Lithium ion secondary battery, assembly for preparing lithium ion secondary battery, preparation method, lithium supplementing negative plate and power utilization device

Abstract

The invention relates to a lithium ion secondary battery, a component for preparing the lithium ion secondary battery, a preparation method, a lithium supplementing negative plate and an electric device. The assembly for preparing the lithium ion secondary battery comprises a lithium supplementing negative plate, the lithium supplementing negative plate comprises a negative current collector, and a second negative active initial layer, a second lithium supplementing layer, a first negative active initial layer and a first lithium supplementing layer which are sequentially arranged on at least one side of the negative current collector; a first negative electrode active material in the first negative electrode active initial layer comprises non-agglomerated primary particles, and the non-agglomerated primary particles account for 80%-100% of the first negative electrode active material in quantity or mass; the non-agglomerated primary particles comprise a coated carbon-based material, the coated carbon-based material comprises a carbon-based body and a carbon coating layer located on at least one part of the surface of the carbon-based body, the carbon-based body comprises graphite, and the carbon coating layer comprises one or more of amorphous carbon, soft carbon and hard carbon. The related lithium ion secondary battery has significantly improved cycle life.

Description

Technical Field

[0001] The present application relates to the technical field of lithium-ion secondary batteries, and further to a lithium-ion secondary battery, a component for preparing the same, a preparation method, a lithium-supplemented negative electrode sheet, and an electrical device. Background Art

[0002] The statements herein merely provide background information related to the present application and do not necessarily constitute prior art.

[0003] With the development of secondary battery technology, secondary batteries represented by lithium-ion batteries are widely used in many fields such as power tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, aerospace, etc. They are also widely used in energy storage power systems such as hydropower, thermal power, wind power and solar power stations. The demand for the cycle life and endurance of lithium-ion secondary batteries is also increasing. Summary of the invention

[0004] According to various embodiments and examples of the present application, the present application provides a lithium ion secondary battery, a component for preparing the same, a preparation method, a lithium supplemented negative electrode sheet and an electric device. The lithium ion secondary battery involved has a significantly improved cycle life.

[0005] In some embodiments of the first aspect of the present application, a component for preparing a lithium-ion secondary battery is provided, which includes a lithium-supplemented negative electrode sheet; the lithium-supplemented negative electrode sheet includes a negative electrode current collector and a second negative electrode active initial layer, a second lithium-supplemented layer, a first negative electrode active initial layer and a first lithium-supplemented layer sequentially arranged on at least one side of the negative electrode current collector;

[0006] The first negative electrode active initial layer includes a first negative electrode active material, the first negative electrode active material includes non-agglomerated primary particles, and the number ratio or mass ratio of the non-agglomerated primary particles in the first negative electrode active material is 80% to 100%;

[0007] The non-agglomerated primary particles include a coated carbon-based material, which includes a carbon base body and a carbon coating layer located on at least a portion of the surface of the carbon base body, the carbon base body includes graphite, and the carbon coating layer includes one or more of amorphous carbon, soft carbon and hard carbon.

[0008] The first negative electrode active initial layer located at the upper layer and the second negative electrode active initial layer located at the lower layer are arranged in the negative electrode active layer of the lithium supplemented negative electrode sheet (the direction away from the negative electrode current collector surface is the upper layer, and the direction toward the negative electrode current collector surface is the lower layer), and further, not only a lithium supplement layer (referred to as the first lithium supplement layer) is arranged on the surface of the first negative electrode active initial layer away from the negative electrode current collector, but also a lithium supplement layer (referred to as the second lithium supplement layer) is arranged between the first negative electrode active initial layer and the second negative electrode active initial layer, and after the component for preparing a lithium ion secondary battery is subjected to infiltration and formation treatment, the first lithium supplement layer The first negative electrode active initial layer and the second negative electrode active initial layer release active lithium, and the released active lithium migrates and is embedded in the negative electrode active material, thereby realizing the lithium insertion treatment, so that the first negative electrode active initial layer and the second negative electrode active initial layer are pre-inserted with lithium respectively, forming the corresponding first negative electrode active layer and the second negative electrode active layer, and at the same time obtaining a lithium ion secondary battery with efficient lithium replenishment of the negative electrode; the component design has a good overall lithium replenishment effect on the negative electrode plate, so that the lithium replenishment effect of the prepared negative electrode plate in the thickness direction is more uniform, and the second negative electrode active initial layer located in the lower layer can also be fully replenished with lithium; on the other hand, the negative electrode plate is On the one hand, the second lithium replenishing layer can pre-embed lithium more evenly and fully, forming a more stable and uniform solid electrolyte interface (SEI) film as a whole; on the other hand, the gas generated in the lithium embedding process of the second lithium replenishing layer can form a path during the discharge process to promote the first lithium replenishing layer to be more fully and evenly infiltrated, so that the first negative electrode active layer located on the upper layer can be better pre-embedded with lithium, and the distribution uniformity of the SEI film in the first negative electrode active layer can be improved; on the other hand, by providing a high content of non-agglomerated primary particles in the first negative electrode active material located on the upper layer, it is beneficial to reduce the embedding of the embeddable surface caused by particle agglomeration, which is beneficial to improve the More lithium insertion sites are provided. Furthermore, by arranging coated carbon-based materials in non-agglomerated primary particles, the carbon coating layer can be used to optimize the lithium ion transmission channel, thereby promoting faster and more lithium ion insertion. Through the aforementioned multiple effects, it is beneficial to store more lithium in the negative electrode, improve the lithium replenishment efficiency, and thus replenish active lithium more sustainably during the charge and discharge cycle. It is also beneficial to enhance the structural stability of the upper and lower negative electrode active materials when they are in contact with the electrolyte, and promote the upper and lower negative electrode active materials to be able to supply capacity more sustainably, thereby giving the lithium ion secondary battery a significantly extended cycle life.

[0009] The effects described in any part of this application are not intended to be limited by any theory.

[0010] In some embodiments, the negative electrode plate is more fully and evenly infiltrated throughout the thickness direction, and is then more evenly and fully pre-embedded with lithium, forming a more stable and uniform solid electrolyte interface (SEI) film as a whole, which is beneficial to improving the charge transfer performance on the surface of the negative electrode active material in the negative electrode plate as a whole; in addition, after the infiltration and formation to achieve lithium insertion treatment, the second lithium replenishment layer is consumed, and a pore channel can be formed between the first negative electrode active layer and the second negative electrode active layer, which is beneficial to electrolyte filling, and can promote the infiltration of the electrolyte into the second negative electrode active layer located at the lower layer, which is beneficial to the formation of a SEI film with better stability, which can reduce the polarization inside the negative electrode plate, and can also take into account the electronic conductivity between the first negative electrode active layer and the second negative electrode active layer in the lithium-ion secondary battery; through the aforementioned multiple effects, it is beneficial to improve the fast charging performance of the battery.

[0011] In some embodiments, the second lithium replenishing layer and the first lithium replenishing layer each independently include single substance lithium.

[0012] By selecting a lithium replenishing layer including single-substance lithium (a non-limiting example such as a lithium film) as the first lithium replenishing layer and the second lithium replenishing layer, the preparation process is more controllable and the lithium replenishing efficiency is high.

[0013] In some embodiments, the coverage area percentage of the second lithium supplement layer relative to the second negative electrode active initial layer is recorded as f, measured along the projection of the thickness direction of the lithium supplement negative electrode sheet and on a single side of the negative electrode current collector. M0 The coverage area percentage of the first lithium supplement layer relative to the first negative electrode active initial layer is recorded as f U0 The thickness of the second lithium supplement layer on one side is d 02 The thickness of the first lithium supplement layer on one side is d 01 The surface density of the second lithium replenishing layer and the first lithium replenishing layer relative to the first negative electrode active initial layer is respectively denoted as p 02 and ρ 01 , where ρ 02 and ρ 01 Respectively measured on both sides of the negative electrode current collector;

[0014] The lithium-supplemented negative electrode sheet meets one or more of the following characteristics:

[0015] The single-side thickness d of the second lithium supplement layer 02 Less than the single-side thickness d of the first lithium supplement layer 01 ;

[0016] The second lithium replenishing layer satisfies 0 <f M0 ≤f U0 ;

[0017] The single-side thickness d of the second lithium supplement layer 020.5μm~4μm;

[0018] The second lithium replenishing layer satisfies 0 <f M0 ≤70%;

[0019] The second lithium replenishing layer satisfies 0<ρ 02 ≤ρ 01 ;

[0020] ρ 02 0.5mg / 1540.25mm 2 ~6mg / 1540.25mm 2 .

[0021] After the components used to prepare lithium-ion secondary batteries are infiltrated and formed to achieve lithium insertion treatment, the active lithium released by the second lithium replenishment layer is embedded into the negative electrode active layer of the negative electrode plate along with the transmission of the electrolyte, which can achieve a good lithium replenishment effect on the second negative electrode active initial layer; at the same time, the active lithium released by the second lithium replenishment layer may be inactivated before being embedded in the negative electrode active material, thereby, a lithium replenishment residual layer including inactive lithium may be formed at the position of the second lithium replenishment layer (referred to as the second lithium replenishment residual layer). On this basis, by controlling the second lithium replenishment layer to meet one or more of the aforementioned characteristics, it is helpful to reduce or avoid the obstruction of the second lithium replenishment residual layer to the ion transmission between the first negative electrode active layer and the second negative electrode active layer; at the same time, the passage formed when the gas generated by the second lithium replenishment layer is discharged during the lithium insertion process can be utilized, so that the first negative electrode active layer located on the upper layer and the second negative electrode active layer located on the lower layer can be better infiltrated and pre-inserted with lithium, thereby improving the uniformity of lithium insertion and forming a better SEI film, thereby better playing the role of the pre-inserted lithium in the first negative electrode active layer and the second negative electrode active layer in supplementing capacity; the ion transmission between the first negative electrode active layer and the second negative electrode active layer and the wetting effect of the electrolyte in the first and second negative electrode active layers can be taken into account, which is conducive to better improving the cycle life of the battery.

[0022] In some embodiments, by controlling the single-side thickness (d 02 ), the coverage area percentage of the second lithium replenishing layer relative to the second negative electrode active initial layer (f M0 , calculated on one side of the negative electrode current collector) and the surface density of the second lithium supplement layer relative to the first negative electrode active initial layer (ρ 02 , measured on both sides of the negative electrode current collector) is within the aforementioned range, the gas generated during the lithium insertion process is conducive to being discharged more evenly and fully, forming a better and more evenly distributed gas passage, which is conducive to improving the lithium insertion uniformity of the first negative electrode active layer, improving the uniformity of the negative electrode interface in the first negative electrode active layer, and promoting the second negative electrode active layer to be better infiltrated and form a SEI film, thereby better improving the cycle life of the battery.

[0023] In some embodiments, by reducing or avoiding the second lithium supplement residual layer's hindrance to ion transport between the first negative electrode active layer and the second negative electrode active layer, the battery can achieve better dynamics and provide better fast charging performance.

[0024] In some embodiments, the lithium-supplemented negative electrode sheet satisfies one or more of the following characteristics:

[0025] The single-side thickness d of the second lithium supplement layer 02 1μm~4μm;

[0026] The second lithium replenishment layer satisfies 10%≤f M0 ≤f U0 ;

[0027] The second lithium replenishment layer satisfies 10%≤f M0 ≤70%;

[0028] ρ 02 1mg / 1540.25mm 2 ~6mg / 1540.25mm 2 .

[0029] By controlling the single-side thickness of the second lithium replenishment layer (d 02 ), the coverage area percentage of the second lithium replenishing layer relative to the second negative electrode active initial layer (f M0 , calculated on one side of the negative electrode current collector) and the surface density of the second lithium supplement layer relative to the first negative electrode active initial layer (ρ 02 , measured on both sides of the negative electrode current collector) within the aforementioned range is beneficial to taking into account the ion transport between the first negative electrode active layer and the second negative electrode active layer, the wetting effect of the electrolyte in the first and second negative electrode active layers, and the amount of lithium supplement supplied by the second negative electrode active layer, which is beneficial to better improve the cycle life of the battery.

[0030] In some embodiments, the lithium-supplemented negative electrode sheet satisfies one or more of the following characteristics:

[0031] The single-side thickness d of the first lithium supplement layer 01 Less than or equal to 8μm;

[0032] The first lithium replenishing layer satisfies 0 <f U0 ≤70%;

[0033] ρ 01 0.5mg / 1540.25mm 2 ~6mg / 1540.25mm 2 ;

[0034] CLi 1mg / 1540.25mm 2 ~12mg / 1540.25mm 2 Among them, C Li is the total surface density of the second lithium replenishing layer and the first lithium replenishing layer relative to the first negative electrode active initial layer, C Li It is calculated based on the total amount on both sides of the negative electrode current collector.

[0035] By controlling the single-side thickness of the first lithium replenishment layer (d 01 ) and the surface density of the first lithium replenishment layer relative to the first negative electrode active initial layer (ρ 01 , measured on both sides of the negative electrode current collector) is within the aforementioned range, while the first lithium replenishing layer is used to provide pre-embedded lithium, the active lithium provided by the first lithium replenishing layer can be fully embedded in the negative electrode, and the length of the lithium embedding path can be taken into account, which is conducive to better controlling the gas production, so that the active lithium provided by the first lithium replenishing layer is more evenly embedded in the negative electrode, which is conducive to forming a SEI film with better stability, and is conducive to reducing or avoiding lithium plating on the surface of the negative electrode active material caused by uneven lithium embedding, and reducing or avoiding the deterioration of the battery cycle life due to surface lithium plating.

[0036] By controlling the coverage area percentage of the first lithium replenishing layer relative to the first negative electrode active initial layer (f U0 , measured on one side of the negative electrode current collector), the surface density of the first lithium supplement layer relative to the first negative electrode active initial layer (ρ 01 , measured on both sides of the negative electrode current collector) is within the aforementioned range, while utilizing the first lithium replenishing layer to provide pre-intercalated lithium, it is also beneficial for the electrolyte to better infiltrate the first negative electrode active layer, and is beneficial for providing more sufficient exhaust channels for the gas generated during the lithium insertion process, and the exhaust channels can further improve the infiltration of the electrolyte into the first negative electrode active layer, thereby being beneficial for achieving better and more sufficient negative electrode lithium replenishment and better improving the battery cycle life.

[0037] In some embodiments, by providing more sufficient exhaust channels for the gas generated during the lithium insertion process, the electrolyte is better promoted to infiltrate the negative electrode, which is beneficial for the battery to achieve better dynamics and provide better fast charging performance.

[0038] On the basis of introducing the second lithium replenishment layer, the total surface density (C Li ) Within the aforementioned range, the cycle life of the battery can be better improved.

[0039] In some embodiments, the lithium-supplemented negative electrode sheet satisfies one or more of the following characteristics:

[0040] The single-side thickness d of the first lithium supplement layer 01 2μm~5μm;

[0041] The first lithium replenishing layer satisfies 30%≤f U0 ≤70%;

[0042] ρ 01 2mg / 1540.25mm 2 ~6mg / 1540.25mm 2 ;

[0043] C Li 3mg / 1540.25mm 2 ~12mg / 1540.25mm 2 .

[0044] By controlling the single-side thickness of the first lithium replenishment layer (d 01 ), the surface density of the first lithium supplement layer relative to the first negative electrode active initial layer (ρ 01 When one or two of the parameters (measured on the total amount on both sides of the negative electrode current collector) are within the aforementioned range, the battery cycle life may be better reduced or avoided from being deteriorated due to surface lithium deposition; in addition, it is also more conducive to making the processing technology of the first lithium replenishing layer easier to implement.

[0045] By controlling the coverage area percentage of the first lithium replenishing layer relative to the first negative electrode active initial layer (f U0 , measured on one side of the negative electrode current collector), the surface density of the first lithium supplement layer relative to the first negative electrode active initial layer (ρ 01 , measured on both sides of the negative electrode current collector) is within the aforementioned range, while utilizing the first lithium replenishment layer to provide pre-embedded lithium, the gas production can be better controlled, and the infiltration of the electrolyte into the first negative electrode active layer can be better improved, thereby achieving better and more sufficient negative electrode lithium replenishment, and taking into account the amount of lithium replenishment supplied by the first lithium replenishment layer, which is beneficial to better improve the battery cycle life.

[0046] In some embodiments, the second lithium replenishing layer and the first lithium replenishing layer each independently include a plurality of lithium replenishing micro-domains;

[0047] The lithium-supplemented negative electrode sheet meets one or more of the following characteristics:

[0048] Measured by projection along the thickness direction of the lithium-supplemented negative electrode sheet, the one-dimensional size of at least a portion of the lithium-supplemented micro-regions is 20 μm to 2000 μm, and can be optionally 20 μm to 1000 μm;

[0049] Measured by projection along the thickness direction of the lithium-supplemented negative electrode sheet, the spacing between at least a portion of the lithium-supplemented micro-regions is 20 μm to 2000 μm, and can be optionally 20 μm to 1000 μm;

[0050] The lithium supplement micro-regions in the first lithium supplement layer are distributed in stripe shape or grid shape;

[0051] The lithium replenishing micro-regions in the second lithium replenishing layer are distributed in stripe shape or grid shape.

[0052] In some embodiments, the lithium supplement micro-regions in the first lithium supplement layer are distributed in stripes; the stripe spacing of the lithium supplement micro-regions in the first lithium supplement layer is 20 μm to 2000 μm, and the stripe width is 20 μm to 2000 μm;

[0053] The lithium replenishing micro-regions in the second lithium replenishing layer are distributed in a grid shape; the stripe spacing of the lithium replenishing micro-regions in the first lithium replenishing layer is 20 μm to 2000 μm, and the stripe width is 20 μm to 2000 μm.

[0054] In some embodiments, the lithium supplement micro-regions in the first lithium supplement layer are distributed in stripes; the stripe spacing of the lithium supplement micro-regions in the first lithium supplement layer is 20 μm to 500 μm; the stripe width is 20 μm to 500 μm;

[0055] The lithium replenishing micro-regions in the second lithium replenishing layer are distributed in a grid shape; the stripe spacing of the lithium replenishing micro-regions in the first lithium replenishing layer is 20 μm to 500 μm, and the stripe width is 20 μm to 500 μm.

[0056] By controlling the lithium-replenishing micro-areas in the lithium-replenishing negative electrode sheet to conform to one or more of the aforementioned sizes and shapes, it is beneficial to provide a more sufficient contact area for the electrolyte to infiltrate the electrode sheet, to control the gas production during the lithium insertion process within a more appropriate range to produce a more uniform and sufficient exhaust channel, to optimize the ion transfer between the first negative electrode active layer and the second negative electrode active layer, and to increase the adhesion strength of the lithium-replenishing layer to the adjacent negative electrode active layer. It can also take into account the amount of lithium replenishment. Through the aforementioned multiple effects, it is beneficial to better improve the battery cycle life.

[0057] In some embodiments, the lithium-supplemented negative electrode sheet satisfies one or more of the following characteristics:

[0058] The compaction density of the second negative electrode active initial layer is higher than the compaction density of the first negative electrode active initial layer;

[0059] The powder compaction density of the second negative electrode active initial layer is higher than the powder compaction density of the first negative electrode active initial layer.

[0060] By adjusting the compaction density of the second negative electrode active initial layer to be higher than that of the first negative electrode active initial layer, the second negative electrode active layer in the lithium-ion secondary battery can have a higher compaction density, which is beneficial to improving the energy density of the lithium-ion secondary battery. On the other hand, the first negative electrode active initial layer has a lower compaction density, which is beneficial to quickly embedding active lithium into the negative electrode active material after electrolyte infiltration, and is beneficial to reducing or avoiding lithium precipitation on the surface of the negative electrode active material. Therefore, it is beneficial to take into account both high lithium replenishment efficiency and high energy density, and to take into account both improving cycle life and increasing energy density.

[0061] By controlling the powder compaction density of the second negative electrode active initial layer to be higher than the powder compaction density of the first negative electrode active initial layer, it is beneficial to give the second negative electrode active initial layer a higher compaction density during the cold pressing process of the electrode sheet, so that the second negative electrode active layer in the lithium-ion secondary battery has a higher compaction density.

[0062] In some embodiments, the lithium-supplemented negative electrode sheet satisfies one or more of the following characteristics:

[0063] The compaction density of the second negative electrode active initial layer is 1.3 g / cm 3 ~1.8g / cm 3 ;

[0064] The overall compaction density of the lithium-supplemented negative electrode sheet is 1.3 g / cm 3 ~1.7g / cm 3 .

[0065] By controlling the powder compaction density of the second negative electrode active initial layer within the aforementioned range, it is advantageous to control the compaction density of the second negative electrode active layer within a more appropriate range, which is advantageous for enabling the lithium-ion secondary battery to achieve a higher energy density.

[0066] By controlling the overall compaction density of the lithium-supplemented negative electrode sheet within the aforementioned range, it is beneficial to control the overall compaction density of the negative electrode sheet in the lithium-ion secondary battery within a more appropriate range, which is beneficial to taking into account both the battery energy density and the higher negative electrode lithium replenishment efficiency.

[0067] Exemplarily, by adjusting the overall compaction density of the lithium-supplemented negative electrode sheet within the aforementioned range, it is beneficial to balance battery kinetics and energy density.

[0068] Exemplarily, by adjusting the overall compaction density of the lithium-supplemented negative electrode sheet within the aforementioned range, it is beneficial to improve both the energy density and the lithium-supplementing efficiency.

[0069] In some embodiments, the first negative electrode active initial layer includes a first negative electrode active material, and the second negative electrode active initial layer includes a second negative electrode active material; v50 represents the particle size corresponding to when the cumulative volume distribution percentage of the multi-particle mixture reaches 50%;

[0070] The lithium-supplemented negative electrode sheet meets one or more of the following characteristics:

[0071] The D of the first negative electrode active material v 50 lower than the D of the second negative electrode active material v 50;

[0072] The D of the first negative electrode active material v 50: 7μm ~14μm;

[0073] The D of the second negative electrode active material v 50: 8μm ~14μm;

[0074] The porosity of the first negative electrode active initial layer is higher than the porosity of the second negative electrode active initial layer;

[0075] The porosity of the first negative electrode active initial layer is 20% to 45%;

[0076] The porosity of the second negative electrode active initial layer is 15% to 45%.

[0077] In some embodiments, the lithium-supplemented negative electrode sheet satisfies one or more of the following characteristics:

[0078] The D of the first negative electrode active material v 50: 8μm ~13μm;

[0079] The D of the second negative electrode active material v 50 is 9μm ~13μm.

[0080] By arranging negative electrode active materials with smaller particle sizes in the first negative electrode active initial layer, the second negative electrode active layer includes negative electrode active materials with smaller particle sizes, which is beneficial to reducing the solid phase diffusion path of the first negative electrode active layer and optimizing battery kinetics.

[0081] By adding D of the first negative electrode active material v 50 is set within the aforementioned range, which is beneficial to reducing the solid phase diffusion path of the first negative electrode active layer, thereby optimizing the battery kinetics.

[0082] By matching the particle sizes of the first negative electrode active material and the second negative electrode active material, it can be achieved that the upper layer in the first negative electrode active layer and the lower layer in the second negative electrode active layer have a low compaction density, and have a suitable compaction density difference, which is beneficial to taking into account both the lithium replenishment efficiency of the lithium replenishment negative electrode sheet and the battery energy density.

[0083] By controlling the porosity of the first negative electrode active initial layer to be higher than the porosity of the second negative electrode active initial layer, the high porosity of the upper layer can provide more channels for lithium ion embedding, which is beneficial for the rapid embedding of lithium ions into the negative electrode active material, thereby helping to reduce or avoid lithium deposition on the surface of the negative electrode active material.

[0084] By controlling the porosity of the first negative electrode active initial layer within the aforementioned range, it is beneficial for lithium ions to be quickly embedded in the negative electrode active material, thereby helping to reduce or avoid lithium deposition on the surface of the negative electrode active material.

[0085] On the basis of controlling the compaction density of the first negative electrode active initial layer (upper layer) to be lower than that of the second negative electrode active initial layer (lower layer), further introducing non-agglomerated primary particles into the first negative electrode active material is beneficial to exposing more lithium insertion sites and further improving the lithium replenishment efficiency.

[0086] In some embodiments, the second negative electrode active layer includes a second negative electrode active material, and the second negative electrode active material includes secondary particles; the number ratio or mass ratio of the secondary particles in the second negative electrode active material may be 80% to 100%.

[0087] By providing the secondary particles in the second negative electrode active material, it is advantageous to control the manufacturing cost.

[0088] In some embodiments, the amount ratio or mass ratio of the coated carbon-based material in the non-agglomerated primary particles in the first negative electrode active material is 80% to 100%.

[0089] In some embodiments, the coated carbon-based material in the non-agglomerated primary particles includes non-agglomerated coated graphite; the quantity ratio or mass ratio of the non-agglomerated coated graphite in the first negative electrode active material is 80% to 100%.

[0090] In some embodiments, the lithium-supplemented negative electrode sheet satisfies one or more of the following characteristics:

[0091] The thickness of the first negative electrode active initial layer is 50 μm to 120 μm, based on the total thickness on both sides of the lithium supplemented negative electrode sheet;

[0092] The thickness of the first negative electrode active initial layer on one side is 25 μm to 60 μm;

[0093] The ratio of the thickness of the first negative electrode active initial layer to the sum of the thickness of the first negative electrode active initial layer and the second negative electrode active initial layer on one side of the negative electrode current collector is denoted as f H0 , satisfying 20%≤f H0 ≤70%.

[0094] In some embodiments, the lithium-supplemented negative electrode sheet satisfies one or more of the following characteristics:

[0095] The thickness of the first negative electrode active initial layer is 50 μm to 100 μm, based on the total thickness on both sides of the lithium supplemented negative electrode sheet;

[0096] The thickness of the first negative electrode active initial layer on one side is 25 μm to 50 μm;

[0097] 30%≤f H0 ≤50%.

[0098] The thickness of one side of the first negative electrode active initial layer and the total thickness of both sides of the first negative electrode active initial layer (H 01 ) and the ratio of the thickness of the first negative electrode active initial layer to the sum of the thickness of the first negative electrode active initial layer and the second negative electrode active initial layer (f H0 ) is controlled within the aforementioned range, which is conducive to better balancing the higher lithium replenishment efficiency provided by the first negative electrode active initial layer and the overall energy density of the negative electrode sheet. In addition, by controlling f H0 Further, by adjusting the compaction density of the second negative electrode active initial layer and / or the compaction density of the powder of the second negative electrode active initial layer, the comprehensive requirements of improving lithium replenishment efficiency, extending cycle life and improving energy density can be better balanced.

[0099] In some embodiments, the components for preparing lithium-ion secondary batteries also include a positive electrode plate, the positive electrode plate includes a positive electrode active material, the positive electrode active material includes one or more of a ternary positive electrode material, a modified ternary positive electrode material, lithium iron phosphate, a modified lithium iron phosphate, lithium iron manganese phosphate, and a modified lithium iron manganese phosphate; the modified material includes one or more of a doping element and a coating element.

[0100] In some embodiments, the positive electrode active material includes carbon-coated lithium iron phosphate, which includes a lithium iron phosphate body and a carbon coating layer located on at least a portion of the surface of the lithium iron phosphate body, and the carbon coating layer includes one or more of soft carbon, hard carbon and amorphous carbon.

[0101] When the positive electrode active material includes carbon-coated lithium iron phosphate, the material has good stability under charge and discharge cycles, which is beneficial to provide more charge and discharge cycles and to better extend the battery cycle life.

[0102] In some embodiments, the components for preparing a lithium-ion secondary battery further include a positive electrode sheet;

[0103] The components for preparing a lithium-ion secondary battery satisfy the following formula:

[0104] 1.03≤C N_A / (α·(m L1 / A L1 + m L2 / A L2 )×C Li / g +C P_A )≤1.2;

[0105] Among them, C N_A is the preset surface capacity of the negative electrode, C P_A is the preset surface capacity of the positive electrode, m L1 is the total mass of the first lithium supplement layer on both sides of the negative electrode current collector, A L1 is the spreading area of ​​the first lithium supplement layer on the first negative electrode active initial layer, m L2 A is the total mass of the second lithium supplement layer on both sides of the negative electrode current collector, L2 is the spreading area of ​​the first lithium supplement layer on the second negative electrode active initial layer, C Li / g is the theoretical gram capacity of lithium, α is the lithium replenishment coefficient, 0.6≤α≤1.

[0106] In some embodiments, the components for preparing a lithium-ion secondary battery meet one or more of the following characteristics:

[0107] 1.1≤C N_A / (α·(m L1 / A L1 + m L2 / A L2 )×C Li / g +C P_A )≤1.2;

[0108] 0.6≤α≤0.9.

[0109] Without being limited to any theory, by controlling the total thickness (d Li ) satisfies the aforementioned formula, and while the battery cycle life can be extended by lithium replenishment, the total thickness of the lithium replenishment residual layer can be controlled to have a more suitable thickness, which is beneficial to better balance the wettability of the electrolyte to the first negative electrode active layer and the second negative electrode active layer and the ion transport performance on the surfaces of both sides of the first negative electrode active layer, and the capacity matching between the positive and negative electrodes is better, which is more conducive to improving the lithium replenishment efficiency and the battery cycle life.

[0110] In some embodiments, by controlling the lithium supplement layer to have a more appropriate total thickness, it is helpful to better control the heat generation caused by the reaction between water and lithium, thereby facilitating improving production safety.

[0111] In some embodiments, the positive electrode active material includes carbon-coated lithium iron phosphate, and the carbon-coated lithium iron phosphate includes a lithium iron phosphate body and a carbon coating layer located on at least a portion of the surface of the lithium iron phosphate body; the total surface density of the second lithium supplement layer and the first lithium supplement layer relative to the first negative electrode active initial layer is recorded as C Li , the surface density of the positive electrode active material in the positive electrode sheet is recorded as A, and the surface density of the negative electrode active material in the lithium supplemented negative electrode sheet is recorded as B; C Li , A and B are respectively calculated based on the total amount on both sides of the negative electrode current collector; the first lithium replenishing layer and the second lithium replenishing layer are both lithium films;

[0112] The lithium supplemented negative electrode sheet satisfies the following formula: (18×C Li +A) / B≤2.3;

[0113] Optionally, the carbon coating layer includes one or more of soft carbon, hard carbon and amorphous carbon.

[0114] In some embodiments, the components for preparing a lithium-ion secondary battery meet one or both of the following characteristics:

[0115] 1.9≤(18×C Li +A) / B≤2.3;

[0116] C Li 1mg / 1540.25mm 2 ~12mg / 1540.25mm 2 .

[0117] On the basis that the positive electrode active material includes carbon-coated lithium iron phosphate, by controlling the total surface density (C Li ) and the surface density of the active materials in the positive and negative electrode sheets satisfy the aforementioned formula, which is conducive to controlling the lithium supplement residual layer to have a more appropriate total thickness, and is conducive to better taking into account the wettability of the electrolyte to the first negative electrode active layer and the second negative electrode active layer and the ion transport performance of the surfaces on both sides of the first negative electrode active layer, and the capacity matching between the positive and negative electrodes is better, which is more conducive to improving the lithium supplement efficiency and battery cycle life. In some embodiments, it is also conducive to better controlling the heat generation caused by the reaction of water and lithium, thereby improving production safety.

[0118] In a second aspect of the present application, a lithium-supplemented negative electrode sheet is provided, the lithium-supplemented negative electrode sheet comprising a negative electrode current collector and a second negative electrode active initial layer, a second lithium-supplemented layer, a first negative electrode active initial layer and a first lithium-supplemented layer sequentially arranged on at least one side of the negative electrode current collector;

[0119] The first negative electrode active initial layer includes a first negative electrode active material, the first negative electrode active material includes non-agglomerated primary particles, and the number ratio or mass ratio of the non-agglomerated primary particles in the first negative electrode active material is 80% to 100%;

[0120] The non-agglomerated primary particles include a coated carbon-based material, which includes a carbon base body and a carbon coating layer located on at least a portion of the surface of the carbon base body, the carbon base body includes graphite, and the carbon coating layer includes one or more of amorphous carbon, soft carbon and hard carbon.

[0121] In some embodiments, the lithium-supplemented negative electrode sheet is the lithium-supplemented negative electrode sheet defined in the first aspect of the present application. In this case, the lithium-supplemented negative electrode sheet has the same characteristics as the lithium-supplemented negative electrode sheet in the component for preparing a lithium-ion secondary battery described in the first aspect of the present application.

[0122] By arranging a first negative electrode active initial layer located at an upper layer and a second negative electrode active initial layer located at a lower layer in the negative electrode active layer of the lithium-supplemented negative electrode sheet (the direction away from the surface of the negative electrode current collector is the upper layer, and the direction toward the surface of the negative electrode current collector is the lower layer), further, not only the first lithium-supplementing layer is arranged on the surface of the first negative electrode active initial layer away from the negative electrode current collector, but also the second lithium-supplementing layer is arranged between the first negative electrode active initial layer and the second negative electrode active initial layer, after being wetted and formed to achieve lithium insertion treatment, the first negative electrode active initial layer and the second negative electrode active initial layer are respectively pre-inserted with lithium to form corresponding first negative electrode active layers and second negative electrode active layers; the lithium-supplemented negative electrode sheet has a good overall lithium-supplementing effect, so that the prepared negative electrode sheet has a more uniform lithium-supplementing effect in the thickness direction, and the second negative electrode active initial layer located at the lower layer can also be fully lithium-supplemented; on the other hand, the negative electrode sheet is more uniformly and fully pre-inserted with lithium in the thickness direction, forming a more stable and uniform solid electrolyte interface (SEI) film as a whole; on the other hand, the second lithium-supplementing layer The gas generated during the lithium insertion process of the layer can form a path during the discharge process to promote the first lithium replenishment layer to be more fully and evenly infiltrated, so that the first negative electrode active layer located on the upper layer can be better pre-inserted with lithium, and the distribution uniformity of the SEI film in the first negative electrode active layer is improved; on the other hand, by setting a high content of non-agglomerated primary particles in the first negative electrode active material located on the upper layer, it is beneficial to reduce the embedding of the embeddable surface caused by particle agglomeration, which is beneficial to provide more lithium insertion sites. Further, by setting a coated carbon-based material in the non-agglomerated primary particles, the carbon coating layer can be used to optimize the lithium ion transmission channel and promote faster and more lithium ion insertion; through the aforementioned multiple effects, it is beneficial to store more lithium in the negative electrode, improve the lithium replenishment efficiency, and thus replenish the active lithium more sustainably during the charge and discharge cycle. It is also beneficial to enhance the structural stability of the negative electrode active materials located in the upper and lower layers when they are in contact with the electrolyte, and promote the negative electrode active materials located in the upper and lower layers to be able to supply capacity more sustainably, thereby giving the lithium-ion secondary battery a significantly extended cycle life.

[0123] In a third aspect of the present application, a method for preparing a lithium ion secondary battery is provided, comprising the following steps:

[0124] Assemble a positive electrode plate, a separator and a lithium-supplemented negative electrode plate into an electrode assembly, so that the separator is arranged between the positive electrode plate and the lithium-supplemented negative electrode plate; wherein the lithium-supplemented negative electrode plate comprises a negative electrode current collector and a second negative electrode active initial layer, a second lithium-supplemented layer, a first negative electrode active initial layer and a first lithium-supplemented layer arranged in sequence on at least one side of the negative electrode current collector; the first negative electrode active initial layer comprises a first negative electrode active material, the first negative electrode active material comprises non-agglomerated primary particles, and the number ratio or mass ratio of the non-agglomerated primary particles in the first negative electrode active material is 80% to 100%; the non-agglomerated primary particles comprise a coated carbon-based material, the coated carbon-based material comprises a carbon base body and a carbon coating layer located at least a portion of the surface of the carbon base body, the carbon base body comprises graphite, and the carbon coating layer comprises one or more of amorphous carbon, soft carbon and hard carbon;

[0125] The electrode assembly is placed in the accommodating cavity of the shell, and the electrolyte is injected to obtain an assembly for preparing a lithium-ion secondary battery, and the electrolyte is allowed to infiltrate the positive electrode plate and the lithium-supplemented negative electrode plate, and the formation is carried out to prepare a lithium-ion secondary battery; wherein the lithium-supplemented negative electrode plate forms a negative electrode plate, the second negative electrode active initial layer forms a second negative electrode active layer, and the first negative electrode active initial layer forms a first negative electrode active layer.

[0126] By contacting the electrode assembly including the aforementioned lithium-supplemented negative electrode sheet with an electrolyte, impregnating, and forming, a negative electrode sheet including the negative electrode lithium-supplemented treatment can be prepared. The lithium-supplemented negative electrode sheet is provided with a first negative electrode active initial layer located on the upper layer and a second negative electrode active initial layer located on the lower layer (the direction away from the surface of the negative electrode current collector is the upper side, and the direction toward the surface of the negative electrode current collector is the lower side). Further, by using the first lithium-supplemented layer located above the first negative electrode active initial layer and the second lithium-supplemented layer located between the first negative electrode active initial layer and the second negative electrode active initial layer, after impregnation and formation, the first negative electrode active initial layer and the second negative electrode active initial layer are respectively pre-embedded with lithium, and the lithium-supplemented negative electrode sheet in the assembly for preparing a lithium-ion secondary battery forms a negative electrode sheet in a lithium-ion battery, and the first negative electrode active initial layer and the second negative electrode active initial layer in the lithium-supplemented negative electrode sheet are respectively converted into a first negative electrode active layer and a second negative electrode active layer, and the first negative electrode active layer and the second negative electrode active layer each independently include lithium pre-embedded by the negative electrode lithium-supplemented. The method has a good overall lithium replenishment effect on the negative electrode plate, so that the prepared negative electrode plate has a more uniform lithium replenishment effect in the thickness direction, and the second negative electrode active initial layer located in the lower layer can also be fully replenished with lithium; on the other hand, the negative electrode plate is more uniformly and fully pre-embedded with lithium in the thickness direction, forming a more stable and uniform solid electrolyte interface (SEI) film as a whole; on the other hand, the gas generated in the second lithium replenishment layer during the lithium insertion process can form a passage during the discharge process to promote the first lithium replenishment layer to be more fully and uniformly infiltrated, so that the first negative electrode active layer located in the upper layer is better pre-embedded with lithium, and the distribution uniformity of the SEI film in the first negative electrode active layer is improved; on the other hand, by Providing a high content of non-agglomerated primary particles in the material is beneficial to reducing the embedding of embeddable surfaces caused by particle agglomeration, and is beneficial to providing more lithium embedding sites. Furthermore, by providing a coated carbon-based material in the non-agglomerated primary particles, the carbon coating layer can be used to optimize the lithium ion transmission channel, thereby promoting faster and more lithium ion embedding; through the aforementioned multiple effects, it is beneficial to store more lithium in the negative electrode, improve the lithium replenishment efficiency, and thus replenish active lithium more sustainably during the charge and discharge cycle, and is also beneficial to enhance the structural stability of the upper and lower negative electrode active materials when they are in contact with the electrolyte, and promote the upper and lower negative electrode active materials to be able to supply capacity more sustainably, thereby giving the lithium-ion secondary battery a significantly extended cycle life.

[0127] In some embodiments, the lithium-supplemented negative electrode sheet is prepared by a method comprising the following steps:

[0128] A second negative electrode active dry layer, a second lithium film, a first negative electrode active dry layer and a first lithium film are stacked on at least one side surface of the negative electrode substrate to obtain a multilayer body to be rolled;

[0129] The multilayer body to be rolled is subjected to a rolling process to obtain the lithium supplemented negative electrode sheet.

[0130] In some embodiments, the roller pressing is performed at a pressure of 60T to 100T.

[0131] In some embodiments, the roller pressing is performed at a pressure of 60T to 80T.

[0132] In some embodiments, the method for preparing the lithium-ion secondary battery satisfies one or both of the following characteristics:

[0133] In the step of making the electrolyte infiltrate the positive electrode sheet and the lithium-supplemented negative electrode sheet, the infiltration temperature is 20° C. to 60° C., and can be optionally 30° C. to 50° C.;

[0134] In the step of allowing the electrolyte to infiltrate the positive electrode sheet and the lithium-supplemented negative electrode sheet, the infiltration time is 10 hours to 50 hours, and can be optionally 10 hours to 30 hours.

[0135] In some embodiments, the component for preparing a lithium ion secondary battery is the component for preparing a lithium ion secondary battery described in the first aspect of the present application.

[0136] In a fourth aspect of the present application, a lithium-ion secondary battery is provided, comprising a negative electrode plate; the negative electrode plate comprises a negative electrode current collector and a second negative electrode active layer, a second lithium supplement residual layer, a first negative electrode active layer and a first lithium supplement residual layer sequentially arranged on at least one side of the negative electrode current collector;

[0137] The first negative electrode active layer and the second negative electrode active layer each independently include lithium pre-embedded by negative electrode lithium supplementation;

[0138] The first negative electrode active initial layer includes a first negative electrode active material, the first negative electrode active material includes non-agglomerated primary particles, and the number ratio or mass ratio of the non-agglomerated primary particles in the first negative electrode active material is 80% to 100%;

[0139] The non-agglomerated primary particles include a coated carbon-based material, which includes a carbon base body and a carbon coating layer located on at least a portion of the surface of the carbon base body, the carbon base body includes graphite, and the carbon coating layer includes one or more of amorphous carbon, soft carbon and hard carbon.

[0140] The negative electrode plate in the lithium-ion secondary battery provided in the fourth aspect of the present application has been treated with lithium replenishment, and a first negative electrode active layer located in the upper layer and a second negative electrode active layer located in the lower layer are arranged on the negative electrode active layer of the negative electrode plate (the direction away from the surface of the negative electrode current collector is the upper side, and the direction toward the surface of the negative electrode current collector is the lower side), further, the lithium replenishment layer (which can be recorded as the first lithium replenishment layer) is treated with lithium replenishment above the first negative electrode active layer, and the lithium replenishment layer (which can be recorded as the second lithium replenishment layer) is also treated with lithium replenishment between the first negative electrode active layer and the second negative electrode active layer, and non-agglomerated primary particles that can provide more lithium insertion sites are arranged in the first negative electrode active material located in the upper layer, and particles that promote faster and more lithium ion insertion are arranged in the non-agglomerated primary particles. The multi-embedded coated carbon-based material enables the first negative electrode active layer and the second negative electrode active layer to independently include rich and uniform pre-embedded lithium, the first negative electrode active layer and the second negative electrode active layer are both fully replenished with lithium, the negative electrode plate has a good overall lithium replenishment effect, and can form a more stable and more uniform solid electrolyte interface (SEI) film as a whole; through the aforementioned multiple effects, it is beneficial to store more lithium in the negative electrode, thereby replenishing active lithium more lastingly during the charge and discharge cycle, and it is also beneficial to enhance the structural stability of the negative electrode active materials in the upper and lower layers when they are in contact with the electrolyte, and promote the negative electrode active materials in the upper and lower layers to be able to supply capacity more lastingly, thereby giving the lithium-ion secondary battery a significantly extended cycle life.

[0141] In some embodiments, the first lithium replenishing residual layer and the second lithium replenishing residual layer each independently include inactive lithium.

[0142] During the lithium insertion process, if the active lithium provided by the lithium replenishment layer is not able to be inserted into the negative electrode active material in time and becomes inactivated, a lithium replenishment residual layer including inactive lithium may be formed at the lithium replenishment layer position. Accordingly, a first lithium replenishment residual layer may be formed at the aforementioned first lithium replenishment layer position, and a second lithium replenishment residual layer may be formed at the aforementioned second lithium replenishment layer position. Based on this, the lithium replenishment method used by the lithium-ion secondary battery can be analyzed.

[0143] In some embodiments, the coverage area percentage of the second lithium supplement residual layer relative to the second negative electrode active layer is recorded as f, measured along the projection in the thickness direction of the negative electrode sheet and on one side of the negative electrode current collector. M The coverage area percentage of the first lithium supplement residual layer relative to the first negative electrode active layer is recorded as f U ; The single-side thickness of the second lithium-supplementing residual layer is recorded as d2; the single-side thickness of the first lithium-supplementing residual layer is recorded as d1;

[0144] The negative electrode plate meets one or more of the following characteristics:

[0145] The single-side thickness d2 of the second lithium-replenishing residual layer is smaller than the single-side thickness d1 of the first lithium-replenishing residual layer;

[0146] The second lithium supplement residual layer satisfies 0 <f M ≤f U ;

[0147] The second lithium supplement residual layer satisfies 0 <f M ≤70%;

[0148] The single-side thickness d2 of the second lithium supplement residual layer is less than 1 μm;

[0149] The first lithium supplement residual layer satisfies 0 <f U ≤70%;

[0150] The single-side thickness d1 of the first lithium replenishing residual layer is less than 1 μm.

[0151] By controlling the second lithium replenishment residual layer to meet one or more of the aforementioned characteristics, it is helpful to reduce or avoid the second lithium replenishment residual layer's obstruction to ion transmission between the first negative electrode active layer and the second negative electrode active layer, so that the first negative electrode active layer and the second negative electrode active layer have good ion transmission capacity during the charge and discharge cycle, which is helpful to better improve the cycle life of the battery.

[0152] In some embodiments, by controlling the single-side thickness (d2) of the second lithium replenishing residual layer and the coverage area percentage (f M , measured on a single side of the negative electrode current collector) within the aforementioned range is beneficial to promoting better wetting of the second negative electrode active layer during the charge and discharge cycle, thereby better improving the cycle life of the battery.

[0153] In some embodiments, by reducing or avoiding the second lithium supplement residual layer's hindrance to ion transport between the first negative electrode active layer and the second negative electrode active layer, the battery can achieve better dynamics and provide better fast charging performance.

[0154] By controlling the single-side thickness (d1) of the first lithium supplement residual layer within the aforementioned range, while realizing lithium insertion in the negative electrode active layer, during the charge and discharge cycle, it is also beneficial to enable the first negative electrode active layer and the electrolyte to have good ion transmission ability and wetting effect, which is beneficial to better improve the cycle life of the battery.

[0155] By controlling the coverage area percentage (f U , measured on a single side of the negative electrode current collector) within the aforementioned range, during the charge and discharge cycle, it is beneficial for the upper surface of the first negative electrode active layer to have good ion transmission ability, which is beneficial to better improve the battery cycle life.

[0156] In some embodiments, during the charge and discharge cycle, by making the upper surface of the first negative electrode active layer have good ion transport capability, it is beneficial to provide better fast charging performance.

[0157] In some embodiments, the negative electrode plate satisfies one or more of the following characteristics:

[0158] The single-side thickness d2 of the second lithium supplement residual layer is less than 0.1 μm;

[0159] The second lithium supplement residual layer satisfies 10%≤f M ≤70%;

[0160] The single-side thickness d1 of the first lithium supplement residual layer is less than 0.1 μm;

[0161] The first lithium supplement residual layer satisfies 30%≤f U ≤70%.

[0162] By controlling the single-side thickness (d2) of the second lithium replenishment residual layer and the coverage area percentage (f M , measured on a single side of the negative electrode current collector) within the aforementioned range, during the charge and discharge cycle, it is beneficial to have better ion transmission ability between the first negative electrode active layer and the second negative electrode active layer, which is beneficial to better improve the cycle life of the battery.

[0163] By controlling the single-side thickness (d1) of the first lithium replenishment residual layer and the coverage area percentage (f U , measured on a single side of the negative electrode current collector) is within the aforementioned range, during the charge and discharge cycle, it is also beneficial to have better ion transmission ability and wetting effect between the first negative electrode active layer and the electrolyte, which is beneficial to better improve the cycle life of the battery.

[0164] In some embodiments, the second lithium replenishment residual layer and the first lithium replenishment residual layer each independently include a plurality of lithium replenishment residual micro-regions;

[0165] The negative electrode plate meets one or more of the following characteristics:

[0166] Measured by projection along the thickness direction of the negative electrode sheet, at least a portion of the lithium-supplemented residual micro-regions has a one-dimensional size of 20 μm to 2000 μm;

[0167] Measured by projection along the thickness direction of the negative electrode sheet, the spacing between at least a portion of the lithium-supplemented residual micro-regions is 20 μm to 2000 μm;

[0168] The lithium-supplement residual micro-regions in the first lithium-supplement residual layer are distributed in a stripe shape or a grid shape;

[0169] The lithium replenishment residual micro-regions in the second lithium replenishment residual layer are distributed in a stripe shape or a grid shape.

[0170] In some embodiments, the negative electrode plate satisfies one or more of the following characteristics:

[0171] Measured by projection along the thickness direction of the negative electrode sheet, a one-dimensional size of at least a portion of the lithium-supplemented residual micro-region is 20 μm to 1000 μm;

[0172] Measured by projection along the thickness direction of the negative electrode sheet, the spacing between at least a portion of the lithium-supplemented residual micro-regions is 20 μm to 1000 μm.

[0173] In some embodiments, the lithium-replenishing residual micro-regions in the first lithium-replenishing residual layer are distributed in stripes; the stripe spacing of the lithium-replenishing residual micro-regions in the first lithium-replenishing residual layer is 20 μm to 2000 μm, and the stripe width is 20 μm to 2000 μm;

[0174] The lithium replenishment residual micro-regions in the second lithium replenishment residual layer are distributed in a grid shape; the grid spacing of the lithium replenishment residual micro-regions in the second lithium replenishment residual layer is 20 μm-2000 μm, and the grid line width is 20 μm-2000 μm.

[0175] In some embodiments, the lithium-replenishing residual micro-regions in the first lithium-replenishing residual layer are distributed in stripes; the stripe spacing of the lithium-replenishing residual micro-regions in the first lithium-replenishing residual layer is 20 μm to 500 μm, and the stripe width is 20 μm to 500 μm;

[0176] The lithium replenishment residual micro-regions in the second lithium replenishment residual layer are distributed in a grid shape; the grid spacing of the lithium replenishment residual micro-regions in the second lithium replenishment residual layer is 20 μm-500 μm, and the grid line width is 20 μm-500 μm.

[0177] By controlling the lithium-replenished residual micro-areas in the negative electrode plate to conform to one or more of the aforementioned sizes and shapes, it is beneficial to provide a more sufficient contact area for the electrolyte to infiltrate the negative electrode plate, which is beneficial to optimizing the ion transfer between the first negative electrode active layer and the second negative electrode active layer, and can also take into account the amount of lithium replenishment. Through the aforementioned multiple effects, it is beneficial to better improve the battery cycle life.

[0178] In some embodiments, the negative electrode plate satisfies one or more of the following characteristics:

[0179] The thickness of the first negative electrode active layer is 50 μm to 120 μm, based on the total thickness in the negative electrode sheet;

[0180] The thickness of the first negative electrode active layer on one side is 25 μm to 60 μm;

[0181] The ratio of the thickness of the first negative electrode active layer to the sum of the thickness of the first negative electrode active layer and the second negative electrode active layer is denoted as f H , satisfying 10%≤f H ≤70%.

[0182] In some embodiments, the negative electrode plate satisfies one or more of the following characteristics:

[0183] The thickness of the first negative electrode active layer on one side is 25 μm to 50 μm;

[0184] The thickness of the first negative electrode active layer is 50 μm to 100 μm, based on the total thickness in the negative electrode sheet;

[0185] 30%≤f H ≤50%.

[0186] By calculating the thickness of the first negative electrode active layer (D1) and the ratio of the thickness of the first negative electrode active layer to the sum of the thicknesses of the first negative electrode active layer and the second negative electrode active layer (f H ) is controlled within the aforementioned range, which is beneficial to better balance the high lithium replenishment amount provided by the first negative electrode active layer and the overall energy density of the negative electrode sheet, and further beneficial to better balance the battery cycle life and energy density.

[0187] In some embodiments, the negative electrode plate satisfies one or more of the following characteristics:

[0188] The compaction density of the second negative electrode active layer is higher than the compaction density of the first negative electrode active layer;

[0189] The powder compaction density of the second negative electrode active layer is higher than the powder compaction density of the first negative electrode active layer.

[0190] By adjusting the compaction density of the second negative electrode active layer to be higher than that of the first negative electrode active layer, the energy density of the lithium-ion secondary battery can be improved. On the other hand, the first negative electrode active initial layer has a lower compaction density, which is beneficial to both prolonging the cycle life and improving the energy density.

[0191] By controlling the powder compaction density of the second negative electrode active layer to be higher than the powder compaction density of the first negative electrode active layer, it is beneficial to give the second negative electrode active layer in the lithium ion secondary battery a higher compaction density.

[0192] In some embodiments, the negative electrode plate satisfies one or more of the following characteristics:

[0193] The compaction density of the second negative electrode active layer is 1.04 g / cm 3 ~1.71g / cm 3 ;

[0194] The overall compaction density of the negative electrode sheet is 1.04 g / cm 3 ~1.62g / cm 3 .

[0195] By controlling the overall compaction density of the negative electrode plate within the aforementioned range, it is beneficial to take into account both battery energy density and higher lithium replenishment efficiency.

[0196] Exemplarily, by adjusting the overall compaction density of the negative electrode sheet within the aforementioned range, it is beneficial to balance battery dynamics and energy density.

[0197] Exemplarily, by adjusting the overall compaction density of the negative electrode sheet within the aforementioned range, it is beneficial to balance improving energy density and extending cycle life.

[0198] By regulating the compaction density of the second negative electrode active layer and / or the compaction density of the powder of the second negative electrode active layer, the comprehensive requirements of extending the cycle life and improving the energy density can be better balanced.

[0199] In some embodiments, the second negative electrode active layer includes a second negative electrode active material; the lithium ion secondary battery further includes a positive electrode sheet, and the positive electrode sheet includes a positive electrode active material;

[0200] The lithium-ion secondary battery meets one or more of the following characteristics:

[0201] The D of the first negative electrode active material v 50 lower than the D of the second negative electrode active material v 50; among them, D v 50 represents the particle size corresponding to when the cumulative volume distribution percentage of the multi-particle mixture reaches 50%;

[0202] The D of the first negative electrode active material v 50: 7μm ~14μm;

[0203] The D of the second negative electrode active material v 50: 8μm ~14μm;

[0204] The porosity of the first negative electrode active layer is higher than the porosity of the second negative electrode active layer;

[0205] The porosity of the first negative electrode active layer is 20% to 45%;

[0206] The porosity of the second negative electrode active layer is 15% to 45%;

[0207] The positive electrode active material includes one or more of a ternary positive electrode material, a modified product of a ternary positive electrode material, lithium iron phosphate, a modified product of lithium iron phosphate, lithium iron manganese phosphate and a modified product of lithium iron manganese phosphate; the modified product includes one or more of a doping element and a coating element.

[0208] In some embodiments, the lithium-ion secondary battery satisfies one or more of the following characteristics:

[0209] The D of the first negative electrode active material v 50: 8μm ~13μm;

[0210] The D of the second negative electrode active material v 50 is 9μm ~13μm;

[0211] The amount or mass proportion of the coated carbon-based material in the non-agglomerated primary particles in the first negative electrode active material is 80% to 100%;

[0212] The positive electrode active material includes carbon-coated lithium iron phosphate, which includes a lithium iron phosphate body and a carbon coating layer located on at least a portion of the surface of the lithium iron phosphate body, and the carbon coating layer includes one or more of soft carbon, hard carbon and amorphous carbon.

[0213] By arranging the negative electrode active material with a smaller particle size in the first negative electrode active layer, it is beneficial to reduce the solid phase diffusion path of the first negative electrode active layer, which is beneficial to optimize the battery dynamics.

[0214] By v 50 is set within the aforementioned range, which is beneficial to reducing the solid phase diffusion path of the first negative electrode active layer, thereby optimizing the battery kinetics.

[0215] By matching the particle sizes of the first negative electrode active material and the second negative electrode active material, it can be achieved that the upper layer in the first negative electrode active layer and the lower layer in the second negative electrode active layer have a low compaction density and have a suitable compaction density difference, which is beneficial to taking into account the battery cycle life, battery dynamics and energy density.

[0216] By controlling the porosity of the first negative electrode active layer to be higher than that of the second negative electrode active layer, the high porosity of the upper layer can provide more channels for lithium ion transmission, which is beneficial to improving battery kinetics.

[0217] By controlling the porosity of the first negative electrode active layer within the aforementioned range, it is beneficial to take both battery kinetics and energy density into account.

[0218] By introducing a coated carbon-based material into the first negative electrode active material located in the upper layer, amorphous carbon is coated on at least a portion of the surface of the carbon base body, which is beneficial to provide a better lithium ion transmission channel for the carbon base body, thereby promoting lithium ion transmission and improving lithium replenishment efficiency, and further beneficial to improving battery dynamics and cycle life.

[0219] In some embodiments, the first negative electrode active material satisfies one or more of the following characteristics:

[0220] The coated carbon-based material in the non-agglomerated primary particles includes non-agglomerated coated graphite; the non-agglomerated coated graphite accounts for 80% to 100% in number or mass in the first negative electrode active material;

[0221] The amount or mass proportion of the coated carbon-based material in the first negative electrode active material is 80% to 100%.

[0222] By introducing non-agglomerated coated graphite into the first negative electrode active material located in the upper layer, it is beneficial to expose more lithium insertion sites, and the carbon coating layer can also be used to promote faster and more lithium ion insertion, which is beneficial to improve the lithium replenishment efficiency.

[0223] In some embodiments, the lithium ion secondary battery further includes a positive electrode plate, and the NP ratio of the lithium ion secondary battery is 1.03-1.2, and can be optionally 1.05-1.2, and the NP ratio of the lithium ion secondary battery is equal to the ratio of the negative electrode surface capacity to the positive electrode surface capacity.

[0224] In some embodiments, the NP ratio of the lithium ion secondary battery is 1.1 to 1.2.

[0225] By controlling the NP ratio of the lithium-ion secondary battery within the aforementioned range, it is beneficial for the negative electrode to store more lithium ions, which is convenient for continuously releasing the supplementary capacity in the later stages of cycling or storage, and can better extend the battery cycle life.

[0226] In some embodiments, the lithium ion secondary battery is prepared by the method for preparing a lithium ion secondary battery described in the third aspect of the present application.

[0227] In a fifth aspect of the present application, an electrical device is provided, which includes the lithium-ion secondary battery described in the fourth aspect of the present application.

[0228] The details of one or more implementations or embodiments of the present application are set forth in the following drawings and description. Other features, objects and advantages of the present application will become apparent from the description, drawings and claims. BRIEF DESCRIPTION OF THE DRAWINGS

[0229] In order to better describe and illustrate the implementation methods, embodiments or examples provided in this application, reference may be made to one or more drawings. The additional details or examples used to describe the drawings should not be considered as limitations on the scope of the disclosed application, the implementation methods, embodiments or examples currently described, and any of the best modes of these applications currently understood. Moreover, in all the drawings, the same figure numbers are used to represent the same components. It should also be noted that the drawings are all drawn in a simplified form and are only used to facilitate and clearly assist in explaining this application. The various sizes of each component shown in the drawings are arbitrarily shown and may be accurate or may not be drawn according to the actual scale. For example, in order to make the illustration clearer, the size of the components is appropriately exaggerated in some places in the drawings. Unless otherwise specified, the components in the figures are not drawn to scale. This application does not limit every size of each component.

[0230] In the attached picture:

[0231] Figure 1 1 is a schematic diagram of the structure of a lithium-supplemented negative electrode sheet in an embodiment of the present application, and corresponds to a side view showing a cross section of the lithium-supplemented negative electrode sheet.

[0232] Figure 2 yes Figure 1 A schematic diagram of the structure of the lithium-supplemented negative electrode sheet, corresponding to the top view, shows the surface of one side of the lithium-supplemented negative electrode sheet where the lithium-supplemented layer is provided.

[0233] Figure 3 It is a schematic diagram of the structure of a lithium-supplemented negative electrode sheet in another embodiment of the present application, and corresponds to a top view, showing a surface of one side of the lithium-supplemented negative electrode sheet on which a lithium-supplemented layer is provided.

[0234] Figure 4 It is a schematic diagram of the structure of a lithium-supplemented negative electrode sheet in another embodiment of the present application, and corresponds to a top view, showing a surface of one side of the lithium-supplemented negative electrode sheet on which a lithium-supplemented layer is provided.

[0235] Figure 5 It is a schematic diagram of a battery cell according to an embodiment of the present application.

[0236] Figure 6 for Figure 5 An exploded view of a battery cell according to an embodiment of the present application is shown.

[0237] Figure 7 FIG. 1 is a schematic diagram of a battery device according to an embodiment of the present application.

[0238] Figure 8 A schematic diagram of a battery pack according to an embodiment of the present application.

[0239] Fig. 9 for Figure 8 An exploded view of a battery pack according to an embodiment of the present application is shown.

[0240] Fig.10 A schematic diagram of an electrical device using a lithium-ion secondary battery according to an embodiment of the present application as a power source.

[0241] Description of reference numerals:

[0242] X is the X direction; Y is the Y direction; Z is the Z direction; 12, lithium supplement negative electrode sheet; 102, negative electrode current collector; 104, second negative electrode active initial layer; 106, first negative electrode active initial layer; 108, first lithium supplement layer; 110, second lithium supplement layer; 1, battery pack; 2, upper box; 3, lower box; 4, battery device; 5, battery cell; 51, shell; 52, electrode assembly; 53, cover plate; 6, power-consuming device.

[0243] Among them, the X direction corresponds to the width direction of the pole piece (which can be consistent with the height direction of the wound battery cell), the Y direction corresponds to the length direction of the pole piece, and the Z direction corresponds to the thickness direction of the pole piece. DETAILED DESCRIPTION

[0244] Below, some embodiments and examples of the lithium-ion secondary battery of the present application, the components for preparing the same, the preparation method, the lithium-supplementing negative electrode sheet and the electrical device are described in detail with appropriate reference to the drawings. However, there are cases where unnecessary detailed descriptions are omitted. For example, there are cases where detailed descriptions of well-known matters and repeated descriptions of actually the same structure are omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate the understanding of those skilled in the art. In addition, the drawings and the following descriptions are provided for those skilled in the art to fully understand the present application and are not intended to limit the subject matter described in the claims.

[0245] "Scope" disclosed in the present application can be limited in the form of lower limit and upper limit, and a given range is limited by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundary of a special range. The scope limited in this way can be including end values ​​or excluding end values, and any end value can be included or not included independently, and can be combined arbitrarily, that is, any lower limit can be combined with any upper limit to form a scope. For example, if the scope of 60-120 and 80-110 is listed for a specific parameter, it is understood that the scope of 60-110 and 80-120 is also expected. In addition, if the minimum range values ​​1 and 2 are listed, and if the maximum range values ​​3, 4 and 5 are also listed, the following scope can be all expected: 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5. In the present application, unless otherwise specified, the numerical range "ab" represents the abbreviation of any real number combination between a and b, wherein a and b are real numbers. For example, the numerical range "0-5" means that all real numbers between "0-5" are listed in this document, and "0-5" is just an abbreviation for these numerical combinations. In addition, when a parameter is expressed as an integer ≥ 2, it is equivalent to listing the parameter as, for example, integers 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc. For example, when a parameter is expressed as an integer selected from "2-10", it is equivalent to listing the integers 2, 3, 4, 5, 6, 7, 8, 9 and 10.

[0246] In this application, when "multiple", "multiple", "multiple", "several", etc. are involved, unless otherwise specified, it means that the number is greater than 2 or equal to 2. For example, "one or more" means one or ≥ (greater than or equal to) two. It is understood that when "any number" of items are involved, it means any suitable combination of multiple items, that is, the combination of "any number" of items is performed in a way that does not conflict and can implement this application.

[0247] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0248] Reference to "embodiments" herein means that a particular feature, structure, or characteristic described in conjunction with the embodiments may be included in at least one embodiment or implementation of the present application. The appearance of the phrase in various locations in the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment that is mutually exclusive with other embodiments. It is explicitly and implicitly understood by those skilled in the art that the embodiments described herein may be combined with other embodiments. The "implementation methods" mentioned herein have a similar understanding.

[0249] In the present application, in the open technical features or technical solutions described by the words "contain", "include", "include", etc., if there is no other explanation, additional members other than the listed members are not excluded, and it can be regarded as providing both closed features or solutions consisting of the listed members and open features or solutions including additional members in addition to the listed members. For example, a includes a1, a2 and a3. If there is no other explanation, it may also include other members or may not include additional members. It can be regarded as providing both the feature or solution of "a consists of a1, a2 and a3" or "a is selected from a1, a2 and a3", and the feature or solution of "a includes not only a1, a2 and a3, but also other members".

[0250] In the present application, unless otherwise specified, M (such as m1) means that m1 is a non-limiting example of M, and it can be understood that M is not limited to m1.

[0251] In this application, "optionally" and "optional" mean optional, that is, any one of the two parallel solutions of "yes" or "no". If there are multiple "optional" in a technical solution, unless otherwise specified and there is no contradiction or mutual restriction, each "optional" is independent. Unless otherwise specified, the descriptions of "optionally including, etc. in this application, taking "optionally including" as an example, means "may include or not include".

[0252] In the present application, unless otherwise specified, the features or solutions corresponding to "and / or" include any one of two or more related listed items, and also include any and all combinations of the related listed items, wherein any and all combinations include any two related listed items, any more related listed items, or a combination of all related listed items. For example, "M and / or N" means a group consisting of M, N, and "a combination of M and N". Among them, "including M and / or N" can mean "including M, including N, and including M and N", and can also mean "including M, including N, or including M and N", which can be properly understood according to the sentence in which it is located.

[0253] Herein, the word “suitable” in “suitable manner” etc. refers to the technical solution that can implement the present application.

[0254] Herein, "better", "preferable" and the like are only used to describe implementation methods or embodiments with better effects, and it should be understood that they do not constitute a limitation on the scope of protection of this application. If there are multiple "preferred" items in a technical solution, unless otherwise specified and there are no contradictions or mutual constraints, each "preferred" item is independent.

[0255] In the present application, “further”, “furthermore”, “particularly”, “for example”, “such as”, “example”, etc. are used for descriptive purposes to indicate differences in content, but should not be understood as limiting the scope of protection of the present application.

[0256] In the present application, the terms "first", "second", "third", "fourth", etc. in "the first aspect", "the second aspect", "the third aspect", "the fourth aspect", etc. are used only for descriptive purposes and cannot be understood as indicating or implying relative importance or quantity, nor can they be understood as implicitly indicating the importance or quantity of the indicated technical features. Moreover, "first", "second", "third", "fourth", etc. only serve the purpose of non-exhaustive enumeration and description, and it should be understood that they do not constitute a closed limitation on quantity.

[0257] In the description of the present application, it should be understood that the terms "length", "width", "thickness", "height", "up", "down", "top", "bottom", "inside", "outside", etc., indicating orientation or positional relationships, are based on the orientation or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as a limitation on the present application.

[0258] In this application, unless otherwise clearly specified and limited, the term "connection" and other terms should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection. For ordinary technicians in this field, the appropriate meanings of the above terms in this application can be understood according to the circumstances.

[0259] In the present application, unless otherwise clearly specified and limited, a first feature being "above" or "below" a second feature may mean that the first and second features are in direct contact, or the first and second features are in indirect contact through an intermediate medium. In the present application, unless otherwise clearly specified and limited, a first feature being "above" or "below" a second feature may mean a relative positional relationship in terms of horizontal height, or may mean that there is an attachment relationship without limiting the relative positional relationship in terms of horizontal height.

[0260] In this application, the term "room temperature" generally refers to 4°C to 35°C, and may refer to 20°C ± 5°C. In some embodiments or examples of this application, room temperature refers to 20°C to 30°C.

[0261] In this application, when referring to the unit of a data range, if there is a unit only after the right endpoint, it means that the units of the left endpoint and the right endpoint are the same. For example, 3~5 μm or 3-5 μm both mean that the units of the left endpoint "3" and the right endpoint "5" are both μm (micrometers), which have the same meaning as 3 μm ~5 μm. In addition, similar descriptions of other parameters such as temperature and size are also understood in the same way.

[0262] In this application, "greater than or equal to" and "≥" have the same meaning and can be used interchangeably; "less than or equal to" and "≤" have the same meaning and can be used interchangeably; "greater than" can be equivalently expressed as ">", and "less than" can be equivalently expressed as "<". In this application, unless otherwise specified, "greater than or equal to" and "≥" can be regarded as providing two solutions of "greater than" and "equal to". In this application, unless otherwise specified, "less than or equal to" and "≤" can be regarded as providing two solutions of "less than" and "equal to".

[0263] In the present application, exemplary descriptions such as "in some implementation modes (or examples)" and "in one implementation mode (or example)" may include but are not limited to the following meanings: these solutions may be combined with other solutions in a suitable manner to form a new technical solution.

[0264] The improved effects described in this application, unless otherwise stated, are not intended to be limited to any theory.

[0265] At present, the demand for the cycle life of lithium-ion secondary batteries is getting higher and higher. The lithium replenishment technology can be used to extend the battery cycle life. As a non-limiting example, in the process of preparing the negative electrode plate, a lithium replenishment layer containing a lithium replenishment material can be provided on the surface of the negative electrode active material layer, and the active lithium ions released by the lithium replenishment material are embedded in the negative electrode active material after being infiltrated with the electrolyte, so as to replenish the negative electrode lithium. The lithium stored in the negative electrode can play a role in supplementing the capacity, thereby extending the battery cycle life. However, the distribution of active lithium along the different thickness positions of the negative electrode plate is not uniform enough, especially the lithium replenishment effect at the position far away from the lithium replenishment layer is not ideal. When the negative electrode plate is provided with a negative electrode active material layer having an upper and lower layer structure, and the compaction density of the lower layer is higher, it is easy to further deteriorate the lithium replenishment effect of the lower layer.

[0266] According to various embodiments and examples of the present application, the present application provides a lithium ion secondary battery, a component for preparing the same, a preparation method, a lithium supplemented negative electrode sheet and an electric device. The lithium ion secondary battery involved has a significantly improved cycle life.

[0267] In some embodiments, the components for preparing a lithium-ion secondary battery include a lithium-supplemented negative electrode sheet; the lithium-supplemented negative electrode sheet includes a negative electrode current collector and a second negative electrode active initial layer, a second lithium-supplemented layer, a first negative electrode active initial layer and a first lithium-supplemented layer sequentially disposed on at least one side of the negative electrode current collector. The prepared lithium-ion secondary battery has a significantly improved cycle life.

[0268] In this application, unless otherwise specified, the term "lithium-ion secondary battery" refers to a secondary battery whose active ions include lithium ions, and "lithium-ion battery cell" refers to a battery cell whose active ions include lithium ions. Typically, a lithium-ion secondary battery includes a positive electrode sheet, a negative electrode sheet, an electrolyte, and a separator. During the battery charge and discharge process, the active ions are embedded and removed back and forth between the positive electrode sheet and the negative electrode sheet. The electrolyte plays the role of conducting ions between the positive electrode sheet and the negative electrode sheet. The separator is arranged between the positive electrode sheet and the negative electrode sheet, mainly to prevent the positive and negative electrodes from short-circuiting, while allowing ions to pass through. In some embodiments, the active ions are lithium ions.

[0269] In the present application, unless otherwise specified, the "electrode active material layer" includes at least one of the positive electrode active material layer of the positive electrode sheet and the negative electrode active material layer of the negative electrode sheet. Depending on the detailed circumstances, the electrode active material layer may refer to the positive electrode active material layer or the negative electrode active material layer.

[0270] In the present application, the term "negative electrode sheet" includes a negative electrode active material layer, and the negative electrode active material layer includes a negative electrode active material. The term "negative electrode active material" refers to a material used in a negative electrode sheet that can reversibly insert and remove active ions.

[0271] In this application, unless otherwise specified, "negative electrode sheet" includes a negative electrode current collector. "Negative electrode current collector" refers to a structure responsible for collecting and conducting electrons at the negative electrode. In the negative electrode sheet, the negative electrode active material layer is located on at least one side of the negative electrode current collector, which can be one side or both sides of the negative electrode current collector.

[0272] In the present application, the term "positive electrode sheet" includes a positive electrode active material layer, and the positive electrode active material layer includes a positive electrode active material. The term "positive electrode active material" refers to a material used in a positive electrode sheet that is capable of reversibly extracting and inserting active ions.

[0273] In this application, unless otherwise specified, "positive electrode sheet" includes positive electrode current collector. "Positive electrode current collector" refers to the structure responsible for collecting and conducting electrons at the positive electrode. In the positive electrode sheet, the positive electrode active material layer is located on at least one side of the positive electrode current collector, which can be one side or both sides of the positive electrode current collector.

[0274] In the present application, unless otherwise specified, "separation membrane" and "diaphragm" have the same meaning and can be used interchangeably.

[0275] In some embodiments of the first aspect of the present application, a component for preparing a lithium-ion secondary battery is provided, which includes a lithium-supplemented negative electrode sheet; the lithium-supplemented negative electrode sheet includes a negative electrode current collector and a second negative electrode active initial layer, a second lithium-supplemented layer, a first negative electrode active initial layer and a first lithium-supplemented layer sequentially arranged on at least one side of the negative electrode current collector;

[0276] Furthermore, the first negative electrode active initial layer includes a first negative electrode active material, the first negative electrode active material includes non-agglomerated primary particles, and the number ratio or mass ratio of the non-agglomerated primary particles in the first negative electrode active material may be 80% to 100%;

[0277] The non-agglomerated primary particles include coated carbon-based materials, which include a carbon base body and a carbon coating layer located on at least a portion of the surface of the carbon base body. The carbon base body includes graphite, and the carbon coating layer includes one or more of amorphous carbon, soft carbon and hard carbon.

[0278] In the present application, unless otherwise specified, "components for preparing lithium-ion secondary batteries" may include assembled electrode assemblies and electrolytes, or may include positive electrode sheets, lithium-supplementing negative electrode sheets and separators for assembling electrode assemblies, wherein the positive electrode sheets and negative electrode sheets are separated by separators. The assembly may be in a state before the electrolyte is injected, in which case the electrode assembly and the electrolyte are placed separately. The assembly may also be in a state before the electrolyte has been injected but before it is fully wetted. In the assembly for preparing lithium-ion secondary batteries, the negative electrode lithium-supplementing material in the lithium-supplementing layer has not been consumed or has only been partially consumed.

[0279] In the present application, the lithium supplement negative electrode sheet includes a negative electrode active initial layer and a lithium supplement layer, the negative electrode active initial layer includes a second negative electrode active initial layer and a first negative electrode active initial layer, and the lithium supplement layer includes a second lithium supplement layer and a first lithium supplement layer. Further, the second negative electrode active initial layer, the second lithium supplement layer, the first negative electrode active initial layer and the first lithium supplement layer are sequentially arranged in a direction away from the negative electrode current collector.

[0280] In the present application, unless otherwise specified, the "first negative electrode active initial layer" corresponds to the intermediate state of preparing the first negative electrode active layer, and the "second negative electrode active initial layer" corresponds to the intermediate state of preparing the second negative electrode active layer. It can be understood that the first negative electrode active initial layer and the second negative electrode active initial layer each independently include negative electrode active materials. The first negative electrode active initial layer and the second negative electrode active initial layer may be in a state without pre-embedded lithium.

[0281] In this application, unless otherwise specified, the "first lithium replenishing layer" and the "second lithium replenishing layer" are each independently a structural layer including a lithium replenishing material. The lithium replenishing material disposed in any lithium replenishing layer of the lithium replenishing negative electrode sheet may also be referred to as a negative electrode lithium replenishing material.

[0282] In the present application, unless otherwise specified, the "lithium-supplemented negative electrode sheet" referred to in the present application corresponds to a state in which the first lithium-supplemented layer and the second lithium-supplemented layer are introduced but the corresponding negative electrode active material layer has not yet been intercalated with lithium. After the lithium-supplemented negative electrode sheet is intercalated with lithium, the negative electrode lithium-supplemented materials in the first lithium-supplemented layer and the second lithium-supplemented layer are consumed, releasing active lithium, and the released active lithium is embedded in the negative electrode active initial layer to achieve intercalation with lithium, and the lithium-supplemented negative electrode sheet is converted into a negative electrode sheet, and the second negative electrode active initial layer and the first negative electrode active initial layer are respectively converted into the second negative electrode active layer and the first negative electrode active layer. It can be understood that the second negative electrode active layer and the first negative electrode active layer each independently include lithium pre-embedded by negative electrode lithium-supplementation. The location of the consumed lithium replenishment layer usually produces residues produced as the lithium replenishment proceeds. Non-limiting examples of the residues include lithium that has been deactivated because it has no time to be embedded in the negative electrode active material. In this way, a lithium replenishment residual layer including inactive lithium is formed at the location of the lithium replenishment layer; accordingly, the lithium replenishment residual layer formed at the location of the first lithium replenishment layer is called the first lithium replenishment residual layer, and the lithium replenishment residual layer formed at the location of the second lithium replenishment layer is called the second lithium replenishment residual layer.

[0283] In the present application, unless otherwise specified, the negative electrode active material in the first negative electrode active initial layer and the first negative electrode active layer is referred to as the “first negative electrode active material”; the negative electrode active material in the second negative electrode active initial layer and the second negative electrode active layer is referred to as the “second negative electrode active material”.

[0284] In the context of the present application, unless otherwise specified, the "first" and "second" in "first negative electrode active initial layer", "second negative electrode active initial layer", "first negative electrode active layer", "second negative electrode active layer", "first negative electrode active material", "second negative electrode active material", "first lithium replenishment layer", "second lithium replenishment layer", "first lithium replenishment residual layer" and "second lithium replenishment residual layer" are used for descriptive purposes only and cannot be understood as indicating or implying relative importance or quantity, nor can they be understood as implicitly indicating the importance or quantity of the indicated technical features.

[0285] The first negative electrode active initial layer located at the upper layer and the second negative electrode active initial layer located at the lower layer are arranged in the negative electrode active layer of the lithium supplemented negative electrode sheet (the direction away from the negative electrode current collector surface is the upper layer, and the direction toward the negative electrode current collector surface is the lower layer), and further, not only a lithium supplement layer (referred to as the first lithium supplement layer) is arranged on the surface of the first negative electrode active initial layer away from the negative electrode current collector, but also a lithium supplement layer (referred to as the second lithium supplement layer) is arranged between the first negative electrode active initial layer and the second negative electrode active initial layer, and after the component for preparing a lithium ion secondary battery is subjected to infiltration and formation treatment, the first lithium supplement layer The first negative electrode active initial layer and the second negative electrode active initial layer release active lithium, and the released active lithium migrates and is embedded in the negative electrode active material, thereby realizing the lithium insertion treatment, so that the first negative electrode active initial layer and the second negative electrode active initial layer are pre-inserted with lithium respectively, forming the corresponding first negative electrode active layer and the second negative electrode active layer, and at the same time obtaining a lithium ion secondary battery with efficient lithium replenishment of the negative electrode; the component design has a good overall lithium replenishment effect on the negative electrode plate, so that the lithium replenishment effect of the prepared negative electrode plate in the thickness direction is more uniform, and the second negative electrode active initial layer located in the lower layer can also be fully replenished with lithium; on the other hand, the negative electrode plate is On the one hand, the second lithium replenishing layer can pre-embed lithium more evenly and fully, forming a more stable and uniform solid electrolyte interface (SEI) film as a whole; on the other hand, the gas generated in the lithium embedding process of the second lithium replenishing layer can form a path during the discharge process to promote the first lithium replenishing layer to be more fully and evenly infiltrated, so that the first negative electrode active layer located on the upper layer can be better pre-embedded with lithium, and the distribution uniformity of the SEI film in the first negative electrode active layer can be improved; on the other hand, by providing a high content of non-agglomerated primary particles in the first negative electrode active material located on the upper layer, it is beneficial to reduce the embedding of the embeddable surface caused by particle agglomeration, which is beneficial to improve the More lithium insertion sites are provided. Furthermore, by arranging coated carbon-based materials in non-agglomerated primary particles, the carbon coating layer can be used to optimize the lithium ion transmission channel, thereby promoting faster and more lithium ion insertion. Through the aforementioned multiple effects, it is beneficial to store more lithium in the negative electrode, improve the lithium replenishment efficiency, and thus replenish active lithium more sustainably during the charge and discharge cycle. It is also beneficial to enhance the structural stability of the upper and lower negative electrode active materials when they are in contact with the electrolyte, and promote the upper and lower negative electrode active materials to be able to supply capacity more sustainably, thereby giving the lithium ion secondary battery a significantly extended cycle life.

[0286] The effects described in any part of this application are not intended to be limited by any theory.

[0287] In some embodiments, the negative electrode plate is more fully and evenly infiltrated throughout the thickness direction, and is then more evenly and fully pre-embedded with lithium, forming a more stable and uniform solid electrolyte interface (SEI) film as a whole, which is beneficial to improving the charge transfer performance on the surface of the negative electrode active material in the negative electrode plate as a whole; in addition, after the infiltration and formation to achieve lithium insertion treatment, the second lithium replenishment layer is consumed, and a pore channel can be formed between the first negative electrode active layer and the second negative electrode active layer, which is beneficial to electrolyte filling, and can promote the infiltration of the electrolyte into the second negative electrode active layer located at the lower layer, which is beneficial to the formation of a SEI film with better stability, which can reduce the polarization inside the negative electrode plate, and can also take into account the electronic conductivity between the first negative electrode active layer and the second negative electrode active layer in the lithium-ion secondary battery; through the aforementioned multiple effects, it is beneficial to improve the fast charging performance of the battery.

[0288] In the present application, in the lithium-supplemented negative electrode sheet, the second lithium-supplemented layer and the first lithium-supplemented layer each independently include negative electrode lithium-supplemented materials.

[0289] In a non-limiting manner, the second lithium replenishing layer and the first lithium replenishing layer can each independently include one or more of simple lithium and lithium alloys. A non-limiting example of a lithium alloy is a lithium-tin alloy. In some embodiments, the lithium replenishing layer includes simple lithium, and in this case, the negative electrode lithium replenishing material includes simple lithium.

[0290] In some embodiments, the second lithium replenishing layer and the first lithium replenishing layer each independently include single lithium.

[0291] By selecting a lithium replenishing layer including single-substance lithium (a non-limiting example such as a lithium film) as the first lithium replenishing layer and the second lithium replenishing layer, the preparation process is more controllable and the lithium replenishing efficiency is high.

[0292] In this application, the coverage area percentage of the second lithium supplement layer relative to the second negative electrode active initial layer is recorded as f, measured along the thickness direction of the lithium supplement negative electrode sheet and on one side of the negative electrode current collector. M0 The coverage percentage of the first lithium supplement layer relative to the first negative electrode active initial layer is recorded as f U0 The thickness of the second lithium supplement layer on one side is d 02 The thickness of the first lithium supplement layer on one side is d 01 The surface density of the second lithium replenishment layer and the first lithium replenishment layer relative to the first negative electrode active initial layer is respectively denoted as ρ 02 and ρ 01 , where ρ 02 and ρ 01 The total surface density of the second lithium replenishment layer and the first lithium replenishment layer relative to the first negative electrode active initial layer is recorded as C Li , where C Li Measured on the total amount on both sides of the negative electrode current collector.

[0293] In the present application, the lithium-supplemented negative electrode sheet has two surfaces facing away from each other, which are respectively recorded as the first surface and the second surface. The distance between the two surfaces corresponds to the thickness of the lithium-supplemented negative electrode sheet. When the thickness of the lithium-supplemented negative electrode sheet is basically the same at all places, the first surface and the second surface are basically parallel. The "thickness direction of the lithium-supplemented negative electrode sheet" can be recorded as the Z direction. For some embodiments, please refer to Figure 1 .

[0294] In the present application, "measured by projection along the thickness direction of the lithium-supplemented negative electrode sheet" is equivalent to "measured by projection on a plane perpendicular to the Z direction", which may correspond to a projection on the first surface or the second surface, or to a projection on a plane parallel to the first surface or the second surface.

[0295] In this application, unless otherwise specified, “the single-side thickness d of the first lithium supplementation layer” 01 ", ", "The single-side thickness of the second lithium supplement layer d 02 "," the thickness of the first lithium-replenishing residual layer on one side d1," and the thickness of the second lithium-replenishing residual layer on one side d2" all refer to the thickness on one side of the negative electrode current collector.

[0296] In this application, unless otherwise specified, “the total thickness H of the first negative electrode active initial layer on both sides” 01 ", "The total thickness of the second negative electrode active initial layer on both sides H 02 "," the total thickness of the first negative electrode active layer on both sides H1," and "the total thickness of the second negative electrode active layer on both sides H2" all refer to the total thickness on both sides of the negative electrode current collector.

[0297] In this application, f M0 and f U0 All are defined on one side of the negative electrode current collector, f M0 It is equal to the ratio of the actual area of ​​the second lithium supplement layer on one side of the negative electrode current collector to the area of ​​the second negative electrode active initial layer, f U0 is equal to the ratio of the actual area of ​​the first lithium replenishment layer on one side of the negative electrode current collector to the area of ​​the first negative electrode active initial layer. When the second lithium replenishment layer or the first lithium replenishment layer has a hollow area that does not cover the corresponding negative electrode active initial layer, f M0 and f U0 The “actual area” refers to the area of ​​the corresponding negative electrode active initial layer minus the area of ​​the corresponding hollowed-out region.

[0298] In the present application, “on both sides of the negative electrode current collector” and “on both sides of the negative electrode current collector” have the same meaning and can be used interchangeably.

[0299] In this application, it is related to 02 and ρ 01 , C Li 、m L1 and mL2 Both are defined on both sides of the negative electrode current collector.

[0300] With ρ 02 and ρ 01 For example, ρ 02 It refers to the sum of the surface densities of the second lithium supplement layer on both sides of the negative electrode current collector, which can be numerically equal to the total mass of the second lithium supplement layer on both sides of the negative electrode current collector divided by the area of ​​the first negative electrode active initial layer. The “area of ​​the first negative electrode active initial layer” can numerically correspond to the area of ​​the aforementioned first surface or second surface; ρ 01 It refers to the sum of the surface densities of the first lithium replenishing layer on both sides of the negative electrode current collector, which can be numerically equal to the total mass of the first lithium replenishing layer on both sides of the negative electrode current collector divided by the area of ​​the first negative electrode active initial layer.

[0301] m L1 and m L2 For example, m L1 is the total mass of the first lithium supplement layer on both sides of the negative electrode current collector; m L2 is the total mass of the second lithium supplement layer on both sides of the negative electrode current collector.

[0302] C Li For example, "C Li It refers to the total surface density of the second lithium replenishment layer and the first lithium replenishment layer relative to the first negative electrode active initial layer, C Li "Measured on both sides of the negative electrode current collector" means the sum of the total mass of the second lithium supplement layer on both sides of the negative electrode current collector and the total mass of the first lithium supplement layer on both sides of the negative electrode current collector divided by the area of ​​the first negative electrode active initial layer. In some embodiments, the single-side thickness d of the second lithium supplement layer 02 Less than the single-side thickness d of the first lithium replenishment layer 01 .

[0303] In some embodiments, 0 <f M0 ≤f U0 , optionally, 10%≤f M0 ≤f U0 .

[0304] In some embodiments, the single-side thickness d of the second lithium supplementing layer is 02 It can be 0.5 μm to 4 μm, and can be 1 μm to 4 μm. In a non-limiting manner, the single-side thickness d of the second lithium supplementation layer is 02 It can also be any of the following values ​​or a range consisting of any two of the following values: 0.5 μm, 1 μm, 1.5 μm, 2 μm, 2.5 μm, 3 μm, 3.5 μm, 4 μm, etc.

[0305] In some embodiments, 0 <f M0 ≤70%, optionally, 10%≤f M0≤70%. Non-limitingly, the coverage area percentage (f M0 ) can also be any of the following percentages or a range consisting of any two of the following percentages: 10%, 15%, 20%, 25%, 30%, 40%, 50%, 60%, 70%, etc.

[0306] In some embodiments, 0<ρ 02 ≤ρ 01 , optionally, 0<ρ 02 < 01 .

[0307] In some embodiments, 02 0.5mg / 1540.25mm 2 ~6mg / 1540.25mm 2 , optional: 1mg / 1540.25mm 2 ~6mg / 1540.25mm 2 , can also be any of the following values ​​or selected from the range consisting of any two of the following values: 0.5 mg / 1540.25mm 2 , 0.6 mg / 1540.25 mm 2 , 0.7 mg / 1540.25 mm 2 , 0.8 mg / 1540.25 mm 2 、0.9mg / 1540.25mm 2 、1.0 mg / 1540.25mm 2 、1.1 mg / 1540.25mm 2 、1.2 mg / 1540.25mm 2 、1.5 mg / 1540.25mm 2 、1.6 mg / 1540.25mm 2 、1.8 mg / 1540.25mm 2 、2.0 mg / 1540.25mm 2 、2.5 mg / 1540.25mm 2 、3mg / 1540.25mm 2 、3.5 mg / 1540.25mm 2 , 4 mg / 1540.25 mm 2 4.5 mg / 1540.25 mm 2 、5mg / 1540.25mm 2 、5.5 mg / 1540.25mm 2、6mg / 1540.25mm 2 Etc. Without limitation, ρ 02 It can also be any of the following values ​​or a range consisting of any two of the following values: 0.5 mg / 1540.25 mm 2 、1 mg / 1540.25mm 2 , 2mg / 1540.25mm 2 、3mg / 1540.25mm 2 , 4 mg / 1540.25 mm 2 、5mg / 1540.25mm 2 、6mg / 1540.25mm 2 wait.

[0308] In this application, unless otherwise specified, the surface density (ρ 02 ) is defined as a two-sided total, ρ 02 It is numerically equal to the total mass of the second lithium supplement layer on both sides of the negative electrode current collector (equivalent to the total mass of both sides of the second lithium film in the third aspect of the present application) divided by the area of ​​the first negative electrode active initial layer.

[0309] In the present application, unless otherwise specified, the surface density (ρ 01 ) is defined as a two-sided total, ρ 01 It is numerically equal to the total mass of the first lithium supplement layer on both sides of the negative electrode current collector (equivalent to the total mass of both sides of the first lithium film in the third aspect of the present application) divided by the area of ​​the first negative electrode active initial layer.

[0310] In the present application, the total surface density (C Li ) is numerically equal to the total mass of the first lithium replenishing layer and the second lithium replenishing layer on both sides of the negative electrode current collector (equivalent to the total mass of the first lithium film and the second lithium film in the third aspect of the present application) divided by the area of ​​the first negative electrode active initial layer, that is, the total amount on both sides of the negative electrode current collector. In terms of numerical value, C Li Equal to ρ 02 and ρ 01 sum.

[0311] In some embodiments, the lithium-supplemented negative electrode sheet satisfies one or more of the following characteristics (any numerical parameter in the following characteristics can also be selected from any suitable numerical value or range in the context):

[0312] The single-side thickness d of the second lithium supplementation layer 02 Less than the single-side thickness d of the first lithium replenishment layer 01 ;

[0313] The second lithium replenishment layer meets 0 <f M0 ≤f U0 , optionally, 10%≤f M0 ≤f U0 ;

[0314] The single-side thickness d of the second lithium supplementation layer 02 0.5μm~4μm, optional 1μm~4μm;

[0315] The second lithium replenishment layer meets 0 <f M0 ≤70%, optionally, 10%≤f M0 ≤70%;

[0316] The second lithium replenishment layer satisfies 0<ρ 02 ≤ρ 01 , optionally, 0<ρ 02 < 01 ;

[0317] ρ 02 0.5mg / 1540.25mm 2 ~6mg / 1540.25mm 2 , optional: 1mg / 1540.25mm 2 ~6mg / 1540.25mm 2 .

[0318] Without limitation, the single-sided thickness of the first lithium replenishment layer and the second lithium replenishment layer can be measured and analyzed based on the cross-sectional SEM image of the lithium replenishment negative electrode sheet, and can also be measured using a laser thickness gauge. In the present application, the cross-section of the lithium replenishment negative electrode sheet can be subjected to microscopic morphology observation. The microscopic morphology of each negative electrode active initial layer in the lithium replenishment negative electrode sheet and the boundaries between different negative electrode active initial layers can be observed, and then the thickness of different negative electrode active initial layers can be determined. "The cross-section of the lithium replenishment negative electrode sheet" refers to the cross-section perpendicular to the thickness direction of the lithium replenishment negative electrode sheet. Furthermore, the cross-section of the lithium replenishment negative electrode sheet can also be subjected to microscopic morphology observation and combined with component analysis (such as energy dispersion spectrum (EDS), X-ray diffraction (XRD) analysis, etc.) to identify the type of elements to confirm the composition of different negative electrode active initial layers. Non-limitingly, instruments or equipment including but not limited to focused electron beam (FIB) electron microscope (non-limiting examples such as FEI Scios 2HiVac equipment, etc.), ion cross-section polisher (non-limiting examples such as IB-09010 CP argon ion cross-section polisher, IB-19500CP ion cross-section polisher, etc. of JEOL, Japan) can be used to obtain the cross section of the lithium-supplemented negative electrode sheet, and the cross section of the lithium-supplemented negative electrode sheet can also be obtained by plasma quenching method. The microscopic morphology observation method can use instruments or equipment including but not limited to scanning electron microscope (SEM) technology, and non-limitingly, a high-resolution field emission scanning electron microscope can be used; non-limiting examples of SEM instruments are Sigma 300 scanning electron microscope, Apreo 2 SEM field emission scanning electron microscope, etc. of ZEISS, Germany. In the SEM microscopic morphology image of the cross section of the lithium-supplemented negative electrode sheet, the boundaries between different negative electrode active initial layers and the thickness of each negative electrode active initial layer can be confirmed according to the obvious discontinuous changes in the microscopic morphology. In the present application, unless otherwise specified, the “cross section of the lithium-supplemented negative electrode sheet” refers to the cross section of the lithium-supplemented negative electrode sheet.

[0319] The shape and size of the first lithium replenishment layer in the lithium replenishment negative electrode sheet (such as stripe spacing, grid spacing, etc.) can be measured using a ruler or CCD (inductively coupled device). In addition, the first negative electrode active initial layer and the first lithium replenishment layer above it can be peeled off from the lithium replenishment negative electrode sheet, and SEM combined with EDS testing can be performed. Based on the element difference between the covered area and the uncovered area of ​​the second lithium replenishment layer, the morphology and size of the second lithium replenishment layer above the second negative electrode active initial layer can be observed and measured using CCD, and the coverage area percentage (f M0 ). It can be combined with the grid method to measure and analyze the area percentage.

[0320] After the components used to prepare lithium-ion secondary batteries are infiltrated and formed to achieve lithium insertion treatment, the active lithium released by the second lithium replenishment layer is embedded into the negative electrode active layer of the negative electrode plate along with the transmission of the electrolyte, which can achieve a good lithium replenishment effect on the second negative electrode active initial layer; at the same time, the active lithium released by the second lithium replenishment layer may be inactivated before being embedded in the negative electrode active material, thereby, a lithium replenishment residual layer including inactive lithium may be formed at the position of the second lithium replenishment layer (referred to as the second lithium replenishment residual layer). On this basis, by controlling the second lithium replenishment layer to meet one or more of the aforementioned characteristics, it is helpful to reduce or avoid the obstruction of the second lithium replenishment residual layer to the ion transmission between the first negative electrode active layer and the second negative electrode active layer; at the same time, the passage formed when the gas generated by the second lithium replenishment layer is discharged during the lithium insertion process can be utilized, so that the first negative electrode active layer located on the upper layer and the second negative electrode active layer located on the lower layer can be better infiltrated and pre-inserted with lithium, thereby improving the uniformity of lithium insertion and forming a better SEI film, thereby better playing the role of the pre-inserted lithium in the first negative electrode active layer and the second negative electrode active layer in supplementing capacity; the ion transmission between the first negative electrode active layer and the second negative electrode active layer and the wetting effect of the electrolyte in the first and second negative electrode active layers can be taken into account, which is conducive to better improving the cycle life of the battery.

[0321] In some embodiments, by controlling the single-side thickness (d 02 ), the coverage area percentage of the second lithium replenishing layer relative to the second negative electrode active initial layer (f M0 , calculated on one side of the negative electrode current collector) and the surface density of the second lithium supplement layer relative to the first negative electrode active initial layer (ρ 02 , measured on both sides of the negative electrode current collector) is within the aforementioned range, the gas generated during the lithium insertion process is conducive to being discharged more evenly and fully, forming a better and more evenly distributed gas passage, which is conducive to improving the lithium insertion uniformity of the first negative electrode active layer, improving the uniformity of the negative electrode interface in the first negative electrode active layer, and promoting the second negative electrode active layer to be better infiltrated and form a SEI film, thereby better improving the cycle life of the battery.

[0322] In some embodiments, by reducing or avoiding the second lithium supplement residual layer's hindrance to ion transport between the first negative electrode active layer and the second negative electrode active layer, the battery can achieve better dynamics and provide better fast charging performance.

[0323] In some embodiments, the lithium-supplemented negative electrode sheet satisfies one or more of the following characteristics (any numerical parameter in the following characteristics can also be selected from any suitable numerical value or range in the context):

[0324] The single-side thickness d of the second lithium supplementation layer 02 1μm~4μm;

[0325] The second lithium replenishment layer meets 10%≤f M0 ≤f U0 ;

[0326] The second lithium replenishment layer meets 10%≤f M0 ≤70%;

[0327] ρ 02 1mg / 1540.25mm 2 ~6mg / 1540.25mm 2 .

[0328] By controlling the single-side thickness of the second lithium replenishment layer (d 02 ), the coverage area percentage of the second lithium replenishing layer relative to the second negative electrode active initial layer (f M0 , calculated on one side of the negative electrode current collector) and the surface density of the second lithium supplement layer relative to the first negative electrode active initial layer (ρ 02 , measured on both sides of the negative electrode current collector) within the aforementioned range is beneficial to taking into account the ion transport between the first negative electrode active layer and the second negative electrode active layer, the wetting effect of the electrolyte in the first and second negative electrode active layers, and the amount of lithium supplement supplied by the second negative electrode active layer, which is beneficial to better improve the cycle life of the battery.

[0329] In some embodiments, the single-side thickness d of the first lithium replenishing layer is 01 Less than or equal to 8 μm, can be 0.5 μm to 8 μm, can be 2 μm to 8 μm, can be 2 μm to 6 μm, can be 2 μm to 5 μm. In a non-limiting manner, the single-side thickness d of the first lithium supplementation layer is 01 It can also be any of the following values ​​or a range consisting of any two of the following values: 0.5μm, 1μm, 1.5μm, 2μm, 2.5μm, 3μm, 3.5μm, 4μm, 4.5μm, 5μm, 6μm, 7μm, 8μm, etc.

[0330] In some embodiments, the coverage area percentage (f U0 ) satisfies 0 <f U0 ≤70%, optionally, 30% <f U0 ≤70%. Without limitation, f U0 It can also be any of the following percentages or a range consisting of any two of the following percentages: 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, etc.

[0331] In some embodiments, 01 0.5mg / 1540.25mm2 ~6mg / 1540.25mm 2 , optional: 2mg / 1540.25mm 2 ~6mg / 1540.25mm 2 , can also be any of the following values ​​or selected from the range consisting of any two of the following values: 0.5 mg / 1540.25mm 2 , 0.6 mg / 1540.25 mm 2 , 0.7 mg / 1540.25 mm 2 , 0.8 mg / 1540.25 mm 2 、0.9mg / 1540.25mm 2 、1.0 mg / 1540.25mm 2 、1.1 mg / 1540.25mm 2 、1.2 mg / 1540.25mm 2 、1.5 mg / 1540.25mm 2 、1.6 mg / 1540.25mm 2 、1.8 mg / 1540.25mm 2 、2.0 mg / 1540.25mm 2 、2.5 mg / 1540.25mm 2 、3mg / 1540.25mm 2 、3.5 mg / 1540.25mm 2 , 4 mg / 1540.25 mm 2 4.5 mg / 1540.25 mm 2 、5mg / 1540.25mm 2 、5.5 mg / 1540.25mm 2 、6mg / 1540.25mm 2 Etc. Without limitation, ρ 01 It can also be any of the following values ​​or a range consisting of any two of the following values: 0.5 mg / 1540.25 mm 2 、1 mg / 1540.25mm 2 , 2mg / 1540.25mm 2 、3mg / 1540.25mm 2 , 4 mg / 1540.25 mm 2 、5mg / 1540.25mm 2 、6mg / 1540.25mm 2 wait.

[0332] In some embodiments, CLi 0.5mg / 1540.25mm 2 ~12mg / 1540.25mm 2 , can be selected as greater than 0.5mg / 1540.25mm 2 And less than or equal to 12mg / 1540.25mm 2 , further optional 1mg / 1540.25mm 2 ~12mg / 1540.25mm 2 , further optional 3mg / 1540.25mm 2 ~12mg / 1540.25mm 2 Without limitation, C Li It can be any of the following values ​​or a range consisting of any two of the following values: 0.5 mg / 1540.25 mm 2 , 0.6 mg / 1540.25 mm 2 , 0.7 mg / 1540.25 mm 2 , 0.8 mg / 1540.25 mm 2 , 0.9 mg / 1540.25 mm 2 、1.0 mg / 1540.25mm 2 、1.1 mg / 1540.25mm 2 、1.2 mg / 1540.25mm 2 、1.5 mg / 1540.25mm 2 、1.6 mg / 1540.25mm 2 、1.8 mg / 1540.25mm 2 、2.0 mg / 1540.25mm 2 、2.5 mg / 1540.25mm 2 、3mg / 1540.25mm 2 、3.5 mg / 1540.25mm 2 , 4 mg / 1540.25 mm 2 4.5 mg / 1540.25 mm 2 、5mg / 1540.25mm 2 、5.5 mg / 1540.25mm 2 、6mg / 1540.25mm 2 、7mg / 1540.25mm 2 、8mg / 1540.25mm 2 、9mg / 1540.25mm 2 、10mg / 1540.25mm2 、11 mg / 1540.25mm 2 、12mg / 1540.25mm 2 Etc. Without limitation, C Li It can also be any of the following values ​​or a range consisting of any two of the following values: 0.5 mg / 1540.25 mm 2 、1mg / 1540.25mm 2 , 2 mg / 1540.25 mm 2 、3mg / 1540.25mm 2 、3.5 mg / 1540.25mm 2 , 4 mg / 1540.25 mm 2 、5mg / 1540.25mm 2 、6mg / 1540.25mm 2 、8mg / 1540.25mm 2 、10mg / 1540.25mm 2 、11.5 mg / 1540.25 mm 2 、12mg / 1540.25mm 2 wait.

[0333] In some embodiments, the lithium-supplemented negative electrode sheet satisfies one or more of the following characteristics (any numerical parameter in the following characteristics can also be selected from any suitable numerical value or range in the context):

[0334] The single-side thickness d of the first lithium supplementation layer 01 Less than or equal to 8 μm, optionally 0.5 μm to 8 μm, further optionally 2 μm to 8 μm, further optionally 2 μm to 6 μm, further optionally 2 μm to 5 μm;

[0335] The first lithium replenishment layer meets 0 <f U0 ≤70%, optionally, 30% <f U0 ≤70%;

[0336] ρ 01 0.5mg / 1540.25mm 2 ~6mg / 1540.25mm 2 , optional: 2mg / 1540.25mm 2 ~6mg / 1540.25mm 2 ;

[0337] C Li 0.5mg / 1540.25mm 2 ~12mg / 1540.25mm 2, can be selected as greater than 0.5mg / 1540.25mm 2 And less than or equal to 12mg / 1540.25mm 2 , further optional 1mg / 1540.25mm 2 ~12mg / 1540.25mm 2 , further optional 3mg / 1540.25mm 2 ~12mg / 1540.25mm 2 .

[0338] By controlling the single-side thickness of the first lithium replenishment layer (d 01 ) and the surface density of the first lithium replenishment layer relative to the first negative electrode active initial layer (ρ 01 , measured on both sides of the negative electrode current collector) is within the aforementioned range, while the first lithium replenishing layer is used to provide pre-embedded lithium, the active lithium provided by the first lithium replenishing layer can be fully embedded in the negative electrode, and the length of the lithium embedding path can be taken into account, which is conducive to better controlling the gas production, so that the active lithium provided by the first lithium replenishing layer is more evenly embedded in the negative electrode, which is conducive to forming a SEI film with better stability, and is conducive to reducing or avoiding lithium plating on the surface of the negative electrode active material caused by uneven lithium embedding, and reducing or avoiding the deterioration of the battery cycle life due to surface lithium plating.

[0339] By controlling the coverage area percentage of the first lithium replenishing layer relative to the first negative electrode active initial layer (f U0 , measured on one side of the negative electrode current collector), the surface density of the first lithium supplement layer relative to the first negative electrode active initial layer (ρ 01 , measured on both sides of the negative electrode current collector) is within the aforementioned range, while utilizing the first lithium replenishing layer to provide pre-intercalated lithium, it is also beneficial for the electrolyte to better infiltrate the first negative electrode active layer, and is beneficial for providing more sufficient exhaust channels for the gas generated during the lithium insertion process, and the exhaust channels can further improve the infiltration of the electrolyte into the first negative electrode active layer, thereby being beneficial for achieving better and more sufficient negative electrode lithium replenishment and better improving the battery cycle life.

[0340] In some embodiments, by providing more sufficient exhaust channels for the gas generated during the lithium insertion process, the electrolyte is better promoted to infiltrate the negative electrode, which is beneficial for the battery to achieve better dynamics and provide better fast charging performance.

[0341] On the basis of introducing the second lithium replenishment layer, the total surface density (C Li ) Within the aforementioned range, the cycle life of the battery can be better improved.

[0342] In some embodiments, the lithium-supplemented negative electrode sheet satisfies one or more of the following characteristics (any numerical parameter in the following characteristics can also be selected from any suitable numerical value or range in the context):

[0343] The single-side thickness d of the first lithium supplementation layer 01 2μm~5μm;

[0344] The first lithium replenishment layer meets 30%≤f U0 ≤70%;

[0345] ρ 01 2mg / 1540.25mm 2 ~6mg / 1540.25mm 2 ;

[0346] C Li 3mg / 1540.25mm 2 ~12mg / 1540.25mm 2 .

[0347] By controlling the single-side thickness of the first lithium replenishment layer (d 01 ), the surface density of the first lithium supplement layer relative to the first negative electrode active initial layer (ρ 01 When one or two of the parameters (measured on the total amount on both sides of the negative electrode current collector) are within the aforementioned range, the battery cycle life may be better reduced or avoided from being deteriorated due to surface lithium deposition; in addition, it is also more conducive to making the processing technology of the first lithium replenishing layer easier to implement.

[0348] By controlling the coverage area percentage of the first lithium replenishing layer relative to the first negative electrode active initial layer (f U0 , measured on one side of the negative electrode current collector), the surface density of the first lithium supplement layer relative to the first negative electrode active initial layer (ρ 01 , measured on both sides of the negative electrode current collector) is within the aforementioned range, while utilizing the first lithium replenishment layer to provide pre-embedded lithium, the gas production can be better controlled, and the infiltration of the electrolyte into the first negative electrode active layer can be better improved, thereby achieving better and more sufficient negative electrode lithium replenishment, and taking into account the amount of lithium replenishment supplied by the first lithium replenishment layer, which is beneficial to better improve the battery cycle life.

[0349] In some embodiments, the second lithium replenishing layer and the first lithium replenishing layer each independently include a plurality of lithium replenishing micro-domains.

[0350] Taking the first lithium replenishment layer as an example, according to the projection along the thickness direction of the lithium replenishment negative electrode sheet, there are blank areas on the surface of the first negative electrode active initial layer that are not covered by the first lithium replenishment layer. These blank areas isolate at least the first lithium replenishment layer into a number of lithium replenishment micro-regions. There is a certain distance between the isolated lithium replenishment micro-regions. The minimum width of the lithium replenishment micro-region located between two blank areas can correspond to the "one-dimensional size" of the lithium replenishment micro-region. Taking the lithium replenishment micro-region in stripe shape as an example, the one-dimensional size of the lithium replenishment micro-region can correspond to the width of the lithium replenishment stripe. Taking the lithium replenishment micro-region in grid shape as an example, the one-dimensional size of the lithium replenishment micro-region can correspond to the width of the grid line in the lithium replenishment grid.

[0351] In some embodiments, the one-dimensional size of at least a portion of the lithium-supplementing micro-regions can be 20 μm to 2000 μm, or can be 20 μm to 1000 μm, as measured by the projection along the thickness direction of the lithium-supplementing negative electrode sheet. Without limitation, the one-dimensional size of at least a portion of the lithium-supplementing micro-regions can also be any of the following values ​​or a range selected from any two of the following values, as measured by the projection along the thickness direction of the lithium-supplementing negative electrode sheet: 20 μm, 40 μm, 50 μm, 60 μm, 80 μm, 100 μm, 150 μm, 200 μm, 300 μm, 400 μm, 500 μm, 600 μm, 800 μm, 1000 μm, 1200 μm, 1500 μm, 1600 μm, 1800 μm, 2000 μm, etc.

[0352] In some embodiments, measured along the projection of the thickness direction of the lithium-supplemented negative electrode sheet, the spacing between at least a portion of the lithium-supplemented micro-regions is 20μm~2000μm, and can be optionally 20μm~1000μm, or can be any of the following values ​​or a range consisting of any two of the following values: 20μm, 40μm, 50μm, 60μm, 80μm, 100μm, 150μm, 200μm, 300μm, 400μm, 500μm, 600μm, 800μm, 1000μm, 1200μm, 1500μm, 1600μm, 1800μm, 2000μm, etc.

[0353] In some embodiments, the lithium replenishment micro-regions in the first lithium replenishment layer are distributed in stripes; the stripe spacing of the lithium replenishment micro-regions in the first lithium replenishment layer is 20 μm to 500 μm; the stripe width is 20 μm to 500 μm;

[0354] The lithium replenishment micro-regions in the second lithium replenishment layer are distributed in a grid shape; the stripe spacing of the lithium replenishment micro-regions in the first lithium replenishment layer is 20 μm to 500 μm, and the stripe width is 20 μm to 500 μm.

[0355] In some embodiments, the lithium replenishment micro-domains in the first lithium replenishment layer are distributed in a stripe shape or a grid shape.

[0356] In some embodiments, the lithium replenishing micro-domains in the second lithium replenishing layer are distributed in a stripe shape or a grid shape.

[0357] In some embodiments, the lithium-replenishing micro-domains in the first lithium-replenishing layer are distributed in a stripe shape, and the lithium-replenishing micro-domains in the second lithium-replenishing layer are distributed in a grid shape.

[0358] In some embodiments, in the lithium replenishment layer of the lithium replenishment negative electrode sheet, there are a number of discontinuous stripe-shaped blank areas in the stripe-shaped distribution, and the stripe-shaped blank areas are distributed alternately with the stripe-shaped lithium replenishment micro-areas.

[0359] In some embodiments, in the lithium replenishment layer of the lithium replenishment negative electrode sheet, there are several discontinuous rectangular blank areas in the grid-like distribution, and the lithium replenishment micro-areas are connected to each other. In some of these embodiments, there are several discontinuous square blank areas in the grid-like distribution, and the lithium replenishment micro-areas are connected to each other.

[0360] In some embodiments, the lithium-supplemented negative electrode sheet satisfies one or more of the following characteristics (any numerical parameter in the following characteristics can also be selected from any suitable numerical value or range in the context):

[0361] Measured by projection along the thickness direction of the lithium-supplemented negative electrode sheet, the one-dimensional size of at least a portion of the lithium-supplemented micro-regions is 20 μm to 2000 μm, and can be optionally 20 μm to 1000 μm;

[0362] Measured by projection along the thickness direction of the lithium-supplemented negative electrode sheet, the spacing between at least a portion of the lithium-supplemented micro-regions is 20 μm to 2000 μm, and can be optionally 20 μm to 1000 μm;

[0363] The lithium supplement micro-regions in the first lithium supplement layer are distributed in stripe shape or grid shape;

[0364] The lithium replenishment micro-regions in the second lithium replenishment layer are distributed in stripe shape or grid shape.

[0365] In some embodiments, the lithium-replenishing micro-regions in the first lithium-replenishing layer are distributed in stripes. In a non-limiting manner, the stripe spacing of the lithium-replenishing micro-regions in the first lithium-replenishing layer can be 20 μm to 2000 μm, optionally 20 μm to 1000 μm, or any of the following values ​​or a range selected from any two of the following values: 20 μm, 40 μm, 50 μm, 60 μm, 80 μm, 100 μm, 150 μm, 200 μm, 300 μm, 400 μm, 500 μm, 600 μm, 800 μm, 1000 μm, 1200 μm, 1500 μm, 1600 μm, 1800 μm, 2000 μm, etc. Without limitation, the stripe width of the lithium replenishing microregion in the first lithium replenishing layer can be 20μm~2000μm, optionally 20μm~1000μm, or any of the following values ​​or a range consisting of any two of the following values: 20μm, 40μm, 50μm, 60μm, 80μm, 100μm, 150μm, 200μm, 300μm, 400μm, 500μm, 600μm, 800μm, 1000μm, 1200μm, 1500μm, 1600μm, 1800μm, 2000μm, etc.

[0366] In some embodiments, the lithium-replenishing micro-regions in the second lithium-replenishing layer are distributed in a grid shape. In a non-limiting manner, the grid spacing of the lithium-replenishing micro-regions in the second lithium-replenishing layer can be 20 μm to 2000 μm, optionally 20 μm to 1000 μm, or any of the following values ​​or a range selected from any two of the following values: 20 μm, 40 μm, 50 μm, 60 μm, 80 μm, 100 μm, 150 μm, 200 μm, 300 μm, 400 μm, 500 μm, 600 μm, 800 μm, 1000 μm, 1200 μm, 1500 μm, 1600 μm, 1800 μm, 2000 μm, etc. Without limitation, the grid line width of the lithium replenishing micro-region in the second lithium replenishing layer can be 20μm~2000μm, optionally 20μm~1000μm, or any of the following values ​​or a range selected from any two of the following values: 20μm, 40μm, 50μm, 60μm, 80μm, 100μm, 150μm, 200μm, 300μm, 400μm, 500μm, 600μm, 800μm, 1000μm, 1200μm, 1500μm, 1600μm, 1800μm, 2000μm, etc.

[0367] In some embodiments, the lithium-replenishing microregions in the first lithium-replenishing layer are distributed in stripes; the stripe spacing of the lithium-replenishing microregions in the first lithium-replenishing layer is 20μm~2000μm, which can be optionally 20μm~1000μm, and further can be optionally 20μm~500μm, and the stripe width is 20μm~2000μm, which can be optionally 20μm~1000μm, and further can be optionally 20μm~500μm; the lithium-replenishing microregions in the second lithium-replenishing layer are distributed in a grid shape; the grid spacing of the lithium-replenishing microregions in the second lithium-replenishing layer is 20μm~2000μm, which can be optionally 20μm~1000μm, and further can be optionally 20μm~500μm, and the grid line width is 20μm~2000μm, which can be optionally 20μm~1000μm, and further can be optionally 20μm~500μm.

[0368] In some embodiments, the lithium-replenishing micro-regions in the first lithium-replenishing layer and the second lithium-replenishing layer are independently distributed in stripes. In a non-limiting manner, the stripe spacing and stripe width of the lithium-replenishing micro-regions in the first lithium-replenishing layer can be independently 20 μm to 2000 μm, optionally 20 μm to 1000 μm, further optionally 20 μm to 500 μm, and can also be any of the following values ​​or a range selected from any two of the following values: 20 μm, 40 μm, 50 μm, 60 μm, 80 μm, 100 μm, 150 μm, 200 μm, 300 μm, 400 μm, 500 μm, 600 μm, 800 μm, 1000 μm, 1200 μm, 1500 μm, 1600 μm, 1800 μm, 2000 μm, etc. In a non-limiting manner, the stripe spacing and stripe width of the lithium-replenishing micro-region in the second lithium-replenishing layer can be independently 20 μm to 2000 μm, optionally 20 μm to 1000 μm, further optionally 20 μm to 500 μm, and can also be any of the following values ​​or a range consisting of any two of the following values: 20 μm, 40 μm, 50 μm, 60 μm, 80 μm, 100 μm, 150 μm, 200 μm, 300 μm, 400 μm, 500 μm, 600 μm, 800 μm, 1000 μm, 1200 μm, 1500 μm, 1600 μm, 1800 μm, 2000 μm, etc. In some embodiments, the stripe spacing of the lithium-replenishing micro-region in the second lithium-replenishing layer is greater than the stripe spacing of the lithium-replenishing micro-region in the first lithium-replenishing layer, which means that there are more blank areas in the second lithium-replenishing layer.

[0369] In some embodiments, the morphology control of the first lithium replenishing region and the second lithium replenishing region on the corresponding surface can be achieved by selecting the raw materials of the first lithium film and the second lithium film having corresponding morphologies, respectively, as required.

[0370] By controlling the lithium-replenishing micro-areas in the lithium-replenishing negative electrode sheet to conform to one or more of the aforementioned sizes and shapes, it is beneficial to provide a more sufficient contact area for the electrolyte to infiltrate the electrode sheet, to control the gas production during the lithium insertion process within a more appropriate range to produce a more uniform and sufficient exhaust channel, to optimize the ion transfer between the first negative electrode active layer and the second negative electrode active layer, and to increase the adhesion strength of the lithium-replenishing layer to the adjacent negative electrode active layer. It can also take into account the amount of lithium replenishment. Through the aforementioned multiple effects, it is beneficial to better improve the battery cycle life.

[0371] In some embodiments, the lithium-supplemented negative electrode sheet satisfies one or more of the following characteristics:

[0372] The compaction density of the second negative electrode active initial layer is higher than the compaction density of the first negative electrode active initial layer;

[0373] The powder compaction density of the second negative electrode active initial layer is higher than the powder compaction density of the first negative electrode active initial layer.

[0374] In some embodiments, in the lithium-supplemented negative electrode sheet, the compaction density of the second negative electrode active initial layer is higher than the compaction density of the first negative electrode active initial layer.

[0375] In the present application, unless otherwise specified, the "compacted density" of the second negative electrode active initial layer refers to the ratio of the mass to the volume of the second negative electrode active initial layer, the compacted density of the "first negative electrode active initial layer" refers to the ratio of the mass to the volume of the first negative electrode active initial layer, the compacted density of the "second negative electrode active layer" refers to the ratio of the mass to the volume of the second negative electrode active layer, and the compacted density of the "first negative electrode active layer" refers to the ratio of the mass to the volume of the first negative electrode active layer.

[0376] By adjusting the compaction density of the second negative electrode active initial layer to be higher than that of the first negative electrode active initial layer, the second negative electrode active layer in the lithium-ion secondary battery can have a higher compaction density, which is beneficial to improving the energy density of the lithium-ion secondary battery. On the other hand, the first negative electrode active initial layer has a lower compaction density, which is beneficial to quickly embedding active lithium into the negative electrode active material after electrolyte infiltration, and is beneficial to reducing or avoiding lithium precipitation on the surface of the negative electrode active material. Therefore, it is beneficial to take into account both high lithium replenishment efficiency and high energy density, and to take into account both improving cycle life and increasing energy density.

[0377] In a non-limiting manner, the compaction density of the first negative electrode active initial layer and the compaction density of the second negative electrode active initial layer can be tested by the following method: the lithium supplemented negative electrode sheet is punched into small discs of a certain area A0, and a certain thickness h of the first negative electrode active initial layer is scraped from the corresponding thickness position. 01 The first negative electrode material powder is weighed, and the powder mass M 01 , the compaction density PD of the first negative electrode active initial layer can be calculated01 =M 01 / (A0×h 01 ), test multiple small discs and take the average value. Also scrape a certain thickness h of the second negative electrode active initial layer from the corresponding thickness position 02 The second negative electrode material powder is weighed, and the powder mass M 02 , the compaction density PD of the second negative electrode active initial layer can be calculated 02 =M 02 (A0×h 02 ), test multiple small discs and take the average value.

[0378] In this application, unless otherwise specified, the constituent material of the negative electrode active material layer is recorded as the negative electrode material, the constituent material of the first negative electrode active initial layer is recorded as the first negative electrode material, and the constituent material of the second negative electrode active initial layer is recorded as the second negative electrode material. The first negative electrode material includes the first negative electrode active material, and the second negative electrode material includes the second negative electrode active material. The "first" and "second" in "first negative electrode material" and "second negative electrode material" are only used for descriptive purposes and cannot be understood as indicating or implying relative importance or quantity, nor can they be understood as implicitly indicating the importance or quantity of the indicated technical features.

[0379] In some embodiments, the powder compaction density of the second negative electrode active initial layer is higher than the powder compaction density of the first negative electrode active initial layer.

[0380] In the present application, unless otherwise specified, the "powder compaction density" of the second negative electrode active initial layer refers to the powder compaction density of the powder material constituting the second negative electrode active initial layer.

[0381] "Powder compaction density" has a well-known meaning in the art, and refers to the ratio of the mass to the volume of the powder material after compaction under a certain pressure. The "powder compaction density" of the negative electrode material can be measured using instruments and methods known in the art. For example, it can be measured by an electronic pressure testing machine (such as UTM7305) with reference to standard GB / T24533-2009. An exemplary test method is as follows: weigh a negative electrode material with a mass of M (such as 1g), add a bottom area of ​​A (such as 1.327cm 2 ) in a mold, pressurize to a certain pressure P0 (such as 3 tons (3T), etc.), maintain the pressure for a certain time (such as 3T for 30s), then release the pressure, maintain for a period of time (such as 10s), and then record and calculate the powder compaction density of the negative electrode material under the pressure P0. The first negative electrode material powder in the first negative electrode active initial layer and the second negative electrode material powder in the second negative electrode active initial layer can be obtained by the above method.

[0382] By controlling the powder compaction density of the second negative electrode active initial layer to be higher than the powder compaction density of the first negative electrode active initial layer, it is beneficial to give the second negative electrode active initial layer a higher compaction density during the cold pressing process of the electrode sheet, so that the second negative electrode active layer in the lithium-ion secondary battery has a higher compaction density.

[0383] It can be understood that the relative size of the powder compaction density of the negative electrode material in different negative electrode active initial layers of the lithium-supplemented negative electrode sheet can be judged based on the relative size of the powder compaction density test value obtained under the same sample parameters and test conditions. Generally, the comparison can be made based on the relative size of the powder compaction density test value under the same test pressure. Similarly, the relative size of the powder compaction density of different negative electrode active layers of the negative electrode sheet in the lithium-ion secondary battery can also be judged based on the relative size of the powder compaction density test value obtained under the same sample parameters and test conditions.

[0384] For the powder compaction density of the negative electrode active material, the state in the negative electrode sheet of the lithium-ion secondary battery can be recorded as the first state, the state in the cold-pressed negative electrode sheet (without the addition of the lithium supplement layer) or the state in the lithium supplemented negative electrode sheet with the additional lithium supplement layer after rolling can be recorded as the second state, and the state of the negative electrode active material used to prepare the negative electrode sheet before being subjected to cold pressing can be recorded as the third state. The third state can include the state of powder raw materials, the state of being suspended in the negative electrode slurry, and the state of being coated on the surface of the negative electrode current collector; the powder compaction density of the negative electrode active material in the third state is equal to or close to the powder compaction density in the powder raw material state in terms of value. In the second state, after the cold pressing treatment (without the addition of the lithium supplement layer) or the addition of the lithium supplement layer after rolling, the particles of the negative electrode active material may be deformed or even broken. Therefore, after re-extracting the powder sample of the negative electrode active material and re-measuring the powder compaction density, the powder compaction density may be different in value from the powder compaction density in the powder raw material state. In the first state, the negative electrode active material is in contact with the electrolyte and is soaked by the electrolyte; after formation, the negative electrode active material is charged for the first time, and there are embedded lithium ions. In addition, an SEI film is formed on the surface of the negative electrode active material; if the battery undergoes a charge and discharge cycle, the negative electrode active material undergoes reversible insertion and extraction of lithium ions. In the charging state, the negative electrode active material is embedded with lithium ions, and in the discharging state, the lithium ions embedded in the negative electrode active material are extracted; therefore, it can be understood that in the first state and the third state, the powder compaction density of the negative electrode active material may also be different to a certain extent. The "first", "second" and "third" in the aforementioned "first state", "second state" and "third state" are only used for descriptive purposes and cannot be understood as indicating or implying relative importance or quantity, nor can they be understood as implicitly indicating the importance or quantity of the indicated technical features.

[0385] In the present application, unless otherwise specified, "negative electrode sheet obtained by cold pressing (without addition of lithium supplement layer)" refers to a state where the first negative electrode active initial layer located on the upper layer has been cold pressed, but the first lithium supplement layer has not been added to the first negative electrode active initial layer.

[0386] Although the compaction density of the negative electrode active material powder may have certain numerical differences under different conditions, it does not affect the judgment of the relative size of the compaction density of the negative electrode material powder in different negative electrode active layers.

[0387] In some embodiments, the lithium-supplemented negative electrode sheet satisfies one or more of the following characteristics (any numerical parameter in the following characteristics can also be selected from any suitable numerical value or range in the context):

[0388] The compaction density of the second negative electrode active initial layer is 1.3 g / cm 3 ~1.8g / cm 3 ;

[0389] The overall compaction density of the lithium-supplemented negative electrode sheet is 1.3g / cm 3 ~1.7g / cm 3 .

[0390] In a non-limiting manner, the compaction density of the second negative electrode active initial layer may be 1.3 g / cm 3 ~1.7g / cm 3 , can also be any of the following values ​​or a range consisting of any two of the following values: 1.3 g / cm 3 , 1.35 g / cm 3 , 1.4 g / cm 3 , 1.45 g / cm 3 , 1.5 g / cm 3 , 1.55 g / cm 3 , 1.6 g / cm 3 , 1.65 g / cm 3 , 1.7 g / cm 3 , 1.8 g / cm 3 wait.

[0391] In some embodiments, the overall compaction density of the lithium-supplemented negative electrode sheet can be 1.3 g / cm 3 ~1.7g / cm 3 , can also be any of the following values ​​or a range consisting of any two of the following values: 1.3 g / cm 3 , 1.35 g / cm 3 , 1.4 g / cm 3 , 1.45 g / cm 3 , 1.5 g / cm 3, 1.55 g / cm 3 , 1.6 g / cm 3 , 1.65 g / cm 3 , 1.7 g / cm 3 wait.

[0392] In the present application, unless otherwise specified, the “overall compaction density of the lithium-supplemented negative electrode sheet” refers to the ratio of the total mass to the total volume of each negative electrode active initial layer in the lithium-supplemented negative electrode sheet.

[0393] Without limitation, the overall compaction density of the lithium-supplemented negative electrode sheet can be tested by the following method: the lithium-supplemented negative electrode sheet is punched into a piece with an area of ​​S (e.g., 1540.25 mm 2 ) and measure the mass M of the small disc. A and thickness L A , peel off the first lithium replenishing layer and the second lithium replenishing layer, weigh the total mass M of the first lithium replenishing layer and the second lithium replenishing layer L Take the lithium-supplemented negative electrode sheet from another area, wipe off the negative electrode active initial layer on the surface and remove the remaining negative electrode current collector foil (which can be recorded as empty negative electrode current collector foil), and also punch it into small discs with an area of ​​S. Weigh the mass of the empty negative electrode current collector foil and record it as M0 and the thickness L0. The overall compaction density PD of the lithium-supplemented negative electrode sheet is A =(M A -M0-M L ) / [S×(L A -L0)-M L / ρ Li ]. Among them, ρ Li The volume density of lithium can be calculated as 0.534 g / cm 3 count.

[0394] By controlling the powder compaction density of the second negative electrode active initial layer within the aforementioned range, it is advantageous to control the compaction density of the second negative electrode active layer within a more appropriate range, which is advantageous for enabling the lithium-ion secondary battery to achieve a higher energy density.

[0395] By controlling the overall compaction density of the lithium-supplemented negative electrode sheet within the aforementioned range, it is beneficial to control the overall compaction density of the negative electrode sheet in the lithium-ion secondary battery within a more appropriate range, which is beneficial to taking into account both the battery energy density and the higher negative electrode lithium replenishment efficiency.

[0396] Exemplarily, by adjusting the overall compaction density of the lithium-supplemented negative electrode sheet within the aforementioned range, it is beneficial to balance battery kinetics and energy density.

[0397] Exemplarily, by adjusting the overall compaction density of the lithium-supplemented negative electrode sheet within the aforementioned range, it is beneficial to improve both the energy density and the lithium-supplementing efficiency.

[0398] It can be understood that the first negative electrode active initial layer includes a first negative electrode active material, and the second negative electrode active initial layer includes a second negative electrode active material.

[0399] In some embodiments, the lithium-supplemented negative electrode sheet satisfies one or more of the following characteristics (any numerical parameter in the following characteristics can also be selected from any suitable numerical value or range in the context):

[0400] D of the first negative electrode active material v 50 lower than the D of the second negative electrode active material v 50; among them, D v 50 represents the particle size corresponding to when the cumulative volume distribution percentage of the multi-particle mixture reaches 50%;

[0401] D of the first negative electrode active material v 50 is 7μm ~14μm, optional is 8μm ~13μm;

[0402] D of the second negative electrode active material v 50 is 8μm ~14μm, and can be selected as 9μm ~13μm;

[0403] The porosity of the first negative electrode active initial layer is higher than the porosity of the second negative electrode active initial layer;

[0404] The porosity of the first negative electrode active initial layer is 20%~45%;

[0405] The porosity of the second negative electrode active initial layer is 15% to 45%.

[0406] In some embodiments, the lithium-supplemented negative electrode sheet satisfies one or more of the following characteristics (any numerical parameter in the following characteristics can also be selected from any suitable numerical value or range in the context):

[0407] D of the first negative electrode active material v 50: 8μm ~13μm;

[0408] D of the second negative electrode active material v 50 is 9μm ~13μm.

[0409] In some embodiments, in the lithium-supplemented negative electrode sheet, D of the first negative electrode active material is v 50 lower than the D of the second negative electrode active material v 50.

[0410] In some embodiments, in the lithium-supplemented negative electrode sheet, D of the first negative electrode active material is v50 can be 7μm ~14μm, optionally 8μm ~13μm, or any of the following values ​​or a range consisting of any two of the following values: 7μm, 7.5μm, 8μm, 8.5μm, 9μm, 10μm, 11μm, 12μm, 12.5μm, 13μm, 13.5μm, 14μm, etc.

[0411] In some embodiments, in the lithium-supplemented negative electrode sheet, D of the second negative electrode active material is v 50 can be 8μm ~14μm, optionally 9μm ~13μm, or any of the following values ​​or a range consisting of any two of the following values: 8μm, 8.5μm, 9μm, 10μm, 11μm, 12μm, 12.5μm, 13μm, 13.5μm, 14μm, etc.

[0412] In this application, unless otherwise specified, D v 50 refers to the particle size corresponding to when the cumulative volume distribution percentage of the material reaches 50%. This parameter indicates that the particle size of particles accounting for 50% of the volume of the material is less than or equal to D v 50, and 50% of the particles by volume are larger than D v 50. D v 50 can be obtained from the volume cumulative distribution curve of the material particle size. If there is no other explanation, the volume cumulative distribution curve starts from zero from the small particle size side. Those skilled in the art can understand that D v 50, and can be measured by instruments and methods known in the art. For example, it can be conveniently measured by laser particle size analyzer, such as Mastersizer 2000E laser particle size analyzer and LS-909 laser particle size analyzer (OMEC) of Malvern Instruments Ltd., UK. It can be tested with reference to the standard process GB / T19077-2016 / ISO13320:2009.

[0413] By arranging negative electrode active materials with smaller particle sizes in the first negative electrode active initial layer, the second negative electrode active layer includes negative electrode active materials with smaller particle sizes, which is beneficial to reducing the solid phase diffusion path of the first negative electrode active layer and optimizing battery kinetics.

[0414] By adding D of the first negative electrode active material v 50 is set within the aforementioned range, which is beneficial to reducing the solid phase diffusion path of the first negative electrode active layer, thereby optimizing the battery kinetics.

[0415] By matching the particle sizes of the first negative electrode active material and the second negative electrode active material, it can be achieved that the upper layer in the first negative electrode active layer and the lower layer in the second negative electrode active layer have a low compaction density, and have a suitable compaction density difference, which is beneficial to taking into account both the lithium replenishment efficiency of the lithium replenishment negative electrode sheet and the battery energy density.

[0416] In some embodiments, in the lithium supplemented negative electrode sheet, the porosity of the first negative electrode active initial layer (which can be recorded as P 01 ) is higher than the porosity of the second negative electrode active initial layer (which can be recorded as P 02 ).

[0417] In some embodiments, in the lithium-supplemented negative electrode sheet, the porosity of the first negative electrode active initial layer is 20% to 45%, and can also be any of the following percentages or a range selected from any two of the following percentages: 20%, 25%, 30%, 35%, 40%, 45%, etc.

[0418] In some embodiments, in the lithium-supplemented negative electrode sheet, the porosity of the second negative electrode active initial layer is 15% to 45%, and can also be any of the following percentages or a range selected from any two of the following percentages: 15%, 20%, 25%, 30%, 35%, 40%, 45%, etc.

[0419] In this application, unless otherwise specified, "porosity" refers to the percentage of pore volume in a material to the total volume.

[0420] The following method can be used to test the porosity of the first negative electrode active initial layer and the second negative electrode active initial layer: punch the lithium-supplemented negative electrode sheet into small discs, use the nano-space dynamic resolution and layer-by-layer cutting technology of FIB-SEM (focused electron beam electron microscope-scanning electron microscope) to reconstruct the three-dimensional structure of the sample, and use the energy dispersive spectrometer (EDS, Energy Dispersive Spectrometer) to analyze the distribution and proportion of each element. According to the component boundaries, the second negative electrode active initial layer, the second lithium-supplemented layer, the first negative electrode active initial layer and the first lithium-supplemented layer can be identified. Finally, the porosity of the first negative electrode active initial layer and the second negative electrode active initial layer is obtained by software quantitative analysis. The FEI Scios 2HiVac device can be used for testing.

[0421] In addition, the porosity of the first negative electrode active initial layer and the second negative electrode active initial layer can be qualitatively compared by means of cross-sectional morphology observation methods. The lithium-supplemented negative electrode sheet can be cut by plasma quenching, and the cross-sectional morphology of the obtained cross section can be observed under a scanning electron microscope (SEM). The cross-sectional morphology can also be observed in conjunction with an energy dispersive spectrometer (EDS), the position of each structural layer can be identified, the thickness of each structural layer can be obtained, the pore size and number of different structural layers can be observed and compared, and then the porosity can be qualitatively compared.

[0422] By controlling the porosity of the first negative electrode active initial layer to be higher than the porosity of the second negative electrode active initial layer, the high porosity of the upper layer can provide more channels for lithium ion embedding, which is beneficial for the rapid embedding of lithium ions into the negative electrode active material, thereby helping to reduce or avoid lithium deposition on the surface of the negative electrode active material.

[0423] By controlling the porosity of the first negative electrode active initial layer within the aforementioned range, it is beneficial for lithium ions to be quickly embedded in the negative electrode active material, thereby helping to reduce or avoid lithium deposition on the surface of the negative electrode active material.

[0424] In some embodiments, in the lithium supplemented negative electrode sheet or the negative electrode sheet, the first negative electrode active material includes non-agglomerated primary particles. Without limitation, the number ratio or mass ratio of the non-agglomerated primary particles in the first negative electrode active material can be 80% to 100%, or can be any of the following percentages or a range selected from any two of the following percentages: 80%, 85%, 90%, 95%, 98%, 99%, 100%, etc.

[0425] In some embodiments, the first negative electrode active material simultaneously satisfies the requirements of including non-agglomerated primary particles and including carbon-based materials; at this time, the first negative electrode active material may include non-agglomerated primary particles, the non-agglomerated primary particles include carbon-based materials, or the first negative electrode active material may include carbon-based materials, the carbon-based materials include non-agglomerated primary particles.

[0426] In this application, unless otherwise specified, "primary particles" are the basic units of particles in a material. In a material, a primary particle can be in a non-agglomerated state, referred to as a "non-agglomerated primary particle"; multiple primary particles can be aggregated into an aggregated particle, referred to as a "secondary particle".

[0427] The first negative electrode active material for preparing the lithium supplement negative electrode sheet can be laid and adhered to the conductive glue, and the particle morphology can be tested by a scanning electron microscope (such as ZEISS Sigma 300). The number of particles in the obtained SEM image is counted to determine whether they are non-agglomerated primary particles or secondary particles, and the number ratio of non-agglomerated primary particles in the first negative electrode active material can be obtained. The number ratio of secondary particles in the second negative electrode active material can be obtained by a similar method.

[0428] By introducing non-agglomerated primary particles into the first negative electrode active material, it is helpful to reduce the embeddable surface being buried due to particle agglomeration, which is beneficial to expose more lithium insertion sites, and further helps to improve the lithium replenishment efficiency.

[0429] On the basis of controlling the compaction density of the first negative electrode active initial layer (upper layer) to be lower than that of the second negative electrode active initial layer (lower layer), further introducing non-agglomerated primary particles into the first negative electrode active material is beneficial to exposing more lithium insertion sites and further improving the lithium replenishment efficiency.

[0430] In some embodiments, in the lithium supplemented negative electrode sheet or the negative electrode sheet, the second negative electrode active material includes secondary particles. In a non-limiting manner, the number ratio or mass ratio of the secondary particles in the second negative electrode active material can be 80% to 100%, and can also be any of the following percentages or a range selected from any two of the following percentages: 80%, 85%, 90%, 95%, 98%, 99%, 100%, etc.

[0431] By providing the secondary particles in the second negative electrode active material, it is advantageous to control the manufacturing cost.

[0432] In some embodiments, in the lithium-supplemented negative electrode sheet or the negative electrode sheet, the first negative electrode active material includes a carbon-based material. The carbon-based material may include a coated carbon-based material.

[0433] In some embodiments, in a lithium-supplemented negative electrode sheet or a negative electrode sheet, the first negative electrode active material includes a coated carbon-based material, the coated carbon-based material includes a carbon matrix and a carbon coating layer located on at least a portion of the surface of the carbon matrix. Optionally, the carbon matrix includes graphite, and the carbon coating layer includes one or more of amorphous carbon, soft carbon and hard carbon.

[0434] In some embodiments, in a lithium-supplemented negative electrode sheet or a negative electrode sheet, the first negative electrode active material includes non-agglomerated primary particles, the non-agglomerated primary particles include coated carbon-based materials, the coated carbon-based materials include a carbon matrix and a carbon coating layer located on at least a portion of the surface of the carbon matrix. Optionally, the carbon matrix includes graphite, and the carbon coating layer includes one or more of amorphous carbon, soft carbon and hard carbon.

[0435] In some embodiments, the quantity ratio or mass ratio of the coated carbon-based material in the non-agglomerated primary particles in the first negative electrode active material can be 80% to 100%, or can be any of the following percentages or a range selected from any two of the following percentages: 80%, 85%, 90%, 95%, 98%, 99%, 100%, etc.

[0436] In this application, unless otherwise specified, "amorphous carbon" refers to a transitional carbon material with a very low degree of graphitization and crystallization, which is close to an amorphous state (or has no fixed shape and periodic structural regularity). In this application, "amorphous carbon" refers to the product of carbonization treatment of an organic carbon source.

[0437] In the present application, the confirmation of "amorphous carbon coating" can be obtained by testing the conventional method of testing the crystalline form of carbon substances in the art, such as Raman spectroscopy testing and analysis, and the characteristic peak information of the carbon component in the spectrum (such as the intensity ratio of D peak / G peak, I D / G ) to analyze whether an amorphous carbon layer is formed. Among them, the D peak and the G peak are both Raman characteristic peaks of carbon atom crystals. The D peak represents the defects of the carbon atom crystals. The more defects there are, the greater the D peak intensity is. The D peak intensity can reflect the content of the amorphous (turbostratified stacking) region. The G peak represents the in-plane stretching vibration of the sp2 hybridization of carbon atoms. The G peak intensity can reflect the content of the graphitized (layered structure) region. As the degree of disorder of carbon atoms increases, the intensity ratio of the D peak to the G peak also increases. The Raman spectrum of the specific structural layer of the particle to be tested can also be compared. D / G Standard Raman spectrum of graphite I D / G The difference between the two can be used to determine whether the coating layer of the material to be tested contains amorphous carbon. It is also possible to compare the Raman spectra I D / G Standard Raman spectrum of graphite I D / G The difference between the two can be used to determine whether the material to be tested contains amorphous carbon.

[0438] In addition, graphite and amorphous carbon can also be distinguished based on X-ray diffraction (XRD) pattern analysis. Graphite has a relatively strong diffraction peak near 2θ of 26.5°, corresponding to the (002) crystal plane of graphite; while amorphous carbon has no obvious crystal structure and appears as a broadened peak in the XRD pattern.

[0439] In some embodiments, in the lithium-supplemented negative electrode sheet or the negative electrode sheet, the mass proportion of graphite in the coated carbon-based material can be 90% to 98%, or can be any of the following percentages or a range consisting of any two of the following percentages: 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, etc.

[0440] In some embodiments, in the coated carbon-based material of the lithium-supplemented negative electrode sheet or the negative electrode sheet, the mass proportion of amorphous carbon in the coated carbon-based material can be 2%~10%, or it can be any of the following percentages or a range selected from any two of the following percentages: 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, etc.

[0441] In some embodiments, in the coated carbon-based material of the lithium-supplemented negative electrode sheet or the negative electrode sheet, the average thickness of the carbon coating layer may be 1 nm to 5 nm, but is not limited thereto.

[0442] In some embodiments, in the coated carbon-based material of the lithium-supplemented negative electrode sheet or the negative electrode sheet, the carbon matrix includes one or more of artificial graphite and natural graphite.

[0443] Natural graphite and artificial graphite can be distinguished by the appearance of the particles; further X-ray diffraction (XRD) analysis and testing can be performed. In the XRD spectrum, if the characteristic peak near 2θ 26.5° is very sharp and has a high intensity, it is natural graphite; if the characteristic peak near 2θ 26.5° is relatively broad and has a weak intensity, it is artificial graphite.

[0444] In some embodiments, in the lithium-supplemented negative electrode sheet or the negative electrode sheet, the first negative electrode active material satisfies one or more of the following characteristics (any numerical parameter in the following characteristics can also be selected from any suitable numerical value or range in the context):

[0445] The coated carbon-based material in the non-agglomerated primary particles includes non-agglomerated coated graphite; the quantity or mass proportion of the non-agglomerated coated graphite in the first negative electrode active material is 80% to 100%;

[0446] The amount or mass proportion of the coated carbon-based material in the first negative electrode active material is 80% to 100%.

[0447] In some embodiments, in the lithium supplemented negative electrode sheet or the negative electrode sheet, the coated carbon-based material in the non-agglomerated primary particles includes non-agglomerated coated graphite. Without limitation, the amount or mass proportion of the non-agglomerated coated graphite in the first negative electrode active material can be 80% to 100%, or any of the following percentages or a range selected from any two of the following percentages: 80%, 85%, 90%, 95%, 98%, 99%, 100%, etc.

[0448] In the present application, "non-agglomerated coated graphite" refers to graphite with a carbon coating layer on the surface, and the non-agglomerated coated graphite belongs to non-agglomerated primary particles, and the definition of the carbon coating layer can be found in the previous text. Unless otherwise specified, the non-agglomerated coated graphite includes a graphite body and a carbon coating layer located on at least a portion of the surface of the graphite body. The carbon coating layer in the non-agglomerated coated graphite may include one or more of amorphous carbon, soft carbon and hard carbon. It can be understood that the non-agglomerated coated graphite is a type of carbon-based material, and further, it is a type of coated carbon-based material.

[0449] In some embodiments, in a lithium-supplemented negative electrode sheet or a negative electrode sheet, the first negative electrode active material includes non-agglomerated primary particles, the non-agglomerated primary particles include non-agglomerated coated graphite, the non-agglomerated coated graphite includes a graphite body and a carbon coating layer located on at least a portion of the surface of the graphite body, and the carbon coating layer includes one or more of amorphous carbon, soft carbon and hard carbon.

[0450] In some embodiments, in the lithium-supplemented negative electrode sheet or the negative electrode sheet, the quantity ratio or mass ratio of the coated carbon-based material in the first negative electrode active material is 80% to 100%, and can also be any of the following percentages or a range selected from any two of the following percentages: 80%, 85%, 90%, 95%, 98%, 99%, 100%, etc.

[0451] By introducing a coated carbon-based material into the first negative electrode active material located in the upper layer, and coating at least a portion of the surface of the carbon base body with one or more of amorphous carbon, soft carbon and hard carbon, it is beneficial to provide a better lithium ion transmission channel for the carbon base body, thereby promoting lithium ion transmission and improving lithium replenishment efficiency, and further improving battery cycle life and battery dynamics.

[0452] Without limitation, the test samples of the lithium-supplemented negative electrode sheet or the coated carbon-based material in the negative electrode sheet can be obtained and analyzed by the following method: the lithium-supplemented negative electrode sheet is soaked and cleaned with a solvent (such as dimethyl carbonate (DMC)), and powder is scraped from different thickness positions to obtain powder samples of the first negative electrode material and the second negative electrode material respectively;

[0453] After cutting the powder into sections using FIB (focused ion beam), the particle cross-sectional morphology was observed under TEM (transmission electron microscope). A clear boundary was observed at the coating interface. The thickness and average thickness of the coating layer could be analyzed and calculated based on the TEM image.

[0454] In some embodiments, the lithium-supplemented negative electrode sheet satisfies one or more of the following characteristics (any numerical parameter in the following characteristics can also be selected from any suitable numerical value or range in the context):

[0455] The thickness of the first negative electrode active initial layer is 50 μm to 120 μm, and can be 50 μm to 100 μm, based on the total thickness in the lithium supplemented negative electrode sheet;

[0456] The single-side thickness of the first negative electrode active initial layer is 25 μm to 60 μm, and can be optionally 25 μm to 50 μm;

[0457] The ratio of the thickness of the first negative electrode active initial layer to the sum of the thickness of the first negative electrode active initial layer and the second negative electrode active initial layer is denoted as f H0 , satisfying 20%≤f H0 ≤70%, optionally, 30%≤f H0 ≤50%.

[0458] In some embodiments, the lithium-supplemented negative electrode sheet satisfies one or more of the following characteristics (any numerical parameter in the following characteristics can also be selected from any suitable numerical value or range in the context):

[0459] The thickness of the first negative electrode active initial layer is 50 μm to 100 μm, based on the total thickness in the lithium supplemented negative electrode sheet;

[0460] 30%≤f H0 ≤50%.

[0461] In some embodiments, based on the total thickness in the lithium-supplemented negative electrode sheet, the thickness of the first negative electrode active initial layer is 50 μm to 120 μm, and can be optionally 50 μm to 100 μm, or can be any of the following values ​​or a range consisting of any two of the following values: 50 μm, 55 μm, 60 μm, 65 μm, 70 μm, 75 μm, 80 μm, 85 μm, 90 μm, 95 μm, 100 μm, 110 μm, 120 μm, etc.

[0462] In the present application, the ratio of the thickness of the first negative electrode active initial layer to the sum of the thickness of the first negative electrode active initial layer and the second negative electrode active initial layer is denoted as f H0 .

[0463] In some embodiments, 20%≤f H0 ≤70%, optionally, 30%≤f H0 ≤50%. Without limitation, f H0 It can also be any of the following percentages or a range consisting of any two of the following percentages: 20%, 30%, 40%, 50%, 60%, 70%, etc.

[0464] The thickness of one side of the first negative electrode active initial layer and the total thickness of both sides of the first negative electrode active initial layer (H 01 ) and the ratio of the thickness of the first negative electrode active initial layer to the sum of the thickness of the first negative electrode active initial layer and the second negative electrode active initial layer (f H0 ) is controlled within the aforementioned range, which is conducive to better balancing the higher lithium replenishment efficiency provided by the first negative electrode active initial layer and the overall energy density of the negative electrode sheet. In addition, by controlling f H0 Further, by adjusting the compaction density of the second negative electrode active initial layer and / or the compaction density of the powder of the second negative electrode active initial layer, the comprehensive requirements of improving lithium replenishment efficiency, extending cycle life and improving energy density can be better balanced.

[0465] In some embodiments, the components for preparing lithium-ion secondary batteries also include a positive electrode sheet, which includes a positive electrode active material. Further, the positive electrode active material may include one or more of a ternary positive electrode material, lithium iron phosphate, lithium iron manganese phosphate, and a modified product of any of the foregoing positive electrode active materials, but is not limited thereto; the modified product may include one or more of a doping element and a coating element. In some embodiments, the components for preparing lithium-ion secondary batteries also include a positive electrode sheet, which includes a positive electrode active material, which includes one or more of a ternary positive electrode material, a modified product of a ternary positive electrode material, lithium iron phosphate, a modified product of lithium iron phosphate, lithium iron manganese phosphate, and a modified product of lithium iron manganese phosphate; the modified product includes one or more of a doping element and a coating element.

[0466] In this application, unless otherwise specified, "positive electrode active material" and "positive electrode active substance" have the same meaning, and "a modified substance of a positive electrode active substance" includes the positive electrode active substance itself and a modified element. Furthermore, the modified element may exist in the form of a doping element, a coating element, or a combination of a doping element and a coating element. Unless otherwise specified, "a modified substance of a positive electrode active substance" still falls within the scope of positive electrode active substances.

[0467] In the present application, unless otherwise specified, the "doping element" involved in the positive electrode active material refers to the modified element doped in the positive electrode active material; unless otherwise specified, the "coating element" involved in the positive electrode active material refers to the positive electrode active material including the positive electrode active particle body and the coating layer located at least a part of the surface of the positive electrode active particle body, wherein the coating element is the modified element located in the coating layer. As a non-limiting example, in the positive electrode active material, "the modified element exists in a combination of the doping element and the coating element" means that the positive electrode active material includes the positive electrode active particle body and the coating layer located at least a part of the surface of the positive electrode active particle body, at least a part of the modified element is doped in the positive electrode active material body, and at least a part of the modified element is also contained in the coating layer. The doping modification method of introducing the doping element and the coating modification method of introducing the coating element can adopt or refer to the existing modification methods in the art, including but not limited to the selection of element type, doping amount, and coating amount. In some embodiments, the positive electrode active particle body can be the positive electrode active material itself or its doped modified product. In some embodiments, the doping element may include one or more of Na, K, Ca, Ba, Sb, Ti, Zr, W, Sr, Nb, Mo, Si, Mg, B, Cr, Ta, etc. In some embodiments, the coating element may include one or more of Ti, Mg, Nb, C, etc.

[0468] In this application, unless otherwise specified, "ternary cathode material" refers to one or more of lithium nickel cobalt manganese oxide and lithium nickel cobalt aluminum oxide. The chemical formula of the ternary cathode material can be: The ternary cathode material is a lithium ion active material.

[0469] In the present application, unless otherwise specified, "lithium ion active material" refers to a positive electrode active material that can provide active lithium ions in the positive electrode.

[0470] In some embodiments, the positive electrode active material includes a lithium iron phosphate-based positive electrode active material. The "lithium iron phosphate-based positive electrode active material" includes at least a lithium iron phosphate body, and further may include a carbon coating layer located at least a portion of the surface of the lithium iron phosphate body, and optionally, the carbon coating layer may include one or more of soft carbon, hard carbon and amorphous carbon.

[0471] In some embodiments, the positive electrode active material includes carbon-coated lithium iron phosphate, which includes a lithium iron phosphate body and a carbon coating layer located on at least a portion of the surface of the lithium iron phosphate body. Optionally, the carbon coating layer may include one or more of soft carbon, hard carbon and amorphous carbon.

[0472] When the positive electrode active material includes carbon-coated lithium iron phosphate, the material has good stability under charge and discharge cycles, which is beneficial to provide more charge and discharge cycles and to better extend the battery cycle life.

[0473] Those skilled in the art can use conventional techniques to select and regulate the mass proportion of the carbon coating layer in the lithium iron phosphate-based positive electrode active material (an example of the lithium iron phosphate-based positive electrode active material is carbon-coated lithium iron phosphate) and the thickness or average thickness of the carbon coating layer. Non-limitingly, the mass proportion of the carbon coating layer in the lithium iron phosphate-based positive electrode active material can be 0.5%~2%, but is not limited to this. Non-limitingly, in the lithium iron phosphate-based positive electrode active material, the average thickness of the carbon coating layer can be 10nm~20nm, but is not limited to this. Non-limitingly, the mass proportion of the carbon coating layer in the carbon-coated lithium iron phosphate can be 0.5%~2%, but is not limited to this. Non-limitingly, in the carbon-coated lithium iron phosphate, the average thickness of the carbon coating layer can be 10nm~20nm, but is not limited to this.

[0474] In some embodiments, the components for preparing a lithium-ion secondary battery further include a positive electrode sheet;

[0475] The components used to prepare lithium-ion secondary batteries satisfy the following formula:

[0476] 1.03≤C N_A / (α·(m L1 / A L1 + m L2 / A L2 )×CLi / g +C P_A )≤1.2;

[0477] Among them, C N_A is the preset surface capacity of the negative electrode, C P_A is the preset surface capacity of the positive electrode, m L1 is the total mass of the first lithium supplement layer on both sides of the negative electrode current collector, A L1 is the spreading area of ​​the first lithium supplement layer on the first negative electrode active initial layer, m L2 is the total mass of the second lithium supplement layer on both sides of the negative electrode current collector, A L2 is the spreading area of ​​the first lithium supplement layer on the second negative electrode active initial layer, C Li / g is the theoretical gram capacity of lithium, α is the lithium replenishment coefficient, 0.6≤α≤1. When the first lithium replenishment layer is disposed on both sides of the negative electrode current collector, m L1 / A L1 The sum of the mass of the first lithium replenishment layer on both sides and its spreading area can be taken; when the second lithium replenishment layer is arranged on both sides of the negative electrode current collector, m L2 / A L2 The sum of the mass of the second lithium replenishing layer on both sides and its spreading area can be taken.

[0478] Unless otherwise specified, the spread area includes the area of ​​covered and uncovered areas.

[0479] In some embodiments, the components used to prepare a lithium-ion secondary battery meet one or more of the following characteristics:

[0480] 1.05≤C N_A / (α·(m L1 / A L1 + m L2 / A L2 )×C Li / g +C P_A )≤1.2;

[0481] 0.6≤α≤0.9.

[0482] In some embodiments, the components used to prepare a lithium-ion secondary battery meet one or more of the following characteristics:

[0483] 1.1≤C N_A / (α·(m L1 / A L1 + m L2 / A L2 )×C Li / g +C P_A )≤1.2;

[0484] 0.6≤α≤0.9.

[0485] The negative electrode preset surface capacity can be calculated based on the theoretical gram capacity of the negative electrode active material and the surface density of the negative electrode active material in the negative electrode sheet. N_A =Theoretical gram capacity of negative electrode active material × surface density of negative electrode active material in the negative electrode sheet.

[0486] The positive electrode preset surface capacity can be calculated based on the theoretical gram capacity of the positive electrode active material and the surface density of the positive electrode active material in the positive electrode sheet. P_A =Theoretical gram capacity of positive electrode active material × surface density of positive electrode active material in the positive electrode sheet.

[0487] In this application, unless otherwise specified, the theoretical gram capacity of lithium is C Li / g It can be calculated as 3860 mAh / g. In addition, the volume density of lithium can be calculated as 0.534 g / cm 3 count.

[0488] Without limitation, C N_A / (α·(m L1 / A L1 + m L2 / A L2 )×C Li / g +C P_A ) can be any of the following values ​​or a range consisting of any two of the following values: 1.03, 1.04, 1.05, 1.06, 1.08, 1.10, 1.12, 1.14, 1.15, 1.16, 1.18, 1.20, etc. In a non-limiting manner, C N_A / (α·(m L1 / A L1 + m L2 / A L2 )×C Li / g +C P_A ) can also be any of the following values ​​or a range consisting of any two of the following values: 1.03, 1.04, 1.05, 1.06, 1.08, 1.1, 1.16, 1.18, 1.19, 1.2, etc. The value of the lithium supplement coefficient α can be found in the context of this application.

[0489] In the present application, the lithium replenishment coefficient α may correspond to the ratio of the active lithium actually embedded in the negative electrode in the lithium replenishment layer to the theoretical total amount of active lithium that the lithium replenishment layer can provide. The higher the lithium replenishment coefficient α, the higher the lithium replenishment efficiency.

[0490] Without limitation, the lithium supplement coefficient α can be any of the following values ​​or a range selected from any two of the following values: 0.6, 0.7, 0.8, 0.9, 1, etc. In some embodiments, 0.6≤α≤1, optionally, 0.6≤α<1, further optionally, 0.6≤α≤0.9. In some embodiments, α=0.8.

[0491] Without being limited to any theory, by controlling the total thickness (d Li ) satisfies the aforementioned formula, and while the battery cycle life can be extended by lithium replenishment, the total thickness of the lithium replenishment residual layer can be controlled to have a more suitable thickness, which is beneficial to better balance the wettability of the electrolyte to the first negative electrode active layer and the second negative electrode active layer and the ion transport performance on the surfaces of both sides of the first negative electrode active layer, and the capacity matching between the positive and negative electrodes is better, which is more conducive to improving the lithium replenishment efficiency and the battery cycle life.

[0492] In some embodiments, by controlling the lithium supplement layer to have a more appropriate total thickness, it is helpful to better control the heat generation caused by the reaction between water and lithium, thereby facilitating improving production safety.

[0493] In this application, the total surface density of the second lithium replenishing layer and the first lithium replenishing layer relative to the first negative electrode active initial layer is recorded as C Li , the surface density of the positive electrode active material in the positive electrode sheet is recorded as A, the surface density of the negative electrode active material in the lithium supplemented negative electrode sheet is recorded as B, C Li , A and B are measured based on the total amount on both sides of the negative electrode current collector.

[0494] In this application, unless otherwise specified, the total surface density (C Li ) is equal to the ratio of the total mass of the second lithium replenishing layer and the first lithium replenishing layer on both sides of the negative electrode current collector to the area of ​​the first negative electrode active initial layer.

[0495] In this application, unless otherwise specified, the surface density of the positive electrode active material in the positive electrode sheet refers to the surface density of the positive electrode active material in the positive electrode sheet, which is equal to the ratio of the total mass of the positive electrode active material on both sides of the negative electrode current collector to its area.

[0496] In this application, unless otherwise specified, the surface density of the negative electrode active material in the lithium-supplemented negative electrode sheet refers to the surface density of the negative electrode active material in the negative electrode sheet, which is equal to the ratio of the total mass of the negative electrode active material on both sides of the negative electrode current collector to its area.

[0497] In some embodiments, the first lithium replenishing layer and the second lithium replenishing layer are both lithium films; the lithium replenishing negative electrode sheet satisfies the following formula: (18×C Li+A) / B≤2.3. Further, the positive electrode active material includes carbon-coated lithium iron phosphate. Unless otherwise specified, the carbon-coated lithium iron phosphate includes a lithium iron phosphate body and a carbon coating layer located on at least a portion of the surface of the lithium iron phosphate body. Optionally, the carbon coating layer may include one or more of soft carbon, hard carbon and amorphous carbon. Further optionally, the carbon coating layer may include soft carbon.

[0498] In some embodiments, 1.9≤(18×C Li +A) / B≤2.3.

[0499] Without limitation, (18×C Li +A) / B can be any of the following values ​​or a range consisting of any two of the following values: 1.9, 2.0, 2.1, 2.2, 2.3, etc.

[0500] In some embodiments, 1.9≤(18×C Li +A) / B≤2.3 and C Li 0.5mg / 1540.25mm 2 ~12mg / 1540.25mm 2 . C Li The value of can also refer to the context of this application. In some embodiments, C Li Greater than 0.5mg / 1540.25mm 2 And less than or equal to 12mg / 1540.25mm 2 In other embodiments, C Li 1mg / 1540.25mm 2 ~12mg / 1540.25mm 2 .

[0501] C Li The definition of can be found in the previous text.

[0502] On the basis that the positive electrode active material includes carbon-coated lithium iron phosphate, by controlling the total surface density (C Li ) and the surface density of the positive and negative electrodes satisfy the aforementioned formula, which is conducive to controlling the lithium supplement residual layer to have a more appropriate total thickness, and is conducive to better taking into account the wettability of the electrolyte to the first negative electrode active layer and the second negative electrode active layer and the ion transport performance of the surfaces on both sides of the first negative electrode active layer, and the capacity matching between the positive and negative electrodes is better, which is more conducive to improving the lithium supplement efficiency and battery cycle life. In some embodiments, it is also conducive to better controlling the heat generation caused by the reaction of water and lithium, thereby improving production safety.

[0503] In a second aspect of the present application, a lithium-supplemented negative electrode sheet is provided, the lithium-supplemented negative electrode sheet comprising a negative electrode current collector and a second negative electrode active initial layer, a second lithium-supplemented layer, a first negative electrode active initial layer and a first lithium-supplemented layer sequentially arranged on at least one side of the negative electrode current collector;

[0504] Furthermore, the first negative electrode active initial layer includes a first negative electrode active material, the first negative electrode active material includes non-agglomerated primary particles, and the number ratio or mass ratio of the non-agglomerated primary particles in the first negative electrode active material may be 80% to 100%;

[0505] The non-agglomerated primary particles include coated carbon-based materials, which include a carbon base body and a carbon coating layer located on at least a portion of the surface of the carbon base body. The carbon base body includes graphite, and the carbon coating layer includes one or more of amorphous carbon, soft carbon and hard carbon.

[0506] In some embodiments, the lithium-supplemented negative electrode sheet is the lithium-supplemented negative electrode sheet defined in the first aspect of the present application. In this case, the lithium-supplemented negative electrode sheet has the same characteristics as the lithium-supplemented negative electrode sheet in the component for preparing a lithium-ion secondary battery described in the first aspect of the present application.

[0507] By arranging a first negative electrode active initial layer located at an upper layer and a second negative electrode active initial layer located at a lower layer in the negative electrode active layer of the lithium-supplemented negative electrode sheet (the direction away from the surface of the negative electrode current collector is the upper layer, and the direction toward the surface of the negative electrode current collector is the lower layer), further, not only the first lithium-supplementing layer is arranged on the surface of the first negative electrode active initial layer away from the negative electrode current collector, but also the second lithium-supplementing layer is arranged between the first negative electrode active initial layer and the second negative electrode active initial layer, after being wetted and formed to achieve lithium insertion treatment, the first negative electrode active initial layer and the second negative electrode active initial layer are respectively pre-inserted with lithium to form corresponding first negative electrode active layers and second negative electrode active layers; the lithium-supplemented negative electrode sheet has a good overall lithium-supplementing effect, so that the prepared negative electrode sheet has a more uniform lithium-supplementing effect in the thickness direction, and the second negative electrode active initial layer located at the lower layer can also be fully lithium-supplemented; on the other hand, the negative electrode sheet is more uniformly and fully pre-inserted with lithium in the thickness direction, forming a more stable and uniform solid electrolyte interface (SEI) film as a whole; on the other hand, the second lithium-supplementing layer The gas generated during the lithium insertion process of the layer can form a path during the discharge process to promote the first lithium replenishment layer to be more fully and evenly infiltrated, so that the first negative electrode active layer located on the upper layer can be better pre-inserted with lithium, and the distribution uniformity of the SEI film in the first negative electrode active layer is improved; on the other hand, by setting a high content of non-agglomerated primary particles in the first negative electrode active material located on the upper layer, it is beneficial to reduce the embedding of the embeddable surface caused by particle agglomeration, which is beneficial to provide more lithium insertion sites. Further, by setting a coated carbon-based material in the non-agglomerated primary particles, the carbon coating layer can be used to optimize the lithium ion transmission channel and promote faster and more lithium ion insertion; through the aforementioned multiple effects, it is beneficial to store more lithium in the negative electrode, improve the lithium replenishment efficiency, and thus replenish the active lithium more sustainably during the charge and discharge cycle. It is also beneficial to enhance the structural stability of the negative electrode active materials located in the upper and lower layers when they are in contact with the electrolyte, and promote the negative electrode active materials located in the upper and lower layers to be able to supply capacity more sustainably, thereby giving the lithium-ion secondary battery a significantly extended cycle life.

[0508] Figure 1 It is a schematic diagram of the structure of the lithium-supplemented negative electrode sheet in one embodiment of the present application, corresponding to the side view. Figure 2 yes Figure 1 Schematic diagram of the structure of the lithium-supplemented negative electrode sheet, corresponding to the top view. Figure 1 The lithium supplement negative electrode sheet 12 in the illustrated embodiment includes a negative electrode current collector 102 and a second negative electrode active initial layer 104 , a second lithium supplement layer 110 , a first negative electrode active layer 106 and a first lithium supplement layer 108 sequentially disposed on one side of the negative electrode current collector 102 . Figure 1 In the figure, the second negative electrode active initial layer 104, the second lithium replenishing layer 110, the first negative electrode active initial layer 106 and the first lithium replenishing layer 108 are stacked in sequence along the thickness direction Z of the negative electrode plate, and the covering area of ​​the first lithium replenishing layer on the first negative electrode active initial layer is in the shape of a strip.

[0509] In the present application, unless otherwise specified, the X direction corresponds to the width direction of the lithium-supplemented negative electrode sheet or the negative electrode sheet in the lithium-ion secondary battery (which may be consistent with the height direction of the wound battery cell), the Y direction corresponds to the length direction of the lithium-supplemented negative electrode sheet or the negative electrode sheet in the lithium-ion secondary battery, and the Z direction corresponds to the thickness direction of the lithium-supplemented negative electrode sheet or the negative electrode sheet in the lithium-ion secondary battery.

[0510] Taking the electrode assembly assembled in a winding manner as an example, the Y direction may correspond to the winding direction of the electrode sheet, and the X direction may correspond to the extending direction of the electrode ear, that is, the X direction may correspond to the height direction of the electrode assembly or the bare cell.

[0511] Figure 3 This is a schematic diagram of the structure of a lithium-supplemented negative electrode sheet in another embodiment of the present application, corresponding to a top view, Figure 3 In the embodiment, the covering area of ​​the first lithium replenishing layer on the first negative electrode active initial layer is in the shape of a strip.

[0512] Figure 4 This is a schematic diagram of the structure of a lithium-supplemented negative electrode sheet in another embodiment of the present application, corresponding to a top view, Figure 4 In the embodiment, the shape of the covering area of ​​the first lithium replenishing layer on the first negative electrode active initial layer is a grid shape.

[0513] In some embodiments, the preparation method of the lithium-supplemented negative electrode sheet can refer to the third aspect of the present application.

[0514] In a third aspect of the present application, a method for preparing a lithium ion secondary battery is provided, which can be used to prepare the lithium ion secondary battery of the fourth aspect of the present application.

[0515] In some embodiments, a method for preparing a lithium ion secondary battery is provided, comprising the following steps:

[0516] S200: Assembling a positive electrode sheet, a separator and a lithium-supplemented negative electrode sheet into an electrode assembly, so that a separator is provided between the positive electrode sheet and the lithium-supplemented negative electrode sheet; wherein the lithium-supplemented negative electrode sheet comprises a negative electrode current collector and a second negative electrode active initial layer, a second lithium-supplemented layer, a first negative electrode active initial layer and a first lithium-supplemented layer sequentially provided on at least one side of the negative electrode current collector; further, the first negative electrode active initial layer comprises a first negative electrode active material, the first negative electrode active material comprises non-agglomerated primary particles, and the number proportion or mass proportion of the non-agglomerated primary particles in the first negative electrode active material may be 80% to 100%; the non-agglomerated primary particles comprise a coated carbon-based material, the coated carbon-based material comprises a carbon base body and a carbon coating layer located at least a portion of the surface of the carbon base body, the carbon base body comprises graphite, and the carbon coating layer comprises one or more of amorphous carbon, soft carbon and hard carbon;

[0517] S400: placing the electrode assembly in the accommodating cavity of the shell, injecting the electrolyte to obtain an assembly for preparing a lithium-ion secondary battery, allowing the electrolyte to infiltrate the positive electrode plate and the lithium-supplemented negative electrode plate, and forming them to prepare a lithium-ion secondary battery; wherein the lithium-supplemented negative electrode plate forms the negative electrode plate, the second negative electrode active initial layer forms the second negative electrode active layer, and the first negative electrode active initial layer forms the first negative electrode active layer.

[0518] In step 400, after being infiltrated and formed, the negative electrode lithium replenishing materials in the first lithium replenishing layer and the second lithium replenishing layer react with the electrolyte and are consumed, releasing active lithium, and the released active lithium is embedded in the negative electrode active initial layer to achieve lithium insertion, and the lithium replenishing negative electrode sheet is converted into a negative electrode sheet, and the second negative electrode active initial layer and the first negative electrode active initial layer are respectively converted into the second negative electrode active layer and the first negative electrode active layer. It can be understood that the second negative electrode active layer and the first negative electrode active layer each independently include lithium pre-embedded by the negative electrode lithium replenishment. The location of the consumed lithium replenishing layer usually produces residues generated as the lithium replenishment proceeds, and non-limiting examples of the residues include lithium that is inactivated because it is not able to be embedded in the negative electrode active material in time. In this way, a lithium replenishing residual layer including inactive lithium is formed at the location of the lithium replenishing layer; accordingly, the lithium replenishing residual layer formed at the location of the first lithium replenishing layer is called the first lithium replenishing residual layer, and the lithium replenishing residual layer formed at the location of the second lithium replenishing layer is called the second lithium replenishing residual layer.

[0519] In step 400, the negative electrode lithium supplement material may generate gas while releasing active lithium. For example, when the negative electrode lithium supplement material is single substance lithium, the single substance lithium reacts with the electrolyte to form lithium ions, and the electrolyte decomposes to generate gas.

[0520] By contacting the electrode assembly including the aforementioned lithium-supplemented negative electrode sheet with an electrolyte, impregnating, and forming, a negative electrode sheet including the negative electrode lithium-supplemented treatment can be prepared. The lithium-supplemented negative electrode sheet is provided with a first negative electrode active initial layer located on the upper layer and a second negative electrode active initial layer located on the lower layer (the direction away from the surface of the negative electrode current collector is the upper side, and the direction toward the surface of the negative electrode current collector is the lower side). Further, by using the first lithium-supplemented layer located above the first negative electrode active initial layer and the second lithium-supplemented layer located between the first negative electrode active initial layer and the second negative electrode active initial layer, after impregnation and formation, the first negative electrode active initial layer and the second negative electrode active initial layer are respectively pre-embedded with lithium, and the lithium-supplemented negative electrode sheet in the assembly for preparing a lithium-ion secondary battery forms a negative electrode sheet in a lithium-ion battery, and the first negative electrode active initial layer and the second negative electrode active initial layer in the lithium-supplemented negative electrode sheet are respectively converted into a first negative electrode active layer and a second negative electrode active layer, and the first negative electrode active layer and the second negative electrode active layer each independently include lithium pre-embedded by the negative electrode lithium-supplemented. The method has a good overall lithium replenishment effect on the negative electrode plate, so that the prepared negative electrode plate has a more uniform lithium replenishment effect in the thickness direction, and the second negative electrode active initial layer located in the lower layer can also be fully replenished with lithium; on the other hand, the negative electrode plate is more uniformly and fully pre-embedded with lithium in the thickness direction, forming a more stable and uniform solid electrolyte interface (SEI) film as a whole; on the other hand, the gas generated in the second lithium replenishment layer during the lithium insertion process can form a passage during the discharge process to promote the first lithium replenishment layer to be more fully and uniformly infiltrated, so that the first negative electrode active layer located in the upper layer is better pre-embedded with lithium, and the distribution uniformity of the SEI film in the first negative electrode active layer is improved; on the other hand, by Providing a high content of non-agglomerated primary particles in the material is beneficial to reducing the embedding of embeddable surfaces caused by particle agglomeration, and is beneficial to providing more lithium embedding sites. Furthermore, by providing a coated carbon-based material in the non-agglomerated primary particles, the carbon coating layer can be used to optimize the lithium ion transmission channel, thereby promoting faster and more lithium ion embedding; through the aforementioned multiple effects, it is beneficial to store more lithium in the negative electrode, improve the lithium replenishment efficiency, and thus replenish active lithium more sustainably during the charge and discharge cycle, and is also beneficial to enhance the structural stability of the upper and lower negative electrode active materials when they are in contact with the electrolyte, and promote the upper and lower negative electrode active materials to be able to supply capacity more sustainably, thereby giving the lithium-ion secondary battery a significantly extended cycle life.

[0521] In some embodiments, the lithium-supplemented negative electrode sheet is prepared by a method comprising the following steps:

[0522] S120: stacking a second negative electrode active dry layer, a second lithium film, a first negative electrode active dry layer and a first lithium film on at least one side surface of the negative electrode substrate to obtain a multilayer body to be rolled;

[0523] S130: Roll-pressing the multilayer body to be rolled to obtain a lithium-supplemented negative electrode sheet.

[0524] According to the aforementioned C N_A / (α·(m L1 / A L1 + m L2 / A L2 )×C Li / g +C P_A ) value controls the selection of appropriate C Li / g .

[0525] By adjusting one or more parameters such as the thickness, quality and morphology of the first lithium film and the second lithium film, rolling conditions, etc., the thickness (d 01 ,d 02 ), the coverage area percentage of the first lithium supplement layer on the first negative electrode active initial layer (f U0 ), the coverage area percentage of the second lithium supplement layer on the second negative electrode active initial layer (f M0 ), the surface density of the first lithium replenishing layer and the second lithium replenishing layer relative to the first negative electrode active initial layer (ρ 01 , 02 ) and other parameters.

[0526] The NP ratio of the prepared lithium-ion secondary battery can be tested and the measured value can be compared with the preset NP ratio. When there is a deviation, a more suitable NP ratio of the lithium-ion secondary battery can be obtained by adjusting the thickness, mass and morphology of the first lithium film and the second lithium film, the rolling conditions and other parameters, but not limited to this.

[0527] In some embodiments, in step S120, the negative electrode substrate includes a negative electrode current collector. In some embodiments, the negative electrode substrate is a negative electrode current collector, and further can be a copper foil.

[0528] In some implementations, step S120 includes the following steps:

[0529] S122: coating a second negative electrode slurry on at least one side of the negative electrode substrate, drying, and cold pressing to form a second negative electrode active dry layer on at least one side of the negative electrode substrate;

[0530] S124: stacking a second lithium film on a surface of the second negative electrode active dry layer away from the negative electrode substrate;

[0531] S126: coating the first negative electrode slurry on the surface of the second lithium film away from the second negative electrode active dry layer, drying, and cold pressing to form the first negative electrode active dry layer on the surface of the second lithium film away from the second negative electrode active dry layer;

[0532] S128: stacking the first lithium film on the surface of the first negative electrode active dry layer away from the second lithium film to obtain a multilayer body to be rolled.

[0533] In some embodiments, the composition of the first negative electrode slurry may refer to the composition of the first negative electrode active initial layer.

[0534] In some embodiments, the composition of the first negative electrode slurry may refer to the composition of the first negative electrode active layer.

[0535] In some embodiments, the composition of the second negative electrode slurry may refer to the composition of the second negative electrode active initial layer.

[0536] In some embodiments, the composition of the second negative electrode slurry may refer to the composition of the second negative electrode active layer.

[0537] In some embodiments, the first negative electrode slurry can be prepared by dispersing the above components for preparing the first negative electrode active initial layer, such as the first negative electrode active material, the conductive agent, the binder and any other components (such as a thickener) in a solvent (a non-limiting example of the solvent is deionized water) to form a first negative electrode slurry.

[0538] In some embodiments, the second negative electrode slurry may be prepared by dispersing the components for preparing the second negative electrode active initial layer, such as the second negative electrode active material, the conductive agent, the binder and any other components (such as a thickener) in a solvent (a non-limiting example of the solvent is deionized water) to form a second negative electrode slurry.

[0539] Without limitation, the solid content of the first negative electrode slurry and the second slurry can be independently 30 wt% to 70 wt%, and can be optionally 40 wt% to 70 wt%. The viscosity of the first negative electrode slurry and the second slurry at room temperature can be independently adjusted to 2000 mPa·s to 10000 mPa·s, and can be optionally 3000 mPa·s to 10000 mPa·s.

[0540] In the present application, "wt%" means weight percentage or mass percentage.

[0541] The required mass of the second lithium film and the first lithium film can refer to the first aspect of the present application, and can be calculated according to formula C N_A / (α·(m L1 / A L1 +m L2 / A L2 )×C Li / g +C P_A ) is controlled by the value of . In some embodiments, according to the formula (18×C Li +A) / B value to control.

[0542] By controlling the morphology of the first lithium film and the second lithium film, the morphology of the first lithium replenishment layer and the second lithium replenishment layer formed after the rolling process can be achieved. For example, a lithium film with hollow stripes can be selected to form a stripe-shaped lithium replenishment micro-region, and a lithium film with a hollow rectangle can also be selected to form a lithium replenishment micro-region with a grid-like morphology. After the lithium insertion treatment, the lithium replenishment residual layer usually also presents the same or similar morphology as the corresponding lithium replenishment layer. For example, a stripe-shaped lithium replenishment micro-region can form a stripe-shaped lithium replenishment residual micro-region, and a grid-shaped lithium replenishment micro-region can form a grid-shaped lithium replenishment residual micro-region.

[0543] In step S140 , by controlling the rolling parameters, the second lithium film and the first lithium film can be pressed to a preset thickness, corresponding to the second lithium replenishing layer and the first lithium replenishing layer, respectively.

[0544] In some embodiments, the pressure of the roller pressing is 60T to 100T. In some embodiments, the pressure of the roller pressing is 60T to 80T. Without limitation, the pressure of the roller pressing can also be any one of the following pressures or a range consisting of any two of the following pressures: 60T, 65T, 70T, 75T, 80T, 85T, 90T, 95T, 100T, etc.

[0545] In this application, unless otherwise specified, "1T pressure" means "1 ton pressure".

[0546] In some embodiments, during the roller pressing step, the roller pressing speed is also controlled to be 20 m / min to 100 m / min, and can also be any of the following roller pressing speeds or a range consisting of any two of the following roller pressing speeds: 20 m / min, 30 m / min, 40 m / min, 50 m / min, 60 m / min, 70 m / min, 80 m / min, 90 m / min, 100 m / min, etc.

[0547] In some embodiments, the method for preparing a lithium-ion secondary battery satisfies one or two of the following characteristics (any numerical parameter in the following characteristics can also be selected from any appropriate numerical value or range in the context):

[0548] In the step of allowing the electrolyte to infiltrate the positive electrode sheet and the lithium-supplemented negative electrode sheet, the infiltration temperature is 30° C. to 50° C.;

[0549] In the step of allowing the electrolyte to infiltrate the positive electrode sheet and the lithium-supplemented negative electrode sheet, the infiltration time is 10 hours to 30 hours.

[0550] Non-limitingly, in step S200 , the soaking method may be high temperature soaking, but is not limited thereto.

[0551] Without limitation, in step S200, the soaking temperature may be 30°C to 50°C, or any one of the following temperatures or a range consisting of any two of the following temperatures: 30°C, 35°C, 40°C, 45°C, 50°C, etc.

[0552] Without limitation, in step S200, the immersion time may be 10 h to 30 h, or any of the following durations or a range consisting of any two of the following durations: 10 h, 12 h, 15 h, 16 h, 18 h, 20 h, 24 h, 25 h, 26 h, 28 h, 30 h, etc.

[0553] By controlling the wetting parameters within the aforementioned range, it is beneficial for the electrolyte to more fully infiltrate the negative electrode plate.

[0554] In some embodiments, the components for preparing a lithium ion secondary battery are the components for preparing a lithium ion secondary battery described in the first aspect of the present application.

[0555] In a fourth aspect of the present application, a lithium-ion secondary battery is provided, comprising a negative electrode plate; the negative electrode plate comprises a negative electrode current collector and a second negative electrode active layer, a second lithium supplement residual layer, a first negative electrode active layer and a first lithium supplement residual layer sequentially arranged on at least one side of the negative electrode current collector;

[0556] The first negative electrode active layer and the second negative electrode active layer independently include lithium pre-embedded by negative electrode lithium supplementation;

[0557] Furthermore, the first negative electrode active initial layer includes a first negative electrode active material, the first negative electrode active material includes non-agglomerated primary particles, and the number ratio or mass ratio of the non-agglomerated primary particles in the first negative electrode active material may be 80% to 100%;

[0558] The non-agglomerated primary particles include coated carbon-based materials, which include a carbon base body and a carbon coating layer located on at least a portion of the surface of the carbon base body. The carbon base body includes graphite, and the carbon coating layer includes one or more of amorphous carbon, soft carbon and hard carbon.

[0559] In the present application, "the negative electrode plate includes lithium pre-embedded by negative electrode lithium supplementation" means that the negative electrode plate of the lithium-ion secondary battery has been treated with negative electrode lithium supplementation, so that the negative electrode plate includes not only the lithium embedded in the negative electrode during the formation process, but also the lithium additionally introduced by the negative electrode lithium supplementation treatment. During the negative electrode lithium supplementation process, the lithium supplementation material carried by the negative electrode plate releases active lithium ions, and the released active lithium ions are embedded in the negative electrode active material, thereby obtaining a negative electrode plate treated with negative electrode lithium supplementation, and the lithium embedded in the negative electrode during the negative electrode lithium supplementation process can be called "pre-embedded lithium"; after the negative electrode plate treated with negative electrode lithium supplementation is introduced into the lithium-ion secondary battery, the negative electrode plate can release the pre-embedded lithium during the charge and discharge process of the lithium-ion secondary battery, thereby replenishing the lithium continuously consumed by the battery system. Compared with the case where the negative electrode plate has not been treated with lithium supplementation, the lithium-ion secondary battery provided in the fourth aspect of the present application has a significantly extended cycle life.

[0560] In the present application, the negative electrode sheet includes a negative electrode active material layer and a lithium supplement residual layer, the negative electrode active material layer includes a second negative electrode active layer and a first negative electrode active layer, and the lithium supplement residual layer includes a second lithium supplement residual layer and a first lithium supplement residual layer. Further, the second negative electrode active layer, the second lithium supplement residual layer, the first negative electrode active layer and the first lithium supplement residual layer are sequentially arranged in a direction away from the negative electrode current collector.

[0561] The negative electrode plate in the lithium-ion secondary battery provided in the fourth aspect of the present application has been treated with lithium replenishment, and a first negative electrode active layer located in the upper layer and a second negative electrode active layer located in the lower layer are arranged on the negative electrode active layer of the negative electrode plate (the direction away from the surface of the negative electrode current collector is the upper side, and the direction toward the surface of the negative electrode current collector is the lower side), further, the lithium replenishment layer (which can be recorded as the first lithium replenishment layer) is treated with lithium replenishment above the first negative electrode active layer, and the lithium replenishment layer (which can be recorded as the second lithium replenishment layer) is also treated with lithium replenishment between the first negative electrode active layer and the second negative electrode active layer, and non-agglomerated primary particles that can provide more lithium insertion sites are arranged in the first negative electrode active material located in the upper layer, and particles that promote faster and more lithium ion insertion are arranged in the non-agglomerated primary particles. The multi-embedded coated carbon-based material enables the first negative electrode active layer and the second negative electrode active layer to independently include rich and uniform pre-embedded lithium, the first negative electrode active layer and the second negative electrode active layer are both fully replenished with lithium, the negative electrode plate has a good overall lithium replenishment effect, and can form a more stable and more uniform solid electrolyte interface (SEI) film as a whole; through the aforementioned multiple effects, it is beneficial to store more lithium in the negative electrode, thereby replenishing active lithium more lastingly during the charge and discharge cycle, and it is also beneficial to enhance the structural stability of the negative electrode active materials in the upper and lower layers when they are in contact with the electrolyte, and promote the negative electrode active materials in the upper and lower layers to be able to supply capacity more lastingly, thereby giving the lithium-ion secondary battery a significantly extended cycle life.

[0562] In the present application, the cross section of the negative electrode sheet can be subjected to microscopic morphology observation to observe the microscopic morphology of each negative electrode active layer in the negative electrode active material layer in the negative electrode sheet and the boundary between different negative electrode active layers, and then the thickness of different negative electrode active layers can be determined. "Cross section of the negative electrode sheet" refers to a cross section perpendicular to the thickness of the negative electrode sheet. Further, the cross section of the negative electrode sheet can also be subjected to microscopic morphology observation and combined with component analysis (such as energy dispersive spectrometer (EDS) etc.) to identify the element type to confirm the composition of different negative electrode active layers in the negative electrode active material layer. Non-limitingly, instruments or equipment including but not limited to focused electron beam (FIB) electron microscope (non-limiting examples such as FEI Scios 2HiVac equipment, etc.), ion cross section polisher (non-limiting examples such as IB-09010 CP argon ion cross section polisher, IB-19500CP ion cross section polisher, etc. of JEOL, Japan) can be used to obtain the cross section of the negative electrode sheet, and the cross section of the negative electrode sheet can also be obtained by plasma quenching method. Microscopic morphology observation methods may use instruments or equipment including but not limited to scanning electron microscopy (SEM) technology, and non-limitingly, a high-resolution field emission scanning electron microscope may be used; non-limiting examples of SEM instruments include the Sigma 300 scanning electron microscope and Apreo 2 SEM field emission scanning electron microscope of the German ZEISS company.

[0563] In the SEM microscopic morphology image of the cross section of the negative electrode sheet, the boundaries between different negative electrode active layers and the thickness of each negative electrode active layer can be confirmed based on the obvious discontinuous changes in the microscopic morphology.

[0564] In the present application, unless otherwise specified, the “section of the negative electrode sheet” refers to the cross section of the negative electrode sheet.

[0565] As an example, the cross section of the negative electrode sheet can be microscopically observed to confirm the single-side thickness of each negative electrode active layer and each lithium supplement residual layer. The definition of "cross section of the negative electrode sheet" is consistent with the above. The surface of the negative electrode sheet can also be microscopically observed and combined with elemental analysis to confirm the coverage area percentage (f) of the first lithium supplement residual layer relative to the first negative electrode active layer. U ).

[0566] In a non-limiting manner, the coverage area percentage of the first lithium supplement residual layer relative to the first negative electrode active layer (f U ) According to the element difference between the covered area and the uncovered area of ​​the first lithium replenishment residual layer in the SEM combined with EDS test image, the surface of the negative electrode piece can be measured using a CCD (inductively coupled device) to obtain the coverage area percentage of the first lithium replenishment residual layer relative to the first negative electrode active layer.

[0567] The following method can be used to analyze the coverage area of ​​the second lithium replenishment residual layer: the first negative electrode active layer and the first lithium replenishment residual layer above it can be peeled off from the negative electrode plate, based on the element difference between the covered area and the uncovered area of ​​the second lithium replenishment residual layer in the SEM combined with EDS test image, the morphology of the second lithium replenishment residual layer above the second negative electrode active layer is observed and measured using CCD, and then the coverage area percentage of the second lithium replenishment residual layer relative to the second negative electrode active layer (f M ). It can be combined with the grid method to measure and analyze the area percentage.

[0568] In the present application, the characteristics of negative electrode lithium replenishment technology can be combined. For example, by detecting the area covered by the lithium replenishment residue and the uncovered area, it can be judged whether the negative electrode plate has been treated with negative electrode lithium replenishment and the area covered by the lithium replenishment residue can be identified. Taking the use of metal lithium foil for negative electrode lithium replenishment as a non-limiting example, the lithium foil and the negative electrode active material are reacted under the action of the electrolyte, so that the lithium ions released by the lithium foil are embedded in the negative electrode active material, and lithium replenishment can be achieved. After lithium replenishment using this type of method, a residual area with the same shape as the lithium foil coverage area is usually formed at the position where the lithium foil is initially set. The residual area may contain inactive substances such as lithium oxide (Li2O) and other by-products. In addition, the residual area may also contain unreacted metallic lithium. Non-restrictively, SEM and EDS can be used in combination to distinguish the residual area from the area not covered by the lithium foil. For example, the distribution difference of carbon elements and / or silicon elements can be used to distinguish the residual area from the area not covered by the lithium foil. The above test analysis can be performed on the battery to be tested after it is fully discharged, or on a battery that has been through a smaller number of cycles (for example, a non-limiting example, the number of cycles does not exceed 5) .

[0569] In some embodiments, the first lithium replenishing residual layer and the second lithium replenishing residual layer each independently include inactive lithium.

[0570] A non-limiting example of inactive lithium is lithium oxide.

[0571] During the lithium insertion process, if the active lithium provided by the lithium replenishment layer is not able to be inserted into the negative electrode active material in time and becomes inactivated, a lithium replenishment residual layer including inactive lithium may be formed at the lithium replenishment layer position. Accordingly, a first lithium replenishment residual layer may be formed at the aforementioned first lithium replenishment layer position, and a second lithium replenishment residual layer may be formed at the aforementioned second lithium replenishment layer position. Based on this, the lithium replenishment method used by the lithium-ion secondary battery can be analyzed.

[0572] In the present application, the coverage area percentage of the second lithium supplement residual layer relative to the second negative electrode active layer is recorded as f, measured along the thickness direction of the negative electrode sheet and on one side of the negative electrode current collector. M The coverage area percentage of the first lithium supplement residual layer relative to the first negative electrode active layer is recorded as f U; The single-side thickness of the second lithium-replenishing residual layer is recorded as d2; the single-side thickness of the first lithium-replenishing residual layer is recorded as d1.

[0573] In some embodiments, the negative electrode plate satisfies one or more of the following characteristics (any numerical parameter in the following characteristics can also be selected from any suitable numerical value or range in the context):

[0574] The single-side thickness d2 of the second lithium-replenishing residual layer is less than the single-side thickness d1 of the first lithium-replenishing residual layer;

[0575] The second lithium supplement residual layer satisfies 0 <f M ≤f U ;

[0576] The second lithium supplement residual layer satisfies 0 <f M ≤70%, optionally, 10%≤f M ≤70%;

[0577] The single-side thickness d2 of the second lithium supplement residual layer is less than 1 μm, optionally, less than 0.1 μm, further optionally, less than 0.08 μm, and further optionally, less than 0.05 μm;

[0578] The first lithium supplement residual layer satisfies 0 <f U ≤70%, optionally, 30%≤f U ≤70%;

[0579] The single-side thickness d1 of the first lithium replenishing residual layer is less than 1 μm, optionally, less than 0.1 μm, further optionally, less than 0.08 μm, and further optionally, less than 0.05 μm.

[0580] In some embodiments, the single-side thickness d2 of the second lithium-replenishing residual layer is smaller than the single-side thickness d1 of the first lithium-replenishing residual layer.

[0581] In some embodiments, the second lithium supplement residual layer satisfies 0 <f M ≤f U .

[0582] In some embodiments, the second lithium supplement residual layer satisfies 0 <f M ≤70%, optionally, 10%≤f M ≤70%. Without limitation, f M It can also be any of the following percentages or a range consisting of any two of the following percentages: 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, etc.

[0583] In some embodiments, the thickness d2 of the second lithium supplement residual layer on one side is less than 1 μm, and optionally, d2 is less than 0.1 μm, further optionally, less than 0.08 μm, and further optionally, less than 0.05 μm. In a non-limiting manner, the thickness d2 of the second lithium supplement residual layer on one side can also be any of the following values, less than any of the following values, or selected from the range consisting of any two of the following values: 0.01 μm, 0.02 μm, 0.03 μm, 0.04 μm, 0.05 μm, 0.06 μm, 0.07 μm, 0.08 μm, 0.09 μm, 0.1 μm, etc.

[0584] In some embodiments, the first lithium supplement residual layer satisfies 0 <f U ≤70%, optionally, 30%≤f U ≤70%. Without limitation, f U It can also be any of the following percentages or a range consisting of any two of the following percentages: 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, etc.

[0585] In some embodiments, the thickness d1 of the first lithium supplement residual layer on one side is less than 1 μm, and optionally, d1 is less than 0.1 μm, further optionally, less than 0.08 μm, and further optionally, less than 0.05 μm. Without limitation, the thickness d1 of the first lithium supplement residual layer on one side can also be any of the following values, less than any of the following values, or selected from the range consisting of any two of the following values: 0.01 μm, 0.02 μm, 0.03 μm, 0.04 μm, 0.05 μm, 0.06 μm, 0.07 μm, 0.08 μm, 0.09 μm, 0.1 μm, etc.

[0586] By controlling the second lithium replenishment residual layer to meet one or more of the aforementioned characteristics, it is helpful to reduce or avoid the second lithium replenishment residual layer's obstruction to ion transmission between the first negative electrode active layer and the second negative electrode active layer, so that the first negative electrode active layer and the second negative electrode active layer have good ion transmission capacity during the charge and discharge cycle, which is helpful to better improve the cycle life of the battery.

[0587] In some embodiments, by controlling the single-side thickness (d2) of the second lithium replenishing residual layer and the coverage area percentage (f M , measured on a single side of the negative electrode current collector) within the aforementioned range is beneficial to promoting better wetting of the second negative electrode active layer during the charge and discharge cycle, thereby better improving the cycle life of the battery.

[0588] In some embodiments, by reducing or avoiding the second lithium supplement residual layer's hindrance to ion transport between the first negative electrode active layer and the second negative electrode active layer, the battery can achieve better dynamics and provide better fast charging performance.

[0589] By controlling the single-side thickness (d1) of the first lithium supplement residual layer within the aforementioned range, while realizing lithium insertion in the negative electrode active layer, during the charge and discharge cycle, it is also beneficial to enable the first negative electrode active layer and the electrolyte to have good ion transmission ability and wetting effect, which is beneficial to better improve the cycle life of the battery.

[0590] By controlling the coverage area percentage (f U , measured on a single side of the negative electrode current collector) within the aforementioned range, during the charge and discharge cycle, it is beneficial for the upper surface of the first negative electrode active layer to have good ion transmission ability, which is beneficial to better improve the battery cycle life.

[0591] In some embodiments, during the charge and discharge cycle, by making the upper surface of the first negative electrode active layer have good ion transport capability, it is beneficial to provide better fast charging performance.

[0592] In some embodiments, the negative electrode plate satisfies one or more of the following characteristics (any numerical parameter in the following characteristics can also be selected from any suitable numerical value or range in the context):

[0593] The single-side thickness d2 of the second lithium supplement residual layer is less than 0.1 μm, optionally, less than 0.08 μm, and further optionally, less than 0.05 μm;

[0594] The second lithium supplement residual layer meets 10%≤f M ≤70%;

[0595] The single-side thickness d1 of the first lithium supplement residual layer is less than 0.1 μm, optionally, less than 0.08 μm, and further optionally, less than 0.05 μm;

[0596] The first lithium supplement residual layer meets 30%≤f U ≤70%.

[0597] By controlling the single-side thickness (d2) of the second lithium replenishment residual layer and the coverage area percentage (f M , measured on a single side of the negative electrode current collector) within the aforementioned range, during the charge and discharge cycle, it is beneficial to have better ion transmission ability between the first negative electrode active layer and the second negative electrode active layer, which is beneficial to better improve the cycle life of the battery.

[0598] By controlling the single-side thickness (d1) of the first lithium replenishment residual layer and the coverage area percentage (f U , measured on a single side of the negative electrode current collector) is within the aforementioned range, during the charge and discharge cycle, it is also beneficial to have better ion transmission ability and wetting effect between the first negative electrode active layer and the electrolyte, which is beneficial to better improve the cycle life of the battery.

[0599] In some embodiments, the second lithium replenishing residual layer and the first lithium replenishing residual layer each independently include a plurality of lithium replenishing residual micro-regions.

[0600] Taking the first lithium supplement residual layer as an example, in terms of projection along the thickness direction of the negative electrode sheet, there are blank areas on the surface of the first negative electrode active layer that are not covered by the first lithium supplement residual layer. These blank areas isolate at least the first lithium supplement residual layer into a number of lithium supplement residual micro-regions. There is a certain distance between the isolated lithium supplement residual micro-regions. The minimum width of the lithium supplement residual micro-region between two blank areas can correspond to the "one-dimensional size" of the lithium supplement residual micro-region. Taking the lithium supplement residual micro-region in the form of stripes as an example, the one-dimensional size of the lithium supplement residual micro-region can correspond to the width of the lithium supplement residual stripes. Taking the lithium supplement residual micro-region in the form of a grid as an example, the one-dimensional size of the lithium supplement residual micro-region can correspond to the width of the grid lines in the lithium supplement residual grid.

[0601] In some embodiments, the negative electrode plate satisfies one or more of the following characteristics (any numerical parameter in the following characteristics can also be selected from any suitable numerical value or range in the context):

[0602] Measured by projection along the thickness direction of the negative electrode sheet, at least a portion of the lithium supplement residual micro-region has a one-dimensional size of 20 μm to 2000 μm;

[0603] The spacing between at least a portion of the lithium supplement residual micro-regions is 20 μm to 2000 μm, measured along the thickness direction of the negative electrode sheet;

[0604] The lithium supplement residual micro-regions in the first lithium supplement residual layer are distributed in a stripe shape or a grid shape;

[0605] The lithium replenishment residual micro-regions in the second lithium replenishment residual layer are distributed in a stripe shape or a grid shape.

[0606] In some embodiments, the negative electrode plate satisfies one or more of the following characteristics (any numerical parameter in the following characteristics can also be selected from any suitable numerical value or range in the context):

[0607] Measured by projection along the thickness direction of the negative electrode sheet, the one-dimensional size of at least a portion of the lithium supplement residual micro-region is 20 μm to 1000 μm;

[0608] Measured by projection along the thickness direction of the negative electrode sheet, the spacing between at least a portion of the lithium supplement residual micro-regions is 20 μm to 1000 μm.

[0609] In some embodiments, measured by the projection along the thickness direction of the negative electrode sheet, the one-dimensional size of at least a portion of the lithium-supplemented residual microregion is 20μm~2000μm, and can be optionally 20μm~1000μm, or can be any of the following values ​​or a range consisting of any two of the following values: 20μm, 40μm, 50μm, 60μm, 80μm, 100μm, 150μm, 200μm, 300μm, 400μm, 500μm, 600μm, 800μm, 1000μm, 1200μm, 1500μm, 1600μm, 1800μm, 2000μm, etc.

[0610] In some embodiments, measured by projection along the thickness direction of the negative electrode sheet, the spacing between at least a portion of the lithium-supplemented residual micro-regions is 20μm~2000μm, and can be optionally 20μm~1000μm, or can be any of the following values ​​or a range consisting of any two of the following values: 20μm, 40μm, 50μm, 60μm, 80μm, 100μm, 150μm, 200μm, 300μm, 400μm, 500μm, 600μm, 800μm, 1000μm, 1200μm, 1500μm, 1600μm, 1800μm, 2000μm, etc.

[0611] In some embodiments, the lithium-replenishing residual micro-regions in the first lithium-replenishing residual layer are distributed in a stripe shape or a grid shape.

[0612] In some embodiments, the lithium-replenishing residual micro-regions in the second lithium-replenishing residual layer are distributed in a stripe shape or a grid shape.

[0613] In some embodiments, the lithium-replenishing residual micro-regions in the first lithium-replenishing residual layer are distributed in a stripe shape, and the lithium-replenishing residual micro-regions in the second lithium-replenishing residual layer are distributed in a grid shape.

[0614] In some embodiments, in the lithium-supplemented residual layer of the negative electrode plate, there are a number of discontinuous stripe-shaped blank areas in the stripe-shaped distribution, and the stripe-shaped blank areas are distributed alternately with the stripe-shaped lithium-supplemented residual micro-areas.

[0615] In some embodiments, in the lithium-supplemented residual layer of the negative electrode sheet, there are a number of discontinuous rectangular blank areas in the grid-like distribution, and the lithium-supplemented residual micro-regions are connected to each other. In some of these embodiments, there are a number of discontinuous regular blank areas in the grid-like distribution, and the lithium-supplemented residual micro-regions are connected to each other.

[0616] In some embodiments, the lithium-replenishing residual micro-regions in the first lithium-replenishing residual layer are distributed in stripes. In a non-limiting manner, the stripe spacing of the lithium-replenishing residual micro-regions in the first lithium-replenishing residual layer can be 20 μm to 2000 μm, optionally 20 μm to 1000 μm, or any of the following values ​​or a range selected from any two of the following values: 20 μm, 40 μm, 50 μm, 60 μm, 80 μm, 100 μm, 150 μm, 200 μm, 300 μm, 400 μm, 500 μm, 600 μm, 800 μm, 1000 μm, 1200 μm, 1500 μm, 1600 μm, 1800 μm, 2000 μm, etc. Without limitation, the stripe width of the lithium-replenishing residual microregion in the first lithium-replenishing residual layer can be 20μm~2000μm, optionally 20μm~1000μm, or any of the following values ​​or a range consisting of any two of the following values: 20μm, 40μm, 50μm, 60μm, 80μm, 100μm, 150μm, 200μm, 300μm, 400μm, 500μm, 600μm, 800μm, 1000μm, 1200μm, 1500μm, 1600μm, 1800μm, 2000μm, etc.

[0617] In some embodiments, the lithium-supplementing residual micro-regions in the second lithium-supplementing residual layer are distributed in a grid shape. In a non-limiting manner, the grid spacing of the lithium-supplementing residual micro-regions in the second lithium-supplementing residual layer can be 20 μm to 2000 μm, optionally 20 μm to 1000 μm, or any of the following values ​​or a range selected from any two of the following values: 20 μm, 40 μm, 50 μm, 60 μm, 80 μm, 100 μm, 150 μm, 200 μm, 300 μm, 400 μm, 500 μm, 600 μm, 800 μm, 1000 μm, 1200 μm, 1500 μm, 1600 μm, 1800 μm, 2000 μm, etc. Without limitation, the grid line width of the lithium-replenishing residual micro-region in the second lithium-replenishing residual layer can be 20μm~2000μm, optionally 20μm~1000μm, or any of the following values ​​or a range selected from any two of the following values: 20μm, 40μm, 50μm, 60μm, 80μm, 100μm, 150μm, 200μm, 300μm, 400μm, 500μm, 600μm, 800μm, 1000μm, 1200μm, 1500μm, 1600μm, 1800μm, 2000μm, etc.

[0618] In some embodiments, the lithium-replenishing residual micro-regions in the first lithium-replenishing residual layer are distributed in stripes; the stripe spacing of the lithium-replenishing residual micro-regions in the first lithium-replenishing residual layer is 20μm~2000μm, which can be optionally 20μm~1000μm, and further can be optionally 20μm~500μm, and the stripe width is 20μm~2000μm, which can be optionally 20μm~1000μm, and further can be optionally 20μm~500μm; the lithium-replenishing residual micro-regions in the second lithium-replenishing residual layer are distributed in a grid shape; the grid spacing of the lithium-replenishing residual micro-regions in the second lithium-replenishing residual layer is 20μm~2000μm, which can be optionally 20μm~1000μm, and further can be optionally 20μm~500μm, and the grid line width is 20μm~2000μm, which can be optionally 20μm~1000μm, and further can be optionally 20μm~500μm.

[0619] In some embodiments, the lithium-replenishing residual micro-regions in the first lithium-replenishing residual layer and the second lithium-replenishing residual layer are independently distributed in stripes. Without limitation, the stripe spacing and stripe width of the lithium-replenishing residual micro-regions in the first lithium-replenishing residual layer can be independently 20μm~2000μm, optionally 20μm~1000μm, and further optionally 20μm~500μm. Without limitation, the stripe spacing and stripe width of the lithium-replenishing residual micro-regions in the second lithium-replenishing residual layer can be independently 20μm~2000μm, optionally 20μm~1000μm, and further optionally 20μm~500μm. In some embodiments, the stripe spacing of the lithium-replenishing residual micro-regions in the second lithium-replenishing residual layer is greater than the stripe spacing of the lithium-replenishing residual micro-regions in the first lithium-replenishing residual layer.

[0620] In some embodiments, the lithium-replenishing residual micro-regions in the first lithium-replenishing residual layer are distributed in stripes; the stripe spacing of the lithium-replenishing residual micro-regions in the first lithium-replenishing residual layer is 20 μm to 500 μm, and the stripe width is 20 μm to 500 μm;

[0621] The lithium replenishment residual micro-regions in the second lithium replenishment residual layer are distributed in a grid shape; the grid spacing of the lithium replenishment residual micro-regions in the second lithium replenishment residual layer is 20 μm-500 μm, and the grid line width is 20 μm-500 μm.

[0622] By controlling the lithium-replenished residual micro-areas in the negative electrode plate to conform to one or more of the aforementioned sizes and shapes, it is beneficial to provide a more sufficient contact area for the electrolyte to infiltrate the negative electrode plate, which is beneficial to optimizing the ion transfer between the first negative electrode active layer and the second negative electrode active layer, and can also take into account the amount of lithium replenishment. Through the aforementioned multiple effects, it is beneficial to better improve the battery cycle life.

[0623] In some embodiments, the negative electrode plate satisfies one or more of the following characteristics (any numerical parameter in the following characteristics can also be selected from any suitable numerical value or range in the context):

[0624] The thickness of the first negative electrode active layer is 50 μm to 120 μm, and can be 50 μm to 100 μm, based on the total thickness in the negative electrode sheet;

[0625] The thickness of one side of the first negative electrode active layer is 25 μm to 60 μm, and can be 25 μm to 50 μm;

[0626] The ratio of the thickness of the first negative electrode active layer to the sum of the thickness of the first negative electrode active layer and the second negative electrode active layer is denoted as f H , satisfying 10%≤f H ≤70%, optionally, 20%≤f H ≤70%, further optionally, 30%≤f H ≤50%.

[0627] In some embodiments, the negative electrode plate satisfies one or more of the following characteristics (any numerical parameter in the following characteristics can also be selected from any suitable numerical value or range in the context):

[0628] The thickness of the first negative electrode active layer is 50 μm to 100 μm, based on the total thickness in the negative electrode sheet;

[0629] The thickness of the first negative electrode active layer on one side is 25 μm to 50 μm;

[0630] 30%≤f H ≤50%.

[0631] In some embodiments, the thickness of the first negative electrode active layer is 50 μm to 120 μm, and can be optionally 50 μm to 100 μm, and can also be any of the following values ​​or a range consisting of any two of the following values: 50 μm, 55 μm, 60 μm, 65 μm, 70 μm, 75 μm, 80 μm, 85 μm, 90 μm, 95 μm, 100 μm, 110 μm, 120 μm, etc., based on the total thickness in the negative electrode sheet.

[0632] In some embodiments, the single-side thickness of the first negative electrode active layer can be 25μm~60μm, optionally 25μm~50μm, or any of the following values ​​or a range consisting of any two of the following values: 25μm, 30μm, 35μm, 40μm, 45μm, 50μm, 55μm, 60μm, etc.

[0633] In the present application, the ratio of the thickness of the first negative electrode active layer to the sum of the thickness of the first negative electrode active layer and the second negative electrode active layer is denoted as f H .

[0634] In some embodiments, 10%≤f H≤70%, optionally, 20%≤f H ≤70%, further optionally, 30%≤f H ≤50%. Without limitation, f H It can also be any of the following percentages or a range consisting of any two of the following percentages: 10%, 15%, 20%, 30%, 40%, 50%, 60%, 70%, etc.

[0635] By calculating the thickness of the first negative electrode active layer (D1) and the ratio of the thickness of the first negative electrode active layer to the sum of the thicknesses of the first negative electrode active layer and the second negative electrode active layer (f H ) is controlled within the aforementioned range, which is beneficial to better balance the high lithium replenishment amount provided by the first negative electrode active layer and the overall energy density of the negative electrode sheet, and further beneficial to better balance the battery cycle life and energy density.

[0636] In some embodiments, the negative electrode plate satisfies one or more of the following characteristics:

[0637] The compaction density of the second negative electrode active layer is higher than the compaction density of the first negative electrode active layer;

[0638] The powder compaction density of the second negative electrode active layer is higher than the powder compaction density of the first negative electrode active layer.

[0639] In some embodiments, the compaction density of the second negative electrode active layer is higher than the compaction density of the first negative electrode active layer.

[0640] In the present application, unless otherwise specified, the compaction density of the “second negative electrode active layer” refers to the ratio of the mass to the volume of the second negative electrode active layer, and the compaction density of the “first negative electrode active layer” refers to the ratio of the mass to the volume of the first negative electrode active layer.

[0641] Without limitation, the following method can be used to test the compaction density of the first negative electrode active layer and the second negative electrode active layer in the negative electrode sheet of a lithium-ion secondary battery: disassemble the battery to obtain the negative electrode sheet, and punch it into small discs of a certain area A0. Scrape a certain thickness d1 of powder in the first negative electrode active layer from the corresponding thickness position, weigh the powder mass M1, and calculate the compaction density of the first negative electrode active layer PD1=M1 / (A0×d1). Test multiple small discs and take the average value. Also scrape a certain thickness d2 of powder in the second negative electrode active layer from the corresponding thickness position, weigh the powder mass M2, and calculate the compaction density of the second negative electrode active layer PD2=M2(A0×d2). Test multiple small discs and take the average value.

[0642] By adjusting the compaction density of the second negative electrode active layer to be higher than that of the first negative electrode active layer, the energy density of the lithium-ion secondary battery can be improved. On the other hand, the first negative electrode active initial layer has a lower compaction density, which is beneficial to both prolonging the cycle life and improving the energy density.

[0643] In some embodiments, the powder compaction density of the second negative electrode active layer is higher than the powder compaction density of the first negative electrode active layer.

[0644] In the present application, unless otherwise specified, the "powder compaction density" of the second negative electrode active layer refers to the powder compaction density of the powder material constituting the second negative electrode active layer. The definition of "powder compaction density" can be found in the first aspect of the present application.

[0645] By controlling the powder compaction density of the second negative electrode active layer to be higher than the powder compaction density of the first negative electrode active layer, it is beneficial to give the second negative electrode active layer in the lithium ion secondary battery a higher compaction density.

[0646] In some embodiments, the negative electrode plate satisfies one or more of the following characteristics:

[0647] The compaction density of the second negative electrode active layer is 1.04 g / cm 3 ~1.71g / cm 3 ;

[0648] The overall compaction density of the negative electrode is 1.04g / cm 3 ~1.62g / cm 3 .

[0649] In a non-limiting manner, the compaction density of the second negative electrode active layer may be 1.04 g / cm 3 ~1.71g / cm 3 , can also be any of the following values ​​or a range consisting of any two of the following values: 1.04 g / cm 3 , 1.05 g / cm 3 , 1.06 g / cm 3 , 1.08 g / cm 3 , 1.10 g / cm 3 , 1.15 g / cm 3 , 1.20 g / cm 3 , 1.25 g / cm 3 , 1.30 g / cm 3 , 1.35 g / cm 3 , 1.40 g / cm 3 , 1.45 g / cm 3 , 1.50 g / cm 3 , 1.55 g / cm3 , 1.60 g / cm 3 , 1.65 g / cm 3 , 1.70 g / cm 3 , 1.71 g / cm 3 .

[0650] In some embodiments, the overall compaction density of the negative electrode sheet can be 1.04 g / cm 3 ~1.62g / cm 3 , can also be any of the following values ​​or a range consisting of any two of the following values: 1.04 g / cm 3 , 1.05 g / cm 3 , 1.06 g / cm 3 , 1.08 g / cm 3 , 1.10 g / cm 3 , 1.15 g / cm 3 , 1.20 g / cm 3 , 1.25 g / cm 3 , 1.30 g / cm 3 , 1.35 g / cm 3 , 1.40 g / cm 3 , 1.45 g / cm 3 , 1.50 g / cm 3 , 1.55 g / cm 3 , 1.60 g / cm 3 , 1.62 g / cm 3 .

[0651] In the present application, unless otherwise specified, the “overall compaction density of the negative electrode sheet” refers to the ratio of the total mass to the total volume of the negative electrode active layer in the negative electrode sheet.

[0652] Without limitation, the overall compaction density of the negative electrode sheet can be tested by the following method: disassemble the battery to obtain the negative electrode sheet, and punch the obtained negative electrode sheet into 1540.25 mm 2 The mass M of the small disc is measured. B and thickness L B Take the negative electrode sheet from another area, wipe off the negative electrode active layer on the surface and remove the remaining negative electrode current collector foil (which can be recorded as empty negative electrode current collector foil), and also punch it into 1540.25mm 2 The mass of the empty negative electrode current collector foil is weighed as M0 and the thickness is L0, then the overall compaction density of the negative electrode sheet is PD B =(M B -M0) / [1.54025×(L B -L0)].

[0653] By controlling the overall compaction density of the negative electrode plate within the aforementioned range, it is beneficial to take into account both battery energy density and higher lithium replenishment efficiency.

[0654] Exemplarily, by adjusting the overall compaction density of the negative electrode sheet within the aforementioned range, it is beneficial to balance battery dynamics and energy density.

[0655] Exemplarily, by adjusting the overall compaction density of the negative electrode sheet within the aforementioned range, it is beneficial to balance improving energy density and extending cycle life.

[0656] By regulating the compaction density of the second negative electrode active layer and / or the compaction density of the powder of the second negative electrode active layer, the comprehensive requirements of extending the cycle life and improving the energy density can be better balanced.

[0657] It can be understood that the negative electrode sheet in the lithium-ion secondary battery usually rebounds after being infiltrated with the electrolyte, compared with the lithium-supplemented negative electrode sheet that is rolled and has a lithium-supplemented layer but is not in contact with the electrolyte, resulting in the compaction density of the negative electrode sheet in the battery being usually lower than the compaction density of the lithium-supplemented negative electrode sheet. Furthermore, after the formation process, the negative electrode active material reacts with the electrolyte at the interface to form a solid electrolyte interface (SEI) film on the surface of the negative electrode active material. The SEI film will also have a certain effect on the compaction density of the negative electrode active material, but the effect is relatively small. In addition, in lithium-ion secondary batteries, the compaction density of the negative electrode sheet and the negative electrode active layers it contains is also related to the charge and discharge state. The negative electrode sheet expands in the charging state, and the negative electrode sheet shrinks in the discharging state. Without limitation, based on the volume of the lithium-supplemented negative electrode sheet or the negative electrode active initial layer therein which has been rolled to add a lithium-supplemented layer but has not contacted the electrolyte, the volume expansion coefficient of the negative electrode sheet or the negative electrode active layer therein in the fully discharged state of the lithium-ion secondary battery can be 1.05-1.3, optionally 1.05-1.25, further optionally 1.05-1.2, and can also be any of the following values ​​or a range selected from any two of the following values: 1.05, 1.06, 1.07, 1.08, 1.09, 1.10, 1.11, 1.12, 1.13, 1.14, 1.15, 1.16, 1.17, 1.18, 1.19, 1.20, 1.22, 1.24, 1.25, 1.26, 1.28, etc. Without limitation, based on the volume of the lithium-supplemented negative electrode sheet or the negative electrode active initial layer thereof which has been rolled to add a lithium-supplemented layer but has not contacted the electrolyte, the volume expansion coefficient of the negative electrode sheet or the negative electrode active layer thereof in the fully discharged state of the lithium-ion secondary battery can also be any of the following values ​​or a range consisting of any two of the following values: 1.05, 1.1, 1.2, 1.25, 1.26, 1.27, 1.28, etc. It can be understood that the compaction density of the negative electrode sheet or the negative electrode active layer thereof in the lithium-ion secondary battery can be calculated by dividing the compaction density of the lithium-supplemented negative electrode sheet or the negative electrode active initial layer thereof by the corresponding volume expansion coefficient. In some embodiments, the compaction density of the "lithium-supplemented negative electrode sheet which has been rolled to add a lithium-supplemented layer but has not contacted the electrolyte" is 1.3 g / cm 3 ~1.7 g / cm 3 .

[0658] In some embodiments, when the battery is fully discharged, the compaction density of the negative electrode sheet is 1.04 g / cm 3 ~1.62g / cm 3 , which can be obtained by fully discharging the lithium-ion secondary battery, disassembling the battery cell, and taking out the negative electrode plate for measurement.

[0659] It can be understood that the first negative electrode active layer includes a first negative electrode active material, and the second negative electrode active layer includes a second negative electrode active material; the lithium-ion secondary battery also includes a positive electrode plate, and the positive electrode plate includes a positive electrode active material.

[0660] The following method can be used to obtain the first negative electrode material in the first negative electrode active layer and the second negative electrode material in the second negative electrode active layer: disassemble the battery cell to take out the negative electrode sheet, scrape the powder at the thickness position of the first negative electrode active layer and the second negative electrode active layer in the negative electrode sheet respectively, and obtain the first negative electrode material (taken from the first negative electrode active layer) and the second negative electrode material (taken from the second negative electrode active layer) respectively after drying. The first negative electrode material includes the first negative electrode active material, and the second negative electrode material includes the second negative electrode active material. Those skilled in the art can further extract the first negative electrode active material and the second negative electrode active material by existing methods. The corresponding negative electrode active materials can be extracted from different negative electrode active layers of the negative electrode sheet by solvent washing, ultrasonic dispersion, graded sedimentation and other methods, and the samples can be obtained by drying. Taking the extraction of the first negative electrode active material from the first negative electrode material as an example, the following method can be used, but is not limited to this: use a solvent (such as dimethyl carbonate) to fully soak the first negative electrode material, so that the organic components such as binders and thickeners therein are dissolved in the solvent (it can also be combined with ultrasonic dispersion to promote dissolution), and after washing and filtering, the collected solid phase is used as the powder to be tested for the negative electrode active material. It should be noted that the small amount of conductive agent that may be contained in the test sample does not affect the type of negative electrode active material in the first negative electrode active layer and the second negative electrode active layer, D v 50. Test, analysis and comparison of agglomeration morphology, etc.

[0661] In some embodiments, the lithium-ion secondary battery satisfies one or more of the following characteristics (any numerical parameter in the following characteristics can also be selected from any suitable numerical value or range in the context):

[0662] D of the first negative electrode active material v 50 lower than the D of the second negative electrode active material v 50; among them, D v 50 represents the particle size corresponding to when the cumulative volume distribution percentage of the multi-particle mixture reaches 50%;

[0663] D of the first negative electrode active material v 50 is 7μm ~14μm, optional is 8μm ~13μm;

[0664] D of the second negative electrode active material v 50 is 8μm ~14μm, and can be selected as 9μm ~13μm;

[0665] The porosity of the first negative electrode active layer is higher than the porosity of the second negative electrode active layer;

[0666] The porosity of the first negative electrode active layer is 20%~45%;

[0667] The porosity of the second negative electrode active layer is 15%~45%;

[0668] The first negative electrode active material includes non-agglomerated primary particles, and the non-agglomerated primary particles include carbon-based materials; the non-agglomerated primary particles may account for 80% to 100% of the first negative electrode active material;

[0669] The positive electrode active material includes one or more of a ternary positive electrode material, a modified product of a ternary positive electrode material, lithium iron phosphate, a modified product of lithium iron phosphate, lithium iron manganese phosphate and a modified product of lithium iron manganese phosphate; the modified product includes one or more of a doping element and a coating element.

[0670] In some embodiments, the lithium-ion secondary battery satisfies one or more of the following characteristics (any numerical parameter in the following characteristics can also be selected from any suitable numerical value or range in the context):

[0671] D of the first negative electrode active material v 50: 8μm ~13μm;

[0672] D of the second negative electrode active material v 50 is 9μm ~13μm;

[0673] The first negative electrode active material includes non-agglomerated primary particles, the non-agglomerated primary particles include coated carbon-based materials, the coated carbon-based materials include a carbon base body and a carbon coating layer (which may be recorded as a first carbon coating layer) located at least a portion of the surface of the carbon base body, the carbon base body includes graphite, and the first carbon coating layer includes one or more of amorphous carbon, soft carbon and hard carbon; further, the coated carbon-based material in the non-agglomerated primary particles accounts for 80% to 100% in number or mass in the first negative electrode active material;

[0674] The positive electrode active material includes carbon-coated lithium iron phosphate, which includes a lithium iron phosphate body and a carbon coating layer (which can be recorded as a second carbon coating layer) located on at least a portion of the surface of the lithium iron phosphate body, and the second carbon coating layer includes one or more of soft carbon, hard carbon and amorphous carbon. Optionally, the carbon coating layer includes soft carbon.

[0675] In some embodiments, D of the first negative electrode active material v 50 lower than the D of the second negative electrode active material v 50; among them, D v 50 represents the particle size corresponding to the cumulative volume distribution percentage of the multi-particle mixture reaching 50%. v The definition and test method of 50 can be found in the previous article.

[0676] By arranging the negative electrode active material with a smaller particle size in the first negative electrode active layer, it is beneficial to reduce the solid phase diffusion path of the first negative electrode active layer, which is beneficial to optimize the battery dynamics.

[0677] In some embodiments, D of the first negative electrode active material v 50 is 7μm ~14μm, and can be 8μm ~13μm, or any of the following values ​​or a range consisting of any two of the following values: 7μm, 7.5μm, 8μm, 8.5μm, 9μm, 10μm, 11μm, 12μm, 12.5μm, 13μm, 13.5μm, 14μm, etc.

[0678] In some embodiments, D of the second negative electrode active material v 50 is 8μm ~14μm, and can be optionally 9μm ~13μm. It can also be any of the following values ​​or a range consisting of any two of the following values: 8μm, 8.5μm, 9μm, 10μm, 11μm, 12μm, 12.5μm, 13μm, 13.5μm, 14μm, etc.

[0679] By v 50 is set within the aforementioned range, which is beneficial to reducing the solid phase diffusion path of the first negative electrode active layer, thereby optimizing the battery kinetics.

[0680] By matching the particle sizes of the first negative electrode active material and the second negative electrode active material, it can be achieved that the upper layer in the first negative electrode active layer and the lower layer in the second negative electrode active layer have a low compaction density and have a suitable compaction density difference, which is beneficial to taking into account the battery cycle life, battery dynamics and energy density.

[0681] In some embodiments, the porosity of the first negative electrode active layer is higher than the porosity of the second negative electrode active layer.

[0682] By controlling the porosity of the first negative electrode active layer to be higher than that of the second negative electrode active layer, the high porosity of the upper layer can provide more channels for lithium ion transmission, which is beneficial to improving battery kinetics.

[0683] In some embodiments, the porosity of the first negative electrode active layer is 20% to 45%, and can also be any of the following percentages or a range consisting of any two of the following percentages: 20%, 25%, 30%, 35%, 40%, 45%, etc.

[0684] In some embodiments, the porosity of the second negative electrode active layer is 15% to 45%, and can also be any of the following percentages or a range consisting of any two of the following percentages: 15%, 20%, 25%, 30%, 35%, 40%, 45%, etc.

[0685] The definition of "porosity" can be found above.

[0686] The following method can be used to test the porosity of the first negative electrode active layer and the second negative electrode active layer: punch the negative electrode plate into small discs, use the nano-space dynamic resolution and layer-by-layer cutting technology of FIB-SEM (focused electron beam electron microscope-scanning electron microscope) to reconstruct the three-dimensional structure of the sample, and use the energy dispersive spectrometer (EDS, Energy Dispersive Spectrometer) to analyze the distribution and proportion of each element. According to the component boundaries, the second negative electrode active layer, the second lithium supplement residual layer, the first negative electrode active layer and the first lithium supplement residual layer can be identified. Finally, the porosity of the first negative electrode active layer and the second negative electrode active layer is obtained by quantitative analysis through software. The FEI Scios 2HiVac device can be used for testing.

[0687] In addition, the porosity of the first negative electrode active layer and the second negative electrode active layer can be qualitatively compared by means of cross-sectional morphology observation methods. The negative electrode sheet can be cut by plasma quenching, and the cross-sectional morphology of the obtained cross section can be observed under a scanning electron microscope (SEM). The cross-sectional morphology can also be observed in conjunction with an energy dispersive spectrometer (EDS), the position of each structural layer can be identified, the thickness of each structural layer can be obtained, the pore size and number of different structural layers can be observed and compared, and then the porosity can be qualitatively compared.

[0688] By controlling the porosity of the first negative electrode active layer within the aforementioned range, it is beneficial to take both battery kinetics and energy density into account.

[0689] In some embodiments, the first negative electrode active material includes non-agglomerated primary particles. Without limitation, the number ratio or mass ratio of the non-agglomerated primary particles in the first negative electrode active material can be 80% to 100%, or can be any of the following percentages or a range selected from any two of the following percentages: 80%, 85%, 90%, 95%, 98%, 99%, 100%, etc.

[0690] In some embodiments, the second negative electrode active material includes secondary particles. Without limitation, the number ratio or mass ratio of the secondary particles in the second negative electrode active material can be 80% to 100%, or can be any of the following percentages or a range selected from any two of the following percentages: 80%, 85%, 90%, 95%, 98%, 99%, 100%, etc.

[0691] The first negative electrode active material extracted from the disassembled battery cell can be laid and adhered to the conductive glue, and the particle morphology can be tested by a scanning electron microscope (such as ZEISS Sigma 300). The number of particles in the obtained SEM image is counted to determine whether they are non-agglomerated primary particles or secondary particles, and the number ratio of non-agglomerated primary particles in the first negative electrode active material can be obtained. The number ratio of secondary particles in the first negative electrode active material can be obtained by taking statistics from multiple regions. A similar method can be used to obtain the number ratio of secondary particles in the first negative electrode active material.

[0692] In some embodiments, the first negative electrode active material includes a carbon-based material.

[0693] In some embodiments, the positive electrode active material includes one or more of a ternary positive electrode material, lithium iron phosphate, lithium manganese iron phosphate, and a modified form of any of the foregoing positive electrode active materials; the modified form includes one or more of a doping element and a coating element.

[0694] By introducing a coated carbon-based material into the first negative electrode active material located in the upper layer, amorphous carbon is coated on at least a portion of the surface of the carbon base body, which is beneficial to provide a better lithium ion transmission channel for the carbon base body, thereby promoting lithium ion transmission and improving lithium replenishment efficiency, and further beneficial to improving battery dynamics and cycle life.

[0695] In some embodiments, the first negative electrode active material satisfies one or more of the following characteristics (any numerical parameter in the following characteristics can also be selected from any suitable numerical value or range in the context):

[0696] The first negative electrode active material includes non-agglomerated primary particles, the non-agglomerated primary particles include coated carbon-based materials, and the coated carbon-based materials include non-agglomerated coated graphite; the number ratio or mass ratio of the non-agglomerated coated graphite in the first negative electrode active material is 80% to 100%;

[0697] The amount or mass proportion of the coated carbon-based material in the first negative electrode active material is 80% to 100%.

[0698] In some embodiments, the coated carbon-based material in the non-agglomerated primary particles includes non-agglomerated coated graphite; without limitation, the quantity ratio or mass ratio of the non-agglomerated coated graphite in the first negative electrode active material can be 80% to 100%, or can be any of the following percentages or a range selected from any two of the following percentages: 80%, 85%, 90%, 95%, 98%, 99%, 100%, etc.

[0699] In some embodiments, the amount or mass proportion of the coated carbon-based material in the first negative electrode active material is 80% to 100%, and can also be any of the following percentages or a range selected from any two of the following percentages: 80%, 85%, 90%, 95%, 98%, 99%, 100%, etc.

[0700] By introducing non-agglomerated coated graphite into the first negative electrode active material located in the upper layer, it is beneficial to expose more lithium insertion sites, and the carbon coating layer can also be used to promote faster and more lithium ion insertion, which is beneficial to improve the lithium replenishment efficiency.

[0701] In some embodiments, the lithium ion secondary battery further includes a positive electrode plate, and the NP ratio of the lithium ion secondary battery is 1.03-1.2, and can be optionally 1.05-1.2. The NP ratio of the lithium ion secondary battery is equal to the ratio of the negative electrode surface capacity to the positive electrode surface capacity.

[0702] In some embodiments, the NP ratio of the lithium ion secondary battery is 1.1 to 1.2.

[0703] Without limitation, the NP ratio of the lithium ion secondary battery can also be any of the following values ​​or a range consisting of any two of the following values: 1.03, 1.04, 1.05, 1.06, 1.08, 1.10, 1.12, 1.14, 1.15, 1.16, 1.18, 1.20, etc. Without limitation, the NP ratio of the lithium ion secondary battery can also be any of the following values ​​or a range consisting of any two of the following values: 1.03, 1.04, 1.05, 1.06, 1.08, 1.1, 1.15, 1.18, 1.19, 1.2, etc.

[0704] In some embodiments, the NP ratio of the lithium ion secondary battery may be in any of the following ranges: 1.03-1.2, 1.04-1.2, 1.05-1.2, 1.06-1.2, 1.08-1.2, 1.1-1.2, etc.

[0705] In this application, unless otherwise specified, the "NP ratio" of a lithium-ion secondary battery refers to the ratio of the negative electrode capacity to the positive electrode capacity, which can be expressed in English as Negative / Positive Ratio. The "NP ratio" of a lithium-ion secondary battery can be obtained by testing using conventional methods in the art.

[0706] In some embodiments, the following methods can be used to test the negative electrode capacity and the positive electrode capacity respectively:

[0707] Negative electrode capacity test: fully charge the battery, disassemble the cell, take the negative electrode sheet, and punch it into small discs with a diameter of 14 mm (corresponding to area A N), separate the small disc from the lithium sheet with an isolation film, add electrolyte and package into 4 button-type half-cells; use a 0.1C rate to charge and discharge for 1 cycle in the voltage range of 0.005V~2V, and take the average of the discharge capacity of the 4 batteries to get the negative electrode capacity C N , negative electrode surface capacity = negative electrode capacity ÷ area A N .

[0708] Positive electrode capacity test: disassemble the battery cell, take the positive electrode sheet and punch it into small discs with a diameter of 14 mm (corresponding to area A P ), separate the small disc from the lithium sheet with an isolation film, add electrolyte and package into 4 button-type half-cells; use a 0.1C rate to charge and discharge for 1 cycle in the voltage range of 2.5V~3.65V, and take the average of the discharge capacities of the 4 batteries to get the positive electrode capacity C P , positive electrode surface capacity = positive electrode capacity ÷ area A P .

[0709] NP ratio of lithium-ion secondary battery = negative electrode surface capacity / positive electrode surface capacity; N Equal to A P In the case of , the following formula can also be used: NP ratio = C N / C P .

[0710] By controlling the NP ratio of the lithium-ion secondary battery within the aforementioned range, it is beneficial for the negative electrode to store more lithium ions, which...

Claims

1. A component for preparing a lithium-ion secondary battery, It is characterized in that It comprises a lithium-supplemented negative electrode sheet; the lithium-supplemented negative electrode sheet comprises a negative electrode current collector and a second negative electrode active initial layer, a second lithium-supplemented layer, a first negative electrode active initial layer and a first lithium-supplemented layer sequentially arranged on at least one side of the negative electrode current collector; The first negative electrode active initial layer includes a first negative electrode active material, the first negative electrode active material includes non-agglomerated primary particles, and the number ratio or mass ratio of the non-agglomerated primary particles in the first negative electrode active material is 80% to 100%; The non-agglomerated primary particles include a coated carbon-based material, which includes a carbon base body and a carbon coating layer located on at least a portion of the surface of the carbon base body, the carbon base body includes graphite, and the carbon coating layer includes one or more of amorphous carbon, soft carbon and hard carbon.

2. The component for preparing a lithium ion secondary battery according to claim 1, It is characterized in that The second lithium replenishing layer and the first lithium replenishing layer each independently include single substance lithium.

3. The component for preparing a lithium ion secondary battery according to claim 1, It is characterized in that The coverage area percentage of the second lithium supplement layer relative to the second negative electrode active initial layer is recorded as f, measured along the thickness direction of the lithium supplement negative electrode sheet and on one side of the negative electrode current collector. M0 The coverage area percentage of the first lithium supplement layer relative to the first negative electrode active initial layer is recorded as f U0 The thickness of the second lithium supplement layer on one side is d 02 The thickness of the first lithium supplement layer on one side is d 01 The surface density of the second lithium replenishing layer and the first lithium replenishing layer relative to the first negative electrode active initial layer is respectively denoted as p 02 and ρ 01 , where ρ 02 and ρ 01 Respectively measured on both sides of the negative electrode current collector; The lithium-supplemented negative electrode sheet meets one or more of the following characteristics: The single-side thickness d of the second lithium supplement layer 02 Less than the single-side thickness d of the first lithium supplement layer 01 ; The second lithium replenishing layer satisfies 0 <f M0 ≤f U0 ; The single-side thickness d of the second lithium supplement layer 02 0.5μm~4μm; The second lithium replenishing layer satisfies 0 <f M0 ≤70%; The second lithium replenishing layer satisfies 0<ρ 02 ≤ρ 01 ; ρ 02 0.5mg / 1540.25mm 2 ~6mg / 1540.25mm 2 .

4. The component for preparing a lithium ion secondary battery according to claim 3, It is characterized in that The lithium-supplemented negative electrode sheet meets one or more of the following characteristics: The single-side thickness d of the second lithium supplement layer 02 1μm~4μm; The second lithium replenishment layer satisfies 10%≤f M0 ≤f U0 ; The second lithium replenishment layer satisfies 10%≤f M0 ≤70%; ρ 02 1mg / 1540.25mm 2 ~6mg / 1540.25mm 2 .

5. The component for preparing a lithium ion secondary battery according to claim 3, It is characterized in that The lithium-supplemented negative electrode sheet meets one or more of the following characteristics: The single-side thickness d of the first lithium supplement layer 01 Less than or equal to 8μm; The first lithium replenishing layer satisfies 0 <f U0 ≤70%; ρ 01 0.5mg / 1540.25mm 2 ~6mg / 1540.25mm 2 ; C Li 1mg / 1540.25mm 2 ~12mg / 1540.25mm 2 Among them, C Li is the total surface density of the second lithium replenishing layer and the first lithium replenishing layer relative to the first negative electrode active initial layer, C Li It is calculated based on the total amount on both sides of the negative electrode current collector.

6. The component for preparing a lithium ion secondary battery according to claim 5, It is characterized in that The lithium-supplemented negative electrode sheet meets one or more of the following characteristics: The single-side thickness d of the first lithium supplement layer 01 2μm~5μm; The first lithium replenishing layer satisfies 30%≤f U0 ≤70%; ρ 01 2mg / 1540.25mm 2 ~6mg / 1540.25mm 2 ; C Li 3mg / 1540.25mm 2 ~12mg / 1540.25mm 2 .

7. The component for preparing a lithium ion secondary battery according to claim 1, It is characterized in that The second lithium replenishing layer and the first lithium replenishing layer each independently include a plurality of lithium replenishing micro-regions; The lithium-supplemented negative electrode sheet meets one or more of the following characteristics: Measured by projection along the thickness direction of the lithium-supplemented negative electrode sheet, at least a portion of the lithium-supplemented micro-regions has a one-dimensional size of 20 μm to 2000 μm; Measured by projection along the thickness direction of the lithium-supplemented negative electrode sheet, the spacing between at least a portion of the lithium-supplemented micro-regions is 20 μm to 2000 μm; The lithium supplement micro-regions in the first lithium supplement layer are distributed in stripe shape or grid shape; The lithium replenishing micro-regions in the second lithium replenishing layer are distributed in stripe shape or grid shape.

8. The component for preparing a lithium ion secondary battery according to claim 7, It is characterized in that The lithium-supplemented negative electrode sheet meets one or more of the following characteristics: Measured by projection along the thickness direction of the lithium-supplemented negative electrode sheet, at least a portion of the lithium-supplemented micro-regions has a one-dimensional size of 20 μm to 1000 μm; Measured by projection along the thickness direction of the lithium-supplemented negative electrode sheet, the spacing between at least a portion of the lithium-supplemented micro-regions is 20 μm to 1000 μm.

9. The component for preparing a lithium ion secondary battery according to claim 7, It is characterized in that The lithium replenishing micro-regions in the first lithium replenishing layer are distributed in stripes; the stripe spacing of the lithium replenishing micro-regions in the first lithium replenishing layer is 20 μm to 2000 μm, and the stripe width is 20 μm to 2000 μm; The lithium replenishing micro-regions in the second lithium replenishing layer are distributed in a grid shape; the grid spacing of the lithium replenishing micro-regions in the second lithium replenishing layer is 20 μm to 2000 μm, and the grid line width is 20 μm to 2000 μm.

10. The component for preparing a lithium ion secondary battery according to claim 9, It is characterized in that The lithium replenishing micro-regions in the first lithium replenishing layer are distributed in stripes; the stripe spacing of the lithium replenishing micro-regions in the first lithium replenishing layer is 20 μm to 500 μm, and the stripe width is 20 μm to 500 μm; The lithium replenishing micro-regions in the second lithium replenishing layer are distributed in a grid shape; the grid spacing of the lithium replenishing micro-regions in the second lithium replenishing layer is 20 μm to 500 μm, and the grid line width is 20 μm to 500 μm.

11. The component for preparing a lithium ion secondary battery according to any one of claims 1 to 10, It is characterized in that The lithium-supplemented negative electrode sheet meets one or more of the following characteristics: The compaction density of the second negative electrode active initial layer is higher than the compaction density of the first negative electrode active initial layer; The powder compaction density of the second negative electrode active initial layer is higher than the powder compaction density of the first negative electrode active initial layer.

12. The component for preparing a lithium ion secondary battery according to claim 11, It is characterized in that The lithium-supplemented negative electrode sheet meets one or more of the following characteristics: The compaction density of the second negative electrode active initial layer is 1.3 g / cm 3 ~1.8g / cm 3 ; The overall compaction density of the lithium-supplemented negative electrode sheet is 1.3 g / cm 3 ~1.7g / cm 3 .

13. The component for preparing a lithium ion secondary battery according to claim 12, It is characterized in that The second negative electrode active initial layer comprises a second negative electrode active material; v 50 represents the particle size corresponding to when the cumulative volume distribution percentage of the multi-particle mixture reaches 50%; The lithium-supplemented negative electrode sheet meets one or more of the following characteristics: The D of the first negative electrode active material v 50 lower than the D of the second negative electrode active material v 50; The D of the first negative electrode active material v 50: 7μm ~14μm; The D of the second negative electrode active material v 50: 8μm ~14μm; The porosity of the first negative electrode active initial layer is higher than the porosity of the second negative electrode active initial layer; The porosity of the first negative electrode active initial layer is 20% to 45%; The porosity of the second negative electrode active initial layer is 15% to 45%.

14. The component for preparing a lithium ion secondary battery according to claim 13, It is characterized in that The lithium-supplemented negative electrode sheet meets one or more of the following characteristics: The D of the first negative electrode active material v 50: 8μm ~13μm; The D of the second negative electrode active material v 50 is 9μm ~13μm.

15. The component for preparing a lithium ion secondary battery according to any one of claims 1 to 10, It is characterized in that The second negative electrode active layer includes a second negative electrode active material, and the second negative electrode active material includes secondary particles; the number ratio or mass ratio of the secondary particles in the second negative electrode active material may be 80% to 100%.

16. The component for preparing a lithium ion secondary battery according to any one of claims 1 to 10, It is characterized in that The amount ratio or mass ratio of the coated carbon-based material in the non-agglomerated primary particles in the first negative electrode active material is 80% to 100%.

17. The component for preparing a lithium ion secondary battery according to claim 16, It is characterized in that The coated carbon-based material in the non-agglomerated primary particles includes non-agglomerated coated graphite; the quantity ratio or mass ratio of the non-agglomerated coated graphite in the first negative electrode active material is 80% to 100%.

18. The component for preparing a lithium ion secondary battery according to claim 1, It is characterized in that The lithium-supplemented negative electrode sheet meets one or more of the following characteristics: The thickness of the first negative electrode active initial layer is 50 μm to 120 μm, based on the total thickness of the lithium supplemented negative electrode sheet; The thickness of the first negative electrode active initial layer on one side is 25 μm to 60 μm; The ratio of the thickness of the first negative electrode active initial layer to the sum of the thickness of the first negative electrode active initial layer and the second negative electrode active initial layer is denoted as f H0 , satisfying 20%≤f H0 ≤70%.

19. The component for preparing a lithium ion secondary battery according to claim 18, It is characterized in that The lithium-supplemented negative electrode sheet meets one or more of the following characteristics: The thickness of the first negative electrode active initial layer is 50 μm to 100 μm, based on the total thickness of the lithium supplemented negative electrode sheet; The thickness of the first negative electrode active initial layer on one side is 25 μm to 50 μm; 30%≤f H0 ≤50%。 20. The component for preparing a lithium ion secondary battery according to claim 1, It is characterized in that The components for preparing lithium-ion secondary batteries also include a positive electrode plate, which includes a positive electrode active material, which includes one or more of a ternary positive electrode material, a modified ternary positive electrode material, lithium iron phosphate, a modified lithium iron phosphate, lithium iron manganese phosphate, and a modified lithium iron manganese phosphate; the modified material includes one or more of a doping element and a coating element.

21. The component for preparing a lithium ion secondary battery according to claim 20, It is characterized in that The positive electrode active material includes carbon-coated lithium iron phosphate, which includes a lithium iron phosphate body and a carbon coating layer located on at least a portion of the surface of the lithium iron phosphate body, and the carbon coating layer includes one or more of soft carbon, hard carbon and amorphous carbon.

22. The component for preparing a lithium ion secondary battery according to any one of claims 1 to 10 and 18 to 21, It is characterized in that The components for preparing lithium-ion secondary batteries also include a positive electrode sheet; The components for preparing lithium-ion secondary batteries satisfy the following formula: 1.03≤C N_A / (α·(m L1 / A L1 + m L2 / A L2 )×C Li / g +C P_A )≤1.2; Among them, C N_A is the preset surface capacity of the negative electrode, C P_A is the preset surface capacity of the positive electrode, m L1 is the total mass of the first lithium supplement layer on both sides of the negative electrode current collector, A L1 is the spreading area of ​​the first lithium supplement layer on the first negative electrode active initial layer, m L2 A is the total mass of the second lithium supplement layer on both sides of the negative electrode current collector, L2 is the spreading area of ​​the first lithium supplement layer on the second negative electrode active initial layer, C Li / g is the theoretical gram capacity of lithium, α is the lithium replenishment coefficient, 0.6≤α≤1.

23. The component for preparing a lithium ion secondary battery according to claim 22, It is characterized in that The components for preparing a lithium-ion secondary battery meet one or more of the following characteristics: (t1) 1.1≤C N_A / (α·(m L1 / A L1 + m L2 / A L2 )×C Li / g +C P_A )≤1.2; （t2）0.6≤α≤0.9。 24. The component for preparing a lithium ion secondary battery according to claim 21, It is characterized in that The total surface density of the second lithium replenishing layer and the first lithium replenishing layer relative to the first negative electrode active initial layer is denoted as C Li , the surface density of the positive electrode active material in the positive electrode sheet is recorded as A, and the surface density of the negative electrode active material in the lithium-supplemented negative electrode sheet is recorded as B; the first lithium-supplementing layer and the second lithium-supplementing layer are both lithium films; C Li , A and B are respectively calculated based on the total amount on both sides of the negative electrode current collector; The lithium supplemented negative electrode sheet satisfies the following formula: (18×C Li +A) / B≤2.

3.

25. The component for preparing a lithium ion secondary battery according to claim 24, It is characterized in that Meet one or both of the following characteristics: (t1') 1.9≤(18×C Li +A) / B≤2.3; (t2')C Li 1mg / 1540.25mm 2 ~12mg / 1540.25mm 2 .

26. A lithium-supplemented negative electrode sheet, It is characterized in that The lithium supplement negative electrode sheet comprises a negative electrode current collector and a second negative electrode active initial layer, a second lithium supplement layer, a first negative electrode active initial layer and a first lithium supplement layer sequentially arranged on at least one side of the negative electrode current collector; The first negative electrode active initial layer includes a first negative electrode active material, the first negative electrode active material includes non-agglomerated primary particles, and the number ratio or mass ratio of the non-agglomerated primary particles in the first negative electrode active material is 80% to 100%; The non-agglomerated primary particles include a coated carbon-based material, which includes a carbon base body and a carbon coating layer located on at least a portion of the surface of the carbon base body, the carbon base body includes graphite, and the carbon coating layer includes one or more of amorphous carbon, soft carbon and hard carbon.

27. The lithium-supplemented negative electrode sheet according to claim 26, It is characterized in that The lithium-supplemented negative electrode sheet has the same characteristics as the lithium-supplemented negative electrode sheet in the component for preparing a lithium-ion secondary battery described in any one of claims 1 to 19.

28. A method for preparing a lithium ion secondary battery, It is characterized in that The steps include: Assemble a positive electrode plate, a separator and a lithium-supplemented negative electrode plate into an electrode assembly, so that the separator is arranged between the positive electrode plate and the lithium-supplemented negative electrode plate; wherein the lithium-supplemented negative electrode plate comprises a negative electrode current collector and a second negative electrode active initial layer, a second lithium-supplemented layer, a first negative electrode active initial layer and a first lithium-supplemented layer arranged in sequence on at least one side of the negative electrode current collector; the first negative electrode active initial layer comprises a first negative electrode active material, the first negative electrode active material comprises non-agglomerated primary particles, and the number ratio or mass ratio of the non-agglomerated primary particles in the first negative electrode active material is 80% to 100%; the non-agglomerated primary particles comprise a coated carbon-based material, the coated carbon-based material comprises a carbon base body and a carbon coating layer located at least a portion of the surface of the carbon base body, the carbon base body comprises graphite, and the carbon coating layer comprises one or more of amorphous carbon, soft carbon and hard carbon; The electrode assembly is placed in the accommodating cavity of the shell, and the electrolyte is injected to obtain an assembly for preparing a lithium-ion secondary battery, and the electrolyte is allowed to infiltrate the positive electrode plate and the lithium-supplemented negative electrode plate, and they are formed to prepare a lithium-ion secondary battery; wherein the lithium-supplemented negative electrode plate forms a negative electrode plate, the second negative electrode active initial layer forms a second negative electrode active layer, and the first negative electrode active initial layer forms a first negative electrode active layer.

29. The method for preparing a lithium ion secondary battery according to claim 28, It is characterized in that The lithium-supplemented negative electrode sheet is prepared by a method comprising the following steps: A second negative electrode active dry layer, a second lithium film, a first negative electrode active dry layer and a first lithium film are stacked on at least one side surface of the negative electrode substrate to obtain a multilayer body to be rolled; The multilayer body to be rolled is subjected to a rolling process to obtain the lithium supplemented negative electrode sheet.

30. The method for preparing a lithium ion secondary battery according to claim 29, It is characterized in that The pressure of the roller pressing process is 60T~100T.

31. The method for preparing a lithium ion secondary battery according to claim 30, It is characterized in that The pressure of the roller pressing process is 60T~80T.

32. The method for preparing a lithium ion secondary battery according to claim 28, It is characterized in that Meet one or both of the following characteristics: In the step of allowing the electrolyte to infiltrate the positive electrode sheet and the lithium-supplemented negative electrode sheet, the infiltration temperature is 20° C. to 60° C.; In the step of allowing the electrolyte to infiltrate the positive electrode sheet and the lithium-supplemented negative electrode sheet, the infiltration time is 10 hours to 50 hours.

33. The method for preparing a lithium ion secondary battery according to any one of claims 28 to 32, It is characterized in that The component for preparing a lithium ion secondary battery is the component for preparing a lithium ion secondary battery described in any one of claims 2 to 25.

34. A lithium ion secondary battery, It is characterized in that It comprises a negative electrode plate; the negative electrode plate comprises a negative electrode current collector and a second negative electrode active layer, a second lithium supplement residual layer, a first negative electrode active layer and a first lithium supplement residual layer sequentially arranged on at least one side of the negative electrode current collector; The first negative electrode active layer and the second negative electrode active layer each independently include lithium pre-embedded by negative electrode lithium supplementation; The first negative electrode active layer includes a first negative electrode active material, the first negative electrode active material includes non-agglomerated primary particles, and the number ratio or mass ratio of the non-agglomerated primary particles in the first negative electrode active material is 80% to 100%; The non-agglomerated primary particles include a coated carbon-based material, which includes a carbon base body and a carbon coating layer located on at least a portion of the surface of the carbon base body, the carbon base body includes graphite, and the carbon coating layer includes one or more of amorphous carbon, soft carbon and hard carbon.

35. The lithium ion secondary battery according to claim 34, It is characterized in that The first lithium replenishment residual layer and the second lithium replenishment residual layer each independently include inactive lithium.

36. The lithium ion secondary battery according to claim 35, It is characterized in that The coverage area percentage of the second lithium supplement residual layer relative to the second negative electrode active layer is recorded as f, measured along the thickness direction of the negative electrode sheet and on one side of the negative electrode current collector. M The coverage area percentage of the first lithium supplement residual layer relative to the first negative electrode active layer is recorded as f U The thickness of the second lithium supplement residual layer on one side is d 2 The thickness of the first lithium supplement residual layer on one side is d 1 ; The negative electrode plate meets one or more of the following characteristics: The single-side thickness d of the second lithium supplement residual layer 2 Less than the single-side thickness d of the first lithium supplement residual layer 1 ; The second lithium supplement residual layer satisfies 0 <f M ≤f U ; The second lithium supplement residual layer satisfies 0 <f M ≤70%; The single-side thickness d of the second lithium supplement residual layer 2 Less than 1 μm; The first lithium supplement residual layer satisfies 0 <f U ≤70%; The single-side thickness d of the first lithium supplement residual layer 1 Less than 1μm.

37. The lithium ion secondary battery according to claim 36, It is characterized in that The negative electrode plate meets one or more of the following characteristics: The single-side thickness d of the second lithium supplement residual layer 2 Less than 0.1 μm; The second lithium supplement residual layer satisfies 10%≤f M ≤70%; The single-side thickness d of the first lithium supplement residual layer 1 Less than 0.1 μm; The first lithium supplement residual layer satisfies 30%≤f U ≤70%.

38. The lithium ion secondary battery according to claim 35, It is characterized in that The second lithium replenishment residual layer and the first lithium replenishment residual layer each independently include a plurality of lithium replenishment residual micro-regions; The negative electrode plate meets one or more of the following characteristics: Measured by projection along the thickness direction of the negative electrode sheet, at least a portion of the lithium-supplemented residual micro-regions has a one-dimensional size of 20 μm to 2000 μm; Measured by projection along the thickness direction of the negative electrode sheet, the spacing between at least a portion of the lithium-supplemented residual micro-regions is 20 μm to 2000 μm; The lithium-supplement residual micro-regions in the first lithium-supplement residual layer are distributed in a stripe shape or a grid shape; The lithium replenishment residual micro-regions in the second lithium replenishment residual layer are distributed in a stripe shape or a grid shape.

39. The lithium ion secondary battery according to claim 38, It is characterized in that The negative electrode plate meets one or more of the following characteristics: Measured by projection along the thickness direction of the negative electrode sheet, at least a portion of the lithium-supplemented residual micro-regions has a one-dimensional size of 20 μm to 1000 μm; Measured by projection along the thickness direction of the negative electrode sheet, the spacing between at least a portion of the lithium-supplemented residual micro-regions is 20 μm to 1000 μm.

40. The lithium ion secondary battery according to claim 38, It is characterized in that The lithium-replenishing residual micro-regions in the first lithium-replenishing residual layer are distributed in stripes; the stripe spacing of the lithium-replenishing residual micro-regions in the first lithium-replenishing residual layer is 20 μm to 2000 μm, and the stripe width is 20 μm to 2000 μm; The lithium replenishment residual micro-regions in the second lithium replenishment residual layer are distributed in a grid shape; the grid spacing of the lithium replenishment residual micro-regions in the second lithium replenishment residual layer is 20 μm-2000 μm, and the grid line width is 20 μm-2000 μm.

41. The lithium ion secondary battery according to claim 40, It is characterized in that The lithium-replenishing residual micro-regions in the first lithium-replenishing residual layer are distributed in stripes; the stripe spacing of the lithium-replenishing residual micro-regions in the first lithium-replenishing residual layer is 20 μm to 500 μm, and the stripe width is 20 μm to 500 μm; The lithium replenishment residual micro-regions in the second lithium replenishment residual layer are distributed in a grid shape; the grid spacing of the lithium replenishment residual micro-regions in the second lithium replenishment residual layer is 20 μm-500 μm, and the grid line width is 20 μm-500 μm.

42. The lithium ion secondary battery according to claim 36, It is characterized in that The negative electrode plate meets one or more of the following characteristics: The thickness of the first negative electrode active layer is 50 μm to 120 μm, based on the total thickness in the negative electrode sheet; The thickness of the first negative electrode active layer on one side is 25 μm to 60 μm; The ratio of the thickness of the first negative electrode active layer to the sum of the thickness of the first negative electrode active layer and the second negative electrode active layer is denoted as f H , satisfying 20%≤f H ≤70%.

43. The lithium ion secondary battery according to claim 42, It is characterized in that The negative electrode plate meets one or more of the following characteristics: The thickness of the first negative electrode active layer is 50 μm to 100 μm, based on the total thickness in the negative electrode sheet; The thickness of the first negative electrode active layer on one side is 25 μm to 50 μm; 30%≤f H ≤50%。 44. The lithium ion secondary battery according to any one of claims 34 to 43, It is characterized in that The negative electrode plate meets one or more of the following characteristics: The compaction density of the second negative electrode active layer is higher than the compaction density of the first negative electrode active layer; The powder compaction density of the second negative electrode active layer is higher than the powder compaction density of the first negative electrode active layer.

45. The lithium ion secondary battery according to claim 44, It is characterized in that The negative electrode plate meets one or more of the following characteristics: The compaction density of the second negative electrode active layer is 1.04 g / cm 3 ~1.71g / cm 3 ; The overall compaction density of the negative electrode sheet is 1.04 g / cm 3 ~1.62g / cm 3 .

46. ​​The lithium ion secondary battery according to any one of claims 34 to 43, It is characterized in that The second negative electrode active layer includes a second negative electrode active material; the lithium ion secondary battery also includes a positive electrode sheet, and the positive electrode sheet includes a positive electrode active material; The lithium-ion secondary battery meets one or more of the following characteristics: The D of the first negative electrode active material v 50 lower than the D of the second negative electrode active material v 50; among them, D v 50 represents the particle size corresponding to when the cumulative volume distribution percentage of the multi-particle mixture reaches 50%; The D of the first negative electrode active material v 50: 7μm ~14μm; The D of the second negative electrode active material v 50: 8μm ~14μm; The porosity of the first negative electrode active layer is higher than the porosity of the second negative electrode active layer; The porosity of the first negative electrode active layer is 20% to 45%; The porosity of the second negative electrode active layer is 15% to 45%; The positive electrode active material includes one or more of a ternary positive electrode material, a modified product of a ternary positive electrode material, lithium iron phosphate, a modified product of lithium iron phosphate, lithium iron manganese phosphate and a modified product of lithium iron manganese phosphate; the modified product includes one or more of a doping element and a coating element.

47. The lithium ion secondary battery according to claim 46, It is characterized in that The lithium-ion secondary battery meets one or more of the following characteristics: The D of the first negative electrode active material v 50: 8μm ~13μm; The D of the second negative electrode active material v 50 is 9μm ~13μm; The amount or mass proportion of the coated carbon-based material in the non-agglomerated primary particles in the first negative electrode active material is 80% to 100%; The positive electrode active material includes carbon-coated lithium iron phosphate, which includes a lithium iron phosphate body and a carbon coating layer located on at least a portion of the surface of the lithium iron phosphate body, and the carbon coating layer includes one or more of soft carbon, hard carbon and amorphous carbon.

48. The lithium ion secondary battery according to claim 47, It is characterized in that The first negative electrode active material satisfies one or more of the following characteristics: The coated carbon-based material in the non-agglomerated primary particles includes non-agglomerated coated graphite; the non-agglomerated coated graphite accounts for 80% to 100% in number or mass in the first negative electrode active material; The amount or mass proportion of the coated carbon-based material in the first negative electrode active material is 80% to 100%.

49. The lithium ion secondary battery according to any one of claims 34 to 43, It is characterized in that The lithium ion secondary battery also includes a positive electrode plate. The NP ratio of the lithium ion secondary battery is 1.03-1.

2. The NP ratio of the lithium ion secondary battery is equal to the ratio of the negative electrode surface capacity to the positive electrode surface capacity.

50. The lithium ion secondary battery according to claim 49, It is characterized in that The NP ratio of the lithium ion secondary battery is 1.1-1.

2.

51. The lithium ion secondary battery according to any one of claims 34 to 43, It is characterized in that The lithium ion secondary battery is prepared by the method for preparing a lithium ion secondary battery described in any one of claims 28 to 33.

52. An electrical device, It is characterized in that A lithium ion secondary battery comprising any one of claims 34 to 51.

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