Secondary battery and electric device

Abstract

The invention discloses a secondary battery and an electric device, and belongs to the technical field of batteries. The secondary battery provided by the invention comprises a positive pole piece, a negative pole piece, a diaphragm and an electrolyte, the positive pole piece comprises a positive current collector and a positive active material layer arranged on at least one surface of the positive current collector, and the positive active material layer comprises a positive active material and a lithium supplement agent; according to the secondary battery provided by the invention, the lithium supplementing agent is introduced into the positive electrode active material layer, and the non-Faraday capacitance of the positive electrode plate, the particle dispersity of the lithium supplementing agent and the average grain size of the lithium supplementing agent are reasonably controlled, so that the prepared secondary battery has excellent cycle performance, rate capability and safety performance; and meanwhile, the material also has rapid charge-discharge performance.

Description

Technical Field

[0001] The present application relates to the field of battery technology, in particular to a secondary battery and an electrical device. Background Art

[0002] In the context of the current rapid development of science and technology, as an important component of energy storage equipment and core components of electric vehicles, the improvement of energy density and cycle performance of secondary batteries is crucial. Especially in the field of energy storage, with the increase of market demand and the promotion of policies, the requirements for battery energy density and cycle life are more stringent. In order to meet this challenge, lithium supplementation technology has emerged as a key technology, which plays a key role in improving battery energy density and cycle life.

[0003] The core goal of lithium replenishment technology is to make up for the problem of active lithium loss and capacity reduction caused by the formation of solid electrolyte interface (SEI) at the negative electrode during the first charge and discharge process of secondary batteries. The overall performance of the battery can be significantly improved through positive electrode lithium replenishment technology. However, the addition of lithium replenishment materials to conventional positive electrode plates may lead to a decrease in compaction density, which has a potential impact on cycle performance and rate performance. At the same time, during the preparation of lithium-supplemented batteries, insufficient liquid absorption and retention of lithium replenisher particles, uneven current distribution during battery operation, and insufficient transient current resistance can easily lead to insufficient decomposition of the lithium replenisher during the formation process of lithium-supplemented batteries, resulting in severe lithium precipitation and battery swelling during the cycle of lithium-supplemented batteries. These problems directly affect the performance and safety of lithium-supplemented batteries. Summary of the invention

[0004] The purpose of the present application is to solve the problem of severe lithium deposition and poor cycle performance of lithium-supplemented batteries during the cycle caused by existing lithium-supplementing technologies, and to provide a secondary battery and an electrical device with excellent cycle performance and rate performance and good lithium deposition.

[0005] To achieve the above-mentioned object, in a first aspect of the present application, a secondary battery is provided, comprising a positive electrode sheet, a negative electrode sheet, a separator and an electrolyte, wherein the positive electrode sheet comprises a positive electrode current collector and a positive electrode active material layer disposed on at least one surface of the positive electrode current collector, wherein the positive electrode active material layer comprises a positive electrode active material and a lithium supplement;

[0006] The positive electrode sheet satisfies: 5≤Y≤53;

[0007] Where, Y = Cdl × N × S -0.5 ;

[0008] Cdl nF is the non-Faraday capacitance of the positive electrode;

[0009] N is the particle dispersion of the lithium supplement;

[0010] Sμm is the average crystal size of the lithium supplement.

[0011] As an implementation scheme of the present application, the non-Faraday capacitance Cdl nF of the positive electrode plate is 0.5 to 3 nF.

[0012] As an embodiment of the present application, the particle dispersion degree N of the lithium supplement agent is 4-20.

[0013] As an embodiment of the present application, the average grain size Sμm of the lithium supplement is 0.01 to 3μm.

[0014] As an embodiment of the present application, in the positive electrode active material layer, the mass percentage of the lithium supplement agent is 0.5-5%.

[0015] As an embodiment of the present application, the lithium supplement comprises Li 5 FeO 5 , Li 6 CoO 4 , Li 2 NiO 2 At least one of .

[0016] As an embodiment of the present application, the positive electrode active material satisfies: 5≤Dv99≤15.

[0017] As an embodiment of the present application, a carbon layer is provided on at least a portion of the surface of the positive electrode active material, and a thickness C of the carbon layer is 5 to 200 nm.

[0018] As an embodiment of the present application, the positive electrode active material satisfies: 1≤C / Dv99≤14.

[0019] As an embodiment of the present application, the positive electrode active material satisfies at least one of the following characteristics: (1) 0.1≤Dv10≤0.5; (2) 0.6≤Dv50≤1.5.

[0020] As an embodiment of the present application, the thickness of the positive electrode active material layer is 60 to 85 μm.

[0021] In a second aspect of the present application, an electrical device is provided, comprising the secondary battery described above.

[0022] Compared with the prior art, the beneficial effects of this application are:

[0023] In the secondary battery provided in the present application, by introducing a lithium supplement agent into the positive electrode active material layer, and reasonably controlling the non-Faraday capacitance of the positive electrode plate, the particle dispersion of the lithium supplement agent, and the average grain size of the lithium supplement agent, the positive electrode plate satisfies a specific relationship: 4≤Cdl×N×S -0.5≤53, which can effectively shorten the reaction path and reaction voltage of the lithium supplement agent in the formation process, improve the wetting effect of the lithium supplement agent, thereby improving the reactivity of the lithium supplement agent in the formation stage of the secondary battery, and reducing the lithium plating phenomenon of the negative electrode of the secondary battery during the cycle, so that the prepared secondary battery has excellent cycle performance and rate performance, and also has fast charge and discharge performance. DETAILED DESCRIPTION

[0024] In order to make the purpose, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application are described clearly and completely below. Obviously, the described embodiments are part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present application.

[0025] In the present application, the technical features described in an open manner include closed technical solutions composed of the listed features, and also include open technical solutions containing the listed features.

[0026] In this application, when it comes to numerical ranges, unless otherwise specified, the above numerical ranges are deemed to be continuous and include the minimum and maximum values ​​of the range, as well as each value between such minimum and maximum values. Further, when a range refers to an integer, each integer between the minimum and maximum values ​​of the range is included. In addition, when multiple ranges are provided to describe features or characteristics, the ranges can be merged. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all subranges included therein.

[0027] The reagents or instruments used in this application without indicating the manufacturer are all conventional products that can be obtained through commercial purchase.

[0028] In one embodiment of the present application, the present application proposes a secondary battery, including a positive electrode sheet, a negative electrode sheet, a separator and an electrolyte, wherein the positive electrode sheet includes a positive electrode collector and a positive electrode active material layer disposed on at least one surface of the positive electrode collector, wherein the positive electrode active material layer includes a positive electrode active material and a lithium supplement;

[0029] The positive electrode sheet satisfies: 5≤Y≤53;

[0030] Where, Y = Cdl × N × S -0.5 ;

[0031] Cdl nF is the non-Faraday capacitance of the positive electrode;

[0032] N is the particle dispersion of the lithium supplement;

[0033] Sμm is the average crystal size of the lithium supplement.

[0034] The present application has found that the non-Faraday capacitance of the positive electrode, the particle dispersion of the lithium supplement and the average grain size of the lithium supplement will have a significant impact on the performance of the secondary battery. The present application makes the positive electrode satisfy a specific relationship: 5≤Cdl×N×S -0.5 ≤53, which reduces the lithium plating phenomenon of the negative electrode of the secondary battery during the cycle process, so that the prepared secondary battery has excellent cycle performance and rate performance, as well as fast charge and discharge performance.

[0035] Specifically, the present application makes the positive electrode sheet satisfy a specific relationship: 5≤Cdl×N×S -0.5 ≤53 improves the performance of secondary batteries from the following aspects: first, improves the uniformity and stability of the specific surface area of ​​the positive electrode sheet, increases the effective tap density of the lithium-supplemented positive electrode material, and optimizes the microstructure of the lithium-supplemented positive electrode sheet so that the positive electrode sheet has high uniformity while reducing overvoltage damage to the positive electrode sheet, thereby helping to improve the cycle performance of the secondary battery; second, a more uniform lithium supplement ensures better consistency in the contact area between the lithium supplement agent particles and the electrolyte. Under the same conditions, the wetting effect and liquid retention performance of the lithium supplement agent in the positive electrode sheet are improved, thereby improving the rate performance of the secondary battery; third, the lithium supplement agent can release more lithium ions in the formation stage, and the lithium release reaction of the lithium supplement agent is more thorough, which can avoid gas production of the secondary battery and lithium precipitation of the negative electrode sheet during the cycle, thereby greatly improving the cycle performance, rate performance and safety performance of the battery; fourth, the secondary battery provided by the present application can effectively balance the liquid retention performance of the positive electrode sheet and the wetting effect of the electrolyte, so that the fast charging performance and cycle stability of the secondary battery are significantly improved.

[0036] Exemplarily, the positive electrode plate satisfies 5≤Y≤53, wherein Y can be any point value or any two point range values ​​within the range of 5≤Y≤53, for example, Y can be one of 5, 8, 10, 12, 14, 16, 18, 20, 22, 24, 26, 28, 30, 32, 34, 36, 38, 40, 42, 44, 46, 48, 50, 53 or any two range values; when the Y value of the positive electrode plate is within the above range, the degree of lithium plating of the obtained secondary battery during the cycle process is greatly improved, the cycle stability of the secondary battery can be effectively improved, and the obtained secondary battery has excellent rate performance and fast charge and discharge performance.

[0037] In one embodiment, the positive electrode sheet satisfies 13.5≤Y≤25.5. For example, Y can be a range of one or any two of 13.5, 14.5, 15.5, 16.5, 17.5, 18.5, 19.5, 20.5, 21.5, 22.5, 23.5, 24.5, and 25.5. The present application has found that when the positive electrode sheet is further selected to satisfy 13.5≤Y≤25.5, the comprehensive performance of the secondary battery obtained is better.

[0038] In one embodiment, the non-Faraday capacitance Cdl nF of the positive electrode plate is 0.5-3 nF.

[0039] It should be noted that the test method of the non-Faraday capacitance Cdl of the positive electrode plate includes the following steps:

[0040] S1: Clean the surface of the positive electrode with electrolyte to remove surface impurities, dry, cut into discs, transfer to a vacuum oven after weighing, dry at 90-105°C for 6h, and assemble the battery symmetrically in a glove box;

[0041] S2: The battery assembled from S1 is tested by cyclic voltammetry (CV) to obtain the non-Faraday potential interval of the corresponding battery. The test voltage range is 0.05-3.0 V and the scan rate is 0.1-2 mV / s.

[0042] S3: Select the flat potential interval (2.5-2.7 V) in S2 to perform cyclic voltammetry (CV) test and collect voltage-current curves, wherein the scan rate is 0.5-10 mV / s and the scan direction is from low potential to high potential;

[0043] S4: Obtain the median U of the potential interval of five specific scan rates V1 in S3 (the specific scan rate can be 1mV / s, 2mV / s, 3mV / s, 5mV / s and 10mV / s, etc.), and obtain the corresponding current value, obtain a scan rate-current scatter plot, and fit a linear function. The slope of the linear function is the non-Faraday capacitance value (Cdl) of the positive electrode plate.

[0044] Non-Faradaic capacitance refers to the ability of an electrode material to store charge in an electrolyte by physical adsorption of charge or intercalation of ions; the present application has found that in a secondary battery, the size of the non-Faradaic capacitance directly affects the diffusion of lithium ions and the reaction on the electrode surface, and has a great influence on the instantaneous charging rate and instantaneous power output of the battery; the present application can improve the rapid charging and discharging performance of the secondary battery and enhance the cycle stability of the battery by optimizing the non-Faradaic capacitance of the positive electrode plate, by protecting the positive electrode active material from strong current attacks.

[0045] Exemplarily, the Cdl may be any point value or any two point range values ​​between 0.5 and 3, for example, Cdl may be one of 0.5, 1.0, 1.2, 1.4, 1.6, 1.8, 2.0, 2.2, 2.4, 2.6, 2.8, 3.0 or any two range values.

[0046] In one embodiment, the non-Faradaic capacitance Cdl nF of the positive electrode plate is 1.3-1.5 nF. For example, Cdl may be a range of one or any two of 1.30, 1.32, 1.34, 1.36, 1.38, 1.40, 1.42, 1.44, 1.46, 1.48, 1.50. The present application has found that when the non-Faradaic capacitance Cdl nF of the positive electrode plate is further selected to be 1.3-1.5 nF, the charge and discharge performance, rate performance and cycle performance of the secondary battery obtained are better.

[0047] In one embodiment, the particle dispersion N of the lithium supplement agent is 4-20.

[0048] It should be noted that the particle dispersion N of the lithium supplement is obtained by testing with a laser particle size analyzer.

[0049] The dispersion of lithium supplement agent particles refers to the spatial distribution between lithium supplement agent particles. The more concentrated the particle size, the higher the dispersion. The research in this application found that the dispersion of lithium supplement agent particles has an important influence on the performance of secondary batteries. Lithium supplement agents with low dispersion have more uniform electrode surface area, which can increase the surface path of electrons / ions in the reaction process, shorten the reaction path of electrons / ions inside the lithium supplement agent particles, and play a role in reducing the internal resistance of the battery, increasing the reaction speed, and reducing the reaction voltage, thereby affecting the lithium supplement efficiency of the secondary battery. At the same time, the dispersion of lithium supplement agent particles will also affect whether the lithium supplement agent can be evenly and completely consumed before capacity separation, thereby affecting the lithium precipitation and cycle performance of the secondary battery.

[0050] Exemplarily, the particle dispersion N of the lithium supplement may be any point value or any two point range values ​​between 4 and 20, for example, N may be one of 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20 or any two range values.

[0051] In one embodiment, the particle dispersion N of the lithium supplement agent is 10 to 16. For example, N can be a range of one or any two of 10.0, 10.5, 11.5, 12.5, 13.5, 14.5, 15.5, and 16.0. The present application has found that when the particle dispersion N of the lithium supplement agent is further selected to be 10 to 16, the cycle performance of the secondary battery obtained is better and the lithium precipitation is better.

[0052] In one embodiment, the average grain size S μm of the lithium supplement is 0.01-3 μm.

[0053] It should be noted that the average grain size S of the lithium supplement material is measured by an X-ray diffractometer using Cu Kα rays, and the diffraction angle 2θ is analyzed to show peaks (crystal planes) belonging to the lithium supplement material in the range of 5 to 90°, and then the grain size of the lithium supplement material is calculated using the Scherrer formula.

[0054] Grains are the basic structural units at the microscopic level. They are formed by atoms or molecules arranged according to a certain rule. Grain size refers to the size of a single grain. The present application found that in the positive electrode sheet, the grain size of the lithium supplement not only affects the processability of the positive electrode sheet, but also affects the reaction potential and specific surface area of ​​the lithium supplement. The grain size affects the distribution of active sites of the lithium supplement in the positive electrode of the secondary battery, thereby affecting the reaction potential and active ion release of the lithium supplement.

[0055] Exemplarily, the average grain size Sμm of the lithium supplement may be any point value or any two point range values ​​between 0.01 and 3μm, for example, S may be one of 0.01, 0.05, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.8, 1.0, 1.2, 1.4, 1.6, 1.8, 2.0, 2.2, 2.4, 2.6, 2.8, 3.0 or any two range values.

[0056] In one embodiment, the average grain size Sμm of the lithium supplement is 1.5 to 2.5μm. For example, S can be a range of one or any two of 1.5, 1.6, 1.7, 1.8, 1.9, 2.0, 2.1, 2.2, 2.3, 2.4, 2.5. The present application has found that when the average grain size Sμm of the lithium supplement is further selected to be 1.5 to 2.5μm, the cycle performance and rate performance of the secondary battery obtained are better, and the charge and discharge performance is also better.

[0057] In the present application, lithium iron phosphate with a specific particle size and a lithium supplement with a specific dispersion can be obtained by the following method:

[0058] S1: re-granulating the lithium iron phosphate and / or lithium supplement particles using a ball mill;

[0059] Optionally, a jet ball mill is used to manufacture lithium iron phosphate and / or lithium supplement particles with a particle size of 10 to 50 μm, a planetary ball mill is used to manufacture lithium iron phosphate and / or lithium supplement particles with a particle size of 0.1 to 10 μm, and a nano ball mill is used to manufacture lithium iron phosphate and / or lithium supplement particles with a particle size of 0.01 to 0.1 μm;

[0060] S2: Use a sieving machine to sieve the crushed particles;

[0061] Optionally, an electromagnetic vibration sieving device is used to separate lithium iron phosphate and / or lithium supplement particles with a particle size of 5 μm or more, an ultrasonic vibration sieving device is used to separate lithium iron phosphate and / or lithium supplement particles with a particle size of 0.1 to 5 μm, and an ultracentrifugation method is used to separate lithium iron phosphate and / or lithium supplement particles with a particle size of less than 0.1 μm.

[0062] In one embodiment, the mass percentage of the lithium supplement in the positive electrode active material layer is 0.5-5%.

[0063] The present application study found that adding a lithium supplement in an appropriate amount range can help achieve better overall performance of secondary batteries.

[0064] Exemplarily, in the positive electrode active material layer, the mass percentage of the lithium supplement agent can be any point value or any two point range values ​​between 0.5 and 5%, for example, it can be one of 0.5%, 0.8%, 1.0%, 1.2%, 1.4%, 1.6%, 1.8%, 2.0%, 2.2%, 2.4%, 2.6%, 2.8%, 3.0% or any two range values.

[0065] In one embodiment, the lithium supplement comprises Li 5 FeO 5 , Li 6 CoO 4 , Li 2 NiO 2 At least one of .

[0066] In one embodiment, the positive electrode active material satisfies: 5≤Dv99≤15.

[0067] In one embodiment, a carbon layer is disposed on at least part of the surface of the positive electrode active material, and the thickness C of the carbon layer is 5 to 200 nm.

[0068] In one embodiment, the positive electrode active material satisfies: 1≤C / Dv99≤14.

[0069] In one embodiment, the positive electrode active material satisfies: 0.1≤Dv10≤0.5.

[0070] In one embodiment, the positive electrode active material satisfies: 0.6≤Dv50≤1.5.

[0071] It should be noted that the Dv99, Dv10 and Dv50 of the positive electrode active material are tested by a laser particle size analyzer; Dv10 is the particle size corresponding to when the cumulative volume percentage of the positive electrode active material reaches 10%; Dv50 is the particle size corresponding to when the cumulative volume percentage of the positive electrode active material reaches 50%; Dv99 is the particle size corresponding to when the cumulative volume percentage of the positive electrode active material reaches 99%.

[0072] Exemplarily, the Dv99 of the positive electrode active material may be any point value or any two point range values ​​between 5 and 15, for example, it may be one of 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, and 15 or any two range values; the Dv10 of the positive electrode active material may be any point value or any two point range values ​​between 0.1 and 0.5, for example, it may be one of 0.1, 0.2, 0.3, 0.4, and 0.5 or any two range values; the Dv50 of the positive electrode active material may be any point value or any two point range values ​​between 0.6 and 1.5, for example, it may be one of 0.6, 0.7, 0.8, 0.9, 1.0, 1.1, 1.2, 1.3, 1.4, and 1.5 or any two range values.

[0073] Exemplarily, the thickness C of the carbon layer can be any point value or any two point range values ​​between 5 and 200 nm, for example, it can be one or any two range values ​​of 5 nm, 10 nm, 15 nm, 20 nm, 30 nm, 40 nm, 50 nm, 60 nm, 70 nm, 80 nm, 90 nm, 100 nm, 110 nm, 120 nm, 130 nm, 140 nm, 150 nm, 160 nm, 170 nm, 180 nm, 190 nm, and 200 nm.

[0074] In one embodiment, the thickness of the positive electrode active material layer is 60-85 μm. It should be noted that the thickness of the positive electrode active material layer in the present application refers to the thickness of the positive electrode coating layer on one side of the positive electrode current collector.

[0075] Exemplarily, the thickness of the positive electrode active material layer may be any point value or any two point range values ​​between 60 and 85 μm, for example, it may be one or any two range values ​​of 60 μm, 65 μm, 70 μm, 75 μm, 80 μm, 85 μm.

[0076] In one embodiment, the positive electrode active material includes a lithium-containing phosphate having an olivine structure.

[0077] In one embodiment, the sphericity of the lithium supplement is 0.7-0.85. For example, the sphericity of the lithium supplement can be in the range of 0.7, 0.75, 0.8, 0.85 or any two of them.

[0078] In one embodiment, the negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer disposed on at least one surface of the negative electrode current collector; the negative electrode active material layer includes a negative electrode active material. The present application has no limitation on the negative electrode active material, and any known negative electrode active material can be used.

[0079] In one embodiment, the electrolyte includes an organic solvent, a lithium salt and an additive. The present application has no limitation on the organic solvent, lithium salt and additive in the electrolyte, and any known organic solvent, lithium salt and additive can be used.

[0080] Exemplarily, the organic solvent includes at least one of ethylene carbonate, propylene carbonate, diethyl carbonate, ethyl methyl carbonate, and dimethyl carbonate; the lithium salt includes at least one of lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, and lithium bis(trifluoromethylsulfonyl)imide; and the additive includes at least one of a film-forming additive, a conductive additive, and a flame retardant additive.

[0081] In one embodiment, the separator of the secondary battery is disposed between the positive electrode and the negative electrode.

[0082] In one embodiment of the present application, the present application proposes an electrical device, and the electrical device includes the secondary battery described in the present application.

[0083] Exemplarily, the above-mentioned electrical devices may include mobile devices (such as mobile phones, laptops, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc., but are not limited thereto.

[0084] Example 1

[0085] The present invention provides a secondary battery, wherein a method for preparing the secondary battery comprises the following steps:

[0086] (1) Preparation of positive electrode sheet

[0087] Lithium iron phosphate (Dv10 is 0.2μm, Dv50 is 0.9μm, Dv99 is 14.9μm), Li 5 FeO 5 (particle dispersion N is 16, grain size S is 1.5μm), conductive carbon black (SP), and PVDF are mixed in a weight ratio of 96.5:0.5:0.7:2.3, then added into NMP for thorough mixing, and after evenly mixing, coated on both sides on a 14μm carbon-coated aluminum foil, and then the electrode is dried, rolled, slit and cut to obtain a positive electrode;

[0088] Among them, the thickness of the single-sided positive electrode active material layer is about 70μm, and the non-Faraday capacitance is 0.87nF; Li 5 FeO 5 The sphericity is 0.75;

[0089] (2) Preparation of negative electrode sheet

[0090] Artificial graphite, conductive carbon black (SP), CMC and SBR are mixed evenly in a mass ratio of 96.3:0.7:1.1:1.9, and then water is added to the above mixture in batches and continued to be fully mixed and stirred to obtain a negative electrode slurry, and then the homogeneous negative electrode slurry is evenly coated on both sides of a 6μm copper foil, and after drying, rolling, slitting and cutting, a negative electrode sheet is obtained;

[0091] (3) Preparation of electrolyte

[0092] Ethylene carbonate, ethyl methyl carbonate and propyl propionate solvent are uniformly mixed in a mass ratio of 1:1:1, and then 1 mol / L lithium hexafluorophosphate and an appropriate amount of additives are added, wherein the additives include a first additive and a second additive, the first additive is 1 wt% of fluoroethylene carbonate, the second additive is 1 wt% of LiFSI, and the total amount of the additives accounts for 2 wt% of the electrolyte;

[0093] (4) Preparation of secondary batteries

[0094] The prepared positive electrode sheet, negative electrode sheet, separator and other battery components are assembled, and a secondary battery is obtained through processes such as shaping, baking, packaging, liquid injection, formation, and capacity division.

[0095] Embodiments 2 to 6

[0096] Embodiments 2 to 6 provide a secondary battery, which differs from Embodiment 1 in that the non-Faraday capacitance of the positive electrode sheet is changed by adjusting the content ratio of the positive electrode material in the positive electrode sheet, the particle size distribution of the positive electrode material, the compaction density of the positive electrode material powder, and the porosity and compaction density of the positive electrode sheet, as well as the positive electrode formulation (such as the conductive agent content and the lithium supplement agent content).

[0097] Embodiments 7 to 11

[0098] Embodiments 7 to 11 provide a secondary battery. The difference between the secondary battery and embodiment 1 is that the particle dispersion of the lithium supplement agent is changed by adjusting the preparation process of the lithium supplement agent.

[0099] Embodiments 12 to 16

[0100] Embodiments 12 to 16 provide a secondary battery, which is different from Embodiment 1 in that the average grain size of the lithium supplement is changed by adjusting the preparation process of the lithium supplement.

[0101] Embodiment 17

[0102] Example 17 provides a secondary battery, which is different from Example 1 in that the non-Faraday capacitance of the positive electrode sheet, the particle dispersion and the average grain size of the lithium supplement are changed by adjusting the content ratio of the positive electrode material in the positive electrode sheet, the particle size distribution of the positive electrode material, the powder compaction density of the positive electrode material, the porosity and compaction density of the positive electrode sheet, the positive electrode formula (such as the conductive agent content, the lithium supplement content) and the preparation process of the lithium supplement.

[0103] Embodiments 18 to 19

[0104] Embodiments 18 to 19 provide a secondary battery, which is different from Embodiment 1 in that the mass percentage of the lithium supplement is changed by adjusting the amount of the lithium supplement added.

[0105] Embodiment 20-21

[0106] Embodiments 20 to 21 provide a secondary battery, which differs from Embodiment 1 in that the changes in the positive electrode active material Dv99, Dv10, and Dv50 are achieved by adjusting the preparation of the positive electrode active material, and the thickness of the positive electrode active material layer and the coated carbon layer are changed by adjusting the preparation process.

[0107] Comparative Examples 1-2

[0108] Comparative Examples 1 to 2 provide a secondary battery, which is different from Example 1 in that the non-Faraday capacitance of the positive electrode sheet, the particle dispersion of the lithium supplement and the average grain size of the lithium supplement are changed by adjusting the content ratio of the positive electrode material in the positive electrode sheet, the particle size distribution of the positive electrode material, the powder compaction density of the positive electrode material, the porosity and compaction density of the positive electrode sheet, the positive electrode formula (such as the conductive agent content, the lithium supplement content) and the preparation process of the lithium supplement.

[0109] Comparative Example 3

[0110] The embodiment of the present application provides a secondary battery, which is different from the embodiment 1 in that no lithium supplement is added.

[0111] The non-Faraday capacitance Cdl of the positive electrode sheet, the particle dispersion N of the lithium supplement, the average grain size S of the lithium supplement, the Dv10 of the positive electrode active material, the Dv50 of the positive electrode active material, the Dv99 of the positive electrode active material, the thickness B of the positive electrode active material layer, the thickness C of the carbon layer, the ratio of the thickness C of the carbon layer to the Dv99 of the positive electrode active material, and the mass percentage m of the lithium supplement in the embodiments and comparative examples are shown in Table 1;

[0112] Table 1

[0113] Cdl / nF N S / μm Y Dv10 Dv50 Dv99 B / μm C / nm C / Dv99 m / ％ Example 1 1.3 16 1.5 22.0 0.2 0.9 14.9 70 40 2.7 2.5 Example 2 1.5 16 1.5 25.2 0.2 0.9 14.9 70 40 2.7 2.5 Example 3 3 16 1.5 49.2 0.2 0.9 14.9 70 40 2.7 2.5 Example 4 0.5 16 1.5 9.2 0.2 0.9 14.9 70 40 2.7 2.5 Example 5 3.2 16 1.5 52.4 0.2 0.9 14.9 70 40 2.7 2.5 Example 6 0.3 16 1.5 6.0 0.2 0.9 14.9 70 40 2.7 2.5 Example 7 1.3 10 1.5 14.2 0.2 0.9 14.9 70 40 2.7 2.5 Example 8 1.3 4 1.5 6.4 0.2 0.9 14.9 70 40 2.7 2.5 Example 9 1.3 20 1.5 27.2 0.2 0.9 14.9 70 40 2.7 2.5 Example 10 1.3 22 1.5 29.8 0.2 0.9 14.9 70 40 2.7 2.5 Embodiment 11 1.3 3 1.5 5.1 0.2 0.9 14.9 70 40 2.7 2.5 Example 12 1.3 16 2.5 22.4 0.2 0.9 14.9 70 40 2.7 2.5 Embodiment 13 1.3 16 3 22.5 0.2 0.9 14.9 70 40 2.7 2.5 Embodiment 14 1.3 16 0.02 20.9 0.2 0.9 14.9 70 40 2.7 2.5 Embodiment 15 1.3 16 3.5 22.7 0.2 0.9 14.9 70 40 2.7 2.5 Example 16 1.3 16 0.008 20.9 0.2 0.9 14.9 70 40 2.7 2.5 Embodiment 17 1 10 2 11.4 0.2 0.9 14.9 70 40 2.7 2.5 Embodiment 18 1.3 16 1.5 22.0 0.2 0.9 14.9 70 40 2.7 0.5 Embodiment 19 1.3 16 1.5 22.0 0.2 0.9 14.9 70 40 2.7 5 Embodiment 20 1.3 16 1.5 22.0 0.1 0.6 5 60 5 1.0 2.5 Embodiment 21 1.3 16 1.5 22.0 0.5 1.5 15 85 200 13.3 2.5 Comparative Example 1 3 20 3 61.7 0.2 0.9 14.9 70 40 4.0 2.5 Comparative Example 2 0.5 4 1 3.0 0.2 0.9 14.9 70 40 4.0 2.5 Comparative Example 3 1.3 / / / 0.2 0.9 14.9 70 40 4.0 2.5

[0114] The cycle performance, rate performance and lithium deposition of the secondary batteries prepared in the examples and comparative examples are shown in Table 2; wherein the test method comprises the following steps:

[0115] 1) Cycle capacity retention rate: The nominal capacity of the battery is C0. After 6000 cycles at 0.5C / 0.5C at 25°C, the discharge capacity C is obtained. The capacity retention rate = C / C0×100%;

[0116] 2) 1C lithium deposition: At 25°C, the battery was disassembled after 3 cycles of charge and discharge at a rate of 0.5C and 10 cycles of charge and discharge at a rate of 1C to observe the lithium deposition at the interface of the negative electrode. According to the degree of lithium deposition, it was divided into four levels: no lithium deposition, slight lithium deposition, moderate lithium deposition and severe lithium deposition; among them, no lithium deposition means that the lithium deposition area is less than 2%, slight lithium deposition means 2-10%, moderate lithium deposition means 10-30%, and severe lithium deposition means more than 30%;

[0117] 3) 2C lithium deposition: At 25°C, the battery was disassembled after 3 cycles of charge and discharge at a rate of 0.5C and 10 cycles of charge and discharge at a rate of 2C to observe the lithium deposition at the interface of the negative electrode. According to the degree of lithium deposition, the battery was divided into four levels: no lithium deposition, slight lithium deposition, moderate lithium deposition and severe lithium deposition; among them, no lithium deposition means that the lithium deposition area is less than 2%, slight lithium deposition means 2-10%, moderate lithium deposition means 10-30%, and severe lithium deposition means more than 30%;

[0118] Table 2

[0119]

[0120]

[0121] As can be seen from Table 2, the present application controls the secondary battery to satisfy 4≤Cdl×N×S -0.5 When ≤53, the obtained secondary battery has good cycle performance, rate performance and safety performance; specifically, the obtained secondary battery has a cycle capacity retention rate of more than 87% after 6000 cycles at 0.5C / 0.5C at 25°C, and no lithium deposition is shown in 1C / 2C lithium deposition tests;

[0122] The results of Examples 1 to 21 and Comparative Examples 1 to 3 of the present application also show that when Y satisfies 4≤Y≤53, the secondary battery can be guaranteed to have excellent cycle performance, rate performance and good lithium deposition conditions.

[0123] Finally, it should be noted that the above embodiments are intended to illustrate the technical solution of the present application rather than to limit the scope of protection of the present application. Although the present application has been described in detail with reference to the preferred embodiments, a person of ordinary skill in the art should understand that the technical solution of the present application may be modified or replaced by equivalents without departing from the essence and scope of the technical solution of the present application.

Claims

1. A secondary battery, comprising a positive electrode sheet, a negative electrode sheet, a separator and an electrolyte, wherein the positive electrode sheet comprises a positive electrode current collector and a positive electrode active material layer disposed on at least one surface of the positive electrode current collector, characterized in that: The positive electrode active material layer includes a positive electrode active material and a lithium supplement; The positive electrode sheet satisfies: 5≤Y≤53; Where, Y = Cdl × N × S -0.5 ; Cdl nF is the non-Faraday capacitance of the positive electrode; N is the particle dispersion of the lithium supplement; Sμm is the average crystal size of the lithium supplement.

2. The secondary battery according to claim 1, characterized in that: At least one of the following is met: a. The non-Faraday capacitance Cdl nF of the positive electrode plate is 0.5 to 3 nF; b. The particle dispersion N of the lithium supplement agent is 4 to 20; c. The average grain size Sμm of the lithium supplement is 0.01 to 3μm.

3. The secondary battery according to claim 1, characterized in that: In the positive electrode active material layer, the mass percentage of the lithium supplement agent is 0.5-5%.

4. The secondary battery according to claim 1, characterized in that: The lithium supplement includes at least one of Li5FeO5, Li6CoO4, and Li2NiO2.

5. The secondary battery according to claim 1, characterized in that: The positive electrode active material satisfies: 5≤Dv99≤15.

6. The secondary battery according to claim 5, characterized in that: At least part of the surface of the positive electrode active material is provided with a carbon layer, and the thickness C of the carbon layer is 5 to 200 nm.

7. The secondary battery according to claim 6, characterized in that: The positive electrode active material satisfies: 1≤C / Dv99≤14.

8. The secondary battery according to claim 1, characterized in that: The positive electrode active material satisfies at least one of the following characteristics: (1) 0.1≤Dv10≤0.5; (2) 0.6≤Dv50≤1.

5.

9. The secondary battery according to claim 1, characterized in that: The thickness of the positive electrode active material layer is 60 to 85 μm.

10. An electrical device, characterized in that: The invention comprises the secondary battery according to any one of claims 1 to 9.

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