Lithium ion secondary battery, power utilization device and application

Abstract

The invention relates to a lithium ion secondary battery, a power utilization device and application. A lithium ion secondary battery according to some embodiments includes a negative electrode tab; the negative electrode plate comprises a negative electrode current collector, and a second negative electrode active layer and a first negative electrode active layer which are sequentially arranged on at least one side of the negative electrode current collector; the second negative electrode active layer is positioned between the negative electrode current collector and the first negative electrode active layer; the second negative electrode active layer comprises a second negative electrode active material and a quaternary ammonium salt type compound, and the quaternary ammonium salt type compound comprises quaternary ammonium cations. The second negative active material may include a carbon-based material. The lithium ion secondary battery has significantly improved fast charge performance.

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, an electrical device and applications. 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 lithium-ion secondary battery technology, lithium-ion batteries are increasingly used in power tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, aerospace and other fields, and are also widely used in energy storage power systems such as hydropower, thermal power, wind power and solar power stations. The demand for fast charging performance of lithium-ion secondary batteries is also increasing. Summary of the invention

[0004] According to various implementations and examples of the present application, the present application provides a lithium ion secondary battery, an electric device and an application. The lithium ion secondary battery has significantly improved fast charging performance.

[0005] In a first aspect of the present application, a lithium-ion secondary battery is provided, wherein a quaternary ammonium salt compound is disposed in a negative electrode active material layer of a negative electrode plate of the lithium-ion secondary battery.

[0006] In some embodiments, a lithium-ion secondary battery is provided, comprising a negative electrode plate and an electrolyte; the negative electrode plate comprises a negative electrode current collector and a second negative electrode active layer and a first negative electrode active layer sequentially disposed on at least one side of the negative electrode current collector, wherein the second negative electrode active layer is located between the negative electrode current collector and the first negative electrode active layer;

[0007] The second negative electrode active layer includes a second negative electrode active material and a quaternary ammonium salt compound, wherein the second negative electrode active material includes a carbon-based material, and the quaternary ammonium salt compound includes a quaternary ammonium cation.

[0008] In the lithium-ion secondary battery, a first negative electrode active layer located in the upper layer and a second negative electrode active layer located in the lower layer (the direction away from the surface of the negative electrode collector is the upper layer, and the direction toward the surface of the negative electrode collector is the lower layer) can be arranged in the negative electrode active material layer in the negative electrode plate, and a quaternary ammonium salt compound is further arranged in the second negative electrode active layer located in the lower layer. The quaternary ammonium salt compound includes a hydrophilic, positively charged quaternary ammonium root. For the negative electrode plate immersed in the electrolyte, the electrostatic effect based on the quaternary ammonium root can be used to attract the electrolyte anions in the electrolyte, promote the rapid dissociation of the electrolyte lithium salt in the electrolyte, and significantly improve the electrolyte wettability of the second negative electrode active layer and the dynamics of the negative electrode plate, thereby significantly improving the fast charging performance of the battery.

[0009] In some embodiments, the electrolyte includes a non-aqueous solvent.

[0010] In some embodiments, the electrolyte includes an electrolyte lithium salt and a non-aqueous solvent.

[0011] In some embodiments, the quaternary ammonium salt compound includes a quaternary ammonium cation and a hydrocarbon chain covalently bonded to the quaternary ammonium cation.

[0012] In some embodiments, the hydrocarbyl chain in the quaternary ammonium salt compound includes an alkyl chain.

[0013] By setting a hydrocarbon chain in the quaternary ammonium salt compound, for example, the hydrocarbon chain may include an alkyl chain, the chain structure of the hydrocarbon chain is conducive to making the quaternary ammonium salt compound better and more stably loaded and wrapped on the surface of the second negative electrode active material, and the carbon-carbon skeleton provided by the hydrocarbon chain is conducive to making the quaternary ammonium salt compound better and more stably adsorbed on the surface of the carbon-based material (the carbon-based material has a certain lipophilicity), further combined with the electrostatic attraction of the quaternary ammonium root in the quaternary ammonium salt compound, it is conducive to guiding the lithium ions in the electrolyte to be guided to the surface of the second negative electrode active material more quickly, which is conducive to further improving the negative electrode plate dynamics and the battery fast charging performance.

[0014] In some embodiments, the quaternary ammonium salt compound satisfies one or more of the following characteristics:

[0015] (ta1) the hydrocarbon chain is an alkyl chain;

[0016] (ta2) the number of carbon atoms in the hydrocarbon chain is 12 to 18;

[0017] (ta3) The molecular weight of the quaternary ammonium salt compound is less than or equal to 600Da.

[0018] In some embodiments, the hydrocarbon chain in the quaternary ammonium salt compound is C 12-18 Alkyl chain.

[0019] By controlling the number of carbon atoms in the hydrocarbon chain of the quaternary ammonium salt compound and / or the molecular weight of the quaternary ammonium salt compound within the aforementioned range, the length of the hydrocarbon chain can be adjusted within a more appropriate range. On the one hand, it is beneficial to better and more stably wrap the quaternary ammonium salt compound on the surface of the second negative electrode active material, and to inhibit the quaternary ammonium salt compound from falling off from the surface of the second negative electrode active material during the charging and discharging process. Further combined with the quaternary ammonium roots exposed to the electrolyte, it can promote the lithium ions in the electrolyte to be guided to the surface of the second negative electrode active material faster and more stably, thereby improving the transmission rate of lithium ions inside the negative electrode plate. On the other hand, the degree of wrapping of the hydrocarbon chain on the surface of the second negative electrode active material can be better controlled, so that the active sites on the surface of the second negative electrode active material can better contact the electrolyte, thereby helping to better improve the negative electrode plate dynamics and battery fast charging performance.

[0020] In some embodiments, the quaternary ammonium salt compound satisfies one or more of the following characteristics:

[0021] (tb1) The structure of the quaternary ammonium cation is -N + (R 1 R 2 R 3 ), where R 1 and R 2 Each independently is C 1-3 Alkyl, R 3 C 1-3 alkyl or hydroxyethyl; optionally, R 1 and R 2 are each independently methyl, R 3 is methyl or hydroxyethyl;

[0022] (tb2) The quaternary ammonium salt compound includes anions, and the anions include one or more of nitrate, carbonate, bicarbonate and phosphate.

[0023] In some embodiments, the quaternary ammonium salt compound includes one or more of octadecyl dimethyl hydroxyethyl quaternary ammonium nitrate, N,N-dimethyl-N-(2-hydroxyethyl) hexadecyl quaternary ammonium phosphate, dodecyl trimethyl quaternary ammonium nitrate, octadecyl trimethyl quaternary ammonium phosphate, dodecyl trimethyl quaternary ammonium phosphate, dodecyl trimethyl quaternary ammonium carbonate, and dodecyl trimethyl quaternary ammonium bicarbonate.

[0024] By introducing one or more of nitrate, carbonate, bicarbonate and phosphate into the anions of quaternary ammonium salt compounds, it is beneficial to better control the binding ability between the anions and the quaternary ammonium roots in the quaternary ammonium salt compounds, making the quaternary ammonium roots more easily dissociated. These anions may have lower electronegativity than electrolyte anions, thereby being more conducive to promoting the formation of the quaternary ammonium root-electrolyte anion structure, and more conducive to the quaternary ammonium root-electrolyte anion structure to guide the lithium ions in the electrolyte to aggregate toward the second negative electrode active material, which is beneficial to better improve the negative electrode plate dynamics and battery fast charging performance.

[0025] In some embodiments, the mass percentage of the quaternary ammonium salt compound in the second negative electrode active layer is 0.2% to 2%.

[0026] In some embodiments, the mass percentage of the quaternary ammonium salt compound in the second negative electrode active layer is 0.2% to 1.5%.

[0027] By controlling the mass proportion of the quaternary ammonium salt compound in the second negative electrode active layer within the aforementioned range, it is not only beneficial to better exert the role of the quaternary ammonium salt compound in improving the fast charging performance of the battery, but also to better control the decrease in the electronic conductivity of the surface of the second negative electrode active material caused by the quaternary ammonium salt compound wrapping, which is beneficial to better improve the fast charging performance of the battery. Furthermore, it is also beneficial to maintain a high lithium storage capacity of the second negative electrode active layer, which is beneficial to take into account the energy density of the negative electrode and the battery.

[0028] In some embodiments, the carbon-based material accounts for 80% to 100% by mass of the second negative electrode active material.

[0029] In some embodiments, the negative electrode plate satisfies one or more of the following characteristics:

[0030] (tc1) the carbon-based material comprises one or more of artificial graphite, natural graphite, soft carbon and hard carbon;

[0031] (tc2) The mass proportion of the carbon-based material in the second negative electrode active layer is 94.5% to 97.5%.

[0032] In some embodiments, the carbon-based material includes one or more of artificial graphite, natural graphite, graphite, soft carbon, and hard carbon.

[0033] Natural graphite is prone to lateral deformation when subjected to cold pressing. Introducing natural graphite into the second negative electrode active material is beneficial for increasing the compaction density and surface capacity of the second negative electrode active layer, thereby helping to increase the energy density of the negative electrode sheet.

[0034] The structure of artificial graphite is more stable than that of natural graphite, and it has relatively fewer internal defects, which slows down the decay of available storage sites for lithium ions during the cycle and makes the cycle performance more stable.

[0035] Both hard carbon and soft carbon have a large degree of disorder, which is conducive to the entry of lithium ions. Hard carbon can provide abundant lithium insertion sites and fast transmission channels; the carbon layers in soft carbon are disorderly stacked, which allows lithium ions to be transmitted relatively quickly. The introduction of at least one of hard carbon and soft carbon is beneficial to improving the negative electrode and battery dynamics.

[0036] In some embodiments, the mass proportion of the carbon-based material in the second negative electrode active layer is 94.5% to 97.5%, and can be optionally 95.0% to 97.0%.

[0037] By controlling the mass proportion of the carbon-based material in the second negative electrode active layer within the aforementioned range, it is beneficial to better wrap the quaternary ammonium salt compound on the surface of the second negative electrode active material. In addition, the energy density of the negative electrode and the battery can also be taken into account.

[0038] In some embodiments, the second negative active layer includes a binder, and the binder includes styrene-butadiene rubber.

[0039] By introducing styrene butadiene rubber into the binder of the second negative electrode active layer, the styrene butadiene rubber can have a non-chain structure. In terms of occupying the wrapping sites on the surface of the second negative electrode active material, the styrene butadiene rubber is not easy to compete with the quaternary ammonium salt compound, which is conducive to better realizing the wrapping of the binder and the quaternary ammonium salt compound on the surface of the second negative electrode active material at the same time, which can not only realize a good electrical contact network, but also give full play to the role of the quaternary ammonium salt compound in guiding lithium ions in the electrolyte, which is conducive to better improving the fast charging performance of the battery.

[0040] In some embodiments, the second negative electrode active layer includes a carbon-based material and a binder, and the binder includes styrene-butadiene rubber.

[0041] By introducing carbon-based materials into the second negative electrode active material of the second negative electrode active layer and introducing styrene-butadiene rubber into the binder, styrene-butadiene rubber has a more suitable lipophilicity and can better coordinate the mutual binding effect between the binder and the carbon-based material and the quaternary ammonium salt compound; relative to the strong binding effect of oily binders (such as polyvinylidene fluoride (PVDF)) on quaternary ammonium salt compounds, styrene-butadiene rubber is conducive to better exerting the binding effect between quaternary ammonium salt compounds and carbon-based materials, and better exerting the role of quaternary ammonium salt compounds in improving the fast charging performance of batteries.

[0042] In some embodiments, the glass transition temperature of the styrene-butadiene rubber is 5°C to 70°C.

[0043] In some embodiments, the glass transition temperature of the styrene-butadiene rubber is 30°C to 50°C.

[0044] By controlling the glass transition temperature of the styrene-butadiene rubber within the aforementioned range, the second negative electrode active layer can have a better pore structure after rolling, which is beneficial for promoting the electrolyte to better infiltrate the second negative electrode active layer.

[0045] In some embodiments, the first negative electrode active layer includes a first negative electrode active material, which includes a negative electrode active body and a coating layer located at least a portion of a surface of the negative electrode active body, wherein the coating layer includes one or more of soft carbon, hard carbon and amorphous carbon.

[0046] By arranging a coating layer on the surface of the first negative electrode active material of the first negative electrode active layer and arranging one or more of soft carbon, hard carbon and amorphous carbon in the coating layer, the lithium ion transmission channel on the surface of the first negative electrode active material can be optimized, lithium ion transmission can be promoted, and battery dynamics and battery fast charging performance can be further improved.

[0047] In some embodiments, the first negative electrode active layer includes a first negative electrode active material;

[0048] The lithium-ion secondary battery meets one or more of the following characteristics:

[0049] (td1) the first negative electrode active material includes coated graphite, the coated graphite includes a graphite body and a coating layer located on at least a portion of a surface of the graphite body, the coating layer includes one or more of soft carbon, hard carbon and amorphous carbon;

[0050] (td2) the first negative electrode active material includes secondary particulate graphite, the secondary particulate graphite includes a secondary particulate graphite body, the amount of the secondary particulate graphite in the first negative electrode active material is greater than or equal to 20%, and can be optionally 30% to 80%; optionally, the secondary particulate graphite includes carbon-coated secondary particulate graphite, the carbon-coated secondary particulate graphite includes the secondary particulate graphite body and a carbon coating layer located on at least a portion of the surface of the secondary particulate graphite body, and the carbon coating layer in the carbon-coated secondary particulate graphite includes one or more of soft carbon, hard carbon and amorphous carbon;

[0051] (td3) the first negative electrode active material includes a graphite material, and the OI value of the graphite material is 2 to 15, and can be optionally 2 to 10;

[0052] (td4) D of the first negative electrode active material v 50 is 10μm~18μm, and can be 12μm~16μm;

[0053] (td5) the porosity of the first negative electrode active layer is higher than the porosity of the second negative electrode active layer;

[0054] (td6) The powder compaction density of the first negative electrode active material or the powder compaction density of the first negative electrode active layer is 1.60 g / cm 3 ~1.80g / cm 3 ;

[0055] (td7) the charge rate of the first negative electrode active layer is higher than the charge rate of the second negative electrode active layer; optionally, the charge rate of the first negative electrode active layer is higher than the charge rate of the second negative electrode active layer;

[0056] (td8) Under at least one temperature condition between 20°C and 35°C, the ionic conductivity of the electrolyte is 13mS / cm to 18mS / cm; optionally, at 25°C, the ionic conductivity of the electrolyte is 13mS / cm to 18mS / cm.

[0057] By making the lithium-ion secondary battery satisfy one or more of the characteristics (td1), (td2), (td3), (td4), (td5), (td6), (td7) and (td8), the fast charging performance of the battery can be better improved.

[0058] By introducing coated graphite into the first negative electrode active layer and arranging one or more of soft carbon, hard carbon and amorphous carbon in the coating layer, the lithium ion transmission channel on the surface of the first negative electrode active material can be optimized, lithium ion transmission can be promoted, and battery dynamics and battery fast charging performance can be further improved.

[0059] By introducing secondary particle-type graphite into the first negative electrode active layer, utilizing the property that secondary particles are formed by agglomeration of primary particles, and based on the disordered orientation of each primary particle, it is beneficial to improve the isotropic characteristics of lithium ions when embedded in the first negative electrode active material, increase the lithium ion embedding sites on the surface of the first negative electrode active material, increase the lithium ion embedding rate, and improve the battery fast charging performance.

[0060] By controlling the OI value of the graphite material in the first negative electrode active material within the aforementioned range, it is beneficial to enhance the isotropic characteristics of the first negative electrode active material, increase the lithium ion embedding channels, and make the lithium ion diffusion kinetics in the first negative electrode active layer better, which is beneficial to improve the battery fast charging performance.

[0061] By adding D of the first negative electrode active material v 50 is controlled within the aforementioned range, which is beneficial to better control the degree of particle stacking in the first negative electrode active layer, is beneficial to better control the pores between particles, provides a better lithium ion transmission channel, and better improves the battery dynamics and fast charging performance.

[0062] By controlling the porosity of the first negative electrode active layer to be higher than that of the second negative electrode active layer, it is beneficial to take into account both the fast charging performance and the energy density of the battery. The relatively high porosity of the first negative electrode active layer can be used to promote the rapid transmission of lithium ions, while the relatively low porosity of the second negative electrode active layer can be used to improve the energy density of the negative electrode.

[0063] By controlling the powder compaction density of the first negative electrode active material or the powder compaction density of the first negative electrode active layer within the aforementioned range, it is beneficial to make the particle stacking degree of the first negative electrode active layer provide a better lithium ion transmission channel, thereby better improving the battery dynamics and fast charging performance; in addition, the second negative electrode active layer can also be used to provide a higher energy density, which is beneficial to take into account the fast charging performance and energy density of the lithium-ion secondary battery.

[0064] By controlling the charge rate of the first negative electrode active layer to be higher than that of the second negative electrode active layer, it is beneficial to promote the faster embedding of lithium ions into the first negative electrode active layer, and it is more beneficial to improve the fast charging performance of the battery. By controlling the charge rate of the first negative electrode active layer to be higher than that of the second negative electrode active layer, it is beneficial to promote the faster embedding of lithium ions into the first negative electrode active layer, and it is more beneficial to improve the fast charging performance of the battery.

[0065] By controlling the ionic conductivity of the electrolyte within the aforementioned range, it is beneficial to promote the rapid transmission of lithium ions, which is beneficial to better improve battery dynamics and battery fast charging performance.

[0066] In some embodiments, the negative electrode plate in the lithium-ion secondary battery satisfies one or more of the following characteristics:

[0067] (te1) D of the second negative electrode active material v 50 is 12μm~21μm, and can be selected as 14μm~20μm;

[0068] (te2) The first negative electrode active layer includes a first negative electrode active material, and the second negative electrode active material D v 50 higher than the D of the first negative electrode active material v 50;

[0069] (te3) the compaction density of the second negative electrode active layer is higher than the compaction density of the first negative electrode active layer;

[0070] (te4) the powder compaction density of the second negative electrode active material is higher than the powder compaction density of the first negative electrode active material, or 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; optionally, the ratio of the powder compaction density of the second negative electrode active material to the powder compaction density of the first negative electrode active material is 1.05-1.35, further optionally 1.10-1.30, further optionally 1.10-1.28 or 1.15-1.30; optionally, the ratio of the powder compaction density of the second negative electrode active layer to the powder compaction density of the first negative electrode active layer is 1.05-1.35, further optionally 1.10-1.30, further optionally 1.10-1.28 or 1.15-1.30;

[0071] (te5) The powder compaction density of the second negative electrode active material or the powder compaction density of the second negative electrode active layer is 1.85 g / cm 3 ~2.05g / cm 3 .

[0072] By making the lithium-ion secondary battery meet one or more of the characteristics (te1), (te2), (te3), (te4) and (te5), it is beneficial for the lithium-ion secondary battery to have improved fast charging performance while also taking into account energy density requirements.

[0073] By adding the D v 50 is controlled within the aforementioned range, which is beneficial for the second negative electrode active layer to obtain a higher compaction density, thereby helping to improve the energy density.

[0074] By controlling the D v 50 higher than the D of the first negative electrode active material v 50, which is beneficial to making the second negative electrode active layer obtain a higher compaction density, thereby helping to improve the energy density.

[0075] By regulating the compaction density of the second negative electrode active layer in the lithium ion secondary battery to be higher than that of the first negative electrode active layer, the energy density of the lithium ion secondary battery can be improved.

[0076] By controlling the powder compaction density of the second negative electrode active material in the lithium-ion secondary battery to be higher than the powder compaction density of the first negative electrode active material or 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 a higher compaction density during the cold pressing process of the pole piece, so that the second negative electrode active layer in the lithium-ion secondary battery has a higher compaction density. Further, by controlling the ratio of the powder compaction density of the second negative electrode active material to the powder compaction density of the first negative electrode active material or controlling the ratio of the powder compaction density of the second negative electrode active layer to the powder compaction density of the first negative electrode active layer within the aforementioned range, it is beneficial to better balance the fast charging performance and energy density of the lithium-ion secondary battery.

[0077] By controlling the powder compaction density of the second negative electrode active material or the powder compaction density of the second negative electrode active layer within the aforementioned range, it is beneficial to make the secondary battery have a higher energy density. In addition, the particle stacking can be relatively compact, and at this time, the quaternary ammonium salt compound introduced into the second negative electrode active layer may have a more obvious effect on improving the fast charging performance of the battery.

[0078] In some embodiments, the negative electrode plate in the lithium-ion secondary battery satisfies one or more of the following characteristics:

[0079] (tf1) based on one side of the negative electrode current collector, the ratio of the surface density of the second negative electrode active layer to the surface density of the first negative electrode active layer is 3:2 to 2:3;

[0080] (tf2) The thickness ratio of the first negative electrode active layer to the second negative electrode active layer on one side of the negative electrode current collector is denoted by f H , satisfying f H ≤1.6, optionally, 1.1≤f H ≤1.6, further optionally, 1.1≤f H ≤1.3;

[0081] (tf3) Based on a single side of the negative electrode current collector, the thickness of the first negative electrode active layer is less than or equal to 50 μm, and may be 20 μm to 50 μm, and may be 30 μm to 40 μm.

[0082] By controlling the ratio of the surface density of the second negative electrode active layer to the surface density of the first negative electrode active layer within the aforementioned range, it is beneficial to take into account both the fast charging performance and the energy density of the battery.

[0083] By controlling the thickness of the first negative electrode active layer to satisfy one or more of the above characteristics (tf2) and (tf3), the distance between the quaternary ammonium salt compound and the surface of the negative electrode plate can be adjusted, which is beneficial to better promote the transmission of lithium ions to the second negative electrode active layer located in the lower layer, thereby helping to better improve the fast charging performance of the battery.

[0084] In the first aspect of the present application, a lithium ion secondary battery is provided, which comprises a negative electrode plate and an electrolyte; the negative electrode plate comprises a negative electrode current collector and a negative electrode active material layer located on at least one side of the negative electrode current collector;

[0085] The negative electrode active material layer includes a negative electrode active material and a quaternary ammonium salt compound, the negative electrode active material includes a negative electrode active body and a coating layer located at least a portion of the surface of the negative electrode active body, the coating layer includes one or more of soft carbon, hard carbon and amorphous carbon, and the quaternary ammonium salt compound includes a quaternary ammonium cation.

[0086] By arranging a coating layer on the surface of the negative electrode active material of the negative electrode active material layer, and arranging one or more of soft carbon, hard carbon and amorphous carbon in the coating layer, the lithium ion transmission channel on the surface of the negative electrode active material can be optimized, lithium ion transmission can be promoted, and battery dynamics and battery fast charging performance can be improved; further, by arranging a quaternary ammonium salt compound in the negative electrode active material layer, the electrostatic effect based on the quaternary ammonium root can be used to attract electrolyte anions in the electrolyte, promote the rapid dissociation of the electrolyte lithium salt in the electrolyte, and the formed quaternary ammonium root-electrolyte anion structure can also guide the rapid transmission of lithium ions in the electrolyte to the surface of the negative electrode active material; based on the aforementioned multiple effects, the fast charging performance of the battery can be better improved.

[0087] In some embodiments, the negative electrode plate satisfies one or more of the following characteristics:

[0088] (tg1) the quaternary ammonium salt compound is as defined above;

[0089] (tg2) the mass proportion of the quaternary ammonium salt compound in the negative electrode active material layer is 0.2% to 2%, and can be 0.2% to 1.5%;

[0090] (tg3) the negative electrode active material comprises a carbon-based material; optionally, the carbon-based material comprises one or more of artificial graphite, natural graphite, soft carbon and hard carbon;

[0091] (tg4) the negative electrode active material includes a carbon-based material, and the mass proportion of the carbon-based material in the negative electrode active material layer is 94.5% to 97.5%, and can be 95.0% to 97.0%;

[0092] (tg5) The negative electrode active material layer includes a binder, and the binder includes styrene-butadiene rubber; optionally, the glass transition temperature of the styrene-butadiene rubber is 5°C to 70°C, and further optionally 30°C to 50°C;

[0093] (tg6) The negative electrode active material includes coated graphite, and the coated graphite includes a graphite body and a coating layer located on at least a part of the surface of the graphite body, and the coating layer includes one or more of soft carbon, hard carbon, and amorphous carbon;

[0094] (tg7) The negative electrode active material includes secondary particle graphite, and the secondary particle graphite includes a secondary particle graphite body. The proportion of the secondary particle graphite in the negative electrode active material is greater than or equal to 20%, and optionally 30% to 60%; optionally, the secondary particle graphite includes carbon-coated secondary particle graphite, and the carbon-coated secondary particle graphite includes the secondary particle graphite body and a carbon coating layer located on at least a part of the surface of the secondary particle graphite body. The carbon coating layer in the carbon-coated secondary particle graphite includes one or more of soft carbon, hard carbon, and amorphous carbon;

[0095] (tg8) The negative electrode active material includes a graphite material, and the OI value of the graphite material is 2 to 15, and optionally 2 to 10;

[0096] (tg9) The D v 50 of the negative electrode active material is 11 μm to 20 μm, and optionally 13 μm to 18 μm;

[0097] (tg10) The porosity of the negative electrode active material layer is 15% to 35%, and optionally 25% to 30%;

[0098] (tg11) Under at least one temperature condition of 20°C to 35°C, the ionic conductivity of the electrolyte is 13 mS / cm to 18 mS / cm; optionally, at 25°C, the ionic conductivity of the electrolyte is 13 mS / cm to 18 mS / cm;

[0099] (tg12) The negative electrode active material layer includes a second negative electrode active layer, and the second negative electrode active layer is defined as in the first aspect of the present application.

[0100] By controlling the mass ratio of the quaternary ammonium salt-type compound in the negative electrode active material layer within the foregoing range, the role of the quaternary ammonium salt-type compound in improving the fast charging performance of the battery can be better exerted, and the decrease in the electronic conductivity of the surface of the negative electrode active material caused by the wrapping of the quaternary ammonium salt-type compound can be better controlled, which is beneficial to better improving the fast charging performance of the battery. Further, it is also beneficial to keep the negative electrode active material layer having a high lithium storage capacity and is beneficial to taking into account the energy density of the negative electrode and the battery.

[0101] Carbon-based materials are conducive to better adsorbing hydrocarbon chains in quaternary ammonium salt compounds, thereby promoting better wrapping of quaternary ammonium salt compounds on the surface of negative electrode active materials, thereby helping to better guide lithium ions in the electrolyte to the surface of negative electrode active materials more quickly; on the other hand, carbon-based materials also have good electronic conductivity; on the other hand, carbon-based materials are also conducive to providing better stability of negative electrode active materials during fast charging and are not easy to pulverize; through the aforementioned multiple effects, it is conducive to better improving the negative electrode plate dynamics and battery fast charging performance.

[0102] By introducing natural graphite into the negative electrode active material, it is beneficial to improve the compaction density and surface capacity of the negative electrode active material layer, thereby improving the energy density of the negative electrode sheet. By introducing artificial graphite into the negative electrode active material, it is beneficial to make the cycle performance more stable. By introducing at least one of hard carbon and soft carbon into the negative electrode active material, it is beneficial to improve the negative electrode sheet and battery dynamics.

[0103] By controlling the mass proportion of the carbon-based material in the negative electrode active material layer within the aforementioned range, it is beneficial to better wrap the quaternary ammonium salt compound on the surface of the negative electrode active material. In addition, the energy density of the negative electrode and the battery can also be taken into account.

[0104] By introducing carbon-based materials into the negative electrode active material of the negative electrode active material layer and introducing styrene-butadiene rubber into the binder, it is beneficial to better realize the simultaneous wrapping of the binder and the quaternary ammonium salt compound on the surface of the negative electrode active material, which can not only realize a good electrical contact network, but also give full play to the role of the quaternary ammonium salt compound in guiding lithium ions in the electrolyte, which is beneficial to better improve the fast charging performance of the battery.

[0105] By controlling the glass transition temperature of the styrene-butadiene rubber within the aforementioned range, the negative electrode active material layer can have a better pore structure after rolling, which is beneficial for promoting the electrolyte to better infiltrate the negative electrode active material layer.

[0106] By setting a coating layer on the surface of the negative electrode active material in the negative electrode active material layer and setting one or more of soft carbon, hard carbon and amorphous carbon in the coating layer, the lithium ion transmission channel on the surface of the negative electrode active material can be optimized, lithium ion transmission can be promoted, and battery dynamics and battery fast charging performance can be further improved.

[0107] By introducing coated graphite into the negative electrode active material layer and arranging one or more of soft carbon, hard carbon and amorphous carbon in the coating layer, the lithium ion transmission channel on the surface of the negative electrode active material can be optimized, lithium ion transmission can be promoted, and battery dynamics and battery fast charging performance can be further improved.

[0108] By introducing secondary particle-type graphite into the negative electrode active material layer, taking advantage of the characteristic that secondary particles are formed by the aggregation of primary particles, and based on the disordered orientation of each primary particle, it is beneficial to improve the isotropic characteristics when lithium ions are inserted into the negative electrode active material, increase the lithium ion insertion sites on the surface of the negative electrode active material, enhance the lithium ion insertion rate, and improve the fast charging performance of the battery.

[0109] By controlling the OI value of the graphite material in the negative electrode active material within the aforementioned range, it is beneficial to enhance the isotropic characteristics of the negative electrode active material, increase the lithium ion insertion channels, make the lithium ion diffusion kinetics in the negative electrode active material layer better, and thus is beneficial to improving the fast charging performance of the battery.

[0110] By controlling the D v 50 of the negative electrode active material within the aforementioned range, it is beneficial to better control the packing degree of the particles in the negative electrode active material layer, beneficial to better control the pores between the particles, provide a better lithium ion transmission channel, and better improve the battery kinetics and fast charging performance.

[0111] When the porosity of the negative electrode active material layer is controlled within the aforementioned range, the particle packing is relatively tight. At this time, the improvement effect of the quaternary ammonium salt-type compound introduced into the negative electrode active material layer on the fast charging performance of the battery is more obvious.

[0112] By controlling the ionic conductivity of the electrolyte within the aforementioned range, it is beneficial to promote the rapid transmission of lithium ions, beneficial to better improving the battery kinetics and the fast charging performance of the battery.

[0113] In some embodiments, on one side of the negative electrode current collector, the areal density of the negative electrode plate is 5 mg / cm 2 ~15 mg / cm 2 .

[0114] By controlling the areal density of the negative electrode plate within the aforementioned range, it is beneficial to balance the fast charging performance and energy density of the battery.

[0115] In some embodiments, the electrolyte includes an electrolyte salt, and the electrolyte salt includes an electrolyte anion;

[0116] The electrolyte anion includes one or more of tetrafluoroborate, hexafluoroarsenate, hexafluorophosphate, trifluoromethanesulfonate, difluorophosphate, difluorooxaloborate, tetrafluorooxalophosphate, difluorodioxalophosphate, bis(fluorosulfonyl)imide, and bis(trifluoromethanesulfonyl)imide.

[0117] By selecting the aforementioned types of electrolyte anions, the electrolyte anions can have a stronger binding ability to the quaternary ammonium roots, which can better promote the dissociation of the quaternary ammonium roots and anions in the quaternary ammonium salt type compound, promote the attraction of the quaternary ammonium salt type compound to the electrolyte anions and the guidance of the lithium ions in the electrolyte, and improve the transmission rate of lithium ions to the second negative electrode active material, which can better improve the negative electrode plate dynamics and battery fast charging performance.

[0118] The above-mentioned electrolyte anion types have stronger electronegativity than one or more of nitrate, carbonate, bicarbonate and phosphate, and have stronger binding properties to quaternary ammonium.

[0119] In some embodiments, the electrolyte salt includes one or more of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bisfluorosulfonyl imide, lithium bistrifluoromethanesulfonyl imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalatoborate, lithium dioxalatoborate, lithium difluorodioxalatophosphate, and lithium tetrafluorooxalatophosphate.

[0120] In some embodiments, the lithium-ion secondary battery further includes a positive electrode plate, the positive electrode plate includes a positive electrode active layer, the positive electrode active layer includes a positive electrode active material, and the positive electrode active material includes one or more of a lithium phosphate active material and a lithium composite metal oxide active material.

[0121] By introducing lithium-containing phosphate active materials into the positive electrode active materials, it is beneficial to improve the structural stability of the positive electrode active materials during the charge and discharge cycle process, which is beneficial to extend the cycle life of the battery.

[0122] Introducing lithium composite metal oxide active materials into the positive electrode active material is beneficial to improving the positive electrode and battery energy density.

[0123] In some embodiments, the positive electrode active material includes a lithium-containing phosphate active material, and the positive electrode active material satisfies one or more of the following characteristics:

[0124] (th1) the mass proportion of the lithium-phosphate active material in the positive electrode active layer is greater than or equal to 80%, and can be 80% to 97%;

[0125] (th2) the lithium phosphate active material includes one or more of lithium iron phosphate, a composite material of lithium iron phosphate and carbon, lithium manganese phosphate, a composite material of lithium manganese phosphate and carbon, lithium iron manganese phosphate, and a composite material of lithium iron manganese phosphate and carbon;

[0126] (th3) The lithium phosphate active material includes a lithium phosphate active body and a carbon coating layer located on at least a portion of the surface of the lithium phosphate active body, and the carbon coating layer in the lithium phosphate active material includes one or more of soft carbon, hard carbon and amorphous carbon.

[0127] By controlling the mass proportion of lithium-phosphate active materials in the positive electrode active layer within the aforementioned range, it is beneficial to better extend the cycle life of the battery.

[0128] The types of lithium phosphate active materials can be flexibly selected to meet different application requirements.

[0129] By setting a carbon coating layer including one or more of soft carbon, hard carbon and amorphous carbon on the surface of the lithium phosphate active material, the conductivity of the material can also be improved, which is beneficial to improving the electrical contact network within the positive electrode plate and providing a fast and stable channel for electron transmission within the positive electrode plate, thereby helping to improve the battery's rate performance and improve the battery's fast charging capability.

[0130] In a second aspect of the present application, an electrical device is provided, which includes the lithium-ion secondary battery described in the first aspect of the present application.

[0131] In a third aspect of the present application, there is provided a use of the lithium ion secondary battery described in the first aspect of the present application in supplying electric energy and / or storing electric energy;

[0132] The application includes a process of charging the lithium-ion secondary battery at a rate higher than or equal to 2C.

[0133] In some embodiments, the application includes a process of charging the lithium-ion secondary battery at at least one rate of 2C to 6C or 4C to 6C;

[0134] Optionally, the application includes a process of charging the lithium-ion secondary battery under at least one rate condition of 2C to 4C;

[0135] Optionally, the maximum charging rate of the lithium-ion secondary battery is greater than or equal to 2C, and may be 2C to 6C, and may be further 2C to 4C or 4C to 6C.

[0136] The lithium-ion secondary battery provided in the first aspect of the present application can provide higher rate performance and good fast charging capability.

[0137] 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

[0138] 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.

[0139] In the attached picture:

[0140] Figure 1 It is a schematic diagram of the structure of the negative electrode plate in one embodiment of the present application.

[0141] Figure 2 It is a schematic diagram of the structure of the negative electrode plate in another embodiment of the present application.

[0142] Figure 3 It is a schematic diagram of the structure of the negative electrode plate in another embodiment of the present application.

[0143] Figure 4 It is a schematic diagram of a battery cell according to an embodiment of the present application.

[0144] Figure 5 for Figure 4 An exploded view of a battery cell according to an embodiment of the present application is shown.

[0145] Figure 6 FIG. 1 is a schematic diagram of a battery device according to an embodiment of the present application.

[0146] Figure 7 A schematic diagram of a battery pack according to an embodiment of the present application.

[0147] Figure 8 for Figure 7 An exploded view of a battery pack according to an embodiment of the present application is shown.

[0148] Fig. 9 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.

[0149] Description of reference numerals:

[0150] 202, negative electrode active particles; 208, quaternary ammonium salt compound; 200, negative electrode plate; 210, negative electrode current collector; 220, negative electrode active material layer; 222, second negative electrode active layer; 224, first negative electrode active layer; 1, battery pack; 2, upper case; 3, lower case; 4, battery device; 5, battery cell; 51, shell; 52, electrode assembly; 53, cover plate; 6, electrical device.

[0151] It should be noted that Figure 1-3 The shapes and sizes of the negative electrode active particles 202, quaternary ammonium salt compounds 208, etc. involved do not represent or are not used to limit the shapes and sizes of actual materials, and the numbers shown in the figures do not represent or are not used to limit the actual numbers and quantity ratios. DETAILED DESCRIPTION

[0152] Below, some embodiments and examples of the lithium-ion secondary battery, electrical device and application of the present application are described in detail with appropriate reference to the drawings. However, there may be 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 description 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.

[0153] "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.

[0154] In this application, unless otherwise specified, "about" means within a reasonable range above and below the number, and the fluctuation range may vary depending on the type and value of the number. For example, it may be allowed to be within a range of ±10%, ±5%, ±2%, ±1%, etc. For example, taking "about 20°C" and its approximate value of ±1°C as an example, the approximate values ​​of 19°C, 19.5°C, etc. within the approximate range shown in "about 20°C" should also be included in the range indicated by "about 20°C".

[0155] In the present 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 carried out in a way that does not conflict and can implement the present application.

[0156] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0157] 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.

[0158] 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".

[0159] 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.

[0160] In this application, "optionally", "optional", 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 include", "optionally include", etc. in this application, taking "optionally include" as an example, mean "may include or not include".

[0161] 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.

[0162] Herein, the word “suitable” in “suitable combination”, “suitable method”, etc., shall be based on the technical solution that can implement the present application.

[0163] Herein, "preferred", "better", "better", "comparatively better", "preferred" and "preferred" are only used to describe implementation methods or examples with better effects, and it should be understood that they do not constitute a limitation on the scope of protection of this application. If multiple "preferred" items appear in a technical solution, unless otherwise specified and there is no contradiction or mutual restriction, each "preferred" item is independent.

[0164] 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.

[0165] 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.

[0166] 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.

[0167] 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.

[0168] In the present 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 the present application, room temperature refers to 20°C to 30°C.

[0169] In this application, when the units of a data range are mentioned, 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, 3-5μm or 3-5μm 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 3μm-5μm. In addition, similar descriptions of other parameters such as temperature and size are also understood in the same way.

[0170] 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".

[0171] 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 new technical solutions.

[0172] In the present application, for a certain parameter, when two or more test methods are provided, as long as the test result of at least one test method is within the described range, they are all included in the protection scope of the present application.

[0173] The improved effects described in this application, unless otherwise stated, are not intended to be limited to any theory.

[0174] According to various implementations and examples of the present application, the present application provides a lithium ion secondary battery, an electric device and an application. The lithium ion secondary battery has significantly improved fast charging performance.

[0175] 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, 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, which mainly prevents the positive and negative electrodes from short-circuiting, while allowing ions to pass through.

[0176] In this 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 specific circumstances, the electrode active material layer may refer to the positive electrode active material layer or the negative electrode active material layer. In this application, the "positive electrode active material layer" may also be recorded as the "positive electrode active layer", and the "negative electrode active material layer" may also be recorded as the "negative electrode active layer".

[0177] 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 extract active ions.

[0178] 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 layer is located on at least one side of the negative electrode current collector, and can be located on one side or both sides of the negative electrode current collector.

[0179] 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 can reversibly extract and insert active ions.

[0180] 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 layer is located on at least one side of the positive electrode current collector, and can be located on one side or both sides of the positive electrode current collector.

[0181] In the present application, unless otherwise specified, "separation membrane" and "diaphragm" have the same meaning and can be used interchangeably.

[0182] In a first aspect of the present application, a lithium-ion secondary battery is provided, which includes a negative electrode plate, the negative electrode plate includes a negative electrode active material layer, and a quaternary ammonium salt compound is provided in the negative electrode active material layer.

[0183] In some embodiments, a lithium ion secondary battery is provided, comprising a negative electrode plate and an electrolyte, comprising a first negative electrode active layer and a second negative electrode active layer, wherein the second negative electrode active layer is located on a side of the first negative electrode active layer away from the surface of the negative electrode plate. That is, the second negative electrode active layer is further away from the surface of the negative electrode plate than the first negative electrode active layer.

[0184] In some embodiments, a lithium-ion secondary battery is provided, which includes a negative electrode plate and an electrolyte, the negative electrode plate includes a negative electrode active material layer, the negative electrode active material layer includes a first negative electrode active layer and a second negative electrode active layer, and the second negative electrode active layer is located on a side of the first negative electrode active layer away from the surface of the negative electrode plate.

[0185] In some embodiments, a lithium ion secondary battery is provided, comprising a negative electrode plate and an electrolyte; the negative electrode plate comprises a negative electrode current collector and a second negative electrode active layer and a first negative electrode active layer sequentially disposed on at least one side of the negative electrode current collector, the second negative electrode active layer being located between the negative electrode current collector and the first negative electrode active layer; the second negative electrode active layer comprises a second negative electrode active material and a quaternary ammonium salt compound, the quaternary ammonium salt compound comprises a quaternary ammonium cation. The second negative electrode active material may comprise a carbon-based material.

[0186] In the present application, in the thickness direction of the negative electrode sheet, for the negative electrode active material layer, the direction close to the surface of the negative electrode sheet can be recorded as "upward", and the direction away from the surface of the negative electrode sheet can be recorded as "downward". Taking the negative electrode sheet including the negative electrode current collector as an example, the direction away from the surface of the negative electrode current collector is upward, and the direction toward the surface of the negative electrode current collector is downward.

[0187] In the present application, unless otherwise specified, “a second negative electrode active layer and a first negative electrode active layer are sequentially disposed on at least one side of the negative electrode current collector” means that the second negative electrode active layer is located between the negative electrode current collector and the first negative electrode active layer.

[0188] In the present application, unless otherwise specified, a "quaternary ammonium salt compound" is a compound including a quaternary ammonium root, which at least includes a quaternary ammonium cation and has the ability to bind to electrolyte anions in an electrolyte by ion exchange. Unless otherwise specified, the nitrogen atom of the quaternary ammonium cation in the quaternary ammonium salt compound is covalently bonded to a carbon atom, that is, the quaternary ammonium salt compound includes a quaternary ammonium cation and a carbon atom covalently bonded to the quaternary ammonium cation. Without limitation, the quaternary ammonium salt compound can be selected to include an antistatic agent for a quaternary ammonium root. Without limitation, the quaternary ammonium salt compound is a small molecule compound, and unless otherwise specified, the molecular weight of the quaternary ammonium salt compound is less than or equal to 600Da. Unless otherwise specified, the "molecular weight" of the quaternary ammonium salt compound refers to the molecular mass measured in Daltons (Da), and 1 Dalton is equal to 12 One twelfth of the atomic mass of C. Without limitation, the molecular weight of the quaternary ammonium salt compound is 150Da to 600Da, optionally 160Da to 500Da, further optionally 200Da to 500Da, and can also be any of the following molecular weights or a range consisting of any two of the following molecular weights: 180Da, 190Da, 200Da, 220Da, 250Da, 260Da, 280Da, 300Da, 350Da, 400Da, 450Da, 500Da, 600Da, etc.

[0189] In some embodiments, the quaternary ammonium salt compound has a low solubility in the electrolyte or is insoluble in the electrolyte, so that the adsorption of the quaternary ammonium salt compound on the surface of the negative electrode active material is relatively stable.

[0190] In the present application, unless otherwise specified, "electrolyte anions" refer to anions carried by electrolyte lithium salts in an electrolyte.

[0191] In the lithium-ion secondary battery, a first negative electrode active layer located in the upper layer and a second negative electrode active layer located in the lower layer (the direction away from the surface of the negative electrode collector is the upper layer, and the direction toward the surface of the negative electrode collector is the lower layer) can be arranged in the negative electrode active material layer in the negative electrode plate, and a quaternary ammonium salt compound is further arranged in the second negative electrode active layer located in the lower layer. The quaternary ammonium salt compound includes a hydrophilic, positively charged quaternary ammonium root. For the negative electrode plate immersed in the electrolyte, the electrostatic effect based on the quaternary ammonium root can be used to attract the electrolyte anions in the electrolyte, promote the rapid dissociation of the electrolyte lithium salt in the electrolyte, and significantly improve the electrolyte wettability of the second negative electrode active layer and the dynamics of the negative electrode plate, thereby significantly improving the fast charging performance of the battery.

[0192] 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-09010CP 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. The microscopic morphology observation method can use instruments or equipment including but not limited to scanning electron microscopy (SEM) technology. Without limitation, a high-resolution field emission scanning electron microscope can be used; non-limiting examples of SEM instruments include the Sigma 300 scanning electron microscope and Apreo 2SEM field emission scanning electron microscope of ZEISS Company of Germany.

[0193] Those skilled in the art can identify the components in the negative electrode active material layer, the first negative electrode active layer, and the second negative electrode active layer by one or more of the following detection methods known in the art, including but not limited to: Fourier transform infrared (FT-IR) spectroscopy, ultraviolet spectroscopy, nuclear magnetic resonance spectroscopy (HNMR), 1 H NMR) method, gel permeation chromatography (GPC) method, high performance liquid chromatography (HPLC) method, mass spectrometry, X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD) method, Raman spectroscopy (Raman) method, single crystal X-ray diffraction (SCXRD) method, inductively coupled plasma spectroscopy (ICP) method, energy dispersive spectrometer (EDS) analysis, etc. The sample preparation methods and test methods of these test methods are known to those skilled in the art, and the test parameters can be appropriately adjusted according to the structure of the material or substance and the sample characteristics.

[0194] In the present application, unless otherwise specified, the following method can be used to extract a sample from the negative active material layer of the negative electrode plate to further detect whether it contains a quaternary ammonium salt compound and the type of the quaternary ammonium salt compound. The detailed steps can be as follows: disassemble the battery cell, scrape a certain amount of powder (such as a certain mass M0) from the second negative active layer position of the negative electrode plate, use acetone as an extractant, and use a Soxhlet extractor to continuously extract to obtain an extract (mass is recorded as M1) as a sample to be tested. Non-restrictively, a sample with a thickness of such as 10 μm can be scraped. Non-restrictively, an Agilent liquid chromatography-mass spectrometry instrument can be used to detect the composition of quaternary ammonium salt compounds.

[0195] Without limitation, the following method can be used to determine the content of the identified type of quaternary ammonium salt compound: a Waters ACQUITY ARC high performance liquid chromatography (HPLC) instrument equipped with a PDA detector can be used, and the GB / T 32268-2015 method can be referred to. The content of the quaternary ammonium salt compound is confirmed by comparative analysis of the retention time and peak area in the high performance liquid chromatogram, and the content of the quaternary ammonium salt compound in the second negative electrode active layer is further calculated in combination with the mass M0 of the scraped powder, the mass M1 of the extract, and the amount M2 of the test sample, such as the mass proportion of the quaternary ammonium salt compound in the second negative electrode active layer.

[0196] In this application, unless otherwise specified, the constituent materials of the negative electrode active material layer are recorded as negative electrode materials, the constituent materials of the first negative electrode active layer are recorded as first negative electrode materials, and the constituent materials of the second negative electrode active layer are recorded as second negative electrode materials. 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", "second negative electrode material", "first negative electrode active material", and "second negative electrode active 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.

[0197] In the present application, the following method can be used to detect and analyze the content of the quaternary ammonium salt compound in the second negative electrode active layer, and a similar method can also be used to detect and analyze the content of the quaternary ammonium salt compound in the entire negative electrode active material layer of the negative electrode sheet:

[0198] (S1) Scraping powder: disassemble the battery cell, take the negative electrode plate, and use a micrometer to test the thickness L of the plate; take another negative electrode plate, wipe off the negative electrode active material layer on both sides of the surface to remove the remaining empty collector foil, and test the thickness L0. The total thickness of the negative electrode active material layer on both sides of the negative electrode collector is L-L0; scrape the negative electrode active material layer on one surface of the negative electrode plate to expose the negative electrode collector surface, and scrape the negative electrode material on the surface of the other negative electrode plate until the plate thickness is L1=L0+Δd, and collect the powder of the Δd thickness part of the negative electrode active material layer under the thickness of L1 to test the content of quaternary ammonium salt compounds. The thickness of the second negative electrode active layer can be determined in advance in combination with the observation results of the cross-sectional morphology of the plate, and then the first negative electrode active layer is completely removed when the thickness is controlled to be L1, and the remaining negative electrode active material layer corresponds to part or all of the second negative electrode active layer. For example, Δd can be 20μm.

[0199] (S2) Separation: Weigh the mass of the powder (corresponding to the second negative electrode material) collected in the Δd thickness portion in step (S1) (denoted as M0), mix the powder with an organic solvent (the mass of the organic solvent is denoted as M1) at a ratio of 1 g of powder to 100 g of organic solvent, perform ultrasonication, vortexing, centrifugation, and membrane filtration, and obtain a filtrate of mass M2.

[0200] Those skilled in the art can select a suitable organic solvent to collect the sample to be tested of the quaternary ammonium salt compound. Taking Example 1 as an example, the ammonium salt compound is dodecyl trimethyl quaternary ammonium phosphate, which is soluble in an alcohol aqueous solution of an alcohol reagent such as methanol and ethanol. In step (S2), the powder can be ultrasonicated, vortexed, centrifuged, and filtered with a 0.22 μm organic filter membrane using a methanol aqueous solution.

[0201] (S3) Detection: A high performance liquid chromatography Acquit H class UPLC-mass spectrometer waters Xevo G2-XSQtof instrument is used, and the high performance liquid chromatography detection can be operated according to the GB / T 16631-2008 method and the mass spectrometry detection can be operated according to GB / T-6041-2002. A reverse phase chromatographic column C18 column is selected for separation, and a solvent that can dissolve quaternary ammonium salt compounds is selected as the mobile phase (taking Example 1 as an example, dodecyl trimethyl quaternary ammonium phosphate is selected from 0.5% (v / v) methanol aqueous solution as the mobile phase).

[0202] The selected quaternary ammonium salt of different concentrations is used as a standard sample to prepare a standard curve of detection signal-quaternary ammonium salt concentration. The selected quaternary ammonium salt can be dodecyl trimethyl quaternary ammonium phosphate. The concentration gradient can be selected to be 0.02, 0.05, 0.08, 0.1, 0.2, 0.4, 0.6, 0.8, 1.0, 2.0 times (M2-M1) / M1.

[0203] The filtrate in step (S2) is tested and compared with the retention time and peak area of ​​the standard sample, and the concentration of the quaternary ammonium salt compound separated in step (S2) is calculated to be C. The mass of the quaternary ammonium salt compound is calculated according to the formula M3=M2×C, and then the mass proportion of the quaternary ammonium salt compound in the second negative electrode active layer can be calculated to be M3 / M0×100%.

[0204] It should be noted that, in step (S2), the conductive agent and other components in the second negative electrode active layer are insoluble in the organic solvent, and some binder components (such as styrene-butadiene rubber) may be soluble in the organic solvent, but the molecular weight of the binder component is usually high, for example, more than 10kDa (1kDa=1000Da), and the polarity is usually weaker than the quaternary ammonium salt compound. In step (S3), when performing high performance liquid chromatography detection, a chromatographic column (such as a C18 chromatographic column) can be used to separate the binder component from the quaternary ammonium salt compound.

[0205] In some embodiments, the electrolyte includes an electrolyte lithium salt and a non-aqueous solvent.

[0206] In some embodiments, the second negative electrode active material includes a carbon-based material. The carbon atoms in the quaternary ammonium salt compound can make the quaternary ammonium salt compound adsorbed on the surface of the carbon-based material better.

[0207] In some embodiments, a carbon material is disposed on the particle surface of the second negative electrode active material, and the carbon material may include one or more of artificial graphite, natural graphite, soft carbon, and hard carbon.

[0208] In some embodiments, the quaternary ammonium salt compound includes a quaternary ammonium cation, a hydrocarbyl chain covalently bonded to the quaternary ammonium cation, and an anion.

[0209] In this application, unless otherwise specified, "hydrocarbon chain" refers to a chain structure composed of carbon atoms and hydrogen atoms; the hydrocarbon chain in the quaternary ammonium salt type compound can provide a carbon-carbon skeleton, and the hydrocarbon chain has a weak polarity or a non-polar structure.

[0210] By providing a hydrocarbon chain in the quaternary ammonium salt type compound, for example, the hydrocarbon chain may include an alkyl chain. The chain structure of the hydrocarbon chain is beneficial to better and more stably loading and wrapping the quaternary ammonium salt type compound on the surface of the second negative electrode active material. The carbon-carbon skeleton provided by the hydrocarbon chain is beneficial to better and more stably adsorbing the quaternary ammonium salt type compound on the surface of the carbon-based material (the carbon-based material has a certain lipophilicity). Further combined with the electrostatic attraction of the quaternary ammonium group in the quaternary ammonium salt type compound, it is beneficial to guide the lithium ions in the electrolyte to the surface of the second negative electrode active material faster, which is beneficial to further improving the kinetics of the negative electrode sheet and the fast charging performance of the battery.

[0211] In some embodiments, the hydrocarbon chain in the quaternary ammonium salt type compound includes an alkyl chain. In some of these embodiments, the hydrocarbon chain in the quaternary ammonium salt type compound is an alkyl chain.

[0212] In this application, unless otherwise specified, "alkyl chain" refers to a saturated chain structure composed of carbon atoms and hydrogen atoms, and the alkyl chain in the quaternary ammonium salt type compound can provide a saturated carbon-carbon skeleton.

[0213] In this application, the term "hydrocarbyl" refers to a monovalent residue formed by removing a hydrogen atom from a hydrocarbon compound containing primary (normal) carbon atoms, or secondary carbon atoms, or tertiary carbon atoms, or quaternary carbon atoms, or a combination thereof. A phrase containing this term, for example, "C 12-18 hydrocarbyl" refers to a hydrocarbyl group containing 12 to 18 carbon atoms, and each occurrence may independently be a C 12 hydrocarbyl, C 13 hydrocarbyl, C 14 hydrocarbyl, C 15 hydrocarbyl, C 16 hydrocarbyl, C 17 hydrocarbyl or C 18 hydrocarbyl.

[0214] In this application, the term "alkyl" refers to a monovalent residue formed by removing a hydrogen atom from a saturated hydrocarbon containing primary (normal) carbon atoms, or secondary carbon atoms, or tertiary carbon atoms, or quaternary carbon atoms, or a combination thereof. A phrase containing this term, for example, "C 12-18 alkyl" refers to an alkyl group containing 12 to 18 carbon atoms, and each occurrence may independently be a C 12 alkyl, C 13 alkyl, C 14 alkyl, C 15 alkyl, C 16 alkyl, C17 Alkyl or C 18 alkyl.

[0215] In this application, unless otherwise specified, the number of carbon atoms in a compound or group can be described using the subscript "C". For example, "C 12-18 " means having 12 to 18 carbon atoms, "C 12-18 "Each time it appears, it can be independently C 12 , C 13 , C 14 , C 15 , C 16 , C 17 or C 18 .

[0216] In some embodiments, the hydrocarbyl chain is a linear chain.

[0217] In some embodiments, the alkyl chain is a linear chain.

[0218] Unless otherwise specified, "linear chain" refers to a chain structure in which the main chain atoms are connected in sequence, and in this case, there is no ring structure and no branch chain.

[0219] In some embodiments, the quaternary ammonium salt compound satisfies one or more of the following characteristics (any numerical parameter in the following characteristics can also be selected from any suitable value or range in the context):

[0220] (ta1) The hydrocarbon chain is an alkyl chain;

[0221] (ta2) the number of carbon atoms in the hydrocarbon chain is 12 to 18 (optionally 12, 13, 14, 15, 16, 17, 18 or a range consisting of any two of the foregoing integers);

[0222] (ta3) the molecular weight of the quaternary ammonium salt compound is less than or equal to 600 Da;

[0223] (ta4) The hydrocarbon chain is a linear chain;

[0224] (ta5) The length of the hydrocarbon chain in the ammonium salt type compound is 12 to 18 main chain carbon atoms.

[0225] In some embodiments, the hydrocarbon chain in the quaternary ammonium salt compound is C 12-18 Alkyl chain. 12-18 The number of carbon atoms in the alkyl chain may be 12 to 18, or may be 12, 13, 14, 15, 16, 17, 18 or a range consisting of any two of the foregoing integers.

[0226] In some embodiments, the length of the hydrocarbyl chain in the ammonium salt type compound is 12 to 18 main chain carbon atoms. Alternatively, the length of the hydrocarbyl chain can also be 12, 13, 14, 15, 16, 17, 18 or a range consisting of any two of the foregoing integers, in terms of the number of main chain carbon atoms. Further optionally, the hydrocarbyl chain can be an alkyl chain.

[0227] By controlling the number of carbon atoms in the hydrocarbon chain of the quaternary ammonium salt compound and / or the molecular weight of the quaternary ammonium salt compound within the aforementioned range, the length of the hydrocarbon chain can be adjusted within a more appropriate range. On the one hand, it is beneficial to better and more stably wrap the quaternary ammonium salt compound on the surface of the second negative electrode active material during the slurry stirring process, and it is beneficial to inhibit the quaternary ammonium salt compound from falling off from the surface of the second negative electrode active material during the charging and discharging process. Further combined with the quaternary ammonium roots exposed to the electrolyte, it can promote the lithium ions in the electrolyte to be guided to the surface of the second negative electrode active material faster and more stably, thereby improving the transmission rate of lithium ions inside the negative electrode plate. On the other hand, the degree of wrapping of the hydrocarbon chain on the surface of the second negative electrode active material can be better controlled, so that the active sites on the surface of the second negative electrode active material can better contact the electrolyte, thereby helping to better improve the negative electrode plate dynamics and battery fast charging performance.

[0228] In some embodiments, the quaternary ammonium salt compound satisfies one or more of the following characteristics:

[0229] (tb1) The structure of the quaternary ammonium cation is -N + (R 1 R 2 R 3 ), where R 1 and R 2 Each independently is C 1-3 Alkyl, R 3 C 1-3 alkyl or hydroxyethyl; optionally, R 1 and R 2 are each independently methyl, R 3 is methyl or hydroxyethyl;

[0230] (tb2) The quaternary ammonium salt type compound includes anions, and the anions include one or more of nitrate, carbonate, bicarbonate and phosphate.

[0231] In this application, the term “C 1-3 The "alkyl" may be methyl, ethyl or propyl.

[0232] In some embodiments, the anion in the quaternary ammonium salt type compound includes one or more of nitrate, carbonate, bicarbonate and phosphate.

[0233] According to the Pauling electronegativity scale theory, it is generally believed that the Pauling electronegativity scale of nitrate, carbonate, bicarbonate and phosphate is as follows: nitrate 3.0> carbonate 2.5> bicarbonate 2.5> phosphate 2.0. According to the Pauling electronegativity scale theory, it is generally believed that the Pauling electronegativity scale of some common electrolyte anions usually has the following values: tetrafluoroborate 4.0≈hexafluoroarsenate 4.0≈hexafluorophosphate 4.0≈bis(fluorosulfonyl)imide 4.0≈bis(trifluoromethanesulfonyl)imide 4.0≈trifluoromethanesulfonate 4.0≈lithium difluorophosphate 4.0≈difluorooxalatoborate 4.0≈lithium tetrafluorooxalatophosphate 4.0≈lithium difluorobis(oxalatophosphate) 4.0>perchlorate 3.5≈lithium dioxalatoborate 3.5. The Pauling electronegativity scale of anions can be determined based on the Pauling electronegativity scale value of the most electronegative element in the anion. The Pauling electronegativity scale for different elements can be found in manuals or existing literature.

[0234] In some embodiments, the quaternary ammonium salt compound includes one or more of octadecyldimethylhydroxyethyl quaternary ammonium nitrate, N,N-dimethyl-N-(2-hydroxyethyl)hexadecyl quaternary ammonium phosphate, dodecyltrimethyl quaternary ammonium nitrate, octadecyltrimethyl quaternary ammonium phosphate, dodecyltrimethyl quaternary ammonium phosphate, dodecyltrimethyl quaternary ammonium carbonate, and dodecyltrimethyl quaternary ammonium bicarbonate.

[0235] By introducing one or more of nitrate, carbonate, bicarbonate and phosphate into the anions of quaternary ammonium salt compounds, it is beneficial to better control the binding ability between the anions and the quaternary ammonium roots in the quaternary ammonium salt compounds, making the quaternary ammonium roots more easily dissociated. These anions may have lower electronegativity than electrolyte anions, thereby being more conducive to promoting the formation of the quaternary ammonium root-electrolyte anion structure, and more conducive to the quaternary ammonium root-electrolyte anion structure to guide the lithium ions in the electrolyte to aggregate toward the second negative electrode active material, which is beneficial to better improve the negative electrode plate dynamics and battery fast charging performance.

[0236] In some embodiments, the mass proportion of the quaternary ammonium salt compound in the second negative electrode active layer may be 0.2% to 2%, and may be 0.2% to 1.5%.

[0237] In some embodiments, the mass percentage of the quaternary ammonium salt compound in the second negative electrode active layer is 0.2% to 1.5%.

[0238] Without limitation, the mass proportion of the quaternary ammonium salt compound in the second negative electrode active layer can also be any of the following percentages or a range consisting of any two of the following percentages: 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, 1.0%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2.0%, 2%, etc.

[0239] By controlling the mass proportion of the quaternary ammonium salt compound in the second negative electrode active layer within the aforementioned range, it is not only beneficial to better exert the role of the quaternary ammonium salt compound in improving the fast charging performance of the battery, but also to better control the decrease in the electronic conductivity of the surface of the second negative electrode active material caused by the quaternary ammonium salt compound wrapping, which is beneficial to better improve the fast charging performance of the battery. Furthermore, it is also beneficial to maintain a high lithium storage capacity of the second negative electrode active layer, which is beneficial to take into account the energy density of the negative electrode and the battery.

[0240] In some embodiments, the mass proportion of the carbon-based material in the second negative electrode active material can be 80% to 100%, optionally 90% to 100%, or any of the following percentages or a range consisting of any two of the following percentages: 80%, 82%, 84%, 85%, 86%, 88%, 90%, 92%, 94%, 95%, 96%, 97%, 98%, 99%, 100%, etc.

[0241] In some embodiments, the second negative electrode active material includes a graphite material. The graphite material may include one or more of artificial graphite and natural graphite.

[0242] In some embodiments, the mass proportion of graphite-based material in the second negative electrode active material can be 80% to 100%, optionally 90% to 100%, or any of the following percentages or a range consisting of any two of the following percentages: 80%, 82%, 84%, 85%, 86%, 88%, 90%, 92%, 94%, 95%, 96%, 97%, 98%, 99%, 100%, etc.

[0243] In some embodiments, graphite is disposed on the surface of particles of the second negative electrode active material, and the graphite may include one or more of artificial graphite and natural graphite.

[0244] 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):

[0245] (tc1) The carbon-based material includes one or more of artificial graphite, natural graphite, soft carbon and hard carbon;

[0246] The mass proportion of (tc2) carbon-based materials in the second negative electrode active layer is 94.5% to 97.5%, and can be optionally 95.0% to 97.0%.

[0247] In some embodiments, the carbon-based material includes one or more of artificial graphite, natural graphite, graphite, soft carbon, and hard carbon.

[0248] In some embodiments, the carbon-based material includes graphite. Further, the graphite may include one or more of artificial graphite and natural graphite.

[0249] Natural graphite is prone to lateral deformation when subjected to cold pressing. Introducing natural graphite into the second negative electrode active material is beneficial for increasing the compaction density and surface capacity of the second negative electrode active layer, thereby helping to increase the energy density of the negative electrode sheet.

[0250] The structure of artificial graphite is more stable than that of natural graphite, and it has relatively fewer internal defects, which slows down the decay of available storage sites for lithium ions during the cycle and makes the cycle performance more stable.

[0251] Both hard carbon and soft carbon have a large degree of disorder, which is conducive to the entry of lithium ions. Hard carbon can provide abundant lithium insertion sites and fast transmission channels; the carbon layers in soft carbon are disorderly stacked, which allows lithium ions to be transmitted relatively quickly. The introduction of at least one of hard carbon and soft carbon is beneficial to improving the negative electrode and battery dynamics.

[0252] In some embodiments, the mass proportion of carbon-based materials in the second negative electrode active layer is 94.5% to 97.5%, optionally 95.0% to 97.0%, or any of the following percentages or a range consisting of any two of the following percentages: 95%, 95.5%, 96%, 96.5%, 97%, 97.5%, etc.

[0253] By controlling the mass proportion of the carbon-based material in the second negative electrode active layer within the aforementioned range, it is beneficial to better wrap the quaternary ammonium salt compound on the surface of the second negative electrode active material. In addition, the energy density of the negative electrode and the battery can also be taken into account.

[0254] In some embodiments, the second negative active layer includes a binder, and the binder includes styrene-butadiene rubber (SBR).

[0255] By introducing styrene butadiene rubber into the binder of the second negative electrode active layer, the styrene butadiene rubber can have a non-chain structure. In terms of occupying the wrapping sites on the surface of the second negative electrode active material, the styrene butadiene rubber is not easy to compete with the quaternary ammonium salt compound, which is conducive to better realizing the wrapping of the binder and the quaternary ammonium salt compound on the surface of the second negative electrode active material at the same time, which can not only realize a good electrical contact network, but also give full play to the role of the quaternary ammonium salt compound in guiding lithium ions in the electrolyte, which is conducive to better improving the fast charging performance of the battery.

[0256] In some embodiments, the second negative electrode active layer includes a carbon-based material and a binder, and the binder includes styrene-butadiene rubber.

[0257] By introducing carbon-based materials into the second negative electrode active material of the second negative electrode active layer and introducing styrene-butadiene rubber into the binder, styrene-butadiene rubber has relatively suitable lipophilicity and can better coordinate the mutual binding effect between the binder and the carbon-based material and the quaternary ammonium salt compound; relative to the strong binding effect of oily binders (such as polyvinylidene fluoride (PVDF)) on quaternary ammonium salt compounds, styrene-butadiene rubber is conducive to better exerting the binding effect between quaternary ammonium salt compounds and carbon-based materials, and better exerting the role of quaternary ammonium salt compounds in improving the fast charging performance of batteries.

[0258] In some embodiments, the glass transition temperature of styrene-butadiene rubber is 5°C to 70°C, and can be optionally 30°C to 50°C, and can further be any of the following temperatures or within the range consisting of any two of the following temperatures: 5°C, 10°C, 15°C, 20°C, 25°C, 30°C, 35°C, 40°C, 45°C, 50°C, etc.

[0259] In some embodiments, the glass transition temperature of the styrene-butadiene rubber is 30°C to 50°C.

[0260] In the present application, "glass transition temperature (Tg)" has a well-known meaning in the art, and refers to the temperature at which a polymer changes from a glassy state to a highly elastic state, or the temperature range at which a polymer changes from a highly elastic state to a glassy state. Generally, the higher the glass transition temperature, the greater the molecular weight. A polymer can undergo molecular chain motion above its Tg. The glass transition temperature can be measured by conventional methods in the art, including but not limited to differential scanning calorimetry (DSC) and the like.

[0261] By controlling the glass transition temperature of the styrene-butadiene rubber within the aforementioned range, the second negative electrode active layer can have a better pore structure after rolling, which is beneficial for promoting the electrolyte to better infiltrate the second negative electrode active layer.

[0262] It can be understood that the first negative electrode active layer includes a first negative electrode active material.

[0263] In some embodiments, the first negative electrode active layer includes a first negative electrode active material, the first negative electrode active material includes a negative electrode active body and a coating layer located at least a portion of the surface of the negative electrode active body, and the coating layer includes one or more of soft carbon, hard carbon and amorphous carbon. Without limitation, the mass percentage of the coating layer in the first negative electrode active material may be 0.1% to 4.0%, and may be 1.0% to 2.0%. Without limitation, the sum of the mass percentages of soft carbon, hard carbon and amorphous carbon in the coating layer in the first negative electrode active material may be 0.1% to 3.0%, and may be 1.0% to 2.0%.

[0264] "Soft carbon" and "hard carbon" have well-known meanings in the art. Soft carbon can be graphitized after further high-temperature treatment, while hard carbon is difficult to graphitize even after further high-temperature treatment. The carbon layers in soft carbon are stacked in a disordered manner, allowing lithium ions to be transported relatively quickly. The crystals inside hard carbon are arranged in a disordered manner and have many pores, which can provide abundant lithium insertion sites and fast transmission channels.

[0265] 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" may refer to the product of carbonization treatment of an organic carbon source.

[0266] By arranging a coating layer on the surface of the first negative electrode active material of the first negative electrode active layer and arranging one or more of soft carbon, hard carbon and amorphous carbon in the coating layer, the lithium ion transmission channel on the surface of the first negative electrode active material can be optimized, lithium ion transmission can be promoted, and battery dynamics and battery fast charging performance can be further improved.

[0267] 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):

[0268] (td1) the first negative electrode active material includes coated graphite, the coated graphite includes a graphite body and a coating layer located on at least a portion of a surface of the graphite body, and the coating layer in the coated graphite includes one or more of soft carbon, hard carbon and amorphous carbon;

[0269] (td2) the first negative electrode active material includes secondary particulate graphite, the secondary particulate graphite includes a secondary particulate graphite body, the amount of the secondary particulate graphite in the first negative electrode active material accounts for greater than or equal to 20%, and can be optionally 30% to 80%; optionally, the secondary particulate graphite includes carbon-coated secondary particulate graphite, the carbon-coated secondary particulate graphite includes a secondary particulate graphite body and a carbon coating layer (which can be recorded as a first carbon coating layer) located at least a portion of the surface of the secondary particulate graphite body, and the carbon coating layer in the carbon-coated secondary particulate graphite (i.e., the first carbon coating layer) includes one or more of soft carbon, hard carbon and amorphous carbon;

[0270] (td3) the first negative electrode active material includes a graphite material, and the OI value of the graphite material may be 2 to 15, and may be 2 to 10;

[0271] (td4) D of the first negative electrode active material v 50 is 10μm~18μm, and can be 12μm~16μm;

[0272] (td5) the porosity of the first negative electrode active layer is higher than the porosity of the second negative electrode active layer;

[0273] (td6) The powder compaction density of the first negative electrode active material or the powder compaction density of the first negative electrode active layer is 1.60 g / cm 3 ~1.80g / cm 3 ;

[0274] (td7) the charge rate of the first negative electrode active layer is higher than the charge rate of the second negative electrode active layer; optionally, the charge rate of the first negative electrode active layer is higher than the charge rate of the second negative electrode active layer;

[0275] (td8) Under at least one temperature condition between 20°C and 35°C, the ionic conductivity of the electrolyte is 13mS / cm to 18mS / cm; optionally, at 25°C, the ionic conductivity of the electrolyte is 13mS / cm to 18mS / cm.

[0276] By making the lithium-ion secondary battery satisfy one or more of the characteristics (td1), (td2), (td3), (td4), (td5), (td6), (td7) and (td8), the fast charging performance of the battery can be better improved.

[0277] In some embodiments, the first negative electrode active material includes coated graphite, which includes a graphite body and a coating layer located on at least a portion of the surface of the graphite body, and the coating layer may include one or more of soft carbon, hard carbon and amorphous carbon.

[0278] In the present application, a "graphite body" consists of graphite.

[0279] By introducing coated graphite into the first negative electrode active layer and arranging one or more of soft carbon, hard carbon and amorphous carbon in the coating layer, the lithium ion transmission channel on the surface of the first negative electrode active material can be optimized, lithium ion transmission can be promoted, and battery dynamics and battery fast charging performance can be further improved.

[0280] The test samples of coated graphite can be tested by the following method: the negative electrode plates obtained by disassembling the battery cells are soaked and cleaned with a solvent (such as dimethyl carbonate (DMC)) to remove residual electrolyte; powders are scraped from different thickness positions of the negative electrode plates to obtain powder samples of the first negative electrode material and the second negative electrode material respectively; the powder is cut into sections using FIB (focused ion beam), and the cross-sectional morphology of the particles is observed under TEM (transmission electron microscope). A clear boundary can be observed at the coating interface, and the thickness and average thickness of the coating layer can be analyzed and calculated based on the TEM image; further combined with one or more methods such as energy dispersive spectroscopy (EDS) analysis, Raman spectroscopy, X-ray diffraction (XRD) and the like, the material types of the coating layer and the graphite body can be confirmed.

[0281] The elemental composition and component types of the coating layer in coated graphite can be analyzed by using or referring to the above-mentioned method.

[0282] Taking the distinction between natural graphite and artificial graphite as a non-limiting example, natural graphite and artificial graphite can be distinguished by X-ray diffraction (XRD) analysis test. In the XRD spectrum, if the characteristic peak near 2θ26.5° is very sharp and has a high intensity, it is natural graphite; if the characteristic peak near 2θ26.5° is relatively broad and has a weak intensity, it is artificial graphite.

[0283] Taking the distinction between graphite and amorphous carbon as an example, Raman spectroscopy can be used for testing and analysis. The characteristic peak information of the carbon component in the spectrum (such as the intensity ratio of the D peak / G peak, I D / G ) to analyze amorphous carbon. Both D peak and G peak are Raman characteristic peaks of carbon atom crystals. D peak represents the defects of carbon atom crystals. The more defects there are, the greater the intensity of D peak. The intensity of D peak can reflect the content of amorphous (such as chaotic layer stacking) areas. G peak represents the in-plane stretching vibration of sp2 hybridization of carbon atoms. The intensity of G peak can reflect the content of graphitized (layered structure) areas. As the degree of disorder of carbon atoms increases, the intensity ratio of D peak to G peak also increases. You can also compare Raman spectra I D / G Standard Raman spectrum of graphite I D / G The difference between the D peak and the G peak of the Raman spectrum can be used to distinguish natural graphite from artificial graphite.

[0284] In some embodiments, the first negative electrode active material includes secondary particulate graphite. In a non-limiting manner, the amount of secondary particulate graphite in the first negative electrode active material may be greater than or equal to 20%, optionally 20% to 80%, further optionally 30% to 60%, or any of the following percentages or a range selected from any two of the following percentages: 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, etc.

[0285] In the present application, "secondary particle type graphite" is a graphite-based material including a secondary particle type graphite body, which includes at least a secondary particle type graphite body and optionally includes a coating layer located at least a portion of the surface of the secondary particle type graphite body. The secondary particle type graphite can be non-coated graphite, coated graphite, or a combination of non-coated graphite and coated graphite.

[0286] In the present application, "uncoated graphite" refers to graphite without a coating layer.

[0287] 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", that is, "secondary particles" refer to aggregates of primary particles. Secondary particles are aggregated from primary particles, and the secondary particles can have a relatively random or relatively disordered orientation on the whole particle, so the secondary particles are more isotropic.

[0288] In the present application, "secondary graphite particle body" or "secondary graphite particle" refers to the agglomerate of primary graphite particles, and "primary graphite particle" is a basic graphite grain unit. It can be understood that secondary graphite particles belong to secondary graphite particles.

[0289] In a non-limiting manner, the "number ratio of secondary particle-type graphite in the first negative electrode active material" can be obtained by statistical analysis based on the SEM scan of the first negative electrode active material. The following method can be used: the first negative electrode active material is laid and adhered to the conductive glue, and the particle morphology is tested by a scanning electron microscope (such as ZEISS Sigma 300), and the number of particles in the obtained SEM image is counted as secondary particles or non-agglomerated primary particles. Multiple areas are randomly selected for scanning tests, and the number of secondary particles and non-agglomerated primary particles in each area is counted, and the number ratio of secondary particles in each area is calculated, and then the test values ​​of the number ratio of secondary particles in multiple test areas are averaged as the test value of "secondary particles in the first negative electrode active material". Taking the first negative electrode active material as graphite material as an example, it corresponds to "the number ratio of secondary particle-type graphite in the first negative electrode active material"; taking the first negative electrode active material as graphite as an example, it corresponds to "the number ratio of secondary particle graphite in the first negative electrode active material". A similar method can be used to test and obtain the "quantity ratio of secondary particles in the second negative electrode active material", "quantity ratio of secondary particle-type graphite in the second negative electrode active material", and "quantity ratio of secondary particle-type graphite in the first negative electrode active material". In addition, a similar method can also be used to obtain parameters such as "quantity ratio of secondary particle-type graphite in negative electrode active materials" and "quantity ratio of secondary particles in negative electrode active materials".

[0290] In the present application, "graphite material" refers to a negative electrode active material containing a graphite body, which includes at least a graphite body and optionally includes a coating layer located on at least a portion of the surface of the graphite body. The graphite material can be non-coated graphite, coated graphite, or a combination of non-coated graphite and coated graphite. The graphite material can be secondary particles, non-agglomerated primary particles, or a combination of secondary particles and non-agglomerated primary particles. When the graphite material can be a secondary particle, it corresponds to a secondary particle-type graphite.

[0291] By introducing secondary particle-type graphite into the first negative electrode active layer, utilizing the property that secondary particles are formed by agglomeration of primary particles, and based on the disordered orientation of each primary particle, it is beneficial to improve the isotropic characteristics of lithium ions when embedded in the first negative electrode active material, increase the lithium ion embedding sites on the surface of the first negative electrode active material, increase the lithium ion embedding rate, and improve the battery fast charging performance.

[0292] In some embodiments, the first negative electrode active material includes a graphite material, and the OI value of the graphite material can be 2 to 15, optionally 2 to 10, or any of the following values ​​or a range consisting of any two of the following values: 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, etc.

[0293] In this application, unless otherwise specified, the "OI value" of a graphite material refers to the intensity ratio of the (004) crystal plane to the (110) crystal plane in the X-ray diffraction spectrum of the graphite material rolled into sheets. The OI value can be used to characterize the orientation of the graphite material particle stacking and reflect the degree of isotropy of the graphite material particle stacking.

[0294] The OI value (GOI) of graphite materials can be tested by X-ray diffraction (XRD) according to Appendix F of the national standard GB / T 24533-2019 "Graphite Anode Materials for Lithium-ion Batteries". The powder sample to be tested can be rolled into sheets, and then the sheet sample can be tested by XRD to obtain an X-ray diffraction spectrum. After the sample is rolled, the arrangement orientation (OI value) of artificial or natural hexagonal graphite on the pole piece is analyzed by X-ray polycrystalline diffraction. The peak area C of the (004) crystal plane diffraction peak is obtained after analysis and calculation by XRD spectrum analysis software such as Highscore Plus or Jade. 004 and the peak area C of the (110) crystal plane diffraction peak 110 OI value = C 004 / C 110 . An X-ray diffractometer (such as Bruker-D8 advance, etc.) can be used for testing.

[0295] Without limitation, the sample for OI value test can be obtained by the following method: disassemble the battery cell, take the negative electrode plate, soak and clean it with a solvent such as dimethyl carbonate; scrape the powder from the first negative electrode active layer, and then use a solvent (such as N-methylpyrrolidone (NMP) etc.) to fully soak the powder material extracted from the first negative electrode active layer, so that the organic components such as binder, thickener, etc. 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 of the first negative electrode active material. After rolling the powder sample to be tested into a sheet, the sheet sample is subjected to XRD test. The powder to be tested of the first negative electrode active material can also be used to test the compaction density of the powder.

[0296] By controlling the OI value of the graphite material in the first negative electrode active material within the aforementioned range, it is beneficial to enhance the isotropic characteristics of the first negative electrode active material, increase the lithium ion embedding channels, and make the lithium ion diffusion kinetics in the first negative electrode active layer better, which is beneficial to improve the battery fast charging performance.

[0297] The above features (td1) to (td6) can be combined in any suitable manner. For example, the first negative electrode active material can satisfy features (td1) and (td2) at the same time, in which case the coated graphite can be secondary particle graphite at the same time. Exemplarily, the first negative electrode active material includes secondary particles, and the secondary particle graphite includes carbon-coated secondary particle graphite. Without limitation, the carbon-coated secondary particle graphite includes a carbon coating layer (i.e., a first carbon coating layer) located in the secondary particle graphite body and at least a portion of the surface of the secondary particle graphite body. Furthermore, the carbon coating layer (i.e., the first carbon coating layer) in the carbon-coated secondary particle graphite can include one or more of soft carbon, hard carbon, and amorphous carbon. For another example, the first negative electrode active material can simultaneously satisfy characteristics (td2) and (td3). Exemplarily, the first negative electrode active material includes a graphite material, the graphite material includes secondary particle graphite, and the OI value of the graphite material can be 2 to 15, optionally 2 to 10, or any of the following values ​​or a range selected from any two of the following values: 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, etc.

[0298] In the present application, the “first”, “third”, “fourth” and “fifth” in “first carbon coating layer”, “third carbon coating layer”, “fourth carbon coating layer” and “fifth carbon coating 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.

[0299] In some embodiments, D of the first negative electrode active material v 50 can be 10μm to 18μm, optionally 12μm to 16μm, or any of the following values ​​or a range consisting of any two of the following values: 10μm, 11μm, 12μm, 13μm, 14μm, 15μm, 16μm, 17μm, 18μm, etc.

[0300] 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 50% of the material volume is less than or equal to D v 50, and 50% of the particles by volume are larger than D v 50. Those skilled in the art will appreciate that v50, and can be measured by instruments and methods known in the art. For example, it can be conveniently measured by a laser particle size analyzer, such as the Mastersizer 2000E laser particle size analyzer of Malvern Instruments Ltd., UK, or the LS-909 laser particle size analyzer (Europe and America). The D of the first negative electrode active material can be measured with reference to the GB / T19077-2016 / ISO 13320:2009 standard process. v 50 for testing. The detailed test process includes: taking an appropriate amount of the sample to be tested, adding a solvent (the solvent can be deionized water, and the sample concentration can be controlled at 8% to 12% shading), ultrasonic treatment for 5 minutes (53KHz / 120W) to fully disperse the sample, and then measuring the sample in accordance with GB / T19077-2016 / ISO13320:2009 standard. After the sample is poured into the injection tower, it circulates with the solution to the test optical path system. When the particles are irradiated by the laser beam, the particle size distribution characteristics of the particles can be obtained by receiving and measuring the energy distribution of the scattered light. The particle size volume distribution diagram is drawn according to the test data, and D is obtained from the distribution diagram. v 50. In order to avoid the influence of agglomeration during the drying process on the particle size test, the wet sample after washing was taken for dispersion test.

[0301] By adding D of the first negative electrode active material v 50 is controlled within the aforementioned range, which is beneficial to better control the degree of particle stacking in the first negative electrode active layer, is beneficial to better control the pores between particles, provides a better lithium ion transmission channel, and better improves the battery dynamics and fast charging performance.

[0302] In some embodiments, the porosity of the first negative electrode active layer is higher than the porosity of the second negative electrode active layer.

[0303] In the present application, the "porosity" of the membrane layer refers to the ratio of the pore volume in the membrane layer to the total volume, which can be expressed as a percentage. The "porosity" of the second negative electrode active layer refers to the ratio of the pore volume in the second negative electrode active layer to the volume of the second negative electrode active layer. The "porosity" of the first negative electrode active layer refers to the ratio of the pore volume in the first negative electrode active layer to the volume of the first negative electrode active layer. The "porosity" of the negative active material layer of the negative electrode sheet refers to the ratio of the pore volume in the negative active material layer to the volume of the entire negative active material layer, which can also be recorded as the "porosity of the negative electrode sheet".

[0304] By controlling the porosity of the first negative electrode active layer to be higher than that of the second negative electrode active layer, it is beneficial to take into account both the fast charging performance and the energy density of the battery. The relatively high porosity of the first negative electrode active layer can be used to promote the rapid transmission of lithium ions, while the relatively low porosity of the second negative electrode active layer can be used to improve the energy density of the negative electrode.

[0305] In the present application, for the overall negative electrode sheet, the porosity (δ N ) can be measured using instruments and methods known in the art. For example, GB / T 24586-2009 can be referred to and the gas displacement method can be used for measurement. Not only can the negative electrode sheet taken out after disassembling the battery cell be tested, but also the negative electrode sheet obtained after cold pressing can be tested.

[0306] Pretreatment: Punch the negative electrode discs. In a drying room, use tweezers to select ≥20 discs with good appearance and no powder falling off the edges and put them into the sample cup. The test sample is n negative electrode discs. Record the number of discs n and calculate the apparent volume V of the test sample. N2 . V N2 =S N ×D N ×n.

[0307] Test analysis: Place the sample cup containing the test sample in the true density tester, close the test system, introduce helium according to the program, detect the pressure of the gas in the sample chamber and the expansion chamber, and then calculate the true volume V of the test sample according to Bohr's law (PV=nRT). N1 , and thus the porosity δ of the test sample is calculated N =(V N2 -V N1 ) / V N2 × 100%, which can be recorded as the porosity of the negative electrode active material layer.

[0308] The test sample is n negative electrode discs; S N is the area of ​​the negative electrode active material layer in a single negative electrode disc, in cm 2 ;D N , the thickness of the negative electrode active material layer in a single negative electrode disc, in cm; V N1 , true volume of the test sample, cm 3 ; V N2 , the apparent volume of the test sample, in cm 3 .

[0309] For example, the porosity of the second negative electrode active layer can be measured by the following method:

[0310] (1) Obtain a sample to be tested including at least a portion of the second negative electrode active layer and excluding the first negative electrode active layer: disassemble the battery cell, take the negative electrode plate, and use a micrometer to test the plate thickness L; take another negative electrode plate, wipe off the negative electrode active material layer on both sides of the surface to leave the remaining empty collector foil, and test the thickness L0, then the total thickness of the negative electrode active material layer on both sides of the negative electrode collector is L-L0; scrape the negative electrode active material layer on one surface of the negative electrode plate to expose the negative electrode collector surface, scrape the negative electrode material on the other surface until the plate thickness is L1=L0+Δd, and collect the powder of the Δd thickness portion of the negative electrode active material layer under the thickness of L1. The thickness of the second negative electrode active layer can be determined in advance in combination with the observation results of the cross-sectional morphology of the plate, and then the first negative electrode active layer is completely removed when the thickness is controlled to be L1, and the remaining negative electrode active material layer portion corresponds to part or all of the second negative electrode active layer. For example, Δd can be exemplarily 15μm, 20μm, etc. In the sample to be tested, only the second negative electrode active layer on one side of the negative electrode current collector is retained.

[0311] (2) The porosity of the second negative electrode active layer (δ 2 ): The porosity of the sample to be tested is obtained by referring to the method for testing the porosity of the negative electrode sheet, and is recorded as the porosity of the second negative electrode active layer.

[0312] When δ N Greater than δ 2 When , it can be considered that "the porosity of the first negative electrode active material layer is higher than the porosity of the second negative electrode active layer". In addition, illustratively, the porosity of the first negative electrode active layer (δ 1 ) can be calculated according to formula D N ×δ N =D 1 ×δ 1 +D 2 ×δ 2 Calculated; where δ N is the porosity of the entire negative electrode active material layer, δ 2 is the porosity of the second negative electrode active layer, D N is the total thickness of the negative electrode active material layer, D 2 is the thickness of the second negative electrode active layer, D 1 is the thickness of the first negative electrode active layer.

[0313] In addition, illustratively, the following method can be used to test the porosity of the negative electrode active material layer in the negative electrode sheet, and the porosity of the first negative electrode active layer and the second negative electrode active layer can also be tested and / or compared: disassemble the battery cell and take the negative electrode sheet; punch the negative electrode sheet into small discs, and 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 an energy dispersive spectrometer (EDS) to analyze the distribution and proportion of each element, and obtain the porosity of the first negative electrode active layer, the second negative electrode active layer and the overall negative electrode active material layer through software quantitative analysis. The FEI Scios 2HiVac device can be used for testing.

[0314] In some embodiments, the powder compaction density of the first negative electrode active material or the powder compaction density of the first negative electrode active layer is 1.60 g / cm 3 ~1.80g / cm 3 , can also be any of the following values ​​or a range consisting of any two of the following values: 1.60 g / cm 3 、1.62g / cm 3 , 1.64g / cm 3 , 1.65g / cm 3 、1.66g / cm 3 、1.68g / cm 3 , 1.70g / cm 3 , 1.72g / cm 3 , 1.74g / cm 3 , 1.75g / cm 3 , 1.76g / cm 3 , 1.78g / cm 3 , 1.80g / cm 3 wait.

[0315] In the present application, unless otherwise specified, the “powder compaction density” of the first negative electrode active layer refers to the powder compaction density of the powder material constituting the first negative electrode active layer, and 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.

[0316] In this application, the "powder compaction density" of a powder material has a well-known meaning in the art, and refers to the ratio of the mass to the volume of the powder material after compacting it under a certain pressure. In this application, the powder compaction density of the negative electrode active layer in the negative electrode active material layer refers to the powder compaction density of the negative electrode material constituting the negative electrode active layer. "Powder material" and "powder material" have the same meaning and can be used interchangeably.

[0317] The "powder compaction density" of a powder 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 material to be tested with a mass of M (such as 1 g), add a bottom area of ​​A (such as 1.327 cm 2 ) in the mold, pressurized to a certain pressure P 0 (such as 3 to 5 tons (3T to 5T), such as 3T, 4T, 5T), maintain pressure for a certain time (such as 5T for 30s), then release the pressure, maintain for a period of time (such as 10s), and then record and calculate the material under pressure P 0 Unless otherwise specified, the pressure for testing the compaction density of powders is 5T.

[0318] 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 are tested for powder compaction density, and the powder compaction density of the first negative electrode active layer and the second negative electrode active layer can be compared or obtained. The first negative electrode material and the second negative electrode material can be extracted from the negative electrode sheet after disassembling the battery cell, or extracted from the negative electrode sheet obtained after cold pressing. Before testing, the first negative electrode material and the second negative electrode material can be ultrasonically dispersed in a solvent and then dried.

[0319] The powder raw material of the first negative electrode active material or the second negative electrode active material can also be tested to obtain the powder compaction density of the first negative electrode active material and the second negative electrode active material. The battery can also be disassembled to obtain the powder to be tested of the first negative electrode active material and / or the powder to be tested of the second negative electrode active material and then perform the powder compaction density test. The preparation method of the powder to be tested can refer to the OI test section.

[0320] In the present application, unless otherwise specified, "the negative electrode sheet obtained after cold pressing" refers to the state of the negative electrode sheet obtained after cold pressing just after the cold pressing. It can be considered that in this state, no or almost no rebound of the electrode sheet volume has occurred.

[0321] By controlling the powder compaction density of the first negative electrode active material or the powder compaction density of the first negative electrode active layer within the aforementioned range, it is beneficial to make the particle stacking degree of the first negative electrode active layer provide a better lithium ion transmission channel, thereby better improving the battery dynamics and fast charging performance; in addition, the second negative electrode active layer can also be used to provide a higher energy density, which is beneficial to take into account the fast charging performance and energy density of the lithium-ion secondary battery.

[0322] Generally, in lithium-ion secondary batteries, the powder compaction density of the first negative electrode active material is close to the tested value of the powder compaction density of the first negative electrode active layer, and the powder compaction density of the second negative electrode active material is close to the tested value of the powder compaction density of the second negative electrode active layer.

[0323] In some embodiments, the ratio of the first negative electrode active layer is higher than the ratio of the second negative electrode active layer.

[0324] In some embodiments, the charge rate of the first negative electrode active layer is higher than the charge rate of the second negative electrode active layer.

[0325] In the present application, the "rate" of the first negative electrode active layer and the second negative electrode active layer is a parameter reflecting the charge and discharge capabilities, and the "charging rate" is a parameter reflecting the charging capability. The higher the charging rate, the better the fast charging performance.

[0326] The following method can be used to prepare the first active layer electrode sheet and the second active layer electrode sheet: based on the negative electrode sheet obtained by cold pressing or the negative electrode sheet obtained by disassembling the battery cell, extract the first negative electrode material from the first negative electrode active layer, extract the second negative electrode material from the second negative electrode active layer, and resuspend them into uniform slurries with deionized water, respectively, and record them as the first resuspended slurry and the second resuspended slurry, respectively. The second resuspended slurry is applied to one side surface of the negative electrode collector copper foil, dried, and cold pressed to obtain the second active layer electrode sheet. The first resuspended slurry is applied to one side surface of the negative electrode collector copper foil, dried, and cold pressed to obtain the first active layer electrode sheet. The difference between the first resuspended slurry and the second resuspended slurry is the difference between the first negative electrode material and the second negative electrode material, and the coating weight, drying and cold pressing parameters are the same. Further, the first active layer electrode sheet and the second active layer electrode sheet are respectively combined with lithium sheets to form a buckle battery for rate testing. If the charge rate of the first active layer electrode sheet is higher than the charge rate of the second active layer electrode sheet, it is considered that "the rate of the first negative electrode active layer is higher than the rate of the second negative electrode active layer". The existing method for testing the charge rate can be used for testing. If the charge rate of the first active layer electrode sheet is higher than the charge rate of the second active layer electrode sheet, it is considered that "the rate of the first negative electrode active layer is higher than the rate of the second negative electrode active layer". The existing method for testing the charge rate can be used for testing.

[0327] In this application, unless otherwise specified, the rate or charge rate of the first negative electrode active layer and the second negative electrode active layer may be compared using the following method:

[0328] The first negative electrode active material, conductive carbon black (Super P), stabilizer sodium carboxymethyl cellulose and binder styrene-butadiene rubber (SBR) are dispersed in deionized water in a mass ratio of 97.3:0.7:1.2:0.8 to form a first slurry.

[0329] The second negative electrode active material, conductive carbon black (Super P), stabilizer sodium carboxymethyl cellulose and binder SBR were dispersed in deionized water in a mass ratio of 97.3:0.7:1.2:0.8 to form a second slurry.

[0330] The first slurry and the second slurry are respectively coated on a single side surface of a copper foil current collector and dried in an oven for later use.

[0331] A metal lithium plate is used as a counter electrode; a polypropylene (PP) film is used as a separator; ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) are mixed in a volume ratio of 1:1:1 to obtain a mixed solvent, and then lithium hexafluorophosphate (LiPF6) is dissolved in the above mixed solvent to obtain an electrolyte, wherein the concentration of LiPF6 is 1 mol / L.

[0332] All components were assembled into a CR2430 button cell in an argon-protected glove box. "CR" represents the international IEC number of button-type lithium manganese batteries, with a diameter of 24 mm and a thickness of 30 mm. After standing for 12 hours, the obtained button cell was discharged at a constant current of 0.05C to 0.005V, and then discharged at a constant current of 10μA to 0.005V. Then stand for 5 minutes, charge the obtained button cell at a constant current of 0.1C to 2V, stand for 5 minutes, and record the charging capacity C0. The battery was placed at a constant temperature of 25°C for 2h, and the charge and discharge tests were carried out at 1C0, 2C0, 3C0, 4C0, and 5C0 rates to obtain the capacity retention rate. Under the same cycle conditions and number of cycles, the higher the capacity retention rate, the better the rate performance, and it can be considered that the "rate" is higher.

[0333] In addition, using the same charging conditions and charging at the same rate to the same SOC (such as 80% SOC, the cut-off current can be 0.01C), the shorter the time used, the better the charging rate performance, and it can be considered that the "charging rate" is higher.

[0334] By controlling the rate of the first negative electrode active layer to be higher than that of the second negative electrode active layer, it is beneficial to promote faster embedding of lithium ions into the first negative electrode active layer, and is more beneficial to improving the fast charging performance of the battery.

[0335] By controlling the charging rate of the first negative electrode active layer to be higher than the charging rate of the second negative electrode active layer, it is beneficial to promote the faster embedding of lithium ions into the first negative electrode active layer, and is more beneficial to improving the fast charging performance of the battery.

[0336] In some embodiments, at at least one temperature condition of 20°C to 35°C, the ionic conductivity of the electrolyte can be 13 mS / cm to 18 mS / cm, and can also be any one of the following values or a range composed of any two of the following values: 13 mS / cm, 14 mS / cm, 15 mS / cm, 16 mS / cm, 17 mS / cm, 18 mS / cm, etc. The test temperature can be 25°C. Without limitation, at 25°C, the ionic conductivity of the electrolyte can be 13 mS / cm to 18 mS / cm, and can also be any one of the following values or a range composed of any two of the following values: 13 mS / cm, 14 mS / cm, 15 mS / cm, 16 mS / cm, 17 mS / cm, 18 mS / cm, etc.

[0337] In this application, unless otherwise specified, the "ionic conductivity" of the electrolyte has the well-known meaning in the art and can be tested and analyzed by the existing methods in the art. The ionic conductivity can be obtained by testing with a conductivity tester, such as a DDSJ-318 conductivity meter. The test temperature can be 25 ± 0.1°C. The method of HG-T 4067-2015 can be referred to for testing. Without limitation, the method including the following steps can be used for testing:

[0338] Pretreatment: Take the standard liquid and keep it at a constant temperature of 25°C (deviation ±0.1°C), and take the test solution and keep it at the test temperature (deviation ±0.1°C);

[0339] Testing: Calibrate the instrument with two standard solutions at 25°C. After calibration and cleaning the electrode, vertically place the sample electrode into the test liquid, click to start the test, and record the test result after the data is stable for more than 10 s.

[0340] By controlling the ionic conductivity of the electrolyte within the aforementioned range, it is beneficial to better improve the battery kinetics and the fast charging performance of the battery.

[0341] The ionic conductivity of the electrolyte in some embodiments can be referred to the context of this application. An electrolyte with a higher conductivity can be obtained by selecting a solvent with low viscosity characteristics, but not limited thereto.

[0342] Without limitation, the electrolyte includes a non-aqueous solvent, the non-aqueous solvent includes a low-viscosity solvent, and the low-viscosity solvent can include ethyl acetate, methyl acetate, dimethyl carbonate, ethyl methyl carbonate, etc. and one or more solvents with a viscosity less than or equal to at least one of the aforementioned reagents at 25°C.

[0343] In this application, unless otherwise specified, conventional methods in the art can be used to test the viscosity of the solvent or electrolyte, and the measurement can be carried out using instruments and methods well-known in the art. For example, reference can be made to the national standard GB / T 10247-2008 "Viscosity Measurement Method", and the test can be based on the rotational viscometer in Appendix D of the national standard GB / T 10247-2008. Without limitation, the following method can be used to test the viscosity of the solvent or electrolyte: Take a certain mass of the sample to be tested and place it in a sample container, and use a rotational viscometer with the instrument model DV2TLV produced by Brookfield Company for testing.

[0344] In some embodiments, the negative electrode sheet in 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):

[0345] (te1) The D v 50 of the second negative electrode active material is 12 μm to 21 μm, optionally 14 μm to 20 μm, and further optionally 14 μm to 19 μm;

[0346] (te2) The D v 50 of the second negative electrode active material is higher than the D v 50 of the first negative electrode active material;

[0347] (te3) The compaction density of the second negative electrode active layer is higher than that of the first negative electrode active layer;

[0348] (te4) The powder compaction density of the second negative electrode active material is higher than that of the first negative electrode active material, or the powder compaction density of the second negative electrode active layer is higher than that of the first negative electrode active layer; Optionally, the ratio of the powder compaction density of the second negative electrode active material to the powder compaction density of the first negative electrode active material is 1.05 to 1.35, further optionally 1.10 to 1.30, still further optionally 1.10 to 1.28 or 1.15 to 1.30, and still further optionally 1.15 to 1.28; Optionally, the ratio of the powder compaction density of the second negative electrode active layer to the powder compaction density of the first negative electrode active layer is 1.05 to 1.35, further optionally 1.10 to 1.30, still further optionally 1.10 to 1.28 or 1.15 to 1.30;

[0349] (te5) The powder compaction density of the second negative electrode active layer is 1.85 g / cm 3 ~2.05 g / cm 3 .

[0350] By making the lithium-ion secondary battery meet one or more of the characteristics (te1), (te2), (te3), (te4) and (te5), it is beneficial for the lithium-ion secondary battery to have improved fast charging performance while also taking into account energy density requirements.

[0351] In some embodiments, the second negative electrode active material includes secondary particulate graphite. In a non-limiting manner, the amount of secondary particulate graphite in the second negative electrode active material is not particularly limited, and can be 0-100%, optionally 20%-100%, further optionally 50%-100%, further optionally 80%-100%, 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%, 50%, 55%, 60%, etc.

[0352] In some embodiments, D of the second negative electrode active material v 50 can be 12μm to 21μm, optionally 14μm to 20μm, further optionally 14μm to 19μm, or any of the following values ​​or a range consisting of any two of the following values: 12μm, 13μm, 14μm, 15μm, 16μm, 17μm, 18μm, 19μm, 20μm, 21μm, etc.

[0353] By adding the D v 50 is controlled within the aforementioned range, which is beneficial for the second negative electrode active layer to obtain a higher compaction density, thereby helping to improve the energy density.

[0354] In some embodiments, D of the second negative electrode active material v 50 higher than the D of the first negative electrode active material v 50.

[0355] By controlling the D v 50 higher than the D of the first negative electrode active material v 50, which is beneficial to making the second negative electrode active layer obtain a higher compaction density, thereby helping to improve the energy density.

[0356] In some embodiments, the compaction density of the negative electrode sheet in the lithium ion secondary battery is greater than or equal to 1.40 g / cm 3 , optional 1.50g / cm 3 ~1.75g / cm 3 , can also be any of the following compaction densities or a range consisting of any two of the following compaction densities: 1.40 g / cm 3 , 1.45g / cm 3 , 1.50g / cm 3, 1.55g / cm 3 , 1.60g / cm 3 , 1.65g / cm 3 , 1.70g / cm 3 , 1.75g / cm 3 wait.

[0357] In this application, unless otherwise specified, the "compacted density" of a negative electrode sheet refers to the ratio of the mass to the volume of the negative electrode active material layer in the negative electrode sheet.

[0358] In a non-limiting manner, the compaction density of the negative electrode sheet in the lithium-ion secondary battery can be tested by the following method: dismantling the battery to obtain the negative electrode sheet, punching the obtained negative electrode sheet into a size S 0 (such as 1540.25mm 2 ) and measure the mass M of the small disc. B and thickness L B Take the negative electrode sheet from another area, wipe off the negative electrode active material 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 out into an area S 0 The mass of the empty negative electrode current collector foil is weighed and recorded as M 0 and thickness L 0 , then the compaction density PD of the negative electrode sheet B =(M B -M 0 ) / [S 0 ×(L B -L 0 )]. Test several small discs and take the average value.

[0359] By controlling the compaction density of the negative electrode plate in the lithium-ion secondary battery within the aforementioned range, the liquid phase impedance accounts for a higher proportion of the impedance inside the negative electrode plate, and the quaternary ammonium salt compound improves the liquid phase impedance by guiding the lithium ions in the electrolyte. Therefore, by controlling the compaction density of the negative electrode plate within the aforementioned range, it is beneficial to better play the role of the quaternary ammonium salt compound in improving the fast charging performance of the battery.

[0360] Compared with the negative electrode sheet obtained after cold pressing, the volume of the negative electrode sheet in the lithium-ion secondary battery will have a certain rebound, so that the compaction density of the negative electrode sheet in the lithium-ion secondary battery is lower than that of the negative electrode sheet obtained after cold pressing.

[0361] 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.

[0362] In the present application, unless otherwise specified, 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.

[0363] For example, the compaction density of the second negative electrode active layer in the negative electrode sheet of a lithium-ion secondary battery can be tested by the following method: dismantling the battery to obtain the negative electrode sheet, erasing part of the negative electrode active material layer, obtaining a sheet sample including at least a part of the second negative electrode active layer and excluding the first negative electrode active layer, and punching out the sheet sample into an area S 0 (such as 1540.25mm 2 ) small disc. The mass M of the pole piece samples were measured respectively. 2 and thickness L 2 , the same area S 0 The mass M of the empty negative electrode current collector foil 0 and thickness L 0 , then the compaction density PD of the pole piece sample is 2 =(M 2 -M 0 ) / [S 0 ×(L 2 -L 0 )], which can be used as the compaction density of the second negative electrode active layer.

[0364] When the compaction density of the negative electrode sheet PD B Lower than the compaction density PD of the second negative electrode active layer 2 , it can be considered that "the compaction density of the second negative electrode active layer is higher than the compaction density of the first negative electrode active layer".

[0365] By regulating the compaction density of the second negative electrode active layer in the lithium ion secondary battery to be higher than that of the first negative electrode active layer, the energy density of the lithium ion secondary battery can be improved.

[0366] In some embodiments, the powder compaction density of the second negative electrode active material is higher than the powder compaction density of the first negative electrode active material.

[0367] In some embodiments, the ratio of the compacted density of the powder of the second negative electrode active material to the compacted density of the powder of the first negative electrode active material can be 1.05-1.35, optionally 1.10-1.30, further optionally 1.10-1.28 or 1.15-1.30, and can also be any of the following ratios or a range selected from any two of the following ratios: 1.05, 1.06, 1.08, 1.10, 1.11, 1.12, 1.14, 1.15, 1.16, 1.18, 1.20, 1.22, 1.24, 1.25, 1.26, 1.28, 1.30, etc., and can also be selected from the following ranges: 1.05-1.28, 1.05-1.30, 1.1-1.3, 1.10-1.35, 1.15-1.28, etc.

[0368] 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.

[0369] In some embodiments, the ratio of the compacted density of the powder of the second negative electrode active layer to the compacted density of the powder of the first negative electrode active layer can be 1.05-1.35, can be 1.10-1.30, can be further 1.10-1.28 or 1.15-1.30, can be any of the following ratios or a range selected from any two of the following ratios: 1.05, 1.06, 1.08, 1.10, 1.11, 1.12, 1.14, 1.15, 1.16, 1.18, 1.20, 1.22, 1.24, 1.25, 1.26, 1.28, 1.30, etc., can also be selected from the following ranges: 1.05-1.30, 1.05-1.28, 1.1-1.3, 1.10-1.35, 1.15-1.28, etc.

[0370] By controlling the powder compaction density of the second negative electrode active material in the lithium-ion secondary battery to be higher than the powder compaction density of the first negative electrode active material or 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 a higher compaction density during the cold pressing process of the pole piece, so that the second negative electrode active layer in the lithium-ion secondary battery has a higher compaction density. Further, by controlling the ratio of the powder compaction density of the second negative electrode active material to the powder compaction density of the first negative electrode active material or controlling the ratio of the powder compaction density of the second negative electrode active layer to the powder compaction density of the first negative electrode active layer within the aforementioned range, it is beneficial to better balance the fast charging performance and energy density of the lithium-ion secondary battery.

[0371] In some embodiments, the powder compaction density of the second negative electrode active material or the powder compaction density of the second negative electrode active layer is 1.85 g / cm 3 ~2.05g / cm3 , can also be any of the following values ​​or a range consisting of any two of the following values: 1.85 g / cm 3 , 1.86g / cm 3 、1.88g / cm 3 , 1.90g / cm 3 、1.92g / cm 3 , 1.94g / cm 3 , 1.95g / cm 3 , 1.96g / cm 3 、1.98g / cm 3 , 2.00g / cm 3 , 2.02g / cm 3 , 2.04g / cm 3 , 2.05g / cm 3 wait.

[0372] By controlling the powder compaction density of the second negative electrode active material or the powder compaction density of the second negative electrode active layer within the aforementioned range, it is beneficial to make the secondary battery have a higher energy density. In addition, the particle stacking can be relatively compact, and at this time, the quaternary ammonium salt compound introduced into the second negative electrode active layer may have a more obvious effect on improving the fast charging performance of the battery.

[0373] 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):

[0374] (tf1) the ratio of the surface density of the second negative electrode active layer to the surface density of the first negative electrode active layer on a single side of the negative electrode current collector is 3:2 to 2:3;

[0375] (tf2) The thickness ratio of the first negative electrode active layer to the second negative electrode active layer is denoted as f on one side of the negative electrode current collector. H , satisfying f H ≤1.6, optionally, 1.1≤f H ≤1.6, further optionally, 1.1≤f H ≤1.3;

[0376] (tf3) The thickness of the first negative electrode active layer on one side of the negative electrode current collector is less than or equal to 50 μm, and can be 30 μm to 40 μm.

[0377] In the present application, unless otherwise specified, “on a single side of the negative electrode current collector” means that the described features are located on the same side of the negative electrode current collector.

[0378] In some embodiments, based on a single side of the negative electrode current collector, the ratio of the surface density of the second negative electrode active layer to the surface density of the first negative electrode active layer is 3:2 to 2:3, and can also be any of the following ratios or a range consisting of any two of the following ratios: 2:3, 0.67, 0.7, 0.75, 0.8, 0.75, 0.9, 0.95, 1 (corresponding to 1:1), 1.05, 1.1, 1.2, 1.25, 1.3, 1.35, 1.4, 1.45, 1.5 (i.e. 3:2), etc.

[0379] In the present application, unless otherwise specified, "the surface density of the second negative electrode active layer measured on a single side of the negative electrode current collector" refers to the ratio of the mass of the second negative electrode active layer on a single side of the negative electrode current collector to the area of ​​the second negative electrode active layer on that side, and "the surface density of the first negative electrode active layer" refers to the ratio of the mass of the first negative electrode active layer on a single side of the negative electrode current collector to the area of ​​the first negative electrode active layer on that side, and the corresponding "area" is equal to the positive projection area of ​​the second negative electrode active layer and the first negative electrode active layer along the thickness direction of the electrode sheet. Numerically, the surface density of the second negative electrode active layer measured on a single side of the negative electrode current collector is equal to the product of the compaction density of the second negative electrode active layer and the thickness of the second negative electrode active layer. The mass and area data can be obtained by referring to the test method for the compaction density of the second negative electrode active layer. Numerically, the surface density of the first negative electrode active layer measured on a single side of the negative electrode current collector is equal to the product of the compaction density of the first negative electrode active layer and the thickness of the second negative electrode active layer. The mass and area data can be obtained by referring to the test method for the compaction density of the first negative electrode active layer.

[0380] By controlling the ratio of the surface density of the second negative electrode active layer to the surface density of the first negative electrode active layer within the aforementioned range, it is beneficial to take into account both the fast charging performance and the energy density of the battery.

[0381] In some embodiments, the thickness ratio of the first negative electrode active layer to the second negative electrode active layer on a single side of the negative electrode current collector is denoted as f H , satisfying f H ≤1.6, optionally, 1.1≤f H ≤1.6, further optionally, 1.1≤f H ≤1.3, f H It can also be any of the following values ​​or a range consisting of any two of the following values: 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, etc.

[0382] In some embodiments, measured on a single side of the negative electrode current collector, the thickness of the first negative electrode active layer is less than or equal to 50 μm, and can be selected from 20 μm to 50 μm, further selected from 30 μm to 50 μm, and further selected from 30 μm to 40 μm. It can also be any of the following values ​​or a range consisting of any two of the following values: 20 μm, 25 μm, 30 μm, 35 μm, 40 μm, 45 μm, 50 μm, etc.

[0383] In the present application, unless otherwise specified, "the thickness ratio of the first negative electrode active layer to the second negative electrode active layer on a single side of the negative electrode current collector" means the thickness ratio of the first negative electrode active layer to the second negative electrode active layer on the same side of the negative electrode current collector. In the present application, unless otherwise specified, "the first negative electrode active layer on a single side of the negative electrode current collector" means the thickness of the first negative electrode active layer on a single side of the negative electrode current collector.

[0384] By controlling the thickness of the first negative electrode active layer to satisfy one or more of the above characteristics (tf2) and (tf3), the distance between the quaternary ammonium salt compound and the surface of the negative electrode plate can be adjusted, which is beneficial to better promote the transmission of lithium ions to the second negative electrode active layer located in the lower layer, thereby helping to better improve the fast charging performance of the battery.

[0385] In the first aspect of the present application, a lithium ion secondary battery is provided, which includes a negative electrode plate and an electrolyte; the negative electrode plate includes a negative electrode active material layer, and the negative electrode active material layer includes a negative electrode active material and a quaternary ammonium salt compound. As defined above, the quaternary ammonium salt compound includes a quaternary ammonium cation.

[0386] By setting a quaternary ammonium salt compound in the negative electrode active material layer, the electrostatic effect based on the quaternary ammonium root can be used to attract the electrolyte anions in the electrolyte, thereby promoting the rapid dissociation of the electrolyte lithium salt in the electrolyte. The formed quaternary ammonium root-electrolyte anion structure can also guide the lithium ions in the electrolyte to be rapidly transferred to the surface of the negative electrode active material, which can significantly improve the dynamics of the negative electrode plate, and thus significantly improve the fast charging performance of the battery.

[0387] In some embodiments, the negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer located on at least one side of the negative electrode current collector.

[0388] In some embodiments, a lithium-ion secondary battery is also provided, which includes a negative electrode plate and an electrolyte; the negative electrode plate includes a negative electrode current collector and a negative electrode active material layer located on at least one side of the negative electrode current collector;

[0389] The negative electrode active material layer includes a negative electrode active material and a quaternary ammonium salt compound. The negative electrode active material includes a negative electrode active body and a coating layer located on at least a portion of the surface of the negative electrode active body. The coating layer includes one or more of soft carbon, hard carbon and amorphous carbon. The quaternary ammonium salt compound includes a quaternary ammonium cation.

[0390] By arranging a coating layer on the surface of the negative electrode active material of the negative electrode active material layer, and arranging one or more of soft carbon, hard carbon and amorphous carbon in the coating layer, the lithium ion transmission channel on the surface of the negative electrode active material can be optimized, lithium ion transmission can be promoted, and battery dynamics and battery fast charging performance can be improved; further, by arranging a quaternary ammonium salt compound in the negative electrode active material layer, the electrostatic effect based on the quaternary ammonium root can be used to attract electrolyte anions in the electrolyte, promote the rapid dissociation of the electrolyte lithium salt in the electrolyte, and the formed quaternary ammonium root-electrolyte anion structure can also guide the rapid transmission of lithium ions in the electrolyte to the surface of the negative electrode active material; based on the aforementioned multiple effects, the fast charging performance of the battery can be better improved.

[0391] The negative electrode active material layer may include one or more negative electrode active layers, that is, the negative electrode active material layer may have a single-layer structure or a multi-layer structure.

[0392] In some embodiments, the negative electrode active material layer has a single layer structure.

[0393] In some embodiments, the negative electrode active material includes a carbon-based material.

[0394] In some embodiments, the mass proportion of carbon-based materials in the negative electrode active material can be 80% to 100%, optionally 90% to 100%, or any of the following percentages or a range consisting of any two of the following percentages: 80%, 82%, 84%, 85%, 86%, 88%, 90%, 92%, 94%, 95%, 96%, 97%, 98%, 99%, 100%, etc.

[0395] In some embodiments, a carbon material is disposed on the surface of particles of the negative electrode active material, and the carbon material may include one or more of artificial graphite, natural graphite, soft carbon, and hard carbon.

[0396] In some embodiments, the negative electrode active material includes a graphite material. The graphite material may include one or more of artificial graphite and natural graphite.

[0397] In some embodiments, the mass proportion of graphite-based materials in the negative electrode active material can be 80% to 100%, optionally 90% to 100%, or any of the following percentages or a range consisting of any two of the following percentages: 80%, 82%, 84%, 85%, 86%, 88%, 90%, 92%, 94%, 95%, 96%, 97%, 98%, 99%, 100%, etc.

[0398] In some embodiments, graphite is disposed on the surface of the particles of the negative electrode active material, and the graphite may include one or more of artificial graphite and natural graphite.

[0399] In some embodiments, the negative electrode plate satisfies one or more of the following characteristics:

[0400] (tg1) quaternary ammonium salt compound is as defined above;

[0401] (tg2) the mass proportion of the quaternary ammonium salt compound in the negative electrode active material layer is 0.2% to 2%, which can be 0.2% to 1.5%, or any of the following percentages or a range selected from any two of the following percentages: 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, 1.0%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2.0%, 2%, etc.;

[0402] (tg3) the negative electrode active material includes a carbon-based material; optionally, the carbon-based material includes one or more of artificial graphite, natural graphite, soft carbon and hard carbon;

[0403] (tg4) the negative electrode active material includes a carbon-based material, and the mass proportion of the carbon-based material in the negative electrode active material layer is 94.5% to 97.5%, which can be 95.0% to 97.0%, or any of the following percentages or a range selected from any two of the following percentages: 95%, 95.5%, 96%, 96.5%, 97%, 97.5%, etc.;

[0404] (tg5) the negative electrode active material layer includes a binder, and the binder includes styrene-butadiene rubber; optionally, the glass transition temperature of the styrene-butadiene rubber is 5°C to 70°C, further optionally 30°C to 50°C, and can also be any one of the following temperatures or a range consisting of any two of the following temperatures: 5°C, 10°C, 15°C, 20°C, 25°C, 30°C, 35°C, 40°C, 45°C, 50°C, etc.;

[0405] (tg6) the negative electrode active material includes coated graphite, the coated graphite includes a graphite body and a coating layer located on at least a portion of the surface of the graphite body, the coating layer includes one or more of soft carbon, hard carbon and amorphous carbon;

[0406] (tg7) The negative electrode active material includes secondary particle-type graphite, the secondary particle-type graphite includes a secondary particle-type graphite body, the amount of the secondary particle-type graphite in the negative electrode active material accounts for greater than or equal to 20%, and can be optionally 30% to 60%, 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%, 50%, 55%, 60%, etc.; Optionally, the secondary particle-type graphite includes carbon-coated secondary particle-type graphite, the carbon-coated secondary particle-type graphite includes a secondary particle-type graphite body and a carbon coating layer located at least a portion of the surface of the secondary particle-type graphite body, and the carbon coating layer in the carbon-coated secondary particle-type graphite includes one or more of soft carbon, hard carbon and amorphous carbon;

[0407] (tg8) The negative electrode active material includes a graphite material, and the OI value of the graphite material is 2 to 15, and can be 2 to 10, or any of the following values ​​or a range consisting of any two of the following values: 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, etc.;

[0408] (tg9) D of negative electrode active material v 50 is 11 μm to 20 μm, and can be 13 μm to 18 μm, and can also be any of the following values ​​or a range consisting of any two of the following values: 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, 16 μm, 17 μm, 18 μm, 19 μm, 20 μm, etc.;

[0409] (tg10) the porosity of the negative electrode active material layer is 15% to 35%, and can be 25% to 30%, and can also be any of the following porosities or a range consisting of any two of the following porosities: 15%, 16%, 18%, 20%, 22%, 24%, 25%, 26%, 8%, 30%, 32%, 34%, 35%, etc.;

[0410] (tg11) the ionic conductivity of the electrolyte is 13mS / cm to 18mS / cm at at least one temperature condition of 20°C to 35°C; optionally, at 25°C, the ionic conductivity of the electrolyte is 13mS / cm to 18mS / cm, and can also be any of the following values ​​or a range consisting of any two of the following values: 13mS / cm, 14mS / cm, 15mS / cm, 16mS / cm, 17mS / cm, 18mS / cm, etc.;

[0411] (tg12) The negative electrode active material layer includes a second negative electrode active layer. The definition of the second negative electrode active layer can refer to the first aspect of the present application.

[0412] For the test methods of the relevant parameters in features (tg1) to (tg11), please refer to the relevant test methods in the context.

[0413] By controlling the mass proportion of the quaternary ammonium salt compound in the negative electrode active material layer within the aforementioned range, the quaternary ammonium salt compound can better play the role of improving the fast charging performance of the battery, and can also better control the decrease in electronic conductivity on the surface of the negative electrode active material caused by the quaternary ammonium salt compound wrapping, which is conducive to better improving the fast charging performance of the battery. Furthermore, it is also conducive to maintaining a high lithium storage capacity of the negative electrode active material layer, which is conducive to taking into account the energy density of the negative electrode and the battery.

[0414] Carbon-based materials are conducive to better adsorbing hydrocarbon chains in quaternary ammonium salt compounds, thereby promoting better wrapping of quaternary ammonium salt compounds on the surface of negative electrode active materials, thereby helping to better guide lithium ions in the electrolyte to the surface of negative electrode active materials more quickly; on the other hand, carbon-based materials also have good electronic conductivity; on the other hand, carbon-based materials are also conducive to providing better stability of negative electrode active materials during fast charging and are not easy to pulverize; through the aforementioned multiple effects, it is conducive to better improving the negative electrode plate dynamics and battery fast charging performance.

[0415] By introducing natural graphite into the negative electrode active material, it is beneficial to improve the compaction density and surface capacity of the negative electrode active material layer, thereby improving the energy density of the negative electrode sheet. By introducing artificial graphite into the negative electrode active material, it is beneficial to make the cycle performance more stable. By introducing at least one of hard carbon and soft carbon into the negative electrode active material, it is beneficial to improve the negative electrode sheet and battery dynamics.

[0416] By controlling the mass proportion of the carbon-based material in the negative electrode active material layer within the aforementioned range, it is beneficial to better wrap the quaternary ammonium salt compound on the surface of the negative electrode active material. In addition, the energy density of the negative electrode and the battery can also be taken into account.

[0417] By introducing carbon-based materials into the negative electrode active material of the negative electrode active material layer and introducing styrene-butadiene rubber into the binder, it is beneficial to better realize the simultaneous wrapping of the binder and the quaternary ammonium salt compound on the surface of the negative electrode active material, which can not only realize a good electrical contact network, but also give full play to the role of the quaternary ammonium salt compound in guiding lithium ions in the electrolyte, which is beneficial to better improve the fast charging performance of the battery.

[0418] By controlling the glass transition temperature of the styrene-butadiene rubber within the aforementioned range, the negative electrode active material layer can have a better pore structure after rolling, which is beneficial for promoting the electrolyte to better infiltrate the negative electrode active material layer.

[0419] By setting a coating layer on the surface of the negative electrode active material in the negative electrode active material layer and setting one or more of soft carbon, hard carbon and amorphous carbon in the coating layer, the lithium ion transmission channel on the surface of the negative electrode active material can be optimized, lithium ion transmission can be promoted, and battery dynamics and battery fast charging performance can be further improved.

[0420] By introducing coated graphite into the negative electrode active material layer and arranging one or more of soft carbon, hard carbon and amorphous carbon in the coating layer, the lithium ion transmission channel on the surface of the negative electrode active material can be optimized, lithium ion transmission can be promoted, and battery dynamics and battery fast charging performance can be further improved.

[0421] By introducing secondary particle-type graphite into the negative electrode active material layer, utilizing the property that secondary particles are formed by agglomeration of primary particles, and based on the disordered orientation of each primary particle, it is beneficial to improve the isotropic characteristics of lithium ions when embedded in the negative electrode active material, increase the lithium ion embedding sites on the surface of the negative electrode active material, increase the lithium ion embedding rate, and improve the fast charging performance of the battery.

[0422] By controlling the OI value of the graphite material in the negative electrode active material within the aforementioned range, it is beneficial to enhance the isotropic characteristics of the negative electrode active material, increase the lithium ion embedding channels, and make the lithium ion diffusion kinetics in the negative electrode active material layer better, which is beneficial to improve the battery fast charging performance.

[0423] By increasing the D v 50 is controlled within the aforementioned range, which is beneficial to better control the stacking degree of particles in the negative electrode active material layer, is beneficial to better control the pores between particles, provides a better lithium ion transmission channel, and better improves the battery dynamics and fast charging performance.

[0424] When the porosity of the negative electrode active material layer is controlled within the aforementioned range, the particles are relatively densely packed. At this time, the quaternary ammonium salt compound introduced into the negative electrode active material layer has a more obvious effect on improving the fast charging performance of the battery.

[0425] By controlling the ionic conductivity of the electrolyte within the aforementioned range, it is beneficial to promote the rapid transmission of lithium ions, which is beneficial to better improve battery dynamics and battery fast charging performance.

[0426] In some embodiments, the surface density of the negative electrode sheet is 5 mg / cm 2 ~15mg / cm 2, can also be any of the following values ​​or a range consisting of any two of the following values: 5 mg / cm 2 , 6mg / cm 2 , 7mg / cm 2 , 8mg / cm 2 , 9mg / cm 2 、10mg / cm 2 、11mg / cm 2 , 12mg / cm 2 、13mg / cm 2 、14mg / cm 2 、15mg / cm 2 wait.

[0427] In this application, unless otherwise specified, "the surface density of the negative electrode sheet measured on one side of the negative electrode current collector" is equal to the ratio of the mass of the negative electrode active material layer on one side of the negative electrode current collector to the area of ​​the negative electrode active material layer, and the corresponding "area" is equal to the positive projection area of ​​the negative electrode active material layer along the thickness direction of the electrode sheet. Reference can be made to the test method for the compaction density of the negative electrode sheet, according to (M B -M 0 ) / S 0 Calculated.

[0428] By controlling the surface density of the negative electrode plate within the aforementioned range, it is beneficial to take into account both the fast charging performance and energy density of the battery.

[0429] In some embodiments, the electrolyte includes an electrolyte salt, and the electrolyte salt includes an electrolyte anion. Without limitation, the electrolyte anion may include one or more of tetrafluoroborate, hexafluoroarsenate, hexafluorophosphate, trifluoromethanesulfonate, difluorophosphate, difluorooxalatoborate, tetrafluorooxalatophosphate, difluorobisoxalatophosphate, bisfluorosulfonimide, and bistrifluoromethanesulfonimide.

[0430] By selecting the aforementioned types of electrolyte anions, the electrolyte anions can have a stronger binding ability to the quaternary ammonium roots, which can better promote the dissociation of the quaternary ammonium roots and anions in the quaternary ammonium salt type compound, promote the attraction of the quaternary ammonium salt type compound to the electrolyte anions and the guidance of the lithium ions in the electrolyte, and improve the transmission rate of lithium ions to the second negative electrode active material, which can better improve the negative electrode plate dynamics and battery fast charging performance.

[0431] The above-mentioned electrolyte anion types have stronger electronegativity than one or more of nitrate, carbonate, bicarbonate and phosphate, and have stronger binding properties to quaternary ammonium.

[0432] In some embodiments, the electrolyte salt includes one or more of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bisfluorosulfonyl imide, lithium bistrifluoromethanesulfonyl imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalatoborate, lithium dioxalatoborate, lithium difluorodioxalatophosphate, and lithium tetrafluorooxalatophosphate.

[0433] In some embodiments, the lithium-ion secondary battery further includes a positive electrode plate, the positive electrode plate includes a positive electrode active layer, the positive electrode active layer includes a positive electrode active material, and the positive electrode active material includes one or more of a lithium phosphate active material and a lithium composite metal oxide active material.

[0434] In some embodiments, the positive electrode active material includes a lithium-containing phosphate-based active material.

[0435] In the present application, unless otherwise specified, the lithium-containing phosphate active material may include at least one of lithium-containing phosphate and its modified product. The lithium-containing phosphate active material may have an olivine structure. Unless otherwise specified, "lithium-containing phosphate" refers to a material including lithium, transition metal elements and phosphate ions (PO 4 3- ) positive electrode active material. Non-limiting examples of olivine-structured lithium-containing phosphates may include, but are not limited to, one or more of lithium iron phosphate, a composite material of lithium iron phosphate and carbon, lithium manganese phosphate, a composite material of lithium manganese phosphate and carbon, lithium iron manganese phosphate, and a composite material of lithium iron manganese phosphate and carbon.

[0436] By introducing lithium-containing phosphate active materials into the positive electrode active materials, it is beneficial to improve the structural stability of the positive electrode active materials during the charge and discharge cycle process, which is beneficial to extend the cycle life of the battery.

[0437] In some embodiments, the positive electrode active material includes a lithium composite metal oxide-based active material.

[0438] In the present application, unless otherwise specified, the lithium composite metal oxide type active material includes at least one of lithium composite metal oxide and its modified product. Unless otherwise specified, "lithium composite metal oxide" refers to a positive electrode active material including lithium element, non-lithium metal element and oxygen element. Generally, the non-lithium metal elements of lithium composite metal oxide include transition metal elements, and therefore, lithium composite metal oxide can also be referred to as "lithium transition metal oxide". The lithium composite metal oxide type active material can have a crystal structure such as a layered structure and a spinel structure suitable for positive electrode active materials. In some embodiments, the lithium composite metal oxide type active material comprises a layered structure. In some embodiments, the lithium composite metal oxide type active material is a layered structure.

[0439] Introducing lithium composite metal oxide active materials into the positive electrode active material is beneficial to improving the positive electrode and battery energy density.

[0440] In this application, unless otherwise specified, "a modified substance of a positive electrode active material" includes the positive electrode active material itself and the 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 material" still falls within the scope of positive electrode active material.

[0441] 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 particle 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.

[0442] In some embodiments, the positive electrode active material includes a lithium phosphate-based active material, and the positive 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):

[0443] (th1) the mass proportion of lithium phosphate active materials in the positive electrode active layer is greater than or equal to 80%, and can be 80% to 97%;

[0444] (th2) lithium phosphate active materials including one or more of lithium iron phosphate, a composite material of lithium iron phosphate and carbon, lithium manganese phosphate, a composite material of lithium manganese phosphate and carbon, lithium iron manganese phosphate, and a composite material of lithium iron manganese phosphate and carbon;

[0445] (th3) The lithium phosphate active material includes a lithium phosphate active body and a carbon coating layer (which can be recorded as a third carbon coating layer) located on at least a portion of the surface of the lithium phosphate active body. The carbon coating layer (third carbon coating layer) in the lithium phosphate active material includes one or more of soft carbon, hard carbon and amorphous carbon.

[0446] In some embodiments, the mass proportion of lithium-phosphate active materials in the positive electrode active layer may be greater than or equal to 80%, optionally 80% to 97%, and further optionally 95% to 97%. Without limitation, the mass proportion of lithium-phosphate active materials in the positive electrode active layer may also be any of the following percentages or a range selected from any two of the following percentages: 80%, 82%, 84%, 85%, 86%, 88%, 90%, 92%, 93%, 94%, 95%, 95.2%, 95.4%, 95.5%, 96%, 96.5%, 96.6%, 96.8%, 96.9%, 97%, etc.

[0447] By controlling the mass proportion of lithium-phosphate active materials in the positive electrode active layer within the aforementioned range, it is beneficial to better extend the cycle life of the battery.

[0448] In some embodiments, the lithium phosphate-based active material includes one or more of lithium iron phosphate (LFP), a composite material of lithium iron phosphate and carbon, lithium manganese phosphate, a composite material of lithium manganese phosphate and carbon, lithium iron manganese phosphate, and a composite material of lithium iron manganese phosphate and carbon. Examples of lithium iron phosphate include LiFePO 4 Examples of lithium manganese phosphate include LiMnPO 4 .

[0449] The types of lithium phosphate active materials can be flexibly selected to meet different application requirements.

[0450] In some embodiments, the lithium phosphate-containing active material includes a lithium phosphate-containing active body and a carbon coating layer (i.e., a third carbon coating layer) located on at least a portion of the surface of the lithium phosphate-containing active body. Optionally, the carbon coating layer (i.e., the third carbon coating layer) in the lithium phosphate-containing active material includes one or more of soft carbon, hard carbon and amorphous carbon.

[0451] By setting a carbon coating layer including one or more of soft carbon, hard carbon and amorphous carbon on the surface of the lithium phosphate active material, the conductivity of the material can also be improved, which is beneficial to improving the electrical contact network within the positive electrode plate and providing a fast and stable channel for electron transmission within the positive electrode plate, thereby helping to improve the battery's rate performance and improve the battery's fast charging capability.

[0452] In some embodiments, the lithium phosphate-containing active entity includes at least one of lithium iron phosphate, lithium manganese phosphate, lithium manganese iron phosphate, and the like.

[0453] 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 (which may be recorded as a fourth carbon coating layer) located at least a portion of the surface of the lithium iron phosphate body. Optionally, the carbon coating layer (i.e., the fourth carbon coating layer) in the lithium iron phosphate-based positive electrode active material may include one or more of soft carbon, hard carbon, and amorphous carbon. Without limitation, the lithium iron phosphate-based positive electrode active material may include carbon-coated lithium iron phosphate.

[0454] 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 (which can be recorded as the fifth carbon coating layer) located at least a portion of the surface of the lithium iron phosphate body. Further, the carbon coating layer (that is, the fifth carbon coating layer) in the carbon-coated lithium iron phosphate can include one or more of soft carbon, hard carbon and amorphous carbon. In some embodiments, the carbon coating layer includes soft carbon. At this time, the positive electrode active material includes a lithium-containing phosphate active material, and the lithium-containing phosphate active material includes carbon-coated lithium iron phosphate.

[0455] 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 (such as carbon-coated lithium iron phosphate) can be 0.2% to 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 to 20nm, but is not limited to this.

[0456] In some embodiments, the positive electrode active material includes soft carbon-coated lithium iron phosphate. Further, the soft carbon-coated lithium iron phosphate includes a lithium iron phosphate body and soft carbon located at least partially on the surface of the lithium iron phosphate body.

[0457] The positive electrode active material in the positive electrode active layer can be detected by fully discharging the battery, disassembling the battery cell, taking out the positive electrode plate, scraping the material of the positive electrode active layer, and using elemental analysis methods such as inductively coupled plasma (ICP) spectroscopy to test and analyze the type and proportion of elements, thereby confirming the elemental composition and chemical formula of the positive electrode active material.

[0458] In some embodiments, the positive electrode active material includes a positive electrode active body and a coating layer located on the positive electrode active body.

[0459] For positive electrode active materials including a coating layer (an example of a coating layer is a carbon coating layer), the cross-section can be cut using FIB (focused ion beam) and the particle cross-sectional morphology can be observed under TEM (transmission electron microscope). A clear boundary can be observed at the coating interface, and the thickness and average thickness of the coating layer can be analyzed and calculated based on the TEM image. Further combined with one or more methods such as energy dispersive spectroscopy (EDS) analysis and Raman spectroscopy, the types of substances in the coating layer and the positive electrode active body can be confirmed respectively.

[0460] The following are some additional descriptions about the positive electrode.

[0461] The positive electrode sheet includes a positive electrode current collector and a positive electrode active layer disposed on at least one surface of the positive electrode current collector, wherein the positive electrode active layer includes a positive electrode active material.

[0462] The definitions of the positive electrode sheet, positive electrode active layer, and positive electrode active material in some embodiments may refer to the context of this application.

[0463] Without limitation, the mass fraction of the positive electrode active material in the positive electrode active layer may be greater than or equal to 80%, and further may be greater than or equal to 90%.

[0464] As a non-limiting example, the positive electrode current collector has two surfaces that are opposite to each other in its thickness direction, and the positive electrode active layer is disposed on any one or both of the two surfaces of the positive electrode current collector that are opposite to each other.

[0465] In some embodiments, the positive electrode current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. In the positive electrode current collector, the composite current collector may include a polymer material base layer and a metal layer formed on at least one surface of the polymer material base layer. In the positive electrode current collector, the composite current collector may be obtained by forming a metal material on a polymer material base layer. In the positive electrode current collector, non-limiting examples of the metal material may include at least one of aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy. In a non-limiting manner, in the positive electrode current collector, the polymer material base layer may include one or more of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.

[0466] The types of positive electrode active materials can be found in the above text. The positive electrode active materials may also include other types of positive electrode active materials known in the art for lithium ion secondary batteries. The positive electrode active materials may be used alone or in combination of two or more.

[0467] As non-limiting examples, the positive electrode active material may include, but is not limited to, one or more of the following materials: olivine-structured lithium-containing phosphates, lithium transition metal oxides, and modifications thereof.

[0468] In some embodiments, the positive electrode active material includes a lithium phosphate containing an olivine structure. Non-limiting examples of lithium phosphate containing an olivine structure may include, but are not limited to, one or more of lithium iron phosphate, a composite material of lithium iron phosphate and carbon, lithium manganese phosphate, a composite material of lithium manganese phosphate and carbon, lithium iron manganese phosphate, and a composite material of lithium iron manganese phosphate and carbon. Examples of lithium iron phosphate include LiFePO 4 Examples of lithium manganese phosphate include LiMnPO 4 .

[0469] In some embodiments, the positive electrode active material includes a lithium transition metal oxide. Examples of lithium transition metal oxides may include, but are not limited to, one or more of lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, and modified compounds thereof. Non-limiting examples of lithium cobalt oxides may include LiCoO 2 Non-limiting examples of lithium nickel oxides may include LiNiO 2 Non-limiting examples of lithium manganese oxides may include LiMnO 2 、LiMn 2 O 4 etc.; Non-limiting examples of lithium nickel cobalt manganese oxides may include LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O 2 (Also referred to as NCM 333 )、LiNi 0.5 Co 0.2 Mn 0.3 O 2 (Also referred to as NCM 523 )、LiNi 0.5 Co 0.25 Mn 0.25 O 2 (Also referred to as NCM 211 )、LiNi 0.6 Co 0.2 Mn 0.2 O 2 (Also referred to as NCM 622 )、LiNi 0.8 Co 0.1 Mn 0.1 O 2 (Also referred to as NCM 811) etc. Non-limiting examples of lithium nickel cobalt aluminum oxide may include LiNi 0.80 Co 0.15 Al 0.05 O 2 .

[0470] It is understandable that the battery will be accompanied by lithium (Li) deintercalation and consumption during the charging and discharging process, and the content of Li in the positive electrode sheet is different when the battery is discharged to different states. In the exemplary description of the positive electrode active material in this application, unless otherwise specified, the content of Li can be the initial state of the material or the non-initial state after the charge and discharge cycle. The positive electrode active material is applied to the positive electrode in the battery system, and after the charge and discharge cycle, the content of Li in the positive electrode active material at the positive electrode usually changes. Among them, the content of Li can be measured by atomic molar content, but is not limited to this. Regarding "the content of Li is the initial state of the material", the initial state of the material refers to the state before being made into a positive electrode active layer. It can be understood that the new material or new substance obtained by appropriately modifying the listed positive electrode active materials is also within the scope of the positive electrode active material. The aforementioned appropriate modification refers to the acceptable modification method for the positive electrode active material, and non-limiting examples include one or more of coating modification and doping modification.

[0471] In the exemplary description of the positive electrode active material in this application, the content of oxygen (O) is only a theoretical state value. The release of oxygen from the lattice will cause the atomic molar content of oxygen to change, and the actual content of O will fluctuate. Among them, the content of O can be measured by atomic molar content, but is not limited to this.

[0472] In some embodiments, the positive electrode active layer optionally includes a binder. As a non-limiting example, the binder may include one or more of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer and fluorine-containing acrylate resin. Generally, the mass fraction of the binder in the positive electrode active layer can be 0 to 10%, further 0 to 8%, and further 1% to 5%, based on the total mass of the positive electrode active layer.

[0473] In some embodiments, the positive electrode active layer optionally includes a conductive agent. As a non-limiting example, the conductive agent may include one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. Typically, the mass fraction of the conductive agent in the positive electrode active layer may be 0 to 10%, further 0 to 8%, and further 0 to 5%, based on the total mass of the positive electrode active layer.

[0474] In some embodiments, the positive electrode sheet can be prepared by the following method: the components for preparing the positive electrode sheet, such as the positive active material, the conductive agent, the binder and any other components, are dispersed in a solvent to form a positive electrode slurry. Further, the positive electrode slurry is coated on at least one side of the positive electrode collector, and after drying, cold pressing and other processes, the positive electrode sheet can be obtained. Cold pressing can be performed by a cold rolling mill. The type of solvent in the positive electrode slurry can include but is not limited to any of the aforementioned embodiments, for example, it can include N-methylpyrrolidone (NMP), and further can be NMP. The surface of the positive electrode collector coated with the positive electrode slurry can be on a single surface of the positive electrode collector, or on both surfaces of the positive electrode collector. The solid content of the positive electrode slurry can be 40wt% to 80wt%. The viscosity of the positive electrode slurry at room temperature can be adjusted to 5000mPa·s to 25000mPa·s.

[0475] In some embodiments, the positive electrode active material includes a lithium-containing phosphate active material, and further, the mass proportion of the lithium-containing phosphate active material in the positive electrode active material can be greater than or equal to 50%, but is not limited thereto. When applying the positive electrode slurry, the coating surface density (based on the coating surface density on both sides) on a dry weight basis (excluding the solvent) can also be (0.1-0.6) g / 1540.25 mm 2 , but not limited to this. The compaction density of the positive electrode sheet can be 1.9g / cm 3 ~3.0g / cm 3 .

[0476] In some embodiments, the positive electrode active material includes a lithium composite metal oxide active material, and further, the mass proportion of the lithium composite metal oxide active material in the positive electrode active material may be greater than or equal to 50%, but is not limited thereto. When the positive electrode slurry is coated, the coating surface density on a dry weight basis (excluding the solvent) may be 15 mg / cm 2 ~35mg / cm 2 , measured by the double-sided coating surface density. The compacted density of the positive electrode sheet can be 3.0g / cm 3 ~3.6g / cm 3 , optional 3.3g / cm 3 ~3.5g / cm 3 .

[0477] In the present application, unless otherwise specified, the compaction density of the positive electrode sheet refers to the ratio of the mass of the positive electrode active layer to its volume.

[0478] The following are some additional descriptions about the negative electrode.

[0479] 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, wherein the negative electrode active material layer includes a negative electrode active material.

[0480] In the present application, the "negative electrode active material layer" in the negative electrode sheet may include one or more negative electrode active layers, that is, the negative electrode active material layer may be a single-layer structure or a multi-layer structure.

[0481] In some embodiments, the negative electrode active material layer includes a second negative electrode active layer. The definition of the second negative electrode active layer can be found in the context of this application.

[0482] In some embodiments, the negative electrode active material layer on at least one side includes a first negative electrode active layer and a second negative electrode active layer, and the second negative electrode active layer is located between the first negative electrode active layer and the negative electrode current collector.

[0483] The first negative electrode active layer includes a first negative electrode active material. The second negative electrode active layer includes a second negative electrode active material. The types of the first negative electrode active material and the second negative electrode active material may be the same or different, and the description above may be referred to.

[0484] The definitions of the negative electrode sheet, the negative electrode active material layer, the first negative electrode active layer and the second negative electrode active layer, the negative electrode active material, the first negative electrode active material and the second negative electrode active material in some embodiments can be referred to in the context of this application.

[0485] As a non-limiting example, the negative electrode sheet includes a negative current collector and a second negative active layer and a first negative active layer sequentially disposed on at least one side of the negative current collector, wherein the second negative active layer is located between the negative current collector and the first negative active layer.

[0486] Without limitation, the mass percentage of the negative electrode active material in the negative electrode active material layer may be greater than or equal to 80%, and further may be greater than or equal to 90%.

[0487] Without limitation, the mass fraction of the first negative electrode active material in the first negative electrode active layer may be greater than or equal to 80%, and further may be greater than or equal to 90%.

[0488] Without limitation, the mass fraction of the second negative electrode active material in the second negative electrode active layer may be greater than or equal to 80%, and further may be greater than or equal to 90%.

[0489] As a non-limiting example, the negative electrode current collector has two surfaces facing each other in its thickness direction, and the negative electrode active material layer is disposed on any one or both of the two surfaces facing each other of the negative electrode current collector.

[0490] Figure 1It is a schematic structural diagram of a negative electrode plate in an embodiment of the present application. The negative electrode plate 200 includes a negative electrode current collector 210, and a second negative electrode active layer 222 and a first negative electrode active layer 224 are sequentially arranged on one side of the negative electrode current collector 210. The second negative electrode active layer 222 includes negative electrode active particles 202 and a quaternary ammonium salt-type compound 208. At this time, the second negative electrode active material in the second negative electrode active layer includes negative electrode active particles 202. At this time, the negative electrode active material layer includes the first negative electrode active layer and the second negative electrode active layer. The negative electrode active material layer can also be located on both sides of the negative electrode current collector.

[0491] Figure 2 It is a schematic structural diagram of a negative electrode plate in another embodiment of the present application. The negative electrode plate 200 includes a negative electrode current collector 210, and a second negative electrode active layer 222 and a first negative electrode active layer 224 are sequentially arranged on both sides of the negative electrode current collector 210. The second negative electrode active layer 222 includes negative electrode active particles 202 and a quaternary ammonium salt-type compound 208. At this time, the second negative electrode active material in the second negative electrode active layer includes negative electrode active particles 202. At this time, the negative electrode active material layer includes the first negative electrode active layer and the second negative electrode active layer. The negative electrode active material layer can also be located on both sides of the negative electrode current collector.

[0492] Figure 3 It is a schematic structural diagram of a negative electrode plate in an embodiment of the present application. The negative electrode plate 200 includes a negative electrode current collector 210 and a negative electrode active material layer 220 located on one side of the negative electrode current collector 210. The negative electrode active material layer 220 includes negative electrode active particles 202 and a quaternary ammonium salt-type compound 208. At this time, the negative electrode active material in the negative electrode active material layer includes negative electrode active particles 202. The negative electrode active material layer can also be located on both sides of the negative electrode current collector.

[0493] In the present application, unless otherwise specified, the negative electrode active particles are the particulate matters in the negative electrode active material.

[0494] In some embodiments, the negative electrode current collector can adopt a metal foil or a composite current collector. For example, as the metal foil, copper foil can be adopted. In the negative electrode current collector, the composite current collector can include a polymer material base layer and a metal layer formed on at least one surface of the polymer material base layer. In the negative electrode current collector, the composite current collector can be formed by forming a metal material on the polymer material base layer. In the negative electrode current collector, non-limiting examples of the metal material can include one or more of copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy, etc. Non-limitingly, in the negative electrode current collector, the polymer material base layer can include one or more of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.

[0495] In addition to the types of negative electrode active materials involved in the context implementation methods and examples, the negative electrode active materials in the negative electrode active material layer, the first negative electrode active layer and the second negative electrode active layer may also independently include other types of negative electrode active materials suitable for lithium-ion secondary batteries that are well known in the art. In the negative electrode active material layer, these negative electrode active materials can be used alone or in combination of two or more. In the first negative electrode active layer and the second negative electrode active layer, each independently, these negative electrode active materials can be used alone or in combination of two or more. In some embodiments, the negative electrode active material also includes one or more of tin-based materials and lithium titanate.

[0496] In some embodiments, the negative active material layer may optionally include a binder.

[0497] In some embodiments, the first negative electrode active layer and the second negative electrode active layer each independently optionally include a binder.

[0498] Without limitation, in the negative electrode sheet, the binder may include one or more of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA) and carboxymethyl chitosan (CMCS). The binder types in the first negative electrode active layer and the second negative electrode active layer may be the same or different.

[0499] Without limitation, the mass percentage of the binder in the negative electrode active material layer may be 0% to 20%, further 0% to 10%, further 0 to 5%, further 1% to 5%, further optionally 1% to 3%.

[0500] Without limitation, the mass fraction of the binder in the first negative electrode active layer may be 0% to 20%, further 0% to 10%, further 0 to 5%, further 1% to 5%, further optionally 1% to 3%.

[0501] Without limitation, the mass fraction of the binder in the second negative electrode active layer may be 0% to 20%, further 0% to 10%, further 0 to 5%, further 1% to 5%, further optionally 1% to 3%.

[0502] The definition of the binder of some embodiments can be found in the context of this application.

[0503] In some embodiments, the negative active material layer may optionally include a conductive agent.

[0504] In some embodiments, the first negative electrode active layer and the second negative electrode active layer each independently optionally include a conductive agent.

[0505] Without limitation, in the negative electrode sheet, the conductive agent may include one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene and carbon nanofibers. The types of conductive agents in the first negative electrode active layer and the second negative electrode active layer may be the same or different.

[0506] Without limitation, the mass percentage of the conductive agent in the negative electrode active material layer may be 0% to 15%, further optionally 0% to 10%, and further optionally 0% to 5%.

[0507] In a non-limiting manner, the mass fraction of the conductive agent in the first negative electrode active layer may be 0% to 15%, further optionally 0% to 10%, and further optionally 0% to 5%.

[0508] In a non-limiting manner, the mass fraction of the conductive agent in the second negative electrode active layer may be 0% to 15%, further optionally 0% to 10%, and further optionally 0% to 5%.

[0509] In some embodiments, the negative electrode active material layer may optionally include other additives, such as a thickener (e.g., sodium carboxymethyl cellulose (CMC-Na)), etc. In a non-limiting manner, the mass percentage of other additives in the negative electrode active material layer may be 0% to 15%, further optionally 0% to 10%, further optionally 0% to 5%, further optionally 0% to 3%, further optionally 0% to 2%.

[0510] In some embodiments, the first negative electrode active layer and the second negative electrode active layer may each independently optionally include other additives, such as a thickener (such as sodium carboxymethyl cellulose (CMC-Na)), etc. Non-limitingly, the mass fraction of other additives in the first negative electrode active layer or the second negative electrode active layer may independently be 0% to 15%, further optionally 0% to 10%, further optionally 0% to 5%, further optionally 0% to 3%, further optionally 0% to 2%.

[0511] In some embodiments, a negative electrode sheet is prepared by a method comprising the following steps, which can be used to prepare a negative electrode sheet with a single-layer structure of a negative electrode active material layer:

[0512] S110: preparing negative electrode slurry. The above components for preparing the negative electrode active material layer, such as the negative electrode active material, the quaternary ammonium salt compound, the conductive agent, the binder and any other components are dispersed in a solvent (a non-limiting example of the solvent is deionized water) to form a negative electrode slurry.

[0513] S120: Prepare negative electrode sheets. The negative electrode slurry is coated on at least one side of the negative electrode current collector. After drying, cold pressing and other processes, a negative electrode active material layer can be formed accordingly to obtain a negative electrode sheet. Cold pressing can be performed using a cold rolling mill. The surface of the negative electrode current collector coated with the negative electrode slurry can be on a single surface of the negative electrode current collector or on both surfaces of the negative electrode current collector. The solid content of the negative electrode slurry can be 30wt% to 70wt%, and can be optionally 40wt% to 60wt%. The viscosity of the negative electrode slurry at room temperature can be adjusted to 2000mPa·s to 10000mPa·s, and can be optionally 3000mPa·s to 10000mPa·s.

[0514] In some embodiments, a negative electrode sheet is prepared by a method comprising the following steps: S100' and S200'; which can be used to prepare a negative electrode sheet having a negative electrode active material layer including a first negative electrode active layer and a second negative electrode active layer.

[0515] S100': Prepare a first negative electrode slurry and a second negative electrode slurry. The above components for preparing the first negative electrode active layer, such as the first negative electrode active material, the conductive agent, the binder and any other components are dispersed in a solvent (a non-limiting example of the solvent is deionized water) to form a first negative electrode slurry. The above components for preparing the second negative electrode active layer, such as the second negative electrode active material, the quaternary ammonium salt compound, the conductive agent, the binder and any other components are dispersed in a solvent (a non-limiting example of the solvent is deionized water) to form a second negative electrode slurry.

[0516] S200': Prepare the negative electrode sheet. Use a double-layer coating machine to coat the second negative electrode slurry and the first negative electrode slurry on at least one side of the negative electrode collector. Apply the second negative electrode slurry first and then the first negative electrode slurry. After drying, cold pressing and other processes, the second negative electrode active layer and the first negative electrode active layer can be formed accordingly. The second negative electrode active layer is located between the first negative electrode active layer and the negative electrode collector; wherein the non-solvent component of the first negative electrode slurry forms the first negative electrode active layer, and the non-solvent component of the second negative electrode slurry forms the second negative electrode active layer. Cold pressing can be performed using a cold rolling mill. The surface of the negative electrode collector coated with the first negative electrode slurry and the second negative electrode slurry can be on a single surface of the negative electrode collector or on both surfaces of the negative electrode collector. The solid content of the first negative electrode slurry and the second negative electrode slurry can be independently 30wt% to 70wt%, and can be independently 40wt% to 60wt%. The viscosity of the first negative electrode slurry and the second negative electrode slurry at room temperature can be independently adjusted to 2000 mPa·s to 10000 mPa·s, and can be independently selected to be 3000 mPa·s to 10000 mPa·s.

[0517] The coating surface density of the negative electrode sheet and the compaction density of the negative electrode sheet can be found in the context of this application.

[0518] The electrolyte solution is exemplarily described below.

[0519] The electrolyte has the function of conducting ions between the positive electrode and the negative electrode. The appropriate electrolyte can be selected according to the needs.

[0520] The electrolyte solution includes an electrolyte salt and a solvent. The solvent includes a non-aqueous solvent.

[0521] In some embodiments, the electrolyte is a non-aqueous electrolyte. The non-aqueous electrolyte may include an electrolyte salt and a solvent.

[0522] The concentration of the electrolyte salt in the electrolyte solution may generally be 0.5 mol / L to 5 mol / L.

[0523] In some embodiments, the electrolyte salt comprises an electrolyte lithium salt. The definition of the electrolyte salt of some embodiments can be found in the context of this application.

[0524] In some embodiments, the solvent in the non-aqueous electrolyte may include ethylene carbonate (EC, ), propylene carbonate (PC, ), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butylene carbonate (BC, ), one or more of fluoroethylene carbonate (FEC), methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, cyclopentane, dimethyl sulfone, methyl ethyl sulfone and diethyl sulfone.

[0525] In some embodiments, the electrolyte may optionally include additives. For example, the additives may include negative electrode film-forming additives, positive electrode film-forming additives, and may also include additives that can improve certain battery properties, such as additives that improve battery overcharge performance, additives that improve battery high or low temperature performance, etc.

[0526] In some embodiments, the additives in the electrolyte may include, but are not limited to, one or more of fluoroethylene carbonate (FEC), difluoroethylene carbonate (DFEC), trifluoromethylethylene carbonate (TFPC), and the like.

[0527] The separator is exemplarily described below.

[0528] The definition of the isolation membrane of some embodiments may be found in the context of this application.

[0529] The present application has no particular limitation on the type of diaphragm membrane, and any known diaphragm membrane with a porous structure having good chemical stability and mechanical stability may be selected.

[0530] In some embodiments, the material of the diaphragm membrane may include one or more of glass fiber, non-woven fabric, polyethylene, polypropylene and polyvinylidene fluoride. The diaphragm membrane may be a single-layer film or a multi-layer composite film, without particular limitation. When the diaphragm membrane is a multi-layer composite film, the materials of each layer may be the same or different, without particular limitation.

[0531] In some embodiments, the thickness of the separator film is 4 μm to 40 μm, and optionally 7 μm to 15 μm.

[0532] In some embodiments, the positive electrode sheet, the negative electrode sheet, and the separator may be formed into an electrode assembly by a winding process or a lamination process.

[0533] In some embodiments, the lithium-ion secondary battery may include an outer package, which may be used to encapsulate the electrode assembly and the electrolyte.

[0534] In some embodiments, the outer packaging of the lithium ion secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer packaging of the lithium ion secondary battery can also be a soft package, such as a bag-type soft package. The material of the soft package can be plastic, and further, non-limiting examples of plastic can include one or more of polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0535] A lithium-ion secondary battery includes at least one battery cell. A lithium-ion secondary battery may include one or more battery cells.

[0536] The present application has no particular limitation on the shape of the battery cell, which may be cylindrical, square or any other shape. Figure 4 The battery cell 5 is a square structure as an example.

[0537] In some embodiments, reference Figure 5 , the outer packaging may include a shell 51 and a cover plate 53. Among them, the shell 51 may include a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plate enclose a receiving cavity. The shell 51 has an opening connected to the receiving cavity, and the cover plate 53 can be covered on the opening to close the receiving cavity. The positive electrode sheet, the negative electrode sheet and the isolation membrane can form an electrode assembly 52 through a winding process or a lamination process. The electrode assembly 52 is encapsulated in the receiving cavity. The electrolyte is infiltrated in the electrode assembly 52. ​​The number of electrode assemblies 52 contained in the battery cell 5 can be one or more, and those skilled in the art can select according to actual needs.

[0538] The lithium-ion secondary battery may be a battery device 4 or a battery pack 1 .

[0539] The battery device includes at least one battery cell. The number of battery cells contained in the battery device can be one or more, and those skilled in the art can select a suitable number according to the application and capacity of the battery device.

[0540] Figure 6 4 is an example of a battery device. Figure 6 In the battery device 4, the plurality of battery cells 5 may be arranged in sequence along the length direction of the battery device 4. Of course, they may also be arranged in any other manner. Further, the plurality of battery cells 5 may be fixed by fasteners.

[0541] Optionally, the battery device 4 may further include a housing having a receiving space, and the plurality of battery cells 5 are received in the receiving space.

[0542] In some embodiments, the battery devices described above may also be assembled into a battery pack. The number of battery devices contained in the battery pack may be one or more. Those skilled in the art may select a suitable number according to the application and capacity of the battery pack.

[0543] Figure 7 and Figure 8 1 is a battery pack 1 as an example. Figure 7 and Figure 8 The battery pack 1 may include a battery box and a plurality of battery devices 4 disposed in the battery box. The battery box includes an upper box body 2 and a lower box body 3. The upper box body 2 can cover the lower box body 3 and form a closed space for accommodating the battery devices 4. The plurality of battery devices 4 can be arranged in the battery box in any manner.

[0544] In another aspect of the present application, a negative electrode plate is provided, which may have the same characteristics as the negative electrode plate described in the first aspect of the present application, or may be in the state after cold pressing and before being soaked in electrolyte corresponding to the negative electrode plate described in the first aspect of the present application.

[0545] In some embodiments, a negative electrode plate is provided, which includes a negative electrode current collector and a negative electrode active material layer located on at least one side of the negative electrode current collector, the negative electrode active material layer; the negative electrode active material layer includes a negative electrode active material and a quaternary ammonium salt compound, and the quaternary ammonium salt compound includes a quaternary ammonium cation.

[0546] In some embodiments, a negative electrode sheet is provided, comprising a negative electrode current collector and a second negative electrode active layer and a first negative electrode active layer sequentially disposed on at least one side of the negative electrode current collector, wherein the second negative electrode active layer is located between the negative electrode current collector and the first negative electrode active layer;

[0547] The second negative electrode active layer includes a second negative electrode active material and a quaternary ammonium salt compound.

[0548] After introducing the quaternary ammonium salt compound into the second negative electrode active layer, the electrolyte wettability of the second negative electrode active layer can be significantly improved. The effect of "whether the quaternary ammonium salt compound is introduced" on the electrolyte wettability of the second negative electrode active layer can be compared by changing the liquid absorption rate. The greater the liquid absorption rate, the better the electrolyte wettability can be considered. The following method can be used for testing and analysis.

[0549] Based on the negative electrode sheet obtained by cold pressing or the negative electrode sheet obtained by disassembling the battery cell, the second negative electrode material can be extracted from the second negative electrode active layer by the method of the first aspect of the application, and resuspended into a uniform slurry using deionized water, which is recorded as the second resuspended slurry. The second resuspended slurry is applied to one side surface of the negative electrode collector copper foil, dried, and cold pressed to obtain the second active layer electrode sheet. The non-solvent component in the second resuspended slurry is substantially the same as the non-solvent component in the second negative electrode slurry. In addition, the second negative electrode slurry used in preparing the negative electrode sheet can be used instead of the second resuspended slurry to prepare the second active layer electrode sheet.

[0550] The following method can be used to test the liquid absorption rate: fix the electrode to be tested on the sample table, drip the electrolyte, and use a stopwatch to time; record the weight increase and time; calculate the liquid absorption rate of the electrode by the change of weight over time. Non-limiting examples of electrolytes include the electrolyte formula of Example 1. The liquid absorption rate can also be tested with an electrolyte with the same composition as the electrolyte in the lithium-ion secondary battery, and a commercially available electrolyte such as electrolyte E30 can also be used. In some examples, the electrolyte is composed of a solvent and 1 mol / L lithium hexafluorophosphate (LiPF6), and the solvent is composed of ethylene carbonate (EC), dimethyl carbonate (DMC) and ethyl methyl carbonate (EMC) in a volume ratio of 1:1:1.

[0551] In some embodiments, a negative electrode plate is provided, which includes a negative electrode current collector and a negative electrode active material layer located on at least one side of the negative electrode current collector; the negative electrode active material layer includes a negative electrode active material and a quaternary ammonium salt compound, the negative electrode active material includes a negative electrode active body and a coating layer located on at least a portion of the surface of the negative electrode active body, the coating layer includes one or more of soft carbon, hard carbon and amorphous carbon, and the quaternary ammonium salt compound includes a quaternary ammonium cation.

[0552] By arranging a coating layer on the surface of the negative electrode active material of the negative electrode active material layer, and arranging one or more of soft carbon, hard carbon and amorphous carbon in the coating layer, the lithium ion transmission channel on the surface of the negative electrode active material can be optimized, lithium ion transmission can be promoted, and battery dynamics and battery fast charging performance can be improved. Furthermore, by arranging a quaternary ammonium salt compound in the negative electrode active material layer, the electrostatic effect based on the quaternary ammonium root can be used to attract the electrolyte anions in the electrolyte, promote the rapid dissociation of the electrolyte lithium salt in the electrolyte, and the formed quaternary ammonium root-electrolyte anion structure can also guide the lithium ions in the electrolyte to the surface of the negative electrode active material for rapid transmission; based on the aforementioned multiple effects, the fast charging performance of the battery can be better improved.

[0553] In some embodiments, the negative electrode plate is the negative electrode plate defined in the first aspect of the present application.

[0554] In a second aspect of the present application, an electrical device is provided, which includes the lithium-ion secondary battery described in the first aspect of the present application.

[0555] An electrical device including the aforementioned lithium ion secondary battery may have the advantages of the aforementioned lithium ion secondary battery, including but not limited to having improved fast charging performance.

[0556] An electrical device including the aforementioned negative electrode plate may have the advantages of the aforementioned negative electrode plate, including but not limited to having improved fast charging performance.

[0557] In some embodiments, an electric device includes a lithium-ion secondary battery according to any embodiment of the present application.

[0558] Lithium-ion secondary batteries can be used as power sources for electrical devices, or as energy storage units for electrical devices. Electrical devices may include mobile devices, electric vehicles, electric trains, ships and satellites, energy storage systems, etc., but are not limited thereto. Among them, mobile devices may be, for example, mobile phones, laptop computers, etc.; electric vehicles may be, for example, pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, electric motorcycles, electric tools, etc., but are not limited thereto. The electrical device may also be used in the fields of military equipment, aerospace, etc., and may also be used in energy storage power supply systems such as hydropower, thermal power, wind power and solar power stations.

[0559] As an electrical device, a lithium-ion secondary battery can be selected according to its usage requirements.

[0560] Fig. 9 The power consumption device 6 is taken as an example. The power consumption device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. In order to meet the power consumption device's requirements for high power and high energy density of lithium-ion secondary batteries, a battery device or a battery pack can be used.

[0561] Another example of a device may be a mobile phone, a tablet computer, a notebook computer, etc. Such a device is usually required to be thin and light, and a lithium-ion secondary battery may be used as a power source.

[0562] In a third aspect of the present application, there is provided a use of the lithium ion secondary battery described in the first aspect of the present application in supplying electric energy and / or storing electric energy;

[0563] The application includes a process of charging a lithium-ion secondary battery at a rate greater than or equal to 2C, that is, the lithium-ion secondary battery can provide a charging rate greater than or equal to 2C.

[0564] In this application, unless otherwise specified, the "rate" of a battery has a well-known meaning in the art, which refers to the current value required for the battery to charge to its rated capacity or discharge its rated capacity within a specified time, and the unit is expressed in C. Unless otherwise specified, the "specified time" is 1 hour (h), 1C means that charging and discharging are completed in 1 hour, and 1 / 3C means that charging and discharging are completed in 3 hours. The battery rate reflects the charging and discharging capabilities of the battery under different currents. A high rate means that the battery can charge and discharge quickly in a short time. The higher the rate, the better the fast charging performance.

[0565] In this application, unless otherwise specified, for the rate, "1C" means the current value required to charge the battery from zero to full or from full to empty within 1 hour. For the charging rate, when charging from zero at a rate of 1C, the battery will be fully charged in 1 hour.

[0566] In some embodiments, the application includes a process of charging a lithium ion secondary battery under at least one rate condition of 2C to 6C, that is, the lithium ion secondary battery can provide a charging rate of 2C to 6C.

[0567] In some embodiments, the application includes a process of charging a lithium-ion secondary battery under at least one rate condition of 2C to 4C.

[0568] In some embodiments, the application includes a process of charging a lithium-ion secondary battery under at least one rate condition of 4C to 6C.

[0569] Without limitation, the lithium-ion secondary battery can be charged at any of the following rates, or can be charged at a rate greater than or equal to any of the following rates, or can be charged at a rate within a range consisting of any two of the following rates: 2C, 3C, 4C, 5C, 6C, etc.

[0570] In some embodiments, the lithium-ion secondary battery can provide a charge rate greater than or equal to 2C.

[0571] In some embodiments, the lithium-ion secondary battery can provide a charge rate of 2C to 6C.

[0572] In the present application, “capable of providing a charging rate Cx” means that the battery cell can be charged under the condition of a charging rate Cx; for example, it can be charged to 97% SOC, but is not limited to this SOC state.

[0573] In some embodiments, the maximum charge rate of the lithium ion secondary battery may be greater than or equal to 2C, and may be 2C to 6C, and may be 2C to 4C or 4C to 6C.

[0574] In some embodiments, the maximum charge rate of the lithium-ion secondary battery can be greater than 2C (C max >2C), can be greater than 2C and less than or equal to 6C (2 <C max ≤6C), and can further be greater than 2C and less than or equal to 4C (2 <C max ≤4C) or can be greater than or equal to 4C and less than or equal to 6C (4C≤C max ≤6C).

[0575] Without limitation, the maximum charge rate of the lithium-ion secondary battery may also be any one of the following charge rates or a range consisting of any two of the following charge rates: 2C, 3C, 4C, 5C, 6C, etc.

[0576] In this application, the maximum charge rate (which can be recorded as C) of a lithium-ion secondary battery is max )" has a well-known meaning in the industry and can be obtained by testing using conventional methods in the art. For example, the lithium precipitation window curve can be obtained by testing at different charging rates, and the critical charging rate at which lithium precipitation occurs is used as the test value of the maximum charging rate of the battery. The test parameters can be as follows: the battery to be tested is charged to a voltage of 4.4V at different rates (such as 1C, 2C, 2.5C, 3C, 3.5C, 4C, ...), then charged at a constant voltage to a current of ≤0.05C, left to stand for 5 minutes, and then charged to 4.4V at a constant current of 0.33C, left to stand for 5 minutes, and the battery is disassembled to observe the lithium precipitation of the negative electrode. Exemplarily, a series of parallel samples can be prepared, starting from 1C, and tested at intervals of 0.1C until lithium precipitation occurs at the negative electrode. In order to reduce the amount of samples, a large interval can be selected to determine the range of the maximum charging rate, and then a small interval can be selected to more accurately determine the maximum charging rate. The intervals of the rate can be selected from 1C, 0.5C, 0.2C, and 0.1C, respectively.

[0577] Below, some embodiments of the present application are described. The described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. The embodiments described below are exemplary and are only used to explain the present application, and should not be understood as limitations on the present application and its applications. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in the field without creative work are within the scope of protection of the present application.

[0578] If the techniques or conditions are not specified in the examples, the above description, or the techniques or conditions described in the literature in the field, or the product instructions are used. If the manufacturer of the reagents or instruments is not specified, they are all conventional products that can be obtained commercially, or can be synthesized in a conventional manner from commercially available products.

[0579] In the following specific embodiments, the measured parameters of raw material components may have slight deviations within the range of weighing accuracy unless otherwise specified. For temperature and time parameters, acceptable deviations caused by instrument test accuracy or operation accuracy are allowed.

[0580] In the following examples, room temperature refers to 20°C to 30°C.

[0581] The glass transition temperature of the styrene-butadiene rubber used in the following examples is about 40°C, within the range of 40°C to 50°C.

[0582] In the following examples, unless otherwise specified, the parameters involved can be confirmed by referring to the test methods described above. For example, the percentage of secondary particle-type graphite in the first negative electrode active material and the percentage of secondary particle-type graphite in the negative electrode active material can be confirmed based on the SEM (Sigma 300 scanning electron microscope of ZEISS, Germany) test results; the D v50 can be tested by Malvern 2000 (MasterSizer 2000) laser particle size analyzer; OI values ​​involving the first negative electrode active material and the second negative electrode active material can be obtained by X-ray diffraction (XRD) instrument Bruker-D8 advance test. Carbon coating layer can be tested by transmission electron microscope JEM-F200 combined with EDS (Energy Dispersive Spectrometer, spectrometer). For example, the compaction density of the negative electrode sheet, the comparison of the compaction density of the first negative electrode active layer and the second negative electrode active layer, the comparison of the surface density of the first negative electrode active layer and the second negative electrode active layer (measured on a single side of the negative electrode current collector), the comparison of the porosity of the first negative electrode active layer and the second negative electrode active layer, the porosity of the negative electrode active material layer, the compaction density of the powder of the second negative electrode active material and the first negative electrode active material and the ratio of the compaction density of the two powders, the compaction density of the powder of the second negative electrode active layer and the first negative electrode active layer and the ratio of the compaction density of the two powders, the ratio of the rate of the first negative electrode active layer and the second negative electrode active layer, the comparison of the charge rate of the first negative electrode active layer and the second negative electrode active layer, etc. For example, the ion conductivity test of the electrolyte is carried out using a DDSJ-318 conductivity meter and referring to the HG-T 4067-2015 detection method.

[0583] In the following examples, unless otherwise specified, the alkyl chain is taken as a linear chain. For example, the octadecyl group in octadecyl trimethyl quaternary aminophosphate is a normal octadecyl group.

[0584] Example 1.

[0585] 1. Preparation of positive electrode sheet:

[0586] The positive electrode plate is composed of powder including lithium iron phosphate-based positive electrode active material and a positive electrode current collector.

[0587] The positive electrode active material LFP (lithium iron phosphate, surface coated with soft carbon), the conductive agent carbon black (Super P), and the binder polyvinylidene fluoride (PVDF) were mixed uniformly in a proper amount of solvent N-methylpyrrolidone (NMP) according to a mass ratio of 97.9:0.3:1.8 to obtain a positive electrode slurry with a solid content of 60wt%; according to the coating weight (double-sided) 0.360g / 1540.25mm 2 (about 23.4mg / cm 2 ) The positive electrode slurry is coated on both sides of the positive electrode current collector aluminum foil, and the positive electrode sheet is obtained through drying, cold pressing, slitting, cutting and other processes. The compaction density of the positive electrode sheet is 2.60g / cm 3 .

[0588] The lithium iron phosphate-based positive electrode active material is lithium iron phosphate coated with soft carbon, and the mass proportion of soft carbon in the positive electrode active material is about 1%.

[0589] 2. Preparation of negative electrode sheet:

[0590] The second negative electrode active material, quaternary ammonium salt compound, conductive carbon black (Super P), stabilizer sodium carboxymethyl cellulose (CMC-Na) and binder styrene-butadiene rubber (SBR) are dispersed in deionized water in a mass ratio of 96.0:0.5:0.4:1.1:2.0 to form a second negative electrode slurry (corresponding to the second negative electrode active layer in the lower layer) with a solid content of 50wt%.

[0591] The first negative electrode active material, conductive carbon black (Super P), stabilizer sodium carboxymethyl cellulose and binder SBR are dispersed in deionized water in a mass ratio of 97.3:0.7:1.2:0.8 to form a first negative electrode slurry (corresponding to the first negative electrode active layer on the upper layer), excluding quaternary ammonium salt compounds, and having a solid content of 50wt%.

[0592] The second negative electrode slurry and the first negative electrode slurry are evenly coated on the two side surfaces of the negative electrode current collector copper foil by an extrusion coater (the coating parameters on both sides of the negative electrode current collector are basically the same). The second negative electrode slurry (corresponding to the second negative electrode active layer) is coated first, and then the first negative electrode slurry (corresponding to the first negative electrode active layer) is coated. The coating weight of the upper and lower layers (one side) is controlled to be 0.08g / 1540.25mm 2 and 0.08g / 1540.25mm 2 After drying in an oven, the negative electrode is compacted using a cold press to control the compaction density of the negative electrode to 1.65g / cm 3 The cold pressed electrode sheet is subjected to striping and cutting processes to obtain the negative electrode sheet. Based on the single side of the negative electrode current collector, the surface density of the negative electrode sheet is about 10.4 mg / cm 2 .

[0593] First negative electrode active layer (upper layer): The first negative electrode active material is coated graphite, and further is artificial graphite coated with soft carbon (the mass percentage of soft carbon in the coating layer in the first negative electrode active material is about 2%), D v 50 is 14 μm, the first negative electrode active material includes secondary graphite particles, and the amount of secondary graphite particles in the first negative electrode active material accounts for about 50%; the OI value of the first negative electrode active material is 5.

[0594] Second negative electrode active layer (lower layer): The second negative electrode active material is artificial graphite (without coating layer), D v 50 is 18 μm, the second negative electrode active material includes secondary graphite particles, and the amount of the secondary graphite particles in the second negative electrode active material accounts for about 100%; the OI value of the second negative electrode active material is 12.

[0595] The thickness ratio (f) of the first negative electrode active layer (upper layer) to the second negative electrode active layer (lower layer) in the negative electrode sheet H ) is greater than 1, and f H is in the range of 1.1 to 1.3, and f H is about 1.2. The thickness of the first negative electrode active layer on one side is in the range of 30 μm to 40 μm. At this time, the compaction density of the second negative electrode active layer is higher than that of the first negative electrode active layer.

[0596] 3. Separator: A polypropylene film with a thickness of 12 μm is used as the separator.

[0597] 4. Preparation of electrolyte: Ethylene carbonate (EC) and ethyl methyl carbonate (EMC) are mixed in a mass ratio of 30:70 to obtain an organic solvent. LiPF 6 is dissolved in the above organic solvent, and vinylene carbonate (VC), fluoroethylene carbonate (FEC), and divinyl sulfite (DTD) are added to prepare an electrolyte with a LiPF 6 concentration of 1 mol / L. The electrolyte contains VC with a mass concentration of 2.5 wt%, FEC with a mass concentration of 1 wt%, and DTD with a mass concentration of 0.5 wt%.

[0598] The ionic conductivity of the electrolyte at 25 °C is 15 mS / cm.

[0599] 5. Preparation of secondary battery: The positive electrode sheet, separator, and negative electrode sheet are stacked and wound in sequence to obtain an electrode assembly; the electrode assembly is placed in an outer package, dried, and then injected with electrolyte, and after vacuum packaging, standing, formation, shaping and other processes, a lithium-ion secondary battery is obtained.

[0600] Example 2-4. The negative electrode sheet and the lithium-ion secondary battery are prepared by a method basically the same as that of Example 1, except that: in the step of preparing the negative electrode sheet, the mass ratio of the quaternary ammonium salt-type compound in the second negative electrode active layer is changed, and different negative electrode sheets are used to prepare the lithium-ion secondary battery. See Table 1 for details.

[0601] Examples 5-8. The negative electrode sheet and the lithium-ion secondary battery are prepared by a method basically the same as that of Example 1, except that: in the step of preparing the negative electrode sheet, the types of the quaternary ammonium salt-type compounds are changed, and different negative electrode sheets are used to prepare the lithium-ion secondary battery. See Table 1 for details. The quaternary ammonium salt-type compounds in Examples 5-8 are octadecyltrimethylammonium phosphate, dodecyltrimethylammonium nitrate, dodecyltrimethylammonium carbonate, and dodecyltrimethylammonium bicarbonate, respectively.

[0602] Examples 9-10. Negative electrode sheets and lithium-ion secondary batteries were prepared by the same method as in Example 1, except that the composition of the electrolyte was changed in the step of preparing the electrolyte, and different electrolytes were used to prepare lithium-ion secondary batteries. See Table 1.

[0603] Example 9 uses lithium hexafluorophosphate (LiPF 6 ) and lithium bis(fluorosulfonyl)imide (LiFSI), the molar volume concentrations in the electrolyte were 1 mol / L and 0.1 mol / L, respectively; the type of solvent, the type of additive and the amount used were the same as those in Example 1.

[0604] In Example 10, the type of solvent is changed, and the solvent is ethylene carbonate (EC), dimethyl carbonate (DMC) and ethyl methyl carbonate (EMC) in a volume ratio of 1:2:1; the type and amount of the electrolyte lithium salt, the type and amount of the additive are the same as in Example 1.

[0605] The 25°C ionic conductivity of the electrolytes of Examples 9-10 is all within the range of 16 mS / cm to 18 mS / cm.

[0606] Example 11-12. A negative electrode sheet and a lithium-ion secondary battery are prepared by a method substantially the same as that of Example 1, except that in the step of preparing the negative electrode sheet, the thickness ratio of the first negative electrode active layer to the second negative electrode active layer is changed, that is, the thickness ratio of the first negative electrode active layer to the second negative electrode active layer is changed (f H ), the sum of the coating surface density on both sides of the negative electrode sheet is substantially the same as that in Example 1; lithium-ion secondary batteries are prepared using different negative electrode sheets. See Table 1.

[0607] Example 13-14. A negative electrode sheet and a lithium-ion secondary battery were prepared by the same method as in Example 1, except that in the step of preparing the negative electrode sheet, the type of the second negative electrode active material was changed, and the coating weight of the first negative electrode slurry and the second negative electrode slurry was changed by adjusting the coating weight of the first negative electrode slurry and the second negative electrode slurry. H The sum of the coating surface densities on both sides of the negative electrode sheet is substantially the same as that in Example 1; different negative electrode sheets are used to prepare lithium-ion secondary batteries. Please refer to Table 1.

[0608] In Example 13, the second negative electrode active material is a combination of artificial graphite and soft carbon in a mass ratio of 1:5%, and the mass proportion of the second negative electrode active material in the second negative electrode active layer is kept the same as that in Example 1.

[0609] In Example 14, the second negative electrode active material is a combination of artificial graphite and hard carbon in a mass ratio of 1:5%, and the mass proportion of the second negative electrode active material in the second negative electrode active layer is kept the same as that in Example 1.

[0610] Example 15. A negative electrode sheet and a lithium-ion secondary battery are prepared by a method substantially the same as that of Example 1, except that: in the step of preparing the negative electrode sheet, D of the first negative electrode active material v 50 is 12 μm, and the D of the second negative electrode active material v 50 is 20 μm; the coating surface density ratio is adjusted so that the thickness ratio of the first negative electrode active layer to the second negative electrode active layer is substantially the same as that in Example 1; different negative electrode sheets are used to prepare lithium ion secondary batteries. Please refer to Table 1.

[0611] Example 16. A negative electrode sheet and a lithium-ion secondary battery are prepared by the same method as in Example 1, except that in the step of preparing the positive electrode sheet, the type of positive electrode active material is changed to a ternary positive electrode material NCM811 (LiNi 0.8 Co 0.1 Mn 0.1 O 2 ), using different positive electrode sheets to prepare lithium-ion secondary batteries. See Table 1.

[0612] Example 17. A negative electrode sheet is prepared by a method substantially the same as that of Example 1, except that the negative electrode active material layer of the negative electrode sheet adopts a single-layer structure, and a lithium-ion secondary battery is prepared using a different negative electrode sheet. In this example, the negative electrode sheet is prepared by the following method:

[0613] The negative electrode active material, quaternary ammonium salt compound, conductive carbon black (Super P), stabilizer sodium carboxymethyl cellulose (CMC-Na) and binder styrene-butadiene rubber (SBR) are dispersed in deionized water in a mass ratio of 96.0:0.5:0.4:1.1:2.0 to form a negative electrode slurry with a solid content of 50wt%.

[0614] The negative electrode slurry is evenly coated on both sides of the negative electrode current collector copper foil by an extrusion coater (the coating parameters on both sides of the negative electrode current collector are basically the same), and the coating weight on one side of the negative electrode current collector is 0.16g / 1540.25mm 2 After drying in an oven, the negative electrode is compacted using a cold press to control the compaction density of the negative electrode to 1.65g / cm 3 The cold pressed electrode sheet is subjected to striping and cutting processes to obtain the negative electrode sheet. Based on the single side of the negative electrode current collector, the surface density of the negative electrode sheet is about 10.4 mg / cm 2 .

[0615] The negative electrode active material is artificial graphite coated with soft carbon (the mass percentage of soft carbon in the coating layer in the first negative electrode active material is 2%), D v50 is 14 μm, the first negative electrode active material includes secondary graphite particles, and the amount of secondary graphite particles in the first negative electrode active material accounts for about 50%; the OI value of the first negative electrode active material is 5.

[0616] Comparative Example 1: The second negative electrode active layer does not contain a quaternary ammonium salt compound.

[0617] The negative electrode sheet and the lithium ion secondary battery were prepared by the method basically the same as that in Example 1, except that: in the step of preparing the negative electrode sheet, the second negative electrode slurry omitted the quaternary ammonium salt compound, the mass ratio of the second negative electrode active material, the conductive agent, the stabilizer and the binder was the same as that in Example 1, and the remaining operation steps were the same as those in Example 1; different negative electrode sheets were used to prepare the lithium ion secondary battery. The sum of the double-sided coating surface density of the negative electrode sheet was the same as that in Example 1.

[0618] Comparative Example 2: The second negative electrode active layer does not include a quaternary ammonium salt compound.

[0619] The negative electrode sheet and the lithium-ion secondary battery were prepared by the method basically the same as that in Example 1, except that: in the step of preparing the negative electrode sheet, the second negative electrode slurry was replaced by the first negative electrode slurry (that is, the second negative electrode active layer was not provided with a quaternary ammonium salt compound), and the remaining operation steps were the same as those in Example 1; different negative electrode sheets were used to prepare the lithium-ion secondary battery. The sum of the coating surface densities on both sides of the negative electrode sheet was the same as that in Example 1.

[0620] Comparative Example 3: The second negative electrode active layer does not include a quaternary ammonium salt compound.

[0621] The negative electrode sheet and the lithium ion secondary battery were prepared by the method basically the same as that in Example 16, except that: in the step of preparing the negative electrode sheet, the second negative electrode slurry omitted the quaternary ammonium salt compound, the mass ratio of the second negative electrode active material, the conductive agent, the stabilizer and the binder was the same as that in Example 16, and the remaining operation steps were the same as those in Example 16; different negative electrode sheets were used to prepare the lithium ion secondary battery. The sum of the double-sided coating surface density of the negative electrode sheet was the same as that in Example 16.

[0622] Comparative Example 4: The second negative electrode active layer does not include a quaternary ammonium salt compound.

[0623] The negative electrode sheet and the lithium ion secondary battery were prepared by the method basically the same as that in Example 16, except that: in the step of preparing the negative electrode sheet, the second negative electrode slurry was replaced by the first negative electrode slurry (that is, the second negative electrode active layer was not provided with a quaternary ammonium salt compound), and the remaining operation steps were the same as those in Example 16; different negative electrode sheets were used to prepare the lithium ion secondary battery. The sum of the double-sided coating surface densities of the negative electrode sheet was the same as that in Example 16.

[0624] Comparative Example 5. A negative electrode sheet and a lithium-ion secondary battery were prepared by a method substantially the same as that in Example 17, except that: in the step of preparing the negative electrode sheet, the negative electrode slurry omitted the quaternary ammonium salt compound, the mass ratio of the negative electrode active material, the conductive agent, the stabilizer and the binder was the same as that in Example 17, and the remaining operation steps were the same as those in Example 17; different negative electrode sheets were used to prepare lithium-ion secondary batteries. The sum of the double-sided coating surface densities of the negative electrode sheet was the same as that in Example 17.

[0625] The porosity of the first negative electrode active layer in Examples 1-16 is higher than the porosity of the second negative electrode active layer. The porosity of the negative electrode sheets in Examples 1-17 is in the range of 15% to 35%. Taking Example 1 and Example 17 as examples, the porosity of the negative electrode sheet in Example 1 is about 25%, and the porosity of the negative electrode sheet in Example 1 is about 22%.

[0626] The powder compaction density of the second negative electrode active material in Examples 1-16 is higher than that of the first negative electrode active material. The powder compaction density of the second negative electrode active material is 1.85 g / cm 3 ~2.05g / cm 3 In the range, the ratio of the powder compaction density of the second negative electrode active material to the powder compaction density of the first negative electrode active material is in the range of 1.05 to 1.35. Taking Example 1 as an example, the powder compaction density of the second negative electrode active material is about 1.9 g / cm 3 In the range, the powder compaction density of the first negative electrode active material is about 1.7 g / cm 3 within the range.

[0627] Table 1.

[0628]

[0629]

[0630] Test Methods and Analysis

[0631] (I) Negative electrode performance test

[0632] Liquid absorption rate test

[0633] Disassemble the battery cell, take the negative electrode plate, soak and clean it with solvent dimethyl carbonate (DMC), scrape the powder from the second negative electrode active layer close to the negative electrode current collector, and obtain a powder sample of the second negative electrode material. Use deionized water to resuspend the second negative electrode material into a uniform slurry, which is recorded as the second resuspended slurry. Apply the second resuspended slurry to one side of the negative electrode current collector copper foil, dry it, and cold press it to obtain the second active layer plate. The following method is used to test the liquid absorption rate: fix the plate to be tested on the sample table, drip the electrolyte E30 (commercially available), and use a stopwatch to time; record the weight increase and time; calculate the liquid absorption rate of the plate by the change in weight over time. The measured liquid absorption rate can be recorded as the "liquid absorption rate of the second negative electrode active layer".

[0634] (II) Battery performance test

[0635] 1. Battery energy density

[0636] At 25°C, the battery to be tested was charged to 3.8V at a constant current and constant voltage of 0.33C, with a cut-off current of 0.05C. After standing for 30 minutes, it was discharged at 0.33C to the designed 2.0V, and the discharge energy P was recorded. X (Wh), record the cell volume as V X (unit is liter (L)), then the energy density of the battery (Wh / L) = P X / V X .

[0637] 2. Fast charging capability test

[0638] The lithium-ion secondary battery to be tested is placed at room temperature of 25°C, and charged to 3.8V with a constant current of 0.33C, then charged to a current of 0.05C at a constant voltage, left for 5 minutes, and then discharged to 2.0V with a constant current of 0.33C, and the constant current discharge capacity is recorded as the initial capacity C0. The battery is charged to a full battery potential of 3.8V or a negative electrode cutoff potential of 0mV at a constant current of 0.5C0, 1C0, 1.5C0, 2C0, 2.0C0, 3C0, and 3.5C0 in sequence (reaching any of these conditions indicates that charging is completed), and discharged to 2.0V at 0.33C0 after each charge is completed. At every interval of 10% SOC, the corresponding negative electrode potential at different charging rates is recorded, and the rate-negative electrode potential curve at different SOCs is plotted. After linear fitting, the corresponding charging rate when the negative electrode potential is 0mV at different SOCs is obtained, which is recorded as Cx (x=2~8). According to the formula (1 / C2+1 / C3+1 / C4+1 / C5+1 / C6+1 / C7+1 / C8)×0.1×60, the charging time t of the lithium-ion secondary battery from 10% SOC to 80% SOC is calculated. c (min).

[0639] The test results can be found in “Charging time t from 10% SOC to 80% SOC”. c ”.

[0640] The shorter the time t0 is, the better the fast charging performance of the battery is.

[0641] SOC (State of Charge) indicates the state of charge. When "SOC=0", it means that the battery is fully discharged, and when "SOC=100%", it means that the battery is fully charged.

[0642] 3. Fast charging cycle performance test

[0643] Place the battery cell in a three-piece steel plate fixture with a pressure sensor. The initial pressure of the fixture is 3000N.

[0644] At 25°C, the battery to be tested is charged at a constant current of 0.33C to a charging cut-off voltage of 3.8V, then charged at a constant voltage to a current of 0.05C, left to stand for 5 minutes, and then discharged at a constant current of 0.33C to a discharge cut-off voltage of 2.0V, and its initial capacity is recorded as C0. Then the battery cell is charged to 10% SOC at 0.33C0, and the 10% SOC-80% SOC interval is charged according to the fast charging strategy of the "Fast Charging Capacity Test" as above, and then charged to a cut-off voltage of 4.25V at 0.33C0, and then charged at a constant voltage to a current of 0.05C, left to stand for 5 minutes, and then discharged at 0.33C0, and the discharge capacity Cn of each cycle is recorded until 1000 cycles, and the cycle capacity retention rate (i.e. C1000 / C1×100%) is calculated.

[0645] For the test results, please refer to “Capacity retention after 1000 cycles of fast charging at 25°C”.

[0646] The higher the cycle retention rate, the better the fast charging cycle life.

[0647] 4. Rate performance

[0648] The first negative electrode slurry and the second negative electrode slurry corresponding to each embodiment and comparative example were respectively coated on the single-side surface of the copper foil current collector and dried in an oven for later use.

[0649] A metal lithium plate was used as a counter electrode, a polypropylene (PP) film was used as a separator, ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) were mixed in a volume ratio of 1:1:1 to obtain a mixed solvent, and then LiPF 6 is uniformly dissolved in the above-mentioned mixed solvent to obtain an electrolyte solution, wherein the concentration of LiPF 6 The concentration is 1 mol / L.

[0650] All components were assembled into a CR2430 button cell in an argon-protected glove box. "CR" represents the international IEC code for button-type lithium manganese batteries, with a diameter of 24 mm and a thickness of 30 mm.

[0651] After standing for 12 hours, the obtained button battery was discharged at a constant current of 0.05C to 0.005V, and then discharged at a constant current of 10μA to 0.005V. Then it was left to stand for 5 minutes, and the obtained button battery was charged to 2V at a constant current of 0.1C, and then stood for 5 minutes, and the charging capacity C0 was recorded. The battery was placed at a constant temperature of 25℃ for 2h, and the charge and discharge tests were carried out at 1C0, 2C0, 3C0, 4C0, and 5C0 rates to obtain the capacity retention rate. At the same rate, the higher the capacity retention rate, the better the rate performance.

[0652] 5. "Maximum charging rate" of lithium-ion secondary batteries

[0653] A series of parallel samples of the battery to be tested are tested at different charging rates to obtain the lithium precipitation window curve, and the critical charging rate at which lithium precipitation occurs is used as the test value of the maximum charging rate of the battery. The test parameters are as follows: the battery to be tested is charged at a target rate (such as 1C, 2C, 2.5C, 3C, 3.5C, 4C, ...) at a constant current to a voltage of 3.8V, then charged at a constant voltage to a current ≤ 0.05C, left to stand for 5 minutes, and then charged at a constant current of 0.33C to 3.8V, left to stand for 5 minutes, and the battery is disassembled to observe the lithium precipitation of the negative electrode. In order to reduce the amount of samples, a large interval rate condition is first selected to determine the range of the maximum charging rate, and then a small interval rate condition is selected to more accurately determine the maximum charging rate. The interval of the rate can be reduced in turn according to the accuracy requirements, for example, one or more intervals of 1C, 0.5C, 0.2C, and 0.1C can be selected.

[0654] In the tests of Examples 1-17 and Comparative Examples 1-4, the selected rate intervals are 1C, 0.5C, 0.2C, and 0.1C, respectively.

[0655] Some test results on battery performance can be found in Table 2-3.

[0656] Test results and analysis

[0657] According to the test results of the liquid absorption rate, after introducing the quaternary ammonium salt compound into the second negative electrode active layer, the liquid absorption rate of the second negative electrode active layer in Examples 1-17 is significantly improved compared with Comparative Examples 1-4, and the electrolyte wettability of the second negative electrode active layer is significantly improved.

[0658] The lithium ion secondary batteries of Examples 1-17 are all provided with a quaternary ammonium salt compound in the second negative electrode active layer. The fast charging performance of Examples 1-15 relative to Comparative Examples 1-2, Example 16 relative to Comparative Examples 3-4, and Example 17 relative to Comparative Example 5 are all significantly improved, and the charging time t from 10% SOC to 80% SOC is c Significantly shortened.

[0659] The maximum charge rates of the lithium ion secondary batteries of Examples 1-17 are all higher than 2C. Taking Example 1 as an example, the maximum charge rate of the lithium ion secondary battery of Example 1 is 2.8C. The maximum charge rates of Examples 1-17 are in the range of 2.4C to 3.3C. The maximum charge rates of Comparative Examples 1-5 are in the range of 1.7C to 2.0C.

[0660] According to the "rate performance" test, the rate performance of the CR2430 button cells assembled with the first negative electrode slurries of Examples 1 to 17 is higher than that of the CR2430 button cells assembled with the first negative electrode slurries of Comparative Examples 1 to 4. After the quaternary ammonium salt compound is introduced into the second negative electrode active layer, the rate performance of the second negative electrode active layer is improved.

[0661] In addition, in Examples 1-16, the ratio of the first negative electrode active layer is higher than that of the second negative electrode active layer.

[0662] The cycle performance of Examples 1-15 relative to Comparative Examples 1-2, Example 16 relative to Comparative Examples 3-4, and Example 17 relative to Comparative Example 5 are also improved.

[0663] The lithium ion secondary batteries of Examples 1-17 also have a relatively high energy density. Some test results can be found in Table 3.

[0664] Table 2.

[0665]

[0666]

[0667] Table 3.

[0668]

[0669] The description of each embodiment and example above tends to emphasize the differences between each embodiment and example, and the same or similar parts can be referenced to each other. For the sake of brevity, this article will not repeat them. The technical features of the above-described embodiments and examples can be combined arbitrarily. For the sake of brevity, all possible combinations of the technical features in the above-described embodiments are not described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0670] It should be noted that the present application is not limited to the above-mentioned embodiments and examples. The above-mentioned embodiments and examples are only examples. Within the scope of the technical solution of the present application, the embodiments and examples that have the same structure as the technical idea and play the same effect are all included in the technical scope of the present application. The above-described embodiments and examples only express several embodiments and examples of the present application, and the description is relatively detailed, but it cannot be understood as a limitation on the scope of the patent. In addition, without departing from the scope of the subject matter of the present application, various modifications that can be thought of by a person skilled in the art to the embodiments or examples, and other methods of combining some of the constituent elements in the embodiments or examples are also included in the scope of the present application.

Claims

1. A lithium ion secondary battery, characterized in that: The invention comprises a negative electrode plate and an electrolyte; the negative electrode plate comprises a negative electrode current collector and a second negative electrode active layer and a first negative electrode active layer sequentially arranged on at least one side of the negative electrode current collector, wherein the second negative electrode active layer is located between the negative electrode current collector and the first negative electrode active layer; The second negative electrode active layer includes a second negative electrode active material and a quaternary ammonium salt compound, wherein the second negative electrode active material includes a carbon-based material, and the quaternary ammonium salt compound includes a quaternary ammonium cation.

2. The lithium ion secondary battery according to claim 1, characterized in that: The quaternary ammonium salt compound further includes a hydrocarbon chain covalently bonded to the quaternary ammonium cation.

3. The lithium ion secondary battery according to claim 2, characterized in that: The hydrocarbyl chain in the quaternary ammonium salt type compound includes an alkyl chain.

4. The lithium ion secondary battery according to claim 2 or 3, characterized in that: The quaternary ammonium salt compound satisfies one or more of the following characteristics: (ta1) the hydrocarbon chain is an alkyl chain; (ta2) the number of carbon atoms in the hydrocarbon chain is 12 to 18; (ta3) The molecular weight of the quaternary ammonium salt compound is less than or equal to 600Da.

5. The lithium ion secondary battery according to any one of claims 2 to 4, characterized in that The quaternary ammonium salt compound satisfies one or more of the following characteristics: (tb1) The structure of the quaternary ammonium cation is -N + (R1R2R3), wherein R1 and R2 are each independently C 1-3 Alkyl, R3 is C 1-3 Alkyl or hydroxyethyl; optionally, R1 and R2 are each independently methyl, and R3 is methyl or hydroxyethyl; (tb2) The quaternary ammonium salt compound also includes anions, and the anions include one or more of nitrate, carbonate, bicarbonate and phosphate.

6. The lithium ion secondary battery according to claim 1, characterized in that: The quaternary ammonium salt compound includes one or more of octadecyl dimethyl hydroxyethyl quaternary ammonium nitrate, N,N-dimethyl-N-(2-hydroxyethyl) hexadecyl quaternary ammonium phosphate, octadecyl trimethyl quaternary ammonium phosphate, dodecyl trimethyl quaternary ammonium phosphate, dodecyl trimethyl quaternary ammonium nitrate, dodecyl trimethyl quaternary ammonium carbonate, and dodecyl trimethyl quaternary ammonium hydrogen carbonate.

7. The lithium ion secondary battery according to any one of claims 1 to 6, characterized in that The mass percentage of the quaternary ammonium salt compound in the second negative electrode active layer is 0.2% to 2%.

8. The lithium ion secondary battery according to claim 7, characterized in that: The mass percentage of the quaternary ammonium salt compound in the second negative electrode active layer is 0.2% to 1.5%.

9. The lithium ion secondary battery according to any one of claims 1 to 8, characterized in that The mass proportion of the carbon-based material in the second negative electrode active material is 80% to 100%.

10. The lithium ion secondary battery according to any one of claims 1 to 9, characterized in that The negative electrode plate meets one or more of the following characteristics: (tc1) the carbon-based material comprises one or more of artificial graphite, natural graphite, soft carbon and hard carbon; (tc2) The mass proportion of the carbon-based material in the second negative electrode active layer is 94.5% to 97.5%.

11. The lithium ion secondary battery according to claim 9 or 10, characterized in that: The mass proportion of the carbon-based material in the second negative electrode active layer is 95.0% to 97.0%.

12. The lithium ion secondary battery according to any one of claims 1 to 11, characterized in that: The second negative electrode active layer includes a binder, and the binder includes styrene-butadiene rubber.

13. The lithium ion secondary battery according to claim 12, characterized in that: The glass transition temperature of the styrene-butadiene rubber is 5°C to 70°C, and can be optionally 30°C to 50°C.

14. The lithium ion secondary battery according to any one of claims 1 to 13, characterized in that: The first negative electrode active layer includes a first negative electrode active material, which includes a negative electrode active body and a coating layer located at at least a portion of the surface of the negative electrode active body, wherein the coating layer includes one or more of soft carbon, hard carbon and amorphous carbon.

15. The lithium ion secondary battery according to any one of claims 1 to 14, characterized in that: The first negative electrode active layer includes a first negative electrode active material; The lithium-ion secondary battery meets one or more of the following characteristics: (td1) the first negative electrode active material includes coated graphite, the coated graphite includes a graphite body and a coating layer located on at least a portion of a surface of the graphite body, the coating layer includes one or more of soft carbon, hard carbon and amorphous carbon; (td2) the first negative electrode active material includes secondary particulate graphite, the secondary particulate graphite includes a secondary particulate graphite body, the amount of the secondary particulate graphite in the first negative electrode active material is greater than or equal to 20%, and can be optionally 30% to 80%; optionally, the secondary particulate graphite includes carbon-coated secondary particulate graphite, the carbon-coated secondary particulate graphite includes the secondary particulate graphite body and a carbon coating layer located on at least a portion of the surface of the secondary particulate graphite body, and the carbon coating layer in the carbon-coated secondary particulate graphite includes one or more of soft carbon, hard carbon and amorphous carbon; (td3) the first negative electrode active material includes a graphite material, and the OI value of the graphite material is 2 to 15, and can be optionally 2 to 10; (td4) D of the first negative electrode active material v 50 is 10μm~18μm, and can be 12μm~16μm; (td5) the porosity of the first negative electrode active layer is higher than the porosity of the second negative electrode active layer; (td6) The powder compaction density of the first negative electrode active material or the powder compaction density of the first negative electrode active layer is 1.60 g / cm 3 ~1.80g / cm 3 ; (td7) the charge rate of the first negative electrode active layer is higher than the charge rate of the second negative electrode active layer; optionally, the charge rate of the first negative electrode active layer is higher than the charge rate of the second negative electrode active layer; (td8) Under at least one temperature condition between 20°C and 35°C, the ionic conductivity of the electrolyte is 13mS / cm to 18mS / cm; optionally, at 25°C, the ionic conductivity of the electrolyte is 13mS / cm to 18mS / cm.

16. The lithium ion secondary battery according to any one of claims 1 to 15, characterized in that: The negative electrode plate meets one or more of the following characteristics: (te1) D of the second negative electrode active material v 50 is 12μm~21μm, and can be selected as 14μm~20μm; (te2) The first negative electrode active layer includes a first negative electrode active material, and the second negative electrode active material D v 50 higher than the D of the first negative electrode active material v 50; (te3) the compaction density of the second negative electrode active layer is higher than the compaction density of the first negative electrode active layer; (te4) the powder compaction density of the second negative electrode active material is higher than the powder compaction density of the first negative electrode active material, or 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; optionally, the ratio of the powder compaction density of the second negative electrode active material to the powder compaction density of the first negative electrode active material is 1.05 to 1.35, further optionally 1.10 to 1.30, and further optionally 1.10 to 1.28; optionally, the ratio of the powder compaction density of the second negative electrode active layer to the powder compaction density of the first negative electrode active layer is 1.05 to 1.35, further optionally 1.10 to 1.30, and further optionally 1.10 to 1.28; (te5) The powder compaction density of the second negative electrode active material or the powder compaction density of the second negative electrode active layer is 1.85 g / cm 3 ~2.05g / cm 3 .

17. The lithium ion secondary battery according to any one of claims 1 to 16, characterized in that: The negative electrode plate meets one or more of the following characteristics: (tf1) based on one side of the negative electrode current collector, the ratio of the surface density of the second negative electrode active layer to the surface density of the first negative electrode active layer is 3:2 to 2:3; (tf2) The thickness ratio of the first negative electrode active layer to the second negative electrode active layer on one side of the negative electrode current collector is denoted as f H , satisfying f H ≤1.6, optionally, 1.1≤f H ≤1.6, further optionally, 1.1≤f H ≤1.3; (tf3) Based on a single side of the negative electrode current collector, the thickness of the first negative electrode active layer is less than or equal to 50 μm, and may be 20 μm to 50 μm, and may be 30 μm to 40 μm.

18. A lithium ion secondary battery, characterized in that: It includes a negative electrode plate and an electrolyte; the negative electrode plate includes a negative electrode current collector and a negative electrode active material layer located on at least one side of the negative electrode current collector; The negative electrode active material layer includes a negative electrode active material and a quaternary ammonium salt compound, the negative electrode active material includes a negative electrode active body and a coating layer located at least a portion of the surface of the negative electrode active body, the coating layer includes one or more of soft carbon, hard carbon and amorphous carbon, and the quaternary ammonium salt compound includes a quaternary ammonium cation.

19. The lithium ion secondary battery according to claim 18, characterized in that: The negative electrode plate meets one or more of the following characteristics: (tg1) the quaternary ammonium salt compound as defined in any one of claims 2 to 6; (tg2) the mass proportion of the quaternary ammonium salt compound in the negative electrode active material layer is 0.2% to 2%, and can be 0.2% to 1.5%; (tg3) the negative electrode active material comprises a carbon-based material; optionally, the carbon-based material comprises one or more of artificial graphite, natural graphite, soft carbon and hard carbon; (tg4) the negative electrode active material includes a carbon-based material, and the mass proportion of the carbon-based material in the negative electrode active material layer is 94.5% to 97.5%, and can be 95.0% to 97.0%; (tg5) the negative electrode active material layer includes a binder, and the binder includes styrene-butadiene rubber; optionally, the styrene-butadiene rubber has a glass transition temperature of 5° C. to 70° C., and further optionally 30° C. to 50° C.; (tg6) the negative electrode active material includes coated graphite, the coated graphite includes a graphite body and a coating layer located on at least a portion of the surface of the graphite body, the coating layer includes one or more of soft carbon, hard carbon and amorphous carbon; (tg7) The negative electrode active material includes secondary particle-type graphite, the secondary particle-type graphite includes a secondary particle-type graphite body, the amount of the secondary particle-type graphite in the negative electrode active material is greater than or equal to 20%, and can be optionally 30% to 60%; optionally, the secondary particle-type graphite includes carbon-coated secondary particle-type graphite, the carbon-coated secondary particle-type graphite includes the secondary particle-type graphite body and a carbon coating layer located at least a portion of the surface of the secondary particle-type graphite body, and the carbon coating layer in the carbon-coated secondary particle-type graphite includes one or more of soft carbon, hard carbon and amorphous carbon; (tg8) The negative electrode active material includes a graphite material, and the OI value of the graphite material is 2 to 15, and can be optionally 2 to 10; (tg9) D of the negative electrode active material v 50 is 11μm~20μm, and can be selected as 13μm~18μm; (tg10) The porosity of the negative electrode active material layer is 15% to 35%, and can be 25% to 30%; (tg11) at least one temperature condition between 20°C and 35°C, the ionic conductivity of the electrolyte is 13mS / cm to 18mS / cm; optionally, at 25°C, the ionic conductivity of the electrolyte is 13mS / cm to 18mS / cm; (tg12) The negative electrode active material layer includes a second negative electrode active layer, and the second negative electrode active layer is defined in any one of claims 1 to 13 and 16.

20. The lithium ion secondary battery according to any one of claims 1 to 19, characterized in that The surface density of the negative electrode sheet is 5 mg / cm 2 ~15mg / cm 2 .

21. The lithium ion secondary battery according to any one of claims 1 to 20, characterized in that: The electrolyte solution includes an electrolyte salt, and the electrolyte salt includes an electrolyte anion; The electrolyte anion includes one or more of tetrafluoroborate, hexafluoroarsenate, hexafluorophosphate, trifluoromethanesulfonate, difluorophosphate, difluorooxalatoborate, tetrafluorooxalatophosphate, difluorobisoxalatophosphate, bisfluorosulfonimide and bistrifluoromethanesulfonimide.

22. The lithium ion secondary battery according to claim 21, characterized in that: The electrolyte salt includes one or more of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bisfluorosulfonyl imide, lithium bistrifluoromethanesulfonyl imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalatoborate, lithium dioxalatoborate, lithium difluorobisoxalatophosphate and lithium tetrafluorooxalatophosphate.

23. The lithium ion secondary battery according to any one of claims 1 to 22, characterized in that: The lithium-ion secondary battery further comprises a positive electrode sheet, the positive electrode sheet comprises a positive electrode active layer, the positive electrode active layer comprises a positive electrode active material, and the positive electrode active material comprises one or more of a lithium-containing phosphate active material and a lithium composite metal oxide active material.

24. The lithium ion secondary battery according to claim 23, characterized in that: The positive electrode active material includes a lithium-containing phosphate active material, and the positive electrode active material satisfies one or more of the following characteristics: (th1) the mass proportion of the lithium-phosphate active material in the positive electrode active layer is greater than or equal to 80%, and can be 80% to 97%; (th2) the lithium phosphate active material includes one or more of lithium iron phosphate, a composite material of lithium iron phosphate and carbon, lithium manganese phosphate, a composite material of lithium manganese phosphate and carbon, lithium iron manganese phosphate, and a composite material of lithium iron manganese phosphate and carbon; (th3) The lithium phosphate active material includes a lithium phosphate active body and a carbon coating layer located on at least a portion of the surface of the lithium phosphate active body, and the carbon coating layer in the lithium phosphate active material includes one or more of soft carbon, hard carbon and amorphous carbon.

25. An electrical device, characterized in that: A lithium ion secondary battery comprising the lithium ion secondary battery according to any one of claims 1 to 24.

26. Use of the lithium ion secondary battery according to any one of claims 1 to 24 in supplying and / or storing electric energy; The application includes a process of charging the lithium-ion secondary battery at a rate higher than or equal to 2C.

27. The use according to claim 26, characterized in that The application includes a process of charging the lithium-ion secondary battery under at least one rate condition of 2C to 6C; Optionally, the application includes a process of charging the lithium-ion secondary battery under at least one rate condition of 2C to 4C or 4C to 6C; Optionally, the maximum charging rate of the lithium-ion secondary battery is greater than or equal to 2C, and may be 2C to 6C, and may be further 2C to 4C or 4C to 6C.

Images