Lithium-ion secondary battery, electric device, and application

Abstract

The present application relates to a lithium ion secondary battery, an electric device, and an application. The lithium ion secondary battery of some embodiments includes a negative electrode sheet; the negative electrode sheet includes a negative electrode current collector and, sequentially arranged on at least one side of the negative electrode current collector, a second negative electrode active layer and a first negative electrode active layer, 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 includes a second negative electrode active material and a quaternary ammonium salt type compound, the quaternary ammonium salt type compound including a quaternary ammonium cation. The second negative electrode active material can include a carbon-based material. The lithium ion secondary battery has significantly improved fast charging performance.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of lithium ion secondary batteries, and further relates to a lithium ion secondary battery, a power utilization device and application. BACKGROUND

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

[0003] With the development of lithium ion secondary battery technology, lithium ion batteries are increasingly widely used in electric tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, aerospace and other fields, and are also widely used in hydropower, thermal power, wind power and solar power station energy storage power systems. The demand for fast charging performance of lithium ion secondary batteries is also increasing. SUMMARY

[0004] According to various embodiments and various examples of the present application, the present application provides a lithium ion secondary battery, a power utilization device and 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, which has a quaternary ammonium salt type compound arranged in the negative electrode active material layer of the negative electrode sheet.

[0006] In some embodiments, a lithium ion secondary battery is provided, which includes a negative electrode sheet and an electrolyte; the negative electrode sheet includes a negative electrode current collector and a second negative electrode active layer and a first negative electrode active layer arranged in sequence on at least one side of the negative electrode current collector, 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 type compound, the second negative electrode active material includes a carbon-based material, and the quaternary ammonium salt type compound includes a quaternary ammonium cation.

[0008] In the lithium ion secondary battery, the first negative electrode active layer located in the upper layer and the second negative electrode active layer located in the lower layer (with the direction away from the surface of the negative electrode current collector as upward and the direction toward the surface of the negative electrode current collector as downward) can be arranged in the negative electrode active material layer in the negative electrode sheet, and the quaternary ammonium salt type compound is further arranged in the second negative electrode active layer located in the lower layer. The quaternary ammonium salt type compound includes a hydrophilic and positively charged quaternary ammonium cation, which can attract the electrolyte anions in the electrolyte by using the electrostatic action based on the quaternary ammonium cation for the negative electrode sheet soaked in the electrolyte, promote the rapid dissociation of the electrolyte lithium salt in the electrolyte, and significantly improve the electrolyte wetting property of the second negative electrode active layer and the kinetics of the negative electrode sheet. In turn, the fast charging performance of the battery can be significantly improved.

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

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

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

[0012] In some embodiments, the hydrocarbon chain in the quaternary ammonium salt type compound comprises an alkyl chain.

[0013] By providing a hydrocarbon chain in the quaternary ammonium salt type compound, for example, the hydrocarbon chain can comprise an alkyl chain, the chain structure of the hydrocarbon chain is conducive to better and more stable loading and wrapping of the quaternary ammonium salt type compound on the surface of the second negative active material, and the carbon-carbon skeleton provided by the hydrocarbon chain is conducive to better and more stable adsorption of the quaternary ammonium salt type compound on the surface of the carbon-based material (the carbon-based material has a certain lipophilicity), and further combined with the electrostatic attraction of the quaternary ammonium group in the quaternary ammonium salt type compound, it is conducive to guiding the lithium ions in the electrolyte to be guided to the surface of the second negative active material more quickly, and is conducive to further improving the negative electrode sheet kinetics and the battery fast charging performance.

[0014] In some embodiments, the quaternary ammonium salt type 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 12-18;

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

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

[0019] By controlling the number of carbon atoms in the hydrocarbon group chain of the quaternary ammonium salt type compound and / or the molecular weight of the quaternary ammonium salt type compound within the aforementioned ranges, the length of the hydrocarbon group chain can be adjusted within a more suitable range, on the one hand, it is beneficial to make the quaternary ammonium salt type compound better and more stably wrapped on the surface of the second negative electrode active material, and it is beneficial to inhibit the quaternary ammonium salt type compound from falling off the surface of the second negative electrode active material during the charging and discharging process, further combined with the quaternary ammonium group exposed to the electrolyte, it can promote the lithium ions in the electrolyte to be more quickly and stably guided to the surface of the second negative electrode active material, improve the transmission rate of lithium ions inside the negative electrode sheet, and on the other hand, it can also better control the wrapping degree of the hydrocarbon group chain on the surface of the second negative electrode active material, so that the active sites on the surface of the second negative electrode active material can better contact the electrolyte, thereby, it is beneficial to better improve the negative electrode sheet kinetics and the battery fast charging performance.

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

[0021] (tb1) the structure of the quaternary ammonium group cation is -N + (R1R2R3), wherein R1 and R2 are each independently C 1-3 alkyl, and R3 is C 1-3 alkyl or hydroxyethyl; optionally, R1 and R2 are each independently methyl, and R3 is methyl or hydroxyethyl.

[0022] (tb2) the quaternary ammonium salt type compound includes an anion, and the anion includes one or more of nitrate, carbonate, bicarbonate, and phosphate.

[0023] In some embodiments, the quaternary ammonium salt type 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.

[0024] By introducing one or more of nitrate, carbonate, bicarbonate, and phosphate into the anion of the quaternary ammonium salt type compound, it is beneficial to better control the binding ability between the anion and the quaternary ammonium group in the quaternary ammonium salt type compound, so that the quaternary ammonium group is more easily dissociated. These anions can have lower electronegativity than electrolyte anions, thereby more favorably promoting the formation of quaternary ammonium group-electrolyte anion structures, more favorably playing the role of guiding lithium ions in the electrolyte to the second negative electrode active material, and more favorably improving the negative electrode sheet kinetics and the battery fast charging performance.

[0025] In some embodiments, the mass percentage of the quaternary ammonium salt type 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 type compound in the second negative electrode active layer is 0.2% to 1.5%.

[0027] By controlling the mass percentage of the quaternary ammonium salt type compound in the second negative electrode active layer within the aforementioned range, it is not only conducive to better exerting the role of the quaternary ammonium salt type compound in improving the fast charging performance of the battery, but also conducive to better controlling the decrease in the electronic conductivity of the surface of the second negative electrode active material caused by the wrapping of the quaternary ammonium salt type compound, thereby being conducive to better improving the fast charging performance of the battery. Further, it is also conducive to keeping the second negative electrode active layer at a high lithium storage capacity, thereby being conducive to giving consideration to the energy density of the negative electrode and the battery.

[0028] In some embodiments, the mass percentage of the carbon-based material in the second negative electrode active material is 80% to 100%.

[0029] In some embodiments, the negative electrode sheet 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 percentage 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 comprises 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. By introducing natural graphite into the second negative electrode active material, it is conducive to providing an increase in the compaction density and surface capacity of the second negative electrode active layer, thereby being conducive to improving the energy density of the negative electrode sheet.

[0034] The structure of artificial graphite is more stable than that of natural graphite, and the internal defects are relatively few, so that the available storage sites of lithium ions in the cycle process attenuate slowly, and the cycle performance is 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 intercalation sites and fast transmission channels. The carbon layers in soft carbon are stacked in disorder, which can enable relatively fast transmission of lithium ions. The introduction of at least one of hard carbon and soft carbon is conducive to improving the dynamics of the negative electrode sheet and the battery.

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

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

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

[0039] By introducing styrene-butadiene rubber into the binder of the second negative electrode active layer, the styrene-butadiene rubber has a non-chain structure, and is not easy to form competition with the quaternary ammonium salt type compound in occupying the wrapping site on the surface of the second negative electrode active material, which is conducive to better achieving the wrapping of the binder and the quaternary ammonium salt type compound on the surface of the second negative electrode active material at the same time, achieving a good electrical contact network, and fully playing the role of the quaternary ammonium salt type 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 comprises a carbon-based material and a binder, and the binder comprises styrene-butadiene rubber.

[0041] By introducing the carbon-based material into the second negative electrode active material of the second negative electrode active layer and introducing the styrene-butadiene rubber into the binder, the styrene-butadiene rubber has a suitable lipophilicity, which can better synergize the mutual bonding effect between the binder, the carbon-based material and the quaternary ammonium salt type compound; compared with the strong bonding effect of the oil-based binder (such as polyvinylidene fluoride (PVDF)) on the quaternary ammonium salt type compound, the styrene-butadiene rubber is conducive to better playing the bonding effect between the quaternary ammonium salt type compound and the carbon-based material, and better playing the role of the quaternary ammonium salt type compound in improving the fast charging performance of the battery.

[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 has a better pore structure after being rolled, which is conducive to promoting the electrolyte to better infiltrate the second negative electrode active layer.

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

[0046] By arranging the 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 of the surface of the first negative electrode active material can be optimized, the lithium ion transmission can be promoted, and the battery dynamics and the battery fast charging performance can be further improved.

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

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

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

[0050] (td2) the first negative electrode active material comprises secondary particle type graphite, the secondary particle type graphite comprises a secondary particle graphite body, and the amount of the secondary particle type graphite in the first negative electrode active material is greater than or equal to 20%, and optionally 30% to 80%; optionally, the secondary particle type graphite comprises carbon-coated secondary particle type graphite, the carbon-coated secondary particle type graphite comprises 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, and the carbon coating layer in the carbon-coated secondary particle type graphite comprises one or more of soft carbon, hard carbon and amorphous carbon;

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

[0052] (td4) the D v 50 is 10 μm to 18 μm, and optionally 12 μm to 16 μm;

[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 to 1.80 g / cm 3 ;

[0055] (td7) the rate of the first negative electrode active layer is higher than the 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) the ionic conductivity of the electrolyte is 13 mS / cm to 18 mS / cm at at least one temperature in the range of 20 °C to 35 °C; optionally, the ionic conductivity of the electrolyte is 13 mS / cm to 18 mS / cm at 25 °C.

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

[0058] By introducing the coated graphite in the first negative electrode active 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 first negative electrode active material can be optimized, the lithium ion transmission is promoted, and the battery dynamics and the battery fast charging performance are further improved.

[0059] By introducing the secondary particle type graphite in the first negative electrode active layer, and using the characteristics that the secondary particles are formed by agglomeration of primary particles, based on the disordered orientation of each primary particle, the isotropic feature when lithium ions are embedded in the first negative electrode active material is improved, the lithium ion embedding site on the surface of the first negative electrode active material is increased, the embedding rate of lithium ions is improved, and the battery fast charging performance is improved.

[0060] By controlling the OI value of the graphite material in the first negative electrode active material in the above range, the isotropic feature of the first negative electrode active material is improved, the lithium ion embedding channel is increased, the lithium ion diffusion dynamics in the first negative electrode active layer is better, and the battery fast charging performance is further improved.

[0061] By controlling the D v 50 in the above range, the accumulation degree of the particles in the first negative electrode active layer is better controlled, the inter-particle pores are better controlled, better lithium ion transmission channels are provided, and the battery dynamics and the fast charging performance are better improved.

[0062] By controlling the porosity of the first negative electrode active layer to be higher than the porosity of the second negative electrode active layer, the fast charging performance and the energy density of the battery can be considered, the fast transmission of lithium ions can be promoted by using the relatively high porosity of the first negative electrode active layer, and the energy density of the negative electrode can be improved by using the relatively low porosity of the second negative electrode active layer.

[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 packing degree of the first negative electrode active layer provide better lithium ion transmission channels, thereby better improving the battery kinetics and fast charging performance; in addition, the second negative electrode active layer can also provide higher energy density, thereby being beneficial to taking into account the fast charging performance and energy density of the lithium ion secondary battery.

[0064] By controlling the rate of the first negative electrode active layer to be higher than the 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 improve the fast charging performance of the battery. 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 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, and is beneficial to better improve the battery kinetics and the fast charging performance of the battery.

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

[0067] (te1) the D50 of the second negative electrode active material is higher than the D50 of the first negative electrode active material; v 50 is 12 μm to 21 μm, and can be selected to be 14 μm to 20 μm;

[0068] (te2) the first negative electrode active layer comprises a first negative electrode active material, and the D50 of the second negative electrode active material is higher than the D50 of the first negative electrode active material; v 50 of the second negative electrode active material is higher than the D50 of the first negative electrode active material; v 50 of the second negative electrode active material is higher than the D50 of the first negative electrode active material;

[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 to 1.35, further optionally 1.10 to 1.30, and more further optionally 1.10 to 1.28 or 1.15 to 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 to 1.35, further optionally 1.10 to 1.30, and more further optionally 1.10 to 1.28 or 1.15 to 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 ~ 2.05 g / cm 3 .

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

[0073] By controlling the D v 50 of the second negative electrode active material to be within the aforementioned range, it is beneficial to make the second negative electrode active layer obtain a higher compaction density, and further beneficial to improve the energy density.

[0074] By controlling the D v 50 of the second negative electrode active material to be higher than the D v 50 of the first negative electrode active material, it is beneficial to make the second negative electrode active layer obtain a higher compaction density, and further beneficial to improve the energy density.

[0075] By regulating the second negative electrode active layer in the lithium ion secondary battery to have a higher compaction density than the first negative electrode active layer, it is beneficial to improve the energy density of the lithium ion secondary battery.

[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 of the electrode sheet, 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 to be within the aforementioned range, it is beneficial to better balance the fast charging performance and the 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 to be within the aforementioned range, it is beneficial to make the secondary battery have a higher energy density. In addition, the particle packing can be relatively tight, at which time the improvement effect of the quaternary ammonium salt type compound introduced in the second negative electrode active layer on the fast charging performance of the battery can be more obvious.

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

[0079] (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 is 3:2 to 2:3, in terms of a single side of the negative electrode current collector;

[0080] (tf2) the ratio of the thickness of the first negative electrode active layer to the second negative electrode active layer is f H , which satisfies f H ≤ 1.6, optionally, 1.1 ≤ f H ≤ 1.6, further optionally, 1.1 ≤ f H ≤ 1.3;

[0081] (tf3) the thickness of the first negative electrode active layer is less than or equal to 50 μm, optionally 20 μm to 50 μm, further optionally 30 μm to 40 μm, in terms of a single side of the negative electrode current collector.

[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, the battery fast charging performance and energy density can be taken into account.

[0083] By controlling the thickness of the first negative electrode active layer to satisfy one or more of the aforementioned features (tf2) and (tf3), the distance of the quaternary ammonium salt type compound from the surface of the negative electrode sheet can be adjusted, which is conducive to better promoting the transmission of lithium ions to the second negative electrode active layer located in the lower layer, thereby being conducive to better improving the fast charging performance of the battery.

[0084] In the first aspect of the present application, a lithium ion secondary battery is also provided, which comprises a negative electrode sheet and an electrolyte; the negative electrode sheet 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 comprises a negative electrode active material and a quaternary ammonium salt type compound, the negative electrode active material comprises a negative electrode active body and a coating layer located on at least a part of the surface of the negative electrode active body, the coating layer comprises one or more of soft carbon, hard carbon and amorphous carbon, and the quaternary ammonium salt type compound comprises a quaternary ammonium cation.

[0086] By setting the coating layer on the surface of the negative active material layer of the negative active material, 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 active material can be optimized, the lithium ion transmission can be promoted, and the battery dynamics and the battery fast charging performance can be improved; further, by setting the quaternary ammonium salt type compound in the negative active material layer, the electrolyte anion in the electrolyte can be attracted by the electrostatic action based on the quaternary ammonium group, the electrolyte lithium salt in the electrolyte can be quickly dissociated, and the quaternary ammonium group-electrolyte anion structure formed can guide the lithium ion in the electrolyte to quickly transmit to the surface of the negative active material; based on the foregoing multiple effects, the fast charging performance of the battery can be better improved.

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

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

[0089] (tg2) the mass ratio of the quaternary ammonium salt type compound in the negative active material layer is 0.2% to 2%, and optionally 0.2% to 1.5%;

[0090] (tg3) the negative 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 active material comprises a carbon-based material, and the mass ratio of the carbon-based material in the negative active material layer is 94.5% to 97.5%, and optionally 95.0% to 97.0%;

[0092] (tg5) the negative active material layer comprises a binder, and the binder comprises a 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 active material comprises a coated graphite, and the coated graphite comprises a graphite body and a coating layer on at least a portion of the surface of the graphite body, and the coating layer comprises one or more of soft carbon, hard carbon and amorphous carbon;

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

[0095] (tg8) the negative active material comprises graphite material, and the OI value of the graphite material is 2-15, and optionally 2-10;

[0096] (tg9) the D v 50 is 11 μm-20 μm, and optionally 13 μm-18 μm;

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

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

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

[0100] By controlling the mass content of the quaternary ammonium salt type compound in the negative active material layer within the aforementioned range, the quaternary ammonium salt type compound can better improve the fast charging performance of the battery, and the decrease in the electronic conductivity of the surface of the negative active material caused by the wrapping of the quaternary ammonium salt type compound can be better controlled, which is conducive to better improving the fast charging performance of the battery. Further, it is also conducive to maintaining a high lithium storage capacity of the negative active material layer, and is conducive to balancing the energy density of the negative electrode and the battery.

[0101] The carbon-based material is conducive to better adsorbing the hydrocarbon chain in the quaternary ammonium salt type compound, thereby facilitating the better wrapping of the quaternary ammonium salt type compound on the surface of the negative active material, and thereby facilitating the faster guiding of lithium ions in the electrolyte to the surface of the negative active material; on the other hand, the carbon-based material also has good electronic conductivity; on the other hand, the carbon-based material is also conducive to providing better stability of the negative active material during fast charging and is not easy to pulverize; through the aforementioned multiple effects, the negative electrode sheet kinetics and the battery fast charging performance can be better improved.

[0102] By introducing natural graphite into the negative active material, it is beneficial to provide improved compaction density and surface capacity of the negative active material layer, and further to improve the energy density of the negative electrode sheet. By introducing artificial graphite into the negative 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 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 active material layer within the aforementioned range, it is beneficial to better wrap the quaternary ammonium salt type compound on the surface of the negative active material, and in addition, the energy density of the negative electrode and the battery can also be taken into account.

[0104] By introducing a carbon-based material into the negative active material of the negative active material layer and introducing butadiene styrene rubber into the binder, it is beneficial to better simultaneously realize the wrapping of the binder and the quaternary ammonium salt type compound on the surface of the negative active material, which can realize a good electrical contact network, and also fully play the role of the quaternary ammonium salt type compound in guiding lithium ions in the electrolyte, and is beneficial to better improve the fast charging performance of the battery.

[0105] By controlling the glass transition temperature of butadiene styrene rubber within the aforementioned range, it is beneficial to make the negative active material layer have a better pore structure after being rolled, and is beneficial to promote the electrolyte to better infiltrate the negative active material layer.

[0106] By providing a coating layer on the surface of the negative active material of the negative active material layer and providing 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 active material can be optimized, lithium ion transmission is promoted, and battery dynamics and battery fast charging performance are further improved.

[0107] By introducing a coated graphite into the negative active material layer and providing 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 active material can be optimized, lithium ion transmission is promoted, and battery dynamics and battery fast charging performance are further improved.

[0108] By introducing a secondary particle type graphite into the negative active material layer, and using the characteristic that the secondary particles are formed by agglomeration of primary particles, based on the disordered orientation of each primary particle, it is beneficial to improve the isotropic feature when lithium ions are inserted into the negative active material, increase the lithium ion insertion site on the surface of the negative active material, improve the insertion rate of lithium ions, and improve the battery fast charging performance.

[0109] By controlling the OI value of the graphite material in the negative electrode active material within the aforementioned range, the isotropic characteristics of the negative electrode active material are enhanced, the lithium ion insertion channel is increased, the lithium ion diffusion kinetics in the negative electrode active material layer is better, and the battery fast charging performance is improved.

[0110] By controlling the D v 50 within the aforementioned range, the degree of particle accumulation in the negative electrode active material layer is better controlled, the inter-particle pores are better controlled, better lithium ion transmission channels are provided, and the battery kinetics and fast charging performance are better improved.

[0111] When the porosity of the negative electrode active material layer is controlled within the aforementioned range, the particles are relatively tightly packed, and at this time, the improvement effect of the quaternary ammonium salt type compound introduced into the negative electrode active material layer on the battery fast charging performance is more obvious.

[0112] By controlling the ionic conductivity of the electrolyte within the aforementioned range, the rapid transmission of lithium ions is promoted, and the battery kinetics and battery fast charging performance are better improved.

[0113] In some embodiments, the areal density of the negative electrode tab is 5 mg / cm 2 ~ 15 mg / cm 2 .

[0114] By controlling the areal density of the negative electrode tab within the aforementioned range, the battery fast charging performance and energy density are taken into account.

[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, triflate, difluorophosphate, difluoro oxalate borate, tetrafluoro oxalate phosphate, difluoro di-oxalate phosphate, bisfluorosulfonylimide, and bis-trifluoromethanesulfonylimide.

[0117] By selecting the aforementioned electrolyte anion species, the electrolyte anion has a stronger binding capacity for the quaternary ammonium group, the dissociation of the quaternary ammonium group and the anion in the quaternary ammonium salt type compound is better promoted, the attraction of the quaternary ammonium salt type compound to the electrolyte anion and the guidance of lithium ions in the electrolyte are promoted, the transmission rate of lithium ions to the second negative electrode active material is improved, the negative electrode tab kinetics and the battery fast charging performance are better improved.

[0118] The aforementioned listed anion species have stronger electronegativity and stronger binding to quaternary ammonium than one or more of nitrate, carbonate, bicarbonate, and phosphate.

[0119] In some embodiments, the electrolyte salt comprises one or more of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bisfluorosulfonylimide, lithium bis-trifluoromethylsulfonylimide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluoroboric oxalate, lithium difluoroboric bisoxalate, lithium difluorophosphoric bisoxalate, and lithium tetrafluorophosphoric oxalate.

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

[0121] By introducing lithium-containing phosphate-based active material into the positive electrode active material, the structural stability of the positive electrode active material during charge and discharge cycles is improved, and the cycle life of the battery is prolonged.

[0122] By introducing lithium composite metal oxide-based active material into the positive electrode active material, the energy density of the positive electrode and the battery is improved.

[0123] In some embodiments, the positive electrode active material comprises lithium-containing phosphate-based active material, the positive electrode active material satisfying one or more of the following characteristics:

[0124] (th1) the mass fraction of the lithium-containing phosphate-based active material in the positive electrode active layer is greater than or equal to 80%, optionally 80% to 97%;

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

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

[0127] By controlling the mass fraction of lithium-containing phosphate-based active material in the positive electrode active layer within the aforementioned range, the cycle life of the battery is better prolonged.

[0128] The type of lithium-containing phosphate-based active material can be flexibly selected to meet different application requirements.

[0129] By setting a carbon-coated layer including one or more of soft carbon, hard carbon and amorphous carbon on the surface of the lithium-containing phosphate-based active material, the conductivity of the material can also be improved, which is conducive to improving the electrical contact network in the positive electrode sheet, providing a fast and stable channel for electron transmission in the positive electrode sheet, thereby facilitating the improvement of the rate performance of the battery and the improvement of the fast charging capability of the battery.

[0130] In a second aspect of the present application, a lithium ion secondary battery is provided.

[0131] In a third aspect of the present application, the lithium ion secondary battery described in the first aspect of the present application is applied to supply and / or store electric energy.

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

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

[0134] Optionally, the application includes charging the lithium ion secondary battery at a rate of at least one of 2C-4C.

[0135] Optionally, the maximum charge rate of the lithium ion secondary battery is greater than or equal to 2C, optionally 2C-6C, further optionally 2C-4C or 4C-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] Details of one or more embodiments or examples of the present application are presented 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 DRAWINGS

[0138] For a better understanding of the embodiments, examples, or examples provided by the present application, one or more drawings are referred to. Additional details or examples used to describe the drawings should not be considered as limiting the scope of the disclosed application, the presently described embodiments, examples, or examples, and the best mode of these applications currently understood. Moreover, in all the drawings, the same reference numbers are used to represent the same components. It should be noted that the drawings are all drawn in a simplified form, only for the convenience, clarity of the description of the present application. The various sizes of each component shown in the drawings are arbitrarily shown, which can be accurate, or can not be drawn according to the actual proportion. For example, in order to make the drawing clearer, the size of the components is appropriately exaggerated in some places of the drawing. Unless otherwise specified, the various components in the drawing are not drawn to scale. The present application does not limit each size of each component.

[0139] In the drawings:

[0140] Figure 1 is a structural schematic diagram of the negative electrode tab in an embodiment of the present application.

[0141] Figure 2 is a structural schematic diagram of the negative electrode tab in another embodiment of the present application.

[0142] Figure 3 is a structural schematic diagram of the negative electrode tab in another embodiment of the present application.

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

[0144] Figure 5 is a schematic diagram of the battery cell in an embodiment of the present application. Figure 4 is an exploded view of the battery cell in an embodiment of the present application.

[0145] Figure 6 is a schematic diagram of the battery device in an embodiment of the present application.

[0146] Figure 7 is a schematic diagram of the battery pack in an embodiment of the present application.

[0147] Figure 8 is a schematic diagram of the battery pack in an embodiment of the present application. Figure 7 is an exploded view of the battery pack in an embodiment of the present application.

[0148] Figure 9 is a schematic diagram of the power consuming device using the lithium ion secondary battery as a power source in an embodiment of the present application.

[0149] Explanation of reference numerals:

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

[0151] It should be noted that, Figures 1-3 The shape and size of the negative active particle 202, the quaternary ammonium salt type compound 208, and the like involved are not intended to limit or represent the shape and size of the actual substance, and the number illustrated is also not intended to limit or represent the actual number and the number ratio. DETAILED DESCRIPTION

[0152] Hereinafter, some embodiments and some examples of the lithium ion secondary battery, the electric device, and the application of the present application are described in detail with appropriate reference to the accompanying drawings. However, there are cases where unnecessary detailed description is omitted. For example, there are cases where detailed description of matters that are well known, repeated description of actually the same structure are omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate understanding by those skilled in the art. In addition, the accompanying drawings and the following description are provided so that those skilled in the art can fully understand the present application, and are not intended to limit the subject matter recited in the claims.

[0153] The ranges disclosed herein can be limited by both a lower limit and an upper limit, to define a range by selecting a lower limit and an upper limit, the selected lower limit and upper limit define the boundaries of the particular range. Ranges defined by such limits can be either inclusive or exclusive of the end values, either end value can be included or excluded independently, and can be combined in any manner, i.e., any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a particular parameter, it is understood that ranges of 60-110 and 80-120 are also contemplated. In addition, if minimum range values of 1 and 2 are listed, and if maximum range values of 3, 4, and 5 are also listed, then the following ranges are all contemplated: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, unless otherwise indicated, a numerical range "a-b" indicates a shorthand way of describing each and every intervening real number, integer or combination thereof between the upper and lower limits of that range, in which "a" and "b" are both real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been listed herein, "0-5" is merely a shorthand way of describing those numerical combinations. In addition, when a parameter is stated to be an integer ≥ 2, it is equivalent to listing the parameter as, for example, integer 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc. For example, when a parameter is stated to be 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, the fluctuation range can vary depending on the type and value of the number. For example, it can be allowed within the range of ±10%, ±5%, ±2%, ±1%, etc. For example, taking "about 20°C" and its approximation ±1°C as an example, the approximation values of 19°C, 19.5°C, etc. within the approximation range indicated by "about 20°C" should also be included in the range indicated by "about 20°C".

[0155] In this application, unless otherwise specified, "a plurality of", "a plurality of", "a plurality of", "several", etc. means more than 2 or equal to 2 in quantity. For example, "one or more" means one or ≥(greater than or equal to) two. It can be understood that when referring to "any number of" items, it means any suitable combination of a plurality of items, i.e., in a manner that does not conflict and can implement the present application.

[0156] If not specifically stated, all embodiments and optional embodiments of the present application can be combined to form new technical solutions.

[0157] Reference to "an embodiment" herein means that a particular feature, structure, or characteristic described in connection with the embodiment can be included in at least one embodiment or implementation of the application. The appearances of the phrase that the phrase in various places in the specification are not necessarily all referring to the same embodiment, nor are they necessarily mutually exclusive of other embodiments. It is explicitly contemplated that embodiments described herein can be combined with other embodiments in combinations that are not explicitly stated nor inherently opposed.

[0158] In the present application, the open technical features or technical solutions described with "containing", "including", "comprising" and the like, if no other description, do not exclude additional members outside the listed members, which can be regarded as providing both the closed features or solutions composed of the listed members, and the open features or solutions including additional members outside the listed members. For example, a includes a1, a2 and a3, if no other description, can also include other members, or can not include additional members, which can be regarded as providing both the features or solutions of "a is composed of a1, a2 and a3" or "a is selected from a1, a2 and a3", and the features or solutions of "a includes not only a1, a2 and a3, but also other members".

[0159] In the present application, 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, if no other description.

[0160] In the present application, "optionally", "optional" and "optional" mean that it can or can not be, that is, it is selected from "have" or "no" two parallel solutions. If there are multiple "optional" in a technical solution, if no special description, and no contradictory or mutual restrictive relationship, each "optional" is independent. If no other description, "optionally includes", "optionally contains" and the like are described in the present application, for example, "optionally includes" means "may include or not include".

[0161] In the present application, if no other description, 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 related listed items, wherein any and all combinations include any two related listed items, any more related listed items, or all related listed items. For example, "M and / or N" means that M, N and "combination of M and N" constitute a group. Wherein "including M and / or N" can mean "including M, including N, and including M and N", and also can mean "including M, including N, or including M and N", which can be understood according to the sentence.

[0162] In the present application, “suitable” in “suitable combination”, “suitable manner” and the like is subject to the ability to implement the technical solutions of the present application.

[0163] In the present application, “preferably”, “more preferably”, “even more preferably”, “more preferably”, “more preferably” and the like are only used to describe embodiments or examples with better effects, and it should be understood that they do not constitute a limitation on the protection scope of the present application. If there are multiple “preferably” in a technical solution, each “preferably” is independent of each other unless otherwise specified, and there is no contradictory relationship or mutual restriction.

[0164] In the present application, “further”, “more further”, “in particular”, “for example”, “such as”, “example” and the like are used for description purposes, indicating differences in content, but should not be understood as limiting the protection scope of the present application.

[0165] In the present application, the terms “first”, “second”, “third”, “fourth” and the like in “first aspect”, “second aspect”, “third aspect”, “fourth aspect” and the like are only used for description purposes, and should not be understood as indicating or implying relative importance or quantity, nor should it be understood as implying the importance or quantity of the indicated technical features. Moreover, “first”, “second”, “third”, “fourth” and the like only serve the purpose of non-exhaustive enumeration and description, and should be understood as not constituting a closed limitation on the quantity.

[0166] In the present application, unless otherwise specified and limited, the term “connection” and the like should be understood broadly, for example, it can be fixed connection, or detachable connection, or integral. For those skilled in the art, the appropriate meaning of the above-mentioned terms in the present application can be understood according to the situation.

[0167] In the present application, unless otherwise specified and limited, the first feature is “on” or “under” the second feature, which can be direct contact between the first and second features, or indirect contact between the first and second features through an intermediate medium. In the present application, unless otherwise specified and limited, the first feature is “on” or “under” the second feature, which can represent the mutual position relationship of horizontal height, or only represent the existence of the attachment relationship without limiting the mutual position relationship of horizontal height.

[0168] In the present application, the term “room temperature” generally refers to 4℃-35℃, which can refer to 20℃±5℃. In some embodiments or examples of the present application, room temperature refers to 20℃-30℃.

[0169] In the present application, when a unit of data range is mentioned, if only the right end point has a unit, it means that the units of the left end point and the right end point are the same. For example, 3-5 μm or 3-5 μm both mean that the units of the left end point "3" and the right end point "5" are both μm (micrometer), and both have the same meaning as 3 μm-5 μm. In addition, similar descriptions of other parameters such as temperature, size, etc. are also understood in the same way.

[0170] In the present 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 equivalent to ">"; "less than" can be equivalent to "<". In the present application, unless otherwise stated, "greater than or equal to" and "≥" can be considered to also provide both "greater than" and "equal to" options. In the present application, unless otherwise stated, "less than or equal to" and "≤" can be considered to also provide both "less than" and "equal to" options.

[0171] In the present application, with regard to the exemplary descriptions such as "in some embodiments (or examples)", "in one embodiment (or example)", etc., the following meanings can be covered, but are not limited thereto: these options can be combined with other options in a suitable manner to form new technical options.

[0172] In the present application, for a certain parameter, when 2 or more test methods are provided, as long as the test results of at least one test method are within the described range, they are all included in the protection scope of the present application.

[0173] The improvement effects described in the present application are not intended to be limited by any theory, unless otherwise stated.

[0174] According to various embodiments and various 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 the present application, unless otherwise stated, the term "lithium ion secondary battery" refers to a secondary battery in which active ions include lithium ions, and the term "lithium ion battery cell" refers to a battery cell in which active ions include lithium ions. Generally, a lithium ion secondary battery includes a positive electrode sheet, a negative electrode sheet, an electrolyte, and a separator. During the charging and discharging of the battery, active ions are inserted and extracted between the positive electrode sheet and the negative electrode sheet. The electrolyte plays a role in conducting ions between the positive electrode sheet and the negative electrode sheet. The separator is disposed between the positive electrode sheet and the negative electrode sheet, and mainly plays a role in preventing short circuiting between the positive and negative electrodes, while allowing ions to pass through.

[0176] In the present application, unless otherwise specified, the "electrode active material layer" includes at least one of the positive electrode active material layer of the positive electrode sheet and the negative electrode active material layer of the negative electrode sheet, and depending on the detailed circumstances, the electrode active material layer can refer to the positive electrode active material layer or the negative electrode active material layer. In the present application, the "positive electrode active material layer" can also be referred to as the "positive electrode active layer", and the "negative electrode active material layer" can also be referred to 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 for the negative electrode sheet, which can reversibly intercalate and deintercalate active ions.

[0178] In the present application, unless otherwise specified, the "negative electrode sheet" includes a negative electrode current collector. The "negative electrode current collector" refers to a structure responsible for collecting and conducting electrons in 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 a single 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 for the positive electrode sheet, which can reversibly deintercalate and intercalate active ions.

[0180] In the present application, unless otherwise specified, the "positive electrode sheet" includes a positive electrode current collector. The "positive electrode current collector" refers to a structure responsible for collecting and conducting electrons in 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 a single side or both sides of the positive electrode current collector.

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

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

[0183] In some embodiments, a lithium ion secondary battery is provided, which includes a negative electrode sheet and an electrolyte, and the negative electrode sheet 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 sheet. That is, the second negative electrode active layer is further away from the surface of the negative electrode sheet than the first negative electrode active layer.

[0184] In some embodiments, a lithium ion secondary battery is provided, which includes a negative electrode sheet and an electrolyte, and the negative electrode sheet includes a negative electrode active material layer, and 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 sheet.

[0185] In some embodiments, a lithium ion secondary battery is provided, which includes a negative electrode sheet and an electrolyte; the negative electrode sheet includes a negative electrode current collector and, sequentially disposed on at least one side of the negative electrode current collector, a second negative electrode active layer and a first negative electrode active layer, 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 includes a second negative electrode active material and a quaternary ammonium salt type compound, the quaternary ammonium salt type compound including a quaternary ammonium cation. The second negative electrode active material can include a carbon-based material.

[0186] In the present application, for the negative electrode active material layer, the direction close to the surface of the negative electrode sheet can be referred to as "upward", and the direction away from the surface of the negative electrode sheet can be referred to as "downward" in the thickness direction of the negative electrode sheet. 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, "the second negative electrode active layer and the first negative electrode active layer 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, the "quaternary ammonium salt type compound" is a compound including a quaternary ammonium group, which at least includes a quaternary ammonium cation and has the ability to bind to electrolyte anions in the electrolyte through ion exchange. Unless otherwise specified, the nitrogen atom of the quaternary ammonium cation in the quaternary ammonium salt type compound is covalently bonded to a carbon atom, that is, the quaternary ammonium salt type compound includes a quaternary ammonium cation and a carbon atom covalently bonded to the quaternary ammonium cation. Non-limitingly, the quaternary ammonium salt type compound can be selected to include an antistatic agent of a quaternary ammonium group. Non-limitingly, the quaternary ammonium salt type compound is a small molecule compound, and unless otherwise specified, the molecular weight of the quaternary ammonium salt type compound is less than or equal to 600 Da. Unless otherwise specified, the "molecular weight" of the quaternary ammonium salt type compound refers to the molecular mass measured in units of Daltons (Da), and 1 Dalton is equal to 12 twelfth of the mass of a C atom. Non-limitingly, the molecular weight of the quaternary ammonium salt type compound is 150 Da to 600 Da, which can be selected to be 160 Da to 500 Da, further selected to be 200 Da to 500 Da, and can also be any one of the following molecular weights or selected from a range consisting of any two of the following molecular weights: 180 Da, 190 Da, 200 Da, 220 Da, 250 Da, 260 Da, 280 Da, 300 Da, 350 Da, 400 Da, 450 Da, 500 Da, 600 Da, etc.

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

[0190] In the present application, unless otherwise specified, "electrolyte anion" refers to the anion carried by the lithium salt of the electrolyte in the electrolyte.

[0191] In the lithium ion secondary battery, the first negative electrode active layer located in the upper layer and the second negative electrode active layer located in the lower layer can be arranged in the negative electrode active material layer in the negative electrode sheet (with the direction away from the surface of the negative electrode current collector as upward and the direction toward the surface of the negative electrode current collector as downward), and the quaternary ammonium salt type compound is further arranged in the second negative electrode active layer located in the lower layer. The quaternary ammonium salt type compound includes a hydrophilic and positively charged quaternary ammonium group. For the negative electrode sheet soaked in the electrolyte, the quaternary ammonium group can attract the electrolyte anion in the electrolyte based on the electrostatic effect, promote the rapid dissociation of the lithium salt of the electrolyte in the electrolyte, and significantly improve the electrolyte wettability of the second negative electrode active layer and the kinetics of the negative electrode sheet, 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 observed for micro-morphology observation to observe the micro-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. The "cross section of the negative electrode sheet" refers to the cross section perpendicular to the thickness of the negative electrode sheet. Further, the cross section of the negative electrode sheet can be observed for micro-morphology observation and combined with composition analysis (such as energy dispersive spectrometer (EDS) and the like) to identify the types of elements to confirm the composition of different negative electrode active layers in the negative electrode active material layer. Non-limitingly, the cross section of the negative electrode sheet can be obtained by using instruments or devices including but not limited to focused electron beam (FIB) electron microscope (non-limiting examples such as FEI Scios 2HiVac device and the like), ion cross-section polisher (non-limiting examples such as IB-09010CP argon ion cross-section polisher and IB-19500CP ion cross-section polisher of Japan JEOL Co., Ltd. and the like), and the like. The micro-morphology observation method can use instruments or devices including but not limited to scanning electron microscope (SEM) technology, and non-limitingly, a high-resolution field emission scanning electron microscope can be used; non-limiting examples of SEM instruments include Sigma 300 scanning electron microscope and Apreo 2SEM field emission scanning electron microscope of Germany ZEISS Co., Ltd.

[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 using 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, and proton nuclear magnetic resonance (NMR) spectroscopy. 1 Methods include 1H NMR, gel permeation chromatography (GPC), high performance liquid chromatography (HPLC), mass spectrometry, X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), Raman spectroscopy, single crystal X-ray diffraction (SCXRD), inductively coupled plasma optical emission spectrometry (ICP), and energy dispersive spectroscopy (EDS). The sample preparation and testing methods for these 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 characteristics of the sample.

[0194] Unless otherwise specified in this application, the following method can be used to extract samples from the negative electrode active material layer of the negative electrode sheet to further detect whether it contains quaternary ammonium salt compounds and the types of quaternary ammonium salt compounds. The detailed steps are as follows: disassemble the battery cell, scrape a certain amount of powder (e.g., a certain mass M0) from the second negative electrode active layer of the negative electrode sheet, use acetone as the extractant, and continuously extract using a Soxhlet extractor to obtain the extract (mass denoted as M1), which is used as the sample to be tested. Non-limitingly, a sample thickness of 10 μm can be scraped. Non-limitingly, an Agilent liquid chromatography-mass spectrometry instrument can be used to detect the components of the quaternary ammonium salt compounds.

[0195] Non-limitingly, the content of identified quaternary ammonium salt compounds can be determined by the following method: A Waters ACQUITY ARC high-performance liquid chromatograph with a PDA detector can be used, referring to the method in GB / T 32268-2015, to confirm the content of quaternary ammonium salt compounds by comparing the retention time and peak area in the high-performance liquid chromatogram. The content of quaternary ammonium salt compounds in the second negative electrode active layer can be further calculated by combining the mass of the scraped powder M0, the mass of the extract M1, and the amount of test sample M2, such as the mass percentage of quaternary ammonium salt compounds in the second negative electrode active layer.

[0196] In the present application, the constituent materials of the negative active material layer are referred to as negative materials, the constituent materials of the first negative active layer are referred to as first negative materials, and the constituent materials of the second negative active layer are referred to as second negative materials, unless otherwise specified. The first negative materials include first negative active materials, and the second negative materials include second negative active materials. The terms "first" and "second" in "first negative material", "second negative material", "first negative active material", and "second negative active material" are only for descriptive purposes and cannot be understood as indicating or implying relative importance or quantity, nor can they be understood as implying the importance or quantity of the indicated technical features.

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

[0198] (S1) Scraping: disassemble the battery cell, take the negative electrode sheet, and use a micrometer to test the thickness L of the sheet. Take another negative electrode sheet, and scrape off the negative active material layer on both sides to leave the bare current collector foil, and test the thickness L0. The total thickness of the negative active material layer on both sides of the negative current collector is L-L0. Scrape off the negative active material layer on one surface of the negative electrode sheet to the surface of the bare negative current collector, and scrape off the negative material on the other surface of the negative electrode sheet until the thickness of the sheet is L1=L0+Δd. Collect the powder of the negative active material layer with a thickness of Δd under the thickness of L1 for testing the content of the quaternary ammonium salt compound. The thickness of the second negative active layer can be determined in advance in combination with the observation results of the cross-sectional morphology of the sheet, so as to control the thickness of L1, so that the first negative active layer has been completely removed, and the remaining part of the negative active material layer corresponds to part or all of the second negative active layer. For example, Δd can be 20 μm.

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

[0200] The skilled person can select a suitable organic solvent to collect the test sample 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 alcohol reagent alcohol aqueous solution such as methanol or ethanol. In step (S2), methanol aqueous solution can be used for ultrasonic, vortex, centrifugation, and 0.22 μm organic filter membrane filtration.

[0201] (S3) Detection: The high performance liquid chromatography method can be operated according to the GB / T 16631-2008 method and the mass spectrometry method can be operated according to the GB / T-6041-2002. A reversed-phase chromatographic column C18 column is selected for separation, and a solvent that can dissolve the quaternary ammonium salt compound is selected as the mobile phase (for example, 0.5% (v / v) methanol aqueous solution is selected as the mobile phase for the quaternary ammonium phosphorus salt dodecyl trimethyl ammonium).

[0202] A standard curve of the detection signal-quaternary ammonium salt concentration is prepared by using different concentrations of selected quaternary ammonium salts as standard samples. The selected quaternary ammonium salt can be quaternary ammonium phosphorus salt dodecyl trimethyl ammonium. The concentration gradient can be selected as 0.02, 0.05, 0.08, 0.1, 0.2, 0.4, 0.6, 0.8, 1.0, 2.0 times of (M2-M1) / M1.

[0203] The filtrate in step (S2) is detected, and the retention time and peak area of the standard sample are compared to calculate the concentration C of the quaternary ammonium salt compound separated in step (S2). The mass M3 of the quaternary ammonium salt compound is calculated according to the formula M3=M2xC, and the mass ratio of the quaternary ammonium salt compound in the second negative electrode active layer is calculated as M3 / M0x100%.

[0204] It should be noted that in step (S2), the conductive agent and other components in the second negative electrode active layer are not soluble in the organic solvent, and some adhesive components (such as butyl rubber) can be dissolved in the organic solvent. However, the molecular weight of the adhesive component is usually higher than 10 kDa (1 kDa=1000 Da), and the polarity is usually weaker than that of the quaternary ammonium salt compound. In step (S3), when performing high performance liquid chromatography detection, the adhesive component can be separated from the quaternary ammonium salt compound by using a chromatographic column (such as a C18 chromatographic column).

[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 enable the quaternary ammonium salt compound to be better adsorbed on the surface of the carbon-based material.

[0207] In some embodiments, the surface of the particles of the second negative electrode active material is provided with a carbon substance. The carbon substance can 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 hydrocarbon chain covalently bonded to the quaternary ammonium cation, and an anion.

[0209] In the present application, "hydrocarbyl chain" refers to a chain structure composed of carbon atoms and hydrogen atoms; the hydrocarbyl chain in the quaternary ammonium salt type compound can provide a carbon-carbon skeleton, and the hydrocarbyl chain has weak polarity or a nonpolar structure.

[0210] By providing a hydrocarbyl chain in the quaternary ammonium salt type compound, for example, the hydrocarbyl chain can include an alkyl chain, the chain structure of the hydrocarbyl chain is beneficial to better and more stably load and wrap the quaternary ammonium salt type compound on the surface of the second negative electrode active material, and the carbon-carbon skeleton provided by the hydrocarbyl chain is beneficial to better and more stably adsorb the quaternary ammonium salt type compound on the surface of the carbon-based material (the carbon-based material has a certain lipophilicity), and 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 be more quickly guided to the surface of the second negative electrode active material, and is beneficial to further improve the negative electrode sheet kinetics and the battery fast charging performance.

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

[0212] In the present application, "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 the present application, the term "hydrocarbyl" refers to a monovalent residue of a hydrocarbon compound containing primary (normal) carbon atoms, or secondary carbon atoms, or tertiary carbon atoms, or quaternary carbon atoms, or a combination thereof, which loses one hydrogen atom. The phrases containing this term, for example, "C 12-18 hydrocarbyl" refers to a hydrocarbyl containing 12 to 18 carbon atoms, and each occurrence can be independently of each other C 12 hydrocarbyl, C 13 hydrocarbyl, C 14 hydrocarbyl, C 15 hydrocarbyl, C 16 hydrocarbyl, C 17 hydrocarbyl or C 18 hydrocarbyl.

[0214] In the present application, the term "alkyl" refers to a monovalent residue of a saturated hydrocarbon containing primary (normal) carbon atoms, or secondary carbon atoms, or tertiary carbon atoms, or quaternary carbon atoms, or a combination thereof, which loses one hydrogen atom. The phrases containing this term, for example, "C 12-18 alkyl" refers to an alkyl containing 12 to 18 carbon atoms, and each occurrence can be independently of each other C 12 alkyl, C 13 alkyl, C 14 alkyl, C 15 alkyl, C 16 alkyl, C17 alkyl or C 18 alkyl.

[0215] In the present application, the number of carbon atoms in a compound or a group can be described using a subscript of "C" if not otherwise specified. For example, "C 12-18 " means having 12 to 18 carbon atoms, and "C 12-18 " can be, independently of each other, 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" means that the main chain atoms are connected in series to form a chain structure, at this time, no cyclic structure is contained, and no branch chain is present.

[0219] In some embodiments, the quaternary ammonium salt type compound 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) :

[0220] (ta1) the hydrocarbyl chain is an alkyl chain;

[0221] (ta2) the number of carbon atoms in the hydrocarbyl chain is 12 to 18 (which can be 12, 13, 14, 15, 16, 17, 18, or a range selected from any two of the foregoing integers);

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

[0223] (ta4) the hydrocarbyl chain is a linear chain;

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

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

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

[0227] By controlling the number of carbon atoms in the hydrocarbyl chain of the quaternary ammonium salt type compound and / or the molecular weight of the quaternary ammonium salt type compound to be within the aforementioned ranges, the length of the hydrocarbyl chain can be adjusted to a more suitable range, which on one hand is conducive to better and more stable wrapping of the quaternary ammonium salt type compound on the surface of the second negative active material during stirring of the slurry, is conducive to inhibiting the quaternary ammonium salt type compound from falling off the surface of the second negative active material during charging and discharging, further in combination with the quaternary ammonium group exposed to the electrolyte, can promote the lithium ions in the electrolyte to be more quickly and stably guided to the surface of the second negative active material, thereby improving the transmission rate of lithium ions inside the negative electrode sheet, and on the other hand, can also better control the wrapping degree of the hydrocarbyl chain on the surface of the second negative active material, so that the active sites on the surface of the second negative active material can better contact the electrolyte, thereby being conducive to better improving the kinetics of the negative electrode sheet and the fast charging performance of the battery.

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

[0229] (tb1) the structure of the quaternary ammonium group is -N + (R1R2R3), wherein R1and R2are each independently C 1-3 alkyl, and R3is C 1-3 alkyl or hydroxyethyl; alternatively, R1and R2are each independently methyl, and R3is methyl or hydroxyethyl.

[0230] (tb2) the quaternary ammonium salt type compound comprises an anion, and the anion comprises one or more of nitrate, carbonate, bicarbonate, and phosphate.

[0231] In the present application, the term "C 1-3 alkyl" can be methyl, ethyl, or propyl.

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

[0233] According to the Pauling electronegativity scale theory, it is generally considered 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 considered that the Pauling electronegativity scale of some common electrolyte anions usually has the following values: tetrafluoroborate 4.0 ≈ hexafluoroarsenate 4.0 ≈ hexafluorophosphate 4.0 ≈ bisfluorosulfonylimide 4.0 ≈ bis-trifluoromethylsulfonylimide 4.0 ≈ trifluoromethanesulfonate 4.0 ≈ lithium difluorophosphate 4.0 ≈ difluoro oxalate borate 4.0 ≈ tetrafluoro oxalate lithium phosphate 4.0 ≈ difluoro di-oxalate lithium phosphate 4.0 > perchlorate 3.5 ≈ lithium bis-oxalate borate 3.5. The Pauling electronegativity scale of anions can be determined according to the Pauling electronegativity scale value of the element with the strongest electronegativity in the anion. The Pauling electronegativity scale of different elements can be consulted in manuals or existing literature.

[0234] In some embodiments, the quaternary ammonium salt type 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, dodecyltrimethyl quaternary ammonium bicarbonate.

[0235] By introducing one or more of nitrate, carbonate, bicarbonate and phosphate into the anion of the quaternary ammonium salt type compound, it is beneficial to better control the binding ability between the anion and the quaternary ammonium cation in the quaternary ammonium salt type compound, so that the quaternary ammonium cation is more easily dissociated. These anions can have lower electronegativity than electrolyte anions, thereby more favorably promoting the formation of quaternary ammonium cation-electrolyte anion structures, more favorably playing the role of guiding lithium ions in the electrolyte to the second negative electrode active material, and better improving the negative electrode sheet kinetics and battery fast charging performance.

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

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

[0238] Non-limitingly, the mass percentage of the quaternary ammonium salt type compound in the second negative electrode active layer can also be any of the following percentages or selected from the following 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 percentage of the quaternary ammonium salt type compound in the second negative electrode active layer within the aforementioned range, it is not only conducive to better exerting the role of the quaternary ammonium salt type compound in improving the fast charging performance of the battery, but also conducive to better controlling the decrease in the electronic conductivity of the surface of the second negative electrode active material caused by the wrapping of the quaternary ammonium salt type compound, and conducive to better improving the fast charging performance of the battery. Further, it is also conducive to keeping the second negative electrode active layer with a relatively high lithium storage capacity, and conducive to giving consideration to the energy density of the negative electrode and the battery.

[0240] In some embodiments, the mass percentage of the carbon-based material in the second negative electrode active material can be 80% to 100%, optionally 90% to 100%, and can also be any of the following percentages or selected from the following 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 can include one or more of artificial graphite and natural graphite.

[0242] In some embodiments, the mass percentage of the graphite-based material in the second negative electrode active material can be 80% to 100%, optionally 90% to 100%, and can also be any of the following percentages or selected from the following 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, the surface of the particles of the second negative electrode active material is provided with graphite. The graphite can include one or more of artificial graphite, natural graphite.

[0244] In some embodiments, the negative electrode sheet satisfies one or more of the following characteristics (any numerical parameter in the following characteristics can also be selected from any suitable numerical value or range in the context):

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

[0246] The mass percentage of the carbon-based material in the second negative electrode active layer is 94.5% to 97.5%, and can be 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, and further, the graphite can include one or more of artificial graphite and natural graphite.

[0249] Natural graphite is prone to lateral deformation when subjected to cold pressing. By introducing natural graphite into the second negative electrode active material, it is beneficial to provide improved compaction density and surface capacity of the second negative electrode active layer, and further to improve the energy density of the negative electrode sheet.

[0250] The structure of artificial graphite is more stable than that of natural graphite, and the internal defects are relatively less, so that the available storage sites of lithium ions in the cycle process are slow to decay, and the cycle performance is more stable.

[0251] Both hard carbon and soft carbon have a large degree of disorder, which is beneficial to the entry of lithium ions. Hard carbon can provide abundant lithium intercalation sites and fast transport channels. The disordered stacking of carbon layers in soft carbon can enable relatively fast transport of lithium ions. The introduction of at least one of hard carbon and soft carbon is beneficial to improve the dynamics of the negative electrode sheet and the battery.

[0252] In some embodiments, the mass percentage of the carbon-based material in the second negative electrode active layer is 94.5% to 97.5%, and can be 95.0% to 97.0%, and can also be any one of the following percentages or selected from 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 percentage 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 type 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 electrode active layer includes a binder, and the binder includes styrene-butadiene rubber (SBR).

[0255] By introducing the styrene-butadiene rubber into the binder of the second negative electrode active layer, the styrene-butadiene rubber can have a non-chain structure, and the styrene-butadiene rubber is not prone to form competition with the quaternary ammonium salt type compound in occupying the wrapping sites on the surface of the second negative electrode active material, which is conducive to better achieving the wrapping of the binder and the quaternary ammonium salt type compound on the surface of the second negative electrode active material at the same time, so that good electrical contact network can be achieved, and the role of the quaternary ammonium salt type compound in guiding lithium ions in the electrolyte can be fully played, which is conducive to better improving the fast charging performance of the battery.

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

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

[0258] In some embodiments, the glass transition temperature of the styrene-butadiene rubber is 5-70°C, which can be 30-50°C, and further can be any one of the following temperatures or a range selected from 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 30-50°C.

[0260] In the present application, the "glass transition temperature (Tg)" has the known meaning in the art, which refers to the temperature interval at which a high polymer changes from a glassy state to a high-elastic state, or from a high-elastic state to a glassy state. Generally, the higher the glass transition temperature, the greater the molecular weight. The polymer can perform molecular chain movement above its Tg. The glass transition temperature can be determined 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 being rolled, which is conducive to promoting the electrolyte to better infiltrate the second negative electrode active layer.

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

[0263] In some embodiments, the first negative active layer comprises a first negative active material, the first negative active material comprises a negative active body and a coating layer located on at least a portion of the surface of the negative active body, the coating layer comprises one or more of soft carbon, hard carbon and amorphous carbon. Non-limitingly, the mass percentage of the coating layer in the first negative active material can be 0.1% to 4.0%, optionally 1.0% to 2.0%. Non-limitingly, the sum of the mass percentages of soft carbon, hard carbon and amorphous carbon in the coating layer in the first negative active material can be 0.1% to 3.0%, optionally 1.0% to 2.0%.

[0264] “Soft carbon” and “hard carbon” have the meanings well known in the art, soft carbon can be graphitized by further high temperature treatment, while hard carbon is difficult to be graphitized even by further high temperature treatment. The carbon layers in soft carbon are disordered stacked, so that lithium ions can be transported therein relatively fast. The internal crystal arrangement of hard carbon is disordered, and has many pores, which can provide abundant lithium intercalation sites and fast transport channels.

[0265] In the present application, “amorphous carbon” refers to a transition state carbon material with very low graphitization and crystallization degree, and an approximate amorphous state (or a structure with no fixed shape and periodicity). In the present application, “amorphous carbon” can refer to the product after carbonization treatment of an organic carbon source.

[0266] By providing a coating layer on the surface of the first negative active material of the first negative active layer, and providing one or more of soft carbon, hard carbon and amorphous carbon in the coating layer, the lithium ion transport channels on the surface of the first negative active material can be optimized, the lithium ion transport can be promoted, and the battery dynamics and the 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 active material comprises a coated graphite, the coated graphite comprises a graphite body and a coating layer located on at least a portion of the surface of the graphite body, the coating layer in the coated graphite comprises one or more of soft carbon, hard carbon and amorphous carbon;

[0269] (td2) The first negative active material comprises secondary particle type graphite, the secondary particle type graphite comprises a secondary particle graphite body, the proportion of the secondary particle type graphite in the first negative active material is greater than or equal to 20%, and is optionally 30%-80%; optionally, the secondary particle type graphite comprises carbon-coated secondary particle type graphite, the carbon-coated secondary particle type graphite comprises a secondary particle graphite body and a carbon coating layer (which can be referred to as a first carbon coating layer) located on at least a portion of the surface of the secondary particle graphite body, and the carbon coating layer (i.e., the first carbon coating layer) in the carbon-coated secondary particle type graphite comprises one or more of soft carbon, hard carbon and amorphous carbon;

[0270] (td3) The first negative active material comprises graphite material, and the OI value of the graphite material can be 2-15, and is optionally 2-10;

[0271] (td4) The D v 50 is 10 μm-18 μm, and is optionally 12 μm-16 μm;

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

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

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

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

[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 active material comprises coated graphite, the coated graphite comprises a graphite body and a coating layer located on at least a portion of the surface of the graphite body, and the coating layer can comprise one or more of soft carbon, hard carbon and amorphous carbon.

[0278] In the present application, the "graphite body" is composed of graphite.

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

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

[0281] The element composition and component type of the coating layer in the coated graphite can be analyzed by using or referring to the foregoing 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. In the XRD spectrum, the characteristic peak near 2θ 26.5° is very sharp and has high intensity, which is natural graphite; the characteristic peak near 2θ 26.5° is relatively wide and has low intensity, which 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 amorphous carbon can be analyzed according to the characteristic peak information (such as the intensity ratio of D peak / G peak, I D / G ) of the carbon component in the spectrum. Both D peak and G peak are Raman characteristic peaks of carbon atom crystals. D peak represents the defects of carbon atom crystals, and the more defects, the greater the intensity of D peak. The intensity of D peak can reflect the content of amorphous (such as random layer stacking) region, and the intensity of G peak can reflect the content of graphitized (layered structure) region. With the increase of the disorder degree of carbon atoms, the intensity ratio of D peak to G peak also increases. The difference between the Raman spectrum I D / G and the standard Raman spectrum I D / G of graphite can also be used to judge whether the material to be tested contains amorphous carbon. Similarly, according to the intensity difference of D peak and G peak in Raman spectrum, natural graphite and artificial graphite can also be distinguished.

[0284] In some embodiments, the first negative active material comprises secondary particle type graphite. Non-limitingly, the amount of secondary particle type graphite in the first negative active material can be greater than or equal to 20%, optionally 20% to 80%, further optionally 30% to 60%, and can also be any one 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%, and the like.

[0285] In the present application, the "secondary particle type graphite" refers to a graphite-based material comprising a secondary particle graphite body, which at least comprises a secondary particle graphite body, and optionally further comprises a coating layer on at least a portion of the surface of the secondary particle graphite body. The secondary particle type graphite can be a non-coated graphite, a coated graphite, or a combination of the non-coated graphite and the coated graphite.

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

[0287] In the present application, unless otherwise specified, the "primary particle" is the basic unit of particles in a material. In a material, the primary particle can be in a non-agglomerated state, which is referred to as a "non-agglomerated primary particle". A plurality of primary particles can be agglomerated into an agglomerated particle, which is referred to as a "secondary particle", i.e., the "secondary particle" refers to an agglomeration of primary particles. The secondary particle is formed by the aggregation of primary particles, and the secondary particle has a relatively random or relatively disordered orientation on the whole particle, and thus the secondary particle has stronger isotropy.

[0288] In the present application, the "secondary particle graphite body" or "secondary particle graphite" refers to an agglomeration of primary particle graphite, and the "primary particle graphite" is the basic unit of graphite crystalline grains. It can be understood that the secondary particle graphite belongs to the secondary particle type graphite.

[0289] Non-limitingly, the "quantity ratio of secondary particle type graphite in the first negative electrode active material" can be obtained by statistical analysis according to the SEM scanning diagram of the first negative electrode active material. The following method can be used: the first negative electrode active material is laid and adhered on conductive glue, the particle morphology is tested by a scanning electron microscope (such as ZEISS Sigma 300), and the number of particles in the obtained SEM picture is counted as secondary particles or non-agglomerated primary particles. Randomly select multiple regions for scanning test, count the number of secondary particles and non-agglomerated primary particles in each region, calculate the quantity ratio of secondary particles in each region, and then take the average value of the quantity ratio of secondary particles in multiple test regions as the test value of the "quantity ratio of secondary particles in the first negative electrode active material". For example, if the first negative electrode active material is graphite material, it corresponds to the "quantity ratio of secondary particle type graphite in the first negative electrode active material"; if the first negative electrode active material is graphite, it corresponds to the "quantity ratio of secondary particle graphite in the first negative electrode active material". The "quantity ratio of secondary particles in the second negative electrode active material", the "quantity ratio of secondary particle type graphite in the second negative electrode active material", and the "quantity ratio of secondary particle graphite in the first negative electrode active material" can be obtained by similar methods. In addition, the "quantity ratio of secondary particle type graphite in the negative electrode active material" and the "quantity ratio of secondary particles in the negative electrode active material" can also be obtained by similar methods.

[0290] In the present application, the "graphite material" refers to a negative electrode active material containing a graphite body, which at least includes a graphite body and optionally includes a coating layer on at least a part 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 is secondary particles, it corresponds to secondary particle type graphite.

[0291] By introducing secondary particle type graphite into the first negative electrode active layer, taking advantage of the characteristics 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 when lithium ions are embedded into the first negative electrode active material, increase the lithium ion embedding sites on the surface of the first negative electrode active material, improve the embedding rate of lithium ions, 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 2-15, optionally 2-10, and can also be 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.

[0293] In the present application, the "OI value" of the graphite material refers to the intensity ratio of the (004) crystal face to the (110) crystal face in the X-ray diffraction pattern of the graphite material rolled into a sheet, unless otherwise specified. The OI value can be used to characterize the orientation degree of the graphite material particle accumulation, and can reflect the isotropic degree of the graphite material particle accumulation.

[0294] The OI value (GOI) of the graphite material can be tested by X-ray diffraction (XRD) according to the content of Appendix F in the national standard GB / T 24533-2019 "Lithium ion battery graphite negative electrode material". After the powder sample to be tested is rolled into a sheet, the sheet-shaped sample is subjected to XRD testing to obtain an X-ray diffraction spectrum. After the sample is rolled, the arrangement orientation (OI value) of the artificial or natural hexagonal graphite on the pole sheet is analyzed by X-ray polycrystalline diffraction on the crystal structure, and the peak area C 004 of the (004) crystal face diffraction peak and the peak area C 110 of the (110) crystal face diffraction peak are obtained after analysis and calculation by Highscore Plus or Jade XRD spectrum analysis software. OI value = C 004 / C 110 . The X-ray diffractometer (such as Bruker-D8 advance) can be used for testing.

[0295] Non-limitingly, the sample for OI value testing can be obtained by the following method: disassembling the battery cell, taking the negative pole sheet, and soaking and cleaning with a solvent such as dimethyl carbonate; scraping the powder from the first negative active layer, and fully soaking the powder material extracted from the first negative active layer with a solvent (such as N-methyl pyrrolidone (NMP) and the like) to dissolve the organic components such as binders, thickeners and the like in the solvent (ultrasonic dispersion can also be combined to promote dissolution), and after washing and filtering, the collected solid phase is used as the first negative active material to be tested. After the powder sample to be tested is rolled into a sheet, the sheet-shaped sample is subjected to XRD testing. The powder compacted density test can also be performed on the first negative active material to be tested.

[0296] By controlling the OI value of the graphite material in the first negative active material in the above range, the isotropic characteristics of the first negative active material are enhanced, the lithium ion insertion channel is increased, the lithium ion diffusion kinetics in the first negative active layer is better, and the battery fast charging performance is improved.

[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 a secondary particle type graphite at the same time. Illustratively, the first negative electrode active material includes secondary particles, and the secondary particle type graphite includes carbon-coated secondary particle type graphite. Non-limitingly, the carbon-coated secondary particle type graphite includes a carbon coating layer (i.e., a first carbon coating layer) located on at least a portion of the graphite body of the secondary particle and on the surface of the graphite body of the secondary particle, and further, the carbon coating layer (i.e., the first carbon coating layer) in the carbon-coated secondary particle type graphite can include one or more of soft carbon, hard carbon, and amorphous carbon. As another example, the first negative electrode active material can satisfy features (td2) and (td3) at the same time, illustratively, the first negative electrode active material includes a graphite material, the graphite material includes secondary particle type graphite, and the graphite material can have an OI value of 2 to 15, optionally 2 to 10, and also can have 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, "first", "third", "fourth", and "fifth" in "first carbon coating layer", "third carbon coating layer", "fourth carbon coating layer", and "fifth carbon coating layer" are only for descriptive purposes and cannot be understood as indicating or implying relative importance or quantity, nor can they be understood as implying the importance or quantity of the indicated technical features.

[0299] In some embodiments, the D50 of the first negative electrode active material is 10 to 18 pm, optionally 12 to 16 pm, and also can have any of the following values or a range selected from any two of the following values: 10 pm, 11 pm, 12 pm, 13 pm, 14 pm, 15 pm, 16 pm, 17 pm, 18 pm, etc. v 50 can be 10 pm to 18 pm, optionally 12 pm to 16 pm, and also can have any of the following values or a range selected from any two of the following values: 10 pm, 11 pm, 12 pm, 13 pm, 14 pm, 15 pm, 16 pm, 17 pm, 18 pm, etc.

[0300] In the present application, D v 50 refers to the particle size corresponding to the cumulative volume distribution percentage of 50% of the material, which indicates that 50% of the volume of the material has a particle size less than or equal to D v 50, and 50% of the volume of the material has a particle size greater than D v 50. Those skilled in the art can understand that D v50, and can be determined using instruments and methods known in the art. For example, laser particle size analyzers can be used conveniently, such as the Mastersizer 2000E laser particle size analyzer from Malvern Instruments Ltd., UK, and the LS-909 laser particle size analyzer (Microtrac). The D v 50. The detailed test procedure 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 to be 8% to 12% in optical density), ultrasonic treatment for 5 min (53 KHz / 120 W) to disperse the sample sufficiently, and then determining the sample according to the GB / T 19077-2016 / ISO 13320:2009 standard. After the sample is poured into the sample tower, it is circulated to the test light path system with the solution, and the particle size distribution characteristics of the particles can be obtained by receiving and measuring the energy distribution of the scattered light under the irradiation of the laser beam. The particle size volume distribution graph is drawn according to the test data, and the D v 50 is obtained from the distribution graph. In order to avoid the influence of agglomeration in the drying process on the test of the particle size, the wet sample after washing is taken for dispersion test.

[0301] By controlling the D v 50 of the first negative electrode active material to be within the aforementioned range, the accumulation degree of the particles in the first negative electrode active layer can be controlled better, the inter-particle pores can be controlled better, better lithium ion transmission channels can be provided, and the battery dynamics and fast charging performance can be improved better.

[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 this application, the "porosity" of a film layer refers to the proportion of the pore volume in the film layer to the total volume, which can be expressed in percentage. The "porosity" of the second negative electrode active layer refers to the proportion 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 proportion 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 electrode active material layer of the negative electrode sheet refers to the proportion of the pore volume in the negative electrode active material layer to the volume of the entire negative electrode active material layer, which can also be referred to as the "porosity of the negative electrode sheet".

[0304] By controlling the porosity of the first negative electrode active layer to be higher than the porosity of the second negative electrode active layer, the fast charging performance and the energy density of the battery can be taken into account, the relatively high porosity of the first negative electrode active layer can be used to promote the rapid transmission of lithium ions, and 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, the porosity (δ N ) of the negative active material layer of the whole negative electrode sheet can be determined by 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 the negative electrode sheet taken out after disassembling the battery cell can be tested, but also the negative electrode sheet obtained after cold pressing can be tested.

[0306] Pre-treatment: The negative electrode sheet is punched, and in the dry room, ≥20 pieces of round sheets with good appearance and no powder falling off the edges are selected by using tweezers and loaded into the sample cup. The test sample is n pieces of negative electrode sheet round sheets. Record the number n of pieces, and calculate the apparent volume V N2 of the test sample. N2 = S N × D N × n.

[0307] Test analysis: The sample cup loaded with the test sample is placed in the true density tester, and the closed test system is used to pass in helium gas according to the program. The pressure of the gas in the sample chamber and the expansion chamber is detected, and then the true volume V N1 of the test sample is calculated according to the Boyle law (PV = nRT), so as to calculate the porosity δ N of the test sample = (V N2 -V N1 ) / V N2 × 100%, which can be recorded as the porosity of the negative active material layer.

[0308] Wherein, the test sample is n pieces of negative electrode sheet round sheets; S N is the area of the negative active material layer in a single negative electrode sheet round sheet, with a unit of cm 2 ; D N is the thickness of the negative active material layer in a single negative electrode sheet round sheet, with a unit of cm; V N1 is the true volume of the test sample, cm 3 ; V N2 is the apparent volume of the test sample, with a unit of cm 3 .

[0309] Exemplarily, the porosity of the second negative active layer can be obtained by testing using the following method:

[0310] (1) Obtain a test sample 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 sheet, and use a micrometer to measure the electrode sheet thickness L; take another negative electrode sheet, wipe off the negative electrode active material layer on both sides of the remaining empty current collector foil, and measure the thickness L0. The total thickness of the negative electrode active material layer on both sides of the negative electrode current collector is L-L0; scrape off the negative electrode active material layer on one surface of the negative electrode sheet to expose the negative electrode current collector surface, and scrape off the negative electrode material on the other surface until the electrode sheet thickness is L1 = L0 + Δd. Collect the powder of the Δd thickness portion of the negative electrode active material layer below the L1 thickness. The thickness of the second negative electrode active layer can be determined in advance based on the observation results of the electrode sheet cross-sectional morphology, thereby controlling that when the thickness is L1, the first negative electrode active layer has been completely removed, 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 exemplarily 15μm, 20μm, etc. The sample to be tested retains only the second negative electrode active layer on one side of the negative electrode current collector.

[0311] (2) Test the porosity (δ2) of the second negative electrode active layer: Test the porosity of the sample to be tested by referring to the method for testing the porosity of the negative electrode sheet, and record it as the porosity of the second negative electrode active layer.

[0312] When δ N When the porosity is greater than δ2, 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". Furthermore, for example, the porosity (δ1) of the first negative electrode active layer can be determined according to formula D. N ×δ N =D1×δ1+D2×δ2 is calculated; where δ N δ1 represents the porosity of the entire negative electrode active material layer, δ2 represents the porosity of the second negative electrode active layer, and D represents the porosity of the second negative electrode active layer. N D1 is the total thickness of the negative electrode active material layer, D2 is the thickness of the second negative electrode active layer, and D1 is the thickness of the first negative electrode active layer.

[0313] In addition, by way of example, the porosity of the negative electrode active material layer in the negative electrode sheet can also be tested, 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 remove the negative electrode sheet; punch the negative electrode sheet into small discs, and use the nanoscale spatial dynamic resolution and layer-by-layer cutting technique of FIB-SEM (Focused Electron Beam Electron Microscopy-Scanning Electron Microscopy) to reconstruct the three-dimensional structure of the sample; use energy dispersive spectroscopy (EDS) to analyze the distribution and proportion of each element; and use software to quantitatively analyze the porosity of the first negative electrode active layer, the second negative electrode active layer, and the overall negative electrode active material layer. The FEI Scios 2HiVac instrument 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 / cm³. 3 ~1.80g / cm 3 It can also be any of the following values ​​or a range selected from any two of the following values: 1.60 g / cm³ 3 1.62g / cm 3 1.64 g / cm 3 1.65g / cm 3 1.66 g / cm 3 1.68g / cm 3 1.70g / cm 3 1.72g / cm 3 1.74 g / cm 3 1.75g / cm 3 1.76 g / cm 3 1.78g / cm 3 1.80g / cm 3 wait.

[0315] In this 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 term "powder compaction density" has a well-known meaning in the art, referring to the ratio of mass to volume of a powder material after compaction 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 that negative electrode active layer. "Powder material" and "powder material" have the same meaning and can be used interchangeably.

[0317] The "powder compaction density" of powder materials can be determined using instruments and methods known in the art. For example, it can be determined using an electronic pressure testing machine (e.g., UTM7305 model) according to standard GB / T24533-2009. An exemplary test method is as follows: Weigh out a mass M (e.g., 1g) of the material to be tested, and add a bottom area A (e.g., 1.327cm²). 2 In a mold, pressure is applied to a certain pressure P0 (e.g., 3-5 tons (3T-5T), such as 3T, 4T, 5T), and held for a certain time (e.g., 5T for 30s). Then the pressure is released, and the pressure is maintained for a period of time (e.g., 10s). The compacted density of the powder under pressure P0 is then recorded and calculated. Unless otherwise specified, the pressure for testing the compacted density of the powder is 5T.

[0318] The powder compaction density test is performed on 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, so as to compare or obtain the powder compaction densities of the first negative electrode active layer and the second negative electrode active layer. The first negative electrode material and the second negative electrode material can be extracted from the negative electrode sheet after the disassembled battery, or can be extracted from the negative electrode sheet obtained after cold pressing. The first negative electrode material and the second negative electrode material can be ultrasonically dispersed in a solvent before the test, and then dried.

[0319] The powder compaction densities of the first negative electrode active material and the second negative electrode active material can also be obtained by testing the powder raw materials of the first negative electrode active material or the second negative electrode active material. The powder compaction density test can also be performed after disassembling the battery to obtain the to-be-tested powder of the first negative electrode active material and / or the to-be-tested powder of the second negative electrode active material. The preparation method of the to-be-tested powder can refer to the OI test part.

[0320] In the present application, unless otherwise stated, the "negative electrode sheet obtained after cold pressing" refers to the state of the negative electrode sheet obtained after cold pressing when the cold pressing is just completed. It can be considered that in this state, the volume rebound of the electrode sheet has not occurred or almost has not 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 above range, the particle packing degree of the first negative electrode active layer can be facilitated to provide better lithium ion transmission channels, thereby better improving the battery kinetics and fast charging performance. In addition, the second negative electrode active layer can also be used to provide higher energy density, thereby facilitating the consideration of the fast charging performance and energy density of the lithium ion secondary battery.

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

[0323] In some embodiments, the rate of the first negative electrode active layer is higher than the rate 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 capacity, and the "charge rate" is a parameter reflecting the charging capacity. The higher the charge rate, the better the fast charging performance.

[0326] The first active layer pole piece and the second active layer pole piece can be prepared by the following method: based on the negative electrode pole piece obtained by cold pressing or the negative electrode pole piece obtained by disassembling the battery cell, the first negative electrode material is extracted from the first negative electrode active layer, and the second negative electrode material is extracted from the second negative electrode active layer, and then the deionized water is used to resuspend the first negative electrode material and the second negative electrode material into uniform slurries, respectively, which are denoted as the first resuspended slurry and the second resuspended slurry. The second resuspended slurry is coated on one side surface of the negative electrode current collector copper foil, dried, cold-pressed, and the second active layer pole piece is obtained. The first resuspended slurry is coated on one side surface of the negative electrode current collector copper foil, dried, cold-pressed, and the first active layer pole piece is obtained. The difference between the first resuspended slurry and the second resuspended slurry lies in the difference between the first negative electrode material and the second negative electrode material, and the parameters of coating weight, drying and cold pressing are the same. Further, the first active layer pole piece and the second active layer pole piece are respectively combined with lithium sheets to form a button cell, and a rate test is performed. If the rate of the button cell prepared by the first active layer pole piece is higher than that of the button cell prepared by the second active layer pole piece, it is considered that “the rate of the first negative electrode active layer is higher than that of the second negative electrode active layer”. The existing method for testing the rate of the button cell in the art can be used for testing. If the charge rate of the button cell prepared by the first active layer pole piece is higher than that of the button cell prepared by the second active layer pole piece, it is considered that “the rate of the first negative electrode active layer is higher than that of the second negative electrode active layer”. The existing method for testing the charge rate of the button cell in the art can be used for testing.

[0327] In the present application, the rate or charge rate of the first negative electrode active layer and the second negative electrode active layer can be compared by the following method unless otherwise stated:

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

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

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

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

[0332] Assemble all components into CR2430 button cell in a glove box under argon protection. "CR" represents the international IEC number of button lithium-manganese battery, 24 mm in diameter, 30 mm in thickness. After standing for 12 hours, the obtained button cell is discharged at 0.05C constant current to 0.005V, and then discharged at 10μA constant current to 0.005V. Then stand for 5 minutes, the obtained button cell is charged at 0.1C constant current to 2V, stand for 5 minutes, and record the charge capacity C0. The battery is placed at 25℃ for 2h, and then subjected to charge-discharge test at 1C0, 2C0, 3C0, 4C0, 5C0 rate, to obtain the capacity retention rate. Under the same cycle conditions and cycle number, the higher the capacity retention rate, the better the rate performance, which can be considered as the higher "rate".

[0333] In addition, under the same charging conditions, the shorter the time taken to charge to the same SOC (such as 80% SOC, and the cutoff current can be 0.01C) at the same rate, the better the charging rate performance, which can be considered as the higher "charging rate".

[0334] By controlling the rate of the first negative electrode active layer to be higher than the 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 it is more beneficial to improve 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 it is more beneficial to improve the fast charging performance of the battery.

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

[0337] In the present application, unless otherwise specified, the "ionic conductivity" of the electrolyte has the 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 using a conductivity tester, such as DDSJ-318 conductivity meter. The test temperature can be 25±0.1℃. The test can be performed according to the method of HG-T 4067-2015. Without limitation, the test can be performed by a method comprising the following steps:

[0338] Pre-treatment: take the standard liquid to constant temperature at 25℃ (deviation ±0.1℃), and take the test liquid to constant temperature at the test temperature (deviation ±0.1℃);

[0339] Test: test the two kinds of standard liquid calibration calibration instrument at 25℃, after calibration and cleaning the electrode, test the sample electrode vertically into the test liquid, click start test, and record the test results after the data is stable for more than 10s.

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

[0341] The ionic conductivity of the electrolyte of some embodiments can be referred to the context of the present application. The electrolyte with higher conductivity can be obtained by selecting solvents with low viscosity characteristics, but is not limited thereto.

[0342] Non-limitingly, the electrolyte includes a non-aqueous solvent, the non-aqueous solvent includes a low viscosity solvent, the low viscosity solvent can include one or more of ethyl acetate, methyl acetate, dimethyl carbonate, methyl ethyl carbonate, etc., and a solvent with a viscosity less than or equal to at least one of the aforementioned reagents at 25℃.

[0343] In the present application, without other instructions, the viscosity of the solvent or electrolyte can be tested by the conventional method in the art, and can be determined by the instrument and method known in the art, for example, the viscosity can be tested according to the national standard GB / T10247-2008 "Viscosity Measurement Method", and can be tested based on the rotary viscometer in the appendix D of the national standard GB / T10247-2008. Non-limitingly, the viscosity of the solvent or electrolyte can be tested by the following method: a certain mass of the sample to be tested is placed in a sample container, and a rotary viscometer produced by Brookfield Company with model number DV2TLV is used 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 of the second negative electrode active material v 50 is 12μm~21μm, which can be selected as 14μm~20μm, and further selected as 14μm~19μm;

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

[0347] (te3) the second negative electrode active layer has a higher compaction density than the first negative electrode active layer;

[0348] (te4) the second negative electrode active material has a higher powder compaction density than the first negative electrode active material, or the second negative electrode active layer has a higher powder compaction density than 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, more further optionally 1.10-1.28 or 1.15-1.30, more further optionally 1.15-1.28; 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 1.05-1.35, further optionally 1.10-1.30, more further optionally 1.10-1.28 or 1.15-1.30;

[0349] (te5) the second negative electrode active layer has a powder compaction density of 1.85 g / cm 3 -2.05 g / cm 3 .

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

[0351] In some embodiments, the second negative electrode active material comprises secondary particle type graphite. Without limitation, the amount of the secondary particle type graphite in the second negative electrode active material can be 0-100%, optionally 20-100%, further optionally 50-100%, more further optionally 80-100%, or any one 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.

[0352] In some embodiments, the D50 of the second negative electrode active material is 12-21 μm, optionally 14-20 μm, further optionally 14-19 μm, or any one of the following values or a range consisting of any two of the following values: 12 μm, 13 μm, 14 μm, 15 μm, 16 μm, 17 μm, 18 μm, 19 μm, 20 μm, 21 μm, etc. v

[0353] By making the D50 of the second negative electrode active material 12-21 μm, optionally 14-20 μm, further optionally 14-19 μm, or any one of the following values or a range consisting of any two of the following values: 12 μm, 13 μm, 14 μm, 15 μm, 16 μm, 17 μm, 18 μm, 19 μm, 20 μm, 21 μm, etc. v ​Keeping 50 within the aforementioned range is beneficial for achieving a higher compaction density in the second negative electrode active layer, which in turn helps to improve the energy density.

[0354] In some embodiments, the 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 of the second negative electrode active material v 50 higher than the D of the first negative electrode active material v 50 is beneficial for achieving a higher compaction density in the second negative electrode active layer, which in turn helps 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 / cm³. 3 1.50g / cm³ is an optional value. 3 ~1.75g / cm 3 It can also be any of the following compaction densities or a range selected from any two of the following compaction densities: 1.40 g / cm³ 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 the 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] Non-limitingly, the compaction density of the negative electrode sheet in a lithium-ion secondary battery can be tested using the following method: disassemble the battery to obtain the negative electrode sheet, and punch the obtained negative electrode sheet into a piece with an area S0 (e.g., 1540.25 mm²). 2 The small circular disc is used to measure its mass M. B and thickness L B Take another negative electrode sheet from a different region, wipe off the surface negative electrode active material layer, and cut the remaining negative electrode current collector foil (which can be denoted as empty negative electrode current collector foil) into small circular pieces with an area of ​​S0. Weigh the empty negative electrode current collector foil and record the mass as M0 and the thickness as L0. Then, the compaction density PD of the negative electrode sheet is... B =(M B -M0) / [S0×(L B -L0)]. Test multiple small discs and take the average value.

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

[0360] The volume of the negative electrode sheet in the lithium ion secondary battery will have a certain rebound relative to the negative electrode sheet obtained after cold pressing, 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 active layer is higher than the compaction density of the first negative active layer.

[0362] In the present application, unless otherwise specified, the "compaction density" of the second negative active layer refers to the ratio of the mass to the volume of the second negative active layer, and the compaction density of the first negative active layer refers to the ratio of the mass to the volume of the first negative active layer.

[0363] Exemplarily, the compaction density of the second negative active layer in the negative electrode sheet of the lithium ion secondary battery can be tested by the following method: disassembling the battery to obtain the negative electrode sheet, wiping off part of the material of the negative active material layer to obtain a sheet sample including at least part of the second negative active layer and not including the first negative active layer, and punching into a small disc with an area S0 (such as 1540.25mm 2 ). The mass M2 and thickness L2 of the sheet sample are measured respectively, and the mass M0 and thickness L0 of the empty negative current collector foil with the same area S0, then the compaction density PD2 of the sheet sample = (M2-M0) / [S0x (L2-L0)], which can be taken as the compaction density of the second negative active layer.

[0364] When the compaction density PD B of the negative electrode sheet is lower than the compaction density PD2 of the second negative active layer, it can be considered that "the compaction density of the second negative active layer is higher than the compaction density of the first negative active layer".

[0365] By regulating the second negative active layer in the lithium ion secondary battery to have a higher compaction density than the first negative active layer, it is beneficial to improve the energy density of the lithium ion secondary battery.

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

[0367] In some embodiments, the ratio of the tap density of the second negative active material to the tap density of the first negative 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 values or a range selected from any two of the following values: 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 tap density of the second negative active layer is higher than the tap density of the first negative active layer.

[0369] In some embodiments, the ratio of the tap density of the second negative active layer to the tap density of the first negative active layer 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 values or a range selected from any two of the following values: 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: 1.05-1.30, 1.05-1.28, 1.1-1.3, 1.10-1.35, 1.15-1.28, etc.

[0370] By controlling the tap density of the second negative active material to be higher than the tap density of the first negative active material in the lithium ion secondary battery or controlling the tap density of the second negative active layer to be higher than the tap density of the first negative active layer, it is beneficial to give the second negative active layer a higher tap density during the cold pressing of the electrode sheet, so that the second negative active layer in the lithium ion secondary battery has a higher tap density. Further by controlling the ratio of the tap density of the second negative active material to the tap density of the first negative active material or controlling the ratio of the tap density of the second negative active layer to the tap density of the first negative active layer to be 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 tap density of the second negative active material or the tap density of the second negative active layer is 1.85 g / cm 3 ~2.05 g / cm3 Also, any one of the following values or a range selected from any two of the following values can be used: 1.85 g / cm 3 , 1.86 g / cm 3 , 1.88 g / cm 3 , 1.90 g / cm 3 , 1.92 g / cm 3 , 1.94 g / cm 3 , 1.95 g / cm 3 , 1.96 g / cm 3 , 1.98 g / cm 3 , 2.00 g / cm 3 , 2.02 g / cm 3 , 2.04 g / cm 3 , 2.05 g / cm 3 , etc.

[0372] By controlling the powder compaction density of the second negative active material or the powder compaction density of the second negative active layer within the aforementioned range, it is beneficial to make the secondary battery have a higher energy density. In addition, the particle packing can be relatively tight, at which time the improvement effect of the quaternary ammonium salt type compound introduced in the second negative active layer on the fast charging performance of the battery can be more obvious.

[0373] In some embodiments, the negative electrode sheet satisfies one or more of the following features (any numerical parameter in the following features can also be selected from any suitable value or range in the context):

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

[0375] (tf2) the thickness ratio of the first negative active layer to the second negative active layer, calculated on a single side of the negative current collector, is denoted as f H , satisfies 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 active layer, calculated on a single side of the negative current collector, is less than or equal to 50 μm, optionally 30 μm to 40 μm.

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

[0378] In some embodiments, the ratio of the areal density of the second negative active layer to the areal density of the first negative active layer, calculated on the single side of the negative current collector, is 3:2 to 2:3, and can also be any of the following values or a range selected from any two of the following values: 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), and the like.

[0379] In the present application, unless otherwise specified, the "areal density of the second negative active layer, calculated on the single side of the negative current collector" refers to the ratio of the mass of the second negative active layer on the single side of the negative current collector to the area of the second negative active layer on the same side, and the "areal density of the first negative active layer" refers to the ratio of the mass of the first negative active layer on the single side of the negative current collector to the area of the first negative active layer on the same side, and the corresponding "area" is equal to the orthogonal projection area of the second negative active layer and the first negative active layer in the thickness direction of the electrode plate. Numerically, the areal density of the second negative active layer, calculated on the single side of the negative current collector, is equal to the product of the compacted density of the second negative active layer and the thickness of the second negative active layer, and the mass and area data can be obtained by referring to the test method for the compacted density of the second negative active layer. Numerically, the areal density of the first negative active layer, calculated on the single side of the negative current collector, is equal to the product of the compacted density of the first negative active layer and the thickness of the second negative active layer, and the mass and area data can be obtained by referring to the test method for the compacted density of the first negative active layer.

[0380] By controlling the ratio of the areal density of the second negative active layer to the areal density of the first negative active layer within the aforementioned range, the battery fast charging performance and the energy density can be considered.

[0381] In some embodiments, the ratio of the thickness of the first negative active layer to the thickness of the second negative active layer, calculated on the single side of the negative current collector, is denoted as f H , and satisfies f H ≤1.6, and optionally, 1.1≤f H ≤1.6, and further optionally, 1.1≤f H ≤1.3, and f H may also be any of the following values or a range selected from any two of the following values: 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, and the like.

[0382] In some embodiments, the thickness of the first negative active layer is less than or equal to 50 pm, optionally 20 pm to 50 pm, further optionally 30 pm to 50 pm, still further optionally 30 pm to 40 pm, and / or in a range defined by any two of the following values: 20 pm, 25 pm, 30 pm, 35 pm, 40 pm, 45 pm, 50 pm, etc., in terms of a single side of the negative current collector.

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

[0384] By controlling the thickness of the first negative active layer to satisfy one or more of the above features (tf2) and (tf3), the distance of the quaternary ammonium salt type compound from the surface of the negative electrode sheet can be adjusted, which is conducive to better promoting the transmission of lithium ions to the second negative active layer located in the lower layer, thereby being conducive to better improving the fast charging performance of the battery.

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

[0386] By providing the quaternary ammonium salt type compound in the negative active material layer, the electrolyte anions in the electrolyte can be attracted by the electrostatic action based on the quaternary ammonium cation, the rapid dissociation of the electrolyte lithium salt in the electrolyte is promoted, and the quaternary ammonium cation-electrolyte anion structure formed can also guide the rapid transmission of lithium ions in the electrolyte to the surface of the negative active material, which can significantly improve the kinetics of the negative electrode sheet, and in turn can significantly improve the fast charging performance of the battery.

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

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

[0389] The negative electrode active material layer comprises a negative electrode active material and a quaternary ammonium salt type compound, the negative electrode active material comprises 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 comprises one or more of soft carbon, hard carbon and amorphous carbon, and the quaternary ammonium salt type compound comprises a quaternary ammonium cation.

[0390] By arranging the coating layer on the surface of the negative electrode active material in 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, the lithium ion transmission can be promoted, and the battery kinetics and the battery fast charging performance can be improved. Further, by arranging the quaternary ammonium salt type compound in the negative electrode active material layer, the electrolyte anions in the electrolyte can be attracted by the electrostatic action based on the quaternary ammonium cation, the electrolyte lithium salt in the electrolyte can be quickly dissociated, and the quaternary ammonium cation-electrolyte anion structure formed can guide the lithium ions in the electrolyte to quickly transmit to the surface of the negative electrode active material. Based on the foregoing multiple effects, the fast charging performance of the battery can be better improved.

[0391] The negative electrode active material layer can comprise one or more negative electrode active layers, that is, the negative electrode active material layer can 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 comprises a carbon-based material.

[0394] In some embodiments, the mass percentage of the carbon-based material in the negative electrode active material can be 80% to 100%, optionally 90% to 100%, or any one of the following percentages or a range formed by 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, the surface of the particles of the negative electrode active material is provided with carbon substances. The carbon substances can comprise one or more of artificial graphite, natural graphite, soft carbon and hard carbon.

[0396] In some embodiments, the negative electrode active material comprises a graphite material. The graphite material can comprise one or more of artificial graphite and natural graphite.

[0397] In some embodiments, the mass percentage of the graphite-based material in the negative active material can be 80% to 100%, optionally 90% to 100%, and can also be any one of the following percentages or a range selected from any two of the following percentages: 80%, 82%, 84%, 85%, 86%, 88%, 90%, 92%, 94%, 95%, 96%, 97%, 98%, 99%, 100%, and the like.

[0398] In some embodiments, the surface of the particles of the negative active material is provided with graphite. The graphite can include one or more of artificial graphite, natural graphite.

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

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

[0401] (tg2) the mass percentage of the quaternary ammonium salt type compound in the negative active material layer is 0.2% to 2%, optionally 0.2% to 1.5%, and can also be any one 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%, and the like;

[0402] (tg3) the negative 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 active material includes a carbon-based material, and the mass percentage of the carbon-based material in the negative active material layer is 94.5% to 97.5%, optionally 95.0% to 97.0%, and can also be any one of the following percentages or a range selected from any two of the following percentages: 95%, 95.5%, 96%, 96.5%, 97%, 97.5%, and the like;

[0404] (tg5) the negative active material layer includes a binder, and the binder includes a 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 selected from 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, and the like;

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

[0406] (tg7) The negative active material comprises secondary particle type graphite, the secondary particle type graphite comprises a secondary particle graphite body, the amount of the secondary particle type graphite in the negative active material is greater than or equal to 20%, optionally 30% to 60%, and can also be any one 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.; optionally, the secondary particle type graphite comprises carbon-coated secondary particle type graphite, the carbon-coated secondary particle type graphite comprises a secondary particle graphite body and a carbon coating layer on at least a part of the surface of the secondary particle graphite body, the carbon coating layer in the carbon-coated secondary particle type graphite comprises one or more of soft carbon, hard carbon and amorphous carbon;

[0407] (tg8) The negative active material comprises a graphite material, the OI value of the graphite material is 2 to 15, optionally 2 to 10, and can also be any one 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.;

[0408] (tg9) The D v 50 is 11 μm to 20 μm, optionally 13 μm to 18 μm, and can also be any one of the following values or a range selected from 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 active material layer is 15% to 35%, optionally 25% to 30%, and can also be any one of the following porosities or a range selected from 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 13 mS / cm to 18 mS / cm at least one of the temperature conditions of 20°C to 35°C; optionally, the ionic conductivity of the electrolyte is 13 mS / cm to 18 mS / cm at 25°C, and can also be any one of the following values or a range selected from 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.;

[0411] The negative active material layer (tg12) comprises a second negative active layer, and the definition of the second negative active layer can refer to the first aspect of the application.

[0412] The test method of the related parameters in features (tg1) to (tg11) can refer to the related test method in the context.

[0413] By controlling the mass ratio of the quaternary ammonium salt type compound in the negative active material layer within the aforementioned range, the role of the quaternary ammonium salt type compound in improving the fast charging performance of the battery can be better played, and the decrease of the electronic conductivity of the surface of the negative active material caused by the wrapping of the quaternary ammonium salt type compound can be better controlled, which is conducive to better improving the fast charging performance of the battery. Further, it is also conducive to keeping the negative active material layer with a high lithium storage capacity, and is conducive to balancing the energy density of the negative electrode and the battery.

[0414] The carbon-based material is conducive to better adsorbing the hydrocarbon chain in the quaternary ammonium salt type compound, thereby facilitating the quaternary ammonium salt type compound to better wrap the surface of the negative active material, and thereby facilitating the lithium ions in the electrolyte to be better guided to the surface of the negative active material; on the other hand, the carbon-based material also has good electronic conductivity; on the other hand, the carbon-based material is also conducive to providing better stability of the negative active material during fast charging, and is not easy to be pulverized; through the aforementioned multiple effects, it is conducive to better improving the kinetics of the negative electrode sheet and the fast charging performance of the battery.

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

[0416] By controlling the mass ratio of the carbon-based material in the negative active material layer within the aforementioned range, the quaternary ammonium salt type compound is better wrapped on the surface of the negative active material, and in addition, the energy density of the negative electrode and the battery can be balanced.

[0417] By introducing the carbon-based material into the negative active material of the negative active material layer and introducing the butadiene styrene rubber into the binder, it is conducive to better simultaneously realizing the wrapping of the binder and the quaternary ammonium salt type compound on the surface of the negative active material, which can realize a good electrical contact network, and fully play the role of the quaternary ammonium salt type compound in guiding the lithium ions in the electrolyte, and is conducive to better improving the fast charging performance of the battery.

[0418] By controlling the glass transition temperature of the styrene-butadiene rubber in the aforementioned range, it is beneficial to make the negative electrode active material layer have a better pore structure after being rolled, and it is beneficial to promote the electrolyte to better infiltrate the negative electrode active material layer.

[0419] By providing a coating layer on the surface of the negative electrode active material in the negative electrode active material layer, and providing 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, the lithium ion transmission is promoted, and the battery dynamics and battery fast charging performance are further improved.

[0420] By introducing a coated graphite into the negative electrode active material layer, and providing 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, the lithium ion transmission is promoted, and the battery dynamics and battery fast charging performance are further improved.

[0421] By introducing secondary particle type graphite into the negative electrode active material layer, and utilizing the characteristics that the secondary particles are formed by agglomeration of primary particles, 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, improve the insertion rate of lithium ions, and improve the battery fast charging performance.

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

[0423] By controlling the D v 50 in the aforementioned range, it is beneficial to better control the degree of particle accumulation in the negative electrode active material layer, better control the inter-particle pores, provide a better lithium ion transmission channel, and better improve the battery dynamics and fast charging performance.

[0424] When the porosity of the negative electrode active material layer is controlled in the aforementioned range, the particles are relatively tightly packed, and at this time, the improvement effect of the quaternary ammonium salt type compound introduced into the negative electrode active material layer on the battery fast charging performance is more obvious.

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

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

[0427] In the present application, unless otherwise specified, the "areal density of the negative electrode tab, calculated on the single side of the negative electrode current collector" is equal to the ratio of the mass of the negative active material layer on the single side of the negative electrode current collector to the area of the negative active material layer, and the corresponding "area" is equal to the orthographic projection area of the negative active material layer along the thickness direction of the tab. Reference can be made to the test method for the compaction density of the negative electrode tab, and the value is calculated according to (M B -M0) / S0.

[0428] By controlling the areal density of the negative electrode tab within the aforementioned range, the battery fast-charging performance and the energy density can be taken into account.

[0429] In some embodiments, the electrolyte includes an electrolyte salt, and the electrolyte salt includes an electrolyte anion. Without limitation, the electrolyte anion can include one or more of tetrafluoroborate, hexafluoroarsenate, hexafluorophosphate, triflate, difluorophosphate, difluoro oxalate borate, tetrafluoro oxalate phosphate, difluoro di-oxalate phosphate, bisfluorosulfonylimide, and bis-trifluoromethanesulfonylimide.

[0430] By selecting the aforementioned electrolyte anion species, the electrolyte anion has a stronger binding capacity for the quaternary ammonium cation, which is conducive to better promoting the dissociation of the quaternary ammonium cation and the anion in the quaternary ammonium salt type compound, promoting the attraction of the quaternary ammonium salt type compound to the electrolyte anion and the guidance of lithium ions in the electrolyte, improving the transmission rate of lithium ions to the second negative electrode active material, and better improving the kinetics of the negative electrode tab and the battery fast-charging performance.

[0431] The aforementioned listed electrolyte anion species has a stronger electronegativity and stronger binding capacity for the quaternary ammonium cation relative to one or more of nitrate, carbonate, bicarbonate, and phosphate.

[0432] In some embodiments, the electrolyte salt includes one or more of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalate borate, lithium dioxalate borate, lithium difluorodioxalate phosphate, and lithium tetrafluorooxalate phosphate.

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

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

[0435] In this application, unless otherwise specified, lithium phosphate-containing active materials may include at least one of lithium phosphates and their modifications. Lithium phosphate-containing active materials may have an olivine structure. Unless otherwise specified, "lithium phosphate" refers to materials containing lithium, transition metal elements, and phosphate ions (PO4). 3- The positive electrode active material is olivine-structured lithium phosphate. Non-limiting examples of lithium phosphates may include, but are not limited to, one or more of lithium iron phosphate, lithium iron phosphate and carbon composites, lithium manganese phosphate, lithium manganese phosphate and carbon composites, lithium iron manganese phosphate, and lithium iron manganese phosphate and carbon composites.

[0436] Introducing lithium phosphate-containing active materials into the positive electrode active material can improve the structural stability of the positive electrode active material during charge-discharge cycles and extend the cycle life of the battery.

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

[0438] In this application, unless otherwise specified, lithium composite metal oxide active materials include at least one of lithium composite metal oxides and their modified forms. Unless otherwise specified, "lithium composite metal oxide" refers to a positive electrode active material comprising lithium, non-lithium metal elements, and oxygen. Typically, the non-lithium metal elements in lithium composite metal oxides include transition metal elements; therefore, lithium composite metal oxides can also be called "lithium transition metal oxides." Lithium composite metal oxide active materials can have crystal structures suitable for positive electrode active materials, such as layered structures and spinel structures. In some embodiments, the lithium composite metal oxide active material comprises a layered structure. In some embodiments, the lithium composite metal oxide active material has a layered structure.

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

[0440] In the present application, unless otherwise specified, the "modified material of a certain positive electrode active material" includes the positive electrode active material itself and the modifying element, and further, the modifying element can exist in the form of a doping element, in the form of a coating element, or in the form of a combination of the doping element and the coating element. Unless otherwise specified, the "modified material of a certain positive electrode active material" still belongs to the category of positive electrode active materials.

[0441] In the present application, unless otherwise specified, the "doping element" involved in the positive electrode active material refers to the modifying element doped in the positive electrode active material; unless otherwise specified, the "coating element" involved in the positive electrode active material refers to that the positive electrode active material includes a positive electrode active particle body and a coating layer located on at least a portion of the surface of the positive electrode active particle body, wherein the coating element is the modifying element located in the coating layer. As a non-limiting example, in the positive electrode active material, "the modifying element exists in the form of a combination of the doping element and the coating element" means that the positive electrode active material includes a positive electrode active particle body and a coating layer located on at least a portion of the surface of the positive electrode active particle body, at least a portion of the modifying element is doped in the positive electrode active particle body, and at least a portion of the modifying element is also contained in the coating layer. Both 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 modification method known 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 a doped modified material thereof. In some embodiments, the doping element can 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 can include one or more of Ti, Mg, Nb, C, etc.

[0442] In some embodiments, the positive electrode active material includes a lithium-containing 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 fraction of the lithium-containing phosphate-based active material in the positive electrode active layer is greater than or equal to 80%, and can be 80% to 97%;

[0444] (th2) the lithium-containing phosphate-based 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 manganese iron phosphate, and a composite material of lithium manganese iron phosphate and carbon;

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

[0446] In some embodiments, the mass percentage of the lithium-containing phosphate-based active material in the positive active layer can be greater than or equal to 80%, optionally 80% to 97%, and further optionally 95% to 97%. Without limitation, the mass percentage of the lithium-containing phosphate-based active material in the positive active layer can also be any one 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%, and the like.

[0447] By controlling the mass percentage of the lithium-containing phosphate-based active material in the positive active layer within the aforementioned range, the cycle life of the battery can be better extended.

[0448] In some embodiments, the lithium-containing phosphate-based active material includes one or more of lithium iron phosphate (LFP), a composite of lithium iron phosphate and carbon, lithium manganese phosphate, a composite of lithium manganese phosphate and carbon, lithium manganese iron phosphate, and a composite of lithium manganese iron phosphate and carbon. An example of lithium iron phosphate is LiFePO4. An example of lithium manganese phosphate is LiMnPO4.

[0449] The type of lithium-containing phosphate-based active material can be flexibly selected to meet different application requirements.

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

[0451] By providing a carbon coating layer including one or more of soft carbon, hard carbon, and amorphous carbon on the surface of the lithium-containing phosphate-based active material, the electrical conductivity of the material can also be improved, which is beneficial for improving the electrical contact network in the positive electrode sheet and providing a fast and stable channel for electron transmission in the positive electrode sheet, thereby being beneficial for improving the rate performance of the battery and improving the fast charging capability of the battery.

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

[0453] In some embodiments, the positive active material comprises a lithium iron phosphate-based positive active material. The lithium iron phosphate-based positive active material comprises a lithium iron phosphate bulk, and further comprises a carbon coating layer (which can be referred to as a fourth carbon coating layer) on at least a portion of the surface of the lithium iron phosphate bulk. Optionally, the carbon coating layer (i.e., the fourth carbon coating layer) in the lithium iron phosphate-based positive active material can comprise one or more of soft carbon, hard carbon, and amorphous carbon. Without limitation, the lithium iron phosphate-based positive active material can comprise carbon-coated lithium iron phosphate.

[0454] In some embodiments, the positive active material comprises carbon-coated lithium iron phosphate, which comprises a lithium iron phosphate bulk and a carbon coating layer (which can be referred to as a fifth carbon coating layer) on at least a portion of the surface of the lithium iron phosphate bulk. Further, the carbon coating layer (i.e., the fifth carbon coating layer) in the carbon-coated lithium iron phosphate can comprise one or more of soft carbon, hard carbon, and amorphous carbon. In some embodiments, the carbon coating layer comprises soft carbon. In this case, the positive active material comprises a lithium-containing phosphate-based active material, which comprises the carbon-coated lithium iron phosphate.

[0455] The skilled person can select and regulate the mass ratio of the carbon coating layer in the lithium iron phosphate-based positive active material (for example, the carbon-coated lithium iron phosphate) and the thickness or average thickness of the carbon coating layer using conventional techniques. Without limitation, the mass ratio of the carbon coating layer in the lithium iron phosphate-based positive active material (for example, the carbon-coated lithium iron phosphate) can be 0.2% to 2%, but is not limited thereto. Without limitation, the average thickness of the carbon coating layer in the lithium iron phosphate-based positive active material can be 10 nm to 20 nm, but is not limited thereto.

[0456] In some embodiments, the positive active material comprises soft carbon-coated lithium iron phosphate. Further, the soft carbon-coated lithium iron phosphate comprises a lithium iron phosphate bulk and soft carbon on at least a portion of the surface of the lithium iron phosphate bulk.

[0457] The detection of the positive active material in the positive active layer can be performed by disassembling the battery cell after the battery is fully discharged, removing the positive electrode sheet, scraping the material of the positive active layer, and testing and analyzing the types and proportions of elements using an inductively coupled plasma (ICP) spectroscopy method or other elemental analysis method, thereby confirming the elemental composition and chemical formula of the positive active material.

[0458] In some embodiments, the positive active material comprises a positive active bulk and a coating layer on the positive active.

[0459] For the positive electrode active material including a coating layer (an example of the coating layer is a carbon coating layer), after the FIB (focused ion beam) cross-section is cut, the cross-sectional morphology of the particle is observed under the TEM (transmission electron microscope), and a clear boundary at the coating interface can be observed. Based on the TEM image, the thickness and average thickness of the coating layer can be analyzed and calculated. Further, one or more of energy dispersive spectroscopy (EDS) analysis, Raman spectroscopy, and the like can be used to identify the types of substances in the coating layer and the positive electrode active body, respectively.

[0460] The following is some other description of the positive electrode tab.

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

[0462] The definitions of the positive electrode tab, the positive electrode active layer, and the positive electrode active material of some embodiments can be found in the context of the present application.

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

[0464] As a non-limiting example, the positive electrode current collector has two surfaces facing away from each other in the thickness direction thereof, and the positive electrode active layer is disposed on any one or both of the two surfaces of the positive electrode current collector facing away from each other.

[0465] In some embodiments, the positive electrode current collector can adopt a metal foil or a composite current collector. For example, as a metal foil, an aluminum foil can be used. In the positive 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 positive electrode current collector, the composite current collector can be obtained by forming a metal material on the polymer material base layer. In the positive electrode current collector, non-limiting examples of the metal material can include at least one of aluminum, an aluminum alloy, nickel, a nickel alloy, titanium, a titanium alloy, silver, a silver alloy, and the like. Without limitation, in the positive 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), and the like.

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

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

[0468] In some embodiments, the positive active material includes lithium-containing phosphates of olivine structure. Non-limiting examples of lithium-containing phosphates of olivine structure can include, but are not limited to, one or more of: lithium iron phosphate, a composite of lithium iron phosphate and carbon, lithium manganese phosphate, a composite of lithium manganese phosphate and carbon, lithium manganese iron phosphate, a composite of lithium manganese iron phosphate and carbon. An example of lithium iron phosphate is LiFeP04. An example of lithium manganese phosphate is LiMnP04.

[0469] In some embodiments, the positive active material includes lithium transition metal oxides. Examples of lithium transition metal oxides can 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 modifications thereof. Non-limiting examples of lithium cobalt oxide can include LiCo02; non-limiting examples of lithium nickel oxide can include LiNi02; non-limiting examples of lithium manganese oxide can include LiMn02, LiMn204, and the like; non-limiting examples of lithium nickel cobalt manganese oxide can include LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 02(also can be referred to simply as NCM 333 ), LiNi 0.5 Co 0.2 Mn 0.3 02(also can be referred to simply as NCM 523 ), LiNi 0.5 Co 0.25 Mn 0.25 02(also can be referred to simply as NCM 211 ), LiNi 0.6 Co 0.2 Mn 0.2 02(also can be referred to simply as NCM 622 ), LiNi 0.8 Co 0.1 Mn 0.1 02(also can be referred to simply as NCM 811 ), and the like. Non-limiting examples of lithium nickel cobalt aluminum oxide can include LiNi 0.80 Co 0.15 Al 0.05 02.

[0470] It can be understood that the battery will be accompanied by lithium (Li) deintercalation and consumption during charging and discharging, and the content of Li in the positive plate is different when the battery is discharged to different states. In the exemplary description of the positive active material in this application, unless otherwise stated, the content of Li can be the initial state of the material or the non-initial state after charging and discharging cycle. The positive active material is applied to the positive electrode in the battery system, and after charging and discharging cycle, the content of Li in the positive active material of the positive electrode will usually change. Among them, the content of Li can be quantified by atomic molar content, but not limited to this. As for "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 active layer. It can be understood that the new material or new substance obtained by proper modification of the listed positive active material is also within the scope of the positive active material, and the foregoing proper modification refers to acceptable modification methods for the positive active material, and non-limiting examples include one or more of coating modification and doping modification.

[0471] In the exemplary description of the positive active material in this application, the content of oxygen (O) is only the theoretical state value, and 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 quantified by atomic molar content, but not limited to this.

[0472] In some embodiments, the positive active layer optionally includes a binder. As a non-limiting example, the binder can 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 acrylic ester resin. Typically, the mass fraction of the binder in the positive active layer can be 0-10%, further can be 0-8%, and more further can be 1-5%, based on the total mass of the positive active layer.

[0473] In some embodiments, the positive active layer optionally includes a conductive agent. As a non-limiting example, the conductive agent can include one or more of super conductive 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 active layer can be 0-10%, further can be 0-8%, and more further can be 0-5%, based on the total mass of the positive active layer.

[0474] In some embodiments, the positive electrode sheet can be prepared by dispersing the above-mentioned components for preparing the positive electrode sheet, such as the positive electrode active material, the conductive agent, the binder and any other components, in a solvent to form a positive electrode slurry. Further, the positive electrode slurry is coated on at least one side surface of the positive electrode current collector, and after processes such as drying, cold pressing, etc., the positive electrode sheet can be obtained. The cold pressing can be performed using a cold rolling machine. The type of solvent in the positive electrode slurry can include, but is not limited to, any of the above-mentioned embodiments, such as N-methyl pyrrolidone (NMP), and further can be NMP. The surface of the positive electrode current collector to which the positive electrode slurry is coated can be a single surface of the positive electrode current collector, or can be both surfaces of the positive electrode current 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-based active material, and further, the mass ratio of the lithium-containing phosphate-based active material in the positive electrode active material can be greater than or equal to 50%, but is not limited thereto. When coating the positive electrode slurry, the coating surface density (calculated based on the coating surface density of both sides) can be (0.1 to 0.6) g / 1540.25mm 2 , but is not limited thereto. The compaction density of the positive electrode sheet can be 1.9g / cm 3 to 3.0g / cm 3 .

[0476] In some embodiments, the positive electrode active material includes a lithium complex metal oxide-based active material, and further, the mass ratio of the lithium complex metal oxide-based active material in the positive electrode active material can be greater than or equal to 50%, but is not limited thereto. When coating the positive electrode slurry, the coating surface density (calculated based on the coating surface density of both sides) can be 15mg / cm 2 to 35mg / cm 2 . The compaction density of the positive electrode sheet can be 3.0g / cm 3 to 3.6g / cm 3 , and optionally 3.3g / cm 3 to 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 other descriptions regarding the negative electrode sheet.

[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, the negative electrode active material layer including a negative electrode active material.

[0480] In the present application, the “negative electrode active material layer” in the negative electrode sheet can include one or more negative electrode active layers, i.e., the negative electrode active material layer can 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 which can be found in the context of the present 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, the second negative electrode active layer being 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 can be the same or different, which can be found in the context of the present application.

[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 of some embodiments can be found in the context of the present application.

[0485] As a non-limiting example, the negative electrode sheet includes a negative electrode current collector and a second negative electrode active layer and a first negative electrode active layer disposed in sequence 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.

[0486] Non-limitingly, the mass percentage of the negative electrode active material in the negative electrode active material layer can be greater than or equal to 80%, further can be greater than or equal to 90%.

[0487] Non-limitingly, the mass fraction of the first negative electrode active material in the first negative electrode active layer can be greater than or equal to 80%, further can be greater than or equal to 90%.

[0488] Non-limitingly, the mass fraction of the second negative electrode active material in the second negative electrode active layer can be greater than or equal to 80%, further can be greater than or equal to 90%.

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

[0490] Figure 1is a structural schematic diagram of a negative electrode tab in an embodiment of the present application. The negative electrode tab 200 includes a negative electrode current collector 210 and a second negative electrode active layer 222 and a first negative electrode active layer 224 disposed in sequence 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 compound 208. At this time, the second negative electrode active material in the second negative electrode active layer includes the 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 is a structural schematic diagram of a negative electrode tab in another embodiment of the present application. The negative electrode tab 200 includes a negative electrode current collector 210 and a second negative electrode active layer 222 and a first negative electrode active layer 224 disposed in sequence 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 compound 208. At this time, the second negative electrode active material in the second negative electrode active layer includes the 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 is a structural schematic diagram of a negative electrode tab in an embodiment of the present application. The negative electrode tab 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 compound 208. At this time, the negative electrode active material in the negative electrode active material layer includes the 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 particle matters in the negative electrode active material.

[0494] In some embodiments, the negative electrode current collector can employ a metal foil or a composite current collector. For example, as the metal foil, a copper foil can be employed. 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, silver alloy, and the like. 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), and the like.

[0495] In addition to the negative active material types referred to in the context of the embodiments and examples, the negative active material in the negative active material layer, the first negative active layer, and the second negative active layer can each independently include other types of negative active materials known in the art to be suitable for lithium-ion secondary batteries. In the negative active material layer, these negative active materials can be used singly or in combination of two or more. In the first negative active layer and the second negative active layer, each independently, these negative active materials can be used singly or in combination of two or more. In some embodiments, the negative active material further includes one or more of tin-based materials and lithium titanate, etc.

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

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

[0498] Without limitation, the binder in the negative electrode tab can 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 active layer and the second negative active layer can be the same or different.

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

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

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

[0502] The definition of the binder of some embodiments can be referred to the context of the present application.

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

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

[0505] Non-limitingly, the conductive agent in the negative electrode tab can include one or more of super-P, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. The type of conductive agent in the first negative active layer and the second negative active layer can be the same or different.

[0506] Non-limitingly, the mass percentage of the conductive agent in the negative active material layer can be 0% to 15%, further optionally 0% to 10%, and more further optionally 0% to 5%.

[0507] Non-limitingly, the mass percentage of the conductive agent in the first negative active layer can be 0% to 15%, further optionally 0% to 10%, and more further optionally 0% to 5%.

[0508] Non-limitingly, the mass percentage of the conductive agent in the second negative active layer can be 0% to 15%, further optionally 0% to 10%, and more further optionally 0% to 5%.

[0509] In some embodiments, the negative active material layer optionally includes other additives, such as thickening agents (e.g., sodium carboxymethyl cellulose (CMC-Na)) and the like. Non-limitingly, the mass percentage of the other additives in the negative active material layer can be 0% to 15%, further optionally 0% to 10%, more further optionally 0% to 5%, more further optionally 0% to 3%, and more further optionally 0% to 2%.

[0510] In some embodiments, the first negative active layer and the second negative active layer each independently optionally includes other additives, such as thickening agents (e.g., sodium carboxymethyl cellulose (CMC-Na)) and the like. Non-limitingly, the mass percentage of the other additives in the first negative active layer or the second negative active layer can independently be 0% to 15%, further optionally 0% to 10%, more further optionally 0% to 5%, more further optionally 0% to 3%, and more further optionally 0% to 2%.

[0511] In some embodiments, the negative electrode tab is prepared using a method comprising the following steps:

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

[0513] S120: preparing the negative electrode sheet. The negative electrode slurry is coated on at least one side surface of the negative electrode current collector, and after processes such as drying, cold pressing, etc., the negative electrode active material layer is formed accordingly, and the negative electrode sheet is obtained. Cold pressing can be performed using a cold rolling machine. 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%-70wt%, and can be optionally 40wt%-60wt%. The viscosity of the negative electrode slurry at room temperature can be adjusted to 2000mPa-s-10000mPa-s, and can be optionally 3000mPa-s-10000mPa-s.

[0514] In some embodiments, the negative electrode sheet is prepared using a method comprising S100' and S200'; the negative electrode sheet comprising a first negative electrode active layer and a second negative electrode active layer can be prepared.

[0515] S100': preparing a first negative electrode slurry and a second negative electrode slurry. The 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 the first negative electrode slurry. The components for preparing the second negative electrode active layer, such as the second negative electrode active material, the quaternary ammonium salt type 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 the second negative electrode slurry.

[0516] S200': preparing the negative electrode sheet. The second negative electrode slurry and the first negative electrode slurry are coated on at least one side surface of the negative electrode current collector using a double-layer coating machine, the second negative electrode slurry is coated first and then the first negative electrode slurry is coated, and after processes such as drying, cold pressing, etc., the second negative electrode active layer and the first negative electrode active layer are formed accordingly, and the second negative electrode active layer is located between the first negative electrode active layer and the negative electrode current collector; wherein the non-solvent components of the first negative electrode slurry form the first negative electrode active layer, and the non-solvent components of the second negative electrode slurry form the second negative electrode active layer. Cold pressing can be performed using a cold rolling machine. The surface of the negative electrode current collector coated with the first negative electrode slurry and the second 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 first negative electrode slurry and the second negative electrode slurry can each independently be 30wt%-70wt%, and can each independently be optionally 40wt%-60wt%. The viscosity of the first negative electrode slurry and the second negative electrode slurry at room temperature can each independently be adjusted to 2000mPa-s-10000mPa-s, and can each independently be optionally 3000mPa-s-10000mPa-s.

[0517] The coating area density of the negative electrode sheet and the compaction density of the negative electrode sheet can be referred to the context of the present application.

[0518] The electrolyte is described illustratively below.

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

[0520] The electrolyte includes an electrolyte salt and a solvent. The solvent includes a nonaqueous solvent.

[0521] In some embodiments, the electrolyte is a nonaqueous electrolyte. The nonaqueous electrolyte can include an electrolyte salt and a solvent.

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

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

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

[0525] In some embodiments, the electrolyte optionally includes an additive. For example, the additive can include a negative electrode film-forming additive, a positive electrode film-forming additive, and can also include an additive capable of improving certain properties of the battery, such as an additive capable of improving overcharge performance of the battery, an additive capable of improving high-temperature or low-temperature performance of the battery, etc.

[0526] In some embodiments, the additive in the electrolyte can include, but is not limited to, one or more of fluoroethylene carbonate (FEC), difluoroethylene carbonate (DFEC), trifluoromethyl ethylene carbonate (TFPC), etc.

[0527] The separator is described illustratively below.

[0528] The definition of the separator of some embodiments can be found in the context of the present application.

[0529] The type of the separator film is not particularly limited in the present application, and any known porous structure separator film having good chemical stability and mechanical stability can be used.

[0530] In some embodiments, the material of the separator film can include one or more of glass fiber, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator film can be a single-layer film or a multi-layer composite film, and is not particularly limited. When the separator film is a multi-layer composite film, the materials of the layers can be the same or different, and are not particularly limited.

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

[0532] In some embodiments, the positive electrode sheet, the negative electrode sheet, and the separator film can be used to form an electrode assembly by a winding process or a stacking process.

[0533] In some embodiments, the lithium ion secondary battery can include an outer package. The outer package can be used to package the electrode assembly and the electrolyte described above.

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

[0535] The lithium ion secondary battery includes at least one battery cell. The lithium ion secondary battery can include one or more battery cells.

[0536] The shape of the battery cell is not particularly limited in the present application, and can be cylindrical, square, or any other shape. For example, Figure 4 is a square structure battery cell 5 as an example.

[0537] In some embodiments, referring to Figure 5 , the outer package can include a shell 51 and a cover plate 53. The shell 51 can 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 communicating with the receiving cavity, and the cover plate 53 can be arranged on the opening to close the receiving cavity. The positive electrode sheet, the negative electrode sheet, and the separator film can be used to form an electrode assembly 52 by a winding process or a stacking process. The electrode assembly 52 is packaged in the receiving cavity. The electrolyte is impregnated in the electrode assembly 52. The number of the electrode assembly 52 contained in the battery cell 5 can be one or more, which can be selected by a person skilled in the art according to actual needs.

[0538] The lithium ion secondary battery can 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 included in the battery device can be one or more, and a person skilled in the art can select a suitable number according to the application and capacity of the battery device.

[0540] Figure 6 The battery device 4 is an example. Referring to Figure 6 In the battery device 4, a plurality of battery cells 5 can be arranged in sequence along the length direction of the battery device 4. Of course, other arbitrary arrangements can also be made. Further, the plurality of battery cells 5 can be fixed by fasteners.

[0541] Optionally, the battery device 4 can also include a housing having an accommodation space, and the plurality of battery cells 5 are accommodated in the accommodation space.

[0542] In some embodiments, the above-mentioned battery device can also be assembled into a battery pack, and the number of battery devices included in the battery pack can be one or more, and a person skilled in the art can select a suitable number according to the application and capacity of the battery pack.

[0543] Figure 7 And Figure 8 The battery pack 1 is an example. Referring to Figure 7 And Figure 8 In the battery pack 1, a battery box and a plurality of battery devices 4 arranged in the battery box can be included. The battery box includes an upper box body 2 and a lower box body 3, and the upper box body 2 can be arranged on the lower box body 3 and form a closed space for accommodating the battery device 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 sheet is provided, which can have the same features as the negative electrode sheet described in the first aspect of the present application, or can be the state of the negative electrode sheet described in the first aspect of the present application after cold pressing and before impregnation of electrolyte.

[0545] In some embodiments, a negative electrode sheet 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 type compound, the quaternary ammonium salt type compound includes a quaternary ammonium cation.

[0546] In some embodiments, a negative electrode sheet is provided, which includes a negative electrode current collector and a second negative electrode active layer and a first negative electrode active layer arranged in sequence on at least one side of the negative electrode current collector, 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 type compound.

[0548] By introducing the quaternary ammonium salt type 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 to introduce the quaternary ammonium salt type compound" on the electrolyte wettability of the second negative electrode active layer can be compared by the change of 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 the deionized water is used to resuspend into a uniform slurry, which is recorded as the second resuspended slurry. The second resuspended slurry is coated on one side surface of the negative electrode current collector copper foil, dried, cold pressed, and a second active layer sheet is obtained. The non-solvent components in the second resuspended slurry are basically the same as those in the second negative electrode slurry. In addition, the second active layer sheet can be prepared by using the second negative electrode slurry used in the preparation of the negative electrode sheet instead of the second resuspended slurry.

[0550] The liquid absorption rate can be tested by the following method: fixing the test sheet on the sample stage, dropping the electrolyte, and timing with a stopwatch; recording the weight gain and time; calculating the liquid absorption rate of the sheet by the change of weight with time. Non-limiting examples of electrolyte are the electrolyte formula of Example 1, and the electrolyte with the same composition as the electrolyte in lithium ion secondary batteries can also be used to test the liquid absorption rate, and commercially available electrolyte such as electrolyte E30 can also be used. In some examples, the composition of the electrolyte is solvent and 1 moL / L lithium hexafluorophosphate (LiPF6), and the solvent composition is 1:1:1 by volume of ethylene carbonate (EC), dimethyl carbonate (DMC) and methyl ethyl carbonate (EMC).

[0551] In some embodiments, a negative electrode sheet 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 type compound, the negative electrode active material includes a negative electrode active body and a coating layer located on at least a part 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 type compound includes a quaternary ammonium cation.

[0552] By disposing the coating layer on the surface of the negative active material of the negative active material layer, and disposing 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 active material can be optimized, the lithium ion transmission can be promoted, and the battery kinetics and the battery fast charging performance can be improved. Further, by disposing the quaternary ammonium salt type compound in the negative active material layer, the electrolyte anions in the electrolyte can be attracted by the electrostatic action based on the quaternary ammonium group, the electrolyte lithium salt in the electrolyte can be quickly dissociated, and the quaternary ammonium group-electrolyte anion structure formed can guide the lithium ions in the electrolyte to quickly transmit to the surface of the negative active material; based on the foregoing multiple effects, the fast charging performance of the battery can be better improved.

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

[0554] In the second aspect of the application, a power utilization device is provided, which comprises the lithium ion secondary battery described in the first aspect of the application.

[0555] The power utilization device comprising the foregoing lithium ion secondary battery can have the advantageous effects of the foregoing lithium ion secondary battery, including but not limited to, can have improved fast charging performance.

[0556] The power utilization device comprising the foregoing negative electrode sheet can have the advantageous effects of the foregoing negative electrode sheet, including but not limited to, can have improved fast charging performance.

[0557] In some embodiments, the power utilization device comprises the lithium ion secondary battery of any of the embodiments provided in the application.

[0558] The lithium ion secondary battery can be used as a power source of a power utilization device, or can be used as an energy storage unit of a power utilization device. The power utilization device can include a mobile device, an electric vehicle, an electric train, a ship and a satellite, an energy storage system, etc., but is not limited thereto. Among them, the mobile device can be a mobile phone, a notebook computer, etc.; the electric vehicle can be a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, an electric bicycle, an electric scooter, an electric golf cart, an electric truck, an electric motorcycle, an electric tool, etc., but is not limited thereto. The power utilization device can also be applied to military equipment, aerospace, etc., and can also be applied to hydroelectric, thermal, wind and solar power station energy storage power systems.

[0559] As a power utilization device, the lithium ion secondary battery can be selected according to its use requirements.

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

[0561] As another example, the device can be a mobile phone, a tablet, a notebook computer, etc. The device generally requires thinness, and a lithium ion secondary battery can 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 and / or storing electric energy;

[0563] The use includes a process of charging the lithium ion secondary battery at a rate higher than or equal to 2C, i.e., the lithium ion secondary battery is capable of providing a charge rate of greater than or equal to 2C.

[0564] In the present application, unless otherwise specified, the "rate" of a battery has the meaning commonly known in the art, and refers to the current value required for charging or discharging the battery to its rated capacity within a specified time, with the unit expressed in C. Unless otherwise specified, the "specified time" is 1 hour (h), 1C indicates that the charging and discharging is completed in 1 hour, and 1 / 3C indicates that the charging and discharging is completed in 3 hours. The rate of a battery reflects the charging and discharging capacity of the battery at different currents. A high rate means that the battery can be quickly charged and discharged in a short time. The higher the rate, the better the fast charging performance.

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

[0566] In some embodiments, the use includes a process of charging the lithium ion secondary battery at at least one rate selected from the group consisting of 2C, 3C, 4C, 5C, 6C, etc.

[0567] In some embodiments, the use includes a process of charging the lithium ion secondary battery at at least one rate selected from the group consisting of 2C, 3C, 4C, 5C, 6C, etc.

[0568] In some embodiments, the use includes a process of charging the lithium ion secondary battery at at least one rate selected from the group consisting of 2C, 3C, 4C, 5C, 6C, etc.

[0569] Without limitation, the lithium ion secondary battery can be charged at any one of the following rates, or can be charged at a rate greater than or equal to any one of the following rates, or can be charged at a rate selected from 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 is capable of providing a charge rate of greater than or equal to 2C.

[0571] In some implementations, lithium-ion secondary batteries can provide charging rates of 2C to 6C.

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

[0573] In some embodiments, the maximum charging rate of the lithium-ion secondary battery can be greater than or equal to 2C, and can be selected as 2C to 6C, or further selected as 2C to 4C or 4C to 6C.

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

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

[0576] In this application, the "maximum charging rate (which can be denoted as C)" of the lithium-ion secondary battery is defined as... max The term "lithium plating" has a well-known meaning within the industry and can be obtained through testing using conventional methods within the field. For example, tests can be conducted at different charging rates to obtain a lithium plating window curve, and the critical charging rate at which lithium plating occurs can be used as the test value of the battery's maximum charging rate. Test parameters can be as follows: The battery under test is charged at a constant current to 4.4V at different rates (e.g., 1C, 2C, 2.5C, 3C, 3.5C, 4C, ...), then charged at a constant voltage until the current is ≤0.05C, left to stand for 5 minutes, and then charged at a constant current of 0.33C to 4.4V, left to stand for 5 minutes, and then disassembled to observe the lithium plating at the negative electrode. For example, a series of parallel samples can be prepared, starting from 1C and tested at 0.1C intervals until lithium plating appears at the negative electrode. To reduce the sample size, a larger interval can be selected first to determine the range of the maximum charging rate, and then a smaller interval can be selected to more accurately determine the maximum charging rate. The intervals can be 1C, 0.5C, 0.2C, and 0.1C, respectively.

[0577] Hereinafter, some embodiments of the present application will be described. The embodiments described are only some of the embodiments of the present application, and are not all the embodiments. The embodiments described below are exemplary and are for the purpose of explanation of the present application only, and are not to be understood as limiting the present application and its applications. All other embodiments obtained by those of ordinary skill in the art based on the embodiments in the present application without creative labor are within the scope of the present application.

[0578] Unless otherwise noted in the embodiments, the techniques or conditions are performed according to the descriptions above, or according to the techniques or conditions described in the literature in the art, or according to the product instructions. Unless otherwise noted, the reagents or instruments used are all conventional products that can be obtained commercially, or can be synthesized according to conventional methods using commercially available products.

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

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

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

[0582] In the following examples, unless otherwise specified, the parameters involved can be confirmed according to the test methods described above. For example, the amount of secondary particle type graphite in the first negative electrode active material, the amount of secondary particle type graphite in the negative electrode active material, can be confirmed according to the SEM (Sigma 300 type scanning electron microscope of Germany ZEISS company) test results; the D v50The test can be performed using a Malvern 2000 laser particle size analyzer; the OI value related to the first negative electrode active material and the second negative electrode active material can be obtained by testing using an X-ray diffraction (XRD) instrument Bruker-D8 advance. Related to the carbon coating layer, the test can be performed using a transmission electron microscope JEM-F200 combined with an EDS (Energy Dispersive Spectrometer). For example, the compaction density of the negative electrode tab, the compaction density comparison of the first negative electrode active layer and the second negative electrode active layer, the surface density comparison of the first negative electrode active layer and the second negative electrode active layer (calculated on the single side of the negative electrode current collector), the porosity comparison of the first negative electrode active layer and the second negative electrode active layer, the porosity of the negative electrode active material layer, the powder compaction density of the second negative electrode active material and the first negative electrode active material and the ratio of the two powder compaction densities, the powder compaction density of the second negative electrode active layer and the first negative electrode active layer and the ratio of the two powder compaction densities, the rate comparison of the first negative electrode active layer and the second negative electrode active layer, the charge rate comparison of the first negative electrode active layer and the second negative electrode active layer, etc. For example, the ionic conductivity test related to the electrolyte is performed using a DDSJ-318 conductivity meter, and the detection method is referred to HG-T 4067-2015.

[0583] In each of the following examples, unless otherwise specified, the alkyl chain is taken as a linear chain. For example, the octadecyl group in octadecyl trimethyl quaternary ammonium phosphate is n-octadecyl.

[0584] Example 1.

[0585] 1. Preparation of the positive electrode tab:

[0586] The positive electrode tab is composed of a powder including a 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) are mixed uniformly in an appropriate amount of solvent N-methyl pyrrolidone (NMP) at a mass ratio of 97.9:0.3:1.8 to obtain a positive electrode slurry with a solid content of 60wt%; the coating weight (calculated on both sides) is 0.360g / 1540.25mm 2 (approximately 23.4mg / cm 2 ) The positive electrode slurry is coated on the double-sided surface of the positive electrode current collector aluminum foil, and through processes such as drying, cold pressing, slitting, and cutting, the positive electrode tab is obtained. The compaction density of the positive electrode tab is 2.60g / cm 3 .

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

[0589] 2. Preparation of the negative electrode tab:

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

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

[0592] The second negative electrode slurry and the first negative electrode slurry are uniformly coated on the two side surfaces of the negative electrode current collector copper foil (the coating parameters of the two sides of the negative electrode current collector are basically the same) by an extrusion coater, the second negative electrode slurry is coated first (corresponding to the second negative electrode active layer), and then the first negative electrode slurry is coated (corresponding to the first negative electrode active layer), and the coating weights (calculated on one side) of the upper and lower layers are controlled to be 0.08g / 1540.25mm 2 and 0.08g / 1540.25mm 2 , respectively. 3 After drying in an oven and compaction using a cold press, the compaction density of the negative electrode tab is controlled to be 1.65g / cm 2 .

[0593] The first negative electrode active layer (upper layer): the first negative electrode active material is coated graphite, further 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 14μm, the first negative electrode active material includes secondary particle graphite, and the amount of secondary particle graphite in the first negative electrode active material accounts for about 50%; the OI value of the first negative electrode active material is 5.

[0594] The second negative electrode active layer (lower layer): the second negative electrode active material is artificial graphite (without coating layer), D v 50 is 18μm, the second negative electrode active material includes secondary particle graphite, and the amount of secondary particle graphite 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 H ) of the first negative electrode active layer (upper layer) to the second negative electrode active layer (lower layer) in the negative electrode sheet is greater than 1, f H is in the range of 1.1 to 1.3, f H is about 1.2, and the single-sided thickness of the first negative electrode active layer is in the range of 30 to 40 μm. At this time, the second negative electrode active layer has a higher compaction density than the first negative electrode active layer.

[0596] 3. Separation film: A polypropylene film having a thickness of 12 μm was used as the separation film.

[0597] 4. Preparation of electrolyte: Ethylene carbonate (EC) and methyl ethyl carbonate (EMC) were mixed in a mass ratio of 30:70 to obtain an organic solvent, and LiPF6 that was sufficiently dried was dissolved in the organic solvent. Vinylene carbonate (VC), fluoroethylene carbonate (FEC), and vinyl ethyl sulfate (DTD) were added to prepare an electrolyte having a LiPF6 concentration of 1 mol / L. The electrolyte contained 2.5 wt% of VC, 1 wt% of FEC, and 0.5 wt% of DTD.

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

[0599] 5. Preparation of secondary battery: The positive electrode sheet, the separation film, and the negative electrode sheet were stacked in order and wound to obtain an electrode assembly. The electrode assembly was placed in an outer package, and after drying, the electrolyte was injected. The secondary battery was obtained by performing processes such as vacuum packaging, standing, formation, and shaping.

[0600] Examples 2-4. The negative electrode sheet and the lithium ion secondary battery were prepared using substantially the same method as in Example 1, except that in the step of preparing the negative electrode sheet, the mass ratio of the quaternary ammonium salt compound in the second negative electrode active layer was changed, and the lithium ion secondary battery was prepared using different negative electrode sheets. See Table 1.

[0601] Examples 5-8. The negative electrode sheet and the lithium ion secondary battery were prepared using substantially the same method as in Example 1, except that in the step of preparing the negative electrode sheet, the type of the quaternary ammonium salt compound was changed, and the lithium ion secondary battery was prepared using different negative electrode sheets. See Table 1. The quaternary ammonium salt compounds of Examples 5-8 were octadecyl trimethyl quaternary ammonium phosphonate, dodecyl trimethyl quaternary ammonium nitrate, dodecyl trimethyl quaternary ammonium carbonate, and dodecyl trimethyl quaternary ammonium bicarbonate, respectively.

[0602] Examples 9-10. The negative electrode sheet and the lithium ion secondary battery were prepared using substantially the same method as in Example 1, except that in the step of preparing the electrolyte, the composition of the electrolyte was changed, and the lithium ion secondary battery was prepared using different electrolytes. See Table 1.

[0603] Example 9 uses lithium hexafluorophosphate (LiPF6) and lithium bisfluorosulfonylimide (LiFSI) with a molar ratio of 1:0.1, and the molar volume concentration in the electrolyte is 1 mol / L and 0.1 mol / L respectively; the solvent type, additive type and amount are the same as in Example 1.

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

[0605] The 25°C ionic conductivities of the electrolytes of Examples 9-10 are all in the range of 16 mS / cm-18 mS / cm.

[0606] Examples 11-12. The negative electrode sheet and lithium ion secondary battery are prepared by substantially the same method as in 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, i.e. the thickness ratio of the first negative electrode active layer to the second negative electrode active layer (f H ) is changed, and the sum of the coating surface densities of the two sides of the negative electrode sheet is substantially the same as in Example 1; different negative electrode sheets are used to prepare lithium ion secondary batteries. See Table 1.

[0607] Examples 13-14. The negative electrode sheet and lithium ion secondary battery are prepared by substantially 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 is changed, and f H is also changed by adjusting the coating weights of the first negative electrode slurry and the second negative electrode slurry, and the sum of the coating surface densities of the two sides of the negative electrode sheet is substantially the same as in Example 1; different negative electrode sheets are used to prepare lithium ion secondary batteries. See Table 1.

[0608] In Example 13, the second negative electrode active material uses a combination of artificial graphite and soft carbon with 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 the same as in Example 1.

[0609] In Example 14, the second negative electrode active material uses a combination of artificial graphite and hard carbon with 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 the same as in Example 1.

[0610] Example 15. The negative electrode sheet and lithium ion secondary battery are prepared by substantially the same method as in Example 1, except that in the step of preparing the negative electrode sheet, the D v 50 of the first negative electrode active material is 12 μm, and the D v50 is 20 pm; the coating surface density ratio is adjusted to make the thickness ratio of the first negative electrode active layer to the second negative electrode active layer substantially the same as that in Example 1; and different negative electrode tabs are used to prepare lithium ion secondary batteries. See Table 1.

[0611] Example 16. The negative electrode tab and lithium ion secondary battery are prepared by substantially the same method as in Example 1, except that in the step of preparing the positive electrode tab, 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 O2), and different positive electrode tabs are used to prepare lithium ion secondary batteries. See Table 1.

[0612] Example 17. The negative electrode tab is prepared by substantially the same method as in Example 1, except that the negative electrode active material layer of the negative electrode tab adopts a single-layer structure, and different negative electrode tabs are used to prepare lithium ion secondary batteries. In this example, the negative electrode tab is prepared by the following method:

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

[0614] The negative electrode slurry is uniformly 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 substantially the same), and the coating weight on one side of the negative electrode current collector is 0.16 g / 1540.25 mm 2 After drying in an oven and compaction using a cold press, the compaction density of the negative electrode tab is controlled to be 1.65 g / cm 3 After cold pressing, the tab is subjected to slitting and cutting processes to obtain the negative electrode tab. The area density of the negative electrode tab is about 10.4 mg / cm 2 .

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

[0616] Comparative Example 1. The second negative electrode active layer is not provided with a quaternary ammonium salt type compound.

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

[0618] Comparative Example 2. The second negative electrode active layer was not provided with the quaternary ammonium salt type compound.

[0619] The negative electrode sheet and the lithium ion secondary battery were prepared by substantially the same method as 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 (i.e., the second negative electrode active layer was not provided with the quaternary ammonium salt type compound), and the remaining operation steps were the same as in Example 1; and the lithium ion secondary battery was prepared using the different negative electrode sheet. The sum of the double-sided coating surface densities of the negative electrode sheet was the same as in Example 1.

[0620] Comparative Example 3. The second negative electrode active layer was not provided with the quaternary ammonium salt type compound.

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

[0622] Comparative Example 4. The second negative electrode active layer was not provided with the quaternary ammonium salt type compound.

[0623] The negative electrode sheet and the lithium ion secondary battery were prepared by substantially the same method as 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 (i.e., the second negative electrode active layer was not provided with the quaternary ammonium salt type compound), and the remaining operation steps were the same as in Example 16; and the lithium ion secondary battery was prepared using the different negative electrode sheet. The sum of the double-sided coating surface densities of the negative electrode sheet was the same as in Example 16.

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

[0625] The porosities of the first negative active layers in Examples 1-16 are all higher than the porosities of the second negative active layers. The porosities of the negative electrode sheets of Example 1-17 are all 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 densities of the second negative active materials in Examples 1-16 are all higher than the powder compaction densities of the first negative active materials, and the powder compaction densities of the second negative active materials are all in the range of 1.85 g / cm 3 to 2.05 g / cm 3 , and the ratios of the powder compaction densities of the second negative active materials to the powder compaction densities of the first negative active materials are all in the range of 1.05 to 1.35. Taking Example 1 as an example, the powder compaction density of the second negative active material is about 1.9 g / cm 3 , and the powder compaction density of the first negative active material is about 1.7 g / cm 3 .

[0627] Table 1.

[0628]

[0629]

[0630] Test Methods and Analysis

[0631] (I) Negative electrode performance test

[0632] Liquid absorption rate test

[0633] The cell was disassembled, the negative electrode sheet was taken out, and the negative electrode sheet was cleaned by soaking in solvent dimethyl carbonate (DMC), and the powder was scraped from the second negative active layer close to the negative electrode current collector to obtain a powder sample of the second negative active material. The second negative active material was resuspended into a uniform slurry with deionized water, and was recorded as the second resuspended slurry. The second resuspended slurry was coated on one side surface of the negative electrode current collector copper foil, dried, cold-pressed, and the second active layer sheet was obtained. The liquid absorption rate was tested by the following method: the test sheet was fixed on the sample stage, and electrolyte E30 (commercially available) was dropped, and a stopwatch was used to time; the weight increase and the time were recorded; and the liquid absorption rate of the sheet was calculated by the change of the weight with time. The measured liquid absorption rate can be recorded as the "liquid absorption rate of the second negative active layer".

[0634] (II) Battery performance test

[0635] 1. Battery energy density

[0636] The battery to be tested was charged at a current of 0.33 C to 3.8 V at 25°C, the cutoff current was 0.05 C, and after standing for 30 min, it was discharged to the designed 2.0 V at 0.33 C, and the discharge energy P was recorded X (Wh) X , and the volume of the battery cell was recorded as V X (unit: L), then the energy density of the battery (Wh / L) = P X .

[0637] 2. Fast charging capacity test

[0638] The lithium ion secondary battery to be tested was placed at room temperature of 25°C, and after constant current charging to 3.8 V at a rate of 0.33 C, constant voltage charging was performed until the current was 0.05 C, and after standing for 5 min, constant current discharging was performed to 2.0 V at 0.33 C, and the initial capacity C0 was recorded. The battery was sequentially charged at 0.5C0, 1C0, 1.5C0, 2C0, 2.0C0, 3C0, and 3.5C0 to the full cell potential of 3.8 V or the negative electrode cutoff potential of 0 mV (any one of which indicates that the charging is completed), and after each charging was completed, it was discharged to 2.0 V at 0.33C0. Every 10% SOC, the corresponding negative electrode potential under different charging rates was recorded, and the rate-negative electrode potential curve under different SOC was drawn, and after linear fitting, the charging rate corresponding to the negative electrode potential of 0 mV under different SOC was obtained, denoted as Cx (x = 2-8). According to the formula (1 / C2 + 1 / C3 + 1 / C4 + 1 / C5 + 1 / C6 + 1 / C7 + 1 / C8) x 0.1 x 60, the charging time t c (min) from 10% SOC to 80% SOC of the lithium ion secondary battery was calculated.

[0639] The test results can be referred to "Charging time t c from 10% SOC to 80% SOC".

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

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

[0642] 3. Fast charging cycle performance test

[0643] The battery cell was placed in a three-piece steel plate clamp with a pressure sensor, and the initial pressure of the clamp was 3000 N.

[0644] 25℃, the battery to be tested is charged at 0.33C to a charge cut-off voltage of 3.8V, then charged at a constant voltage to a current of 0.05C, left for 5min, then discharged at 0.33C to a discharge cut-off voltage of 2.0V, and the initial capacity is recorded as C0. Then the battery is charged at 0.33C0to 10% SOC, and the interval of 10% SOC-80% SOC is charged according to the "fast charging capacity test" charging strategy as above, then charged at 0.33C0to a cut-off voltage of 4.25V, and then charged at a constant voltage to a current of 0.05C, left for 5min, and then discharged at 0.33C0, and the discharge capacity Cnof each cycle is recorded, until after 1000 cycles, the cycle capacity retention rate (i.e. C1000 / C1x 100%) is calculated.

[0645] The test results can be referred to as "capacity retention rate after 1000 cycles of fast charging at 25℃".

[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 example and comparative example are respectively coated on the single-sided surface of a copper foil current collector, and dried in an oven for later use.

[0649] A metal lithium plate is used as a counter electrode, a polypropylene (PP) film is used as a separator, ethylene carbonate (EC), methyl ethyl carbonate (EMC) and diethyl carbonate (DEC) are mixed in a volume ratio of 1:1:1 to obtain a mixed solvent, and then LiPF6 is uniformly dissolved in the mixed solvent to obtain an electrolyte, wherein the concentration of LiPF6 is 1 mol / L.

[0650] All components are assembled into a CR2430 type button cell in an argon glove box. "CR" represents the international IEC number of the button lithium manganese battery, with a diameter of 24 mm and a thickness of 30 mm.

[0651] After standing for 12 hours, the obtained button cell is 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 charge capacity C0. The battery is placed at 25℃ for 2h, and the charge-discharge test is carried out at 1C0, 2C0, 3C0, 4C0, 5C0 rate, and the capacity retention rate is obtained. The higher the capacity retention rate under the same rate, the better the rate performance.

[0652] 5, "maximum charge rate" of lithium ion secondary battery

[0653] A series of parallel samples of the battery to be tested are tested at different charge rates to obtain the lithium precipitation window curve, and the critical charge rate at which lithium precipitation occurs is taken as the test value of the maximum charge 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, …) to 3.8V, then charged at a constant voltage to a current of ≤0.05C, left for 5 minutes, then charged at a constant current of 0.33C to 3.8V, left for 5 minutes, disassembled, and the negative electrode lithium precipitation condition was observed. To reduce the sample size, first select a large interval rate condition to determine the range of the maximum charge rate, and then select a small interval rate condition to more accurately determine the maximum charge rate. The interval of the rate can be reduced according to the accuracy requirement, for example, one or more 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 were 1C, 0.5C, 0.2C, and 0.1C in turn.

[0655] Some test results of the battery performance can be seen in Tables 2-3.

[0656] Test results and analysis

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

[0658] The lithium ion secondary batteries of Examples 1-17 all have a quaternary ammonium salt type compound in the second negative electrode active layer, and 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. The charging time t c is significantly shortened.

[0659] The maximum charge rate of the lithium ion secondary batteries of Examples 1-17 is 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 rate of Examples 1-17 is in the range of 2.4C-3.3C. The maximum charge rate of Comparative Examples 1-5 is in the range of 1.7C-2.0C.

[0660] According to the "rate performance" test, the rate performance of the CR2430 type button cell batteries assembled by the first negative electrode slurry of Examples 1-17 is all higher than that of the CR2430 type button cell batteries assembled by the first negative electrode slurry of Comparative Examples 1-4. After introducing a quaternary ammonium salt type compound into the second negative electrode active layer, the rate performance of the second negative electrode active layer is improved.

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

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

[0663] The lithium ion secondary battery of Example 1-17 also has a relatively high energy density. Some test results are shown in Table 3.

[0664] Table 2.

[0665]

[0666]

[0667] Table 3.

[0668]

[0669] The above description of various embodiments and examples tends to emphasize the differences between various embodiments and examples, and the same or similar parts can be referred to each other, and for brevity, will not be described herein. Each of the technical features of the above-described embodiments and examples can be combined arbitrarily, and for brevity, each of the technical features of the above-described embodiments is not described in all possible combinations, however, as long as the combination of the technical features does not contradict, it should be considered within the scope of the present disclosure.

[0670] It should be noted that the present application is not limited to the above-described embodiments and examples. The above-described embodiments and examples are merely examples, and embodiments and examples having substantially the same configuration and playing the same role and effect as the technical idea within the scope of the technical solution of the present application 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 should not be construed as limiting the scope of the patent. In addition, within the scope of the main idea of the present application, various modifications that can be thought of by those skilled in the art, combinations of part of the components of the embodiments or examples to construct other ways are also included in the scope of the present application.

Claims

1. A lithium-ion secondary battery, characterized by comprising: The lithium ion secondary battery comprises a negative electrode sheet and an electrolyte; the negative electrode sheet comprises a negative electrode current collector and a second negative electrode active layer and a first negative electrode active layer arranged in sequence on at least one side of the negative electrode current collector, and 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 comprises a second negative electrode active material and a quaternary ammonium salt type compound, the second negative electrode active material comprises a carbon-based material, and the quaternary ammonium salt type compound comprises a quaternary ammonium cation.

2. The lithium-ion secondary battery according to claim 1, characterized by The quaternary ammonium salt type compound further comprises a hydrocarbon chain covalently bonded to the quaternary ammonium cation.

3. The lithium-ion secondary battery according to claim 2, characterized by The hydrocarbon chain in the quaternary ammonium salt type compound comprises an alkyl chain.

4. The lithium-ion secondary battery according to claim 2, characterized by The quaternary ammonium salt type 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 12-18; (ta3) the molecular weight of the quaternary ammonium salt type compound is less than or equal to 600 Da.

5. The lithium-ion secondary battery according to claim 2, characterized by The quaternary ammonium salt type compound satisfies one or more of the following characteristics: (tb1) the quaternary ammonium cation has the structure -N + (R1R2R3), wherein R1and R2are each independently C 1-3 alkyl, and R3is C 1-3 alkyl or hydroxyethyl; (tb2) the quaternary ammonium salt type compound further comprises an anion, and the anion comprises one or more of nitrate, carbonate, bicarbonate and phosphate.

6. The lithium-ion secondary battery according to claim 5, characterized by R1 and R2 are each independently methyl, and R3 is methyl or hydroxyethyl.

7. The lithium-ion secondary battery according to claim 1, characterized by The quaternary ammonium salt type compound comprises one or more of octadecyldimethylhydroxyethyl quaternary ammonium nitrate, N,N-dimethyl-N-(2-hydroxyethyl) hexadecyl quaternary ammonium phosphate, octadecyltrimethyl quaternary ammonium phosphate, dodecyltrimethyl quaternary ammonium phosphate, dodecyltrimethyl quaternary ammonium nitrate, dodecyltrimethyl quaternary ammonium carbonate, and dodecyltrimethyl quaternary ammonium bicarbonate.

8. The lithium-ion secondary battery according to claim 1, characterized by The mass fraction of the quaternary ammonium salt type compound in the second negative electrode active layer is 0.2%-2%.

9. The lithium-ion secondary battery according to claim 1, characterized by The mass fraction of the quaternary ammonium salt type compound in the second negative electrode active layer is 0.2%-1.5%.

10. The lithium-ion secondary battery according to claim 1, characterized by The mass fraction of the carbon-based material in the second negative electrode active material is 80%-100%.

11. The lithium-ion secondary battery according to claim 1, characterized by The negative electrode sheet satisfies 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 fraction of the carbon-based material in the second negative electrode active layer is 94.5%-97.5%.

12. The lithium-ion secondary battery according to claim 11, characterized by The mass fraction of the carbon-based material in the second negative electrode active layer is 95.0%-97.0%.

13. The lithium-ion secondary battery according to any one of claims 1 to 12, characterized by The second negative electrode active layer comprises a binder, and the binder comprises styrene-butadiene rubber.

14. The lithium-ion secondary battery according to claim 13, characterized by The glass transition temperature of the styrene-butadiene rubber is 5°C-70°C.

15. The lithium-ion secondary battery according to claim 13, characterized by The glass transition temperature of the styrene-butadiene rubber is 30°C-50°C.

16. The lithium-ion secondary battery according to any one of claims 1 to 12, characterized by The first negative electrode active layer comprises a first negative electrode active material, and the first negative electrode active material comprises a negative electrode active body and a coating layer located on at least a portion of the surface of the negative electrode active body, and the coating layer comprises one or more of soft carbon, hard carbon and amorphous carbon.

17. The lithium-ion secondary battery according to any one of claims 1 to 12, characterized by The first negative electrode active layer comprises a first negative electrode active material; The lithium ion secondary battery satisfies one or more of the following characteristics: (td1) the first negative electrode active material comprises a coated graphite, the coated graphite comprises a graphite body and a coating layer on at least a part of the surface of the graphite body, the coating layer comprises one or more of soft carbon, hard carbon and amorphous carbon; (td2) the first negative electrode active material comprises secondary particle type graphite, the secondary particle type graphite comprises a secondary particle graphite body, and the amount of the secondary particle type graphite in the first negative electrode active material accounts for more than or equal to 20%; (td3) the first negative electrode active material comprises a graphite material, and the OI value of the graphite material is 2-15; (td4) D50 of the first negative electrode active material v 50 is 10 to 18 μm; (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 1.80 g / cm 3 ; (td7) the rate of the first negative electrode active layer is higher than the rate of the second negative electrode active layer; (td8) the ionic conductivity of the electrolyte is 13-18 mS / cm at least one temperature condition of 20-35°C.

18. The lithium-ion secondary battery according to claim 17, characterized by The first negative electrode active material comprises secondary particle type graphite, and the amount of the secondary particle type graphite in the first negative electrode active material accounts for 30-80%.

19. The lithium-ion secondary battery according to claim 17, characterized by The secondary particle type graphite comprises carbon-coated secondary particle type graphite, the carbon-coated secondary particle type graphite comprises the secondary particle graphite body and a carbon coating layer on at least a part of the surface of the secondary particle graphite body, and the carbon coating layer in the carbon-coated secondary particle type graphite comprises one or more of soft carbon, hard carbon and amorphous carbon.

20. The lithium-ion secondary battery according to claim 17, characterized by The lithium ion secondary battery satisfies one or more of the following characteristics: (1) the first negative electrode active material comprises a graphite material, and the OI value of the graphite material is 2-10; (2) the D50 of the first negative electrode active material is 1.0 to 2.0 pm v 50 is 12 to 16 pm; (3) the charging rate of the first negative electrode active layer is higher than the charging rate of the second negative electrode active layer; (4) the ionic conductivity of the electrolyte is 13-18 mS / cm at 25°C.

21. The lithium-ion secondary battery according to any one of claims 1 to 12, characterized by The negative electrode sheet satisfies one or more of the following characteristics: (te1) D of the second negative electrode active material v 50 is 12 to 21 μm; (te2) the first negative electrode active layer includes a first negative electrode active material, the second negative electrode active material has a D50 v 50 higher than the D50 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; (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 2.05 g / cm 3 .

22. The lithium-ion secondary battery according to claim 21, characterized by The negative electrode sheet satisfies one or more of the following characteristics: (1) the D50 of the second negative electrode active material is 0.5 to 5.0 μm v 50 is 14 to 20 μm; (2) 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; and 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.

23. The lithium-ion secondary battery according to claim 22, characterized by 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 1.10-1.30; and 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 1.10-1.

30.

24. The lithium-ion secondary battery according to claim 22, characterized by 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 1.10-1.28; and 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 1.10-1.

28.

25. The lithium-ion secondary battery according to any one of claims 1 to 12, characterized by The negative electrode sheet satisfies one or more of the following characteristics: (tf1) the ratio of the area density of the second negative electrode active layer to the area density of the first negative electrode active layer is 3:2 to 2:3, calculated on a single side of the negative electrode current collector; (tf2) a thickness ratio of the first negative electrode active layer with respect to the second negative electrode active layer is denoted as f, per one side of the negative electrode current collector H , f H ≤ 1.6 is satisfied. (tf3) the thickness of the first negative electrode active layer is less than or equal to 50 μm, calculated on a single side of the negative electrode current collector.

26. The lithium-ion secondary battery according to claim 25, characterized by The negative electrode sheet satisfies one or more of the following characteristics: (1) 1.1 < f < 1.6, where f is the ratio of the thickness of the negative electrode to the thickness of the positive electrode, measured on one side of the negative electrode current collector H ≤1.6; (2) the thickness of the first negative electrode active layer is 20 μm-50 μm, calculated on a single side of the negative electrode current collector.

27. The lithium-ion secondary battery according to claim 25, characterized by The negative electrode sheet satisfies one or more of the following characteristics: (1) 1.1 < f < 1.3, where f is the ratio of the thickness of the negative electrode to the thickness of the positive electrode, measured on one side of the negative electrode current collector H ≤ 1.3; (2) the thickness of the first negative electrode active layer is 30 μm-40 μm, calculated on a single side of the negative electrode current collector.

28. A lithium-ion secondary battery, characterized by comprising: The negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer 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 type compound, the negative electrode active material includes a negative electrode active body and a coating layer on at least a part 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 type compound includes a quaternary ammonium cation.

29. The lithium-ion secondary battery according to claim 28, characterized by The negative electrode sheet satisfies one or more of the following characteristics: (tg1) the quaternary ammonium salt type compound is the quaternary ammonium salt type compound in the lithium ion secondary battery of any one of claims 2-7; (tg2) the mass proportion of the quaternary ammonium salt type compound in the negative electrode active material layer is 0.2%-2%; (tg3) the negative electrode active material includes a carbon-based material; (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%-97.5%; (tg5) the negative electrode active material layer includes a binder, and the binder includes a styrene-butadiene rubber; the glass transition temperature of the styrene-butadiene rubber is 5°C-70°C; (tg6) the negative electrode active material includes coated graphite, and the coated graphite includes a graphite body and a coating layer 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; (tg7) the negative electrode active material includes secondary particle type graphite, and the secondary particle type graphite includes a secondary particle graphite body, and the amount proportion of the secondary particle type graphite in the negative electrode active material is greater than or equal to 20%; (tg8) the negative electrode active material includes a graphite material, and the OI value of the graphite material is 2-15; (tg9) the D50 of the negative active material is 10 μm or less v 50 is 11 μm to 20 μm; (tg10) the porosity of the negative electrode active material layer is 15%-35%. (tg11) the ionic conductivity of the electrolyte is 13 mS / cm to 18 mS / cm at at least one temperature in the range of 20°C to 35°C; (tg12) the negative active material layer comprises a second negative active layer, the second negative active layer being the second negative active layer in the lithium ion secondary battery of any one of claims 1 to 15, 21 to 24.

30. The lithium-ion secondary battery according to claim 29, characterized by The negative electrode sheet satisfies one or more of the following characteristics: (1) the mass fraction of the quaternary ammonium salt type compound in the negative active material layer is 0.2% to 1.5%; (2) the carbon-based material comprises one or more of artificial graphite, natural graphite, soft carbon, and hard carbon; (3) the mass fraction of the carbon-based material in the negative active material layer is 95.0% to 97.0%; (4) the glass transition temperature of the styrene-butadiene rubber is 30°C to 50°C; (5) the negative active material comprises secondary particle type graphite, the secondary particle type graphite comprises a secondary particle graphite body, and the amount of the secondary particle type graphite in the negative active material is 30% to 60%; (6) the negative active material comprises graphite material, and the OI value of the graphite material is 2 to 10; (7) the D50 of the negative active material is 5 to 15 μm v 50 is 13 to 18 μm; (8) the porosity of the negative active material layer is 25% to 30%; (9) the ionic conductivity of the electrolyte is 13 mS / cm to 18 mS / cm at at least one temperature in the range of 20°C to 35°C.

31. The lithium-ion secondary battery according to claim 30, characterized by The ionic conductivity of the electrolyte is 13 mS / cm to 18 mS / cm at 25°C.

32. The lithium-ion secondary battery according to claim 30, characterized by The secondary particle type graphite comprises carbon-coated secondary particle type graphite, the carbon-coated secondary particle type graphite comprises the secondary particle graphite body and a carbon coating layer on at least a portion of the surface of the secondary particle graphite body, and the carbon coating layer in the carbon-coated secondary particle type graphite comprises one or more of soft carbon, hard carbon, and amorphous carbon.

33. The lithium-ion secondary battery according to any one of claims 1 to 12, 28, wherein The area density of the negative electrode tab is 5 mg / cm2 or more and 15 mg / cm2 or less, per one side of the negative electrode current collector 2 15 mg / cm2 2 .

34. The lithium-ion secondary battery according to any one of claims 1 to 12, 28, wherein The electrolyte comprises an electrolyte salt, and the electrolyte salt comprises an electrolyte anion; The electrolyte anion comprises one or more of tetrafluoroborate, hexafluoroarsenate, hexafluorophosphate, triflate, difluorophosphate, difluoro oxalate borate, tetrafluoro oxalate phosphate, difluoro di-oxalate phosphate, bisfluorosulfonylimide, and bis-trifluoromethanesulfonylimide.

35. The lithium-ion secondary battery according to claim 34, characterized by The electrolyte salt comprises one or more of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bisfluorosulfonylimide, lithium bis-trifluoromethanesulfonylimide, lithium triflate, lithium difluorophosphate, lithium difluoro oxalate borate, lithium di-oxalate borate, lithium difluoro di-oxalate phosphate, and lithium tetrafluoro oxalate phosphate.

36. The lithium-ion secondary battery according to any one of claims 1 to 12, 28, wherein The lithium ion secondary battery further comprises a positive electrode sheet, the positive electrode sheet comprises a positive active layer, the positive active layer comprises a positive active material, and the positive active material comprises one or more of lithium-containing phosphate-based active material and lithium complex metal oxide-based active material.

37. The lithium-ion secondary battery according to claim 36, characterized by The positive active material comprises lithium-containing phosphate-based active material, and the positive active material satisfies one or more of the following characteristics: (th1) the mass ratio of the lithium-containing phosphate-based active material in the positive active layer is greater than or equal to 80%; (th2) the lithium-containing phosphate-based active material comprises one or more of lithium iron phosphate, a composite of lithium iron phosphate and carbon, lithium manganese phosphate, a composite of lithium manganese phosphate and carbon, lithium manganese iron phosphate, and a composite of lithium manganese iron phosphate and carbon; (th3) the lithium-containing phosphate-based active material comprises a lithium-containing phosphate-based active body and a carbon coating layer located on at least a portion of the surface of the lithium-containing phosphate-based active body, the carbon coating layer in the lithium-containing phosphate-based active material comprises one or more of soft carbon, hard carbon, and amorphous carbon.

38. The lithium-ion secondary battery according to claim 37, characterized by, The positive active material comprises a lithium-containing phosphate-based active material, and the mass ratio of the lithium-containing phosphate-based active material in the positive active layer is 80% to 97%.

39. An electrical device, comprising: The lithium ion secondary battery as claimed in any one of claims 1 to 38.

40. Use of the lithium ion secondary battery as claimed in any one of claims 1 to 38 for supplying and / or storing electric energy. The use comprises charging the lithium ion secondary battery at a rate higher than or equal to 2C.

41. The use of claim 40, wherein, The use comprises charging the lithium ion secondary battery at a rate of at least one of 2C to 6C.

42. The use of claim 40, wherein, The use comprises charging the lithium ion secondary battery at a rate of at least one of 2C to 4C or 4C to 6C.

43. The use of claim 40, wherein, The maximum charging rate of the lithium ion secondary battery is greater than or equal to 2C.

44. The use of claim 43, wherein, The maximum charging rate of the lithium ion secondary battery is 2C to 6C.

45. The use of claim 43, wherein, The maximum charging rate of the lithium ion secondary battery is 2C to 4C or 4C to 6C.

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