Battery cell, battery device, and electrical device

Abstract

The present application relates to a battery cell, a battery device and an electrical device. The battery cell includes an electrode assembly, the electrode assembly includes a positive electrode tab, a negative electrode tab and a separator, the separator is located between the positive electrode tab and the negative electrode tab. The positive electrode tab includes a positive electrode ear, a positive current collector portion and a positive electrode film layer disposed on at least one surface of the positive current collector portion along the thickness direction of the positive electrode tab and containing a positive electrode active material, and the positive electrode ear is disposed on at least one side of the positive current collector portion; the negative electrode tab includes a negative electrode ear, a negative current collector portion and a negative electrode film layer disposed on at least one surface of the negative current collector portion along the thickness direction of the negative electrode tab and containing a negative electrode active material, and the negative electrode ear is disposed on at least one side of the negative current collector portion. Wherein, when the battery cell is in a 100% charged state, the ratio of the total thickness of the negative electrode film layer in the negative electrode tab to the thickness of the negative electrode tab is 0.95 to 0.97. The present application can improve the fast charging performance and cycling performance of the battery cell and the energy density is improved.

Description

[0001] This application claims the priority of the PCT international application PCT / CN2024 / 106977, titled "Battery Cell, Battery Device and Electrical Device", filed on July 23, 2024, the entire content of which is incorporated herein by reference. Technical Field

[0002] This application relates to a battery cell, a battery device and an electrical device. Background Art

[0003] Battery cells have characteristics such as high capacity and long life, and are thus widely used in electronic devices, such as mobile phones, laptop computers, battery cars, electric vehicles, electric airplanes, electric ships, electric toy cars, electric toy ships, electric toy airplanes and electric tools, etc. Due to the great progress made in the battery field, higher requirements are put forward for the performance of batteries. The fast charging performance, cycling performance and energy density of battery cells still need to be further improved. Summary of the Invention

[0004] This application provides a battery cell, a battery device and an electrical device, which can improve the fast charging performance, cycling performance and energy density of the battery cell.

[0005] In a first aspect, this application proposes a battery cell, which includes an electrode assembly. The electrode assembly includes a positive electrode tab, a negative electrode tab and a separator. The separator is located between the positive electrode tab and the negative electrode tab. The positive electrode tab includes a positive electrode ear, a positive current collector and at least one positive electrode film layer disposed on at least one surface of the positive current collector along the thickness direction of the positive electrode tab and containing a positive electrode active material. The positive electrode ear is disposed on at least one side of the positive current collector; the negative electrode tab includes a negative electrode ear, a negative current collector and at least one negative electrode film layer disposed on at least one surface of the negative current collector along the thickness direction of the negative electrode tab and containing a negative electrode active material. The negative electrode ear is disposed on at least one side of the negative current collector. Wherein, when the battery cell is in a 100% charged state, the ratio of the total thickness of the negative electrode film layer in the negative electrode tab to the thickness of the negative electrode tab is 0.95 to 0.97.

[0006] Thus, when the ratio of the total thickness of the negative electrode film layer in the negative electrode tab to the thickness of the negative electrode tab is 0.95 to 0.97 in the embodiments of this application, during the charging process of the negative electrode tab, the volume expansion of the negative electrode tab is relatively small, so that the electrolyte can fully infiltrate the negative electrode tab, improving the migration performance of lithium ions in the negative electrode tab. The risk of lithium deposition on the negative electrode tab is reduced, which can effectively improve the use reliability and cycling performance of the battery cell, and is beneficial to improving the energy density of the battery cell; and the proportion of the negative current collector is small and the thickness is thin, which is beneficial to improving the fast charging performance of the battery cell and can also take into account the improvement of the energy density of the battery cell.

[0007] In some embodiments, when the battery cell is in a 100% charged state, the ratio of the total thickness of the positive electrode film layer to the thickness of the positive electrode tab in the positive electrode tab is 0.88 to 0.94.

[0008] In some embodiments, the thickness of the negative current collector is 4 μm to 6 μm. When the thickness of the negative current collector is within the above range, the current-carrying capacity of the negative current collector is relatively excellent, and the battery cell can have a relatively high energy density.

[0009] In some embodiments, the negative electrode film layer is disposed on two surfaces of the negative current collector. When the battery cell is in a 100% charged state, the thickness of the negative electrode film layer on both sides is 110 μm to 178 μm.

[0010] In some embodiments, the thickness of the positive current collector is 10 μm to 15 μm. When the thickness of the positive current collector is within the above range, the current-carrying capacity of the positive current collector is relatively excellent, and the battery cell can have a relatively high energy density.

[0011] In some embodiments, the positive electrode film layer is disposed on two surfaces of the positive current collector. When the battery cell is in a 100% charged state, the thickness of the positive electrode film layer on both sides is 128 μm to 191 μm. When the thickness of the negative electrode film layer on both sides is within the above range, it is beneficial to improve the energy density of the battery cell.

[0012] In some embodiments, the coating weight of the single-sided positive electrode film layer is 200 mg / 1540.25 mm 2 to 370 mg / 1540.25 mm 2 . When the coating weight of the single-sided positive electrode film layer is within the above range, the heat generation per unit area of the positive electrode tab will not be too large, and the energy density of the battery cell can be improved while taking into account.

[0013] In some embodiments, the coating weight of the single-sided negative electrode film layer is 90 mg / 1540.25 mm 2 to 170 mg / 1540.25 mm 2 . When the coating weight of the single-sided negative electrode film layer is within the above range, the heat generation per unit area of the negative electrode tab will not be too large, and the energy density of the battery cell can be improved while taking into account.

[0014] In some embodiments, when the battery cell is in a 100% charged state, the compaction density of the single-sided positive electrode film layer is 2.5 g / cm 3 to 2.8 g / cm 3 . When the compaction density of the positive electrode film layer is within the above range, it is beneficial to improve the energy density of the battery cell; and since the positive active materials in the positive electrode film layer are stacked relatively tightly, the contact resistance between particles is small, which can further reduce the resistance of the electrode tab and thus reduce heat generation.

[0015] In some embodiments, when the battery cell is in a 100% state of charge, the compaction density of the single-sided negative electrode film layer is 1.15 g / cm 3 to 1.36 g / cm 3 . When the compaction density of the negative electrode film layer is within the above range, it is beneficial to improve the energy density of the battery cell; and since the negative electrode active material in the negative electrode film layer is stacked relatively tightly, the contact resistance between particles is small, which can further reduce the resistance of the electrode sheet, thereby reducing heat generation.

[0016] In some embodiments, the powder resistivity of the negative electrode active material is 0.005 Ω•cm to 0.043 Ω•cm. The relatively low powder resistivity of the negative electrode active material results in a relatively low resistance of the negative electrode sheet and less heat generation of the battery cell.

[0017] In some embodiments, the powder compaction density of the negative electrode active material under 20000 N is 1.5 g / cm 3 to 1.85 g / cm 3 . When the powder compaction density of the negative electrode active material under 20000 N is within the above range, it can improve the energy density of the battery cell, and since the negative electrode active material in the negative electrode film layer can be stacked more tightly, the contact resistance between particles is small, which can further reduce the resistance of the electrode sheet, thereby reducing heat generation.

[0018] In some embodiments, the charging specific capacity of the negative electrode active material at a 0.1C rate is 350 mAh / g to 480 mAh / g. When the charging specific capacity of the negative electrode active material at a 0.1C rate is within the above range, the energy density of the battery cell is relatively high.

[0019] In some embodiments, the negative electrode active material includes a carbon-based material, the carbon-based material includes graphite particles, and the graphitization degree of the graphite particles is 92.0% to 94.5%. When the graphitization degree of the graphite particles is within the above range, the conductive performance of the graphite particles is relatively excellent, which can reduce the heat generation of the negative electrode sheet and the battery cell; and can improve the fast charging performance of the battery cell.

[0020] In some embodiments, the graphite particles include artificial graphite and a carbon coating layer, the artificial graphite includes secondary particles, and the carbon coating layer covers the surface of the artificial graphite. The carbon coating layer has more end faces and defects, so that the number of sites capable of intercalating and deintercalating lithium ions is more, and the conductivity of the carbon coating layer is relatively excellent, which can reduce the internal resistance of the negative electrode sheet and the heat generation of the battery cell.

[0021] In some embodiments, based on the mass of the graphite particles, the mass content of the carbon coating layer is 2% to 5%. When the mass content of the carbon coating layer is within the above range, the internal resistance of the negative electrode sheet can be further reduced, and the heat generation of the battery cell can be reduced.

[0022] In some embodiments, the negative electrode film layer includes a first negative electrode film layer and a second negative electrode film layer. The first negative electrode film layer is disposed on the surface of the negative electrode current collector portion. The first negative electrode film layer includes a carbon-based material. The second negative electrode film layer is connected to the side of the first negative electrode film layer facing away from the negative electrode current collector portion. The second negative electrode film layer includes a carbon-based material. The carbon-based materials in the first negative electrode film layer and the second negative electrode film layer each independently include graphite particles, and the volume average particle diameter Dv50 of the graphite particles in the first negative electrode film layer is greater than or equal to the volume average particle diameter Dv50 of the graphite particles in the second negative electrode film layer.

[0023] Thus, in the embodiments of the present application, there is a difference in the particle sizes of the first negative electrode film layer and the second negative electrode film layer, which can improve the fast charging performance of the battery cell. Specifically, during the fast charging process, the overpotential of the second negative electrode film layer is usually higher, and the bottleneck of fast charging mainly lies in the second negative electrode film layer. In the embodiments of the present application, the particle size in the second negative electrode film layer is relatively small, which can shorten the solid-phase transmission path of lithium ions, improve the fast charging performance, and can improve the problem of lithium deposition on the surface layer of the negative electrode sheet.

[0024] In some embodiments, the carbon-based material in the first negative electrode film layer further includes natural graphite.

[0025] In some embodiments, the tapped density of the carbon-based material in the first negative electrode film layer is less than or equal to the tapped density of the carbon-based material in the second negative electrode film layer. When the tapped density of the carbon-based material in the second negative electrode film layer is greater than the tapped density of the carbon-based material in the first negative electrode film layer, the second negative electrode film layer is filled more densely, which improves the energy density of the battery cell. The first negative electrode film layer is filled relatively sparsely, and the pores are more abundant, which can improve the fast charging performance of the battery cell.

[0026] In some embodiments, the tapped density of the carbon-based material in the first negative electrode film layer is 0.82 g / cm 3 to 1.21 g / cm 3 . When the tapped density of the carbon-based material in the first negative electrode film layer is within a suitable range, the fast charging performance of the battery cell can be improved.

[0027] In some embodiments, the tapped density of the carbon-based material in the second negative electrode film layer is 0.90 g / cm 3 to 1.25 g / cm 3 . When the tapped density of the carbon-based material in the second negative electrode film layer is within a suitable range, the energy density of the battery cell can be improved.

[0028] In some embodiments, the volume average particle size Dv50 of the graphite particles in the first negative electrode film layer is 9.5 μm to 18.5 μm. When the volume average particle size Dv50 of the negative electrode active material in the first negative electrode film layer is within the above range, the fast charging performance can be improved.

[0029] In some embodiments, the volume average particle size Dv50 of the graphite particles in the second negative electrode film layer is 7.8 μm to 14.3 μm. When the volume average particle size Dv50 of the negative electrode active material in the second negative electrode film layer is within the above range, the tortuosity of lithium ion transport can be reduced, and the fast charging performance of the battery cell can be improved.

[0030] In some embodiments, the first negative electrode film layer further includes a first lithium-containing binder, and the second negative electrode film layer further includes a second lithium-containing binder. The mass content of the first lithium-containing binder relative to the mass of the first negative electrode film layer is less than or equal to the mass content of the second lithium-containing binder relative to the mass of the second negative electrode film layer.

[0031] Thus, in the embodiments of the present application, the mass content of the second lithium-containing binder in the second negative electrode film layer is relatively high, and the number of freely movable lithium ions provided by the second lithium-containing binder for the second negative electrode film layer is relatively large, which can further improve the fast charging performance of the battery cell.

[0032] In some embodiments, the mass content of the first lithium-containing binder relative to the mass of the first negative electrode film layer is 0.1% to 1%. When the mass content of the first lithium-containing binder is within the above range, the intercalation and deintercalation rate of lithium ions can be improved, and the fast charging performance of the battery cell can be improved.

[0033] In some embodiments, the mass content of lithium element in the first lithium-containing binder is 3% to 10%, and can be optionally 3% to 8%. When the mass content of lithium element is within the above range, the number of freely movable lithium ions in the negative electrode film layer can be relatively large, which can further shorten the distance for lithium ions to diffuse to the surface of the negative electrode film layer, improve the intercalation and deintercalation rate of lithium ions, and improve the fast charging performance of the battery cell.

[0034] In some embodiments, the mass content of the second lithium-containing binder relative to the mass of the second negative electrode film layer is 0.1% to 1%. When the mass content of lithium element in the second lithium-containing binder is within the above range, the intercalation and deintercalation rate of lithium ions is improved, and the fast charging performance of the battery cell is improved.

[0035] In some embodiments, the mass content of lithium element in the second lithium-containing binder is 3% to 10%, and can be optionally 3% to 8%. When the mass content of lithium element is within the above range, the number of freely movable lithium ions in the negative electrode film layer can be relatively large, which can further shorten the distance for lithium ions to diffuse to the surface of the negative electrode film layer, improve the intercalation and deintercalation rate of lithium ions, and improve the fast charging performance of the battery cell.

[0036] In some embodiments, the first lithium-containing binder comprises a lithium acrylate-acrylonitrile-acrylamide-2-hydroxyethyl acrylate copolymer, which is derived from a lithium acrylate monomer, an acrylonitrile monomer, an acrylamide monomer, and a 2-hydroxyethyl acrylate monomer, and the molar percentages of the lithium acrylate monomer, the acrylonitrile monomer, the acrylamide monomer, and the 2-hydroxyethyl acrylate monomer are 30% to 50%: 15% to 45%: 5% to 20%: 20% to 35%.

[0037] Thus, the lithium-containing binder of the above material can provide a certain amount of lithium ions for the negative electrode film layer, improve the fast charging performance of the battery cell, and is not prone to swelling during charge and discharge, with a stable structure, so that the cycle performance of the negative electrode film layer is improved during fast charge and discharge.

[0038] In some embodiments, the second lithium-containing binder comprises a lithium acrylate-acrylonitrile-acrylamide-2-hydroxyethyl acrylate copolymer, which is derived from a lithium acrylate monomer, an acrylonitrile monomer, an acrylamide monomer, and a 2-hydroxyethyl acrylate monomer, and the molar percentages of the lithium acrylate monomer, the acrylonitrile monomer, the acrylamide monomer, and the 2-hydroxyethyl acrylate monomer are 30% to 50%: 15% to 45%: 5% to 20%: 20% to 35%.

[0039] Thus, the lithium-containing binder of the above material can provide a certain amount of lithium ions for the negative electrode film layer, improve the fast charging performance of the battery cell, and is not prone to swelling during charge and discharge, with a stable structure, so that the cycle performance of the negative electrode film layer is improved during fast charge and discharge.

[0040] In some embodiments, the negative electrode film layer is a single-layer film layer, the negative electrode active material is granular, and the volume average particle size of the negative electrode active material is 8.2 μm to 13.5 μm. When the volume average particle size of the negative electrode active material is in the above range, the negative electrode film layer can have an excellent pore structure, which is beneficial to improving the fast charging performance of the battery cell.

[0041] In some embodiments, the porosity of the negative electrode film layer is 40% to 55%. When the porosity of the negative electrode film layer is in the above range, it is beneficial to improve the migration rate of lithium ions and improve the fast charging performance of the battery cell.

[0042] In some embodiments, the negative electrode plate further comprises a negative electrode conductive layer, and the negative electrode conductive layer is located between the negative electrode film layer and the negative electrode current collector.

[0043] In some embodiments, the thickness of the negative electrode conductive layer is 0.5 μm to 2 μm. The negative electrode conductive layer can further improve the electrical conductivity of the negative electrode sheet, reduce the heat generation of the negative electrode sheet, and thus reduce the heat generation of the battery cell.

[0044] In some embodiments, the negative electrode conductive layer includes one or more of a negative electrode conductive agent and a negative electrode binder. The negative electrode conductive agent in the negative electrode conductive layer can improve the electrical conductivity of the negative electrode conductive layer, thereby improving the electrical conductivity of the negative electrode sheet and reducing the heat generation of the battery cell; the negative electrode binder in the negative electrode conductive layer can improve the bonding performance between the negative electrode current collector portion and the negative electrode film layer and improve the structural stability of the negative electrode sheet.

[0045] In some embodiments, the negative electrode conductive agent includes one or more of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0046] In some embodiments, the negative electrode binder includes one or more of styrene-butadiene rubber, water-soluble unsaturated resin SR-1B, water-based acrylic resin, polyvinyl alcohol, sodium alginate, and carboxymethyl chitosan.

[0047] In some embodiments, the powder resistivity of the positive electrode active material is 1 Ω•cm to 27.5 Ω•cm. The relatively low powder resistivity of the positive electrode active material results in a relatively low resistance of the positive electrode sheet and less heat generation of the battery cell.

[0048] In some embodiments, the powder compaction density of the positive electrode active material under 30000 N is 2.46 g / cm 3 to 2.8 g / cm 3 . When the powder compaction density of the positive electrode active material under 30000 N is within the above range, the energy density of the battery cell can be improved, and since the positive electrode active materials in the positive electrode film layer can be stacked more tightly and the contact resistance between particles is small, the resistance of the electrode sheet can be further reduced, thereby reducing heat generation.

[0049] In some embodiments, the charging specific capacity of the positive electrode active material at a 0.1C rate is 150 mAh / g to 170 mAh / g. When the charging specific capacity of the positive electrode active material at a 0.1C rate is within the above range, the energy density of the battery cell is relatively high.

[0050] In some embodiments, the positive electrode active material includes lithium-containing phosphate with an olivine structure.

[0051] In some embodiments, the lithium-containing phosphate with olivine structure includes a core and an ion-conducting layer. The core includes the lithium-containing phosphate with olivine structure, and the ion-conducting layer coats the surface of the lithium-containing phosphate with olivine structure. The ion-conducting layer contains one or more elements among C, Fe, Ti, Zr, Hf, Ge, and Sn. By coating the core with the ion-conducting layer, the conductivity of the lithium-containing phosphate with olivine structure can be improved, the powder resistivity of the material can be reduced, and it is beneficial to the migration rate of lithium ions, reducing the heat generation of the battery cell.

[0052] In some embodiments, the lithium-containing phosphate with olivine structure includes phosphate particles and a coating layer. The coating layer coats the phosphate particles, and the coating layer contains one or more elements among C, Fe, Ti, Zr, Hf, Ge, and Sn. By coating the surface of the phosphate particles with the coating layer, the conductivity of the lithium-containing phosphate with olivine structure can be improved, the powder resistivity of the material can be reduced, and it is beneficial to the migration rate of lithium ions, reducing the heat generation of the battery cell.

[0053] In some embodiments, the phosphate particles include a compound with the general formula Li x1 A y1 Me a M b P 1-c X c Y z where 0.5 ≤ x1 ≤ 1.3, 0 ≤ y1 ≤ 1.3, and 0.9 ≤ x1 + y1 ≤ 1.3, 0.9 ≤ a ≤ 1.5, 0 ≤ b ≤ 0.5, and 0.9 ≤ a + b ≤ 1.5, 0 ≤ c ≤ 0.5, 3 ≤ z ≤ 5. A includes one or more of Na, K, and Mg, Me includes one or more of Mn, Fe, Co, and Ni, M includes one or more of B, Mg, Al, Si, P, S, Ca, Sc, Ti, V, Cr, Cu, Zn, Sr, Y, Zr, Nb, Mo, Cd, Sn, Sb, Te, Ba, Ta, W, Yb, La, and Ce, X includes one or more of S, Si, Cl, B, C, and N, and Y includes one or more of O and F. The phosphate particles have excellent cycle stability, which is beneficial to improving the cycle performance of the battery cell.

[0054] In some embodiments, the coating layer includes a compound with the general formula Li 3-d Fe 2-d M2 d (PO x2 ) y2The fast ion conductor, M2 includes one or more elements of Ti, Zr, Hf, Ge, and Sn, 0 ≤ d ≤ 1, 0 < x2 < 5, 0 < y2 < 4. Coating the fast ion conductor on the surface of the phosphate particles can significantly improve the transport rate of lithium ions during multiple deintercalation / insertion at the positive electrode, improve the ionic conductivity of the positive electrode active material, and thus increase the specific capacity. Further, the energy density of the corresponding battery cell is increased.

[0055] In some embodiments, the graphitization degree of the positive electrode active material is from 0.15 to 0.32, and can be optionally from 0.19 to 0.26. When the graphitization degree of the positive electrode active material is within the above range, it is beneficial to improve the conductivity of the positive electrode active material, reduce the heat generation of the positive electrode sheet, and thus reduce the heat generation of the battery cell.

[0056] In some embodiments, the mass content of carbon element in the lithium-containing phosphate with olivine structure is 1% to 2%, and the specific surface area of the lithium-containing phosphate with olivine structure is 5m 2 / g to 18m 2 / g, and can be optionally 7.5m 2 / g to 14m 2 / g.

[0057] Thus, in the embodiments of the present application, the carbon element with the above mass content and the material with the above specific surface area are more conducive to the effective contact between the electrolyte and the lithium-containing phosphate with olivine structure, and are conducive to the transport of lithium ions at the phase interface.

[0058] In some embodiments, the lithium-containing phosphate with olivine structure is in particulate form, and its volume distribution particle size satisfies: 1 µm ≤ Dv50 ≤ 2 µm, 0.4 µm ≤ Dv10 ≤ 0.7 µm. The particle size of the lithium-containing phosphate with olivine structure is relatively small, the deintercalation / insertion path of lithium ions in the positive electrode active material is short, the heat generation is less, and the particle size of the above positive electrode active material is not too small, and basically no agglomeration occurs during the processing and preparation, so that the performance of the positive electrode active material is stable.

[0059] In some embodiments, the lithium-containing phosphate with olivine structure is in particulate form, the lithium-containing phosphate with olivine structure includes secondary particles, and the secondary particles include a plurality of primary particles, and the average particle size of the primary particles is from 200 nm to 500 nm. The average particle size of the primary particles is relatively small, the deintercalation / insertion path of lithium ions in the positive electrode active material is short, and the heat generation is less.

[0060] In some embodiments, the particle size of the smallest particle in the lithium-containing phosphate with olivine structure is from 0.1 µm to 0.4 µm.

[0061] In some embodiments, the particle size of the largest particle in the lithium-containing phosphate with olivine structure is from 15 µm to 25 µm.

[0062] In some embodiments, the positive electrode film layer further includes a first material, which includes one or more of ternary materials, lithium phosphate, lithium hydrogen phosphate, lithium sulfate, lithium sulfite, lithium molybdate, lithium oxalate, lithium titanate, lithium tetraborate, lithium metasilicate, lithium manganate, lithium tartrate, trilithium citrate, lithium nickelate, and lithium ferrate. The above-mentioned first material can be used as a lithium supplement agent, which can supplement lithium ions for the positive electrode film layer, make up for the irreversible loss of lithium ions in the system, improve the capacity, and thus improve the energy density of the battery cell.

[0063] In some embodiments, the mass content of the lithium supplement agent in the positive electrode film layer is 0.5% to 5%. When the mass content of the lithium supplement agent is within the above range, it can supplement lithium ions for the positive electrode film layer, make up for the irreversible loss of lithium ions in the system, improve the capacity, and thus improve the energy density of the battery cell.

[0064] In some embodiments, the positive electrode plate further includes a positive electrode conductive layer, which is located between the positive electrode film layer and the positive electrode current collector. The positive electrode conductive layer can further improve the conductivity of the positive electrode plate, reduce the heat generation of the positive electrode plate, and thus reduce the heat generation of the battery cell.

[0065] In some embodiments, the thickness of the positive electrode conductive layer is 0.5 μm to 2 μm. When the thickness of the positive electrode conductive layer is within the above range, it can further improve the conductivity of the positive electrode plate, reduce the heat generation of the positive electrode plate, and thus reduce the heat generation of the battery cell; and it can also take into account the improvement of the energy density of the battery cell.

[0066] In some embodiments, the positive electrode conductive layer includes one or more of a positive electrode conductive agent and a positive electrode binder. The positive electrode conductive agent in the positive electrode conductive layer can improve the conductivity of the positive electrode conductive layer, thereby improving the conductivity of the positive electrode plate and reducing the heat generation of the battery cell; the positive electrode binder in the positive electrode conductive layer can improve the bonding performance between the positive electrode current collector and the positive electrode film layer and improve the structural stability of the positive electrode plate.

[0067] In some embodiments, the positive electrode conductive agent includes one or more of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0068] In some embodiments, the positive electrode binder includes one or more of polyvinylidene fluoride, polytetrafluoroethylene, vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, polyacrylic acid, and fluorinated acrylate resins.

[0069] In some embodiments, the conductivity of the electrolyte at room temperature is from 13 mS / cm to 20 mS / cm. When the conductivity of the electrolyte is within the above range, the migration rate of lithium ions in the electrolyte is relatively high, which can further reduce the internal resistance of the battery cell, thereby reducing heat generation and improving the fast charging performance of the battery cell.

[0070] In some embodiments, the viscosity of the electrolyte at room temperature is from 2.3 mPa·s to 3.5 mPa·s. When the viscosity of the electrolyte is within the above range, the migration rate of lithium ions in the electrolyte is relatively high, which can further reduce the internal resistance of the battery cell, thereby reducing heat generation and improving the fast charging performance of the battery cell.

[0071] In some embodiments, the density of the electrolyte at room temperature is from 1.05 g / mL to 1.35 g / mL. When the density of the electrolyte is within the above range, the migration rate of lithium ions in the electrolyte is relatively high, which can further reduce the internal resistance of the battery cell, thereby reducing heat generation and improving the fast charging performance of the battery cell.

[0072] In some embodiments, the carboxylic ester solvent includes a chain carboxylic ester solvent, and the mass content of the chain carboxylic ester solvent in the organic solvent is greater than or equal to 5% and less than or equal to 75%, and can be optionally 30% to 75%. When the mass content of the chain carboxylic ester solvent is within the above range, the viscosity of the electrolyte system is relatively small, which is beneficial to the migration of lithium ions.

[0073] In some embodiments, the chain carboxylic ester solvent includes a compound represented by Formula I,

[0074] Formula I,

[0075] In Formula I,

[0076] R1 includes a hydrogen atom, a halogen atom, a C1-C5 alkyl group or a C1-C5 haloalkyl group, and R2 includes a C1-C5 alkyl group or a C1-C5 haloalkyl group. Thus, the conductivity of the above chain carboxylic ester solvent in the embodiments of the present application is relatively high, which is beneficial to improving the fast charging ability of the battery cell.

[0077] In some embodiments, R1 includes a hydrogen atom, a halogen atom, a C1-C3 alkyl group or a C1-C3 haloalkyl group.

[0078] In some embodiments, R2 includes a C1-C3 alkyl group or a C1-C3 haloalkyl group.

[0079] In some embodiments, the chain carboxylic ester solvent includes one or more of the compounds represented by Formula I-1 to Formula I-8,

[0080]

[0081] In some embodiments, the organic solvent further includes a carbonate solvent, and the carbonate solvent includes one or more of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate. The above-mentioned carbonate solvent and the chain carboxylic acid ester solvent are used in combination, so that the conductivity of the electrolyte is improved, which is beneficial to the migration of lithium ions.

[0082] In some embodiments, the carbonate solvent includes one or more of ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate.

[0083] In some embodiments, the mass content of the carbonate solvent in the organic solvent is 25% to 95%. The carbonate solvent with the above mass content can further improve the conductivity of the electrolyte, which is beneficial to the migration of lithium ions.

[0084] In some embodiments, the electrolyte further includes an additive, and the additive includes one or more of a carbonate additive, a sulfur-containing additive, and a lithium salt additive. The above-mentioned additive can improve the interfacial film performance on the positive electrode side and / or the negative electrode side, which is beneficial to improving the fast charging performance of the battery cell and improving the cycle performance.

[0085] In some embodiments, the carbonate additive includes one or more of vinylene carbonate VC and fluoroethylene carbonate FEC.

[0086] In some embodiments, the sulfur-containing additive includes one or more of ethylene sulfate DTD, bis(ethylene sulfate) 2-DTD, butene sulfite BS, 1,3-propane sultone PS, ethylene sulfite ES, and methylene methanedisulfonate MMDS.

[0087] In some embodiments, the lithium salt additive includes one or more of lithium difluorophosphate LiPO2F2, lithium difluorooxalate borate LiDFOB, lithium tetrafluoroborate LiBF4, and lithium bis(oxalate) borate LiBOB.

[0088] In some embodiments, the mass content of the additive in the electrolyte is 1% to 10%, and can be optionally 2% to 8%. The additive with the above mass content can effectively improve the interfacial film performance on the positive electrode side and / or the negative electrode side, which is beneficial to improving the fast charging performance of the battery cell and improving the cycle performance.

[0089] In some embodiments, the electrolyte further includes a lithium salt, and the lithium salt includes one or more of a fluorosulfonylimide salt and lithium hexafluorophosphate LiPF6. The above-mentioned lithium salt is easy to dissociate, which is beneficial to the rapid migration of lithium ions, and the electrolyte system is relatively stable and not easy to decompose, which can improve the cycle performance of the battery cell.

[0090] In some embodiments, the fluorosulfonylimide salt includes one or more of lithium bis(fluorosulfonyl)imide (LiFSI) and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI).

[0091] In some embodiments, the lithium salt includes lithium bis(fluorosulfonyl)imide (LiFSI) and lithium hexafluorophosphate (LiPF6). The molar concentration of lithium bis(fluorosulfonyl)imide (LiFSI) is from 0.2 mol / L to 0.5 mol / L, and the molar concentration of lithium hexafluorophosphate (LiPF6) is from 0.5 mol / L to 1.0 mol / L.

[0092] In some embodiments, the ratio of the molar concentration of lithium bis(fluorosulfonyl)imide to the molar concentration of lithium hexafluorophosphate (LiPF6) is from 0.2 to 1.0.

[0093] In some embodiments, the thickness of the base film does not exceed 12 μm, and can be optionally 5 μm to 12 μm. When the thickness of the base film is within the above range, the migration path of lithium ions in the base film is shorter, which can further reduce the internal resistance of the battery cell, thereby reducing heat generation.

[0094] In some embodiments, the separator includes a base film with a porous structure, and the porosity of the base film is from 20% to 70%. When the porosity of the separator in the embodiments of the present application is within the above range, the migration ability of lithium ions in the separator can be improved, the internal resistance of the battery cell can be further reduced, thereby reducing heat generation.

[0095] In some embodiments, the separator includes a base film with a porous structure, and the porosity of the base film is from 35% to 60%. When the porosity of the separator in the embodiments of the present application is within the above range, the migration ability of lithium ions in the separator can be improved, the internal resistance of the battery cell can be further reduced, thereby reducing heat generation.

[0096] In some embodiments, the thickness of the base film is from 6 μm to 12 μm. When the thickness of the base film is within the above range, the migration path of lithium ions in the base film is shorter, which can further reduce the internal resistance of the battery cell, thereby reducing heat generation.

[0097] In some embodiments, the thickness of the base film is from 6 μm to 9 μm. When the thickness of the base film is within the above range, the migration path of lithium ions in the base film is shorter, which can further reduce the internal resistance of the battery cell, thereby reducing heat generation.

[0098] In some embodiments, the separator membrane includes a base film and a functional layer disposed on at least one side of the base film. The functional layer includes a first functional layer and a second functional layer. The first functional layer is located on one side of the base film and includes first inorganic particles. The second functional layer is located on the other side of the base film and includes composite particles. The composite particles include second inorganic particles and a plurality of non-fluoropolymer particles. The second inorganic particles are attached to the surface of and / or dispersed inside the non-fluoropolymer particles. The first functional layer and the second functional layer have good heat resistance, which can improve the heat resistance of the separator membrane.

[0099] In some embodiments, the non-fluoropolymer particles include acrylate copolymers. Acrylate copolymers have excellent adhesion properties and high adhesion stability with the base film.

[0100] In some embodiments, the first inorganic particles include one or more of silica, alumina, boehmite, barium sulfate, calcium oxide, titanium oxide, zinc oxide, magnesium oxide, zirconium oxide, and tin oxide. The above first inorganic particles can improve the heat resistance of the first functional layer.

[0101] In some embodiments, the second inorganic particles include one or more of silica, alumina, boehmite, barium sulfate, calcium oxide, titanium oxide, zinc oxide, magnesium oxide, zirconium oxide, and tin oxide. The above second inorganic particles can improve the heat resistance of the first functional layer.

[0102] In some embodiments, the average particle size of the second inorganic particles is 5 nm to 100 nm. When the average particle size of the second inorganic particles is in the above range, it is beneficial to improve the heat resistance and compression modulus of the composite particles.

[0103] In some embodiments, the positive electrode tabs are disposed on both sides of the positive current collector along the length direction of the electrode assembly. The positive electrode tabs are disposed on both sides of the positive current collector along the length direction, so that the current in the length direction of the positive current collector is evenly divided by the positive electrode tabs on both sides, the electron transmission path is short, and the current distribution is more uniform. The delithiation state of each part of the positive electrode plate is uniform, and the charging performance of the battery cell can be improved.

[0104] In some embodiments, the number of positive electrode tabs on the same side of the positive current collector is one or more. The positive electrode tab includes a first end surface connected to the positive current collector. The dimension of the first end surface in the width direction is W1. The sum of the dimensions of all the first end surfaces in the width direction on the same side of the positive current collector is n×W1. The dimension of the positive current collector in the width direction is W2, and n×W1 / W2 is greater than or equal to 1 / 3, where n represents the number of all positive electrode tabs on the same side of the positive current collector. Optionally, n×W1 / W2 is greater than or equal to 2 / 3, where n represents the number of all positive electrode tabs on the same side of the positive current collector.

[0105] Thus, when n×W1 / W2 meets the above range, the current-carrying area of the positive electrode tab is relatively large, which is beneficial to improving the fast charging performance of the battery cell.

[0106] In some embodiments, the negative electrode tabs are disposed on both sides of the negative current collector along the length direction of the electrode assembly. The negative electrode tabs are disposed on both sides of the negative current collector along the length direction, so that the current in the length direction of the negative current collector is evenly divided by the negative electrode tabs on both sides, the electron transmission path is short, and the current distribution is more uniform. The lithium intercalation state of each part of the negative electrode plate is uniform, and the charging performance of the battery cell can be improved.

[0107] In some embodiments, the number of negative electrode tabs on the same side of the negative current collector is one or more. The negative electrode tab includes a second end face connected to the negative current collector. The dimension of the second end face in the width direction is W3. The sum of the dimensions of all the second end faces on the same side of the negative current collector in the width direction is m×W3. The dimension of the negative current collector in the width direction is W4, and m×W3 / W4 is greater than or equal to 1 / 3, where m represents the number of all negative electrode tabs on the same side of the negative current collector. Optionally, m×W3 / W4 is greater than or equal to 2 / 3, where m represents the number of all negative electrode tabs on the same side of the negative current collector.

[0108] Thus, when m×W3 / W4 meets the above range, the current-carrying area of the negative electrode tab is relatively large, which is beneficial to improving the fast charging performance of the battery cell.

[0109] In some embodiments, the battery cell further includes a positive terminal, and the positive terminal is electrically connected to the positive electrode tab.

[0110] In some embodiments, the positive terminal is directly welded to the positive electrode tab. The internal resistance of the battery cell is reduced, which is beneficial to improving the fast charging performance.

[0111] In some embodiments, the number of positive terminals on the same side of the positive current collector is at least two. The current-carrying capacity of the positive terminal is enhanced, which is beneficial to improving the fast charging performance.

[0112] In some embodiments, the current-carrying area of a single positive terminal is greater than or equal to 200mm 2 . The current-carrying capacity of the positive terminal is enhanced, which is beneficial to improving the fast charging performance.

[0113] In some embodiments, the battery cell further includes a negative terminal, and the negative terminal is electrically connected to the negative electrode tab.

[0114] In some embodiments, the negative terminal is directly welded to the negative electrode tab. The internal resistance of the battery cell is reduced, which is beneficial to improving the fast charging performance.

[0115] In some embodiments, the number of negative terminals on the same side of the negative current collector is at least two. The enhanced over-current capacity of the negative terminals is beneficial to the improvement of fast charging performance.

[0116] In some embodiments, the over-current area of a single negative terminal is greater than or equal to 200 mm 2 . The enhanced over-current capacity of the negative terminals is beneficial to the improvement of fast charging performance.

[0117] In some embodiments, the positive electrode sheet, the separator, and the negative electrode sheet are stacked in the thickness direction of the electrode assembly. The stacked electrode assembly is beneficial to the improvement of energy density.

[0118] In some embodiments, the charging time of the battery cell from 10% state of charge to 80% state of charge is less than or equal to 12.5 min, and can be optionally 6 min to 12.5 min. The charging speed of the battery cell is relatively fast, which is more beneficial to the improvement of fast charging ability.

[0119] In a second aspect, the present application provides a battery device, and the battery device includes the battery cell according to any one of the embodiments in the first aspect of the present application.

[0120] In some embodiments, the charging time of the battery device from 10% state of charge to 80% state of charge is less than or equal to 12.5 min, and can be optionally 6 min to 12.5 min. The charging speed of the battery device is relatively fast, which is more beneficial to the improvement of fast charging ability.

[0121] In a third aspect, the present application provides an electrical device, and the electrical device includes the battery device according to any one of the embodiments in the second aspect of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0122] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings required to be used in the embodiments of the present application will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For those of ordinary skill in the art, other drawings can be obtained according to the drawings without creative efforts.

[0123] Figure 1 Schematic structural diagram of a battery cell provided in some embodiments of the present application;

[0124] Figure 2 Explosion diagram of a battery cell provided in some embodiments of the present application;

[0125] Figure 3 Schematic structural diagram of a battery module provided in some embodiments of the present application;

[0126] Figure 4Schematic diagram of the structure of the battery pack provided for some embodiments of the present application;

[0127] Figure 5 Schematic diagram of the structure of the electrical device provided for some embodiments of the present application.

[0128] The drawings are not necessarily drawn to actual scale.

[0129] The reference numerals are explained as follows:

[0130] 1. Electrical device; 2. Battery pack; 3. Controller; 4. Motor; 5. Box body; 5a. First box body part; 5b. Second box body part; 5c. Accommodating space; 6. Battery module;

[0131] 7. Battery cell;

[0132] 10. Electrode assembly; 111. Positive electrode tab; 112. Negative electrode tab; 12. Main body part;

[0133] 20. Outer shell; 21. Housing; 22. End cover;

[0134] 31. Positive terminal; 32. Negative terminal. Specific embodiments

[0135] Hereinafter, embodiments of the battery cell, battery device, and electrical device of the present application specifically disclosed will be described in detail with appropriate reference to the drawings. However, there may be cases where unnecessary detailed descriptions are omitted. For example, there are cases where detailed descriptions of well-known matters and repeated descriptions of actually identical structures are omitted. This is to avoid making the following description unnecessarily lengthy and to facilitate the understanding of those skilled in the art. In addition, the drawings and the following description are provided for those skilled in the art to fully understand the present application and are not intended to limit the subject matter recited in the claims.

[0136] The "ranges" disclosed in this application are defined in the form of a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundaries of a particular range. The ranges defined in this way can include or exclude the end values, and can be combined arbitrarily, that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60 to 120 and 80 to 110 are listed for a specific parameter, ranges of 60 to 110 and 80 to 120 are also contemplated. In addition, if the minimum range values 1 and 2 are listed, and if the maximum range values 3, 4, and 5 are listed, the following ranges are all contemplated: 1 to 3, 1 to 4, 1 to 5, 2 to 3, 2 to 4, and 2 to 5. In this application, unless otherwise specified, the numerical range "a to b" represents an abbreviated representation of any real number combination between a and b, where a and b are both real numbers. For example, the numerical range "0 to 5" means that all real numbers between "0 to 5" are fully listed herein, and "0 to 5" is only an abbreviated representation of these numerical combinations. Additionally, when stating that a certain parameter is an integer ≥2, it is equivalent to disclosing that the parameter is, for example, the integers 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0137] If there is no special instruction, all embodiments and optional embodiments of this application can be combined with each other to form new technical solutions.

[0138] If there is no special instruction, all technical features and optional technical features of this application can be combined with each other to form new technical solutions.

[0139] If there is no special instruction, all steps of this application can be carried out sequentially or randomly, preferably sequentially. For example, if a method includes steps (a) and (b), it means that the method can include steps (a) and (b) carried out sequentially, or can also include steps (b) and (a) carried out sequentially. For example, if it is mentioned that the method may further include step (c), it means that step (c) can be added to the method in any order. For example, the method can include steps (a), (b), and (c), or can also include steps (a), (c), and (b), or can also include steps (c), (a), and (b), etc.

[0140] With the development of the battery field, the performance requirements for batteries are getting higher and higher, especially the requirements for the energy density and fast charging performance of batteries are gradually increasing. During the charging process, the negative electrode film layer containing the negative electrode active material in the negative electrode tab may undergo volume expansion and contraction. During the volume change of the negative electrode film layer, it is easy to cause the electrolyte in the negative electrode film layer to be extruded and difficult to flow back, resulting in insufficient electrolyte infiltration in the negative electrode film layer, making the negative electrode tab prone to problems such as lithium deposition, and shortening the cycle life of the battery cell. During fast charging, the above problems are more prominent, making it difficult for the battery cell to improve the cycle performance and energy density under fast charging conditions.

[0141] In view of the above problems, the embodiments of the present application design the system of the battery cell. By designing the thickness ratio of the negative electrode film layer and the negative electrode current collector part in the negative electrode tab, during the charging process of the negative electrode tab, the volume expansion of the negative electrode tab is relatively small, so that the electrolyte can fully infiltrate the negative electrode tab, improving the migration performance of lithium ions in the negative electrode tab, reducing the risk of lithium deposition in the negative electrode tab, and effectively improving the use reliability and cycle performance of the battery cell. And the above technical solution is also applicable to the battery system for fast charging, so that the cycle performance and energy density of the battery cell can be improved under fast charging conditions.

[0142] battery cell

[0143] In a first aspect, the embodiments of the present application propose a battery cell.

[0144] The battery cell includes an electrode assembly. The electrode assembly includes a positive electrode tab, a negative electrode tab, and a separator. The separator is located between the positive electrode tab and the negative electrode tab. The positive electrode tab includes a positive electrode tab ear, a positive electrode current collector part, and a positive electrode film layer disposed on at least one surface of the positive electrode current collector part along the thickness direction of the positive electrode tab and containing a positive electrode active material. The positive electrode tab ear is disposed on at least one side of the positive electrode current collector part; the negative electrode tab includes a negative electrode tab ear, a negative electrode current collector part, and a negative electrode film layer disposed on at least one surface of the negative electrode current collector part along the thickness direction of the negative electrode tab and containing a negative electrode active material. The negative electrode tab ear is disposed on at least one side of the negative electrode current collector part. When the battery cell is in a 100% charged state, the ratio of the total thickness of the negative electrode film layer in the negative electrode tab to the thickness of the negative electrode tab is from 0.95 to 0.97.

[0145] The negative electrode current collector part includes two surfaces opposite to each other along the thickness direction of the negative electrode tab. The negative electrode film layer can be disposed on any one of the two surfaces or on both surfaces. When the negative electrode film layer is disposed on one of the two surfaces, the total thickness of the negative electrode film layer in the negative electrode tab refers to the thickness of the negative electrode film layer on this surface. When the negative electrode film layer is disposed on both surfaces, the total thickness of the negative electrode film layer in the negative electrode tab refers to the sum of the thicknesses of the negative electrode film layers on the two surfaces.

[0146] When the battery cell is in a 100% state of charge, the ratio of the total thickness of the negative electrode film layer to the thickness of the negative electrode tab in the negative electrode tab is relatively small, for example, when it is less than 0.95, the thickness of the negative electrode film layer is relatively thin, resulting in a lower energy density of the battery cell; as the total thickness of the negative electrode film layer in the negative electrode tab increases, the amount of active material that can be accommodated increases, which is beneficial to the improvement of the energy density. However, when the total thickness of the negative electrode film layer is too thick, for example, when the ratio of the total thickness of the negative electrode film layer to the thickness of the negative electrode tab in the negative electrode tab is relatively large, for example, greater than 0.97, the volume expansion of the negative electrode tab is too large, and it is difficult for the electrolyte to flow back, resulting in insufficient electrolyte infiltration in the negative electrode film layer, making it easy for the negative electrode tab to have problems such as lithium plating, resulting in a shortened cycle life of the battery cell;

[0147] In the embodiments of the present application, the ratio of the total thickness of the negative electrode film layer to the thickness of the negative electrode tab in the negative electrode tab is 0.95 to 0.97, for example, 0.95, 0.955, 0.958, 0.96, 0.962, 0.965, 0.968, 0.970 or the range composed of any two of the above values. During the charging process of the negative electrode tab, the volume expansion of the negative electrode tab is relatively small, enabling the electrolyte to fully infiltrate the negative electrode tab, improving the migration performance of lithium ions in the negative electrode tab, reducing the risk of lithium plating in the negative electrode tab, effectively improving the use reliability and cycle performance of the battery cell, and being beneficial to improving the energy density of the battery cell; and the proportion of the negative electrode current collector part is relatively small and the thickness is relatively thin, which is beneficial to improving the fast charging performance and energy density of the battery cell.

[0148] The charging upper limit voltage and the discharge cut-off voltage of the battery cell vary according to the different positive electrode active materials. For example, when the phosphate material includes lithium iron phosphate, the charging upper limit voltage can be 3.65V and the discharge cut-off voltage can be 2.0V. Another example is when the phosphate material includes lithium manganese iron phosphate, the charging upper limit voltage can be 4.3V and the discharge cut-off voltage can be 2.0V. Next, taking the charging upper limit voltage of 3.65V and the discharge cut-off voltage of 2.0V as an example, the state of the battery cell is described as follows: In the embodiments of the present application, the 100% state of charge SOC and the 0% state of charge SOC of the battery cell are defined as follows,

[0149] The battery cell is charged at a constant current charging rate of 0.33C to the charging upper limit voltage, and then charged at a constant voltage to 0.05C, corresponding to the state of 100% SOC of the battery cell. The battery cell is discharged at a constant current discharge rate of 0.33C to the cut-off voltage, corresponding to the state of 0% SOC of the battery cell.

[0150] Optionally, the thickness of the negative current collector portion is 4 μm to 6 μm, such as 4 μm, 4.2 μm, 4.5 μm, 4.8 μm, 5 μm, 5.2 μm, 5.5 μm, 5.8 μm, 6 μm or a range composed of any two of the above values. When the thickness of the negative current collector portion is within the above range, the current-carrying capacity of the negative current collector portion is relatively excellent, and the battery cell can have a relatively high energy density.

[0151] The negative current collector portion can be made of a metal foil or a composite current collector. As an example of the metal foil, at least one of copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy foils can be used. The composite current collector can include a polymer material base layer and a metal material layer formed on at least one surface of the polymer material base layer. As an example, the metal material in the metal material layer can include at least one of copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy. As an example, the polymer material base layer can include at least one of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0152] Optionally, when the negative electrode film layers are disposed on two surfaces of the negative current collector portion, at 100% state of charge of the battery cell, the total thickness of the negative electrode film layers on both sides is 110 μm to 178 μm, such as 110 μm, 115 μm, 120 μm, 125 μm, 130 μm, 135 μm, 140 μm, 145 μm, 150 μm, 155 μm, 160 μm, 165 μm, 170 μm, 175 μm, 178 μm or a range composed of any two of the above values.

[0153] The total thickness of the negative electrode film layers on both sides refers to the sum of the thicknesses of the negative electrode film layers on two surfaces of the negative current collector portion. When the thickness of the negative electrode film layer meets the above range, the service reliability and energy density of the battery cell can be effectively improved.

[0154] In some embodiments, at 100% state of charge of the battery cell, the ratio of the total thickness of the positive electrode film layer in the positive electrode tab to the thickness of the positive electrode tab is 0.88 to 0.94, such as 0.88, 0.89, 0.90, 0.905, 0.91, 0.915, 0.92, 0.925, 0.93, 0.935, 0.94 or a range composed of any two of the above values.

[0155] The positive current collector portion includes two surfaces that face each other along the thickness direction of the positive electrode plate. The positive electrode film layer can be disposed on either one of the two surfaces or on both surfaces. When the positive electrode film layer is disposed on one of the two surfaces, the total thickness of the positive electrode film layer in the positive electrode plate refers to the thickness of the positive electrode film layer on that surface. When the positive electrode film layer is disposed on both surfaces, the total thickness of the positive electrode film layer in the positive electrode plate refers to the sum of the thicknesses of the positive electrode film layers on the two surfaces.

[0156] When the ratio of the total thickness of the positive electrode film layer in the positive electrode plate to the thickness of the positive electrode plate is within the above range, it is beneficial to increase the coating weight of the positive active material and improve the energy density of the battery cell; because the proportion of the positive current collector portion is small and the thickness is thin, it is beneficial to improve the fast charging performance of the battery cell.

[0157] Optionally, the thickness of the positive current collector portion is 10 μm to 15 μm, such as 10 μm, 10.5 μm, 11 μm, 11.5 μm, 12 μm, 12.5 μm, 13 μm, 13.5 μm, 14 μm, 14.5 μm, 15 μm or the range composed of any two of the above values. When the thickness of the positive current collector portion is within the above range, the current-carrying capacity of the positive current collector portion is relatively excellent, and the battery cell can have a high energy density.

[0158] The positive current collector portion can adopt a metal foil or a composite current collector. As an example of the metal foil, at least one of aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy foils can be used. The composite current collector can include a polymer material base layer and a metal material layer formed on at least one surface of the polymer material base layer. As an example, the metal material of the metal material layer can include at least one of aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy. As an example, the polymer material base layer can include at least one of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS) and polyethylene (PE).

[0159] Optionally, when the positive electrode film layer is disposed on both surfaces of the positive current collector portion, at 100% state of charge of the battery cell, the thickness of the positive electrode film layers on both sides is 128 μm to 191 μm, such as 128 μm, 130 μm, 135 μm, 140 μm, 145 μm, 150 μm, 155 μm, 160 μm, 165 μm, 170 μm, 175 μm, 180 μm, 185 μm, 190 μm, 191 μm or the range composed of any two of the above values.

[0160] The thickness of the two-sided positive electrode film layer refers to the sum of the thicknesses of the positive electrode film layers on the two surfaces of the positive electrode current collector part. When the thickness of the positive electrode film layer meets the above range, the energy density and fast charging performance of the battery cell can be effectively improved.

[0161] In the embodiments of the present application, the thicknesses of the film layer and the current collector part have meanings well-known in the art, and can be detected by devices and methods well-known in the art. For example, a micrometer is used to measure the thickness of the electrode sheet. After removing the film layer on the surface of the current collector part, a micrometer is used to measure the thickness of the current collector part. When the film layer is coated on one side, the thickness of the film layer is the thickness of the electrode sheet minus the thickness of the current collector part; when the film layer is coated on both sides, the thickness of the film layer is (the thickness of the electrode sheet minus the thickness of the current collector part) / 2.

[0162] Optionally, the coating weight of the single-sided negative electrode film layer is 90 mg / 1540.25 mm 2 to 170 mg / 1540.25 mm 2 , and can be optionally 110 mg / 1540.25 mm 2 to 150 mg / 1540.25 mm 2 . Exemplarily, the single-sided coating weight of the negative electrode film layer is 90 mg / 1540.25 mm 2 , 92 mg / 1540.25 mm 2 , 95 mg / 1540.25 mm 2 , 96 mg / 1540.25 mm 2 , 100 mg / 1540.25 mm 2 , 102 mg / 1540.25 mm 2 , 104 mg / 1540.25 mm 2 , 105 mg / 1540.25 mm 2 , 108 mg / 1540.25 mm 2 , 110 mg / 1540.25 mm 2 , 112 mg / 1540.25 mm 2 , 114 mg / 1540.25 mm 2 , 115 mg / 1540.25 mm 2 , 116 mg / 1540.25 mm 2 , 118 mg / 1540.25 mm 2 , 120 mg / 1540.25 mm 2 , 122 mg / 1540.25 mm 2 , 125 mg / 1540.25 mm 2 , 128 mg / 1540.25 mm 2 , 130 mg / 1540.25 mm 2, 132 mg / 1540.25 mm 2 , 135 mg / 1540.25 mm 2 , 137 mg / 1540.25 mm 2 , 140 mg / 1540.25 mm 2 , 142 mg / 1540.25 mm 2 , 145 mg / 1540.25 mm 2 , 148 mg / 1540.25 mm 2 , 150 mg / 1540.25 mm 2 , 152 mg / 1540.25 mm 2 , 155 mg / 1540.25 mm 2 , 160 mg / 1540.25 mm 2 , 165 mg / 1540.25 mm 2 , 170 mg / 1540.25 mm 2 Or a range composed of any two of the above values.

[0163] When the single-sided coating weight of the negative electrode film layer is within the above range, the heat generation amount per unit area of the negative electrode plate will not be too large, and it can take into account improving the energy density and fast charging performance of the battery cell.

[0164] Optionally, the coating weight of the single-sided positive electrode film layer is 200 mg / 1540.25 mm 2 to 370 mg / 1540.25 mm 2 ; it can be 240 mg / 1540.25 mm 2 to 330 mg / 1540.25 mm 2 . Exemplarily, the coating weight of the single-sided positive electrode film layer is 200 mg / 1540.25 mm 2 , 210 mg / 1540.25 mm 2 , 220 mg / 1540.25 mm 2 , 230 mg / 1540.25 mm 2 , 240 mg / 1540.25 mm 2 , 250 mg / 1540.25 mm 2 , 260 mg / 1540.25 mm 2 , 270 mg / 1540.25 mm 2 , 280 mg / 1540.25 mm 2 , 290 mg / 1540.25 mm 2 , 300 mg / 1540.25 mm 2 , 310 mg / 1540.25 mm2 、320 mg / 1540.25 mm 2 、330 mg / 1540.25 mm 2 、340 mg / 1540.25 mm 2 、350 mg / 1540.25 mm 2 、360 mg / 1540.25 mm 2 、370 mg / 1540.25 mm 2 or a range composed of any two of the above values.

[0165] When the single-sided coating weight of the positive electrode film layer is within the above range, the heat generation per unit area of the positive electrode plate will not be excessive, and it can take into account the improvement of the energy density and fast charging performance of the battery cell.

[0166] In some embodiments, when the battery cell is in a 100% charged state, the tap density of the negative electrode film layer is 1.15 g / cm 3 to 1.36 g / cm 3 ; optionally 1.25 g / cm 3 to 1.36 g / cm 3 . Exemplarily, the tap density of the negative electrode film layer of the battery cell in a 100% charged state is 1.15 g / cm 3 、1.18 g / cm 3 、1.20 g / cm 3 、1.22 g / cm 3 、1.25 g / cm 3 、1.28 g / cm 3 、1.3 g / cm 3 、1.32 g / cm 3 、1.35 g / cm 3 、1.36 g / cm 3 or a range composed of any two of the above values.

[0167] When the tap density of the negative electrode film layer is within the above range, it is beneficial to improve the energy density of the battery cell; and since the negative electrode active materials in the negative electrode film layer are stacked relatively tightly, the contact resistance between particles is small, which can further reduce the resistance of the electrode plate, thereby reducing heat generation.

[0168] In some embodiments, when the battery cell is in a 100% charged state SOC, the tap density of the positive electrode film layer is 2.50 g / cm 3 to 2.80 g / cm 3 ; optionally 2.55 g / cm 3 to 2.70 g / cm 3. Exemplarily, when the battery cell is at 100% state of charge (SOC), the tap density of the positive electrode film layer is 2.50 g / cm 3 , 2.52 g / cm 3 , 2.55 g / cm 3 , 2.56 g / cm 3 , 2.57 g / cm 3 , 2.58 g / cm 3 , 2.60 g / cm 3 , 2.62 g / cm 3 , 2.65 g / cm 3 , 2.68 g / cm 3 , 2.70 g / cm 3 , 2.72 g / cm 3 , 2.75 g / cm 3 , 2.78 g / cm 3 , 2.80 g / cm 3 or a range composed of any two of the above values.

[0169] When the tap density of the positive electrode film layer is within the above range, it is beneficial to improve the energy density of the battery cell; and since the positive electrode active material in the positive electrode film layer is stacked relatively tightly, the contact resistance between particles is small, which can further reduce the resistance of the electrode sheet, thereby reducing heat generation during fast charging. Therefore, by adjusting the tap density of the positive electrode film layer to a reasonable range, the battery cell has both high energy density and high charging rate performance.

[0170] In the embodiments of the present application, the tap density of the positive electrode film layer of the battery cell at 100% state of charge (SOC) has the meaning well known in the art, that is, the positive electrode sheet of the battery cell at 100% state of charge (SOC) is disassembled, and the tap density of the positive electrode film layer is measured. For example, a single-sided coated positive electrode sheet (if it is a double-sided coated sheet, the positive electrode film layer on one side can be wiped off first) is punched into small round pieces with an area of S1, weighed, recorded as M1, and its thickness H1 is measured. Then, the positive electrode film layer of the above-mentioned weighed positive electrode sheet is wiped off, and the weight of the positive electrode current collector is weighed and recorded as M0, and its thickness H0 is measured. The single-sided coating weight of the positive electrode film layer = (the weight M1 of the positive electrode sheet - the weight M0 of the positive electrode current collector) / S1, the thickness of the positive electrode film layer = the thickness H1 of the positive electrode sheet - the thickness H0 of the positive electrode current collector, and the tap density of the positive electrode film layer = the single-sided coating weight of the positive electrode film layer / the thickness of the positive electrode film layer.

[0171] [Positive electrode sheet]

[0172] In some embodiments, the powder resistivity of the positive electrode active material is from 1 Ω·cm to 27.5 Ω·cm, optionally less than or equal to 20 Ω·cm, and optionally less than or equal to 11 Ω·cm. Exemplarily, the powder resistivity of the positive electrode active material can be 27.5 Ω·cm, 20 Ω·cm, 19 Ω·cm, 18 Ω·cm, 17 Ω·cm, 16 Ω·cm, 15 Ω·cm, 14 Ω·cm, 13 Ω·cm, 12 Ω·cm, 11 Ω·cm, 10 Ω·cm, 9 Ω·cm, 8 Ω·cm, 7 Ω·cm, 6 Ω·cm, 5 Ω·cm, 4 Ω·cm, 3 Ω·cm, 2 Ω·cm, 1 Ω·cm or the range composed of any two of the above values.

[0173] The relatively low powder resistivity of the positive electrode active material results in a relatively low resistance of the positive electrode sheet and less heat generation of the battery cell.

[0174] In the embodiments of the present application, the powder resistivity of the material has the meaning well known in the art and can be detected by the methods and equipment well known in the art. For example, according to the test standard GB / T30835-2014, a PRCD1100 powder resistivity meter is used for testing.

[0175] In some embodiments, the powder compacting density of the positive electrode active material under 30000 N is greater than or equal to 2.46 g / cm 3 , optionally 2.46 g / cm 3 to 2.80 g / cm 3 . Exemplarily, the powder compacting density of the positive electrode active material under 30000 N is 2.46 g / cm 3 , 2.47 g / cm 3 , 2.48 g / cm 3 , 2.49 g / cm 3 , 2.5 g / cm 3 , 2.51 g / cm 3 , 2.55 g / cm 3 , 2.58 g / cm 3 , 2.60 g / cm 3 , 2.65 g / cm 3 , 2.68 g / cm 3 , 2.70 g / cm 3 , 2.72 g / cm 3 , 2.75 g / cm 3 , 2.78 g / cm 3 , 2.80 g / cm 3 or the range composed of any two of the above values.

[0176] When the powder compaction density of the positive electrode active material is within the above range under 30000N, the energy density of the battery cell can be improved. Moreover, since the positive electrode active material in the positive electrode film layer can be stacked more closely, the contact resistance between particles is small, which can further reduce the resistance of the electrode sheet and thus reduce heat generation.

[0177] In the embodiments of the present application, the powder compaction density of the material has the meaning well-known in the art and can be detected by methods and equipment well-known in the art. Detection is carried out according to the test standard GB / T24533-2009. For example, a certain amount of positive electrode active material is taken as a sample and added to a mold with a bottom area of 1.327 cm 2 in the UTM7305 type electronic pressure testing machine, pressurized to 3000 kg (equivalent to 30000N), kept under pressure for 30 s, then depressurized, kept for 10 s, and then the powder compaction density of the positive electrode active material under the action of 30000N is recorded and calculated.

[0178] In some embodiments, the charging specific capacity of the positive electrode active material at a rate of 0.1C is 150 mAh / g to 170 mAh / g. Exemplarily, the charging specific capacity of the positive electrode active material at a rate of 0.1C is 150 mAh / g, 151 mAh / g, 152 mAh / g, 153 mAh / g, 154 mAh / g, 155 mAh / g, 156 mAh / g, 157 mAh / g, 158 mAh / g, 159 mAh / g, 160 mAh / g, 161 mAh / g, 162 mAh / g, 163 mAh / g, 164 mAh / g, 165 mAh / g, 166 mAh / g, 167 mAh / g, 168 mAh / g, 169 mAh / g, 170 mAh / g or the range composed of any two of the above values.

[0179] When the charging specific capacity of the positive electrode active material at a rate of 0.1C is within the above range, the energy density of the battery cell is relatively high.

[0180] In the embodiments of the present application, the specific capacity of the active material has the meaning well-known in the art and can be tested by equipment and methods well-known in the art. The test method of the first Coulomb efficiency and the first discharge specific capacity in Appendix G of the national standard GB / T 24533-2019 can be adopted. Using metallic lithium as the negative electrode and the sample electrode sheet containing the above materials as the positive electrode, a half-button battery is assembled. Under the condition of 23℃±2℃, the half-button battery is placed on a battery tester or other test equipment with the same performance, and the discharge capacity is obtained through charge and discharge at a rate of 0.1C, and then the capacity is divided by the mass of the active material of the electrode sheet to obtain the charging specific capacity parameter.

[0181] In some embodiments, the mass percentage of the lithium-containing phosphate with an olivine structure in the positive electrode active material can be greater than or equal to 80% and less than or equal to 100%. It can be considered that the positive electrode active material of the present application is a lithium-containing phosphate system with an olivine structure. When the mass percentage of the lithium-containing phosphate with an olivine structure is less than 100%, the positive electrode active material may further include common positive electrode active materials, such as at least one of lithium-containing transition metal oxides. Examples of the lithium-containing transition metal oxides may include but are not limited to at least one 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 their respective modified compounds.

[0182] Optionally, the mass percentage of the lithium-containing phosphate with an olivine structure in the positive electrode active material is 100%.

[0183] In the embodiments of the present application, the lithium-containing phosphate with an olivine structure can be phosphate particles or a material obtained by coating and modifying them. For example, the lithium-containing phosphate with an olivine structure includes phosphate particles and a coating layer. The coating layer is coated on the surface of the phosphate particles, and the coating layer contains one or more elements of C, Fe, Ti, Zr, Hf, Ge, and Sn.

[0184] By surface coating the phosphate particles with a coating layer, the conductivity of the lithium-containing phosphate with an olivine structure can be improved, the powder resistivity of the material can be reduced, and it is beneficial to the migration rate of lithium ions, improving the fast charging ability of the battery and reducing the heat generation of the battery cell.

[0185] In some embodiments, the phosphate particles include a compound with the general formula Li x1 A y1 Me a M b P 1-c X c Y z where 0.5 ≤ x1 ≤ 1.3, 0 ≤ y1 ≤ 1.3, and 0.9 ≤ x1 + y1 ≤ 1.3, 0.9 ≤ a ≤ 1.5, 0 ≤ b ≤ 0.5, and 0.9 ≤ a + b ≤ 1.5, 0 ≤ c ≤ 0.5, 3 ≤ z ≤ 5, A includes one or more of Na, K, Mg, Me includes one or more of Mn, Fe, Co, Ni, M includes one or more of B, Mg, Al, Si, P, S, Ca, Sc, Ti, V, Cr, Cu, Zn, Sr, Y, Zr, Nb, Mo, Cd, Sn, Sb, Te, Ba, Ta, W, Yb, La, Ce, X includes one or more of S, Si, Cl, B, C, N, and Y includes one or more of O, F. The phosphate particles have relatively excellent cycle stability, which is beneficial to improving the cycle performance of the battery cell.

[0186] Exemplarily, the phosphate particles include one or more of LiFePO4, LiMnPO4, LiNiPO4, and LiCoPO4. The battery cells are accompanied by the deintercalation and consumption of active ions such as Li during the charge and discharge process, and the molar content of Li in the battery cells is different when discharged to different states. In the enumeration of positive electrode active materials LiFePO4, LiMnPO4, LiNiPO4, LiCoPO4, etc., the molar content of Li is the initial state of the material, that is, the state before feeding. The positive electrode active material is used in the battery system, and the molar content of Li may change after charge and discharge cycles. In the enumeration of positive electrode active materials LiFePO4, LiMnPO4, LiNiPO4, LiCoPO4, etc. in the embodiment of the present application, the molar content of oxygen O is only a theoretical state value. Lattice oxygen release will cause the molar content of oxygen O to change. In practice, the molar content of oxygen O will fluctuate. The above situations are all within the scope of protection of this application.

[0187] In some embodiments, the coating layer comprises a Li 3-d Fe 2-d M2 d (PO x2 ) y2 The fast ion conductor M2 includes one or more elements selected from Ti, Zr, Hf, Ge and Sn, 0≤d≤1, 0<x2<5, 0<y2<4.

[0188] Exemplarily, the fast ion conductor is a material having a NASICON structure, such as one or more of lithium iron titanium phosphate Li2FeTi(PO4)3, lithium iron zirconium phosphate Li2FeZr(PO4)3, and lithium iron tin phosphate Li2FeSn(PO4)3.

[0189] Fast ion conductors with a NASICON structure are materials with ultrafast ion conduction capabilities. They possess abundant three-dimensional lithium ion diffusion and transport channels, and exhibit advantages such as high ion conduction efficiency and strong structural stability during multiple lithium de- and intercalation processes. Coating phosphate particles with a fast ion conductor containing a NASICON structure can significantly increase the lithium ion transport rate at the positive electrode during multiple lithium de- and intercalation processes, improving the ionic conductivity of the positive electrode active material and the rapid charging capability of the battery cell. Furthermore, it can increase the specific capacity and the energy density of the corresponding battery cell.

[0190] In some embodiments, the coating layer further includes carbon.

[0191] The carbon element and the fast ion conductor can be arranged in layers. For example, the carbon element serves as an independent carbon coating layer, and the fast ion conductor serves as an independent fast ion conductor layer. The carbon coating layer can be coated on the surface of the phosphate particles, and the fast ion conductor layer is located on the surface of the carbon coating layer, that is, the fast ion conductor layer is located on the side of the carbon coating layer facing away from the phosphate particles. Alternatively, the fast ion conductor layer can be coated on the surface of the phosphate particles, and the carbon coating layer is located on the surface of the fast ion conductor layer, that is, the carbon coating layer is located on the side of the fast ion conductor layer facing away from the phosphate particles. Of course, the carbon element and the fast ion conductor can also be arranged in the same layer.

[0192] Optionally, a carbon coating can be formed by carbonizing an organic carbon source (e.g., glucose, polyethylene glycol, etc.) and coating the surface of the fast ion conductor layer. The carbon coating can partially or completely cover the fast ion conductor layer. The carbon coating can significantly improve the electronic conductivity of the phosphate particles, compensating for their poor electronic conductivity and increasing the energy density of the battery cell.

[0193] Specifically, the provision of the carbon coating layer enables the positive electrode active material of the present application to have the following advantages:

[0194] The carbon coating layer in the positive electrode active material of the present application provides a suitable channel for the transmission of electrons, which can significantly improve the conduction rate of electrons in multiple lithium delithiation and lithium insertion processes, improve the electronic conductivity of lithium-containing phosphates, improve the charging capacity of the corresponding battery cells, and also improve the energy density.

[0195] The carbon coating layer of the positive electrode active material of the present application is loose and porous, which enables the electrolyte to be in full and effective contact with the lithium-containing phosphate, thereby increasing the transmission rate of lithium ions at the phase interface and improving the charging capacity of the battery cell.

[0196] Coating a carbon coating layer on the surface of the lithium-containing phosphate can not only improve the conductivity of the lithium-containing phosphate, but also improve the structural stability of the positive electrode active material, effectively alleviate the iron dissolution of the positive electrode active material during long-term storage and cyclic use of the battery cell, thereby improving the cycle life of the battery cell.

[0197] The cathode active material of this application, based on a lithium-containing phosphate, leverages the advantages of lithium-containing phosphates: low cost, high reliability, and excellent cycling stability. It also utilizes coating layers (fast ion conductor layer and carbon coating layer) to address their poor electronic and ionic conductivity. Battery cells prepared with this cathode active material can improve the energy density of the battery cells while maintaining excellent cycling performance.

[0198] In the embodiments of the present application, the content of elements in the positive electrode active material has the meaning well-known in the art, and can be detected by equipment and methods well-known in the art. For example, referring to EPA 6010D-2014, it is tested by inductively coupled plasma atomic emission spectrometry, and determined by inductively coupled plasma optical emission spectrometry (ICP-OES, instrument model: Thermo ICAP7400). After discharging the battery cell to 0% state of charge (SOC) and disassembling the positive electrode sheet, it is cleaned with DMC, dried, and then calcined at high temperature to remove impurities. Then, 0.4 g of the positive electrode active material is weighed, and 10 ml (50% concentration) of aqua regia is added thereto. Then it is placed on a flat plate at 180 °C for 30 min. After digestion on the flat plate, it is fixed to a volume of 100 mL, and quantitative testing is carried out by the standard curve method.

[0199] In some embodiments, the graphitization degree of the positive electrode active material is from 0.15 to 0.32, and can be optionally from 0.19 to 0.26. Exemplarily, the graphitization degree of the positive electrode active material is 0.15, 0.16, 0.17, 0.18, 0.19, 0.20, 0.21, 0.22, 0.23, 0.24, 0.25, 0.26, 0.27, 0.28, 0.29, 0.30, 0.31, 0.32 or a range composed of any two of the above values.

[0200] When the graphitization degree of the positive electrode active material is within the above range, it is beneficial to improve the conductivity of the positive electrode active material, reduce the heat generation of the positive electrode sheet, and thus reduce the heat generation of the battery cell.

[0201] In the embodiments of the present application, the higher the graphitization degree of the material, the lower the degree of disorder, and it can be tested according to the general rules of X-ray diffraction analysis method in JIS / K 0131-1996.

[0202] In some embodiments, the mass content of carbon element in the lithium-containing phosphate with olivine structure is 1% to 2%, and the specific surface area of the lithium-containing phosphate with olivine structure is 5 m 2 / g to 18 m 2 / g.

[0203] Optionally, the mass content of carbon element in the lithium-containing phosphate with olivine structure is 1% to 2%, and the specific surface area of the lithium-containing phosphate with olivine structure is 7.5 m 2 / g to 14 m 2 / g.

[0204] Exemplarily, the mass content of carbon element in the lithium-containing phosphate with olivine structure is 1%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2% or a range composed of any two of the above values.

[0205] Exemplarily, the specific surface area of the lithium-containing phosphate with an olivine structure is 5 m 2 / g, 6 m 2 / g, 7 m 2 / g, 8 m 2 / g, 9 m 2 / g, 10 m 2 / g, 11 m 2 / g, 12 m 2 / g, 13 m 2 / g, 14 m 2 / g, 15 m 2 / g, 16 m 2 / g, 17 m 2 / g, 18 m 2 / g or a range composed of any two of the above values.

[0206] Carbon elements mainly exist in the coating layer in the form of a carbon coating layer. The carbon coating layer is loose and porous, which is beneficial to increasing the specific surface area of the material, more beneficial to the effective contact between the electrolyte and the phosphate particles, and beneficial to the transmission of lithium ions at the phase interface. In addition, when the mass content of carbon elements is within the above range, it can significantly improve the conductivity of the lithium-containing phosphate with an olivine structure, which is beneficial to enhancing the ionic conductivity and electronic conductivity of the lithium-containing phosphate with an olivine structure, and can improve the fast charging ability and energy density of a single battery cell.

[0207] In the embodiments of the present application, the specific surface area of the material has the meaning well-known in the art and can be detected by equipment and methods well-known in the art. For example, it can be detected according to the test standard GB / T 19587-2017. Taking the positive electrode active material as a sample, the specific surface area is tested by a Tri-Star 3020 specific surface area and pore size analyzer produced by Micromeritics Company of the United States.

[0208] In some embodiments, the volume distribution particle size of the positive electrode active material satisfies: 1 µm ≤ Dv50 ≤ 2 µm, 0.4 µm ≤ Dv10 ≤ 0.7 µm.

[0209] Exemplarily, Dv50 of the positive electrode active material can be 1 µm, 1.1 µm, 1.15 µm, 1.2 µm, 1.25 µm, 1.3 µm, 1.35 µm, 1.4 µm, 1.45 µm, 1.5 µm, 1.55 µm, 1.6 µm, 1.65 µm, 1.7 µm, 1.75 µm, 1.8 µm, 1.85 µm, 1.9 µm, 1.95 µm, 2 µm or a range composed of any two of the above values.

[0210] Exemplarily, the Dv10 of the positive electrode active material can be 0.4 µm, 0.45 µm, 0.5 µm, 0.55 µm, 0.6 µm, 0.65 µm, 0.7 µm, or a range composed of any two of the above values.

[0211] The particle size of the positive electrode active material is relatively small, the lithium deintercalation / insertion path of lithium ions in the positive electrode active material is short, and the heat generation is less; moreover, the particle size of the above positive electrode active material is not too small, and agglomeration basically does not occur during the processing and preparation process, making the performance of the positive electrode active material stable.

[0212] In the embodiments of the present application, the volume average particle size Dv50 of the material refers to the particle size corresponding to 50% in the volume distribution, and the volume average particle size Dv10 of the material refers to the particle size corresponding to 10% in the volume distribution. It can be detected by using equipment and methods well-known in the art. For example, taking the positive electrode active material as a sample, according to the test standard GB / T 19077-2016, the Dv50 and Dv10 of the particles are tested by a Mastersizer 2000E laser particle size analyzer, etc.

[0213] When the positive electrode active material includes other materials in addition to the lithium-containing phosphate with an olivine structure, the volume distribution particle size of the positive electrode active material refers to the volume distribution particle size of all positive electrode active materials.

[0214] In some embodiments, the lithium-containing phosphate with an olivine structure is in a granular form, and the lithium-containing phosphate with an olivine structure is composed of secondary particles formed by agglomeration of primary particles. The average particle size of the primary particles is 200 nm to 500 nm. Exemplarily, the average particle size of the primary particles is 200 nm, 220 nm, 250 nm, 280 nm, 300 nm, 320 nm, 350 nm, 380 nm, 400 nm, 420 nm, 450 nm, 480 nm, 500 nm, or a range composed of any two of the above values.

[0215] The average particle size of the primary particles is relatively small, the lithium deintercalation / insertion path of lithium ions in the positive electrode active material is short, and the heat generation is less.

[0216] In the embodiments of the present application, the primary particles and secondary particles are terms well-known in the art. The secondary particles refer to aggregated particles formed by the aggregation of two or more primary particles. The primary particles and secondary particles can be easily distinguished by experimental means (such as taking SEM images using a scanning electron microscope), and the average particle size of the primary particles can be obtained by testing in the SEM image of the scanning electron microscope SSEM. The SEM test parameters can be set as follows: the working voltage (EHT) is 10.00 kV, the InLens detector is used, the working distance is 4.6 mm, and the magnification is 1000X.

[0217] The positive electrode film layer usually includes a plurality of positive electrode active material particles, that is, the lithium-containing phosphate in the olivine structure is in the form of a plurality of particles, and the particle sizes of the plurality of particles are different. The plurality of particles include the smallest particle and the largest particle. The smallest particle is the particle with the smallest particle size, and the largest particle is the particle with the largest particle size. By matching the large and small particles, the compaction density of the positive electrode film layer can be improved, and the pore structure of the positive electrode film layer can be increased, so that the fast charging performance of the battery cell is improved.

[0218] In some embodiments, the particle size of the smallest particle in the lithium-containing phosphate in the olivine structure is from 0.1 μm to 0.4 μm. Exemplarily, 0.1 μm, 0.15 μm, 0.2 μm, 0.25 μm, 0.3 μm, 0.35 μm, 0.4 μm or a range composed of any two of the above values. When the particle size of the smallest particle is within the above range, agglomeration is not likely to occur during the preparation of the positive electrode film layer 113.

[0219] In some embodiments, the particle size of the largest particle in the lithium-containing phosphate in the olivine structure is from 15 μm to 25 μm. Exemplarily, 15 μm, 16 μm, 17 μm, 18 μm, 19 μm, 20 μm, 21 μm, 22 μm, 23 μm, 24 μm, 25 μm or a range composed of any two of the above values. When the particle size of the largest particle is within the above range, the migration path of lithium ions during charge and discharge will not be too long, and the fast charge and discharge performance of the battery cell can be improved.

[0220] In some embodiments, the positive electrode film layer further includes one or more of ternary materials, lithium phosphate, lithium hydrogen phosphate, lithium sulfate, lithium sulfite, lithium molybdate, lithium oxalate, lithium titanate, lithium tetraborate, lithium metasilicate, lithium manganate, lithium tartrate, lithium citrate, lithium nickelate, and lithium ferrate. The above materials can be used as lithium supplement agents. The lithium supplement agents can supplement lithium ions for the positive electrode film layer, make up for the irreversible loss of lithium ions in the system, and improve the capacity, thereby improving the energy density of the battery cell.

[0221] Optionally, the ternary material includes Li x3 A y3 Ni a3 Co b3 Mn c M3 (1-a3-b3-c3) Y3 z3, wherein, 0 < x3 ≤ 2.1, 0 < y3 ≤ 2.1, and 0.9 ≤ x3 + y3 ≤ 2.1, 0 ≤ a3 ≤ 1, 0 ≤ b3 ≤ 1, 0 ≤ c3 ≤ 1, and 0.1 ≤ a3 + b3 + c3 ≤ 1, 1.8 ≤ z3 ≤ 3.5, A includes one or more of Na, K, and Mg, M3 includes one or more of B, Mg, Al, Si, P, S, Ca, Sc, Ti, V, Cr, Fe, Cu, Zn, Sr, Y, Zr, Nb, Mo, Cd, Sn, Sb, Te, Ba, Ta, W, Yb, La, and Ce, and Y3 includes one or more of O and F.

[0222] Exemplarily, the ternary material includes LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (NCM333), LiNi 0.5 Co 0.2 Mn 0.3 O2 (NCM523), LiNi 0.6 Co 0.2 Mn 0.2 O2 (NCM622), LiNi 0.8 Co 0.1 Mn 0.1 O2 (NCM811), LiNi 0.80 Co 0.15 Al 0.05 at least one of O2.

[0223] In some embodiments, the mass content of the lithium supplement in the positive electrode film layer is 0.5% to 5%, such as 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5% or a range composed of any two of the above values. When the mass content of the lithium supplement is within the above range, it can supplement lithium ions to the positive electrode film layer, make up for the irreversible lithium ion loss in the system, and improve the capacity, thereby improving the energy density of the battery cell.

[0224] The lithium supplement can be in the same layer as the positive electrode active material or in different layers. When the lithium supplement and the positive electrode active material are in different layers, the lithium supplement can be in the lithium supplement layer, and the positive electrode active material can be in the positive electrode active material layer. In other words, the positive electrode film layer includes a lithium supplement layer and a positive electrode active material layer. The positive electrode active material layer can be disposed on at least one side of the positive electrode current collector, and the lithium supplement layer can be located between the positive electrode active material layer and the positive electrode current collector. Alternatively, the lithium supplement layer can be disposed on at least one side of the positive electrode current collector, and the positive electrode active material layer can be located between the lithium supplement layer and the positive electrode current collector. Optionally, the lithium supplement layer can be located between the positive electrode active material layer and the positive electrode current collector. During the charge and discharge cycling of the battery cell, the lithium supplement in the lithium supplement layer can be gradually released into the system to make up for the lithium loss in the battery system.

[0225] In some embodiments, the positive electrode film layer may further optionally include a positive electrode conductive agent. There is no particular limitation on the type of the positive electrode conductive agent in the embodiments of the present application. By way of example, the positive electrode conductive agent includes at least one of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. In some embodiments, based on the mass of the positive electrode film layer, the mass content of the positive electrode conductive agent is ≤5%.

[0226] In some embodiments, the positive electrode film layer may further optionally include a positive electrode binder. There is no particular limitation on the type of the positive electrode binder in the embodiments of the present application. By way of example, the positive electrode binder may include at least one of polyvinylidene fluoride, polytetrafluoroethylene, vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, polyacrylic acid, and fluorinated acrylate resins. In some embodiments, based on the mass of the positive electrode film layer, the mass content of the positive electrode binder is ≤5%.

[0227] In the embodiments of the present application, the thicknesses of the positive electrode film layer and the positive electrode current collector are of meanings well-known in the art, and can be detected by using equipment and methods well-known in the art. For example, the thickness of the positive electrode plate is measured with a micrometer, the film layer on the surface of the positive electrode current collector is removed, and the thickness of the positive electrode current collector is measured with a micrometer. When the positive electrode film layer is coated on one side, the thickness of the positive electrode film layer is the thickness of the positive electrode plate minus the thickness of the positive electrode current collector. When the positive electrode film layer is coated on both sides, the thickness of the positive electrode film layer is (the thickness of the positive electrode plate minus the thickness of the positive electrode current collector) / 2.

[0228] The positive electrode film layer is usually formed by coating a positive electrode slurry on the positive electrode current collector and then drying and cold pressing. The positive electrode slurry is usually formed by dispersing a positive electrode active material, an optional conductive agent, an optional binder, and any other components in a solvent and stirring evenly. The solvent can be N-methylpyrrolidone (NMP), but is not limited thereto.

[0229] The positive electrode plate does not exclude other additional functional layers other than the positive electrode film layer. For example, in some embodiments, the positive electrode plate of the embodiments of the present application further includes a positive electrode conductive layer sandwiched between the positive electrode current collector and the positive electrode film layer and disposed on the surface of the positive electrode current collector. In some other embodiments, the positive electrode plate of the embodiments of the present application further includes a protective layer covering the surface of the positive electrode film layer.

[0230] In some embodiments, the positive electrode plate further includes a positive electrode conductive layer, and the positive electrode conductive layer is located between the positive electrode film layer and the positive electrode current collector. The positive electrode conductive layer can further improve the conductive performance of the positive electrode plate and reduce the heat generation of the positive electrode plate, thereby reducing the heat generation amount of the battery cell.

[0231] In some embodiments, the thickness of the positive electrode conductive layer is 0.5 μm to 2 μm. For example, the thickness of the positive electrode conductive layer can be 0.5 μm, 0.8 μm, 1 μm, 1.2 μm, 1.5 μm, 1.6 μm, 1.8 μm, 2 μm, or a range consisting of any two of the above values.

[0232] When the thickness of the positive electrode conductive layer is within the above range, the conductivity of the positive electrode sheet can be further improved, the heat generation of the positive electrode sheet can be reduced, thereby reducing the heat generation of the battery cell, and the energy density of the battery cell can be improved.

[0233] In the embodiment of the present application, the thickness of the positive electrode conductive layer has a meaning well known in the art and can be detected using equipment and methods well known in the art, for example, performing a tomographic scan on the positive electrode sheet to directly measure the thickness of the positive electrode conductive layer.

[0234] In some embodiments, the positive electrode conductive layer includes one or more of a positive electrode conductive agent and a positive electrode binder.

[0235] Optionally, the mass content of the positive electrode conductive agent in the positive electrode conductive layer is 30% to 50%. Exemplarily, the mass content of the positive electrode conductive agent is 30%, 35%, 40%, 45%, 50%, or a range consisting of any two of the above values.

[0236] Illustratively, the positive electrode conductive agent includes one or more of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. The positive electrode conductive agent in the positive electrode conductive layer can improve the conductivity of the positive electrode conductive layer, thereby improving the conductivity of the positive electrode sheet and reducing heat generation in the battery cell.

[0237] Optionally, the mass content of the positive electrode binder in the positive electrode conductive layer is 50% to 70%, illustratively, 50%, 60%, 65%, 70%, or a range consisting of any two of the above values.

[0238] Illustratively, the positive electrode binder includes one or more of polyvinylidene fluoride, polytetrafluoroethylene, a vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, a vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, a tetrafluoroethylene-hexafluoropropylene copolymer, polyacrylic acid, and a fluorine-containing acrylate resin. The positive electrode binder in the positive electrode conductive layer can improve the bonding performance between the positive electrode current collector and the positive electrode film layer, thereby improving the structural stability of the positive electrode sheet.

[0239] [Negative electrode]

[0240] In some embodiments, the powder resistivity of the negative electrode active material is from 0.005 Ω·cm to 0.043 Ω·cm, and may be optionally 0.04 Ω·cm. Exemplarily, the powder resistivity of the negative electrode active material may be 0.043 Ω·cm, 0.04 Ω·cm, 0.035 Ω·cm, 0.03 Ω·cm, 0.025 Ω·cm, 0.02 Ω·cm, 0.015 Ω·cm, 0.01 Ω·cm, 0.005 Ω·cm, or a range composed of any two of the above values.

[0241] The relatively low powder resistivity of the negative electrode active material results in a relatively low resistance of the negative electrode plate and less heat generation in the battery cell.

[0242] In the embodiments of the present application, the powder resistivity of the negative electrode active material has the meaning well-known in the art and can be detected by the equipment and methods well-known in the art. The detection method is the same as the powder resistivity test method of the positive electrode active material described above.

[0243] In some embodiments, the powder compaction density of the negative electrode active material under a pressure of 20000 N is 1.5 g / cm 3 to 1.85 g / cm 3, , and may be optionally 1.55 g / cm 3 to 1.65 g / cm 3 . Exemplarily, the powder compaction density of the negative electrode active material under a pressure of 20000 N is 1.5 g / cm 3 , 1.55 g / cm 3 , 1.6 g / cm 3 , 1.65 g / cm 3 , 1.7 g / cm 3 , 1.75 g / cm 3 , 1.8 g / cm 3 , 1.85 g / cm 3 or a range composed of any two of the above values.

[0244] When the powder compaction density of the negative electrode active material under 20000 N is within the above range, the energy density of the battery cell can be improved, and since the negative electrode active material in the negative electrode film layer can be stacked more closely and the contact resistance between particles is small, the resistance of the electrode plate can be further reduced, thereby reducing heat generation.

[0245] In the embodiments of the present application, the powder compaction density of the material has the meaning well-known in the art and can be detected by the methods and equipment well-known in the art, and is detected according to the test standard GB / T24533-2009. As an example, a certain amount of the negative electrode active material is taken as a sample and added to the UTM7305 type electronic pressure testing machine with a bottom area of 1.327 cm 2In the mold, it is pressurized to 2000 kg (equivalent to 20000 N), the pressure is maintained for 30 s, then the pressure is released, and it is kept for 10 s. Then, the powder compaction density of the negative electrode active material under the action of 20000 N is recorded and calculated.

[0246] In some embodiments, the charging specific capacity of the negative electrode active material at a rate of 0.1 C is 350 mAh / g to 480 mAh / g. Exemplarily, the charging specific capacity of the negative electrode active material at a rate of 0.1 C is 350 mAh / g, 355 mAh / g, 360 mAh / g, 365 mAh / g, 370 mAh / g, 375 mAh / g, 380 mAh / g, 385 mAh / g, 390 mAh / g, 395 mAh / g, 400 mAh / g, 410 mAh / g, 420 mAh / g, 430 mAh / g, 440 mAh / g, 450 mAh / g, 460 mAh / g, 470 mAh / g, 480 mAh / g or a range composed of any two of the above values.

[0247] When the charging specific capacity of the negative electrode active material at a rate of 0.1 C is within the above range, the energy density of the battery cell is relatively high.

[0248] In the embodiments of the present application, the charging specific capacity of the negative electrode active material at a rate of 0.1 C has the meaning well-known in the art, and can be detected by using the equipment and methods well-known in the art. Its detection method is the same as the charging specific capacity test method of the positive electrode active material at a rate of 0.1 C described above.

[0249] In some embodiments, the negative electrode active material includes a carbon-based material with a layered structure. The carbon-based material has high cycle stability and can improve the cycle performance of the battery cell. Optionally, the mass ratio of the carbon-based material in the negative electrode active material can be greater than or equal to 80% and less than or equal to 100%.

[0250] The positive electrode active material of the present application is mainly a lithium-containing phosphate system with an olivine structure, and the negative electrode active material is mainly a carbon-based material system. When the two are used in combination, the battery cell has excellent cycle performance.

[0251] Optionally, the carbon-based material includes graphite particles, and the graphitization degree of the graphite particles is 92.0% to 94.5%. Exemplarily, the graphitization degree of the graphite particles is 92.0%, 92.5%, 93%, 93.5%, 94%, 94.5% or a range composed of any two of the above values.

[0252] When the graphitization degree of the graphite particles is within the above range, the graphite particles have excellent electrical conductivity, can reduce the heat generation of the negative electrode sheet and the battery cell; and can improve the fast charging performance of the battery cell.

[0253] In some embodiments, the graphite particles include artificial graphite and a carbon coating layer. The artificial graphite includes secondary particles, the secondary particles include a plurality of primary particles, and the carbon coating layer coats the surface of the artificial graphite. The carbon in the carbon coating layer is mainly amorphous carbon, and amorphous carbon refers to a transition carbon material with a very low degree of graphitization crystallization and an approximate amorphous form (or no fixed shape and periodic structural rules). In the present application, amorphous carbon refers to the product after carbonization treatment of an organic carbon source.

[0254] The artificial graphite includes secondary particles. There are many migration paths of lithium ions in the artificial graphite, and the migration path in the primary particles is short, which can improve the migration rate of lithium ions. The carbon coating layer has many end faces and defects, so that the number of sites capable of intercalating and deintercalating lithium ions is larger, and the conductivity of the carbon coating layer is relatively excellent, which can reduce the internal resistance of the negative electrode sheet and reduce the heat generation of the battery cell.

[0255] Optionally, based on the mass of the graphite particles, the mass content of the carbon coating layer is 2% to 5%. Exemplarily, the mass content of the carbon coating layer is 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5% or a range composed of any two of the above values.

[0256] When the mass content of the carbon coating layer is within the above range, it can further reduce the internal resistance of the negative electrode sheet and reduce the heat generation of the battery cell.

[0257] In the embodiments of the present application, the graphite particles can be prepared by methods well known in the art. For example, the preparation method includes: providing artificial graphite and an organic carbon source, mixing the two, and after carbonization treatment, forming a carbon coating layer on at least part of the surface of the artificial graphite particles.

[0258] Optionally, the organic carbon source includes one or more of coal tar pitch, petroleum pitch, phenolic resin, and coconut shell. Further optionally, the organic carbon source includes petroleum pitch. Optionally, the softening point of coal tar pitch and petroleum pitch is below 250 °C.

[0259] Optionally, the carbonization treatment temperature is 700 °C to 1800 °C. Optionally, the carbonization treatment temperature is 1000 °C to 1300 °C. When the carbonization treatment temperature is within a suitable range, the organic carbon source can be carbonized and a coating layer containing amorphous carbon can be formed on at least a part of the surface of the artificial graphite.

[0260] Optionally, the carbonization treatment time is 1 h to 6 h.

[0261] In some embodiments, the carbon-based material may further include natural graphite. Specifically, the carbon-based material may include graphite particles, or the carbon-based material may include graphite particles and natural graphite. Optionally, the carbon-based material is graphite particles.

[0262] In some embodiments, the negative electrode active material may further include a silicon-based material. The introduction of the silicon-based material can increase the capacity of the negative electrode active material and improve the energy density of the battery cell.

[0263] Optionally, based on the mass of the negative electrode active material, the mass content of silicon element in the silicon-based material is 0.3% to 10.0%, and may be optionally 1% to 6%. Exemplarily, the mass content of silicon element in the silicon-based material is 0.3%, 0.5%, 0.8%, 1%, 1.2%, 1.5%, 1.8%, 2%, 2.2%, 2.5%, 2.8%, 3%, 3.2%, 3.5%, 3.8%, 4%, 4.2%, 4.5%, 4.8%, 5%, 5.2%, 5.5%, 5.8%, 6%, 6.2%, 6.5%, 6.8%, 7%, 7.2%, 7.5%, 7.8%, 8%, 8.2%, 8.5%, 8.8%, 9%, 9.2%, 9.5%, 9.8%, 10% or any range composed of any two of the above values.

[0264] When the mass content of silicon element in the silicon-based material is within the above range, it can increase the capacity of the negative electrode active material and improve the energy density of the battery cell.

[0265] Optionally, the silicon-based material may include at least one of elemental silicon, silicon oxide, silicon-carbon composite, silicon-nitrogen composite, and silicon alloy material.

[0266] In some embodiments, in addition to the above-mentioned carbon-based material and the optional silicon-based material, the negative electrode active material may further include at least one of a tin-based material and lithium titanate. The tin-based material may include at least one of elemental tin, tin oxide, and tin alloy material.

[0267] In this application, the qualitative and quantitative determination of each substance or each element can be detected by suitable equipment and methods known to those skilled in the art. The relevant detection methods can refer to domestic and foreign detection standards, domestic and foreign enterprise standards, etc. And those skilled in the art can also adaptively change some detection steps / instrument parameters, etc. from the perspective of detection accuracy to obtain more accurate detection results. One detection method can be used for qualitative or quantitative determination, or several detection methods can be used in combination for qualitative or quantitative determination.

[0268] For example, this application can perform X-ray powder diffraction testing and qualitative analysis on the negative electrode sheet or the negative electrode active material in combination with the General Rules for X-ray Diffraction Analysis of JIS / K0131-1996.

[0269] Artificial graphite and natural graphite can be distinguished by the SEM cross-sectional views taken by a scanning electron microscope (SEM). In the SEM cross-sectional view of natural graphite, there are voids between flake structures. The SEM cross-sectional view of artificial graphite is dense and has no obvious gaps, or they can be distinguished by the XRD spectra obtained by X-ray diffraction method. In the XRD spectra of natural graphite, there are obvious 2H phase and 3R phase, while the XRD spectra of artificial graphite only have 2H phase.

[0270] In the embodiments of the present application, the negative electrode film layer includes at least one film layer, which can be a single film layer or at least two film layers. Optionally, the negative electrode film layer includes at least two film layers.

[0271] When the negative electrode film layer is a single film layer, the negative electrode active material in the negative electrode film layer includes a carbon-based material, and optionally also includes a silicon-based material. When a single film layer is used, the volume average particle size Dv50 of the negative electrode active material is 8.2 μm to 13.5 μm. Exemplarily, the volume average particle size Dv50 of the negative electrode active material is 8.2 μm, 8.5 μm, 8.8 μm, 9 μm, 9.2 μm, 9.5 μm, 9.8 μm, 10 μm, 10.2 μm, 10.5 μm, 10.8 μm, 11 μm, 11.2 μm, 11.5 μm, 11.8 μm, 12 μm, 12.2 μm, 12.5 μm, 12.8 μm, 13 μm, 13.2 μm, 13.5 μm or the range composed of any two of the above values.

[0272] When the negative electrode film layer is at least two film layers, the negative electrode active material in the negative electrode film layer includes a carbon-based material, and optionally also includes a silicon-based material. The silicon-based material can be located in one of the at least two film layers or in at least two of the at least two film layers. The negative electrode film layer can include two film layers, three film layers, four film layers, or even more film layers.

[0273] In some embodiments, the negative electrode film layer includes a first negative electrode film layer and a second negative electrode film layer. The first negative electrode film layer is disposed on the surface of the negative electrode current collector portion. The carbon-based material in the first negative electrode film layer includes graphite particles. The second negative electrode film layer is connected to the side of the first negative electrode film layer facing away from the negative electrode current collector portion. The carbon-based material in the second negative electrode film layer includes graphite particles. The graphite particles in the first negative electrode film layer and the graphite particles in the second negative electrode film layer can be the same or different.

[0274] The interface between the first negative electrode film layer and the second negative electrode film layer can be regular or irregular, and optionally it is irregular.

[0275] Optionally, the carbon-based material in the first negative electrode film layer further includes natural graphite.

[0276] The negative electrode film layer includes at least two film layers, and layered coating is beneficial to improving the fast charging performance of the battery cell. Especially when there are differences between the first negative electrode film layer and the second negative electrode film layer, it is possible to construct pore differences in the negative electrode film layer, reduce the tortuosity of lithium ion transport, and improve the fast charging performance of the battery cell.

[0277] Optionally, the volume average particle size Dv50 of the negative electrode active material in the first negative electrode film layer is greater than or equal to the volume average particle size Dv50 of the negative electrode active material in the second negative electrode film layer. Further optionally, the volume average particle size Dv50 of the negative electrode active material in the first negative electrode film layer is greater than the volume average particle size Dv50 of the negative electrode active material in the second negative electrode film layer, which is beneficial to improving the tap density of the negative electrode film layer. When the negative electrode active material includes graphite particles, the volume average particle size Dv50 of the graphite particles in the first negative electrode film layer is greater than or equal to the volume average particle size Dv50 of the graphite particles in the second negative electrode film layer.

[0278] There are differences in the particle sizes in the first negative electrode film layer and the second negative electrode film layer, which can improve the fast charging performance of the battery cell. Specifically, during fast charging, the overpotential of the second negative electrode film layer is usually relatively high, and the bottleneck of fast charging mainly lies in the second negative electrode film layer. In the embodiments of the present application, the particle size in the second negative electrode film layer is relatively small, which can shorten the solid-phase transport path of lithium ions, improve the fast charging performance, and can improve the problem of lithium deposition on the surface layer of the negative electrode sheet.

[0279] Optionally, the negative electrode active material in the first negative electrode film layer is in particulate form, and its volume average particle size Dv50 is from 9.5 μm to 18.5 μm, and can be from 9.5 μm to 14.6 μm. Exemplarily, the volume average particle size of the negative electrode active material in the first negative electrode film layer is 9.5 μm, 10 μm, 10.5 μm, 11 μm, 11.5 μm, 12 μm, 12.5 μm, 13 μm, 13.5 μm, 14 μm, 14.5 μm, 14.6 μm, 15 μm, 15.5 μm, 16 μm, 16.5 μm, 17 μm, 17.5 μm, 18 μm, 18.5 μm or a range composed of any two of the above values. When the first negative electrode film layer includes graphite particles, the volume average particle size Dv50 of the graphite particles in the first negative electrode film layer is from 9.5 μm to 18.5 μm, and can be from 9.5 μm to 14.6 μm.

[0280] When the volume average particle size Dv50 of the negative electrode active material in the first negative electrode film layer is within the above range, on the one hand, it can shorten the solid-phase transport path of lithium ions and improve the fast charging performance. On the other hand, the material is not prone to agglomeration during the preparation process, which can improve the stability of the material.

[0281] Optionally, the negative electrode active material in the second negative electrode film layer is granular, and its volume average particle size Dv50 is from 7.8 μm to 14.3 μm, and may be optionally from 7.8 μm to 11.3 μm. Exemplarily, the volume average particle size Dv50 of the negative electrode active material is 7.8 μm, 8.0 μm, 8.2 μm, 8.5 μm, 8.8 μm, 9 μm, 9.2 μm, 9.5 μm, 9.8 μm, 10 μm, 10.2 μm, 10.5 μm, 10.8 μm, 11 μm, 11.3 μm, 11.2 μm, 11.5 μm, 11.8 μm, 12 μm, 12.2 μm, 12.5 μm, 12.8 μm, 13 μm, 13.2 μm, 13.5 μm, 13.8 μm, 14 μm, 14.1 μm, 14.3 μm or a range composed of any two of the above values. When the second negative electrode film layer includes graphite particles, the volume average particle size Dv50 of the graphite particles in the second negative electrode film layer is from 7.8 μm to 14.3 μm, and may be optionally from 7.8 μm to 11.3 μm.

[0282] When the volume average particle size Dv50 of the negative electrode active material in the second negative electrode film layer is within the above range, on the one hand, it can shorten the solid-phase transmission path of lithium ions and improve the fast charging performance. On the other hand, the material is not prone to agglomeration during the preparation process, which can improve the stability of the material. On the other hand, the cooperation of the negative electrode active material in the second negative electrode film layer with the volume average particle size range and the negative electrode active material in the first negative electrode film layer is conducive to constructing the gradient pore difference between the second negative electrode film layer and the first negative electrode film layer, reducing the tortuosity of lithium ion transmission, and improving the fast charging performance of the battery cell.

[0283] In the embodiments of the present application, the volume average particle size Dv50 of the negative electrode active material has the meaning well-known in the art, and can be detected by the equipment and methods well-known in the art. The detection method is the same as the test method for the volume average particle size Dv50 of the positive electrode active material described above.

[0284] Optionally, the tapped density of the carbon-based material in the first negative electrode film layer is less than or equal to the tapped density of the carbon-based material in the second negative electrode film layer. The tapped density can reflect the filling density of the active material in the film layer. When the tapped density of the carbon-based material in the second negative electrode film layer is greater than the tapped density of the carbon-based material in the first negative electrode film layer, the second negative electrode film layer is filled more densely, so that the energy density of the battery cell is improved. The filling of the first negative electrode film layer is relatively sparse and the pores are richer, which can improve the fast charging performance of the battery cell. When the negative electrode active material includes graphite particles, the tapped density of the graphite particles in the first negative electrode film layer is less than or equal to the tapped density of the graphite particles in the second negative electrode film layer.

[0285] Optionally, the tapped density of the carbon-based material in the first negative electrode film layer is 0.82 g / cm 3 to 1.21 g / cm3 , such as 0.82 g / cm 3 , 0.85 g / cm 3 , 0.88 g / cm 3 , 0.90 g / cm 3 , 0.92 g / cm 3 , 0.95 g / cm 3 , 0.98 g / cm 3 , 1.00 g / cm 3 , 1.05 g / cm 3 , 1.08 g / cm 3 , 1.10 g / cm 3 , 1.12 g / cm 3 , 1.15 g / cm 3 , 1.18 g / cm 3 , 1.20 g / cm 3 , 1.21 g / cm 3 or a range composed of any two of the above values. When the tap density of the carbon-based material in the first negative electrode film layer is within a suitable range, the fast charging performance of the battery cell can be improved.

[0286] Optionally, the tap density of the carbon-based material in the second negative electrode film layer is 0.90 g / cm 3 to 1.25 g / cm 3 , such as 0.90 g / cm 3 , 0.92 g / cm 3 , 0.95 g / cm 3 , 0.98 g / cm 3 , 1.00 g / cm 3 , 1.05 g / cm 3 , 1.08 g / cm 3 , 1.10 g / cm 3 , 1.12 g / cm 3 , 1.15 g / cm 3 , 1.18 g / cm 3 , 1.20 g / cm 3 , 1.21 g / cm 3 , 1.22 g / cm 3 , 1.23 g / cm 3 , 1.24 g / cm 3 , 1.25 g / cm 3 or a range composed of any two of the above values. When the tap density of the carbon-based material in the second negative electrode film layer is within a suitable range, the energy density of the battery cell can be improved.

[0287] In the embodiments of the present application, the tapped density of the material has the meaning well-known in the art and can be measured by instruments and methods known in the art. For example, reference can be made to GB / T5162-2006, and a powder tapped density tester can be used for measurement. The test instrument can be BT-301 produced by Dandong BETOP.

[0288] Optionally, the ratio of the thickness of the second negative electrode film layer to the thickness of the first negative electrode film layer is from 3:7 to 7:3, and can be optionally from 4:6 to 6:4. Exemplarily, the ratio of the thickness of the second negative electrode film layer to the thickness of the first negative electrode film layer is 3:7, 4:6, 5:5, 6:4, 7:3 or a range composed of any two of the above values. By adjusting the thickness ratio of the first negative electrode film layer and the second negative electrode film layer, the gradient pore difference between the upper and lower layers can be further increased, the tortuosity of lithium ion transport can be reduced, and the fast charging ability of the battery cell can be improved.

[0289] In some embodiments, after the battery cell undergoes 10 full charge test cycles at the beginning of life (BOL), the thickness of the first negative electrode film layer is from 15 μm to 65 μm, such as 15 μm, 17 μm, 18 μm, 20 μm, 25 μm, 30 μm, 35 μm, 40 μm, 45 μm, 50 μm, 55 μm, 57 μm, 58 μm, 60 μm, 61 μm, 62 μm, 63 μm, 64 μm, 65 μm or a range composed of any two of the above values. When the thickness of the first negative electrode film layer is within the above range, the gradient pore difference between the first negative electrode film layer and the second negative electrode film layer can be increased, the tortuosity of lithium ion transport can be reduced, and the fast charging ability of the battery cell can be improved.

[0290] In some embodiments, after the battery cell undergoes 10 full charge test cycles at the beginning of life (BOL), the thickness of the second negative electrode film layer is from 15 μm to 65 μm, such as 15 μm, 17 μm, 18 μm, 20 μm, 25 μm, 30 μm, 35 μm, 40 μm, 45 μm, 50 μm, 55 μm, 57 μm, 58 μm, 60 μm, 61 μm, 62 μm, 63 μm, 64 μm, 65 μm or a range composed of any two of the above values. When the thickness of the second negative electrode film layer is within the above range, the gradient pore difference between the first negative electrode film layer and the second negative electrode film layer can be regulated and increased, the tortuosity of lithium ion transport can be reduced, and the fast charging ability of the battery cell can be improved.

[0291] In the embodiments of the present application, for example, taking the upper limit voltage of battery charging as 3.65 V and the cut-off voltage of battery discharging as 2.0 V as an example for illustration,

[0292] The specific steps of the BOL full charge test are as follows: At 25 °C, charge at a charging rate of 0.33C of the battery nominal capacity until 3.65V, then charge at a constant voltage of 3.65V until 0.05C, let it stand for 10 min, then discharge at a discharge rate of 0.33C until 2.0V, and let it stand for 10 min. The above one charge and discharge cycle is one cycle, and cycle 10 times. Then charge at a charging rate of 0.33C of the nominal capacity until 3.65V, and then charge at a constant voltage of 3.65V until 0.05C, which is the BOL full charge state. In the BOL full charge state, disassemble the negative electrode sheet, use a tomography scanning electron microscope to observe the cross-section in the thickness direction of the middle area of the negative electrode sheet, distinguish the regions of the first negative electrode film layer and the second negative electrode film layer according to the interface between them, and measure their thicknesses respectively. For example, measure the thicknesses at 10 positions of the first negative electrode film layer, calculate their average value as the average value of the first negative electrode film layer, measure the thicknesses at 10 positions of the second negative electrode film layer, and calculate their average value as the average value of the second negative electrode film layer.

[0293] In some embodiments, after the battery cell undergoes the End Of Life (EOL) full charge test, the thickness of the first negative electrode film layer is 15 μm to 70 μm, such as 15 μm, 16 μm, 17 μm, 18 μm, 19 μm, 20 μm, 21 μm, 22 μm, 23 μm, 24 μm, 25 μm, 26 μm, 27 μm, 28 μm, 29 μm, 30 μm, 35 μm, 40 μm, 43 μm, 45 μm, 50 μm, 55 μm, 60 μm, 65 μm, 66 μm, 67 μm, 68 μm, 69 μm, 70 μm or the range composed of any two of the above values. When the thickness of the first negative electrode film layer is within the above range, the first negative electrode film layer and the second negative electrode film layer can regulate and increase the gradient pore difference between the upper and lower layers, reduce the tortuosity of lithium ion transmission, and improve the fast charging ability of the battery cell.

[0294] In some embodiments, after the battery cell undergoes the End Of Life (EOL) full charge test, the thickness of the second negative electrode film layer is 15 μm to 70 μm, such as 15 μm, 16 μm, 17 μm, 18 μm, 19 μm, 20 μm, 21 μm, 22 μm, 23 μm, 24 μm, 25 μm, 26 μm, 27 μm, 28 μm, 29 μm, 30 μm, 35 μm, 40 μm, 43 μm, 45 μm, 50 μm, 55 μm, 60 μm, 65 μm, 66 μm, 67 μm, 68 μm, 69 μm, 70 μm or the range composed of any two of the above values. When the thickness of the second negative electrode film layer is within the above range, the first negative electrode film layer and the second negative electrode film layer can regulate and increase the gradient pore difference between the upper and lower layers, reduce the tortuosity of lithium ion transmission, and improve the fast charging ability of the battery cell.

[0295] In an embodiment of the present application, for example, taking the battery charging upper limit voltage of 3.65V and the battery discharge cut-off voltage of 2.0V as an example for illustration,

[0296] The EOL full charge test steps are as follows: At 60°C, charge at a charging rate of 0.33C of the battery nominal capacity to 3.65V, then charge at a constant voltage of 3.65V to 0.05C, stand for 10 minutes, then discharge at a discharge rate of 0.33C to 2.0V, stand for 10 minutes. The above one charge and discharge is one cycle until the battery capacity decays to 80% of the nominal capacity and the test stops. Then at 25°C, charge at a constant current of 0.33C to 3.65V, and charge at a constant voltage of 0.05C to 3.65V, which is the EOL full charge state. In the EOL full charge state, disassemble the negative electrode sheet, use a tomography scanning electron microscope to observe the cross-section in the thickness direction of the middle area of the negative electrode sheet, distinguish the regions of the first negative electrode film layer and the second negative electrode film layer according to the interface between them, measure their thicknesses respectively. For example, measure the thicknesses of 10 positions of the first negative electrode film layer, calculate their average value as the average value of the first negative electrode film layer, measure the thicknesses of 10 positions of the second negative electrode film layer, and calculate their average value as the average value of the second negative electrode film layer.

[0297] In some embodiments, when the negative electrode film layer adopts a single-layer film layer (different from the above double-layer film layer), the negative electrode film layer further includes a lithium-containing binder. Optionally, the mass content of the lithium-containing binder relative to the mass of the negative electrode film layer is 0.1% to 1%. Exemplarily, the mass content of the lithium-containing binder relative to the mass of the negative electrode film layer is 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1% or a range composed of any two of the above values. The lithium element in the lithium-containing binder can exist in an ionic form, which can increase the number of free-moving lithium ions in the negative electrode film layer, shorten the distance for lithium ions to diffuse to the surface of the negative electrode film layer, improve the intercalation and deintercalation rate of lithium ions, and improve the fast charging performance of the battery cell. Optionally, the negative electrode film layer can further include a negative electrode binder. For example, the negative electrode binder includes at least one of styrene-butadiene rubber (SBR), water-soluble unsaturated resin SR-1B, water-based acrylic resin (such as polyacrylic acid PAA, polymethacrylic acid PMAA, sodium polyacrylate PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), and carboxymethyl chitosan (CMCS).

[0298] Optionally, the mass content of lithium element in the lithium-containing binder is 3% to 10%. Exemplarily, the mass content of lithium element in the lithium-containing binder is 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10% or the range composed of any two of the above values. The mass content of lithium element is calculated based on the mass of the lithium-containing binder. When the mass content of lithium element is within the above range, the number of free-moving lithium ions in the negative electrode film layer can be relatively large, which can further shorten the distance for lithium ions to diffuse to the surface of the negative electrode film layer, improve the intercalation and deintercalation rate of lithium ions, and improve the fast charging performance of the battery cell.

[0299] Exemplarily, the lithium-containing binder includes a lithium acrylate-acrylonitrile-acrylamide-2-hydroxyethyl acrylate copolymer, and the lithium acrylate-acrylonitrile-acrylamide-2-hydroxyethyl acrylate copolymer is derived from a lithium acrylate monomer, an acrylonitrile monomer, an acrylamide monomer, and a 2-hydroxyethyl acrylate monomer. The molar percentages of the lithium acrylate monomer, the acrylonitrile monomer, the acrylamide monomer, and the 2-hydroxyethyl acrylate monomer are 30% to 50%: 15% to 45%: 5% to 20%: 20% to 35%. For example, the molar percentages of the lithium acrylate monomer, the acrylonitrile monomer, the acrylamide monomer, and the 2-hydroxyethyl acrylate monomer are 35%: 30%: 15%: 20%, or 40%, 20%, 10%, 30%, or 45%, 15%, 20%, 20%, etc.

[0300] The lithium-containing binder of the above material can provide a certain number of lithium ions for the negative electrode film layer, improve the fast charging performance of the battery cell, and is not prone to swelling during the charge and discharge process, with a stable structure, so that the cycle performance of the negative electrode film layer is improved during the fast charge and discharge process.

[0301] In some other embodiments, when the negative electrode film layer adopts at least two layers of film layers, the negative electrode film layer further includes a lithium-containing binder.

[0302] Optionally, the first negative electrode film layer further includes a first lithium-containing binder, and the second negative electrode film layer further includes a second lithium-containing binder. The mass content of the first lithium-containing binder relative to the mass of the first negative electrode film layer is less than or equal to the mass content of the second lithium-containing binder relative to the mass of the second negative electrode film layer. Further optionally, the mass content of the first lithium-containing binder relative to the mass of the first negative electrode film layer is less than the mass content of the second lithium-containing binder relative to the mass of the second negative electrode film layer.

[0303] The mass content of the second lithium-containing binder in the second negative electrode film layer is relatively high, and the number of free-moving lithium ions provided by the second lithium-containing binder for the second negative electrode film layer is relatively more, which can further improve the fast charging performance of the battery cell.

[0304] Optionally, the mass content of the first lithium-containing binder relative to the mass of the first negative electrode film layer is 0.1% to 1%. Exemplarily, the mass content of the first lithium-containing binder relative to the mass of the first negative electrode film layer is 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1% or a range composed of any two of the above values. The lithium element in the first lithium-containing binder can exist in the form of ions, which can increase the number of free-moving lithium ions in the negative electrode film layer, shorten the distance for lithium ions to diffuse to the surface of the negative electrode film layer, increase the insertion / extraction rate of lithium ions, and improve the fast charging performance of the battery cell.

[0305] Optionally, the mass content of the lithium element in the first lithium-containing binder is 3% to 10%, and can be 3% to 8%. Exemplarily, the mass content of the lithium element in the first lithium-containing binder is 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10% or a range composed of any two of the above values. When the mass content of the lithium element is within the above range, the number of free-moving lithium ions in the negative electrode film layer can be relatively large, which can further shorten the distance for lithium ions to diffuse to the surface of the negative electrode film layer, increase the insertion / extraction rate of lithium ions, and improve the fast charging performance of the battery cell.

[0306] Exemplarily, the first lithium-containing binder includes a lithium acrylate-acrylonitrile-acrylamide-2-hydroxyethyl acrylate copolymer, and the lithium acrylate-acrylonitrile-acrylamide-2-hydroxyethyl acrylate copolymer is derived from a lithium acrylate monomer, an acrylonitrile monomer, an acrylamide monomer, and a 2-hydroxyethyl acrylate monomer. The molar percentages of the lithium acrylate monomer, the acrylonitrile monomer, the acrylamide monomer, and the 2-hydroxyethyl acrylate monomer are 30% to 50%: 15% to 45%: 5% to 20%: 20% to 35%. For example, the molar percentages of the lithium acrylate monomer, the acrylonitrile monomer, the acrylamide monomer, and the 2-hydroxyethyl acrylate monomer are 35%: 30%: 15%: 20%, or 40%, 20%, 10%, 30%, or 45%, 15%, 20%, 20%, etc.

[0307] The lithium-containing binder of the above material can provide a certain number of lithium ions for the negative electrode film layer, improve the fast charging performance of the battery cell, and is not prone to swelling during the charge and discharge process, with a stable structure, so that the cycle performance of the negative electrode film layer is improved during the fast charge and discharge process.

[0308] Optionally, the mass content of the second lithium-containing binder relative to the mass of the second negative electrode film layer is 0.1% to 1%. Exemplarily, the mass content of the second lithium-containing binder relative to the mass of the second negative electrode film layer is 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1% or a range composed of any two of the above values. The lithium element in the second lithium-containing binder can exist in an ionic form, which can increase the number of free-moving lithium ions in the negative electrode film layer, shorten the distance for lithium ions to diffuse to the surface of the negative electrode film layer, increase the intercalation and deintercalation rate of lithium ions, and improve the fast charging performance of the battery cell.

[0309] The first lithium-containing binder and the second lithium-containing binder can be made of the same material or different materials.

[0310] Optionally, the mass content of lithium element in the second lithium-containing binder is 3% to 10%, and can be optionally 3% to 8%. Exemplarily, the mass content of lithium element in the second lithium-containing binder is 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10% or a range composed of any two of the above values. When the mass content of lithium element is within the above range, the number of free-moving lithium ions in the negative electrode film layer can be relatively large, which can further shorten the distance for lithium ions to diffuse to the surface of the negative electrode film layer, increase the intercalation and deintercalation rate of lithium ions, and improve the fast charging performance of the battery cell.

[0311] Exemplarily, the second lithium-containing binder includes a lithium acrylate-acrylonitrile-acrylamide-2-hydroxyethyl acrylate copolymer, and the lithium acrylate-acrylonitrile-acrylamide-2-hydroxyethyl acrylate copolymer is derived from a lithium acrylate monomer, an acrylonitrile monomer, an acrylamide monomer and a 2-hydroxyethyl acrylate monomer. The molar percentages of the lithium acrylate monomer, the acrylonitrile monomer, the acrylamide monomer and the 2-hydroxyethyl acrylate monomer are 30% to 50%: 15% to 45%: 5% to 20%: 20% to 35%. For example, the molar percentages of the lithium acrylate monomer, the acrylonitrile monomer, the acrylamide monomer and the 2-hydroxyethyl acrylate monomer are 35%: 30%: 15%: 20%, or 40%, 20%, 10%, 30%, or 45%, 15%, 20%, 20%, etc.

[0312] The lithium-containing binder of the above material can provide a certain number of lithium ions for the negative electrode film layer, improve the fast charging performance of the battery cell, and is not prone to swelling during charge and discharge, with a stable structure, so that the cycling performance of the negative electrode film layer is improved during fast charge and discharge.

[0313] In some embodiments, the first negative electrode film layer further includes a negative electrode binder, and the second negative electrode film layer further includes a negative electrode binder. The negative electrode binder in the first negative electrode film layer and the negative electrode binder in the second negative electrode film layer independently include at least one of styrene-butadiene rubber (SBR), water-soluble unsaturated resin SR-1B, water-based acrylic resin (e.g., polyacrylic acid PAA, polymethacrylic acid PMAA, sodium polyacrylate PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), and carboxymethyl chitosan (CMCS).

[0314] In some embodiments, the total content of the first lithium-containing binder and the negative electrode binder in the first negative electrode film layer is greater than the total content of the second lithium-containing binder and the negative electrode binder in the second negative electrode film layer, and the mass content of the first lithium-containing binder relative to the mass of the first negative electrode film layer is less than the mass content of the second lithium-containing binder relative to the mass of the second negative electrode film layer.

[0315] In some embodiments, the negative electrode film layer may further optionally include a negative electrode conductive agent. There is no particular limitation on the type of the negative electrode conductive agent in the embodiments of the present application. As an example, the negative electrode conductive agent may include at least one of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. In some embodiments, based on the total weight of the negative electrode film layer, the mass content of the negative electrode conductive agent is ≤5%.

[0316] In some embodiments, the negative electrode film layer may further optionally include a negative electrode binder. In some embodiments, based on the total weight of the negative electrode film layer, the mass content of the negative electrode binder is ≤5%.

[0317] In some embodiments, the negative electrode film layer may further optionally include other additives. As an example, the other additives may include thickeners, dispersants, etc., such as sodium carboxymethyl cellulose (CMC-Na), PTC thermistor materials, etc. In some embodiments, based on the total weight of the negative electrode film layer, the mass content of the other additives is ≤2%.

[0318] In some embodiments, the porosity of the negative electrode film layer is 40% to 55%. Exemplarily, the porosity of the negative electrode film layer is 40%, 45%, 50%, 55% or a range composed of any two of the above values.

[0319] When the porosity of the negative electrode film layer in the embodiments of the present application is within the above range, the migration ability of lithium ions in the negative electrode film layer can be improved, and the fast charging performance can be improved.

[0320] In the embodiments of the present application, the porosity of the negative electrode film layer can be measured by the gas displacement method in accordance with Standard GB / T 24586. The porosity P = (V1 - V2) / V1 × 100%, where V1 is the apparent volume of the sample and V2 is the true volume of the sample.

[0321] The negative electrode film layer is usually formed by coating a negative electrode slurry on a negative electrode current collector and then drying and cold pressing. The negative electrode slurry is usually formed by dispersing negative electrode active materials, optional conductive agents, optional binders, and other optional additives in a solvent and stirring evenly. The solvent can be N-methylpyrrolidone (NMP) or deionized water, but is not limited thereto.

[0322] The negative electrode plate does not exclude other additional functional layers in addition to the negative electrode film layer. For example, in some embodiments, the negative electrode plate of the embodiments of the present application further includes a negative electrode conductive layer disposed on the surface of the negative electrode current collector and sandwiched between the negative electrode current collector and the negative electrode film layer. In some other embodiments, the negative electrode plate of the embodiments of the present application further includes a protective layer covering the surface of the negative electrode film layer.

[0323] In some embodiments, the negative electrode plate further includes a negative electrode conductive layer, and the negative electrode conductive layer is located between the negative electrode film layer and the negative electrode current collector. The negative electrode conductive layer can further improve the conductivity of the negative electrode plate, reduce the heat generation of the negative electrode plate, and thus reduce the heat generation of the battery cell.

[0324] In some embodiments, the thickness of the negative electrode conductive layer is 0.5 μm to 2 μm. Exemplarily, the thickness of the negative electrode conductive layer can be 0.5 μm, 0.8 μm, 1 μm, 1.2 μm, 1.5 μm, 1.6 μm, 1.8 μm, 2 μm or a range composed of any two of the above values.

[0325] When the thickness of the negative electrode conductive layer is within the above range, it can further improve the conductivity of the negative electrode plate, reduce the heat generation of the negative electrode plate, and thus reduce the heat generation of the battery cell, and can also take into account the improvement of the energy density of the battery cell.

[0326] In the embodiments of the present application, the thickness of the negative electrode conductive layer has the meaning well known in the art, can be detected by equipment and methods well known in the art, and the test method of the negative electrode conductive layer in the foregoing can be adopted.

[0327] In some embodiments, the negative electrode conductive layer includes one or more of a negative electrode conductive agent and a negative electrode binder. The negative electrode conductive agent in the negative electrode conductive layer can improve the conductivity of the negative electrode conductive layer, thereby improving the conductivity of the negative electrode plate and reducing the heat generation of the battery cell. The negative electrode binder in the negative electrode conductive layer can improve the bonding performance between the negative electrode current collector and the negative electrode film layer and improve the structural stability of the negative electrode plate.

[0328] In some embodiments, the negative electrode conductive layer may also optionally include other additives. As an example, the other additives may include thickeners, such as sodium carboxymethyl cellulose (CMC), PTC thermistor materials, and the like.

[0329] Optionally, the mass content of the negative electrode conductive agent in the negative electrode conductive layer is 20% to 40%. Exemplarily, the mass content of the negative electrode conductive agent is 20%, 25%, 30%, 35%, 40% or a range composed of any two of the above values.

[0330] Exemplarily, the negative electrode conductive agent includes one or more of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0331] Optionally, the mass content of the negative electrode binder in the negative electrode conductive layer is 60% to 80%. Exemplarily, 60%, 65%, 70%, 75%, 80% or a range composed of any two of the above values.

[0332] Exemplarily, the negative electrode binder includes one or more of styrene-butadiene rubber SBR, water-soluble unsaturated resin SR-1B, water-based acrylic resin, polyvinyl alcohol, sodium alginate, and carboxymethyl chitosan.

[0333] In some embodiments, the ratio CB of the capacity of the negative electrode film layer per unit area to the capacity of the positive electrode film layer per unit area in the battery cell is 1.05 to 1.30, and may be optionally 1.07 to 1.15. Exemplarily, the ratio CB of the capacity of the negative electrode film layer per unit area to the capacity of the positive electrode film layer per unit area in the battery cell is 1.05, 1.07, 1.1, 1.12, 1.15, 1.18, 1.2, 1.22, 1.25, 1.28, 1.3 or a range composed of any two of the above values.

[0334] When the ratio CB of the capacity of the negative electrode film layer per unit area to the capacity of the positive electrode film layer per unit area in the battery cell is within the above range, there are sufficient sites in the negative electrode film layer for lithium insertion, which can reduce the risk of lithium deposition and is beneficial for fast charging.

[0335] In the embodiments of the present application, the meaning of the CB value is well-known in the art, and it can be detected by using well-known equipment and methods in the art. For example, the capacity of the negative electrode film layer per unit area and the capacity of the positive electrode film layer per unit area are calculated respectively, and then the ratio of the two is calculated to obtain the CB value.

[0336] Specifically, taking the battery charging upper limit voltage of 3.65V and the battery discharge cut-off voltage of 2.0V as an example for illustration,

[0337] The capacity of the positive electrode film layer per unit area refers to the actual de-lithiation capacity of the positive electrode active material. The test method is as follows: Disassemble the battery in a PRS340 / 11-119-11 Braun glove box, take the positive electrode plate, assemble it into a CR2430 type half-button battery of positive electrode-lithium sheet, and the area of the positive electrode plate used is amm 2 , where the electrolyte is a solution of 1mol / L LiPF6 in EC / EMC / DEC = 3 / 5 / 2 (mass ratio). Then, let the assembled half-button battery stand for 3h. The test is carried out at 25°C. First, charge (Charge) and de-lithiate at a current of 0.1C in the voltage range of 2.0V to 3.65V, and then discharge (Discharge) and intercalate lithium at a current of 0.05C to 2.0V. Cycle 2 times. Record the discharge and charge capacity of the second cycle as YmAh. The actual length of the positive electrode plate designed for the battery is bmm, the width is cmm, and the number of sides d where the positive electrode active material is coated on the positive electrode current collector part. Then, the capacity of the positive electrode film layer per unit area = Y / a × b × c × d.

[0338] Specifically, the capacity of the negative electrode film layer per unit area refers to the actual lithium intercalation capacity of the negative electrode active material. The test method is: Disassemble the battery in a PRS340 / 11-119-11 Braun glove box, take the negative electrode plate, assemble it into a CR2430 type half-button battery of negative electrode-lithium sheet, and the area of the negative electrode plate used is fmm 2 , where the electrolyte is a solution of 1mol / L LiPF6 in EC / EMC / DEC = 3 / 5 / 2 (mass ratio). Then, let the assembled half-button battery stand for 3h. The test is carried out at 25°C. First, discharge (Discharge) and intercalate lithium at a current of 0.1C in the voltage range of 2V - 0V, and then charge (Discharge) and de-lithiate at a current of 0.05C to 2V. Cycle 2 times. Record the discharge and charge capacity of the second cycle as ZmAh. The actual length of the negative electrode plate designed for the battery is hmm, the width is imm, and the number of sides d where the negative electrode active material is coated on the negative electrode current collector part. Then, the lithium intercalation capacity of the negative electrode = Z / f × h × i × d.

[0339] [Separator membrane]

[0340] In the embodiments of the present application, the separator membrane includes a base membrane with a porous structure.

[0341] In some embodiments, the base membrane includes at least one of glass fiber, non-woven fabric, and polyolefin. The base membrane can be a single-layer film or a multi-layer composite film, without particular limitation. When the base membrane is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0342] Optionally, the polyolefin includes at least one of polyethylene, polypropylene, and polyvinylidene fluoride.

[0343] In some embodiments, the porosity of the base film is from 20% to 70%, optionally from 35% to 60%. Exemplarily, the porosity of the base film is 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70% or a range composed of any two of the above values.

[0344] When the porosity of the base film in the embodiments of the present application is within the above range, the migration ability of lithium ions in the separator can be improved, the internal resistance of the battery cell can be further reduced, and thus the heat generation can be reduced.

[0345] In the embodiments of the present application, the porosity refers to the percentage of the internal pore volume of the separator occupying the total volume of the separator. The porosity can be tested in accordance with the standard GB / T36363-2018 "Polyolefin Separator for Battery Cells". It should be noted that in the actual test process, the test process slightly different from the standard can be adopted according to the differences in test instruments, test errors, and in order to eliminate the test influence on the porosity as much as possible, so as to obtain a more accurate test value.

[0346] In some embodiments, the thickness of the base film is from 6μm to 12μm, optionally from 6μm to 9μm. Exemplarily, the thickness of the base film is 6μm, 6.5μm, 7μm, 7.5μm, 8μm, 8.5μm, 9μm, 9.5μm, 10μm, 10.5μm, 11μm, 11.5μm, 12μm or a range composed of any two of the above values.

[0347] When the thickness of the base film is within the above range, the migration path of lithium ions in the base film is shorter, the internal resistance of the battery cell can be further reduced, and thus the heat generation can be reduced.

[0348] In the embodiments of the present application, the separator can be a base film. Optionally, the separator further includes a functional layer disposed on at least one side of the base film. The functional layer can include inorganic particles to improve the heat resistance of the separator. Optionally, the functional layer is disposed on both sides of the base film.

[0349] In some embodiments, the functional layer includes a first functional layer and a second functional layer. The first functional layer is located on one side of the base film and includes first inorganic particles. The second functional layer is located on the other side of the base film and includes composite particles. The composite particles include second inorganic particles and a plurality of non-fluoropolymer particles, and the second inorganic particles are attached to the surface of and / or dispersed in the non-fluoropolymer particles.

[0350] The first functional layer and the second functional layer have good heat resistance, which can improve the heat resistance of the separator.

[0351] Optionally, the first functional layer may include a binder, optionally including at least one of a fluorine-containing binder or a polyacrylic acid binder, such as polyvinylidene fluoride.

[0352] Optionally, the first inorganic particles include one or more of silica, alumina, boehmite, barium sulfate, calcium oxide, titanium oxide, zinc oxide, magnesium oxide, zirconium oxide, and tin oxide. The above first inorganic particles can improve the heat resistance of the first functional layer.

[0353] In the embodiments of the present application, the meaning of the thickness of the base film is the meaning well known in the art, and it can be detected by using the meaning and equipment well known in the art. For example, a newly prepared separator can be taken as a sample, or a battery cell that has been discharged (discharged to the lower cut-off voltage so that the charged state of the battery is about 0% SOC) can be disassembled in reverse, the separator is obtained from the battery cell, and the separator is dried and used as a sample. The separator is cut off with an ion beam cutter to form a cross-section. Subsequently, a scanning electron microscope is used to measure the thickness of the cross-section of the separator and its respective layers.

[0354] The non-fluoropolymer particles in the second functional layer refer to polymers that are non-fluorinated polymers. For example, the non-fluoropolymer particles include acrylate copolymers. Optionally, the acrylate copolymers include acrylate-acrylonitrile-acrylamide-acrylonitrile copolymers. The acrylate copolymers have excellent adhesion properties and relatively high adhesion stability with the base film. The molar percentages of the monomers in the copolymer can be in any ratio, such as a molar percentage of 35%:30%:15%:20%, or 40%, 20%, 10%, 30%, or 45%, 15%, 20%, 20%, etc.

[0355] The second inorganic particles in the composite particles make it difficult for the non-fluoropolymer particles to adhere to each other due to the high-temperature treatment during the granulation process, resulting in pores in the composite particles, which is beneficial to the transmission of lithium ions and improves the ionic conductivity of the separator. Moreover, the second inorganic particles can also increase the compression modulus of the composite particles. During the charge and discharge process, the composite particles are not easily deformed, making the structure of the separator more stable, which can improve the kinetic performance of the battery cell and enhance the fast charging performance. Optionally, compared with the first functional layer, the second functional layer is disposed closer to the negative electrode tab. Since the composite particles are not easily deformed, the separator basically does not cause side effects such as extrusion to the negative electrode tab, making the kinetic performance of the negative electrode tab stable. Correspondingly, the first functional layer is disposed closer to the positive electrode tab.

[0356] Optionally, the second inorganic particles include one or more of silica, alumina, boehmite, barium sulfate, calcium oxide, titanium oxide, zinc oxide, magnesium oxide, zirconium oxide, and tin oxide. Optionally, the second inorganic particles include silica. The above-mentioned second inorganic particles can improve the heat resistance of the second functional layer and can form composite particles in combination with the non-fluoropolymer, further improving the cycle stability and kinetic performance of the separator membrane, and improving the cycle performance and fast charging performance of the battery cell.

[0357] The average particle size of the second inorganic particles is 5 nm to 100 nm, optionally 10 nm to 100 nm, and optionally 5 nm to 20 nm. Exemplarily, the average particle size of the second inorganic particles is 5 nm, 10 nm, 15 nm, 20 nm, 25 nm, 30 nm, 35 nm, 40 nm, 45 nm, 50 nm, 55 nm, 60 nm, 65 nm, 70 nm, 75 nm, 80 nm, 85 nm, 90 nm, 95 nm, 100 nm or a range composed of any two of the above values. When the average particle size of the second inorganic particles is within the above range, it is beneficial to improve the heat resistance and compression modulus of the composite particles.

[0358] In the embodiments of the present application, the average particle size of the second inorganic particles has the meaning well-known in the art and can be detected by using the equipment and methods well-known in the art. For example, after obtaining the separator membrane and drying the separator membrane as a sample, use an ion beam cutter to cut the separator membrane to form a cross-section. Subsequently, use a scanning electron microscope to measure the particle size of the second inorganic particles in the separator membrane, measure the particle sizes of multiple, for example, 50 second inorganic particles, and calculate their average value as the average particle size of the second inorganic particles.

[0359] In some embodiments, the ionic conductivity of the separator membrane is 0.3 mS / cm to 0.6 mS / cm. Exemplarily, the ionic conductivity of the separator membrane is 0.3 mS / cm, 0.35 mS / cm, 0.4 mS / cm, 0.45 mS / cm, 0.5 mS / cm, 0.55 mS / cm, 0.6 mS / cm or a range composed of any two of the above values.

[0360] When the ionic conductivity of the separator membrane is within the above range, it can further improve the migration ability of lithium ions in the separator membrane and improve the fast charging performance of the battery cell.

[0361] In the embodiments of the present application, the ionic conductivity of the separator membrane has the meaning well-known in the art and can be detected by using the equipment and methods well-known in the art. For example,

[0362] Preparation of 2025 type button battery for testing: In a vacuum glove box, put a lithium sheet into the negative electrode case of the battery, add 150 μL of electrolyte, the electrolyte is a solution of 1 mol / L LiPF6 in EC / EMC / DEC = 3 / 5 / 2 (mass ratio), then put in a separator (with an area of 3.14 cm 2 , with a thickness of 12 μm) to make it close to the lithium sheet, add another 25 μL of electrolyte, and finally place the positive electrode sheet (the positive electrode sheet can be the positive electrode sheet in Example 1) on it and seal. Take out the assembled button battery from the vacuum glove box and place it for 24 h for the next test.

[0363] Testing: On an electrochemical workstation, conduct tests in the frequency range of 10 -1 ~10 6 Hz to obtain the separator resistance Rb, and calculate the ionic conductivity σ (unit: mS / cm) through the following formula,

[0364] σ = L / (R b ×S)

[0365] where: R b is the separator resistance, and L and S are the thickness and area of the separator to be measured, respectively.

[0366] [Electrolyte]

[0367] In some embodiments, the battery cell further includes an electrolyte.

[0368] During the charge and discharge process of the battery cell, active ions are embedded and removed back and forth between the positive electrode sheet and the negative electrode sheet, and the electrolyte plays a role in conducting active ions between the positive electrode sheet and the negative electrode sheet.

[0369] In the embodiments of the present application, the conductivity of the electrolyte at room temperature is 13 mS / cm to 20 mS / cm, and can be optionally 15 mS / cm to 20 mS / cm. Exemplarily, the conductivity of the electrolyte at room temperature is 13 mS / cm, 13.5 mS / cm, 14 mS / cm, 14.5 mS / cm, 15 mS / cm, 15.5 mS / cm, 16 mS / cm, 16.5 mS / cm, 17 mS / cm, 17.5 mS / cm, 18 mS / cm, 18.5 mS / cm, 19 mS / cm, 19.5 mS / cm, 20 mS / cm or the range composed of any two of the above values.

[0370] When the conductivity of the electrolyte at room temperature, such as 25 °C, is within the above range, the migration rate of lithium ions in the electrolyte is relatively high, which can further reduce the internal resistance of the battery cell, thereby reducing heat generation, and can improve the fast charging performance of the battery cell.

[0371] In the embodiments of the present application, the conductivity of the electrolyte at room temperature, such as 25°C, is the ionic conductivity, and it can be detected by using the equipment and methods well-known in the art. For example, it can be tested with reference to the industry standard HG-T 4067-2015.

[0372] In some embodiments, the viscosity of the electrolyte at room temperature is from 2.3 mPa·s to 3.5 mPa·s. Exemplarily, the viscosity of the electrolyte is 2.3 mPa·s, 2.4 mPa·s, 2.5 mPa·s, 2.6 mPa·s, 2.7 mPa·s, 2.8 mPa·s, 2.9 mPa·s, 3.0 mPa·s, 3.1 mPa·s, 3.2 mPa·s, 3.3 mPa·s, 3.4 mPa·s, 3.5 mPa·s or the range composed of any two of the above values.

[0373] When the viscosity of the electrolyte at room temperature, such as 25°C, is within the above range, the migration rate of lithium ions in the electrolyte is relatively high, which can further reduce the internal resistance of the battery cell, thereby reducing heat generation, and can improve the fast charging performance of the battery cell.

[0374] In the embodiments of the present application, the viscosity of the electrolyte has the meaning well-known in the art, and it can be detected by using the equipment and methods well-known in the art. For example, it can be detected according to GB / T10247-2008.

[0375] In some embodiments, the density of the electrolyte at room temperature, such as 25°C, is from 1.05 g / mL to 1.35 g / mL. Exemplarily, the density of the electrolyte is 1.05 g / mL, 1.10 g / mL, 1.15 g / mL, 1.2 g / mL, 1.25 g / mL, 1.3 g / mL, 1.35 g / mL or the range composed of any two of the above values.

[0376] When the density of the electrolyte is within the above range, the migration rate of lithium ions in the electrolyte is relatively high, which can further reduce the internal resistance of the battery cell, thereby reducing heat generation, and can improve the fast charging performance of the battery cell.

[0377] In the embodiments of the present application, the density of the electrolyte has the meaning well-known in the art, and it can be detected by using the equipment and methods well-known in the art. For example, it can be tested with reference to GB / T 2013-2010.

[0378] The electrolyte includes an organic solvent and an electrolyte salt. The types of the organic solvent and the electrolyte salt are not specifically limited and can be selected according to actual needs.

[0379] In some embodiments, the organic solvent includes a chain carboxylic acid ester solvent, and the mass content of the chain carboxylic acid ester solvent relative to the mass of the organic solvent is greater than or equal to 5% and less than or equal to 75%, optionally 30% to 75%. Exemplarily, the mass content of the chain carboxylic acid ester solvent is 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75% or a range composed of any two of the above values.

[0380] When the mass content of the chain carboxylic acid ester solvent is within the above range, the viscosity of the electrolyte system is relatively small, which is beneficial to the migration of lithium ions.

[0381] When the mass content of the chain carboxylic acid ester solvent is within the above range, the viscosity of the electrolyte system is relatively small, which is beneficial to the migration of lithium ions.

[0382] In some embodiments, the chain carboxylic acid ester solvent includes a compound represented by Formula I,

[0383] Formula I,

[0384] In Formula I,

[0385] R1 includes a hydrogen atom, a halogen atom, a C1-C5 alkyl group or a C1-C5 haloalkyl group,

[0386] R2 includes a C1-C5 alkyl group or a C1-C5 haloalkyl group.

[0387] The above chain carboxylic acid ester solvent has a high conductivity, which is beneficial to improving the fast charging ability of the battery monomer.

[0388] Optionally, R1 includes a hydrogen atom, a halogen atom, a C1-C3 alkyl group or a C1-C3 haloalkyl group. Further optionally, R1 includes a hydrogen atom, a halogen atom, a C1-C2 alkyl group or a C1-C2 haloalkyl group.

[0389] Optionally, R2 includes a C1-C3 alkyl group or a C1-C3 haloalkyl group. Further optionally, R2 includes a C1-C2 alkyl group or a C1-C2 haloalkyl group.

[0390] In the above embodiments, the halogen atom includes one or more of a fluorine atom, a chlorine atom, a bromine atom and an iodine atom. Optionally, the halogen atom includes a fluorine atom.

[0391] In the above embodiments, the haloalkyl group includes one or more of a fluoroalkyl group, a chloroalkyl group, a bromoalkyl group and an iodoalkyl group. Optionally, the haloalkyl group includes a fluoroalkyl group.

[0392] Exemplarily, the chain carboxylic acid ester solvents include one or more of the compounds represented by Formula I-1 to Formula I-8.

[0393]

[0394] In some embodiments, the organic solvent further includes carbonate solvents.

[0395] Optionally, the carbonate solvents include one or more of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate. Further optionally, the carbonate solvents include one or more of ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate. The above carbonate solvents and chain carboxylic acid ester solvents are used in combination to improve the conductivity of the electrolyte, which is beneficial to the migration of lithium ions.

[0396] Further optionally, the mass content of the carbonate solvent in the organic solvent is 25% to 95%, and can be 25% to 70%. Exemplarily, the mass content of the carbonate solvent in the organic solvent is 25%, 30%, 31%, 32%, 33%, 34%, 35%, 36%, 37%, 38%, 40%, 45%, 48%, 50%, 55%, 60%, 65%, 70% or a range composed of any two of the above values. The carbonate solvent with the above mass content can further improve the conductivity of the electrolyte at room temperature, which is beneficial to the migration of lithium ions.

[0397] Exemplarily, the carbonate solvents include one or more of ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate, and the mass content of the carbonate solvent is 25% to 95%.

[0398] In some embodiments, the electrolyte further contains additives. The additives can include negative electrode film-forming additives, or can include positive electrode film-forming additives, and can also include additives that can improve certain performance of the battery, such as additives that improve the overcharge performance of the battery, additives that improve the high-temperature performance of the battery, additives that improve the low-temperature power performance of the battery, etc.

[0399] In some embodiments, the additives include one or more of carbonate additives, sulfur-containing additives, and lithium salt additives, and can be at least two. The above additives can improve the interfacial film performance on the positive electrode side and / or the negative electrode side, which is beneficial to improving the fast charging performance of the battery monomer and improving the cycle performance.

[0400] In some embodiments, the mass content of the additive in the electrolyte is 1% to 10%, optionally 2% to 8%, and further optionally 3.5% to 8%. Exemplarily, the mass content of the additive in the electrolyte is 1%, 2%, 3%, 3.5%, 4%, 5%, 6%, 7%, 8%, 9%, 10% or a range composed of any two of the above values.

[0401] The additive with the above mass content can effectively improve the interfacial film performance on the positive electrode side and / or the negative electrode side, which is beneficial to improving the fast charging performance of the battery cell and improving the cycle performance.

[0402] Exemplarily, the carbonate additives include one or more of vinylene carbonate (VC) and fluoroethylene carbonate (FEC).

[0403] Exemplarily, the sulfur-containing additives include one or more of ethylene sulfate (DTD), bis(ethylene sulfate) (2-DTD), butene sulfite (BS), 1,3-propane sultone (PS), ethylene sulfite (ES), and methylene methyl disulfonate (MMDS).

[0404] Optionally, the lithium salt additives include one or more of lithium difluorophosphate (LiPO2F2), lithium difluorooxalate borate (LiDFOB), lithium tetrafluoroborate (LiBF4), and lithium bis(oxalate) borate (LiBOB).

[0405] Optionally, the mass content of vinylene carbonate (VC) in the electrolyte is 0.5% to 9%, and optionally 2% to 6%.

[0406] Optionally, the mass content of fluoroethylene carbonate (FEC) in the electrolyte is 0.1% to 4%, and optionally 0.5% to 3%.

[0407] Optionally, the mass content of vinylene carbonate (VC) in the electrolyte is 0.5% to 9%, and the mass content of fluoroethylene carbonate (FEC) in the electrolyte is 0.1% to 4%.

[0408] Further optionally, the mass content of vinylene carbonate (VC) in the electrolyte is 2% to 6%, and the mass content of fluoroethylene carbonate (FEC) in the electrolyte is 0.5% to 3%.

[0409] In some embodiments, the electrolyte salt includes a lithium salt, and the lithium salt includes one or more of fluorosulfonimide salts and lithium hexafluorophosphate (LiPF6). The above lithium salts are easy to dissociate, which is beneficial to the rapid migration of lithium ions, and the electrolyte system is relatively stable and not easy to decompose, which can improve the cycle performance of the battery cell.

[0410] Optionally, the fluorosulfonimide salts include one or more of lithium bis(fluorosulfonyl)imide (LiFSI) and lithium bis(trifluoromethylsulfonyl)imide (LiTFSI).

[0411] Optionally, the lithium salt includes lithium bis(fluorosulfonyl)imide (LiFSI) and lithium hexafluorophosphate (LiPF6). The molar concentration of lithium bis(fluorosulfonyl)imide (LiFSI) is from 0.2 mol / L to 0.5 mol / L, and the molar concentration of lithium hexafluorophosphate (LiPF6) is from 0.5 mol / L to 1.0 mol / L.

[0412] Exemplarily, the molar concentration of lithium bis(fluorosulfonyl)imide (LiFSI) is from 0.4 mol / L to 0.5 mol / L, and the molar concentration of lithium hexafluorophosphate (LiPF6) is 0.7 mol / L.

[0413] Exemplarily, the molar concentration of lithium bis(fluorosulfonyl)imide (LiFSI) is 0.5 mol / L, and the molar concentration of lithium hexafluorophosphate (LiPF6) is 0.5 mol / L.

[0414] Exemplarily, the molar concentration of lithium bis(fluorosulfonyl)imide (LiFSI) is 0.2 mol / L, and the molar concentration of lithium hexafluorophosphate (LiPF6) is 0.8 mol / L.

[0415] Optionally, the ratio of the molar concentration of lithium bis(fluorosulfonyl)imide to the molar concentration of lithium hexafluorophosphate (LiPF6) is from 0.2 to 1.0, and can be optionally from 0.2 to 0.5. Exemplarily, the ratio of the molar concentration of lithium bis(fluorosulfonyl)imide to the molar concentration of lithium hexafluorophosphate (LiPF6) is 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1 or a range composed of any two of the above values.

[0416] In the embodiments of the present application, the types and contents of the inorganic components / lithium salt concentration in the electrolyte have the meanings well-known in the art, and can be detected by devices and methods well-known in the art. For example, reference can be made to the standard JY / T 020-1996 "General Rules for Ion Chromatography Analysis Methods" to qualitatively or quantitatively analyze the inorganic components / lithium salt concentration in the electrolyte by ion chromatography analysis method. In the embodiments of the present application, freshly prepared electrolyte can be taken as a sample, the free electrolyte of a fresh battery can be taken as a sample, or a discharged battery (discharged to the lower cut-off voltage so that the charged state of the battery is about 0% SOC) can be reverse disassembled, and the free electrolyte obtained from the battery can be taken as a sample, and detected by ion chromatography analysis method.

[0417] In the embodiments of the present application, the types and contents of the organic components in the electrolyte have meanings well-known in the art, and can be detected by devices and methods well-known in the art. For example, qualitative and quantitative analysis of the organic components in the electrolyte can be carried out by gas chromatography with reference to GB / T9722-2006 General Rules for Chemical Reagents - Gas Chromatography. In the embodiments of the present application, newly prepared electrolyte can be taken as a sample, free electrolyte of a fresh battery can be taken as a sample, or a battery that has been fully discharged (discharged to the lower cut-off voltage so that the charged state of the battery is about 0% SOC) can be reversely disassembled, and the free electrolyte obtained from the battery can be taken as a sample, and detected by ion chromatography analysis method.

[0418] In the embodiments of the present application, after quantitatively and qualitatively detecting each component in the electrolyte, each component is classified. Chain carboxylic ester solvents and carbonate solvents (such as ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate) are used as constituent components of the organic solvent. Based on the mass of the organic solvent being 100%, the mass content of each component is calculated.

[0419] Carbonate additives (such as vinylene carbonate, fluoroethylene carbonate), sulfur-containing additives, and lithium salt additives are used as additives of the electrolyte. Based on the mass of the electrolyte being 100%, the mass content of each component is calculated.

[0420] In some embodiments, the battery cell satisfies: d / A ≤ 3.5 g / Ah, and optionally 2.40 g / Ah ≤ d / A ≤ 3.3 g / Ah, where d represents the mass of the electrolyte in the battery cell, in g; A represents the rated capacity of the battery cell, in Ah. Exemplarily, d / A can be 3.5 g / Ah, 3.3 g / Ah, 3.2 g / Ah, 3.0 g / Ah, 2.8 g / Ah, 2.5 g / Ah, 2.45 g / Ah, 2.4 g / Ah, or a range composed of any two of the above values.

[0421] d / A can reflect the liquid retention ability of the electrolyte. When d / A is in the above range, the electrolyte can play a better wetting role on the positive electrode plate and the negative electrode plate, and can also improve the migration rate of lithium ions in the liquid phase, which is beneficial to improving the fast charging ability of the battery cell.

[0422] In the embodiments of the present application, d / A of the battery cell can be understood as the liquid retention coefficient, and can be detected by devices and methods well-known in the art. For example, taking the upper charge voltage of the battery as 3.65V and the discharge cut-off voltage of the battery as 2.0V as an example in accordance with GB / T31486-2015 Electrical Performance Requirements and Test Methods for Power Batteries for Electric Vehicles.

[0423] At 25 °C, the battery cell is charged at 0.33C to 3.65V, then charged at a constant voltage until 0.05C, and then discharged at a constant current of 0.33C to 2.0V. The discharged capacity A is used as the denominator. The battery cell is weighed as M0, and then the positive electrode plate, negative electrode plate, separator, and electrolyte are disassembled. The free electrolyte is stored in a bag. All the above solid components are placed in an oven at 60 °C and baked for more than 4 hours (including but not limited to the positive electrode plate, negative electrode plate, and separator, and also including other mechanical components of the disassembled battery cell that contribute to M0). Then, all the components of the battery cell are weighed as M1. The weight difference between M0 and M1 is used as the numerator. The liquid retention coefficient is equal to the value obtained by dividing the weight difference d between M0 and M1 by the capacity A.

[0424] In some embodiments, the positive electrode plate, separator, and negative electrode plate can be made into an electrode assembly by a winding process and / or a stacking process.

[0425] Figure 1 and Figure 2 shows a schematic structural diagram of the battery cell.

[0426] In some embodiments, the battery cell 7 may include a housing 20.

[0427] In some embodiments, the housing 20 of the battery cell 7 can be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The housing 20 of the battery cell 7 can also be a soft package, such as a pouch soft package. The material of the soft package can be plastic, such as at least one of polypropylene (PP), polybutylene terephthalate (PBT), and polybutylene succinate (PBS).

[0428] The housing 20 is a hollow structure, and the housing 20 can be used to encapsulate the above electrode assembly 10 and the electrolyte.

[0429] The preparation method of the battery cell 7 according to the embodiments of the present application is well-known. In some embodiments, the positive electrode plate, separator, negative electrode plate, and electrolyte can be assembled to form the battery cell 7. As an example, the positive electrode plate, separator, and negative electrode plate can be formed into an electrode assembly 10 by a winding process and / or a stacking process. The electrode assembly 10 is placed in the housing 20, and after drying, the electrolyte is injected. After processes such as vacuum packaging, standing, forming, and shaping, the battery cell 7 is obtained.

[0430] Optionally, the positive electrode sheet, the separator, and the negative electrode sheet are formed into an electrode assembly 10 through a stacking process, that is, the electrode assembly 10 is a stacked electrode assembly. The thickness direction of the electrode assembly 10, the thickness direction of the positive electrode sheet, and the thickness direction of the negative electrode sheet are parallel. The width direction of the electrode assembly 10, the width direction of the positive electrode sheet, and the width direction of the negative electrode sheet are parallel. The length direction of the electrode assembly 10, the length direction of the positive electrode sheet, and the length direction of the negative electrode sheet are parallel. The stacked electrode assembly 10 is more conducive to improving the energy density of the battery cell.

[0431] When the electrode assembly 10 is of a stacked structure, from the appearance, the electrode assembly 10 includes a flat region. Optionally, the electrode assembly 10 may also include a bent region. For example, when the separator adopts a one-piece structure, the separator is bent multiple times and then laminated with the positive electrode sheet and the negative electrode sheet to form the electrode assembly 10. Or when the negative electrode sheet adopts a one-piece structure, the negative electrode sheet is bent multiple times and then laminated with the positive electrode sheet and the separator to form the electrode assembly. Next, an example in which the electrode assembly 10 only includes a flat region will be described.

[0432] Structurally, the electrode assembly 10 includes a positive electrode sheet, a separator, and a negative electrode sheet that are stacked. The negative current collector part and the negative electrode film layer of the negative electrode sheet correspond to the flat region. Optionally, after the battery cell is charged and discharged cyclically 100 times, the lithium deposition area in the flat region accounts for 0% to 3% of the area of the flat region. The lithium deposition area is small, making the use reliability of the battery cell relatively high.

[0433] When the electrode assembly 10 is of a wound structure, structurally, the electrode assembly 10 includes a positive electrode sheet, a negative electrode sheet, and a separator. The positive electrode sheet can be a one-piece structure, the negative electrode sheet is a one-piece structure, and the separator is a one-piece structure. The separator is disposed between the positive electrode sheet and the negative electrode sheet.

[0434] After the positive electrode sheet is wound, the positive electrode sheet includes a first flat section and a positive electrode tab 111. The number of the first flat sections is at least one, preferably at least two. The positive electrode sheet further includes a first bent section. The first bent section and the first flat section are arranged along the winding direction of the electrode assembly 10, and the first bent section is connected to the first flat section. The positive electrode tab is connected to the first flat section. The first flat section and the first bent section constitute part of the main body 12.

[0435] After the negative electrode tab is wound, the negative electrode tab includes a second straight section and a negative electrode tab 112. The number of the second straight sections is at least one, and can be selected as at least two. The negative electrode tab further includes a second bent section. The second bent section and the second straight section are arranged along the winding direction of the electrode assembly 10, and the second bent section is connected to the second straight section. The negative electrode tab 112 is connected to the second straight section. The second straight section and the second bent section form a part of the main body 12. The first straight section and the second straight section are alternately stacked, and the first bent section and the second bent section are alternately stacked.

[0436] In terms of appearance, the electrode assembly 10 includes a straight region and a bent region. The straight region includes a first straight section and a second straight section. The number of the first straight sections is at least one, and can be selected as at least two. The number of the second straight sections is at least one, and can be selected as at least two. The bent region includes a first bent section and a second bent section. The number of the first bent sections is at least one, and can be selected as at least two. The number of the second bent sections is at least one, and can be selected as at least two. Optionally, after the battery cell is cycled 100 times for charge and discharge, the lithium deposition area in the straight region occupies 0% to 3% of the area of the straight region. The lithium deposition area is small, making the use reliability of the battery cell relatively high.

[0437] In some embodiments, the housing 20 includes a housing body 21 and an end cap 22. The housing body 21 has an opening, and the end cap 22 covers the opening.

[0438] The shape of the housing body 21 can be determined according to the specific shape of the electrode assembly 10. For example, if the electrode assembly 10 is a cylindrical structure, a cylindrical housing can be selected; if the electrode assembly 10 is a cuboid structure, a cuboid housing can be selected. Optionally, both the electrode assembly 10 and the housing body 21 are cuboid structures.

[0439] In some embodiments, the base material of the housing body 21 includes steel. Steel has relatively high mechanical strength and is not easily deformed, which can improve the use reliability and cycle performance of the battery cell. In the embodiments of the present application, the base material refers to the material with the highest proportion in the housing body 21.

[0440] Optionally, the thickness of the housing body 21 is 0.1 mm to 0.5 mm, and can be selected as 0.2 mm to 0.35 mm. Exemplarily, the thickness of the housing body 21 is 0.1 mm, 0.15 mm, 0.2 mm, 0.25 mm, 0.3 mm, 0.35 mm, 0.4 mm, 0.45 mm, 0.5 mm or a range composed of any two of the above values. When the thickness of the housing body 21 is within the above range, the housing body 21 has relatively high mechanical strength, which can improve the use reliability and cycle performance of the battery cell; and the housing body 21 occupies less space and there is more internal space in the housing body 21, which is beneficial to improving the energy density of the battery cell.

[0441] Viewed from the outer shape of the electrode assembly 10, the electrode assembly 10 includes a main body portion 12, a positive electrode tab 111 and a negative electrode tab 112. The positive electrode tab 111 and the negative electrode tab 112 protrude from the main body portion 12. The positive electrode tab 111 is the portion of the positive electrode plate that is not coated with the active material layer, and the negative electrode tab 112 is the portion of the negative electrode plate that is not coated with the active material layer. The positive electrode tab 111 and the negative electrode tab 112 are used to lead out the current in the main body portion 12. The polarities of the positive electrode plate and the negative electrode plate are opposite.

[0442] The positive electrode tab 111 and the negative electrode tab 112 can extend from the same side of the main body portion 12, or can extend from opposite sides respectively.

[0443] Optionally, the positive electrode tab 111 is disposed on at least one side of the main body portion 12. Specifically, the positive electrode tab 111 is disposed on at least one side of the positive current collector portion, and can be optionally disposed on both sides of the positive current collector portion, and can be disposed on both sides of the positive current collector portion along the length direction of the positive electrode plate, or disposed on at least one side of the positive current collector portion along the width direction of the positive electrode plate; optionally, the positive electrode tab 111 is disposed on both sides of the positive current collector portion along the length direction.

[0444] Optionally, the number of positive electrode tabs 111 on the same side of the main body portion 12 is at least one, and can be optionally at least two. Specifically, the number of positive electrode tabs 111 on the same side of the positive current collector portion can be at least one, such as one or at least two. When the number of positive electrode tabs 111 on the same side of the positive current collector portion is at least two, at least two positive electrode tabs 111 can increase the current-carrying area, and can evenly distribute the current, improving the current uniformity in the positive electrode plate 11, which is beneficial to further improving the fast charging performance of the battery cell 7.

[0445] In some embodiments, the number of positive electrode tabs 111 on the same side of the positive current collector portion is one or more. The positive electrode tab 111 includes a first end face connected to the positive current collector portion. The dimension of the first end face along the width direction is W1, and the sum of the dimensions of all the first end faces along the width direction on the same side of the positive current collector portion is n×W1. The dimension of the positive current collector portion along the width direction is W2, and n×W1 / W2 is greater than or equal to 1 / 3, where n represents the number of all positive electrode tabs 111 on the same side of the positive current collector portion. Optionally, n×W1 / W2 is greater than or equal to 2 / 3, where n represents the number of all positive electrode tabs 111 on the same side of the positive current collector portion.

[0446] Exemplarily, n×W1 / W2 is 1 / 3, 0.35, 0.4, 0.45, 0.5, 0.5, 0.55, 0.6, 2 / 3, 0.7, 0.75, 0.8, 0.85, 0.9 or a range composed of any two of the above values.

[0447] When \(n\times W1 / W2\) satisfies the above range, the current-carrying area of the positive electrode tab 111 is relatively large, which is beneficial to improving the fast charging performance of the battery cell 7.

[0448] Optionally, the negative electrode tab 112 is disposed on at least one side of the negative current collector part, and can be disposed on both sides of the negative current collector part, and can be disposed on both sides of the negative current collector part along the length direction of the negative electrode plate, or disposed on at least one side of the negative current collector part along the width direction of the negative electrode plate; optionally, the negative electrode tab 112 is disposed on both sides of the negative current collector part along the length direction.

[0449] Optionally, the number of the negative electrode tabs 112 on the same side of the main body part 12 is at least one, and can be at least two. Specifically, the number of the negative electrode tabs 112 on the same side of the negative current collector part can be at least one, such as one or at least two. When the number of the negative electrode tabs 112 on the same side of the negative current collector part is at least two, the at least two negative electrode tabs 112 can increase the current-carrying area, and can evenly distribute the current, improving the current uniformity in the negative electrode plate, which is beneficial to further improving the fast charging performance of the battery cell 7.

[0450] In some embodiments, the number of the negative electrode tabs 112 on the same side of the negative current collector part is one or more. The negative electrode tab 112 includes a second end face connected to the negative current collector part. The dimension of the second end face along the width direction is W3. The sum of the dimensions of all the second end faces along the width direction on the same side of the negative current collector part is \(m\times W3\). The dimension of the negative current collector part along the width direction is W4. \(m\times W3 / W4\geq1 / 3\), where \(m\) represents the number of all the negative electrode tabs 112 on the same side of the negative current collector part. Optionally, \(m\times W3 / W4\geq2 / 3\), where \(m\) represents the number of all the negative electrode tabs 112 on the same side of the negative current collector part.

[0451] Exemplarily, \(m\times W3 / W4\) is 1 / 3, 0.35, 0.4, 0.45, 0.5, 0.55, 0.6, 2 / 3, 0.7, 0.75, 0.8, 0.85, 0.9 or a range composed of any two of the above values.

[0452] When \(m\times W3 / W4\) satisfies the above range, the current-carrying area of the negative electrode tab 112 is relatively large, which is beneficial to improving the fast charging performance of the battery cell 7.

[0453] In some embodiments, the battery cell 7 further includes a positive terminal 31, and the positive terminal 31 is electrically connected to the positive current collector tab 111. Optionally, the positive terminal 31 and the positive current collector tab 111 are welded. The positive terminal 31 and the positive current collector tab 111 can be connected through an adapter, or can be connected without using an adapter. Optionally, the positive terminal 31 and the positive current collector tab 111 are connected without using an adapter, that is, the positive terminal 31 and the positive current collector tab 111 are directly welded, which can reduce the resistance at the connection and is beneficial to reducing the overall internal resistance of the battery cell 7.

[0454] Optionally, the number of the positive terminals 31 is at least one, and can be at least two.

[0455] Optionally, the number of the positive terminals 31 on the same side of the positive current collector part is at least one, and can be at least two. At least two positive terminals 31 can increase the overall current-carrying capacity of the positive terminals 31.

[0456] Further optionally, the current-carrying area of a single positive terminal 31 is greater than or equal to 200 mm 2 , and can be 200 mm 2 to 800 mm 2 . The current-carrying area of the positive terminal 31 can be understood as the cross-sectional area of the positive terminal 31, and this cross-section is perpendicular to the thickness direction of the positive terminal 31.

[0457] Exemplarily, the current-carrying area of a single positive terminal 31 can be 200 mm 2 , 210 mm 2 , 250 mm 2 , 280 mm 2 , 300 mm 2 , 320 mm 2 , 350 mm 2 , 380 mm 2 , 400 mm 2 , 450 mm 2 , 500 mm 2 , 550 mm 2 , 600 mm 2 , 650 mm 2 , 700 mm 2 , 750 mm 2 , 800 mm 2 or a range composed of any two of the above values.

[0458] In some embodiments, the battery cell 7 further includes a negative terminal 32, and the negative terminal 32 is electrically connected to the negative electrode tab 112. Optionally, the negative terminal 32 and the negative electrode tab 112 are welded. The negative terminal 32 and the negative electrode tab 112 can be connected through an adapter, or can be connected without using an adapter; optionally, the negative terminal 32 and the negative electrode tab 112 are not connected through an adapter, that is, the negative terminal 32 and the negative electrode tab 112 are directly welded, which can reduce the resistance at the connection and is beneficial to reducing the overall internal resistance of the battery cell 7.

[0459] Optionally, the number of the negative terminals 32 is at least one, and can be at least two.

[0460] Optionally, the number of the negative terminals 32 on the same side of the negative current collector is at least one, and can be at least two. At least two negative terminals 32 can increase the current-carrying capacity of the negative terminals 32.

[0461] Further optionally, the current-carrying area of a single negative terminal 32 is greater than or equal to 200 mm 2 , and can be 200 mm 2 to 800 mm 2 . The current-carrying area of the negative terminal 32 can be understood as the cross-sectional area of the negative terminal 32, and this cross-section is perpendicular to the thickness direction of the negative terminal 32.

[0462] Exemplarily, the current-carrying area of a single negative terminal 32 can be 200 mm 2 , 210 mm 2 , 250 mm 2 , 280 mm 2 , 300 mm 2 , 320 mm 2 , 350 mm 2 , 380 mm 2 , 400 mm 2 , 450 mm 2 , 500 mm 2 , 550 mm 2 , 600 mm 2 , 650 mm 2 , 700 mm 2 , 750 mm 2 , 800 mm 2 or a range composed of any two of the above values.

[0463] As Figure 3 shown, in some embodiments of the present application, the battery cell 7 according to the embodiments of the present application can be assembled into a battery module 6. The number of battery cells 7 included in the battery module 6 can be one or more, and the specific number can be adjusted according to the application and capacity of the battery module 6.

[0464] If there are multiple battery cells 7, the multiple battery cells 7 can be connected in series, in parallel, or in a combined series-parallel configuration. A combined series-parallel configuration means that there are both series and parallel connections among the multiple battery cells 7. The multiple battery cells 7 can be directly connected in series, in parallel, or in a combined series-parallel configuration together, and then the whole formed by the multiple battery cells 7 is accommodated in the accommodation part of the battery module 6; of course, it is also possible that the multiple battery cells 7 are first connected in series, in parallel, or in a combined series-parallel configuration to form battery modules 6, and then the multiple battery modules 6 are connected in series, in parallel, or in a combined series-parallel configuration to form a whole and are accommodated in the accommodation part. Optionally, the battery module 6 can also include an accommodation part with an accommodation space, and the multiple battery cells 7 are accommodated in this accommodation space.

[0465] As Figure 4 shown, in some embodiments, the above-mentioned battery module 6 can also be assembled into a battery pack 2, and the number of battery modules 6 included in the battery pack 2 can be adjusted according to the application and capacity of the battery pack. The battery device in this article can be either the battery module 6 or the battery pack 2.

[0466] The battery pack 2 can include a box body 5 and a plurality of battery modules 6 arranged in the box body 5. The box body 5 includes a first box body part 5a and a second box body part 5b. The box body 5 has an accommodation space 5c. The first box body part 5a is used to cover the second box body part 5b and form a closed space for accommodating the battery module 6. The plurality of battery modules 6 can be arranged in the box body 5 in any manner.

[0467] The first box body part 5a and the second box body part 5b are covered with each other, and the first box body part 5a and the second box body part 5b jointly define an accommodation space 5c for accommodating the battery cells. The second box body part 5b can be a hollow structure with one end open, and the first box body part 5a is a plate-like structure. The first box body part 5a covers the open side of the second box body part 5b to form the box body 5 with the accommodation space 5c; both the first box body part 5a and the second box body part 5b can also be hollow structures with one side open, and the open side of the first box body part 5a covers the open side of the second box body part 5b to form the box body 5 with the accommodation space 5c. Of course, the first box body part 5a and the second box body part 5b can be in various shapes, such as a cylinder, a cuboid, etc.

[0468] To improve the sealing performance after the connection between the first box body part 5a and the second box body part 5b, a sealing member, such as sealant, sealing ring, etc., can also be provided between the first box body part 5a and the second box body part 5b.

[0469] Assume that the first box body part 5a covers the top of the second box body part 5b. The first box body part 5a can also be called the upper box cover, and the second box body part 5b can also be called the lower box body.

[0470] In some embodiments, during the process of the battery pack 2 or any battery cell constituting the battery pack 2 from 0% state of charge (SOC) to 100% SOC, the temperature of the external environment where the battery pack 2 is located is room temperature, such as 30°C.

[0471] In some embodiments, during the charging process of the battery pack 2 or any battery cell constituting the battery pack 2 from 10% SOC to 80% SOC, it includes multiple charging steps, and the difference between the maximum SOC of any charging step and the maximum SOC of its adjacent charging step in the multiple charging steps is less than or equal to 5% SOC, such as 1% SOC, 1.5% SOC, 2% SOC, 2.5% SOC, 3% SOC, 3.5% SOC, 4% SOC, 4.5% SOC, 5% SOC, or a range composed of any two of the above values.

[0472] The battery pack 2 or any battery cell constituting the battery pack 2 from 10% SOC to 40% SOC includes multiple charging steps. For any charging step, it can be charged at any rate between 5C and 10C. The charging rate corresponding to each charging step can be any value among 5C, 5.5C, 6C, 6.5C, 7C, 7.5C, 8C, 8.5C, 9C, 9.5C, 10C, or a value within a range composed of any two of the above values.

[0473] Exemplarily, the charging steps of the battery pack 2 or any battery cell constituting the battery pack 2 from 10% to 80% can be carried out as follows:

[0474] Charge at a constant current of 5.0C from 10% SOC to 15% SOC;

[0475] Charge at a constant current of 5.0C from 15% SOC to 20% SOC;

[0476] Charge at a constant current of 5.0C from 20% SOC to 25% SOC;

[0477] Charge at a constant current of 5.0C from 25% SOC to 30% SOC;

[0478] Charge at a constant current of 5.0C from 30% SOC to 35% SOC;

[0479] Charge at a constant current of 5.0C from 35% SOC to 40% SOC;

[0480] Charge at a constant current of 4.6C from 40% SOC to 45% SOC;

[0481] Charge at a constant current of 4.3C from 45% SOC to 50% SOC;

[0482] Charge at a constant current of 4.0C from 50% SOC to 55% SOC;

[0483] Charge from 55% SOC to 60% SOC at a constant current of 3.7C;

[0484] Charge from 60% SOC to 65% SOC at a constant current of 3.4C;

[0485] Charge from 65% SOC to 70% SOC at a constant current of 3.1C;

[0486] Charge from 70% SOC to 75% SOC at a constant current of 2.9C;

[0487] Charge from 75% SOC to 80% SOC at a constant current of 2.7C.

[0488] In some embodiments, the charging time of the battery pack 2 or any battery cell constituting the battery pack 2 from 20% state of charge to 80% state of charge is less than or equal to 12.5 min, and can be optionally 6 min to 12.5 min. The temperature of the external environment of the battery pack 2 at 10% state of charge is room temperature, such as 30°C. Exemplarily, the charging time of the battery pack 2 from 10% state of charge to 80% state of charge is 12.5 min, 12 min, 11.5 min, 11 min, 10.5 min, 10 min, 9.5 min, 9 min, 8.5 min, 8 min, 7.5 min, 7 min, 6.5 min, 6 min or the range composed of any two of the above values.

[0489] In some embodiments, the volumetric energy density of the battery cell is 390 Wh / L to 500 Wh / L, and can be optionally 410 Wh / L to 470 Wh / L. Exemplarily, the volumetric energy density of the battery cell is 390 Wh / L, 400 Wh / L, 410 Wh / L, 420 Wh / L, 430 Wh / L, 440 Wh / L, 450 Wh / L, 460 Wh / L, 470 Wh / L, 480 Wh / L, 490 Wh / L, 500 Wh / L or the range composed of any two of the above values. The volumetric energy density of the battery cell is relatively high.

[0490] In the embodiments of the present application, the volumetric energy density of the battery cell has the meaning well-known in the art, and can be detected by using the equipment and methods well-known in the art. For example, taking the upper limit voltage of battery charging as 3.65V and the cut-off voltage of battery discharging as 2.0V as an example for illustration,

[0491] The battery cell is placed at 25°C and charged at a constant current of 0.33C to 3.65V, then charged at a constant voltage until 0.05C, and discharged at a constant current of 0.33C to 2.0V. Record the discharge capacity A0 at this time, unit: Ah. Use a caliper to measure the length, width, and height of the battery cell (generally calculated based on the outer shell size of the battery, excluding the height of the electrode terminals and the insulating film outside the shell), and calculate the volume V0 of the single battery cell, unit: L. The volume energy density VED of the battery cell = (A0 × discharge platform voltage) / V0, unit: Wh / L.

[0492] electrical device

[0493] The second aspect of the embodiments of the present application provides an electrical device. The electrical device includes at least one of the battery cell, battery module, or battery pack of the embodiments of the present application. The battery cell, battery module, or battery pack can be used as the power source of the electrical device or as the energy storage unit of the electrical device. The electrical device can be a vehicle, mobile phone, portable device, laptop computer, ship, spacecraft, electric toy, and electric tool, etc. The vehicle can be a fuel vehicle, gas vehicle, or new energy vehicle. The new energy vehicle can be a pure electric vehicle, hybrid electric vehicle, or range-extended electric vehicle, etc.; the spacecraft includes airplanes, rockets, space shuttles, and spaceships, etc.; the electric toy includes fixed or mobile electric toys, for example, game consoles, electric vehicle toys, electric ship toys, and electric airplane toys, etc.; the electric tool includes metal cutting electric tools, grinding electric tools, assembly electric tools, and railway electric tools, for example, electric drills, electric grinders, electric wrenches, electric screwdrivers, electric hammers, impact electric drills, concrete vibrators, and electric planers, etc. The embodiments of the present application do not impose special restrictions on the above electrical devices.

[0494] The electrical device can select a battery cell, battery module, or battery pack according to its usage requirements.

[0495] Figure 5 It is a schematic diagram of an electrical device 1 as an example. The electrical device 1 is a pure electric vehicle, hybrid electric vehicle, or plug-in hybrid electric vehicle, etc. To meet the requirements of the electrical device 1 for high power and high energy density, a battery pack or battery module can be used.

[0496] A battery pack 2 is provided inside the electrical device 1. The battery pack 2 can be provided at the bottom, head, or tail of the electrical device 1. The battery pack 2 can be used for the power supply of the electrical device 1. For example, the battery pack 2 can be used as the operating power source of the electrical device 1 and can also be used as the driving power source of the electrical device 1, replacing or partially replacing fuel or natural gas to provide driving power for the electrical device 1.

[0497] The electrical device 1 may further include a controller 3 and a motor 4. The controller 3 is used to control the battery pack 2 to supply power to the motor 4. For example, it is used for the working power requirements during the startup, navigation, and driving of the electrical device 1.

[0498] As another example, the electrical device can be a mobile phone, a tablet computer, a laptop computer, etc. This electrical device usually requires being thin and light, and battery cells can be used as the power source.

[0499] The charging process of the electrical device can select the following charging methods:

[0500] Charge from 10% SOC to 15% SOC at a constant current of 5.0C;

[0501] Charge from 15% SOC to 20% SOC at a constant current of 5.0C;

[0502] Charge from 20% SOC to 25% SOC at a constant current of 5.0C;

[0503] Charge from 25% SOC to 30% SOC at a constant current of 5.0C;

[0504] Charge from 30% SOC to 35% SOC at a constant current of 5.0C;

[0505] Charge from 35% SOC to 40% SOC at a constant current of 5.0C;

[0506] Charge from 40% SOC to 45% SOC at a constant current of 4.6C;

[0507] Charge from 45% SOC to 50% SOC at a constant current of 4.3C;

[0508] Charge from 50% SOC to 55% SOC at a constant current of 4.0C;

[0509] Charge from 55% SOC to 60% SOC at a constant current of 3.7C;

[0510] Charge from 60% SOC to 65% SOC at a constant current of 3.4C;

[0511] Charge from 65% SOC to 70% SOC at a constant current of 3.1C;

[0512] Charge from 70% SOC to 75% SOC at a constant current of 2.9C;

[0513] Charge from 75% SOC to 80% SOC at a constant current of 2.7C.

[0514] In some embodiments, the charging time of the electrical device from 10% state of charge to 80% state of charge is less than or equal to 12.5 min, and can be optionally 6 min to 12.5 min. The temperature of the external environment of the battery pack 2 in the electrical device at 20% state of charge is room temperature, such as 30 °C. Exemplarily, the charging time of the battery pack 2 in the electrical device from 10% state of charge to 80% state of charge is 12.5 min, 12 min, 11.5 min, 11 min, 10.5 min, 10 min, 9.5 min, 9 min, 8.5 min, 8 min, 7.5 min, 7 min, 6.5 min, 6 min or the range composed of any two of the above values.

[0515] embodiment

[0516] The following examples more specifically describe the content disclosed in the embodiments of the present application. These examples are only for illustrative purposes, because various modifications and changes within the scope of the content disclosed in the embodiments of the present application are obvious to those skilled in the art. Unless otherwise stated, all parts, percentages and ratios reported in the following examples are based on mass, and all reagents used in the examples are commercially available or synthesized according to conventional methods, and can be used directly without further treatment, and all instruments used in the examples are commercially available.

[0517] Example 1

[0518] 1. Preparation of the positive electrode plate

[0519] The positive electrode plate includes a positive current collector, a positive conductive layer on the positive current collector, and a positive electrode film layer. The positive current collector is aluminum foil.

[0520] The positive conductive layer on the positive current collector is a film layer formed by uniformly coating a mixture of a positive conductive agent, superconducting carbon, a positive binder, polyvinylidene fluoride (PVDF), and a solvent, N-methylpyrrolidone (NMP), on the surface of the current collector and drying. The thickness is 1 μm. The mass content of the positive conductive agent in the positive conductive layer is 40%, and the mass content of the positive binder is 60%.

[0521] The positive electrode film layer includes a film layer formed by uniformly coating a positive electrode slurry (solvent is N-methylpyrrolidone NMP) on the surface of the positive conductive layer, followed by drying and cold pressing. The positive electrode film layer includes a positive active material, a binder polyvinylidene fluoride (PVDF), and a conductive agent acetylene black with a weight ratio of 97:2:1.

[0522] The positive electrode active material includes lithium iron phosphate and a coating layer. The coating layer coats the surface of the lithium iron phosphate. The coating layer includes lithium iron titanium phosphate Li2FeTi(PO4)3 and amorphous carbon. The Dv50 of the positive electrode active material is 1.6 μm, the Dv10 is 0.64 μm, the particle size of the smallest particle is 0.2 μm, and the particle size of the largest particle is 18 μm.

[0523] 2. Preparation of the negative electrode sheet

[0524] The negative electrode sheet includes a negative electrode current collector, a negative electrode conductive layer on the negative electrode current collector, and a negative electrode film layer. The negative electrode current collector is a copper foil.

[0525] The negative electrode conductive layer on the negative electrode current collector is a film layer formed by uniformly mixing a negative electrode conductive agent, superconducting carbon, a negative electrode binder, styrene-butadiene rubber SBR, a thickening agent, sodium carboxymethyl cellulose (CMC-Na), and a solvent, water, and then coating it on the surface of the negative electrode current collector and drying it. The thickness is 1 μm. The mass content of the negative electrode conductive agent in the negative electrode conductive layer is 35%, the mass content of the negative electrode binder in the negative electrode conductive layer is 60%, and the mass content of the thickening agent in the negative electrode conductive layer is 5%;

[0526] The negative electrode film layer includes a film layer formed by uniformly coating a negative electrode slurry (the solvent is deionized water) on the surface of the negative electrode conductive layer, followed by drying and cold pressing.

[0527] The negative electrode film layer includes a first negative electrode film layer and a second negative electrode film layer. The first negative electrode film layer is located on the surface of the negative electrode conductive layer, and the second negative electrode film layer is located on the surface of the first negative electrode film layer.

[0528] The first negative electrode film layer includes graphite particles, conductive agent acetylene black, a first lithium-containing binder (a copolymer of lithium acrylate - acrylonitrile - acrylamide - 2 - hydroxyethyl acrylate, where the molar ratio of lithium acrylate monomer, acrylonitrile monomer, acrylamide monomer, and 2 - hydroxyethyl acrylate monomer is 35%:30%:15%:20%), negative electrode binder styrene-butadiene rubber, and thickening agent sodium carboxymethyl cellulose, with a mass ratio of 96.5:0.5:0.5:1.5:1. The mass content of lithium element in the first lithium-containing binder is 4.8%. The Dv50 of the graphite particles is 11.3 μm. The graphite particles include artificial graphite and a carbon coating layer. The carbon coating layer coats the surface of the artificial graphite, and the mass content of the carbon coating layer is 3.5%.

[0529] The second negative electrode film layer comprises graphite particles, conductive agent acetylene black, second lithium-containing binder (lithium acrylate-acrylonitrile-acrylamide-2-hydroxyethyl acrylate copolymer, wherein the molar ratio of lithium acrylate monomer, acrylonitrile monomer, acrylamide monomer and 2-hydroxyethyl acrylate monomer is 35%:30%:15%:20%), negative electrode binder styrene-butadiene rubber, and thickening agent sodium carboxymethyl cellulose, the mass content of lithium element in the second lithium-containing binder is 4.8%, the Dv50 of the graphite particles is 11.3 μm, the graphite particles include artificial graphite and a carbon coating layer, the carbon coating layer is coated on the surface of the artificial graphite, and the mass content of the carbon coating layer is 3.5%.

[0530] 3. Separator

[0531] The separator comprises a base film, the base film is a 7-μm polyethylene film layer, and the porosity is 42%.

[0532] 4. Preparation of electrolyte

[0533] The electrolyte comprises an organic solvent, a lithium salt, and an additive.

[0534] The organic solvent comprises 60% chain carboxylic ester solvent (ethyl acetate) and 40% carbonate solvent (30% ethylene carbonate EC and 10% dimethyl carbonate), and the mass content of each component in the organic solvent is calculated based on the mass of the organic solvent.

[0535] Based on the mass of the electrolyte, the mass content of the additive is 6.5%, which comprises vinylene carbonate VC, fluoroethylene carbonate FEC, ethylene sulfite ES, and lithium difluorooxalate borate LiDFOB with a mass ratio of 5:0.5:0.5:0.5.

[0536] The lithium salt comprises 1 mol / L lithium hexafluorophosphate LiPF6.

[0537] The conductivity of the electrolyte at room temperature is 16.4 mS / cm.

[0538] 5. Preparation of battery cell

[0539] Stack the above-mentioned positive electrode sheet, separator, and negative electrode sheet in sequence, with the separator placed between the positive electrode sheet and the negative electrode sheet to play an isolation role, obtaining an electrode assembly. Place the electrode assembly in an outer packaging shell, inject the electrolyte after drying, and go through processes such as vacuum packaging, standing, forming, and shaping to obtain the battery cell.

[0540] Comparative Example 1 and Comparative Example 2

[0541] The battery single cells were prepared by a method similar to that of Example 1. Different from Example 1, the thickness, compaction density, coating weight, etc. of the positive electrode plate and the negative electrode plate were adjusted, as specifically shown in Table 1 and Table 2.

[0542] Examples 2 to 11

[0543] The battery single cells were prepared by a method similar to that of Example 1. Different from Example 1, the thickness, compaction density, coating weight, etc. of the positive electrode plate and the negative electrode plate were adjusted, as specifically shown in Table 1 and Table 2.

[0544] performance test

[0545] 1. Charging time of the battery single cell

[0546] The charging time of the battery single cell from 10% SOC to 80% SOC was specifically carried out by the following charging steps.

[0547] At 30 °C, charging was carried out from the state of 10% SOC of the battery.

[0548] Constant current charging at 5.0C from 10% SOC to 15% SOC;

[0549] Constant current charging at 5.0C from 15% SOC to 20% SOC;

[0550] Constant current charging at 5.0C from 20% SOC to 25% SOC;

[0551] Constant current charging at 5.0C from 25% SOC to 30% SOC;

[0552] Constant current charging at 5.0C from 30% SOC to 35% SOC;

[0553] Constant current charging at 5.0C from 35% SOC to 40% SOC;

[0554] Constant current charging at 4.6C from 40% SOC to 45% SOC;

[0555] Constant current charging at 4.3C from 45% SOC to 50% SOC;

[0556] Constant current charging at 4.0C from 50% SOC to 55% SOC;

[0557] Constant current charging at 3.7C from 55% SOC to 60% SOC;

[0558] Constant current charging at 3.4C from 60% SOC to 65% SOC;

[0559] Constant current charging at 3.1C from 65% SOC to 70% SOC;

[0560] Charge from 70% SOC to 75% SOC at a constant current of 2.9C;

[0561] Charge from 75% SOC to 80% SOC at a constant current of 2.7C.

[0562] Record the total charging time.

[0563] The difference in charging time between different embodiments is adjusted based on the charging rate of Embodiment 1 to achieve the corresponding charging time.

[0564] 2. Cycle performance of battery cells

[0565] At 30°C, charge the battery cell from 10% SOC to 80% SOC according to the above charging process, then charge to 3.65V at 0.33C, let it stand for 30 minutes, and then discharge to 10% SOC at 1C. This is one charge-discharge cycle. Repeat the above charge-discharge cycle 1000 times, and calculate the cycle capacity retention rate of the battery cell. The higher the cycle capacity retention rate, the better the cycle performance of the battery cell. Based on the charging rate adjustment of Embodiment 1, the actual rate of different embodiments is adjusted due to the charging time adjustment from 10% to 80% SOC.

[0566] The test results are shown in Tables 1 to 3.

[0567] Table 1

[0568]

[0569] Table 2

[0570]

[0571] Table 3

[0572]

[0573] As can be seen from Tables 1 to 3,

[0574] In Comparative Example 1, the ratio of the total thickness of the negative electrode film layer to the thickness of the negative electrode plate in the negative electrode plate is less than 0.95, and the thickness of the negative electrode film layer is relatively thin, resulting in a lower energy density of the battery cell.

[0575] In Comparative Example 2, the ratio of the total thickness of the negative electrode film layer to the thickness of the negative electrode plate in the negative electrode plate is greater than 0.97. The internal impedance may be relatively high, resulting in a longer charging time. Moreover, the volume expansion of the negative electrode plate is too large, and it is difficult for the electrolyte to flow back, resulting in insufficient electrolyte infiltration in the negative electrode film layer, making it easy for lithium deposition to occur on the negative electrode plate, etc., resulting in a shortened cycle life of the battery cell;

[0576] In the embodiments of the present application, the ratio of the total thickness of the negative electrode film layer to the thickness of the negative electrode sheet in the negative electrode sheet is 0.95 to 0.97, such that during the charging process of the negative electrode sheet, the volume expansion of the negative electrode sheet is relatively small, enabling the electrolyte to fully infiltrate the negative electrode sheet, improving the migration performance of lithium ions in the negative electrode sheet, reducing the risk of lithium deposition on the negative electrode sheet, effectively improving the reliability and cycle performance of the battery cell, and being conducive to improving the energy density of the battery cell; and the proportion of the negative electrode current collector part is small and the thickness is thin, which is conducive to improving the fast charging performance of the battery cell.

[0577] In the embodiments of the present application, by further adjusting the ratio of the total thickness of the positive electrode film layer to the thickness of the positive electrode sheet in the positive electrode sheet to be 0.88 to 0.94, it is possible to further balance and improve the fast charging performance, cycle performance, and energy density of the battery cell.

[0578] In the embodiments of the present application, by further adjusting the thickness of the positive electrode current collector part to be 10 μm to 15 μm; and / or the thickness of the negative electrode current collector part to be 4 μm to 6 μm, it is possible to further balance and improve the fast charging performance, cycle performance, and energy density of the battery cell.

[0579] In the embodiments of the present application, by further adjusting the coating weight of the single-sided positive electrode film layer to be 200 mg / 1540.25 mm 2 to 370 mg / 1540.25 mm 2 ; and / or the coating weight of the single-sided negative electrode film layer to be 90 mg / 1540.25 mm 2 to 170 mg / 1540.25 mm 2 , it is possible to further balance and improve the fast charging performance, cycle performance, and energy density of the battery cell.

[0580] In the embodiments of the present application, by further adjusting the compaction density of the single-sided positive electrode film layer to be 2.5 g / cm 3 to 2.8 g / cm 3 ; and / or the compaction density of the single-sided negative electrode film layer to be 1.15 g / cm 3 to 1.36 g / cm 3 when the battery cell is in a 100% charged state, it is possible to further balance and improve the fast charging performance, cycle performance, and energy density of the battery cell.

[0581] Although the illustrative embodiments have been demonstrated and described, those skilled in the art should understand that the above embodiments should not be construed as limitations on the present application, and changes, substitutions, and modifications can be made to the embodiments without departing from the spirit, principle, and scope of the present application.

Claims

1. A battery cell, characterized in that, The electrode assembly includes a positive electrode sheet, a negative electrode sheet, and a separator, wherein the separator is located between the positive electrode sheet and the negative electrode sheet. The positive electrode sheet includes a positive electrode tab, a positive electrode current collecting portion, and a positive electrode film layer provided on at least one surface of the positive electrode current collecting portion along the thickness direction of the positive electrode sheet and containing a positive electrode active material, wherein the positive electrode tab is provided on at least one side of the positive electrode current collecting portion; The negative electrode sheet includes a negative electrode tab, a negative electrode current collector, and a negative electrode film layer provided on at least one surface of the negative electrode current collector along the thickness direction of the negative electrode sheet and containing a negative electrode active material. The negative electrode tab is provided on at least one side of the negative electrode current collector. Among them, when the battery cell is in a 100% charged state, the ratio of the total thickness of the negative electrode film layer in the negative electrode plate to the thickness of the negative electrode plate is 0.95 to 0.97; when the battery cell is in a 100% charged state, the ratio of the total thickness of the positive electrode film layer in the positive electrode plate to the thickness of the positive electrode plate is 0.88 to 0.

94.

2. The battery cell according to claim 1, wherein: The thickness of the negative electrode current collector is 4 μm to 6 μm; and / or The negative electrode film layer is arranged on both surfaces of the negative electrode current collecting portion. When the battery cell is in a 100% charged state, the thickness of the negative electrode film layer on both sides is 110 μm to 178 μm.

3. The battery cell according to claim 1, wherein: The thickness of the positive electrode current collecting portion is 10 μm to 15 μm; and / or The positive electrode film layer is arranged on both surfaces of the positive electrode current collecting portion. When the battery cell is in a 100% charged state, the thickness of the positive electrode film layer on both sides is 128 μm to 191 μm.

4. The battery cell according to claim 1, wherein The coating weight of the single-sided positive electrode film layer is 200 mg / 1540.25 mm 2 to 370 mg / 1540.25 mm 2 .

5. The battery cell according to claim 1, characterized in that, The coating weight of the single-sided negative electrode film layer is 90 mg / 1540.25 mm 2 to 170 mg / 1540.25 mm 2 .

6. The battery cell according to claim 1, characterized in that, When the battery cell is in a 100% state of charge, the tap density of the positive electrode film layer on one side is 2.5 g / cm 3 to 2.8 g / cm 3 ; and / or When the battery cell is in a 100% state of charge, the compaction density of the negative electrode film layer on one side is 1.15 g / cm 3 to 1.36 g / cm 3 .

7. The battery cell according to claim 1, characterized in that, The powder resistivity of the negative electrode active material is 0.005 Ω·cm to 0.043 Ω·cm.

8. The battery cell according to claim 1, characterized in that, The powder compaction density of the negative electrode active material under a pressure of 20,000 N is 1.5 g / cm 3 to 1.85 g / cm 3 .

9. The battery cell according to claim 1, wherein The negative electrode active material has a charge capacity of 350 mAh / g to 480 mAh / g at a 0.1 C rate.

10. The battery cell according to claim 1, wherein, The negative electrode active material includes a carbon-based material, the carbon-based material includes graphite particles, and the graphite particles have a degree of graphitization of 92.0% to 94.5%.

11. The battery cell according to claim 10, wherein The graphite particles include: Artificial graphite, including secondary particles, and The carbon coating layer is coated on the surface of the artificial graphite.

12. The battery cell according to claim 11, wherein, The mass content of the carbon coating layer is 2% to 5% based on the mass of the graphite particles.

13. The battery cell according to claim 10, characterized in that, The negative electrode film layer comprises: a first negative electrode film layer, disposed on the surface of the negative electrode current collecting portion, wherein the first negative electrode film layer comprises a carbon-based material, and A second negative electrode film layer is connected to a side of the first negative electrode film layer away from the negative electrode current collecting portion, wherein the second negative electrode film layer comprises a carbon-based material. The carbon-based material in the first negative electrode film layer and the carbon-based material in the second negative electrode film layer each independently include graphite particles, and the volume average particle size Dv50 of the graphite particles in the first negative electrode film layer is greater than or equal to the volume average particle size Dv50 of the graphite particles in the second negative electrode film layer.

14. The battery cell according to claim 13, characterized in that The volume average particle size Dv50 of the graphite particles in the first negative electrode film layer is 9.5 μm to 18.5 μm, and / or The volume average particle size Dv50 of the graphite particles in the second negative electrode film layer is 7.8 μm to 14.3 μm.

15. The battery cell according to claim 13, wherein, The first negative electrode film layer further includes a first lithium-containing binder, and the second negative electrode film layer further includes a second lithium-containing binder. The mass content of the first lithium-containing binder relative to the mass of the first negative electrode film layer is less than or equal to the mass content of the second lithium-containing binder relative to the mass of the second negative electrode film layer.

16. The battery cell according to claim 15, wherein The mass content of the first lithium-containing binder relative to the mass of the first negative electrode film layer is 0.1% to 1%, and / or The mass content of the second lithium-containing binder relative to the mass of the second negative electrode film layer is 0.1% to 1%.

17. The battery cell according to claim 15, wherein The mass content of lithium element in the first lithium-containing binder is 3% to 10%, and / or The mass content of lithium element in the second lithium-containing binder is 3% to 10%.

18. The battery cell according to claim 15, wherein The first lithium-containing binder includes a lithium acrylate-acrylonitrile-acrylamide-2-hydroxyethyl acrylate copolymer, and the lithium acrylate-acrylonitrile-acrylamide-2-hydroxyethyl acrylate copolymer is derived from lithium acrylate monomer, acrylonitrile monomer, acrylamide monomer and 2-hydroxyethyl acrylate monomer. The molar percentages of the lithium acrylate monomer, the acrylonitrile monomer, the acrylamide monomer and the 2-hydroxyethyl acrylate monomer are 30% to 50%: 15% to 45%: 5% to 20%: 20% to 35%, and / or The second lithium-containing binder includes a lithium acrylate-acrylonitrile-acrylamide-2-hydroxyethyl acrylate copolymer, and the lithium acrylate-acrylonitrile-acrylamide-2-hydroxyethyl acrylate copolymer is derived from lithium acrylate monomer, acrylonitrile monomer, acrylamide monomer and 2-hydroxyethyl acrylate monomer. The molar percentages of the lithium acrylate monomer, the acrylonitrile monomer, the acrylamide monomer and the 2-hydroxyethyl acrylate monomer are 30% to 50%: 15% to 45%: 5% to 20%: 20% to 35%.

19. The battery cell according to claim 1, wherein The negative electrode active material is a single-layer film layer, the negative electrode active material is granular, and the volume average particle size of the negative electrode active material is 8.2 μm to 13.5 μm.

20. The battery cell according to claim 1, wherein, The porosity of the negative electrode film layer is 40% to 55%.

21. The battery cell according to claim 1, wherein The negative electrode active material further includes a silicon-based material, and the content of silicon element in the silicon-based material is 0.3% to 10.0% based on the mass of the negative electrode active material.

22. The battery cell according to claim 1, wherein ,, The powder resistivity of the positive electrode active material is 1 Ω•cm to 27.5 Ω•cm.

23. The battery cell according to claim 1, wherein The powder compaction density of the positive electrode active material under 30,000 N is 2.46 g / cm 3 to 2.8 g / cm 3 .

24. The battery cell according to claim 1, wherein, The charging specific capacity of the positive electrode active material at a rate of 0.1C is 150 mAh / g to 170 mAh / g.

25. The battery cell according to claim 1, characterized in that, The positive electrode active material includes a lithium-containing phosphate in an olivine structure.

26. The battery cell according to claim 25, wherein, The lithium-containing phosphate in the olivine structure includes: Phosphate particles, and A coating layer that coats the phosphate particles, and the coating layer contains one or more elements of C, Fe, Ti, Zr, Hf, Ge, and Sn.

27. The battery cell according to claim 26, characterized in that, The phosphate particles include a compound with the general formula Li x1 A y1 Me a M b P 1-c X c Y z , where 0.5 ≤ x1 ≤ 1.3, 0 ≤ y1 ≤ 1.3, and 0.9 ≤ x1 + y1 ≤ 1.3, 0.9 ≤ a ≤ 1.5, 0 ≤ b ≤ 0.5, and 0.9 ≤ a + b ≤ 1.5, 0 ≤ c ≤ 0.5, 3 ≤ z ≤ 5, A includes one or more of Na, K, and Mg, Me includes one or more of Mn, Fe, Co, and Ni, M includes one or more of B, Mg, Al, Si, P, S, Ca, Sc, Ti, V, Cr, Cu, Zn, Sr, Y, Zr, Nb, Mo, Cd, Sn, Sb, Te, Ba, Ta, W, Yb, La, and Ce, X includes one or more of S, Si, Cl, B, C, and N, and Y includes one or more of O and F.

28. The battery cell according to claim 26, characterized in that, The coating layer comprises a fast ion conductor with the general formula Li 3-d Fe 2-d M2 d (PO x2 ) y2 , where M2 comprises one or more elements of Ti, Zr, Hf, Ge, and Sn, 0 ≤ d ≤ 1, 0 < x2 < 5, and 0 < y2 < 4.

29. The battery cell according to claim 25, wherein, The graphitization degree of the lithium-containing phosphate with olivine structure is 0.15 to 0.

32.

30. The battery cell according to claim 29, wherein, The graphitization degree of the lithium-containing phosphate with olivine structure is 0.19 to 0.

26.

31. The battery cell according to claim 25, wherein The mass content of carbon element in the lithium-containing phosphate with olivine structure is 1.0% to 2%; The specific surface area of the lithium-containing phosphate with an olivine structure is 5 m 2 / g to 18 m 2 / g.

32. The battery cell according to claim 25, wherein, The lithium-containing phosphate with olivine structure is granular, and its volume distribution particle size satisfies: 1μm ≤ Dv50 ≤ 2μm, 0.4μm ≤ Dv10 ≤ 0.7μm.

33. The battery cell according to claim 32, wherein The particle size of the smallest particle in the lithium-containing phosphate with olivine structure is 0.1μm to 0.4μm; and / or The particle size of the largest particle in the lithium-containing phosphate with olivine structure is 15μm to 25μm.

34. The battery cell according to claim 1, characterized in that, The positive electrode film layer further includes a first material, and the first material includes one or more of ternary materials, lithium phosphate, lithium hydrogen phosphate, lithium sulfate, lithium sulfite, lithium molybdate, lithium oxalate, lithium titanate, lithium tetraborate, lithium metasilicate, lithium manganate, lithium tartrate, lithium citrate, lithium nickelate, and lithium ferrate.

35. The battery cell according to claim 34, wherein, The mass content of the first material in the positive electrode film layer is 0.5% to 5%.

36. The battery cell according to claim 1, wherein The battery cell includes an electrolyte, and the conductivity of the electrolyte at room temperature is 13 mS / cm to 20 mS / cm; and / or The battery cell includes an electrolyte, and the viscosity of the electrolyte at room temperature is 2.3 mPa·s to 3.5 mPa·s; and / or The battery cell includes an electrolyte, and the density of the electrolyte at room temperature is 1.05 g / mL to 1.35 g / mL.

37. The battery cell according to claim 1, characterized in that, The battery cell includes an electrolyte, and the electrolyte includes an organic solvent, and the organic solvent includes a chain carboxylic ester solvent, and the mass content of the chain carboxylic ester solvent in the organic solvent is 5% to 75%.

38. The battery cell according to claim 37, wherein The mass content of the chain carboxylic ester solvent in the organic solvent is 30% to 75%.

39. The battery cell according to claim 37, characterized in that, The chain carboxylic ester solvent includes a compound represented by Formula I, Formula I, In Formula I, R1 includes a hydrogen atom, a halogen atom, a C1 to C5 alkyl group, or a C1 to C5 haloalkyl group, R2 includes a C1 to C5 alkyl group or a C1 to C5 haloalkyl group.

40. The battery cell according to claim 39, wherein R1 includes a hydrogen atom, a halogen atom, a C1 to C3 alkyl group, or a C1 to C3 haloalkyl group, and / or R2 includes a C1 to C3 alkyl group or a C1 to C3 haloalkyl group.

41. The battery cell according to claim 40, wherein, The chain carboxylic ester solvent includes one or more of the compounds represented by Formula I-1 to Formula I-8, 。 42. The battery cell according to claim 37, wherein The organic solvent further includes a carbonate solvent, and the carbonate solvent includes one or more of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate.

43. The battery cell according to claim 42, wherein, The carbonate solvent includes one or more of ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate.

44. The battery cell according to claim 42, wherein, The mass content of the carbonate solvent in the organic solvent is 25% to 95%.

45. The battery cell according to claim 1, wherein The battery cell includes an electrolyte, and the electrolyte further includes additives, and the additives include one or more of carbonate additives, sulfur-containing additives, and lithium salt additives.

46. The battery cell according to claim 45, wherein, The carbonate additives include one or more of vinylene carbonate and fluoroethylene carbonate, and / or The sulfur-containing additives include one or more of ethylene sulfate, bis(ethylene sulfate), butene sulfite, 1,3-propane sultone, ethylene sulfite, and methylene methanedisulfonate, and / or The lithium salt additives include one or more of lithium difluorophosphate, lithium difluorooxalate borate, lithium tetrafluoroborate, and lithium bis(oxalate) borate.

47. The battery cell according to claim 45, characterized in that, The mass content of the additives in the electrolyte is 1% to 10%.

48. The battery cell according to claim 47, wherein The mass content of the additives in the electrolyte is 2% to 8%.

49. The battery cell according to claim 1, wherein The battery cell includes an electrolyte, and the electrolyte further includes a lithium salt, and the lithium salt includes one or more of fluorosulfonylimide salts and lithium hexafluorophosphate.

50. The battery cell according to claim 49, wherein, The fluorosulfonylimide salts include one or more of lithium bis(fluorosulfonyl)imide and lithium bis(trifluoromethylsulfonyl)imide.

51. The battery cell according to claim 50, wherein The lithium salt includes lithium bis(fluorosulfonyl)imide and lithium hexafluorophosphate. The molar concentration of lithium bis(fluorosulfonyl)imide is 0.2 mol / L to 0.5 mol / L, and the molar concentration of lithium hexafluorophosphate is 0.5 mol / L to 1.0 mol / L.

52. The battery cell according to claim 51, wherein, The ratio of the molar concentration of lithium bis(fluorosulfonyl)imide to the molar concentration of lithium hexafluorophosphate is 0.2 to 1.

0.

53. The battery cell according to claim 1, wherein The separator includes a base film with a porous structure, and the thickness of the base film is 6 μm to 12 μm.

54. The battery cell according to claim 53, characterized in that, The separator includes a base film and a functional layer provided on at least one side of the base film. The functional layer includes: A first functional layer located on one side of the base film. The first functional layer includes first inorganic particles. A second functional layer located on the other side of the base film. The second functional layer includes composite particles. The composite particles include second inorganic particles and a plurality of non-fluoropolymer particles. The second inorganic particles are attached to the surface of the non-fluoropolymer particles and / or dispersed inside the non-fluoropolymer particles.

55. The battery cell according to claim 54, characterized in that, The non-fluoropolymer particles include acrylate copolymers.

56. The battery cell according to claim 54, wherein, The first inorganic particles include one or more of silicon oxide, aluminum oxide, boehmite, barium sulfate, calcium oxide, titanium oxide, zinc oxide, magnesium oxide, zirconium oxide, and tin oxide.

57. The battery cell according to claim 54, wherein, The second inorganic particles include one or more of silicon oxide, aluminum oxide, boehmite, barium sulfate, calcium oxide, titanium oxide, zinc oxide, magnesium oxide, zirconium oxide, and tin oxide, and / or The average particle size of the second inorganic particles is 5 nm to 100 nm.

58. The battery cell according to claim 1, wherein The positive electrode tab is provided on both sides of the positive electrode current collector portion along the length direction of the electrode assembly.

59. The battery cell according to claim 58, wherein, The positive electrode tabs on the same side of the positive electrode current collector part are one or more. The positive electrode tab includes a first end face connected to the positive electrode current collector part. The dimension of the first end face in the width direction is W1. The sum of the dimensions of all the first end faces on the same side of the positive electrode current collector part in the width direction is n×W1. The dimension of the positive electrode current collector part in the width direction is W2, and n×W1 / W2 is greater than or equal to 1 / 3, where n represents the number of all the positive electrode tabs on the same side of the positive electrode current collector part.

60. The battery cell according to claim 1, wherein The negative electrode tabs are arranged on both sides of the negative electrode current collector part along the length direction of the electrode assembly.

61. The battery cell according to claim 60, characterized in that, The negative electrode tabs on the same side of the negative electrode current collector part are one or more. The negative electrode tab includes a second end face connected to the negative electrode current collector part. The dimension of the second end face in the width direction is W3. The sum of the dimensions of all the second end faces on the same side of the negative electrode current collector part in the width direction is m×W3. The dimension of the negative electrode current collector part in the width direction is W4, and m×W3 / W4 is greater than or equal to 1 / 3, where m represents the number of all the negative electrode tabs on the same side of the negative electrode current collector part.

62. The battery cell according to claim 1, characterized in that, The battery cell further includes a positive terminal, and the positive terminal is electrically connected to the positive electrode tab.

63. The battery cell according to claim 62, characterized in that, The positive terminal is directly welded to the positive electrode tab.

64. The battery cell according to claim 62, wherein The number of positive terminals on the same side of the positive electrode current collector part is at least two.

65. The battery cell according to claim 62, characterized in that, The overcurrent area of a single positive terminal is 200 mm 2 to 800 mm 2 .

66. The battery cell according to claim 1, characterized in that, The battery cell further includes a negative terminal, and the negative terminal is electrically connected to the negative electrode tab.

67. The battery cell according to claim 66, wherein The negative terminal is directly welded to the negative electrode tab.

68. The battery cell according to claim 66, wherein, The number of negative terminals on the same side of the negative electrode current collector part is at least two.

69. The battery cell according to claim 66, wherein, The overcurrent area of a single said negative terminal is 200 mm 2 to 800 mm 2 .

70. The battery cell according to claim 1, characterized in that, The positive electrode plate, the separator, and the negative electrode plate are stacked along the thickness direction of the electrode assembly.

71. The battery cell according to claim 1, wherein, The charging time of the battery cell from 10% state of charge to 80% state of charge is 6 min to 12.5 min.

72. A battery device, characterized in that, Including the battery cell according to any one of claims 1 to 71.

73. The battery device according to claim 72, wherein, The charging time of the battery device from 10% state of charge to 80% state of charge is 6 min to 12.5 min.

74. An electrical device, characterized in that, Including the battery device according to claim 72.

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