Battery cell, battery device and electric device

Abstract

The invention relates to a battery monomer, a battery device and a power utilization device, the battery monomer comprises an electrode assembly and an electrolyte, the electrode assembly comprises a positive pole piece and a negative pole piece, the positive pole piece comprises a positive current collector and a positive film layer, the positive film layer comprises a positive active material, the positive active material comprises lithium-containing phosphate of an olivine structure, and the electrolyte is a lithium-containing lithium-containing phosphate of a lithium-containing lithium-containing lithium-containing lithium-containing lithium-containing lithium-containing lithium-containing lithium-containing lithium-containing lithium-containing lithium-containing lithium-containing lithium-containing electrolyte. The resistance of the positive pole piece is 0.1 ohm to 30 ohm, the negative pole piece comprises a negative current collector and a negative film layer, the resistance of the negative pole piece is 0.001 ohm to 0.01 ohm, the electrolyte comprises an organic solvent, the organic solvent comprises a chain ester solvent, and the mass content of the chain ester solvent in the organic solvent is 5% to 75%; the conductivity of the electrolyte at room temperature is 13 mS / cm to 20 mS / cm. The heat production amount of the battery monomer can be reduced, and the use reliability and the cycle performance of the battery monomer can be improved.

Description

[0001] This application claims the priority of International Patent Application PCT / CN2024 / 102652, titled "Battery Cell, Battery Device and Electrical Device", filed on June 28, 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] Lithium-ion batteries have characteristics such as high capacity and long life, and thus are widely used in electronic devices, such as mobile phones, laptop computers, battery cars, electric vehicles, electric airplanes, electric ships, and power tools, etc. With the development of the application fields of lithium-ion batteries, higher requirements are put forward for the performance of lithium-ion batteries, such as fast charging performance, cycling performance, etc. Summary of the Invention

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

[0005] In a first aspect, this application proposes a battery cell. The battery cell includes an electrode assembly, an electrolyte and a housing. The electrode assembly and the electrolyte are accommodated in the housing. The electrode assembly includes a positive electrode plate, a negative electrode plate and a separator. The positive electrode plate includes a positive current collector and a positive electrode film layer provided on at least one side of the positive current collector. The positive electrode film layer includes a positive electrode active material capable of providing lithium. The positive electrode active material includes a lithium-containing phosphate with an olivine structure. The resistance of the positive electrode plate is 0.1 Ω to 30 Ω. The negative electrode plate includes a negative current collector and a negative electrode film layer provided on at least one side of the negative current collector. The negative electrode film layer includes a negative electrode active material capable of receiving lithium. The resistance of the negative electrode plate is 0.001 Ω to 0.01 Ω. The separator is located between the positive electrode plate and the negative electrode plate. The electrolyte includes an organic solvent. The organic solvent includes a chain ester solvent. The mass content of the chain carboxylic ester solvent in the organic solvent is 5% to 75%. The conductivity of the electrolyte at room temperature is 13 mS / cm to 20 mS / cm.

[0006] Accordingly, in the embodiments of the present application, the positive electrode active material includes lithium-containing phosphate with an olivine structure. This material system has relatively high cycle stability. Further, by synergistically controlling the resistance of the positive electrode sheet, the resistance of the negative electrode sheet, and the conductivity of the electrolyte within a reasonable range, on the one hand, it can reduce the transmission resistance of lithium ions inside the battery cell, improve the fast charging ability of the battery cell, and reduce the internal resistance DCR of the battery cell. On the other hand, it can improve the cycle attenuation caused by excessive temperature rise during the fast charging process of the battery cell. On the further hand, it can also improve the problem of uneven temperature rise during the fast charging process of the battery cell and reduce the cycle attenuation problem caused by lithium precipitation in the battery cell. Moreover, 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%. 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.

[0007] In addition, by controlling the resistance of the positive and negative electrode sheets within a reasonable range, the internal temperature of the battery cell can be controlled within the reasonable range tolerated by the high-conductivity electrolyte, which can reduce the risk of weakening the fast charging performance of the battery due to the volatilization of the solvent components of the electrolyte.

[0008] In some embodiments, the conductivity of the electrolyte at room temperature is 15 mS / cm to 20 mS / cm. When the conductivity of the electrolyte at room temperature 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.

[0009] In some embodiments, the resistance of the positive electrode sheet is 0.1 Ω to 5 Ω. When the resistance of the positive electrode sheet is within the above range, the resistance of the positive electrode sheet is relatively small, which is beneficial to reducing the internal resistance of the battery cell.

[0010] In some embodiments, the resistance of the positive electrode sheet is 0.1 Ω to 1 Ω. When the resistance of the positive electrode sheet is within the above range, the resistance of the positive electrode sheet is relatively small, which is beneficial to reducing the internal resistance of the battery cell.

[0011] In some embodiments, the resistance of the negative electrode sheet is 0.001 Ω to 0.005 Ω. When the resistance of the negative electrode sheet is within the above range, the resistance of the negative electrode sheet is relatively small, which is beneficial to reducing the internal resistance of the battery cell.

[0012] In some embodiments, the viscosity of the electrolyte at room temperature is 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.

[0013] In some embodiments, the density of the electrolyte at room temperature is 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.

[0014] In some embodiments, when the battery cell is in a 100% charged state, the compaction 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 . 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. Moreover, since the positive electrode active materials in the positive electrode film layer are stacked relatively tightly and the contact resistance between particles is small, the resistance of the electrode sheet can be further reduced, thereby reducing heat generation.

[0015] In some embodiments, the single-sided coating weight of the positive electrode film layer is 240 mg / 1540.25 mm 2 to 330 mg / 1540.25 mm 2 . 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 sheet will not be too large, and the energy density of the battery cell can be improved while taking it into account.

[0016] In some embodiments, when the battery cell is in a 100% charged state, the compaction 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 . 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. Moreover, since the negative electrode active materials in the negative electrode film layer are stacked relatively tightly and the contact resistance between particles is small, the resistance of the electrode sheet can be further reduced, thereby reducing heat generation.

[0017] In some embodiments, the single-sided coating weight of the negative electrode film layer is 90 mg / 1540.25 mm 2 to 170 mg / 1540.25 mm 2 , optionally 110 mg / 1540.25 mm 2 to 150 mg / 1540.25 mm 2 . When the single-sided coating weight of the negative electrode film layer is within the above range, the heat generation per unit area of the negative electrode sheet will not be too large, and the energy density of the battery cell can be improved while taking it into account.

[0018] In some embodiments, the powder resistivity of the positive electrode active material is from 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 in the battery cell.

[0019] 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 packed more tightly, the contact resistance between particles is small, which can further reduce the resistance of the electrode sheet, thereby reducing heat generation.

[0020] In some embodiments, the charging specific capacity of the positive electrode active material at a rate of 0.1 C is from 150 mAh / g to 170 mAh / g. When the charging specific capacity of the positive 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.

[0021] In some embodiments, the powder resistivity of the negative electrode active material is from 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 in the battery cell.

[0022] 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, the energy density of the battery cell can be improved, and since the negative electrode active materials in the negative electrode film layer can be packed more tightly, the contact resistance between particles is small, which can further reduce the resistance of the electrode sheet, thereby reducing heat generation.

[0023] In some embodiments, the charging specific capacity of the negative electrode active material at a rate of 0.1 C is greater than or equal to 350 mAh / g. 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.

[0024] In some embodiments, the lithium-containing phosphate in 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 of 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 in 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 amount of the battery cell.

[0025] In some embodiments, the phosphate particles comprise a compound of the general formula Li x1 A y1 Me a M b P 1-c X c Y z where 0.5 ≤ x 1 ≤ 1.3, 0 ≤ y 1 ≤ 1.3, and 0.9 ≤ x 1 + y 1 ≤ 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 comprises one or more of Na, K, Mg, Me comprises one or more of Mn, Fe, Co, Ni, M comprises 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 comprises one or more of S, Si, Cl, B, C, N, and Y comprises one or more of O, F. The phosphate particles have excellent cycle stability, which is beneficial to improving the cycle performance of the battery cell.

[0026] In some embodiments, the coating layer comprises a fast ion conductor of 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 < x 2 < 5, 0 < y 2 < 4. Coating the phosphate particles with the fast ion conductor can significantly increase the transport rate of lithium ions during multiple deintercalation / insertion of lithium 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.

[0027] In some embodiments, the graphitization degree of the positive electrode active material is from 0.15 to 0.32, and may be selected 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 and reduce the heat generation of the positive electrode sheet, thereby reducing the heat generation of the battery cell.

[0028] 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, and may be 7.5 m2 / g to 14 m 2 / g.

[0029] Thus, in the embodiments of the present application, the carbon element with the above mass content in combination with the material with the above specific surface area is more conducive to the effective contact between the electrolyte and the lithium-containing phosphate in the olivine structure, and is conducive to the transport of lithium ions at the phase interface.

[0030] In some embodiments, the lithium-containing phosphate in the olivine structure is granular, 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 in the olivine structure is relatively small, the lithium 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 process, so that the performance of the positive electrode active material is stable.

[0031] In some embodiments, the lithium-containing phosphate in the olivine structure is granular, the lithium-containing phosphate in the olivine structure includes secondary particles, the secondary particles include a plurality of primary particles, and the average particle size of the primary particles is 200 nm to 500 nm. 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.

[0032] 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, trilithium citrate, lithium nickelate, and lithium ferrate. The above materials can supplement lithium ions to 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.

[0033] In some embodiments, the thickness of the positive electrode current collector is 10 µm to 15 µm. When the thickness of the positive electrode current collector is within the above range, the current-carrying capacity of the positive electrode current collector is relatively excellent, and the battery cell can have a relatively high energy density.

[0034] 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 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.

[0035] 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 can also take into account the improvement of the energy density of the battery cell.

[0036] 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 sheet, reducing the heat generation of the battery cell, and the positive electrode binder in the positive electrode conductive layer can improve the adhesion performance between the positive electrode current collector and the positive electrode film layer, and improve the structural stability of the positive electrode sheet.

[0037] 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.

[0038] 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.

[0039] 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.

[0040] 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.

[0041] 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.

[0042] 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, 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, 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.

[0043] Therefore, there are differences in the particle sizes of the first negative electrode film layer and the second negative electrode film layer in the embodiments of the present application, 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 transmission path of lithium ions, improve the fast charging performance, and can also improve the problem of lithium plating on the surface layer of the negative electrode sheet.

[0044] In some embodiments, the carbon-based material in the first negative electrode film layer further includes natural graphite.

[0045] 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 filling of the second negative electrode film layer is more dense, which improves the energy density of the battery cell. The filling of the first negative electrode film layer is relatively sparse and has more pores, which can improve the fast charging performance of the battery cell.

[0046] 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.

[0047] 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. 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.

[0048] 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 transmission can be reduced, and the fast charging performance of the battery cell can be improved.

[0049] 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.

[0050] 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 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.

[0051] 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 insertion and extraction rate of lithium ions can be improved, and the fast charging performance of the battery cell can be improved.

[0052] 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 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 insertion and extraction rate of lithium ions, and improve the fast charging performance of the battery cell.

[0053] 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 insertion and extraction rate of lithium ions is improved, and the fast charging performance of the battery cell is improved.

[0054] 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 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 insertion and extraction rate of lithium ions, and improve the fast charging performance of the battery cell.

[0055] In some embodiments, 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 ratio of the lithium acrylate monomer, the acrylonitrile monomer, the acrylamide monomer, and the 2-hydroxyethyl acrylate monomer is 30% to 50%: 15% to 45%: 5% to 20%: 20% to 35%.

[0056] Thus, the lithium-containing binder of the above material can provide a certain amount of lithium ions for the negative electrode film layer, improving the fast charging performance of the battery cell. Moreover, it is not prone to swelling during the charge and discharge process, with a stable structure, enabling the negative electrode film layer to have improved cycling performance during fast charging and discharging.

[0057] In some embodiments, the second lithium-containing binder includes a lithium acrylate-acrylonitrile-acrylamide-2-hydroxyethyl acrylate copolymer, which is derived from lithium acrylate monomer, acrylonitrile monomer, acrylamide monomer, and 2-hydroxyethyl acrylate monomer. The molar ratio of the lithium acrylate monomer, acrylonitrile monomer, acrylamide monomer, and 2-hydroxyethyl acrylate monomer is 30% to 50%: 15% to 45%: 5% to 20%: 20% to 35%.

[0058] Thus, the lithium-containing binder of the above material can provide a certain amount of lithium ions for the negative electrode film layer, improving the fast charging performance of the battery cell. Moreover, it is not prone to swelling during the charge and discharge process, with a stable structure, enabling the negative electrode film layer to have improved cycling performance during fast charging and discharging.

[0059] In some embodiments, the negative electrode active material further includes a silicon-based material, and the mass 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. 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.

[0060] In some embodiments, the thickness of the negative electrode current collector is 4 μm to 6 μm. When the thickness of the negative electrode current collector is within the above range, the current-carrying capacity of the negative electrode current collector is relatively excellent, and it can enable the battery cell to have a high energy density.

[0061] In some embodiments, the negative electrode sheet further includes a negative electrode conductive layer, which is located between the negative electrode film layer and the negative electrode current collector.

[0062] 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 conductivity of the negative electrode sheet and reduce the heat generation of the negative electrode sheet, thereby reducing the heat generation amount of the battery cell.

[0063] 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 sheet and reducing the heat generation amount 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 enhance the structural stability of the negative electrode sheet.

[0064] In some embodiments, the anode 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.

[0065] In some embodiments, the anode 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.

[0066] In some embodiments, the separator includes a base film with a porous structure, and the porosity of the base film is 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, and thus the heat generation can be reduced.

[0067] In some embodiments, the separator includes a base film with a porous structure, and the porosity of the base film is 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, and thus the heat generation can be reduced.

[0068] In some embodiments, the thickness of the base film is 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, the internal resistance of the battery cell can be further reduced, and thus the heat generation can be reduced.

[0069] In some embodiments, the thickness of the base film is 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, the internal resistance of the battery cell can be further reduced, and thus the heat generation can be reduced.

[0070] In some embodiments, the separator 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 the non-fluoropolymer particles 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.

[0071] In some embodiments, the non-fluoropolymer particles include acrylate copolymers. Acrylate copolymers have excellent adhesion properties and high adhesion stability with the base film.

[0072] 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-mentioned first inorganic particles can improve the heat resistance of the first functional layer.

[0073] 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-mentioned second inorganic particles can improve the heat resistance of the first functional layer.

[0074] 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 within the above range, it is beneficial to improve the heat resistance and compression modulus of the composite particles.

[0075] 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 10% and less than or equal to 75%, optionally 30% to 70%, and optionally 50% to 70%. 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.

[0076] In some embodiments, the chain carboxylic ester solvent includes a compound represented by Formula I, Formula I, In Formula I, R 1 includes a hydrogen atom, a halogen atom, a C1-C5 alkyl group, or a C1-C5 haloalkyl group, R 2 includes a C1-C5 alkyl group or a C1-C5 haloalkyl group.

[0077] Therefore, the conductivity of the above-mentioned 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.

[0078] In some embodiments, R 1 includes a hydrogen atom, a halogen atom, a C1-C3 alkyl group, or a C1-C3 haloalkyl group.

[0079] In some embodiments, in some embodiments, R 2 includes a C1-C3 alkyl group or a C1-C3 haloalkyl group.

[0080] In some embodiments, the chain carboxylic ester solvent includes one or more of the compounds represented by Formula I-1 to Formula I-8,

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

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

[0083] In some embodiments, the mass content of the carbonate solvents in the organic solvent is 30% to 70%, and may be optionally 30% to 50%. The carbonate solvents with the above mass content can further improve the conductivity of the electrolyte and are beneficial to the migration of lithium ions.

[0084] In some embodiments, the electrolyte further includes additives, and the additives include one or more of carbonate additives, sulfur-containing additives, and lithium salt additives. 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 cell and improving the cycle performance.

[0085] In some embodiments, the carbonate additives include one or more of vinylene carbonate (VC) and fluoroethylene carbonate (FEC).

[0086] In some embodiments, 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 methanedisulfonate (MMDS).

[0087] In some embodiments, the lithium salt additives include lithium difluorophosphate LiPO 2 F 2 , lithium difluorooxalate borate LiDFOB, lithium tetrafluoroborate LiBF 4 , and one or more of lithium bis(oxalate) borate LiBOB.

[0088] In some embodiments, the mass content of the additives in the electrolyte is 1% to 10%, and may be optionally 2% to 8%. The additives 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 fluorosulfonylimide salts and lithium hexafluorophosphate LiPF 6 . 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.

[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 (LiPF 6 , 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 (LiPF 6 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 (LiPF 6 is from 0.2 to 1.0.

[0093] In some embodiments, the base material of the housing includes steel, the thickness of the housing is from 0.1 mm to 0.5 mm, and may be selected from 0.2 mm to 0.35 mm. When the thickness of the housing is within the above range, the mechanical strength of the housing is relatively high, which can improve the use reliability and cycle performance of the battery cell, and the housing occupies less space and there is more internal space in the housing, which is beneficial to improving the energy density of the battery cell.

[0094] In some embodiments, the battery cell further includes an electrode terminal, and the electrode assembly includes a tab, and the tab is directly welded to the electrode terminal. Direct welding can reduce the resistance at the connection, which is beneficial to reducing the overall internal resistance of the battery cell.

[0095] In some embodiments, the charging time of the battery cell from 10% state of charge to 80% state of charge is from 5 min to 10.5 min. The charging speed of the battery cell is relatively fast, which is more beneficial to improving the fast charging ability.

[0096] In a second aspect, the present application provides a battery device, and the battery device includes a plurality of battery cells according to any one of the embodiments of the first aspect of the present application.

[0097] In some embodiments, the charging time of the battery device from 10% state of charge to 80% state of charge is from 5 min to 10.5 min. The charging speed of the battery device is relatively fast, which is more beneficial to improving the fast charging ability.

[0098] 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 of the second aspect of the present application. Description of the Drawings

[0099] To more clearly illustrate the technical solutions of the embodiments of the present application, the following will briefly introduce the drawings required for use in the embodiments of the present application. Obviously, the following described drawings are only some embodiments of the present application. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on the drawings.

[0100] Figure 1 It is a schematic structural diagram of a battery cell provided in some embodiments of the present application. Figure 2 It is an exploded schematic diagram of a battery cell provided in some embodiments of the present application. Figure 3 It is a schematic structural diagram of a battery module provided in some embodiments of the present application. Figure 4 It is a schematic structural diagram of a battery pack provided in some embodiments of the present application. Figure 5 It is a schematic structural diagram of an electrical device provided in some embodiments of the present application.

[0101] The drawings are not necessarily drawn to actual scale.

[0102] The descriptions of the reference numerals are as follows: 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, 7. Battery cell, 10. Electrode assembly, 111. First tab, 112. Second tab, 12. Main body part, 20. Outer shell, 21. Housing, 22. End cover, 31. First electrode terminal, 32. Second electrode terminal. Specific embodiments

[0103] Hereinafter, embodiments of the battery cell, battery device, and electrical device of the present application will be specifically disclosed 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 the following description from becoming unnecessarily lengthy and to facilitate the understanding of those skilled in the art. In addition, the drawings and the following description are provided for those skilled in the art to fully understand the present application and are not intended to limit the subject matter described in the claims.

[0104] 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" have been 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.

[0105] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined with each other to form new technical solutions.

[0106] Unless otherwise specified, all technical features and optional technical features of this application can be combined with each other to form new technical solutions.

[0107] Unless otherwise specified, all steps of this application can be carried out sequentially or randomly, preferably sequentially. For example, if the 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.

[0108] During the charge and discharge process of a battery cell, a thermal effect will occur. Specifically, during the charging process, the external power supply provides electrical energy to the battery cell, and a series of chemical reactions are triggered inside the battery, generating heat energy, which causes the temperature of the battery cell to rise during the charging process. During the discharging process, the battery cell converts chemical energy into electrical energy and simultaneously generates heat energy, which causes the temperature of the battery cell to rise during the discharging process. The increase in the temperature of the battery cell reduces the reliability of the battery cell during use, and even triggers thermal runaway, and deteriorates the cycle performance. And these problems are particularly significant in the batteries of fast charging systems.

[0109] In view of the above problems, the embodiments of the present application reasonably design the system of the battery cell, reduce the internal resistance of the battery cell, and reduce the heat generation of the battery cell. Specifically, by reasonably configuring the characteristics of the positive electrode sheet, negative electrode sheet, and electrolyte that affect the internal resistance of the battery, the internal resistance of the battery cell can be further reduced, thereby reducing heat generation, and the use reliability and cycle performance of the battery cell can be improved.

[0110] Battery cell In a first aspect, an embodiment of the present application provides a battery cell.

[0111] The battery cell includes an electrode assembly, an electrolyte, and a housing. The electrode assembly and the electrolyte are accommodated in the housing. The electrode assembly includes a positive electrode sheet, a negative electrode sheet, and a separator. The positive electrode sheet includes a positive current collector and a positive electrode film layer provided on at least one side of the positive current collector. The positive electrode film layer includes a positive active material. The positive active material includes a lithium phosphate with an olivine structure. The resistance of the positive electrode sheet is 0.1 Ω to 30 Ω. The negative electrode sheet includes a negative current collector and a negative electrode film layer provided on at least one side of the negative current collector. The negative electrode film layer includes a negative active material. The resistance of the negative electrode sheet is 0.001 Ω to 0.01 Ω. The separator is located between the positive electrode sheet and the negative electrode sheet. The electrolyte includes an organic solvent. The organic solvent includes a chain carboxylic ester solvent. The conductivity of the electrolyte at room temperature is 13 mS / cm to 20 mS / cm.

[0112] In the embodiment of the present application, the positive active material includes a lithium phosphate with an olivine structure, and the cycle stability of this material system is relatively high. Further, by synergistically controlling the resistance of the positive electrode sheet, the resistance of the negative electrode sheet, and the conductivity of the electrolyte within a reasonable range, on the one hand, the transmission resistance of lithium ions inside the battery cell can be reduced, the fast charging ability of the battery can be improved, and the internal resistance DCR of the battery can be reduced. On the other hand, the cycle attenuation caused by excessive temperature rise during the fast charging process of the battery cell can be improved. On the other hand, the problem of uneven temperature rise during the fast charging process of the battery can also be improved, and the cycle attenuation problem caused by lithium plating of the battery cell can be reduced. In addition, by controlling the resistance of the positive and negative electrode sheets within a reasonable range, the internal temperature of the battery cell can be controlled within the reasonable range tolerated by the high-conductivity electrolyte, and the risk of weakening the fast charging performance of the battery due to the volatilization of the solvent components of the electrolyte can be reduced.

[0113] In summary, the battery cell of the embodiment of the present application has the advantages of fast charging, low DCR, and good cycle performance.

[0114] In the embodiment of the present application, the resistance of the positive electrode sheet can be adjusted by adjusting the material of the positive active material, such as adjusting the graphitization degree, powder resistivity, etc. of the positive active material.

[0115] In the embodiments of the present application, the resistance of the negative electrode sheet can be adjusted by adjusting the material of the negative electrode active material. For example, the graphitization degree, powder resistivity, etc. of the negative electrode active material can be adjusted.

[0116] In the embodiments of the present application, the conductivity of the electrolyte can be adjusted by adjusting the mass content of the chain carboxylic ester solvent in the organic solvent in the electrolyte.

[0117] The upper charge limit voltage and the lower discharge cut-off voltage of the battery cell are different according to the different positive electrode active materials. For example, when the phosphate material includes lithium iron phosphate, the upper charge limit voltage can be 3.65 V and the lower discharge cut-off voltage can be 2.0 V. Also, for example, when the phosphate material includes lithium manganese iron phosphate, the upper charge limit voltage can be 4.3 V and the lower discharge cut-off voltage can be 2.0 V. Next, taking the upper charge limit voltage of 3.65 V and the lower discharge cut-off voltage of 2.0 V as an example, the state of the battery cell will be described: In the embodiments of the present application, the 100% state of charge (SOC) and 0% SOC of the battery cell are defined as follows. Charge the battery cell at a constant current charge rate of 0.33 C to the upper charge limit voltage, and then charge at a constant voltage until 0.05 C, corresponding to the state of 100% SOC of the battery cell. Discharge the battery cell at a constant current discharge rate of 0.33 C to the cut-off voltage, corresponding to the state of 0% SOC of the battery cell.

[0118] In the embodiments of the present application, the sheet resistance refers to the ability of current to flow through the sheet (the overcurrent area is the cross-section along the thickness direction of the current collector and the film layers containing electrode materials on both sides of the current collector). The following equipment and methods can be used for detection: As an example, after discharging the battery to 0% SOC, disassemble the sheet. Clean the sheet more than three times with a solvent such as dimethyl carbonate (DMC). Twenty parallel samples can be taken along the central axis of the sheet. Each sample is symmetric about the central axis, and the size of each sample is 4 cm × 25 cm. Among them, the central axis can be parallel to the length direction of the sheet. Use a film resistance tester (Yueneng Technology, model BER2500) to test the above 20 parallel samples, and after calculating the average value, it is used as the sheet resistance of this sheet.

[0119] [Positive electrode sheet] The positive electrode sheet includes a positive electrode current collector and a positive electrode film layer provided on at least one surface of the positive electrode current collector and including a positive electrode active material. For example, the positive electrode current collector has two opposite surfaces in its own thickness direction, and the positive electrode film layer is provided on any one or both of the two opposite surfaces of the positive electrode current collector.

[0120] In the embodiments of the present application, the resistance of the positive electrode plate is from 0.1 Ω to 30 Ω, optionally from 0.1 Ω to 5 Ω, and further optionally from 0.1 Ω to 1 Ω. Exemplarily, the resistance of the positive electrode plate is 0.1 Ω, 0.5 Ω, 1 Ω, 1.5 Ω, 2 Ω, 2.5 Ω, 3 Ω, 3.5 Ω, 4 Ω, 4.5 Ω, 5 Ω, 5.5 Ω, 6 Ω, 6.5 Ω, 7 Ω, 7.5 Ω, 8 Ω, 8.5 Ω, 9 Ω, 9.5 Ω, 10 Ω, 10.5 Ω, 11 Ω, 11.5 Ω, 12 Ω, 12.5 Ω, 13 Ω, 13.5 Ω, 14 Ω, 14.5 Ω, 15 Ω, 15.5 Ω, 16 Ω, 16.5 Ω, 17 Ω, 17.5 Ω, 18 Ω, 18.5 Ω, 19 Ω, 20 Ω, 21 Ω, 22 Ω, 23 Ω, 24 Ω, 25 Ω, 26 Ω, 27 Ω, 28 Ω, 29 Ω, 30 Ω or a range composed of any two of the above values.

[0121] When the resistance of the positive electrode plate is within the above range, the resistance of the positive electrode plate is more adaptable to the resistance of the negative electrode plate of the battery cell and the electrolyte system, which is beneficial to reducing the internal resistance of the battery cell and optimizing the electrical performance of the battery cell.

[0122] In some embodiments, 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 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.

[0123] 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. Moreover, since the positive electrode active materials in the positive electrode film layer are stacked relatively closely, 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 compaction density of the positive electrode film layer to a reasonable range, the battery cell has both high energy density and high charging rate performance.

[0124] In some embodiments, the single-sided coating weight of the positive electrode film layer is 200 mg / 1540.25 mm 2 to 370 mg / 1540.25 mm 2 , and can be optionally 240 mg / 1540.25 mm 2 to 330 mg / 1540.25 mm 2 . Exemplarily, the single-sided coating weight of the 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 mm 2 , 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.

[0125] 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 sheet will not be excessive, and it can balance the improvement of the energy density and charging rate performance of the battery cell.

[0126] In the embodiments of the present application, the compaction density of the positive electrode film layer of the battery cell at 100% state of charge (SOC) can be detected by the following method. Disassemble the positive electrode plate from the battery cell at 100% SOC, and measure the compaction density of the positive electrode film layer. For example, take a positive electrode plate with single-sided coating (if it is a double-sided coated electrode plate, the positive electrode film layer on one side can be wiped off first), punch it into small round pieces with an area of S1, weigh it, record it as M1, and measure its thickness H1. Then wipe off the positive electrode film layer of the above-mentioned weighed positive electrode plate, weigh the weight of the positive electrode current collector, record it as M0, and measure its thickness H0. The single-sided coating weight of the positive electrode film layer = (the weight M1 of the positive electrode plate - 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 plate - the thickness H0 of the positive electrode current collector, and the compaction 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.

[0127] In some embodiments, the powder resistivity of the positive electrode active material is from 1 Ω·cm to 27.5 Ω·cm. Optionally, it is less than or equal to 20 Ω·cm. Optionally, it is 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.

[0128] The relatively low powder resistivity of the positive electrode active material results in a relatively low resistance of the positive electrode plate and less heat generation of the battery cell.

[0129] 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, use a PRCD1100 powder resistivity meter for testing.

[0130] 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 . Exemplarily, the powder compaction 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 / cm3 , 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 a range composed of any two of the above values.

[0131] When the powder compaction density of the positive electrode active material is within the above range under 30000 N, 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 tightly and the contact resistance between particles is small, the resistance of the electrode sheet can be further reduced, thereby reducing heat generation.

[0132] 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 a UTM7305 type electronic pressure testing machine, pressurized to 3000 kg (equivalent to 30000 N), kept under pressure for 30 s, then the pressure is released, kept for 10 s, and then the powder compaction density of the positive electrode active material under the action of 30000 N is recorded and calculated.

[0133] 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, and can be optionally 157 mAh / g to 170 mAh / g. Exemplarily, the charging specific capacity of the positive electrode active material at a 0.1C rate 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 a range composed of any two of the above values.

[0134] 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.

[0135] 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 the 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 cell is assembled. Under the condition of 23°C ± 2°C, the half-button cell 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. Then, the capacity is divided by the mass of the active material of the electrode sheet to obtain the charging specific capacity parameter.

[0136] In some embodiments, the mass ratio 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 ratio of the lithium-containing phosphate with an olivine structure is less than 100%, the positive electrode active material can also include common positive electrode active materials, such as, but not limited to, at least one of lithium-containing transition metal oxides. Examples of the lithium-containing transition metal oxides can include, but 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.

[0137] Optionally, the mass ratio of the lithium-containing phosphate with an olivine structure in the positive electrode active material is 100%.

[0138] In the embodiments of the present application, the lithium-containing phosphate with an olivine structure can be phosphate particles or the 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 coats the surface of the phosphate particles, and the coating layer contains one or more elements of C, Fe, Ti, Zr, Hf, Ge, and Sn.

[0139] By surface coating the coating layer on the phosphate particles, 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.

[0140] 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 ≤ x 1 ≤ 1.3, 0 ≤ y1 ≤1.3, and 0.9 ≤ x 1 + y 1 ≤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 cyclic stability of the phosphate particles is relatively excellent, which is beneficial to improving the cyclic performance of the battery cell.

[0141] Exemplarily, the phosphate particles include LiFePO 4 , LiMnPO 4 , LiNiPO 4 , LiCoPO 4 or one or more of them. During the charge and discharge process of the battery cell, the insertion and extraction and consumption of active ions such as Li will occur, and the molar content of Li is different when the battery cell is discharged to different states. Regarding the positive electrode active materials LiFePO 4 , LiMnPO 4 , LiNiPO 4 , LiCoPO 4 etc., the molar content of Li is the initial state of the material, that is, the state before feeding. When the positive electrode active material is applied to the battery system and undergoes charge and discharge cycles, the molar content of Li may change. In the embodiments of the present application, regarding the positive electrode active materials LiFePO 4 , LiMnPO 4 , LiNiPO 4 , LiCoPO 4 etc., the molar content of oxygen O is only the theoretical state value, and the release of oxygen from the lattice will cause the molar content of oxygen O to change. Actually, the molar content of oxygen O will fluctuate, and the above situations are all within the protection scope of the present application.

[0142] In some embodiments, the coating layer includes a fast ion conductor with the general formula Li 3-d Fe 2-d M2 d (PO x2 ) y2 , M2 includes one or more elements of Ti, Zr, Hf, Ge, and Sn, 0 ≤ d ≤ 1, 0 < x 2 <5, 0 < y 2 <4.

[0143] Exemplarily, the fast ion conductor is a material having a NASICON structure, such as including 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.

[0144] The fast ion conductor having a NASICON structure is a material with ultrafast ion conduction ability, having rich three-dimensional lithium ion diffusion and transport channels, and having advantages such as high ion conduction efficiency and strong structural stability during multiple de-lithiation and lithiation processes. Coating the surface of the phosphate particles with a fast ion conductor containing a NASICON structure can significantly improve the transport rate of lithium ions during multiple de-lithiation / insertion at the positive electrode, improve the ion conductivity of the positive electrode active material, improve the fast charging ability of the battery cell, and in addition, can also improve the specific capacity and the energy density of the corresponding battery cell.

[0145] In some embodiments, the coating layer further includes elemental carbon.

[0146] The elemental carbon and the fast ion conductor can be arranged in layers. For example, the elemental carbon 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 away from the phosphate particles. Or, 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 away from the phosphate particles. Of course, the elemental carbon and the fast ion conductor can also be arranged in the same layer.

[0147] Optionally, the carbon coating layer can be formed by carbonizing an organic carbon source (such as glucose, polyethylene glycol, etc.) on the surface of the fast ion conductor layer. The carbon coating layer can partially coat the fast ion conductor layer or can completely coat the fast ion conductor layer. The setting of the carbon coating layer can significantly improve the electronic conductivity of the phosphate particles, make up for the defect of poor electronic conduction performance of the phosphate particles, and improve the energy density of the battery cell. Specifically, the setting of the carbon coating layer endows the positive electrode active material of the present application with the following advantages: The carbon coating layer in the positive electrode active material of the present application provides a suitable channel for the transport of electrons, can significantly improve the conduction rate of electrons during multiple de-lithiation and lithiation processes, improve the electronic conductivity of the lithium-containing phosphate, improve the charging ability of the corresponding battery cell, and can also improve the energy density.

[0148] The carbon coating layer of the positive electrode active material of the present application is loose and porous, enabling the electrolyte to come into full and effective contact with the lithium-containing phosphate, thereby improving the lithium ion transport rate at the phase interface and enhancing the charging capacity of the battery cell.

[0149] Coating a layer of carbon coating on the surface of the lithium-containing phosphate can not only improve the electrical conductivity of the lithium-containing phosphate, but also enhance the structural stability of the positive electrode active material, effectively alleviating the iron dissolution phenomenon of the positive electrode active material during the long-term storage and cyclic use of the battery cell, thereby improving the cycle life of the battery cell. The positive electrode active material of the present application uses lithium-containing phosphate as the base material, giving full play to the advantages of low cost, high use reliability, and good cycle stability of the lithium-containing phosphate. At the same time, the coating layer (fast ion conductor layer and carbon coating layer) is used to solve the disadvantages of poor electronic and ionic conductivity. The battery cell prepared from the positive electrode active material of the present application can improve the energy density of the battery cell on the premise of excellent cycle performance. 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 the battery cell is discharged to 0% state of charge (SOC) and the positive electrode plate is disassembled, it is washed with DMC and dried, and then after high-temperature calcination to remove impurities, 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.

[0150] In some embodiments, the graphitization degree of the positive electrode active material is 0.15 to 0.32, and can be selected as 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 the range composed of any two of the above values.

[0151] When the graphitization degree of the positive electrode active material is within the above range, it is beneficial to improve the electrical conductivity of the positive electrode active material, reduce the heat generation of the positive electrode plate, and thus reduce the heat generation of the battery cell.

[0152] 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 of JIS / K 0131-1996.

[0153] In some embodiments, the mass content of carbon 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.

[0154] Optionally, the mass content of carbon 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.

[0155] Exemplarily, the mass content of carbon 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.

[0156] Exemplarily, the specific surface area of the lithium-containing phosphate with 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.

[0157] Carbon mainly exists 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 transport of lithium ions at the phase interface. In addition, when the mass content of carbon is within the above range, it can significantly improve the conductivity of the lithium-containing phosphate with olivine structure, which is beneficial to enhancing the ionic conductivity and electronic conductivity of the lithium-containing phosphate with olivine structure, and can improve the rapid charging ability and energy density of the battery cell.

[0158] 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 devices and methods well-known in the art. For example, detection is carried out in accordance with 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 of Micromeritics Corporation of the United States.

[0159] 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.

[0160] 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.

[0161] Exemplarily, 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.

[0162] 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 basically no agglomeration occurs during the processing and preparation process, making the performance of the positive electrode active material stable.

[0163] 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 devices and methods well-known in the art. For example, taking the positive electrode active material as a sample, in accordance with the test standard GB / T 19077-2016, the Dv50 and Dv10 of the particles are tested by a Mastersizer 2000E laser particle size analyzer.

[0164] When the positive electrode active material includes other materials in addition to the lithium 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.

[0165] In some embodiments, the lithium-containing phosphate of olivine structure is granular. The lithium-containing phosphate of olivine structure includes secondary particles, and the secondary particles include a plurality of primary particles. The average particle size of the primary particles is from 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.

[0166] The average particle size of the primary particles is relatively small, the lithium deintercalation / insertion path of lithium ions in the cathode active material is short, and the heat generation is less.

[0167] In the embodiments of the present application, the secondary particles refer to agglomerated particles formed by aggregation of two or more primary particles. The primary particles and the 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 images of the scanning electron microscope. The SEM test parameters can be set as: 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.

[0168] In some embodiments, the cathode 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 to the cathode 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.

[0169] Optionally, the ternary material includes Li x3 A y3 Ni a3 Co b3 Mn c M3 (1-a3-b3-c3) Y3 z3 where 0 < x 3 ≤ 2.1, 0 < y 3 ≤ 2.1, and 0.9 ≤ x 3 + y 3 ≤ 2.1, 0 ≤ a 3 ≤ 1, 0 ≤ b 3 ≤ 1, 0 ≤ c 3 ≤ 1, and 0.1 ≤ a 3 + b 3 + c 3 ≤ 1, 1.8 ≤ z 3≤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.

[0170] Exemplarily, the ternary material includes LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O 2 (NCM333), LiNi 0.5 Co 0.2 Mn 0.3 O 2 (NCM523), LiNi 0.6 Co 0.2 Mn 0.2 O 2 (NCM622), LiNi 0.8 Co 0.1 Mn 0.1 O 2 (NCM811), LiNi 0.80 Co 0.15 Al 0.05 O 2 at least one of.

[0171] 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.

[0172] 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 cycle 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.

[0173] 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%.

[0174] 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%.

[0175] In some embodiments, the positive electrode current collector may be a metal foil or a composite current collector. By way of example of the metal foil, at least one foil of aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy may be used. The composite current collector may include a polymer material base layer and a metal material layer formed on at least one surface of the polymer material base layer. By way of example, the metal material of the metal material layer may include at least one of aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy. By way of example, the polymer material base layer may include at least one of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0176] In some embodiments, the ratio of the thickness of the positive electrode current collector to the thickness of the single-sided positive electrode film layer is 0.05 to 0.3. Exemplarily, the ratio of the thickness of the positive electrode current collector to the thickness of the single-sided positive electrode film layer is 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, 0.12, 0.15, 0.18, 0.2, 0.22, 0.25, 0.28, 0.3 or a range composed of any two of the above values.

[0177] When the ratio of the thickness of the positive electrode current collector to the thickness of the single-sided positive electrode film layer is within the above range, the fast charging ability and energy density of the battery cell can be improved.

[0178] In some embodiments, the thickness of the positive current collector is from 10 μm to 15 μm, optionally from 12 μm to 15 μm. Exemplarily, the thickness of the positive current collector is 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 a range composed of any two of the above values.

[0179] 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 it can enable the battery cell to have a relatively high energy density.

[0180] In the embodiments of the present application, the thicknesses of the positive electrode film layer and the positive current collector have meanings well-known in the art, and can be detected by devices 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 current collector is removed, and the thickness of the positive 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 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 current collector) / 2.

[0181] The positive electrode film layer is usually formed by coating a positive electrode slurry on a positive 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.

[0182] The positive electrode plate does not exclude other additional functional layers in addition to 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 current collector and the positive electrode film layer and disposed on the surface of the positive 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.

[0183] 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 current collector. The positive electrode conductive layer can further improve the conductivity of the positive electrode plate and reduce the heat generation of the positive electrode plate, thereby reducing the heat generation of the battery cell.

[0184] In some embodiments, the thickness of the positive electrode conductive layer is from 0.5 μm to 2 μm. Exemplarily, 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 composed of any two of the above values.

[0185] 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 while taking into account.

[0186] In the embodiments of the present application, the thickness of the positive electrode conductive layer 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, tomographic scanning is performed on the positive electrode sheet to directly measure the thickness of the positive electrode conductive layer.

[0187] In some embodiments, the positive electrode conductive layer includes one or more of a positive electrode conductive agent and a positive electrode binder.

[0188] 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 composed of any two of the above values.

[0189] Exemplarily, 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 the heat generation amount of the battery cell.

[0190] Optionally, the mass content of the positive electrode binder in the positive electrode conductive layer is 50% to 70%. Exemplarily, 50%, 60%, 65%, 70% or a range composed of any two of the above values.

[0191] Exemplarily, 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. 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 sheet.

[0192] [Negative electrode sheet] The negative electrode sheet includes a negative electrode current collector and a negative electrode film layer provided on at least one surface of the negative electrode current collector and including a negative electrode active material. For example, the negative electrode current collector has two surfaces opposite to each other in its own thickness direction, and the negative electrode film layer is provided on any one or both of the two opposite surfaces of the negative electrode current collector.

[0193] In the embodiments of the present application, the resistance of the negative electrode plate is from 0.001 Ω to 0.01 Ω, and may be optionally from 0.001 Ω to 0.005 Ω. Exemplarily, the resistance of the negative electrode plate is 0.001 Ω, 0.002 Ω, 0.003 Ω, 0.004 Ω, 0.005 Ω, 0.006 Ω, 0.007 Ω, 0.008 Ω, 0.009 Ω, 0.01 Ω or the range composed of any two of the above values.

[0194] When the resistance of the negative electrode plate is within the above range, the resistance of the negative electrode plate is relatively small, which is beneficial to reducing the internal resistance of the battery cell.

[0195] In the embodiments of the present application, the resistance of the negative electrode plate 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 resistance test method of the positive electrode plate described above.

[0196] 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 , and may be optionally 1.25 g / cm 3 to 1.36 g / cm 3 . Exemplarily, 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 , 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 the range composed of any two of the above values.

[0197] 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 active materials in the negative electrode film layer are stacked relatively closely, the contact resistance between particles is small, which can further reduce the resistance of the electrode plate and thus reduce heat generation.

[0198] In the embodiments of the present application, the tap density of the negative electrode film layer when the battery cell is in a 100% charged state 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 tap density test method of the positive electrode film layer described above.

[0199] In some embodiments, the single-sided coating weight of the negative electrode film layer is 90 mg / 1540.25 mm2 to 170 mg / 1540.25 mm 2 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 mm2 、165 mg / 1540.25 mm 2 、170 mg / 1540.25 mm 2 Or a range composed of any two of the above values.

[0200] When the single-sided coating weight of the negative electrode film layer is within the above range, the heat generation per unit area of the negative electrode sheet will not be excessive, and it can also take into account the improvement of the energy density of the battery cell.

[0201] In the embodiments of the present application, the single-sided coating weight of the negative electrode film layer has the meaning well-known in the art and can be detected by using the equipment and methods well-known in the art. The detection method is as described in the single-sided coating weight test method of the film layer above.

[0202] In some embodiments, the powder resistivity of the negative electrode active material is from 0.005 Ω·cm to 0.043 Ω·cm, and can be 0.04 Ω·cm. Exemplarily, the powder resistivity of the negative electrode active material can 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.

[0203] The relatively low powder resistivity of the negative electrode active material makes the resistance of the negative electrode sheet relatively low, and the heat generation of the battery cell is less.

[0204] 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 using the equipment and methods well-known in the art. The detection method is as described in the powder resistivity test method of the positive electrode active material above.

[0205] 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 can be 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.

[0206] When the powder compaction density of the negative electrode active material under 20000N is within the above range, the energy density of the battery cell can be improved. Moreover, since the negative electrode active materials in the negative 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, thereby reducing heat generation.

[0207] 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, and the detection is carried out according to the test standard GB / T24533-2009. As an example, a certain amount of negative 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 2000 kg (equivalent to 20000N), kept under pressure for 30 s, then depressurized, kept for 10 s, and then the powder compaction density of the negative electrode active material under the action of 20000N is recorded and calculated.

[0208] 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. Exemplarily, the charging specific capacity of the negative electrode active material at a 0.1C rate 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 the range composed of any two of the above values.

[0209] 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.

[0210] In the embodiments of the present application, the charging specific capacity of the negative electrode active material at a 0.1C rate has the meaning well-known in the art, and can be detected by equipment and methods well-known in the art. The detection method is the same as the charging specific capacity test method of the positive electrode active material at a 0.1C rate described above.

[0211] In some embodiments, the negative electrode active material includes a carbon-based material, and the carbon-based material has high cycle stability, which 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%.

[0212] The positive electrode active material of this 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 relatively excellent cycling performance.

[0213] 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.

[0214] When the graphitization degree of the graphite particles is within the above range, the graphite particles have relatively excellent electrical conductivity, can reduce the heat generation of the negative electrode sheet, reduce the heat generation of the battery cell, and can improve the fast charging performance of the battery cell.

[0215] In some embodiments, the graphite particles include artificial graphite and a carbon coating layer. The artificial graphite includes secondary particles, and the secondary particles include a plurality of primary particles. The carbon coating layer is coated on the surface of the artificial graphite. The carbon in the carbon coating layer is mainly amorphous carbon. 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 this application, amorphous carbon refers to the product after carbonization treatment of an organic carbon source.

[0216] The artificial graphite includes secondary particles. There are more migration paths for lithium ions in the artificial graphite, and the migration path in the primary particles is shorter, which can improve the migration rate of lithium ions. The carbon coating layer has more end faces and defects, so that the number of sites where lithium ions can be intercalated and deintercalated is more, making the electrical conductivity of the carbon coating layer relatively excellent, and can reduce the internal resistance of the negative electrode sheet and the heat generation of the battery cell.

[0217] 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.

[0218] 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 the heat generation of the battery cell.

[0219] In the embodiments of this 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.

[0220] 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 points of the coal tar pitch and petroleum pitch are below 250°C.

[0221] Optionally, the carbonization temperature is from 700°C to 1800°C. Optionally, the carbonization temperature is from 1000°C to 1300°C. Within a suitable range of the carbonization temperature, 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.

[0222] Optionally, the carbonization time is from 1 h to 6 h.

[0223] 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.

[0224] 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.

[0225] Optionally, based on the mass of the negative electrode active material, the mass content of silicon element in the silicon-based material is from 0.3% to 10.0%, and may be optionally from 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.

[0226] When the mass content of silicon element in the silicon-based material is within the above range, the capacity of the negative electrode active material can be increased, and the energy density of the battery cell can be improved.

[0227] 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.

[0228] In some embodiments, in addition to the above-mentioned carbon-based material and optionally the 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.

[0229] The qualitative and quantitative analysis of various substances or elements in this application can be detected by suitable equipment and methods known to those skilled in the art. 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 certain detection steps / instrument parameters from the perspective of detection accuracy to obtain more accurate detection results. One detection method can be used for qualitative or quantitative analysis, or several detection methods can be used in combination for qualitative or quantitative determination.

[0230] For example, this application can combine the general rules of X-ray diffraction analysis method in JIS / K0131-1996 to conduct X-ray powder diffraction test and qualitative analysis on the negative electrode sheet or negative electrode active material.

[0231] Artificial graphite and natural graphite can be distinguished by the SEM cross-sectional view taken by scanning electron microscope (SEM). There are voids between flaky structures in the SEM cross-sectional view of natural graphite, while the SEM cross-sectional view of artificial graphite is dense and has no obvious gaps, or they can be distinguished by the XRD spectrum obtained by X-ray diffraction method. There are obvious 2H phase and 3R phase in the XRD spectrum of natural graphite, while only 2H phase exists in the XRD spectrum of artificial graphite.

[0232] In the embodiments of this application, the negative electrode film layer includes at least one layer of film layer, which can be a single-layer film layer or at least two layers of film layers. Optionally, the negative electrode film layer includes at least two layers of film layers.

[0233] When the negative electrode film layer adopts a single-layer film layer, the negative electrode active material in the negative electrode film layer includes carbon-based materials, and optionally also includes silicon-based materials. When a single-layer film layer is adopted, 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.

[0234] When the negative electrode film layer adopts at least two layers of film layers, the negative electrode active material in the negative electrode film layer includes carbon-based materials, and optionally also includes silicon-based materials. The silicon-based materials can be located in one of the at least two layers of film layers or in at least two of the at least two layers of film layers. The negative electrode film layer can include two layers of film layers, three layers of film layers, four layers of film layers, or even more layers of film layers.

[0235] 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. 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. 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 may be the same or different.

[0236] The interface between the first negative electrode film layer and the second negative electrode film layer may be regular or irregular, and optionally is irregular.

[0237] Optionally, the carbon-based material in the first negative electrode film layer further includes natural graphite.

[0238] The negative electrode film layer includes at least two film layers. 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.

[0239] 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 compaction 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.

[0240] The difference in particle size between the first negative electrode film layer and the second negative electrode film layer 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 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 transport path of lithium ions, improve the fast charging performance, and can also improve the problem of lithium deposition on the surface layer of the negative electrode sheet.

[0241] Optionally, the negative active material in the first negative electrode film layer is granular, and its volume average particle size Dv50 is from 9.5 μm to 18.5 μm, optionally from 9.5 μm to 14.6 μm. Exemplarily, the volume average particle size of the negative 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, optionally from 9.5 μm to 14.6 μm.

[0242] When the volume average particle size Dv50 of the negative active material in the first 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.

[0243] Optionally, the negative 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, optionally from 7.8 μm to 11.3 μm. Exemplarily, the volume average particle size Dv50 of the negative 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, optionally from 7.8 μm to 11.3 μm.

[0244] When the volume average particle size Dv50 of the negative 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 further hand, the cooperation of the negative active material in the second negative electrode film layer and the negative active material in the first negative electrode film layer within the above volume average particle size range is beneficial 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.

[0245] 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 using the equipment and methods well-known in the art. The detection method is the same as the volume average particle size Dv50 test method of the positive electrode active material described above.

[0246] 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 packing 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 that in the first negative electrode film layer, the second negative electrode film layer is more densely packed, which improves the energy density of the battery cell. The first negative electrode film layer is relatively sparsely packed and has more pores, 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.

[0247] 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 / cm 3 , for example, 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 the range composed of any two of the above values. 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.

[0248] Optionally, 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 , for example, 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.

[0249] In the embodiments of the present application, the tap density of the material has a well-known meaning 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 tap density tester can be used for measurement. The test instrument can be BT-301 produced by Dandong BETTER.

[0250] Optionally, 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 to 7:3, and can be optionally 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.

[0251] 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 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.

[0252] 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 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.

[0253] 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, The specific steps of the BOL full charge test are as follows: At 25 °C, charge at a charging rate of 0.33 C of the nominal capacity of the battery to 3.65 V, then charge at a constant voltage of 3.65 V to 0.05 C, stand for 10 min, then discharge at a discharging rate of 0.33 C to 2.0 V, stand for 10 min. The above one charge and discharge is one cycle, and cycle 10 times. Then charge at a charging rate of 0.33 C of the nominal capacity to 3.65 V, and then charge at a constant voltage of 3.65 V to 0.05 C to obtain the BOL full charge state. In the BOL full charge state, disassemble the negative electrode plate, use a tomography scanning electron microscope to observe the cross-section in the thickness direction of the middle area of the negative electrode plate, distinguish the two regions according to the interface between the first negative electrode film layer and the second negative electrode film layer, and measure the thicknesses of the two 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.

[0254] In some embodiments, after the full charge test at the end of life (EOL) of the battery cell, 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 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 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 transport, and improve the fast charging ability of the battery cell.

[0255] In some embodiments, after the full charge test at the end of life (EOL) of the battery cell, 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 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 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 transport, and improve the fast charging ability of the battery cell.

[0256] 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, The specific steps for the EOL full charge test are as follows: At 60 °C, charge at a charging rate of 0.33C of the battery nominal capacity until 3.65V, then perform constant voltage charging at 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 repeated 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 until 3.65V, and perform constant voltage charging at a rate of 0.05C until 3.65V, which is the EOL full charge state. In the EOL full charge state, disassemble the negative electrode plate, and use a tomography scanning electron microscope to observe the cross-section in the thickness direction of the middle area of the negative electrode plate. Distinguish the areas 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 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.

[0257] In some embodiments, when the negative electrode film layer adopts a single-layer film layer (different from the above-mentioned 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 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 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 (e.g., polyacrylic acid PAA, polymethacrylic acid PMAA, sodium polyacrylate PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), and carboxymethyl chitosan (CMCS).

[0258] 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 a 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, it can make the number of free-moving lithium ions in the negative electrode film layer relatively large, 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.

[0259] Exemplarily, the lithium-containing binder includes 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. The molar ratio of the lithium acrylate monomer, the acrylonitrile monomer, the acrylamide monomer, and the 2-hydroxyethyl acrylate monomer is 30% to 50%: 15% to 45%: 5% to 20%: 20% to 35%. For example, the molar ratio of the lithium acrylate monomer, the acrylonitrile monomer, the acrylamide monomer, and the 2-hydroxyethyl acrylate monomer is 35%: 30%: 15%: 20%, or 40%, 20%, 10%, 30%, or 45%, 15%, 20%, 20%, etc.

[0260] 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 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.

[0261] In some other embodiments, when the negative electrode film layer adopts at least two film layers, the negative electrode film layer further includes a lithium-containing binder.

[0262] 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.

[0263] 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 more, which can further improve the fast charging performance of the battery cell.

[0264] 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 an ionic form, which can increase the number of freely movable 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 deintercalation rate of lithium ions, and improve the fast charging performance of the battery cell.

[0265] Optionally, the mass content of lithium element in the first lithium-containing binder is 3% to 10%, and can be optionally 3% to 8%. Exemplarily, the mass content of 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 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.

[0266] 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, and the molar ratio of the lithium acrylate monomer, the acrylonitrile monomer, the acrylamide monomer and the 2-hydroxyethyl acrylate monomer is 30% to 50%: 15% to 45%: 5% to 20%: 20% to 35%. For example, the molar ratio of the lithium acrylate monomer, the acrylonitrile monomer, the acrylamide monomer and the 2-hydroxyethyl acrylate monomer is 35%: 30%: 15%: 20%, or 40%, 20%, 10%, 30%, or 45%, 15%, 20%, 20%, etc.

[0267] 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.

[0268] 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 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, improve the intercalation and deintercalation rate of lithium ions, and improve the fast charging performance of the battery cell.

[0269] The first lithium-containing binder and the second lithium-containing binder can be made of the same material or different materials.

[0270] 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, improve the intercalation and deintercalation rate of lithium ions, and improve the fast charging performance of the battery cell.

[0271] 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 ratio of the lithium acrylate monomer, the acrylonitrile monomer, the acrylamide monomer, and the 2-hydroxyethyl acrylate monomer is 30% to 50%: 15% to 45%: 5% to 20%: 20% to 35%. For example, the molar ratio of the lithium acrylate monomer, the acrylonitrile monomer, the acrylamide monomer, and the 2-hydroxyethyl acrylate monomer is 35%: 30%: 15%: 20%, or 40%, 20%, 10%, 30%, or 45%, 15%, 20%, 20%, etc.

[0272] 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.

[0273] 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 (for example, polyacrylic acid PAA, polymethacrylic acid PMAA, sodium polyacrylate PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), and carboxymethyl chitosan (CMCS).

[0274] 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.

[0275] 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%.

[0276] 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%.

[0277] 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., for example, 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%.

[0278] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. As an example of the metal foil, at least one foil of copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy may be used. The composite current collector may 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 may 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 may include at least one of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0279] In some embodiments, the thickness of the negative electrode current collector is 4 μm to 6 μm. Exemplarily, the thickness of the negative electrode current collector is 4 μm, 4.5 μm, 5 μm, 5.5 μm, 6 μm or a range composed of any two of the above values.

[0280] When the thickness of the negative electrode current collector is within the above range, the current-carrying capacity of the negative electrode current collector is relatively excellent, and the battery cell can have a relatively high energy density.

[0281] In the embodiments of the present application, the thickness of the negative electrode current collector 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, the film layer on the surface of the negative electrode current collector is washed away with a solvent, and the thickness of the negative electrode current collector is measured with a micrometer.

[0282] 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.

[0283] The negative electrode sheet does not exclude other additional functional layers besides the negative electrode film layer. For example, in some embodiments, the negative electrode sheet of the embodiment of the present application further includes a negative electrode conductive layer sandwiched between the negative electrode current collector and the negative electrode film layer and disposed on the surface of the negative electrode current collector. In some other embodiments, the negative electrode sheet of the embodiment of the present application further includes a protective layer covering the surface of the negative electrode film layer.

[0284] In some embodiments, the negative electrode sheet 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 sheet, reduce the heat generation of the negative electrode sheet, and thus reduce the heat generation of the battery cell.

[0285] 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.

[0286] When the thickness of the negative electrode conductive layer is within the above range, it can further improve the 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, and can also take into account improving the energy density of the battery cell.

[0287] In the embodiment 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.

[0288] 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 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 and the negative electrode film layer and improve the structural stability of the negative electrode sheet.

[0289] In some embodiments, the negative electrode conductive layer may further optionally include other additives. As an example, the other additives may include thickeners, such as sodium carboxymethyl cellulose (CMC), PTC thermistor materials, etc.

[0290] 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.

[0291] 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.

[0292] 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.

[0293] 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.

[0294] 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 can 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.

[0295] 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 intercalation, which can reduce the risk of lithium deposition and is beneficial for fast charging.

[0296] 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, calculate the capacity of the negative electrode film layer per unit area and the capacity of the positive electrode film layer per unit area respectively, and then calculate the ratio of the two to obtain the CB value.

[0297] 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, 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 am 2 where the electrolyte uses 1mol / L LiPF 6In a solution with EC / EMC / DEC = 3 / 5 / 2 (mass ratio), then the assembled half-button battery is left standing for 3 h, the test is carried out at 25 °C, first charge (Charge) to de-lithiate in the voltage range of 2.0 V to 3.65 V at 0.1C, and then discharge (Discharge) to intercalate lithium to 2.0 V at 0.05C, cycle 2 times, and record the discharge capacity of the second cycle as Y mAh. The actual length of the positive electrode tab of the battery design is b mm, the width is c mm, and the number of sides d of the positive active material coated on the positive current collector, then the capacity of the positive electrode film layer per unit area = Y / a * b * c * d.

[0298] Specifically, the capacity of the negative electrode film layer per unit area refers to the actual lithium intercalation capacity of the negative active material. The test method is as follows: disassemble the battery in a PRS340 / 11-119-11 Braun glove box, take the negative electrode tab, and assemble it into a CR2430 type half-button battery of negative electrode-lithium sheet. The area of the negative electrode tab used is f mm 2 , where the electrolyte uses 1 mol / L LiPF 6 In a solution with EC / EMC / DEC = 3 / 5 / 2 (mass ratio), then the assembled half-button battery is left standing for 3 h, the test is carried out at 25 °C, first discharge (Discharge) to intercalate lithium in the voltage range of 2 V - 0 V at 0.1C, and then charge (Discharge) to de-lithiate to 2 V at 0.05C, cycle 2 times, and record the discharge capacity of the second cycle as Z mAh. The actual length of the negative electrode tab of the battery design is h mm, the width is i mm, and the number of sides d of the negative active material coated on the negative current collector, then the lithium intercalation capacity of the negative electrode = Z / f * h * i * d.

[0299] [Separator membrane] In the embodiments of the present application, the separator membrane includes a base membrane with a porous structure.

[0300] 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.

[0301] Optionally, the polyolefin includes at least one of polyethylene, polypropylene, and polyvinylidene fluoride.

[0302] In some embodiments, the porosity of the base membrane is 20% to 70%, and can be optionally 35% to 60%. Exemplarily, the porosity of the base membrane is 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70% or a range composed of any two of the above values.

[0303] 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.

[0304] In the embodiments of the present application, the porosity refers to the percentage of the internal pore volume in the separator occupying the total volume of the separator. The porosity can be tested in accordance with the standard GB / T36363-2018 "Polyolefin Separators for Battery Cells". It should be noted that in the actual testing process, the testing process slightly different from the standard can be adopted according to the differences in testing instruments, testing errors, and in order to eliminate the testing influence on the porosity as much as possible, so as to obtain a more accurate test value.

[0305] In some embodiments, the thickness of the base film is 6 μm to 12 μm, and can be optionally 6 μm to 9 μm. Exemplarily, the thickness of the base film is 6 μm, 6.5 μm, 7 μm, 7.5 μm, 8 μm, 8.5 μm, 9 μm, 9.5 μm, 10 μm, 10.5 μm, 11 μm, 11.5 μm, 12 μm or the range composed of any two of the above values.

[0306] 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.

[0307] In the embodiments of the present application, the separator can be a base film. Optionally, the separator further includes a functional layer provided 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 provided on both sides of the base film.

[0308] 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 the non-fluoropolymer particles and / or dispersed inside the non-fluoropolymer particles.

[0309] The first functional layer and the second functional layer have good heat resistance, and can improve the heat resistance of the separator.

[0310] Optionally, the first functional layer can include a binder, and can optionally include at least one of a fluorine-containing binder or a polyacrylic acid binder, such as polyvinylidene fluoride.

[0311] Optionally, 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. The above first inorganic particles can improve the heat resistance of the first functional layer.

[0312] 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 film 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 film is obtained from the battery cell, and after drying the separator film, it is used as a sample. The separator film is cut by 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 film and its respective layers.

[0313] 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-propylene copolymers. The acrylate copolymers have excellent adhesion properties and relatively high adhesion stability with the base film. The molar ratio of each monomer in the copolymer can be any ratio, such as a molar ratio of 35%:30%:15%:20%, or 40%, 20%, 10%, 30%, or 45%, 15%, 20%, 20%, etc.

[0314] The second inorganic particles in the composite particles prevent the non-fluoropolymer particles from adhering to each other easily due to the high-temperature treatment during the granulation process, resulting in pores in the composite particles, which is beneficial to the transport of lithium ions, improving the ionic conductivity of the separator film. 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 prone to deformation, making the structure of the separator film 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 arranged closer to the negative electrode tab. Since the composite particles are not prone to deformation, the separator film 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 arranged closer to the positive electrode tab.

[0315] Optionally, 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. Optionally, the second inorganic particles include silicon oxide. The above-mentioned second inorganic particles can improve the heat resistance of the second functional layer and can form composite particles in cooperation with the non-fluoropolymer, further improving the cycle stability and kinetic performance of the separator film, and improving the cycle performance and fast charging performance of the battery cell.

[0316] The average particle size of the second inorganic particles is from 5 nm to 100 nm, optionally from 10 nm to 100 nm, and optionally from 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.

[0317] 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 and drying the separator as a sample, the separator is cut by an ion beam cutter to form a cross-section. Subsequently, a scanning electron microscope is used to measure the particle size of the second inorganic particles in the separator, and the particle sizes of multiple, such as 50, second inorganic particles are measured, and the average value thereof is calculated as the average particle size of the second inorganic particles.

[0318] In some embodiments, the ionic conductivity of the separator is from 0.3 mS / cm to 0.6 mS / cm. Exemplarily, the ionic conductivity of the separator 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.

[0319] When the ionic conductivity of the separator is within the above range, the migration ability of lithium ions in the separator can be further improved, and the fast charging performance of the battery cell can be improved.

[0320] In the embodiments of the present application, the ionic conductivity of the separator 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, Prepare a 2025-type button battery for testing: In a vacuum glove box, put a lithium sheet into the battery negative electrode case, add 150 μL of electrolyte thereto, and the electrolyte is a solution in EC / EMC / DEC = 3 / 5 / 2 (mass ratio), and then put the separator (with an area of 3.14 cm 6 and a thickness of 12 μm) to make it close to the lithium sheet, then add 25 μL of electrolyte, and finally place the positive electrode sheet (the positive electrode sheet can be the positive electrode sheet in Example 1) thereon and encapsulate. Take out the assembled button battery from the vacuum glove box and place it for 24 h for the next test. 2 Test: On an electrochemical workstation, at 10

[0321] Test: On an electrochemical workstation, at 10-1 ~10 6 It is tested within the frequency range of Hz to obtain the separator resistance Rb, and the ionic conductivity σ (unit: mS / cm) is calculated by the following formula σ = L / (R b ×S) where: R b is the separator resistance, and L and S are the thickness and area of the separator to be measured, respectively.

[0322] [Electrolyte] In some embodiments, the battery cell further includes an electrolyte.

[0323] During the charge and discharge process of the battery cell, active ions such as lithium ions are intercalated and deintercalated back and forth between the positive electrode plate and the negative electrode plate, and the electrolyte plays a role in conducting active ions between the positive electrode plate and the negative electrode plate.

[0324] In the embodiments of the present application, the conductivity of the electrolyte at room temperature is 13 mS / cm to 20 mS / cm, and may 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 a range composed of any two of the above values.

[0325] 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.

[0326] 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.

[0327] In some embodiments, the viscosity of the electrolyte at room temperature is 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 a range composed of any two of the above values.

[0328] 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 improving the fast charging performance of the battery cell.

[0329] In the embodiments of the present application, the viscosity of the electrolyte 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, it can be detected according to GB / T10247-2008.

[0330] In some embodiments, the density of the electrolyte at room temperature, such as 25 °C, is 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.

[0331] 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.

[0332] In the embodiments of the present application, the density of the electrolyte 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, it can be tested with reference to GB / T 2013-2010.

[0333] 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.

[0334] In some embodiments, the organic solvent includes a chain carboxylic ester solvent, and the mass content of the chain carboxylic 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 greater than or equal to 10% and less than or equal to 75%, optionally 30% to 70%, optionally 50% to 70%. Exemplarily, the mass content of the chain carboxylic ester solvent is 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75% or the range composed of any two of the above values.

[0335] 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.

[0336] In some embodiments, the chain carboxylic ester solvent includes a compound represented by Formula I, Formula I, In formula I, R 1 includes a hydrogen atom, a halogen atom, a C1-C5 alkyl group or a C1-C5 haloalkyl group, R 2 includes a C1-C5 alkyl group or a C1-C5 haloalkyl group.

[0337] The above-mentioned chain carboxylic ester solvents have relatively high conductivity, which is beneficial to improving the fast charging ability of battery monomers.

[0338] Optionally, R 1 includes a hydrogen atom, a halogen atom, a C1-C3 alkyl group or a C1-C3 haloalkyl group. Further optionally, R 1 includes a hydrogen atom, a halogen atom, a C1-C2 alkyl group or a C1-C2 haloalkyl group.

[0339] Optionally, R 2 includes a C1-C3 alkyl group or a C1-C3 haloalkyl group. Further optionally, R 2 includes a C1-C2 alkyl group or a C1-C2 haloalkyl group.

[0340] 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.

[0341] 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.

[0342] Exemplarily, the chain carboxylic ester solvents include one or more of the compounds shown in Formula I-1 to Formula I-8,

[0343] In some embodiments, the organic solvent further includes a carbonate solvent.

[0344] Optionally, the carbonate solvent includes one or more of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate and methyl ethyl carbonate. Further optionally, the carbonate solvent includes one or more of ethylene carbonate, dimethyl carbonate and methyl ethyl carbonate. The above carbonate solvents and chain carboxylic ester solvents are used in combination, so that the conductivity of the electrolyte at room temperature is improved, which is beneficial to the migration of lithium ions.

[0345] Further optionally, the mass content of the carbonate solvent in the organic solvent is 30% to 70%, and may be optionally 30% to 50%. Exemplarily, the mass content of the carbonate solvent in the organic solvent is 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.

[0346] Exemplarily, the carbonate solvent includes one or more of ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate, and the mass content of the carbonate solvent is 30% to 50%.

[0347] In some embodiments, the electrolyte further contains additives. The additives may include negative electrode film-forming additives, or may include positive electrode film-forming additives, or may also include additives that can improve certain battery performance, such as additives for improving the overcharge performance of the battery, additives for improving the high-temperature performance of the battery, additives for improving the low-temperature power performance of the battery, etc.

[0348] In some embodiments, the additives include one or more of carbonate additives, sulfur-containing additives, and lithium salt additives, and may be optionally 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.

[0349] In some embodiments, the mass content of the additives in the electrolyte is 1% to 10%, optionally 2% to 8%, and further optionally 3.5% to 8%. Exemplarily, the mass content of the additives 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.

[0350] The additives 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 monomer and improving the cycle performance.

[0351] Exemplarily, the carbonate additives include one or more of vinylene carbonate VC and fluoroethylene carbonate FEC.

[0352] 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 methanedisulfonate MMDS.

[0353] Optionally, the lithium salt additives include lithium difluorophosphate LiPO2 F 2 、 lithium difluoro(oxalato)borate LiDFOB, lithium tetrafluoroborate LiBF 4 、 lithium bis(oxalato)borate LiBOB or one or more of them.

[0354] Optionally, the mass content of vinylene carbonate VC in the electrolyte is 0.5% to 9%, and may be optionally 2% to 6%.

[0355] Optionally, the mass content of fluoroethylene carbonate FEC in the electrolyte is 0.1% to 4%, and may be optionally 0.5% to 3%.

[0356] 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%.

[0357] 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%.

[0358] In some embodiments, the electrolyte salt includes a lithium salt, and the lithium salt includes a fluorosulfonylimide salt and lithium hexafluorophosphate LiPF 6 or one or more of them. 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 cycling performance of the battery cell.

[0359] Optionally, the fluorosulfonylimide salt includes one or more of lithium bis(fluorosulfonyl)imide LiFSI and lithium bis(trifluoromethylsulfonyl)imide LiTFSI.

[0360] Optionally, the lithium salt includes lithium bis(fluorosulfonyl)imide LiFSI and lithium hexafluorophosphate LiPF 6 , the molar concentration of lithium bis(fluorosulfonyl)imide LiFSI is 0.2 mol / L to 0.5 mol / L, and the molar concentration of lithium hexafluorophosphate LiPF 6 is 0.5 mol / L to 1.0 mol / L.

[0361] Exemplarily, the molar concentration of lithium bis(fluorosulfonyl)imide LiFSI is 0.4 mol / L to 0.5 mol / L, and the molar concentration of lithium hexafluorophosphate LiPF 6 is 0.7 mol / L.

[0362] Exemplarily, the molar concentration of lithium bis(fluorosulfonyl)imide LiFSI is 0.5 mol / L, and the molar concentration of lithium hexafluorophosphate LiPF 6 is 0.5 mol / L.

[0363] Exemplarily, the molar concentration of lithium bis(fluorosulfonyl)imide LiFSI is 0.2 mol / L, and the molar concentration of lithium hexafluorophosphate LiPF 6 is 0.8 mol / L.

[0364] Optionally, the ratio of the molar concentration of lithium bis(fluorosulfonyl)imide to the molar concentration of lithium hexafluorophosphate LiPF 6 is 0.2 to 1.0, and can be optionally 0.2 to 0.5. Exemplarily, the ratio of the molar concentration of lithium bis(fluorosulfonyl)imide to the molar concentration of lithium hexafluorophosphate LiPF 6 is 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1 or the range composed of any two of the above values.

[0365] In the embodiments of the present application, the types and contents of inorganic components / lithium salt concentrations in the electrolyte have meanings well-known in the art, and can be detected by equipment 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 concentrations in the electrolyte by ion chromatography analysis methods. In the embodiments of the present application, freshly 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 disassembled in reverse, and the free electrolyte obtained from the battery can be taken as a sample, and ion chromatography analysis methods are used for detection.

[0366] In the embodiments of the present application, the types and contents of organic components in the electrolyte have meanings well-known in the art, and can be detected by equipment and methods well-known in the art. For example, reference can be made to GB / T 9722-2006 "General Rules for Gas Chromatography of Chemical Reagents" to qualitatively and quantitatively analyze the organic components in the electrolyte by gas chromatography. In the embodiments of the present application, freshly 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 disassembled in reverse, and the free electrolyte obtained from the battery can be taken as a sample, and ion chromatography analysis methods are used for detection.

[0367] In the embodiments of the present application, after quantitatively and qualitatively detecting each component in the electrolyte, each component is classified, and chain carboxylic ester solvents and carbonate solvents (such as ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate) are used as the constituent components of the organic solvent. Based on the mass of the organic solvent being 100%, the mass content of each component is calculated. Use carbonate additives (such as vinylene carbonate, fluoroethylene carbonate), sulfur-containing additives, and lithium salt additives as additives for the electrolyte, and calculate the mass content of each component based on the mass of the electrolyte being 100%.

[0368] In some embodiments, the battery cell satisfies: 2.45 g / Ah ≤ d / A ≤ 3.5 g / Ah, optionally 2.45 g / Ah ≤ d / A ≤ 3.3 g / Ah, where d represents the mass of the electrolyte in the battery cell, in g, and 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, or a range composed of any two of the above values.

[0369] d / A can reflect the liquid retention ability of the electrolyte. When d / A is within the above range, the electrolyte can play a good 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.

[0370] 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 using equipment and methods well-known in the art. For example, taking the upper charging voltage of the battery as 3.65 V and the discharge cut-off voltage of the battery as 2.0 V in accordance with GB / T31486-2015 "Electrical Performance Requirements and Test Methods for Power Batteries for Electric Vehicles" for illustration, At 25°C, charge the battery cell at 0.33C to 3.65 V, then charge it at a constant voltage to 0.05C, and then discharge it at a constant current of 0.33C to 2.0 V. Take the discharged capacity A as the denominator, weigh the battery cell as M0, and then disassemble the positive electrode plate, the negative electrode plate, the separator, and the electrolyte. The free electrolyte is placed in a bag. Put all the above solid components into an oven at 60°C and bake for more than 4 hours (including but not limited to the positive electrode plate, the negative electrode plate, the separator, and other mechanical parts of the disassembled battery cell that contribute to M0), and then weigh all the components of the battery cell 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.

[0371] In some embodiments, the positive electrode plate, the separator, and the negative electrode plate can be made into an electrode assembly by a winding process and / or a stacking process.

[0372] Figure 1 and Figure 2 shows a schematic structural diagram of the battery cell.

[0373] In some embodiments, the battery cell 7 may include a housing 20.

[0374] 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).

[0375] The housing 20 is a hollow structure, and the housing 20 can be used to encapsulate the above-mentioned electrode assembly 10 and electrolyte.

[0376] 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 sheet, the separator, the negative electrode sheet, and the electrolyte can be assembled to form the battery cell 7. As an example, the positive electrode sheet, the separator, and the negative electrode sheet can be formed into the electrode assembly 10 through 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, and through processes such as vacuum packaging, standing, formation, and shaping, the battery cell 7 is obtained.

[0377] In some embodiments, the housing 20 includes a housing body 21 and an end cover 22, the housing body 21 has an opening, and the end cover 22 covers the opening.

[0378] 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.

[0379] In some embodiments, the material of the housing body 21 includes steel. Steel has high mechanical strength and is not easily deformed, which can improve the service reliability and cycle performance of the battery cell. Optionally, the mass ratio of steel is the highest among the materials in the housing body 21.

[0380] Optionally, the thickness of the housing body 21 is from 0.1 mm to 0.5 mm, and can be selected from 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 high mechanical strength, which can improve the service reliability and cycle performance of the battery cell 7, and the housing body 21 occupies less space and has more internal space, which is beneficial to improving the energy density of the battery cell 7.

[0381] Viewed from the outer shape of the electrode assembly 10, the electrode assembly 10 includes a main body portion 12, a first tab 111 and a second tab 112, and the first tab 111 and the second tab 112 protrude from the main body portion 12. The first tab 111 is the part of the first electrode plate where the active material layer is not coated, and the second tab 112 is the part of the second electrode plate where the active material layer is not coated. The first tab 111 and the second tab 112 are used to lead out the current in the main body portion 12. The polarities of the first electrode plate and the second electrode plate are opposite. In other words, one of the first electrode plate and the second electrode plate is the positive electrode plate, and the other of the first electrode plate and the second electrode plate is the negative electrode plate. Of course, the first tab 111 can be the positive tab, and the second tab 112 can be the negative tab.

[0382] Taking the first tab 111 as the negative tab and the second tab 112 as the positive tab as an example for illustration, the negative current collector part of the negative electrode plate where the active material layer is not coated is the negative tab. The active material coated on the negative current collector of the negative electrode plate forms the negative electrode film layer. The negative electrode film layer and the negative current collector coated with the active material are part of the main body portion 12. The positive current collector part of the positive electrode plate where the active material layer is not coated is the positive tab. The active material coated on the positive current collector of the positive electrode plate forms the positive electrode film layer. The positive electrode film layer and the positive current collector coated with the active material are part of the main body portion 12.

[0383] The first tab 111 and the second tab 112 can extend from the same side of the main body portion 12, or can extend from opposite sides respectively.

[0384] Optionally, the number of the first tabs 111 located on the same side of the main body portion 12 is at least one, optionally at least two. At least two first tabs 111 can increase the current-carrying capacity of the first tab 111.

[0385] Optionally, the number of the second tabs 112 located on the same side of the main body portion 12 is at least one, optionally at least two. At least two second tabs 112 can increase the current-carrying capacity of the second tab 112.

[0386] In some embodiments, the battery cell 7 further includes a first electrode terminal 31, and the first electrode terminal 31 is electrically connected to the first tab 111. Optionally, the first electrode terminal 31 and the first tab 111 are welded. The first electrode terminal 31 and the first tab 111 can be connected through an adapter, or can be connected without using an adapter. Optionally, the first electrode terminal 31 and the first tab 111 are connected without using an adapter, that is, the first electrode terminal 31 and the first tab 111 are directly welded, which can reduce the resistance at the connection point and is beneficial to reducing the overall internal resistance of the battery cell 7.

[0387] When the first tab 111 is the negative electrode tab, the first electrode terminal 31 is the negative terminal. When the first tab 111 is the positive electrode tab, the first electrode terminal 31 is the positive terminal.

[0388] In some embodiments, the battery cell 7 further includes a second electrode terminal 32, and the second electrode terminal 32 is electrically connected to the second tab 112. Optionally, the second electrode terminal 32 and the second tab 112 are welded. The second electrode terminal 32 and the second tab 112 can be connected through an adapter, or can be connected without using an adapter. Optionally, no adapter is used between the second electrode terminal 32 and the second tab 112, that is, the second electrode terminal 32 and the second 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.

[0389] When the second tab 112 is the negative electrode tab, the second electrode terminal 32 is the negative terminal. When the second tab 112 is the positive electrode tab, the second electrode terminal 32 is the positive terminal.

[0390] Optionally, the number of the first electrode terminals 31 on the same side of the main body portion 12 is at least one, and can be at least two. At least two first electrode terminals 31 can increase the current-carrying capacity of the first electrode terminals 31.

[0391] Further optionally, the current-carrying area of the first electrode terminals 31 on one side is 150 mm 2 to 1000 mm 2 , and can be 200 mm 2 to 1000 mm 2 . The current-carrying area of the first electrode terminals 31 refers to the sum of the current-carrying areas of all the first electrode terminals 31 on the same side of the main body portion 12. The current-carrying area of the first electrode terminals 31 can be understood as the cross-sectional area of the first electrode terminals 31, and this cross-section is perpendicular to the thickness direction of the end cover 22.

[0392] Exemplarily, the current-carrying area of the first electrode terminals 31 on one side can be 150 mm 2 , 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 mm2 , 700 mm 2 , 750 mm 2 , 800 mm 2 , 850 mm 2 , 900 mm 2 , 950 mm 2 , 1000 mm 2 or a range composed of any two of the above values.

[0393] Optionally, the number of the second electrode terminals 32 on the same side of the main body 12 is at least one, and may be at least two. The at least two second electrode terminals 32 can increase the over-current capacity of the second electrode terminals 32.

[0394] Further optionally, the over-current area of the second electrode terminals 32 on one side is 150 mm 2 to 1000 mm 2 , and may be 200 mm 2 to 1000 mm 2 . The over-current area of the second electrode terminals 32 refers to the sum of the over-current areas of all the second electrode terminals 32 on the same side of the main body 12. The over-current area of the second electrode terminals 32 can be understood as the cross-sectional area of the second electrode terminals 32, and this cross-section is perpendicular to the thickness direction of the end cover 22.

[0395] Exemplarily, the over-current area of the second electrode terminals 32 on one side can be 150 mm 2 , 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 , 850 mm 2 , 900 mm 2 , 950 mm 2 , 1000 mm 2 or a range composed of any two of the above values.

[0396] Such as Figure 3As shown, in some embodiments of the present application, the battery cell 7 according to the implementation manner 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.

[0397] If there are multiple battery cells 7, the multiple battery cells 7 can be connected in series, in parallel, or in a series-parallel combination. A series-parallel combination 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 series-parallel combination together, and then the whole formed by the multiple battery cells 7 is accommodated in the accommodating 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 series-parallel combination to form battery modules 6, and then the multiple battery modules 6 are connected in series, in parallel, or in a series-parallel combination to form a whole and are accommodated in the accommodating part. Optionally, the battery module 6 can further include an accommodating part with an accommodating space, and the multiple battery cells 7 are accommodated in this accommodating space.

[0398] As Figure 4 shown, in some implementation manners, the above-mentioned battery module 6 can also be assembled into a battery pack 2. 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 described herein can be either the battery module 6 or the battery pack 2.

[0399] The battery pack 2 can include a box body 5 and multiple battery modules 6 disposed 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 accommodating 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 multiple battery modules 6 can be arranged in the box body 5 in any manner.

[0400] The first box body part 5a and the second box body part 5b cover each other, and the first box body part 5a and the second box body part 5b jointly define an accommodating 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 accommodating space 5c. The first box body part 5a and the second box body part 5b can also both 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 accommodating space 5c. Of course, the first box body part 5a and the second box body 5b can be in various shapes, such as a cylinder, a cuboid, etc.

[0401] 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 can also be provided between the first box body part 5a and the second box body part 5b, such as sealant, sealing ring, etc.

[0402] 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. In some embodiments, during the charging 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 30°C.

[0403] 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, the temperature of the external environment where the battery pack 2 is located is 30°C.

[0404] 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. The difference between the maximum state of charge of any charging step and the maximum state of charge of its adjacent charging step 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.

[0405] 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 of 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.

[0406] The battery pack 2 or any battery cell constituting the battery pack 2 from 40% SOC to 80% SOC also includes multiple charging steps. The charging rate of any charging step is less than the charging rate of any charging step from 10% SOC to 40% SOC, and the charging rate of the step when charging to 80% SOC is any value between 2.5C and 5C. For example, it can be 2.7C.

[0407] 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 in the following manner: Charge from 10% SOC to 15% SOC at a constant current of 5.0C, Charge from 15% SOC to 20% SOC at a constant current of 5.0C, Charge from 20% SOC to 25% SOC at a constant current of 5.0C, Charge from 25% SOC to 30% SOC at a constant current of 5.0C, Charge from 30% SOC to 35% SOC at a constant current of 5.0C, Charge from 35% SOC to 40% SOC at a constant current of 5.0C, Charge from 40% SOC to 45% SOC at a constant current of 4.6C, Charge from 45% SOC to 50% SOC at a constant current of 4.3C, Charge from 50% SOC to 55% SOC at a constant current of 4.0C, Charge from 55% SOC to 60% SOC at a constant current of 3.7C, Charge from 60% SOC to 65% SOC at a constant current of 3.4C, Charge from 65% SOC to 70% SOC at a constant current of 3.1C, Charge from 70% SOC to 75% SOC at a constant current of 2.9C, Charge from 75% SOC to 80% SOC at a constant current of 2.7C.

[0408] In some embodiments, the charging time of the battery pack 2 or any battery cell constituting the battery pack 2 from 10% state of charge to 80% state of charge is less than or equal to 10.5 min, optionally 5 min to 10.5 min, and the temperature of the external environment of the battery pack 2 at 10% state of charge is room temperature, for example 30°C. Exemplarily, the charging time of the battery pack 2 from 10% state of charge to 80% state of charge is 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, 5.5 min, 5 min or a range composed of any two of the above values. In some embodiments, the volumetric energy density of the battery cell is 390 Wh / L to 500 Wh / L, 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 a range composed of any two of the above values. The volumetric energy density of the battery cell is relatively high.

[0409] 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 charging limit voltage of the battery as 3.65V and the discharge cut-off voltage of the battery as 2.0V as an example for illustration, 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 the current reaches 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 outer shell), and calculate the volume V0 of the single battery cell, unit: L. The volumetric energy density VED of the battery cell = (A0 × discharge platform voltage) / V0, unit: Wh / L.

[0410] Electrical device The second aspect of the embodiments of the present application provides an electrical device. The electrical device includes the battery device of the embodiments of the present application, such as a battery cell, a battery module, or a battery pack. The battery cell, the battery module, or the 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, a mobile phone, a portable device, a laptop computer, a ship, a spacecraft, an electric toy, and an electric tool, etc. The vehicle can be a fuel vehicle, a gas vehicle, or a new energy vehicle. The new energy vehicle can be a pure electric vehicle, a hybrid electric vehicle, or an extended-range electric vehicle, etc. The spacecraft includes an airplane, a rocket, a space shuttle, and a spaceship, etc. The electric toy includes a fixed or mobile electric toy, such as a game console, an electric vehicle toy, an electric ship toy, and an electric airplane toy, etc. The electric tool includes a metal cutting electric tool, a grinding electric tool, an assembly electric tool, and a railway electric tool, such as a drill, an electric grinding wheel, an electric wrench, an electric screwdriver, a hammer drill, an impact drill, a concrete vibrator, and a planer, etc. The embodiments of the present application do not impose special restrictions on the above-mentioned electrical devices. The electrical device can select a battery cell, a battery module, or a battery pack according to its usage requirements.

[0411] Figure 5 It is a schematic diagram of an electrical device 1 as an example. The electrical device 1 is a pure electric vehicle, a hybrid electric vehicle, or a 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 a battery module can be used.

[0412] Inside the electrical device 1, there is a battery pack 2, which can be arranged at the bottom, head or tail of the electrical device 1. The battery pack 2 can be used to supply power to the electrical device 1. For example, the battery pack 2 can serve as the operating power source of the electrical device 1 and also 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.

[0413] 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 start-up, navigation and driving of the electrical device 1.

[0414] As another example, the electrical device can be a mobile phone, a tablet computer, a laptop computer, etc. Such an electrical device usually requires being thin and light, and battery cells can be used as the power source.

[0415] The charging process of the electrical device can select the following charging methods: Charge from 10% SOC to 15% SOC at a constant current of 5.0C, Charge from 15% SOC to 20% SOC at a constant current of 5.0C, Charge from 20% SOC to 25% SOC at a constant current of 5.0C, Charge from 25% SOC to 30% SOC at a constant current of 5.0C, Charge from 30% SOC to 35% SOC at a constant current of 5.0C, Charge from 35% SOC to 40% SOC at a constant current of 5.0C, Charge from 40% SOC to 45% SOC at a constant current of 4.6C, Charge from 45% SOC to 50% SOC at a constant current of 4.3C, Charge from 50% SOC to 55% SOC at a constant current of 4.0C, Charge from 55% SOC to 60% SOC at a constant current of 3.7C, Charge from 60% SOC to 65% SOC at a constant current of 3.4C, Charge from 65% SOC to 70% SOC at a constant current of 3.1C, Charge from 70% SOC to 75% SOC at a constant current of 2.9C, Charge from 75% SOC to 80% SOC at a constant current of 2.7C.

[0416] 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 10.5 min, optionally 5 min to 10.5 min, and 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 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, 5.5 min, 5 min or the range composed of any two of the above values.

[0417] Embodiment 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 the instruments used in the examples are all commercially available.

[0418] Example 1 1. Preparation of the positive electrode sheet The positive electrode sheet includes a positive electrode current collector, a positive electrode conductive layer on the positive electrode current collector, and a positive electrode film layer. The positive electrode current collector is an aluminum foil with a thickness of 10 μm.

[0419] The positive electrode conductive layer on the positive electrode current collector is a film layer formed by uniformly mixing a positive electrode conductive agent, superconducting carbon, a positive electrode binder, polyvinylidene fluoride (PVDF), and a solvent, N-methylpyrrolidone (NMP), and then coating and drying on the surface of the current collector. The thickness is 1 μm. The mass content of the positive electrode conductive agent in the positive electrode conductive layer is 40%, and the mass content of the positive electrode binder is 60%.

[0420] 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 electrode conductive layer, followed by drying and cold pressing. The positive electrode film layer includes a positive electrode active material, a binder polyvinylidene fluoride (PVDF), and a conductive agent acetylene black in a weight ratio of 97:2:1.

[0421] The positive electrode active material includes lithium iron phosphate and a coating layer. The coating layer is coated on the surface of lithium iron phosphate. The coating layer includes lithium iron titanium phosphate Li 2 FeTi(PO 4 ) 3 and amorphous carbon. The Dv50 of the positive electrode active material is 1.6 μm, and the Dv10 is 0.64 μm.

[0422] The single-sided coating weight of the positive electrode film layer is 300 mg / 1540.25 mm 2 。

[0423] 2. Preparation of the negative electrode sheet 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 with a thickness of 5 μm

[0424] 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 thickener, sodium carboxymethyl cellulose (CMC-Na), and a solvent, water, and then coating it on the surface of the negative electrode current collector and drying. 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 thickener in the negative electrode conductive layer is 5%

[0425] 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

[0426] The single-sided coating weight of the negative electrode film layer is 138 mg / 1540.25 mm 2 。

[0427] 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

[0428] The first negative electrode film layer includes graphite particles, conductive agent acetylene black, a first lithium-containing binder (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 thickener 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, and the carbon coating layer covers the surface of the artificial graphite, with a mass content of 3.5%

[0429] The second negative electrode film layer includes graphite particles, conductive agent acetylene black, second lithium-containing binder (lithium acrylate-acrylonitrile-acrylamide-2-hydroxyethyl acrylate copolymer, 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. 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 covers the surface of the artificial graphite, and the mass content of the carbon coating layer is 3.5%.

[0430] 3. Separator The separator includes a base film, which is a 7-μm polyethylene film layer with a porosity of 42%.

[0431] 4. Preparation of electrolyte The electrolyte includes organic solvents, lithium salts and additives.

[0432] The organic solvents include 60% chain carboxylic ester solvents (ethyl acetate) and 40% carbonate solvents (30% ethylene carbonate EC, 10% dimethyl carbonate). The mass content of each component in the organic solvents is calculated based on the mass of the organic solvents.

[0433] Based on the mass of the electrolyte, the mass content of the additives is 6.5%, which includes 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.

[0434] The lithium salt includes 1 mol / L lithium hexafluorophosphate LiPF 6 .

[0435] The conductivity of the electrolyte at room temperature is 16.4 mS / cm.

[0436] 5. Preparation of battery cell Stack the above-mentioned positive electrode plate, separator, and negative electrode plate in sequence, with the separator placed between the positive electrode plate and the negative electrode plate to play an isolation role, obtaining an electrode assembly. Place the electrode assembly in an outer packaging shell, inject the electrolyte after drying, and through processes such as vacuum packaging, standing, formation, and shaping, obtain a battery cell. The compaction density of the positive electrode film layer of the battery cell at 100% SOC is 2.72 g / cm 3 , and the compaction density of the negative electrode film layer at 100% SOC is 1.26 g / cm 3 .

[0437] Comparative Example 1 The battery monomer was prepared by a method similar to that of Example 1. Different from Example 1, the mass content of carbon element in the positive electrode active material was adjusted to adjust the resistance of the positive electrode sheet.

[0438] Comparative Example 2 The battery monomer was prepared by a method similar to that of Example 1. Different from Example 1, the mass content of the carbon coating layer in the negative electrode active material was adjusted to adjust the resistance of the negative electrode sheet.

[0439] Examples 2-1 to 2-4 The battery monomer was prepared by a method similar to that of Example 1. Different from Example 1, the mass content of carbon element in the positive electrode active material was adjusted to adjust the resistance of the positive electrode sheet.

[0440] Examples 2-5 and 2-6 The battery monomer was prepared by a method similar to that of Example 1. Different from Example 1, the mass content of the carbon coating layer in the negative electrode active material was adjusted to adjust the resistance of the negative electrode sheet.

[0441] Examples 3-1 and 3-2 The battery monomer was prepared by a method similar to that of Example 1. Different from Example 1, the thickness of the separator was adjusted.

[0442] Examples 3-3 to 3-4 The battery monomer was prepared by a method similar to that of Example 1. Different from Example 1, the porosity of the separator was adjusted.

[0443] Performance test 1. The charging time of the battery monomer from 10% SOC to 80% SOC was specifically carried out by the following charging steps. At 30 °C, charging was carried out from the 10% SOC state of the battery. Constant current charging was carried out at 5.0C from 10% SOC to 15% SOC. Constant current charging was carried out at 5.0C from 15% SOC to 20% SOC. Constant current charging was carried out at 5.0C from 20% SOC to 25% SOC. Constant current charging was carried out at 5.0C from 25% SOC to 30% SOC. Constant current charging was carried out at 5.0C from 30% SOC to 35% SOC. Constant current charging was carried out at 5.0C from 35% SOC to 40% SOC. Constant current charging was carried out at 4.6C from 40% SOC to 45% SOC. Constant current charging was carried out at 4.3C from 45% SOC to 50% SOC. Charge from 50% SOC to 55% SOC at a constant current of 4.0C, charge from 55% SOC to 60% SOC at a constant current of 3.7C, charge from 60% SOC to 65% SOC at a constant current of 3.4C, charge from 65% SOC to 70% SOC at a constant current of 3.1C, charge from 70% SOC to 75% SOC at a constant current of 2.9C, charge from 75% SOC to 80% SOC at a constant current of 2.7C, Record the total charging time.

[0444] 2. DC internal resistance DCR test of battery cells The method in GB / T 31467 "Performance Test Specification for High-Power Lithium-Ion Power Batteries for HEV" can be referred to.

[0445] For example, at room temperature, charge the battery cell to 3.65V at a constant current of 0.33C, let it stand for 1 min, then charge it to 3.65V at a constant current of 0.1C, let it stand for 30 min, discharge it to 2.0V at a constant current of 0.33C, and record the discharge capacity A 0 , in the unit of Ah, then charge it at a constant current of 0.33C for 0.5A 0 Ah, and adjust the SOC to 50%.

[0446] After placing the battery cell at 20 °C for 2 h, discharge it at a constant current of 4C for 10s, and record ∆U 放电 , ∆I 放电 , and calculate the discharge DCR data of the lithium-ion battery through the following formula, R 放电 = ∆U 放电 / ∆I 放电 , where, ∆U 放电 represents the voltage change within the first 10s of discharge, and ∆I 放电 represents the current value within the first 10s of discharge.

[0447] 3. Number of cycles for the battery cell to cycle to 80% SOH At room temperature, charge the battery cell to the charging cut-off voltage of 3.65V at a constant current of 1C, and then discharge it to 2.0V at a constant current of 1C. This is one charge-discharge cycle. Repeat the above charge-discharge cycle steps until the cycle capacity retention rate (i.e., Cn / C0×100%) is 80%, and record the number of cycles. The more the number of cycles, the better the cycle performance of the battery cell.

[0448] The test results are shown in Table 1.

[0449] Table 1

[0450] In Table 1, In Comparative Example 1, the mass content of carbon element on the surface of the positive active material is relatively low, resulting in relatively poor conductivity of the positive active material and a relatively large internal resistance of the positive electrode sheet.

[0451] In Comparative Example 2, the mass content of amorphous carbon on the surface of the graphite particles is relatively low, resulting in relatively poor conductivity of the graphite particles and a relatively large internal resistance of the negative electrode sheet.

[0452] In the case where the internal resistances of Comparative Example 1 and Comparative Example 2 are relatively large, it is not conducive to the rapid charging of the battery cell, and the DCR of the battery cell is relatively high. The battery cell generates more heat, making the electrolyte system unstable and the organic solvent easy to volatilize, resulting in an increase in the internal pressure of the battery cell and being not conducive to cycling.

[0453] In the examples of the present application, the resistance of the positive electrode sheet is 0.1 Ω to 30 Ω, optionally 0.1 Ω to 25 Ω, and optionally 0.1 Ω to 5 Ω. The resistance of the negative electrode sheet is 0.001 Ω to 0.01 Ω, optionally 0.001 Ω to 0.005 Ω, and optionally 0.001 Ω to 0.004 Ω. The resistances of the positive electrode sheet and the negative electrode sheet are controlled within a reasonable range, making the DCR of the battery cell relatively low and the battery cell generating less heat, making the electrolyte system relatively stable and the organic solvent not easy to volatilize, which is beneficial to improving the cycling performance.

[0454] In Examples 3-1 to 3-4, by adjusting the porosity or thickness of the base film in the separator, when the porosity of the base film is 20% to 70%, optionally 35% to 60%, and the thickness of the base film is 6 μm to 12 μm, optionally 6 μm to 9 μm, the migration ability of lithium ions in the separator is relatively strong, which is beneficial to rapid charging, and can reduce the internal resistance of the battery cell, thereby reducing heat generation and being beneficial to improving the cycling performance.

[0455] Comparative Example 3 and Comparative Example 4 The battery cell was prepared by a method similar to that of Example 1. Different from Example 1, the composition of the organic solvent in the electrolyte was adjusted.

[0456] Examples 4-1 to 4-3 The battery cell was prepared by a method similar to that of Example 1. Different from Example 1, In Example 4-1, The single-sided coating weight of the positive electrode film layer is 231 mg / 1540.25 mm 2 , and the compaction density at 100% SOC is 2.72 g / cm 3 , The single-sided coating weight of the negative electrode film layer is 110 mg / 1540.25 mm 2 , and the compaction density at 100% SOC is 1.21 g / cm 3 , and the composition of the organic solvent in the electrolyte was adjusted.

[0457] In Example 4-2, The single-sided coating weight of the positive electrode film layer is 258 mg / 1540.25 mm 2 , and the compaction density at 100% SOC is 2.72 g / cm 3 , The single-sided coating weight of the negative electrode film layer is 123 mg / 1540.25 mm 2 , and the compaction density at 100% SOC is 1.21 g / cm 3 , and the composition of the organic solvent in the electrolyte was adjusted.

[0458] In Example 4-3, The single-sided coating weight of the positive electrode film layer is 300 mg / 1540.25 mm 2 , and the compaction density at 100% SOC is 2.72 g / cm 3 , The single-sided coating weight of the negative electrode film layer is 138 mg / 1540.25 mm 2 , and the compaction density at 100% SOC is 1.26 g / cm 3 , and the composition of the organic solvent in the electrolyte was adjusted.

[0459] The performance test procedure is the same as that described above and will not be elaborated here. The test results are shown in Table 2.

[0460] Table 2 In Table 2, In Comparative Example 3, Example 4-1 and Example 4-2, the mass content of ethylene carbonate in the carbonate solvent is 30%, and the rest is dimethyl carbonate.

[0461] In Comparative Example 3, the conductivity of the electrolyte is too low. Even if the resistance of the positive and negative electrode plates is set within a reasonable range, it makes the migration of lithium ions difficult, the charging ability of the electrolyte is insufficient, and cyclic voltage decay is likely to occur.

[0462] In Comparative Example 4, the conductivity of the electrolyte is too high, and the proportion of low-boiling organic solvents is relatively high. It is extremely easy to volatilize during cycling, which increases the internal pressure of the battery cell and deteriorates the cycle.

[0463] Examples 4-1 to 4-3, by setting the positive and negative electrode sheet resistances within a reasonable range, and in combination with setting the conductivity of the electrolyte to 13 mS / cm to 20 mS / cm, optionally 15 mS / cm to 20 mS / cm, the migration rate of lithium ions is relatively fast, which is beneficial to fast charging, and the electrolyte system is stable, which can improve the cycle performance of the battery cell, etc. Through Examples 4-1 to 4-3, when the conductivity of the electrolyte is relatively low, further in combination with a relatively small compaction density and / or coating weight of the positive electrode film layer, and / or a relatively small compaction density and / or coating weight of the negative electrode film layer, it is beneficial to fast charging.

[0464] Example 5 The battery cell was prepared by a method similar to that of Example 1. Different from Example 1, The preparation of the positive electrode sheet includes: The positive electrode sheet includes a positive electrode current collector, a positive electrode conductive layer on the positive electrode current collector, a positive electrode lithium supplement layer, and a positive electrode film layer. The positive electrode current collector is an aluminum foil with a thickness of 10 μm. The positive electrode conductive layer on the positive electrode current collector is composed of a positive electrode conductive agent, superconducting carbon, and a positive electrode binder, polyvinylidene fluoride (PVDF), and a solvent, N-methylpyrrolidone (NMP). After being mixed evenly, it is coated on the surface of the current collector with a thickness of 1 μm. The mass content of the positive electrode conductive agent in the positive electrode conductive layer is 40%, and the mass content of the positive electrode binder is 60%.

[0465] The positive electrode lithium supplement layer is a film layer formed by coating a mixture of lithium phosphate, a positive electrode binder, polyvinylidene fluoride (PVDF), and a solvent, N-methylpyrrolidone (NMP), evenly on the surface of the positive electrode conductive layer, with a thickness of 0.5 μm. The mass content of lithium phosphate in the positive electrode lithium supplement layer is 80%.

[0466] The positive electrode film layer includes a film layer formed by evenly coating a positive electrode slurry (with a solvent of N-methylpyrrolidone (NMP)) on the surface of the positive electrode lithium supplement layer and then drying and cold pressing. The positive electrode film layer includes a positive electrode active material, a binder, polyvinylidene fluoride (PVDF), and a conductive agent, acetylene black, with a weight ratio of 97:2:1.

[0467] 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 Li 2 FeTi(PO 4 ) 3 and amorphous carbon. The Dv50 of the positive electrode active material is 1.6 μm, and the Dv10 is 0.64 μm.

[0468] Example 6 The battery cell was prepared by a method similar to that of Example 1. Different from Example 1, The preparation of the negative electrode sheet includes: The negative electrode plate includes a negative current collector, a negative conductive layer on the negative current collector, and a negative film layer. The negative current collector is a copper foil with a thickness of 5 μm. The negative conductive layer on the negative current collector is composed of a negative conductive agent, superconducting carbon, a negative binder, styrene-butadiene rubber (SBR), a thickening agent, sodium carboxymethyl cellulose (CMC-Na), and a solvent, water. After being mixed evenly, it is coated on the surface of the negative current collector with a thickness of 1 μm. The mass content of the negative conductive agent in the negative conductive layer is 35%, the mass content of the negative binder in the negative conductive layer is 60%, and the mass content of the thickening agent in the negative conductive layer is 5%.

[0469] The negative film layer includes a film layer formed by evenly coating a negative electrode paste (with deionized water as the solvent) on the surface of the negative conductive layer and then drying and cold-pressing it.

[0470] The negative film layer includes a first negative film layer and a second negative film layer. The first negative film layer is located on the surface of the negative conductive layer, and the second negative film layer is located on the surface of the first negative film layer.

[0471] The first negative film layer includes a negative active material, conductive agent acetylene black, a first lithium-containing binder (a copolymer of lithium acrylate - acrylonitrile - acrylamide - 2-hydroxyethyl acrylate), a negative binder styrene-butadiene rubber, and a 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 negative active material includes graphite particles and silicon oxide compounds. The mass content of silicon element in the silicon oxide compounds in the negative active material is 1.5%. The Dv50 of the graphite particles is 11.6 μm. The graphite particles include artificial graphite and a carbon coating layer. The carbon coating layer covers the surface of the artificial graphite, and the mass content of amorphous carbon is 3.5%.

[0472] The second negative film layer includes a negative active material, conductive agent acetylene black, a second lithium-containing binder (a copolymer of lithium acrylate - acrylonitrile - acrylamide - 2-hydroxyethyl acrylate), a negative binder styrene-butadiene rubber, and a thickening agent sodium carboxymethyl cellulose with a mass ratio of 97.5:0.5:0.5:0.5:1. The mass content of lithium element in the second lithium-containing binder is 4.8%. The negative active material includes graphite particles and silicon oxide compounds. The mass content of silicon element in the silicon oxide compounds in the negative active material is 1.5%. The Dv50 of the graphite particles is 11.6 μm. The graphite particles include artificial graphite and a carbon coating layer. The carbon coating layer covers the surface of the artificial graphite, and the mass content of amorphous carbon is 3.5%.

[0473] The performance test steps are the same as those in the previous text and will not be elaborated here. The test results are shown in Table 3.

[0474] Table 3

[0475] In Example 5, a lithium supplement is added to the positive electrode plate, which can make up for lithium loss in the battery system and increase the cycle life.

[0476] In Example 6, a silicon-based material is added to the negative electrode plate, which is beneficial to improving the energy density of the battery cell and can maintain excellent fast charging performance and cycle performance.

[0477] 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 the embodiments can be changed, substituted, and modified without departing from the spirit, principle, and scope of the present application.

Claims

1. A battery cell, characterized in that: The invention comprises an electrode assembly, an electrolyte and a shell, wherein the electrode assembly and the electrolyte are contained in the shell, the electrode assembly comprises a positive electrode sheet, a negative electrode sheet and a separator, and the separator is located between the positive electrode sheet and the negative electrode sheet. The positive electrode plate comprises a positive electrode current collector and a positive electrode film layer disposed on at least one side of the positive electrode current collector, the positive electrode film layer comprises a positive electrode active material, the positive electrode active material comprises a lithium-containing phosphate with an olivine structure, and the resistance of the positive electrode plate is 0.1Ω to 30Ω. The negative electrode plate comprises a negative electrode current collector and a negative electrode film layer disposed on at least one side of the negative electrode current collector, the negative electrode film layer comprises a negative electrode active material, and the resistance of the negative electrode plate is 0.001Ω to 0.01Ω. The electrolyte includes an organic solvent, the organic solvent includes a chain carboxylate solvent, and the mass content of the chain carboxylate solvent in the organic solvent is 5% to 75%; the conductivity of the electrolyte at room temperature is 13mS / cm to 20mS / cm.

2. The battery cell according to claim 1, characterized in that: The conductivity of the electrolyte at room temperature is 15 mS / cm to 20 mS / cm.

3. The battery cell according to any one of claims 1 to 2, characterized in that: The resistance of the positive electrode plate is 0.1Ω to 5Ω.

4. The battery cell according to claim 3, characterized in that: The resistance of the positive electrode plate is 0.1Ω to 1Ω.

5. The battery cell according to any one of claims 1 to 2, characterized in that: The resistance of the negative electrode plate is 0.001Ω to 0.005Ω.

6. The battery cell according to any one of claims 1 to 2, characterized in that: The viscosity of the electrolyte at room temperature is 2.3 mPa·s to 3.5 mPa·s.

7. The battery cell according to any one of claims 1 to 2, characterized in that: The electrolyte has a density of 1.05 g / mL to 1.35 g / mL at room temperature.

8. The battery cell according to any one of claims 1 to 2, characterized in that: The battery cell is at 100% charge state, and the compaction density of the positive electrode film layer is 2.50 g / cm 3 Up to 2.80g / cm 3 , and / or The single-sided coating weight of the positive electrode film layer is 200 mg / 1540.25 mm 2 Up to 370mg / 1540.25mm 2 .

9. The battery cell according to any one of claims 1 to 2, characterized in that: The compaction density of the positive electrode film layer of the battery cell is 2.55g / cm 3 Up to 2.70g / cm 3 , and / or The single-sided coating weight of the positive electrode film layer is 240 mg / 1540.25 mm 2 Up to 330mg / 1540.25mm 2 .

10. The battery cell according to any one of claims 1 to 2, characterized in that: The compaction density of the negative electrode film layer of the battery cell is 1.15 g / cm 3 Up to 1.36g / cm 3 , and / or The single-sided coating weight of the negative electrode film layer is 90 mg / 1540.25 mm 2 Up to 170mg / 1540.25mm 2 .

11. The battery cell according to any one of claims 1 to 2, characterized in that: The compaction density of the negative electrode film layer of the battery cell is 1.25 g / cm 3 Up to 1.36g / cm 3 , and / or The single-sided coating weight of the negative electrode film layer is 110 mg / 1540.25 mm 2 Up to 150mg / 1540.25mm 2 .

12. The battery cell according to any one of claims 1 to 2, characterized in that: The powder resistivity of the positive electrode active material is 1 Ω·cm to 27.5 Ω·cm.

13. The battery cell according to any one of claims 1 to 2, characterized in that: The powder compaction density of the positive electrode active material at 30000N is 2.46g / cm 3 Up to 2.8g / cm 3 .

14. The battery cell according to any one of claims 1 to 2, characterized in that: The positive electrode active material has a charge capacity of 150 mAh / g to 170 mAh / g at a charge rate of 0.1C.

15. The battery cell according to any one of claims 1 to 2, characterized in that: The powder resistivity of the negative electrode active material is 0.005 Ω·cm to 0.043 Ω·cm.

16. The battery cell according to any one of claims 1 to 2, characterized in that: The powder compaction density of the negative electrode active material under 20000N is 1.5g / cm 3 Up to 1.85g / cm 3 .

17. The battery cell according to any one of claims 1 to 2, characterized in that: The negative electrode active material has a charge capacity of 350 mAh / g to 480 mAh / g at a 0.1C rate.

18. The battery cell according to any one of claims 1 to 2, characterized in that: The lithium-containing phosphate of the olivine structure comprises: Phosphate particles, and A coating layer, wherein the coating layer covers the phosphate particles, and the coating layer contains one or more elements selected from the group consisting of C, Fe, Ti, Zr, Hf, Ge and Sn.

19. The battery cell according to claim 18, characterized in that: The phosphate particles include a general formula of Li x1 A y1 Me a M b P 1-c X c Y z A compound wherein 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.

20. The battery cell according to claim 18, characterized in that: The coating layer includes a general formula of Li 3-d Fe 2-d M2 d (PO x2 ) y2 The 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.

21. The battery cell according to claim 18, characterized in that: The graphitization degree of the lithium-containing phosphate with an olivine structure is 0.15 to 0.

32.

22. The battery cell according to claim 21, characterized in that: The graphitization degree of the lithium-containing phosphate with an olivine structure is 0.19 to 0.

26.

23. The battery cell according to claim 18, characterized in that: The mass content of carbon in the lithium-containing phosphate with olivine structure is 1% to 2%. The specific surface area of ​​the lithium-containing phosphate of the olivine structure is 5m 2 / g to 18m 2 / g.

24. The battery cell according to claim 23, characterized in that: The specific surface area of ​​the lithium-containing phosphate with olivine structure is 7.5 m 2 / g to 14m 2 / g.

25. The battery cell according to any one of claims 1 to 2, characterized in that: The lithium-containing phosphate with olivine structure is in granular form, and its volume distribution particle size satisfies: 1µm≤Dv50≤2µm, 0.4µm≤Dv10≤0.7µm.

26. The battery cell according to any one of claims 1 to 2, characterized in that: The lithium-containing phosphate with an olivine structure is in a granular form, and includes secondary particles. The secondary particles include a plurality of primary particles, and the average particle size of the primary particles is 200 nm to 500 nm.

27. The battery cell according to any one of claims 1 to 2, characterized in that: The positive electrode film layer also 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 metamanganate, lithium tartrate, trilithium citrate, lithium nickelate and lithium ferrite.

28. The battery cell according to any one of claims 1 to 2, characterized in that: The thickness of the positive electrode current collector is 10 μm to 15 μm.

29. The battery cell according to any one of claims 1 to 2, characterized in that: 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.

30. The battery cell according to claim 29, characterized in that The thickness of the positive electrode conductive layer is 0.5 μm to 2 μm.

31. The battery cell according to claim 29, characterized in that: The positive electrode conductive layer includes a positive electrode conductive agent, and 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, and / or The positive electrode conductive layer includes a positive electrode binder, and 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 fluorine-containing acrylic resin.

32. The battery cell according to any one of claims 1 to 2, characterized in that: 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%.

33. The battery cell according to claim 32, characterized in that: The graphite particles include: Artificial graphite, including secondary particles, and The carbon coating layer is coated on the surface of the artificial graphite.

34. The battery cell according to claim 33, characterized in that: The mass content of the carbon coating layer is 2% to 5% based on the mass of the graphite particles.

35. The battery cell according to any one of claims 1 to 2, characterized in that: The negative electrode film layer comprises: a first negative electrode film layer, disposed on the surface of the negative electrode current collector, 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 collector, and 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.

36. The battery cell according to claim 35, characterized in that The carbon-based material in the first negative electrode film layer also includes natural graphite.

37. The battery cell according to claim 35, characterized in that: The tap density of the carbon-based material in the first negative electrode film layer is less than or equal to the tap density of the carbon-based material in the second negative electrode film layer.

38. The battery cell according to claim 37, characterized in that: The tap density of the carbon-based material in the first negative electrode film layer is 0.82 g / cm 3 Up to 1.21g / cm 3 , and / or The tap density of the carbon-based material in the second negative electrode film layer is 0.90 g / cm 3 Up to 1.25g / cm 3 .

39. The battery cell according to claim 35, 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.

40. The battery cell according to claim 35, characterized in that The first negative electrode film layer also includes a first lithium-containing binder, and the second negative electrode film layer also 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.

41. The battery cell according to claim 40, characterized in that 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%.

42. The battery cell according to claim 40, characterized in that The mass content of lithium 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%.

43. The battery cell according to claim 40, characterized in that The first lithium-containing binder comprises a lithium acrylate-acrylonitrile-acrylamide-hydroxyethyl acrylate copolymer, wherein the lithium acrylate-acrylonitrile-acrylamide-hydroxyethyl acrylate copolymer is derived from a lithium acrylate monomer, an acrylonitrile monomer, an acrylamide monomer and a hydroxyethyl acrylate monomer, and the molar ratio of the lithium acrylate monomer, the acrylonitrile monomer, the acrylamide monomer and the hydroxyethyl acrylate monomer is 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-hydroxyethyl acrylate copolymer, wherein the lithium acrylate-acrylonitrile-acrylamide-hydroxyethyl acrylate copolymer is derived from a lithium acrylate monomer, an acrylonitrile monomer, an acrylamide monomer and a hydroxyethyl acrylate monomer, and the molar ratio of the lithium acrylate monomer, the acrylonitrile monomer, the acrylamide monomer and the hydroxyethyl acrylate monomer is 30% to 50%: 15% to 45%: 5% to 20%: 20% to 35%.

44. The battery cell according to any one of claims 1 to 2, characterized in that: The negative electrode active material further comprises a silicon-based material, and the mass 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.

45. The battery cell according to any one of claims 1 to 2, characterized in that: The thickness of the negative electrode current collector is 4 μm to 6 μm.

46. ​​The battery cell according to any one of claims 1 to 2, characterized in that: 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.

47. The battery cell according to claim 46, characterized in that The thickness of the negative electrode conductive layer is 0.5 μm to 2 μm.

48. The battery cell according to claim 46, characterized in that The negative electrode conductive layer includes a negative electrode conductive agent, and 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, and / or The negative electrode conductive layer includes a negative electrode binder, and the negative electrode binder includes one or more of styrene-butadiene rubber, water-soluble unsaturated resin, water-based acrylic resin, polyvinyl alcohol, sodium alginate and carboxymethyl chitosan.

49. The battery cell according to any one of claims 1 to 2, characterized in that: The isolation membrane includes a base membrane with a porous structure, and the porosity of the base membrane is 20% to 70%.

50. The battery cell according to claim 49, characterized in that The porosity of the base film is 35% to 60%.

51. The battery cell according to claim 49, characterized in that The base film has a thickness of 6 μm to 12 μm.

52. The battery cell according to claim 51, characterized in that The base film has a thickness of 6 μm to 9 μm.

53. The battery cell according to any one of claims 1 to 2, characterized in that: The isolation film includes a base film and a functional layer disposed on at least one side of the base film, wherein the functional layer includes: a first functional layer, located on one side of the base film, wherein the first functional layer comprises first inorganic particles, The second functional layer is located on the other side of the base film, and 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.

54. The battery cell according to claim 53, characterized in that The non-fluorinated polymer particles include acrylic copolymers.

55. The battery cell according to claim 53, characterized in that 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.

56. The battery cell according to claim 53, characterized in that 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.

57. The battery cell according to any one of claims 1 to 2, characterized in that: The mass content of the chain carboxylic acid ester solvent in the organic solvent is 30% to 70%.

58. The battery cell according to claim 57, characterized in that The chain carboxylic acid ester solvent includes a compound shown in 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 halogenated alkyl group, R2 includes a C1 to C5 alkyl group or a C1 to C5 halogenated alkyl group.

59. The battery cell according to claim 58, characterized in that R1 includes a hydrogen atom, a halogen atom, a C1 to C3 alkyl group or a C1 to C3 halogenated alkyl group, and / or R2 includes C1 to C3 alkyl or C1 to C3 halogenated alkyl.

60. The battery cell according to any one of claims 58 to 59, characterized in that: The chain carboxylic acid ester solvent includes one or more of the compounds represented by formula I-1 to the compounds represented by formula I-8, 。 61. The battery cell according to any one of claims 1 to 2, characterized in that: 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.

62. The battery cell according to claim 61, characterized in that The mass content of the carbonate solvent in the organic solvent is 30% to 70%.

63. The battery cell according to any one of claims 1 to 2, characterized in that: The electrolyte further includes additives, and the additives include one or more of carbonate additives, sulfur-containing additives and lithium salt additives.

64. The battery cell according to claim 63, characterized in that The carbonate additive includes one or more of vinylene carbonate, fluoroethylene carbonate, and / or The sulfur-containing additive includes one or more of vinyl sulfate, vinyl disulfate, butylene sulfite, 1,3-propane sultone, vinyl sulfite, and methylene disulfonate, and / or The lithium salt additive includes one or more of lithium difluorophosphate, lithium difluorooxalatoborate, lithium tetrafluoroborate, and lithium bis(oxalatoborate).

65. The battery cell according to claim 63, characterized in that The mass content of the additive in the electrolyte is 1% to 10%.

66. The battery cell according to claim 63, characterized in that The mass content of the additive in the electrolyte is 2% to 8%.

67. The battery cell according to any one of claims 1 to 2, characterized in that: The electrolyte further includes a lithium salt, and the lithium salt includes one or more of a fluorine-containing sulfonyl imide salt and lithium hexafluorophosphate.

68. The battery cell according to claim 67, characterized in that The fluorine-containing sulfonyl imide salt includes one or more of lithium bis(fluorosulfonyl)imide and lithium bis(trifluoromethanesulfonyl)imide.

69. The battery cell according to claim 67, characterized in that The lithium salt includes lithium bis(fluorosulfonyl)imide and lithium hexafluorophosphate. The molar concentration of the lithium bis(fluorosulfonyl)imide is 0.2 mol / L to 0.5 mol / L, and the molar concentration of the lithium hexafluorophosphate is 0.5 mol / L to 1.0 mol / L.

70. The battery cell according to claim 69, characterized in that The ratio of the molar concentration of the lithium bis(fluorosulfonyl)imide to the molar concentration of the lithium hexafluorophosphate is 0.2 to 1.

0.

71. The battery cell according to any one of claims 1 to 2, characterized in that: The shell is made of steel, and has a thickness of 0.1 mm to 0.5 mm.

72. The battery cell according to claim 71, characterized in that The thickness of the shell is 0.2 mm to 0.35 mm.

73. The battery cell according to any one of claims 1 to 2, characterized in that: The battery cell further includes an electrode terminal, and the electrode assembly includes a pole ear portion, and the pole ear portion is directly welded to the electrode terminal.

74. The battery cell according to any one of claims 1 to 2, characterized in that: The charging time of the battery cell from 10% state of charge to 80% state of charge is 5 minutes to 10.5 minutes.

75. A battery device, characterized in that: Comprising a plurality of battery cells as claimed in any one of claims 1 to 74.

76. The battery device according to claim 75, characterized in that The charging time of the battery device from a 10% state of charge to an 80% state of charge is 5 minutes to 10.5 minutes.

77. An electrical device, characterized in that: Comprising a battery device as described in claim 75 or 76.

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