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 a shell, an electrolyte and an electrode assembly, the shell comprises a shell and an end cover, the electrolyte and the electrode assembly are accommodated in the shell, the shell is provided with an opening, the end cover covers the opening, the electrode assembly comprises a positive pole piece and a negative pole piece, the positive electrode plate comprises a positive electrode current collector and a positive electrode film layer which is arranged on at least one side of the positive electrode current collector along the thickness direction of the positive electrode plate and contains a positive electrode active material, and the positive electrode active material comprises lithium-containing phosphate with an olivine structure; the negative electrode plate comprises a negative electrode current collector and a negative electrode film layer which is arranged on at least one side of the negative electrode current collector along the thickness direction of the negative electrode plate and contains a negative electrode active material, and the discharge capacity of the positive electrode film layer per unit area is 2.0 mAh / cm < 2 > to 3.7 mAh / cm < 2 >; the size of the positive electrode film layer in the first direction is 75-105 mm, and the first direction is parallel to the direction from the shell to the end cover. According to the invention, the energy density of the battery monomer can be further improved.

Description

[0001] This application claims the priority of the patent application PCT / CN2024 / 102651 titled "Battery Cell, Battery Device and Electrical Device" filed on June 28, 2024, and the entire content of this application 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 electric 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 volumetric energy density and fast charging performance. Summary of the Invention This application provides a battery cell, a battery device and an electrical device, and this application can further improve the energy density of the battery cell.

[0004] In a first aspect, this application proposes a battery cell. The battery cell includes a housing, an electrolyte and an electrode assembly. The housing includes a shell and an end cap. The shell houses the electrolyte and the electrode assembly. The shell has an opening, and the end cap covers the opening. The electrode assembly includes a positive electrode plate, a negative electrode plate and a separator. The separator is located between the positive electrode plate and the negative electrode plate. 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 along the thickness direction of the positive electrode plate and containing a positive electrode active material. The positive electrode active material includes a lithium-containing phosphate with an olivine structure; 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 along the thickness direction of the negative electrode plate and containing a negative electrode active material. Wherein, the discharge capacity per unit area of the positive electrode film layer is 2.0 mAh / cm 2 to 3.7 mAh / cm 2 ; the size of the positive electrode film layer in a first direction is 75 mm to 105 mm, and the first direction is parallel to the direction pointing from the shell to the end cap.

[0005] Thus, in the embodiments of this application, when the size of the positive electrode film layer in the first direction is less than 75 mm, the coating size of the positive electrode active material is relatively small, which is not conducive to improving the energy density of the battery cell; as the size of the positive electrode film layer in the first direction increases, the coating size of the positive electrode active material can be increased, further making the discharge capacity per unit area of the positive electrode film layer greater than or equal to 2.0 mAh / cm 2 , which can improve the energy density of the battery cell; however, when the discharge capacity per unit area of the positive electrode film layer is greater than 3.7 mAh / cm 2When the coating amount of the positive electrode film layer is too large, the migration resistance of lithium ions is relatively high, which is not conducive to improving the fast charging performance of the battery cell. Further limiting the size of the positive electrode film layer in the first direction to be less than or equal to 105 mm is beneficial to comprehensively improving the energy density and fast charging performance of the battery cell to a certain extent. Therefore, when the size of the positive electrode film layer in the first direction in the embodiment of the present application is 75 mm to 105 mm, the discharge capacity per unit area of the positive electrode film layer is synergistically regulated to be 2.0 mAh / cm 2 to 3.7 mAh / cm 2 , which can effectively improve the energy density of the battery cell and is applicable to the battery cell in the fast charging system.

[0006] In some embodiments, the discharge capacity per unit area of the positive electrode film layer is 2.4 mAh / cm 2 to 3.4 mAh / cm 2 . When the discharge capacity per unit area of the positive electrode film layer is within the above range, it is beneficial to further improve the energy density of the battery cell.

[0007] In some embodiments, the ratio of the discharge capacity per unit area of the negative electrode film layer to the discharge capacity per unit area of the positive electrode film layer is 1.05 to 1.15, and can be optionally 1.07 to 1.13.

[0008] Thus, when the ratio of the discharge capacity per unit area of the negative electrode film layer to the discharge capacity per unit area of the positive electrode film layer is within the above range, the lithium ions released from the positive electrode film layer can basically be embedded in the negative electrode film layer, reducing the risk of lithium deposition in the negative electrode film layer and improving the use reliability of the battery cell; and due to the low risk of lithium deposition and less lithium loss, the capacity loss of the battery cell can be reduced, and its cycle performance and fast charging performance can be improved.

[0009] In some embodiments, the discharge capacity per unit area of the negative electrode film layer is 2.0 mAh / cm 2 to 4.1 mAh / cm 2 , and can be optionally 2.4 mAh / cm 2 to 3.7 mAh / cm 2 . When the discharge capacity per unit area of the negative electrode film layer is within the above range, there are sufficient sites in the negative electrode film layer for lithium to be embedded, which can reduce the risk of lithium deposition; and it is beneficial to fast charging.

[0010] In some embodiments, the conductivity of the electrolyte is 13 mS / cm to 20 mS / cm, and can be optionally 15 mS / cm to 20 mS / cm. The migration rate of lithium ions in this 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.

[0011] In some embodiments, the dimension of the battery cell in the first direction is 90 mm to 130 mm. When the dimension of the battery cell in the first direction is within the above range, in cooperation with the dimension of the positive electrode film layer in the first direction, the positive electrode active material coated on the positive electrode film layer increases, which is beneficial to improving the energy density of the battery cell.

[0012] 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 , and can be 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, and since the positive electrode active material in the positive electrode film layer is 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.

[0013] 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 . 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.

[0014] In some embodiments, the powder resistivity of the positive electrode active material is 1 Ω•cm to 27.5 Ω•cm. The relatively low powder resistivity of the positive electrode active material results in a relatively low resistance of the positive electrode sheet and less heat generation of the battery cell.

[0015] 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 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.

[0016] In some embodiments, the charging specific capacity of the positive electrode active material at a 0.1C rate is 150 mAh / g to 170 mAh / g. When the charging specific capacity of the positive electrode active material at a 0.1C rate is within the above range, the energy density of the battery cell is relatively high.

[0017] In some embodiments, the lithium-containing phosphate with an olivine structure includes phosphate particles and a coating layer. The coating layer coats the phosphate particles, and the coating layer contains one or more elements among C, Fe, Ti, Zr, Hf, Ge, and Sn. By coating the surface of the phosphate particles with the coating layer, the conductivity of the lithium-containing phosphate with an olivine structure can be improved, the powder resistivity of the material can be reduced, the migration rate of lithium ions is facilitated, and the heat generation of a single battery can be reduced.

[0018] 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 ≤ 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 includes one or more of Na, K, and Mg, Me includes one or more of Mn, Fe, Co, and Ni, M includes one or more of B, Mg, Al, Si, P, S, Ca, Sc, Ti, V, Cr, Cu, Zn, Sr, Y, Zr, Nb, Mo, Cd, Sn, Sb, Te, Ba, Ta, W, Yb, La, and Ce, X includes one or more of S, Si, Cl, B, C, and N, and Y includes one or more of O and F. The phosphate particles have relatively excellent cycle stability, which is beneficial to improving the cycle performance of a single battery.

[0019] 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 , where M2 includes one or more elements among Ti, Zr, Hf, Ge, and Sn, 0 ≤ d ≤ 1, 0 < x 2 <5, 0 < y 2 <4. Coating the fast ion conductor on the surface of the phosphate particles can significantly improve the transmission 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 further improve the specific capacity, and further improve the energy density of the corresponding single battery.

[0020] In some embodiments, the graphitization degree of the positive electrode active material is from 0.15 to 0.32, and optionally from 0.19 to 0.26. When the graphitization degree of the positive electrode active material is within the above range, it is beneficial to improve the conductivity of the positive electrode active material, reduce the heat generation of the positive electrode sheet, and thus reduce the heat generation of the battery cell.

[0021] In some embodiments, the mass content of carbon element in the lithium-containing phosphate with olivine structure is from 1% to 2%, and the specific surface area of the lithium-containing phosphate with olivine structure is 5m 2 / g to 18m 2 / g, and optionally from 7.5m 2 / g to 14m 2 / g.

[0022] Thus, in the embodiments of the present application, the carbon element with the above mass content cooperates with the material with the above specific surface area, which is more beneficial to the effective contact between the electrolyte and the lithium-containing phosphate with olivine structure, and is beneficial to the transport of lithium ions at the phase interface.

[0023] In some embodiments, the lithium-containing phosphate with olivine structure is granular, and its volume distribution particle size satisfies: 1μm ≤ Dv50 ≤ 2μm, 0.4μm ≤ Dv10 ≤ 0.7μm. The particle size of the lithium-containing phosphate with 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.

[0024] In some embodiments, the lithium-containing phosphate with olivine structure is granular, the lithium-containing phosphate with olivine structure includes secondary particles, and the secondary particles include a plurality of primary particles, and the average particle size of the primary particles is from 200nm to 500nm. 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.

[0025] In some embodiments, the positive electrode film layer further includes one or more of ternary materials, lithium phosphate, lithium hydrogen phosphate, lithium sulfate, lithium sulfite, lithium molybdate, lithium oxalate, lithium titanate, lithium tetraborate, lithium metasilicate, lithium manganate, lithium tartrate, lithium citrate, lithium nickelate, and lithium ferrate. The above materials can supplement lithium ions for 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.

[0026] In some embodiments, the thickness of the positive electrode current collector is from 10μm to 15μm. 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.

[0027] In some embodiments, the positive electrode tab further includes a positive electrode conductive layer, which is located between the positive electrode film layer and the positive electrode current collector. The positive electrode conductive layer can further improve the conductivity of the positive electrode tab, reduce the heat generation of the positive electrode tab, and thus reduce the heat generation of the battery cell.

[0028] 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 tab, reduce the heat generation of the positive electrode tab, 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.

[0029] 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 tab and reducing the heat generation of the battery cell. The positive electrode binder in the positive electrode conductive layer can improve the bonding performance between the positive electrode current collector and the positive electrode film layer and improve the structural stability of the positive electrode tab.

[0030] 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.

[0031] 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.

[0032] In some embodiments, when the battery cell is in a 100% charged state, the tap density of the negative electrode film layer is 1.15 g / cm 3 to 1.36 g / cm 3 , optionally 1.25 g / cm 3 to 1.36 g / cm 3 . When the tap density of the negative electrode film layer is within the above range, it is beneficial to improve the energy density of the battery cell, and since the negative electrode active material in the negative electrode film layer is stacked relatively tightly and the contact resistance between particles is small, it can further reduce the resistance of the electrode tab and thus reduce heat generation.

[0033] 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 2When 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.

[0034] In some embodiments, the powder resistivity of the negative electrode active material is 0.005 Ω·cm to 0.043 Ω·cm. The relatively low powder resistivity of the negative electrode active material results in a relatively low resistance of the negative electrode sheet, and less heat generation of the battery cell.

[0035] In some embodiments, the powder compaction density of the negative electrode active material under 20000 N is 1.5 g / cm 3 to 1.85 g / cm 3 When the powder compaction density of the negative electrode active material under 20000 N is within the above range, it can improve the energy density of the battery cell. 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.

[0036] In some embodiments, the charging specific capacity of the negative electrode active material at 0.1 C rate is greater than or equal to 350 mAh / g. When the charging specific capacity of the negative electrode active material at 0.1 C rate is within the above range, the energy density of the battery cell is relatively high.

[0037] 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 electrical conductivity of the graphite particles is relatively excellent, which can reduce the heat generation of the negative electrode sheet, reduce the heat generation of the battery cell, and improve the fast charging performance of the battery cell.

[0038] 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 coats 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 electrical conductivity of the carbon coating layer is relatively excellent, which can reduce the internal resistance of the negative electrode sheet and reduce the heat generation of the battery cell.

[0039] 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, it can further reduce the internal resistance of the negative electrode sheet and reduce the heat generation of the battery cell.

[0040] 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 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.

[0041] Thus, 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. However, in the embodiments of the present application, the particle size of the second negative electrode film layer is relatively small, which can shorten the solid-phase transmission path of lithium ions, improve the fast charging performance, and can improve the problem of lithium deposition on the surface layer of the negative electrode plate.

[0042] In some embodiments, the carbon-based material in the first negative electrode film layer further includes natural graphite.

[0043] In some embodiments, the tapped density of the carbon-based material in the first negative electrode film layer is less than or equal to the tapped density of the carbon-based material in the second negative electrode film layer. When the tapped density of the carbon-based material in the second negative electrode film layer is greater than the tapped density of the carbon-based material in the first negative electrode film layer, the second negative electrode film layer is filled more densely, which improves the energy density of the battery cell. The first negative electrode film layer is filled relatively sparsely with richer pores, which can improve the fast charging performance of the battery cell.

[0044] 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, it can improve the fast charging performance of the battery cell.

[0045] 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, it can improve the energy density of the battery cell. 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, it can improve the fast charging performance.

[0046] In some embodiments, the volume average particle size Dv50 of the graphite particles in the second negative electrode film layer is 7.8 μm to 14.3 μm. When the volume average particle size Dv50 of the negative electrode active material in the second negative electrode film layer is within the above range, the tortuosity of lithium ion transport can be reduced, and the fast charging performance of the battery cell can be improved.

[0047] 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.

[0048] Therefore, in the embodiments of the present application, the mass content of the second lithium-containing binder in the second negative electrode film layer is relatively high, and the number of freely movable lithium ions provided by the second lithium-containing binder for the second negative electrode film layer is relatively large, which can further improve the fast charging performance of the battery cell.

[0049] 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 / extraction rate of lithium ions can be improved, and the fast charging performance of the battery cell can be improved.

[0050] In some embodiments, the mass content of lithium element in the first lithium-containing binder is 3% to 10%, and may be 3% to 8%. When the mass content of lithium element is within the above range, the number of freely movable lithium ions in the negative electrode film layer can be relatively large, which can further shorten the distance for lithium ions to diffuse to the surface of the negative electrode film layer, improve the insertion / extraction rate of lithium ions, and improve the fast charging performance of the battery cell.

[0051] 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 / extraction rate of lithium ions is improved, and the fast charging performance of the battery cell is improved.

[0052] In some embodiments, the mass content of lithium element in the second lithium-containing binder is 3% to 10%, and may be 3% to 8%. When the mass content of lithium element is within the above range, the number of freely movable lithium ions in the negative electrode film layer can be relatively large, which can further shorten the distance for lithium ions to diffuse to the surface of the negative electrode film layer, improve the insertion / extraction rate of lithium ions, and improve the fast charging performance of the battery cell.

[0053] In some embodiments, the first lithium-containing binder comprises a lithium acrylate-acrylonitrile-acrylamide-2-hydroxyethyl acrylate copolymer, which is derived from a lithium acrylate monomer, an acrylonitrile monomer, an acrylamide monomer, and a 2-hydroxyethyl acrylate monomer, and the molar 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%.

[0054] 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, and is not prone to swelling during charge and discharge, with a stable structure, so that the cycling performance of the negative electrode film layer is improved during fast charge and discharge.

[0055] In some embodiments, the second lithium-containing binder comprises a lithium acrylate-acrylonitrile-acrylamide-2-hydroxyethyl acrylate copolymer, which is derived from a lithium acrylate monomer, an acrylonitrile monomer, an acrylamide monomer, and a 2-hydroxyethyl acrylate monomer, and the molar 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, and is not prone to swelling during charge and discharge, with a stable structure, so that the cycling performance of the negative electrode film layer is improved during fast charge and discharge.

[0057] In some embodiments, 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. The introduction of the silicon-based material can improve the capacity of the negative electrode active material and increase the energy density of the battery cell.

[0058] 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 the battery cell can have a high energy density.

[0059] In some embodiments, the negative electrode sheet further comprises a negative electrode conductive layer, and the negative electrode conductive layer is located between the negative electrode film layer and the negative electrode current collector.

[0060] In some embodiments, the thickness of the negative electrode conductive layer is 0.5 μm to 2 μm. The negative electrode conductive layer can further improve the electrical conductivity of the negative electrode sheet, reduce the heat generation of the negative electrode sheet, and thus reduce the heat generation of the battery cell.

[0061] 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.

[0062] In some embodiments, the negative electrode conductive agent includes one or more of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0063] In some embodiments, the negative electrode binder includes one or more of styrene-butadiene rubber, water-soluble unsaturated resin SR-1B, water-based acrylic resin, polyvinyl alcohol, sodium alginate, and carboxymethyl chitosan.

[0064] 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.

[0065] In some embodiments, the carboxylic acid ester solvent includes a chain carboxylic acid ester solvent, and the mass content of the chain carboxylic acid ester solvent in 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%. When the mass content of the chain carboxylic acid ester solvent is within the above range, the viscosity of the electrolyte system is relatively small, which is beneficial to the migration of lithium ions.

[0066] In some embodiments, the chain carboxylic acid 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 to C5 alkyl group, or a C1 to C5 haloalkyl group, R 2 includes a C1 to C5 alkyl group or a C1 to C5 haloalkyl group.

[0067] Thus, the conductivity of the above chain carboxylic acid 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.

[0068] In some embodiments, R 1 includes a hydrogen atom, a halogen atom, a C1 to C3 alkyl group, or a C1 to C3 haloalkyl group.

[0069] In some embodiments, R 2 comprises a C1-C3 alkyl or a C1-C3 haloalkyl.

[0070] In some embodiments, the chain carboxylic ester solvents include one or more of the compounds represented by Formula I-1 to Formula I-8,

[0071] In some embodiments, the organic solvent further includes a carbonate solvent, and the carbonate solvent includes one or more of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate. The above-mentioned carbonate solvents and chain carboxylic ester solvents are used in combination to improve the conductivity of the electrolyte, which is beneficial to the migration of lithium ions.

[0072] In some embodiments, the carbonate solvent includes one or more of ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate.

[0073] In some embodiments, the mass content of the carbonate solvent in the organic solvent is 30% to 70%, and may be 30% to 50%. The carbonate solvent with the above mass content can further improve the conductivity of the electrolyte, which is beneficial to the migration of lithium ions.

[0074] In some embodiments, the electrolyte further includes an additive, and the additive includes one or more of a carbonate additive, a sulfur-containing additive, and a lithium salt additive. The above 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.

[0075] In some embodiments, the carbonate additive includes one or more of vinylene carbonate VC and fluoroethylene carbonate FEC.

[0076] In some embodiments, the sulfur-containing additive includes one or more of ethylene sulfate DTD, bis(ethylene sulfate) 2-DTD, butene sulfite BS, 1,3-propane sultone PS, ethylene sulfite ES, and methylene methanedisulfonate MMDS.

[0077] In some embodiments, the lithium salt additive includes lithium difluorophosphate LiPO 2 F 2 , lithium difluorooxalate borate LiDFOB, lithium tetrafluoroborate LiBF 4 , and lithium bis(oxalate) borate LiBOB.

[0078] In some embodiments, the mass content of the additive in the electrolyte is 1% to 10%, optionally 2% to 8%. The additive with the above mass content can effectively improve the interfacial film performance on the positive electrode side and / or the negative electrode side, is beneficial to improving the fast charging performance of the battery cell, and improves the cycle performance.

[0079] In some embodiments, the electrolyte further includes a lithium salt, and the lithium salt includes a fluorosulfonylimide salt and lithium hexafluorophosphate LiPF 6 One or more of them. The above lithium salt is easy to dissociate, which is beneficial to the rapid migration of lithium ions, and the electrolyte system is relatively stable and not easy to decompose, which can improve the cycle performance of the battery cell.

[0080] In some embodiments, the fluorosulfonylimide salt includes one or more of lithium bis(fluorosulfonyl)imide LiFSI and lithium bis(trifluoromethylsulfonyl)imide LiTFSI.

[0081] 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 0.2 mol / L to 0.5 mol / L, and lithium hexafluorophosphate LiPF 6 The molar concentration of is 0.5 mol / L to 1.0 mol / L.

[0082] In some embodiments, the ratio of the molar concentration of lithium bis(fluorosulfonyl)imide to the molar concentration of lithium hexafluorophosphate LiPF 6 in is 0.2 to 1.0.

[0083] 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.

[0084] 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.

[0085] 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.

[0086] In some embodiments, the separator membrane comprises a base film and a functional layer disposed on at least one side of the base film. The functional layer comprises a first functional layer and a second functional layer. The first functional layer is located on one side of the base film and comprises first inorganic particles. The second functional layer is located on the other side of the base film and comprises composite particles. The composite particles comprise 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 membrane.

[0087] In some embodiments, the non-fluoropolymer particles comprise acrylate copolymers. Acrylate copolymers have excellent adhesion properties and high adhesion stability to the base film.

[0088] In some embodiments, the first inorganic particles comprise one or more of silica, alumina, boehmite, barium sulfate, calcium oxide, titanium oxide, zinc oxide, magnesium oxide, zirconium oxide, and tin oxide. The above first inorganic particles can improve the heat resistance of the first functional layer.

[0089] In some embodiments, the second inorganic particles comprise one or more of silica, alumina, boehmite, barium sulfate, calcium oxide, titanium oxide, zinc oxide, magnesium oxide, zirconium oxide, and tin oxide. The above second inorganic particles can improve the heat resistance of the first functional layer.

[0090] In some embodiments, the average particle size of the second inorganic particles is 5 nm to 100 nm. When the average particle size of the second inorganic particles is in the above range, it is beneficial to improve the heat resistance and compression modulus of the composite particles.

[0091] 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 in 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.

[0092] 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 in 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.

[0093] In some embodiments, the base material of the housing includes steel, and the thickness of the housing is from 0.1 mm to 0.5 mm, and may be optionally 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 cycling 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 group margin of the battery cell is greater than or equal to 96% and less than 100%, and may be optionally from 96.5% to 99.5%. When the group margin is within the above range, it is beneficial to improve the energy density 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 12.5 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 12.5 min. The charging speed of the battery device is relatively fast, which is more beneficial to improving the fast charging ability.

[0098] In some embodiments, the battery device includes a box body, and the box body houses the battery cells. Among them, the dimension of the box body in the first direction is from 110 mm to 170 mm.

[0099] 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. BRIEF DESCRIPTION OF THE DRAWINGS

[0100] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following will briefly introduce the drawings required to be used 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, other drawings can be obtained according to the drawings without creative efforts.

[0101] Figure 1 It is a schematic structural diagram of a battery cell provided for some embodiments of the present application; Figure 2 It is an exploded view of a battery cell provided for some embodiments of the present application; Figure 3 It is a schematic structural diagram of a battery module provided for some embodiments of the present application; Figure 4Schematic diagram of the structure of a battery pack provided for some embodiments of the present application; Figure 5 For Figure 4 Explosion diagram of the battery pack shown; Figure 6 Schematic diagram of the structure of an electrical device provided for some embodiments of the present application.

[0102] The drawings are not necessarily drawn to actual scale.

[0103] The drawings are not necessarily drawn to actual scale.

[0104] Explanation of reference numerals in the drawings is as follows: X, the first direction; 1, electrical device; 2, battery pack; 3, controller; 4, motor; 5, housing; 5a, first housing part; 5b, second housing part; 5c, accommodation space; 6, battery module; 7, battery cell; 10, electrode assembly; 111, positive electrode tab; 112, negative electrode tab; 12, main body part; 20, outer shell; 21, housing; 22, end cap; 31, positive terminal; 32, negative terminal. Specific embodiments

[0105] Hereinafter, embodiments of the battery cell, battery device, and electrical device of the present application specifically disclosed will be described in detail with appropriate reference to the drawings. However, there may be cases where unnecessary detailed descriptions are omitted. For example, there are cases where detailed descriptions of well-known matters and repeated descriptions of actually identical structures are omitted. This is to avoid 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 recited in the claims.

[0106] 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 the end values or not include 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 understood to be anticipated. In addition, if the minimum range values 1 and 2 are listed, and if the maximum range values 3, 4, and 5 are listed, then the following ranges are all anticipated: 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 both a and b are 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.

[0107] If there is no special instruction, all embodiments and optional embodiments of this application can be combined with each other to form a new technical solution.

[0108] If there is no special instruction, all technical features and optional technical features of this application can be combined with each other to form a new technical solution.

[0109] If there is no special instruction, all steps of this application can be carried out in sequence or randomly, preferably in sequence. For example, if the method includes steps (a) and (b), it means that the method can include steps (a) and (b) carried out in sequence, or can also include steps (b) and (a) carried out in sequence. 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.

[0110] With the development of the battery field, the requirements for the energy density of battery cells are gradually increasing. Especially when the battery cells are relatively small, it is more difficult to improve the energy density of battery cells.

[0111] In view of the above problems, the embodiments of this application reasonably design the system of battery cells, and improve the energy density of battery cells by increasing the discharge capacity of the positive electrode film layer and the coating size of the positive electrode film layer in the battery cells.

[0112] Battery cell In a first aspect, an embodiment of the present application provides a battery cell.

[0113] As Figure 1 and Figure 2 shown, the battery cell 7 includes an electrolyte, an electrode assembly 10, and a housing 20. The electrode assembly 10 includes a positive electrode tab, a negative electrode tab, and a separator. The separator is located between the positive electrode tab and the negative electrode tab. The positive electrode tab includes a positive current collector and a positive electrode film layer provided on at least one side of the positive current collector along the thickness direction of the positive electrode tab and containing a positive electrode active material. The positive electrode active material includes a lithium-containing phosphate having an olivine structure. The negative electrode tab includes a negative current collector and a negative electrode film layer provided on at least one side of the negative current collector along the thickness direction of the negative electrode tab and containing a negative electrode active material. The housing 20 includes a housing body 21 and an end cap 22. The housing body 21 has an opening and houses the electrolyte and the electrode assembly 10. The end cap 22 covers the opening. Wherein, the discharge capacity per unit area of the positive electrode film layer is 2.0 mAh / cm 2 to 3.7 mAh / cm 2 , the size of the positive electrode film layer along a first direction X is 75 mm to 105 mm, and the first direction X is parallel to the direction pointing from the housing body 21 to the end cap 22.

[0114] Generally, when the battery cell 7 is assembled into a box body, the battery cell 7 is placed vertically, and the height direction of the battery cell 7 is parallel to the direction pointing from the housing body 21 to the end cap 22, that is, the height direction of the battery cell 7 is parallel to the first direction X.

[0115] When the size of the positive electrode film layer along the first direction X is relatively small, for example, less than 75 mm, the coating size of the positive electrode active material is relatively small, which is not conducive to improving the energy density of the battery cell 7. As the size of the positive electrode film layer along the first direction X increases, the coating size of the positive electrode active material can be increased, further making the discharge capacity per unit area of the positive electrode film layer greater than or equal to 2.0 mAh / cm 2 , which can improve the energy density of the battery cell 7. However, when the discharge capacity per unit area of the positive electrode film layer is greater than 3.7 mAh / cm 2 , the coating amount of the positive electrode film layer may be too large, resulting in a large migration resistance of lithium ions, which is not conducive to improving the fast charging performance of the battery cell 7. Further limiting the size of the positive electrode film layer along the first direction X to be less than or equal to 105 mm is beneficial to comprehensively improving the energy density and fast charging performance of the battery cell 7 to a certain extent.

[0116] Therefore, when the size of the positive electrode film layer of the embodiment of the present application along the first direction X is 75 mm to 105 mm, the discharge capacity per unit area of the positive electrode film layer is coordinately regulated to be 2.0 mAh / cm 2To 3.7 mAh / cm 2 , which can effectively improve the energy density of the battery cell 7 and is applicable to the battery cell 7 in a fast charging system.

[0117] In the embodiment of the present application, the discharge capacity of the positive electrode film layer per unit area is 2.0 mAh / cm 2 to 3.7 mAh / cm 2 , and can be optionally 2.4 mAh / cm 2 to 3.4 mAh / cm 2 . For example, the discharge capacity of the positive electrode film layer per unit area is 2.0 mAh / cm 2 , 2.1 mAh / cm 2 , 2.2 mAh / cm 2 , 2.3 mAh / cm 2 , 2.4 mAh / cm 2 , 2.5 mAh / cm 2 , 2.6 mAh / cm 2 , 2.7 mAh / cm 2 , 2.8 mAh / cm 2 , 2.9 mAh / cm 2 , 3.0 mAh / cm 2 , 3.1 mAh / cm 2 , 3.2 mAh / cm 2 , 3.3 mAh / cm 2 , 3.4 mAh / cm 2 , 3.5 mAh / cm 2 , 3.6 mAh / cm 2 , 3.7 mAh / cm 2 or a range composed of any two of the above values.

[0118] In some embodiments, the ratio CB of the discharge capacity of the negative electrode film layer per unit area to the discharge capacity of the positive electrode film layer per unit area is 1.05 to 1.15, and can be optionally 1.07 to 1.13. Exemplarily, the ratio CB of the discharge capacity of the negative electrode film layer per unit area to the discharge capacity of the positive electrode film layer per unit area in the battery cell 7 is 1.05, 1.07, 1.1, 1.12, 1.13, 1.14, 1.15 or a range composed of any two of the above values.

[0119] When the ratio CB of the discharge capacity of the negative electrode film layer per unit area to the discharge capacity of the positive electrode film layer per unit area is within the above range, the lithium ions released from the positive electrode film layer can basically be embedded in the negative electrode film layer, reducing the risk of lithium deposition in the negative electrode film layer and improving the reliability of the use of the battery cell 7; and due to the lower risk of lithium deposition and less lithium loss, the capacity loss of the battery cell 7 can be reduced, and its cycle performance and fast charging performance can be improved.

[0120] In some embodiments, the discharge capacity of the negative electrode film layer per unit area is 2.0 mAh / cm 2 to 4.1 mAh / cm 2 . It can be optionally 2.4 mAh / cm 2 to 3.7 mAh / cm 2 . Exemplarily, the discharge capacity of the negative electrode film layer per unit area is 2.0 mAh / cm 2 , 2.1 mAh / cm 2 , 2.2 mAh / cm 2 , 2.3 mAh / cm 2 , 2.4 mAh / cm 2 , 2.5 mAh / cm 2 , 2.6 mAh / cm 2 , 2.7 mAh / cm 2 , 2.8 mAh / cm 2 , 2.9 mAh / cm 2 , 3.0 mAh / cm 2 , 3.1 mAh / cm 2 , 3.2 mAh / cm 2 , 3.3 mAh / cm 2 , 3.4 mAh / cm 2 , 3.5 mAh / cm 2 , 3.6 mAh / cm 2 , 3.7 mAh / cm 2 , 3.8 mAh / cm 2 , 3.9 mAh / cm 2 , 4.0 mAh / cm 2 , 4.1 mAh / cm 2 or the range composed of any two of the above values.

[0121] When the discharge capacity of the negative electrode film layer per unit area is within the above range, there are sufficient sites in the negative electrode film layer for lithium to be embedded, which can reduce the risk of lithium deposition; and it is beneficial for fast charging.

[0122] In the embodiments of the present application, the CB value can be detected by using devices and methods well-known in the art. For example, the discharge capacity per unit area of the negative electrode film layer and the discharge capacity per unit area of the positive electrode film layer are calculated respectively, and the ratio of the two is calculated to obtain the CB value. The upper charge limit voltage and the lower discharge cut-off voltage of the battery cell 7 vary 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. Another example is that 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 for illustration: The discharge capacity per unit area of the positive electrode film layer 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 actual battery electrode sheet, which is double-sided coated. It is necessary to scrub off the substances in the film layer on one side with DMC solvent. Assemble the side with the film layer and the lithium sheet to form a CR2430 type half-button cell of positive electrode - lithium sheet. The area of the positive electrode sheet used for discharging is a cm 2 , and the electrolyte used is 1mol / LLiPF 6 in a solution of EC / EMC / DEC = 3 / 5 / 2 (mass ratio); then let the assembled half-button cell stand for 3 h, the test is carried out at 25 °C, first charge (Charge) and de-lithiate in the voltage range of 2.0 V to 4.0 V at 0.05C, and then discharge (Discharge) and 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 discharge capacity per unit area of the positive electrode film layer = Y / a.

[0123] Specifically, the discharge capacity per unit area of the negative electrode film layer refers to the actual intercalation capacity of the negative electrode active material. The test method is: Disassemble the battery in a PRS340 / 11-119-11 Braun glove box, take the actual battery electrode sheet, which is double-sided coated. It is necessary to scrub off the substances in the film layer on one side with DMC solvent. Assemble the side with the film layer and the lithium sheet to form a CR2430 type half-button cell of negative electrode - lithium sheet. The area of the negative electrode sheet used for discharging is f cm 2 , and the electrolyte used is 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 discharging (Discharge) and inserting lithium in the voltage range of 2 V - 0.04 V at 0.05 C, and then charging (charge) and extracting lithium to 2 V at 0.05 C for 2 cycles. The discharge and charge capacity of the second cycle is recorded as Z mAh, and the discharge capacity per unit area of the negative electrode film layer = Z / f.

[0124] In some embodiments, the size of the negative electrode film layer along the length direction of the negative electrode tab is larger than the size of the positive electrode film layer along the length direction of the positive electrode tab, and the difference between the two is 0.5 mm to 3.0 mm, such as 0.5 mm, 1.0 mm, 1.5 mm, 2.0 mm, 2.5 mm, 3.0 mm or a range composed of any two of the above values. Since the size of the negative electrode film layer is relatively large, it can provide sufficient lithium insertion sites for lithium ions, reduce the risk of lithium deposition, and improve the reliability of use of the battery cell 7.

[0125] In some embodiments, the size of the negative electrode film layer along the width direction of the negative electrode tab is larger than the size of the positive electrode film layer along the width direction of the positive electrode tab, and the difference between the two is 0.5 mm to 3.0 mm, such as 1.0 mm, 1.5 mm, 2.0 mm, 2.5 mm, 3.0 mm or a range composed of any two of the above values. Since the size of the negative electrode film layer is relatively large, it can provide sufficient lithium insertion sites for lithium ions, reduce the risk of lithium deposition, and improve the reliability of use of the battery cell 7.

[0126] In some embodiments, the conductivity of the electrolyte at room temperature is 13 mS / cm to 20 mS / cm, and can be optionally 15 mS / cm to 20 mS / cm. Exemplarily, the conductivity of the electrolyte at room temperature is 13 mS / cm, 13.5 mS / cm, 14 mS / cm, 14.5 mS / cm, 15 mS / cm, 15.5 mS / cm, 16 mS / cm, 16.5 mS / cm, 17 mS / cm, 17.5 mS / cm, 18 mS / cm, 18.5 mS / cm, 19 mS / cm, 19.5 mS / cm, 20 mS / cm or a range composed of any two of the above values.

[0127] 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 improving the fast charging performance of the battery cell.

[0128] 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.

[0129] The conductivity of the electrolyte can be regulated by adjusting the type and content of the organic solvent in the electrolyte; it can also be regulated by adjusting the type and content of lithium salts and the like in the electrolyte.

[0130] [Electrolyte] During the charge and discharge process of the battery cell, the active 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 the active ions between the positive electrode plate and the negative electrode plate.

[0131] 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 the range composed of any two of the above values.

[0132] When the viscosity of the electrolyte at room temperature, such as 25 °C, is within the above range, the migration rate of lithium ions in the electrolyte is relatively high, which can further reduce the internal resistance of the battery cell, thereby reducing heat generation, and can improve the fast charging performance of the battery cell.

[0133] In the embodiments of the present application, the viscosity of the electrolyte has the meaning well-known in the art, and it can be detected by using the equipment and methods well-known in the art. For example, it can be detected according to GB / T10247-2008.

[0134] 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.

[0135] When the density of the electrolyte is within the above range, the migration rate of lithium ions in the electrolyte is relatively high, which can further reduce the internal resistance of the battery cell, thereby reducing heat generation, and can improve the fast charging performance of the battery cell.

[0136] 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.

[0137] 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.

[0138] In some embodiments, the organic solvent includes a chain carboxylic acid ester solvent, and the mass content of the chain carboxylic acid ester solvent relative to the mass of the organic solvent is greater than or equal to 5% and less than or equal to 75%, optionally greater than or equal to 10% and less than or equal to 90%, optionally 30% to 70%, and optionally 50% to 70%. Exemplarily, the mass content of the chain carboxylic acid ester solvent is 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75% or a range composed of any two of the above values.

[0139] When the mass content of the chain carboxylic acid ester solvent is within the above range, the viscosity of the electrolyte system is relatively small, which is beneficial to the migration of lithium ions.

[0140] In some embodiments, the chain carboxylic acid 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.

[0141] The above chain carboxylic acid ester solvent has a relatively high conductivity, which is beneficial to improving the fast charging ability of the battery cell.

[0142] 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.

[0143] 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.

[0144] 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.

[0145] In the above embodiments, the haloalkyl group includes one or more of fluoroalkyl group, chloroalkyl group, bromoalkyl group and iodoalkyl group. Optionally, the haloalkyl group includes a fluoroalkyl group.

[0146] Exemplarily, the chain carboxylic ester solvents include one or more of the compounds represented by Formula I-1 to the compounds represented by Formula I-8.

[0147] In some embodiments, the organic solvent further includes carbonate solvents.

[0148] Optionally, the carbonate solvents include one or more of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate and ethyl methyl carbonate. Further optionally, the carbonate solvents include one or more of ethylene carbonate, dimethyl carbonate and ethyl methyl carbonate. The above carbonate solvents and chain carboxylic 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.

[0149] Further optionally, the mass content of the carbonate solvents in the organic solvent is 30% to 70%, and can be 30% to 50%. Exemplarily, the mass content of the carbonate solvents 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 solvents 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.

[0150] Exemplarily, the carbonate solvents include one or more of ethylene carbonate, dimethyl carbonate and ethyl methyl carbonate, and the mass content of the carbonate solvents is 30% to 50%.

[0151] In some embodiments, the electrolyte further contains additives. The additives can include negative electrode film-forming additives, or can include positive electrode film-forming additives, or can also include additives that can improve certain performance of the battery, 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.

[0152] In some embodiments, the additives include one or more of carbonate additives, sulfur-containing additives and lithium salt additives, and can be at least two. The above additives can improve the interfacial film performance on the positive electrode side and / or the negative electrode side, which is beneficial to improving the fast charging performance of the battery monomer and improving the cycle performance.

[0153] In some embodiments, the mass content of the additive in the electrolyte is from 1% to 10%, optionally from 2% to 8%, and further optionally from 3.5% to 8%. Exemplarily, the mass content of the additive in the electrolyte is 1%, 2%, 3%, 3.5%, 4%, 5%, 6%, 7%, 8%, 9%, 10% or a range composed of any two of the above values.

[0154] The additive with the above mass content can effectively improve the interfacial film performance on the positive electrode side and / or the negative electrode side, which is beneficial to enhancing the fast charging performance of the battery cell and improving the cycling performance.

[0155] Exemplarily, the carbonate additives include one or more of vinylene carbonate (VC) and fluoroethylene carbonate (FEC).

[0156] Exemplarily, the sulfur-containing additives include one or more of ethylene sulfate (DTD), bis(ethylene sulfate) (2-DTD), butene sulfite (BS), 1,3-propane sultone (PS), ethylene sulfite (ES), and methylene methyl disulfonate (MMDS).

[0157] Optionally, the lithium salt additives include lithium difluorophosphate LiPO 2 F 2 , lithium difluorooxalate borate (LiDFOB), lithium tetrafluoroborate LiBF 4 , and lithium bis(oxalate) borate (LiBOB), or one or more of them.

[0158] Optionally, the mass content of vinylene carbonate (VC) in the electrolyte is from 0.5% to 9%, and can be from 2% to 6%.

[0159] Optionally, the mass content of fluoroethylene carbonate (FEC) in the electrolyte is from 0.1% to 4%, and can be from 0.5% to 3%.

[0160] Optionally, the mass content of vinylene carbonate (VC) in the electrolyte is from 0.5% to 9%, and the mass content of fluoroethylene carbonate (FEC) in the electrolyte is from 0.1% to 4%.

[0161] Further optionally, the mass content of vinylene carbonate (VC) in the electrolyte is from 2% to 6%, and the mass content of fluoroethylene carbonate (FEC) in the electrolyte is from 0.5% to 3%.

[0162] In some embodiments, the electrolyte salt 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 cycling performance of the battery cell.

[0163] Optionally, the fluorosulfonylimide salt includes one or more of lithium bis(fluorosulfonyl)imide LiFSI and lithium bis(trifluoromethanesulfonyl)imide LiTFSI.

[0164] 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 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.

[0165] Exemplarily, the molar concentration of lithium bis(fluorosulfonyl)imide LiFSI is from 0.4 mol / L to 0.5 mol / L, and the molar concentration of lithium hexafluorophosphate LiPF 6 is 0.7 mol / L.

[0166] 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.

[0167] 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.

[0168] Optionally, 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, and may be from 0.2 to 0.5. Exemplarily, the ratio of the molar concentration of lithium bis(fluorosulfonyl)imide to the molar concentration of lithium hexafluorophosphate LiPF 6 is 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1 or a range composed of any two of the above values.

[0169] In the embodiments of the present application, the types and contents of the inorganic components / lithium salt concentration in the electrolyte have the meanings well known in the art, and can be detected by using the 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 concentration in the electrolyte by ion chromatography analysis method. In the embodiments of the present application, freshly prepared electrolyte can be taken as a sample, free electrolyte of a fresh battery can be taken as a sample, or a discharged battery (discharged to the lower cut-off voltage so that the charged state of the battery is about 0% SOC) can be disassembled in reverse, and the free electrolyte obtained from the battery can be taken as a sample, and detected by ion chromatography analysis method.

[0170] In the embodiments of the present application, the types and contents of the organic components in the electrolyte have meanings well-known in the art, and can be detected by devices and methods well-known in the art. For example, qualitative and quantitative analysis of the organic components in the electrolyte can be carried out by gas chromatography with reference to GB / T9722-2006 General Rules for Chemical Reagents - Gas Chromatography. In the embodiments of the present application, freshly prepared electrolyte can be taken as a sample, or the 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 for detection by ion chromatography analysis method.

[0171] In the embodiments of the present application, after quantitatively and qualitatively detecting each component in the electrolyte, each component is classified. Chain carboxylic ester solvents and carbonate solvents (such as ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate) are used as 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. Carbonate additives (such as vinylene carbonate, fluoroethylene carbonate), sulfur-containing additives, and lithium salt additives are used as additives in the electrolyte. Based on the mass of the electrolyte being 100%, the mass content of each component is calculated.

[0172] In some embodiments, the battery cell satisfies: 2.45 g / Ah ≤ d / A ≤ 3.5 g / Ah, and 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.

[0173] d / A can reflect the liquid retention ability of the electrolyte. When d / A is within the above range, the electrolyte can play a better wetting role on the positive electrode plate and the negative electrode plate, and can also improve the migration rate of lithium ions in the liquid phase, which is beneficial to improving the fast charging ability of the battery cell.

[0174] In the embodiments of the present application, d / A of the battery cell can be understood as the liquid retention coefficient, and can be detected by devices and methods well-known in the art. For example, taking the upper charge voltage of the battery as 3.65 V and the discharge cut-off voltage of the battery as 2.0 V as an example in accordance with GB / T31486-2015 Electrical Performance Requirements and Test Methods for Power Batteries for Electric Vehicles. At 25°C, the battery cell is charged at 0.33C to 3.65V, then charged at a constant voltage to 0.05C, and then discharged at a constant current of 0.33C to 2.0V. The discharged capacity A is used as the denominator. The battery cell is weighed as M0, and then the positive electrode plate, negative electrode plate, separator, and electrolyte are disassembled. The free electrolyte is stored in a bag. All the above solid components are placed in an oven at 60°C and baked for more than 4 hours (including but not limited to the positive electrode plate, negative electrode plate, and separator, and also including other mechanical parts of the disassembled battery cell that contribute to M0). Then, all the components of the battery cell are weighed as M1. The weight difference between M0 and M1 is used as the numerator. The liquid retention coefficient is equal to the value obtained by dividing the weight difference d between M0 and M1 by the capacity A.

[0175] [Positive electrode plate] The positive electrode plate includes a positive current collector and a positive electrode film layer provided on at least one surface of the positive current collector and including a positive active material. For example, the positive current collector has two surfaces opposite to each other in its own thickness direction, and the positive electrode film layer is provided on either or both of the two opposite surfaces of the positive current collector.

[0176] 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 the range composed of any two of the above values.

[0177] 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, the contact resistance between particles is small, which can further reduce the resistance of the electrode sheet and thus reduce the 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.

[0178] In the embodiments of the present application, the 100% state of charge (SOC) and 0% SOC of the battery cell are defined as follows: The battery cell is charged at a constant current charging rate of 0.33C to the upper charging voltage, and then charged at a constant voltage to 0.05C, corresponding to the state of 100% SOC of the battery cell; the battery cell is discharged at a constant current discharge rate of 0.33C to the cut-off voltage, corresponding to the state of 0% SOC of the battery cell.

[0179] 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.

[0180] 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 take into account improving the energy density and charging rate performance of the battery cell.

[0181] In the embodiments of the present application, the compaction density of the positive electrode film layer of the battery cell in the 100% state of charge (SOC) can be detected by the following method. Disassemble the positive electrode sheet from the battery cell in the 100% state of charge (SOC), and measure the compaction density of the positive electrode film layer. For example, take a single-sided coated positive electrode sheet (if it is a double-sided coated sheet, one side of the positive electrode film layer can be wiped off first), punch it into small circular 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 sheet, 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 sheet - the weight M0 of the positive electrode current collector) / S1, the thickness of the positive electrode film layer = the thickness H1 of the positive electrode sheet - the thickness H0 of the positive electrode current collector, and the 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.

[0182] 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 a range composed of any two of the above values.

[0183] The relatively low powder resistivity of the positive electrode active material makes the resistance of the positive electrode sheet relatively low, and the heat generation of the battery cell is less.

[0184] 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.

[0185] 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 / cm3 Exemplarily, the powder tap density of the positive electrode active material under 30,000 N is 2.46 g / cm 3 、2.47 g / cm 3 、2.48 g / cm 3 、2.49 g / cm 3 、2.5 g / cm 3 、2.51 g / cm 3 、2.55 g / cm 3 、2.58 g / cm 3 、2.60 g / cm 3 、2.65 g / cm 3 、2.68 g / cm 3 、2.70 g / cm 3 、2.72 g / cm 3 、2.75 g / cm 3 、2.78 g / cm 3 、2.80 g / cm 3 or a range composed of any two of the above values.

[0186] When the powder tap density of the positive electrode active material under 30,000 N is within the above range, the energy density of the battery cell can be improved, and since the positive electrode active material in the positive electrode film layer can be stacked more closely, the contact resistance between particles is small, which can further reduce the resistance of the electrode sheet, thereby reducing heat generation.

[0187] In the embodiments of the present application, the powder tap 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 30,000 N), kept under pressure for 30 s, then depressurized, kept for 10 s, and then the powder tap density of the positive electrode active material under the action of 30,000 N is recorded and calculated.

[0188] In some embodiments, the charging specific capacity of the positive electrode active material at a rate of 0.1C is from 150 mAh / g to 170 mAh / g, and optionally from 157 mAh / g to 170 mAh / g. Exemplarily, the charging specific capacity of the positive electrode active material at a rate of 0.1C is 150 mAh / g, 151 mAh / g, 152 mAh / g, 153 mAh / g, 154 mAh / g, 155 mAh / g, 156 mAh / g, 157 mAh / g, 158 mAh / g, 159 mAh / g, 160 mAh / g, 161 mAh / g, 162 mAh / g, 163 mAh / g, 164 mAh / g, 165 mAh / g, 166 mAh / g, 167 mAh / g, 168 mAh / g, 169 mAh / g, 170 mAh / g or a range composed of any two of the above values.

[0189] When the charging specific capacity of the positive electrode active material at a rate of 0.1C is within the above range, the energy density of the battery cell is relatively high.

[0190] In the embodiments of the present application, the specific capacity of the active material has the meaning well-known in the art, and can be tested by equipment and methods well-known in the art. The test method for 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 charge-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.

[0191] 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 at least one of lithium-containing transition metal oxides. Examples of the lithium-containing transition metal oxides can include but are not limited to at least one of lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide and their respective modified compounds.

[0192] Optionally, the mass ratio of the lithium-containing phosphate with an olivine structure in the positive electrode active material is 100%.

[0193] In the embodiments of the present application, the lithium-containing phosphate of olivine structure can be phosphate particles or a material obtained by coating and modifying them. For example, the lithium-containing phosphate of 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.

[0194] By coating the surface of the phosphate particles with a coating layer, the conductivity of the lithium-containing phosphate of 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, improve the fast charging ability of the battery, and reduce the heat generation of the battery cell.

[0195] 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 ≤ 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 includes one or more of Na, K, Mg, Me includes one or more of Mn, Fe, Co, Ni, M includes one or more of B, Mg, Al, Si, P, S, Ca, Sc, Ti, V, Cr, Cu, Zn, Sr, Y, Zr, Nb, Mo, Cd, Sn, Sb, Te, Ba, Ta, W, Yb, La, Ce, X includes one or more of S, Si, Cl, B, C, N, and Y includes one or more of O, F. The phosphate particles have excellent cycle stability, which is beneficial to improving the cycle performance of the battery cell.

[0196] Exemplarily, the phosphate particles include one or more of LiFePO 4 、LiMnPO 4 、LiNiPO 4 、LiCoPO 4 . 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 in the battery cell is different when the battery cell is discharged to different states. Regarding the cathode active materials LiFePO 4 、LiMnPO 4 、LiNiPO 4 、LiCoPO 4In the examples of the present invention, 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 used in the battery system, the molar content of Li may change after charge and discharge cycles. 4 、LiMnPO 4 、LiNiPO 4 、LiCoPO 4 In the enumeration of etc., the molar content of oxygen O is only a theoretical value. The release of oxygen from the lattice will cause the molar content of oxygen O to change. In reality, the molar content of oxygen O will fluctuate. The above situations are all within the protection scope of the present application.

[0197] In some embodiments, 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 selected from Ti, Zr, Hf, Ge and Sn, 0≤d≤1, 0<x 2 <5,0<y 2 <4.

[0198] Exemplarily, the fast ion conductor is a material having a NASICON structure, for example, 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.

[0199] Fast ion conductors with NASICON structures are materials with ultrafast ion conduction capabilities, rich three-dimensional lithium ion diffusion and transmission channels, and have the advantages of high ion conduction efficiency and strong structural stability during multiple lithium removal and insertion processes. Coating fast ion conductors with NASICON structures on the surface of phosphate particles can significantly increase the transmission rate of lithium ions during multiple lithium removal / insertion at the positive terminal, improve the ionic conductivity of the positive electrode active material, and improve the fast charging capability of the battery cell. In addition, it can also increase the gram capacity and the energy density of the corresponding battery cell.

[0200] In some embodiments, the coating layer further includes carbon.

[0201] The carbon element and the fast ion conductor can be arranged in layers, for example, the carbon element is used as an independent carbon coating layer, and the fast ion conductor is used 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. Alternatively, the fast ion conductor layer can be coated on the surface of the phosphate particles, and the carbon coating layer is located on the surface of the fast ion conductor layer, that is, the carbon coating layer is located on the side of the fast ion conductor layer away from the phosphate particles. Of course, the carbon element and the fast ion conductor can also be arranged in the same layer.

[0202] Optionally, the carbon coating layer can be coated on the surface of the fast ion conductor layer by a carbonization process of an organic carbon source (e.g., glucose, polyethylene glycol, etc.). The carbon coating layer can partially coat the fast ion conductor layer, or it can completely coat the fast ion conductor layer. The provision of the carbon coating layer can significantly improve the electronic conductivity of the phosphate particles, make up for the defect of poor electronic conductivity of the phosphate particles, and improve the energy density of the battery cell. Specifically, the provision of the carbon coating layer enables the positive electrode active material of the present application to have the following advantages: The carbon coating layer in the positive electrode active material of the present application provides a suitable channel for the transmission of electrons, which can significantly improve the conduction rate of electrons in multiple lithium de- and lithium insertion processes, improve the electronic conductivity of lithium-containing phosphates, improve the charging capacity of the corresponding battery cells, and also improve the energy density.

[0203] The carbon coating layer of the positive electrode active material of the present application is loose and porous, which enables the electrolyte to be in full and effective contact with the lithium-containing phosphate, thereby increasing the transmission rate of lithium ions at the interface and improving the charging capacity of the battery cell.

[0204] Coating a carbon coating on the surface of the lithium-containing phosphate can not only improve the conductivity of the lithium-containing phosphate, but also improve the structural stability of the positive electrode active material, effectively alleviate the iron dissolution of the positive electrode active material during long-term storage and cyclic use of the battery cell, thereby improving the cycle life of the battery cell. The positive electrode active material of the present application uses lithium-containing phosphate as a base material, giving full play to the advantages of low cost, high reliability and good cycle stability of lithium-containing phosphate, while using the coating layer (fast ion conductor layer and carbon coating layer) to solve the disadvantages of poor electronic conductivity and ion conductivity. The battery cell prepared by the positive electrode active material of the present application can improve the energy density of the battery cell while having 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 devices 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 atomic emission (ICP-OES, instrument model: Thermo ICAP7400). After discharging the battery cell to 0% state of charge (SOC) and disassembling the positive electrode sheet, it is cleaned with DMC, dried, and then calcined at high temperature to remove impurities. Then, 0.4 g of the positive electrode active material is weighed, and 10 ml (50% concentration) of aqua regia is added thereto. Then it is placed on a flat plate at 180 °C for 30 min. After digestion on the flat plate, it is made up to a volume of 100 mL, and quantitative testing is carried out by the standard curve method.

[0205] In some embodiments, the graphitization degree of the positive electrode active material is from 0.15 to 0.32, and can be optionally from 0.19 to 0.26. Exemplarily, the graphitization degree of the positive electrode active material is 0.15, 0.16, 0.17, 0.18, 0.19, 0.20, 0.21, 0.22, 0.23, 0.24, 0.25, 0.26, 0.27, 0.28, 0.29, 0.30, 0.31, 0.32 or the range composed of any two of the above values.

[0206] When the graphitization degree of the positive electrode active material is within the above range, it is beneficial to improve the conductivity of the positive electrode active material, reduce the heat generation of the positive electrode sheet, and thus reduce the heat generation of the battery cell.

[0207] In the embodiments of the present application, the higher the graphitization degree of the material, the lower the degree of disorder. It can be tested according to the general rules of X-ray diffraction analysis method of JIS / K 0131-1996.

[0208] In some embodiments, the mass content of carbon element in the lithium-containing phosphate with olivine structure is from 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.

[0209] Optionally, the mass content of carbon element in the lithium-containing phosphate with olivine structure is from 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.

[0210] Exemplarily, the mass content of carbon element in the lithium-containing phosphate with olivine structure is 1%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2% or the range composed of any two of the above values.

[0211] Exemplarily, the specific surface area of the lithium-containing phosphate in the 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.

[0212] The carbon element 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 the carbon element is within the above range, the conductivity of the lithium-containing phosphate in the olivine structure can be significantly improved, which is beneficial to enhancing the ionic conductivity and electronic conductivity of the lithium-containing phosphate in the olivine structure, and can improve the rapid charging ability and energy density of the battery cell.

[0213] 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 using the equipment and methods well-known in the art. For example, it can be detected according to the test standard GB / T 19587-2017. The positive electrode active material is used as a sample, and the specific surface area is tested by a Tri-Star 3020 specific surface area and pore size analyzer of Micromeritics Company, USA.

[0214] 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.

[0215] 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.

[0216] Exemplarily, the Dv10 of the positive electrode active material may 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.

[0217] The particle size of the positive electrode active material is relatively small, the lithium intercalation / deintercalation path of lithium ions in the positive electrode active material is short, and the heat generation is less. Moreover, the particle size of the above positive electrode active material is not too small, and agglomeration basically does not occur during the processing and preparation process, so that the performance of the positive electrode active material is stable.

[0218] In the embodiments of the present application, the volume average particle size Dv50 of the material refers to the particle size corresponding to 50% in the volume distribution, and the volume average particle size Dv10 of the material refers to the particle size corresponding to 10% in the volume distribution. It can be detected by using equipment and methods well-known in the art. For example, taking the positive electrode active material as a sample, according to the test standard GB / T 19077-2016, the Dv50 and Dv10 of the particles are tested by a Mastersizer 2000E laser particle size analyzer, etc.

[0219] When the positive electrode active material includes other materials in addition to the lithium-containing phosphate with an olivine structure, the volume distribution particle size of the positive electrode active material refers to the volume distribution particle size of all the positive electrode active materials.

[0220] In some embodiments, the lithium-containing phosphate with an olivine structure is granular, and the lithium-containing phosphate with an olivine structure includes secondary particles, and the secondary particles include a plurality of primary particles. The average particle size of the primary particles is 200 nm to 500 nm. Exemplarily, the average particle size of the primary particles is 200 nm, 220 nm, 250 nm, 280 nm, 300 nm, 320 nm, 350 nm, 380 nm, 400 nm, 420 nm, 450 nm, 480 nm, 500 nm, or a range composed of any two of the above values.

[0221] The average particle size of the primary particles is relatively small, the lithium intercalation / deintercalation path of lithium ions in the positive electrode active material is short, and the heat generation is less.

[0222] In the embodiments of the present application, the secondary particles refer to aggregated particles formed by the 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 image of the scanning electron microscope. The SEM test parameters can be set as follows: the working voltage (EHT) is 10.00 kV, the InLens detector is used, the working distance is 4.6 mm, and the magnification is 1000X.

[0223] 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 be used as lithium supplement agents, which can supplement lithium ions to the positive electrode film layer, make up for the irreversible lithium ion loss in the system, and improve the capacity, thereby improving the energy density of the battery cell.

[0224] 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 several of Na, K, Mg, M3 includes one or several 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, Ce, and Y3 includes one or several of O, F.

[0225] 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 0.05O 2 at least one of

[0226] 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.

[0227] 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 cyclic charge and discharge process 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.

[0228] 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. As an 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%.

[0229] 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. As an 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%.

[0230] In some embodiments, the positive 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 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. As an 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. 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).

[0231] 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.

[0232] 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.

[0233] In some embodiments, the thickness of the positive electrode current collector is 10 μm to 15 μm, and may be optionally 12 μm to 15 μm. Exemplarily, the thickness of the positive electrode 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.

[0234] 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 high energy density.

[0235] In the embodiments of the present application, the thicknesses of the positive electrode film layer and the positive electrode current collector have meanings well-known in the art, and can be detected by equipment and methods well-known in the art. For example, the thickness of the positive electrode plate is measured using a micrometer, the film layer on the surface of the positive electrode current collector is removed, and the thickness of the positive electrode current collector is measured using a micrometer. When the positive electrode film layer is coated on one side, the thickness of the positive electrode film layer is the thickness of the positive electrode plate minus the thickness of the positive electrode current collector. When the positive electrode film layer is coated on both sides, the thickness of the positive electrode film layer is (the thickness of the positive electrode plate minus the thickness of the positive electrode current collector) / 2.

[0236] The positive electrode film layer is usually formed by coating a positive electrode slurry on a positive electrode current collector and then drying and cold pressing. The positive electrode slurry is usually formed by dispersing a positive electrode active material, an optional conductive agent, an optional binder, and any other components in a solvent and stirring evenly. The solvent can be N-methylpyrrolidone (NMP), but is not limited thereto.

[0237] The positive electrode tab does not exclude other additional functional layers besides the positive electrode film layer. For example, in some embodiments, the positive electrode tab of the embodiment of the present application further includes a positive electrode conductive layer disposed on the surface of the positive electrode current collector and sandwiched between the positive electrode current collector and the positive electrode film layer. In some other embodiments, the positive electrode tab of the embodiment of the present application further includes a protective layer covering the surface of the positive electrode film layer.

[0238] In some embodiments, the positive electrode tab 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 tab, reduce the heat generation of the positive electrode tab, and thus reduce the heat generation of the battery cell.

[0239] 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.

[0240] When the thickness of the positive electrode conductive layer is within the above range, it can further improve the conductivity of the positive electrode tab, reduce the heat generation of the positive electrode tab, 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.

[0241] In the embodiment 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, the positive electrode tab is subjected to tomography to directly measure the thickness of the positive electrode conductive layer.

[0242] In some embodiments, the positive electrode conductive layer includes one or more of a positive electrode conductive agent and a positive electrode binder.

[0243] Optionally, the mass content of the positive electrode conductive agent in the positive electrode conductive layer is from 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.

[0244] 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 tab and reducing the heat generation of the battery cell.

[0245] 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.

[0246] 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 adhesion performance between the positive electrode current collector and the positive electrode film layer, and improve the structural stability of the positive electrode plate.

[0247] [Negative electrode plate] The negative electrode plate 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.

[0248] In some embodiments, when the battery cell is in a 100% charged state, the tap density of the negative electrode film layer is 1.15 g / cm 3 to 1.36 g / cm 3 , optionally 1.25 g / cm 3 to 1.36 g / cm 3 . Exemplarily, 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 a range composed of any two of the above values.

[0249] When the tap density of the negative electrode film layer is within the above range, it is beneficial to improve the energy density of the battery cell, and since the negative electrode active materials in the negative electrode film layer are stacked relatively tightly and the contact resistance between particles is small, the resistance of the electrode plate can be further reduced, thereby reducing heat generation.

[0250] In the embodiments of the present application, the compaction density of the negative electrode film layer in the 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 compaction density test method of the positive electrode film layer described above.

[0251] 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 , and can be optionally 110 mg / 1540.25 mm 2 to 150 mg / 1540.25 mm 2 . Exemplarily, the single-sided coating weight of the negative electrode film layer is 90 mg / 1540.25 mm 2 , 92 mg / 1540.25 mm 2 , 95 mg / 1540.25 mm 2 , 96 mg / 1540.25 mm 2 , 100 mg / 1540.25 mm 2 , 102 mg / 1540.25 mm 2 , 104 mg / 1540.25 mm 2 , 105 mg / 1540.25 mm 2 , 108 mg / 1540.25 mm 2 , 110 mg / 1540.25 mm 2 , 112 mg / 1540.25 mm 2 , 114 mg / 1540.25 mm 2 , 115 mg / 1540.25 mm 2 , 116 mg / 1540.25 mm 2 , 118 mg / 1540.25 mm 2 , 120 mg / 1540.25 mm 2 , 122 mg / 1540.25 mm 2 , 125 mg / 1540.25 mm 2 , 128 mg / 1540.25 mm 2 , 130 mg / 1540.25 mm 2 , 132 mg / 1540.25 mm 2 , 135 mg / 1540.25 mm 2 , 137 mg / 1540.25 mm 2 , 140 mg / 1540.25 mm 2 , 142 mg / 1540.25 mm 2, 145 mg / 1540.25 mm 2 , 148 mg / 1540.25 mm 2 , 150 mg / 1540.25 mm 2 , 152 mg / 1540.25 mm 2 , 155 mg / 1540.25 mm 2 , 160 mg / 1540.25 mm 2 , 165 mg / 1540.25 mm 2 , 170 mg / 1540.25 mm 2 Or a range composed of any two of the above values.

[0252] 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 plate will not be excessive, and the energy density of the battery cell can be improved while taking it into account.

[0253] 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 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.

[0254] 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.

[0255] The relatively low powder resistivity of the negative electrode active material results in a relatively low resistance of the negative electrode plate and less heat generation of the battery cell.

[0256] In the embodiments of the present application, the powder resistivity of the negative electrode active material has the meaning well known in the art, and can be detected by the equipment and methods well known in the art. The detection method is as described in the powder resistivity test method of the positive electrode active material above.

[0257] 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.

[0258] When the powder compaction density of the negative electrode active material is within the above range under 20,000 N, the energy density of the battery cell can be improved. And because 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.

[0259] In the embodiments of the present application, the powder compaction density of the material has the meaning well-known in the art, and can be detected by the methods and equipment well-known in the art, and detected 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 20,000 N), 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 20,000 N is recorded and calculated.

[0260] In some embodiments, the charging specific capacity of the negative electrode active material at 0.1 C rate is 350 mAh / g to 480 mAh / g. Exemplarily, the charging specific capacity of the negative electrode active material at 0.1 C 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 a range composed of any two of the above values.

[0261] When the charging specific capacity of the negative electrode active material at 0.1 C rate is within the above range, the energy density of the battery cell is relatively high.

[0262] In the embodiments of the present application, the charging specific capacity of the negative electrode active material at a rate of 0.1C 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 charging specific capacity test method of the positive electrode active material at a rate of 0.1C described above.

[0263] In some embodiments, the negative electrode active material includes a carbon-based material. The carbon-based material has high cycle stability and can improve the cycle performance of the battery cell. Optionally, the mass ratio of the carbon-based material in the negative electrode active material can be greater than or equal to 80% and less than or equal to 100%.

[0264] The positive electrode active material of the present application is mainly a lithium-containing phosphate system with an olivine structure, and the negative electrode active material is mainly a carbon-based material system. When used in combination, the battery cell has excellent cycle performance.

[0265] 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 the range composed of any two of the above values.

[0266] When the graphitization degree of the graphite particles is within the above range, the graphite particles have excellent electrical conductivity, can reduce the heat generation of the negative electrode sheet and the battery cell, and can improve the fast charging performance of the battery cell.

[0267] 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 covers the surface of the artificial graphite. The carbon in the carbon coating layer is mainly amorphous carbon. Amorphous carbon refers to a transitional carbon material with a very low degree of graphitization crystallization and an approximate amorphous form (or no fixed shape and periodic structural rules). In the present application, amorphous carbon refers to the product after carbonization treatment of an organic carbon source.

[0268] The artificial graphite includes secondary particles. In the artificial graphite, there are more migration paths for lithium ions, 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, and the electrical conductivity of the carbon coating layer is excellent, which can reduce the internal resistance of the negative electrode sheet and the heat generation of the battery cell.

[0269] 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 the range composed of any two of the above values.

[0270] 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.

[0271] In the embodiments of the present application, the graphite particles can be prepared by methods well known in the art. For example, the preparation method includes: providing artificial graphite and an organic carbon source, mixing the two, and after carbonization treatment, a carbon coating layer is formed on at least part of the surface of the artificial graphite particles.

[0272] Optionally, the organic carbon source includes one or more of coal tar pitch, petroleum pitch, phenolic resin, and coconut shell. Further optionally, the organic carbon source includes petroleum pitch. Optionally, the softening point of the coal tar pitch and petroleum pitch is below 250 °C.

[0273] Optionally, the carbonization treatment temperature is 700 °C to 1800 °C. Optionally, the carbonization treatment temperature is 1000 °C to 1300 °C. When the carbonization treatment temperature is within a suitable range, the organic carbon source can be carbonized, and a coating layer containing amorphous carbon is formed on at least part of the surface of the artificial graphite.

[0274] Optionally, the carbonization treatment time is 1 h to 6 h.

[0275] 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.

[0276] 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.

[0277] Optionally, based on the mass of the negative electrode active material, the mass content of silicon element in the silicon-based material is 0.3% to 10.0%, and may be optionally 1% to 6%. Exemplarily, the mass content of silicon element in the silicon-based material is 0.3%, 0.5%, 0.8%, 1%, 1.2%, 1.5%, 1.8%, 2%, 2.2%, 2.5%, 2.8%, 3%, 3.2%, 3.5%, 3.8%, 4%, 4.2%, 4.5%, 4.8%, 5%, 5.2%, 5.5%, 5.8%, 6%, 6.2%, 6.5%, 6.8%, 7%, 7.2%, 7.5%, 7.8%, 8%, 8.2%, 8.5%, 8.8%, 9%, 9.2%, 9.5%, 9.8%, 10% or any range composed of any two of the above values.

[0278] 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.

[0279] 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.

[0280] In some embodiments, in addition to the above-mentioned carbon-based material and optional silicon-based material, the negative electrode active material may further include at least one of a tin-based material and lithium titanate. The tin-based material may include at least one of elemental tin, tin oxide, and tin alloy material.

[0281] The qualitative and quantitative determination of each substance or element 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, etc. from the perspective of detection accuracy to obtain more accurate detection results. One detection method can be used for qualitative or quantitative determination, or several detection methods can be used in combination for qualitative or quantitative determination.

[0282] For example, this application can perform X-ray powder diffraction testing and qualitative analysis on the negative electrode sheet or the negative electrode active material in combination with the general rules of X-ray diffraction analysis method JIS / K0131-1996.

[0283] Artificial graphite and natural graphite can be distinguished by the SEM cross-sectional view taken by scanning electron microscope (SEM). There are voids between the flake structures in the SEM cross-sectional view of natural graphite, and the SEM cross-sectional view of artificial graphite is dense and has no obvious gaps, or 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, and only 2H phase exists in the XRD spectrum of artificial graphite.

[0284] 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.

[0285] When the negative electrode film layer adopts a single-layer film layer, the negative electrode active material in the negative electrode film layer includes a carbon-based material, and optionally also includes a silicon-based material. When adopting a single-layer film layer, the volume average particle diameter Dv50 of the negative electrode active material is 8.2 μm to 13.5 μm. Exemplarily, the volume average particle diameter 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.

[0286] When the negative electrode film layer adopts at least two film layers, the negative electrode active material in the negative electrode film layer includes a carbon-based material, and optionally also includes a silicon-based material. The silicon-based material can be located in one of the at least two film layers or in at least two of the at least two film layers. The negative electrode film layer can include two film layers, three film layers, four film layers, or even more film layers.

[0287] 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 can be the same or different.

[0288] The interface between the first negative electrode film layer and the second negative electrode film layer can be regular or irregular, and is optionally irregular.

[0289] Optionally, the carbon-based material in the first negative electrode film layer further includes natural graphite.

[0290] The negative electrode film layer includes at least two film layers, and layer-by-layer 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.

[0291] 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.

[0292] The difference in particle sizes 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 lies mainly in the second negative electrode film layer. In the embodiments of the present application, the particle size in the second negative electrode film layer is relatively small, which can shorten the solid-phase transport path of lithium ions, improve the fast charging performance, and can improve the problem of lithium deposition on the surface layer of the negative electrode plate.

[0293] 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, and can be 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, and can be optionally from 9.5 μm to 14.6 μm.

[0294] 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.

[0295] 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, and can be 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, and can be optionally from 7.8 μm to 11.3 μm.

[0296] 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 other 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.

[0297] In the embodiments of the present application, the volume average particle size Dv50 of the negative electrode active material has the meaning well known in the art, and can be detected by the equipment and methods well known in the art. The detection method is the same as the volume average particle size Dv50 test method of the positive electrode active material described above.

[0298] Optionally, 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. The tap density can reflect the packing density of the active material in the film layer. When the tap 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, improving the energy density of the battery cell. The first negative electrode film layer is relatively sparsely packed with more pores, which can enhance the fast charging performance of the battery cell. When the negative electrode active material includes graphite particles, the tap density of the graphite particles in the first negative electrode film layer is less than or equal to the tap density of the graphite particles in the second negative electrode film layer.

[0299] Optionally, the tap 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 , such as 0.82 g / cm 3 , 0.85 g / cm 3 , 0.88 g / cm 3 , 0.90 g / cm 3 , 0.92 g / cm 3 , 0.95 g / cm 3 , 0.98 g / cm 3 , 1.00 g / cm 3 , 1.05 g / cm 3 , 1.08 g / cm 3 , 1.10 g / cm 3 , 1.12 g / cm 3 , 1.15 g / cm 3 , 1.18 g / cm 3 , 1.20 g / cm 3 , 1.21 g / cm 3 or the range composed of any two of the above values. When the tap density of the carbon-based material in the first negative electrode film layer is within a suitable range, the fast charging performance of the battery cell can be improved.

[0300] Optionally, the tap density of the carbon-based material in the second negative electrode film layer is 0.90 g / cm 3 to 1.25 g / cm 3 , such as 0.90 g / cm 3 , 0.92 g / cm 3, 0.95 g / cm 3 , 0.98 g / cm 3 , 1.00 g / cm 3 , 1.05 g / cm 3 , 1.08 g / cm 3 , 1.10 g / cm 3 , 1.12 g / cm 3 , 1.15 g / cm 3 , 1.18 g / cm 3 , 1.20 g / cm 3 , 1.21 g / cm 3 , 1.22 g / cm 3 , 1.23 g / cm 3 , 1.24 g / cm 3 , 1.25 g / cm 3 Or a range composed of any two of the above values. When the tap density of the carbon-based material in the second negative electrode film layer is within a suitable range, the energy density of the battery cell can be improved.

[0301] 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.

[0302] 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.

[0303] 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.

[0304] 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.

[0305] 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 at 10 positions of the first negative electrode film layer, calculate their average value as the average value of the first negative electrode film layer, measure the thicknesses at 10 positions of the second negative electrode film layer, and calculate their average value as the average value of the second negative electrode film layer.

[0306] 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.

[0307] 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.

[0308] 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 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 minutes, then discharge at a discharge rate of 0.33C until 2.0V, and let it stand for 10 minutes. 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, 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.

[0309] In some embodiments, when the negative electrode film layer adopts a single-layer film layer (different from the above double-layer film layer), the negative electrode film layer further includes a lithium-containing binder. Optionally, the mass content of the lithium-containing binder relative to the mass of the negative electrode film layer is 0.1% to 1%. Exemplarily, the mass content of the lithium-containing binder relative to the mass of the negative electrode film layer is 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1% or a range composed of any two of the above values. The lithium element in the lithium-containing binder can exist in an ionic form, which can increase the number of free-moving lithium ions in the negative electrode film layer, shorten the distance for lithium ions to diffuse to the surface of the negative electrode film layer, 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).

[0310] 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.

[0311] 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.

[0312] The lithium-containing binder of the above materials 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 cycling performance of the negative electrode film layer is improved during the fast charge and discharge process.

[0313] 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.

[0314] 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.

[0315] The mass content of the second lithium-containing binder in the second negative electrode film layer is relatively high, and the second lithium-containing binder provides a relatively larger number of freely movable lithium ions for the second negative electrode film layer, which can further improve the fast charging performance of the battery cell.

[0316] 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.

[0317] 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.

[0318] 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.

[0319] 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.

[0320] 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.

[0321] The first lithium-containing binder and the second lithium-containing binder can be made of the same material or different materials.

[0322] 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.

[0323] 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.

[0324] 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.

[0325] 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).

[0326] 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.

[0327] In some embodiments, the negative electrode film layer may optionally further 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%.

[0328] In some embodiments, the negative electrode film layer may optionally further 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%.

[0329] In some embodiments, the negative electrode film layer may optionally further 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%.

[0330] 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).

[0331] 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.

[0332] 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.

[0333] 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 off with a solvent, and the thickness of the negative electrode current collector is measured with a micrometer.

[0334] 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.

[0335] 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.

[0336] 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.

[0337] 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.

[0338] 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 the improvement of the energy density of the battery cell.

[0339] 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 testing method of the negative electrode conductive layer in the foregoing can be adopted.

[0340] 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.

[0341] In some embodiments, the negative electrode conductive layer may also optionally include other additives. As an example, the other additives may include thickeners, such as sodium carboxymethyl cellulose (CMC), PTC thermistor materials, etc.

[0342] 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.

[0343] 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.

[0344] 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.

[0345] 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.

[0346] 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.

[0347] When the ratio CB of the capacity of the negative electrode film layer per unit area to the capacity of the positive electrode film layer per unit area in the battery cell is within the above range, there are sufficient sites in the negative electrode film layer for lithium insertion, which can reduce the risk of lithium deposition and is beneficial for fast charging.

[0348] 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.

[0349] 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. Its 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 cell 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.

[0350] 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 cell 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 cell 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.

[0351] [Separator membrane] In the embodiments of the present application, the separator membrane includes a base membrane with a porous structure.

[0352] 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.

[0353] Optionally, the polyolefin includes at least one of polyethylene, polypropylene, and polyvinylidene fluoride.

[0354] 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.

[0355] 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.

[0356] In the embodiments of the present application, the porosity refers to the percentage of the internal pore volume of the separator occupying the total volume of the separator. The porosity can be tested in accordance with the standard GB / T36363-2018 "Polyolefin Separator for Battery Cells". It should be noted that in the actual testing process, due to differences in testing instruments, testing errors, and in order to eliminate the influence on the porosity test as much as possible, a testing process slightly different from the standard can be adopted to obtain a more accurate test value.

[0357] In some embodiments, the thickness of the base film is 6μm to 12μm, and can be optionally 6μm to 9μm. Exemplarily, the thickness of the base film is 6μm, 6.5μm, 7μm, 7.5μm, 8μm, 8.5μm, 9μm, 9.5μm, 10μm, 10.5μm, 11μm, 11.5μm, 12μm or a range composed of any two of the above values.

[0358] 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.

[0359] 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.

[0360] 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.

[0361] The first functional layer and the second functional layer have good heat resistance, which can improve the heat resistance of the separator.

[0362] Optionally, the first functional layer can include a binder, optionally including at least one of a fluorine-containing binder or a polyacrylic acid binder, such as polyvinylidene fluoride.

[0363] 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.

[0364] 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 the thickness 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 the separator film is dried, 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.

[0365] 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 35%:30%:15%:20%, or 40%, 20%, 10%, 30%, or 45%, 15%, 20%, 20%, etc.

[0366] The second inorganic particles in the composite particles prevent the non-fluoropolymer particles from sticking to each other due to the high-temperature treatment during the granulation process, resulting in pores in the composite particles, which is beneficial to the transport of lithium ions and improves 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 easily deformed, making the structure of the separator film more stable, which can improve the kinetic performance of the battery cell and 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 easily deformed, 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.

[0367] 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.

[0368] 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.

[0369] 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, for example, 50 second inorganic particles are measured, and the average value thereof is calculated as the average particle size of the second inorganic particles.

[0370] 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.

[0371] 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.

[0372] 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, place a lithium sheet in the negative electrode case of the battery, add 150 μL of electrolyte thereto, and the electrolyte is a solution in EC / EMC / DEC = 3 / 5 / 2 (mass ratio), and then place the separator (with an area of 3.14 cm 6 and a thickness of 12 μm) to make it close to the lithium sheet, add another 25 μL of electrolyte, and finally place the positive electrode sheet (the positive electrode sheet can be the positive electrode sheet in Example 1) thereon and seal it. Take out the assembled button battery from the vacuum glove box and place it for 24 h for the next test. 2 Testing: On an electrochemical workstation, at 10

[0373] Testing: 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.

[0374] In some embodiments, the positive electrode sheet, the separator, and the negative electrode sheet can be made into an electrode assembly through a winding process and / or a stacking process.

[0375] Please continue to refer to Figure 1 and Figure 2 , and the battery cell 7 can include a housing 20.

[0376] 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).

[0377] The housing 20 is a hollow structure, and the housing 20 can be used to encapsulate the above electrode assembly 10 and the electrolyte.

[0378] 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 an electrode assembly 10 through a winding process and / or a stacking process, the electrode assembly 10 is placed in the housing 20, the electrolyte is injected after drying, and the battery cell 7 is obtained through processes such as vacuum packaging, standing, formation, and shaping.

[0379] In the embodiments of the present application, 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. 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.

[0380] In some embodiments, the material of the housing body 21 includes steel, and the mechanical strength of the steel is relatively high, not easily deformed, and can improve the use reliability and cycle performance of the battery cell 7. Optionally, the mass ratio of the steel is the highest among the materials in the housing body 21.

[0381] Optionally, the thickness of the housing 21 is from 0.1 mm to 0.5 mm, and may be optionally from 0.2 mm to 0.35 mm. Exemplarily, the thickness of the housing 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 21 is within the above range, the mechanical strength of the housing 21 is relatively high, which can improve the reliability and cycling performance of the battery cell 7; and the housing 21 occupies less space and has more internal space, which is beneficial to improving the energy density of the battery cell 7.

[0382] Viewed from the outer shape of the electrode assembly 10, the electrode assembly 10 includes a main body portion 12, a positive electrode tab 111 and a negative electrode tab 112, and the positive electrode tab 111 and the negative electrode tab 112 protrude from the main body portion 12. The positive electrode tab 111 is the part of the positive electrode plate where the active material layer is not coated, and the negative electrode tab 112 is the part of the negative electrode plate where the active material layer is not coated. The positive electrode tab 111 and the negative electrode tab 112 are used to lead out the current in the main body portion 12.

[0383] The positive electrode tab 111 and the negative electrode tab 112 may extend from the same side of the main body portion 12, or may extend from opposite sides respectively.

[0384] Optionally, the number of the positive electrode tabs 111 on the same side of the main body portion 12 is at least one, and may be optionally at least two. At least two positive electrode tabs 111 can increase the current-carrying capacity of the positive electrode tabs 111.

[0385] Optionally, the positive electrode tab 111 may be disposed on at least one side of the main body portion 12, and may be optionally at least two sides.

[0386] Optionally, the number of the negative electrode tabs 112 on the same side of the main body portion 12 is at least one, and may be optionally at least two. At least two negative electrode tabs 112 can increase the current-carrying capacity of the negative electrode tabs 112.

[0387] Optionally, the negative electrode tab 112 may be disposed on at least one side of the main body portion 12, and may be optionally at least two sides.

[0388] In some embodiments, the battery cell 7 further includes a positive terminal 31, and the positive terminal 31 is electrically connected to the positive electrode tab 111. Optionally, the positive terminal 31 and the positive electrode tab 111 are welded. The positive terminal 31 and the positive electrode tab 111 may be connected through an adapter, or may not be connected through an adapter; optionally, the positive terminal 31 and the positive electrode tab 111 are not connected through an adapter, that is, the positive terminal 31 and the positive electrode tab 111 are directly welded, which can reduce the resistance at the connection, and is beneficial to reducing the overall internal resistance of the battery cell 7.

[0389] In some embodiments, the battery cell 7 further includes a negative terminal 32, and the negative terminal 32 is electrically connected to the negative electrode tab 112. Optionally, the negative terminal 32 and the negative electrode tab 112 are welded. The negative terminal 32 and the negative electrode tab 112 can be connected through an adapter, or can be connected without using an adapter; optionally, the negative terminal 32 and the negative electrode tab 112 are not connected through an adapter, that is, the negative terminal 32 and the negative electrode tab 112 are directly welded, which can reduce the resistance at the connection, and is beneficial to reducing the overall internal resistance of the battery cell 7.

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

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

[0392] Exemplarily, the current-carrying area of the positive 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 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.

[0393] Optionally, the number of negative terminals 32 on the same side of the main body 12 is at least one, optionally at least two. At least two negative terminals 32 can increase the over-current capacity of the negative terminals 32.

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

[0395] Exemplarily, the over-current area of the single-sided negative terminal 32 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] In some embodiments, the dimension of the battery cell 7 in the first direction X is 90 mm to 130 mm, such as 90 mm, 95 mm, 100 mm, 105 mm, 110 mm, 115 mm, 120 mm, 125 mm, 130 mm or a range composed of any two of the above values. Figure 1 The L shown in 1 represents the dimension of the battery cell 7 in the first direction X, and can be understood as when the battery cell 7 is placed vertically, L 1 is the dimension from the bottom of the housing 21 to the top of the end cover 22.

[0397] When the size of the battery cell 7 in the first direction X is within the above range, in combination with the size of the positive electrode film layer in the first direction X, the positive electrode active material coated on the positive electrode film layer increases, which is beneficial to improving the energy density of the battery cell 7.

[0398] As Figure 3 shown, in some embodiments of the present application, the battery cell 7 according to the embodiment 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.

[0399] 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 can also be that multiple battery cells 7 are first connected in series, in parallel, or in a series-parallel combination to form a battery module 6, and then 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 also include an accommodating part with an accommodating space, and multiple battery cells 7 are accommodated in this accommodating space.

[0400] As Figure 4 and Figure 5 shown, in some embodiments, the above battery module 6 can be further 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.

[0401] The battery pack 2 may include a box body 5 and a plurality of 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 plurality of battery modules 6 can be arranged in the box body 5 in any manner.

[0402] In some embodiments, the size of the box body 5 in the first direction X is 110 mm to 170 mm, such as 110 mm, 115 mm, 120 mm, 125 mm, 130 mm, 135 mm, 140 mm, 145 mm, 150 mm, 155 mm, 160 mm, 165 mm, 168 mm, 170 mm or the range composed of any two of the above values. Figure 4 The L shown in 2 represents the size of the box body 5 in the first direction X, and can also be understood as the height size of the box body 5.

[0403] 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 a receiving space 5c for receiving 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 a box body 5 with a receiving space 5c; both the first box body part 5a and the second box body part 5b can also be hollow structures with one side open, and the open side of the first box body part 5a covers the open side of the second box body part 5b to form a box body 5 with a receiving space 5c. Of course, the first box body part 5a and the second box body part 5b can be of various shapes, such as a cylinder, a cuboid, etc.

[0404] 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.

[0405] 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 a 0% state of charge (SOC) to a 100% state of charge (SOC), the temperature of the external environment where the battery pack 2 is located is room temperature, such as 30°C.

[0406] In some embodiments, during the process of the battery pack 2 or any battery cell constituting the battery pack 2 from a 10% state of charge (SOC) to an 80% state of charge (SOC), the temperature of the external environment where the battery pack 2 is located is room temperature, such as 30°C.

[0407] In some embodiments, during the charging process of the battery pack 2 or any battery cell constituting the battery pack 2 from a 10% state of charge to an 80% state of charge, 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% state of charge, such as 1% state of charge, 1.5% state of charge, 2% state of charge, 2.5% state of charge, 3% state of charge, 3.5% state of charge, 4% state of charge, 4.5% state of charge, 5% state of charge, or a range composed of any two of the above values.

[0408] The battery pack 2 or any battery cell that makes up the battery pack 2 includes multiple charging steps from a state of charge (SOC) of 10% to 40%. For any one of the charging steps, it can be charged at any rate between 5C and 10C. The charging rate corresponding to each charging step can be any value among 5C, 5.5C, 6C, 6.5C, 7C, 7.5C, 8C, 8.5C, 9C, 9.5C, 10C, or a value within the range composed of any two of the above values.

[0409] The battery pack 2 or any battery cell that makes up the battery pack 2 also includes multiple charging steps from a state of charge (SOC) of 40% to 80%. The charging rate of any one of the charging steps is less than the charging rate of any one of the charging steps from a state of charge (SOC) of 10% to 40%, and the charging rate of the step when charging to 80% state of charge is any value between 2.5C and 5C. For example, it can be 2.7C.

[0410] Exemplarily, the charging steps of the battery pack 2 or any battery cell that makes up the battery pack 2 from 10% to 80% can be carried out as follows: Constant current charging at 5.0C from 10% SOC to 15% SOC; Constant current charging at 5.0C from 15% SOC to 20% SOC; Constant current charging at 5.0C from 20% SOC to 25% SOC; Constant current charging at 5.0C from 25% SOC to 30% SOC; Constant current charging at 5.0C from 30% SOC to 35% SOC; Constant current charging at 5.0C from 35% SOC to 40% SOC; Constant current charging at 4.6C from 40% SOC to 45% SOC; Constant current charging at 4.3C from 45% SOC to 50% SOC; Constant current charging at 4.0C from 50% SOC to 55% SOC; Constant current charging at 3.7C from 55% SOC to 60% SOC; Constant current charging at 3.4C from 60% SOC to 65% SOC; Constant current charging at 3.1C from 65% SOC to 70% SOC; Constant current charging at 2.9C from 70% SOC to 75% SOC; Constant current charging at 2.7C from 75% SOC to 80% SOC.

[0411] 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 12.5 min, and can be optionally 5 min to 12.5 min. The temperature of the external environment of the battery pack 2 at 10% state of charge is room temperature, such as 30°C. Exemplarily, the charging time of the battery pack 2 from 10% state of charge to 80% state of charge is 12.5 min, 12 min, 11.5 min, 11 min, 10.5 min, 10 min, 9.5 min, 9 min, 8.5 min, 8 min, 7.5 min, 7 min, 6.5 min, 6 min, 5.5 min, 5 min or the range composed of any two of the above values In some embodiments, the volumetric energy density of the battery cell is 380 Wh / L to 470 Wh / L, and can be optionally 390 Wh / L to 450 Wh / L. Exemplarily, the volumetric energy density of the battery cell is 380 Wh / L, 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 or the range composed of any two of the above values. The volumetric energy density of the battery cell is relatively high.

[0412] 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 the equipment and methods well-known in the art. 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 battery cell is placed at 25°C and charged at a constant current of 0.33C to 3.65 V, and then charged at a constant voltage to 0.05C; discharged at a constant current of 0.33C to 2.0 V, and 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 terminal and excluding the insulating film outside the outer shell), 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.

[0413] In some embodiments, the group margin of the battery cell at 100% state of charge is greater than or equal to 96% and less than 100%, and can be optionally 96.5% to 99.5%. For example, the group margin of the battery cell is 96%, 96.5%, 97%, 97.5%, 98%, 98.5%, 99%, 99.5% or the range composed of any two of the above values. When the group margin of the battery cell is within the above range, the volume proportion of the electrode assembly is relatively high, and the energy density of the battery cell is relatively high.

[0414] In the embodiments of the present application, the group margin refers to the ratio of the actual internal cross-sectional area of the battery cell to the maximum internal cross-sectional area, that is, the filling rate. The calculation method of the group margin is: group margin = electrode assembly thickness / internal thickness of the battery housing.

[0415] 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, for example, 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, for example, an electric drill, an electric grinding wheel, an electric wrench, an electric screwdriver, a hammer drill, an impact drill, a concrete vibrator and a power planer, etc. The embodiments of the present application do not impose special restrictions on the above electrical devices. The electrical device can select a battery cell, a battery module or a battery pack according to its usage requirements.

[0416] 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, a plug-in hybrid electric vehicle, etc. In order 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 adopted.

[0417] A battery pack 2 is arranged inside the electrical device 1. The battery pack 2 can be arranged at the bottom, the head or the tail of the electrical device 1. The battery pack 2 can be used for power supply of the electrical device 1. For example, the battery pack 2 can be used as the operating power source of the electrical device 1 and can also be used as the driving power source of the electrical device 1, replacing or partially replacing fuel or natural gas to provide driving power for the electrical device 1.

[0418] 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, navigation and driving of the electrical device 1.

[0419] Another example of the electrical device can be a mobile phone, a tablet computer, a laptop computer, etc. This type of electrical device usually requires being thin and light, and a battery cell can be used as the power source.

[0420] 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.

[0421] In some embodiments, the charging time of the electrical device from 10% state of charge to 80% state of charge is less than or equal to 12.5 min, and can be selected as 5 min to 12.5 min. The temperature of the external environment of the battery pack 2 at 10% state of charge is 30°C. Exemplarily, the charging time of the battery pack 2 from 10% state of charge to 80% state of charge is 12.5 min, 12 min, 11.5 min, 11 min, 10.5 min, 10 min, 9.5 min, 9 min, 8.5 min, 8 min, 7.5 min, 7 min, 6.5 min, 6 min, 5.5 min, 5 min or the range composed of any two of the above values Embodiment The following embodiments more specifically describe the content disclosed in the embodiments of the present application. These embodiments 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 embodiments are based on mass, and all reagents used in the embodiments are commercially available or synthesized according to conventional methods and can be used directly without further treatment, and the instruments used in the embodiments are all commercially available.

[0422] Example 1 1. Preparation of the positive electrode sheet The positive electrode sheet includes a positive current collector, a positive conductive layer on the positive current collector, and a positive electrode film layer. The positive current collector is aluminum foil.

[0423] The positive conductive layer on the positive current collector is a film layer formed by uniformly mixing a positive conductive agent, superconducting carbon, a positive binder, polyvinylidene fluoride (PVDF), and a solvent, N-methylpyrrolidone (NMP), and then coating it on the surface of the current collector and drying. The thickness is 1 μm. The mass content of the positive conductive agent in the positive conductive layer is 40%, and the mass content of the positive binder is 60%.

[0424] The positive electrode film layer is a film layer formed by uniformly coating a positive electrode paste (solvent: N-methylpyrrolidone NMP) on the surface of the positive conductive layer, followed by drying and cold pressing. The positive electrode film layer includes a positive active material, a binder, polyvinylidene fluoride (PVDF), and a conductive agent, acetylene black, with a weight ratio of 97:2:1.

[0425] The positive 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 titanium iron phosphate Li2FeTi(PO4)3 and amorphous carbon. The Dv50 of the positive active material is 1.6 μm, and the Dv10 is 0.64 μm.

[0426] The single-sided coating weight of the positive electrode film layer is 300 mg / 1540.25 mm 2 。

[0427] 2. Preparation of the negative electrode sheet The negative electrode sheet includes a negative current collector, a negative conductive layer on the negative current collector, and a negative electrode film layer. The negative current collector is copper foil.

[0428] The negative electrode conductive layer on the negative electrode current collector is a film layer formed by uniformly mixing a negative electrode conductive agent, superconducting carbon, a negative electrode binder, styrene-butadiene rubber (SBR), a thickening agent, sodium carboxymethyl cellulose (CMC-Na), and a solvent, water, and then coating the mixture on the surface of the negative electrode current collector and drying it. The thickness of the film layer is 1 μm. The mass content of the negative electrode conductive agent in the negative electrode conductive layer is 35%, the mass content of the negative electrode binder in the negative electrode conductive layer is 60%, and the mass content of the thickening agent in the negative electrode conductive layer is 5%.

[0429] The negative electrode film layer includes a film layer formed by uniformly coating a negative electrode slurry (with deionized water as the solvent) on the surface of the negative electrode conductive layer and then drying and cold-pressing it.

[0430] The single-sided coating weight of the negative electrode film layer is 138 mg / 1540.25 mm 2 。

[0431] 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.

[0432] 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 thickening agent sodium carboxymethyl cellulose, with a mass ratio of 96.5:0.5:0.5:1.5:1. The mass content of lithium element in the first lithium-containing binder is 4.8%. The Dv50 of the graphite particles is 11.3 μm. The graphite particles include artificial graphite and a carbon coating layer, and the carbon coating layer covers the surface of the artificial graphite, with a mass content of 3.5%.

[0433] The second negative electrode film layer includes graphite particles, conductive agent acetylene black, a second 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 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 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%.

[0434] 3. Separator The separator includes a base film, which is a 7-μm polyethylene film layer with a porosity of 42%.

[0435] 4. Preparation of electrolyte The organic solvent includes 60% chain carboxylic acid ester solvents (ethyl acetate) and 40% carbonate solvents (30% ethylene carbonate EC, 10% dimethyl carbonate). The mass content of each component in the organic solvent is calculated based on the mass of the organic solvent.

[0436] Based on the mass of the electrolyte, the mass content of the additive 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.

[0437] The lithium salt includes 1 mol / L of lithium hexafluorophosphate LiPF 6 。

[0438] The conductivity of the electrolyte at room temperature is 16.4 mS / cm.

[0439] 5. Preparation of the battery cell Stack the above positive electrode sheet, separator, and negative electrode sheet in sequence, with the separator placed between the positive electrode sheet and the negative electrode sheet to play an isolation role, obtaining an electrode assembly; place the electrode assembly in an outer packaging shell, inject the electrolyte after drying, and through processes such as vacuum packaging, standing, formation, and shaping, obtain the battery cell. Place the battery cell vertically, with the end cover located on the upper side of the housing. The height direction of the battery cell is parallel to the first direction. The height of the battery is 97 mm, and the width of the battery is 71 mm. 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 。

[0440] Comparative Example 1 and Comparative Example 2 Prepare the battery cell using a method similar to that of Example 1. Different from Example 1, the coating weight of the positive electrode film layer and the coating weight of the negative electrode film layer are adjusted.

[0441] Examples 2-1 to 2-3 Prepare the battery cell using a method similar to that of Example 1. Different from Example 1, the coating weight of the positive electrode film layer and the coating weight of the negative electrode film layer are adjusted.

[0442] Examples 3-1 to 3-3 Prepare the battery cell using a method similar to that of Example 1. Different from Example 1, the coating weight of the negative electrode film layer is adjusted.

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

[0444] Test result The test results are shown in Table 1.

[0445] Table 1

[0446] In Table 1, the height (dimension along the first direction) of the battery cell is 97 mm, and the thickness of the battery cell is 71 mm. The height (dimension along the first direction) of the positive electrode film layer is 80 mm, and the height (dimension along the first direction) of the negative electrode film layer is 83 mm. The height of the negative electrode film layer is greater than that of the positive electrode film layer, and the difference between the two is 3 mm.

[0447] The discharge capacity per gram of the positive electrode active material in the positive electrode film layer at a rate of 0.1C is 157 mAh / g, and the discharge capacity per gram of the negative electrode active material in the negative electrode film layer at a rate of 0.1C is 355 mAh / g.

[0448] In Comparative Example 1, the coating weight of the positive electrode film layer is small, resulting in too small discharge capacity and too small volume energy density of the battery cell, which cannot meet the requirements; while in Comparative Example 2, the coating weight of the positive electrode film layer is too large. Although it can significantly improve the discharge capacity of the positive electrode film layer and the volume energy density of the battery cell, due to the increase in the impedance of the positive electrode film layer, the fast charging performance of the battery cell decreases.

[0449] In the embodiment of the present application, the discharge capacity of the positive electrode film layer per unit area is 2.0 mAh / cm 2 to 3.7 mAh / cm 2 , which can effectively balance the improvement of the volume energy density and fast charging performance of the battery cell; the discharge capacity can be effectively regulated by the coating weight. For example, when the coating weight of the positive electrode film layer is 200 mg / 1540.25 mm 2 to 370 mg / 1540.25 mm 2 , the discharge capacity of the positive electrode film layer is within an appropriate range.

[0450] In the embodiment of the present application, the discharge capacity of the negative electrode film layer can be further regulated to 2.0 mAh / cm 2 to 4.1 mAh / cm 2 . When used in combination with the positive electrode film layer, it can, on the basis of improving the volume energy density and fast charging performance of the battery cell, also make the CB value within the range of 1.05 to 1.15, reduce the risk of lithium deposition, and improve the use reliability of the battery cell. The discharge capacity of the negative electrode film layer can also be effectively regulated by the coating weight. For example, when the coating weight of the negative electrode film layer is 90 mg / 1540.25 mm 2 to 170 mg / 1540.25 mm 2 , the discharge capacity of the negative electrode film layer is within an appropriate range.

[0451] Example 4 A battery cell was prepared by a method similar to that of Example 1. Different from Example 1, the component contents of the organic solvent were adjusted.

[0452] The test results are shown in Table 2.

[0453] Table 2

[0454] When the conductivity of the electrolyte is 13 mS / cm to 20 mS / cm, and can be selected as 15 mS / cm to 20 mS / cm, with the increase in conductivity, the migration rate of lithium ions in the battery cell accelerates, which is beneficial to improving the fast charging performance of the battery cell.

[0455] Comparative Example 3 The battery single cell was prepared by a method similar to that of Example 1. Different from Example 1, the size of the battery single cell was adjusted, and the sizes of the positive electrode film layer and the negative electrode film layer were adjusted accordingly.

[0456] Example 5 The battery single cell was prepared by a method similar to that of Example 1. Different from Example 1, the size of the battery single cell was adjusted, and the sizes of the positive electrode film layer and the negative electrode film layer were adjusted accordingly.

[0457] The test results are shown in Table 3.

[0458] Table 3

[0459] In Comparative Example 3, since the height of the battery single cell was relatively short, the volumetric energy density of the battery single cell could not be effectively improved. In the embodiments of the present application, the height of the positive electrode film layer was adjusted to 75 mm to 105 mm, which was beneficial to improving the volumetric energy density of the battery single cell.

[0460] 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 limiting 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 battery cell comprises a housing, an electrolyte and an electrode assembly, wherein the housing comprises a shell and an end cap, wherein the shell contains the electrolyte and the electrode assembly, the shell has an opening, and the end cap covers the opening. The electrode assembly comprises a positive electrode sheet, a negative electrode sheet and a separator, wherein the separator is located between the positive electrode sheet and the negative electrode sheet, the positive electrode sheet comprises a positive electrode current collector and a positive electrode film layer disposed on at least one side of the positive electrode current collector along the thickness direction of the positive electrode sheet and containing a positive electrode active material, wherein the positive electrode active material comprises a lithium-containing phosphate with an olivine structure; the negative electrode sheet comprises a negative electrode current collector and a negative electrode film layer disposed on at least one side of the negative electrode current collector along the thickness direction of the negative electrode sheet and containing a negative electrode active material, wherein: The discharge capacity per unit area of ​​the positive electrode film is 2.0 mAh / cm 2 Up to 3.7 mAh / cm 2 ; The dimension of the positive electrode film layer along a first direction is 75 mm to 105 mm, and the first direction is parallel to a direction from the shell to the end cover.

2. The battery cell according to claim 1, characterized in that: The discharge capacity of the positive electrode film layer per unit area is 2.4 mAh / cm 2 Up to 3.4 mAh / cm 2 .

3. The battery cell according to claim 1 or 2, characterized in that: The ratio of the discharge capacity per unit area of ​​the negative electrode film layer to the discharge capacity per unit area of ​​the positive electrode film layer is 1.05 to 1.

15.

4. The battery cell according to claim 3, characterized in that: The ratio of the discharge capacity per unit area of ​​the negative electrode film layer to the discharge capacity per unit area of ​​the positive electrode film layer is 1.07 to 1.

13.

5. The battery cell according to claim 1, characterized in that: The discharge capacity of the negative electrode film layer per unit area is 2.0 mAh / cm 2 Up to 4.1mAh / cm 2 .

6. The battery cell according to claim 5, characterized in that: The discharge capacity of the negative electrode film layer per unit area is 2.4 mAh / cm 2 Up to 3.7 mAh / cm 2 .

7. The battery cell according to claim 1, characterized in that: The conductivity of the electrolyte is 13 mS / cm to 20 mS / cm.

8. The battery cell according to claim 7, characterized in that: The conductivity of the electrolyte is 15 mS / cm to 20 mS / cm.

9. The battery cell according to claim 1, characterized in that: The dimension of the battery cell along the first direction is 90 mm to 130 mm.

10. The battery cell according to claim 1, 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 .

11. The battery cell according to claim 1, characterized in that: The powder resistivity of the positive electrode active material is 1 Ω·cm to 27.5 Ω·cm.

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

13. The battery cell according to claim 1, 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.

14. The battery cell according to claim 1, 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.

15. The battery cell according to claim 14, 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.

16. The battery cell according to claim 14 or 15, 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.

17. The battery cell according to claim 14, characterized in that: The graphitization degree of the lithium-containing phosphate with an olivine structure is 0.15 to 0.

32.

18. The battery cell according to claim 14, 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.

19. The battery cell according to claim 1, characterized in that: The volume distribution particle size of the positive electrode active material satisfies: 1µm≤Dv50≤2µm, 0.4µm≤Dv10≤0.7µm.

20. The battery cell according to claim 1, 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.

21. The battery cell according to claim 1, 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.

22. The battery cell according to claim 1, characterized in that: The thickness of the positive electrode current collector is 10 μm to 15 μm.

23. The battery cell according to claim 1, 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.

24. The battery cell according to claim 23, characterized in that: The thickness of the positive electrode conductive layer is 0.5 μm to 2 μm.

25. The battery cell according to claim 23 or 24, 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.

26. The battery cell according to claim 1, 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 .

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

28. The battery cell according to claim 1, 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 .

29. The battery cell according to claim 1, 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.

30. The battery cell according to claim 1, 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%.

31. The battery cell according to claim 30, 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.

32. The battery cell according to claim 31, characterized in that The mass content of the carbon coating layer is 2% to 5% based on the total mass of the graphite particles.

33. The battery cell according to claim 30, 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.

34. The battery cell according to claim 33, characterized in that: The carbon-based material in the first negative electrode film layer also includes natural graphite.

35. The battery cell according to claim 33 or 34, 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.

36. The battery cell according to claim 33, 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 .

37. The battery cell according to claim 33, 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.

38. The battery cell according to claim 33, 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, and the mass content of the first lithium-containing binder relative to the total 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 total mass of the second negative electrode film layer.

39. The battery cell according to claim 38, characterized in that The mass content of the first lithium-containing binder relative to the total 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 total mass of the second negative electrode film layer is 0.1% to 1%.

40. The battery cell according to claim 38 or 39, 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%.

41. The battery cell according to claim 38, 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%.

42. The battery cell according to claim 1, characterized in that The negative electrode active material further comprises a silicon-based material, and the mass content of silicon in the silicon-based material is 0.3% to 10.0%, based on the total mass of the negative electrode active material.

43. The battery cell according to claim 1, characterized in that The thickness of the negative electrode current collector is 4 μm to 6 μm.

44. The battery cell according to claim 1, 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.

45. The battery cell according to claim 44, characterized in that The thickness of the negative electrode conductive layer is 0.5 μm to 2 μm.

46. ​​The battery cell according to claim 44 or 45, 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.

47. The battery cell according to claim 1, characterized in that The viscosity of the electrolyte at room temperature is 2.3 mPa·s to 3.5 mPa·s.

48. The battery cell according to claim 1, characterized in that The electrolyte has a density of 1.05 g / mL to 1.35 g / mL at room temperature.

49. The battery cell according to claim 1, characterized in that 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 greater than or equal to 5% to 75%.

50. The battery cell according to claim 49, characterized in that The mass content of the chain carboxylic acid ester solvent in the organic solvent is 30% to 70%.

51. The battery cell according to claim 49 or 50, 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.

52. The battery cell according to claim 51, 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.

53. The battery cell according to claim 51, 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, 。 54. The battery cell according to claim 49, 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.

55. The battery cell according to claim 54, characterized in that The mass content of the carbonate solvent in the organic solvent is 30% to 70%.

56. The battery cell according to claim 1, 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.

57. The battery cell according to claim 56, 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, methylene disulfonate, and / or The lithium salt additive includes one or more of lithium difluorophosphate, lithium difluorooxalatoborate, lithium tetrafluoroborate, and lithium bis(oxalatoborate).

58. The battery cell according to claim 56 or 57, characterized in that: The mass content of the additive in the electrolyte is 1% to 10%.

59. The battery cell according to claim 58, characterized in that The mass content of the additive in the electrolyte is 2% to 8%.

60. The battery cell according to claim 1, 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.

61. The battery cell according to claim 60, characterized in that The fluorine-containing sulfonyl imide salt includes one or more of lithium bis(fluorosulfonyl)imide and lithium bis(trifluoromethanesulfonyl)imide.

62. The battery cell according to claim 60 or 61, 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.

63. The battery cell according to claim 62, characterized in that The ratio of the molar concentration of the lithium bis(fluorosulfonyl)imide to the molar concentration of the lithium hexafluorophosphate LiPF6 is 0.2 to 1.

0.

64. The battery cell according to claim 1, 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%.

65. The battery cell according to claim 64, characterized in that The base film has a thickness of 6 μm to 12 μm.

66. The battery cell according to claim 1, 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.

67. The battery cell according to claim 66, characterized in that The non-fluorinated polymer particles include acrylic copolymers.

68. The battery cell according to claim 66 or 67, 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; and / or 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.

69. The battery cell according to claim 66, characterized in that The average particle size of the second inorganic particles is 5 nm to 100 nm.

70. The battery cell according to claim 1, characterized in that The base material of the shell includes steel, and the thickness of the shell is 0.1 mm to 0.5 mm.

71. The battery cell according to claim 70, characterized in that The thickness of the shell is 0.2 mm to 0.35 mm.

72. The battery cell according to claim 1, characterized in that The group margin of the battery cells is greater than or equal to 96% and less than 100%.

73. The battery cell according to claim 72, characterized in that The group margin of the battery cells is 96.5% to 99.5%.

74. The battery cell according to claim 1, characterized in that The charging time of the battery cell from 10% state of charge to 80% state of charge is 5 minutes to 12.5 minutes.

75. A battery device, characterized in that: The battery device comprises the battery cell according to any one of claims 1 to 74.

76. The battery device according to claim 75, characterized in that The charging time of the battery from 10% state of charge to 80% state of charge is 5 min to 12.5 min.

77. The battery device according to claim 75 or 76, characterized in that: The battery device includes a box body, the box body accommodating the battery cells, wherein a dimension of the box body along a first direction is 110 mm to 170 mm.

78. An electrical device, characterized in that: The electrical device includes a battery device as described in claim 76 or 77.

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