Battery cells, battery devices, and power-consuming devices

Abstract

The present application relates to a battery cell, a battery device, and an electrical device. The battery cell includes a shell, an electrolyte, and an electrode assembly. The shell includes a shell and an end cover. The shell contains the electrolyte and the electrode assembly. The shell has an opening, and the end cover covers the opening. The electrode assembly includes a positive electrode sheet and a negative electrode sheet. The positive electrode sheet includes a positive electrode collector and a positive electrode film layer provided on at least one side of the positive electrode collector along the thickness direction of the positive electrode sheet and containing a positive electrode active material. The positive electrode active material includes a lithium phosphate containing an olivine structure. The negative electrode sheet includes a negative electrode collector and a negative electrode film layer provided on at least one side of the negative electrode collector along the thickness direction of the negative electrode sheet and containing a negative electrode active material. The discharge capacity per unit area of ​​the positive electrode film layer is 2.0 mAh / cm 2 Up to 3.7 mAh / cm 2 The positive electrode film layer has a dimension of 75 mm to 105 mm along a first direction, which is parallel to the direction from the housing to the end cap. This application can further increase the energy density of the battery cell.

Description

[0001] This application claims priority to patent application PCT / CN2024 / 102651, entitled “Battery Cell, Battery Device, and Electrical Device,” filed on June 28, 2024, the entire contents of which are incorporated herein by reference. Technical Field

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

[0003] Lithium-ion batteries, with their high capacity and long lifespan, are widely used in electronic devices such as mobile phones, laptops, electric bicycles, electric cars, electric aircraft, electric ships, and power tools. With the development of lithium-ion battery applications, higher requirements are being placed on lithium-ion battery performance, such as volumetric energy density and fast charging performance. Summary of the Invention

[0004] The present application provides a battery cell, a battery device and an electrical device, which can further improve the energy density of the battery cell.

[0005] In the first aspect, the present application proposes a battery cell, which includes a shell, an electrolyte and an electrode assembly. The shell includes a shell and an end cover, the shell contains the electrolyte and the electrode assembly, the shell has an opening, and the end cover covers the opening. The electrode assembly includes a positive electrode sheet, a negative electrode sheet and a separator, the separator is located between the positive electrode sheet and the negative electrode sheet, the positive electrode sheet includes a positive electrode collector and a positive electrode film layer provided on at least one side of the positive electrode collector along the thickness direction of the positive electrode sheet and containing a positive electrode active material, the positive electrode active material includes an olivine-structured lithium phosphate; the negative electrode sheet includes a negative electrode collector and a negative electrode film layer provided on at least one side of the negative electrode 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 layer is 2.0 mAh / cm 2 Up to 3.7 mAh / cm 2 The size of the positive electrode film along the first direction is 75 mm to 105 mm, and the first direction is parallel to the direction from the shell to the end cover.

[0006] Therefore, in the embodiment of the present application, when the size of the positive electrode film layer along 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 the improvement of the energy density of the battery cell; as the size of the positive electrode film layer along 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 battery cells; however, the discharge capacity of the positive electrode film layer per unit area is greater than 3.7 mAh / cm 2When the positive electrode film layer is coated with a large amount of material, the amount of material coated may be too large, resulting in a large resistance to the migration of lithium ions, which is not conducive to improving the fast charging performance of the battery cell. Further limiting the size of the positive electrode film layer along the first direction to be less than or equal to 105mm is conducive 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 along the first direction of the embodiment of the present application is 75mm to 105mm, the discharge capacity of the positive electrode film layer per unit area is coordinated and controlled to be 2.0mAh / cm 2 Up to 3.7 mAh / cm 2 , which can effectively improve the energy density of battery cells and is suitable for battery cells in fast charging systems.

[0007] In some embodiments, the discharge capacity per unit area of ​​the positive electrode film layer is 2.4 mAh / cm 2 Up 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.

[0008] 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.

[0009] Therefore, when the ratio 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 plating in the negative electrode film and improving the reliability of the battery cell. Moreover, since the risk of lithium plating is low and the lithium loss is small, the capacity loss of the battery cell can be reduced, and its cycle performance and fast charging performance can be improved.

[0010] In some embodiments, the discharge capacity per unit area of ​​the negative electrode film layer is 2.0 mAh / cm 2 to 4.1mAh / cm 2 , optional 2.4mAh / cm 2 Up 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 embedding, which can reduce the risk of lithium plating and is conducive to fast charging.

[0011] In some embodiments, the electrolyte has a conductivity of 13 mS / cm to 20 mS / cm, optionally 15 mS / cm to 20 mS / cm. The high migration rate of lithium ions in this electrolyte can further reduce the internal resistance of the battery cell, thereby reducing heat generation and improving the fast charging performance of the battery cell.

[0012] In some embodiments, the battery cell has a dimension along the first direction of 90 mm to 130 mm. When the battery cell has a dimension along the first direction within the above range, the dimension of the positive electrode film along the first direction increases the amount of positive electrode active material coated on the positive electrode film, thereby improving the energy density of the battery cell.

[0013] In some embodiments, the compaction density of the positive electrode film layer of the battery cell at 100% state of charge is 2.50 g / cm 3 to 2.80g / cm 3 , optional 2.55g / cm 3 to 2.70g / cm 3 When the compaction density of the positive electrode film layer is within the above range, it is beneficial to improve the energy density of the battery cell. Moreover, since the positive electrode active material in the positive electrode film layer is densely packed, the contact resistance between particles is small, which can further reduce the resistance of the electrode sheet and thus reduce heat generation.

[0014] In some embodiments, the single-sided coating weight of the positive electrode film layer is 200 mg / 1540.25 mm 2 Up to 370mg / 1540.25mm 2 , optional 240mg / 1540.25mm 2 Up to 330mg / 1540.25mm 2 When the single-sided coating weight of the positive electrode film layer is within the above range, the heat generated per unit area of ​​the positive electrode sheet will not be too large, and the energy density of the battery cell can be improved.

[0015] In some embodiments, the positive electrode active material has a powder resistivity of 1 Ω·cm to 27.5 Ω·cm. The relatively low powder resistivity of the positive electrode active material results in a relatively low resistance of the positive electrode sheet and less heat generation in the battery cell.

[0016] In some embodiments, the powder compaction density of the positive electrode active material at 30,000 N is 2.46 g / cm 3 Up to 2.8g / cm 3 When the powder compaction density of the positive electrode active material at 30,000N is within the above range, the energy density of the battery cell can be improved. Moreover, since the positive electrode active material in the positive electrode film layer can be more densely packed, the contact resistance between particles is smaller, which can further reduce the resistance of the electrode sheet and thus reduce heat generation.

[0017] In some embodiments, the positive electrode active material has a charge capacity of 150 mAh / g to 170 mAh / g at a rate of 0.1 C. When the charge capacity of the positive electrode active material at a rate of 0.1 C is within the above range, the energy density of the battery cell is relatively high.

[0018] In some embodiments, the olivine-structured lithium-containing phosphate includes phosphate particles and a coating layer, wherein the coating layer coats the phosphate particles and contains one or more elements selected from the group consisting of C, Fe, Ti, Zr, Hf, Ge, and Sn. The coating layer coating the phosphate particles improves the conductivity of the olivine-structured lithium-containing phosphate, reduces the powder resistivity of the material, and facilitates the migration rate of lithium ions, thereby reducing heat generation in the battery cells.

[0019] In some embodiments, the phosphate particles include a general formula of Li x1 A y1 Me a M b P 1-c X c Y z Compounds 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 comprises one or more of Na, K, and Mg, Me comprises one or more of Mn, Fe, Co, and Ni, M comprises one or more of B, Mg, Al, Si, P, S, Ca, Sc, Ti, V, Cr, Cu, Zn, Sr, Y, Zr, Nb, Mo, Cd, Sn, Sb, Te, Ba, Ta, W, Yb, La, and Ce, X comprises one or more of S, Si, Cl, B, C, and N, and Y comprises one or more of O and F. The phosphate particles have excellent cycling stability, which is beneficial for improving the cycling performance of battery cells.

[0020] In some embodiments, the coating layer comprises a Li 3-d Fe 2-d M2 d (PO x2 ) y2 The fast ion conductor M2 comprises one or more elements selected from Ti, Zr, Hf, Ge, and Sn, with 0≤d≤1, 0<x²<5, and 0<y²<4. Coating the phosphate particles with the fast ion conductor significantly increases the rate of lithium ion transport during multiple lithium insertions and extractions at the positive electrode, improving the ionic conductivity of the positive electrode active material, thereby increasing the specific capacity and, further, the energy density of the corresponding battery cell.

[0021] In some embodiments, the degree of graphitization of the positive electrode active material is 0.15 to 0.32, and optionally 0.19 to 0.26. When the degree of graphitization 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 generated by the positive electrode sheet, and thus reduce the heat generated by the battery cell.

[0022] In some embodiments, the mass content of carbon in the lithium-containing phosphate with olivine structure is 1% to 2%, and the specific surface area of ​​the lithium-containing phosphate with olivine structure is 5m 2 / g to 18m 2 / g, optional 7.5m 2 / g to 14m 2 / g.

[0023] Therefore, in the embodiment of the present application, the above-mentioned mass content of carbon elements combined with the above-mentioned specific surface area material is more conducive to the effective contact between the electrolyte and the lithium-containing phosphate with olivine structure, and is conducive to the transmission of lithium ions at the phase interface.

[0024] In some embodiments, the olivine-structured lithium-containing phosphate is in granular form, with a volume distribution particle size satisfying the following conditions: 1µm ≤ Dv50 ≤ 2µm, and 0.4µm ≤ Dv10 ≤ 0.7µm. The relatively small particle size of the olivine-structured lithium-containing phosphate shortens the lithium ion insertion and deintercalation pathways within the positive electrode active material, resulting in less heat generation. Furthermore, the particle size of the positive electrode active material is not excessively small, and agglomeration is substantially avoided during processing and preparation, resulting in stable performance of the positive electrode active material.

[0025] In some embodiments, the olivine-structured lithium-containing phosphate is in a granular form, comprising secondary particles, each of which comprises a plurality of primary particles, with the primary particles having an average particle size of 200 nm to 500 nm. The relatively small average particle size of the primary particles shortens the lithium ion insertion and extraction pathways in the positive electrode active material, resulting in less heat generation.

[0026] In some embodiments, the positive electrode film layer further comprises one or more of a ternary material, lithium phosphate, lithium dihydrogen 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. These materials can replenish lithium ions in the positive electrode film layer, compensating for irreversible lithium ion loss within the system, increasing capacity, and thereby improving the energy density of the battery cell.

[0027] In some embodiments, the thickness of the positive electrode current collector is 10 μm to 15 μm. When the thickness of the positive electrode current collector is within the above range, the positive electrode current collector has excellent current flow capacity and can enable the battery cell to have a higher energy density.

[0028] In some embodiments, the positive electrode plate further includes a positive electrode conductive layer, which is located between the positive electrode film layer and the positive electrode current collector. The positive electrode conductive layer can further improve the conductivity of the positive electrode plate, reduce the heat generated by the positive electrode plate, and thus reduce the heat generated by the battery cell.

[0029] 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, the conductivity of the positive electrode sheet can be further improved, the heat generation of the positive electrode sheet can be reduced, and thus the heat generation of the battery cell can be reduced, while also improving the energy density of the battery cell.

[0030] 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 pole piece 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, thereby improving the structural stability of the positive electrode pole piece.

[0031] 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.

[0032] 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 fluorine-containing acrylic resin.

[0033] In some embodiments, the negative electrode layer has a compaction density of 1.15 g / cm2 at 100% state of charge. 3 to 1.36g / cm 3 , optional 1.25g / cm 3 to 1.36g / cm 3 When the compaction density of the negative electrode film layer is within the above range, it is beneficial to improve the energy density of the battery cell. Moreover, since the negative electrode active material in the negative electrode film layer is densely packed, the contact resistance between particles is small, which can further reduce the resistance of the electrode sheet and thus reduce heat generation.

[0034] In some embodiments, the single-side coating weight of the negative electrode film layer is 90 mg / 1540.25 mm 2 Up to 170mg / 1540.25mm 2 , optional 110mg / 1540.25mm 2 Up to 150mg / 1540.25mm 2 When the coating weight on one side of the negative electrode film layer is within the above range, the heat generated per unit area of ​​the negative electrode sheet will not be too large, and the energy density of the battery cell can be improved.

[0035] 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 relatively low resistance of the negative electrode sheet and less heat generation in the battery cell.

[0036] In some embodiments, the powder compaction density of the negative electrode active material at 20,000 N is 1.5 g / cm 3 Up to 1.85g / cm 3 When the powder compaction density of the negative electrode active material at 20,000 N is within the above range, the energy density of the battery cell can be improved. Moreover, since the negative electrode active material in the negative electrode film layer can be more densely packed, the contact resistance between particles is smaller, which can further reduce the resistance of the electrode sheet and thus reduce heat generation.

[0037] In some embodiments, the charge capacity of the negative electrode active material at a rate of 0.1 C is greater than or equal to 350 mAh / g. When the charge capacity of the negative electrode active material at a rate of 0.1 C is within the above range, the energy density of the battery cell is relatively high.

[0038] In some embodiments, the negative electrode active material includes a carbon-based material, which includes graphite particles having a degree of graphitization of 92.0% to 94.5%. When the degree of graphitization of the graphite particles is within this range, the graphite particles have excellent electrical conductivity, can reduce heat generation of the negative electrode sheet and the battery cell, and can improve the fast charging performance of the battery cell.

[0039] In some embodiments, the graphite particles include artificial graphite and a carbon coating, wherein the artificial graphite includes secondary particles, and the carbon coating is coated on the surface of the artificial graphite. The carbon coating has a large number of end faces and defects, which increase the number of sites for lithium ion insertion and extraction, resulting in excellent conductivity of the carbon coating, which can reduce the internal resistance of the negative electrode sheet and reduce the heat generation of the battery cell.

[0040] In some embodiments, the mass content of the carbon coating layer is 2% to 5% based on the mass of the graphite particles. When the mass content of the carbon coating layer is within the above range, the internal resistance of the negative electrode plate can be further reduced, and the heat generation of the battery cell can be reduced.

[0041] 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 arranged 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 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.

[0042] Therefore, in the embodiment of the present application, there is a difference in the particle size of the first negative electrode film layer and the second negative electrode film layer, which can improve the fast charging performance of the battery cell. Specifically, during the fast charging process, the overpotential of the second negative electrode film layer is usually higher, and the bottleneck of fast charging mainly lies in the second negative electrode film layer. In the embodiment 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 improve the problem of lithium plating on the surface of the negative electrode plate.

[0043] In some embodiments, the carbon-based material in the first negative electrode film layer further includes natural graphite.

[0044] In some embodiments, 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. When the tap density of the carbon-based material in the second negative electrode film layer is greater than the tap density of the carbon-based material in the first negative electrode film layer, the second negative electrode film layer is more densely packed, thereby improving the energy density of the battery cell. The first negative electrode film layer is relatively sparsely packed, with more pores, which can improve the fast charging performance of the battery cell.

[0045] In some embodiments, the tap density of the carbon-based material in the first negative electrode film layer is 0.82 g / cm 3 to 1.21g / cm 3 When the tap density of the carbon-based material in the first negative electrode film layer is within an appropriate range, the fast charging performance of the battery cell can be improved.

[0046] In some embodiments, 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 When the tap density of the carbon-based material in the second negative electrode film layer is within an appropriate range, the energy density of the battery cell can be improved.

[0047] In some embodiments, the volume average particle size Dv50 of the graphite particles in the first negative electrode film layer is 9.5 μm to 18.5 μm. When the volume average particle size Dv50 of the negative electrode active material in the first negative electrode film layer is within the above range, the fast charging performance can be improved.

[0048] In some embodiments, the volume average particle size Dv50 of the graphite particles in the second negative electrode film layer is 7.8 μm to 14.3 μm. When the volume average particle size Dv50 of the negative electrode active material in the second negative electrode film layer is within the above range, the tortuosity of lithium ion transport can be reduced, thereby improving the fast charging performance of the battery cell.

[0049] In some embodiments, 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 mass of the first negative electrode film layer is less than or equal to the mass content of the second lithium-containing binder relative to the mass of the second negative electrode film layer.

[0050] Therefore, in the embodiment 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 second lithium-containing binder provides the second negative electrode film layer with a relatively larger number of freely movable lithium ions, which can further improve the fast charging performance of the battery cell.

[0051] In some embodiments, the mass content of the first lithium-containing binder relative to the mass of the first negative electrode film layer is 0.1% to 1%. When the mass content of the first lithium-containing binder is within the above range, the rate of lithium ion insertion and extraction can be increased, thereby improving the fast charging performance of the battery cell.

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

[0053] In some embodiments, the mass content of the second lithium-containing binder relative to the mass of the second negative electrode film layer is 0.1% to 1%. When the mass content of lithium in the second lithium-containing binder is within the above range, the rate of lithium ion insertion and extraction is increased, thereby improving the fast charging performance of the battery cell.

[0054] In some embodiments, the second lithium-containing binder has a lithium content of 3% to 10% by mass, and optionally 3% to 8% by mass. When the lithium content is within this range, a relatively large number of lithium ions can freely move within the negative electrode film layer, further shortening the distance for lithium ions to diffuse to the surface of the negative electrode film layer, increasing the rate of lithium ion insertion and extraction, and improving the fast charging performance of the battery cell.

[0055] In some embodiments, the first 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%.

[0056] Therefore, the lithium-containing binder of the above material can provide a certain amount of lithium ions for the negative electrode film layer, thereby improving the fast charging performance of the battery cell. In addition, it is not easy to swell during the charging and discharging process, and has a stable structure, thereby improving the cycle performance of the negative electrode film layer during the fast charging and discharging process.

[0057] In some embodiments, 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%.

[0058] Therefore, the lithium-containing binder of the above material can provide a certain amount of lithium ions for the negative electrode film layer, thereby improving the fast charging performance of the battery cell. In addition, it is not easy to swell during the charging and discharging process, and has a stable structure, thereby improving the cycle performance of the negative electrode film layer during the fast charging and discharging process.

[0059] In some embodiments, the negative electrode active material further comprises a silicon-based material, wherein the silicon content of the silicon-based material is 0.3% to 10.0% by weight, based on the mass of the negative electrode active material. The introduction of the silicon-based material can increase the capacity of the negative electrode active material and improve the energy density of the battery cell.

[0060] In some embodiments, the thickness of the negative electrode current collector is 4 μm to 6 μm. When the thickness of the negative electrode current collector is within the above range, the negative electrode current collector has a relatively good current flow capacity and can enable the battery cell to have a higher energy density.

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

[0062] In some embodiments, the thickness of the negative electrode conductive layer is 0.5 μm to 2 μm. The negative electrode conductive layer can further improve the conductivity of the negative electrode plate, reduce the heat generation of the negative electrode plate, and thus reduce the heat generation of the battery cell.

[0063] In some embodiments, the negative electrode conductive layer includes one or more of a negative electrode conductive agent and a negative electrode binder. The negative electrode conductive agent in the negative electrode conductive layer can improve the conductivity of the negative electrode conductive layer, thereby improving the conductivity of the negative electrode pole piece 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, thereby improving the structural stability of the negative electrode pole piece.

[0064] 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.

[0065] 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.

[0066] In some embodiments, the separator includes a porous base membrane having a porosity of 20% to 70%. In embodiments of the present application, when the porosity of the separator is within the above range, the migration of lithium ions through the separator can be enhanced, further reducing the internal resistance of the battery cell and thereby reducing heat generation.

[0067] In some embodiments, the carboxylate solvent includes a linear carboxylate solvent, and the mass content of the linear carboxylate 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%, and optionally 50% to 70%. When the mass content of the linear carboxylate solvent is within the above range, the viscosity of the electrolyte system is relatively low, which is conducive to the migration of lithium ions.

[0068] In some embodiments, the linear carboxylate solvent includes a compound represented by Formula I,

[0069] Formula I,

[0070] In Formula I,

[0071] R1 includes a hydrogen atom, a halogen atom, a C1 to C5 alkyl group or a C1 to C5 halogenated alkyl group,

[0072] R2 includes C1 to C5 alkyl or C1 to C5 halogenated alkyl.

[0073] Therefore, in the embodiment of the present application, the above-mentioned chain carboxylic acid ester solvent has a high conductivity, which is beneficial to improving the fast charging capability of the battery cell.

[0074] In some embodiments, R1 includes a hydrogen atom, a halogen atom, a C1 to C3 alkyl group, or a C1 to C3 haloalkyl group.

[0075] In some embodiments, in some embodiments, R2 comprises C1 to C3 alkyl or C1 to C3 haloalkyl.

[0076] In some embodiments, the chain carboxylate solvent includes one or more compounds represented by formula I-1 to formula I-8.

[0077]

[0078] In some embodiments, the organic solvent further comprises a carbonate solvent, and the carbonate solvent comprises one or more of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate. The use of the carbonate solvent and the chain carboxylate solvent in combination improves the conductivity of the electrolyte, facilitating the migration of lithium ions.

[0079] In some embodiments, the carbonate solvent includes one or more of ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate.

[0080] In some embodiments, the mass content of the carbonate solvent in the organic solvent is 30% to 70%, and optionally 30% to 50%. The above mass content of the carbonate solvent can further improve the conductivity of the electrolyte, which is beneficial to the migration of lithium ions.

[0081] In some embodiments, the electrolyte further includes additives, including one or more of carbonate additives, sulfur-containing additives, and lithium salt additives. These additives can improve the interfacial film properties on the positive and / or negative electrode sides, thereby enhancing the rapid charging performance of the battery cell and improving the cycling performance.

[0082] In some embodiments, the carbonate additive includes one or more of vinylene carbonate (VC) and fluoroethylene carbonate (FEC).

[0083] In some embodiments, the sulfur-containing additive includes one or more of vinyl sulfate DTD, vinyl disulfate 2-DTD, butylene sulfite BS, 1,3-propane sultone PS, vinyl sulfite ES, and methylene disulfonate MMDS.

[0084] In some embodiments, the lithium salt additive includes one or more of lithium difluorophosphate LiPO2F2, lithium difluorooxalatoborate LiDFOB, lithium tetrafluoroborate LiBF4, and lithium bis(oxalatoborate) LiBOB.

[0085] In some embodiments, the additive content in the electrolyte is 1% to 10%, optionally 2% to 8%. The additive content above can effectively improve the interfacial film performance on the positive electrode side and / or the negative electrode side, thereby enhancing the fast charging performance of the battery cell and improving the cycling performance.

[0086] In some embodiments, the electrolyte further includes a lithium salt, including one or more of a fluorinated sulfonyl imide salt and lithium hexafluorophosphate (LiPF6). These lithium salts readily dissociate, facilitating rapid lithium ion migration. Furthermore, the electrolyte system is relatively stable and resistant to decomposition, thereby enhancing the cycling performance of the battery cells.

[0087] In some embodiments, the fluorine-containing sulfonyl imide salt includes one or more of lithium bis(fluorosulfonyl)imide (LiFSI) and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI).

[0088] In some embodiments, the lithium salt includes lithium bis(fluorosulfonyl)imide LiFSI and lithium hexafluorophosphate LiPF6, the molar concentration of lithium bis(fluorosulfonyl)imide LiFSI is 0.2 mol / L to 0.5 mol / L, and the molar concentration of lithium hexafluorophosphate LiPF6 is 0.5 mol / L to 1.0 mol / L.

[0089] In some embodiments, the ratio of the molar concentration of lithium bis(fluorosulfonyl)imide to the molar concentration of lithium hexafluorophosphate (LiPF6) is 0.2 to 1.0.

[0090] In some embodiments, the separator includes a porous base membrane having a porosity of 35% to 60%. In embodiments of the present application, when the porosity of the separator is within the above range, the migration of lithium ions through the separator can be enhanced, further reducing the internal resistance of the battery cell, thereby reducing heat generation.

[0091] In some embodiments, the base film has a thickness of 6 μm to 12 μm. When the base film thickness is within the above range, the migration path of lithium ions in the base film is shorter, which can further reduce the internal resistance of the battery cell and thus reduce heat generation.

[0092] In some embodiments, the base film has a thickness of 6 μm to 9 μm. When the base film has a thickness within the above range, the migration path of lithium ions in the base film is shorter, which can further reduce the internal resistance of the battery cell and thus reduce heat generation.

[0093] In some embodiments, a separator includes a base film and a functional layer disposed on at least one side of the base film, the functional layer including a first functional layer and a second functional layer, the first functional layer being located on one side of the base film and including first inorganic particles, the second functional layer being located on the other side of the base film, the second functional layer including composite particles, the composite particles including second inorganic particles and a plurality of non-fluoropolymer particles, the second inorganic particles being attached to the surface of the non-fluoropolymer particles and / or dispersed within the non-fluoropolymer particles. The first and second functional layers have good heat resistance, thereby improving the heat resistance of the separator.

[0094] In some embodiments, the non-fluorinated polymer particles include acrylic copolymers, which have excellent bonding properties and high bonding stability with the base film.

[0095] In some embodiments, 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 first inorganic particles can improve the heat resistance of the first functional layer.

[0096] In some embodiments, 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. The second inorganic particles can improve the heat resistance of the first functional layer.

[0097] In some embodiments, the average particle size of the second inorganic particles is 5 nm to 100 nm. When the average particle size of the second inorganic particles is within the above range, it is beneficial to improve the heat resistance and compression modulus of the composite particles.

[0098] In some embodiments, the electrolyte has a viscosity of 2.3 mPa·s to 3.5 mPa·s at room temperature. When the viscosity of the electrolyte is within this range, the migration rate of lithium ions in the electrolyte is 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.

[0099] In some embodiments, the electrolyte has a density of 1.05 g / mL to 1.35 g / mL at room temperature. When the electrolyte density is within this range, the migration rate of lithium ions in the electrolyte is 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.

[0100] In some embodiments, the base material of the housing includes steel, and the thickness of the housing is 0.1 mm to 0.5 mm, optionally 0.2 mm to 0.35 mm. When the housing thickness is within the above range, the housing has high mechanical strength, which can improve the reliability and cycle performance of the battery cell. The housing also occupies less space, leaving more space inside the housing, which is conducive to improving the energy density of the battery cell.

[0101] In some embodiments, the group margin of the battery cells is greater than or equal to 96% and less than 100%, and can be optionally 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 cells.

[0102] In some embodiments, the charging time of the battery cell from 10% state of charge to 80% state of charge is 5 minutes to 12.5 minutes. The charging speed of the battery cell is faster, which is more conducive to improving the fast charging capability.

[0103] In a second aspect, the present application proposes a battery device, which includes a plurality of battery cells according to any embodiment of the first aspect of the present application.

[0104] In some embodiments, the battery device can be charged from a 10% state of charge to an 80% state of charge in a time range of 5 to 12.5 minutes. The faster the charging speed of the battery device, the better the fast charging capability.

[0105] In some embodiments, the battery device includes a case housing the battery cells, wherein a dimension of the case along the first direction is 110 mm to 170 mm.

[0106] In a third aspect, the present application proposes an electrical device, which includes a battery device according to any embodiment of the second aspect of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0107] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following is a brief introduction to the drawings required for use in the embodiments of the present application. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on the drawings without creative work.

[0108] Figure 1 A schematic structural diagram of a battery cell provided in some embodiments of the present application;

[0109] Figure 2 An exploded schematic diagram of a battery cell provided in some embodiments of the present application;

[0110] Figure 3 A schematic diagram of the structure of a battery module provided in some embodiments of the present application;

[0111] Figure 4 A schematic diagram of the structure of a battery pack provided in some embodiments of the present application;

[0112] Figure 5 for Figure 4 An exploded diagram of the battery pack shown;

[0113] Figure 6 It is a schematic diagram of the structure of an electrical device provided in some embodiments of the present application.

[0114] The drawings are not necessarily drawn to scale.

[0115] The drawings are not necessarily drawn to scale.

[0116] The following are the descriptions of the reference numerals:

[0117] X, first direction;

[0118] 1. Power-consuming device; 2. Battery pack; 3. Controller; 4. Motor; 5. Box; 5a. First box portion; 5b. Second box portion; 5c. Accommodation space; 6. Battery module;

[0119] 7. Battery cells;

[0120] 10. Electrode assembly; 111. Positive electrode tab; 112. Negative electrode tab; 12. Main body;

[0121] 20. Housing; 21. Shell; 22. End cover;

[0122] 31. Positive terminal; 32. Negative terminal. DETAILED DESCRIPTION

[0123] Below, the embodiments of the battery cells, battery devices, and electrical devices of the present application are described in detail with appropriate reference to the accompanying drawings. However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repeated descriptions of substantially the same structures may be omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate understanding by those skilled in the art. In addition, the drawings and the following description are provided to enable those skilled in the art to fully understand the present application and are not intended to limit the subject matter described in the claims.

[0124] " Range " disclosed in this application is limited in the form of lower limit and upper limit, and given range is limited by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundary of special range. The scope limited in this way can be inclusive or exclusive of end values, and can be arbitrarily combined, that is, any lower limit can form a range with any upper limit combination. For example, if the range of 60 to 120 and 80 to 110 is listed for a particular parameter, it is understood that the range of 60 to 110 and 80 to 120 is also expected. In addition, if the minimum range values ​​1 and 2 are listed, and if the maximum range values ​​3,4 and 5 are listed, then the following ranges can all be expected: 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 abbreviation of any real number combination between a and b, wherein a and b are real numbers. For example, a numerical range of "0 to 5" indicates that all real numbers between "0 and 5" are listed herein, and "0 to 5" is merely an abbreviation for a combination of these values. Furthermore, when a parameter is expressed as an integer ≥ 2, this is equivalent to disclosing that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0125] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0126] Unless otherwise specified, all technical features and optional technical features of this application can be combined with each other to form a new technical solution.

[0127] Unless otherwise specified, all steps of the present application may be performed sequentially or randomly, preferably sequentially. For example, a method includes steps (a) and (b), which indicates that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially. For example, a method may further include step (c), which indicates that step (c) may be added to the method in any order, for example, the method may include steps (a), (b), and (c), or may include steps (a), (c), and (b), or may include steps (c), (a), and (b), etc.

[0128] With the development of the battery field, the energy density requirements for battery cells are gradually increasing. Especially when the battery cells are relatively small, the energy density of the battery cells is more difficult to improve.

[0129] In view of the above problems, the embodiments of the present application rationally design the battery cell system, and improve the energy density of the battery cell by increasing the discharge capacity of the positive electrode film layer in the battery cell and the coating size of the positive electrode film layer.

[0130] battery cells

[0131] In a first aspect, an embodiment of the present application provides a battery cell.

[0132] like Figure 1 and Figure 2 As shown, the battery cell 7 includes an electrolyte, an electrode assembly 10 and a shell 20, the electrode assembly 10 includes a positive electrode sheet, a negative electrode sheet and a separator, the separator is located between the positive electrode sheet and the negative electrode sheet, the positive electrode sheet includes a positive electrode collector and a positive electrode film layer provided on at least one side of the positive electrode collector along the thickness direction of the positive electrode sheet and containing a positive electrode active material, the positive electrode active material includes an olivine structure containing lithium phosphate; the negative electrode sheet includes a negative electrode collector and a negative electrode film layer provided on at least one side of the negative electrode collector along the thickness direction of the negative electrode sheet and containing a negative electrode active material, the shell 20 includes a shell 21 and an end cover 22, the shell 21 has an opening and accommodates the electrolyte and the electrode assembly 10, the end cover 22 covers the opening; wherein, the discharge capacity per unit area of ​​the positive electrode film layer is 2.0 mAh / cm 2 Up to 3.7 mAh / cm 2 The size of the positive electrode film layer along the first direction X is 75 mm to 105 mm, and the first direction X is parallel to the direction from the shell 21 to the end cover 22.

[0133] Generally speaking, when the battery cell 7 is assembled into the box, the battery cell 7 is placed vertically, and the height direction of the battery cell 7 is parallel to the direction from the shell 21 to the end cover 22, that is, the height direction of the battery cell 7 is parallel to the first direction X.

[0134] When the size of the positive electrode film layer along the first direction X is 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, the discharge capacity of the positive electrode film layer per unit area is greater than 3.7 mAh / cm 2 When the positive electrode film layer is coated, the coating amount may be too large, resulting in a large resistance to the migration 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 improve the energy density and fast charging performance of the battery cell 7 to a certain extent.

[0135] Therefore, when the size of the positive electrode film layer along the first direction X of the embodiment of the present application is 75mm to 105mm, the discharge capacity of the positive electrode film layer per unit area is coordinated and controlled to be 2.0mAh / cm 2 Up to 3.7 mAh / cm 2 , which can effectively improve the energy density of the battery cell 7 and is suitable for the battery cell 7 of the fast charging system.

[0136] In the embodiment of the present application, the discharge capacity per unit area of ​​the positive electrode film layer is 2.0 mAh / cm 2 Up to 3.7 mAh / cm 2 , optional 2.4mAh / cm 2 Up to 3.4 mAh / cm 2 For example, the discharge capacity per unit area of ​​the positive electrode film layer is 2.0 mAh / cm 2 , 2.1mAh / cm 2 , 2.2mAh / cm 2 , 2.3mAh / cm 2 , 2.4mAh / cm 2 , 2.5mAh / cm 2 , 2.6mAh / cm 2 , 2.7mAh / cm 2 , 2.8mAh / cm 2 , 2.9mAh / cm 2 、3.0mAh / cm 2 、3.1mAh / cm 2 、3.2mAh / cm 2 、3.3mAh / cm 2 、3.4mAh / cm 2 、3.5mAh / cm 2 、3.6mAh / cm 2 、3.7mAh / cm 2 Or a range consisting of any two of the above values.

[0137] In some embodiments, the ratio CB 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 optionally be 1.07 to 1.13. For example, the ratio CB 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 in the battery cell 7 is 1.05, 1.07, 1.1, 1.12, 1.13, 1.14, 1.15, or a range consisting of any two of the foregoing values.

[0138] When the ratio CB 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 plating in the negative electrode film and improving the reliability of the battery cell 7; and because the risk of lithium plating is low and the lithium loss is less, the capacity loss of the battery cell 7 can be reduced, and its cycle performance and fast charging performance can be improved.

[0139] In some embodiments, the discharge capacity per unit area of ​​the negative electrode film layer is 2.0 mAh / cm 2 to 4.1mAh / cm 2 Optional 2.4mAh / cm 2 Up to 3.7 mAh / cm 2 For example, the discharge capacity per unit area of ​​the negative electrode film is 2.0 mAh / cm 2 , 2.1mAh / cm 2 , 2.2mAh / cm 2 , 2.3mAh / cm 2 , 2.4mAh / cm 2 , 2.5mAh / cm 2 , 2.6mAh / cm 2 , 2.7mAh / cm 2 , 2.8mAh / cm 2 , 2.9mAh / cm 2 、3.0mAh / cm 2 、3.1mAh / cm 2 、3.2mAh / cm 2 、3.3mAh / cm 2 、3.4mAh / cm 2 、3.5mAh / cm 2 、3.6mAh / cm 2 、3.7mAh / cm 2 、3.8mAh / cm 2 、3.9mAh / cm 2 , 4.0mAh / cm 2 , 4.1mAh / cm 2 Or a range consisting of any two of the above values.

[0140] 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 embedding, which can reduce the risk of lithium plating and is conducive to fast charging.

[0141] In the embodiment of the present application, the CB value can be detected using equipment and methods 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, and the ratio of the two is calculated to obtain the CB value.

[0142] The upper limit charge voltage and the discharge cut-off voltage of the battery cell 7 vary depending on the positive electrode active material. For example, when the phosphate material includes lithium iron phosphate, the upper limit charge voltage may be 3.65V and the discharge cut-off voltage may be 2.0V. For another example, when the phosphate material includes lithium manganese iron phosphate, the upper limit charge voltage may be 4.3V and the discharge cut-off voltage may be 2.0V. The following is an example of an upper limit charge voltage of 3.65V and a discharge cut-off voltage of 2.0V:

[0143] The discharge capacity per unit area of ​​the positive electrode film layer refers to the actual lithium-removable capacity of the positive electrode active material. The test method is as follows: the battery is disassembled in a Braun PRS340 / 11-119-11 glove box. The actual battery electrode is taken. It is double-sided coated. The film material on one side needs to be scrubbed with DMC solvent. The film-containing side is then assembled with the lithium sheet to form a CR2430 semi-button battery with a positive electrode and lithium sheet. The positive electrode sheet area used in the button battery is a cm 2 The electrolyte is a solution of 1 mol / L LiPF6 in EC / EMC / DEC = 3 / 5 / 2 (mass ratio); the assembled half-button battery is then left to stand for 3 hours and tested at 25°C. It is first charged (charge) at 0.05C in the voltage range of 2.0V to 4.0V to remove lithium, and then discharged (discharge) at 0.05C to insert lithium to 2.0V. This cycle is repeated twice. The discharge capacity of the second cycle is recorded as YmAh. The discharge capacity per unit area of ​​the positive electrode film layer = Y / a.

[0144] Specifically, the discharge capacity per unit area of ​​the negative electrode film layer refers to the actual lithium-insertable capacity of the negative electrode active material. The test method is as follows: the battery is disassembled in a PRS340 / 11-119-11 Braun glove box, and the actual battery electrode is taken. It is double-sided coated, and the material in the film layer on one side needs to be wiped off with DMC solvent. The side containing the film layer is assembled with the lithium sheet to form a CR2430 model semi-button battery with a negative electrode and a lithium sheet. The negative electrode sheet area used for the button battery is f cm 2The electrolyte used was a solution of 1 mol / L LiPF6 in EC / EMC / DEC = 3 / 5 / 2 (mass ratio); the assembled half-button battery was then left to stand for 3 hours and tested at 25°C. It was first discharged (Discharge) in the voltage range of 2V-0.04V at 0.05C to insert lithium, and then charged (Charge) to 2V at 0.05C to remove lithium. This cycle was repeated twice, and the discharge capacity of the second cycle was recorded as ZmAh. The discharge capacity per unit area of ​​the negative electrode film layer = Z / f.

[0145] In some embodiments, the negative electrode film layer has a larger dimension along the length of the negative electrode sheet than the positive electrode film layer, with the difference between the two being 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 consisting of any two of these values. Due to the relatively large size of the negative electrode film layer, sufficient lithium insertion sites can be provided for lithium ions, reducing the risk of lithium plating and improving the reliability of the battery cell 7.

[0146] In some embodiments, the negative electrode film layer has a larger dimension along the width of the negative electrode sheet than the positive electrode film layer, with the difference between the two being 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 consisting of any two of these values. Due to the relatively large size of the negative electrode film layer, sufficient lithium insertion sites can be provided for lithium ions, reducing the risk of lithium plating and improving the reliability of the battery cell 7.

[0147] In some embodiments, the electrolyte has a conductivity of 13 mS / cm to 20 mS / cm at room temperature, and optionally 15 mS / cm to 20 mS / cm. For example, the electrolyte has a conductivity of 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 consisting of any two of the foregoing values.

[0148] 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 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.

[0149] In the embodiment of the present application, the conductivity of the electrolyte at room temperature, for example, 25° C., is ionic conductivity, which can be tested using equipment and methods known in the art, for example, by referring to the industry standard HG-T 4067-2015.

[0150] The conductivity of the electrolyte can be controlled by adjusting the type and content of the organic solvent in the electrolyte; it can also be controlled by adjusting the type and content of the lithium salt in the electrolyte.

[0151] [Electrolyte]

[0152] During the charge and discharge process of the battery cell, active ions are embedded and released back and forth between the positive electrode and the negative electrode, and the electrolyte plays the role of conducting active ions between the positive electrode and the negative electrode.

[0153] In some embodiments, the viscosity of the electrolyte at room temperature is 2.3 mPa·s to 3.5 mPa·s. For example, the viscosity of the electrolyte is 2.3 mPa·s, 2.4 mPa·s, 2.5 mPa·s, 2.6 mPa·s, 2.7 mPa·s, 2.8 mPa·s, 2.9 mPa·s, 3.0 mPa·s, 3.1 mPa·s, 3.2 mPa·s, 3.3 mPa·s, 3.4 mPa·s, 3.5 mPa·s, or a range consisting of any two of the foregoing values.

[0154] 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 higher, 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.

[0155] In the embodiments of the present application, the viscosity of the electrolyte has a well-known meaning in the art and can be detected using equipment and methods well-known in the art, for example, it can be detected according to GB / T10247-2008.

[0156] In some embodiments, the density of the electrolyte at room temperature, e.g., 25° C., is between 1.05 g / mL and 1.35 g / mL. For example, 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 a range consisting of any two of the foregoing values.

[0157] When the density of the electrolyte is within the above range, the migration rate of lithium ions in the electrolyte is 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.

[0158] In the embodiments of the present application, the density of the electrolyte has a well-known meaning in the art and can be tested using equipment and methods well-known in the art, for example, by referring to GB / T 2013-2010.

[0159] The electrolyte includes an organic solvent and an electrolyte salt. The types of the organic solvent and the electrolyte salt are not particularly limited and can be selected according to actual needs.

[0160] In some embodiments, the organic solvent includes a linear carboxylate solvent, and the mass content of the linear carboxylate 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 linear carboxylate solvent is 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, or a range consisting of any two of the above values.

[0161] 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.

[0162] In some embodiments, the linear carboxylate solvent includes a compound represented by Formula I,

[0163] Formula I,

[0164] In Formula I, R1 includes a hydrogen atom, a halogen atom, a C1 to C5 alkyl group or a C1 to C5 haloalkyl group,

[0165] R2 includes C1 to C5 alkyl or C1 to C5 halogenated alkyl.

[0166] The above-mentioned chain carboxylic acid ester solvents have high electrical conductivity, which is beneficial to improving the fast charging capability of battery cells.

[0167] Alternatively, R1 includes a hydrogen atom, a halogen atom, a C1 to C3 alkyl group, or a C1 to C3 haloalkyl group. Further alternatively, R1 includes a hydrogen atom, a halogen atom, a C1 to C2 alkyl group, or a C1 to C2 haloalkyl group.

[0168] Alternatively, R2 comprises a C1 to C3 alkyl group or a C1 to C3 haloalkyl group. Further alternatively, R2 comprises a C1 to C2 alkyl group or a C1 to C2 haloalkyl group.

[0169] 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.

[0170] In each of the above embodiments, the haloalkyl group includes one or more of a fluoroalkyl group, a chloroalkyl group, a bromoalkyl group and an iodoalkyl group. Optionally, the haloalkyl group includes a fluoroalkyl group.

[0171] Illustratively, the chain carboxylate solvent includes one or more compounds represented by formula I-1 to formula I-8.

[0172]

[0173] In some embodiments, the organic solvent further includes a carbonate solvent.

[0174] Optionally, the carbonate solvent includes one or more of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate. Further optionally, the carbonate solvent includes one or more of ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate. The use of the above carbonate solvent and the chain carboxylate solvent in combination improves the conductivity of the electrolyte at room temperature, which is beneficial to the migration of lithium ions.

[0175] Further optionally, the mass content of the carbonate solvent in the organic solvent is 30% to 70%, optionally 30% to 50%. Exemplarily, the mass content of the carbonate solvent in the organic solvent is 30%, 31%, 32%, 33%, 34%, 35%, 36%, 37%, 38%, 40%, 45%, 48%, 50%, 55%, 60%, 65%, 70%, or a range consisting of any two of the above values. The above mass content of carbonate solvent can further improve the conductivity of the electrolyte at room temperature, which is beneficial to the migration of lithium ions.

[0176] Illustratively, the carbonate solvent includes one or more of ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate, and the mass content of the carbonate solvent is 30% to 50%.

[0177] In some embodiments, the electrolyte further contains additives, which may include negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain battery properties, such as additives that improve battery overcharge performance, additives that improve battery high temperature performance, additives that improve battery low temperature power performance, etc.

[0178] In some embodiments, the additives include one or more of carbonate additives, sulfur-containing additives, and lithium salt additives, and optionally at least two of these additives. These additives can improve the interfacial film properties on the positive and / or negative electrode sides, thereby enhancing the fast charging performance of the battery cells and improving the cycling performance.

[0179] In some embodiments, the weight content of the additive in the electrolyte is 1% to 10%, optionally 2% to 8%, and further optionally 3.5% to 8%. For example, the weight content of the additive in the electrolyte is 1%, 2%, 3%, 3.5%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, or a range consisting of any two of the above values.

[0180] The additives in the above mass content can effectively improve the interfacial film performance on the positive electrode side and / or the negative electrode side, which is beneficial to improving the fast charging performance of the battery cell and improving the cycle performance.

[0181] Illustratively, the carbonate additive includes one or more of vinylene carbonate VC and fluoroethylene carbonate FEC.

[0182] For example, the sulfur-containing additive includes one or more of vinyl sulfate DTD, vinyl disulfate 2-DTD, butylene sulfite BS, 1,3-propane sultone PS, vinyl sulfite ES, and methylene disulfonate MMDS.

[0183] Optionally, the lithium salt additive includes one or more of lithium difluorophosphate LiPO2F2, lithium difluorooxalatoborate LiDFOB, lithium tetrafluoroborate LiBF4, and lithium bis(oxalatoborate) LiBOB.

[0184] Optionally, the mass content of vinylene carbonate VC in the electrolyte is 0.5% to 9%, optionally 2% to 6%.

[0185] Optionally, the mass content of fluoroethylene carbonate FEC in the electrolyte is 0.1% to 4%, and optionally 0.5% to 3%.

[0186] Optionally, the mass content of vinylene carbonate VC in the electrolyte is 0.5% to 9%, and the mass content of fluoroethylene carbonate FEC in the electrolyte is 0.1% to 4%.

[0187] Further optionally, the mass content of vinylene carbonate VC in the electrolyte is 2% to 6%, and the mass content of fluoroethylene carbonate FEC in the electrolyte is 0.5% to 3%.

[0188] In some embodiments, the electrolyte salt includes a lithium salt, which includes one or more of a fluorinated sulfonyl imide salt and lithium hexafluorophosphate (LiPF6). These lithium salts are easily dissociated, facilitating rapid lithium ion migration. Furthermore, the electrolyte system is relatively stable and resistant to decomposition, thereby improving the cycling performance of the battery cell.

[0189] Optionally, the fluorine-containing sulfonyl imide salt includes one or more of lithium bis(fluorosulfonyl)imide LiFSI and lithium bis(trifluoromethanesulfonyl)imide LiTFSI.

[0190] Optionally, the lithium salt includes lithium bis(fluorosulfonyl)imide LiFSI and lithium hexafluorophosphate LiPF6, the molar concentration of lithium bis(fluorosulfonyl)imide LiFSI is 0.2 mol / L to 0.5 mol / L, and the molar concentration of lithium hexafluorophosphate LiPF6 is 0.5 mol / L to 1.0 mol / L.

[0191] Illustratively, the molar concentration of lithium bis(fluorosulfonyl)imide LiFSI is 0.4 mol / L to 0.5 mol / L, and the molar concentration of lithium hexafluorophosphate LiPF6 is 0.7 mol / L.

[0192] For example, the molar concentration of lithium bis(fluorosulfonyl)imide LiFSI is 0.5 mol / L, and the molar concentration of lithium hexafluorophosphate LiPF6 is 0.5 mol / L.

[0193] For example, the molar concentration of lithium bis(fluorosulfonyl)imide LiFSI is 0.2 mol / L, and the molar concentration of lithium hexafluorophosphate LiPF6 is 0.8 mol / L.

[0194] Optionally, the ratio of the molar concentration of lithium bis(fluorosulfonyl)imide to the molar concentration of lithium hexafluorophosphate (LiPF6) is 0.2 to 1.0, and optionally 0.2 to 0.5. Exemplarily, the ratio of the molar concentration of lithium bis(fluorosulfonyl)imide to the molar concentration of lithium hexafluorophosphate (LiPF6) is 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, or a range consisting of any two of the foregoing values.

[0195] In the embodiments of the present application, the types and contents of the inorganic components / lithium salt concentrations in the electrolyte are well known in the art and can be detected using equipment and methods well known in the art. For example, the inorganic components / lithium salt concentrations in the electrolyte can be qualitatively or quantitatively analyzed by ion chromatography analysis methods in accordance with the standard JY / T020-1996 "General Rules for Ion Chromatography Analysis Methods". In the embodiments of the present application, a freshly prepared electrolyte can be taken as a sample, 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 battery's state of charge is approximately 0% SOC) can be reversely disassembled, and the free electrolyte obtained from the battery can be used as a sample for detection using ion chromatography analysis methods.

[0196] In the embodiments of the present application, the types and contents of organic components in the electrolyte are well known in the art and can be detected using equipment and methods well known in the art. For example, qualitative and quantitative analysis of organic components in the electrolyte can be performed by gas chromatography with reference to GB / T9722-2006, "General Rules for Gas Chromatography of Chemical Reagents." In the embodiments of the present application, a freshly prepared electrolyte can be taken as a sample, free electrolyte from a fresh battery can be taken as a sample, or a battery that has been fully discharged (discharged to the lower cutoff voltage so that the battery's state of charge is approximately 0%) can be disassembled in reverse, and free electrolyte obtained from the battery can be used as a sample for detection using ion chromatography.

[0197] In the embodiment of the present application, after quantitative and qualitative detection of each component in the electrolyte, the components are classified, and the chain carboxylate solvent and the carbonate solvent (such as ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate and ethyl methyl carbonate) are used as the components of the organic solvent. The mass content of each component is calculated based on the mass of the organic solvent as 100%.

[0198] Carbonate additives (such as vinylene carbonate, fluoroethylene carbonate), sulfur-containing additives and lithium salt additives are used as additives for the electrolyte. The mass content of each component is calculated based on the mass of the electrolyte being 100%.

[0199] In some embodiments, the battery cell satisfies the following conditions: 2.45g / Ah ≤ d / A ≤ 3.5g / Ah, optionally 2.45g / Ah ≤ d / A ≤ 3.3g / 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. For example, d / A can be 3.5g / Ah, 3.3g / Ah, 3.2g / Ah, 3.0g / Ah, 2.8g / Ah, 2.5g / Ah, 2.45g / Ah, or a range consisting of any two of the foregoing values.

[0200] d / A can reflect the electrolyte's ability to retain liquid. When d / A is within the above range, the electrolyte can better wet the positive and negative electrodes, and can increase the migration rate of lithium ions in the liquid phase, which is beneficial to improving the fast charging capability of the battery cell.

[0201] In the embodiment of the present application, the d / A of the battery cell can be understood as the liquid retention coefficient, which can be tested using equipment and methods known in the art. For example, it can be described in accordance with GB / T31486-2015 "Electrical Performance Requirements and Test Methods for Power Batteries for Electric Vehicles", taking the battery charging upper limit voltage of 3.65V and the battery discharge cut-off voltage of 2.0V as an example.

[0202] At 25°C, charge a battery cell at 0.33C to 3.65V, then charge it at a constant voltage to 0.05C, and then discharge it at a constant current of 0.33C to 2.0V. The discharged capacity A is used as the denominator, and the battery cell is weighed as M0. The positive electrode sheet, negative electrode sheet, separator, and electrolyte, with the free electrolyte contained in a bag, are then disassembled and baked in a 60°C oven for at least 4 hours (including but not limited to the positive electrode sheet, negative electrode sheet, separator, and other mechanical parts of the disassembled battery cell that contribute to M0). The total weight of the battery cell is then weighed as M1, with the weight difference between M0 and M1 as the numerator. The liquid retention coefficient is equal to the weight difference d between M0 and M1 divided by the capacity A.

[0203] [Positive electrode]

[0204] The positive electrode sheet includes a positive electrode current collector and a positive electrode film layer disposed on at least one surface of the positive electrode current collector and comprising a positive electrode active material. For example, the positive electrode current collector may have two opposing surfaces in its thickness direction, and the positive electrode film layer may be disposed on either or both of the two opposing surfaces of the positive electrode current collector.

[0205] In some embodiments, the compaction density of the positive electrode film layer of the battery cell at 100% state of charge (SOC) is 2.50 g / cm 3 to 2.80g / cm 3 , optional 2.55g / cm 3 to 2.70g / cm 3 For example, when the battery cell is at 100% state of charge (SOC), the compaction density of the positive electrode film is 2.50 g / cm 3 , 2.52g / cm 3 , 2.55g / cm 3 , 2.56g / cm 3 , 2.57g / cm 3 , 2.58g / cm 3 , 2.60g / cm 3 , 2.62g / cm 3 , 2.65g / cm 3 , 2.68g / cm 3 , 2.70g / cm 3 , 2.72g / cm 3 , 2.75g / cm 3 , 2.78g / cm 3 , 2.80g / cm 3 Or a range consisting of any two of the above values.

[0206] 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, because the positive electrode active material in the positive electrode film layer is relatively densely packed, the contact resistance between particles is relatively low, which can further reduce the resistance of the electrode sheet and thus reduce the heat generated during rapid charging. Therefore, by regulating the compaction density of the positive electrode film layer to a reasonable range, the battery cell has both high energy density and high charge rate performance.

[0207] In the embodiment of the present application, the 100% state of charge SOC and 0% state of charge SOC of the battery cell are defined as follows:

[0208] The battery cell is charged at a constant current charge rate of 0.33C to the upper limit of the charge 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.

[0209] In some embodiments, the single-sided coating weight of the positive electrode film layer is 200 mg / 1540.25 mm 2 Up to 370mg / 1540.25mm 2 , optional 240mg / 1540.25mm 2 Up to 330mg / 1540.25mm 2 For example, the coating weight of the positive electrode film on one side is 200 mg / 1540.25 mm 2 、210mg / 1540.25mm 2 、220mg / 1540.25mm 2 、230mg / 1540.25mm 2 、240mg / 1540.25mm 2 、250mg / 1540.25mm 2 、260mg / 1540.25mm 2 、270mg / 1540.25mm 2 、280mg / 1540.25mm 2 、290mg / 1540.25mm 2 、300mg / 1540.25mm 2 、310mg / 1540.25mm 2 、320mg / 1540.25mm 2 、330mg / 1540.25mm 2 、340mg / 1540.25mm 2 、350mg / 1540.25mm 2 、360mg / 1540.25mm2 、370mg / 1540.25mm 2 Or a range consisting of any two of the above values.

[0210] When the single-sided coating weight of the positive electrode film layer is within the above range, the heat generated per unit area of ​​the positive electrode sheet will not be too large, and both the energy density and the charge rate performance of the battery cell can be improved.

[0211] In the embodiments of the present application, the compaction density of the positive electrode film layer of a battery cell at 100% state of charge (SOC) can be tested using the following method: The positive electrode sheet of the battery cell at 100% state of charge (SOC) is disassembled and the compaction density of the positive electrode film layer is measured. For example, a single-sided coated positive electrode sheet (if a double-sided coated sheet, the positive electrode film layer on one side can be wiped off first) is punched into small discs with an area of ​​S1. The discs are weighed and recorded as M1, and their thickness H1 is measured. The positive electrode film layer of the weighed positive electrode sheet is then wiped off, and the weight of the positive current collector is weighed and recorded as M0, and its thickness H0 is measured. The single-sided coating weight of the positive electrode film layer = (weight of the positive electrode sheet M1 - weight of the positive current collector M0) / S1. The thickness of the positive electrode film layer = thickness of the positive electrode sheet H1 - thickness of the positive current collector H0. The compaction density of the positive electrode film layer = single-sided coating weight of the positive electrode film layer / thickness of the positive electrode film layer.

[0212] In some embodiments, the powder resistivity of the positive electrode active material is 1 Ω·cm to 27.5 Ω·cm, optionally, less than or equal to 20 Ω·cm, optionally, less than or equal to 11 Ω·cm. For example, the powder resistivity of the positive electrode active material may 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 consisting of any two of the foregoing values.

[0213] The powder resistivity of the positive electrode active material is relatively low, which makes the resistance of the positive electrode sheet relatively low and the heat generation of the battery cell less.

[0214] In the embodiments of the present application, the powder resistivity of the material is well known in the art and can be tested using methods and equipment well known in the art, for example, using a PRCD1100 powder resistivity meter according to the test standard GB / T30835-2014.

[0215] In some embodiments, the powder compaction density of the positive electrode active material at 30,000 N is 2.46 g / cm 3Up to 2.8 g / cm 3 For example, the powder compaction density of the positive electrode active material at 30000N is 2.46g / cm 3 , 2.47g / cm 3 , 2.48g / cm 3 , 2.49g / cm 3 , 2.5g / cm 3 , 2.51g / cm 3 , 2.55g / cm 3 , 2.58g / cm 3 , 2.60g / cm 3 , 2.65g / cm 3 , 2.68g / cm 3 , 2.70g / cm 3 , 2.72g / cm 3 , 2.75g / cm 3 , 2.78g / cm 3 , 2.80g / cm 3 Or a range consisting of any two of the above values.

[0216] When the powder compaction density of the positive electrode active material at 30,000 N is within the above range, the energy density of the battery cell can be improved. Moreover, since the positive electrode active material in the positive electrode film layer can be stacked more densely and the contact resistance between particles is smaller, the resistance of the electrode sheet can be further reduced, thereby reducing heat generation.

[0217] In the embodiment of the present application, the powder compaction density of the material is a well-known meaning in the art and can be tested using methods and equipment known in the art. For example, a certain amount of positive electrode active material is taken as a sample and added to a UTM7305 electronic pressure testing machine with a bottom area of ​​1.327 cm 2 The mold was pressurized to 3000 kg (equivalent to 30000 N), maintained for 30 seconds, then released and maintained for 10 seconds, and then the powder compaction density of the positive electrode active material under a force of 30000 N was recorded and calculated.

[0218] In some embodiments, the positive electrode active material has a charge capacity of 150 mAh / g to 170 mAh / g at a 0.1 C rate, optionally 157 mAh / g to 170 mAh / g. For example, the positive electrode active material has a charge capacity of 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 consisting of any two of the above values.

[0219] When the charge gram 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.

[0220] In the embodiment of the present application, the gram capacity of the active material has a meaning well known in the art and can be tested using equipment and methods well known in the art. The test method for the first coulombic efficiency and the first discharge specific capacity in Appendix G of the national standard GB / T 24533-2019 can be used. Metal lithium is used as the negative electrode and a sample electrode comprising the above-mentioned material is used as the positive electrode to assemble a half-button battery. Under the conditions of 23°C±2°C, the half-button battery is charged and discharged at a rate of 0.1C on a battery tester or other test equipment of equivalent performance to obtain the charge capacity, and then the capacity is divided by the mass of the active material of the electrode to obtain the charge gram capacity parameter.

[0221] In some embodiments, the mass proportion of the lithium-containing phosphate with an olivine structure in the positive electrode active material may be greater than or equal to 80% and less than or equal to 100%, and the positive electrode active material of the present application may be considered to be a lithium-containing phosphate system with an olivine structure. When the mass proportion of the lithium-containing phosphate with an olivine structure is less than 100%, the positive electrode active material may also include a commonly used positive electrode active material, for example, it may include but is not limited to at least one of lithium-containing transition metal oxides. Examples of lithium-containing transition metal oxides may include but are not limited to at least one of lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, and their respective modified compounds.

[0222] Optionally, the mass proportion of the lithium-containing phosphate with an olivine structure in the positive electrode active material is 100%.

[0223] In an embodiment of the present application, the lithium-containing phosphate with an olivine structure may be phosphate particles, or a material obtained by coating and modifying the phosphate particles. For example, the lithium-containing phosphate with an olivine structure includes phosphate particles and a coating layer, the coating layer is coated on the surface of the phosphate particles, and the coating layer contains one or more elements of C, Fe, Ti, Zr, Hf, Ge and Sn.

[0224] By coating the surface of the phosphate particles with a coating layer, the conductivity of the lithium-containing phosphate with an olivine structure can be improved, the powder resistivity of the material can be reduced, and the migration rate of lithium ions can be promoted, thereby improving the fast charging capability of the battery and reducing the heat generation of the battery cell.

[0225] In some embodiments, the phosphate particles include a general formula of Li x1 A y1 Me a M b P 1-c X c Y z Compounds 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 comprises one or more of Na, K, and Mg, Me comprises one or more of Mn, Fe, Co, and Ni, M comprises one or more of B, Mg, Al, Si, P, S, Ca, Sc, Ti, V, Cr, Cu, Zn, Sr, Y, Zr, Nb, Mo, Cd, Sn, Sb, Te, Ba, Ta, W, Yb, La, and Ce, X comprises one or more of S, Si, Cl, B, C, and N, and Y comprises one or more of O and F. The phosphate particles have excellent cycling stability, which is beneficial for improving the cycling performance of battery cells.

[0226] Exemplarily, the phosphate particles include one or more of LiFePO4, LiMnPO4, LiNiPO4, and LiCoPO4. The battery cells are accompanied by the deintercalation and consumption of active ions such as Li during the charge and discharge process, and the molar content of Li in the battery cells is different when discharged to different states. In the enumeration of positive electrode active materials LiFePO4, LiMnPO4, LiNiPO4, LiCoPO4, etc., the molar content of Li is the initial state of the material, that is, the state before feeding. The positive electrode active material is used in the battery system, and the molar content of Li may change after charge and discharge cycles. In the enumeration of positive electrode active materials LiFePO4, LiMnPO4, LiNiPO4, LiCoPO4, etc. in the embodiment of the present application, the molar content of oxygen O is only a theoretical state value. Lattice oxygen release will cause the molar content of oxygen O to change. In practice, the molar content of oxygen O will fluctuate. The above situations are all within the scope of protection of this application.

[0227] In some embodiments, the coating layer comprises a 3-d Fe 2-d M2 d (PO x2 ) y2 The fast ion conductor M2 includes one or more elements selected from Ti, Zr, Hf, Ge and Sn, 0≤d≤1, 0<x2<5, 0<y2<4.

[0228] Exemplarily, the fast ion conductor is a material having a NASICON structure, such as one or more of lithium iron titanium phosphate Li2FeTi(PO4)3, lithium iron zirconium phosphate Li2FeZr(PO4)3, and lithium iron tin phosphate Li2FeSn(PO4)3.

[0229] Fast ion conductors with a NASICON structure are materials with ultrafast ion conduction capabilities. They possess abundant three-dimensional lithium ion diffusion and transport channels, and exhibit advantages such as high ion conduction efficiency and strong structural stability during multiple lithium de- and intercalation processes. Coating phosphate particles with a fast ion conductor containing a NASICON structure can significantly increase the lithium ion transport rate at the positive electrode during multiple lithium de- and intercalation processes, improving the ionic conductivity of the positive electrode active material and the rapid charging capability of the battery cell. Furthermore, it can increase the specific capacity and the energy density of the corresponding battery cell.

[0230] In some embodiments, the coating layer further includes carbon.

[0231] The carbon element and the fast ion conductor can be arranged in layers. For example, the carbon element serves as an independent carbon coating layer, and the fast ion conductor serves as an independent fast ion conductor layer. The carbon coating layer can be coated on the surface of the phosphate particles, and the fast ion conductor layer is located on the surface of the carbon coating layer, that is, the fast ion conductor layer is located on the side of the carbon coating layer facing away from the phosphate particles. Alternatively, the fast ion conductor layer can be coated on the surface of the phosphate particles, and the carbon coating layer is located on the surface of the fast ion conductor layer, that is, the carbon coating layer is located on the side of the fast ion conductor layer facing away from the phosphate particles. Of course, the carbon element and the fast ion conductor can also be arranged in the same layer.

[0232] Optionally, a carbon coating can be formed by carbonizing an organic carbon source (e.g., glucose, polyethylene glycol, etc.) and coating the surface of the fast ion conductor layer. The carbon coating can partially or completely cover the fast ion conductor layer. The carbon coating can significantly improve the electronic conductivity of the phosphate particles, compensating for their poor electronic conductivity and increasing the energy density of the battery cell.

[0233] Specifically, the provision of the carbon coating layer enables the positive electrode active material of the present application to have the following advantages:

[0234] The carbon coating layer in the positive electrode active material of the present application provides a suitable channel for the transmission of electrons, which can significantly improve the conduction rate of electrons in multiple lithium delithiation and lithium insertion processes, improve the electronic conductivity of lithium-containing phosphates, improve the charging capacity of the corresponding battery cells, and also improve the energy density.

[0235] The carbon coating layer of the positive electrode active material of the present application is loose and porous, which enables the electrolyte to be in full and effective contact with the lithium-containing phosphate, thereby increasing the transmission rate of lithium ions at the phase interface and improving the charging capacity of the battery cell.

[0236] Coating a carbon coating layer on the surface of the lithium-containing phosphate can not only improve the conductivity of the lithium-containing phosphate, but also improve the structural stability of the positive electrode active material, effectively alleviate the iron dissolution of the positive electrode active material during long-term storage and cyclic use of the battery cell, thereby improving the cycle life of the battery cell.

[0237] The cathode active material of this application, based on a lithium-containing phosphate, leverages the advantages of lithium-containing phosphates: low cost, high reliability, and excellent cycling stability. It also utilizes coating layers (fast ion conductor layer and carbon coating layer) to address their poor electronic and ionic conductivity. Battery cells prepared with this cathode active material can improve the energy density of the battery cells while maintaining excellent cycling performance.

[0238] In the embodiments of this application, the element content in the positive electrode active material has a meaning well known in the art and can be measured using equipment and methods well known in the art. For example, in accordance with EPA 6010D-2014, it can be measured by inductively coupled plasma atomic emission spectrometry (ICP-OES, Thermo ICAP7400). After discharging the battery cell to 0% state of charge (SOC), the positive electrode sheet is disassembled, cleaned with DMC, dried, and calcined at high temperature to remove impurities. Then, 0.4g of the positive electrode active material is weighed and 10ml (50% concentration) of aqua regia is added. The sample is then placed on a plate at 180°C for 30 minutes. After digestion on the plate, the volume is adjusted to 100ml, and quantitative analysis is performed using a standard curve method.

[0239] In some embodiments, the degree of graphitization of the positive electrode active material is 0.15 to 0.32, optionally 0.19 to 0.26. For example, the degree of graphitization of the positive electrode active material is 0.15, 0.16, 0.17, 0.18, 0.19, 0.20, 0.21, 0.22, 0.23, 0.24, 0.25, 0.26, 0.27, 0.28, 0.29, 0.30, 0.31, 0.32, or a range consisting of any two of the above values.

[0240] 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.

[0241] In the embodiment of the present application, a higher degree of graphitization of the material indicates a lower degree of disorder, which can be tested according to the test standard JIS / K 0131-1996 X-ray diffraction analysis method general rules.

[0242] In some embodiments, the mass content of carbon in the lithium-containing phosphate with olivine structure is 1% to 2%, and the specific surface area of ​​the lithium-containing phosphate with olivine structure is 5m 2 / g to 18m 2 / g.

[0243] Optionally, the mass content of carbon in the lithium-containing phosphate with olivine structure is 1% to 2%, and the specific surface area of ​​the lithium-containing phosphate with olivine structure is 7.5m 2 / g to 14m 2 / g.

[0244] Illustratively, the mass content of carbon in the olivine-structured lithium-containing phosphate is 1%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2%, or a range consisting of any two of the above values.

[0245] For example, the specific surface area of ​​the lithium-containing phosphate with olivine structure is 5m 2 / g、6m 2 / g、7m 2 / g、8m 2 / g、9m 2 / g、10m 2 / g、11m 2 / g、12m 2 / g、13m 2 / g、14m 2 / g、15m 2 / g、16m 2 / g、17m 2 / g、18m 2 / g or a range consisting of any two of the above values.

[0246] 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 conducive to effective contact between the electrolyte and phosphate particles, and conducive to the transmission of lithium ions at the phase interface. In addition, when the mass content of the carbon element is within the above range, it can significantly improve the conductivity of the lithium-containing phosphate with an olivine structure, which is beneficial to improving the ionic conductivity and electronic conductivity of the lithium-containing phosphate with an olivine structure, and can improve the rapid charging capability and energy density of the battery cell.

[0247] In the embodiments of the present application, the specific surface area of ​​the material has a meaning well known in the art and can be detected using equipment and methods well known in the art. For example, 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 using a Tri-Star 3020 specific surface area pore size analyzer produced by Micromeritics, USA.

[0248] 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.

[0249] Illustratively, the Dv50 of the positive electrode active material can be 1µm, 1.1µm, 1.15µm, 1.2µm, 1.25µm, 1.3µm, 1.35µm, 1.4µm, 1.45µm, 1.5µm, 1.55µm, 1.6µm, 1.65µm, 1.7µm, 1.75µm, 1.8µm, 1.85µm, 1.9µm, 1.95µm, 2µm, or a range consisting of any two of the above values.

[0250] For example, 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 consisting of any two of the above values.

[0251] The particle size of the positive electrode active material is relatively small, the lithium ion deintercalation path in the positive electrode active material is short, and the heat generation is less. Moreover, the particle size of the above-mentioned positive electrode active material is not too small, and basically no agglomeration will occur during the processing and preparation process, making the performance of the positive electrode active material stable.

[0252] In the embodiment of the present application, the volume average particle size Dv50 of the material refers to the particle size corresponding to 50% of the volume distribution, and the volume average particle size Dv10 of the material refers to the particle size corresponding to 10% of the volume distribution. It can be detected by equipment and methods known in the art. For example, the positive electrode active material is used as a sample, and the Dv50 and Dv10 of the particles are tested by a Mastersizer 2000E laser particle size analyzer according to the test standard GB / T 19077-2016.

[0253] When the positive electrode active material includes other materials in addition to the lithium-containing phosphate having 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.

[0254] In some embodiments, the olivine-structured lithium-containing phosphate is in a granular form, comprising secondary particles, each of which comprises a plurality of primary particles, and the average particle size of the primary particles is between 200 nm and 500 nm. For example, 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 consisting of any two of the foregoing values.

[0255] The average particle size of the primary particles is relatively small, the lithium ion deintercalation path in the positive electrode active material is shorter, and the heat generated is less.

[0256] In the embodiments of the present application, secondary particles refer to particles in an agglomerated state formed by the aggregation of two or more primary particles. Primary particles and secondary particles can be easily distinguished by experimental means (such as using a scanning electron microscope to take SEM images), and the average particle size of the primary particles can be obtained by testing in the scanning electron microscope SEM images. The SEM test parameters can be set to: an operating voltage (EHT) of 10.00 kV, an InLens detector, a working distance of 4.6 mm, and a magnification of 1000X.

[0257] In some embodiments, the positive electrode film layer further comprises one or more of a ternary material, lithium phosphate, lithium dihydrogen 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. These materials can serve as lithium replenishers, which can replenish lithium ions in the positive electrode film layer, compensating for irreversible lithium ion loss within the system, increasing capacity, and thereby improving the energy density of the battery cell.

[0258] Optionally, the ternary material includes Li x3 A y3 Ni a3 Co b3 Mn c M3 (1-a3-b3-c3) Y3 z3 , wherein, 0<x3≤2.1, 0<y3≤2.1, and 0.9≤x3+y3≤2.1, 0≤a3≤1, 0≤b3≤1, 0≤c3≤1, and 0.1≤a3+b3+c3≤1, 1.8≤z3≤3.5, A includes one or more of Na, K, and Mg, M3 includes one or more of B, Mg, Al, Si, P, S, Ca, Sc, Ti, V, Cr, Fe, Cu, Zn, Sr, Y, Zr, Nb, Mo, Cd, Sn, Sb, Te, Ba, Ta, W, Yb, La, and Ce, and Y3 includes one or more of O and F.

[0259] For example, the ternary material includes LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (NCM333), LiNi 0.5 Co 0.2 Mn 0.3 O2 (NCM523), LiNi 0.6 Co 0.2 Mn 0.2 O2 (NCM622), LiNi 0.8 Co 0.1 Mn 0.1 O2 (NCM811), LiNi 0.80 Co 0.15 Al 0.05 At least one of O2.

[0260] In some embodiments, the lithium supplement agent comprises 0.5% to 5% by weight of the positive electrode film layer, for example, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, or a range consisting of any two of these values. When the lithium supplement agent comprises within the above range, it can replenish lithium ions in the positive electrode film layer, compensating for irreversible lithium ion loss in the system, increasing capacity, and thereby improving the energy density of the battery cell.

[0261] The lithium replenisher can be located in the same layer as the positive electrode active material, or in different layers. When the lithium replenisher and the positive electrode active material are located in different layers, the lithium replenisher can be located in the lithium replenisher layer, and the positive electrode active material can be located in the positive electrode active material layer. In other words, the positive electrode film layer includes a lithium replenisher layer and a positive electrode active material layer. The positive electrode active material layer can be arranged on at least one side of the positive electrode current collector, and the lithium replenisher layer can be located between the positive electrode active material layer and the positive electrode current collector. Alternatively, the lithium replenisher layer can be arranged on at least one side of the positive electrode current collector, and the positive electrode active material layer can be located between the lithium replenisher layer and the positive electrode current collector. Optionally, the lithium replenisher 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 replenisher in the lithium replenisher layer can be gradually released into the system to compensate for the lithium loss of the battery system.

[0262] In some embodiments, the positive electrode film layer may further optionally include a positive electrode conductive agent. The present application does not particularly limit the type of positive electrode conductive agent. For example, the positive 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, the mass content of the positive electrode conductive agent is ≤5% based on the mass of the positive electrode film layer.

[0263] In some embodiments, the positive electrode film layer may further optionally include a positive electrode binder. The embodiments of the present application do not particularly limit the type of positive electrode binder. 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 fluorine-containing acrylic resin. In some embodiments, based on the mass of the positive electrode film layer, the mass content of the positive electrode binder is ≤5%.

[0264] In some embodiments, the positive electrode current collector may be a metal foil or a composite current collector. Examples of metal foils include at least one of aluminum, aluminum alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys. The composite current collector may include a polymer base layer and a metal layer formed on at least one surface of the polymer base layer. For example, the metal material of the metal layer may include at least one of aluminum, aluminum alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys. For example, the polymer base layer may include at least one of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0265] In some embodiments, the ratio of the thickness of the positive electrode current collector to the thickness of the positive electrode film layer on one side is 0.05 to 0.3. For example, the ratio of the thickness of the positive electrode current collector to the thickness of the positive electrode film layer on one side 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 consisting of any two of the above values.

[0266] 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 capability and energy density of the battery cell can be improved.

[0267] In some embodiments, the thickness of the positive electrode current collector is 10 μm to 15 μm, optionally 12 μm to 15 μm. For example, 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 consisting of any two of the above values.

[0268] When the thickness of the positive electrode current collector is within the above range, the positive electrode current collector has a relatively excellent current flow capacity and can enable the battery cell to have a higher energy density.

[0269] In the embodiment of the present application, the thickness of the positive electrode film layer and the positive electrode current collector has a meaning 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 sheet is measured with a micrometer, the film layer on the surface of the positive electrode current collector is removed, and the thickness of the positive electrode current collector is measured with a micrometer. When the positive electrode film layer is coated on one side, the thickness of the positive electrode film layer is the thickness of the positive electrode sheet 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 sheet minus the thickness of the positive electrode current collector) / 2.

[0270] The positive electrode film layer is typically formed by coating a positive electrode slurry onto a positive electrode current collector, drying it, and cold pressing it. The positive electrode slurry is typically formed by dispersing the positive electrode active material, an optional conductive agent, an optional binder, and any other components in a solvent and stirring them uniformly. The solvent can be, but is not limited to, N-methylpyrrolidone (NMP).

[0271] The positive electrode sheet does not exclude other additional functional layers in addition to the positive electrode film layer. For example, in some embodiments, the positive electrode sheet of the embodiments of the present application further includes a positive electrode conductive layer sandwiched between the positive electrode current collector and the positive electrode film layer and disposed on the surface of the positive electrode current collector. In other embodiments, the positive electrode sheet of the embodiments of the present application further includes a protective layer covering the surface of the positive electrode film layer.

[0272] In some embodiments, the positive electrode plate further includes a positive electrode conductive layer, which is located between the positive electrode film layer and the positive electrode current collector. The positive electrode conductive layer can further improve the conductivity of the positive electrode plate, reduce the heat generated by the positive electrode plate, and thus reduce the heat generated by the battery cell.

[0273] In some embodiments, the thickness of the positive electrode conductive layer is 0.5 μm to 2 μm. For example, the thickness of the positive electrode conductive layer can be 0.5 μm, 0.8 μm, 1 μm, 1.2 μm, 1.5 μm, 1.6 μm, 1.8 μm, 2 μm, or a range consisting of any two of the above values.

[0274] When the thickness of the positive electrode conductive layer is within the above range, the conductivity of the positive electrode sheet can be further improved, the heat generation of the positive electrode sheet can be reduced, thereby reducing the heat generation of the battery cell, and the energy density of the battery cell can be improved.

[0275] In the embodiment of the present application, the thickness of the positive electrode conductive layer has a meaning well known in the art and can be detected using equipment and methods well known in the art, for example, performing a tomographic scan on the positive electrode sheet to directly measure the thickness of the positive electrode conductive layer.

[0276] In some embodiments, the positive electrode conductive layer includes one or more of a positive electrode conductive agent and a positive electrode binder.

[0277] Optionally, the mass content of the positive electrode conductive agent in the positive electrode conductive layer is 30% to 50%. Exemplarily, the mass content of the positive electrode conductive agent is 30%, 35%, 40%, 45%, 50%, or a range consisting of any two of the above values.

[0278] Illustratively, the positive electrode conductive agent includes one or more of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. The positive electrode conductive agent in the positive electrode conductive layer can improve the conductivity of the positive electrode conductive layer, thereby improving the conductivity of the positive electrode sheet and reducing heat generation in the battery cell.

[0279] Optionally, the mass content of the positive electrode binder in the positive electrode conductive layer is 50% to 70%, illustratively, 50%, 60%, 65%, 70%, or a range consisting of any two of the above values.

[0280] Illustratively, the positive electrode binder includes one or more of polyvinylidene fluoride, polytetrafluoroethylene, a vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, a vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, a tetrafluoroethylene-hexafluoropropylene copolymer, polyacrylic acid, and a fluorinated acrylic resin. The positive electrode binder in the positive electrode conductive layer can improve the bonding between the positive electrode current collector and the positive electrode film layer, thereby enhancing the structural stability of the positive electrode sheet.

[0281] [Negative electrode]

[0282] The negative electrode sheet includes a negative electrode current collector and a negative electrode film layer disposed on at least one surface of the negative electrode current collector and comprising a negative electrode active material. For example, the negative electrode current collector has two opposing surfaces in the thickness direction of the negative electrode current collector, and the negative electrode film layer is disposed on either or both of the two opposing surfaces of the negative electrode current collector.

[0283] In some embodiments, the negative electrode layer has a compaction density of 1.15 g / cm2 at 100% state of charge. 3 to 1.36g / cm 3 , optional 1.25g / cm 3 to 1.36g / cm 3 For example, the compaction density of the negative electrode film layer of the battery cell at 100% charge state is 1.15g / cm 3 , 1.18g / cm 3 , 1.20g / cm 3 , 1.22g / cm 3 , 1.25g / cm 3 , 1.28g / cm 3 , 1.3g / cm 3 , 1.32g / cm 3 , 1.35g / cm 3 , 1.36g / cm 3 Or a range consisting of any two of the above values.

[0284] When the compaction density of the negative electrode film layer is within the above range, it is beneficial to improve the energy density of the battery cell. Moreover, since the negative electrode active material in the negative electrode film layer is stacked relatively densely, the contact resistance between particles is small, which can further reduce the resistance of the electrode sheet and thus reduce heat generation.

[0285] In the embodiment of the present application, the compaction density of the negative electrode film layer of the battery cell at 100% charge state has a meaning well known in the art and can be detected using equipment and methods well known in the art, and the detection method is the same as the compaction density test method of the positive electrode film layer mentioned above.

[0286] In some embodiments, the single-side coating weight of the negative electrode film layer is 90 mg / 1540.25 mm 2 Up to 170mg / 1540.25mm 2 , optional 110mg / 1540.25mm 2 Up to 150mg / 1540.25mm 2 For example, the coating weight of the negative electrode film on one side is 90 mg / 1540.25 mm 2 、92mg / 1540.25mm 2 、95mg / 1540.25mm 2 、96mg / 1540.25mm 2 、100mg / 1540.25mm 2 、102mg / 1540.25mm 2 、104mg / 1540.25mm 2 、105mg / 1540.25mm 2 、108mg / 1540.25mm 2 、110mg / 1540.25mm 2 、112mg / 1540.25mm 2 、114mg / 1540.25mm 2 、115mg / 1540.25mm 2 、116mg / 1540.25mm 2 、118mg / 1540.25mm 2 、120mg / 1540.25mm 2 、122mg / 1540.25mm 2 、125mg / 1540.25mm 2 、128mg / 1540.25mm 2 、130mg / 1540.25mm 2 、132mg / 1540.25mm 2 、135mg / 1540.25mm 2 、137mg / 1540.25mm 2 、140mg / 1540.25mm 2 、142mg / 1540.25mm 2、145mg / 1540.25mm 2 、148mg / 1540.25mm 2 、150mg / 1540.25mm 2 、152mg / 1540.25mm 2 、155mg / 1540.25mm 2 、160mg / 1540.25mm 2 、165mg / 1540.25mm 2 、170mg / 1540.25mm 2 Or a range consisting of any two of the above values.

[0287] When the single-side coating weight of the negative electrode film layer is within the above range, the heat generated per unit area of ​​the negative electrode sheet will not be too large, and the energy density of the battery cell can be improved.

[0288] In the embodiment of the present application, the single-sided coating weight of the negative electrode film layer has a meaning well known in the art and can be detected using equipment and methods well known in the art, such as the single-sided coating weight test method of the film layer described above.

[0289] In some embodiments, the powder resistivity of the negative electrode active material is 0.005 Ω·cm to 0.043 Ω·cm, and may be 0.04 Ω·cm. For example, the powder resistivity of the negative electrode active material may be 0.043 Ω·cm, 0.04 Ω·cm, 0.035 Ω·cm, 0.03 Ω·cm, 0.025 Ω·cm, 0.02 Ω·cm, 0.015 Ω·cm, 0.01 Ω·cm, 0.005 Ω·cm, or a range consisting of any two of the foregoing values.

[0290] The powder resistivity of the negative electrode active material is relatively low, which makes the resistance of the negative electrode sheet relatively low and the heat generation of the battery cell less.

[0291] In the embodiment of the present application, the powder resistivity of the negative electrode active material is well known in the art and can be detected using equipment and methods well known in the art, such as the powder resistivity test method of the positive electrode active material described above.

[0292] In some embodiments, the powder compaction density of the negative electrode active material under a pressure of 20,000 N is 1.5 g / cm 3 Up to 1.85g / cm 3 , optional 1.55g / cm 3 Up to 1.65g / cm 3 For example, the powder compaction density of the negative electrode active material under a pressure of 20,000 N is 1.5 g / cm 3, 1.55g / cm 3 , 1.6g / cm 3 , 1.65g / cm 3 , 1.7g / cm 3 , 1.75g / cm 3 , 1.8g / cm 3 , 1.85g / cm 3 Or a range consisting of any two of the above values.

[0293] When the powder compaction density of the negative electrode active material at 20,000 N is within the above range, the energy density of the battery cell can be improved. Moreover, since the negative electrode active material in the negative electrode film layer can be stacked more densely and the contact resistance between particles is smaller, the resistance of the electrode sheet can be further reduced, thereby reducing heat generation.

[0294] In the embodiments of the present application, the powder compaction density of the material is a well-known meaning in the art and can be tested using methods and equipment known in the art in accordance with the test standard GB / T24533-2009. As an example, a certain amount of negative electrode active material is taken as a sample and placed in a UTM7305 electronic pressure testing machine with a bottom area of ​​1.327 cm 2 The mold was pressurized to 2000 kg (equivalent to 20000 N), maintained for 30 seconds, then released and maintained for 10 seconds, and then the powder compaction density of the negative electrode active material under a force of 20000 N was recorded and calculated.

[0295] In some embodiments, the negative electrode active material has a charge capacity in the range of 350 mAh / g to 480 mAh / g at a 0.1 C rate. For example, the negative electrode active material has a charge capacity in the range of 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 consisting of any two of the foregoing values.

[0296] When the charge gram capacity of the negative electrode active material at a 0.1C rate is within the above range, the energy density of the battery cell is relatively high.

[0297] In the embodiment of the present application, the charge gram capacity of the negative electrode active material at a rate of 0.1C has a meaning well known in the art and can be detected using equipment and methods well known in the art. The detection method is the same as the charge gram capacity test method of the positive electrode active material at a rate of 0.1C mentioned above.

[0298] In some embodiments, the negative electrode active material includes a carbon-based material. Carbon-based materials have high cycle stability and can improve the cycle performance of the battery cell. Optionally, the mass proportion 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%.

[0299] 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. The two are used in combination, and the cycle performance of the battery cell is relatively excellent.

[0300] Optionally, the carbon-based material includes graphite particles, and the graphite particles have a degree of graphitization of 92.0% to 94.5%. Exemplarily, the degree of graphitization of the graphite particles is 92.0%, 92.5%, 93%, 93.5%, 94%, 94.5%, or a range consisting of any two of the foregoing values.

[0301] When the graphitization degree of the graphite particles is within the above range, the graphite particles have relatively excellent electrical conductivity, can reduce the heat generation of the negative electrode sheet, reduce the heat generation of the battery cell, and can improve the fast charging performance of the battery cell.

[0302] In some embodiments, the graphite particles include artificial graphite and a carbon coating. The artificial graphite includes secondary particles, each of which includes a plurality of primary particles. The carbon coating is coated on the surface of the artificial graphite. The carbon in the carbon coating is primarily amorphous carbon. Amorphous carbon refers to a transitional carbon material with a very low degree of graphitization and crystallization, nearly an amorphous form (or lacking a fixed shape and periodic structural regularity). In this application, amorphous carbon refers to the product of carbonization of an organic carbon source.

[0303] Artificial graphite includes secondary particles. There are more migration paths for lithium ions in artificial graphite, and the migration paths in primary particles are shorter, which can improve the migration rate of lithium ions. The carbon coating has more end faces and defects, which increases the number of sites for lithium ion insertion and extraction, making the carbon coating more conductive, which can reduce the internal resistance of the negative electrode and reduce the heat generation of the battery cell.

[0304] Optionally, the mass content of the carbon coating layer is 2% to 5% based on the mass of the graphite particles. Exemplarily, the mass content of the carbon coating layer is 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, or a range consisting of any two of the above values.

[0305] When the mass content of the carbon coating layer is within the above range, the internal resistance of the negative electrode plate can be further reduced, and the heat generation of the battery cell can be reduced.

[0306] In an embodiment of the present application, the graphite particles can be prepared by methods known in the art. For example, the preparation method includes: providing artificial graphite and an organic carbon source, mixing the two, and forming a carbon coating layer on at least a portion of the surface of the artificial graphite particles after carbonization treatment.

[0307] Optionally, the organic carbon source includes one or more of coal tar, petroleum tar, phenolic resin, and coconut shell. Further, the organic carbon source includes petroleum tar. Optionally, the softening point of the coal tar or petroleum tar is below 250°C.

[0308] Optionally, the carbonization temperature is 700° C. to 1800° C. Optionally, the carbonization temperature is 1000° C. to 1300° C. When the carbonization temperature is within a suitable range, the organic carbon source can be carbonized and a coating layer containing amorphous carbon can be formed on at least a portion of the surface of the artificial graphite.

[0309] Optionally, the carbonization treatment time is 1 hour to 6 hours.

[0310] 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.

[0311] 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.

[0312] Optionally, based on the mass of the negative electrode active material, the mass content of silicon in the silicon-based material is 0.3% to 10.0%, optionally 1% to 6%. Exemplarily, the mass content of silicon 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 a range consisting of any two of the above values.

[0313] When the mass content of silicon in the silicon-based material is within the above range, the capacity of the negative electrode active material can be increased, thereby improving the energy density of the battery cell.

[0314] Alternatively, the silicon-based material may include at least one of elemental silicon, silicon oxide, a silicon-carbon composite, a silicon-nitrogen composite, and a silicon alloy material.

[0315] In some embodiments, the negative electrode active material may include at least one of a tin-based material and lithium titanate in addition to the aforementioned carbon-based material and optionally a silicon-based material. The tin-based material may include at least one of elemental tin, tin oxide, and a tin alloy.

[0316] The qualitative and quantitative properties of each substance or element in this application can be detected using appropriate equipment and methods known to those skilled in the art. The relevant detection methods can refer to domestic and international detection standards, domestic and international enterprise standards, etc., and those skilled in the art can also adapt certain detection steps / instrument parameters, etc. from the perspective of detection accuracy to obtain more accurate detection results. A single detection method can be used for qualitative or quantitative determination, or several detection methods can be used in combination for qualitative or quantitative determination.

[0317] For example, the present application may combine JIS / K0131-1996 General Rules for X-ray Diffraction Analysis Methods to perform X-ray powder diffraction testing and qualitative analysis on the negative electrode sheet or negative electrode active material.

[0318] Artificial graphite and natural graphite can be distinguished by the SEM cross-section taken by a scanning electron microscope (SEM). The SEM cross-section of natural graphite shows gaps between the flake structures, while the SEM cross-section of artificial graphite is dense and has no obvious gaps. They can also be distinguished by the XRD spectrum obtained by the X-ray diffraction method. The XRD spectrum of natural graphite shows obvious 2H phase and 3R phase, while the XRD spectrum of artificial graphite only shows 2H phase.

[0319] In the embodiment of the present application, the negative electrode film layer includes at least one film layer, which can be a single film layer or at least two film layers. Optionally, the negative electrode film layer includes at least two film layers.

[0320] In the case where 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. In the case of a single-layer film layer, the volume average particle size Dv50 of the negative electrode active material is 8.2μm to 13.5μm. Exemplarily, the volume average particle size Dv50 of the negative electrode active material is 8.2μm, 8.5μm, 8.8μm, 9μm, 9.2μm, 9.5μm, 9.8μm, 10μm, 10.2μm, 10.5μm, 10.8μm, 11μm, 11.2μm, 11.5μm, 11.8μm, 12μm, 12.2μm, 12.5μm, 12.8μm, 13μm, 13.2μm, 13.5μm or a range consisting of any two of the above values.

[0321] When the negative electrode film layer comprises 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 may 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 may include two film layers, three film layers, four film layers, or even more film layers.

[0322] 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 arranged 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 away from the negative electrode current collector, the carbon-based material in the second negative electrode film layer includes graphite particles, and 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.

[0323] The interface between the first negative electrode film layer and the second negative electrode film layer may be regular or irregular, and optionally irregular.

[0324] Optionally, the carbon-based material in the first negative electrode film layer further includes natural graphite.

[0325] The negative electrode film comprises at least two layers, and layered coating can improve the rapid charging performance of the battery cell. In particular, when the first and second negative electrode film layers are different, the pores of the negative electrode film layers can be differentiated, reducing the tortuosity of lithium-ion transport and improving the rapid charging performance of the battery cell.

[0326] 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 for 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.

[0327] There is a difference in the particle size between the first negative electrode film layer and the second negative electrode film layer, which can improve the fast charging performance of the battery cell. Specifically, during the fast charging process, the overpotential of the second negative electrode film layer is usually higher, and the bottleneck of fast charging mainly lies in the second negative electrode film layer. In the embodiment 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 improve the problem of lithium plating on the surface of the negative electrode plate.

[0328] Optionally, the negative electrode active material in the first negative electrode film layer is in a granular form, and its volume average particle size Dv50 is 9.5 μm to 18.5 μm, and optionally 9.5 μm to 14.6 μm. Exemplarily, the volume average particle size of the negative electrode active material in the first negative electrode film layer is 9.5 μm, 10 μm, 10.5 μm, 11 μm, 11.5 μm, 12 μm, 12.5 μm, 13 μm, 13.5 μm, 14 μm, 14.5 μm, 14.6 μm, 15 μm, 15.5 μm, 16 μm, 16.5 μm, 17 μm, 17.5 μm, 18 μm, 18.5 μm, or a range consisting 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 9.5 μm to 18.5 μm, and optionally 9.5 μm to 14.6 μm.

[0329] When the volume average particle size Dv50 of the negative electrode active material in the first negative electrode film layer is within the above range, on the one hand, the solid phase transmission path of lithium ions can be shortened and the fast charging performance can be improved; on the other hand, the material is not easy to agglomerate during the preparation process, which can improve the stability of the material.

[0330] Optionally, the negative electrode active material in the second negative electrode film layer is in a granular form, and a volume average particle size Dv50 thereof is 7.8 μm to 14.3 μm, and optionally 7.8 μm to 11.3 μm. Illustratively, the volume average particle size Dv50 of the negative electrode active material is 7.8 μm, 8.0 μm, 8.2 μm, 8.5 μm, 8.8 μm, 9 μm, 9.2 μm, 9.5 μm, 9.8 μm, 10 μm, 10.2 μm, 10.5 μm, 10.8 μm, 11 μm, 11.3 μm, 11.2 μm, 11.5 μm, 11.8 μm, 12 μm, 12.2 μm, 12.5 μm, 12.8 μm, 13 μm, 13.2 μm, 13.5 μm, 13.8 μm, 14 μm, 14.1 μm, 14.3 μm, or a range consisting 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 7.8 μm to 14.3 μm, and optionally 7.8 μm to 11.3 μm.

[0331] When the volume average particle size Dv50 of the negative electrode active material in the second negative electrode film layer is within the above range, on the one hand, it can shorten the solid phase transmission path of lithium ions and improve the fast charging performance; on the other hand, the material is not easy to agglomerate during the preparation process, which can improve the stability of the material; on the other hand, the combination of the negative electrode active material in the second negative electrode film layer within the above volume average particle size range and the negative electrode active material in the first negative electrode film layer is conducive to constructing a 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.

[0332] In the embodiment of the present application, the volume average particle size Dv50 of the negative electrode active material has a meaning well known in the art and can be detected using equipment and methods well known in the art, and its detection method is the same as the volume average particle size Dv50 test method of the positive electrode active material mentioned above.

[0333] 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 filling 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 the tap density of the carbon-based material in the first negative electrode film layer, the second negative electrode film layer is filled more densely, thereby improving the energy density of the battery cell. The first negative electrode film layer is filled relatively sparsely and has more abundant pores, which can improve 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.

[0334] Optionally, the tap density of the carbon-based material in the first negative electrode film layer is 0.82 g / cm 3 to 1.21g / cm 3 , for example 0.82 g / cm 3 , 0.85g / cm 3 、0.88g / cm 3 , 0.90g / cm 3 , 0.92g / cm 3 , 0.95g / cm 3 , 0.98g / cm 3 , 1.00g / cm 3 , 1.05g / cm 3 、1.08g / cm 3 , 1.10g / cm 3 , 1.12g / cm 3 , 1.15g / cm 3 , 1.18g / cm 3 , 1.20g / cm 3 , 1.21g / cm 3 When the tap density of the carbon-based material in the first negative electrode film layer is within an appropriate range, the fast charging performance of the battery cell can be improved.

[0335] Optionally, 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 , for example 0.90g / cm 3 , 0.92g / cm 3, 0.95g / cm 3 , 0.98g / cm 3 , 1.00g / cm 3 , 1.05g / cm 3 、1.08g / cm 3 , 1.10g / cm 3 , 1.12g / cm 3 , 1.15g / cm 3 , 1.18g / cm 3 , 1.20g / cm 3 , 1.21g / cm 3 , 1.22g / cm 3 , 1.23g / cm 3 , 1.24g / cm 3 , 1.25g / cm 3 When the tap density of the carbon-based material in the second negative electrode film layer is within an appropriate range, the energy density of the battery cell can be increased.

[0336] In the embodiments of this application, the tap density of a material is a term generally known in the art and can be measured using instruments and methods known in the art. For example, it can be measured using a powder tap density tester, as described in GB / T 5162-2006. A Dandong Better BT-301 can be used as the tester.

[0337] 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, or 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 consisting of any two of the foregoing values. By adjusting the thickness ratio of the first negative electrode film layer to the second negative electrode film layer, the gradient porosity difference between the upper and lower layers can be further increased, reducing the tortuosity of lithium ion transport and improving the fast charging capability of the battery cell.

[0338] In some embodiments, after the battery cell undergoes 10 full charge cycles in the Beginning of Life (BOL) test, 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 consisting of any two of the foregoing values. When the thickness of the first negative electrode film layer is within the foregoing range, the gradient porosity difference between the first and second negative electrode film layers can be increased, thereby reducing the tortuosity of lithium ion transport and improving the fast charging capability of the battery cell.

[0339] In some embodiments, after the battery cell undergoes 10 full charge cycles in the Beginning of Life (BOL) test, 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 consisting of any two of the foregoing values. When the thickness of the second negative electrode film layer is within the foregoing range, the gradient porosity difference between the first and second negative electrode film layers can be increased, thereby reducing the tortuosity of lithium ion transport and improving the fast charging capability of the battery cell.

[0340] In the embodiment of the present application, for example, the battery charging upper limit voltage is 3.65V and the battery discharging cut-off voltage is 2.0V.

[0341] The BOL full charge test steps are as follows: at 25°C, charge the battery to 3.65V at a charge rate of 0.33C of the nominal capacity, then charge it to 0.05C at a constant voltage of 3.65V, let it stand for 10 minutes, then discharge it to 2.0V at a discharge rate of 0.33C, let it stand for 10 minutes. The above charge and discharge is one cycle, and the cycle is 10 circles. Then charge it to 3.65V at a charge rate of 0.33C of the nominal capacity, and then charge it to 0.05C at a constant voltage of 3.65V. In the BOL fully charged state, the negative electrode sheet is disassembled, and a cross-section in the thickness direction of the middle area of ​​the negative electrode sheet is observed using a tomographic scanning electron microscope. The first negative electrode film layer and the second negative electrode film layer are distinguished according to the interface between the two areas, and the thickness of the two is measured respectively. For example, the thickness of 10 positions of the first negative electrode film layer is measured respectively, and the average value thereof is calculated as the average value of the first negative electrode film layer; the thickness of 10 positions of the second negative electrode film layer is measured, and the average value thereof is calculated as the average value of the second negative electrode film layer.

[0342] In some embodiments, after a battery cell undergoes an end-of-life (EOL) full charge test, the thickness of the first negative electrode film layer is 15 μm to 70 μm, such as 15 μm, 16 μm, 17 μm, 18 μm, 19 μm, 20 μm, 21 μm, 22 μm, 23 μm, 24 μm, 25 μm, 26 μm, 27 μm, 28 μm, 29 μm, 30 μm, 35 μm, 40 μm, 43 μm, 45 μm, 50 μm, 55 μm, 60 μm, 65 μm, 66 μm, 67 μm, 68 μm, 69 μm, or 70 μm, or a range consisting of any two of the foregoing values. When the thickness of the first negative electrode film layer is within the foregoing range, the first and second negative electrode film layers can be controlled to increase the gradient porosity difference between the upper and lower layers, thereby reducing the tortuosity of lithium ion transmission and improving the fast charging capability of the battery cell.

[0343] In some embodiments, after a battery cell undergoes an end-of-life (EOL) full charge test, the thickness of the second negative electrode film layer is 15 μm to 70 μm, such as 15 μm, 16 μm, 17 μm, 18 μm, 19 μm, 20 μm, 21 μm, 22 μm, 23 μm, 24 μm, 25 μm, 26 μm, 27 μm, 28 μm, 29 μm, 30 μm, 35 μm, 40 μm, 43 μm, 45 μm, 50 μm, 55 μm, 60 μm, 65 μm, 66 μm, 67 μm, 68 μm, 69 μm, 70 μm, or a range consisting of any two of the foregoing values. When the thickness of the second negative electrode film layer is within the foregoing range, the first negative electrode film layer and the second negative electrode film layer can be controlled to increase the gradient porosity difference between the upper and lower layers, thereby reducing the tortuosity of lithium ion transmission and improving the fast charging capability of the battery cell.

[0344] In the embodiment of the present application, for example, the battery charging upper limit voltage is 3.65V and the battery discharging cut-off voltage is 2.0V.

[0345] The EOL full charge test steps are as follows: at 60°C, charge the battery to 3.65V at a charge rate of 0.33C of the nominal capacity, then charge it to 0.05C at a constant voltage of 3.65V, let it stand for 10 minutes, and then discharge it to 2.0V at a discharge rate of 0.33C, let it stand for 10 minutes. The above charge and discharge cycle is one cycle, and the test is stopped when the battery capacity decays to 80% of the nominal capacity. Then, at 25°C, charge to 3.65V at a constant current of 0.33C and charge to 3.65V at a constant voltage of 0.05C, which is the EOL fully charged state. In the EOL fully charged state, disassemble the negative electrode sheet, and use a tomographic scanning electron microscope to observe the cross-section in the thickness direction of the middle area of ​​the negative electrode sheet. The first negative electrode film layer and the second negative electrode film layer are distinguished according to the interface between the two areas, and the thickness of the two is measured respectively. For example, the thickness of 10 positions of the first negative electrode film layer is measured respectively, and the average value thereof is calculated as the average value of the first negative electrode film layer. The thickness of 10 positions of the second negative electrode film layer is measured, and the average value thereof is calculated as the average value of the second negative electrode film layer.

[0346] In some embodiments, when the negative electrode film layer adopts a single-layer film layer (as distinguished from the double-layer film layer described above), 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 consisting of any two of the above values. The lithium element in the lithium-containing binder can exist in the form of ions, which can increase the number of freely 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 rate of lithium ion insertion and extraction, and improve the fast charging performance of the battery cell. Optionally, the negative electrode film layer may 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 (for example, polyacrylic acid PAA, polymethacrylic acid PMAA, sodium polyacrylate PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA) and carboxymethyl chitosan (CMCS).

[0347] Optionally, the mass content of lithium in the lithium-containing binder is 3% to 10%. Exemplarily, the mass content of lithium in the lithium-containing binder is 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, or a range consisting of any two of the above values. The mass content of lithium is calculated based on the mass of the lithium-containing binder. When the mass content of lithium is within the above range, the number of lithium ions that can freely move in the negative electrode film layer is relatively large, which can further shorten the distance that lithium ions 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.

[0348] Exemplarily, the 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, wherein 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%. For example, the molar ratio of the lithium acrylate monomer, the acrylonitrile monomer, the acrylamide monomer, and the hydroxyethyl acrylate monomer is 35%: 30%: 15%: 20%, or 40%, 20%, 10%, 30%, or 45%, 15%, 20%, 20%, etc.

[0349] The lithium-containing binder of the above material can provide a certain amount of lithium ions for the negative electrode film layer, thereby improving the fast charging performance of the battery cell. In addition, it is not easy to swell during the charging and discharging process and has a stable structure, thereby improving the cycle performance of the negative electrode film layer during the fast charging and discharging process.

[0350] In other embodiments, when the negative electrode film layer comprises at least two film layers, the negative electrode film layer further comprises a lithium-containing binder.

[0351] 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, wherein 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.

[0352] 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 the second negative electrode film layer with a relatively larger number of freely movable lithium ions, which can further improve the fast charging performance of the battery cell.

[0353] 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 consisting of any two of the above values. The lithium element in the first lithium-containing binder can exist in ionic form, which can increase the number of freely mobile lithium ions in the negative electrode film layer, shorten the distance lithium ions diffuse to the surface of the negative electrode film layer, increase the lithium ion deintercalation rate, and improve the fast charging performance of the battery cell.

[0354] Optionally, the mass content of lithium in the first lithium-containing binder is 3% to 10%, optionally 3% to 8%. Exemplarily, the mass content of lithium in the first lithium-containing binder is 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, or a range consisting of any two of the above values. When the mass content of lithium is within the above range, a relatively large number of lithium ions can freely move in the negative electrode film layer, further shortening the distance for lithium ions to diffuse to the surface of the negative electrode film layer, increasing the rate of lithium ion insertion and extraction, and improving the fast charging performance of the battery cell.

[0355] Illustratively, the first 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, wherein 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%. For example, the molar ratio of the lithium acrylate monomer, the acrylonitrile monomer, the acrylamide monomer, and the hydroxyethyl acrylate monomer is 35%: 30%: 15%: 20%, or 40%, 20%, 10%, 30%, or 45%, 15%, 20%, 20%, etc.

[0356] The lithium-containing binder of the above material can provide a certain amount of lithium ions for the negative electrode film layer, thereby improving the fast charging performance of the battery cell. In addition, it is not easy to swell during the charging and discharging process and has a stable structure, thereby improving the cycle performance of the negative electrode film layer during the fast charging and discharging process.

[0357] 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 consisting of any two of the above values. The lithium element in the second lithium-containing binder can exist in ionic form, which can increase the number of freely mobile lithium ions in the negative electrode film layer, shorten the distance lithium ions diffuse to the surface of the negative electrode film layer, increase the lithium ion deintercalation rate, and improve the fast charging performance of the battery cell.

[0358] The first lithium-containing binder and the second lithium-containing binder may be made of the same material or different materials.

[0359] Optionally, the mass content of lithium in the second lithium-containing binder is 3% to 10%, optionally 3% to 8%. Exemplarily, the mass content of lithium in the second lithium-containing binder is 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, or a range consisting of any two of the above values. When the mass content of lithium is within the above range, the number of lithium ions that can freely move in the negative electrode film layer is relatively large, which can further shorten the distance that lithium ions diffuse to the surface of the negative electrode film layer, increase the rate of lithium ion insertion and extraction, and improve the fast charging performance of the battery cell.

[0360] Exemplarily, 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, wherein 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%. For example, the molar ratio of the lithium acrylate monomer, the acrylonitrile monomer, the acrylamide monomer, and the hydroxyethyl acrylate monomer is 35%: 30%: 15%: 20%, or 40%, 20%, 10%, 30%, or 45%, 15%, 20%, 20%, etc.

[0361] The lithium-containing binder of the above material can provide a certain amount of lithium ions for the negative electrode film layer, thereby improving the fast charging performance of the battery cell. In addition, it is not easy to swell during the charging and discharging process and has a stable structure, thereby improving the cycle performance of the negative electrode film layer during the fast charging and discharging process.

[0362] 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 each independently include at least one of styrene-butadiene rubber (SBR), a water-soluble unsaturated resin SR-1B, a 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).

[0363] 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.

[0364] In some embodiments, the negative electrode film layer may further optionally include a negative electrode conductive agent. The present application does not particularly limit the type of negative electrode conductive agent. For 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, the weight content of the negative electrode conductive agent is ≤5% based on the total weight of the negative electrode film layer.

[0365] In some embodiments, the negative electrode film layer may further include a negative electrode binder. In some embodiments, the negative electrode binder has a mass content of ≤5% based on the total weight of the negative electrode film layer.

[0366] In some embodiments, the negative electrode film layer may also optionally include other additives. Examples of these additives include thickeners, dispersants, and the like, such as sodium carboxymethylcellulose (CMC-Na) and PTC thermistor materials. In some embodiments, the weight content of these additives is ≤ 2% based on the total weight of the negative electrode film layer.

[0367] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. Examples of metal foils include at least one of copper, copper alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys. The composite current collector may include a polymer base layer and a metal layer formed on at least one surface of the polymer base layer. For example, the metal layer may include at least one of copper, copper alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys. For example, the polymer base layer may include at least one of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0368] In some embodiments, the thickness of the negative electrode current collector is 4 μm to 6 μm. For example, the thickness of the negative electrode current collector is 4 μm, 4.5 μm, 5 μm, 5.5 μm, 6 μm, or a range consisting of any two of the above values.

[0369] When the thickness of the negative electrode current collector is within the above range, the negative electrode current collector has a relatively excellent current flow capacity and can enable the battery cell to have a higher energy density.

[0370] In the embodiment of the present application, the thickness of the negative electrode current collector has a meaning well known in the art and can be detected using equipment and methods well known in the art, for example, using a solvent to wash away the film layer on the surface of the negative electrode current collector and measuring the thickness of the negative electrode current collector with a micrometer.

[0371] The negative electrode film layer is typically formed by coating the negative electrode slurry onto the negative electrode current collector, drying it, and cold pressing it. The negative electrode slurry is typically formed by dispersing the negative electrode active material, an optional conductive agent, an optional binder, and other optional additives in a solvent and stirring them uniformly. The solvent can be, but is not limited to, N-methylpyrrolidone (NMP) or deionized water.

[0372] The negative electrode sheet does not exclude other additional functional layers in addition to the negative electrode film layer. For example, in some embodiments, the negative electrode sheet of the embodiments of the present application further includes a negative 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 other embodiments, the negative electrode sheet of the embodiments of the present application further includes a protective layer covering the surface of the negative electrode film layer.

[0373] In some embodiments, the negative electrode plate further includes a negative electrode conductive layer, which is located between the negative electrode film layer and the negative electrode current collector. The negative electrode conductive layer can further improve the conductivity of the negative electrode plate, reduce the heat generated by the negative electrode plate, and thus reduce the heat generated by the battery cell.

[0374] In some embodiments, the thickness of the negative electrode conductive layer is 0.5 μm to 2 μm. For example, 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 consisting of any two of the above values.

[0375] When the thickness of the negative electrode conductive layer is within the above range, the conductivity of the negative electrode sheet can be further improved, the heat generation of the negative electrode sheet can be reduced, thereby reducing the heat generation of the battery cell, and the energy density of the battery cell can be improved.

[0376] In the embodiment of the present application, the thickness of the negative electrode conductive layer has a meaning well known in the art and can be detected using equipment and methods well known in the art, and the test method for the negative electrode conductive layer mentioned above can be used.

[0377] 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 pole piece 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, thereby improving the structural stability of the negative electrode pole piece.

[0378] In some embodiments, the negative electrode conductive layer may further include other additives, such as thickeners, sodium carboxymethyl cellulose (CMC), PTC thermistor materials, and the like.

[0379] 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 consisting of any two of the above values.

[0380] Illustratively, 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.

[0381] Optionally, the mass content of the negative electrode binder in the negative electrode conductive layer is 60% to 80%, illustratively 60%, 65%, 70%, 75%, 80%, or a range consisting of any two of the above values.

[0382] Illustratively, the negative electrode binder includes one or more of styrene-butadiene rubber (SBR), water-soluble unsaturated resin SR-1B, aqueous acrylic resin, polyvinyl alcohol, sodium alginate, and carboxymethyl chitosan.

[0383] In some embodiments, the ratio CB of the capacity per unit area of ​​the negative electrode film layer to the capacity per unit area of ​​the positive electrode film layer in the battery cell is 1.05 to 1.30, and can optionally be 1.07 to 1.15. For example, the ratio CB of the capacity per unit area of ​​the negative electrode film layer to the capacity per unit area of ​​the positive electrode film layer 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 consisting of any two of the foregoing values.

[0384] When the ratio CB of the capacity per unit area of ​​the negative electrode film layer to the capacity per unit area of ​​the positive electrode film layer in the battery cell is within the above range, there are sufficient sites in the negative electrode film layer for lithium embedding, which can reduce the risk of lithium plating and is conducive to fast charging.

[0385] In the embodiment of the present application, the CB value has a well-known meaning in the art and can be detected using equipment and methods well-known in the art. For example, the capacity per unit area of ​​the negative electrode film layer and the 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.

[0386] Specifically, take the battery charging upper limit voltage as 3.65V and the battery discharging cut-off voltage as 2.0V as an example for explanation.

[0387] The capacity per unit area of ​​the positive electrode film layer refers to the actual lithium-removable capacity of the positive electrode active material. The test method is as follows: the battery is disassembled in a PRS340 / 11-119-11 Braun glove box, the positive electrode sheet is removed, and assembled into a CR2430 model semi-button battery with a positive electrode-lithium sheet. The area of ​​the positive electrode sheet used is amm 2The electrolyte is a solution of 1 mol / L LiPF6 in EC / EMC / DEC=3 / 5 / 2 (mass ratio), and then the assembled half-button battery is left to stand for 3 hours. The test is carried out at 25°C, and 0.1C is used to charge (Charge) in the voltage range of 2.0V to 3.65V to delithiate, and then 0.05C is used to discharge (Discharge) lithium to 2.0V, and the cycle is repeated twice. The discharge capacity of the second cycle is recorded as YmAh. The actual battery design has a positive electrode sheet length of bmm and a width of cmm. The number of surfaces of the positive electrode active material coated on the positive electrode current collector is d, then the capacity of the positive electrode film layer per unit area = Y / a*b*c*d.

[0388] Specifically, the capacity per unit area of ​​the negative electrode film layer refers to the actual lithium-insertable capacity of the negative electrode active material. The test method is as follows: disassemble the battery in a PRS340 / 11-119-11 Braun glove box, remove the negative electrode plate, and assemble it into a CR2430 model semi-button battery with a negative electrode-lithium plate. The area of ​​the negative electrode plate used is fmm 2 , where the electrolyte uses a solution of 1 mol / L LiPF6 in EC / EMC / DEC=3 / 5 / 2 (mass ratio), and then the assembled half-button battery is left to stand for 3 hours. The test is carried out at 25°C, and 0.1C is used to discharge (Discharge) in the voltage range of 2V-0V to insert lithium, and then 0.05C is used to charge (Discharge) to 2V for lithium removal, and the cycle is repeated twice. The discharge capacity of the second cycle is recorded as ZmAh. The actual battery design has a negative electrode sheet length of hmm and a width of imm. The number of surfaces of the negative electrode active material coated on the negative electrode current collector is d, then the negative electrode lithium insertion capacity = Z / f*h*i*d.

[0389] [Isolation film]

[0390] In the embodiment of the present application, the isolation membrane includes a base membrane with a porous structure.

[0391] In some embodiments, the base film comprises at least one of glass fiber, non-woven fabric, and polyolefin. The base film may be a single-layer film or a multi-layer composite film, without particular limitation. When the base film is a multi-layer composite film, the materials of each layer may be the same or different, without particular limitation.

[0392] Optionally, the polyolefin includes at least one of polyethylene, polypropylene and polyvinylidene fluoride.

[0393] In some embodiments, the porosity of the base film is 20% to 70%, optionally 35% to 60%. Exemplarily, the porosity of the base film is 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, or a range consisting of any two of the above values.

[0394] In the embodiment of the present application, when the porosity of the base film is within the above range, the migration ability of lithium ions in the separator can be improved, and the internal resistance of the battery cell can be further reduced, thereby reducing heat generation.

[0395] In the embodiments of this application, porosity refers to the percentage of the pore volume within the separator to the total volume of the separator. Porosity can be tested in accordance with the standard GB / T36363-2018, "Polyolefin Separators for Battery Cells." It should be noted that the actual testing process may vary slightly from the standard to obtain a more accurate test value, depending on instrument differences, test errors, and to minimize the impact of porosity testing.

[0396] In some embodiments, the base film has a thickness of 6 μm to 12 μm, optionally 6 μm to 9 μm. For example, the base film has a thickness of 6 μm, 6.5 μm, 7 μm, 7.5 μm, 8 μm, 8.5 μm, 9 μm, 9.5 μm, 10 μm, 10.5 μm, 11 μm, 11.5 μm, 12 μm, or a range consisting of any two of the above values.

[0397] When the thickness of the base film is within the above range, the migration path of lithium ions in the base film is shorter, which can further reduce the internal resistance of the battery cell and thus reduce heat generation.

[0398] In the embodiment of the present application, the isolation membrane may be a base membrane. Optionally, the isolation membrane further includes a functional layer disposed on at least one side of the base membrane. The functional layer may include inorganic particles to enhance the heat resistance of the isolation membrane. Optionally, the functional layer is disposed on both sides of the base membrane.

[0399] 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, the first functional layer includes first inorganic particles, the second functional layer is located on the other side of the base film, the second functional layer includes composite particles, the composite particles include second inorganic particles and multiple 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.

[0400] The first functional layer and the second functional layer have good heat resistance, which can improve the heat resistance of the isolation film.

[0401] Optionally, the first functional layer may include a binder, optionally including at least one of a fluorine-containing binder or a polyacrylic binder, such as polyvinylidene fluoride.

[0402] 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 first inorganic particles can improve the heat resistance of the first functional layer.

[0403] In the embodiments of the present application, the thickness of the base film has a meaning well known in the art, and can be tested using the meanings and equipment well known in the art. For example, a newly prepared isolation membrane can be taken as a sample, or a battery cell that has been discharged (discharged to the lower cut-off voltage so that the battery's charged state is approximately 0% SOC) can be reversely disassembled, and the isolation membrane can be obtained from the battery cell. The isolation membrane is dried and used as a sample, and the isolation membrane is cut with an ion beam cutter to form a cross section. Subsequently, a scanning electron microscope is used to measure the thickness of the cross section of the isolation membrane and its various layers.

[0404] The non-fluorinated polymer particles in the second functional layer refer to polymers that are non-fluorinated polymers. For example, the non-fluorinated polymer particles include an acrylic copolymer. Optionally, the acrylic copolymer includes an acrylate-acrylonitrile-acrylamide-propylene copolymer. Acrylic copolymers have excellent bonding properties and high bonding 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.

[0405] The second inorganic particles in the composite particles make it difficult for the non-fluoropolymer particles to adhere to each other due to the high temperature treatment during the granulation process, so that the composite particles have pores, which is conducive to the transmission of lithium ions and improves the ion conductivity of the separator. The second inorganic particles can also increase the compression modulus of the composite particles. During the charge and discharge process, the composite particles are not easily deformed, making the structure of the separator more stable, which can improve the dynamic performance of the battery cell and improve the fast charging performance. Optionally, compared to the first functional layer, the second functional layer is arranged close to the negative electrode sheet. Since the composite particles are not easily deformed, the separator basically does not cause side effects such as extrusion on the negative electrode sheet, which stabilizes the dynamic performance of the negative electrode sheet. Accordingly, the first functional layer is arranged close to the positive electrode sheet.

[0406] 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. These second inorganic particles can enhance the heat resistance of the second functional layer and can form composite particles with non-fluoropolymers to further improve the cycle stability and dynamic performance of the separator, thereby improving the cycle performance and fast charging performance of the battery cell.

[0407] The average particle size of the second inorganic particles is 5 nm to 100 nm, optionally 10 nm to 100 nm, optionally 5 nm to 20 nm. Exemplarily, the average particle size of the second inorganic particles is 5 nm, 10 nm, 15 nm, 20 nm, 25 nm, 30 nm, 35 nm, 40 nm, 45 nm, 50 nm, 55 nm, 60 nm, 65 nm, 70 nm, 75 nm, 80 nm, 85 nm, 90 nm, 95 nm, 100 nm, or a range consisting 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.

[0408] In the embodiment of the present application, the average particle size of the second inorganic particles has a meaning well known in the art and can be detected using equipment and methods well known in the art. For example, after obtaining the isolation film and drying the isolation film as a sample, the isolation film is cut with 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 isolation film. The particle sizes of multiple, for example, 50, second inorganic particles are measured, and the average value is calculated as the average particle size of the second inorganic particles.

[0409] In some embodiments, the ionic conductivity of the separator is 0.3 mS / cm to 0.6 mS / cm. For example, 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 consisting of any two of the foregoing values.

[0410] 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, thereby improving the fast charging performance of the battery cell.

[0411] In the embodiments of the present application, the ionic conductivity of the isolation membrane has a meaning known in the art and can be detected using equipment and methods known in the art, for example,

[0412] Preparation of 2025 button cells for testing: In a vacuum glove box, a lithium sheet was placed in the negative electrode shell of the battery, and 150 μL of electrolyte was added thereto. The electrolyte was a solution of 1 mol / L LiPF6 in EC / EMC / DEC = 3 / 5 / 2 (mass ratio). Then, an isolation membrane (area of ​​3.14 cm) was placed in the negative electrode shell of the battery. 2 , 12μm thick) to ensure close contact with the lithium sheet. 25μL of electrolyte was then added. Finally, a positive electrode sheet (the one described in Example 1 can be used) was placed on top and packaged. The assembled button cell was removed from the vacuum glove box and allowed to rest for 24 hours before the next test.

[0413] Test: On an electrochemical workstation, at 10 -1 ~10 6 The test is carried out in the frequency range of Hz to obtain the isolation membrane resistance Rb, and the ionic conductivity σ (unit: mS / cm) is calculated by the following formula:

[0414] σ=L / (R b ×S)

[0415] Where: R b is the isolation film resistance, L and S are the thickness and area of ​​the isolation film to be measured respectively.

[0416] In some embodiments, the positive electrode sheet, the separator, and the negative electrode sheet may be formed into an electrode assembly through a winding process and / or a lamination process.

[0417] Please continue to refer to Figure 1 and Figure 2 , the battery cell 7 may include a housing 20 .

[0418] In some embodiments, the outer shell 20 of the battery cell 7 can be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell. Alternatively, the outer shell 20 of the battery cell 7 can be a soft shell, such as a pouch-type soft shell. The soft shell can be made of plastic, such as at least one of polypropylene (PP), polybutylene terephthalate (PBT), and polybutylene succinate (PBS).

[0419] The shell 20 is a hollow structure, and the shell 20 can be used to encapsulate the electrode assembly 10 and the electrolyte.

[0420] The preparation method of the battery cell 7 according to the embodiments of the present application is well known. In some embodiments, a positive electrode sheet, a separator, a negative electrode sheet, and an electrolyte can be assembled to form a battery cell 7. As an example, the positive electrode sheet, separator, and negative electrode sheet can be wound and / or laminated to form an electrode assembly 10. The electrode assembly 10 is placed in a housing 20, dried, and then injected with electrolyte. The battery cell 7 is then vacuum packaged, allowed to stand, formed, and shaped.

[0421] In the embodiment of the present application, the housing 20 includes a shell 21 and an end cap 22. The shell 21 has an opening, and the end cap 22 covers the opening. The shape of the shell 21 can be determined according to the specific shape of the electrode assembly 10. For example, if the electrode assembly 10 has a cylindrical structure, a cylindrical shell can be selected; if the electrode assembly 10 has a rectangular structure, a rectangular shell can be selected. Optionally, both the electrode assembly 10 and the shell 21 have a rectangular structure.

[0422] In some embodiments, the housing 21 is made of steel, which has high mechanical strength and is not easily deformed, thereby improving the reliability and cycle performance of the battery cell 7. Optionally, steel accounts for the largest proportion of the housing 21 by mass.

[0423] Optionally, the thickness of the shell 21 is 0.1mm to 0.5mm, and optionally 0.2mm to 0.35mm. For example, the thickness of the shell is 0.1mm, 0.15mm, 0.2mm, 0.25mm, 0.3mm, 0.35mm, 0.4mm, 0.45mm, 0.5mm, or a range consisting of any two of the above values. When the thickness of the shell 21 is within the above range, the mechanical strength of the shell 21 is high, which can improve the reliability and cycle performance of the battery cell 7. In addition, the shell 21 occupies less space, and the internal space of the shell 21 is larger, which is conducive to improving the energy density of the battery cell 7.

[0424] From the appearance of the electrode assembly 10, the electrode assembly 10 includes a main body 12, a positive electrode tab 111, and a negative electrode tab 112. The positive electrode tab 111 and the negative electrode tab 112 protrude from the main body 12. The positive electrode tab 111 is the portion of the positive electrode sheet not coated with the active material layer, and the negative electrode tab 112 is the portion of the negative electrode sheet not coated with the active material layer. The positive electrode tab 111 and the negative electrode tab 112 are used to draw current from the main body 12.

[0425] The positive electrode tab 111 and the negative electrode tab 112 may extend from the same side of the main body 12 or from opposite sides thereof.

[0426] Optionally, the number of the positive electrode tabs 111 located on the same side of the main body 12 is at least one, and optionally at least two. At least two positive electrode tabs 111 can increase the current capacity of the positive electrode tab 111 .

[0427] Optionally, the positive electrode tab 111 may be provided on at least one side of the main body 12 , and optionally on at least two sides.

[0428] Optionally, the number of the negative electrode tabs 112 located on the same side of the main body 12 is at least one, and optionally at least two. At least two negative electrode tabs 112 can increase the current capacity of the negative electrode tabs 112 .

[0429] Optionally, the negative electrode tab 112 may be provided on at least one side of the main body 12 , and optionally at least two sides.

[0430] In some embodiments, the battery cell 7 further includes a positive terminal 31, which is electrically connected to the positive electrode tab 111. Optionally, the positive terminal 31 and the positive electrode tab 111 are welded, and the positive terminal 31 and the positive electrode tab 111 can be connected via an adapter or without an adapter. Optionally, the positive terminal 31 and the positive electrode tab 111 are connected without 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 point and help reduce the internal resistance of the battery cell 7 as a whole.

[0431] In some embodiments, the battery cell 7 further includes a negative terminal 32, which is electrically connected to the negative electrode tab 112. Optionally, the negative terminal 32 and the negative electrode tab 112 are welded, and the negative terminal 32 and the negative electrode tab 112 may be connected via an adapter or without an adapter. Optionally, the negative terminal 32 and the negative electrode tab 112 are connected without 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 point and help reduce the internal resistance of the battery cell 7 as a whole.

[0432] Optionally, the number of the positive terminals 31 located on the same side of the main body 12 is at least one, and optionally at least two. At least two positive terminals 31 can increase the current capacity of the positive terminal 31 .

[0433] Further optionally, the flow area of ​​the single-side positive terminal 31 is 150mm 2 Up to 1000mm 2 , 200mm is optional 2 Up to 1000mm 2 The flow area of ​​a single-sided positive terminal 31 refers to the sum of the flow areas of all positive terminals 31 located on the same side of the main body 12. The flow area of ​​the positive terminal 31 can be understood as the cross-sectional area of ​​the positive terminal 31, where the cross-section of the positive terminal 31 is perpendicular to the thickness direction of the end cap 22.

[0434] For example, the flow area of ​​the single-sided positive terminal 31 can be 150 mm 2 , 200mm 2 , 210mm 2 , 250mm 2 , 280mm 2 , 300mm 2 , 320mm 2 , 350mm 2 , 380mm 2 , 400mm 2 , 450mm 2 , 500mm 2 , 550mm 2 , 600mm 2、650mm 2 , 700mm 2 , 750mm 2 , 800mm 2 , 850mm 2 , 900mm 2 , 950mm 2 , 1000mm 2 Or a range consisting of any two of the above values.

[0435] Optionally, the number of the negative terminals 32 located on the same side of the main body 12 is at least one, and optionally at least two. At least two negative terminals 32 can increase the current capacity of the negative terminal 32 .

[0436] Alternatively, the flow area of ​​the single-side negative terminal 32 is 150 mm 2 Up to 1000mm 2 , 200mm is optional 2 Up to 1000mm 2 The flow area of ​​a single-sided negative terminal 32 refers to the sum of the flow areas of all negative terminals 32 located on the same side of the main body 12. The flow area of ​​the negative terminal 32 can be understood as the cross-sectional area of ​​the negative terminal 32, where the cross-section of the negative terminal 32 is perpendicular to the thickness direction of the end cap 22.

[0437] For example, the flow area of ​​the single-side negative terminal 32 may be 150 mm 2 , 200mm 2 , 210mm 2 , 250mm 2 , 280mm 2 , 300mm 2 , 320mm 2 , 350mm 2 , 380mm 2 , 400mm 2 , 450mm 2 , 500mm 2 , 550mm 2 , 600mm 2 、650mm 2 , 700mm 2 , 750mm 2 , 800mm 2 , 850mm 2 , 900mm 2 , 950mm 2 , 1000mm 2 Or a range consisting of any two of the above values.

[0438] In some embodiments, the dimension of the battery cell 7 along 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 consisting of any two of the above values. Figure 1 L1 shown in the figure represents the dimension of the battery cell 7 along the first direction X. It can be understood that when the battery cell 7 is placed vertically, L1 is the dimension from the bottom of the shell 21 to the top of the end cover 22.

[0439] When the size of the battery cell 7 along the first direction X is within the above range, the size of the positive electrode film along the first direction X is matched, so that the positive electrode active material coated on the positive electrode film is increased, which is beneficial to improving the energy density of the battery cell 7.

[0440] like Figure 3 As shown, in some embodiments of the present application, the battery cells 7 according to the embodiments of the present application can be assembled into a battery module 6. The number of battery cells 7 contained 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.

[0441] If there are multiple battery cells 7, they can be connected in series, in parallel, or in a hybrid connection. A hybrid connection refers to a combination of series and parallel connections within the battery cells 7. Multiple battery cells 7 can be directly connected in series, in parallel, or in a hybrid connection, and then the entire battery cell 7 is housed within the housing of the battery module 6. Alternatively, multiple battery cells 7 can be first connected in series, in parallel, or in a hybrid connection to form a battery module 6, and then the battery modules 6 are further connected in series, in parallel, or in a hybrid connection to form a single unit and housed within the housing. Optionally, the battery module 6 may further include a housing portion having a storage space, and the multiple battery cells 7 are housed within the storage space.

[0442] like Figure 4 and Figure 5 As shown, in some embodiments, the battery modules 6 can also be assembled into a battery pack 2. The number of battery modules 6 contained 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 a battery module 6 or a battery pack 2.

[0443] The battery pack 2 may include a housing 5 and a plurality of battery modules 6 disposed within the housing 5. The housing 5 includes a first housing portion 5a and a second housing portion 5b. The housing 5 defines a receiving space 5c. The first housing portion 5a covers the second housing portion 5b and forms an enclosed space for receiving the battery modules 6. The plurality of battery modules 6 may be arranged in any manner within the housing 5.

[0444] In some embodiments, the size of the box 5 along the first direction X is 110 mm to 170 mm, for example, 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 a range consisting of any two of the above values. Figure 4 L2 shown in the figure represents the dimension of the box 5 along the first direction X, which can also be understood as the height dimension of the box 5.

[0445] The first and second housing portions 5a, 5b overlap each other, and together they define a storage space 5c for accommodating the battery cells. The second housing portion 5b can be a hollow structure with one end open. The first housing portion 5a is a plate-like structure, and the first housing portion 5a overlaps the open side of the second housing portion 5b to form the housing 5 with the storage space 5c. Alternatively, both the first and second housing portions 5a, 5b can be hollow structures with one end open, and the open side of the first housing portion 5a overlaps the open side of the second housing portion 5b to form the housing 5 with the storage space 5c. Of course, the first and second housing portions 5a, 5b can have various shapes, such as a cylinder, a rectangular parallelepiped, etc.

[0446] In order to improve the sealing performance after the first box body portion 5a and the second box body portion 5b are connected, a sealing member, such as a sealant, a sealing ring, etc., may also be provided between the first box body portion 5a and the second box body portion 5b.

[0447] Assuming that the first box portion 5a covers the top of the second box portion 5b, the first box portion 5a can also be called an upper box cover, and the second box portion 5b can also be called a lower box.

[0448] In some embodiments, during the charging process of the battery pack 2 or any battery cell constituting the battery pack 2 from 0% state of charge (SOC) to 100% state of charge (SOC), the temperature of the external environment of the battery pack 2 is room temperature, for example, 30°C.

[0449] In some embodiments, during the process of the battery pack 2 or any battery cell constituting the battery pack 2 changing from a state of charge (SOC) of 10% to a state of charge (SOC) of 80%, the temperature of the external environment of the battery pack 2 is room temperature, for example, 30°C.

[0450] In some embodiments, the charging process of the battery pack 2 or any battery cell constituting the battery pack 2 from 10% state of charge to 80% state of charge includes multiple charging steps, and 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 consisting of any two of the above values.

[0451] The battery pack 2 or any battery cell constituting the battery pack 2 includes multiple charging steps from a 10% state of charge to a 40% state of charge. For any charging step, it can be charged at any rate between 5C and 10C. The charging rate corresponding to each charging step can be any value of 5C, 5.5C, 6C, 6.5C, 7C, 7.5C, 8C, 8.5C, 9C, 9.5C, 10C, or a value in the range consisting of any two of the above values.

[0452] The battery pack 2 or any battery cell constituting the battery pack 2 also includes multiple charging steps from 40% state of charge to 80% state of charge, the charging rate of any charging step is less than the charging rate of any charging step from 10% state of charge to 40% state of charge, and the charging rate of the step of charging to 80% state of charge is any value between 2.5C and 5C, for example, it can be 2.7C.

[0453] For example, the charging step of the battery pack 2 or any battery cell constituting the battery pack 2 from 10% to 80% can be performed as follows:

[0454] Charge from 10% SOC to 15% SOC at 5.0C constant current;

[0455] Charge from 15% SOC to 20% SOC at 5.0C constant current;

[0456] Charge from 20% SOC to 25% SOC at 5.0C constant current;

[0457] Charge from 25% SOC to 30% SOC at 5.0C constant current;

[0458] Charge from 30% SOC to 35% SOC at 5.0C constant current;

[0459] Charge from 35% SOC to 40% SOC at 5.0C constant current;

[0460] Charge from 40% SOC to 45% SOC at 4.6C constant current;

[0461] Charge from 45% SOC to 50% SOC at 4.3C constant current;

[0462] Charge from 50% SOC to 55% SOC at 4.0C constant current;

[0463] Charge from 55% SOC to 60% SOC at 3.7C constant current;

[0464] Charge from 60% SOC to 65% SOC at 3.4C constant current;

[0465] Charge from 65% SOC to 70% SOC at 3.1C constant current;

[0466] Charge from 70% SOC to 75% SOC at 2.9C constant current;

[0467] Charge from 75% SOC to 80% SOC at 2.7C constant current.

[0468] 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 minutes, and can be optionally 5 minutes to 12.5 minutes. 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 minutes, 12 minutes, 11.5 minutes, 11 minutes, 10.5 minutes, 10 minutes, 9.5 minutes, 9 minutes, 8.5 minutes, 8 minutes, 7.5 minutes, 7 minutes, 6.5 minutes, 6 minutes, 5.5 minutes, 5 minutes, or a range consisting of any two of the above values.

[0469] In some embodiments, the volumetric energy density of the battery cell is 380Wh / L to 470Wh / L, optionally 390Wh / L to 450Wh / L. For example, the volumetric energy density of the battery cell is 380Wh / L, 390Wh / L, 400Wh / L, 410Wh / L, 420Wh / L, 430Wh / L, 440Wh / L, 450Wh / L, 460Wh / L, 470Wh / L, or a range consisting of any two of the foregoing values. The volumetric energy density of the battery cell is relatively high.

[0470] In the embodiments of the present application, the volume energy density of a battery cell has a meaning well known in the art and can be detected using equipment and methods well known in the art. For example, the battery charging upper limit voltage is 3.65V and the battery discharge cut-off voltage is 2.0V.

[0471] Place the battery cell at 25°C, charge at a constant current of 0.33C to 3.65V, and then charge at a constant voltage of 0.05C; discharge at a constant current of 0.33C to 2.0V, and record the discharge capacity A0 at this time, unit: Ah; use calipers to measure the length, width, and height of the battery cell (generally calculated based on the battery casing size, excluding the electrode terminal height and the insulating film outside the casing), and calculate the volume of the single battery V0, unit: L; the volume energy density of the battery cell VED = (A0 × discharge platform voltage) / V0, unit: Wh / L.

[0472] In some embodiments, the cell group margin at 100% state of charge is greater than or equal to 96% and less than 100%, and may be between 96.5% and 99.5%. For example, the cell group margin is 96%, 96.5%, 97%, 97.5%, 98%, 98.5%, 99%, 99.5%, or a range consisting of any two of these values. When the cell group margin is within the above range, the volume ratio of the electrode assembly is high, and the energy density of the battery cell is high.

[0473] In 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 fill rate. The group margin is calculated as follows: group margin = electrode assembly thickness / battery case internal thickness.

[0474] Electrical devices

[0475] A second aspect of the embodiments of the present application provides an electrical device, comprising a battery device according to the embodiments of the present application, such as a battery cell, battery module, or battery pack. The battery cell, battery module, or battery pack can serve as a power source for the electrical device or as an energy storage unit for 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, an electric tool, and the like. The vehicle can be a fuel-powered vehicle, a gas-powered vehicle, or a new energy vehicle; the new energy vehicle can be a pure electric vehicle, a hybrid vehicle, or an extended-range vehicle; the spacecraft can include an airplane, a rocket, a space shuttle, and a spacecraft; the electric toy can include fixed or mobile electric toys, such as game consoles, electric car toys, electric ship toys, and electric airplane toys; and the electric tools can include metal cutting power tools, grinding power tools, assembly power tools, and railway power tools, such as electric drills, electric grinders, electric wrenches, electric screwdrivers, electric hammers, impact drills, concrete vibrators, and electric planers. The embodiments of the present application do not impose any particular limitations on the above-mentioned electrical devices.

[0476] The electrical device can select battery cells, battery modules or battery packs according to its usage requirements.

[0477] Figure 51 is a schematic diagram of an exemplary electric device 1. The electric device 1 is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the high power and high energy density requirements of the electric device 1, a battery pack or battery module may be used.

[0478] A battery pack 2 is disposed within the electrical device 1. The battery pack 2 can be located at the bottom, top, or rear of the electrical device 1. The battery pack 2 can be used to power the electrical device 1. For example, the battery pack 2 can serve as the operating power source of the electrical device 1 or 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.

[0479] The electric 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, to meet the power requirements of the electric device 1 during startup, navigation, and driving.

[0480] As another example, an electric device may be a mobile phone, a tablet computer, a laptop computer, etc. Such an electric device is usually required to be lightweight and thin, and may use a battery cell as a power source.

[0481] The charging process of the electric device can select the following charging methods:

[0482] Charge from 10% SOC to 15% SOC at 5.0C constant current;

[0483] Charge from 15% SOC to 20% SOC at 5.0C constant current;

[0484] Charge from 20% SOC to 25% SOC at 5.0C constant current;

[0485] Charge from 25% SOC to 30% SOC at 5.0C constant current;

[0486] Charge from 30% SOC to 35% SOC at 5.0C constant current;

[0487] Charge from 35% SOC to 40% SOC at 5.0C constant current;

[0488] Charge from 40% SOC to 45% SOC at 4.6C constant current;

[0489] Charge from 45% SOC to 50% SOC at 4.3C constant current;

[0490] Charge from 50% SOC to 55% SOC at 4.0C constant current;

[0491] Charge from 55% SOC to 60% SOC at 3.7C constant current;

[0492] Charge from 60% SOC to 65% SOC at 3.4C constant current;

[0493] Charge from 65% SOC to 70% SOC at 3.1C constant current;

[0494] Charge from 70% SOC to 75% SOC at 2.9C constant current;

[0495] Charge from 75% SOC to 80% SOC at 2.7C constant current.

[0496] 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 minutes, and can be optionally 5 minutes to 12.5 minutes, and 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 minutes, 12 minutes, 11.5 minutes, 11 minutes, 10.5 minutes, 10 minutes, 9.5 minutes, 9 minutes, 8.5 minutes, 8 minutes, 7.5 minutes, 7 minutes, 6.5 minutes, 6 minutes, 5.5 minutes, 5 minutes, or a range consisting of any two of the above values.

[0497] Example

[0498] The following examples describe the disclosure of the present invention in more detail. These examples are intended for illustrative purposes only, as various modifications and variations within the scope of the disclosure of the present invention will be apparent to those skilled in the art. Unless otherwise stated, all parts, percentages, and ratios reported in the following examples are by mass, and all reagents used in the examples are commercially available or synthesized according to conventional methods and can be used directly without further processing, and the instruments used in the examples are commercially available.

[0499] Example 1

[0500] 1. Preparation of positive electrode sheet

[0501] The positive electrode sheet includes a positive electrode current collector, a positive electrode conductive layer on the positive electrode current collector and a positive electrode film layer. The positive electrode current collector is aluminum foil.

[0502] The positive conductive layer on the positive current collector is formed by evenly mixing the positive conductive agent superconducting carbon, the positive electrode binder polyvinylidene fluoride (PVDF) and the solvent N-methylpyrrolidone NMP, and then coating it on the surface of the current collector and drying it to form a film layer with a thickness of 1μm. 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%.

[0503] The positive electrode film layer includes a positive electrode slurry (the solvent is N-methylpyrrolidone NMP) uniformly coated on the surface of the positive electrode conductive layer, and a film layer formed after drying and cold pressing. The positive electrode film layer includes a positive electrode active material, a binder polyvinylidene fluoride (PVDF) and a conductive agent acetylene black in a weight ratio of 97:2:1.

[0504] The positive electrode active material includes lithium iron phosphate and a coating layer, which is coated on the surface of the lithium iron phosphate and includes lithium iron titanium phosphate (Li2FeTi(PO4)3) and amorphous carbon. The Dv50 of the positive electrode active material is 1.6μm and the Dv10 is 0.64μm.

[0505] The single-sided coating weight of the positive electrode film is 300mg / 1540.25mm 2 .

[0506] 2. Preparation of negative electrode sheet

[0507] The negative electrode plate includes a negative electrode current collector, a negative electrode conductive layer on the negative electrode current collector and a negative electrode film layer. The negative electrode current collector is copper foil.

[0508] The negative electrode conductive layer on the negative electrode current collector is formed by evenly mixing the negative electrode conductive agent superconducting carbon, the negative electrode binder styrene-butadiene rubber SBR, the thickener sodium carboxymethyl cellulose (CMC-Na) and the solvent water, and then coating it on the surface of the negative electrode current collector and drying it to form a film layer with a thickness of 1 μm. The mass content of the negative electrode conductive agent in the negative electrode conductive layer is 35%, the mass content of the negative electrode binder in the negative electrode conductive layer is 60%, and the mass content of the thickener in the negative electrode conductive layer is 5%.

[0509] The negative electrode film layer includes a film layer formed by uniformly coating the negative electrode slurry (the solvent is deionized water) on the surface of the negative electrode conductive layer, drying, and cold pressing.

[0510] The single-sided coating weight of the negative electrode film is 138mg / 1540.25mm 2 .

[0511] 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.

[0512] The first negative electrode film layer includes graphite particles with a mass ratio of 96.5:0.5:0.5:1.5:1, a conductive agent acetylene black, a first lithium-containing binder (lithium acrylate-acrylonitrile-acrylamide-hydroxyethyl acrylate copolymer, wherein the molar ratio of lithium acrylate monomer, acrylonitrile monomer, acrylamide monomer and hydroxyethyl acrylate monomer is 35%:30%:15%:20%), a negative electrode binder styrene-butadiene rubber, and a thickener sodium carboxymethyl cellulose. The mass content of lithium element in the first lithium-containing binder is 4.8%, the Dv50 of the graphite particles is 11.3μm, and the graphite particles include artificial graphite and a carbon coating layer. The carbon coating layer is coated on the surface of the artificial graphite, and the mass content of the carbon coating layer is 3.5%.

[0513] The second negative electrode film layer includes graphite particles with a mass ratio of 97.5:0.5:0.5:0.5:1, a conductive agent acetylene black, a second lithium-containing binder (lithium acrylate-acrylonitrile-acrylamide-hydroxyethyl acrylate copolymer, wherein the molar ratio of lithium acrylate monomer, acrylonitrile monomer, acrylamide monomer and hydroxyethyl acrylate monomer is 35%:30%:15%:20%), a negative electrode binder styrene-butadiene rubber, and a thickener sodium carboxymethyl cellulose. The mass content of lithium element in the second lithium-containing binder is 4.8%, the Dv50 of the graphite particles is 11.3μm, and the graphite particles include artificial graphite and a carbon coating layer. The carbon coating layer is coated on the surface of the artificial graphite, and the mass content of the carbon coating layer is 3.5%.

[0514] 3. Isolation film

[0515] The isolation film includes a base film, which is a 7 μm polyethylene film layer with a porosity of 42%.

[0516] 4. Preparation of electrolyte

[0517] The organic solvent includes 60% of a chain carboxylic acid ester solvent (ethyl acetate) and 40% of a carbonate solvent (30% of ethylene carbonate EC, 10% of dimethyl carbonate), and the mass content of each component in the organic solvent is calculated based on the mass of the organic solvent.

[0518] Based on the mass of the electrolyte, the mass content of the additive is 6.5%, which includes vinylene carbonate VC, fluoroethylene carbonate FEC, vinyl sulfite ES and lithium difluorooxalatoborate LiDFOB in a mass ratio of 5:0.5:0.5:0.5.

[0519] The lithium salt includes 1 mol / L lithium hexafluorophosphate LiPF6.

[0520] The conductivity of the electrolyte at room temperature is 16.4 mS / cm.

[0521] 5. Preparation of battery cells

[0522] The positive electrode sheet, separator, and negative electrode sheet are stacked in order, with the separator placed between the positive and negative electrode sheets to serve as an isolation to obtain an electrode assembly; the electrode assembly is placed in an outer packaging shell, dried, and then injected with electrolyte. After vacuum packaging, standing, forming, and shaping, a battery cell is obtained. The battery cell is placed vertically with the end cap located on the upper side of the shell. The height direction of the battery cell is parallel to the first direction. The battery height is 97mm and the battery width is 71mm. The compaction density of the positive electrode film layer of the battery cell at 100% SOC is 2.72g / cm 3 The compaction density of the negative electrode film layer at 100% SOC is 1.26g / cm 3 .

[0523] Comparative Example 1 and Comparative Example 2

[0524] A battery cell was prepared using a method similar to that of Example 1. The difference from Example 1 was that the coating weight of the positive electrode film layer and the coating weight of the negative electrode film layer were adjusted.

[0525] Example 2-1 to Example 2-3

[0526] A battery cell was prepared using a method similar to that of Example 1. The difference from Example 1 was that the coating weight of the positive electrode film layer and the coating weight of the negative electrode film layer were adjusted.

[0527] Example 3-1 to Example 3-3

[0528] A battery cell was prepared using a method similar to that of Example 1. The difference from Example 1 was that the coating weight of the negative electrode film layer was adjusted.

[0529] Performance Testing

[0530] 1. The charging time of the battery cell from 10% SOC to 80% SOC is specifically charged in the following steps:

[0531] At 30°C, charge from 10% SOC state.

[0532] Charge from 10% SOC to 15% SOC at 5.0C constant current.

[0533] Charge from 15% SOC to 20% SOC at 5.0C constant current.

[0534] Charge from 20% SOC to 25% SOC at 5.0C constant current.

[0535] Charge from 25% SOC to 30% SOC at 5.0C constant current.

[0536] Charge from 30% SOC to 35% SOC at 5.0C constant current.

[0537] Charge from 35% SOC to 40% SOC at 5.0C constant current.

[0538] Charge from 40% SOC to 45% SOC at 4.6C constant current.

[0539] Charge from 45% SOC to 50% SOC at 4.3C constant current.

[0540] Charge from 50% SOC to 55% SOC at 4.0C constant current.

[0541] Charge from 55% SOC to 60% SOC at 3.7C constant current.

[0542] Charge from 60% SOC to 65% SOC at 3.4C constant current.

[0543] Charge from 65% SOC to 70% SOC at 3.1C constant current.

[0544] Charge from 70% SOC to 75% SOC at 2.9C constant current.

[0545] Charge from 75% SOC to 80% SOC at 2.7C constant current.

[0546] Record the total charging time.

[0547] Test results

[0548] The test results are shown in Table 1.

[0549] Table 1

[0550]

[0551] In Table 1,

[0552] 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, with a difference of 3 mm between the two.

[0553] The discharge capacity of the positive electrode active material in the positive electrode film layer at a rate of 0.1 is 157 mAh / g, and the discharge capacity of the negative electrode active material in the negative electrode film layer at a rate of 0.1 is 355 mAh / g.

[0554] In Comparative Example 1, the coating weight of the positive electrode film layer is relatively small, resulting in its discharge capacity being too small and the volume energy density of the battery cell being too small to meet the demand; 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, the impedance of the positive electrode film layer increases, which reduces the fast charging performance of the battery cell.

[0555] The discharge capacity per unit area of ​​the positive electrode film layer in the embodiment of the present application is 2.0 mAh / cm 2 Up to 3.7 mAh / cm 2 , which can effectively improve the volume energy density and fast charging performance of battery cells; the discharge capacity can be effectively controlled by coating weight, for example, the coating weight of the positive electrode film layer is 200mg / 1540.25mm 2 Up to 370mg / 1540.25mm 2 Under such circumstances, the discharge capacity of the positive electrode film layer is within an appropriate range.

[0556] The embodiment of the present application can further adjust the discharge capacity of the negative electrode film layer to 2.0 mAh / cm 2 to 4.1mAh / cm 2 When used in conjunction with the positive electrode film, it can improve the volumetric energy density and fast charging performance of the battery cell, while also making the CB value within the range of 1.05 to 1.15, reducing the risk of lithium plating and improving the reliability of the battery cell. The discharge capacity of the negative electrode film can also be effectively controlled by the coating weight. For example, the coating weight of the negative electrode film is 90mg / 1540.25mm 2 Up to 170mg / 1540.25mm 2 Under such circumstances, the discharge capacity of the negative electrode film layer is within an appropriate range.

[0557] Example 4

[0558] A battery cell was prepared using a method similar to that of Example 1. The difference from Example 1 was that the contents of the components of the organic solvent were adjusted.

[0559] The test results are shown in Table 2.

[0560] Table 2

[0561]

[0562] When the conductivity of the electrolyte is 13mS / cm to 20mS / cm, and can be optionally 15mS / cm to 20mS / cm, as the conductivity increases, the migration rate of lithium ions in the battery cell is accelerated, which is beneficial to improving the fast charging performance of the battery cell.

[0563] Comparative Example 3

[0564] A battery cell was prepared using a method similar to that of Example 1. The difference from Example 1 was that the size of the battery cell was adjusted, and the sizes of the positive electrode film layer and the negative electrode film layer were also adjusted.

[0565] Example 5

[0566] A battery cell was prepared using a method similar to that of Example 1. The difference from Example 1 was that the size of the battery cell was adjusted, and the sizes of the positive electrode film layer and the negative electrode film layer were also adjusted.

[0567] The test results are shown in Table 3.

[0568] Table 3

[0569]

[0570] In Comparative Example 3, the volumetric energy density of the battery cell cannot be effectively improved due to the relatively short height of the battery cell. However, in the embodiment of the present application, the height of the positive electrode film layer is adjusted to 75 mm to 105 mm, which is conducive to improving the volumetric energy density of the battery cell.

[0571] Although illustrative embodiments have been shown and described, those skilled in the art should understand that the above embodiments should not be construed as limitations on the present application, and that changes, substitutions, and modifications may be made to the embodiments without departing from the spirit, principles, and scope of the present application.

Claims

1. A battery cell, characterized in that: The battery cell includes a shell, an electrolyte and an electrode assembly. The shell includes a housing and an end cover. The housing contains the electrolyte and the electrode assembly. The housing has an opening, and the end cover covers the opening. The electrode assembly includes a positive electrode sheet, a negative electrode sheet and a separator, wherein the separator is located between the positive electrode sheet and the negative electrode sheet, the positive electrode sheet includes a positive electrode current collector and a positive electrode film layer provided 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 includes a lithium-containing phosphate with an olivine structure; the negative electrode sheet includes a negative electrode current collector and a negative electrode film layer provided 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 of the positive electrode film layer per unit area is 2.0 mAh / cm 2 Up to 3.7 mAh / cm 2 ; The size of the positive electrode film layer along a first direction is 75 mm to 105 mm, and the first direction is parallel to the direction from the shell to the end cover; The single-sided coating weight of the negative electrode film layer is 90 mg / 1540.25 mm 2 Up to 170mg / 1540.25mm 2 ; The discharge capacity of the negative electrode film layer per unit area is 2.0 mAh / cm 2 to 4.1mAh / cm 2 ; The single-sided coating weight of the positive electrode film layer is 200 mg / 1540.25 mm 2 Up to 370mg / 1540.25mm 2 .

2. The battery cell according to claim 1, wherein: 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 2.4 mAh / cm 2 Up to 3.7 mAh / cm 2 .

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

7. The battery cell according to claim 6, characterized in that The conductivity of the electrolyte is 15 mS / cm to 20 mS / cm.

8. The battery cell according to claim 1, wherein: The dimension of the battery cell along the first direction is 90 mm to 130 mm.

9. 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 to 2.80g / cm 3 .

10. 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.

11. 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 .

12. The battery cell according to claim 1, wherein The positive electrode active material has a charge capacity of 150 mAh / g to 170 mAh / g at a 0.1 C rate.

13. The battery cell according to claim 1, characterized in that The lithium-containing phosphate of the olivine structure includes: Phosphate particles, and 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.

14. The battery cell according to claim 13, 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.

15. The battery cell according to claim 13 or 14, 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 selected from Ti, Zr, Hf, Ge and Sn, 0≤d≤1, 0<x2<5, 0<y2<4.

16. The battery cell according to claim 13, characterized in that The graphitization degree of the lithium-containing phosphate with an olivine structure is 0.15 to 0.

32.

17. The battery cell according to claim 13, characterized in that The mass content of carbon element in the olivine-structured lithium-containing phosphate is 1% to 2%.

18. The battery cell according to claim 13 or 14, characterized in that: The specific surface area of ​​the lithium-containing phosphate with 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 the following requirements: 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. 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 dihydrogen 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, carbon black, carbon dots, carbon nanotubes, graphene and carbon nanofibers, and / or The positive electrode conductive layer includes a positive electrode binder, which 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 battery cell is at 100% charge state, and the compaction density of the negative electrode film layer is 1.15 g / cm 3 to 1.36g / cm 3 .

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 at 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 0.1 C 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 graphite particles have a degree of graphitization of 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 that is away from the negative electrode current collector, and 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.

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 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. 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 includes a silicon-based material, and the mass content of silicon element in the silicon-based material is 0.3% to 10.0%, based on the 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, carbon 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 carboxylate 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 C1 to C5 alkyl or C1 to C5 halogenated alkyl.

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 haloalkyl group, and / or R2 includes C1 to C3 alkyl or C1 to C3 haloalkyl.

53. The battery cell according to claim 51, characterized in that The chain carboxylate solvent includes one or more compounds represented by formula I-1 to 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 additive has a mass content of 1% to 10% in the electrolyte.

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 provided on at least one side of the base film, wherein the functional layer includes: A first functional layer is located on one side of the base film, and the first functional layer includes 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 multiple 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-fluoropolymer 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 includes 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 minutes to 12.5 minutes.

77. The battery device according to claim 75 or 76, characterized in that The battery device includes a box body that accommodates 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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