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 an electrode assembly and an electrolyte. The electrode assembly includes a positive electrode sheet and a negative electrode sheet. The positive electrode sheet includes a positive electrode current collector and a positive electrode film layer. The positive electrode film layer includes a positive electrode active material. The positive electrode active material includes a lithium-containing phosphate with an olivine structure. The positive electrode sheet has a resistance of 0.1Ω to 30Ω. The negative electrode sheet includes a negative electrode current collector and a negative electrode film layer. The resistance of the negative electrode sheet is 0.001Ω to 0.01Ω. The electrolyte includes an organic solvent, including a chain ester solvent. The mass content of the chain carboxylate solvent in the organic solvent is 5% to 75%. The electrolyte has an electrical conductivity of 13mS / cm to 20mS / cm at room temperature. The present application can reduce the heat generation of the battery cell and improve the reliability and cycle performance of the battery cell.

Description

[0001] This application claims priority to international patent application PCT / CN2024 / 102652, filed on June 28, 2024, entitled “Battery Cell, Battery Device, and Electrical Device,” 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 fast charging performance and cycle performance. Summary of the Invention

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

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

[0006] Therefore, in the embodiment of the present application, the positive electrode active material includes a lithium phosphate containing an olivine structure. The cycle stability of this material system is relatively high. By further coordinating the positive electrode sheet resistance, the negative electrode sheet resistance, and the electrolyte conductivity within a reasonable range, on the one hand, the transmission resistance of lithium ions inside the battery cell can be reduced, the fast charging capability of the battery cell can be improved, and the internal resistance DCR of the battery cell can be reduced. On the other hand, the cycle attenuation caused by excessive temperature rise of the battery cell during fast charging can be improved. On the other hand, the uneven temperature rise problem of the battery cell during fast charging can be improved, and the cycle attenuation problem caused by decomposition of the battery cell can be reduced. The mass content of the chain carboxylic acid ester solvent in the organic solvent is greater than or equal to 5% and less than or equal to 75%. 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 conducive to the migration of lithium ions.

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

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

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

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

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

[0012] 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.

[0013] 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.

[0014] 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.

[0015] In some embodiments, the single-sided coating weight of the positive electrode film layer is 240 mg / 1540.25 mm 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.

[0016] 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.

[0017] 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.

[0018] 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.

[0019] 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.

[0020] 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.

[0021] 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.

[0022] 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.

[0023] 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.

[0024] 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.

[0025] 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.

[0026] 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.

[0027] 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.

[0028] 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.

[0029] 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.

[0030] 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.

[0031] 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.

[0032] 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.

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

[0034] 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.

[0035] In some embodiments, the thickness of the positive electrode conductive layer is 0.5 μm to 2 μm. When the thickness of the positive electrode conductive layer is within the above range, 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.

[0036] In some embodiments, the positive electrode conductive layer includes one or more of a positive electrode conductive agent and a positive electrode binder. The positive electrode conductive agent in the positive electrode conductive layer can improve the conductivity of the positive electrode conductive layer, thereby improving the conductivity of the positive electrode 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.

[0037] In some embodiments, the positive electrode conductive agent includes one or more of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0038] In some embodiments, the positive electrode binder includes one or more of polyvinylidene fluoride, polytetrafluoroethylene, vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, polyacrylic acid, and fluorine-containing acrylic resin.

[0039] 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.

[0040] 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.

[0041] 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.

[0042] In some embodiments, the negative electrode film layer includes a first negative electrode film layer and a second negative electrode film layer, the first negative electrode film layer is 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.

[0043] 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.

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

[0045] 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.

[0046] 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.

[0047] 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.

[0048] 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.

[0049] 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.

[0050] 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.

[0051] 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.

[0052] 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.

[0053] 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.

[0054] 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.

[0055] 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.

[0056] 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%.

[0057] 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.

[0058] 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%.

[0059] 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.

[0060] 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 weight 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.

[0061] 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.

[0062] 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.

[0063] 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 generated by the negative electrode plate, and thus reduce the heat generated by the battery cell.

[0064] 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.

[0065] 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.

[0066] 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.

[0067] 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.

[0068] 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.

[0069] 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.

[0070] 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.

[0071] 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.

[0072] In some embodiments, the non-fluorinated polymer particles include acrylic copolymers, which have excellent bonding properties and high bonding stability with the base film.

[0073] 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.

[0074] 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.

[0075] 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.

[0076] 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 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.

[0077] In some embodiments, the linear carboxylate solvent includes a compound represented by Formula I,

[0078] Formula I,

[0079] In Formula I,

[0080] R1 includes a hydrogen atom, a halogen atom, a C1 to C5 alkyl group or a C1 to C5 halogenated alkyl group,

[0081] R2 includes C1 to C5 alkyl or C1 to C5 halogenated alkyl.

[0082] 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.

[0083] In some embodiments, R1 includes a hydrogen atom, a halogen atom, a C1 to C3 alkyl group, or a C1 to C3 haloalkyl group.

[0084] In some embodiments, in some embodiments, R2 comprises C1 to C3 alkyl or C1 to C3 haloalkyl.

[0085] In some embodiments, the chain carboxylate solvent includes one or more compounds represented by formula I-1 to formula I-8.

[0086]

[0087] 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.

[0088] In some embodiments, the carbonate solvent includes one or more of ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate.

[0089] 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.

[0090] 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.

[0091] In some embodiments, the carbonate additive includes one or more of vinylene carbonate (VC) and fluoroethylene carbonate (FEC).

[0092] 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.

[0093] 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.

[0094] 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.

[0095] 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.

[0096] 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).

[0097] 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.

[0098] 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.

[0099] 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.

[0100] In some embodiments, the battery cell further includes an electrode terminal, the electrode assembly includes a tab portion, and the tab portion is directly welded to the electrode terminal. Direct welding can reduce the resistance at the connection, which is beneficial for reducing the internal resistance of the battery cell as a whole.

[0101] In some embodiments, the charging time of the battery cell from 10% state of charge to 80% state of charge is 5 minutes to 10.5 minutes. The charging speed of the battery cell is faster, which is more conducive to improving the fast charging capability.

[0102] 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.

[0103] 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 10.5 minutes. The faster the charging speed of the battery device, the better the fast charging capability.

[0104] 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

[0105] 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.

[0106] Figure 1 This is a schematic diagram of the structure of a battery cell provided in some embodiments of the present application.

[0107] Figure 2 Schematic diagram of an explosion of a battery cell provided in some embodiments of the present application,

[0108] Figure 3 This is a schematic diagram of the structure of the battery module provided in some embodiments of the present application.

[0109] Figure 4 This is a schematic diagram of the structure of the battery pack provided in some embodiments of the present application.

[0110] Figure 5 It is a schematic diagram of the structure of an electrical device provided in some embodiments of the present application.

[0111] The drawings are not necessarily drawn to scale.

[0112] The following are the descriptions of the reference numerals:

[0113] 1. Power device, 2. Battery pack, 3. Controller, 4. Motor, 5. Box, 5a. First box part, 5b. Second box part, 5c. Accommodation space, 6. Battery module,

[0114] 7. Battery cells,

[0115] 10. Electrode assembly, 111. First electrode tab, 112. Second electrode tab, 12. Main body,

[0116] 20. Shell, 21. Housing, 22. End cover,

[0117] 31. First electrode terminal, 32. Second electrode terminal. DETAILED DESCRIPTION

[0118] 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.

[0119] " 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.

[0120] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0121] 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.

[0122] 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.

[0123] Battery cells generate thermal effects during the charging and discharging process. Specifically, during charging, an external power source provides electrical energy to the battery cells, triggering a series of chemical reactions within the battery, generating heat energy, which causes the battery cells to heat up during charging. During discharge, the battery cells convert chemical energy into electrical energy, simultaneously generating heat energy, which also causes the battery cells to heat up during discharge. This increase in battery cell temperature reduces the battery's reliability, can even cause thermal runaway, and worsen cycle performance. This problem is particularly pronounced in batteries with fast-charging systems.

[0124] In view of the above problems, the embodiments of the present application rationally design the system of battery cells, reduce the internal resistance of the battery cells, and reduce the heat generation of the battery cells. Specifically, by rationally configuring the characteristics of the positive electrode plate, negative electrode plate and electrolyte that affect the internal resistance of the battery, the internal resistance of the battery cells can be further reduced, thereby reducing heat generation and improving the reliability and cycle performance of the battery cells.

[0125] battery cells

[0126] In a first aspect, an embodiment of the present application provides a battery cell.

[0127] The battery cell includes an electrode assembly, an electrolyte and a shell. The electrode assembly and the electrolyte are contained in the shell. The electrode assembly includes a positive electrode sheet, a negative electrode sheet and a separator. The positive electrode sheet includes a positive electrode collector and a positive electrode film layer arranged on at least one side of the positive electrode collector. The positive electrode film layer includes a positive electrode active material. The positive electrode active material includes a lithium phosphate with an olivine structure. The resistance of the positive electrode sheet is 0.1Ω to 30Ω. The negative electrode sheet includes a negative electrode collector and a negative electrode film layer arranged on at least one side of the negative electrode collector. The negative electrode film layer includes a negative electrode active material. The resistance of the negative electrode sheet is 0.001Ω to 0.01Ω. The separator is located between the positive electrode sheet and the negative electrode sheet. The electrolyte includes an organic solvent. The organic solvent includes a chain carboxylic acid ester solvent. The conductivity of the electrolyte at room temperature is 13mS / cm to 20mS / cm.

[0128] In the embodiment of the present application, the positive electrode active material includes a lithium phosphate containing an olivine structure. The cycle stability of this material system is relatively high. By further controlling the positive electrode sheet resistance, the negative electrode sheet resistance, and the electrolyte conductivity in a reasonable range, on the one hand, the transmission resistance of lithium ions inside the battery cell can be reduced, the fast charging capability of the battery can be improved, and the battery internal resistance DCR can be reduced. On the other hand, the cycle attenuation caused by excessive temperature rise of the battery cell during fast charging can be improved. On the other hand, the problem of uneven temperature rise of the battery during fast charging can also be improved, and the cycle attenuation problem caused by analysis of the battery cell can be reduced. In addition, by controlling the positive and negative electrode sheet resistance within a reasonable range, the internal temperature of the battery cell is controlled within a reasonable range that can be tolerated by the high-conductivity electrolyte, which can reduce the risk of weakening the fast charging performance of the battery due to volatilization of the solvent components of the electrolyte.

[0129] In summary, the battery cells of the embodiments of the present application have the advantages of fast charging, low DCR, and good cycle performance.

[0130] In the embodiment of the present application, the resistance of the positive electrode sheet can be adjusted by adjusting the material of the positive electrode active material, for example, adjusting the graphitization degree and powder resistivity of the positive electrode active material.

[0131] In the embodiment of the present application, the resistance of the negative electrode sheet can be adjusted by adjusting the material of the negative electrode active material, for example, adjusting the graphitization degree and powder resistivity of the negative electrode active material.

[0132] In the embodiment of the present application, the conductivity of the electrolyte can be adjusted by adjusting the mass content of the chain carboxylate solvent in the organic solvent in the electrolyte.

[0133] The upper limit voltage for charging and the cut-off voltage for discharging of the battery cell vary depending on the different positive electrode active materials. For example, when the phosphate material includes lithium iron phosphate, the upper limit voltage for charging may be 3.65V and the cut-off voltage for discharging may be 2.0V. For another example, when the phosphate material includes lithium manganese iron phosphate, the upper limit voltage for charging may be 4.3V and the cut-off voltage for discharging may be 2.0V. Next, the state of the battery cell will be described by taking the upper limit voltage for charging of 3.65V and the cut-off voltage for discharging of 2.0V as an example: In the embodiment of the present application, the 100% state of charge SOC and the 0% state of charge SOC of the battery cell are defined as follows:

[0134] 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.

[0135] In the embodiments of the present application, the electrode sheet resistance refers to the ability of current to flow through the electrode sheet (the flow area is the cross-section of the current collector and the film layer containing electrode material located on both sides of the current collector along the thickness direction), which can be detected using the following equipment and methods:

[0136] As an example, after discharging the battery to 0% SOC, remove the electrode sheet and clean it three or more times with a solvent such as dimethyl carbonate (DMC). Twenty parallel samples can be taken along the center axis of the electrode sheet. Each sample is symmetrical along the center axis and measures 4 cm x 25 cm. The center axis can be parallel to the length of the electrode sheet. These 20 parallel samples are tested using a sheet resistance meter (Yuanneng Technology, BER2500 model). The average value is calculated and used as the electrode sheet resistance.

[0137] [Positive electrode]

[0138] 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.

[0139] In the embodiment of the present application, the resistance of the positive electrode plate is 0.1Ω to 30Ω, optionally 0.1Ω to 5Ω, and further optionally 0.1Ω to 1Ω. Exemplarily, the resistance of the positive electrode plate is 0.1Ω, 0.5Ω, 1Ω, 1.5Ω, 2Ω, 2.5Ω, 3Ω, 3.5Ω, 4Ω, 4.5Ω, 5Ω, 5.5Ω, 6Ω, 6.5Ω, 7Ω, 7.5Ω, 8Ω, 8.5Ω, 9Ω, 9.5Ω, 10Ω, 10.5Ω, 11Ω, 11.5Ω, 12Ω, 12.5Ω, 13Ω, 13.5Ω, 14Ω, 14.5Ω, 15Ω, 15.5Ω, 16Ω, 16.5Ω, 17Ω, 17.5Ω, 18Ω, 18.5Ω, 19Ω, 20Ω, 21Ω, 22Ω, 23Ω, 24Ω, 25Ω, 26Ω, 27Ω, 28Ω, 29Ω, 30Ω or a range consisting of any two of the above values.

[0140] When the resistance of the positive electrode sheet is within the above range, the resistance of the positive electrode sheet is more compatible with the negative electrode sheet resistance and electrolyte system of the battery cell, which is beneficial to reducing the internal resistance of the battery cell and optimizing the electrical performance of the battery cell.

[0141] 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 3For 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.

[0142] 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 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.

[0143] 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 / 1540.25mm2 、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 / 1540.25mm 2 、370mg / 1540.25mm 2 Or a range consisting of any two of the above values.

[0144] 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.

[0145] 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.

[0146] 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.

[0147] 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.

[0148] 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.

[0149] 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 2.8 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.

[0150] 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.

[0151] 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 2The 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.

[0152] 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.

[0153] 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.

[0154] 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.

[0155] 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.

[0156] Optionally, the mass proportion of the lithium-containing phosphate with an olivine structure in the positive electrode active material is 100%.

[0157] 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.

[0158] 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.

[0159] 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.

[0160] 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 the present application.

[0161] In some embodiments, the coating layer comprises a Li 3-d Fe 2-d M2 d (PO x2 ) y2 The fast ion conductor M2 includes one or more elements selected from Ti, Zr, Hf, Ge and Sn, 0≤d≤1, 0<x2<5, 0<y2<4.

[0162] 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.

[0163] 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.

[0164] In some embodiments, the coating layer further includes carbon.

[0165] 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.

[0166] 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.

[0167] Specifically, the provision of the carbon coating layer enables the positive electrode active material of the present application to have the following advantages:

[0168] 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.

[0169] 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.

[0170] 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.

[0171] 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.

[0172] 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, instrument model: Thermo ICAP7400). After discharging the battery cell to 0% state of charge (SOC), the positive electrode sheet is disassembled, cleaned with DMC and dried, and then 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.

[0173] 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.

[0174] 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.

[0175] 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.

[0176] 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.

[0177] 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.

[0178] 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.

[0179] 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.

[0180] 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.

[0181] 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.

[0182] 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.

[0183] 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.

[0184] 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.

[0185] 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, which makes the performance of the positive electrode active material stable.

[0186] 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.

[0187] 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.

[0188] 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, or 500 nm, or a range consisting of any two of the foregoing values.

[0189] 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 generation is less.

[0190] 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.

[0191] 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.

[0192] 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.

[0193] 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.

[0194] 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.

[0195] 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.

[0196] 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.

[0197] 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%.

[0198] 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).

[0199] 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.

[0200] 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.

[0201] 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.

[0202] 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.

[0203] 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.

[0204] 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).

[0205] 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.

[0206] 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.

[0207] 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.

[0208] 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.

[0209] 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.

[0210] In some embodiments, the positive electrode conductive layer includes one or more of a positive electrode conductive agent and a positive electrode binder.

[0211] 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.

[0212] 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.

[0213] 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.

[0214] 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.

[0215] [Negative electrode]

[0216] 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.

[0217] In the embodiment of the present application, the resistance of the negative electrode plate is 0.001Ω to 0.01Ω, and can be 0.001Ω to 0.005Ω. For example, the resistance of the negative electrode plate is 0.001Ω, 0.002Ω, 0.003Ω, 0.004Ω, 0.005Ω, 0.006Ω, 0.007Ω, 0.008Ω, 0.009Ω, 0.01Ω, or a range consisting of any two of the above values.

[0218] When the resistance of the negative electrode sheet is within the above range, the resistance of the negative electrode sheet is relatively small, which is beneficial to reducing the internal resistance of the battery cell.

[0219] In the embodiment of the present application, the resistance of the negative electrode plate 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 resistance test method of the positive electrode plate mentioned above.

[0220] 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 / cm3 , 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.

[0221] 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.

[0222] 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.

[0223] 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.

[0224] 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.

[0225] 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.

[0226] 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.

[0227] 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.

[0228] 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.

[0229] 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.

[0230] 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.

[0231] 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.

[0232] 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.

[0233] 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.

[0234] 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.

[0235] 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%.

[0236] 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.

[0237] 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.

[0238] 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.

[0239] In some embodiments, the graphite particles include artificial graphite and a carbon coating. The artificial graphite includes secondary particles, which include multiple 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.

[0240] 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.

[0241] 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.

[0242] 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.

[0243] 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.

[0244] 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.

[0245] 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.

[0246] Optionally, the carbonization treatment time is 1 hour to 6 hours.

[0247] 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.

[0248] 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.

[0249] 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.

[0250] 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.

[0251] 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.

[0252] 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.

[0253] 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.

[0254] 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.

[0255] 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.

[0256] 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.

[0257] 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.

[0258] 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.

[0259] 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.

[0260] The interface between the first negative electrode film layer and the second negative electrode film layer may be regular or irregular, and may optionally be irregular.

[0261] Optionally, the carbon-based material in the first negative electrode film layer further includes natural graphite.

[0262] 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.

[0263] 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.

[0264] 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.

[0265] 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.

[0266] 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.

[0267] 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.

[0268] 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.

[0269] 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.

[0270] 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.

[0271] 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 / cm3 , 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.

[0272] 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.

[0273] 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.

[0274] 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.

[0275] 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.

[0276] 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.

[0277] 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.

[0278] 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.

[0279] 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.

[0280] 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.

[0281] 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.

[0282] 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.

[0283] 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).

[0284] 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.

[0285] 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.

[0286] 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.

[0287] 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.

[0288] 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.

[0289] 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.

[0290] 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.

[0291] 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.

[0292] 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.

[0293] 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.

[0294] 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.

[0295] The first lithium-containing binder and the second lithium-containing binder may be made of the same material or different materials.

[0296] 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.

[0297] 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.

[0298] 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.

[0299] 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).

[0300] 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.

[0301] 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.

[0302] 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.

[0303] 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.

[0304] 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).

[0305] 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.

[0306] 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.

[0307] 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.

[0308] 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.

[0309] 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.

[0310] 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.

[0311] 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.

[0312] 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.

[0313] 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.

[0314] 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.

[0315] 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.

[0316] 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.

[0317] 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.

[0318] 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.

[0319] 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.

[0320] 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.

[0321] 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.

[0322] 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.

[0323] 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.

[0324] 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 2 The 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.

[0325] 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.

[0326] [Isolation film]

[0327] In the embodiment of the present application, the isolation membrane includes a base membrane with a porous structure.

[0328] 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.

[0329] Optionally, the polyolefin includes at least one of polyethylene, polypropylene and polyvinylidene fluoride.

[0330] 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.

[0331] 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.

[0332] 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 due to differences in testing instrumentation, testing errors, and to minimize the impact of porosity testing, in order to obtain a more accurate test value.

[0333] 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.

[0334] 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.

[0335] 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.

[0336] 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.

[0337] The first functional layer and the second functional layer have good heat resistance, which can improve the heat resistance of the isolation film.

[0338] 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.

[0339] 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.

[0340] 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.

[0341] 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.

[0342] 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.

[0343] 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.

[0344] 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.

[0345] 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.

[0346] 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.

[0347] 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.

[0348] 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,

[0349] 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.

[0350] 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:

[0351] σ=L / (R b ×S)

[0352] Where: R b is the isolation film resistance, L and S are the thickness and area of ​​the isolation film to be measured respectively.

[0353] [Electrolyte]

[0354] In some embodiments, the battery cell further includes an electrolyte.

[0355] During the charge and discharge process of a battery cell, active ions such as lithium 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.

[0356] In an embodiment of the present application, the conductivity of the electrolyte at room temperature is 13 mS / cm to 20 mS / cm, and can be 15 mS / cm to 20 mS / cm. For example, the conductivity of the electrolyte at room temperature is 13 mS / cm, 13.5 mS / cm, 14 mS / cm, 14.5 mS / cm, 15 mS / cm, 15.5 mS / cm, 16 mS / cm, 16.5 mS / cm, 17 mS / cm, 17.5 mS / cm, 18 mS / cm, 18.5 mS / cm, 19 mS / cm, 19.5 mS / cm, 20 mS / cm, or a range consisting of any two of the above values.

[0357] 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.

[0358] 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.

[0359] 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.

[0360] 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.

[0361] 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.

[0362] In some embodiments, the density of the electrolyte at room temperature, e.g., 25° C., is from 1.05 g / mL to 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.

[0363] 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.

[0364] 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.

[0365] 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.

[0366] 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 75%, 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.

[0367] 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.

[0368] In some embodiments, the linear carboxylate solvent includes a compound represented by Formula I,

[0369] Formula I,

[0370] In Formula I,

[0371] R1 includes a hydrogen atom, a halogen atom, a C1 to C5 alkyl group or a C1 to C5 halogenated alkyl group,

[0372] R2 includes C1 to C5 alkyl or C1 to C5 halogenated alkyl.

[0373] The above-mentioned chain carboxylic acid ester solvents have high electrical conductivity, which is beneficial to improving the fast charging capability of battery cells.

[0374] 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.

[0375] 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.

[0376] 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.

[0377] 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.

[0378] Illustratively, the chain carboxylate solvent includes one or more compounds represented by formula I-1 to formula I-8.

[0379]

[0380] In some embodiments, the organic solvent further includes a carbonate solvent.

[0381] 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.

[0382] 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.

[0383] 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%.

[0384] 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.

[0385] 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.

[0386] 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.

[0387] 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.

[0388] Illustratively, the carbonate additive includes one or more of vinylene carbonate VC and fluoroethylene carbonate FEC.

[0389] 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.

[0390] Optionally, the lithium salt additive includes one or more of lithium difluorophosphate LiPO2F2, lithium difluorooxalatoborate LiDFOB, lithium tetrafluoroborate LiBF4, and lithium bis(oxalatoborate) LiBOB.

[0391] Optionally, the mass content of vinylene carbonate VC in the electrolyte is 0.5% to 9%, optionally 2% to 6%.

[0392] Optionally, the mass content of fluoroethylene carbonate FEC in the electrolyte is 0.1% to 4%, and optionally 0.5% to 3%.

[0393] 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%.

[0394] 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%.

[0395] 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.

[0396] Optionally, the fluorine-containing sulfonyl imide salt includes one or more of lithium bis(fluorosulfonyl)imide LiFSI and lithium bis(trifluoromethanesulfonyl)imide LiTFSI.

[0397] 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.

[0398] 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.

[0399] 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.

[0400] 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.

[0401] 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.

[0402] 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.

[0403] 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.

[0404] 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%.

[0405] 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%.

[0406] 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.

[0407] 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.

[0408] 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.

[0409] 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.

[0410] 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.

[0411] Figure 1 and Figure 2 A schematic structural diagram of a battery cell is shown.

[0412] In some embodiments, the battery cell 7 may include a housing 20 .

[0413] 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).

[0414] The shell 20 is a hollow structure, and the shell 20 can be used to encapsulate the electrode assembly 10 and the electrolyte.

[0415] 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.

[0416] In some embodiments, the housing 20 includes a shell 21 and an end cover 22 . The shell 21 has an opening, and the end cover 22 covers the opening.

[0417] The shape of the housing 21 can be determined based on the specific shape of the electrode assembly 10. For example, if the electrode assembly 10 has a cylindrical structure, a cylindrical housing can be used; if the electrode assembly 10 has a rectangular parallelepiped structure, a rectangular parallelepiped housing can be used. Alternatively, both the electrode assembly 10 and the housing 21 have a rectangular parallelepiped structure.

[0418] 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 cells. Optionally, steel accounts for the largest proportion of the housing 21 by mass.

[0419] 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 21 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 more, which is conducive to improving the energy density of the battery cell 7.

[0420] From the appearance of the electrode assembly 10, the electrode assembly 10 includes a main body 12, a first pole tab 111 and a second pole tab 112, and the first pole tab 111 and the second pole tab 112 protrude from the main body 12. The first pole tab 111 is the portion of the first pole piece that is not coated with the active material layer, and the second pole tab 112 is the portion of the second pole piece that is not coated with the active material layer. The first pole tab 111 and the second pole tab 112 are used to draw current from the main body 12. The polarities of the first pole piece and the second pole piece are opposite. In other words, one of the first pole piece and the second pole piece is a positive pole piece, and the other of the first pole piece and the second pole piece is a negative pole piece. Of course, the first pole tab 111 can be a positive pole tab, and the second pole tab 112 can be a negative pole tab.

[0421] Taking the first electrode tab 111 as the negative electrode tab and the second electrode tab 112 as the positive electrode tab as an example, the portion of the negative electrode current collector in the negative electrode sheet that is not coated with the active material layer is the negative electrode tab, the active material coated on the negative electrode current collector in the negative electrode sheet constitutes the negative electrode film layer, and the negative electrode film layer and the negative electrode current collector coated with the active material are part of the main body 12. The portion of the positive electrode current collector in the positive electrode sheet that is not coated with the active material layer is the positive electrode tab, the active material coated on the positive electrode current collector in the positive electrode sheet constitutes the positive electrode film layer, and the positive electrode film layer and the positive electrode current collector coated with the active material are part of the main body 12.

[0422] The first electrode tab 111 and the second electrode tab 112 may extend from the same side of the main body 12 , or may extend from opposite sides thereof.

[0423] Optionally, the number of the first 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 first electrode tabs 111 can increase the current capacity of the first electrode tab 111 .

[0424] Optionally, the number of the second 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 second electrode tabs 112 can increase the current capacity of the second electrode tabs 112 .

[0425] In some embodiments, the battery cell 7 further includes a first electrode terminal 31, which is electrically connected to the first tab 111. Optionally, the first electrode terminal 31 and the first tab 111 are welded, and the first electrode terminal 31 and the first tab 111 may be connected via an adapter or may not be connected via an adapter. Optionally, the first electrode terminal 31 and the first tab 111 are connected without an adapter, that is, the first electrode terminal 31 and the first tab 111 are directly welded, which can reduce the resistance at the connection point and help reduce the overall internal resistance of the battery cell 7.

[0426] When the first electrode tab 111 is a negative electrode tab, the first electrode terminal 31 is a negative electrode terminal. When the first electrode tab 111 is a positive electrode tab, the first electrode terminal 31 is a positive electrode terminal.

[0427] In some embodiments, the battery cell 7 further includes a second electrode terminal 32, which is electrically connected to the second electrode tab 112. Optionally, the second electrode terminal 32 and the second electrode tab 112 are welded. The second electrode terminal 32 and the second electrode tab 112 may be connected via an adapter or may not be connected via an adapter. Optionally, the second electrode terminal 32 and the second electrode tab 112 are connected without an adapter, that is, the second electrode terminal 32 and the second electrode tab 112 are directly welded, which can reduce the resistance at the connection point and help reduce the overall internal resistance of the battery cell 7.

[0428] When the second electrode tab 112 is a negative electrode tab, the second electrode terminal 32 is a negative electrode terminal. When the second electrode tab 112 is a positive electrode tab, the second electrode terminal 32 is a positive electrode terminal.

[0429] Optionally, the number of the first electrode terminals 31 located on the same side of the main body 12 is at least one, and optionally at least two. At least two first electrode terminals 31 can increase the current capacity of the first electrode terminals 31 .

[0430] Further optionally, the flow area of ​​the first electrode terminal 31 on one side is 150mm 2 Up to 1000mm 2 , 200mm is optional 2 Up to 1000mm2 The flow area of ​​a single-side first electrode terminal 31 refers to the sum of the flow areas of all first electrode terminals 31 located on the same side of the main body 12. The flow area of ​​a first electrode terminal 31 can be understood as the cross-sectional area of ​​the first electrode terminal 31, which is perpendicular to the thickness direction of the end cap 22.

[0431] For example, the flow area of ​​the first electrode terminal 31 on one side 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.

[0432] Optionally, the number of the second electrode terminals 32 located on the same side of the main body 12 is at least one, and optionally at least two. At least two second electrode terminals 32 can increase the current capacity of the second electrode terminals 32 .

[0433] Alternatively, the flow area of ​​the second electrode terminal 32 on one side is 150 mm 2 Up to 1000mm 2 , 200mm is optional 2 Up to 1000mm 2 The flow area of ​​a single-side second electrode terminal 32 refers to the sum of the flow areas of all second electrode terminals 32 located on the same side of the main body 12. The flow area of ​​a second electrode terminal 32 can be understood as the cross-sectional area of ​​the second electrode terminal 32, which is perpendicular to the thickness direction of the end cap 22.

[0434] For example, the flow area of ​​the second electrode terminal 32 on one side may be 150 mm 2 , 200mm 2 , 210mm2 , 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] 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.

[0436] 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.

[0437] like Figure 4 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.

[0438] 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.

[0439] The first housing portion 5a and the second housing portion 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 housing portion 5a and the second housing portion 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 housing portion 5a and the second housing portion 5b can have various shapes, such as a cylinder, a rectangular parallelepiped, etc.

[0440] 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.

[0441] 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.

[0442] 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 30° C.

[0443] In some embodiments, during the charging process of the battery pack 2 or any battery cell constituting the battery pack 2 from 10% state of charge (SOC) to 80% state of charge (SOC), the temperature of the external environment of the battery pack 2 is 30° C.

[0444] 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.

[0445] 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.

[0446] 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.

[0447] 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:

[0448] Charge from 10% SOC to 15% SOC at 5.0C constant current.

[0449] Charge from 15% SOC to 20% SOC at 5.0C constant current.

[0450] Charge from 20% SOC to 25% SOC at 5.0C constant current.

[0451] Charge from 25% SOC to 30% SOC at 5.0C constant current.

[0452] Charge from 30% SOC to 35% SOC at 5.0C constant current.

[0453] Charge from 35% SOC to 40% SOC at 5.0C constant current.

[0454] Charge from 40% SOC to 45% SOC at 4.6C constant current.

[0455] Charge from 45% SOC to 50% SOC at 4.3C constant current.

[0456] Charge from 50% SOC to 55% SOC at 4.0C constant current.

[0457] Charge from 55% SOC to 60% SOC at 3.7C constant current.

[0458] Charge from 60% SOC to 65% SOC at 3.4C constant current.

[0459] Charge from 65% SOC to 70% SOC at 3.1C constant current.

[0460] Charge from 70% SOC to 75% SOC at 2.9C constant current.

[0461] Charge from 75% SOC to 80% SOC at 2.7C constant current.

[0462] In some embodiments, the charging time of the battery pack 2 or any battery cell constituting the battery pack 2 from 10% state of charge to 80% state of charge is less than or equal to 10.5 minutes, and can be optionally 5 minutes to 10.5 minutes. The temperature of the external environment of the battery pack 2 at 10% state of charge is room temperature, for example, 30°C. Exemplarily, the charging time of the battery pack 2 from 10% state of charge to 80% state of charge is 10.5 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.

[0463] In some embodiments, the volumetric energy density of the battery cell is 390Wh / L to 500Wh / L, optionally 410Wh / L to 470Wh / L. For example, the volumetric energy density of the battery cell is 390Wh / L, 400Wh / L, 410Wh / L, 420Wh / L, 430Wh / L, 440Wh / L, 450Wh / L, 460Wh / L, 470Wh / L, 480Wh / L, 490Wh / L, 500Wh / L, or a range consisting of any two of the foregoing values. The volumetric energy density of the battery cell is relatively high.

[0464] 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.

[0465] Place the battery cell at 25°C, charge at a constant current of 0.33C to 3.65V, then charge at a constant voltage to 0.05C, and discharge at a constant current of 0.33C to 2.0V. 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), calculate the volume of the single battery V0, unit L, and the volume energy density of the battery cell VED = (A0 × discharge platform voltage) / V0, unit Wh / L.

[0466] Electrical devices

[0467] According to a second aspect of the embodiments of the present application, there is provided an electrical device, which includes a battery device according to the embodiments of the present application, such as a battery cell, a battery module, or a battery pack. The battery cell, battery module, or battery pack can be used 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, etc. The vehicle can be a fuel vehicle, a gas vehicle, or a new energy vehicle. The new energy vehicle can be a pure electric vehicle, a hybrid vehicle, or an extended-range vehicle. The spacecraft includes an airplane, a rocket, a space shuttle, and a spacecraft. The electric toy includes a fixed or mobile electric toy, such as a game console, an electric car toy, an electric ship toy, and an electric airplane toy. The electric tool includes a metal cutting electric tool, a grinding electric tool, an assembly electric tool, and a railway electric tool, such as an electric drill, an electric grinder, an electric wrench, an electric screwdriver, an electric hammer, an impact drill, a concrete vibrator, and an electric planer. The embodiments of the present application do not impose any special restrictions on the above-mentioned electrical devices.

[0468] The electrical device can select battery cells, battery modules or battery packs according to its usage requirements.

[0469] Figure 5 1 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.

[0470] 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.

[0471] 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.

[0472] 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.

[0473] The charging process of the electric device can select the following charging methods:

[0474] Charge from 10% SOC to 15% SOC at 5.0C constant current.

[0475] Charge from 15% SOC to 20% SOC at 5.0C constant current.

[0476] Charge from 20% SOC to 25% SOC at 5.0C constant current.

[0477] Charge from 25% SOC to 30% SOC at 5.0C constant current.

[0478] Charge from 30% SOC to 35% SOC at 5.0C constant current.

[0479] Charge from 35% SOC to 40% SOC at 5.0C constant current.

[0480] Charge from 40% SOC to 45% SOC at 4.6C constant current.

[0481] Charge from 45% SOC to 50% SOC at 4.3C constant current.

[0482] Charge from 50% SOC to 55% SOC at 4.0C constant current.

[0483] Charge from 55% SOC to 60% SOC at 3.7C constant current.

[0484] Charge from 60% SOC to 65% SOC at 3.4C constant current.

[0485] Charge from 65% SOC to 70% SOC at 3.1C constant current.

[0486] Charge from 70% SOC to 75% SOC at 2.9C constant current.

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

[0488] In some embodiments, the charging time of the electric device from 10% state of charge to 80% state of charge is less than or equal to 10.5 minutes, and can be optionally 5 minutes to 10.5 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 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.

[0489] Example

[0490] 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.

[0491] Example 1

[0492] 1. Preparation of positive electrode sheet

[0493] The positive electrode sheet includes a positive electrode current collector, a positive electrode conductive layer on the positive electrode current collector and a positive electrode film layer. The positive electrode current collector is an aluminum foil with a thickness of 10 μm.

[0494] The positive conductive layer on the positive current collector is a film layer formed by evenly mixing the positive electrode conductive agent superconducting carbon, the positive electrode binder polyvinylidene fluoride (PVDF) and the solvent N-methylpyrrolidone NMP, and then coating it on the current collector surface and drying it. The thickness is 1μm. The mass content of the positive electrode conductive agent in the positive conductive layer is 40%, and the mass content of the positive electrode binder is 60%.

[0495] 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.

[0496] 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.

[0497] The single-sided coating weight of the positive electrode film is 300mg / 1540.25mm 2 .

[0498] 2. Preparation of negative electrode sheet

[0499] The negative electrode sheet includes a negative electrode current collector, a negative electrode conductive layer on the negative electrode current collector and a negative electrode film layer. The negative electrode current collector is a copper foil with a thickness of 5 μm.

[0500] The negative electrode conductive layer on the negative electrode current collector is a film layer 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. The thickness is 1 μm, the mass content of the negative electrode conductive agent in the negative electrode conductive layer is 35%, the mass content of the negative electrode binder in the negative electrode conductive layer is 60%, and the mass content of the thickener in the negative electrode conductive layer is 5%.

[0501] 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.

[0502] The single-sided coating weight of the negative electrode film is 138mg / 1540.25mm 2 .

[0503] 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.

[0504] 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%.

[0505] 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%.

[0506] 3. Isolation film

[0507] The isolation film includes a base film, which is a 7 μm polyethylene film layer with a porosity of 42%.

[0508] 4. Preparation of electrolyte

[0509] The electrolyte includes an organic solvent, lithium salt and additives.

[0510] 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.

[0511] 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.

[0512] The lithium salt includes 1 mol / L lithium hexafluorophosphate LiPF6.

[0513] The conductivity of the electrolyte at room temperature is 16.4 mS / cm.

[0514] 5. Preparation of battery cells

[0515] 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 compaction density of the positive electrode film layer of the battery cell at 100% SOC is 2.72 g / cm 3 The compaction density of the negative electrode film layer at 100% SOC is 1.26g / cm 3 .

[0516] Comparative Example 1

[0517] A battery cell was prepared using a method similar to that of Example 1. The difference from Example 1 was that the mass content of carbon in the positive electrode active material was adjusted to adjust the resistance of the positive electrode sheet.

[0518] Comparative Example 2

[0519] A battery cell was prepared using a method similar to that of Example 1. The difference from Example 1 was that the mass content of the carbon coating layer in the negative electrode active material was adjusted to adjust the resistance of the negative electrode sheet.

[0520] Example 2-1 to Example 2-4

[0521] A battery cell was prepared using a method similar to that of Example 1. The difference from Example 1 was that the mass content of carbon in the positive electrode active material was adjusted to adjust the resistance of the positive electrode sheet.

[0522] Example 2-5 and Example 2-6

[0523] A battery cell was prepared using a method similar to that of Example 1. The difference from Example 1 was that the mass content of the carbon coating layer in the negative electrode active material was adjusted to adjust the resistance of the negative electrode sheet.

[0524] Example 3-1 and Example 3-2

[0525] A battery cell was prepared using a method similar to that of Example 1. The difference from Example 1 was that the thickness of the separator was adjusted.

[0526] Example 3-3 to Example 3-4

[0527] A battery cell was prepared using a method similar to that of Example 1. The difference from Example 1 was that the porosity of the separator was adjusted.

[0528] Performance Testing

[0529] 1. The charging time of the battery cell from 10% SOC to 80% SOC is specifically charged in the following steps:

[0530] At 30°C, charge from 10% SOC state.

[0531] Charge from 10% SOC to 15% SOC at 5.0C constant current.

[0532] Charge from 15% SOC to 20% SOC at 5.0C constant current.

[0533] Charge from 20% SOC to 25% SOC at 5.0C constant current.

[0534] Charge from 25% SOC to 30% SOC at 5.0C constant current.

[0535] Charge from 30% SOC to 35% SOC at 5.0C constant current.

[0536] Charge from 35% SOC to 40% SOC at 5.0C constant current.

[0537] Charge from 40% SOC to 45% SOC at 4.6C constant current.

[0538] Charge from 45% SOC to 50% SOC at 4.3C constant current.

[0539] Charge from 50% SOC to 55% SOC at 4.0C constant current.

[0540] Charge from 55% SOC to 60% SOC at 3.7C constant current.

[0541] Charge from 60% SOC to 65% SOC at 3.4C constant current.

[0542] Charge from 65% SOC to 70% SOC at 3.1C constant current.

[0543] Charge from 70% SOC to 75% SOC at 2.9C constant current.

[0544] Charge from 75% SOC to 80% SOC at 2.7C constant current.

[0545] Record the total charging time.

[0546] 2. DC internal resistance DCR test of battery cells

[0547] You can refer to the methods in GB / T 31467 "Performance test specification for high-power lithium-ion power batteries for HEV".

[0548] For example, at room temperature, charge the battery cell to 3.65 V at a constant current of 0.33 C, let it stand for 1 min, then charge it to 3.65 V at a constant current of 0.1 C, let it stand for 30 min, and discharge it to 2.0 V at a constant current of 0.33 C. Record the discharge capacity A0 at this time in Ah, and then charge it at a constant current of 0.33 C for 0.5A0Ah, and adjust the SOC to 50%.

[0549] After the battery cell is placed at 20 ℃ for 2 hours, it is discharged at a constant current of 4C for 10 seconds and the ∆U 放电 , ∆I 放电 , the discharge DCR data of lithium-ion batteries is calculated by the following formula, R 放电 =∆U 放电 / ∆I 放电 ,

[0550] Where ∆U 放电 Indicates the voltage change within 10s after the discharge starts, ∆I 放电 Indicates the current value within 10 seconds after the start of discharge.

[0551] 3. Number of cycles of battery cells until 80% SOH

[0552] At room temperature, charge the battery cell at a constant current of 1C to a charge cutoff voltage of 3.65V, then discharge it at a constant current of 1C to 2.0V. This constitutes one charge-discharge cycle. Repeat these charge-discharge cycle steps until the cycle capacity retention rate (i.e., Cn / C0 × 100%) reaches 80%. Record the number of cycles. A higher number of cycles indicates better cycling performance of the battery cell.

[0553] The test results are shown in Table 1.

[0554] Table 1

[0555]

[0556] In Table 1,

[0557] In Comparative Example 1, the mass content of carbon elements on the surface of the positive electrode active material is relatively low, resulting in relatively poor conductivity of the positive electrode active material and a relatively large internal resistance of the positive electrode sheet.

[0558] In Comparative Example 2, the mass content of amorphous carbon on the surface of the graphite particles is relatively low, resulting in relatively poor conductivity of the graphite particles and a large internal resistance of the negative electrode sheet.

[0559] When the internal resistance of Comparative Examples 1 and 2 is large, it is not conducive to the rapid charging of the battery cells. In addition, the DCR of the battery cells is high, and the battery cells are more likely to generate heat, making the electrolyte system unstable and the organic solvent easily volatilized, resulting in an increase in the internal pressure of the battery cells, which is not conducive to circulation.

[0560] In the embodiment of the present application, the resistance of the positive electrode sheet is 0.1Ω to 30Ω, optionally 0.1Ω to 25Ω, optionally 0.1Ω to 5Ω, and the resistance of the negative electrode sheet is 0.001Ω to 0.01Ω, optionally 0.001Ω to 0.005Ω, and optionally 0.001Ω to 0.004Ω. The resistance of the positive electrode sheet and the resistance of the negative electrode sheet are controlled within a reasonable range, so that the DCR of the battery cell is relatively low, the battery cell generates less heat, the electrolyte system is relatively stable, the organic solvent is not easy to volatilize, and it is beneficial to improve the cycle performance.

[0561] In Examples 3-1 to 3-4, the porosity or thickness of the base film in the isolation membrane is adjusted so that the porosity of the base film is 20% to 70%, optionally 35% to 60%, and the thickness of the base film is 6μm to 12μm, optionally 6μm to 9μm. In this case, the migration ability of lithium ions in the isolation membrane is strong, which is conducive to fast charging, and can reduce the internal resistance of the battery cell, thereby reducing heat generation, which is conducive to improving the cycle performance.

[0562] Comparative Example 3 and Comparative Example 4

[0563] A battery cell was prepared using a method similar to that of Example 1. The difference from Example 1 was that the composition of the organic solvent in the electrolyte was adjusted.

[0564] Example 4-1 to Example 4-3

[0565] A battery cell was prepared using a method similar to that of Example 1, except that:

[0566] In Example 4-1,

[0567] The single-sided coating weight of the positive electrode film is 231mg / 1540.25mm 2 The compacted density at 100% SOC is 2.72 g / cm 3 ,

[0568] The single-sided coating weight of the negative electrode film is 110mg / 1540.25mm 2 The compacted density at 100% SOC is 1.21 g / cm 3 ,

[0569] The composition of the organic solvent in the electrolyte was also adjusted.

[0570] In Example 4-2,

[0571] The single-sided coating weight of the positive electrode film is 258mg / 1540.25mm 2 The compacted density at 100% SOC is 2.72 g / cm 3 ,

[0572] The single-sided coating weight of the negative electrode film is 123mg / 1540.25mm 2 The compacted density at 100% SOC is 1.21 g / cm 3 ,

[0573] The composition of the organic solvent in the electrolyte was also adjusted.

[0574] In Example 4-3,

[0575] The single-sided coating weight of the positive electrode film is 300mg / 1540.25mm2 The compacted density at 100% SOC is 2.72 g / cm 3 ,

[0576] The single-sided coating weight of the negative electrode film is 138mg / 1540.25mm 2 The compacted density at 100% SOC is 1.26 g / cm 3 ,

[0577] The composition of the organic solvent in the electrolyte was also adjusted.

[0578] The performance test steps are the same as above and will not be repeated here. The test results are shown in Table 2.

[0579] Table 2

[0580] In Table 2,

[0581] In Comparative Example 3, Example 4-1 and Example 4-2, the mass content of ethylene carbonate in the carbonate solvent is 30%, and the remainder is dimethyl carbonate.

[0582] In Comparative Example 3, the conductivity of the electrolyte is too small. Even if the resistance of the positive and negative electrode sheets is set within a reasonable range, lithium ion migration is difficult, the electrolyte charging capacity is insufficient, and cycle drop is prone to occur.

[0583] In Comparative Example 4, the conductivity of the electrolyte is too high, and the low-boiling-point organic solvent accounts for a high proportion, which is very easy to volatilize during the cycle, causing the internal pressure of the battery cell to increase and worsening the cycle.

[0584] In Examples 4-1 to 4-3, by setting the positive and negative electrode sheet resistance within a reasonable range and setting the electrolyte conductivity to 13mS / cm to 20mS / cm, optionally 15mS / cm to 20mS / cm, the lithium ion migration rate is faster, which is conducive to fast charging. The electrolyte system is stable, which can improve the cycle performance of the battery cell. In Examples 4-1 to 4-3, when the electrolyte conductivity is relatively low, further combining a lower compaction density and / or coating weight of the positive electrode film layer, and / or a lower compaction density and / or coating weight of the negative electrode film layer, facilitates fast charging.

[0585] Example 5

[0586] A battery cell was prepared using a method similar to that of Example 1, except that:

[0587] The preparation of the positive electrode sheet includes:

[0588] The positive electrode sheet includes a positive electrode current collector, a positive electrode conductive layer on the positive electrode current collector, a positive electrode lithium replenishing layer and a positive electrode film layer. The positive electrode current collector is an aluminum foil with a thickness of 10μm. The positive electrode conductive layer on the positive electrode current collector is composed of a positive electrode conductive agent superconducting carbon, a positive electrode binder polyvinylidene fluoride (PVDF) and a solvent N-methylpyrrolidone NMP. After being evenly mixed, it is coated on the surface of the current collector with a thickness of 1μm. The mass content of the positive electrode conductive agent in the positive electrode conductive layer is 40%, and the mass content of the positive electrode binder is 60%.

[0589] The positive electrode lithium replenishment layer is a film formed by mixing lithium phosphate, positive electrode binder polyvinylidene fluoride (PVDF) and solvent N-methylpyrrolidone NMP evenly and then coating it on the surface of the positive electrode conductive layer. The thickness is 0.5μm, and the mass content of lithium phosphate in the positive electrode lithium replenishment layer is 80%.

[0590] 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 lithium replenishment 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.

[0591] 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.

[0592] Example 6

[0593] A battery cell was prepared using a method similar to that of Example 1, except that:

[0594] The preparation of the negative electrode sheet includes:

[0595] The negative electrode sheet includes a negative electrode current collector, a negative electrode conductive layer on the negative electrode current collector and a negative electrode film layer. The negative electrode current collector is a copper foil with a thickness of 5μm. The negative electrode conductive layer on the negative electrode current collector is composed of a negative electrode conductive agent superconducting carbon, a negative electrode binder styrene-butadiene rubber SBR, a thickener sodium carboxymethyl cellulose (CMC-Na) and solvent water. After mixing evenly, it is coated on the surface of the negative electrode current collector with a thickness of 1μm. 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%.

[0596] 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.

[0597] 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.

[0598] The first negative electrode film layer includes a negative electrode active material 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), 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 negative electrode active material includes graphite particles and silicon oxide compounds. The mass content of silicon element in the silicon oxide compounds in the negative electrode active material is 1.5%. The Dv50 of the graphite particles is 11.6μm. The graphite particles include artificial graphite and a carbon coating layer. The carbon coating layer is coated on the surface of the artificial graphite. The mass content of amorphous carbon is 3.5%.

[0599] The second negative electrode film layer includes a negative electrode active material 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), 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 negative electrode active material includes graphite particles and silicon oxide compounds. The mass content of silicon element in the silicon oxide compounds in the negative electrode active material is 1.5%. The Dv50 of the graphite particles is 11.6μm. The graphite particles include artificial graphite and a carbon coating layer. The carbon coating layer is coated on the surface of the artificial graphite. The mass content of amorphous carbon is 3.5%.

[0600] The performance test steps are the same as above and will not be repeated here. The test results are shown in Table 3.

[0601] Table 3

[0602]

[0603] In Example 5, the addition of a lithium replenisher to the positive electrode plate can compensate for lithium loss in the battery system and increase the cycle life.

[0604] In Example 6, the addition of silicon-based materials to the negative electrode plate is beneficial to improving the energy density of the battery cell and can maintain excellent fast charging performance and cycle performance.

[0605] 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 comprises an electrode assembly, an electrolyte and a shell, wherein the electrode assembly and the electrolyte are contained in the shell, the electrode assembly comprises a positive electrode sheet, a negative electrode sheet and a separator, and the separator is located between the positive electrode sheet and the negative electrode sheet. The positive electrode plate includes a positive electrode current collector and a positive electrode film layer provided on at least one side of the positive electrode current collector. The positive electrode film layer includes a positive electrode active material. The positive electrode active material includes lithium iron phosphate with an olivine structure. The resistance of the positive electrode plate is 0.1Ω to 30Ω. The negative electrode plate includes a negative electrode current collector and a negative electrode film layer disposed on at least one side of the negative electrode current collector. The negative electrode film layer includes a negative electrode active material. The resistance of the negative electrode plate is 0.001Ω to 0.01Ω, and the powder resistivity of the negative electrode active material is 0.005Ω·cm to 0.043Ω·cm. The negative electrode active material includes a carbon-based material, and the carbon-based material includes graphite particles. The degree of graphitization of the graphite particles is 92.0% to 94.5%. The electrolyte includes an organic solvent, the organic solvent includes a chain carboxylate solvent, and the mass content of the chain carboxylate solvent in the organic solvent is 5% to 75%; the conductivity of the electrolyte at room temperature is 13mS / cm to 20mS / cm.

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

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

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

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

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

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

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

9. The battery cell according to any one of claims 1 to 2, characterized in that: The battery cell is at 100% charge state, and the compaction density of the positive electrode film layer is 2.55 g / cm 3 to 2.70g / cm 3 , and / or, The single-sided coating weight of the positive electrode film layer is 240 mg / 1540.25 mm 2 Up to 330mg / 1540.25mm 2 .

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

11. The battery cell according to any one of claims 1 to 2, characterized in that: The battery cell is at 100% charge state, and the compaction density of the negative electrode film layer is 1.25 g / cm 3 to 1.36g / cm 3 , and / or, The single-sided coating weight of the negative electrode film layer is 110 mg / 1540.25 mm 2 Up to 150mg / 1540.25mm 2 .

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

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

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

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

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

17. The battery cell according to any one of claims 1 to 2, characterized in that: The olivine-structured lithium iron phosphate comprises: lithium iron phosphate particles, and The coating layer covers the lithium iron 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.

18. The battery cell according to claim 17, 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.

19. The battery cell according to claim 17, characterized in that The graphitization degree of the olivine-structured lithium iron phosphate is 0.15 to 0.

32.

20. The battery cell according to claim 19, characterized in that The graphitization degree of the olivine-structured lithium iron phosphate is 0.19 to 0.

26.

21. The battery cell according to claim 17, wherein: The mass content of carbon in the olivine-structured lithium iron phosphate is 1% to 2%. The specific surface area of ​​the olivine-structured lithium iron phosphate is 5m 2 / g to 18m 2 / g.

22. The battery cell according to claim 21, characterized in that The specific surface area of ​​the olivine-structured lithium iron phosphate is 7.5 m 2 / g to 14m 2 / g.

23. The battery cell according to any one of claims 1 to 2, characterized in that: The lithium iron phosphate with an olivine structure is in a granular form, and its volume distribution particle size satisfies the following requirements: 1µm≤Dv50≤2µm, 0.4µm≤Dv10≤0.7µm.

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

25. The battery cell according to any one of claims 1 to 2, characterized in that: The positive electrode film layer also includes one or more of ternary materials, lithium phosphate, lithium 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.

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

27. The battery cell according to any one of claims 1 to 2, characterized in that: The positive electrode plate further includes a positive electrode conductive layer, and the positive electrode conductive layer is located between the positive electrode film layer and the positive electrode current collector.

28. The battery cell according to claim 27, characterized in that The thickness of the positive electrode conductive layer is 0.5 μm to 2 μm.

29. The battery cell according to claim 27, characterized in that The positive electrode conductive layer includes a positive electrode conductive agent, and the positive electrode conductive agent includes one or more of superconducting carbon, conductive graphite, acetylene black, Ketjen 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.

30. The battery cell according to any one of claims 1 to 2, 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.

31. The battery cell according to claim 30, characterized in that The mass content of the carbon coating layer is 2% to 5% based on the mass of the graphite particles.

32. The battery cell according to any one of claims 1 to 2, characterized in that: The negative electrode film layer comprises: a first negative electrode film layer, disposed on the surface of the negative electrode current collector, wherein the first negative electrode film layer comprises a carbon-based material, and A second negative electrode film layer is connected to a side of the first negative electrode film layer 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.

33. The battery cell according to claim 32, characterized in that The carbon-based material in the first negative electrode film layer also includes natural graphite.

34. The battery cell according to claim 32, 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.

35. The battery cell according to claim 34, 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 .

36. The battery cell according to claim 32, 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.

37. The battery cell according to claim 32, characterized in that The first negative electrode film layer also includes a first lithium-containing binder, and the second negative electrode film layer also includes a second lithium-containing binder. The mass content of the first lithium-containing binder relative to the mass of the first negative electrode film layer is less than or equal to the mass content of the second lithium-containing binder relative to the mass of the second negative electrode film layer.

38. The battery cell according to claim 37, characterized in that The mass content of the first lithium-containing binder relative to the mass of the first negative electrode film layer is 0.1% to 1%, and / or The mass content of the second lithium-containing binder relative to the mass of the second negative electrode film layer is 0.1% to 1%.

39. The battery cell according to claim 37, characterized in that The mass content of lithium element in the first lithium-containing binder is 3% to 10%, and / or The mass content of lithium element in the second lithium-containing binder is 3% to 10%.

40. The battery cell according to claim 37, wherein: 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%.

41. The battery cell according to any one of claims 1 to 2, 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 mass of the negative electrode active material.

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

43. The battery cell according to any one of claims 1 to 2, characterized in that The negative electrode plate further includes a negative electrode conductive layer, and the negative electrode conductive layer is located between the negative electrode film layer and the negative electrode current collector.

44. The battery cell according to claim 43, characterized in that The thickness of the negative electrode conductive layer is 0.5 μm to 2 μm.

45. The battery cell according to claim 43, characterized in that The negative electrode conductive layer includes a negative electrode conductive agent, and the negative electrode conductive agent includes one or more of superconducting carbon, conductive graphite, acetylene black, Ketjen black, carbon dots, carbon nanotubes, graphene and carbon nanofibers, and / or, The negative electrode conductive layer includes a negative electrode binder, and the negative electrode binder includes one or more of styrene-butadiene rubber, water-based acrylic resin, polyvinyl alcohol, sodium alginate, and carboxymethyl chitosan.

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

47. The battery cell according to claim 46, characterized in that The porosity of the base film is 35% to 60%.

48. The battery cell according to claim 46, characterized in that The base film has a thickness of 6 μm to 12 μm.

49. The battery cell according to claim 48, characterized in that The base film has a thickness of 6 μm to 9 μm.

50. The battery cell according to any one of claims 1 to 2, characterized in that: The isolation film includes a base film and a functional layer 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.

51. The battery cell according to claim 50, characterized in that The non-fluoropolymer particles include acrylic copolymers.

52. The battery cell according to claim 50, 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.

53. The battery cell according to claim 50, characterized in that The second inorganic particles include one or more of silicon oxide, aluminum oxide, boehmite, barium sulfate, calcium oxide, titanium oxide, zinc oxide, magnesium oxide, zirconium oxide and tin oxide, and / or The average particle size of the second inorganic particles is 5 nm to 100 nm.

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

55. The battery cell according to claim 54, 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.

56. The battery cell according to claim 55, 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.

57. The battery cell according to any one of claims 55 to 56, characterized in that The chain carboxylate solvent includes one or more compounds represented by formula I-1 to formula I-8, 。 58. The battery cell according to any one of claims 1 to 2, characterized in that The organic solvent further includes a carbonate solvent, and the carbonate solvent includes one or more of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate and ethyl methyl carbonate.

59. The battery cell according to claim 58, characterized in that The mass content of the carbonate solvent in the organic solvent is 30% to 70%.

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

61. The battery cell according to claim 60, characterized in that The carbonate additive includes one or more of vinylene carbonate, fluoroethylene carbonate, and / or The sulfur-containing additive includes one or more of vinyl sulfate, vinyl disulfate, butylene sulfite, 1,3-propane sultone, vinyl sulfite, and methylene disulfonate, and / or, The lithium salt additive includes one or more of lithium difluorophosphate, lithium difluorooxalatoborate, lithium tetrafluoroborate, and lithium bis(oxalatoborate).

62. The battery cell according to claim 60, characterized in that The additive has a mass content of 1% to 10% in the electrolyte.

63. The battery cell according to claim 60, characterized in that The mass content of the additive in the electrolyte is 2% to 8%.

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

65. The battery cell according to claim 64, characterized in that The fluorine-containing sulfonyl imide salt includes one or more of lithium bis(fluorosulfonyl)imide and lithium bis(trifluoromethanesulfonyl)imide.

66. The battery cell according to claim 64, 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.

67. The battery cell according to claim 66, characterized in that The ratio of the molar concentration of the lithium bis(fluorosulfonyl)imide to the molar concentration of the lithium hexafluorophosphate is 0.2 to 1.

0.

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

69. The battery cell according to claim 68, characterized in that The thickness of the shell is 0.2 mm to 0.35 mm.

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

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

72. A battery device, characterized in that The invention comprises a plurality of battery cells according to any one of claims 1 to 71.

73. The battery device according to claim 72, characterized in that The battery device has a charging time from 10% state of charge to 80% state of charge of 5 minutes to 10.5 minutes.

74. An electrical device, characterized in that: Comprising a battery device as claimed in claim 72 or 73.

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