Battery monomer and charging method thereof, battery device and power utilization device

Abstract

The invention relates to a battery monomer and a charging method thereof, a battery device and a power utilization device, the battery monomer comprises an electrolyte and an electrode assembly, the electrode assembly comprises a positive pole piece, a negative pole piece and an isolating membrane, the positive pole piece comprises a positive current collector and a positive membrane layer containing a positive active material, and the negative pole piece comprises a negative current collector and a negative membrane layer containing a negative active material; the positive electrode active material comprises lithium-containing phosphate with an olivine structure, the negative electrode plate comprises a negative electrode current collector and a negative electrode film layer, and the charging process of the battery monomer from a 0% state of charge to a 100% state of charge comprises N charging steps, the difference value between the maximum charge state of any one of the N charging steps and the maximum charge state of the adjacent charging step is smaller than or equal to 5% of the charge state, and N is a positive integer larger than or equal to 2; in the N charging steps, the cut-off voltage of any one of the N-1 charging steps is smaller than the cut-off voltage of the Nth charging step, and the cut-off voltage of the Nth charging step does not exceed 4.4 V. The use reliability of the battery monomer can be improved.

Description

[0001] This application claims the priority of the PCT international application PCT / CN2024 / 102640, titled "Battery Cell, Its Charging Method, Battery Device, and Electrical Device", filed on June 28, 2024. The entire content of this application is incorporated herein by reference. Technical Field

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

[0003] Battery cells have characteristics such as high capacity and long life, and thus are widely used in electronic devices, such as mobile phones, laptop computers, battery cars, electric vehicles, electric airplanes, electric ships, electric toy cars, electric toy ships, electric toy airplanes, and electric tools, etc. With the development of the battery field, higher requirements are put forward for the use reliability of battery cells. Summary of the Invention

[0004] This application provides a battery cell, its charging method, a battery device, and an electrical device, which can reduce the risk of lithium plating during the fast charging process of the battery cell and improve the use reliability of the battery cell.

[0005] In a first aspect, this application provides a battery cell, including an electrolyte and an electrode assembly. The electrode assembly includes a positive electrode plate, a negative electrode plate, and a separator located between the positive electrode plate and the negative electrode plate. The positive electrode plate includes a positive current collector and a positive electrode film layer provided on at least one side of the positive current collector and containing a positive electrode active material. The positive electrode active material includes a lithium-containing phosphate with an olivine structure. The negative electrode plate includes a negative current collector and a negative electrode film layer provided on at least one side of the negative current collector and containing a negative electrode active material. The negative electrode film layer includes a carbon-based material. The charging process of the battery cell from 0% state of charge to 100% state of charge includes N charging steps. The difference between the maximum state of charge of any charging step in the N charging steps and the maximum state of charge of its adjacent charging step is less than or equal to 5% state of charge, where N is a positive integer greater than or equal to 2; among the N charging steps, the cut-off voltage of any charging step in N - 1 charging steps is less than the cut-off voltage of the Nth charging step, and the cut-off voltage of the Nth charging step does not exceed 4.4V. At room temperature, the charging of the battery cell from 10% state of charge to 80% state of charge takes 5 minutes to 10.5 minutes.

[0006] Therefore, in the embodiments of the present application, during the rapid charging process of the battery cell, the difference in the maximum state of charge between adjacent charging steps is less than or equal to 5% state of charge, resulting in less polarization during the charging process; before the Nth charging step, that is, the cut-off voltage of any charging step from the 1st charging step to the (N - 1)th charging step is relatively small, so that during the charging process, the voltage does not rise sharply, and the lithium ions released from the positive electrode film layer can basically be embedded in the negative electrode film layer, and lithium deposition is not likely to occur on the surface of the negative electrode plate, which can improve the reliability of the battery cell during use.

[0007] In some embodiments, the cut-off voltage of the Nth charging step is greater than the cut-off voltage of any charging step among the (N - 1) charging steps, and the difference between the cut-off voltage of the Nth charging step and the cut-off voltage of any charging step among the (N - 1) charging steps is greater than or equal to 0.02V.

[0008] Therefore, when the battery cell in the embodiments of the present application meets the above conditions, it can further make it less likely for lithium deposition to occur on the surface of the negative electrode plate, and can improve the reliability of the battery cell during use.

[0009] In some embodiments, the cut-off voltage of the Nth charging step is greater than the cut-off voltage of any charging step among the (N - 1) charging steps, and the difference between the cut-off voltage of the Nth charging step and the cut-off voltage of any charging step among the (N - 1) charging steps is greater than or equal to 0.05V.

[0010] Therefore, when the battery cell in the embodiments of the present application meets the above conditions, it can further make it less likely for lithium deposition to occur on the surface of the negative electrode plate, and can improve the reliability of the battery cell during use.

[0011] In some embodiments, the cut-off voltage of the Nth charging step is greater than the cut-off voltage of any charging step among the (N - 1) charging steps, and the difference between the cut-off voltage of the Nth charging step and the cut-off voltage of any charging step among the (N - 1) charging steps is 0.05V to 0.2V.

[0012] Therefore, when the battery cell in the embodiments of the present application meets the above conditions, it can further make it less likely for lithium deposition to occur on the surface of the negative electrode plate, and can improve the reliability of the battery cell during use.

[0013] In some embodiments, the cut-off voltage of the Nth charging step is 3.65V to 4.4V.

[0014] Therefore, when the cut-off voltage of the Nth charging step is within the above range, the risk of lithium deposition in the battery cell is small, and the energy density of the battery cell can be improved.

[0015] In some embodiments, the charging rate of the Nth charging step is 0.05C to 0.30C, and can be optionally 0.10C to 0.30C.

[0016] Therefore, at the end stage of charging, the risk of lithium plating on the negative electrode plate increases. When charging at the above-mentioned rate in the Nth charging step, the risk of lithium plating on the negative electrode plate can be further reduced, and the reliability of use of the battery cell can be improved.

[0017] In some embodiments, the charging rate of the battery cell in the Mth charging step is 3.5C to 6C. The state of charge of the battery cell in the Mth charging step includes a 50% state of charge. M is less than N, and M is a positive integer greater than or equal to 1.

[0018] Therefore, in the middle stage of charging, the risk of lithium plating on the negative electrode plate is relatively small, and the charging rate can be increased by high-rate charging. For example, when the battery cell is charged at the above-mentioned rate in the Mth charging step, the reliability of use and the fast charging performance of the battery cell can be improved.

[0019] In some embodiments, the charging rate of the battery cell in the charging step from 0% state of charge to 40% state of charge is 4C to 8C. When the battery cell is charged at the above-mentioned rate in the early stage of charging, the reliability of use and the fast charging performance of the battery cell can be improved.

[0020] In some embodiments, the constant current value in the Qth charging step among the N charging steps is less than the constant current value in the (Q - 1)th charging step. Q is less than or equal to N, and Q is a positive integer greater than or equal to 2.

[0021] Therefore, the constant current value in any charging step among the N charging steps is less than the constant current value in the previous charging step. As the state of charge increases, the risk of lithium plating on the negative electrode plate is relatively small, which is beneficial to improving the reliability of use of the battery cell.

[0022] In some embodiments, the lithium-containing phosphate with an olivine structure includes phosphate particles and a coating layer. The phosphate particles include phosphate particles, and the coating layer is coated on the surface of the phosphate particles. The coating layer contains one or more elements of C, Fe, Ti, Zr, Hf, Ge, and Sn. By coating the surface of the phosphate particles with the coating layer, the conductivity of the lithium-containing phosphate with an olivine structure can be improved, the powder resistivity of the material can be reduced, and it is beneficial to the migration rate of lithium ions and reduces the heat generation of the battery cell.

[0023] In some embodiments, the phosphate particles include a compound with the general formula Li x1 A y1 Me a M b P 1-c X c Y z where 0.5 ≤ x 1 ≤ 1.3, 0 ≤ y 1 ≤ 1.3, and 0.9 ≤ x1 +y 1 ≤1.3, 0.9 ≤ a ≤ 1.5, 0 ≤ b ≤ 0.5, and 0.9 ≤ a + b ≤ 1.5, 0 ≤ c ≤ 0.5, 3 ≤ z ≤ 5, A includes one or more of Na, K, and Mg, Me includes one or more of Mn, Fe, Co, and Ni, M includes one or more of B, Mg, Al, Si, P, S, Ca, Sc, Ti, V, Cr, Cu, Zn, Sr, Y, Zr, Nb, Mo, Cd, Sn, Sb, Te, Ba, Ta, W, Yb, La, Ce, X includes one or more of S, Si, Cl, B, C, N, and Y includes one or more of O, F.

[0024] In some embodiments, the coating layer comprises a fast ion conductor having the general formula Li 3-d Fe 2-d M2 d (PO x2 ) y2 , where M2 includes one or more elements of Ti, Zr, Hf, Ge, and Sn, 0 ≤ d ≤ 1, 0 < x 2 <5, 0 < y 2 <4.

[0025] Coating the phosphate particles with the fast ion conductor can significantly improve the transport rate of lithium ions during multiple deintercalation / insertion of lithium at the positive electrode, improve the ionic conductivity of the positive electrode active material, and thus increase the specific capacity, and further increase the energy density of the corresponding battery cell.

[0026] In some embodiments, the graphitization degree of the positive electrode active material is from 0.15 to 0.32; optionally from 0.19 to 0.26. When the graphitization degree of the positive electrode active material is within the above range, it is beneficial to improve the conductivity of the positive electrode active material and reduce the heat generation of the positive electrode sheet, thereby reducing the heat generation of the battery cell.

[0027] In some embodiments, the mass content of carbon element in the lithium-containing phosphate with olivine structure is from 1% to 2%; the specific surface area of the lithium-containing phosphate with olivine structure is 5m 2 / g to 18m 2 / g; optionally 7.5m 2 / g to 14m 2 / g.

[0028] Thus, in the embodiments of the present application, the carbon element with the above mass content and the material with the above specific surface area are more conducive to the effective contact between the electrolyte and the phosphate particles of the phosphate particles, and are conducive to the transport of lithium ions at the phase interface.

[0029] In some embodiments, the volume-based particle size distribution of the positive electrode active material satisfies: 1 µm ≤ Dv50 ≤ 2 µm, and 0.4 µm ≤ Dv10 ≤ 0.7 µm. The particle size of the positive electrode active material is relatively small, the lithium deintercalation / insertion path in the positive electrode active material is short, and the heat generation is less; moreover, the particle size of the above positive electrode active material is not too small, and basically no agglomeration occurs during the processing and preparation process, so that the performance of the positive electrode active material is stable.

[0030] In some embodiments, the lithium-containing phosphate in the olivine structure is granular. The lithium-containing phosphate in the olivine structure includes secondary particles formed by the agglomeration of primary particles, and the average particle size of the primary particles is 200 nm to 500 nm. The average particle size of the primary particles is relatively small, the lithium deintercalation / insertion path in the positive electrode active material is short, and the heat generation is less.

[0031] In some embodiments, the positive electrode film layer further includes one or more of a ternary material, lithium phosphate, lithium hydrogen phosphate, lithium sulfate, lithium sulfite, lithium molybdate, lithium oxalate, lithium titanate, lithium tetraborate, lithium metasilicate, lithium manganate, lithium tartrate, trilithium citrate, lithium nickelate, and lithium ferrate. The above materials can supplement lithium ions to the positive electrode film layer, make up for the irreversible lithium ion loss in the system, and improve the capacity, thereby improving the energy density of the battery cell.

[0032] In some embodiments, the single-sided coating weight of the positive electrode film layer is 200 mg / 1540.25 mm 2 to 370 mg / 1540.25 mm 2 , and can be optionally 240 mg / 1540.25 mm 2 to 330 mg / 1540.25 mm 2 . When the single-sided coating weight of the positive electrode film layer is within the above range, the heat generation per unit area of the positive electrode sheet is not too large, and the energy density of the battery cell can be improved while taking it into account.

[0033] In some embodiments, when the battery cell is in a 100% charged state, the tap density of the positive electrode film layer is 2.50 g / cm 3 to 2.80 g / cm 3 , and can be optionally 2.55 g / cm 3 to 2.70 g / cm 3 . When the tap density of the positive electrode film layer is within the above range, it is beneficial to improve the energy density of the battery cell; and since the positive electrode active materials in the positive electrode film layer are stacked relatively tightly and the contact resistance between particles is small, the resistance of the electrode sheet can be further reduced, thereby reducing heat generation.

[0034] In some embodiments, the single-sided coating weight of the negative electrode film layer is 90 mg / 1540.25 mm 2 to 170 mg / 1540.25 mm2 ; Optionally 110 mg / 1540.25 mm 2 to 150 mg / 1540.25 mm 2 . When the single-sided coating weight of the negative electrode film layer is within the above range, the heat generation per unit area of the negative electrode plate will not be too large, and it can take into account the improvement of the energy density of the battery cell.

[0035] In some embodiments, when the battery cell is in a 100% charged state, the compaction density of the negative electrode film layer is 1.15 g / cm 3 to 1.36 g / cm 3 ; Optionally 1.25 g / cm 3 to 1.36 g / cm 3 . When the compaction density of the negative electrode film layer is within the above range, it is beneficial to improve the energy density of the battery cell; and because the negative electrode active materials in the negative electrode film layer are stacked relatively tightly, the contact resistance between particles is small, which can further reduce the resistance of the electrode plate, thereby reducing heat generation.

[0036] In some embodiments, the negative electrode active material includes a carbon-based material, the carbon-based material includes graphite particles, and the graphitization degree of the graphite particles is 92.0% to 94.5%. When the graphitization degree of the graphite particles is within the above range, the conductive performance of the graphite particles is relatively excellent, which can reduce the heat generation of the negative electrode plate and the battery cell; and it can improve the fast charging performance of the battery cell.

[0037] In some embodiments, the graphite particles include artificial graphite and a carbon coating layer. The artificial graphite includes secondary particles aggregated by a plurality of primary particles; the carbon coating layer covers the surface of the artificial graphite. The carbon coating layer has more end faces and defects, so that the number of sites capable of intercalating and deintercalating lithium ions is more, and the conductivity of the carbon coating layer is relatively excellent, which can reduce the internal resistance of the negative electrode plate and the heat generation amount of the battery cell.

[0038] In some embodiments, based on the mass of the graphite particles, the mass content of the carbon coating layer is 2% to 5%. When the mass content of the carbon coating layer is within the above range, it can further reduce the internal resistance of the negative electrode plate and the heat generation amount of the battery cell.

[0039] In some embodiments, the negative electrode film layer includes a first negative electrode film layer and a second negative electrode film layer. The first negative electrode film layer is disposed on the surface of the negative electrode current collector. The carbon-based material in the first negative electrode film layer includes graphite particles. The second negative electrode film layer is connected to the side of the first negative electrode film layer facing away from the negative electrode current collector. The carbon-based material in the second negative electrode film layer includes graphite particles. The 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.

[0040] Therefore, in the embodiments of the present application, there are differences in the particle sizes of the first negative electrode film layer and the second negative electrode film layer, which can improve the fast charging performance of the battery cell. Specifically, during fast charging, the overpotential of the second negative electrode film layer is usually relatively high, and the bottleneck of fast charging mainly lies in the second negative electrode film layer. In the embodiments of the present application, the particle size of the second negative electrode film layer is relatively small, which can shorten the solid-phase transport path of lithium ions, improve the fast charging performance, and can improve the problem of lithium deposition on the surface layer of the negative electrode sheet.

[0041] 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.

[0042] In some embodiments, the volume average particle size Dv50 of the graphite particles in the second negative electrode film layer is 7.8 μm to 14.3 μm. When the volume average particle size Dv50 of the negative electrode active material in the second negative electrode film layer is within the above range, the tortuosity of lithium ion transport can be reduced, and the fast charging performance of the battery cell can be improved.

[0043] In some embodiments, the tapped density of the carbon-based material in the first negative electrode film layer is less than or equal to the tapped density of the carbon-based material in the second negative electrode film layer. When the tapped density of the carbon-based material in the second negative electrode film layer is greater than the tapped density of the carbon-based material in the first negative electrode film layer, the second negative electrode film layer is filled more densely, so that the energy density of the battery cell is improved; the filling of the first negative electrode film layer is relatively sparse and the pores are more abundant, which can improve the fast charging performance of the battery cell.

[0044] In some embodiments, the tapped density of the carbon-based material in the first negative electrode film layer is 0.82 g / cm 3 to 1.21 g / cm 3 . When the tapped density of the carbon-based material in the first negative electrode film layer is within a suitable range, the fast charging performance of the battery cell can be improved.

[0045] In some embodiments, the tapped density of the carbon-based material in the second negative electrode film layer is 0.90 g / cm 3 to 1.25 g / cm 3 . When the tapped density of the carbon-based material in the second negative electrode film layer is within a suitable range, the energy density of the battery cell can be improved.

[0046] In some embodiments, the ratio of the thickness of the second negative electrode film layer to the thickness of the first negative electrode film layer is 3:7 to 7:3, and can be optionally 4:6 to 6:4. By adjusting the thickness ratio of the first negative electrode film layer and the second negative electrode film layer, the gradient pore difference between the upper and lower layers can be further increased, the tortuosity of lithium ion transport can be reduced, and the fast charging ability of the battery cell can be improved.

[0047] In some embodiments, after the battery cell undergoes 10 full charge test cycles at the beginning of life (BOL), the thickness of the first negative electrode film layer is 15 μm to 65 μm. When the thickness of the first negative electrode film layer is within the above range, the first negative electrode film layer and the second negative electrode film layer can regulate and increase the gradient pore difference between the upper and lower layers, reduce the tortuosity of lithium ion transport, and improve the fast charging ability of the battery cell.

[0048] In some embodiments, after the battery cell undergoes 10 full charge test cycles at the beginning of life (BOL), the thickness of the second negative electrode film layer is 15 μm to 65 μm. When the thickness of the second negative electrode film layer is within the above range, the first negative electrode film layer and the second negative electrode film layer can regulate and increase the gradient pore difference between the upper and lower layers, reduce the tortuosity of lithium ion transport, and improve the fast charging ability of the battery cell.

[0049] In some embodiments, after the battery cell undergoes a full charge test at the end of life (EOL), the thickness of the first negative electrode film layer is 15 μm to 70 μm. When the thickness of the first negative electrode film layer is within the above range, the first negative electrode film layer and the second negative electrode film layer can regulate and increase the gradient pore difference between the upper and lower layers, reduce the tortuosity of lithium ion transport, and improve the fast charging ability of the battery cell.

[0050] In some embodiments, after the battery cell undergoes a full charge test at the end of life (EOL), the thickness of the second negative electrode film layer is 15 μm to 70 μm. When the thickness of the second negative electrode film layer is within the above range, the first negative electrode film layer and the second negative electrode film layer can regulate and increase the gradient pore difference between the upper and lower layers, reduce the tortuosity of lithium ion transport, and improve the fast charging ability of the battery cell.

[0051] In some embodiments, the first negative electrode film layer further includes a first lithium-containing binder, and the second negative electrode film layer further includes a second lithium-containing binder. The mass content of the first lithium-containing binder relative to the mass of the first negative electrode film layer is less than or equal to the mass content of the second lithium-containing binder relative to the mass of the second negative electrode film layer.

[0052] Therefore, in the embodiments of the present application, the mass content of the second lithium-containing binder in the second negative electrode film layer is relatively high, and the number of freely movable lithium ions provided by the second lithium-containing binder for the second negative electrode film layer is relatively more, which can further improve the fast charging performance of the battery cell.

[0053] 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 deintercalation rate of lithium ions can be improved, and the fast charging performance of the battery cell can be improved.

[0054] In some embodiments, the mass content of lithium element in the first lithium-containing binder is 3% to 10%, optionally 3% to 8%. When the mass content of lithium element is within the above range, the number of free-moving lithium ions in the negative electrode film layer can be relatively large, which can further shorten the distance for lithium ions to diffuse to the surface of the negative electrode film layer, improve the intercalation and deintercalation rate of lithium ions, and improve the fast charging performance of the battery cell.

[0055] In some embodiments, the mass content of the second lithium-containing binder relative to the mass of the second negative electrode film layer is 0.1% to 1%. When the mass content of lithium element in the second lithium-containing binder is within the above range, the intercalation and deintercalation rate of lithium ions is improved, and the fast charging performance of the battery cell is improved.

[0056] In some embodiments, the mass content of lithium element in the second lithium-containing binder is 3% to 10%, optionally 3% to 8%. When the mass content of lithium element is within the above range, the number of free-moving lithium ions in the negative electrode film layer can be relatively large, which can further shorten the distance for lithium ions to diffuse to the surface of the negative electrode film layer, improve the intercalation and deintercalation rate of lithium ions, and improve the fast charging performance of the battery cell.

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

[0058] Thus, the lithium-containing binder of the above material can provide a certain number of lithium ions for the negative electrode film layer, improve the fast charging performance of the battery cell; and is not prone to swelling during charge and discharge, with a stable structure, so that the cycle performance of the negative electrode film layer is improved during fast charge and discharge.

[0059] In some embodiments, the second lithium-containing binder includes a lithium acrylate-acrylonitrile-acrylamide-2-hydroxyethyl acrylate copolymer, and the lithium acrylate-acrylonitrile-acrylamide-2-hydroxyethyl acrylate copolymer is derived from a lithium acrylate monomer, an acrylonitrile monomer, an acrylamide monomer, and a 2-hydroxyethyl acrylate monomer. The molar ratio of the lithium acrylate monomer, the acrylonitrile monomer, the acrylamide monomer, and the 2-hydroxyethyl acrylate monomer is 30% to 50%: 15% to 45%: 5% to 20%: 20% to 35%.

[0060] Thus, the lithium-containing binder of the above material can provide a certain amount of lithium ions for the negative electrode film layer, improving the fast charging performance of the battery cell; and it is not prone to swelling during the charge and discharge process, with a stable structure, so that the cycle performance of the negative electrode film layer is improved during the fast charge and discharge process.

[0061] In some embodiments, the negative electrode active material further includes a silicon-based material, and the mass content of silicon element in the silicon-based material is 0.3% to 10.0% based on the mass of the negative electrode active material. The introduction of the silicon-based material can improve the capacity of the negative electrode active material and increase the energy density of the battery cell.

[0062] In some embodiments, the separator includes a base film with a porous structure, and the porosity of the base film is 20% to 70%. When the porosity of the separator in the embodiments of the present application is within the above range, the migration ability of lithium ions in the separator can be improved, and the internal resistance of the battery cell can be further reduced, thereby reducing heat generation.

[0063] In some embodiments, the separator includes a base film with a porous structure, and the porosity of the base film is 35% to 60%. When the porosity of the separator in the embodiments of the present application is within the above range, the migration ability of lithium ions in the separator can be improved, and the internal resistance of the battery cell can be further reduced, thereby reducing heat generation.

[0064] In some embodiments, the thickness of the base film does not exceed 12 μm. When the thickness of the base film is within the above range, the migration path of lithium ions in the base film is shorter, which can further reduce the internal resistance of the battery cell, thereby reducing heat generation.

[0065] In some embodiments, the thickness of the base film does not exceed 9 μm. When the thickness of the base film is within the above range, the migration path of lithium ions in the base film is shorter, which can further reduce the internal resistance of the battery cell, thereby reducing heat generation.

[0066] In some embodiments, the separator includes a base film and a functional layer provided on at least one side of the base film. The functional layer includes a first functional layer and a second functional layer. The first functional layer is located on one side of the base film and includes first inorganic particles. The second functional layer is located on the other side of the base film and includes composite particles. The composite particles include second inorganic particles and a plurality of non-fluoropolymer particles, and the second inorganic particles are attached to the surface of the non-fluoropolymer particles and / or dispersed inside the non-fluoropolymer particles. The first functional layer and the second functional layer have good heat resistance, which can improve the heat resistance of the separator.

[0067] In some embodiments, the non-fluoropolymer particles include acrylate copolymers. Acrylate copolymers have excellent adhesion properties and high adhesion stability with the base film.

[0068] In some embodiments, the first inorganic particles include one or more of silica, alumina, boehmite, barium sulfate, calcium oxide, titanium oxide, zinc oxide, magnesium oxide, zirconium oxide, and tin oxide. The above-mentioned first inorganic particles can improve the heat resistance of the first functional layer.

[0069] In some embodiments, the second inorganic particles include one or more of silica, alumina, boehmite, barium sulfate, calcium oxide, titanium oxide, zinc oxide, magnesium oxide, zirconium oxide, and tin oxide. The above-mentioned second inorganic particles can improve the heat resistance of the first functional layer.

[0070] 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.

[0071] In some embodiments, the conductivity of the electrolyte is 13 mS / cm to 20 mS / cm. When the conductivity of the electrolyte is within the above range, the migration rate of lithium ions in the electrolyte is relatively high, which can further reduce the internal resistance of the battery cell, thereby reducing heat generation and improving the fast charging performance of the battery cell.

[0072] In some embodiments, the viscosity of the electrolyte at room temperature is 2.3 mPa·s to 3.5 mPa·s. When the viscosity of the electrolyte is within the above range, the migration rate of lithium ions in the electrolyte is relatively high, which can further reduce the internal resistance of the battery cell, thereby reducing heat generation and improving the fast charging performance of the battery cell.

[0073] In some embodiments, the density of the electrolyte at room temperature is 1.05 g / mL to 1.35 g / mL. When the density of the electrolyte is within the above range, the migration rate of lithium ions in the electrolyte is relatively high, which can further reduce the internal resistance of the battery cell, thereby reducing heat generation and improving the fast charging performance of the battery cell.

[0074] In some embodiments, the carboxylic acid ester solvent includes a chain carboxylic acid ester solvent, and the mass content of the chain carboxylic acid ester solvent in the organic solvent is greater than or equal to 5% and less than 75%, optionally greater than or equal to 10%, optionally 30% to 70%, optionally 50% to 70%. When the mass content of the chain carboxylic acid ester solvent is within the above range, the viscosity of the electrolyte system is relatively small, which is beneficial to the migration of lithium ions.

[0075] In some embodiments, the chain carboxylic acid ester solvent includes a compound represented by Formula I, Formula I, In Formula I, R 1including a hydrogen atom, a halogen atom, a C1-C5 alkyl group or a C1-C5 haloalkyl group, R 2 including a C1-C5 alkyl group or a C1-C5 haloalkyl group.

[0076] Thus, in the embodiments of the present application, the chain carboxylic ester solvent has a relatively high conductivity, which is beneficial to improving the fast charging ability of the battery monomer.

[0077] In some embodiments, R 1 includes a hydrogen atom, a halogen atom, a C1-C3 alkyl group or a C1-C3 haloalkyl group.

[0078] In some embodiments, in some embodiments, R 2 includes a C1-C3 alkyl group or a C1-C3 haloalkyl group.

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

[0080] In some embodiments, the organic solvent further includes a carbonate solvent, and the carbonate solvent includes one or more of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate and ethyl methyl carbonate. The above carbonate solvent and the chain carboxylic ester solvent are used in combination, so that the conductivity of the electrolyte is improved, which is beneficial to the migration of lithium ions.

[0081] In some embodiments, the carbonate solvent includes one or more of ethylene carbonate, dimethyl carbonate and ethyl methyl carbonate.

[0082] In some embodiments, the mass content of the carbonate solvent in the organic solvent is 30% to 70%, and can be selected from 30% to 50%. The carbonate solvent with the above mass content can further improve the conductivity of the electrolyte, which is beneficial to the migration of lithium ions.

[0083] In some embodiments, the electrolyte further includes an additive, and the additive includes one or more of a carbonate additive, a sulfur-containing additive and a lithium salt additive. The above additive can improve the interfacial film performance on the positive electrode side and / or the negative electrode side, which is beneficial to improving the fast charging performance of the battery monomer and improving the cycle performance.

[0084] In some embodiments, the carbonate additive includes one or more of vinylene carbonate VC and fluoroethylene carbonate FEC.

[0085] In some embodiments, the sulfur-containing additive includes one or more of vinylene sulfate DTD, bis(vinylene sulfate) 2-DTD, butylene sulfite BS, 1,3-propane sultone PS, ethylene sulfite ES, and methylene methanedisulfonate MMDS.

[0086] In some embodiments, the lithium salt additive includes lithium difluorophosphate LiPO 2 F 2 , lithium difluoro(oxalato)borate LiDFOB, lithium tetrafluoroborate LiBF 4 , and one or more of lithium bis(oxalato)borate LiBOB.

[0087] In some embodiments, the mass content of the additive in the electrolyte is 1% to 10%, and can be optionally 2% to 8%. The additive with the above mass content can effectively improve the interfacial film performance on the positive electrode side and / or the negative electrode side, is beneficial to improving the fast charging performance of the battery cell, and improves the cycle performance.

[0088] In some embodiments, the electrolyte further includes a lithium salt, and the lithium salt includes one or more of fluorosulfonylimide salts and lithium hexafluorophosphate LiPF 6 . The above lithium salts are easy to dissociate, which is beneficial to the rapid migration of lithium ions; and the electrolyte system is relatively stable and not easy to decompose, which can improve the cycle performance of the battery cell.

[0089] In some embodiments, the fluorosulfonylimide salt includes one or more of lithium bis(fluorosulfonyl)imide LiFSI and lithium bis(trifluoromethanesulfonyl)imide LiTFSI.

[0090] In some embodiments, the lithium salt includes lithium bis(fluorosulfonyl)imide LiFSI and lithium hexafluorophosphate LiPF 6 , the molar concentration of lithium bis(fluorosulfonyl)imide LiFSI is 0.2 mol / L to 0.5 mol / L, and the molar concentration of lithium hexafluorophosphate LiPF 6 is 0.5 mol / L to 1.0 mol / L.

[0091] In some embodiments, the ratio of the molar concentration of lithium bis(fluorosulfonyl)imide to the molar concentration of lithium hexafluorophosphate LiPF 6 is 0.2 to 1.0.

[0092] In some embodiments, the material of the housing includes steel, and the thickness of the housing is 0.1 mm to 0.5 mm, and can be optionally 0.2 mm to 0.35 mm. When the thickness of the housing is within the above range, the mechanical strength of the housing is relatively high, which can improve the usage reliability and cycle performance of the battery cell; and the housing occupies less space and there is more internal space in the housing, which is beneficial to improving the energy density of the battery cell.

[0093] In some embodiments, the current-carrying area of a single said first electrode terminal is 25 mm 2 to 315 mm 2 ; the relatively large current-carrying area of the first electrode terminal results in a relatively small resistance, which is beneficial to reducing the overall internal resistance of the battery cell.

[0094] In some embodiments, the current-carrying area of a single said second electrode terminal is 25 mm 2 to 315 mm 2 . The relatively large current-carrying area of the second electrode terminal results in a relatively small resistance, which is beneficial to reducing the overall internal resistance of the battery cell.

[0095] In some embodiments, the battery cell includes a first electrode terminal, the positive electrode tab includes a positive electrode lug, and the first electrode terminal and the positive electrode lug are directly welded. Direct welding can reduce the resistance at the connection, which is beneficial to reducing the overall internal resistance of the battery cell.

[0096] In some embodiments, the battery cell includes a second electrode terminal, the negative electrode tab includes a negative electrode lug, and the second electrode terminal and the negative electrode lug are directly welded. Direct welding can reduce the resistance at the connection, which is beneficial to reducing the overall internal resistance of the battery cell.

[0097] In a second aspect, the present application provides a battery device, which includes the battery cell according to any one of the embodiments in the first aspect of the present application.

[0098] In some embodiments, at room temperature, the charging time of the battery device from 10% state of charge to 80% state of charge is 5 min to 10.5 min. The charging speed of the battery device is relatively fast, which is more beneficial to improving the fast charging ability.

[0099] In a third aspect, the present application provides an electrical device, which includes the battery device according to any one of the embodiments in the second aspect of the present application.

[0100] In a fourth aspect, the present application provides a charging method for a battery cell, the charging method including charging a battery cell in a first state of charge so that the increase in the state of charge of the battery cell is less than or equal to 5% state of charge; repeating the above steps at least once until the battery cell is charged to a second state of charge, where the second state of charge is greater than the first state of charge, and the second state of charge is greater than or equal to 95% state of charge and less than 100% state of charge; charging the battery cell in the second state of charge to 100% state of charge, where the cut-off voltage of any step before charging to the second state of charge is less than the cut-off voltage of the step of charging to 100% state of charge, and the cut-off voltage of the step of charging to 100% state of charge does not exceed the theoretical voltage upper limit of the lithium-containing phosphate in the olivine structure. BRIEF DESCRIPTION OF THE DRAWINGS

[0101] To more clearly illustrate the technical solutions of the embodiments of the present application, the drawings required for use in the embodiments of the present application will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on these drawings.

[0102] Figure 1 Schematic structural diagram of a battery cell provided in some embodiments of the present application; Figure 2 Explosion schematic diagram of a battery cell provided in some embodiments of the present application; Figure 3 Schematic structural diagram of a battery module provided in some embodiments of the present application; Figure 4 Schematic structural diagram of a battery pack provided in some embodiments of the present application; Figure 5 Schematic structural diagram of an electrical device provided in some embodiments of the present application.

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

[0104] The reference numerals are explained as follows: 1. Electrical device; 2. Battery pack; 3. Controller; 4. Motor; 5. Box body; 5a. First box body part; 5b. Second box body part; 5c. Accommodating space; 6. Battery module; 7. Battery cell; 10. Electrode assembly; 111. First tab; 112. Second tab; 12. Main body part; 20. Outer shell; 21. Housing; 22. End cap; 31. First electrode terminal; 32. Second electrode terminal. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0105] Hereinafter, embodiments of the battery cell, its charging method, battery device, and electrical device of the present application will be specifically disclosed in detail with appropriate reference to the drawings. However, there may be cases where unnecessary detailed descriptions are omitted. For example, there are cases where detailed descriptions of well-known matters and repeated descriptions of actually identical structures are omitted. This is to avoid the following description from becoming unnecessarily long and to facilitate the understanding of those skilled in the art. In addition, the drawings and the following description are provided for those skilled in the art to fully understand the present application and are not intended to limit the subject matter described in the claims.

[0106] The "ranges" disclosed in this application are defined in the form of a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundaries of a particular range. The ranges defined in this way can include or exclude the end values, and can be combined arbitrarily, that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60 to 120 and 80 to 110 are listed for a specific parameter, ranges of 60 to 110 and 80 to 120 are understood to be anticipated. In addition, if the minimum range values 1 and 2 are listed, and if the maximum range values 3, 4, and 5 are listed, then the following ranges are all anticipated: 1 to 3, 1 to 4, 1 to 5, 2 to 3, 2 to 4, and 2 to 5. In this application, unless otherwise specified, the numerical range "a to b" represents an abbreviated representation of any real number combination between a and b, where both a and b are real numbers. For example, the numerical range "0 to 5" means that all real numbers between "0 to 5" are fully listed herein, and "0 to 5" is only an abbreviated representation of these numerical combinations. Additionally, when stating that a certain parameter is an integer ≥2, it is equivalent to disclosing that the parameter is, for example, the integers 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

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

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

[0109] If there is no special instruction, all steps of this application can be carried out sequentially or randomly, preferably sequentially. For example, if a method includes steps (a) and (b), it means that the method can include steps (a) and (b) carried out sequentially, or can also include steps (b) and (a) carried out sequentially. For example, if it is mentioned that the method may further include step (c), it means that step (c) can be added to the method in any order. For example, the method can include steps (a), (b), and (c), or can also include steps (a), (c), and (b), or can also include steps (c), (a), and (b), etc.

[0110] The battery cell includes a positive electrode plate and a negative electrode plate. During the charging process, lithium ions in the positive electrode film layer of the positive electrode plate are released and migrate to the negative electrode plate, and are embedded in the negative electrode film layer of the negative electrode plate after obtaining electrons. The degree of lithium intercalation in each region of the negative electrode film layer in the negative electrode plate may vary, especially during fast charging, and the difference in the degree of lithium intercalation is greater, resulting in differences in the state of charge (SOC) corresponding to different regions of the negative electrode plate; correspondingly, a part of the region of the positive electrode film layer is in a lithium-rich state, and another part of the region is in a lithium-poor state.

[0111] The positive electrode film layer includes lithium-containing phosphate with an olivine structure. Such materials have an obvious voltage plateau during the charging process. At the beginning of charging, the positive electrode voltage remains unchanged, and at the end of charging, the positive electrode voltage upturns, causing lithium ions in the lithium-rich state to rapidly escape, increasing the local lithium ion activity. The lithium deposition rate is greater than the lithium intercalation rate, resulting in lithium deposition on the surface of the negative electrode sheet and triggering problems with the reliability of the use of the battery cell.

[0112] In view of the above problems, the embodiments of the present application design the system of the battery cell so that lithium deposition basically does not occur during the charging process of the battery cell, which can improve the reliability of the use of the battery cell.

[0113] battery cell In a first aspect, an embodiment of the present application provides a battery cell.

[0114] The battery cell includes an electrolyte and an electrode assembly. The electrode assembly includes a positive electrode sheet, a negative electrode sheet, and a separator located between the positive electrode sheet and the negative electrode sheet. The positive electrode sheet includes a positive electrode current collector and a positive electrode film layer disposed on at least one side of the positive electrode current collector and containing a positive electrode active material. The positive electrode active material includes lithium-containing phosphate with an olivine structure. The negative electrode sheet 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 carbon-based material. The charging process of the battery cell from the 0% state of charge to the 100% state of charge includes N charging steps. The difference between the maximum state of charge of any one of the N charging steps and the maximum state of charge of its adjacent charging step is less than or equal to 5% state of charge. N is a positive integer greater than or equal to 2. Among the N charging steps, the cut-off voltage of any one of the N - 1 charging steps is less than the cut-off voltage of the Nth charging step, and the cut-off voltage of the Nth charging step does not exceed 4.4V.

[0115] In other words, the charging method of the battery cell includes: Charging the battery cell in the first state of charge so that the increase in the state of charge of the battery cell is less than or equal to 5% state of charge; that is, in each charging step of the battery cell, the difference between the maximum state of charge and the minimum state of charge of the battery cell is less than or equal to 5% state of charge. Optionally, the first state of charge is less than or equal to 5% state of charge. Repeat the above steps at least once until charging to the second state of charge, where the second state of charge is greater than or equal to 95% state of charge and less than 100% state of charge. Charge the battery cell in the second state of charge to 100% state of charge. The cut-off voltage of the step of charging to 100% state of charge does not exceed the upper limit of the theoretical voltage of the lithium-containing phosphate with olivine structure. The cut-off voltage of any step before charging to the third state of charge is less than the cut-off voltage of the step of charging to 100% state of charge. Correspondingly, the step of charging to 100% state of charge corresponds to the Nth charging step, that is, the last charging step; any step before charging to the second state of charge refers to the N - 1 charging steps.

[0116] In the embodiments of the present application, N is a positive integer greater than or equal to 2, and can be selected from 20 to 30, such as 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30 or the range composed of any two of the above values.

[0117] The N charging steps refer to the 1st charging step to the Nth charging step; the N - 1 charging steps refer to the 1st charging step to the N - 1th charging step, and any charging step in the N - 1 charging steps refers to any charging step from the 1st charging step to the N - 1th charging step. The Nth charging step is the last charging step of the N charging steps.

[0118] During the charging process of the battery cell, the difference in the maximum state of charge between adjacent charging steps is less than or equal to 5% state of charge, so that the polarization during the charging process is small; before the Nth charging step, that is, the cut-off voltage of any charging step from the 1st charging step to the N - 1th charging step is relatively small, so that during the charging process, the voltage does not rise upward, and the lithium ions released from the positive electrode film layer can basically be embedded in the negative electrode film layer, and lithium deposition is not likely to occur on the surface of the negative electrode plate, which can improve the use reliability of the battery cell. During the charging process of the battery cell, the state of charge of the battery cell can be used as the basis for jumping to the next charging step. The increase in the state of charge in each step does not exceed 5% state of charge. When the increase in the state of charge is 5% state of charge, it will jump to the next charging step; of course, when the increase in the state of charge does not reach 5% state of charge, it can also jump to the next charging step, which can be specifically set according to the actual charging strategy. For example, when the increase in the state of charge is set to 4% state of charge for jumping, then when the state of charge increases by 4% state of charge in each charging step, it will jump to the next charging step. However, it should be noted that the cut-off voltage of any charging step in the N - 1 charging steps is less than the cut-off voltage of the Nth charging step.

[0119] In the embodiments of the present application, the cut-off voltage of any one of the N-1 charging steps does not exceed the cut-off voltage of the Nth charging step. In other words, the cut-off voltage of the Nth charging step is greater than or equal to the cut-off voltage of any one of the N-1 charging steps. Optionally, the cut-off voltage of the Nth charging step is greater than the cut-off voltage of any one of the N-1 charging steps. Further optionally, the difference between the cut-off voltage of the Nth charging step and the cut-off voltage of any one of the N-1 charging steps is greater than or equal to 0.02V; even further optionally, the difference between the cut-off voltage of the Nth charging step and the cut-off voltage of any one of the N-1 charging steps is greater than or equal to 0.05V. In some embodiments, the cut-off voltage of the Nth charging step is greater than the cut-off voltage of any one of the N-1 charging steps, and the difference between the cut-off voltage of the Nth charging step and the cut-off voltage of any one of the N-1 charging steps is greater than or equal to 0.05V and less than or equal to 0.2V.

[0120] The embodiments of the present application adopt a lithium-containing phosphate with an olivine structure, and its charging cut-off voltage is less than or equal to 4.4V. In the last step of charging the battery device, the cut-off voltage is less than or equal to 4.4V, and in the remaining steps, it is less than 4.4V. During the charging process of the battery cell, the cut-off voltage of each charging step can be used as the basis for jumping to the next charging step. For example, it is set that the cut-off voltage of each of the N-1 charging steps is less than the cut-off voltage of the Nth charging step. Specifically, the cut-off voltage of the Nth charging step is 3.65V, and the cut-off voltage of each of the N-1 charging steps is 3.6V. When charging to 3.6V during any one of the N-1 charging steps, it jumps to the next charging step; it should be noted that the increase in the state of charge in each charging step is less than or equal to 5% of the state of charge.

[0121] In the embodiments of the present application, the difference between the maximum state of charge of any one of the N charging steps and the maximum state of charge of its adjacent charging step is less than or equal to 5% of the state of charge, such as 1% of the state of charge, 1.5% of the state of charge, 2% of the state of charge, 2.5% of the state of charge, 3% of the state of charge, 3.5% of the state of charge, 4% of the state of charge, 4.5% of the state of charge, or a range composed of any two of the above values.

[0122] In the embodiments of the present application, the lithium-containing phosphate with an olivine structure may include a lithium iron phosphate system or a lithium manganese iron phosphate system.

[0123] Exemplarily, the difference between the cut-off voltage of the Nth charging step and the cut-off voltage of any one of the N-1 charging steps is 0.02V, 0.025V, 0.03V, 0.035V, 0.04V, 0.045V, 0.05V, 0.055V, 0.06V, 0.065V, 0.07V, 0.075V, 0.08V, 0.085V, 0.09V, 0.095V, 0.1V, 0.12V, 0.15V, 0.18V, 0.20V or a range composed of any two of the above values.

[0124] When the difference between the cut-off voltage of the Nth charging step and the cut-off voltage of any one of the N-1 charging steps is within the above range, the risk of lithium plating on the negative electrode plate can be further reduced, and the reliability of use of the battery cell can be improved.

[0125] In the embodiment of the present application, the cut-off voltage of the Nth charging step does not exceed the theoretical voltage upper limit of the lithium-containing phosphate of the olivine structure. In other words, the cut-off voltage of the Nth charging step is less than or equal to the theoretical voltage upper limit of the lithium-containing phosphate of the olivine structure. In some embodiments, the cut-off voltage of the Nth charging step is 3.65V to 4.4V. Exemplarily, the cut-off voltage of the Nth charging step is 3.65V, 3.7V, 3.75V, 3.8V, 3.85V, 3.9V, 3.95V, 4V, 4.05V, 4.1V, 4.15V, 4.2V, 4.25V, 4.3V, 4.35V, 4.4V or a range composed of any two of the above values.

[0126] When the cut-off voltage of the Nth charging step is within the above range, the risk of lithium plating in the battery cell is small, and the energy density of the battery cell can be increased.

[0127] In some embodiments, the charging rate in the Nth charging step is between 0.05C and 0.30C; optionally, the charging rate in the Nth charging step is 0.10C to 0.30C. Exemplarily, the charging rate in the Nth charging step is 0.05C, 0.10C, 0.15C, 0.20C, 0.25C, 0.30C or a range composed of any two of the above values.

[0128] At the end of charging, the risk of lithium plating on the negative electrode plate increases. When the Nth charging step is charged at the above rate, the risk of lithium plating on the negative electrode plate can be further reduced, and the reliability of use of the battery cell can be improved.

[0129] In some embodiments, the battery cell is charged at a rate of 3.5C to 6C in the Mth charging step. The state of charge of the battery cell in the Mth charging step includes 50% state of charge. M is less than N and M is a positive integer greater than or equal to 1. Exemplarily, the charging rate of the battery cell in the Mth charging step is 3.5C, 4C, 4.5C, 5C, 5.5C, 6C or a range composed of any two of the above values. For example, M is 8, 9, 10, 11, 12, 13, 14 or 15, etc. When M is 10, it is charged at any charging rate between 3.5C and 6C in the 10th charging step.

[0130] In the middle stage of charging, the risk of lithium plating on the negative electrode plate is relatively small, and the charging rate can be increased by high-rate charging. For example, when the battery cell is charged at the above rate in the Mth charging step, the reliability of use and fast charging performance of the battery cell can be improved.

[0131] In some embodiments, the battery cell is charged at a rate of 4C to 8C in any charging step from 0% state of charge to 40% state of charge. Exemplarily, if the adjacent charging steps are spaced 5% state of charge apart, in any charging step from 0% state of charge to 5% state of charge, from 5% state of charge to 10% state of charge, from 10% state of charge to 15% state of charge... from 35% state of charge to 40% state of charge, the charging rate is 4C, 4.5C, 5C, 5.5C, 6C, 6.5C, 7C, 7.5C, 8C or a range composed of any two of the above values. The state of charge of the battery cell in the Pth charging step includes 40% state of charge. The charging rate from the 1st charging step to the Pth charging step is 4C to 8C. P is less than M and P is a positive integer greater than or equal to 1. Exemplarily, P is 6, 7, 8 or 9, etc. When P is 8, in the 9 charging steps from the 1st charging step to the 9th charging step, it is charged at any charging rate between 4C and 8C.

[0132] In the early stage of charging, the risk of lithium plating on the negative electrode plate is relatively small, and the charging rate can be increased by high-rate charging. For example, when the battery cell is charged at the above rate in the early stage of charging, the reliability of use and fast charging performance of the battery cell can be improved.

[0133] Optionally, during the charging step of the battery cell from 10% state of charge to 40% state of charge, the charging rate is 4C to 8C. Exemplarily, the charging rate during the charging step of the battery cell from 10% state of charge to 40% state of charge is 4C, 4.5C, 5C, 5.5C, 6C, 6.5C, 7C, 7.5C, 8C or a range composed of any two of the above values. The state of charge of the battery cell in the P2 charging step includes 40% state of charge, the state of charge in the P1 charging step includes 10% state of charge, the charging rate from the P1 charging step to the P2 charging step is 4C to 8C, P2 is less than M, P1 is less than P2, and P1 and P2 are positive integers greater than or equal to 1.

[0134] In some embodiments, the constant current value of the Qth charging step in the N charging steps is less than the constant current value of the Q - 1th charging step, Q is less than or equal to N, and Q is a positive integer greater than or equal to 2. For example, Q can be any positive integer among 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, N. In any charging step of the N charging steps, the constant current value is less than the constant current value of the previous charging step. As the state of charge increases, the risk of lithium plating on the negative electrode plate is relatively small, which is beneficial to improving the usage reliability of the battery cell.

[0135] With the development of the battery cell field, the requirements for the fast charging performance of battery cells are gradually increasing. The embodiments of the present application are particularly applicable to battery cells for fast charging. For example, in an environment of 30°C, the charging time of the battery cell from 10% state of charge to 80% state of charge is less than or equal to 10.5 min, and can be optionally 5 min to 10.5 min. Exemplarily, the charging time of the battery cell from 10% state of charge to 80% state of charge is 10.5 min, 10 min, 9.5 min, 9 min, 8.5 min, 8 min, 7.5 min, 7 min, 6.5 min, 6 min, 5.5 min, 5 min or a range composed of any two of the above values.

[0136] In some embodiments, during the charging process of the battery cell from 10% state of charge to 80% state of charge, 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 or a range composed of any two of the above values. This charging process can be carried out at room temperature, such as 30°C.

[0137] In some embodiments, the volumetric energy density of the battery cell is from 390 Wh / L to 500 Wh / L, optionally from 410 Wh / L to 470 Wh / L. Exemplarily, the volumetric energy density of the battery cell is 390 Wh / L, 400 Wh / L, 410 Wh / L, 420 Wh / L, 430 Wh / L, 440 Wh / L, 450 Wh / L, 460 Wh / L, 470 Wh / L, 480 Wh / L, 490 Wh / L, 500 Wh / L or a range composed of any two of the above values. The volumetric energy density of the battery cell is relatively high.

[0138] The upper charge cut-off voltage and the lower discharge cut-off voltage of the battery cell vary according to the different cathode active materials. For example, when the phosphate material includes lithium iron phosphate, the upper charge cut-off voltage (i.e., the theoretical voltage upper limit) is 3.65 V, the lower discharge cut-off voltage is 2.0 V, or the upper charge cut-off voltage is 3.7 V, or the upper charge cut-off voltage is 3.8 V; again, for example, when the phosphate material includes lithium manganese iron phosphate, the upper charge cut-off voltage is 4.2 V, the lower discharge cut-off voltage is 2.5 V, or the upper charge cut-off voltage is 4.25 V, or the upper charge cut-off voltage is 4.35 V, or the upper charge cut-off voltage is 4.4 V.

[0139] In the embodiments of the present application, the volumetric energy density of the battery cell has the meaning well-known in the art and can be detected by using the equipment and methods well-known in the art. Taking the upper charge cut-off voltage of the battery cell being 3.65 V and the lower discharge cut-off voltage of the battery cell being 2.0 V as an example, the battery cell is placed at 25 °C and charged at a constant current of 0.33C to 3.65 V, and then charged at a constant voltage to 0.05C; discharged at a constant current of 0.33C to 2.0 V, and record the discharge capacity A0 at this time, unit: Ah; use a caliper to measure the length, width, and height of the battery cell (generally calculated based on the outer shell size of the battery device, excluding the height of the electrode terminal and excluding the insulating film outside the outer shell), calculate the volume V0 of the single battery device, unit: L; the volumetric energy density VED of the battery cell = (A0 × discharge platform voltage) / V0, unit: Wh / L.

[0140] [Positive electrode plate] The positive electrode plate includes a positive current collector and a positive electrode film layer provided on at least one surface of the positive current collector and including a positive cathode active material. For example, the positive current collector has two surfaces opposite to each other in its own thickness direction, and the positive electrode film layer is provided on any one or both of the two opposite surfaces of the positive current collector.

[0141] Next, taking the upper charge cut-off voltage being 3.65 V and the lower discharge cut-off voltage being 2.0 V as an example, the state of the battery cell is described. In the embodiments of the present application, the 0% state of charge SOC and the 100% state of charge SOC are defined as follows: Charge the battery cell at a constant current charge rate of 0.33C to the upper limit voltage of the battery cell, and then charge it at a constant voltage to 0.05C, corresponding to the state of 100% SOC of the battery cell; discharge the battery cell 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.

[0142] In some embodiments, when the battery cell is at 100% state of charge (SOC), the compaction density of the positive electrode film layer is 2.50 g / cm 3 to 2.80 g / cm 3 ; optionally 2.55 g / cm 3 to 2.70 g / cm 3 . Exemplarily, when the battery cell is at 100% state of charge (SOC), the compaction density of the positive electrode film layer is 2.50 g / cm 3 , 2.52 g / cm 3 , 2.55 g / cm 3 , 2.56 g / cm 3 , 2.57 g / cm 3 , 2.58 g / cm 3 , 2.60 g / cm 3 , 2.62 g / cm 3 , 2.65 g / cm 3 , 2.68 g / cm 3 , 2.70 g / cm 3 , 2.72 g / cm 3 , 2.75 g / cm 3 , 2.78 g / cm 3 , 2.80 g / cm 3 or a range composed of any two of the above values.

[0143] When the compaction density of the positive electrode film layer is within the above range, it is beneficial to improve the energy density of the battery cell; and since the positive electrode active materials in the positive electrode film layer are stacked relatively tightly, the contact resistance between particles is small, which can further reduce the resistance of the electrode sheet, thereby reducing heat generation.

[0144] In some embodiments, the single-sided coating weight of the positive electrode film layer is 200 mg / 1540.25 mm 2 to 370 mg / 1540.25 mm 2 ; optionally 240 mg / 1540.25 mm 2 to 330 mg / 1540.25 mm 2 . Exemplarily, the single-sided coating weight of the positive electrode film layer is 200 mg / 1540.25 mm 2 , 210 mg / 1540.25 mm 2, 220 mg / 1540.25 mm 2 , 230 mg / 1540.25 mm 2 , 240 mg / 1540.25 mm 2 , 250 mg / 1540.25 mm 2 , 260 mg / 1540.25 mm 2 , 270 mg / 1540.25 mm 2 , 280 mg / 1540.25 mm 2 , 290 mg / 1540.25 mm 2 , 300 mg / 1540.25 mm 2 , 310 mg / 1540.25 mm 2 , 320 mg / 1540.25 mm 2 , 330 mg / 1540.25 mm 2 , 340 mg / 1540.25 mm 2 , 350 mg / 1540.25 mm 2 , 360 mg / 1540.25 mm 2 , 370 mg / 1540.25 mm 2 Or a range composed of any two of the above values.

[0145] When the single-sided coating weight of the positive electrode film layer is within the above range, the heat generation amount per unit area of the positive electrode plate will not be too large, and it can take into account improving the energy density of the battery cell.

[0146] In the embodiments of the present application, the compaction density of the positive electrode film layer of the battery cell in the 100% state of charge (SOC) can be detected by the following method. Disassemble the positive electrode plate from the battery cell in the 100% state of charge (SOC), and measure the compaction density of the positive electrode film layer. For example, take a single-sided coated positive electrode plate (if it is a double-sided coated plate, one side of the positive electrode film layer can be wiped off first), punch it into small round pieces with an area of S1, weigh it, record it as M1, and measure its thickness H1. Then wipe off the positive electrode film layer of the above weighed positive electrode plate, weigh the weight of the positive electrode current collector, record it as M0, and measure its thickness H0. The single-sided coating weight of the positive electrode film layer = (the weight M1 of the positive electrode plate - the weight M0 of the positive electrode current collector) / S1, the thickness of the positive electrode film layer = the thickness H1 of the positive electrode plate - the thickness H0 of the positive electrode current collector, and the compaction density of the positive electrode film layer = the single-sided coating weight of the positive electrode film layer / the thickness of the positive electrode film layer.

[0147] In some embodiments, the powder resistivity of the positive electrode active material is from 1 Ω·cm to 27.5 Ω·cm, optionally less than or equal to 20 Ω·cm, and optionally less than or equal to 11 Ω·cm. Exemplarily, the powder resistivity of the positive electrode active material can be 27.5 Ω·cm, 20 Ω·cm, 19 Ω·cm, 18 Ω·cm, 17 Ω·cm, 16 Ω·cm, 15 Ω·cm, 14 Ω·cm, 13 Ω·cm, 12 Ω·cm, 11 Ω·cm, 10 Ω·cm, 9 Ω·cm, 8 Ω·cm, 7 Ω·cm, 6 Ω·cm, 5 Ω·cm, 4 Ω·cm, 3 Ω·cm, 2 Ω·cm, 1 Ω·cm or the range composed of any two of the above values.

[0148] The relatively low powder resistivity of the positive electrode active material results in a relatively low resistance of the positive electrode sheet and less heat generation of the battery cell.

[0149] In the embodiments of the present application, the powder resistivity of the material has the meaning well-known in the art and can be detected by the methods and equipment well-known in the art. For example, according to the test standard GB / T30835-2014, a PRCD1100 powder resistivity meter is used for testing.

[0150] In some embodiments, the powder compaction density of the positive electrode active material under 30000 N is 2.46 g / cm 3 to 2.8 g / cm 3 . Exemplarily, the powder compaction density of the positive electrode active material under 30000 N is 2.46 g / cm 3 , 2.47 g / cm 3 , 2.48 g / cm 3 , 2.49 g / cm 3 , 2.5 g / cm 3 , 2.51 g / cm 3 , 2.55 g / cm 3 , 2.58 g / cm 3 , 2.60 g / cm 3 , 2.65 g / cm 3 , 2.68 g / cm 3 , 2.70 g / cm 3 , 2.72 g / cm 3 , 2.75 g / cm 3 , 2.78 g / cm 3 , 2.80 g / cm 3 or the range composed of any two of the above values.

[0151] When the powder compaction density of the positive electrode active material is within the above range under 30000N, the energy density of the battery cell can be improved. Moreover, since the positive electrode active material in the positive electrode film layer can be stacked more closely, the contact resistance between particles is small, which can further reduce the resistance of the electrode sheet and thus reduce heat generation.

[0152] In the embodiments of the present application, the powder compaction density of the material has the meaning well-known in the art and can be detected by methods and equipment well-known in the art. Detection is carried out according to the test standard GB / T24533-2009. For example, a certain amount of positive electrode active material is taken as a sample and added to a mold with a bottom area of 1.327 cm 2 in a UTM7305 type electronic pressure testing machine, pressurized to 3000 kg (equivalent to 30000N), kept under pressure for 30 s, then depressurized, kept for 10 s, and then the powder compaction density of the positive electrode active material under the action of 30000N is recorded and calculated.

[0153] In some embodiments, the charging specific capacity of the positive electrode active material at a 0.1C rate is 150 mAh / g to 170 mAh / g, and can be optionally 157 mAh / g to 170 mAh / g. Exemplarily, the charging specific capacity of the positive electrode active material at a 0.1C rate is 150 mAh / g, 151 mAh / g, 152 mAh / g, 153 mAh / g, 154 mAh / g, 155 mAh / g, 156 mAh / g, 157 mAh / g, 158 mAh / g, 159 mAh / g, 160 mAh / g, 161 mAh / g, 162 mAh / g, 163 mAh / g, 164 mAh / g, 165 mAh / g, 166 mAh / g, 167 mAh / g, 168 mAh / g, 169 mAh / g, 170 mAh / g or the range composed of any two of the above values.

[0154] When the charging specific capacity of the positive electrode active material at a 0.1C rate is within the above range, the energy density of the battery cell is relatively high.

[0155] In the embodiments of the present application, the specific capacity of the active material has the meaning well-known in the art, and can be tested by equipment and methods well-known in the art. The test method of the first Coulomb efficiency and the first discharge specific capacity in Appendix G of the national standard GB / T 24533-2019 can be adopted. Using metallic lithium as the negative electrode and the sample electrode sheet containing the above materials as the positive electrode, a half-button cell is assembled. Under the condition of 23°C ± 2°C, the half-button cell is placed on a battery tester or other test equipment with the same performance, and the discharge capacity is obtained through charge and discharge at a 0.1C rate, and then the capacity is divided by the mass of the active material of the electrode sheet to obtain the charging specific capacity parameter.

[0156] In some embodiments, the mass percentage of lithium-containing phosphate with an olivine structure in the positive electrode active material can be greater than or equal to 80% and less than or equal to 100%. It can be considered that the positive electrode active material of this application is a lithium-containing phosphate system with an olivine structure. When the mass percentage of lithium-containing phosphate with an olivine structure is less than 100%, the positive electrode active material can also include common positive electrode active materials, such as at least one of lithium-containing transition metal oxides, for example, but not limited to. Examples of lithium-containing transition metal oxides can include but are not limited to at least one of lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, and their respective modified compounds.

[0157] Optionally, the mass percentage of lithium-containing phosphate with an olivine structure in the positive electrode active material is 100%.

[0158] In the embodiments of this application, the lithium-containing phosphate with an olivine structure can be phosphate particles or a material obtained by coating and modifying them. For example, the lithium-containing phosphate with an olivine structure includes phosphate particles and a coating layer. The coating layer is coated on the surface of the phosphate particles, and the coating layer contains one or more elements of C, Fe, Ti, Zr, Hf, Ge, and Sn.

[0159] By surface coating the phosphate particles with a coating layer, the conductivity of the lithium-containing phosphate with an olivine structure can be improved, the powder resistivity of the material can be reduced, and it is beneficial to the migration rate of lithium ions, improving the fast charging ability of the battery and reducing the heat generation of the battery cell.

[0160] In some embodiments, the phosphate particles include a compound with the general formula Li x1 A y1 Me a M b P 1-c X c Y z where 0.5 ≤ x 1 ≤ 1.3, 0 ≤ y 1 ≤ 1.3, and 0.9 ≤ x 1 + y 1≤1.3, 0.9 ≤ a ≤ 1.5, 0 ≤ b ≤ 0.5, and 0.9 ≤ a + b ≤ 1.5, 0 ≤ c ≤ 0.5, 3 ≤ z ≤ 5, A includes one or more of Na, K, and Mg, Me includes one or more of Mn, Fe, Co, and Ni, M includes one or more of B, Mg, Al, Si, P, S, Ca, Sc, Ti, V, Cr, Cu, Zn, Sr, Y, Zr, Nb, Mo, Cd, Sn, Sb, Te, Ba, Ta, W, Yb, La, and Ce, X includes one or more of S, Si, Cl, B, C, and N, and Y includes one or more of O and F. The cyclic stability of the phosphate particles is relatively excellent, which is beneficial to improving the cyclic performance of the battery cell.

[0161] Exemplarily, the phosphate particles include LiFePO 4 , LiMnPO 4 , LiNiPO 4 , LiCoPO 4 or one or more of them. During the charge and discharge process of the battery cell, the insertion and extraction and consumption of active ions such as Li will occur, and the molar content of Li is different when the battery cell is discharged to different states. Regarding the positive electrode active materials LiFePO 4 , LiMnPO 4 , LiNiPO 4 , LiCoPO 4 etc., the molar content of Li is the initial state of the material, that is, the state before feeding. When the positive electrode active material is applied to the battery system and undergoes charge and discharge cycles, the molar content of Li may change. In the embodiments of the present application, regarding the positive electrode active materials LiFePO 4 , LiMnPO 4 , LiNiPO 4 , LiCoPO 4 etc., the molar content of oxygen O is only the theoretical state value, and the release of oxygen from the lattice will cause the molar content of oxygen O to change. Actually, the molar content of oxygen O will show fluctuations, and the above situations are all within the protection scope of the present application.

[0162] In some embodiments, the coating layer includes a fast ion conductor with the general formula Li 3-d Fe 2-d M2 d (PO x2 ) y2 , M2 includes one or more elements of Ti, Zr, Hf, Ge, and Sn, 0 ≤ d ≤ 1, 0 < x 2 < 5, 0 < y 2 < 4.

[0163] Exemplarily, the fast ion conductor is a material having a NASICON structure, such as including lithium iron titanium phosphate Li 2 FeTi(PO 4 ) 3 , lithium iron zirconium phosphate Li 2 FeZr(PO 4 ) 3 , or one or more of lithium iron tin phosphate Li2FeSn(PO4)3.

[0164] The fast ion conductor having a NASICON structure is a material with ultrafast ion conduction ability, having abundant three-dimensional lithium ion diffusion and transport channels, and having advantages such as high ion conduction efficiency and strong structural stability during multiple de-lithiation and intercalation processes. Coating the surface of phosphate particles with a fast ion conductor containing a NASICON structure can significantly improve the transport rate of lithium ions during multiple de- / intercalation at the positive electrode, improve the ion conductivity of the positive electrode active material, improve the fast charging ability of the battery cell, and in addition, can also improve the specific capacity and the energy density of the corresponding battery cell.

[0165] In some embodiments, the coating layer further includes elemental carbon.

[0166] The elemental carbon and the fast ion conductor can be arranged in layers. For example, the elemental carbon serves as an independent carbon coating layer, and the fast ion conductor serves as an independent fast ion conductor layer. The carbon coating layer can be coated on the surface of the phosphate particles, and the fast ion conductor layer is located on the surface of the carbon coating layer, that is, the fast ion conductor layer is located on the side of the carbon coating layer away from the phosphate particles. Or, the fast ion conductor layer can be coated on the surface of the phosphate particles, and the carbon coating layer is located on the surface of the fast ion conductor layer, that is, the carbon coating layer is located on the side of the fast ion conductor layer away from the phosphate particles. Of course, the elemental carbon and the fast ion conductor can also be arranged in the same layer.

[0167] Optionally, the carbon coating layer can be formed by carbonizing an organic carbon source (such as glucose, polyethylene glycol, etc.) on the surface of the fast ion conductor layer. The carbon coating layer can partially coat the fast ion conductor layer or can completely coat the fast ion conductor layer. The setting of the carbon coating layer can significantly improve the electronic conductivity of the phosphate particles, make up for the defect of poor electronic conduction performance of the phosphate particles, and improve the energy density of the battery cell. Specifically, the setting of the carbon coating layer endows the positive electrode active material of the present application with the following advantages: The carbon coating layer in the positive electrode active material of the present application provides a suitable channel for the transport of electrons, can significantly improve the conduction rate of electrons during multiple de-lithiation and intercalation processes, improve the electronic conductivity of lithium-containing phosphates, improve the charging ability of the corresponding battery cell, and can also improve the energy density.

[0168] The carbon coating layer of the positive electrode active material of the present application has a loose and porous structure, which enables the electrolyte to come into full and effective contact with the lithium-containing phosphate, thereby improving the lithium ion transport rate at the phase interface and enhancing the charging capacity of the battery cell.

[0169] Coating a layer of carbon coating on the surface of the lithium-containing phosphate can not only improve the electrical conductivity of the lithium-containing phosphate, but also enhance the structural stability of the positive electrode active material, effectively alleviating the iron dissolution phenomenon of the positive electrode active material during the long-term storage and cyclic use of the battery cell, thereby improving the cycle life of the battery cell. The positive electrode active material of the present application uses lithium-containing phosphate as the base material, giving full play to the advantages of low cost, high reliability in use, and good cycle stability of the lithium-containing phosphate. At the same time, the coating layer (fast ion conductor layer and carbon coating layer) is used to solve the disadvantages of poor electronic conductivity and ionic conductivity. The battery cell prepared from the positive electrode active material of the present application can improve the energy density of the battery cell on the premise of excellent cycle performance. In the embodiments of the present application, the content of elements in the positive electrode active material has the meaning well-known in the art and can be detected by equipment and methods well-known in the art. For example, referring to EPA 6010D-2014, it is tested by inductively coupled plasma atomic emission spectrometry, and determined by inductively coupled plasma optical emission spectrometry (ICP-OES, instrument model: Thermo ICAP7400). After discharging the battery cell to 0% state of charge (SOC), the positive electrode plate is disassembled, washed with DMC and dried, and then after removing impurities by high-temperature calcination, 0.4 g of the positive electrode active material is weighed, and 10 ml (50% concentration) of aqua regia is added thereto. Then it is placed on a flat plate at 180 °C for 30 min. After digestion on the flat plate, it is fixed to a volume of 100 mL, and quantitative testing is carried out by the standard curve method.

[0170] In some embodiments, the graphitization degree of the positive electrode active material is from 0.15 to 0.32, and can be selected from 0.19 to 0.26. Exemplarily, the graphitization degree of the positive electrode active material is 0.15, 0.16, 0.17, 0.18, 0.19, 0.20, 0.21, 0.22, 0.23, 0.24, 0.25, 0.26, 0.27, 0.28, 0.29, 0.30, 0.31, 0.32 or the range composed of any two of the above values.

[0171] When the graphitization degree of the positive electrode active material is within the above range, it is beneficial to improve the electrical conductivity of the positive electrode active material, reduce the heat generation of the positive electrode plate, and thus reduce the heat generation of the battery cell.

[0172] In the embodiments of the present application, the higher the graphitization degree of the material, the lower the degree of disorder, and it can be tested according to the general rules of X-ray diffraction analysis method of JIS / K 0131-1996.

[0173] In some embodiments, the mass content of carbon in the lithium-containing phosphate with olivine structure is 1% to 2%, and the specific surface area of the lithium-containing phosphate with olivine structure is 5 m 2 / g to 18 m 2 / g.

[0174] Optionally, the mass content of carbon in the lithium-containing phosphate with olivine structure is 1% to 2%, and the specific surface area of the lithium-containing phosphate with olivine structure is 7.5 m 2 / g to 14 m 2 / g.

[0175] Exemplarily, the mass content of carbon in the lithium-containing phosphate with olivine structure is 1%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2% or a range composed of any two of the above values.

[0176] Exemplarily, the specific surface area of the lithium-containing phosphate with olivine structure is 5 m 2 / g, 6 m 2 / g, 7 m 2 / g, 8 m 2 / g, 9 m 2 / g, 10 m 2 / g, 11 m 2 / g, 12 m 2 / g, 13 m 2 / g, 14 m 2 / g, 15 m 2 / g, 16 m 2 / g, 17 m 2 / g, 18 m 2 / g or a range composed of any two of the above values.

[0177] Carbon mainly exists in the coating layer in the form of a carbon coating layer. The carbon coating layer is porous and loose, which is beneficial to increasing the specific surface area of the material, more beneficial to the effective contact between the electrolyte and the phosphate particles, and beneficial to the transport of lithium ions at the phase interface. In addition, when the mass content of carbon is within the above range, the conductivity of the lithium-containing phosphate with olivine structure can be significantly improved, which is beneficial to enhancing the ionic conductivity and electronic conductivity of the lithium-containing phosphate with olivine structure, and can improve the rapid charging ability and energy density of the battery cell.

[0178] In the embodiments of the present application, the specific surface area of the material has the meaning well-known in the art, and can be detected by equipment and methods well-known in the art. For example, detection is carried out according to the test standard GB / T 19587-2017. The positive electrode active material is used as a sample, and the specific surface area is tested by a Tri-Star 3020 specific surface area and pore size analyzer of Micromeritics Corporation, USA.

[0179] 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.

[0180] Exemplarily, Dv50 of the positive electrode active material can be 1 µm, 1.1 µm, 1.15 µm, 1.2 µm, 1.25 µm, 1.3 µm, 1.35 µm, 1.4 µm, 1.45 µm, 1.5 µm, 1.55 µm, 1.6 µm, 1.65 µm, 1.7 µm, 1.75 µm, 1.8 µm, 1.85 µm, 1.9 µm, 1.95 µm, 2 µm or a range composed of any two of the above values.

[0181] Exemplarily, Dv10 of the positive electrode active material can be 0.4 µm, 0.45 µm, 0.5 µm, 0.55 µm, 0.6 µm, 0.65 µm, 0.7 µm or a range composed of any two of the above values.

[0182] The particle size of the positive electrode active material is relatively small, the lithium deintercalation / insertion path of lithium ions in the positive electrode active material is short, and the heat generation is less. Moreover, the particle size of the above positive electrode active material is not too small, and basically no agglomeration occurs during the processing and preparation process, making the performance of the positive electrode active material stable.

[0183] In the embodiments of the present application, the volume average particle size Dv50 of the material refers to the particle size corresponding to 50% in the volume distribution, and the volume average particle size Dv10 of the material refers to the particle size corresponding to 10% in the volume distribution. It can be detected by equipment and methods well-known in the art. For example, the positive electrode active material is used as a sample, and according to the test standard GB / T 19077-2016, the Dv50 and Dv10 of the particles are tested by a Mastersizer 2000E laser particle size analyzer.

[0184] When the positive electrode active material includes other materials in addition to the lithium phosphate with olivine structure, the volume distribution particle size of the positive electrode active material refers to the volume distribution particle size of all positive electrode active materials.

[0185] In some embodiments, the lithium-containing phosphate of the olivine structure is granular. The lithium-containing phosphate of the olivine structure includes secondary particles, and the secondary particles include a plurality of primary particles. The average particle size of the primary particles is from 200 nm to 500 nm. Exemplarily, the average particle size of the primary particles is 200 nm, 220 nm, 250 nm, 280 nm, 300 nm, 320 nm, 350 nm, 380 nm, 400 nm, 420 nm, 450 nm, 480 nm, 500 nm or a range composed of any two of the above values.

[0186] The average particle size of the primary particles is relatively small, the lithium deintercalation / insertion path of lithium ions in the cathode active material is short, and the heat generation is less.

[0187] In the embodiments of the present application, the secondary particles refer to agglomerated particles formed by the aggregation of two or more primary particles. The primary particles and the secondary particles can be easily distinguished by experimental means (such as taking SEM images using a scanning electron microscope), and the average particle size of the primary particles can be obtained by testing in the SEM images of the scanning electron microscope. The SEM test parameters can be set as follows: the working voltage (EHT) is 10.00 kV, the InLens detector is used, the working distance is 4.6 mm, and the magnification is 1000X.

[0188] In some embodiments, the cathode film layer further includes one or more of a ternary material, lithium phosphate, lithium hydrogen phosphate, lithium sulfate, lithium sulfite, lithium molybdate, lithium oxalate, lithium titanate, lithium tetraborate, lithium metasilicate, lithium manganate, lithium tartrate, trilithium citrate, lithium nickelate, and lithium ferrate. The above materials can be used as a lithium supplement agent, and the lithium supplement agent can supplement lithium ions to the cathode film layer, make up for the irreversible lithium ion loss in the system, and improve the capacity, thereby improving the energy density of the battery cell.

[0189] Optionally, the ternary material includes Li x3 A y3 Ni a3 Co b3 Mn c M3 (1-a3-b3-c3) Y3 z3 where 0 < x 3 ≤ 2.1, 0 < y 3 ≤ 2.1, and 0.9 ≤ x 3 + y 3 ≤ 2.1, 0 ≤ a 3 ≤ 1, 0 ≤ b 3 ≤ 1, 0 ≤ c 3 ≤ 1, and 0.1 ≤ a 3 + b 3 + c 3 ≤ 1, 1.8 ≤ z 3≤3.5, A includes one or more of Na, K, and Mg, M3 includes one or more of B, Mg, Al, Si, P, S, Ca, Sc, Ti, V, Cr, Fe, Cu, Zn, Sr, Y, Zr, Nb, Mo, Cd, Sn, Sb, Te, Ba, Ta, W, Yb, La, and Ce, and Y3 includes one or more of O and F.

[0190] Exemplarily, the ternary material includes LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O 2 (NCM333), LiNi 0.5 Co 0.2 Mn 0.3 O 2 (NCM523), LiNi 0.6 Co 0.2 Mn 0.2 O 2 (NCM622), LiNi 0.8 Co 0.1 Mn 0.1 O 2 (NCM811), LiNi 0.80 Co 0.15 Al 0.05 O 2 at least one of them.

[0191] In some embodiments, the mass content of the lithium supplement in the positive electrode film layer is 0.5% to 5%, such as 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5% or the range composed of any two of the above values. When the mass content of the lithium supplement is within the above range, it can supplement lithium ions to the positive electrode film layer, make up for the irreversible lithium ion loss in the system, and improve the capacity, thereby improving the energy density of the battery cell.

[0192] The lithium supplement can be in the same layer as the positive electrode active material or in different layers. When the lithium supplement and the positive electrode active material are in different layers, the lithium supplement can be in the lithium supplement layer, and the positive electrode active material can be in the positive electrode active material layer. In other words, the positive electrode film layer includes a lithium supplement layer and a positive electrode active material layer. The positive electrode active material layer can be disposed on at least one side of the positive electrode current collector, and the lithium supplement layer can be located between the positive electrode active material layer and the positive electrode current collector. Or, the lithium supplement layer can be disposed on at least one side of the positive electrode current collector, and the positive electrode active material layer can be located between the lithium supplement layer and the positive electrode current collector. Optionally, the lithium supplement layer can be located between the positive electrode active material layer and the positive electrode current collector. During the charge and discharge cycling of the battery cell, the lithium supplement in the lithium supplement layer can be gradually released into the system to make up for the lithium loss in the battery system.

[0193] In some embodiments, the positive electrode film layer may further optionally include a positive electrode conductive agent. There is no particular limitation on the type of the positive electrode conductive agent in the embodiments of the present application. As an example, the positive electrode conductive agent includes at least one of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. In some embodiments, based on the mass of the positive electrode film layer, the mass content of the positive electrode conductive agent is ≤5%.

[0194] In some embodiments, the positive electrode film layer may further optionally include a positive electrode binder. There is no particular limitation on the type of the positive electrode binder in the embodiments of the present application. As an example, the positive electrode binder may include at least one of polyvinylidene fluoride, polytetrafluoroethylene, vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, polyacrylic acid, and fluorinated acrylate resins. In some embodiments, based on the mass of the positive electrode film layer, the mass content of the positive electrode binder is ≤5%.

[0195] In some embodiments, the positive electrode current collector may be a metal foil or a composite current collector. As an example of the metal foil, at least one foil of aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy may be used. The composite current collector may include a polymer material base layer and a metal material layer formed on at least one surface of the polymer material base layer. As an example, the metal material of the metal material layer may include at least one of aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy. As an example, the polymer material base layer may include at least one of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0196] In some embodiments, the ratio of the thickness of the positive electrode current collector to the thickness of the single-sided positive electrode film layer is 0.05 to 0.3. Exemplarily, the ratio of the thickness of the positive electrode current collector to the thickness of the single-sided positive electrode film layer is 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, 0.12, 0.15, 0.18, 0.2, 0.22, 0.25, 0.28, 0.3 or a range composed of any two of the above values.

[0197] When the ratio of the thickness of the positive electrode current collector to the thickness of the single-sided positive electrode film layer is within the above range, the fast charging ability and energy density of the battery cell can be improved.

[0198] In some embodiments, the thickness of the positive current collector is from 10 μm to 15 μm, optionally from 12 μm to 15 μm. Exemplarily, the thickness of the positive current collector is 10 μm, 10.5 μm, 11 μm, 11.5 μm, 12 μm, 12.5 μm, 13 μm, 13.5 μm, 14 μm, 14.5 μm, 15 μm or a range composed of any two of the above values.

[0199] When the thickness of the positive current collector is within the above range, the current-carrying capacity of the positive current collector is relatively excellent, and it can enable the battery cell to have a relatively high energy density.

[0200] In the embodiments of the present application, the thicknesses of the positive electrode film layer and the positive current collector have the meanings well-known in the art, and can be detected by using the equipment and methods well-known in the art. For example, a micrometer is used to measure the thickness of the positive electrode sheet, the film layer on the surface of the positive current collector is removed, and a micrometer is used to measure the thickness of the positive current collector. 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 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 current collector) / 2.

[0201] The positive electrode film layer is usually formed by coating a positive electrode slurry on a positive current collector and drying and cold pressing it. The positive electrode slurry is usually formed by dispersing a positive electrode active material, an optional conductive agent, an optional binder, and any other components in a solvent and stirring evenly. The solvent can be N-methylpyrrolidone (NMP), but is not limited thereto.

[0202] 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 disposed on the surface of the positive current collector and sandwiched between the positive current collector and the positive electrode film layer. In some 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.

[0203] In some embodiments, the positive electrode sheet further includes a positive electrode conductive layer, and the positive electrode conductive layer is located between the positive electrode film layer and the positive current collector. The positive electrode conductive layer can further improve the conductivity of the positive electrode sheet and reduce the heat generation of the positive electrode sheet, thereby reducing the heat generation amount of the battery cell.

[0204] In some embodiments, the thickness of the positive electrode conductive layer is from 0.5 μm to 2 μm. Exemplarily, the thickness of the positive electrode conductive layer can be 0.5 μm, 0.8 μm, 1 μm, 1.2 μm, 1.5 μm, 1.6 μm, 1.8 μm, 2 μm or a range composed of any two of the above values.

[0205] 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 increased while taking into account.

[0206] In the embodiments of the present application, the thickness of the positive electrode conductive layer has the meaning well known in the art and can be detected by using the equipment and methods well known in the art. For example, tomographic scanning is performed on the positive electrode sheet to directly measure the thickness of the positive electrode conductive layer.

[0207] In some embodiments, the positive electrode conductive layer includes one or more of a positive electrode conductive agent and a positive electrode binder.

[0208] Optionally, the mass content of the positive electrode conductive agent in the positive electrode conductive layer is 30% to 50%. Exemplarily, the mass content of the positive electrode conductive agent is 30%, 35%, 40%, 45%, 50% or a range composed of any two of the above values.

[0209] Exemplarily, the positive electrode conductive agent includes one or more of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. The positive electrode conductive agent in the positive electrode conductive layer can improve the conductivity of the positive electrode conductive layer, thereby improving the conductivity of the positive electrode sheet and reducing the heat generation amount of the battery cell.

[0210] Optionally, the mass content of the positive electrode binder in the positive electrode conductive layer is 50% to 70%. Exemplarily, 50%, 60%, 65%, 70% or a range composed of any two of the above values.

[0211] Exemplarily, the positive electrode binder includes one or more of polyvinylidene fluoride, polytetrafluoroethylene, vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, polyacrylic acid, and fluorinated acrylate resins. The positive electrode binder in the positive electrode conductive layer can improve the bonding performance between the positive electrode current collector and the positive electrode film layer and improve the structural stability of the positive electrode sheet.

[0212] [Negative electrode sheet] The negative electrode sheet includes a negative electrode current collector and a negative electrode film layer provided on at least one surface of the negative electrode current collector and including a negative electrode active material. For example, the negative electrode current collector has two surfaces opposite to each other in its own thickness direction, and the negative electrode film layer is provided on any one or both of the two opposite surfaces of the negative electrode current collector.

[0213] In some embodiments, when the battery cell is in a 100% charged state, the compaction density of the negative electrode film layer is 1.15 g / cm 3 to 1.36 g / cm 3 , and optionally 1.25 g / cm3 to 1.36 g / cm 3 。Exemplarily, the compaction density of the negative electrode film layer of the battery cell at 100% state of charge is 1.15 g / cm 3 , 1.18 g / cm 3 , 1.20 g / cm 3 , 1.22 g / cm 3 , 1.25 g / cm 3 , 1.28 g / cm 3 , 1.3 g / cm 3 , 1.32 g / cm 3 , 1.35 g / cm 3 , 1.36 g / cm 3 or a range composed of any two of the above values.

[0214] When the compaction density of the negative electrode film layer is within the above range, it is beneficial to improve the energy density of the battery cell, and since the negative electrode active material in the negative electrode film layer is stacked relatively tightly, the contact resistance between particles is small, which can further reduce the resistance of the electrode sheet, thereby reducing heat generation.

[0215] In the embodiments of the present application, the compaction density of the negative electrode film layer of the battery cell at 100% state of charge has the meaning well known in the art, and can be detected by using the equipment and methods well known in the art. The detection method is as described in the above-mentioned compaction density test method of the positive electrode film layer.

[0216] In some embodiments, the single-sided coating weight of the negative electrode film layer is 90 mg / 1540.25 mm 2 to 170 mg / 1540.25 mm 2 , and can be optionally 110 mg / 1540.25 mm 2 to 150 mg / 1540.25 mm 2 。Exemplarily, the single-sided coating weight of the negative electrode film layer is 90 mg / 1540.25 mm 2 , 92 mg / 1540.25 mm 2 , 95 mg / 1540.25 mm 2 , 96 mg / 1540.25 mm 2 , 100 mg / 1540.25 mm 2 , 102 mg / 1540.25 mm 2 , 104 mg / 1540.25 mm 2 , 105 mg / 1540.25 mm 2 , 108 mg / 1540.25 mm 2 , 110 mg / 1540.25 mm 2, 112 mg / 1540.25 mm 2 , 114 mg / 1540.25 mm 2 , 115 mg / 1540.25 mm 2 , 116 mg / 1540.25 mm 2 , 118 mg / 1540.25 mm 2 , 120 mg / 1540.25 mm 2 , 122 mg / 1540.25 mm 2 , 125 mg / 1540.25 mm 2 , 128 mg / 1540.25 mm 2 , 130 mg / 1540.25 mm 2 , 132 mg / 1540.25 mm 2 , 135 mg / 1540.25 mm 2 , 137 mg / 1540.25 mm 2 , 140 mg / 1540.25 mm 2 , 142 mg / 1540.25 mm 2 , 145 mg / 1540.25 mm 2 , 148 mg / 1540.25 mm 2 , 150 mg / 1540.25 mm 2 , 152 mg / 1540.25 mm 2 , 155 mg / 1540.25 mm 2 , 160 mg / 1540.25 mm 2 , 165 mg / 1540.25 mm 2 , 170 mg / 1540.25 mm 2 Or a range composed of any two of the above values.

[0217] When the single-sided coating weight of the negative electrode film layer is within the above range, the heat generation per unit area of the negative electrode plate will not be excessive, and it can also take into account the improvement of the energy density of the battery cell.

[0218] In the embodiments of the present application, the single-sided coating weight of the negative electrode film layer has the meaning well-known in the art, and can be detected by using the equipment and methods well-known in the art. The detection method is as described in the single-sided coating weight test method of the film layer above.

[0219] In some embodiments, the powder resistivity of the negative electrode active material is from 0.005 Ω·cm to 0.043 Ω·cm, and may be optionally 0.04 Ω·cm. Exemplarily, the powder resistivity of the negative electrode active material may be 0.043 Ω·cm, 0.04 Ω·cm, 0.035 Ω·cm, 0.03 Ω·cm, 0.025 Ω·cm, 0.02 Ω·cm, 0.015 Ω·cm, 0.01 Ω·cm, 0.005 Ω·cm or the range composed of any two of the above values.

[0220] The relatively low powder resistivity of the negative electrode active material results in a relatively low resistance of the negative electrode plate and less heat generation of the battery cell.

[0221] In the embodiments of the present application, the powder resistivity of the negative electrode active material has the meaning well-known in the art, and can be detected by the equipment and methods well-known in the art. The detection method is the same as the powder resistivity test method of the positive electrode active material described above.

[0222] In some embodiments, the powder compaction density of the negative electrode active material under a pressure of 20000 N is 1.5 g / cm 3 to 1.85 g / cm 3 and may be optionally 1.55 g / cm 3 to 1.65 g / cm 3 . Exemplarily, the powder compaction density of the negative electrode active material under a pressure of 20000 N is 1.5 g / cm 3 , 1.55 g / cm 3 , 1.6 g / cm 3 , 1.65 g / cm 3 , 1.7 g / cm 3 , 1.75 g / cm 3 , 1.8 g / cm 3 , 1.85 g / cm 3 or the range composed of any two of the above values.

[0223] When the powder compaction density of the negative electrode active material under 20000 N is within the above range, the energy density of the battery cell can be improved, and since the negative electrode active material in the negative electrode film layer can be stacked more closely, the contact resistance between particles is small, which can further reduce the resistance of the electrode plate and thus reduce heat generation.

[0224] In the embodiments of the present application, the powder compaction density of the material has the meaning well-known in the art, and can be detected by the methods and equipment well-known in the art, and is detected according to the test standard GB / T24533-2009. As an example, a certain amount of the negative electrode active material is taken as a sample and added to the bottom area of the UTM7305 type electronic pressure testing machine, which is 1.327 cm 2In the mold, it is pressurized to 2000 kg (equivalent to 20000 N), the pressure is maintained for 30 s, then the pressure is released, and it is kept for 10 s, and then the powder compaction density of the negative electrode active material under the action of 20000 N is recorded and calculated.

[0225] In some embodiments, the charging specific capacity of the negative electrode active material at a rate of 0.1 C is greater than or equal to 350 mAh / g, and can be optionally 350 mAh / g to 480 mAh / g. Exemplarily, the charging specific capacity of the negative electrode active material at a rate of 0.1 C is 350 mAh / g, 355 mAh / g, 360 mAh / g, 365 mAh / g, 370 mAh / g, 375 mAh / g, 380 mAh / g, 385 mAh / g, 390 mAh / g, 395 mAh / g, 400 mAh / g, 410 mAh / g, 420 mAh / g, 430 mAh / g, 440 mAh / g, 450 mAh / g, 460 mAh / g, 470 mAh / g, 480 mAh / g or the range composed of any two of the above values.

[0226] When the charging specific capacity of the negative electrode active material at a rate of 0.1 C is within the above range, the energy density of the battery cell is relatively high.

[0227] In the embodiments of the present application, the charging specific capacity of the negative electrode active material at a rate of 0.1 C has the meaning well-known in the art, and can be detected by using the equipment and methods well-known in the art. Its detection method is the same as the charging specific capacity test method of the positive electrode active material at a rate of 0.1 C described above.

[0228] In some embodiments, the negative electrode active material includes a carbon-based material. The carbon-based material has relatively high cycle stability and can improve the cycle performance of the battery cell. Optionally, the mass ratio of the carbon-based material in the negative electrode active material can be greater than or equal to 80% and less than or equal to 100%.

[0229] The positive electrode active material of the present application is mainly a lithium-containing phosphate system with an olivine structure, and the negative electrode active material is mainly a carbon-based material system. When the two are used in combination, the cycle performance of the battery cell is relatively excellent.

[0230] Optionally, the carbon-based material includes graphite particles, and the graphitization degree of the graphite particles is 92.0% to 94.5%. Exemplarily, the graphitization degree of the graphite particles is 92.0%, 92.5%, 93%, 93.5%, 94%, 94.5% or the range composed of any two of the above values.

[0231] 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 plate and the heat generation of the battery cell; and can improve the fast charging performance of the battery cell.

[0232] In some embodiments, the graphite particles include artificial graphite and a carbon coating layer. The artificial graphite includes secondary particles, and the secondary particles include a plurality of primary particles. The plurality of primary particles aggregate to form secondary particles, and the carbon coating layer coats the surface of the artificial graphite. Amorphous carbon refers to a transitional carbon material with a very low degree of graphitization crystallization, approximately an amorphous form (or without a fixed shape and periodic structural rules). In the present application, amorphous carbon refers to the product after carbonization treatment of an organic carbon source.

[0233] The artificial graphite includes secondary particles. In the artificial graphite, there are more migration paths for lithium ions, and the migration path in the primary particles is shorter, which can improve the migration rate of lithium ions. The carbon coating layer has more end faces and defects, so that the number of sites where lithium ions can be deintercalated is more, and the conductivity of the carbon coating layer is relatively excellent, which can reduce the internal resistance of the negative electrode sheet and reduce the heat generation of the battery cell.

[0234] Optionally, based on the mass of the graphite particles, the mass content of the carbon coating layer is 2% to 5%. Exemplarily, the mass content of the carbon coating layer is 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5% or the range composed of any two of the above values.

[0235] When the mass content of the carbon coating layer is within the above range, the internal resistance of the negative electrode sheet can be further reduced, and the heat generation of the battery cell can be reduced.

[0236] In the embodiments of the present application, the graphite particles can be prepared by methods well known in the art. For example, the preparation method includes: providing artificial graphite and an organic carbon source, mixing the two, and after carbonization treatment, forming a carbon coating layer on at least part of the surface of the artificial graphite particles.

[0237] Optionally, the organic carbon source includes one or more of coal tar pitch, petroleum pitch, phenolic resin, and coconut shell. Further optionally, the organic carbon source includes petroleum pitch. Optionally, the softening point of the coal tar pitch and petroleum pitch is below 250 °C.

[0238] Optionally, the carbonization treatment temperature is 700 °C to 1800 °C. Optionally, the carbonization treatment temperature is 1000 °C to 1300 °C. When the carbonization treatment temperature is within a suitable range, the organic carbon source can be carbonized, and a coating layer containing amorphous carbon can be formed on at least part of the surface of the artificial graphite.

[0239] Optionally, the carbonization treatment time is 1 h to 6 h.

[0240] In the embodiments of the present application, the morphology and mass content of amorphous carbon have meanings well-known in the art, and can be detected by devices and methods well-known in the art. For example, the confirmation of the amorphous carbon layer can be obtained by using conventional methods for testing the crystallization form of carbon substances in the art. For example, Raman spectroscopy can be used for testing and analysis. The formation of the amorphous carbon layer can be analyzed based on the characteristic peak information of the carbon component in the spectrum (such as the intensity ratio of the D peak to the G peak, I D / G ). Among them, both the D peak and the G peak are Raman characteristic peaks of the carbon atom crystal. The D peak represents the defects of the carbon atom crystal. The more defects, the greater the intensity of the D peak. The intensity of the D peak can reflect the content of the amorphous (disordered stacking) region. The G peak represents the in-plane stretching vibration of the sp2 hybridization of carbon atoms. The intensity of the G peak can reflect the content of the graphitized (layered structure) region. As the degree of disorder of carbon atoms increases, the intensity ratio of the D peak to the G peak also increases. It can be determined whether an amorphous carbon layer is formed based on whether the I D / G (intensity ratio of the D peak to the G peak) of the surface composition of the particles before and after coating constitutes a statistically significant change (such as p < 0.05, p < 0.01, etc.), that is, based on the deviation degree of the layer structure introduced after coating from the I D / G before coating. This is easy for those skilled in the art to judge. It is also possible to compare the Raman spectrum I D / G of a specific structural layer of the particle to be tested with the standard Raman spectrum I D / G of graphite to determine whether it is an amorphous carbon layer.

[0241] The graphitization degree of graphite particles can be detected by using the detection method for the graphitization degree of the cathode active material.

[0242] In the embodiments of the present application, regarding the mass ratio of the "amorphous carbon layer" in graphite particles, it can be obtained by combining TEM (transmission electron microscopy) morphology observation and data analysis. The negative electrode sheet is cut, and powder samples are scraped from the cross-section for TEM testing. By comparing graphite particles with and without an amorphous carbon layer coating, an obvious interface can be observed on the surface of the graphite particles coated with an amorphous carbon layer. Thus, the thickness of the amorphous carbon layer at this position can be estimated from the TEM photo. Analysis can be carried out at multiple different cross-section positions, and the average value is taken as the thickness of the amorphous carbon layer. Assuming that the graphite particles are spherical, based on the thickness of the amorphous carbon layer and the particle size statistical data of the graphite particles, the volume ratio of the amorphous carbon layer in the carbon-based particles can be estimated according to the volume of the carbon-based particles and the volume of the carbon-based core. Further, based on the average mass of a single graphite particle, the volume of artificial graphite (which can be deduced or can also be statistically obtained from the TEM test photo) and the density of artificial graphite, the mass content of the amorphous carbon layer in the graphite particles can be estimated.

[0243] 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.

[0244] In some embodiments, the negative electrode active material may further include a silicon-based material. The introduction of the silicon-based material can improve the capacity of the negative electrode active material and increase the energy density of the battery cell.

[0245] Optionally, based on the mass of the negative electrode active material, the mass content of silicon element in the silicon-based material is 0.3% to 10.0%, optionally 1% to 6%. Exemplarily, the mass content of silicon element in the silicon-based material is 0.3%, 0.5%, 0.8%, 1%, 1.2%, 1.5%, 1.8%, 2%, 2.2%, 2.5%, 2.8%, 3%, 3.2%, 3.5%, 3.8%, 4%, 4.2%, 4.5%, 4.8%, 5%, 5.2%, 5.5%, 5.8%, 6%, 6.2%, 6.5%, 6.8%, 7%, 7.2%, 7.5%, 7.8%, 8%, 8.2%, 8.5%, 8.8%, 9%, 9.2%, 9.5%, 9.8%, 10% or any range composed of any two of the above values.

[0246] When the mass content of silicon element in the silicon-based material is within the above range, it can improve the capacity of the negative electrode active material and make the cycle stability of the negative electrode active material better, thereby improving the energy density and cycle performance of the battery cell.

[0247] Optionally, the silicon-based material may include at least one of elemental silicon, silicon oxide, silicon-carbon composite, silicon-nitrogen composite, and silicon alloy material.

[0248] In some embodiments, in addition to the above-mentioned carbon-based material and optionally the silicon-based material, the negative electrode active material may further include at least one of a tin-based material and lithium titanate. The tin-based material may include at least one of elemental tin, tin oxide, and tin alloy material.

[0249] In this application, the qualitative and quantitative determination of each substance or each element can be performed using suitable equipment and methods known to those skilled in the art. Relevant detection methods can refer to domestic and foreign detection standards, domestic and foreign enterprise standards, etc. And those skilled in the art can also adaptively change certain detection steps / instrument parameters, etc. from the perspective of detection accuracy to obtain more accurate detection results. One detection method can be used for qualitative or quantitative determination, or several detection methods can be used in combination for qualitative or quantitative determination.

[0250] For example, the carbon-based material in the present application can be used to perform X-ray powder diffraction testing and qualitative analysis on the negative electrode sheet or the negative electrode active material in combination with the General Rules for X-ray Diffraction Analysis of JIS / K0131-1996.

[0251] Artificial graphite and natural graphite can be distinguished by the SEM cross-sectional view taken by scanning electron microscopy (SEM). In the SEM cross-sectional view of natural graphite, there are voids between flake structures, while the SEM cross-sectional view of artificial graphite is dense and seamless; or they can be distinguished by the XRD pattern obtained by X-ray diffraction method (XRD). In the XRD pattern of natural graphite, obvious 2H phase and 3R phase exist, while only 2H phase exists in the XRD pattern of artificial graphite.

[0252] In the embodiments of the present application, the negative electrode film layer includes at least one layer of film layer, which can be a single-layer film layer or at least two layers of film layers. Optionally, the negative electrode film layer includes at least two layers of film layers.

[0253] When the negative electrode film layer is a single-layer film layer, the negative electrode active material in the negative electrode film layer includes a carbon-based material, and optionally also includes a silicon-based material. When a single-layer film layer is used, the volume average particle size Dv50 of the negative electrode active material is 8.2 μm to 13.5 μm. Exemplarily, the volume average particle size Dv50 of the negative electrode active material is 8.2 μm, 8.5 μm, 8.8 μm, 9 μm, 9.2 μm, 9.5 μm, 9.8 μm, 10 μm, 10.2 μm, 10.5 μm, 10.8 μm, 11 μm, 11.2 μm, 11.5 μm, 11.8 μm, 12 μm, 12.2 μm, 12.5 μm, 12.8 μm, 13 μm, 13.2 μm, 13.5 μm or the range composed of any two of the above values.

[0254] When the negative electrode film layer is at least two layers of film layers, the negative electrode active material in the negative electrode film layer includes a carbon-based material, and optionally also includes a silicon-based material. The silicon-based material can be located in one of the at least two layers of film layers or in at least two of the at least two layers of film layers. The negative electrode film layer can include two layers of film layers, three layers of film layers, four layers of film layers, or even more layers of film layers.

[0255] In some embodiments, the negative electrode film layer includes a first negative electrode film layer and a second negative electrode film layer. The first negative electrode film layer is disposed on the surface of the negative electrode current collector, and the carbon-based material in the first negative electrode film layer includes graphite particles. The second negative electrode film layer is connected to the side of the first negative electrode film layer facing away from the negative electrode current collector, and the carbon-based material in the second negative electrode film layer includes graphite particles.

[0256] The interface between the first negative electrode film layer and the second negative electrode film layer can be regular or irregular; optionally, it is irregular.

[0257] Optionally, the carbon-based material in the first negative electrode film layer further includes natural graphite.

[0258] The negative electrode film layer includes at least two film layers, and layer-by-layer coating is beneficial to improving the fast charging performance of the battery cell. Especially when there are differences between the first negative electrode film layer and the second negative electrode film layer, the pore differences of the negative electrode film layer can be constructed, the tortuosity of lithium ion transmission can be reduced, and the fast charging performance of the battery cell can be improved.

[0259] Optionally, the volume average particle size Dv50 of the negative electrode active material in the first negative electrode film layer is greater than or equal to the volume average particle size Dv50 of the negative electrode active material in the second negative electrode film layer. Further optionally, the volume average particle size Dv50 of the negative electrode active material in the first negative electrode film layer is greater than the volume average particle size Dv50 of the negative electrode active material in the second negative electrode film layer, which is beneficial to improving the compaction density of the negative electrode film layer. When the negative electrode active material includes graphite particles, the volume average particle size Dv50 of the graphite particles in the first negative electrode film layer is greater than or equal to the volume average particle size Dv50 of the graphite particles in the second negative electrode film layer.

[0260] The difference in particle sizes between the first negative electrode film layer and the second negative electrode film layer can improve the fast charging performance of the battery cell; specifically, during fast charging, the overpotential of the second negative electrode film layer is usually higher, and the bottleneck of fast charging lies mainly in the second negative electrode film layer. In the embodiments of the present application, the particle size in the second negative electrode film layer is relatively small, which can shorten the solid-phase transmission path of lithium ions, improve the fast charging performance, and can improve the problem of lithium deposition on the surface layer of the negative electrode plate.

[0261] Optionally, the negative electrode active material in the first negative electrode film layer is granular, and its volume average particle size Dv50 is 9.5 μm to 18.5 μm, and can be 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 the range composed of any two of the above values. When the first negative electrode film layer includes graphite particles, the volume average particle size Dv50 of the graphite particles in the first negative electrode film layer is 9.5 μm to 18.5 μm, and can be 9.5 μm to 14.6 μm.

[0262] When the volume average particle size Dv50 of the negative electrode active material in the first negative electrode film layer is within the above range, on the one hand, it can shorten the solid-phase transmission path of lithium ions and improve the fast charging performance; on the other hand, the material is not prone to agglomeration during the preparation process, which can improve the stability of the material.

[0263] Optionally, the negative active material in the second negative electrode film layer is granular, and its volume average particle size Dv50 is from 7.8 μm to 14.3 μm, optionally from 7.8 μm to 11.3 μm. Exemplarily, the volume average particle size Dv50 of the negative active material is 7.8 μm, 8.0 μm, 8.2 μm, 8.5 μm, 8.8 μm, 9 μm, 9.2 μm, 9.5 μm, 9.8 μm, 10 μm, 10.2 μm, 10.5 μm, 10.8 μm, 11 μm, 11.3 μm, 11.2 μm, 11.5 μm, 11.8 μm, 12 μm, 12.2 μm, 12.5 μm, 12.8 μm, 13 μm, 13.2 μm, 13.5 μm, 13.8 μm, 14 μm, 14.1 μm, 14.3 μm or a range composed of any two of the above values. When the second negative electrode film layer includes graphite particles, the volume average particle size Dv50 of the graphite particles in the second negative electrode film layer is from 7.8 μm to 14.3 μm, optionally from 7.8 μm to 11.3 μm.

[0264] When the volume average particle size Dv50 of the negative active material in the second negative electrode film layer is within the above range, on the one hand, it can shorten the solid-phase transmission path of lithium ions and improve the fast charging performance; on the other hand, the material is not easily agglomerated during the preparation process, which can improve the stability of the material; on the other hand, the negative active material in the second negative electrode film layer with the above volume average particle size range cooperates with the negative active material in the first negative electrode film layer, which is beneficial to constructing the gradient pore difference between the second negative electrode film layer and the first negative electrode film layer, reducing the tortuosity of lithium ion transmission, and improving the fast charging performance of the battery cell.

[0265] In the embodiments of the present application, the volume average particle size Dv50 of the negative active material has the meaning well known in the art, and can be detected by the equipment and methods well known in the art. Its detection method is the same as the test method for the volume average particle size Dv50 of the positive active material described above.

[0266] Optionally, the tapped density of the carbon-based material in the first negative electrode film layer is less than or equal to the tapped density of the carbon-based material in the second negative electrode film layer. The tapped density can reflect the packing density of the active material in the film layer. When the tapped density of the carbon-based material in the second negative electrode film layer is greater than the tapped density of the carbon-based material in the first negative electrode film layer, the second negative electrode film layer is more densely packed, resulting in an increase in the energy density of the battery cell; the packing of the first negative electrode film layer is relatively sparse and the pores are more abundant, which can improve the fast charging performance of the battery cell. When the negative active material includes graphite particles, the tapped density of the graphite particles in the first negative electrode film layer is less than or equal to the tapped density of the graphite particles in the second negative electrode film layer.

[0267] Optionally, the tapped density of the carbon-based material in the first negative electrode film layer is 0.82 g / cm 3 to 1.21 g / cm3 , such as 0.82 g / cm 3 , 0.85 g / cm 3 , 0.88 g / cm 3 , 0.90 g / cm 3 , 0.92 g / cm 3 , 0.95 g / cm 3 , 0.98 g / cm 3 , 1.00 g / cm 3 , 1.05 g / cm 3 , 1.08 g / cm 3 , 1.10 g / cm 3 , 1.12 g / cm 3 , 1.15 g / cm 3 , 1.18 g / cm 3 , 1.20 g / cm 3 , 1.21 g / cm 3 or a range composed of any two of the above values. When the tap density of the carbon-based material in the first negative electrode film layer is within a suitable range, the fast charging performance of the battery cell can be improved.

[0268] Optionally, the tap density of the carbon-based material in the second negative electrode film layer is 0.90 g / cm 3 to 1.25 g / cm 3 , such as 0.90 g / cm 3 , 0.92 g / cm 3 , 0.95 g / cm 3 , 0.98 g / cm 3 , 1.00 g / cm 3 , 1.05 g / cm 3 , 1.08 g / cm 3 , 1.10 g / cm 3 , 1.12 g / cm 3 , 1.15 g / cm 3 , 1.18 g / cm 3 , 1.20 g / cm 3 , 1.21 g / cm 3 , 1.22 g / cm 3 , 1.23 g / cm 3 , 1.24 g / cm 3 , 1.25 g / cm 3 or a range composed of any two of the above values. When the tap density of the carbon-based material in the second negative electrode film layer is within a suitable range, the energy density of the battery cell can be improved.

[0269] In the embodiments of the present application, the tapped density of the material has the meaning well-known in the art and can be measured by instruments and methods known in the art. For example, reference can be made to GB / T5162-2006 and a powder tapped density tester can be used for measurement. The test instrument can be BT-301 produced by Dandong BETOP.

[0270] Optionally, the ratio of the thickness of the second negative electrode film layer to the thickness of the first negative electrode film layer is from 3:7 to 7:3, and can be optionally from 4:6 to 5:5. Exemplarily, the ratio of the thickness of the second negative electrode film layer to the thickness of the first negative electrode film layer is 3:7, 4:6, 5:5, 6:4, 7:3 or a range composed of any two of the above values. By adjusting the thickness ratio of the first negative electrode film layer and the second negative electrode film layer, the gradient pore difference between the upper and lower layers can be further increased, the tortuosity of lithium ion transport can be reduced, and the fast charging ability of the battery cell can be improved.

[0271] In some embodiments, after the battery cell has undergone 10 full charge test cycles at the beginning of life (BOL), the thickness of the first negative electrode film layer is from 15 μm to 65 μm, such as 15 μm, 17 μm, 18 μm, 20 μm, 25 μm, 30 μm, 35 μm, 40 μm, 45 μm, 50 μm, 55 μm, 57 μm, 58 μm, 60 μm, 61 μm, 62 μm, 63 μm, 64 μm, 65 μm or a range composed of any two of the above values. When the thickness of the first negative electrode film layer is within the above range, the first negative electrode film layer and the second negative electrode film layer can regulate and increase the gradient pore difference between the upper and lower layers, reduce the tortuosity of lithium ion transport, and improve the fast charging ability of the battery cell.

[0272] In some embodiments, after the battery cell has undergone 10 full charge test cycles at the beginning of life (BOL), the thickness of the second negative electrode film layer is from 15 μm to 65 μm, such as 15 μm, 17 μm, 18 μm, 20 μm, 25 μm, 30 μm, 35 μm, 40 μm, 45 μm, 50 μm, 55 μm, 57 μm, 58 μm, 60 μm, 61 μm, 62 μm, 63 μm, 64 μm, 65 μm or a range composed of any two of the above values. When the thickness of the second negative electrode film layer is within the above range, the first negative electrode film layer and the second negative electrode film layer can regulate and increase the gradient pore difference between the upper and lower layers, reduce the tortuosity of lithium ion transport, and improve the fast charging ability of the battery cell.

[0273] In the embodiments of the present application, for example, taking the charging upper limit voltage of the battery cell as 3.65 V and the discharge cut-off voltage of the battery cell as 2.0 V as an example for illustration, The BOL full charge test steps are as follows: At 25°C, charge at a charging rate of 0.33C of the battery nominal capacity until 3.65V, then perform constant voltage charging at 3.65V until 0.05C, let it stand for 10 minutes, then discharge at a discharge rate of 0.33C until 2.0V, and let it stand for 10 minutes. The above one charge and discharge cycle is one cycle, repeat 10 cycles, and then charge at a charging rate of 0.33C of the nominal capacity until 3.65V, and then perform constant voltage charging at 3.65V until 0.05C to reach the BOL full charge state. In the BOL full charge state, disassemble the negative electrode sheet, use a tomography electron microscope to observe the cross-section in the thickness direction of the middle area of the negative electrode sheet, distinguish the areas of the first negative electrode film layer and the second negative electrode film layer according to the interface between them, and measure their thicknesses respectively. For example, measure the thicknesses at 10 positions of the first negative electrode film layer, and calculate their average value as the average value of the first negative electrode film layer; measure the thicknesses at 10 positions of the second negative electrode film layer, and calculate their average value as the average value of the second negative electrode film layer.

[0274] In some embodiments, after the battery cell undergoes the End Of Life (EOL) full charge test, the thickness of the first negative electrode film layer is 15μm to 70μm, such as 15μm, 16μm, 17μm, 18μm, 19μm, 20μm, 21μm, 22μm, 23μm, 24μm, 25μm, 26μm, 27μm, 28μm, 29μm, 30μm, 35μm, 40μm, 43μm, 45μm, 50μm, 55μm, 60μm, 65μm, 66μm, 67μm, 68μm, 69μm, 70μm or the range composed of any two of the above values. When the thickness of the first negative electrode film layer is within the above range, the first negative electrode film layer and the second negative electrode film layer can regulate and increase the gradient pore difference between the upper and lower layers, reduce the tortuosity of lithium ion transmission, and improve the fast charging ability of the battery cell.

[0275] In some embodiments, after the battery cell undergoes the End Of Life (EOL) full charge test, the thickness of the second negative electrode film layer is 15μm to 70μm, such as 15μm, 16μm, 17μm, 18μm, 19μm, 20μm, 21μm, 22μm, 23μm, 24μm, 25μm, 26μm, 27μm, 28μm, 29μm, 30μm, 35μm, 40μm, 43μm, 45μm, 50μm, 55μm, 60μm, 65μm, 66μm, 67μm, 68μm, 69μm, 70μm or the range composed of any two of the above values. When the thickness of the second negative electrode film layer is within the above range, the first negative electrode film layer and the second negative electrode film layer can regulate and increase the gradient pore difference between the upper and lower layers, reduce the tortuosity of lithium ion transmission, and improve the fast charging ability of the battery cell.

[0276] In an embodiment of the present application, for example, taking the charge upper limit voltage of the battery cell as 3.65V and the discharge cut-off voltage of the battery cell as 2.0V as an example for illustration, The specific steps of the EOL full charge test are as follows: At 60°C, charge at a charging rate of 0.33C of the battery nominal capacity to 3.65V, then charge at a constant voltage of 3.65V to 0.05C, let it stand for 10 minutes, then discharge at a discharge rate of 0.33C to 2.0V, and let it stand for 10 minutes. The above one charge and discharge cycle is repeated until the battery capacity decays to 80% of the nominal capacity and the test stops. Then at 25°C, charge at a constant current of 0.33C to 3.65V, and charge at a constant voltage of 0.05C to 3.65V, which is the EOL full charge state. In the EOL full charge state, disassemble the negative electrode sheet, use a tomography scanning electron microscope to observe the cross-section in the thickness direction of the middle area of the negative electrode sheet, distinguish the regions of the first negative electrode film layer and the second negative electrode film layer according to the interface between them, measure their thicknesses respectively. For example, measure the thicknesses at 10 positions of the first negative electrode film layer, and calculate their average value as the average value of the first negative electrode film layer; measure the thicknesses at 10 positions of the second negative electrode film layer, and calculate their average value as the average value of the second negative electrode film layer.

[0277] In some embodiments, when the negative electrode film layer adopts a single-layer film layer, the negative electrode film layer further includes a lithium-containing binder. Optionally, the mass content of the lithium-containing binder relative to the mass of the negative electrode film layer is 0.1% to 1%. Exemplarily, the mass content of the lithium-containing binder relative to the mass of the negative electrode film layer is 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1% or a range composed of any two of the above values. The lithium element in the lithium-containing binder can exist in ionic form, which can increase the number of free-moving lithium ions in the negative electrode film layer, shorten the distance for lithium ions to diffuse to the surface of the negative electrode film layer, improve the intercalation and deintercalation rate of lithium ions, and improve the fast charging performance of the battery cell. Optionally, the negative electrode film layer can further include a negative electrode binder. For example, the negative electrode binder includes at least one of styrene-butadiene rubber (SBR), water-soluble unsaturated resin SR-1B, water-based acrylic resin (such as polyacrylic acid PAA, polymethacrylic acid PMAA, sodium polyacrylate PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), and carboxymethyl chitosan (CMCS).

[0278] Optionally, the mass content of lithium element in the lithium-containing binder is 3% to 10%. Exemplarily, the mass content of lithium element in the lithium-containing binder is 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10% or the range composed of any two of the above values. The mass content of lithium element is calculated based on the mass of the lithium-containing binder. When the mass content of lithium element is within the above range, the number of free-moving lithium ions in the negative electrode film layer can be relatively large, which can further shorten the distance for lithium ions to diffuse to the surface of the negative electrode film layer, improve the intercalation and deintercalation rate of lithium ions, and improve the fast charging performance of the battery cell.

[0279] Exemplarily, the lithium-containing binder includes a lithium acrylate-acrylonitrile-acrylamide-2-hydroxyethyl acrylate copolymer, and the lithium acrylate-acrylonitrile-acrylamide-2-hydroxyethyl acrylate copolymer is derived from a lithium acrylate monomer, an acrylonitrile monomer, an acrylamide monomer, and a 2-hydroxyethyl acrylate monomer. The molar ratio of the lithium acrylate monomer, the acrylonitrile monomer, the acrylamide monomer, and the 2-hydroxyethyl acrylate monomer is 30% to 50%: 15% to 45%: 5% to 20%: 20% to 35%. For example, the molar ratio of the lithium acrylate monomer, the acrylonitrile monomer, the acrylamide monomer, and the 2-hydroxyethyl acrylate monomer is 35%: 30%: 15%: 20%, or 40%, 20%, 10%, 30%, or 45%, 15%, 20%, 20%, etc.

[0280] The lithium-containing binder of the above materials can provide a certain number of lithium ions for the negative electrode film layer, improving the fast charging performance of the battery cell; and it is not easy to swell during the charge and discharge process, with a stable structure, so that the cycle performance of the negative electrode film layer is improved during the fast charge and discharge process.

[0281] In some other embodiments, when the negative electrode film layer adopts at least two layers of film layers, the negative electrode film layer further includes a lithium-containing binder.

[0282] Optionally, the first negative electrode film layer further includes a first lithium-containing binder, and the second negative electrode film layer further includes a second lithium-containing binder. The mass content of the first lithium-containing binder relative to the mass of the first negative electrode film layer is less than or equal to the mass content of the second lithium-containing binder relative to the mass of the second negative electrode film layer. Further optionally, the mass content of the first lithium-containing binder relative to the mass of the first negative electrode film layer is less than the mass content of the second lithium-containing binder relative to the mass of the second negative electrode film layer.

[0283] The mass content of the second lithium-containing binder in the second negative electrode film layer is relatively high, and the number of free-moving lithium ions provided by the second lithium-containing binder for the second negative electrode film layer is relatively more, which can further improve the fast charging performance of the battery cell.

[0284] Optionally, the mass content of the first lithium-containing binder relative to the mass of the first negative electrode film layer is 0.1% to 1%. Exemplarily, the mass content of the first lithium-containing binder relative to the mass of the first negative electrode film layer is 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1% or a range composed of any two of the above values. The lithium element in the first lithium-containing binder can exist in ionic form, which can increase the number of free-moving lithium ions in the negative electrode film layer, shorten the distance for lithium ions to diffuse to the surface of the negative electrode film layer, increase the intercalation and deintercalation rate of lithium ions, and improve the fast charging performance of the battery cell.

[0285] Optionally, the mass content of lithium element in the first lithium-containing binder is 3% to 10%, and can be optionally 3% to 8%. Exemplarily, the mass content of lithium element in the first lithium-containing binder is 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10% or a range composed of any two of the above values. When the mass content of lithium element is within the above range, the number of free-moving lithium ions in the negative electrode film layer can be relatively large, which can further shorten the distance for lithium ions to diffuse to the surface of the negative electrode film layer, increase the intercalation and deintercalation rate of lithium ions, and improve the fast charging performance of the battery cell.

[0286] Exemplarily, the first lithium-containing binder includes a lithium acrylate-acrylonitrile-acrylamide-2-hydroxyethyl acrylate copolymer, and the lithium acrylate-acrylonitrile-acrylamide-2-hydroxyethyl acrylate copolymer is derived from lithium acrylate monomer, acrylonitrile monomer, acrylamide monomer and 2-hydroxyethyl acrylate monomer. The molar ratio of lithium acrylate monomer, acrylonitrile monomer, acrylamide monomer and 2-hydroxyethyl acrylate monomer is 30% to 50%: 15% to 45%: 5% to 20%: 20% to 35%. For example, the molar ratio of lithium acrylate monomer, acrylonitrile monomer, acrylamide monomer and 2-hydroxyethyl acrylate monomer is 35%: 30%: 15%: 20%, or 40%, 20%, 10%, 30%, or 45%, 15%, 20%, 20%, etc.

[0287] The lithium-containing binder of the above materials can provide a certain number of lithium ions for the negative electrode film layer, improving the fast charging performance of the battery cell; and it is not prone to swelling during charge and discharge, with a stable structure, so that the cycle performance of the negative electrode film layer is improved during fast charge and discharge.

[0288] Optionally, the mass content of the second lithium-containing binder relative to the mass of the second negative electrode film layer is 0.1% to 1%. Exemplarily, the mass content of the second lithium-containing binder relative to the mass of the second negative electrode film layer is 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1% or a range composed of any two of the above values. The lithium element in the second lithium-containing binder can exist in an ionic form, which can increase the number of free-moving lithium ions in the negative electrode film layer, shorten the distance for lithium ions to diffuse to the surface of the negative electrode film layer, increase the intercalation and deintercalation rate of lithium ions, and improve the fast charging performance of the battery cell.

[0289] The first lithium-containing binder and the second lithium-containing binder can be made of the same material or different materials.

[0290] Optionally, the mass content of lithium element in the second lithium-containing binder is 3% to 10%, and can be optionally 3% to 8%. Exemplarily, the mass content of lithium element in the second lithium-containing binder is 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10% or a range composed of any two of the above values. When the mass content of lithium element is within the above range, the number of free-moving lithium ions in the negative electrode film layer can be relatively large, which can further shorten the distance for lithium ions to diffuse to the surface of the negative electrode film layer, increase the intercalation and deintercalation rate of lithium ions, and improve the fast charging performance of the battery cell.

[0291] Exemplarily, the second lithium-containing binder includes a lithium acrylate-acrylonitrile-acrylamide-2-hydroxyethyl acrylate copolymer, and the lithium acrylate-acrylonitrile-acrylamide-2-hydroxyethyl acrylate copolymer is derived from a lithium acrylate monomer, an acrylonitrile monomer, an acrylamide monomer, and a 2-hydroxyethyl acrylate monomer. The molar ratio of the lithium acrylate monomer, the acrylonitrile monomer, the acrylamide monomer, and the 2-hydroxyethyl acrylate monomer is 30% to 50%: 15% to 45%: 5% to 20%: 20% to 35%. For example, the molar ratio of the lithium acrylate monomer, the acrylonitrile monomer, the acrylamide monomer, and the 2-hydroxyethyl acrylate monomer is 35%: 30%: 15%: 20%, or 40%, 20%, 10%, 30%, or 45%, 15%, 20%, 20%, etc.

[0292] The lithium-containing binder of the above material can provide a certain number of lithium ions for the negative electrode film layer, improving the fast charging performance of the battery cell; and it is not prone to swelling during the charge and discharge process, with a stable structure, so that the cycling performance of the negative electrode film layer is improved during the fast charge and discharge process.

[0293] In some embodiments, the first negative electrode film layer further includes a negative electrode binder, and the second negative electrode film layer further includes a negative electrode binder. The negative electrode binder in the first negative electrode film layer and the negative electrode binder in the second negative electrode film layer independently include at least one of styrene-butadiene rubber (SBR), water-soluble unsaturated resin SR-1B, water-based acrylic resin (e.g., polyacrylic acid PAA, polymethacrylic acid PMAA, sodium polyacrylate PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), and carboxymethyl chitosan (CMCS).

[0294] 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.

[0295] In some embodiments, the negative electrode film layer may further optionally include a negative electrode conductive agent. There is no particular limitation on the type of the negative electrode conductive agent in the embodiments of the present application. As an example, the negative electrode conductive agent may include at least one of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. In some embodiments, based on the total weight of the negative electrode film layer, the mass content of the negative electrode conductive agent is ≤5%.

[0296] In some embodiments, the negative electrode film layer may further optionally include a negative electrode binder. There is no particular limitation on the type of the negative electrode binder in the embodiments of the present application. As an example, the negative electrode binder may include at least one of styrene-butadiene rubber (SBR), water-soluble unsaturated resin SR-1B, water-based acrylic resin (e.g., polyacrylic acid PAA, polymethacrylic acid PMAA, sodium polyacrylate PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), and carboxymethyl chitosan (CMCS). In some embodiments, based on the total weight of the negative electrode film layer, the mass content of the negative electrode binder is ≤5%.

[0297] In some embodiments, the negative electrode film layer may further optionally include other additives. As an example, the other additives may include thickeners, dispersants, etc., such as sodium carboxymethyl cellulose (CMC-Na), PTC thermistor materials, etc. In some embodiments, based on the total weight of the negative electrode film layer, the mass content of the other additives is ≤2%.

[0298] In some embodiments, the negative electrode current collector can be a metal foil or a composite current collector. As an example of the metal foil, at least one foil of copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy can be used. The composite current collector can include a polymer material base layer and a metal material layer formed on at least one surface of the polymer material base layer. As an example, the metal material in the metal material layer can include at least one of copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy. As an example, the polymer material base layer can include at least one of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0299] In some embodiments, the thickness of the negative electrode current collector is 4 μm to 6 μm. Exemplarily, the thickness of the negative electrode current collector is 4 μm, 4.5 μm, 5 μm, 5.5 μm, 6 μm, or a range composed of any two of the above values.

[0300] When the thickness of the negative electrode current collector is within the above range, the current-carrying capacity of the negative electrode current collector is relatively excellent, and the battery cell can have a relatively high energy density.

[0301] In the embodiments of the present application, the thickness of the negative electrode current collector has the meaning well-known in the art, and can be detected by using equipment and methods well-known in the art. For example, the film layer on the surface of the negative electrode current collector is washed away with an organic solvent such as water, and the thickness of the positive electrode current collector is measured with a micrometer.

[0302] The negative electrode film layer is usually formed by coating a negative electrode slurry on the negative electrode current collector and then drying and cold pressing. The negative electrode slurry is usually formed by dispersing a negative electrode active material, an optional conductive agent, an optional binder, and other optional additives in a solvent and stirring evenly. The solvent can be N-methylpyrrolidone (NMP) or deionized water, but is not limited thereto.

[0303] The negative electrode plate does not exclude other additional functional layers in addition to the negative electrode film layer. For example, in some embodiments, the negative electrode plate of the embodiments of the present application further includes a negative electrode conductive layer disposed on the surface of the negative electrode current collector and sandwiched between the negative electrode current collector and the negative electrode film layer. In some other embodiments, the negative electrode plate of the embodiments of the present application further includes a protective layer covering the surface of the negative electrode film layer.

[0304] In some embodiments, the negative electrode plate further includes a negative electrode conductive layer, and the negative electrode conductive layer is located between the negative electrode film layer and the negative electrode current collector. The negative electrode conductive layer can further improve the conductivity of the negative electrode plate and reduce the heat generation of the negative electrode plate, thereby reducing the heat generation of the battery cell.

[0305] 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.

[0306] When the thickness of the negative electrode conductive layer is within the above range, the conductivity of the negative electrode plate can be further improved, the heat generation of the negative electrode plate can be reduced, thereby reducing the heat generation of the battery cell; and the energy density of the battery cell can be improved.

[0307] In the embodiment of the present application, the thickness of the negative electrode conductive layer has a well-known meaning in the art and can be detected by using equipment and methods well-known in the art, and the test method for the negative electrode conductive layer mentioned above can be used.

[0308] 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 and improve the structural stability of the negative electrode pole piece.

[0309] In some embodiments, the negative electrode conductive layer may further include other additives, such as, for example, thickeners, such as sodium carboxymethyl cellulose (CMC), PTC thermistor materials, and the like.

[0310] 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.

[0311] 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.

[0312] 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.

[0313] 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.

[0314] In some embodiments, the ratio CB of the capacity of the negative electrode film layer per unit area to the capacity of the positive electrode film layer per unit area in the battery cell is 1.05 to 1.30, and can be optionally 1.07 to 1.15. Exemplarily, the ratio CB of the capacity of the negative electrode film layer per unit area to the capacity of the positive electrode film layer per unit area in the battery cell is 1.05, 1.07, 1.1, 1.12, 1.15, 1.18, 1.2, 1.22, 1.25, 1.28, 1.3 or the range composed of any two of the above values.

[0315] When the ratio CB of the capacity of the negative electrode film layer per unit area to the capacity of the positive electrode film layer per unit area in the battery cell is within the above range, there are sufficient sites in the negative electrode film layer for lithium insertion, which can reduce the risk of lithium plating; and it is beneficial for fast charging.

[0316] In the embodiments of the present application, the meaning of the CB value is well-known in the art, and it can be detected by using equipment and methods well-known in the art. For example, calculate the capacity of the negative electrode film layer per unit area and the capacity of the positive electrode film layer per unit area respectively, and then calculate the ratio of the two to obtain the CB value.

[0317] Specifically, taking the upper limit voltage of battery charging as 3.65V and the cut-off voltage of battery discharging as 2.0V as an example for illustration, The capacity of the positive electrode film layer per unit area refers to the actual lithium-deintercalation capacity of the positive electrode active material. Its test method is as follows: Disassemble the battery in a PRS340 / 11-119-11 Braun glove box, take the positive electrode plate, assemble it into a CR2430 type half-button battery of positive electrode-lithium sheet, and the area of the positive electrode plate used is amm 2 , where the electrolyte uses a solution of 1M LiPF 6 in EC / EMC / DEC = 3 / 5 / 2 (mass ratio); then let the assembled half-button battery stand for 3h, the test is carried out at 25°C, first charge (Charge) and deintercalate lithium in the voltage range of 2.0V to 3.65V at 0.1C, and then discharge (Discharge) and insert lithium to 2.0V at 0.05C, cycle 2 times, and record the discharge and charge capacity of the second cycle as YmAh. The actual length of the positive electrode plate designed for the battery is bmm, the width is cmm, and the number of sides d of the positive electrode active material coated on the positive electrode current collector, then the capacity of the positive electrode film layer per unit area = Y / a*b*c*d.

[0318] Specifically, the capacity of the negative electrode film layer per unit area refers to the actual lithium-insertion capacity of the negative electrode active material. Its test method is: Disassemble the battery in a PRS340 / 11-119-11 Braun glove box, take the negative electrode plate, assemble it into a CR2430 type half-button battery of negative electrode-lithium sheet, and the area of the negative electrode plate used is fmm 2 , where the electrolyte uses a solution of 1M LiPF 6In a solution with EC / EMC / DEC=3 / 5 / 2 (mass ratio); then the assembled half-button battery is left to stand for 3h, and the test is carried out at 25℃, 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 button 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.

[0319] [Isolation film] In the embodiment of the present application, the isolation membrane includes a base membrane with a porous structure.

[0320] In some embodiments, the base film includes at least one of glass fiber, non-woven fabric, and polyolefin. The base film can 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 can be the same or different, without particular limitation.

[0321] Optionally, the polyolefin includes at least one of polyethylene, polypropylene and polyvinylidene fluoride.

[0322] 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.

[0323] When the porosity of the base film in the embodiment of the present application is within the above range, the migration ability of lithium ions in the isolation film can be improved, and the internal resistance of the battery cell can be further reduced, thereby reducing heat generation.

[0324] In the embodiments of the present application, porosity refers to the percentage of the pore volume in the separator to the total volume of the separator. The porosity can be tested in accordance with the standard GB / T36363-2018 "Polyolefin separator for battery monomers". It should be noted that the actual test process can be slightly different from the standard test process according to the difference in test instruments, test errors, and in order to eliminate the test influence on porosity as much as possible, so as to obtain a more accurate test value.

[0325] In some embodiments, the thickness of the base film is from 5 μm to 12 μm, optionally not exceeding 9 μm, and optionally from 6 μm to 9 μm. Exemplarily, the thickness of the base film is 6 μm, 6.5 μm, 7 μm, 7.5 μm, 8 μm, 8.5 μm, 9 μm, 9.5 μm, 10 μm, 10.5 μm, 11 μm, 11.5 μm, 12 μm or a range composed of any two of the above values.

[0326] When the thickness of the base film is within the above range, the migration path of lithium ions in the base film is shorter, which can further reduce the internal resistance of the battery cell, thereby reducing heat generation.

[0327] In the embodiments of the present application, the separator membrane may be the base film; optionally, the separator membrane further includes a functional layer provided on at least one side of the base film, and the functional layer may include inorganic particles to improve the heat resistance of the separator membrane. Optionally, the functional layer is provided on both sides of the base film.

[0328] In some embodiments, the functional layer includes a first functional layer and a second functional layer. The first functional layer is located on one side of the base film and includes first inorganic particles. The second functional layer is located on the other side of the base film and includes composite particles. The composite particles include second inorganic particles and a plurality of non-fluoropolymer particles, and the second inorganic particles are attached to the surface of the non-fluoropolymer particles and / or dispersed inside the non-fluoropolymer particles.

[0329] The first functional layer and the second functional layer have good heat resistance, which can improve the heat resistance of the separator membrane.

[0330] Optionally, the first functional layer may include a binder, optionally at least one of a fluorine-containing binder or a polyacrylic acid binder, such as polyvinylidene fluoride.

[0331] Optionally, the first inorganic particles include one or more of silicon oxide, aluminum oxide, boehmite, barium sulfate, calcium oxide, titanium oxide, zinc oxide, magnesium oxide, zirconium oxide, and tin oxide. The above first inorganic particles can improve the heat resistance of the first functional layer.

[0332] In the embodiments of the present application, the meaning of the thickness of the base film is the meaning well-known in the art, and it can be detected by the meaning and equipment well-known in the art. For example, a newly prepared separator membrane can be taken as a sample, or a discharged battery cell (discharged to the lower cut-off voltage so that the charged state of the battery is 0% SOC) can be disassembled in reverse, the separator membrane is obtained from the battery cell, and the separator membrane is dried and used as a sample. The separator membrane is cut off with an ion beam cutter to form a cross-section; subsequently, a scanning electron microscope is used to measure the thickness of the cross-section of the separator membrane and its respective layers.

[0333] The non-fluoropolymer particles in the second functional layer refer to polymers that are non-fluorinated polymers. For example, the non-fluoropolymer particles include acrylate copolymers. Optionally, the acrylate copolymers include acrylate-acrylonitrile-acrylamide-propylene copolymers. The acrylate copolymers have excellent adhesion properties and relatively high adhesion stability with the base film. The molar ratio of each monomer in the copolymer can be any ratio, such as 35%:30%:15%:20%, or 40%, 20%, 10%, 30%, or 45%, 15%, 20%, 20%, etc.

[0334] The second inorganic particles in the composite particles prevent the non-fluoropolymer particles from easily adhering to each other during the high-temperature treatment in the granulation process, creating pores in the composite particles, which is beneficial for the transport of lithium ions and improves the ionic conductivity of the separator. Moreover, the second inorganic particles can also increase the compression modulus of the composite particles. During the charge and discharge process, the composite particles are not easily deformed, making the structure of the separator more stable, capable of enhancing the kinetic performance of the battery monomer and improving the fast charging performance. Optionally, compared with the first functional layer, the second functional layer is arranged closer to the negative electrode tab. Since the composite particles are not easily deformed, the separator basically does not cause side effects such as extrusion to the negative electrode tab, ensuring the stable kinetic performance of the negative electrode tab. Correspondingly, the first functional layer is arranged closer to the positive electrode tab.

[0335] Optionally, the second inorganic particles include one or more of silicon oxide, aluminum oxide, boehmite, barium sulfate, calcium oxide, titanium oxide, zinc oxide, magnesium oxide, zirconium oxide, and tin oxide; optionally, the second inorganic particles include silicon oxide. The above-mentioned second inorganic particles can enhance the heat resistance of the second functional layer and can form composite particles in cooperation with the non-fluoropolymer, further improving the cycle stability and kinetic performance of the separator, and improving the cycle performance and fast charging performance of the battery monomer.

[0336] The average particle size of the second inorganic particles is 5 nm to 100 nm, optionally 10 nm to 100 nm, and optionally 5 nm to 20 nm. Exemplarily, the average particle size of the second inorganic particles is 5 nm, 10 nm, 15 nm, 20 nm, 25 nm, 30 nm, 35 nm, 40 nm, 45 nm, 50 nm, 55 nm, 60 nm, 65 nm, 70 nm, 75 nm, 80 nm, 85 nm, 90 nm, 95 nm, 100 nm or a range composed of any two of the above values. When the average particle size of the second inorganic particles is within the above range, it is beneficial to improve the heat resistance and compression modulus of the composite particles.

[0337] In the embodiments of the present application, the average particle size of the second inorganic particles has the meaning well-known in the art and can be detected by using the equipment and methods well-known in the art. For example, after obtaining the separator membrane and drying it as a sample, the separator membrane is cut by an ion beam cutter to form a cross-section; subsequently, a scanning electron microscope is used to measure the particle size of the second inorganic particles in the separator membrane, and the particle sizes of multiple, for example, 50 second inorganic particles are measured, and the average value thereof is calculated as the average particle size of the second inorganic particles.

[0338] In some embodiments, the ionic conductivity of the separator membrane is from 0.3 mS / cm to 0.6 mS / cm. Exemplarily, the ionic conductivity of the separator membrane is 0.3 mS / cm, 0.35 mS / cm, 0.4 mS / cm, 0.45 mS / cm, 0.5 mS / cm, 0.55 mS / cm, 0.6 mS / cm or the range composed of any two of the above values.

[0339] When the ionic conductivity of the separator membrane is within the above range, the migration ability of lithium ions in the separator membrane can be further improved, and the fast charging performance of the battery cell can be improved.

[0340] In the embodiments of the present application, the ionic conductivity of the separator membrane has the meaning well-known in the art and can be detected by using the equipment and methods well-known in the art. For example, Prepare a 2025-type button battery for testing: In a vacuum glove box, put a lithium sheet into the negative electrode case of the battery, add 150 μL of electrolyte thereto, and the electrolyte is a solution of 1 M LiPF 6 in EC / EMC / DEC = 3 / 5 / 2 (mass ratio), then put the separator membrane (with an area of 3.14 cm 2 , a thickness of 12 μm) to make it close to the lithium sheet, then add 25 μL of electrolyte, and finally place the positive electrode sheet (the positive electrode sheet can be the positive electrode sheet in Example 1) thereon and seal. Take out the assembled button battery from the vacuum glove box and place it for 24 h for the next test.

[0341] Testing: On an electrochemical workstation, test is carried out in the frequency range of 10 -1 ~10 6 Hz to obtain the separator membrane resistance R b , and the ionic conductivity σ (unit: mS / cm) is calculated through the following formula, σ = L / (R b ×S) wherein: R b is the separator membrane resistance, and L and S are the thickness and area of the separator membrane to be tested, respectively.

[0342] [Electrolyte] In some embodiments, the battery cell further includes an electrolyte.

[0343] During the charge and discharge process of the battery cell, active ions such as lithium ions are intercalated and deintercalated back and forth between the positive electrode plate and the negative electrode plate, and the electrolyte plays a role in conducting active ions between the positive electrode plate and the negative electrode plate.

[0344] In the embodiments of the present application, the conductivity of the electrolyte at room temperature is from 13 mS / cm to 20 mS / cm, and may be optionally from 15 mS / cm to 20 mS / cm. Exemplarily, the conductivity of the electrolyte at room temperature is 13 mS / cm, 13.5 mS / cm, 14 mS / cm, 14.5 mS / cm, 15 mS / cm, 15.5 mS / cm, 16 mS / cm, 16.5 mS / cm, 17 mS / cm, 17.5 mS / cm, 18 mS / cm, 18.5 mS / cm, 19 mS / cm, 19.5 mS / cm, 20 mS / cm or a range composed of any two of the above values.

[0345] When the conductivity of the electrolyte at room temperature, such as 25 °C, is within the above range, the migration rate of lithium ions in the electrolyte is relatively high, which can further reduce the internal resistance of the battery cell, thereby reducing heat generation and improving the fast charging performance of the battery cell.

[0346] In the embodiments of the present application, the conductivity of the electrolyte at room temperature, such as 25 °C, is the ionic conductivity, and it can be detected by using equipment and methods well-known in the art. For example, it can be tested with reference to the industry standard HG-T 4067-2015.

[0347] In some embodiments, the viscosity of the electrolyte at room temperature is from 2.3 mPa·s to 3.5 mPa·s. Exemplarily, the viscosity of the electrolyte is 2.3 mPa·s, 2.4 mPa·s, 2.5 mPa·s, 2.6 mPa·s, 2.7 mPa·s, 2.8 mPa·s, 2.9 mPa·s, 3.0 mPa·s, 3.1 mPa·s, 3.2 mPa·s, 3.3 mPa·s, 3.4 mPa·s, 3.5 mPa·s or a range composed of any two of the above values.

[0348] When the viscosity of the electrolyte at room temperature, such as 25 °C, is within the above range, the migration rate of lithium ions in the electrolyte is relatively high, which can further reduce the internal resistance of the battery cell, thereby reducing heat generation and improving the fast charging performance of the battery cell.

[0349] In the embodiments of the present application, the viscosity of the electrolyte has the meaning well-known in the art and can be detected by using equipment and methods well-known in the art. For example, it can be detected in accordance with GB / T10247-2008.

[0350] In some embodiments, the density of the electrolyte at room temperature, such as 25 °C, is 1.05 g / mL to 1.35 g / mL. Exemplarily, the density of the electrolyte is 1.05 g / mL, 1.10 g / mL, 1.15 g / mL, 1.2 g / mL, 1.25 g / mL, 1.3 g / mL, 1.35 g / mL or a range composed of any two of the above values.

[0351] When the density of the electrolyte is within the above range, the migration rate of lithium ions in the electrolyte is relatively high, which can further reduce the internal resistance of the battery cell, thereby reducing heat generation and improving the fast charging performance of the battery cell.

[0352] In the embodiments of the present application, the density of the electrolyte has the meaning well-known in the art and can be detected by devices and methods well-known in the art. For example, it can be tested with reference to GB / T 2013-2010.

[0353] The electrolyte includes an organic solvent and an electrolyte salt. The types of the organic solvent and the electrolyte salt are not specifically limited and can be selected according to actual needs.

[0354] In some embodiments, the organic solvent includes a chain carboxylic ester solvent, and the mass content of the chain carboxylic ester solvent relative to the mass of the organic solvent is greater than or equal to 5% and less than or equal to 75%, optionally greater than or equal to 10% and less than or equal to 75%, optionally 30% to 70%, optionally 50% to 70%. Exemplarily, the mass content of the chain carboxylic ester solvent is 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75% or a range composed of any two of the above values.

[0355] When the mass content of the chain carboxylic ester solvent is within the above range, the viscosity of the electrolyte system is relatively small, which is beneficial to the migration of lithium ions.

[0356] In some embodiments, the chain carboxylic ester solvent includes a compound represented by Formula I, Formula I, In Formula I, R 1 includes a hydrogen atom, a halogen atom, a C1-C5 alkyl group or a C1-C5 haloalkyl group, R 2 includes a C1-C5 alkyl group or a C1-C5 haloalkyl group.

[0357] The above chain carboxylic ester solvent has a relatively high conductivity, which is beneficial to improving the fast charging ability of the battery cell.

[0358] Optionally, R 1include a hydrogen atom, a halogen atom, a C1-C3 alkyl group, or a C1-C3 haloalkyl group. Further optionally, R 1 include a hydrogen atom, a halogen atom, a C1-C2 alkyl group, or a C1-C2 haloalkyl group.

[0359] Optionally, R 2 include a C1-C3 alkyl group or a C1-C3 haloalkyl group. Further optionally, R 2 include a C1-C2 alkyl group or a C1-C2 haloalkyl group.

[0360] In each of 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.

[0361] 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.

[0362] Exemplarily, the chain carboxylic ester solvents include one or more of the compounds represented by Formula I-1 to Formula I-8,

[0363] In some embodiments, the organic solvent further includes a carbonate solvent.

[0364] 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 above carbonate solvents and chain carboxylic ester solvents are used in combination, so that the conductivity of the electrolyte at room temperature is improved, which is beneficial to the migration of lithium ions.

[0365] Further optionally, the mass content of the carbonate solvent in the organic solvent is 30% to 70%, and can be 30% to 50%. Exemplarily, the mass content of the carbonate solvent in the organic solvent is 30%, 31%, 32%, 33%, 34%, 35%, 36%, 37%, 38%, 40%, 45%, 48%, 50%, 55%, 60%, 65%, 70% or a range composed of any two of the above values. The carbonate solvent with the above mass content can further improve the conductivity of the electrolyte at room temperature, which is beneficial to the migration of lithium ions.

[0366] Exemplarily, the carbonate solvent includes one or more of ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate, and the mass content of the carbonate solvent is 30% to 50%.

[0367] In some embodiments, the electrolyte further comprises an additive, which may include a negative electrode film-forming additive, a positive electrode film-forming additive, or an additive capable of improving certain battery performance, such as an additive for improving the overcharge performance of the battery, an additive for improving the high-temperature performance of the battery, an additive for improving the low-temperature power performance of the battery, etc.

[0368] In some embodiments, the additive comprises one or more of a carbonate additive, a sulfur-containing additive, and a lithium salt additive, and may be selected as at least two. The above additives can improve the interfacial film performance on the positive electrode side and / or the negative electrode side, which is beneficial to enhancing the fast charging performance of the battery cell and improving the cycling performance.

[0369] In some embodiments, the mass content of the additive in the electrolyte is 1% to 10%, optionally 2% to 8%, and further optionally 3.5% to 8%. Exemplarily, the mass content of the additive in the electrolyte is 1%, 2%, 3%, 3.5%, 4%, 5%, 6%, 7%, 8%, 9%, 10% or a range composed of any two of the above values.

[0370] The additive with the above mass content can effectively improve the interfacial film performance on the positive electrode side and / or the negative electrode side, which is beneficial to enhancing the fast charging performance of the battery cell and improving the cycling performance.

[0371] Exemplarily, the carbonate additive includes one or more of vinylene carbonate (VC) and fluoroethylene carbonate (FEC).

[0372] Exemplarily, the sulfur-containing additive includes one or more of ethylene sulfate (DTD), bis(ethylene sulfate) (2-DTD), butene sulfite (BS), 1,3-propane sultone (PS), ethylene sulfite (ES), and methylene methyl disulfonate (MMDS).

[0373] Optionally, the lithium salt additive includes lithium difluorophosphate (LiPO 2 F 2 , lithium difluorooxalate borate (LiDFOB), lithium tetrafluoroborate (LiBF 4 , and lithium bis(oxalate) borate (LiBOB).

[0374] Optionally, the mass content of vinylene carbonate (VC) in the electrolyte is 0.5% to 9%, and may be 2% to 6%.

[0375] Optionally, the mass content of fluoroethylene carbonate (FEC) in the electrolyte is 0.1% to 4%, and may be 0.5% to 3%.

[0376] 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%.

[0377] 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%.

[0378] In some embodiments, the electrolyte salt includes a lithium salt, and the lithium salt includes a fluorosulfonylimide salt and lithium hexafluorophosphate LiPF 6 or one or more of them. The above lithium salts are easy to dissociate, which is beneficial to the rapid migration of lithium ions, and the electrolyte system is relatively stable and not easy to decompose, which can improve the cycle performance of the battery monomer.

[0379] Optionally, the fluorosulfonylimide salt includes one or more of lithium bis(fluorosulfonyl)imide LiFSI and lithium bis(trifluoromethylsulfonyl)imide LiTFSI.

[0380] Optionally, the lithium salt includes lithium bis(fluorosulfonyl)imide LiFSI and lithium hexafluorophosphate LiPF 6 , the molar concentration of lithium bis(fluorosulfonyl)imide LiFSI is 0.2 mol / L to 0.5 mol / L, and the molar concentration of lithium hexafluorophosphate LiPF 6 is 0.5 mol / L to 1.0 mol / L.

[0381] Exemplarily, the molar concentration of lithium bis(fluorosulfonyl)imide LiFSI is 0.4 mol / L to 0.5 mol / L, and the molar concentration of lithium hexafluorophosphate LiPF 6 is 0.7 mol / L.

[0382] Exemplarily, the molar concentration of lithium bis(fluorosulfonyl)imide LiFSI is 0.5 mol / L, and the molar concentration of lithium hexafluorophosphate LiPF 6 is 0.5 mol / L.

[0383] Exemplarily, the molar concentration of lithium bis(fluorosulfonyl)imide LiFSI is 0.2 mol / L, and the molar concentration of lithium hexafluorophosphate LiPF 6 is 0.8 mol / L.

[0384] Optionally, the ratio of the molar concentration of lithium bis(fluorosulfonyl)imide and the molar concentration of lithium hexafluorophosphate LiPF 6 is 0.2 to 1.0, and can be optionally 0.2 to 0.5. Exemplarily, the ratio of the molar concentration of lithium bis(fluorosulfonyl)imide and the molar concentration of lithium hexafluorophosphate LiPF 6 is 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1 or the range composed of any two of the above values.

[0385] In the embodiments of the present application, the types and contents of the inorganic components / lithium salts in the electrolyte have meanings well-known in the art, and can be detected by devices and methods well-known in the art. For example, reference can be made to the General Rules for Ion Chromatography Analysis (JY / T 020-1996) to qualitatively or quantitatively analyze the concentration of inorganic components / lithium salts in the electrolyte by ion chromatography. In the embodiments of the present application, freshly prepared electrolyte can be taken as a sample, the free electrolyte of a fresh battery can be taken as a sample, or a battery that has been fully discharged (discharged to the lower cut-off voltage so that the charged state of the battery is approximately 0% SOC) can be disassembled in reverse, and the free electrolyte obtained from the battery can be taken as a sample for detection using ion chromatography analysis method.

[0386] In the embodiments of the present application, the types and contents of the organic components in the electrolyte have meanings well-known in the art, and can be detected by devices and methods well-known in the art. For example, reference can be made to the General Rules for Gas Chromatography of Chemical Reagents (GB / T 9722-2006) to qualitatively and quantitatively analyze the organic components in the electrolyte by gas chromatography. In the embodiments of the present application, freshly prepared electrolyte can be taken as a sample, the free electrolyte of a fresh battery can be taken as a sample, or a battery that has been fully discharged (discharged to the lower cut-off voltage so that the charged state of the battery is approximately 0% SOC) can be disassembled in reverse, and the free electrolyte obtained from the battery can be taken as a sample for detection using ion chromatography analysis method.

[0387] In the embodiments of the present application, after quantitatively and qualitatively detecting each component in the electrolyte, each component is classified. Chain carboxylic ester solvents and carbonate solvents (such as ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate) are used as the constituent components of the organic solvent. Based on the mass of the organic solvent being 100%, the mass content of each component is calculated. Carbonate additives (such as vinylene carbonate, fluoroethylene carbonate), sulfur-containing additives, and lithium salt additives are used as additives in the electrolyte. Based on the mass of the electrolyte being 100%, the mass content of each component is calculated.

[0388] In some embodiments, the battery cell satisfies: 2.45 g / Ah ≤ d / A ≤ 3.5 g / Ah, and can be optionally 2.45 g / Ah ≤ d / A ≤ 3.3 g / Ah, where d represents the mass of the electrolyte in the battery cell, in g, and A represents the rated capacity of the battery cell, in Ah. Exemplarily, d / A can be 3.5 g / Ah, 3.3 g / Ah, 3.2 g / Ah, 3.0 g / Ah, 2.8 g / Ah, 2.5 g / Ah, 2.45 g / Ah, or a range composed of any two of the above values.

[0389] d / A can reflect the liquid retention ability of the electrolyte. When d / A is within the above range, the electrolyte can play a good wetting role on the positive electrode plate and the negative electrode plate, and can also improve the migration rate of lithium ions in the liquid phase, which is beneficial to improving the fast charging ability of the battery cell.

[0390] In the embodiments of the present application, the d / A of the battery cell can be understood as the liquid retention coefficient, and can be detected by using the equipment and methods well-known in the art. For example, taking the upper limit voltage of battery charging as 3.65V and the cut-off voltage of battery discharging as 2.0V in accordance with GB / T31486-2015 "Power Battery Electrical Performance Requirements and Test Methods for Electric Vehicles" for illustration, At 25°C, the battery cell is charged to 3.65V at 0.33C, then charged at a constant voltage until 0.05C, and then discharged at a constant current of 0.33C to 2.0V. The discharged capacity A is used as the denominator. The battery cell is weighed as M0, and then the positive electrode plate, the negative electrode plate, the separator and the electrolyte are disassembled. The free electrolyte is placed in a bag. All the above solid components are placed in an oven at 60°C and baked for more than 4 hours (including but not limited to the positive electrode plate, the negative electrode plate, the separator, and other mechanical parts contributing to M0 in the disassembled battery cell), and then all the components of the battery cell are weighed as M1. The weight difference between M0 and M1 is used as the numerator. The liquid retention coefficient is the value obtained by dividing the weight difference d between M0 and M1 by the capacity A.

[0391] In some embodiments, the positive electrode plate, the separator and the negative electrode plate can be made into an electrode assembly by a winding process and / or a stacking process.

[0392] Figure 1 and Figure 2 shows a schematic structural diagram of the battery cell.

[0393] In some embodiments, the battery cell 7 may include a housing 20.

[0394] In some embodiments, the housing 20 of the battery cell 7 can be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The housing 20 of the battery cell 7 can also be a soft package, such as a pouch soft package. The material of the soft package can be plastic, such as at least one of polypropylene (PP), polybutylene terephthalate (PBT) and polybutylene succinate (PBS).

[0395] The housing 20 is a hollow structure, and the housing 20 can be used to encapsulate the above electrode assembly 10 and the electrolyte.

[0396] The preparation method of the battery cell 7 according to the embodiments of the present application is well-known. In some embodiments, the positive electrode sheet, the separator, the negative electrode sheet and the electrolyte can be assembled to form the battery cell 7. As an example, the positive electrode sheet, the separator and the negative electrode sheet can be formed into the electrode assembly 10 through a winding process and / or a stacking process, the electrode assembly 10 is placed in the housing 20, and after drying, the electrolyte is injected, and through processes such as vacuum packaging, standing, forming, and shaping, the battery cell 7 is obtained.

[0397] In some embodiments, the housing 20 includes a housing body 21 and an end cap 22, the housing body 21 has an opening, and the end cap 22 covers the opening.

[0398] The shape of the housing body 21 can be determined according to the specific shape of the electrode assembly 10. For example, if the electrode assembly 10 is a cylindrical structure, a cylindrical housing can be selected; if the electrode assembly 10 is a cuboid structure, a cuboid housing can be selected. Optionally, both the electrode assembly 10 and the housing body 21 are cuboid structures.

[0399] In some embodiments, the material of the housing body 21 includes steel. Steel has high mechanical strength and is not easily deformed, which can improve the use reliability of the battery cell 7. In the embodiments of the present application, steel refers to the material with the highest proportion in the housing body 21.

[0400] Optionally, the thickness of the housing body 21 is 0.1 mm to 0.5 mm, and can be 0.2 mm to 0.35 mm. Exemplarily, the thickness of the housing body 21 is 0.1 mm, 0.15 mm, 0.2 mm, 0.25 mm, 0.3 mm, 0.35 mm, 0.4 mm, 0.45 mm, 0.5 mm or a range composed of any two of the above values. When the thickness of the housing body 21 is within the above range, the housing body 21 has high mechanical strength, which can improve the use reliability of the battery cell 7; and the housing body 21 occupies less space and there is more internal space in the housing body 21, which is beneficial to improving the energy density of the battery cell 7.

[0401] Viewed from the outer shape of the electrode assembly 10, the electrode assembly 10 includes a main body portion 12, a first pole ear 111 and a second pole ear 112, and the first pole ear 111 and the second pole ear 112 protrude from the main body portion 12. The first pole ear 111 is the part of the first electrode sheet without the coated active material layer, and the second pole ear 112 is the part of the second electrode sheet without the coated active material layer. The first pole ear 111 and the second pole ear 112 are used to lead out the current in the main body portion 12. The polarities of the first electrode sheet and the second electrode sheet are opposite. In other words, one of the first electrode sheet and the second electrode sheet is the positive electrode sheet, and the other of the first electrode sheet and the second electrode sheet is the negative electrode sheet.

[0402] Taking the first tab 111 as the negative tab and the second tab 112 as the positive tab as an example for illustration; the part of the negative current collector in the negative electrode plate that is not coated with the active material layer is the negative tab, and the active material coated on the negative current collector in the negative electrode plate constitutes the negative electrode film layer. The negative electrode film layer and the negative current collector coated with the active material are part of the main body 12. The part of the positive current collector in the positive electrode plate that is not coated with the active material layer is the positive tab, and the active material coated on the positive current collector in the positive electrode plate constitutes the positive electrode film layer. The positive electrode film layer and the positive current collector coated with the active material are part of the main body 12. Of course, the first tab 111 can be the positive electrode plate, and the second tab 112 can be the negative electrode plate.

[0403] The first tab 111 and the second tab 112 can extend from the same side of the main body 12, or can extend from opposite sides respectively.

[0404] Optionally, the number of the first tabs 111 located on the same side of the main body 12 is at least one, optionally at least two. At least two first tabs 111 can increase the current-carrying capacity of the first tab 111.

[0405] Optionally, the number of the second tabs 112 located on the same side of the main body 12 is at least one, optionally at least two. At least two second tabs 112 can increase the current-carrying capacity of the second tab 112.

[0406] In some embodiments, the battery cell 7 further includes a first electrode terminal 31, and the first electrode terminal 31 is electrically connected to the first tab 111. Optionally, the first electrode terminal 31 and the first tab 111 are welded. The first electrode terminal 31 and the first tab 111 can be connected through an adapter, or can be connected without using an adapter; optionally, the first electrode terminal 31 and the first tab 111 are not connected through 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 and is beneficial to reducing the overall internal resistance of the battery cell 7. When the first tab 111 is the negative tab, the first electrode terminal 31 is the negative terminal. When the first tab 111 is the positive tab, the first electrode terminal 31 is the positive terminal.

[0407] In some embodiments, the battery cell 7 further includes a second electrode terminal 32, and the second electrode terminal 32 is electrically connected to the second tab 112. Optionally, the second electrode terminal 32 and the second tab 112 are welded. The second electrode terminal 32 and the second tab 112 can be connected through an adapter, or can be connected without using an adapter; optionally, the second electrode terminal 32 and the second tab 112 are not connected through an adapter, that is, the second electrode terminal 32 and the second tab 112 are directly welded, which can reduce the resistance at the connection and is beneficial to reducing the overall internal resistance of the battery cell 7. When the second tab 112 is a negative tab, the second electrode terminal 32 is a negative terminal. When the second tab 112 is a positive tab, the second electrode terminal 32 is a positive terminal.

[0408] Optionally, the number of the first electrode terminals 31 on the same side of the main body 12 is at least one, and can be at least two. At least two first electrode terminals 31 can increase the current-carrying capacity of the first electrode terminals 31.

[0409] Further optionally, the current-carrying area of a single first electrode terminal 31 is greater than or equal to 25 mm 2 , and can be 25 mm 2 to 315 mm 2 . The current-carrying area of the first electrode terminal 31 can be understood as the cross-sectional area of the first electrode terminal 31, and this cross-section is perpendicular to the thickness direction of the end cap 22.

[0410] Exemplarily, the current-carrying area of a single first electrode terminal 31 can be 25 mm 2 , 30 mm 2 , 35 mm 2 , 40 mm 2 , 45 mm 2 , 50 mm 2 , 55 mm 2 , 60 mm 2 , 62 mm 2 , 64 mm 2 , 65 mm 2 , 70 mm 2 , 75 mm 2 , 80 mm 2 , 85 mm 2 , 90 mm 2 , 95 mm 2 , 100 mm 2 , 105 mm 2 , 110 mm 2 , 115 mm 2 , 120 mm 2 , 125 mm 2 , 130 mm 2 , 135 mm2 、140 mm 2 、145 mm 2 、150 mm 2 、155 mm 2 、160 mm 2 、165 mm 2 、170 mm 2 、175 mm 2 、180 mm 2 、185 mm 2 、190 mm 2 、195 mm 2 、200 mm 2 、205 mm 2 、210 mm 2 、215 mm 2 、220 mm 2 、225 mm 2 、230 mm 2 、235 mm 2 、240 mm 2 、245 mm 2 、250 mm 2 、255 mm 2 、260 mm 2 、265 mm 2 、270 mm 2 、275 mm 2 、280 mm 2 、285 mm 2 、290 mm 2 、295 mm 2 、300 mm 2 、305 mm 2 、310 mm 2 、315 mm 2 or a range composed of any two of the above values.

[0411] Optionally, the number of the second electrode terminals 32 on the same side of the main body 12 is at least one, optionally at least two. The at least two second electrode terminals 32 can increase the over-current capacity of the second electrode terminals 32.

[0412] Further optionally, the over-current area of a single second electrode terminal 32 is greater than or equal to 25 mm 2 , optionally 25 mm 2 to 315 mm 2 . The over-current area of the second electrode terminal 32 can be understood as the cross-sectional area of the second electrode terminal 32, and this cross-section is perpendicular to the thickness direction of the end cover 22.

[0413] Exemplarily, the overcurrent area of a single second electrode terminal 32 can be 25 mm 2 , 30 mm 2 , 35 mm 2 , 40 mm 2 , 45 mm 2 , 50 mm 2 , 55 mm 2 , 60 mm 2 , 62 mm 2 , 64 mm 2 , 65 mm 2 , 70 mm 2 , 75 mm 2 , 80 mm 2 , 85 mm 2 , 90 mm 2 , 95 mm 2 , 100 mm 2 , 105 mm 2 , 110 mm 2 , 115 mm 2 , 120 mm 2 , 125 mm 2 , 130 mm 2 , 135 mm 2 , 140 mm 2 , 145 mm 2 , 150 mm 2 , 155 mm 2 , 160 mm 2 , 165 mm 2 , 170 mm 2 , 175 mm 2 , 180 mm 2 , 185 mm 2 , 190 mm 2 , 195 mm 2 , 200 mm 2 , 205 mm 2 , 210 mm 2 , 215 mm 2 , 220 mm 2 , 225 mm 2 , 230 mm 2 , 235 mm 2 , 240 mm 2 , 245 mm 2 , 250 mm 2 , 255 mm 2 , 260 mm 2 , 265 mm 2 , 270 mm 2 , 275 mm2 , 280 mm 2 , 285 mm 2 , 290 mm 2 , 295 mm 2 , 300 mm 2 , 305 mm 2 , 310 mm 2 , 315 mm 2 or a range formed by any two of the above values.

[0414] As Figure 3 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 included in the battery module 6 can be one or more, and the specific number can be adjusted according to the application and capacity of the battery module 6.

[0415] If there are multiple battery cells 7, the multiple battery cells 7 can be connected in series, parallel or in a hybrid connection. A hybrid connection means that there are both series and parallel connections among the multiple battery cells 7. The multiple battery cells 7 can be directly connected in series, parallel or in a hybrid connection together, and then the whole formed by the multiple battery cells 7 is accommodated in the accommodating part of the battery module 6; of course, it is also possible that the multiple battery cells 7 are first connected in series, parallel or in a hybrid connection to form a battery module 6, and then the multiple battery modules 6 are connected in series, parallel or in a hybrid connection to form a whole and are accommodated in the accommodating part. Optionally, the battery module 6 can also include an accommodating part with an accommodating space, and the multiple battery cells 7 are accommodated in this accommodating space.

[0416] As Figure 4 shown, in some embodiments, the above battery module 6 can also be assembled into a battery pack 2. The number of battery modules 6 included in the battery pack 2 can be adjusted according to the application and capacity of the battery pack. The multiple battery modules 6 can be arranged in the box body 5 in any manner. The battery device can be in the form of a battery pack 2 or a battery module 6, etc.

[0417] The battery pack 2 can include a box body 5 and multiple battery modules 6 arranged in the box body 5. The box body 5 includes a first box body part 5a and a second box body part 5b. The box body 5 has an accommodating space 5c. The first box body part 5a is used to cover the second box body part 5b and form a closed space for accommodating the battery module 6. The multiple battery modules 6 can be arranged in the box body 5 in any manner.

[0418] The first box body part 5a and the second box body part 5b cover each other, and the first box body part 5a and the second box body part 5b jointly define an accommodation space 5c for accommodating battery cells. The second box body part 5b can be a hollow structure with an opening at one end, and the first box body part 5a is a plate-like structure. The first box body part 5a covers the opening side of the second box body part 5b to form a box body 5 with the accommodation space 5c; both the first box body part 5a and the second box body part 5b can also be hollow structures with an opening on one side, and the opening side of the first box body part 5a covers the opening side of the second box body part 5b to form a box body 5 with the accommodation space 5c. Of course, the first box body part 5a and the second box body part 5b can be in various shapes, such as a cylinder, a cuboid, etc.

[0419] To improve the sealing performance after the connection between the first box body part 5a and the second box body part 5b, a sealing member can also be provided between the first box body part 5a and the second box body part 5b, such as sealant, sealing ring, etc.

[0420] Assume that the first box body part 5a covers the top of the second box body part 5b. The first box body part 5a can also be called the upper box cover, and the second box body part 5b can also be called the lower box body.

[0421] The battery pack 2 or any battery cell that makes up 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 from 2.5C to 5C. For example, it can be 2.7C.

[0422] In some embodiments, the charging time of the battery pack 2 or any battery cell that makes up the battery pack 2 from 10% state of charge to 80% state of charge is less than or equal to 10.5 min, and can be selected from 5 min to 10.5 min. The temperature of the external environment where the battery pack 2 is located is room temperature, such as 30°C. Exemplarily, the charging time of the battery pack 2 from 10% state of charge to 80% state of charge is 10.5 min, 10 min, 9.5 min, 9 min, 8.5 min, 8 min, 7.5 min, 7 min, 6.5 min, 6 min, 5.5 min, 5 min or any range composed of any two of the above values.

[0423] electrical device The second aspect of the embodiments of the present application provides an electrical device, which includes at least one of the battery cells, battery modules or battery packs of the embodiments of the present application. The battery cells, battery modules or battery packs can be used as the power source of the electrical device or as the energy storage unit of the electrical device. The electrical device can be a vehicle, a mobile phone, a portable device, a laptop computer, a ship, a spacecraft, an electric toy and an electric tool, etc. The vehicle can be a fuel vehicle, a gas vehicle or a new energy vehicle, and the new energy vehicle can be a pure electric vehicle, a hybrid electric vehicle or an extended-range electric vehicle, etc.; the spacecraft includes an airplane, a rocket, a space shuttle and a spaceship, etc.; the electric toy includes a fixed or mobile electric toy, for example, a game console, an electric vehicle toy, an electric ship toy and an electric airplane toy, etc.; the electric tool includes a metal cutting electric tool, a grinding electric tool, an assembly electric tool and a railway electric tool, for example, an electric drill, an electric grinding wheel, an electric wrench, an electric screwdriver, a hammer drill, an impact drill, a concrete vibrator and a planer, etc. The embodiments of the present application do not impose special restrictions on the above-mentioned electrical devices.

[0424] The electrical device can select battery cells, battery modules or battery packs according to its usage requirements.

[0425] Figure 5 It is a schematic diagram of an electrical device 1 as an example. The electrical device 1 is a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, etc. In order to meet the requirements of the electrical device 1 for high power and high energy density, a battery pack or a battery module can be used.

[0426] A battery pack 2 is provided inside the electrical device 1, and the battery pack 2 can be arranged at the bottom, head or tail of the electrical device 1. The battery pack 2 can be used for power supply of the electrical device 1. For example, the battery pack 2 can be used as the operating power source of the electrical device 1 and can also be used as the driving power source of the electrical device 1, replacing or partially replacing fuel or natural gas to provide driving power for the electrical device 1.

[0427] The electrical device 1 may further include a controller 3 and a motor 4. The controller 3 is used to control the battery pack 2 to supply power to the motor 4. For example, it is used for the working power requirements during the start, navigation and driving of the electrical device 1.

[0428] Another example of the electrical device can be a mobile phone, a tablet computer, a laptop computer, etc. This type of electrical device usually requires thin and light design, and battery cells can be used as the power source.

[0429] In some embodiments, the charging time of the electrical device from 10% state of charge to 80% state of charge is less than or equal to 10.5 min, and can be optionally 5 min to 10.5 min. The temperature of the external environment where the electrical device is located is room temperature, such as 30°C. Exemplarily, the charging time of the battery pack 2 from 10% state of charge to 80% state of charge is 10.5 min, 10 min, 9.5 min, 9 min, 8.5 min, 8 min, 7.5 min, 7 min, 6.5 min, 6 min, 5.5 min, 5 min or the range composed of any two of the above values. The electrical device can adopt the same charging strategy as the battery pack 2 or the battery cell.

[0430] embodiment The following examples more specifically describe the content disclosed in the embodiments of the present application. These examples are only for illustrative purposes, because various modifications and changes within the scope of the content disclosed in the embodiments of the present application are obvious to those skilled in the art. Unless otherwise stated, all parts, percentages and ratios reported in the following examples are based on mass, and all reagents used in the examples are commercially available or synthesized according to conventional methods and can be used directly without further treatment, and the instruments used in the examples are all commercially available.

[0431] Example 1 Preparation of the battery pack 1. Preparation of the positive electrode plate The positive electrode plate includes a positive current collector, a positive conductive layer on the positive current collector, and a positive electrode film layer. The positive current collector is an aluminum foil with a thickness of 10 μm. The positive conductive layer on the positive current collector is a film layer formed by uniformly coating a positive conductive agent, superconducting carbon, a positive binder, polyvinylidene fluoride (PVDF), and a solvent, N-methylpyrrolidone (NMP), on the surface of the current collector, with a thickness of 1 μm. The mass content of the positive conductive agent in the positive conductive layer is 40%, and the mass content of the positive binder is 60%.

[0432] The positive electrode film layer includes a film layer formed by uniformly coating a positive electrode slurry (with a solvent of N-methylpyrrolidone NMP) on the surface of the positive conductive layer and then drying and cold pressing. The positive electrode film layer includes a positive active material, a binder, polyvinylidene fluoride (PVDF), and a conductive agent, acetylene black, with a weight ratio of 97:2:1.

[0433] The positive active material includes lithium iron phosphate and a coating layer. The coating layer is coated on the surface of the lithium iron phosphate. The coating layer includes lithium iron titanium phosphate Li 2 FeTi(PO 4 ) 3 and amorphous carbon. The Dv50 of the positive active material is 1.6 μm, and the Dv10 is 0.64 μm.

[0434] The single-sided coating weight of the positive electrode film layer is 300 mg / 1540.25 mm 2 。

[0435] 2. Preparation of the negative electrode sheet The negative electrode sheet includes a negative electrode current collector, a negative electrode conductive layer on the negative electrode current collector, and a negative electrode film layer. The negative electrode current collector is a copper foil with a thickness of 5 μm. The negative electrode conductive layer on the negative electrode current collector is a film layer formed by uniformly coating a mixture of a negative electrode conductive agent superconducting carbon, a negative electrode binder styrene-butadiene rubber (SBR), a thickener sodium carboxymethyl cellulose (CMC-Na), and a solvent water on the surface of the negative electrode current collector, with a thickness of 1 μm; the mass content of the negative electrode conductive agent in the negative electrode conductive layer is 35%, the mass content of the negative electrode binder in the negative electrode conductive layer is 60%, and the mass content of the thickener in the negative electrode conductive layer is 5%; The negative electrode film layer includes a film layer formed by uniformly coating a negative electrode slurry (with deionized water as the solvent) on the surface of the negative electrode conductive layer, followed by drying and cold pressing.

[0436] The single-sided coating weight of the negative electrode film layer is 138 mg / 1540.25 mm 2 。

[0437] 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.

[0438] The first negative electrode film layer includes graphite particles, conductive agent acetylene black, a first lithium-containing binder (copolymer of lithium acrylate - acrylonitrile - acrylamide - 2-hydroxyethyl acrylate), negative electrode binder styrene-butadiene rubber, and thickener sodium carboxymethyl cellulose with a mass ratio of 96.5:0.5:0.5:1.5:1; the mass content of lithium element in the first lithium-containing binder is 4.8%; the Dv50 of the graphite particles is 11.3 μm. The graphite particles include artificial graphite and a carbon coating layer, and the carbon coating layer covers the surface of the artificial graphite, and the mass content of amorphous carbon is 3.5%.

[0439] The second negative electrode film layer includes graphite particles, conductive agent acetylene black, a second lithium-containing binder (copolymer of lithium acrylate - acrylonitrile - acrylamide - 2-hydroxyethyl acrylate), negative electrode binder styrene-butadiene rubber, and thickener sodium carboxymethyl cellulose with a mass ratio of 97.5:0.5:0.5:0.5:1; the mass content of lithium element in the second lithium-containing binder is 4.8%; the Dv50 of the graphite particles is 11.3 μm. The graphite particles include artificial graphite and a carbon coating layer, and the carbon coating layer covers the surface of the artificial graphite, and the mass content of amorphous carbon is 3.5%.

[0440] 3. Separator membrane The separator membrane includes a base film, and the base film is a polyethylene film layer with a thickness of 7 μm and a porosity of 42%.

[0441] 4. Preparation of Electrolyte The electrolyte includes organic solvents, lithium salts and additives.

[0442] The organic solvents include 60% chain carboxylic ester solvents (ethyl acetate) and 40% carbonate solvents (30% ethylene carbonate EC, 10% dimethyl carbonate). The mass content of each component in the organic solvents is calculated based on the mass of the organic solvents.

[0443] Based on the mass of the electrolyte, the mass content of the additives is 6.5%, which includes vinylene carbonate VC, fluoroethylene carbonate FEC, ethylene sulfite ES and lithium difluorooxalate borate LiDFOB with a mass ratio of 5:0.5:0.5:0.5.

[0444] The lithium salt includes 1 mol / L lithium hexafluorophosphate LiPF 6 .

[0445] The conductivity of the electrolyte at room temperature is 16.4 mS / cm.

[0446] 5. Preparation of Battery Cell Stack the above-mentioned positive electrode plate, separator and negative electrode plate in sequence, with the separator placed between the positive electrode plate and the negative electrode plate to play an isolation role, obtaining an electrode assembly; place the electrode assembly in an outer packaging shell, inject the electrolyte after drying, and go through processes such as vacuum packaging, standing, formation, and shaping to obtain a battery cell. The compaction density of the positive electrode film layer at 100% SOC is 2.72 g / cm 3 , and the compaction density of the negative electrode film layer at 100% SOC is 1.26 g / cm 3 .

[0447] 6. Preparation of Battery Pack Divide multiple battery cells into two groups, connect them in series inside each group, and assemble them into a battery module after connecting them in parallel between the two groups. Then connect the battery module and the battery management system BMS, and assemble them into a box to form a battery pack. The battery management system BMS is configured to monitor the charging state and / or discharging state of multiple battery cells, and can adjust the charging current and voltage as needed.

[0448] It should be noted that the battery pack can be charged separately, and each independent battery cell in the battery pack can also be charged separately. Both the battery pack and the battery cell can adopt the following charging strategy for charging. Next, the charging strategy will be described taking the battery pack as an example.

[0449] Charging Strategy 1 After assembling the battery cell prepared in Example 1 with the battery management system BMS into a battery pack, charge it at an external temperature of 30°C. The charging steps include the following steps: Charge at a constant current of 5.0C from 0% SOC to 5% SOC; Charge from 5% SOC to 10% SOC at a constant current of 5.0C; Charge from 10% SOC to 15% SOC at a constant current of 5.0C; Charge from 15% SOC to 20% SOC at a constant current of 5.0C; Charge from 20% SOC to 25% SOC at a constant current of 5.0C; Charge from 25% SOC to 30% SOC at a constant current of 5.0C; Charge from 30% SOC to 35% SOC at a constant current of 5.0C; Charge from 35% SOC to 40% SOC at a constant current of 5.0C; Charge from 40% SOC to 45% SOC at a constant current of 4.6C; Charge from 45% SOC to 50% SOC at a constant current of 4.3C; Charge from 50% SOC to 55% SOC at a constant current of 4.0C; Charge from 55% SOC to 60% SOC at a constant current of 3.7C; Charge from 60% SOC to 65% SOC at a constant current of 3.4C; Charge from 65% SOC to 70% SOC at a constant current of 3.1C; Charge from 70% SOC to 75% SOC at a constant current of 2.9C; Charge from 75% SOC to 80% SOC at a constant current of 2.7C; Charge from 80% SOC to 85% SOC at a constant current of 1.8C; Charge from 85% SOC to 90% SOC at a constant current of 1.3C; Charge from 90% SOC to 95% SOC at a constant current of 0.7C; Charge from 95% SOC to 98% SOC at a constant current of 0.33C; Charge from 98% SOC to 100% SOC at a constant current of 0.1C.

[0450] In the above charging steps, the cut-off voltage of the last charging step is 3.65V. The difference between the cut-off voltage of any one of the N - 1 charging steps and the cut-off voltage of the last charging step is less than or equal to 0.05V. The cut-off voltage of each of the N - 1 charging steps is 3.6V, and the difference in the maximum state of charge between two adjacent charging steps is less than or equal to 5% SOC.

[0451] charging strategy 2 After assembling the battery cells prepared in Example 1 with the battery management system BMS into a battery pack, charge at an external temperature of 30°C. The charging steps include the following steps: Charge from 0% SOC to 5% SOC at a constant current of 5.0 C; Charge from 5% SOC to 10% SOC at a constant current of 5.0 C; Charge from 10% SOC to 15% SOC at a constant current of 5.0 C; Charge from 15% SOC to 20% SOC at a constant current of 5.0 C; Charge from 20% SOC to 25% SOC at a constant current of 5.0 C; Charge from 25% SOC to 30% SOC at a constant current of 5.0 C; Charge from 30% SOC to 35% SOC at a constant current of 5.0 C; Charge from 35% SOC to 40% SOC at a constant current of 5.0 C; Charge from 40% SOC to 45% SOC at a constant current of 4.6 C; Charge from 45% SOC to 50% SOC at a constant current of 4.3 C; Charge from 50% SOC to 55% SOC at a constant current of 4.0 C; Charge from 55% SOC to 60% SOC at a constant current of 3.7 C; Charge from 60% SOC to 65% SOC at a constant current of 3.4 C; Charge from 65% SOC to 70% SOC at a constant current of 3.1 C; Charge from 70% SOC to 75% SOC at a constant current of 2.9 C; Charge from 75% SOC to 80% SOC at a constant current of 2.7 C; Charge from 80% SOC to 85% SOC at a constant current of 1.8 C; Charge from 85% SOC to 90% SOC at a constant current of 1.3 C; Charge from 90% SOC to 95% SOC at a constant current of 0.7 C; Charge from 95% SOC to 98% SOC at a constant current of 0.33 C; Charge from 98% SOC to 100% SOC at a constant current of 0.01 C.

[0452] The cut-off voltage of the last charging step in the above charging steps is 3.65 V. The difference between the cut-off voltage of any charging step in the N - 1 charging steps and the cut-off voltage of the last charging step is less than or equal to 0.05 V. The cut-off voltage of each charging step in the N - 1 steps is 3.6 V, and the difference in the maximum state of charge between two adjacent charging steps is less than or equal to 5% SOC.

[0453] charging strategy 3 After assembling the battery monomer prepared in Example 1 with the battery management system BMS into a battery pack, charging is carried out at an external temperature of 30°C. The charging steps include the following steps: Constant current charge at 5.0C from 0% SOC to 5% SOC; Constant current charge at 5.0C from 5% SOC to 10% SOC; Constant current charge at 5.0C from 10% SOC to 15% SOC; Constant current charge at 5.0C from 15% SOC to 20% SOC; Constant current charge at 5.0C from 20% SOC to 25% SOC; Constant current charge at 5.0C from 25% SOC to 30% SOC; Constant current charge at 5.0C from 30% SOC to 35% SOC; Constant current charge at 5.0C from 35% SOC to 40% SOC; Constant current charge at 4.6C from 40% SOC to 45% SOC; Constant current charge at 4.3C from 45% SOC to 50% SOC; Constant current charge at 4.0C from 50% SOC to 55% SOC; Constant current charge at 3.7C from 55% SOC to 60% SOC; Constant current charge at 3.4C from 60% SOC to 65% SOC; Constant current charge at 3.1C from 65% SOC to 70% SOC; Constant current charge at 2.9C from 70% SOC to 75% SOC; Constant current charge at 2.7C from 75% SOC to 80% SOC; Constant current charge at 1.8C from 80% SOC to 85% SOC; Constant current charge at 1.3C from 85% SOC to 90% SOC; Constant current charge at 0.7C from 90% SOC to 95% SOC; Constant current charge at 0.33C from 95% SOC to 98% SOC; Constant current charge at 0.05C from 98% SOC to 100% SOC.

[0454] In the above charging steps, the cut-off voltage of the last charging step is 3.65V. The difference between the cut-off voltage of any one of the N - 1 charging steps and the cut-off voltage of the last charging step is less than or equal to 0.05V. The cut-off voltage of each of the N - 1 steps is 3.6V, and the difference in the maximum state of charge between two adjacent charging steps is less than or equal to 5% SOC.

[0455] charging strategy 4 After assembling the battery cell prepared in Example 1 with the battery management system BMS into a battery pack, charging is carried out at an external temperature of 30°C, and the charging steps include the following steps: Constant current charging at 5.0C from 0% SOC to 5% SOC; Constant current charging at 5.0C from 5% SOC to 10% SOC; Constant current charging at 5.0C from 10% SOC to 15% SOC; Constant current charging at 5.0C from 15% SOC to 20% SOC; Constant current charging at 5.0C from 20% SOC to 25% SOC; Constant current charging at 5.0C from 25% SOC to 30% SOC; Constant current charging at 5.0C from 30% SOC to 35% SOC; Constant current charging at 5.0C from 35% SOC to 40% SOC; Constant current charging at 4.6C from 40% SOC to 45% SOC; Constant current charging at 4.3C from 45% SOC to 50% SOC; Constant current charging at 4.0C from 50% SOC to 55% SOC; Constant current charging at 3.7C from 55% SOC to 60% SOC; Constant current charging at 3.4C from 60% SOC to 65% SOC; Constant current charging at 3.1C from 65% SOC to 70% SOC; Constant current charging at 2.9C from 70% SOC to 75% SOC; Constant current charging at 2.7C from 75% SOC to 80% SOC; Constant current charging at 1.8C from 80% SOC to 85% SOC; Constant current charging at 1.3C from 85% SOC to 90% SOC; Constant current charging at 0.7C from 90% SOC to 95% SOC; Constant current charging at 0.33C from 95% SOC to 98% SOC; Constant current charging at 0.3C from 98% SOC to 100% SOC.

[0456] The cut-off voltage of the last charging step in the above charging steps is 3.65 V. The difference between the cut-off voltage of any one of the N - 1 charging steps and the cut-off voltage of the last charging step is less than or equal to 0.05 V. The cut-off voltage of each of the N - 1 charging steps is 3.6 V, and the difference in the state of charge of the maximum between two adjacent charging steps is less than or equal to 5% SOC.

[0457] charging strategy 5 After assembling the battery cell prepared in Example 1 with the battery management system BMS into a battery pack, charging is carried out at an external temperature of 30 °C. The charging steps include the following steps: Constant current charging at 5.0 C from 0% SOC to 5% SOC; Constant current charging at 5.0 C from 5% SOC to 10% SOC; Constant current charging at 5.0 C from 10% SOC to 15% SOC; Constant current charging at 5.0 C from 15% SOC to 20% SOC; Constant current charging at 5.0 C from 20% SOC to 25% SOC; Constant current charging at 5.0 C from 25% SOC to 30% SOC; Constant current charging at 5.0 C from 30% SOC to 35% SOC; Constant current charging at 5.0 C from 35% SOC to 40% SOC; Constant current charging at 4.6 C from 40% SOC to 45% SOC; Constant current charging at 4.3 C from 45% SOC to 50% SOC; Constant current charging at 4.0 C from 50% SOC to 55% SOC; Constant current charging at 3.7 C from 55% SOC to 60% SOC; Constant current charging at 3.4 C from 60% SOC to 65% SOC; Constant current charging at 3.1 C from 65% SOC to 70% SOC; Constant current charging at 2.9 C from 70% SOC to 75% SOC; Constant current charging at 2.7 C from 75% SOC to 80% SOC; Constant current charging at 1.8 C from 80% SOC to 85% SOC; Constant current charging at 1.3 C from 85% SOC to 90% SOC; Constant current charging at 0.7 C from 90% SOC to 95% SOC; Constant current charging at 0.33 C from 95% SOC to 98% SOC; Charge from 98% SOC to 100% SOC at a constant current of 0.1C.

[0458] The cut-off voltage of the last charging step in the above charging steps is 3.65V. The difference between the cut-off voltage of any one of the N - 1 charging steps and the cut-off voltage of the last charging step is less than or equal to 0.02V. The cut-off voltage of each of the N - 1 charging steps is 3.63V. The difference in the state of charge between two adjacent charging steps is less than or equal to 5% SOC.

[0459] charging strategy 6 After assembling the battery cells prepared in Example 1 with the battery management system BMS into a battery pack, charge it at an external temperature of 30°C. The charging steps include the following steps: Charge from 0% SOC to 5% SOC at a constant current of 5.0C; Charge from 5% SOC to 10% SOC at a constant current of 5.0C; Charge from 10% SOC to 15% SOC at a constant current of 5.0C; Charge from 15% SOC to 20% SOC at a constant current of 5.0C; Charge from 20% SOC to 25% SOC at a constant current of 5.0C; Charge from 25% SOC to 30% SOC at a constant current of 5.0C; Charge from 30% SOC to 35% SOC at a constant current of 5.0C; Charge from 35% SOC to 40% SOC at a constant current of 5.0C; Charge from 40% SOC to 45% SOC at a constant current of 4.6C; Charge from 45% SOC to 50% SOC at a constant current of 4.3C; Charge from 50% SOC to 55% SOC at a constant current of 4.0C; Charge from 55% SOC to 60% SOC at a constant current of 3.7C; Charge from 60% SOC to 65% SOC at a constant current of 3.4C; Charge from 65% SOC to 70% SOC at a constant current of 3.1C; Charge from 70% SOC to 75% SOC at a constant current of 2.9C; Charge from 75% SOC to 80% SOC at a constant current of 2.7C; Charge from 80% SOC to 85% SOC at a constant current of 1.8C; Charge from 85% SOC to 90% SOC at a constant current of 1.3C; Charge from 90% SOC to 95% SOC at a constant current of 0.7C; Charge from 95% SOC to 98% SOC at a constant current of 0.33C; Charge from 98% SOC to 100% SOC at a constant current of 0.1C.

[0460] In the above charging steps, the cut-off voltage of the last charging step is 3.65V. The difference between the cut-off voltage of any one of the N - 1 charging steps and the cut-off voltage of the last charging step is less than or equal to 0.08V, and the cut-off voltage of each of the N - 1 steps is 3.57V. The difference in the maximum state of charge between two adjacent charging steps is less than or equal to 5% SOC.

[0461] Charging Strategy 7 (Slow Charging Comparison) After assembling the battery cell prepared in Example 1 with the battery management system BMS into a battery pack, charge it at an external temperature of 30°C. The charging steps include the following: Charge from 0% SOC to 30% SOC at a constant current of 3.0C; Charge from 30% SOC to 35% SOC at a constant current of 2.8C; Charge from 35% SOC to 40% SOC at a constant current of 2.6C; Charge from 40% SOC to 45% SOC at a constant current of 2.4C; Charge from 45% SOC to 50% SOC at a constant current of 2.2C; Charge from 50% SOC to 55% SOC at a constant current of 2.0C; Charge from 55% SOC to 60% SOC at a constant current of 1.8C; Charge from 60% SOC to 65% SOC at a constant current of 1.6C; Charge from 65% SOC to 70% SOC at a constant current of 1.4C; Charge from 70% SOC to 75% SOC at a constant current of 1.3C; Charge from 75% SOC to 80% SOC at a constant current of 1.2C; Charge from 80% SOC to 85% SOC at a constant current of 0.8C; Charge from 85% SOC to 90% SOC at a constant current of 0.6C; Charge from 90% SOC to 95% SOC at a constant current of 0.4C; Charge from 95% SOC to 98% SOC at a constant current of 0.33C; Charge from 98% SOC to 100% SOC at a constant current of 0.3C.

[0462] The cut-off voltage of the last charging step in the above charging steps is 3.65V. The difference between the cut-off voltage of any one of the N-1 charging steps and the cut-off voltage of the last charging step is equal to 0V, that is, the cut-off voltage of each charging step is 3.65V, and the difference in the maximum state of charge between two adjacent charging steps is less than or equal to 5% SOC.

[0463] Charging strategy 8 After assembling the battery monomer prepared in Example 1 with the battery management system BMS into a battery pack, charging is carried out at an external temperature of 30°C. The charging steps include the following steps: Constant current charge at 5.0C from 0% SOC to 5% SOC; Constant current charge at 5.0C from 5% SOC to 10% SOC; Constant current charge at 5.0C from 10% SOC to 15% SOC; Constant current charge at 5.0C from 15% SOC to 20% SOC; Constant current charge at 5.0C from 20% SOC to 25% SOC; Constant current charge at 5.0C from 25% SOC to 30% SOC; Constant current charge at 5.0C from 30% SOC to 35% SOC; Constant current charge at 5.0C from 35% SOC to 40% SOC; Constant current charge at 5C from 40% SOC to 45% SOC; Constant current charge at 4.3C from 45% SOC to 50% SOC; Constant current charge at 4.0C from 50% SOC to 55% SOC; Constant current charge at 3.7C from 55% SOC to 60% SOC; Constant current charge at 3.4C from 60% SOC to 65% SOC; Constant current charge at 3.1C from 65% SOC to 70% SOC; Constant current charge at 2.9C from 70% SOC to 75% SOC; Constant current charge at 2.7C from 75% SOC to 80% SOC; Constant current charge at 1.8C from 80% SOC to 85% SOC; Constant current charge at 1.3C from 85% SOC to 90% SOC; Constant current charge at 0.7C from 90% SOC to 95% SOC; Constant current charge at 0.33C from 95% SOC to 98% SOC; Constant current charge at 0.33C from 98% SOC to 100% SOC.

[0464] In the above charging steps, the cut-off voltage of the last charging step is 3.65 V, and the difference between the cut-off voltage of any one of the N - 1 charging steps and the cut-off voltage of the last charging step is equal to 0 V, that is, the cut-off voltage of each charging step is 3.65 V, and the difference in the state of charge (SOC) between two adjacent charging steps is less than or equal to 5% SOC.

[0465] Preparation of the battery pack in Example 2 The battery cells and the battery pack were prepared by a method similar to that in Example 1. Different from Example 1, the positive electrode active material includes lithium iron manganese phosphate and a coating layer, and the coating layer coats the surface of the lithium iron manganese phosphate. The coating layer includes lithium 2 FeTi(PO 4 ) 3 and amorphous carbon.

[0466] Charging strategy 9 After assembling the battery cells prepared in Example 2 with the battery management system (BMS) into a battery pack, charging was carried out at an external temperature of 30 °C. The charging steps include the following steps: Constant current charging at 5.0 C from 0% SOC to 5% SOC; Constant current charging at 5.0 C from 5% SOC to 10% SOC; Constant current charging at 5.0 C from 10% SOC to 15% SOC; Constant current charging at 5.0 C from 15% SOC to 20% SOC; Constant current charging at 5.0 C from 20% SOC to 25% SOC; Constant current charging at 5.0 C from 25% SOC to 30% SOC; Constant current charging at 5.0 C from 30% SOC to 35% SOC; Constant current charging at 5.0 C from 35% SOC to 40% SOC; Constant current charging at 5.0 C from 40% SOC to 45% SOC; Constant current charging at 4.3 C from 45% SOC to 50% SOC; Constant current charging at 4.0 C from 50% SOC to 55% SOC; Constant current charging at 3.7 C from 55% SOC to 60% SOC; Constant current charging at 3.4 C from 60% SOC to 65% SOC; Constant current charging at 3.1 C from 65% SOC to 70% SOC; Constant current charging at 2.9 C from 70% SOC to 75% SOC; Constant current charging at 2.7 C from 75% SOC to 80% SOC; Charge from 80% SOC to 85% SOC at a constant current of 1.8C; Charge from 85% SOC to 90% SOC at a constant current of 1.3C; Charge from 90% SOC to 95% SOC at a constant current of 0.7C; Charge from 95% SOC to 98% SOC at a constant current of 0.33C; Charge from 98% SOC to 100% SOC at a constant current of 0.33C.

[0467] In the above charging steps, the cut-off voltage of the last charging step is 4.25V. The difference between the cut-off voltage of any one of the N - 1 charging steps and the cut-off voltage of the last charging step is less than or equal to 0.05V. The cut-off voltage of each charging step in the N - 1 steps is 4.2V, and the difference in the maximum state of charge between two adjacent charging steps is less than or equal to 5% SOC.

[0468] Performance Test 1. Lithium plating area test of battery cells After each battery pack of each embodiment is cycled 20 times according to its respective charge and discharge strategy, the following strategy is adopted for discharging: discharge at a constant current of 0.33C to 2.0V, and then fully charge to 100% SOC according to the corresponding charging strategy. Disassemble the negative electrode plate in the battery pack, unfold the negative electrode plate, observe the lithium plating area (grayish-white area), and measure the lithium plating area. No lithium plating: Lithium plating area < 0.05%.

[0469] Slight lithium plating: Lithium plating area < 2%.

[0470] Severe lithium plating: Lithium plating area ≥ 2%.

[0471] Test Results The test results are shown in Table 1.

[0472] Table 1

[0473] As can be seen from Table 1, when adopting a slower charging strategy (charging strategy 7), although there is basically no lithium plating on the negative electrode plate, its charging time is relatively long and it cannot meet the requirements of fast charging.

[0474] When adopting a faster charging strategy (charging strategy 8), when charging to the cut-off voltage in each step, the risk of lithium plating in each step is relatively large, resulting in severe lithium plating on the negative electrode plate during the entire charging process, which is very likely to shorten the service life of the battery pack, etc.

[0475] During the charging process of the battery pack according to the embodiment of the present application, the difference in the maximum state of charge between adjacent charging steps is less than or equal to 5% state of charge, resulting in less polarization during the charging process; before the Nth charging step, that is, the cut-off voltage of any charging step from the 1st charging step to the (N - 1)th charging step is relatively small, so that during the charging process, the voltage does not rise sharply, and the lithium ions released from the positive electrode film layer can basically be embedded in the negative electrode film layer, and lithium deposition is not likely to occur on the surface of the negative electrode plate, which can improve the reliability of the battery cell in use.

[0476] Moreover, the embodiment of the present application is applicable to different phosphate systems, such as lithium iron phosphate, lithium manganese iron phosphate, lithium manganese phosphate, etc. The corresponding battery cut-off voltages are different, which means that the embodiment of the present application is applicable to batteries with different cut-off voltages, such as batteries less than or equal to 4.4V, and the battery system can be optionally 3.65V to 4.4V. For the above battery systems adopting the charging strategy of the present application, fast charging can be achieved, and the risk of lithium deposition can be reduced.

[0477] Although the illustrative embodiments have been demonstrated and described, those skilled in the art should understand that the above embodiments should not be construed as limitations of the present application, and the embodiments can be changed, substituted, and modified without departing from the spirit, principle, and scope of the present application.

Claims

1. A battery cell, characterized in that: The invention comprises an electrolyte and an electrode assembly, wherein the electrode assembly comprises a positive electrode sheet, a negative electrode sheet and a separator between the positive electrode sheet and the negative electrode sheet. The positive electrode sheet comprises a positive electrode current collector and a positive electrode film layer disposed on at least one side of the positive electrode current collector and containing a positive electrode active material, wherein the positive electrode active material comprises a lithium-containing phosphate with an olivine structure; the negative electrode sheet comprises a negative electrode current collector and a negative electrode film layer disposed on at least one side of the negative electrode current collector and containing a negative electrode active material, wherein the negative electrode film layer comprises a carbon-based material; The charging process of the battery cell from 0% state of charge to 100% state of charge includes N charging steps, the difference between the maximum state of charge of any charging step in the N charging steps and the maximum state of charge in the adjacent charging step is less than or equal to 5% state of charge, and N is a positive integer greater than or equal to 2; In the N charging steps, the cut-off voltage of any charging step in the N-1 charging steps is less than the cut-off voltage of the Nth charging step, and the cut-off voltage of the Nth charging step does not exceed 4.4V. At room temperature, the charging time of the battery cell from 10% state of charge to 80% state of charge is 5 minutes to 10.5 minutes.

2. The battery cell according to claim 1, characterized in that: The cut-off voltage of the Nth charging step is greater than the cut-off voltage of any charging step in the N-1 charging steps, and the difference between the cut-off voltage of the Nth charging step and the cut-off voltage of any charging step in the N-1 charging steps is greater than or equal to 0.02V.

3. The battery cell according to claim 1 or 2, characterized in that: The cut-off voltage of the Nth charging step is greater than the cut-off voltage of any charging step in the N-1 charging steps, and the difference between the cut-off voltage of the Nth charging step and the cut-off voltage of any charging step in the N-1 charging steps is greater than or equal to 0.05V.

4. The battery cell according to claim 3, characterized in that: The cut-off voltage of the Nth charging step is greater than the cut-off voltage of any charging step in the N-1 charging steps, and the difference between the cut-off voltage of the Nth charging step and the cut-off voltage of any charging step in the N-1 charging steps is 0.05V to 0.2V.

5. The battery cell according to claim 1, characterized in that: The cut-off voltage of the Nth charging step is 3.65V to 4.4V.

6. The battery cell according to claim 1, characterized in that: The charging rate of the Nth charging step is 0.05C to 0.30C.

7. The battery cell according to claim 6, characterized in that: The charging rate of the Nth charging step is 0.1C to 0.30C.

8. The battery cell according to claim 1, characterized in that: The charging rate of the battery cell in the Mth charging step is 3.5C to 6C, the state of charge of the battery cell in the Mth charging step includes a 50% state of charge, M is less than N, and M is a positive integer greater than or equal to 1.

9. The battery cell according to claim 1, characterized in that: The charging rate of the battery cell in any charging step from 0% state of charge to 40% state of charge is 4C to 8C.

10. The battery cell according to claim 1, characterized in that: The constant current value of the Qth charging step in the N charging steps is less than the constant current value of the Q-1th charging step, Q is less than or equal to N, and Q is a positive integer greater than or equal to 2.

11. The battery cell according to claim 1, characterized in that: The lithium-containing phosphate of the olivine structure comprises: Phosphate particles, and The coating layer is coated on the surface of the phosphate particles, and the coating layer contains one or more elements selected from the group consisting of C, Fe, Ti, Zr, Hf, Ge and Sn.

12. The battery cell according to claim 11, characterized in that: The phosphate particles include a general formula of Li x1 A y1 Me a M b P 1-c X c Y z A compound wherein 0.5≤x1≤1.3, 0≤y1≤1.3, and 0.9≤x1+y1≤1.3, 0.9≤a≤1.5, 0≤b≤0.5, and 0.9≤a+b≤1.5, 0≤c≤0.5, 3≤z≤5, A includes one or more of Na, K, and Mg, Me includes one or more of Mn, Fe, Co, and Ni, M includes one or more of B, Mg, Al, Si, P, S, Ca, Sc, Ti, V, Cr, Cu, Zn, Sr, Y, Zr, Nb, Mo, Cd, Sn, Sb, Te, Ba, Ta, W, Yb, La, and Ce, X includes one or more of S, Si, Cl, B, C, and N, and Y includes one or more of O and F.

13. The battery cell according to claim 11 or 12, characterized in that: The coating layer includes a general formula of Li 3- d Fe 2-d M2 d (PO x2 ) y2 The fast ion conductor M2 includes one or more elements of Ti, Zr, Hf, Ge and Sn, 0≤d≤1, 0<x2<5, 0<y2<4.

14. The battery cell according to claim 11, characterized in that: The mass content of carbon in the lithium-containing phosphate with an olivine structure is 1% to 2%; The specific surface area of ​​the lithium-containing phosphate of the olivine structure is 5m 2 / g to 18m 2 / g.

15. The battery cell according to claim 1, characterized in that: The single-sided coating weight of the positive electrode film layer is 200 mg / 1540 mm 2 Up to 370mg / 1540 / mm 2 ; and / or The battery cell is at 100% charge state, and the compaction density of the positive electrode film layer is 2.50 g / cm 3 Up to 2.80g / cm 3 .

16. The battery cell according to claim 1, characterized in that: The single-sided coating weight of the negative electrode film layer is 90 mg / 1540 mm 2 Up to 170mg / 1540mm 2 ; and / or The battery cell is at 100% charge state, and the compaction density of the negative electrode film layer is 1.15 g / cm 3 Up to 1.36g / cm 3 .

17. The battery cell according to claim 16, 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 Up to 1.36g / cm 3 .

18. The battery cell according to claim 1, characterized in that: The carbon-based material includes graphite particles, and the graphite particles have a degree of graphitization of 92.0% to 94.5%.

19. The battery cell according to claim 18, 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.

20. The battery cell according to claim 18 or 19, characterized in that: The negative electrode film layer comprises: a first negative electrode film layer, disposed on the surface of the negative electrode current collector, wherein the first negative electrode film layer comprises a carbon-based material, and A second negative electrode film layer is connected to a side of the first negative electrode film layer away from the negative electrode current collector, and the second negative electrode film layer comprises a carbon-based material. The carbon-based material in the first negative electrode film layer and the carbon-based material in the second negative electrode film layer each independently include graphite particles, and the volume average particle size Dv50 of the graphite particles in the first negative electrode film layer is greater than or equal to the volume average particle size Dv50 of the graphite particles in the second negative electrode film layer.

21. The battery cell according to claim 20, 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.

22. The battery cell according to claim 20, 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.

23. The battery cell according to claim 22, characterized in that: The tap density of the carbon-based material in the first negative electrode film layer is 0.82 g / cm 3 Up to 1.21g / cm 3 , and / or The tap density of the carbon-based material in the second negative electrode film layer is 0.90 g / cm 3 Up to 1.25g / cm 3 .

24. The battery cell according to claim 20, characterized in that: 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.

25. The battery cell according to claim 24, characterized in that: The ratio of the thickness of the second negative electrode film layer to the thickness of the first negative electrode film layer is 4:6 to 6:

4.

26. The battery cell according to claim 20, characterized in that: After the battery cell has been subjected to 10 cycles of the BOL full charge test at the beginning of life, the thickness of the first negative electrode film layer is 15 μm to 65 μm, and / or the thickness of the second negative electrode film layer is 15 μm to 65 μm.

27. The battery cell according to claim 20, characterized in that: After the battery cell is subjected to an end-of-life (EOL) full charge test, the thickness of the first negative electrode film layer is 15 μm to 70 μm, and / or the thickness of the second negative electrode film layer is 15 μm to 70 μm.

28. The battery cell according to claim 20, 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.

29. The battery cell according to claim 28, 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%.

30. The battery cell according to claim 28 or 29, characterized in that: The mass content of lithium in the first lithium-containing binder is 3% to 10%, and / or The mass content of lithium element in the second lithium-containing binder is 3% to 10%.

31. The battery cell according to claim 28, characterized in that The first lithium-containing binder comprises a lithium acrylate-acrylonitrile-acrylamide-hydroxyethyl acrylate copolymer, wherein the lithium acrylate-acrylonitrile-acrylamide-hydroxyethyl acrylate copolymer is derived from a lithium acrylate monomer, an acrylonitrile monomer, an acrylamide monomer and a hydroxyethyl acrylate monomer, and the molar ratio of the lithium acrylate monomer, the acrylonitrile monomer, the acrylamide monomer and the hydroxyethyl acrylate monomer is 30% to 50%: 15% to 45%: 5% to 20%: 20% to 35%; and / or The second lithium-containing binder includes a lithium acrylate-acrylonitrile-acrylamide-hydroxyethyl acrylate copolymer, wherein the lithium acrylate-acrylonitrile-acrylamide-hydroxyethyl acrylate copolymer is derived from a lithium acrylate monomer, an acrylonitrile monomer, an acrylamide monomer and a hydroxyethyl acrylate monomer, and the molar ratio of the lithium acrylate monomer, the acrylonitrile monomer, the acrylamide monomer and the hydroxyethyl acrylate monomer is 30% to 50%: 15% to 45%: 5% to 20%: 20% to 35%.

32. The battery cell according to claim 1, characterized in that The negative electrode active material further includes a silicon-based material, and a 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.

33. The battery cell according to claim 1, characterized in that: The isolation membrane includes a base membrane with a porous structure, the porosity of the base membrane is 20% to 70%; and / or the thickness of the base membrane is 6 μm to 12 μm.

34. The battery cell according to claim 33, characterized in that: The isolation film further includes a functional layer disposed on at least one side of the base film, and the functional layer includes: a first functional layer, located on one side of the base film, wherein the first functional layer comprises first inorganic particles, The second functional layer is located on the other side of the base film, and the second functional layer includes composite particles. The composite particles include second inorganic particles and a plurality of non-fluoropolymer particles. The second inorganic particles are attached to the surface of the non-fluoropolymer particles and / or dispersed inside the non-fluoropolymer particles.

35. The battery cell according to claim 34, characterized in that: The non-fluorinated polymer particles include acrylic copolymers.

36. The battery cell according to claim 34 or 35, characterized in that: The first inorganic particles include one or more of silicon oxide, aluminum oxide, boehmite, barium sulfate, calcium oxide, titanium oxide, zinc oxide, magnesium oxide, zirconium oxide and tin oxide, and / or The second inorganic particles include one or more of silicon oxide, aluminum oxide, boehmite, barium sulfate, calcium oxide, titanium oxide, zinc oxide, magnesium oxide, zirconium oxide, and tin oxide.

37. The battery cell according to claim 34, characterized in that The average particle size of the second inorganic particles is 5 nm to 100 nm.

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

39. The battery cell according to claim 1, characterized in that: The electrolyte includes an organic solvent, and the organic solvent includes one or more of a carbonate solvent and a carboxylate solvent.

40. The battery cell according to claim 39, characterized in that The carboxylate ester solvent includes a chain carboxylate ester solvent, and the mass content of the chain carboxylate ester solvent relative to the mass of the organic solvent is greater than or equal to 5% and less than 75%.

41. The battery cell according to claim 1, characterized in that The ratio of the negative electrode capacity per unit area to the positive electrode capacity per unit area in the battery cell is 1.05 to 1.

20.

42. The battery cell according to claim 1, characterized in that The battery cell comprises a positive terminal, the positive electrode sheet comprises a positive electrode tab, and the positive terminal and the positive electrode tab are directly welded; and / or The battery cell includes a negative electrode terminal, the negative electrode plate includes a negative electrode tab, and the negative electrode terminal and the negative electrode tab are directly welded.

43. The battery cell according to claim 42, characterized in that The flow area of ​​a single positive terminal is 25mm 2 Up to 315mm 2 ; and / or The flow area of ​​a single negative terminal is 25mm 2 Up to 315mm 2 .

44. The battery cell according to claim 1, characterized in that It also includes a shell, which accommodates the electrode assembly. The material of the shell includes steel, and the thickness of the shell is 0.1mm to 0.5mm.

45. A battery device, characterized in that: Comprising the battery cell according to any one of claims 1 to 44.

46. ​​The battery device according to claim 45, characterized in that At room temperature, the battery device has a charging time of 5 min to 10.5 min from a 10% state of charge to an 80% state of charge.

47. An electrical device, characterized in that: Comprising a battery device as claimed in claim 45 or 46.

48. A method for charging a battery cell, characterized in that: A battery cell according to any one of claims 1 to 44, comprising: Charging a battery cell in a first state of charge so that an increase in the state of charge of the battery cell is less than or equal to 5% state of charge; Repeat the above steps at least once until the battery cell is charged to a second state of charge, wherein the second state of charge is greater than the first state of charge, and the second state of charge is greater than or equal to 95% state of charge and less than 100% state of charge; The battery cell in the second state of charge is charged to 100% state of charge, wherein: The cut-off voltage of any step before charging to the second state of charge is less than the cut-off voltage of the step of charging to 100% state of charge, and the cut-off voltage of the step of charging to 100% state of charge does not exceed the theoretical voltage upper limit of the lithium-containing phosphate with an olivine structure.

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