Battery cell, battery device and electrical device

Abstract

The present application relates to a battery cell, a battery device and an electrical device. The battery cell includes an electrolyte, a positive electrode plate and a negative electrode plate. The positive electrode plate includes a positive current collector portion and a positive electrode film layer containing a positive electrode active material on at least one surface of the positive current collector portion. The positive electrode active material includes a lithium-containing phosphate with an olivine structure. The single-sided coating weight of the positive electrode film layer is from 200 mg / 1540.25 mm<supgt;2< / supgt> to 370 mg / 1540.25 mm<supgt;2< / supgt>. The negative electrode plate includes a negative current collector portion and a negative electrode film layer containing a negative electrode active material on at least one surface of the negative current collector portion. The negative electrode active material includes a carbon-based material. The conductivity of the electrolyte is 13 - 20 mS / cm. When the battery cell is discharged at a constant current of 0.33C from a 100% state of charge to 2.0V at 25°C, there is a discharge platform voltage V<subgt;1< / subgt>, and V<subgt;1 is 3.19 - 3.235V. The present application can improve the fast charging performance, energy density and cycling performance of the battery cell.

Description

[0001] This application claims the priority of the PCT international application PCT / CN2024 / 107009, titled "Battery Cell, Battery Device and Electrical Device", filed on July 23, 2024, the entire content of which is incorporated herein by reference. Technical Field

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

[0003] Battery cells have characteristics such as high capacity and long life, and are thus 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 power tools, etc. Due to the great progress in the battery field, higher requirements are put forward for the performance of batteries. The fast charging performance, energy density and cycling performance of battery cells still need to be further improved. Summary of the Invention

[0004] This application provides a battery cell, a battery device and an electrical device, which can improve the fast charging performance of the battery cell and enable the battery cell to have a relatively high energy density and cycling performance.

[0005] In a first aspect, this application proposes a battery cell. The battery cell includes an electrode assembly and an electrolyte. The electrode assembly includes a positive electrode tab, a negative electrode tab and a separator. The separator is located between the positive electrode tab and the negative electrode tab. The positive electrode tab includes a positive current collector and at least one surface disposed on the positive current collector along the thickness direction of the positive electrode tab and including a positive electrode film layer containing a positive electrode active material. The positive electrode active material includes a lithium-containing phosphate with an olivine structure. 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 , the negative electrode tab includes a negative current collector and at least one surface disposed on the negative current collector along the thickness direction of the negative electrode tab and including a negative electrode film layer containing a negative electrode active material. The negative electrode active material includes a carbon-based material. The conductivity of the electrolyte at room temperature is 13 mS / cm to 20 mS / cm. In an external environment at 25 °C, during the discharge process of the battery cell from 100% state of charge at a constant current rate of 0.33C to 2.0V, it has a discharge platform voltage V1, and V1 is 3.19V to 3.235V.

[0006] Thus, in the embodiments of this application, the positive electrode active material in the positive electrode tab includes a lithium-containing phosphate with an olivine structure, and the negative electrode active material in the negative electrode tab includes a carbon-based material. The material system structure is more stable, and the cycling stability of the material system is relatively excellent; the single-sided coating weight of the positive electrode film layer is 200 mg / 1540.25 mm2 Up to 370mg / 1540.25mm 2 The conductivity of the electrolyte at room temperature is 13mS / cm to 20mS / cm, which is conducive to achieving fast charging performance and excellent cycle performance of the battery cell; and the battery cell has a discharge platform voltage V1 during the discharge process, which makes the energy density of the battery cell relatively high.

[0007] In some embodiments, the electrode assembly is a laminated structure, with the positive electrode sheet, separator, and negative electrode sheet stacked, and V1 is 3.19 V to 3.225 V. The battery cell has a discharge platform voltage V1 during discharge, resulting in a relatively high energy density of the battery cell.

[0008] In some embodiments, the electrode assembly is a laminated structure, and the positive electrode sheet further includes a positive electrode tab, which is disposed on at least one side of the positive current collecting portion along the length direction of the positive electrode sheet.

[0009] In some embodiments, the electrode assembly has a laminated structure, with positive electrode tabs disposed on either side of the positive current collecting portion along the length of the positive electrode sheet. This arrangement evenly divides the current flowing along the length of the positive current collecting portion between the tabs, shortening the electron transmission path and providing a more uniform current distribution. This also results in a more uniform delithiation state across the positive electrode sheet, improving the charging performance of the battery cells.

[0010] In some embodiments, the electrode assembly has a laminated structure, the positive electrode film layer has a length (i.e., the length of the positive electrode film layer) along the length of the positive electrode sheet, which is 200 mm to 400 mm, and a V1 range of 3.20 V to 3.225 V. Positive electrode film layers of these dimensions, combined with the aforementioned discharge platform voltage, can further enhance the energy density of the battery cell.

[0011] In some embodiments, the electrode assembly has a laminated structure, the length of the positive electrode film is greater than 400 mm and less than or equal to 1000 mm, and V1 is 3.19 V to 3.218 V. The above-mentioned dimensions of the positive electrode film, combined with the above-mentioned discharge platform voltage, are conducive to further improving the energy density of the battery cell.

[0012] In some embodiments, the electrode assembly has a wound structure, with the positive electrode sheet, separator, and negative electrode sheet wound in the same direction, and V1 is 3.215 V to 3.235 V. The wound electrode assembly, combined with the above-mentioned discharge platform voltage, is conducive to further improving the energy density of the battery cell.

[0013] In some embodiments, the negative electrode active material further comprises a silicon-based material, and V1 is 3.190 V to 3.230 V. The above-mentioned negative electrode active material, combined with the discharge platform voltage, is conducive to further improving the energy density of the battery cell.

[0014] In some embodiments, the silicon-based material contains 0.3% to 10.0% silicon by weight, based on the weight of the negative electrode active material. The above-mentioned negative electrode active material, combined with the discharge platform voltage, is conducive to further improving the energy density of the battery cell.

[0015] In some embodiments, the electrode assembly has a laminated structure, and V1 is 3.190 V to 3.218 V. The laminated electrode assembly, combined with the silicon-containing negative electrode active material and the above-mentioned discharge platform voltage, is conducive to further improving the energy density of the battery cell.

[0016] In some embodiments, the electrode assembly is a wound structure, and V1 is 3.210 V to 3.230 V. The wound electrode assembly, combined with the silicon-containing negative electrode active material and the above-mentioned discharge platform voltage, is conducive to further improving the energy density of the battery cell.

[0017] In some embodiments, when discharging a battery cell at an ambient temperature of 25°C, the battery cell exhibits a discharge platform voltage V2 when discharged from a 100% state of charge to 2.0V at a constant current rate of 2C, and V2 / V1 is 0.942 to 0.975. In the embodiments of the present application, the discharge platform voltages of the battery cell during discharge at a 0.33 rate and at a 2C rate are similar. The battery cell is relatively completely discharged at both the 0.33 and 2C rates, exhibiting good rate performance and facilitating the utilization of the battery cell's energy density.

[0018] In some embodiments, V2 is 3.05V to 3.15V.

[0019] In some embodiments, the single-sided coating weight of the positive electrode film layer is 240 mg / 1540.25 mm 2 Up to 330mg / 1540.25mm 2 When the single-sided coating weight of the positive electrode film layer is within the above range, the heat generated per unit area of the positive electrode sheet will not be too large, and the energy density of the battery cell can be improved.

[0020] In some embodiments, the single-side coating weight of the negative electrode film layer is 90 mg / 1540.25 mm 2 Up to 170mg / 1540.25mm 2 , optional 110mg / 1540.25mm 2 Up to 150mg / 1540.25mm 2 When the coating weight on one side of the negative electrode film layer is within the above range, the heat generated per unit area of the negative electrode sheet will not be too large, and the energy density of the battery cell can be improved.

[0021] In some embodiments, the compaction density of the positive electrode film layer of the battery cell at 100% state of charge is 2.50 g / cm 3 to 2.80 g / cm 3 . When the compaction density of the positive electrode film layer is within the above range, it is beneficial to improve the energy density of the battery cell. Moreover, since the positive electrode active materials in the positive electrode film layer are stacked relatively closely and the contact resistance between particles is relatively small, the resistance of the electrode sheet can be further reduced, thereby reducing heat generation.

[0022] In some embodiments, the compaction density of the negative electrode film layer of the battery cell at 100% state of charge is 1.15 g / cm 3 to 1.36 g / cm 3 . When the compaction density of the negative electrode film layer is within the above range, it is beneficial to improve the energy density of the battery cell. Moreover, since the negative electrode active materials in the negative electrode film layer are stacked relatively closely and the contact resistance between particles is relatively small, the resistance of the electrode sheet can be further reduced, thereby reducing heat generation.

[0023] In some embodiments, the powder resistivity of the positive electrode active material is 1 Ω•cm to 27.5 Ω•cm. The relatively low powder resistivity of the positive electrode active material results in a relatively low resistance of the positive electrode sheet and less heat generation of the battery cell.

[0024] In some embodiments, the powder compaction density of the positive electrode active material under 30000 N is 2.46 g / cm 3 to 2.8 g / cm 3 . When the powder compaction density of the positive electrode active material under 30000 N is within the above range, the energy density of the battery cell can be improved. Moreover, since the positive electrode active materials in the positive electrode film layer can be stacked more closely and the contact resistance between particles is relatively small, the resistance of the electrode sheet can be further reduced, thereby reducing heat generation.

[0025] In some embodiments, the charging specific capacity of the positive electrode active material at 0.1C rate is 150 mAh / g to 170 mAh / g. When the charging specific capacity of the positive electrode active material at 0.1C rate is within the above range, the energy density of the battery cell is relatively high.

[0026] In some embodiments, the lithium-containing phosphate in olivine structure includes phosphate particles and a coating layer. The coating layer coats the phosphate particles, and the coating layer contains one or more elements of C, Fe, Ti, Zr, Hf, Ge, and Sn. By coating the surface of the phosphate particles with the coating layer, the conductivity of the lithium-containing phosphate in olivine structure can be improved, the powder resistivity of the material can be reduced, and it is beneficial to the migration rate of lithium ions, reducing the heat generation amount of the battery cell.

[0027] In some embodiments, the phosphate particles include a general formula of Lix1 A y1 Me a M b P 1-c X c Y z The 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. The cyclic stability of the phosphate particles is relatively excellent, which is beneficial to improving the cyclic performance of the battery cell.

[0028] In some embodiments, the coating layer includes a fast ion conductor with the general formula Li 3-d Fe 2-d M2 d (PO x2 ) y2 , where M2 includes one or more elements of Ti, Zr, Hf, Ge, and Sn, 0 ≤ d ≤ 1, 0 < x2 < 5, and 0 < y2 < 4. Coating the fast ion conductor on the surface of the phosphate particles can significantly improve the transmission rate of lithium ions during multiple deintercalation / insertion of lithium at the positive electrode, improve the ionic conductivity of the positive electrode active material, and further improve the specific capacity, and further improve the energy density of the corresponding battery cell.

[0029] 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, reduce the heat generation of the positive electrode sheet, and thus reduce the heat generation of the battery cell.

[0030] In some embodiments, the mass content of carbon element in the lithium-containing phosphate with olivine structure is from 1% to 2%, and the specific surface area of the lithium-containing phosphate with olivine structure is from 5 m 2 / g to 18 m 2 / g, optionally from 7.5 m 2 / g to 14 m 2 / g.

[0031] Therefore, in the embodiments of the present application, the carbon element with the above mass content in combination with the material with the above specific surface area is more conducive to the effective contact between the electrolyte and the lithium-containing phosphate in the olivine structure, and is conducive to the transport of lithium ions at the phase interface.

[0032] In some embodiments, the volume distribution particle size of the positive electrode active material satisfies: 1 µm ≤ Dv50 ≤ 2 µm, and / or 0.4 µm ≤ Dv10 ≤ 0.7 µm, and / or 15 µm ≤ Dv99 ≤ 25 µm.

[0033] The particle size of the positive electrode active material is relatively small, the lithium insertion / extraction path of lithium ions in the positive electrode active material is short, and the heat generation is less; moreover, the particle size of the above positive electrode active material is not too small, and agglomeration basically does not occur during the processing and preparation process, so that the performance of the positive electrode active material is stable.

[0034] In some embodiments, the lithium-containing phosphate in the olivine structure is granular. The lithium-containing phosphate in 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 200 nm to 500 nm. The average particle size of the primary particles is relatively small, the lithium insertion / extraction path of lithium ions in the positive electrode active material is short, and the heat generation is less.

[0035] In some embodiments, the ratio of the thickness of the positive electrode current collector part to the total thickness of the single-sided positive electrode film layer is 0.06 to 0.10. When the positive electrode sheet meets the above range, the thickness of the positive electrode current collector part is relatively thin, which can provide more coating space for the positive electrode film layer, thereby improving the energy density of the battery cell and being beneficial to improving the fast charging performance of the battery cell.

[0036] In some embodiments, the positive electrode film layer further includes a first material, and the first material includes one or more of ternary materials, lithium phosphate, lithium hydrogen phosphate, lithium sulfate, lithium sulfite, lithium molybdate, lithium oxalate, lithium titanate, lithium tetraborate, lithium metasilicate, lithium manganate, lithium tartrate, lithium citrate, lithium nickelate, and lithium ferrate. The first material as a lithium supplementing agent can supplement lithium ions for the positive electrode film layer, make up for the irreversible lithium ion loss in the system, and improve the capacity, thereby improving the energy density of the battery cell.

[0037] In some embodiments, the mass content of the first material in the positive electrode film layer is 0.5% to 5%. When the mass content of the lithium supplementing agent is within the above range, it can supplement lithium ions for the positive electrode film layer, make up for the irreversible lithium ion loss in the system, and improve the capacity, thereby improving the energy density of the battery cell.

[0038] In some embodiments, the thickness of the positive electrode current collector part is 10 µm to 15 µm. When the thickness of the positive electrode current collector part is within the above range, the current-carrying capacity of the positive electrode current collector part is relatively excellent, and the battery cell can have a relatively high energy density.

[0039] In some embodiments, the positive electrode tab further includes a positive electrode conductive layer, which is located between the positive electrode film layer and the positive electrode current collector. The positive electrode conductive layer can further improve the conductivity of the positive electrode tab, reduce the heat generation of the positive electrode tab, and thus reduce the heat generation of the battery cell.

[0040] In some embodiments, the thickness of the positive electrode conductive layer is 0.5 μm to 2 μm. When the thickness of the positive electrode conductive layer is within the above range, it can further improve the conductivity of the positive electrode tab, reduce the heat generation of the positive electrode tab, and thus reduce the heat generation of the battery cell; moreover, it can take into account the improvement of the energy density of the battery cell.

[0041] In some embodiments, the positive electrode conductive layer includes one or more of a positive electrode conductive agent and a positive electrode binder. The positive electrode conductive agent in the positive electrode conductive layer can improve the conductivity of the positive electrode conductive layer, thereby improving the conductivity of the positive electrode tab and reducing the heat generation of the battery cell; the positive electrode binder in the positive electrode conductive layer can improve the bonding performance between the positive electrode current collector and the positive electrode film layer and improve the structural stability of the positive electrode tab.

[0042] In some embodiments, the positive electrode conductive agent includes one or more of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0043] In some embodiments, the positive electrode binder includes one or more of polyvinylidene fluoride, polytetrafluoroethylene, vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, polyacrylic acid, and fluorinated acrylate resins.

[0044] In some embodiments, the powder resistivity of the negative electrode active material is 0.005 Ω•cm to 0.043 Ω•cm. The relatively low powder resistivity of the negative electrode active material results in a relatively low resistance of the negative electrode tab and less heat generation of the battery cell.

[0045] In some embodiments, the powder compaction density of the negative electrode active material under 20000 N is 1.5 g / cm 3 to 1.85 g / cm 3 . When the powder compaction density of the negative electrode active material under 20000 N is within the above range, it can improve the energy density of the battery cell, and since the negative electrode active material in the negative electrode film layer can be stacked more tightly and the contact resistance between particles is small, it can further reduce the resistance of the electrode tab and thus reduce heat generation.

[0046] In some embodiments, the charging specific capacity of the negative electrode active material at a rate of 0.1C is greater than or equal to 350 mAh / g. When the charging specific capacity of the negative electrode active material at a rate of 0.1C is within the above range, the energy density of the battery cell is relatively high.

[0047] In some embodiments, the negative electrode active material includes a carbon-based material, the carbon-based material includes graphite particles, and the graphitization degree of the graphite particles is 92.0% to 94.5%. When the graphitization degree of the graphite particles is within the above range, the electrical conductivity of the graphite particles is relatively excellent, which can reduce the heat generation of the negative electrode sheet and the battery cell, and can improve the fast charging performance of the battery cell.

[0048] In some embodiments, the graphite particles include artificial graphite and a carbon coating layer, the artificial graphite includes secondary particles, and the carbon coating layer covers the surface of the artificial graphite. The carbon coating layer has more end faces and defects, so that the number of sites capable of intercalating and deintercalating lithium ions is larger, and the electrical conductivity of the carbon coating layer is relatively excellent, which can reduce the internal resistance of the negative electrode sheet and the heat generation of the battery cell.

[0049] In some embodiments, based on the mass of the graphite particles, the mass content of the carbon coating layer is 2% to 5%. When the mass content of the carbon coating layer is within the above range, the internal resistance of the negative electrode sheet can be further reduced, and the heat generation of the battery cell can be reduced.

[0050] In some embodiments, the porosity of the negative electrode film layer is 40% to 55%. When the porosity of the negative electrode film layer is within the above range, it is beneficial to improve the migration rate of lithium ions and the fast charging performance of the battery cell.

[0051] In some embodiments, the negative electrode film layer is a single-layer film layer, the negative electrode active material is granular, and the volume average particle size of the negative electrode active material is 8.2 μm to 13.5 μm. When the volume average particle size of the negative electrode active material is within the above range, the negative electrode film layer can have an excellent pore structure, which is beneficial to improving the fast charging performance of the battery cell.

[0052] In some embodiments, the negative electrode film layer includes a first negative electrode film layer and a second negative electrode film layer. The first negative electrode film layer is disposed on the surface of the negative electrode current collector. The first negative electrode film layer includes a carbon-based material. The second negative electrode film layer is connected to the side of the first negative electrode film layer facing away from the negative electrode current collector. The second negative electrode film layer includes a carbon-based material. The carbon-based materials in the first negative electrode film layer and the second negative electrode film layer 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.

[0053] Therefore, in the embodiments of the present application, there are differences in the particle sizes of the particles in the first negative electrode film layer and the second negative electrode film layer, which can improve the fast charging performance of the battery cell. Specifically, during the fast charging process, the overpotential of the second negative electrode film layer is usually 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 particles 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 improve the problem of lithium deposition on the surface layer of the negative electrode sheet.

[0054] In some embodiments, the carbon-based material in the first negative electrode film layer further includes natural graphite.

[0055] In some embodiments, the tapped density of the carbon-based material in the first negative electrode film layer is less than or equal to the tapped density of the carbon-based material in the second negative electrode film layer. When the tapped density of the carbon-based material in the second negative electrode film layer is greater than the tapped density of the carbon-based material in the first negative electrode film layer, the second negative electrode film layer is filled more densely, which improves the energy density of the battery cell. The first negative electrode film layer is filled relatively sparsely with richer pores, which can improve the fast charging performance of the battery cell.

[0056] 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.

[0057] 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.

[0058] 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 active material in the first negative electrode film layer is within the above range, the fast charging performance can be improved.

[0059] 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 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.

[0060] 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.

[0061] Thus, in the embodiments of the present application, the mass content of the second lithium-containing binder in the second negative electrode film layer is relatively high, and the number of freely movable lithium ions provided by the second lithium-containing binder for the second negative electrode film layer is relatively large, which can further improve the fast charging performance of the battery cell.

[0062] In some embodiments, the mass content of the first lithium-containing binder relative to the mass of the first negative electrode film layer is 0.1% to 1%. When the mass content of the first lithium-containing binder is within the above range, the insertion and extraction rate of lithium ions can be improved, and the fast charging performance of the battery cell can be improved.

[0063] In some embodiments, the mass content of lithium element in the first lithium-containing binder is 3% to 10%, and can be optionally 3% to 8%. When the mass content of lithium element is within the above range, the number of freely movable lithium ions in the negative electrode film layer can be relatively large, which can further shorten the distance for lithium ions to diffuse to the surface of the negative electrode film layer, improve the insertion and extraction rate of lithium ions, and improve the fast charging performance of the battery cell.

[0064] In some embodiments, the mass content of the second lithium-containing binder relative to the mass of the second negative electrode film layer is 0.1% to 1%. When the mass content of lithium element in the second lithium-containing binder is within the above range, the insertion and extraction rate of lithium ions is improved, and the fast charging performance of the battery cell is improved.

[0065] In some embodiments, the mass content of lithium element in the second lithium-containing binder is 3% to 10%, and can be optionally 3% to 8%. When the mass content of lithium element is within the above range, the number of freely movable lithium ions in the negative electrode film layer can be relatively large, which can further shorten the distance for lithium ions to diffuse to the surface of the negative electrode film layer, improve the insertion and extraction rate of lithium ions, and improve the fast charging performance of the battery cell.

[0066] 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 (0.3 - 0.5):(0.15 - 0.45):(0.05 - 0.2):(0.2 - 0.35).

[0067] Thus, the lithium-containing binder of the above material can provide a certain amount of lithium ions for the negative electrode film layer, improving the fast charging performance of the battery cell; moreover, it is not prone to swelling during the charge and discharge process, with a stable structure, so that the cycle performance of the negative electrode film layer is improved during the fast charge and discharge process.

[0068] 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 (0.3-0.5):(0.15-0.45):(0.05-0.2):(0.2-0.35).

[0069] Thus, the lithium-containing binder of the above material can provide a certain amount of lithium ions for the negative electrode film layer, improving the fast charging performance of the battery cell; moreover, it is not prone to swelling during the charge and discharge process, with a stable structure, so that the cycle performance of the negative electrode film layer is improved during the fast charge and discharge process.

[0070] In some embodiments, the thickness of the negative electrode current collector is 4 μm to 6 μm. When the thickness of the negative electrode current collector is within the above range, the current-carrying capacity of the negative electrode current collector is relatively excellent, and it can make the battery cell have a high energy density.

[0071] In some embodiments, the negative electrode sheet further includes a negative electrode conductive layer, and the negative electrode conductive layer is located between the negative electrode film layer and the negative electrode current collector.

[0072] In some embodiments, the thickness of the negative electrode conductive layer is 0.5 μm to 2 μm. The negative electrode conductive layer can further improve the conductivity of the negative electrode sheet, reduce the heat generation of the negative electrode sheet, and thus reduce the heat generation of the battery cell.

[0073] In some embodiments, the negative electrode conductive layer includes one or more of a negative electrode conductive agent and a negative electrode binder. The negative electrode conductive agent in the negative electrode conductive layer can improve the conductivity of the negative electrode conductive layer, thereby improving the conductivity of the negative electrode sheet and reducing the heat generation of the battery cell; the negative electrode binder in the negative electrode conductive layer can improve the bonding performance between the negative electrode current collector and the negative electrode film layer, and improve the structural stability of the negative electrode sheet.

[0074] In some embodiments, the negative electrode conductive agent includes one or more of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0075] In some embodiments, the negative electrode binder includes one or more of styrene-butadiene rubber, water-soluble unsaturated resin SR-1B, water-based acrylic resin, polyvinyl alcohol, sodium alginate, and carboxymethyl chitosan.

[0076] In some embodiments, the conductivity of the electrolyte at room temperature is 15 mS / cm to 20 mS / cm. When the conductivity of the electrolyte 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.

[0077] 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.

[0078] 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.

[0079] In some embodiments, the carboxylic ester solvent includes a chain carboxylic ester solvent, and the mass content of the chain carboxylic ester solvent in the organic solvent is greater than or equal to 5% and less than or equal to 75%, optionally greater than or equal to 10% and less than or equal to 75%, and optionally 30% to 75%. When the mass content of the chain carboxylic ester solvent is within the above range, the viscosity of the electrolyte system is relatively small, which is beneficial to the migration of lithium ions.

[0080] In some embodiments, the chain carboxylic ester solvent includes a compound represented by Formula I,

[0081] Formula I,

[0082] In Formula I,

[0083] R1 includes a hydrogen atom, a halogen atom, a C1-C5 alkyl group, or a C1-C5 haloalkyl group,

[0084] R2 includes a C1-C5 alkyl group or a C1-C5 haloalkyl group.

[0085] Thus, the conductivity of the above chain carboxylic ester solvent in the embodiments of the present application is relatively high, which is beneficial to improving the fast charging ability of the battery cell.

[0086] In some embodiments, R1 includes a hydrogen atom, a halogen atom, a C1-C3 alkyl group, or a C1-C3 haloalkyl group.

[0087] In some embodiments, R2 includes C1-C3 alkyl or C1-C3 haloalkyl.

[0088] In some embodiments, the chain carboxylic ester solvent includes one or more of the compounds represented by Formula I-1 to Formula I-8.

[0089]

[0090] 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 solvents and chain carboxylic ester solvents are used in combination, which improves the conductivity of the electrolyte and is beneficial to the migration of lithium ions.

[0091] In some embodiments, the carbonate solvent includes one or more of ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate.

[0092] In some embodiments, the mass content of the carbonate solvent in the organic solvent is 25% to 95%, and can be optionally 25% to 70%. The carbonate solvent with the above mass content can further improve the conductivity of the electrolyte and is beneficial to the migration of lithium ions.

[0093] In some embodiments, the electrolyte further includes additives, and the additives include one or more of carbonate additives, sulfur-containing additives, and lithium salt additives. The above additives can improve the interfacial film performance on the positive electrode side and / or negative electrode side, which is beneficial to improving the fast charging performance of the battery cell and improving the cycling performance.

[0094] In some embodiments, the carbonate additives include one or more of vinylene carbonate (VC) and fluoroethylene carbonate (FEC).

[0095] In some embodiments, the sulfur-containing additives include one or more of ethylene sulfate (DTD), bis(ethylene sulfate) (2-DTD), butene sulfite (BS), 1,3-propane sultone (PS), ethylene sulfite (ES), and methylene methanedisulfonate (MMDS).

[0096] In some embodiments, the lithium salt additives include one or more of lithium difluorophosphate (LiPO2F2), lithium difluorooxalate borate (LiDFOB), lithium tetrafluoroborate (LiBF4), and lithium bis(oxalate) borate (LiBOB).

[0097] In some embodiments, the mass content of the additive in the electrolyte is 1% to 10%, optionally 2% to 8%. The additive with the above mass content can effectively improve the interfacial film performance on the positive electrode side and / or the negative electrode side, which is beneficial to improving the fast charging performance of the battery cell and improving the cycle performance.

[0098] In some embodiments, the electrolyte further includes a lithium salt, and the lithium salt includes one or more of a fluorosulfonylimide salt and lithium hexafluorophosphate LiPF6. The above lithium salt is easy to dissociate, which is beneficial to the rapid migration of lithium ions; and the electrolyte system is relatively stable and not easy to decompose, which can improve the cycle performance of the battery cell.

[0099] In some embodiments, the fluorosulfonylimide salt includes one or more of lithium bis(fluorosulfonyl)imide LiFSI and lithium bis(trifluoromethylsulfonyl)imide LiTFSI.

[0100] In some embodiments, the lithium salt includes lithium bis(fluorosulfonyl)imide LiFSI and lithium hexafluorophosphate LiPF6. The molar concentration of lithium bis(fluorosulfonyl)imide LiFSI is 0.2 mol / L to 0.5 mol / L, and the molar concentration of lithium hexafluorophosphate LiPF6 is 0.5 mol / L to 1.0 mol / L.

[0101] In some embodiments, the ratio of the molar concentration of lithium bis(fluorosulfonyl)imide to the molar concentration of lithium hexafluorophosphate LiPF6 is 0.2 to 1.0.

[0102] In some embodiments, the thickness of the base film does not exceed 12 μm, optionally 5 μm to 12 μm. When the thickness of the base film is within the above range, the migration path of lithium ions in the base film is shorter, which can further reduce the internal resistance of the battery cell and thus reduce heat generation.

[0103] 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. The second inorganic particles are attached to the surface 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.

[0104] In some embodiments, the non-fluoropolymer particles include an acrylate copolymer. The acrylate copolymer has excellent adhesion performance and high adhesion stability with the base film.

[0105] 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.

[0106] 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.

[0107] 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.

[0108] In some embodiments, the volume energy density of the battery cell is 390 Wh / L to 550 Wh / L. The volume energy density of the battery cell is relatively high.

[0109] In some embodiments, the charging time of the battery cell from 10% state of charge to 80% state of charge is less than or equal to 12.5 min, and can be optionally 6 min to 12.5 min. The charging speed of the battery cell is relatively fast, which is more beneficial to improving the fast charging ability.

[0110] 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.

[0111] In some embodiments, the charging time of the battery device from 10% state of charge to 80% state of charge is less than or equal to 12.5 min, and can be optionally 6 min to 12.5 min. The charging speed of the battery device is relatively fast, which is more beneficial to improving the fast charging ability.

[0112] 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. BRIEF DESCRIPTION OF THE DRAWINGS

[0113] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following will briefly introduce the drawings required to be used in the embodiments of the present application. Obviously, the following described drawings are only some embodiments of the present application. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained according to the drawings.

[0114] Figure 1 It is a schematic structural diagram of a battery cell provided in some embodiments of the present application;

[0115] Figure 2Explosion schematic diagram of a battery cell provided for some embodiments of the present application;

[0116] Figure 3 Schematic structural diagram of a battery module provided for some embodiments of the present application;

[0117] Figure 4 Schematic structural diagram of a battery pack provided for some embodiments of the present application;

[0118] Figure 5 Schematic structural diagram of an electrical device provided for some embodiments of the present application.

[0119] The drawings are not necessarily drawn to actual scale.

[0120] Explanation of reference numerals is as follows:

[0121] 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;

[0122] 7. Battery cell;

[0123] 10. Electrode assembly; 111. Positive electrode tab; 112. Negative electrode tab; 12. Main body part;

[0124] 20. Outer shell; 21. Housing; 22. End cover;

[0125] 31. Positive terminal; 32. Negative terminal. Specific embodiments

[0126] Hereinafter, embodiments of the battery cell, battery device, and electrical device of the present application that are specifically disclosed will be described in detail with appropriate reference to the drawings. However, there may be cases where unnecessary detailed descriptions are omitted. For example, there are cases where detailed descriptions of well-known matters and repeated descriptions of actually identical structures are omitted. This is to prevent 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 recited in the claims.

[0127] 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 contemplated. In addition, if the minimum range values 1 and 2 are listed, and if the maximum range values 3, 4, and 5 are listed, then the following ranges are all contemplated: 1 to 3, 1 to 4, 1 to 5, 2 to 3, 2 to 4, and 2 to 5. In this application, unless otherwise specified, the numerical range "a to b" represents an abbreviated representation of any real number combination between a and b, where a and b are both real numbers. For example, the numerical range "0 to 5" means that all real numbers between "0 to 5" 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.

[0128] 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.

[0129] 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.

[0130] 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.

[0131] With the development of the battery field, the performance requirements for batteries are getting higher and higher, especially the requirements for the energy density and fast charging performance of batteries are gradually increasing, while the related technologies are difficult to balance the energy density and fast charging performance of batteries.

[0132] In view of the above problems, the embodiments of this application have designed the system of the battery cell. The electrode has a small resistance, which is beneficial to improving the fast charging performance of the battery cell; by adjusting the discharge voltage platform of the battery cell, the battery cell has a high energy density.

[0133] battery cell

[0134] In a first aspect, an embodiment of the present application provides a battery cell.

[0135] The battery cell includes an electrode assembly and an electrolyte. The electrode assembly includes a positive electrode sheet, a negative electrode sheet and a separator. The separator is located between the positive electrode sheet and the negative electrode sheet. The positive electrode sheet includes a positive current collector and a positive electrode film layer provided on at least one surface of the positive current collector along the thickness direction of the positive electrode sheet and containing a positive electrode active material. The positive electrode active material includes a lithium phosphate containing an olivine structure. The negative electrode sheet includes a negative current collector and a negative electrode film layer provided on at least one surface of the negative current collector along the thickness direction of the negative electrode sheet and containing a negative electrode active material. The negative electrode active material includes a carbon-based material. The single-sided coating weight of the positive electrode film layer is 200 mg / 1540.25 mm 2 Up to 370mg / 1540.25mm 2 The conductivity of the electrolyte at room temperature is 13mS / cm to 20mS / cm. In an external environment of 25°C, the battery cell has a discharge platform voltage V1 during the discharge process from 100% state of charge to 2.0V at a constant current rate of 0.33C, and V1 is 3.19V to 3.235V.

[0136] The positive electrode active material in the positive electrode sheet can provide lithium, which can be in ionic form. Lithium ions escape from the positive electrode active material and migrate to the negative electrode sheet through the electrolyte, where they gain electrons. The negative electrode active material in the negative electrode sheet can accept lithium, and lithium can be embedded in the negative electrode active material in the form of a metal element, or form an alloy with the negative electrode active material. The positive electrode active material in the positive electrode sheet includes lithium-containing phosphate with an olivine structure, and the negative electrode active material in the negative electrode sheet includes a carbon-based material. The material system structure is more stable, and the cycle stability of the material system is relatively excellent.

[0137] The single-sided coating weight of the positive electrode film is 200mg / 1540.25mm 2 Up to 370mg / 1540.25mm 2 The conductivity of the electrolyte at room temperature is 13mS / cm to 20mS / cm, which is conducive to achieving fast charging performance and excellent cycle performance of the battery cell; and it has a discharge platform voltage V1 during the discharge process, which makes the energy density of the battery cell relatively high.

[0138] The upper charge limit voltage and the discharge cut-off voltage of the battery cell vary depending on the cathode active material. For example, when the phosphate material includes lithium iron phosphate, the upper charge limit voltage can be 3.65 V and the discharge cut-off voltage can be 2.0 V. Another example is when the phosphate material includes lithium iron manganese phosphate, the upper charge limit voltage can be 4.3 V and the discharge cut-off voltage can be 2.0 V. Next, taking the upper charge limit voltage of 3.65 V and the discharge cut-off voltage of 2.0 V as an example, the discharge platform voltage V1 of the battery cell will be described:

[0139] Charge the battery cell at a constant current charge rate of 0.33C to the upper charge limit voltage, 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.

[0140] Place the battery cell at 25°C and discharge it at a constant current rate of 0.33C to 2.0 V. Let it stand for 30 min, then charge it at a constant current rate of 0.33 to 3.65 V, and then charge it at a constant voltage of 3.65 V to 0.05C. After standing for 2 h, discharge it at a constant current rate of 0.33C to 2.0 V, and record the discharge energy W, the discharge capacity A0 at this time. The calculation method of the discharge platform voltage V1 is W / A0. The unit of W is Wh, and the unit of A0 is Ah.

[0141] Place the battery cell at 25°C and discharge it at a constant current rate of 0.33C to 2.0 V. Let it stand for 2 h, then charge it at a constant current rate of 0.33 to 3.65 V, and then charge it at a constant voltage of 3.65 V to 0.05C. Record the charge energy W, the charge capacity A0 at this time. The calculation method of the charge platform voltage is W / A0. The unit of W is Wh, and the unit of A0 is Ah.

[0142] In some embodiments, when discharging the battery cell in an external environment of 25°C, during the discharge process of the battery cell from 100% state of charge at a constant current rate of 2C to 2.0 V, there is a discharge platform voltage V2, and V2 / V1 ranges from 0.942 to 0.975, such as 0.942, 0.945, 0.948, 0.950, 0.952, 0.955, 0.958, 0.960, 0.962, 0.965, 0.968, 0.970, 0.972, 0.975 or the range composed of any two of the above values.

[0143] Taking the upper charge limit voltage of 3.65 V and the discharge cut-off voltage of 2.0 V as an example, the discharge platform voltage V2 of the battery cell will be described:

[0144] Charge the battery cell at a constant current charge rate of 0.33C to the upper charge limit voltage, and then charge it at a constant voltage to 0.05C, corresponding to the state of 100% SOC of the battery cell.

[0145] The battery cell is placed at 25°C and discharged at a constant current of 0.33C until 2.0V, then left standing for 30 minutes. It is charged at a constant current of 0.33 until 3.65V, and then charged at a constant voltage of 3.65V until 0.05C. After standing for 2 hours, it is discharged at a rate of 2C until 2.0V. Record the discharge energy W, discharge capacity A0 at this time. The calculation method of the discharge platform voltage V2 is W / A0. The unit of W is Wh, and the unit of A0 is Ah.

[0146] As the discharge rate increases, the current is relatively large, which easily causes the polarization of the battery cell to increase during discharge, resulting in the discharge voltage decreasing to the discharge cut-off voltage in advance, making the discharge incomplete and the capacity not fully utilized. In the embodiment of the present application, the discharge platform voltages of the battery cell during discharge at a rate of 0.33 and during discharge at a rate of 2C are similar. The battery cell is discharged relatively completely during discharge at a rate of 0.33 and at a rate of 2C, and has good rate performance, which is beneficial to the utilization of the energy density of the battery cell.

[0147] Optionally, V2 can be from 3.05V to 3.15V, such as 3.05V, 3.06V, 3.07V, 3.08V, 3.09V, 3.10V, 3.11V, 3.12V, 3.13V, 3.14V, 3.15V or the range composed of any two of the above values.

[0148] The electrode assembly can be a wound electrode assembly or a stacked electrode assembly.

[0149] In some embodiments, the electrode assembly is a stacked electrode assembly, and the electrode assembly includes a positive electrode tab, a separator, and a negative electrode tab arranged in a stacked manner.

[0150] When the electrode assembly is a stacked electrode assembly, V1 is from 3.19V to 3.225V. Optionally, V1 is from 3.200V to 3.225V. Exemplarily, the discharge platform voltages of the electrode assembly are 3.190V, 3.195V, 3.200V, 3.205V, 3.215V, 3.220V, 3.225V or the range composed of any two of the above values.

[0151] When the discharge platform voltage V1 of the stacked electrode assembly is within the above range, it can improve the energy density of the battery cell, and the discharge platform voltage is not too high. The interfacial side reaction rate in the battery cell is relatively low, which is beneficial to reducing the internal resistance DCR of the battery cell and improving the fast charging performance of the battery cell.

[0152] The negative electrode active material includes a carbon-based material. Optionally, the negative electrode active material further includes a silicon-based material. When the negative electrode active material includes a silicon-based material, the electrode assembly is a stacked electrode assembly, and V1 is from 3.19 V to 3.225 V. The discharge platform voltage of the battery cell is relatively small, resulting in fewer side reactions and a lower reaction rate at the interface between the negative electrode active material and the electrolyte, which can improve the fast charging performance of the battery cell. Moreover, since the negative electrode active material includes a silicon-based material, the energy density of the battery cell is relatively high.

[0153] The positive electrode tab further includes a positive electrode tab, and the positive electrode tab is disposed on at least one side of the positive current collector portion. The positive electrode tab is disposed on at least one side of the positive current collector portion along the width direction of the positive electrode plate. Optionally, the positive electrode tab is disposed on both sides of the positive current collector portion along the width direction of the positive electrode plate. Alternatively, the positive electrode tab is disposed on at least one side of the positive current collector portion along the length direction of the positive electrode plate. Optionally, the positive electrode tab is disposed on both sides of the positive current collector portion along the length direction of the positive electrode plate.

[0154] The current transmission path in the length direction is relatively long, and the current distribution in the length direction is uneven. The positive electrode tab is disposed on both sides of the positive current collector portion along the length direction, so that the current in the length direction of the positive current collector portion is evenly divided by the positive electrode tabs on both sides. The electron transmission path is relatively short, and the current distribution is more uniform. The de-lithiation state of each part of the positive electrode plate is uniform, and the charging performance of the battery cell can be improved.

[0155] The negative electrode tab is disposed on at least one side of the negative current collector portion. The negative electrode tab is disposed on at least one side of the negative current collector portion along the width direction of the negative electrode plate. Optionally, the negative electrode tab is disposed on both sides of the negative current collector portion along the width direction of the negative electrode plate. Alternatively, the negative electrode tab is disposed on at least one side of the negative current collector portion along the length direction of the negative electrode plate. Optionally, the negative electrode tab is disposed on both sides of the negative current collector portion along the length direction of the negative electrode plate.

[0156] The current transmission path in the length direction is relatively long, and the current distribution in the length direction is uneven. The negative electrode tab is disposed on both sides of the negative current collector portion along the length direction, so that the current in the length direction of the negative current collector portion is evenly divided by the negative electrode tabs on both sides. The electron transmission path is relatively short, and the current distribution is more uniform. The lithium intercalation state of each part of the negative electrode plate is uniform, and the charging performance of the battery cell can be improved.

[0157] Optionally, the length of the positive electrode film layer is from 200 mm to 1000 mm, such as 200 mm, 250 mm, 300 mm, 350 mm, 400 mm, 450 mm, 500 mm, 550 mm, 600 mm, 650 mm, 700 mm, 750 mm, 800 mm, 850 mm, 900 mm, 950 mm, 1000 mm or the range composed of any two of the above values.

[0158] When the length of the positive electrode film layer is relatively short, such as 200 mm to 400 mm, the coating weight of the positive electrode film layer is relatively low, which is not conducive to the improvement of energy density. In the embodiment of the present application, V1 is 3.20 V to 3.225 V, so that the capacity of the battery cell is more fully utilized during the discharge process, and the improvement of energy density can be further enhanced.

[0159] When the length of the positive electrode film layer is relatively long, such as greater than 400 mm and less than or equal to 1000 mm, the coating weight of the positive electrode film layer is relatively high, resulting in a relatively large energy density. In this case, with a discharge platform voltage of 3.19 V to 3.218 V, a relatively low interfacial side reaction rate can be achieved, the internal resistance DCR of the battery cell can be reduced, which is beneficial to improving the fast charging performance of the battery cell.

[0160] In the case where the electrode assembly is a wound electrode assembly, the positive electrode tab can be a single-piece structure, the separator can be a single-piece structure, and the negative electrode tab can be a single-piece structure. The positive electrode tab, the separator, and the negative electrode tab are wound in the same direction to form an electrode assembly.

[0161] The coating weight of the wound electrode assembly is relatively low, which is not conducive to the improvement of energy density. In the embodiment of the present application, V1 is 3.215 V to 3.235 V, so that the capacity of the battery cell is more fully utilized during the discharge process, and the improvement of energy density can be further enhanced.

[0162] The negative electrode active material includes a carbon-based material. Optionally, the negative electrode active material further includes a silicon-based material. When the negative electrode active material includes a carbon-based material and a silicon-based material, the electrode assembly is a wound electrode assembly, and V1 is 3.190 V to 3.230 V. The discharge platform voltage of the battery cell is relatively small, resulting in fewer interfacial side reactions between the negative electrode active material and the electrolyte and a lower reaction rate, which can improve the fast charging performance of the battery cell. Moreover, since the negative electrode active material includes a silicon-based material, the energy density of the battery cell is relatively high.

[0163] The positive electrode tab further includes a positive electrode ear, and the positive electrode ear is disposed on at least one side of the positive electrode current collector portion. The positive electrode ear is disposed on at least one side of the positive electrode current collector portion along the width direction of the positive electrode tab. Optionally, the positive electrode ear is disposed on both sides of the positive electrode current collector portion along the width direction of the positive electrode tab. Alternatively, the positive electrode ear is disposed on at least one side of the positive electrode current collector portion along the length direction of the positive electrode tab. Optionally, the positive electrode ear is disposed on both sides of the positive electrode current collector portion along the width direction of the positive electrode tab.

[0164] The negative electrode tab is disposed on at least one side of the negative current collector portion. The negative electrode tab is disposed on at least one side of the negative current collector portion along the width direction of the negative electrode plate. Optionally, the negative electrode tab is disposed on both sides of the negative current collector portion along the width direction of the negative electrode plate. Alternatively, the negative electrode tab is disposed on at least one side of the negative current collector portion along the length direction of the negative electrode plate. Optionally, the negative electrode tab is disposed on both sides of the negative current collector portion along the width direction of the negative electrode plate.

[0165] From an appearance perspective, the electrode assembly includes a main body portion, a positive electrode tab, and a negative electrode tab. The positive electrode tab and the negative electrode tab protrude from the main body portion. The positive electrode tab is the portion of the positive electrode plate where the active material layer is not coated, and the negative electrode tab is the portion of the negative electrode plate where the active material layer is not coated. The positive electrode tab and the negative electrode tab are used to draw out the current in the main body portion. The positive electrode tab and the negative electrode tab can extend from the same side of the main body portion, or can extend from opposite sides respectively.

[0166] Optionally, the positive electrode tab can extend from both sides of the main body portion. The current is evenly distributed in the main body portion, so that the de-lithiation state of each part of the positive electrode plate is uniform, and the charging performance of the battery cell can be improved.

[0167] Optionally, the negative electrode tab can extend from both sides of the main body portion. The current is evenly distributed in the main body portion, so that the lithium insertion state of each part of the negative electrode plate is uniform, and the charging performance of the battery cell can be improved.

[0168] The negative active material in the embodiments of the present application includes a carbon-based material.

[0169] 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.

[0170] 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 can improve the fast charging performance of the battery cell.

[0171] In some embodiments, the graphite particles include artificial graphite and a carbon coating layer. The artificial graphite includes secondary particles, and the secondary particles include a plurality of primary particles. The carbon coating layer covers the surface of the artificial graphite. The carbon in the carbon coating layer is mainly amorphous carbon. Amorphous carbon refers to a transition carbon material with a very low degree of graphitization crystallization and an approximate amorphous form (or no fixed shape and periodic structural rules). In the present application, amorphous carbon refers to the product after carbonization treatment of an organic carbon source.

[0172] 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, resulting in a larger number of sites where lithium ions can be intercalated and deintercalated, making the conductivity of the carbon coating layer relatively excellent, capable of reducing the internal resistance of the negative electrode sheet and the heat generation of the battery cell.

[0173] Optionally, based on the mass of the graphite particles, the mass content of the carbon coating layer is 2% to 5%. Exemplarily, the mass content of the carbon coating layer is 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5% or a range composed of any two of the above values.

[0174] When the mass content of the carbon coating layer is within the above range, it can further reduce the internal resistance of the negative electrode sheet and the heat generation of the battery cell.

[0175] 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.

[0176] 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 coal tar pitch and petroleum pitch is below 250°C.

[0177] Optionally, the carbonization treatment temperature is 700°C to 1800°C. Optionally, the carbonization treatment temperature is 1000°C to 1300°C. Within the appropriate range of the carbonization treatment temperature, 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.

[0178] Optionally, the carbonization treatment time is 1h to 6h.

[0179] 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.

[0180] 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. When the negative electrode active material includes a carbon-based material and a silicon-based material, V1 is 3.190V to 3.230V, and the discharge platform voltage of the battery cell is relatively small, resulting in fewer side reactions and a lower reaction rate at the interface between the negative electrode active material and the electrolyte, which can improve the fast charging performance of the battery cell. Moreover, since the negative electrode active material includes a silicon-based material, the energy density of the battery cell is relatively high.

[0181] Optionally, based on the mass of the negative electrode active material, the mass content of silicon element in the silicon-based material is 0.3% to 10.0%, and 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 the range composed of any two of the above values.

[0182] When the mass content of silicon element in the silicon-based material is within the above range, the capacity of the negative electrode active material can be improved, and the energy density of the battery cell can be improved.

[0183] 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.

[0184] In some embodiments, in addition to the above-mentioned carbon-based material and the optional silicon-based material, the negative electrode active material may further include at least one of a tin-based material and lithium titanate. The tin-based material may include at least one of elemental tin, tin oxide and tin alloy material.

[0185] In this application, the qualitative and quantitative determination of each substance or each element can be detected by suitable equipment and methods known to those skilled in the art. The 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 some 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.

[0186] For example, the carbon-based material in this application can be combined with the general rules of X-ray diffraction analysis method in JIS / K0131-1996 to perform X-ray powder diffraction test and qualitative analysis on the negative electrode plate or the negative electrode active material.

[0187] [Positive electrode plate]

[0188] The positive electrode plate includes a positive electrode current collector portion and a positive electrode film layer provided on at least one surface of the positive electrode current collector portion and including a positive electrode active material. For example, the positive electrode current collector portion 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 electrode current collector portion.

[0189] In some embodiments, when the battery cell is in the 100% state of charge (SOC), the tap density of the positive electrode film layer is 2.50 g / cm 3 to 2.80 g / cm 3 ; optionally 2.55 g / cm 3 to 2.70 g / cm 3 Exemplarily, when the battery cell is in the 100% state of charge (SOC), the tap density of the positive electrode film layer is 2.50 g / cm 3 , 2.52 g / cm 3 , 2.55 g / cm 3 , 2.56 g / cm 3 , 2.57 g / cm 3 , 2.58 g / cm 3 , 2.60 g / cm 3 , 2.62 g / cm 3 , 2.65 g / cm 3 , 2.68 g / cm 3 , 2.70 g / cm 3 , 2.72 g / cm 3 , 2.75 g / cm 3 , 2.78 g / cm 3 , 2.80 g / cm 3 or a range composed of any two of the above values.

[0190] 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 active material in the positive 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.

[0191] In the embodiments of the present application, the tap density of the positive electrode film layer when the battery cell is in the 100% state of charge (SOC) has the meaning well-known in the art, and can be detected by using the equipment and methods well-known in the art. For example, the battery cell is charged at a constant current charging rate of 0.33C to the cut-off voltage, left standing for 1 min, and then continued to be charged at a constant current charging rate of 0.1C to the cut-off voltage. At this time, the battery cell is in 100% SOC, and then the positive electrode sheet is disassembled to measure the tap density of the positive electrode film layer.

[0192] 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 2Exemplarily, 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.

[0193] 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 tab will not be too large, and it can also take into account the improvement of the energy density of the battery cell. In the embodiments of the present application, the compaction density of the positive electrode film layer in the 100% state of charge (SOC) of the battery cell has the meaning well known in the art, that is, the positive electrode tab is disassembled from the battery cell in the 100% state of charge (SOC), and the compaction density of the positive electrode film layer is measured. For example, for a single-sided coated positive electrode tab (if it is a double-sided coated tab, one side of the positive electrode film layer can be wiped off first), it is punched into small circular pieces with an area of S1, weighed, recorded as M1, and its thickness H1 is measured. Then, the positive electrode film layer of the above weighed positive electrode tab is wiped off, and the weight of the positive electrode current collector is weighed, recorded as M0, and its thickness H0 is measured. The single-sided coating weight of the positive electrode film layer = (the weight M1 of the positive electrode tab - 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 tab - 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.

[0194] 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.

[0195] 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.

[0196] 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.

[0197] In some embodiments, the powder compaction density of the positive electrode active material under 30000 N is greater than or equal to 2.46 g / cm 3 , optionally 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.

[0198] When the powder compaction density of the positive electrode active material under 30,000 N is within the above range, the energy density of the battery cell can be improved. 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.

[0199] 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 the UTM7305 type electronic pressure testing machine, pressurize to 3000 kg (equivalent to 30,000 N), keep the pressure for 30 s, then relieve the pressure, keep for 10 s, and then record and calculate the powder compaction density of the positive electrode active material under the action of 30,000 N.

[0200] 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.

[0201] 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.

[0202] 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 GB / T 24533-2019 can be adopted. Using metallic lithium as the negative electrode and the sample electrode sheet containing the above materials as the positive electrode, a half-button cell is assembled. Under the condition of 23°C ± 2°C, the half-button cell is placed on a battery tester or other test equipment with the same performance, and the discharge capacity is obtained through charge and discharge at a rate of 0.1C, and then the capacity is divided by the mass of the active material of the electrode sheet to obtain the charging specific capacity parameter.

[0203] In some embodiments, the mass percentage of the lithium-containing phosphate with an olivine structure in the positive electrode active material can be greater than or equal to 80% and less than or equal to 100%. It can be considered that the positive electrode active material of the present application is a lithium-containing phosphate system with an olivine structure. When the mass percentage of the lithium-containing phosphate with an olivine structure is less than 100%, the positive electrode active material can further 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 the lithium-containing transition metal oxides can include but not limited to at least one of lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide and their respective modified compounds.

[0204] Optionally, the mass percentage of the lithium-containing phosphate with an olivine structure in the positive electrode active material is 100%.

[0205] In the embodiments of the present 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.

[0206] By surface coating the coating layer on the phosphate particles, the conductivity of the lithium-containing phosphate with an olivine structure can be improved, the powder resistivity of the material can be reduced, and it is beneficial to the migration rate of lithium ions, improving the fast charging ability of the battery and reducing the heat generation of the battery cell.

[0207] 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 ≤ 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, Mg, Me includes one or more of Mn, Fe, Co, Ni, M includes one or more of B, Mg, Al, Si, P, S, Ca, Sc, Ti, V, Cr, Cu, Zn, Sr, Y, Zr, Nb, Mo, Cd, Sn, Sb, Te, Ba, Ta, W, Yb, La, Ce, X includes one or more of S, Si, Cl, B, C, N, and Y includes one or more of O, F. The phosphate particles have excellent cycle stability, which is beneficial to improving the cycle performance of the battery cell.

[0208] Exemplarily, the phosphate particles include one or more of LiFePO4, LiMnPO4, LiNiPO4, and LiCoPO4. The battery cells are accompanied by the deintercalation and consumption of active ions such as Li during the charge and discharge process, and the molar content of Li in the battery cells is different when discharged to different states. In the enumeration of positive electrode active materials LiFePO4, LiMnPO4, LiNiPO4, LiCoPO4, etc., the molar content of Li is the initial state of the material, that is, the state before feeding. The positive electrode active material is used in the battery system, and the molar content of Li may change after charge and discharge cycles. In the enumeration of positive electrode active materials LiFePO4, LiMnPO4, LiNiPO4, LiCoPO4, etc. in the embodiment of the present application, the molar content of oxygen O is only a theoretical state value. Lattice oxygen release will cause the molar content of oxygen O to change. In practice, the molar content of oxygen O will fluctuate. The above situations are all within the scope of protection of this application.

[0209] In some embodiments, the coating layer comprises a Li 3-d Fe 2-d M2 d (PO x2 ) y2 The fast ion conductor M2 includes one or more elements selected from Ti, Zr, Hf, Ge and Sn, 0≤d≤1, 0<x2<5, 0<y2<4.

[0210] Exemplarily, the fast ion conductor is a material having a NASICON structure, such as one or more of lithium iron titanium phosphate Li2FeTi(PO4)3, lithium iron zirconium phosphate Li2FeZr(PO4)3, and lithium iron tin phosphate Li2FeSn(PO4)3.

[0211] Fast ion conductors with a NASICON structure are materials with ultrafast ion conduction capabilities. They possess abundant three-dimensional lithium ion diffusion and transport channels, and exhibit advantages such as high ion conduction efficiency and strong structural stability during multiple lithium de- and intercalation processes. Coating phosphate particles with a fast ion conductor containing a NASICON structure can significantly increase the lithium ion transport rate at the positive electrode during multiple lithium de- and intercalation processes, improving the ionic conductivity of the positive electrode active material and the rapid charging capability of the battery cell. Furthermore, it can increase the specific capacity and the energy density of the corresponding battery cell.

[0212] In some embodiments, the ion-conducting layer further includes carbon.

[0213] The carbon element and the fast ion conductor can be arranged in layers. For example, the carbon element serves as an independent carbon coating layer, and the fast ion conductor serves as an independent fast ion conductor layer. The carbon coating layer can be coated on the surface of the core part, 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 core part; alternatively, the fast ion conductor layer can be coated on the surface of the core part, 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 core part. Of course, the carbon element and the fast ion conductor can also be arranged in the same layer.

[0214] 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 completely coat the fast ion conductor layer. The setting of the carbon coating layer can significantly improve the electronic conductivity of the core part, make up for the defect of poor electronic conduction performance of the core part, and improve the energy density of the battery cell.

[0215] Specifically, the setting of the carbon coating layer endows the positive electrode active material of the present application with the following advantages:

[0216] The carbon coating layer in the positive electrode active material of the present application provides a suitable channel for the transmission of electrons, can significantly improve the conduction rate of electrons during multiple de-lithiation and intercalation processes, improve the electronic conductivity of the lithium-containing phosphate, improve the charging ability of the corresponding battery cell, and can also improve the energy density.

[0217] The carbon coating layer of the positive electrode active material of the present application has loose pores, which enables the electrolyte to come into full and effective contact with the lithium-containing phosphate, thereby improving the transmission rate of lithium ions at the phase interface and improving the charging ability of the battery cell.

[0218] Coating a layer of carbon coating layer on the surface of the lithium-containing phosphate can not only improve the conductivity of the lithium-containing phosphate, but also improve the structural stability of the positive electrode active material, effectively alleviate the iron dissolution 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.

[0219] The positive electrode active material of the present application is based on lithium-containing phosphate, giving full play to the advantages of low cost, high use reliability, and good cycle stability of lithium-containing phosphate. At the same time, the ion-conducting layer (fast ion conductor layer and carbon coating layer) is used to solve the disadvantages of poor electronic conductivity and ion 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.

[0220] 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) and disassembling the positive electrode plate, it is cleaned with DMC and dried, and then the binder is burned off at high temperature to obtain the positive electrode active material to be tested. Weigh 0.4 g of the positive electrode active material, and add 10 ml (50% concentration) of aqua regia to it. Then place it on a flat plate at 180 °C for 30 min. After digestion on the flat plate, it is made up to a volume of 100 mL, and quantitative testing is carried out by the standard curve method.

[0221] In some embodiments, the graphitization degree of the positive electrode active material is 0.15 to 0.32, and can be optionally 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.

[0222] When the graphitization degree of the positive electrode active material is within the above range, it is beneficial to improve the conductivity of the positive electrode active material, reduce the heat generation of the positive electrode plate, and thus reduce the heat generation of the battery cell.

[0223] In the embodiments of the present application, the graphitization degree 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, it can be tested according to the test standards JIS K 0131-1996 and JB / T 4220-2011. After drying the positive electrode active material as a sample, it is tested with a Bruker D8 Discover X-ray diffractometer to obtain the interlayer spacing d of the (002) crystal plane of carbon in the positive electrode active material. 002 , and then according to the formula g = (0.344 - d 002 ) / (0.344 - 0.3354) × 100%, the graphitization degree of the positive electrode active material is calculated.

[0224] In some embodiments, the mass content of carbon element in the lithium-containing phosphate with olivine structure is 1% to 2%; the specific surface area of the lithium-containing phosphate with olivine structure is 5 m 2 / g to 18 m 2 / g.

[0225] Optionally, the mass content of carbon element in the lithium-containing phosphate with olivine structure is 1% to 2%; the specific surface area of the lithium-containing phosphate with olivine structure is 7.5m 2 / g to 14m 2 / g.

[0226] Exemplarily, the mass content of carbon element in the lithium-containing phosphate with olivine structure is 1%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2% or the range composed of any two of the above values.

[0227] Exemplarily, the specific surface area of the lithium-containing phosphate with olivine structure is 5m 2 / g, 6m 2 / g, 7m 2 / g, 8m 2 / g, 9m 2 / g, 10m 2 / g, 11m 2 / g, 12m 2 / g, 13m 2 / g, 14m 2 / g, 15m 2 / g, 16m 2 / g, 17m 2 / g, 18m 2 / g or the range composed of any two of the above values.

[0228] The carbon element mainly exists in the coating layer in the form of a carbon coating layer. The carbon coating layer is loose and porous, which is beneficial to increasing the specific surface area of the material, more beneficial to the effective contact between the electrolyte and the phosphate particles, and beneficial to the transmission of lithium ions at the phase interface. In addition, when the mass content of the carbon element is within the above range, it can significantly improve the conductivity of the lithium-containing phosphate with olivine structure, which is beneficial to enhancing the ionic conductivity and electronic conductivity of the lithium-containing phosphate with olivine structure, and can improve the rapid charging ability and energy density of the battery monomer.

[0229] In the embodiments of the present application, the specific surface area of the material has the meaning well-known in the art, and can be detected by using the equipment and methods well-known in the art. For example, it is detected according to the test standard GB / T 19587-2017. The positive electrode active material is used as a sample, and the specific surface area is tested by a Tri-Star 3020 specific surface area and pore size analyzer of Micromeritics Company in the United States.

[0230] In some embodiments, the volume distribution particle size of the positive electrode active material satisfies: 1µm ≤ Dv50 ≤ 2µm, and / or 0.4µm ≤ Dv10 ≤ 0.7µm, and / or 15µm ≤ Dv99 ≤ 25µm.

[0231] Exemplarily, the Dv50 of the positive electrode active material may 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.

[0232] Exemplarily, the Dv10 of the positive electrode active material may be 0.4 µm, 0.45 µm, 0.5 µm, 0.55 µm, 0.6 µm, 0.65 µm, 0.7 µm or a range composed of any two of the above values.

[0233] Exemplarily, the Dv99 of the positive electrode active material may be 15 µm, 16 µm, 17 µm, 18 µm, 19 µm, 20 µm, 21 µm, 22 µm, 23 µm, 24 µm, 25 µm or a range composed of any two of the above values.

[0234] 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, so that the performance of the positive electrode active material is stable.

[0235] 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, the volume average particle size Dv10 of the material refers to the particle size corresponding to 10% in the volume distribution, and the volume average particle size Dv99 of the material refers to the particle size corresponding to 99% in the volume distribution. It can be detected by using the equipment and methods well-known in the art. For example, taking the positive electrode active material as a sample, according to the test standard GB / T 19077-2016, the Dv50 and Dv10 of the particles are tested by a Mastersizer 2000E laser particle size analyzer.

[0236] When the positive electrode active material includes other materials in addition to the lithium-containing phosphate with an olivine structure, the volume distribution particle size of the positive electrode active material refers to the volume distribution particle size of all positive electrode active materials.

[0237] In some embodiments, the lithium-containing phosphate with olivine structure is granular. The lithium-containing phosphate with olivine structure includes secondary particles, and the secondary particles include a plurality of primary particles. 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.

[0238] 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.

[0239] 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.

[0240] In some embodiments, the cathode film layer further includes a first material. The first material includes one or more of ternary materials, lithium phosphate, lithium hydrogen phosphate, lithium sulfate, lithium sulfite, lithium molybdate, lithium oxalate, lithium titanate, lithium tetraborate, lithium metasilicate, lithium manganate, lithium tartrate, trilithium citrate, lithium nickelate, and lithium ferrate. As a lithium supplement agent, the first material can supplement lithium ions for 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.

[0241] Optionally, the ternary material includes Li x3 A y3 Ni a3 Co b3 Mn c M3 (1-a3-b3-c3) Y3 z3 , where 0 < x3 ≤ 2.1, 0 < y3 ≤ 2.1, and 0.9 ≤ x3 + y3 ≤ 2.1, 0 ≤ a3 ≤ 1, 0 ≤ b3 ≤ 1, 0 ≤ c3 ≤ 1, and 0.1 ≤ a3 + b3 + c3 ≤ 1, 1.8 ≤ z3 ≤ 3.5, A includes one or several of Na, K, and Mg, M3 includes one or several of B, Mg, Al, Si, P, S, Ca, Sc, Ti, V, Cr, Fe, Cu, Zn, Sr, Y, Zr, Nb, Mo, Cd, Sn, Sb, Te, Ba, Ta, W, Yb, La, Ce, and Y3 includes one or several of O and F.

[0242] Exemplarily, the ternary material includes LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (NCM333), LiNi 0.5 Co 0.2 Mn 0.3 O2 (NCM523), LiNi 0.6 Co 0.2 Mn 0.2 O2 (NCM622), LiNi 0.8 Co 0.1 Mn 0.1 O2 (NCM811), LiNi 0.80 Co 0.15 Al 0.05 O2, or at least one of them.

[0243] In some embodiments, the mass content of the lithium supplement agent 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 agent 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, improve the capacity, and thus improve the energy density of the battery cell.

[0244] The lithium supplement agent can be in the same layer as the positive electrode active material or in different layers. When the lithium supplement agent and the positive electrode active material are in different layers, the lithium supplement agent can be in the lithium supplement layer, and the positive electrode active material can be in the positive electrode active material layer. In other words, the positive electrode film layer includes a lithium supplement layer and a positive electrode active material layer. The positive electrode active material layer can be disposed on at least one side of the positive electrode current collector, and the lithium supplement layer can be located between the positive electrode active material layer and the positive electrode current collector. Alternatively, the lithium supplement layer can be disposed on at least one side of the positive electrode current collector, and the positive electrode active material layer can be located between the lithium supplement layer and the positive electrode current collector. Optionally, the lithium supplement layer can be located between the positive electrode active material layer and the positive electrode current collector. During the charge and discharge cycle of the battery cell, the lithium supplement agent in the lithium supplement layer can be gradually released into the system to make up for the lithium loss of the battery system.

[0245] In some embodiments, the positive electrode film layer may optionally further include a positive electrode conductive agent. The type of the positive electrode conductive agent is not particularly limited 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%.

[0246] 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 resin. In some embodiments, based on the mass of the positive electrode film layer, the mass content of the positive electrode binder is ≤5%.

[0247] 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 of foils 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).

[0248] 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 0.30, and may be optionally 0.06 to 0.10. 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.

[0249] 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.

[0250] ]In some embodiments, the thickness of the positive electrode current collector is 10 μm to 15 μm, and may be optionally 12 μm to 15 μm. Exemplarily, the thickness of the positive electrode current collector is 10 μm, 10.5 μm, 11 μm, 11.5 μm, 12 μm, 12.5 μm, 13 μm, 13.5 μm, 14 μm, 14.5 μm, 15 μm or a range composed of any two of the above values.

[0251] When the thickness of the positive electrode current collector is within the above range, the current-carrying capacity of the positive electrode current collector is relatively excellent, and the battery cell can have a high energy density.

[0252] In the embodiments of the present application, the thicknesses of the positive electrode film layer and the positive electrode current collector are of meanings well-known in the art and can be detected by devices and methods well-known in the art. For example, the thickness of the positive electrode plate is measured using a micrometer, the film layer on the surface of the positive electrode current collector is washed off with an organic solvent such as alcohol, and the thickness of the positive electrode current collector is measured using a micrometer. When the positive electrode film layer is coated on one side, the thickness of the positive electrode film layer is the thickness of the positive electrode plate minus the thickness of the positive electrode current collector; when the positive electrode film layer is coated on both sides, the thickness of the positive electrode film layer is (the thickness of the positive electrode plate minus the thickness of the positive electrode current collector) / 2.

[0253] The positive electrode film layer is usually formed by coating a positive electrode slurry on the positive electrode current collector and then drying and cold pressing. The positive electrode slurry is usually formed by dispersing a positive electrode active material, an optional conductive agent, an optional binder, and any other components in a solvent and stirring evenly. The solvent can be N-methylpyrrolidone (NMP), but is not limited thereto.

[0254] The positive electrode plate does not exclude other additional functional layers in addition to the positive electrode film layer. For example, in some embodiments, the positive electrode plate of the embodiments of the present application further includes a positive electrode conductive layer sandwiched between the positive electrode current collector and the positive electrode film layer and disposed on the surface of the positive electrode current collector. In some other embodiments, the positive electrode plate of the embodiments of the present application further includes a protective layer covering the surface of the positive electrode film layer.

[0255] In some embodiments, the positive electrode plate further includes a positive electrode conductive layer, and the positive electrode conductive layer is located between the positive electrode film layer and the positive electrode current collector. The positive electrode conductive layer can further improve the conductivity of the positive electrode plate, reduce the heat generation of the positive electrode plate, and thus reduce the heat generation of the battery cell.

[0256] In some embodiments, the thickness of the positive electrode conductive layer is 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.

[0257] When the thickness of the positive electrode conductive layer is within the above range, it can further improve the conductivity of the positive electrode plate, reduce the heat generation of the positive electrode plate, and thus reduce the heat generation of the battery cell; and it can also take into account the improvement of the energy density of the battery cell.

[0258] In the embodiments of the present application, the thickness of the positive electrode conductive layer is of a meaning well-known in the art and can be detected by devices and methods well-known in the art. For example, the positive electrode plate is subjected to tomographic scanning to directly measure the thickness of the positive electrode conductive layer.

[0259]

[0260] ​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.

[0261] 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 of the battery cell.

[0262] 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.

[0263] Exemplarily, the positive electrode binder includes one or more of polyvinylidene fluoride, polytetrafluoroethylene, vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, polyacrylic acid, and fluorinated acrylate resins. The positive electrode binder in the positive electrode conductive layer can improve the adhesion performance between the positive electrode current collector part and the positive electrode film layer, and improve the structural stability of the positive electrode sheet.

[0264] [Negative electrode sheet]

[0265] The negative electrode sheet includes a negative electrode current collector part and a negative electrode film layer provided on at least one surface of the negative electrode current collector part and including a negative electrode active material. For example, the negative electrode current collector part 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 part.

[0266] In some embodiments, when the battery cell is in a 100% charged state, the tap density of the negative electrode film layer is 1.15 g / cm 3 to 1.36 g / cm 3 ; it can be optionally 1.25 g / cm 3 to 1.36 g / cm 3 . Exemplarily, when the battery cell is in a 100% charged state, the tap density of the negative electrode film layer is 1.15 g / cm 3 , 1.18 g / cm 3 , 1.20 g / cm 3 , 1.22 g / cm 3 , 1.25 g / cm 3 , 1.28 g / cm 3 , 1.3 g / cm 3 , 1.32 g / cm 3 , 1.35 g / cm3 、 1.36 g / cm 3 or a range composed of any two of the above values.

[0267] 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 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.

[0268] In the embodiments of the present application, the compaction density of the negative electrode film layer of the battery cell in the 100% charged state has the meaning well known in the art, and can be detected by equipment and methods well known in the art. The detection method is the same as the compaction density test method of the positive electrode film layer described above.

[0269] 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.

[0270] 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 the energy density of the battery cell can be improved while taking it into account.

[0271] In the embodiments of the present application, the single-sided coating weight of the negative electrode film layer has the meaning well-known in the art, and can be detected by the equipment and methods well-known in the art. The detection method is as described in the single-sided coating weight test method of the film layer above.

[0272] In some embodiments, the powder resistivity of the negative electrode active material is from 0.005 Ω·cm to 0.043 Ω·cm, and can be 0.04 Ω·cm. Exemplarily, the powder resistivity of the negative electrode active material can be 0.043 Ω·cm, 0.04 Ω·cm, 0.035 Ω·cm, 0.03 Ω·cm, 0.025 Ω·cm, 0.02 Ω·cm, 0.015 Ω·cm, 0.01 Ω·cm, 0.005 Ω·cm or a range composed of any two of the above values.

[0273] 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.

[0274] In the embodiments of the present application, the powder resistivity of the negative electrode active material has the meaning well-known in the art, and can be detected by the equipment and methods well-known in the art. The detection method is as described in the powder resistivity test method of the positive electrode active material above.

[0275] In some embodiments, the powder compaction density of the negative electrode active material under a pressure of 20,000 N is 1.5 g / cm 3 to 1.85 g / cm 3 , 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 20,000 N is 1.5 g / cm 3 , 1.55 g / cm 3 , 1.6 g / cm 3 , 1.65 g / cm 3 , 1.7 g / cm 3 , 1.75 g / cm 3 , 1.8 g / cm 3 , 1.85 g / cm 3 or a range composed of any two of the above values.

[0276] When the powder compaction density of the negative electrode active material under 20,000 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 tightly, the contact resistance between particles is small, the resistance of the electrode sheet can be further reduced, thereby reducing heat generation.

[0277] 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. Detection is carried out according to the test standard GB / T24533-2009. For example, a certain amount of negative electrode active material is taken as a sample and added to a mold with a bottom area of 1.327 cm 2 in a UTM7305 type electronic pressure testing machine, pressurized to 2000 kg (equivalent to 20,000 N), held for 30 s, then depressurized, held for 10 s, and then the powder compaction density of the negative electrode active material under a force of 20,000 N is recorded and calculated.

[0278] In some embodiments, the charging specific capacity of the negative electrode active material at a rate of 0.1 C is 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 a range composed of any two of the above values.

[0279] When the charging specific capacity of the negative electrode active material at a rate of 0.1C is within the above range, the energy density of the battery cell is relatively high.

[0280] In the embodiments of the present application, the charging specific capacity of the negative electrode active material at a rate of 0.1C has the meaning well-known in the art, and can be detected by the equipment and methods well-known in the art. The detection method is the same as the charging specific capacity test method of the positive electrode active material at a rate of 0.1C described above.

[0281] In some embodiments, the negative electrode active material includes a carbon-based material. The carbon-based material has high cycle stability and can improve the cycle performance of the battery cell. Optionally, the mass ratio of the carbon-based material in the negative electrode active material can be greater than or equal to 80% and less than or equal to 100%.

[0282] 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 battery cell has excellent cycle performance.

[0283] Optionally, the carbon-based material includes graphite particles.

[0284] In some embodiments, the negative electrode active material may further include a silicon-based material. The introduction of the silicon-based material can increase the capacity of the negative electrode active material and improve the energy density of the battery cell.

[0285] In the present application, the qualitative and quantitative determination of each substance or each element can be detected by suitable equipment and methods known to those skilled in the art. The 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 some 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.

[0286] For example, the present application can combine the general rules of X-ray diffraction analysis method in JIS / K0131-1996 to perform X-ray powder diffraction test and qualitative analysis on the negative electrode sheet or the negative electrode active material.

[0287] Artificial graphite and natural graphite can be distinguished by the SEM cross-section diagram taken by scanning electron microscope SEM. There are voids between the flaky structures in the SEM cross-section diagram of natural graphite, and the SEM cross-section diagram of artificial graphite is dense and has no obvious gaps, or can be distinguished by the XRD spectrum obtained by the X-ray diffraction method. There are obvious 2H phase and 3R phase in the XRD spectrum of natural graphite, and only 2H phase exists in the XRD spectrum of artificial graphite.

[0288] In the embodiments of the present application, the negative electrode film layer includes at least one film layer, which can be a single-layer film layer or at least two film layers. Optionally, the negative electrode film layer includes at least two film layers.

[0289] 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 diameter Dv50 of the negative electrode active material is 8.2 μm to 13.5 μm. Exemplarily, the volume average particle diameter Dv50 of the negative electrode active material is 8.2 μm, 8.5 μm, 8.8 μm, 9 μm, 9.2 μm, 9.5 μm, 9.8 μm, 10 μm, 10.2 μm, 10.5 μm, 10.8 μm, 11 μm, 11.2 μm, 11.5 μm, 11.8 μm, 12 μm, 12.2 μm, 12.5 μm, 12.8 μm, 13 μm, 13.2 μm, 13.5 μm or a range composed of any two of the above values.

[0290] When the negative electrode film layer is at least two film layers, the negative electrode active material in the negative electrode film layer includes a carbon-based material, and optionally also includes a silicon-based material. The silicon-based material can be located in one of the at least two film layers or in at least two of the at least two film layers. The negative electrode film layer can include two film layers, three film layers, four film layers, or even more film layers.

[0291] 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.

[0292] 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.

[0293] Optionally, the carbon-based material in the first negative electrode film layer further includes natural graphite.

[0294] The negative electrode film layer includes at least two film layers. Layered coating is beneficial to improving the fast charging performance of the battery cell. Especially when there are differences between the first negative electrode film layer and the second negative electrode film layer, it is possible to construct pore differences in the negative electrode film layer, reduce the tortuosity of lithium ion transport, and improve the fast charging performance of the battery cell.

[0295] Optionally, the volume average particle size Dv50 of the negative active material in the first negative electrode film layer is greater than or equal to the volume average particle size Dv50 of the negative active material in the second negative electrode film layer. Further optionally, the volume average particle size Dv50 of the negative active material in the first negative electrode film layer is greater than the volume average particle size Dv50 of the negative 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 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.

[0296] 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 the fast charging process, the overpotential of the second negative electrode film layer is usually relatively high, and the bottleneck of fast charging mainly lies in the second negative electrode film layer. In the embodiments of the present application, the particle size in the second negative electrode film layer is relatively small, which can shorten the solid-phase transmission path of lithium ions, improve the fast charging performance, and can also improve the problem of lithium deposition on the surface layer of the negative electrode sheet.

[0297] Optionally, the negative active material in the first negative electrode film layer is in particulate form, and its volume average particle size Dv50 is from 9.5 μm to 18.5 μm, and can be optionally from 9.5 μm to 14.6 μm. Exemplarily, the volume average particle size of the negative active material in the first negative electrode film layer is 9.5 μm, 10 μm, 10.5 μm, 11 μm, 11.5 μm, 12 μm, 12.5 μm, 13 μm, 13.5 μm, 14 μm, 14.5 μm, 14.6 μm, 15 μm, 15.5 μm, 16 μm, 16.5 μm, 17 μm, 17.5 μm, 18 μm, 18.5 μm or a range composed of any two of the above values. When the first negative electrode film layer includes graphite particles, the volume average particle size Dv50 of the graphite particles in the first negative electrode film layer is from 9.5 μm to 18.5 μm, and can be optionally from 9.5 μm to 14.6 μm.

[0298] When the volume average particle size Dv50 of the negative active material in the first negative electrode film layer is within the above range, on the one hand, it can shorten the solid-phase transmission path of lithium ions and improve the fast charging performance; on the other hand, the material is not prone to agglomeration during the preparation process, which can improve the stability of the material.

[0299] Optionally, the negative electrode active material in the second negative electrode film layer is granular, and its volume average particle size Dv50 is from 7.8 μm to 14.3 μm, and can be optionally from 7.8 μm to 11.3 μm. Exemplarily, the volume average particle size Dv50 of the negative electrode active material is 7.8 μm, 8.0 μm, 8.2 μm, 8.5 μm, 8.8 μm, 9 μm, 9.2 μm, 9.5 μm, 9.8 μm, 10 μm, 10.2 μm, 10.5 μm, 10.8 μm, 11 μm, 11.3 μm, 11.2 μm, 11.5 μm, 11.8 μm, 12 μm, 12.2 μm, 12.5 μm, 12.8 μm, 13 μm, 13.2 μm, 13.5 μm, 13.8 μm, 14 μm, 14.1 μm, 14.3 μm or a range composed of any two of the above values. When the second negative electrode film layer includes graphite particles, the volume average particle size Dv50 of the graphite particles in the second negative electrode film layer is from 7.8 μm to 14.3 μm, and can be optionally from 7.8 μm to 11.3 μm.

[0300] When the volume average particle size Dv50 of the negative electrode active material in the second negative electrode film layer is within the above range, on the one hand, it can shorten the solid-phase transmission path of lithium ions and improve the fast charging performance. On the other hand, the material is not prone to agglomeration during the preparation process, which can improve the stability of the material. On the other hand, the negative electrode active material in the second negative electrode film layer with the above volume average particle size range cooperates with the negative electrode 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.

[0301] In the embodiments of the present application, the volume average particle size Dv50 of the negative electrode active material has the meaning well-known in the art, and can be detected by equipment and methods well-known in the art. The detection method is the same as the test method for the volume average particle size Dv50 of the positive electrode active material described above.

[0302] Optionally, the tap density of the carbon-based material in the first negative electrode film layer is less than or equal to the tap density of the carbon-based material in the second negative electrode film layer. The tap density can reflect the filling density of the active material in the film layer. When the tap density of the carbon-based material in the second negative electrode film layer is greater than the tap density of the carbon-based material in the first negative electrode film layer, the second negative electrode film layer is filled more densely, which improves the energy density of the battery cell. The filling of the first negative electrode film layer is relatively sparse and the pores are richer, which can improve the fast charging performance of the battery cell. When the negative electrode active material includes graphite particles, the tap density of the graphite particles in the first negative electrode film layer is less than or equal to the tap density of the graphite particles in the second negative electrode film layer.

[0303] Optionally, the tap density of the carbon-based material in the first negative electrode film layer is 0.82 g / cm 3 to 1.21 g / 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.

[0304] 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. <S <S

[0305] In the embodiments of the present application, the tapped density of the material has a 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.

[0306] 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 6:4. Exemplarily, the ratio of the thickness of the second negative electrode film layer to the thickness of the first negative electrode film layer is 3:7, 4:6, 5:5, 6:4, 7:3 or a range composed of any two of the above values. By adjusting the thickness ratio of the first negative electrode film layer and the second negative electrode film layer, the gradient pore difference between the upper and lower layers can be further increased, the tortuosity of lithium ion transport can be reduced, and the fast charging ability of the battery cell can be improved.

[0307] 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 gradient pore difference between the first negative electrode film layer and the second negative electrode film layer can be increased, the tortuosity of lithium ion transport can be reduced, and the fast charging ability of the battery cell can be improved.

[0308] 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 gradient pore difference between the first negative electrode film layer and the second negative electrode film layer can be regulated and increased, the tortuosity of lithium ion transport can be reduced, and the fast charging ability of the battery cell can be improved.

[0309] In the embodiments of the present application, for example, taking the battery charging upper limit voltage of 3.65 V and the battery discharge cut-off voltage of 2.0 V as an example for explanation,

[0310] The specific steps of the BOL full charge test are as follows: At 25°C, charge at a charging rate of 0.33C of the battery nominal capacity until 3.65V, then charge at a constant voltage of 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 charge at a constant voltage of 3.65V until 0.05C, which is the BOL full charge state. In the BOL 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 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, 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.

[0311] 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 transport, and improve the fast charging ability of the battery cell.

[0312] 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 transport, and improve the fast charging ability of the battery cell.

[0313] In the embodiments of the present application, for example, taking the battery charging upper limit voltage as 3.65V and the battery discharge cut-off voltage as 2.0V as an example for illustration,

[0314] The EOL full charge test steps are specifically 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, stand for 10 min, then discharge at a discharge rate of 0.33C to 2.0V, stand for 10 min. The above one charge and discharge cycle is one cycle 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 of 10 positions of the first negative electrode film layer, calculate their average value as the average value of the first negative electrode film layer, measure the thicknesses of 10 positions of the second negative electrode film layer, and calculate their average value as the average value of the second negative electrode film layer.

[0315] In some embodiments, when the negative electrode film layer adopts a single-layer film layer (different from the above double-layer film layer), the negative electrode film layer further includes a lithium-containing binder. Optionally, the mass content of the lithium-containing binder relative to the mass of the negative electrode film layer is 0.1% to 1%. Exemplarily, the mass content of the lithium-containing binder relative to the mass of the negative electrode film layer is 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1% or the range composed of any two of the above values. The lithium element in the lithium-containing binder can exist in an ionic form, which can increase the number of free-moving lithium ions in the negative electrode film layer, shorten the distance for lithium ions to diffuse to the surface of the negative electrode film layer, 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 (for example, polyacrylic acid PAA, polymethacrylic acid PMAA, sodium polyacrylate PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), and carboxymethyl chitosan (CMCS).

[0316] 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.

[0317] 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 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 (0.3-0.5):(0.15-0.45):(0.05-0.2):(0.2-0.35). For example, the molar ratio of lithium acrylate monomer, acrylonitrile monomer, acrylamide monomer and 2-hydroxyethyl acrylate monomer is 0.35:0.3:0.15:0.2, or 0.4:0.2:0.1:0.3, or 0.45:0.15:0.2:0.2, etc.

[0318] 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.

[0319] 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.

[0320] 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.

[0321] 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.

[0322] 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 the form of ions, which can increase the number of free-moving lithium ions in the negative electrode film layer, shorten the distance for lithium ions to diffuse to the surface of the negative electrode film layer, increase the intercalation and deintercalation rate of lithium ions, and improve the fast charging performance of the battery cell.

[0323] 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.

[0324] Exemplarily, the first lithium-containing binder includes a lithium acrylate-acrylonitrile-acrylamide-2-hydroxyethyl acrylate copolymer, and the lithium acrylate-acrylonitrile-acrylamide-2-hydroxyethyl acrylate copolymer is derived from a lithium acrylate monomer, an acrylonitrile monomer, an acrylamide monomer, and a 2-hydroxyethyl acrylate monomer. The molar ratio of the lithium acrylate monomer, the acrylonitrile monomer, the acrylamide monomer, and the 2-hydroxyethyl acrylate monomer is (0.3 - 0.5):(0.15 - 0.45):(0.05 - 0.2):(0.2 - 0.35). For example, the molar ratio of the lithium acrylate monomer, the acrylonitrile monomer, the acrylamide monomer, and the 2-hydroxyethyl acrylate monomer is 0.35:0.3:0.15:0.2, or 0.4:0.2:0.1:0.3, or 0.45:0.15:0.2:0.2, etc.

[0325] 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 cycle performance of the negative electrode film layer is improved during the fast charge and discharge process.

[0326] 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 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 insertion / extraction rate of lithium ions, and improve the fast charging performance of the battery cell.

[0327] The first lithium-containing binder and the second lithium-containing binder can be made of the same material or different materials.

[0328] 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 insertion / extraction rate of lithium ions, and improve the fast charging performance of the battery cell.

[0329] 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 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 (0.3 - 0.5):(0.15 - 0.45):(0.05 - 0.2):(0.2 - 0.35). For example, the molar ratio of lithium acrylate monomer, acrylonitrile monomer, acrylamide monomer and 2-hydroxyethyl acrylate monomer is 0.35:0.3:0.15:0.2, or 0.4:0.2:0.1:0.3, or 0.45:0.15:0.2:0.2, etc.

[0330] 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.

[0331] 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).

[0332] 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.

[0333] 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%.

[0334] 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%.

[0335] 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%.

[0336] In some embodiments, the negative current collector may be a metal foil or a composite current collector. As an example of the metal foil, at least one of copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy foils may be used. The composite current collector may include a polymer material base layer and a metal material layer formed on at least one surface of the polymer material base layer. As an example, the metal material in the metal material layer may include at least one of copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy. As an example, the polymer material base layer may include at least one of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0337] In some embodiments, the thickness of the negative current collector is 4 μm to 6 μm. Exemplarily, the thickness of the negative 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.

[0338] When the thickness of the negative current collector is within the above range, the current-carrying capacity of the negative current collector is relatively excellent, and the battery cell can have a high energy density.

[0339] In the embodiments of the present application, the thickness of the negative 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 current collector is washed away with an organic solvent such as water, and the thickness of the positive current collector is measured with a micrometer.

[0340] The negative electrode film layer is usually formed by coating a negative electrode slurry on the negative current collector and drying and cold pressing it. The negative electrode slurry is usually formed by dispersing negative electrode active materials, optional conductive agents, optional binders, and other optional additives in a solvent and stirring evenly. The solvent can be N-methylpyrrolidone (NMP) or deionized water, but is not limited thereto.

[0341] The negative electrode plate does not exclude other additional functional layers besides 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 sandwiched between the negative current collector and the negative electrode film layer and disposed on the surface of the negative current collector. In 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.

[0342] 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 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.

[0343] In some embodiments, the thickness of the negative electrode conductive layer is from 0.5 μm to 2 μm. Exemplarily, the thickness of the negative electrode conductive layer can be 0.5 μm, 0.8 μm, 1 μm, 1.2 μm, 1.5 μm, 1.6 μm, 1.8 μm, 2 μm or a range composed of any two of the above values.

[0344] When the thickness of the negative electrode conductive layer is within the above range, the conductivity of the negative electrode sheet can be further improved, the heat generation of the negative electrode sheet can be reduced, thereby reducing the heat generation of the battery cell; and the energy density of the battery cell can be improved while taking into account.

[0345] In the embodiments of the present application, the thickness of the negative electrode conductive layer has the meaning well known in the art, and can be detected by equipment and methods well known in the art, and the test method of the negative electrode conductive layer in the foregoing can be adopted.

[0346] In some embodiments, the negative electrode conductive layer includes one or more of a negative electrode conductive agent and a negative electrode binder. The negative electrode conductive agent in the negative electrode conductive layer can improve the conductivity of the negative electrode conductive layer, thereby improving the conductivity of the negative electrode sheet and reducing the heat generation amount of the battery cell; the negative electrode binder in the negative electrode conductive layer can improve the bonding performance between the negative electrode current collecting part and the negative electrode film layer and improve the structural stability of the negative electrode sheet.

[0347] In some embodiments, the negative electrode conductive layer may optionally further include other additives. As an example, the other additives may include thickeners, such as sodium carboxymethyl cellulose (CMC), PTC thermistor materials, etc.

[0348] Optionally, the mass content of the negative electrode conductive agent in the negative electrode conductive layer is from 20% to 40%. Exemplarily, the mass content of the negative electrode conductive agent is 20%, 25%, 30%, 35%, 40% or a range composed of any two of the above values.

[0349] Exemplarily, the negative electrode conductive agent includes one or more of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0350] Optionally, the mass content of the negative electrode binder in the negative electrode conductive layer is from 60% to 80%. Exemplarily, 60%, 65%, 70%, 75%, 80% or a range composed of any two of the above values.

[0351] Exemplarily, the negative electrode binder includes one or more of styrene-butadiene rubber SBR, water-soluble unsaturated resin SR-1B, water-based acrylic resin, polyvinyl alcohol, sodium alginate, and carboxymethyl chitosan.

[0352] 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.

[0353] 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.

[0354] 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.

[0355] 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,

[0356] The capacity of the positive electrode film layer per unit area refers to the actual de-lithiation capacity of the positive electrode active material. The test method is as follows: Disassemble the battery in a PRS340 / 11-119-11 Braun glove box, take the positive electrode plate, assemble it into a CR2430 type half-button battery of positive electrode - lithium sheet, and the area of the positive electrode plate used is am 2 , where the electrolyte is a solution of 1mol / L LiPF6 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 de-lithiate 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 for 2 cycles, and record the discharge and charge capacity of the second cycle as YmAh. The actual designed length of the positive electrode plate of 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 part, then the capacity of the positive electrode film layer per unit area = Y / a*b*c*d.

[0357] 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. The 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 1 mol / L LiPF6 in EC / EMC / DEC=3 / 5 / 2 (mass ratio), and then the assembled half-button battery is left to stand for 3 hours. The test is carried out at 25°C, and 0.1C is used to discharge (Discharge) in the voltage range of 2V-0V to insert lithium, and then 0.05C is used to charge (Discharge) to 2V for lithium removal, and the cycle is repeated twice. The discharge capacity of the second cycle is recorded as ZmAh. The actual battery design has a negative electrode sheet length of hmm and a width of imm. The number of surfaces of the negative electrode active material coated on the negative electrode current collector is d, then the negative electrode lithium insertion capacity = Z / f*h*i*d.

[0358] [Isolation film]

[0359] In the embodiment of the present application, the isolation membrane includes a base membrane with a porous structure.

[0360] In some embodiments, the base film comprises at least one of glass fiber, non-woven fabric, and polyolefin. The base film may be a single-layer film or a multi-layer composite film, without particular limitation. When the base film is a multi-layer composite film, the materials of each layer may be the same or different, without particular limitation.

[0361] Optionally, the polyolefin includes at least one of polyethylene, polypropylene and polyvinylidene fluoride.

[0362] 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.

[0363] In the embodiment of the present application, when the porosity of the base film is within the above range, the migration ability of lithium ions in the separator can be improved, and the internal resistance of the battery cell can be further reduced, thereby reducing heat generation.

[0364] In the embodiments of this application, porosity refers to the percentage of the pore volume within the separator to the total volume of the separator. Porosity can be tested in accordance with the standard GB / T36363-2018, "Polyolefin Separators for Battery Cells." It should be noted that the actual testing process may vary slightly from the standard to obtain a more accurate test value, depending on instrument differences, test errors, and to minimize the impact of porosity testing.

[0365] In some embodiments, the thickness of the base film is from 6 μm to 12 μm, 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.

[0366] 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.

[0367] In the embodiments of the present application, the separator membrane can be a base film. Optionally, the separator membrane further includes a functional layer provided on at least one side of the base film. The functional layer can include inorganic particles to improve the heat resistance of the separator membrane. Optionally, the functional layer is provided on both sides of the base film.

[0368] 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 the first functional layer includes first inorganic particles. The second functional layer is located on the other side of the base film, and the second functional layer includes composite particles. The composite particles include second inorganic particles and 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.

[0369] The first functional layer and the second functional layer have good heat resistance, which can improve the heat resistance of the separator membrane.

[0370] Optionally, the first functional layer can include a binder, optionally at least one of a fluorine-containing binder or a polyacrylic acid binder, such as polyvinylidene fluoride.

[0371] 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.

[0372] In the embodiments of the present application, the meaning of the thickness of the base film is the meaning well-known in the art, and it can be detected by using the meaning and equipment well-known in the art. For example, a newly prepared separator 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 about 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 by an ion beam cutter to form a cross-section. Subsequently, a scanning electron microscope is used to measure the thickness of the cross-section of the separator membrane and its respective layers.

[0373] 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 0.35:0.3:0.15:0.2, or 0.4:0.2:0.1:0.3, or 0.45:0.15:0.2:0.2, etc.

[0374] The second inorganic particles in the composite particles prevent the non-fluoropolymer particles from sticking to each other due to the high-temperature treatment during the granulation process, creating pores in the composite particles, which is beneficial for the transport of lithium ions and improves the ionic conductivity of the separator. Additionally, the second inorganic particles can also increase the compression modulus of the composite particles. During the charge and discharge process, the composite particles are less likely to deform, making the structure of the separator more stable and capable of enhancing the kinetic performance of the battery cell and improving the fast charging performance. Optionally, compared with the first functional layer, the second functional layer is disposed closer to the negative electrode tab. Since the composite particles are less likely to deform, 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 disposed closer to the positive electrode tab.

[0375] Optionally, the second inorganic particles include one or more of silicon oxide, aluminum oxide, boehmite, barium sulfate, calcium oxide, titanium oxide, zinc oxide, magnesium oxide, zirconium oxide, and tin oxide. Optionally, the second inorganic particles include silicon oxide. The above-mentioned second inorganic particles can improve the heat resistance of the second functional layer and can form composite particles in combination with the non-fluoropolymer, further improving the cycle stability and kinetic performance of the separator, as well as the cycle performance and fast charging performance of the battery cell.

[0376] The average particle size of the second inorganic particles is from 5 nm to 100 nm, optionally from 10 nm to 100 nm, and optionally from 5 nm to 20 nm. Exemplarily, the average particle size of the second inorganic particles is 5 nm, 10 nm, 15 nm, 20 nm, 25 nm, 30 nm, 35 nm, 40 nm, 45 nm, 50 nm, 55 nm, 60 nm, 65 nm, 70 nm, 75 nm, 80 nm, 85 nm, 90 nm, 95 nm, 100 nm or any 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.

[0377] 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 the separator membrane 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.

[0378] 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 a range composed of any two of the above values.

[0379] 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.

[0380] 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,

[0381] Prepare a 2025-type button battery for testing: In a vacuum glove box, a lithium sheet is placed in the battery negative electrode case, 150 μL of electrolyte is added thereto, and the electrolyte is a solution of 1 mol / L LiPF6 in EC / EMC / DEC = 3 / 5 / 2 (mass ratio), and then the separator membrane (with an area of 3.14 cm 2 , a thickness of 12 μm) is placed so as to closely adhere to the lithium sheet, 25 μL of electrolyte is added, and finally a positive electrode plate (the positive electrode plate can be the positive electrode plate in Example 1) is placed thereon and encapsulated. The assembled button battery is taken out of the vacuum glove box and left for 24 h for the next test.

[0382] Test: On an electrochemical workstation, test is carried out in the frequency range of 10 -1 ~10 6 Hz to obtain the separator membrane resistance Rb, and the ionic conductivity σ (unit: mS / cm) is calculated by the following formula,

[0383] σ = L / (R b ×S)

[0384] 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.

[0385] [Electrolyte]

[0386] In some embodiments, the battery cell further includes an electrolyte.

[0387] During the charge and discharge process of the battery cell, active ions such as lithium ions are inserted into and extracted from 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.

[0388] In the embodiments of the present application, the conductivity of the electrolyte at room temperature is 13 mS / cm to 20 mS / cm, and may be optionally 15 mS / cm to 20 mS / cm. Exemplarily, the conductivity of the electrolyte at room temperature is 13 mS / cm, 13.5 mS / cm, 14 mS / cm, 14.5 mS / cm, 15 mS / cm, 15.5 mS / cm, 16 mS / cm, 16.5 mS / cm, 17 mS / cm, 17.5 mS / cm, 18 mS / cm, 18.5 mS / cm, 19 mS / cm, 19.5 mS / cm, 20 mS / cm or a range composed of any two of the above values.

[0389] When the conductivity of the electrolyte at room temperature, such as 25 °C, is within the above range, the migration rate of lithium ions in the electrolyte is relatively high, which can further reduce the internal resistance of the battery cell, thereby reducing heat generation, and can improve the fast charging performance of the battery cell.

[0390] In the embodiments of the present application, the conductivity of the electrolyte at room temperature, such as 25 °C, is the ionic conductivity, and 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.

[0391] In some embodiments, the viscosity of the electrolyte at room temperature is 2.3 mPa·s to 3.5 mPa·s. Exemplarily, the viscosity of the electrolyte is 2.3 mPa·s, 2.4 mPa·s, 2.5 mPa·s, 2.6 mPa·s, 2.7 mPa·s, 2.8 mPa·s, 2.9 mPa·s, 3.0 mPa·s, 3.1 mPa·s, 3.2 mPa·s, 3.3 mPa·s, 3.4 mPa·s, 3.5 mPa·s or a range composed of any two of the above values.

[0392] When the viscosity of the electrolyte at room temperature, such as 25 °C, is within the above range, the migration rate of lithium ions in the electrolyte is relatively high, which can further reduce the internal resistance of the battery cell, thereby reducing heat generation, and can improve the fast charging performance of the battery cell.

[0393] 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 according to GB / T10247-2008.

[0394] 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.

[0395] 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.

[0396] In the embodiments of the present application, the density of the electrolyte has the meaning well known in the art, and can be detected by using the equipment and methods well known in the art. For example, it can be tested with reference to GB / T 2013-2010.

[0397] 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.

[0398] [[ID=I4]]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%, and can be optionally 30% to 75%. 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.

[0399] 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.

[0400] In some embodiments, the chain carboxylic ester solvent includes a compound represented by Formula I,

[0401] Formula I,

[0402] In Formula I,

[0403] R1 includes a hydrogen atom, a halogen atom, a C1-C5 alkyl group or a C1-C5 haloalkyl group,

[0404] R2 includes a C1-C5 alkyl group or a C1-C5 haloalkyl group.

[0405] The above chain carboxylic ester solvent has a relatively high conductivity, which is beneficial to improving the fast charging ability of the battery cell.

[0406] Optionally, R1 includes a hydrogen atom, a halogen atom, a C1-C3 alkyl group, or a C1-C3 haloalkyl group. Further optionally, R1 includes a hydrogen atom, a halogen atom, a C1-C2 alkyl group, or a C1-C2 haloalkyl group.

[0407] Optionally, R2 includes a C1-C3 alkyl group or a C1-C3 haloalkyl group. Further optionally, R2 includes a C1-C2 alkyl group or a C1-C2 haloalkyl group.

[0408] 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.

[0409] 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.

[0410] Exemplarily, the chain carboxylic acid ester solvents include one or more of the compounds represented by Formula I-1 to Formula I-8.

[0411]

[0412] In some embodiments, the organic solvent further includes a carbonate solvent.

[0413] 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 acid 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.

[0414] Further optionally, the mass content of the carbonate solvent in the organic solvent is 25% to 95%, and can be 25% to 70%. Exemplarily, the mass content of the carbonate solvent in the organic solvent is 25%, 30%, 31%, 32%, 33%, 34%, 35%, 36%, 37%, 38%, 40%, 45%, 48%, 50%, 55%, 60%, 65%, 70%, 75%, 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.

[0415] 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 25% to 70%.

[0416] In some embodiments, the electrolyte further contains additives, which may include negative electrode film-forming additives, positive electrode film-forming additives, or additives that can improve certain battery performance, such as additives for improving the overcharge performance of the battery, additives for improving the high-temperature performance of the battery, additives for improving the low-temperature power performance of the battery, and the like.

[0417] In some embodiments, the additives include one or more of carbonate additives, sulfur-containing additives, and lithium salt additives, 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 improving the fast charging performance of the battery cell and the cycle performance.

[0418] In some embodiments, the mass content of the additives in the electrolyte is 1% to 10%, optionally 2% to 8%, and further optionally 3.5% to 8%. Exemplarily, the mass content of the additives in the electrolyte is 1%, 2%, 3%, 3.5%, 4%, 5%, 6%, 7%, 8%, 9%, 10% or a range composed of any two of the above values.

[0419] The additives with the above mass content can effectively improve the interfacial film performance on the positive electrode side and / or the negative electrode side, which is beneficial to improving the fast charging performance of the battery cell and the cycle performance.

[0420] Exemplarily, the carbonate additives include one or more of vinylene carbonate (VC) and fluoroethylene carbonate (FEC).

[0421] Exemplarily, the sulfur-containing additives include one or more of ethylene sulfate (DTD), bis(ethylene sulfate) (2-DTD), butene sulfite (BS), 1,3-propane sultone (PS), ethylene sulfite (ES), and methylene methanedisulfonate (MMDS).

[0422] Optionally, the lithium salt additives include one or more of lithium difluorophosphate (LiPO2F2), lithium difluoro(oxalato)borate (LiDFOB), lithium tetrafluoroborate (LiBF4), and lithium bis(oxalato)borate (LiBOB).

[0423] Optionally, the mass content of vinylene carbonate (VC) in the electrolyte is 0.5% to 9%, and may be 2% to 6%.

[0424] Optionally, the mass content of fluoroethylene carbonate (FEC) in the electrolyte is 0.1% to 4%, and may be 0.5% to 3%.

[0425] 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%.

[0426] 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%.

[0427] In some embodiments, the electrolyte salt includes a lithium salt, and the lithium salt includes one or more of a fluorosulfonylimide salt and lithium hexafluorophosphate LiPF6. The above lithium salts are easy to dissociate, which is beneficial to the rapid migration of lithium ions, and the electrolyte system is relatively stable and not easy to decompose, which can improve the cycling performance of the battery cell.

[0428] Optionally, the fluorosulfonylimide salt includes one or more of lithium bis(fluorosulfonyl)imide LiFSI and lithium bis(trifluoromethylsulfonyl)imide LiTFSI.

[0429] Optionally, the lithium salt includes lithium bis(fluorosulfonyl)imide LiFSI and lithium hexafluorophosphate LiPF6. The molar concentration of lithium bis(fluorosulfonyl)imide LiFSI is 0.2 mol / L to 0.5 mol / L, and the molar concentration of lithium hexafluorophosphate LiPF6 is 0.5 mol / L to 1.0 mol / L.

[0430] 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 LiPF6 is 0.7 mol / L.

[0431] Exemplarily, the molar concentration of lithium bis(fluorosulfonyl)imide LiFSI is 0.5 mol / L, and the molar concentration of lithium hexafluorophosphate LiPF6 is 0.5 mol / L.

[0432] Exemplarily, the molar concentration of lithium bis(fluorosulfonyl)imide LiFSI is 0.2 mol / L, and the molar concentration of lithium hexafluorophosphate LiPF6 is 0.8 mol / L.

[0433] Optionally, the ratio of the molar concentration of lithium bis(fluorosulfonyl)imide to the molar concentration of lithium hexafluorophosphate LiPF6 is 0.2 to 1.0, and can be optionally 0.2 to 0.5. Exemplarily, the ratio of the molar concentration of lithium bis(fluorosulfonyl)imide to the molar concentration of lithium hexafluorophosphate LiPF6 is 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1 or a range composed of any two of the above values.

[0434] In the embodiments of the present application, the types and contents of the inorganic components / lithium salt concentration in the electrolyte have meanings well-known in the art, and can be detected by equipment and methods well-known in the art. For example, reference can be made to the standard JY / T 020-1996 "General Rules for Ion Chromatographic Analysis Methods" to qualitatively or quantitatively analyze the inorganic components / lithium salt concentration in the electrolyte by ion chromatography. In the embodiments of the present application, newly prepared electrolyte can be taken as a sample, free electrolyte of a fresh battery can be taken as a sample, or a battery that has been fully discharged (discharged to the lower cut-off voltage so that the charged state of the battery is about 0% SOC) can be disassembled in reverse, and the free electrolyte obtained from the battery can be taken as a sample, and detected by ion chromatography.

[0435] 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 equipment and methods well-known in the art. For example, reference can be made to GB / T 9722-2006 "General Rules for Gas Chromatography of Chemical Reagents" to qualitatively and quantitatively analyze the organic components in the electrolyte by gas chromatography. In the embodiments of the present application, newly prepared electrolyte can be taken as a sample, free electrolyte of a fresh battery can be taken as a sample, or a battery that has been fully discharged (discharged to the lower cut-off voltage so that the charged state of the battery is about 0% SOC) can be disassembled in reverse, and the free electrolyte obtained from the battery can be taken as a sample, and detected by ion chromatography.

[0436] 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.

[0437] Carbonate additives (such as vinylene carbonate, fluoroethylene carbonate), sulfur-containing additives, and lithium salt additives are used as additives for the electrolyte. Based on the mass of the electrolyte being 100%, the mass content of each component is calculated.

[0438] 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.

[0439] The d / A can reflect the liquid retention ability of the electrolyte. When the d / A is within the above range, the electrolyte can wet the positive electrode plate and the negative electrode plate well, 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.

[0440] 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 "Electrical Performance Requirements and Test Methods for Power Batteries for Electric Vehicles" for illustration.

[0441] At 25°C, charge the battery cell at 0.33C to 3.65V, then charge at constant voltage to 0.05C, and then discharge at 0.33C constant current to 2.0V. Take the discharged capacity A as the denominator. Weigh the battery cell as M0, then disassemble the positive electrode plate, the negative electrode plate, the separator and the electrolyte. The free electrolyte is in a bag. Put all the above solid components into an oven at 60°C and bake for more than 4 hours (including but not limited to the positive electrode plate, the negative electrode plate, the separator, and other mechanical parts contributing to M0 in the disassembled battery cell), and then weigh all the components of the battery cell as M1. The weight difference between M0 and M1 is used as the numerator. The liquid retention coefficient is the value obtained by dividing the weight difference d between M0 and M1 by the capacity A.

[0442] In some embodiments, the positive electrode plate, the separator and the negative electrode plate can be made into an electrode assembly by winding process and / or stacking process.

[0443] In some embodiments, the battery cell 7 may further include a housing 20.

[0444] 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 bag-type 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).

[0445] The housing 20 is a hollow structure, and the housing 20 can be used to encapsulate the above electrode assembly 10 and the electrolyte.

[0446] The preparation method of the battery cell 7 according to the embodiments of the present application is well-known. In some embodiments, a positive electrode sheet, a separator, a negative electrode sheet, and an electrolyte can be assembled to form the battery cell 7. As an example, the positive electrode sheet, the separator, and the negative electrode sheet can be formed into an electrode assembly 10 through a winding process and / or a stacking process, the electrode assembly 10 is placed in a housing 20, dried, and then the electrolyte is injected. After vacuum packaging, standing, formation, shaping and other processes, the battery cell 7 is obtained.

[0447] From the perspective of appearance, the electrode assembly 10 includes a main body portion 12, a positive electrode tab 111, and a negative electrode tab 112, and the positive electrode tab 111 and the negative electrode tab 112 protrude from the main body portion 12.

[0448] 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.

[0449] 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.

[0450] In some embodiments, the base material of the housing body 21 includes steel, and the mechanical strength of the steel is relatively high, not easily deformed, which can improve the use reliability of the battery cell 7. In the embodiments of the present application, the base material refers to the material with the highest proportion in the housing body 21.

[0451] Optionally, when the base material of the housing body 21 includes steel, the thickness of the housing body 21 is 0.1 mm to 0.5 mm, and can be selected as 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 mechanical strength of the housing body 21 is relatively high, 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.

[0452] In some embodiments, the battery cell 7 further includes a positive terminal 31, and the positive terminal 31 is electrically connected to the positive electrode tab 111. Optionally, the positive terminal 31 and the positive electrode tab 111 are welded, and the positive terminal 31 and the positive electrode tab 111 can be connected through an adapter, or can be connected without using an adapter. In

[0453] When the positive electrode tab 111 is a negative electrode tab, the positive terminal 31 is a positive terminal. When the positive electrode tab 111 is a positive electrode tab, the positive terminal 31 is a negative terminal.

[0454] In some embodiments, the battery cell 7 further includes a negative terminal 32, and the negative terminal 32 is electrically connected to the negative tab 112. Optionally, the negative terminal 32 and the negative tab 112 are welded, and the negative terminal 32 and the negative tab 112 can be connected through an adapter, or can be connected without using an adapter. When the negative tab 112 is a negative tab, the negative terminal 32 is a positive terminal. When the negative tab 112 is a positive tab, the negative terminal 32 is a negative terminal.

[0455] Optionally, the number of positive terminals 31 on the same side of the main body 12 is at least one, optionally at least two, and at least two positive terminals 31 can increase the current-carrying capacity of the positive terminals 31.

[0456] Further optionally, the current-carrying area of all the positive terminals 31 on one side is greater than or equal to 200 mm 2 and can be optionally 200 mm 2 to 1000 mm 2 The current-carrying area of all the positive terminals 31 on one side refers to the sum of the current-carrying areas of all the positive terminals 31 on the same side of the main body 12.

[0457] Optionally, the number of negative terminals 32 on the same side of the main body 12 is at least one, optionally at least two, and at least two negative terminals 32 can increase the current-carrying capacity of the negative terminals 32.

[0458] Further optionally, the current-carrying area of all the negative terminals 32 on one side is greater than or equal to 200 mm 2 and can be optionally 200 mm 2 to 1000 mm 2 The current-carrying area of the negative terminals 32 on one side refers to the sum of the current-carrying areas of all the negative terminals 32 on the same side of the main body 12.

[0459] As Figure 3 shown, in some embodiments of the present application, the battery cell 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.

[0460] If there are multiple battery cells 7, the multiple battery cells 7 can be connected in series, in parallel, or in a combined series-parallel connection. A combined series-parallel 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, in parallel, or in a combined series-parallel 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, in parallel, or in a combined series-parallel connection to form battery modules 6, and then the multiple battery modules 6 are connected in series, in parallel, or in a combined series-parallel 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.

[0461] As Figure 4 shown, in some embodiments, the above-mentioned battery module 6 can also be assembled into a battery pack 2, and the number of battery modules 6 included in the battery pack 2 can be adjusted according to the application and capacity of the battery pack. The battery device in this article can be either the battery module 6 or the battery pack 2.

[0462] 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.

[0463] The first box body part 5a and the second box body part 5b cover each other, and the first box body part 5a and the second box body part 5b jointly define an accommodating space 5c for accommodating the battery cells. The second box body part 5b can be a hollow structure with one end open, and the first box body part 5a is a plate-like structure. The first box body part 5a covers the opening side of the second box body part 5b to form the box body 5 with the accommodating space 5c. Both the first box body part 5a and the second box body part 5b can also be hollow structures with one side open, and the opening side of the first box body part 5a covers the opening side of the second box body part 5b to form the box body 5 with the accommodating space 5c. Of course, the first box body part 5a and the second box body part 5b can be in various shapes, such as a cylinder, a cuboid, etc.

[0464] 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.

[0465] 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.

[0466] In some embodiments, during the process of the battery pack 2 or any battery cell constituting the battery pack 2 from 0% state of charge (SOC) to 100% SOC, the temperature of the external environment where the battery pack 2 is located is room temperature, such as 30°C.

[0467] In some embodiments, during the charging process of the battery pack 2 or any battery cell constituting the battery pack 2 from 10% SOC to 80% SOC, it includes multiple charging steps. The difference between the maximum SOC of any charging step and the maximum SOC of its adjacent charging step in the multiple charging steps is less than or equal to 5% SOC, such as 1% SOC, 1.5% SOC, 2% SOC, 2.5% SOC, 3% SOC, 3.5% SOC, 4% SOC, 4.5% SOC, 5% SOC, or a range composed of any two of the above values.

[0468] The battery pack 2 or any battery cell constituting the battery pack 2 from 10% SOC to 40% SOC includes multiple charging steps. For any charging step, it can be charged at any rate between 5C and 10C. The charging rate corresponding to each charging step can be any value among 5C, 5.5C, 6C, 6.5C, 7C, 7.5C, 8C, 8.5C, 9C, 9.5C, 10C, or a value within a range composed of any two of the above values.

[0469] Exemplarily, the charging steps of the battery pack 2 or any battery cell constituting the battery pack 2 from 10% to 80% can be carried out as follows:

[0470] Constant current charge at 5.0C from 10% SOC to 15% SOC;

[0471] Constant current charge at 5.0C from 15% SOC to 20% SOC;

[0472] Constant current charge at 5.0C from 20% SOC to 25% SOC;

[0473] Constant current charge at 5.0C from 25% SOC to 30% SOC;

[0474] Constant current charge at 5.0C from 30% SOC to 35% SOC;

[0475] Constant current charge at 5.0C from 35% SOC to 40% SOC;

[0476] Constant current charge at 4.6C from 40% SOC to 45% SOC;

[0477] Constant current charge at 4.3C from 45% SOC to 50% SOC;

[0478] Constant current charge at 4.0C from 50% SOC to 55% SOC;

[0479] Charge from 55% SOC to 60% SOC at a constant current of 3.7C;

[0480] Charge from 60% SOC to 65% SOC at a constant current of 3.4C;

[0481] Charge from 65% SOC to 70% SOC at a constant current of 3.1C;

[0482] Charge from 70% SOC to 75% SOC at a constant current of 2.9C;

[0483] Charge from 75% SOC to 80% SOC at a constant current of 2.7C.

[0484] In some embodiments, the charging time of the battery pack 2 or any battery cell constituting the battery pack 2 from 20% state of charge to 80% state of charge is less than or equal to 12.5 min, and can be optionally 6 min to 12.5 min. The temperature of the external environment of the battery pack 2 at 10% state of charge is room temperature, such as 30°C. Exemplarily, the charging time of the battery pack 2 from 10% state of charge to 80% state of charge is 12.5 min, 12 min, 11.5 min, 11 min, 10.5 min, 10 min, 9.5 min, 9 min, 8.5 min, 8 min, 7.5 min, 7 min, 6.5 min, 6 min or the range composed of any two of the above values.

[0485] In some embodiments, the volumetric energy density of the battery cell is 390 Wh / L to 500 Wh / L, and can be optionally 410 Wh / L to 470 Wh / L. Exemplarily, the volumetric energy density of the battery cell is 390 Wh / L, 400 Wh / L, 410 Wh / L, 420 Wh / L, 430 Wh / L, 440 Wh / L, 450 Wh / L, 460 Wh / L, 470 Wh / L, 480 Wh / L, 490 Wh / L, 500 Wh / L or the range composed of any two of the above values. The volumetric energy density of the battery cell is relatively high.

[0486] In the embodiments of the present application, the volumetric energy density of the battery cell has the meaning well-known in the art, and can be detected by using the equipment and methods well-known in the art. For example, taking the upper charging voltage of the battery as 3.65V and the cut-off discharge voltage of the battery as 2.0V as an example for illustration,

[0487] The battery cell is placed at 25°C and charged at a constant current of 0.33C to 3.65V, then charged at a constant voltage to 0.05C, and discharged at a constant current of 0.33C to 2.0V. Record the discharge capacity A0 at this time, unit: Ah. Use a caliper to measure the length, width, and height of the battery cell (generally calculated based on the outer shell size of the battery, excluding the height of the electrode terminals and the insulation film outside the shell), and calculate the volume V0 of the single battery cell, unit: L. The volume energy density VED of the battery cell = (A0 × discharge platform voltage) / V0, unit: Wh / L.

[0488] electrical device

[0489] The second aspect of the embodiments of the present application provides an electrical device. The electrical device includes at least one of the battery cell, battery module, or battery pack of the embodiments of the present application. The battery cell, battery module, or battery pack can be used as the power source of the electrical device or as the energy storage unit of the electrical device. The electrical device can be a vehicle, mobile phone, portable device, laptop computer, ship, spacecraft, electric toy, and electric tool, etc. The vehicle can be a fuel vehicle, gas vehicle, or new energy vehicle. The new energy vehicle can be a pure electric vehicle, hybrid electric vehicle, or range-extended electric vehicle, etc.; the spacecraft includes airplanes, rockets, space shuttles, and spaceships, etc.; the electric toy includes fixed or mobile electric toys, for example, game consoles, electric vehicle toys, electric ship toys, and electric airplane toys, etc.; the electric tool includes metal cutting electric tools, grinding electric tools, assembly electric tools, and railway electric tools, for example, electric drills, electric grinders, electric wrenches, electric screwdrivers, electric hammers, impact electric drills, concrete vibrators, and electric planers, etc. The embodiments of the present application do not impose special restrictions on the above electrical devices.

[0490] The electrical device can select the battery cell, battery module, or battery pack according to its usage requirements.

[0491] Figure 5 It is a schematic diagram of an electrical device 1 as an example. The electrical device 1 is a pure electric vehicle, hybrid electric vehicle, or plug-in hybrid electric vehicle, etc. To meet the requirements of the electrical device 1 for high power and high energy density, a battery pack or battery module can be used.

[0492] A battery pack 2 is provided inside the electrical device 1. The battery pack 2 can be provided 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.

[0493] The electrical device 1 may also 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 startup, navigation, and driving of the electrical device 1.

[0494] As another example, the electrical device can be a mobile phone, a tablet computer, a laptop computer, etc. This electrical device usually requires being thin and light, and battery cells can be used as the power source.

[0495] The charging process of the electrical device can select the following charging methods:

[0496] Charge at a constant current of 5.0C from 10% SOC to 15% SOC;

[0497] Charge at a constant current of 5.0C from 15% SOC to 20% SOC;

[0498] Charge at a constant current of 5.0C from 20% SOC to 25% SOC;

[0499] Charge at a constant current of 5.0C from 25% SOC to 30% SOC;

[0500] Charge at a constant current of 5.0C from 30% SOC to 35% SOC;

[0501] Charge at a constant current of 5.0C from 35% SOC to 40% SOC;

[0502] Charge at a constant current of 4.6C from 40% SOC to 45% SOC;

[0503] Charge at a constant current of 4.3C from 45% SOC to 50% SOC;

[0504] Charge at a constant current of 4.0C from 50% SOC to 55% SOC;

[0505] Charge at a constant current of 3.7C from 55% SOC to 60% SOC;

[0506] Charge at a constant current of 3.4C from 60% SOC to 65% SOC;

[0507] Charge at a constant current of 3.1C from 65% SOC to 70% SOC;

[0508] Charge at a constant current of 2.9C from 70% SOC to 75% SOC;

[0509] Charge at a constant current of 2.7C from 75% SOC to 80% SOC.

[0510] In some embodiments, the charging time of the electrical device from 10% state of charge to 80% state of charge is less than or equal to 12.5 min, and can be optionally 6 min to 12.5 min. The temperature of the external environment of the battery pack 2 in the electrical device at 20% state of charge is room temperature, such as 30°C. Exemplarily, the charging time of the battery pack 2 in the electrical device from 10% state of charge to 80% state of charge is 12.5 min, 12 min, 11.5 min, 11 min, 10.5 min, 10 min, 9.5 min, 9 min, 8.5 min, 8 min, 7.5 min, 7 min, 6.5 min, 6 min or a range composed of any two of the above values.

[0511] embodiment

[0512] 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 all instruments used in the examples are commercially available.

[0513] Example 1-1 Battery Cell (Wound Electrode Assembly)

[0514] 1. Preparation of the Positive Electrode Plate

[0515] 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 15 μm.

[0516] The positive conductive layer on the positive current collector is a film layer formed by uniformly mixing a positive conductive agent, superconducting carbon, a positive binder, polyvinylidene fluoride (PVDF), and a solvent, N-methylpyrrolidone (NMP), and then coating it on the surface of the current collector and drying. The thickness is 1 μm. The mass content of the positive conductive agent in the positive conductive layer is 40%, and the mass content of the positive binder is 60%.

[0517] The positive electrode film layer includes a film layer formed by uniformly coating a positive electrode slurry (solvent: N-methylpyrrolidone (NMP)) on the surface of the positive conductive layer, followed by drying and cold pressing. The positive electrode film layer includes a positive active material, a binder, polyvinylidene fluoride (PVDF), and a conductive agent, acetylene black, with a weight ratio of 97:2:1.

[0518] The positive electrode active material includes lithium iron phosphate and a coating layer. The coating layer coats the surface of the lithium iron phosphate. The coating layer includes lithium iron titanium phosphate Li2FeTi(PO4)3 and amorphous carbon. The Dv50 of the positive electrode active material is 1.6 μm, and the Dv10 is 0.64 μm.

[0519] 2. Preparation of the negative electrode sheet

[0520] The negative electrode sheet includes a negative electrode current collector portion, a negative electrode conductive layer on the negative electrode current collector portion, and a negative electrode film layer. The negative electrode current collector portion is a copper foil with a thickness of 6 μm.

[0521] The negative electrode conductive layer on the negative electrode current collector portion 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 thickening agent, sodium carboxymethyl cellulose (CMC-Na), and a solvent, water, on the surface of the negative electrode current collector portion and drying. The thickness is 1 μm. The mass content of the negative electrode conductive agent in the negative electrode conductive layer is 35%, the mass content of the negative electrode binder in the negative electrode conductive layer is 60%, and the mass content of the thickening agent in the negative electrode conductive layer is 5%.

[0522] The negative electrode film layer includes a film layer formed by uniformly coating a negative electrode slurry (with deionized water as the solvent) on the surface of the negative electrode conductive layer and then drying and cold pressing.

[0523] The negative electrode film layer includes a film layer formed by uniformly coating a negative electrode slurry (with deionized water as the solvent) on the surface of the negative electrode conductive layer and then drying and cold pressing.

[0524] 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.

[0525] The first negative electrode film layer includes graphite particles, conductive agent acetylene black, a first lithium-containing binder (copolymer of lithium acrylate - acrylonitrile - acrylamide - 2-hydroxyethyl acrylate, where the molar ratio of lithium acrylate monomer, acrylonitrile monomer, acrylamide monomer, and 2-hydroxyethyl acrylate monomer is 0.35:0.3:0.15:0.2), negative electrode binder styrene-butadiene rubber, and thickening agent sodium carboxymethyl cellulose with a mass ratio of 96.5:0.5:0.5:1.5:1. The mass content of lithium element in the first lithium-containing binder is 4.8%. The Dv50 of the graphite particles is 11.3 μm. The graphite particles include artificial graphite and a carbon coating layer. The carbon coating layer coats the surface of the artificial graphite, and the mass content of the carbon coating layer is 3.5%.

[0526] The second negative electrode film layer includes graphite particles, conductive agent acetylene black, second lithium-containing binder (lithium acrylate-acrylonitrile-acrylamide-hydroxyethyl acrylate copolymer, where the molar ratio of lithium acrylate monomer, acrylonitrile monomer, acrylamide monomer, and hydroxyethyl acrylate monomer is 0.35:0.3:0.15:0.2), negative electrode binder styrene-butadiene rubber, and thickening agent sodium carboxymethyl cellulose. The mass content of lithium element in the second lithium-containing binder is 4.8%. The Dv50 of the graphite particles is 11.3 μm. The graphite particles include artificial graphite and a carbon coating layer. The carbon coating layer is coated on the surface of the artificial graphite, and the mass content of the carbon coating layer is 3.5%.

[0527] 3. Separator

[0528] The separator includes a base film, which is a 7-μm polyethylene film layer with a porosity of 42%.

[0529] 4. Preparation of electrolyte

[0530] The electrolyte includes organic solvents, lithium salts, and additives.

[0531] The organic solvents include 60% chain carboxylic ester solvents (ethyl acetate) and 40% carbonate solvents (30% ethylene carbonate EC and 10% dimethyl carbonate). The mass content of each component in the organic solvents is calculated based on the mass of the organic solvents.

[0532] 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.

[0533] The lithium salt includes 1 mol / L lithium hexafluorophosphate LiPF6.

[0534] The conductivity of the electrolyte at room temperature is 16.4 mS / cm.

[0535] 5. Preparation of battery cell

[0536] 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 a separating role, and obtain an electrode assembly through a winding process; place the electrode assembly in an outer packaging shell, inject the electrolyte after drying, and obtain a battery cell through processes such as vacuum packaging, standing, forming, and shaping.

[0537] At 100% SOC, the tap density of the positive electrode film layer of the battery cell is 2.63 g / cm 3 and the tap density of the negative electrode film layer is 1.26 g / cm 3 .

[0538] Comparative Example 1-1 and Comparative Example 1-2

[0539] The battery monomer was prepared by a method similar to that of Example 1-1. Different from Example 1-1, the coating weights of the positive electrode film layer and the negative electrode film layer were adjusted.

[0540] Comparative Example 1-3

[0541] The battery monomer was prepared by a method similar to that of Example 1-1. Different from Example 1-1, the conductivity of the electrolyte was adjusted.

[0542] Examples 1-2 to 1-6

[0543] The battery monomer was prepared by a method similar to that of Example 1-1. Different from Example 1-1, at least one of the coating weights of the positive electrode film layer and the negative electrode film layer and the conductivity of the electrolyte was adjusted, as specifically shown in Table 1.

[0544] Among them,

[0545] In Example 1-4, the organic solvent in the electrolyte included 30% chain carboxylic ester solvent (ethyl acetate) and 70% carbonate solvent (30% ethylene carbonate EC and 40% dimethyl carbonate). The mass content of each component in the organic solvent was calculated based on the mass of the organic solvent, and the conductivity was 13.1 mS / cm;

[0546] In Example 1-5, the organic solvent in the electrolyte included 70% chain carboxylic ester solvent (methyl acetate) and 30% carbonate solvent (ethylene carbonate EC), and the mass content of each component in the organic solvent was calculated based on the mass of the organic solvent, and the conductivity was 18.7 mS / cm.

[0547] In Example 1-6, the negative electrode active material further included a silicon-based material, and the mass content of silicon element in the silicon-based material relative to the mass of the negative electrode active material was 3%.

[0548] performance test

[0549] 1. Charging time of the battery monomer

[0550] For the battery monomer of Example 1, the charging time from 10% SOC to 80% SOC was specifically carried out by the following charging steps. At 30 °C, charging was carried out from the 10% SOC state of the battery.

[0551] Constant current charging at 5.0C from 10% SOC to 15% SOC;

[0552] Constant current charging at 5.0C from 15% SOC to 20% SOC;

[0553] Charge from 20% SOC to 25% SOC at 5.0C constant current;

[0554] Charge from 25% SOC to 30% SOC at 5.0C constant current;

[0555] Charge from 30% SOC to 35% SOC at 5.0C constant current;

[0556] Charge from 35% SOC to 40% SOC at 5.0C constant current;

[0557] Charge from 40% SOC to 45% SOC at 4.6C constant current;

[0558] Charge from 45% SOC to 50% SOC at 4.3C constant current;

[0559] Charge from 50% SOC to 55% SOC at 4.0C constant current;

[0560] Charge from 55% SOC to 60% SOC at 3.7C constant current;

[0561] Charge from 60% SOC to 65% SOC at 3.4C constant current;

[0562] Charge from 65% SOC to 70% SOC at 3.1C constant current;

[0563] Charge from 70% SOC to 75% SOC at 2.9C constant current;

[0564] Charge from 75% SOC to 80% SOC at 2.7C constant current.

[0565] Record the total charging time.

[0566] Based on the charging rate adjustment in Example 1, different embodiments adjust the actual rate according to the charging time from 10% to 80% SOC.

[0567] 2. Battery cell cycle performance

[0568] At 30°C, the battery cell was charged from 10% SOC to 80% SOC using the above charging process, then charged to 3.65V at 0.33C. After standing for 30 minutes, it was discharged to 10% SOC at 1C. This constituted one charge-discharge cycle. This charge-discharge cycle was repeated 1000 times to calculate the cycle capacity retention rate of the battery cell. A higher cycle capacity retention rate indicates better cycle performance of the battery cell. Based on the charge rate adjustment in Example 1, the actual charge rate was adjusted according to the charging time from 10% to 80% SOC in different examples.

[0569] The test results are shown in Table 1.

[0570] Table 1

[0571]

[0572] As can be seen from Table 1, the single-sided coating weight of the positive electrode film layer in Comparative Example 1-1 is 150 mg / 1540.25 mm 2 , and its coating weight is small, resulting in a small energy density of the battery cell; while the single-sided coating weight of the positive electrode film layer in Comparative Example 1-2 is 400 mg / 1540.25 mm 2 , and its coating weight is high, which may result in a large resistance to lithium ion migration and poor fast charging performance. In Comparative Example 1-3, the conductivity of the electrolyte is small, the resistance to lithium ion migration is large, and the fast charging performance is poor.

[0573] In the embodiment of the present application, 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 , the conductivity of the electrolyte at room temperature is 13 mS / cm to 20 mS / cm, which can make the discharge platform voltage of the battery cell during the discharge process from 100% state of charge at a constant current rate of 0.33C to 2.0V be 3.19V to 3.235V, preferably 3.215V to 3.235V, and the discharge platform voltage of the battery cell during the discharge process from 100% state of charge at a constant current rate of 2C to 2.0V be 3.05V to 3.15V. Thus, it is possible to take into account the improvement of the energy density, fast charging performance and cycle performance of the battery cell.

[0574] In Example 1-6, since the negative electrode active material contains a silicon-based material, its energy density is significantly improved. However, due to its volume expansion effect, the cycle performance may be slightly worse than that of Example 1-1.

[0575] Example 2-1 Battery cell (laminated electrode assembly)

[0576] A battery cell was prepared by a method similar to that of Example 1-1. Different from Example 1-1, a laminated process was used to prepare the electrode assembly.

[0577] Examples 2-2 to 2-6

[0578] A battery cell was prepared by a method similar to that of Example 2-1. Different from Example 2-1, at least one of the coating weights of the positive electrode film layer and the negative electrode film layer and the conductivity of the electrolyte was adjusted, as shown in Table 2 specifically.

[0579] Examples 2-1 to 2-6 were tested for battery performance by a method similar to that of Example 1-1, and the test results are shown in Table 2.

[0580] Among them, in Examples 2-5 and 2-6, the negative electrode active material further includes a silicon-based material, and the mass content of silicon element in the silicon-based material relative to the mass of the negative electrode active material is 3%.

[0581] Table 2

[0582]

[0583] As can be seen from Table 2, in the examples of the present application, 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 , the conductivity of the electrolyte at room temperature is 13 mS / cm to 20 mS / cm, which can make the discharge platform voltage of the battery cell during the constant current discharge process from 100% state of charge at a rate of 0.33C to 2.0V be 3.19V to 3.235V, optionally 3.19 to 3.225V, and the discharge platform voltage of the battery cell during the constant current discharge process from 100% state of charge at a rate of 2C to 2.0V be 3.05V to 3.15V. Thus, it is possible to balance the improvement of the energy density, fast charging performance and cycling performance of the battery cell.

[0584] In Examples 2-5 and 2-6, the negative electrode active material further includes a silicon-based material, and its energy density is significantly improved. However, due to its volume expansion effect, the cycling performance may be slightly worse than that of Example 2-1.

[0585] 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, It includes an electrode assembly and an electrolyte. The electrode assembly includes a positive electrode plate, a negative electrode plate, and a separator. The separator is located between the positive electrode plate and the negative electrode plate. The positive electrode sheet includes a positive current collector portion and a positive electrode film layer disposed on at least one surface of the positive current collector portion along the thickness direction of the positive electrode sheet and containing a positive electrode active material. The positive electrode active material includes a lithium-containing phosphate having an olivine structure, and 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 , The negative electrode plate includes a negative current collector and at least one surface of the negative current collector along the thickness direction of the negative electrode plate and a negative electrode film layer containing a negative active material. The negative active material includes a carbon-based material. The conductivity of the electrolyte at room temperature is 13 mS / cm to 20 mS / cm. The electrolyte includes an organic solvent, and the organic solvent includes a chain carboxylic ester solvent. In an external environment at 25 °C, during the discharge process of the battery cell from 100% state of charge at a constant current rate of 0.33C to 2.0V, it has a discharge platform voltage V1, and V1 is 3.19V to 3.235V.

2. The battery cell according to claim 1, wherein 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 .

3. The battery cell according to claim 1, characterized in that, The electrode assembly is a stacked structure, and the positive electrode plate, the separator, and the negative electrode plate are stacked. V1 is 3.19V to 3.225V.

4. The battery cell according to claim 3, wherein The positive electrode plate further includes a positive electrode tab, and the positive electrode tab is arranged on at least one side of the positive current collector along the length direction of the positive electrode plate.

5. The battery cell according to claim 4, characterized in that, The positive electrode tab is arranged on both sides of the positive current collector along the length direction of the positive electrode plate.

6. The battery cell according to claim 3, wherein, The size of the positive electrode film layer along the length direction of the positive electrode plate is 200 mm to 400 mm, and V1 is 3.20V to 3.225V.

7. The battery cell according to claim 3, characterized in that, The size of the positive electrode film layer along the length direction is greater than 400 mm and less than or equal to 1000 mm, and V1 is 3.19V to 3.218V.

8. The battery cell according to claim 1, wherein The electrode assembly is a wound structure, and the positive electrode plate, the separator, and the negative electrode plate are wound in the same direction. V1 is 3.215V to 3.235V.

9. The battery cell according to claim 1, wherein, The negative active material further includes a silicon-based material, and V1 is 3.190V to 3.230V.

10. The battery cell according to claim 9, characterized in that, The mass content of silicon element in the silicon-based material is 0.3% to 10.0% based on the mass of the negative active material.

11. The battery cell according to claim 9, characterized in that, The electrode assembly is a stacked structure, and V1 is 3.190V to 3.218V.

12. The battery cell according to claim 9, wherein, The electrode assembly is a wound structure, and V1 is 3.210V to 3.230V.

13. The battery cell according to claim 1, characterized in that, When discharging the battery cell in an external environment at 25 °C, during the discharge process of the battery cell from 100% state of charge at a constant current rate of 2C to 2.0V, it has a discharge platform voltage V2, and V2 / V1 is 0.942 to 0.

975.

14. The battery cell according to claim 12, wherein V2 is 3.05V to 3.15V.

15. The battery cell according to claim 1, wherein, The single-sided coating weight of the positive electrode film layer is 240 mg / 1540.25 mm 2 to 330 mg / 1540.25 mm 2 .

16. The battery cell according to claim 1, characterized in that, The single-sided coating weight of the negative electrode film layer is 110 mg / 1540.25 mm 2 to 150 mg / 1540.25 mm 2 .

17. The battery cell according to claim 1, wherein When the battery cell is in a 100% state of charge, the tap density of the positive electrode film layer is 2.50 g / cm 3 to 2.80 g / cm 3 .

18. The battery cell according to claim 1, wherein, 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 .

19. The battery cell according to claim 1, wherein the powder resistivity of the positive active material is 1 Ω•cm to 27.5 Ω•cm; and / or The powder tap density of the positive electrode active material under 30,000 N is 2.46 g / cm 3 to 2.8 g / cm 3 ; and / or the charging specific capacity of the positive active material at a rate of 0.1C is 150 mAh / g to 170 mAh / g.

20. The battery cell according to claim 1, characterized in that, The lithium-containing phosphate with an olivine structure includes: phosphate particles, and a coating layer that coats the phosphate particles, and the coating layer contains one or more elements of C, Fe, Ti, Zr, Hf, Ge, and Sn.

21. The battery cell according to claim 20, wherein The phosphate particles comprise a compound of the general formula Li x1 A y1 Me a M b P 1-c X c Y z wherein 0.5 ≤ x1 ≤ 1.3, 0 ≤ y1 ≤ 1.3, and 0.9 ≤ x1 + y1 ≤ 1.3, 0.9 ≤ a ≤ 1.5, 0 ≤ b ≤ 0.5, and 0.9 ≤ a + b ≤ 1.5, 0 ≤ c ≤ 0.5, 3 ≤ z ≤ 5, A comprises one or more of Na, K, Mg, Me comprises one or more of Mn, Fe, Co, Ni, M comprises one or more of B, Mg, Al, Si, P, S, Ca, Sc, Ti, V, Cr, Cu, Zn, Sr, Y, Zr, Nb, Mo, Cd, Sn, Sb, Te, Ba, Ta, W, Yb, La, Ce, X comprises one or more of S, Si, Cl, B, C, N, and Y comprises one or more of O, F.

22. The battery cell according to claim 20, wherein, The coating layer includes a fast ion conductor with the general formula Li 3-d Fe 2-d M2 d (PO x2 ) y2 , where M2 includes one or more elements of Ti, Zr, Hf, Ge, and Sn, 0 ≤ d ≤ 1, 0 < x2 < 5, and 0 < y2 < 4.

23. The battery cell according to claim 20, characterized in that, The graphitization degree of the lithium-containing phosphate with an olivine structure is 0.15 to 0.

32.

24. The battery cell according to claim 23, characterized in that, The graphitization degree of the lithium-containing phosphate with olivine structure is 0.19 to 0.

26.

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

26. The battery cell according to claim 25, wherein The specific surface area of the lithium-containing phosphate with olivine structure is 7.5 m 2 / g to 14 m 2 / g.

27. The battery cell according to claim 1, wherein The lithium-containing phosphate with olivine structure is granular, and its volume distribution particle size satisfies: 1μm ≤ Dv50 ≤ 2μm, 0.4μm ≤ Dv10 ≤ 0.7μm.

28. The battery cell according to claim 1, wherein, The lithium-containing phosphate with olivine structure is granular, the lithium-containing phosphate with olivine structure includes secondary particles, the secondary particles include a plurality of primary particles, and the average particle size of the primary particles is 200nm to 500nm.

29. The battery cell according to claim 1, wherein, The ratio of the thickness of the positive electrode current collector part to the total thickness of the single-sided positive electrode film layer is 0.06 to 0.

10.

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

31. The battery cell according to claim 1, characterized in that, 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 electrode current collector part.

32. The battery cell according to claim 31, characterized in that, The thickness of the positive electrode conductive layer is 0.5μm to 2μm.

33. The battery cell according to claim 31, wherein The positive electrode conductive layer includes a positive electrode conductive agent, and the positive electrode conductive agent includes one or more of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers, and / or The positive electrode conductive layer includes a positive electrode binder, and the positive electrode binder includes one or more of polyvinylidene fluoride, polytetrafluoroethylene, vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, polyacrylic acid, and fluorinated acrylate resins.

34. The battery cell according to claim 1, characterized in that, The positive electrode film layer further includes a first material, and the first material includes one or more of ternary materials, lithium phosphate, lithium hydrogen phosphate, lithium sulfate, lithium sulfite, lithium molybdate, lithium oxalate, lithium titanate, lithium tetraborate, lithium metasilicate, lithium manganate, lithium tartrate, lithium citrate, lithium nickelate, and lithium ferrate.

35. The battery cell according to claim 34, wherein The mass content of the first material in the positive electrode film layer is 0.5% to 5.0%.

36. According to the battery cell of claim 1, characterized in that, The powder resistivity of the negative electrode active material is 0.005Ω•cm to 0.043Ω•cm; and / or The powder compaction density of the negative electrode active material under 20,000 N is 1.5 g / cm 3 to 1.85 g / cm 3 .

37. The battery cell according to claim 1, characterized in that, The charging specific capacity of the negative electrode active material at 0.1C rate is 350mAh / g to 480mAh / g.

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

39. The battery cell according to claim 38, wherein The graphite particles include: Artificial graphite, including secondary particles, and A carbon coating layer, coated on the surface of the artificial graphite.

40. The battery cell according to claim 39, wherein Based on the mass of the graphite particles, the mass content of amorphous carbon in the coating layer is 2% to 5%.

41. The battery cell according to claim 1, wherein The porosity of the negative electrode film layer is 40% to 55%.

42. The battery cell according to claim 1, wherein The negative electrode film layer is a single-layer film layer, the negative electrode active material is granular, and the volume average particle size of the negative electrode active material is 8.2μm to 13.5μm.

43. The battery cell according to claim 1, characterized in that, The negative electrode film layer includes: A first negative electrode film layer, disposed on the surface of the negative electrode current collector part, the first negative electrode film layer includes a carbon-based material, and The second negative electrode film layer is connected to a side of the first negative electrode film layer facing away from the negative electrode current collector portion. The second negative electrode film layer includes a carbon-based material. The carbon-based material in the first negative electrode film layer and the carbon-based material in the second negative electrode film layer each independently include graphite particles, and the volume average particle diameter Dv50 of the graphite particles in the first negative electrode film layer is greater than or equal to the volume average particle diameter Dv50 of the graphite particles in the second negative electrode film layer.

44. The battery cell according to claim 43, wherein the volume average particle diameter 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 diameter Dv50 of the graphite particles in the second negative electrode film layer is 7.8 μm to 14.3 μm.

45. The battery cell according to claim 43, wherein, 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.

46. The battery cell according to claim 45, wherein 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%.

47. The battery cell according to claim 45, wherein the mass content of lithium element in the first lithium-containing binder is 3% to 10%, and / or the mass content of lithium element in the second lithium-containing binder is 3% to 10%.

48. The battery cell according to claim 45, wherein 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 the lithium acrylate monomer, the acrylonitrile monomer, the acrylamide monomer and the 2-hydroxyethyl acrylate monomer is (0.3 - 0.5):(0.15 - 0.45):(0.05 - 0.2):(0.2 - 0.35); and / or 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 lithium acrylate monomer, acrylonitrile monomer, acrylamide monomer and 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 (0.3 - 0.5):(0.15 - 0.45):(0.05 - 0.2):(0.2 - 0.35).

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

50. The battery cell according to claim 1, characterized in that, The negative electrode tab 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 portion.

51. The battery cell according to claim 50, wherein, The thickness of the negative electrode conductive layer is 0.5 μm to 2 μm.

52. The battery cell according to claim 50, wherein, The negative electrode conductive layer includes a negative electrode conductive agent, and the negative electrode conductive agent includes one or more of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers, and / or The negative electrode conductive layer includes a negative electrode binder, and the negative electrode binder includes one or more of styrene-butadiene rubber, water-soluble unsaturated resin, water-based acrylic resin, polyvinyl alcohol, sodium alginate, and carboxymethyl chitosan.

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

54. The battery cell according to claim 1, wherein The viscosity of the electrolyte at room temperature is 2.3 mPa·s to 3.5 mPa·s; and / or The density of the electrolyte at room temperature is 1.05 g / mL to 1.35 g / mL.

55. The battery cell according to claim 1, characterized in that, The mass content of the chain carboxylic acid ester solvent in the organic solvent is 5% to 75%.

56. The battery cell according to claim 55, characterized in that, The mass content of the chain carboxylic acid ester solvent in the organic solvent is 30% to 75%.

57. The battery cell according to claim 55, characterized in that, The chain carboxylic acid ester solvent includes a compound represented by Formula I, Formula I, In Formula I, R1 includes a hydrogen atom, a halogen atom, a C1-C5 alkyl group, or a C1-C5 haloalkyl group, R2 includes a C1-C5 alkyl group or a C1-C5 haloalkyl group.

58. The battery cell according to claim 57, wherein R1 includes a hydrogen atom, a halogen atom, a C1-C3 alkyl group, or a C1-C3 haloalkyl group, and / or R2 includes a C1-C3 alkyl group or a C1-C3 haloalkyl group.

59. The battery cell according to claim 58, wherein, The chain carboxylic acid ester solvent includes one or more of the compounds represented by Formula I-1 to Formula I-8, 。 60. The battery cell according to claim 55, wherein, 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.

61. The battery cell according to claim 60, characterized in that, The mass content of the carbonate solvent in the organic solvent is greater than or equal to 25% and less than or equal to 95%.

62. The battery cell according to claim 1, characterized in that, 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.

63. The battery cell according to claim 62, wherein The carbonate additive includes one or more of vinylene carbonate and fluoroethylene carbonate, and / or The sulfur-containing additive includes one or more of ethylene sulfate, bis(ethylene sulfate), butene sulfite, 1,3-propane sultone, ethylene sulfite, and methylene methanedisulfonate, and / or The lithium salt additive includes one or more of lithium difluorophosphate, lithium difluorooxalate borate, lithium tetrafluoroborate, and lithium bis(oxalate) borate.

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

65. The battery cell according to claim 64, characterized in that, The mass content of the additive in the electrolyte is 2% to 8%.

66. The battery cell according to claim 1, characterized in that, The electrolyte further includes a lithium salt, and the lithium salt includes one or more of a fluorosulfonylimide salt and lithium hexafluorophosphate.

67. The battery cell according to claim 66, wherein, The fluorosulfonylimide salt includes one or more of lithium bis(fluorosulfonyl)imide and lithium bis(trifluoromethylsulfonyl)imide.

68. The battery cell according to claim 67, wherein, The lithium salts include lithium bis(fluorosulfonyl)imide and lithium hexafluorophosphate. The molar concentration of lithium bis(fluorosulfonyl)imide is from 0.2 mol / L to 0.5 mol / L, and the molar concentration of lithium hexafluorophosphate is from 0.5 mol / L to 1.0 mol / L.

69. The battery cell according to claim 68, wherein The ratio of the molar concentration of lithium bis(fluorosulfonyl)imide to the molar concentration of lithium hexafluorophosphate (LiPF6) is from 0.2 to 1.

0.

70. The battery cell according to claim 1, characterized in that, The separator includes a base film with a porous structure, and the thickness of the base film is from 5 μm to 12 μm.

71. The battery cell according to claim 70, wherein, The separator further includes a functional layer disposed on at least one side of the base film. The functional layer includes: A first functional layer located on one side of the base film. The first functional layer includes first inorganic particles. A second functional layer located on the other side of the base film. 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 and / or dispersed inside the non-fluoropolymer particles.

72. The battery cell according to claim 71, wherein, The non-fluoropolymer particles include acrylate copolymers.

73. The battery cell according to claim 71, 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.

74. The battery cell according to claim 71, characterized in that, The second inorganic particles include one or more of silicon oxide, aluminum oxide, boehmite, barium sulfate, calcium oxide, titanium oxide, zinc oxide, magnesium oxide, zirconium oxide, and tin oxide, and / or The average particle size of the second inorganic particles is from 5 nm to 100 nm.

75. The battery cell according to claim 1, wherein, The volume energy density of the battery cell is from 390 Wh / L to 550 Wh / L.

76. The battery cell according to claim 1, wherein The charging time of the battery cell from 10% state of charge to 80% state of charge is from 6 min to 12.5 min.

77. A battery device, characterized in that, It includes a battery cell as described in any one of claims 1 to 76.

78. The battery device according to claim 77, wherein, The charging time of the battery device from 10% state of charge to 80% state of charge is from 6 min to 12.5 min.

79. An electrical device, characterized in that, It includes a battery device as described in claim 77.

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