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 electrode assembly, the electrode assembly includes a positive electrode tab and a negative electrode tab. The positive electrode tab includes a positive current collector portion and a positive electrode film layer, the positive electrode film layer includes a positive active material, and the positive active material includes a lithium-containing phosphate with an olivine structure; the negative electrode tab includes a negative current collector portion and a negative electrode film layer, a negative electrode tab is connected to at least one side of the negative current collector portion along a first direction, the negative electrode film layer includes two ends opposite to each other along the first direction, a first region includes one end of the two ends facing the negative electrode tab, the ratio of the size of the first region along the first direction to the size of the negative electrode film layer along the first direction is 0.05 to 0.20, and the negative active material in the first region includes artificial graphite and natural graphite. The first direction is perpendicular to the thickness direction. The present application can improve the cycle performance and use reliability of the battery cell.

Description

[0001] This application claims the priority of the PCT international application PCT / CN2024 / 109011, titled "Monomer, Battery Device and Electrical Device", filed on July 31, 2024, the entire content of which is incorporated herein by reference. Technical Field

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

[0003] Lithium-ion batteries have characteristics such as high capacity and long life, and thus are widely used in electronic devices, such as mobile phones, laptop computers, battery cars, electric vehicles, electric airplanes, electric ships and electric tools, etc. With the development of the application fields of lithium-ion batteries, higher requirements are put forward for the performance of lithium-ion batteries, such as cycle performance and use reliability. Summary of the Invention

[0004] This application provides a battery monomer, a battery device and an electrical device, which can improve the cycle performance and use reliability of the battery monomer.

[0005] In a first aspect, this application proposes a battery monomer, which includes an electrode assembly. The electrode assembly includes a positive electrode tab and a negative electrode tab. The positive electrode tab includes a positive current collector and a positive electrode film layer. The positive electrode film layer is disposed on at least one side of the positive current collector along the thickness direction of the positive current collector. The positive electrode film layer includes a positive active material, and the positive active material includes a lithium-containing phosphate with an olivine structure; the negative electrode tab includes a negative electrode tab ear, a negative current collector and a negative electrode film layer. The negative electrode film layer is disposed on at least one side of the negative current collector along the thickness direction. The negative electrode film layer contains a negative active material. The negative electrode tab ear is connected to at least one side of the negative current collector along a first direction. The negative electrode film layer includes two ends opposite to each other along the first direction. A first region includes one of the two ends facing the negative electrode tab ear. The ratio of the size of the first region along the first direction to the size of the negative electrode film layer along the first direction is 0.05 to 0.20. The negative active material in the first region includes artificial graphite and natural graphite, wherein the first direction is perpendicular to the thickness direction.

[0006] Thus, after the battery monomer in the embodiment of this application is cyclically charged and discharged, the lithium deposition area is small, or even no lithium deposition occurs, which significantly improves the use reliability of the battery monomer and can also improve the cycle performance of the battery monomer.

[0007] In some embodiments, the mass content of natural graphite relative to the mass of the negative active material in the first region is 5% to 45%, and can be optionally 20% to 45%, which can further improve the use reliability and cycle performance of the battery monomer.

[0008] In some embodiments, the mass content of artificial graphite relative to the mass of the negative electrode active material in the first region is 55% to 95%, which can further improve the service reliability and cycling performance of the battery cell.

[0009] In some embodiments, the first region includes a first sub-layer and a second sub-layer. The first sub-layer is disposed on at least one side of the negative electrode current collector portion, and the second sub-layer is disposed on the side of the first sub-layer away from the negative electrode current collector portion. The first sub-layer includes artificial graphite and natural graphite, and the second sub-layer includes artificial graphite, which is beneficial to improving the fast charging ability.

[0010] In some embodiments, the mass content of artificial graphite in the second sub-layer relative to the mass of the negative electrode active material in the first region is 30% to 70%, which can further improve the service reliability and cycling performance of the battery cell.

[0011] In some embodiments, when the battery cell is in a 100% charged state, the tap density of the first sub-layer is greater than or equal to the tap density of the second sub-layer. In the embodiments of the present application, the tap density of the first sub-layer is relatively large, and the tap density of the second sub-layer is relatively small, which can improve the tortuosity of the first region, thereby improving the concentration polarization phenomenon during the charging process, especially the fast charging process, and reducing the risk of lithium deposition in the first region.

[0012] In some embodiments, when the battery cell is in a 100% charged state, the tap density of the first sub-layer is 1.25 g / cm 3 to 1.65 g / cm 3 .

[0013] In some embodiments, when the battery cell is in a 100% charged state, the tap density of the second sub-layer is 1.1 g / cm 3 to 1.5 g / cm 3 .

[0014] In some embodiments, the first sub-layer includes a lithium-containing binder, and the mass content of the lithium-containing binder relative to the mass of the first sub-layer is 0.1% to 3%. The lithium in the lithium-containing binder can form a delocalized structure with the graphite material, which is beneficial to improving the kinetic performance, especially beneficial to improving the kinetic performance at low temperature and room temperature.

[0015] In some embodiments, the second sub-layer includes a lithium-containing binder, and the mass content of the lithium-containing binder relative to the mass of the second sub-layer is 0.1% to 3%. The lithium in the lithium-containing binder can form a delocalized structure with the graphite material, which is beneficial to improving the kinetic performance, especially beneficial to improving the kinetic performance at low temperature and room temperature.

[0016] In some embodiments, the mass content of lithium element in the lithium-containing binder is 4% to 10%.

[0017] In some embodiments, the lithium-containing binder includes a lithium acrylate-acrylonitrile-acrylamide-2-hydroxyethyl acrylate copolymer, which is derived from a lithium acrylate monomer, an acrylonitrile monomer, an acrylamide monomer, and a 2-hydroxyethyl acrylate monomer. The molar percentages of the lithium acrylate monomer, the acrylonitrile monomer, the acrylamide monomer, and the 2-hydroxyethyl acrylate monomer are 30% to 50%: 15% to 45%: 5% to 20%: 20% to 35%.

[0018] In some embodiments, the volume average particle size Dv50 of the artificial graphite in the first region is 7 μm to 15 μm.

[0019] In some embodiments, the volume average particle size Dv50 of the natural graphite in the first region is 7 μm to 15 μm.

[0020] In some embodiments, the specific surface area of the natural graphite in the first region is greater than that of the artificial graphite in the first region, which is beneficial to improving the fast charging performance.

[0021] In some embodiments, the specific surface area of the natural graphite in the first region is 1.5 m 2 / g to 4.5 m 2 / g.

[0022] In some embodiments, the specific surface area of the artificial graphite in the first region is 0.7 m 2 / g to 3.0 m 2 / g.

[0023] In some embodiments, the ratio of the size of the first region in the first direction to the size of the negative electrode film layer in the first direction is 0.05 to 0.20, and can be optionally 0.10 to 0.20. When the proportion of the first region is within the above range, the risk of lithium plating is small, and the cycle performance and service reliability of the battery cell can be further improved.

[0024] In some embodiments, the electrode assembly has a laminated structure, and the positive electrode sheet and the negative electrode sheet are laminated in the thickness direction.

[0025] In some embodiments, the electrode assembly has a laminated structure, the negative electrode tab is connected to both sides of the negative current collector in the first direction, and the first region includes two ends.

[0026] In some embodiments, the electrode assembly has a laminated structure, the negative electrode tab is connected to one side of the negative current collector in the first direction, and the first region is one of the two ends facing the negative electrode tab.

[0027] In some embodiments, the electrode assembly has a wound structure, and the positive electrode sheet and the negative electrode sheet are wound in one direction.

[0028] In some embodiments, the negative electrode tab is connected to one side of the negative current collector along the first direction, and the first region includes two ends.

[0029] In some embodiments, after the battery cell undergoes 500 cycles of charge and discharge, based on the surface area of the negative electrode film layer, the lithium deposition area of the negative electrode film layer is 0 to 13.5%, optionally 0 to 6%.

[0030] In some embodiments, the positive electrode sheet further includes an insulating layer, the insulating layer is disposed on the positive current collector and connected to the positive electrode film layer, the insulating layer is disposed opposite to the first region in the thickness direction, and the insulating layer can further reduce the risk of lithium deposition.

[0031] In some embodiments, the negative electrode film layer further includes a second region, the second region and the first region are continuously arranged, the second region 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 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 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 each independently include graphite particles, and the volume average particle size Dv50 of the graphite particles in the first negative electrode film layer is greater than or equal to the volume average particle size Dv50 of the graphite particles in the second negative electrode film layer. The graphite particles include artificial graphite and a carbon coating layer, the artificial graphite includes secondary particles, and the carbon coating layer coats the surface of the artificial graphite.

[0032] Thus, there is a difference in the particle sizes of the first negative electrode film layer and the second negative electrode film layer in the embodiments of the present application, which can improve the fast charging performance of the battery cell. Specifically, during fast charging, the overpotential of the second negative electrode film layer is usually high, and the bottleneck of fast charging mainly lies in the second negative electrode film layer. In the embodiments of the present application, the particle size of the second negative electrode film layer is relatively small, which can shorten the solid-phase transmission path of lithium ions, improve the fast charging performance, and improve the lithium deposition problem on the surface layer of the negative electrode sheet.

[0033] In some embodiments, the graphitization degree of the graphite particles is 92.0% to 94.5%. When the graphitization degree of the graphite particles is within the above range, the conductive performance of the graphite particles is relatively excellent, which can reduce the heat generation of the negative electrode sheet, reduce the heat generation of the battery cell, and improve the fast charging performance of the battery cell.

[0034] 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 amount of the battery cell can be reduced.

[0035] In some embodiments, the powder compaction density of the graphite particles under 20000N is 1.5g / cm3 to 1.85 g / cm 3 When the powder compaction density of the graphite particles is within the above range under 20,000 N, the energy density of the battery cell can be improved. Moreover, since the negative active materials in the negative electrode film layer can be packed more closely, the contact resistance between particles is small, which can further reduce the resistance of the electrode sheet, thereby reducing heat generation.

[0036] In some embodiments, when the battery cell is in a 100% charged state, the compaction density of the first negative electrode film layer is 1.15 g / cm 3 to 1.36 g / cm 3 .

[0037] In some embodiments, when the battery cell is in a 100% charged state, the compaction density of the second negative electrode film layer is 1.15 g / cm 3 to 1.36 g / cm 3 .

[0038] In some embodiments, 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. When the volume average particle diameter Dv50 of the negative active materials in the first negative electrode film layer is within the above range, the fast charging performance can be improved.

[0039] In some embodiments, 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. When the volume average particle diameter Dv50 of the negative active materials 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.

[0040] 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.

[0041] Therefore, in the embodiments of the present application, the mass content of the second lithium-containing binder in the second negative electrode film layer is relatively high, and the number of 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.

[0042] 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 3%. When the mass content of the first lithium-containing binder is within the above range, the deintercalation rate of lithium ions can be improved, and the fast charging performance of the battery cell can be improved.

[0043] 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 3%. When the mass content of lithium element in the second lithium-containing binder is within the above range, the intercalation and deintercalation rate of lithium ions is improved, and the fast charging performance of the battery cell is improved.

[0044] In some embodiments, the mass content of lithium element in the first lithium-containing binder is 3% to 10%. When the mass content of lithium element is within the above range, the number of freely moving lithium ions in the negative electrode film layer can be relatively large, the distance for lithium ions to diffuse to the surface of the negative electrode film layer can be further shortened, the intercalation and deintercalation rate of lithium ions is improved, and the fast charging performance of the battery cell is improved.

[0045] In some embodiments, the mass content of lithium element in the second lithium-containing binder is 3% to 10%. When the mass content of lithium element is within the above range, the number of freely moving lithium ions in the negative electrode film layer can be relatively large, the distance for lithium ions to diffuse to the surface of the negative electrode film layer can be further shortened, the intercalation and deintercalation rate of lithium ions is improved, and the fast charging performance of the battery cell is improved.

[0046] In some embodiments, the first lithium-containing binder includes a lithium acrylate-acrylonitrile-acrylamide-2-hydroxyethyl acrylate copolymer. 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 percentages of the lithium acrylate monomer, the acrylonitrile monomer, the acrylamide monomer, and the 2-hydroxyethyl acrylate monomer are 30% to 50%: 15% to 45%: 5% to 20%: 20% to 35%. Thus, the lithium-containing binder of the above materials 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.

[0047] In some embodiments, the second lithium-containing binder includes a lithium acrylate-acrylonitrile-acrylamide-2-hydroxyethyl acrylate copolymer. 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 percentages of the lithium acrylate monomer, the acrylonitrile monomer, the acrylamide monomer, and the 2-hydroxyethyl acrylate monomer are 30% to 50%: 15% to 45%: 5% to 20%: 20% to 35%.

[0048] Thus, the lithium-containing binder of the above materials 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.

[0049] 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 . When the single-sided coating weight of the negative electrode film layer is within the above range, the heat generation per unit area of the negative electrode plate will not be too large, and it can take into account the improvement of the energy density of the battery cell.

[0050] In some embodiments, the negative electrode plate further includes a negative electrode conductive layer, and the negative electrode conductive layer is located between the negative electrode film layer and the negative electrode current collector. The negative electrode conductive layer can further improve the conductivity of the negative electrode plate and reduce the heat generation of the negative electrode plate, thereby reducing the heat generation of the battery cell.

[0051] In some embodiments, the thickness of the negative electrode conductive layer is 0.1 μm to 2 μm. 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.

[0052] In some embodiments, 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. 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 plate and reducing the heat generation of the battery cell.

[0053] In some embodiments, 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. 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 plate

[0054] In some embodiments, when the battery cell is in a 100% charged state, the tap density of the positive electrode film layer is 2.50 g / cm 3 to 2.80 g / cm 3 , when the tap density of the positive electrode film layer is within the above range, it is beneficial to improve the energy density of the battery cell, and since the positive electrode active materials in the positive electrode film layer are stacked relatively tightly and the contact resistance between particles is small, the resistance of the electrode plate can be further reduced, thereby reducing heat generation.

[0055] 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 . 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 plate will not be too large, and it can take into account the improvement of the energy density of the battery cell.

[0056] In some embodiments, when the battery cell is in a 100% state of charge, the tap density of the positive electrode film layer is 2.55 g / cm 3 to 2.70 g / cm 3 . When the tap density of the positive electrode film layer is within the above range, it is beneficial to improve the energy density of the battery cell. Moreover, since the positive electrode active materials in the positive electrode film layer are stacked relatively tightly and the contact resistance between particles is small, the resistance of the electrode sheet can be further reduced, thereby reducing heat generation.

[0057] In some embodiments, 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 . When the single-sided coating weight of the positive electrode film layer is within the above range, the heat generation per unit area of the positive electrode sheet will not be too large, and the energy density of the battery cell can be improved while taking it into account.

[0058] In some embodiments, the tap density of the positive electrode active material under 30000 N is 2.46 g / cm 3 to 2.8 g / cm 3 . When the tap 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 tightly and the contact resistance between particles is small, the resistance of the electrode sheet can be further reduced, thereby reducing heat generation.

[0059] In some embodiments, the lithium-containing phosphate in the 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 the 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 of the battery cell.

[0060] In some embodiments, the phosphate particles include a general formula of Li x1 A y1 Me a M b P 1-c X c Y zcompounds, 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 cyclic stability of the phosphate particles is relatively excellent, which is beneficial to improving the cyclic performance of the battery single cell.

[0061] In some embodiments, the coating layer comprises 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, 0 < y2 < 4. Coating the fast ion conductor on the surface of the phosphate particles can significantly improve the transport rate of lithium ions during multiple deintercalation / insertion of lithium at the positive electrode, improve the ionic conductivity of the positive electrode active material, and further improve the specific capacity, and further improve the energy density of the corresponding battery single cell.

[0062] In some embodiments, the graphitization degree of the positive electrode active material is from 0.15 to 0.32, and can be selected from 0.19 to 0.26. 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 single cell.

[0063] In some embodiments, the mass content of carbon element in the lithium-containing phosphate with olivine structure is 1% to 2%, and the specific surface area of the lithium-containing phosphate with olivine structure is 5m 2 / g to 18m 2 / g, and can be selected from 7.5m 2 / g to 14m 2 / g.

[0064] Thus, in the embodiments of the present application, the carbon element with the above mass content cooperates with the material with the above specific surface area, which is more beneficial to the effective contact between the electrolyte and the lithium-containing phosphate with olivine structure, and is beneficial to the transport of lithium ions at the phase interface.

[0065] In some embodiments, the lithium-containing phosphate in the olivine structure is granular, and its volume distribution particle size satisfies: 1 µm ≤ Dv50 ≤ 2 µm, 0.4 µm ≤ Dv10 ≤ 0.7 µm. The particle size of the lithium-containing phosphate in the olivine structure 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.

[0066] 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 deintercalation / insertion path of lithium ions in the positive electrode active material is short, and the heat generation is less.

[0067] In some embodiments, the positive electrode film layer further includes one or more of ternary materials, lithium phosphate, lithium hydrogen phosphate, lithium sulfate, lithium sulfite, lithium molybdate, lithium oxalate, lithium titanate, lithium tetraborate, lithium metasilicate, lithium manganate, lithium tartrate, lithium citrate, lithium nickelate, and lithium ferrate. The above materials can supplement lithium ions to the positive electrode film layer, make up for the irreversible lithium ion loss in the system, and improve the capacity, thereby improving the energy density of the battery cell.

[0068] In some embodiments, the thickness of the positive electrode current collector is 10 µm to 15 µm. When the thickness of the positive electrode current collector is within the above range, the current-carrying capacity of the positive electrode current collector is relatively excellent, and the battery cell can have a high energy density.

[0069] 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.

[0070] In some embodiments, the thickness of the positive electrode conductive layer is 0.1 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 plate, reduce the heat generation of the positive electrode plate, and thus reduce the heat generation of the battery cell, and can also take into account improving the energy density of the battery cell.

[0071] 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 plate 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 plate.

[0072] 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.

[0073] 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.

[0074] In some embodiments, the charging time of the battery cell from 10% state of charge to 80% state of charge is 5 min to 10.5 min. The charging speed of the battery cell is relatively fast, which is more conducive to improving the fast charging ability.

[0075] In a second aspect, the present application provides a battery device, which includes a plurality of battery cells according to any one of the embodiments in the first aspect of the present application.

[0076] In some embodiments, the charging time of the battery device from 10% state of charge to 80% state of charge is 5 min to 10.5 min. The charging speed of the battery device is relatively fast, which is more conducive to improving the fast charging ability.

[0077] 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. Description of the Drawings

[0078] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings required for the embodiments of the present application will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For those of ordinary skill in the art, other drawings can be obtained according to the drawings without creative efforts.

[0079] Figure 1 It is a schematic structural diagram of a battery cell provided in some embodiments of the present application.

[0080] Figure 2 It is an exploded view of a battery cell provided in some embodiments of the present application.

[0081] Figure 3 It is a schematic structural diagram of an electrode assembly of a battery cell provided in some embodiments of the present application.

[0082] Figure 4 It is a schematic structural diagram of a negative electrode sheet of an electrode assembly provided in some embodiments of the present application.

[0083] Figure 5Schematic diagram of the negative electrode tab of the electrode assembly provided for some other embodiments of the present application;

[0084] Figure 6 Schematic diagram of the negative electrode tab of the electrode assembly provided for some other embodiments of the present application;

[0085] Figure 7 Schematic diagram of the positive electrode tab of the electrode assembly provided for some embodiments of the present application;

[0086] Figure 8 Schematic diagram of the electrode assembly of the battery cell provided for some other embodiments of the present application;

[0087] Figure 9 Schematic diagram of the unfolded structure of the negative electrode tab of the electrode assembly provided for some embodiments of the present application;

[0088] Figure 10 Schematic diagram of the battery module provided for some embodiments of the present application,

[0089] Figure 11 Schematic diagram of the battery pack provided for some embodiments of the present application;

[0090] Figure 12 Schematic diagram of the electrical device provided for some embodiments of the present application.

[0091] The drawings are not necessarily drawn to actual scale.

[0092] Explanation of the reference numerals is as follows:

[0093] X, thickness direction; Y, first direction; Z, second direction;

[0094] 1, electrical device; 2, battery pack; 3, controller; 4, motor; 5, housing; 5a, first housing part; 5b, second housing part; 5c, accommodation space; 6, battery module;

[0095] 7, battery cell;

[0096] 10, electrode assembly; 111, positive electrode tab; 112, negative electrode tab; 12, main body part;

[0097] 13, positive electrode tab; 131, positive current collector part; 132, positive electrode film layer; 133, insulating layer;

[0098] 14, negative electrode tab;

[0099] 140, first region; 1401, first sub-layer; 1402, second sub-layer;

[0100] 141, negative current collector part;

[0101] 142. Negative electrode film layer;

[0102] 145. First negative electrode film layer; 146. Second negative electrode film layer;

[0103] 147. Second region;

[0104] 15. Separator;

[0105] 20. Outer shell; 21. Housing; 22. End cap;

[0106] 31. Positive terminal; 32. Negative terminal. Detailed implementation manners

[0107] Hereinafter, embodiments of the battery cell, battery device, and electrical device of the present application will be specifically disclosed in detail with appropriate reference to the accompanying drawings. However, there may be cases where unnecessary detailed descriptions are omitted. For example, there are cases where detailed descriptions of well-known matters and repeated descriptions of actually identical structures are omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate the understanding of those skilled in the art. In addition, the accompanying drawings and the following description are provided for those skilled in the art to fully understand the present application and are not intended to limit the subject matter described in the claims.

[0108] The "range" disclosed in the present application is 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 boundary of a specific range. The range defined in this way can include the end values or not include the end values, and can be combined arbitrarily, that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60 to 120 and 80 to 110 are listed for a specific parameter, it is understood that ranges of 60 to 110 and 80 to 120 are also 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 the present 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" have been fully listed herein, and "0 to 5" is only an abbreviated representation of these numerical combinations. In addition, when it is stated that a certain parameter is an integer ≥2, it is equivalent to disclosing that the parameter is, for example, the integer 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0109] If there is no special description, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0110] Unless otherwise specified, all technical features and optional technical features of this application can be combined with each other to form new technical solutions.

[0111] Unless otherwise specified, 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.

[0112] During the charging process of a battery cell, lithium ions in the positive electrode plate escape and migrate to the negative electrode plate to gain electrons and form lithium metal; during the formation of lithium metal, some lithium ions may not be embedded in the negative electrode plate in time, resulting in the precipitation of lithium dendrites on the surface of the negative electrode plate. The lithium dendrites may pierce the separator, causing a short circuit between the positive and negative electrodes and deteriorating the reliability of the battery cell; moreover, since the lithium dendrites occupy the gap between the electrode plates, the swelling force of the battery cell increases and the cycle life deteriorates. As the charging rate of the battery cell increases, the risk of lithium precipitation in the battery cell increases, which will further deteriorate the reliability of the battery cell and shorten the cycle life of the battery cell.

[0113] In view of this, the embodiments of this application reasonably design the system of the battery cell, so that the battery cell basically does not precipitate lithium or has a small lithium precipitation area after cycling, significantly improving the reliability of the battery cell and also improving the cycle life of the battery cell.

[0114] Battery cell

[0115] In a first aspect, the embodiments of this application provide a battery cell.

[0116] As Figures 1 to 4As shown, the battery cell 7 includes an electrode assembly 10. The electrode assembly 10 includes a positive electrode tab 13 and a negative electrode tab 14. The positive electrode tab 13 includes a positive current collector portion 131 and a positive electrode film layer 132. The positive electrode film layer 132 is disposed on at least one side of the positive current collector portion 131 along the thickness direction X of the positive current collector portion 131. The positive electrode film layer 132 includes a positive electrode active material, and the positive electrode active material includes a lithium-containing phosphate having an olivine structure. The negative electrode tab 14 includes a negative electrode tab 112, a negative current collector portion 141, and a negative electrode film layer 142. The negative electrode film layer 142 is disposed on at least one side of the negative current collector portion 141 along the thickness direction and contains a negative electrode active material. The negative electrode film layer 142 includes a first region 140. The negative electrode film layer 142 includes two ends opposite to each other in a first direction Y. The first region 140 includes one end of the two ends facing the negative electrode tab 112. The ratio of the dimension of the first region 140 in the first direction Y to the dimension of the negative electrode film layer 142 in the first direction Y is 0.05 to 0.20. The negative electrode active material in the first region 140 includes artificial graphite and natural graphite, wherein the first direction Y is perpendicular to the thickness direction X. Optionally, the electrode assembly further includes a separator 15, and the separator 15 is located between the positive electrode tab 13 and the negative electrode tab 14.

[0117] Optionally, the negative electrode film layer 142 includes a first region 140 and a second region 147. The first region 140 and the second region 147 are continuously arranged. It can be understood that the other regions of the negative electrode film layer 142 except the first region 140 are the second region.

[0118] In the embodiment of the present application, the end of the negative electrode film layer 142 refers to the end of the negative electrode film layer 142 in the first direction Y; when the first direction Y is parallel to the length direction of the negative electrode film layer 142, the end of the negative electrode film layer 142 refers to the end of the negative electrode film layer 142 along the length direction. When the first direction Y is parallel to the width direction of the negative electrode film layer 142, the end of the negative electrode film layer 142 refers to the end of the negative electrode film layer 142 along the width direction.

[0119] Since the current density of the part close to the negative electrode tab 112 is relatively high and the risk of lithium deposition is relatively high, the embodiment of the present application reduces the risk of lithium deposition in the first region 140 through a specific design of the first region 140. Specifically, the first region 140 includes artificial graphite and natural graphite. The artificial graphite and natural graphite are used in combination, which is beneficial to increasing the diffusion channels of lithium ions, improving the charging capacity of the first region 140, and reducing the risk of lithium deposition.

[0120] In some embodiments, the mass content of natural graphite relative to the mass of the negative electrode active material in the first region 140 is 5% to 45%, optionally 20% to 45%, such as 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45% or a range composed of any two of the above values. When the mass content of natural graphite is within the above range, it is more conducive to improving the fast charging ability and further reducing the risk of lithium plating.

[0121] In some embodiments, the mass content of artificial graphite relative to the mass of the negative electrode active material in the first region is 55% to 95%, such as 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95% or a range composed of any two of the above values.

[0122] In some embodiments, the first region 140 in the negative electrode film layer 142 can be a single-layer film structure or a double-layer film structure, optionally a double-layer film structure. For example, the first region 140 includes a first sub-layer 1401 and a second sub-layer 1402. The first sub-layer 1401 is disposed on at least one side of the negative electrode current collector 141, and the second sub-layer 1402 is disposed on the side of the first sub-layer 1401 away from the negative electrode current collector 141. The double-layer setting is beneficial to reducing the risk of film cracking, improving the stability of the film structure, and further improving the fast charging ability.

[0123] In some embodiments, the second region 147 in the negative electrode film layer 142 can be a single-layer film structure or a double-layer film structure, optionally a double-layer film structure. For example, the second region 147 includes a first negative electrode film layer 145 and a second negative electrode film layer 146. The first negative electrode film layer 145 is disposed on at least one side of the negative electrode current collector १4१, and the second negative electrode film layer 146 is disposed on the side of the first negative electrode film layer 145 away from the negative electrode current collector 141. The double-layer setting is beneficial to reducing the risk of film cracking, improving the stability of the film structure, and further improving the fast charging ability.

[0124] In some embodiments, the negative electrode active material of the first sub-layer 1401 includes natural graphite and artificial graphite. The specific surface area of natural graphite is relatively large, which is beneficial to increasing the diffusion channels of lithium ions, improving the charging ability of the first region 140, and reducing the risk of lithium plating.

[0125] In some embodiments, the negative electrode active material of the second sub-layer 1402 includes artificial graphite, which is beneficial to improving the fast charging ability.

[0126] In some embodiments, the mass content of artificial graphite in the second sub-layer 1402 relative to the mass of the negative electrode active material in the first region 140 is 30% to 70%, such as 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70% or a range composed of any two of the above values.

[0127] In some embodiments, when the battery cell 7 is in a 100% charged state, the tap density of the first sub-layer 1401 is greater than or equal to the tap density of the second sub-layer 1402.

[0128] When the first region 140 adopts a relatively thick coating, serious concentration polarization phenomenon is likely to occur. In the embodiments of the present application, the tap density of the first sub-layer 1401 is relatively large, and the tap density of the second sub-layer 1402 is relatively small, which can improve the tortuosity of the first region 140, thereby improving the concentration polarization phenomenon during the charging process, especially during the fast charging process, and reducing the risk of lithium deposition in the first region 140.

[0129] Optionally, when the battery cell 7 is in a 100% charged state, the tap density of the first sub-layer 1401 is 1.25 g / cm 3 to 1.65 g / cm 3 , for example, 1.25 g / cm 3 , 1.3 g / cm 3 , 1.35 g / cm 3 , 1.4 g / cm 3 , 1.45 g / cm 3 , 1.5 g / cm 3 , 1.55 g / cm 3 , 1.6 g / cm 3 , 1.65 g / cm 3 or a range composed of any two of the above values.

[0130] Optionally, when the battery cell 7 is in a 100% charged state, the tap density of the second sub-layer 1402 is 1.1 g / cm 3 to 1.5 g / cm 3 , for example, 1.1 g / cm 3 , 1.15 g / cm 3 , 1.2 g / cm 3 , 1.25 g / cm 3 , 1.3 g / cm 3 , 1.35 g / cm 3 , 1.4 g / cm 3 , 1.45 g / cm 3 , 1.5 g / cm 3 or a range composed of any two of the above values.

[0131] In some embodiments, the first region 140 includes a lithium-containing binder, and the mass content of lithium element in the lithium-containing binder is 4% to 10%, such as 4%, 4.5%, 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 8%, 8.5%, 9%, 9.5%, 10% or a range composed of any two of the above values.

[0132] The lithium in the lithium-containing binder can form a delocalized structure with the graphite material, which is beneficial to improving the kinetic performance, especially beneficial to improving the kinetic performance at low temperature and normal temperature, and can improve the fast charging performance of the battery cell 7 and reduce the risk of lithium plating.

[0133] Exemplarily, the lithium-containing binder includes a lithium acrylate-acrylonitrile-acrylamide-2-hydroxyethyl acrylate copolymer, and the lithium acrylate-acrylonitrile-acrylamide-2-hydroxyethyl acrylate copolymer is derived from a lithium acrylate monomer, an acrylonitrile monomer, an acrylamide monomer, and a 2-hydroxyethyl acrylate monomer. The molar percentages of the lithium acrylate monomer, the acrylonitrile monomer, the acrylamide monomer, and the 2-hydroxyethyl acrylate monomer are 30% to 50%: 15% to 45%: 5% to 20%: 20% to 35%.

[0134] In some embodiments, the first sub-layer 1401 includes a lithium-containing binder, and the mass content of the lithium-containing binder relative to the mass of the first sub-layer is 0.1% to 3%, such as 0.1%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3% or a range composed of any two of the above values.

[0135] In some embodiments, the second sub-layer 1402 includes a lithium-containing binder, and the mass content of the lithium-containing binder relative to the mass of the second sub-layer is 0.1% to 3%, such as 0.1%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3% or a range composed of any two of the above values.

[0136] In some embodiments, the volume average particle size Dv50 of the artificial graphite in the first region 140 is 7 μm to 15 μm, such as 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm or a range composed of any two of the above values.

[0137] Optionally, the volume average particle size Dv50 of the artificial graphite in the first sub-layer 1401 is 7 μm to 15 μm, such as 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm or a range composed of any two of the above values.

[0138] Optionally, the volume average particle size Dv50 of the artificial graphite in the second sub-layer 1402 is 7 μm to 15 μm, such as 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, or a range composed of any two of the above values.

[0139] In some embodiments, the volume average particle size Dv50 of the natural graphite in the first region 140 is 7 μm to 15 μm, such as 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, or a range composed of any two of the above values. When the volume average particle size Dv50 of the artificial graphite is within the above range, the fast charging ability can be improved, and the risk of lithium plating can be reduced.

[0140] Optionally, the volume average particle size Dv50 of the negative electrode active material in the second sub-layer 1402 is less than or equal to the volume average particle size Dv50 of the negative electrode active material in the first sub-layer 1401.

[0141] During the charging process of the battery cell 7, the chemical reaction region of the negative electrode active material gradually extends from near the separator to near the negative electrode current collector; the volume average particle size Dv50 of the negative electrode active material in the second sub-layer 1402 is relatively small, and the solid-phase transport ability is strong, which can improve the fast charging ability and can also increase the anode potential of the second sub-layer 1402 and reduce the risk of lithium plating in this region.

[0142] In some embodiments, the specific surface area of the natural graphite in the first region 140 is greater than the specific surface area of the artificial graphite in the first region 140, which is beneficial to improving the fast charging performance.

[0143] In some embodiments, the specific surface area of the natural graphite in the first sub-layer 1401 is greater than the specific surface area of the artificial graphite in the first sub-layer 1401, which is beneficial to improving the fast charging performance.

[0144] Optionally, the specific surface area of the natural graphite in the first sub-layer 1401 is 1.5 m 2 / g to 4.5 m 2 / g, such as 1.5 m 2 / g, 1.6 m 2 / g, 1.7 m 2 / g, 1.8 m 2 / g, 1.9 m 2 / g, 2.0 m 2 / g, 2.1 m 2 / g, 2.2 m 2 / g, 2.3 m 2 / g, 2.4 m 2 / g, 2.5 m 2 / g, 2.6 m2 / g, 3.0 m 2 / g, 3.5 m 2 / g, 4.0 m 2 / g, 4.5 m 2 / g or a range composed of any two of the above values.

[0145] Optionally, the specific surface area of the artificial graphite in the first sub-layer 1401 is 0.7 m 2 / g to 3.0 m 2 / g; for example, 0.7 m 2 / g, 0.8 m 2 / g, 0.9 m 2 / g, 1.0 m 2 / g, 1.1 m 2 / g, 1.2 m 2 / g, 1.5 m 2 / g, 1.8 m 2 / g, 2.0 m 2 / g, 2.5 m 2 / g, 3.0 m 2 / g or a range composed of any two of the above values.

[0146] Optionally, the specific surface area of the artificial graphite in the second sub-layer 1402 is 0.7 m 2 / g to 3.0 m 2 / g; for example, 0.7 m 2 / g, 0.8 m 2 / g, 0.9 m 2 / g, 1.0 m 2 / g, 1.1 m 2 [[ID=�5]] / g, 1.2 m 2 / g, 1.5 m 2 / g, 1.8 m 2 / g, 2.0 m 2 / g, 2.5 m 2 / g, 3.0 m 2 / g or a range composed of any two of the above values.

[0147] In the embodiments of the present application, other parameters not mentioned in the first region can be the same as those in the second region.

[0148] By specifically designing the first region in the embodiments of the present application, the lithium deposition area can be effectively reduced. In some embodiments, after the battery cell 7 is cycled 500 times, based on the surface area of the negative electrode film layer, the lithium deposition area of the negative electrode film layer is 0 to 13.5%, such as 0, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 8%, 8.5%, 9%, 9.5%, 10%, 10.5%, 11%, 11.5%, 12%, 12.5%, 13%, 13.5% or the range composed of any two of the above values.

[0149] The lithium deposition area is less than or equal to 13.5%. After the battery cell 7 is cycled 500 times, the lithium deposition area is small, or even no lithium deposition occurs, which significantly improves the usage reliability of the battery cell 7 and can also improve the cycle life of the battery cell 7.

[0150] The upper charge cut-off voltage and the lower discharge cut-off voltage of the battery cell vary depending on the different cathode active materials. For example, when the phosphate material includes lithium iron phosphate, the upper charge cut-off voltage can be 3.65V and the lower discharge cut-off voltage can be 2.0V. Another example is that when the phosphate material includes lithium manganese iron phosphate, the upper charge cut-off voltage can be 4.3V and the lower discharge cut-off voltage can be 2.0V. Next, taking the upper charge cut-off voltage of 3.65V and the lower discharge cut-off voltage of 2.0V as an example, the charging and discharging of the battery cell will be described:

[0151] At room temperature, for example, at a temperature of 30°C in the external environment, the battery cell is charged, and the charging steps include the following steps:

[0152] Constant current charge at 5.0C from 0% SOC to 5% SOC;

[0153] Constant current charge at 5.0C from 5% SOC to 10% SOC;

[0154] Constant current charge at 5.0C from 10% SOC to 15% SOC;

[0155] Constant current charge at 5.0C from 15% SOC to 20% SOC;

[0156] Constant current charge at 5.0C from 20% SOC to 25% SOC;

[0157] Constant current charge at 5.0C from 25% SOC to 30% SOC;

[0158] Constant current charge at 5.0C from 30% SOC to 35% SOC;

[0159] Constant current charge at 5.0C from 35% SOC to 40% SOC;

[0160] Charge from 40% SOC to 45% SOC at a constant current of 4.6C;

[0161] Charge from 45% SOC to 50% SOC at a constant current of 4.3C;

[0162] Charge from 50% SOC to 55% SOC at a constant current of 4.0C;

[0163] Charge from 55% SOC to 60% SOC at a constant current of 3.7C;

[0164] Charge from 60% SOC to 65% SOC at a constant current of 3.4C;

[0165] Charge from 65% SOC to 70% SOC at a constant current of 3.1C;

[0166] Charge from 70% SOC to 75% SOC at a constant current of 2.9C;

[0167] Charge from 75% SOC to 80% SOC at a constant current of 2.7C;

[0168] Charge from 80% SOC to 85% SOC at a constant current of 1.8C;

[0169] Charge from 85% SOC to 90% SOC at a constant current of 1.3C;

[0170] Charge from 90% SOC to 95% SOC at a constant current of 0.7C;

[0171] Charge from 95% SOC to 98% SOC at a constant current of 0.33C;

[0172] Charge from 98% SOC to 100% SOC at a constant current of 0.1C.

[0173] The cut-off voltage of the last charging step in the above charging steps is 3.65V.

[0174] The discharging strategy is as follows: discharge at a constant current of 0.33C to the cut-off voltage, such as 2.0V.

[0175] According to the above cycling strategy, perform 500 cycles on the battery cell 7; then charge the battery cell 7 to 100% state of charge SOC according to the above charging steps, disassemble the negative electrode plate 14. The golden yellow area in the negative electrode plate 14 is the normal area, and the grayish white area is the lithium deposition area. After taking pictures with a high-power microscope, analyze different areas, use the gray level difference to count the lithium deposition area, obtain the total area of the lithium deposition area, and the ratio of the total area of the lithium deposition area to the surface area of the negative electrode film layer is the area ratio of the lithium deposition area in the negative electrode film layer, that is, the lithium deposition area.

[0176] The electrode assembly 10 can be a stacked electrode assembly or a wound electrode assembly. The difference in the structure of the electrode assembly 10 results in differences in the lithium plating process, which will be described in detail below.

[0177] [Stacked electrode assembly]

[0178] As Figures 3 to 6 shown, when the electrode assembly 10 is of a stacked structure, the positive electrode tab 13 and the negative electrode tab 14 are stacked in the thickness direction. Optionally, the lithium plating area of the electrode assembly 10 of the stacked structure is less than or equal to 13.5%. The thickness direction of the electrode assembly 10, the thickness direction of the positive electrode tab 13, and the thickness direction of the negative electrode tab 14 are parallel. The thickness direction of the positive electrode tab 13 is parallel to the thickness direction of the positive current collector 131. The length direction of the electrode assembly 10, the length direction of the positive electrode tab 13, and the length direction of the negative electrode tab 14 are parallel. The width direction of the electrode assembly 10, the width direction of the positive electrode, and the width direction of the negative electrode tab 14 are parallel. Figures 3 to 6 The X direction shown in

[0179] In some embodiments, the negative electrode tab 112 is connected to at least one side of the negative current collector 141 along the first direction Y.

[0180] The negative electrode tab 112 is connected to one side of the negative current collector 141 along the first direction Y, or the negative electrode tab 112 is connected to both sides of the negative current collector 141 along the first direction Y. The first direction Y can be parallel to the length direction of the electrode assembly 10, or the first direction Y is parallel to the width direction of the electrode assembly 10. Optionally, the first direction Y is parallel to the length direction of the electrode assembly 10. For example Figures 3 to 6 shown, the Y direction represents the length direction of the electrode assembly 10, and the Z direction represents the width direction of the electrode assembly 10. For example, the negative electrode tab 112 is connected to both sides of the negative current collector 141 along the length direction. Another example is that the negative electrode tab 112 is connected to one side of the negative current collector 141 along the width direction.

[0181] In some embodiments, the first region 140 includes one of the two ends facing the negative electrode tab 112.

[0182] The negative electrode film layer 142 and the negative electrode current collector 141 are oppositely arranged along the thickness direction X. The negative electrode current collector 141 and the negative electrode tab 112 are connected along the first direction Y, and the current can conduct along the first direction Y. The current can converge from the negative electrode current collector 141 towards the negative electrode tab 112. The electrochemical polarization is the largest at the end of the negative electrode film layer 142 close to the negative electrode tab 112, and lithium deposition is likely to occur. However, the lithium deposition area in the first region 140 is less than or equal to 13.5%, and can be selected from 0 to 6%, such as 13.5%, 12%, 11%, 10%, 9%, 8%, 7%, 6%, 5%, 4%, 3%, 2.9%, 2.8%, 2.5%, 2.3%, 2.0%, 1.8%, 1.5%, 1.2%, 1%, 0.8%, 0.6%, 0.5%, 0.3%, 0.2%, 0.1%, 0 or the range composed of any two of the above values. When the lithium deposition area is 0, it means that no lithium deposition occurs on the negative electrode plate 14.

[0183] Optionally, the ratio of the dimension of the first region 140 along the first direction Y to the dimension of the negative electrode film layer 142 along the first direction Y is 0.05 to 0.20, such as 0.05, 0.06, 0.07, 0.08, 0.09, 0.10, 0.15, 0.18, 0.20 or the range composed of any two of the above values.

[0184] For example Figure 5 In, the negative electrode tab 112 is arranged on one side of the negative electrode current collector 141. The first region 140 is one of the two ends facing the negative electrode tab 112. L1 represents the dimension of the first region 140 along the first direction Y, L0 represents the dimension of the negative electrode film layer 142 along the first direction Y, and L1 / L0 is the ratio of the dimension of the first region 140 along the first direction Y to the dimension of the negative electrode film layer 142 along the first direction Y. The ratio is 0.05 to 0.20, can be selected from 0.05 to 0.15, and can be selected from 0.05 to 0.10.

[0185] Another example[[ID=l2]] Figure 6 In, the negative electrode tab 112 is arranged on both sides of the negative electrode current collector 141. The first region 140 includes two ends. 2 times L2 represents the dimension of each first region 140 along the first direction Y. 2L2 / L0 is the ratio of the dimension of the first region 140 along the first direction Y to the dimension of the negative electrode film layer 142 along the first direction Y. The ratio is 0.05 to 0.20, and can be selected from 0.10 to 0.20.

[0186] As Figure 7 shown, in some embodiments, the positive electrode plate 13 further includes an insulating layer 133. The insulating layer 133 is arranged on the positive electrode current collector 131 and connected to the positive electrode film layer 132. The insulating layer 133 is oppositely arranged with the first region 140 along the thickness direction.

[0187] The positive active material is basically not provided at the insulating layer 133, which is beneficial to increasing the size of the negative electrode film layer 142 exceeding the positive electrode film layer 132, and further reducing the risk of lithium plating on the negative electrode tab 14.

[0188] [Wound Electrode Assembly]

[0189] As Figures 8 to 10 shown, when the electrode assembly 10 is of a wound structure, the positive electrode tab 13 and the negative electrode tab 14 are wound in one direction to form a wound structure, which can be presented as a cylindrical structure or a flat structure, and preferably a flat structure. The flat structure includes a bent area and a straight area, and the thickness direction, length direction, and width direction of the flat structure are perpendicular to each other in pairs.

[0190] In the wound electrode assembly 10, the end of the negative electrode film layer 142 close to the negative electrode tab 112 may also undergo lithium plating due to current concentration and relatively high local current density. However, in the embodiments of the present application, the lithium plating area of the wound electrode assembly 10 is less than or equal to 13.5%, and can be optionally 0 to 6%.

[0191] In some embodiments, the negative electrode tab 14 further includes a negative electrode tab 112, and the negative electrode tab 112 is connected to at least one side of the negative current collector 141 along the first direction Y, and the first direction Y is perpendicular to the thickness direction of the negative electrode tab 14; the thickness direction of the negative electrode tab 14 is parallel to the thickness direction of the positive electrode tab 13. The first direction Y can be parallel to the length direction of the electrode assembly 10 or parallel to the width direction of the electrode assembly 10.

[0192] The negative electrode tab 112 is connected to one side of the negative current collector 141 along the first direction Y, or the negative electrode tab 112 is connected to both sides of the negative current collector 141 along the first direction Y.

[0193] In the case where the negative electrode tab 112 is connected to one side of the negative current collector 141 along the first direction Y, the first region 140 includes two ends.

[0194] In the case where the negative electrode tab 112 is connected to both sides of the negative current collector 141 along the first direction Y, the first region 140 includes two ends.

[0195] When the negative electrode tab 112 is connected to one side of the negative current collector 141 along the first direction Y, in the wound electrode assembly 10, the gap between the electrode sheets in the bent region is relatively large, and the transport path of the active ions in space is relatively long, resulting in the polarization in the bent region being prone to intensify and the risk of lithium deposition increasing. In particular, the risk of lithium deposition is relatively high in the part of the negative electrode film layer 142 in the bent region that faces away from the negative electrode tab 112. Generally speaking, after the electrode assembly 10 is assembled into the housing of the battery cell 7, the battery cell 7 is placed vertically in the box to be assembled into a battery pack, and the vertical direction is parallel to the first direction Y, that is, the negative electrode tab 112 is located above the first region 140 in the vertical direction. And the heat dissipation capacity of the bottom of the box is usually better than that of the top of the box, resulting in a temperature difference in the negative electrode sheet 14 in the vertical direction. One end of the two ends that faces away from the negative electrode tab 112 has a lower temperature, and the polarization is more likely to intensify and lithium deposition is more likely to occur during charging. And one end of the two ends that faces the negative electrode tab 112 is prone to lithium deposition due to the relatively large current density. However, in the embodiment of the present application, the first region 140 is designed in terms of materials and the like, so that the lithium deposition area is relatively small.

[0196] Optionally, the ratio of the size of the first region 140 along the first direction Y to the size of the negative electrode film layer 142 along the first direction Y is 0.05 to 0.20, such as 0.05, 0.06, 0.07, 0.08, 0.09, 0.10, 0.15, 0.20 or the range composed of any two of the above values. For example Figure 9 In, the negative electrode tab 112 is disposed on one side of the negative current collector 141, 2L3 represents the size of the first region 140 along the first direction Y, L0 represents the size of the negative electrode film layer 142 along the first direction Y, and 2L3 / L0 is the ratio of the size of the first region 140 along the first direction Y to the size of the negative electrode film layer 142 along the first direction Y, and the ratio is 0.05 to 0.20, and can be selected as 0.10 to 0.20.

[0197] [Negative electrode sheet]

[0198] 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 and including a negative active material. For example, the negative current collector has two surfaces opposite to each other in its own thickness direction, and the negative electrode film layer is provided on any one or both of the two opposite surfaces of the negative current collector.

[0199] Next, the relevant parameters such as the material and structure of the second region in the negative electrode film layer will be mainly described.

[0200] In some embodiments, when the battery cell is in a 100% charged state, the compaction density of the second region in the negative electrode film layer is 1.15 g / cm 3 to 1.36 g / cm 3 , and can be selected as 1.25 g / cm3 to 1.36 g / cm 3 。Exemplarily, the compaction density of the second region in the negative electrode film layer of the battery cell at 100% state of charge is 1.15 g / cm 3 、1.18 g / cm 3 、1.20 g / cm 3 、1.22 g / cm 3 、1.25 g / cm 3 、1.28 g / cm 3 、1.3 g / cm 3 、1.32 g / cm 3 、1.35 g / cm 3 、1.36 g / cm 3 or a range composed of any two of the above values.

[0201] When the compaction density of the second region in the negative electrode film layer is within the above range, it is beneficial to improve the energy density of the battery cell. Moreover, since the negative electrode active material in the negative electrode film layer is stacked relatively tightly and the contact resistance between particles is small, the resistance of the electrode sheet can be further reduced, thereby reducing heat generation.

[0202] In the embodiments of the present application, the 100% state of charge SOC and 0% state of charge SOC of the battery cell are defined as follows.

[0203] The battery cell is charged at a constant current charging rate of 0.33C to the upper charging voltage, and then charged at a constant voltage to 0.05C, corresponding to the state of 100% SOC of the battery cell. The battery cell is discharged at a constant current discharge rate of 0.33C to the cut-off voltage, corresponding to the state of 70% SOC of the battery cell.

[0204] In the embodiments of the present application, the compaction density of the negative electrode film layer of the battery cell at 100% state of charge has the meaning well known in the art, and can be detected by using the equipment and methods well known in the art. The detection method is the same as the compaction density test method of the positive electrode film layer described above.

[0205] 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.

[0206] When the single-sided coating weight of the negative electrode film layer is within the above range, the heat generation per unit area of the negative electrode plate will not be too large, and it can also take into account the improvement of the energy density of the battery cell.

[0207] 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 the same as the single-sided coating weight test method of the film layer described above.

[0208] In some embodiments, the powder resistivity of the negative electrode active material in the negative electrode film layer is from 0.005 Ω·cm to 0.043 Ω·cm, and can be optionally 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 the range composed of any two of the above values.

[0209] The relatively low powder resistivity of the negative electrode active material makes the resistance of the negative electrode plate relatively low and the heat generation of the battery cell less.

[0210] In the embodiments of the present application, the powder resistivity of the negative electrode active material has the meaning well-known in the art and can be detected by the equipment and methods well-known in the art. The detection method is the same as the powder resistivity test method of the positive electrode active material described above.

[0211] In some embodiments, the powder compaction density of the negative electrode active material in the negative electrode film layer under a pressure of 20000 N is 1.5 g / cm 3 to 1.85 g / cm 3 , and can be optionally 1.55 g / cm 3 to 1.65 g / cm 3 . Exemplarily, the powder compaction density of the negative electrode active material under a pressure of 20000 N is 1.5 g / cm 3 , 1.55 g / cm 3 , 1.6 g / cm 3 , 1.65 g / cm 3 , 1.7 g / cm 3 , 1.75 g / cm 3 , 1.8 g / cm 3 , 1.85 g / cm 3 or the range composed of any two of the above values.

[0212] When the powder compaction density of the negative electrode active material under 20000 N is within the above range, the energy density of the battery cell can be improved, and since the negative electrode active material in the negative electrode film layer can be stacked more closely and the contact resistance between particles is smaller, the resistance of the electrode plate can be further reduced, thereby reducing heat generation.

[0213] 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, and is detected according to the test standard GB / T24533-2009. As an example, a certain amount of negative electrode active material is taken as a sample and added to a mold with a bottom area of 1.327 cm 2 in a UTM7305 type electronic pressure testing machine, pressurized to 2000 kg (equivalent to 20000 N), kept under pressure for 30 s, then depressurized, kept for 10 s, and then the powder compaction density of the negative electrode active material under the action of 20000 N is recorded and calculated.

[0214] In some embodiments, the charging specific capacity of the negative electrode active material in the negative electrode film layer at a 0.1C rate is 350 mAh / g to 390 mAh / g. Exemplarily, the charging specific capacity of the negative electrode active material at a 0.1C rate is 350 mAh / g, 355 mAh / g, 360 mAh / g, 365 mAh / g, 370 mAh / g, 375 mAh / g, 380 mAh / g, 385 mAh / g, 390 mAh / g or the range composed of any two of the above values.

[0215] When the charging specific capacity of the negative electrode active material at a 0.1C rate is within the above range, the energy density of the battery cell is relatively high.

[0216] In the embodiments of the present application, the charging specific capacity of the negative electrode active material at a 0.1C rate has the meaning well-known in the art, and can be detected by equipment and methods well-known in the art, and its detection method is the same as the charging specific capacity test method of the positive electrode active material at a 0.1C rate described above.

[0217] In some embodiments, the negative electrode active material in the second region includes a carbon-based material, and 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%.

[0218] The positive electrode active material of the present application is mainly a lithium-containing phosphate system with an olivine structure, and the negative electrode active material is mainly a carbon-based material system. When the two are used in combination, the cycle performance of the battery cell is relatively excellent.

[0219] 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.

[0220] 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.

[0221] 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 coats 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, similar to an amorphous form (or a structure without a fixed shape and periodic structure rules). In the present application, amorphous carbon refers to the product after carbonization treatment of an organic carbon source.

[0222] The artificial graphite includes secondary particles. There are more migration paths for lithium ions in the artificial graphite, and the migration path in the primary particles is shorter, which can improve the migration rate of lithium ions. The carbon coating layer has more end faces and defects, so that the number of sites where lithium ions can be deintercalated is more, and the 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.

[0223] 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.

[0224] 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.

[0225] 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 a part of the surface of the artificial graphite particles.

[0226] 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 points of coal tar pitch and petroleum pitch are below 250°C.

[0227] Optionally, the carbonization treatment temperature is 700°C to 1800°C. Optionally, the carbonization treatment temperature is 1000°C to 1300°C. When the carbonization treatment temperature is within a suitable range, the organic carbon source can be carbonized and a coating layer containing amorphous carbon can be formed on at least a part of the surface of the artificial graphite.

[0228] Optionally, the carbonization treatment time is 1h to 6h.

[0229] 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.

[0230] In this application, the qualitative and quantitative determination of each substance or element can be detected by suitable equipment and methods known to those skilled in the art. Relevant detection methods can refer to domestic and foreign detection standards, domestic and foreign enterprise standards, etc. And those skilled in the art can also adaptively change certain detection steps / instrument parameters, etc. from the perspective of detection accuracy to obtain more accurate detection results. One detection method can be used for qualitative or quantitative determination, or several detection methods can be used in combination for qualitative or quantitative determination.

[0231] For example, this application can combine the General Rules for X-ray Diffraction Analysis Method of JIS / K0131-1996 to perform X-ray powder diffraction testing and qualitative analysis on the negative electrode sheet or the negative electrode active material.

[0232] Artificial graphite and natural graphite can be distinguished by the SEM cross-sectional view taken by scanning electron microscope (SEM). There are voids between flaky structures in the SEM cross-sectional view of natural graphite, and the SEM cross-sectional view of artificial graphite is dense and has no obvious gaps, or can be distinguished by the XRD spectrum obtained by X-ray diffraction method. There are obvious 2H phase and 3R phase in the XRD spectrum of natural graphite, and only 2H phase exists in the XRD spectrum of artificial graphite.

[0233] In the embodiments of this application, the negative electrode film layer in the second region includes at least one layer of film layer, which can be a single-layer film layer or at least two layers of film layers. Optionally, the negative electrode film layer includes at least two layers of film layers.

[0234] When the negative electrode film layer in the second region adopts a single-layer film layer, the negative electrode active material in the negative electrode film layer includes a carbon-based material. When a single-layer film layer is adopted, the volume average particle size Dv50 of the negative electrode active material is 8.2 μm to 13.5 μm.

[0235] Exemplarily, the volume average particle size Dv50 of the negative electrode active material is 8.2 μm, 8.5 μm, 8.8 μm, 9 μm, 9.2 μm, 9.5 μm, 9.8 μm, 10 μm, 10.2 μm, 10.5 μm, 10.8 μm, 11 μm, 11.2 μm, 11.5 μm, 11.8 μm, 12 μm, 12.2 μm, 12.5 μm, 12.8 μm, 13 μm, 13.2 μm, 13.5 μm or the range composed of any two of the above values.

[0236] When the negative electrode film layer adopts at least two film layers, the negative electrode active material in the negative electrode film layer includes a carbon-based material, and optionally also includes a silicon-based material. The silicon-based material can be located in one of the at least two film layers, or can be located 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.

[0237] In some embodiments, the second region in the negative electrode film layer includes a first negative electrode film layer and a second negative electrode film layer. The first negative electrode film layer is disposed on the surface of the negative electrode current collector. The carbon-based material in the first negative electrode film layer includes graphite particles. The second negative electrode film layer is connected to the side of the first negative electrode film layer facing away from the negative electrode current collector. The carbon-based material in the second negative electrode film layer includes graphite particles. The graphite particles in the first negative electrode film layer and the graphite particles in the second negative electrode film layer can be the same or different.

[0238] The interface between the first negative electrode film layer and the second negative electrode film layer can be regular or irregular, and is optionally irregular.

[0239] Optionally, the carbon-based material in the first negative electrode film layer further includes natural graphite.

[0240] The negative electrode film layer includes at least two film layers, and layer-by-layer coating is beneficial to improving the fast charging performance of the battery cell. Especially when there are differences between the first negative electrode film layer and the second negative electrode film layer, the pore differences of the negative electrode film layer can be constructed, the tortuosity of lithium ion transmission can be reduced, and the fast charging performance of the battery cell can be improved.

[0241] Optionally, the volume average particle size Dv50 of the negative electrode active material in the first negative electrode film layer is greater than or equal to the volume average particle size Dv50 of the negative electrode active material in the second negative electrode film layer. Further optionally, the volume average particle size Dv50 of the negative electrode active material in the first negative electrode film layer is greater than the volume average particle size Dv50 of the negative electrode active material in the second negative electrode film layer, which is beneficial to improving the compaction density of the negative electrode film layer. When the negative electrode active material includes graphite particles, the volume average particle size Dv50 of the graphite particles in the first negative electrode film layer is greater than or equal to the volume average particle size Dv50 of the graphite particles in the second negative electrode film layer.

[0242] The difference in particle sizes between the first negative electrode film layer and the second negative electrode film layer can improve the fast charging performance of the battery cell. Specifically, during fast charging, the overpotential of the second negative electrode film layer is usually 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 improve the problem of lithium deposition on the surface layer of the negative electrode plate.

[0243] Optionally, the negative electrode active material in the first negative electrode film layer is granular, and its volume average particle size Dv50 is from 9.5 μm to 18.5 μm, optionally from 9.5 μm to 14.6 μm. Exemplarily, the volume average particle size of the negative electrode active material in the first negative electrode film layer is 9.5 μm, 10 μm, 10.5 μm, 11 μm, 11.5 μm, 12 μm, 12.5 μm, 13 μm, 13.5 μm, 14 μm, 14.5 μm, 14.6 μm, 15 μm, 15.5 μm, 16 μm, 16.5 μm, 17 μm, 17.5 μm, 18 μm, 18.5 μm or a range 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, optionally from 9.5 μm to 14.6 μm.

[0244] When the volume average particle size Dv50 of the negative electrode active material in the first negative electrode film layer is within the above range, on the one hand, it can shorten the solid-phase transmission path of lithium ions and improve the fast charging performance. On the other hand, the material is not prone to agglomeration during the preparation process, which can improve the stability of the material.

[0245] 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, 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, optionally from 7.8 μm to 11.3 μm.

[0246] 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 cooperation of the negative electrode active material in the second negative electrode film layer with the volume average particle size range and the negative electrode active material in the first negative electrode film layer 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.

[0247] 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 using the equipment and methods well-known in the art. The detection method is the same as the volume average particle size Dv50 test method of the positive electrode active material described above.

[0248] Optionally, the tapped density of the carbon-based material in the first negative electrode film layer is less than or equal to the tapped density of the carbon-based material in the second negative electrode film layer. The tapped density can reflect the packing density of the active material in the film layer. When the tapped density of the carbon-based material in the second negative electrode film layer is greater than that in the first negative electrode film layer, the second negative electrode film layer is more densely packed, improving the energy density of the battery cell. The first negative electrode film layer is relatively sparsely packed with more pores, which can enhance the fast charging performance of the battery cell. When the negative electrode active material includes graphite particles, the tapped density of the graphite particles in the first negative electrode film layer is less than or equal to the tapped density of the graphite particles in the second negative electrode film layer.

[0249] Optionally, the tapped density of the carbon-based material in the first negative electrode film layer is 0.82 g / cm 3 to 1.21 g / cm 3 , such as 0.82 g / cm 3 , 0.85 g / cm 3 , 0.88 g / cm 3 , 0.90 g / cm 3 , 0.92 g / cm 3 , 0.95 g / cm 3 , 0.98 g / cm 3 , 1.00 g / cm 3 , 1.05 g / cm 3 , 1.08 g / cm 3 , 1.10 g / cm 3 , 1.12 g / cm 3 , 1.15 g / cm 3 , 1.18 g / cm 3 , 1.20 g / cm 3 , 1.21 g / cm 3 or the range composed of any two of the above values. When the 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.

[0250] Optionally, 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 , 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 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.

[0251] In the embodiments of the present application, the tapped density of the material has the meaning well known in the art and can be measured by instruments and methods known in the art. For example, reference can be made to GB / T5162-2006, and a powder tapped density tester can be used for measurement. The test instrument can be BT-301 produced by Dandong BETOP.

[0252] Optionally, the ratio of the thickness of the second negative electrode film layer to the thickness of the first negative electrode film layer is 3:7 to 7:3, and can be optionally 4:6 to 6:4. Exemplarily, the ratio of the thickness of the second negative electrode film layer to the thickness of the first negative electrode film layer is 3:7, 4:6, 5:5, 6:4, 7:3 or a range composed of any two of the above values. By adjusting the thickness ratio of the first negative electrode film layer and the second negative electrode film layer, the gradient pore difference between the upper and lower layers can be further increased, the tortuosity of lithium ion transport can be reduced, and the fast charging ability of the battery cell can be improved.

[0253] In some embodiments, after the battery cell undergoes 10 full charge test cycles at the beginning of life (BOL), a 100% SOC disassembly test is performed. The thickness of the first negative electrode film layer is 15 μm to 100 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, 70 μm, 75 μm, 80 μm, 85 μm, 90 μm, 95 μm, 100 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.

[0254] In some embodiments, after the battery cell undergoes 10 full charge test cycles at the beginning of life (BOL), the thickness of the second negative electrode film layer is 15 μm to 80 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, 70 μm, 75 μm, 80 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.

[0255] 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 illustration,

[0256] 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, and cycle 10 times. 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, and 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, and measure their thicknesses respectively. For example, measure the thicknesses at 10 positions of the first negative electrode film layer, and calculate their average value as the average value of the first negative electrode film layer. Measure the thicknesses at 10 positions of the second negative electrode film layer, and calculate their average value as the average value of the second negative electrode film layer.

[0257] 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 110μm, 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, 75μm, 80μm, 85μm, 90μm, 95μm, 100μm, 105μm, 110μm 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.

[0258] In some embodiments, after the battery cell undergoes a full charge test at the end of its life (EOL), the thickness of the second negative electrode film layer is 15 μm to 90 μm, such as 15 μm, 16 μm, 17 μm, 18 μm, 19 μm, 20 μm, 21 μm, 22 μm, 23 μm, 24 μm, 25 μm, 26 μm, 27 μm, 28 μm, 29 μm, 30 μm, 35 μm, 40 μm, 43 μm, 45 μm, 50 μm, 55 μm, 60 μm, 65 μm, 66 μm, 67 μm, 68 μm, 69 μm, 70 μm, 75 μm, 80 μm, 85 μm, 90 μm or a range composed of any two of the above values. When the thickness of the second negative electrode film layer is within the above range, the first negative electrode film layer and the second negative electrode film layer can regulate and increase the gradient pore difference between the upper and lower layers, reduce the tortuosity of lithium-ion transport, and improve the fast charging ability of the battery cell.

[0259] In the embodiments of the present application, for example, taking the upper limit voltage of battery charging as 3.65 V and the cut-off voltage of battery discharging as 2.0 V as an example for illustration,

[0260] The specific steps of the EOL full charge test are as follows: At 60 °C, charge at a charging rate of 0.33C of the nominal capacity of the battery to 3.65 V, then charge at a constant voltage of 3.65 V to 0.05C, stand for 10 min, then discharge at a discharging rate of 0.33C to 2.0 V, stand for 10 min. The above one charge and discharge cycle is repeated until the battery capacity decays to 80% of the nominal capacity and the test stops. Then, at 25 °C, charge at a constant current of 0.33C to 3.65 V, and charge at a constant voltage of 0.05C to 3.65 V, which is the EOL full charge state. In the EOL full charge state, disassemble the negative electrode plate and use a tomography electron microscope to observe the cross-section in the thickness direction of the middle area of the negative electrode plate. Distinguish the two regions according to the interface between the first negative electrode film layer and the second negative electrode film layer, and measure the thicknesses of the two respectively. For example, measure the thicknesses at 10 positions of the first negative electrode film layer, calculate their average value as the average value of the first negative electrode film layer, measure the thicknesses at 10 positions of the second negative electrode film layer, and calculate their average value as the average value of the second negative electrode film layer.

[0261] In some embodiments, when a single-layer film layer (different from the above-mentioned double-layer film layer) is adopted in the second region of the negative electrode 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 3%. 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%, 2%, 2.5%, 3% or a range composed of any two of the above values. The lithium element in the lithium-containing binder can exist in an ionic form, which can increase the number of free-moving lithium ions in the negative electrode film layer, shorten the distance for lithium ions to diffuse to the surface of the negative electrode film layer, increase the intercalation and deintercalation rate of lithium ions, and improve the fast charging performance of the battery cell. Optionally, the negative electrode film layer may further include a negative electrode binder. For example, the negative electrode binder includes at least one of styrene-butadiene rubber (SBR), water-soluble unsaturated resin SR-1B, water-based acrylic resin (such as polyacrylic acid PAA, polymethacrylic acid PMAA, sodium polyacrylate PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), and carboxymethyl chitosan (CMCS).

[0262] Optionally, the mass content of the lithium element in the lithium-containing binder is 3% to 10%. Exemplarily, the mass content of the lithium element in the lithium-containing binder is 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10% or a range composed of any two of the above values. The mass content of the lithium element is calculated based on the mass of the lithium-containing binder. When the mass content of the 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.

[0263] Exemplarily, the lithium-containing binder includes a copolymer of lithium acrylate-acrylonitrile-acrylamide-2-hydroxyethyl acrylate, and the copolymer of lithium acrylate-acrylonitrile-acrylamide-2-hydroxyethyl acrylate is derived from lithium acrylate monomer, acrylonitrile monomer, acrylamide monomer, and 2-hydroxyethyl acrylate monomer. The molar percentages of the lithium acrylate monomer, acrylonitrile monomer, acrylamide monomer, and 2-hydroxyethyl acrylate monomer are 30% to 50%: 15% to 45%: 5% to 20%: 20% to 3%. For example, the molar percentages of the lithium acrylate monomer, acrylonitrile monomer, acrylamide monomer, and 2-hydroxyethyl acrylate monomer are 35%: 30%: 15%: 20%, or 40%, 20%, 10%, 30%, or 45%, 15%, 20%, 20%, etc.

[0264] The lithium-containing binder of the above material can provide a certain number of lithium ions for the negative electrode film layer, improve the fast charging performance of the battery cell, and is not prone to swelling during the charge and discharge process, with a stable structure, so that the cycle performance of the negative electrode film layer is improved during the fast charge and discharge process.

[0265] In some other embodiments, when at least two layers of film layers are used in the second region of the negative electrode film layer, the second region of the negative electrode film layer further includes a lithium-containing binder.

[0266] 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.

[0267] The mass content of the second lithium-containing binder in the second negative electrode film layer is relatively high, and the number of freely movable lithium ions provided by the second lithium-containing binder for the second negative electrode film layer is relatively more, which can further improve the fast charging performance of the battery cell.

[0268] Optionally, the mass content of the lithium element in the first lithium-containing binder relative to the mass of the first negative electrode film layer is 0.1% to 3%. 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%, 2%, 3% 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 freely movable lithium ions in the negative electrode film layer, shorten the distance for lithium ions to diffuse to the surface of the negative electrode film layer, increase the intercalation and deintercalation rate of lithium ions, and improve the fast charging performance of the battery cell.

[0269] Optionally, the mass content of the lithium element in the first lithium-containing binder is 3% to 10%, and can be 3% to 8%. Exemplarily, the mass content of the 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 the lithium element is in 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, increase the intercalation and deintercalation rate of lithium ions, and improve the fast charging performance of the battery cell.

[0270] Exemplarily, the first lithium-containing binder includes a lithium acrylate-acrylonitrile-acrylamide-2-hydroxyethyl acrylate copolymer, which is derived from lithium acrylate monomer, acrylonitrile monomer, acrylamide monomer and 2-hydroxyethyl acrylate monomer, and the molar percentages of lithium acrylate monomer, acrylonitrile monomer, acrylamide monomer and 2-hydroxyethyl acrylate monomer are 30% to 50%: 15% to 45%: 5% to 20%: 20% to 35%. For example, the molar percentages of lithium acrylate monomer, acrylonitrile monomer, acrylamide monomer and 2-hydroxyethyl acrylate monomer are 35%: 30%: 15%: 20%, or 40%, 20%, 10%, 30%, or 45%, 15%, 20%, 20%, etc.

[0271] The lithium-containing binder of the above materials can provide a certain number of lithium ions for the negative electrode film layer, improve the fast charging performance of the battery cell, and is not prone to swelling during the charge and discharge process, with a stable structure, so that the cycle performance of the negative electrode film layer is improved during the fast charge and discharge process.

[0272] 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 3%. 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%, 2%, 3% or a range composed of any two of the above values. The lithium element in the second lithium-containing binder can exist in the form of ions, which can increase the number of freely moving lithium ions in the negative electrode film layer, shorten the distance for lithium ions to diffuse to the surface of the negative electrode film layer, increase the deintercalation rate of lithium ions, and improve the fast charging performance of the battery cell.

[0273] The first lithium-containing binder and the second lithium-containing binder can be made of the same material or different materials.

[0274] Optionally, the mass content of lithium element in the second lithium-containing binder is 3% to 10%, and can be 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 in the above range, the number of freely 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 deintercalation rate of lithium ions, and improve the fast charging performance of the battery cell.

[0275] Exemplarily, the second lithium-containing binder includes a lithium acrylate-acrylonitrile-acrylamide-2-hydroxyethyl acrylate copolymer, which is derived from a lithium acrylate monomer, an acrylonitrile monomer, an acrylamide monomer, and a 2-hydroxyethyl acrylate monomer. The molar percentages of the lithium acrylate monomer, acrylonitrile monomer, acrylamide monomer, and 2-hydroxyethyl acrylate monomer are 30% to 50%: 15% to 45%: 5% to 20%: 20% to 35%. For example, the molar percentages of the lithium acrylate monomer, acrylonitrile monomer, acrylamide monomer, and 2-hydroxyethyl acrylate monomer are 35%: 30%: 15%: 20%, or 40%, 20%, 10%, 30%, or 45%, 15%, 20%, 20%, etc.

[0276] The lithium-containing binder of the above materials can provide a certain amount of lithium ions for the negative electrode film layer, improve the fast charging performance of the battery cell, and is not prone to swelling during charge and discharge, with a stable structure, so that the cycling performance of the negative electrode film layer is improved during fast charge and discharge.

[0277] 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 resins (e.g., polyacrylic acid PAA, polymethacrylic acid PMAA, sodium polyacrylate PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), and carboxymethyl chitosan (CMCS).

[0278] 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.

[0279] 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%.

[0280] In some embodiments, the negative electrode film layer may further optionally include a negative electrode binder. In some embodiments, based on the total weight of the negative electrode film layer, the mass content of the negative electrode binder is ≤5%.

[0281] In some embodiments, the negative electrode film layer may also optionally include other additives. As an example, other additives may include thickeners, dispersants, etc. For example, sodium carboxymethyl cellulose (CMC-Na), PTC thermistor materials, etc. In some embodiments, based on the total weight of the negative electrode film layer, the mass content of other additives is ≤2%.

[0282] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. As an example of the metal foil, at least one foil of copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy may be used. The composite current collector may include a polymer material base layer and a metal material layer formed on at least one surface of the polymer material base layer. As an example, the metal material in the metal material layer may include at least one of copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy. As an example, the polymer material base layer may include at least one of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0283] In some embodiments, the thickness of the negative electrode current collector is 4 μm to 6 μm. Exemplarily, the thickness of the negative electrode current collector is 4 μm, 4.5 μm, 5 μm, 5.5 μm, 6 μm, or a range composed of any two of the above values.

[0284] 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 enable the battery cell to have a high energy density.

[0285] In the embodiments of the present application, the thickness of the negative electrode current collector has the meaning well-known in the art, and it can be detected by the equipment and methods well-known in the art. For example, the film layer on the surface of the negative electrode current collector is washed away with a solvent, and the thickness of the negative electrode current collector is measured with a micrometer.

[0286] The negative electrode film layer is usually formed by coating a negative electrode slurry on the negative electrode current collector, followed by drying and cold pressing. The negative electrode slurry is usually formed by dispersing negative electrode active materials, optional conductive agents, optional binders, and other optional additives in a solvent and stirring evenly. The solvent can be N-methylpyrrolidone (NMP) or deionized water, but is not limited thereto.

[0287] 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 electrode current collector and the negative electrode film layer and disposed on the surface of the negative electrode current collector. In other embodiments, the negative electrode plate of the embodiments of the present application further includes a protective layer covering the surface of the negative electrode film layer.

[0288] In some embodiments, the negative electrode tab further includes a negative electrode conductive layer, which is located between the negative electrode film layer and the negative electrode current collector. The negative electrode conductive layer can further improve the conductivity of the negative electrode tab, reduce the heat generation of the negative electrode tab, and thus reduce the heat generation of the battery cell.

[0289] In some embodiments, the thickness of the negative electrode conductive layer is from 0.1 μm to 2 μm. Exemplarily, the thickness of the negative electrode conductive layer can be 0.1 μm, 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.

[0290] When the thickness of the negative electrode conductive layer is within the above range, it can further improve the conductivity of the negative electrode tab, reduce the heat generation of the negative electrode tab, and thus reduce the heat generation of the battery cell, and can also take into account the improvement of the energy density of the battery cell.

[0291] 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.

[0292] 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 tab 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 tab.

[0293] 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), calcium hydroxide, etc.

[0294] 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.

[0295] 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.

[0296] 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.

[0297] Exemplarily, the negative electrode binder includes one or more of styrene-butadiene rubber (SBR), water-soluble unsaturated resin SR-1B, aqueous acrylic resin, polyvinyl alcohol, sodium alginate, and carboxymethyl chitosan.

[0298] 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 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.

[0299] 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 is beneficial to rapid charging.

[0300] In the embodiments of the present application, the meaning of the CB value is well-known in the art, and it can be detected by using well-known equipment and methods in the art. For example, calculate the capacity of the negative electrode film layer per unit area and the capacity of the positive electrode film layer per unit area respectively, and then calculate the ratio of the two to obtain the CB value.

[0301] Specifically, taking the battery charging upper limit voltage of 3.65V and the battery discharge cut-off voltage of 2.0V as an example for illustration,

[0302] 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, and assemble it into a CR2430 type half-button battery of positive electrode-lithium sheet. 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, cycle 2 times, 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, then the capacity of the positive electrode film layer per unit area = Y / a × b × c × d.

[0303] 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 testing method is as follows: Disassemble the battery in a PRS340 / 11-119-11 Braun glove box, take the negative electrode plate, and assemble it into a CR2430-type half-button battery with a negative electrode-lithium sheet. The area of the negative electrode plate used is f mm 2 , where the electrolyte is a solution of 1 mol / L LiPF6 in EC / EMC / DEC = 3 / 5 / 2 (mass ratio). Then, let the assembled half-button battery stand for 3 h. The test is carried out at 25 °C. First, discharge (Discharge) and insert lithium in the voltage range of 2 V - 0 V at 0.1 C, and then charge (Discharge) and de-lithiate to 2 V at 0.05 C for 2 cycles. Record the discharge and charge capacity of the second cycle as Z mAh. The actual length of the negative electrode plate designed for the battery is h mm, the width is i mm, and the number of surfaces of the negative electrode active material coated on the negative electrode current collector is d. Then, the lithium-insertion capacity of the negative electrode = Z / f × h × i × d.

[0304] [Positive electrode plate]

[0305] The positive electrode plate includes a positive electrode current collector and a positive electrode film layer provided on at least one surface of the positive electrode current collector and including the positive electrode active material. For example, the positive electrode current collector has two surfaces opposite to each other in its own thickness direction, and the positive electrode film layer is provided on either one or both of the two opposite surfaces of the positive electrode current collector.

[0306] In some embodiments, when the battery cell is at 100% state of charge (SOC), the tap density of the positive electrode film layer is 2.50 g / cm 3 to 2.80 g / cm 3 , and can be optionally 2.55 g / cm 3 to 2.70 g / cm 3 . Exemplarily, when the battery cell is at 100% state of charge (SOC), the tap density of the positive electrode film layer is 2.50 g / cm 3 , 2.52 g / cm 3 , 2.55 g / cm 3 , 2.56 g / cm 3 , 2.57 g / cm 3 , 2.58 g / cm 3 , 2.60 g / cm 3 , 2.62 g / cm 3 , 2.65 g / cm 3 , 2.68 g / cm 3 , 2.70 g / cm 3 , 2.72 g / cm 3 , 2.75 g / cm 3 , 2.78 g / cm 3, 2.80 g / cm 3 Or a range composed of any two of the above values.

[0307] When the compaction density of the positive electrode film layer is within the above range, it is beneficial to improve the energy density of the battery cell. Moreover, since the positive electrode active materials in the positive electrode film layer are stacked relatively tightly and the contact resistance between particles is small, the resistance of the electrode sheet can be further reduced, thereby reducing the heat generation during fast charging. Therefore, by adjusting the compaction density of the positive electrode film layer to a reasonable range, the battery cell has both high energy density and high charging rate performance.

[0308] In some embodiments, the single-sided coating weight of the positive electrode film layer is 200 mg / 1540.25 mm 2 to 370 mg / 1540.25 mm 2 , and can be optionally 240 mg / 1540.25 mm 2 to 330 mg / 1540.25 mm 2 . Exemplarily, the single-sided coating weight of the positive electrode film layer is 200 mg / 1540.25 mm 2 , 210 mg / 1540.25 mm 2 , 220 mg / 1540.25 mm 2 , 230 mg / 1540.25 mm 2 , 240 mg / 1540.25 mm 2 , 250 mg / 1540.25 mm 2 , 260 mg / 1540.25 mm 2 , 270 mg / 1540.25 mm 2 , 280 mg / 1540.25 mm 2 , 290 mg / 1540.25 mm 2 , 300 mg / 1540.25 mm 2 , 310 mg / 1540.25 mm 2 , 320 mg / 1540.25 mm 2 , 330 mg / 1540.25 mm 2 , 340 mg / 1540.25 mm 2 , 350 mg / 1540.25 mm 2 , 360 mg / 1540.25 mm 2 , 370 mg / 1540.25 mm 2 Or a range composed of any two of the above values.

[0309] 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 plate will not be excessive, and it is possible to balance the improvement of the energy density and charge rate performance of the battery cell.

[0310] In the embodiments of the present application, the compaction density of the positive electrode film layer of the battery cell in the 100% state of charge (SOC) can be detected by the following method. Disassemble the positive electrode plate from the battery cell in the 100% state of charge (SOC), and measure the compaction density of the positive electrode film layer. For example, take a single-sided coated positive electrode plate (if it is a double-sided coated plate, one side of the positive electrode film layer can be wiped off first), punch it into small round pieces with an area of S1, weigh it, record it as M1, and measure its thickness H1. Then wipe off the positive electrode film layer of the above-mentioned weighed positive electrode plate, weigh the weight of the positive electrode current collector, record it as M0, and measure its thickness H0. The single-sided coating weight of the positive electrode film layer = (the weight M1 of the positive electrode plate - the weight M0 of the positive electrode current collector) / S1, the thickness of the positive electrode film layer = the thickness H1 of the positive electrode plate - the thickness H0 of the positive electrode current collector, and the compaction density of the positive electrode film layer = the single-sided coating weight of the positive electrode film layer / the thickness of the positive electrode film layer.

[0311] In some embodiments, the powder resistivity of the positive electrode active material is 1 Ω·cm to 27.5 Ω·cm. Optionally, it is less than or equal to 20 Ω·cm. Optionally, it is less than or equal to 11 Ω·cm. Exemplarily, the powder resistivity of the positive electrode active material can be 27.5 Ω·cm, 20 Ω·cm, 19 Ω·cm, 18 Ω·cm, 17 Ω·cm, 16 Ω·cm, 15 Ω·cm, 14 Ω·cm, 13 Ω·cm, 12 Ω·cm, 11 Ω·cm, 10 Ω·cm, 9 Ω·cm, 8 Ω·cm, 7 Ω·cm, 6 Ω·cm, 5 Ω·cm, 4 Ω·cm, 3 Ω·cm, 2 Ω·cm, 1 Ω·cm or a range composed of any two of the above values.

[0312] The relatively low powder resistivity of the positive electrode active material makes the resistance of the positive electrode plate relatively low and the heat generation of the battery cell less.

[0313] 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 methods and equipment well-known in the art. For example, according to the test standard GB / T30835-2014, use a PRCD1100 powder resistivity meter for testing.

[0314] In some embodiments, the powder compaction density of the positive electrode active material under 30000 N is 2.46 g / cm 3 to 2.8 g / cm 3 . Exemplarily, the powder compaction density of the positive electrode active material under 30000 N is 2.46 g / cm 3 、2.47 g / cm3 , 2.48 g / cm 3 , 2.49 g / cm 3 , 2.5 g / cm 3 , 2.51 g / cm 3 , 2.55 g / cm 3 , 2.58 g / cm 3 , 2.60 g / cm 3 , 2.65 g / cm 3 , 2.68 g / cm 3 , 2.70 g / cm 3 , 2.72 g / cm 3 , 2.75 g / cm 3 , 2.78 g / cm 3 , 2.80 g / cm 3 or a range composed of any two of the above values.

[0315] When the powder compaction density of the positive electrode active material is within the above range under 30000 N, the energy density of the battery cell can be improved, and since the positive electrode active material in the positive electrode film layer can be stacked more closely, the contact resistance between particles is small, which can further reduce the resistance of the electrode sheet, thereby reducing heat generation.

[0316] In the embodiments of the present application, the powder compaction density of the material has the meaning well-known in the art, and can be detected by methods and equipment well-known in the art. Detection is carried out according to the test standard GB / T24533-2009. For example, a certain amount of positive electrode active material is taken as a sample and added to a mold with a bottom area of 1.327 cm 2 in a UTM7305 type electronic pressure testing machine, pressurized to 3000 kg (equivalent to 30000 N), kept under pressure for 30 s, then the pressure is released, kept for 10 s, and then the powder compaction density of the positive electrode active material under the action of 30000 N is recorded and calculated.

[0317] In some embodiments, the charging specific capacity of the positive electrode active material at a rate of 0.1C is from 150 mAh / g to 170 mAh / g, and optionally from 157 mAh / g to 170 mAh / g. Exemplarily, the charging specific capacity of the positive electrode active material at a rate of 0.1C is 150 mAh / g, 151 mAh / g, 152 mAh / g, 153 mAh / g, 154 mAh / g, 155 mAh / g, 156 mAh / g, 157 mAh / g, 158 mAh / g, 159 mAh / g, 160 mAh / g, 161 mAh / g, 162 mAh / g, 163 mAh / g, 164 mAh / g, 165 mAh / g, 166 mAh / g, 167 mAh / g, 168 mAh / g, 169 mAh / g, 170 mAh / g or a range composed of any two of the above values.

[0318] When the charging specific capacity of the positive electrode active material at a rate of 0.1C is within the above range, the energy density of the battery cell is relatively high.

[0319] In the embodiments of the present application, the specific capacity of the active material has the meaning well-known in the art, and can be tested by equipment and methods well-known in the art. The test method for the first Coulomb efficiency and the first discharge specific capacity in Appendix G of the national standard GB / T 24533-2019 can be adopted. Using metallic lithium as the negative electrode and the sample electrode sheet containing the above materials as the positive electrode, a half-button cell is assembled. Under the condition of 23°C ± 2°C, the half-button cell is placed on a battery tester or other test equipment with the same performance, and the charge-discharge capacity is obtained through charging and discharging at a rate of 0.1C. Then, the capacity is divided by the mass of the active material of the electrode sheet to obtain the charging specific capacity parameter.

[0320] 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. Examples of the lithium-containing transition metal oxides can include but are not limited to at least one of lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide and their respective modified compounds.

[0321] Optionally, the mass percentage of the lithium-containing phosphate with an olivine structure in the positive electrode active material is 100%.

[0322] 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 the same. For example, the lithium-containing phosphate with an olivine structure includes phosphate particles and a coating layer, the coating layer coats the surface of the phosphate particles, and the coating layer contains one or more elements among C, Fe, Ti, Zr, Hf, Ge, and Sn.

[0323] By coating the surface of the phosphate particles with a coating layer, the conductivity of the lithium-containing phosphate with an olivine structure can be improved, the powder resistivity of the material can be reduced, which is beneficial to the migration rate of lithium ions, improves the fast charging ability of the battery, and reduces the heat generation of the battery cell.

[0324] 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, and Mg, Me includes one or more of Mn, Fe, Co, and Ni, M includes one or more of B, Mg, Al, Si, P, S, Ca, Sc, Ti, V, Cr, Cu, Zn, Sr, Y, Zr, Nb, Mo, Cd, Sn, Sb, Te, Ba, Ta, W, Yb, La, and Ce, X includes one or more of S, Si, Cl, B, C, and N, and Y includes one or more of O and F. The phosphate particles have excellent cycle stability, which is beneficial to improving the cycle performance of the battery cell.

[0325] 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.

[0326] 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.

[0327] 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.

[0328] 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.

[0329] In some embodiments, the coating layer further includes carbon.

[0330] The carbon element and the fast ion conductor can be arranged in layers. For example, the carbon element serves as an independent carbon coating layer, and the fast ion conductor serves as an independent fast ion conductor layer. The carbon coating layer can be coated on the surface of the phosphate particles, and the fast ion conductor layer is located on the surface of the carbon coating layer, that is, the fast ion conductor layer is located on the side of the carbon coating layer away from the phosphate particles. Alternatively, the fast ion conductor layer can be coated on the surface of the phosphate particles, and the carbon coating layer is located on the surface of the fast ion conductor layer, that is, the carbon coating layer is located on the side of the fast ion conductor layer away from the phosphate particles. Of course, the carbon element and the fast ion conductor can also be arranged in the same layer.

[0331] 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 phosphate particles, make up for the defect of poor electronic conduction performance of the phosphate particles, and improve the energy density of the battery cell.

[0332] Specifically, the setting of the carbon coating layer endows the positive electrode active material of the present application with the following advantages:

[0333] 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.

[0334] 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.

[0335] 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, and thus improve the cycle life of the battery cell.

[0336] 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 coating layers (fast ion conductor layer and carbon coating layer) are used to solve the drawbacks 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.

[0337] 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, dried, and then calcined at high temperature to remove impurities. Then, 0.4 g of the positive electrode active material is weighed, and 10 ml (50% concentration) of aqua regia is added thereto. Then it is placed on a flat plate at 180 °C for 30 min. After digestion on the flat plate, it is fixed to a volume of 100 mL, and quantitative testing is carried out by the standard curve method.

[0338] In some embodiments, the graphitization degree of the positive electrode active material is from 0.15 to 0.32, and can be optionally from 0.19 to 0.26. Exemplarily, the graphitization degree of the positive electrode active material is 0.15, 0.16, 0.17, 0.18, 0.19, 0.20, 0.21, 0.22, 0.23, 0.24, 0.25, 0.26, 0.27, 0.28, 0.29, 0.30, 0.31, 0.32 or a range composed of any two of the above values.

[0339] 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.

[0340] In the embodiments of the present application, the higher the graphitization degree of the material, the lower the degree of disorder, and it can be tested according to the general rules of X-ray diffraction analysis method of JIS / K 0131-1996.

[0341] In some embodiments, the mass content of carbon element in the lithium-containing phosphate with olivine structure is 1% to 2%, and the specific surface area of the lithium-containing phosphate with olivine structure is 5 m 2 / g to 18 m 2 / g.

[0342] Optionally, the mass content of carbon element in the lithium-containing phosphate with olivine structure is 1% to 2%, and the specific surface area of the lithium-containing phosphate with olivine structure is 7.5 m 2 / g to 14 m 2 / g.

[0343] 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 a range composed of any two of the above values.

[0344] Exemplarily, the specific surface area of the lithium-containing phosphate in the olivine structure is 5 m 2 / g, 6 m 2 / g, 7 m 2 / g, 8 m 2 / g, 9 m 2 / g, 10 m 2 / g, 11 m 2 / g, 12 m 2 / g, 13 m 2 / g, 14 m 2 / g, 15 m 2 / g, 16 m 2 / g, 17 m 2 / g, 18 m 2 / g or a range composed of any two of the above values.

[0345] 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, the conductivity of the lithium-containing phosphate in the olivine structure can be significantly improved, which is beneficial to enhancing the ionic conductivity and electronic conductivity of the lithium-containing phosphate in the olivine structure, and can improve the fast charging ability and energy density of the battery cell.

[0346] In the embodiments of the present application, the specific surface area of the material has the meaning well-known in the art, and can be detected by using the equipment and methods well-known in the art. For example, it can be detected according to the test standard GB / T 19587-2017. Taking the positive electrode active material as a sample, 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.

[0347] In some embodiments, the volume distribution particle size of the positive electrode active material satisfies: 1 µm ≤ Dv50 ≤ 2 µm, 0.4 µm ≤ Dv10 ≤ 0.7 µm.

[0348] Exemplarily, Dv50 of the positive electrode active material can be 1 µm, 1.1 µm, 1.15 µm, 1.2 µm, 1.25 µm, 1.3 µm, 1.35 µm, 1.4 µm, 1.45 µm, 1.5 µm, 1.55 µm, 1.6 µm, 1.65 µm, 1.7 µm, 1.75 µm, 1.8 µm, 1.85 µm, 1.9 µm, 1.95 µm, 2 µm or a range composed of any two of the above values.

[0349] Exemplarily, the Dv10 of the positive electrode active material can be 0.4 µm, 0.45 µm, 0.5 µm, 0.55 µm, 0.6 µm, 0.65 µm, 0.7 µm, or a range composed of any two of the above values.

[0350] 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 basically no agglomeration occurs during the processing and preparation process, making the performance of the positive electrode active material stable.

[0351] In the embodiments of the present application, the volume average particle size Dv50 of the material refers to the particle size corresponding to 50% in the volume distribution, and the volume average particle size Dv10 of the material refers to the particle size corresponding to 10% in the volume distribution. It can be detected by using equipment and methods well-known in the art. For example, taking the positive electrode active material as a sample, according to the test standard GB / T 19077-2016, the Dv50 and Dv10 of the particles are tested by a Mastersizer 2000E laser particle size analyzer, etc.

[0352] 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.

[0353] In some embodiments, the lithium-containing phosphate with an olivine structure is granular. The lithium-containing phosphate with an olivine structure includes secondary particles, and the secondary particles include a plurality of primary particles. The average particle size of the primary particles is 200 nm to 500 nm. Exemplarily, the average particle size of the primary particles is 200 nm, 220 nm, 250 nm, 280 nm, 300 nm, 320 nm, 350 nm, 380 nm, 400 nm, 420 nm, 450 nm, 480 nm, 500 nm, or a range composed of any two of the above values.

[0354] 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.

[0355] 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). The average particle size of the primary particles can be obtained by testing in the SEM image of the scanning electron microscope. The SEM test parameters can be set as follows: the working voltage (EHT) is 10.00 kV, the InLens detector is used, the working distance is 4.6 mm, and the magnification is 1000X.

[0356] In some embodiments, the positive electrode film layer further includes one or more of ternary materials, lithium phosphate, lithium hydrogen phosphate, lithium sulfate, lithium sulfite, lithium molybdate, lithium oxalate, lithium titanate, lithium tetraborate, lithium metasilicate, lithium manganate, lithium tartrate, lithium citrate, lithium nickelate, and lithium ferrate. The above materials can be used as a lithium supplement agent, which can supplement lithium ions to the positive electrode film layer, make up for the irreversible lithium ion loss in the system, and improve the capacity, thereby improving the energy density of the battery cell.

[0357] 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.

[0358] Exemplarily, the ternary materials include at least one of 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.

[0359] 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 a 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, and improve the capacity, thereby improving the energy density of the battery cell.

[0360] 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 cyclic charge and discharge process 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 in the battery system.

[0361] In some embodiments, the positive electrode film layer may further optionally include a positive electrode conductive agent. The embodiments of the present application do not particularly limit the type of the positive electrode conductive agent. 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%.

[0362] In some embodiments, the positive electrode film layer may further optionally include a positive electrode binder. The embodiments of the present application do not particularly limit the type of the positive electrode binder. As an example, the positive electrode binder may include at least one of polyvinylidene fluoride, polytetrafluoroethylene, vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, polyacrylic acid, and fluorinated acrylate resins. In some embodiments, based on the mass of the positive electrode film layer, the mass content of the positive electrode binder is ≤5%.

[0363] In some embodiments, the positive current collector can be a metal foil or a composite current collector. As an example of the metal foil, at least one foil of aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy can be used. The composite current collector can include a polymer material base layer and a metal material layer formed on at least one surface of the polymer material base layer. As an example, the metal material of the metal material layer can 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 can include at least one of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0364] In some embodiments, the ratio of the thickness of the positive current collector to the thickness of the single-sided positive electrode film layer is 0.05 to 0.3. Exemplarily, the ratio of the thickness of the positive 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.

[0365] When the ratio of the thickness of the positive current collector to the thickness of the single-sided positive electrode film layer is within the above range, the rapid charging ability and energy density of the battery cell can be improved.

[0366] In some embodiments, the thickness of the positive current collector is 10 μm to 15 μm, and can be optionally 12 μm to 15 μm. Exemplarily, the thickness of the positive current collector is 10 μm, 10.5 μm, 11 μm, 11.5 μm, 12 μm, 12.5 μm, 13 μm, 13.5 μm, 14 μm, 14.5 μm, 15 μm or a range composed of any two of the above values.

[0367] When the thickness of the positive current collector is within the above range, the current-carrying capacity of the positive current collector is relatively excellent, and the battery cell can have a high energy density.

[0368] In the embodiments of the present application, the thicknesses of the positive electrode film layer and the positive current collector have the meanings well-known in the art, and can be detected by using the equipment and methods well-known in the art. For example, a micrometer is used to measure the thickness of the positive electrode sheet, the film layer on the surface of the positive current collector is removed, and a micrometer is used to measure the thickness of the positive current collector. When the positive electrode film layer is coated on one side, the thickness of the positive electrode film layer is the thickness of the positive electrode sheet minus the thickness of the positive current collector. When the positive electrode film layer is coated on both sides, the thickness of the positive electrode film layer is (the thickness of the positive electrode sheet minus the thickness of the positive current collector) / 2.

[0369] The positive electrode film layer is usually formed by coating a positive electrode slurry on a positive electrode current collector and then drying and cold pressing. The positive electrode slurry is usually formed by dispersing a positive electrode active material, an optional conductive agent, an optional binder, and any other components in a solvent and stirring evenly. The solvent can be N-methylpyrrolidone (NMP), but is not limited thereto.

[0370] The positive electrode tab does not exclude other additional functional layers besides the positive electrode film layer. For example, in some embodiments, the positive electrode tab of the embodiment of the present application further includes a positive electrode conductive layer 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 tab of the embodiment of the present application further includes a protective layer covering the surface of the positive electrode film layer.

[0371] In some embodiments, the positive electrode tab further includes a positive electrode conductive layer, and the positive electrode conductive layer is located between the positive electrode film layer and the positive electrode current collector. The positive electrode conductive layer can further improve the conductivity of the positive electrode tab, reduce the heat generation of the positive electrode tab, and thus reduce the heat generation of the battery cell.

[0372] In some embodiments, the thickness of the positive electrode conductive layer is 0.1 μm to 2 μm. Exemplarily, the thickness of the positive electrode conductive layer can be 0.1 μm, 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.

[0373] When the thickness of the positive electrode conductive layer is within the above range, it can further improve the conductivity of the positive electrode tab, reduce the heat generation of the positive electrode tab, and thus reduce the heat generation of the battery cell, and can also take into account the improvement of the energy density of the battery cell.

[0374] In the embodiment of the present application, the thickness of the positive electrode conductive layer has the meaning well known in the art, and can be detected by using the equipment and methods well known in the art. For example, tomographic scanning of the positive electrode tab can be performed to directly measure the thickness of the positive electrode conductive layer.

[0375] In some embodiments, the positive electrode conductive layer includes one or more of a positive electrode conductive agent and a positive electrode binder.

[0376] 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.

[0377] 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 plate and reducing the heat generation of the battery cell.

[0378] 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.

[0379] Exemplarily, the positive electrode binder includes one or more of polyvinylidene fluoride, polytetrafluoroethylene, vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, polyacrylic acid, and fluorinated acrylate resins. The positive electrode binder in the positive electrode conductive layer can improve the bonding performance between the positive electrode current collector and the positive electrode film layer, and improve the structural stability of the positive electrode plate.

[0380] [Separator film]

[0381] In the embodiments of the present application, the separator film includes a base film with a porous structure.

[0382] In some embodiments, the base film includes at least one of glass fiber, non-woven fabric, and polyolefin. The base film can be a single-layer film or a multi-layer composite film, without particular limitation. When the base film is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0383] Optionally, the polyolefin includes at least one of polyethylene, polypropylene, and polyvinylidene fluoride.

[0384] In some embodiments, the porosity of the base film is 20% to 70%, and can be 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 composed of any two of the above values.

[0385] When the porosity of the base film in the embodiments of the present application is within the above range, it can improve the migration ability of lithium ions in the separator film, further reduce the internal resistance of the battery cell, and thus reduce heat generation.

[0386] In the embodiments of the present application, the porosity refers to the percentage of the internal pore volume in the separator membrane occupying the total volume of the separator membrane. The porosity can be tested in accordance with the standard GB / T36363-2018 "Polyolefin Separator for Battery Cells". It should be noted that in the actual testing process, due to differences in testing instruments, testing errors, and in order to eliminate the influence on the porosity test as much as possible, a testing process slightly different from the standard can be adopted to obtain a more accurate test value.

[0387] In some embodiments, the thickness of the base film is 6 μm to 12 μm, and can be optionally 6 μm to 9 μm. Exemplarily, the thickness of the base film is 6 μm, 6.5 μm, 7 μm, 7.5 μm, 8μm, 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.

[0388] 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.

[0389] 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.

[0390] In some embodiments, the functional layer includes a first functional layer and a second functional layer. The first functional layer is located on one side of the base film and includes first inorganic particles. The second functional layer is located on the other side of the base film and includes composite particles. The composite particles include second inorganic particles and a plurality of non-fluoropolymer particles, and the second inorganic particles are attached to the surface of the non-fluoropolymer particles and / or dispersed inside the non-fluoropolymer particles.

[0391] The first functional layer and the second functional layer have good heat resistance, which can improve the heat resistance of the separator membrane.

[0392] Optionally, the first functional layer can include a binder, optionally including at least one of a fluorine-containing binder or a polyacrylic acid binder, such as polyvinylidene fluoride.

[0393] 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.

[0394] 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 film can be taken as a sample, or a battery cell that has been discharged (discharged to the lower cut-off voltage so that the charged state of the battery is about 0% SOC) can be disassembled in reverse, the separator film is obtained from the battery cell, and the separator film is dried and used as a sample. The separator film is cut off with an ion beam cutter to form a cross-section. Subsequently, a scanning electron microscope is used to measure the thickness of the cross-section of the separator film and its respective layers.

[0395] 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-acrylonitrile copolymers. The acrylate copolymers have excellent adhesion properties and relatively high adhesion stability with the base film. The molar percentages of the monomers in the copolymer can be in any ratio, such as 35%:30%:15%:20%, or 40%, 20%, 10%, 30%, or 45%, 15%, 20%, 20%, etc.

[0396] The second inorganic particles in the composite particles prevent the non-fluoropolymer particles from sticking to each other due to the high-temperature treatment during the granulation process, resulting in pores in the composite particles, which is beneficial to the transmission of lithium ions, improving the ion-conducting ability of the separator film. Moreover, the second inorganic particles can also increase the compression modulus of the composite particles. During the charge and discharge process, the composite particles are not easily deformed, making the structure of the separator film more stable, capable of improving the kinetic performance of the battery cell and enhancing 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 not easily deformed, the separator film basically does not cause side effects such as extrusion to the negative electrode tab, making the kinetic performance of the negative electrode tab stable. Correspondingly, the first functional layer is disposed closer to the positive electrode tab.

[0397] Optionally, the second inorganic particles include one or more of silicon oxide, aluminum oxide, boehmite, barium sulfate, calcium oxide, titanium oxide, zinc oxide, magnesium oxide, zirconium oxide, and tin oxide. Optionally, the second inorganic particles include silicon oxide. The above-mentioned second inorganic particles can improve the heat resistance of the second functional layer and can form composite particles in cooperation with the non-fluoropolymer, further improving the cycle stability and kinetic performance of the separator film, and improving the cycle performance and fast-charging performance of the battery cell.

[0398] The average particle size of the second inorganic particles is from 5 nm to 100 nm, optionally from 10 nm to 100 nm, and optionally from 5 nm to 20 nm. Exemplarily, the average particle size of the second inorganic particles is 5 nm, 10 nm, 15 nm, 20 nm, 25 nm, 30 nm, 35 nm, 40 nm, 45 nm, 50 nm, 55 nm, 60 nm, 65 nm, 70 nm, 75 nm, 80 nm, 85 nm, 90 nm, 95 nm, 100 nm or a range composed of any two of the above values. When the average particle size of the second inorganic particles is within the above range, it is beneficial to improve the heat resistance and compression modulus of the composite particles.

[0399] In the embodiments of the present application, the average particle size of the second inorganic particles has the meaning well known in the art and can be detected by using the equipment and methods well known in the art. For example, after obtaining the separator and drying the separator as a sample, the separator is cut by an ion beam cutter to form a cross-section. Subsequently, a scanning electron microscope is used to measure the particle size of the second inorganic particles in the separator, and the particle sizes of 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.

[0400] In some embodiments, the ionic conductivity of the separator is from 0.3 mS / cm to 0.6 mS / cm. Exemplarily, the ionic conductivity of the separator is 0.3 mS / cm, 0.35 mS / cm, 0.4 mS / cm, 0.45 mS / cm, 0.5 mS / cm, 0.55 mS / cm, 0.6 mS / cm or a range composed of any two of the above values.

[0401] When the ionic conductivity of the separator is within the above range, the migration ability of lithium ions in the separator can be further improved, and the fast charging performance of the battery cell can be improved.

[0402] In the embodiments of the present application, the ionic conductivity of the separator has the meaning well known in the art and can be detected by using the equipment and methods well known in the art. For example,

[0403] Prepare a 2025 type button battery for testing: In a vacuum glove box, put a lithium sheet into the battery negative electrode case, add 150 μL of electrolyte thereto. The electrolyte is a solution of 1 mol / L LiPF6 in EC / EMC / DEC = 3 / 5 / 2 (mass ratio), and then put the separator (with an area of 3.14 cm 2 , a thickness of 12 μm) to make it close to the lithium sheet, add another 25 μL of electrolyte, and finally place the positive electrode sheet (the positive electrode sheet can be the positive electrode sheet in Example 1) thereon and encapsulate. Take out the assembled button battery from the vacuum glove box and place it for 24 h for the next test.

[0404] Test: Conduct the test on an electrochemical workstation within a frequency range of 10 -1 ~10 6 Hz to obtain the separator resistance Rb, and calculate the ionic conductivity σ (unit: mS / cm) through the following formula:

[0405] σ = L / (R b ×S)

[0406] where: R b is the separator resistance, and L and S are the thickness and area of the separator to be measured, respectively.

[0407] [Electrolyte]

[0408] In some embodiments, the battery cell further includes an electrolyte.

[0409] During the charge and discharge process of the battery cell, active ions such as lithium ions are embedded and extracted back and forth between the positive electrode plate and the negative electrode plate, and the electrolyte plays a role in conducting active ions between the positive electrode plate and the negative electrode plate.

[0410] In the embodiments of the present application, the conductivity of the electrolyte at room temperature is 13 mS / cm to 20 mS / cm, and can be optionally 15 mS / cm to 20 mS / cm. Exemplarily, the conductivity of the electrolyte at room temperature is 13 mS / cm, 13.5 mS / cm, 14 mS / cm, 14.5 mS / cm, 15 mS / cm, 15.5 mS / cm, 16 mS / cm, 16.5 mS / cm, 17 mS / cm, 17.5 mS / cm, 18 mS / cm, 18.5 mS / cm, 19 mS / cm, 19.5 mS / cm, 20 mS / cm or a range composed of any two of the above values.

[0411] 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.

[0412] In the embodiments of the present application, the conductivity of the electrolyte at room temperature, such as 25 °C, is the ionic conductivity, and it can be detected by using equipment and methods well-known in the art, for example, tested with reference to the industry standard HG-T 4067-2015.

[0413] In some embodiments, the viscosity of the electrolyte at room temperature is from 2.3 mPa·s to 3.5 mPa·s. Exemplarily, the viscosity of the electrolyte is 2.3 mPa·s, 2.4 mPa·s, 2.5 mPa·s, 2.6 mPa·s, 2.7 mPa·s, 2.8 mPa·s, 2.9 mPa·s, 3.0 mPa·s, 3.1 mPa·s, 3.2 mPa·s, 3.3 mPa·s, 3.4 mPa·s, 3.5 mPa·s or a range composed of any two of the above values.

[0414] 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.

[0415] 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 devices and methods well-known in the art. For example, it can be detected according to GB / T10247-2008.

[0416] In some embodiments, the density of the electrolyte at room temperature, such as 25 °C, is from 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.

[0417] When the density of the electrolyte is within the above range, the migration rate of lithium ions in the electrolyte is relatively high, which can further reduce the internal resistance of the battery cell, thereby reducing heat generation, and can improve the fast charging performance of the battery cell.

[0418] In the embodiments of the present application, the density of the electrolyte has the meaning well-known in the art, and can be detected by devices and methods well-known in the art. For example, it can be tested with reference to GB / T 2013-2010.

[0419] 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.

[0420] In some embodiments, the organic solvent includes a chain carboxylic acid ester solvent, and the mass content of the chain carboxylic acid ester solvent relative to the mass of the electrolyte is greater than or equal to 4% and less than or equal to 65%, optionally greater than or equal to 8.5% and less than or equal to 65%, and optionally 25% to 60%. Exemplarily, the mass content of the chain carboxylic acid ester solvent is 4%, 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 65% or a range composed of any two of the above values.

[0421] When the mass content of the chain carboxylic acid ester solvent is within the above range, the viscosity of the electrolyte system is relatively small, which is beneficial to the migration of lithium ions.

[0422] In some embodiments, the chain carboxylic acid ester solvent includes a compound represented by Formula I,

[0423] Formula I,

[0424] In Formula I,

[0425] R1 includes a hydrogen atom, a halogen atom, a C1-C5 alkyl group or a C1-C5 haloalkyl group,

[0426] R2 includes a C1-C5 alkyl group or a C1-C5 haloalkyl group.

[0427] The above chain carboxylic acid ester solvent has a relatively high conductivity, which is beneficial to improving the fast charging ability of the battery monomer.

[0428] 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.

[0429] 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.

[0430] In the above embodiments, the halogen atom includes one or more of a fluorine atom, a chlorine atom, a bromine atom and an iodine atom. Optionally, the halogen atom includes a fluorine atom.

[0431] In 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.

[0432] Exemplarily, the chain carboxylic acid ester solvent includes one or more of the compounds represented by Formula I-1 to Formula I-8,

[0433]

[0434] In some embodiments, the organic solvent further includes carbonate solvents.

[0435] Optionally, the carbonate solvents include one or more of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, and methyl ethyl carbonate. Further optionally, the carbonate solvents include one or more of ethylene carbonate, dimethyl carbonate, and methyl ethyl carbonate. The above-mentioned 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.

[0436] Further optionally, the mass content of the carbonate solvents in the electrolyte is 25% to 60%, and can be 25% to 42.5%. Exemplarily, the mass content of the carbonate solvents in the electrolyte is 25%, 28%, 30%, 31%, 32%, 33%, 34%, 35%, 36%, 37%, 38%, 40%, 45%, 48%, 50%, 55%, 60% or a range composed of any two of the above values. The carbonate solvents with the above mass content can further improve the conductivity of the electrolyte at room temperature, which is beneficial to the migration of lithium ions.

[0437] Exemplarily, the carbonate solvents include one or more of ethylene carbonate, dimethyl carbonate, and methyl ethyl carbonate, and the mass content of the carbonate solvents is 25% to 42.5%.

[0438] In some embodiments, the electrolyte further contains additives. The additives can include negative electrode film-forming additives, or can include positive electrode film-forming additives, and can also include additives that can improve certain battery performances, such as additives for improving the overcharge performance of the battery, additives for improving the high-temperature performance of the battery, additives for improving the low-temperature power performance of the battery, etc.

[0439] In some embodiments, the additives include one or more of carbonate additives, sulfur-containing additives, and lithium salt additives, and can be at least two. The above-mentioned additives can improve the interfacial film performance on the positive electrode side and / or the negative electrode side, which is beneficial to improving the fast charging performance of the battery monomer and improving the cycle performance.

[0440] 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.

[0441] The additives with the above mass contents can effectively improve the interfacial film properties on the positive electrode side and / or the negative electrode side, which is beneficial to enhancing the fast charging performance of the battery cell and improving the cycle performance.

[0442] Exemplarily, the carbonate additives include one or more of vinylene carbonate (VC) and fluoroethylene carbonate (FEC).

[0443] Exemplarily, the sulfur-containing additives include one or more of ethylene sulfate (DTD), bis(ethylene sulfate) (2-DTD), butene sulfite (BS), 1,3-propane sultone (PS), ethylene sulfite (ES), and methylene methyl disulfonate (MMDS).

[0444] 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).

[0445] Optionally, the mass content of vinylene carbonate (VC) in the electrolyte is 0.5% to 9%, and optionally 2% to 6%.

[0446] Optionally, the mass content of fluoroethylene carbonate (FEC) in the electrolyte is 0.1% to 4%, and optionally 0.5% to 3%.

[0447] 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%.

[0448] 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%.

[0449] In some embodiments, the electrolyte salt includes a lithium salt, and the lithium salt includes one or more of fluorosulfonimide salts 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 cycle performance of the battery cell.

[0450] Optionally, the fluorosulfonimide salts include one or more of lithium bis(fluorosulfonyl)imide (LiFSI) and lithium bis(trifluoromethylsulfonyl)imide (LiTFSI).

[0451] 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.

[0452] 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.

[0453] 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.

[0454] 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.

[0455] 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.

[0456] 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 devices 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, freshly prepared electrolyte can be taken as a sample, the free electrolyte of a fresh battery can be taken as a sample, or a battery that has been fully discharged (discharged to the lower cut-off voltage so that the charged state of the battery is about 0% SOC) can be reverse disassembled, and the free electrolyte obtained from the battery can be taken as a sample for detection by ion chromatography.

[0457] In the embodiments of the present application, the types and contents of the organic components in the electrolyte have meanings well-known in the art, and can be detected by devices and methods well-known in the art. For example, reference can be made to 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, freshly prepared electrolyte can be taken as a sample, the free electrolyte of a fresh battery can be taken as a sample, or a battery that has been fully discharged (discharged to the lower cut-off voltage so that the charged state of the battery is about 0% SOC) can be reverse disassembled, and the free electrolyte obtained from the battery can be taken as a sample for detection by ion chromatography.

[0458] In the embodiments of the present application, after quantitatively and qualitatively detecting each component in the electrolyte, each component is classified. Chain carboxylic acid ester solvents and carbonate solvents (such as ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate) are used as constituent components of the organic solvent. Based on the mass of the electrolyte being 100%, the mass content of each component is calculated.

[0459] Vinylene carbonate additives (such as vinylene carbonate, fluoroethylene carbonate), sulfur-containing additives, and lithium salt additives are used as additives in the electrolyte. Based on the mass of the electrolyte being 100%, the mass content of each component is calculated.

[0460] 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.

[0461] d / A can reflect the liquid retention ability of the electrolyte. When d / A is within the above range, the electrolyte can play a good wetting role on the positive electrode plate and the negative electrode plate, and can also improve the migration rate of lithium ions in the liquid phase, which is beneficial to improving the fast charging ability of the battery cell.

[0462] In the embodiments of the present application, d / A of the battery cell can be understood as the liquid retention coefficient, and can be detected by using equipment and methods well-known in the art. For example, taking the upper limit voltage of battery charging as 3.65 V and the cut-off voltage of battery discharging as 2.0 V in accordance with GB / T31486-2015 "Electric Performance Requirements and Test Methods for Power Batteries for Electric Vehicles" for illustration.

[0463] At 25 °C, the battery cell is charged to 3.65 V at 0.33 C, then charged at a constant voltage until 0.05 C, and then discharged at a constant current of 0.33 C to 2.0 V. The discharged capacity A is used as the denominator. The battery cell is weighed as M0, and then the positive electrode plate, the negative electrode plate, the separator, and the electrolyte are disassembled. The free electrolyte is placed in a bag. All the above solid components are placed in an oven at 60 °C and baked for more than 4 hours (including but not limited to the positive electrode plate, the negative electrode plate, the separator, and other mechanical parts contributing to M0 in the disassembled battery cell), and then all the components of the battery cell are weighed as M1. The weight difference between M0 and M1 is used as the numerator. The liquid retention coefficient is equal to the value obtained by dividing the weight difference d between M0 and M1 by the capacity A.

[0464] In some embodiments, the positive electrode sheet, the separator, and the negative electrode sheet can be made into an electrode assembly by a winding process and / or a stacking process.

[0465] Figure 1 and Figure 2 shows a schematic structural view of a battery cell.

[0466] In some embodiments, the battery cell 7 may include a housing 20.

[0467] In some embodiments, the housing 20 of the battery cell 7 may 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 may also be a soft package, such as a pouch soft package. The material of the soft package may be plastic, such as at least one of polypropylene (PP), polybutylene terephthalate (PBT), and polybutylene succinate (PBS).

[0468] The housing 20 has a hollow structure, and the housing 20 can be used to encapsulate the above-mentioned electrode assembly 10 and the electrolyte.

[0469] The preparation method of the battery cell 7 according to the embodiments of the present application is well-known. In some embodiments, the positive electrode sheet, the separator, the negative electrode sheet, and the electrolyte can be assembled to form the battery cell 7. As an example, the positive electrode sheet, the separator, and the negative electrode sheet can be formed into an electrode assembly 10 by a winding process and / or a stacking process, the electrode assembly 10 is placed in the housing 20, the electrolyte is injected after drying, and after processes such as vacuum packaging, standing, forming, and shaping, the battery cell 7 is obtained.

[0470] 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.

[0471] 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.

[0472] In some embodiments, the material of the housing body 21 includes steel, and the mechanical strength of the steel is relatively high, not easily deformed, and can improve the use reliability and cycle performance of the battery cell. Optionally, the mass ratio of the steel is the highest among the materials in the housing body 21.

[0473] Optionally, the thickness of the housing 21 is from 0.1 mm to 0.5 mm, optionally from 0.2 mm to 0.35 mm. Exemplarily, the thickness of the housing 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 21 is within the above range, the mechanical strength of the housing 21 is relatively high, which can improve the use reliability and cycling performance of the battery cell 7, and the housing 21 occupies less space and has more internal space, which is beneficial to improving the energy density of the battery cell 7.

[0474] Viewed from the outer shape of the electrode assembly 10, the electrode assembly 10 includes a main body portion 12, a positive electrode tab 111 and a negative electrode tab 112, and the positive electrode tab 111 and the negative electrode tab 112 protrude from the main body portion 12. The positive electrode tab 111 is the part of the positive electrode plate where the active material layer is not coated, and the negative electrode tab 112 is the part of the negative electrode plate where the active material layer is not coated. The positive electrode tab 111 and the negative electrode tab 112 are used to lead out the current in the main body portion 12.

[0475] The positive electrode tab 111 and the negative electrode tab 112 can extend from the same side of the main body portion 12, or can extend from opposite sides respectively.

[0476] Optionally, the number of the positive electrode tabs 111 on the same side of the main body portion 12 is at least one, optionally at least two, and at least two positive electrode tabs 111 can increase the current-carrying capacity of the positive electrode tabs 111.

[0477] Optionally, the number of the negative electrode tabs 112 on the same side of the main body portion 12 is at least one, optionally at least two, and at least two negative electrode tabs 112 can increase the current-carrying capacity of the negative electrode tabs 112.

[0478] In some embodiments, the battery cell 7 further includes a positive terminal 31, and the positive terminal 31 is electrically connected to the positive electrode tab 111. Optionally, the positive terminal 31 and the positive electrode tab 111 are welded. The positive terminal 31 and the positive electrode tab 111 can be connected through an adapter, or can be connected without using an adapter. Optionally, the positive terminal 31 and the positive electrode tab 111 are connected without using an adapter, that is, the positive terminal 31 and the positive electrode tab 111 are directly welded, which can reduce the resistance at the connection and is beneficial to reducing the overall internal resistance of the battery cell 7.

[0479] In some embodiments, the battery cell 7 further includes a negative terminal 32, and the negative terminal 32 is electrically connected to the negative electrode tab 112. Optionally, the negative terminal 32 and the negative electrode tab 112 are welded. The negative terminal 32 and the negative electrode tab 112 can be connected through an adapter, or can be connected without using an adapter. Optionally, the negative terminal 32 and the negative electrode tab 112 are directly welded without using an adapter, which can reduce the resistance at the connection and is beneficial to reducing the overall internal resistance of the battery cell 7.

[0480] Optionally, the number of positive terminals 31 on the same side of the main body 12 is at least one, and can be at least two. At least two positive terminals 31 can increase the current-carrying capacity of the positive terminals 31.

[0481] Further optionally, the current-carrying area of the positive terminals 31 on one side is 150 mm 2 to 1000 mm 2 and can be 200 mm 2 to 1000 mm 2 The current-carrying area of the positive terminals 31 on one side refers to the sum of the current-carrying areas of all the positive terminals 31 on the same side of the main body 12. The current-carrying area of the positive terminals 31 can be understood as the cross-sectional area of the positive terminals 31, and this cross-section is perpendicular to the thickness direction of the end cover 22.

[0482] Exemplarily, the current-carrying area of the positive terminals 31 on one side can be 150 mm 2 、200 mm 2 、210 mm 2 、250 mm 2 、280 mm 2 、300 mm 2 、320 mm 2 、350 mm 2 、380 mm 2 、400 mm 2 、450 mm 2 、500 mm 2 、550 mm 2 、600 mm 2 、650 mm 2 、700 mm 2 、750 mm 2 、800 mm 2 、850 mm 2 、900 mm 2 、950 mm 2 、1000 mm 2 or the range composed of any two of the above values.

[0483] Optionally, the number of negative extreme terminals 32 on the same side of the main body 12 is at least one, optionally at least two. The at least two negative extreme terminals 32 can increase the over-current capacity of the negative extreme terminals 32.

[0484] Further optionally, the over-current area of the single-sided negative extreme terminal 32 is 150 mm 2 to 1000 mm 2 , optionally 200 mm 2 to 1000 mm 2 . The over-current area of the single-sided negative extreme terminal 32 refers to the sum of the over-current areas of all negative extreme terminals 32 on the same side of the main body 12. The over-current area of the negative extreme terminal 32 can be understood as the cross-sectional area of the negative extreme terminal 32, and this cross-section is perpendicular to the thickness direction of the end cover 22.

[0485] Exemplarily, the over-current area of the single-sided negative extreme terminal 32 can be 150 mm 2 , 200 mm 2 , 210 mm 2 , 250 mm 2 , 280 mm 2 , 300 mm 2 , 320 mm 2 , 350 mm 2 , 380 mm 2 , 400 mm 2 , 450 mm 2 , 500 mm 2 , 550 mm 2 , 600 mm 2 , 650 mm 2 , 700 mm 2 , 750 mm 2 , 800 mm 2 , 850 mm 2 , 900 mm 2 , 950 mm 2 , 1000 mm 2 or a range composed of any two of the above values.

[0486] As Figure 10 shown, in some embodiments of the present application, the battery cell 7 according to the implementation manner 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.

[0487] If there are multiple battery cells 7, the multiple battery cells 7 can be connected in series, in parallel, or in a combination of series and parallel. A combination of series and parallel 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 combination of series and parallel together, and then the whole formed by the multiple battery cells 7 is accommodated in the accommodation 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 combination of series and parallel to form battery modules 6, and then the multiple battery modules 6 are connected in series, in parallel, or in a combination of series and parallel to form a whole and are accommodated in the accommodation part. Optionally, the battery module 6 can also include an accommodation part with an accommodation space, and the multiple battery cells 7 are accommodated in this accommodation space.

[0488] As Figure 11 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.

[0489] 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 accommodation 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.

[0490] The first box body part 5a and the second box body part 5b cover each other, and the first box body part 5a and the second box body part 5b jointly define an accommodation space 5c for accommodating 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 accommodation 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 accommodation space 5c. Of course, the first box body part 5a and the second box body part 5b can be in various shapes, such as a cylinder, a cuboid, etc.

[0491] To improve the sealing performance after the first box body part 5a and the second box body part 5b are connected, 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.

[0492] 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.

[0493] In some embodiments, during the charging process of the battery pack 2 or any battery cell that makes up the battery pack 2 from a state of charge (SOC) of 0% to 100% SOC, the temperature of the external environment where the battery pack 2 is located is 30°C.

[0494] In some embodiments, during the charging process of the battery pack 2 or any battery cell that makes up the battery pack 2 from a state of charge (SOC) of 10% to 80% SOC, the temperature of the external environment where the battery pack 2 is located is 30°C.

[0495] In some embodiments, during the charging process of the battery pack 2 or any battery cell that makes up the battery pack 2 from 10% state of charge to 80% state of charge, it includes multiple charging steps. The difference between the maximum state of charge of any charging step and the maximum state of charge of its adjacent charging step is less than or equal to 5% state of charge, such as 1% state of charge, 1.5% state of charge, 2% state of charge, 2.5% state of charge, 3% state of charge, 3.5% state of charge, 4% state of charge, 4.5% state of charge, 5% state of charge, or a range composed of any two of the above values.

[0496] The charging process of the battery pack 2 or any battery cell that makes up the battery pack 2 from 10% state of charge to 40% state of charge 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.

[0497] Exemplarily, the charging steps of the battery pack 2 or any battery cell that makes up the battery pack 2 from 10% to 80% can be carried out in the following manner:

[0498] Constant current charging at 5.0C from 10% SOC to 15% SOC,

[0499] Constant current charging at 5.0C from 15% SOC to 20% SOC,

[0500] Constant current charging at 5.0C from 20% SOC to 25% SOC,

[0501] Constant current charging at 5.0C from 25% SOC to 30% SOC,

[0502] Constant current charging at 5.0C from 30% SOC to 35% SOC,

[0503] Constant current charging at 5.0C from 35% SOC to 40% SOC,

[0504] Charge from 40% SOC to 45% SOC at a constant current of 4.6C,

[0505] Charge from 45% SOC to 50% SOC at a constant current of 4.3C,

[0506] Charge from 50% SOC to 55% SOC at a constant current of 4.0C,

[0507] Charge from 55% SOC to 60% SOC at a constant current of 3.7C,

[0508] Charge from 60% SOC to 65% SOC at a constant current of 3.4C,

[0509] Charge from 65% SOC to 70% SOC at a constant current of 3.1C,

[0510] Charge from 70% SOC to 75% SOC at a constant current of 2.9C,

[0511] Charge from 75% SOC to 80% SOC at a constant current of 2.7C.

[0512] In some embodiments, the charging time of the battery pack 2 or any battery cell constituting the battery pack 2 from 10% state of charge to 80% state of charge is less than or equal to 10.5 min, and can be optionally 5 min to 10.5 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 10.5 min, 10 min, 9.5 min, 9 min, 8.5 min, 8 min, 7.5 min, 7 min, 6.5 min, 6 min, 5.5 min, 5 min or the range composed of any two of the above values

[0513] 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.

[0514] 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,

[0515] 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 insulating 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.

[0516] Electrical device

[0517] The second aspect of the embodiments of the present application provides an electrical device. The electrical device includes the battery device of the embodiments of the present application, such as a battery cell, a battery module, or a battery pack. The battery cell, the battery module, or the battery pack can be used as the power source of the electrical device or as the energy storage unit of the electrical device. The electrical device can be a vehicle, a mobile phone, a portable device, a laptop computer, a ship, a spacecraft, an electric toy, and an electric tool, etc. The vehicle can be a fuel vehicle, a gas vehicle, or a new energy vehicle. The new energy vehicle can be a pure electric vehicle, a hybrid electric vehicle, or an extended-range electric vehicle, etc. The spacecraft includes an airplane, a rocket, a space shuttle, and a spaceship, etc. The electric toy includes a fixed or mobile electric toy, for example, a game console, an electric vehicle toy, an electric ship toy, and an electric airplane toy, etc. The electric tool includes a metal cutting electric tool, a grinding electric tool, an assembly electric tool, and a railway electric tool, for example, an electric drill, an electric grinding wheel, an electric wrench, an electric screwdriver, a hammer drill, an impact drill, a concrete vibrator, and a planer, etc. The embodiments of the present application do not impose special restrictions on the above electrical devices.

[0518] The electrical device can select a battery cell, a battery module, or a battery pack according to its usage requirements.

[0519] Figure 12 It is a schematic diagram of an electrical device 1 as an example. The electrical device 1 is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. In order to meet the requirements of the electrical device 1 for high power and high energy density, a battery pack or a battery module can be used.

[0520] A battery pack 2 is provided inside the electrical device 1. The battery pack 2 can be provided at the bottom, the head, or the tail of the electrical device 1. The battery pack 2 can be used for power supply of the electrical device 1. For example, the battery pack 2 can be used as the operating power source of the electrical device 1 and can also be used as the driving power source of the electrical device 1, replacing or partially replacing fuel or natural gas to provide driving power for the electrical device 1.

[0521] The electrical device 1 may further include a controller 3 and a motor 4. The controller 3 is used to control the battery pack 2 to supply power to the motor 4. For example, it is used for the power consumption requirements during the startup, navigation, and driving of the electrical device 1.

[0522] Another example of an electrical device can be a mobile phone, a tablet computer, a laptop computer, etc. Such an electrical device usually requires being thin and light, and battery cells can be used as the power source.

[0523] The charging process of the electrical device can select the following charging methods:

[0524] Charge from 10% SOC to 15% SOC at a constant current of 5.0C,

[0525] Charge from 15% SOC to 20% SOC at a constant current of 5.0C,

[0526] Charge from 20% SOC to 25% SOC at a constant current of 5.0C,

[0527] Charge from 25% SOC to 30% SOC at a constant current of 5.0C,

[0528] Charge from 30% SOC to 35% SOC at a constant current of 5.0C,

[0529] Charge from 35% SOC to 40% SOC at a constant current of 5.0C,

[0530] Charge from 40% SOC to 45% SOC at a constant current of 4.6C,

[0531] Charge from 45% SOC to 50% SOC at a constant current of 4.3C,

[0532] Charge from 50% SOC to 55% SOC at a constant current of 4.0C,

[0533] Charge from 55% SOC to 60% SOC at a constant current of 3.7C,

[0534] Charge from 60% SOC to 65% SOC at a constant current of 3.4C,

[0535] Charge from 65% SOC to 70% SOC at a constant current of 3.1C,

[0536] Charge from 70% SOC to 75% SOC at a constant current of 2.9C,

[0537] Charge from 75% SOC to 80% SOC at a constant current of 2.7C.

[0538] In some embodiments, the charging time of the electrical device from 10% state of charge to 80% state of charge is less than or equal to 10.5 min, and can be optionally 5 min to 10.5 min. The temperature of the external environment of the battery pack 2 at 10% state of charge is room temperature, such as 30°C. Exemplarily, the charging time of the battery pack 2 from 10% state of charge to 80% state of charge is 10.5 min, 10 min, 9.5 min, 9 min, 8.5 min, 8 min, 7.5 min, 7 min, 6.5 min, 6 min, 5.5 min, 5 min or the range composed of any two of the above values.

[0539] Embodiment

[0540] 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.

[0541] Example 1-1 (laminated battery cell)

[0542] 1. Preparation of the positive electrode plate

[0543] 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 aluminum foil.

[0544] 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 and drying on the surface of the current collector. 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%.

[0545] The positive electrode film layer includes a film layer formed by uniformly coating a positive electrode slurry (solvent is 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.

[0546] The positive active material includes lithium iron phosphate and a coating layer. The coating layer covers the surface of the lithium iron phosphate. The coating layer includes lithium titanium iron phosphate Li2FeTi(PO4)3 and amorphous carbon. The Dv50 of the positive active material is 1.6 μm, and the Dv10 is 0.64 μm.

[0547] The single-sided coating weight of the positive electrode film layer is 300 mg / 1540.25 mm 2 。

[0548] 2. Preparation of the negative electrode sheet

[0549] The negative electrode sheet includes a negative electrode current collector, a negative electrode conductive layer on the negative electrode current collector, and a negative electrode film layer. The negative electrode current collector is a copper foil

[0550] The negative electrode conductive layer on the negative electrode current collector is a film layer formed by uniformly mixing a negative electrode conductive agent, superconducting carbon, a negative electrode binder, styrene-butadiene rubber (SBR), a thickening agent, sodium carboxymethyl cellulose (CMC-Na), and a solvent, water, and then coating and drying on the surface of the negative electrode current collector. 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%

[0551] The negative electrode film layer includes a film layer formed by uniformly coating a negative electrode slurry (with deionized water as the solvent) on the surface of the negative electrode conductive layer, followed by drying and cold pressing

[0552] The single-sided coating weight of the negative electrode film layer is 138 mg / 1540.25 mm 2 。

[0553] The negative electrode film layer includes a first region and a second region. The ratio of the length of the first region to the length of the negative electrode film layer is 0.15

[0554] The first region includes a first sub-layer and a second sub-layer. The first sub-layer is located on the surface of the negative electrode conductive layer, and the second sub-layer is located on the surface of the first sub-layer. After being fabricated into a battery cell, the tap density of the first sub-layer of the battery cell at 100% SOC is 1.35 g / cm 3 ,and the tap density of the second sub-layer is 1.28 g / cm 3 。

[0555] The first sub-layer includes a negative electrode active material, conductive agent acetylene black, a lithium-containing binder (copolymer of lithium acrylate - acrylonitrile - acrylamide - 2-hydroxyethyl acrylate, where the molar percentages of lithium acrylate monomer, acrylonitrile monomer, acrylamide monomer, and 2-hydroxyethyl acrylate monomer are 35%:30%:15%:20%), negative electrode binder styrene-butadiene rubber, and thickening agent sodium carboxymethyl cellulose, with a mass ratio of 96.5:0.5:2.5:0.3:0.2. The mass content of lithium element in the lithium-containing binder is 9%. The negative electrode active material includes artificial graphite and natural graphite. The volume average particle size Dv50 of the artificial graphite is 1l.8 μm, and the volume average particle size Dv50 of the natural graphite is 12 μm

[0556] The second sub-layer includes artificial graphite, conductive agent acetylene black, lithium-containing binder (lithium acrylate-acrylonitrile-acrylamide-2-hydroxyethyl acrylate copolymer, where the molar percentages of lithium acrylate monomer, acrylonitrile monomer, acrylamide monomer, and 2-hydroxyethyl acrylate monomer are 35%:30%:15%:20%), negative electrode binder styrene-butadiene rubber, and thickener sodium carboxymethyl cellulose with a mass ratio of 96.5:0.5:0.5:1.5:1. The mass content of lithium element in the first lithium-containing binder is 9%, and the volume average particle size Dv50 of the artificial graphite is 11.8 μm; the mass content of the lithium-containing binder in the second sub-layer is 0.50%.

[0557] The second region 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. After being prepared into a battery monomer, the compaction density of the first negative electrode film layer of the battery monomer at 100% SOC is 1.28 g / cm 3 , and the compaction density of the second negative electrode film layer is 1.28 g / cm 3 .

[0558] The first negative electrode film layer includes graphite particles, conductive agent acetylene black, first lithium-containing binder (lithium acrylate-acrylonitrile-acrylamide-2-hydroxyethyl acrylate copolymer, where the molar percentages of lithium acrylate monomer, acrylonitrile monomer, acrylamide monomer, and 2-hydroxyethyl acrylate monomer are 35%:30%:15%:20%), negative electrode binder styrene-butadiene rubber, and thickener sodium carboxymethyl cellulose with a mass ratio of 96.5:0.5:2.5:0.3:0.2. The mass content of lithium element in the first lithium-containing binder is 9%, the Dv50 of the graphite particles is 11.8 μm, the graphite particles include artificial graphite and a carbon coating layer, the carbon coating layer covers the surface of the artificial graphite, and the mass content of the carbon coating layer is 3.5%.

[0559] The second negative electrode film layer includes graphite particles, conductive agent acetylene black, second lithium-containing binder (lithium acrylate-acrylonitrile-acrylamide-2-hydroxyethyl acrylate copolymer, where the molar percentages of lithium acrylate monomer, acrylonitrile monomer, acrylamide monomer, and 2-hydroxyethyl acrylate monomer are 35%:30%:15%:20%), negative electrode binder styrene-butadiene rubber, and thickener sodium carboxymethyl cellulose with a mass ratio of 96.5:0.5:0.5:1.5:1. The mass content of lithium element in the second lithium-containing binder is 9%, the Dv50 of the graphite particles is 11.8 μm, the graphite particles include artificial graphite and a carbon coating layer, the carbon coating layer covers the surface of the artificial graphite, and the mass content of the carbon coating layer is 3.5%.

[0560] 3. Separator

[0561] The separator includes a base film, and the base film is a 7-μm polyethylene film layer with a porosity of 42%.

[0562] 4. Preparation of electrolyte

[0563] The electrolyte includes organic solvents, lithium salts and additives.

[0564] The organic solvents include 48.5% chain carboxylic ester solvents (ethyl acetate) and 32.5% carbonate solvents (24.5% ethylene carbonate EC, 8% dimethyl carbonate). The mass contents of each component in the organic solvents are calculated based on the mass of the electrolyte.

[0565] 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.

[0566] The lithium salt includes 1 mol / L lithium hexafluorophosphate LiPF6.

[0567] The conductivity of the electrolyte at room temperature is 16.4 mS / cm.

[0568] 5. Preparation of battery cells

[0569] Stack the above-mentioned positive electrode sheet, separator, and negative electrode sheet in sequence, with the separator placed between the positive electrode sheet and the negative electrode sheet to play an isolation role. An electrode assembly is obtained through the stacking process. Place the electrode assembly in the outer packaging shell, inject the electrolyte after drying, and go through processes such as vacuum packaging, standing, formation, and shaping to obtain the battery cell. The compaction density of the positive electrode film layer of the battery cell at 100% SOC is 2.72 g / cm 3 .

[0570] Comparative Example 1-1, Examples 1-2 to 1-11

[0571] Battery cells were prepared using a method similar to that of Example 1-1. Different from Example 1-1, the composition of the first sub-layer was adjusted, etc., as shown in Table 1 specifically.

[0572] Performance test

[0573] 1. Number of cycles for the battery cell to cycle to 70% SOH

[0574] At room temperature, the battery cell was charged at a constant current of 1C to the charging cut-off voltage of 3.65V, and then discharged at a constant current of 1C to 2.0V. This is one charge-discharge cycle. Repeat the above charge-discharge cycle steps until the cycle capacity retention rate (i.e., Cn / C0×100%) is 70%, and record the number of cycles. The more the number of cycles, the better the cycle performance of the battery cell.

[0575] The test results are shown in Table 1.

[0576] Table 1

[0577]

[0578] In Table 1, the tabs are located on both sides of the current collector along the length direction.

[0579] The compaction density refers to the compaction density of the battery cell at 100% SOC.

[0580] The mass content of artificial graphite and the mass content of natural graphite are based on the mass of the negative active material in the first region.

[0581] In Comparative Example 1-1, the first region did not include natural graphite, the lithium deposition area of the battery cell was relatively large, and the cycle performance deteriorated; while in the embodiment of the present application, through the design of the first region, the first sub-layer in the first region includes artificial graphite and natural graphite, so that the fast charging performance of the first sub-layer is improved, the lithium deposition area is reduced, and the cycle performance is enhanced; and further by appropriately increasing the mass content of natural graphite, for example, increasing it to 5% to 45%, optionally 20% to 45%, as the mass content of natural graphite increases, the compaction density increases accordingly, and the lithium deposition risk can be further improved, and the cycle performance can be enhanced; while when the mass content of natural graphite is further increased, the cycle performance will deteriorate.

[0582] In the embodiment of the present application, by appropriately adjusting the distribution content of artificial graphite in the first sub-layer and the second sub-layer, the lithium deposition risk can be further improved and the cycle performance can be enhanced.

[0583] In the embodiment of the present application, by appropriately adjusting the volume average particle size Dv50 of natural graphite, for example, Dv50 is 12 μm, and its specific surface area is 2.1 m 2 / g, the cycle performance and lithium deposition risk of the battery cell can be improved. In the case where Dv50 is relatively small, for example, 8 μm, the charging ability of natural graphite is enhanced, and its specific surface area is relatively large, for example, 4.0 m 2 / g, and there are relatively more side reactions, resulting in relatively poor cycle performance; in the case where Dv50 is relatively large, for example, 15 μm, its specific surface area is relatively small, for example, 1.85 m 2 / g, the side reactions of natural graphite are less, and the cycle performance is optimized, but the charging ability is weakened. In the embodiment of the present application, by appropriately reducing the volume average particle size Dv50 of artificial graphite, for example, 7 μm to 15 μm, optionally 7 μm to 12 μm, the solid-phase transmission path is shorter, which is beneficial to improving the fast charging ability and reducing the lithium deposition risk. When the volume average particle size of artificial graphite is 11.8 μm, its specific surface area is 0.9 m 2 / g; when the volume average particle size of artificial graphite is 7 μm, its specific surface area is 2.6 m 2 / g.

[0584] In the embodiments of the present application, by appropriately increasing the mass content of the lithium-containing binder, it is beneficial to further improve the risk of lithium plating and enhance the cycling performance.

[0585] In the embodiments of the present application, the length ratio of the first region occupying the negative electrode film layer is 0.05 to 0.20, and can be optionally 0.10 to 0.20. As the size of the first region increases, the risk of lithium plating decreases, but due to the capacity decline, the cycling may deteriorate.

[0586] Example 2-1 (Wound battery cell)

[0587] A battery cell was prepared by a method similar to that of Example 1-1. Different from Example 1-1, the electrode assembly was prepared by a winding process to obtain the battery cell. Among them, the negative electrode film layer includes a first region and a second region, and the length ratio of the first region to the negative electrode film layer is 0.08.

[0588] Comparative Example 2-1, Examples 2-2 to 2-7

[0589] A battery cell was prepared by a method similar to that of Example 2-1. Different from Example 2-1, the composition of the first sub-layer was adjusted, etc., as shown in Table 2 specifically.

[0590] Table 2

[0591]

[0592] In Table 2, the tab is located on one side of the current collector.

[0593] The compaction density refers to the compaction density of the battery cell at 100% SOC.

[0594] The mass content of artificial graphite and the mass content of natural graphite are based on the mass of the negative electrode active material in the first region.

[0595] In Comparative Example 2-1, the first region does not include natural graphite, and the lithium plating area of the battery cell is large, and the cycling shows a significant decline; while in the embodiments of the present application, through the design of the first region, the first sub-layer in the first region includes artificial graphite and natural graphite, so that the fast charging performance of the first sub-layer is improved, the lithium plating area is reduced, and the cycling performance is enhanced; and further by appropriately increasing the mass content of natural graphite, for example, increasing it to 5% to 45%, and can be optionally 20% to 45%, as the mass content of natural graphite increases, the compaction density increases accordingly, and the risk of lithium plating can be further improved, and the cycling performance is enhanced; while when the mass content of natural graphite is further increased, the cycling will deteriorate.

[0596] In the embodiments of the present application, by appropriately increasing the mass content of the lithium-containing binder, it is beneficial to further improve the risk of lithium plating and enhance the cycling performance.

[0597] Although the illustrative embodiments have been shown and described, those skilled in the art should understand that the above embodiments should not be construed as limiting the present application, and changes, substitutions, and modifications can be made to the embodiments without departing from the spirit, principles, and scope of the present application.

Claims

1. A battery cell, characterized in that, Comprising an electrode assembly, the electrode assembly comprising: A positive electrode tab, including a positive current collector portion and a positive electrode film layer, the positive electrode film layer being disposed on at least one side of the positive current collector portion along the thickness direction of the positive current collector portion, the positive electrode film layer including a positive active material, the positive active material including a lithium-containing phosphate having an olivine structure; and A negative electrode tab, including a negative electrode tab, a negative current collector portion and a negative electrode film layer, the negative electrode film layer being disposed on at least one side of the negative current collector portion along the thickness direction of the negative current collector portion, the negative electrode film layer containing a negative active material, the negative electrode tab being connected to at least one side of the negative current collector portion along a first direction, the negative electrode film layer including two ends opposite to each other along the first direction, a first region including the end facing the negative electrode tab among the two ends, the ratio of the size of the first region along the first direction to the size of the negative electrode film layer along the first direction being 0.05 to 0.20, the negative active material in the first region including artificial graphite and natural graphite, the mass content of the natural graphite relative to the mass of the negative active material in the first region being 5% to 45%, wherein the first direction is perpendicular to the thickness direction.

2. The battery cell according to claim 1, wherein The mass content of the natural graphite relative to the mass of the negative active material in the first region is 20% to 45%.

3. The battery cell according to claim 1, characterized in that, The mass content of the artificial graphite relative to the mass of the negative active material in the first region is 55% to 95%.

4. The battery cell according to claim 1, characterized in that, The first region includes a first sub-layer and a second sub-layer, the first sub-layer being disposed on at least one side of the negative current collector portion, the second sub-layer being disposed on the side of the first sub-layer facing away from the negative current collector portion, the first sub-layer including artificial graphite and natural graphite, the second sub-layer including artificial graphite.

5. The battery cell according to claim 4, characterized in that, The mass content of the artificial graphite in the second sub-layer relative to the mass of the negative active material in the first region is 30% to 70%.

6. The battery cell according to claim 4, wherein, When the battery cell is in a 100% state of charge, the compaction density of the first sub-layer is greater than or equal to the compaction density of the second sub-layer.

7. The battery cell according to claim 4, wherein, When the battery cell is in a 100% state of charge, the tap density of the first sub-layer is 1.25 g / cm 3 to 1.65 g / cm 3 ; and / or, When the battery cell is in a 100% state of charge, the compaction density of the second sub-layer is 1.1 g / cm 3 to 1.5 g / cm 3 .

8. The battery cell according to claim 4, characterized in that, The first sub-layer includes a lithium-containing binder, the mass content of the lithium-containing binder relative to the mass of the first sub-layer being 0.1% to 3%; and / or, The second sub-layer includes a lithium-containing binder, the mass content of the lithium-containing binder relative to the mass of the second sub-layer being 0.1% to 3%.

9. The battery cell according to claim 8, wherein, The mass content of lithium element in the lithium-containing binder is 4% to 10%.

10. The battery cell according to claim 8, characterized in that, The lithium-containing binder includes a copolymer of lithium acrylate - acrylonitrile - acrylamide - 2 - hydroxyethyl acrylate, and the copolymer of lithium acrylate - acrylonitrile - acrylamide - 2 - hydroxyethyl acrylate is derived from lithium acrylate monomer, acrylonitrile monomer, acrylamide monomer and 2 - hydroxyethyl acrylate monomer, and the molar percentages of lithium acrylate monomer, acrylonitrile monomer, acrylamide monomer and 2 - hydroxyethyl acrylate monomer are 30% to 50%: 15% to 45%: 5% to 20%: 20% to 35%.

11. The battery cell according to claim 1, wherein, The volume average particle size Dv50 of the artificial graphite in the first region is 7 μm to 15 μm; and / or, The volume average particle size Dv50 of the natural graphite in the first region is 7 μm to 15 μm.

12. The battery cell according to claim 1, wherein, The specific surface area of natural graphite in the first region is greater than that of artificial graphite in the first region.

13. The battery cell according to claim 1, characterized in that, The specific surface area of natural graphite in the first region is 1.5 m 2 / g to 4.5 m 2 / g; and / or, The specific surface area of the artificial graphite in the first region is 0.7 m 2 / g to 3.0 m 2 / g.

14. The battery cell according to claim 1, wherein, The ratio of the dimension of the first region in the first direction to the dimension of the negative electrode film layer in the first direction is 0.10 to 0.

20.

15. The battery cell according to claim 1, wherein The electrode assembly is of a stacked structure, and the positive electrode plate and the negative electrode plate are stacked along the thickness direction.

16. The battery cell according to claim 15, wherein, The negative electrode tab is connected to both sides of the negative current collector in the first direction, and the first region includes two of the ends.

17. The battery cell according to claim 15, wherein, The negative electrode tab is connected to one side of the negative current collector in the first direction, and the first region is one of the two ends facing the negative electrode tab.

18. The battery cell according to claim 1, characterized in that, The electrode assembly is of a wound structure, and the positive electrode plate and the negative electrode plate are wound in one direction.

19. The battery cell according to claim 18, wherein, The negative electrode tab is connected to one side of the negative current collector in the first direction, and the first region includes one of the two ends facing the negative electrode tab.

20. The battery cell according to claim 1, characterized in that, After the battery cell is subjected to 500 cycles of charge and discharge, based on the surface area of the negative electrode film layer, the lithium deposition area of the negative electrode film layer is 0 to 13.5%.

21. The battery cell according to claim 1, characterized in that, The lithium deposition area of the negative electrode film layer is 0 to 6%.

22. The battery cell according to claim 1, characterized in that, The positive electrode plate further includes an insulating layer, the insulating layer is disposed on the positive current collector and connected to the positive electrode film layer, and the insulating layer is disposed opposite to the first region in the thickness direction.

23. The battery cell according to claim 1, wherein The negative electrode film layer further includes a second region continuously provided with the first region, and the second region includes: a first negative electrode film layer disposed on the surface of the negative current collector, the first negative electrode film layer including a carbon-based material, and a second negative electrode film layer connected to a side of the first negative electrode film layer facing away from the negative current collector, the second negative electrode film layer including 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, The graphite particles include artificial graphite and a carbon coating layer, the artificial graphite includes secondary particles, and the carbon coating layer coats the surface of the artificial graphite.

24. The battery cell according to claim 23, characterized in that, The graphitization degree of the graphite particles is 92.0% to 94.5%.

25. The battery cell according to claim 23, wherein Based on the mass of the graphite particles, the mass content of the carbon coating layer is 2% to 5%.

26. The battery cell according to claim 24, wherein The powder compaction density of the graphite particles under 20,000 N is 1.5 g / cm 3 to 1.85 g / cm 3 .

27. The battery cell according to claim 23, wherein When the battery cell is in a 100% state of charge, the tap density of the first negative electrode film layer is 1.15 g / cm 3 to 1.36 g / cm 3 , and / or When the battery cell is in a 100% state of charge, the compaction density of the second negative electrode film layer is 1.15 g / cm 3 to 1.36 g / cm 3 .

28. The battery cell according to claim 23, 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.

29. The battery cell according to claim 23, wherein, The first negative electrode film layer further includes a first lithium-containing binder, the second negative electrode film layer further includes a second lithium-containing binder, and the mass content of the first lithium-containing binder relative to the mass of the first negative electrode film layer is less than or equal to the mass content of the second lithium-containing binder relative to the mass of the second negative electrode film layer.

30. The battery cell according to claim 29, 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 3%, 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 3%.

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

32. The battery cell according to claim 29, wherein the first lithium-containing binder comprises a lithium acrylate-acrylonitrile-acrylamide-2-hydroxyethyl acrylate copolymer, the lithium acrylate-acrylonitrile-acrylamide-2-hydroxyethyl acrylate copolymer is derived from a lithium acrylate monomer, an acrylonitrile monomer, an acrylamide monomer and a 2-hydroxyethyl acrylate monomer, and the molar percentages of the lithium acrylate monomer, the acrylonitrile monomer, the acrylamide monomer and the 2-hydroxyethyl acrylate monomer are 30% to 50%: 15% to 45%: 5% to 20%: 20% to 35%, and / or the second lithium-containing binder comprises a lithium acrylate-acrylonitrile-acrylamide-2-hydroxyethyl acrylate copolymer, the lithium acrylate-acrylonitrile-acrylamide-2-hydroxyethyl acrylate copolymer is derived from a lithium acrylate monomer, an acrylonitrile monomer, an acrylamide monomer and a 2-hydroxyethyl acrylate monomer, and the molar percentages of the lithium acrylate monomer, the acrylonitrile monomer, the acrylamide monomer and the 2-hydroxyethyl acrylate monomer are 30% to 50%: 15% to 45%: 5% to 20%: 20% to 35%.

33. 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 .

34. The battery cell according to claim 1, wherein, The negative electrode sheet further comprises a negative electrode conductive layer, and the negative electrode conductive layer is located between the negative electrode film layer and the negative electrode current collector portion.

35. The battery cell according to claim 34, wherein The thickness of the negative electrode conductive layer is 0.1 μm to 2 μm.

36. The battery cell according to claim 34, wherein The negative electrode conductive layer comprises a negative electrode conductive agent, and the negative electrode conductive agent comprises one or more of superconducting carbon, conductive graphite, acetylene black, Ketjen black, carbon dots, carbon nanotubes, graphene and carbon nanofibers, and / or The negative electrode conductive layer comprises a negative electrode binder, and the negative electrode binder comprises one or more of styrene-butadiene rubber, water-based acrylic resin, polyvinyl alcohol, sodium alginate and carboxymethyl chitosan.

37. 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 , and / or 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 .

38. 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 2.55 g / cm 3 to 2.70 g / cm 3 , and / or 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 .

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

40. The battery cell according to claim 1, wherein the olivine-structured lithium-containing phosphate comprises: 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.

41. The battery cell according to claim 40, characterized in that, 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 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 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.

42. The battery cell according to claim 40 or 41, characterized in that, The coating layer comprises a fast ion conductor with the general formula Li 3- d Fe 2-d M2 d (PO x2 ) y2 , where M2 comprises one or more elements of Ti, Zr, Hf, Ge, and Sn, 0 ≤ d ≤ 1, 0 < x2 < 5, and 0 < y2 < 4.

43. The battery cell according to claim 40, characterized in that, The graphitization degree of the olivine-structured lithium-containing phosphate is 0.15 to 0.

32.

44. The battery cell according to claim 40, wherein The mass content of carbon element in the olivine-structured lithium-containing phosphate 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.

45. The battery cell according to claim 40, characterized in that, The specific surface area of the lithium-containing phosphate with olivine structure is 7.5 m 2 / g to 14 m 2 / g.

46. The battery cell according to claim 1, characterized in that, the olivine-structured lithium-containing phosphate is in a granular shape, and its volume distribution particle size satisfies: 1 µm ≤ Dv50 ≤ 2 µm, 0.4 µm ≤ Dv10 ≤ 0.7 µm.

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

48. 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 portion.

49. The battery cell according to claim 48, wherein, The thickness of the positive electrode conductive layer is 0.1 μm to 2 μm.

50. The battery cell according to claim 48, 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, 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.

51. The battery cell according to claim 1, characterized in that, The charging time of the battery monomer from 10% state of charge to 80% state of charge is 5 min to 10.5 min.

52. A battery device, characterized in that, It includes a plurality of battery monomers as described in any one of claims 1 to 51.

53. The battery device according to claim 52, characterized in that, The charging time of the battery device from 10% state of charge to 80% state of charge is 5 min to 10.5 min.

54. An electrical device, characterized in that, It includes the battery device as described in claim 52.

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