Battery cell, battery device and electric device

Abstract

The present application relates to a battery cell, a battery device and an electric device. The battery cell comprises an electrode assembly; the electrode assembly comprises a positive electrode sheet and a negative electrode sheet; the positive electrode sheet comprises a positive electrode current collecting portion and a positive electrode film layer; the positive electrode film layer comprises a positive electrode active material; the positive electrode active material comprises a lithium-containing phosphate having an olivine structure; the negative electrode sheet comprises a negative electrode current collecting portion and a negative electrode film layer; a negative electrode tab is connected to at least one side of the negative electrode current collecting portion in a first direction; the negative electrode film layer comprises two end portions which are opposite to each other in the first direction; a first region comprises one of the two end portions facing the negative electrode tab; 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; a negative electrode active material in the first region comprises artificial graphite and natural graphite; and 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

Battery cells, battery packs and electrical devices Technical Field

[0001] This application relates to a battery cell, a battery device, and an electrical device. Background Technology

[0002] Lithium-ion batteries are widely used in electronic devices such as mobile phones, laptops, electric vehicles, electric cars, electric airplanes, electric ships, and power tools due to their high capacity and long lifespan. With the development of lithium-ion battery applications, higher demands are being placed on their performance, such as cycle life and reliability.

[0003] Summary of the Invention

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

[0005] In a first aspect, this application proposes a battery cell, which includes an electrode assembly comprising a positive electrode and a negative electrode. The positive electrode includes a positive current collector and a positive electrode film. The positive electrode film is disposed on at least one side of the positive current collector along its thickness direction and includes a positive active material, which includes a lithium phosphate with an olivine structure. The negative electrode includes a negative electrode tab, a negative current collector, and a negative electrode film. The negative electrode film is disposed on at least one side of the negative current collector along its thickness direction and contains a negative active material. The negative electrode tab is connected to at least one side of the negative current collector along a first direction. The negative electrode film 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. The ratio of the size of the first region along the first direction to the size of the negative electrode film along the first direction is 0.05 to 0.20. The negative active material of the first region includes artificial graphite and natural graphite, wherein the first direction is perpendicular to the thickness direction.

[0006] Therefore, in the embodiments of this application, the lithium plating area of ​​the battery cell is small or even non-existent after cyclic charging and discharging, which significantly improves the reliability of the battery cell and also improves the cycle performance of the battery cell.

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

[0008] In some embodiments, the mass content of artificial graphite relative to the negative electrode active material in the first region is 55% to 95%, which can further improve the reliability and cycle 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, and the second sub-layer is disposed on the side of the first sub-layer opposite to the negative electrode current collector. The first sub-layer includes artificial graphite and natural graphite, and the second sub-layer includes artificial graphite, which is beneficial to improving fast charging capability.

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

[0011] In some embodiments, when a battery cell is 100% charged, the compaction density of the first sublayer is greater than or equal to the compaction density of the second sublayer. In the embodiments of this application, the larger compaction density of the first sublayer and the smaller compaction density of the second sublayer can improve the tortuosity of the first region, thereby improving the charging process, especially the concentration polarization phenomenon during fast charging, and reducing the risk of lithium plating in the first region.

[0012] In some embodiments, the compaction density of the first sublayer of the battery cell at 100% charge is 1.25 g / cm³. 3 Up to 1.65 g / cm 3 .

[0013] In some embodiments, the compaction density of the second sublayer of the battery cell at 100% charge is 1.1 g / cm³. 3 Up to 1.5g / cm 3 .

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

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

[0016] In some embodiments, the lithium-containing binder contains 4% to 10% lithium by mass.

[0017] In some embodiments, the lithium-containing binder comprises a lithium acrylate-acrylonitrile-acrylamide-hydroxyethyl acrylate copolymer, which is derived from lithium acrylate monomer, acrylonitrile monomer, acrylamide monomer and hydroxyethyl acrylate monomer, wherein the molar percentages of lithium acrylate monomer, acrylonitrile monomer, acrylamide monomer and 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 implementations, the specific surface area of ​​natural graphite in the first region is greater than that of artificial graphite in the first region, which is beneficial to improving fast charging performance.

[0021] In some implementations, the specific surface area of ​​natural graphite in the first region is 1.5 m². 2 / g to 4.5m 2 / g.

[0022] In some implementations, the specific surface area of ​​the artificial graphite in the first region is 0.7 m². 2 / g to 3.0m 2 / g.

[0023] In some embodiments, 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, optionally 0.10 to 0.20. When the proportion of the first region is within the above range, the risk of lithium plating is relatively low, which can further improve the cycle performance and reliability of the battery cell.

[0024] In some embodiments, the electrode assembly has a stacked structure, with positive and negative electrode sheets stacked along the thickness direction.

[0025] In some embodiments, the electrode assembly has a stacked structure, with the negative electrode tab connected to both sides of the negative electrode current collector along a first direction, and the first region including two ends.

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

[0027] In some implementations, the electrode assembly has a wound structure, with the positive and negative electrode sheets wound in one direction.

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

[0029] In some implementations, after 500 charge-discharge cycles of a single battery cell, the lithium plating area of ​​the negative electrode film is 0 to 13.5%, optionally 0 to 6%, based on the surface area of ​​the negative electrode film.

[0030] In some embodiments, the positive electrode sheet further includes an insulating layer disposed on the positive current collector and connected to the positive electrode film layer. The insulating layer and the first region are disposed opposite each other along the thickness direction. The insulating layer can further reduce the risk of lithium plating.

[0031] In some embodiments, the negative electrode film layer further includes a second region, which is continuously disposed with the first region. 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 electrode current collector and includes a carbon-based material. The second negative electrode film layer is connected to the side of the first negative electrode film layer away from the negative electrode current collector and also includes a carbon-based material. The carbon-based material in the first negative electrode film layer and the carbon-based material in the second negative electrode film layer each independently include graphite particles, and the volume average particle size Dv50 of the graphite particles in the first negative electrode film layer is greater than or equal to the volume average particle size Dv50 of the graphite particles in the second negative electrode film layer. 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] Therefore, the particle size difference between the first negative electrode film layer and the second negative electrode film layer in the embodiments of this application can improve the fast charging performance of the battery cell. Specifically, during fast charging, the overpotential of the second negative electrode film layer is usually higher, and the bottleneck of fast charging is mainly in the second negative electrode film layer. However, in the embodiments of this application, the particle size of the second negative electrode film layer is relatively small, which can shorten the solid-phase transport path of lithium ions, improve fast charging performance, and improve the problem of lithium deposition on the surface of the negative electrode sheet.

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

[0034] In some embodiments, the carbon coating content is 2% to 5% by mass, based on the mass of the graphite particles. When the carbon coating content is within the above range, the internal resistance of the negative electrode sheet can be further reduced, and the heat generation of the battery cell can be reduced.

[0035] In some embodiments, the powder compaction density of graphite particles at 20000 N is 1.5 g / cm³. 3Up to 1.85 g / cm 3 When the powder compaction density of graphite particles at 20000N is within the above range, it can improve the energy density of the battery cell. Furthermore, because the negative electrode active material in the negative electrode film can be stacked more tightly, the contact resistance between particles is smaller, which can further reduce the resistance of the electrode sheet, thereby reducing heat generation.

[0036] In some embodiments, the compaction density of the first negative electrode film layer is 1.15 g / cm³ when the battery cell is 100% charged. 3 Up to 1.36 g / cm 3 .

[0037] In some embodiments, the compaction density of the second negative electrode film layer is 1.15 g / cm³ when the battery cell is 100% charged. 3 Up to 1.36 g / cm 3 .

[0038] In some embodiments, the volume average particle size Dv50 of the graphite particles in the first negative electrode film layer is 9.5 μm to 18.5 μm. When the volume average particle size Dv50 of the negative electrode active material in the first negative electrode film layer is within the above range, the fast charging performance can be improved.

[0039] In some embodiments, the volume average particle size Dv50 of the graphite particles in the second negative electrode film is between 7.8 μm and 14.3 μm. When the volume average particle size Dv50 of the negative electrode active material in the second negative electrode film is within the above range, the lithium-ion transport tortuosity can be reduced, thereby improving the fast charging performance of the battery cell.

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

[0041] Therefore, in the embodiments of this application, the mass content of the second lithium-containing binder in the second negative electrode film layer is relatively high, and the second lithium-containing binder provides a relatively larger number of freely movable lithium ions for the second negative electrode film layer, 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 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, it can improve the lithium-ion insertion / extraction rate and improve the fast charging performance of the battery cell.

[0043] In some embodiments, the mass content of the second lithium-containing binder relative to the second negative electrode film layer is 0.1% to 3%. When the mass content of lithium in the second lithium-containing binder is within the above range, the lithium-ion insertion / extraction rate is increased, thereby improving the fast charging performance of the battery cell.

[0044] In some embodiments, the lithium content in the first lithium-containing binder is 3% to 10% by mass. When the lithium content is within the above range, the number of freely moving lithium ions in the negative electrode film layer is relatively large, which can further shorten the distance of lithium ions to diffuse to the surface of the negative electrode film layer, improve the lithium ion insertion / extraction rate, and improve the fast charging performance of the battery cell.

[0045] In some embodiments, the lithium content in the second lithium-containing binder is 3% to 10% by mass. When the lithium content is within the above range, the number of freely moving lithium ions in the negative electrode film layer is relatively large, which can further shorten the distance for lithium ions to diffuse to the surface of the negative electrode film layer, improve the lithium ion insertion / extraction rate, and improve the fast charging performance of the battery cell.

[0046] In some embodiments, the first lithium-containing binder comprises a lithium acrylate-acrylonitrile-acrylamide-hydroxyethyl acrylate copolymer, which is derived from lithium acrylate monomer, acrylonitrile monomer, acrylamide monomer and hydroxyethyl acrylate monomer. The molar percentages of lithium acrylate monomer, acrylonitrile monomer, acrylamide monomer and hydroxyethyl acrylate monomer are 30% to 50%: 15% to 45%: 5% to 20%: 20% to 35%. Thus, the lithium-containing binder of the above material can provide a certain number of lithium ions to the negative electrode film layer, improve the fast charging performance of the battery cell, and is not prone to swelling during charging and discharging, with a stable structure, thereby improving the cycle performance of the negative electrode film layer during fast charging and discharging.

[0047] In some embodiments, the second lithium-containing binder comprises a lithium acrylate-acrylonitrile-acrylamide-hydroxyethyl acrylate copolymer, which is derived from lithium acrylate monomer, acrylonitrile monomer, acrylamide monomer and hydroxyethyl acrylate monomer, wherein the molar percentages of lithium acrylate monomer, acrylonitrile monomer, acrylamide monomer and hydroxyethyl acrylate monomer are 30% to 50%: 15% to 45%: 5% to 20%: 20% to 35%.

[0048] Therefore, the lithium-containing binder of the above material can provide a certain number of lithium ions to the negative electrode film layer, improve the fast charging performance of the battery cell, and is not prone to swelling during charging and discharging, with a stable structure, which improves the cycle performance of the negative electrode film layer during fast charging and discharging.

[0049] In some embodiments, the single-sided coating weight of the negative electrode film is 90 mg / 1540.25 mm. 2 Up to 170mg / 1540.25mm 2 When the single-sided coating weight of the negative electrode film is within the above range, the heat generation per unit area of ​​the negative electrode sheet will not be too large, and the energy density of the battery cell can be improved at the same time.

[0050] In some embodiments, the negative electrode sheet 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 sheet and reduce the heat generation of the negative electrode sheet, thereby reducing the heat generation of the battery cell.

[0051] In some embodiments, the thickness of the negative electrode conductive layer is from 0.1 μm to 2 μm. The negative electrode conductive layer can further improve the conductivity of the negative electrode sheet and reduce the heat generation of the negative electrode sheet, thereby reducing the heat generation of the battery cell.

[0052] In some embodiments, the negative electrode conductive layer includes a negative electrode conductive agent, which may be one or more selected from 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 sheet and reducing the heat generation of the battery cell.

[0053] In some embodiments, the negative electrode conductive layer includes a negative electrode binder, which may be 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 adhesion between the negative electrode current collector and the negative electrode film layer, thereby enhancing the structural stability of the negative electrode sheet.

[0054] In some embodiments, the compaction density of the positive electrode film layer is 2.50 g / cm³ when the battery cell is 100% charged. 3 Up to 2.80 g / cm 3 When the compaction density of the positive electrode film is within the above range, it is beneficial to improve the energy density of the battery cell. Furthermore, since the positive electrode active material in the positive electrode film is packed more tightly, the contact resistance between particles is smaller, which can further reduce the resistance of the electrode sheet, thereby reducing heat generation.

[0055] In some embodiments, the single-sided coating weight of the positive electrode film is 200 mg / 1540.25 mm. 2 Up to 370mg / 1540.25mm 2 When the single-sided coating weight of the positive electrode film 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 at the same time.

[0056] In some embodiments, the compaction density of the positive electrode film layer is 2.55 g / cm³ when the battery cell is 100% charged. 3 Up to 2.70 g / cm 3 When the compaction density of the positive electrode film is within the above range, it is beneficial to improve the energy density of the battery cell. Furthermore, since the positive electrode active material in the positive electrode film is packed more tightly, the contact resistance between particles is smaller, which can further reduce the resistance of the electrode sheet, thereby reducing heat generation.

[0057] In some embodiments, the single-sided coating weight of the positive electrode film is 240 mg / 1540.25 mm. 2 Up to 330mg / 1540.25mm 2 When the single-sided coating weight of the positive electrode film 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 at the same time.

[0058] In some embodiments, the powder compaction density of the positive electrode active material at 30000 N is 2.46 g / cm³. 3 Up to 2.8 g / cm 3 When the powder compaction density of the positive electrode active material at 30000N is within the above range, it can improve the energy density of the battery cell. Furthermore, because the positive electrode active material in the positive electrode film can be stacked more tightly, the contact resistance between particles is smaller, which can further reduce the resistance of the electrode sheet, thereby reducing heat generation.

[0059] In some embodiments, the olivine-structured lithium phosphate comprises phosphate particles and a coating layer. The coating layer coats the phosphate particles and contains one or more elements selected from C, Fe, Ti, Zr, Hf, Ge, and Sn. The surface coating of the phosphate particles enhances the conductivity of the olivine-structured lithium phosphate, reduces the powder resistivity of the material, and facilitates the migration rate of lithium ions, thereby reducing the heat generation of the battery cell.

[0060] In some embodiments, the phosphate particles comprise the general formula Li x1 A y1 Me a M b P 1-c X c Y zThe compound contains 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, where 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. Phosphate particles exhibit excellent cycle stability, which is beneficial for improving the cycle performance of battery cells.

[0061] In some embodiments, the coating layer includes a general formula 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, where 0 ≤ d ≤ 1, 0 < x2 < 5, and 0 < y2 < 4. Coating the phosphate particles with the fast ion conductor can significantly improve the lithium-ion transport rate during multiple lithium intercalation / deintercalation at the positive electrode, enhance the ionic conductivity of the positive electrode active material, thereby increasing the specific capacity and, further, improving the energy density of the corresponding battery cell.

[0062] In some embodiments, the degree of graphitization of the positive electrode active material is 0.15 to 0.32, optionally 0.19 to 0.26. When the degree of graphitization of the positive electrode active material is within the above range, it is beneficial to improve the conductivity of the positive electrode active material, reduce the heat generation of the positive electrode sheet, and thus reduce the heat generation of the battery cell.

[0063] In some embodiments, the carbon content in the olivine-structured lithium phosphate is 1% to 2% by mass, and the specific surface area of ​​the olivine-structured lithium phosphate is 5 m². 2 / g to 18m 2 / g, optional 7.5m 2 / g to 14m 2 / g.

[0064] Therefore, the carbon content of the above-mentioned mass content in the embodiments of this application, combined with the material with the above-mentioned specific surface area, is more conducive to the effective contact between the electrolyte and the lithium phosphate with olivine structure, and is conducive to the transport of lithium ions at the phase interface.

[0065] In some embodiments, the olivine-structured lithium phosphate is in particulate form, with a volume distribution particle size satisfying: 1μm≤Dv50≤2μm, 0.4μm≤Dv10≤0.7μm. The relatively small particle size of the olivine-structured lithium phosphate results in a shorter lithium ion insertion / extraction pathway in the cathode active material, less heat generation, and the particle size of the cathode active material is not excessively small, thus preventing agglomeration during processing and preparation, thereby ensuring stable performance of the cathode active material.

[0066] In some embodiments, the olivine-structured lithium phosphate is particulate, comprising secondary particles, which in turn include multiple primary particles. The average particle size of the primary particles is 200 nm to 500 nm. The relatively small average particle size of the primary particles results in a shorter lithium ion insertion / extraction pathway in the positive electrode active material, leading to less heat generation.

[0067] In some embodiments, the positive electrode film layer further includes one or more of the following: ternary materials, lithium phosphate, lithium hydrogen phosphate, lithium sulfate, lithium sulfite, lithium molybdate, lithium oxalate, lithium titanate, lithium tetraborate, lithium metasilicate, lithium metamanganese oxide, lithium tartrate, lithium trilithium citrate, lithium nickel oxide, and lithium ferrite. These materials can replenish lithium ions to the positive electrode film layer, compensate for irreversible lithium ion loss within the system, increase capacity, and thereby improve 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 this range, the current-carrying capacity of the positive electrode current collector is excellent, and the battery cell can have a high energy density.

[0069] In some embodiments, the positive electrode further includes a positive conductive layer located between the positive electrode film and the positive current collector. The positive conductive layer can further improve the conductivity of the positive electrode and reduce the heat generation of the positive electrode, thereby reducing the heat generation of the battery cell.

[0070] In some embodiments, the thickness of the positive electrode conductive layer is from 0.1 μm to 2 μm. When the thickness of the positive electrode conductive layer is within the above range, the conductivity of the positive electrode sheet can be further improved, the heat generation of the positive electrode sheet can be reduced, thereby reducing the heat generation of the battery cell, and at the same time, the energy density of the battery cell can be improved.

[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 sheet and reducing the heat generation of the battery cell. The positive electrode binder in the positive electrode conductive layer can improve the adhesion between the positive electrode current collector and the positive electrode film layer, thereby improving the structural stability of the positive electrode sheet.

[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 implementations, the charging time for a single battery cell from 10% state of charge to 80% state of charge is 5 to 10.5 minutes. The faster charging speed of the battery cell is more conducive to improving fast charging capability.

[0075] Secondly, this application proposes a battery device comprising a plurality of battery cells according to any embodiment of the first aspect of this application.

[0076] In some implementations, the charging time for the battery device from 10% state of charge to 80% state of charge is 5 to 10.5 minutes. A faster charging speed improves the device's fast-charging capability.

[0077] Thirdly, this application proposes an electrical device, which includes the battery device according to any embodiment of the second aspect of this application. Attached Figure Description

[0078] To more clearly illustrate the technical solutions of the embodiments of this application, the drawings used in the embodiments of this application will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on the drawings without creative effort.

[0079] Figure 1 is a schematic diagram of the structure of a battery cell provided in some embodiments of this application.

[0080] Figure 2 is an exploded schematic diagram of a battery cell provided in some embodiments of this application.

[0081] Figure 3 is a schematic diagram of the structure of the electrode assembly of a battery cell provided in some embodiments of this application;

[0082] Figure 4 is a schematic diagram of the structure of the negative electrode sheet of the electrode assembly provided in some embodiments of this application;

[0083] Figure 5 is a schematic diagram of the structure of the negative electrode sheet of the electrode assembly provided in some other embodiments of this application;

[0084] Figure 6 is a schematic diagram of the structure of the negative electrode sheet of the electrode assembly provided in some other embodiments of this application;

[0085] Figure 7 is a schematic diagram of the structure of the positive electrode sheet of the electrode assembly provided in some embodiments of this application;

[0086] Figure 8 is a schematic diagram of the structure of the electrode assembly of a battery cell provided in some other embodiments of this application;

[0087] Figure 9 is a schematic diagram of the unfolded structure of the negative electrode sheet of the electrode assembly provided in some embodiments of this application;

[0088] Figure 10 is a schematic diagram of the structure of a battery module provided in some embodiments of this application.

[0089] Figure 11 is a schematic diagram of the structure of a battery pack provided in some embodiments of this application.

[0090] Figure 12 is a schematic diagram of the structure of an electrical device provided in some embodiments of this application.

[0091] The accompanying drawings may not be drawn to scale.

[0092] The reference numerals in the attached drawings are explained as follows: X, thickness direction; Y, first direction; Z, second direction; 1, electrical device; 2, battery pack; 3, controller; 4, motor; 5, housing; 5a, first housing section; 5b, second housing section; 5c, accommodating space; 6, battery module; 7, battery cell; 10, electrode assembly; 111, positive electrode tab; 112, negative electrode tab; 12, main body section; 13, positive electrode sheet; 131, positive current collector; 132, positive electrode film layer; 133, insulating layer; 14, negative electrode sheet; 140, first region; 1401, first sublayer; 1402, second sublayer; 141, negative current collector; 142, negative electrode film layer; 145, first negative electrode film layer; 146, second negative electrode film layer; 147, second region; 15, separator; 20. Outer shell; 21. Housing; 22. End cap; 31. Positive terminal; 32. Negative terminal. Detailed Implementation

[0093] The following detailed description, with appropriate reference to the accompanying drawings, specifically discloses embodiments of the battery cell, battery device, and power-consuming device of this application. However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of practically identical structures may be omitted. This is to avoid unnecessarily lengthy descriptions and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided to enable those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0094] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of the particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; 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 also expected that ranges of 60 to 110 and 80 to 120 are also included. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1 to 3, 1 to 4, 1 to 5, 2 to 3, 2 to 4, and 2 to 5. In this application, unless otherwise stated, the numerical range "a to b" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0 to 5" means that all real numbers between "0 and 5" have been listed in this article; "0 to 5" is just a shortened representation of these numerical combinations. In addition, when a parameter is stated as an integer ≥ 2, it is equivalent to disclosing that the parameter is, for example, an integer 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0095] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0096] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0097] Unless otherwise specified, all steps of this application may be performed sequentially or randomly, preferably sequentially. For example, if the method includes steps (a) and (b), it means that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, if the method may also include step (c), it means that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0098] During the charging process of a battery cell, lithium ions in the positive electrode are released and migrate to the negative electrode to gain electrons and form lithium metal. During this process, some lithium ions may not be embedded in the negative electrode in time, leading to the precipitation of lithium dendrites on the surface of the negative electrode. These dendrites may puncture the separator, causing a short circuit between the positive and negative electrodes and deteriorating the reliability of the battery cell. Furthermore, because lithium dendrites occupy the gaps between the electrodes, the expansion force of the battery cell increases, worsening its cycle life. As the charging rate of the battery cell increases, the risk of lithium deposition increases, further deteriorating the reliability of the battery cell and shortening its cycle life.

[0099] In view of this, the embodiments of this application rationally design the system of the battery cell so that the battery cell basically does not deposit lithium after cycling, or the lithium deposit area is small, which significantly improves the reliability of the battery cell and also improves the cycle life of the battery cell.

[0100] battery cell

[0101] In one aspect, this application proposes a battery cell.

[0102] As shown in Figures 1 to 4, the battery cell 7 includes an electrode assembly 10, which includes a positive electrode 13 and a negative electrode 14. The positive electrode 13 includes a positive current collector 131 and a positive electrode film 132. The positive electrode film 132 is disposed on at least one side of the positive current collector 131 along the thickness direction X of the positive current collector 131, and includes a positive active material, which includes a lithium phosphate with an olivine structure. The negative electrode 14 includes a negative electrode tab 112, a negative current collector 141, and a negative electrode film 142. The negative electrode film 142 is disposed on... The negative electrode current collector 141 has at least one side along its thickness direction and contains a negative electrode active material. The negative electrode film layer 142 includes a first region 140 and two ends opposite each other along a first direction Y. The first region 140 includes one of the two ends facing the negative electrode tab 112. 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. The negative electrode active material of 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 located between the positive electrode 13 and the negative electrode 14.

[0103] Optionally, the negative electrode film layer 142 includes a first region 140 and a second region 147, and the first region 140 and the second region 147 are continuously arranged. It can be understood that all regions in the negative electrode film layer 142 other than the first region 140 are the second region.

[0104] In this embodiment, the end of the negative electrode film layer 142 refers to the end of the negative electrode film layer 142 along 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.

[0105] Since the current density is higher near the negative electrode tab 112, the risk of lithium plating is higher. In this embodiment, the risk of lithium plating in the first region 140 is reduced by a specific design. Specifically, the first region 140 includes artificial graphite and natural graphite. The combination of artificial graphite and natural graphite is beneficial to increase the diffusion channels of lithium ions, improve the charging capacity of the first region 140, and reduce the risk of lithium plating.

[0106] In some embodiments, the mass content of natural graphite relative to the negative electrode active material in the first region 140 is 5% to 45%, optionally 20% to 45%, for example 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, or any combination of two of the above values. A mass content of natural graphite within the above range is more conducive to improving fast charging capability and further reducing the risk of lithium plating.

[0107] In some embodiments, the mass content of artificial graphite relative to the negative electrode active material in the first region is 55% to 95%, for example, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, or any combination of two of the above values.

[0108] 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, preferably 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 opposite to the negative electrode current collector 141. The double-layer configuration helps reduce the risk of film cracking, improves the stability of the film structure, and further enhances the fast charging capability.

[0109] 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, preferably 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 141, and the second negative electrode film layer 146 is disposed on the side of the first negative electrode film layer 145 opposite to the negative electrode current collector 141. The double-layer configuration helps reduce the risk of film cracking, improves the stability of the film structure, and further enhances the fast charging capability.

[0110] In some embodiments, the negative electrode active material of the first sublayer 1401 includes natural graphite and artificial graphite. Natural graphite has a relatively large specific surface area, which is beneficial to increase the diffusion channels of lithium ions, improve the charging capacity of the first region 140, and reduce the risk of lithium plating.

[0111] In some embodiments, the negative electrode active material of the second sublayer 1402 includes artificial graphite, which is beneficial for improving fast charging capability.

[0112] In some embodiments, the mass content of artificial graphite in the second sublayer 1402 relative to the mass of the negative electrode active material in the first region 140 is 30% to 70%, for example, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, or any combination of two of the above values.

[0113] In some embodiments, when the battery cell 7 is 100% charged, the compaction density of the first sublayer 1401 is greater than or equal to the compaction density of the second sublayer 1402.

[0114] When the first region 140 uses a thicker coating, severe concentration polarization is likely to occur. However, in the embodiments of this application, the first sublayer 1401 has a larger compaction density and the second sublayer 1402 has a smaller compaction density, 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 plating in the first region 140.

[0115] Optionally, when the battery cell 7 is at 100% charge, the compaction density of the first sublayer 1401 is 1.25 g / cm³. 3 Up to 1.65 g / cm 3 For example, 1.25 g / cm³ 3 1.3g / cm 3 1.35g / cm 3 1.4g / cm 3 1.45g / cm 3 1.5g / cm 3 1.55g / cm 31.6g / cm 3 1.65g / cm 3 Or a range consisting of any two of the above values.

[0116] Optionally, when the battery cell 7 is at 100% charge, the compaction density of the second sublayer 1402 is 1.1 g / cm³. 3 Up to 1.5g / cm 3 For example, 1.1 g / cm³ 3 1.15g / cm 3 1.2g / cm 3 1.25g / cm 3 1.3g / cm 3 1.35g / cm 3 1.4g / cm 3 1.45g / cm 3 1.5g / cm 3 Or a range consisting of any two of the above values.

[0117] In some embodiments, the first region 140 includes a lithium-containing binder, wherein the lithium content of the lithium element in the lithium-containing binder is 4% to 10% by mass, for example 4%, 4.5%, 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 8%, 8.5%, 9%, 9.5%, 10%, or any combination of two of the above values.

[0118] 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 the low-temperature and room-temperature kinetic performance, and can also improve the fast charging performance of the battery cell 7 and reduce the risk of lithium plating.

[0119] For example, the lithium-containing binder includes a lithium acrylate-acrylonitrile-acrylamide-hydroxyethyl acrylate copolymer, which is derived from lithium acrylate monomer, acrylonitrile monomer, acrylamide monomer and hydroxyethyl acrylate monomer, wherein the molar percentages of lithium acrylate monomer, acrylonitrile monomer, acrylamide monomer and hydroxyethyl acrylate monomer are 30% to 50%: 15% to 45%: 5% to 20%: 20% to 35%.

[0120] In some embodiments, the first sublayer 1401 includes a lithium-containing binder, the lithium-containing binder having a mass content of 0.1% to 3% relative to the mass of the first sublayer, such as 0.1%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, or any combination of two of the above values.

[0121] In some embodiments, the second sublayer 1402 includes a lithium-containing binder, the lithium-containing binder having a mass content of 0.1% to 3% relative to the mass of the second sublayer, such as 0.1%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, or any combination of two of the above values.

[0122] In some embodiments, the volume average particle size Dv50 of the artificial graphite in the first region 140 is 7 μm to 15 μm, for example 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm or any combination of two of the above values.

[0123] Optionally, the volume average particle size Dv50 of the artificial graphite in the first sublayer 1401 is 7 μm to 15 μm, for example, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm or any combination of two of the above values.

[0124] Optionally, the volume average particle size Dv50 of the artificial graphite in the second sublayer 1402 is 7 μm to 15 μm, for example, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm or any combination of two of the above values.

[0125] In some embodiments, the volume average particle size Dv50 of the natural graphite in the first region 140 is from 7 μm to 15 μm, for example, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, or any combination of two of the above values. When the volume average particle size Dv50 of the artificial graphite is within the above range, it can improve fast charging capability and reduce the risk of lithium plating.

[0126] Optionally, the volume average particle size Dv50 of the negative electrode active material of the second sublayer 1402 is less than or equal to the volume average particle size Dv50 of the negative electrode active material of the first sublayer 1401.

[0127] During the charging process of 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 of the second sublayer 1402 is small, and the solid phase transport capability is strong, which can improve the fast charging capability and increase the anode potential of the second sublayer 1402, reducing the risk of lithium plating in this region.

[0128] In some implementations, the specific surface area of ​​natural graphite in the first region 140 is greater than that of artificial graphite in the first region 140, which is beneficial to improving fast charging performance.

[0129] In some embodiments, the specific surface area of ​​natural graphite in the first sublayer 1401 is greater than that of artificial graphite in the first sublayer 1401, which is beneficial to improving fast charging performance.

[0130] Optionally, the specific surface area of ​​the natural graphite in the first sublayer 1401 is 1.5 m². 2 / g to 4.5m 2 / g, for example 1.5m 2 / g, 1.6m 2 / g, 1.7m 2 / g, 1.8m 2 / g, 1.9m 2 / g, 2.0m 2 / g、2.1m 2 / g, 2.2m 2 / g, 2.3m 2 / g, 2.4m 2 / g, 2.5m 2 / g, 2.6m 2 / g, 3.0m 2 / g, 3.5m 2 / g, 4.0m 2 / g, 4.5m 2 / g or a range consisting of any two of the above values.

[0131] Optionally, the specific surface area of ​​the artificial graphite in the first sublayer 1401 is 0.7 m². 2 / g to 3.0m 2 / g; for example, 0.7m 2 / g, 0.8m 2 / g, 0.9m 2 / g, 1.0m 2 / g, 1.1m 2 / g, 1.2m 2 / g, 1.5m 2 / g, 1.8m 2 / g, 2.0m 2 / g, 2.5m 2 / g, 3.0m 2 / g or a range consisting of any two of the above values.

[0132] Optionally, the specific surface area of ​​the artificial graphite in the second sublayer 1402 is 0.7 m². 2 / g to 3.0m 2 / g; for example, 0.7m 2 / g, 0.8m 2 / g, 0.9m 2 / g, 1.0m 2 / g, 1.1m 2 / g, 1.2m 2 / g, 1.5m 2 / g, 1.8m 2 / g, 2.0m 2 / g, 2.5m 2 / g, 3.0m 2 / g or a range consisting of any two of the above values.

[0133] In the embodiments of this application, all other parameters not mentioned in the first region can be the same as the parameters in the second region.

[0134] The embodiments of this application can effectively reduce the lithium plating area by specifically designing the first region. In some embodiments, after 500 charge-discharge cycles of the battery cell 7, the lithium plating area of ​​the negative electrode film is 0 to 13.5% based on the surface area of ​​the negative electrode film, for example, 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 a range of any two of the above values.

[0135] With a lithium plating area of ​​less than or equal to 13.5%, the lithium plating area of ​​battery cell 7 is small or even non-existent after 500 charge-discharge cycles, which significantly improves the reliability of battery cell 7 and also improves the cycle life of battery cell 7.

[0136] The upper limit voltage for charging and the lower limit voltage for discharging a single battery cell vary depending on the positive electrode active material. For example, when using phosphate materials, including lithium iron phosphate, the upper limit voltage for charging can be 3.65V and the lower limit voltage for discharging can be 2.0V. Similarly, when using phosphate materials, including lithium manganese iron phosphate, the upper limit voltage for charging can be 4.3V and the lower limit voltage for discharging can be 2.0V. The following explanation uses a charging upper limit voltage of 3.65V and a discharging lower limit voltage of 2.0V as an example to illustrate the charging and discharging process of a single battery cell:

[0137] The battery cells are charged at room temperature, such as 30°C. The charging process includes the following steps:

[0138] Charge from 0% SOC to 5% SOC at a constant current of 5.0C;

[0139] Charge from 5% SOC to 10% SOC at a constant current of 5.0C;

[0140] Charge from 10% SOC to 15% SOC at a constant current of 5.0C;

[0141] Charge from 15% SOC to 20% SOC at a constant current of 5.0C;

[0142] Charge from 20% SOC to 25% SOC at a constant current of 5.0C;

[0143] Charge from 25% SOC to 30% SOC at a constant current of 5.0C;

[0144] Charge from 30% SOC to 35% SOC at a constant current of 5.0C;

[0145] Charge from 35% SOC to 40% SOC at a constant current of 5.0C;

[0146] Charge from 40% SOC to 45% SOC at a constant current of 4.6C;

[0147] Charge from 45% SOC to 50% SOC at a constant current of 4.3C;

[0148] Charge from 50% SOC to 55% SOC at a constant current of 4.0C;

[0149] Charge from 55% SOC to 60% SOC at a constant current of 3.7C;

[0150] Charge from 60% SOC to 65% SOC at a constant current of 3.4C;

[0151] Charge from 65% SOC to 70% SOC at a constant current of 3.1C;

[0152] Charge from 70% SOC to 75% SOC at a constant current of 2.9C;

[0153] Charge from 75% SOC to 80% SOC at a constant current of 2.7C;

[0154] Charge from 80% SOC to 85% SOC at a constant current of 1.8C;

[0155] Charge from 85% SOC to 90% SOC at a constant current of 1.3C;

[0156] Charge from 90% SOC to 95% SOC at a constant current of 0.7C;

[0157] Charge from 95% SOC to 98% SOC at a constant current of 0.33C;

[0158] Charge from 98% SOC to 100% SOC at a constant current of 0.1C.

[0159] The cutoff voltage for the final charging step in the above charging process is 3.65V.

[0160] The discharge strategy is as follows: discharge at a constant current of 0.33C until the cutoff voltage, for example, 2.0V.

[0161] Following the above-described cycling strategy, the battery cell 7 is cycled 500 times. Then, the battery cell 7 is charged to 100% SOC using the above-described charging steps. The negative electrode 14 is then disassembled. The golden yellow area in the negative electrode 14 is the normal area, and the grayish-white area is the lithium plating area. After taking pictures using a high-magnification microscope, the different areas are analyzed. The grayscale difference is used to statistically analyze the lithium plating areas to obtain the total area of ​​the lithium plating areas. The ratio of the total area of ​​the lithium plating areas to the surface area of ​​the negative electrode film is the area proportion of the lithium plating areas in the negative electrode film, i.e., the lithium plating area.

[0162] 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 leads to differences in the lithium plating process, which will be explained in detail below.

[0163] [Stacked Electrode Assembly]

[0164] As shown in Figures 3 to 6, when the electrode assembly 10 has a stacked structure, the positive electrode 13 and the negative electrode 14 are stacked along the thickness direction. Optionally, the lithium plating area of ​​the stacked electrode assembly 10 is less than or equal to 13.5%. The thickness direction of the electrode assembly 10, the thickness direction of the positive electrode 13, and the thickness direction of the negative electrode 14 are parallel. The thickness direction of the positive electrode 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 13, and the length direction of the negative electrode 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 14 are parallel. The X direction shown in Figures 3 to 6 indicates that the X direction is parallel to the thickness direction of the electrode assembly 10.

[0165] In some embodiments, the negative electrode tab 112 is connected to at least one side of the negative electrode current collector 141 along the first direction Y.

[0166] 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 can be 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, in Figures 3 to 6, 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.

[0167] In some embodiments, the first region 140 includes one of the two ends facing the negative electrode tab 112.

[0168] The negative electrode film layer 142 and the negative electrode current collector 141 are arranged opposite each other along the thickness direction X. The negative electrode current collector 141 and the negative electrode tab 112 are connected along the first direction Y. Current can be conducted along the first direction Y, and current can be gathered from the negative electrode current collector 141 to the negative electrode tab 112. The electrochemical polarization is greatest at the end of the negative electrode film layer 142 near the negative electrode tab 112, making lithium deposition easier. However, the lithium deposition area in the first region 140 is less than or equal to 13.5%, selectable from 0 to 6%, for example 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 any range of two of the above values. When the lithium deposition area is 0, it means that the negative electrode 14 does not deposit lithium.

[0169] 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, for example, 0.05, 0.06, 0.07, 0.08, 0.09, 0.10, 0.15, 0.18, 0.20 or any two of the above values.

[0170] For example, in Figure 5, the negative electrode tab 112 is disposed on one side of the negative electrode current collector 141, the first region 140 is one end of the two ends facing the negative electrode tab 112, L1 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 L1 / 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. The ratio is 0.05 to 0.20, and can be selected from 0.05 to 0.15, or can be selected from 0.05 to 0.10.

[0171] For example, in Figure 6, the negative electrode tab 112 is disposed on both sides of the negative electrode current collector 141, the first region 140 includes two ends, 2L2 represents the size of each first region 140 along the first direction Y, and 2L2 / 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. The ratio is 0.05 to 0.20, and can be selected as 0.10 to 0.20.

[0172] As shown in FIG7, in some embodiments, the positive electrode 13 further includes an insulating layer 133, which is disposed on the positive current collector 131 and connected to the positive electrode film layer 132. The insulating layer 133 and the first region 140 are disposed opposite each other in the thickness direction.

[0173] The insulating layer 133 is basically not provided with positive electrode active material, which is conducive to increasing the size of the negative electrode film 142 beyond the positive electrode film 132, and further reducing the risk of lithium plating on the negative electrode sheet 14.

[0174] [Roll-up electrode assembly]

[0175] As shown in Figures 8 to 10, when the electrode assembly 10 is a wound structure, the positive electrode 13 and the negative electrode 14 are wound in one direction to form a wound structure. This structure can be a cylindrical structure or a flat structure, and can be a flat structure. The flat structure includes a bent area and a straight area. The thickness direction, length direction and width direction of the flat structure are perpendicular to each other.

[0176] In the wound electrode assembly 10, the end of the negative electrode film layer 142 near the negative electrode tab 112 may have a large local current density due to current accumulation, which may lead to lithium plating. However, in the embodiments of this application, the lithium plating area of ​​the wound electrode assembly 10 is less than or equal to 13.5%, and can be selected as 0 to 6%.

[0177] In some embodiments, the negative electrode 14 further includes a negative electrode tab 112, which is connected to at least one side of the negative current collector 141 along a first direction Y, the first direction Y being perpendicular to the thickness direction of the negative electrode 14; the thickness direction of the negative electrode 14 is parallel to the thickness direction of the positive electrode 13. The first direction Y may be parallel to the length direction of the electrode assembly 10 or parallel to the width direction of the electrode assembly 10.

[0178] The negative electrode tab 112 is connected to one side of the negative electrode current collector 141 along the first direction Y, or the negative electrode tab 112 is connected to both sides of the negative electrode current collector 141 along the first direction Y.

[0179] When the negative electrode tab 112 is connected to the negative electrode current collector 141 on one side along the first direction Y, the first region 140 includes two ends.

[0180] When the negative electrode tab 112 is connected to both sides of the negative electrode current collector 141 along the first direction Y, the first region 140 includes two ends.

[0181] When the negative electrode tab 112 is connected to the negative electrode current collector 141 on one side along the first direction Y, the gap between the electrodes in the bent region of the wound electrode assembly 10 is relatively large, resulting in a longer transport path for active ions in space. This leads to increased polarization in the bent region and a higher risk of lithium plating, especially in the portion of the negative electrode film layer 142 located away from the negative electrode tab 112 in the bent region. Typically, after assembling the electrode assembly 10 into the casing of the battery cell 7, the battery cell 7 is placed vertically in the housing to form a battery pack, with the vertical direction parallel to the first direction Y, meaning the negative electrode tab 112 is located above the first region 140 in the vertical direction. The heat dissipation capacity at the bottom of the housing is usually better than that at the top, resulting in a temperature difference in the negative electrode 14 in the vertical direction. The end away from the negative electrode tab 112 has a lower temperature, making it more prone to increased polarization and lithium plating during charging. The end facing the negative electrode tab 112, due to its higher current density, is more susceptible to lithium plating. However, in the embodiments of this application, the first region 140 is designed with materials, etc., so that the lithium plating area is relatively small.

[0182] 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, for example, 0.05, 0.06, 0.07, 0.08, 0.09, 0.10, 0.15, 0.20, or any range of two of the above values. For example, in Figure 9, the negative electrode tab 112 is disposed on one side of the negative electrode 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, optionally 0.10 to 0.20.

[0183] [Negative electrode plate]

[0184] The negative electrode sheet includes a negative current collector and a negative electrode film layer disposed on at least one surface of the negative current collector and comprising a negative electrode active material. For example, the negative current collector has two surfaces opposite each other in its thickness direction, and the negative electrode film layer is disposed on either or both of the two opposite surfaces of the negative current collector.

[0185] The following section will mainly explain the material, structure, and other relevant parameters of the second region in the negative electrode film.

[0186] In some embodiments, when the battery cell is 100% charged, the compaction density of the second region in the negative electrode film is 1.15 g / cm³. 3 Up to 1.36 g / cm 3 The option is 1.25g / cm³. 3Up to 1.36 g / cm 3 For example, the compaction density of the second region in the negative electrode film layer of a single battery cell at 100% charge is 1.15 g / cm³. 3 1.18 g / cm 3 1.20g / cm 3 1.22g / cm 3 1.25g / cm 3 1.28g / cm 3 1.3g / cm 3 1.32g / cm 3 1.35g / cm 3 1.36 g / cm 3 Or a range consisting of any two of the above values.

[0187] When the compaction density of the second region in the negative electrode film is within the above range, it is beneficial to improve the energy density of the battery cell. Furthermore, since the negative electrode active material in the negative electrode film is packed more tightly, the contact resistance between particles is smaller, which can further reduce the resistance of the electrode sheet, thereby reducing heat generation.

[0188] In this application embodiment, the 100% state of charge (SOC) and 0% state of charge (SOC) of a single battery cell are defined as follows:

[0189] The battery cell is charged at a constant current charging rate of 0.33C to the upper limit of the charging voltage, and then charged at a constant voltage to 0.05C, which corresponds to the battery cell being at 100% SOC. The battery cell is then discharged at a constant current discharging rate of 0.33C to the cutoff voltage, which corresponds to the battery cell being at 70% SOC.

[0190] In the embodiments of this application, the compaction density of the negative electrode film layer of a single battery cell under 100% charge state has a well-known meaning in the art and can be detected using well-known equipment and methods in the art. The detection method is as described above for the compaction density test method of the positive electrode film layer.

[0191] In some embodiments, the single-sided coating weight of the negative electrode film is 90 mg / 1540.25 mm. 2 Up to 170mg / 1540.25mm 2 The option is 110mg / 1540.25mm. 2 Up to 150mg / 1540.25mm 2 For example, the single-sided coating weight of the negative electrode film is 90 mg / 1540.25 mm. 2 92mg / 1540.25mm 2 95mg / 1540.25mm 2 96mg / 1540.25mm2 100mg / 1540.25mm 2 102mg / 1540.25mm 2 104mg / 1540.25mm 2 105mg / 1540.25mm 2 108mg / 1540.25mm 2 110mg / 1540.25mm 2 112mg / 1540.25mm 2 114mg / 1540.25mm 2 115mg / 1540.25mm 2 116mg / 1540.25mm 2 118mg / 1540.25mm 2 120mg / 1540.25mm 2 122mg / 1540.25mm 2 125mg / 1540.25mm 2 128mg / 1540.25mm 2 130mg / 1540.25mm 2 132mg / 1540.25mm 2 135mg / 1540.25mm 2 137mg / 1540.25mm 2 140mg / 1540.25mm 2 142mg / 1540.25mm 2 145mg / 1540.25mm 2 148mg / 1540.25mm 2 150mg / 1540.25mm 2 152mg / 1540.25mm 2 155mg / 1540.25mm 2 160mg / 1540.25mm 2 165mg / 1540.25mm 2 170mg / 1540.25mm 2 Or a range consisting of any two of the above values.

[0192] When the single-sided coating weight of the negative electrode film is within the above range, the heat generation per unit area of ​​the negative electrode sheet will not be too large, and the energy density of the battery cell can be improved at the same time.

[0193] In the embodiments of this application, the single-sided coating weight of the negative electrode film layer has a meaning known in the art and can be detected using equipment and methods known in the art, such as the single-sided coating weight test method of the film layer described above.

[0194] 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, 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 a range consisting of any two of the above values.

[0195] The powder resistivity of the negative electrode active material is relatively low, which results in relatively low resistance of the negative electrode sheet and less heat generation in the battery cell.

[0196] In the embodiments of this application, the powder resistivity of the negative electrode active material has a well-known meaning in the art and can be detected using equipment and methods well-known in the art, such as the powder resistivity test method for the positive electrode active material described above.

[0197] In some embodiments, the powder compaction density of the negative electrode active material in the negative electrode film layer under a pressure of 20000N is 1.5 g / cm³. 3 Up to 1.85 g / cm 3 1.55g / cm³ is an optional value. 3 Up to 1.65 g / cm 3 For example, the compacted density of the negative electrode active material powder under a pressure of 20000N is 1.5 g / cm³. 3 1.55g / cm 3 1.6g / cm 3 1.65g / cm 3 1.7g / cm 3 1.75g / cm 3 1.8g / cm 3 1.85g / cm 3 Or a range consisting of any two of the above values.

[0198] When the powder compaction density of the negative electrode active material at 20000N is within the above range, it can improve the energy density of the battery cell. Furthermore, since the negative electrode active material in the negative electrode film can be stacked more tightly, the contact resistance between particles is smaller, which can further reduce the resistance of the electrode sheet, thereby reducing heat generation.

[0199] In this application, the powder compaction density of the material has a meaning known in the art and can be tested using methods and equipment known in the art, according to the testing standard GB / T24533-2009. As an example, a certain amount of negative electrode active material is taken as a sample and added to a UTM7305 electronic pressure testing machine with a base area of ​​1.327 cm². 2 In the mold, the pressure is increased to 2000 kg (equivalent to 20000 N), held for 30 s, then depressurized and held for 10 s. The compaction density of the negative electrode active material under a force of 20000 N is then recorded and calculated.

[0200] In some embodiments, the specific charge capacity of the negative electrode active material in the negative electrode film layer at a 0.1C rate is between 350 mAh / g and 390 mAh / g. Exemplarily, the specific charge 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 a range consisting of any two of the above values.

[0201] When the 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.

[0202] In the embodiments of this application, the charging capacity of the negative electrode active material at a rate of 0.1C is a well-known concept in the art and can be detected using well-known equipment and methods in the art. The detection method is as described above for the charging capacity test method of the positive electrode active material at a rate of 0.1C.

[0203] In some embodiments, the negative electrode active material in the second region includes a carbon-based material. Carbon-based materials have high cycle stability and can improve the cycle performance of the battery cell. Optionally, the mass percentage of carbon-based material in the negative electrode active material can be greater than or equal to 80% and less than or equal to 100%.

[0204] The positive electrode active material of this application is mainly a lithium phosphate system with an olivine structure, and the negative electrode active material is mainly a carbon-based material system. When used together, the cycle performance of the battery cell is excellent.

[0205] Optionally, the carbon-based material includes graphite particles with a graphitization degree of 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 a range consisting of any two of the above values.

[0206] When the degree of graphitization of graphite particles is within the above range, the graphite particles have excellent electrical conductivity, 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.

[0207] In some embodiments, the graphite particles include artificial graphite and a carbon coating layer. The artificial graphite includes secondary particles, which in turn include multiple primary particles. The carbon coating layer coats the surface of the artificial graphite. The carbon in the carbon coating layer is primarily amorphous carbon, which refers to transitional carbon materials with a very low degree of graphitization and crystallization, exhibiting an approximately amorphous morphology (or lacking a fixed shape and periodic structural regularity). In this application, amorphous carbon refers to the product of carbonization treatment of an organic carbon source.

[0208] Artificial graphite includes secondary particles. There are more migration paths for lithium ions in artificial graphite, and the migration paths in primary particles are shorter, which can improve the migration rate of lithium ions. The carbon coating layer has more end faces and defects, which increases the number of sites where lithium ions can be inserted and extracted, resulting in better conductivity of the carbon coating layer. This can reduce the internal resistance of the negative electrode and reduce the heat generation of the battery cell.

[0209] Optionally, the carbon coating content is 2% to 5% by mass, based on the mass of the graphite particles. For example, the carbon coating content is 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, or any range of two of the above values.

[0210] When the mass content of the carbon coating is within the above range, it can further reduce the internal resistance of the negative electrode and reduce the heat generation of the battery cell.

[0211] In the embodiments of this application, the graphite particles can be prepared using methods known in the art, such as: providing artificial graphite and an organic carbon source, mixing the two, and then carbonizing them to form a carbon coating layer on at least a portion of the surface of the artificial graphite particles.

[0212] Optionally, the organic carbon source includes one or more of coal tar pitch, petroleum asphalt, phenolic resin, and coconut shell. More preferably, the organic carbon source includes petroleum asphalt. Optionally, the softening point of coal tar pitch or petroleum asphalt is below 250°C.

[0213] Optionally, the carbonization temperature is between 700°C and 1800°C. Optionally, the carbonization temperature is between 1000°C and 1300°C. Within a suitable range, the carbonization temperature allows the organic carbon source to be carbonized, forming a coating layer containing amorphous carbon on at least a portion of the surface of the artificial graphite.

[0214] Optionally, the carbonization treatment time is 1 hour to 6 hours.

[0215] In some embodiments, the carbon-based material may further include natural graphite. Specifically, the carbon-based material may include graphite particles, or it may include both graphite particles and natural graphite. Optionally, the carbon-based material is graphite particles.

[0216] The qualitative and quantitative analysis of each substance or element in this application can be performed using suitable equipment and methods known to those skilled in the art. Relevant testing methods can be referenced from domestic and international testing standards and enterprise standards. Furthermore, those skilled in the art can adaptively modify certain testing steps / instrument parameters from the perspective of testing accuracy to obtain more accurate results. One testing method can be used for qualitative or quantitative analysis, or several testing methods can be used in combination for qualitative or quantitative determination.

[0217] For example, this application can combine the general rules of X-ray diffraction analysis in JIS / K0131-1996 to perform X-ray powder diffraction tests and qualitative analysis on negative electrode sheets or negative electrode active materials.

[0218] Artificial graphite and natural graphite can be distinguished by SEM cross-sectional images taken by scanning electron microscope (SEM). Natural graphite has gaps between the sheet-like structures in its SEM cross-section, while artificial graphite has a dense structure with no obvious gaps. Alternatively, they can be distinguished by XRD patterns obtained by X-ray diffraction. Natural graphite has obvious 2H and 3R phases in its XRD pattern, while artificial graphite only has the 2H phase in its XRD pattern.

[0219] In the embodiments of this application, the negative electrode film layer in the second region includes at least one film layer, which can be a single film layer or at least two film layers. Optionally, the negative electrode film layer includes at least two film layers.

[0220] In the second region, when the negative electrode film layer is a single layer, the negative electrode active material in the negative electrode film layer includes carbon-based materials. When a single layer film layer is used, the volume average particle size Dv50 of the negative electrode active material is 8.2 μm to 13.5 μm.

[0221] For example, 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 any range of two of the above values.

[0222] When the negative electrode film layer comprises at least two film layers, the negative electrode active material in the negative electrode film layer includes a carbon-based material, and optionally also includes a silicon-based material. The silicon-based material may be located in one of the at least two film layers, or in at least two of the at least two film layers. The negative electrode film layer may include two film layers, three film layers, four film layers, or even more film layers.

[0223] 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, and the carbon-based material in the first negative electrode film layer includes graphite particles. The second negative electrode film layer is connected to the side of the first negative electrode film layer away from the negative electrode current collector, and 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 may be the same or different.

[0224] The interface between the first negative electrode film and the second negative electrode film can be regular or irregular, and can optionally be irregular.

[0225] Optionally, the carbon-based material in the first negative electrode film layer may also include natural graphite.

[0226] The negative electrode film consists of at least two layers, and layered coating is beneficial for improving the fast charging performance of the battery cell. In particular, when there are differences between the first and second negative electrode films, it can create porosity differences in the negative electrode films, reduce the tortuosity of lithium-ion transport, and improve the fast charging performance of the battery cell.

[0227] 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. More preferably, the volume average particle size Dv50 of the negative electrode active material in the first negative electrode film layer is greater than the volume average particle size Dv50 of the negative electrode active material in the second negative electrode film layer, which is beneficial for increasing 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.

[0228] The difference in particle size between the first and second negative electrode layers can improve the fast charging performance of the battery cell. Specifically, during fast charging, the overpotential of the second negative electrode layer is usually higher, and the bottleneck of fast charging is mainly in the second negative electrode layer. However, in the embodiments of this application, the particle size of the second negative electrode layer is relatively small, which can shorten the solid-phase transport path of lithium ions, improve fast charging performance, and improve the problem of lithium deposition on the surface of the negative electrode sheet.

[0229] Optionally, the negative electrode active material in the first negative electrode film layer is particulate, and its volume average particle size Dv50 is 9.5 μm to 18.5 μm, optionally 9.5 μm to 14.6 μm. Exemplarily, the volume average particle size of the negative electrode active material in the first negative electrode film layer is 9.5 μm, 10 μm, 10.5 μm, 11 μm, 11.5 μm, 12 μm, 12.5 μm, 13 μm, 13.5 μm, 14 μm, 14.5 μm, 14.6 μm, 15 μm, 15.5 μm, 16 μm, 16.5 μm, 17 μm, 17.5 μm, 18 μm, 18.5 μm, or a range consisting of any two of the above values. When the first negative electrode film layer includes graphite particles, the volume average particle size Dv50 of the graphite particles in the first negative electrode film layer is 9.5 μm to 18.5 μm, and can be selected as 9.5 μm to 14.6 μm.

[0230] 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, it can shorten the solid-phase transport path of lithium ions and improve fast charging performance. On the other hand, the material is less prone to agglomeration during the preparation process, which can improve the stability of the material.

[0231] Optionally, the negative electrode active material in the second negative electrode film layer is particulate, and its volume average particle size Dv50 is 7.8 μm to 14.3 μm, optionally 7.8 μm to 11.3 μm. For example, 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 of any two of the above values. When the second negative electrode film layer includes graphite particles, the volume average particle size Dv50 of the graphite particles in the second negative electrode film layer is 7.8 μm to 14.3 μm, and can be selected as 7.8 μm to 11.3 μm.

[0232] When the volume average particle size Dv50 of the negative electrode active material in the second negative electrode film is within the above-mentioned range, it can shorten the solid-phase transport path of lithium ions and improve fast charging performance. On the other hand, the material is less prone to agglomeration during the preparation process, which can improve the stability of the material. Furthermore, the combination of the negative electrode active material in the second negative electrode film within the above-mentioned volume average particle size range and the negative electrode active material in the first negative electrode film is conducive to building a gradient porosity difference between the second negative electrode film and the first negative electrode film, reducing the tortuosity of lithium ion transport, and improving the fast charging performance of the battery cell.

[0233] In the embodiments of this application, the volume average particle size Dv50 of the negative electrode active material has a meaning known in the art and can be detected using equipment and methods known in the art, such as the volume average particle size Dv50 test method for positive electrode active materials described above.

[0234] Optionally, the tap density of the carbon-based material in the first negative electrode film layer is less than or equal to the tap density of the carbon-based material in the second negative electrode film layer. Tap density reflects the compactness of the active material within the film layer. When the tap 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, thus increasing the energy density of the battery cell. Conversely, the first negative electrode film layer is relatively sparsely packed with more pores, which improves the fast-charging performance of the battery cell. When the negative electrode active material includes graphite particles, the tap density of the graphite particles in the first negative electrode film layer is less than or equal to that in the second negative electrode film layer.

[0235] Optionally, the tap density of the carbon-based material in the first negative electrode film layer is 0.82 g / cm³. 3 Up to 1.21 g / cm 3 For example, 0.82 g / cm³ 3 0.85g / cm 3 0.88g / cm 3 0.90g / cm 3 0.92g / cm 3 0.95g / cm 3 0.98g / cm 3 1.00g / cm 3 1.05g / cm 3 1.08g / cm 3 1.10 g / cm 3 1.12 g / cm 3 1.15g / cm 3 1.18 g / cm 3 1.20g / cm 3 1.21 g / cm 3 Or it can be a range consisting of any two of the above values. When the tap density of the carbon-based material in the first negative electrode film is within a suitable range, it can improve the fast charging performance of the battery cell.

[0236] Optionally, the tap density of the carbon-based material in the second negative electrode film is 0.90 g / cm³. 3 Up to 1.25 g / cm 3 For example, 0.90 g / cm³ 3 0.92g / cm 30.95g / cm 3 0.98g / cm 3 1.00g / cm 3 1.05g / cm 3 1.08g / cm 3 1.10 g / cm 3 1.12 g / cm 3 1.15g / cm 3 1.18 g / cm 3 1.20g / cm 3 1.21 g / cm 3 1.22g / cm 3 1.23g / cm 3 1.24 g / cm 3 1.25g / cm 3 Or it can be a range consisting of any two of the above values. When the tap density of the carbon-based material in the second negative electrode film is within a suitable range, it can improve the energy density of the battery cell.

[0237] In the embodiments of this application, the tap density of the material has a meaning known in the art and can be determined using instruments and methods known in the art. For example, it can be determined using a powder tap density tester according to GB / T5162-2006. The testing instrument can be the Dandong Baite BT-301.

[0238] Optionally, the thickness ratio of the second negative electrode film to the first negative electrode film is 3:7 to 7:3, and optionally 4:6 to 6:4. For example, the thickness ratio of the second negative electrode film to the first negative electrode film is 3:7, 4:6, 5:5, 6:4, 7:3, or any range of two of the above values. By adjusting the thickness ratio of the first and second negative electrode films, the gradient porosity difference between the upper and lower layers can be further increased, reducing the tortuosity of lithium-ion transport and improving the fast charging capability of the battery cell.

[0239] In some implementations, after 10 full-charge cycles during the Beginning of Life (BOL) test, the battery cell is disassembled and tested at 100% SOC. The thickness of the first negative electrode film layer is between 15 μm and 100 μm, for example, 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 any combination of two of the above values. When the thickness of the first negative electrode film layer is within the above range, it can increase the gradient porosity difference between the first and second negative electrode film layers, reduce the tortuosity of lithium-ion transport, and improve the fast charging capability of the battery cell.

[0240] In some implementations, after 10 full-charge cycles during the Beginning of Life (BOL) test, the thickness of the second negative electrode film is between 15 μm and 80 μm, for example, 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 any combination of two of the above values. When the thickness of the second negative electrode film is within the above range, the gradient porosity difference between the first and second negative electrode films can be increased, reducing lithium-ion transport tortuosity and improving the fast-charging capability of the battery cell.

[0241] In this embodiment, for example, a battery charging upper limit voltage of 3.65V and a battery discharging cutoff voltage of 2.0V will be used for explanation.

[0242] The BOL full charge test procedure is as follows: At 25℃, charge the battery to 3.65V at a charging rate of 0.33C (the nominal capacity), then charge it to 0.05C at a constant voltage of 3.65V, let it rest for 10 minutes, then discharge it to 2.0V at a discharging rate of 0.33C, let it rest for 10 minutes. One charge-discharge cycle constitutes one cycle; complete 10 cycles. Then charge the battery to 3.65V again at a charging rate of 0.33C (the nominal capacity), and then charge it to 0.05C at a constant voltage of 3.65V. With the BOL fully charged, the negative electrode sheet is disassembled. A tomographic scanning electron microscope is used to observe the cross-section of the thickness direction in the middle region of the negative electrode sheet. The two regions are distinguished according to the interface between the first negative electrode film layer and the second negative electrode film layer. The thickness of each is measured separately. For example, the thickness of the first negative electrode film layer is measured at 10 locations, and the average value is calculated as the average value of the first negative electrode film layer. The thickness of the second negative electrode film layer is measured at 10 locations, and the average value is calculated as the average value of the second negative electrode film layer.

[0243] In some embodiments, after the battery cell undergoes an end-of-life (EOL) full-charge test, the thickness of the first negative electrode film layer is 15 μm to 110 μm, for example, 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, 95 μm, 100 μm, 105 μm, 110 μm, or any range of two of the above values. When the thickness of the first negative electrode film is within the above range, the first negative electrode film and the second negative electrode film can be controlled to increase the gradient porosity difference between the upper and lower layers, reduce the tortuosity of lithium-ion transport, and improve the fast charging capability of the battery cell.

[0244] In some implementations, after the battery cell undergoes an end-of-life (EOL) full-charge test, the thickness of the second negative electrode film is 15 μm to 90 μm, for example, 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 any range of two of the above values. When the thickness of the second negative electrode film is within the above range, the first negative electrode film and the second negative electrode film can regulate and increase the gradient porosity difference between the upper and lower layers, reduce the tortuosity of lithium-ion transport, and improve the fast charging capability of the battery cell.

[0245] In this embodiment, for example, a battery charging upper limit voltage of 3.65V and a battery discharging cutoff voltage of 2.0V will be used for explanation.

[0246] The EOL full charge test procedure is as follows: At 60℃, charge the battery to 3.65V at a charging rate of 0.33C (the nominal capacity), then charge it to 0.05C at a constant voltage of 3.65V, let it stand for 10 minutes, then discharge it to 2.0V at a discharging rate of 0.33C, and let it stand for 10 minutes. One charge and discharge cycle is one cycle. The test is stopped when the battery capacity decays to 80% of the nominal capacity. Then, charge at 25°C with a constant current of 0.33C to 3.65V, and then charge at a constant voltage of 0.05C to 3.65V, which is the EOL full charge state. In the EOL full charge state, disassemble the negative electrode plate and use a tomographic scanning electron microscope to observe the cross-section of the thickness direction of the middle region of the negative electrode plate. Distinguish the two regions according to the interface of the first negative electrode film layer and the second negative electrode film layer, and measure the thickness of each. For example, measure the thickness of the first negative electrode film layer at 10 locations and calculate the average value as the average value of the first negative electrode film layer. Measure the thickness of the second negative electrode film layer at 10 locations and calculate the average value as the average value of the second negative electrode film layer.

[0247] In some embodiments, when the second region of the negative electrode film layer uses a single-layer film layer (as opposed to the double-layer film layer described above), the negative electrode film layer further includes a lithium-containing binder. Optionally, the mass content of the lithium-containing binder relative to the negative electrode film layer is 0.1% to 3%. Exemplarily, the mass content of the lithium-containing binder relative to 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 any combination of two of the above values. The lithium element in the lithium-containing binder can exist in ionic form, 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, improve the lithium ion insertion / extraction rate, and improve the fast charging performance of the battery cell. Optionally, the negative electrode film layer may further include a negative electrode binder, such as at least one of styrene-butadiene rubber (SBR), water-soluble unsaturated resin SR-1B, waterborne 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).

[0248] Optionally, the lithium content in the lithium-containing binder is 3% to 10% by mass. For example, the lithium content in the lithium-containing binder is 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, or any combination of two of the above values. The lithium content is calculated based on the mass of the lithium-containing binder. When the lithium content is within the above range, a relatively large number of freely moving lithium ions can be achieved in the negative electrode film, further shortening the distance that lithium ions diffuse to the surface of the negative electrode film, increasing the lithium ion insertion / extraction rate, and improving the fast-charging performance of the battery cell.

[0249] For example, lithium-containing binders include lithium acrylate-acrylonitrile-acrylamide-hydroxyethyl acrylate copolymers, which are derived from lithium acrylate monomers, acrylonitrile monomers, acrylamide monomers, and hydroxyethyl acrylate monomers, wherein the molar percentages of lithium acrylate monomers, acrylonitrile monomers, acrylamide monomers, and hydroxyethyl acrylate monomers are 30% to 50%: 15% to 45%: 5% to 20%: 20% to 35%. For example, the molar percentages of lithium acrylate monomers, acrylonitrile monomers, acrylamide monomers, and hydroxyethyl acrylate monomers are 35%: 30%: 15%: 20%, or 40%, 20%, 10%, 30%, or 45%, 15%, 20%, 20%, etc.

[0250] The lithium-containing binder of the above-mentioned material can provide a certain number of lithium ions to the negative electrode film layer, improve the fast charging performance of the battery cell, and is not prone to swelling during charging and discharging, with a stable structure, which improves the cycle performance of the negative electrode film layer during fast charging and discharging.

[0251] In other embodiments, where the second region of the negative electrode film layer employs at least two film layers, the second region of the negative electrode film layer further includes a lithium-containing binder.

[0252] Optionally, the first negative electrode film layer further includes a first lithium-containing binder, and the second negative electrode film layer further includes a second lithium-containing binder, wherein the mass content of the first lithium-containing binder relative to the mass of the first negative electrode film layer is less than or equal to the mass content of the second lithium-containing binder relative to the mass of the second negative electrode film layer. More 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.

[0253] The second lithium-containing binder has a relatively high mass content in the second negative electrode film layer. The second lithium-containing binder provides a relatively larger number of freely movable lithium ions to the second negative electrode film layer, which can further improve the fast charging performance of the battery cell.

[0254] Optionally, the mass content of the first lithium-containing binder relative to the first negative electrode film layer is 0.1% to 3%. For example, the mass content of the first lithium-containing binder relative to 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 any combination of two of the above values. The lithium element in the first lithium-containing binder can exist in ionic form, which can increase the number of freely moving lithium ions in the negative electrode film layer, shorten the distance for lithium ions to diffuse to the surface of the negative electrode film layer, improve the lithium ion insertion / extraction rate, and improve the fast charging performance of the battery cell.

[0255] Optionally, the lithium content in the first lithium-containing binder is 3% to 10% by mass, and optionally 3% to 8%. For example, the lithium content in the first lithium-containing binder is 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, or any combination of two of the above values. When the lithium content is within the above range, a relatively large number of freely moving lithium ions can be achieved in the negative electrode film layer, further shortening the distance that lithium ions diffuse to the surface of the negative electrode film layer, increasing the lithium ion insertion / extraction rate, and improving the fast charging performance of the battery cell.

[0256] For example, the first lithium-containing binder comprises a lithium acrylate-acrylonitrile-acrylamide-hydroxyethyl acrylate copolymer, which is derived from lithium acrylate monomer, acrylonitrile monomer, acrylamide monomer, and hydroxyethyl acrylate monomer, wherein the molar percentages of lithium acrylate monomer, acrylonitrile monomer, acrylamide monomer, and 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 hydroxyethyl acrylate monomer are 35%: 30%: 15%: 20%, or 40%, 20%, 10%, 30%, or 45%, 15%, 20%, 20%, etc.

[0257] The lithium-containing binder of the above-mentioned material can provide a certain number of lithium ions to the negative electrode film layer, improve the fast charging performance of the battery cell, and is not prone to swelling during charging and discharging, with a stable structure, which improves the cycle performance of the negative electrode film layer during fast charging and discharging.

[0258] Optionally, the mass content of the second lithium-containing binder relative to the second negative electrode film layer is from 0.1% to 3%. For example, the mass content of the second lithium-containing binder relative to 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 any combination of two of the above values. The lithium element in the second lithium-containing binder can exist in ionic form, which can increase the number of freely moving lithium ions in the negative electrode film layer, shorten the distance for lithium ions to diffuse to the surface of the negative electrode film layer, improve the lithium ion insertion / extraction rate, and improve the fast charging performance of the battery cell.

[0259] The first lithium-containing binder and the second lithium-containing binder can be made of the same material or different materials.

[0260] Optionally, the lithium content in the second lithium-containing binder is 3% to 10% by mass, and optionally 3% to 8%. For example, the lithium content in the second lithium-containing binder is 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, or any combination of two of the above values. When the lithium content is within the above range, a relatively large number of freely moving lithium ions can be achieved in the negative electrode film layer, further shortening the distance that lithium ions diffuse to the surface of the negative electrode film layer, increasing the lithium ion insertion / extraction rate, and improving the fast charging performance of the battery cell.

[0261] For example, the second lithium-containing binder comprises a lithium acrylate-acrylonitrile-acrylamide-hydroxyethyl acrylate copolymer, which is derived from lithium acrylate monomers, acrylonitrile monomers, acrylamide monomers, and hydroxyethyl acrylate monomers, wherein the molar percentages of lithium acrylate monomers, acrylonitrile monomers, acrylamide monomers, and hydroxyethyl acrylate monomers are 30% to 50%: 15% to 45%: 5% to 20%: 20% to 35%. For example, the molar percentages of lithium acrylate monomers, acrylonitrile monomers, acrylamide monomers, and hydroxyethyl acrylate monomers are 35%: 30%: 15%: 20%, or 40%, 20%, 10%, 30%, or 45%, 15%, 20%, 20%, etc.

[0262] The lithium-containing binder of the above-mentioned material can provide a certain number of lithium ions to the negative electrode film layer, improve the fast charging performance of the battery cell, and is not prone to swelling during charging and discharging, with a stable structure, which improves the cycle performance of the negative electrode film layer during fast charging and discharging.

[0263] In some embodiments, the first negative electrode film layer further includes a negative electrode binder, and the second negative electrode film layer further includes a negative electrode binder. The negative electrode binder in the first negative electrode film layer and the negative electrode binder in the second negative electrode film layer each independently include at least one of styrene-butadiene rubber (SBR), water-soluble unsaturated resin SR-1B, waterborne 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).

[0264] 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.

[0265] In some embodiments, the negative electrode film layer may optionally include a negative electrode conductive agent. This application does not impose particular limitations on the type of negative electrode conductive agent. As an example, the negative electrode conductive agent may include at least one selected from superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. In some embodiments, the mass content of the negative electrode conductive agent is ≤5% based on the total weight of the negative electrode film layer.

[0266] In some embodiments, the negative electrode film layer may optionally include a negative electrode binder. In some embodiments, the mass content of the negative electrode binder is ≤5% based on the total weight of the negative electrode film layer.

[0267] In some embodiments, the negative electrode film layer may optionally include other additives. As examples, other additives may include thickeners, dispersants, etc., such as sodium carboxymethyl cellulose (CMC-Na), PTC thermistor materials, etc. In some embodiments, the mass content of other additives is ≤2% based on the total weight of the negative electrode film layer.

[0268] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. Examples of metal foils include at least one foil selected from copper, copper alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys. The composite current collector may include a polymeric material substrate and a metal material layer formed on at least one surface of the polymeric material substrate. As an example, the metal material layer may include at least one selected from copper, copper alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys. As an example, the polymeric material substrate may include at least one selected from polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0269] In some embodiments, the thickness of the negative electrode current collector is 4 μm to 6 μm. For example, the thickness of the negative electrode current collector is 4 μm, 4.5 μm, 5 μm, 5.5 μm, 6 μm, or any range of two of the above values.

[0270] 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 excellent, and it can enable the battery cell to have a high energy density.

[0271] In the embodiments of this application, the thickness of the negative electrode current collector has a meaning known in the art and can be detected using equipment and methods known in the art. For example, the film layer on the surface of the negative electrode current collector can be washed away with a solvent, and the thickness of the negative electrode current collector can be measured with a micrometer.

[0272] The negative electrode film is typically formed by coating a negative electrode slurry onto a negative electrode current collector, followed by drying and cold pressing. The negative electrode slurry is usually formed by dispersing the negative electrode active material, optional conductive agent, optional binder, and other optional additives in a solvent and stirring until homogeneous. The solvent can be N-methylpyrrolidone (NMP) or deionized water, but is not limited to these.

[0273] The negative electrode sheet does not exclude other additional functional layers besides the negative electrode film layer. For example, in some embodiments, the negative electrode sheet of this 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 sheet of this application further includes a protective layer covering the surface of the negative electrode film layer.

[0274] In some embodiments, the negative electrode sheet 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 sheet and reduce the heat generation of the negative electrode sheet, thereby reducing the heat generation of the battery cell.

[0275] In some embodiments, the thickness of the negative electrode conductive layer is from 0.1 μm to 2 μm. For example, 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 any combination of two of the above values.

[0276] When the thickness of the negative electrode conductive layer is within the above range, the conductivity of the negative electrode sheet can be further improved, the heat generation of the negative electrode sheet can be reduced, thereby reducing the heat generation of the battery cell, and the energy density of the battery cell can also be improved.

[0277] In the embodiments of this application, the thickness of the negative electrode conductive layer has a meaning known in the art and can be detected using equipment and methods known in the art, such as the test method for the negative electrode conductive layer described above.

[0278] In some embodiments, the negative electrode conductive layer includes one or more of a negative electrode conductive agent and a negative electrode binder. The negative electrode conductive agent in the negative electrode conductive layer can improve the conductivity of the negative electrode conductive layer, thereby improving the conductivity of the negative electrode sheet and reducing the heat generation of the battery cell. The negative electrode binder in the negative electrode conductive layer can improve the adhesion between the negative electrode current collector and the negative electrode film layer, thereby improving the structural stability of the negative electrode sheet.

[0279] In some embodiments, the negative electrode conductive layer may optionally include other additives. As an example, other additives may include thickeners, such as sodium carboxymethyl cellulose (CMC), calcium hydroxide, etc.

[0280] Optionally, the mass content of the negative electrode conductive agent in the negative electrode conductive layer is 20% to 40%. For example, the mass content of the negative electrode conductive agent is 20%, 25%, 30%, 35%, 40%, or any combination of two of the above values.

[0281] For example, 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.

[0282] Optionally, the negative electrode binder has a mass content of 60% to 80% in the negative electrode conductive layer. For example, 60%, 65%, 70%, 75%, 80%, or any range of two of the above values.

[0283] For example, the negative electrode binder includes one or more of styrene-butadiene rubber (SBR), water-soluble unsaturated resin SR-1B, water-based acrylic resin, polyvinyl alcohol, sodium alginate, and carboxymethyl chitosan.

[0284] In some embodiments, the ratio CB of the capacity of the negative electrode film per unit area to the capacity of the positive electrode film per unit area in a single battery cell is from 1.05 to 1.30, and optionally from 1.07 to 1.15. Exemplarily, the ratio CB of the capacity of the negative electrode film per unit area to the capacity of the positive electrode film per unit area in a single battery cell is 1.05, 1.07, 1.1, 1.12, 1.15, 1.18, 1.2, 1.22, 1.25, 1.28, 1.3, or a range of any two of the above values.

[0285] When the ratio CB of the capacity of the negative electrode film per unit area to the capacity of the positive electrode film per unit area in a single battery cell is within the above range, there are sufficient sites in the negative electrode film for lithium insertion, which can reduce the risk of lithium plating and facilitate fast charging.

[0286] In the embodiments of this application, the CB value has a well-known meaning in the art and can be detected using well-known equipment and methods in the art. For example, the capacity of the negative electrode film per unit area and the capacity of the positive electrode film per unit area can be calculated respectively, and the ratio between the two can be calculated to obtain the CB value.

[0287] Specifically, this explanation will be based on an example where the upper limit of battery charging voltage is 3.65V and the battery discharge cutoff voltage is 2.0V.

[0288] The capacity per unit area of ​​the positive electrode film refers to the actual lithium-depleting capacity of the positive electrode active material. The testing method is as follows: The battery is disassembled in a Braun glove box (PRS340 / 11-119-11), the positive electrode sheet is removed, and assembled into a CR2430 model semi-button battery with a positive electrode and lithium sheet. The positive electrode sheet area used is a mm². 2 The electrolyte used was a solution of 1 mol / L LiPF6 in EC / EMC / DEC = 3 / 5 / 2 (mass ratio). The assembled semi-coin cells were then left to stand for 3 hours. The test was conducted at 25°C. The cells were first charged at 0.1C in the voltage range of 2.0V to 3.65V to remove lithium, and then discharged at 0.05C to insert lithium to 2.0V. This cycle was repeated twice. The discharge coin capacity of the second cycle was recorded as YmAh. The actual battery design had a positive electrode length of bmm and a width of cmm. The number of surfaces of the positive electrode active material coated on the positive electrode current collector was d. Therefore, the capacity of the positive electrode film per unit area was Y / a*b*c*d.

[0289] Specifically, the capacity per unit area of ​​the negative electrode film refers to the actual lithium intercalation capacity of the negative electrode active material. The testing method is as follows: The battery is disassembled in a PRS340 / 11-119-11 Braun glove box, the negative electrode sheet is removed, and it is assembled into a CR2430 model semi-button battery with a negative electrode and lithium sheet. The area of ​​the negative electrode sheet used is fmm². 2 The electrolyte used was a solution of 1 mol / L LiPF6 in EC / EMC / DEC = 3 / 5 / 2 (mass ratio). The assembled semi-coin cells were then left to stand for 3 hours. The test was conducted at 25°C. Lithium insertion was performed by discharging at 0.1C in the voltage range of 2V-0V, followed by lithium extraction by charging at 0.05C to 2V. This cycle was repeated twice. The discharge capacity of the second cycle was recorded as ZmAh. The actual battery design had a negative electrode length of hmm and a width of imm. The number of surfaces of the negative electrode active material coated on the negative electrode current collector was d. Therefore, the lithium insertion capacity of the negative electrode was Z / f*h*i*d.

[0290] [Positive electrode plate]

[0291] The positive electrode includes a positive current collector and a positive electrode film layer disposed on at least one surface of the positive current collector and comprising a positive electrode active material. For example, the positive current collector has two surfaces opposite each other in its thickness direction, and the positive electrode film layer is disposed on either or both of the two opposite surfaces of the positive current collector.

[0292] In some embodiments, the compaction density of the positive electrode film layer is 2.50 g / cm³ when the battery cell is at 100% state of charge (SOC). 3 Up to 2.80 g / cm 3 2.55g / cm³ is an optional value. 3 Up to 2.70 g / cm 3 For example, when the battery cell is at 100% state of charge (SOC), the compaction density of the positive electrode film is 2.50 g / cm³. 3 2.52g / cm 3 2.55g / cm 3 2.56 g / cm 3 2.57g / cm 3 2.58g / cm 3 2.60g / cm 3 2.62 g / cm 3 2.65g / cm 3 2.68g / cm 3 2.70 g / cm 3 2.72 g / cm 3 2.75g / cm 3 2.78g / cm 32.80g / cm 3 Or a range consisting of any two of the above values.

[0293] When the compaction density of the positive electrode film is within the aforementioned range, it is beneficial to improve the energy density of the battery cell. Furthermore, because the positive electrode active material in the positive electrode film is densely packed, the contact resistance between particles is low, which can further reduce the resistance of the electrode sheet, thereby reducing heat generation during fast charging. Therefore, by adjusting the compaction density of the positive electrode film to a reasonable range, the battery cell can achieve both high energy density and high charging rate performance.

[0294] In some embodiments, the single-sided coating weight of the positive electrode film is 200 mg / 1540.25 mm. 2 Up to 370mg / 1540.25mm 2 The option is 240mg / 1540.25mm. 2 Up to 330mg / 1540.25mm 2 For example, the single-sided coating weight of the positive electrode film is 200 mg / 1540.25 mm. 2 210mg / 1540.25mm 2 220mg / 1540.25mm 2 230mg / 1540.25mm 2 240mg / 1540.25mm 2 250mg / 1540.25mm 2 260mg / 1540.25mm 2 270mg / 1540.25mm 2 280mg / 1540.25mm 2 290mg / 1540.25mm 2 300mg / 1540.25mm 2 310mg / 1540.25mm 2 320mg / 1540.25mm 2 330mg / 1540.25mm 2 340mg / 1540.25mm 2 350mg / 1540.25mm 2 360mg / 1540.25mm 2 370mg / 1540.25mm 2 Or a range consisting of any two of the above values.

[0295] When the single-sided coating weight of the positive electrode film is within the above range, the heat generation per unit area of ​​the positive electrode sheet will not be too large, and it can also improve the energy density and charging rate performance of the battery cell.

[0296] In this embodiment, the compaction density of the positive electrode film layer of a single battery cell at 100% State of Charge (SOC) can be detected by the following method: The positive electrode sheet of the single battery cell at 100% SOC is disassembled, and the compaction density of the positive electrode film layer is measured. For example, a single-sided coated positive electrode sheet (if double-sided coated, the positive electrode film layer on one side can be wiped off first) is taken, cut into small circular pieces with an area of ​​S1, weighed, and recorded as M1, and its thickness H1 is measured. Then, the positive electrode film layer of the weighed positive electrode sheet is wiped off, the weight of the positive current collector is weighed and recorded as M0, and its thickness H0 is measured. The single-sided coating weight of the positive electrode film layer = (weight of the positive electrode sheet M1 - weight of the positive current collector M0) / S1, the thickness of the positive electrode film layer = thickness of the positive electrode sheet H1 - thickness of the positive current collector H0, and the compaction density of the positive electrode film layer = single-sided coating weight of the positive electrode film layer / thickness of the positive electrode film layer.

[0297] In some embodiments, the resistivity of the positive electrode active material powder is from 1 Ω·cm to 27.5 Ω·cm, optionally less than or equal to 20 Ω·cm, and optionally less than or equal to 11 Ω·cm. Exemplarily, the resistivity of the positive electrode active material powder 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 consisting of any two of the above values.

[0298] The powder resistivity of the positive electrode active material is relatively low, which results in relatively low resistance of the positive electrode sheet and less heat generation in the battery cell.

[0299] In the embodiments of this application, the powder resistivity of the material has a well-known meaning in the art and can be tested using methods and equipment well-known in the art, such as using a PRCD1100 powder resistivity meter according to the test standard GB / T30835-2014.

[0300] In some embodiments, the powder compaction density of the positive electrode active material at 30000 N is 2.46 g / cm³. 3 Up to 2.8 g / cm 3 For example, the compacted density of the positive electrode active material at 30000 N is 2.46 g / cm³. 3 2.47 g / cm3 2.48 g / cm 3 2.49 g / cm 3 2.5g / cm 3 2.51g / cm 3 2.55g / cm 3 2.58g / cm 3 2.60g / cm 3 2.65g / cm 3 2.68g / cm 3 2.70 g / cm 3 2.72 g / cm 3 2.75g / cm 3 2.78g / cm 3 2.80g / cm 3 Or a range consisting of any two of the above values.

[0301] When the powder compaction density of the positive electrode active material at 30000N is within the above range, it can improve the energy density of the battery cell. Furthermore, since the positive electrode active material in the positive electrode film can be stacked more tightly, the contact resistance between particles is smaller, which can further reduce the resistance of the electrode sheet, thereby reducing heat generation.

[0302] In the embodiments of this application, the powder compaction density of the material has a meaning known in the art and can be tested using methods and equipment known in the art, according to the testing standard GB / T24533-2009. For example, a certain amount of positive electrode active material is taken as a sample and added to a UTM7305 electronic pressure testing machine with a bottom area of ​​1.327 cm². 2 In the mold, the pressure is increased to 3000 kg (equivalent to 30000 N), held for 30 s, then depressurized and held for 10 s. The compaction density of the positive electrode active material under a force of 30000 N is then recorded and calculated.

[0303] In some embodiments, the specific charge capacity of the positive electrode active material at a 0.1C rate is 150 mAh / g to 170 mAh / g, optionally 157 mAh / g to 170 mAh / g. Exemplarily, the specific charge capacity of the positive electrode active material at a 0.1C rate is 150 mAh / g, 151 mAh / g, 152 mAh / g, 153 mAh / g, 154 mAh / g, 155 mAh / g, 156 mAh / g, 157 mAh / g, 158 mAh / g, 159 mAh / g, 160 mAh / g, 161 mAh / g, 162 mAh / g, 163 mAh / g, 164 mAh / g, 165 mAh / g, 166 mAh / g, 167 mAh / g, 168 mAh / g, 169 mAh / g, 170 mAh / g, or a range consisting of any two of the above values.

[0304] When the specific capacity of the positive electrode active material at a 0.1C rate is within the above range, the energy density of the battery cell is relatively high.

[0305] In the embodiments of this application, the specific capacity of the active material has a meaning known in the art and can be tested using equipment and methods known in the art. The test methods for the first coulombic efficiency and the first discharge specific capacity in Appendix G of the national standard GB / T24533-2019 can be used. A half-coin cell is assembled with lithium metal as the negative electrode and a sample electrode containing the above-mentioned material as the positive electrode. The half-coin cell is tested on a battery tester or other test equipment with equivalent performance at 23℃±2℃ by charging and discharging at a rate of 0.1C to obtain the coin capacity. The capacity is then divided by the mass of the electrode active material to obtain the charging specific capacity parameter.

[0306] In some embodiments, the mass percentage of olivine-structured lithium phosphate in the positive electrode active material can be greater than or equal to 80% and less than or equal to 100%, and the positive electrode active material of this application can be considered as an olivine-structured lithium phosphate system. When the mass percentage of olivine-structured lithium phosphate is less than 100%, the positive electrode active material may also include commonly used positive electrode active materials, such as, but not limited to, at least one of lithium transition metal oxides. Examples of lithium transition metal oxides 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.

[0307] Optionally, the lithium phosphate with an olivine structure in the positive electrode active material accounts for 100% by mass.

[0308] In this application, the lithium phosphate with olivine structure can be phosphate particles or a material obtained by coating and modifying them. For example, the lithium phosphate with olivine structure includes phosphate particles and a coating layer. The coating layer is coated on the surface of the phosphate particles and contains one or more elements selected from C, Fe, Ti, Zr, Hf, Ge and Sn.

[0309] Phosphate particles, through surface coating, can improve the conductivity of lithium phosphates with olivine structure, reduce the powder resistivity of the material, facilitate the migration rate of lithium ions, improve the fast charging capability of the battery, and reduce the heat generation of the battery cell.

[0310] In some embodiments, the phosphate particles comprise the general formula Li x1 A y1 Me a M b P 1-c X c Y z The compound contains 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, where 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. Phosphate particles exhibit excellent cycle stability, which is beneficial for improving the cycle performance of battery cells.

[0311] For example, phosphate particles include one or more of LiFePO4, LiMnPO4, LiNiPO4, and LiCoPO4. During the charging and discharging process, active ions such as Li are de-intercalated and consumed in a single battery cell, resulting in different molar contents of Li in different discharged states. In the examples of positive electrode active materials such as LiFePO4, LiMnPO4, LiNiPO4, and LiCoPO4, the molar contents of Li represent the initial state of the material, i.e., the state before feeding. When the positive electrode active material is applied to the battery system, the molar contents of Li may change after charge-discharge cycles. In the embodiments of this application, the molar contents of oxygen (O) in the examples of positive electrode active materials such as LiFePO4, LiMnPO4, LiNiPO4, and LiCoPO4 are only theoretical values. Lattice oxygen release can cause changes in the molar contents of oxygen (O). In reality, the molar contents of oxygen (O) may fluctuate, and all of the above situations are within the scope of protection of this application.

[0312] In some embodiments, the coating layer includes a general formula Li 3-d Fe 2-d M2 d (PO x2 ) y2 A fast ion conductor, M2 includes one or more elements from Ti, Zr, Hf, Ge and Sn, 0≤d≤1, 0<x2<5, 0<y2<4.

[0313] For example, the fast ion conductor is a material having a NASICON structure, such as one or more of lithium iron phosphate (Li2FeTi(PO4)3), lithium zirconium iron phosphate (Li2FeZr(PO4)3), and lithium iron tin phosphate (Li2FeSn(PO4)3).

[0314] Fast ion conductors with a NASICON structure are materials with ultrafast ion conduction capabilities, possessing abundant three-dimensional lithium-ion diffusion and transport channels. They exhibit advantages such as high ion conduction efficiency and strong structural stability during multiple lithium delithiation and lithium intercalation processes. Coating the surface of phosphate particles with fast ion conductors containing a NASICON structure can significantly improve the lithium-ion transport rate during multiple lithium delithiation / intercalation at the positive electrode, enhance the ionic conductivity of the positive electrode active material, improve the fast charging capability of the battery cell, and further increase the specific capacity and energy density of the corresponding battery cell.

[0315] In some embodiments, the coating layer also includes all-carbon.

[0316] The carbon element and the fast ion conductor can be layered. For example, the carbon element can be an independent carbon coating layer, and the fast ion conductor can be an independent fast ion conductor layer. The carbon coating layer can be applied to the surface of the phosphate particles, and the fast ion conductor layer can be located on the surface of the carbon coating layer, i.e., 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 applied to the surface of the phosphate particles, and the carbon coating layer can be located on the surface of the fast ion conductor layer, i.e., 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 layered together.

[0317] Optionally, the carbon coating layer can be formed by carbonizing an organic carbon source (e.g., glucose, polyethylene glycol, etc.) onto the surface of the fast ion conductor layer. The carbon coating layer can partially or completely cover the fast ion conductor layer. The carbon coating layer can significantly improve the electronic conductivity of phosphate particles, compensating for the poor electronic conductivity of phosphate particles and increasing the energy density of the battery cell.

[0318] Specifically, the carbon coating layer gives the positive electrode active material of this application the following advantages:

[0319] The carbon coating layer in the positive electrode active material of this application provides a suitable channel for electron transport, which can significantly improve the electron conduction rate during multiple lithium delithiation and lithium insertion processes, improve the electronic conductivity of lithium phosphate, improve the charging capacity of the corresponding battery cell, and also improve the energy density.

[0320] The carbon coating layer of the positive electrode active material in this application is porous, which allows the electrolyte to come into full and effective contact with the lithium phosphate, thereby improving the lithium ion transport rate at the phase interface and enhancing the charging capacity of the battery cell.

[0321] Coating the surface of lithium phosphate with a carbon coating layer can not only improve the conductivity of lithium phosphate, but also improve the structural stability of the positive electrode active material. This effectively alleviates the iron dissolution phenomenon of the positive electrode active material during long-term storage and cyclic use of battery cells, thereby improving the cycle life of battery cells.

[0322] The positive electrode active material of this application uses lithium phosphate as a substrate, fully leveraging the advantages of lithium phosphate such as low cost, high reliability, and good cycle stability. Simultaneously, it utilizes coating layers (a fast ion conductor layer and a carbon coating layer) to overcome the drawbacks of poor electronic and ionic conductivity. Battery cells prepared using the positive electrode active material of this application can improve the energy density of battery cells while maintaining excellent cycle performance.

[0323] In this application embodiment, the element content in the positive electrode active material has a meaning known in the art and can be detected using equipment and methods known in the art. For example, referring to EPA6010D-2014, it can be tested by inductively coupled plasma atomic emission spectrometry (ICP-OES, instrument model: Thermo ICAP7400). After discharging the battery cell to 0% state of charge (SOC), the positive electrode sheet is disassembled, cleaned and dried with DMC, and then calcined at high temperature to remove impurities. 0.4g of positive electrode active material is weighed and 10ml (50% concentration) of aqua regia is added. Then it is placed on a plate at 180℃ for 30min. After digestion on the plate, the volume is adjusted to 100mL, and quantitative testing is performed using the standard curve method.

[0324] In some embodiments, the degree of graphitization of the positive electrode active material is 0.15 to 0.32, optionally 0.19 to 0.26. Exemplarily, the degree of graphitization of the positive electrode active material is 0.15, 0.16, 0.17, 0.18, 0.19, 0.20, 0.21, 0.22, 0.23, 0.24, 0.25, 0.26, 0.27, 0.28, 0.29, 0.30, 0.31, 0.32, or a range consisting of any two of the above values.

[0325] When the degree of graphitization of the positive electrode active material is within the above range, it is beneficial to improve the conductivity of the positive electrode active material, reduce the heat generation of the positive electrode sheet, and thus reduce the heat generation of the battery cell.

[0326] In the embodiments of this application, the higher the degree of graphitization of the material, the lower the degree of disorder, and the test can be carried out according to the general rules of X-ray diffraction analysis method JIS / K0131-1996.

[0327] In some embodiments, the carbon content in the olivine-structured lithium phosphate is 1% to 2% by mass, and the specific surface area of ​​the olivine-structured lithium phosphate is 5 m². 2 / g to 18m 2 / g.

[0328] Optionally, the carbon content in the olivine-structured lithium phosphate is 1% to 2% by mass, and the specific surface area of ​​the olivine-structured lithium phosphate is 7.5 m². 2 / g to 14m 2 / g.

[0329] For example, the mass content of carbon in the lithium 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 any combination of two of the above values.

[0330] For example, the specific surface area of ​​lithium phosphate with an olivine structure is 5 m². 2 / g、6m 2 / g、7m 2 / g、8m 2 / g、9m 2 / g, 10m 2 / g、11m 2 / g、12m 2 / g、13m 2 / g、14m 2 / g, 15m 2 / g, 16m 2 / g、17m 2 / g、18m 2 / g or a range consisting of any two of the above values.

[0331] Carbon mainly exists in the form of a carbon coating layer. The carbon coating layer is loose and porous, which helps to increase the specific surface area of ​​the material, facilitates effective contact between the electrolyte and phosphate particles, and promotes the transport of lithium ions at the phase interface. In addition, when the mass content of carbon is within the above range, it can significantly improve the conductivity of lithium phosphate with olivine structure, which is beneficial to improving the ionic and electronic conductivity of lithium phosphate with olivine structure, and can improve the rapid charging capability and energy density of battery cells.

[0332] In the embodiments of this application, the specific surface area of ​​the material has a meaning known in the art and can be detected using equipment and methods known in the art. For example, it can be detected according to the testing standard GB / T19587-2017, using the positive electrode active material as a sample, and the specific surface area is tested using a Tri-Star3020 specific surface area and pore size analyzer from Micromeritics, USA.

[0333] In some embodiments, the volume distribution particle size of the positive electrode active material satisfies: 1μm≤Dv50≤2μm, 0.4μm≤Dv10≤0.7μm.

[0334] For example, the 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 any range of two of the above values.

[0335] For example, 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 any combination of two of the above values.

[0336] The positive electrode active material has a relatively small particle size, resulting in a shorter lithium ion insertion / extraction path and less heat generation. Furthermore, the particle size of the positive electrode active material is not too small, so it will not agglomerate during the processing and preparation process, thus ensuring the stable performance of the positive electrode active material.

[0337] In the embodiments of this application, the volume average particle size Dv50 of the material refers to the particle size corresponding to 50% of the volume distribution, and the volume average particle size Dv10 of the material refers to the particle size corresponding to 10% of the volume distribution. They can be detected using equipment and methods known in the art. For example, the positive electrode active material can be used as a sample, and the Dv50 and Dv10 of the particles can be tested using a Mastersizer2000E laser particle size analyzer according to the test standard GB / T19077-2016.

[0338] When the positive electrode active material includes other materials besides lithium phosphate with olivine structure, the volume distribution particle size of the positive electrode active material refers to the volume distribution particle size of all positive electrode active materials.

[0339] In some embodiments, the olivine-structured lithium phosphate is particulate, comprising secondary particles, which in turn include multiple primary particles. The average particle size of the primary particles is between 200 nm and 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 consisting of any two of the above values.

[0340] The average particle size of primary particles is relatively small, the lithium ion insertion / extraction path in the positive electrode active material is shorter, and the heat generation is less.

[0341] In this embodiment, secondary particles refer to aggregated particles formed by the aggregation of two or more primary particles. Primary and secondary particles can be easily distinguished experimentally (e.g., by taking SEM images using a scanning electron microscope). The average particle size of primary particles can be obtained by testing the SEM images. The SEM test parameters can be set as follows: operating voltage (EHT) of 10.00 kV, using an InLens detector, operating distance of 4.6 mm, and magnification of 1000X.

[0342] In some embodiments, the positive electrode film layer further includes one or more of the following: ternary materials, lithium phosphate, lithium hydrogen phosphate, lithium sulfate, lithium sulfite, lithium molybdate, lithium oxalate, lithium titanate, lithium tetraborate, lithium metasilicate, lithium metamanganese oxide, lithium tartrate, lithium trilithium citrate, lithium nickel oxide, and lithium ferrite. These materials can act as lithium replenishing agents, which can replenish lithium ions to the positive electrode film layer, compensate for irreversible lithium ion losses within the system, increase capacity, and thereby improve the energy density of the battery cell.

[0343] Optionally, ternary materials include Li x3 A y3 Ni a3 Co b3 Mn c M3(1-a3-b3-c3)Y3 z3 Wherein, 0 < x3 ≤ 2.1, 0 < y3 ≤ 2.1, and 0.9 ≤ x3 + y3 ≤ 2.1, 0 ≤ a3 ≤ 1, 0 ≤ b3 ≤ 1, 0 ≤ c3 ≤ 1, and 0.1 ≤ a3 + b3 + c3 ≤ 1, 1.8 ≤ z3 ≤ 3.5, A includes one or more of Na, K, and Mg, M3 includes one or more of B, Mg, Al, Si, P, S, Ca, Sc, Ti, V, Cr, Fe, Cu, Zn, Sr, Y, Zr, Nb, Mo, Cd, Sn, Sb, Te, Ba, Ta, W, Yb, La, and Ce, and Y3 includes one or more of O and F.

[0344] For example, ternary materials include LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2(NCM333), LiNi 0.5 Co 0.2 Mn 0.3 O2(NCM523), LiNi 0.6 Co 0.2 Mn 0.2 O2(NCM622), LiNi 0.8 Co 0.1 Mn 0.1 O2(NCM811), LiNi 0.80 Co 0.15 Al 0.05 At least one of O2.

[0345] In some embodiments, the lithium replenishing agent has a mass content of 0.5% to 5% in the positive electrode film, for example, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, or any combination of two of the above values. When the mass content of the lithium replenishing agent is within the above range, it can replenish lithium ions to the positive electrode film, compensate for irreversible lithium ion loss in the system, increase capacity, and thereby increase the energy density of the battery cell.

[0346] The lithium replenishing agent can be located in the same layer as the positive electrode active material or in a different layer. When the lithium replenishing agent and the positive electrode active material are in different layers, the lithium replenishing agent can be located in the lithium replenishing layer, and the positive electrode active material can be located in the positive electrode active material layer. In other words, the positive electrode film layer includes a lithium replenishing 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 replenishing layer can be located between the positive electrode active material layer and the positive electrode current collector. Alternatively, the lithium replenishing 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 replenishing layer and the positive electrode current collector. Optionally, the lithium replenishing layer can be located between the positive electrode active material layer and the positive electrode current collector. During the cycle charging and discharging of the battery cell, the lithium replenishing agent in the lithium replenishing layer can be gradually released into the system to compensate for the lithium loss of the battery system.

[0347] In some embodiments, the positive electrode film layer may optionally include a positive electrode conductive agent. This application does not impose particular limitations on the type of positive electrode conductive agent. As an example, the positive electrode conductive agent includes at least one selected from superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. In some embodiments, the mass content of the positive electrode conductive agent is ≤5% based on the mass of the positive electrode film layer.

[0348] In some embodiments, the positive electrode film layer may optionally include a positive electrode binder. This application does not impose particular limitations on the type of positive electrode binder. As an example, the positive electrode binder may include at least one selected from polyvinylidene fluoride, polytetrafluoroethylene, a terpolymer of vinylidene fluoride-tetrafluoroethylene-propylene, a terpolymer of vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene, a tetrafluoroethylene-hexafluoropropylene copolymer, polyacrylic acid, and fluorinated acrylate resins. In some embodiments, the mass content of the positive electrode binder is ≤5% based on the mass of the positive electrode film layer.

[0349] In some embodiments, the positive current collector may be a metal foil or a composite current collector. Examples of metal foils include at least one foil selected from aluminum, aluminum alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys. The composite current collector may include a polymeric material substrate and a metal material layer formed on at least one surface of the polymeric material substrate. As an example, the metal material layer may include at least one selected from aluminum, aluminum alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys. As an example, the polymeric material substrate may include at least one selected from polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0350] In some embodiments, the ratio of the thickness of the positive current collector to the thickness of the positive electrode film on one side is 0.05 to 0.3. Exemplarily, the ratio of the thickness of the positive current collector to the thickness of the positive electrode film on one side is 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, 0.12, 0.15, 0.18, 0.2, 0.22, 0.25, 0.28, 0.3, or a range consisting of any two of the above values.

[0351] When the ratio of the thickness of the positive current collector to the thickness of the positive electrode film layer on one side is within the above range, the fast charging capability and energy density of the battery cell can be improved.

[0352] In some embodiments, the thickness of the positive current collector is 10 μm to 15 μm, 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 consisting of any two of the above values.

[0353] 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 excellent, and it can enable the battery cell to have a high energy density.

[0354] In the embodiments of this application, the thickness of the positive electrode film and the positive electrode current collector are known in the art and can be detected using equipment and methods known in the art. For example, the thickness of the positive electrode sheet can be measured with a micrometer, the film layer on the surface of the positive electrode current collector can be removed, and the thickness of the positive electrode current collector can be measured with a micrometer. When the positive electrode film is coated on one side, the thickness of the positive electrode film is the thickness of the positive electrode sheet minus the thickness of the positive electrode current collector. When the positive electrode film is coated on both sides, the thickness of the positive electrode film is (the thickness of the positive electrode sheet minus the thickness of the positive electrode current collector) / 2.

[0355] The positive electrode film is typically formed by coating a positive electrode slurry onto a positive electrode current collector, followed by drying and cold pressing. The positive electrode slurry is usually formed by dispersing the positive electrode active material, optional conductive agent, optional binder, and any other components in a solvent and stirring until homogeneous. The solvent can be N-methylpyrrolidone (NMP), but is not limited to it.

[0356] The positive electrode sheet does not exclude other additional functional layers besides the positive electrode film layer. For example, in some embodiments, the positive electrode sheet of this application further includes a positive conductive layer sandwiched between the positive current collector and the positive electrode film layer and disposed on the surface of the positive current collector. In other embodiments, the positive electrode sheet of this application further includes a protective layer covering the surface of the positive electrode film layer.

[0357] In some embodiments, the positive electrode further includes a positive conductive layer located between the positive electrode film and the positive current collector. The positive conductive layer can further improve the conductivity of the positive electrode and reduce the heat generation of the positive electrode, thereby reducing the heat generation of the battery cell.

[0358] In some embodiments, the thickness of the positive electrode conductive layer is from 0.1 μm to 2 μm. For example, 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 any combination of two of the above values.

[0359] When the thickness of the positive electrode conductive layer is within the above range, the conductivity of the positive electrode sheet can be further improved, the heat generation of the positive electrode sheet can be reduced, thereby reducing the heat generation of the battery cell, and the energy density of the battery cell can also be improved.

[0360] In the embodiments of this application, the thickness of the positive electrode conductive layer has a meaning known in the art and can be detected using equipment and methods known in the art, such as performing a tomographic scan on the positive electrode sheet to directly measure the thickness of the positive electrode conductive layer.

[0361] In some embodiments, the positive conductive layer includes one or more of a positive conductive agent and a positive binder.

[0362] Optionally, the mass content of the positive electrode conductive agent in the positive electrode conductive layer is 30% to 50%. For example, the mass content of the positive electrode conductive agent is 30%, 35%, 40%, 45%, 50%, or any combination of two of the above values.

[0363] For example, the positive electrode conductive agent includes one or more of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. The positive electrode conductive agent in the positive electrode conductive layer can improve the conductivity of the positive electrode conductive layer, thereby improving the conductivity of the positive electrode sheet and reducing the heat generation of the battery cell.

[0364] Optionally, the positive electrode binder has a mass content of 50% to 70% in the positive electrode conductive layer. For example, 50%, 60%, 65%, 70%, or any combination of two of the above values.

[0365] For example, the positive electrode binder includes one or more of polyvinylidene fluoride, polytetrafluoroethylene, a terpolymer of vinylidene fluoride-tetrafluoroethylene-propylene, a terpolymer of vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene, a tetrafluoroethylene-hexafluoropropylene copolymer, polyacrylic acid, and fluorinated acrylate resins. The positive electrode binder in the positive electrode conductive layer can improve the adhesion between the positive electrode current collector and the positive electrode film layer, thereby enhancing the structural stability of the positive electrode sheet.

[0366] [Isolation membrane]

[0367] In this embodiment, the separator includes a porous base membrane.

[0368] In some embodiments, the base film includes at least one of glass fiber, nonwoven 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.

[0369] Optionally, the polyolefin includes at least one of polyethylene, polypropylene, and polyvinylidene fluoride.

[0370] In some embodiments, the porosity of the base membrane is 20% to 70%, optionally 35% to 60%. Exemplarily, the porosity of the base membrane is 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, or any range of two of the above values.

[0371] When the porosity of the base film in the embodiments of this application is within the above-mentioned range, it can enhance the migration ability of lithium ions in the separator, further reduce the internal resistance of the battery cell, and thus reduce heat generation.

[0372] In this embodiment, porosity refers to the percentage of the volume of the pores in the separator to the total volume of the separator. Porosity can be tested according to the standard GB / T36363-2018 "Polyolefin Separators for Battery Cells". It should be noted that the actual testing process may differ slightly from the standard due to differences in testing instruments, testing errors, and to minimize the impact on porosity testing, in order to obtain more accurate test values.

[0373] In some embodiments, the thickness of the base film is 6 μm to 12 μm, optionally 6 μm to 9 μm. Exemplarily, the thickness of the base film is 6 μm, 6.5 μm, 7 μm, 7.5 μm, 8 μm, 8.5 μm, 9 μm, 9.5 μm, 10 μm, 10.5 μm, 11 μm, 11.5 μm, 12 μm, or any range of two of the above values.

[0374] When the thickness of the base film is within the above range, the migration path of lithium ions in the base film is shorter, which can further reduce the internal resistance of the battery cell and thus reduce heat generation.

[0375] In this embodiment, the separator can be a base film. Optionally, the separator further includes a functional layer disposed on at least one side of the base film. The functional layer may include inorganic particles to improve the heat resistance of the separator. Optionally, the functional layer is disposed on both sides of the base film.

[0376] 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. The second inorganic particles are attached to the surface of the non-fluoropolymer particles and / or dispersed inside the non-fluoropolymer particles.

[0377] The first and second functional layers have good heat resistance, which can improve the heat resistance of the separator.

[0378] Optionally, the first functional layer may include an adhesive, optionally including at least one of a fluorinated adhesive or a polyacrylic adhesive, such as polyvinylidene fluoride.

[0379] 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. These first inorganic particles can improve the heat resistance of the first functional layer.

[0380] In the embodiments of this application, the thickness of the base film has a meaning known in the art and can be detected using known meanings and equipment. For example, a newly prepared separator can be taken as a sample, or a battery cell that has been completely discharged (discharged to the lower limit cutoff voltage so that the battery's state of charge is about 0% SOC) can be disassembled in reverse, the separator can be obtained from the battery cell, and the separator can be dried and used as a sample. The separator can be cut with an ion beam cutter to form a cross section, and then the thickness of the separator and its various layers can be measured using a scanning electron microscope.

[0381] In the second functional layer, the non-fluorinated polymer particles refer to polymers that are non-fluorinated polymers. For example, non-fluorinated polymer particles include acrylate copolymers. Optionally, acrylate copolymers include acrylate-acrylonitrile-acrylamide-propylene copolymers. Acrylate copolymers have excellent adhesion properties and high adhesion stability to the base film. The molar percentage of each monomer in the copolymer can be any ratio, for example, 35%:30%:15%:20%, or 40%, 20%, 10%, 30%, or 45%, 15%, 20%, 20%, etc.

[0382] The second inorganic particle in the composite particles prevents the non-fluoropolymer particles from sticking together due to the high-temperature treatment during granulation. This creates porosity within the composite particles, facilitating lithium-ion transport and enhancing the ion-conductivity of the separator. Furthermore, the second inorganic particle increases the compressive modulus of the composite particles, reducing their deformation during charging and discharging, resulting in a more stable separator structure and improved kinetic performance of the battery cells, as well as faster charging performance. Optionally, compared to the first functional layer, the second functional layer is positioned closer to the negative electrode. Because the composite particles are less prone to deformation, the separator exerts minimal pressure or other side effects on the negative electrode, ensuring stable kinetic performance of the negative electrode. Correspondingly, the first functional layer is positioned closer to the positive electrode.

[0383] Optionally, the second inorganic particles include one or more of silicon oxide, aluminum oxide, boehmite, barium sulfate, calcium oxide, titanium oxide, zinc oxide, magnesium oxide, zirconium oxide, and tin oxide. Optionally, the second inorganic particles include silicon oxide. These second inorganic particles can improve the heat resistance of the second functional layer and can combine with non-fluoropolymers to form composite particles, further improving the cycle stability and kinetic performance of the separator, and improving the cycle performance and fast-charging performance of the battery cells.

[0384] The average particle size of the second inorganic particles is 5 nm to 100 nm, optionally 10 nm to 100 nm, or optionally 5 nm to 20 nm. For example, the average particle size of the second inorganic particles is 5 nm, 10 nm, 15 nm, 20 nm, 25 nm, 30 nm, 35 nm, 40 nm, 45 nm, 50 nm, 55 nm, 60 nm, 65 nm, 70 nm, 75 nm, 80 nm, 85 nm, 90 nm, 95 nm, 100 nm, or any combination of 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 compressive modulus of the composite particles.

[0385] In the embodiments of this application, the average particle size of the second inorganic particles has a meaning known in the art and can be detected using equipment and methods known in the art. For example, after obtaining the separator membrane and drying it as a sample, the separator membrane is cut with an ion beam cutter to form a cross-section. Subsequently, the particle size of the second inorganic particles in the separator membrane is measured using a scanning electron microscope. The particle size of multiple, for example, 50, second inorganic particles is measured, and their average value is calculated as the average particle size of the second inorganic particles.

[0386] 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 consisting of any two of the above values.

[0387] When the ionic conductivity of the separator is within the above range, the lithium-ion migration ability of the separator can be further improved, thereby enhancing the fast charging performance of the battery cell.

[0388] In this application embodiment, the ionic conductivity of the separator has a meaning known in the art and can be detected using equipment and methods known in the art, for example,

[0389] Preparation of the 2025-type button cell for testing: In a vacuum glove box, a lithium sheet was placed in the negative electrode case of the battery, and 150 μL of electrolyte was added. The electrolyte was a solution of 1 mol / L LiPF6 in EC / EMC / DEC = 3 / 5 / 2 (mass ratio). Then, a separator (with an area of ​​3.14 cm²) was placed inside. 2 The electrode (12 μm thick) is tightly attached to the lithium sheet, then 25 μL of electrolyte is added, and finally the positive electrode (which can be the positive electrode from Example 1) is placed on top and sealed. The assembled button battery is removed from the vacuum glove box and left for 24 hours for further testing.

[0390] Test: At an electrochemical workstation, at 10-1 ~10 6 The isolation film resistance Rb was obtained by testing within a frequency range of Hz, and the ionic conductivity σ (unit: mS / cm) was calculated using the following formula: σ=L / (R b ×S)

[0391] Where: R b Let L be the resistance of the isolation membrane, and S be the thickness and area of ​​the isolation membrane under test, respectively.

[0392] Electrolyte

[0393] In some implementations, the battery cell also includes an electrolyte.

[0394] During the charging and discharging process of a single battery cell, active ions such as lithium ions are inserted and extracted back and forth between the positive and negative electrode plates, and the electrolyte plays the role of conducting active ions between the positive and negative electrode plates.

[0395] In this embodiment of the application, the conductivity of the electrolyte at room temperature is 13 mS / cm to 20 mS / cm, 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 any range of two of the above values.

[0396] When the conductivity of the electrolyte at room temperature, such as 25°C, is within the above range, the migration rate of lithium ions in the electrolyte is relatively high, which can further reduce the internal resistance of the battery cell, thereby reducing heat generation and improving the fast charging performance of the battery cell.

[0397] In the embodiments of this application, the conductivity of the electrolyte at room temperature, such as 25°C, is the ionic conductivity, which can be detected using equipment and methods known in the art, such as by referring to industry standard HG-T4067-2015.

[0398] 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 consisting of any two of the above values.

[0399] When the viscosity of the electrolyte at room temperature, such as 25°C, is within the above range, the migration rate of lithium ions in the electrolyte is relatively high, which can further reduce the internal resistance of the battery cell, thereby reducing heat generation and improving the fast charging performance of the battery cell.

[0400] In the embodiments of this application, the viscosity of the electrolyte has a meaning known in the art and can be detected using equipment and methods known in the art, such as in accordance with GB / T10247-2008.

[0401] In some embodiments, the electrolyte has a density of 1.05 g / mL to 1.35 g / mL at room temperature, such as 25°C. Exemplarily, the electrolyte density 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 of any two of the above values.

[0402] When the electrolyte density is within the above range, the migration rate of lithium ions in the electrolyte is relatively high, which can further reduce the internal resistance of the battery cell, thereby reducing heat generation and improving the fast charging performance of the battery cell.

[0403] In the embodiments of this application, the density of the electrolyte has a meaning known in the art and can be detected using equipment and methods known in the art, such as referring to GB / T2013-2010 for testing.

[0404] Electrolytes consist of organic solvents and electrolyte salts. The types of organic solvents and electrolyte salts are not specifically limited and can be selected according to actual needs.

[0405] In some embodiments, the organic solvent includes a chain carboxylic acid ester solvent, wherein the mass content of the chain carboxylic acid ester solvent relative to 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%, optionally from 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 of any two of the above values.

[0406] When the mass content of chain carboxylic acid ester solvents is within the above range, the viscosity of the electrolyte system is relatively low, which is conducive to the migration of lithium ions.

[0407] In some embodiments, the chain carboxylic acid ester solvent includes compounds represented by Formula I.

[0408] In formula I,

[0409] R1 includes a hydrogen atom, a halogen atom, a C1 to C5 alkyl group, or a C1 to C5 haloalkyl group.

[0410] R2 includes C1 to C5 alkyl or C1 to C5 haloalkyl.

[0411] The aforementioned chain-like carboxylic acid ester solvents have high conductivity, which is beneficial for improving the fast charging capability of battery cells.

[0412] Optionally, R1 includes a hydrogen atom, a halogen atom, a C1 to C3 alkyl group, or a C1 to C3 haloalkyl group. Further optionally, R1 includes a hydrogen atom, a halogen atom, a C1 to C2 alkyl group, or a C1 to C2 haloalkyl group.

[0413] Optionally, R2 comprises a C1 to C3 alkyl group or a C1 to C3 haloalkyl group. More optionally, R2 comprises a C1 to C2 alkyl group or a C1 to C2 haloalkyl group.

[0414] In the above embodiments, the halogen atom includes one or more of fluorine, chlorine, bromine and iodine atoms, and optionally, the halogen atom includes fluorine atom.

[0415] In the above embodiments, the halogenated alkyl group includes one or more of fluoroalkyl, chloroalkyl, bromoalkyl and iodoalkyl groups, and optionally, the halogenated alkyl group includes fluoroalkyl.

[0416] For example, the chain carboxylic acid ester solvent includes one or more compounds of formula I-1 to formula I-8.

[0417] In some embodiments, the organic solvent also includes carbonate solvents.

[0418] Optionally, the carbonate solvent includes one or more of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, and methyl ethyl carbonate. More preferably, the carbonate solvent includes one or more of ethylene carbonate, dimethyl carbonate, and methyl ethyl carbonate. The combined use of the above-mentioned carbonate solvents and chain carboxylic acid ester solvents improves the conductivity of the electrolyte at room temperature, which is beneficial for lithium ion migration.

[0419] Further optionally, the carbonate solvent in the electrolyte has a mass content of 25% to 60%, optionally 25% to 42.5%. Exemplarily, the mass content of the carbonate solvent in the electrolyte is 25%, 28%, 30%, 31%, 32%, 33%, 34%, 35%, 36%, 37%, 38%, 40%, 45%, 48%, 50%, 55%, 60%, or any combination of two of the above values. The carbonate solvent at the above mass contents can further improve the conductivity of the electrolyte at room temperature, which is beneficial for lithium ion migration.

[0420] For example, the carbonate solvent includes one or more of ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate, and the mass content of the carbonate solvent is 25% to 42.5%.

[0421] In some embodiments, the electrolyte also contains additives, which may include negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain battery performance, such as additives that improve battery overcharge performance, additives that improve battery high-temperature performance, and additives that improve battery low-temperature power performance.

[0422] In some embodiments, the additive comprises one or more of carbonate additives, sulfur-containing additives, and lithium salt additives, optionally at least two. These additives can improve the interfacial film performance on the positive and / or negative electrode sides, which is beneficial for improving the fast-charging performance of individual battery cells and enhancing cycle performance.

[0423] In some embodiments, the additive has a mass content of 1% to 10% in the electrolyte, optionally 2% to 8%, and more preferably 3.5% to 8%. Exemplarily, the additive has a mass content of 1%, 2%, 3%, 3.5%, 4%, 5%, 6%, 7%, 8%, 9%, 10% in the electrolyte, or a range of any two of the above values.

[0424] The additives mentioned above can effectively improve the interfacial film performance on the positive and / or negative electrode sides, which is beneficial to improving the fast charging performance of battery cells and improving cycle performance.

[0425] For example, carbonate additives include one or more of vinylene carbonate (VC) and fluoroethylene carbonate (FEC).

[0426] For example, sulfur-containing additives include one or more of vinyl sulfate DTD, vinyl disulfate 2-DTD, butenyl sulfite BS, 1,3-propanesulfonate lactone PS, vinyl sulfite ES, and methylene disulfonate MMDS.

[0427] Optionally, the lithium salt additive includes one or more of lithium difluorophosphate (LiPO2F2), lithium difluorooxalate borate (LiDFOB), lithium tetrafluoroborate (LiBF4), and lithium dioxalate borate (LiBOB).

[0428] Optionally, the mass content of vinylene carbonate (VC) in the electrolyte is 0.5% to 9%, and optionally 2% to 6%.

[0429] Optionally, the mass content of fluoroethylene carbonate (FEC) in the electrolyte is 0.1% to 4%, and optionally 0.5% to 3%.

[0430] 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%.

[0431] 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%.

[0432] In some embodiments, the electrolyte salt includes a lithium salt, which includes one or more of fluorosulfonylimide salts and lithium hexafluorophosphate (LiPF6). These lithium salts are readily dissociated, facilitating rapid lithium-ion migration, and the electrolyte system is relatively stable and not easily decomposed, thus improving the cycle performance of the battery cells.

[0433] Optionally, the fluorosulfonyl imide salt includes one or more of lithium bisfluorosulfonyl imide (LiFSI) and lithium bistrifluoromethanesulfonate (LiTFSI).

[0434] Optionally, the lithium salt includes lithium bis(fluorosulfonyl)imide (LiFSI) and lithium hexafluorophosphate (LiPF6), wherein the molar concentration of lithium bis(fluorosulfonyl)imide (LiFSI) is from 0.2 mol / L to 0.5 mol / L, and the molar concentration of lithium hexafluorophosphate (LiPF6) is from 0.5 mol / L to 1.0 mol / L.

[0435] For example, 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.

[0436] For example, the molar concentration of lithium bis(fluorosulfonyl)imide (LiFSI) is 0.5 mol / L, and the molar concentration of lithium hexafluorophosphate (LiPF6) is 0.5 mol / L.

[0437] For example, the molar concentration of lithium bis(fluorosulfonyl)imide (LiFSI) is 0.2 mol / L, and the molar concentration of lithium hexafluorophosphate (LiPF6) is 0.8 mol / L.

[0438] Optionally, the molar ratio of lithium bis(fluorosulfonyl)imide to lithium hexafluorophosphate (LiPF6) is from 0.2 to 1.0, and optionally from 0.2 to 0.5. Exemplarily, the molar ratio of lithium bis(fluorosulfonyl)imide to lithium hexafluorophosphate (LiPF6) is 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, or a range of any two of the above values.

[0439] In the embodiments of this application, the types and contents of inorganic components / lithium salt concentrations in the electrolyte are well-known in the art and can be detected using well-known equipment and methods. For example, the concentrations of inorganic components / lithium salts in the electrolyte can be qualitatively or quantitatively analyzed by ion chromatography using the standard JY / T020-1996 "General Rules for Ion Chromatography Analysis". In the embodiments of this application, freshly prepared electrolyte can be used as a sample, the free electrolyte of a fresh battery can be used as a sample, or a battery that has been completely discharged (discharged to the lower limit cutoff voltage so that the battery's state of charge is approximately 0% SOC) can be disassembled in reverse, and the free electrolyte obtained from the battery can be used as a sample for detection by ion chromatography analysis.

[0440] In the embodiments of this application, the types and contents of organic components in the electrolyte are defined in the art and can be detected using equipment and methods known in the art. For example, the organic components in the electrolyte can be qualitatively and quantitatively analyzed by gas chromatography using GB / T9722-2006 "General Rules for Gas Chromatography of Chemical Reagents". In the embodiments of this application, freshly prepared electrolyte can be used as a sample, the free electrolyte of a fresh battery can be used as a sample, or a battery that has been completely discharged (discharged to the lower limit cutoff voltage so that the battery's state of charge is approximately 0% SOC) can be disassembled in reverse, and the free electrolyte obtained from the battery can be used as a sample for detection using ion chromatography.

[0441] In this embodiment, after quantitative and qualitative detection of each component in the electrolyte, the components are classified. Chain-like carboxylic acid ester solvents and carbonate solvents (e.g., ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, and methyl ethyl carbonate) are considered as components of the organic solvent. The mass content of each component is calculated based on the electrolyte mass as 100%.

[0442] Carbonate additives (such as vinylene carbonate and fluoroethylene carbonate), sulfur-containing additives, and lithium salt additives are used as additives in the electrolyte. The mass content of each component is calculated based on the mass of the electrolyte as 100%.

[0443] In some embodiments, the battery cell satisfies: 2.45 g / Ah ≤ d / A ≤ 3.5 g / Ah, optionally 2.45 g / Ah ≤ d / A ≤ 3.3 g / Ah, where d represents the mass of electrolyte in the battery cell in grams (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 of any two of the above values.

[0444] d / A reflects the electrolyte's liquid retention capacity. When d / A is within the above range, the electrolyte can effectively wet the positive and negative electrode plates and improve the migration rate of lithium ions in the liquid phase, which is beneficial to improving the fast charging capability of the battery cell.

[0445] In the embodiments of this application, the d / A ratio of a single battery cell can be understood as the liquid retention coefficient, which can be tested using equipment and methods known in the art. For example, it can be described using GB / T31486-2015 "Electrical Performance Requirements and Test Methods for Power Batteries for Electric Vehicles", taking a battery charging upper limit voltage of 3.65V and a battery discharge cut-off voltage of 2.0V as an example.

[0446] At 25°C, the battery cell is charged to 3.65V at 0.33C, then charged at a constant voltage to 0.05C, and then discharged at a constant current of 0.33C to 2.0V. The discharged capacity A is used as the denominator. The battery cell is weighed as M0. Then, the positive electrode, negative electrode, separator, and electrolyte are disassembled, with the free electrolyte remaining in a bag. All the solid components are placed in a 60°C oven and baked for at least 4 hours (including but not limited to the positive electrode, negative electrode, separator, and other mechanical parts of the disassembled battery cell that contribute to M0). Then, all components of the battery cell are weighed again as M1, with the weight difference between M0 and M1 as the numerator. The liquid retention coefficient is equal to the weight difference d between M0 and M1 divided by the capacity A.

[0447] In some implementations, the positive electrode, separator, and negative electrode can be fabricated into an electrode assembly using a winding process and / or a stacking process.

[0448] Figures 1 and 2 show schematic diagrams of the structure of a single battery cell.

[0449] In some embodiments, the battery cell 7 may include a housing 20.

[0450] In some embodiments, the casing 20 of the battery cell 7 can be a rigid casing, such as a hard plastic casing, an aluminum casing, a steel casing, etc. The casing 20 of the battery cell 7 can also be a pouch, such as a pouch-type pouch. The material of the pouch can be plastic, such as at least one of polypropylene (PP), polybutylene terephthalate (PBT), and polybutylene succinate (PBS).

[0451] The outer shell 20 is a hollow structure, and the outer shell 20 can be used to encapsulate the electrode assembly 10 and the electrolyte.

[0452] The method for preparing the battery cell 7 according to the embodiments of this application is well known. In some embodiments, a positive electrode, a separator, a negative electrode, and an electrolyte can be assembled to form a battery cell 7. As an example, the positive electrode, the separator, and the negative electrode can be formed into an electrode assembly 10 by a winding process and / or a stacking process. The electrode assembly 10 is placed in a housing 20, dried, and then injected with electrolyte. After vacuum sealing, settling, formation, shaping, and other processes, the battery cell 7 is obtained.

[0453] In some embodiments, the housing 20 includes a housing 21 and an end cap 22, the housing 21 having an opening and the end cap 22 closing the opening.

[0454] The shape of the housing 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 21 are cuboid structures.

[0455] In some embodiments, the casing 21 is made of steel, which has high mechanical strength, is not easily deformed, and can improve the reliability and cycle performance of the battery cells. Optionally, steel is the material with the highest mass percentage in the casing 21.

[0456] Optionally, the thickness of the casing 21 is 0.1 mm to 0.5 mm, and optionally 0.2 mm to 0.35 mm. For example, the thickness of the casing 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 any combination of two of the above values. When the thickness of the casing 21 is within the above range, the mechanical strength of the casing 21 is high, which can improve the reliability and cycle performance of the battery cell 7. Furthermore, the casing 21 occupies less space, and the internal space of the casing 21 is larger, which is beneficial to improving the energy density of the battery cell 7.

[0457] From the external shape of the electrode assembly 10, the electrode assembly 10 includes a main body 12, a positive electrode tab 111, and a negative electrode tab 112, with the positive electrode tab 111 and negative electrode tab 112 protruding from the main body 12. The positive electrode tab 111 is the portion of the positive electrode sheet without an active material layer, and the negative electrode tab 112 is the portion of the negative electrode sheet without an active material layer. The positive electrode tab 111 and negative electrode tab 112 are used to draw out the current from the main body 12.

[0458] The positive electrode tab 111 and the negative electrode tab 112 can extend from the same side of the main body 12, or they can extend from opposite sides respectively.

[0459] Optionally, the number of positive electrode tabs 111 located on the same side of the main body 12 is at least one, and optionally at least two. At least two positive electrode tabs 111 can increase the current carrying capacity of the positive electrode tabs 111.

[0460] Optionally, the number of negative electrode tabs 112 located on the same side of the main body 12 is at least one, and optionally at least two. At least two negative electrode tabs 112 can increase the current carrying capacity of the negative electrode tabs 112.

[0461] In some embodiments, the battery cell 7 further includes a positive terminal 31, which is electrically connected to a positive electrode tab 111. Optionally, the positive terminal 31 and the positive electrode tab 111 are welded together. The positive terminal 31 and the positive electrode tab 111 can be connected by an adapter, or they can be connected without an adapter. Optionally, the positive terminal 31 and the positive electrode tab 111 are directly welded together without an adapter, which can reduce the resistance at the connection point and help reduce the overall internal resistance of the battery cell 7.

[0462] In some embodiments, the battery cell 7 further includes a negative terminal 32, which is electrically connected to a negative electrode tab 112. Optionally, the negative terminal 32 and the negative electrode tab 112 are welded together. The negative terminal 32 and the negative electrode tab 112 can be connected by an adapter, or they can be connected without an adapter. Optionally, the negative terminal 32 and the negative electrode tab 112 are directly welded together without an adapter, which can reduce the resistance at the connection point and help reduce the overall internal resistance of the battery cell 7.

[0463] Optionally, the number of positive terminals 31 located on the same side of the main body 12 is at least one, and optionally at least two. At least two positive terminals 31 can increase the current carrying capacity of the positive terminals 31.

[0464] Alternatively, the flow area of ​​the single-sided positive terminal 31 is 150 mm². 2 Up to 1000mm 2 200mm is optional2 Up to 1000mm 2 The flow area of ​​a single positive terminal 31 refers to the sum of the flow areas of all positive terminals 31 located on the same side of the main body 12. The flow area of ​​a positive terminal 31 can be understood as the cross-sectional area of ​​the positive terminal 31, which is perpendicular to the thickness direction of the end cap 22.

[0465] For example, the flow area of ​​the single-sided positive terminal 31 can be 150 mm². 2 200mm 2 210mm 2 250mm 2 280mm 2 300mm 2 320mm 2 350mm 2 380mm 2 400mm 2 450mm 2 500mm 2 550mm 2 600mm 2 650mm 2 700mm 2 750mm 2 800mm 2 850mm 2 900mm 2 950mm 2 1000mm 2 Or a range consisting of any two of the above values.

[0466] Optionally, the number of negative terminals 32 located on the same side of the main body 12 is at least one, and optionally at least two. At least two negative terminals 32 can increase the current carrying capacity of the negative terminals 32.

[0467] Alternatively, the flow area of ​​the single-sided negative terminal 32 is 150 mm². 2 Up to 1000mm 2 200mm is optional 2 Up to 1000mm 2 The flow area of ​​a single negative terminal 32 refers to the sum of the flow areas of all negative terminals 32 located on the same side of the main body 12. The flow area of ​​a negative terminal 32 can be understood as the cross-sectional area of ​​the negative terminal 32, which is perpendicular to the thickness direction of the end cap 22.

[0468] For example, the flow area of ​​the single-sided negative terminal 32 can be 150 mm². 2 200mm 2 210mm 2250mm 2 280mm 2 300mm 2 320mm 2 350mm 2 380mm 2 400mm 2 450mm 2 500mm 2 550mm 2 600mm 2 650mm 2 700mm 2 750mm 2 800mm 2 850mm 2 900mm 2 950mm 2 1000mm 2 Or a range consisting of any two of the above values.

[0469] As shown in Figure 10, in some embodiments of this application, the battery cell 7 according to the implementation of this application can be assembled into a battery module 6. The number of battery cells 7 contained in the battery module 6 can be one or more, and the specific number can be adjusted according to the application and capacity of the battery module 6.

[0470] If there are multiple battery cells 7, they can be connected in series, parallel, or in a mixed configuration. A mixed configuration means that some battery cells 7 are connected in series while others are connected in parallel. Multiple battery cells 7 can be directly connected in series, parallel, or in a mixed configuration, and then the entire assembly of these battery cells 7 is housed within the housing of the battery module 6. Alternatively, multiple battery cells 7 can first be connected in series, parallel, or in a mixed configuration to form the battery module 6, and then the multiple battery modules 6 can be connected in series, parallel, or in a mixed configuration to form a whole, which is then housed within the housing. Optionally, the battery module 6 may also include a housing with a accommodating space, within which multiple battery cells 7 are housed.

[0471] As shown in Figure 11, in some embodiments, the battery module 6 can also be assembled into a battery pack 2, and the number of battery modules 6 contained in the battery pack 2 can be adjusted according to the application and capacity of the battery pack. The battery device described herein can be either a battery module 6 or a battery pack 2.

[0472] The battery pack 2 may include a housing 5 and a plurality of battery modules 6 disposed within the housing 5. The housing 5 includes a first housing portion 5a and a second housing portion 5b, and the housing 5 has a receiving space 5c. The first housing portion 5a is used to cover the second housing portion 5b and form a closed space for accommodating the battery modules 6. The plurality of battery modules 6 can be arranged in the housing 5 in any manner.

[0473] The first housing portion 5a and the second housing portion 5b overlap each other, and together they define a receiving space 5c for accommodating a single battery cell. The second housing portion 5b can be a hollow structure with one open end, and the first housing portion 5a can be a plate-like structure. The first housing portion 5a covers the open side of the second housing portion 5b to form a housing 5 with the receiving space 5c. Alternatively, both the first housing portion 5a and the second housing portion 5b can be hollow structures with one open side, with the open side of the first housing portion 5a covering the open side of the second housing portion 5b to form a housing 5 with the receiving space 5c. Of course, the first housing portion 5a and the second housing portion 5b can be of various shapes, such as cylinders, cuboids, etc.

[0474] To improve the sealing performance after the first housing part 5a and the second housing part 5b are connected, a sealing element, such as sealant or sealing ring, can also be provided between the first housing part 5a and the second housing part 5b.

[0475] Assuming that the first box section 5a covers the top of the second box section 5b, the first box section 5a can also be called the upper box cover, and the second box section 5b can also be called the lower box.

[0476] In some embodiments, during the charging process of the battery pack 2 or any individual battery cell comprising the battery pack 2 from 0% state of charge (SOC) to 100% state of charge (SOC), the ambient temperature of the external environment in which the battery pack 2 is located is 30°C.

[0477] In some embodiments, during the charging process of the battery pack 2 or any individual battery cell comprising the battery pack 2 from 10% state of charge (SOC) to 80% SOC, the ambient temperature of the external environment in which the battery pack 2 is located is 30°C.

[0478] In some embodiments, the charging process of the battery pack 2 or any individual battery cell comprising the battery pack 2 from 10% state of charge to 80% state of charge 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 any range of any two of the above values.

[0479] The battery pack 2 or any individual battery cell comprising the battery pack 2 includes multiple charging steps from 10% state of charge to 40% state of charge. For any charging step, the battery can be charged at any rate between 5C and 10C. The charging rate corresponding to each charging step can be any value of 5C, 5.5C, 6C, 6.5C, 7C, 7.5C, 8C, 8.5C, 9C, 9.5C, or 10C, or a value within the range of any two of the above values.

[0480] For example, the charging steps from 10% to 80% for the battery pack 2 or any individual battery cell comprising the battery pack 2 can be performed as follows:

[0481] Charge from 10% SOC to 15% SOC at a constant current of 5.0C.

[0482] Charge from 15% SOC to 20% SOC at a constant current of 5.0C.

[0483] Charge from 20% SOC to 25% SOC at a constant current of 5.0C.

[0484] Charge from 25% SOC to 30% SOC at a constant current of 5.0C.

[0485] Charge from 30% SOC to 35% SOC at a constant current of 5.0C.

[0486] Charge from 35% SOC to 40% SOC at a constant current of 5.0C.

[0487] Charge from 40% SOC to 45% SOC at a constant current of 4.6C.

[0488] Charge from 45% SOC to 50% SOC at a constant current of 4.3C.

[0489] Charge from 50% SOC to 55% SOC at a constant current of 4.0C.

[0490] Charge from 55% SOC to 60% SOC at a constant current of 3.7C.

[0491] Charge from 60% SOC to 65% SOC at a constant current of 3.4C.

[0492] Charge from 65% SOC to 70% SOC at a constant current of 3.1C.

[0493] Charge from 70% SOC to 75% SOC at a constant current of 2.9C.

[0494] Charge from 75% SOC to 80% SOC at a constant current of 2.7C.

[0495] In some embodiments, the charging time for the battery pack 2 or any individual battery cell comprising the battery pack 2 from 10% state of charge to 80% state of charge is less than or equal to 10.5 minutes, optionally ranging from 5 minutes to 10.5 minutes, and the ambient temperature of the battery pack 2 at 10% state of charge is room temperature, for example, 30°C. Exemplarily, the charging time for the battery pack 2 from 10% state of charge to 80% state of charge is 10.5 minutes, 10 minutes, 9.5 minutes, 9 minutes, 8.5 minutes, 8 minutes, 7.5 minutes, 7 minutes, 6.5 minutes, 6 minutes, 5.5 minutes, 5 minutes, or a range of any two of the above values.

[0496] In some embodiments, the volumetric energy density of the battery cell is from 390 Wh / L to 500 Wh / L, optionally from 410 Wh / L to 470 Wh / L. Exemplarily, the volumetric energy density of the battery cell is 390 Wh / L, 400 Wh / L, 410 Wh / L, 420 Wh / L, 430 Wh / L, 440 Wh / L, 450 Wh / L, 460 Wh / L, 470 Wh / L, 480 Wh / L, 490 Wh / L, 500 Wh / L, or a range of any two of the above values. The volumetric energy density of the battery cell is relatively high.

[0497] In the embodiments of this application, the volumetric energy density of a single battery cell has a meaning known in the art and can be detected using equipment and methods known in the art. For example, the following description uses a battery charging upper limit voltage of 3.65V and a battery discharging cutoff voltage of 2.0V as an example.

[0498] Place the battery cell at 25°C and charge it to 3.65V with a constant current of 0.33C, then charge it to 0.05C with a constant voltage, and discharge it to 2.0V with a constant current of 0.33C. Record the discharge capacity A0 at this point, in Ah. Use calipers to measure the length, width, and height of the battery cell (generally calculated based on the battery casing dimensions, excluding the height of the electrode terminals and the insulating film outside the casing). Calculate the volume of the battery cell V0, in L. The volumetric energy density of the battery cell VED = (A0 × discharge plateau voltage) / V0, in Wh / L.

[0499] Electrical appliances

[0500] The second aspect of this application provides an electrical device, which includes a battery device as described in this application, such as a battery cell, battery module, or battery pack. The battery cell, battery module, or battery pack can be the power source of the electrical device or the energy storage unit of the electrical device. The electrical device can be a vehicle, mobile phone, portable device, laptop computer, ship, spacecraft, electric toy, and power tool, etc. Vehicles can be gasoline-powered vehicles, natural gas-powered vehicles, or new energy vehicles; new energy vehicles can be pure electric vehicles, hybrid electric vehicles, or range-extended electric vehicles, etc.; spacecraft include airplanes, rockets, space shuttles, and spacecraft, etc.; electric toys include stationary or mobile electric toys, such as game consoles, electric car toys, electric ship toys, and electric airplane toys, etc.; power tools include metal cutting power tools, grinding power tools, assembly power tools, and railway power tools, such as electric drills, electric grinders, electric wrenches, electric screwdrivers, electric hammers, impact drills, concrete vibrators, and electric planers, etc. This application does not impose any special limitations on the above-described electrical device.

[0501] Electrical devices can be equipped with individual battery cells, battery modules, or battery packs depending on their usage requirements.

[0502] Figure 12 is a schematic diagram of an example electrical device 1. This electrical device 1 is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. To meet the high power and high energy density requirements of this electrical device 1, a battery pack or battery module can be used.

[0503] The electrical device 1 is equipped with a battery pack 2, which can be located at the bottom, head, or tail of the electrical device 1. The battery pack 2 can be used to supply power to the electrical device 1. For example, the battery pack 2 can serve as the operating power source for the electrical device 1, and can also serve as the driving power source for the electrical device 1, replacing or partially replacing fuel oil or natural gas to provide driving power for the electrical device 1.

[0504] Electrical device 1 may also include controller 3 and motor 4. Controller 3 is used to control battery pack 2 to supply power to motor 4, for example, to meet the power needs of electrical device 1 during startup, navigation and driving.

[0505] Another example of an electrical device could be a mobile phone, tablet, or laptop. These devices typically require a slim and lightweight design and can use a single battery cell as their power source.

[0506] The following charging methods can be selected for the charging process of electrical devices:

[0507] Charge from 10% SOC to 15% SOC at a constant current of 5.0C.

[0508] Charge from 15% SOC to 20% SOC at a constant current of 5.0C.

[0509] Charge from 20% SOC to 25% SOC at a constant current of 5.0C.

[0510] Charge from 25% SOC to 30% SOC at a constant current of 5.0C.

[0511] Charge from 30% SOC to 35% SOC at a constant current of 5.0C.

[0512] Charge from 35% SOC to 40% SOC at a constant current of 5.0C.

[0513] Charge from 40% SOC to 45% SOC at a constant current of 4.6C.

[0514] Charge from 45% SOC to 50% SOC at a constant current of 4.3C.

[0515] Charge from 50% SOC to 55% SOC at a constant current of 4.0C.

[0516] Charge from 55% SOC to 60% SOC at a constant current of 3.7C.

[0517] Charge from 60% SOC to 65% SOC at a constant current of 3.4C.

[0518] Charge from 65% SOC to 70% SOC at a constant current of 3.1C.

[0519] Charge from 70% SOC to 75% SOC at a constant current of 2.9C.

[0520] Charge from 75% SOC to 80% SOC at a constant current of 2.7C.

[0521] In some embodiments, the charging time for the electrical device from 10% state of charge to 80% state of charge is less than or equal to 10.5 minutes, optionally ranging from 5 minutes to 10.5 minutes, and the ambient temperature of the battery pack 2 at 10% state of charge is room temperature, for example, 30°C. Exemplarily, the charging time for the battery pack 2 from 10% state of charge to 80% state of charge is 10.5 minutes, 10 minutes, 9.5 minutes, 9 minutes, 8.5 minutes, 8 minutes, 7.5 minutes, 7 minutes, 6.5 minutes, 6 minutes, 5.5 minutes, 5 minutes, or a range of any two of the above values.

[0522] Example

[0523] The following embodiments describe the contents disclosed in this application in more detail. These embodiments are merely illustrative, as various modifications and variations will be apparent to those skilled in the art within the scope of the disclosure of the embodiments of this application. Unless otherwise stated, all parts, percentages, and ratios reported in the following embodiments are based on mass, and all reagents used in the embodiments are commercially available or synthesized by conventional methods and can be used directly without further processing, and the instruments used in the embodiments are commercially available.

[0524] Example 1-1 (Stacked Battery Cell)

[0525] 1. Preparation of positive electrode sheet

[0526] The positive electrode includes a positive current collector, a positive conductive layer on the positive current collector, and a positive film layer. The positive current collector is aluminum foil.

[0527] The positive electrode conductive layer on the positive electrode current collector is a film formed by uniformly mixing the positive electrode conductive agent superconducting carbon, the positive electrode binder polyvinylidene fluoride (PVDF), and the solvent N-methylpyrrolidone (NMP), coating it on the surface of the current collector, and drying it. The thickness is 1 μm. The positive electrode conductive layer contains 40% positive electrode conductive agent by mass and 60% positive electrode binder by mass.

[0528] The positive electrode film layer comprises a film layer formed by uniformly coating a positive electrode slurry (solvent being N-methylpyrrolidone, NMP) onto the surface of a positive electrode conductive layer, followed by drying and cold pressing. The positive electrode film layer comprises positive electrode active material, binder polyvinylidene fluoride (PVDF), and conductive agent acetylene black in a weight ratio of 97:2:1.

[0529] The positive electrode active material includes lithium iron phosphate and a coating layer. The coating layer is coated on the surface of the lithium iron phosphate and includes lithium titanium iron phosphate (Li2FeTi(PO4)3) and amorphous carbon. The Dv50 of the positive electrode active material is 1.6 μm, and the Dv10 is 0.64 μm.

[0530] The single-sided coating weight of the positive electrode film is 300 mg / 1540.25 mm. 2 .

[0531] 2. Preparation of negative electrode sheet

[0532] The negative electrode sheet includes a negative current collector, a negative conductive layer on the negative current collector, and a negative film layer. The negative current collector is copper foil.

[0533] The negative electrode conductive layer on the negative electrode current collector is a film formed by uniformly mixing the negative electrode conductive agent superconducting carbon, the negative electrode binder styrene-butadiene rubber SBR, the thickener sodium carboxymethyl cellulose (CMC-Na), and the solvent water, coating it on the surface of the negative electrode current collector, and drying it. The thickness is 1μm. The negative electrode conductive agent has a mass content of 35% in the negative electrode conductive layer, the negative electrode binder has a mass content of 60% in the negative electrode conductive layer, and the thickener has a mass content of 5% in the negative electrode conductive layer.

[0534] The negative electrode film layer comprises a film layer formed by uniformly coating a negative electrode slurry (with deionized water as the solvent) onto the surface of a negative electrode conductive layer, followed by drying and cold pressing.

[0535] The single-sided coating weight of the negative electrode film is 138 mg / 1540.25 mm. 2 .

[0536] 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 0.15.

[0537] The first region comprises a first sublayer and a second sublayer. The first sublayer is located on the surface of the negative electrode conductive layer, and the second sublayer is located on the surface of the first sublayer. After being fabricated into a battery cell, the compaction density of the first sublayer of the battery cell at 100% SOC is 1.35 g / cm³. 3 The compaction density of the second sublayer is 1.28 g / cm³. 3 .

[0538] The first sublayer comprises a negative electrode active material in a mass ratio of 96.5:0.5:2.5:0.3:0.2, a conductive agent acetylene black, a lithium-containing binder (lithium acrylate-acrylonitrile-acrylamide-hydroxyethyl acrylate copolymer, wherein the molar percentages of lithium acrylate monomer, acrylonitrile monomer, acrylamide monomer and hydroxyethyl acrylate monomer are 35%:30%:15%:20%), a negative electrode binder styrene-butadiene rubber, and a thickener sodium carboxymethyl cellulose. The lithium-containing binder contains 9% lithium by mass. The negative electrode active material includes artificial graphite and natural graphite. The volume average particle size Dv50 of artificial graphite is 11.8 μm, and the volume average particle size Dv50 of natural graphite is 12 μm.

[0539] The second sublayer comprises artificial graphite in a mass ratio of 96.5:0.5:0.5:1.5:1, conductive agent acetylene black, lithium-containing binder (lithium acrylate-acrylonitrile-acrylamide-hydroxyethyl acrylate copolymer, wherein the molar percentages of lithium acrylate monomer, acrylonitrile monomer, acrylamide monomer and hydroxyethyl acrylate monomer are 35%:30%:15%:20%), negative electrode binder styrene-butadiene rubber, and thickener sodium carboxymethyl cellulose. The lithium content in the first lithium-containing binder is 9% by mass, and the volume average particle size Dv50 of the artificial graphite is 11.8 μm. The lithium-containing binder in the second sublayer has a mass content of 0.50%.

[0540] 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 fabricated into a battery cell, the compaction density of the first negative electrode film layer of the battery cell at 100% SOC is 1.28 g / cm³. 3 The compaction density of the second negative electrode film is 1.28 g / cm³. 3 .

[0541] The first negative electrode film layer comprises graphite particles in a mass ratio of 96.5:0.5:2.5:0.3:0.2, conductive agent acetylene black, a first lithium-containing binder (lithium acrylate-acrylonitrile-acrylamide-hydroxyethyl acrylate copolymer, wherein the molar percentages of lithium acrylate monomer, acrylonitrile monomer, acrylamide monomer and hydroxyethyl acrylate monomer are 35%:30%:15%:20%), negative electrode binder styrene-butadiene rubber, and thickener sodium carboxymethyl cellulose. The lithium content 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 coats the surface of the artificial graphite, and the mass content of the carbon coating layer is 3.5%.

[0542] The second negative electrode film layer comprises graphite particles in a mass ratio of 96.5:0.5:0.5:1.5:1, conductive agent acetylene black, a second lithium-containing binder (lithium acrylate-acrylonitrile-acrylamide-hydroxyethyl acrylate copolymer, wherein the molar percentages of lithium acrylate monomer, acrylonitrile monomer, acrylamide monomer and hydroxyethyl acrylate monomer are 35%:30%:15%:20%), negative electrode binder styrene-butadiene rubber, and thickener sodium carboxymethyl cellulose. The lithium content 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 coats the surface of the artificial graphite, and the mass content of the carbon coating layer is 3.5%.

[0543] 3. Separating membrane

[0544] The separator includes a base membrane, which is a 7μm polyethylene film layer with a porosity of 42%.

[0545] 4. Preparation of electrolyte

[0546] The electrolyte consists of organic solvents, lithium salts, and additives.

[0547] The organic solvents include 48.5% chain carboxylic acid ester solvents (ethyl acetate) and 32.5% carbonate solvents (24.5% ethylene carbonate EC, 8% dimethyl carbonate). The mass content of each component in the organic solvents is calculated based on the mass of the electrolyte.

[0548] Based on the mass of the electrolyte, the additive content is 6.5%, which includes vinylene carbonate (VC), fluoroethylene carbonate (FEC), vinyl sulfite (ES), and lithium difluorooxalate borate (LiDFOB) in a mass ratio of 5:0.5:0.5:0.5.

[0549] The lithium salts include 1 mol / L lithium hexafluorophosphate (LiPF6).

[0550] The electrolyte has a conductivity of 16.4 mS / cm at room temperature.

[0551] 5. Preparation of battery cells

[0552] The positive electrode, separator, and negative electrode are stacked in sequence, with the separator positioned between the positive and negative electrodes to provide isolation. This stacking process yields an electrode assembly. The electrode assembly is then placed in an outer packaging shell, dried, and injected with electrolyte. Following vacuum sealing, settling, formation, and shaping processes, a battery cell is obtained. The compaction density of the positive electrode film layer at 100% SOC is 2.72 g / cm³. 3 .

[0553] Comparative Example 1-1, Examples 1-2 to 1-11

[0554] Battery cells were prepared using a method similar to that of Example 1-1. The difference from Example 1-1 is that the composition of the first sublayer was adjusted, as shown in Table 1.

[0555] Performance testing

[0556] 1. Number of cycles required for a single battery cell to reach 70% SOH

[0557] At room temperature, charge a single battery cell at a constant current of 1C to the charging cutoff voltage of 3.65V, and then discharge it at a constant current of 1C to 2.0V. This constitutes 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 cycles, the better the cycle performance of the battery cell.

[0558] The test results are shown in Table 1.

[0559] Table 1

[0560] In Table 1, the tabs are located on both sides of the current collector along its length.

[0561] Compacted density refers to the compacted density of a single cell at 100% SOC.

[0562] 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.

[0563] In Comparative Example 1-1, the first region does not include natural graphite, resulting in a large lithium plating area in the battery cell and a significant drop in cycle performance. However, the embodiments of this application, through designing the first region, include both artificial and natural graphite in the first sublayer, improving the fast-charging performance of the first sublayer, reducing the lithium plating area, and enhancing cycle performance. Furthermore, by appropriately increasing the mass content of natural graphite, for example to 5% to 45%, or optionally 20% to 45%, the compaction density increases with the increase in the mass content of natural graphite, further mitigating the risk of lithium plating and improving cycle performance. Conversely, further increasing the mass content of natural graphite worsens cycle performance.

[0564] The embodiments of this application can further improve the risk of lithium plating and enhance cycle performance by appropriately adjusting the distribution content of artificial graphite in the first and second sublayers.

[0565] In this embodiment, the volume average particle size Dv50 of natural graphite is appropriately adjusted, for example, Dv50 is 12 μm, and its specific surface area is 2.1 m². 2 / g can improve the cycle performance and lithium plating risk of individual cells. With a relatively small Dv50 (e.g., 8μm), the charging capability of natural graphite is enhanced, and its specific surface area is relatively large (e.g., 4.0m²). 2 / g, with relatively more side reactions, resulting in relatively poor cycle performance; when Dv50 is relatively large, such as 15μm, its specific surface area is relatively small, such as 1.85m². 2 While natural graphite exhibits fewer side reactions and optimized cycle performance, its charging capability is weakened. In this application, by appropriately reducing the volume average particle size (Dv50) of the artificial graphite, for example from 7 μm to 15 μm (selectively from 7 μm to 12 μm), the solid-phase transport path is shorter, which is beneficial for improving fast charging capability and reducing the risk of lithium plating. When the volume average particle size of the artificial graphite is 11.8 μm, its specific surface area is 0.9 m². 2 / g; When the volume average particle size of artificial graphite is 7μm, its specific surface area is 2.6m². 2 / g.

[0566] The embodiments of this application, by appropriately increasing the mass content of lithium-containing binder, are beneficial to further improve the risk of lithium plating and enhance cycle performance.

[0567] In the embodiments of this application, the length ratio of the first region to the negative electrode film is 0.05 to 0.20, and can be selected as 0.10 to 0.20. As the size of the first region increases, the risk of lithium plating decreases, but the cycle life may deteriorate due to the decrease in capacity.

[0568] Example 2-1 (Wound Battery Cell)

[0569] Battery cells were prepared using a method similar to that in Example 1-1, except that an electrode assembly was prepared using a winding process, thereby obtaining the battery cell. The negative electrode film layer includes a first region and a second region, with the length ratio of the first region to the negative electrode film layer being 0.08.

[0570] Comparative Example 2-1, Examples 2-2 to 2-7

[0571] Battery cells were prepared using a method similar to that of Example 2-1. The difference from Example 2-1 is that the composition of the first sublayer was adjusted, as shown in Table 2.

[0572] Table 2

[0573] In Table 2, the tab is located on one side of the current collector.

[0574] Compacted density refers to the compacted density of a single cell at 100% SOC.

[0575] 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.

[0576] In Comparative Example 2-1, the first region did not include natural graphite, resulting in a large lithium plating area in the battery cell and a significant drop in cycle performance. However, the embodiments of this application, through designing the first region, include both artificial and natural graphite in the first sublayer, improving the fast-charging performance of the first sublayer, reducing the lithium plating area, and enhancing cycle performance. Furthermore, by appropriately increasing the mass content of natural graphite, for example to 5% to 45%, or optionally 20% to 45%, the compaction density increases with the increase in the mass content of natural graphite, further mitigating the risk of lithium plating and improving cycle performance. Conversely, further increasing the mass content of natural graphite worsens cycle performance.

[0577] The embodiments of this application, by appropriately increasing the mass content of lithium-containing binder, are beneficial to further improve the risk of lithium plating and enhance cycle performance.

[0578] Although illustrative embodiments have been demonstrated and described, those skilled in the art should understand that the above embodiments should not be construed as limiting the present application, and that changes, substitutions and modifications can be made to the embodiments without departing from the spirit, principles and scope of the present application.

Claims

A battery cell includes an electrode assembly including: a positive electrode tab including a positive current collector and a positive film layer disposed on at least one side of the positive current collector in a thickness direction of the positive current collector, the positive film layer including a positive active material including a lithium-containing phosphate of olivine structure; and a negative electrode tab including a negative current collector and a negative film layer disposed on at least one side of the negative current collector in the thickness direction, the negative film layer containing a negative active material, the negative electrode tab being connected to at least one side of the negative current collector in a first direction, the negative film layer including two end portions opposite to each other in the first direction, a first region including one end portion of the two end portions facing the negative electrode tab, a ratio of a dimension of the first region in the first direction to a dimension of the negative film layer in the first direction being 0.05 to 0.20, the negative active material of the first region including artificial graphite and natural graphite, wherein the first direction is perpendicular to the thickness direction. The battery cell of claim 1, wherein, A mass content of the natural graphite with respect to a mass of the negative active material in the first region is 5% to 45%. The battery cell according to claim 1 or 2, wherein, A mass content of the natural graphite with respect to a mass of the negative active material in the first region is 20% to 45%. The battery cell according to claim 1 or 2, wherein A mass content of the artificial graphite with respect to a mass of the negative active material in the first region is 55% to 95%. The battery cell of any one of claims 1 to 4, wherein, The first region includes a first sub-layer disposed on at least one side of the negative current collector and a second sub-layer disposed on a side of the first sub-layer facing away from the negative current collector, the first sub-layer including artificial graphite and natural graphite, the second sub-layer including artificial graphite. The battery cell of claim 5, wherein, A mass content of the artificial graphite in the second sub-layer with respect to a mass of the negative active material in the first region is 30% to 70%. The battery cell according to claim 5 or 6, wherein The first sub-layer has a compaction density greater than or equal to a compaction density of the second sub-layer at 100% state of charge of the battery cell. The battery cell of any one of claims 5 to 7, wherein, The battery cell has a compaction density of the first sub-layer of 1.25 g / cm3 3 to 1.65 g / cm3 3 ; and / or The battery cell has a compaction density of the second sub-layer of 1.1 g / cm 3 to 1.5 g / cm 3 . The battery cell of any one of claims 5 to 8, wherein, The first sub-layer includes a lithium-containing binder having a mass content of 0.1% to 3% with respect to a mass of the first sub-layer; and / or The second sub-layer includes a lithium-containing binder having a mass content of 0.1% to 3% with respect to a mass of the second sub-layer. The battery cell of claim 9, wherein, A mass content of lithium in the lithium-containing binder is 4% to 10%. The battery cell according to claim 9 or 10, wherein The lithium-containing binder includes a lithium acrylate-acrylonitrile-acrylamide-hydroxyethyl acrylate copolymer derived from lithium acrylate monomers, acrylonitrile monomers, acrylamide monomers, and hydroxyethyl acrylate monomers, the lithium acrylate monomers, the acrylonitrile monomers, the acrylamide monomers, and the hydroxyethyl acrylate monomers having a mole percentage of 30% to 50%: 15% to 45%: 5% to 20%: 20% to 35%. The battery cell of any one of claims 1 to 11, wherein A volume average particle diameter Dv50 of the artificial graphite in the first region is 7 μm to 15 μm; and / or A volume average particle diameter Dv50 of the natural graphite in the first region is 7 μm to 15 μm. The battery cell of any one of claims 1 to 12, wherein, The specific surface area of the natural graphite in the first region is greater than the specific surface area of the artificial graphite in the first region. The battery cell of any one of claims 1 to 13, wherein, The specific surface area of the 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 of the first region is 0.7 m 2 / g to 3.0 m 2 / g. The battery cell of any one of claims 1 to 14, wherein, The ratio of the dimension of the first region along the first direction to the dimension of the negative electrode film layer along the first direction is 0.10 to 0.

20. The battery cell of any one of claims 1 to 15, wherein, The electrode assembly is of a jelly-roll structure, and the positive electrode tab and the negative electrode tab are wound along one direction. The battery cell of claim 16, wherein, The negative electrode tab is connected to one side of the negative electrode current collector along the first direction, and the first region includes both of the end portions. The battery cell of claim 16, wherein, The negative electrode tab is connected to one side of the negative electrode current collector along the first direction, and the first region is one of the end portions facing the negative electrode tab. The battery cell of any one of claims 1 to 18, wherein, The electrode assembly is of a jelly-roll structure, and the positive electrode tab and the negative electrode tab are wound along one direction. The battery cell of claim 19, wherein, The negative electrode tab is connected to one side of the negative electrode current collector along the first direction, and the first region includes both of the end portions. The battery cell of any one of claims 1 to 20, wherein, After the battery cell is cycled for 500 times, the lithium precipitation area of the negative electrode film layer accounts for 0 to 13.5% of the surface area of the negative electrode film layer. The battery cell of any one of claims 1 to 21, wherein, The lithium precipitation area of the negative electrode film layer accounts for 0 to 6%. The battery cell of any one of claims 1 to 22, wherein, The positive electrode tab further comprises an insulating layer disposed on the positive electrode current collector and connected to the positive electrode film layer, and the insulating layer and the first region are oppositely disposed along the thickness direction. The battery cell of any one of claims 1 to 23, wherein, The negative electrode film layer further comprises a second region continuously disposed with the first region, and the second region comprises: a first negative electrode film layer disposed on the surface of the negative electrode current collector, the first negative electrode film layer comprising a carbon-based material, and a second negative electrode film layer connected to the side of the first negative electrode film layer away from the negative electrode current collector, the second negative electrode film layer comprising 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 comprise 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 comprise artificial graphite and a carbon coating layer, the artificial graphite comprises secondary particles, and the carbon coating layer is coated on the surface of the artificial graphite. The battery cell of claim 24, wherein, The graphitization degree of the graphite particles is 92.0% to 94.5%. The battery cell according to claim 24 or 25, wherein The mass content of the carbon coating layer is 2% to 5% based on the mass of the graphite particles. The battery cell of any one of claims 24-26, wherein, The powder compaction density of the graphite particles under 20000N is 1.5g / cm 3 to 1.85g / cm 3 . The battery cell according to any one of claims 24 to 27, wherein The compacted density of the first negative electrode film layer is 1.15 g / cm 3 to 1.36 g / cm 3 , and / or The compacted density of the second negative electrode film layer is 1.15 g / cm 3 to 1.36 g / cm 3 . The battery cell according to any one of claims 24 to 28, wherein the volume average particle size Dv50 of the graphite particles in the first negative electrode film layer is 9.5 μm to 18.5 μm, and / or the volume average particle size Dv50 of the graphite particles in the second negative electrode film layer is 7.8 μm to 14.3 μm. The battery cell of any one of claims 24-29, wherein, The first negative electrode film layer further comprises a first lithium-containing binder, and the second negative electrode film layer further comprises 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. The battery cell according to claim 30, wherein a mass content of lithium element in the first lithium-containing binder is 3% to 10%, and / or a mass content of lithium element in the second lithium-containing binder is 3% to 10%. The battery cell of claim 30 or 31, wherein a mass content of lithium element in the first lithium-containing binder is 3% to 10%, and / or a mass content of lithium element in the second lithium-containing binder is 3% to 10%. The battery cell of any one of claims 30 to 32, wherein the first lithium-containing binder comprises a lithium acrylate-acrylonitrile-acrylamide-hydroxyethyl acrylate copolymer derived from lithium acrylate monomers, acrylonitrile monomers, acrylamide monomers, and hydroxyethyl acrylate monomers, the mole percentages of the lithium acrylate monomers, the acrylonitrile monomers, the acrylamide monomers, and the hydroxyethyl acrylate monomers being 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-hydroxyethyl acrylate copolymer derived from lithium acrylate monomers, acrylonitrile monomers, acrylamide monomers, and hydroxyethyl acrylate monomers, the mole percentages of the lithium acrylate monomers, the acrylonitrile monomers, the acrylamide monomers, and the hydroxyethyl acrylate monomers being 30% to 50%: 15% to 45%: 5% to 20%: 20% to 35%. The negative electrode tab further comprises a negative electrode conductive layer, the negative electrode conductive layer being located between the negative electrode film layer and the negative electrode current collector. The battery cell according to any one of claims 1 to 33, 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 . The battery cell of any one of claims 1 to 34, wherein, The negative electrode conductive layer has a thickness of 0.1 pm to 2 pm. The battery cell of claim 35, wherein, The negative electrode conductive layer comprises a negative electrode conductive agent, the negative electrode conductive agent comprising one or more of super conductive carbon, conductive graphite, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers, and / or The battery cell of claim 35 or 36, wherein, The negative electrode conductive layer comprises a negative electrode binder, the negative electrode binder comprising one or more of styrene butadiene rubber, water-soluble unsaturated resin, water-based acrylic resin, polyvinyl alcohol, sodium alginate, and carboxymethyl chitosan. The battery cell of any one of claims 1 to 37, wherein The battery cell of any one of claims 1 to 38, wherein The compacted density of the positive electrode film layer is 2.50 g / cm 3 to 2.80 g / cm 3 , and / or The single-side coating weight of the positive electrode film layer is 200 mg / 1540.25 mm 2 to 370 mg / 1540.25 mm 2 . The lithium-containing phosphate of olivine structure comprises: The compacted density of the positive electrode film layer is 2.55 g / cm 3 to 2.70 g / cm 3 , and / or The single-side coating weight of the positive electrode film layer is 240 mg / 1540.25 mm 2 to 330 mg / 1540.25 mm 2 . The battery cell of any one of claims 1 to 39, wherein, The powder compaction density of the positive electrode active material at 30000 N is 2.46 g / cm 3 to 2.8 g / cm 3 . The battery cell of any one of claims 1-40, wherein, phosphate particles, and a coating layer, the coating layer coating the phosphate particles, the coating layer containing one or more elements of C, Fe, Ti, Zr, Hf, Ge, and Sn. one or more of 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. The battery cell of claim 41, wherein, The phosphate particles include a compound of the general formula Li x1 A y1 Me a M b P 1-c X c Y z wherein 0.5≤x1≤1.3, 0≤y1≤1.3, and 0.9≤x1+y1≤1.3, 0.9≤a≤1.5, 0≤b≤0.5, and 0.9≤a+b≤1.5, 0≤c≤0.5, 3≤z≤5, A includes one or more of Na, K, Mg, Me includes one or more of Mn, Fe, Co, Ni, M includes B, Mg, Al, Si, P, The graphitization degree of the lithium-containing phosphate of olivine structure is 0.15 to 0.

32. The battery cell of claim 41 or 42, wherein, The coating layer includes a fast ion conductor of the general formula Li 3-d Fe 2- d M2 d (PO x2 ) y2 M2 includes one or more of Ti, Zr, Hf, Ge, and Sn, 0≤d≤1, 0 The battery cell of any one of claims 41 to 43, wherein, ​ The battery cell of any one of claims 41 to 44, wherein, The mass content of carbon element in the olivine-structured lithium-containing phosphate is 1% to 2%, The lithium-containing phosphate of olivine structure has a specific surface area of 5 m 2 / g to 18 m 2 / g. The battery cell of any one of claims 41-45, wherein, The lithium-containing phosphate of olivine structure has a specific surface area of 7.5 m 2 / g to 14 m 2 / g. The battery cell of any one of claims 1 to 46, wherein, The olivine-structured lithium-containing phosphate is in a granular form, and the volume distribution particle size satisfies 1 μm≤Dv50≤2 μm and 0.4 μm≤Dv10≤0.7 μm. The battery cell of any one of claims 1 to 47, wherein, The olivine-structured lithium-containing phosphate is in a granular form, and the olivine-structured lithium-containing phosphate 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. The battery cell of any one of claims 1 to 48, wherein, 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. The battery cell of claim 49, wherein, The thickness of the positive electrode conductive layer is 0.1 μm to 2 μm. The battery cell of claim 49 or 50, wherein, The positive electrode conductive layer includes a positive electrode conductive agent, and the positive electrode conductive agent includes one or more of super-conductive carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers, and / or The positive electrode conductive layer includes a positive electrode binder, and the positive electrode binder includes one or more of polyvinylidene fluoride, polytetrafluoroethylene, a vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, a vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, a tetrafluoroethylene-hexafluoropropylene copolymer, polyacrylic acid, and a fluorine-containing acrylic ester resin. The battery cell of any one of claims 1 to 51, wherein, The charging time of the battery cell from 10% state of charge to 80% state of charge is 5 min to 10.5 min. A battery device includes a plurality of battery cells as claimed in any one of claims 1 to 52. The battery device of claim 53, wherein, The charging time of the battery device from 10% state of charge to 80% state of charge is 5 min to 10.5 min. An electric device includes the battery device as claimed in claim 53 or 54.

Images