Battery cell, battery device and electric device

Abstract

The invention provides a battery monomer, a battery device and a power utilization device, the battery monomer comprises an electrode assembly and an electrolyte, the electrode assembly comprises a first pole piece and a second pole piece, each of the first pole piece and the second pole piece comprises a coating part and a tab, the coating part is coated with an active material layer, and the tab is not coated with the active material layer; one of the first pole piece and the second pole piece is a positive pole piece, and a positive active material of the positive pole piece comprises lithium-containing phosphate with an olivine structure; the coating part of the first pole piece comprises a first straight section, the coating part of the second pole piece comprises a second straight section, the first straight section and the second straight section are stacked in the thickness direction of the electrode assembly, and the ratio of the number of the tabs of the first pole piece to the number of the first straight sections of the first pole piece is 0.5-2; an organic solvent of the electrolyte comprises a chain carboxylic ester solvent, and the mass content of the chain carboxylic ester solvent in the organic solvent is 8-90%. The use reliability and the cycle performance of the battery monomer can be improved.

Description

[0001] This application claims the priority of International Patent Application PCT / CN2024 / 102646 titled "Battery Cell, Battery Device and Electrical Device" filed on June 28, 2024, the entire content of which is incorporated herein by reference. Technical Field

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

[0003] Lithium-ion batteries have characteristics such as high capacity and long life, and are therefore widely used in electronic devices, such as mobile phones, laptop computers, battery cars, electric vehicles, electric airplanes, electric ships, and electric tools, etc. With the development of the application fields of lithium-ion batteries, the performance of lithium-ion batteries is required. However, the current reliability in use and cycling performance of battery cells need to be further improved. Summary of the Invention

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

[0005] In a first aspect, this application provides a battery cell. The battery cell includes a housing assembly, an electrode assembly and an electrolyte. The electrode assembly and the electrolyte are accommodated in the housing assembly, and the housing assembly is provided with electrode terminals; the electrode assembly includes a first electrode tab, a second electrode tab and a separator located between the first electrode tab and the second electrode tab. Both the first electrode tab and the second electrode tab include a coated portion and an electrode ear, the coated portion is coated with an active material layer, and the electrode ear is not coated with the active material layer; the polarities of the first electrode tab and the second electrode tab are opposite, and one of the first electrode tab and the second electrode tab is a positive electrode tab. The active material layer of the positive electrode tab includes a positive electrode active material, and the positive electrode active material includes a lithium-containing phosphate with an olivine structure; the electrode assembly is electrically connected to the electrode terminals through the electrode ears. Among them, the coated portion of the first electrode tab includes a first flat section, the coated portion of the second electrode tab includes a second flat section, the first flat section and the second flat section are stacked along the thickness direction of the electrode assembly, the ratio of the number of electrode ears of the first electrode tab to the number of first flat sections of the first electrode tab is 0.5 to 2, the electrolyte includes an organic solvent, and the organic solvent includes a chain carboxylic ester solvent. The mass content of the chain carboxylic ester solvent in the organic solvent is 8% to 75%.

[0006] Therefore, in the embodiments of the present application, the electrolyte includes the chain carboxylic ester solvent with the above mass content. The conductivity of this solvent system is relatively high, which is conducive to the rapid migration of lithium ions and improves the fast charging performance of the battery cell. In the fast charging system of the battery cell, the current density of the tab is usually relatively large, resulting in increased heat generation and a relatively high temperature in the battery cell, which easily leads to the attenuation of the active material and the decomposition of the organic solvent in the electrolyte, deteriorating the cycle performance. The positive active material includes lithium-containing phosphate with an olivine structure, and this material has a stable structure during charge and discharge and is not prone to capacity attenuation, which is beneficial to improving the cycle performance of the battery cell. At the same time, when the ratio of the number of tabs of the first electrode tab to the number of the first flat sections of the first electrode tab is within the above range, the shunt capacity of the tab can be increased, and the fast charging performance of the battery cell can be further improved. However, since the connection area between the tab and other components such as the coated part is relatively large, the overcurrent impedance can be effectively reduced, and the overcurrent temperature rise can be reduced, so that the temperature rise inside the battery cell will not be too high, improving the stability of the electrolyte system and the stability of the active material, which is beneficial to improving the use reliability of the battery cell and can improve the cycle performance. And there are more connection sites between the tab and the coated part, etc., which can increase connection redundancy such as welding redundancy and effectively improve the product yield. Therefore, the embodiments of the present application can improve the cycle performance and fast charging performance of the battery cell.

[0007] In some embodiments, the mass content of the chain carboxylic ester solvent in the organic solvent is 30% to 70%.

[0008] In some embodiments, the ratio of the number of tabs of the second electrode tab to the number of the second flat sections of the second electrode tab is 0.5 to 2. The embodiments of the present application can improve the cycle performance and fast charging performance of the battery cell.

[0009] In some embodiments, the electrode assembly is of a wound structure, the first electrode tab and the second electrode tab are wound in one direction, and the first electrode tab has a plurality of tabs.

[0010] In some embodiments, the ratio of the number of tabs of the first electrode tab to the number of the first flat sections of the first electrode tab is 0.5 to 1. The embodiments of the present application can improve the cycle performance and fast charging performance of the battery cell.

[0011] In some embodiments, the electrode assembly is of a stacked structure, there are a plurality of first electrode tabs and second electrode tabs, and each first electrode tab has at least one tab.

[0012] In some embodiments, the ratio of the number of tabs of the first electrode tab to the number of the first flat sections of the first electrode tab is 1 to 2. The embodiments of the present application can improve the cycle performance and fast charging performance of the battery cell.

[0013] In some embodiments, the first pole piece has multiple pole tabs, and the multiple pole tabs of the first pole piece are arranged on the same side of the coating portion. The first pole tabs can be arranged on the same side of the first coating portion, which can increase welding redundancy and effectively improve product yield.

[0014] In some embodiments, the first pole piece has multiple pole ears, and the multiple pole ears of the first pole piece are respectively arranged on both sides of the coating portion. The embodiments of the present application can improve the cycle performance and fast charging performance of the battery cell. The first pole ear can share the current density of a single first pole piece, especially when the area of ​​the first pole piece is relatively large, the shunting inside the first pole piece is more uniform, which is conducive to uniform reaction and reduces impedance.

[0015] In some embodiments, the tab includes a tab body and a plurality of tab protrusions, wherein the tab body is connected to the coating portion; the plurality of tab protrusions are all connected to the side of the tab body away from the coating portion, and there is a gap between two adjacent tab protrusions, and each tab protrusion is used to be electrically connected to the electrode terminal.

[0016] Therefore, in the embodiment of the present application, the arrangement of multiple pole lug protrusions allows the first pole lug to have multiple connection sites. For example, when connecting the first pole lug to the first adapter, the multiple pole lug protrusions can be respectively connected to different positions of the first adapter, such as by welding, which can increase the welding positions of the first pole lug and the first adapter, improve the welding yield, and enhance the stability of the connection between the two.

[0017] In some embodiments, the electrode tab in the first pole piece is a positive electrode tab, and the thickness of the positive electrode tab is 10 μm to 20 μm.

[0018] When the thickness of the positive electrode tab is within the above range, the positive electrode tab has a relatively excellent current carrying capacity, can reduce heat generation, and is beneficial to improving the fast charging performance of the battery cell.

[0019] In some embodiments, the electrode tab in the first electrode sheet is a negative electrode tab, and the thickness of the negative electrode tab is 4 μm to 10 μm.

[0020] When the thickness of the negative electrode tab is within the above range, the negative electrode tab has excellent current carrying capacity, can reduce heat generation, and is beneficial to improving the fast charging performance of the battery cell.

[0021] In some embodiments, the conductivity of the electrolyte is 10.5 mS / cm to 20 mS / cm, and optionally 15 mS / cm to 20 mS / cm.

[0022] When the conductivity of the electrolyte at room temperature 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.

[0023] In some embodiments, the carboxylic acid ester solvent includes a chain carboxylic acid ester solvent, and the mass content of the chain carboxylic acid ester solvent in the organic solvent is 8% to 75%, optionally greater than or equal to 10%, and optionally 50% to 70%. When the mass content of the chain carboxylic acid ester solvent is within the above range, the viscosity of the electrolyte system is relatively small, which is beneficial to the migration of lithium ions.

[0024] In some embodiments, the chain carboxylic acid ester solvent includes a compound represented by Formula I, Formula I, In Formula I, R 1 includes a hydrogen atom, a halogen atom, a C1-C5 alkyl group or a C1-C5 haloalkyl group, R 2 includes a C1-C5 alkyl group or a C1-C5 haloalkyl group.

[0025] Thus, the conductivity of the above chain carboxylic acid ester solvent in the embodiments of the present application is relatively high, which is beneficial to improving the fast charging ability of the battery monomer.

[0026] In some embodiments, R 1 includes a hydrogen atom, a halogen atom, a C1-C3 alkyl group or a C1-C3 haloalkyl group.

[0027] In some embodiments, in some embodiments, R 2 includes a C1-C3 alkyl group or a C1-C3 haloalkyl group.

[0028] In some embodiments, the chain carboxylic acid ester solvent includes one or more of the compounds represented by Formula I-1 to Formula I-8,

[0029] In some embodiments, the organic solvent further includes a carbonate solvent, and the carbonate solvent includes one or more of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate. The above carbonate solvent and the chain carboxylic acid ester solvent are used in combination, so that the conductivity of the electrolyte is improved, which is beneficial to the migration of lithium ions.

[0030] In some embodiments, the carbonate solvent includes one or more of ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate.

[0031] In some embodiments, the mass content of the carbonate solvent in the organic solvent is 25% to 92%, optionally 30% to 50%. The carbonate solvent with the above mass content can further improve the conductivity of the electrolyte, which is beneficial to the migration of lithium ions.

[0032] In some embodiments, the electrolyte further includes additives, and the additives include one or more of carbonate additives, sulfur-containing additives, and lithium salt additives. The above additives can improve the interfacial film properties on the positive electrode side and / or the negative electrode side, which is beneficial to improving the fast charging performance of the battery cell and improving the cycle performance.

[0033] In some embodiments, the carbonate additives include one or more of vinylene carbonate (VC) and fluoroethylene carbonate (FEC).

[0034] In some embodiments, the sulfur-containing additives include one or more of ethylene sulfate (DTD), bis(ethylene sulfate) (2-DTD), butene sulfite (BS), 1,3-propane sultone (PS), ethylene sulfite (ES), and methylene methyl disulfonate (MMDS).

[0035] In some embodiments, the lithium salt additives include lithium difluorophosphate LiPO 2 F 2 , lithium difluoro(oxalato)borate (LiDFOB), lithium tetrafluoroborate LiBF 4 , and one or more of lithium bis(oxalato)borate (LiBOB).

[0036] In some embodiments, the mass content of the additives in the electrolyte is 1% to 10%, and can be optionally 2% to 8%. The additives with the above mass content can effectively improve the interfacial film properties on the positive electrode side and / or the negative electrode side, which is beneficial to improving the fast charging performance of the battery cell and improving the cycle performance.

[0037] In some embodiments, the electrolyte further includes a lithium salt, and the lithium salt includes one or more of fluorosulfonylimide salts and lithium hexafluorophosphate LiPF 6 . The above lithium salts are easy to dissociate, which is beneficial to the rapid migration of lithium ions; and the electrolyte system is relatively stable and not easy to decompose, which can improve the cycle performance of the battery cell.

[0038] In some embodiments, the fluorosulfonylimide salts include one or more of lithium bis(fluorosulfonyl)imide (LiFSI) and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI).

[0039] In some embodiments, the lithium salt includes lithium bis(fluorosulfonyl)imide (LiFSI) and lithium hexafluorophosphate LiPF 6 , the molar concentration of lithium bis(fluorosulfonyl)imide (LiFSI) is 0.2 mol / L to 0.5 mol / L, and the molar concentration of lithium hexafluorophosphate LiPF 6 is 0.5 mol / L to 1.0 mol / L.

[0040] In some embodiments, the molar concentration of lithium bis(fluorosulfonyl)imide and lithium hexafluorophosphate LiPF 6The ratio of molar concentrations therein is from 0.2 to 1.0, optionally from 0.2 to 0.5.

[0041] In some embodiments, the viscosity of the electrolyte at room temperature is from 2.3 mPa·s to 3.5 mPa·s. When the viscosity of the electrolyte is within the above range, the migration rate of lithium ions in the electrolyte is relatively high, which can further reduce the internal resistance of the battery cell, thereby reducing heat generation and improving the fast charging performance of the battery cell.

[0042] In some embodiments, the density of the electrolyte at room temperature is from 1.05 g / mL to 1.35 g / mL. When the density of the electrolyte is within the above range, the migration rate of lithium ions in the electrolyte is relatively high, which can further reduce the internal resistance of the battery cell, thereby reducing heat generation and improving the fast charging performance of the battery cell.

[0043] In some embodiments, the lithium-containing phosphate of olivine structure includes phosphate particles and a coating layer, the coating layer coats the phosphate particles, and the coating layer contains one or more elements of C, Fe, Ti, Zr, Hf, Ge, and Sn. By surface coating with the coating layer, the conductivity of the lithium-containing phosphate of olivine structure can be improved, the powder resistivity of the material can be reduced, and it is beneficial to the migration rate of lithium ions, reducing the heat generation of the battery cell.

[0044] In some embodiments, 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 ≤ x 1 ≤ 1.3, 0 ≤ y 1 ≤ 1.3, and 0.9 ≤ x 1 + y 1 ≤ 1.3, 0.9 ≤ a ≤ 1.5, 0 ≤ b ≤ 0.5, and 0.9 ≤ a + b ≤ 1.5, 0 ≤ c ≤ 0.5, 3 ≤ z ≤ 5, A includes one or more of Na, K, Mg, Me includes one or more of Mn, Fe, Co, Ni, M includes one or more of B, Mg, Al, Si, P, S, Ca, Sc, Ti, V, Cr, Cu, Zn, Sr, Y, Zr, Nb, Mo, Cd, Sn, Sb, Te, Ba, Ta, W, Yb, La, Ce, X includes one or more of S, Si, Cl, B, C, N, and Y includes one or more of O, F. The lithium-containing phosphate of olivine structure has relatively excellent cycle stability, which is beneficial to improving the cycle performance of the battery cell.

[0045] In some embodiments, the coating layer includes a compound of the general formula Li3-d Fe 2-d M2 d (PO x2 ) y2 fast ionic conductor, M2 includes one or more elements of Ti, Zr, Hf, Ge, and Sn, 0 ≤ d ≤ 1, 0 < x 2 <5, 0 < y 2 <4. Coating the surface of phosphate particles with a fast ionic conductor can significantly improve the transmission rate of lithium ions during multiple deintercalation / insertion at the positive electrode, improve the ionic conductivity of the positive electrode active material, and thus increase the specific capacity. Further, the energy density of the corresponding battery cell is increased.

[0046] In some embodiments, the graphitization degree of the positive electrode active material is from 0.15 to 0.32; optionally from 0.19 to 0.26. When the graphitization degree of the positive electrode active material is within the above range, it is beneficial to improve the conductivity of the positive electrode active material and reduce the heat generation of the positive electrode sheet, thereby reducing the heat generation of the battery cell.

[0047] In some embodiments, the mass content of carbon element in the lithium-containing phosphate with olivine structure is 1% to 2%; the specific surface area of the lithium-containing phosphate with olivine structure is 5m 2 / g to 18m 2 / g; optionally 7.5m 2 / g to 14m 2 / g.

[0048] Thus, in the embodiments of the present application, the carbon element with the above mass content in combination with the material with the above specific surface area is more conducive to the effective contact between the electrolyte and the lithium-containing phosphate with olivine structure in the core, and is conducive to the transmission of lithium ions at the phase interface.

[0049] In some embodiments, the volume distribution particle size of the positive electrode active material satisfies: 1 µm ≤ Dv50 ≤ 2 µm, 0.4 µm ≤ Dv10 ≤ 0.7 µm. The particle size of the positive electrode active material is relatively small, the deintercalation / insertion path of lithium ions in the positive electrode active material is shorter, and the heat generation is less; moreover, the particle size of the above positive electrode active material is not too small, and basically no agglomeration occurs during the processing and preparation process, so that the performance of the positive electrode active material is stable.

[0050] In some embodiments, the lithium-containing phosphate with olivine structure is in granular form, and the lithium-containing phosphate with olivine structure includes secondary particles formed by the aggregation of primary particles, and the average particle size of the primary particles is from 200 nm to 500 nm. The average particle size of the primary particles is relatively small, the deintercalation / insertion path of lithium ions in the positive electrode active material is shorter, and the heat generation is less.

[0051] In some embodiments, the coated portion of the negative electrode tab includes a negative electrode film layer, the negative electrode film layer includes a negative electrode active material, the negative electrode active material includes a carbon-based material, the carbon-based material includes graphite particles, and the graphitization degree of the graphite particles is 92.0% to 94.5%.

[0052] When the graphitization degree of the graphite particles is within the above range, the electrical conductivity of the graphite particles is relatively excellent, which can reduce the heat generation of the negative electrode tab and the heat generation of the battery cell; and can improve the fast charging performance of the battery cell.

[0053] In some embodiments, the graphite particles include artificial graphite and amorphous carbon. The artificial graphite includes secondary particles aggregated by a plurality of primary particles; the amorphous carbon layer is coated on the surface of the artificial graphite. The amorphous carbon layer has more end faces and defects, so that the number of sites capable of intercalating and deintercalating lithium ions is more, and the electrical conductivity of the amorphous carbon layer is relatively excellent, which can reduce the internal resistance of the negative electrode tab and the heat generation amount of the battery cell.

[0054] In some embodiments, based on the mass of the graphite particles, the mass content of the amorphous carbon layer is 2% to 5%. When the mass content of the amorphous carbon layer is within the above range, the internal resistance of the negative electrode tab can be further reduced, and the heat generation amount of the battery cell can be reduced.

[0055] In some embodiments, the coated portion negative electrode film layer of the negative electrode tab 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 portion. The carbon-based material in the first negative electrode film layer includes graphite particles. The second negative electrode film layer is connected to the side of the first negative electrode film layer facing away from the negative electrode current collector portion. The carbon-based material in the second negative electrode film layer includes graphite particles. The volume average particle diameter Dv50 of the graphite particles in the first negative electrode film layer is greater than or equal to the volume average particle diameter Dv50 of the graphite particles in the second negative electrode film layer.

[0056] Therefore, in the embodiments of the present application, there are differences in the particle sizes of the first negative electrode film layer and the second negative electrode film layer, which can improve the fast charging performance of the battery cell; specifically, during fast charging, the overpotential of the second negative electrode film layer is usually relatively high, and the bottleneck of fast charging lies mainly in the second negative electrode film layer. In the embodiments of the present application, the particle size in the second negative electrode film layer is relatively small, which can shorten the solid-phase transmission path of lithium ions, can improve the fast charging performance, and can improve the problem of lithium deposition on the surface layer of the negative electrode tab.

[0057] In some embodiments, the carbon-based material in the first negative electrode film layer further includes natural graphite.

[0058] In some embodiments, the tap density of the carbon-based material in the first negative electrode film layer is less than or equal to the tap density of the carbon-based material in the second negative electrode film layer. When the tap density of the carbon-based material in the second negative electrode film layer is greater than that in the first negative electrode film layer, the second negative electrode film layer is more densely packed, improving the energy density of the battery cell; the first negative electrode film layer is relatively sparsely packed with richer pores, enhancing the fast charging performance of the battery cell.

[0059] In some embodiments, the tap density of the carbon-based material in the first negative electrode film layer is 0.82 g / cm 3 to 1.21 g / cm 3 . When the tap density of the carbon-based material in the first negative electrode film layer is within a suitable range, the fast charging performance of the battery cell can be improved.

[0060] In some embodiments, the tap density of the carbon-based material in the second negative electrode film layer is 0.90 g / cm 3 to 1.25 g / cm 3 . When the tap density of the carbon-based material in the second negative electrode film layer is within a suitable range, the energy density of the battery cell can be improved. 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.

[0061] In some embodiments, the volume average particle size Dv50 of the graphite particles in the second negative electrode film layer is 7.8 μm to 14.3 μm. When the volume average particle size Dv50 of the negative electrode active material in the second negative electrode film layer is within the above range, the tortuosity of lithium ion transport can be reduced, improving the fast charging performance of the battery cell.

[0062] In some embodiments, the first negative electrode film layer further includes a first lithium-containing binder, and the second negative electrode film layer further includes a second lithium-containing binder. The mass content of the first lithium-containing binder relative to the mass of the first negative electrode film layer is less than or equal to the mass content of the second lithium-containing binder relative to the mass of the second negative electrode film layer.

[0063] Thus, in the embodiments of the present application, the mass content of the second lithium-containing binder in the second negative electrode film layer is relatively high, and the number of freely movable lithium ions provided by the second lithium-containing binder for the second negative electrode film layer is relatively more, further improving the fast charging performance of the battery cell.

[0064] In some embodiments, the mass content of the first lithium-containing binder relative to the mass of the first negative electrode film layer is 0.1% to 1%. When the mass content of the first lithium-containing binder is within the above range, the deintercalation rate of lithium ions can be improved, enhancing the fast charging performance of the battery cell.

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

[0066] In some embodiments, the mass content of the second lithium-containing binder relative to the mass of the second negative electrode film layer is 0.1% to 1%. When the mass content of lithium element in the second lithium-containing binder is within the above range, the intercalation and deintercalation rate of lithium ions is improved, and the fast charging performance of the battery cell is improved.

[0067] In some embodiments, the mass content of lithium element in the second lithium-containing binder is 3% to 10%, and optionally 3% to 8%. When the mass content of lithium element is within the above range, the number of free-moving lithium ions in the negative electrode film layer can be relatively large, which can further shorten the distance for lithium ions to diffuse to the surface of the negative electrode film layer, improve the intercalation and deintercalation rate of lithium ions, and improve the fast charging performance of the battery cell.

[0068] In some embodiments, the first lithium-containing binder includes a lithium acrylate-acrylonitrile-acrylamide-2-hydroxyethyl acrylate copolymer, and the lithium acrylate-acrylonitrile-acrylamide-2-hydroxyethyl acrylate copolymer is derived from a lithium acrylate monomer, an acrylonitrile monomer, an acrylamide monomer, and a 2-hydroxyethyl acrylate monomer. The molar ratio of the lithium acrylate monomer, the acrylonitrile monomer, the acrylamide monomer, and the 2-hydroxyethyl acrylate monomer is 30% to 50%: 15% to 45%: 5% to 20%: 20% to 35%.

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

[0070] In some embodiments, the second lithium-containing binder includes a lithium acrylate-acrylonitrile-acrylamide-2-hydroxyethyl acrylate copolymer, and the lithium acrylate-acrylonitrile-acrylamide-2-hydroxyethyl acrylate copolymer is derived from a lithium acrylate monomer, an acrylonitrile monomer, an acrylamide monomer, and a 2-hydroxyethyl acrylate monomer. The molar ratio of the lithium acrylate monomer, the acrylonitrile monomer, the acrylamide monomer, and the 2-hydroxyethyl acrylate monomer is 30% to 50%: 15% to 45%: 5% to 20%: 20% to 35%.

[0071] Thus, the lithium-containing binder of the above materials can provide a certain amount of lithium ions for the negative electrode film layer, improving the fast charging performance of the battery cell; moreover, it is not prone to swelling during the charge and discharge process, with a stable structure, so that the cycling performance of the negative electrode film layer is improved during the fast charge and discharge process.

[0072] In some embodiments, the negative electrode active material further includes a silicon-based material, and the mass content of silicon element in the silicon-based material is 0.3% to 10.0% based on the mass of the negative electrode active material. The introduction of the silicon-based material can improve the capacity of the negative electrode active material and increase the energy density of the battery cell.

[0073] In some embodiments, the battery cell includes a separator, and the separator includes a base film with a porous structure, and the porosity of the base film is 20% to 70%. When the porosity of the separator in the embodiments of the present application is within the above range, the migration ability of lithium ions in the separator can be improved, and the internal resistance of the battery cell can be further reduced, thereby reducing heat generation.

[0074] In some embodiments, the separator includes a base film with a porous structure, and the porosity of the base film is 35% to 60%. When the porosity of the separator in the embodiments of the present application is within the above range, the migration ability of lithium ions in the separator can be improved, and the internal resistance of the battery cell can be further reduced, thereby reducing heat generation.

[0075] In some embodiments, the thickness of the base film is 6 μm to 12 μm. When the thickness of the base film is within the above range, the migration path of lithium ions in the base film is shorter, which can further reduce the internal resistance of the battery cell, thereby reducing heat generation.

[0076] In some embodiments, the thickness of the base film is 6 μm to 9 μm. When the thickness of the base film is within the above range, the migration path of lithium ions in the base film is shorter, which can further reduce the internal resistance of the battery cell, thereby reducing heat generation.

[0077] In some embodiments, the separator includes a base film and a functional layer provided on at least one side of the base film. The functional layer includes a first functional layer and a second functional layer. The first functional layer is located on one side of the base film and includes first inorganic particles. The second functional layer is located on the other side of the base film and includes composite particles. The composite particles include second inorganic particles and a plurality of non-fluoropolymer particles, and the second inorganic particles are attached to the surface of the non-fluoropolymer particles and / or dispersed inside the non-fluoropolymer particles. The first functional layer and the second functional layer have good heat resistance, which can improve the heat resistance of the separator.

[0078] In some embodiments, the non-fluoropolymer particles include acrylate copolymers. Acrylate copolymers have excellent adhesion properties and relatively high adhesion stability with the base film.

[0079] In some embodiments, the first inorganic particles include one or more of silica, alumina, boehmite, barium sulfate, calcium oxide, titanium oxide, zinc oxide, magnesium oxide, zirconium oxide, and tin oxide. The above-mentioned first inorganic particles can improve the heat resistance of the first functional layer.

[0080] In some embodiments, the second inorganic particles include one or more of silica, alumina, boehmite, barium sulfate, calcium oxide, titanium oxide, zinc oxide, magnesium oxide, zirconium oxide, and tin oxide. The above-mentioned second inorganic particles can improve the heat resistance of the first functional layer.

[0081] In some embodiments, the average particle size of the second inorganic particles is 5 nm to 100 nm. When the average particle size of the second inorganic particles is within the above range, it is beneficial to improve the heat resistance and compression modulus of the composite particles.

[0082] In some embodiments, the base material of the housing includes steel, and the thickness of the housing is 0.1 mm to 0.5 mm, and can be optionally 0.2 mm to 0.35 mm. When the thickness of the housing is within the above range, the mechanical strength of the housing is relatively high, which can improve the use reliability and cycle performance of the battery cell; and the housing occupies less space and there is more internal space in the housing, which is beneficial to improving the energy density of the battery cell.

[0083] In some embodiments, the charging time of the battery cell from 10% state of charge to 80% state of charge is 5 min to 10.5 min. The charging speed of the battery cell is relatively fast, which is more beneficial to improving the fast charging ability.

[0084] In a second aspect, the present application provides a battery device, which includes a plurality of battery cells according to any one of the embodiments in the first aspect of the present application.

[0085] In some embodiments, the charging time of the battery device from 10% state of charge to 80% state of charge is 5 min to 10.5 min. The charging speed of the battery device is relatively fast, which is more beneficial to improving the fast charging ability.

[0086] In a third aspect, the present application provides an electrical device, which includes the battery device according to any one of the embodiments in the second aspect of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0087] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following will briefly introduce the drawings required to be used in the embodiments of the present application. Obviously, the following described drawings are only some embodiments of the present application. For those of ordinary skill in the art, other drawings can be obtained according to the drawings without creative efforts.

[0088] Figure 1Schematic diagram of the structure of a battery cell provided for some embodiments of the present application; Figure 2 Explosion diagram of the battery cell provided for some embodiments of the present application; Figure 3 Schematic diagram of the structure of the electrode assembly of the battery cell provided for some embodiments of the present application; Figure 4 Schematic diagram of the structure of the electrode assembly of the battery cell provided for other embodiments of the present application; Figure 5 Schematic diagram of the structure of the electrode assembly of the battery cell provided for still other embodiments of the present application; Figure 6 Expanded schematic diagram of the first electrode tab of the electrode assembly in the battery cell provided for some embodiments of the present application; Figure 7 Expanded schematic diagram of the first electrode tab of the electrode assembly in the battery cell provided for other embodiments of the present application; Figure 8 Explosion diagram of the battery cell provided for other embodiments of the present application; Figure 9 Schematic diagram of the structure of the electrode assembly of the battery cell provided for other embodiments of the present application; Figure 10 Schematic diagram of the structure of the first electrode tab of the battery cell provided for some embodiments of the present application; Figure 11 Schematic diagram of the structure of the first electrode tab of the battery cell provided for other embodiments of the present application; Figure 12 Schematic diagram of the structure of the second electrode tab of the battery cell provided for some embodiments of the present application; Figure 13 Expanded structure schematic diagram of the first electrode tab of the battery cell provided for other embodiments of the present application; Figure 14 For Figure 13 Partial enlarged structure schematic diagram of the first electrode tab shown at A; Figure 15 Explosion diagram of the battery cell provided for other embodiments of the present application; Figure 16 Schematic diagram of the structure of the battery module provided for some embodiments of the present application; Figure 17 Schematic diagram of the structure of the battery pack provided for some embodiments of the present application; Figure 18 Schematic diagram of the structure of the electrical device provided for some embodiments of the present application.

[0089] The drawings are not necessarily drawn to actual scale.

[0090] The description of the reference numerals is as follows: Y, the thickness direction; 1, electrical device; 2, battery pack; 3, controller; 4, motor; 5, housing; 5a, first housing part; 5b, second housing part; 5c, accommodation space; 6, battery module; 7, battery cell; 10, electrode assembly; 111, first tab; 1111, tab body; 1112, tab protrusion; 112, second tab; 13, first electrode plate; 131, first straight section; 132, first bent section; 130, first coating part; 14, second electrode plate; 141, second straight section; 142, second bent section; 140, second coating part; 15, separator; 200, housing assembly; 20, housing; 21, shell; 22, end cover; 31, first electrode terminal; 32, second electrode terminal; 41, first adapter; 42, second adapter. Detailed implementation manners

[0091] Hereinafter, embodiments of the battery cell, battery device, and electrical device of the present application are specifically disclosed in detail with appropriate reference to the accompanying drawings. However, there may be cases where unnecessary detailed descriptions are omitted. For example, there may be cases where detailed descriptions of well-known matters and repeated descriptions of actually identical structures are omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate the understanding of those skilled in the art. In addition, the accompanying drawings and the following description are provided for those skilled in the art to fully understand the present application and are not intended to limit the subject matter recited in the claims.

[0092] The "range" disclosed in this application is defined in the form of a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundaries of a particular range. The ranges defined in this way can include or exclude the end values, and can be combined arbitrarily, that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60 to 120 and 80 to 110 are listed for a specific parameter, ranges of 60 to 110 and 80 to 120 are also contemplated. In addition, if the minimum range values 1 and 2 are listed, and if the maximum range values 3, 4, and 5 are listed, the following ranges are all contemplated: 1 to 3, 1 to 4, 1 to 5, 2 to 3, 2 to 4, and 2 to 5. In this application, unless otherwise stated, the numerical range "a to b" represents an abbreviated representation of any real number combination between a and b, where a and b are both real numbers. For example, the numerical range "0 to 5" means that all real numbers between "0 to 5" are fully listed herein, and "0 to 5" is only an abbreviated representation of these numerical combinations. In addition, when stating that a certain parameter is an integer ≥ 2, it is equivalent to disclosing that the parameter is, for example, the integers 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0093] If there is no special instruction, all embodiments and optional embodiments of this application can be combined with each other to form a new technical solution.

[0094] If there is no special instruction, all technical features and optional technical features of this application can be combined with each other to form a new technical solution.

[0095] If there is no special instruction, all steps of this application can be carried out sequentially or randomly, preferably sequentially. For example, a method includes steps (a) and (b), which means that the method can include steps (a) and (b) carried out sequentially, or can also include steps (b) and (a) carried out sequentially. For example, it is mentioned that the method may further include step (c), which means that step (c) can be added to the method in any order. For example, the method can include steps (a), (b), and (c), or can also include steps (a), (c), and (b), or can also include steps (c), (a), and (b), etc.

[0096] With the development of the field of battery cells, the requirements for the fast charging performance of battery cells are gradually increasing; during the fast charge and discharge process, the charge and discharge rate is relatively large, resulting in a relatively large amount of heat generated inside the battery cell, a relatively high temperature rise inside the battery cell. At high temperatures, the stability of the electrolyte system is poor and it is easy to decompose and volatilize, increasing the internal pressure of the battery cell, reducing the reliability of the battery cell in use, and even possibly triggering thermal runaway.

[0097] In view of the above problems, the embodiments of the present application design the system of the battery cell. The electrolyte includes a chain carboxylic acid ester solvent. The conductivity of this solvent system is relatively high, which is conducive to the rapid migration of lithium ions and improves the rapid charging performance of the battery cell. The battery cell is provided with a certain number of tabs to increase the shunt capacity of the tabs, further improving the rapid charging performance of the battery cell. Moreover, it can also reduce the over-current impedance and the over-current temperature rise, and the temperature rise in the battery cell system will not be too high, so that the electrolyte system is more stable, which is conducive to improving the use reliability of the battery cell and the cycle performance.

[0098] Battery cell In a first aspect, an embodiment of the present application provides a battery cell.

[0099] As Figures 1 to 3 shown, the battery cell 7 includes a housing assembly 200, an electrode assembly 10, and an electrolyte. The electrode assembly 10 and the electrolyte are accommodated in the housing assembly 200, and the housing assembly 200 is provided with electrode terminals. The electrode assembly 10 includes a first electrode plate 13, a second electrode plate 14, and a separator 15 located between the first electrode plate 13 and the second electrode plate 14. Both the first electrode plate 13 and the second electrode plate 14 include a coated portion and a tab, the coated portion is coated with an active material layer, and the tab is not coated with the active material layer. The polarities of the first electrode plate 13 and the second electrode plate 14 are opposite, one of the first electrode plate 13 and the second electrode plate 14 is a positive electrode plate, and the other is a negative electrode plate. The active material layer of the positive electrode plate includes a positive electrode active material, and the positive electrode active material includes a lithium-containing phosphate with an olivine structure. The electrode assembly 10 is electrically connected to the electrode terminals through the tabs. Among them, the coated portion of the first electrode plate 13 includes a first flat section 131, the coated portion of the second electrode plate 14 includes a second flat section 141, the first flat section 131 and the second flat section 141 are stacked along the thickness direction Y of the electrode assembly 10, and the ratio of the number of tabs of the first electrode plate 13 to the number of the first flat sections 131 of the first electrode plate 13 is 0.5 to 2. The electrolyte includes an organic solvent, and the organic solvent includes a chain carboxylic acid ester solvent. The mass content of the chain carboxylic acid ester solvent in the organic solvent is 8% to 75%.

[0100] The electrolyte includes the chain carboxylic acid ester solvent with the above mass content. The conductivity of this solvent system is relatively high, which is conducive to the rapid migration of lithium ions and improves the rapid charging performance of the battery cell 7. Under the rapid charging system of the battery cell 7, the current density of the tabs is usually relatively large, resulting in increased heat generation, making the temperature in the battery cell 7 relatively high, which easily leads to the attenuation of the active material and the decomposition of the organic solvent in the electrolyte, deteriorating the cycle. The positive electrode active material includes a lithium-containing phosphate with an olivine structure. This material has a stable structure during charge and discharge and is not prone to capacity attenuation, which is conducive to improving the cycle performance of the battery cell 7. Meanwhile, when the ratio of the number of tabs of the first electrode tab 13 to the number of first flat segments 131 of the first electrode tab 13 is within the above range, the shunting ability of the tabs can be increased, and the fast charging performance of the battery cell 7 can be further improved; however, since the connection area between the tabs and other components such as the coated part is relatively large, the overcurrent impedance can be effectively reduced, the overcurrent temperature rise can be reduced, so that the temperature rise inside the battery cell 7 will not be too high, the stability of the electrolyte system and the stability of the active material can be improved, which is beneficial to the improvement of the usage reliability of the battery cell 7, and the cycle performance can be improved; and there are more connection sites between the tabs and the coated part, etc., which can increase connection redundancy such as welding redundancy and effectively improve the product yield.

[0101] Therefore, the embodiments of the present application can improve the cycle performance and fast charging performance of the battery cell 7.

[0102] The housing assembly 200 has an accommodation space for accommodating the electrode assembly 10 and the electrolyte. In some embodiments, the housing assembly 200 includes a housing 20, the housing 20 includes an end cap 22 and a housing body 21, the housing body 21 has an opening, the end cap 22 covers the opening, and the electrode terminal is disposed on the end cap 22. The shape of the housing body 21 can be determined according to the specific shape of the electrode assembly 10. For example, if the electrode assembly 10 is a cylindrical structure, the housing body 21 of a cylindrical structure can be selected; if the electrode assembly 10 is a cuboid structure, the housing body 21 of a cuboid structure can be selected. Optionally, both the electrode assembly 10 and the housing body 21 are of cuboid structures.

[0103] To illustrate the present application more clearly, the tab of the first electrode tab 13 is defined as the first tab 111, and the coated part of the first electrode tab 13 is defined as the first coated part 130. The tab of the second electrode tab 14 is defined as the second tab 112, and the coated part of the second electrode tab 14 is defined as the second coated part 140. The electrode terminal that is electrically connected and has the same electrical property as the first tab 111 is defined as the first electrode terminal 31, and the electrode terminal that is electrically connected and has the same electrical property as the second tab 112 is defined as the second electrode terminal 32.

[0104] The polarities of the first electrode tab 13 and the second electrode tab 14 are opposite. When the first electrode tab 13 is the positive electrode tab, the second electrode tab 14 is the negative electrode tab, the first electrode terminal 31 is the positive terminal, and the second electrode terminal 32 is the negative terminal; or when the first electrode tab 13 is the negative electrode tab, the second electrode tab 14 is the positive electrode tab, the first electrode terminal 31 is the negative terminal, and the second electrode terminal 32 is the positive terminal.

[0105] The coated portion in the positive electrode tab corresponds to the positive electrode coating portion, the tab corresponds to the positive electrode tab, the active material layer corresponds to the positive electrode film layer containing the positive electrode active material, the positive electrode coating portion includes a positive electrode current collector portion and a positive electrode film layer provided on at least one side of the positive electrode current collector portion. When the positive electrode coating portion includes a positive electrode flat section, the positive electrode flat section includes a positive electrode current collector portion and a positive electrode film layer provided on at least one side of the positive electrode current collector portion.

[0106] The coated portion in the negative electrode tab corresponds to the negative electrode coating portion, the tab corresponds to the negative electrode tab, the active material layer corresponds to the negative electrode film layer containing the negative electrode active material, the negative electrode coating portion includes a negative electrode current collector portion and a negative electrode film layer provided on at least one side of the negative electrode current collector portion. When the negative electrode coating portion includes a negative electrode flat section, the negative electrode flat section includes a negative electrode current collector portion and a negative electrode film layer provided on at least one side of the negative electrode current collector portion.

[0107] In an embodiment of the present application, the first tab 111 is electrically connected to the first flat section 131 and the first electrode terminal 31. The ratio of the number of the first tabs 111 of the first electrode tab 13 to the number of the first flat sections 131 of the first electrode tab 13 is 0.5 to 2, such as 0.5, 0.55, 0.6, 0.7, 0.8, 0.9, 1, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2 or a range composed of any two of the above values. When the ratio of the number of the first tabs 111 of the first electrode tab 13 to the number of the first flat sections 131 of the first electrode tab 13 is within the above range, the number of the first tabs 111 is relatively large, which can improve the current shunting effect, reduce the over-current impedance between the first tab 111 and the first flat section 131, reduce the over-current temperature rise, and make the temperature rise inside the battery cell 7 relatively low.

[0108] In an embodiment of the present application, the electrode assembly 10 includes a second flat section 141. The second flat section 141 and the first flat section 131 are stacked, and are alternately stacked along the thickness direction Y of the electrode assembly 10. The second tab 112 is used to electrically connect the second flat section 141 and the second electrode terminal 32. Optionally, the battery cell 7 further includes a separator 15. The first flat section 131, the separator 15 and the second flat section 141 are alternately stacked.

[0109] In some embodiments, the ratio of the number of the second tabs 112 of the second electrode tab 14 to the number of the second flat segments 141 of the second electrode tab 14 is from 0.5 to 2, such as 0.5, 0.6, 0.7, 0.8, 0.9, 1, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2 or a range composed of any two of the above values. When the ratio of the number of the second tabs 112 of the second electrode tab 14 to the number of the second flat segments 141 of the second electrode tab 14 is from 0.5 to 2, the number of the second tabs 112 is relatively large, which can improve the current shunting effect, reduce the over-current impedance between the second tabs 112 and the second flat segments 141, reduce the over-current temperature rise, and make the temperature rise inside the battery cell 7 relatively low.

[0110] When the number of the first tabs 111 is the same as that of the second tabs 112, the over-current density of a single tab is the same, and the performance matching is more excellent, which is beneficial to improving the homogenized reaction of the battery cell 7, enhancing the current shunting effect, and improving the charge and discharge capacity of the battery cell 7.

[0111] In some embodiments, the first tab 111 is a positive electrode tab; the first flat segment 131 includes a positive electrode active material, and the positive electrode active material includes a lithium-containing phosphate with an olivine structure for providing lithium ions. The relatively large number of positive electrode tabs can improve the current shunting effect, reduce the over-current impedance between the first tabs 111 and the first flat segments 131, reduce the over-current temperature rise, and make the temperature rise inside the battery cell 7 relatively low.

[0112] In some embodiments, the second tab 112 is a negative electrode tab, the second flat segment 141 includes a negative electrode active material, and the negative electrode active material includes a carbon-based material for receiving lithium ions from the first flat segment 131.

[0113] The electrode assembly 10 can be a wound electrode assembly 10 or a stacked electrode assembly 10.

[0114] In the case where the electrode assembly 10 is of a wound structure, structurally, the electrode assembly 10 includes a first electrode tab 13, a second electrode tab 14, and a separator 15. The first electrode tab 13 can be a whole piece structure, the second electrode tab 14 is a whole piece structure, and the separator 15 is a whole piece structure. The separator 15 is disposed between the first electrode tab 13 and the second electrode tab 14, and the first electrode tab 13, the separator 15, and the second electrode tab 14 are wound in one direction to form the electrode assembly 10. The first electrode tab 13 includes a first coating portion 130 and a plurality of first tabs 111. The second electrode tab 14 includes a second coating portion 140 and a plurality of second tabs 112.

[0115] After the electrode assembly 10 is formed by winding, the first coating portion 130 of the first electrode sheet 13 may include a plurality of first straight segments 131 and a plurality of first curved segments 132. The first curved segments 132 and the first straight segments 131 are arranged along the winding direction of the electrode assembly 10, and the first curved segments 132 are connected to the first straight segments 131. The first tab 111 is connected to the first straight segment 131. During the formation of the wound electrode assembly 10, one first straight segment 131 can be formed when the first electrode sheet 13 is wound half a turn.

[0116] The second coating portion 140 of the second electrode sheet 14 may include a plurality of second straight segments 141 and a plurality of second curved segments 142. The second curved segments 142 and the second straight segments 141 are arranged along the winding direction of the electrode assembly 10, and the second curved segments 142 are connected to the second straight segments 141. The second tab 112 is connected to the second straight segment 141. The first straight segments 131 and the second straight segments 141 are alternately stacked, and the first curved segments 132 and the second curved segments 142 are alternately stacked.

[0117] Viewed from the appearance, the electrode assembly 10 includes a flat region, a bent region, and tabs. The flat region includes the first straight segments 131 and the second straight segments 141. The bent region includes the first curved segments 132 and the second curved segments 142.

[0118] When the electrode assembly 10 is of a wound structure, the ratio of the number of the first tabs 111 of the first electrode sheet 13 to the number of the first straight segments 131 of the first electrode sheet 13 may be selected from 0.5 to 1, may be greater than 0.5 and less than 1, and may further be selected from 0.6 to 0.99. It can further cooperate with a chain carboxylic ester solvent with a mass content of 8% to 75% to improve the cycle performance and fast charging performance of the battery cell 7. Exemplarily, when the electrode assembly 10 is of a wound structure, the ratio of the number of the first tabs 111 of the first electrode sheet 13 to the number of the first straight segments 131 of the first electrode sheet 13 is 0.5, 0.55, 0.6, 0.7, 0.8, 0.9, 0.95, 0.99, 1 or a range composed of any two of the above values.

[0119] Figure 3 The case where the ratio of the number of the first tabs 111 of the first electrode sheet 13 to the number of the first straight segments 131 of the first electrode sheet 13 is 0.5 is shown. When the first electrode sheet 13 is wound one turn, two first straight segments 131 can be formed. One of the two first straight segments 131 is connected to a first tab 111, which means that there is one first tab 111 corresponding to the two first straight segments 131, that is, one of the two first straight segments 131 is provided with a first tab 111, and the other first straight segment 131 is not provided with a first tab 111. It can be converted to that 0.5 first tab 111 is provided on each first straight segment 131.

[0120] Figure 4 It shows a case where the ratio of the number of the first tabs 111 of the first electrode tab 13 to the number of the first flat segments 131 of the first electrode tab 13 is 1. When the first electrode tab 13 is wound around one circle, two first flat segments 131 can be formed, and each first flat segment 131 is connected with a first tab 111. It can be converted that one first tab 111 is arranged on each first flat segment 131.

[0121] Figure 5 It shows a case where the ratio of the number of the first tabs 111 of the first electrode tab 13 to the number of the first flat segments 131 of the first electrode tab 13 is greater than 0.5 and less than 1. The first electrode tab 13 is wound around multiple circles, and two first flat segments 131 can be formed in each circle. One first tab 111 can be arranged on the two first flat segments 131 of at least one circle among the multiple circles, that is, one first tab 111 is arranged in one circle; two first tabs 111 can be arranged on the two first flat segments 131 of at least another circle among the multiple circles, that is, two first tabs 111 are arranged in one circle; in the electrode assembly 10, it can be converted that there are more than 0.5 and less than 1 first tabs 111 arranged on each first flat segment 131.

[0122] When the battery cell 7 meets the above conditions, the conductivity of the solvent system is relatively high, which is beneficial to the rapid migration of lithium ions and can improve the fast charging performance of the battery cell 7; moreover, the protection effect of the electrolyte system on the negative active material is relatively excellent, which is beneficial to the improvement of the cycle performance of the battery cell 7; when the ratio of the number of the first tabs 111 to the number of the first flat segments 131 is within the above range, the shunt capacity of the first tabs 111 can be increased, which is beneficial to the uniform reaction of the first electrode tab 13 and the reduction of impedance, and can further improve the fast charging performance of the battery cell 7. Moreover, it can also increase the connection sites between the first tabs 111 and other components, increase the welding redundancy, and effectively improve the product yield; since the connection area between the first tabs 111 and other components is relatively large, the overcurrent impedance can be reduced, the overcurrent temperature rise can be reduced, and the temperature rise in the battery cell 7 system will not be too high, so that the electrolyte system is more stable, which is beneficial to the improvement of the use reliability of the battery cell 7 and can improve the cycle performance.

[0123] Optionally, the number of the first tabs 111 in the first electrode tab 13 is multiple, and the first tabs 111 are located on at least one side of the first coating part 130.

[0124] As Figure 6 shown, exemplarily, multiple first tabs 111 can be located on the same side of the first coating part 130.

[0125] As Figure 7 shown, exemplarily, multiple first tabs 111 can be respectively located on both sides of the first coating part 130.

[0126] As Figure 7 and Figure 8 shown, optionally, all the first tabs 111 on the same side of the first coating portion 130 are stacked in the thickness direction Y of the electrode assembly 10. Such an arrangement is beneficial for connecting the stacked first tabs 111 together with other components, such as the first adapter 41 of the battery cell 7.

[0127] Optionally, the first adapter 41 is connected to the first tab 111, and the first adapter 41 is used to electrically connect the first tab 111 and the first electrode terminal 31 of the battery cell 7. After all the first tabs 111 on the same side of the first coating portion 130 are stacked, they can be connected to the first adapter 41 as a whole, for example, by welding.

[0128] The arrangement of the second tab 112 can be the same as or similar to that of the first tab 111, and will not be elaborated here.

[0129] Optionally, the battery cell 7 further includes a second adapter 42. The second adapter 42 is connected to the second tab 112, and the second adapter 42 is used to electrically connect the second tab 112 and the second electrode terminal 32 of the battery cell 7. After all the second tabs 112 on the same side of the second coating portion 140 are stacked, they can be connected to the second adapter 42 as a whole, for example, by welding.

[0130] The electrode assembly 10 can be provided as at least one, optionally at least two, such as two, three, four, etc., and optionally two. At least two electrode assemblies 10 can be stacked in the thickness direction Y of the electrode assembly 10. Figure 8 Two stacked electrode assemblies 10 are shown.

[0131] As Figures 9 to 12 shown, when the electrode assembly 10 is a laminated structure, there can be multiple first electrode plates 13 and multiple second electrode plates 14. Each first electrode plate 13 respectively has a first flat section 131 and a first tab 111. The first flat sections 131 of the multiple first electrode plates 13 and the second flat sections 141 of the multiple second electrode plates 14 are stacked in the thickness direction Y of the electrode assembly 10.

[0132] In the case where the electrode assembly 10 is a laminated structure, from the appearance, the electrode assembly 10 includes a flat region. Optionally, the electrode assembly 10 can also include a bent region. For example, when the separator 15 adopts a one-piece structure, the separator 15 is bent multiple times and then stacked with the first electrode plate 13 and the second electrode plate 14 to form the electrode assembly 10, or when the negative electrode plate adopts a one-piece structure, the negative electrode plate is bent multiple times and then stacked with the positive electrode plate and the separator to form the electrode assembly; Next, an example will be given with the electrode assembly 10 only including a flat region.

[0133] Structurally, the electrode assembly 10 includes a first pole piece 13, a second pole piece 14, and a separator 15. The separator 15 is disposed between the first pole piece 13 and the second pole piece 14, and the first pole piece 13, the separator 15, and the second pole piece 14 are stacked.

[0134] There may be multiple first pole pieces 13 and multiple second pole pieces 14. Each first pole piece 13 includes a first flat section 131 and a first tab 111, and the first tab 111 is connected to the first flat section 131. Each second pole piece 14 includes a second flat section 141 and a second tab 112, and the second tab 112 is connected to the second flat section 141. The multiple first flat sections 131 and the multiple second flat sections 141 are alternately stacked in the thickness direction Y of the electrode assembly 10.

[0135] When the electrode assembly 10 is of a stacked structure, the ratio of the number of the first tabs 111 of the first pole piece 13 to the number of the first flat sections 131 of the first pole piece 13 is 1 to 2, and can be selected to be greater than 1 and less than or equal to 2. In combination with a chain carboxylic ester solvent with a mass content of 8% to 75%, the performance of the battery cell 7 can be effectively improved. Exemplarily, when the electrode assembly 10 is of a stacked structure, the ratio of the number of the first tabs 111 of the first pole piece 13 to the number of the first flat sections 131 of the first pole piece 13 is 1, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2, or a range composed of any two of the above values.

[0136] When the ratio of the number of the first tabs 111 of the first pole piece 13 to the number of the first flat sections 131 of the first pole piece 13 is 1, it means that the first tabs 111 and the first flat sections 131 are arranged in one-to-one correspondence, and it can be converted to that one first tab 111 is provided on each first flat section 131. Figure 10 The structural schematic diagram showing that one first tab 111 is provided on each first flat section 131 is shown.

[0137] When the ratio of the number of the first tabs 111 of the first pole piece 13 to the number of the first flat sections 131 of the first pole piece 13 is 2, it can be converted to that two first tabs 111 are provided on each first flat section 131. In this case, one first tab 111 can be provided on each side of the first flat section 131. Figure 11 The structural schematic diagram showing that two first tabs 111 are provided on each first flat section 131 is shown.

[0138] When the ratio of the number of the first tabs 111 of the first electrode tab 13 to the number of the first flat sections 131 of the first electrode tab 13 is selected to be greater than 1 and less than or equal to 2, it can be converted to that there are more than 1 and less than or equal to 2 first tabs 111 arranged on each first flat section 131. For example, the electrode assembly 10 includes two first electrode tabs 13, one of the first electrode tabs 13 is provided with one first tab 111, and the other first electrode tab 13 is provided with two first tabs 111, which is converted to that there are 1.5 first tabs 111 arranged on each first electrode tab 13.

[0139] When the battery cell 7 meets the above conditions, the conductivity of the solvent system is relatively high, which is beneficial to the rapid migration of lithium ions and can improve the rapid charging performance of the battery cell 7; moreover, the protection effect of the electrolyte system on the negative active material is relatively excellent, which is beneficial to the improvement of the cycle performance of the battery cell 7; the number of the first tabs 111 is relatively large, which can increase the shunt capacity of the first tabs 111, make the internal shunt of the first flat section 131 uniform, and can further improve the rapid charging performance of the battery cell 7. Moreover, it can also increase the connection sites between the first tabs 111 and other components, increase the welding redundancy, and effectively improve the product yield; because the connection area between the first tabs 111 and other components is relatively large, it can reduce the overcurrent impedance and the overcurrent temperature rise, and the temperature rise in the battery cell 7 system will not be too high, so that the electrolyte system is more stable, which is beneficial to the improvement of the use reliability of the battery cell 7 and can improve the cycle performance.

[0140] Optionally, when the ratio of the number of the first tabs 111 of the first electrode tab 13 to the number of the first flat sections 131 of the first electrode tab 13 is greater than 1, after conversion, there are more than 1 first tabs 111 arranged on the first flat section 131 on average. The more than 1 first tabs 111 can be respectively arranged on both sides of the first flat section 131. In this case, the more than 1 first tabs 111 can share the current density of a single first electrode tab 13. Especially when the area of the first electrode tab 13 is relatively large, the internal shunt of the first electrode tab 13 is relatively uniform, which is beneficial to the homogenization reaction and reduces the impedance.

[0141] Optionally, when the ratio of the number of the first tabs 111 of the first electrode tab 13 to the number of the first flat sections 131 of the first electrode tab 13 is greater than 1, after conversion, when there are more than 1 first tabs 111 arranged on the first flat section 131 on average, the more than 1 first tabs 111 can be all arranged on the same side of the first flat section 131. In this case, the welding redundancy can be increased and the product yield can be effectively improved.

[0142] The arrangement of the second pole tab 112 can be the same or similar to that of the first pole tab 111, which will not be described in detail. For example, the ratio of the number of the second pole tabs 112 of the second pole piece 14 to the number of the second straight sections 141 of the second pole piece 14 is 1 to 2, which can be greater than 1 and less than or equal to 2.

[0143] When the electrode assembly 10 is a laminated structure, when the number of the first pole lugs 111 and the second pole lugs 112 are the same, the overcurrent density of a single pole lug is the same, and the performance matching is more excellent, which is beneficial to improving the uniform reaction of the battery cell 7, enhancing the shunt effect, and improving the charge and discharge capacity of the battery cell 7.

[0144] Regardless of whether the electrode assembly 10 is a wound structure or a laminated structure, the first electrode tab 111 is connected to at least one side of the first coating portion 130 .

[0145] like Figure 13 and Figure 14 As shown, in some embodiments, the first pole tab 111 includes a pole tab body 1111 and a plurality of pole tab protrusions 1112, the plurality of pole tab protrusions 1112 are all connected to a side of the pole tab body 1111 away from the first coating portion 130, and there is a gap between two adjacent pole tab protrusions 1112. Of course, the first pole tab 111 may also include only the pole tab body 1111. Figure 13 A schematic diagram of unfolding the first pole piece 13 in the electrode assembly 10 of the wound structure is shown.

[0146] The arrangement of multiple pole lug protrusions 1112 enables the first pole lug 111 to have multiple connection sites. For example, when connecting the first pole lug 111 to the first adapter 41, the multiple pole lug protrusions 1112 can be respectively connected to different positions of the first adapter 41, such as by welding. This can increase the welding positions of the first pole lug 111 and the first adapter 41, improve the welding yield, and enhance the stability of the connection between the two.

[0147] The structure of the second electrode tab 112 may be the same as or similar to that of the first electrode tab 111 , and will not be described in detail herein.

[0148] In some embodiments, the first pole ear 111 is a positive pole ear, and the thickness of the positive pole ear is 10 μm to 20 μm, and can be 10 μm to 15 μm. Exemplarily, the thickness of the positive pole ear 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, 16 μm, 17 μm, 18 μm, 19 μm, 20 μm, or a range consisting of any two of the above values. When the thickness of the positive pole ear is within the above range, the positive pole ear has excellent current capacity, can reduce heat generation, and is conducive to improving the fast charging performance of the battery cell.

[0149] In some embodiments, the first tab 111 is a negative tab, and the thickness of the negative tab is 4 μm to 10 μm, optionally 4 μm to 6 μm. Exemplarily, the thickness of the negative tab is 4 μm, 4.5 μm, 5 μm, 5.5 μm, 6 μm, 6.5 μm, 7 μm, 7.5 μm, 8 μm, 8.5 μm, 9 μm, 9.5 μm, 10 μm, or a range composed of any two of the above values. When the thickness of the negative tab is within the above range, the current-carrying capacity of the negative tab is relatively excellent, which can reduce heat generation and is beneficial to improving the fast charging performance of the battery cell.

[0150] In the embodiments of the present application, the thickness of the tab has the meaning in the art and can be detected by using equipment and methods well-known in the art. For example, the thickness measured by a micrometer can be used.

[0151] [Positive electrode plate] The positive electrode plate includes a positive current collector portion and a positive electrode film layer provided on at least one surface of the positive current collector portion and including a positive active material. For example, the positive current collector portion has two surfaces opposite to each other in its own thickness direction, and the positive electrode film layer is provided on any one or both of the two opposite surfaces of the positive current collector portion.

[0152] In the embodiments of the present application, the upper charge voltage and the discharge cut-off voltage of the battery cell are different according to the different positive active materials. For example, when the phosphate material includes lithium iron phosphate, the upper charge voltage can be 3.65 V and the discharge cut-off voltage can be 2.0 V. Another example is that when the phosphate material includes lithium manganese iron phosphate, the upper charge voltage can be 4.3 V and the discharge cut-off voltage can be 2.0 V.

[0153] The 100% state of charge (SOC) and 0% state of charge (SOC) of the battery cell are defined as follows: The battery cell is charged at a constant current charge rate of 0.33C to the upper voltage of the battery, and then charged at a constant voltage to 0.05C, corresponding to the state of 100% SOC of the battery cell; the battery cell is discharged at a constant current discharge rate of 0.33C to the cut-off voltage, corresponding to the state of 0% SOC of the battery cell.

[0154] In some embodiments, when the battery cell is at 100% state of charge (SOC), the tap density of the positive electrode film layer is 2.50 g / cm 3 to 2.80 g / cm 3 ; optionally 2.55 g / cm 3 to 2.70 g / cm 3 . Exemplarily, when the battery cell is at 100% state of charge (SOC), the tap density of the positive electrode film layer is 2.50 g / cm 3 、2.52 g / cm3 , 2.55 g / cm 3 , 2.56 g / cm 3 , 2.57 g / cm 3 , 2.58 g / cm 3 , 2.60 g / cm 3 , 2.62 g / cm 3 , 2.65 g / cm 3 , 2.68 g / cm 3 , 2.70 g / cm 3 , 2.72 g / cm 3 , 2.75 g / cm 3 , 2.78 g / cm 3 , 2.80 g / cm 3 or a range composed of any two of the above values.

[0155] When the compaction density of the positive electrode film layer is within the above range, it is beneficial to improve the energy density of the single battery cell; and because the positive electrode active material in the positive electrode film layer is stacked relatively tightly, the contact resistance between particles is small, which can further reduce the resistance of the electrode sheet, thereby reducing heat generation.

[0156] In some embodiments, the single-sided coating weight of the positive electrode film layer is 200 mg / 1540.25 mm 2 to 370 mg / 1540.25 mm 2 ; optionally 240 mg / 1540.25 mm 2 to 330 mg / 1540.25 mm 2 . Exemplarily, the single-sided coating weight of the positive electrode film layer is 200 mg / 1540.25 mm 2 , 210 mg / 1540.25 mm 2 , 220 mg / 1540.25 mm 2 , 230 mg / 1540.25 mm 2 , 240 mg / 1540.25 mm 2 , 250 mg / 1540.25 mm 2 , 260 mg / 1540.25 mm 2 , 270 mg / 1540.25 mm 2 , 280 mg / 1540.25 mm 2 , 290 mg / 1540.25 mm 2 , 300 mg / 1540.25 mm 2 , 310 mg / 1540.25 mm 2 , 320 mg / 1540.25 mm 2 , 330 mg / 1540.25 mm2 、 340 mg / 1540.25 mm 2 、 350 mg / 1540.25 mm 2 、 360 mg / 1540.25 mm 2 、 370 mg / 1540.25 mm 2 or a range composed of any two of the above values.

[0157] When the single-sided coating weight of the positive electrode film layer is within the above range, the heat generation per unit area of the positive electrode sheet is not excessive, and the energy density of the battery cell can be improved while taking it into account.

[0158] In the embodiments of the present application, the compaction density of the positive electrode film layer of the battery cell in the 100% state of charge (SOC) has the meaning well-known in the art, that is, the positive electrode sheet is disassembled from the battery cell in the 100% state of charge (SOC), and the compaction density of the positive electrode film layer is measured. For example, a single-sided coated positive electrode sheet (if it is a double-sided coated sheet, the positive electrode film layer on one side can be wiped off first) is punched into small round pieces with an area of S1, weighed, recorded as M1, and its thickness H1 is measured. Then, the positive electrode film layer of the above-mentioned weighed positive electrode sheet is wiped off, the weight of the positive electrode current collector is weighed, recorded as M0, and its thickness H0 is measured. The single-sided coating weight of the positive electrode film layer = (the weight M1 of the positive electrode sheet - the weight M0 of the positive electrode current collector) / S1, the thickness of the positive electrode film layer = the thickness H1 of the positive electrode sheet - the thickness H0 of the positive electrode current collector, and the compaction density of the positive electrode film layer = the single-sided coating weight of the positive electrode film layer / the thickness of the positive electrode film layer.

[0159] In some embodiments, the powder resistivity of the positive electrode active material is from 1 Ω·cm to 27.5 Ω·cm; optionally, less than or equal to 20 Ω·cm; optionally, less than or equal to 11 Ω·cm. Exemplarily, the powder resistivity of the positive electrode active material can be 27.5 Ω·cm, 20 Ω·cm, 19 Ω·cm, 18 Ω·cm, 17 Ω·cm, 16 Ω·cm, 15 Ω·cm, 14 Ω·cm, 13 Ω·cm, 12 Ω·cm, 11 Ω·cm, 10 Ω·cm, 9 Ω·cm, 8 Ω·cm, 7 Ω·cm, 6 Ω·cm, 5 Ω·cm, 4 Ω·cm, 3 Ω·cm, 2 Ω·cm, 1 Ω·cm or a range composed of any two of the above values.

[0160] The relatively low powder resistivity of the positive electrode active material results in a relatively low resistance of the positive electrode sheet and less heat generation of the battery cell.

[0161] In the embodiments of the present application, the powder resistivity of the material has the meaning well-known in the art, and can be detected by methods and equipment well-known in the art. For example, according to the test standard GB / T30835-2014, a PRCD1100 powder resistivity meter is used for testing.

[0162] In some embodiments, the powder tap density of the positive electrode active material under 30000 N is 2.46 g / cm 3 to 2.8 g / cm 3 . Exemplarily, the powder tap density of the positive electrode active material under 30000 N is 2.46 g / cm 3 , 2.47 g / cm 3 , 2.48 g / cm 3 , 2.49 g / cm 3 , 2.5 g / cm 3 , 2.51 g / cm 3 , 2.55 g / cm 3 , 2.58 g / cm 3 , 2.60 g / cm 3 , 2.65 g / cm 3 , 2.68 g / cm 3 , 2.70 g / cm 3 , 2.72 g / cm 3 , 2.75 g / cm 3 , 2.78 g / cm 3 , 2.80 g / cm 3 or a range composed of any two of the above values.

[0163] When the powder tap density of the positive electrode active material under 30000 N is within the above range, the energy density of the battery cell can be improved. Moreover, since the positive electrode active material in the positive electrode film layer can be stacked more closely and the contact resistance between particles is smaller, the resistance of the electrode sheet can be further reduced, thereby reducing heat generation.

[0164] In the embodiments of the present application, the powder tap density of the material has the meaning well-known in the art and can be detected by methods and equipment well-known in the art. Detection is carried out in accordance with the test standard GB / T24533-2009. For example, a certain amount of positive electrode active material is taken as a sample and added to a mold with a bottom area of 1.327 cm 2 in a UTM7305 type electronic pressure testing machine, pressurized to 3000 kg (equivalent to 30000 N), held for 30 s, then depressurized, held for 10 s, and then the powder tap density of the positive electrode active material under the action of 30000 N is recorded and calculated.

[0165] In some embodiments, the specific charge capacity of the positive electrode active material at a rate of 0.1C is from 150 mAh / g to 170 mAh / g, and may be optionally from 157 mAh / g to 170 mAh / g. Exemplarily, the specific charge capacity of the positive electrode active material at a rate of 0.1C is 150 mAh / g, 151 mAh / g, 152 mAh / g, 153 mAh / g, 154 mAh / g, 155 mAh / g, 156 mAh / g, 157 mAh / g, 158 mAh / g, 159 mAh / g, 160 mAh / g, 161 mAh / g, 162 mAh / g, 163 mAh / g, 164 mAh / g, 165 mAh / g, 166 mAh / g, 167 mAh / g, 168 mAh / g, 169 mAh / g, 170 mAh / g or a range composed of any two of the above values.

[0166] When the specific charge capacity of the positive electrode active material at a rate of 0.1C is within the above range, the energy density of the battery cell is relatively high.

[0167] In the embodiments of the present application, the specific capacity of the active material has the meaning well-known in the art, and can be tested by using the equipment and methods well-known in the art. The test method for the initial coulombic efficiency and the initial discharge specific capacity in Appendix G of the national standard GB / T 24533-2019 can be adopted. Using metallic lithium as the negative electrode and the sample electrode sheet containing the above materials as the positive electrode, a half-button cell is assembled. Under the condition of 23°C ± 2°C, the half-button cell is placed on a battery tester or other test equipment with the same performance, and the charge-discharge capacity is obtained through charge and discharge at a rate of 0.1C, and then the capacity is divided by the mass of the active material of the electrode sheet to obtain the specific charge capacity parameter.

[0168] In some embodiments, the mass ratio of the lithium-containing phosphate with an olivine structure in the positive electrode active material may be greater than or equal to 80% and less than or equal to 100%. It can be considered that the positive electrode active material of the present application is a lithium-containing phosphate system with an olivine structure. When the mass ratio of the lithium-containing phosphate with an olivine structure is less than 100%, the positive electrode active material may further include common positive electrode active materials, such as but not limited to at least one of lithium-containing transition metal oxides and lithium-containing phosphates. Examples of the lithium-containing transition metal oxides may include but are not limited to at least one of lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide and their respective modified compounds. Examples of the lithium-containing phosphates may include but are not limited to at least one of lithium iron phosphate, a composite material of lithium iron phosphate and carbon, lithium manganese phosphate, a composite material of lithium manganese phosphate and carbon, lithium manganese iron phosphate, and a composite material of lithium manganese iron phosphate and carbon.

[0169] Optionally, the mass percentage of the lithium-containing phosphate with an olivine structure in the positive electrode active material is 100%.

[0170] In the embodiments of the present application, the lithium-containing phosphate with an olivine structure can be phosphate particles or a material obtained by coating and modifying them. For example, the lithium-containing phosphate with an olivine structure includes phosphate particles and a coating layer, and the coating layer covers the surface of the phosphate particles, and the coating layer contains one or more elements of C, Fe, Ti, Zr, Hf, Ge, and Sn.

[0171] By coating the surface of the phosphate particles with a coating layer, the conductivity of the lithium-containing phosphate with an olivine structure can be improved, the powder resistivity of the material can be reduced, and it is beneficial to the migration rate of lithium ions, improving the fast charging ability of the battery and reducing the heat generation of the battery cell.

[0172] In some embodiments, the phosphate particles include a compound with the general formula Li x1 A y1 Me a M b P 1-c X c Y z where 0.5 ≤ x 1 ≤ 1.3, 0 ≤ y 1 ≤ 1.3, and 0.9 ≤ x 1 + y 1 ≤ 1.3, 0.9 ≤ a ≤ 1.5, 0 ≤ b ≤ 0.5, and 0.9 ≤ a + b ≤ 1.5, 0 ≤ c ≤ 0.5, 3 ≤ z ≤ 5, A includes one or more of Na, K, Mg, Me includes one or more of Mn, Fe, Co, Ni, M includes one or more of B, Mg, Al, Si, P, S, Ca, Sc, Ti, V, Cr, Cu, Zn, Sr, Y, Zr, Nb, Mo, Cd, Sn, Sb, Te, Ba, Ta, W, Yb, La, Ce, X includes one or more of S, Si, Cl, B, C, N, and Y includes one or more of O, F. The cyclic stability of the phosphate particles is relatively excellent, which is beneficial to improving the cyclic performance of the battery cell.

[0173] Exemplarily, the phosphate particles include one or more of LiFePO 4 、LiMnPO 4 、LiNiPO 4 、LiCoPO 4 . During the charge and discharge process of the battery cell, the insertion and extraction and consumption of active ions such as Li will occur, and the molar content of Li in the battery cell is different when the battery cell is discharged to different states. Regarding the positive electrode active materials LiFePO 4 、LiMnPO 4 、LiNiPO4 、LiCoPO 4 In the examples of the present invention, the molar content of Li is the initial state of the material, that is, the state before feeding. When the positive electrode active material is used in the battery system, the molar content of Li may change after charge and discharge cycles. 4 、LiMnPO 4 、LiNiPO 4 、LiCoPO 4 In the enumeration of etc., the molar content of oxygen O is only a theoretical value. The release of oxygen from the lattice will cause the molar content of oxygen O to change. In reality, the molar content of oxygen O will fluctuate. The above situations are all within the protection scope of the present application.

[0174] In some embodiments, the coating layer includes a general formula of Li 3-d Fe 2-d M2 d (PO x2 ) y2 The fast ion conductor M2 includes one or more elements selected from Ti, Zr, Hf, Ge and Sn, 0≤d≤1, 0<x 2 <5,0<y 2 <4.

[0175] Exemplarily, the fast ion conductor is a material having a NASICON structure, for example, one or more of lithium iron titanium phosphate Li2FeTi(PO4)3, lithium iron zirconium phosphate Li2FeZr(PO4)3, and lithium iron tin phosphate Li2FeSn(PO4)3.

[0176] Fast ion conductors with NASICON structures are materials with ultrafast ion conduction capabilities, rich three-dimensional lithium ion diffusion and transmission channels, and have the advantages of high ion conduction efficiency and strong structural stability during multiple lithium removal and insertion processes. Coating fast ion conductors with NASICON structures on the surface of phosphate particles can significantly increase the transmission rate of lithium ions during multiple lithium removal / insertion at the positive terminal, improve the ionic conductivity of the positive electrode active material, and improve the fast charging capability of the battery cell. In addition, it can also increase the gram capacity and the energy density of the corresponding battery cell.

[0177] In some embodiments, the coating layer further includes carbon.

[0178] The carbon element and the fast ion conductor can be arranged in layers. For example, the carbon element serves as an independent carbon coating layer, and the fast ion conductor serves as an independent fast ion conductor layer. The carbon coating layer can coat the surface of the phosphate particles, and the fast ion conductor layer is located on the surface of the carbon coating layer, that is, the fast ion conductor layer is located on the side of the carbon coating layer away from the phosphate particles. Or, the fast ion conductor layer can coat the surface of the phosphate particles, and the carbon coating layer is located on the surface of the fast ion conductor layer, that is, the carbon coating layer is located on the side of the fast ion conductor layer away from the phosphate particles. Of course, the carbon element and the fast ion conductor can also be arranged in the same layer.

[0179] Optionally, the carbon coating layer can be formed by carbonizing an organic carbon source (such as glucose, polyethylene glycol, etc.) on the surface of the fast ion conductor layer. The carbon coating layer can partially coat the fast ion conductor layer or completely coat the fast ion conductor layer. The setting of the carbon coating layer can significantly improve the electronic conductivity of the phosphate particles, make up for the defect of poor electronic conduction performance of the phosphate particles, and improve the energy density of the battery cell. Specifically, the setting of the carbon coating layer endows the positive electrode active material of the present application with the following advantages: The carbon coating layer in the positive electrode active material of the present application provides a suitable channel for the transmission of electrons, can significantly improve the conduction rate of electrons during multiple de-lithiation and intercalation processes, improve the electronic conductivity of lithium-containing phosphate, improve the charging ability of the corresponding battery cell, and can also improve the energy density.

[0180] The carbon coating layer of the positive electrode active material of the present application is porous and loose, which enables the electrolyte to come into full and effective contact with the lithium-containing phosphate, thereby improving the transmission rate of lithium ions at the phase interface and improving the charging ability of the battery cell.

[0181] Coating a layer of carbon coating layer on the surface of the lithium-containing phosphate can not only improve the conductivity of the lithium-containing phosphate, but also improve the structural stability of the positive electrode active material, effectively alleviate the iron dissolution phenomenon of the positive electrode active material during the long-term storage and cyclic use of the battery cell, and thus improve the cycle life of the battery cell. The positive electrode active material of the present application uses lithium-containing phosphate as the base material, giving full play to the advantages of low cost, high use reliability, and good cycle stability of lithium-containing phosphate. At the same time, the coating layers (fast ion conductor layer and carbon coating layer) are used to solve the disadvantages of poor electronic conductivity and ion conductivity. The battery cell prepared from the positive electrode active material of the present application can improve the energy density of the battery cell on the premise of excellent cycle performance. In the embodiments of the present application, the content of elements in the positive electrode active material has the meaning well-known in the art and can be detected by equipment and methods well-known in the art. For example, referring to EPA 6010D-2014, it is tested by inductively coupled plasma atomic emission spectrometry and determined by inductively coupled plasma optical emission spectrometry (ICP-OES, instrument model: Thermo ICAP7400). After discharging the battery cell to 0% state of charge (SOC), the positive electrode plate is disassembled, washed with DMC and dried, and then after removing impurities by high-temperature calcination, 0.4 g of the positive electrode active material is weighed, and 10 ml (50% concentration) of aqua regia is added thereto. Then it is placed on a flat plate at 180 °C for 30 min. After digestion on the flat plate, it is made up to a volume of 100 mL, and quantitative testing is carried out by the standard curve method.

[0182] In some embodiments, the graphitization degree of the positive electrode active material is from 0.15 to 0.32, and can be optionally from 0.19 to 0.26. Exemplarily, the graphitization degree of the positive electrode active material is 0.15, 0.16, 0.17, 0.18, 0.19, 0.20, 0.21, 0.22, 0.23, 0.24, 0.25, 0.26, 0.27, 0.28, 0.29, 0.30, 0.31, 0.32 or the range composed of any two of the above values.

[0183] When the graphitization degree of the positive electrode active material is within the above range, it is beneficial to improve the conductivity of the positive electrode active material, reduce the heat generation of the positive electrode plate, and thus reduce the heat generation of the battery cell.

[0184] In the embodiments of the present application, the higher the graphitization degree of the material, the lower the degree of disorder, and it can be tested according to the general rules of X-ray diffraction analysis method of JIS / K 0131-1996.

[0185] In some embodiments, the mass content of carbon element in the lithium-containing phosphate with olivine structure is 1% to 2%, and the specific surface area of the lithium-containing phosphate with olivine structure is 5 m 2 / g to 18 m 2 / g.

[0186] Optionally, the mass content of carbon element in the lithium-containing phosphate with olivine structure is 1% to 2%, and the specific surface area of the lithium-containing phosphate with olivine structure is 7.5 m 2 / g to 14 m 2 / g.

[0187] Exemplarily, the mass content of carbon element in the lithium-containing phosphate with olivine structure is 1%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2% or the range composed of any two of the above values.

[0188] Exemplarily, the specific surface area of the lithium-containing phosphate with olivine structure is 5 m 2 / g, 6 m 2 / g, 7 m 2 / g, 8 m 2 / g, 9 m 2 / g, 10 m 2 / g, 11 m 2 / g, 12 m 2 / g, 13 m 2 / g, 14 m 2 / g, 15 m 2 / g, 16 m 2 / g, 17 m 2 / g, 18 m 2 / g or a range composed of any two of the above values.

[0189] Carbon mainly exists in the form of a carbon coating layer in the coating layer. The carbon coating layer is loose and porous, which is beneficial to increasing the specific surface area of the material, more beneficial to the effective contact between the electrolyte and the phosphate particles, and beneficial to the transmission of lithium ions at the phase interface. In addition, when the mass content of carbon is within the above range, the conductivity of the lithium-containing phosphate with olivine structure can be significantly improved, which is beneficial to enhancing the ionic conductivity and electronic conductivity of the lithium-containing phosphate with olivine structure, and can improve the rapid charging ability and energy density of a single battery cell.

[0190] In the embodiments of the present application, the specific surface area of the material has the meaning well-known in the art, and can be detected by using the equipment and methods well-known in the art. For example, it can be detected according to the test standard GB / T 19587-2017. Taking the positive electrode active material as a sample, the specific surface area is tested by a Tri-Star 3020 specific surface area and pore size analyzer of Micromeritics Company in the United States.

[0191] In some embodiments, the volume distribution particle size of the positive electrode active material satisfies: 1 µm ≤ Dv50 ≤ 2 µm, 0.4 µm ≤ Dv10 ≤ 0.7 µm.

[0192] Exemplarily, Dv50 of the positive electrode active material can be 1 µm, 1.1 µm, 1.15 µm, 1.2 µm, 1.25 µm, 1.3 µm, 1.35 µm, 1.4 µm, 1.45 µm, 1.5 µm, 1.55 µm, 1.6 µm, 1.65 µm, 1.7 µm, 1.75 µm, 1.8 µm, 1.85 µm, 1.9 µm, 1.95 µm, 2 µm or a range composed of any two of the above values.

[0193] Exemplarily, the Dv10 of the positive electrode active material may be 0.4 µm, 0.45 µm, 0.5 µm, 0.55 µm, 0.6 µm, 0.65 µm, 0.7 µm, or a range composed of any two of the above values.

[0194] The particle size of the positive electrode active material is relatively small, the lithium deintercalation / insertion path of lithium ions in the positive electrode active material is short, and the heat generation is less. Moreover, the particle size of the above positive electrode active material is not too small, and basically no agglomeration occurs during the processing and preparation process, making the performance of the positive electrode active material stable.

[0195] In the embodiments of the present application, the volume average particle size Dv50 of the material refers to the particle size corresponding to 50% in the volume distribution, and the volume average particle size Dv10 of the material refers to the particle size corresponding to 10% in the volume distribution. It can be detected by using equipment and methods well-known in the art. For example, taking the positive electrode active material as a sample, according to the test standard GB / T 19077-2016, the Dv50 and Dv10 of the particles are tested by a Mastersizer 2000E laser particle size analyzer, etc.

[0196] When the positive electrode active material includes other materials in addition to the lithium-containing phosphate with an olivine structure, the volume distribution particle size of the positive electrode active material refers to the volume distribution particle size of all positive electrode active materials.

[0197] In some embodiments, the lithium-containing phosphate with an olivine structure is in a granular form. The lithium-containing phosphate with an olivine structure includes secondary particles, and the secondary particles include a plurality of primary particles. The average particle size of the primary particles is 200 nm to 500 nm. Exemplarily, the average particle size of the primary particles is 200 nm, 220 nm, 250 nm, 280 nm, 300 nm, 320 nm, 350 nm, 380 nm, 400 nm, 420 nm, 450 nm, 480 nm, 500 nm, or a range composed of any two of the above values.

[0198] The average particle size of the primary particles is relatively small, the lithium deintercalation / insertion path of lithium ions in the positive electrode active material is short, and the heat generation is less.

[0199] In the embodiments of the present application, the secondary particles refer to aggregated particles formed by more than two primary particles. The primary particles and the secondary particles can be easily distinguished by experimental means (such as taking SEM images using a scanning electron microscope). The average particle size of the primary particles can be obtained by testing in the SEM image of the scanning electron microscope. The SEM test parameters can be set as follows: the working voltage (EHT) is 10.00 kV, the InLens detector is used, the working distance is 4.6 mm, and the magnification is 1000X.

[0200] In some embodiments, the positive electrode film layer further includes one or more of ternary materials, lithium phosphate, lithium hydrogen phosphate, lithium sulfate, lithium sulfite, lithium molybdate, lithium oxalate, lithium titanate, lithium tetraborate, lithium metasilicate, lithium manganate, lithium tartrate, trilithium citrate, lithium nickelate, and lithium ferrate. The above materials can be used as lithium supplement agents. The lithium supplement agent can supplement lithium ions to the positive electrode film layer, make up for the irreversible loss of lithium ions in the system, and improve the capacity, thereby enhancing the energy density of the battery cell.

[0201] Optionally, the ternary material includes Li x3 A y3 Ni a3 Co b3 Mn c M3 (1-a3-b3-c3) Y3 z3 , where 0 < x 3 ≤2.1, 0 < y 3 ≤2.1, and 0.9 ≤ x 3 +y 3 ≤2.1, 0 ≤ a 3 ≤1, 0 ≤ b 3 ≤1, 0 ≤ c 3 ≤1, and 0.1 ≤ a 3 +b 3 +c 3 ≤1, 1.8 ≤ z 3 ≤3.5, A includes one or several of Na, K, and Mg, M3 includes one or several of B, Mg, Al, Si, P, S, Ca, Sc, Ti, V, Cr, Fe, Cu, Zn, Sr, Y, Zr, Nb, Mo, Cd, Sn, Sb, Te, Ba, Ta, W, Yb, La, Ce, and Y3 includes one or several of O and F.

[0202] Exemplarily, the ternary material includes LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O 2 (NCM333), LiNi 0.5 Co 0.2 Mn 0.3 O 2 (NCM523), LiNi 0.6 Co 0.2 Mn 0.2 O 2 (NCM622), LiNi 0.8 Co 0.1 Mn 0.1 O 2 (NCM811), LiNi 0.80 Co 0.15 Al 0.05O 2 at least one of

[0203] In some embodiments, the mass content of the lithium supplement in the positive electrode film layer is 0.5% to 5%, such as 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5% or the range composed of any two of the above values. When the mass content of the lithium supplement is within the above range, it can supplement lithium ions to the positive electrode film layer, make up for the irreversible lithium ion loss in the system, improve the capacity, and thus improve the energy density of the battery cell.

[0204] The lithium supplement can be in the same layer as the positive electrode active material or in different layers. When the lithium supplement and the positive electrode active material are in different layers, the lithium supplement can be in the lithium supplement layer, and the positive electrode active material can be in the positive electrode active material layer. In other words, the positive electrode film layer includes a lithium supplement layer and a positive electrode active material layer. The positive electrode active material layer can be disposed on at least one side of the positive electrode current collector, and the lithium supplement layer can be located between the positive electrode active material layer and the positive electrode current collector. Alternatively, the lithium supplement layer can be disposed on at least one side of the positive electrode current collector, and the positive electrode active material layer can be located between the lithium supplement layer and the positive electrode current collector. Optionally, the lithium supplement layer can be located between the positive electrode active material layer and the positive electrode current collector. During the cyclic charge and discharge process of the battery cell, the lithium supplement in the lithium supplement layer can be gradually released into the system to make up for the lithium loss in the battery system.

[0205] In some embodiments, the positive electrode film layer may further optionally include a positive electrode conductive agent. There is no particular limitation on the type of the positive electrode conductive agent in the embodiments of the present application. As an example, the positive electrode conductive agent includes at least one of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. In some embodiments, based on the mass of the positive electrode film layer, the mass content of the positive electrode conductive agent is ≤5%.

[0206] In some embodiments, the positive electrode film layer may further optionally include a positive electrode binder. There is no particular limitation on the type of the positive electrode binder in the embodiments of the present application. As an example, the positive electrode binder may include at least one of polyvinylidene fluoride, polytetrafluoroethylene, vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, polyacrylic acid, and fluorinated acrylate resins. In some embodiments, based on the mass of the positive electrode film layer, the mass content of the positive electrode binder is ≤5%.

[0207] In some embodiments, the positive current collector may be a metal foil or a composite current collector. As an example of the metal foil, at least one of aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy foils may be used. The composite current collector may include a polymer material base layer and a metal material layer formed on at least one surface of the polymer material base layer. As an example, the metal material of the metal material layer may include at least one of aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy. As an example, the polymer material base layer may include at least one of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0208] In some embodiments, the ratio of the thickness of the positive current collector to the thickness of the single-sided positive electrode film layer is 0.05 to 0.3. Exemplarily, the ratio of the thickness of the positive current collector to the thickness of the single-sided positive electrode film layer is 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, 0.12, 0.15, 0.18, 0.2, 0.22, 0.25, 0.28, 0.3, or a range composed of any two of the above values.

[0209] When the ratio of the thickness of the positive current collector to the thickness of the single-sided positive electrode film layer is within the above range, the rapid charging ability and energy density of the battery cell can be improved.

[0210] In some embodiments, the thickness of the positive current collector is 10 μm to 20 μm, 10 μm to 15 μm, and may be optionally 12 μm to 15 μm. Exemplarily, the thickness of the positive current collector is 10 μm, 10.5 μm, 11 μm, 11.5 μm, 12 μm, 12.5 μm, 13 μm, 13.5 μm, 14 μm, 14.5 μm, 15 μm, 20 μm, or a range composed of any two of the above values.

[0211] When the thickness of the positive current collector is within the above range, the current-carrying capacity of the positive current collector is relatively excellent, and the battery cell can have a high energy density.

[0212] In the embodiments of the present application, the thicknesses of the positive electrode film layer and the positive current collector have meanings well-known in the art, and can be detected by devices and methods well-known in the art. For example, a micrometer is used to measure the thickness of the positive electrode plate, the film layer on the surface of the positive current collector is removed, and a micrometer is used to measure the thickness of the positive current collector. When the positive electrode film layer is coated on one side, the thickness of the positive electrode film layer is the thickness of the positive electrode plate minus the thickness of the positive current collector. When the positive electrode film layer is coated on both sides, the thickness of the positive electrode film layer is (the thickness of the positive electrode plate minus the thickness of the positive current collector) / 2.

[0213] The positive electrode film layer is usually formed by coating a positive electrode slurry on a positive electrode current collector and then drying and cold pressing. The positive electrode slurry is usually formed by dispersing a positive electrode active material, an optional conductive agent, an optional binder, and any other components in a solvent and stirring evenly. The solvent can be N-methylpyrrolidone (NMP), but is not limited thereto.

[0214] The positive electrode tab does not exclude other additional functional layers besides the positive electrode film layer. For example, in some embodiments, the positive electrode tab of the embodiment of the present application further includes a positive electrode conductive layer disposed on the surface of the positive electrode current collector and sandwiched between the positive electrode current collector and the positive electrode film layer. In some other embodiments, the positive electrode tab of the embodiment of the present application further includes a protective layer covering the surface of the positive electrode film layer.

[0215] In some embodiments, the positive electrode tab further includes a positive electrode conductive layer, and the positive electrode conductive layer is located between the positive electrode film layer and the positive electrode current collector. The positive electrode conductive layer can further improve the conductivity of the positive electrode tab, reduce the heat generation of the positive electrode tab, and thus reduce the heat generation of the battery cell.

[0216] In some embodiments, the thickness of the positive electrode conductive layer is 0.5 μm to 2 μm. Exemplarily, the thickness of the positive electrode conductive layer can be 0.5 μm, 0.8 μm, 1 μm, 1.2 μm, 1.5 μm, 1.6 μm, 1.8 μm, 2 μm, or a range composed of any two of the above values.

[0217] When the thickness of the positive electrode conductive layer is within the above range, it can further improve the conductivity of the positive electrode tab, reduce the heat generation of the positive electrode tab, and thus reduce the heat generation of the battery cell, and can also take into account the improvement of the energy density of the battery cell.

[0218] In the embodiment of the present application, the thickness of the positive electrode conductive layer has the meaning well-known in the art, and can be detected by using equipment and methods well-known in the art. For example, tomographic scanning of the positive electrode tab can be performed to directly measure the thickness of the positive electrode conductive layer.

[0219] In some embodiments, the positive electrode conductive layer includes one or more of a positive electrode conductive agent and a positive electrode binder.

[0220] Optionally, the mass content of the positive electrode conductive agent in the positive electrode conductive layer is 30% to 50%. Exemplarily, the mass content of the positive electrode conductive agent is 30%, 35%, 40%, 45%, 50%, or a range composed of any two of the above values.

[0221] Exemplarily, the positive electrode conductive agent includes one or more of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. The positive electrode conductive agent in the positive electrode conductive layer can improve the conductivity of the positive electrode conductive layer, thereby improving the conductivity of the positive electrode tab and reducing the heat generation of the battery cell.

[0222] Optionally, the mass content of the positive electrode binder in the positive electrode conductive layer is 50% to 70%. Exemplarily, 50%, 60%, 65%, 70% or a range composed of any two of the above values.

[0223] Exemplarily, the positive electrode binder includes one or more of polyvinylidene fluoride, polytetrafluoroethylene, vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, polyacrylic acid, and fluorinated acrylate resins. The positive electrode binder in the positive electrode conductive layer can improve the bonding performance between the positive electrode current collector part and the positive electrode film layer, and improve the structural stability of the positive electrode plate.

[0224] [Negative electrode plate] The negative electrode plate includes a negative electrode current collector part and a negative electrode film layer provided on at least one surface of the negative electrode current collector part and including a negative electrode active material. For example, the negative electrode current collector part has two surfaces opposite to each other in its own thickness direction, and the negative electrode film layer is provided on any one or both of the two opposite surfaces of the negative electrode current collector part.

[0225] In some embodiments, when the battery cell is in a 100% charged state, the tap density of the negative electrode film layer is 1.15 g / cm 3 to 1.36 g / cm 3 ; optionally 1.25 g / cm 3 to 1.36 g / cm 3 . Exemplarily, when the battery cell is in a 100% charged state, the tap density of the negative electrode film layer is 1.15 g / cm 3 , 1.18 g / cm 3 , 1.20 g / cm 3 , 1.22 g / cm 3 , 1.25 g / cm 3 , 1.28 g / cm 3 , 1.3 g / cm 3 , 1.32 g / cm 3 , 1.35 g / cm 3 , 1.36 g / cm 3 or a range composed of any two of the above values.

[0226] When the tap density of the negative electrode film layer is within the above range, it is beneficial to improve the energy density of the battery cell; and since the negative electrode active materials in the negative electrode film layer are stacked relatively tightly and the contact resistance between particles is small, the resistance of the electrode plate can be further reduced, thereby reducing heat generation.

[0227] In the embodiments of the present application, the compaction density of the negative electrode film layer in the 100% charged state has the meaning well-known in the art, and can be detected by using the equipment and methods well-known in the art. The detection method is the same as the compaction density test method of the positive electrode film layer described above.

[0228] In some embodiments, the single-sided coating weight of the negative electrode film layer is 90 mg / 1540.25 mm 2 to 170 mg / 1540.25 mm 2 , and can be optionally 110 mg / 1540.25 mm 2 to 150 mg / 1540.25 mm 2 . Exemplarily, the single-sided coating weight of the negative electrode film layer is 90 mg / 1540.25 mm 2 , 92 mg / 1540.25 mm 2 , 95 mg / 1540.25 mm 2 , 96 mg / 1540.25 mm 2 , 100 mg / 1540.25 mm 2 , 102 mg / 1540.25 mm 2 , 104 mg / 1540.25 mm 2 , 105 mg / 1540.25 mm 2 , 108 mg / 1540.25 mm 2 , 110 mg / 1540.25 mm 2 , 112 mg / 1540.25 mm 2 , 114 mg / 1540.25 mm 2 , 115 mg / 1540.25 mm 2 , 116 mg / 1540.25 mm 2 , 118 mg / 1540.25 mm 2 , 120 mg / 1540.25 mm 2 , 122 mg / 1540.25 mm 2 , 125 mg / 1540.25 mm 2 , 128 mg / 1540.25 mm 2 , 130 mg / 1540.25 mm 2 , 132 mg / 1540.25 mm 2 , 135 mg / 1540.25 mm 2 , 137 mg / 1540.25 mm 2 , 140 mg / 1540.25 mm 2 , 142 mg / 1540.25 mm 2, 145 mg / 1540.25 mm 2 , 148 mg / 1540.25 mm 2 , 150 mg / 1540.25 mm 2 , 152 mg / 1540.25 mm 2 , 155 mg / 1540.25 mm 2 , 160 mg / 1540.25 mm 2 , 165 mg / 1540.25 mm 2 , 170 mg / 1540.25 mm 2 Or a range composed of any two of the above values.

[0229] When the single-sided coating weight of the negative electrode film layer is within the above range, the heat generation per unit area of the negative electrode sheet will not be too large, and it can take into account the improvement of the energy density of the battery cell.

[0230] In the embodiments of the present application, the single-sided coating weight of the negative electrode film layer has the meaning well-known in the art, and can be detected by the equipment and methods well-known in the art. The detection method is as described in the single-sided coating weight test method of the film layer above.

[0231] In some embodiments, the powder resistivity of the negative electrode active material is from 0.005 Ω·cm to 0.043 Ω·cm, and can be 0.04 Ω·cm. Exemplarily, the powder resistivity of the negative electrode active material can be 0.043 Ω·cm, 0.04 Ω·cm, 0.035 Ω·cm, 0.03 Ω·cm, 0.025 Ω·cm, 0.02 Ω·cm, 0.015 Ω·cm, 0.01 Ω·cm, 0.005 Ω·cm or a range composed of any two of the above values.

[0232] The relatively low powder resistivity of the negative electrode active material makes the resistance of the negative electrode sheet relatively low, and the heat generation of the battery cell is less.

[0233] In the embodiments of the present application, the powder resistivity of the negative electrode active material has the meaning well-known in the art, and can be detected by the equipment and methods well-known in the art. The detection method is as described in the powder resistivity test method of the positive electrode active material above.

[0234] In some embodiments, the powder compaction density of the negative electrode active material under a pressure of 20000 N is 1.5 g / cm 3 to 1.85 g / cm 3 , and can be 1.55 g / cm 3 to 1.65 g / cm 3 . Exemplarily, the powder compaction density of the negative electrode active material under a pressure of 20000 N is 1.5 g / cm 3, 1.55 g / cm 3 , 1.6 g / cm 3 , 1.65 g / cm 3 , 1.7 g / cm 3 , 1.75 g / cm 3 , 1.8 g / cm 3 , 1.85 g / cm 3 or a range composed of any two of the above values.

[0235] When the powder compaction density of the negative electrode active material is within the above range under 20,000 N, the energy density of the battery cell can be improved. And because the negative electrode active material in the negative electrode film layer can be stacked more closely, the contact resistance between particles is small, which can further reduce the resistance of the electrode sheet, thereby reducing heat generation.

[0236] In the embodiments of the present application, the powder compaction density of the material has the meaning well-known in the art, and can be detected by the methods and equipment well-known in the art, and detected according to the test standard GB / T24533-2009. As an example, take a certain amount of negative electrode active material as a sample, add it into a mold with a bottom area of 1.327 cm 2 in the UTM7305 type electronic pressure testing machine, pressurize to 2000 kg (equivalent to 20,000 N), keep the pressure for 30 s, then release the pressure, keep it for 10 s, and then record and calculate the powder compaction density of the negative electrode active material under the action of 20,000 N.

[0237] In some embodiments, the charging specific capacity of the negative electrode active material at a 0.1C rate is 350 mAh / g to 480 mAh / g. Exemplarily, the charging specific capacity of the negative electrode active material at a 0.1C rate is 350 mAh / g, 355 mAh / g, 360 mAh / g, 365 mAh / g, 370 mAh / g, 375 mAh / g, 380 mAh / g, 385 mAh / g, 390 mAh / g, 395 mAh / g, 400 mAh / g, 410 mAh / g, 420 mAh / g, 430 mAh / g, 440 mAh / g, 450 mAh / g, 460 mAh / g, 470 mAh / g, 480 mAh / g or a range composed of any two of the above values.

[0238] When the charging specific capacity of the negative electrode active material at a 0.1C rate is within the above range, the energy density of the battery cell is relatively high.

[0239] In the embodiments of the present application, the charging capacity per gram of the negative electrode active material at a rate of 0.1C has the meaning well-known in the art, and can be detected by the equipment and methods well-known in the art. The detection method is the same as the charging capacity per gram test method of the positive electrode active material at a rate of 0.1C described above.

[0240] In some embodiments, the negative electrode active material includes a carbon-based material, and the carbon-based material has high cycle stability and can improve the cycle performance of the battery cell. Optionally, the mass percentage of the carbon-based material in the negative electrode active material can be greater than or equal to 80% and less than or equal to 100%.

[0241] The positive electrode active material of the present application is mainly a lithium-containing phosphate system with an olivine structure, and the negative electrode active material is mainly a carbon-based material system. When used in combination, the battery cell has excellent cycle performance.

[0242] Optionally, the carbon-based material includes graphite particles, and the graphitization degree of the graphite particles is 92.0% to 94.5%. Exemplarily, the graphitization degree of the graphite particles is 92.0%, 92.5%, 93%, 93.5%, 94%, 94.5% or the range composed of any two of the above values.

[0243] When the graphitization degree of the graphite particles is within the above range, the graphite particles have excellent electrical conductivity, can reduce the heat generation of the negative electrode sheet and the battery cell, and can improve the fast charging performance of the battery cell.

[0244] In some embodiments, the graphite particles include artificial graphite and a carbon coating layer. The artificial graphite includes secondary particles, and the secondary particles include a plurality of primary particles. The carbon coating layer covers the surface of the artificial graphite. The carbon in the carbon coating layer is mainly amorphous carbon, and amorphous carbon refers to a transition carbon material with a very low degree of graphitization crystallization and an approximate amorphous form (or no fixed shape and periodic structural rules). In the present application, amorphous carbon refers to the product after carbonization treatment of an organic carbon source.

[0245] The artificial graphite includes secondary particles. In the artificial graphite, there are more migration paths for lithium ions, and the migration path in the primary particles is shorter, which can improve the migration rate of lithium ions. The carbon coating layer has more end faces and defects, so that the number of sites where lithium ions can be intercalated and deintercalated is more, and the electrical conductivity of the carbon coating layer is excellent, which can reduce the internal resistance of the negative electrode sheet and the heat generation of the battery cell.

[0246] Optionally, based on the mass of the graphite particles, the mass content of the carbon coating layer is 2% to 5%. Exemplarily, the mass content of the carbon coating layer is 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5% or the range composed of any two of the above values.

[0247] When the mass content of the carbon coating layer is within the above range, the internal resistance of the negative electrode sheet can be further reduced, and the heat generation of the battery cell can be reduced.

[0248] In the embodiments of the present application, the graphite particles can be prepared by methods well known in the art. For example, the preparation method includes: providing artificial graphite and an organic carbon source, mixing the two, and after carbonization treatment, a carbon coating layer is formed on at least part of the surface of the artificial graphite particles.

[0249] Optionally, the organic carbon source includes one or more of coal tar pitch, petroleum pitch, phenolic resin, and coconut shell. Further optionally, the organic carbon source includes petroleum pitch. Optionally, the softening point of coal tar pitch and petroleum pitch is below 250 °C.

[0250] Optionally, the carbonization treatment temperature is 700 °C to 1800 °C. Optionally, the carbonization treatment temperature is 1000 °C to 1300 °C. When the carbonization treatment temperature is within a suitable range, the organic carbon source can be carbonized, and a coating layer containing amorphous carbon is formed on at least a part of the surface of the artificial graphite.

[0251] Optionally, the carbonization treatment time is 1 h to 6 h.

[0252] In some embodiments, the carbon-based material may further include natural graphite. Specifically, the carbon-based material may include graphite particles, or the carbon-based material may include graphite particles and natural graphite. Optionally, the carbon-based material is graphite particles.

[0253] In some embodiments, the negative electrode active material may further include a silicon-based material. The introduction of the silicon-based material can improve the capacity of the negative electrode active material and increase the energy density of the battery cell.

[0254] Optionally, based on the mass of the negative electrode active material, the mass content of silicon element in the silicon-based material is 0.3% to 10.0%, and may be 1% to 6%. Exemplarily, the mass content of silicon element in the silicon-based material is 0.3%, 0.5%, 0.8%, 1%, 1.2%, 1.5%, 1.8%, 2%, 2.2%, 2.5%, 2.8%, 3%, 3.2%, 3.5%, 3.8%, 4%, 4.2%, 4.5%, 4.8%, 5%, 5.2%, 5.5%, 5.8%, 6%, 6.2%, 6.5%, 6.8%, 7%, 7.2%, 7.5%, 7.8%, 8%, 8.2%, 8.5%, 8.8%, 9%, 9.2%, 9.5%, 9.8%, 10% or any range composed of any two of the above values.

[0255] When the mass content of silicon element in the silicon-based material is within the above range, the capacity of the negative electrode active material can be improved, and the energy density of the battery cell can be improved.

[0256] Optionally, the silicon-based material may include at least one of elemental silicon, silicon oxide, silicon-carbon composite, silicon-nitrogen composite, and silicon alloy material.

[0257] In some embodiments, in addition to the above-mentioned carbon-based material and optional silicon-based material, the negative electrode active material may further include at least one of a tin-based material and lithium titanate. The tin-based material may include at least one of elemental tin, tin oxide, and tin alloy material.

[0258] In this application, the qualitative and quantitative determination of each substance or element can be detected by suitable equipment and methods known to those skilled in the art. Relevant detection methods can refer to domestic and foreign detection standards, domestic and foreign enterprise standards, etc. And those skilled in the art can also adaptively change certain detection steps / instrument parameters, etc. from the perspective of detection accuracy to obtain more accurate detection results. One detection method can be used for qualitative or quantitative determination, or several detection methods can be used in combination for qualitative or quantitative determination.

[0259] For example, this application can combine the general rules of X-ray diffraction analysis method in JIS / K0131-1996 to perform X-ray powder diffraction test and qualitative analysis on the negative electrode sheet or the negative electrode active material.

[0260] Artificial graphite and natural graphite can be distinguished by the SEM cross-sectional view taken by scanning electron microscope (SEM). There are voids between flake structures in the SEM cross-sectional view of natural graphite, and the SEM cross-sectional view of artificial graphite is dense and has no obvious gaps, or can be distinguished by the XRD spectrum obtained by X-ray diffraction method. There are obvious 2H phase and 3R phase in the XRD spectrum of natural graphite, and only 2H phase exists in the XRD spectrum of artificial graphite.

[0261] In the embodiments of this application, the negative electrode film layer includes at least one layer of film layer, and a single-layer film layer can be used, or at least two layers of film layers can be used. Optionally, the negative electrode film layer includes at least two layers of film layers.

[0262] When the negative electrode film layer adopts a single-layer film layer, the negative electrode active material in the negative electrode film layer includes a carbon-based material, and optionally also includes a silicon-based material. When a single-layer film layer is adopted, the volume average particle size Dv50 of the negative electrode active material is 8.2 μm to 13.5 μm. Exemplarily, the volume average particle size Dv50 of the negative electrode active material is 8.2 μm, 8.5 μm, 8.8 μm, 9 μm, 9.2 μm, 9.5 μm, 9.8 μm, 10 μm, 10.2 μm, 10.5 μm, 10.8 μm, 11 μm, 11.2 μm, 11.5 μm, 11.8 μm, 12 μm, 12.2 μm, 12.5 μm, 12.8 μm, 13 μm, 13.2 μm, 13.5 μm or the range composed of any two of the above values.

[0263] When the negative electrode film layer adopts at least two film layers, the negative electrode active material in the negative electrode film layer includes a carbon-based material, and optionally also includes a silicon-based material. The silicon-based material can be located in one of the at least two film layers or in at least two of the at least two film layers. The negative electrode film layer can include two film layers, three film layers, four film layers, or even more film layers.

[0264] In some embodiments, the negative electrode film layer includes a first negative electrode film layer and a second negative electrode film layer. The first negative electrode film layer is disposed on the surface of the negative electrode current collector. The carbon-based material in the first negative electrode film layer includes graphite particles. The second negative electrode film layer is connected to the side of the first negative electrode film layer facing away from the negative electrode current collector. The carbon-based material in the second negative electrode film layer includes graphite particles. The graphite particles in the first negative electrode film layer and the graphite particles in the second negative electrode film layer can be the same or different.

[0265] The interface between the first negative electrode film layer and the second negative electrode film layer can be regular or irregular, and is optionally irregular.

[0266] Optionally, the carbon-based material in the first negative electrode film layer further includes natural graphite.

[0267] The negative electrode film layer includes at least two film layers, and layer-by-layer coating is beneficial to improving the fast charging performance of the battery cell. Especially when there are differences between the first negative electrode film layer and the second negative electrode film layer, the pore differences of the negative electrode film layer can be constructed, the tortuosity of lithium ion transmission can be reduced, and the fast charging performance of the battery cell can be improved.

[0268] Optionally, the volume average particle size Dv50 of the negative electrode active material in the first negative electrode film layer is greater than or equal to the volume average particle size Dv50 of the negative electrode active material in the second negative electrode film layer. Further optionally, the volume average particle size Dv50 of the negative electrode active material in the first negative electrode film layer is greater than the volume average particle size Dv50 of the negative electrode active material in the second negative electrode film layer, which is beneficial to improving the compaction density of the negative electrode film layer. When the negative electrode active material includes graphite particles, the volume average particle size Dv50 of the graphite particles in the first negative electrode film layer is greater than or equal to the volume average particle size Dv50 of the graphite particles in the second negative electrode film layer.

[0269] The difference in particle sizes between the first negative electrode film layer and the second negative electrode film layer can improve the fast charging performance of the battery cell. Specifically, during fast charging, the overpotential of the second negative electrode film layer is usually relatively high, and the bottleneck of fast charging mainly lies in the second negative electrode film layer. In the embodiments of the present application, the particle size in the second negative electrode film layer is relatively small, which can shorten the solid-phase transmission path of lithium ions, improve the fast charging performance, and can improve the problem of lithium deposition on the surface layer of the negative electrode plate.

[0270] Optionally, the negative electrode active material in the first negative electrode film layer is granular, and its volume average particle size Dv50 is from 9.5 μm to 18.5 μm, optionally from 9.5 μm to 14.6 μm. Exemplarily, the volume average particle size of the negative electrode active material in the first negative electrode film layer is 9.5 μm, 10 μm, 10.5 μm, 11 μm, 11.5 μm, 12 μm, 12.5 μm, 13 μm, 13.5 μm, 14 μm, 14.5 μm, 14.6 μm, 15 μm, 15.5 μm, 16 μm, 16.5 μm, 17 μm, 17.5 μm, 18 μm, 18.5 μm or a range composed of any two of the above values. When the first negative electrode film layer includes graphite particles, the volume average particle size Dv50 of the graphite particles in the first negative electrode film layer is from 9.5 μm to 18.5 μm, optionally from 9.5 μm to 14.6 μm.

[0271] When the volume average particle size Dv50 of the negative electrode active material in the first negative electrode film layer is within the above range, on the one hand, it can shorten the solid-phase transmission path of lithium ions and improve the fast charging performance. On the other hand, the material is not prone to agglomeration during the preparation process, which can improve the stability of the material.

[0272] Optionally, the negative electrode active material in the second negative electrode film layer is granular, and its volume average particle size Dv50 is from 7.8 μm to 14.3 μm, optionally from 7.8 μm to 11.3 μm. Exemplarily, the volume average particle size Dv50 of the negative electrode active material is 7.8 μm, 8.0 μm, 8.2 μm, 8.5 μm, 8.8 μm, 9 μm, 9.2 μm, 9.5 μm, 9.8 μm, 10 μm, 10.2 μm, 10.5 μm, 10.8 μm, 11 μm, 11.3 μm, 11.2 μm, 11.5 μm, 11.8 μm, 12 μm, 12.2 μm, 12.5 μm, 12.8 μm, 13 μm, 13.2 μm, 13.5 μm, 13.8 μm, 14 μm, 14.1 μm, 14.3 μm or a range composed of any two of the above values. When the second negative electrode film layer includes graphite particles, the volume average particle size Dv50 of the graphite particles in the second negative electrode film layer is from 7.8 μm to 14.3 μm, optionally from 7.8 μm to 11.3 μm.

[0273] When the volume average particle size Dv50 of the negative electrode active material in the second negative electrode film layer is within the above range, on the one hand, it can shorten the solid-phase transmission path of lithium ions and improve the fast charging performance. On the other hand, the material is not prone to agglomeration during the preparation process, which can improve the stability of the material. On the other hand, the cooperation of the negative electrode active material in the second negative electrode film layer with the volume average particle size range and the negative electrode active material in the first negative electrode film layer is conducive to constructing the gradient pore difference between the second negative electrode film layer and the first negative electrode film layer, reducing the tortuosity of lithium ion transmission, and improving the fast charging performance of the battery cell.

[0274] In the embodiments of the present application, the volume average particle size Dv50 of the negative electrode active material has the meaning well known in the art and can be detected by using the equipment and methods well known in the art. The detection method is the same as the volume average particle size Dv50 test method of the positive electrode active material described above.

[0275] Optionally, the tapped density of the carbon-based material in the first negative electrode film layer is less than or equal to the tapped density of the carbon-based material in the second negative electrode film layer. The tapped density can reflect the packing density of the active material in the film layer. When the tapped density of the carbon-based material in the second negative electrode film layer is greater than that in the first negative electrode film layer, the second negative electrode film layer is packed more densely, improving the energy density of the battery cell. The first negative electrode film layer is relatively sparsely packed with richer pores, which can enhance the fast charging performance of the battery cell. When the negative electrode active material includes graphite particles, the tapped density of the graphite particles in the first negative electrode film layer is less than or equal to the tapped density of the graphite particles in the second negative electrode film layer.

[0276] Optionally, the tapped density of the carbon-based material in the first negative electrode film layer is 0.82 g / cm 3 to 1.21 g / cm 3 , such as 0.82 g / cm 3 , 0.85 g / cm 3 , 0.88 g / cm 3 , 0.90 g / cm 3 , 0.92 g / cm 3 , 0.95 g / cm 3 , 0.98 g / cm 3 , 1.00 g / cm 3 , 1.05 g / cm 3 , 1.08 g / cm 3 , 1.10 g / cm 3 , 1.12 g / cm 3 , 1.15 g / cm 3 , 1.18 g / cm 3 , 1.20 g / cm 3 , 1.21 g / cm 3 or the range composed of any two of the above values. When the tapped density of the carbon-based material in the first negative electrode film layer is within a suitable range, the fast charging performance of the battery cell can be improved.

[0277] Optionally, the tapped density of the carbon-based material in the second negative electrode film layer is 0.90 g / cm 3 to 1.25 g / cm 3 , such as 0.90 g / cm 3 , 0.92 g / cm 3, 0.95 g / cm 3 , 0.98 g / cm 3 , 1.00 g / cm 3 , 1.05 g / cm 3 , 1.08 g / cm 3 , 1.10 g / cm 3 , 1.12 g / cm 3 , 1.15 g / cm 3 , 1.18 g / cm 3 , 1.20 g / cm 3 , 1.21 g / cm 3 , 1.22 g / cm 3 , 1.23 g / cm 3 , 1.24 g / cm 3 , 1.25 g / cm 3 or a range composed of any two of the above values. When the tap density of the carbon-based material in the second negative electrode film layer is within a suitable range, the energy density of the battery cell can be improved.

[0278] In the embodiments of the present application, the tap density of the material has the meaning well known in the art and can be measured by instruments and methods known in the art. For example, reference can be made to GB / T5162-2006, and a powder tap density tester can be used for measurement. The test instrument can be BT-301 produced by Dandong BETTER.

[0279] Optionally, the ratio of the thickness of the second negative electrode film layer to the thickness of the first negative electrode film layer is 3:7 to 7:3, and can be optionally 4:6 to 6:4. Exemplarily, the ratio of the thickness of the second negative electrode film layer to the thickness of the first negative electrode film layer is 3:7, 4:6, 5:5, 6:4, 7:3 or a range composed of any two of the above values. By adjusting the thickness ratio of the first negative electrode film layer and the second negative electrode film layer, the gradient pore difference between the upper and lower layers can be further increased, the tortuosity of lithium ion transport can be reduced, and the fast charging ability of the battery cell can be improved.

[0280] In some embodiments, after the battery cell undergoes 10 full charge test cycles at the beginning of life (BOL), the thickness of the first negative electrode film layer is 15 μm to 65 μm, such as 15 μm, 17 μm, 18 μm, 20 μm, 25 μm, 30 μm, 35 μm, 40 μm, 45 μm, 50 μm, 55 μm, 57 μm, 58 μm, 60 μm, 61 μm, 62 μm, 63 μm, 64 μm, 65 μm or a range composed of any two of the above values. When the thickness of the first negative electrode film layer is within the above range, the gradient pore difference between the first negative electrode film layer and the second negative electrode film layer can be increased, the tortuosity of lithium ion transport can be reduced, and the fast charging ability of the battery cell can be improved.

[0281] In some embodiments, after the battery cell undergoes 10 full charge test cycles at the beginning of life (BOL), the thickness of the second negative electrode film layer is 15 μm to 65 μm, such as 15 μm, 17 μm, 18 μm, 20 μm, 25 μm, 30 μm, 35 μm, 40 μm, 45 μm, 50 μm, 55 μm, 57 μm, 58 μm, 60 μm, 61 μm, 62 μm, 63 μm, 64 μm, 65 μm, or a range composed of any two of the above values. When the thickness of the second negative electrode film layer is within the above range, the gradient pore difference between the first negative electrode film layer and the second negative electrode film layer can be regulated and increased, the tortuosity of lithium ion transport can be reduced, and the fast charging ability of the battery cell can be improved.

[0282] In the embodiments of the present application, for example, taking the upper limit voltage of battery charging as 3.65 V and the cut-off voltage of battery discharging as 2.0 V as an example for illustration, The specific steps of the BOL full charge test are as follows: At 25 °C, charge at a charging rate of 0.33 C of the nominal capacity of the battery to 3.65 V, then charge at a constant voltage of 3.65 V to 0.05 C, stand for 10 min, then discharge at a discharging rate of 0.33 C to 2.0 V, stand for 10 min. The above one charge and discharge is one cycle, and cycle 10 times. Then charge at a charging rate of 0.33 C of the nominal capacity to 3.65 V, and then charge at a constant voltage of 3.65 V to 0.05 C to obtain the BOL full charge state. In the BOL full charge state, disassemble the negative electrode plate, use a tomography scanning electron microscope to observe the cross-section in the thickness direction of the middle area of the negative electrode plate, distinguish the two regions according to the interface between the first negative electrode film layer and the second negative electrode film layer, and measure the thicknesses of the two respectively. For example, measure the thicknesses of 10 positions of the first negative electrode film layer, calculate their average value as the average value of the first negative electrode film layer, measure the thicknesses of 10 positions of the second negative electrode film layer, and calculate their average value as the average value of the second negative electrode film layer.

[0283] In some embodiments, after the full charge test at the end of life (EOL) of the battery cell, the thickness of the first negative electrode film layer is 15 μm to 70 μm, such as 15 μm, 16 μm, 17 μm, 18 μm, 19 μm, 20 μm, 21 μm, 22 μm, 23 μm, 24 μm, 25 μm, 26 μm, 27 μm, 28 μm, 29 μm, 30 μm, 35 μm, 40 μm, 43 μm, 45 μm, 50 μm, 55 μm, 60 μm, 65 μm, 66 μm, 67 μm, 68 μm, 69 μm, 70 μm or a range composed of any two of the above values. When the thickness of the first negative electrode film layer is within the above range, the first negative electrode film layer and the second negative electrode film layer can regulate and increase the gradient pore difference between the upper and lower layers, reduce the tortuosity of lithium ion transport, and improve the fast charging ability of the battery cell.

[0284] In some embodiments, after the full charge test at the end of life (EOL) of the battery cell, the thickness of the second negative electrode film layer is 15 μm to 70 μm, such as 15 μm, 16 μm, 17 μm, 18 μm, 19 μm, 20 μm, 21 μm, 22 μm, 23 μm, 24 μm, 25 μm, 26 μm, 27 μm, 28 μm, 29 μm, 30 μm, 35 μm, 40 μm, 43 μm, 45 μm, 50 μm, 55 μm, 60 μm, 65 μm, 66 μm, 67 μm, 68 μm, 69 μm, 70 μm or a range composed of any two of the above values. When the thickness of the second negative electrode film layer is within the above range, the first negative electrode film layer and the second negative electrode film layer can regulate and increase the gradient pore difference between the upper and lower layers, reduce the tortuosity of lithium ion transport, and improve the fast charging ability of the battery cell.

[0285] In the embodiments of the present application, for example, taking the upper limit voltage of battery charging as 3.65 V and the cut-off voltage of battery discharging as 2.0 V as an example for illustration, The specific steps for the EOL full charge test are as follows: At 60 °C, charge at a charging rate of 0.33C of the battery's nominal capacity until 3.65V, then perform constant voltage charging at 3.65V until 0.05C, let it stand for 10 minutes, then discharge at a discharge rate of 0.33C until 2.0V, and let it stand for 10 minutes. One cycle of the above charge and discharge is considered one cycle, and the test stops until the battery capacity decays to 80% of the nominal capacity. Then, at 25 °C, charge at a constant current of 0.33C until 3.65V, and perform constant voltage charging at a rate of 0.05C until 3.65V, which is the EOL full charge state. In the EOL full charge state, disassemble the negative electrode plate, use a tomography scanning electron microscope to observe the cross-section in the thickness direction of the middle area of the negative electrode plate, distinguish the regions of the first negative electrode film layer and the second negative electrode film layer according to the interface between them, and measure their thicknesses respectively. For example, measure the thicknesses of 10 positions of the first negative electrode film layer, calculate their average value as the average value of the first negative electrode film layer, measure the thicknesses of 10 positions of the second negative electrode film layer, and calculate their average value as the average value of the second negative electrode film layer.

[0286] In some embodiments, when the negative electrode film layer adopts a single-layer film layer (different from the above double-layer film layer), the negative electrode film layer further includes a lithium-containing binder. Optionally, the mass content of the lithium-containing binder relative to the mass of the negative electrode film layer is 0.1% to 1%. Exemplarily, the mass content of the lithium-containing binder relative to the mass of the negative electrode film layer is 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1% or a range composed of any two of the above values. The lithium element in the lithium-containing binder can exist in an ionic form, which can increase the number of free-moving lithium ions in the negative electrode film layer, shorten the distance for lithium ions to diffuse to the surface of the negative electrode film layer, increase the insertion and extraction rate of lithium ions, and improve the fast charging performance of the battery cell. Optionally, the negative electrode film layer can further include a negative electrode binder. For example, the negative electrode binder includes at least one of styrene-butadiene rubber (SBR), water-soluble unsaturated resin SR-1B, water-based acrylic resin (e.g., polyacrylic acid PAA, polymethacrylic acid PMAA, sodium polyacrylate PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), and carboxymethyl chitosan (CMCS).

[0287] Optionally, the mass content of lithium element in the lithium-containing binder is 3% to 10%. Exemplarily, the mass content of lithium element in the lithium-containing binder is 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10% or a range composed of any two of the above values. The mass content of lithium element is calculated based on the mass of the lithium-containing binder. When the mass content of lithium element is within the above range, it can make the number of free-moving lithium ions in the negative electrode film layer relatively large, further shorten the distance for lithium ions to diffuse to the surface of the negative electrode film layer, increase the insertion and extraction rate of lithium ions, and improve the fast charging performance of the battery cell.

[0288] Exemplarily, the lithium-containing binder includes a lithium acrylate-acrylonitrile-acrylamide-2-hydroxyethyl acrylate copolymer, which is derived from a lithium acrylate monomer, an acrylonitrile monomer, an acrylamide monomer, and a 2-hydroxyethyl acrylate monomer. The molar ratio of the lithium acrylate monomer, the acrylonitrile monomer, the acrylamide monomer, and the 2-hydroxyethyl acrylate monomer is 30% to 50%: 15% to 45%: 5% to 20%: 20% to 35%. For example, the molar ratio of the lithium acrylate monomer, the acrylonitrile monomer, the acrylamide monomer, and the 2-hydroxyethyl acrylate monomer is 35%: 30%: 15%: 20%, or 40%, 20%, 10%, 30%, or 45%, 15%, 20%, 20%, etc.

[0289] The lithium-containing binder of the above materials can provide a certain number of lithium ions for the negative electrode film layer, improve the fast charging performance of the battery cell, and is not prone to swelling during the charge and discharge process, with a stable structure, so that the cycle performance of the negative electrode film layer is improved during the fast charge and discharge process.

[0290] In some other embodiments, when the negative electrode film layer adopts at least two layers of film layers, the negative electrode film layer further includes a lithium-containing binder.

[0291] Optionally, the first negative electrode film layer further includes a first lithium-containing binder, and the second negative electrode film layer further includes a second lithium-containing binder. The mass content of the first lithium-containing binder relative to the mass of the first negative electrode film layer is less than or equal to the mass content of the second lithium-containing binder relative to the mass of the second negative electrode film layer. Further optionally, the mass content of the first lithium-containing binder relative to the mass of the first negative electrode film layer is less than the mass content of the second lithium-containing binder relative to the mass of the second negative electrode film layer.

[0292] The mass content of the second lithium-containing binder in the second negative electrode film layer is relatively high, and the number of freely movable lithium ions provided by the second lithium-containing binder for the second negative electrode film layer is relatively more, which can further improve the fast charging performance of the battery cell.

[0293] Optionally, the mass content of the first lithium-containing binder relative to the mass of the first negative electrode film layer is 0.1% to 1%. Exemplarily, the mass content of the first lithium-containing binder relative to the mass of the first negative electrode film layer is 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1% or a range composed of any two of the above values. The lithium element in the first lithium-containing binder can exist in an ionic form, which can increase the number of freely movable lithium ions in the negative electrode film layer, shorten the distance for lithium ions to diffuse to the surface of the negative electrode film layer, increase the deintercalation rate of lithium ions, and improve the fast charging performance of the battery cell.

[0294] Optionally, the mass content of lithium element in the first lithium-containing binder is 3% to 10%, and can be optionally 3% to 8%. Exemplarily, the mass content of lithium element in the first lithium-containing binder is 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10% or the range composed of any two of the above values. When the mass content of lithium element is within the above range, the number of free-moving lithium ions in the negative electrode film layer can be relatively large, which can further shorten the distance for lithium ions to diffuse to the surface of the negative electrode film layer, improve the insertion / extraction rate of lithium ions, and improve the fast charging performance of the battery cell.

[0295] Exemplarily, the first lithium-containing binder includes a lithium acrylate-acrylonitrile-acrylamide-2-hydroxyethyl acrylate copolymer, and the lithium acrylate-acrylonitrile-acrylamide-2-hydroxyethyl acrylate copolymer is derived from a lithium acrylate monomer, an acrylonitrile monomer, an acrylamide monomer and a 2-hydroxyethyl acrylate monomer, and the molar ratio of the lithium acrylate monomer, the acrylonitrile monomer, the acrylamide monomer and the 2-hydroxyethyl acrylate monomer is 30% to 50%: 15% to 45%: 5% to 20%: 20% to 35%. For example, the molar ratio of the lithium acrylate monomer, the acrylonitrile monomer, the acrylamide monomer and the 2-hydroxyethyl acrylate monomer is 35%: 30%: 15%: 20%, or 40%, 20%, 10%, 30%, or 45%, 15%, 20%, 20%, etc.

[0296] The lithium-containing binder of the above material can provide a certain number of lithium ions for the negative electrode film layer, improve the fast charging performance of the battery cell, and is not prone to swelling during charge and discharge, with a stable structure, so that the cycle performance of the negative electrode film layer is improved during fast charge and discharge.

[0297] Optionally, the mass content of the second lithium-containing binder relative to the mass of the second negative electrode film layer is 0.1% to 1%. Exemplarily, the mass content of the second lithium-containing binder relative to the mass of the second negative electrode film layer is 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1% or the range composed of any two of the above values. The lithium element in the second lithium-containing binder can exist in the form of ions, which can increase the number of free-moving lithium ions in the negative electrode film layer, shorten the distance for lithium ions to diffuse to the surface of the negative electrode film layer, improve the insertion / extraction rate of lithium ions, and improve the fast charging performance of the battery cell.

[0298] The first lithium-containing binder and the second lithium-containing binder can be made of the same material or different materials.

[0299] Optionally, the mass content of lithium element in the second lithium-containing binder is 3% to 10%, and can be optionally 3% to 8%. Exemplarily, the mass content of lithium element in the second lithium-containing binder is 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10% or the range composed of any two of the above values. When the mass content of lithium element is within the above range, the number of free-moving lithium ions in the negative electrode film layer can be relatively large, which can further shorten the distance for lithium ions to diffuse to the surface of the negative electrode film layer, improve the intercalation and deintercalation rate of lithium ions, and improve the fast charging performance of the battery cell.

[0300] Exemplarily, the second lithium-containing binder includes a lithium acrylate-acrylonitrile-acrylamide-2-hydroxyethyl acrylate copolymer, and the lithium acrylate-acrylonitrile-acrylamide-2-hydroxyethyl acrylate copolymer is derived from a lithium acrylate monomer, an acrylonitrile monomer, an acrylamide monomer, and a 2-hydroxyethyl acrylate monomer. The molar ratio of the lithium acrylate monomer, the acrylonitrile monomer, the acrylamide monomer, and the 2-hydroxyethyl acrylate monomer is 30% to 50%: 15% to 45%: 5% to 20%: 20% to 35%. For example, the molar ratio of the lithium acrylate monomer, the acrylonitrile monomer, the acrylamide monomer, and the 2-hydroxyethyl acrylate monomer is 35%: 30%: 15%: 20%, or 40%, 20%, 10%, 30%, or 45%, 15%, 20%, 20%, etc.

[0301] The lithium-containing binder of the above material can provide a certain number of lithium ions for the negative electrode film layer, improve the fast charging performance of the battery cell, and is not prone to swelling during the charge and discharge process, with a stable structure, so that the cycle performance of the negative electrode film layer is improved during the fast charge and discharge process.

[0302] 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, water-based acrylic resin (for example, polyacrylic acid PAA, polymethacrylic acid PMAA, sodium polyacrylate PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), and carboxymethyl chitosan (CMCS).

[0303] 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.

[0304] In some embodiments, the negative electrode film layer may optionally further include a negative electrode conductive agent. There is no particular limitation on the type of the negative electrode conductive agent in the embodiments of the present application. As an example, the negative electrode conductive agent may include at least one of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. In some embodiments, based on the total weight of the negative electrode film layer, the mass content of the negative electrode conductive agent is ≤5%.

[0305] In some embodiments, the negative electrode film layer may optionally further include a negative electrode binder. In some embodiments, based on the total weight of the negative electrode film layer, the mass content of the negative electrode binder is ≤5%.

[0306] In some embodiments, the negative electrode film layer may optionally further include other additives. As an example, the other additives may include a thickener, a dispersant, etc., for example, sodium carboxymethyl cellulose (CMC-Na), PTC thermistor materials, etc. In some embodiments, based on the total weight of the negative electrode film layer, the mass content of the other additives is ≤2%.

[0307] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. As an example of the metal foil, at least one foil of copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy may be used. The composite current collector may include a polymer material base layer and a metal material layer formed on at least one surface of the polymer material base layer. As an example, the metal material in the metal material layer may include at least one of copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy. As an example, the polymer material base layer may include at least one of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0308] In some embodiments, the thickness of the negative electrode current collector is 4 μm to 10 μm, and may be optionally 4 μm to 6 μm. Exemplarily, the thickness of the negative electrode current collector is 4 μm, 4.5 μm, 5 μm, 5.5 μm, 6 μm, 10 μm, or a range composed of any two of the above values.

[0309] When the thickness of the negative electrode current collector is within the above range, the current-carrying capacity of the negative electrode current collector is relatively excellent, and the battery cell can have a high energy density.

[0310] In the embodiments of the present application, the thickness of the negative electrode current collector has the meaning well known in the art, and can be detected by using the equipment and methods well known in the art. For example, the film layer on the surface of the negative electrode current collector is washed off with a solvent, and the thickness of the negative electrode current collector is measured with a micrometer.

[0311] The negative electrode film layer is usually formed by coating a negative electrode paste on a negative electrode current collector and then drying and cold pressing. The negative electrode paste is usually formed by dispersing negative electrode active materials, optional conductive agents, optional binders, and other optional additives in a solvent and stirring evenly. The solvent can be N-methylpyrrolidone (NMP) or deionized water, but is not limited thereto.

[0312] The negative electrode sheet does not exclude other additional functional layers other than the negative electrode film layer. For example, in some embodiments, the negative electrode sheet of the embodiment of the present application further includes a negative electrode conductive layer disposed on the surface of the negative electrode current collector and sandwiched between the negative electrode current collector and the negative electrode film layer. In some other embodiments, the negative electrode sheet of the embodiment of the present application further includes a protective layer covering the surface of the negative electrode film layer.

[0313] In some embodiments, the negative electrode sheet further includes a negative electrode conductive layer, and the negative electrode conductive layer is located between the negative electrode film layer and the negative electrode current collector. 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.

[0314] In some embodiments, the thickness of the negative electrode conductive layer is 0.5 μm to 2 μm. Exemplarily, the thickness of the negative electrode conductive layer can be 0.5 μm, 0.8 μm, 1 μm, 1.2 μm, 1.5 μm, 1.6 μm, 1.8 μm, 2 μm or a range composed of any two of the above values.

[0315] When the thickness of the negative electrode conductive layer is within the above range, it can further improve the conductivity of the negative electrode sheet, reduce the heat generation of the negative electrode sheet, thereby reducing the heat generation of the battery cell, and can also take into account the improvement of the energy density of the battery cell.

[0316] In the embodiment of the present application, the thickness of the negative electrode conductive layer has the meaning well known in the art, and can be detected by equipment and methods well known in the art, and the test method of the negative electrode conductive layer in the foregoing can be adopted.

[0317] In some embodiments, the negative electrode conductive layer includes one or more of a negative electrode conductive agent and a negative electrode binder. The negative electrode conductive agent in the negative electrode conductive layer can improve the conductivity of the negative electrode conductive layer, thereby improving the conductivity of the negative electrode sheet and reducing the heat generation of the battery cell. The negative electrode binder in the negative electrode conductive layer can improve the bonding performance between the negative electrode current collector and the negative electrode film layer and improve the structural stability of the negative electrode sheet.

[0318] In some embodiments, the negative electrode conductive layer may further optionally include other additives. As an example, the other additives may include thickeners, such as sodium carboxymethyl cellulose (CMC), PTC thermistor materials, etc.

[0319] Optionally, the mass content of the negative electrode conductive agent in the negative electrode conductive layer is 20% to 40%. Exemplarily, the mass content of the negative electrode conductive agent is 20%, 25%, 30%, 35%, 40% or a range composed of any two of the above values.

[0320] Exemplarily, the negative electrode conductive agent includes one or more of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0321] Optionally, the mass content of the negative electrode binder in the negative electrode conductive layer is 60% to 80%. Exemplarily, 60%, 65%, 70%, 75%, 80% or a range composed of any two of the above values.

[0322] Exemplarily, the negative electrode binder includes one or more of styrene-butadiene rubber SBR, water-soluble unsaturated resin SR-1B, water-based acrylic resin, polyvinyl alcohol, sodium alginate, and carboxymethyl chitosan.

[0323] In some embodiments, the ratio CB of the capacity of the negative electrode film layer per unit area to the capacity of the positive electrode film layer per unit area in the battery cell is 1.05 to 1.30, and can be optionally 1.07 to 1.15. Exemplarily, the ratio CB of the capacity of the negative electrode film layer per unit area to the capacity of the positive electrode film layer per unit area in the battery cell is 1.05, 1.07, 1.1, 1.12, 1.15, 1.18, 1.2, 1.22, 1.25, 1.28, 1.3 or a range composed of any two of the above values.

[0324] When the ratio CB of the capacity of the negative electrode film layer per unit area to the capacity of the positive electrode film layer per unit area in the battery cell is within the above range, there are sufficient sites in the negative electrode film layer for lithium intercalation, which can reduce the risk of lithium deposition and is beneficial for fast charging.

[0325] In the embodiments of the present application, the meaning of the CB value is well-known in the art, and it can be detected by using well-known equipment and methods in the art. For example, the capacity of the negative electrode film layer per unit area and the capacity of the positive electrode film layer per unit area are calculated respectively, and then the ratio of the two is calculated to obtain the CB value.

[0326] Specifically, taking the battery charging upper limit voltage of 3.65V and the battery discharge cut-off voltage of 2.0V as an example for illustration, The capacity of the positive electrode film layer per unit area refers to the actual de-lithiation capacity of the positive electrode active material. The test method is as follows: Disassemble the battery in a PRS340 / 11-119-11 Braun glove box, take the positive electrode plate, assemble it into a CR2430 type half-button battery of positive electrode-lithium sheet, and the area of the positive electrode plate used is amm 2 where the electrolyte is 1mol / L LiPF 6In a solution with EC / EMC / DEC = 3 / 5 / 2 (mass ratio), then the assembled half-button battery is left standing for 3 h, the test is carried out at 25 °C, first charge (Charge) to remove lithium in the voltage range of 2.0 V to 3.65 V at 0.1C, and then discharge (Discharge) to insert lithium to 2.0 V at 0.05C, cycle 2 times, and record the discharge capacity of the second cycle as Y mAh. The actual length of the positive electrode plate of the battery design is b mm, the width is c mm, and the number of sides d of the positive active material coated on the positive current collector part, then the capacity of the positive electrode film layer per unit area = Y / a * b * c * d.

[0327] Specifically, the capacity of the negative electrode film layer per unit area refers to the actual lithium-inserting capacity of the negative active material. The test method is as follows: disassemble the battery in a PRS340 / 11-119-11 Braun glove box, take the negative electrode plate, and assemble it into a CR2430 type half-button battery of negative electrode-lithium sheet. The area of the negative electrode plate used is f mm 2 , where the electrolyte uses 1 mol / L LiPF 6 In a solution with EC / EMC / DEC = 3 / 5 / 2 (mass ratio), then the assembled half-button battery is left standing for 3 h, the test is carried out at 25 °C, first discharge (Discharge) to insert lithium in the voltage range of 2 V - 0 V at 0.1C, and then charge (Discharge) to remove lithium to 2 V at 0.05C, cycle 2 times, and record the discharge capacity of the second cycle as Z mAh. The actual length of the negative electrode plate of the battery design is h mm, the width is i mm, and the number of sides d of the negative active material coated on the negative current collector part, then the lithium-inserting capacity of the negative electrode = Z / f * h * i * d.

[0328] [Separator membrane] In the embodiments of the present application, the separator membrane includes a base membrane with a porous structure.

[0329] In some embodiments, the base membrane includes at least one of glass fiber, non-woven fabric, and polyolefin. The base membrane can be a single-layer film or a multi-layer composite film, without particular limitation. When the base membrane is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0330] Optionally, the polyolefin includes at least one of polyethylene, polypropylene, and polyvinylidene fluoride.

[0331] In some embodiments, the porosity of the base membrane is 20% to 70%, and can be optionally 35% to 60%. Exemplarily, the porosity of the base membrane is 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70% or a range composed of any two of the above values.

[0332] When the porosity of the base film in the embodiments of the present application is within the above range, the migration ability of lithium ions in the separator can be improved, the internal resistance of the battery cell can be further reduced, and thus heat generation can be reduced.

[0333] In the embodiments of the present application, the porosity refers to the percentage of the internal pore volume in the separator occupying the total volume of the separator. The porosity can be tested in accordance with the standard GB / T36363-2018 "Polyolefin Separator for Battery Cells". It should be noted that in the actual testing process, the testing process slightly different from the standard can be adopted according to the differences in testing instruments, testing errors, and in order to eliminate the influence on the porosity test as much as possible, so as to obtain a more accurate test value.

[0334] In some embodiments, the thickness of the base film is 6μm to 12μm, and can be optionally 6μm to 9μm. Exemplarily, the thickness of the base film is 6μm, 6.5μm, 7μm, 7.5μm, 8μm, 8.5μm, 9μm, 9.5μm, 10μm, 10.5μm, 11μm, 11.5μm, 12μm or the range composed of any two of the above values.

[0335] When the thickness of the base film is within the above range, the migration path of lithium ions in the base film is shorter, the internal resistance of the battery cell can be further reduced, and thus heat generation can be reduced.

[0336] In the embodiments of the present application, the separator can be a base film. Optionally, the separator further includes a functional layer provided on at least one side of the base film. The functional layer can include inorganic particles to improve the heat resistance of the separator. Optionally, the functional layer is provided on both sides of the base film.

[0337] In some embodiments, the functional layer includes a first functional layer and a second functional layer. The first functional layer is located on one side of the base film and includes first inorganic particles. The second functional layer is located on the other side of the base film and includes composite particles. The composite particles include second inorganic particles and a plurality of non-fluoropolymer particles, and the second inorganic particles are attached to the surface of the non-fluoropolymer particles and / or dispersed inside the non-fluoropolymer particles.

[0338] The first functional layer and the second functional layer have good heat resistance, and can improve the heat resistance of the separator.

[0339] Optionally, the first functional layer can include a binder, and can optionally include at least one of a fluorine-containing binder or a polyacrylic acid binder, such as polyvinylidene fluoride.

[0340] Optionally, the first inorganic particles include one or more of silicon oxide, aluminum oxide, boehmite, barium sulfate, calcium oxide, titanium oxide, zinc oxide, magnesium oxide, zirconium oxide, and tin oxide. The above first inorganic particles can improve the heat resistance of the first functional layer.

[0341] In the embodiments of the present application, the meaning of the thickness of the base film is the meaning well-known in the art, and the meaning well-known in the art and equipment can be used for detection. For example, a newly prepared separator film can be taken as a sample, or a battery cell that has been discharged (discharged to the lower cut-off voltage so that the charged state of the battery is about 0% SOC) can be disassembled in reverse, the separator film is obtained from the battery cell, and the separator film is dried and used as a sample. The separator film is cut off with an ion beam cutter to form a cross-section. Subsequently, a scanning electron microscope is used to measure the thickness of the cross-section of the separator film and its respective layers.

[0342] The non-fluoropolymer particles in the second functional layer refer to polymers that are non-fluorinated polymers. For example, the non-fluoropolymer particles include acrylate copolymers. Optionally, the acrylate copolymers include acrylate-acrylonitrile-acrylamide-acrylonitrile copolymers. The acrylate copolymers have excellent adhesion properties and relatively high adhesion stability with the base film. The molar ratio of each monomer in the copolymer can be any ratio, such as a molar ratio of 35%:30%:15%:20%, or 40%, 20%, 10%, 30%, or 45%, 15%, 20%, 20%, etc.

[0343] The second inorganic particles in the composite particles prevent the non-fluoropolymer particles from adhering to each other easily due to the high-temperature treatment during the granulation process, resulting in pores in the composite particles, which is beneficial to the transmission of lithium ions and improves the ion-conducting ability of the separator film. Moreover, the second inorganic particles can also increase the compression modulus of the composite particles. During the charge and discharge process, the composite particles are not easily deformed, making the structure of the separator film more stable, which can improve the kinetic performance of the battery cell and the fast charging performance. Optionally, compared with the first functional layer, the second functional layer is disposed closer to the negative electrode tab. Since the composite particles are not easily deformed, the separator film basically does not cause side effects such as extrusion to the negative electrode tab, making the kinetic performance of the negative electrode tab stable. Correspondingly, the first functional layer is disposed closer to the positive electrode tab.

[0344] Optionally, the second inorganic particles include one or more of silicon oxide, aluminum oxide, boehmite, barium sulfate, calcium oxide, titanium oxide, zinc oxide, magnesium oxide, zirconium oxide, and tin oxide. Optionally, the second inorganic particles include silicon oxide. The above-mentioned second inorganic particles can improve the heat resistance of the second functional layer and can cooperate with the non-fluoropolymer to form composite particles, further improving the cycle stability and kinetic performance of the separator film, and improving the cycle performance and fast charging performance of the battery cell.

[0345] The average particle size of the second inorganic particles is from 5 nm to 100 nm, optionally from 10 nm to 100 nm, and optionally from 5 nm to 20 nm. Exemplarily, the average particle size of the second inorganic particles is 5 nm, 10 nm, 15 nm, 20 nm, 25 nm, 30 nm, 35 nm, 40 nm, 45 nm, 50 nm, 55 nm, 60 nm, 65 nm, 70 nm, 75 nm, 80 nm, 85 nm, 90 nm, 95 nm, 100 nm or a range composed of any two of the above values. When the average particle size of the second inorganic particles is within the above range, it is beneficial to improve the heat resistance and compression modulus of the composite particles.

[0346] In the embodiments of the present application, the average particle size of the second inorganic particles has the meaning well-known in the art and can be detected by using the equipment and methods well-known in the art. For example, after obtaining the separator and drying the separator as a sample, the separator is cut by an ion beam cutter to form a cross-section. Subsequently, a scanning electron microscope is used to measure the particle size of the second inorganic particles in the separator, and the particle sizes of, for example, 50 second inorganic particles are measured, and the average value thereof is calculated as the average particle size of the second inorganic particles.

[0347] In some embodiments, the ionic conductivity of the separator is from 0.3 mS / cm to 0.6 mS / cm. Exemplarily, the ionic conductivity of the separator is 0.3 mS / cm, 0.35 mS / cm, 0.4 mS / cm, 0.45 mS / cm, 0.5 mS / cm, 0.55 mS / cm, 0.6 mS / cm or a range composed of any two of the above values.

[0348] When the ionic conductivity of the separator is within the above range, the migration ability of lithium ions in the separator can be further improved, and the fast charging performance of the battery cell can be improved.

[0349] In the embodiments of the present application, the ionic conductivity of the separator has the meaning well-known in the art and can be detected by using the equipment and methods well-known in the art. For example, Prepare a 2025-type button battery for testing: In a vacuum glove box, place a lithium sheet in the negative electrode case of the battery, add 150 μL of electrolyte thereto, and the electrolyte is a solution in EC / EMC / DEC = 3 / 5 / 2 (mass ratio), and then place the separator (with an area of 3.14 cm 6 and a thickness of 12 μm) to make it close to the lithium sheet, add another 25 μL of electrolyte, and finally place the positive electrode sheet (the positive electrode sheet can be the positive electrode sheet in Example 1) thereon and encapsulate. Take out the assembled button battery from the vacuum glove box and place it for 24 h for the next test. 2 Test: On an electrochemical workstation, at 10

[0350] Test: On an electrochemical workstation, at 10-1 ~10 6 It is tested in the frequency range of ~10 Hz to obtain the separator resistance Rb, and the ionic conductivity σ (unit: mS / cm) is calculated by the following formula: σ = L / (R b ×S) where: R b is the separator resistance, and L and S are the thickness and area of the separator to be measured, respectively.

[0351] [Electrolyte] In some embodiments, the battery cell further includes an electrolyte.

[0352] During the charge and discharge process of the battery cell, active ions such as lithium ions are inserted and extracted back and forth between the positive electrode plate and the negative electrode plate, and the electrolyte plays a role in conducting active ions between the positive electrode plate and the negative electrode plate.

[0353] In the embodiments of the present application, the conductivity of the electrolyte at room temperature, such as 25°C, is 10.5 mS / cm to 20 mS / cm, and can be optionally 15 mS / cm to 20 mS / cm. Exemplarily, the conductivity of the electrolyte at room temperature is 10.5 mS / cm, 11 mS / cm, 11.5 mS / cm, 12 mS / cm, 12.5 mS / cm, 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 the range composed of any two of the above values.

[0354] When the conductivity of the electrolyte at room temperature 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.

[0355] In the embodiments of the present application, the conductivity of the electrolyte at room temperature is the ionic conductivity, and it can be detected by using the equipment and methods well-known in the art, such as testing with reference to the industry standard HG-T 4067-2015.

[0356] In some embodiments, the viscosity of the electrolyte at room temperature, such as 25 °C, is from 2.3 mPa·s to 3.5 mPa·s. Exemplarily, the viscosity of the electrolyte is 2.3 mPa·s, 2.4 mPa·s, 2.5 mPa·s, 2.6 mPa·s, 2.7 mPa·s, 2.8 mPa·s, 2.9 mPa·s, 3.0 mPa·s, 3.1 mPa·s, 3.2 mPa·s, 3.3 mPa·s, 3.4 mPa·s, 3.5 mPa·s or a range composed of any two of the above values.

[0357] When the viscosity of the electrolyte is within the above range, the migration rate of lithium ions in the electrolyte is relatively high, which can further reduce the internal resistance of the battery cell, thereby reducing heat generation and improving the fast charging performance of the battery cell.

[0358] In the embodiments of the present application, the viscosity of the electrolyte has the meaning well known in the art and can be detected by devices and methods well known in the art. For example, it can be detected according to GB / T10247-2008.

[0359] In some embodiments, the density of the electrolyte at room temperature, such as 25 °C, is from 1.05 g / mL to 1.35 g / mL. Exemplarily, the density of the electrolyte is 1.05 g / mL, 1.10 g / mL, 1.15 g / mL, 1.2 g / mL, 1.25 g / mL, 1.3 g / mL, 1.35 g / mL or a range composed of any two of the above values.

[0360] When the density of the electrolyte is within the above range, the migration rate of lithium ions in the electrolyte is relatively high, which can further reduce the internal resistance of the battery cell, thereby reducing heat generation and improving the fast charging performance of the battery cell.

[0361] In the embodiments of the present application, the density of the electrolyte has the meaning well known in the art and can be detected by devices and methods well known in the art. For example, it can be tested with reference to GB / T 2013-2010.

[0362] The electrolyte includes an organic solvent and an electrolyte salt. The types of the organic solvent and the electrolyte salt are not specifically limited and can be selected according to actual needs.

[0363] In some embodiments, the organic solvent includes a chain carboxylic acid ester solvent, and the mass content of the chain carboxylic acid ester solvent relative to the mass of the organic solvent is greater than or equal to 8% and less than or equal to 75%, optionally greater than or equal to 10% and less than or equal to 75%, optionally 30% to 70%, and optionally 50% to 70%. Exemplarily, the mass content of the chain carboxylic acid ester solvent is 8%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75% or a range composed of any two of the above values.

[0364] When the mass content of the chain carboxylic acid ester solvent is within the above range, the viscosity of the electrolyte system is relatively small, which is beneficial to the migration of lithium ions.

[0365] In some embodiments, the chain carboxylic acid ester solvent includes a compound represented by Formula I, Formula I, In Formula I, R 1 includes a hydrogen atom, a halogen atom, a C1-C5 alkyl group or a C1-C5 haloalkyl group, R 2 includes a C1-C5 alkyl group or a C1-C5 haloalkyl group.

[0366] The above chain carboxylic acid ester solvent has a high conductivity, which is beneficial to improving the fast charging ability of the battery monomer.

[0367] Optionally, R 1 includes a hydrogen atom, a halogen atom, a C1-C3 alkyl group or a C1-C3 haloalkyl group. Further optionally, R 1 includes a hydrogen atom, a halogen atom, a C1-C2 alkyl group or a C1-C2 haloalkyl group.

[0368] Optionally, R 2 includes a C1-C3 alkyl group or a C1-C3 haloalkyl group. Further optionally, R 2 includes a C1-C2 alkyl group or a C1-C2 haloalkyl group.

[0369] In the above embodiments, the halogen atom includes one or more of a fluorine atom, a chlorine atom, a bromine atom and an iodine atom. Optionally, the halogen atom includes a fluorine atom.

[0370] In the above embodiments, the haloalkyl group includes one or more of a fluoroalkyl group, a chloroalkyl group, a bromoalkyl group and an iodoalkyl group. Optionally, the haloalkyl group includes a fluoroalkyl group.

[0371] Exemplarily, the chain carboxylic acid ester solvent includes one or more of the compounds represented by Formula I-1 to Formula I-8,

[0372] In some embodiments, the organic solvent further includes a carbonate solvent.

[0373] Optionally, the carbonate solvent includes one or more of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, and methyl ethyl carbonate. Further optionally, the carbonate solvent includes one or more of ethylene carbonate, dimethyl carbonate, and methyl ethyl carbonate. The above carbonate solvents and chain carboxylic acid ester solvents are used in combination to improve the conductivity of the electrolyte at room temperature, which is beneficial to the migration of lithium ions.

[0374] Further optionally, the mass content of the carbonate solvent in the organic solvent is 25% to 92%, and can be optionally 30% to 50%. Exemplarily, the mass content of the carbonate solvent in the organic solvent is 25%, 30%, 31%, 32%, 33%, 34%, 35%, 36%, 37%, 38%, 40%, 45%, 48%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 92% or a range composed of any two of the above values. The carbonate solvent with the above mass content can further improve the conductivity of the electrolyte at room temperature, which is beneficial to the migration of lithium ions.

[0375] Exemplarily, the carbonate solvent includes one or more of ethylene carbonate, dimethyl carbonate, and methyl ethyl carbonate, and the mass content of the carbonate solvent is 30% to 50%.

[0376] In some embodiments, the electrolyte further contains an additive. The additive can include a negative electrode film-forming additive, or can include a positive electrode film-forming additive, or can also include an additive that can improve certain battery performances, such as an additive for improving the overcharge performance of the battery, an additive for improving the high-temperature performance of the battery, an additive for improving the low-temperature power performance of the battery, etc.

[0377] In some embodiments, the additive includes one or more of a carbonate additive, a sulfur-containing additive, and a lithium salt additive, and can be optionally at least two. The above additives can improve the interfacial film performance on the positive electrode side and / or the negative electrode side, which is beneficial to improving the fast charging performance of the battery cell and improving the cycle performance.

[0378] In some embodiments, the mass content of the additive in the electrolyte is 1% to 10%, optionally 2% to 8%, and further optionally 3.5% to 8%. Exemplarily, the mass content of the additive in the electrolyte is 1%, 2%, 3%, 3.5%, 4%, 5%, 6%, 7%, 8%, 9%, 10% or a range composed of any two of the above values.

[0379] The additives with the above mass contents can effectively improve the interfacial film properties on the positive electrode side and / or the negative electrode side, which is beneficial to enhancing the fast charging performance of the battery cell and improving the cycle performance.

[0380] Exemplarily, the carbonate additives include one or more of vinylene carbonate (VC) and fluoroethylene carbonate (FEC).

[0381] Exemplarily, the sulfur-containing additives include one or more of ethylene sulfate (DTD), bis(ethylene sulfate) (2-DTD), butene sulfite (BS), 1,3-propane sultone (PS), ethylene sulfite (ES), and methylene methyl disulfonate (MMDS).

[0382] Optionally, the lithium salt additives include lithium difluorophosphate LiPO 2 F 2 , lithium difluorooxalate borate (LiDFOB), lithium tetrafluoroborate LiBF 4 , and one or more of lithium bis(oxalate) borate (LiBOB).

[0383] Optionally, the mass content of vinylene carbonate (VC) in the electrolyte is 0.5% to 9%, and can be optionally 2% to 6%.

[0384] Optionally, the mass content of fluoroethylene carbonate (FEC) in the electrolyte is 0.1% to 4%, and can be optionally 0.5% to 3%.

[0385] 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%.

[0386] 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%.

[0387] In some embodiments, the electrolyte salt includes a lithium salt, and the lithium salt includes one or more of fluorosulfonylimide salts and lithium hexafluorophosphate LiPF 6 . The above lithium salts are easy to dissociate, which is beneficial to the rapid migration of lithium ions, and the electrolyte system is relatively stable and not easy to decompose, which can improve the cycle performance of the battery cell.

[0388] Optionally, the fluorosulfonylimide salts include one or more of lithium bis(fluorosulfonyl)imide (LiFSI) and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI).

[0389] Optionally, the lithium salt includes lithium bis(fluorosulfonyl)imide (LiFSI) and lithium hexafluorophosphate LiPF 6 , the molar concentration of lithium bis(fluorosulfonyl)imide (LiFSI) is 0.2 mol / L to 0.5 mol / L, and lithium hexafluorophosphate LiPF6 The molar concentration is from 0.5 mol / L to 1.0 mol / L.

[0390] Exemplarily, the molar concentration of lithium bis(fluorosulfonyl)imide LiFSI is from 0.4 mol / L to 0.5 mol / L, and that of lithium hexafluorophosphate LiPF 6 is 0.7 mol / L.

[0391] Exemplarily, the molar concentration of lithium bis(fluorosulfonyl)imide LiFSI is 0.5 mol / L, and that of lithium hexafluorophosphate LiPF 6 is 0.5 mol / L.

[0392] Exemplarily, the molar concentration of lithium bis(fluorosulfonyl)imide LiFSI is 0.2 mol / L, and that of lithium hexafluorophosphate LiPF 6 is 0.8 mol / L.

[0393] Optionally, the ratio of the molar concentration of lithium bis(fluorosulfonyl)imide and the molar concentration of lithium hexafluorophosphate LiPF 6 is from 0.2 to 1.0, and can be from 0.2 to 0.5. Exemplarily, the ratio of the molar concentration of lithium bis(fluorosulfonyl)imide and the molar concentration of lithium hexafluorophosphate LiPF 6 is 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1 or a range composed of any two of the above values.

[0394] In the embodiments of the present application, the types and contents of the inorganic components / lithium salt concentration in the electrolyte have the meanings well-known in the art, and can be detected by the equipment and methods well-known in the art. For example, reference can be made to the standard JY / T 020-1996 "General Rules for Ion Chromatography Analysis Methods" to qualitatively or quantitatively analyze the inorganic components / lithium salt concentration in the electrolyte by ion chromatography analysis method. In the embodiments of the present application, newly prepared electrolyte can be taken as a sample, free electrolyte of a fresh battery can be taken as a sample, or a discharged battery (discharged to the lower cut-off voltage so that the charged state of the battery is about 0% SOC) can be disassembled in reverse, and the free electrolyte obtained from the battery can be taken as a sample, and detected by ion chromatography analysis method.

[0395] In the embodiments of the present application, the types and contents of the organic components in the electrolyte have meanings well-known in the art, and can be detected by devices and methods well-known in the art. For example, qualitative and quantitative analysis of the organic components in the electrolyte can be carried out by gas chromatography with reference to GB / T9722-2006 General Rules for Gas Chromatography of Chemical Reagents. In the embodiments of the present application, freshly prepared electrolyte can be taken as a sample, the free electrolyte of a fresh battery can be taken as a sample, or a battery that has been fully discharged (discharged to the lower cut-off voltage so that the charged state of the battery is about 0% SOC) can be disassembled in reverse, and the free electrolyte obtained from the battery can be taken as a sample, and detected by ion chromatography analysis method.

[0396] In the embodiments of the present application, after quantitatively and qualitatively detecting each component in the electrolyte, each component is classified. Chain carboxylic acid ester solvents and carbonate solvents (such as ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate) are used as the constituent components of the organic solvent. Based on the mass of the organic solvent being 100%, the mass content of each component is calculated. Carbonate additives (such as vinylene carbonate, fluoroethylene carbonate), sulfur-containing additives, and lithium salt additives are used as additives in the electrolyte. Based on the mass of the electrolyte being 100%, the mass content of each component is calculated.

[0397] In some embodiments, the battery cell satisfies: 2.45 g / Ah ≤ d / A ≤ 3.5 g / Ah, and can be optionally 2.45 g / Ah ≤ d / A ≤ 3.3 g / Ah, where d represents the mass of the electrolyte in the battery cell, in g, and A represents the rated capacity of the battery cell, in Ah. Exemplarily, d / A can be 3.5 g / Ah, 3.3 g / Ah, 3.2 g / Ah, 3.0 g / Ah, 2.8 g / Ah, 2.5 g / Ah, 2.45 g / Ah or a range composed of any two of the above values.

[0398] d / A can reflect the liquid retention ability of the electrolyte. When d / A is within the above range, the electrolyte can play a better wetting role on the positive electrode plate and the negative electrode plate, and can also improve the migration rate of lithium ions in the liquid phase, which is beneficial to improving the fast charging ability of the battery cell.

[0399] In the embodiments of the present application, d / A of the battery cell can be understood as the liquid retention coefficient, and can be detected by devices and methods well-known in the art. For example, taking the upper charge voltage of the battery as 3.65 V and the discharge cut-off voltage of the battery as 2.0 V as an example in accordance with GB / T31486-2015 Electrical Performance Requirements and Test Methods for Power Batteries for Electric Vehicles. At 25°C, the battery cell is charged at 0.33C to 3.65V, then charged at a constant voltage until 0.05C, and then discharged at a constant current of 0.33C to 2.0V. The discharged capacity A is used as the denominator. The battery cell is weighed as M0, and then the positive electrode plate, negative electrode plate, separator, and electrolyte are disassembled. The free electrolyte is stored in a bag. All the above solid components are placed in an oven at 60°C for more than 4 hours (including but not limited to the positive electrode plate, negative electrode plate, and separator, and also including other mechanical components of the disassembled battery cell that contribute to M0). Then, all the components of the battery cell are weighed as M1. The weight difference between M0 and M1 is used as the numerator. The liquid retention coefficient is equal to the value obtained by dividing the weight difference d between M0 and M1 by the capacity A.

[0400] In some embodiments, the positive electrode plate, separator, and negative electrode plate can be made into an electrode assembly through a winding process and / or a stacking process.

[0401] As Figure 15 shown, the housing 21 of the battery cell 7 can be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The housing 21 of the battery cell 7 can also be a soft package, such as a pouch soft package. The material of the soft package can be plastic, such as at least one of polypropylene (PP), polybutylene terephthalate (PBT), and polybutylene succinate (PBS).

[0402] In some embodiments, the base material of the housing 21 includes steel, which has high mechanical strength and is not easily deformed, and can improve the use reliability of the battery cell 7. In the embodiments of the present application, the base material refers to the material with the highest proportion in the housing 21.

[0403] When the housing 21 has a cuboid structure, the housing 21 includes two first shell parts 211 and two second shell parts 212. The two first shell parts 211 are arranged opposite to each other, and the two second shell parts 212 are arranged opposite to each other. The first shell part 211 is connected between the two second shell parts 212, and the area of the first shell part 211 is larger than the area of the second shell part 212.

[0404] In some embodiments, the base material of the housing 21 includes steel, which has high mechanical strength and is not easily deformed, and can improve the use reliability and cycling performance of the battery cell. In the embodiments of the present application, the base material refers to the material with the highest proportion in the housing 21.

[0405] Optionally, when the base material of the housing 21 includes steel, the thickness of the housing 21 is from 0.1 mm to 0.5 mm, and optionally from 0.2 mm to 0.35 mm. Exemplarily, the thickness of the housing 21 is 0.1 mm, 0.15 mm, 0.2 mm, 0.25 mm, 0.3 mm, 0.35 mm, 0.4 mm, 0.45 mm, 0.5 mm or a range composed of any two of the above values. When the thickness of the housing 21 is within the above range, the mechanical strength of the housing 21 is relatively high, which can improve the reliability of use of the battery cell 7; and the housing 21 occupies less space and there is more internal space in the housing 21, which is beneficial to improving the energy density of the battery cell 7.

[0406] In some embodiments, the base material of the housing 21 includes aluminum.

[0407] Optionally, when the base material of the housing includes aluminum, the thickness of the first housing portion 211 is less than or equal to the thickness of the second housing portion 212.

[0408] Exemplarily, the thickness of the first housing portion 211 is from 0.1 mm to 1.0 mm, and optionally from 0.3 mm to 0.8 mm. Exemplarily, the thickness of the first housing portion 211 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, 0.55 mm, 0.6 mm, 0.65 mm, 0.7 mm, 0.75 mm, 0.8 mm, 0.85 mm, 0.9 mm, 0.95 mm, 1.0 mm or a range composed of any two of the above values.

[0409] The relatively thin thickness of the first housing portion 211 makes the housing 21 occupy less space and can further improve the energy density of the battery cell 7.

[0410] Exemplarily, the thickness of the second housing portion 212 is from 0.1 mm to 1.0 mm, and optionally from 0.5 mm to 0.8 mm. Exemplarily, the thickness of the second housing portion 212 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, 0.55 mm, 0.6 mm, 0.65 mm, 0.7 mm, 0.75 mm, 0.8 mm, 0.85 mm, 0.9 mm, 0.95 mm, 1.0 mm or a range composed of any two of the above values.

[0411] The relatively thick thickness of the second housing portion 212 can improve the overall mechanical strength of the housing 21 and reduce the risk of deformation of the housing 21.

[0412] In some embodiments, the battery cell 7 further includes a first electrode terminal 31 and a second electrode terminal 32.

[0413] Optionally, the number of the first electrode terminals 31 on the same side of the first coating part is at least one, and can be at least two. At least two first electrode terminals 31 can increase the current-carrying capacity of the first electrode terminals 31.

[0414] Further optionally, the current-carrying area of all the first electrode terminals 31 on one side is greater than or equal to 150 mm 2 , and can be 200 mm 2 to 1000 mm 2 . The current-carrying area of all the first electrode terminals 31 on one side refers to the sum of the current-carrying areas of all the first electrode terminals 31 on the same side of the first coating part. The current-carrying area of the first electrode terminal 31 can be understood as the cross-sectional area of the first electrode terminal 31, and this cross-section is perpendicular to the thickness direction of the end cover 22.

[0415] Exemplarily, the current-carrying area of the first electrode terminals 31 on one side can be 150 mm 2 , 200 mm 2 , 210 mm 2 , 250 mm 2 , 280 mm 2 , 300 mm 2 , 320 mm 2 , 350 mm 2 , 380 mm 2 , 400 mm 2 , 450 mm 2 , 500 mm 2 , 550 mm 2 , 600 mm 2 , 650 mm 2 , 700 mm 2 , 750 mm 2 , 800 mm 2 , 850 mm 2 , 900 mm 2 , 950 mm 2 , 1000 mm 2 or the range composed of any two of the above values.

[0416] Optionally, the number of the second electrode terminals 32 on the same side of the first coating part is at least one, and can be at least two. At least two second electrode terminals 32 can increase the current-carrying capacity of the second electrode terminals 32.

[0417] Further optionally, the current-carrying area of all the second electrode terminals 32 on one side is greater than or equal to 150 mm 2 , and can be 200 mm 2 to 1000 mm 2, the overcurrent area of the second electrode terminals 32 on one side refers to the sum of the overcurrent areas of all the second electrode terminals 32 on the same side of the second coating portion. The overcurrent area of the second electrode terminals 32 can be understood as the cross-sectional area of the second electrode terminals 32, and this cross-section is perpendicular to the thickness direction of the end cover 22.

[0418] Exemplarily, the overcurrent area of the second electrode terminals 32 on one side can be 150 mm 2 , 200 mm 2 , 210 mm 2 , 250 mm 2 , 280 mm 2 , 300 mm 2 , 320 mm 2 , 350 mm 2 , 380 mm 2 , 400 mm 2 , 450 mm 2 , 500 mm 2 , 550 mm 2 , 600 mm 2 , 650 mm 2 , 700 mm 2 , 750 mm 2 , 800 mm 2 , 850 mm 2 , 900 mm 2 , 950 mm 2 , 1000 mm 2 or a range composed of any two of the above values.

[0419] As Figure 16 shown, in some embodiments of the present application, the battery cells 7 according to the implementation manner of the present application can be assembled into a battery module 6. The number of battery cells 7 included in the battery module 6 can be one or more, and the specific number can be adjusted according to the application and capacity of the battery module 6.

[0420] If there are multiple battery cells 7, the multiple battery cells 7 can be connected in series, parallel, or in a series-parallel combination. A series-parallel combination means that there are both series and parallel connections among the multiple battery cells 7. The multiple battery cells 7 can be directly connected in series, parallel, or in a series-parallel combination together, and then the whole formed by the multiple battery cells 7 is accommodated in the accommodating portion of the battery module 6; of course, it is also possible that multiple battery cells 7 are first connected in series, parallel, or in a series-parallel combination to form a battery module 6, and then multiple battery modules 6 are connected in series, parallel, or in a series-parallel combination to form a whole and are accommodated in the accommodating portion. Optionally, the battery module 6 can further include an accommodating portion having an accommodating space, and the multiple battery cells 7 are accommodated in this accommodating space.

[0421] As Figure 17As shown, in some embodiments, the above battery module 6 can also be assembled into a battery pack 2, and the number of battery modules 6 included in the battery pack 2 can be adjusted according to the application and capacity of the battery pack. The battery device herein can be either the battery module 6 or the battery pack 2.

[0422] The battery pack 2 may include a box body 5 and a plurality of battery modules 6 disposed in the box body 5. The box body 5 includes a first box body part 5a and a second box body part 5b. The box body 5 has an accommodation space 5c. The first box body part 5a is used to cover the second box body part 5b and form a closed space for accommodating the battery module 6. The plurality of battery modules 6 can be arranged in the box body 5 in any manner.

[0423] The first box body part 5a and the second box body part 5b cover each other, and the first box body part 5a and the second box body part 5b jointly define an accommodation space 5c for accommodating battery cells. The second box body part 5b can be a hollow structure with one end open, and the first box body part 5a is a plate-like structure. The first box body part 5a covers the open side of the second box body part 5b to form the box body 5 with the accommodation space 5c. Both the first box body part 5a and the second box body part 5b can also be hollow structures with one side open, and the open side of the first box body part 5a covers the open side of the second box body part 5b to form the box body 5 with the accommodation space 5c. Of course, the first box body part 5a and the second box body part 5b can be of various shapes, such as a cylinder, a cuboid, etc.

[0424] To improve the sealing performance after the connection between the first box body part 5a and the second box body part 5b, a sealing member can also be provided between the first box body part 5a and the second box body part 5b, such as sealant, sealing ring, etc.

[0425] Assuming that the first box body part 5a covers the top of the second box body part 5b, the first box body part 5a can also be called the upper box cover, and the second box body part 5b can also be called the lower box body. In some embodiments, during the charging process of the battery pack 2 or any battery cell constituting the battery pack 2 from 0% state of charge (SOC) to 100% state of charge (SOC), the temperature of the external environment where the battery pack 2 is located is room temperature, for example, 30°C.

[0426] In some embodiments, during the charging process of the battery pack 2 or any battery cell constituting the battery pack 2 from 10% state of charge (SOC) to 80% state of charge (SOC), the temperature of the external environment where the battery pack 2 is located is 30°C.

[0427] In some embodiments, during the charging process of the battery pack 2 or any battery cell constituting the battery pack 2 from a state of charge of 10% to 80%, it includes multiple charging steps. The difference between the maximum state of charge of any charging step and the maximum state of charge of its adjacent charging step in the multiple charging steps is less than or equal to 5% state of charge, such as 1% state of charge, 1.5% state of charge, 2% state of charge, 2.5% state of charge, 3% state of charge, 3.5% state of charge, 4% state of charge, 4.5% state of charge, 5% state of charge, or a range composed of any two of the above values.

[0428] The battery pack 2 or any battery cell constituting the battery pack 2 from a state of charge of 10% to 40% includes multiple charging steps. For any charging step, it can be charged at any rate between 5C and 10C. The charging rate corresponding to each charging step can be any value of 5C, 5.5C, 6C, 6.5C, 7C, 7.5C, 8C, 8.5C, 9C, 9.5C, 10C, or a value within a range composed of any two of the above values.

[0429] The battery pack 2 or any battery cell constituting the battery pack 2 from a state of charge of 40% to 80% also includes multiple charging steps. The charging rate of any charging step is less than the charging rate of any charging step from a state of charge of 10% to 40%, and the charging rate of the step of charging to 80% state of charge is any value between 2.5C and 5C. For example, it can be 2.7C.

[0430] Exemplarily, the charging steps of the battery pack 2 or any battery cell constituting the battery pack 2 from 10% to 80% can be carried out as follows: Constant current charge from 10% SOC to 15% SOC at 5.0C, Constant current charge from 15% SOC to 20% SOC at 5.0C, Constant current charge from 20% SOC to 25% SOC at 5.0C, Constant current charge from 25% SOC to 30% SOC at 5.0C, Constant current charge from 30% SOC to 35% SOC at 5.0C, Constant current charge from 35% SOC to 40% SOC at 5.0C, Constant current charge from 40% SOC to 45% SOC at 4.6C, Constant current charge from 45% SOC to 50% SOC at 4.3C, Constant current charge from 50% SOC to 55% SOC at 4.0C, Constant current charge from 55% SOC to 60% SOC at 3.7C, Charge from 60% SOC to 65% SOC at a constant current of 3.4C, Charge from 65% SOC to 70% SOC at a constant current of 3.1C, Charge from 70% SOC to 75% SOC at a constant current of 2.9C, Charge from 75% SOC to 80% SOC at a constant current of 2.7C.

[0431] In some embodiments, the charging time of the battery pack 2 or any battery cell constituting the battery pack 2 from 10% state of charge to 80% state of charge is less than or equal to 10.5 min, optionally 5 min to 10.5 min. The external environment of the battery pack 2 at 10% state of charge is room temperature, for example, the temperature is 30°C. Exemplarily, the charging time of the battery pack 2 from 10% state of charge to 80% state of charge is 10.5 min, 10 min, 9.5 min, 9 min, 8.5 min, 8 min, 7.5 min, 7 min, 6.5 min, 6 min, 5.5 min, 5 min or the range composed of any two of the above values. In some embodiments, the volumetric energy density of the battery cell is 390 Wh / L to 500 Wh / L, optionally 410 Wh / L to 470 Wh / L. Exemplarily, the volumetric energy density of the battery cell is 390 Wh / L, 400 Wh / L, 410 Wh / L, 420 Wh / L, 430 Wh / L, 440 Wh / L, 450 Wh / L, 460 Wh / L, 470 Wh / L, 480 Wh / L, 490 Wh / L, 500 Wh / L or the range composed of any two of the above values. The volumetric energy density of the battery cell is relatively high.

[0432] In the embodiments of the present application, the volumetric energy density of the battery cell has the meaning well-known in the art and can be detected by using the equipment and methods well-known in the art. For example, taking the upper charging voltage of the battery as 3.65V and the discharge cut-off voltage of the battery as 2.0V as an example for illustration, Place the battery cell at 25°C, charge it at a constant current of 0.33C to 3.65V, then charge it at a constant voltage to 0.05C, discharge it at a constant current of 0.33C to 2.0V, record the discharge capacity A0 at this time, unit: Ah, measure the length, width, and height of the battery cell using a caliper (generally calculated based on the outer shell size of the battery, excluding the height of the electrode terminals and excluding the insulating film outside the outer shell), calculate the volume V0 of the single battery cell, unit: L, and the volumetric energy density VED of the battery cell = (A0 × discharge platform voltage) / V0, unit: Wh / L.

[0433] Electrical device In the second aspect of the embodiments of the present application, an electrical device is provided. The electrical device includes the battery device of the embodiments of the present application, such as a battery cell, a battery module, or a battery pack. The battery cell, the battery module, or the battery pack can be used as the power source of the electrical device or as the energy storage unit of the electrical device. The electrical device can be a vehicle, a mobile phone, a portable device, a laptop computer, a ship, a spacecraft, an electric toy, an electric tool, etc. The vehicle can be a fuel vehicle, a gas vehicle, or a new energy vehicle. The new energy vehicle can be a pure electric vehicle, a hybrid electric vehicle, or an extended-range electric vehicle, etc. The spacecraft includes an airplane, a rocket, a space shuttle, a spaceship, etc. The electric toy includes a fixed or mobile electric toy, for example, a game console, an electric vehicle toy, an electric ship toy, an electric airplane toy, etc. The electric tool includes a metal cutting electric tool, a grinding electric tool, an assembly electric tool, and a railway electric tool, for example, an electric drill, an electric grinder, an electric wrench, an electric screwdriver, a hammer drill, an impact drill, a concrete vibrator, and a planer, etc. The embodiments of the present application do not impose special restrictions on the above electrical devices. The electrical device can select a battery cell, a battery module, or a battery pack according to its usage requirements.

[0434] Figure 18 It is a schematic diagram of an electrical device 1 as an example. The electrical device 1 is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. In order to meet the requirements of the electrical device 1 for high power and high energy density, a battery pack or a battery module can be used.

[0435] A battery pack 2 is arranged inside the electrical device 1. The battery pack 2 can be arranged at the bottom, the head, or the tail of the electrical device 1. The battery pack 2 can be used for power supply of the electrical device 1. For example, the battery pack 2 can be used as the operating power source of the electrical device 1 and can also be used as the driving power source of the electrical device 1, replacing or partially replacing fuel or natural gas to provide driving power for the electrical device 1.

[0436] The electrical device 1 may further include a controller 3 and a motor 4. The controller 3 is used to control the battery pack 2 to supply power to the motor 4. For example, it is used for the working power requirements during the start, navigation, and driving of the electrical device 1.

[0437] As another example, the electrical device can be a mobile phone, a tablet computer, a laptop computer, etc. This electrical device usually requires a thin and light design, and a battery cell can be used as the power source.

[0438] The charging process of the electrical device can select the following charging methods: Charge from 10% SOC to 15% SOC at a constant current of 5.0C, Charge from 15% SOC to 20% SOC at a constant current of 5.0C, Charge from 20% SOC to 25% SOC at a constant current of 5.0C, Charge from 25% SOC to 30% SOC at a constant current of 5.0C, Charge from 30% SOC to 35% SOC at a constant current of 5.0C, Charge from 35% SOC to 40% SOC at a constant current of 5.0C, Charge from 40% SOC to 45% SOC at a constant current of 4.6C, Charge from 45% SOC to 50% SOC at a constant current of 4.3C, Charge from 50% SOC to 55% SOC at a constant current of 4.0C, Charge from 55% SOC to 60% SOC at a constant current of 3.7C, Charge from 60% SOC to 65% SOC at a constant current of 3.4C, Charge from 65% SOC to 70% SOC at a constant current of 3.1C, Charge from 70% SOC to 75% SOC at a constant current of 2.9C, Charge from 75% SOC to 80% SOC at a constant current of 2.7C.

[0439] In some embodiments, the charging time of the electrical device from 10% state of charge to 80% state of charge is less than or equal to 10.5 min, optionally 5 min to 10.5 min. The temperature of the external environment of the battery pack 2 at 10% state of charge is room temperature, for example, the temperature is 30°C. Exemplarily, the charging time of the battery pack 2 from 10% state of charge to 80% state of charge is 10.5 min, 10 min, 9.5 min, 9 min, 8.5 min, 8 min, 7.5 min, 7 min, 6.5 min, 6 min, 5.5 min, 5 min or the range composed of any two of the above values.

[0440] Embodiment The following examples more specifically describe the content disclosed in the embodiments of the present application. These examples are only for illustrative purposes, because various modifications and changes within the scope of the content disclosed in the embodiments of the present application are obvious to those skilled in the art. Unless otherwise stated, all parts, percentages, and ratios reported in the following examples are based on mass, and all reagents used in the examples are commercially available or synthesized according to conventional methods and can be used directly without further treatment, and all instruments used in the examples are commercially available.

[0441] Example 1 1. Preparation of the positive electrode plate The positive electrode plate includes a positive current collector part, a positive conductive layer on the positive current collector part, and a positive electrode film layer. The positive current collector part is an aluminum foil, and the thickness of the aluminum foil is the same as that of the positive electrode tab. The positive conductive layer on the positive current collector part is a film layer formed by uniformly coating a mixture of a positive conductive agent, superconducting carbon, a positive binder, polyvinylidene fluoride (PVDF), and a solvent, N-methylpyrrolidone (NMP), on the surface of the current collector part. The thickness is 1 μm. The mass content of the positive conductive agent in the positive conductive layer is 40%, and the mass content of the positive binder is 60%.

[0442] The positive electrode film layer includes a film layer formed by uniformly coating a positive electrode slurry (with a solvent of N-methylpyrrolidone NMP) on the surface of the positive conductive layer and then drying and cold pressing. The positive electrode film layer includes a positive active material, a binder polyvinylidene fluoride (PVDF), and a conductive agent acetylene black in a weight ratio of 97:2:1.

[0443] The positive active material includes lithium iron phosphate and a coating layer. The coating layer coats the surface of the lithium iron phosphate. The coating layer includes lithium iron titanium phosphate Li2FeTi(PO4)3 and amorphous carbon. The Dv50 of the positive active material is 1.6 μm, and the Dv10 is 0.64 μm.

[0444] The single-sided coating weight of the positive electrode film layer is 290 mg / 1540.25 mm 2 。

[0445] 2. Preparation of the negative electrode plate The negative electrode plate includes a negative current collector part, a negative conductive layer on the negative current collector part, and a negative electrode film layer. The negative current collector part is a copper foil, and the thickness of the copper foil is the same as that of the negative electrode tab. The negative conductive layer on the negative current collector part is a film layer formed by uniformly coating a mixture of a negative conductive agent, superconducting carbon, a negative binder, styrene-butadiene rubber (SBR), a thickener, sodium carboxymethyl cellulose (CMC-Na), and a solvent, water, on the surface of the negative current collector part. The thickness is 1 μm; the mass content of the negative conductive agent in the negative conductive layer is 35%, the mass content of the negative binder in the negative conductive layer is 60%, and the mass content of the thickener in the negative conductive layer is 5%; The negative electrode film layer includes a film layer formed by uniformly coating a negative electrode slurry (with a solvent of deionized water) on the surface of the negative conductive layer and then drying and cold pressing.

[0446] The single-sided coating weight of the negative electrode film layer is 135 mg / 1540.25 mm 2 。

[0447] The negative electrode film layer includes a first negative electrode film layer and a second negative electrode film layer. The first negative electrode film layer is located on the surface of the negative conductive layer, and the second negative electrode film layer is located on the surface of the first negative electrode film layer.

[0448] The first negative electrode film layer comprises graphite particles, conductive agent acetylene black, first lithium-containing binder (lithium acrylate-acrylonitrile-acrylamide-hydroxyethyl acrylate copolymer), negative electrode binder styrene-butadiene rubber, and thickening agent sodium carboxymethyl cellulose in a mass ratio of 96.5:0.5:0.5:1.5:1; the mass content of lithium element in the first lithium-containing binder is 4.8%; the Dv50 of the graphite particles is 11.3 μm, the graphite particles include artificial graphite and an amorphous carbon layer, the amorphous carbon layer coats the surface of the artificial graphite, and the mass content of the amorphous carbon is 3.5%.

[0449] The second negative electrode film layer comprises graphite particles, conductive agent acetylene black, second lithium-containing binder (lithium acrylate-acrylonitrile-acrylamide-hydroxyethyl acrylate copolymer), negative electrode binder styrene-butadiene rubber, and thickening agent sodium carboxymethyl cellulose in a mass ratio of 97.5:0.5:0.5:0.5:1; the mass content of lithium element in the second lithium-containing binder is 4.8%; the Dv50 of the graphite particles is 11.3 μm, the graphite particles include artificial graphite and an amorphous carbon layer, the amorphous carbon layer coats the surface of the artificial graphite, and the mass content of the amorphous carbon is 3.5%.

[0450] 3. Separator The separator includes a base film, which is a 7-μm polyethylene film layer with a porosity of 42%.

[0451] 4. Preparation of electrolyte The electrolyte includes organic solvents, lithium salts, and additives. The organic solvents include 60% chain carboxylic ester solvents (ethyl acetate) and 40% carbonate solvents (30% ethylene carbonate EC and 10% dimethyl carbonate by mass); the mass content of the additives is 6.5%, which includes vinylene carbonate VC, fluoroethylene carbonate FEC, ethylene sulfite ES, and lithium difluorooxalate borate LiDFOB in a mass ratio of 5:0.5:0.5:0.5; the lithium salt includes 1 mol / L lithium hexafluorophosphate LiPF 6 . The conductivity of the electrolyte is 16.4 mS / cm.

[0452] 5. Preparation of battery cell Stack the above-mentioned positive electrode sheet, separator, and negative electrode sheet in sequence, with the separator between the positive electrode sheet and the negative electrode sheet to play an isolation role, and obtain an electrode assembly through the winding process; place the electrode assembly in an outer packaging shell, inject the electrolyte after drying, and obtain a battery cell through processes such as vacuum packaging, standing, formation, and shaping. The compaction density of the positive electrode film layer at 100% SOC is 2.60 / cm 3 , and the compaction density of the negative electrode film layer at 100% SOC is 1.25 g / cm 3 .

[0453] The ratio of the number of the first tabs to the number of the first flat segments in the positive electrode tab is 0.75. For example, Figure 5 the arrangement of the tabs in the first electrode sheet in

[0454] The ratio of the number of the second tabs to the number of the second flat segments in the negative electrode tab is 0.75. Refer to Figure 5 the arrangement of the tabs in the first electrode sheet in

[0455] Examples 2-1 to 2-4 The battery cells were prepared by a method similar to that of Example 1. Different from Example 1, the ratio of the number of the first tabs to the number of the first flat segments was adjusted; the ratio of the number of the second tabs to the number of the second flat segments in the negative electrode tab was adjusted.

[0456] In Example 2-1, The ratio of the number of the first tabs to the number of the first flat segments in the positive electrode tab is 0.5. For example, Figure 3 the arrangement of the tabs in the first electrode sheet in

[0457] The ratio of the number of the second tabs to the number of the second flat segments in the negative electrode tab is 0.5. Refer to Figure 3 the arrangement of the tabs in the first electrode sheet in

[0458] In Example 2-2, The ratio of the number of the first tabs to the number of the first flat segments in the positive electrode tab is 0.8. For example, the positive electrode tab is wound 5 turns, each turn includes 2 first flat segments, a total of 10 first flat segments; 8 of the 10 first flat segments are connected with the first tabs, and the number of the first tabs is 8.

[0459] The ratio of the number of the second tabs to the number of the second flat segments in the negative electrode tab is 0.8. For example, the negative electrode tab is wound 5 turns, each turn includes 2 second flat segments, a total of 10 second flat segments; 8 of the 10 second flat segments are connected with the second tabs, and the number of the second tabs is 8.

[0460] In Example 2-3, The ratio of the number of the first tabs to the number of the first flat segments in the positive electrode tab is 1. For example, Figure 4 the arrangement of the tabs in the first electrode sheet in

[0461] The ratio of the number of the second tabs to the number of the second flat segments in the negative electrode tab is 1. Refer to Figure 4 the arrangement of the tabs in the first electrode sheet in

[0462] In Example 2-4, Compared with the positive electrode tab in Examples 2-3, the positive electrode tab in Example 2-4 is equivalent to cutting the positive electrode tab in Example 2-3, but the roots of the tabs are still connected together, that is, the ratio of the number of the first tabs in the positive electrode plate to the number of the first flat sections is 1. For example, the positive electrode tab in Example 2-3 is as shown in Figure 6 and the positive electrode tab in Example 2-4 is as shown in Figure 13 .

[0463] The setting method of the negative electrode tab is the same as that of the positive electrode tab and will not be elaborated here.

[0464] Example 3 A battery cell was prepared by a method similar to that in Example 1. Different from Example 1, the thickness of the positive electrode tab and the thickness of the negative electrode tab were adjusted.

[0465] Comparative Example 1-1 A battery cell was prepared by a method similar to that in Example 1. Different from Example 1, the number of the positive electrode tabs and the number of the negative electrode tabs were adjusted.

[0466] Performance test 1. Lithium deposition area test of the battery cell After each battery cell in each example and comparative example was cycled 50 times according to the following charge and discharge strategy, and then fully charged to 100% SOC according to the corresponding charging strategy, the negative electrode plate in the battery pack was disassembled, the negative electrode plate was unfolded, the lithium deposition area (grayish-white area) was observed, and the lithium deposition area was measured. The degree of lithium deposition is as follows: No lithium deposition: Lithium deposition area < 0.05%.

[0467] Slight lithium deposition: Lithium deposition area < 2%.

[0468] Severe lithium deposition: Lithium deposition area ≥ 2%.

[0469] At an external environmental temperature of 30°C, the battery cell was charged. The charging steps included the following steps: Constant current charging at 5.0C from 0% SOC to 5% SOC; Constant current charging at 5.0C from 5% SOC to 10% SOC; Constant current charging at 5.0C from 10% SOC to 15% SOC; Constant current charging at 5.0C from 15% SOC to 20% SOC; Constant current charging at 5.0C from 20% SOC to 25% SOC; Constant current charging at 5.0C from 25% SOC to 30% SOC; Constant current charging at 5.0C from 30% SOC to 35% SOC; Charge from 35% SOC to 40% SOC at a constant current of 5.0C; Charge from 40% SOC to 45% SOC at a constant current of 4.6C; Charge from 45% SOC to 50% SOC at a constant current of 4.3C; Charge from 50% SOC to 55% SOC at a constant current of 4.0C; Charge from 55% SOC to 60% SOC at a constant current of 3.7C; Charge from 60% SOC to 65% SOC at a constant current of 3.4C; Charge from 65% SOC to 70% SOC at a constant current of 3.1C; Charge from 70% SOC to 75% SOC at a constant current of 2.9C; Charge from 75% SOC to 80% SOC at a constant current of 2.7C; Charge from 80% SOC to 85% SOC at a constant current of 1.8C; Charge from 85% SOC to 90% SOC at a constant current of 1.3C; Charge from 90% SOC to 95% SOC at a constant current of 0.7C; Charge from 95% SOC to 98% SOC at a constant current of 0.33C; Charge from 98% SOC to 100% SOC at a constant current of 0.1C.

[0470] The cut-off voltage of the last charging step in the above charging steps is 3.65V.

[0471] The discharging strategy is as follows: discharge at a constant current of 0.33C to the cut-off voltage, such as 2.0V.

[0472] 2. DC internal resistance DCR test of battery cells The method in GB / T 31467 "Performance Test Specification for High-power Lithium-ion Power Batteries for HEV" can be referred to.

[0473] For example, at 25 °C, charge the battery cell to 3.65V at a constant current of 0.33C, and let it stand for 1 min; then charge it to 3.65V at a constant current of 0.1C and let it stand for 30 min; discharge it to 2.0V at a constant current of 0.33C, and record the discharge capacity A 0 , in the unit of Ah, then charge 0.5A at a constant current of 0.33C 0 Ah, and adjust the SOC to 50%.

[0474] After leaving the battery cell at 25 °C for 2 h, discharge it at a constant current of 4C for 10s, and record ∆U 放电 , ∆I 放电, the discharge DCR data of the lithium-ion battery is calculated by the following formula.

[0475] R 放电 =∆U 放电 / ∆I 放电 , where ∆U 放电 represents the voltage change within 10 s at the start of discharge, and ∆I 放电 represents the current value within 10 s at the start of discharge.

[0476] 3. Number of cycles for the battery cell to reach 80% SOH At 35 °C, the battery cell is charged at a constant current of 1C to the charging cut-off voltage of 3.65 V, and then discharged at a constant current of 1C to 2.0 V. This is one charge-discharge cycle; repeat the above charge-discharge cycle steps until the cycle capacity retention rate (i.e., Cn / C0×100%) is 80%, and record the number of cycles. The more the number of cycles, the better the cycle performance of the battery cell.

[0477] The test results are shown in Table 1.

[0478] Table 1

[0479] As can be seen from Table 1, in Comparative Example 1-1, the number of tabs is relatively small, resulting in a longer current conduction path and higher impedance, making it easier for lithium to deposit on the negative electrode tab.

[0480] In the embodiment of the present application, by setting the ratio of the number of tabs to the number of straight sections to be 0.5:1 to 2:1, the shunting ability of the tabs can be improved, the current conduction path can be shortened, and it is not easy for lithium to deposit on the negative electrode tab; moreover, the organic solvent in the electrolyte is not easily decomposed, the electrolyte system is more stable, which is beneficial to improving the use reliability of the battery cell and the cycle performance.

[0481] When the thickness of the positive electrode tab is 10 to 20 μm and the thickness of the negative electrode tab is 5 to 10 μm, the impedance of the battery is relatively low, lithium is not easily deposited on the negative electrode, and the cycle performance is better.

[0482] Examples 4-1 to 4-3 Battery cells were prepared using a method similar to that of Example 1. Different from Example 1, the composition of the organic solvent in the electrolyte was adjusted.

[0483] Comparative Example 2-1 Battery cells were prepared using a method similar to that of Example 1. Different from Example 1, the composition of the organic solvent in the electrolyte was adjusted.

[0484] The test results are shown in Table 2.

[0485] Table 2

[0486] In Table 2, In Example 4-3, the mass content ratio of ethyl acetate to methyl acetate is 2:7.

[0487] In Example 4-1, Example 4-2 and Comparative Example 2-1, the mass content of ethylene carbonate is 30%, and the rest is dimethyl carbonate.

[0488] As can be seen from Table 2, in Comparative Example 2-1, the mass content of the chain carboxylic acid ester solvent is relatively low, the conductivity is low, and the impedance of the battery cell is too large, which will seriously deteriorate the cycle performance and lead to cycle diving. Compared with Comparative Example 2-1, the conductivity of the electrolyte in Example 4-2 is improved, which is beneficial to the improvement of the cycle performance.

[0489] Compared with Comparative Example 2-1, when the mass content of the chain carboxylic acid ester solvent relative to the mass of the organic solvent increases, for example, when it is greater than or equal to 8%, the conductivity of the solvent system is high, which is beneficial to the rapid migration of lithium ions and improves the rapid charging performance of the battery cell. However, the conductivity of the electrolyte cannot be too low. For example, when the mass content of the chain carboxylic acid ester solvent is less than 5%, the conductivity is low, which is not conducive to the rapid migration of lithium ions and makes the battery cell unable to charge and discharge quickly. Examples 5-1 to 5-3 The battery cell was prepared by a method similar to that of Example 1. Different from Example 1, a stacked electrode assembly was prepared by a stacking process to obtain a battery cell.

[0490] In Example 5-1, The ratio of the number of the first tabs to the number of the first straight sections in the positive electrode tab is 1. The first tab is the positive electrode tab, and the first straight section is the positive electrode straight section. The positive electrode tabs and the positive electrode straight sections are connected in one-to-one correspondence, as Figure 10 the tab setting in

[0491] The ratio of the number of the second tabs to the number of the second straight sections in the negative electrode tab is 1. The second tab is the negative electrode tab, and the second straight section is the negative electrode straight section. The negative electrode tabs and the negative electrode straight sections are connected in one-to-one correspondence. Refer to Figure 10 the tab setting in

[0492] In Example 5-2, Compared with the positive electrode tab of Example 5-1, the positive electrode tab in Example 5-2 is equivalent to cutting the positive electrode tab of Example 5-1, but the tab roots are still connected together. Refer to Figure 10 the tab structure in

[0493] The arrangement of the positive electrode tab in comparison with that in Embodiment 5-1, such as the arrangement of the positive electrode tab, will not be elaborated herein again.

[0494] In Embodiment 5-3, The ratio of the number of the first tabs in the positive electrode sheet to the number of the first flat segments is 2. The first tabs are positive electrode tabs, and the first flat segments are positive electrode flat segments. One positive electrode tab is arranged on each of the two sides of one positive electrode flat segment along the length direction, which is equivalent to that the number of the positive electrode tabs is twice the number of the positive electrode flat segments, as Figure 11 the arrangement of the middle tabs.

[0495] The ratio of the number of the second tabs in the negative electrode sheet to the number of the second flat segments is 2. The second tabs are negative electrode tabs, and the second flat segments are negative electrode flat segments. One negative electrode tab is arranged on each of the two sides of one negative electrode flat segment, which is equivalent to that the number of the negative electrode tabs is twice the number of the negative electrode flat segments, as Figure 12 the arrangement of the middle tabs.

[0496] The test results are shown in Table 3.

[0497] Table 3

[0498] In Embodiments 5-1 to 5-3, the thickness of the positive electrode tabs is 15 μm, and the thickness of the negative electrode tabs is 6 μm.

[0499] In the embodiments of the present application, by setting the ratio of the number of the tabs to the number of the flat segments to be 0.5:1 to 2:1, the current shunting capacity of the tabs can be improved, the current conduction path can be shortened, and lithium deposition is not likely to occur on the negative electrode sheet; moreover, the organic solvents in the electrolyte are not easily decomposed, the electrolyte system is more stable, which is beneficial to improving the use reliability of the battery cell and the cycle performance.

[0500] Although the illustrative embodiments have been demonstrated and described, those skilled in the art should understand that the above embodiments cannot be construed as a limitation to the present application, and the embodiments can be changed, substituted, and modified without departing from the spirit, principle, and scope of the present application.

Claims

1. A battery cell, characterized in that: The invention comprises a housing component, an electrode component and an electrolyte, wherein the electrode component and the electrolyte are contained in the housing component. The housing assembly is provided with electrode terminals; The electrode assembly comprises a first pole piece, a second pole piece and a separator between the first pole piece and the second pole piece, wherein the first pole piece and the second pole piece each comprise a coating portion and a pole ear, wherein the coating portion is coated with an active material layer, and the pole ear is not coated with an active material layer; The first electrode sheet and the second electrode sheet have opposite polarities, one of the first electrode sheet and the second electrode sheet is a positive electrode sheet, the active material layer of the positive electrode sheet includes a positive electrode active material, and the positive electrode active material includes a lithium-containing phosphate with an olivine structure; the electrode assembly is electrically connected to the electrode terminal through the electrode tab, wherein: The coated portion of the first pole piece includes a first straight segment, and the coated portion of the second pole piece includes a second straight segment. The first straight segment and the second straight segment are stacked along the thickness direction of the electrode assembly. The ratio of the number of pole ears of the first pole piece to the number of first straight segments of the first pole piece is 0.5 to 2. The electrolyte includes an organic solvent, and the organic solvent includes a chain carboxylate solvent. The mass content of the chain carboxylate solvent in the organic solvent is 8% to 75%.

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

3. The battery cell according to claim 1 or 2, characterized in that: The ratio of the number of the pole ears of the second pole piece to the number of the second straight sections of the second pole piece is 0.5 to 2.

4. The battery cell according to any one of claims 1 to 2, characterized in that: The electrode assembly is a wound structure, the first pole sheet and the second pole sheet are wound in one direction, and the first pole sheet has a plurality of pole ears.

5. The battery cell according to claim 4, characterized in that: The ratio of the number of the pole ears of the first pole piece to the number of the first straight sections of the first pole piece is 0.5 to 1.

6. The battery cell according to any one of claims 1 to 2, characterized in that: The electrode assembly is a laminated structure, and the first pole piece and the second pole piece each have a plurality of them, and each of the first pole pieces has at least one pole lug.

7. The battery cell according to claim 6, characterized in that: The ratio of the number of the pole ears of the first pole piece to the number of the first straight sections of the first pole piece is 1 to 2.

8. The battery cell according to any one of claims 1 to 2, characterized in that: The first pole piece has a plurality of pole ears, and the plurality of pole ears of the first pole piece are arranged on the same side of the coating portion.

9. The battery cell according to any one of claims 1 to 2, characterized in that: The first pole piece has a plurality of pole ears, and the plurality of pole ears of the first pole piece are respectively arranged on both sides of the coating portion.

10. The battery cell according to any one of claims 1 to 2, characterized in that: The tab comprises: a tab body connected to the coating portion; and A plurality of tab protrusions are connected to a side of the tab body away from the coating portion, and a gap is provided between two adjacent tab protrusions. Each tab protrusion is used for being electrically connected to the electrode terminal.

11. The battery cell according to any one of claims 1 to 2, characterized in that: The pole tab in the first pole piece is a positive pole tab, and the thickness of the positive pole tab is 10 μm to 20 μm.

12. The battery cell according to any one of claims 1 to 2, characterized in that: The tab in the first pole piece is a negative pole tab, and the thickness of the negative pole tab is 4 μm to 10 μm.

13. The battery cell according to any one of claims 1 to 2, characterized in that: The conductivity of the electrolyte at room temperature is 10.5 mS / cm to 20 mS / cm.

14. The battery cell according to claim 13, characterized in that: The conductivity of the electrolyte at room temperature is 15 mS / cm to 20 mS / cm.

15. The battery cell according to any one of claims 1 to 2, characterized in that: The chain carboxylic acid ester solvent includes a compound shown in Formula I, Formula I, In Formula I, R1 includes a hydrogen atom, a halogen atom, a C1 to C5 alkyl group or a C1 to C5 halogenated alkyl group, R2 includes a C1 to C5 alkyl group or a C1 to C5 halogenated alkyl group.

16. The battery cell according to claim 15, characterized in that: R1 includes a hydrogen atom, a halogen atom, a C1 to C3 alkyl group or a C1 to C3 halogenated alkyl group, R2 includes C1 to C3 alkyl or C1 to C3 halogenated alkyl.

17. The battery cell according to claim 15, characterized in that: The halogen atom includes a fluorine atom, and / or the halogenated alkyl group includes a fluorinated alkyl group.

18. The battery cell according to claim 15, characterized in that: The chain carboxylic acid ester solvent includes one or more of the compounds represented by formula I-1 to the compounds represented by formula I-8, 。 19. The battery cell according to any one of claims 1 to 2, characterized in that: The organic solvent further includes a carbonate solvent, and the carbonate solvent includes one or more of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate and ethyl methyl carbonate.

20. The battery cell according to claim 19, characterized in that: The mass content of the carbonate solvent in the organic solvent is 30% to 50%.

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

22. The battery cell according to claim 21, characterized in that: The carbonate additive includes one or more of vinylene carbonate, fluoroethylene carbonate, and / or The sulfur-containing additive includes one or more of vinyl sulfate, vinyl disulfate, butylene sulfite, 1,3-propane sultone, vinyl sulfite, and methylene disulfonate, and / or The lithium salt additive includes one or more of lithium difluorophosphate, lithium difluorooxalatoborate, lithium tetrafluoroborate, and lithium bis(oxalatoborate).

23. The battery cell according to claim 21, characterized in that: The mass content of the additive in the electrolyte is 1% to 10%.

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

25. The battery cell according to claim 24, characterized in that: The fluorine-containing sulfonyl imide salt includes one or more of lithium bis(fluorosulfonyl)imide and lithium bis(trifluoromethanesulfonyl)imide.

26. The battery cell according to claim 25, characterized in that: The lithium salt includes lithium bis(fluorosulfonyl)imide and lithium hexafluorophosphate. The molar concentration of the lithium bis(fluorosulfonyl)imide is 0.2 mol / L to 0.5 mol / L, and the molar concentration of the lithium hexafluorophosphate is 0.5 mol / L to 1.0 mol / L.

27. The battery cell according to any one of claims 1 to 2, characterized in that: The viscosity of the electrolyte at room temperature is 2.3 mPa·s to 3.5 mPa·s; and / or The electrolyte has a density of 1.05 g / mL to 1.35 g / mL at room temperature.

28. The battery cell according to any one of claims 1 to 2, characterized in that: The lithium-containing phosphate of the olivine structure comprises: Phosphate particles, and The coating layer covers the phosphate particles, and the coating layer contains one or more elements of C, Fe, Ti, Zr, Hf, Ge and Sn.

29. The battery cell according to claim 28, characterized in that: The phosphate particles include a general formula of Li x1 A y1 Me a M b P 1-c X c Y z A compound wherein 0.5≤x1≤1.3, 0≤y1≤1.3, and 0.9≤x1+y1≤1.3, 0.9≤a≤1.5, 0≤b≤0.5, and 0.9≤a+b≤1.5, 0≤c≤0.5, 3≤z≤5, A includes one or more of Na, K, and Mg, Me includes one or more of Mn, Fe, Co, and Ni, M includes one or more of B, Mg, Al, Si, P, S, Ca, Sc, Ti, V, Cr, Cu, Zn, Sr, Y, Zr, Nb, Mo, Cd, Sn, Sb, Te, Ba, Ta, W, Yb, La, and Ce, X includes one or more of S, Si, Cl, B, C, and N, and Y includes one or more of O and F.

30. The battery cell according to claim 28, characterized in that The coating layer includes a general formula of Li 3-d Fe 2-d M2 d (PO x2 ) y2 The fast ion conductor M2 includes one or more elements of Ti, Zr, Hf, Ge and Sn, 0≤d≤1, 0<x2<5, 0<y2<4.

31. The battery cell according to claim 28, characterized in that The graphitization degree of the lithium-containing phosphate with an olivine structure is 0.15 to 0.

32.

32. The battery cell according to claim 31, characterized in that: The graphitization degree of the lithium-containing phosphate with an olivine structure is 0.19 to 0.

26.

33. The battery cell according to claim 28, characterized in that The mass content of carbon in the lithium-containing phosphate with olivine structure is 1% to 2%. The specific surface area of ​​the lithium-containing phosphate with olivine structure is 5m 2 / g to 18m 2 / g.

34. The battery cell according to claim 33, characterized in that: The specific surface area of ​​the lithium-containing phosphate with olivine structure is 7.5 m 2 / g to 14m 2 / g.

35. The battery cell according to any one of claims 1 to 2, characterized in that: The lithium-containing phosphate with olivine structure is in granular form, and its volume distribution particle size satisfies: 1µm≤Dv50≤2µm, 0.4µm≤Dv10≤0.7µm.

36. The battery cell according to any one of claims 1 to 2, characterized in that: The lithium-containing phosphate with an olivine structure is in a granular form, and 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.

37. The battery cell according to any one of claims 1 to 2, characterized in that: The other of the first pole sheet and the second pole sheet is a negative pole sheet, the negative pole sheet includes a negative electrode active material, the negative electrode active material includes a carbon-based material, the carbon-based material includes graphite particles, and the graphitization degree of the graphite particles is 92.0% to 94.5%.

38. The battery cell according to claim 37, characterized in that: The graphite particles include: Artificial graphite, including secondary particles, and The carbon coating layer is coated on the surface of the artificial graphite.

39. The battery cell according to claim 38, characterized in that The mass content of the carbon coating layer is 2% to 5% based on the mass of the graphite particles.

40. The battery cell according to any one of claims 1 to 2, characterized in that: The other of the first electrode sheet and the second electrode sheet is a negative electrode sheet, and the coating portion of the negative electrode sheet includes a negative electrode film layer, and the negative electrode film layer is coated on the surface of the negative electrode current collector, and the negative electrode film layer includes: a first negative electrode film layer, disposed on the surface of the negative electrode current collecting portion, wherein the first negative electrode film layer comprises a carbon-based material, and A second negative electrode film layer is connected to a side of the first negative electrode film layer away from the negative electrode current collecting portion, wherein the second negative electrode film layer comprises a carbon-based material. The carbon-based material in the first negative electrode film layer and the carbon-based material in the second negative electrode film layer each independently include graphite particles, and the volume average particle size Dv50 of the graphite particles in the first negative electrode film layer is greater than or equal to the volume average particle size Dv50 of the graphite particles in the second negative electrode film layer.

41. The battery cell according to claim 40, characterized in that The carbon-based material in the first negative electrode film layer also includes natural graphite.

42. The battery cell according to claim 40, characterized in that The tap density of the carbon-based material in the first negative electrode film layer is less than or equal to the tap density of the carbon-based material in the second negative electrode film layer.

43. The battery cell according to claim 42, characterized in that The tap density of the carbon-based material in the first negative electrode film layer is 0.82 g / cm 3 Up to 1.21g / cm 3 , and / or The tap density of the carbon-based material in the second negative electrode film layer is 0.90 g / cm 3 Up to 1.25g / cm 3 .

44. The battery cell according to claim 40, characterized in that The volume average particle size Dv50 of the graphite particles in the first negative electrode film layer is 9.5 μm to 18.5 μm, and / or The volume average particle size Dv50 of the graphite particles in the second negative electrode film layer is 7.8 μm to 14.3 μm.

45. The battery cell according to claim 40, characterized in that The first negative electrode film layer also includes a first lithium-containing binder, and the second negative electrode film layer also includes a second lithium-containing binder. The mass content of the first lithium-containing binder relative to the mass of the first negative electrode film layer is less than or equal to the mass content of the second lithium-containing binder relative to the mass of the second negative electrode film layer.

46. ​​The battery cell according to claim 45, characterized in that The mass content of the first lithium-containing binder relative to the mass of the first negative electrode film layer is 0.1% to 1%, and / or The mass content of the second lithium-containing binder relative to the mass of the second negative electrode film layer is 0.1% to 1%.

47. The battery cell according to claim 45 or 46, characterized in that: The mass content of lithium in the first lithium-containing binder is 3% to 10%, and / or The mass content of lithium element in the second lithium-containing binder is 3% to 10%.

48. The battery cell according to any one of claims 45 to 46, characterized in that: The first lithium-containing binder comprises a lithium acrylate-acrylonitrile-acrylamide-hydroxyethyl acrylate copolymer, wherein the lithium acrylate-acrylonitrile-acrylamide-hydroxyethyl acrylate copolymer is derived from a lithium acrylate monomer, an acrylonitrile monomer, an acrylamide monomer and a hydroxyethyl acrylate monomer, and the molar ratio of the lithium acrylate monomer, the acrylonitrile monomer, the acrylamide monomer and the hydroxyethyl acrylate monomer is 30% to 50%: 15% to 45%: 5% to 20%: 20% to 35%, and / or The second lithium-containing binder includes a lithium acrylate-acrylonitrile-acrylamide-hydroxyethyl acrylate copolymer, wherein the lithium acrylate-acrylonitrile-acrylamide-hydroxyethyl acrylate copolymer is derived from a lithium acrylate monomer, an acrylonitrile monomer, an acrylamide monomer and a hydroxyethyl acrylate monomer, and the molar ratio of the lithium acrylate monomer, the acrylonitrile monomer, the acrylamide monomer and the hydroxyethyl acrylate monomer is 30% to 50%: 15% to 45%: 5% to 20%: 20% to 35%.

49. The battery cell according to claim 37, characterized in that The negative electrode active material further comprises a silicon-based material, and the mass content of silicon element in the silicon-based material is 0.3% to 10.0%, based on the mass of the negative electrode active material.

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

51. The battery cell according to claim 50, characterized in that The base film has a thickness of 6 μm to 12 μm.

52. The battery cell according to claim 51, characterized in that The base film has a thickness of 6 μm to 9 μm.

53. The battery cell according to any one of claims 1 to 2, characterized in that: The isolation film includes a base film and a functional layer disposed on at least one side of the base film, wherein the functional layer includes: a first functional layer, located on one side of the base film, the first functional layer comprising first inorganic particles, The second functional layer is located on the other side of the base film, and the second functional layer includes composite particles. The composite particles include second inorganic particles and a plurality of non-fluoropolymer particles. The second inorganic particles are attached to the surface of the non-fluoropolymer particles and / or dispersed inside the non-fluoropolymer particles.

54. The battery cell according to claim 53, characterized in that The non-fluorine polymer particles include acrylic copolymers.

55. The battery cell according to claim 53, characterized in that The first inorganic particles include one or more of silicon oxide, aluminum oxide, boehmite, barium sulfate, calcium oxide, titanium oxide, zinc oxide, magnesium oxide, zirconium oxide, and tin oxide.

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

57. The battery cell according to any one of claims 1 to 2, characterized in that: The battery cell includes a case that accommodates the electrode assembly, the case includes steel, and a thickness of the case is 0.1 mm to 0.5 mm.

58. The battery cell according to claim 57, characterized in that The thickness of the shell is 0.2 mm to 0.35 mm.

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

60. A battery device, characterized in that: The invention comprises a plurality of battery cells as claimed in any one of claims 1 to 59.

61. The battery device according to claim 60, characterized in that The charging time of the battery device from a 10% state of charge to an 80% state of charge is 5 minutes to 10.5 minutes.

62. An electrical device, characterized in that: Comprising a battery device as claimed in claim 60 or 61.

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