Battery cell, battery device, and electric device

Abstract

A battery cell, a battery device, and an electric device. The battery cell comprises an electrode assembly and an electrolyte. The electrode assembly comprises a first electrode sheet and a second electrode sheet. The first electrode sheet and the second electrode sheet each comprise a coating portion and tabs. The coating portion is coated with an active material layer, and the tabs are not coated with the active material layer. One of the first electrode sheet and the second electrode sheet is a positive electrode sheet, and a positive electrode active material of the positive electrode sheet comprises lithium-containing phosphate having an olivine structure. The coating portion of the first electrode sheet comprises first straight sections, and the coating portion of the second electrode sheet comprises second straight sections. The first straight sections and the second straight sections are stacked in the thickness direction of the electrode assembly. The ratio of the number of the tabs of the first electrode sheet to the number of the first straight sections of the first electrode sheet is 0.5 to 2. An organic solvent of the electrolyte comprises a linear carboxylic ester solvent. The mass content of the linear carboxylic ester solvent in the organic solvent is 8% to 90%. The present application can improve the use reliability and cycle performance of battery cells.

Description

Battery cells, battery packs and electrical devices Technical Field

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

[0002] Lithium-ion batteries are widely used in electronic devices such as mobile phones, laptops, electric vehicles, electric cars, electric airplanes, electric ships, and power tools due to their high capacity and long lifespan. However, with the development of lithium-ion battery applications, there is a growing demand for improved battery performance; however, the reliability and cycle life of individual battery cells still need further improvement.

[0003] Summary of the Invention

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

[0005] In a first aspect, this application proposes a battery cell, comprising a casing assembly, an electrode assembly, and an electrolyte. The electrode assembly and electrolyte are housed within the casing assembly, which is provided with electrode terminals. The electrode assembly includes a first electrode, a second electrode, and a separator membrane located between the first and second electrodes. Both the first and second electrodes include a coated portion and a tab. The coated portion is coated with an active material layer, while the tab is not coated with an active material layer. The first and second electrodes have opposite polarities, with one of them being a positive electrode. The active material layer of the positive electrode includes a positive electrode... The electrode assembly includes a positive electrode active material, comprising a lithium phosphate with an olivine structure; the electrode assembly is electrically connected to the electrode terminals via tabs, wherein the coating portion of the first electrode includes a first straight section, the coating portion of the second electrode includes a second straight section, the first straight section and the second straight section are stacked along the thickness direction of the electrode assembly, the ratio of the number of tabs of the first electrode to the number of the first straight sections of the first electrode is 0.5 to 2, the electrolyte includes an organic solvent, the organic 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%.

[0006] Therefore, in this embodiment, the electrolyte includes the aforementioned mass content of a chain-like carboxylic acid ester solvent. This solvent system has high conductivity, which is beneficial for the rapid migration of lithium ions and improves the fast-charging performance of the battery cell. In a fast-charging system for a battery cell, the current density of the tab is usually high, leading to increased heat generation and higher temperatures within the battery cell. This can easily cause the degradation of the active material and the decomposition of the organic solvent in the electrolyte, worsening the cycle life. The positive electrode active material includes a lithium phosphate with an olivine structure. This material is structurally stable during charge and discharge, is not prone to capacity decay, and is beneficial for improving the cycle performance of the battery cell. Meanwhile, the first electrode... When the ratio of the number of tabs to the number of the first straight sections of the first electrode is within the aforementioned range, the current shunting capacity of the tabs can be increased, further improving the fast-charging performance of the battery cell. Furthermore, because the connection area between the tabs and other components, such as the coating, is relatively large, overcurrent resistance and overcurrent temperature rise can be effectively reduced, preventing excessive temperature rise inside the battery cell. This improves the stability of the electrolyte system and the active materials, enhancing the reliability of the battery cell and improving cycle performance. Additionally, the numerous connection points between the tabs and the coating increase connection redundancy, such as welding redundancy, effectively improving product yield. Therefore, the embodiments of this application can improve the cycle performance and fast-charging performance of the battery cell.

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

[0008] In some embodiments, the ratio of the number of tabs to the number of second straight segments of the second electrode is 0.5 to 2. Embodiments of this application can improve the cycle performance and fast-charging performance of individual battery cells.

[0009] In some embodiments, the electrode assembly has a wound structure, with the first electrode and the second electrode wound in one direction, and the first electrode having multiple tabs.

[0010] In some embodiments, the ratio of the number of tabs on the first electrode to the number of the first straight segments of the first electrode is 0.5 to 1. Embodiments of this application can improve the cycle performance and fast-charging performance of a single battery cell.

[0011] In some embodiments, the electrode assembly has a stacked structure, with multiple first and second electrodes, and each first electrode having at least one tab.

[0012] In some embodiments, the ratio of the number of tabs on the first electrode to the number of the first straight segments of the first electrode is 1 to 2. Embodiments of this application can improve the cycle performance and fast-charging performance of a single battery cell.

[0013] In some embodiments, the first electrode has multiple tabs, which are disposed on the same side of the coating portion. The first tabs being disposed on the same side of the first coating portion increases welding redundancy and effectively improves product yield.

[0014] In some embodiments, the first electrode has multiple tabs, which are respectively disposed on both sides of the coated portion. The embodiments of this application can improve the cycle performance and fast charging performance of a single battery cell. The first tabs can share the current density of a single first electrode, especially when the area of ​​the first electrode is relatively large, resulting in more uniform current distribution within the first electrode, which is beneficial for homogenizing the reaction and reducing impedance.

[0015] In some embodiments, the tab includes a tab body and a plurality of tab protrusions, the tab body being 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, each tab protrusion being used for electrical connection with an electrode terminal.

[0016] Therefore, in the embodiments of this application, the arrangement of multiple electrode protrusions allows the first electrode to have multiple connection points. For example, when connecting the first electrode to the first adapter, the multiple electrode protrusions can be connected to different positions of the first adapter, such as by welding. This increases the number of welding positions between the first electrode and the first adapter, improves the welding yield, and enhances the stability of the connection between the two.

[0017] In some embodiments, the tab in the first electrode is a positive tab, and the thickness of the positive 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 excellent overcurrent capacity, which can reduce heat generation and help improve the fast charging performance of the battery cell.

[0019] In some embodiments, the tab in the first electrode is a negative tab, and the thickness of the negative 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 overcurrent capacity, which can reduce heat generation and help improve the fast charging performance of the battery cell.

[0021] In some embodiments, the conductivity of the electrolyte is from 10.5 mS / cm to 20 mS / cm, optionally from 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, wherein the chain carboxylic acid ester solvent has a mass content of 8% to 75% in the organic solvent, optionally greater than or equal to 10%, 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 low, which is beneficial to the migration of lithium ions.

[0024] In some embodiments, the chain carboxylic acid ester solvent includes compounds represented by Formula I.

[0025] In formula I,

[0026] R1 includes a hydrogen atom, a halogen atom, a C1 to C5 alkyl group, or a C1 to C5 haloalkyl group.

[0027] R2 includes C1 to C5 alkyl or C1 to C5 haloalkyl.

[0028] Therefore, the above-mentioned chain carboxylic acid ester solvents in the embodiments of this application have high conductivity, which is beneficial to improving the fast charging capability of battery cells.

[0029] In some embodiments, R1 includes a hydrogen atom, a halogen atom, a C1 to C3 alkyl group, or a C1 to C3 haloalkyl group.

[0030] In some embodiments, R2 includes C1 to C3 alkyl or C1 to C3 haloalkyl.

[0031] In some embodiments, the chain carboxylic acid ester solvent includes one or more compounds of formulas I-1 to I-8.

[0032] In some embodiments, the organic solvent further includes carbonate solvents, including one or more of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, and methyl ethyl carbonate. The combined use of these carbonate solvents and chain carboxylic acid ester solvents improves the conductivity of the electrolyte, which is beneficial for lithium ion migration.

[0033] In some embodiments, the carbonate solvent includes one or more of ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate.

[0034] In some embodiments, the carbonate solvent comprises 25% to 92% by mass in the organic solvent, optionally 30% to 50%. The carbonate solvent content described above can further improve the conductivity of the electrolyte, which is beneficial for lithium ion migration.

[0035] In some embodiments, the electrolyte further includes additives, including one or more of carbonate additives, sulfur-containing additives, and lithium salt additives. These additives can improve the interfacial film performance on the positive and / or negative electrode sides, which is beneficial for improving the fast-charging performance of individual battery cells and enhancing cycle performance.

[0036] In some embodiments, the carbonate additives include one or more of vinylene carbonate (VC) and fluoroethylene carbonate (FEC).

[0037] In some embodiments, the sulfur-containing additives include one or more of vinyl sulfate DTD, vinyl disulfate 2-DTD, butenyl sulfite BS, 1,3-propanesulfonate lactone PS, vinyl sulfite ES, and methylene disulfonate MMDS.

[0038] In some embodiments, the lithium salt additive includes one or more of lithium difluorophosphate (LiPO2F2), lithium difluorooxalate borate (LiDFOB), lithium tetrafluoroborate (LiBF4), and lithium dioxalate borate (LiBOB).

[0039] In some embodiments, the additive has a mass content of 1% to 10% in the electrolyte, optionally 2% to 8%. The above-mentioned mass content of the additive can effectively improve the interfacial film performance on the positive and / or negative electrode sides, which is beneficial to improving the fast charging performance of the battery cell and improving cycle performance.

[0040] In some embodiments, the electrolyte further includes a lithium salt, which includes one or more of fluorosulfonyl imide salts and lithium hexafluorophosphate (LiPF6). These lithium salts are readily dissociated, facilitating rapid lithium-ion migration; and the electrolyte system is relatively stable and not easily decomposed, thus improving the cycle performance of the battery cells.

[0041] In some embodiments, the fluorosulfonyl imide salt includes one or more of lithium bisfluorosulfonyl imide (LiFSI) and lithium bistrifluoromethanesulfonate (LiTFSI).

[0042] In some embodiments, the lithium salt includes lithium bis(fluorosulfonyl)imide (LiFSI) and lithium hexafluorophosphate (LiPF6), wherein the molar concentration of lithium bis(fluorosulfonyl)imide (LiFSI) is from 0.2 mol / L to 0.5 mol / L, and the molar concentration of lithium hexafluorophosphate (LiPF6) is from 0.5 mol / L to 1.0 mol / L.

[0043] In some embodiments, the molar concentration ratio of lithium bis(fluorosulfonyl)imide to lithium hexafluorophosphate (LiPF6) is 0.2 to 1.0, optionally 0.2 to 0.5.

[0044] In some embodiments, the electrolyte has a viscosity of 2.3 mPa·s to 3.5 mPa·s at room temperature. When the electrolyte viscosity is within this range, the migration rate of lithium ions in the electrolyte is higher, which can further reduce the internal resistance of the battery cells, thereby reducing heat generation and improving the fast charging performance of the battery cells.

[0045] In some embodiments, the electrolyte density at room temperature is between 1.05 g / mL and 1.35 g / mL. When the electrolyte density is within this range, the migration rate of lithium ions in the electrolyte is higher, which can further reduce the internal resistance of the battery cells, thereby reducing heat generation and improving the fast charging performance of the battery cells.

[0046] In some embodiments, the olivine-structured lithium phosphate comprises phosphate particles and a coating layer. The coating layer coats the phosphate particles and contains one or more elements selected from C, Fe, Ti, Zr, Hf, Ge, and Sn. By coating the surface, the conductivity of the olivine-structured lithium phosphate can be improved, the powder resistivity of the material can be reduced, and the migration rate of lithium ions can be facilitated, thereby reducing the heat generation of the battery cell.

[0047] In some embodiments, the phosphate particles comprise the general formula Li x1 A y1 Me a M b P 1-c X c Y z The compound contains olivine-structured lithium phosphates, 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 including one or more of Na, K, and Mg, Me including one or more of Mn, Fe, Co, and Ni, M including 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 including one or more of S, Si, Cl, B, C, and N, and Y including one or more of O and F. The olivine-structured lithium phosphate exhibits superior cycle stability, which is beneficial for improving the cycle performance of battery cells.

[0048] In some embodiments, the coating layer includes a general formula Li 3-d Fe 2-d M2 d (PO x2 ) y2The fast ion conductor, M2, includes one or more elements selected from Ti, Zr, Hf, Ge, and Sn, where 0 ≤ d ≤ 1, 0 < x2 < 5, and 0 < y2 < 4. Coating the phosphate particles with the fast ion conductor can significantly improve the lithium-ion transport rate during multiple lithium intercalation / deintercalation at the positive electrode, enhance the ionic conductivity of the positive electrode active material, thereby increasing the specific capacity and, further, improving the energy density of the corresponding battery cell.

[0049] In some embodiments, the degree of graphitization of the positive electrode active material is 0.15 to 0.32; optionally, it is 0.19 to 0.26. When the degree of graphitization of the positive electrode active material is within the above range, it is beneficial to improve the conductivity of the positive electrode active material, reduce the heat generation of the positive electrode sheet, and thus reduce the heat generation of the battery cell.

[0050] In some embodiments, the carbon content in the olivine-structured lithium phosphate is 1% to 2% by mass; the specific surface area of ​​the olivine-structured lithium phosphate is 5 m². 2 / g to 18m 2 / g; optional 7.5m 2 / g to 14m 2 / g.

[0051] Therefore, the carbon content of the above-mentioned mass content in the embodiments of this application, combined with the material with the above-mentioned specific surface area, is more conducive to the effective contact between the electrolyte and the lithium phosphate containing the olivine structure in the core, and is conducive to the transport of lithium ions at the phase interface.

[0052] In some embodiments, the volume distribution particle size of the positive electrode active material satisfies: 1μm≤Dv50≤2μm, 0.4μm≤Dv10≤0.7μm. The relatively small particle size of the positive electrode active material results in a shorter lithium-ion insertion / extraction path and less heat generation. Furthermore, the particle size of the aforementioned positive electrode active material is not too small, preventing agglomeration during processing and preparation, thus ensuring stable performance of the positive electrode active material.

[0053] In some embodiments, the olivine-structured lithium phosphate is particulate, comprising secondary particles formed by the agglomeration of primary particles, with the average particle size of the primary particles ranging from 200 nm to 500 nm. The relatively small average particle size of the primary particles results in a shorter lithium-ion insertion / extraction pathway in the positive electrode active material, leading to less heat generation.

[0054] In some embodiments, the coating portion of the negative electrode sheet 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%.

[0055] When the degree of graphitization of graphite particles is within the above range, the graphite particles have excellent electrical conductivity, which can reduce the heat generation of the negative electrode sheet and the heat generation of the battery cell; and can also improve the fast charging performance of the battery cell.

[0056] In some embodiments, the graphite particles include artificial graphite and amorphous carbon. The artificial graphite comprises secondary particles formed by the aggregation of multiple primary particles; an amorphous carbon layer coats the surface of the artificial graphite. The amorphous carbon layer has more end faces and defects, resulting in a greater number of sites for lithium ion insertion and extraction, which in turn improves the conductivity of the amorphous carbon layer, reduces the internal resistance of the negative electrode, and reduces the heat generation of the battery cell.

[0057] In some embodiments, the mass content of the amorphous carbon layer is 2% to 5% based on the mass of the graphite particles. When the mass content of the amorphous carbon 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.

[0058] In some embodiments, the negative electrode sheet is coated with a partial negative electrode film layer including a first negative electrode film layer and a second negative electrode film layer. The first negative electrode film layer is disposed on the surface of the negative electrode current collector, and the carbon-based material in the first negative electrode film layer includes graphite particles. The second negative electrode film layer is connected to the side of the first negative electrode film layer away from the negative electrode current collector, and the carbon-based material in the second negative electrode film layer includes graphite particles. The 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.

[0059] Therefore, the particle size difference between the first and second negative electrode film layers in the embodiments of this application can improve the fast charging performance of the battery cell. Specifically, during fast charging, the overpotential of the second negative electrode film layer is usually higher, and the bottleneck of fast charging is mainly in the second negative electrode film layer. However, in the embodiments of this application, the particle size of the second negative electrode film layer is relatively small, which can shorten the solid-phase transport path of lithium ions, improve fast charging performance, and improve the problem of lithium deposition on the surface of the negative electrode sheet.

[0060] In some embodiments, the carbon-based material in the first negative electrode film layer also includes natural graphite.

[0061] In some embodiments, the tap density of the carbon-based material in the first negative electrode film is less than or equal to the tap density of the carbon-based material in the second negative electrode film. When the tap density of the carbon-based material in the second negative electrode film is greater than that in the first negative electrode film, the second negative electrode film is more densely packed, thereby increasing the energy density of the battery cell; the first negative electrode film is relatively sparsely packed with more pores, which can improve the fast charging performance of the battery cell.

[0062] In some embodiments, the tap density of the carbon-based material in the first negative electrode film layer is 0.82 g / cm³. 3 Up to 1.21 g / cm 3 When the tap density of the carbon-based material in the first negative electrode film is within a suitable range, it can improve the fast charging performance of the battery cell.

[0063] In some embodiments, the tap density of the carbon-based material in the second negative electrode film is 0.90 g / cm³. 3 Up to 1.25 g / cm 3 When the tap density of the carbon-based material in the second negative electrode film is within a suitable range, it can improve the energy density of the battery cell.

[0064] In some embodiments, the volume average particle size Dv50 of the graphite particles in the first negative electrode film layer is between 9.5 μm and 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, fast charging performance can be improved.

[0065] In some embodiments, the volume average particle size Dv50 of the graphite particles in the second negative electrode film is between 7.8 μm and 14.3 μm. When the volume average particle size Dv50 of the negative electrode active material in the second negative electrode film is within the above range, the lithium-ion transport tortuosity can be reduced, thereby improving the fast charging performance of the battery cell.

[0066] In some embodiments, the first negative electrode film layer further includes a first lithium-containing binder, and the second negative electrode film layer further includes a second lithium-containing binder, wherein the mass content of the first lithium-containing binder relative to the mass of the first negative electrode film layer is less than or equal to the mass content of the second lithium-containing binder relative to the mass of the second negative electrode film layer.

[0067] Therefore, in the embodiments of this application, the mass content of the second lithium-containing binder in the second negative electrode film layer is relatively high, and the second lithium-containing binder provides a relatively larger number of freely movable lithium ions for the second negative electrode film layer, which can further improve the fast charging performance of the battery cell.

[0068] In some embodiments, the mass content of the first lithium-containing binder relative to 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, it can improve the lithium-ion insertion / extraction rate and enhance the fast charging performance of the battery cell.

[0069] In some embodiments, the lithium content in the first lithium-containing binder is 3% to 10% by mass, optionally 3% to 8%. When the lithium content is within the above range, the number of freely moving lithium ions in the negative electrode film layer is relatively large, which can further shorten the distance that lithium ions diffuse to the surface of the negative electrode film layer, improve the lithium ion insertion / extraction rate, and improve the fast charging performance of the battery cell.

[0070] In some embodiments, the mass content of the second lithium-containing binder relative to the second negative electrode film layer is 0.1% to 1%. When the mass content of lithium in the second lithium-containing binder is within the above range, the lithium-ion insertion / extraction rate is increased, thereby improving the fast charging performance of the battery cell.

[0071] In some embodiments, the lithium content in the second lithium-containing binder is 3% to 10% by mass, optionally 3% to 8%. When the lithium content is within the above range, the number of freely moving lithium ions in the negative electrode film layer is relatively large, which can further shorten the distance that lithium ions diffuse to the surface of the negative electrode film layer, improve the lithium ion insertion / extraction rate, and improve the fast charging performance of the battery cell.

[0072] In some embodiments, the first lithium-containing binder comprises a lithium acrylate-acrylonitrile-acrylamide-hydroxyethyl acrylate copolymer, which is derived from lithium acrylate monomer, acrylonitrile monomer, acrylamide monomer and hydroxyethyl acrylate monomer, wherein the molar ratio of lithium acrylate monomer, acrylonitrile monomer, acrylamide monomer and hydroxyethyl acrylate monomer is 30% to 50% : 15% to 45% : 5% to 20% : 20% to 35%.

[0073] Therefore, the lithium-containing binder of the above material can provide a certain number of lithium ions to the negative electrode film layer, thereby improving the fast charging performance of the battery cell; moreover, it is not prone to swelling during charging and discharging, and its structure is stable, which improves the cycle performance of the negative electrode film layer during fast charging and discharging.

[0074] In some embodiments, the second lithium-containing binder comprises a lithium acrylate-acrylonitrile-acrylamide-hydroxyethyl acrylate copolymer, which is derived from lithium acrylate monomer, acrylonitrile monomer, acrylamide monomer and hydroxyethyl acrylate monomer, wherein the molar ratio of lithium acrylate monomer, acrylonitrile monomer, acrylamide monomer and hydroxyethyl acrylate monomer is 30% to 50% : 15% to 45% : 5% to 20% : 20% to 35%.

[0075] Therefore, the lithium-containing binder of the above material can provide a certain number of lithium ions to the negative electrode film layer, thereby improving the fast charging performance of the battery cell; moreover, it is not prone to swelling during charging and discharging, and its structure is stable, which improves the cycle performance of the negative electrode film layer during fast charging and discharging.

[0076] In some embodiments, the negative electrode active material further includes a silicon-based material, wherein the silicon content in the silicon-based material is 0.3% to 10.0% by mass, based on the mass of the negative electrode active material. The introduction of the silicon-based material can increase the capacity of the negative electrode active material and improve the energy density of the battery cell.

[0077] In some embodiments, the battery cell includes a separator, which comprises a porous base film with a porosity of 20% to 70%. When the porosity of the separator in the embodiments of this application is within the above range, it can enhance the migration ability of lithium ions within the separator, further reduce the internal resistance of the battery cell, and thus reduce heat generation.

[0078] In some embodiments, the separator includes a porous base film with a porosity of 35% to 60%. When the porosity of the separator in the embodiments of this application is within the above range, it can improve the migration ability of lithium ions in the separator, further reduce the internal resistance of the battery cells, and thus reduce heat generation.

[0079] In some embodiments, the thickness of the base film is between 6 μm and 12 μm. When the thickness of the base film is within this range, the migration path of lithium ions in the base film is shorter, which can further reduce the internal resistance of the battery cell and thus reduce heat generation.

[0080] In some embodiments, the thickness of the base film is 6 μm to 9 μm. When the thickness of the base film is within this 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.

[0081] In some embodiments, the separator includes a base film and a functional layer disposed on at least one side of the base film. The functional layer includes a first functional layer and a second functional layer. The first functional layer is located on one side of the base film and includes first inorganic particles. The second functional layer is located on the other side of the base film and includes composite particles. The composite particles include second inorganic particles and a plurality of non-fluoropolymer particles. The second inorganic particles are attached to the surface of the non-fluoropolymer particles and / or dispersed inside the non-fluoropolymer particles. The first and second functional layers have good heat resistance, which can improve the heat resistance of the separator.

[0082] In some embodiments, the non-fluoropolymer particles include acrylate copolymers. Acrylate copolymers have excellent adhesion properties and high adhesion stability to the base film.

[0083] In some embodiments, the first inorganic particles include one or more of silicon oxide, aluminum oxide, boehmite, barium sulfate, calcium oxide, titanium oxide, zinc oxide, magnesium oxide, zirconium oxide, and tin oxide. These first inorganic particles can improve the heat resistance of the first functional layer.

[0084] In some embodiments, 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. These second inorganic particles can improve the heat resistance of the first functional layer.

[0085] In some embodiments, the average particle size of the second inorganic particles is between 5 nm and 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 compressive modulus of the composite particles.

[0086] In some embodiments, the base material of the casing includes steel, and the thickness of the casing is 0.1 mm to 0.5 mm, optionally 0.2 mm to 0.35 mm. A casing thickness within this range results in higher mechanical strength, improving the reliability and cycle performance of the battery cell; furthermore, the casing occupies less space, allowing for more internal space, which is beneficial for increasing the energy density of the battery cell.

[0087] In some implementations, the charging time for a single battery cell from 10% state of charge to 80% state of charge is 5 to 10.5 minutes. The faster charging speed of the battery cell is more conducive to improving fast charging capability.

[0088] Secondly, this application proposes a battery device comprising a plurality of battery cells according to any embodiment of the first aspect of this application.

[0089] In some implementations, the charging time for the battery device from 10% state of charge to 80% state of charge is 5 to 10.5 minutes. A faster charging speed improves the device's fast-charging capability.

[0090] Thirdly, this application proposes an electrical device, which includes the battery device according to any embodiment of the second aspect of this application. Attached Figure Description

[0091] To more clearly illustrate the technical solutions of the embodiments of this application, the drawings used in the embodiments of this application will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on the drawings without creative effort.

[0092] Figure 1 is a schematic diagram of the structure of a battery cell provided in some embodiments of this application;

[0093] Figure 2 is an exploded schematic diagram of a battery cell provided in some embodiments of this application;

[0094] Figure 3 is a schematic diagram of the structure of the electrode assembly of a battery cell provided in some embodiments of this application;

[0095] Figure 4 is a schematic diagram of the structure of the electrode assembly of a battery cell provided in some other embodiments of this application;

[0096] Figure 5 is a schematic diagram of the structure of the electrode assembly of a battery cell provided in some embodiments of this application;

[0097] Figure 6 is a schematic diagram showing the unfolded first electrode of the electrode assembly in a battery cell provided in some embodiments of this application;

[0098] Figure 7 is a schematic diagram showing the unfolded first electrode of the electrode assembly in a battery cell provided in some other embodiments of this application;

[0099] Figure 8 is an explosion diagram of a battery cell provided in some other embodiments of this application;

[0100] Figure 9 is a schematic diagram of the structure of the electrode assembly of a battery cell provided in some other embodiments of this application;

[0101] Figure 10 is a schematic diagram of the structure of the first electrode of a battery cell provided in some embodiments of this application;

[0102] Figure 11 is a schematic diagram of the structure of the first electrode of a battery cell provided in some other embodiments of this application;

[0103] Figure 12 is a schematic diagram of the structure of the second electrode of a battery cell provided in some embodiments of this application;

[0104] Figure 13 is a schematic diagram of the unfolded structure of the first electrode of a battery cell provided in some other embodiments of this application;

[0105] Figure 14 is a partially enlarged structural diagram of the first electrode plate shown in Figure 13 at point A;

[0106] Figure 15 is an exploded schematic diagram of a battery cell provided in some other embodiments of this application;

[0107] Figure 16 is a schematic diagram of the structure of a battery module provided in some embodiments of this application;

[0108] Figure 17 is a schematic diagram of the structure of a battery pack provided in some embodiments of this application;

[0109] Figure 18 is a schematic diagram of the structure of an electrical device provided in some embodiments of this application.

[0110] The accompanying drawings may not be drawn to scale.

[0111] The annotations in the attached figures are explained as follows:

[0112] Y, thickness direction;

[0113] 1. Electrical device; 2. Battery pack; 3. Controller; 4. Motor; 5. Housing; 5a. First housing section; 5b. Second housing section; 5c. Storage space; 6. Battery module;

[0114] 7. Battery cells;

[0115] 10. Electrode assembly;

[0116] 111. First electrode tab; 1111. Electrode body; 1112. Electrode protrusion;

[0117] 112. Second pole ear;

[0118] 13. First electrode; 131. First straight section; 132. First curved section; 130. First coating section;

[0119] 14. Second electrode; 141. Second straight section; 142. Second curved section; 140. Second coating section;

[0120] 15. Separating membrane;

[0121] 200. Housing components;

[0122] 20. Outer shell; 21. Housing; 22. End cap;

[0123] 31. First electrode terminal; 32. Second electrode terminal;

[0124] 41. First adapter;

[0125] 42. Second adapter. Detailed Implementation

[0126] The following detailed description, with appropriate reference to the accompanying drawings, specifically discloses embodiments of the battery cell, battery device, and power-consuming device of this application. However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of practically identical structures may be omitted. This is to avoid unnecessarily lengthy descriptions and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided to enable those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0127] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of the particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60 to 120 and 80 to 110 are listed for a specific parameter, it is also expected that ranges of 60 to 110 and 80 to 120 are also included. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1 to 3, 1 to 4, 1 to 5, 2 to 3, 2 to 4, and 2 to 5. In this application, unless otherwise stated, the numerical range "a to b" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0 to 5" means that all real numbers between "0 and 5" have been listed in this article; "0 to 5" is just a shortened representation of these numerical combinations. In addition, when a parameter is stated as an integer ≥ 2, it is equivalent to disclosing that the parameter is, for example, an integer 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0128] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0129] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0130] Unless otherwise specified, all steps of this application may be performed sequentially or randomly, preferably sequentially. For example, if the method includes steps (a) and (b), it means that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, if the method may also include step (c), it means that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0131] With the development of the battery cell field, the requirements for the fast charging performance of battery cells are gradually increasing. During the fast charging and discharging process, the charge and discharge rate is relatively large, which results in a large amount of heat generated inside the battery cell and a high internal temperature rise. At high temperatures, the stability of the electrolyte system is poor and it is easy to decompose and volatilize, which increases the internal pressure of the battery cell, reduces the reliability of the battery cell, and may even lead to thermal runaway.

[0132] In view of the above problems, the embodiments of this application design the system of the battery cell. The electrolyte includes a chain-like carboxylic acid ester solvent. This solvent system has high conductivity, which is conducive to the rapid migration of lithium ions and improves the fast charging performance of the battery cell. The battery cell is provided with a certain number of tabs to increase the current shunting capacity of the tabs, further improving the fast charging performance of the battery cell. It can also reduce overcurrent resistance and reduce overcurrent temperature rise. The temperature rise within the battery cell system will not be too high, thereby making the electrolyte system more stable, which is conducive to improving the reliability of the battery cell and the cycle performance.

[0133] battery cell

[0134] In one aspect, this application proposes a battery cell.

[0135] As shown in Figures 1 to 3, the battery cell 7 includes a housing assembly 200, an electrode assembly 10, and an electrolyte. The electrode assembly 10 and the electrolyte are housed within the housing assembly 200, which is provided with electrode terminals. The electrode assembly 10 includes a first electrode 13 and a second electrode 14, as well as a separator 15 located between the first electrode 13 and the second electrode 14. Both the first electrode 13 and the second electrode 14 include a coated portion and a tab. The coated portion is coated with an active material layer, while the tab is not coated with an active material layer. The first electrode 13 and the second electrode 14 have opposite polarities; one of the first electrode 13 and the second electrode 14 is a positive electrode, and the other is a negative electrode. The positive electrode has an active... The material layer includes a positive electrode active material, which includes a lithium phosphate with an olivine structure. The electrode assembly 10 is electrically connected to the electrode terminal via tabs. The coating portion of the first electrode 13 includes a first straight section 131, and the coating portion of the second electrode 14 includes a second straight section 141. The first straight section 131 and the second straight section 141 are stacked along the thickness direction Y of the electrode assembly 10. The ratio of the number of tabs of the first electrode 13 to the number of the first straight sections 131 of the first electrode 13 is 0.5 to 2. The electrolyte includes an organic solvent, which 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%.

[0136] The electrolyte includes the chain carboxylic acid ester solvent of the above-mentioned mass content. This solvent system has high conductivity, which is conducive to the rapid migration of lithium ions and improves the fast charging performance of the battery cell 7.

[0137] In the fast charging system of battery cell 7, the current density of the tab is usually large, which leads to increased heat generation and higher temperature in battery cell 7. This can easily lead to the degradation of active materials and the decomposition of organic solvents in the electrolyte, thus worsening the cycle performance. On the other hand, the positive electrode active material includes lithium phosphate with an olivine structure. This material is structurally stable during charging and discharging and is not prone to capacity decay, which is beneficial to improving the cycle performance of battery cell 7.

[0138] Meanwhile, when the ratio of the number of tabs to the number of the first straight sections 131 of the first electrode 13 is within the above range, the current shunting capacity of the tabs can be increased, which can further improve the fast charging performance of the battery cell 7. However, since the connection area between the tabs and other components such as the coating is relatively large, the overcurrent resistance can be effectively reduced, the overcurrent temperature rise can be reduced, and the internal temperature rise of the battery cell 7 will not be too high, which improves the stability of the electrolyte system and the stability of the active materials, which is conducive to improving the reliability of the battery cell 7 and improving the cycle performance. In addition, there are more connection points between the tabs and the coating, which can increase connection redundancy, such as welding redundancy, and effectively improve the product yield.

[0139] Therefore, the embodiments of this application can improve the cycle performance and fast charging performance of the battery cell 7.

[0140] The housing assembly 200 has a receiving space for accommodating the electrode assembly 10 and the electrolyte. In some embodiments, the housing assembly 200 includes a housing 20, which includes an end cap 22 and a shell 21. The shell 21 has an opening, which is closed by the end cap 22, and electrode terminals are disposed on the end cap 22. The shape of the shell 21 can be determined according to the specific shape of the electrode assembly 10. For example, if the electrode assembly 10 is a cylindrical structure, a cylindrical shell 21 can be selected; if the electrode assembly 10 is a cuboid structure, a cuboid shell 21 can be selected. Optionally, both the electrode assembly 10 and the shell 21 are cuboid structures.

[0141] To more clearly illustrate this application, the tab of the first electrode 13 is defined as the first tab 111, and the coated portion of the first electrode 13 is defined as the first coated portion 130. The tab of the second electrode 14 is defined as the second tab 112, and the coated portion of the second electrode 14 is defined as the second coated portion 140. The electrode terminal with the same electrical charge and electrically connected to the first tab 111 is defined as the first electrode terminal 31, and the electrode terminal with the same electrical charge and electrically connected to the second tab 112 is defined as the second electrode terminal 32.

[0142] The first electrode 13 and the second electrode 14 have opposite polarities. When the first electrode 13 is the positive electrode, the second electrode 14 is the negative electrode, the first electrode terminal 31 is the positive terminal, and the second electrode terminal 32 is the negative terminal; or when the first electrode 13 is the negative electrode, the second electrode 14 is the positive electrode, the first electrode terminal 31 is the negative terminal, and the second electrode terminal 32 is the positive terminal.

[0143] The coating portion in the positive electrode sheet corresponds to the positive electrode coating portion, the tab corresponds to the positive electrode tab, and the active material layer corresponds to the positive electrode film layer containing positive electrode active material. The positive electrode coating portion includes a positive electrode current collector and a positive electrode film layer disposed on at least one side of the positive electrode current collector. When the positive electrode coating portion includes a positive electrode straight section, the positive electrode straight section includes a positive electrode current collector and a positive electrode film layer disposed on at least one side of the positive electrode current collector.

[0144] The coating portion in the negative electrode sheet corresponds to the negative electrode coating portion, the tab corresponds to the negative electrode tab, and 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 and a negative electrode film layer disposed on at least one side of the negative electrode current collector. When the negative electrode coating portion includes a negative electrode straight section, the negative electrode straight section includes a negative electrode current collector and a negative electrode film layer disposed on at least one side of the negative electrode current collector.

[0145] In this embodiment, the first tab 111 is electrically connected to the first straight section 131 and the first electrode terminal 31. The ratio of the number of first tabs 111 to the number of first straight sections 131 of the first electrode 13 is 0.5 to 2, for example, 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 any two of the above values. When the ratio of the number of first tabs 111 to the number of first straight sections 131 of the first electrode 13 is within the above range, the number of first tabs 111 is relatively large, which can improve the current shunting effect, reduce the overcurrent resistance between the first tabs 111 and the first straight section 131, reduce the overcurrent temperature rise, and make the internal temperature rise of the battery cell 7 lower.

[0146] In this embodiment, the electrode assembly 10 includes a second straight section 141, and the second straight section 141 and the first straight section 131 are stacked and arranged alternately along the thickness direction Y of the electrode assembly 10. The second tab 112 is used to electrically connect the second straight section 141 and the second electrode terminal 32. Optionally, the battery cell 7 also includes a separator 15, and the first straight section 131, the separator 15 and the second straight section 141 are stacked alternately.

[0147] In some embodiments, the ratio of the number of second tabs 112 to the number of second straight sections 141 of the second electrode 14 is 0.5 to 2, for example, 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 any range of two of the above values. When the ratio of the number of second tabs 112 to the number of second straight sections 141 of the second electrode 14 is 0.5 to 2, the number of second tabs 112 is relatively large, which can improve the current shunting effect, reduce the overcurrent resistance between the second tabs 112 and the second straight section 141, reduce the overcurrent temperature rise, and make the temperature rise inside the battery cell 7 lower.

[0148] When the number of first tabs 111 and second tabs 112 is the same, the overcurrent density of a single tab is the same, and the performance matching is better, which is conducive to improving the uniformity reaction of the battery cell 7, improving the current shunting effect, and improving the charging and discharging capability of the battery cell 7.

[0149] In some embodiments, the first tab 111 is a positive tab; the first straight section 131 includes a positive active material, which includes a lithium phosphate with an olivine structure, for providing lithium ions. The relatively large number of positive tabs can improve the current shunting effect, reduce the overcurrent resistance between the first tab 111 and the first straight section 131, reduce the overcurrent temperature rise, and make the temperature rise inside the battery cell 7 lower.

[0150] In some embodiments, the second tab 112 is a negative tab, and the second flat section 141 includes a negative electrode active material, which includes a carbon-based material, for receiving lithium ions from the first flat section 131.

[0151] The electrode assembly 10 can be a wound electrode assembly 10 or a stacked electrode assembly 10.

[0152] In the case where the electrode assembly 10 has a wound structure, structurally, the electrode assembly 10 includes a first electrode 13, a second electrode 14, and a separator 15. The first electrode 13, the second electrode 14, and the separator 15 are all integral structures, disposed between the first electrode 13 and the second electrode 14. The first electrode 13, the separator 15, and the second electrode 14 are wound in one direction to form the electrode assembly 10. The first electrode 13 includes a first coating portion 130 and a plurality of first tabs 111. The second electrode 14 includes a second coating portion 140 and a plurality of second tabs 112.

[0153] After the electrode assembly 10 is formed by winding, the first coating portion 130 of the first electrode 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 segments 131. During the winding process of the electrode assembly 10, the first electrode 13 can form a first straight segment 131 by winding half a turn.

[0154] The second coating portion 140 of the second electrode 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 segments 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.

[0155] In terms of shape, the electrode assembly 10 includes a flat region, a bent region, and a tab. The flat region includes a first flat segment 131 and a second flat segment 141. The bent region includes a first bent segment 132 and a second bent segment 142.

[0156] When the electrode assembly 10 has a wound structure, the ratio of the number of first tabs 111 of the first electrode 13 to the number of first straight segments 131 of the first electrode 13 can be selected from 0.5 to 1, can be greater than 0.5 and less than 1, and can be further selected from 0.6 to 0.99; it can be further combined with 8% to 75% by mass of chain carboxylic acid ester solvent to improve the cycle performance and fast charging performance of the battery cell 7. For example, when the electrode assembly 10 has a wound structure, the ratio of the number of first tabs 111 of the first electrode 13 to the number of first straight segments 131 of the first electrode 13 is 0.5, 0.55, 0.6, 0.7, 0.8, 0.9, 0.95, 0.99, 1 or any two of the above values.

[0157] Figure 3 shows the case where the ratio of the number of first tabs 111 of the first electrode 13 to the number of first straight segments 131 of the first electrode 13 is 0.5. The first electrode 13 can form two first straight segments 131 by winding it around once. One of the two first straight segments 131 is connected to a first tab 111, which means that there is one first tab 111 on each of 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. This can be converted to each first straight segment 131 having 0.5 first tabs 111.

[0158] Figure 4 shows the case where the ratio of the number of first tabs 111 of the first electrode 13 to the number of first straight segments 131 of the first electrode 13 is 1. The first electrode 13 can form two first straight segments 131 by winding it around once. Each first straight segment 131 is connected to a first tab 111. This can be converted to the case where each first straight segment 131 is provided with a first tab 111.

[0159] Figure 5 shows the case where the ratio of the number of first tabs 111 to the number of first straight segments 131 of the first electrode 13 is greater than 0.5 and less than 1. The first electrode 13 is wound multiple times, and each turn can form two first straight segments 131. At least one turn of the multiple turns can have one first tab 111 on the two first straight segments 131, that is, one first tab 111 is set in one turn; at least another turn of the multiple turns can have two first tabs 111 on the two first straight segments 131, that is, two first tabs 111 are set in one turn; the electrode assembly 10 can be converted to each first straight segment 131 having more than 0.5 and less than 1 first tab 111.

[0160] When the battery cell 7 meets the above conditions, the solvent system has a high conductivity, which is conducive to the rapid migration of lithium ions and can improve the fast charging performance of the battery cell 7. Moreover, the electrolyte system has a good protective effect on the negative electrode active material, which is conducive to improving the cycle performance of the battery cell 7. When the ratio of the number of first tabs 111 to the number of first straight sections 131 is within the above range, it can increase the current shunting capacity of the first tabs 111, which is conducive to the homogenization reaction of the first electrode 13 and the reduction of impedance, which can further improve the fast charging performance of the battery cell 7. It can also increase the connection points between the first tabs 111 and other components, increase welding redundancy, and effectively improve product yield. Since the connection area between the first tabs 111 and other components is relatively large, it can reduce the overcurrent resistance and reduce the overcurrent temperature rise. The temperature rise in the battery cell 7 system will not be too high, thus making the electrolyte system more stable, which is conducive to improving the reliability of the battery cell 7 and improving cycle performance.

[0161] Optionally, the number of first tabs 111 in the first electrode 13 is multiple, and the first tabs 111 are located on at least one side of the first coating portion 130.

[0162] As shown in FIG6, by way of example, a plurality of first tabs 111 may be located on the same side of the first coating portion 130.

[0163] As shown in FIG7, by way of example, a plurality of first tabs 111 may be located on both sides of the first coating portion 130 respectively.

[0164] As shown in Figures 7 and 8, optionally, all the first tabs 111 on the same side of the first coating portion 130 are stacked along the thickness direction Y of the electrode assembly 10. This arrangement facilitates the connection of the stacked first tabs 111 together with other components, such as the first adapter 41 of the battery cell 7.

[0165] 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 being stacked, all the first tabs 111 located on the same side of the first coating portion 130 can be connected to the first adapter 41 as a whole, for example, by welding.

[0166] The setting method of the second electrode 112 can be the same as or similar to that of the first electrode 111, and will not be described in detail here.

[0167] Optionally, the battery cell 7 further includes a second adapter 42, which is connected to the second tab 112. The second adapter 42 is used to electrically connect the second tab 112 and the second electrode terminal 32 of the battery cell 7. All the second tabs 112 located on the same side of the second coating portion 140 can be connected to the second adapter 42 after being stacked, for example, by welding.

[0168] The electrode assembly 10 can be configured as at least one, and optionally at least two, such as two, three, four, etc., with two being optional. At least two electrode assemblies 10 can be stacked along the thickness direction Y of the electrode assembly 10, as shown in Figure 8.

[0169] As shown in Figures 9 to 12, when the electrode assembly 10 has a stacked structure, there can be multiple first electrode plates 13 and multiple second electrode plates 14. Each first electrode plate 13 has a first straight section 131 and a first tab 111. The first straight sections 131 of the multiple first electrode plates 13 and the second straight sections 141 of the multiple second electrode plates 14 are stacked along the thickness direction Y of the electrode assembly 10.

[0170] When the electrode assembly 10 has a stacked structure, from the perspective of its shape, the electrode assembly 10 includes a flat area. Optionally, the electrode assembly 10 may also include a bent area. 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 13 and the second electrode 14 to form the electrode assembly 10. Or when the negative electrode adopts a one-piece structure, the negative electrode is bent multiple times and then stacked with the positive electrode and the separator to form the electrode assembly. The following description will take the example of the electrode assembly 10 only having a flat area.

[0171] Structurally, the electrode assembly 10 includes a first electrode 13, a second electrode 14, and a separator 15. The separator 15 is disposed between the first electrode 13 and the second electrode 14, and the first electrode 13, the separator 15, and the second electrode 14 are stacked.

[0172] There may be multiple first electrode plates 13 and multiple second electrode plates 14. Each first electrode plate 13 includes a first straight section 131 and a first tab 111, with the first tab 111 connected to the first straight section 131. Each second electrode plate 14 includes a second straight section 141 and a second tab 112, with the second tab 112 connected to the second straight section 141. Multiple first straight sections 131 and multiple second straight sections 141 are alternately stacked along the thickness direction Y of the electrode assembly 10.

[0173] When the electrode assembly 10 has a stacked structure, the ratio of the number of first tabs 111 of the first electrode 13 to the number of first straight segments 131 of the first electrode 13 is 1 to 2, preferably greater than 1 and less than or equal to 2; combined with a chain carboxylic acid ester solvent with a mass content of 8% to 75%, the performance of the battery cell 7 can be effectively improved. For example, when the electrode assembly 10 has a stacked structure, the ratio of the number of first tabs 111 of the first electrode 13 to the number of first straight segments 131 of the first electrode 13 is 1, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2, or any combination of two of the above values.

[0174] When the ratio of the number of first tabs 111 to the number of first straight segments 131 of the first electrode 13 is 1, it means that the first tabs 111 and the first straight segments 131 are arranged in a one-to-one correspondence, which can be converted into one first tab 111 being provided on each first straight segment 131. Figure 10 shows a schematic diagram of the structure in which one first tab 111 is provided on each first straight segment 131.

[0175] When the ratio of the number of first tabs 111 of the first electrode 13 to the number of first straight segments 131 of the first electrode 13 is 2, it can be converted to two first tabs 111 being provided on each first straight segment 131. In this case, one first tab 111 can be provided on each side of the first straight segment 131. Figure 11 shows a schematic diagram of the structure in which two first tabs 111 are provided on each first straight segment 131.

[0176] The ratio of the number of first tabs 111 on the first electrode 13 to the number of first straight segments 131 on the first electrode 13 can be selected to be greater than 1 and less than or equal to 2. This can be converted to each first straight segment 131 having more than 1 and less than or equal to 2 first tabs 111. For example, the electrode assembly 10 includes two first electrodes 13, one of which has one first tab 111 and the other has two first tabs 111, which can be converted to each first electrode 13 having 1.5 first tabs 111.

[0177] When the battery cell 7 meets the above conditions, the solvent system has a high conductivity, which is conducive to the rapid migration of lithium ions and can improve the fast charging performance of the battery cell 7. Moreover, the electrolyte system has a good protective effect on the negative electrode active material, which is conducive to improving the cycle performance of the battery cell 7. The number of first tabs 111 is relatively large, which can increase the current shunting capacity of the first tabs 111, making the current shunting within the first straight section 131 uniform, which can further improve the fast charging performance of the battery cell 7. It can also increase the connection points between the first tabs 111 and other components, increase welding redundancy, and effectively improve product yield. Since the connection area between the first tabs 111 and other components is relatively large, it can reduce the overcurrent resistance and reduce the overcurrent temperature rise. The temperature rise within the battery cell 7 system will not be too high, thus making the electrolyte system more stable, which is conducive to improving the reliability of the battery cell 7 and improving cycle performance.

[0178] Optionally, when the ratio of the number of first tabs 111 of the first electrode 13 to the number of first straight sections 131 of the first electrode 13 is greater than 1, after conversion, more than one first tab 111 is provided on average on the first straight section 131. More than one first tab 111 can be respectively provided on both sides of the first straight section 131. In this case, more than one first tab 111 can share the current density of a single first electrode 13. Especially when the area of ​​the first electrode 13 is relatively large, the current distribution inside the first electrode 13 is more uniform, which is conducive to homogenization of the reaction and reduction of impedance.

[0179] Optionally, when the ratio of the number of first tabs 111 of the first electrode 13 to the number of first straight sections 131 of the first electrode 13 is greater than 1, after conversion, if more than one first tab 111 is provided on average on the first straight section 131, the more than one first tab 111 can be provided on the same side of the first straight section 131. In this case, welding redundancy can be increased and product yield can be effectively improved.

[0180] The setting method of the second electrode tab 112 can be the same as or similar to that of the first electrode tab 111, and will not be described in detail here. For example, the ratio of the number of second electrode tabs 112 to the number of second straight segments 141 of the second electrode plate 14 is 1 to 2, and can be greater than 1 and less than or equal to 2.

[0181] When the electrode assembly 10 has a stacked structure, with the same number of first tabs 111 and second tabs 112, the overcurrent density of a single tab is the same, resulting in better performance matching. This is beneficial for improving the uniformity of the battery cell 7, enhancing the current shunting effect, and improving the charge and discharge capability of the battery cell 7.

[0182] Regardless of whether the electrode assembly 10 has a wound structure or a stacked structure, the first tab 111 is connected to at least one side of the first coating portion 130.

[0183] As shown in Figures 13 and 14, in some embodiments, the first tab 111 includes a tab body 1111 and a plurality of tab protrusions 1112. The plurality of tab protrusions 1112 are all connected to the side of the tab body 1111 facing away from the first coating portion 130, and there is a gap between adjacent tab protrusions 1112. Of course, the first tab 111 may also consist only of the tab body 1111. Figure 13 shows a schematic diagram of the unfolded first electrode 13 in the wound electrode assembly 10.

[0184] The arrangement of multiple tab protrusions 1112 allows the first tab 111 to have multiple connection points. For example, when connecting the first tab 111 to the first adapter 41, the multiple tab protrusions 1112 can be connected to different positions of the first adapter 41, such as by welding. This increases the number of welding positions between the first tab 111 and the first adapter 41, improves the welding yield, and enhances the stability of the connection between the two.

[0185] The structure of the second electrode 112 can be the same as or similar to that of the first electrode 111, and will not be described in detail here.

[0186] In some embodiments, the first tab 111 is a positive tab, and the thickness of the positive tab is 10 μm to 20 μm, optionally 10 μm to 15 μm. Exemplarily, the thickness of the positive tab 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 of any two of the above values. When the thickness of the positive tab is within the above range, the positive tab has excellent current-carrying capacity, which can reduce heat generation and improve the fast-charging performance of the battery cell.

[0187] In some embodiments, the first tab 111 is a negative tab, and the thickness of the negative tab is 4μm to 10μm, optionally 4μm to 6μm. Exemplarily, the thickness of the negative tab is 4μm, 4.5μm, 5μm, 5.5μm, 6μm, 6.5μm, 7μm, 7.5μm, 8μm, 8.5μm, 9μm, 9.5μm, 10μm, or any combination of two of the above values. When the thickness of the negative tab is within the above range, the negative tab has excellent overcurrent capacity, which can reduce heat generation and improve the fast charging performance of the battery cell.

[0188] In the embodiments of this application, the thickness of the tab is as defined in the art, and can be detected by means of equipment and methods known in the art, such as thickness measured by a micrometer.

[0189] [Positive electrode plate]

[0190] The positive electrode includes a positive current collector and a positive electrode film layer disposed on at least one surface of the positive current collector and comprising a positive electrode active material. For example, the positive current collector has two surfaces opposite each other in its own thickness direction, and the positive electrode film layer is disposed on either or both of the two opposite surfaces of the positive current collector.

[0191] In the embodiments of this application, the upper limit voltage for charging and the lower limit voltage for discharging of a single battery cell vary depending on the positive electrode active material. For example, when the phosphate material includes lithium iron phosphate, the upper limit voltage for charging can be 3.65V and the lower limit voltage for discharging can be 2.0V. Another example is when the phosphate material includes lithium manganese iron phosphate, the upper limit voltage for charging can be 4.3V and the lower limit voltage for discharging can be 2.0V.

[0192] The 100% state of charge (SOC) and 0% state of charge (SOC) of a single battery cell are defined as follows:

[0193] The battery cell is charged at a constant current charging rate of 0.33C to the upper limit voltage of the battery, and then charged at a constant voltage to 0.05C, which corresponds to the 100% SOC state of the battery cell; the battery cell is discharged at a constant current discharging rate of 0.33C to the cutoff voltage, which corresponds to the 0% SOC state of the battery cell.

[0194] In some embodiments, the compaction density of the positive electrode film layer is 2.50 g / cm³ when the battery cell is at 100% state of charge (SOC). 3 Up to 2.80 g / cm 3 ; 2.55g / cm³ is optional 3 Up to 2.70 g / cm 3 For example, when the battery cell is at 100% state of charge (SOC), the compaction density of the positive electrode film is 2.50 g / cm³. 3 2.52g / cm3 2.55g / cm 3 2.56 g / cm 3 2.57g / cm 3 2.58g / cm 3 2.60g / cm 3 2.62 g / cm 3 2.65g / cm 3 2.68g / cm 3 2.70 g / cm 3 2.72 g / cm 3 2.75g / cm 3 2.78g / cm 3 2.80g / cm 3 Or a range consisting of any two of the above values.

[0195] When the compaction density of the positive electrode film is within the above range, it is beneficial to improve the energy density of the battery cell; and because the positive electrode active material in the positive electrode film is packed more tightly, the contact resistance between particles is smaller, which can further reduce the resistance of the electrode sheet, thereby reducing heat generation.

[0196] In some embodiments, the single-sided coating weight of the positive electrode film is 200 mg / 1540.25 mm. 2 Up to 370mg / 1540.25mm 2 ; 240mg / 1540.25mm is optional. 2 Up to 330mg / 1540.25mm 2 For example, the single-sided coating weight of the positive electrode film is 200 mg / 1540.25 mm. 2 210mg / 1540.25mm 2 220mg / 1540.25mm 2 230mg / 1540.25mm 2 240mg / 1540.25mm 2 250mg / 1540.25mm 2 260mg / 1540.25mm 2 270mg / 1540.25mm 2 280mg / 1540.25mm 2 290mg / 1540.25mm 2 300mg / 1540.25mm 2 310mg / 1540.25mm 2 320mg / 1540.25mm 2 330mg / 1540.25mm2 340mg / 1540.25mm 2 350mg / 1540.25mm 2 360mg / 1540.25mm 2 370mg / 1540.25mm 2 Or a range consisting of any two of the above values.

[0197] When the single-sided coating weight of the positive electrode film is within the above range, the heat generation per unit area of ​​the positive electrode sheet will not be too large, and the energy density of the battery cell can be improved at the same time.

[0198] In this embodiment, the compaction density of the positive electrode film layer of a single battery cell at 100% State of Charge (SOC) is a well-known concept in the art. This means that the positive electrode sheet is disassembled from the single battery cell at 100% SOC, and the compaction density of the positive electrode film layer is measured. For example, a single-sided coated positive electrode sheet (if double-sided coated, the positive electrode film layer on one side can be wiped off first) is cut into small circular pieces with an area of ​​S1, weighed, and recorded as M1, and its thickness H1 is measured. Then, the positive electrode film layer of the weighed positive electrode sheet is wiped off, the weight of the positive current collector is weighed and recorded as M0, and its thickness H0 is measured. The single-sided coating weight of the positive electrode film = (weight of the positive electrode sheet M1 - weight of the positive current collector M0) / S1, the thickness of the positive electrode film = the thickness of the positive electrode sheet H1 - the thickness of the positive current collector H0, and the compaction density of the positive electrode film = the single-sided coating weight of the positive electrode film / the thickness of the positive electrode film.

[0199] 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 consisting of any two of the above values.

[0200] The powder resistivity of the positive electrode active material is relatively low, which results in relatively low resistance of the positive electrode sheet and less heat generation in the battery cell.

[0201] In the embodiments of this application, the powder resistivity of the material has a well-known meaning in the art and can be tested using methods and equipment well-known in the art, such as using a PRCD1100 powder resistivity meter according to the test standard GB / T30835-2014.

[0202] In some embodiments, the powder compaction density of the positive electrode active material at 30000N is 2.46 g / cm³. 3 Up to 2.8 g / cm 3 For example, the compacted density of the positive electrode active material at 30000 N is 2.46 g / cm³. 3 2.47 g / cm 3 2.48 g / cm 3 2.49 g / cm 3 2.5g / cm 3 2.51g / cm 3 2.55g / cm 3 2.58g / cm 3 2.60g / cm 3 2.65g / cm 3 2.68g / cm 3 2.70 g / cm 3 2.72 g / cm 3 2.75g / cm 3 2.78g / cm 3 2.80g / cm 3 Or a range consisting of any two of the above values.

[0203] When the powder compaction density of the positive electrode active material at 30000N is within the above range, it can improve the energy density of the battery cell. Furthermore, since the positive electrode active material in the positive electrode film can be stacked more tightly, the contact resistance between particles is smaller, which can further reduce the resistance of the electrode sheet, thereby reducing heat generation.

[0204] In the embodiments of this application, the powder compaction density of the material has a meaning known in the art and can be tested using methods and equipment known in the art, according to the testing standard GB / T24533-2009. For example, a certain amount of positive electrode active material is taken as a sample and added to a UTM7305 electronic pressure testing machine with a bottom area of ​​1.327 cm². 2 In the mold, the pressure is increased to 3000 kg (equivalent to 30000 N), held for 30 s, then depressurized and held for 10 s. The compaction density of the positive electrode active material under a force of 30000 N is then recorded and calculated.

[0205] In some embodiments, the specific charge capacity of the positive electrode active material at a 0.1C rate is 150 mAh / g to 170 mAh / g, optionally 157 mAh / g to 170 mAh / g. Exemplarily, the specific charge capacity of the positive electrode active material at a 0.1C rate is 150 mAh / g, 151 mAh / g, 152 mAh / g, 153 mAh / g, 154 mAh / g, 155 mAh / g, 156 mAh / g, 157 mAh / g, 158 mAh / g, 159 mAh / g, 160 mAh / g, 161 mAh / g, 162 mAh / g, 163 mAh / g, 164 mAh / g, 165 mAh / g, 166 mAh / g, 167 mAh / g, 168 mAh / g, 169 mAh / g, 170 mAh / g, or a range consisting of any two of the above values.

[0206] When the specific capacity of the positive electrode active material at a 0.1C rate is within the above range, the energy density of the battery cell is relatively high.

[0207] In the embodiments of this application, the specific capacity of the active material has a meaning known in the art and can be tested using equipment and methods known in the art. The test methods for the first coulombic efficiency and the first discharge specific capacity in Appendix G of the national standard GB / T 24533-2019 can be adopted. A half-coin cell is assembled with lithium metal as the negative electrode and a sample electrode containing the above-mentioned material as the positive electrode. The half-coin cell is tested on a battery tester or other test equipment with equivalent performance at 23℃±2℃ by charging and discharging at a rate of 0.1C to obtain the coin capacity. The capacity is then divided by the mass of the electrode active material to obtain the charging specific capacity parameter.

[0208] In some embodiments, the mass percentage of olivine-structured lithium phosphate in the positive electrode active material can be greater than or equal to 80% and less than or equal to 100%, and the positive electrode active material of this application can be considered as an olivine-structured lithium phosphate system. When the mass percentage of olivine-structured lithium phosphate is less than 100%, the positive electrode active material may also include commonly used positive electrode active materials, such as, but not limited to, at least one of lithium transition metal oxides and lithium phosphates. Examples of lithium transition metal oxides include, but are not limited to, at least one of lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, and their respective modified compounds. Examples of lithium phosphates include, but are not limited to, at least one of lithium iron phosphate, lithium iron phosphate and carbon composites, lithium manganese phosphate, lithium manganese phosphate and carbon composites, lithium manganese iron phosphate, and lithium manganese iron phosphate and carbon composites.

[0209] Optionally, the lithium phosphate with an olivine structure in the positive electrode active material accounts for 100% by mass.

[0210] In this application, the lithium phosphate with olivine structure can be phosphate particles or a material obtained by coating and modifying them. For example, the lithium phosphate with olivine structure includes phosphate particles and a coating layer. The coating layer is coated on the surface of the phosphate particles and contains one or more elements selected from C, Fe, Ti, Zr, Hf, Ge and Sn.

[0211] Phosphate particles, through surface coating, can improve the conductivity of lithium phosphates with olivine structure, reduce the powder resistivity of the material, facilitate the migration rate of lithium ions, improve the fast charging capability of the battery, and reduce the heat generation of the battery cell.

[0212] In some embodiments, the phosphate particles comprise the general formula Li x1 A y1 Me a M b P 1-c X c Y z The compound contains 0.5 ≤ x1 ≤ 1.3, 0 ≤ y1 ≤ 1.3, and 0.9 ≤ x1 + y1 ≤ 1.3, 0.9 ≤ a ≤ 1.5, 0 ≤ b ≤ 0.5, and 0.9 ≤ a + b ≤ 1.5, 0 ≤ c ≤ 0.5, 3 ≤ z ≤ 5, where A includes one or more of Na, K, and Mg; Me includes one or more of Mn, Fe, Co, and Ni; M includes one or more of B, Mg, Al, Si, P, S, Ca, Sc, Ti, V, Cr, Cu, Zn, Sr, Y, Zr, Nb, Mo, Cd, Sn, Sb, Te, Ba, Ta, W, Yb, La, and Ce; X includes one or more of S, Si, Cl, B, C, and N; and Y includes one or more of O and F. Phosphate particles exhibit excellent cycle stability, which is beneficial for improving the cycle performance of battery cells.

[0213] For example, phosphate particles include one or more of LiFePO4, LiMnPO4, LiNiPO4, and LiCoPO4. During the charging and discharging process, active ions such as Li are de-intercalated and consumed in a single battery cell, resulting in different molar contents of Li in different discharged states. In the examples of positive electrode active materials such as LiFePO4, LiMnPO4, LiNiPO4, and LiCoPO4, the molar contents of Li represent the initial state of the material, i.e., the state before feeding. When the positive electrode active material is applied to the battery system, the molar contents of Li may change after charge-discharge cycles. In the embodiments of this application, the molar contents of oxygen (O) in the examples of positive electrode active materials such as LiFePO4, LiMnPO4, LiNiPO4, and LiCoPO4 are only theoretical values. Lattice oxygen release can cause changes in the molar contents of oxygen (O). In reality, the molar contents of oxygen (O) may fluctuate, and all of the above situations are within the scope of protection of this application.

[0214] In some embodiments, the coating layer includes a general formula Li 3-d Fe 2-d M2 d (PO x2 ) y2 A fast ion conductor, M2 includes one or more elements from Ti, Zr, Hf, Ge and Sn, 0≤d≤1, 0<x2<5, 0<y2<4.

[0215] For example, the fast ion conductor is a material having a NASICON structure, such as one or more of lithium iron phosphate (Li2FeTi(PO4)3), lithium zirconium iron phosphate (Li2FeZr(PO4)3), and lithium iron tin phosphate (Li2FeSn(PO4)3).

[0216] Fast ion conductors with a NASICON structure are materials with ultrafast ion conduction capabilities, possessing abundant three-dimensional lithium-ion diffusion and transport channels. They exhibit advantages such as high ion conduction efficiency and strong structural stability during multiple lithium delithiation and lithium intercalation processes. Coating the surface of phosphate particles with fast ion conductors containing a NASICON structure can significantly improve the lithium-ion transport rate during multiple lithium delithiation / intercalation at the positive electrode, enhance the ionic conductivity of the positive electrode active material, improve the fast charging capability of the battery cell, and further increase the specific capacity and energy density of the corresponding battery cell.

[0217] In some embodiments, the coating layer also includes elemental carbon.

[0218] The carbon element and the fast ion conductor can be layered. For example, the carbon element can be an independent carbon coating layer, and the fast ion conductor can be an independent fast ion conductor layer. The carbon coating layer can be applied to the surface of the phosphate particles, and the fast ion conductor layer can be located on the surface of the carbon coating layer, i.e., the fast ion conductor layer is located on the side of the carbon coating layer away from the phosphate particles. Alternatively, the fast ion conductor layer can be applied to the surface of the phosphate particles, and the carbon coating layer can be located on the surface of the fast ion conductor layer, i.e., the carbon coating layer is located on the side of the fast ion conductor layer away from the phosphate particles. Of course, the carbon element and the fast ion conductor can also be layered together.

[0219] Optionally, the carbon coating layer can be formed by carbonizing an organic carbon source (e.g., glucose, polyethylene glycol, etc.) onto the surface of the fast ion conductor layer. The carbon coating layer can partially or completely cover the fast ion conductor layer. The carbon coating layer can significantly improve the electronic conductivity of phosphate particles, compensating for the poor electronic conductivity of phosphate particles and increasing the energy density of the battery cell.

[0220] Specifically, the carbon coating layer gives the positive electrode active material of this application the following advantages:

[0221] The carbon coating layer in the positive electrode active material of this application provides a suitable channel for electron transport, which can significantly improve the electron conduction rate during multiple lithium delithiation and lithium insertion processes, improve the electronic conductivity of lithium phosphate, improve the charging capacity of the corresponding battery cell, and also improve the energy density.

[0222] The carbon coating layer of the positive electrode active material in this application is porous, which allows the electrolyte to come into full and effective contact with the lithium phosphate, thereby improving the lithium ion transport rate at the phase interface and enhancing the charging capacity of the battery cell.

[0223] Coating the surface of lithium phosphate with a carbon coating layer can not only improve the conductivity of lithium phosphate, but also improve the structural stability of the positive electrode active material. This effectively alleviates the iron dissolution phenomenon of the positive electrode active material during long-term storage and cyclic use of battery cells, thereby improving the cycle life of battery cells.

[0224] The positive electrode active material of this application uses lithium phosphate as a substrate, fully leveraging the advantages of lithium phosphate such as low cost, high reliability, and good cycle stability. Simultaneously, it utilizes coating layers (a fast ion conductor layer and a carbon coating layer) to overcome the drawbacks of poor electronic and ionic conductivity. Battery cells prepared using the positive electrode active material of this application can improve the energy density of battery cells while maintaining excellent cycle performance.

[0225] In this embodiment, the elemental content in the positive electrode active material is defined in a way known in the art and can be detected using equipment and methods known in the art. For example, referring to EPA 6010D-2014, it can be tested by inductively coupled plasma atomic emission spectrometry (ICP-OES, instrument model: Thermo ICAP7400). After discharging the battery cell to 0% state of charge (SOC), the positive electrode sheet is disassembled, cleaned and dried with DMC, and then calcined at high temperature to remove impurities. 0.4g of the positive electrode active material is weighed and 10ml (50% concentration) of aqua regia is added. Then it is placed on a plate at 180°C for 30min. After digestion on the plate, the volume is adjusted to 100mL, and quantitative testing is performed using the standard curve method.

[0226] In some embodiments, the degree of graphitization of the positive electrode active material is 0.15 to 0.32, optionally 0.19 to 0.26. Exemplarily, the degree of graphitization of the positive electrode active material is 0.15, 0.16, 0.17, 0.18, 0.19, 0.20, 0.21, 0.22, 0.23, 0.24, 0.25, 0.26, 0.27, 0.28, 0.29, 0.30, 0.31, 0.32, or a range consisting of any two of the above values.

[0227] When the degree of graphitization of the positive electrode active material is within the above range, it is beneficial to improve the conductivity of the positive electrode active material, reduce the heat generation of the positive electrode sheet, and thus reduce the heat generation of the battery cell.

[0228] In the embodiments of this application, the higher the degree of graphitization of the material, the lower the degree of disorder, and the test can be carried out according to the general rules of X-ray diffraction analysis method JIS / K 0131-1996.

[0229] In some embodiments, the carbon content in the olivine-structured lithium phosphate is 1% to 2% by mass, and the specific surface area of ​​the olivine-structured lithium phosphate is 5 m². 2 / g to 18m 2 / g.

[0230] Optionally, the carbon content in the olivine-structured lithium phosphate is 1% to 2% by mass, and the specific surface area of ​​the olivine-structured lithium phosphate is 7.5 m². 2 / g to 14m 2 / g.

[0231] For example, the mass content of carbon in the lithium phosphate with olivine structure is 1%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2%, or any combination of two of the above values.

[0232] For example, the specific surface area of ​​lithium phosphate with an olivine structure is 5 m². 2 / g、6m 2 / g、7m 2 / g、8m 2 / g、9m 2 / g, 10m 2 / g、11m 2 / g、12m 2 / g、13m 2 / g、14m 2 / g, 15m 2 / g, 16m 2 / g、17m 2 / g、18m 2 / g or a range consisting of any two of the above values.

[0233] Carbon mainly exists in the form of a carbon coating layer. The carbon coating layer is loose and porous, which helps to increase the specific surface area of ​​the material, facilitates effective contact between the electrolyte and phosphate particles, and promotes the transport of lithium ions at the phase interface. In addition, when the mass content of carbon is within the above range, it can significantly improve the conductivity of lithium phosphate with olivine structure, which is beneficial to improving the ionic and electronic conductivity of lithium phosphate with olivine structure, and can improve the rapid charging capability and energy density of battery cells.

[0234] In the embodiments of this application, the specific surface area of ​​the material has a meaning known in the art and can be detected using equipment and methods known in the art. For example, it can be detected according to the testing standard GB / T 19587-2017, using the positive electrode active material as a sample, and the specific surface area is tested using a Tri-Star 3020 specific surface area and pore size analyzer from Micromeritics, USA.

[0235] In some embodiments, the volume distribution particle size of the positive electrode active material satisfies: 1μm≤Dv50≤2μm, 0.4μm≤Dv10≤0.7μm.

[0236] For example, the Dv50 of the positive electrode active material can be 1 μm, 1.1 μm, 1.15 μm, 1.2 μm, 1.25 μm, 1.3 μm, 1.35 μm, 1.4 μm, 1.45 μm, 1.5 μm, 1.55 μm, 1.6 μm, 1.65 μm, 1.7 μm, 1.75 μm, 1.8 μm, 1.85 μm, 1.9 μm, 1.95 μm, 2 μm, or any range of two of the above values.

[0237] For example, the Dv10 of the positive electrode active material can be 0.4 μm, 0.45 μm, 0.5 μm, 0.55 μm, 0.6 μm, 0.65 μm, 0.7 μm, or any combination of two of the above values.

[0238] The positive electrode active material has a relatively small particle size, resulting in a shorter lithium ion insertion / extraction path and less heat generation. Furthermore, the particle size of the positive electrode active material is not too small, so it will not agglomerate during the processing and preparation process, thus ensuring the stable performance of the positive electrode active material.

[0239] In the embodiments of this application, the volume average particle size Dv50 of the material refers to the particle size corresponding to 50% of the volume distribution, and the volume average particle size Dv10 of the material refers to the particle size corresponding to 10% of the volume distribution. They can be detected using equipment and methods known in the art. For example, the positive electrode active material can be used as a sample, and the Dv50 and Dv10 of the particles can be tested using a Mastersizer 2000E laser particle size analyzer according to the test standard GB / T 19077-2016.

[0240] When the positive electrode active material includes other materials besides lithium phosphate with olivine structure, the volume distribution particle size of the positive electrode active material refers to the volume distribution particle size of all positive electrode active materials.

[0241] In some embodiments, the olivine-structured lithium phosphate is particulate, comprising secondary particles, which in turn include a plurality of primary particles, the average particle size of which 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 consisting of any two of the above values.

[0242] The average particle size of primary particles is relatively small, the lithium ion insertion / extraction path in the positive electrode active material is shorter, and the heat generation is less.

[0243] In this embodiment, secondary particles refer to aggregated particles formed by the aggregation of two or more primary particles. Primary and secondary particles can be easily distinguished experimentally (e.g., by taking SEM images using a scanning electron microscope). The average particle size of primary particles can be obtained by testing the SEM images. The SEM test parameters can be set as follows: operating voltage (EHT) of 10.00 kV, using an InLens detector, operating distance of 4.6 mm, and magnification of 1000X.

[0244] In some embodiments, the positive electrode film layer further includes one or more of the following: ternary materials, lithium phosphate, lithium hydrogen phosphate, lithium sulfate, lithium sulfite, lithium molybdate, lithium oxalate, lithium titanate, lithium tetraborate, lithium metasilicate, lithium metamanganese oxide, lithium tartrate, lithium trilithium citrate, lithium nickel oxide, and lithium ferrite. These materials can act as lithium replenishing agents, which can replenish lithium ions to the positive electrode film layer, compensate for irreversible lithium ion losses within the system, increase capacity, and thereby improve the energy density of the battery cell.

[0245] Optionally, ternary materials include Li x3 A y3 Ni a3 Co b3 Mn c M3(1-a3-b3-c3)Y3 z3 Wherein, 0 < x3 ≤ 2.1, 0 < y3 ≤ 2.1, and 0.9 ≤ x3 + y3 ≤ 2.1, 0 ≤ a3 ≤ 1, 0 ≤ b3 ≤ 1, 0 ≤ c3 ≤ 1, and 0.1 ≤ a3 + b3 + c3 ≤ 1, 1.8 ≤ z3 ≤ 3.5, A includes one or more of Na, K, and Mg, M3 includes one or more of B, Mg, Al, Si, P, S, Ca, Sc, Ti, V, Cr, Fe, Cu, Zn, Sr, Y, Zr, Nb, Mo, Cd, Sn, Sb, Te, Ba, Ta, W, Yb, La, and Ce, and Y3 includes one or more of O and F.

[0246] For example, ternary materials include LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2(NCM333), LiNi 0.5 Co 0.2 Mn 0.3 O2(NCM523), LiNi 0.6 Co 0.2 Mn 0.2 O2(NCM622), LiNi 0.8 Co 0.1 Mn 0.1 O2(NCM811), LiNi 0.80 Co 0.15 Al 0.05 At least one of O2.

[0247] In some embodiments, the lithium replenishing agent has a mass content of 0.5% to 5% in the positive electrode film, for example, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, or any combination of two of the above values. When the mass content of the lithium replenishing agent is within the above range, it can replenish lithium ions to the positive electrode film, compensate for irreversible lithium ion loss in the system, increase capacity, and thereby increase the energy density of the battery cell.

[0248] The lithium replenishing agent can be located in the same layer as the positive electrode active material or in a different layer. When the lithium replenishing agent and the positive electrode active material are in different layers, the lithium replenishing agent can be located in the lithium replenishing layer, and the positive electrode active material can be located in the positive electrode active material layer. In other words, the positive electrode film layer includes a lithium replenishing layer and a positive electrode active material layer. The positive electrode active material layer can be disposed on at least one side of the positive electrode current collector, and the lithium replenishing layer can be located between the positive electrode active material layer and the positive electrode current collector. Alternatively, the lithium replenishing layer can be disposed on at least one side of the positive electrode current collector, and the positive electrode active material layer can be located between the lithium replenishing layer and the positive electrode current collector. Optionally, the lithium replenishing layer can be located between the positive electrode active material layer and the positive electrode current collector. During the cycle charging and discharging of the battery cell, the lithium replenishing agent in the lithium replenishing layer can be gradually released into the system to compensate for the lithium loss of the battery system.

[0249] In some embodiments, the positive electrode film layer may optionally include a positive electrode conductive agent. This application does not impose particular limitations on the type of positive electrode conductive agent. As an example, the positive electrode conductive agent includes at least one selected from superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. In some embodiments, the mass content of the positive electrode conductive agent is ≤5% based on the mass of the positive electrode film layer.

[0250] In some embodiments, the positive electrode film layer may optionally include a positive electrode binder. This application does not impose particular limitations on the type of positive electrode binder. As an example, the positive electrode binder may include at least one selected from polyvinylidene fluoride, polytetrafluoroethylene, a terpolymer of vinylidene fluoride-tetrafluoroethylene-propylene, a terpolymer of vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene, a tetrafluoroethylene-hexafluoropropylene copolymer, polyacrylic acid, and fluorinated acrylate resins. In some embodiments, the mass content of the positive electrode binder is ≤5% based on the mass of the positive electrode film layer.

[0251] In some embodiments, the positive current collector may be a metal foil or a composite current collector. Examples of metal foils include at least one foil selected from aluminum, aluminum alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys. A composite current collector may include a polymer base material and a metal material layer formed on at least one surface of the polymer base material. As an example, the metal material layer may include at least one selected from aluminum, aluminum alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys. As an example, the polymer base material may include at least one selected from polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0252] In some embodiments, the ratio of the thickness of the positive current collector to the thickness of the positive electrode film on one side is 0.05 to 0.3. For example, the ratio of the thickness of the positive current collector to the thickness of the positive electrode film on one side is 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, 0.12, 0.15, 0.18, 0.2, 0.22, 0.25, 0.28, 0.3, or a range consisting of any two of the above values.

[0253] When the ratio of the thickness of the positive current collector to the thickness of the positive electrode film layer on one side is within the above range, the fast charging capability and energy density of the battery cell can be improved.

[0254] In some embodiments, the thickness of the positive current collector is 10 μm to 20 μm, 10 μm to 15 μm, or 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 consisting of any two of the above values.

[0255] When the thickness of the positive electrode current collector is within the above range, the current carrying capacity of the positive electrode current collector is excellent, and it can enable the battery cell to have a high energy density.

[0256] In the embodiments of this application, the thickness of the positive electrode film layer and the positive electrode current collector are known in the art and can be detected using equipment and methods known in the art. For example, the thickness of the positive electrode sheet can be measured with a micrometer, the film layer on the surface of the positive electrode current collector can be removed, and the thickness of the positive electrode current collector can be measured with a micrometer. When the positive electrode film layer is coated on one side, the thickness of the positive electrode film layer is the thickness of the positive electrode sheet minus the thickness of the positive electrode current collector. When the positive electrode film layer is coated on both sides, the thickness of the positive electrode film layer is (the thickness of the positive electrode sheet minus the thickness of the positive electrode current collector) / 2.

[0257] The positive electrode film is typically formed by coating a positive electrode slurry onto the positive electrode current collector, followed by drying and cold pressing. The positive electrode slurry is usually formed by dispersing the positive electrode active material, optional conductive agent, optional binder, and any other components in a solvent and stirring until homogeneous. The solvent can be N-methylpyrrolidone (NMP), but is not limited to it.

[0258] The positive electrode sheet does not exclude other additional functional layers besides the positive electrode film layer. For example, in some embodiments, the positive electrode sheet of the present application further includes a positive electrode conductive layer sandwiched between the positive electrode current collector and the positive electrode film layer and disposed on the surface of the positive electrode current collector. In other embodiments, the positive electrode sheet of the present application further includes a protective layer covering the surface of the positive electrode film layer.

[0259] In some embodiments, the positive electrode further includes a positive conductive layer located between the positive electrode film and the positive current collector. The positive conductive layer can further improve the conductivity of the positive electrode and reduce the heat generation of the positive electrode, thereby reducing the heat generation of the battery cell.

[0260] In some embodiments, the thickness of the positive electrode conductive layer is from 0.5 μm to 2 μm. For example, 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 any combination of two of the above values.

[0261] When the thickness of the positive electrode conductive layer is within the above range, the conductivity of the positive electrode sheet can be further improved, the heat generation of the positive electrode sheet can be reduced, thereby reducing the heat generation of the battery cell, and the energy density of the battery cell can also be improved.

[0262] In the embodiments of this application, the thickness of the positive electrode conductive layer has a meaning known in the art and can be detected using equipment and methods known in the art, such as performing a tomographic scan on the positive electrode sheet to directly measure the thickness of the positive electrode conductive layer.

[0263] In some embodiments, the positive conductive layer includes one or more of a positive conductive agent and a positive binder.

[0264] Optionally, the mass content of the positive electrode conductive agent in the positive electrode conductive layer is 30% to 50%. For example, the mass content of the positive electrode conductive agent is 30%, 35%, 40%, 45%, 50%, or any combination of two of the above values.

[0265] For example, the positive electrode conductive agent includes one or more of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. The positive electrode conductive agent in the positive electrode conductive layer can improve the conductivity of the positive electrode conductive layer, thereby improving the conductivity of the positive electrode sheet and reducing the heat generation of the battery cell.

[0266] Optionally, the positive electrode binder has a mass content of 50% to 70% in the positive electrode conductive layer. For example, 50%, 60%, 65%, 70%, or any combination of two of the above values.

[0267] For example, the positive electrode binder includes one or more of polyvinylidene fluoride, polytetrafluoroethylene, a terpolymer of vinylidene fluoride-tetrafluoroethylene-propylene, a terpolymer of vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene, a tetrafluoroethylene-hexafluoropropylene copolymer, polyacrylic acid, and fluorinated acrylate resins. The positive electrode binder in the positive electrode conductive layer can improve the adhesion between the positive electrode current collector and the positive electrode film layer, thereby enhancing the structural stability of the positive electrode sheet.

[0268] [Negative electrode plate]

[0269] The negative electrode sheet includes a negative current collector and a negative electrode film layer disposed on at least one surface of the negative current collector and comprising a negative electrode active material. For example, the negative current collector has two surfaces opposite to each other in its own thickness direction, and the negative electrode film layer is disposed on either or both of the two opposite surfaces of the negative current collector.

[0270] In some embodiments, the compaction density of the negative electrode film layer is 1.15 g / cm³ when the battery cell is 100% charged. 3 Up to 1.36 g / cm 3 ; 1.25g / cm³ is optional 3 Up to 1.36 g / cm 3 For example, the compaction density of the negative electrode film layer of a single battery cell at 100% charge is 1.15 g / cm³. 3 1.18 g / cm 3 1.20g / cm 3 1.22g / cm 3 1.25g / cm 3 1.28g / cm 3 1.3g / cm 3 1.32g / cm 3 1.35g / cm 3 1.36 g / cm 3 Or a range consisting of any two of the above values.

[0271] When the compaction density of the negative electrode film is within the above range, it is beneficial to improve the energy density of the battery cell; and because the negative electrode active material in the negative electrode film is packed more tightly, the contact resistance between particles is smaller, which can further reduce the resistance of the electrode sheet, thereby reducing heat generation.

[0272] In the embodiments of this application, the compaction density of the negative electrode film layer of a single battery cell under 100% charge state has a well-known meaning in the art and can be detected using well-known equipment and methods in the art. The detection method is as described above for the compaction density test method of the positive electrode film layer.

[0273] In some embodiments, the single-sided coating weight of the negative electrode film is 90 mg / 1540.25 mm. 2 Up to 170mg / 1540.25mm 2 The option is 110mg / 1540.25mm. 2 Up to 150mg / 1540.25mm 2 For example, the single-sided coating weight of the negative electrode film is 90 mg / 1540.25 mm. 2 92mg / 1540.25mm 2 95mg / 1540.25mm 2 96mg / 1540.25mm 2 100mg / 1540.25mm 2 102mg / 1540.25mm 2 104mg / 1540.25mm 2 105mg / 1540.25mm 2 108mg / 1540.25mm 2 110mg / 1540.25mm 2 112mg / 1540.25mm 2 114mg / 1540.25mm 2 115mg / 1540.25mm 2 116mg / 1540.25mm 2 118mg / 1540.25mm 2 120mg / 1540.25mm 2 122mg / 1540.25mm 2 125mg / 1540.25mm 2 128mg / 1540.25mm 2 130mg / 1540.25mm 2 132mg / 1540.25mm 2 135mg / 1540.25mm 2 137mg / 1540.25mm 2 140mg / 1540.25mm 2 142mg / 1540.25mm 2145mg / 1540.25mm 2 148mg / 1540.25mm 2 150mg / 1540.25mm 2 152mg / 1540.25mm 2 155mg / 1540.25mm 2 160mg / 1540.25mm 2 165mg / 1540.25mm 2 170mg / 1540.25mm 2 Or a range consisting of any two of the above values.

[0274] When the single-sided coating weight of the negative electrode film is within the above range, the heat generation per unit area of ​​the negative electrode sheet will not be too large, and the energy density of the battery cell can be improved at the same time.

[0275] In the embodiments of this application, the single-sided coating weight of the negative electrode film layer has a meaning known in the art and can be detected using equipment and methods known in the art, such as the single-sided coating weight test method of the film layer described above.

[0276] In some embodiments, the resistivity of the negative electrode active material powder is from 0.005 Ω·cm to 0.043 Ω·cm, optionally 0.04 Ω·cm. Exemplarily, the resistivity of the negative electrode active material powder can be 0.043 Ω·cm, 0.04 Ω·cm, 0.035 Ω·cm, 0.03 Ω·cm, 0.025 Ω·cm, 0.02 Ω·cm, 0.015 Ω·cm, 0.01 Ω·cm, 0.005 Ω·cm, or a range consisting of any two of the above values.

[0277] The powder resistivity of the negative electrode active material is relatively low, which results in relatively low resistance of the negative electrode sheet and less heat generation in the battery cell.

[0278] In the embodiments of this application, the powder resistivity of the negative electrode active material has a well-known meaning in the art and can be detected using equipment and methods well-known in the art, such as the powder resistivity test method for the positive electrode active material described above.

[0279] In some embodiments, the powder compaction density of the negative electrode active material under a pressure of 20,000 N is 1.5 g / cm³. 3 Up to 1.85 g / cm 3 1.55g / cm³ is an optional value. 3 Up to 1.65 g / cm 3 For example, the compacted density of the negative electrode active material powder under a pressure of 20000N is 1.5 g / cm³. 31.55g / cm 3 1.6g / cm 3 1.65g / cm 3 1.7g / cm 3 1.75g / cm 3 1.8g / cm 3 1.85g / cm 3 Or a range consisting of any two of the above values.

[0280] When the powder compaction density of the negative electrode active material at 20000N is within the above range, it can improve the energy density of the battery cell. Furthermore, since the negative electrode active material in the negative electrode film can be stacked more tightly, the contact resistance between particles is smaller, which can further reduce the resistance of the electrode sheet, thereby reducing heat generation.

[0281] In this application, the powder compaction density of the material has a meaning known in the art and can be tested using methods and equipment known in the art, according to the testing standard GB / T24533-2009. As an example, a certain amount of negative electrode active material is taken as a sample and added to a UTM7305 electronic pressure testing machine with a base area of ​​1.327 cm². 2 In the mold, the pressure is increased to 2000 kg (equivalent to 20000 N), held for 30 s, then depressurized and held for 10 s. The compaction density of the negative electrode active material under a force of 20000 N is then recorded and calculated.

[0282] In some embodiments, the specific charge capacity of the negative electrode active material at a 0.1C rate is between 350 mAh / g and 480 mAh / g. Exemplarily, the specific charge capacity of the negative electrode active material at a 0.1C rate is 350 mAh / g, 355 mAh / g, 360 mAh / g, 365 mAh / g, 370 mAh / g, 375 mAh / g, 380 mAh / g, 385 mAh / g, 390 mAh / g, 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 consisting of any two of the above values.

[0283] When the charge 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.

[0284] In the embodiments of this application, the charging capacity of the negative electrode active material at a rate of 0.1C is a well-known concept in the art and can be detected using well-known equipment and methods in the art. The detection method is as described above for the charging capacity test method of the positive electrode active material at a rate of 0.1C.

[0285] In some embodiments, the negative electrode active material includes a carbon-based material, which 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%.

[0286] The positive electrode active material of this application is mainly a lithium phosphate system with an olivine structure, and the negative electrode active material is mainly a carbon-based material system. When used together, the cycle performance of the battery cell is excellent.

[0287] Optionally, the carbon-based material includes graphite particles with a graphitization degree of 92.0% to 94.5%. Exemplarily, the graphitization degree of the graphite particles is 92.0%, 92.5%, 93%, 93.5%, 94%, 94.5%, or a range consisting of any two of the above values.

[0288] When the degree of graphitization of graphite particles is within the above range, the graphite particles have excellent electrical conductivity, which can reduce the heat generation of the negative electrode sheet, reduce the heat generation of the battery cell, and improve the fast charging performance of the battery cell.

[0289] In some embodiments, the graphite particles include artificial graphite and a carbon coating layer. The artificial graphite includes secondary particles, which in turn include multiple primary particles. The carbon coating layer coats the surface of the artificial graphite. The carbon in the carbon coating layer is primarily amorphous carbon, which refers to transitional carbon materials with a very low degree of graphitization and crystallization, exhibiting an approximately amorphous morphology (or lacking a fixed shape and periodic structural regularity). In this application, amorphous carbon refers to the product of carbonization treatment of an organic carbon source.

[0290] Artificial graphite includes secondary particles. There are more migration paths for lithium ions in artificial graphite, and the migration paths in primary particles are shorter, which can improve the migration rate of lithium ions. The carbon coating layer has more end faces and defects, which increases the number of sites where lithium ions can be inserted and extracted, resulting in better conductivity of the carbon coating layer. This can reduce the internal resistance of the negative electrode and reduce the heat generation of the battery cell.

[0291] Optionally, the carbon coating content is 2% to 5% by mass, based on the mass of the graphite particles. For example, the carbon coating content is 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, or any range of two of the above values.

[0292] When the mass content of the carbon coating is within the above range, it can further reduce the internal resistance of the negative electrode and reduce the heat generation of the battery cell.

[0293] In the embodiments of this application, the graphite particles can be prepared using methods known in the art, such as: providing artificial graphite and an organic carbon source, mixing the two, and then carbonizing them to form a carbon coating layer on at least a portion of the surface of the artificial graphite particles.

[0294] Optionally, the organic carbon source includes one or more of coal tar pitch, petroleum asphalt, phenolic resin, and coconut shell. More preferably, the organic carbon source includes petroleum asphalt. Optionally, the softening point of coal tar pitch or petroleum asphalt is below 250°C.

[0295] Optionally, the carbonization temperature is between 700°C and 1800°C. Optionally, the carbonization temperature is between 1000°C and 1300°C. Within a suitable range, the carbonization temperature allows the organic carbon source to be carbonized, forming a coating layer containing amorphous carbon on at least a portion of the surface of the artificial graphite.

[0296] Optionally, the carbonization treatment time is 1 hour to 6 hours.

[0297] In some embodiments, the carbon-based material may further include natural graphite. Specifically, the carbon-based material may include graphite particles, or it may include both graphite particles and natural graphite. Optionally, the carbon-based material is graphite particles.

[0298] In some embodiments, the negative electrode active material may also include a silicon-based material. The introduction of silicon-based materials can increase the capacity of the negative electrode active material and improve the energy density of the battery cell.

[0299] Optionally, based on the mass of the negative electrode active material, the mass content of silicon element in the silicon-based material is 0.3% to 10.0%, optionally 1% to 6%. Exemplarily, the mass content of silicon element in the silicon-based material is 0.3%, 0.5%, 0.8%, 1%, 1.2%, 1.5%, 1.8%, 2%, 2.2%, 2.5%, 2.8%, 3%, 3.2%, 3.5%, 3.8%, 4%, 4.2%, 4.5%, 4.8%, 5%, 5.2%, 5.5%, 5.8%, 6%, 6.2%, 6.5%, 6.8%, 7%, 7.2%, 7.5%, 7.8%, 8%, 8.2%, 8.5%, 8.8%, 9%, 9.2%, 9.5%, 9.8%, 10%, or a range consisting of any two of the above values.

[0300] When the mass content of silicon in silicon-based materials is within the above range, it can improve the capacity of the negative electrode active material, thereby improving the energy density of the battery cell.

[0301] Optionally, the silicon-based material may include at least one of elemental silicon, silicon oxide, silicon-carbon composite, silicon-nitrogen composite, and silicon alloy.

[0302] In some embodiments, the negative electrode active material may include, in addition to the carbon-based materials and optionally silicon-based materials described above, at least one of tin-based materials and lithium titanate. Tin-based materials may include at least one of elemental tin, tin oxides, and tin alloys.

[0303] The qualitative and quantitative analysis of each substance or element in this application can be performed using suitable equipment and methods known to those skilled in the art. Relevant testing methods can be referenced from domestic and international testing standards and enterprise standards. Furthermore, those skilled in the art can adaptively modify certain testing steps / instrument parameters from the perspective of testing accuracy to obtain more accurate results. One testing method can be used for qualitative or quantitative analysis, or several testing methods can be used in combination for qualitative or quantitative determination.

[0304] For example, this application can combine JIS / K0131-1996 General Rules for X-ray Diffraction Analysis to perform X-ray powder diffraction tests and qualitative analysis on negative electrode sheets or negative electrode active materials.

[0305] Artificial graphite and natural graphite can be distinguished by SEM cross-sectional images taken by scanning electron microscope (SEM). Natural graphite has gaps between the sheet-like structures in its SEM cross-section, while artificial graphite has a dense structure with no obvious gaps. Alternatively, they can be distinguished by XRD patterns obtained by X-ray diffraction. Natural graphite has obvious 2H and 3R phases in its XRD pattern, while artificial graphite only has the 2H phase in its XRD pattern.

[0306] In the embodiments of this application, the negative electrode film layer includes at least one film layer, which can be a single film layer or at least two film layers. Optionally, the negative electrode film layer includes at least two film layers.

[0307] When a single-layer negative electrode film is used, the negative electrode active material in the negative electrode film includes a carbon-based material, and optionally also includes a silicon-based material. When a single-layer film is used, the volume average particle size Dv50 of the negative electrode active material is from 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 a range consisting of any two of the above values.

[0308] When the negative electrode film layer comprises at least two film layers, the negative electrode active material in the negative electrode film layer includes a carbon-based material, and optionally also includes a silicon-based material. The silicon-based material may be located in one of the at least two film layers, or in at least two of the at least two film layers. The negative electrode film layer may include two film layers, three film layers, four film layers, or even more film layers.

[0309] 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 away from the negative electrode current collector. The carbon-based material in the second negative electrode film layer also includes graphite particles. The graphite particles in the first negative electrode film layer and the graphite particles in the second negative electrode film layer may be the same or different.

[0310] The interface between the first negative electrode film and the second negative electrode film can be regular or irregular, and can optionally be irregular.

[0311] Optionally, the carbon-based material in the first negative electrode film layer may also include natural graphite.

[0312] The negative electrode film consists of at least two layers, and layered coating is beneficial for improving the fast charging performance of the battery cell. In particular, when there are differences between the first and second negative electrode films, it can create porosity differences in the negative electrode films, reduce the tortuosity of lithium-ion transport, and improve the fast charging performance of the battery cell.

[0313] Optionally, the volume average particle size Dv50 of the negative electrode active material in the first negative electrode film layer is greater than or equal to the volume average particle size Dv50 of the negative electrode active material in the second negative electrode film layer. More preferably, the volume average particle size Dv50 of the negative electrode active material in the first negative electrode film layer is greater than the volume average particle size Dv50 of the negative electrode active material in the second negative electrode film layer, which is beneficial for increasing the compaction density of the negative electrode film layer. When the negative electrode active material includes graphite particles, the volume average particle size Dv50 of the graphite particles in the first negative electrode film layer is greater than or equal to the volume average particle size Dv50 of the graphite particles in the second negative electrode film layer.

[0314] The difference in particle size between the first and second negative electrode layers can improve the fast charging performance of the battery cell. Specifically, during fast charging, the overpotential of the second negative electrode layer is usually higher, and the bottleneck of fast charging is mainly in the second negative electrode layer. However, in the embodiments of this application, the particle size of the second negative electrode layer is relatively small, which can shorten the solid-phase transport path of lithium ions, improve fast charging performance, and improve the problem of lithium deposition on the surface of the negative electrode sheet.

[0315] Optionally, the negative electrode active material in the first negative electrode film layer is particulate, and its volume average particle size Dv50 is 9.5 μm to 18.5 μm, optionally 9.5 μm to 14.6 μm. Exemplarily, the volume average particle size of the negative electrode active material in the first negative electrode film layer is 9.5 μm, 10 μm, 10.5 μm, 11 μm, 11.5 μm, 12 μm, 12.5 μm, 13 μm, 13.5 μm, 14 μm, 14.5 μm, 14.6 μm, 15 μm, 15.5 μm, 16 μm, 16.5 μm, 17 μm, 17.5 μm, 18 μm, 18.5 μm, or a range consisting of any two of the above values. When the first negative electrode film layer includes graphite particles, the volume average particle size Dv50 of the graphite particles in the first negative electrode film layer is 9.5 μm to 18.5 μm, and can be selected as 9.5 μm to 14.6 μm.

[0316] When the volume average particle size Dv50 of the negative electrode active material in the first negative electrode film layer is within the above range, it can shorten the solid-phase transport path of lithium ions and improve fast charging performance. On the other hand, the material is less prone to agglomeration during the preparation process, which can improve the stability of the material.

[0317] Optionally, the negative electrode active material in the second negative electrode film layer is particulate, and its volume average particle size Dv50 is 7.8 μm to 14.3 μm, optionally 7.8 μm to 11.3 μm. For example, the volume average particle size Dv50 of the negative electrode active material is 7.8 μm, 8.0 μm, 8.2 μm, 8.5 μm, 8.8 μm, 9 μm, 9.2 μm, 9.5 μm, 9.8 μm, 10 μm, 10.2 μm, 10.5 μm, 10.8 μm, 11 μm, 11.3 μm, 11.2 μm, 11.5 μm, 11.8 μm, 12 μm, 12.2 μm, 12.5 μm, 12.8 μm, 13 μm, 13.2 μm, 13.5 μm, 13.8 μm, 14 μm, 14.1 μm, 14.3 μm, or a range of any two of the above values. When the second negative electrode film layer includes graphite particles, the volume average particle size Dv50 of the graphite particles in the second negative electrode film layer is 7.8 μm to 14.3 μm, and can be selected as 7.8 μm to 11.3 μm.

[0318] When the volume average particle size Dv50 of the negative electrode active material in the second negative electrode film is within the above-mentioned range, it can shorten the solid-phase transport path of lithium ions and improve fast charging performance. On the other hand, the material is less prone to agglomeration during the preparation process, which can improve the stability of the material. Furthermore, the combination of the negative electrode active material in the second negative electrode film within the above-mentioned volume average particle size range and the negative electrode active material in the first negative electrode film is conducive to building a gradient porosity difference between the second negative electrode film and the first negative electrode film, reducing the tortuosity of lithium ion transport, and improving the fast charging performance of the battery cell.

[0319] In the embodiments of this application, the volume average particle size Dv50 of the negative electrode active material has a meaning known in the art and can be detected using equipment and methods known in the art, such as the volume average particle size Dv50 test method for positive electrode active materials described above.

[0320] Optionally, the tap density of the carbon-based material in the first negative electrode film layer is less than or equal to the tap density of the carbon-based material in the second negative electrode film layer. Tap density reflects the compactness of the active material within the film layer. When the tap density of the carbon-based material in the second negative electrode film layer is greater than that in the first negative electrode film layer, the second negative electrode film layer is more densely packed, thus increasing the energy density of the battery cell. Conversely, the first negative electrode film layer is relatively sparsely packed with more pores, which improves the fast-charging performance of the battery cell. When the negative electrode active material includes graphite particles, the tap density of the graphite particles in the first negative electrode film layer is less than or equal to that in the second negative electrode film layer.

[0321] Optionally, the tap density of the carbon-based material in the first negative electrode film layer is 0.82 g / cm³. 3 Up to 1.21 g / cm 3 For example, 0.82 g / cm³ 3 0.85g / cm 3 0.88g / cm 3 0.90g / cm 3 0.92g / cm 3 0.95g / cm 3 0.98g / cm 3 1.00g / cm 3 1.05g / cm 3 1.08g / cm 3 1.10 g / cm 3 1.12 g / cm 3 1.15g / cm 3 1.18 g / cm 3 1.20g / cm 3 1.21 g / cm 3 Or it can be a range consisting of any two of the above values. When the tap density of the carbon-based material in the first negative electrode film is within a suitable range, it can improve the fast charging performance of the battery cell.

[0322] Optionally, the tap density of the carbon-based material in the second negative electrode film is 0.90 g / cm³. 3 Up to 1.25 g / cm 3 For example, 0.90 g / cm³ 3 0.92g / cm 30.95g / cm 3 0.98g / cm 3 1.00g / cm 3 1.05g / cm 3 1.08g / cm 3 1.10 g / cm 3 1.12 g / cm 3 1.15g / cm 3 1.18 g / cm 3 1.20g / cm 3 1.21 g / cm 3 1.22g / cm 3 1.23g / cm 3 1.24 g / cm 3 1.25g / cm 3 Or it can be a range consisting of any two of the above values. When the tap density of the carbon-based material in the second negative electrode film is within a suitable range, it can improve the energy density of the battery cell.

[0323] In the embodiments of this application, the tap density of the material has a meaning known in the art and can be determined using instruments and methods known in the art. For example, it can be determined using a powder tap density tester according to GB / T5162-2006. The testing instrument can be Dandong Baite BT-301.

[0324] Optionally, the thickness ratio of the second negative electrode film to the first negative electrode film is 3:7 to 7:3, and optionally 4:6 to 6:4. For example, the thickness ratio of the second negative electrode film to the first negative electrode film is 3:7, 4:6, 5:5, 6:4, 7:3, or any range of two of the above values. By adjusting the thickness ratio of the first and second negative electrode films, the gradient porosity difference between the upper and lower layers can be further increased, reducing the tortuosity of lithium-ion transport and improving the fast charging capability of the battery cell.

[0325] In some implementations, after 10 full-charge cycles during the Beginning of Life (BOL) test, the thickness of the first negative electrode film layer in a single battery cell is between 15 μm and 65 μm, for example, 15 μm, 17 μm, 18 μm, 20 μm, 25 μm, 30 μm, 35 μm, 40 μm, 45 μm, 50 μm, 55 μm, 57 μm, 58 μm, 60 μm, 61 μm, 62 μm, 63 μm, 64 μm, 65 μm, or any combination of two of the above values. When the thickness of the first negative electrode film layer is within the above range, it can increase the gradient porosity difference between the first and second negative electrode film layers, reduce the tortuosity of lithium-ion transport, and improve the fast-charging capability of the battery cell.

[0326] In some implementations, after 10 full-charge cycles during the Beginning of Life (BOL) test, the thickness of the second negative electrode film is between 15 μm and 65 μm, for example, 15 μm, 17 μm, 18 μm, 20 μm, 25 μm, 30 μm, 35 μm, 40 μm, 45 μm, 50 μm, 55 μm, 57 μm, 58 μm, 60 μm, 61 μm, 62 μm, 63 μm, 64 μm, 65 μm, or any combination of two of the above values. When the thickness of the second negative electrode film is within the above range, the gradient porosity difference between the first and second negative electrode films can be increased, reducing lithium-ion transport tortuosity and improving the fast-charging capability of the battery cell.

[0327] In the embodiments of this application, for example, a battery charging upper limit voltage of 3.65V and a battery discharging cutoff voltage of 2.0V will be used for explanation.

[0328] The BOL full charge test procedure is as follows: At 25℃, charge the battery to 3.65V at a charging rate of 0.33C (the nominal capacity), then charge it to 0.05C at a constant voltage of 3.65V, let it rest for 10 minutes, then discharge it to 2.0V at a discharging rate of 0.33C, let it rest for 10 minutes. One charge-discharge cycle constitutes one cycle; complete 10 cycles. Then charge the battery to 3.65V again at a charging rate of 0.33C (the nominal capacity), and then charge it to 0.05C at a constant voltage of 3.65V. With the BOL fully charged, the negative electrode sheet is disassembled. A tomographic scanning electron microscope is used to observe the cross-section of the thickness direction in the middle region of the negative electrode sheet. The two regions are distinguished according to the interface between the first negative electrode film layer and the second negative electrode film layer. The thickness of each is measured separately. For example, the thickness of the first negative electrode film layer is measured at 10 locations, and the average value is calculated as the average value of the first negative electrode film layer. The thickness of the second negative electrode film layer is measured at 10 locations, and the average value is calculated as the average value of the second negative electrode film layer.

[0329] In some embodiments, after a full-charge test at the end of life (EOL) of the battery cell, the thickness of the first negative electrode film is between 15 μm and 70 μm, for example, 15 μm, 16 μm, 17 μm, 18 μm, 19 μm, 20 μm, 21 μm, 22 μm, 23 μm, 24 μm, 25 μm, 26 μm, 27 μm, 28 μm, 29 μm, 30 μm, 35 μm, 40 μm, 43 μm, 45 μm, 50 μm, 55 μm, 60 μm, 65 μm, 66 μm, 67 μm, 68 μm, 69 μm, 70 μm, or any combination of two of the above values. When the thickness of the first negative electrode film is within the above range, the first and second negative electrode films can be modulated to increase the gradient porosity difference between the upper and lower layers, reduce the tortuosity of lithium-ion transport, and improve the fast charging capability of the battery cell.

[0330] In some embodiments, after the battery cell undergoes an end-of-life (EOL) full-charge test, the thickness of the second negative electrode film is between 15 μm and 70 μm, for example, 15 μm, 16 μm, 17 μm, 18 μm, 19 μm, 20 μm, 21 μm, 22 μm, 23 μm, 24 μm, 25 μm, 26 μm, 27 μm, 28 μm, 29 μm, 30 μm, 35 μm, 40 μm, 43 μm, 45 μm, 50 μm, 55 μm, 60 μm, 65 μm, 66 μm, 67 μm, 68 μm, 69 μm, 70 μm, or any combination of two of the above values. When the thickness of the second negative electrode film is within the above range, the first and second negative electrode films can be modulated to increase the gradient porosity difference between the upper and lower layers, reduce the tortuosity of lithium-ion transport, and improve the fast charging capability of the battery cell.

[0331] In the embodiments of this application, for example, a battery charging upper limit voltage of 3.65V and a battery discharging cutoff voltage of 2.0V will be used for explanation.

[0332] The EOL full charge test procedure is as follows: At 60℃, charge the battery to 3.65V at a charging rate of 0.33C (the nominal capacity), then charge it to 0.05C at a constant voltage of 3.65V, let it stand for 10 minutes, then discharge it to 2.0V at a discharging rate of 0.33C, and let it stand for 10 minutes. One charge and discharge cycle is one cycle. The test is stopped when the battery capacity decays to 80% of the nominal capacity. Then, charge at 25°C with a constant current of 0.33C to 3.65V, and then charge at a constant voltage of 0.05C to 3.65V, which is the EOL full charge state. In the EOL full charge state, disassemble the negative electrode plate and use a tomographic scanning electron microscope to observe the cross-section of the thickness direction of the middle region of the negative electrode plate. Distinguish the two regions according to the interface of the first negative electrode film layer and the second negative electrode film layer, and measure the thickness of each. For example, measure the thickness of the first negative electrode film layer at 10 locations and calculate the average value as the average value of the first negative electrode film layer. Measure the thickness of the second negative electrode film layer at 10 locations and calculate the average value as the average value of the second negative electrode film layer.

[0333] In some embodiments, when the negative electrode film layer is a single-layer film (as opposed to the double-layer film layer described above), the negative electrode film layer further includes a lithium-containing binder. Optionally, the mass content of the lithium-containing binder relative to the negative electrode film layer is 0.1% to 1%. Exemplarily, the mass content of the lithium-containing binder relative to the negative electrode film layer is 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, or any combination of two of the above values. The lithium element in the lithium-containing binder can exist in ionic form, which can increase the number of freely moving lithium ions in the negative electrode film layer, shorten the distance for lithium ions to diffuse to the surface of the negative electrode film layer, improve the lithium ion insertion / extraction rate, and improve the fast charging performance of the battery cell. Optionally, the negative electrode film layer may further include a negative electrode binder, such as at least one of styrene-butadiene rubber (SBR), water-soluble unsaturated resin SR-1B, waterborne acrylic resins (e.g., polyacrylic acid PAA, polymethacrylic acid PMAA, sodium polyacrylate PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), and carboxymethyl chitosan (CMCS).

[0334] Optionally, the lithium content in the lithium-containing binder is 3% to 10% by mass. For example, the lithium content in the lithium-containing binder is 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, or any combination of two of the above values. The lithium content is calculated based on the mass of the lithium-containing binder. When the lithium content is within the above range, a relatively large number of freely moving lithium ions can be achieved in the negative electrode film, further shortening the distance that lithium ions diffuse to the surface of the negative electrode film, increasing the lithium ion insertion / extraction rate, and improving the fast-charging performance of the battery cell.

[0335] For example, lithium-containing binders include lithium acrylate-acrylonitrile-acrylamide-hydroxyethyl acrylate copolymers, which are derived from lithium acrylate monomers, acrylonitrile monomers, acrylamide monomers, and hydroxyethyl acrylate monomers, wherein the molar ratio of lithium acrylate monomers, acrylonitrile monomers, acrylamide monomers, and hydroxyethyl acrylate monomers is 30% to 50%: 15% to 45%: 5% to 20%: 20% to 35%. For example, the molar ratio of lithium acrylate monomers, acrylonitrile monomers, acrylamide monomers, and hydroxyethyl acrylate monomers is 35%: 30%: 15%: 20%, or 40%, 20%, 10%, 30%, or 45%, 15%, 20%, 20%, etc.

[0336] The lithium-containing binder of the above-mentioned material can provide a certain number of lithium ions to the negative electrode film layer, improve the fast charging performance of the battery cell, and is not prone to swelling during charging and discharging, with a stable structure, which improves the cycle performance of the negative electrode film layer during fast charging and discharging.

[0337] In other embodiments, where the negative electrode film layer comprises at least two layers, the negative electrode film layer further includes a lithium-containing binder.

[0338] Optionally, the first negative electrode film layer further includes a first lithium-containing binder, and the second negative electrode film layer further includes a second lithium-containing binder, wherein the mass content of the first lithium-containing binder relative to the mass of the first negative electrode film layer is less than or equal to the mass content of the second lithium-containing binder relative to the mass of the second negative electrode film layer. More optionally, the mass content of the first lithium-containing binder relative to the mass of the first negative electrode film layer is less than the mass content of the second lithium-containing binder relative to the mass of the second negative electrode film layer.

[0339] The second lithium-containing binder has a relatively high mass content in the second negative electrode film layer. The second lithium-containing binder provides a relatively larger number of freely movable lithium ions to the second negative electrode film layer, which can further improve the fast charging performance of the battery cell.

[0340] Optionally, the mass content of the first lithium-containing binder relative to the first negative electrode film layer is 0.1% to 1%. For example, the mass content of the first lithium-containing binder relative to the first negative electrode film layer is 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, or any combination of two of the above values. The lithium element in the first lithium-containing binder can exist in ionic form, which can increase the number of freely moving lithium ions in the negative electrode film layer, shorten the distance for lithium ions to diffuse to the surface of the negative electrode film layer, improve the lithium ion insertion / extraction rate, and improve the fast charging performance of the battery cell.

[0341] Optionally, the lithium content in the first lithium-containing binder is 3% to 10% by mass, and optionally 3% to 8%. For example, the lithium content in the first lithium-containing binder is 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, or any combination of two of the above values. When the lithium content is within the above range, a relatively large number of freely moving lithium ions can be achieved in the negative electrode film layer, further shortening the distance that lithium ions diffuse to the surface of the negative electrode film layer, increasing the lithium ion insertion / extraction rate, and improving the fast charging performance of the battery cell.

[0342] For example, the first lithium-containing binder comprises a lithium acrylate-acrylonitrile-acrylamide-hydroxyethyl acrylate copolymer, which is derived from lithium acrylate monomer, acrylonitrile monomer, acrylamide monomer, and hydroxyethyl acrylate monomer, wherein the molar ratio of lithium acrylate monomer, acrylonitrile monomer, acrylamide monomer, and hydroxyethyl acrylate monomer is 30% to 50%: 15% to 45%: 5% to 20%: 20% to 35%. For example, the molar ratio of lithium acrylate monomer, acrylonitrile monomer, acrylamide monomer, and hydroxyethyl acrylate monomer is 35%: 30%: 15%: 20%, or 40%, 20%, 10%, 30%, or 45%, 15%, 20%, 20%, etc.

[0343] The lithium-containing binder of the above-mentioned material can provide a certain number of lithium ions to the negative electrode film layer, improve the fast charging performance of the battery cell, and is not prone to swelling during charging and discharging, with a stable structure, which improves the cycle performance of the negative electrode film layer during fast charging and discharging.

[0344] Optionally, the mass content of the second lithium-containing binder relative to the second negative electrode film layer is 0.1% to 1%. For example, the mass content of the second lithium-containing binder relative to the second negative electrode film layer is 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, or any combination of two of the above values. The lithium element in the second lithium-containing binder can exist in ionic form, which can increase the number of freely moving lithium ions in the negative electrode film layer, shorten the distance for lithium ions to diffuse to the surface of the negative electrode film layer, improve the lithium ion insertion / extraction rate, and improve the fast charging performance of the battery cell.

[0345] The first lithium-containing binder and the second lithium-containing binder can be made of the same material or different materials.

[0346] Optionally, the lithium content in the second lithium-containing binder is 3% to 10% by mass, and optionally 3% to 8%. For example, the lithium content in the second lithium-containing binder is 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, or any combination of two of the above values. When the lithium content is within the above range, a relatively large number of freely moving lithium ions can be achieved in the negative electrode film layer, further shortening the distance that lithium ions diffuse to the surface of the negative electrode film layer, increasing the lithium ion insertion / extraction rate, and improving the fast charging performance of the battery cell.

[0347] For example, the second lithium-containing binder includes a lithium acrylate-acrylonitrile-acrylamide-hydroxyethyl acrylate copolymer, which is derived from lithium acrylate monomer, acrylonitrile monomer, acrylamide monomer, and hydroxyethyl acrylate monomer, wherein the molar ratio of lithium acrylate monomer, acrylonitrile monomer, acrylamide monomer, and hydroxyethyl acrylate monomer is 30% to 50%: 15% to 45%: 5% to 20%: 20% to 35%. For example, the molar ratio of lithium acrylate monomer, acrylonitrile monomer, acrylamide monomer, and hydroxyethyl acrylate monomer is 35%: 30%: 15%: 20%, or 40%, 20%, 10%, 30%, or 45%, 15%, 20%, 20%, etc.

[0348] The lithium-containing binder of the above-mentioned material can provide a certain number of lithium ions to the negative electrode film layer, improve the fast charging performance of the battery cell, and is not prone to swelling during charging and discharging, with a stable structure, which improves the cycle performance of the negative electrode film layer during fast charging and discharging.

[0349] In some embodiments, the first negative electrode film layer further includes a negative electrode binder, and the second negative electrode film layer further includes a negative electrode binder. The negative electrode binder in the first negative electrode film layer and the negative electrode binder in the second negative electrode film layer each independently include at least one of styrene-butadiene rubber (SBR), water-soluble unsaturated resin SR-1B, waterborne acrylic resins (e.g., polyacrylic acid PAA, polymethacrylic acid PMAA, sodium polyacrylate PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), and carboxymethyl chitosan (CMCS).

[0350] 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.

[0351] In some embodiments, the negative electrode film layer may optionally include a negative electrode conductive agent. This application does not impose particular limitations on the type of negative electrode conductive agent. As an example, the negative electrode conductive agent may include at least one selected from superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. In some embodiments, the mass content of the negative electrode conductive agent is ≤5% based on the total weight of the negative electrode film layer.

[0352] In some embodiments, the negative electrode film layer may optionally include a negative electrode binder. In some embodiments, the mass content of the negative electrode binder is ≤5% based on the total weight of the negative electrode film layer.

[0353] In some embodiments, the negative electrode film layer may optionally include other additives. As examples, other additives may include thickeners, dispersants, etc., such as sodium carboxymethyl cellulose (CMC-Na), PTC thermistor materials, etc. In some embodiments, the mass content of other additives is ≤2% based on the total weight of the negative electrode film layer.

[0354] In some embodiments, the negative current collector may be a metal foil or a composite current collector. Examples of metal foils include at least one foil selected from copper, copper alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys. A composite current collector may include a polymer base material and a metal material layer formed on at least one surface of the polymer base material. As an example, the metal material layer may include at least one of copper, copper alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys. As an example, the polymer base material may include at least one of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0355] In some embodiments, the thickness of the negative current collector is 4 μm to 10 μm, optionally 4 μm to 6 μm. Exemplarily, the thickness of the negative current collector is 4 μm, 4.5 μm, 5 μm, 5.5 μm, 6 μm, 10 μm, or any combination of two of the above values.

[0356] When the thickness of the negative electrode current collector is within the above range, the current carrying capacity of the negative electrode current collector is excellent, and it can enable the battery cell to have a high energy density.

[0357] In the embodiments of this application, the thickness of the negative electrode current collector has a meaning known in the art and can be detected using equipment and methods known in the art. For example, the film layer on the surface of the negative electrode current collector can be washed away with a solvent, and the thickness of the negative electrode current collector can be measured with a micrometer.

[0358] The negative electrode film is typically formed by coating a negative electrode slurry onto the negative electrode current collector, followed by drying and cold pressing. The negative electrode slurry is usually formed by dispersing the negative electrode active material, optional conductive agent, optional binder, and other optional additives in a solvent and stirring until homogeneous. The solvent can be N-methylpyrrolidone (NMP) or deionized water, but is not limited to these.

[0359] The negative electrode sheet does not exclude other additional functional layers besides the negative electrode film layer. For example, in some embodiments, the negative electrode sheet of the present application further includes a negative electrode conductive layer sandwiched between the negative electrode current collector and the negative electrode film layer and disposed on the surface of the negative electrode current collector. In other embodiments, the negative electrode sheet of the present application further includes a protective layer covering the surface of the negative electrode film layer.

[0360] In some embodiments, the negative electrode sheet further includes a negative electrode conductive layer, which is located between the negative electrode film layer and the negative electrode current collector. The negative electrode conductive layer can further improve the conductivity of the negative electrode sheet and reduce the heat generation of the negative electrode sheet, thereby reducing the heat generation of the battery cell.

[0361] In some embodiments, the thickness of the negative electrode conductive layer is from 0.5 μm to 2 μm. For example, the thickness of the negative electrode conductive layer can be 0.5 μm, 0.8 μm, 1 μm, 1.2 μm, 1.5 μm, 1.6 μm, 1.8 μm, 2 μm, or any combination of two of the above values.

[0362] When the thickness of the negative electrode conductive layer is within the above range, the conductivity of the negative electrode sheet can be further improved, the heat generation of the negative electrode sheet can be reduced, thereby reducing the heat generation of the battery cell, and the energy density of the battery cell can also be improved.

[0363] In the embodiments of this application, the thickness of the negative electrode conductive layer has a meaning known in the art and can be detected using equipment and methods known in the art, such as the test method for the negative electrode conductive layer described above.

[0364] 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, thereby improving the structural stability of the negative electrode sheet.

[0365] In some embodiments, the negative electrode conductive layer may optionally include other additives. As an example, other additives may include thickeners, such as sodium carboxymethyl cellulose (CMC), PTC thermistor materials, etc.

[0366] Optionally, the mass content of the negative electrode conductive agent in the negative electrode conductive layer is 20% to 40%. For example, the mass content of the negative electrode conductive agent is 20%, 25%, 30%, 35%, 40%, or any combination of two of the above values.

[0367] For example, the negative electrode conductive agent includes one or more of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0368] Optionally, the negative electrode binder has a mass content of 60% to 80% in the negative electrode conductive layer. For example, 60%, 65%, 70%, 75%, 80%, or any range of two of the above values.

[0369] For example, the negative electrode binder includes one or more of styrene-butadiene rubber (SBR), water-soluble unsaturated resin SR-1B, water-based acrylic resin, polyvinyl alcohol, sodium alginate, and carboxymethyl chitosan.

[0370] In some embodiments, the ratio CB of the capacity of the negative electrode film per unit area to the capacity of the positive electrode film per unit area in a single battery cell is from 1.05 to 1.30, and optionally from 1.07 to 1.15. Exemplarily, the ratio CB of the capacity of the negative electrode film per unit area to the capacity of the positive electrode film per unit area in a single battery cell is 1.05, 1.07, 1.1, 1.12, 1.15, 1.18, 1.2, 1.22, 1.25, 1.28, 1.3, or a range of any two of the above values.

[0371] When the ratio CB of the capacity of the negative electrode film per unit area to the capacity of the positive electrode film per unit area in a single battery cell is within the above range, there are sufficient sites in the negative electrode film for lithium insertion, which can reduce the risk of lithium plating and facilitate fast charging.

[0372] In the embodiments of this application, the CB value has a well-known meaning in the art and can be detected using well-known equipment and methods in the art. For example, the capacity of the negative electrode film per unit area and the capacity of the positive electrode film per unit area can be calculated respectively, and the ratio between the two can be calculated to obtain the CB value.

[0373] Specifically, this explanation will be based on an example where the upper limit of battery charging voltage is 3.65V and the battery discharge cutoff voltage is 2.0V.

[0374] The capacity per unit area of ​​the positive electrode film refers to the actual lithium-depleting capacity of the positive electrode active material. The testing method is as follows: The battery is disassembled in a Braun glove box (PRS340 / 11-119-11), the positive electrode sheet is removed, and assembled into a CR2430 model semi-button battery with a positive electrode and lithium sheet. The positive electrode sheet area used is a mm². 2The electrolyte used was a solution of 1 mol / L LiPF6 in EC / EMC / DEC = 3 / 5 / 2 (mass ratio). The assembled semi-coin cells were then left to stand for 3 hours. The test was conducted at 25°C. The cells were first charged at 0.1C in the voltage range of 2.0V to 3.65V to remove lithium, and then discharged at 0.05C to insert lithium to 2.0V. This cycle was repeated twice. The discharge coin capacity of the second cycle was recorded as YmAh. The actual battery design had a positive electrode length of bmm and a width of cmm. The number of surfaces of the positive electrode active material coated on the positive electrode current collector was d. Therefore, the capacity of the positive electrode film per unit area was Y / a*b*c*d.

[0375] Specifically, the capacity per unit area of ​​the negative electrode film refers to the actual lithium intercalation capacity of the negative electrode active material. The testing method is as follows: The battery is disassembled in a PRS340 / 11-119-11 Braun glove box, the negative electrode sheet is removed, and it is assembled into a CR2430 model semi-button battery with a negative electrode and lithium sheet. The area of ​​the negative electrode sheet used is fmm². 2 The electrolyte used was a 1 mol / L LiPF6 solution in EC / EMC / DEC = 3 / 5 / 2 (mass ratio). The assembled semi-coin cells were then left to stand for 3 hours. The test was conducted at 25°C. Lithium insertion was first performed by discharging at 0.1C in the voltage range of 2V-0V, followed by lithium extraction by charging at 0.05C to 2V. This cycle was repeated twice. The discharge capacity of the second cycle was recorded as ZmAh. The actual battery design had a negative electrode length of h mm and a width of i mm. The number of surfaces of the negative electrode active material coated on the negative electrode current collector was d. Therefore, the lithium insertion capacity of the negative electrode was Z / f*h*i*d.

[0376] [Isolation membrane]

[0377] In this embodiment, the separator includes a porous base membrane.

[0378] In some embodiments, the base film includes at least one of glass fiber, nonwoven fabric, and polyolefin. The base film can be a single-layer film or a multi-layer composite film, without particular limitation. When the base film is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0379] Optionally, the polyolefin includes at least one of polyethylene, polypropylene, and polyvinylidene fluoride.

[0380] In some embodiments, the porosity of the base membrane is 20% to 70%, optionally 35% to 60%. Exemplarily, the porosity of the base membrane is 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, or any range of two of the above values.

[0381] When the porosity of the base film in the embodiments of this application is within the above-mentioned range, it can enhance the migration ability of lithium ions in the separator, further reduce the internal resistance of the battery cell, and thus reduce heat generation.

[0382] In this embodiment, porosity refers to the percentage of the volume of the pores in the separator to the total volume of the separator. Porosity can be tested according to the standard GB / T 36363-2018 "Polyolefin Separators for Battery Cells". It should be noted that the actual testing process may differ slightly from the standard due to differences in testing instruments, testing errors, and to minimize the impact on porosity testing, in order to obtain more accurate test values.

[0383] In some embodiments, the thickness of the base film is 6 μm to 12 μm, optionally 6 μm to 9 μm. Exemplarily, the thickness of the base film is 6 μm, 6.5 μm, 7 μm, 7.5 μm, 8 μm, 8.5 μm, 9 μm, 9.5 μm, 10 μm, 10.5 μm, 11 μm, 11.5 μm, 12 μm, or any range of two of the above values.

[0384] When the thickness of the base film is within the above range, the migration path of lithium ions in the base film is shorter, which can further reduce the internal resistance of the battery cell and thus reduce heat generation.

[0385] In this embodiment, the separator can be a base film. Optionally, the separator further includes a functional layer disposed on at least one side of the base film. The functional layer may include inorganic particles to improve the heat resistance of the separator. Optionally, the functional layer is disposed on both sides of the base film.

[0386] In some embodiments, the functional layer includes a first functional layer and a second functional layer. The first functional layer is located on one side of the base film and includes first inorganic particles. The second functional layer is located on the other side of the base film and includes composite particles. The composite particles include second inorganic particles and a plurality of non-fluoropolymer particles. The second inorganic particles are attached to the surface of the non-fluoropolymer particles and / or dispersed inside the non-fluoropolymer particles.

[0387] The first and second functional layers have good heat resistance, which can improve the heat resistance of the separator.

[0388] Optionally, the first functional layer may include an adhesive, optionally including at least one of a fluorinated adhesive or a polyacrylic adhesive, such as polyvinylidene fluoride.

[0389] Optionally, the first inorganic particles include one or more of silicon oxide, aluminum oxide, boehmite, barium sulfate, calcium oxide, titanium oxide, zinc oxide, magnesium oxide, zirconium oxide, and tin oxide. These first inorganic particles can improve the heat resistance of the first functional layer.

[0390] In the embodiments of this application, the thickness of the base film has a meaning known in the art and can be detected using known meanings and equipment. For example, a newly prepared separator can be taken as a sample, or a battery cell that has been completely discharged (discharged to the lower limit cutoff voltage so that the battery's state of charge is about 0% SOC) can be disassembled in reverse, the separator can be obtained from the battery cell, and the separator can be dried and used as a sample. The separator can be cut with an ion beam cutter to form a cross section, and then the thickness of the separator and its various layers can be measured using a scanning electron microscope.

[0391] In the second functional layer, the non-fluorinated polymer particles refer to polymers that are non-fluorinated polymers. For example, non-fluorinated polymer particles include acrylate copolymers. Optionally, acrylate copolymers include acrylate-acrylonitrile-acrylamide-propylene copolymers. Acrylate copolymers have excellent adhesion properties and high adhesion stability to the base film. The molar ratio of each monomer in the copolymer can be arbitrary, for example, a molar ratio of 35%:30%:15%:20%, or 40%, 20%, 10%, 30%, or 45%, 15%, 20%, 20%, etc.

[0392] The second inorganic particle in the composite particles prevents the non-fluoropolymer particles from sticking together due to the high-temperature treatment during granulation. This creates porosity within the composite particles, facilitating lithium-ion transport and enhancing the ion-conductivity of the separator. Furthermore, the second inorganic particle increases the compressive modulus of the composite particles, reducing their deformation during charging and discharging, resulting in a more stable separator structure and improved kinetic performance of the battery cells, as well as faster charging performance. Optionally, compared to the first functional layer, the second functional layer is positioned closer to the negative electrode. Because the composite particles are less prone to deformation, the separator exerts minimal pressure or other side effects on the negative electrode, ensuring stable kinetic performance of the negative electrode. Correspondingly, the first functional layer is positioned closer to the positive electrode.

[0393] Optionally, the second inorganic particles include one or more of silicon oxide, aluminum oxide, boehmite, barium sulfate, calcium oxide, titanium oxide, zinc oxide, magnesium oxide, zirconium oxide, and tin oxide. Optionally, the second inorganic particles include silicon oxide. These second inorganic particles can improve the heat resistance of the second functional layer and can combine with non-fluoropolymers to form composite particles, further improving the cycle stability and kinetic performance of the separator, and improving the cycle performance and fast-charging performance of the battery cells.

[0394] The average particle size of the second inorganic particles is 5 nm to 100 nm, optionally 10 nm to 100 nm, or optionally 5 nm to 20 nm. For example, the average particle size of the second inorganic particles is 5 nm, 10 nm, 15 nm, 20 nm, 25 nm, 30 nm, 35 nm, 40 nm, 45 nm, 50 nm, 55 nm, 60 nm, 65 nm, 70 nm, 75 nm, 80 nm, 85 nm, 90 nm, 95 nm, 100 nm, or any combination of two of the above values. When the average particle size of the second inorganic particles is within the above range, it is beneficial to improve the heat resistance and compressive modulus of the composite particles.

[0395] In the embodiments of this application, the average particle size of the second inorganic particles has a meaning known in the art and can be detected using equipment and methods known in the art. For example, after obtaining the separator membrane and drying it as a sample, the separator membrane is cut with an ion beam cutter to form a cross-section. Subsequently, the particle size of the second inorganic particles in the separator membrane is measured using a scanning electron microscope. The particle size of multiple, for example, 50, second inorganic particles is measured, and their average value is calculated as the average particle size of the second inorganic particles.

[0396] In some embodiments, the ionic conductivity of the separator is from 0.3 mS / cm to 0.6 mS / cm. Exemplarily, the ionic conductivity of the separator is 0.3 mS / cm, 0.35 mS / cm, 0.4 mS / cm, 0.45 mS / cm, 0.5 mS / cm, 0.55 mS / cm, 0.6 mS / cm, or a range consisting of any two of the above values.

[0397] When the ionic conductivity of the separator is within the above range, the lithium-ion migration ability of the separator can be further improved, thereby enhancing the fast charging performance of the battery cell.

[0398] In this application embodiment, the ionic conductivity of the separator has a meaning known in the art and can be detected using equipment and methods known in the art, for example,

[0399] Preparation of the 2025-type button cell for testing: In a vacuum glove box, a lithium sheet was placed in the negative electrode case of the battery, and 150 μL of electrolyte was added. The electrolyte was a solution of 1 mol / L LiPF6 in EC / EMC / DEC = 3 / 5 / 2 (mass ratio). Then, a separator (with an area of ​​3.14 cm²) was placed inside. 2 The electrode (12 μm thick) is tightly attached to the lithium sheet, then 25 μL of electrolyte is added, and finally the positive electrode (which can be the positive electrode from Example 1) is placed on top and sealed. The assembled button battery is removed from the vacuum glove box and left for 24 hours for further testing.

[0400] Test: At an electrochemical workstation, at 10 -1 ~10 6 The isolation film resistance Rb was obtained by testing within a frequency range of Hz, and the ionic conductivity σ (unit: mS / cm) was calculated using the following formula.

[0401] σ=L / (R b ×S)

[0402] Where: R b Let L be the resistance of the isolation membrane, and S be the thickness and area of ​​the isolation membrane under test, respectively.

[0403] Electrolyte

[0404] In some implementations, the battery cell also includes an electrolyte.

[0405] During the charging and discharging process of a single battery cell, active ions such as lithium ions are inserted and extracted back and forth between the positive and negative electrode plates, and the electrolyte plays the role of conducting active ions between the positive and negative electrode plates.

[0406] In this embodiment of the application, the conductivity of the electrolyte at room temperature, such as 25°C, is 10.5 mS / cm to 20 mS / cm, 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 any range of two of the above values.

[0407] 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.

[0408] In the embodiments of this application, the conductivity of the electrolyte at room temperature is the ionic conductivity, which can be detected using equipment and methods known in the art, such as by referring to industry standard HG-T 4067-2015.

[0409] In some embodiments, the viscosity of the electrolyte at room temperature, such as 25°C, is between 2.3 mPa·s and 3.5 mPa·s. Exemplarily, the viscosity of the electrolyte is 2.3 mPa·s, 2.4 mPa·s, 2.5 mPa·s, 2.6 mPa·s, 2.7 mPa·s, 2.8 mPa·s, 2.9 mPa·s, 3.0 mPa·s, 3.1 mPa·s, 3.2 mPa·s, 3.3 mPa·s, 3.4 mPa·s, 3.5 mPa·s, or a range consisting of any two of the above values.

[0410] 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.

[0411] In the embodiments of this application, the viscosity of the electrolyte has a meaning known in the art and can be detected using equipment and methods known in the art, such as in accordance with GB / T10247-2008.

[0412] In some embodiments, the electrolyte has a density of 1.05 g / mL to 1.35 g / mL at room temperature, such as 25°C. Exemplarily, the electrolyte density is 1.05 g / mL, 1.10 g / mL, 1.15 g / mL, 1.2 g / mL, 1.25 g / mL, 1.3 g / mL, 1.35 g / mL, or a range of any two of the above values.

[0413] When the electrolyte density is within the above range, the migration rate of lithium ions in the electrolyte is relatively high, which can further reduce the internal resistance of the battery cell, thereby reducing heat generation and improving the fast charging performance of the battery cell.

[0414] In the embodiments of this application, the density of the electrolyte has a meaning known in the art and can be detected using equipment and methods known in the art, such as referring to GB / T 2013-2010 for testing.

[0415] Electrolytes consist of organic solvents and electrolyte salts. The types of organic solvents and electrolyte salts are not specifically limited and can be selected according to actual needs.

[0416] In some embodiments, the organic solvent includes a chain carboxylic acid ester solvent, wherein the chain carboxylic acid ester solvent comprises, by mass, 8% and 75% of the organic solvent, optionally 10% and 75%, optionally 30% to 70%, or 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 of any two of the above values.

[0417] When the mass content of chain carboxylic acid ester solvents is within the above range, the viscosity of the electrolyte system is relatively low, which is conducive to the migration of lithium ions.

[0418] In some embodiments, the chain carboxylic acid ester solvent includes compounds represented by Formula I.

[0419] In formula I,

[0420] R1 includes a hydrogen atom, a halogen atom, a C1 to C5 alkyl group, or a C1 to C5 haloalkyl group.

[0421] R2 includes C1 to C5 alkyl or C1 to C5 haloalkyl.

[0422] The aforementioned chain-like carboxylic acid ester solvents have high conductivity, which is beneficial for improving the fast charging capability of battery cells.

[0423] Optionally, R1 includes a hydrogen atom, a halogen atom, a C1 to C3 alkyl group, or a C1 to C3 haloalkyl group. Further optionally, R1 includes a hydrogen atom, a halogen atom, a C1 to C2 alkyl group, or a C1 to C2 haloalkyl group.

[0424] Optionally, R2 comprises a C1 to C3 alkyl group or a C1 to C3 haloalkyl group. More optionally, R2 comprises a C1 to C2 alkyl group or a C1 to C2 haloalkyl group.

[0425] In the above embodiments, the halogen atom includes one or more of fluorine, chlorine, bromine and iodine atoms, and optionally, the halogen atom includes fluorine atom.

[0426] In the above embodiments, the halogenated alkyl group includes one or more of fluoroalkyl, chloroalkyl, bromoalkyl and iodoalkyl groups, and optionally, the halogenated alkyl group includes fluoroalkyl.

[0427] For example, the chain carboxylic acid ester solvent includes one or more compounds of formula I-1 to formula I-8.

[0428] In some embodiments, the organic solvent also includes carbonate solvents.

[0429] Optionally, the carbonate solvent includes one or more of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, and methyl ethyl carbonate. More preferably, the carbonate solvent includes one or more of ethylene carbonate, dimethyl carbonate, and methyl ethyl carbonate. The combined use of the above-mentioned carbonate solvents and chain carboxylic acid ester solvents improves the conductivity of the electrolyte at room temperature, which is beneficial for lithium ion migration.

[0430] Further optionally, the carbonate solvent in the organic solvent has a mass content of 25% to 92%, 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 any combination of two of the above values. The carbonate solvent at the above mass content can further improve the conductivity of the electrolyte at room temperature, which is beneficial for lithium ion migration.

[0431] For example, the carbonate solvent includes one or more of ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate, and the carbonate solvent content is 30% to 50% by mass.

[0432] In some embodiments, the electrolyte also contains additives, which may include negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain battery performance, such as additives that improve battery overcharge performance, additives that improve battery high-temperature performance, and additives that improve battery low-temperature power performance.

[0433] In some embodiments, the additive comprises one or more of carbonate additives, sulfur-containing additives, and lithium salt additives, optionally at least two. These additives can improve the interfacial film performance on the positive and / or negative electrode sides, which is beneficial for improving the fast-charging performance of individual battery cells and enhancing cycle performance.

[0434] In some embodiments, the additive has a mass content of 1% to 10% in the electrolyte, optionally 2% to 8%, and more preferably 3.5% to 8%. Exemplarily, the additive has a mass content of 1%, 2%, 3%, 3.5%, 4%, 5%, 6%, 7%, 8%, 9%, 10% in the electrolyte, or a range of any two of the above values.

[0435] The additives mentioned above can effectively improve the interfacial film performance on the positive and / or negative electrode sides, which is beneficial to improving the fast charging performance of battery cells and improving cycle performance.

[0436] For example, carbonate additives include one or more of vinylene carbonate (VC) and fluoroethylene carbonate (FEC).

[0437] For example, sulfur-containing additives include one or more of vinyl sulfate DTD, vinyl disulfate 2-DTD, butenyl sulfite BS, 1,3-propanesulfonate lactone PS, vinyl sulfite ES, and methylene disulfonate MMDS.

[0438] Optionally, the lithium salt additive includes one or more of lithium difluorophosphate (LiPO2F2), lithium difluorooxalate borate (LiDFOB), lithium tetrafluoroborate (LiBF4), and lithium dioxalate borate (LiBOB).

[0439] Optionally, the mass content of vinylene carbonate (VC) in the electrolyte is 0.5% to 9%, and optionally 2% to 6%.

[0440] Optionally, the mass content of fluoroethylene carbonate (FEC) in the electrolyte is 0.1% to 4%, and optionally 0.5% to 3%.

[0441] 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%.

[0442] 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%.

[0443] In some embodiments, the electrolyte salt includes a lithium salt, which includes one or more of fluorosulfonylimide salts and lithium hexafluorophosphate (LiPF6). These lithium salts are readily dissociated, facilitating rapid lithium-ion migration, and the electrolyte system is relatively stable and not easily decomposed, thus improving the cycle performance of the battery cells.

[0444] Optionally, the fluorosulfonyl imide salt includes one or more of lithium bisfluorosulfonyl imide (LiFSI) and lithium bistrifluoromethanesulfonate (LiTFSI).

[0445] Optionally, the lithium salt includes lithium bis(fluorosulfonyl)imide (LiFSI) and lithium hexafluorophosphate (LiPF6), wherein the molar concentration of lithium bis(fluorosulfonyl)imide (LiFSI) is from 0.2 mol / L to 0.5 mol / L, and the molar concentration of lithium hexafluorophosphate (LiPF6) is from 0.5 mol / L to 1.0 mol / L.

[0446] For example, the molar concentration of lithium bis(fluorosulfonyl)imide (LiFSI) is 0.4 mol / L to 0.5 mol / L, and the molar concentration of lithium hexafluorophosphate (LiPF6) is 0.7 mol / L.

[0447] For example, the molar concentration of lithium bis(fluorosulfonyl)imide (LiFSI) is 0.5 mol / L, and the molar concentration of lithium hexafluorophosphate (LiPF6) is 0.5 mol / L.

[0448] For example, the molar concentration of lithium bis(fluorosulfonyl)imide (LiFSI) is 0.2 mol / L, and the molar concentration of lithium hexafluorophosphate (LiPF6) is 0.8 mol / L.

[0449] Optionally, the molar ratio of lithium bis(fluorosulfonyl)imide to lithium hexafluorophosphate (LiPF6) is from 0.2 to 1.0, and optionally from 0.2 to 0.5. Exemplarily, the molar ratio of lithium bis(fluorosulfonyl)imide to lithium hexafluorophosphate (LiPF6) is 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, or a range of any two of the above values.

[0450] In the embodiments of this application, the types and contents of inorganic components / lithium salt concentrations in the electrolyte are well-known in the art and can be detected using well-known equipment and methods. For example, the concentrations of inorganic components / lithium salts in the electrolyte can be qualitatively or quantitatively analyzed by ion chromatography using the standard JY / T020-1996 "General Rules for Ion Chromatography Analysis". In the embodiments of this application, freshly prepared electrolyte can be used as a sample, the free electrolyte of a fresh battery can be used as a sample, or a battery that has been completely discharged (discharged to the lower limit cutoff voltage so that the battery's state of charge is approximately 0% SOC) can be disassembled in reverse, and the free electrolyte obtained from the battery can be used as a sample for detection by ion chromatography analysis.

[0451] In the embodiments of this application, the types and contents of organic components in the electrolyte are defined in the art and can be detected using equipment and methods known in the art. For example, the organic components in the electrolyte can be qualitatively and quantitatively analyzed by gas chromatography using GB / T9722-2006 "General Rules for Gas Chromatography of Chemical Reagents". In the embodiments of this application, freshly prepared electrolyte can be used as a sample, the free electrolyte of a fresh battery can be used as a sample, or a battery that has been completely discharged (discharged to the lower limit cutoff voltage so that the battery's state of charge is approximately 0% SOC) can be disassembled in reverse, and the free electrolyte obtained from the battery can be used as a sample for detection using ion chromatography.

[0452] In this embodiment, after quantitative and qualitative detection of each component in the electrolyte, the components are classified. Chain-like carboxylic acid ester solvents and carbonate solvents (e.g., ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, and methyl ethyl carbonate) are considered as components of the organic solvent. The mass content of each component is calculated with the mass of the organic solvent representing 100%.

[0453] Carbonate additives (such as vinylene carbonate and fluoroethylene carbonate), sulfur-containing additives, and lithium salt additives are used as additives in the electrolyte. The mass content of each component is calculated based on the mass of the electrolyte as 100%.

[0454] In some embodiments, the battery cell satisfies: 2.45 g / Ah ≤ d / A ≤ 3.5 g / Ah, optionally 2.45 g / Ah ≤ d / A ≤ 3.3 g / Ah, where d represents the mass of electrolyte in the battery cell in grams (g), and A represents the rated capacity of the battery cell in Ah. Exemplarily, d / A can be 3.5 g / Ah, 3.3 g / Ah, 3.2 g / Ah, 3.0 g / Ah, 2.8 g / Ah, 2.5 g / Ah, 2.45 g / Ah, or a range of any two of the above values.

[0455] d / A reflects the electrolyte's liquid retention capacity. When d / A is within the above range, the electrolyte can effectively wet the positive and negative electrode plates and improve the migration rate of lithium ions in the liquid phase, which is beneficial to improving the fast charging capability of the battery cell.

[0456] In the embodiments of this application, the d / A ratio of a single battery cell can be understood as the liquid retention coefficient, which can be tested using equipment and methods known in the art. For example, it can be described using GB / T31486-2015 "Electrical Performance Requirements and Test Methods for Power Batteries for Electric Vehicles", taking a battery charging upper limit voltage of 3.65V and a battery discharge cut-off voltage of 2.0V as an example.

[0457] At 25°C, the battery cell is charged to 3.65V at 0.33C, then charged at a constant voltage to 0.05C, and then discharged at a constant current of 0.33C to 2.0V. The discharged capacity A is used as the denominator. The battery cell is weighed as M0. Then, the positive electrode, negative electrode, separator, and electrolyte are disassembled, with the free electrolyte remaining in a bag. All the solid components are placed in a 60°C oven and baked for at least 4 hours (including but not limited to the positive electrode, negative electrode, separator, and other mechanical parts of the disassembled battery cell that contribute to M0). Then, all components of the battery cell are weighed again as M1, with the weight difference between M0 and M1 as the numerator. The liquid retention coefficient is equal to the weight difference d between M0 and M1 divided by the capacity A.

[0458] In some implementations, the positive electrode, separator, and negative electrode can be fabricated into an electrode assembly using a winding process and / or a stacking process.

[0459] As shown in Figure 15, the casing 21 of the battery cell 7 can be a rigid casing, such as a hard plastic casing, an aluminum casing, or a steel casing. The casing 21 of the battery cell 7 can also be a pouch, such as a pouch-type pouch. The material of the pouch can be plastic, such as at least one of polypropylene (PP), polybutylene terephthalate (PBT), and polybutylene succinate (PBS).

[0460] In some embodiments, the base material of the casing 21 includes steel. Steel has high mechanical strength and is not easily deformed, which can improve the reliability of the battery cell 7. In the embodiments of this application, the base material refers to the material with the highest material content in the casing 21.

[0461] When the shell 21 has a cuboid structure, the shell 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 parts 211 are connected between the two second shell parts 212, and the area of ​​the first shell parts 211 is larger than the area of ​​the second shell parts 212.

[0462] In some embodiments, the base material of the casing 21 includes steel. Steel has high mechanical strength, is not easily deformed, and can improve the reliability and cycle performance of the battery cell. In the embodiments of this application, the base material refers to the material with the highest proportion of material in the casing 21.

[0463] Optionally, when the base material of the housing 21 includes steel, the thickness of the housing 21 is 0.1 mm to 0.5 mm, and optionally 0.2 mm to 0.35 mm. For example, 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 any combination of 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 high, which can improve the reliability of the battery cell 7; and the housing 21 occupies less space, with more internal space, which is beneficial to improving the energy density of the battery cell 7.

[0464] In some embodiments, the base material of the housing 21 includes aluminum.

[0465] 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.

[0466] For example, the thickness of the first shell portion 211 is 0.1 mm to 1.0 mm, and optionally 0.3 mm to 0.8 mm. For example, the thickness of the first shell 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 consisting of any two of the above values.

[0467] The thinner thickness of the first shell 211 reduces the space occupied by the shell 21, thereby further increasing the energy density of the battery cell 7.

[0468] For example, the thickness of the second shell portion 212 is 0.1 mm to 1.0 mm, and can be selected as 0.5 mm to 0.8 mm. For example, the thickness of the second shell 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 of any two of the above values.

[0469] The second shell portion 212 is thicker, which can improve the overall mechanical strength of the shell 21 and reduce the risk of deformation of the shell 21.

[0470] In some embodiments, the battery cell 7 further includes a first electrode terminal 31 and a second electrode terminal 32.

[0471] Optionally, the number of first electrode terminals 31 located on the same side of the first coating portion is at least one, and optionally at least two. At least two first electrode terminals 31 can increase the current-carrying capacity of the first electrode terminals 31.

[0472] Further optionally, the overcurrent area of ​​all first electrode terminals 31 on one side is greater than or equal to 150 mm². 2 200mm is optional 2 Up to 1000mm 2 The current-carrying area of ​​all first electrode terminals 31 on one side refers to the sum of the current-carrying areas of all first electrode terminals 31 located on the same side of the first coating portion. The current-carrying area of ​​the first electrode terminal 31 can be understood as the cross-sectional area of ​​the first electrode terminal 31, which is perpendicular to the thickness direction of the end cap 22.

[0473] For example, the current-passing area of ​​the first electrode terminal 31 on one side can be 150 mm². 2 200mm2 210mm 2 250mm 2 280mm 2 300mm 2 320mm 2 350mm 2 380mm 2 400mm 2 450mm 2 500mm 2 550mm 2 600mm 2 650mm 2 700mm 2 750mm 2 800mm 2 850mm 2 900mm 2 950mm 2 1000mm 2 Or a range consisting of any two of the above values.

[0474] Optionally, the number of second electrode terminals 32 located on the same side of the first coating portion is at least one, and optionally at least two. At least two second electrode terminals 32 can increase the current-carrying capacity of the second electrode terminals 32.

[0475] Further optionally, the overcurrent area of ​​all second electrode terminals 32 on one side is greater than or equal to 150 mm². 2 200mm is optional 2 Up to 1000mm 2 The flow area of ​​a single-sided second electrode terminal 32 refers to the sum of the flow areas of all second electrode terminals 32 located on the same side of the second coating portion. The flow area of ​​the second electrode terminal 32 can be understood as the cross-sectional area of ​​the second electrode terminal 32, which is perpendicular to the thickness direction of the end cap 22.

[0476] For example, the current-passing area of ​​the second electrode terminal 32 on one side can be 150 mm². 2 200mm 2 210mm 2 250mm 2 280mm 2 300mm 2 320mm 2 350mm 2 380mm 2 400mm 2 450mm 2 500mm 2 550mm2 600mm 2 650mm 2 700mm 2 750mm 2 800mm 2 850mm 2 900mm 2 950mm 2 1000mm 2 Or a range consisting of any two of the above values.

[0477] As shown in Figure 16, in some embodiments of this application, the battery cell 7 according to the implementation of this application can be assembled into a battery module 6. The number of battery cells 7 contained in the battery module 6 can be one or more, and the specific number can be adjusted according to the application and capacity of the battery module 6.

[0478] If there are multiple battery cells 7, they can be connected in series, parallel, or in a mixed configuration. A mixed configuration means that some battery cells 7 are connected in series while others are connected in parallel. Multiple battery cells 7 can be directly connected in series, parallel, or in a mixed configuration, and then the entire assembly of the multiple battery cells 7 is housed within the housing of the battery module 6. Alternatively, multiple battery cells 7 can first be connected in series, parallel, or in a mixed configuration to form the battery module 6, and then the multiple battery modules 6 can be connected in series, parallel, or in a mixed configuration to form a whole, which is then housed within the housing. Optionally, the battery module 6 may also include a housing with a accommodating space, within which multiple battery cells 7 are housed.

[0479] As shown in Figure 17, in some embodiments, the battery module 6 can also be assembled into a battery 2, and the number of battery modules 6 contained in the battery 2 can be adjusted according to the application and capacity of the battery pack. The battery device described herein can be either a battery module 6 or a battery pack 2.

[0480] The battery pack 2 may include a housing 5 and a plurality of battery modules 6 disposed within the housing 5. The housing 5 includes a first housing portion 5a and a second housing portion 5b, and the housing 5 has a receiving space 5c. The first housing portion 5a is used to cover the second housing portion 5b and form a closed space for accommodating the battery modules 6. The plurality of battery modules 6 can be arranged in the housing 5 in any manner.

[0481] The first housing portion 5a and the second housing portion 5b overlap each other, and together they define a receiving space 5c for accommodating a single battery cell. The second housing portion 5b can be a hollow structure with one open end, and the first housing portion 5a can be a plate-like structure. The first housing portion 5a covers the open side of the second housing portion 5b to form a housing 5 with the receiving space 5c. Alternatively, both the first housing portion 5a and the second housing portion 5b can be hollow structures with one open side, with the open side of the first housing portion 5a covering the open side of the second housing portion 5b to form a housing 5 with the receiving space 5c. Of course, the first housing portion 5a and the second housing portion 5b can be of various shapes, such as cylinders, cuboids, etc.

[0482] To improve the sealing performance after the first housing part 5a and the second housing part 5b are connected, a sealing element, such as sealant or sealing ring, can also be provided between the first housing part 5a and the second housing part 5b.

[0483] Assuming that the first box section 5a covers the top of the second box section 5b, the first box section 5a can also be called the upper box cover, and the second box section 5b can also be called the lower box.

[0484] In some embodiments, during the charging process of the battery pack 2 or any individual battery cell comprising the battery pack 2 from 0% state of charge (SOC) to 100% SOC, the ambient temperature of the external environment in which the battery pack 2 is located is room temperature, for example, 30°C.

[0485] In some embodiments, during the charging process of the battery pack 2 or any individual battery cell comprising the battery pack 2 from 10% state of charge (SOC) to 80% SOC, the ambient temperature of the external environment in which the battery pack 2 is located is 30°C.

[0486] In some embodiments, the charging process of the battery pack 2 or any individual battery cell comprising the battery pack 2 from 10% state of charge to 80% state of charge includes multiple charging steps. The difference between the maximum state of charge of any charging step and the maximum state of charge of its adjacent charging step is less than or equal to 5% state of charge, such as 1% state of charge, 1.5% state of charge, 2% state of charge, 2.5% state of charge, 3% state of charge, 3.5% state of charge, 4% state of charge, 4.5% state of charge, 5% state of charge, or any range of any two of the above values.

[0487] The battery pack 2 or any individual battery cell comprising the battery pack 2 includes multiple charging steps from 10% state of charge to 40% state of charge. For any charging step, the battery can be charged at any rate between 5C and 10C. The charging rate corresponding to each charging step can be any value of 5C, 5.5C, 6C, 6.5C, 7C, 7.5C, 8C, 8.5C, 9C, 9.5C, or 10C, or a value within the range of any two of the above values.

[0488] The charging process from 40% state of charge to 80% state of charge in the battery pack 2 or any individual battery cell comprising the battery pack 2 also includes multiple charging steps. The charging rate of any charging step is less than the charging rate of any charging step from 10% state of charge to 40% state of charge, and the charging rate of the step to 80% state of charge is any value from 2.5C to 5C, for example, it can be 2.7C.

[0489] For example, the charging steps from 10% to 80% for the battery pack 2 or any individual battery cell comprising the battery pack 2 can be performed as follows:

[0490] Charge from 10% SOC to 15% SOC at a constant current of 5.0C.

[0491] Charge from 15% SOC to 20% SOC at a constant current of 5.0C.

[0492] Charge from 20% SOC to 25% SOC at a constant current of 5.0C.

[0493] Charge from 25% SOC to 30% SOC at a constant current of 5.0C.

[0494] Charge from 30% SOC to 35% SOC at a constant current of 5.0C.

[0495] Charge from 35% SOC to 40% SOC at a constant current of 5.0C.

[0496] Charge from 40% SOC to 45% SOC at a constant current of 4.6C.

[0497] Charge from 45% SOC to 50% SOC at a constant current of 4.3C.

[0498] Charge from 50% SOC to 55% SOC at a constant current of 4.0C.

[0499] Charge from 55% SOC to 60% SOC at a constant current of 3.7C.

[0500] Charge from 60% SOC to 65% SOC at a constant current of 3.4C.

[0501] Charge from 65% SOC to 70% SOC at a constant current of 3.1C.

[0502] Charge from 70% SOC to 75% SOC at a constant current of 2.9C.

[0503] Charge from 75% SOC to 80% SOC at a constant current of 2.7C.

[0504] In some embodiments, the charging time for the battery pack 2 or any individual battery cell comprising the battery pack 2 from 10% state of charge to 80% state of charge is less than or equal to 10.5 minutes, optionally ranging from 5 minutes to 10.5 minutes, and the ambient environment for the battery pack 2 at 10% state of charge is room temperature, for example, a temperature of 30°C. Exemplarily, the charging time for the battery pack 2 from 10% state of charge to 80% state of charge is 10.5 minutes, 10 minutes, 9.5 minutes, 9 minutes, 8.5 minutes, 8 minutes, 7.5 minutes, 7 minutes, 6.5 minutes, 6 minutes, 5.5 minutes, 5 minutes, or a range of any two of the above values.

[0505] In some embodiments, the volumetric energy density of the battery cell is from 390 Wh / L to 500 Wh / L, optionally from 410 Wh / L to 470 Wh / L. Exemplarily, the volumetric energy density of the battery cell is 390 Wh / L, 400 Wh / L, 410 Wh / L, 420 Wh / L, 430 Wh / L, 440 Wh / L, 450 Wh / L, 460 Wh / L, 470 Wh / L, 480 Wh / L, 490 Wh / L, 500 Wh / L, or a range of any two of the above values. The volumetric energy density of the battery cell is relatively high.

[0506] In the embodiments of this application, the volumetric energy density of a single battery cell has a meaning known in the art and can be detected using equipment and methods known in the art. For example, the following description uses a battery charging upper limit voltage of 3.65V and a battery discharging cutoff voltage of 2.0V as an example.

[0507] Place the battery cell at 25°C and charge it to 3.65V with a constant current of 0.33C, then charge it to 0.05C with a constant voltage, and discharge it to 2.0V with a constant current of 0.33C. Record the discharge capacity A0 at this point, in Ah. Use calipers to measure the length, width, and height of the battery cell (generally calculated based on the battery casing dimensions, excluding the height of the electrode terminals and the insulating film outside the casing). Calculate the volume of the battery cell V0, in L. The volumetric energy density of the battery cell VED = (A0 × discharge plateau voltage) / V0, in Wh / L.

[0508] Electrical appliances

[0509] The second aspect of this application provides an electrical device, which includes a battery device as described in this application, such as a battery cell, battery module, or battery pack. The battery cell, battery module, or battery pack can be the power source of the electrical device or the energy storage unit of the electrical device. The electrical device can be a vehicle, mobile phone, portable device, laptop computer, ship, spacecraft, electric toy, and power tool, etc. Vehicles can be gasoline-powered vehicles, natural gas-powered vehicles, or new energy vehicles; new energy vehicles can be pure electric vehicles, hybrid electric vehicles, or range-extended electric vehicles, etc.; spacecraft include airplanes, rockets, space shuttles, and spacecraft, etc.; electric toys include stationary or mobile electric toys, such as game consoles, electric car toys, electric ship toys, and electric airplane toys, etc.; power tools include metal cutting power tools, grinding power tools, assembly power tools, and railway power tools, such as electric drills, electric grinders, electric wrenches, electric screwdrivers, electric hammers, impact drills, concrete vibrators, and electric planers, etc. This application does not impose any special limitations on the above-described electrical device.

[0510] Electrical devices can be equipped with individual battery cells, battery modules, or battery packs depending on their usage requirements.

[0511] Figure 18 is a schematic diagram of an example electrical device 1. This electrical device 1 is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. To meet the high power and high energy density requirements of this electrical device 1, a battery pack or battery module can be used.

[0512] The electrical device 1 is equipped with a battery pack 2, which can be located at the bottom, head, or tail of the electrical device 1. The battery pack 2 can be used to supply power to the electrical device 1. For example, the battery pack 2 can serve as the operating power source for the electrical device 1, and can also serve as the driving power source for the electrical device 1, replacing or partially replacing fuel oil or natural gas to provide driving power for the electrical device 1.

[0513] Electrical device 1 may also include controller 3 and motor 4. Controller 3 is used to control battery pack 2 to supply power to motor 4, for example, to meet the power needs of electrical device 1 during startup, navigation and driving.

[0514] Another example of an electrical device could be a mobile phone, tablet, or laptop. These devices typically require a slim and lightweight design and can use a single battery cell as their power source.

[0515] The following charging methods can be selected for the charging process of electrical devices:

[0516] Charge from 10% SOC to 15% SOC at a constant current of 5.0C.

[0517] Charge from 15% SOC to 20% SOC at a constant current of 5.0C.

[0518] Charge from 20% SOC to 25% SOC at a constant current of 5.0C.

[0519] Charge from 25% SOC to 30% SOC at a constant current of 5.0C.

[0520] Charge from 30% SOC to 35% SOC at a constant current of 5.0C.

[0521] Charge from 35% SOC to 40% SOC at a constant current of 5.0C.

[0522] Charge from 40% SOC to 45% SOC at a constant current of 4.6C.

[0523] Charge from 45% SOC to 50% SOC at a constant current of 4.3C.

[0524] Charge from 50% SOC to 55% SOC at a constant current of 4.0C.

[0525] Charge from 55% SOC to 60% SOC at a constant current of 3.7C.

[0526] Charge from 60% SOC to 65% SOC at a constant current of 3.4C.

[0527] Charge from 65% SOC to 70% SOC at a constant current of 3.1C.

[0528] Charge from 70% SOC to 75% SOC at a constant current of 2.9C.

[0529] Charge from 75% SOC to 80% SOC at a constant current of 2.7C.

[0530] In some embodiments, the charging time for the electrical device from 10% state of charge to 80% state of charge is less than or equal to 10.5 minutes, optionally ranging from 5 minutes to 10.5 minutes. The ambient temperature of the battery pack 2 at 10% state of charge is room temperature, for example, 30°C. Exemplarily, the charging time for the battery pack 2 from 10% state of charge to 80% state of charge is 10.5 minutes, 10 minutes, 9.5 minutes, 9 minutes, 8.5 minutes, 8 minutes, 7.5 minutes, 7 minutes, 6.5 minutes, 6 minutes, 5.5 minutes, 5 minutes, or a range of any two of the above values.

[0531] Example

[0532] The following embodiments describe the contents disclosed in this application in more detail. These embodiments are merely illustrative, as various modifications and variations will be apparent to those skilled in the art within the scope of the disclosure of the embodiments of this application. Unless otherwise stated, all parts, percentages, and ratios reported in the following embodiments are based on mass, and all reagents used in the embodiments are commercially available or synthesized by conventional methods and can be used directly without further processing, and the instruments used in the embodiments are commercially available.

[0533] Example 1

[0534] 1. Preparation of positive electrode sheet

[0535] The positive electrode includes a positive current collector, a positive conductive layer on the positive current collector, and a positive film layer. The positive current collector is an aluminum foil with the same thickness as the positive electrode tab. The positive conductive layer on the positive current collector is a film layer formed by uniformly mixing the positive conductive agent superconducting carbon, the positive binder polyvinylidene fluoride (PVDF), and the solvent N-methylpyrrolidone (NMP) and then coating it on the surface of the current collector. The thickness is 1 μm. The positive conductive agent in the positive conductive layer has a mass content of 40%, and the positive binder has a mass content of 60%.

[0536] The positive electrode film layer comprises a film layer formed by uniformly coating a positive electrode slurry (solvent being N-methylpyrrolidone, NMP) onto the surface of a positive electrode conductive layer, followed by drying and cold pressing. The positive electrode film layer comprises positive electrode active material, binder polyvinylidene fluoride (PVDF), and conductive agent acetylene black in a weight ratio of 97:2:1.

[0537] The positive electrode active material includes lithium iron phosphate and a coating layer. The coating layer is coated on the surface of the lithium iron phosphate and includes lithium titanium iron phosphate (Li2FeTi(PO4)3) and amorphous carbon. The Dv50 of the positive electrode active material is 1.6 μm, and the Dv10 is 0.64 μm.

[0538] The single-sided coating weight of the positive electrode film is 290 mg / 1540.25 mm. 2 .

[0539] 2. Preparation of negative electrode sheet

[0540] The negative electrode sheet includes a negative current collector, a negative conductive layer on the negative current collector, and a negative film layer. The negative current collector is a copper foil with the same thickness as the negative electrode tab. The negative conductive layer on the negative current collector is a film layer with a thickness of 1 μm formed by uniformly mixing superconducting carbon as a negative conductive agent, styrene-butadiene rubber (SBR) as a negative binder, sodium carboxymethyl cellulose (CMC-Na) as a thickener, and water as a solvent, and then coating it onto the surface of the negative current collector. The negative conductive agent has a mass content of 35% in the negative conductive layer, the negative binder has a mass content of 60% in the negative conductive layer, and the thickener has a mass content of 5% in the negative conductive layer.

[0541] The negative electrode film layer comprises a film layer formed by uniformly coating a negative electrode slurry (with deionized water as the solvent) onto the surface of a negative electrode conductive layer, followed by drying and cold pressing.

[0542] The single-sided coating weight of the negative electrode film is 135 mg / 1540.25 mm. 2 .

[0543] The negative electrode film layer includes a first negative electrode film layer and a second negative electrode film layer. The first negative electrode film layer is located on the surface of the negative electrode conductive layer, and the second negative electrode film layer is located on the surface of the first negative electrode film layer.

[0544] The first negative electrode film layer comprises graphite particles in a mass ratio of 96.5:0.5:0.5:1.5:1, conductive agent acetylene black, a first lithium-containing binder (lithium acrylate-acrylonitrile-acrylamide-hydroxyethyl acrylate copolymer), negative electrode binder styrene-butadiene rubber, and thickener sodium carboxymethyl cellulose; the lithium content in the first lithium-containing binder is 4.8% by mass; the Dv50 of the graphite particles is 11.3 μm, and the graphite particles include artificial graphite and an amorphous carbon layer, with the amorphous carbon layer coating the surface of the artificial graphite, and the amorphous carbon content is 3.5% by mass.

[0545] The second negative electrode film layer comprises graphite particles in a mass ratio of 97.5:0.5:0.5:0.5:1, conductive agent acetylene black, a second lithium-containing binder (lithium acrylate-acrylonitrile-acrylamide-hydroxyethyl acrylate copolymer), negative electrode binder styrene-butadiene rubber, and thickener sodium carboxymethyl cellulose; the lithium content in the second lithium-containing binder is 4.8% by mass; the Dv50 of the graphite particles is 11.3 μm, and the graphite particles include artificial graphite and an amorphous carbon layer, with the amorphous carbon layer coating the surface of the artificial graphite, and the mass content of the amorphous carbon is 3.5%.

[0546] 3. Separating membrane

[0547] The separator includes a base membrane, which is a 7μm polyethylene film layer with a porosity of 42%.

[0548] 4. Preparation of electrolyte

[0549] The electrolyte comprises an organic solvent, a lithium salt, and additives. The organic solvent consists of 60% chain carboxylic acid esters (ethyl acetate) and 40% carbonates (30% ethylene carbonate EC and 10% dimethyl carbonate by mass). The additives comprise 6.5% by mass and include vinylene carbonate VC, fluoroethylene carbonate FEC, vinyl sulfite ES, and lithium difluorooxalate borate LiDFOB in a mass ratio of 5:0.5:0.5:0.5. The lithium salt comprises 1 mol / L lithium hexafluorophosphate LiPF6. The electrolyte has a conductivity of 16.4 mS / cm.

[0550] 5. Preparation of battery cells

[0551] The positive electrode, separator, and negative electrode are stacked in sequence, with the separator positioned between the positive and negative electrodes to provide isolation. The electrode assembly is then obtained through a winding process. The electrode assembly is placed in an outer packaging shell, dried, and then injected with electrolyte. After vacuum sealing, settling, formation, and shaping, a single battery cell is obtained. The compaction density of the positive electrode film at 100% SOC is 2.60 g / cm³. 3 The compaction density of the negative electrode film at 100% SOC is 1.25 g / cm³. 3 .

[0552] The ratio of the number of first tabs to the number of first straight sections in the positive electrode plate is 0.75, as shown in the tab arrangement of the first electrode plate in Figure 5.

[0553] The ratio of the number of second tabs to the number of second straight sections in the negative electrode plate is 0.75, referring to the tab arrangement in the first electrode plate in Figure 5.

[0554] Examples 2-1 to 2-4

[0555] Battery cells were prepared using a method similar to that of Example 1. The difference from Example 1 is that the ratio of the number of first tabs to the number of first straight sections was adjusted; the ratio of the number of second tabs to the number of second straight sections in the negative electrode was also adjusted.

[0556] In Example 2-1,

[0557] The ratio of the number of first tabs to the number of first straight sections in the positive electrode plate is 0.5, as shown in the tab arrangement of the first electrode plate in Figure 3.

[0558] The ratio of the number of second tabs to the number of second straight sections in the negative electrode plate is 0.5, referring to the tab arrangement in the first electrode plate in Figure 3.

[0559] In Example 2-2,

[0560] The ratio of the number of first tabs to the number of first straight segments in the positive electrode sheet is 0.8. For example, if the positive electrode sheet is wound 5 times, each time there are 2 first straight segments, for a total of 10 first straight segments; 8 of the 10 first straight segments are connected to the first tabs, so the number of first tabs is 8.

[0561] The ratio of the number of second tabs to the number of second straight segments in the negative electrode plate is 0.8. For example, the negative electrode plate is wound 5 times, each turn includes 2 second straight segments, for a total of 10 second straight segments; 8 of the 10 second straight segments are connected to second tabs, so the number of second tabs is 8.

[0562] In Examples 2-3,

[0563] The ratio of the number of first tabs to the number of first straight sections in the positive electrode plate is 1, as shown in the tab arrangement of the first electrode plate in Figure 4.

[0564] The ratio of the number of second tabs to the number of second straight sections in the negative electrode plate is 1, referring to the tab arrangement in the first electrode plate in Figure 4.

[0565] In Examples 2-4,

[0566] Compared to the positive electrode tabs of Examples 2-3, the positive electrode tabs in Examples 2-4 are equivalent to cutting the positive electrode tabs of Examples 2-3, but the roots of the tabs are still connected as one piece, that is, the ratio of the number of first tabs to the number of first straight segments in the positive electrode sheet is 1. For example, the positive electrode tabs in Examples 2-3 are shown in Figure 6, and the positive electrode tabs in Examples 2-4 are shown in Figure 13.

[0567] The negative electrode tab is set up in the same way as the positive electrode tab, and will not be described again here.

[0568] Example 3

[0569] Battery cells were prepared using a method similar to that of Example 1, except that the thickness of the positive electrode tab and the thickness of the negative electrode tab were adjusted.

[0570] Comparative Example 1-1

[0571] Battery cells were prepared using a method similar to that of Example 1, except that the number of positive electrode tabs and the number of negative electrode tabs were adjusted.

[0572] Performance testing

[0573] 1. Lithium plating area test of individual battery cells

[0574] Each battery cell in the embodiment and comparative example was cycled 50 times according to the following charge-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 cleavage area (grayish-white area) was observed, and the cleavage area was measured. The degree of cleavage is as follows:

[0575] No lithium plating: lithium plating area < 0.05%.

[0576] Slight lithium plating: lithium plating area <2%.

[0577] Severe lithium plating: lithium plating area ≥2%.

[0578] The battery cells are charged at an ambient temperature of 30°C. The charging process includes the following steps:

[0579] Charge from 0% SOC to 5% SOC at a constant current of 5.0C;

[0580] Charge from 5% SOC to 10% SOC at a constant current of 5.0C;

[0581] Charge from 10% SOC to 15% SOC at a constant current of 5.0C;

[0582] Charge from 15% SOC to 20% SOC at a constant current of 5.0C;

[0583] Charge from 20% SOC to 25% SOC at a constant current of 5.0C;

[0584] Charge from 25% SOC to 30% SOC at a constant current of 5.0C;

[0585] Charge from 30% SOC to 35% SOC at a constant current of 5.0C;

[0586] Charge from 35% SOC to 40% SOC at a constant current of 5.0C;

[0587] Charge from 40% SOC to 45% SOC at a constant current of 4.6C;

[0588] Charge from 45% SOC to 50% SOC at a constant current of 4.3C;

[0589] Charge from 50% SOC to 55% SOC at a constant current of 4.0C;

[0590] Charge from 55% SOC to 60% SOC at a constant current of 3.7C;

[0591] Charge from 60% SOC to 65% SOC at a constant current of 3.4C;

[0592] Charge from 65% SOC to 70% SOC at a constant current of 3.1C;

[0593] Charge from 70% SOC to 75% SOC at a constant current of 2.9C;

[0594] Charge from 75% SOC to 80% SOC at a constant current of 2.7C;

[0595] Charge from 80% SOC to 85% SOC at a constant current of 1.8C;

[0596] Charge from 85% SOC to 90% SOC at a constant current of 1.3C;

[0597] Charge from 90% SOC to 95% SOC at a constant current of 0.7C;

[0598] Charge from 95% SOC to 98% SOC at a constant current of 0.33C;

[0599] Charge from 98% SOC to 100% SOC at a constant current of 0.1C.

[0600] The cutoff voltage for the final charging step in the above charging process is 3.65V.

[0601] The discharge strategy is as follows: discharge at a constant current of 0.33C until the cutoff voltage, for example, 2.0V.

[0602] 2. DC internal resistance (DCR) test of individual battery cells

[0603] You can refer to the methods in GB / T 31467 "Performance Test Specification for High-Power Lithium-ion Power Batteries for HEVs".

[0604] For example, at 25°C, charge a single battery cell to 3.65V with a constant current of 0.33C and let it stand for 1 minute; then charge it to 3.65V with a constant current of 0.1C and let it stand for 30 minutes; discharge it to 2.0V with a constant current of 0.33C and record the discharge capacity A0 in Ah. Then charge it to 0.5A0Ah with a constant current of 0.33C and adjust the SOC to 50%.

[0605] After placing the battery cell at 25°C for 2 hours, it was discharged at a constant current of 4C for 10 seconds, and ΔU was recorded. 放电 ΔI 放 电 The discharge DCR data of lithium-ion batteries can be calculated using the following formula.

[0606] R 放电 =ΔU 放电 / ΔI 放电 ,

[0607] Wherein, ΔU 放电 ΔI represents the voltage change within 10 seconds of the start of discharge. 放电 This indicates the current value within 10 seconds of the start of discharge.

[0608] 3. Number of cycles required for a single battery cell to reach 80% SOH

[0609] At 35°C, the battery cell is charged at a constant current of 1C to the charging cutoff voltage of 3.65V, and then discharged at a constant current of 1C to 2.0V. This constitutes one charge-discharge cycle. The above charge-discharge cycle steps are repeated until the cycle capacity retention rate (i.e., Cn / C0×100%) is 80%, and the number of cycles is recorded. The more cycles, the better the cycle performance of the battery cell.

[0610] The test results are shown in Table 1.

[0611] Table 1

[0612] As can be seen from Table 1,

[0613] 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 be deposited on the negative electrode.

[0614] In this embodiment, by setting the ratio of the number of tabs to the number of straight sections to 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 plating is less likely to occur on the negative electrode sheet. Moreover, the organic solvent in the electrolyte is less likely to decompose, the electrolyte system is more stable, which is conducive to improving the reliability of the battery cell and the cycle performance.

[0615] 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 battery impedance is relatively low, lithium plating on the negative electrode is not easy, and the cycle performance is good.

[0616] Examples 4-1 to 4-3

[0617] Battery cells were prepared using a similar method to that used in Example 1, except that the composition of the organic solvent in the electrolyte was adjusted.

[0618] Comparative Example 2-1

[0619] Battery cells were prepared using a similar method to that used in Example 1, except that the composition of the organic solvent in the electrolyte was adjusted.

[0620] The test results are shown in Table 2.

[0621] Table 2

[0622] In Table 2,

[0623] In Examples 4-3, the mass ratio of ethyl acetate to methyl acetate was 2:7.

[0624] In Examples 4-1, 4-2 and Comparative Example 2-1, the mass content of ethylene carbonate was 30%, and the remainder was dimethyl carbonate.

[0625] As shown in Table 2, the chain carboxylic acid ester solvent in Comparative Example 2-1 has a relatively low mass content, resulting in low conductivity and excessive impedance of the battery cells, which severely deteriorates cycle performance and leads to a drop in cycle life. Compared to Comparative Example 2-1, the electrolyte in Example 4-2 has improved conductivity, which is beneficial for improving cycle performance.

[0626] Compared to Comparative Example 2-1, when the mass content of the chain carboxylic acid ester solvent relative to the organic solvent increases, for example, to 8% or more, the conductivity of this solvent system is higher, which is beneficial for the rapid migration of lithium ions and improves the fast-charging performance of the battery cells. 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 it impossible for the battery cells to charge and discharge quickly.

[0627] Examples 5-1 to 5-3

[0628] Battery cells were prepared using a method similar to that in Example 1. However, unlike Example 1, a stacked electrode assembly was prepared using a stacking process to obtain the battery cells.

[0629] In Example 5-1,

[0630] The ratio of the number of first tabs to the number of first straight sections in the positive electrode plate 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 positive electrode straight sections are connected in a one-to-one correspondence, as shown in the tab arrangement in Figure 10.

[0631] The ratio of the number of second tabs to the number of second straight sections in the negative electrode plate 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 negative electrode straight sections are connected in a one-to-one correspondence, as shown in the tab configuration in Figure 10.

[0632] In Example 5-2,

[0633] Compared to the positive electrode tab in Example 5-1, the positive electrode tab in Example 5-2 is equivalent to cutting the positive electrode tab in Example 5-1, but the root of the tab is still connected as one piece. Referring to the structure of the tab in Figure 10, the ratio of the number of the first tabs to the number of the first straight segments in the positive electrode sheet is 1.

[0634] The negative electrode tab arrangement in Example 5-1 is similar to the positive electrode tab arrangement, and will not be described again here.

[0635] In Example 5-3,

[0636] The ratio of the number of first tabs to the number of first straight sections in the positive electrode plate is 2. The first tab is the positive electrode tab, and the first straight section is the positive electrode straight section. One positive electrode tab is set on each side along the length direction of a positive electrode straight section, which is equivalent to the number of positive electrode tabs being twice the number of positive electrode straight sections, as shown in the tab arrangement in Figure 11.

[0637] The ratio of the number of second tabs to the number of second straight sections in the negative electrode plate is 2. The second tab is a negative electrode tab, and the second straight section is a negative electrode straight section. One negative electrode tab is set on each side of a negative electrode straight section, which means that the number of negative electrode tabs is twice the number of negative electrode straight sections, as shown in the tab arrangement in Figure 12.

[0638] The test results are shown in Table 3.

[0639] Table 3

[0640] In Examples 5-1 to 5-3, the thickness of the positive electrode tab is 15 μm and the thickness of the negative electrode tab is 6 μm.

[0641] In this embodiment, by setting the ratio of the number of tabs to the number of straight sections to 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 plating is less likely to occur on the negative electrode sheet. Moreover, the organic solvent in the electrolyte is less likely to decompose, the electrolyte system is more stable, which is conducive to improving the reliability of the battery cell and the cycle performance.

[0642] Although illustrative embodiments have been demonstrated and described, those skilled in the art should understand that the above embodiments should not be construed as limiting the present application, and that changes, substitutions and modifications can be made to the embodiments without departing from the spirit, principles and scope of the present application.

Claims

1. A battery cell, comprising a housing assembly, an electrode assembly and an electrolyte, the electrode assembly and the electrolyte being contained in the housing assembly, the housing assembly being provided with an electrode terminal; the electrode assembly comprising a first electrode tab, a second electrode tab and a separator film between the first electrode tab and the second electrode tab, the first electrode tab and the second electrode tab each comprising a coated portion coated with an active material layer and a tab portion not coated with the active material layer; the first electrode tab and the second electrode tab having opposite polarities, one of the first electrode tab and the second electrode tab being a positive electrode tab, the active material layer of the positive electrode tab comprising a positive electrode active material, the positive electrode active material comprising a lithium-containing phosphate with an olivine structure; the electrode assembly being electrically connected to the electrode terminal through the tab portion; wherein the coated portion of the first electrode tab comprises a first flat section, the coated portion of the second electrode tab comprises a second flat section, the first flat section and the second flat section being stacked along a thickness direction of the electrode assembly, a ratio of a number of the tab portions of the first electrode tab to a number of the first flat sections of the first electrode tab is 0.5 to 2, the electrolyte comprises an organic solvent, the organic solvent comprises a chain carboxylic acid ester solvent, a mass content of the chain carboxylic acid ester solvent in the organic solvent is 8% to 75%. The mass content of the chain carboxylic acid ester solvent in the organic solvent is 30% to 70%. A ratio of a number of the tab portions of the second electrode tab to a number of the second flat sections of the second electrode tab is 0.5 to 2. The electrode assembly has a jelly-roll structure, the first electrode tab and the second electrode tab are wound in one direction, and the first electrode tab has a plurality of the tab portions.

2. The battery cell of claim 1, wherein, A ratio of a number of the tab portions of the first electrode tab to a number of the first flat sections of the first electrode tab is 0.5 to 1.

3. The battery cell of claim 1 or 2, wherein, The electrode assembly has a jelly-roll structure, the first electrode tab and the second electrode tab are wound in one direction, and the first electrode tab has a plurality of the tab portions.

4. The battery cell of any one of claims 1 to 3, wherein, A ratio of a number of the tab portions of the first electrode tab to a number of the first flat sections of the first electrode tab is 1 to 2.

5. The battery cell of claim 4, wherein, The first electrode tab has a plurality of the tab portions, and the plurality of the tab portions of the first electrode tab are arranged on the same side of the coated portion.

6. The battery cell of any one of claims 1 to 3, wherein, The first electrode tab has a plurality of the tab portions, and the plurality of the tab portions of the first electrode tab are arranged on both sides of the coated portion.

7. The battery cell of claim 6, wherein, The tab portion comprises:

8. The battery cell of any one of claims 1 to 7, wherein, a tab body connected to the coated portion; and 9. The battery cell of any one of claims 1 to 7, wherein, a plurality of tab protrusions connected to a side of the tab body away from the coated portion, and having a gap between adjacent two of the tab protrusions, each of the tab protrusions being used for electrical connection with the electrode terminal.

10. The battery cell of any one of claims 1 to 9, wherein, The tab portion in the first electrode tab is a positive electrode tab portion, and a thickness of the positive electrode tab portion is 10 μm to 20 μm. The tab portion in the first electrode tab is a negative electrode tab portion, and a thickness of the negative electrode tab portion is 4 μm to 10 μm. The electrolyte has an electrical conductivity of 10.5 mS / cm to 20 mS / cm at room temperature.

11. The battery cell of any one of claims 1-10, wherein, The electrolyte has an electrical conductivity of 15 mS / cm to 20 mS / cm at room temperature.

12. The battery cell of any one of claims 1-10, wherein, In formula I, 13. The battery cell of any one of claims 1-12, wherein, ​ 14. The battery cell of claim 13, wherein, ​ 15. The battery cell of any one of claims 1-14, wherein, The chain carboxylate-based solvent includes a compound represented by Formula I, ​ R1 includes a hydrogen atom, a halogen atom, a C1 to C5 alkyl group, or a C1 to C5 haloalkyl group, R2 includes a C1 to C5 alkyl group or a C1 to C5 haloalkyl group.

16. The battery cell according to claim 15, wherein R1 includes a hydrogen atom, a halogen atom, a C1 to C3 alkyl group, or a C1 to C3 haloalkyl group, R2 includes a C1 to C3 alkyl group or a C1 to C3 haloalkyl group.

17. The battery cell according to claim 15 or 16, wherein the halogen atom includes a fluorine atom, and / or the haloalkyl group includes a fluoroalkyl group.

18. The battery cell of any one of claims 15-17, wherein, The chain carboxylate-based solvent includes one or more of compounds represented by Formula I-1 to Formula I-8, 19. The battery cell of any one of claims 1-18, wherein, The organic solvent further includes a carbonate-based solvent, the carbonate-based solvent including one or more of vinyl carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate.

20. The battery cell of claim 19, wherein, The mass content of the carbonate-based solvent in the organic solvent is 30% to 50%.

21. The battery cell of any one of claims 1-20, wherein, The electrolyte solution further includes an additive, the additive including one or more of a carbonate-based additive, a sulfur-containing additive, and a lithium salt-based additive.

22. The battery cell of claim 21, wherein, The carbonate-based additive includes one or more of vinylene carbonate, fluoro-vinylene carbonate, and / or The sulfur-containing additive includes one or more of vinyl sulfate, bis-vinyl sulfate, butylene sulfite, 1,3-propane sultone, vinyl sulfite, and methyl bis(methylene sulfite), and / or The lithium salt-based additive includes one or more of lithium difluorophosphate, lithium difluoro oxalate borate, lithium tetrafluoroborate, and lithium bis-oxalate borate.

23. The battery cell of claim 21 or 22, wherein, The mass content of the additive in the electrolyte solution is 1% to 10%.

24. The battery cell of any one of claims 1-23, wherein, The electrolyte solution further includes a lithium salt, the lithium salt including one or more of a fluorine-containing sulfimide salt and lithium hexafluorophosphate.

25. The battery cell of claim 24, wherein, The fluorine-containing sulfimide salt includes one or more of lithium bis-fluorosulfimide and lithium bis-trifluoromethylsulfonamide.

26. The battery cell of claim 25, wherein, The lithium salt includes lithium bis-fluorosulfimide and lithium hexafluorophosphate, the molar concentration of the lithium bis-fluorosulfimide being 0.2 mol / L to 0.5 mol / L, and the molar concentration of the lithium hexafluorophosphate being 0.5 mol / L to 1.0 mol / L.

27. The battery cell according to any one of claims 1 to 26, wherein The viscosity of the electrolyte solution at room temperature is 2.3 mPa s to 3.5 mPa s; and / or The density of the electrolyte solution at room temperature is 1.05 g / mL to 1.35 g / mL.

28. The battery cell of any one of claims 1-27, wherein, The lithium-containing phosphate of olivine structure includes: phosphate particles, and a coating layer, the coating layer coating the phosphate particles, the coating layer containing one or more of C, Fe, Ti, Zr, Hf, Ge, and Sn.

29. The battery cell of claim 28, wherein, The phosphate particles include a compound of a general formula of Li x1 A y1 Me a M b P 1-c X c Y z , wherein 0.5≤x1≤1.3, 0≤y1≤1.3, and 0.9≤x1+y1≤1.3, 0.9≤a≤1.5, 0≤b≤0.5, and 0.9≤a+b≤1.5, 0≤c≤0.5, 3≤z≤5, A includes one or more of Na, K, Mg, Me includes one or more of Mn, Fe, Co, Ni, M includes 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.

30. The battery cell of claim 28 or 29, wherein, The coating layer includes a general formula of Li 3-d Fe 2- d M2 d (PO x2 ) y2 a fast ion conductor of a general formula of Li M2Ti2-x2Snx2P2-y2O12, M2 includes one or more elements of Ti, Zr, Hf, Ge, and Sn, 0≤d≤1, 0 31. The battery cell of any one of claims 28-30, wherein, The graphitization degree of the lithium-containing phosphate of olivine structure is 0.15 to 0.

32.

32. The battery cell of claim 31, wherein, The graphitization degree of the lithium-containing phosphate of olivine structure is 0.19 to 0.

26.

33. The battery cell of any one of claims 28-32, wherein, The mass content of carbon element in the lithium-containing phosphate of olivine structure is 1% to 2%, The lithium-containing phosphate of olivine structure has a specific surface area of 5 m 2 / g to 18 m 2 / g.

34. The battery cell of claim 33, wherein, The lithium-containing phosphate of olivine structure has a specific surface area of 7.5 m 2 / g to 14 m 2 / g.

35. The battery cell of any one of claims 1-34, wherein, The lithium-containing phosphate of olivine structure is in a particulate form, the volume distribution particle size thereof satisfying 1 μm ≤ Dv50 ≤ 2 μm, 0.4 μm ≤ Dv10 ≤ 0.7 μm.

36. The battery cell of any one of claims 1-35, wherein, The olivine-structure lithium-containing phosphate is in a particulate form, the olivine-structure lithium-containing phosphate includes secondary particles, the secondary particles include a plurality of primary particles, and the primary particles have an average particle size of 200 nm to 500 nm.

37. The battery cell of any one of claims 1-36, wherein, The negative electrode tab includes a negative electrode active material, the negative electrode active material includes a carbon-based material, and the carbon-based material includes graphite particles having a graphitization degree of 92.0% to 94.5%.

38. The battery cell of claim 37, wherein, The graphite particles include: artificial graphite including secondary particles, and a carbon coating layer coated on a surface of the artificial graphite.

39. The battery cell of claim 38, wherein, A mass content of the carbon coating layer is 2% to 5% based on a mass of the graphite particles.

40. The battery cell of any one of claims 1-39, wherein, The other of the first electrode tab and the second electrode tab is a negative electrode tab, and a coated portion in the negative electrode tab includes a negative electrode film layer including: a first negative electrode film layer disposed on a surface of the negative electrode current collector, the first negative electrode film layer including a carbon-based material, and a second negative electrode film layer connected to a side of the first negative electrode film layer facing away from the negative electrode current collector, the second negative electrode film layer including a carbon-based material, the carbon-based material in the first negative electrode film layer and the carbon-based material in the second negative electrode film layer each independently include graphite particles, and a volume average particle size Dv50 of the graphite particles in the first negative electrode film layer is greater than or equal to a volume average particle size Dv50 of the graphite particles in the second negative electrode film layer.

41. The battery cell of claim 40, wherein, The carbon-based material in the first negative electrode film layer further includes natural graphite.

42. The battery cell of claim 40 or 41, wherein, A tap density of the carbon-based material in the first negative electrode film layer is less than or equal to a tap density of the carbon-based material in the second negative electrode film layer.

43. The battery cell of claim 42, wherein, 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 , and / or 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 .

44. The battery cell of any one of claims 40 to 43, wherein, the volume average particle size Dv50 of the graphite particles in the first negative electrode film layer is 9.5 μm to 18.5 μm, and / or the volume average particle size Dv50 of the graphite particles in the second negative electrode film layer is 7.8 μm to 14.3 μm.

45. The battery cell of any one of claims 40-44, wherein, The first negative electrode film layer further includes a first lithium-containing binder, the second negative electrode film layer further includes a second lithium-containing binder, and a mass content of the first lithium-containing binder with respect to a mass of the first negative electrode film layer is less than or equal to a mass content of the second lithium-containing binder with respect to a mass of the second negative electrode film layer.

46. The battery cell of claim 45, wherein, the mass content of the first lithium-containing binder with respect 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 with respect to the mass of the second negative electrode film layer is 0.1% to 1%.

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

48. The battery cell of any one of claims 45 to 47, wherein, The first lithium-containing binder includes a lithium acrylate-acrylonitrile-acrylamide-hydroxyethyl acrylate copolymer derived from lithium acrylate monomers, acrylonitrile monomers, acrylamide monomers, and hydroxyethyl acrylate monomers in a molar ratio of 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 derived from lithium acrylate monomers, acrylonitrile monomers, acrylamide monomers, and hydroxyethyl acrylate monomers in a molar ratio of 30% to 50%: 15% to 45%: 5% to 20%: 20% to 35%.

49. The battery cell of any one of claims 37-48, wherein, The negative active material further includes a silicon-based material having a mass content of silicon element of 0.3% to 10.0% based on the mass of the negative active material.

50. The battery cell of any one of claims 1 to 49, the separator film comprising a base film of a porous structure, the base film having a porosity of 20% to 70%.

51. The battery cell of claim 49 or 50, wherein, The base film has a thickness of 6 μm to 12 μm.

52. The battery cell of claim 51, wherein, The base film has a thickness of 6 μm to 9 μm.

53. The battery cell of any one of claims 1-52, wherein, The separator film comprises a base film and a functional layer provided on at least one side of the base film, the functional layer comprising: a first functional layer on one side of the base film, the first functional layer comprising first inorganic particles, a second functional layer on the other side of the base film, the second functional layer comprising composite particles comprising second inorganic particles and a plurality of non-fluoropolymer particles, the second inorganic particles being attached to the surface of the non-fluoropolymer particles and / or dispersed inside the non-fluoropolymer particles.

54. The battery cell of claim 53, wherein, The non-fluoropolymer particles comprise an acrylate-based copolymer.

55. The battery cell of claim 53 or 54, wherein, The first inorganic particles comprise 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 of any one of claims 53-55, wherein, The second inorganic particles comprise one or more of silicon oxide, aluminum oxide, boehmite, barium sulfate, calcium oxide, titanium oxide, zinc oxide, magnesium oxide, zirconium oxide, and tin oxide, and / or The second inorganic particles have an average particle diameter of 5 nm to 100 nm.

57. The battery cell of any one of claims 1 to 56, the battery cell comprising a case housing the electrode assembly, the case comprising steel, the case having a thickness of 0.1 mm to 0.5 mm.

58. The battery cell of claim 57, wherein, The case has a thickness of 0.2 mm to 0.35 mm.

59. The battery cell of any one of claims 1-58, wherein, wherein, The battery cell has a charging time from 10% state of charge to 80% state of charge of 5 min to 10.5 min.

60. A battery device comprising a plurality of battery cells according to any one of claims 1 to 59.

61. The battery device of claim 60, wherein, The battery device has a charge time from 10% state of charge to 80% state of charge of 5 min to 10.5 min.

62. An electrical device comprising the battery device of claim 60 or 61.

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