Battery monomer, battery device, power utilization device and energy storage device

Abstract

The invention provides a battery monomer, a battery device, a power utilization device and an energy storage device. The battery monomer is a soft package battery monomer and comprises an electrode assembly and an electrolyte, the electrode assembly comprises a positive pole piece, a negative pole piece and an isolating membrane, and the isolating membrane is located between the positive pole piece and the negative pole piece; the negative electrode plate comprises a negative electrode current collector and a negative electrode film layer arranged on at least one side of the negative electrode current collector, the negative electrode film layer comprises a negative electrode active material, the negative electrode active material comprises graphite, the graphitization degree of the graphite is 94%-98%, and the compaction density of the negative electrode film layer is 1.1 g / cm < 3 >-1.23 g / cm < 3 > when the battery monomer is in a full charge state. And the battery monomer has excellent energy density and cycling stability.

Description

Technical Field

[0001] The present application relates to the technical field of battery cells, and particularly to a battery cell, a battery device, an electrical device, and an energy storage device. Background Art

[0002] In recent years, battery cells have been widely used in energy storage power systems such as hydraulic, thermal, wind, and solar power stations, as well as in multiple fields such as power tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, and aerospace.

[0003] With the increasing demand for the cruising range of electrical devices in the market, higher requirements are also put forward for the energy density of battery cells. However, while improving the energy density, the cycle stability often deteriorates, which has become a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0004] The present application is made in view of the above problems, and its purpose is to provide a battery cell, a battery device, an electrical device, and an energy storage device, in which the battery cell takes into account excellent energy density and cycle life.

[0005] The first aspect of the present application provides a battery cell, which is a soft-pack battery cell and includes an electrode assembly and an electrolyte. The electrode assembly includes a positive electrode plate, a negative electrode plate, and a separator. The separator is located between the positive electrode plate and the negative electrode plate; the negative electrode plate includes a negative current collector and a negative electrode film layer provided on at least one side of the negative current collector. The negative electrode film layer includes a negative active material, and the negative active material includes graphite. The graphitization degree of the graphite is 94% to 98%. When the battery cell is in a fully charged state, the compaction density of the negative electrode film layer is 1.1 g / cm 3 to 1.23 g / cm 3 .

[0006] By using graphite with a graphitization degree in the above range and a negative electrode film layer with a compaction density in the above range in the soft-pack battery cell, the embodiments of the present application achieve a comprehensive improvement in energy density and cycle life.

[0007] In any implementation, the graphitization degree of the graphite is 94% to 96%.

[0008] Graphite with a graphitization degree in the above range enables the battery cell to have excellent energy density while further improving the cycle stability.

[0009] In any implementation, when the battery cell is in a fully charged state, the compaction density of the negative electrode film layer is 1.1 g / cm 3 to 1.17 g / cm 3 .

[0010] The battery cell with the compaction density of the negative electrode film layer within the above range has excellent energy density while the cycle stability is further improved.

[0011] In any embodiment, the single-sided coating mass of the negative electrode film layer is 0.11 g / 1540.25 mm 2 to 0.16 g / 1540.25 mm 2 .

[0012] In any embodiment, the single-sided coating mass of the negative electrode film layer is 0.12 g / 1540.25 mm 2 to 0.135 g / 1540.25 mm 2 .

[0013] The negative electrode film layer with the single-sided coating mass within the above range has a thin thickness and a low pore number. Under the same liquid injection coefficient, it is more conducive to improving the infiltration of the electrolyte into the pores of the film layer and increasing the content of free electrolyte, and the proportion of the electrolyte effectively participating in the reaction is higher. Therefore, the probability of lithium deposition on the negative electrode plate caused by insufficient electrolyte in the film layer and the local lack of electrolyte in the later stage of the cycle, which deteriorates the cycle life, is further reduced. While the cycle stability of the battery cell is further improved, it also has excellent energy density.

[0014] In any embodiment, the cold pressing compaction density of the negative electrode film layer is 1.45 g / cm 3 to 1.6 g / cm 3 .

[0015] When the cold pressing compaction density of the negative electrode film layer is within the above range, the battery cell has both excellent energy density and cycle life.

[0016] In any embodiment, the first charge specific capacity of the negative electrode active material is 379 mAh / g to 385 mAh / g.

[0017] In any embodiment, the first discharge specific capacity of the negative electrode active material is 345 mAh / g to 360 mAh / g.

[0018] When the first charge and discharge specific capacities of the negative electrode active material are within the above range, the battery cell has excellent energy density.

[0019] In any embodiment, the Dv50 of the negative electrode active material is 14 μm to 23 μm.

[0020] In any embodiment, the Dv10 of the negative electrode active material is 6 μm to 18 μm.

[0021] In any embodiment, the Dv90 of the negative electrode active material is 17 μm to 49 μm.

[0022] In any embodiment, the Dv99 of the negative electrode active material is 40 μm to 50 μm.

[0023] In some embodiments, the specific surface area of the negative electrode active material is 1.4 m 2 / g to 1.6 m 2 / g.

[0024] The volume distribution particle size and specific surface area of the negative electrode active material are within the above ranges, enabling the negative electrode active material to have both low reactivity and a short solid-phase migration path for lithium ions, and the battery cell to have both excellent energy density and cycle life.

[0025] In any embodiment, the negative electrode film layer includes a first negative electrode film layer disposed on at least one side of the negative electrode current collector and a second negative electrode film layer disposed on the side of the first negative electrode film layer away from the negative electrode current collector, and the mass ratio of the binder in the first negative electrode film layer is greater than the mass ratio of the binder in the second negative electrode film layer.

[0026] The negative electrode slurry used in the high energy density battery cell often has a high content of active material. When coated on the surface of the current collector, it is prone to powder falling and detaching from the current collector after drying. Moreover, in the step of drying and removing the solvent from the aqueous negative electrode slurry, the binder is prone to float along with the evaporation of the solvent, resulting in insufficient binder content in the lower film layer, and the cohesion between the active material particles and the adhesion between the active material particles and the copper foil substrate deteriorate significantly. In the embodiments of the present application, setting the mass ratio of the binder in the first negative electrode film layer to be greater than the mass ratio of the binder in the second negative electrode film layer helps to improve the adhesion between the negative electrode film layer and the current collector, the cohesion of the negative electrode film layer, and restrain the expansion of the negative electrode active material, thereby further improving the cycle stability of the battery cell.

[0027] In any embodiment, based on the total mass of the first negative electrode film layer, the mass ratio of the binder is 1% - 3%.

[0028] In any embodiment, based on the total mass of the first negative electrode film layer, the mass ratio of the binder is 1.5% - 2.3%.

[0029] When the mass ratio of the binder in the first negative electrode film layer is within the above range, the first negative electrode film layer takes into account the adhesion between the active material particles and the copper foil substrate and the cohesion of the film layer, and the battery cell has both excellent cycle life and energy density.

[0030] In any embodiment, based on the total mass of the second negative electrode film layer, the mass ratio of the binder is 0.3% - 1.5%, and may be optionally 0.3% - 0.8%.

[0031] When the mass proportion of the binder in the second negative electrode film layer is within the above range, the second negative electrode film layer has both excellent cohesion and energy density, and the battery cell has both excellent cycle life and energy density.

[0032] In any implementation, based on the total mass of the first negative electrode film layer, the mass proportion of graphite is 70% - 97%.

[0033] In any implementation, based on the total mass of the second negative electrode film layer, the mass proportion of graphite is 80% - 98%.

[0034] When the mass proportions of graphite in the first negative electrode film layer and the second negative electrode film layer are within the above ranges, the battery cell has both excellent energy density and cycle life.

[0035] In any implementation, the ratio of the thickness of the first negative electrode film layer to the thickness of the second negative electrode film layer is 3:7 to 6:4.

[0036] The first negative electrode film layer with a high binder content and the second negative electrode film layer with a high graphite content, combined with the first and second negative electrode film layers with a thickness ratio within the above range, are beneficial to further improve the energy density and cycle stability of the battery cell, while meeting the processing technology of the electrode sheet.

[0037] In any implementation, the positive electrode sheet includes a positive electrode current collector and a positive electrode film layer provided on at least one side of the positive electrode current collector. When the battery cell is in a fully charged state, the compaction density of the positive electrode film layer is 2.35 g / cm 3 to 2.55 g / cm 3 .

[0038] In any implementation, the cold pressing compaction density of the positive electrode film layer is 2.4 g / cm 3 to 2.6 g / cm 3 .

[0039] The positive electrode film layer with a compaction density within the above range has both excellent liquid retention ability and a thin film layer thickness, enabling the battery cell to further have both excellent energy density and cycle life.

[0040] In any implementation, the single-sided coating mass of the positive electrode film layer is 0.26 g / 1540.25 mm 2 to 0.35 g / 1540.25 mm 2 .

[0041] The positive electrode film layer with a single-sided coating mass within the above range enables the battery cell to further have both excellent energy density and cycle life.

[0042] In any embodiment, the positive electrode film layer includes a positive electrode active material, and the positive electrode active material includes: a lithium-containing phosphate with an olivine structure, and a carbon coating layer located on at least a part of the surface of the lithium-containing phosphate.

[0043] The carbon coating layer is beneficial to improving the electronic conductivity of the lithium-containing phosphate, improving the solid-phase transmission rate of electrons, and thus further improving the energy density and cycling performance of the battery cell.

[0044] In any embodiment, the lithium-containing phosphate includes components shown in Formula I, Li x A y Me a M b P 1-c X c Y z Formula I, where 0.5 ≤ x ≤ 1.3, 0 ≤ y ≤ 1.3, 0.9 ≤ x + y ≤ 1.3; 0.9 ≤ a ≤ 1.5, 0 ≤ b ≤ 0.4, 0.9 ≤ a + b ≤ 1.5; 0 ≤ c ≤ 0.5; 3 ≤ z ≤ 5; A includes one or more of Na, K, and Mg; Me includes one or more of Mn, Fe, Co, and Ni; M includes one or more of Mn, Ti, Ba, Co, Mg, Al, Ni, and Sn; X includes one or more of S, Si, Cl, B, C, N, and P; Y includes one or more of O and F.

[0045] The lithium-containing phosphate with an olivine structure having the above components has good structural stability and further improves the cycling stability of the battery cell.

[0046] In any embodiment, the positive electrode active material includes one or more of lithium iron phosphate, lithium manganese phosphate, lithium manganese iron phosphate, lithium nickel phosphate, lithium cobalt phosphate, and modified forms of any one of the foregoing substances, wherein the modified forms include one or more of doping modification and coating modification.

[0047] In any embodiment, the first charge specific capacity of the positive electrode active material is 150 mAh / g to 170 mAh / g.

[0048] In any embodiment, the first discharge specific capacity of the positive electrode active material is 140 mAh / g to 165 mAh / g.

[0049] The positive electrode active material with the first charge and discharge specific capacities within the above ranges is beneficial to further improving the energy density of the battery cell.

[0050] In some embodiments, in the cumulative particle number distribution curve of the particles obtained from the cross-section of the positive electrode film layer along the thickness direction of the electrode sheet, the particle number distribution particle size D10 is 0.2 μm to 1.2 μm.

[0051] In any embodiment, in the cumulative particle number distribution curve of the particles obtained from the cross-section of the positive electrode film layer along the thickness direction of the electrode sheet, the particle size D50 of the particle number distribution is 0.8 μm to 2 μm.

[0052] In any embodiment, in the cumulative particle number distribution curve of the particles obtained from the cross-section of the positive electrode film layer along the thickness direction of the electrode sheet, the particle size D90 of the particle number distribution is 1 μm to 10 μm.

[0053] In any embodiment, in the cumulative particle number distribution curve of the particles obtained from the cross-section of the positive electrode film layer along the thickness direction of the electrode sheet, the particle size D99 of the particle number distribution is 8 μm to 20 μm.

[0054] In any embodiment, the specific surface area of the positive electrode active material is 11 m 2 / g to 14 m 2 / g.

[0055] The particle size distribution and specific surface area of the positive electrode active material are within the above ranges, enabling the positive electrode active material to have excellent particle size distribution, low reaction activity, and polarization effect. Under the same compaction density, it is beneficial to reduce the fragmentation of the active material particles and lower the degree of side reactions with the electrolyte, and the battery cell further takes into account excellent energy density and cycle life.

[0056] In any embodiment, the electrolyte includes a lithium salt, and the lithium salt includes one or more of lithium difluorophosphate LiPO2F2, lithium bis(fluorosulfonyl)imide LiFSI, lithium bis(trifluoromethylsulfonyl)imide LiTFSI, lithium bis(oxalato)borate LiBOB, and lithium perchlorate LiClO4.

[0057] In any embodiment, the lithium salt includes lithium difluorophosphate LiPO2F2.

[0058] Adding the above lithium salt to the electrolyte is beneficial to improving the stability of the solid electrolyte interface film (SEI film) on the negative electrode, alleviating the repeated rupture and formation of the SEI film caused by the swelling of the negative electrode active material particles, thereby further improving the cycle life of the battery cell. Among them, lithium difluorophosphate LiPO2F2 has excellent effects on improving the cycle life of the battery cell, low cost, and mildness, and is suitable for the industrial preparation of battery cells.

[0059] In any embodiment, the lithium salt further includes one or more of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), and lithium hexafluoroarsenate (LiAsF6).

[0060] The above lithium salts have high solubility and dissociation degree, enabling the electrolyte to have excellent conductivity, providing a transmission channel for lithium ions, and enabling additive lithium salts to play a role in participating in the formation of the SEI film, thereby further improving the cycle life of the battery cell.

[0061] In any implementation, the concentration of the lithium salt in the electrolyte is 0.5 mol / L to 2 mol / L.

[0062] When the concentration of the lithium salt is within the above range, the electrolyte takes into account excellent ionic conductivity and wettability, thereby further improving the cycle stability of the battery cell in the embodiments of the present application.

[0063] In any implementation, based on the total mass of the lithium salt, the mass proportion of lithium difluorophosphate LiPO2F2 is 2% to 30%.

[0064] In any implementation, based on the total mass of the lithium salt, the mass proportion of lithium difluorophosphate LiPO2F2 is 5% to 15%.

[0065] When the mass proportion of lithium difluorophosphate LiPO2F2 is within the above range based on the total mass of the lithium salt, the battery cell takes into account an electrolyte with excellent conductivity and a stable SEI film, thereby further improving the cycle life of the battery cell.

[0066] In any implementation, the electrolyte further includes additives, and the additives include one or more of carbonate additives and sulfur-containing additives.

[0067] In any implementation, the carbonate additives include one or more of vinylene carbonate (VC) and fluorinated ethylene carbonate (FEC).

[0068] The carbonate additives can evolve into organic components in the SEI film, improving the toughness of the SEI film, thereby further enhancing the stability of the SEI film during the cycling of the battery cell, reducing the side reactions between the electrolyte and the negative electrode film layer, and being beneficial to the further improvement of the cycle life of the battery cell.

[0069] In any implementation, the sulfur-containing additives include one or more of ethylene sulfate, vinylene sulfite, propylene sulfate, vinyl methyl sulfate, vinyl methyl sulfite, ethylene sulfite ethyl ester, and sulfonate.

[0070] The sulfur-containing additives can evolve into sulfur-containing inorganic components in the SEI film, further improving the thermal stability of the SEI film at high temperatures, and being beneficial to the further improvement of the cycle stability of the battery cell.

[0071] In any embodiment, the electrolyte further includes a solvent, the solvent includes carbonate solvents, and the carbonate solvents include one or more of linear carbonates, cyclic carbonates, and fluorinated carbonates.

[0072] In any embodiment, the linear carbonates include one or more of diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), and methyl ethyl carbonate (MEC).

[0073] In any embodiment, the cyclic carbonates include one or more of ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), and vinylene ethylene carbonate (VEC).

[0074] In any embodiment, the fluorinated carbonates include one or more of 1,2-difluoroethylene carbonate, 1,1-difluoroethylene carbonate, 1,1,2-trifluoroethylene carbonate, 1,1,2,2-tetrafluoroethylene carbonate, 1-fluoro-2-methylethylene carbonate, 1-fluoro-1-methylethylene carbonate, 1,2-difluoro-1-methylethylene carbonate, 1,1,2-trifluoro-2-methylethylene carbonate, and trifluoromethyl ethylene carbonate.

[0075] In any embodiment, the separator includes a base film, a first functional layer on both sides of the base film, and a second functional layer between the base film and at least one side of the first functional layer. The first functional layer includes polymer particles, and the second functional layer includes inorganic substances.

[0076] The inorganic substances in the second functional layer can improve the wettability of the separator to the electrolyte and the heat resistance. The polymers in the first functional layer can improve the processability and stability of the separator, and prevent the separator from moving in the battery cell to cause internal short circuit. The above separator can further improve the cycle stability and safety performance of the battery cell.

[0077] In any embodiment, the second functional layer is located between the base film and the first functional layer on the side close to the positive electrode tab, and the single-layer thickness of the second functional layer is 1 μm - 3 μm.

[0078] The impedance of the positive electrode active material is relatively large, and more heat is generated during charge and discharge. The second functional layer close to the positive electrode side helps to further reduce the thermal shrinkage of the separator; and the aluminum foil of the positive electrode current collector is more likely to generate burrs during die-cutting. The second functional layer facing the positive electrode helps to improve the toughness and strength of the separator, prevent the burrs from piercing the separator to cause internal short circuit, and thus further improve the cycle stability and safety performance of the battery cell.

[0079] In any embodiment, the second functional layer is located between the base film and the first functional layer on the side close to the negative electrode plate, and the single-layer thickness of the second functional layer is 1 μm - 3 μm.

[0080] In a lithium phosphate cathode active material system with relatively low heat generation, the second functional layer of the separator can also be close to the negative electrode side, which helps to improve the wetting effect of the separator on the electrolyte on the negative electrode side, thereby reducing the generation of lithium dendrites on the negative electrode side, and helps to prevent the lithium dendrites from piercing the separator, thereby further improving the cycle stability and safety performance of the battery cell.

[0081] In any embodiment, the second functional layer is located between the base film and the first functional layers on both sides, and the single-layer thickness of the second functional layer is 1 μm - 2 μm.

[0082] When the thickness of the second functional layer is within the above range, the separator has both excellent wettability and a short lithium ion diffusion distance, which is beneficial to further improving the cycle stability and energy density of the battery cell.

[0083] In any embodiment, the polymer particles include one or more of fluorine-containing polymer particles and non-fluorine polymer particles; among them, the fluorine-containing polymer particles include one or more of vinylidene fluoride homopolymers and vinylidene fluoride copolymers, and the non-fluorine polymer particles include acrylate copolymers.

[0084] In any embodiment, the inorganic substances include one or more of aluminum hydroxide monohydrate, alumina, silica, boehmite, barium sulfate, calcium oxide, titanium oxide, zinc oxide, magnesium oxide, zirconium oxide, and tin oxide.

[0085] In any embodiment, the liquid injection coefficient of the battery cell is 1.8 g / Ah - 3 g / Ah, and can be optionally 2.2 g / Ah - 2.7 g / A.

[0086] Since the soft-pack battery cell has a higher space utilization rate, controlling the liquid injection coefficient within the above range enables the injected electrolyte to provide excellent cycle life for the battery cell while improving the weight energy density, and alleviates the phenomenon that the excessive additives cause too large SEI film impedance and deteriorate the charging DCR, reducing the influence of gas generation due to the reaction of electrolyte components and then causing the swelling of the soft-pack housing with relatively low mechanical strength, etc., thus taking into account the improvement of the safety performance and use stability of the battery cell.

[0087] The second aspect of the present application provides a battery device, including the battery cell provided in the first aspect of the present application, and the battery device includes at least one of a battery module, a battery pack, and an energy storage battery.

[0088] The third aspect of the present application further provides an electrical device, and the electrical device includes the battery device provided in the second aspect of the present application, and the battery device is used to provide electrical energy.

[0089] The fourth aspect of the present application further provides an energy storage device, which includes the battery device provided in the second aspect of the present application, and the battery device is used for storing electric energy. Description of the Drawings

[0090] Figure 1 It is a schematic diagram of a battery cell according to an embodiment of the present application; Figure 2 is Figure 1 A partial cross-sectional view of the battery cell shown in an embodiment of the present application; Figure 3 It is a schematic diagram of an electrical device using the battery cell as a power source according to an embodiment of the present application.

[0091] Description of the Reference Numerals: 1. Electrode assembly; 2. Positive electrode tab; 3. Negative electrode tab; 4. Tab heat-sealing adhesive; 5. Housing. Detailed Embodiments

[0092] Hereinafter, embodiments of the battery cell, battery device, electrical device, and energy storage device of the present application will be specifically disclosed in detail with appropriate reference to the drawings. However, there may be cases where unnecessary detailed descriptions are omitted. For example, there are cases where detailed descriptions of well-known matters and repeated descriptions of actually identical structures are omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate the understanding of those skilled in the art. In addition, the drawings and the following description are provided for those skilled in the art to fully understand the present application and are not intended to limit the subject matter recited in the claims.

[0093] The "ranges" disclosed in this application are defined in the form of a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundaries of a particular range. The ranges defined in this way can include or exclude the end values, and can be combined arbitrarily, that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a specific parameter, ranges of 60-110 and 80-120 are also contemplated. In addition, if the minimum range values 1 and 2 are listed, and if the maximum range values 3, 4, and 5 are listed, then the following ranges are all contemplated: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, unless otherwise stated, the numerical range "a-b" represents an abbreviated representation of any real number combination between a and b, where a and b are both real numbers. For example, the numerical range "0-5" means that all real numbers between "0-5" are fully listed herein, and "0-5" is only an abbreviated representation of these numerical combinations. In addition, when stating that a certain parameter is an integer ≥2, it is equivalent to disclosing that the parameter is, for example, the integers 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

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

[0095] If there is no special instruction, all technical features and optional technical features of this application can be combined with each other to form a new technical solution.

[0096] If there is no special instruction, all steps of this application can be carried out in sequence or randomly, preferably in sequence. For example, the method includes steps (a) and (b), which means that the method can include steps (a) and (b) carried out in sequence, or can also include steps (b) and (a) carried out in sequence. For example, it is mentioned that the method may further include step (c), which means that step (c) can be added to the method in any order. For example, the method can include steps (a), (b), and (c), or can also include steps (a), (c), and (b), or can also include steps (c), (a), and (b), etc.

[0097] If there is no special instruction, the "including" and "comprising" mentioned in this application mean open-ended, and can also be closed-ended. For example, the "including" and "comprising" can mean that other components not listed can also be included or comprised, or can only include or comprise the listed components.

[0098] If not specifically stated, in this application, the term "or" is inclusive. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, any of the following conditions satisfies the condition "A or B": A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0099] Graphite with a high degree of graphitization has a high specific capacity. As a negative electrode active material, it helps to improve the energy density of battery cells. However, when graphite with a high degree of graphitization is deintercalated with lithium, its volume changes more significantly, which increases the expansion force of the battery cells. The increased squeezing force on the positive and negative pole pieces causes the electrolyte in the film layer to be squeezed out, which is not conducive to the cycle stability of the battery cells. This problem is more significant in soft-pack batteries with higher energy density. How to obtain soft-pack battery cells that take into account both high energy density and cycle life is a technical problem that needs to be solved urgently in this field.

[0100] Based on this, the first aspect of the present application provides a battery cell, which is a soft-pack battery cell, including an electrode assembly and an electrolyte, wherein the electrode assembly includes a positive electrode sheet, a negative electrode sheet and a separator, wherein the separator is located between the positive electrode sheet and the negative electrode sheet; the negative electrode sheet includes a negative electrode current collector and a negative electrode film layer arranged on at least one side of the negative electrode current collector, wherein the negative electrode film layer includes a negative electrode active material, wherein the negative electrode active material includes graphite, wherein the graphitization degree of the graphite is 94% to 98%, and when the battery cell is in a fully charged state, the compaction density of the negative electrode film layer is 1.1 g / cm 3 Up to 1.23g / cm 3 .

[0101] The soft-pack battery cell has a high space utilization rate. Moreover, the flexible shell material used is lighter in weight and thinner in thickness compared to hard shell materials such as aluminum shells and steel shells, which is beneficial to improving the energy density of the battery cell. Graphite with a high degree of graphitization means that the carbon layers in the material are more regularly arranged and have fewer lattice defects, which is conducive to the insertion and extraction of lithium ions, reduces the migration resistance of electrons, and reduces the irreversible consumption of lithium ions, enabling it to have excellent specific capacity, thus further facilitating the improvement of the energy density of the battery cell. However, due to the closer interlayer bonding of graphite with a high degree of graphitization, the volume expansion of graphite is more significant after lithium ions are inserted into the graphite interlayers, which easily causes the electrolyte stored in the pore space inside the negative electrode film layer to be extruded. The insufficient electrolyte in the film layer hinders the transmission of lithium ions, easily triggering the growth of lithium dendrites on the surface of the negative electrode sheet, resulting in a decrease in the cycle life of the battery cell. Moreover, the increase in the thickness of the negative electrode film layer due to expansion also causes the positive electrode film layer and the separator to be squeezed, and there is also a problem of electrolyte extrusion, which further disadvantages the cycle life of the battery cell. And because the space for accommodating the electrolyte in the soft-pack battery cell is limited and it is prone to bulging, when there is more electrolyte, it is likely to cause a bulging risk. Therefore, compared with the electrolyte in the hard-shell battery, the electrolyte in the soft-pack battery cell with the same capacity is less, which makes it more likely to have problems such as insufficient electrolyte in the film layer and difficulty in reabsorbing the electrolyte after extrusion, further leading to insufficient infiltration of the electrolyte in the film layer and seriously deteriorating the cycle life. The applicant found through research that the negative electrode film layer with a smaller tap density is more loosely packed. The loose film layer structure can provide space for the volume change of high-graphitization graphite during the lithium deintercalation and intercalation process, thereby reducing the probability of the electrolyte in the negative electrode film layer being extruded. And it reduces the change in the thickness of the negative electrode film layer, thus alleviating the extrusion of the positive electrode film layer and the separator, reducing the extrusion of the electrolyte in the positive electrode film layer and the separator. Moreover, the negative electrode film layer with a smaller tap density has a larger porosity, which is beneficial to improving its liquid retention and reabsorption ability for the electrolyte, further alleviating the insufficient electrolyte in the negative electrode film layer, and significantly improving the cycle life of the battery cell. In summary, the embodiments of the present application achieve a comprehensive improvement in energy density and cycle life by using graphite with a graphitization degree in the above range and a negative electrode film layer with a tap density in the above range in the soft-pack battery cell.

[0102] A soft-pack battery cell refers to a basic unit whose shell uses a flexible material and can realize the mutual conversion between chemical energy and electrical energy.

[0103] The term "degree of graphitization" refers to an index that measures the degree of formation of a close-packed hexagonal graphite crystal structure by carbon atoms.

[0104] In this application, the graphitization degree of the graphite material can be tested by methods known in the art. For example, it can be tested using an X-ray diffractometer (such as Bruker D8 Discover), referring to JIS K0131-1996 and JB / T 4220-2011, to obtain the average layer spacing d002 of the (002) crystal plane in the crystal structure of the graphite material, and then the graphitization degree is calculated according to the formula g=(0.344 - d002) / (0.344 - 0.3354)×100%. In the above formula, d002 is the average layer spacing of the (002) crystal plane in the crystal structure of the graphite material expressed in nanometers (nm). The negative electrode active material can be freshly prepared or obtained by scraping powder from the negative electrode film layer after disassembling the battery cell. For example, the battery cell is placed at 25°C, the battery cell is discharged at a constant current of 0.33C to 2.0V, left standing for 5 minutes, and then discharged at a constant current of 0.04C to 2.0V, which is recorded as the fully discharged state. The battery cell is disassembled to take the negative electrode plate, the negative electrode plate is dissolved, centrifuged at 3000 r / min for more than 30 minutes to remove the binder in the film layer, etc. The graphite will be deposited in the lower layer of the sediment, and the conductive agent will be in the upper layer of the sediment. The graphite in the lower layer is taken for graphitization degree testing.

[0105] Those skilled in the art can regulate the graphitization degree of graphite through any known process. As an example, using petroleum coke as the raw material, heat treatment is carried out at 2400°C - 2800°C, with a gradient of 200°C each, for 2 hours to obtain graphite materials with different graphitization degrees. Among them, the graphite obtained in the 2400°C group has a graphitization degree of 83%, the graphite obtained in the 2600°C group has a graphitization degree of 88%, and the graphite obtained in the 2800°C group has a graphitization degree of 90%. In addition to regulating the treatment temperature, the raw materials for graphitization treatment, the treatment time, and other processes will all affect the graphitization degree of the product.

[0106] In some embodiments, the graphitization degree of graphite can be 94%, 94.5%, 95%, 95.5%, 96%, 96.5%, 97%, 97.5%, 98% or any numerical range between any two of them.

[0107] When the battery cell is in the fully charged state, the compaction density of the negative electrode film layer has the meaning well-known in the art and can be tested by methods known in the art. For example, the battery cell is placed at 25°C, charged at a constant current of 0.33C to 3.65V, and then charged at a constant voltage of 3.65V to 0.05C. At this time, the battery cell is in the fully charged state, and then the negative electrode plate is disassembled to measure the compaction density of the negative electrode film layer. The compaction density of the negative electrode film layer is the single-sided coating mass of the negative electrode film layer after disassembly / the single-sided thickness of the negative electrode film layer.

[0108] In this application, the "single-sided coating mass of the negative electrode film layer" refers to the mass of the negative electrode film layer per unit area on the side of the current collector.

[0109] In this application, the single-sided coating mass of the negative electrode film layer can be tested by methods known in the art. For example, the negative electrode plate can be taken from the disassembled battery (if it is a double-sided coated negative electrode plate, the negative electrode film layer on one side can be wiped off first), punched into small round pieces with an area of S1, weighed, and recorded as M1. Then, wipe off the negative electrode film layer of the above-mentioned weighed negative electrode plate, weigh the mass of the negative electrode current collector, and record it as M0. The single-sided coating mass of the positive electrode plate = (M1 - M0) / S1.

[0110] The thickness of the negative electrode film layer has the meaning well-known in the art and can be tested by methods known in the art. For example, it can be tested using a micrometer (such as Mitutoyo 293-100 type with an accuracy of 0.1 μm). It can be understood that when the battery cell is in a fully charged state, the compaction density of the negative electrode film layer is different from the designed value of the compaction density of the battery cell. Affected by actual operations, when the battery cell is in a fully charged state, the compaction density of the negative electrode film layer is often lower than the designed value of the cold pressing compaction density of the battery cell.

[0111] In some embodiments, the compaction density of the negative electrode film layer can be 1.1 g / cm 3 、1.11 g / cm 3 、1.12 g / cm 3 、1.13 g / cm 3 、1.14 g / cm 3 、1.15 g / cm 3 、1.16 g / cm 3 、1.17 g / cm 3 、1.18 g / cm 3 、1.19 g / cm 3 、1.2 g / cm 3 、1.21 g / cm 3 、1.22 g / cm 3 、1.23 g / cm 3 or any value range between any two of them.

[0112] In some embodiments, the graphitization degree of graphite is 94% to 96%.

[0113] Graphite with a graphitization degree within the above range enables the battery cell to have excellent energy density while further improving the cycle stability.

[0114] In some embodiments, when the battery cell is in a fully charged state, the compaction density of the negative electrode film layer is 1.1 g / cm 3 to 1.17 g / cm 3 .

[0115] The battery cell with the compaction density of the negative electrode film layer within the above range has excellent energy density while the cycle stability is further improved.

[0116] In some embodiments, the single-sided coating mass of the negative electrode film layer is 0.11 g / 1540.25 mm 2 to 0.16 g / 1540.25 mm 2 .

[0117] In some embodiments, the single-sided coating mass of the negative electrode film layer is 0.12 g / 1540.25 mm 2 to 0.135 g / 1540.25 mm 2 .

[0118] In some embodiments, the single-sided coating mass of the negative electrode film layer is 0.11 g / 1540.25 mm 2 , 0.12 g / 1540.25 mm 2 , 0.13 g / 1540.25 mm 2 , 0.14 g / 1540.25 mm 2 , 0.15 g / 1540.25 mm 2 , 0.16 g / 1540.25 mm 2 or a numerical range between any two of them.

[0119] The negative electrode film layer with the single-sided coating mass within the above range has a thin thickness and a low number of pores. Under the same liquid injection coefficient, it is more conducive to improving the infiltration of the electrolyte into the pores of the film layer and increasing the content of free electrolyte, and the proportion of the electrolyte effectively participating in the reaction is higher. Thus, the probability of lithium plating on the negative electrode due to insufficient electrolyte in the film layer and local lack of electrolyte in the later stage of the cycle, which deteriorates the cycle life, is further reduced. While the cycle stability of the battery cell is further improved, it also has excellent energy density.

[0120] In some embodiments, the cold pressing compaction density of the negative electrode film layer is 1.45 g / cm 3 to 1.6 g / cm 3 .

[0121] In some embodiments, the cold pressing compaction density of the negative electrode film layer is 1.45 g / cm 3 , 1.48 g / cm 3 , 1.51 g / cm 3 , 1.54 g / cm 3 , 1.57 g / cm 3 , 1.6 g / cm 3 or a numerical range between any two of them.

[0122] The cold pressed density of the negative electrode film layer is within the above range, and the battery cell has both excellent energy density and cycle life.

[0123] In some embodiments, the first charge gram capacity of the negative electrode active material is 379 mAh / g to 385 mAh / g.

[0124] In the present application, the first charge and discharge gram capacity of the negative electrode active material can be tested by methods known in the art. For example, the negative electrode active material and the conductive agent carbon black and polyvinylidene fluoride (PVDF) are fully stirred and mixed in an appropriate amount of solvent NMP according to a mass ratio of 91.6:1.8:6.6 to form a uniform negative electrode slurry; the negative electrode slurry is evenly coated on the surface of the negative electrode current collector copper foil and dried and cold pressed; then the metal lithium sheet is used as the counter electrode and the polypropylene (PP) film is used as the isolation membrane, and the electrolyte is injected, wherein the electrolyte formula used is as follows: dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), and ethylene carbonate (EC) are mixed in a weight ratio of 1:1:1 to obtain an organic solvent, and then LiPF6 is dissolved in the above organic solvent to prepare an electrolyte with a concentration of 1.0 mol / L. CR2430 button batteries are assembled in an argon-protected glove box. At 25°C, charge at a rate of 0.1C to an upper cutoff voltage of 3.8V, then charge at a constant voltage until the current is less than 0.05C, and record the first charge capacity as Cn; after standing for 30 minutes, discharge at a rate of 0.1C to a lower cutoff voltage of 2.0V, and record the first discharge capacity as Cm. Then the first charge gram capacity of the negative electrode active material = the first charge capacity Cn / the mass m of the negative electrode active material, and the first discharge gram capacity = the first discharge capacity Cm / the mass m of the negative electrode active material. It can be understood that the first charge gram capacity and the first discharge gram capacity of the negative electrode active material can also be obtained by disassembling the battery, obtaining the negative electrode sheet, and assembling it into a button cell according to the method described above and then testing.

[0125] In some embodiments, the first charge gram capacity of the negative electrode active material is 379 mAh / g, 380 mAh / g, 381 mAh / g, 382 mAh / g, 383 mAh / g, 384 mAh / g, 385 mAh / g, or any range therebetween.

[0126] In some embodiments, the first discharge gram capacity of the negative electrode active material is 345 mAh / g to 360 mAh / g.

[0127] In some embodiments, the first discharge gram capacity of the negative electrode active material is 345 mAh / g, 348 mAh / g, 351 mAh / g, 354 mAh / g, 357 mAh / g, 360 mAh / g, or any range therebetween.

[0128] The first charge-discharge specific capacity of the negative electrode active material is within the above range, enabling the battery cell to have excellent energy density.

[0129] In some embodiments, the Dv50 of the negative electrode active material is 14 μm to 23 μm.

[0130] "Dv10, Dv50, Dv90, Dv99" have the meanings well-known in the art, which respectively represent the particle sizes corresponding to when the cumulative volume distribution percentage of the material reaches 10%, 50%, 90%, and 99%, and can be measured by instruments and methods known in the art. For example, it can be conveniently measured by referring to GB / T 19077-2016 Laser diffraction method for particle size distribution and using a laser particle size analyzer. The test instrument can be the Mastersizer 3000 type laser particle size analyzer of Malvern Instruments Limited, UK. The negative electrode active material can be freshly prepared or obtained by scraping powder from the negative electrode film layer after disassembling the battery cell. For example, discharge the battery to 0% SOC, then disassemble to take the negative electrode plate, scrape a certain amount of powder on the electrode plate with a blade, then use deionized water to wash and shake repeatedly for 5 - 10 times, dry it, sinter it in a tube furnace at 400 °C for 2 h, after sintering, take an appropriate amount of the sample to be tested (the sample concentration ensures a light transmittance of 8% - 12%), add deionized water, and disperse it ultrasonically to ensure complete dispersion of the sample, and then measure the sample according to the GB / T19077-2016 / ISO 13320:2009 standard.

[0131] In some embodiments, the Dv50 of the negative electrode active material is 14 μm, 15 μm, 16 μm, 17 μm, 18 μm, 19 μm, 20 μm, 21 μm, 22 μm, 23 μm, 23 μm or the numerical range between any two of them.

[0132] In some embodiments, the Dv10 of the negative electrode active material is 6 μm to 18 μm.

[0133] In some embodiments, the Dv10 of the negative electrode active material is 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, 16 μm, 17 μm, 18 μm or the numerical range between any two of them.

[0134] In some embodiments, the Dv90 of the negative electrode active material is 17 μm to 49 μm.

[0135] In some embodiments, the Dv90 of the negative electrode active material is 17 μm, 21 μm, 25 μm, 29 μm, 33 μm, 37 μm, 41 μm, 45 μm, 49 μm or the numerical range between any two of them.

[0136] In some embodiments, the Dv99 of the negative electrode active material is from 40 μm to 50 μm.

[0137] In some embodiments, the Dv99 of the negative electrode active material is 40 μm, 41 μm, 42 μm, 43 μm, 44 μm, 45 μm, 46 μm, 47 μm, 48 μm, 49 μm, 50 μm, or a numerical range between any two of them.

[0138] In some embodiments, the specific surface area of the negative electrode active material is 1.4 m 2 / g to 1.6 m 2 / g.

[0139] In the present application, the specific surface area has the meaning well-known in the art and can be tested by methods known in the art. The measurement method can refer to GB / T19587-2017, and is tested by the nitrogen adsorption specific surface area analysis test method and calculated by the BET (Brunauer Emmett Teller) method. Among them, the nitrogen adsorption specific surface area analysis test can be carried out by a Tri-Star 3020 specific surface area and pore size analyzer of Micromeritics Company, USA.

[0140] In some embodiments, the specific surface area of the negative electrode active material is 1.4 m 2 / g, 1.42 m 2 / g, 1.44 m 2 / g, 1.46 m 2 / g, 1.48 m 2 / g, 1.5 m 2 / g, 1.52 m 2 / g, 1.54 m 2 / g, 1.56 m 2 / g, 1.58 m 2 / g, 1.6 m 2 / g, or a numerical range between any two of them.

[0141] The volume distribution particle size and specific surface area of the negative electrode active material within the above ranges enable the negative electrode active material to have both low reaction activity and short lithium-ion solid-phase migration paths, and the battery monomer to have excellent energy density and cycle life.

[0142] In some embodiments, the negative electrode film layer includes a first negative electrode film layer disposed on at least one side of the negative electrode current collector and a second negative electrode film layer disposed on the side of the first negative electrode film layer away from the negative electrode current collector, and the mass ratio of the binder in the first negative electrode film layer is greater than the mass ratio of the binder in the second negative electrode film layer.

[0143] In some embodiments, the binder may be selected from at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0144] The mass content of the binder in different film layers of the negative electrode sheet can be tested by any well-known method in the art. As an example, lay a clean copper foil flat on the table, cut the negative electrode sheet to be tested into a sheet of 20 cm × 10 cm; prepare a clean blade, hold the sheet with the left hand, hold the blade with the right hand, set the blade at a 45° angle to the sheet, select the middle of the sheet and scrape the powder from left to right, with the scraping length being 10 cm and the width being 5 cm. If it takes 10 times to scrape the powder from the start until the copper foil is exposed, then take the powder scraped in the first 3 times as the second film layer sample, and the powder scraped in the last 3 times as the first film layer sample, and store the collected samples in a sealed bottle. Weigh 50 mg of the collected sample and place it in an alumina crucible and level it, use a thermogravimetric analyzer to detect the binder content in the sample (the atmosphere is nitrogen, and the flow rate is 20 mL / min), heat the sample from 25 °C to 600 °C at a heating rate of 10 °C / min, and the mass percentage loss of the sample in different regions is the mass ratio of the binder in different regions.

[0145] The negative electrode slurry used in high-energy density battery cells often has a high content of active materials. When coated on the surface of the current collector, it is prone to powder falling and detaching from the current collector after drying. Moreover, in the step of drying and removing the solvent from the aqueous negative electrode slurry, the binder is prone to float along with the evaporation of the solvent, resulting in insufficient binder content in the lower film layer, and the cohesion between active material particles and the adhesion between active material particles and the copper foil substrate deteriorate significantly. In the embodiments of the present application, setting the mass ratio of the binder in the first negative electrode film layer to be greater than the mass ratio of the binder in the second negative electrode film layer helps to improve the adhesion between the negative electrode film layer and the current collector, the cohesion of the negative electrode film layer, and restrain the expansion of the negative electrode active material, thereby further improving the cycle stability of the battery cell.

[0146] In some embodiments, based on the total mass of the first negative electrode film layer, the mass ratio of the binder is 1% - 3%.

[0147] In some embodiments, based on the total mass of the first negative electrode film layer, the mass ratio of the binder is 1.5% - 2.3%.

[0148] In some embodiments, based on the total mass of the first negative electrode film layer, the mass ratio of the binder is 1%, 1.2%, 1.4%, 1.6%, 1.8%, 2%, 2.2%, 2.4%, 2.6%, 2.8%, 3% or the numerical range between any two of them.

[0149] When the mass percentage of the binder in the first negative electrode film layer is within the above range, the first negative electrode film layer takes into account both the adhesion between the active material particles and the copper foil substrate and the cohesion of the film layer, and the battery cell has both excellent cycle life and energy density.

[0150] In some embodiments, based on the total mass of the second negative electrode film layer, the mass percentage of the binder is 0.3% - 1.5%, and can be optionally 0.3% - 0.8%.

[0151] In some embodiments, based on the total mass of the second negative electrode film layer, the mass percentage of the binder can be 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5% or the numerical range between any two of them.

[0152] When the mass percentage of the binder in the second negative electrode film layer is within the above range, the second negative electrode film layer has both excellent cohesion and energy density, and the battery cell has both excellent cycle life and energy density.

[0153] In some embodiments, based on the total mass of the first negative electrode film layer, the mass percentage of graphite is 70% - 97%.

[0154] In some embodiments, based on the total mass of the first negative electrode film layer, the mass percentage of graphite is 70%, 73%, 76%, 79%, 82%, 85%, 88%, 91%, 94%, 97% or the numerical range between any two of them.

[0155] In some embodiments, based on the total mass of the second negative electrode film layer, the mass percentage of graphite is 80% - 98%.

[0156] In some embodiments, based on the total mass of the second negative electrode film layer, the mass percentage of graphite is 80%, 82%, 84%, 86%, 88%, 90%, 92%, 94%, 96%, 98% or the numerical range between any two of them.

[0157] When the mass percentages of graphite in the first negative electrode film layer and the second negative electrode film layer are within the above ranges, the battery cell has both excellent energy density and cycle life.

[0158] In some embodiments, the ratio of the thickness of the first negative electrode film layer to the thickness of the second negative electrode film layer is 3:7 to 6:4.

[0159] In some embodiments, the ratio of the thickness of the first negative electrode film layer to the thickness of the second negative electrode film layer is 3:7, 4:6, 5:5, 6:4 or the ratio range between any two of them.

[0160] The high binder content in the first negative electrode film layer and the high graphite content in the second negative electrode film layer, combined with the first and second negative electrode film layers having a thickness ratio within the above range, are beneficial for further improving the energy density and cycle stability of the battery cell, while meeting the processing technology of the electrode sheet.

[0161] In some embodiments, the negative electrode film layer may further optionally include a conductive agent. The conductive agent may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0162] In some embodiments, the positive electrode sheet includes a positive electrode current collector and a positive electrode film layer provided on at least one side of the positive electrode current collector. When the battery cell is in a fully charged state, the compaction density of the positive electrode film layer is 2.35 g / cm 3 to 2.55 g / cm 3 .

[0163] The compaction density of the positive electrode film layer can be tested by a method similar to that of the compaction density of the negative electrode film layer described above.

[0164] In some embodiments, when the battery cell is in a fully charged state, the compaction density of the positive electrode film layer is 2.35 g / cm 3 , 2.37 g / cm 3 , 2.39 g / cm 3 , 2.41 g / cm 3 , 2.43 g / cm 3 , 2.45 g / cm 3 , 2.47 g / cm 3 , 2.49 g / cm 3 , 2.51 g / cm 3 , 2.53 g / cm 3 , 2.55 g / cm 3 or any numerical range between any two of them.

[0165] In some embodiments, the cold-pressed compaction density of the positive electrode film layer is 2.4 g / cm 3 to 2.6 g / cm 3 .

[0166] In some embodiments, the cold-pressed compaction density of the positive electrode film layer is 2.4 g / cm 3 , 2.42 g / cm 3 , 2.44 g / cm 3 , 2.46 g / cm 3 , 2.48 g / cm 3 , 2.5 g / cm 3 , 2.52 g / cm 3 , 2.54 g / cm 3, 2.56 g / cm 3 , 2.58 g / cm 3 , 2.6 g / cm 3 or a numerical range between any two of them.

[0167] The positive electrode film layer with a compaction density within the above range has both excellent liquid retention ability and a thin film layer thickness, enabling the battery cell to further have excellent energy density and cycle life.

[0168] In some embodiments, the single-sided coating mass of the positive electrode film layer is 0.26 g / 1540.25 mm 2 to 0.35 g / 1540.25 mm 2 .

[0169] In some embodiments, the single-sided coating mass of the positive electrode film layer is 0.26 g / 1540.25 mm 2 , 0.27 g / 1540.25 mm 2 , 0.28 g / 1540.25 mm 2 , 0.29 g / 1540.25 mm 2 , 0.30 g / 1540.25 mm 2 , 0.31 g / 1540.25 mm 2 , 0.32 g / 1540.25 mm 2 , 0.33 g / 1540.25 mm 2 , 0.34 g / 1540.25 mm 2 , 0.35 g / 1540.25 mm 2 or a numerical range between any two of them.

[0170] The positive electrode film layer with a single-sided coating mass within the above range enables the battery cell to further have excellent energy density and cycle life.

[0171] In some embodiments, the positive electrode film layer includes a positive electrode active material, and the positive electrode active material includes: a lithium-containing phosphate with an olivine structure, and a carbon coating layer located on at least part of the surface of the lithium-containing phosphate.

[0172] The lithium-containing phosphate with an olivine structure is an active material with an olivine structure including lithium ions and phosphate groups. The type of the positive electrode active material can be tested by any well-known method in the art. As an example, phase analysis methods such as X-ray diffraction (XRD) can be combined with elemental analysis methods such as energy spectrum and XPS for analysis.

[0173] The carbon coating layer is beneficial to improving the electronic conductivity of the lithium-containing phosphate and improving the solid-phase transmission rate of electrons, thereby further improving the energy density and cycle performance of the battery cell.

[0174] In some embodiments, the lithium-containing phosphate includes components as shown in Formula I, Li x A y Me a M b P 1-c X c Y z Formula I, where 0.5 ≤ x ≤ 1.3, 0 ≤ y ≤ 1.3, 0.9 ≤ x + y ≤ 1.3; 0.9 ≤ a ≤ 1.5, 0 ≤ b ≤ 0.4, 0.9 ≤ a + b ≤ 1.5; 0 ≤ c ≤ 0.5; 3 ≤ z ≤ 5; A includes one or more of Na, K, and Mg; Me includes one or more of Mn, Fe, Co, and Ni; M includes one or more of Mn, Ti, Ba, Co, Mg, Al, Ni, and Sn; X includes one or more of S, Si, Cl, B, C, N, and P; Y includes one or more of O and F.

[0175] In some embodiments, x can be selected from 0.5, 0.6, 0.7, 0.8, 0.9, 1, 1.1, 1.2, 1.3 or the numerical range between any two of them, y can be selected from 0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 1.1, 1.2, 1.3 or the numerical range between any two of them, x + y can be selected from 0.9, 1, 1.1, 1.2, 1.3 or the numerical range between any two of them, a can be selected from 0.9, 1, 1.1, 1.2, 1.3, 1.4, 1.5 or the numerical range between any two of them, b can be selected from 0, 0.1, 0.2, 0.3, 0.4, 0.5 or the numerical range between any two of them, a + b can be selected from 0.9, 1, 1.1, 1.2, 1.3, 1.4, 1.5 or the numerical range between any two of them, c can be selected from 0, 0.1, 0.2, 0.3, 0.4, 0.5 or the numerical range between any two of them, and z can be selected from 3, 3.1, 3.2, 3.3, 3.4, 3.5, 3.6, 3.7, 3.8, 3.9, 4, 4.1, 4.2, 4.3, 4.4, 4.5, 4.6, 4.7, 4.8, 4.9, 5 or the numerical range between any two of them.

[0176] The lithium-containing phosphate with an olivine structure having the above components has good structural stability and further improves the cycle stability of the battery cell.

[0177] In some embodiments, the cathode active material includes one or more of lithium iron phosphate, lithium manganese phosphate, lithium manganese iron phosphate, lithium nickel phosphate, lithium cobalt phosphate, and modified forms of any one of the foregoing substances, wherein the modified forms include one or more of doping modification and coating modification.

[0178] In some embodiments, the first charge specific capacity of the positive electrode active material is 150 mAh / g to 170 mAh / g.

[0179] In this application, the positive electrode active material is assembled into a button cell to test the electrical performance on a Blue Electric Tester. At 25 ± 5 °C and within the voltage range of 2.0 V to 3.8 V, after constant current charging at 1 / 3 C to 3.8 V, pause for 5 minutes, then constant voltage charge until the cut-off current is 50 μA, and then discharge at 1 C to 2.0 V. Divide the first charge capacity of the button cell by the mass of the positive electrode active material to obtain the first charge specific capacity of the positive electrode active material. Divide the first discharge capacity of the button cell by the mass of the positive electrode active material to obtain the first discharge specific capacity of the positive electrode active material.

[0180] The preparation and testing process of the button cell is as follows: Mix 2.0 g of positive electrode active material, conductive carbon black, and PVDF in a mass ratio of 0.9∶0.05∶0.05, then add the organic solvent NMP (N-methylpyrrolidone), mix well, coat with a 150 μm doctor blade, and dry at 100 °C for 2 h. According to the compaction density of 2.0 g / cm 3 -2.2 g / cm 3 Cold press the positive electrode sheet, punch it into a circular sheet with a diameter of 14 mm, then weigh and record the weight. Put the weighed positive electrode sheet into a vacuum drying oven (105 °C, 1 - 12 hrs, -90 kPa). After drying, put the positive electrode sheet into a glove box and assemble it into a battery in the order of negative electrode shell - nickel mesh - lithium sheet - separator - positive electrode sheet - positive electrode shell. Drop 65 - 87 μL (pipette) of electrolyte (the electrolyte is a mixed solvent of EC (ethylene carbonate) and DMC (1,2-dimethyl carbonate) with a volume ratio of 1:1, and the electrolyte is LiPF6). The negative electrode is on the top, place it in the groove of the sealing machine, and the sealing pressure is 650 kg / cm 2 , use insulating tweezers to remove the button cell and put it into a dust-free bag, remove the glove box, and place it in a constant temperature room to stand for 3 h to obtain the button cell for testing. It can be understood that the first charge specific capacity and the first discharge specific capacity of the positive electrode active material can also be obtained by disassembling the battery, obtaining the positive electrode sheet, and assembling it into a button cell according to the method described above for testing.

[0181] In some embodiments, the first charge specific capacity of the positive electrode active material is 150 mAh / g, 152 mAh / g, 154 mAh / g, 156 mAh / g, 158 mAh / g, 160 mAh / g, 162 mAh / g, 164 mAh / g, 166 mAh / g, 168 mAh / g, 170 mAh / g or any numerical range between any two of them.

[0182] In some embodiments, the first discharge specific capacity of the positive electrode active material is from 140 mAh / g to 165 mAh / g.

[0183] In some embodiments, the first discharge specific capacity of the positive electrode active material is 140 mAh / g, 145 mAh / g, 150 mAh / g, 155 mAh / g, 160 mAh / g, 165 mAh / g, or a numerical range between any two of them.

[0184] The positive electrode active material with the first charge-discharge specific capacity within the above range is beneficial to further improve the energy density of the battery cell.

[0185] In some embodiments, in the cumulative particle number distribution curve of the particles obtained from the cross-section of the positive electrode film layer along the thickness direction of the electrode sheet, the particle size D10 of the particle number distribution is from 0.2 μm to 1.2 μm.

[0186] In the present application, the term "particle" refers to a particle with a recognizable complete boundary in the field of view at a certain magnification, such as 10,000 times, of the positive electrode film layer. There may be defects and scratches inside the particle, but no complete boundary sufficient to divide the particle can be recognized inside the particle.

[0187] In the cumulative particle number distribution curve of the particles obtained from the cross-section of the positive electrode film layer along the thickness direction of the electrode sheet, the particle size of the particle number distribution can be measured by methods known in the art. As an example, disassemble the battery cell, take out the positive electrode sheet, perform SEM testing on the cross-section of the electrode sheet (such as a ZEISS electron microscope with a magnification of 10,000X), and count the sizes of all particles on one SEM image. It can be counted by software or manually. Take the longest diameter of the particle as the particle size. The longest diameter of the particle refers to the maximum value among the distances between any two points on the outer peripheral edge line of the particle. Arrange the particle sizes from small to large, and take the particle sizes corresponding to when the cumulative number distribution reaches 10%, 50%, 90%, and 99% as the particle size D10, D50, D90, and D99 of the particle number distribution of the positive electrode active material particles in the particle size number distribution curve of the cross-section of the positive electrode film layer along the thickness direction; repeat the above operation multiple times, and after counting multiple different regions (such as 10) of the same electrode sheet, take the average value as the particle size D10, D50, D90, and D99 of the particle number distribution of the particles obtained from the cross-section of the positive electrode film layer of the sample to be tested along the thickness direction of the electrode sheet.

[0188] During the compaction process of the positive electrode film layer, compaction occurs in the thickness direction. Therefore, the cross-section of the positive electrode film layer along the thickness direction of the electrode sheet can reflect the true compaction condition of the particles inside the film layer on the spatial scale better than the surface of the positive electrode film layer.

[0189] It is understandable that in the prior art, a laser particle size analyzer is usually used to statistically analyze the particle size of the positive electrode active material by the Malvern laser diffraction method. However, the applicant's research shows that due to the easy agglomeration of particles with small particle sizes, the test results obtained by the Malvern laser diffraction method based on the laser scattering principle often measure the particle size of their particle aggregates, and cannot truly reflect the particle size of the particles in the positive electrode active material, let alone reflect the dispersion state of the positive electrode active material in the film layer, because the degree of dispersion of the positive electrode active material in the film layer will increase during the processes of pulping and film forming and rolling. The test results obtained by the Malvern laser diffraction method are affected by the particle size, specific surface area, and agglomeration degree of the positive electrode active material. Compared with the actual dispersion situation in the electrode sheet, the number of large particles obtained by this test is lower than the actual value, and the number of small particles is higher than the actual value. Therefore, the particle size obtained by testing with the Malvern laser diffraction method cannot be equivalent to or analogized to the particle size statistically obtained in the embodiments of the present application.

[0190] In some embodiments, D10 is 0.2 μm, 0.4 μm, 0.6 μm, 0.8 μm, 1.0 μm, 1.2 μm, or a numerical range between any two of them.

[0191] In some embodiments, in the cumulative particle number distribution curve of the particles obtained from the cross-section of the positive electrode film layer along the thickness direction of the electrode sheet, the particle number distribution particle size D50 is from 0.8 μm to 2 μm.

[0192] In some embodiments, D50 is 0.8 μm, 1.0 μm, 1.2 μm, 1.4 μm, 1.6 μm, 1.8 μm, 2 μm, or a numerical range between any two of them.

[0193] In some embodiments, in the cumulative particle number distribution curve of the particles obtained from the cross-section of the positive electrode film layer along the thickness direction of the electrode sheet, the particle number distribution particle size D90 is from 1 μm to 10 μm.

[0194] In some embodiments, D90 is 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, or a numerical range between any two of them.

[0195] In some embodiments, in the cumulative particle number distribution curve of the particles obtained from the cross-section of the positive electrode film layer along the thickness direction of the electrode sheet, the particle number distribution particle size D99 is from 8 μm to 20 μm.

[0196] In some embodiments, D99 is 8 μm, 10 μm, 12 μm, 14 μm, 16 μm, 18 μm, 20 μm, or a numerical range between any two of them.

[0197] In some embodiments, the specific surface area of the positive electrode active material is 11 m 2 / g to 14 m2 / g.

[0198] In some embodiments, the specific surface area of the positive electrode active material is 11 m 2 / g, 11.5 m 2 / g, 12 m 2 / g, 12.5 m 2 / g, 13 m 2 / g, 13.5 m 2 / g, 14 m 2 / g or a numerical range between any two of them.

[0199] The number-average particle size and the specific surface area of the positive electrode active material are within the above ranges, enabling the positive electrode active material to have excellent particle size distribution, low reactivity, and polarization effect. This is beneficial for reducing the fragmentation of active material particles under the same compaction density and decreasing the degree of side reactions with the electrolyte, further enabling the battery cell to have excellent energy density and cycle life.

[0200] In some embodiments, the positive electrode film layer may further optionally include a binder. As an example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0201] In some embodiments, the positive electrode film layer may further optionally include a conductive agent. As an example, the conductive agent may include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0202] In some embodiments, the electrolyte includes a lithium salt, and the lithium salt includes one or more of lithium difluorophosphate LiPO2F2, lithium bis(fluorosulfonyl)imide LiFSI, lithium bis(trifluoromethylsulfonyl)imide LiTFSI, lithium bis(oxalato)borate LiBOB, and lithium perchlorate LiClO4.

[0203] In some embodiments, the lithium salt includes lithium difluorophosphate LiPO2F2.

[0204] The types and quality of lithium salts in the electrolyte can be obtained by detecting the electrolyte through methods well-known to those skilled in the art. In the embodiments of the present application, freshly prepared electrolyte can be taken as a sample, free electrolyte of a fresh battery can be taken as a sample, or a battery cell that has been fully discharged (discharged to the discharge cut-off voltage so that the charged state of the battery cell is approximately 0% SOC) can be disassembled in reverse, and the free electrolyte obtained from the battery cell is taken as a sample, and detected by ion chromatography analysis method. The types and contents of organic components in the electrolyte have meanings well-known in the art, and can be detected by equipment and methods well-known in the art. For example, qualitative and quantitative analysis of the organic components of the electrolyte can be carried out by gas chromatography with reference to GB / T9722-2023 General Rules for Gas Chromatography of Chemical Reagents. The types and contents of inorganic components / lithium salts in the electrolyte have meanings well-known in the art, and can be detected by equipment and methods well-known in the art. For example, qualitative or quantitative analysis of the inorganic components / lithium salts of the electrolyte can be carried out by ion chromatography analysis method with reference to the standard JY / T020-2002 General Rules for Ion Chromatography Analysis Method.

[0205] Adding the above lithium salts to the electrolyte is beneficial to improving the stability of the solid electrolyte interface film (SEI film) on the negative electrode, alleviating the repeated rupture and formation of the SEI film caused by the swelling of the negative electrode active material particles, thereby further improving the cycle life of the battery cell. Among them, lithium difluorophosphate LiPO2F2 has excellent effects on improving the cycle life of the battery cell, low cost and mildness, and is suitable for the industrial preparation of battery cells.

[0206] In some embodiments, the lithium salt further includes one or more of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), and lithium hexafluoroarsenate (LiAsF6).

[0207] The above lithium salts have high solubility and dissociation degree, making the electrolyte have excellent conductivity, providing a transmission channel for lithium ions, and enabling additive lithium salts to play a role in participating in the formation of the SEI film, thereby further improving the cycle life of the battery cell. In some embodiments, the concentration of the lithium salt in the electrolyte is 0.5 mol / L to 2 mol / L.

[0208] In some embodiments, the concentration of the lithium salt in the electrolyte is 0.5 mol / L, 0.6 mol / L, 0.7 mol / L, 0.8 mol / L, 0.9 mol / L, 1.0 mol / L, 1.1 mol / L, 1.2 mol / L, 1.3 mol / L, 1.4 mol / L, 1.5 mol / L, 1.6 mol / L, 1.7 mol / L, 1.8 mol / L, 1.9 mol / L, 2 mol / L or the numerical range between any two of them.

[0209] When the concentration of the lithium salt is within the above range, the electrolyte has both excellent ionic conductivity and wettability, thereby further improving the cycle stability of the battery monomer in the embodiments of the present application.

[0210] In some embodiments, based on the total mass of the lithium salt, the mass proportion of lithium difluorophosphate LiPO2F2 is 2% to 30%.

[0211] In some embodiments, based on the total mass of the lithium salt, the mass proportion of lithium difluorophosphate LiPO2F2 is 5% to 15%.

[0212] It should be noted that since lithium difluorophosphate in the electrolyte will be consumed to some extent during the formation and charge-discharge cycles, generating relevant components in the SEI film, when the content of lithium difluorophosphate is tested by gas chromatography after disassembling the battery monomer to obtain the electrolyte, the content may be 0%.

[0213] Specifically, taking the case where the mass content of lithium difluorophosphate is 0% as an example, it may be that lithium difluorophosphate is not added to the freshly prepared electrolyte, or the electrolyte obtained after disassembling the battery monomer does not contain lithium difluorophosphate. This situation may be that lithium difluorophosphate is not added to the freshly prepared electrolyte, or a small amount of lithium difluorophosphate is added, but it participates in the film-forming reaction of the SEI film during the formation of the battery monomer, resulting in a mass content of 0% of lithium difluorophosphate during the detection. Optionally, the freshly prepared electrolyte includes lithium difluorophosphate.

[0214] Furthermore, for adding certain substances, such as additives, to the electrolyte, due to the characteristic that the additives participate in the film formation on the surface of the active material to play a role, the content of the additives in the electrolyte of the battery monomer is related to the formation, different battery life cycles or different battery storage states. Therefore, there may be a difference in the content of the additives between the freshly prepared electrolyte and the electrolyte obtained by reverse disassembling the battery monomer. However, those skilled in the art can know the approximate range of the content of the relevant substances in the corresponding freshly prepared electrolyte according to the performance expression level (such as the number of cycle times), residual content, etc. of the battery monomer. Similarly, those skilled in the art can also know the approximate range of the content of the non-freshly prepared (i.e., reverse) according to the content of the freshly prepared additives, based on the performance requirements of the battery monomer, storage environment, etc.

[0215] Therefore, the content of lithium difluorophosphate mentioned in the technical solution of the present application can be the content of lithium difluorophosphate actively added to the freshly prepared electrolyte, or the content of the residual lithium difluorophosphate detected by reverse according to the actual battery state.

[0216] It is understandable that in some embodiments, lithium difluorophosphate added to the electrolyte is completely converted into inorganic components in the SEI film during formation. In some embodiments, there is still lithium difluorophosphate remaining in the electrolyte, which forms a reinforcing effect on the SEI film during subsequent cycling of the battery cell.

[0217] In some embodiments, based on the total mass of the lithium salt, the mass fraction of lithium difluorophosphate LiPO2F2 is 2%, 4%, 6%, 8%, 10%, 12%, 14%, 16%, 18%, 20%, 22%, 24%, 26%, 28%, 30% or any value range between any two of them.

[0218] Based on the total mass of the lithium salt, when the mass fraction of lithium difluorophosphate LiPO2F2 is within the above range, the battery cell takes into account an electrolyte with excellent conductivity and a stable SEI film, thereby further improving the cycle life of the battery cell.

[0219] In some embodiments, the electrolyte further includes additives, and the additives include one or more of carbonate additives and sulfur-containing additives.

[0220] Additives refer to components with relatively low content in the electrolyte, generally with a mass fraction in the electrolyte not exceeding 10%. They have the characteristics of strong pertinence and small dosage, and can significantly optimize a certain aspect of the battery performance without changing the production process.

[0221] In the present application, carbonate additives refer to compounds containing a carbonate group (-O-CO-O-) and their derivatives, as well as mixtures containing the above compounds and their derivatives.

[0222] The types of additives in the electrolyte can be obtained by detecting the electrolyte through methods well-known to those skilled in the art. As an example, the testing methods for the types and masses of lithium salts in the electrolyte described above can be used for testing.

[0223] In some embodiments, the carbonate additives include one or more of vinylene carbonate (VC) and fluoroethylene carbonate (FEC).

[0224] Carbonate additives can evolve into organic components in the SEI film, improving the toughness of the SEI film, thereby further enhancing the stability of the SEI film during the cycling of the battery cell, reducing side reactions between the electrolyte and the negative electrode film layer, and being beneficial to further improving the cycle life of the battery cell.

[0225] In some embodiments, the sulfur-containing additives include one or more of ethylene sulfate, vinylene sulfite, propylene sulfate, methyl ethylene sulfate, methyl vinylene sulfite, ethylene sulfite ethyl ester, and sulfonate.

[0226] The sulfur-containing additive can evolve into a sulfur-containing inorganic component in the SEI film, further improving the thermal stability of the SEI film at high temperatures, which is beneficial to further improving the cycle stability of the battery cell.

[0227] In some embodiments, the electrolyte further includes a solvent, the solvent includes a carbonate solvent, and the carbonate solvent includes one or more of a chain carbonate, a cyclic carbonate, and a fluorinated carbonate.

[0228] As used herein, "cyclic carbonate" refers to a compound containing a carbonate group and a cyclic structure in its molecular structure.

[0229] As used herein, "linear carbonate" refers to a compound containing a carbonate group in its molecular structure but not forming a cyclic structure.

[0230] In some embodiments, the chain carbonate includes one or more of diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), and methyl ethyl carbonate (MEC).

[0231] In some embodiments, the cyclic carbonate includes one or more of ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), and vinylene ethylene carbonate (VEC).

[0232] In some embodiments, the fluorinated carbonates include one or more of fluoroethylene carbonate, difluoroethylene carbonate, trifluoroethylene carbonate, tetrafluoroethylene carbonate, fluoromethyl ethylene carbonate, difluoromethyl ethylene carbonate, 1,2-difluoro-1-methyl ethylene carbonate, 1,1,2-trifluoro-2-methyl ethylene carbonate, and trifluoromethyl ethylene carbonate.

[0233] In some embodiments, the separator includes a base film, a first functional layer on both sides of the base film, and a second functional layer between the base film and at least one side of the first functional layer. The first functional layer includes polymer particles, and the second functional layer includes inorganic substances.

[0234] The inorganic substances in the second functional layer can improve the wettability and heat resistance of the separator to the electrolyte. The polymer in the first functional layer can improve the processing performance and stability of the separator, avoiding internal short circuit caused by the movement of the separator in the battery cell. The above separator can further improve the cycle stability and safety performance of the battery cell.

[0235] In some embodiments, the second functional layer is located between the base film and the first functional layer on the side close to the positive electrode tab, and the single-layer thickness of the second functional layer is 1 μm - 3 μm.

[0236] In some embodiments, the single-layer thickness of the second functional layer can be 1 μm, 1.5 μm, 2 μm, 2.5 μm, 3 μm, or a numerical range between any two of them.

[0237] The impedance of the positive electrode active material is relatively large, and more heat is generated during charge and discharge. The second functional layer close to the positive electrode side helps to further reduce the thermal shrinkage of the separator; moreover, the aluminum foil of the positive electrode current collector is more likely to generate burrs during die-cutting. The second functional layer facing the positive electrode helps to improve the toughness and strength of the separator, preventing the burrs from piercing the separator and causing internal short circuit, thereby further improving the cycle stability and safety performance of the battery cell.

[0238] In some embodiments, the second functional layer is located between the base film and the first functional layer on the side close to the negative electrode tab. The single-layer thickness of the second functional layer is 1 μm - 3 μm.

[0239] In the lithium phosphate positive electrode active material system with lower heat generation, the second functional layer of the separator can also be close to the negative electrode side, which helps to improve the wetting effect of the separator on the electrolyte on the negative electrode side, thereby reducing the generation of lithium dendrites on the negative electrode side, and helps to prevent the lithium dendrites from piercing the separator, thereby further improving the cycle stability and safety performance of the battery cell.

[0240] In some embodiments, the second functional layer is located between the base film and the first functional layers on both sides. The single-layer thickness of the second functional layer is 1 μm - 2 μm.

[0241] In some embodiments, the single-layer thickness of the second functional layer can be 1 μm, 1.5 μm, 2 μm, or a numerical range between any two of them.

[0242] When the thickness of the second functional layer is within the above range, the separator has both excellent wettability and a short lithium ion diffusion distance, which is beneficial to further improving the cycle stability and energy density of the battery cell.

[0243] In some embodiments, the polymer particles include one or more of fluoropolymer particles and non-fluoropolymer particles. The fluoropolymer particles include one or more of vinylidene fluoride homopolymers and vinylidene fluoride copolymers. The non-fluoropolymer particles include acrylate copolymers.

[0244] In some embodiments, the inorganic substances include one or more of aluminum hydroxide monohydrate, alumina, silica, boehmite, barium sulfate, calcium oxide, titanium oxide, zinc oxide, magnesium oxide, zirconium oxide, and tin oxide.

[0245] In some embodiments, the liquid injection coefficient of the battery cell is 1.8 g / Ah - 3 g / Ah, and can be optionally 2.2 g / Ah - 2.7 g / A.

[0246] The liquid injection coefficient of a battery cell refers to the ratio of the mass of the electrolyte inside the battery cell to the battery capacity. The liquid injection coefficient of a battery cell can be measured by any well-known method in the art. Exemplarily, the mass of the electrolyte in the battery cell can be measured by the following method: Weigh the battery, and record the mass as M0. Disassemble the battery cell and pour out the free electrolyte. Take out the internal electrode assembly and separate the positive electrode plate, negative electrode plate, separator, and mechanical parts. Immerse and clean the positive electrode plate, negative electrode plate, separator, and mechanical parts with dimethyl carbonate (DMC) solvent for 24h - 48h, and soak repeatedly for more than 3 times. Place the aforementioned positive electrode plate, negative electrode plate, separator, and mechanical parts in an oven at 100°C for more than 24h until completely dried. Weigh the dried positive electrode plate, negative electrode plate, separator, and mechanical parts, and record the mass as M1. Thus, the mass of the electrolyte in the battery cell is (M0 - M1). The liquid injection coefficient is calculated by (M0 - M1) / the rated capacity of the battery cell. The rated capacity is the nominal capacity of the battery, or charge at a charging rate of 0.33C to 3.65V, then charge at a constant voltage of 3.65V to 0.05C, let it stand for 10min, and then discharge at a discharge rate of 0.33C to 2.0V. Take the discharge capacity of the battery cell as the rated capacity.

[0247] In some embodiments, the liquid injection coefficient of the battery cell can be 1.8g / Ah, 1.9g / Ah, 2.0g / Ah, 2.1g / Ah, 2.2g / Ah, 2.3g / Ah, 2.4g / Ah, 2.5g / Ah, 2.6g / Ah, 2.7g / Ah, 2.8g / Ah, 2.9g / Ah, 3.0g / Ah or any value range between any two of them.

[0248] Since the space utilization rate of the soft-pack battery cell is higher, controlling the liquid injection coefficient within the above range enables the injected electrolyte to provide excellent cycle life for the battery cell while improving the weight energy density, and alleviates the phenomenon that the excessive additive causes the too large impedance of the SEI film and deteriorates the charging DCR. It reduces the influence of gas generation due to the reaction of electrolyte components, which in turn causes the swelling of the soft-pack shell with low mechanical strength, etc., thus taking into account the improvement of the safety performance and use stability of the battery cell.

[0249] In some embodiments, the battery cell includes a housing, and the material of the housing includes a soft-pack material, and the soft-pack material includes an aluminum-plastic film.

[0250] In some embodiments, the aluminum-plastic film includes a composite film formed by one or more of polypropylene (PP), polybutylene terephthalate (PBT), polybutylene succinate (PBS), nylon, polyethylene terephthalate (PET), polyethylene (PE) and aluminum.

[0251] The second aspect of the present application provides a battery device, including the battery cell provided by the first aspect of the present application. Additionally, the third aspect of the present application further provides an electrical device, and the electrical device includes the battery device provided by the second aspect of the present application. The battery cell, battery module, or battery pack can be used as the power source of the electrical device or as the energy storage unit of the electrical device. The electrical device can include mobile devices (such as mobile phones, laptops, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships, satellites, energy storage systems, etc., but is not limited thereto.

[0252] As the electrical device, the battery cell, battery module, or battery pack can be selected according to its usage requirements.

[0253] Figure 3 is an electrical device as an example. The electrical device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. In order to meet the requirements of the electrical device for high power and high energy density of the battery cell, a battery pack or a battery module can be adopted.

[0254] Another example of the device can be a mobile phone, a tablet computer, a laptop computer, etc. This device usually requires being thin and light, and a battery cell can be used as the power source.

[0255] The embodiment of the present application further provides an energy storage device using a battery as the power source. The energy storage device can be, but is not limited to, an energy storage container, an energy storage cabinet, an energy storage power station, an energy storage battery pack, or a portable energy storage system, etc.

[0256] Embodiment In order to make the technical problems, technical solutions, and beneficial effects solved by the present application clearer, the present application will be further described in detail below in conjunction with embodiments and the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. The following description of at least one exemplary embodiment is actually only illustrative and in no way constitutes a limitation to the present application and its application. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present application.

[0257] For those not specified in the embodiments regarding specific technologies or conditions, they shall be carried out according to the technologies or conditions described in the literature in the art or according to the product specifications. For reagents or instruments not specified in the manufacturer, they are all conventional products that can be obtained through commercial purchase.

[0258] Embodiment 1 (1) Preparation of the negative electrode sheet The anode active material graphite, conductive agent (SP), thickening agent (CMC), and binder (SBR) are fully stirred and mixed in deionized water as a solvent in a mass ratio of 96.4:0.7:1.1:18 to obtain an anode slurry. Among them, the graphitization degree of graphite is 96%, the first charge specific capacity is 380 mAh / g, the first discharge specific capacity is 350 mAh / g, Dv50 is 15 μm, the specific surface area is 1.43 m 2 / g, Dv10 is 8 μm, Dv90 is 22.4 μm; Dv99 is 42 μm.

[0259] The anode slurry is evenly coated on the anode current collector copper foil, and after drying and cold pressing, an anode electrode sheet is obtained. Among them, the thickness of the copper foil is 6 μm, and the cold pressing compaction density of the anode film layer is 1.52 g / cm 3 , and the single-sided coating mass is 0.1425 g / 1540.25 mm 2 .

[0260] (2) Preparation of the cathode electrode sheet The cathode active material lithium iron phosphate, binder polyvinylidene fluoride, and conductive agent (SP) are mixed in a mass ratio of 97:2:1, and then the solvent N-methylpyrrolidone (NMP) is added and stirred into a cathode slurry. Among them, the first charge specific capacity of the cathode active material is 160 mAh / g, the first discharge specific capacity is 157 mAh / g, Dv50 is 1.4 μm, the specific surface area is 13.1 m 2 / g, Dv10 is 0.6 μm, Dv90 is 5 μm; Dv99 is 8.9 μm. The cathode active material includes lithium iron phosphate and a carbon coating layer on at least part of the surface of lithium iron phosphate. The lithium iron phosphate includes a doping element Ti, and the general formula is LiFe 0.85 Ti 0.15 PO4.

[0261] The cathode slurry is evenly coated on the aluminum foil, and after drying and cold pressing, a cathode electrode sheet is obtained. The thickness of the aluminum foil is 15 μm, and the cold pressing compaction density of the cathode film layer is 2.6 g / cm 3 , and the single-sided coating mass is 0.31 g / 1540.25 mm 2 .

[0262] (3) Preparation of the separator Polyethylene with a thickness of 7 μm is used as the base film, and a 1-μm-thick aluminum oxide monohydrate ceramic material is sprayed on the single-sided surface of the base film close to the cathode electrode sheet. On this basis, 1.85 mg / 1540.25 mm 2 of PVDF is sprayed on both sides to obtain a composite separator.

[0263] (4) Preparation of the electrolyte In a glove box filled with argon (water content < 1 ppm, oxygen content < 1 ppm), EC (ethylene carbonate), DEC (diethyl carbonate), VC (vinylene carbonate), and DTD (divinyl sulfite) with a mass ratio of 38:45:0.5:0.2 were mixed, and a lithium salt with a concentration of 1 mol / L was prepared by adding a fully dried lithium salt. The lithium salt includes LiPF6 (lithium hexafluorophosphate).

[0264] (5) Preparation of battery cells The positive electrode sheet, negative electrode sheet, and separator were stacked in sequence using a laminator, with the separator placed between the positive electrode sheet and the negative electrode sheet to play an isolation role, obtaining a laminated electrode assembly. The laminated battery cell was subjected to gluing treatment to tightly wrap the battery cell. The glued laminated electrode assembly was placed in an outer package, which was a soft-packaging material, an aluminum-plastic film composed of an inner layer of polypropylene, a middle layer of aluminum foil, and an outer layer of nylon. Among them, the aluminum-plastic film outer package was formed and trimmed by a pit-forming machine to obtain the target shape and size. Then, the aluminum-plastic film was heat-sealed, subjected to vacuum baking and standing, injected with electrolyte, and sealed. Then, hot pressing and cold pressing operations were performed on the soft-pack battery. Finally, after processes such as formation, vacuum exhaust, and edge trimming, the battery cells were obtained. The liquid injection coefficient of the battery cells is 2.4 g / Ah, the width of the battery cells is 395 mm, the height is 125 mm, and the thickness is 42 mm. When the battery cells are in a fully charged state, the compaction density of the negative electrode film layer is 1.17 g / cm 3 , and the compaction density of the positive electrode film layer is 2.5 g / cm 3 .

[0265] Examples 2 - 3 The preparation methods of Examples 2 - 3 are basically the same as those of Example 1, except that the graphitization degree of the graphite is changed, as shown in Table 1 specifically.

[0266] Examples 4 - 5 The preparation methods of Examples 4 - 5 are basically the same as those of Example 1, except that the compaction density of the negative electrode film layer is changed, as shown in Table 1 specifically.

[0267] Examples 6 - 9 The preparation methods of Examples 6 - 9 are basically the same as those of Example 1, except that the single-sided coating mass of the negative electrode film layer is changed, and the single-sided coating mass of the positive electrode film layer changes accordingly, as shown in Table 1 specifically.

[0268] Example 10 The preparation method of Example 10 is basically the same as that of Example 1, except that the preparation of the negative electrode sheet is changed, specifically as follows: The negative electrode active material graphite, conductive agent (SP), thickening agent (CMC), and binder (SBR) are fully stirred and mixed in deionized water as the solvent in a mass ratio of 96.1:0.4:1.5:2 to obtain the first negative electrode slurry; The negative electrode active material graphite, conductive agent (SP), thickening agent (CMC), and binder (SBR) are fully stirred and mixed in deionized water as the solvent in a mass ratio of 97.7:0.7:1.1:0.5 to obtain the second negative electrode slurry; The first negative electrode slurry is uniformly coated on the negative electrode current collector copper foil; the second negative electrode slurry is coated on the surface of the first negative electrode slurry, and after drying and cold pressing, a negative electrode plate is obtained. The negative electrode plate includes a negative electrode current collector and a negative electrode film layer on the negative electrode current collector. The negative electrode film layer includes a first negative electrode film layer provided on the surface of the negative electrode current collector and a second negative electrode film layer provided on the side of the first negative electrode film layer away from the negative electrode current collector. The thickness ratio of the first negative electrode film layer to the second negative electrode film layer is 6:4.

[0269] Example 11 The preparation method of Example 11 is basically the same as that of Example 1, except that the compaction density of the positive electrode film layer is changed, as shown in Table 1 specifically.

[0270] Examples 12 - 13 The preparation methods of Examples 12 - 13 are basically the same as that of Example 1, except that the composition of the lithium salt is changed, as shown in Table 1 specifically.

[0271] Example 14 The preparation method of Example 14 is basically the same as that of Example 10, except that the composition of the lithium salt is changed, as shown in Table 1 specifically.

[0272] Examples 15 - 16 The preparation methods of Examples 15 - 16 are basically the same as that of Example 1, except that the liquid injection coefficient is changed, as shown in Table 1 specifically.

[0273] Comparative Examples 1 - 2 The preparation methods of Comparative Examples 1 - 2 are basically the same as that of Example 1, except that the graphitization degree of graphite is changed, and the single-sided coating mass of the positive electrode film layer changes accordingly, as shown in Table 1 specifically.

[0274] Comparative Examples 3 - 4 The preparation methods of Comparative Examples 3 - 4 are basically the same as that of Example 1, except that the compaction density of the negative electrode film layer is changed, as shown in Table 1 specifically.

[0275] Testing Method 1. Cycle Life Test At 25°C, the lithium-ion battery is charged at a constant current of 0.5C until the voltage rises to the rated voltage of 3.65V, and then switched to constant voltage charging until the current drops to 0.05C; it is left standing for 5 minutes, and then the lithium-ion battery is discharged at a constant current of 0.33C. When the voltage drops to 2.0V, the discharge is stopped and the discharge capacity Qc is recorded; the charge-discharge cycle test is carried out with this process step, and the discharge capacity Qn of each cycle is recorded. The life of the battery cell is the number of cycles when Qn / Qc = 70%.

[0276] 2. Energy density test The battery cell is charged at a constant current of 2C to the rated voltage of 3.65V at 25°C, and then charged at a constant voltage until 0.02C, and then left standing for 30 minutes. Subsequently, it is discharged at 0.33C to 2V and left standing for 10 minutes. The volume of the lithium-ion battery = length × width × thickness, with the unit of L; the energy density of the battery is calculated using the discharge capacity, voltage, and volume of the battery. The energy of the battery = ∫UI×dt, where U is the voltage (V), I is the current (A), dt is the time (s), and the unit of energy is Wh. Then the energy density = energy / volume.

[0277] Test results Table 1

[0278] From the comparison between the examples and comparative examples of this application, it can be seen that the battery cell is a soft-pack battery cell, the graphitization degree of graphite is 94% to 98%, and when the battery cell is in a fully charged state, the compaction density of the negative electrode film layer is 1.1 g / cm 3 to 1.23 g / cm 3 , and the battery cell has both excellent energy density and cycle stability.

[0279] From the comparison between Examples 1, 2 and Example 3, it can be seen that the graphitization degree of graphite is 94% to 96%. While the battery cell has excellent energy density, its cycle stability is further improved.

[0280] From the comparison between Examples 1, 4 and Example 5, it can be seen that the compaction density of the negative electrode film layer is 1.1 g / cm 3 to 1.17 g / cm 3 , and while the battery cell has excellent energy density, its cycle stability is further improved.

[0281] From Examples 1, 6 - 9, it can be seen that the single-sided coating mass of the negative electrode film layer is 0.11 g / 1540.25 mm 2 to 0.16 g / 1540.25 mm 2 , and the battery cell has both excellent energy density and cycle stability. The single-sided coating mass of the negative electrode film layer is 0.12 g / 1540.25 mm2 to 0.135 g / 1540.25 mm 2 , the battery cell has both excellent energy density and cycle stability.

[0282] It can be seen from the comparison between Example 10 and Example 1 that the mass ratio of the binder in the first negative electrode film layer is greater than that in the second negative electrode film layer, and the energy density and cycle stability of the battery cell are further improved.

[0283] It can be seen from Examples 1 and 11 that the compaction density of the positive electrode film layer is 2.35 g / cm 3 to 2.55 g / cm 3 , the battery cell has both excellent energy density and cycle stability.

[0284] It can be seen from the comparison between Examples 12, 13 and Example 1 that the lithium salt includes one or more of lithium difluorophosphate LiPO2F2, lithium bis(fluorosulfonyl)imide LiFSI, lithium bis(trifluoromethylsulfonyl)imide LiTFSI, lithium bis(oxalato)borate LiBOB, and lithium perchlorate LiClO4, which helps to improve the cycle stability of the battery cell. It can be seen from the comparison between Example 12 and Example 13 that the lithium salt including LiPO2F2 helps to further improve the cycle stability of the battery cell.

[0285] It can be seen from Examples 1, 15 and 16 that the liquid injection coefficient of the battery cell is 2.2 g / Ah - 2.7 g / A, and the battery cell has both excellent volume energy density, weight energy density, cycle stability and safety performance.

[0286] It should be noted that the present disclosure is not limited to the above embodiments. The above embodiments are only examples, and embodiments having the same structure and the same effect as the technical idea within the scope of the technical solution of the present disclosure are included in the technical scope of the present disclosure. In addition, within the scope not departing from the gist of the present disclosure, various modifications that can be conceived by those skilled in the art to the embodiments and other ways constructed by combining some constituent elements of the embodiments are also included in the scope of the present disclosure.

Claims

1. A battery cell, characterized in that, The battery cell is a soft-pack battery cell, including an electrode assembly and an electrolyte. The electrode assembly includes a positive electrode sheet, a negative electrode sheet, and a separator. The separator is located between the positive electrode sheet and the negative electrode sheet; The negative electrode sheet includes a negative electrode current collector and a negative electrode film layer provided on at least one side of the negative electrode current collector. The negative electrode film layer includes a negative electrode active material, and the negative electrode active material includes graphite. The graphitization degree of the graphite is 94% to 98%. When the battery cell is in a fully charged state, the tap density of the negative electrode film layer is 1.1 g / cm 3 to 1.23 g / cm 3 .

2. The battery cell according to claim 1, wherein The graphitization degree of the graphite is 94% to 96%.

3. The battery cell according to claim 1, wherein, When the battery cell is in a fully charged state, the compaction density of the negative electrode film layer is 1.1 g / cm 3 to 1.17 g / cm 3 .

4. The battery cell according to claim 1, wherein The single-sided coating mass of the negative electrode film layer is 0.11 g / 1540.25 mm 2 to 0.16 g / 1540.25 mm 2 .

5. The battery cell according to claim 1, characterized in that, The single-sided coating mass of the negative electrode film layer is 0.12 g / 1540.25 mm 2 to 0.135 g / 1540.25 mm 2 .

6. The battery cell according to claim 1, wherein, The cold pressing compaction density of the negative electrode film layer is 1.45 g / cm 3 to 1.6 g / cm 3 .

7. The battery cell according to claim 1, wherein The negative active material satisfies at least one of the following conditions: (1) The first charge specific capacity of the negative active material is 379 mAh / g to 385 mAh / g; (2) The first discharge specific capacity of the negative active material is 345 mAh / g to 360 mAh / g; (3) The Dv50 of the negative active material is 14 μm to 23 μm; (4) The specific surface area of the negative electrode active material is 1.4 m 2 / g to 1.6 m 2 / g; (5) The Dv10 of the negative active material is 6 μm to 18 μm; (6) The Dv90 of the negative active material is 17 μm to 49 μm; (7) The Dv99 of the negative active material is 40 μm to 50 μm.

8. The battery cell according to claim 1, characterized in that, The negative electrode film layer includes a first negative electrode film layer provided on at least one side of the negative electrode current collector and a second negative electrode film layer provided on the side of the first negative electrode film layer away from the negative electrode current collector. The mass ratio of the binder in the first negative electrode film layer is greater than the mass ratio of the binder in the second negative electrode film layer.

9. The battery cell according to claim 8, characterized in that, Based on the total mass of the first negative electrode film layer, the mass ratio of the binder is 1% - 3%.

10. The battery cell according to claim 8, characterized in that, Based on the total mass of the first negative electrode film layer, the mass ratio of the binder is 1.5% - 2.3%.

11. The battery cell according to claim 8, wherein, Based on the total mass of the second negative electrode film layer, the mass ratio of the binder is 0.3% - 1.5%.

12. The battery cell according to claim 8, wherein Based on the total mass of the second negative electrode film layer, the mass ratio of the binder is 0.3% - 0.8%.

13. The battery cell according to claim 8, characterized in that, Based on the total mass of the first negative electrode film layer, the mass ratio of the graphite is 70% - 97%; and / or, Based on the total mass of the second negative electrode film layer, the mass ratio of the graphite is 80% - 98%.

14. The battery cell according to claim 8, wherein, The ratio of the thickness of the first negative electrode film layer to the thickness of the second negative electrode film layer is 3:7 to 6:

4.

15. The battery cell according to claim 1, characterized in that, The positive electrode sheet 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 battery cell is in a fully charged state, the compaction density of the positive electrode film layer is 2.35 g / cm 3 to 2.55 g / cm 3 .

16. The battery cell according to claim 15, wherein The cold-pressed compaction density of the positive electrode film layer is 2.4 g / cm 3 to 2.6 g / cm 3 .

17. The battery cell according to claim 15, wherein, The single-sided coating mass of the positive electrode film layer is 0.26 g / 1540.25 mm 2 to 0.35 g / 1540.25 mm 2 .

18. The battery cell according to claim 15, wherein The positive electrode film layer includes a positive active material, and the positive active material includes: Lithium-containing phosphate with an olivine structure and a carbon coating layer located on at least part of the surface of the lithium-containing phosphate.

19. The battery cell according to claim 18, wherein, The lithium-containing phosphate includes the components shown in Formula I, Li x A y Me a M b P 1-c X c Y z Formula Ⅰ where 0.5 ≤ x ≤ 1.3, 0 ≤ y ≤ 1.3, 0.9 ≤ x + y ≤ 1.3; 0.9 ≤ a ≤ 1.5, 0 ≤ b ≤ 0.4, 0.9 ≤ a + b ≤ 1.5; 0 ≤ c ≤ 0.5; 3 ≤ z ≤ 5; A includes one or more of Na, K, and Mg; Me includes one or more of Mn, Fe, Co, and Ni; M includes one or more of Mn, Ti, Ba, Co, Mg, Al, Ni, and Sn; X includes one or more of S, Si, Cl, B, C, N, and P; Y includes one or more of O and F.

20. The battery cell according to claim 18, wherein, The positive active material includes one or more of lithium iron phosphate, lithium manganese phosphate, lithium manganese iron phosphate, lithium nickel phosphate, lithium cobalt phosphate, and modified forms of any one of the foregoing substances. Among them, the modified form includes one or more of doping modification and coating modification.

21. The battery cell according to claim 18, wherein, The positive electrode active material satisfies at least one of the following conditions: (1) The first charge specific capacity of the positive electrode active material is 150 mAh / g to 170 mAh / g; (2) The first discharge specific capacity of the positive electrode active material is 140 mAh / g to 165 mAh / g; (3) In the cumulative particle number distribution curve of the particles obtained from the cross-section of the positive electrode film layer along the thickness direction of the electrode sheet, the particle size D10 of the particle number distribution is 0.2 μm to 1.2 μm; (4) In the cumulative particle number distribution curve of the particles obtained from the cross-section of the positive electrode film layer along the thickness direction of the electrode sheet, the particle size D50 of the particle number distribution is 0.8 μm to 2 μm; (5) In the cumulative particle number distribution curve of the particles obtained from the cross-section of the positive electrode film layer along the thickness direction of the electrode sheet, the particle size D90 of the particle number distribution is 1 μm to 10 μm; (6) In the cumulative particle number distribution curve of the particles obtained from the cross-section of the positive electrode film layer along the thickness direction of the electrode sheet, the particle size D99 of the particle number distribution is 8 μm to 20 μm; The specific surface area of the positive electrode active material is 11 m 2 / g to 14 m 2 / g.

22. The battery cell according to claim 1, wherein, The electrolyte includes a lithium salt, and the lithium salt includes one or more of lithium difluorophosphate (LiPO2F2), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethylsulfonyl)imide (LiTFSI), lithium bis(oxalato)borate (LiBOB), and lithium perchlorate (LiClO4).

23. The battery cell according to claim 22, characterized in that, The lithium salt includes lithium difluorophosphate (LiPO2F2).

24. The battery cell according to claim 22, wherein The lithium salt further includes one or more of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), and lithium hexafluoroarsenate (LiAsF6).

25. The battery cell according to claim 22, wherein The concentration of the lithium salt in the electrolyte is 0.5 mol / L to 2 mol / L.

26. The battery cell according to claim 23, wherein Based on the total mass of the lithium salt, the mass ratio of lithium difluorophosphate (LiPO2F2) is 2% to 30%.

27. The battery cell according to claim 23, wherein Based on the total mass of the lithium salt, the mass ratio of lithium difluorophosphate (LiPO2F2) is 5% to 15%.

28. The battery cell according to claim 1, characterized in that, The electrolyte further includes an additive, and the additive includes one or more of carbonate additives and sulfur-containing additives.

29. The battery cell according to claim 28, wherein the carbonate additives include one or more of vinylene carbonate (VC) and fluorinated ethylene carbonate (FEC); and / or the sulfur-containing additives include one or more of ethylene sulfate, vinylene sulfite, propylene sulfate, methyl ethylene sulfate, methyl vinylene sulfite, ethylene sulfite ethyl ester, and sulfonate ester.

30. The battery cell according to claim 1, wherein, The electrolyte further includes a solvent, and the solvent includes carbonate solvents, and the carbonate solvents include one or more of chain carbonates, cyclic carbonates, and fluorinated carbonate solvents.

31. The battery cell according to claim 30, wherein the chain carbonates include one or more of diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), and methyl ethyl carbonate (MEC); the cyclic carbonates include one or more of ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), and vinylene ethylene carbonate (VEC); and / or The fluorinated carbonates include one or more of vinylene carbonate, 1,1-difluoroethylene carbonate, 1,1,2-trifluoroethylene carbonate, 1,1,2,2-tetrafluoroethylene carbonate, 1-fluoro-2-methylethylene carbonate, 1-fluoro-1-methylethylene carbonate, 1,2-difluoro-1-methylethylene carbonate, 1,1,2-trifluoro-2-methylethylene carbonate, and trifluoromethyl ethylene carbonate.

32. The battery cell according to claim 1, wherein The separator includes a base film, a first functional layer on both sides of the base film, and a second functional layer between the base film and at least one side of the first functional layer. The first functional layer includes polymer particles, and the second functional layer includes inorganic substances.

33. The battery cell according to claim 32, characterized in that, The second functional layer is located between the base film and the first functional layer on the side close to the positive electrode tab, and the single-layer thickness of the second functional layer is 1 μm - 3 μm.

34. The battery cell according to claim 32, wherein, The second functional layer is located between the base film and the first functional layer on the side close to the negative electrode tab, and the single-layer thickness of the second functional layer is 1 μm - 3 μm.

35. The battery cell according to claim 32, wherein The second functional layer is located between the base film and the first functional layers on both sides, and the single-layer thickness of the second functional layer is 1 μm - 2 μm.

36. The battery cell according to claim 32, wherein The polymer particles include one or more of fluorine-containing polymer particles and non-fluorine polymer particles; Among them, the fluorine-containing polymer particles include one or more of vinylidene fluoride homopolymers and vinylidene fluoride copolymers, and the non-fluorine polymer particles include acrylate copolymers.

37. The battery cell according to claim 32, wherein The inorganic substances include one or more of aluminum hydroxide monohydrate, alumina, silica, boehmite, barium sulfate, calcium oxide, titanium oxide, zinc oxide, magnesium oxide, zirconium oxide, and tin oxide.

38. The battery cell according to claim 1, characterized in that, The liquid injection coefficient of the battery cell is 1.8 g / Ah - 3 g / Ah.

39. The battery cell according to claim 1, wherein The liquid injection coefficient of the battery cell is 2.2 g / Ah - 2.7 g / Ah.

40. A battery device, characterized in that, It includes the battery cell according to any one of claims 1 to 39.

41. An electrical device, characterized in that, It includes the battery device according to claim 40, and the battery device is used to provide electrical energy.

42. A energy storage device, characterized in that, It includes the battery device according to claim 40, and the battery device is used to store electrical energy.

Images