Battery cell, battery device, electric device, and energy storage device

Abstract

Provided are a battery cell, a battery device, an electric device, and an energy storage device. On the basis of the total mass of a negative electrode film layer, the mass percentage of silicon ranges from 0.5% to 5%; in a cumulative area distribution curve of particles obtained by means of a section of a positive electrode film layer in the thickness direction of an electrode sheet, the particle size concentration (DA90-DA10) / DA50 of the particles ranges from 1.6 to 8.5; and on the basis of the total number of particles in the section of the positive electrode film layer in the thickness direction of the electrode sheet, the percentage of particles having a particle size greater than or equal to 50 nm and less than 200 nm ranges from 26% to 64%. The battery cell achieves both excellent energy density and excellent power performance in a low-SOC range.

Description

Battery cells, battery packs, electrical devices and energy storage devices Technical Field

[0001] This application relates to the field of battery cell technology, and in particular to a battery cell, battery device, power consumption device and energy storage device. Background Technology

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

[0003] With the market's increasing demands for both extended driving range and efficient recharging of electrical devices, higher requirements are being placed on the energy density of individual battery cells. However, improving energy density performance often leads to a deterioration in power performance, which has become a pressing technical problem that needs to be solved in this field. Summary of the Invention

[0004] This application addresses the aforementioned issues and aims to provide a battery cell, a battery device, an electrical device, and an energy storage device. The battery cell combines excellent energy density with power performance at low SOC, achieving a comprehensive improvement in battery performance.

[0005] The first aspect of this application provides a battery cell, including an electrode assembly and an electrolyte. The electrode assembly includes a positive electrode, a negative electrode, and a separator, with the separator located between the positive and negative electrode. The negative electrode includes a negative current collector and a negative electrode film layer disposed on at least one side of the negative current collector. The negative electrode film layer includes a negative electrode active material, which includes a carbon-based material and a silicon-based material. The silicon element accounts for 0.5% to 5% of the total mass of the negative electrode film layer. The positive electrode includes a positive current collector and a positive electrode film layer disposed on at least one side of the positive current collector. The positive electrode film layer includes a positive electrode active material. The material includes lithium phosphate particles with an olivine structure. In the cumulative area distribution curve of the particles obtained from the cross-section of the positive electrode film along the thickness direction of the electrode sheet, the particle size concentration (DA90-DA10) / DA50 is 1.6 to 8.5. Here, DA90, DA50, and DA10 refer to the particle size corresponding to the cumulative area distribution of the particles reaching 90%, 50%, and 10%, respectively. Based on the total number of particles in the cross-section of the positive electrode film along the thickness direction of the electrode sheet, the proportion of particles with a diameter greater than or equal to 50 nm and less than 200 nm is 26% to 64%.

[0006] The high-specific-capacity silicon-based material of the negative electrode in this application, combined with the lithium-phosphate particles with a wide particle size distribution and excellent gradation in the positive electrode, is beneficial for improving the capacity of the negative electrode and the compaction density of the positive electrode, thereby improving the energy density of the battery. However, silicon-based materials have inherent defects such as low ionic conductivity and high lithium insertion / extraction potential, which leads to high ohmic resistance and diffusion resistance of the silicon-containing negative electrode, resulting in an increase in the overall battery impedance and a significant deterioration in the power performance of the battery cell in the low SOC range. At the same time, the larger particles in the gradation have a larger particle size, resulting in a longer diffusion distance for lithium ions, which reduces the diffusion efficiency of lithium ions and increases the diffusion resistance, also affecting the power performance of the battery cell in the low SOC range. This application limits the number of small-diameter particles in the positive electrode film to a certain range. Particles with a diameter greater than or equal to 50 nm and less than 200 nm have short lithium-ion insertion / extraction distances and low diffusion resistance, mitigating the impact of large particles in silicon-based materials and gradation on the battery cell impedance and power performance in the low SOC range. It also ensures that the particle size concentration in the cross-section is within a suitable range, thereby improving the energy density of the battery cell while maintaining excellent power performance in the low SOC range. In summary, by combining a suitable range of silicon elements in the negative electrode, a wide particle size distribution of lithium phosphate in the positive electrode, and a suitable area ratio of small-diameter particles, high-density positive electrode, high-capacity negative electrode, and high-energy-density battery cells can be obtained while also maintaining good power performance in the low SOC range.

[0007] In any embodiment, the particle size distribution curve obtained from the cross-section of the positive electrode film along the electrode thickness direction shows that the particle size concentration (DA90-DA10) / DA50 is between 1.68 and 4.0.

[0008] In the cross-section of the positive electrode film along the thickness direction of the electrode sheet, an excessively high particle size concentration means that the size difference of the active material particles is significant, making it impossible to achieve optimal close packing of the positive electrode film. This limits the improvement in electrode compaction and makes it difficult to further increase the electrode compaction density. Therefore, by keeping the particle size concentration within the aforementioned range, the energy density of the battery cell can be further improved while maintaining power performance in the low SOC range.

[0009] In any implementation, the mass percentage of silicon element is 1.5% to 3% based on the total mass of the negative electrode film.

[0010] With the silicon content in the negative electrode film within the aforementioned range, the battery cell further balances excellent energy density and power performance in the low SOC range.

[0011] In any embodiment, based on the total number of particles in the cross section of the positive electrode film along the electrode thickness direction, the proportion of particles with a diameter greater than or equal to 50 nm and less than 200 nm is 26% to 45%.

[0012] With the proportion of small particles within the aforementioned range, the impact of large particles in silicon-based materials and gradation on the impedance of individual cells and power performance in the low SOC range is mitigated. On the other hand, it enables the positive electrode film layer to achieve optimal dense packing, resulting in excellent power performance in the low SOC range for individual cells while further improving energy density.

[0013] In any embodiment, the compaction density of the negative electrode film is 1.20 g / cm³. 3 Up to 1.50 g / cm 3 .

[0014] A negative electrode film with a compaction density within the above range enables the battery cell to achieve both excellent energy density and power performance in the low SOC range.

[0015] In any embodiment, the single-sided coating mass of the negative electrode film is 100 mg / 1540.25 mm. 2 Up to 160mg / 1540.25mm 2 .

[0016] Anode films with single-sided coating quality within the above range can further achieve a balance between the energy density of individual battery cells and the power performance in the low SOC range.

[0017] In any embodiment, the compaction density of the positive electrode film is 2.60 g / cm³. 3 Up to 2.83 g / cm 3 .

[0018] A cathode film with a compaction density within the above range can further achieve a balance between the energy density of the battery cell and the power performance in the low SOC range.

[0019] In any embodiment, the single-sided coating mass of the positive electrode film is between 220 mg / 1540.25 mm² and 370 mg / 1540.25 mm². 2 .

[0020] When the single-sided coating quality of the positive electrode film is within the above range, the battery cell has both excellent energy density and power performance in the low SOC range.

[0021] In any embodiment, the silicon-based material includes one or more of elemental silicon, silicon-carbon materials, silicon-oxygen materials, silicon-nitrogen materials, and silicon alloys, and may be selected as one or more of silicon-carbon materials and silicon-oxygen materials.

[0022] In any embodiment, the carbon-based material includes one or more of artificial graphite and natural graphite.

[0023] In any implementation, the mass percentage of silicon-based materials is 1% to 10% based on the total mass of the negative electrode active materials.

[0024] In some implementations, the carbon-based material accounts for 90% to 99% of the total mass of the negative electrode active material.

[0025] In any embodiment, the silicon-based material includes composite silicon-carbon particles, which include a porous carbon matrix and silicon-based particles. The porous carbon matrix has channels with a width of 5 nm to 50 nm inside, and the silicon-based particles are distributed in the channels.

[0026] Silicon-based particles are distributed in the pores of the carbon matrix, which helps to suppress the expansion of silicon particles and improve the structural stability of composite silicon-carbon particles. The pore width of the carbon matrix is ​​within the above range, which makes the particle size of silicon-based particles smaller, and also helps to improve the kinetic performance of composite silicon-carbon particles, thereby improving the cycle stability of battery cells and the power performance in the low SOC range.

[0027] In any embodiment, the carbon-based material includes composite graphite particles, which include graphite bulk particles and a carbon coating layer covering the surface of the graphite bulk particles. The graphite bulk particles include secondary particles, and the carbon coating layer includes amorphous carbon.

[0028] Composite graphite particles, including secondary particles and a surface coating layer including amorphous carbon, are beneficial for improving the wetting performance of the electrolyte in the negative electrode film and enhancing the solid-phase transport capability of active ions, thereby contributing to further improvement of the power performance, fast charging performance and cycle stability of battery cells in the low SOC range.

[0029] In any embodiment, the mass content of amorphous carbon is 2% to 5% based on the total mass of the composite graphite particles.

[0030] When the content of amorphous carbon is within a suitable range, composite graphite materials can have both high specific capacity and high active ion solid-phase transport capability, which is beneficial to further improve the energy density of battery cells, power performance in the low SOC range, and fast charging performance.

[0031] In any embodiment, the powder resistivity of the composite graphite particles is from 0.005 Ω·cm to 0.04 Ω·cm.

[0032] The powder resistivity of composite graphite particles is within a suitable range, which is beneficial to the further improvement of the power performance and fast charging performance of battery cells in the low SOC range.

[0033] 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. The volume average particle size Dv50 of the composite graphite particles in the first negative electrode film layer is 14 μm to 19 μm, and the volume average particle size Dv50 of the composite graphite particles in the second negative electrode film layer is 8 μm to 15 μm.

[0034] The second negative electrode active material layer disposed on the electrolyte side includes negative electrode active materials with smaller particle size, which can further improve the solid-liquid transport rate of lithium ions in the battery electrode, and further improve the power performance and fast charging performance of the battery cell in the low SOC range.

[0035] In any embodiment, the positive electrode active material includes: a lithium phosphate with an olivine structure, and a coating layer located on at least a portion of the surface of the lithium phosphate, the coating layer comprising one or more of carbon, iron, titanium, vanadium, and boron.

[0036] The coating layer contains carbon, which helps improve the electronic conductivity of lithium phosphate and enhances the solid-state electron transport rate, thereby further improving the energy density, power performance in the low SOC range, and fast-charging performance of the battery cell. The coating layer also contains one or more of carbon, iron, titanium, vanadium, and boron, which helps form a fast-ion conductor component with high ionic conductivity. This significantly improves the lithium-ion transport rate during multiple lithium-ion insertion / extraction at the positive electrode, enhances the ionic conductivity of the positive electrode active material, and further improves the energy density, power performance in the low SOC range, and fast-charging performance of the battery cell.

[0037] In any embodiment, the mass percentage of carbon element is 0.8% to 2.3% based on the total mass of the positive electrode active material.

[0038] Based on the total mass of the positive electrode active material, the mass ratio of carbon is within the above range, which makes lithium phosphate have both excellent electronic conductivity and specific capacity, further comprehensively improving the energy density, power performance in the low SOC range, and fast charging performance of the battery cell.

[0039] 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 of the aforementioned substances, wherein the modified forms include one or more of doping modification and coating modification.

[0040] In any embodiment, the positive electrode further includes a positive conductive layer located between the positive electrode film layer and the positive electrode current collector, the thickness of the positive conductive layer being 0.5 μm to 2 μm; and / or, the negative electrode further includes a negative conductive layer located between the negative electrode current collector and at least one side of the negative electrode film layer, the thickness of the negative conductive layer being 0.5 μm to 2 μm.

[0041] The addition of a positive conductive layer and / or a negative conductive layer helps to improve the electronic conductivity of the battery cell electrodes, which in turn helps to further improve the power performance and fast charging performance of the battery cell in the low SOC range.

[0042] In any embodiment, the positive electrode conductive layer includes a conductive agent and a positive electrode binder, and the negative electrode conductive layer includes a conductive agent, which includes one or more of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers; and / or, the positive electrode binder includes one or more of polyvinylidene fluoride, polytetrafluoroethylene, vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, polyacrylic acid, and fluorinated acrylate resins.

[0043] In any embodiment, the electrolyte includes a solvent, which includes carboxylic acid ester solvents.

[0044] Carboxylic acid ester solvents have the advantages of low viscosity and high ionic conductivity, which are beneficial to the wetting of the positive and negative electrode films by the electrolyte and the rapid insertion and extraction of active ions in the negative electrode film, thereby further improving the power performance and fast charging performance of the battery cells in the low SOC range.

[0045] In any embodiment, the carboxylic acid ester solvent has the general structural formula R,-COO-R,, wherein R, includes one or more of hydrogen atoms, halogen atoms, C1-C5 alkyl groups, and C1-C5 haloalkyl groups, and R, includes one or more of C1-C5 alkyl groups and C1-C5 haloalkyl groups.

[0046] In any embodiment, the carboxylic acid ester solvent includes one or more of methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, methyl butyrate, and ethyl butyrate.

[0047] In any embodiment, the mass percentage of the carboxylic acid ester solvent is 10% to 60% based on the total mass of the electrolyte, and optionally 30% to 60%.

[0048] When the mass percentage of carboxylic acid ester solvents is within the above range, the electrolyte has low viscosity, high conductivity, and excellent stability, which is beneficial to the comprehensive improvement of the power performance, fast charging performance, and cycle stability of battery cells in the low SOC range.

[0049] In any embodiment, the solvent further includes carbonate solvents, including one or more of ethylene carbonate, propylene carbonate, butene carbonate, dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate.

[0050] Carbonate solvents have high dielectric constants. Carbonate solvents readily form solvation structures with lithium ions in lithium-containing electrolyte salts to increase the dissociation rate of lithium ions and anions in lithium-containing electrolyte salts, thereby further improving the power performance and fast charging performance of battery cells in the low SOC range.

[0051] In any embodiment, the carbonate solvent accounts for 18% to 70% of the total mass of the electrolyte, and optionally 18% to 40%.

[0052] The mass percentage of carbonate solvents within the above range allows the electrolyte to simultaneously possess suitable viscosity, conductivity, and good dissociation rate and wettability, which is beneficial for comprehensively improving the power performance, fast charging performance, and cycle stability of battery cells in the low SOC range.

[0053] In any embodiment, the electrolyte further includes additives, which include one or more of carbonate additives, sulfur-containing additives, lithium salt additives, and fluorobenzene additives.

[0054] In any embodiment, the carbonate additive includes one or more of vinylene carbonate and ethylene carbonate derivatives.

[0055] Among them, ethylene carbonate derivatives include compounds represented by Formula I.

[0056] R1, R2, R3, and R4 each independently include one or more of hydrogen atoms, halogen atoms, C1-C5 alkyl groups, and C1-C5 haloalkyl groups, and R1, R2, R3, and R4 are not all hydrogen atoms at the same time. Optionally, carbonate additives include one or more of vinylene carbonate and fluorovinyl carbonate.

[0057] Carbonate additives can evolve into organic components in the SEI film, which helps improve the toughness of the SEI film, reduce the probability of SEI film rupture caused by volume changes of silicon-based materials, and cause side reactions between electrolyte and silicon-based materials. They also reduce battery gas production and lower the interface impedance on the negative electrode side, which is beneficial to further improving the cycle life, storage life, power performance in the low SOC range, and fast charging performance of battery cells.

[0058] In any embodiment, the sulfur-containing additive includes one or more of vinyl sulfate, vinyl disulfate, 1,3-propanesulfonate lactone, butene sulfite, vinyl sulfite, and methylene disulfonate.

[0059] Sulfur-containing additives often have high potentials. When added to the electrolyte, these additives preferentially react during formation or subsequent cycling, evolving into sulfur-containing inorganic components in the SEI film. Carbonate-based additives result in SEI films with poor high-temperature stability, which is detrimental to the stability of individual battery cells at high temperatures. The presence of sulfur in the SEI film can further improve its thermal stability at high temperatures, further reduce the interfacial impedance on the negative electrode side, and thus improve the cycle stability of individual battery cells, power performance in the low SOC range, and fast-charging performance.

[0060] In any embodiment, the lithium salt additive includes one or more of lithium difluorophosphate, lithium difluorooxalate borate, lithium tetrafluoroborate, and lithium dioxalate borate.

[0061] Lithium salt additives can evolve into inorganic components in the SEI film, further improving the rigidity and thermal stability of the SEI film, thereby further enhancing the battery's cycle stability, power performance in the low SOC range, and fast-charging performance. Furthermore, these lithium salt additives can also form a positive electrode electrolyte interface film (CEI film) on the surface of the positive electrode active material, further improving the cycle stability of individual battery cells.

[0062] In any embodiment, the fluorobenzene additive includes one or more fluorobenzene and its derivatives.

[0063] Fluorobenzene additives help improve the wettability of the electrolyte to the positive and negative electrode films, thereby further improving the power performance, fast charging performance and cycle stability of the battery cells in the low SOC range.

[0064] In any embodiment, the carbonate additives account for 3% to 10% of the total mass of the electrolyte.

[0065] When the mass percentage of carbonate additives in the electrolyte is within the above range, it can both improve the stability of the SEI film and maintain a suitable electrolyte viscosity, thereby further improving the cycle life of the battery cells, power performance in the low SOC range, and fast charging performance.

[0066] In any embodiment, the mass percentage of sulfur-containing additives is 0.01% to 2% based on the total mass of the electrolyte.

[0067] The mass ratio of sulfur-containing additives in the electrolyte is within the above range, which takes into account both improving the thermal stability of the SEI film and maintaining a suitable electrolyte viscosity, thereby further improving the cycle life of the battery cells, power performance in the low SOC range, and fast charging performance.

[0068] In any embodiment, the lithium salt additive accounts for 0.01% to 1% of the total mass of the electrolyte.

[0069] The lithium salt additives in the electrolyte are within the above-mentioned mass ratio, which takes into account both improving the thermal stability of the SEI film and maintaining the appropriate viscosity of the electrolyte, and further comprehensively improves the cycle life of the battery cells, power performance in the low SOC range and fast charging performance.

[0070] In any embodiment, the fluorobenzene additive accounts for 0.1% to 0.5% of the total mass of the electrolyte.

[0071] When the mass percentage of fluorobenzene additives in the electrolyte is within the above-mentioned range, the wettability of the electrolyte and the appropriate viscosity of the electrolyte are taken into account, thereby further improving the cycle life of the battery cells, the power performance in the low SOC range, and the fast charging performance.

[0072] In any embodiment, the separator includes a base film with a thickness of 4 μm to 7 μm.

[0073] In any embodiment, the porosity of the base membrane is 20% to 70%, optionally 35% to 60%.

[0074] The thickness and porosity of the separator base film within the above range are beneficial for further balancing the energy density and fast charging performance of the battery cells.

[0075] In any embodiment, the separator further includes a functional layer disposed on at least one side of the base membrane. The functional layer includes: a first functional layer located on one side of the base membrane, the first functional layer including first inorganic particles; and a second functional layer located on the other side of the base membrane, the second functional layer including composite particles, the composite particles including second inorganic particles and a plurality of non-fluoropolymer particles, the second inorganic particles being attached to the surface of the non-fluoropolymer particles and / or dispersed inside the non-fluoropolymer particles.

[0076] In any embodiment, the non-fluoropolymer particles comprise acrylate copolymers.

[0077] In any embodiment, the first inorganic particle and the second inorganic particle each independently comprise one or more of silicon oxide, aluminum oxide, boehmite, barium sulfate, calcium oxide, titanium oxide, zinc oxide, magnesium oxide, zirconium oxide, and tin oxide.

[0078] Inorganic particles can improve the wettability and heat resistance of the first and second functional layers to the electrolyte, further comprehensively improving the fast-charging performance, cycle stability, and safety performance of the battery cells. Non-fluoropolymer particles can improve the processing performance and stability of the separator, preventing the separator from migrating within the battery cells and causing internal short circuits, thereby further improving the cycle stability and safety performance of the battery cells.

[0079] In any embodiment, the battery cell includes a housing that accommodates the electrode assembly, and the housing has a wall thickness of 0.2 mm to 0.4 mm.

[0080] A casing wall thickness within the aforementioned range is beneficial for further improvement of the energy density of individual battery cells.

[0081] In any embodiment, the positive electrode includes a positive electrode tab, the negative electrode includes a negative electrode tab, and the battery cell also includes a top cover. The top cover includes a positive electrode terminal and a negative electrode terminal with opposite polarities. The positive electrode terminal is directly welded to the positive electrode tab, and the negative electrode terminal is directly welded to the negative electrode tab.

[0082] Conventional batteries require adapters to connect the electrode terminals and tabs, which reduces the utilization rate of the electrode assembly and lowers the battery's energy density. When the battery cell provided in this application uses the above-described structure, eliminating the adapters and directly welding the electrode terminals and tabs effectively solves this problem and reduces the battery's internal resistance, thereby further improving both battery energy density and fast-charging performance.

[0083] In any embodiment, the volumetric energy density of the battery cell is greater than 410Wh / L and less than or equal to 520Wh / L, and can be selected as 435Wh / L to 465Wh / L.

[0084] This battery cell also has high energy density, which can meet the needs of increasing the driving range of electrical devices.

[0085] In any embodiment, the electrolyte injection coefficient of the battery cell is from 2.2 g / Ah to 2.7 g / Ah.

[0086] Within the above range, the liquid injection coefficient can balance the cycle stability and energy density of the battery cells.

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

[0088] A third aspect of this application also provides an electrical device, which includes the battery device provided in the second aspect of this application.

[0089] The fourth aspect of this application also provides an energy storage device, which includes the battery device provided in the second aspect of this application. Attached Figure Description

[0090] Figure 1 is a schematic diagram of a battery cell according to an embodiment of this application;

[0091] Figure 2 is an exploded view of a battery cell according to an embodiment of this application shown in Figure 1;

[0092] Figure 3 is a schematic diagram of a battery module according to an embodiment of this application;

[0093] Figure 4 is a schematic diagram of a battery pack according to an embodiment of this application;

[0094] Figure 5 is an exploded view of the battery pack of one embodiment of this application shown in Figure 4;

[0095] Figure 6 is a schematic diagram of an electrical device in which a single battery cell is used as a power source according to an embodiment of this application.

[0096] Explanation of reference numerals in the attached diagram: 1 Battery pack; 2 Upper housing; 3 Lower housing; 4 Battery module; 5 Battery cell; 51 Housing; 52 Electrode assembly; 53 Top cover assembly. Detailed Implementation

[0097] The following detailed description, with appropriate reference to the accompanying drawings, discloses embodiments of the battery cell, battery assembly, power consumption device, and energy storage device of this application. However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of practically identical structures may be omitted. This is to avoid unnecessarily lengthy descriptions and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided for the purpose of enabling those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0098] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a specific parameter, it is expected that ranges of 60-110 and 80-120 are also included. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, unless otherwise stated, the numerical range "ab" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been listed in this article; "0-5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0099] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0100] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0101] Unless otherwise specified, all steps in this application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the mention that the method may also include step (c) indicates that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0102] Unless otherwise specified, the terms "comprising" and "including" as used in this application can be open-ended or closed-ended. For example, "comprising" and "including" can mean that other components not listed may also be included, or that only the listed components may be included.

[0103] Unless otherwise specified, the term "or" is inclusive in this application. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, the condition "A or B" is satisfied by any of the following conditions: 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).

[0104] Silicon possesses a high theoretical specific capacity, and silicon-based materials, when used as negative electrode active materials, help improve the energy density of individual battery cells. However, silicon-based materials have lower ionic conductivity and higher lithium insertion / extraction potential than carbon-based materials, resulting in poor power output of battery cells in the low SOC (State of Charge) range. Therefore, obtaining battery cells that balance high energy density and high power performance in the low SOC range is a pressing technical problem that needs to be solved in this field.

[0105] Based on this, a first aspect of this application provides a battery cell, including an electrode assembly and an electrolyte. The electrode assembly includes a positive electrode, a negative electrode, and a separator. The separator is located between the positive and negative electrode. The negative electrode includes a negative current collector and a negative electrode film layer disposed on at least one side of the negative current collector. The negative electrode film layer includes a negative electrode active material, which includes a carbon-based material and a silicon-based material. The silicon element accounts for 0.5% to 5% of the total mass of the negative electrode film layer. The positive electrode includes a positive current collector and a positive electrode film layer disposed on at least one side of the positive current collector. The positive electrode film layer includes a positive electrode active material. The active material includes lithium phosphate particles with an olivine structure. In the cumulative area distribution curve of the particles obtained from the cross-section of the positive electrode film along the thickness direction of the electrode sheet, the particle size concentration (DA90-DA10) / DA50 is 1.6 to 8.5. Here, DA90, DA50, and DA10 refer to the particle size corresponding to the cumulative area distribution of the particles reaching 90%, 50%, and 10%, respectively. Based on the total number of particles in the cross-section of the positive electrode film along the thickness direction of the electrode sheet, the proportion of particles with a diameter greater than or equal to 50 nm and less than 200 nm is 26% to 64%.

[0106] The qualitative and quantitative analysis of each substance or element in this application can be performed using suitable equipment and methods known to those skilled in the art. Relevant testing methods can be referenced from domestic and international testing standards and enterprise standards. Furthermore, those skilled in the art can adaptively modify certain testing steps / instrument parameters from the perspective of testing accuracy to obtain more accurate results. One testing method can be used for qualitative or quantitative analysis, or several testing methods can be used in combination for qualitative or quantitative determination.

[0107] Based on the total mass of the negative electrode film, the mass percentage of silicon is a well-known concept in the art and can be detected using well-known equipment and methods. For example, the negative electrode sheet can be immersed in a solvent such as water to separate the negative electrode active material from the negative electrode current collector. The substances in the negative electrode film can be obtained by filtration and used as a test sample. The test sample can be used with an ICAP7400 inductively coupled plasma atomic emission spectrometer from Thermo Fisher Scientific, USA, in accordance with the GB / T30902-2014 standard, to obtain the mass percentage of silicon.

[0108] In some implementations, based on the total mass of the negative electrode film, the mass percentage of silicon can be selected as 0.5%, 1.0%, 1.5%, 2.0%, 2.5%, 3.0%, 3.5%, 4.0%, 4.5%, 5%, or any value between the two.

[0109] Lithium phosphates with an olivine structure are active materials containing lithium ions and phosphate groups. The types of positive electrode active materials can be tested using any method known in the art. As an example, phase analysis methods such as X-ray diffraction (XRD) combined with elemental analysis methods such as energy dispersive spectroscopy (EDS) and XPS can be used for analysis.

[0110] In this application, the term "particle" refers to a particle in the positive electrode film layer that has a recognizable complete boundary in the field of view at a certain magnification, such as 10,000x. Defects and scratches may exist inside the particle, but a complete boundary sufficient to divide the particle cannot be identified inside the particle.

[0111] The particle identification method is as follows: The positive electrode film layer is cut along the thickness direction of the electrode sheet using an argon ion beam (for example, a Leica EM TIC 3X CP device can be used, operating voltage: 6kV, operating time: 6h). After exposing the cut surface, a scanning electron microscope (SEM) is used (for example, a Hitachi SU8230 device can be used, operating voltage: 3kV, beam current: high, probe model: U (LA100), working distance <5mm) to observe the cut surface along the thickness direction of the electrode sheet. Images are acquired using a field emission scanning electron microscope at a non-edge location in the cut surface of the positive electrode film layer (after observing the electrode edge under the SEM, the field of view is adjusted to the center of the sample) in secondary electron mode. Electron micrographs are taken at 10kx magnification, and the particles in the electron micrographs are analyzed using ImageJ software (1.46r, win64 version). The specific steps for using ImageJ software are as follows: Load the scanning electron microscope (SEM) image to be analyzed; use the Cellpose plugin to identify particles, and then perform manual corrections; use ImageJ to read and analyze data. The specific method for using the Cellpose plugin to identify particles is as follows: Set the segmentation diameter parameter (diameter in the Segmentation module) to 15 pixels, click "run cyto3" to identify particles; manually mark particles in the image that were not identified by the software, were not fully identified, or were identified incorrectly. Particles that were not identified by the software, were not fully identified, or were identified incorrectly mainly include the following: 1. Particles that are too large or have scratches on their surface, making them unidentifiable or incompletely identifiable; 2. During argon ion beam cutting, scratches may be generated on the particle surface, and the software may misinterpret these scratches as particle boundaries, leading to identification errors; 3. Particles that are too small and were not successfully identified; 4. Particles located at the edge of the SEM field of view, with the particle's interior penetrated by the edge, preventing a complete view of the morphology, resulting in identification errors due to partial identification replacing the whole.For the unidentified or misidentified particles mentioned above, manual calibration is performed as follows: Particles located at the edges of the scanning electron microscope that are not fully displayed are deleted; It is determined whether other unidentified or misidentified particles have internal cracks or scratches. If no cracks or scratches are found, the particle is considered a single particle, and its boundary is manually marked based on observation; If cracks or scratches are found within the particle, it is determined whether the cracks or scratches penetrate the particle. If not, it is considered a single particle and manually marked; If the cracks or scratches penetrate the particle, it is determined whether the cracks or scratches are linear or irregular; If the cracks or scratches are irregular, they are considered the boundary between particles, and particles are divided along this boundary; If the cracks or scratches are linear, contrast is compared; If the contrast is not obvious and there is no crack-like appearance, it is considered a scratch and marked as a single particle; If the contrast is strong and there is a crack-like appearance, it is considered the boundary between particles and marked as two particles. After manual marking, irrelevant information from the automatic image processing is deleted, thus completing the particle identification and marking in the image.

[0112] The particle size distribution (DA90-DA10) / DA50 in the cross-section of the positive electrode film along the electrode thickness direction is calculated as follows. After particle identification and labeling, the image is imported into ImageJ software for analysis. The scale is set based on the scanning electron microscope image. The particle size and area in the cross-section of the positive electrode film along the electrode thickness direction are analyzed using the "Feret diameter," "Area," "Round," and "Solidity" analysis functions. According to the software manual (ImageJ User Guide IJ 1.46r), the obtained "Feret" parameter represents the maximum spacing between all parallel lines in the two-dimensional projection of the particle, thus characterizing the particle size; and the obtained "Area" parameter represents the pixel area of ​​the particle. Since particles smaller than 50nm have a large error in the statistical process and are difficult to identify accurately, and the particle size of conductive agents is generally smaller than 50nm, which will cause a large error in the statistical results, particles smaller than 50nm are not counted in the particle size statistics process of this application, and the particle statistics data corresponding to AR, Round or Solidity displayed as "NaN" are deleted.

[0113] Following the above method, to ensure a statistically significant sample size, at least 10 non-overlapping scanning electron microscope (SEM) images were acquired for each electrode, and the particle size within the field of view was statistically analyzed. The obtained particle sizes were arranged in ascending order, and the cumulative area distribution curve of the particles in the positive electrode film was obtained by plotting particle size on the horizontal axis and the cumulative area percentage calculated from the particle's "Area" on the vertical axis. DA90, DA50, and DA10 represent the particle size values ​​corresponding to a cumulative area percentage of 90%, 50%, and 10% on the vertical axis of the cumulative area distribution curve, respectively.

[0114] Among the obtained particle sizes, the number of particles with a diameter greater than or equal to 50 nm and less than 200 nm is divided by the total number of particles counted to obtain the proportion of particles with a diameter greater than or equal to 50 nm and less than 200 nm in the cross-section of the positive electrode film along the thickness direction of the electrode sheet.

[0115] During the cold pressing process, the positive electrode film undergoes compaction in the thickness direction. A cross-section of the positive electrode film along its thickness direction provides a more accurate reflection of the actual compaction of particles within the film on a spatial scale compared to the film's surface. The proportion of particles with a diameter greater than or equal to 50 nm and less than 200 nm in this cross-section directly reflects the ratio of particles in that size range to the total number of particles, indicating the abundance of particles in that size range.

[0116] It is understandable that the particles in the cross-section of the positive electrode film along the thickness direction of the electrode sheet, especially those larger than 50 nm, mainly originate from the positive electrode active material. Therefore, the embodiments of this application can accurately and objectively reflect the distribution of lithium phosphate particles in the positive electrode film within the electrode sheet by observing and statistically analyzing the particle size in the cross-section of the positive electrode film.

[0117] In existing technologies, laser particle size analyzers are typically used to statistically analyze the particle size of positive electrode active materials using Malvern laser diffraction. However, the applicant's research indicates that because lithium phosphate particles are prone to agglomeration, the test results obtained using Malvern laser diffraction, based on the principle of laser scattering, often only reflect the particle size of the agglomerates. This does not accurately reflect the particle size within the positive electrode active material, nor does it reflect the dispersion state of the positive electrode active material in the film layer, as the dispersion of the positive electrode active material in the film layer increases during the film-forming rolling process. The test results obtained by Malvern laser diffraction are affected by the particle size, specific surface area, and degree of agglomeration of the positive electrode active material. Compared to the actual dispersion in the electrode sheet, the number of large particles obtained by this test is lower than the actual value, while the number of small particles is higher. Therefore, the particle size obtained by Malvern laser diffraction cannot be equated with or analogized to the particle size statistically obtained in the embodiments of this application.

[0118] In some implementations, (DA90-DA10) / DA50 can be selected as a range of values ​​between 1.6, 1.9, 2.2, 2.5, 2.8, 3.1, 3.4, 3.7, 4.0, 4.3, 4.6, 4.9, 5.2, 5.5, 5.8, 7.1, 7.4, 7.7, 8.0, 8.2, 8.5, or any two of these values.

[0119] In some embodiments, based on the total number of particles in a cross-section along the thickness direction of the positive electrode film, the percentage of particles with a diameter greater than or equal to 50 nm and less than 200 nm can be selected as 26%, 28%, 30%, 32%, 34%, 36%, 38%, 40%, 42%, 44%, 46%, 48%, 50%, 52%, 54%, 56%, 58%, 60%, 62%, 64%, or any value range between the two.

[0120] Those skilled in the art can control the particle size distribution (DA90-DA10) / DA50 and the proportion of particles with a diameter greater than or equal to 50 nm and less than 200 nm using any known process. For example, particle size distribution can be adjusted through the scientific gradation of particles of different sizes; the mechanical force of crushing and grinding processes can be used to process raw materials to the target particle size distribution range, thereby adjusting particle size and distribution; particle size separation can be achieved by using screening and grading equipment to obtain a particle size distribution that meets the requirements; precise control of the feeding rate and adjustment of the residence time and stress state of particles within the equipment also helps to control particle size; adjusting the sintering temperature or holding time of the positive electrode active material also helps to adjust particle size and distribution.

[0121] "Power performance of a single battery cell in the low SOC range" refers to the power output capability of the battery when the remaining charge is low (e.g., SOC < 10%).

[0122] The high-specific-capacity silicon-based material of the negative electrode in this application, combined with the lithium-phosphate particles with a wide particle size distribution and excellent gradation in the positive electrode, is beneficial for improving the capacity of the negative electrode and the compaction density of the positive electrode, thereby improving the energy density of the battery. However, silicon-based materials have inherent defects such as low ionic conductivity and high lithium insertion / extraction potential, which leads to high ohmic resistance and diffusion resistance of the silicon-containing negative electrode, resulting in an increase in the overall battery impedance and a significant deterioration in the power performance of the battery cell in the low SOC range. At the same time, the larger particles in the gradation have a larger particle size, resulting in a longer diffusion distance for lithium ions, which reduces the diffusion efficiency of lithium ions and increases the diffusion resistance, also affecting the power performance of the battery cell in the low SOC range. This application limits the number of small-diameter particles in the positive electrode film to a certain range. Particles with a diameter greater than or equal to 50 nm and less than 200 nm have short lithium-ion insertion / extraction distances and low diffusion resistance, mitigating the impact of large particles in silicon-based materials and gradation on the battery cell impedance and power performance in the low SOC range. It also ensures that the particle size concentration in the cross-section is within a suitable range, thereby improving the energy density of the battery cell while maintaining excellent power performance in the low SOC range. In summary, by combining a suitable range of silicon elements in the negative electrode, a wide particle size distribution of lithium phosphate in the positive electrode, and a suitable area ratio of small-diameter particles, high-density positive electrode, high-capacity negative electrode, and high-energy-density battery cells can be obtained while also maintaining good power performance in the low SOC range.

[0123] In some embodiments, the particle size distribution curve (DA90-DA10) / DA50 obtained from the cross-section of the positive electrode film along the electrode thickness direction has a particle size concentration (DA90-DA10) / DA50 of 1.68 to 4.0.

[0124] In the cross-section of the positive electrode film along the thickness direction of the electrode sheet, an excessively high particle size concentration means that the size difference of the active material particles is significant, making it impossible to achieve optimal close packing of the positive electrode film. This limits the improvement in electrode compaction and makes it difficult to further increase the electrode compaction density. Therefore, by keeping the particle size concentration within the aforementioned range, the energy density of the battery cell can be further improved while maintaining power performance in the low SOC range.

[0125] In some implementations, the mass percentage of silicon is 1.5% to 3% based on the total mass of the negative electrode film.

[0126] With the silicon content in the negative electrode film within the aforementioned range, the battery cell further balances excellent energy density and power performance in the low SOC range.

[0127] In some implementations, based on the total number of particles in a cross-section of the positive electrode film along the electrode thickness direction, the proportion of particles with a diameter greater than or equal to 50 nm and less than 200 nm is 26% to 45%.

[0128] With the proportion of small particles within the aforementioned range, the impact of large particles in silicon-based materials and gradation on the impedance of individual cells and power performance in the low SOC range is mitigated. On the other hand, it enables the positive electrode film layer to achieve optimal dense packing, resulting in excellent power performance in the low SOC range for individual cells while further improving energy density.

[0129] In some embodiments, the compaction density of the negative electrode film is 1.20 g / cm³. 3 Up to 1.50 g / cm 3 .

[0130] The compaction density of the negative electrode film is a well-known concept in the art and can be tested using methods known in the art. For example, a single battery cell is charged to 3.8V at a constant current charging rate of 0.33C at 25°C, allowed to stand for 1 minute, and then charged at a constant voltage until the current is less than 0.05C. At this point, the battery cell is fully charged. The negative electrode sheet is then disassembled, and the compaction density of the negative electrode film is measured. The compaction density of the negative electrode film is the single-sided coating mass of the negative electrode film measured after disassembly divided by the thickness of the negative electrode film.

[0131] The thickness of the negative electrode film is a well-known concept in the art and can be tested using methods known in the art, such as a micrometer (e.g., a Mitutoyo 293-100 with an accuracy of 0.1 μm). It is understood that the compaction density of the negative electrode film in a fully charged battery cell differs from the designed compaction density of the battery cell. Due to practical operational factors, the compaction density of the negative electrode film in a fully charged battery cell is often slightly lower than the designed compaction density.

[0132] In some embodiments, the compaction density of the negative electrode film can be selected as 1.20 g / cm³. 3 1.25g / cm 3 1.30g / cm 3 1.35g / cm 3 1.40g / cm 3 1.45g / cm 3 1.50g / cm 3 Or the range of values ​​between any two.

[0133] A negative electrode film with a compaction density within the above range enables the battery cell to achieve both excellent energy density and power performance in the low SOC range.

[0134] In some embodiments, the single-sided coating mass of the negative electrode film is 100 mg / 1540.25 mm. 2 Up to 160mg / 1540.25mm 2 .

[0135] "Single-sided coating quality of the negative electrode film" refers to the quality of the negative electrode film per unit area on the current collector side.

[0136] The single-sided coating quality of the negative electrode film can be tested using methods known in the art. For example, a negative electrode sheet can be taken from a disassembled battery cell (if it is a double-sided coated negative electrode sheet, the negative electrode film layer on one side can be wiped off first), cut into a small circular piece with an area of ​​S1, and weighed, recorded as M1. Then, the negative electrode film layer of the weighed negative electrode sheet is wiped off, and the mass of the negative electrode current collector is weighed and recorded as M0. The single-sided coating quality of the negative electrode sheet = (M1 - M0) / S1.

[0137] In some embodiments, the single-sided coating quality of the negative electrode film can be selected as 100 mg / 1540.25 mm. 2 110mg / 1540.25mm 2 120mg / 1540.25mm 2 130mg / 1540.25mm 2 140mg / 1540.25mm 2 150mg / 1540.25mm 2 160mg / 1540.25mm 2 Or the range of values ​​between any two.

[0138] Anode films with single-sided coating quality within the above range can further achieve a balance between the energy density of individual battery cells and the power performance in the low SOC range.

[0139] In some embodiments, the compaction density of the positive electrode film is 2.60 g / cm³. 3 Up to 2.83 g / cm 3 .

[0140] The compaction density of the positive electrode film can be tested using a method similar to that used for the compaction density of the negative electrode film, as described above.

[0141] In some embodiments, the compaction density of the positive electrode film can be selected as 2.60 g / cm³. 3 2.62 g / cm 3 2.64 g / cm 3 2.67 g / cm 3 2.69 g / cm 3 2.71 g / cm 32.73 g / cm 3 2.75g / cm 3 2.77 g / cm 3 2.79 g / cm 3 2.81 g / cm 3 2.83 g / cm 3 Or the range of values ​​between any two.

[0142] A cathode film with a compaction density within the above range can further achieve a balance between the energy density of the battery cell and the power performance in the low SOC range.

[0143] In some embodiments, the single-sided coating mass of the positive electrode film is 220 mg / 1540.25 mm. 2 Up to 370mg / 1540.25mm 2 .

[0144] The single-sided coating quality of the positive electrode film can be tested using a method similar to that used for the single-sided coating quality of the negative electrode film described above.

[0145] In some embodiments, the single-sided coating mass of the positive electrode film can be selected as 220 mg / 1540.25 mm. 2 230mg / 1540.25mm 2 240mg / 1540.25mm 2 250mg / 1540.25mm 2 260mg / 1540.25mm 2 270mg / 1540.25mm 2 280mg / 1540.25mm 2 290mg / 1540.25mm 2 300mg / 1540.25mm 2 310mg / 1540.25mm 2 320mg / 1540.25mm 2 330mg / 1540.25mm 2 340mg / 1540.25mm 2 350mg / 1540.25mm 2 360mg / 1540.25mm 2 370mg / 1540.25mm 2 Or the range of values ​​between any two.

[0146] When the single-sided coating quality of the positive electrode film is within the above range, the battery cell has both excellent energy density and power performance in the low SOC range.

[0147] In some embodiments, the silicon-based material includes one or more of elemental silicon, silicon-carbon materials, silicon-oxygen materials, silicon-nitrogen materials, and silicon alloys, and may be selected as one or more of silicon-carbon materials and silicon-oxygen materials.

[0148] In some implementations, the carbon-based material includes one or more of artificial graphite and natural graphite.

[0149] In some implementations, the silicon-based material accounts for 1% to 10% of the total mass of the negative electrode active material.

[0150] In some implementations, based on the total mass of the negative electrode active material, the mass percentage of silicon-based material can be selected as 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, or any value range between the two.

[0151] In some implementations, the carbon-based material accounts for 90% to 99% of the total mass of the negative electrode active material.

[0152] In some implementations, based on the total mass of the negative electrode active material, the mass percentage of the carbon-based material can be selected as 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or any value range between the two.

[0153] In some embodiments, the silicon-based material includes composite silicon-carbon particles, which include a porous carbon matrix and silicon-based particles. The porous carbon matrix has channels with a width of 5 nm to 50 nm inside, and the silicon-based particles are distributed in the channels.

[0154] In some embodiments, the width of the pores inside the porous carbon matrix can be selected as 5 nm, 10 nm, 15 nm, 20 nm, 25 nm, 30 nm, 35 nm, 40 nm, 45 nm, 50 nm or any value range between the two.

[0155] The width of the internal pores of a porous carbon matrix can be tested using methods known in the art. For example, the pore size can be tested using a gas adsorption method according to the testing standards GB / T19587-2017 & GB / T21650.2-2008, as follows: A silicon-carbon composite is taken as the sample, and the sample tube is immersed in liquid nitrogen at -196℃. Nitrogen gas is adsorbed onto the material under test at a relative pressure of 0-1. The pore size distribution of the porous material is characterized based on the relationship between the volume of each pore size and the corresponding partial pressure.

[0156] Silicon-based particles are distributed in the pores of the carbon matrix, which helps to suppress the expansion of silicon particles and improve the structural stability of composite silicon-carbon particles. The pore width of the carbon matrix is ​​within the above range, which makes the particle size of silicon-based particles smaller, and also helps to improve the kinetic performance of composite silicon-carbon particles, thereby improving the cycle stability of battery cells and the power performance in the low SOC range.

[0157] In some embodiments, the carbon-based material includes composite graphite particles, which include graphite bulk particles and a carbon coating layer covering the surface of the graphite bulk particles. The graphite bulk particles include secondary particles, and the carbon coating layer includes amorphous carbon.

[0158] Secondary particles are particles formed by the aggregation of two or more primary particles.

[0159] Composite graphite particles, including secondary particles and a surface coating layer including amorphous carbon, are beneficial for improving the wetting performance of the electrolyte in the negative electrode film and enhancing the solid-phase transport capability of active ions, thereby contributing to further improvement of the power performance, fast charging performance and cycle stability of battery cells in the low SOC range.

[0160] In some implementations, the mass content of amorphous carbon is 2% to 5% based on the total mass of the composite graphite particles.

[0161] In some implementations, the mass percentage of amorphous carbon, based on the total mass of the composite graphite particles, can be selected as 2%, 3%, 4%, 5%, or any value between the two.

[0162] When the content of amorphous carbon is within a suitable range, composite graphite materials can have both high specific capacity and high active ion solid-phase transport capability, which is beneficial to further improve the energy density of battery cells, power performance in the low SOC range, and fast charging performance.

[0163] In some embodiments, the powder resistivity of the composite graphite particles is from 0.005 Ω·cm to 0.04 Ω·cm.

[0164] In some embodiments, the powder resistivity of the composite graphite particles can be selected as 0.005 Ω·cm, 0.01 Ω·cm, 0.015 Ω·cm, 0.02 Ω·cm, 0.025 Ω·cm, 0.03 Ω·cm, 0.035 Ω·cm, 0.04 Ω·cm, or any value range between the two.

[0165] The powder resistivity of composite graphite particles is within a suitable range, which is beneficial to the further improvement of the power performance and fast charging performance of battery cells in the low SOC range.

[0166] 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. The volume average particle size Dv50 of the composite graphite particles in the first negative electrode film layer is 14 μm to 19 μm, and the volume average particle size Dv50 of the composite graphite particles in the second negative electrode film layer is 8 μm to 15 μm.

[0167] "Volume average particle size Dv50" is a well-known term in the art, representing the particle size corresponding to a cumulative volume distribution percentage of 50% for the material. It can be determined using instruments and methods known in the art. For example, it can be conveniently determined using a laser particle size analyzer, referring to GB / T19077-2016 Particle Size Distribution Laser Diffraction Method. The testing instrument can be the Mastersizer 3000 laser particle size analyzer from Malvern Instruments Ltd., UK. The composite graphite particles can be freshly prepared or obtained by scraping powder from the negative electrode active layer after disassembling a secondary battery.

[0168] In some embodiments, the volume average particle size Dv50 of the composite graphite particles in the first negative electrode film layer can be selected as 14 μm, 15 μm, 16 μm, 17 μm, 18 μm, 19 μm or any value range between the two.

[0169] In some embodiments, the volume average particle size Dv50 of the composite graphite particles in the second negative electrode film layer can be selected as 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm or any value range between the two.

[0170] The second negative electrode active material layer disposed on the electrolyte side includes negative electrode active materials with smaller particle size, which can further improve the solid-liquid transport rate of lithium ions in the battery electrode, and further improve the power performance and fast charging performance of the battery cell in the low SOC range.

[0171] In some embodiments, the positive electrode active material includes: a lithium phosphate with an olivine structure, and a coating layer located on at least a portion of the surface of the lithium phosphate, the coating layer comprising one or more of carbon, iron, titanium, vanadium, and boron.

[0172] The coating layer contains carbon, which helps improve the electronic conductivity of lithium phosphate and enhances the solid-state electron transport rate, thereby further improving the energy density, power performance in the low SOC range, and fast-charging performance of the battery cell. The coating layer also contains one or more of carbon, iron, titanium, vanadium, and boron, which helps form a fast-ion conductor component with high ionic conductivity. This significantly improves the lithium-ion transport rate during multiple lithium-ion insertion / extraction at the positive electrode, enhances the ionic conductivity of the positive electrode active material, and further improves the energy density, power performance in the low SOC range, and fast-charging performance of the battery cell.

[0173] In some implementations, the carbon element accounts for 0.8% to 2.3% of the total mass of the positive electrode active material.

[0174] In some implementations, the mass percentage of carbon element, based on the total mass of the positive electrode active material, can be selected as 0.8%, 1.1%, 1.4%, 1.7%, 2.0%, 2.3%, or any value range between the two.

[0175] Based on the total mass of the positive electrode active material, the mass ratio of carbon is within the above range, which makes lithium phosphate have both excellent electronic conductivity and specific capacity, further comprehensively improving the energy density, power performance in the low SOC range, and fast charging performance of the battery cell.

[0176] In some embodiments, 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 of the foregoing, wherein the modified forms include one or more of doping modification and coating modification.

[0177] In some embodiments, the positive electrode further includes a positive conductive layer located between the positive electrode film and the positive current collector, the thickness of which is 0.5 μm to 2 μm; and / or, the negative electrode further includes a negative conductive layer located between the negative current collector and at least one side of the negative electrode film, the thickness of which is 0.5 μm to 2 μm.

[0178] In some embodiments, the thickness of the positive or negative conductive layer can be selected from 0.5 μm, 0.6 μm, 0.7 μm, 0.8 μm, 0.9 μm, 1.0 μm, 1.1 μm, 1.2 μm, 1.3 μm, 1.4 μm, 1.5 μm, 1.6 μm, 1.7 μm, 1.8 μm, 1.9 μm, 2.0 μm, or any value range between the two.

[0179] The addition of a positive conductive layer and / or a negative conductive layer helps to improve the electronic conductivity of the battery cell electrodes, which in turn helps to further improve the power performance and fast charging performance of the battery cell in the low SOC range.

[0180] In some embodiments, the positive electrode conductive layer includes a conductive agent and a positive electrode binder, and the negative electrode conductive layer includes a conductive agent, which includes one or more of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers; and / or, the positive electrode binder includes one or more of polyvinylidene fluoride, polytetrafluoroethylene, vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, polyacrylic acid, and fluorinated acrylate resins.

[0181] In some embodiments, the electrolyte includes a solvent, which includes carboxylic acid ester solvents.

[0182] The type and quality of solvents in the electrolyte can be obtained by methods known to those skilled in the art. In the embodiments of this application, freshly prepared electrolyte can be used as a sample, or the free electrolyte from a fresh battery can be used as a sample. Alternatively, a fully discharged battery cell (discharged to the discharge cutoff voltage so that the battery cell's state of charge is approximately 0% SOC) can be disassembled in reverse, and the free electrolyte obtained from the battery cell can be used as a sample for detection using ion chromatography. The type and content of organic components in the electrolyte are known in the art and can be detected using equipment and methods known in the art. For example, the organic components of the electrolyte can be qualitatively and quantitatively analyzed by gas chromatography using GB / T9722-2023 "General Rules for Gas Chromatography of Chemical Reagents". The types and contents of inorganic components / lithium salts in the electrolyte are known in the art and can be detected using equipment and methods known in the art. For example, the inorganic components / lithium salts in the electrolyte can be qualitatively or quantitatively analyzed by ion chromatography using the standard JY / T020-2002 "General Rules for Ion Chromatography Analysis".

[0183] Carboxylic acid ester solvents have the advantages of low viscosity and high ionic conductivity, which are beneficial to the wetting of the positive and negative electrode films by the electrolyte and the rapid insertion and extraction of active ions in the negative electrode film, thereby further improving the power performance and fast charging performance of the battery cells in the low SOC range.

[0184] In some embodiments, the carboxylic acid ester solvent has the general structural formula R,-COO-R,, wherein R, includes one or more of hydrogen atoms, halogen atoms, C1-C5 alkyl groups, and C1-C5 haloalkyl groups, and R, includes one or more of C1-C5 alkyl groups and C1-C5 haloalkyl groups.

[0185] "C1-C5 alkyl" refers to unbranched or branched alkyl groups having 1-5 carbon atoms; including but not limited to one or more of methyl, ethyl, propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, n-pentyl, 2-pentyl, 2-methylbutyl, 3-methylbutyl, 1,2-dimethylpropyl, 1,1-dimethylpropyl, 2,2-dimethylpropyl, and 1-ethylpropyl.

[0186] "C1-C5 haloalkyl" refers to an unbranched or branched alkyl group having 1-5 carbon atoms in which at least one hydrogen atom is replaced by a halogen, including but not limited to one or more of chloroalkyl, bromoalkyl, and iodoalkyl.

[0187] "Halogen" refers to elements in Group VIIA of the periodic table. Specifically, halogens include elements such as fluorine, chlorine, bromine, iodine, and astatine.

[0188] In some embodiments, the carboxylic acid ester solvent includes one or more of methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, methyl butyrate, and ethyl butyrate.

[0189] In some embodiments, the mass percentage of carboxylic acid ester solvent is 10% to 60% based on the total mass of the electrolyte, and optionally 30% to 60%.

[0190] When the mass percentage of carboxylic acid ester solvents is within the above range, the electrolyte has low viscosity, high conductivity, and excellent stability, which is beneficial to the comprehensive improvement of the power performance, fast charging performance, and cycle stability of battery cells in the low SOC range.

[0191] In some embodiments, the solvent also includes carbonate solvents, including one or more of ethylene carbonate, propylene carbonate, butene carbonate, dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate.

[0192] Carbonate solvents have high dielectric constants. Carbonate solvents readily form solvation structures with lithium ions in lithium-containing electrolyte salts to increase the dissociation rate of lithium ions and anions in lithium-containing electrolyte salts, thereby further improving the power performance and fast charging performance of battery cells in the low SOC range.

[0193] In some embodiments, the carbonate solvent accounts for 18% to 70% of the total mass of the electrolyte, optionally 18% to 40%.

[0194] In some embodiments, the mass percentage of carbonate solvents, based on the total mass of the electrolyte, can be selected as 18%, 30%, 40%, 50%, 60%, 70%, or any value between the two.

[0195] The mass percentage of carbonate solvents within the above range allows the electrolyte to simultaneously possess suitable viscosity, conductivity, and good dissociation rate and wettability, which is beneficial for comprehensively improving the power performance, fast charging performance, and cycle stability of battery cells in the low SOC range.

[0196] In some embodiments, the electrolyte further includes additives, including one or more of carbonate additives, sulfur-containing additives, lithium salt additives, and fluorobenzene additives.

[0197] Additives refer to components with low content in electrolytes, generally accounting for no more than 10% of the electrolyte by mass. They are characterized by their strong targeting and small dosage, and can significantly optimize a certain aspect of battery performance without changing the production process.

[0198] In this application, carbonate additives refer to compounds and their derivatives that include carbonate groups (-O-CO-O-), as well as mixtures containing the above compounds and their derivatives.

[0199] In this application, fluorobenzene additives refer to organic compounds and their derivatives in which one or more hydrogen atoms on the benzene ring are replaced by fluorine atoms, as well as mixtures containing the above compounds and their derivatives.

[0200] The composition and content of additives can be tested using methods similar to those used for testing the type and quality of solvents described above.

[0201] In some embodiments, the carbonate additives include one or more of vinylene carbonate and ethylene carbonate derivatives.

[0202] Among them, ethylene carbonate derivatives include compounds represented by Formula I.

[0203] R1, R2, R3, and R4 each independently include one or more of hydrogen atoms, halogen atoms, C1-C5 alkyl groups, and C1-C5 haloalkyl groups, and R1, R2, R3, and R4 are not all hydrogen atoms at the same time. Optionally, carbonate additives include one or more of vinylene carbonate and fluorovinyl carbonate.

[0204] Carbonate additives can evolve into organic components in the SEI film, which helps improve the toughness of the SEI film, reduce the probability of SEI film rupture caused by volume changes of silicon-based materials, and cause side reactions between electrolyte and silicon-based materials. They also reduce battery gas production and lower the interface impedance on the negative electrode side, which is beneficial to further improving the cycle life, storage life, power performance in the low SOC range, and fast charging performance of battery cells.

[0205] In some embodiments, the sulfur-containing additive includes one or more of vinyl sulfate, vinyl disulfate, 1,3-propanesulfonate lactone, butene sulfite, vinyl sulfite, and methylene disulfonate.

[0206] Sulfur-containing additives often have high potentials. When added to the electrolyte, these additives preferentially react during formation or subsequent cycling, evolving into sulfur-containing inorganic components in the SEI film. Carbonate-based additives result in SEI films with poor high-temperature stability, which is detrimental to the stability of individual battery cells at high temperatures. The presence of sulfur in the SEI film can further improve its thermal stability at high temperatures, further reduce the interfacial impedance on the negative electrode side, and thus improve the cycle stability of individual battery cells, power performance in the low SOC range, and fast-charging performance.

[0207] In some embodiments, the lithium salt additive includes one or more of lithium difluorophosphate, lithium difluorooxalate borate, lithium tetrafluoroborate, and lithium dioxalate borate.

[0208] Lithium salt additives can evolve into inorganic components in the SEI film, further improving the rigidity and thermal stability of the SEI film, thereby further enhancing the battery's cycle stability, power performance in the low SOC range, and fast-charging performance. Furthermore, these lithium salt additives can also form a positive electrode electrolyte interface film (CEI film) on the surface of the positive electrode active material, further improving the cycle stability of individual battery cells.

[0209] In some embodiments, fluorobenzene additives include one or more fluorobenzene and its derivatives.

[0210] Fluorobenzene additives help improve the wettability of the electrolyte to the positive and negative electrode films, thereby further improving the power performance, fast charging performance and cycle stability of the battery cells in the low SOC range.

[0211] In some implementations, the carbonate additives account for 3% to 10% of the total mass of the electrolyte.

[0212] Based on the total mass of the electrolyte, the mass percentage of additives can be determined using any method known in the art. For example, the method described above for testing the mass percentage of solvent in the electrolyte can be used. It should be understood that, due to the consumption of additives in the electrolyte during formation and cycling, and the formation of components in the SEI and / or CEI films, the mass percentage of additives in the electrolyte may be slightly lower than the initial mass percentage of additives added to the electrolyte.

[0213] In some embodiments, the mass percentage of carbonate additives, based on the total mass of the electrolyte, can be selected as 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, or any range between the two.

[0214] When the mass percentage of carbonate additives in the electrolyte is within the above range, it can both improve the stability of the SEI film and maintain a suitable electrolyte viscosity, thereby further improving the cycle life of the battery cells, power performance in the low SOC range, and fast charging performance.

[0215] In some implementations, the sulfur-containing additive accounts for 0.01% to 2% of the total mass of the electrolyte.

[0216] It should be noted that, since the additives in the electrolyte are consumed during the formation and charge-discharge cycle, and related components are generated in the SEI film and / or CEI film, when the content of sulfur-containing additives and lithium salt additives is tested by gas chromatography after disassembling the battery cell to obtain the electrolyte, the content may be 0%.

[0217] Specifically, taking the case where the mass content of sulfur-containing additives is 0% as an example, this could mean that the freshly prepared electrolyte does not contain sulfur-containing additives, or that the electrolyte obtained after disassembling a battery cell does not contain sulfur-containing additives. In this case, the freshly prepared electrolyte may not have contained sulfur-containing additives, or a small amount of sulfur-containing additives may have been added, but these additives participated in the SEI film formation reaction during the battery cell formation process, resulting in the sulfur-containing additive having a mass content of 0% during the detection process. Optionally, the freshly prepared electrolyte may include sulfur-containing additives.

[0218] Furthermore, regarding the addition of certain substances, such as additives, to the electrolyte, the content of additives in the battery cell electrolyte is related to formation, different battery life cycles, or different battery storage states, due to the additives' role in film formation on the surface of active materials. Therefore, the additive content in freshly prepared electrolyte may differ from that in electrolyte obtained from reverse-engineered battery cells. However, those skilled in the art can determine the approximate range of the relevant substance content in the corresponding fresh electrolyte based on the battery cell's performance level (e.g., cycle count) and residual content. Similarly, those skilled in the art can also determine the approximate range of the content in non-freshly prepared (i.e., reverse-engineered) electrolytes based on the additive content in freshly prepared electrolytes, considering the battery cell's performance requirements and storage environment.

[0219] Therefore, the additive content mentioned in the technical solution of this application can be the content of additives actively added to fresh electrolyte, or the content of residual additives detected by reverse detection based on the actual battery state.

[0220] It is understood that in some embodiments, the sulfur-containing additives added to the electrolyte are completely converted into sulfur-containing components in the SEI film during the formation process, and the amount of sulfur-containing additives added to the electrolyte can be inferred by X-ray photoelectron spectroscopy (XPS) testing of the negative electrode material. In some embodiments, sulfur-containing additives remain in the electrolyte, which form a reinforcing effect on the SEI film during subsequent cell cycling.

[0221] In this application, the X-ray photoelectron spectroscopy (XPS) of the negative electrode material can be tested using any method known in the art. As an example, after disassembling the battery cell, the negative electrode sheet is cleaned three or more times with a solvent such as dimethyl carbonate (DMC), and then powder is scraped off and sampled. The obtained negative electrode material sample powder is adhered to a conductive substrate, and X-ray photoelectron spectroscopy is performed using an X-ray photoelectron spectrometer (e.g., AXIS ULTRA). The scanning rate and time of the X-ray source are adjusted to focus the X-rays and detect elements and functional groups at a depth of 5 nm to 10 nm from the surface of the negative electrode material, thereby obtaining the X-ray photoelectron spectroscopy (XPS) spectrum of the sample. The characteristic peaks of the elements in the spectrum are then analyzed.

[0222] In some implementations, the mass percentage of sulfur-containing additives, based on the total mass of the electrolyte, can be selected as 0.01%, 0.3%, 0.6%, 0.9%, 1.2%, 1.5%, 1.8%, 2%, or any range between the two.

[0223] The mass ratio of sulfur-containing additives in the electrolyte is within the above range, which takes into account both improving the thermal stability of the SEI film and maintaining a suitable electrolyte viscosity, thereby further improving the cycle life of the battery cells, power performance in the low SOC range, and fast charging performance.

[0224] In some implementations, the lithium salt additive accounts for 0.01% to 1% of the total mass of the electrolyte.

[0225] In some embodiments, the mass percentage of lithium salt additives, based on the total mass of the electrolyte, can be selected as 0.01%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, or any range between the two.

[0226] It is understood that, in some embodiments, the lithium salt additives added to the electrolyte are completely converted into inorganic components in the SEI and / or CEI films during the formation process. In some embodiments, lithium salt additives remain in the electrolyte, which reinforce the SEI and / or CEI films during subsequent cell cycling.

[0227] The lithium salt additives in the electrolyte are within the above-mentioned mass ratio, which takes into account both improving the thermal stability of the SEI film and maintaining the appropriate viscosity of the electrolyte, and further comprehensively improves the cycle life of the battery cells, power performance in the low SOC range and fast charging performance.

[0228] In some implementations, the fluorobenzene additives account for 0.1% to 0.5% of the total mass of the electrolyte.

[0229] In some embodiments, the mass percentage of fluorobenzene additives can be selected as 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, or any value between the two, based on the total mass of the electrolyte.

[0230] When the mass percentage of fluorobenzene additives in the electrolyte is within the above-mentioned range, the wettability of the electrolyte and the appropriate viscosity of the electrolyte are taken into account, thereby further improving the cycle life of the battery cells, the power performance in the low SOC range, and the fast charging performance.

[0231] In some embodiments, the separator includes a base film with a thickness of 4 μm to 7 μm.

[0232] In some implementations, the thickness of the base film can be selected as 4 μm, 5 μm, 6 μm, 7 μm or any value between the two.

[0233] In some embodiments, the porosity of the base membrane is 20% to 70%, optionally 35% to 60%.

[0234] In some embodiments, the porosity of the base membrane can be selected as 20%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, or any value range between the two.

[0235] The thickness and porosity of the separator base film within the above range are beneficial for further balancing the energy density and fast charging performance of the battery cells.

[0236] In some embodiments, the base film includes one or more of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The base film can be a single-layer film or a multi-layer composite film, without particular limitation.

[0237] In some embodiments, the separator further includes a functional layer disposed on at least one side of the base membrane. The functional layer includes: a first functional layer located on one side of the base membrane, the first functional layer including first inorganic particles; and a second functional layer located on the other side of the base membrane, the second functional layer including composite particles, the composite particles including second inorganic particles and a plurality of non-fluoropolymer particles, the second inorganic particles being attached to the surface of the non-fluoropolymer particles and / or dispersed inside the non-fluoropolymer particles.

[0238] In some embodiments, the non-fluoropolymer particles include acrylate copolymers.

[0239] In some embodiments, the first inorganic particle and the second inorganic particle each independently comprise one or more of silicon oxide, aluminum oxide, boehmite, barium sulfate, calcium oxide, titanium oxide, zinc oxide, magnesium oxide, zirconium oxide, and tin oxide.

[0240] Inorganic particles can improve the wettability and heat resistance of the first and second functional layers to the electrolyte, further comprehensively improving the fast-charging performance, cycle stability, and safety performance of the battery cells. Non-fluoropolymer particles can improve the processing performance and stability of the separator, preventing the separator from migrating within the battery cells and causing internal short circuits, thereby further improving the cycle stability and safety performance of the battery cells.

[0241] In some embodiments, the battery cell includes a housing that houses the electrode assembly, and the housing has a wall thickness of 0.2 mm to 0.4 mm.

[0242] In some embodiments, the wall thickness of the housing can be selected as 0.2 mm, 0.25 mm, 0.3 mm, 0.35 mm, 0.4 mm, or any value range between the two.

[0243] A casing wall thickness within the aforementioned range is beneficial for further improvement of the energy density of individual battery cells.

[0244] In some embodiments, the positive electrode includes a positive electrode tab, the negative electrode includes a negative electrode tab, and the battery cell also includes a top cover. The top cover includes a positive electrode terminal and a negative electrode terminal with opposite polarities. The positive electrode terminal is directly welded to the positive electrode tab, and the negative electrode terminal is directly welded to the negative electrode tab.

[0245] Conventional batteries require adapters to connect the electrode terminals and tabs, which reduces the utilization rate of the electrode assembly and lowers the battery's energy density. When the battery cell provided in this application uses the above-described structure, eliminating the adapters and directly welding the electrode terminals and tabs effectively solves this problem and reduces the battery's internal resistance, thereby further improving both battery energy density and fast-charging performance.

[0246] In some implementations, the volumetric energy density of the battery cell is greater than 410Wh / L and less than or equal to 520Wh / L.

[0247] In some implementations, the volumetric energy density of the battery cell is between 435 Wh / L and 465 Wh / L.

[0248] The volumetric energy density of a single battery cell can be tested using any method known in the art. As an example, the battery cell is placed at 25°C, charged to 3.8V with a constant current of 0.33C, then charged to 0.05C with a constant voltage, and left to stand for 30 minutes. It is then discharged to 2.0V with a constant current of 0.33C, and the discharge capacity A0 (Ah) is recorded. The length, width, and height of the battery cell are measured using calipers (generally calculated based on the battery casing dimensions, excluding the height of the electrode terminals and the insulating film outside the casing). The volumetric energy density V0 (L) of the battery cell is calculated. The volumetric energy density VED of the battery cell is calculated as (A0 × discharge plateau voltage) / V0 (Wh / L).

[0249] In some implementations, the volumetric energy density of the battery cell can be selected as 420Wh / L, 430Wh / L, 440Wh / L, 450Wh / L, 460Wh / L, 470Wh / L, 480Wh / L, 490Wh / L, 500Wh / L, 510Wh / L, 520Wh / L, or any value range between the two.

[0250] This battery cell also has high energy density, which can meet the needs of increasing the driving range of electrical devices.

[0251] In some implementations, the electrolyte injection coefficient of the battery cell is 2.2 g / Ah to 2.7 g / Ah.

[0252] The electrolyte filling coefficient of a battery cell refers to the ratio of the mass of electrolyte inside the battery cell to the battery capacity. The electrolyte filling coefficient of a battery cell can be obtained by any method known in the art. For example, the mass of electrolyte in a battery cell can be obtained by the following method: Weigh the battery, and record the mass as M0. Disassemble the battery cell and pour out the free electrolyte. Remove the internal electrode assembly and separate the positive electrode, negative electrode, separator, and mechanical components. Soak the positive electrode, negative electrode, separator, and mechanical components in dimethyl carbonate (DMC) solvent for 24-48 hours, repeating the soaking process at least three times. Place the aforementioned positive electrode, negative electrode, separator, and mechanical components in a 100°C oven for at least 24 hours until completely dried. Weigh the dried positive electrode, negative electrode, separator, and mechanical components, and record the mass as M1. The mass of electrolyte in the battery cell is thus obtained as (M0-M1). The electrolyte filling coefficient is calculated by (M0-M1) / rated capacity of the battery cell. The rated capacity is the nominal capacity of the battery, or the rated capacity is obtained by charging the battery to 3.8V at a charging rate of 0.33C, then charging it to 0.05C at a constant voltage of 3.8V, letting it stand for 10 minutes, and then discharging it to 2.0V at a discharging rate of 0.33C.

[0253] In some implementations, the electrolyte injection coefficient of the battery cell can be selected as 2.2 g / Ah, 2.3 g / Ah, 2.4 g / Ah, 2.5 g / Ah, 2.6 g / Ah, 2.7 g / Ah, or any value range between the two.

[0254] Within the above range, the liquid injection coefficient can balance the cycle stability and energy density of the battery cells.

[0255] In some embodiments, the battery cell may include an outer packaging. This outer packaging can be used to encapsulate the electrode assembly and electrolyte described above.

[0256] In some embodiments, the outer packaging of the battery cell can be a rigid shell, such as a hard plastic shell, an aluminum shell, or a steel shell. The outer packaging of the battery cell can also be a flexible package, such as a pouch. The material of the flexible package can be plastic; examples of plastics include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0257] This application does not impose any particular limitation on the shape of the battery cell; it can be cylindrical, square, or any other arbitrary shape. For example, Figure 1 shows a square battery cell 5 as an example.

[0258] In some embodiments, referring to FIG2, the outer packaging may include a housing 51 and a cover plate 53. The housing 51 may include a base plate and side plates connected to the base plate, the base plate and side plates forming a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the cover plate 53 can be placed over the opening to close the receiving cavity. A positive electrode sheet, a negative electrode sheet, and a separator can be formed into an electrode assembly 52 by a winding process or a stacking process. The electrode assembly 52 is encapsulated within the receiving cavity. Electrolyte is immersed in the electrode assembly 52. ​​The number of electrode assemblies 52 contained in a single battery cell 5 can be one or more, which can be selected by those skilled in the art according to specific practical needs.

[0259] In some implementations, individual battery cells can be assembled into a battery module. The number of individual battery cells contained in a battery module can be one or more, and the specific number can be selected by those skilled in the art based on the application and capacity of the battery module.

[0260] Figure 3 shows a battery module 4 as an example. Referring to Figure 3, in the battery module 4, multiple battery cells 5 can be arranged sequentially along the length of the battery module 4. Of course, they can also be arranged in any other manner. Furthermore, the multiple battery cells 5 can be fixed in place using fasteners.

[0261] Optionally, the battery module 4 may also include a housing with a receiving space in which multiple battery cells 5 are received.

[0262] In some embodiments, the battery modules described above can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be one or more, the specific number of which can be selected by those skilled in the art according to the application and capacity of the battery pack.

[0263] Figures 4 and 5 show a battery pack 1 as an example. Referring to Figures 4 and 5, the battery pack 1 may include a battery box and multiple battery modules 4 disposed within the battery box. The battery box includes an upper box 2 and a lower box 3, with the upper box 2 covering the lower box 3 to form a closed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery box.

[0264] The second aspect of this application provides a battery device including the battery cell provided in the first aspect of this application, the battery device including at least one of a battery module, a battery pack, and an energy storage battery.

[0265] Furthermore, a third aspect of this application provides an electrical device, which includes the battery device provided in the second aspect of this application. The battery cell, battery module, or battery pack can be used as a power source for the electrical device, or as an energy storage unit for the electrical device. The electrical device may include, but is not limited to, mobile devices (e.g., mobile phones, laptops, etc.), electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc.

[0266] As the electrical device, a single battery cell, a battery module, or a battery pack can be selected according to its usage requirements.

[0267] Figure 6 shows an example of an electrical device. This device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. To meet the high power and high energy density requirements of the individual battery cells, a battery pack or battery module can be used.

[0268] Another example device could be a mobile phone, tablet, or laptop. These devices typically require a slim and lightweight design and can use a single battery cell as their power source.

[0269] This application also provides an energy storage device that uses a battery as a 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.

[0270] Example

[0271] To make the technical problems, technical solutions, and beneficial effects solved by this application clearer, the application will be further described in detail below with reference to embodiments and accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. The following description of at least one exemplary embodiment is merely illustrative and is in no way intended to limit this application or its applications. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0272] Where specific techniques or conditions are not specified in the examples, they shall be performed in accordance with the techniques or conditions described in the literature in this field or in accordance with the product instructions. Reagents or instruments whose manufacturers are not specified are all commercially available conventional products.

[0273] Example 1

[0274] (1) Preparation of positive electrode active material

[0275] S1, lithium carbonate, iron phosphate, and glucose are added to water and mixed in a premixing tank at 1800 rpm. The mixture is then demagnetized by a demagnetizing rod with a magnetic field strength of 8000-12000 Gs to obtain a mixed raw material. The ratio of lithium carbonate to iron phosphate results in a molar ratio of iron to phosphorus of 0.975. The glucose content is 5.7% of the total raw material mass. The addition of titanium dioxide results in a titanium doping amount of 5000 ppm in the positive electrode active material.

[0276] S2, the mixed raw materials are subjected to two grinding-demagnetization cycles in a sand mill. The first grinding is performed using 0.6mm diameter zirconia balls at a speed of 260rpm for 1 hour, with a grinding chamber pressure of less than 0.2MPa. The raw materials after the first grinding are demagnetized using a permanent magnet separator with a demagnetization intensity greater than or equal to 8000Gs. The demagnetized raw materials are then ground a second time to obtain a mixed slurry with a particle size Dv50 of 0.40μm±0.10μm.

[0277] S3, the mixed slurry is spray-dried to obtain precursor powder;

[0278] S4, the precursor powder is sintered to obtain lithium iron phosphate cathode material. The sintering process includes:

[0279] First sintering: The precursor powder is sintered in a nitrogen atmosphere, heated from 25°C to 760°C at a heating rate of 5°C / min, and held at that temperature for 10 hours. After cooling, the first sintered product is obtained.

[0280] Grinding and mixing: 1.5% glucose and 3.0% polyethylene glycol by mass of the first sintering product were added to the first sintering product. The mixture was then divided into two groups for grinding (third grinding). Grinding in the first group was stopped when the particle Dv50 reached 1.0 ± 0.20 μm (grinding conditions: 550 rpm ± 50 rpm, grinding time 1 h), and grinding in the second group was stopped when the particle Dv50 reached 0.38 μm ± 0.05 μm (grinding conditions: 500 rpm ± 50 rpm, grinding time 4 h). The first and second groups were mixed at a mass ratio of 70:30 to obtain a mixed intermediate product. To ensure uniform mixing, the mixed product was ground a fourth time before spray drying, under the conditions of 500 rpm ± 50 rpm for 1 h, to obtain the target mixture. The target mixture was then spray dried.

[0281] Second sintering: The dried target mixture is sintered in a nitrogen atmosphere, heated from 25°C to 800°C at a heating rate of 5°C / min, and held at that temperature for 8 hours. After cooling, the second sintered product is obtained.

[0282] S5. After sintering, the product is cooled to below 100°C and then crushed using an air jet milling method to obtain carbon-coated lithium iron phosphate cathode active material. The air jet milling stage frequency is 25Hz and the milling pressure is 0.55MPa.

[0283] The prepared positive electrode active material has a coating layer comprising carbon elements, with a mass percentage of 1.12%. The primary particles of the positive electrode active material have an average particle size of 900 nm and a specific surface area of ​​13 m². 2 / g, the compacted density of the powder at 30000N is 2.7g / cm³. 3 .

[0284] (2) Preparation of positive electrode sheet

[0285] The positive electrode includes a positive current collector, a positive conductive layer on the positive current collector, and a positive film layer. The positive current collector is an aluminum foil with a thickness of 13 μm.

[0286] The positive electrode conductive layer on the positive electrode current collector is a film formed by uniformly mixing the positive electrode conductive agent superconducting carbon, the positive electrode binder polyvinylidene fluoride (PVDF), and the solvent N-methylpyrrolidone (NMP), coating it on the surface of the current collector, and drying it. The thickness is 1 μm. The positive electrode conductive layer contains 40% positive electrode conductive agent by mass and 60% positive electrode binder by mass.

[0287] The lithium iron phosphate positive electrode active material, binder polyvinylidene fluoride, conductive agent acetylene black, and dispersant sodium dodecyl sulfate prepared above were mixed in a ratio of 98:1.4:0.1:0.5, and then N-methylpyrrolidone (NMP) solvent was added and stirred to form a positive electrode slurry.

[0288] A positive electrode conductive paste is uniformly coated onto a positive electrode current collector aluminum foil, and after drying, a positive electrode conductive layer is obtained. Then, a positive electrode paste is uniformly coated onto the positive electrode conductive layer, and after drying and cold pressing, a positive electrode sheet is obtained. The single-sided coating weight of the positive electrode film is 340 mg / 1540.25 mm. 2 The single-sided coating weight of the positive electrode film is 320 mg / 1540.25 mm. 2 The cold-pressed compaction density of the positive electrode sheet is the ultimate compaction density of the electrode sheet. The test method for the ultimate compaction density of the electrode sheet is described below; the ultimate compaction density of the electrode sheet in Example 1 is 2.75 g / cm³. 3 .

[0289] In the cumulative area distribution curve of particles obtained from the cross section of the positive electrode film along the thickness direction of the electrode sheet, the particle size concentration (DA90-DA10) / DA50 is 2.8. Based on the total number of particles in the cross section of the positive electrode film along the thickness direction of the electrode sheet, the number of particles with a particle size greater than or equal to 50nm and less than 200nm accounts for 32%.

[0290] (3) Preparation of negative electrode sheet

[0291] The negative electrode sheet includes a negative current collector, a negative conductive layer on the negative current collector, and a negative film layer. The negative current collector is a copper foil with a thickness of 5 μm.

[0292] The negative electrode conductive layer on the negative electrode current collector is a film formed by uniformly mixing the negative electrode conductive agent superconducting carbon, the negative electrode binder styrene-butadiene rubber SBR, the thickener sodium carboxymethyl cellulose (CMC-Na) and the solvent water, coating it on the surface of the negative electrode current collector and drying it. The thickness is 1μm. The mass content of the negative electrode conductive agent in the negative electrode conductive layer is 35%, the mass content of the negative electrode binder in the negative electrode conductive layer is 60%, and the mass content of the thickener in the negative electrode conductive layer is 5%.

[0293] The negative electrode film layer includes a first negative electrode film layer and a second negative electrode film layer, wherein the first negative electrode film layer is located on the surface of the negative electrode conductive layer and the second negative electrode film layer is located on the surface of the first negative electrode film layer.

[0294] The first negative electrode film layer comprises composite graphite particles and composite silicon-carbon particles in a mass ratio of 95.15:2.95:0.5:0.3:1.1, conductive agent acetylene black, thickener sodium carboxymethyl cellulose, and binder styrene-butadiene rubber. The silicon content in the composite silicon-carbon particles is 50%, and the Dv50 of the composite graphite particles is 16 μm.

[0295] The second negative electrode film layer includes composite graphite particles and composite silicon carbide particles in a mass ratio of 95.05:2.95:0.5:0.4:1.1, conductive agent acetylene black, thickener sodium carboxymethyl cellulose, binder styrene-butadiene rubber, and the composite silicon carbide particles contain 50% silicon and the composite graphite particles have a Dv50 of 12μm.

[0296] The composite graphite particles include graphite bulk particles and a carbon coating layer covering at least a portion of the surface of the graphite bulk particles. The carbon coating layer includes amorphous carbon, and the mass percentage of amorphous carbon is 3% based on the total mass of the composite graphite particles. The powder resistivity of the composite graphite particles is 0.01 Ω·cm.

[0297] A first negative electrode slurry is uniformly coated onto the negative electrode conductive layer of the negative electrode current collector copper foil and dried. A second negative electrode slurry is then coated onto the dried first negative electrode slurry surface. After drying and cold pressing, a negative electrode sheet is obtained. The thickness ratio of the first film layer to the second film layer is 1:1. Based on the total mass of the negative electrode film layers, the silicon element accounts for 1.5% of the total mass, and the single-sided coating weight of the negative electrode film layer is 140 mg / 1540.25 mm. 2 .

[0298] (4) Preparation of electrolyte

[0299] Electrolytes consist of solvents, lithium-containing electrolyte salts, and additives.

[0300] The solvents include 39.0% by mass of carboxylic acid ester solvent (ethyl acetate) and 39.0% by mass of carbonate solvent (27.3% by mass of ethylene carbonate EC and 11.7% by mass of dimethyl carbonate DMC). The mass percentage of each component in the solvent is calculated based on the total mass of the electrolyte.

[0301] Based on the total mass of the electrolyte, the total mass content of the additives is 7%, which includes vinylene carbonate VC, fluoroethylene carbonate FEC, vinyl sulfite ES and lithium difluorooxalate borate LiDFOB in a mass ratio of 4.5:1.5:0.5:0.5.

[0302] The lithium-containing electrolyte salt includes lithium bis(fluorosulfonyl)imide (LiFSI) at a mass ratio of 5% and lithium hexafluorophosphate (LiPF6) at a mass ratio of 10%. The mass ratio of the lithium-containing electrolyte salt is calculated based on the total mass of the electrolyte.

[0303] (5) Preparation of the separating membrane

[0304] The separator includes a base membrane, which is a 5μm polyethylene film layer with a porosity of 36%.

[0305] (6) Preparation of battery cells

[0306] The positive electrode, separator, and negative electrode are wound together, with the separator positioned between the positive and negative electrodes to provide insulation, resulting in a wound electrode assembly. This assembly is then placed in a housing, dried, and injected with electrolyte at an injection rate of 2.6 g / Ah. After vacuum sealing, settling, and formation processes, a single battery cell is obtained. The positive electrode terminal is electrically connected to the positive electrode tab, and the negative electrode terminal is electrically connected to the negative electrode tab. The energy density of the single battery cell is 445 Wh / L. Under full charge, the compaction density of the negative electrode film is 1.3 g / cm³. 3 The compaction density of the positive electrode sheet is 2.69 g / cm³. 3 .

[0307] Examples 2-4

[0308] The preparation methods of Examples 2-4 are basically the same as those of Example 1, except that the mass ratio of silicon in the negative electrode film is adjusted, the mass of composite graphite particles is changed accordingly, and the single-sided coating quality of the positive electrode film is adjusted accordingly, as shown in the table.

[0309] Examples 5-7

[0310] The preparation methods of Examples 5-7 are basically the same as those of Example 1, except that the proportion of particles with a diameter greater than or equal to 50 nm and less than 200 nm in the (DA90-DA10) / DA50 and / or positive electrode film layer is adjusted by regulating the grinding particle size and / or sintering holding time during the preparation of the positive electrode active material. This results in a corresponding change in the cold-pressed compaction density of the positive electrode film layer.

[0311] The preparation method of Example 5 is basically the same as that of Example 1, except that in step S4, grinding is stopped when the Dv50 of the particles in the first group reaches 0.80±0.20μm; grinding is stopped when the Dv50 of the particles in the second group reaches 0.6±0.05μm. The holding time for the second sintering is 8h.

[0312] The preparation method of Example 6 is basically the same as that of Example 1, except that in step S4, grinding is stopped when the Dv50 of the particles in the first group reaches 0.80±0.20μm, and grinding is stopped when the Dv50 of the particles in the second group reaches 0.45±0.05μm. The holding time for the second sintering is 6h.

[0313] The preparation method of Example 7 is basically the same as that of Example 1, except that in step S4, grinding is stopped when the Dv50 of the particles in the first group reaches 0.80±0.20μm, and grinding is stopped when the Dv50 of the particles in the second group reaches 0.3±0.05μm. The holding time for the second sintering is 5h.

[0314] Examples 8-9

[0315] The preparation methods of Examples 8-9 are basically the same as those of Example 1, except that the mass ratio of the solvent in the electrolyte is adjusted, as shown in Table 1.

[0316] Comparative Examples 1-2

[0317] The preparation methods of Comparative Examples 1-2 are basically the same as those of Example 1, except that some parameters in the battery cells are adjusted, as shown in Table 1.

[0318] Comparative Examples 3-4

[0319] The preparation methods of Comparative Examples 3-4 are basically the same as those of Example 1, except that the sintering temperature and holding time during the preparation of the positive electrode active material are adjusted, thereby changing the proportion of particles with a diameter greater than or equal to 50 nm and less than 200 nm in the (DA90-DA10) / DA50 and / or positive electrode film layer. The cold-pressed compaction density of the positive electrode film layer is thus changed accordingly.

[0320] The preparation method of Comparative Example 3 is basically the same as that of Example 1, except that the highest temperature of the second sintering is 810℃ and the holding time is 8.5h.

[0321] The preparation method of Comparative Example 4 is basically the same as that of Example 1, except that the highest temperature of the second sintering is 770℃ and the holding time is 7h.

[0322] Test methods

[0323] 1. Power density

[0324] At 25°C, the battery cell is discharged at a constant current of 0.33C to 2.0V, left to stand for 5 minutes, charged at a constant current of 0.33C to the upper limit cutoff voltage of 3.8V, and then charged at a constant voltage to a current of 0.05C, left to stand for 5 minutes; discharged at a constant current of 0.33C to the cutoff voltage of 2.0V, and the discharge capacity C0 and discharge energy E0 are recorded.

[0325] At 25℃, the battery cell is charged at a constant current of 0.33C to 0.1C0 (adjusted to 10% SOC), left to stand for 120 minutes, and the open circuit voltage OCV1 is recorded. The cell is then subjected to constant current discharge for 10 seconds using a stepped current test method until the voltage at the end of the discharge reaches 2.0±0.005V (adjusted to 10% SOC for each test). The discharge power P0 is recorded. The power density (W / Wh) = discharge power P0 / discharge energy E0 can be used to characterize the power performance of the battery cell in the low SOC range.

[0326] 2. Volumetric energy density

[0327] Place the battery cell at 25℃ and charge it to 3.8V with a constant current of 0.33C, then charge it to 0.05C with a constant voltage and let it stand for 30 minutes. Discharge it to 2.0V with a constant current of 0.33C and record the discharge capacity A0 at this time, in Ah. Use calipers to measure the length, width and height of the battery cell (generally calculated based on the battery casing dimensions, excluding the height of the electrode terminals and the insulating film outside the casing). Calculate the volume of the battery cell V0, in L. The volumetric energy density of the battery cell VED = (A0 × discharge plateau voltage) / V0, in Wh / L.

[0328] 3. Ultimate compaction density of electrode sheets

[0329] The double-coated electrode sheets were compacted using a roller press. The elongation of the compacted electrode sheets was tested, and their flexibility was evaluated. By increasing the pressure of the roller press, electrode sheets with different compaction densities were obtained. As the pressure increased, the compaction density of the electrode sheet increased, the elongation of the electrode sheet increased, and the flexibility of the electrode sheet decreased. Excessive elongation of the electrode sheet can easily lead to warping, while insufficient flexibility can easily lead to brittle fracture. Therefore, the lower of the compaction density corresponding to an elongation of 8% or the compaction density corresponding to a flexible fold of 3 times is defined as the ultimate compaction density of the electrode sheet. The compaction density is calculated by dividing the mass of the positive electrode film by the volume of the positive electrode film. The elongation test method is as follows: Lay the electrode flat on a horizontal table and cut it into sections, each about 100cm long; remove the copper foil from the edge of the electrode, making sure the cut edge is parallel to the MD direction of the electrode (perpendicular to the direction of the pressure roller), ensuring that the electrode is completely covered by the coating. Use a steel ruler to measure the length between the marked points at the same position along the length direction of the electrode at the beginning and end, estimating to 0.1mm, and record the length before compaction; after compaction, record the length between the corresponding marked points. The elongation of the electrode is calculated as (length after compaction - length before compaction) / length before compaction.

[0330] The test method for the number of flexible folds is as follows.

[0331] Cut the positive electrode sheet to 20×100mm. 2 Test the size of the sample; fold it in half with the front side facing up, flatten it with a 2kg roller, unfold it and check the gap against the light to see if light passes through. If no light passes through, fold it in half again with the back side facing up, flatten it with a 2kg roller, and check it against the light again. Repeat this process until light passes through the gap. Record the number of folds. Repeat the test three times and take the average value as the reference data for the flexibility of the electrode sheet.

[0332] Test Results

[0333] The test results for each embodiment and comparative example are shown in the table.

[0334] Table 1

[0335] As can be seen from the comparison between the embodiments and comparative examples of this application, based on the total mass of the negative electrode film, the mass ratio of silicon element is 0.5% to 5%; in the cumulative area distribution curve of particles obtained from the cross-section of the positive electrode film along the thickness direction of the electrode sheet, the particle size concentration (DA90-DA10) / DA50 is 1.6 to 8.5; based on the total number of particles in the cross-section of the positive electrode film along the thickness direction of the electrode sheet, the proportion of particles with a particle size greater than or equal to 50nm and less than 200nm is 26% to 64%, which can take into account the improvement of the energy density of the battery cell and the power density in the low SOC range, and achieve a comprehensive improvement in battery performance.

[0336] As can be seen from the comparison between Examples 1 and 3 and Examples 2 and 4, when the mass ratio of silicon element is 1.5% to 3%, the battery cell further combines excellent energy density and high power density in the low SOC range.

[0337] As can be seen from the comparison of Examples 1, 5, 6 and Example 7, (DA90-DA10) / DA50 is 1.68 to 4.0. The battery cell has high power density in the low SOC range, while the energy density is further improved.

[0338] As can be seen from the comparison of Examples 1, 5, 6 and Example 7, based on the total number of particles in the cross section along the thickness direction of the positive electrode film, the proportion of particles with a diameter greater than or equal to 50 nm and less than 200 nm is 26% to 45%. The battery cell has a high power density in the low SOC range, while the energy density is further improved.

[0339] As can be seen from Examples 1, 8, and 9, based on the total mass of the electrolyte, the mass percentage of carboxylic acid ester solvents is 10% to 60%, and the mass percentage of carbonate solvents is 18% to 70%, resulting in a high power density of the battery cell in the low SOC range. A comparison of Examples 1, 8, and 9 shows that, based on the total mass of the electrolyte, the mass percentage of carboxylic acid ester solvents is 30% to 60%, and the mass percentage of carbonate solvents is 18% to 40%, further improving the power density of the battery cell in the low SOC range.

[0340] It should be noted that this disclosure is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same essential structure and achieving the same effect as the technical concept within the scope of this disclosure are included in the technical scope of this disclosure. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, are also included in the scope of this disclosure without departing from the spirit of this disclosure.

Claims

A battery cell, characterized in that, The system includes an electrode assembly and an electrolyte. The electrode assembly includes a positive electrode, a negative electrode, and a separator. The separator is located between the positive and negative electrode. The negative electrode includes a negative current collector and a negative electrode film layer disposed on at least one side of the negative current collector. The negative electrode film layer includes a negative electrode active material, which may be a carbon-based material or a silicon-based material. In this context, based on the total mass of the negative electrode film, the mass percentage of silicon is 0.5% to 5%. The positive electrode sheet includes a positive current collector and a positive electrode film layer disposed on at least one side of the positive current collector. The positive electrode film layer includes a positive active material, which includes lithium phosphate particles with an olivine structure. In the cumulative area distribution curve of the particles obtained by slicing the positive electrode film layer along the thickness direction of the electrode sheet, the particle size concentration (DA90-DA10) / DA50 is 1.6 to 8.

5. Here, DA90, DA50, and DA10 refer to the particle size corresponding to the cumulative area distribution of the particles reaching 90%, 50%, and 10%, respectively, in the cumulative area distribution curve of the particles. Based on the total number of particles in the cross-section of the positive electrode film along the thickness direction of the electrode sheet, the proportion of particles with a diameter greater than or equal to 50 nm and less than 200 nm is 26% to 64%. The battery cell according to claim 1 is characterized in that, In the cumulative area distribution curve of particles obtained from the cross-section of the positive electrode film along the thickness direction of the electrode, the particle size concentration (DA90-DA10) / DA50 is 1.68 to 4.

0. The battery cell according to claim 1 or 2 is characterized in that, Based on the total mass of the negative electrode film, the mass percentage of silicon is 1.5% to 3%. The battery cell according to any one of claims 1 to 3 is characterized in that, Based on the total number of particles in the cross-section of the positive electrode film along the thickness direction of the electrode sheet, the proportion of particles with a diameter greater than or equal to 50 nm and less than 200 nm is 26% to 45%. The battery cell according to any one of claims 1 to 4 is characterized in that, The single-side coating quality of the negative electrode film layer is 100 mg / 1540.25 mm 2 to 160 mg / 1540.25 mm 2 . The battery cell according to any one of claims 1 to 5 is characterized in that, The compaction density of the negative electrode film layer is 1.20 g / cm 3 to 1.50 g / cm 3 . The battery cell according to any one of claims 1 to 6 is characterized in that, The single-side coating quality of the positive electrode film layer is 220 mg / 1540.25 mm 2 to 370 mg / 1540.25 mm 2 . The battery cell according to any one of claims 1 to 7 is characterized in that, The compaction density of the positive electrode film is 2.60 g / cm³. 3 Up to 2.83 g / cm 3 . The battery cell according to any one of claims 1 to 8 is characterized in that, The silicon-based material includes one or more of elemental silicon, silicon-carbon materials, silicon-oxygen materials, silicon-nitrogen materials, and silicon alloys, and may be selected as one or more of silicon-carbon materials and silicon-oxygen materials; and / or the carbon-based material includes one or more of artificial graphite and natural graphite. The battery cell according to any one of claims 1 to 9 is characterized in that, Based on the total mass of the negative electrode active material, the silicon-based material accounts for 1% to 10% of the mass, and / or the carbon-based material accounts for 90% to 99% of the mass. The battery cell according to any one of claims 1 to 10 is characterized in that, The silicon-based material includes composite silicon-carbon particles, which comprise a porous carbon matrix and silicon-based particles. The porous carbon matrix contains channels with a width of 5 nm to 50 nm, and the silicon-based particles are distributed within these channels. The battery cell according to any one of claims 1 to 11 is characterized in that, The carbon-based material includes composite graphite particles, which include graphite bulk particles and a carbon coating layer covering the surface of the graphite bulk particles. The graphite bulk particles include secondary particles, and the carbon coating layer includes amorphous carbon. The battery cell according to claim 12 is characterized in that, The composite graphite particles satisfy at least one of the following conditions: (1) Based on the total mass of the composite graphite particles, the mass content of the amorphous carbon is 2% to 5%; (2) The resistivity of the composite graphite particles is 0.005 Ω·cm to 0.04 Ω·cm. The battery cell according to claim 12 or 13 is characterized in that, 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. The volume average particle size Dv50 of the composite graphite particles in the first negative electrode film layer is 14 μm to 19 μm, and the volume average particle size Dv50 of the composite graphite particles in the second negative electrode film layer is 8 μm to 15 μm. The battery cell according to any one of claims 1 to 14 is characterized in that, The positive electrode active material includes: Lithium phosphates with an olivine structure, and A coating layer located on at least a portion of the surface of the lithium phosphate, the coating layer comprising one or more of the elements carbon, iron, titanium, vanadium, and boron. The battery cell according to claim 15 is characterized in that, Based on the total mass of the positive electrode active material, the mass percentage of carbon is between 0.8% and 2.3%. The battery cell according to claim 15 or 16 is characterized in that, 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 of the aforementioned substances, wherein the modified forms include one or more of doping modification and coating modification. The battery cell according to any one of claims 1 to 17 is characterized in that, The positive electrode further includes a positive conductive layer, which is located between the positive electrode film and the positive electrode current collector, and the thickness of the positive conductive layer is 0.5 μm to 2 μm; and / or, the negative electrode further includes a negative conductive layer, which is located between the negative electrode current collector and at least one side of the negative electrode film, and the thickness of the negative conductive layer is 0.5 μm to 2 μm. The battery cell according to claim 18 is characterized in that, The positive electrode conductive layer includes a conductive agent and a positive electrode binder, and the negative electrode conductive layer includes a conductive agent, which includes one or more of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers; and / or, the positive electrode binder includes one or more of polyvinylidene fluoride, polytetrafluoroethylene, vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, polyacrylic acid, and fluorinated acrylate resins. The battery cell according to any one of claims 1 to 19 is characterized in that, The electrolyte includes a solvent, which includes carboxylic acid ester solvents. The battery cell according to claim 20 is characterized in that, The carboxylic acid ester solvent has the general structural formula R'-COO-R”, wherein R' includes one or more of hydrogen atoms, halogen atoms, C1-C5 alkyl groups, and C1-C5 haloalkyl groups, and R” includes one or more of C1-C5 alkyl groups and C1-C5 haloalkyl groups. The battery cell according to claim 20 or 21 is characterized in that, The carboxylic acid ester solvents include one or more of methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, methyl butyrate, and ethyl butyrate. According to any one of claims 20 to 22, the mass percentage of the carboxylic acid ester solvent is 10% to 60% based on the total mass of the electrolyte, and optionally 30% to 60%. The battery cell according to any one of claims 20 to 23 is characterized in that, The solvent also includes carbonate solvents, which include one or more of ethylene carbonate, propylene carbonate, butene carbonate, dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate. The battery cell according to claim 24 is characterized in that, Based on the total mass of the electrolyte, the carbonate solvent accounts for 18% to 70% by mass, and optionally 18% to 40%. The battery cell according to any one of claims 1 to 25 is characterized in that, The electrolyte also includes additives, which include one or more of carbonate additives, sulfur-containing additives, lithium salt additives, and fluorobenzene additives. The battery cell according to claim 26 is characterized in that, The carbonate additives include one or more vinylene carbonates and ethylene carbonate derivatives. The ethylene carbonate derivatives include compounds represented by Formula I. R1, R2, R3, and R4 each independently include one or more of hydrogen atoms, halogen atoms, C1-C5 alkyl groups, and C1-C5 haloalkyl groups, and R1, R2, R3, and R4 are not all hydrogen atoms at the same time. Optionally, the carbonate additives include one or more of vinylene carbonate and fluorovinyl carbonate. The sulfur-containing additives include one or more of vinyl sulfate, vinyl disulfate, 1,3-propanesulfonate lactone, butene sulfite, vinyl sulfite, and methylene disulfonate. The lithium salt additives include one or more of lithium difluorophosphate, lithium difluorooxalate borate, lithium tetrafluoroborate, and lithium dioxalate borate; and / or, The fluorobenzene additives include one or more fluorobenzene and its derivatives. The battery cell according to claim 26 or 27 is characterized in that, Based on the total mass of the electrolyte, the carbonate additives account for 3% to 10% of the total mass. Based on the total mass of the electrolyte, the sulfur-containing additive accounts for 0.01% to 2% of the total mass. Based on the total mass of the electrolyte, the lithium salt additive accounts for 0.01% to 1% of the total mass; and / or, Based on the total mass of the electrolyte, the fluorobenzene additive accounts for 0.1% to 0.5% of the total mass. The battery cell according to any one of claims 1 to 28 is characterized in that, The separator includes a base membrane, which satisfies at least one of the following conditions: (1) The thickness of the base film is 4 μm to 7 μm; (2) The porosity of the base membrane is 20% to 70%, and can be selected as 35% to 60%. The battery cell according to any one of claims 1 to 29 is characterized in that, The isolation membrane further includes a functional layer disposed on at least one side of the base membrane, the functional layer comprising: A first functional layer is located on one side of the base film, and the first functional layer includes first inorganic particles; The second functional layer is located on the other side of the base film. The second functional layer includes composite particles, which include second inorganic particles and a plurality of non-fluoropolymer particles. The second inorganic particles are attached to the surface of the non-fluoropolymer particles and / or dispersed inside the non-fluoropolymer particles. The battery cell according to claim 30 is characterized in that, The non-fluoropolymer particles include acrylate copolymers. The battery cell according to claim 30 or 31 is characterized in that, The first inorganic particle and the second inorganic particle each independently comprise one or more of the following: silicon oxide, aluminum oxide, boehmite, barium sulfate, calcium oxide, titanium oxide, zinc oxide, magnesium oxide, zirconium oxide, and tin oxide. The battery cell according to any one of claims 1 to 32 is characterized in that, The battery cell includes a housing that accommodates the electrode assembly, and the housing has a wall thickness of 0.2 mm to 0.4 mm. The battery cell according to any one of claims 1 to 33 is characterized in that, The positive electrode includes a positive electrode tab, the negative electrode includes a negative electrode tab, and the battery cell also includes a top cover. The top cover includes a positive electrode terminal and a negative electrode terminal with opposite polarities. The positive electrode terminal is directly welded to the positive electrode tab, and the negative electrode terminal is directly welded to the negative electrode tab. The battery cell according to any one of claims 1 to 34 is characterized in that, The volumetric energy density of the battery cell is greater than 410Wh / L and less than or equal to 520Wh / L. Optionally, the volumetric energy density of the battery cell is between 435Wh / L and 465Wh / L. The battery cell according to any one of claims 1 to 35 is characterized in that, The electrolyte injection coefficient of the battery cell is from 2.2 g / Ah to 2.7 g / Ah. A battery device, characterized in that, The battery device includes any one of the battery cells according to claims 1 to 36, and the battery device is at least one of battery module, battery pack, and energy storage battery. An electrical device, characterized in that, Includes the battery device as described in claim 37. An energy storage device, characterized in that, Includes the battery device of claim 37, the battery device being used for storing electrical energy.

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