Battery cell, battery, and electric apparatus

Abstract

The present disclosure provides a battery cell, a battery, and an electric apparatus. The battery cell comprises an electrode assembly and an electrolyte, wherein the electrode assembly comprises a negative electrode sheet; the negative electrode sheet comprises a negative electrode current collector and a negative electrode film layer located on at least one side of the negative electrode current collector; the negative electrode film layer comprises a negative electrode active material; the negative electrode active material comprises a silicon-carbon composite material, and the silicon-carbon composite material comprises a carbon material matrix having a pore structure and a silicon-based material located in the pore structure of the carbon material matrix; and a ratio of the mass of the electrolyte to the capacity of the battery cell is 1.2 g / Ah-2.0 g / Ah. The battery of the present disclosure can achieve both high energy density and excellent cycle performance.

Description

Battery cells, batteries and electrical devices

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] The present disclosure claims priority to Chinese patent application No. 202410269782.2, filed on March 8, 2024, entitled “Battery Cell, Battery and Electrical Device,” the entire contents of which are incorporated herein by reference. Technical Field

[0003] The present disclosure relates to a battery cell, a battery, and an electric device. Background Art

[0004] As the application range of battery cells expands, the demand for their use is also increasing, with demands for higher energy density being placed on them. A battery cell consists of a positive electrode, a negative electrode, a separator, and an electrolyte. The electrolyte serves to establish an ion conduction path between the positive and negative electrodes. Improving the energy density of battery cells by reducing the mass fraction of the electrolyte is a viable solution. However, the electrolyte has a significant impact on the charge and discharge performance of battery cells. When the electrolyte wetting of a battery cell is poor, the ion transport path becomes longer, and the unwetted portions of the electrode cannot participate in the battery's electrochemical reactions. Currently, large electrolyte injection volumes are typically used to achieve good electrochemical performance in battery cells. A high electrolyte mass in a battery cell reduces the cell's energy density. Reducing electrolyte mass and increasing battery energy density without compromising the electrochemical performance of the battery cell is a pressing technical challenge.

[0005] Summary of the Invention

[0006] The present disclosure provides a battery cell, a battery, and an electrical device, which can enable the battery to have both high energy density and good cycle performance.

[0007] In a first aspect, the present disclosure provides a battery cell, comprising an electrode assembly and an electrolyte, wherein the electrode assembly comprises a negative electrode pole piece, the negative electrode pole piece comprises a negative electrode current collector and a negative electrode film layer located on at least one side of the negative electrode current collector, the negative electrode film layer comprises a negative electrode active material, the negative electrode active material comprises a silicon-carbon composite material, the silicon-carbon composite material comprises a carbon material matrix having a pore structure and a silicon-based material located in the pore structure of the carbon material matrix; the ratio of the mass of the electrolyte to the capacity of the battery cell is 1.2g / Ah-2.0g / Ah.

[0008] The silicon-carbon composite material used in the battery cell provided by the embodiment of the present disclosure includes a carbon material matrix with a pore structure and a silicon-based material located in the pore structure of the carbon material matrix. The carbon material matrix with a pore structure can effectively alleviate the volume expansion of the internal silicon-based material, reduce the problems of breakage and pulverization of the silicon-carbon composite material, and improve the integrity of the SEI film on the surface of the silicon-carbon composite material particles, thereby reducing the consumption of active ions and electrolytes. The consumption of electrolyte is reduced, and the demand for electrolyte during charging and discharging of the battery cell is reduced, thereby enabling the battery cell to have a long cycle life while maintaining a low mass of electrolyte. Therefore, the battery cell provided by the embodiment of the present disclosure can have both high energy density and good cycle performance.

[0009] In some embodiments, the battery cell is a square-shell battery cell, and the ratio of the mass of the electrolyte to the capacity of the square-shell battery cell is 1.5 g / Ah-2.0 g / Ah, and can be optionally 1.7 g / Ah-1.9 g / Ah.

[0010] In some embodiments, the battery cell is a cylindrical battery cell, and the ratio of the mass of the electrolyte to the capacity of the cylindrical battery cell is 1.2 g / Ah-1.5 g / Ah, and can be optionally 1.24 g / Ah-1.5 g / Ah.

[0011] In some embodiments, the average pore size of the pore structure of the carbon material matrix is ​​0.5 nm to 8 nm.

[0012] In some embodiments, the pore structure of the carbon material matrix includes micropores, and the average pore diameter d1 of the micropores satisfies: 0.5 nm ≤ d1 < 2 nm.

[0013] In some embodiments, the pore structure of the carbon material matrix includes mesopores, and the average pore diameter d2 of the mesopores satisfies: 2nm≤d2≤8nm.

[0014] In some embodiments, the pore structure of the carbon material matrix includes micropores and mesopores, wherein the micropores account for 60%-90% of the pore structure, and the mesopores account for 10%-40% of the pore structure. By adjusting the ratio of micropores to mesopores, it is beneficial to better disperse the silicon-based material.

[0015] In some embodiments, the specific surface area of ​​the carbon material matrix having a porous structure is 500 m 2 / g-2000m 2 / g.

[0016] In some embodiments, the silicon-based material accounts for 20%-60% by mass of the silicon-carbon composite material.

[0017] In some embodiments, the silicon-based material in the silicon-carbon composite material includes one or more of amorphous silicon, crystalline silicon, silicon oxides, silicon carbide, and silicon alloys.

[0018] In some embodiments, the silicon-based material in the silicon-carbon composite material includes one or more of amorphous silicon and crystalline silicon.

[0019] In some embodiments, the silicon-based material in the silicon-carbon composite material includes one or more of amorphous silicon and crystalline silicon, and the grain size of the crystalline silicon is less than or equal to 5 nm.

[0020] In some embodiments, the volume distribution particle size Dv50 of the silicon-carbon composite material is 3 μm-15 μm.

[0021] In some embodiments, the volume distribution particle size Dv90 of the silicon-carbon composite material is 15 μm-25 μm.

[0022] In some embodiments, the volume distribution particle size Dv10 of the silicon-carbon composite material is 1 μm-5 μm.

[0023] The volume distribution particle size of the silicon-carbon composite material is within the above range, which helps to reduce surface activity, reduce interface side reactions, reduce electrolyte consumption, and also helps to make the battery cell have a long cycle life while keeping the electrolyte mass small.

[0024] In some embodiments, the particle size distribution of the silicon-carbon composite material satisfies: 1≤(Dv90-Dv10) / Dv50≤3. The particle size distribution of the silicon-carbon composite material within the above range helps the battery cell have a high energy density.

[0025] In some embodiments, the specific surface area of ​​the silicon-carbon composite material is 1 m 2 / g-6m 2 The specific surface area of ​​the silicon-carbon composite material is within the above range, which helps to reduce interface side reactions, reduce electrolyte consumption, and also helps to ensure that the battery cell has a long cycle life while maintaining a small electrolyte mass.

[0026] In some embodiments, the tap density of the silicon-carbon composite material is 0.8 g / cm 3 -1.2g / cm 3 The tap density of the silicon-carbon composite material is within the above range, which helps the battery cell have a high energy density.

[0027] In some embodiments, the powder resistivity of the silicon-carbon composite material at 16 MPa is less than or equal to 5 Ω·cm. The tap density of the silicon-carbon composite material is within the above range, which helps the battery cell have a high energy density.

[0028] In some embodiments, the silicon-carbon composite material includes a coating layer. Located on the outside of the silicon-carbon composite material, the coating layer further prevents direct contact between the silicon-based material and the electrolyte, reducing the reactivity of the silicon-based material upon contact with air, thereby reducing electrolyte consumption and enabling a long cycle life for the battery cell while maintaining a low electrolyte mass. Furthermore, the coating layer can buffer the volume expansion of the silicon-based material, thereby helping to improve the storage performance of the battery cell.

[0029] In some embodiments, the negative electrode active material further comprises graphite. Optionally, the graphite comprises at least one of artificial graphite and natural graphite.

[0030] In some embodiments, the volume distribution particle size Dv50 of the negative electrode active material is 7 μm-12 μm.

[0031] In some embodiments, the volume distribution particle size Dv90 of the negative electrode active material is 15 μm-20 μm.

[0032] In some embodiments, the volume distribution particle size Dv10 of the negative electrode active material is 3 μm-6 μm.

[0033] The overall volume distribution particle size of the negative electrode active material is within the above range, which helps to reduce surface activity, reduce interface side reactions, reduce electrolyte consumption, and also helps to make the battery cell have a long cycle life while keeping the electrolyte mass small.

[0034] In some embodiments, the particle size distribution of the negative electrode active material satisfies: 1.16≤(Dv90-Dv10) / Dv50≤1.71.

[0035] The particle size distribution of the negative electrode active material is within the above range, which helps the battery cell have a high energy density.

[0036] In some embodiments, the electrolyte includes an organic solvent, the organic solvent includes a linear carbonate, and the linear carbonate includes one or both of dimethyl carbonate and ethyl methyl carbonate.

[0037] In some embodiments, the linear carbonate accounts for 60%-85% by mass in the organic solvent.

[0038] By making the chain carbonate in the organic solvent of the electrolyte have a larger mass proportion, the electrolyte can be made to have a low viscosity, which facilitates the flow of the electrolyte, thereby better improving the electrolyte wettability of the electrode assembly, and also making the battery cell have a long cycle life while the electrolyte has a small mass.

[0039] In some embodiments, the mass proportion of dimethyl carbonate in the organic solvent is 60%-85%, thereby better reducing the viscosity of the electrolyte, improving the electrolyte wettability of the electrode assembly, and also ensuring a long cycle life for the battery cell while maintaining a low mass of the electrolyte.

[0040] In some embodiments, the mass proportion of dimethyl carbonate in the organic solvent is greater than the mass proportion of ethyl methyl carbonate in the organic solvent, thereby enabling the electrolyte to have both lower viscosity and lower gas production.

[0041] In some embodiments, the mass proportion of the dimethyl carbonate in the organic solvent is 40%-75%.

[0042] In some embodiments, the mass proportion of the ethyl methyl carbonate in the organic solvent is 5%-25%.

[0043] In some embodiments, the mass proportion of the dimethyl carbonate in the organic solvent is 40%-75%, and the mass proportion of the ethyl methyl carbonate in the organic solvent is 5%-25%.

[0044] In some embodiments, the organic solvent further comprises a cyclic carbonate, and the cyclic carbonate comprises one or both of ethylene carbonate and fluoroethylene carbonate.

[0045] By mixing chain carbonates with cyclic carbonates, the electrolyte can have good fluidity, high ion conductivity and high ion migration rate, thereby making the battery cell have better cycle performance.

[0046] In some embodiments, the mass proportion of the cyclic carbonate in the organic solvent is 15%-40%.

[0047] In some embodiments, the mass proportion of the fluoroethylene carbonate in the organic solvent is 1%-10%.

[0048] By making the electrolyte contain an appropriate amount of fluoroethylene carbonate, the electrolyte can be helped to have a long cycle life of the battery cell while having a small mass.

[0049] In some embodiments, the mass proportion of the ethylene carbonate in the organic solvent is 10%-35%.

[0050] In some embodiments, the electrolyte contains cations and anions, the cations include one or both of lithium ions and sodium ions, the anions include one or more of hexafluorophosphate anions and anions represented by Formula 1, R1 and R2 each independently include a fluorine atom or a C1-C6 fluoroalkyl group,

[0051] In some embodiments, the molar concentration of the anion is 1 mol / L-1.3 mol / L.

[0052] In some embodiments, the anions include both hexafluorophosphate anions and anions represented by Formula 1, and the molar concentration of the anions represented by Formula 1 is greater than the molar concentration of the hexafluorophosphate anions. By increasing the molar concentration of the anions represented by Formula 1 to be greater than the molar concentration of the hexafluorophosphate anions, the electrolyte solution can be reduced in mass while providing a long cycle life for the battery cells.

[0053] In some embodiments, the molar concentration of the anion represented by Formula 1 is 0.6 mol / L-0.9 mol / L. When the molar concentration of the anion represented by Formula 1 is within the above range, the electrolyte can have high ionic conductivity and form a good SEI film on the surface of the negative electrode active material, thereby reducing side reactions between the negative electrode active material and the electrolyte.

[0054] In some embodiments, the molar concentration of the hexafluorophosphate anion is 0.3 mol / L-0.5 mol / L. The molar concentration of the hexafluorophosphate anion within the above range can make the electrolyte have high ionic conductivity and can also reduce the corrosion of the anion represented by Formula 1 on the positive electrode current collector, thereby better exerting the effect of the anion represented by Formula 1.

[0055] In some embodiments, the electrode assembly includes a positive electrode plate, the positive electrode plate includes a positive electrode current collector and a positive electrode film layer located on at least one side of the positive electrode current collector, the positive electrode film layer includes a positive electrode active material, and the positive electrode active material includes a layered lithium-containing transition metal oxide.

[0056] Optionally, the positive electrode active material includes both a layered lithium-containing transition metal oxide with a single crystal morphology and a layered lithium-containing transition metal oxide with a polycrystalline morphology.

[0057] The positive electrode active material includes both single-crystal layered lithium-containing transition metal oxides and polycrystalline layered lithium-containing transition metal oxides, which helps the battery cell to have both good cycle stability and good power performance while having a smaller electrolyte mass and higher energy density.

[0058] In some embodiments, the electrode assembly includes a separator, the separator including a base film and a coating layer disposed on at least one side of the base film, and the coating layer does not contain a fluorine-containing polymer.

[0059] In some embodiments, the base film has a thickness of 3 μm-9 μm.

[0060] In some embodiments, the coating has a thickness of 0.5 μm to 3 μm.

[0061] In some embodiments, the isolation film has a total thickness of 5 μm-14 μm.

[0062] In a second aspect, the present disclosure provides a battery comprising the battery cell according to the first aspect of the present disclosure.

[0063] In a third aspect, the present disclosure provides an electrical device comprising the battery according to the second aspect of the present disclosure, wherein the battery is configured to provide electrical energy.

[0064] The electric device of the present disclosure includes the battery provided by the present disclosure, and thus has at least the same advantages as the battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0065] To more clearly illustrate the technical solutions of the embodiments of the present disclosure, the following briefly introduces the drawings required for use in the embodiments of the present disclosure. Obviously, the drawings described below are only some embodiments of the present disclosure, and those skilled in the art can derive other drawings based on the drawings without inventive effort.

[0066] FIG1 is a schematic structural diagram of a vehicle provided in some embodiments of the present disclosure.

[0067] FIG2 is a schematic diagram of an explosion of a battery provided in some embodiments of the present disclosure.

[0068] FIG3 is a schematic diagram of an explosion of the battery module shown in FIG2 .

[0069] FIG4 is a schematic diagram of a cross-sectional image of a silicon-carbon composite material provided by some embodiments of the present disclosure.

[0070] In the accompanying drawings, the drawings are not necessarily drawn to scale.

[0071] The figure numbers are explained as follows: 1. Vehicle; 2. Battery; 3. Controller; 4. Motor; 5. Box; 5a. First box part; 5b. Second box part; 5c. Accommodation space; 6. Battery module; 7. Battery cell; 100. Silicon-carbon composite material; 101. External area; 102. Internal area; O. Particle core. DETAILED DESCRIPTION

[0072] Below, the embodiments of the battery cell, battery, and electrical device disclosed herein are described in detail with appropriate reference to the accompanying drawings. However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repeated descriptions of substantially identical structures may be omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate understanding by those skilled in the art. In addition, the drawings and the following description are provided to enable those skilled in the art to fully understand the present disclosure and are not intended to limit the subject matter described in the claims.

[0073] " scope " disclosed in the present disclosure is limited in the form of lower limit and upper limit, and given range is limited by selecting a lower limit and an upper limit, and selected lower limit and upper limit define the boundary of special scope.The scope that this mode limits can be to include end value or not include end value, and can be combined arbitrarily, and promptly any lower limit can form a scope with any upper limit combination.For example, if the scope of 60-120 and 80-110 is listed for specific parameter, it is understood that the scope of 60-110 and 80-120 is also expected.In addition, if the minimum range value 1 and 2 listed, and if the maximum range value 3,4 and 5 listed, then the following scope can all be expected: 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5.In the present disclosure, unless otherwise specified, numerical range " ab " represents the abbreviation of any real number combination between a and b, and wherein a and b are all real numbers. For example, a numerical range of "0-5" indicates that all real numbers between "0-5" are listed herein, and "0-5" is simply an abbreviation for these numerical combinations. Furthermore, when a parameter is expressed as an integer ≥ 2, this is equivalent to disclosing that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0074] Unless otherwise specified, all embodiments and optional embodiments of the present disclosure can be combined with each other to form new technical solutions, and such technical solutions should be considered to be included in the disclosure content of the present disclosure.

[0075] Unless otherwise specified, all technical features and optional technical features of the present disclosure can be combined with each other to form new technical solutions, and such technical solutions should be considered to be included in the disclosure content of the present disclosure.

[0076] Unless otherwise specified, all steps of the present disclosure may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), which means that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially. For example, the method may further include step (c), which means that step (c) may be added to the method in any order, for example, the method may include steps (a), (b) and (c), or may include steps (a), (c) and (b), or may include steps (c), (a) and (b), etc.

[0077] If not otherwise specified, in the present disclosure, the terms "first", "second", etc. are used to distinguish different objects rather than to describe a specific order or a primary-secondary relationship.

[0078] In the present disclosure, the terms "plurality" and "multiplicity" refer to two or more.

[0079] In the description of the embodiments of the present disclosure, unless otherwise specified, a first feature being "above" or "below" a second feature may mean that the first and second features are in direct contact, or that the first and second features are in indirect contact through an intermediate medium. Furthermore, a first feature being "above," "above," and "above" a second feature may mean that the first feature is directly above or diagonally above the second feature, or simply means that the first feature is at a higher level than the second feature. A first feature being "below," "below," and "below" a second feature may mean that the first feature is directly below or diagonally below the second feature, or simply means that the first feature is at a lower level than the second feature.

[0080] Unless otherwise defined, terms used in the present disclosure have the common meanings that are commonly understood by those skilled in the art.

[0081] Unless otherwise stated, the numerical values ​​of the various parameters mentioned in this disclosure can be measured using various test methods commonly used in the art, for example, they can be measured according to the test methods given in the examples of this disclosure. Unless otherwise stated, the test temperature of each parameter is 25°C.

[0082] The battery mentioned in the embodiments of the present disclosure may be a single physical module including one or more battery cells to provide higher voltage and capacity. For example, the battery mentioned in the present disclosure may include a battery cell, a battery module or a battery pack, etc. A battery cell is the smallest unit that makes up a battery, which can realize the function of charging and discharging on its own. When there are multiple battery cells, the multiple battery cells are connected in series, in parallel or in mixed connection through a busbar. In some embodiments, the battery may be a battery module; when there are multiple battery cells, the multiple battery cells are arranged and fixed to form a battery module. In some embodiments, the battery may be a battery pack, which includes a case and battery cells, and the battery cells or battery modules are housed in the case. In some embodiments, the case may serve as part of the chassis structure of a vehicle. For example, part of the case may become at least a part of the floor of the vehicle, or part of the case may become at least a part of the crossbeam and longitudinal beam of the vehicle.

[0083] In some embodiments, the battery may be an energy storage device, including an energy storage container, an energy storage cabinet, and the like.

[0084] The technical solutions described in the embodiments of the present disclosure are applicable to batteries and electrical devices using batteries.

[0085] Batteries can be used as power sources or energy storage units for electrical devices. Electrical devices include, but are not limited to, mobile devices (e.g., mobile phones, tablets, laptops, etc.), 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, satellites, and energy storage systems.

[0086] The electrical device can select the type of battery according to its usage requirements, such as a battery cell, a battery module or a battery pack.

[0087] For the convenience of description, the following embodiments are described by taking a vehicle as an example of an electrical device.

[0088] FIG1 is a schematic structural diagram of a vehicle provided in some embodiments of the present disclosure.

[0089] As shown in FIG1 , a battery 2 is provided inside the vehicle 1. The battery 2 may be provided at the bottom, head, or tail of the vehicle 1. The battery 2 may be used to power the vehicle 1. For example, the battery 2 may serve as an operating power source for the vehicle 1.

[0090] The vehicle 1 may further include a controller 3 and a motor 4 . The controller 3 is used to control the battery 2 to supply power to the motor 4 , for example, to meet the power requirements of the vehicle 1 during startup, navigation, and driving.

[0091] In some embodiments, the battery 2 can serve not only as an operating power source for the vehicle 1 , but also as a driving power source for the vehicle 1 , replacing or partially replacing fuel or natural gas to provide driving power for the vehicle 1 .

[0092] FIG2 is an exploded view of a battery according to some embodiments of the present disclosure. As shown in FIG2 , the battery 2 includes a housing 5 and battery cells (not shown), which are housed in the housing 5 .

[0093] The housing 5 is used to house the battery cells and can have various structures. In some embodiments, the housing 5 can include a first housing portion 5a and a second housing portion 5b. The first housing portion 5a and the second housing portion 5b overlap each other and together define a storage space 5c for accommodating the battery cells. The second housing portion 5b can be a hollow structure with one end open. The first housing portion 5a is a plate-like structure, and the first housing portion 5a overlaps the open side of the second housing portion 5b to form the housing 5 with the storage space 5c. Alternatively, both the first housing portion 5a and the second housing portion 5b can be hollow structures with one end open. The open side of the first housing portion 5a overlaps the open side of the second housing portion 5b to form the housing 5 with the storage space 5c. Of course, the first housing portion 5a and the second housing portion 5b can have various shapes, such as a cylinder, a rectangular parallelepiped, etc.

[0094] In order to improve the sealing performance after the first box body 5a and the second box body 5b are connected, a sealing member, such as a sealant, a sealing ring, etc., may also be provided between the first box body 5a and the second box body 5b.

[0095] Assuming that the first box body portion 5a covers the top of the second box body portion 5b, the first box body portion 5a can also be called an upper box cover, and the second box body portion 5b can also be called a lower box body.

[0096] In battery 2, there can be one or more battery cells. If there are multiple battery cells, they can be connected in series, in parallel, or in a hybrid configuration. A hybrid configuration refers to a combination of series and parallel connections. Multiple battery cells can be directly connected in series, in parallel, or in a hybrid configuration, and then the entire battery cell structure can be housed within housing 5. Alternatively, multiple battery cells can be first connected in series, in parallel, or in a hybrid configuration to form a battery module 6, and then multiple battery modules 6 can be connected in series, in parallel, or in a hybrid configuration to form a single unit and housed within housing 5.

[0097] FIG3 is a schematic diagram of an explosion of the battery module shown in FIG2 .

[0098] As shown in FIG3 , in some embodiments, there are multiple battery cells 7, which are first connected in series, in parallel, or in hybrid to form a battery module 6. The multiple battery modules 6 are then connected in series, in parallel, or in hybrid to form a whole and accommodated in a box.

[0099] The multiple battery cells 7 in the battery module 6 can be electrically connected via a busbar component to achieve parallel connection, series connection, or mixed connection of the multiple battery cells 7 in the battery module 6 .

[0100] The battery cells mentioned in the embodiments of the present disclosure may include lithium-ion battery cells.

[0101] The battery cell mentioned in the embodiment of the present disclosure includes an electrode assembly and an electrolyte, and the electrode assembly includes a negative electrode sheet, a positive electrode sheet and a separator.

[0102] The negative electrode plate includes a negative electrode current collector and a negative electrode film layer located on at least one side of the negative electrode current collector, the negative electrode film layer includes a negative electrode active material, the negative electrode active material includes a silicon-carbon composite material, the silicon-carbon composite material includes a carbon material matrix with a pore structure and a silicon-based material located in the pore structure of the carbon material matrix.

[0103] The ratio of the mass of the electrolyte to the capacity of the battery cell is 1.2g / Ah-2.0g / Ah.

[0104] High energy density and long cycle life are currently the common pursuits of battery cells. In order to improve the energy density of battery cells, a feasible strategy is to reduce the mass proportion of each component in the battery cell. The mass proportion of the positive electrode sheet, negative electrode sheet and electrolyte in the battery cell is relatively high, but the positive electrode sheet and negative electrode sheet mainly play the role of contributing to the capacity in the battery cell, and their mass proportion is difficult to further reduce. Therefore, it is a feasible solution to improve the energy density of the battery cell by reducing the mass proportion of the electrolyte. However, the electrolyte has a huge impact on the charge and discharge performance of the battery cell. When the infiltration effect of the electrode assembly is not good, the ion transmission path becomes longer, and the part of the electrode sheet that is not infiltrated by the electrolyte will not be able to participate in the electrochemical reaction of the battery, which will affect the cycle performance of the battery cell.

[0105] Silicon-carbon composites have a high theoretical specific capacity and can significantly increase the energy density of battery cells. However, unlike graphite, silicon-carbon composites react with metals (such as lithium) primarily through alloying reactions during charge and discharge, resulting in a significant volume effect that can easily cause particle breakage and pulverization.

[0106] Silicon-carbon composite materials are composites of carbon materials and silicon-based materials. Currently, silicon-carbon composite materials are mostly obtained by mechanical ball milling. Mechanical ball milling usually uses silicon powder, flake graphite, and coated carbon source as raw materials, and the granulation is followed by carbonization treatment of the carbon source to obtain the obtained product. The silicon-carbon composite materials prepared by this method are still prone to breakage and pulverization problems during repeated charge and discharge of battery cells. In addition, due to the volume effect of the silicon-carbon composite material, the solid electrolyte interface (SEI) film on the surface of its particles will be repeatedly destroyed and reconstructed, thereby increasing the consumption of active ions and electrolytes. The electrolyte consumed in rebuilding the SEI film increases, and the electrolyte available for wetting the electrode assembly decreases, resulting in poor electrolyte wettability of the electrode assembly.

[0107] Therefore, when the negative electrode active material includes a silicon-carbon composite material, in order to make the battery cell have a long cycle life, the amount of electrolyte used is usually relatively large. However, as the amount of electrolyte used increases, the energy density of the battery cell will decrease. Therefore, there is usually a contradiction between the long cycle life and high energy density of the battery cell, and it is difficult to have both.

[0108] The silicon-carbon composite material used in the battery cell provided by the embodiment of the present disclosure is different from the silicon-carbon composite material obtained by mechanical ball milling. It includes a carbon material matrix with a pore structure and a silicon-based material located in the pore structure of the carbon material matrix. The carbon material matrix with a pore structure can effectively alleviate the volume expansion of the internal silicon-based material, reduce the problems of breakage and pulverization of the silicon-carbon composite material, and improve the integrity of the SEI film on the surface of the silicon-carbon composite material particles, thereby reducing the consumption of active ions and electrolytes. The consumption of electrolyte is reduced, and the demand for electrolyte during charge and discharge of the battery cell is reduced, thereby enabling the battery cell to have a long cycle life under the premise of a smaller mass of electrolyte. Therefore, the battery cell provided by the embodiment of the present disclosure can have both high energy density and good cycle performance.

[0109] The quality of the electrolyte can be tested as follows: Weigh the battery cell and record its mass as m0. Then, disassemble the battery cell and separate the electrolyte by centrifugation. Soak all disassembled solid components in acetonitrile for 2 hours, remove them, air dry at room temperature, and bake them in a 60°C oven for at least 4 hours. Weigh again and record its mass as m1. The difference between m0 and m1 is the mass of the electrolyte.

[0110] The capacity of a battery cell can be tested as follows: at 25°C, let the battery cell stand for 5 minutes, and discharge it at a constant current of 0.33C to the lower cut-off voltage; after standing for 5 minutes, charge it at a constant current of 0.33C to the upper cut-off voltage, and then charge it at a constant voltage at the upper cut-off voltage to a current of 0.05C; after standing for 5 minutes, discharge it at a constant current of 0.33C to the lower cut-off voltage, and record the discharge capacity at this time, which is the capacity of the battery cell.

[0111] The upper cut-off voltage and the lower cut-off voltage may adopt the charge and discharge voltages recommended in the product specification of the battery cell.

[0112] For example, the positive electrode active material includes a lithium transition metal oxide with a molar ratio of Ni of less than 0.8, such as LiNi 0.5 Co 0.2 Mn 0.3 When the negative electrode active material includes graphite and silicon-carbon composite material, the upper cut-off voltage of the battery cell can be 4.35V, and the lower cut-off voltage can be 2.8V.

[0113] For example, the positive electrode active material includes a lithium transition metal oxide with a molar ratio of Ni greater than or equal to 0.8, such as LiNi 0.8 Co 0.1 Mn 0.1 O2、LiNi 0.8 Co 0.15 Al 0.05 O2、LiNi 0.9 Co 0.06 Mn 0.04 When the negative electrode active material includes graphite and silicon-carbon composite material, the upper cut-off voltage of the battery cell can be 4.25V, and the lower cut-off voltage can be 2.8V.

[0114] The molar ratio of Ni element refers to the ratio of the molar amount of Ni element in the lithium transition metal oxide to the total molar amount of transition metal elements.

[0115] The battery cell can be a square shell battery cell or a cylindrical battery cell. As shown in FIG3 , the battery cell can be a cylindrical battery cell.

[0116] Optionally, the ratio of the mass of the electrolyte to the capacity of the prismatic battery cell may be 1.5 g / Ah to 2.0 g / Ah, for example, 1.5 g / Ah, 1.55 g / Ah, 1.6 g / Ah, 1.65 g / Ah, 1.7 g / Ah, 1.75 g / Ah, 1.8 g / Ah, 1.85 g / Ah, 1.9 g / Ah, 1.95 g / Ah, 2.0 g / Ah, or a range consisting of any of the foregoing values. More preferably, the ratio of the mass of the electrolyte to the capacity of the prismatic battery cell may be 1.7 g / Ah to 1.9 g / Ah.

[0117] Optionally, the ratio of the mass of the electrolyte to the capacity of the cylindrical battery cell can be 1.2g / Ah-1.5g / Ah, for example, it can be 1.2g / Ah, 1.22g / Ah, 1.24g / Ah, 1.26g / Ah, 1.28g / Ah, 1.3g / Ah, 1.32g / Ah, 1.34g / Ah, 1.36g / Ah, 1.38g / Ah, 1.4g / Ah, 1.42g / Ah, 1.44g / Ah, 1.46g / Ah, 1.48g / Ah, 1.5g / Ah, or a range consisting of any of the above values. More optionally, the ratio of the mass of the electrolyte to the capacity of the cylindrical battery cell may be 1.24 g / Ah-1.5 g / Ah, 1.26 g / Ah-1.46 g / Ah, or 1.26 g / Ah-1.4 g / Ah.

[0118] During the preparation process, the electrode assembly of the square-shell battery cell needs to undergo a cold pressing process to be pressed into a square electrode assembly so that the electrode assembly can be installed in the square shell. In order to ensure uniform bonding between the electrode piece and the isolation membrane and reduce interface contact problems, the isolation membrane coating usually contains a certain amount of fluoropolymer, such as polyvinylidene fluoride (PVDF), which can improve the interface between the isolation membrane and the electrode piece, thereby helping to improve the cycle performance of the battery cell. However, the fluoropolymer will absorb a certain amount of electrolyte, thereby reducing the electrolyte wettability of the electrode piece. In order to fully infiltrate the electrode piece with the electrolyte, the amount of electrolyte used needs to be greater than that of the cylindrical battery cell. The electrode assembly of the cylindrical battery cell does not need to undergo a cold pressing process before being installed in the cylindrical shell, and the isolation membrane coating used usually does not need to contain a fluoropolymer, so the amount of electrolyte used can be less than that of the square-shell battery cell.

[0119] In some embodiments, the battery cell further includes a shell and an end cap assembly, the shell having an opening, and the end cap assembly covers the opening of the shell and forms a sealed connection to form a receiving cavity for accommodating the electrode assembly and the electrolyte.

[0120] In some embodiments, the end cap assembly includes an end cap that covers the opening of the housing.

[0121] In some embodiments, the end cap assembly may further include an electrode terminal mounted on the end cap. There may be two electrode terminals, each defined as a positive electrode terminal and a negative electrode terminal. Both the positive electrode terminal and the negative electrode terminal are used to electrically connect to the electrode assembly to output the electrical energy generated by the electrode assembly.

[0122] In other embodiments, the housing is a hollow structure with two opposing openings. Two end cap assemblies are provided, with one end cap assembly correspondingly covering one opening of the housing and forming a sealed connection to form a chamber for accommodating the electrode assembly and electrolyte. In this structure, one end cap assembly may be provided with two electrode terminals while the other end cap assembly is not provided with an electrode terminal, or both end cap assemblies may each be provided with one electrode terminal.

[0123] The electrode assembly consists of a main body and tabs extending axially from the main body. The tabs are used to conduct current generated by the main body. The main body is the core part of the battery cell that enables charging and discharging, and typically includes the positive electrode sheet, the negative electrode sheet, and the separator.

[0124] The number of tabs may be two. The two tabs are defined as a positive tab and a negative tab, respectively. The two tabs are electrically connected to the positive electrode terminal and the negative electrode terminal, respectively. The positive tab may be formed by stacking multiple positive tabs together, and the negative tab may be formed by stacking multiple negative tabs together.

[0125] In some embodiments, the diameter of the cylindrical battery cell may be greater than or equal to 35 mm, and may be 40 mm to 60 mm, thereby enabling the battery cell to have a high capacity.

[0126] In some embodiments, the axial dimension of the cylindrical battery cell may be greater than or equal to 70 mm, and may be 80 mm to 135 mm, thereby enabling the battery cell to have a high capacity.

[0127] The axial direction of a cylindrical battery cell refers to the direction of the cylinder's central axis of rotation, i.e., the direction shared by the central axis. The radial direction of a cylindrical battery cell is perpendicular to the axial direction and is the direction of the diameter of the cylinder's end face. The axial dimension of a cylindrical battery cell is usually referred to as the length of the cylindrical battery cell.

[0128] The axial dimension of a cylindrical battery cell refers to the distance between the top and bottom outer surfaces of the battery cell. It is understood that the axial dimension of a cylindrical battery cell does not include the dimensions of the electrode terminals.

[0129] In some embodiments, the material of the battery cell housing may include but is not limited to hard plastic, aluminum, or steel.

[0130] [Negative electrode]

[0131] The negative electrode active material includes a silicon-carbon composite material. In some embodiments, the silicon-carbon composite material may account for 4 wt % or more of the negative electrode active material, thereby increasing the energy density of the battery cell.

[0132] Optionally, the mass proportion of the silicon-carbon composite material in the negative electrode active material can be 5wt%-25wt%. When the mass proportion of the silicon-carbon composite material in the negative electrode active material is within the above range, the demand for electrolyte during the battery cell charge and discharge cycle is reduced, thereby reducing the electrolyte mass of the battery cell and thus achieving a higher energy density of the battery cell.

[0133] The silicon-carbon composite material includes a carbon material matrix having a pore structure and a silicon-based material located in the pore structure of the carbon material matrix. In some embodiments, the carbon material matrix having a pore structure may include one or more of activated carbon, biomass carbon, pyrolytic carbon, and resin carbon. In addition to alleviating the volume expansion of the silicon-based material and improving the electronic conductivity of the silicon-based material, the silicon-carbon composite material can also promote ion transport and increase the specific capacity of the silicon-carbon composite material.

[0134] Optionally, the average pore diameter of the pore structure of the carbon material matrix may be 0.5 nm to 8 nm.

[0135] Optionally, the pore structure of the carbon material matrix may include micropores, and the average pore diameter d1 of the micropores may satisfy: 0.5 nm ≤ d1 < 2 nm.

[0136] Optionally, the pore structure of the carbon material matrix may include mesopores, and the average pore diameter d2 of the mesopores may satisfy: 2nm≤d2≤8nm.

[0137] Optionally, the pore structure of the carbon material matrix may include micropores and mesopores, the micropores may account for 60%-90% of the pore structure, and the mesopores may account for 10%-40% of the pore structure.

[0138] By adjusting the ratio of micropores and mesopores, it is beneficial to better disperse silicon-based materials.

[0139] Optionally, the specific surface area of ​​the carbon material matrix with a porous structure can be 500m 2 / g-2000m 2 / g.

[0140] The carbon material matrix can be obtained by high-temperature pyrolysis of an organic carbon source and chemical activation treatment. The organic carbon source can include one or more of biomass materials and polymer materials. The chemical activation treatment can be etching, and the etching can be performed using sodium hydroxide and / or potassium hydroxide.

[0141] In some embodiments, the silicon-based material may include one or more of amorphous silicon, crystalline silicon, silicon oxides, silicon carbide, and silicon alloys.

[0142] Optionally, the silicon-based material may include one or more of amorphous silicon and crystalline silicon.

[0143] Optionally, the grain size of the crystalline silicon may be less than or equal to 5 nm.

[0144] The grain size of crystalline silicon is well known in the art and can be measured using instruments and methods known in the art, such as a high-resolution transmission electron microscope (HRTEM).

[0145] Crystalline silicon helps improve the initial coulombic efficiency of battery cells. Amorphous silicon has a small volume expansion, which helps improve the cycle performance of battery cells and reduce the volume expansion of battery cells.

[0146] In some embodiments, the silicon-based material may include amorphous silicon.

[0147] In some embodiments, the silicon-based material may include crystalline silicon.

[0148] In some embodiments, the silicon-based material may include both crystalline silicon and amorphous silicon.

[0149] In some embodiments, the silicon-based material may include a first crystalline silicon and a second crystalline silicon having different grain sizes, and the ratio of the grain size of the first crystalline silicon to the grain size of the second crystalline silicon may be greater than or equal to 1.6:1.

[0150] The first crystalline silicon has a larger grain size, which helps to improve the first coulombic efficiency of the battery cell; the second crystalline silicon has a smaller grain size, which helps to improve the cycle performance of the battery cell and reduce the volume expansion of the battery cell.

[0151] The silicon-carbon composite material has an inner region and an outer region. The region extending from the outer surface of the silicon-carbon composite particle to the inner portion of the particle by 0.5 times the distance between any point on the outer surface of the particle and the particle core is recorded as the outer region, and the region inside the outer region is recorded as the inner region.

[0152] A cross-section of the silicon-carbon composite material particles can be prepared using a dual beam focused ion beam microscope (Dual Beam FIB-SEM), the cross-section passing through the central area of ​​the silicon-carbon composite material, optionally through the particle core of the silicon-carbon composite material, and then the cross-sectional image characteristics of the silicon-carbon composite material can be observed by a transmission electron microscope (TEM) or a high resolution transmission electron microscope (HRTEM). The cross-sectional image of the silicon-carbon composite material includes a cross-sectional image passing through the particle core of the silicon-carbon composite material. "Particle core" refers to the intersection of the longest diameter (or longest diagonal) and the shortest diameter (or shortest diagonal) of the silicon-carbon composite material particle.

[0153] FIG4 is a schematic diagram of a cross-sectional image of a silicon-carbon composite material 100 provided in some embodiments of the present disclosure, and the cross-sectional image passes through the particle core O of the silicon-carbon composite material 100. As shown in FIG4 , the silicon-carbon composite material 100 includes an outer region 101 and an inner region 102 located inside the outer region 101. The intersection of the longest diameter (or longest diagonal) and the shortest diameter (or shortest diagonal) of the silicon-carbon composite material particle is the particle core O, and the length between any point P on the outer surface of the particle and the particle core O is recorded as R n The length R between any point P on the outer surface of the particle and the particle core O is the length from the outer surface of the silicon-carbon composite material to the inner surface of the particle. n The area formed by the distance of 0.5 times is recorded as the outer area 101. It should be noted that the "length R" here is n " refers to the distance between any point on the outer surface of the particle and the particle core. When the silicon-carbon composite material has a regular or irregular morphology other than an ideal spherical shape, the length R n It is expressed as a variable value, that is, the distance from different positions on the outer surface of the particle to the particle core is a constantly changing value, and thus the distance from different positions on the outer surface of the particle to the inside of the particle is also a constantly changing value. Therefore, all points on the outer surface of the silicon-carbon composite material particle extend the corresponding distance (i.e. 0.5R n The area enclosed by all the points obtained after ) and the outer surface of the particle is the external area.

[0154] The external area and the internal area can be considered as two artificially defined areas, and there may be no obvious boundary between the external area and the internal area.

[0155] Optionally, the silicon-based material may include both crystalline silicon and amorphous silicon, and in a cross-sectional image of the silicon-carbon composite material, the total cross-sectional area of ​​the crystalline silicon in the outer region may be smaller than the total cross-sectional area of ​​the crystalline silicon in the inner region, and the total cross-sectional area of ​​the amorphous silicon in the outer region may be larger than the total cross-sectional area of ​​the amorphous silicon in the inner region.

[0156] Crystalline silicon is mainly located in the inner region of the silicon-carbon composite material, while amorphous silicon is mainly located in the outer region of the silicon-carbon composite material. This can fully exert the effect of crystalline silicon on improving the first coulombic efficiency, and fully exert the effect of amorphous silicon on improving the cycle performance and reducing the volume expansion.

[0157] Optionally, the silicon-based material may simultaneously include a first crystalline silicon and a second crystalline silicon having different grain sizes, and the ratio of the grain size of the first crystalline silicon to the grain size of the second crystalline silicon may be greater than or equal to 1.6:1, and in the cross-sectional image of the silicon-carbon composite material, the total cross-sectional area of ​​the first crystalline silicon in the outer region may be smaller than the total cross-sectional area of ​​the first crystalline silicon in the inner region, and the total cross-sectional area of ​​the second crystalline silicon in the inner region may be smaller than the total cross-sectional area of ​​the second crystalline silicon in the outer region.

[0158] By making the first crystalline silicon with a larger grain size mainly located in the inner region of the silicon-carbon composite material and making the second crystalline silicon with a smaller grain size mainly located in the outer region of the silicon-carbon composite material, the first crystalline silicon can fully exert its effect on improving the first coulombic efficiency, and the second crystalline silicon can fully exert its effect on improving the cycle performance and reducing the volume expansion.

[0159] The process of dispersing silicon-based materials into the pore structure of the carbon material matrix can be a vapor deposition process, and the vapor deposition process includes a chemical vapor deposition process and a physical vapor deposition process. It can be optionally a chemical vapor deposition process, for example, it can be any one of a thermal chemical vapor deposition process, a plasma enhanced chemical vapor deposition process, and a microwave plasma assisted chemical vapor deposition process.

[0160] In some embodiments, the process of dispersing silicon-based materials into the pore structure of a carbon material matrix includes the following steps: placing a carbon material matrix with a pore structure in a reaction furnace, introducing a mixed gas containing a silicon source gas and depositing it at a certain temperature, so that the silicon-based material can be dispersed into the pore structure of the carbon material matrix.

[0161] By adjusting the temperature of vapor deposition, amorphous silicon and crystalline silicon with different grain sizes can be obtained.

[0162] Vapor deposition can be performed in stages. By adjusting parameters such as deposition temperature at different stages, the silicon-based material can include both crystalline silicon and amorphous silicon, or both a first crystalline silicon and a second crystalline silicon with different grain sizes.

[0163] The mixed gas may include a silicon source gas and a protective gas. The protective gas may include nitrogen and a rare gas. The rare gas may include one or more of argon, helium, and the like. The silicon source gas refers to a gas that can form a silicon-based material. Optionally, the silicon source gas may include but is not limited to monosilane (H4Si), disilane (H6Si2), trisilane (H8Si3), silicon tetrachloride (Cl4Si), trichlorosilane (Cl3HSi), dichlorosilane (Cl2H2Si), chlorosilane (ClH3Si), silicon tetrafluoride (F4Si), trifluorosilane (F3HSi), difluorosilane (F2H2Si), fluorosilane (FH3Si), hexachlorodisilane (Cl6Si2), pentachlorodisilane (Cl5HSi2), tetrachlorodisilane (Cl4H2Si2, including 1,1,2,2-tetrachlorodisilane, 1,1,1,2-tetrachlorodisilane), trichlorodisilane (Cl3H3Si2, including 1,1,2-trichlorodisilane, 1,1,1-trichlorodisilane ), dichlorodisilane (Cl2H4Si2, including 1,1-dichlorodisilane, 1,2-dichlorodisilane), monochlorodisilane (ClH5Si2), hexafluorodisilane (F6Si2), pentafluorodisilane (F5HSi2), 1,1,2,2-tetrafluorodisilane (F4H2Si2), 1,1,1-trifluorodisilane (F3H3Si2), difluorodisilane (F2H4Si2, including 1,1-difluorodisilane, 1,2-difluorodisilane), monofluorodisilane (FH5Si2), one or more of methylsilane, ethylsilane, dimethylsilane, trimethylsilane, tetramethylsilane, methyldisilane, dimethyldisilane, trimethyldisilane, tetramethyldisilane, hexamethylsilane, methyltrichlorosilane, methylchlorosilane, chloroethylsilane, dichlorodimethylsilane and dichlorodiethylsilane.

[0164] In some embodiments, the mass proportion of silicon-based materials in the silicon-carbon composite material can be 20%-60%, for example, it can be 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, or a range consisting of any of the above values.

[0165] In some embodiments, the silicon-carbon composite material may further include a coating layer, which is located on at least a portion of the surface of the porous carbon material matrix. The coating layer is located on the outside of the silicon-carbon composite material, thereby further preventing direct contact between the silicon-based material and the electrolyte, reducing the reactivity of the silicon-based material after contact with air, thereby reducing electrolyte consumption and enabling the battery cell to have a long cycle life while maintaining a low electrolyte mass. Furthermore, the coating layer can also buffer the volume expansion of the silicon-based material, thereby helping to improve the storage performance of the battery cell.

[0166] Alternatively, the coating layer may include one or more of a carbon material, a conductive polymer, a metal oxide, and a metal sulfide. Alternatively, the carbon material may include one or more of vapor-deposited carbon, hard carbon, soft carbon, graphene, carbon fiber, and carbon nanotubes. Alternatively, the conductive polymer may include one or more of polyaniline, polypyrrole, and polythiophene. Alternatively, the metal oxide may include one or more of iron oxide, zinc oxide, tin oxide, copper oxide, and titanium oxide. Alternatively, the metal sulfide may include one or more of tin sulfide, molybdenum sulfide, titanium sulfide, iron sulfide, and copper sulfide.

[0167] Alternatively, the coating can be obtained by a vapor deposition process. For example, a carbon coating can be formed by introducing a mixed gas containing a carbon source gas and depositing it at a certain temperature. "Carbon source gas" refers to a gas that can form a carbon coating. Alternatively, the carbon source gas can include, but is not limited to, one or more of methane, ethane, propane, isopropyl ether, butane, isobutane, ethylene, propylene, butene, acetylene, ethyl chloride, fluoroethane, difluoroethane, chloromethane, fluoromethane, difluoromethane, trifluoromethane, vinyl chloride, vinyl fluoride, difluoroethylene, methylamine, formaldehyde, benzene, toluene, xylene, styrene, and phenol.

[0168] In some embodiments, the volume distribution particle size Dv50 of the silicon-carbon composite material may be 3 μm-15 μm.

[0169] In some embodiments, the volume distribution particle size Dv90 of the silicon-carbon composite material may be 15 μm-25 μm.

[0170] In some embodiments, the volume distribution particle size Dv10 of the silicon-carbon composite material may be 1 μm-5 μm.

[0171] The volume distribution particle size of the silicon-carbon composite material is within the above range, which helps to reduce surface activity, reduce interface side reactions, reduce electrolyte consumption, and also helps to make the battery cell have a long cycle life while keeping the electrolyte mass small.

[0172] In some embodiments, the particle size distribution of the silicon-carbon composite material may satisfy: 1≤(Dv90-Dv10) / Dv50≤3. The particle size distribution of the silicon-carbon composite material within the above range helps the battery cell have a high energy density.

[0173] In some embodiments, the specific surface area of ​​the silicon-carbon composite material can be 1 m 2 / g-6m 2 The specific surface area of ​​the silicon-carbon composite material is within the above range, which helps to reduce interface side reactions, reduce electrolyte consumption, and also helps to ensure that the battery cell has a long cycle life while maintaining a small electrolyte mass.

[0174] In some embodiments, the tap density of the silicon-carbon composite material can be 0.8 g / cm 3 -1.2g / cm 3 The tap density of the silicon-carbon composite material is within the above range, which helps the battery cell have a high energy density.

[0175] In some embodiments, the powder resistivity of the silicon-carbon composite material at 16 MPa can be less than or equal to 5Ω·cm. When the powder resistivity of the silicon-carbon composite material is within the above range, it can have good electronic conductivity, thereby enabling the battery cell to have a long cycle life.

[0176] In some embodiments, the negative electrode active material may further include graphite.

[0177] Optionally, the mass proportion of the silicon-carbon composite material in the negative electrode active material may be 5 wt%-25 wt%, and the mass proportion of graphite in the negative electrode active material may be greater than or equal to 75 wt%.

[0178] Optionally, the graphite may include but is not limited to at least one of artificial graphite and natural graphite.

[0179] In some embodiments, the volume distribution particle size Dv50 of the negative electrode active material may be 7 μm to 12 μm.

[0180] In some embodiments, the volume distribution particle size Dv90 of the negative electrode active material may be 15 μm to 20 μm.

[0181] In some embodiments, the volume distribution particle size Dv10 of the negative electrode active material may be 3 μm to 6 μm.

[0182] The overall volume distribution particle size of the negative electrode active material is within the above range, which helps to reduce surface activity, reduce interface side reactions, reduce electrolyte consumption, and also helps to make the battery cell have a long cycle life while keeping the electrolyte mass small.

[0183] In some embodiments, the particle size distribution of the negative electrode active material may satisfy: 1.16≤(Dv90-Dv10) / Dv50≤1.71.

[0184] The particle size distribution of the negative electrode active material is within the above range, which helps the battery cell have a high energy density.

[0185] In some embodiments, the negative electrode film layer may further include a negative electrode conductive agent. As an example, the negative electrode conductive agent may include, but is not limited to, one or more of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0186] In some embodiments, the negative electrode film layer may further include a negative electrode binder. As examples, the negative electrode binder may include, but is not limited to, one or more of styrene-butadiene rubber (SBR), water-soluble unsaturated resin SR-1B, water-based acrylic resins (e.g., polyacrylic acid PAA, polymethacrylic acid PMAA, sodium polyacrylate PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), and carboxymethyl chitosan (CMCS).

[0187] In some embodiments, the negative electrode film layer may further include other additives, such as thickeners, such as sodium carboxymethyl cellulose (CMC), PTC thermistor materials, and the like.

[0188] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. As examples of metal foils, copper foil, copper alloy foil, aluminum foil, and aluminum alloy foil may be used. The composite current collector may include a polymer material base layer and a metal material layer formed on at least one side of the polymer material base layer. As an example, the metal material may include, but is not limited to, one or more of copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy. As an example, the polymer material base layer may include, but is not limited to, one or more of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0189] The negative electrode plate does not exclude other additional functional layers in addition to the negative electrode film layer. For example, in some embodiments, the negative electrode plate may further include a conductive primer layer sandwiched between the negative electrode current collector and the negative electrode film layer and located on the surface of the negative electrode current collector. The primer layer may be composed of, for example, a conductive agent and a binder. In some embodiments, the negative electrode plate may further include a protective layer covering the surface of the negative electrode film layer.

[0190] The negative electrode sheet can be prepared by dispersing the negative electrode active material, negative electrode binder, negative electrode conductive agent, and optional other additives in a solvent and stirring them uniformly to form a negative electrode slurry; the negative electrode slurry is coated on the negative electrode current collector and, after drying and roll pressing, forms the negative electrode sheet. The solvent can be, but is not limited to, N-methylpyrrolidone (NMP) or deionized water.

[0191] [Electrolyte]

[0192] In some embodiments, the electrolyte includes an organic solvent, and the organic solvent includes a linear carbonate.

[0193] Optionally, the chain carbonate includes one or both of dimethyl carbonate (DMC) and ethyl methyl carbonate (EMC).

[0194] Optionally, the mass proportion of the linear carbonate in the organic solvent is greater than or equal to 60%. More preferably, the mass proportion of the linear carbonate in the organic solvent is 60%-85%.

[0195] As the energy density of battery cells increases, their dimensions also become larger, making them more susceptible to electrolyte wetting issues. By increasing the mass fraction of chain carbonates in the organic solvent of the electrolyte, the electrolyte can be made to have a low viscosity, facilitating electrolyte flow. This improves the electrolyte wetting of the electrode assembly and allows for a long cycle life for the battery cells while maintaining a low electrolyte mass.

[0196] The linear carbonate may include one or both of dimethyl carbonate and ethyl methyl carbonate. Dimethyl carbonate has a lower viscosity and a lower boiling point than ethyl methyl carbonate. Dimethyl carbonate is more effective in reducing electrolyte viscosity and reducing electrolyte dosage. Ethyl methyl carbonate is more effective in improving electrolyte stability and reducing gas production.

[0197] In some embodiments, the mass proportion of dimethyl carbonate in the organic solvent can be 60%-85%, optionally 70%-85%, and the mass proportion of ethyl methyl carbonate in the organic solvent can be 0%. A 0% ethyl methyl carbonate content indicates that the organic solvent does not contain ethyl methyl carbonate. This can better reduce the viscosity of the electrolyte, improve the electrolyte wettability of the electrode assembly, and also ensure that the battery cell has a long cycle life while maintaining a low mass of electrolyte.

[0198] In some embodiments, the mass ratio of dimethyl carbonate in the organic solvent may be greater than the mass ratio of ethyl methyl carbonate in the organic solvent, thereby enabling the electrolyte to have both lower viscosity and lower gas production.

[0199] In some embodiments, the mass proportion of dimethyl carbonate in the organic solvent may be 40%-75%, and optionally 45%-70%.

[0200] In some embodiments, the mass proportion of ethyl methyl carbonate in the organic solvent may be 5%-25%.

[0201] In some embodiments, the linear carbonate may include dimethyl carbonate and ethyl methyl carbonate, the mass proportion of dimethyl carbonate in the organic solvent is 40%-75%, optionally 45%-70%, and the mass proportion of ethyl methyl carbonate in the organic solvent is 5%-25%.

[0202] From the perspective of improving the stability of the electrolyte and reducing gas production, the organic solvent may include dimethyl carbonate and ethyl methyl carbonate, thereby making the electrolyte have both lower viscosity and lower gas production.

[0203] In some embodiments, the organic solvent further comprises a cyclic carbonate, and the cyclic carbonate may comprise one or both of ethylene carbonate (EC) and fluoroethylene carbonate (FEC).

[0204] Chain carbonates can make the electrolyte have low viscosity, which facilitates the flow of the electrolyte, but their dielectric constant is small and their ability to dissociate electrolyte salts is slightly weak. By mixing chain carbonates with cyclic carbonates, the electrolyte can have good fluidity while also having high ionic conductivity and high ion migration rate, thereby making the battery cell have better cycle performance.

[0205] Optionally, the cyclic carbonate includes both ethylene carbonate (EC) and fluoroethylene carbonate (FEC).

[0206] Optionally, the mass proportion of the cyclic carbonate in the organic solvent may be 15%-40%, more preferably 15%-38%, 20%-38%.

[0207] In some embodiments, the mass proportion of ethylene carbonate in the organic solvent may be 10%-35%.

[0208] In some embodiments, the mass proportion of fluoroethylene carbonate in the organic solvent may be 1%-10%, optionally 3%-10%, or 3%-8%.

[0209] Fluorinated ethylene carbonate can participate in the formation of SEI film on the surface of the negative electrode active material, improve the composition and properties of the SEI film, and thus effectively protect the negative electrode active material. Especially when the negative electrode active material contains silicon-carbon composite materials, due to the volume expansion characteristics of silicon-carbon composite materials, it is even more necessary to optimize the composition of the SEI film.

[0210] The reduction products of fluoroethylene carbonate at the negative electrode are mainly -CHF-OCO2 compounds and LiF. During the charge and discharge process, the -CHF-OCO2 compound forms an initial SEI film that coats the surface of the silicon-carbon composite material. This SEI film is flexible and resistant to rupture, effectively blocking contact between the silicon-carbon composite material and the electrolyte, thereby reducing electrolyte decomposition and SEI film reconstruction. At the same time, LiF, another reduction product of fluoroethylene carbonate, helps promote the conduction of lithium ions within the SEI film. Therefore, by including an appropriate amount of fluoroethylene carbonate in the electrolyte, the battery cell can have a long cycle life while maintaining a low electrolyte mass.

[0211] In some embodiments, the electrolyte contains cations and anions.

[0212] The cations include one or both of lithium ions and sodium ions.

[0213] The anion includes one or more of a hexafluorophosphate anion and an anion shown in Formula 1, and R1 and R2 each independently include a fluorine atom or a C1-C6 fluoroalkyl group.

[0214] R1 and R2 each independently include a fluorine atom or a C1-C6 fluoroalkyl group. A C1-C6 fluoroalkyl group means that at least one hydrogen atom in the C1-C6 alkyl group is replaced by a fluorine atom, or all hydrogen atoms are replaced by fluorine atoms, and can be, for example, a trifluoromethyl group, a pentafluoroethyl group, a heptafluoropropyl group, or the like.

[0215] Optionally, R1 and R2 each independently include a fluorine atom or a trifluoromethyl group.

[0216] Alternatively, the anion shown in Formula 1 may include a bis(fluorosulfonyl)imide anion (FSI - ), bis(trifluoromethanesulfonyl)imide anion (TFSI - ) or two thereof. More preferably, the anion shown in Formula 1 may include a bis(fluorosulfonyl)imide anion (FSI - ).

[0217] In some embodiments, the anion includes both a hexafluorophosphate anion and an anion of Formula 1.

[0218] The anion shown in Formula 1 is a weakly coordinated anion centered on N, containing a conjugated group and a fluorine atom and / or a fluoroalkyl group with strong charge absorption. The anion charge is highly delocalized, and the interaction between the anion and the cation is weak, which also helps to improve the ionic conductivity of the electrolyte. However, the anion shown in Formula 1 has the problem of corroding the positive electrode current collector (for example, aluminum foil), which will result in poor contact between the positive electrode active material and the positive electrode current collector. The thermal stability of the hexafluorophosphate anion is not as good as that of the anion shown in Formula 1, but it can passivate the positive electrode current collector and reduce the corrosion of the anion shown in Formula 1 on the positive electrode current collector; at the same time, the negative electrode film forming property of the hexafluorophosphate anion is worse than that of the anion shown in Formula 1.

[0219] Therefore, by making the anions include both hexafluorophosphate anions and the anions shown in Formula 1, a synergistic effect between the two can be exerted, thereby reducing the consumption of electrolyte during the cyclic charge and discharge process of the battery cell, thereby helping the battery cell to have a long cycle life while having a smaller electrolyte mass; in addition, the battery cell can also have a lower production cost.

[0220] Optionally, the molar concentration of the anion represented by Formula 1 may be greater than the molar concentration of the hexafluorophosphate anion.

[0221] By increasing the molar concentration of the anion represented by Formula 1 to a greater molar concentration than the hexafluorophosphate anion, the battery cell can achieve a long cycle life, good power performance, and high reliability. This is because the basic process of thermal runaway in a battery cell is as follows: at high temperatures, the SEI film at the negative electrode decomposes. As the temperature rises, the charged layered lithium-containing transition metal oxide violently decomposes and releases oxygen, causing a violent oxidation reaction in the electrolyte. By increasing the molar concentration of the anion represented by Formula 1 to a greater molar concentration than the hexafluorophosphate anion, the redox resistance of the electrolyte can be improved, delaying the thermal runaway temperature of the battery cell.

[0222] Alternatively, the molar concentration of the anion represented by Formula 1 may be 0.6 mol / L-0.9 mol / L. When the molar concentration of the anion represented by Formula 1 is within the above range, the electrolyte may have high ionic conductivity and may form a good SEI film on the surface of the negative electrode active material, thereby reducing side reactions between the negative electrode active material and the electrolyte.

[0223] Optionally, the molar concentration of the hexafluorophosphate anion can be 0.3 mol / L-0.5 mol / L. When the molar concentration of the hexafluorophosphate anion is within the above range, the electrolyte can have high ionic conductivity and can also reduce the corrosion of the anion represented by Formula 1 on the positive electrode current collector, thereby better exerting the effect of the anion represented by Formula 1.

[0224] In some embodiments, the anion may also include other anions, for example, but not limited to tetrafluoroborate anion (BF4 - ), perchlorate anion (ClO4 - ), hexafluoroarsenate anion (AsF6 - ), trifluoromethanesulfonate anion (TFS - ), difluorooxalatoborate anion (DFOB - ), dioxalatoborate anion (BOB - ), difluorophosphate anion (PO2F2 - ), difluorobis(oxaloyl)phosphate anion (DFOP - ) and tetrafluorooxalophosphate anion (TFOP - )

[0225] In some embodiments, the molar concentration of the anion can be 1 mol / L to 1.3 mol / L, optionally 1.05 mol / L to 1.15 mol / L. The molar concentration of the anion is the sum of the molar concentration of the anion shown in Formula 1, the molar concentration of the hexafluorophosphate anion, and the molar concentration of any other anion.

[0226] In some embodiments, the viscosity of the electrolyte at 25° C. may be less than or equal to 5 mPa·s, and may optionally be less than or equal to 3 mPa·s. This helps improve the electrolyte wettability of the electrode assembly and also helps the battery cell have a long cycle life while maintaining a low electrolyte mass.

[0227] The viscosity of the electrolyte can be measured using a viscometer. The shear force applied to the rotor as it rotates continuously at a constant speed in the sample causes the spring to generate torque, which is proportional to the viscosity, thus providing the viscosity value of the sample.

[0228] For example, the viscosity of an electrolyte can be tested as follows: Under ambient humidity conditions of <80%, take a 30mL sample and place it in a water bath at 25°C for at least 30 minutes. Place a spindle (e.g., No. 18) in the sample cup and add the sample to a point approximately 0.3cm from the cup opening. Start the connected viscometer and rotate at 70 RPM for 5 minutes before reading the viscosity value. Ten data points can be collected and averaged during the test. The test instrument can be a Brookfield DV-2TLV viscometer.

[0229] In some embodiments, the conductivity of the electrolyte at 25° C. may be 8 mS / cm-16 mS / cm, optionally 9 mS / cm-12 mS / cm.

[0230] The conductivity of the electrolyte can be measured using a conductivity meter. For example, an appropriate amount of electrolyte can be taken and divided into three equal parts. The conductivity of each sample is then measured at 25°C using a conductivity meter. The average of the test results is then taken as the conductivity of the electrolyte. The measuring instrument can be a DDS-307 conductivity meter.

[0231] Methods for preparing the electrolyte are well known. In some embodiments, the electrolyte solution can be obtained by uniformly mixing an electrolyte salt, an organic solvent, and an additive. The order in which the materials are added is not particularly limited and can be selected according to actual conditions. Alternatively, the molar concentration of the electrolyte salt can be 1 mol / L to 1.3 mol / L, and can be 1.05 mol / L to 1.15 mol / L.

[0232] Electrolyte salts can dissociate into cations and anions in organic solvents.

[0233] The electrolyte salt may include lithium hexafluorophosphate (LiPF6), one or more of the electrolyte salts shown in Formula 2, R1 and R2 each independently include a fluorine atom or a C1-C6 fluoroalkyl group, and M1 is Li. Alternatively, the electrolyte salt shown in Formula 2 may include one or both of lithium bis(fluorosulfonyl)imide (LiFSI) and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI). More optionally, the electrolyte salt shown in Formula 2 may include lithium bis(fluorosulfonyl)imide (LiFSI).

[0234] Furthermore, the electrolyte salt may further include one or more of lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6), lithium trifluoromethanesulfonate (LiTFS), lithium difluorooxalatoborate (LiDFOB), lithium bisoxalatoborate (LiBOB), lithium difluorophosphate (LiPO2F2), lithium difluorobisoxalatophosphate (LiDFOP) and lithium tetrafluorooxalatophosphate (LiTFOP).

[0235] The components and their contents in the electrolyte can be determined using conventional methods in the art. For example, ion chromatography (IC) can be used to qualitatively or quantitatively analyze the type and content of electrolyte salts in the electrolyte, and the testing standards can refer to JY / T020-1996. Gas chromatography-mass spectrometry (GC-MS) can be used to qualitatively and quantitatively analyze organic solvents in the electrolyte, and the testing standards can refer to GB / T9722-2006.

[0236] The electrolyte can be sampled and analyzed during the preparation process, or it can be obtained by disassembling and centrifuging the prepared battery after discharge.

[0237] [Isolation film]

[0238] In some embodiments, the isolation film may include a base film and a coating layer disposed on at least one side of the base film.

[0239] In some embodiments, the coating is free of fluoropolymers.

[0240] In some embodiments, the material of the base film may include polyolefin, and may optionally include polyethylene.

[0241] In some embodiments, the thickness of the base film may be 3 μm-9 μm, optionally 3 μm-7 μm.

[0242] In some embodiments, the puncture strength of the base film may be greater than or equal to 390 gf, and may be optionally 400 gf-480 gf.

[0243] The higher the base film's puncture strength, the better its puncture resistance, effectively reducing the risk of positive and negative electrode particles, as well as metallic foreign matter, piercing the separator and causing a short circuit between the positive and negative electrodes. Therefore, a base film puncture strength within the above range can improve the pass rate of battery cell short-circuit testing and enhance battery cell reliability.

[0244] In some embodiments, the base film may have a machine direction (MD) heat shrinkage rate of less than 3% at 105° C. for 1 hour, and may optionally be 1%-2.5%.

[0245] In some embodiments, the transverse direction (TD) thermal shrinkage of the base film at 105° C. for 1 hour may be less than 2%, and may be optionally 1%-1.8%.

[0246] The reduced thermal shrinkage of the base film indicates that the base film has good heat resistance, which can also increase the short-circuit test pass rate of the battery cell and improve the reliability of the battery cell.

[0247] The thermal shrinkage of the base film has a well-known meaning in the art and can be measured using methods known in the art. For example, the test can be performed with reference to GB / T 36363-2018.

[0248] In some embodiments, the longitudinal tensile strength of the base film may be greater than or equal to 2700 kgf / cm 2 , optional 2800kgf / cm 2 -3500kgf / cm 2 .

[0249] In some embodiments, the transverse tensile strength of the base film can be greater than or equal to 2500 kgf / cm 2 , optional 2600kgf / cm 2 -3200kgf / cm 2 .

[0250] The increased tensile strength of the base film helps to effectively coat the positive and negative electrode particles, thereby effectively reducing the short circuit between the positive and negative electrodes and improving the reliability of the battery cells.

[0251] The tensile strength of the base film has a well-known meaning in the art and can be measured using methods known in the art. For example, it can be tested with reference to GB / T 36363-2018.

[0252] In some embodiments, the average pore size of the base film may be 10 nm-60 nm, optionally 20 nm-40 nm.

[0253] The average pore size of the basement membrane has a well-known meaning in the art and can be measured using methods known in the art, for example, using a capillary flow pore size analyzer, such as a PMIPorometer.

[0254] In some embodiments, the porosity of the base film may be 20%-60%, optionally 30%-50%.

[0255] The porosity of the base film has a well-known meaning in the art and can be measured using methods known in the art. For example, the porosity can be measured with reference to GB / T 36363-2018.

[0256] In some embodiments, the coating includes a particulate inorganic filler. The particulate inorganic filler may include, but is not limited to, boehmite, alumina, silicon oxide SiO x (0<x≤2), one or more of zinc oxide, magnesium oxide, tin dioxide, titanium oxide, calcium oxide, zirconium oxide, yttrium oxide, nickel oxide, hafnium dioxide, cerium oxide, magnesium hydroxide, aluminum hydroxide, silicon carbide, boron carbide, aluminum nitride, silicon nitride, boron nitride, magnesium fluoride, calcium fluoride, barium fluoride, barium sulfate, magnesium aluminum silicate, lithium magnesium silicate, sodium magnesium silicate, bentonite, hectorite, zirconium titanate, and barium titanate.

[0257] In some embodiments, the coating further comprises a non-granular binder. The present disclosure does not particularly limit the type of the non-granular binder, and any known material with good adhesive properties may be selected, such as a linear binder, an emulsion binder, and a mixed linear and emulsion binder.

[0258] Optionally, the non-granular binder may have at least one polar group selected from the group consisting of a hydroxyl group (-OH), a carboxyl group (-COOH), an ester group (-COO-), a cyano group (-CN), an imide group (-CO-NH-CO-), a maleic anhydride group (-COOOC-), a sulfonate group (-SO3H) and a pyrrolidone group (-NCO-).

[0259] Alternatively, the non-particulate binder may include a homopolymer or copolymer selected from the group consisting of allyl polyether sulfate, acrylic acid, methacrylic acid, acrylamide, methyl acrylate, butyl acrylate, ethyl acrylate, glycidyl methacrylate, vinyl alcohol, acrylonitrile, hydroxyethyl acrylate, styrene, acetoxyethyl methacrylate, vinyltrimethoxysilane, lithium acrylate, sodium acrylate, lithium methacrylate, isobutylene, and maleic anhydride.

[0260] Optionally, the non-granular binder may include at least one of: polyacrylic acid, polymethyl methacrylate, polyacrylonitrile, polyvinyl pyrrolidone, polyvinyl acetate, polyethylene-co-vinyl acetate, polystyrene-co-methyl methacrylate, polystyrene-co-butyl acrylate, polyethylene oxide, cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, cyanoethyl pullulan, cyanoethyl polyvinyl alcohol, cyanoethyl cellulose, cyanoethyl sucrose, pullulan, carboxymethyl cellulose, acrylonitrile-styrene-butadiene copolymer, polyimide.

[0261] Optionally, the mass content of the non-particulate binder in the coating layer may be less than or equal to 10 wt %, based on the total mass of the coating layer.

[0262] In some embodiments, the coating may have a thickness of 0.5 μm to 3 μm, optionally 1 μm to 2.5 μm.

[0263] In some embodiments, the isolation film may have a total thickness of 5 μm to 14 μm.

[0264] It should be noted that the above-mentioned isolation film coating parameters (such as thickness, etc.) are the coating parameters of a single side of the base film. When the coating is provided on both sides of the base film, the coating parameters on either side meet the requirements of this disclosure and are considered to fall within the scope of protection of this disclosure.

[0265] [Positive electrode]

[0266] In some embodiments, the positive electrode sheet includes a positive electrode current collector and a positive electrode film layer located on at least one side of the positive electrode current collector, wherein the positive electrode film layer includes a positive electrode active material.

[0267] In some embodiments, the positive electrode active material may include a layered lithium-containing transition metal oxide. Examples of the layered lithium-containing transition metal oxide may include one or more of lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, and modified compounds thereof.

[0268] In some embodiments, the layered lithium-containing transition metal oxide may include a Ni element. The molar amount of the Ni element may account for more than 70% of the total molar amount of the transition metal elements in the layered lithium-containing transition metal oxide; alternatively, the molar amount of the Ni element may account for more than 80% of the total molar amount of the transition metal elements in the layered lithium-containing transition metal oxide; more alternatively, the molar amount of the Ni element may account for more than 90% of the total molar amount of the transition metal elements in the layered lithium-containing transition metal oxide.

[0269] In some embodiments, the layered lithium-containing transition metal oxide may include Li a Ni b Co c M d O e A f , where 0 < a ≤ 1.2; 0.5 ≤ b < 1; 0 < c < 1; 0 < d < 1; 1 ≤ e ≤ 2; 0 ≤ f ≤ 1; M includes, but is not limited to, one or more of Mn, Al, Zr, Zn, Cu, Cr, Mg, Fe, V, Ti, and B; and A includes, but is not limited to, one or more of N, F, S, and Cl. Optionally, 0.7 ≤ b < 1, 0.8 ≤ b < 1, and 0.9 ≤ b < 1. This can further increase the energy density of the battery cell.

[0270] In some embodiments, as an example, the layered lithium-containing transition metal oxide may include but is not limited to LiNi 0.8 Co 0.1 Mn0.1 O2、LiNi 0.80 Co 0.15 Al 0.05 O2、LiNi 0.9 Co 0.06 Mn 0.04 O2、LiNi 0.92 Co 0.06 Mn 0.02 O2、LiNi 0.96 Co 0.02 Mn 0.02 One or more of O2.

[0271] The charge and discharge process of a battery cell is accompanied by the intercalation and deintercalation of Li, and the molar content of Li in the battery cell varies at different discharge states. The molar content of Li in the examples of the present disclosure regarding the positive electrode active materials refers to the material's initial state, i.e., the state before the materials are added. The molar content of Li in the positive electrode active materials used in the battery cell may change after charge and discharge cycles.

[0272] In the examples of the present disclosure regarding the positive electrode active materials, the molar content of O is only a theoretical value. Lattice oxygen release will cause the molar content of O to change, and the actual molar content of O will fluctuate.

[0273] The higher the content of Ni element in the layered lithium-containing transition metal oxide, the higher the energy density of the battery cell.

[0274] The modified compounds of the above-mentioned positive electrode active materials may be used to perform doping modification and / or surface coating modification on the positive electrode active materials.

[0275] In some embodiments, the positive electrode active material may include both a single-crystal layered lithium-containing transition metal oxide and a polycrystalline layered lithium-containing transition metal oxide.

[0276] To achieve higher energy density, higher requirements are typically placed on the compaction density of the positive electrode sheet. Typically, the volume distribution particle size Dv50 of a single-crystal layered lithium-containing transition metal oxide is smaller than the volume distribution particle size Dv50 of a polycrystalline layered lithium-containing transition metal oxide. By including both single-crystal and polycrystalline layered lithium-containing transition metal oxides in the positive electrode active material, the compaction density of the positive electrode sheet can be increased, thereby improving the energy density of the battery cell.

[0277] For the same type of layered lithium-containing transition metal oxide and the same upper charge cutoff voltage for the battery cells, the cycling stability of single-crystal layered lithium-containing transition metal oxides is higher than that of polycrystalline layered lithium-containing transition metal oxides. Polycrystalline layered lithium-containing transition metal oxides have a higher lithium ion diffusion coefficient and better electrolyte wettability, which can improve the power performance of battery cells.

[0278] Therefore, the positive electrode active material includes both single-crystal layered lithium-containing transition metal oxides and polycrystalline layered lithium-containing transition metal oxides, which helps the battery cell to have both good cycle stability and good power performance while having a smaller electrolyte mass and higher energy density.

[0279] Optionally, the proportion of the single-crystal layered lithium-containing transition metal oxide in the positive electrode active material is greater than 0 and less than or equal to 40%, and the proportion of the polycrystalline layered lithium-containing transition metal oxide in the positive electrode active material is greater than or equal to 60% and less than 100%. This helps the battery cell achieve both good cycle stability and good power performance while having a small electrolyte mass and high energy density.

[0280] The terms "layered lithium-containing transition metal oxide with a single crystal morphology" and "layered lithium-containing transition metal oxide with a polycrystalline morphology" have well-known meanings in the art. "Layered lithium-containing transition metal oxide with a single crystal morphology" also includes layered lithium-containing transition metal oxide with a quasi-single crystal (also known as quasi-single crystal) morphology. Quasi-single crystal (quasi-single crystal) is a well-known meaning in the art, generally referring to particles formed by the agglomeration of a small number (e.g., 2-5) primary particles. Layered lithium-containing transition metal oxide with a polycrystalline morphology refers to a layered lithium-containing transition metal oxide with a secondary particle morphology formed by the agglomeration of multiple (e.g., greater than 5) primary particles. "Layered lithium-containing transition metal oxide with a single crystal morphology" and "Layered lithium-containing transition metal oxide with a polycrystalline morphology" can be distinguished by scanning electron microscopy.

[0281] The percentage of layered lithium-containing transition metal oxides with a single crystal (or polycrystalline) morphology in the positive electrode active material is well known in the art and can be measured using instruments and methods known in the art. For example, the positive electrode active material can be laid and adhered to a conductive adhesive to form a test sample with a length × width of 6 cm × 1.1 cm; the particle morphology can be tested using a scanning electron microscope and an energy dispersive spectrometer (such as a ZEISS Sigma300). The test can refer to JY / T010-1996. To ensure the accuracy of the test results, 20 different areas can be randomly selected from the test sample for scanning testing, and at a certain magnification (for example, 1000 times or more), the ratio of the number of layered lithium-containing transition metal oxides with a single crystal (or polycrystalline) morphology to the total number of particles in each area is calculated, which is the percentage of layered lithium-containing transition metal oxides with a single crystal (or polycrystalline) morphology in the area; the average of the test results of the 20 test areas is taken as the percentage of layered lithium-containing transition metal oxides with a single crystal (or polycrystalline) morphology in the positive electrode active material.

[0282] In some embodiments, the positive electrode active material may further include a lithium-containing phosphate. That is, the positive electrode active material may include both a layered lithium-containing transition metal oxide and a lithium-containing phosphate. The lithium-containing phosphate may include one or more of lithium iron phosphate, lithium manganese phosphate, lithium manganese iron phosphate, and modified compounds thereof.

[0283] Optionally, the mass proportion of the layered lithium-containing transition metal oxide in the positive electrode active material can be greater than or equal to 80%, for example, greater than or equal to 80%, greater than or equal to 85%, greater than or equal to 90%, greater than or equal to 95% or greater than or equal to 99%.

[0284] Optionally, the mass proportion of the layered lithium-containing transition metal oxide in the positive electrode active material may be 80%-99%, and the mass proportion of the lithium-containing phosphate in the positive electrode active material may be 1%-20%.

[0285] In some embodiments, the particle size distribution curve of the positive electrode active material has two volume distribution peaks, the volume distribution peak with the maximum peak intensity is recorded as the first peak, and the volume distribution particle size corresponding to the maximum peak intensity of the first peak is recorded as Dv1, and the volume distribution peak with the second maximum peak intensity is recorded as the second peak, and the volume distribution particle size corresponding to the maximum peak intensity of the second peak is recorded as Dv2, Dv1 is between 7μm and 12μm, and Dv2 is between 2μm and 5μm.

[0286] This can increase the actual packing density of the positive electrode active material, increase the compaction density of the positive electrode sheet, and further enable the battery cell to have a higher energy density.

[0287] Optionally, Dv1 is between 8 μm and 11 μm, and Dv2 is between 2 μm and 4 μm.

[0288] In some embodiments, the volume distribution particle size Dv50 of the single-crystal layered lithium-containing transition metal oxide may be less than or equal to 5 μm, and may be optionally 2 μm-4 μm.

[0289] In some embodiments, the volume distribution particle size Dv50 of the polycrystalline layered lithium-containing transition metal oxide may be 7 μm-12 μm, and optionally 8 μm-11 μm.

[0290] In some embodiments, the volume distribution particle size Dv50 of the positive electrode active material may be 6 μm-10 μm, optionally 7 μm-9.5 μm.

[0291] In some embodiments, the positive electrode film layer may further optionally include a positive electrode conductive agent. As an example, the positive electrode conductive agent may include, but is not limited to, one or more of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0292] In some embodiments, the positive electrode film layer may further optionally include a positive electrode binder. As an example, the positive electrode binder may include, but is not limited to, one or more of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorine-containing acrylic resin.

[0293] In some embodiments, the positive electrode current collector may be a metal foil or a composite current collector. As an example of a metal foil, aluminum foil may be used. The composite current collector may include a polymer material base layer and a metal material layer formed on at least one surface of the polymer material base layer. As an example, the metal material may include one or more of aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy. As an example, the polymer material base layer may include, but is not limited to, one or more of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS) and polyethylene (PE).

[0294] The positive electrode film layer is typically formed by coating a positive electrode slurry onto a positive electrode current collector, drying, and cold pressing. The positive electrode slurry is typically formed by dispersing the positive electrode active material, optional positive electrode conductive agent, optional positive electrode binder, and any other components in a solvent and stirring them uniformly. The solvent may be, but is not limited to, N-methylpyrrolidone (NMP).

[0295] The volume distribution particle sizes Dv10, Dv50, and Dv90 of a material are well known in the art and represent the particle sizes corresponding to the 10%, 50%, and 90% cumulative volume distribution percentages, respectively. They can be measured using instruments and methods known in the art. For example, they can be conveniently measured using a laser particle size analyzer, as per GB / T 19077-2016. The testing instrument can be the Mastersizer 3000 laser particle size analyzer from Malvern Instruments Ltd., UK.

[0296] The specific surface area of ​​a material is well known in the art and can be measured using instruments and methods known in the art. For example, it can be measured using the nitrogen adsorption specific surface area analysis test method in accordance with GB / T 19587-2017 and calculated using the BET (Brunauer Emmett Teller) method. The nitrogen adsorption specific surface area analysis test can be performed using a TRISTAR II 3020 specific surface area and porosity analyzer available from Micromeritics, Inc., USA.

[0297] The tap density of a material is well known in the art and can be measured using methods known in the art. For example, it can be measured using a powder tap density tester in accordance with GB / T 5162-2006. For example, a tap density tester model FZS4-4B from the Beijing Iron and Steel Research Institute can be used. The test parameters are as follows: vibration frequency: 250 ± 15 times / minute, amplitude: 3 ± 0.2 mm, number of vibrations: 5000, and a 25 mL graduated cylinder.

[0298] The powder resistivity of a material is well known in the art and can be measured using instruments and methods known in the art. For example, an appropriate amount of the sample to be tested can be placed in the feeding cup of a resistivity tester, pressure applied, and data collected manually. The powder resistivity test results at different pressure points can be recorded. The test pressure is 16 MPa.

[0299] The preparation method of battery cells is well known. In some embodiments, a positive electrode sheet, a separator, a negative electrode sheet, and an electrolyte can be assembled to form a battery cell. As an example, the positive electrode sheet, separator, and negative electrode sheet can be made into an electrode assembly, which is then placed in a housing, dried, and then injected with electrolyte. After standing and forming, a battery cell is obtained.

[0300] Example

[0301] The following examples describe the present disclosure in more detail. These examples are intended to be illustrative only, as various modifications and variations within the scope of the present disclosure will be apparent to those skilled in the art. Unless otherwise stated, all parts, percentages, and ratios reported in the following examples are by mass, and all reagents used in the examples are commercially available or synthesized according to conventional methods and can be used directly without further processing, and the instruments used in the examples are commercially available.

[0302] Example 1-1

[0303] Preparation of positive electrode

[0304] The positive electrode active material LiNi 0.9 Co 0.06 Mn 0.04 O2, binder polyvinylidene fluoride, and conductive agent Super P are mixed in a mass ratio of 97:2:1. An appropriate amount of solvent N-methylpyrrolidone (NMP) is added and stirred evenly to obtain a positive electrode slurry. The positive electrode slurry is coated on both surfaces of the positive electrode current collector aluminum foil. After drying and cold pressing, the positive electrode sheet is obtained.

[0305] The positive electrode active material also includes single crystal morphology of LiNi 0.9 Co 0.06 Mn 0.04 O2 and polycrystalline LiNi 0.9 Co 0.06 Mn 0.04 O2. Single crystal morphology of LiNi 0.9 Co 0.06 Mn 0.04 The amount of O2 accounts for 30%, and the polycrystalline LiNi 0.9 Co 0.06 Mn 0.04 The amount of O2 accounts for 70%. Single crystal morphology of LiNi 0.9 Co 0.06 Mn 0.04 The volume distribution particle size Dv50 of O2 is 4.0μm, and the polycrystalline morphology of LiNi 0.9 Co 0.06 Mn 0.04 The volume distribution particle size Dv50 of O2 was 11.0 μm. The volume distribution particle size Dv50 of the mixed positive electrode active material was 8.9 μm.

[0306] Preparation of negative electrode sheet

[0307] Coconut shell is used as a raw material for sintering to obtain a carbon material; potassium hydroxide is used to perform pore-forming treatment on the carbon material, and then the carbon material matrix is ​​obtained through washing and drying.

[0308] The carbon material substrate is placed in a vapor deposition furnace, the furnace body is kept rotating, and argon is used for purging. After heating to an appropriate temperature, a mixed gas of 30% monosilane + 70% argon (volume ratio) is introduced to deposit amorphous silicon. After deposition for a period of time, the introduction of monosilane is stopped and the temperature is increased. Then, a mixed gas of 20% acetylene + 80% argon (volume ratio) is introduced to deposit a carbon coating layer. After completion, the mixture is cooled, discharged, and sieved to obtain a silicon-carbon composite material.

[0309] The negative electrode active material is a mixture of artificial graphite and the silicon-carbon composite material prepared above, with a mass ratio of 93:7. The volume distribution particle size Dv50 of the silicon-carbon composite material is 8μm, and the volume distribution particle size Dv50 of the artificial graphite is 10μm. The volume distribution particle size Dv50 of the mixed negative electrode active material is 8.9μm. The negative electrode active material, conductive agent Super P, binder styrene-butadiene rubber, and thickener sodium carboxymethyl cellulose are thoroughly stirred and mixed in an appropriate amount of solvent deionized water in a mass ratio of 96.2:0.6:1.3:1.9 to obtain a negative electrode slurry. The negative electrode slurry is coated on both surfaces of the negative electrode current collector copper foil, dried, and cold pressed to obtain a negative electrode sheet.

[0310] Preparation of isolation membrane

[0311] The base membrane is a PE porous membrane with a thickness of 7μm. Aluminum oxide and the binder polyacrylic acid are mixed in a mass ratio of 94:6 in an appropriate amount of deionized water to obtain a coating slurry. The prepared coating slurry is applied to both surfaces of the PE porous membrane using a coating machine, and then dried and cut to obtain a separator. The coating thickness on one side of the PE porous membrane is 1.5μm, the total coating thickness is 3μm, and the total thickness of the separator is 10μm.

[0312] Preparation of electrolyte

[0313] Dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), ethylene carbonate (EC), and fluoroethylene carbonate (FEC) were mixed in a mass ratio of 45:20:30:5 to obtain an organic solvent, and LiPF6 was dissolved in the organic solvent to obtain an electrolyte solution. The concentration of LiPF6 was 1.1 mol / L.

[0314] Preparation of battery cells

[0315] The positive electrode sheet, separator, and negative electrode sheet are stacked in sequence and connected to a winding needle. The winding needle is then rotated to wind the positive electrode sheet, separator, and negative electrode sheet around the winding needle. After winding is completed, the winding needle is withdrawn to form a cylindrical electrode assembly. The electrode assembly is placed in a cylindrical shell with an open end. An end cap assembly is welded to the open end of the cylindrical shell. The electrolyte is then injected, and after standing and forming processes, a cylindrical battery cell is obtained. The diameter of the cylindrical battery cell is 46mm and the length is 95mm. The ratio of the mass of the electrolyte to the capacity of the battery cell is 1.29g / Ah.

[0316] Comparative Example 1-1

[0317] The preparation of the battery cell was the same as that of Example 1-1 except for the following differences.

[0318] The ratio of the mass of the electrolyte to the capacity of the battery cell is 2.10 g / Ah.

[0319] The test methods for the capacity and mass energy density of battery cells are as follows.

[0320] At 25°C, let the battery cell stand for 5 minutes, discharge it at a constant current of 0.33C to 2.8V; after standing for 5 minutes, charge it at a constant current of 0.33C to 4.25V, and then charge it at a constant voltage to a current of 0.05C; after standing for 5 minutes, discharge it at a constant current of 0.33C to 2.8V, and record the discharge capacity at this time, which is the capacity of the battery cell.

[0321] At 25°C, charge the battery cell at a constant current of 0.33C to 4.25V, then charge it at a constant voltage to a current of 0.05C. After standing for 5 minutes, discharge the battery cell at a constant current of 0.33C to 2.8V, and calculate the discharge energy Q. The mass energy density (Wh / kg) of a battery cell is calculated as: discharge energy Q / cell mass.

[0322] Table 1

[0323] It can be seen from the test results in Table 1 that the mass energy density of the battery cell can be improved by reducing the ratio of the mass of the electrolyte to the capacity of the battery cell.

[0324] Comparative Example 1-2

[0325] The preparation of the battery cell was the same as that of Example 1-1 except for the following differences.

[0326] The silicon-carbon composite material is obtained by mechanical ball milling.

[0327] Commercially purchased industrial silicon is ground into nano-silicon, and the nano-silicon suspension is evenly mixed with flake graphite. After granulation and spray drying, nano-silicon spherical graphite is obtained. The nano-silicon spherical graphite is mixed with asphalt and subjected to high-temperature carbonization treatment to obtain a silicon-carbon composite material.

[0328] The negative electrode active material is a mixture of artificial graphite and the silicon-carbon composite material prepared above, with a mass ratio of 93:7. The negative electrode active material, conductive agent Super P, binder styrene-butadiene rubber, and thickener sodium carboxymethyl cellulose are thoroughly mixed in a suitable amount of deionized water as a solvent at a mass ratio of 96.2:0.6:1.3:1.9 to obtain a negative electrode slurry. The negative electrode slurry is coated on both surfaces of the negative electrode current collector copper foil, dried, and cold pressed to obtain a negative electrode sheet.

[0329] Comparative Examples 1-3

[0330] The preparation of the battery cell was the same as that of Example 1-1 except for the following differences.

[0331] The negative electrode active material is a mixture of artificial graphite and silicon oxide, with a mass ratio of 93:10. The negative electrode active material, conductive agent Super P, binder styrene-butadiene rubber, and thickener sodium carboxymethyl cellulose are thoroughly mixed in a suitable amount of deionized water as a solvent at a mass ratio of 96.2:0.6:1.3:1.9 to obtain a negative electrode slurry. The negative electrode slurry is then coated on both surfaces of the negative electrode current collector copper foil. After drying and cold pressing, the negative electrode sheet is obtained.

[0332] The test method for the cycle performance of the battery cell is as follows.

[0333] At 25°C, charge the battery cell at a constant current of 0.5C to 4.25V, then charge it at a constant voltage to a current of 0.05C. After 5 minutes of rest, discharge the battery cell at a constant current of 0.5C to 2.8V. Record the discharge capacity at this point, which is the first cycle discharge capacity. Repeat the battery cell charge and discharge test as described above until the battery cell capacity decays to 80% of the first cycle discharge capacity. Record the number of cycles.

[0334] Table 2

[0335] It can be seen from the test results in Table 2 that, under the premise of the same ratio of the mass of the electrolyte to the capacity of the battery cell and the same energy density of the battery cell, the battery cell using the silicon-carbon composite material provided by the embodiment of the present disclosure can have better cycle performance.

[0336] Example 2-1

[0337] The preparation of the battery cell was the same as that of Example 1-1 except for the following differences.

[0338] The ratio of the mass of the electrolyte to the capacity of the battery cell is 1.39 g / Ah.

[0339] Example 2-2

[0340] The preparation of the battery cell was the same as that of Example 1-1 except for the following differences.

[0341] The ratio of the mass of the electrolyte to the capacity of the battery cell is 1.50 g / Ah.

[0342] Example 2-3

[0343] The preparation of the battery cell was the same as that of Example 1-1 except for the following differences.

[0344] The ratio of the mass of the electrolyte to the capacity of the battery cell is 1.20 g / Ah.

[0345] Examples 2-4

[0346] The preparation of the battery cell was the same as that of Example 1-1 except for the following differences.

[0347] The base film is a PE porous film with a thickness of 7μm. Alumina and binder polyacrylic acid are mixed evenly in an appropriate amount of solvent deionized water in a mass ratio of 94:6 to obtain a first slurry. Polyvinylidene fluoride (PVDF) particles, binder polymethyl methacrylate, dispersant sodium carboxymethyl cellulose (CMC) and surfactant are mixed evenly in an appropriate amount of solvent deionized water in a mass ratio of 87:8:3:2 to obtain a second slurry. The prepared first slurry is applied to both surfaces of the PE porous membrane with a coating machine. After drying, the second slurry is applied to the dried first slurry, and then the isolation membrane is obtained through drying and cutting processes.

[0348] The coating thickness on one side of the PE porous membrane is 2 μm, the total coating thickness is 4 μm, and the total thickness of the separator is 11 μm.

[0349] Table 3

[0350] The test results in Table 3 show that, with other conditions remaining the same, increasing the ratio of electrolyte mass to cell capacity reduces the cell's mass energy density and improves cycle performance. Furthermore, after the ratio reaches a certain level, the electrolyte's further improvement in cell cycle performance becomes less pronounced. Therefore, to achieve high-energy-density cylindrical cells, the electrolyte mass to cell capacity ratio can be between 1.2g / Ah and 1.5g / Ah.

[0351] It can also be seen from the test results of Examples 1-1 and 2-4 that the fluoropolymer PVDF in the isolation membrane coating will absorb a certain amount of electrolyte. When the ratio of the mass of the electrolyte to the capacity of the battery cell is the same, the battery cell using an isolation membrane without fluoropolymer PVDF can have better cycle performance.

[0352] Example 3-1

[0353] The preparation of the battery cell was the same as that of Example 1-1 except for the following differences.

[0354] Dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), ethylene carbonate (EC), and fluoroethylene carbonate (FEC) were mixed in a mass ratio of 20:45:30:5 to obtain an organic solvent, and LiPF6 was dissolved in the organic solvent to obtain an electrolyte solution. The concentration of LiPF6 was 1.1 mol / L.

[0355] Example 3-2

[0356] The preparation of the battery cell was the same as that of Example 1-1 except for the following differences.

[0357] Dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), ethylene carbonate (EC), and fluoroethylene carbonate (FEC) were mixed in a mass ratio of 45:20:30:5 to obtain an organic solvent, and then LiPF6 and LiFSI were dissolved in the above organic solvent to obtain an electrolyte. The concentration of LiPF6 was 0.7 mol / L and the concentration of LiFSI was 0.4 mol / L.

[0358] Example 3-3

[0359] The preparation of the battery cell was the same as that of Example 1-1 except for the following differences.

[0360] Dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), ethylene carbonate (EC), and fluoroethylene carbonate (FEC) were mixed in a mass ratio of 45:20:30:5 to obtain an organic solvent, and then LiPF6 and LiFSI were dissolved in the above organic solvent to obtain an electrolyte. The concentration of LiPF6 was 0.4 mol / L and the concentration of LiFSI was 0.7 mol / L.

[0361] Table 4

[0362] From the test results in Table 4, it can be seen that when the ratio of the mass of the electrolyte to the capacity of the battery cell is the same and the total content of the chain carbonate is the same, by making the content of dimethyl carbonate (DMC) greater than the content of ethyl methyl carbonate (EMC), the battery cell can have better cycle performance.

[0363] From the test results in Table 4, it can be seen that when the ratio of the mass of the electrolyte to the capacity of the battery cell is the same and the total concentration of the electrolyte is the same, the battery cell using the mixed electrolyte of LiPF6 and LiFSI can have better cycle performance.

[0364] The test results in Table 4 also show that when the ratio of the mass of the electrolyte to the capacity of the battery cell is the same and the total concentration of the electrolyte is the same, the battery cell can have better cycle performance by making the concentration of LiFSI greater than the concentration of LiPF6.

[0365] Example 4-1

[0366] The preparation of the battery cell was the same as that of Example 1-1 except for the following differences.

[0367] The positive electrode active material also includes single crystal morphology of LiNi 0.9 Co 0.06 Mn 0.04 O2 and polycrystalline LiNi 0.9 Co 0.06 Mn 0.04 O2. Single crystal morphology of LiNi 0.9 Co 0.06 Mn 0.04 The amount of O2 accounts for 40%, and the polycrystalline LiNi 0.9 Co 0.06 Mn 0.04 The amount of O2 accounts for 60%. Single crystal morphology of LiNi 0.9 Co 0.06 Mn 0.04 The volume distribution particle size Dv50 of O2 is 4.0μm, and the polycrystalline morphology of LiNi 0.9 Co 0.06 Mn 0.04 The volume distribution particle size Dv50 of O2 was 11.0 μm. The volume distribution particle size Dv50 of the mixed positive electrode active material was 8.2 μm.

[0368] Example 4-2

[0369] The preparation of the battery cell was the same as that of Example 1-1 except for the following differences.

[0370] The positive electrode active material also includes single crystal morphology of LiNi 0.9 Co 0.06 Mn 0.04 O2 and polycrystalline LiNi 0.9 Co 0.06 Mn 0.04 O2. Single crystal morphology of LiNi 0.9 Co 0.06 Mn 0.04The amount of O2 accounts for 50%, and the polycrystalline LiNi 0.9 Co 0.06 Mn 0.04 The amount of O2 accounts for 50%. Single crystal morphology of LiNi 0.9 Co 0.06 Mn 0.04 The volume distribution particle size Dv50 of O2 is 4.0μm, and the polycrystalline morphology of LiNi 0.9 Co 0.06 Mn 0.04 The volume distribution particle size Dv50 of O2 was 11.0 μm. The volume distribution particle size Dv50 of the mixed positive electrode active material was 7.5 μm.

[0371] Example 4-3

[0372] The preparation of the battery cell was the same as that of Example 1-1 except for the following differences.

[0373] The positive electrode active material also includes single crystal morphology of LiNi 0.9 Co 0.06 Mn 0.04 O2 and polycrystalline LiNi 0.9 Co 0.06 Mn 0.04 O2. Single crystal morphology of LiNi 0.9 Co 0.06 Mn 0.04 The amount of O2 accounts for 70%, and the polycrystalline LiNi 0.9 Co 0.06 Mn 0.04 The amount of O2 accounts for 30%. Single crystal morphology of LiNi 0.9 Co 0.06 Mn 0.04 The volume distribution particle size Dv50 of O2 is 4.0μm, and the polycrystalline morphology of LiNi 0.9 Co 0.06 Mn 0.04 The volume distribution particle size Dv50 of O2 was 11.0 μm. The volume distribution particle size Dv50 of the mixed positive electrode active material was 6.1 μm.

[0374] The test method for the power performance of a battery cell is as follows.

[0375] At 25°C, charge the battery cell at a constant current and constant voltage of 1C to an upper cutoff voltage of 4.25V, then charge at a constant voltage to a current of 0.05C. After a 5-minute rest, discharge the battery cell at 1C for 30 minutes, adjusting the SOC to 50%, and record the voltage U1. Then discharge the battery cell at a constant current of 3C for 30 seconds, and record the voltage U2. Battery cell power (W) = lower cutoff voltage × (U1 - lower cutoff voltage) / (U1 - U2) / 3C. The lower cutoff voltage is 2.8V.

[0376] Table 5

[0377] The test results in Table 5 show that when the ratio of electrolyte mass to battery cell capacity is low, the proportion of polycrystalline layered lithium-containing transition metal oxides is high, resulting in higher energy density and power density, but slightly lower cycle life. This is because polycrystalline layered lithium-containing transition metal oxides have more side reactions on their surfaces, consuming more electrolyte.

[0378] By adjusting the ratio of single-crystal layered lithium-containing transition metal oxides and polycrystalline layered lithium-containing transition metal oxides in the positive electrode active material, the battery cell can better combine high energy density, good cycle performance and good power performance.

[0379] It should be noted that the present disclosure is not limited to the above-mentioned embodiments. The above-mentioned embodiments are merely examples, and within the scope of the technical solution of the present disclosure, embodiments having substantially the same structure as the technical concept and exerting the same effects are all included in the technical scope of the present disclosure. In addition, within the scope of the present disclosure, various modifications that can be imagined by those skilled in the art to the embodiments, and other methods constructed by combining some of the constituent elements of the embodiments are also included in the scope of the present disclosure.

Claims

1. A battery cell, wherein: The battery cell includes an electrode assembly and an electrolyte, The electrode assembly includes a negative electrode plate, the negative electrode plate includes a negative electrode current collector and a negative electrode film layer located on at least one side of the negative electrode current collector, the negative electrode film layer includes a negative electrode active material, the negative electrode active material includes a silicon-carbon composite material, the silicon-carbon composite material includes a carbon material matrix with a pore structure and a silicon-based material located in the pore structure of the carbon material matrix; The ratio of the mass of the electrolyte to the capacity of the battery cell is 1.2 g / Ah-2.0 g / Ah.

2. The battery cell according to claim 1, wherein: The battery cell is a square-shell battery cell, and the ratio of the mass of the electrolyte to the capacity of the square-shell battery cell is 1.5 g / Ah-2.0 g / Ah.

3. The battery cell according to claim 2, wherein: The ratio of the mass of the electrolyte to the capacity of the square-shell battery cell is 1.7 g / Ah-1.9 g / Ah.

4. The battery cell according to claim 1, wherein: The battery cell is a cylindrical battery cell, and the ratio of the mass of the electrolyte to the capacity of the cylindrical battery cell is 1.2 g / Ah-1.5 g / Ah.

5. The battery cell according to claim 4, wherein: The ratio of the mass of the electrolyte to the capacity of the cylindrical battery cell is 1.24 g / Ah-1.5 g / Ah.

6. The battery cell according to any one of claims 1 to 5, wherein: The carbon material matrix having a porous structure satisfies one or more of the following conditions (1) to (5): (1) The average pore size of the pore structure of the carbon material matrix is ​​0.5 nm to 8 nm; (2) The pore structure of the carbon material matrix includes micropores, and the average pore diameter d1 of the micropores satisfies: 0.5 nm ≤ d1 < 2 nm; (3) The pore structure of the carbon material matrix includes mesopores, and the average pore diameter d2 of the mesopores satisfies: 2nm≤d2≤8nm; (4) The pore structure of the carbon material matrix includes micropores and mesopores, wherein the micropores account for 60% to 90% of the pore structure, and the mesopores account for 10% to 40% of the pore structure; (5) The specific surface area of ​​the carbon material matrix with a porous structure is 500 m 2 / g-2000m 2 / g.

7. The battery cell according to any one of claims 1 to 6, wherein: The silicon-based material satisfies one or more of the following conditions (1) to (4): (1) The mass proportion of the silicon-based material in the silicon-carbon composite material is 20%-60%; (2) The silicon-based material includes one or more of amorphous silicon, crystalline silicon, silicon oxides, silicon carbide, and silicon alloys; (3) The silicon-based material includes one or more of amorphous silicon and crystalline silicon; (4) The silicon-based material includes one or more of amorphous silicon and crystalline silicon, and the grain size of the crystalline silicon is less than or equal to 5 nm.

8. The battery cell according to any one of claims 1 to 7, wherein: The silicon-carbon composite material satisfies one or more of the following conditions (1) to (8): (1) The volume distribution particle size Dv50 of the silicon-carbon composite material is 3 μm-15 μm; (2) The volume distribution particle size Dv90 of the silicon-carbon composite material is 15 μm-25 μm; (3) The volume distribution particle size Dv10 of the silicon-carbon composite material is 1 μm-5 μm; (4) The particle size distribution of the silicon-carbon composite material satisfies: 1≤(Dv90-Dv10) / Dv50≤3; (5) The specific surface area of ​​the silicon-carbon composite material is 1m 2 / g-6m 2 / g; (6) The tap density of the silicon-carbon composite material is 0.8 g / cm 3 -1.2g / cm 3 ; (7) The powder resistivity of the silicon-carbon composite material at 16 MPa is less than or equal to 5 Ω·cm; (8) The silicon-carbon composite material has a coating layer.

9. The battery cell according to any one of claims 1 to 8, wherein: The negative electrode active material satisfies one or more of the following conditions (1) to (6): (1) The negative electrode active material further includes graphite; (2) The negative electrode active material further includes graphite, and the graphite includes at least one of artificial graphite and natural graphite; (3) The volume distribution particle size Dv50 of the negative electrode active material is 7 μm-12 μm; (4) The volume distribution particle size Dv90 of the negative electrode active material is 15 μm-20 μm; (5) The volume distribution particle size Dv10 of the negative electrode active material is 3 μm-6 μm; (6) The particle size distribution of the negative electrode active material satisfies: 1.16≤(Dv90-Dv10) / Dv50≤1.

71.

10. The battery cell according to any one of claims 1 to 9, wherein: The electrolyte includes an organic solvent, the organic solvent includes a chain carbonate, and the chain carbonate includes one or both of dimethyl carbonate and ethyl methyl carbonate.

11. The battery cell according to claim 10, wherein: The mass proportion of the linear carbonate in the organic solvent is 60%-85%.

12. The battery cell according to claim 11, wherein: The linear carbonate satisfies one or more of the following conditions (1) to (5): (1) The mass proportion of the dimethyl carbonate in the organic solvent is 60%-85%; (2) the mass proportion of the dimethyl carbonate in the organic solvent is greater than the mass proportion of the ethyl methyl carbonate in the organic solvent; (3) the mass proportion of the dimethyl carbonate in the organic solvent is 40%-75%; (4) the mass proportion of the ethyl methyl carbonate in the organic solvent is 5%-25%; (5) The mass proportion of the dimethyl carbonate in the organic solvent is 40%-75%, and the mass proportion of the ethyl methyl carbonate in the organic solvent is 5%-25%.

13. The battery cell according to any one of claims 10 to 12, wherein: The organic solvent further comprises a cyclic carbonate, and the cyclic carbonate comprises one or both of ethylene carbonate and fluoroethylene carbonate.

14. The battery cell according to claim 13, wherein: The mass proportion of the cyclic carbonate in the organic solvent is 15%-40%.

15. The battery cell according to any one of claims 13 to 14, wherein: The mass proportion of the fluoroethylene carbonate in the organic solvent is 1%-10%; and / or, The mass proportion of the ethylene carbonate in the organic solvent is 10%-35%.

16. The battery cell according to any one of claims 1 to 15, wherein: The electrolyte contains cations and anions, wherein the cations include one or both of lithium ions and sodium ions, and the anions include one or more of hexafluorophosphate anions and anions represented by Formula 1, wherein R1 and R2 independently include fluorine atoms or C1-C6 fluoroalkyl groups.

17. The battery cell according to claim 16, wherein: The molar concentration of the anion is 1 mol / L-1.3 mol / L.

18. The battery cell according to any one of claims 16 to 17, wherein: The anions include both hexafluorophosphate anions and anions represented by Formula 1, and the molar concentration of the anions represented by Formula 1 is greater than the molar concentration of the hexafluorophosphate anions; and / or, The molar concentration of the anion represented by Formula 1 is 0.6 mol / L-0.9 mol / L; and / or, The molar concentration of the hexafluorophosphate anion is 0.3 mol / L-0.5 mol / L.

19. The battery cell according to any one of claims 1 to 18, wherein: The electrode assembly includes a positive electrode plate, which includes a positive electrode current collector and a positive electrode film layer located on at least one side of the positive electrode current collector. The positive electrode film layer includes a positive electrode active material, and the positive electrode active material includes a layered lithium-containing transition metal oxide.

20. The battery cell according to claim 19, wherein: The positive electrode active material includes layered lithium-containing transition metal oxides in both single crystal and polycrystalline morphologies.

21. The battery cell according to any one of claims 1 to 20, wherein: The electrode assembly includes a separator, wherein the separator includes a base film and a coating layer disposed on at least one side of the base film, and the coating layer does not contain a fluorine-containing polymer.

22. The battery cell according to claim 21, wherein The thickness of the base film is 3 μm-9 μm; and / or, The thickness of the coating is 0.5 μm-3 μm; and / or, The total thickness of the isolation film is 5 μm-14 μm.

23. A battery comprising the battery cell according to any one of claims 1 to 22.

24. An electrical device comprising the battery according to claim 23, wherein the battery is used to provide electrical energy.

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