Battery cell, battery device and power-consuming device

Abstract

Battery cell, including: A negative electrode sheet, wherein the negative electrode sheet comprises a negative electrode current collector and a negative electrode film layer arranged on at least one side of the negative electrode current collector, wherein the negative electrode film layer comprises a negative electrode active material, the negative electrode active material comprising a silicon-based material and a carbon-based material, wherein the mass fraction of the element silicon of the silicon-based material in the negative electrode active material is 0.3% to 15%, and the one-sided coating weight of the negative electrode film layer is 80 mg / 1540.25 mm² 2 up to 150 mg / 1540.25 mm 2 is; and an electrolyte solution comprising an organic solvent, wherein the organic solvent comprises a carboxylic acid ester solvent, wherein the mass fraction of the carboxylic acid ester solvent in the electrolyte solution is 3% to 70%.

Description

Technical field

[0001] The present application relates to a battery cell, a battery device and a power-consuming device. State of the art

[0002] Battery cells are characterized by high capacity, long lifespan, and other properties, and are therefore widely used in electronic devices such as mobile phones, laptops, e-bikes, electric vehicles, electric aircraft, electric boats, electric toy cars, electric toy ships, electric toy airplanes, and power tools. As battery technology has advanced significantly, the demands on battery performance have also increased. However, the high-temperature storage performance and cycle life of battery cells still need to be improved. Disclosure of the invention

[0003] The present application provides a battery cell, a battery device and a power-consuming device, wherein the high-temperature storage performance and the cycle performance of the battery cell of the present application can be further improved.

[0004] In a first aspect, the embodiments of the present application propose a battery cell comprising a negative electrode sheet and an electrolyte solution, wherein the negative electrode sheet comprises a negative electrode current collector and a negative electrode film layer arranged on at least one side of the negative electrode current collector, wherein the negative electrode film layer comprises a negative electrode active material, the negative electrode active material comprising a silicon-based material and a carbon-based material, wherein the mass fraction of the element silicon of the silicon-based material in the negative electrode active material is 0.3% to 15%, and the one-sided coating weight of the negative electrode film layer is 80 mg / 1540.25 mm². 2 up to 150 mg / 1540.25 mm 2is; the electrolyte solution comprises an organic solvent, wherein the organic solvent comprises a carboxylic acid ester solvent, wherein the mass fraction of the carboxylic acid ester solvent in the electrolyte solution is 3% to 70%.

[0005] Therefore, in the embodiments of the present application, the combination of the mass fraction of the element silicon, the coating weight of the negative electrode film layer, and the components in the electrolyte solution can reduce the interfacial side reaction of the negative electrode active material with the electrolyte solution, lower the high-temperature gas evolution quantity, and improve the high-temperature storage performance; furthermore, the migration rate of active ions in the negative electrode film layer and the electrolyte solution is relatively fast, and the side reaction on the negative electrode side is reduced, which is advantageous for improving the cycle performance of the battery cell during fast charging.

[0006] In some embodiments, the specific surface area of ​​the silicon-based material is 1 m². 2 / g up to 4 m 2 / g; if the specific surface area of ​​the silicon-based material is in the above range, the side reaction between the silicon-based material and the electrolyte solution can be reduced to lower the high-temperature gas evolution quantity, thus improving the high-temperature storage performance and the cycle performance of the battery cell.

[0007] In some embodiments, the silicon-based material is in granular form with an average particle size of 4 µm to 12 µm. If the average particle size of the silicon-based material is within the above range, the side reaction between the silicon-based material and the electrolyte solution can be reduced to lower the amount of high-temperature gas evolution, thus improving the high-temperature storage performance and the cycle life of the battery cell.

[0008] In some embodiments, the silicon-based material comprises one or more elements of elemental silicon, silicon-carbon composite, and silicon oxide. The above materials can increase the capacity of the negative electrode active material, which is advantageous for reducing the coating thickness of the negative electrode film layer, thereby shortening the migration path of lithium ions and facilitating fast charging.

[0009] In some embodiments, the negative electrode film layer comprises a first region and a second region. The first region is a region of the negative electrode film layer along its own thickness direction near the negative electrode current collector, wherein the thickness of the first region is 1 / 3 of the thickness of the negative electrode film layer. The second region is a region of the negative electrode film layer facing away from the negative electrode current collector along the thickness direction, wherein the thickness of the second region is also 1 / 3 of the thickness of the negative electrode film layer. In the cross-section of the negative electrode film layer parallel to the thickness direction, the void fraction of the individual carbon-based material located in the first region is smaller than the void fraction of the individual carbon-based material located in the second region.

[0010] Therefore, in the embodiments of the present application, the void fraction of the individual carbon-based material in the first region is less than or equal to the void fraction of the individual carbon-based material in the second region, which further promotes the diffusion of lithium ions in the first region, increases the transport rate and thus facilitates fast charging of the battery cell; during fast charging, the lithium ions diffuse rapidly into the negative electrode active material, thereby reducing the risk of lithium plating on the negative electrode side and thus improving the cycle life of the battery cell.

[0011] In some embodiments, the average particle size of the carbon-based material of the first region is greater than or equal to the average particle size of the carbon-based material of the second region.

[0012] Therefore, in the embodiments of the present application, the particle size in the second region is relatively small, which can shorten the solid-phase transport path of lithium ions, increase the fast-charging power, and improve the problem of lithium plating on the surface of the negative electrode sheet, thereby improving the cycle life of the battery cell.

[0013] In some embodiments, the average particle size of the carbon-based material in the first region is 12 µm to 21 µm, if the average particle size of the carbon-based material in the first region is greater than or equal to the average particle size of the carbon-based material in the second region; if the average particle size of the carbon-based material in the first region is in the above range, the cycle life can be improved.

[0014] In some embodiments, the average particle size of the carbon-based material in the second region is 9 µm to 17 µm, provided that the average particle size of the carbon-based material in the first region is greater than or equal to the average particle size of the carbon-based material in the second region. Having the average particle size of the carbon-based material within the above range is advantageous for improving the high-temperature storage performance and the cycle performance of the battery cell during fast charging.

[0015] In some embodiments, the carbon-based material of the first region comprises synthetic graphite and / or natural graphite, provided that the average particle size of the carbon-based material of the first region is greater than or equal to the average particle size of the carbon-based material of the second region. The above configuration is advantageous for improving the cycle performance of the battery cell.

[0016] In some embodiments, the carbon-based material of the second region comprises synthetic graphite if the average particle size of the carbon-based material of the first region is greater than or equal to the average particle size of the carbon-based material of the second region. The above embodiment is advantageous for improving the cycle performance of the battery cell.

[0017] In some embodiments, the average particle size of the carbon-based material in the second region is larger than the average particle size of the carbon-based material in the first region. The relatively larger average particle size of the carbon-based material in the second region results in higher pressure resistance during the film layer manufacturing process and superior film layer stability, which is advantageous for improving the high-temperature storage performance and cycle life of the battery cell.

[0018] In some embodiments, the average particle size of the carbon-based material in the first region is 9 µm to 17 µm, provided the average particle size of the carbon-based material in the second region is larger than the average particle size of the carbon-based material in the first region. If the average particle size of the carbon-based material in the first region falls within the range mentioned above, the cycle life can be improved.

[0019] In some embodiments, the average particle size of the carbon-based material in the second region is 12 µm to 21 µm, provided that the average particle size of the carbon-based material in the second region is larger than the average particle size of the carbon-based material in the first region. If the average particle size of the carbon-based material in the second region falls within the above range, the cycle life can be improved.

[0020] In some embodiments, the carbon-based material of the second region comprises synthetic graphite and / or natural graphite if the average particle size of the carbon-based material of the second region is larger than the average particle size of the carbon-based material of the first region. The above configuration is advantageous for improving the cycle performance of the battery cell.

[0021] In some embodiments, the carbon-based material of the first region comprises synthetic graphite if the average particle size of the carbon-based material of the second region is larger than the average particle size of the carbon-based material of the first region. The above configuration is advantageous for improving the cycle performance of the battery cell.

[0022] In some embodiments, the negative electrode film layer comprises a first negative electrode film layer and a second negative electrode film layer, wherein the first negative electrode film layer is arranged on the surface of the negative electrode current collector, and the negative electrode active material of the first negative electrode film layer comprises a carbon-based material; wherein the second negative electrode film layer is connected to the side of the first negative electrode film layer facing away from the negative electrode current collector, and the negative electrode active material of the second negative electrode film layer comprises a carbon-based material, wherein at least one of the first negative electrode film layer and the second negative electrode film layer comprises a silicon-based material.The double-layer arrangement is advantageous for simultaneously improving the fast-charging capability and the energy density of the battery cell; the silicon-based material can further increase the energy density.

[0023] In some embodiments, the conductivity of the electrolyte solution at room temperature ranges from 9 mS / cm to 18 mS / cm. The migration rate of lithium ions in the electrolyte solution is relatively high, which can further reduce the internal resistance of the battery cell, thereby reducing heat generation and thus improving the fast-charging performance of the battery cell.

[0024] In some embodiments, the mass fraction of the carboxylic acid ester solvent in the electrolyte solution is 5% to 30%. When the mass fraction of the carboxylic acid ester solvent is in the above range, the conductivity of the electrolyte solution can be increased and the fast-charging capability of the battery cell improved; in addition, the side reaction of the electrolyte solution on the negative electrode side can be reduced, thereby effectively reducing the amount of gas evolution from the battery cell, which is advantageous for improving the high-temperature storage performance and the cycle performance of the battery cell.

[0025] In some embodiments, the carboxylic acid ester solvent comprises a cyclic carboxylic acid ester, wherein the cyclic carboxylic acid ester comprises one or more of γ-butyrolactone, γ-valerolactone, and δ-valerolactone. The above materials exhibit a low viscosity, which can improve the wettability of the electrode sheet and increase the cycle performance during fast charging.

[0026] In some embodiments, the carboxylic acid ester solvent comprises a chain-like carboxylic acid ester, wherein the chain-like carboxylic acid ester comprises one or more of methyl acetate, ethyl acetate, propyl acetate, butyl acetate, propyl propionate, and butyl propionate. The above materials exhibit low viscosity, which can improve the wettability of the electrode sheet and increase cycle performance during fast charging.

[0027] In some embodiments, the organic solvent also comprises a carbonate solvent, wherein the carbonate solvent comprises one or more of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate. The combined use of the carbonate solvent and the carboxylic acid ester solvent can increase the stability of the electrolyte solution and reduce its high-temperature gas evolution rate, which is advantageous for improving the high-temperature storage performance and cycle life of the battery cell.

[0028] In some embodiments, the electrolyte solution also comprises a lithium salt, wherein the lithium salt comprises lithium bis(fluorosulfonyl)imide and lithium hexafluorophosphate, and the ratio of the mass fraction of lithium bis(fluorosulfonyl)imide to the mass fraction of lithium hexafluorophosphate, based on the mass of the electrolyte solution, is 0.3 to 1.2.

[0029] Therefore, if the ratio of the mass fraction of lithium bis(fluorosulfonyl)imide to the mass fraction of lithium hexafluorophosphate in the embodiments of the present application meets the above range, on the one hand the hydrofluoric acid content can be reduced, the interfacial side reaction of the negative electrode slowed down and gas evolution during high-temperature storage reduced; on the other hand the content of the organic components of the interfacial film formed at the interface of the negative electrode is appropriate, which can also reduce the amount of gas evolution during high-temperature storage and is advantageous for improving the cycle life of the battery cell.

[0030] In some embodiments, the mass fraction of lithium bis(fluorosulfonyl)imide is 2% to 11%, based on the mass of the electrolyte solution. When the mass fraction of lithium bis(fluorosulfonyl)imide is within the above range, the hydrofluoric acid content can be reduced, the interfacial side reaction of the negative electrode slowed down, and the amount of gas evolution during high-temperature storage reduced, which is advantageous for improving the cycle life of the battery cell.

[0031] In some embodiments, the mass fraction of lithium hexafluorophosphate is 3% to 14%, based on the mass of the electrolyte solution. When the mass fraction of lithium hexafluorophosphate is in the above range, the conductivity of the electrolyte solution is relatively high, which promotes the migration of lithium ions and improves the fast-charging performance of the battery cell.

[0032] In some embodiments, the electrolyte solution also comprises one or more fluorinated cyclic carbonates and vinylene carbonate. The fluorinated cyclic carbonate can form an interfacial film rich in lithium fluoride (LiF) on the negative electrode surface, thereby reducing the volumetric expansion of silicon, improving the lifetime of the silicon-containing system, and lowering the amount of high-temperature gas evolution, which is advantageous for improving the high-temperature storage performance and the cycle life of the battery cell.The interfacial film formed by the vinylene carbonate on the negative electrode surface exhibits improved density, thereby more effectively protecting the silicon-containing negative electrode, reducing the degree of interfacial side reaction of the negative electrode, and lowering the amount of high-temperature gas evolution, which is advantageous for improving the high-temperature storage performance and the cycle performance of the battery cell.

[0033] In some embodiments, the fluorinated cyclic carbonate comprises at least one of monofluoroethylene carbonate, difluoroethylene carbonate and trifluoropropylene carbonate.

[0034] In some embodiments, the mass fraction of the fluorinated cyclic carbonate is 0.5% to 20%, based on the mass of the electrolyte solution. When the mass fraction of the fluorinated cyclic carbonate is in the above range, an excellent interfacial film can be formed, providing outstanding protection for the negative electrode, which is advantageous for improving the high-temperature storage performance and the cycle life of the battery cell.

[0035] In some embodiments, the mass fraction of vinylene carbonate is 0.1% to 3%, based on the mass of the electrolyte solution. The vinylene carbonate participates in the formation of the interfacial film of the negative electrode, thereby creating an excellent interfacial film that provides outstanding protection for the negative electrode, which is advantageous for improving the high-temperature storage performance and the cycle life of the battery cell.

[0036] In some embodiments, the mass fraction of fluorinated cyclic carbonate is 0.5% to 10%, and the mass fraction of elemental silicon in the silicon-based material within the negative electrode active material is 0.3% to 7.5%, both based on the mass of the electrolyte solution. When the mass fraction of fluorinated cyclic carbonate and the mass fraction of elemental silicon meet the above conditions, the volumetric expansion of silicon can be more effectively reduced, the lifetime of the silicon-containing system improved, and the amount of high-temperature gas evolution decreased, which is advantageous for improving the high-temperature storage performance and the cycle life of the battery cell.

[0037] In some embodiments, the mass fraction of the fluorinated cyclic carbonate is greater than 10% and less than or equal to 20%, and the mass fraction of elemental silicon in the silicon-based material of the negative electrode active material is greater than 7.5% and less than or equal to 15%, both based on the mass of the electrolyte solution. When the mass fraction of the fluorinated cyclic carbonate and the mass fraction of elemental silicon meet the above conditions, the volume expansion of the silicon can be more effectively reduced, the lifetime of the silicon-containing system improved, and the amount of high-temperature gas evolution decreased.

[0038] In some embodiments, the battery cell further comprises a positive electrode sheet, wherein the positive electrode sheet comprises a positive electrode current collector and a positive electrode film layer arranged on at least one side of the positive electrode current collector, wherein the positive electrode film layer comprises a positive electrode active material, and the one-sided coating weight of the positive electrode film layer is 250 mg / 1540.25 mm² 2 up to 300 mg / 1540.25 mm 2 amounts.

[0039] If the one-sided coating weight of the positive electrode film layer is in the above range, the amount of heat generated by the positive electrode sheet per unit area is not too high, thus preventing excessive heat accumulation in the battery cell system, reducing the risk of high-temperature decomposition of the electrolyte solution, and improving the cycle performance of the battery cell.

[0040] In some embodiments, the positive electrode active material comprises one or more lithium-containing transition metal oxides and lithium-containing phosphates.

[0041] In a second aspect, the embodiments of the present application propose a battery device comprising a battery cell according to one of the embodiments of the first aspect of the present application.

[0042] In a third aspect, the embodiments of the present application propose a power-consuming device comprising a battery device according to one of the embodiments of the second or third aspect of the present application. Brief description of the drawings

[0043] To better illustrate the technical solutions in the embodiments of the present application, a brief description of the drawings required in these embodiments is given below. Of course, the drawings described below represent only some embodiments of the present application, and other drawings can be created by a person skilled in the art based on these drawings without any creative effort. Fig. Figure 1 is a schematic representation of the structure of a power-consuming device according to some embodiments of the present application; Fig. Figure 2 is a schematic representation of the structure of a battery pack according to some embodiments of the present application; Fig. Figure 3 is a schematic representation of the structure of a battery module according to some embodiments of the present application; Fig. Figure 4 is a schematic representation of the structure of a battery cell according to some embodiments of the present application; Fig. Figure 5 is a schematic representation of the structure of an electrode arrangement of a battery cell according to some embodiments of the present application; Fig. Figure 6 is a schematic representation of the structure of a negative electrode sheet of a battery cell according to some embodiments of the present application.

[0044] The drawings are not necessarily to scale. Reference symbol list:

[0045] X, thickness direction; 1, current-consuming device; 2, battery pack; 3, controller; 4, motor; 5, box body; 5a, first box body section; 5b, second box body section; 5c, receiving chamber; 6, battery module; 7, battery cell; 10, electrode assembly; 11, positive electrode sheet; 12, negative electrode sheet; 121, negative electrode film layer; 122, negative electrode current collector; 1211, first negative electrode film layer; 1212, second negative electrode film layer; 121a, first area; 121b, second area; 121c, third area; 13, separator; 20, housing assembly; 21, housing body; 22, end cap; 23, electrode terminal. Detailed descriptions

[0046] The following section describes in detail embodiments of a battery cell, a battery device, and a power-consuming device specifically disclosed in the present application, possibly with reference to the drawings. However, an unnecessarily detailed description can be omitted. For example, a detailed description of known facts and a repeated description of essentially the same structure can be avoided. This is to prevent the following description from becoming unnecessarily lengthy, thus facilitating understanding by those skilled in the art. Furthermore, the drawings and the following description serve to enable those skilled in the art to fully understand the present application and are not intended to limit the subject matter described in the claims.

[0047] The “range” disclosed in the present application is defined in terms of a lower bound and an upper bound. A given range is defined by selecting a lower bound and an upper bound. The selected lower bound and upper bound define the limits of the specific range. The ranges thus defined may or may not include the end values ​​and may be specified in any combination; that is, any lower bound can be combined with any upper bound to form a range. For example, if ranges of 60 to 120 and 80 to 110 are listed for a particular parameter, then ranges of 60 to 110 and 80 to 120 are also conceivable. Furthermore, if minimum range values ​​of 1 and 2 and maximum range values ​​of 3, 4, and 5 are listed, then all of the following ranges are conceivable: 1 to 3, 1 to 4, 1 to 5, 2 to 3, 2 to 4, and 2 to 5.In the present application, unless otherwise specified, a range of numbers "a to b" represents an abbreviation for any combination of real numbers between a and b, where a and b are both real numbers. For example, the range "0 to 5" means that all real numbers between "0 to 5" are listed therein, and "0 to 5" is simply an abbreviation for these number combinations. Furthermore, if a particular parameter is specified 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.

[0048] Unless otherwise stated, all embodiments and optional embodiments of the present application may be combined to form a new technical solution. Unless otherwise stated, all technical features and optional technical features of the present application may be combined to form a new technical solution. Unless otherwise stated, all steps of the present application may be carried out sequentially or in any order, but preferably sequentially. For example, a method comprising steps (a) and (b) means that the method may comprise steps (a) and (b) carried out sequentially, or steps (b) and (a) carried out sequentially. For example, if it is mentioned that the method may further comprise step (c), this means that step (c) may be added in any order.For example, the procedure may include steps (a), (b) and (c), or steps (a), (c) and (b), or steps (c), (a) and (b), etc.

[0049] The term ‘several’ used in the present application refers to two or more (including two).

[0050] With the rapid development of battery technology, the performance requirements for battery cells are constantly increasing. For example, the rising demand for fast charging can be met by increasing the conductivity of the electrolyte solution in relevant technologies. However, increased conductivity can lead to decomposition of the electrolyte solution, which can increase the amount of high-temperature gas evolution from the battery cell, increase the volume expansion rate of the battery cell, and reduce the cycle life of the battery cell.

[0051] In light of the above problem, the embodiments of the present application improve the cycle life and fast-charge performance of the battery cell through a coordinated adaptation of the negative electrode sheet and the electrolyte solution. In particular, the negative electrode sheet of the battery cell comprises a negative electrode active material containing the element silicon, which, in combination with a relatively low coating weight, promotes the rapid migration of active ions and increases the fast-charge capability of the battery cell.

[0052] Under fast-charging conditions, the negative electrode active material, which contains the element silicon, is more prone to side reactions with the electrolyte solution, leading to an increase in the amount of high-temperature gas evolution. However, the embodiments of the present application use an electrolyte solution containing a suitable amount of carboxylic esters. Based on the rapid migration of active ions such as lithium ions, this can reduce the side reaction of the negative electrode active material with the electrolyte solution, thereby lowering the amount of high-temperature gas evolution and decreasing the volume expansion rate of the battery cell. This improves the high-temperature storage performance of the battery cell, and since the interfacial side reaction on the negative electrode side is reduced, this is advantageous for increasing the cycle life of the battery cell.

[0053] The battery cell of the present application is applicable to various battery devices and power-consuming devices that use the battery cell.

[0054] The power-consuming device could be, for example, a mobile phone, a portable device, a laptop, an electric vehicle, an electric toy, a power tool, a vehicle, a ship, or a spacecraft. Alternatively, the power-consuming device could be, for example, a spacecraft, where the spacecraft includes an airplane, a rocket, a space shuttle, and a spaceship.

[0055] Fig.Figure 1 is a schematic representation of a power-consuming device 1 as an example. The power-consuming device 1 is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. To meet the power-consuming device 1's requirements for high power and high energy density, a battery pack or battery module can be used.

[0056] Inside the power-consuming device 1, a battery device is arranged, the battery device being located at the bottom, top, or rear of the power-consuming device 1. The battery device can be used to supply power to the power-consuming device 1. For example, the battery device can be used both as an operating power source for the power-consuming device 1 and as a drive power source for the power-consuming device 1, replacing fuel or natural gas wholly or partially to provide the drive for the power-consuming device 1. In the case described in Fig. The battery device shown in Figure 1 is a battery pack.

[0057] The power-consuming device 1 can further comprise a controller 3 and a motor 4, wherein the controller 3 is used to control the battery device in order to supply power to the motor 4, for example to meet the work power requirements of the power-consuming device 1 when starting, navigating and driving.

[0058] The battery apparatus can comprise one or more battery cell assemblies to provide voltage and capacity. The battery cell assembly can comprise multiple battery cells connected in series, parallel, or a mixed configuration via a current collector.

[0059] In some embodiments, a battery cell assembly is generally formed by arranging the multiple battery cells.

[0060] For example, the battery cell arrangement could be a battery module, where the battery module consists of several battery cells arranged and secured to form a self-contained module. For instance, a battery module can be formed by bundling several battery cells together with cable ties.

[0061] As in Fig. As shown in Figure 2, in some embodiments the battery device can be a battery pack 2, wherein the battery pack 2 comprises a box body 5 and one or more battery cell assemblies, the battery cell assemblies being accommodated in the box body 5. For example, the battery cell assembly can also be accommodated in the box body 5 by attaching several battery cells directly to the box body 5.

[0062] As an example, the box body 5 comprises a first box body section 5a and a second box body section 5b. The box body 5 has a receiving space 5c. The first box body section 5a and the second box body section 5b interlock, creating a closed space within the box body 5 for receiving the battery cell assembly. "Closed" here refers to covering or sealing, which can be either airtight or not. The first box body section 5a can be a top cover or a bottom plate.

[0063] For example, the box body 5 can comprise a top cover, a frame, and a base plate. The top cover and the base plate are each connected to the frame, creating an enclosed space inside the box body 5 to accommodate the battery cell arrangement.

[0064] In some embodiments, the box body 5 can be designed as part of a vehicle chassis. For example, part of the box body 5 can become at least part of a floor of the vehicle, or part of the box body 5 can become at least part of a cross member and a longitudinal member of the vehicle.

[0065] For example, the battery cell arrangement can be a battery module 6, and the battery cell arrangement can be accommodated in the box body 5 by attaching the battery module 6 to the box body 5.

[0066] As in Fig. As shown in Figure 3, the battery module 6 comprises several battery cells 7.

[0067] As in the Fig. 4 and Fig. As shown in Figure 5, in some embodiments the battery cell 7 comprises an electrode arrangement 10 and a housing arrangement 20.

[0068] The housing arrangement 20 has a receiving chamber for receiving the electrode arrangement 10 and the electrolyte solution.

[0069] In some embodiments, the housing arrangement 20 comprises a housing and an electrode connection 23, wherein the electrode connection 23 is arranged on the housing.

[0070] The housing can be a steel housing, an aluminum housing, a plastic housing (e.g., made of polypropylene), a composite metal housing (e.g., a copper-aluminum composite housing), or an aluminum-plastic foil. In some embodiments, the housing can have a sealed or an unsealed structure. If, for example, the housing has an unsealed structure, it serves to protect the electrode assembly 10, with a sealing pouch positioned between the housing and the electrode assembly 10 to enclose the electrode assembly 10 and the electrolyte. In particular, the sealing pouch can be a pouch-shaped insulating element or an aluminum-plastic foil. If the housing has a sealed structure, it is used to encapsulate the electrode assembly 10 and other components such as the electrolyte.

[0071] For example, battery cell 7 can be a cylindrical battery cell, a prismatic battery cell, a pouch battery cell, or a battery cell of other shapes, wherein the prismatic battery cell includes a square battery cell, a leaf-shaped battery cell, and a polygonal battery, such as a hexagonal battery. The present application does not impose any specific restrictions in this regard.

[0072] In some embodiments, the housing comprises an end cap 22 and a housing body 21, wherein the housing body 21 is provided with an opening and the end cap 22 covers the opening. The housing body 21 may be provided with one or more openings. One or more end caps 22 may be provided.

[0073] The shape of the housing body 21 can be determined according to the specific shape of the electrode assembly 10. For example, if the electrode assembly 10 has a cylindrical structure, a housing body 21 with a cylindrical structure can be selected; if the electrode assembly 10 has a cuboid structure, a housing body 21 with a cuboid structure can be selected. Optionally, both the electrode assembly 10 and the housing body 21 can have the cuboid structure.

[0074] The electrode connection 23 can be located on the housing body 21, or the electrode connection 23 can be located on the end cap 22. The electrode connection 23 is electrically connected to an electrode tab of an electrode blade. The electrode connection 23 can be connected directly to the electrode tab or indirectly via a current collector component.

[0075] The electrode arrangement 10 can have a wound structure, a stacked structure or a hybrid structure of wound and stacked structure.

[0076] In some embodiments, the electrode arrangement 10 has a wound structure. A positive electrode sheet 11 and a negative electrode sheet 12 are wound together in a coiled structure.

[0077] In some embodiments, the electrode arrangement 10 has a stacked structure.

[0078] For example, several positive electrode sheets 11 and several negative electrode sheets 12 can be provided, wherein the several positive electrode sheets 11 and the several negative electrode sheets 12 are stacked alternately.

[0079] For example, several positive electrode sheets 11 can be provided while a negative electrode sheet 12 is folded to form several stacked folded sections, with a positive electrode sheet 11 being clamped between each adjacent folded section.

[0080] As an example, both the positive electrode sheet 11 and the negative electrode sheet 12 are folded to form several stacked folded segments.

[0081] For example, several separators 13 can be provided, each arranged between any adjacent positive electrode sheets 11 or negative electrode sheets 12.

[0082] For example, a separator 13 can be arranged continuously, which is arranged by folding or winding between any adjacent positive electrode sheets 11 or negative electrode sheets 12.

[0083] In some embodiments, the shape of the electrode arrangement 10 can be cylindrical, flat or polygonal.

[0084] In some embodiments, the electrode arrangement 10 is provided with an electrode tab that can conduct current away from the electrode arrangement 10. The electrode tab comprises a positive electrode tab and a negative electrode tab. The electrode arrangement 10 can have a wound structure or a stacked structure, optionally the stacked structure, which is advantageous for improving the energy density of the battery cell 7.

[0085] In some embodiments, the battery cell 7 comprises a negative electrode sheet 12 and an electrolyte solution, wherein the negative electrode sheet 12 comprises a negative electrode current collector and a negative electrode film layer arranged on at least one side of the negative electrode current collector, wherein the negative electrode film layer comprises a negative electrode active material, the negative electrode active material comprising a silicon-based material and a carbon-based material, wherein the mass fraction of the element silicon of the silicon-based material in the negative electrode active material is 0.3% to 15%, and the one-sided coating weight of the negative electrode film layer is 80 mg / 1540.25 mm². 2 up to 150 mg / 1540.25 mm 2is; wherein the electrolyte solution comprises an organic solvent, wherein the organic solvent comprises a carboxylic acid ester solvent, wherein the mass fraction of the carboxylic acid ester solvent in the electrolyte solution is 3% to 70%.

[0086] During the charging process of the battery cell 7, active ions such as lithium ions migrate from the positive electrode sheet 11 through the electrolyte solution to the negative electrode sheet 12, with the mass fraction of the carboxylic acid ester solvent of the electrolyte solution being greater than or equal to 3%, which results in a relatively fast migration rate of the active ions in the electrolyte solution.

[0087] The negative electrode sheet 12 comprises a silicon-based material, wherein the mass fraction of the element silicon in the negative electrode active material is greater than or equal to 0.3%, which is advantageous for reducing the coating thickness. The coating weight of the negative electrode film layer is 80 mg / 1540.25 mm². 2 up to 150 mg / 1540.25 mm 2 , which is advantageous for shortening the migration path of lithium ions and increasing the migration rate of lithium ions.

[0088] The combination of the coating weight of the negative electrode film layer and the components in the electrolyte solution is advantageous for increasing the fast charging capability of the battery cell 7.

[0089] Increasing the mass fraction of silicon is advantageous for increasing the energy density, and increasing the amount of carboxylic ester solvent is advantageous for increasing the migration rate of lithium ions. However, the interfacial reaction between the silicon-based material and the electrolyte solution intensifies with increasing mass fractions of silicon and carboxylic ester solvent, and the amount of high-temperature gas evolution increases.Accordingly, the embodiments of the present application further adjust the mass fraction of the element silicon so that it is less than or equal to 15%, and the mass fraction of the carboxylic acid ester solvent in the electrolyte solution so that it is less than or equal to 70%, which reduces the interfacial side reaction of the negative electrode active material with the electrolyte solution, lowers the high-temperature gas evolution quantity and can improve the high-temperature storage performance of the battery cell, and since the interfacial side reaction on the negative electrode side is reduced, this is advantageous for improving the cycle performance of the battery cell 7, in particular the cycle performance under fast-charging conditions. Negative electrode sheet

[0090] The negative electrode sheet comprises a negative electrode current collector and a negative electrode film layer, which is arranged on at least one side of the negative electrode current collector and comprises a negative electrode active material. For example, the negative electrode current collector has two surfaces that are opposite each other in its thickness direction, and the negative electrode film layer is arranged on one or both of the two opposite surfaces of the negative electrode current collector.

[0091] The upper charging voltage and the discharge cut-off voltage of the battery cell differ depending on the positive electrode active material. For example, if the phosphate material comprises lithium iron phosphate, the upper charging voltage can be 3.65 V and the discharge cut-off voltage 2.0 V, or the upper charging voltage can be 3.8 V and the discharge cut-off voltage 2.0 V. If the phosphate material also comprises, for example, lithium manganese iron phosphate, the upper charging voltage can be 4.3 V and the discharge cut-off voltage 2.0 V. The state of the battery cell is explained below using the example of an upper charging voltage of 3.8 V and a discharge cut-off voltage of 2.0 V: In the embodiments of the present application, the state of charge (SOC) of 100% and the state of charge (SOC) of the battery cell are defined as follows:

[0092] The battery cell is charged at a constant rate of 0.33C up to the upper charging limit voltage and then further charged at a constant voltage down to 0.05C, which corresponds to a state of 100% SOC (State of Charge). The battery cell is then discharged at a constant rate of 0.33C down to the final voltage, which corresponds to a state of 0% SOC.

[0093] In some embodiments, the density of the negative electrode film layer in the battery cell at a state of charge (SOC) of 0% is 1.1 g / cm³. 3 up to 1.7 g / cm³ 3 For example, the density of the negative electrode film layer when the battery cell is at a charge level of 0% is 1.10 g / cm³. 3 , 1.12 g / cm³ 3 , 1.14 g / cm³ 3 , 1.16 g / cm³ 3 , 1.18 g / cm³ 3 , 1.20 g / cm³ 3 , 1.22 g / cm³ 3 , 1.24 g / cm³ 3 , 1.26 g / cm³ 3 , 1.28 g / cm³ 3, 1.3 g / cm³ 3 , 1.32 g / cm³ 3 , 1.35 g / cm³ 3 , 1.40 g / cm³ 3 , 1.45 g / cm³ 3 , 1.50 g / cm² 3 , 1.55 g / cm³ 3 , 1.60 g / cm³ 3 , 1.65 g / cm³ 3 , 1.66 g / cm³ 3 , 1.68 g / cm³ 3 or 1.70 g / cm² 3 , or lies within a range consisting of any two of the above values.

[0094] If the density of the negative electrode film layer is in the above range, the thickness of the negative electrode film layer is not too thick, which facilitates fast charging of the battery cell; and the particle packing of the negative electrode active material is not excessively dense, which reduces the risk of particle fragmentation and is beneficial for improving the cycle performance of the battery cell.

[0095] In some embodiments, the one-sided coating weight of the negative electrode film layer is 80 mg / 1540.25 mm². 2up to 150 mg / 1540.25 mm 2 For example, the one-sided coating weight of the negative electrode film layer is 80 mg / 1540.25 mm². 2 , 85 mg / 1540.25 mm 2 , 90 mg / 1540.25 mm 2 , 95 mg / 1540.25 mm 2 , 100 mg / 1540.25 mm 2 , 105 mg / 1540.25 mm 2 , 110 mg / 1540.25 mm 2 , 115 mg / 1540.25 mm 2 , 120 mg / 1540.25 mm 2 , 120 mg / 1540.25 mm 2 , 122 mg / 1540.25 mm 2 , 125 mg / 1540.25 mm 2 , 128 mg / 1540.25 mm 2 , 130 mg / 1540.25 mm 2 , 132 mg / 1540.25 mm 2 , 135 mg / 1540.25 mm 2 , 137 mg / 1540.25 mm 2 , 140 mg / 1540.25 mm 2 , 145 mg / 1540.25 mm 2 , 150 mg / 1540.25 mm 2 , 155 mg / 1540.25 mm 2 , 160 mg / 1540.25 mm 2 , 165 mg / 1540.25 mm 2 , 170 mg / 1540.25 mm 2 , 175 mg / 1540.25 mm 2 or 180 mg / 1540.25 mm 2, or lies within a range consisting of any two of the above values.

[0096] If the one-sided coating weight of the negative electrode film layer meets the above range, it is advantageous in combination with a suitable mass fraction of the element silicon for increasing the energy density of the battery cell, so that the migration rate of active ions in the negative electrode film layer is faster, which is advantageous for improving the fast charging capability of the battery cell.

[0097] In the embodiments of the present application, the density of the negative electrode film layer in the battery cell at a state of charge (SOC) of 0% has the meaning known in the art. The negative electrode sheet is thus removed from the battery cell at a state of charge (SOC) of 0%, and the density of the negative electrode film layer is measured. For example, the single-sided coated negative electrode sheet (in the case of a double-sided coated electrode sheet, the negative electrode film layer can first be wiped off one side) is taken, then punched into small discs with an area S1 and weighed, and its weight is recorded as M1. Its thickness H1 is then measured. Subsequently, the negative electrode film layer of the above-weighed negative electrode sheet is wiped off, the negative electrode current collector is weighed, its weight is recorded as M0, and its thickness H0 is measured.The one-sided coating weight of the negative electrode film layer = (the weight of the negative electrode sheet M1 - the weight of the negative electrode current collector M0) / S1, the thickness of the negative electrode film layer = the thickness of the negative electrode sheet H1 - the thickness of the negative electrode current collector H0, the compaction density of the negative electrode film layer = the one-sided coating weight of the negative electrode film layer / the thickness of the negative electrode film layer.

[0098] In some embodiments, the negative electrode active material comprises a silicon-based material, and optionally the silicon-based material comprises at least one of elemental silicon, silicon-carbon composite and silicon dioxide SiO₂. x(0 < x ≤ 2). The above materials can increase the capacity of the negative electrode active material, which is advantageous for reducing the coating thickness of the negative electrode film layer and shortening the migration path of lithium ions.

[0099] In some embodiments, the specific surface area of ​​the silicon-based material is 1 m². 2 / g up to 4 m 2 / g, for example 1 m 2 / g, 1.2 m 2 / g, 1.4 m 2 / g, 1.5 m 2 / g, 1.6 m 2 / g, 1.8 m 2 / g, 2 m 2 / g, 2.2 m 2 / g, 2.4 m 2 / g, 2.5 m 2 / g, 2.6 m 2 / g, 2.8 m 2 / g, 3 m 2 / g, 3.2 m 2 / g, 3, 4 m 2 / g, 3.5 m 2 / g, 3.6 m 2 / g, 3.8 m 2 / g or 4 m 2 / g, or lies within a range consisting of any two of the above values.

[0100] If the specific surface area of ​​the silicon-based material is in the above range, suitable intercalation sites for lithium ions can be provided to improve fast charging capability; and the side reaction between the silicon-based material and the electrolyte solution can also be reduced, thereby lowering the high-temperature gas evolution quantity to improve the cycle performance of the battery cell under fast charging conditions.

[0101] In the embodiments of the present application, the specific surface area of ​​the material has a meaning known in the art and can be determined using devices and methods known in the art, for example according to the test standard GB / T 19587-2017. The negative electrode sheet of the battery cell can be disassembled to obtain the relevant material as a sample, and the specific surface area is measured using a specific surface and pore size analyzer (model: Tri-Star 3020) from the American manufacturer Micromeritics.

[0102] In some embodiments, the silicon-based material is in granular form with an average particle size of 4 µm to 12 µm, for example, 4 µm, 4.5 µm, 5 µm, 5.5 µm, 6 µm, 6.5 µm, 7 µm, 7.5 µm, 8 µm, 8.5 µm, 9 µm, 9.5 µm, 10 µm, 10.5 µm, 11 µm, 11.5 µm or 12 µm, or lies in a range consisting of any two of the above values.

[0103] If the average particle size of the silicon-based material is in the above range, the side reaction between the silicon-based material and the electrolyte solution can be reduced, thereby lowering the amount of high-temperature gas evolution to improve the cycle performance of the battery cell; and suitable intercalation sites for lithium ions can also be provided to improve fast-charging capability.

[0104] In some embodiments, the negative electrode active material comprises a carbon-based material. This carbon-based material exhibits high cycle stability, which can improve the cycle performance of the battery cell.

[0105] Optionally, the carbon-based material includes at least one of synthetic graphite and one of natural graphite.

[0106] In some embodiments, the negative electrode active material can comprise, in addition to the carbon-based material mentioned above and optionally the silicon-based material, at least one tin-based material and one lithium titanate. The tin-based material can comprise at least one elemental tin, tin oxide, and tin alloy material.

[0107] The qualitative and quantitative determination of the individual substances or elements in the present application can be carried out using suitable equipment and methods known to those skilled in the art. The relevant methods of determination may refer to national and international testing standards as well as national and international company standards. Those skilled in the art may also adjust certain test steps / equipment parameters with regard to test accuracy in order to obtain more precise test results. A single method may be used for the qualitative or quantitative determination, or a combination of several methods may be used.

[0108] For example, the present application, in combination with the general rule for X-ray diffraction analysis JIS / K0131-1996, can perform an X-ray powder diffraction test and a qualitative analysis of the negative electrode sheet or the negative electrode active material.

[0109] Artificial and natural graphite can be distinguished using SEM cross-sectional images obtained with a scanning electron microscope (SEM). The SEM cross-sectional image of natural graphite shows gaps between the scaly structures, while the SEM cross-sectional image of artificial graphite is dense and shows no obvious gaps. They can also be distinguished using their XRD spectra obtained by X-ray diffraction. The XRD spectrum of natural graphite shows a distinct 2H phase and a 3R phase, while the XRD spectrum of artificial graphite shows only the 2H phase.

[0110] As in Fig. As shown in Figure 6, in the embodiments of the present application, the negative electrode film layer 121 of the negative electrode sheet 12 comprises at least one film layer, wherein either a single film layer or at least two film layers may be present. Optionally, the negative electrode film layer 121 comprises at least two film layers.

[0111] In the case where the negative electrode film layer 121 comprises a single-layer film layer, the negative electrode active material in the negative electrode film layer 121 comprises a carbon-based material and optionally a silicon-based material.

[0112] In the case that the negative electrode film layer 121 comprises at least two film layers, the negative electrode active material in the negative electrode film layer 121 comprises a carbon-based material and a silicon-based material. The negative electrode film layer 121 can comprise two film layers, three film layers, four film layers, or even more film layers.

[0113] In some embodiments, the negative electrode film layer 121 comprises a first negative electrode film layer 1211 and a second negative electrode film layer 1212, wherein the first negative electrode film layer 1211 is arranged on the surface of the negative electrode current collector 122, and the negative electrode active material of the first negative electrode film layer 1211 comprises a carbon-based material, the second negative electrode film layer 1212 is connected to the side of the first negative electrode film layer 1211 facing away from the negative electrode current collector 122, and the negative electrode active material of the second negative electrode film layer 1212 comprises a carbon-based material.The interface between the first negative electrode film layer 1211 and the second negative electrode film layer 1212 is regular or irregular, optionally irregular; alternatively, there may be no obvious interface between the first negative electrode film layer 1211 and the second negative electrode film layer 1212.

[0114] The negative electrode film layer 121 comprises at least two film layers. This multilayer coating is advantageous for simultaneously improving the fast-charging performance and the cycle life of the battery cell.

[0115] In some embodiments, at least one of the first negative electrode film layer 1211 and the second negative electrode film layer 1212 comprises a silicon-based material.

[0116] Optionally, the first negative electrode film layer 1211 also includes a silicon-based material.

[0117] Optionally, the second negative electrode film layer 1212 also includes a silicon-based material.

[0118] For example, the first negative electrode film layer 1211 comprises a carbon-based material and a silicon-based material, and the second negative electrode film layer 1212 comprises a carbon-based material and a silicon-based material. Alternatively, the first negative electrode film layer 1211 comprises a carbon-based material and a silicon-based material, and the second negative electrode film layer 1212 comprises a carbon-based material. Alternatively, the first negative electrode film layer 1211 comprises a carbon-based material, and the second negative electrode film layer 1212 comprises a carbon-based material and a silicon-based material.

[0119] If both the first negative electrode film layer 1211 and the second negative electrode film layer 1212 comprise a silicon-based material, this is further advantageous for improving the energy density of the battery cell. In the case that the first negative electrode film layer 1211 comprises a silicon-based material and the second negative electrode film layer 1212 does not, the second negative electrode film layer 1212 can reduce the volume expansion of the first negative electrode film layer 1211, decrease the side reaction of the negative electrode film layer 1211 with the electrolyte solution, and improve cycle performance.

[0120] If the negative electrode film layer 121 comprises at least two film layers, the cross-sectional shapes of the negative electrode film layer 121 along the thickness direction X of the negative electrode film layer 121 can be the same or similar, but of course also different.

[0121] Along the thickness direction X of the negative electrode film layer 121, the negative electrode film layer 121 is divided into three regions: a first region 121a, a third region 121c, and a second region 121b. The first region 121a is a region of the negative electrode film layer 121 along its own thickness direction X near the negative electrode current collector 122, wherein the thickness of the first region 121a is 1 / 3 of the thickness of the negative electrode layer 121. The second region 121b is a region of the negative electrode film layer 121 facing away from the negative electrode current collector 122 along the thickness direction X, wherein the thickness of the second region 121b is also 1 / 3 of the thickness of the negative electrode layer 121.

[0122] The cross-sectional shapes of the first area 121a and the second area 121b can be the same or similar, or of course, different. The cross-sectional shapes of the first area 121a and the third area 121c can be the same or similar, or of course, different. The cross-sectional shapes of the second area 121b and the third area 121c can be the same or similar, or of course, different.

[0123] Distinct layer boundaries may or may not exist between the first region 121a, the second region 121b, and the third region 121c. For example, the first negative electrode film layer 1211 comprises a first region 121a, the second negative electrode film layer 1212 comprises a second region 121b, and the third region 121c may be part of the first negative electrode film layer 1211, or the third region 121c may be part of the second negative electrode film layer 1212, or the third region 121c may be part of both the first negative electrode film layer 1211 and the second negative electrode film layer 1212.

[0124] In some embodiments, in the cross-section of the negative electrode film layer 121 parallel to the thickness direction X, the void fraction of the individual carbon-based material located in the first region 121a is greater than or equal to the void fraction of the individual carbon-based material located in the second region 121b. Optionally, the void fraction of the individual carbon-based material located in the first region 121a is less than the void fraction of the individual carbon-based material located in the second region 121b.

[0125] The carbon-based material is in granular form with internal cavities. In the cross-section of the negative electrode film layer 121 parallel to the thickness direction X, the percentage of the cavity area to the total cross-sectional area of ​​the carbon-based material corresponds to the cavity fraction of the individual carbon-based material.

[0126] During the charging process of the battery cell, lithium ions diffuse through the second region 121b to the first region 121a. The void fraction of the individual carbon-based material in the first region 121a is less than or equal to the void fraction of the individual carbon-based material in the second region 121b, which further promotes the diffusion of lithium ions in the first region 121a, increases the transport rate and thus facilitates fast charging of the battery cell.

[0127] Optionally, the average particle size of the carbon-based material in the first region 121a can be greater than or equal to the average particle size of the carbon-based material in the second region 121b. Furthermore, optionally, the average particle size of the carbon-based material in the first region 121a can be larger than the average particle size of the carbon-based material in the second region 121b, which promotes the rapid migration of lithium ions from the second region 121b to the first region 121a and improves the fast-charging capability of the battery cell. Of course, the average particle size of the carbon-based material in the first region 121a can also be smaller than the average particle size of the carbon-based material in the second region 121b.

[0128] Optionally, the average particle size of the carbon-based material of the first negative electrode film layer 1211 can be greater than or equal to the average particle size of the carbon-based material of the second negative electrode film layer 1212. Furthermore, optionally, the average particle size of the carbon-based material of the first negative electrode film layer 1211 can be larger than the average particle size of the carbon-based material of the second negative electrode film layer 1212.

[0129] The particle size in the first electrode film layer 1211 and the second negative electrode film layer 1212 differs, which can improve the fast-charging performance of the battery cell. In particular, during fast charging, the overpotential of the second negative electrode film layer 1212 is typically higher, and the bottleneck during fast charging is mainly in the second negative electrode film layer 1212. In the embodiments of the present application, the particle size in the second negative electrode film layer 1212 is relatively small, which can shorten the solid-phase transport path of lithium ions to improve fast-charging performance and reduce the problem of lithium plating on the surface of the negative electrode sheet 12.

[0130] Optionally, the average particle size of the carbon-based material of the first range 121a is 12 µm to 21 µm, for example 12 µm, 12.5 µm, 13 µm, 13.5 µm, 14 µm, 14.5 µm, 15 µm, 15.5 µm, 16 µm, 16.5 µm, 17 µm, 17.5 µm, 18 µm, 18.5 µm, 19 µm, 19.5 µm, 20 µm, 20.5 µm or 21 µm, or lies in a range consisting of any two of the above values. If the average particle size of the carbon-based material in the first area 121a is within the range above, the cycle life can be improved, and the fast charging performance is not adversely affected.

[0131] Optionally, the average particle size of the carbon-based material in the first negative electrode film layer 1211 is 12 µm to 21 µm. If the average particle size of the carbon-based material in the first negative electrode film layer 1211 is within the above range, the cycle life can be improved, and the fast charging performance is not adversely affected.

[0132] Optionally, the average particle size of the carbon-based material of the second range 121b is 9 µm to 17 µm, for example 9 µm, 9.5 µm, 10 µm, 10.5 µm, 11 µm, 11.5 µm, 12 µm, 12.5 µm, 13 µm, 13.5 µm, 14 µm, 14.5 µm, 15 µm, 15.5 µm, 16 µm, 16.5 µm or 17 µm, or lies in a range consisting of any two of the above values. If the average particle size of the carbon-based material in the second negative electrode film layer 1212 is in the above range, this is advantageous for improving the fast charging capability of the battery cell and improving the stability of the material.

[0133] Optionally, the average particle size of the carbon-based material in the second negative electrode film layer 1212 is 9 µm to 17 µm. If the average particle size of the carbon-based material in the second negative electrode film layer 1212 is within the above range, the solid-phase transport path of lithium ions can be shortened to increase fast charging performance and improve material stability.

[0134] For example, the carbon-based material of the first area 121a comprises synthetic graphite and natural graphite, and the carbon-based material of the second area 121b comprises synthetic graphite. Similarly, the negative electrode active material of the first area 121a comprises a silicon-based material, synthetic graphite, and natural graphite, and the negative electrode active material of the second area 121b comprises a silicon-based material and synthetic graphite.

[0135] For example, the carbon-based material of the first negative electrode film layer 1211 comprises synthetic graphite and natural graphite, and the carbon-based material of the second negative electrode film layer 1212 comprises synthetic graphite. For example, the negative electrode active material of the first negative electrode film layer 1211 comprises a silicon-based material, synthetic graphite, and natural graphite, and the negative electrode active material of the second negative electrode film layer 1212 comprises a silicon-based material and synthetic graphite.

[0136] In some other embodiments, in the cross-section of the negative electrode film layer 121 parallel to the thickness direction X, the void fraction of the individual carbon-based material located in the first region 121a is smaller than the void fraction of the individual carbon-based material located in the second region 121b.

[0137] During the charging process of the battery cell, lithium ions diffuse through the second region 121b to the first region 121a. The void fraction of the individual carbon-based material in the second region 121b is larger, which promotes the rapid transport of lithium ions from the second region 121b to the first region 121a and is therefore advantageous for improving the fast charging of the battery cell.

[0138] Optionally, the average particle size of the carbon-based material in the first area 121a can be smaller than the average particle size of the carbon-based material in the second area 121b. The average particle size of the carbon-based material in the second area 121b is relatively larger, resulting in higher pressure resistance during the film layer manufacturing process, which is advantageous for improving particle density. Conversely, the average particle size of the carbon-based material in the first area 121a is relatively smaller, enabling rapid lithium ion migration and increasing the fast-charging capability of the battery cell. Of course, the average particle size of the carbon-based material in the first area 121a can also be greater than or equal to the average particle size of the carbon-based material in the second area 121b.

[0139] Optionally, the average particle size of the carbon-based material of the first range 121a is 9 µm to 17 µm, for example 9 µm, 9.5 µm, 10 µm, 10.5 µm, 11 µm, 11.5 µm, 12 µm, 12.5 µm, 13 µm, 13.5 µm, 14 µm, 14.5 µm, 15 µm, 15.5 µm, 16 µm, 16.5 µm or 17 µm, or lies in a range consisting of any two of the above values.

[0140] Optionally, the average particle size of the carbon-based material of the first negative electrode film layer is 1211 9 µm to 17 µm.

[0141] Optionally, the average particle size of the carbon-based material of the second range 121b is 12 µm to 21 µm, for example 12 µm, 12.5 µm, 13 µm, 13.5 µm, 14 µm, 14.5 µm, 15 µm, 15.5 µm, 16 µm, 16.5 µm, 17 µm, 17.5 µm, 18 µm, 18.5 µm, 19 µm, 19.5 µm, 20 µm, 20.5 µm or 21 µm, or lies in a range consisting of any two of the above values.

[0142] Optionally, the average particle size of the carbon-based material of the second negative electrode film layer is 12 µm to 21 µm.

[0143] For example, the carbon-based material of the second section 121b comprises synthetic graphite and natural graphite, and the carbon-based material of the first section 121a comprises synthetic graphite. Optionally, the negative electrode active material also includes a silicon-based material. For example, the negative electrode active material of the second section 121b comprises a silicon-based material, synthetic graphite, and natural graphite, and the negative electrode active material of the first section 121a comprises a silicon-based material and synthetic graphite.

[0144] For example, the carbon-based material of the second negative electrode film layer 1212 comprises synthetic graphite and natural graphite, and the carbon-based material of the first negative electrode film layer 1211 comprises synthetic graphite. Optionally, the negative electrode active material also includes a silicon-based material. For example, the negative electrode active material of the second negative electrode film layer 1212 comprises a silicon-based material, synthetic graphite, and natural graphite, and the negative electrode active material of the first negative electrode film layer 1211 comprises a silicon-based material and synthetic graphite.

[0145] In the embodiments of the present application, the average particle size of the active material in the first region 121a and in the second region 121b can be determined using the following devices and methods: The negative electrode sheet 12 is imaged as a sample along the thickness direction X of the negative electrode film layer 121 using a scanning electron microscope (SEM) to obtain an SEM cross-sectional image. The particle sizes of the active material in the SEM cross-section are statistically recorded, and the average particle size of the active material is calculated based on the statistical recording.

[0146] In some embodiments, the negative electrode film layer optionally includes a conductive element of the negative electrode. The embodiments of the present application do not specifically restrict the type of conductive element of the negative electrode. By way of example, the conductive element of the negative electrode may comprise at least one of superconducting carbon, conductive graphite, carbon black, carbon black, Ketjen carbon black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. In some embodiments, the mass fraction of the conductive element of the negative electrode is ≤ 5%, based on the total weight of the negative electrode film layer.

[0147] In some embodiments, the negative electrode film layer optionally also includes a negative electrode binder. In some embodiments, the mass fraction of the negative electrode binder is ≤ 5%, based on the total weight of the negative electrode film layer.

[0148] In some embodiments, the negative electrode film layer optionally includes further excipients. For example, these excipients may include a thickening agent, a dispersing agent, and the like, such as sodium carboxymethylcellulose (CMC-Na), PTC thermistor material, and the like. In some embodiments, the mass fraction of the further excipients, based on the total weight of the negative electrode film layer, is ≤ 2%.

[0149] In some embodiments, the negative electrode current collector can be a metal foil or a composite current collector. For example, the metal foil can include at least one foil made of copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, or silver alloy. The composite current collector can comprise a polymer material base layer and a metal material layer formed on at least one surface of the polymer material base layer. For example, the metal material in the metal material layer can include at least one of copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, or silver alloy. For example, the polymer material base layer can include at least one of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), or polyethylene (PE).

[0150] The negative electrode film layer is typically formed by applying a negative electrode paste to the negative electrode current collector, followed by drying and cold pressing. The negative electrode paste is usually formed by dispersing and uniformly stirring the negative electrode active material, an optional conductive agent, an optional binder, and other optional excipients in a solvent. The solvent may be, but is not limited to, N-methyl-2-pyrrolidone (NMP) or deionized water.

[0151] The negative electrode sheet does not exclude further additional functional layers besides the negative electrode film layer. For example, in some embodiments, the negative electrode sheet according to the embodiments of the present application also includes a conductive layer of the negative electrode, which is enclosed between the negative electrode current collector and the negative electrode film layer and is arranged on the surface of the negative electrode current collector. In some other embodiments, the negative electrode sheet according to the embodiments of the present application also includes a protective layer that covers the surface of the negative electrode film layer. Positive electrode sheet

[0152] In some embodiments, the battery cell also includes a positive electrode sheet.

[0153] The positive electrode sheet comprises a positive electrode current collector and a positive electrode film layer, which is arranged on at least one side of the positive electrode current collector and comprises a positive electrode active material. For example, the positive electrode current collector has two surfaces that are opposite each other in its thickness direction, and the positive electrode film layer is arranged on one or both of the two opposite surfaces of the positive electrode current collector.

[0154] In some embodiments, the dimension of the positive electrode film layer along the longitudinal direction of the positive electrode sheet is 200 mm to 600 mm, for example 200 mm, 250 mm, 300 mm, 350 mm, 400 mm, 450 mm, 500 mm, 550 mm or 600 mm, or lies in a range consisting of any two of the above values.

[0155] In a stacked electrode arrangement, the longitudinal direction of the positive electrode sheet runs parallel to the longitudinal direction of the battery cell, and the dimension of the positive electrode film layer along the longitudinal direction can be understood as the length of the positive electrode film layer. The lateral direction of the positive electrode sheet runs parallel to the lateral direction of the battery cell, and the dimension of the positive electrode film layer along the lateral direction can be understood as the width of the positive electrode film layer.

[0156] For example, the dimensions of the positive electrode film layer along its length range from 200 mm to 600 mm; the electrolyte solution comprises an organic solvent containing a carboxylic ester solvent, and the conductivity of the electrolyte solution at room temperature is 9 mS / cm to 18 mS / cm. The length of the positive electrode film layer, in combination with the electrolyte solution with the above conductivity, is advantageous for increasing the transport rate of lithium ions in the liquid phase, improving the kinetics, and enhancing the fast-charging capability of the battery cell. Furthermore, since the low viscosity of the carboxylic ester solvent ensures uniform wetting of all areas of the positive electrode film layer, the charge level across all areas of the positive electrode film layer is uniform.The lithium ions deinterlated from the positive electrode film layer are distributed evenly on the negative electrode side, thereby reducing the risk of local side reactions on the negative electrode side and improving cycle performance during fast charging.

[0157] In some embodiments, the compaction density of the positive electrode film layer in the battery cell at a state of charge (SOC) of 0% is 2.20 g / cm³. 3 up to 2.85 g / cm³ 3 For example, the density of the positive electrode film layer in a battery cell at a state of charge (SOC) of 0% is 2.20 g / cm³. 3 , 2.25 g / cm³ 3 , 2.30 g / cm³ 3 , 2.32 g / cm³ 3 , 2.35 g / cm³ 3 , 2.38 g / cm³ 3 , 2.40 g / cm³ 3 , 2.42 g / cm³ 3 , 2.45 g / cm³ 3 , 2.48 g / cm³ 3 , 2.50 g / cm³ 3 , 2.52 g / cm³ 3 , 2.55 g / cm³ 3 , 2.56 g / cm³ 3 , 2.57 g / cm³ 3, 2.58 g / cm³ 3 , 2.60 g / cm³ 3 , 2.62 g / cm³ 3 , 2.65 g / cm³ 3 , 2.68 g / cm³ 3 , 2.70 g / cm³ 3 , 2.75 g / cm³ 3 , 2.80 g / cm³ 3 or 2.85 g / cm³ 3 , or lies within a range consisting of any two of the above values.

[0158] If the packing density of the positive electrode film layer is in the above range, this is advantageous for increasing the energy density of the battery cell; and since the positive electrode active material of the positive electrode film layer is relatively densely packed and the contact resistance between the particles is small, the resistance of the electrode sheet can be further reduced, thereby reducing heat generation during fast charging, lowering the amount of high-temperature gas evolution, and improving the cycle performance of the battery cell.

[0159] In some embodiments, the one-sided coating weight of the positive electrode film layer is 250 mg / 1540.25 mm². 2 up to 300 mg / 1540.25 mm 2 For example, the coating weight of the positive electrode film layer on one side is 250 mg / 1540.25 mm². 2 , 260 mg / 1540.25 mm 2 , 270 mg / 1540.25 mm 2 , 280 mg / 1540.25 mm 2 , 290 mg / 1540.25 mm 2 or 300 mg / 1540.25 mm 2 , or lies within a range consisting of any two of the above values.

[0160] If the one-sided coating weight of the positive electrode film layer is in the above range, the amount of heat generated by the positive electrode sheet per unit area is not too large, and both the energy density and the charging rate performance of the battery cell can be improved simultaneously, thus preventing excessive heat accumulation in the battery cell system, reducing the risk of high-temperature decomposition of the electrolyte solution, and improving the cycle performance of the battery cell.

[0161] In the embodiments of the present application, the density of the positive electrode film layer in the battery cell at a state of charge (SOC) of 0% has the meaning known in the art. The positive electrode sheet is thus removed from the battery cell at a state of charge (SOC) of 0%, and the density of the positive electrode film layer is measured. For example, the single-sided coated positive electrode sheet (in the case of a double-sided coated electrode sheet, the positive electrode film layer can first be wiped off one side) is taken, then punched into small discs with an area S1 and weighed, and its weight is recorded as M1. Its thickness H1 is then measured. Subsequently, the positive electrode film layer of the above-weighed positive electrode sheet is wiped off, the positive electrode current collector is weighed, its weight is recorded as M0, and its thickness H0 is measured.The one-sided coating weight of the positive electrode film layer = (the weight of the positive electrode sheet M1 - the weight of the positive electrode current collector M0) / S1, the thickness of the positive electrode film layer = the thickness of the positive electrode sheet H1 - the thickness of the positive electrode current collector H0, the compaction density of the positive electrode film layer = the one-sided coating weight of the positive electrode film layer / the thickness of the positive electrode film layer.

[0162] In some embodiments, the positive electrode active material comprises one or more lithium-containing transition metal oxides and lithium-containing phosphates; optionally, the positive electrode active material comprises a lithium-containing phosphate. The lithium-containing phosphate may have an olivine structure that is stable during charging and discharging and can improve the cycle life of the battery cell.

[0163] Examples of the lithium-containing transition metal oxide may include, but are not limited to, at least one of lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, and their respective modified compounds.

[0164] In some embodiments, the positive electrode film layer also includes a carbon-containing material, wherein the carbon-containing material is a carbon-containing conductive material that can increase the conductivity of the positive electrode film layer and is advantageous for improving the fast charging performance of the battery cell.

[0165] Optionally, the mass fraction of the element carbon in the positive electrode film layer is 0.8% to 3.5%, for example, 0.8%, 0.9%, 1.0%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2.0%, 2.1%, 2.2%, 2.3%, 2.4%, 2.5%, 2.6%, 2.7%, 2.8%, 2.9%, 3.0%, 3.1%, 3.2%, 3.3%, 3.4%, or 3.5%, or lies within a range consisting of any two of the above values. Optionally, the mass fraction of the element carbon in the positive electrode film layer is 1.3% to 3.0%.

[0166] For example, the carbon-containing material can include carbon nanotubes. The carbon nanotubes can serve as a conductive medium in the positive electrode film layer and improve the conductivity of the positive electrode film layer.

[0167] For example, the lithium phosphate with an olivine structure can be an unmodified lithium phosphate, such as lithium iron phosphate, or a material obtained by coating and modifying the lithium phosphate with an olivine structure. For instance, the surface of the lithium phosphate can be coated with a carbon-containing material, which can serve as a coating layer. This increases the conductivity of the lithium phosphate and reduces the powder resistance of the material, thereby improving the migration rate of lithium ions, enhancing the fast-charging capability of the battery cell, and reducing the amount of heat generated by the battery cell.

[0168] In some embodiments, the lithium-containing phosphate comprises a compound with the general formula of Li x1 A y1 Me a M b P 1-cX c Y z , where 0.5 ≤ x1 ≤ 1.3, 0 ≤ y1 ≤ 1.3 and 0.9 ≤ x1 + y1 ≤ 1.3, 0.9 ≤ a ≤ 1.5, 0 ≤ b ≤ 0.5 and 0.9 ≤ a + b ≤ 1.5, 0 ≤ c ≤ 0.5, 3 ≤ z ≤ 5, A comprises one or more of Na, K and Mg, Me comprises one or more of Mn, Fe, Co and Ni, M comprises one or more of B, Mg, Al, Si, P, S, Ca, Sc, Ti, V, Cr, Cu, Zn, Sr, Y, Zr, Nb, Mo, Cd, Sn, Sb, Te, Ba, Ta, W, Yb, La and Ce, X comprises one or more of Cl, C, and N, and Y comprises one or more of O and F. The lithium-containing phosphate exhibits excellent cycle stability, which is advantageous for improving the cycle performance of the battery cell.

[0169] For example, the lithium-containing phosphate comprises one or more of LiFePO4, LiMnPO4, LiNiPO4, and LiCoPO4. During the charging and discharging process of the battery cell, deintercalation and intercalation, as well as the consumption of active ions such as Li, occur, and the molar content of Li varies depending on the state of discharge of the battery cell. When listing positive electrode active materials such as LiFePO4, LiMnPO4, LiNiPO4, LiCoPO4, etc., the molar content of Li refers to the initial state of the material, i.e., the state before it is added. The positive electrode active material is used in the battery system. After the charge-discharge cycle, the molar content of Li can change. When listing positive electrode active materials such as LiFePO4, LiMnPO4, LiNiPO4, LiCoPO4, etc., in the embodiments of the present application, the molar content of oxygen (O) is only a theoretical value.The release of oxygen from the lattice leads to a change in the molar content of oxygen (O), which is why the molar content of oxygen (O) varies in practice. The situations described above all fall within the scope of protection of this application.

[0170] In the embodiments of the present application, the element content in the positive electrode active material has a meaning known in the art and can be determined using devices and methods known in the art. For example, it is measured by inductively coupled plasma atomic emission spectroscopy (ICP-OES, instrument model: Thermo ICAP7400) with reference to EPA 6010D-2014. After the battery cell is discharged to a state of charge (SOC) of 0%, the positive electrode sheet is removed, cleaned with dimethyl carbonate (DMC), and dried. It is then calcined at a high temperature to remove impurities. Next, 0.4 g of positive electrode active material is weighed out and mixed with 10 mL (50% concentration) of aqua regia. It is then placed on a plate at 180 °C for 30 minutes.After digestion on the plate, the volume is made up to 100 mL and the quantitative test is carried out using the standard curve method.

[0171] In some embodiments, the lithium-containing phosphate is in granular form, comprising several first phosphate particles and several second phosphate particles. The longest diameter of the first phosphate particles is greater than or equal to a preset longest diameter of, for example, 1 µm, while the longest diameter of the second phosphate particles is less than 1 µm. It can be understood that all particles with a longest diameter greater than or equal to 1 µm are classified as first phosphate particles, and all particles with a longest diameter less than 1 µm are classified as second phosphate particles.

[0172] The longest diameters of the first phosphate particles are larger than the longest diameters of the second phosphate particles; the average longest diameter of the first phosphate particles is 1 µm to 5 µm, and the average longest diameter of the second phosphate particles is 0.1 µm to 0.5 µm.

[0173] For example, the average longest diameter of the first phosphate particles is 1 µm to 5 µm, for example 1 µm, 1.5 µm, 2 µm, 2.5 µm, 3 µm, 3.5 µm, 4 µm, 4.5 µm or 5 µm, or lies in a range consisting of any two of the above values.

[0174] For example, the average longest diameter of the second phosphate particles is 0.1 µm to 0.5 µm, for instance 0.1 µm, 0.15 µm, 0.2 µm, 0.25 µm, 0.3 µm, 0.35 µm, 0.4 µm, 0.45 µm or 0.5 µm, or lies in a range consisting of any two of the above values.

[0175] If the lithium phosphate meets the above conditions, its longest diameter is relatively small, the de- and intercalation path of lithium ions in the lithium phosphate is shorter, and the amount of heat generated is lower; furthermore, the particle size of the above lithium phosphate is not too small, and agglomeration practically does not occur during the processing and manufacturing process, so the performance stability of the lithium phosphate remains stable; therefore, this is advantageous for improving the high-temperature cycle performance of the battery cell.

[0176] In some embodiments, the mass fraction of the second phosphate particles in the lithium-containing phosphate is 80% to 95%, for example, 80%, 82%, 84%, 85%, 86%, 88%, 90%, 92%, 94%, or 95%, or lies within a range consisting of any two of the above values. If the mass fraction of the second phosphate particles is within a suitable range, for example, 80% to 95%, the amount of heat generated can be further reduced, the amount of heat generated in the battery cell system can be decreased, the risk of decomposition of electrolyte solution components due to heat build-up can be reduced, and the high-temperature cycle performance of the battery cell can be improved.

[0177] In some embodiments, the positive electrode film layer also includes a lithium supplement, wherein the lithium supplement comprises an elemental lithium. During the charging process of the battery cell, lithium ions can be released to compensate for lithium loss and thereby improve the capacity characteristics and high-temperature cycle performance of the battery cell.

[0178] In some embodiments, the lithium supplement comprises at least one of lithium ferrite, lithium nickel oxide and lithium cobalt oxide.

[0179] In some embodiments, the lithium supplement is in granular form with an average longest diameter of 9 µm to 13 µm, for example, 9 µm, 9.5 µm, 10 µm, 10.5 µm, 11 µm, 11.5 µm, 12 µm, 12.5 µm or 13 µm, or lies in a range consisting of any two of the above values.

[0180] In some embodiments, the lithium supplement is in granular form with an average minimum diameter of 5 µm to 9 µm, for example, 5 µm, 5.5 µm, 6 µm, 6.5 µm, 7 µm, 7.5 µm, 8 µm, 8.5 µm or 9 µm, or lies in a range consisting of any two of the above values.

[0181] In the embodiments of the present application, the positive electrode sheet is cut along its thickness direction to expose the cut surface of the positive electrode film layer, which can also be understood as the cross-section of the positive electrode film layer along its own thickness direction. By performing a scanning electron microscope (SEM) test on the cut surface of the positive electrode film layer, the longest and shortest diameters of the lithium supplement particles and the longest diameter of the lithium-containing phosphate particles are determined. For example, the "longest diameter" of a particle refers to the longest straight line passing through the center of the particle and extending to the outer circumference of the particle.The "shortest diameter" of a particle refers to the shortest straight line that passes through the center of the particle and extends to the outer circumference of the particle.

[0182] In the cross-section of the positive electrode film layer along its own thickness direction, the longest diameters of several, for example 10, particles of the lithium supplement are statistically recorded and their average value is calculated as the average longest diameter; the shortest diameters of several, for example 10, particles of the lithium supplement are statistically recorded and their average value is calculated as the average shortest diameter.

[0183] In the cross-section of the positive electrode film layer along its own thickness direction, the longest diameters of several, for example, 50, lithium-containing phosphate particles are statistically recorded. Particles with a longest diameter greater than or equal to 1 µm are assigned to the first phosphate particles, and particles with a longest diameter less than 1 µm are assigned to the second phosphate particles. The average of the longest diameters of all first phosphate particles is calculated, which corresponds to the average longest diameter of the first phosphate particles, and the average of the longest diameters of all second phosphate particles is calculated, which corresponds to the average longest diameter of the second phosphate particles.

[0184] The number of all first phosphate particles and the number of all second phosphate particles are statistically recorded, and the quantity fraction of the second phosphate particles is calculated, which corresponds to the mass fraction of the second phosphate particles in the lithium-containing phosphate.

[0185] In some embodiments, the mass fraction of the lithium supplement, based on the total mass of the positive electrode film layer, is 0.5% to 3%, for example, 0.5%, 0.6%, 0.8%, 1.0%, 1.2%, 1.4%, 1.6%, 1.8%, 2.0%, 2.5%, or 3.0%, or lies within a range consisting of any two of the above values. When the lithium supplement is used within the mass range mentioned above, its stability can be effectively improved while simultaneously achieving good oxygen release.

[0186] In some embodiments, the positive electrode film layer optionally includes a conductive element of the positive electrode. For example, the conductive element of the positive electrode comprises at least one of superconducting carbon, conductive graphite, carbon black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. In some embodiments, the mass fraction of the conductive element of the positive electrode is ≤ 5%, based on the mass of the positive electrode film layer.

[0187] Optionally, the conductive medium of the positive electrode comprises carbon nanotubes, wherein the mass fraction of the carbon nanotubes in the positive electrode film layer is 0.1% to 2%, for example, 0.1%, 0.3%, 0.5%, 0.7%, 0.9%, 1.1%, 1.3%, 1.5%, 1.7%, 1.9%, or 2%, or is in a range consisting of any two of the above values. Optionally, the mass fraction of the carbon nanotubes in the positive electrode film layer is 0.15% to 1.2%.

[0188] If the mass fraction of the carbon nanotubes is in the above range, this is advantageous for improving the conductivity of the positive electrode film layer and improving the fast charging performance of the battery cell.

[0189] Optionally, the specific surface area of ​​the carbon nanotubes is 500 m². 2 / g up to 2500 m 2 / g, for example 500 m 2 / g, 700 m 2 / g, 900 m 2 / g, 1100 m 2 / g, 1300 m2 / g, 1500 m 2 / g, 1700 m 2 / g, 1900 m 2 / g, 2100 m 2 / g, 2300 m 2 / g or 2500 m 2 / g, or lies within a range consisting of any two of the above values.

[0190] If the specific surface area of ​​the carbon nanotubes is in the above range, this is advantageous for improving electron conductivity; moreover, in combination with a suitable content of carbon nanotubes, the degree of side reactions can be reduced to improve gas evolution at high temperature.

[0191] Optionally, the diameter of the carbon nanotubes can be from 0.5 nm to 20 nm, for example, 0.5 nm, 1.5 nm, 2.5 nm, 3.5 nm, 4.5 nm, 5.5 nm, 6.5 nm, 7.5 nm, 8.5 nm, 9.5 nm, 10.5 nm, 11.5 nm, 12.5 nm, 13.5 nm, 14.5 nm, 15.5 nm, 16.5 nm, 17.5 nm, 18.5 nm, 19.5 nm, or 20 nm, or a range consisting of any two of the above values. Optionally, the diameter of the carbon nanotubes can be from 0.5 nm to 7.5 nm.

[0192] If the diameter of the carbon nanotubes is in the range above, the structure is relatively stable and exhibits relatively excellent electron conductivity.

[0193] Carbon nanotubes can generally be considered two-dimensional carbon materials formed by coiling. Coiling into a single layer results in single-walled carbon nanotubes, while coiling into multiple layers results in multi-walled carbon nanotubes. The tube diameter of the carbon nanotubes is the outer diameter of the carbon nanotubes in cross-section perpendicular to their own central axis.

[0194] In some embodiments, the positive electrode film layer optionally also comprises a positive electrode binder. The embodiments of the present application are not subject to any particular restrictions regarding the type of positive electrode binder. By way of example, the positive electrode binder may comprise at least one of the following: polyvinylidene fluoride, polytetrafluoroethylene, a vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, a vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, a tetrafluoroethylene-hexafluoropropylene copolymer, polyacrylic acid, and a fluorine-containing acrylate resin. In some embodiments, the mass fraction of the positive electrode binder is ≤ 5%, based on the mass of the positive electrode film layer.

[0195] In some embodiments, the positive electrode current collector can be a metal foil or a composite current collector. For example, the metal foil can be made of at least one material: aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, or silver alloy. The composite current collector can comprise a polymer base layer and a metal layer formed on at least one surface of the polymer base layer. For example, the metal material of the metal layer can be aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, or silver alloy. For example, the polymer base layer can be polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), or polyethylene (PE).

[0196] The positive electrode film layer is typically formed by applying a positive electrode paste to the positive electrode current collector, followed by drying and cold pressing. The positive electrode paste is generally formed by dispersing and uniformly stirring the positive electrode active material, an optional conductive agent, an optional binder, and any other components in a solvent. The solvent may be, but is not limited to, N-methyl-2-pyrrolidone (NMP).

[0197] The positive electrode sheet does not exclude further additional functional layers besides the positive electrode film layer. For example, in some embodiments, the positive electrode sheet according to the embodiments of the present application also comprises a conductive layer of the positive electrode, which is enclosed between the positive electrode current collector and the positive electrode film layer and is arranged on the surface of the positive electrode current collector. In some other embodiments, the positive electrode sheet according to the embodiments of the present application further comprises a protective layer that covers the surface of the positive electrode film layer. [Electrolyte solution]

[0198] During the charging and discharging process of the battery cell, active ions, such as lithium ions, are intercalated and deintercalated between the positive and negative electrode sheets, and the electrolyte solution facilitates the movement of these active ions between the positive and negative electrode sheets. The electrolyte solution comprises an organic solvent and an electrolyte salt.

[0199] In some embodiments, the conductivity of the electrolyte solution at room temperature is 9 mS / cm to 18 mS / cm. For example, the conductivity of the electrolyte solution at room temperature is 9 mS / cm, 9.5 mS / cm, 10 mS / cm, 10.5 mS / cm, 11 mS / cm, 11.5 mS / cm, 12 mS / cm, 12.5 mS / cm, 13 mS / cm, 13.5 mS / cm, 14 mS / cm, 14.5 mS / cm, 15 mS / cm, 15.5 mS / cm, 16 mS / cm, 16.5 mS / cm, 17 mS / cm, 17.5 mS / cm, or 18 mS / cm, or lies within a range consisting of any two of the above values.

[0200] If the conductivity of the electrolyte solution at room temperature, for example 25 °C, is in the above range, the migration rate of lithium ions in this electrolyte solution is higher, which can further reduce the internal resistance of the battery cell, thereby reducing heat generation and lowering the amount of high-temperature gas evolution due to heat build-up, which can increase the cycle performance of the battery cell during fast charging.

[0201] In the embodiments of the present application, the conductivity of the electrolyte solution at room temperature, for example 25 °C, is the ionic conductivity, which can be determined using devices and methods known in the art, for example with reference to the industry standard HG-T 4067-2015.

[0202] In some embodiments, the organic solvent comprises a carboxylic acid ester solvent.

[0203] Optionally, the mass fraction of the carboxylic acid ester solvent in the electrolyte solution is 3% to 70%. For example, the mass fraction of the carboxylic acid ester solvent is 3%, 5%, 8%, 10%, 13%, 15%, 18%, 20%, 23%, 25%, 28%, 30%, 33%, 35%, 38%, 40%, 43%, 45%, 48%, 50%, 53%, 55%, 58%, 60%, 63%, 65%, 68%, or 70%, or is in a range consisting of any two of the above values. Optionally, the mass fraction of the carboxylic acid ester solvent in the electrolyte solution is 5% to 30%.

[0204] If the mass fraction of the carboxylic acid ester solvent is in the above range, the conductivity of the electrolyte solution can be increased; in addition, the electrolyte solution and the silicon-containing negative electrode are compatible, which can effectively reduce the side reaction on the negative electrode side, lower the high-temperature gas evolution quantity of the battery cell, and improve the cycle performance of the battery cell during fast charging.

[0205] For example, the carboxylic acid ester solvent comprises a cyclic carboxylic acid ester, wherein the cyclic carboxylic acid ester includes one or more of γ-butyrolactone, γ-valerolactone, and δ-valerolactone. The above materials exhibit low viscosity, which can improve the wettability of the electrode sheet and increase cycle performance during fast charging.

[0206] For example, the carboxylic acid ester solvent comprises a chain-like carboxylic acid ester, wherein the chain-like carboxylic acid ester comprises one or more of methyl acetate, ethyl acetate, propyl acetate, butyl acetate, propyl propionate, and butyl propionate. The above materials exhibit low viscosity, which can improve the wettability of the electrode sheet and increase cycle performance during fast charging.

[0207] In some embodiments, the organic solvent comprises a carbonate solvent. The combined use of the carbonate solvent and the carboxylic acid ester solvent can increase the stability of the electrolyte solution, reduce its high-temperature gas evolution, and improve the cycle performance of the battery cell.

[0208] For example, the carbonate solvent comprises one or more of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate. Optionally, the carbonate solvent comprises one or more of ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate.

[0209] In some embodiments, the electrolyte salt comprises a lithium salt, wherein the lithium salt comprises one or more of lithium bis(fluorosulfonyl)imide and lithium hexafluorophosphate. Optionally, the lithium salt comprises lithium bis(fluorosulfonyl)imide and lithium hexafluorophosphate.

[0210] Lithium hexafluorophosphate can decompose to form hydrofluoric acid (HF), whereby the side reaction between the hydrofluoric acid and the negative electrode, especially the silicon-containing negative electrode, can lead to increased gas evolution during high-temperature storage; the combined use of lithium hexafluorophosphate and lithium bis(fluorosulfonyl)imide can reduce the hydrofluoric acid content, slow down the interfacial side reaction of the negative electrode, and lower the amount of gas evolution during high-temperature storage, and this is advantageous for improving the cycle life of the battery cell.

[0211] In some embodiments, the ratio of the mass fraction of lithium bis(fluorosulfonyl)imide to the mass fraction of lithium hexafluorophosphate, based on the mass of the electrolyte solution, is 0.3 to 1.2, for example 0.3, 0.5, 0.7, 0.9, 1.1 or 1.2, or lies in a range consisting of any two of the above values.

[0212] If the ratio of the mass fraction of lithium bis(fluorosulfonyl)imide to the mass fraction of lithium hexafluorophosphate meets the above range, the hydrofluoric acid content can be reduced, the interfacial side reaction of the negative electrode slowed down, and the amount of gas evolution during high-temperature storage lowered; on the other hand, the content of the organic component of the SEI film formed at the negative interface is adequate, which can also reduce the amount of gas evolution during high-temperature storage and is advantageous for increasing the cycle life of the battery cell.

[0213] For example, the mass fraction of lithium bis(fluorosulfonyl)imide, based on the mass of the electrolyte solution, is 2% to 11%, such as 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 8%, 8.5%, 9%, 9.5%, 10%, 10.5%, or 11%, or lies within any two of the above values. When the mass fraction of lithium bis(fluorosulfonyl)imide is within the above range, the hydrofluoric acid content can be reduced, the interfacial side reaction of the negative electrode slowed down, and the amount of gas evolution during high-temperature storage reduced, which is advantageous for improving the cycle life of the battery cell.

[0214] For example, the mass fraction of lithium hexafluorophosphate, based on the mass of the electrolyte solution, is 3% to 14%, such as 3%, 3.5%, 4%, 4.5%, 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 8%, 8.5%, 9%, 9.5%, 10%, 10.5%, 11%, 11.5%, 12%, 12.5%, 13%, 13.5%, or 14%, or lies within any two of the above values. When the mass fraction of lithium hexafluorophosphate is within the above range, the conductivity of the electrolyte solution is relatively high, which promotes the migration of lithium ions and improves the fast-charging performance of the battery cell.

[0215] In some embodiments, the electrolyte solution also contains an additive, which may include a film-forming additive for the negative electrode, a film-forming additive for the positive electrode, and an additive that can improve certain battery performance characteristics, such as an additive that improves the battery's overcharge behavior, an additive that improves the battery's high-temperature performance, and an additive that improves the battery's low-temperature performance.

[0216] In some embodiments, the additive contains a cyclic carbonate additive, for example, it comprises one or more of fluorinated cyclic carbonate and vinylene carbonate, and optionally the additive contains a fluorinated cyclic carbonate and a vinylene carbonate.

[0217] The fluorinated cyclic carbonate can form an interfacial film rich in lithium fluoride (LiF) on the negative electrode surface, thereby reducing the volume expansion of silicon, improving the lifetime of the silicon-containing system, and lowering the amount of high-temperature gas evolution.

[0218] The combined use of fluorinated cyclic carbonate and vinylene carbonate results in a denser interfacial film on the negative electrode surface, which can protect the silicon-containing negative electrode more effectively, reduce the degree of interfacial side reaction of the negative electrode and lower the amount of high-temperature gas evolution.

[0219] Optionally, the fluorinated cyclic carbonate comprises at least one of monofluoroethylene carbonate, difluoroethylene carbonate and trifluoropropylene carbonate.

[0220] Optionally, the mass fraction of the fluorinated cyclic carbonate, based on the mass of the electrolyte solution, is 0.5% to 20%, for example 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 8%, 8.5%, 9%, 9.5%, 10%, 10.5%, 11%, 11.5%, 12%, 12.5%, 13%, 13.5%, 14%, 14.5%, 15%, 15.5%, 16%, 16.5%, 17%, 17.5%, 18%, 18.5%, 19%, 19.5%, or 20%, or lies within a range consisting of any two of the above values. If the mass fraction of the fluorinated cyclic carbonate is in the above range, this is advantageous for improving cycle performance.

[0221] For example, the mass fraction of the fluorinated cyclic carbonate is 0.5% to 10% and the mass fraction of the element silicon of the silicon-based material in the negative electrode active material is 0.3% to 7.5%, each based on the mass of the electrolyte solution.

[0222] When the mass fraction of elemental silicon is relatively high, the volume expansion is relatively large. If the mass fraction of the fluorinated cyclic carbonate and the mass fraction of elemental silicon meet the conditions mentioned above, the volume expansion of silicon can be reduced more effectively, the lifetime of the silicon-containing system improved, and the amount of high-temperature gas evolution reduced.

[0223] As another example, the mass fraction of the fluorinated cyclic carbonate is greater than 10% and less than or equal to 20%, and the mass fraction of the element silicon of the silicon-based material in the negative electrode active material is greater than 7.5% and less than or equal to 15%, each based on the mass of the electrolyte solution.

[0224] If the mass fraction of the fluorinated cyclic carbonate and the mass fraction of the element silicon meet the above conditions, the volume expansion of the silicon can be reduced more effectively, the lifetime of the silicon-containing system can be improved, and the amount of high-temperature gas evolution can be reduced.

[0225] Optionally, the mass fraction of vinylene carbonate, based on the mass of the electrolyte solution, is 0.1% to 3%, for example, 0.1%, 0.5%, 0.6%, 1.0%, 1.1%, 1.5%, 1.6%, 2.0%, 2.1%, 2.5%, 2.6%, or 3%, or lies within any two of the above values. Vinylene carbonate at the above mass fraction results in a denser SEI film on the negative electrode surface, which can more effectively protect the negative electrode active material, reduce the degree of interfacial side reaction of the negative electrode, and improve cycle performance.

[0226] The combined use of vinylene carbonate and fluorinated cyclic carbonate with the above mass fractions leads to a further improved performance of the SEI film on the negative electrode surface, which exhibits excellent sealing and lower resistance, thus protecting the negative electrode active material more effectively, reducing the degree of interfacial side reaction of the negative electrode and improving cycle performance.

[0227] In the embodiments of the present application, the types and concentrations of the inorganic components / lithium salts in the electrolyte solution have meanings known in the art and can be determined using devices and methods known in the art. For example, the inorganic components / lithium salts in the electrolyte solution can be analyzed qualitatively or quantitatively by ion chromatography in accordance with the standard JY / T020-1996 "General rules for ion chromatography analysis methods".In the embodiments of the present application, a newly prepared electrolyte solution can be taken as a sample, a free electrolyte solution from a fresh battery can be taken as a sample, or a completely discharged battery (it has been discharged to the discharge cut-off voltage, so that the state of charge of the battery is approximately 0% SOC) can be reverse disassembled and the free electrolyte solution obtained from the battery taken as a sample. The sample is analyzed using the ion chromatography analytical method.

[0228] In the embodiments of the present application, the types and concentrations of the organic components in the electrolyte solution have meanings known in the art and can be determined using devices and methods known in the art. For example, reference can be made to GB / T9722-2006 "General rules for the gas chromatography of chemical reagents" to carry out a qualitative and quantitative analysis of organic components in the electrolyte solution by means of gas chromatography.

[0229] In the embodiments of the present application, the components are classified after quantitative and qualitative analysis of all components in the electrolyte solution. The carboxylic acid ester solvent and the carbonate solvent are classified as components of the organic solvent. The mass fraction of the individual components is calculated based on the mass of the electrolyte solution at 100%.

[0230] Fluorinated cyclic carbonate and vinylene carbonate are used as additives in the electrolyte solution. The mass fraction of each component is calculated based on the mass of the electrolyte solution at 100%. separator

[0231] In some embodiments, the electrode arrangement also includes a separator, wherein the separator is arranged between the positive electrode sheet and the negative electrode sheet.

[0232] In some embodiments, the separator is formed as a film. The present application does not impose any specific restrictions on the type of separator, and any known separator with good chemical and mechanical stability and a porous structure can be used.

[0233] For example, the main material of the separator can be selected from at least one of the following: glass fiber, nonwoven fabric, polyethylene, polypropylene, polyvinylidene fluoride, and ceramic. The separator can be a single-layer film or a multi-layer composite film, without any particular restriction. If the separator is a multi-layer composite film, the materials of each layer can be the same or different, without any particular restriction. The separator can be a separate component located between the positive and negative electrodes, or it can be attached to the surface of the positive and negative electrodes. The surface of the separator can also be coated with an inorganic particle coating, an organic particle coating, or an organic / inorganic composite coating.

[0234] In some embodiments, the separator is designed as a solid electrolyte. The solid electrolyte is arranged between the positive and negative electrodes and performs the functions of ion transport and insulation of the positive and negative electrodes. Example of implementation

[0235] The following exemplary embodiments describe in more detail the content disclosed in the embodiments of the present application. These exemplary embodiments serve only as an illustration, since various modifications and changes within the scope of the content disclosed in the embodiments of the present application are obvious to the person skilled in the art. Unless otherwise stated, all proportions, percentages, and ratios given in the following exemplary embodiments refer to mass. All reagents used in the exemplary embodiments are commercially available or are synthesized by conventional methods and can be used directly without further treatment. The instruments used in the exemplary embodiments are commercially available. Example 11. Production of the positive electrode sheet

[0236] The positive electrode sheet comprised a positive electrode current collector and positive electrode film layers arranged on both sides of the positive electrode current collector, the positive electrode current collector being an aluminum foil.

[0237] The positive electrode film layer comprised lithium iron phosphate, a binder polyvinylidene fluoride (PVDF) and a conductive agent superP in a mass ratio of 97:2:1, and the positive electrode film layer was formed by uniformly coating the positive electrode paste (the solvent was N-methyl-2-pyrrolidone NMP) on both sides of the positive electrode current collector, followed by drying and cold pressing.

[0238] The lithium iron phosphate came from Hunan Yuneng New Energy Battery Material Co., Ltd. 2. Production of the negative electrode sheet

[0239] The negative electrode sheet comprised a negative electrode current collector and negative electrode film layers arranged on both sides of the negative electrode current collector, the negative electrode current collector being a copper foil.

[0240] The negative electrode film layer was a film layer formed by uniformly applying the negative electrode paste (solvent: deionized water) to the surface of the negative electrode current collector and subsequently drying and cold pressing.

[0241] The negative electrode film layer comprised a first negative electrode film layer and a second negative electrode film layer, wherein the first negative electrode film layer was located on the surface of the negative electrode current collector and the second negative electrode film layer was located on the surface of the first negative electrode film layer.

[0242] The first negative electrode film layer comprised a carbon-based material, a silicon-based material (silicon oxide), a conductive agent (acetylene carbon black), a negative electrode binder (styrene-butadiene rubber), and a thickening agent (sodium carboxymethylcellulose) in a mass ratio of 87:9.5:1:1.5:1. The carbon-based material of the first negative electrode film layer comprised a synthetic graphite and a natural graphite in a mass ratio of 80%:20%. The average particle size of the carbon-based material was 18 µm, and the void content of the individual carbon-based material was 20%.

[0243] The second negative electrode film layer comprised a carbon-based material, a silicon-based material (silicon oxide), a conductive agent (acetylene carbon black), a negative electrode binder (styrene-butadiene rubber), and a thickening agent (sodium carboxymethylcellulose) in a mass ratio of 87:9.5:1:1.5:1. The carbon-based material of the second negative electrode film layer comprised synthetic graphite. The average particle size of the carbon-based material was 15 µm, and the void content of the individual carbon-based material was 25%.

[0244] The carbon-based material came from Guangdong Kaijin New Energy Technology Co., Ltd. 3. Separator

[0245] The separator comprised a base film and a coating arranged on both sides of the base film; the base film was a 7 µm polyethylene film layer, the coating was polyvinylidene fluoride, and the areal density was 1.2 g / m². 2 .

[0246] The separator came from Shanghai Enjie New Material Technology Co., Ltd. 4. Preparation of the electrolyte solution

[0247] The electrolyte solution comprised an organic solvent, a lithium salt, and an additive. After mixing the components of the organic solvent, the lithium salt and the additive were added to prepare the electrolyte solution.

[0248] The organic solvent comprised 25% chain-like carboxylic acid ester solvent ethyl acetate EA and 57% carbonate solvent (27% ethylene carbonate EC, 30% dimethyl carbonate DMC), and the mass fraction of each component of the organic solvent was calculated based on the mass of the electrolyte solution.

[0249] The lithium salt comprised 8% lithium hexafluorophosphate LiPF6 and 6% lithium bis(fluorosulfonyl)imide.

[0250] The additive comprised 2% fluorinated cyclic carbonate, namely monofluoroethylene carbonate FEC, and 2% vinylene carbonate VC.

[0251] The conductivity of the electrolyte solution was 14.2 mS / cm. 5. Manufacturing the battery cell

[0252] The positive electrode sheet, the separator, and the negative electrode sheet were stacked sequentially. The separator was positioned between the positive and negative electrode sheets to provide insulation, thus forming an electrode assembly. The electrode assembly was placed in an outer packaging sleeve. After drying, the electrolyte solution was injected, and a battery cell was obtained by vacuum sealing, standing, formation, and shaping, etc. The compaction density of the positive electrode film layer at 0% state of charge (SOC) of the battery cell was 2.7 g / cm³. 3 was, and the density of the negative electrode film layer at 0% SOC was 1.45 g / cm³ 3 fraud. Comparison example 1-1 and comparison example 1-2

[0253] A battery cell was manufactured using a method similar to that of embodiment 1, the difference being that the mass fraction of the element silicon was adjusted. Comparison example 1-3 and comparison example 1-4

[0254] A battery cell was manufactured using a method similar to that of embodiment 1, the difference being that the coating weight of the negative electrode film layer was adjusted. Exemplary embodiment 2-1 to Exemplary embodiment 2-3

[0255] A battery cell was manufactured using a method similar to that of embodiment 1, the difference being that the mass fraction of the element silicon and the coating weight of the negative electrode film layer were adjusted. Example 2-4

[0256] A battery cell was manufactured using a method similar to that of embodiment 1, the difference being that the coating weights of the positive and negative electrode film layers were adjusted. Exemplary embodiment 3-1 and Exemplary embodiment 3-2

[0257] A battery cell was manufactured using a process similar to that of embodiment 1, the difference being that the average particle size and the specific surface area of ​​the silicon-based material were adjusted. Example 4

[0258] A battery cell was manufactured using a method similar to that of embodiment 1, the difference being that the silicon-based material was adapted. Performance tests: 1. Test of the room temperature cycle performance of the battery cell

[0259] In an environment of 25 °C, a fully discharged battery cell was charged to 10% state of charge (SOC) at a constant current of 0.33 C. It was then charged from 10% SOC to 80% SOC, then charged to the upper charge limit voltage at 0.33 C. After a 30-minute rest period, it was discharged to the discharge cut-off voltage at 1 C. This constituted one charge-discharge cycle. The battery cell was subjected to several such cycles until its discharge capacity decreased to 90% (i.e., the battery state of health reached 90%). The greater the number of cycles, the better the battery cell's cycle life. The charging steps ranged from 10% SOC to 80% SOC: Charging from 10% SOC to 45% SOC at 3.7°C; Charging from 45% SOC to 50% SOC at 3.4°C; Charging from 50% SOC to 55% SOC at 3.2°C; Charging from 55% SOC to 60% SOC at 2.9°C; Charging from 60% SOC to 65% SOC at 2.6°C; Charging from 65% SOC to 70% SOC at 2.4°C; Charging from 70% SOC to 75% SOC at 2.1°C; Charging from 75% SOC to 80% SOC at 1.9°C. 2. Examination of gas evolution during high-temperature storage of the battery cell

[0260] In a 25°C environment, the battery cell was charged to its upper charging limit voltage with a constant current of 0.5C. It was then charged with a constant voltage until the current reached 0.05C. The initial volume of the battery cell at this point was measured using the water displacement method and recorded as V0. The battery cell was then stored in a 60°C thermostatic chamber for 90 days. After storage, it was removed, and its volume was again measured using the water displacement method and recorded as V1. Ten battery cells were tested per group, and the average value was taken.

[0261] The volume expansion rate (%) of the battery cell after 90 days of storage at 60 °C (%) = (V1 - V0) / V0 × 100 %.

[0262] The test results are shown in Table 1. Table 1 Positive electrode film layer Negative electrode film layer Battery power Single-sided coating weight (in mg / 1540.25 mm²) 2 ) Single-sided coating weight (in mg / 1540.25 mm²) 2 ) Silicon-based material Room temperature, number of cycles for 90% SOH High-temperature volume expansion (in %) material Specific surface area (in m²) 2 / G) Average particle size (in µm) Mass fraction of the element silicon in the negative electrode active material (in %) Example 1 280 140 silicon dioxide 1,4 6 5,0 1294 15,5 Example 2-1 280 80 silicon dioxide 1,4 6 15,0 1103 17,1 Example 2-2 280 100 silicon dioxide 1,4 6 10,0 1146 16,5 Example 2-3 280 150 silicon dioxide 1,4 6 0,3 1034 16,7 Example 2-4 270 135 silicon dioxide 1,4 6 5,0 1120 15,9 Example 3-1 280 140 silicon dioxide 1,9 4 5,0 1065 16,9 Example 3-2 280 140 silicon dioxide 1,0 12 5,0 1030 14,8 Example 4 280 140 silicon carbide 2,5 9 5,0 1054 17,0 Comparison example 1-1 280 155 silicon dioxide 1,4 6 0,2 911 17,3 Comparison example 1-2 280 140 silicon dioxide 1,4 6 18,0 842 25,4 Comparison example 1-3 280 75 silicon dioxide 1,4 6 5,0 994 22,5 Comparison example 1-4 280 160 silicon dioxide 1,4 6 5,0 859 24,1

[0263] In comparison example 1-1, the relatively low mass fraction of element silicon resulted in a relatively high coating weight of the negative electrode film layer, and the higher coating weight was unfavorable for lithium ion migration, which was detrimental to fast charging; the mass fraction of element silicon in comparison example 1-2 was too high, which increased the risk of side reactions at the interface on the negative electrode side, worsened gas evolution, and degraded high-temperature storage performance and cycle performance.

[0264] In contrast, the embodiments of the present application, by adjusting the mass fraction of the element silicon within a suitable range, ensured that the coating weight of the negative electrode film layer was not too high, which was advantageous for the rapid migration of lithium ions and improved the fast-charging capability of the battery cell; furthermore, the mass fraction of the element silicon was not too high, which reduced the side reactions on the negative electrode side, thereby decreasing the amount of high-temperature gas evolution and improving the high-temperature storage performance; since the side reaction on the negative electrode side was reduced, the cycle performance of the battery cell, in particular the cycle performance under fast-charging conditions, could be improved.

[0265] The coating weight of the negative electrode film layer in comparative example 1-3 was too low, which made the electrode sheet too thin, making it prone to breakage and worsening the cycle; the coating weight of the negative electrode film layer in comparative example 1-4 was too high, resulting in a greater transport resistance of lithium ions, which was unfavorable for fast charging.

[0266] In embodiments 2-1 to 2-4, the coating weight of the negative electrode film layer and the coating weight of the positive electrode film layer worked together, which was advantageous for improving the migration rate of the lithium ions in the positive and negative electrode film layers, so that the resistance of the battery cell was low under fast charging conditions; and the total amount of active material that participated in side reactions was lower, which was advantageous for improving the high-temperature storage performance and the cycle life of the battery cell.

[0267] The embodiments described in the present application are suitable for various silicon-based materials, for example, silicon oxide materials and silicon-carbon materials (e.g., silicon carbide). By adjusting the average particle size, specific surface area, etc., of the silicon-based material within a suitable range, the active area of ​​the silicon-based material was optimized, which further reduced side reactions on the negative electrode side, thereby decreasing the amount of high-temperature gas evolution and improving the high-temperature storage performance and cycle life of the battery cell.

[0268] The embodiments of the present application are suitable for various positive electrode active materials, for example lithium iron phosphate materials, lithium manganese iron phosphate materials or lithium iron phosphate materials mixed with transition metal oxides. Exemplary embodiment 5-1 and Exemplary embodiment 5-2

[0269] A battery cell was manufactured using a similar process to that described in embodiment 1. The difference compared to embodiment 1 was that the average particle size of the carbon-based material was adjusted. Example 6

[0270] A battery cell was manufactured using a method similar to that of embodiment 1, the difference being that the arrangement of the negative electrode film layer was adapted. In particular, the negative electrode film layer comprised a first negative electrode film layer and a second negative electrode film layer; the first negative electrode film layer was arranged on the surface of the negative electrode current collector, and the second negative electrode film layer was arranged on the surface of the first negative electrode film layer.

[0271] The first negative film layer comprised a carbon-based material, a silicon-based material silicon oxide, a conductive agent acetylene carbon black, a binder of the negative electrode styrene-butadiene rubber and a thickening agent sodium carboxymethylcellulose in a mass ratio of 87:9.5:1:1.5:1, the carbon-based material of the first negative electrode film layer comprised a synthetic graphite, the average particle size of the carbon-based material was 15 µm.

[0272] The second negative electrode film layer comprised a carbon-based material, a silicon-based material silicon oxide, a conductive agent acetylene carbon black, a negative electrode binder styrene-butadiene rubber, and a thickening agent sodium carboxymethylcellulose in a mass ratio of 87:9.5:1:1.5:1. The carbon-based material of the second negative electrode film layer comprised synthetic graphite and natural graphite in a mass ratio of 80%:20%. The average particle size of the carbon-based material was 18 µm.

[0273] The mass fraction of the element silicon in the negative electrode active material of the negative electrode film layer was 5%.

[0274] The test results are shown in Table 2. Table 2 material Negative electrode film layer Battery power First negative electrode film layer Second negative electrode film layer Room temperature, number of cycles for 90% SOH High-temperature volumetric expansion (in %) Carbon-based material Average particle size of the carbon-based material (in µm) Void fraction of the individual carbon-based material (in %) Carbon-based material Average particle size of the carbon-based material (in µm) Void fraction of the individual carbon-based material (in %) Example 5-1 Example 5-2 Artificial graphite and natural graphite 15 24 Artificial graphite 9 28 1087 17,2 21 17 17 22 1062 16,4 Example 6 Artificial graphite 15 22 Artificial graphite and natural graphite 18 27 1035 17,1

[0275] By adjusting the average particle size of the carbon-based material and / or the void fraction of a single carbon-based material, or by ensuring that the average particle size of the carbon-based material of the first negative electrode film layer was larger than the average particle size of the carbon-based material of the second negative electrode film layer, the solid-phase transport path of lithium ions could be shortened and the fast-charging capability improved; and the risk of lithium plating on the surface of the negative electrode side was reduced and the cycle performance and storage performance were improved.

[0276] If the average particle size of the carbon-based material of the first negative electrode film layer was smaller than the average particle size of the carbon-based material of the second negative electrode film layer, a pore difference could be created in the negative electrode film layer, improving the fast charging capability and increasing the cycle performance under fast charging conditions. Comparison example 1-5 and comparison example 1-6

[0277] A battery cell was manufactured using a similar method to that described in embodiment 1. The difference compared to embodiment 1 was that the components and their concentrations in the electrolyte solution were adapted. Exemplary embodiment 7-1 to Exemplary embodiment 11

[0278] A battery cell was manufactured using a similar method to that described in embodiment 1. The difference compared to embodiment 1 was that the components and their concentrations in the electrolyte solution were adapted.

[0279] The test results are shown in Table 3. Table 3 electrolyte solution Battery power Organic solvent lithium salt Additive Room temperature, number of cycles for 90% SOH High-temperature volume expansion (in %) Carboxylic acid ester solvent and mass fraction (in %) Carbonate solvent and mass fraction (in %) Mass fraction of lithium hexafluorophosphate (in %) Mass fraction of lithium bis(fluorosulfonyl)imide (in %) Mass ratio of lithium bis(fluorosulfonyl)imide / lithium hexafluorophosphate Fluorinated cyclic carbonate and mass fraction (in %) Mass fraction of vinylene carbonate (in %) Exemplary embodiment 7-1 EA:5 EC:20EMC:47DMC: 10 8,0 6 0,75 FEC:2 2 1043 14,9 Exemplary embodiment 7-2 MA:57 EC:25.0 8,0 6 0,75 FEC:2 2 1000 17,5 Exemplary embodiment 7-3 EA:3 EC:25EMC:34DMC:20 8,0 6 0,75 FEC:2 2 1012 14,7 Example 7-4 EA:70 EC:12 8,0 6 0,75 FEC:2 2 1065 18,4 Example 8 EA:25 EC:24.5DMC:30 7,5 9 1,20 FEC:2 2 1228 16,3 Example 9 EA:25 EC:28DMC:30 8,0 6 0,75 FEC:2 1 1215 15,2 Example 10 EA:25 EC:27DMC: 17 8,0 6 0,75 FEC: 15 2 989 17,5 Example 11 EA:25 EC:27DMC:30 8,0 6 0,75 DFEC:2 2 1233 16,1 Example 12 EA:25 EC:29DMC:30 8,0 6 0,75 FEC:2 / 1196 14,8 Comparison example 1-5 EA:1 EC:27EMC:24DMC:30 8,0 6 0,75 FEC:2 2 732 18,2 Comparison example 1-6 EA:75 EC:7 8,0 6 0,75 FEC:2 2 653 27,4

[0280] In Table 3 EA stands for ethyl acetate; MA stands for methyl acetate; EC stands for ethylene carbonate; DMC stands for dimethyl carbonate; EMC stands for ethyl methyl carbonate; FEC stands for monofluoroethylene carbonate; DFEC stands for difluoroethylene carbonate;

[0281] EA: 25 means that the mass fraction of EA was 25%; EC: 27 means that the mass fraction of EC was 27%.

[0282] The mass ratio of lithium bis(fluorosulfonyl)imide to lithium hexafluorophosphate refers to the ratio of the mass fraction of lithium bis(fluorosulfonyl)imide to the mass fraction of lithium hexafluorophosphate. The meanings of the other examples are analogous to the explanation above and are not repeated here.

[0283] The conductivity of the electrolyte solution in embodiment 7-1 was 9 mS / cm, and the conductivity of the electrolyte solution in embodiment 7-2 was 18 mS / cm.

[0284] By adjusting the individual components of the electrolyte solution so that the individual components of the electrolyte solution were in a suitable range, the side reaction on the negative electrode side could be effectively improved, the high-temperature gas evolution quantity reduced, and the cycle performance and fast charging performance improved.

[0285] The mass fraction of the carboxylic acid ester solvent in the embodiments of the present application was 3% to 70%, so that the side reaction on the negative electrode side could be effectively improved, thereby reducing the amount of gas evolution during high-temperature storage and improving the high-temperature storage performance, which was advantageous for improving the cycle performance of the battery cell under fast-charging conditions.

[0286] In the embodiments of the present application, lithium hexafluorophosphate and lithium bis(fluorosulfonyl)imide were used together, and, for example, the ratio of the mass fraction of lithium bis(fluorosulfonyl)imide to the mass fraction of lithium hexafluorophosphate was 0.3 to 1.2, so that the hydrofluoric acid content could be reduced, which slowed down the interfacial side reaction of the negative electrode, reduced the amount of gas evolution during high-temperature storage, and was advantageous for improving the cycle life of the battery cell.

[0287] The fluorinated cyclic carbonate exhibited a mass fraction of 0.5% to 20%. This fluorinated cyclic carbonate was able to form a lithium fluoride (LiF)-rich SEI film on the negative electrode surface, which reduced volume expansion on the negative electrode side, improved the lifetime of the negative electrode system, and enhanced cycle performance.

[0288] In embodiment 10, the mass fraction of the element silicon was 12.5%, in combination with 15% monofluoroethylene carbonate, effectively protecting the surface of the negative electrode active material, which further reduced the side reaction on the negative electrode side to improve high-temperature storage performance and cycle performance.

[0289] Although illustrative embodiments have been demonstrated and described, the person skilled in the art should understand that the above embodiments should not be construed as limiting the embodiments of the present application and that changes, substitutions and modifications to the embodiments may be made without departing from the spirit, principles and scope of the embodiments of the present application. QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited non-patent literature

[0000] GB / T 19587-2017

[0101] GB / T9722-2006

[0228]

Claims

[1] Battery cell, comprising: A negative electrode sheet, wherein the negative electrode sheet comprises a negative electrode current collector and a negative electrode film layer arranged on at least one side of the negative electrode current collector, wherein the negative electrode film layer comprises a negative electrode active material, the negative electrode active material comprising a silicon-based material and a carbon-based material, wherein the mass fraction of the element silicon of the silicon-based material in the negative electrode active material is 0.3% to 15%, and the one-sided coating weight of the negative electrode film layer is 80 mg / 1540.25 mm² 2 up to 150 mg / 1540.25 mm 2 is; and an electrolyte solution comprising an organic solvent, wherein the organic solvent comprises a carboxylic acid ester solvent, wherein the mass fraction of the carboxylic acid ester solvent in the electrolyte solution is 3% to 70%. [2] Battery cell according to claim 1, wherein the specific surface area of ​​the silicon-based material is 1 m² 2 / g up to 4 m 2 / g; and / or the silicon-based material is in granular form with an average particle size of 4 µm to 12 µm. [3] Battery cell according to claim 1 or 2, wherein the silicon-based material comprises one or more of elemental silicon, silicon-carbon composite and silicon oxide compound. [4] Battery cell according to any one of claims 1 to 3, wherein the negative electrode film layer comprises: a first region, which is a region of the negative electrode film layer along its own thickness direction near the negative electrode current collector, wherein the thickness of the first region is 1 / 3 of the thickness of the negative electrode film layer; and a second region, which is a region of the negative electrode film layer facing away from the negative electrode current collector along the thickness direction, wherein the thickness of the second region is 1 / 3 of the thickness of the negative electrode film layer, wherein in the cross-section of the negative electrode film layer parallel to the thickness direction the void fraction of the individual carbon-based material located in the first region, smaller than the void fraction of the individual carbon-based material located in the second area. [5] Battery cell according to claim 4, wherein the average particle size of the carbon-based material of the first area is greater than or equal to the average particle size of the carbon-based material of the second area. [6] Battery cell according to claim 4 or 5, wherein the average particle size of the carbon-based material of the first region is 12 µm to 21 µm; and / or the average particle size of the carbon-based material of the second region is 9 µm to 17 µm. [7] Battery cell according to any one of claims 4 to 6, wherein The carbon-based material of the first area comprises artificial graphite and / or natural graphite; and The carbon-based material of the second area includes an artificial graphite. [8] Battery cell according to claim 4, wherein the average particle size of the carbon-based material of the second region is larger than the average particle size of the carbon-based material of the first region. [9] Battery cell according to claim 8, wherein the average particle size of the carbon-based material of the first region is 9 µm to 17 µm; and / or the average particle size of the carbon-based material of the second region is 12 µm to 21 µm. [10] Battery cell according to claim 8 or 9, wherein The carbon-based material of the second area comprises artificial graphite and / or natural graphite; and The carbon-based material of the first area includes artificial graphite. [11] Battery cell according to any one of claims 1 to 10, wherein the negative electrode film layer comprises: a first negative electrode film layer arranged on the surface of the negative electrode current collector, wherein the negative electrode active material of the first negative electrode film layer comprises a carbon-based material; and a second negative electrode film layer connected to the side of the first negative electrode film layer facing away from the negative electrode current collector, wherein the negative electrode active material of the second negative electrode film layer comprises a carbon-based material, wherein at least one of the first negative electrode film layer and the second negative electrode film layer comprises a silicon-based material. [12] Battery cell according to any one of claims 1 to 11, wherein the conductivity of the electrolyte solution at room temperature is 9 mS / cm to 18 mS / cm. [13] Battery cell according to any one of claims 1 to 12, wherein the mass fraction of the carboxylic acid ester solvent in the electrolyte solution is 5% to 30%. [14] Battery cell according to any one of claims 1 to 13, wherein the carboxylic acid ester solvent comprises a cyclic carboxylic acid ester, wherein the cyclic carboxylic acid ester comprises one or more of γ-butyrolactone, γ-valerolactone and δ-valerolactone; and / or the carboxylic acid ester solvent comprises a chain-like carboxylic acid ester, wherein the chain-like carboxylic acid ester comprises one or more of methyl acetate, ethyl acetate, propyl acetate, butyl acetate, propyl propionate and butyl propionate. [15] Battery cell according to any one of claims 1 to 14, wherein the organic solvent also comprises a carbonate solvent, wherein the carbonate solvent comprises one or more of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate and ethyl methyl carbonate. [16] Battery cell according to any one of claims 1 to 15, wherein the electrolyte solution also comprises a lithium salt, wherein the lithium salt comprises lithium bis(fluorosulfonyl)imide and lithium hexafluorophosphate, wherein the ratio of the mass fraction of the lithium bis(fluorosulfonyl)imide to the lithium hexafluorophosphate, based on the mass of the electrolyte solution, is 0.3 to 1.

2. [17] Battery cell according to claim 16, wherein the mass fraction of lithium bis(fluorosulfonyl)imide, based on the mass of the electrolyte solution, is 2% to 11%; and / or the mass fraction of lithium hexafluorophosphate, based on the mass of the electrolyte solution, is 3% to 14%. [18] Battery cell according to any one of claims 1 to 17, wherein the electrolyte solution further comprises one or more of fluorinated cyclic carbonate and vinylene carbonate. [19] Battery cell according to claim 18, wherein the fluorinated cyclic carbonate comprises at least one of monofluoroethylene carbonate, difluoroethylene carbonate and trifluoropropylene carbonate. [20] Battery cell according to claim 18 or 19, wherein the mass fraction of the fluorinated cyclic carbonate, based on the mass of the electrolyte solution, is 0.5% to 20%; and / or The mass fraction of vinylene carbonate, based on the mass of the electrolyte solution, is 0.1% to 3%. [21] Battery cell according to one of claims 18 to 20, wherein the mass fraction of the fluorinated cyclic carbonate, based on the mass of the electrolyte solution, is 0.5% to 10%; and The mass fraction of the element silicon in the silicon-based material in the negative electrode active material is 0.3% to 7.5%. [22] Battery cell according to one of claims 18 to 20, wherein the mass fraction of the fluorinated cyclic carbonate, based on the mass of the electrolyte solution, is greater than 10% and less than or equal to 20%; and the mass fraction of the element silicon in the silicon-based material in the negative electrode active material is greater than 7.5% and less than or equal to 15%. [23] Battery cell according to one of claims 1 to 22, further comprising a positive electrode sheet, wherein the positive electrode sheet comprises a positive electrode current collector and a positive electrode film layer arranged on at least one side of the positive electrode current collector, wherein the positive electrode film layer comprises a positive electrode active material, wherein the one-sided coating weight of the positive electrode film layer is 250 mg / 1540.25 mm² 2 up to 300 mg / 1540.25 mm 2 amounts. [24] Battery cell according to claim 23, wherein the positive electrode active material comprises one or more lithium-containing transition metal oxides and lithium-containing phosphates. [25] Battery device comprising a battery cell according to any one of claims 1 to 24. [26] Power consumption device comprising a battery device according to claim 25.

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