Battery cell, battery device and electric device

Abstract

The invention relates to a battery monomer, a battery device and a power utilization device, the battery monomer comprises a negative pole piece and an electrolyte, the negative pole piece comprises a negative current collector and a negative film layer arranged on at least one side of the negative current collector, the negative film layer comprises a negative active material, the negative active material comprises a silicon-based material and a carbon-based material, and the silicon-based material and the carbon-based material are arranged on the negative current collector. The mass content of the silicon element of the silicon-based material in the negative electrode active material is 0.3%-15%, and the single-side coating weight of the negative electrode film layer is 80 mg / 1540.25 mm < 2 >-150 mg / 1540.25 mm < 2 >; the electrolyte comprises an organic solvent, the organic solvent comprises a carboxylic ester solvent, and the mass content of the carboxylic ester solvent in the electrolyte is 3%-70%. The high-temperature storage performance and the cycle performance of the battery monomer can be further improved.

Description

[0001] This application claims the priority of the international patent application PCT / CN2025 / 071105 titled "Battery Cell, Battery Device and Electrical Device" filed on January 7, 2025, and the entire content of this application is incorporated herein by reference. Technical Field

[0002] This application relates to a battery cell, a battery device and an electrical device. Background Art

[0003] Battery cells have characteristics such as high capacity and long life, and are thus widely used in electronic devices, such as mobile phones, laptop computers, battery-powered vehicles, electric vehicles, electric airplanes, electric ships, electric toy cars, electric toy ships, electric toy airplanes, and power tools, etc. Due to the great progress made in batteries, higher requirements are put forward for the performance of batteries. However, the high-temperature storage performance and cycling performance of battery cells need to be further improved. Summary of the Invention

[0004] This application provides a battery cell, a battery device and an electrical device, and the high-temperature storage performance and cycling performance of the battery cell of this application can be further improved.

[0005] In a first aspect, an embodiment of this application provides a battery cell. The battery cell includes a negative electrode tab and an electrolyte. The negative electrode tab includes a negative electrode current collector and a negative electrode film layer disposed on at least one side of the negative electrode current collector. The negative electrode film layer includes a negative electrode active material. The negative electrode active material includes a silicon-based material and a carbon-based material. The mass content of silicon element in the silicon-based material in the negative electrode active material is 0.3% to 15%. The single-sided coating weight of the negative electrode film layer is 80 mg / 1540.25 mm 2 to 150 mg / 1540.25 mm 2 ; The electrolyte includes an organic solvent. The organic solvent includes a carboxylic acid ester solvent. The mass content of the carboxylic acid ester solvent in the electrolyte is 3% to 70%.

[0006] Thus, through the cooperation of the mass content of silicon element, the coating weight of the negative electrode film layer and the components in the electrolyte, the embodiment of this application can alleviate the interfacial side reaction between the negative electrode active material and the electrolyte, reduce the gas generation amount at high temperature, and improve the high-temperature storage performance; moreover, the migration rate of active ions in the negative electrode film layer and the electrolyte is relatively fast, and the side reaction on the negative electrode side is alleviated, which is beneficial to improving the cycling performance of the battery cell under fast charging.

[0007] In some embodiments, the specific surface area of the silicon-based material is 1 m 2 / g to 4 m 2 / g; When the specific surface area of the silicon-based material is within the above range, the side reaction between the silicon-based material and the electrolyte can be alleviated, the gas generation amount at high temperature can be reduced, and the high-temperature storage performance and cycling performance of the battery cell can be improved.

[0008] In some embodiments, the silicon-based material is granular, and its average particle size is 4 μm to 12 μm. When 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 can be alleviated, the gas generation amount at high temperature can be reduced, and the high-temperature storage performance and cycling performance of the battery cell can be improved.

[0009] In some embodiments, the silicon-based material includes one or more of silicon, silicon-carbon composite, and silicon oxide. The above materials can improve the capacity of the negative electrode active material, help reduce the coating thickness of the negative electrode film layer, shorten the migration path of lithium ions, and facilitate fast charging.

[0010] In some embodiments, the negative electrode film layer includes a first region and a second region. The first region is the region of the negative electrode film layer close to the negative electrode current collector along its own thickness direction, and the thickness of the first region is 1 / 3 of the thickness of the negative electrode film layer; the second region is the region of the negative electrode film layer away from the negative electrode current collector along the thickness direction, and the thickness of the second region is 1 / 3 of the thickness of the negative electrode film layer. Among them, in the cross-section of the negative electrode film layer parallel to the thickness direction, the void ratio of a single carbon-based material in the first region is less than the void ratio of a single carbon-based material in the second region.

[0011] Therefore, in the embodiments of the present application, the void ratio of a single carbon-based material in the first region is less than or equal to the void ratio of a single carbon-based material in the second region, which is more conducive to the diffusion of lithium ions in the first region, improving the transmission rate, and thus facilitating the fast charging of the battery cell; under fast charging, lithium ions quickly diffuse into the negative electrode active material, which can reduce the risk of lithium deposition on the negative electrode side, thereby improving the cycle life of the battery cell.

[0012] In some embodiments, 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.

[0013] Therefore, in the embodiments of the present application, the particle size of the second region is relatively small, which can shorten the solid-phase transmission path of lithium ions, improve the fast charging performance, and can improve the problem of lithium deposition on the surface layer of the negative electrode sheet, thereby improving the cycle life of the battery cell.

[0014] In some embodiments, when 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, the average particle size of the carbon-based material in the first region is 12 μm to 21 μm; when the average particle size of the carbon-based material in the first region is within the above range, the cycle life can be improved.

[0015] In some embodiments, when 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, the average particle size of the carbon-based material in the second region is 9 μm to 17 μm. When the average particle size of the carbon-based material is within the above range, it is beneficial to improve the high-temperature storage performance and cycling performance of the battery cell under fast charging conditions.

[0016] In some embodiments, when 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, the carbon-based material in the first region includes artificial graphite and / or natural graphite. The above setting is beneficial to improving the cycling performance of the battery cell.

[0017] In some embodiments, when 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, the carbon-based material in the second region includes artificial graphite. The above setting is beneficial to improving the cycling performance of the battery cell.

[0018] In some embodiments, the average particle size of the carbon-based material in the second region is greater 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 preparation of the film layer, and the stability of the film layer is relatively excellent, which is beneficial to improving the high-temperature storage performance and cycling performance of the battery cell.

[0019] In some embodiments, when the average particle size of the carbon-based material in the second region is greater than the average particle size of the carbon-based material in the first region, the average particle size of the carbon-based material in the first region is 9 μm to 17 μm. When the average particle size of the carbon-based material in the first region is within the above range, the cycle life can be improved.

[0020] In some embodiments, when the average particle size of the carbon-based material in the second region is greater than the average particle size of the carbon-based material in the first region, the average particle size of the carbon-based material in the second region is 12 μm to 21 μm. When the average particle size of the carbon-based material in the second region is within the above range, the cycle life can be improved.

[0021] In some embodiments, when the average particle size of the carbon-based material in the second region is greater than the average particle size of the carbon-based material in the first region, the carbon-based material in the second region includes artificial graphite and / or natural graphite. The above setting is beneficial to improving the cycling performance of the battery cell.

[0022] In some embodiments, when the average particle size of the carbon-based material in the second region is greater than the average particle size of the carbon-based material in the first region, the carbon-based material in the first region includes artificial graphite. The above setting is beneficial to improving the cycling performance of the battery cell.

[0023] In some embodiments, the negative electrode film layer includes a first negative electrode film layer and a second negative electrode film layer. The first negative electrode film layer is disposed on the surface of the negative electrode current collector, and the negative electrode active material of the first negative electrode film layer includes a carbon-based material; 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 includes a carbon-based material. Among them, at least one of the first negative electrode film layer and the second negative electrode film layer includes a silicon-based material. The double-layer setting is beneficial to taking into account the improvement of the fast charging ability and energy density of the battery cell; the silicon-based material can further improve the energy density.

[0024] In some embodiments, the conductivity of the electrolyte at room temperature is 9 mS / cm to 18 mS / cm. The migration rate of lithium ions in this electrolyte is relatively high, which can further reduce the internal resistance of the battery cell, thereby reducing heat generation and improving the fast charging performance of the battery cell.

[0025] In some embodiments, the mass content of the carboxylic ester solvent in the electrolyte is 5% to 30%. When the mass content of the carboxylic ester solvent is within the above range, the conductivity of the electrolyte can be improved, and the fast charging ability of the battery cell can be improved; moreover, the side reaction of the electrolyte on the negative electrode side can be alleviated, the gas generation amount of the battery cell can be effectively reduced, which is beneficial to improving the high-temperature storage performance and cycling performance of the battery cell.

[0026] In some embodiments, the carboxylic ester solvent includes cyclic carboxylic esters, and the cyclic carboxylic esters include one or more of γ-butyrolactone, γ-valerolactone, and δ-valerolactone. The viscosity of the above materials is relatively low, which can improve the wetting ability of the electrode sheet and improve the cycling performance under fast charging.

[0027] In some embodiments, the carboxylic ester solvent includes chain carboxylic esters, and the chain carboxylic esters include one or more of methyl acetate, ethyl acetate, propyl acetate, butyl acetate, propyl propionate, and butyl propionate. The viscosity of the above materials is relatively low, which can improve the wetting ability of the electrode sheet and improve the cycling performance under fast charging.

[0028] In some embodiments, the organic solvent further includes a carbonate solvent, and the carbonate solvent includes one or more of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate. The mixed use of the carbonate solvent and the carboxylic ester solvent can improve the stability of the electrolyte, reduce its gas generation amount at high temperature, which is beneficial to improving the high-temperature storage performance and cycling performance of the battery cell.

[0029] In some embodiments, the electrolyte further includes a lithium salt, and the lithium salt includes lithium bis(fluorosulfonyl)imide and lithium hexafluorophosphate. Based on the mass of the electrolyte, the ratio of the mass content of lithium bis(fluorosulfonyl)imide to the mass content of lithium hexafluorophosphate is 0.3 to 1.2.

[0030] Therefore, when the ratio of the mass contents of lithium hexafluorophosphate and lithium bis(fluorosulfonyl)imide in the embodiments of the present application satisfies the above range, on the one hand, the content of hydrofluoric acid can be reduced, the side reactions at the negative electrode interface can be slowed down, and the gas generation amount during high-temperature storage can be reduced; on the other hand, the content of the organic components in the interface film formed at the negative electrode interface is appropriate, which can also reduce the gas generation amount during high-temperature storage and is beneficial to improving the cycle life of the battery cell.

[0031] In some embodiments, based on the mass of the electrolyte, the mass content of lithium bis(fluorosulfonyl)imide is 2% to 11%. When the mass content of lithium bis(fluorosulfonyl)imide is in the above range, the content of hydrofluoric acid can be reduced, the side reactions at the negative electrode interface can be slowed down, the gas generation amount during high-temperature storage can be reduced, and it is beneficial to improving the cycle life of the battery cell.

[0032] In some embodiments, based on the mass of the electrolyte, the mass content of lithium hexafluorophosphate is 3% to 14%. When the mass content of lithium hexafluorophosphate is in the above range, the conductivity of the electrolyte is relatively high, which is beneficial to the migration of lithium ions and improves the fast charging performance of the battery cell.

[0033] In some embodiments, the electrolyte further includes one or more of fluorinated cyclic carbonates and vinylene carbonate. The fluorinated cyclic carbonate can form an interface film rich in lithium fluoride (LiF) on the surface of the negative electrode, which can relieve the volume expansion of silicon, improve the life of the silicon-containing system, and reduce the gas generation amount at high temperature, being beneficial to improving the high-temperature storage performance and cycle performance of the battery cell. The interface film formed by vinylene carbonate on the surface of the negative electrode is denser, can more effectively protect the silicon-containing negative electrode, reduce the degree of side reactions at the negative electrode interface, reduce the gas generation amount at high temperature, and is beneficial to improving the high-temperature storage performance and cycle performance of the battery cell.

[0034] In some embodiments, the fluorinated cyclic carbonate includes at least one of fluoroethylene carbonate, difluoroethylene carbonate, and trifluoropropylene carbonate.

[0035] In some embodiments, based on the mass of the electrolyte, the mass content of the fluorinated cyclic carbonate is 0.5% to 20%. When the mass content of the fluorinated cyclic carbonate is in the above range, an excellent interface film can be formed, which has an excellent protective effect on the negative electrode and is beneficial to improving the high-temperature storage performance and cycle performance of the battery cell.

[0036] In some embodiments, based on the mass of the electrolyte, the mass content of vinylene carbonate is 0.1% to 3%. Vinylene carbonate participates in the formation of the negative electrode interface film, can form an excellent interface film, has an excellent protective effect on the negative electrode, and is beneficial to improving the high-temperature storage performance and cycle performance of the battery cell.

[0037] In some embodiments, based on the mass of the electrolyte, the mass content of the fluorinated cyclic carbonate is 0.5% to 10%; the mass content of silicon element of the silicon-based material in the negative electrode active material is 0.3% to 7.5%. When the mass content of the fluorinated cyclic carbonate and the mass content of the silicon element meet the above conditions, the volume expansion of silicon can be more effectively alleviated, the lifespan of the silicon-containing system can be improved, the gas generation amount at high temperature can be reduced, which is beneficial to improving the high-temperature storage performance and cycling performance of the battery cell.

[0038] In some embodiments, based on the mass of the electrolyte, the mass content of the fluorinated cyclic carbonate is greater than 10% and less than or equal to 20%; the mass content of silicon element of the silicon-based material in the negative electrode active material is greater than 7.5% and less than or equal to 15%. When the mass content of the fluorinated cyclic carbonate and the mass content of the silicon element meet the above conditions, the volume expansion of silicon can be more effectively alleviated, the lifespan of the silicon-containing system can be improved, and the gas generation amount at high temperature can be reduced. In some embodiments, the battery cell further includes a positive electrode plate, which includes a positive electrode current collector and a positive electrode film layer disposed on at least one side of the positive electrode current collector. The positive electrode film layer includes a positive electrode active material, and the single-sided coating weight of the positive electrode film layer is 250 mg / 1540.25 mm 2 to 300 mg / 1540.25 mm 2 .

[0039] When the single-sided coating weight of the positive electrode film layer is within the above range, the heat generation amount per unit area of the positive electrode plate will not be too large, so that the heat in the battery cell system will not accumulate too much, reducing the risk of high-temperature decomposition of the electrolyte and improving the cycling performance of the battery cell.

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

[0041] In a second aspect, an embodiment of the present application further provides a battery device, including the battery cell according to any one of the embodiments in the first aspect of the present application.

[0042] In a third aspect, an embodiment of the present application further provides an electrical device, which includes the battery device according to any one of the embodiments in the second or third aspect of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following will briefly introduce the drawings required to be used in the embodiments of the present application. Obviously, the following described drawings are only some embodiments of the present application. For those of ordinary skill in the art, other drawings can be obtained according to the drawings without creative efforts.

[0044] Figure 1It is a schematic structural diagram of an electrical device provided by some embodiments of the present application.

[0045] Figure 2 It is a schematic structural diagram of a battery pack provided by some embodiments of the present application; Figure 3 It is a schematic structural diagram of a battery module provided by some embodiments of the present application; Figure 4 It is a schematic structural diagram of a battery cell provided by some embodiments of the present application; Figure 5 It is a schematic structural diagram of an electrode assembly of a battery cell provided by some embodiments of the present application; Figure 6 It is a schematic structural diagram of a negative electrode tab of a battery cell provided by some embodiments of the present application.

[0046] The drawings are not necessarily drawn to actual scale.

[0047] The description of the reference numerals is as follows: X, the thickness direction; 1, electrical device; 2, battery pack; 3, controller; 4, motor; 5, housing; 5a, first housing part; 5b, second housing part; 5c, accommodation space; 6, battery module; 7, battery cell; 10, electrode assembly; 11, positive electrode tab; 12, negative electrode tab; 121, negative electrode film layer; 122, negative electrode current collector; 1211, first negative electrode film layer; 1212, second negative electrode film layer; 121a, first region; 121b, second region; 121c, third region; 13, separator; 20, outer shell assembly; 21, housing; 22, end cap; 23, electrode terminal. Detailed Embodiments

[0048] Hereinafter, embodiments of the battery cell, battery device, and electrical device of the present application that are specifically disclosed will be described in detail with appropriate reference to the drawings. However, there may be cases where unnecessary detailed descriptions are omitted. For example, there are cases where detailed descriptions of well-known matters and repeated descriptions of actually identical structures are omitted. This is to avoid making the following description unnecessarily lengthy and to facilitate the understanding of those skilled in the art. In addition, the drawings and the following description are provided for those skilled in the art to fully understand the present application and are not intended to limit the subject matter recited in the claims.

[0049] The "ranges" disclosed in this application are defined in the form of a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundaries of a particular range. The ranges defined in this way can include or exclude the end values, and can be combined arbitrarily, that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60 to 120 and 80 to 110 are listed for a specific parameter, ranges of 60 to 110 and 80 to 120 are also contemplated. In addition, if the minimum range values 1 and 2 are listed, and if the maximum range values 3, 4, and 5 are listed, the following ranges are all contemplated: 1 to 3, 1 to 4, 1 to 5, 2 to 3, 2 to 4, and 2 to 5. In this application, unless otherwise specified, the numerical range "a to b" represents an abbreviated representation of any real number combination between a and b, where a and b are both real numbers. For example, the numerical range "0 to 5" means that all real numbers between "0 to 5" are fully listed herein, and "0 to 5" is only an abbreviated representation of these numerical combinations. Additionally, when stating that a certain parameter is an integer ≥2, it is equivalent to disclosing that the parameter is, for example, the integers 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0050] If there is no special instruction, all embodiments and optional embodiments of this application can be combined with each other to form a new technical solution. If there is no special instruction, all technical features and optional technical features of this application can be combined with each other to form a new technical solution. If there is no special instruction, all steps of this application can be carried out sequentially or randomly, preferably sequentially. For example, a method includes steps (a) and (b), which means that the method can include steps (a) and (b) carried out sequentially, or can also include steps (b) and (a) carried out sequentially. For example, when it is mentioned that the method may further include step (c), it means that step (c) can be added to the method in any order. For example, the method can include steps (a), (b), and (c), or can also include steps (a), (c), and (b), or can also include steps (c), (a), and (b), etc.

[0051] The term "a plurality of" as used in this application refers to two or more (including two).

[0052] With the rapid development of the battery field, the performance requirements for battery cells are gradually increasing. For example, with the improvement of the fast charging performance requirements, in the related art, it can be achieved by increasing the conductivity of the electrolyte. However, the increase in conductivity may cause the electrolyte to decompose at high temperatures, resulting in an increase in the gas generation amount of the battery cell at high temperatures, an increase in the volume expansion rate of the battery cell, and may deteriorate the cycle performance of the battery cell.

[0053] In view of the above problems, the embodiments of the present application improve the cycle performance and fast charging performance of battery cells by synergistically regulating the negative electrode sheet and the electrolyte. Specifically, the negative electrode sheet of the battery cell includes a silicon-containing negative electrode active material, which, in combination with a relatively small coating weight, is conducive to the rapid migration of active ions and improves the fast charging ability of the battery cell. Under fast charging conditions, the silicon-containing negative electrode active material is more likely to react with the electrolyte, resulting in an increase in the gas generation at high temperature. However, the embodiments of the present application also cooperate with an electrolyte containing an appropriate amount of carboxylate ester, which can alleviate the side reaction between the negative electrode active material and the electrolyte while enabling the rapid migration of active ions such as lithium ions, reducing the gas generation at high temperature, reducing the volume expansion rate of the battery cell, improving the high-temperature storage performance of the battery cell, and facilitating the improvement of the cycle performance of the battery cell due to the alleviation of the side reaction at the negative electrode interface.

[0054] The battery cell of the present application is applicable to various battery devices and electrical devices that use battery cells.

[0055] Exemplarily, the electrical device can be a mobile phone, a portable device, a laptop computer, an electric vehicle, an electric toy, an electric tool, a vehicle, a ship, a spacecraft, etc. Alternatively, exemplarily, the electrical device is a spacecraft, and the spacecraft includes an airplane, a rocket, a space shuttle, a spaceship, etc.

[0056] Figure 1 It is a schematic diagram of an electrical device 1 as an example. The electrical device 1 is a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, etc. In order to meet the requirements of the electrical device 1 for high power and high energy density, a battery pack or a battery module can be adopted.

[0057] A battery device is provided inside the electrical device 1, and the battery device can be provided at the bottom, the head, or the tail of the electrical device 1. The battery device can be used to supply power to the electrical device 1. For example, the battery device can be used as the operating power source of the electrical device 1 and can also be used as the driving power source of the electrical device 1, replacing or partially replacing fuel or natural gas to provide driving power for the electrical device 1. Figure 1 The battery device shown in is a battery pack 2.

[0058] The electrical device 1 may further include a controller 3 and a motor 4. The controller 3 is used to control the battery device to supply power to the motor 4. For example, it is used for the working power requirements during the start-up, navigation, and driving of the electrical device 1.

[0059] A Battery Apparatus may include one or more Battery Cell Assemblies for providing voltage and capacity. A Battery Cell Assembly may include a plurality of battery cells, and the plurality of battery cells are connected in series, parallel, or in a combined series-parallel manner through busbar components.

[0060] In some embodiments, a Battery Cell Assembly is generally formed by arranging a plurality of battery cells.

[0061] As an example, the Battery Cell Assembly can be a Battery Module, which is formed by arranging and fixing a plurality of battery cells into an independent module. As an example, the Battery Module can be formed by bundling a plurality of battery cells with cable ties.

[0062] As Figure 2 shown, in some embodiments, the Battery Apparatus can be a Battery Pack 2, which includes a housing 5 and one or more Battery Cell Assemblies, and the Battery Cell Assemblies are accommodated in the housing 5. As an example, the Battery Cell Assemblies can also be accommodated in the housing 5 by directly fixing a plurality of battery cells to the housing 5.

[0063] As an example, the housing 5 includes a first housing part 5a and a second housing part 5b, and the housing 5 has an accommodation space 5c. The first housing part 5a and the second housing part 5b are snapped together so that a closed space is formed inside the housing 5 to accommodate the Battery Cell Assembly. Here, "closed" means covered or closed, which can be sealed or non-sealed. The first housing part 5a can be a top cover or a bottom plate.

[0064] As an example, the housing 5 can include a top cover, a frame, and a bottom plate. The top cover and the bottom plate are respectively connected to the frame so that a closed space is formed inside the housing 5 to accommodate the Battery Cell Assembly.

[0065] In some embodiments, the housing 5 can be part of the chassis structure of a vehicle. For example, a part of the housing 5 can become at least a part of the floor of the vehicle, or a part of the housing 5 can become at least a part of the crossbeam and longitudinal beam of the vehicle.

[0066] As an example, the Battery Cell Assembly can be a Battery Module 6, and the Battery Cell Assembly can be accommodated in the housing 5 by fixing the Battery Module 6 to the housing 5.

[0067] As Figure 3 shown, the Battery Module 6 includes a plurality of battery cells 7.

[0068] As Figure 4 and Figure 5As shown, in some embodiments, the battery cell 7 includes an electrode assembly 10 and a housing assembly 20.

[0069] The housing assembly 20 has a receiving cavity for receiving the electrode assembly 10 and the electrolyte.

[0070] In some embodiments, the housing assembly 20 includes a housing and electrode terminals 23, and the electrode terminals 23 are disposed on the housing.

[0071] The housing can be a steel shell, an aluminum shell, a plastic shell (such as polypropylene), a composite metal shell (such as a copper-aluminum composite housing), or an aluminum plastic film, etc. In some embodiments, the housing can be a sealed structure or a non-sealed structure. As an example, when the housing is a non-sealed structure, the housing serves to protect the electrode assembly 10, and a sealing bag is further included between the housing and the electrode assembly 10, and the sealing bag is used to encapsulate the electrode assembly 10 and the electrolyte. Specifically, the sealing bag can be a bag-shaped insulating member or an aluminum plastic film. When the housing is a sealed structure, it is used to encapsulate components such as the electrode assembly 10 and the electrolyte.

[0072] As an example, the battery cell 7 can be a cylindrical battery cell, a prismatic battery cell, a soft-pack battery cell, or a battery cell of other shapes. The prismatic battery cell includes a square-shell battery cell, a blade-shaped battery cell, and a multi-prismatic battery. The multi-prismatic battery is, for example, a hexagonal-prismatic battery, etc., and there is no special limitation in this application.

[0073] In some embodiments, the housing includes an end cap 22 and a housing body 21. The housing body 21 is provided with an opening, and the end cap 22 covers the opening. The housing body 21 can be provided with one or more openings. The end cap 22 can also be provided with one or more.

[0074] 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 is a cylindrical structure, a housing body 21 with a cylindrical structure can be selected; if the electrode assembly 10 is 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 are cuboid structures.

[0075] The electrode terminals 23 can be disposed on the housing body 21, or the electrode terminals 23 are disposed on the end cap 22. The electrode terminals 23 are electrically connected to the tabs of the electrode plates. The electrode terminals 23 can be directly connected to the tabs or indirectly connected to the tabs through a current collector member. The electrode assembly 10 can be a wound structure, a stacked structure, or a hybrid structure of winding and stacking.

[0076] In some embodiments, the electrode assembly 10 is a wound structure. The positive electrode plate 11 and the negative electrode plate 12 are wound into a wound structure.

[0077] In some embodiments, the electrode assembly 10 is a stacked structure.

[0078] As an example, a plurality of positive electrode plates 11 and negative electrode plates 12 can be provided respectively, and the plurality of positive electrode plates 11 and the plurality of negative electrode plates 12 are alternately stacked.

[0079] As an example, a plurality of positive electrode plates 11 can be provided, and the negative electrode plate 12 is folded to form a plurality of stacked folding segments, and a positive electrode plate 11 is clamped between adjacent folding segments.

[0080] As an example, both the positive electrode plate 11 and the negative electrode plate 12 are folded to form a plurality of stacked folding segments.

[0081] As an example, a plurality of separators 13 can be provided and are respectively arranged between any adjacent positive electrode plates 11 or negative electrode plates 12.

[0082] As an example, the separators 13 can be continuously provided and are arranged between any adjacent positive electrode plates 11 or negative electrode plates 12 by folding or winding.

[0083] In some embodiments, the shape of the electrode assembly 10 can be cylindrical, flat, prismatic, etc.

[0084] In some embodiments, the electrode assembly 10 is provided with tabs, and the tabs can lead the current out of the electrode assembly 10. The tabs include a positive tab and a negative tab. The electrode assembly 10 can adopt a wound structure or a stacked structure, and the stacked structure is preferably selected, which is beneficial to improving the energy density of the battery cell 7.

[0085] In some embodiments, the battery cell 7 includes a negative electrode plate 12 and an electrolyte. The negative electrode plate 12 includes a negative current collector and a negative electrode film layer provided on at least one side of the negative current collector. The negative electrode film layer includes a negative electrode active material. The negative electrode active material includes a silicon-based material and a carbon-based material. The mass content of silicon element in the silicon-based material in the negative electrode active material is 0.3% to 15%. The single-sided coating weight of the negative electrode film layer is 80 mg / 1540.25 mm 2 to 150 mg / 1540.25 mm 2 ; The electrolyte includes an organic solvent. The organic solvent includes a carboxylic acid ester solvent. The mass content of the carboxylic acid ester solvent in the electrolyte 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 plate 11 to the negative electrode plate 12 through the electrolyte. The mass content of the carboxylic acid ester solvent in the electrolyte is greater than or equal to 3%, so that the migration rate of the active ions in the electrolyte is relatively fast; The negative electrode plate 12 includes a silicon-based material, and the mass content of silicon element in the negative electrode active material is greater than or equal to 0.3%, which is beneficial to reducing the coating thickness. The coating weight of the negative electrode film layer is 80 mg / 1540.25 mm 2 to 150 mg / 1540.25 mm 2 , which is beneficial to shortening the migration path of lithium ions and improving the migration rate of lithium ions; Through the cooperation of the coating weight of the negative electrode film layer and the components in the electrolyte, it is beneficial to improve the fast charging ability of the battery cell 7; The increase in the mass content of silicon element is beneficial to the improvement of energy density, and the increase in the addition amount of carboxylic ester solvent is beneficial to the improvement of the migration rate of lithium ions. However, with the increase in the mass content of silicon element and the mass content of carboxylic ester solvent, the interfacial reaction between the silicon-based material and the electrolyte intensifies, and the gas generation amount at high temperature increases. Therefore, in the embodiments of the present application, the mass content of silicon element is further controlled to be less than or equal to 15%, and the mass content of carboxylic ester solvent in the electrolyte is less than or equal to 70%, so as to relieve the interfacial side reaction between the negative electrode active material and the electrolyte, reduce the gas generation amount at high temperature, improve the high-temperature storage performance of the battery cell, and since the interfacial side reaction on the negative electrode side is relieved, it is beneficial to improve the cycle performance of the battery cell 7, especially the cycle performance under fast charging conditions.

[0087] Negative electrode sheet The negative electrode plate includes a negative electrode current collector and a negative electrode film layer provided on at least one side of the negative electrode current collector and including a negative electrode active material. For example, the negative electrode current collector has two surfaces opposite to each other in its own thickness direction, and the negative electrode film layer is provided on any one or both of the two opposite surfaces of the negative electrode current collector.

[0088] The charging upper limit voltage and the discharging cut-off voltage of the battery cell are different according to different positive electrode active materials. For example, when the phosphate material includes lithium iron phosphate, the charging upper limit voltage can be 3.65 V and the discharging cut-off voltage can be 2.0 V, or the charging upper limit voltage can be 3.8 V and the discharging cut-off voltage can be 2.0 V; again, for example, when the phosphate material includes lithium manganese iron phosphate, the charging upper limit voltage can be 4.3 V and the discharging cut-off voltage can be 2.0 V. Next, taking the charging upper limit voltage of 3.8 V and the discharging cut-off voltage of 2.0 V as an example, the state of the battery cell will be described: In the embodiments of the present application, the 100% state of charge SOC and the 0% state of charge SOC of the battery cell are defined as follows, The battery cell is charged at a constant current charging rate of 0.33 C to the charging upper limit voltage, and then charged at a constant voltage to 0.05 C, corresponding to the state of 100% SOC of the battery cell. The battery cell is discharged at a constant current discharging rate of 0.33 C to the cut-off voltage, corresponding to the state of 0% SOC of the battery cell.

[0089] In some embodiments, when the battery cell is at 0% state of charge (SOC), the compaction density of the negative electrode film layer is 1.1 g / cm 3 to 1.7 g / cm 3 . Exemplarily, when the battery cell is at 0% state of charge, the compaction density of the negative electrode film layer is 1.10 g / cm³, 1.12 g / cm³, 1.14 g / cm³, 1.16 g / cm³, 1.18 g / cm³, 1.20 g / cm³, 1.22 g / cm³, 1.24 g / cm³, 1.26 g / cm³, 1.28 g / cm³, 1.3 g / cm 3 , 1.32 g / cm 3 , 1.35 g / cm 3 , 1.40 g / cm 3 , 1.45 g / cm 3 , 1.50 g / cm 3 , 1.55 g / cm 3 , 1.60 g / cm 3 , 1.65 g / cm 3 , 1.66 g / cm³, 1.68 g / cm³, 1.70 g / cm³ or a range composed of any two of the above values.

[0090] When the compaction density of the negative electrode film layer is within the above range, the thickness of the negative electrode film layer will not be too thick, which is beneficial to the rapid charging of the battery cell; moreover, the particle packing of the negative electrode active material will not be too tight, reducing the risk of particle crushing and being beneficial to improving the cycling performance of the battery cell.

[0091] In some embodiments, the single-sided coating weight of the negative electrode film layer is 80 mg / 1540.25 mm 2 to 150 mg / 1540.25 mm 2 . Exemplarily, the single-sided coating weight of the negative electrode film layer is 80 mg / 1540.25 mm², 85 mg / 1540.25 mm², 90 mg / 1540.25 mm², 95 mg / 1540.25 mm², 100 mg / 1540.25 mm², 105 mg / 1540.25 mm², 110 mg / 1540.25 mm², 115 mg / 1540.25 mm², 120 mg / 1540.25 mm², 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 mm2 、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 、180 mg / 1540.25 mm 2 or a range composed of any two of the above values.

[0092] When the single-sided coating weight of the negative electrode film layer meets the above range, in combination with an appropriate mass content of silicon element, it is beneficial to improve the energy density of the battery cell, and the migration rate of active ions in the negative electrode film layer is relatively fast, which is beneficial to improving the fast charging ability of the battery cell.

[0093] In the embodiments of the present application, the compaction density of the negative electrode film layer of the battery cell in the 0% state of charge (SOC) has the meaning well-known in the art, that is, the negative electrode pole piece is disassembled from the battery cell in the 0% state of charge (SOC), and the compaction density of the negative electrode film layer is measured. For example, take the negative electrode pole piece with single-sided coating (if it is a pole piece with double-sided coating, one side of the negative electrode film layer can be wiped off first), punch it into small round pieces with an area of S1, weigh it, record it as M1, and measure its thickness H1. Then wipe off the negative electrode film layer of the above-mentioned weighed negative electrode pole piece, weigh the weight of the negative electrode current collector, record it as M0, and measure its thickness H0. The single-sided coating weight of the negative electrode film layer = (the weight M1 of the negative electrode pole piece - the weight M0 of the negative electrode current collector) / S1, the thickness of the negative electrode film layer = the thickness H1 of the negative electrode pole piece - the thickness H0 of the negative electrode current collector, and the compaction density of the negative electrode film layer = the single-sided coating weight of the negative electrode film layer / the thickness of the negative electrode film layer.

[0094] In some embodiments, the negative electrode active material includes a silicon-based material. Optionally, the silicon-based material may include at least one of elemental silicon, silicon-carbon composite, and silicon oxide SiO x (0 < x ≤ 2). The above materials can improve the capacity of the negative electrode active material, which is beneficial to reducing the coating thickness of the negative electrode film layer and shortening the migration path of lithium ions.

[0095] In some embodiments, the specific surface area of the silicon-based material is 1 m 2 / g to 4 m2 / g, such as 1 m² / g, 1.2 m² / g, 1.4 m² / g, 1.5 m² / g, 1.6 m² / g, 1.8 m² / g, 2 m² / g, 2.2 m² / g, 2.4 m² / g, 2.5 m² / g, 2.6 m² / g, 2.8 m² / g, 3 m² / g, 3.2 m² / g, 3.4 m² / g, 3.5 m² / g, 3.6 m² / g, 3.8 m² / g, 4 m² / g or a range composed of any two of the above values.

[0096] When the specific surface area of the silicon-based material is within the above range, it can provide appropriate embedding sites for lithium ions, improving the fast charging ability; it can also alleviate the side reaction between the silicon-based material and the electrolyte, reduce the gas generation amount at high temperature, and improve the cycle performance of the battery cell under fast charging conditions.

[0097] In the embodiments of the present application, the specific surface area of the material has the meaning well-known in the art, and can be detected by using the equipment and methods well-known in the art. For example, it can be detected according to the test standard GB / T 19587-2017. The negative electrode tab in the battery cell can be disassembled to obtain the relevant material as a sample, and the specific surface area can be tested by a Tri-Star 3020 specific surface area and pore size analyzer of Micromeritics Company in the United States.

[0098] In some embodiments, the silicon-based material is granular, and its average particle size is 4 μm to 12 μm, such as 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, 12 μm or a range composed of any two of the above values.

[0099] When the average particle size of the silicon-based material is within the above range, it can alleviate the side reaction between the silicon-based material and the electrolyte, reduce the gas generation amount at high temperature, and improve the cycle performance of the battery cell; and it can provide appropriate embedding sites for lithium ions, improving the fast charging ability.

[0100] In some embodiments, the negative electrode active material includes a carbon-based material, and the carbon-based material has high cycle stability and can improve the cycle performance of the battery cell.

[0101] Optionally, the carbon-based material includes at least one of artificial graphite and natural graphite.

[0102] In some embodiments, in addition to the above-mentioned carbon-based material and optionally the silicon-based material, the negative electrode active material may further include at least one of a tin-based material and lithium titanate. The tin-based material may include at least one of elemental tin, tin oxide and tin alloy material.

[0103] In this application, the qualitative and quantitative analysis of various substances or elements can be detected by suitable equipment and methods known to those skilled in the art. Relevant detection methods can refer to domestic and foreign detection standards, domestic and foreign enterprise standards, etc. And those skilled in the art can also adaptively change certain detection steps / instrument parameters from the perspective of detection accuracy to obtain more accurate detection results. One detection method can be used for qualitative or quantitative analysis, or several detection methods can be used in combination for qualitative or quantitative determination.

[0104] For example, this application can combine the general rules of X-ray diffraction analysis method in JIS / K0131-1996 to conduct X-ray powder diffraction test and qualitative analysis on the negative electrode plate or negative electrode active material.

[0105] Artificial graphite and natural graphite can be distinguished by the SEM cross-section pictures taken by scanning electron microscope (SEM). There are voids between flaky structures in the SEM cross-section picture of natural graphite, while the SEM cross-section picture of artificial graphite is dense and has no obvious gaps, or they can be distinguished by the XRD spectrum obtained by X-ray diffraction method. There are obvious 2H phase and 3R phase in the XRD spectrum of natural graphite, while the XRD spectrum of artificial graphite only has 2H phase.

[0106] Such as Figure 6 As shown, in the embodiment of this application, the negative electrode film layer 121 of the negative electrode plate 12 includes at least one layer of film layer, which can be a single-layer film layer or at least two-layer film layers. Optionally, the negative electrode film layer 121 includes at least two-layer film layers.

[0107] When the negative electrode film layer 121 adopts a single-layer film layer, the negative electrode active material in the negative electrode film layer 121 includes carbon-based material and optional silicon-based material.

[0108] When the negative electrode film layer 121 adopts at least two-layer film layers, the negative electrode active material in the negative electrode film layer 121 includes carbon-based material and silicon-based material. The negative electrode film layer 121 can include two-layer film layers, three-layer film layers, four-layer film layers, or even more film layers.

[0109] In some embodiments, the negative electrode film layer 121 includes a first negative electrode film layer 1211 and a second negative electrode film layer 1212. The first negative electrode film layer 1211 is disposed on the surface of the negative electrode current collector 122, and the negative electrode active material of the first negative electrode film layer 1211 includes 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 includes carbon-based material. The interface between the first negative electrode film layer 1211 and the second negative electrode film layer 1212 can be regular or irregular, optionally irregular; or there is no obvious interface between the first negative electrode film layer 1211 and the second negative electrode film layer 1212.

[0110] The negative electrode film layer 121 includes at least two film layers, and the layered coating is beneficial to taking into account the improvement of the fast charging performance and cycle life of the battery cell.

[0111] In some embodiments, at least one of the first negative electrode film layer 1211 and the second negative electrode film layer 1212 includes a silicon-based material.

[0112] Optionally, the first negative electrode film layer 1211 further includes a silicon-based material.

[0113] Optionally, the second negative electrode film layer 1212 further includes a silicon-based material.

[0114] Exemplarily, the first negative electrode film layer 1211 includes a carbon-based material and a silicon-based material, and the second negative electrode film layer 1212 includes a carbon-based material and a silicon-based material. Or, the first negative electrode film layer 1211 includes a carbon-based material and a silicon-based material, and the second negative electrode film layer 1212 includes a carbon-based material. Or, the first negative electrode film layer 1211 includes a carbon-based material, and the second negative electrode film layer 1212 includes a carbon-based material and a silicon-based material.

[0115] When both the first negative electrode film layer 1211 and the second negative electrode film layer 1212 include a silicon-based material, it is more beneficial to improve the energy density of the battery cell. When the first negative electrode film layer 1211 includes a silicon-based material and the second negative electrode film layer 1212 does not include a silicon-based material, the second negative electrode film layer 1212 can relieve the volume expansion of the first negative electrode film layer 1211, reduce the side reaction between the negative electrode film layer 121 and the electrolyte, and improve the cycle performance.

[0116] When the negative electrode film layer 121 adopts at least two film layers, along the thickness direction X of the negative electrode film layer 121, the cross-sectional morphology of the negative electrode film layer 121 can be the same or similar, and of course, it can also be different.

[0117] Along the thickness direction X of the negative electrode film layer 121, the negative electrode film layer 121 is divided into three regions, namely the first region 121a, the third region 121c, and the second region 121b in sequence. The first region 121a is the region of the negative electrode film layer 121 close to the negative electrode current collector 122 along the thickness direction X, and the thickness of the first region 121a is 1 / 3 of the thickness of the negative electrode film layer 121; the second region 121b is the region of the negative electrode film layer 121 away from the negative electrode current collector 122 along the thickness direction X, and the thickness of the second region 121b is 1 / 3 of the thickness of the negative electrode film layer 121.

[0118] The cross-sectional morphologies of the first region 121a and the second region 121b can be the same or similar, and of course, they can also be different. The cross-sectional morphologies of the first region 121a and the third region 121c can be the same or similar, and of course, they can also be different. The cross-sectional morphologies of the second region 121b and the third region 121c can be the same or similar, and of course, they can also be different.

[0119] There may or may not be an obvious layer interface between the first region 121a, the second region 121b, and the third region 121c. For example, the first negative electrode film layer 1211 includes the first region 121a, the second negative electrode film layer 1212 includes the second region 121b, the third region 121c may be a part of the first negative electrode film layer 1211, or the third region 121c may be a part of the second negative electrode film layer 1212, or the third region 121c may be a part of both the first negative electrode film layer 1211 and the second negative electrode film layer 1212.

[0120] In some embodiments, in a cross-section of the negative electrode film layer 121 parallel to the thickness direction X, the void ratio of a single carbon-based material located in the first region 121a is greater than or equal to the void ratio of a single carbon-based material located in the second region 121b. Optionally, the void ratio of a single carbon-based material located in the first region 121a is less than the void ratio of a single carbon-based material located in the second region 121b.

[0121] The carbon-based material is granular and has voids inside. In a cross-section of the negative electrode film layer 121 parallel to the thickness direction X, the percentage of the void area in the total cross-sectional area of the carbon-based material is the void ratio of a single carbon-based material.

[0122] During the charging process of the battery cell, lithium ions diffuse from the second region 121b to the first region 121a. When the void ratio of a single carbon-based material in the first region 121a is less than or equal to the void ratio of a single carbon-based material in the second region 121b, it is more conducive to the diffusion of lithium ions in the first region 121a, improving the transmission rate, and thus facilitating the rapid charging of the battery cell.

[0123] Optionally, the average particle size of the carbon-based material in the first region 121a may be greater than or equal to the average particle size of the carbon-based material in the second region 121b. Further optionally, the average particle size of the carbon-based material in the first region 121a may be greater than the average particle size of the carbon-based material in the second region 121b, which is beneficial for the rapid migration of lithium ions from the second region 121b to the first region 121a and improves the rapid charging ability of the battery cell. Of course, the average particle size of the carbon-based material in the first region 121a may be less than the average particle size of the carbon-based material in the second region 121b.

[0124] Optionally, the average particle size of the carbon-based material in the first negative electrode film layer 1211 may be greater than or equal to the average particle size of the carbon-based material in the second negative electrode film layer 1212. Further optionally, the average particle size of the carbon-based material in the first negative electrode film layer 1211 may be greater than the average particle size of the carbon-based material in the second negative electrode film layer 1212.

[0125] There are differences in the particle sizes of the first negative electrode film layer 1211 and the second negative electrode film layer 1212, which can improve the fast charging performance of the battery cell. Specifically, during the fast charging process, the overpotential of the second negative electrode film layer 1212 is usually relatively high, and the bottleneck of fast charging mainly lies in the second negative electrode film layer 1212. In the embodiments of the present application, the particle size of the second negative electrode film layer 1212 is relatively small, which can shorten the solid-phase transmission path of lithium ions, improve the fast charging performance, and can also improve the problem of lithium deposition on the surface of the negative electrode sheet 12.

[0126] Optionally, the average particle size of the carbon-based material in the first region 121a is 12 μm to 21 μm, such as 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, 21 μm or the range composed of any two of the above values. When the average particle size of the carbon-based material in the first region 121a is within the above range, the cycle life can be improved, and it will basically not have an adverse impact on the fast charging performance.

[0127] Optionally, the average particle size of the carbon-based material in the first negative electrode film layer 1211 is 12 μm to 21 μm. When 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 it will basically not have an adverse impact on the fast charging performance.

[0128] Optionally, the average particle size of the carbon-based material in the second region 121b is 9 μm to 17 μm, such as 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, 17 μm or the range composed of any two of the above values. When the average particle size of the carbon-based material in the second negative electrode film layer 1212 is within the above range, it is beneficial to improve the fast charging ability of the battery cell and improve the stability of the material.

[0129] Optionally, the average particle size of the carbon-based material in the second negative electrode film layer 1212 is 9 μm to 17 μm. When the average particle size of the carbon-based material in the second negative electrode film layer 1212 is within the above range, it can shorten the solid-phase transmission path of lithium ions, improve the fast charging performance and the stability of the material.

[0130] Exemplarily, the carbon-based material in the first region 121a includes artificial graphite and natural graphite, and the carbon-based material in the second region 121b includes artificial graphite. For example, the negative electrode active material in the first region 121a includes a silicon-based material, artificial graphite, and natural graphite, and the negative electrode active material in the second region 121b includes a silicon-based material and artificial graphite.

[0131] Exemplarily, the carbon-based material in the first negative electrode film layer 1211 includes artificial graphite and natural graphite, and the carbon-based material in the second negative electrode film layer 1212 includes artificial graphite. For example, the negative electrode active material in the first negative electrode film layer 1211 includes a silicon-based material, artificial graphite, and natural graphite, and the negative electrode active material in the second negative electrode film layer 1212 includes a silicon-based material and artificial graphite.

[0132] In some other embodiments, in a cross-section of the negative electrode film layer 121 parallel to the thickness direction X, the void ratio of a single carbon-based material in the first region 121a is less than that of a single carbon-based material in the second region 121b.

[0133] During the charging process of the battery cell, lithium ions diffuse from the second region 121b to the first region 121a. The larger void ratio of a single carbon-based material in the second region 121b is beneficial for the rapid transmission of lithium ions from the second region 121b to the first region 121a, thereby facilitating the rapid charging of the battery cell.

[0134] Optionally, the average particle size of the carbon-based material in the first region 121a may be smaller than that of the carbon-based material in the second region 121b. The relatively larger average particle size of the carbon-based material in the second region 121b results in higher pressure resistance during the preparation of the film layer, which is beneficial for improving the particle compactness; the relatively smaller average particle size of the carbon-based material in the first region 121a enables the rapid migration of lithium ions and can improve the rapid charging ability of the battery cell. Of course, the average particle size of the carbon-based material in the first region 121a may be greater than or equal to that of the carbon-based material in the second region 121b.

[0135] Optionally, the average particle size of the carbon-based material in the first region 121a is 9 μm to 17 μm, such as 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, 17 μm or a range composed of any two of the above values.

[0136] Optionally, the average particle size of the carbon-based material in the first negative electrode film layer 1211 is 9 μm to 17 μm.

[0137] Optionally, the average particle size of the carbon-based material in the second region 121b is from 12 μm to 21 μm, such as 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, 21 μm, or a range composed of any two of the above values.

[0138] Optionally, the average particle size of the carbon-based material in the second negative electrode film layer 1212 is from 12 μm to 21 μm.

[0139] Exemplarily, the carbon-based material in the second region 121b includes artificial graphite and natural graphite, and the carbon-based material in the first region 121a includes artificial graphite. Optionally, the negative electrode active material further includes a silicon-based material. For example, the negative electrode active material in the second region 121b includes a silicon-based material, artificial graphite, and natural graphite, and the negative electrode active material in the first region 121a includes a silicon-based material and artificial graphite.

[0140] Exemplarily, the carbon-based material in the second negative electrode film layer 1212 includes artificial graphite and natural graphite, and the carbon-based material in the first negative electrode film layer 1211 includes artificial graphite. Optionally, the negative electrode active material further includes a silicon-based material. For example, the negative electrode active material in the second negative electrode film layer 1212 includes a silicon-based material, artificial graphite, and natural graphite, and the negative electrode active material in the first negative electrode film layer 1211 includes a silicon-based material and artificial graphite.

[0141] In the embodiments of the present application, for the average particle size of the active material in the first region 121a and the second region 121b, the following equipment and method can be used for detection: taking the negative electrode plate 12 as a sample, and taking a scanning electron microscope (SEM) photograph along the thickness direction X of the negative electrode film layer 121 to obtain an SEM cross-sectional view, counting the particle sizes of the active material in the SEM cross-section, and calculating the average particle size of the active material according to the counted quantity.

[0142] In some embodiments, the negative electrode film layer may optionally further include a negative electrode conductive agent. The embodiments of the present application do not particularly limit the type of the negative electrode conductive agent. As an example, the negative electrode conductive agent may include at least one of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. In some embodiments, based on the total weight of the negative electrode film layer, the mass content of the negative electrode conductive agent is ≤5%.

[0143] In some embodiments, the negative electrode film layer may optionally further include a negative electrode binder. In some embodiments, based on the total weight of the negative electrode film layer, the mass content of the negative electrode binder is ≤5%.

[0144] In some embodiments, the negative electrode film layer may optionally further include other additives. As an example, the other additives may include thickeners, dispersants, etc., for example, sodium carboxymethyl cellulose (CMC-Na), PTC thermistor materials, etc. In some embodiments, based on the total weight of the negative electrode film layer, the mass content of the other additives is ≤2%.

[0145] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. As an example of the metal foil, at least one foil of copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy may be used. The composite current collector may include a polymer material base layer and a metal material layer formed on at least one surface of the polymer material base layer. As an example, the metal material in the metal material layer may include at least one of copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy. As an example, the polymer material base layer may include at least one of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0146] The negative electrode film layer is generally formed by coating a negative electrode slurry on a negative electrode current collector and then drying and cold pressing. The negative electrode slurry is generally formed by dispersing a negative electrode active material, an optional conductive agent, an optional binder, and other optional additives in a solvent and stirring evenly. The solvent may be N-methylpyrrolidone (NMP) or deionized water, but is not limited thereto.

[0147] The negative electrode plate does not exclude other additional functional layers other than the negative electrode film layer. For example, in some embodiments, the negative electrode plate of the present application embodiment further includes a negative electrode conductive layer sandwiched between the negative electrode current collector and the negative electrode film layer and disposed on the surface of the negative electrode current collector. In some other embodiments, the negative electrode plate of the present application embodiment further includes a protective layer covering the surface of the negative electrode film layer.

[0148] Positive electrode sheet In some embodiments, the battery cell further includes a positive electrode plate.

[0149] The positive electrode plate includes a positive electrode current collector and a positive electrode film layer disposed on at least one side of the positive electrode current collector and including a positive electrode active material. For example, the positive electrode current collector has two opposite surfaces in its own thickness direction, and the positive electrode film layer is disposed on any one or both of the two opposite surfaces of the positive electrode current collector.

[0150] In some embodiments, the size of the positive electrode film layer in the length direction of the positive electrode plate is 200 mm to 600 mm, for example, 200 mm, 250 mm, 300 mm, 350 mm, 400 mm, 450 mm, 500 mm, 550 mm, 600 mm, or a range composed of any two of the above values.

[0151] In the case of a laminated structure of the electrode assembly, the length direction of the positive electrode sheet is parallel to the length direction of the battery cell, and the size of the positive electrode film layer along the length direction can be understood as the length of the positive electrode film layer. The width direction of the positive electrode sheet is parallel to the width direction of the battery cell, and the size of the positive electrode film layer along the width direction can be understood as the width of the positive electrode film layer.

[0152] Exemplarily, the dimension of the positive electrode film layer along the length direction is 200mm to 600mm; the electrolyte includes an organic solvent, the organic solvent includes a carboxylic acid ester solvent, and the conductivity of the electrolyte at room temperature is 9mS / cm to 18mS / cm. The length of the positive electrode film layer is matched with the electrolyte of the above conductivity, which is conducive to improving the liquid phase transmission rate of lithium ions, improving the kinetic performance, and improving the fast charging ability of the battery cell; and because the viscosity of the carboxylic acid ester solvent is relatively low, it can evenly infiltrate the positive electrode film layer, so that the charging degree of the positive electrode film layer is uniform, and the lithium ions released from the positive electrode film layer are evenly distributed on the negative electrode side, reducing the risk of local side reactions on the negative electrode side, and improving the cycle performance under fast charging.

[0153] In some embodiments, the compaction density of the positive electrode film layer of the battery cell at 0% state of charge SOC is 2.20 g / cm 3 Up to 2.85g / cm 3 For example, when the battery cell is at 0% state of charge SOC, the compaction density of the positive electrode film layer is 2.20 g / cm 3 , 2.25g / cm 3 , 2.30g / cm 3 , 2.32g / cm 3 , 2.35g / cm 3 , 2.38g / cm 3 , 2.40g / cm 3 , 2.42g / cm 3 , 2.45g / cm 3 , 2.48g / cm 3 , 2.50g / cm 3 , 2.52g / cm 3 , 2.55g / cm 3 , 2.56g / cm 3 , 2.57g / cm 3 , 2.58g / cm 3 , 2.60g / cm 3 , 2.62g / cm 3 , 2.65g / cm 3 , 2.68g / cm 3 , 2.70g / cm 3 , 2.75g / cm 3, 2.80 g / cm 3 , 2.85 g / cm 3 or a range composed of any two of the above values.

[0154] When the compaction density of the positive electrode film layer is within the above range, it is beneficial to improve the energy density of the battery cell; and since the positive active material of the positive electrode film layer is stacked relatively tightly, the contact resistance between particles is small, which can further reduce the resistance of the electrode sheet, thereby reducing the heat generation during rapid charging, reducing the gas generation at high temperature, and improving the cycle performance of the battery cell.

[0155] In some embodiments, the single-sided coating weight of the positive electrode film layer is 250 mg / 1540.25 mm 2 to 300 mg / 1540.25 mm 2 . Exemplarily, the single-sided coating weight of the positive electrode film layer is 250 mg / 1540.25 mm 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 , 300 mg / 1540.25 mm 2 or a range composed of any two of the above values.

[0156] When the single-sided coating weight of the positive electrode film layer is within the above range, the heat generation per unit area of the positive electrode sheet will not be too large, and it can take into account improving the energy density and charging rate performance of the battery cell, and prevent excessive heat accumulation in the battery cell system, reduce the risk of high-temperature decomposition of the electrolyte, and improve the cycle performance of the battery cell.

[0157] In the embodiments of the present application, the compaction density of the positive electrode film layer of the battery cell in the 0% state of charge (SOC) has the meaning well known in the art, that is, the positive electrode sheet is disassembled from the battery cell in the 0% state of charge (SOC), and the compaction density of the positive electrode film layer is measured. For example, for a single-sided coated positive electrode sheet (if it is a double-sided coated sheet, one side of the positive electrode film layer can be wiped off first), it is punched into small round pieces with an area of S1, weighed, recorded as M1, and its thickness H1 is measured. Then, the positive electrode film layer of the above-mentioned weighed positive electrode sheet is wiped off, and the weight of the positive electrode current collector is weighed and recorded as M0, and its thickness H0 is measured. The single-sided coating weight of the positive electrode film layer = (the weight M1 of the positive electrode sheet - the weight M0 of the positive electrode current collector) / S1, the thickness of the positive electrode film layer = the thickness H1 of the positive electrode sheet - the thickness H0 of the positive electrode current collector, and the compaction density of the positive electrode film layer = the single-sided coating weight of the positive electrode film layer / the thickness of the positive electrode film layer.

[0158] In some embodiments, the positive electrode active material includes one or more of a lithium-containing transition metal oxide and a lithium-containing phosphate. Optionally, the positive electrode active material includes a lithium-containing phosphate. The lithium-containing phosphate may have an olivine structure, which is stable in structure during charge and discharge and can improve the cycle life of the battery cell.

[0159] 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.

[0160] In some embodiments, the positive electrode film layer further includes a carbon-containing material, and the carbon-containing material is a carbon-containing conductive material. The above materials can improve the conductivity of the positive electrode film layer and are beneficial to improving the fast charging performance of the battery cell.

[0161] Optionally, the mass content of carbon element in the positive electrode film layer is 0.8% to 3.5%, such as 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%, 3.5% or a range composed of any two of the above values. Optionally, the mass content of carbon element in the positive electrode film layer is 1.3% to 3.0%.

[0162] For example, the carbon-containing material may include carbon nanotubes, and the carbon nanotubes can be used as a conductive agent in the positive electrode film layer to improve the conductivity of the positive electrode film layer.

[0163] For another example, the lithium-containing phosphate with an olivine structure may be an unmodified lithium-containing phosphate such as lithium iron phosphate, or a material obtained by coating and modifying it. For example, a carbon-containing material is provided on the surface of the lithium-containing phosphate, and the carbon-containing material can be used as a coating layer to coat the surface of the lithium-containing phosphate, thereby improving the conductivity of the lithium-containing phosphate, reducing the powder resistivity of the material, being beneficial to the migration rate of lithium ions, improving the fast charging ability of the battery cell, and reducing the heat generation of the battery cell.

[0164] In some embodiments, the lithium-containing phosphate includes a general formula of Li x1 A y1 Me a M b P 1-c X c Y zA compound, 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 includes one or more of Na, K, and Mg, Me includes one or more of Mn, Fe, Co, and Ni, M includes one or more of B, Mg, Al, Si, P, S, Ca, Sc, Ti, V, Cr, Cu, Zn, Sr, Y, Zr, Nb, Mo, Cd, Sn, Sb, Te, Ba, Ta, W, Yb, La, and Ce, X includes one or more of Cl, C, and N, and Y includes one or more of O and F. The lithium-containing phosphate has excellent cycle stability, which is beneficial to improving the cycle performance of the battery cell.

[0165] Exemplarily, the lithium-containing phosphate includes one or more of LiFePO4, LiMnPO4, LiNiPO4, and LiCoPO4. During the charge and discharge process of the battery cell, the insertion and extraction and consumption of active ions such as Li will occur. The molar content of Li is different when the battery cell is discharged to different states. In the listing of the cathode active materials such as LiFePO4, LiMnPO4, LiNiPO4, and LiCoPO4, the molar content of Li is the initial state of the material, that is, the state before feeding. When the cathode active material is applied to the battery system and undergoes charge and discharge cycles, the molar content of Li may change. In the embodiments of the present application, in the listing of the cathode active materials such as LiFePO4, LiMnPO4, LiNiPO4, and LiCoPO4, the molar content of oxygen O is only the theoretical state value. The release of oxygen from the lattice will cause the molar content of oxygen O to change. Actually, the molar content of oxygen O will fluctuate, and the above situations are all within the protection scope of the present application.

[0166] In the embodiments of the present application, the content of elements in the cathode active material has the meaning well-known in the art and can be detected by equipment and methods well-known in the art. For example, referring to EPA 6010D-2014, it is tested by inductively coupled plasma atomic emission spectrometry and determined by inductively coupled plasma optical emission spectrometry (ICP-OES, instrument model: Thermo ICAP7400). After the battery cell is discharged to 0% state of charge (SOC) and the cathode electrode sheet is disassembled, it is cleaned with dimethyl carbonate (DMC) and dried, and then after high-temperature calcination to remove impurities, 0.4 g of the cathode active material is weighed, and 10 ml (50% concentration) of aqua regia is added thereto. Then it is placed on a flat plate at 180 °C for 30 min. After digestion on the flat plate, it is fixed to a volume of 100 mL, and quantitative testing is carried out by the standard curve method.

[0167] In some embodiments, the lithium-containing phosphate is granular. The lithium-containing phosphate includes a plurality of first phosphate particles and a plurality of second phosphate particles. The longest diameter of the first phosphate particles is greater than or equal to a preset longest diameter, such as 1 μm, and the longest diameter of the second phosphate particles is less than 1 μm. It can be understood that the particles with a longest diameter greater than or equal to 1 μm all belong to the first phosphate particles, and the particles with a longest diameter less than 1 μm all belong to the second phosphate particles; The longest diameter of the first phosphate particles is greater than that 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.

[0168] Exemplarily, the average longest diameter of the first phosphate particles is 1 μm to 5 μm, such as 1 μm, 1.5 μm, 2 μm, 2.5 μm, 3 μm, 3.5 μm, 4 μm, 4.5 μm, 5 μm or the range composed of any two of the above values.

[0169] Exemplarily, the average longest diameter of the second phosphate particles is 0.1 μm to 0.5 μm, such as 0.1 μm, 0.15 μm, 0.2 μm, 0.25 μm, 0.3 μm, 0.35 μm, 0.4 μm, 0.45 μm, 0.5 μm or the range composed of any two of the above values.

[0170] When the lithium-containing phosphate meets the above conditions, its longest diameter is relatively small, the lithium deintercalation / insertion path of lithium ions in the lithium-containing phosphate is short, and the heat generation is less; moreover, the particle size of the above lithium-containing phosphate is not too small, and basically no agglomeration occurs during the processing and preparation process, making the performance of the lithium-containing phosphate stable; thus, it is beneficial to improve the high-temperature cycle performance of the battery cell.

[0171] In some embodiments, the mass content of the second phosphate particles in the lithium-containing phosphate is 80% to 95%, such as 80%, 82%, 84%, 85%, 86%, 88%, 90%, 92%, 94%, 95% or the range composed of any two of the above values. When the mass content of the second phosphate particles is within an appropriate range, such as 80% to 95%, it can further reduce the heat generation, reduce the heat generation in the battery cell system, reduce the risk of decomposition of the electrolyte components due to heat accumulation, and improve the high-temperature cycle performance of the battery cell.

[0172] In some embodiments, the positive electrode film layer further includes a lithium supplement agent. The lithium supplement agent includes lithium element and can release lithium ions during the charging process of the battery cell to make up for lithium loss, which is beneficial to improving the capacity characteristics and high-temperature cycle performance of the battery cell.

[0173] In some embodiments, the lithium supplement agent includes at least one of lithium ferrite, lithium nickelate, and lithium cobaltate.

[0174] In some embodiments, the lithium supplement agent is granular, and its average longest diameter is from 9 μm to 13 μm, such as 9 μm, 9.5 μm, 10 μm, 10.5 μm, 11 μm, 11.5 μm, 12 μm, 12.5 μm, 13 μm or the range composed of any two of the above.

[0175] In some embodiments, the lithium supplement agent is granular, and its average shortest diameter is from 5 μm to 9 μm, such as 5 μm, 5.5 μm, 6 μm, 6.5 μm, 7 μm, 7.5 μm, 8 μm, 8.5 μm, 9 μm or the range composed of any two of the above.

[0176] In the embodiments of the present application, the positive electrode sheet is cut along the thickness direction of the sheet 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 diameter and the shortest diameter of the lithium supplement agent particles and the longest diameter of the lithium-containing phosphate are determined. For example, the "longest diameter" of a particle refers to the longest straight line passing through the center point of the particle and extending to the outer periphery of the particle. The "shortest diameter" of a particle refers to the shortest straight line passing through the center point of the particle and extending to the outer periphery of the particle.

[0177] In the cross-section of the positive electrode film layer along its own thickness direction, the longest diameters of multiple, for example, 10 lithium supplement agents are statistically counted, and the average value calculated is the average longest diameter; the shortest diameters of multiple, for example, 10 lithium supplement agents are statistically counted, and the average value calculated is the average shortest diameter.

[0178] In the cross-section of the positive electrode film layer along its own thickness direction, the longest diameters of multiple, for example, 50 lithium-containing phosphate particles are statistically counted. The particles with the longest diameter greater than or equal to 1 μm belong to the first phosphate particles, and the particles with the longest diameter less than 1 μm belong to the second phosphate particles. The average value of the longest diameters of all the first phosphate particles is calculated as the average longest diameter of the first phosphate particles, and the average value of the longest diameters of all the second phosphate particles is calculated as the average longest diameter of the second phosphate particles; The number of all the first phosphate particles and the number of all the second phosphate particles are statistically counted, and the proportion of the number of the second phosphate particles is calculated as the mass content of the second phosphate particles in the lithium-containing phosphate.

[0179] In some embodiments, based on the total mass of the positive electrode film layer, the mass proportion of the lithium supplement agent is from 0.5% to 3%, such as 0.5%, 0.6%, 0.8%, 1.0%, 1.2%, 1.4%, 1.6%, 1.8%, 2.0%, 2.5%, 3.0% or the range composed of any two of the above. When using the lithium supplement agent within the above mass range, it can effectively improve the stability of the lithium supplement agent while also having a good oxygen release effect.

[0180] In some embodiments, the positive electrode film layer may further optionally include a positive electrode conductive agent. As an example, the positive electrode conductive agent includes at least one of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. In some embodiments, based on the mass of the positive electrode film layer, the mass content of the positive electrode conductive agent is ≤5%.

[0181] Optionally, the positive electrode conductive agent includes carbon nanotubes, and the mass content of the carbon nanotubes in the positive electrode film layer is 0.1% to 2%, such as 0.1%, 0.3%, 0.5%, 0.7%, 0.9%, 1.1%, 1.3%, 1.5%, 1.7%, 1.9%, 2% or the range composed of any two of the above. Optionally, the mass content of the carbon nanotubes in the positive electrode film layer is 0.15% to 1.2%.

[0182] When the mass content of the carbon nanotubes is within the above range, it is beneficial to improve the conductivity of the positive electrode film layer and improve the fast charging performance of the battery cell.

[0183] Optionally, the specific surface area of the carbon nanotubes is 500 m 2 / g to 2500 m 2 / g, such as 500 m² / g, 700 m² / g, 900 m² / g, 1100 m² / g, 1300 m² / g, 1500 m² / g, 1700 m² / g, 1900 m² / g, 2100 m² / g, 2300 m² / g, 2500 m² / g or the range composed of any two of the above.

[0184] When the specific surface area of the carbon nanotubes is within the above range, it is beneficial to improve the electron conduction ability; and with an appropriate content of carbon nanotubes, the degree of side reactions can be reduced and the gas generation at high temperature can be improved.

[0185] Optionally, the diameter of the carbon nanotubes is 0.5 nm to 20 nm, 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, 20 nm or the range composed of any two of the above. Optionally, the diameter of the carbon nanotubes is 0.5 nm to 7.5 nm.

[0186] When the diameter of the carbon nanotubes is within the above range, the structure is relatively stable and has relatively excellent electron conduction ability.

[0187] Carbon nanotubes can generally be considered to be formed by curling two-dimensional carbon materials. When the number of curled layers is a single layer, it is a single-walled carbon nanotube; when curled into multiple layers, it is a multi-walled carbon nanotube. The diameter of a carbon nanotube is the outer diameter of the carbon nanotube on a cross-section perpendicular to its own central axis.

[0188] In some embodiments, the positive electrode film layer may optionally further include a positive electrode binder. There is no particular limitation on the type of the positive electrode binder in the embodiments of the present application. As an example, the positive electrode binder may include at least one of polyvinylidene fluoride, polytetrafluoroethylene, vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, polyacrylic acid, and fluorinated acrylate resins. In some embodiments, based on the mass of the positive electrode film layer, the mass content of the positive electrode binder is ≤5%.

[0189] In some embodiments, the positive electrode current collector may be a metal foil or a composite current collector. As an example of the metal foil, at least one foil of aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy may be used. The composite current collector may include a polymer material base layer and a metal material layer formed on at least one surface of the polymer material base layer. As an example, the metal material of the metal material layer may include at least one of aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy. As an example, the polymer material base layer may include at least one of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0190] The positive electrode film layer is usually formed by coating a positive electrode slurry on a positive electrode current collector and then drying and cold pressing. The positive electrode slurry is usually formed by dispersing a positive electrode active material, an optional conductive agent, an optional binder, and any other components in a solvent and stirring evenly. The solvent may be N-methylpyrrolidone (NMP), but is not limited thereto.

[0191] The positive electrode plate does not exclude other additional functional layers besides the positive electrode film layer. For example, in some embodiments, the positive electrode plate of the embodiments of the present application further includes a positive electrode conductive layer sandwiched between the positive electrode current collector and the positive electrode film layer and disposed on the surface of the positive electrode current collector. In some other embodiments, the positive electrode plate of the embodiments of the present application further includes a protective layer covering the surface of the positive electrode film layer.

[0192] [Electrolyte] During the charge and discharge process of the battery cell, active ions such as lithium ions shuttle between the positive electrode plate and the negative electrode plate for insertion and extraction, and the electrolyte plays a role in conducting active ions between the positive electrode plate and the negative electrode plate. The electrolyte includes an organic solvent and an electrolyte salt.

[0193] In some embodiments, the conductivity of the electrolyte at room temperature is from 9 mS / cm to 18 mS / cm. Exemplarily, the conductivity of the electrolyte 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, 18 mS / cm or a range composed of any two of the above values.

[0194] When the conductivity of the electrolyte at room temperature, such as 25 °C, is within the above range, the migration rate of lithium ions in the electrolyte is relatively high, which can further reduce the internal resistance of the battery cell, thereby reducing heat generation and the high-temperature gas generation caused by heat accumulation, and can improve the cycle performance of the battery cell under fast charging.

[0195] In the embodiments of the present application, the conductivity of the electrolyte at room temperature, such as 25 °C, is the ionic conductivity, and it can be detected by using equipment and methods well known in the art. For example, it can be tested with reference to the industry standard HG-T 4067-2015.

[0196] In some embodiments, the organic solvent includes a carboxylic acid ester solvent.

[0197] Optionally, the mass content of the carboxylic acid ester solvent in the electrolyte is from 3% to 70%. Exemplarily, the mass content 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%, 70% or a range composed of any two of the above values. Optionally, the mass content of the carboxylic acid ester solvent in the electrolyte is from 5% to 30%.

[0198] When the mass content of the carboxylic acid ester solvent is within the above range, it can improve the conductivity of the electrolyte; and the electrolyte is compatible with the silicon-containing negative electrode, which can effectively alleviate the side reactions on the negative electrode side, reduce the high-temperature gas generation of the battery cell, and can improve the cycle performance of the battery cell under fast charging.

[0199] Exemplarily, the carboxylic acid ester solvent includes a cyclic carboxylic acid ester, and the cyclic carboxylic acid ester includes one or more of γ-butyrolactone, γ-valerolactone and δ-valerolactone. The viscosity of the above materials is relatively low, which can improve the wetting ability of the electrode sheet and improve the cycle performance under fast charging.

[0200] Exemplarily, the carboxylic acid ester solvents include chain carboxylic acid esters, and the chain carboxylic acid esters include one or more of methyl acetate, ethyl acetate, propyl acetate, butyl acetate, propyl propionate, and butyl propionate. The viscosity of the above materials is relatively low, which can improve the wetting ability of the electrode sheet and improve the cycle performance under fast charging.

[0201] In some embodiments, the organic solvent includes carbonate solvents. The carbonate solvents and carboxylic acid ester solvents are used in combination, which can improve the stability of the electrolyte, reduce its gas generation amount at high temperature, and can improve the cycle performance of the battery cell.

[0202] Exemplarily, the carbonate solvents include one or more of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate. Optionally, the carbonate solvents include one or more of ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate.

[0203] In some embodiments, the electrolyte salt includes lithium salts, and the lithium salts include one or more of lithium bis(fluorosulfonyl)imide and lithium hexafluorophosphate. Optionally, the lithium salts include lithium bis(fluorosulfonyl)imide and lithium hexafluorophosphate.

[0204] Lithium hexafluorophosphate may decompose to produce hydrofluoric acid HF, and the side reaction between hydrofluoric acid and the negative electrode, especially the silicon-containing negative electrode, may lead to an increase in gas generation during high-temperature storage; the compound use of lithium hexafluorophosphate and lithium bis(fluorosulfonyl)imide can reduce the content of hydrofluoric acid, slow down the side reaction at the negative electrode interface, reduce the gas generation amount during high-temperature storage, and is beneficial to improving the cycle life of the battery cell.

[0205] In some embodiments, based on the mass of the electrolyte, the ratio of the mass content of lithium bis(fluorosulfonyl)imide to the mass content of lithium hexafluorophosphate is 0.3 to 1.2, such as 0.3, 0.5, 0.7, 0.9, 1.1, 1.2 or the range composed of any two of the above values.

[0206] When the ratio of the mass contents of lithium hexafluorophosphate and lithium bis(fluorosulfonyl)imide satisfies the above range, on the one hand, it can reduce the content of hydrofluoric acid, slow down the side reaction at the negative electrode interface, and can reduce the gas generation amount during high-temperature storage; on the other hand, the content of the organic component of the SEI film formed at the negative electrode interface is appropriate, which can also reduce the gas generation amount during high-temperature storage and is beneficial to improving the cycle life of the battery cell.

[0207] Exemplarily, based on the mass of the electrolyte, the mass content of lithium bis(fluorosulfonyl)imide 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%, 11% or a range composed of any two of the above values. When the mass content of lithium bis(fluorosulfonyl)imide is within the above range, the content of hydrofluoric acid can be reduced, the side reaction at the negative electrode interface can be slowed down, the gas generation amount during high-temperature storage can be reduced, and it is beneficial to improve the cycle life of the battery cell.

[0208] Exemplarily, based on the mass of the electrolyte, the mass content of lithium hexafluorophosphate 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%, 14% or a range composed of any two of the above values. When the mass content of lithium hexafluorophosphate is within the above range, the conductivity of the electrolyte is relatively high, which is beneficial to the migration of lithium ions and improves the fast charging performance of the battery cell.

[0209] In some embodiments, the electrolyte further includes additives. The additives can include negative electrode film-forming additives, or can include positive electrode film-forming additives, and can also include additives that can improve certain performance of the battery, such as additives for improving the overcharge performance of the battery, additives for improving the high-temperature performance of the battery, additives for improving the low-temperature power performance of the battery, etc.

[0210] In some embodiments, the additives include cyclic carbonate additives, such as including one or more of fluorinated cyclic carbonates and vinylene carbonate. Optionally, the additives include fluorinated cyclic carbonates and vinylene carbonate.

[0211] The fluorinated cyclic carbonate can form an interfacial film rich in lithium fluoride LiF on the surface of the negative electrode, which can relieve the volume expansion of silicon, improve the life of the silicon-containing system, and reduce the gas generation amount at high temperature. The fluorinated cyclic carbonate and vinylene carbonate are used in combination, making the interfacial film on the surface of the negative electrode denser, which can more effectively protect the silicon-containing negative electrode, reduce the degree of side reaction at the negative electrode interface, and reduce the gas generation amount at high temperature.

[0212] Optionally, the fluorinated cyclic carbonate includes at least one of fluoroethylene carbonate, difluoroethylene carbonate, and trifluoropropylene carbonate.

[0213] Optionally, based on the mass of the electrolyte, the mass content of the fluorinated cyclic carbonate 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%, 20% or a range composed of any two of the above values. When the mass content of the fluorinated cyclic carbonate is within the above range, it is beneficial to improve the cycling performance.

[0214] As an example, based on the mass of the electrolyte, the mass content of the fluorinated cyclic carbonate is 0.5% to 10%; the mass content of silicon element in the silicon-based material in the negative electrode active material is 0.3% to 7.5%.

[0215] The mass content of silicon element is relatively high and the volume expansion is relatively larger. When the mass content of the fluorinated cyclic carbonate and the mass content of silicon element meet the above conditions, the volume expansion of silicon can be more effectively alleviated, the life of the silicon-containing system can be improved, and the gas generation amount at high temperature can be reduced. As another example, based on the mass of the electrolyte, the mass content of the fluorinated cyclic carbonate is greater than 10% and less than or equal to 20%, and the mass content of silicon element in the silicon-based material in the negative electrode active material is greater than 7.5% and less than or equal to 15%.

[0216] When the mass content of the fluorinated cyclic carbonate and the mass content of silicon element meet the above conditions, the volume expansion of silicon can be more effectively alleviated, the life of the silicon-containing system can be improved, and the gas generation amount at high temperature can be reduced. Optionally, based on the mass of the electrolyte, the mass content of vinylene carbonate 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%, 3% or a range composed of any two of the above values. The vinylene carbonate with the above mass content makes the SEI film on the negative electrode surface denser, can more effectively protect the negative electrode active material, reduce the degree of side reactions at the negative electrode interface, and improve the cycling performance.

[0217] When the vinylene carbonate and the fluorinated cyclic carbonate with the above mass contents are used in combination, the performance of the SEI film on the negative electrode surface is further optimized, with excellent denseness and low impedance, can more effectively protect the negative electrode active material, reduce the degree of side reactions at the negative electrode interface, and improve the cycling performance.

[0218] In the embodiments of the present application, the types and contents of inorganic components / lithium salts in the electrolyte have meanings well-known in the art and can be detected using equipment and methods well-known in the art. For example, reference can be made to the standard JY / T 020-1996 General Rules for Ion Chromatographic Analysis Methods to qualitatively or quantitatively analyze the inorganic components / lithium salts in the electrolyte by ion chromatography. In the embodiments of the present application, newly prepared electrolyte can be taken as a sample, free electrolyte of a fresh battery can be taken as a sample, or a discharged battery (discharged to the lower cut-off voltage such that the charged state of the battery is approximately 0% SOC) can be reverse disassembled, and the free electrolyte obtained from the battery can be taken as a sample for detection using ion chromatography.

[0219] In the embodiments of the present application, the types and contents of organic components in the electrolyte have meanings well-known in the art and can be detected using equipment and methods well-known in the art. For example, reference can be made to GB / T 9722-2006 General Rules for Gas Chromatography of Chemical Reagents to qualitatively and quantitatively analyze the organic components in the electrolyte by gas chromatography.

[0220] In the embodiments of the present application, after quantitatively and qualitatively detecting each component in the electrolyte, each component is classified. Carboxylic ester solvents and carbonate solvents are used as the constituent components of organic solvents, and based on the mass of the electrolyte being 100%, the mass content of each component is calculated. Fluorinated cyclic carbonates and vinylene carbonate are used as additives to the electrolyte, and based on the mass of the electrolyte being 100%, the mass content of each component is calculated.

[0221] Separator In some embodiments, the electrode assembly further includes a separator disposed between the positive electrode sheet and the negative electrode sheet.

[0222] In some embodiments, the separator is a separator membrane. The present application does not particularly limit the type of the separator membrane, and any well-known porous structure separator membrane with good chemical stability and mechanical stability can be selected.

[0223] As an example, the main material of the separator membrane can be selected from at least one of glass fiber, non-woven fabric, polyethylene, polypropylene, polyvinylidene fluoride, and ceramics. The separator membrane can be a single-layer film or a multi-layer composite film, without particular limitation. When the separator membrane is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation. The separator can be a single component located between the positive and negative electrodes or attached to the surfaces of the positive and negative electrodes. An inorganic particle coating, an organic particle coating, or an organic / inorganic composite coating can also be coated on the surface of the separator membrane.

[0224] In some embodiments, the separator is a solid electrolyte. The solid electrolyte is disposed between the positive electrode and the negative electrode, and functions to transport ions and isolate the positive and negative electrodes simultaneously.

[0225] Example The following examples more specifically describe the content disclosed in the embodiments of the present application. These examples are only for illustrative purposes, because various modifications and changes within the scope of the content disclosed in the embodiments of the present application are obvious to those skilled in the art. Unless otherwise stated, all parts, percentages, and ratios reported in the following examples are based on mass, and all reagents used in the examples are commercially available or synthesized according to conventional methods and can be used directly without further treatment, and the instruments used in the examples are all commercially available.

[0226] Example 1 1. Preparation of the positive electrode sheet The positive electrode sheet includes a positive electrode current collector and positive electrode film layers provided on both sides of the positive electrode current collector. The positive electrode current collector is aluminum foil.

[0227] The positive electrode film layer includes lithium iron phosphate, binder polyvinylidene fluoride (PVDF), and conductive agent super P with a mass ratio of 97:2:1. The positive electrode film layer is a film layer formed by uniformly coating the positive electrode slurry (solvent is N-methylpyrrolidone NMP) on both sides of the positive electrode current collector and drying and cold pressing.

[0228] The lithium iron phosphate is sourced from Hunan Yuneng New Energy Battery Materials Co., Ltd.

[0229] 2. Preparation of the negative electrode sheet The negative electrode sheet includes a negative electrode current collector and negative electrode film layers provided on both sides of the negative electrode current collector. The negative electrode current collector is copper foil.

[0230] The negative electrode film layer is a film layer formed by uniformly coating the negative electrode slurry (solvent is deionized water) on the surface of the negative electrode current collector and drying and cold pressing.

[0231] The negative electrode film layer includes a first negative electrode film layer and a second negative electrode film layer. The first negative electrode film layer is located on the surface of the negative electrode current collector, and the second negative electrode film layer is located on the surface of the first negative electrode film layer.

[0232] The first negative electrode film layer includes a carbon-based material, silicon-based material silicon oxide, conductive agent acetylene black, negative electrode binder styrene-butadiene rubber, and thickening agent sodium carboxymethyl cellulose with a mass ratio of 87:9.5:1:1.5:1. The carbon-based material of the first negative electrode film layer includes artificial graphite and natural graphite with a mass ratio of 80%:20%, the average particle size of the carbon-based material is 18 μm, and the void ratio of a single carbon-based material is 20%.

[0233] The second negative electrode film layer includes a carbon-based material, a silicon-based material silicon oxide, a conductive agent acetylene black, a negative electrode binder styrene-butadiene rubber, and a thickening agent sodium carboxymethyl cellulose with a mass ratio of 87:9.5:1:1.5:1. The carbon-based material of the second negative electrode film layer includes artificial graphite. The average particle size of the carbon-based material is 15 μm, and the void ratio of a single carbon-based material is 25%.

[0234] The carbon-based material is sourced from Guangdong KINGFA New Energy Technology Co., Ltd.

[0235] 3. Separator The separator includes a base film and coatings provided on both sides of the base film. The base film is a 7-μm polyethylene film layer, and the coating is polyvinylidene fluoride with a surface density of 1.2 g / m 2 .

[0236] The separator is sourced from Shanghai Enjie New Materials Technology Co., Ltd.

[0237] 4. Preparation of electrolyte The electrolyte includes an organic solvent, a lithium salt, and an additive. After mixing the components of the organic solvent evenly, the lithium salt and the additive are added to prepare the electrolyte.

[0238] The organic solvent includes 25% of a chain carboxylic acid ester solvent ethyl acetate EA and 57% of a carbonate solvent (27% ethylene carbonate EC, 30% dimethyl carbonate DMC). The mass content of each component in the organic solvent is calculated based on the mass of the electrolyte.

[0239] The lithium salt includes 8% of lithium hexafluorophosphate LiPF6 and 6% of lithium bis(fluorosulfonyl)imide.

[0240] The additive includes 2% of a fluorinated cyclic carbonate fluoroethylene carbonate FEC and 2% of vinylene carbonate VC; The conductivity of the electrolyte is 14.2 mS / cm.

[0241] 5. Preparation of battery cell The above positive electrode sheet, separator, and negative electrode sheet are stacked in sequence, with the separator placed between the positive electrode sheet and the negative electrode sheet to play a separating role, obtaining an electrode assembly. The electrode assembly is placed in an outer packaging shell, dried, and then injected with the electrolyte. After processes such as vacuum packaging, standing, forming, and shaping, a battery cell is obtained. The compaction density of the positive electrode film layer of the battery cell at 0% SOC is 2.7 g / cm 3 , and the compaction density of the negative electrode film layer at 0% SOC is 1.45 g / cm 3 .

[0242] Comparative Example 1-1 and Comparative Example 1-2 Battery cells were prepared using a method similar to that of Example 1. Different from Example 1, the mass content of silicon element was adjusted.

[0243] Comparative Examples 1-3 and Comparative Example 1-4 The battery monomer was prepared by a method similar to that of Example 1. Different from Example 1, the coating weight of the negative electrode film layer was adjusted.

[0244] Examples 2-1 to Example 2-3 The battery monomer was prepared by a method similar to that of Example 1. Different from Example 1, the mass content of silicon element and the coating weight of the negative electrode film layer were adjusted.

[0245] Example 2-4 The battery monomer was prepared by a method similar to that of Example 1. Different from Example 1, the coating weights of the positive and negative electrode film layers were adjusted.

[0246] Examples 3-1 and Example 3-2 The battery monomer was prepared by a method similar to that of Example 1. Different from Example 1, the average particle size and specific surface area of the silicon-based material were adjusted.

[0247] Example 4 The battery monomer was prepared by a method similar to that of Example 1. Different from Example 1, the material of the silicon-based material was adjusted.

[0248] Performance test 1. Room temperature cycle performance test of the battery monomer Under the environment of 25°C, the fully discharged battery monomer was charged from 0.33C constant current to 10% SOC, then charged from 10% SOC to 80% SOC, and then charged to the charging upper limit voltage at 0.33C. After standing for 30 min, it was discharged to the discharge cut-off voltage at 1C. This was one charge-discharge cycle. The battery monomer was cycled for multiple circles until the discharge capacity of the battery monomer decayed to 90% (i.e., the battery health state reached 90% SOH). The more the number of cycle circles, the better the cycle performance of the battery monomer; Among them, the charging step from 10% SOC to 80% SOC includes: 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; Charge from 70% SOC to 75% SOC at 2.1 C; Charge from 75% SOC to 80% SOC at 1.9 C.

[0249] 2. High-temperature storage gas generation test of battery cells Under a 25°C environment, charge the battery cell at a constant current of 0.5 C until the charging upper limit voltage, then charge at a constant voltage until the current is 0.05 C. Use the water displacement method to measure the initial volume of the battery cell at this time and record it as V0. Then place the battery cell in an incubator at 60°C for 90 days. After storage, take it out and measure the volume of the battery cell again using the water displacement method and record it as V1. Test 10 battery cells in each group and take the average value.

[0250] Volume expansion rate (%) of the battery cell after 90 days of storage at 60°C = (V1 - V0) / V0 × 100%.

[0251] The test results are shown in Table 1.

[0252] Table 1

[0253] In Comparative Example 1-1, due to the relatively low mass content of silicon element, the coating weight of the negative electrode film layer is relatively high, and the high coating weight is not conducive to the migration of lithium ions and is not conducive to rapid charging; in Comparative Example 1-2, the mass content of silicon element is too high, resulting in a relatively high risk of side reactions occurring at the negative electrode side interface, gas generation intensifying, and the high-temperature storage performance and cycle performance deteriorating.

[0254] In the examples of the present application, by setting the mass content of silicon element within an appropriate range, the coating weight of the negative electrode film layer will not be too high, which is conducive to the rapid migration of lithium ions and improves the rapid charging ability of the battery cell; moreover, the mass content of silicon element will not be too high, which can alleviate the side reactions on the negative electrode side, reduce the high-temperature gas generation amount, and improve the high-temperature storage performance; because the side reactions on the negative electrode side are alleviated, the cycle performance of the battery cell can be improved, especially the cycle performance under rapid charging conditions.

[0255] In Comparative Example 1-3, the coating weight of the negative electrode film layer is too small, resulting in an overly thin electrode sheet, which is prone to breakage and deteriorates the cycle; in Comparative Example 1-4, the coating weight of the negative electrode film layer is too large, resulting in a relatively large lithium ion transmission resistance and being not conducive to rapid charging.

[0256] In Examples 2-1 to 2-4, the coating weight of the negative electrode film layer and the coating weight of the positive electrode film layer cooperate with each other, which is conducive to improving the migration rate of lithium ions in the positive and negative electrode film layers, making the resistance of the battery cell under rapid charging smaller; and the total amount of active materials participating in side reactions is less, which is conducive to improving the high-temperature storage performance and cycle life of the battery cell.

[0257] The embodiments of the present application are applicable to different silicon-based materials, such as silicon oxide materials and silicon carbide materials (such as silicon carbide). By setting the average particle size, specific surface area, etc. of the silicon-based materials within an appropriate range, the active area of the silicon-based materials is within an appropriate range, which can further alleviate the side reactions on the negative electrode side, reduce the gas generation amount at high temperature, and improve the high-temperature storage performance and cycling performance of the battery cell.

[0258] The embodiments of the present application are applicable to different positive electrode active materials, such as lithium iron phosphate materials, lithium iron manganese ferrite materials, or lithium iron phosphate materials mixed with transition metal oxides.

[0259] Examples 5-1 and 5-2 The battery cell was prepared by a method similar to that of Example 1. Different from Example 1, the average particle size of the carbon-based material was adjusted.

[0260] Example 6 The battery cell was prepared by a method similar to that of Example 1. Different from Example 1, the setting of the negative electrode film layer was adjusted. Specifically: the negative electrode film layer includes a first negative electrode film layer and a second negative electrode film layer. The first negative electrode film layer is located on the surface of the negative electrode current collector, and the second negative electrode film layer is located on the surface of the first negative electrode film layer.

[0261] The first negative electrode film layer includes a carbon-based material, silicon-based material silicon oxide, conductive agent acetylene black, negative electrode binder styrene-butadiene rubber, and thickener sodium carboxymethyl cellulose with a mass ratio of 87:9.5:1:1.5:1. The carbon-based material of the first negative electrode film layer includes artificial graphite, and the average particle size of the carbon-based material is 15 μm.

[0262] The second negative electrode film layer includes a carbon-based material, silicon-based material silicon oxide, conductive agent acetylene black, negative electrode binder styrene-butadiene rubber, and thickener sodium carboxymethyl cellulose with a mass ratio of 87:9.5:1:1.5:1. The carbon-based material of the second negative electrode film layer includes artificial graphite and natural graphite with a mass ratio of 80%:20%, and the average particle size of the carbon-based material is 18 μm.

[0263] The mass content of silicon element in the negative electrode active material of the negative electrode film layer is 5%.

[0264] The test results are shown in Table 2.

[0265] Table 2

[0266] By regulating the average particle size of the carbon-based material and / or the void ratio of a single carbon-based material, or making the average particle size of the carbon-based material in the first negative electrode film layer larger than that of the carbon-based material in the second negative electrode film layer, the solid-phase transport path of lithium ions can be shortened, the fast charging ability can be improved; and the risk of lithium deposition on the negative electrode side surface can be reduced, and the cycle performance and storage performance can be improved.

[0267] When the average particle size of the carbon-based material in the first negative electrode film layer is smaller than that of the carbon-based material in the second negative electrode film layer, the pore difference of the negative electrode film layer can be constructed, the fast charging ability can be improved, and the cycle performance under fast charging conditions can be enhanced.

[0268] Comparative Example 1-5 and Comparative Example 1-6 The battery monomer was prepared by a method similar to that of Example 1. Different from Example 1, the components and contents of the electrolyte were adjusted.

[0269] Examples 7-1 to Example 11 The battery monomer was prepared by a method similar to that of Example 1. Different from Example 1, the components and contents of the electrolyte were adjusted.

[0270] The test results are shown in Table 3.

[0271] Table 3

[0272] In Table 3, EA represents ethyl acetate; MA represents methyl acetate; EC represents ethylene carbonate; DMC represents dimethyl carbonate; EMC represents ethyl methyl carbonate; FEC represents fluoroethylene carbonate; DFEC represents difluoroethylene carbonate; EA: 25 means that the mass content of EA is 25%; EC: 27 means that the mass content of EC is 27%.

[0273] The mass ratio of lithium bis(fluorosulfonyl)imide / lithium hexafluorophosphate refers to the ratio of the mass content of lithium bis(fluorosulfonyl)imide to the mass content of lithium hexafluorophosphate. The meanings of other examples are the same as the above explanation and will not be elaborated here.

[0274] The conductivity of the electrolyte in Example 7-1 was 9 mS / cm, and the conductivity of the electrolyte in Example 7-2 was 18 mS / cm.

[0275] By regulating the components of the electrolyte to make the components of the electrolyte within an appropriate range, the side reactions on the negative electrode side can be effectively improved, the gas generation amount at high temperature can be reduced, and the cycle performance and fast charging performance can be improved.

[0276] The mass content of the carboxylic ester solvent in the embodiments of the present application is 3% to 70%, which can effectively improve the side reactions on the negative electrode side, reduce the gas generation amount during high-temperature storage, improve the high-temperature storage performance, and is beneficial to the improvement of the cycling performance of the battery cell under fast charging; In the embodiments of the present application, by using lithium hexafluorophosphate and lithium bis(fluorosulfonyl)imide in combination, for example, the ratio of the mass content of lithium bis(fluorosulfonyl)imide to the mass content of lithium hexafluorophosphate is 0.3 to 1.2, the content of hydrofluoric acid can be reduced, the side reactions at the negative electrode interface can be slowed down, the gas generation amount during high-temperature storage can be reduced, and it is beneficial to improve the cycle life of the battery cell.

[0277] The mass content of the fluorinated cyclic carbonate is 0.5% to 20%. The fluorinated cyclic carbonate can form a SEI film rich in lithium fluoride (LiF) on the surface of the negative electrode, which can relieve the volume expansion on the negative electrode side, improve the life of the negative electrode system, and improve the cycling performance. In Example 10, the mass content of silicon element is 12.5%, and in combination with 15% of vinylene carbonate fluoride, the surface of the negative electrode active material is effectively protected, which can further reduce the side reactions on the negative electrode side and improve the high-temperature storage performance and cycling performance.

[0278] Although the illustrative embodiments have been demonstrated and described, those skilled in the art should understand that the above embodiments cannot be construed as limitations on the embodiments of the present application, and the embodiments can be changed, substituted, and modified without departing from the spirit, principle, and scope of the embodiments of the present application.

Claims

1. A battery cell, characterized in that: include: A negative electrode sheet, comprising a negative electrode current collector and a negative electrode film layer disposed on at least one side of the negative electrode current collector, wherein the negative electrode film layer comprises a negative electrode active material, wherein the negative electrode active material comprises a silicon-based material and a carbon-based material, wherein the mass content of silicon element of the silicon-based material in the negative electrode active material is 0.3% to 15%, and the single-side coating weight of the negative electrode film layer is 80 mg / 1540.25 mm 2 Up to 150mg / 1540.25mm 2 ;as well as The electrolyte includes an organic solvent, wherein the organic solvent includes a carboxylate solvent, and the mass content of the carboxylate solvent in the electrolyte is 3% to 70%.

2. The battery cell according to claim 1, characterized in that: The specific surface area of ​​the silicon-based material is 1 m 2 / g to 4m 2 / g; and / or The silicon-based material is in granular form, and the average particle size thereof is 4 μm to 12 μm.

3. The battery cell according to claim 1 or 2, characterized in that: The silicon-based material includes one or more of silicon alone, silicon-carbon composites and silicon oxides.

4. The battery cell according to any one of claims 1 to 2, characterized in that: The negative electrode film layer comprises: A first region, which is a region of the negative electrode film layer close to the negative electrode current collector along its own thickness direction, and the thickness of the first region is 1 / 3 of the thickness of the negative electrode film layer; and The second region is a region of the negative electrode film layer away from the negative electrode current collector along the thickness direction, and the thickness of the second region is 1 / 3 of the thickness of the negative electrode film layer. Among them, in the cross section of the negative electrode film layer parallel to the thickness direction, the void ratio of the single carbon-based material located in the first region is smaller than the void ratio of the single carbon-based material located in the second region.

5. The battery cell according to claim 4, characterized in that: An average particle size of the carbon-based material in the first region is greater than or equal to an average particle size of the carbon-based material in the second region.

6. The battery cell according to claim 4, characterized in that: The average particle size of the carbon-based material in the first region is 12 μm to 21 μm; and / or The average particle size of the carbon-based material in the second region is 9 μm to 17 μm.

7. The battery cell according to claim 4, characterized in that: The carbon-based material of the first region includes artificial graphite and / or natural graphite; The carbon-based material of the second region includes artificial graphite.

8. The battery cell according to claim 4, characterized in that: An average particle size of the carbon-based material in the second region is greater than an average particle size of the carbon-based material in the first region.

9. The battery cell according to claim 8, characterized in that: The average particle size of the carbon-based material in the first region is 9 μm to 17 μm; and / or The average particle size of the carbon-based material in the second region is 12 μm to 21 μm.

10. The battery cell according to claim 8 or 9, characterized in that: The carbon-based material of the second region includes artificial graphite and / or natural graphite; The carbon-based material of the first region includes artificial graphite.

11. The battery cell according to any one of claims 1 to 2, characterized in that: The negative electrode film layer comprises: A first negative electrode film layer is disposed on the surface of the negative electrode current collector, wherein the negative electrode active material of the first negative electrode film layer includes a carbon-based material; and A second negative electrode film layer is connected to a side of the first negative electrode film layer away from the negative electrode current collector, wherein the negative electrode active material of the second negative electrode film layer includes 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. The battery cell according to any one of claims 1 to 2, characterized in that: The conductivity of the electrolyte at room temperature is 9 mS / cm to 18 mS / cm.

13. The battery cell according to any one of claims 1 to 2, characterized in that: The mass content of the carboxylic acid ester solvent in the electrolyte is 5% to 30%.

14. The battery cell according to any one of claims 1 to 2, characterized in that: The carboxylate solvent includes cyclic carboxylate, and the cyclic carboxylate includes one or more of γ-butyrolactone, γ-valerolactone and δ-valerolactone; and / or The carboxylate solvent includes chain carboxylate, and the chain carboxylate includes one or more of methyl acetate, ethyl acetate, propyl acetate, butyl acetate, propyl propionate and butyl propionate.

15. The battery cell according to any one of claims 1 to 2, characterized in that: The organic solvent further includes a carbonate solvent, and the carbonate solvent includes one or more of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate.

16. The battery cell according to any one of claims 1 to 2, characterized in that: The electrolyte further includes a lithium salt, which includes lithium bis(fluorosulfonyl)imide and lithium hexafluorophosphate. Based on the mass of the electrolyte, the ratio of the mass content of the lithium bis(fluorosulfonyl)imide to the mass content of the lithium hexafluorophosphate is 0.3 to 1.

2.

17. The battery cell according to claim 16, characterized in that: Based on the mass of the electrolyte, the mass content of the lithium bis(fluorosulfonyl)imide is 2% to 11%; and / or Based on the mass of the electrolyte, the mass content of the lithium hexafluorophosphate is 3% to 14%.

18. The battery cell according to any one of claims 1 to 2, characterized in that: The electrolyte further comprises one or more of fluorinated cyclic carbonate and vinylene carbonate.

19. The battery cell according to claim 18, characterized in that: The fluorinated cyclic carbonate includes at least one of monofluoroethylene carbonate, bisfluoroethylene carbonate and trifluoropropylene carbonate.

20. The battery cell according to claim 18, characterized in that: Based on the mass of the electrolyte, the mass content of the fluorinated cyclic carbonate is 0.5% to 20%; and / or Based on the mass of the electrolyte, the mass content of the vinylene carbonate is 0.1% to 3%.

21. The battery cell according to claim 18, characterized in that: Based on the mass of the electrolyte, the mass content of the fluorinated cyclic carbonate is 0.5% to 10%; The mass content of silicon element of the silicon-based material in the negative electrode active material is 0.3% to 7.5%.

22. The battery cell according to claim 18, characterized in that: Based on the mass of the electrolyte, the mass content of the fluorinated cyclic carbonate is greater than 10% and less than or equal to 20%; The mass content of silicon element of the silicon-based material in the negative electrode active material is greater than 7.5% and less than or equal to 15%.

23. The battery cell according to any one of claims 1 to 2, characterized in that: The invention also includes a positive electrode sheet, wherein the positive electrode sheet includes a positive electrode current collector and a positive electrode film layer disposed on at least one side of the positive electrode current collector, wherein the positive electrode film layer includes a positive electrode active material, and the single-side coating weight of the positive electrode film layer is 250 mg / 1540.25 mm 2 Up to 300mg / 1540.25mm 2 .

24. The battery cell according to claim 23, characterized in that: The positive electrode active material includes one or more of a lithium-containing transition metal oxide and a lithium-containing phosphate.

25. A battery device, characterized in that: The invention comprises the battery cell according to any one of claims 1 to 24.

26. An electrical device, characterized in that: Comprising a battery device as claimed in claim 25.

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