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 positive pole piece, a negative pole piece and an electrolyte, the positive pole piece comprises a positive current collector and a positive film layer arranged on at least one side of the positive current collector, the positive film layer comprises a positive active material and a carbon-containing material, the positive active material comprises lithium-containing phosphate, and the carbon-containing material comprises lithium-containing phosphate. The carbon-containing material comprises a carbon material with a tubular structure, and the mass content of a carbon element in the positive electrode film layer is 0.8%-3.5%; the negative electrode piece comprises a negative electrode current collector and a negative electrode film layer arranged on at least one side of the negative electrode current collector, the negative electrode film layer comprises a negative electrode active material, the negative electrode active material comprises a carbon-based material and a silicon-based material, and the mass content of a silicon element in the silicon-based material in the negative electrode active material is 0.3%-15%; 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 cycle performance of the battery monomer can be further improved.

Description

[0001] This application claims the priority of the PCT international application PCT / CN2025 / 070993, titled "Battery Cell, Battery Device and Electrical Device", filed on January 7, 2025, the entire content of which 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 cars, electric vehicles, electric airplanes, electric ships, electric toy cars, electric toy ships, electric toy airplanes and electric tools, etc. Due to the great progress of batteries, higher requirements are put forward for the performance of batteries. However, the cycling performance of battery cells needs to be further improved. Summary of the Invention

[0004] This application provides a battery cell, a battery device and an electrical device, and the 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 positive electrode tab, a negative electrode tab and an electrolyte. The positive electrode tab 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 a carbon-containing material. The positive electrode active material includes a lithium-containing phosphate. The carbon-containing material includes a carbon material with a tubular structure. The mass content of carbon element in the positive electrode film layer is 0.8% to 3.5% in the positive electrode film layer; 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 carbon-based material and a silicon-based material. The mass content of silicon element in the silicon-based material is 0.3% to 15% in the negative electrode active material; 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] Accordingly, the positive electrode active material of the embodiment of the present application includes lithium-containing phosphate, which has poor conductivity; the positive electrode film layer further includes a carbon-containing material, and the carbon-containing material includes a carbon material with a tubular structure. The carbon material with a tubular structure can improve the conductivity between the positive electrode active material particles in the positive electrode film layer, and at the same time control the carbon element in the positive electrode film layer to be within a reasonable range, making the conductive network in the entire positive electrode film layer more conducive to the rapid conduction of electron conduction; the negative electrode sheet 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%. The high specific capacity of the silicon-based material can make up for the problem of excessive electron and lithium ion transmission resistance caused by the too thick negative electrode film layer; the electrolyte includes an appropriate content of carboxylate solvent, and the viscosity of the electrolyte is low. The carboxylate solvent can quickly infiltrate the electrode sheet, which is beneficial to the rapid transmission of lithium ions between the solid-phase system of the positive and negative electrodes and the liquid-phase electrolyte system, making the transmission rates of lithium ions and electrons match, and is beneficial to improving the cycle performance of the battery cell under fast charging; moreover, the mass content of the carboxylate solvent is not too high and less than or equal to 70%, and the mass content of the silicon element is less than or equal to 15%, so that the side reactions on the negative electrode side are less, and the cycle performance under fast charging conditions can be further improved.

[0007] In some embodiments, the mass content of carbon element in the positive electrode film layer is 1.3% to 3.0%. When the carbon element in the positive electrode film layer meets the above range, the conductivity of the positive electrode film layer can be more effectively improved, which is beneficial to improving the cycle performance of the battery cell under fast charging.

[0008] 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, it can provide appropriate embedding sites for lithium ions, improve the fast charging ability, and can alleviate the side reactions between the silicon-based material and the electrolyte, and improve the cycle performance under fast charging.

[0009] 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, it can provide appropriate embedding sites for lithium ions, improve the fast charging ability, and can alleviate the side reactions between the silicon-based material and the electrolyte, and improve the cycle performance under fast charging.

[0010] 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, are beneficial to reducing the coating thickness of the negative electrode film layer, shortening the migration path of lithium ions, and improving the cycle performance under fast charging.

[0011] 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. Wherein, 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.

[0012] Thus, 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 conducive to improving the cycle performance of the battery cell under fast charging.

[0013] 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. In the embodiments of the present application, the particle size of the second negative electrode film layer 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, and improve the cycle life under fast charging.

[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 cycle life under fast charging.

[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.

[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.

[0018] In some embodiments, the average particle size of the carbon-based material in the second region is greater than that of the carbon-based material in the first region. The relatively smaller average particle size of the carbon-based material in the first region enables the rapid migration of lithium ions, improves the rapid charging ability of the battery cell, and is beneficial to enhancing the cycle life under rapid charging.

[0019] In some embodiments, when the average particle size of the carbon-based material in the second region is greater than that 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.

[0020] In some embodiments, when the average particle size of the carbon-based material in the second region is greater than that 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.

[0021] In some embodiments, when the average particle size of the carbon-based material in the second region is greater than that of the carbon-based material in the first region, the carbon-based material in the second region includes artificial graphite and / or natural graphite.

[0022] In some embodiments, when the average particle size of the carbon-based material in the second region is greater than that of the carbon-based material in the first region, the carbon-based material in the first region includes artificial graphite.

[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, wherein 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 cycle life of the battery cell under rapid charging; 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 is beneficial to enhancing the cycle performance of the battery cell under rapid charging.

[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, it can improve the conductivity of the electrolyte; and the electrolyte is compatible with the silicon-containing negative electrode, which can effectively reduce the gas generation amount of the battery cell and improve the rapid charging ability 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 cycle performance of the battery cell under fast charging.

[0027] In some embodiments, the carboxylic ester solvent includes linear carboxylic esters, and the linear 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 cycle performance of the battery cell under fast charging.

[0028] In some embodiments, the organic solvent further includes carbonate solvents, and the carbonate solvents include one or more of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate. When the carbonate solvent and the carboxylic ester solvent are used in combination, the stability of the electrolyte can be improved, which is beneficial to improving the cycle life 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] Thus, when the ratio of the mass content of lithium hexafluorophosphate and lithium bis(fluorosulfonyl)imide in the embodiments of the present application satisfies the above range, the combined 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, 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 within the above range, the content of hydrofluoric acid can be reduced, the side reaction at the negative electrode interface can be slowed down, and it is beneficial to improving the cycle performance of the battery cell under fast charging.

[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 within the above range, the conductivity of the electrolyte is relatively high, which is beneficial to the migration of lithium ions and is beneficial to improving the cycle performance of the battery cell under fast charging.

[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 interfacial film rich in lithium fluoride (LiF) on the surface of the negative electrode, which can relieve the volume expansion of silicon, and can improve the lifespan of the silicon-containing system; when the fluorinated cyclic carbonate and vinylene carbonate are used in combination, the interfacial film on the surface of the negative electrode has better compactness, can more effectively protect the silicon-containing negative electrode, reduce the degree of side reactions at the negative electrode interface, and can improve the cycle performance of the battery cell under fast charging.

[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 within the above range, an excellent interfacial film can be formed, which can play an excellent protective role for the negative electrode and can improve the cycle performance of the battery cell under fast charging.

[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 interfacial film, can form an excellent interfacial film, can play an excellent protective role for the negative electrode, and can improve the cycle performance of the battery cell under fast charging.

[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 in 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 relieved, the lifespan of the silicon-containing system can be improved, and the cycle performance of the battery cell under fast charging can be improved.

[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 in 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 relieved, the lifespan of the silicon-containing system can be improved, and the cycle performance of the battery cell under fast charging can be improved. In some embodiments, a carbon-containing material is coated on the surface of the lithium-containing phosphate. There is a carbon-containing material on the surface of the lithium-containing phosphate, and the carbon-containing material can be used as a coating layer to coat on the surface of the lithium-containing phosphate, thereby improving the conductivity of the lithium-containing phosphate, reducing the powder resistivity of the material, and being beneficial to the migration rate of lithium ions, and can improve the cycle performance of the battery cell under fast charging.

[0039] In some embodiments, the mass content of carbon element of the carbon-containing material coated on the surface of the lithium-containing phosphate in the positive electrode film layer is 0.5% to 2.0%. When the mass content of the carbon-containing material is within the above range, it is beneficial to improve the electrical conductivity of the lithium-containing phosphate and improve the cycling performance of the battery cell under fast charging conditions.

[0040] In some embodiments, the lithium-containing phosphate includes lithium iron phosphate. Lithium iron phosphate has excellent cycling stability and can improve the cycling performance of the battery cell under fast charging.

[0041] In some embodiments, the tubular carbon material includes carbon nanotubes. Carbon nanotubes can be used as a conductive agent in the positive electrode film layer to improve the electrical conductivity of the positive electrode film layer and improve the cycling performance of the battery cell under fast charging.

[0042] In some embodiments, the mass content of carbon nanotubes in the positive electrode film layer is 0.1% to 2%. When the mass content of carbon nanotubes is within the above range, it is beneficial to improve the electrical conductivity of the positive electrode film layer and improve the cycling performance of the battery cell under fast charging conditions.

[0043] In some embodiments, the diameter of the carbon nanotubes is 0.5 nm to 20 nm. When the diameter of the carbon nanotubes is within the above range, the structure is relatively stable and has excellent electron conduction ability, which can improve the cycling performance of the battery cell under fast charging conditions.

[0044] In some embodiments, the specific surface area of the carbon nanotubes is 500 m 2 / g to 2500 m 2 / g. 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 side reaction degree between the carbon nanotubes and the electrolyte can be reduced, which can improve the cycling performance of the battery cell under fast charging conditions.

[0045] 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.

[0046] 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. Description of the Drawings

[0047] 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, without creative efforts, other drawings can also be obtained according to the drawings.

[0048] Figure 1 is a schematic structural view of an electrical device provided by some embodiments of the present application; Figure 2 is a schematic structural view of a battery pack provided by some embodiments of the present application; Figure 3 is a schematic structural view of a battery module provided by some embodiments of the present application; Figure 4 is a schematic structural view of a battery cell provided by some embodiments of the present application; Figure 5 is a schematic structural view of an electrode assembly of a battery cell provided by some embodiments of the present application; Figure 6 is a schematic structural view of a negative electrode tab of a battery cell provided by some embodiments of the present application.

[0049] The drawings are not necessarily drawn to actual scale.

[0050] The reference numerals are explained as follows: X, thickness direction; 1, electrical device; 2, battery pack; 3, controller; 4, motor; 5, box body; 5a, first box body part; 5b, second box body 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

[0051] Hereinafter, embodiments of the battery cell, battery device, and electrical device of the present application 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 prevent the following descriptions from becoming unnecessarily lengthy and to facilitate the understanding of those skilled in the art. In addition, the drawings and the following descriptions 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.

[0052] 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, then 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 both a and b are 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.

[0053] If there is no special instruction, all embodiments and optional embodiments of this application can be combined with each other to form new technical solutions.

[0054] If there is no special instruction, all technical features and optional technical features of this application can be combined with each other to form new technical solutions.

[0055] If there is no special instruction, all steps of this application can be carried out sequentially or randomly, preferably sequentially. For example, if a method includes steps (a) and (b), it 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, if 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.

[0056] The "plurality" mentioned in this application means two or more (including two).

[0057] In the embodiments of this application, the battery cell can be a secondary battery, and a secondary battery refers to a battery cell that can be activated by charging after discharging so as to be used continuously.

[0058] 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 related technologies, it can be achieved by increasing the conductivity of the electrolyte. However, the increase in conductivity may cause the electrolyte to decompose and undergo side reactions, deteriorating the cycle performance of the battery cell, especially the cycle performance under fast charging.

[0059] In view of the above problems, the embodiments of the present application improve the lithium ion transport rates in the solid phase and the liquid phase by coordinately regulating the positive electrode sheet, the negative electrode sheet, and the electrolyte, thereby enhancing the cycle performance of the battery cell under fast charging; specifically, The positive electrode sheet of the battery cell includes a positive electrode active material containing lithium phosphate and a carbon-containing material. The carbon-containing material includes a carbon material with a tubular structure. The carbon material with a tubular structure can improve the conductivity between the positive electrode active material particles in the positive electrode film layer, and at the same time control the carbon element in the positive electrode film layer within a reasonable range, making the conductive network in the entire positive electrode film layer more conducive to the rapid conduction of electron conduction; the negative electrode sheet includes a silicon-based material, and the high specific capacity of the silicon-based material can compensate for the problem of excessive resistance to electron and lithium ion transport caused by an overly thick negative electrode film layer; The electrolyte includes an appropriate content of carboxylic ester solvents. The viscosity of the electrolyte is low. The carboxylic ester solvents can quickly infiltrate the electrode sheets, which is beneficial to the rapid transport of lithium ions between the solid phase systems of the positive and negative electrodes and the liquid phase electrolyte system, making the transport rates of lithium ions and electrons match, and being beneficial to improving the cycle performance of the battery cell under fast charging; Moreover, the mass content of the carboxylic ester solvents is not too high, and the mass content of the silicon element is not too high, resulting in fewer side reactions on the negative electrode side and being able to further improve the cycle performance under fast charging conditions; Therefore, the embodiments of the present application can enhance the cycle performance of the battery cell under fast charging conditions.

[0060] The battery cell of the present application is applicable to various battery devices and electrical devices that use battery cells.

[0061] 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. Or, exemplarily, the electrical device is a spacecraft, and the spacecraft includes an airplane, a rocket, a space shuttle, a spaceship, etc.

[0062] 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 used.

[0063] The interior of the electrical device 1 is provided with a battery device, which can be arranged at the bottom, head or 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 serve as the operating power source of the electrical device 1 and also 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

[0064] 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.

[0065] The battery device (Battery Apparatus) may include one or more battery cell assemblies for providing voltage and capacity. The battery cell assembly (Battery Cell Assembly) may include a plurality of battery cells, and the plurality of battery cells are connected in series, parallel or in a hybrid connection through a busbar component.

[0066] In some embodiments, the battery cell assembly (Battery Cell Assembly) is generally formed by arranging a plurality of battery cells.

[0067] As an example, the battery cell assembly may be a battery module (Battery Module), and the battery module 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.

[0068] As Figure 2 shown, in some embodiments, the battery device may be a battery pack 2 (battery Pack), and the battery pack 2 includes a box body 5 and one or more battery cell assemblies, and the battery cell assemblies are accommodated in the box body 5.

[0069] As an example, the battery cell assembly can also be accommodated in the box body 5 by directly fixing a plurality of battery cells to the box body 5.

[0070] As an example, the box body 5 includes a first box body part 5a and a second box body part 5b. The box body 5 has an accommodation space 5c. The first box body part 5a and the second box body part 5b are snapped together so that a closed space is formed inside the box body 5 to accommodate the battery cell assembly. The term "closed" here means covering or closing, which can be sealed or non-sealed. The first box body part 5a can be a top cover or a bottom plate.

[0071] As an example, the box body 5 may 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 box body 5 to accommodate the battery cell assembly.

[0072] In some embodiments, the box body 5 can be part of the chassis structure of a vehicle. For example, part of the box body 5 can become at least part of the floor of the vehicle, or part of the box body 5 can become at least part of the cross beams and longitudinal beams of the vehicle.

[0073] As an example, the battery cell assembly can be a battery module 6, and the battery cell assembly can be accommodated in the box body 5 by fixing the battery module 6 in the box body 5.

[0074] As Figure 3 shown, the battery module 6 includes a plurality of battery cells 7.

[0075] As Figure 4 and Figure 5 shown, in some embodiments, the battery cell 7 includes an electrode assembly 10 and a housing assembly 20.

[0076] The housing assembly 20 has a receiving cavity for receiving the electrode assembly 10 and the electrolyte.

[0077] In some embodiments, the housing assembly 20 includes a housing and electrode terminals 23, and the electrode terminals 23 are disposed on the housing.

[0078] 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 shell), 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 plays a role in protecting the electrode assembly 10, and a sealing bag is further included between the housing and the electrode assembly 10 for encapsulating the electrode assembly 10 and the electrolyte. Specifically, the sealing bag can be a bag-shaped insulating part 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.

[0079] 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, a multi-prismatic battery, and the multi-prismatic battery is, for example, a hexagonal prism battery, etc., and there is no special limitation in this application.

[0080] 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.

[0081] The shape of the housing 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, the housing 21 of a cylindrical structure can be selected; if the electrode assembly 10 is a cuboid structure, the housing 21 of a cuboid structure can be selected. Optionally, both the electrode assembly 10 and the housing 21 are of cuboid structure.

[0082] The electrode terminal 23 can be disposed on the housing 21, or the electrode terminal 23 is disposed on the end cap 22. The electrode terminal 23 is electrically connected to the tab of the electrode plate. The electrode terminal 23 can be directly connected to the tab, or indirectly connected to the tab 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.

[0083] 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.

[0084] In some embodiments, the electrode assembly 10 is a stacked structure.

[0085] As an example, a plurality of positive electrode plates 11 and negative electrode plates 12 can be respectively provided, and the plurality of positive electrode plates 11 and the plurality of negative electrode plates 12 are alternately stacked.

[0086] 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.

[0087] 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.

[0088] As an example, a plurality of separators 13 can be provided and are respectively disposed between any adjacent positive electrode plates 11 or negative electrode plates 12.

[0089] As an example, the separator 13 can be continuously provided and is disposed between any adjacent positive electrode plates 11 or negative electrode plates 12 by folding or winding.

[0090] In some embodiments, the shape of the electrode assembly 10 can be cylindrical, flat, prismatic, etc.

[0091] In some embodiments, the electrode assembly 10 is provided with tabs, and the tabs can conduct current out of the electrode assembly 10. The tabs include positive tabs and negative tabs. The electrode assembly 10 can adopt a wound structure or a stacked structure, and the stacked structure is optionally selected, which is beneficial to improving the energy density of the battery cell 7.

[0092] In some embodiments, the battery cell 7 includes a positive electrode plate 11, a negative electrode plate 12 and an electrolyte. The positive electrode tab 11 includes a positive electrode current collector and a positive electrode film layer provided on at least one side of the positive electrode current collector. The positive electrode film layer includes a positive electrode active material and a carbon-containing material. The carbon-containing material includes a carbon material with a tubular structure. The positive electrode active material includes a lithium-containing phosphate. The mass content of carbon element in the positive electrode film layer is 0.8% to 3.5% in the positive electrode film layer; The negative electrode tab 12 includes a negative electrode current collector and a negative electrode film layer provided on at least one side of the negative electrode current collector. The negative electrode film layer includes a negative electrode active material. The negative electrode active material includes a carbon-based material and a silicon-based material. The mass content of silicon element in the silicon-based material is 0.3% to 15% in the negative electrode active material; 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%.

[0093] During the charging process of the battery cell 7, electrons flow from the positive electrode tab 11 to the negative electrode tab 12 through an external circuit. Active ions such as lithium ions migrate from the positive electrode tab 11 to the negative electrode tab 12 through the electrolyte. Both the electron flow resistance and the ion migration resistance are factors restricting the fast charging ability; The positive electrode active material includes a lithium-containing phosphate, which has poor conductivity; the positive electrode film layer also includes a carbon-containing material. The carbon-containing material includes a carbon material with a tubular structure. The carbon material with a tubular structure can improve the conductivity between the positive electrode active material particles in the positive electrode film layer, and at the same time control the carbon element in the positive electrode film layer to remain within a reasonable range, making the conductive network in the entire positive electrode film layer more conducive to the rapid conduction of electron conduction; The negative electrode tab includes a silicon-based material. The mass content of silicon element in the negative electrode active material is greater than or equal to 0.3%. The high specific capacity of the silicon-based material can make up for the problem of excessive electron and lithium ion transmission resistance caused by the too thick negative electrode film layer; The electrolyte includes an appropriate content of carboxylic acid ester solvent. The viscosity of the electrolyte is low. The carboxylic acid ester solvent can quickly infiltrate the electrode tab, which is beneficial to the rapid transmission of lithium ions between the solid phase system of the positive and negative electrodes and the liquid phase electrolyte system, making the transmission rates of lithium ions and electrons match, and is beneficial to improving the cycle performance of the battery cell under fast charging; Moreover, the mass content of the carboxylic acid ester solvent is not too high and less than or equal to 70%, and the mass content of silicon element is less than or equal to 15%, so that the side reactions on the negative electrode side are less, and the cycle performance under fast charging conditions can be further improved.

[0094] Negative electrode sheet 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 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 disposed on any one or both of the two opposite surfaces of the negative electrode current collector.

[0095] The upper charge limit voltage and the discharge cut-off voltage of the battery cell are different according to the different positive electrode active materials. For example, when the phosphate material includes lithium iron phosphate, the upper charge limit voltage can be 3.65V and the discharge cut-off voltage can be 2.0V, or the upper charge limit voltage can be 3.8V and the discharge cut-off voltage can be 2.0V; also for example, when the phosphate material includes lithium manganese iron phosphate, the upper charge limit voltage can be 4.3V and the discharge cut-off voltage can be 2.0V. Next, taking the upper charge limit voltage of 3.8V and the discharge cut-off voltage of 2.0V 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 0.33C to the upper charge limit voltage, and then charged at a constant voltage to 0.05C, corresponding to the state of 100% SOC of the battery cell. The battery cell is discharged at a constant current discharge rate of 0.33C to the cut-off voltage, corresponding to the state of 0% SOC of the battery cell.

[0096] In some embodiments, when the battery cell is in the 0% state of charge (SOC), the tap density of the negative electrode film layer is 1.1 g / cm 3 to 1.7 g / cm 3 . Exemplarily, the tap density of the negative electrode film layer when the battery cell is in the 0% state of charge 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 the range composed of any two of the above values.

[0097] 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, the migration path of lithium ions is short, which is beneficial to the improvement of the cycle performance of the battery cell under fast charging.

[0098] 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 mm 2 、135 mg / 1540.25 mm 2 、137 mg / 1540.25 mm 2 、140 mg / 1540.25 mm 2 、145 mg / 1540.25 mm 2 、150 mg / 1540.25 mm 2 、155 mg / 1540.25 mm 2 、160 mg / 1540.25 mm 2 、165 mg / 1540.25 mm 2 、170 mg / 1540.25 mm 2 、175 mg / 1540.25 mm 2 、180 mg / 1540.25 mm 2 or the range composed of any two of the above values.

[0099] When the single-sided coating weight of the negative electrode film layer meets the above range and is combined 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 the improvement of the cycle performance of the battery cell under fast charging.

[0100] In the embodiments of the present application, the tap density of the negative electrode film layer of the battery cell at 0% state of charge (SOC) has the meaning well-known in the art, that is, the negative electrode tab is disassembled from the battery cell at 0% SOC, and the tap density of the negative electrode film layer is measured. For example, for a single-sided coated negative electrode tab (if it is a double-sided coated tab, the negative electrode film layer on one side can be wiped off first), it is punched into small circular pieces with an area of S1, weighed, and recorded as M1, and its thickness H1 is measured. Then, the negative electrode film layer of the weighed negative electrode tab is wiped off, the weight of the negative electrode current collector is weighed, and recorded as M0, and its thickness H0 is measured. The single-sided coating weight of the negative electrode film layer = (the weight M1 of the negative electrode tab - 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 tab - the thickness H0 of the negative electrode current collector, and the tap 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.

[0101] In some embodiments, the negative electrode active material includes a silicon-based material. Optionally, the silicon-based material may include elemental silicon, silicon-carbon composite, silicon oxide SiO x (where 0 < x ≤ 2), or at least one of them. The above materials can improve the capacity of the negative electrode active material, help reduce the coating thickness of the negative electrode film layer, and shorten the migration path of lithium ions.

[0102] In some embodiments, the specific surface area of the silicon-based material is 1 m 2 ² / g to 4 m 2 ² / 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.

[0103] When the specific surface area of the silicon-based material is within the above range, it can provide appropriate embedding sites for lithium ions, improve the fast charging ability, and can alleviate the side reaction between the silicon-based material and the electrolyte, and improve the cycle performance under fast charging.

[0104] 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 is tested by a Tri-Star 3020 specific surface area and pore size analyzer of Micromeritics Company, USA.

[0105] In some embodiments, the silicon-based material is granular, and its average particle size is from 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.

[0106] When the average particle size of the silicon-based material is within the above range, it can provide appropriate insertion sites for lithium ions, improve the fast charging ability, and can alleviate the side reaction between the silicon-based material and the electrolyte, improving the cycle performance under fast charging.

[0107] 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.

[0108] Optionally, the carbon-based material includes at least one of artificial graphite and natural graphite.

[0109] In some embodiments, in addition to the above-mentioned carbon-based material and optional 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.

[0110] In this application, the qualitative and quantitative determination of each substance or each element can be detected by suitable equipment and methods known to those skilled in the art. The 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 some detection steps / instrument parameters, etc. from the perspective of detection accuracy to obtain more accurate detection results. One detection method can be used for qualitative or quantitative determination, or several detection methods can be used in combination for qualitative or quantitative determination.

[0111] For example, this application can combine the General Rules for X-ray Diffraction Analysis of JIS / K0131-1996 to perform X-ray powder diffraction testing and qualitative analysis on the negative electrode sheet or the negative electrode active material.

[0112] Artificial graphite and natural graphite can be distinguished by the SEM cross-section taken by scanning electron microscope (SEM). There are voids between flake structures in the SEM cross-section of natural graphite, and the SEM cross-section of artificial graphite is dense and has no obvious gaps, or 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, and only 2H phase exists in the XRD spectrum of artificial graphite.

[0113] Such as Figure 6As shown, in the embodiments of the present application, the negative electrode film layer 121 of the negative electrode tab 12 includes at least one film layer, which can be a single film layer or at least two film layers. Optionally, the negative electrode film layer 121 includes at least two film layers.

[0114] When the negative electrode film layer 121 is a single film layer, the negative electrode active material in the negative electrode film layer 121 includes a carbon-based material and an optional silicon-based material.

[0115] When the negative electrode film layer 121 includes at least two film layers, the negative electrode active material in the negative electrode film layer 121 includes a carbon-based material and an optional silicon-based material. The negative electrode film layer 121 can include two film layers, three film layers, four film layers, or even more film layers.

[0116] 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 a carbon-based material. The second negative electrode film layer 1212 is connected to the side of the first negative electrode film layer 1211 facing away from the negative electrode current collector 122, and the negative electrode active material of the second negative electrode film layer 1212 includes a 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.

[0117] The negative electrode film layer 121 includes at least two film layers, and layer-by-layer coating is beneficial to improving the cycle life of the battery cell under fast charging.

[0118] 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.

[0119] Optionally, the first negative electrode film layer 1211 further includes a silicon-based material.

[0120] Optionally, the second negative electrode film layer 1212 further includes a silicon-based material.

[0121] 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.

[0122] When both the first negative electrode film layer 1211 and the second negative electrode film layer 1212 include silicon-based materials, it is more conducive to improving the energy density of the battery cell. When the first negative electrode film layer 1211 includes silicon-based materials and the second negative electrode film layer 1212 does not include silicon-based materials, 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 cycling performance under fast charging.

[0123] 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.

[0124] 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. 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.

[0125] 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.

[0126] There may be an obvious layer interface between the first region 121a, the second region 121b, and the third region 121c, or there may be no obvious layer interface. 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, and the third region 121c can be a part of the first negative electrode film layer 1211, or the third region 121c can be a part of the second negative electrode film layer 1212, or the third region 121c can be a part of both the first negative electrode film layer 1211 and the second negative electrode film layer 1212.

[0127] In some embodiments, in the 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 greater than or equal to the void ratio of a single carbon-based material in the second region 121b. Optionally, the void ratio of a single carbon-based material in the first region 121a is less than the void ratio of a single carbon-based material in the second region 121b.

[0128] The carbon-based material is granular and has voids inside. On the 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.

[0129] During the charging process of the battery cell, lithium ions diffuse through the second region 121b to the first region 121a. 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, which is more conducive to the diffusion of lithium ions in the first region 121a, improving the transmission rate, and thus conducive to the improvement of the cycle life of the battery cell under fast charging.

[0130] Optionally, the average particle size of the carbon-based material in the first region 121a can be greater than or equal to the average particle size of the carbon-based material in the second region 121b. Further optionally, the average particle size of the carbon-based material in the first region 121a can be greater than the average particle size of the carbon-based material in the second region 121b, which is conducive to the rapid migration of lithium ions from the second region 121b to the first region 121a and improves the fast charging ability of the battery cell. Of course, the average particle size of the carbon-based material in the first region 121a can be less than the average particle size of the carbon-based material in the second region 121b.

[0131] Optionally, the average particle size of the carbon-based material in the first negative electrode film layer 1211 can 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 can be greater than the average particle size of the carbon-based material in the second negative electrode film layer 1212.

[0132] There is a difference 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 fast charging, 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 embodiment 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 plating on the surface of the negative electrode sheet 12 and improve the cycle life under fast charging.

[0133] Optionally, the average particle size of the carbon-based material in the first region 121a 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. When the average particle size of the carbon-based material in the first region 121a is within the above range, the cycle life under fast charging can be improved.

[0134] Optionally, the average particle size of the carbon-based material in the first negative electrode film layer 1211 is from 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 under fast charging can be improved.

[0135] Optionally, the average particle size of the carbon-based material in the second region 121b is from 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. 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 cycle life under fast charging.

[0136] Optionally, the average particle size of the carbon-based material in the second negative electrode film layer 1212 is from 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, the solid-phase transmission path of lithium ions can be shortened, the fast charging performance and the stability of the material can be improved, and it is beneficial to improve the cycle life under fast charging.

[0137] 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.

[0138] 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.

[0139] 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 smaller than that of a single carbon-based material in the second region 121b.

[0140] 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 conducive to the rapid transmission of lithium ions from the second region 121b to the first region 121a, thus facilitating the rapid charging of the battery cell.

[0141] Optionally, the average particle size of the carbon-based material in the first region 121a can 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 a higher pressure resistance during the preparation of the film layer, which is conducive to 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, improves the rapid charging ability of the battery cell, and is conducive to enhancing the cycle life under rapid charging. Of course, the average particle size of the carbon-based material in the first region 121a can be greater than or equal to that of the carbon-based material in the second region 121b.

[0142] Optionally, the average particle size of the carbon-based material in the first region 121a is from 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.

[0143] Optionally, the average particle size of the carbon-based material in the first negative electrode film layer 1211 is from 9 μm to 17 μm.

[0144] 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.

[0145] 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.

[0146] Exemplarily, the carbon-based material of the second region 121b includes artificial graphite and natural graphite, and the carbon-based material of 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 of the second region 121b includes a silicon-based material, artificial graphite, and natural graphite, and the negative electrode active material of the first region 121a includes a silicon-based material and artificial graphite.

[0147] Exemplarily, the carbon-based material of the second negative electrode film layer 1212 includes artificial graphite and natural graphite, and the carbon-based material of 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 of the second negative electrode film layer 1212 includes a silicon-based material, artificial graphite, and natural graphite, and the negative electrode active material of the first negative electrode film layer 1211 includes a silicon-based material and artificial graphite.

[0148] In the embodiments of the present application, the average particle size of the active material in the first region 121a and the second region 121b can be detected by the following equipment and method: taking the negative electrode sheet 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 size of the active material in the SEM cross-section, and calculating the average particle size of the active material according to the counted quantity.

[0149] 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%.

[0150] 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%.

[0151] 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., such as 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%.

[0152] 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).

[0153] The negative electrode film layer is usually formed by coating a negative electrode slurry on the negative electrode current collector and then drying and cold pressing. The negative electrode slurry is usually 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.

[0154] The negative electrode plate does not exclude other additional functional layers besides the negative electrode film layer. For example, in some embodiments, the negative electrode plate of the embodiment of the present application further includes a negative electrode conductive layer disposed on the surface of the negative electrode current collector and sandwiched between the negative electrode current collector and the negative electrode film layer. In some other embodiments, the negative electrode plate of the embodiment of the present application further includes a protective layer covering the surface of the negative electrode film layer.

[0155] Positive electrode sheet In some embodiments, the battery cell further includes a positive electrode plate.

[0156] 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 surfaces opposite to each other 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.

[0157] 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, such as 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.

[0158] In the case where the electrode assembly is a stacked structure, the length direction of the positive electrode plate is parallel to the length direction of the battery cell, and the size of the positive electrode film layer in the length direction can be understood as the length of the positive electrode film layer. The width direction of the positive electrode plate is parallel to the width direction of the battery cell, and the size of the positive electrode film layer in the width direction can be understood as the width of the positive electrode film layer.

[0159] 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.

[0160] 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 , 2.80g / cm 3 , 2.85g / cm 3 Or a range consisting of any two of the above values.

[0161] 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 electrode active materials in the positive electrode film layer are stacked relatively tightly, the contact resistance between particles is small, which can further reduce the resistance of the electrode sheet, thereby reducing heat generation during fast charging and improving the cycle performance of the battery cell under fast charging.

[0162] 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.

[0163] 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, improving the cycle performance of the battery cell under fast charging.

[0164] 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 of the battery cell in the 0% state of charge (SOC) is disassembled, and the compaction density of the positive electrode film layer is measured. For example, 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) 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, 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.

[0165] In some embodiments, the positive electrode active material includes one or more of lithium-containing transition metal oxides and lithium-containing phosphates. Optionally, the positive electrode active material includes lithium-containing phosphates. The lithium-containing phosphate can be in an olivine structure, which is stable in structure during charge and discharge and can improve the cycle life of the battery cell.

[0166] Examples of the lithium-containing transition metal oxides 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.

[0167] 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, which is beneficial to improving the cycling performance of the battery cell under fast charging.

[0168] 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 the 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%.

[0169] For example, the carbon-containing material may include carbon materials with a tubular structure, such as carbon nanotubes, carbon nanofibers, etc., and carbon nanotubes can be selected. 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.

[0170] Also, for example, the lithium-containing phosphate with an olivine structure can 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 on the surface of the lithium-containing phosphate, thereby improving the conductivity of the lithium-containing phosphate, reducing the powder resistivity of the material, and being beneficial to the migration rate of lithium ions, and improving the cycling performance of the battery cell under fast charging conditions.

[0171] In some embodiments, the mass content of carbon element of the carbon-containing material of the positive electrode active material in the positive electrode film layer is 0.5% to 2.0%, such as 0.5%, 0.6%, 0.8%, 1.0%, 1.2%, 1.4%, 1.6%, 1.8%, 2.0% or the range composed of any two of the above values. When the mass content of the carbon-containing material meets the above range, it can further improve the fast charging ability of the battery cell and reduce the heat generation of the battery cell.

[0172] In some embodiments, the lithium-containing phosphate includes the general formula Li x1 A y1 Me aM b P 1-c X c Y z compounds, wherein, 0.5 ≤ x 1 ≤ 1.3, 0 ≤ y 1 ≤ 1.3, and 0.9 ≤ x 1 + y 1 ≤ 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, Mg, Me includes one or more of Mn, Fe, Co, 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, Ce, X includes one or more of Cl, C, N, and Y includes one or more of O, F. The lithium-containing phosphate has excellent cycle stability, which is beneficial to improving the cycle performance of the battery cell.

[0173] Exemplarily, the lithium-containing phosphate includes LiFePO 4 , LiMnPO 4 , LiNiPO 4 , LiCoPO 4 or more of them. During the charge and discharge process of the battery cell, the insertion and extraction and consumption of active ions such as Li will occur, and the molar content of Li is different when the battery cell is discharged to different states. Regarding the positive electrode active materials LiFePO 4 , LiMnPO 4 , LiNiPO 4 , LiCoPO 4 etc., the molar content of Li is the initial state of the material, that is, the state before feeding. When the positive electrode active material is applied to the battery system, after charge and discharge cycling, the molar content of Li may change. In the embodiments of the present application, regarding the positive electrode active materials LiFePO 4 , LiMnPO 4 , LiNiPO 4 , LiCoPO 4 etc., the molar content of oxygen O is only the theoretical state value, and 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 show fluctuations, and the above situations are all within the protection scope of the present application.

[0174] In the embodiments of the present application, the content of elements in the positive electrode 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 discharging the battery cell to 0% state of charge (SOC) and disassembling the positive electrode plate, it is cleaned with dimethyl carbonate (DMC) and dried, and then after removing impurities by high-temperature calcination, 0.4 g of the positive electrode 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 made up to a volume of 100 mL, and quantitative testing is carried out by the standard curve method.

[0175] In some embodiments, the positive electrode film layer further includes a lithium supplement agent. The lithium supplement agent contains 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.

[0176] In some embodiments, the lithium supplement agent includes at least one of lithium ferrite, lithium nickelate, and lithium cobaltate.

[0177] 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.

[0178] 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.

[0179] In the embodiments of the present application, the positive electrode plate is cut along the thickness direction of the plate 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 scanning electron microscope (SEM) testing on the cut surface of the positive electrode film layer, the longest diameter and the shortest diameter of the lithium supplement agent particles are determined. For example, the "longest diameter" of the 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 the particle refers to the shortest straight line passing through the center point of the particle and extending to the outer periphery of the particle.

[0180] 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 therefrom is the average longest diameter; the shortest diameters of multiple, for example, 10 lithium supplement agents are statistically counted, and the average value calculated therefrom is the average shortest diameter.

[0181] In some embodiments, based on the total mass of the positive electrode film layer, the mass ratio of the lithium supplementing agent is 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 supplementing agent within the above mass range, it can effectively improve the stability of the lithium supplementing agent while having a good oxygen release effect.

[0182] In some embodiments, the positive electrode film layer includes a carbon material with a tubular structure for use as a positive electrode conductive agent, which can be carbon nanotubes. The positive electrode conductive agent can also optionally include at least one of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, 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%.

[0183] 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%.

[0184] 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 cycling performance of the battery cell under fast charging conditions.

[0185] Optionally, the specific surface area of the carbon nanotubes is 500m 2 / g to 2500m 2 / g, such as 500m² / g, 700m² / g, 900m² / g, 1100m² / g, 1300m² / g, 1500m² / g, 1700m² / g, 1900m² / g, 2100m² / g, 2300m² / g, 2500m² / g or the range composed of any two of the above.

[0186] 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 side reaction degree between the carbon nanotubes and the electrolyte can be reduced, and the cycling performance of the battery cell under fast charging conditions can be improved.

[0187] Optionally, the diameter of the carbon nanotubes is from 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 a range composed of any two of the above. Optionally, the diameter of the carbon nanotubes is from 0.5 nm to 7.5 nm.

[0188] When the diameter of the carbon nanotubes is within the above range, the structure is relatively stable, and it has relatively excellent electron conduction ability, which can improve the cycle performance of the battery cell under fast charging conditions.

[0189] 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 the carbon nanotubes is the outer diameter of the carbon nanotubes on the cross-section perpendicular to its own central axis.

[0190] In some embodiments, the positive electrode film layer may further optionally include a positive electrode binder. The type of the positive electrode binder is not particularly limited 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%.

[0191] In some embodiments, the positive electrode current collector can 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 can 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).

[0192] 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 can be N-methylpyrrolidone (NMP), but is not limited thereto.

[0193] 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 embodiment of the present application further includes a positive electrode conductive layer disposed on the surface of the positive electrode current collector and sandwiched between the positive electrode current collector and the positive electrode film layer. In some other embodiments, the positive electrode plate of the embodiment of the present application further includes a protective layer covering the surface of the positive electrode film layer.

[0194] [Electrolyte] During the charge and discharge process of the battery cell, active ions such as lithium ions shuttle back and forth between the positive electrode plate and the negative electrode plate, 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.

[0195] 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 the range composed of any two of the above values.

[0196] 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 gas generation caused by heat accumulation, and can improve the cycle life of the battery cell under fast charging.

[0197] In the embodiment 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 the equipment and methods well-known in the art. For example, it can be tested with reference to the industry standard HG-T 4067-2015.

[0198] In some embodiments, the organic solvent includes carboxylic ester solvents.

[0199] Optionally, the mass content of the carboxylic ester solvent in the electrolyte is 3% to 70%. Exemplarily, the mass content of the carboxylic 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 ester solvent in the electrolyte is 5% to 30%.

[0200] When the mass content of the carboxylic ester solvent is within the above range, the conductivity of the electrolyte can be improved; 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 gas generation amount of the battery cell, and improve the cycling performance of the battery cell under fast charging. The carboxylic ester solvent with the above mass content can also quickly infiltrate the positive electrode film layer, making the charging state of the positive electrode film layer more uniform, reducing the risk of local side reactions on the negative electrode side, and further improving the cycling performance of the battery cell under fast charging.

[0201] Exemplarily, 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 infiltration ability of the electrode sheet and improve the cycling performance under fast charging.

[0202] Exemplarily, the carboxylic ester solvent includes linear carboxylic esters, and the linear 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 infiltration ability of the electrode sheet and improve the cycling performance under fast charging.

[0203] In some embodiments, the organic solvent includes carbonate solvents.

[0204] When the carbonate solvent and the carboxylic ester solvent are used in combination, the stability of the electrolyte can be improved, its gas generation amount can be reduced, which is beneficial to improving the cycling life of the battery cell.

[0205] Exemplarily, the carbonate solvent includes one or more of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate. Optionally, the carbonate solvent includes one or more of ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate.

[0206] 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.

[0207] Lithium hexafluorophosphate may decompose to produce hydrofluoric acid (HF). 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. When lithium hexafluorophosphate and lithium bis(fluorosulfonyl)imide are used in combination, the content of hydrofluoric acid can be reduced, the side reaction at the negative electrode interface can be slowed down, which is beneficial to improving the cycle life of the battery cell.

[0208] 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 from 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.

[0209] When the ratio of the mass contents of lithium hexafluorophosphate and lithium bis(fluorosulfonyl)imide satisfies the above range, the content of hydrofluoric acid can be reduced, the side reaction at the negative electrode interface can be slowed down, which is beneficial to improving the cycle performance of the battery cell under fast charging.

[0210] Exemplarily, based on the mass of the electrolyte, the mass content of lithium bis(fluorosulfonyl)imide is from 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 the 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, which is beneficial to improving the cycle performance of the battery cell under fast charging.

[0211] Exemplarily, based on the mass of the electrolyte, the mass content of lithium hexafluorophosphate is from 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 the 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 is beneficial to improving the cycle performance of the battery cell under fast charging.

[0212] 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, or 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.

[0213] In some embodiments, the additive comprises a cyclic carbonate additive, such as one or more of a fluorinated cyclic carbonate and vinylene carbonate. Optionally, the additive comprises a fluorinated cyclic carbonate and vinylene carbonate.

[0214] 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 of silicon, improve the lifespan of the silicon-containing system, and improve the cycling performance. When the fluorinated cyclic carbonate and vinylene carbonate are used in combination, the SEI film on the surface of the negative electrode has better compactness, can more effectively protect the silicon-containing negative electrode, reduce the degree of side reactions at the negative electrode interface, and improve the cycling performance.

[0215] Optionally, the fluorinated cyclic carbonate comprises at least one of fluoroethylene carbonate, difluoroethylene carbonate, and trifluoropropylene carbonate.

[0216] Optionally, based on the mass of the electrolyte, the mass content of the fluorinated cyclic carbonate is from 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.

[0217] As an example, based on the mass of the electrolyte, the mass content of the fluorinated cyclic carbonate is from 0.5% to 10%; the mass content of silicon element in the silicon-based material in the negative electrode active material is from 0.3% to 7.5%.

[0218] When the mass content of the fluorinated cyclic carbonate and the mass content of silicon element meet the above conditions, it can more effectively relieve the volume expansion of silicon, improve the lifespan of the silicon-containing system, and improve the cycling performance. 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%.

[0219] When 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, it can more effectively relieve the volume expansion of silicon, improve the lifespan of the silicon-containing system, and improve the cycling performance. Optionally, based on the mass of the electrolyte, the mass content of vinylene carbonate is 0.1% to 3%, such as 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.

[0220] The above-mentioned mass content of vinylene carbonate and fluorinated cyclic carbonate are used in combination, making the interfacial film on the negative electrode surface denser, capable of more effectively protecting the silicon-containing negative electrode, reducing the degree of side reactions at the negative electrode interface, and improving the cycling performance.

[0221] In the embodiments of the present application, the types and contents of inorganic components / lithium salts in the electrolyte have the meanings well-known in the art, and can be detected by devices and methods well-known in the art. For example, reference can be made to the standard JY / T020-1996 "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 battery that has been fully discharged (discharged to the lower cut-off voltage so that the charged state of the battery is about 0% SOC) can be disassembled in reverse, and the free electrolyte obtained from the battery can be taken as a sample and detected by ion chromatography.

[0222] In the embodiments of the present application, the types and contents of organic components in the electrolyte have the meanings well-known in the art, and can be detected by devices and methods well-known in the art. For example, reference can be made to GB / T9722-2006 "General Rules for Gas Chromatography of Chemical Reagents" to qualitatively and quantitatively analyze the organic components in the electrolyte by gas chromatography.

[0223] In the embodiments of the present application, after quantitatively and qualitatively detecting each component in the electrolyte, each component is classified, and carboxylic ester solvents and carbonate solvents are used as the constituent components of organic solvents. Based on the mass of the electrolyte being 100%, the mass content of each component is calculated. Fluorinated cyclic carbonate and vinylene carbonate are used as additives in the electrolyte. Based on the mass of the electrolyte being 100%, the mass content of each component is calculated.

[0224] Separator In some embodiments, the electrode assembly further includes a separator disposed between the positive electrode sheet and the negative electrode sheet.

[0225] In some embodiments, the separator is a separator film. The present application does not particularly limit the type of the separator film, and any well-known porous structure separator film with good chemical stability and mechanical stability can be selected.

[0226] As an example, the main material of the separator can be selected from at least one of glass fiber, non-woven fabric, polyethylene, polypropylene, polyvinylidene fluoride, and ceramics. The separator can be a single-layer film or a multi-layer composite film, without any particular limitation. When the separator is a multi-layer composite film, the materials of each layer can be the same or different, without any particular limitation. The separator can be a single component located between the positive and negative electrodes, or can be 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.

[0227] In some embodiments, the separator is a solid electrolyte. The solid electrolyte is disposed between the positive electrode and the negative electrode, and simultaneously functions to transport ions and isolate the positive and negative electrodes.

[0228] 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 variations 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 all instruments used in the examples are commercially available.

[0229] Example 1 1. Preparation of the positive electrode plate The positive electrode plate 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.

[0230] The positive electrode film layer includes a lithium-containing phosphate, a binder polyvinylidene fluoride (PVDF), a conductive agent acetylene black, and a conductive agent carbon nanotube in a mass ratio of 97:1.5:0.5:1. The positive electrode film layer is a film layer formed by uniformly coating a positive electrode slurry (solvent is N-methylpyrrolidone NMP) on both sides of the positive electrode current collector and drying and cold pressing.

[0231] The lithium-containing phosphate includes lithium iron phosphate, and the surface of the lithium iron phosphate is coated with carbon. The mass content of carbon in the lithium iron phosphate is 1.2%. The lithium iron phosphate is sourced from Guangdong Bump Recycling Technology Co., Ltd.

[0232] The single-sided coating weight of the positive electrode film layer is 280 mg / 1540.25 mm 2 .

[0233] 2. Preparation of the negative electrode plate The negative electrode plate 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.

[0234] The negative electrode film layer is formed by uniformly coating the negative electrode slurry (the solvent is deionized water) on the surface of the negative electrode current collector, and then drying and cold pressing.

[0235] The negative electrode film layer comprises a first negative electrode film layer and a second negative electrode film layer, wherein the first negative electrode film layer is located on the surface of the negative electrode conductive layer, and the second negative electrode film layer is located on the surface of the first negative electrode film layer.

[0236] The first negative electrode film layer includes a carbon-based material with a mass ratio of 87:9.5:1:1.5:1, a silicon-based material silicon oxide, a conductive agent acetylene black, a negative electrode binder styrene-butadiene rubber, and a thickener sodium carboxymethyl cellulose. The carbon-based material of the first 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.

[0237] The second negative electrode film layer includes a carbon-based material with a mass ratio of 87:9.5:1:1.5:1, a silicon-based material silicon oxide, a conductive agent acetylene black, a negative electrode binder styrene-butadiene rubber, and a thickener sodium carboxymethyl cellulose. The carbon-based material of the second negative electrode film layer includes artificial graphite, and the average particle size of the carbon-based material is 15 μm.

[0238] in, In a cross section along the thickness direction of the negative electrode film layer, the void ratio of a single carbon-based material in the second negative electrode film layer is greater than the void ratio of a single carbon-based material in the first negative electrode film layer; The coating weight ratio of the first negative electrode film layer to the second negative electrode film layer is 4:6; The mass content of silicon in the negative electrode active material of the negative electrode film layer is 6%, and the specific surface area of ​​the silicon-based material is 2m 2 / g, and the average particle size is 6μm.

[0239] The single-sided coating weight of the negative electrode film is 135mg / 1540.25mm 2 .

[0240] The carbon-based materials and silicon-based materials are sourced from Shanghai Shanshan Technology Co., Ltd.

[0241] 3. Isolation film The isolation film includes a base film and a coating arranged on both sides of the base film. The base film is a 7μm polyethylene film layer, and the coating includes an alumina ceramic layer and a polyvinylidene fluoride layer. The alumina ceramic layer is located on the surface of the base film and has a thickness of 1μm. The polyvinylidene fluoride layer is located on the surface of the alumina ceramic away from the base film and has a surface density of 1g / m 2 .

[0242] The isolation membrane comes from Taihe New Materials Group Co., Ltd.

[0243] 4. Preparation of electrolyte The electrolyte includes an organic solvent, a lithium salt, and an additive.

[0244] After mixing the components of the organic solvent evenly, the lithium salt and the additive are added to prepare the electrolyte.

[0245] The organic solvent includes 25% chain carboxylic ester solvent (ethyl acetate EA) and 57% carbonate solvent (30% ethyl methyl carbonate, 27% ethylene carbonate EC). The mass content of each component in the organic solvent is calculated based on the mass of the electrolyte.

[0246] The lithium salt includes 8% lithium hexafluorophosphate LiPF 6 and 6% lithium bis(fluorosulfonyl)imide.

[0247] The additive includes 2% fluoroethylene carbonate FEC and 2% vinylene carbonate VC; The conductivity of the electrolyte at room temperature is 14.2 mS / cm.

[0248] 5. Preparation of the 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 an isolation role, obtaining an electrode assembly. The electrode assembly is placed in an outer packaging shell, dried, and then the electrolyte is injected. After processes such as vacuum packaging, standing, formation, and shaping, the 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 .

[0249] Comparative Example 1-1 and Comparative Example 1-2 The battery cell is prepared by a method similar to that of Example 1. Different from Example 1, the mass content of carbon element in the positive electrode film layer is adjusted.

[0250] Examples 2-1 to 2-6 The battery cell is prepared by a method similar to that of Example 1. Different from Example 1, the mass content of carbon element in the positive electrode film layer is adjusted.

[0251] Performance test 1. Room temperature cycle performance test of the battery cell At 25 °C, the battery cell is charged at a constant current of 0.33C from 0% SOC to 10% SOC, then charged from 10% SOC to 80% SOC, and then charged at 0.33C until the charging cut-off voltage of 3.65V. After standing for 30 minutes, it is discharged at 1C until the discharge cut-off voltage of 2.0V. This is one charge-discharge cycle. Record the initial discharge capacity D0. Cycle the battery cell n times and record the discharge capacity D1 after cycling. The cycle capacity retention rate at the 1500th cycle is (D1 - D0) / D0.

[0252] Among them, the charging steps from 10% SOC to 80% SOC include: Charge from 10% SOC to 45% SOC at 3.7 C; Charge from 45% SOC to 50% SOC at 3.4 C; Charge from 50% SOC to 55% SOC at 3.2 C; Charge from 55% SOC to 60% SOC at 2.9 C; Charge from 60% SOC to 65% SOC at 2.6 C; Charge 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.

[0253] The test results are shown in Table 1.

[0254] Table 1

[0255] In Comparative Example 1-1, the mass content of carbon nanotubes in the positive electrode film layer is too high, resulting in a decrease in the mass ratio of lithium iron phosphate and a reduction in the capacity of the positive electrode film layer, which is not conducive to improving the cycle life of the battery cell; In Comparative Example 1-2, the mass content of carbon element is too low. For example, no carbon nanotubes are added to the positive electrode film layer, resulting in too poor conductivity of the positive electrode film layer, which is not conducive to improving the cycle performance of the battery cell under fast charging.

[0256] In the examples of the present application, by adjusting the mass content of carbon nanotubes in the positive electrode film layer to be within a reasonable range, such as 0.1% to 2.0%, an excellent conductive network can be constructed in the positive electrode film layer to improve the electron conduction rate. In combination with an electrolyte containing an appropriate content of carboxylic ester solvent, active ions such as lithium ions can migrate quickly, improving the ion conduction ability. The improvement of the electron conduction ability in combination with the improvement of the lithium ion transmission ability can improve the cycle performance of the battery cell under fast charging conditions; The specific surface area of the carbon nanotubes is within an appropriate range, for example, 500 m 2 / g to 2500 m 2 / g, which is beneficial to improving the electron conduction ability; and with an appropriate content of carbon nanotubes, the side reaction degree between the carbon nanotubes and the electrolyte can be reduced, and the cycle performance of the battery cell under fast charging conditions can be improved.

[0257] The diameter of the carbon nanotubes is within an appropriate range, for example, 0.5 nm to 20 nm, which is beneficial to improving the electron conduction ability; and with an appropriate content of carbon nanotubes, the side reaction degree between the carbon nanotubes and the electrolyte can be reduced, and the cycle performance of the battery cell under fast charging conditions can be improved.

[0258] The mass content of the carbon element coated on the surface of the lithium iron phosphate in the embodiment of the present application is within an appropriate range, for example, 0.5% to 2.0%, which can improve the conductivity of the lithium iron phosphate and can improve the cycle performance of the battery cell under fast charging conditions.

[0259] Comparative Example 2-1 and Comparative Example 2-2 The battery cell was prepared by a method similar to that of Example 1. Similar to Example 1, the mass content of silicon element was adjusted. Among them, the negative electrode active material of Comparative Example 2-1 did not contain silicon-based material.

[0260] Examples 3-1 to 3-4 The battery cell was prepared by a method similar to that of Example 1. Similar to Example 1, the mass content of silicon element and the mass content of fluorinated cyclic carbonate were adjusted.

[0261] Example 3-5 The battery cell was prepared by a method similar to that of Example 1. Similar to Example 1, the fluorinated cyclic carbonate was not added to the electrolyte.

[0262] Example 3-6 The battery cell was prepared by a method similar to that of Example 1. Similar to Example 1, the material of the fluorinated cyclic carbonate was adjusted.

[0263] Examples 4-1 and 4-2 The battery cell was prepared by a method similar to that of Example 1. Similar to Example 1, the average particle size and specific surface area of the silicon-based material were adjusted.

[0264] Example 4-3 The battery cell was prepared by a method similar to that of Example 1. Similar to Example 1, the material of the silicon-based material was adjusted.

[0265] The test results are shown in Table 2.

[0266] Table 2

[0267] In Table 2, DFEC represents difluoroethylene carbonate; FEC represents fluoroethylene carbonate.

[0268] In Comparative Example 2-1, no silicon-based material is added. To meet the preset energy density, the coating amount of the active material on the negative electrode side may be relatively high, resulting in a longer migration path and greater resistance of lithium ions in the negative electrode film layer, which is not conducive to the improvement of the cycle performance under fast charging. In Comparative Example 2-2, the mass content of silicon element is relatively high, resulting in more intense side reactions on the negative electrode side and deteriorating the cycle.

[0269] Silicon element may undergo volume expansion during the charging process. The electrolyte of the embodiment of the present application further includes fluorinated cyclic carbonate, which can form an interfacial film rich in lithium fluoride (LiF) on the surface of the negative electrode, relieve the volume expansion of silicon, improve the life of the silicon-containing system, and improve the cycle performance under fast charging conditions. When the mass content of the fluorinated cyclic carbonate and the mass content of the silicon element meet appropriate conditions, the volume expansion of silicon can be more effectively relieved, the life of the silicon-containing system can be improved, and the cycle performance under fast charging conditions can be improved. The present application is applicable to silicon-based materials of different materials, different specific surface areas and different average particle sizes; and within an appropriate range of the specific surface area and average particle size of the silicon-based material, the side reactions on the negative electrode side can be further relieved, the cycle stability of the silicon-based material can be improved, and the cycle performance under fast charging conditions can be further improved. Comparative Example 3-1 and Comparative Example 3-2 The battery monomers were prepared by a method similar to that of Example 1. Different from Example 1, the components and contents of the electrolyte were adjusted.

[0270] Examples 5-1 to 5-6 The battery monomers were prepared by a method similar to that of Example 1. Different from Example 1, the components and contents of the electrolyte were adjusted.

[0271] The test results are shown in Table 3.

[0272] Table 3

[0273] 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; EA: 25, indicating that the mass content of EA is 25%; EC: 27, indicating that the mass content of EC is 27%.

[0274] 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.

[0275] The meanings of other examples are the same as the above explanations and will not be elaborated here.

[0276] The conductivity of the electrolyte in Example 5-1 is 9 mS / cm, and the conductivity of the electrolyte in Example 5-2 is 18 mS / cm.

[0277] In Comparative Example 3-1, when the mass content of the carboxylic ester solvent is too low, the conductivity of the electrolyte may be too low, which is not conducive to the rapid transmission of lithium ions; in Comparative Example 3-2, when the mass content of the carboxylic ester solvent is too high, the side reactions on the negative electrode side increase, deteriorating the cycle.

[0278] The mass content of the carboxylic ester solvent in the examples of this application is 3% to 70%. The electrolyte can rapidly infiltrate the electrode sheet, improve the transmission rate of lithium ions, and is adapted to the electron conduction ability, which is beneficial to the improvement of the cycle performance of the battery cell under rapid charging; In the examples of this 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, which is beneficial to improving the cycle life of the battery cell under rapid charging conditions.

[0279] 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 cycle life under rapid charging conditions. Example 6-1 and Example 6-2 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.

[0280] Example 7 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.

[0281] 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.

[0282] The first negative electrode film layer comprises 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 in a mass ratio of 87:9.5:1:1.5:1. The carbon-based material of the first negative electrode film layer comprises artificial graphite, and the average particle size of the carbon-based material is 15 μm. The second negative electrode film layer comprises 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 in a mass ratio of 87:9.5:1:1.5:1. The carbon-based material of the second negative electrode film layer comprises artificial graphite and natural graphite in a mass ratio of 80%:20%, and the average particle size of the carbon-based material is 18 μm; Among them, In the cross-section along the thickness direction of the negative electrode film layer, the void ratio of a single carbon-based material in the second negative electrode film layer is greater than that of a single carbon-based material in the first negative electrode film layer; The mass content of silicon element of the silicon-based material in the negative electrode active material of the negative electrode film layer is 6%, the specific surface area of the silicon-based material is 2 m 2 / g, and the average particle size is 6 μm.

[0283] The test results are shown in Table 4.

[0284] Table 4

[0285] In Examples 6-1 and 6-2, by adjusting the average particle size of the carbon-based material, the average particle size of the carbon-based material in the first negative electrode film layer is greater than that of the carbon-based material in the second negative electrode film layer, which can shorten the solid-phase transmission path of lithium ions, improve the fast charging ability; and reduce the risk of lithium deposition on the surface of the negative electrode side, and improve the cycling performance under fast charging.

[0286] In Example 7, 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, and the cycling performance under fast charging can be improved.

[0287] 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 implementation manners of the present application, and the embodiments can be changed, substituted, and modified without departing from the spirit, principle, and scope of the implementation manners of the present application.

Claims

1. A battery cell, characterized in that: include: A positive electrode sheet, comprising 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 comprises a positive electrode active material and a carbonaceous material, wherein the positive electrode active material comprises a lithium-containing phosphate, and the carbonaceous material comprises a carbon material with a tubular structure, and the mass content of the carbon element in the positive electrode film layer is 0.8% to 3.5%; 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 carbon-based material and a silicon-based material, and the mass content of silicon element in the silicon-based material in the negative electrode active material is 0.3% to 15%; and 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 mass content of carbon element in the positive electrode film layer is 1.3% to 3.0%.

3. 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.

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

5. The battery cell according to claim 1, 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.

6. The battery cell according to claim 5, 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.

7. The battery cell according to claim 5, 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.

8. The battery cell according to claim 5, 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.

9. The battery cell according to claim 5, 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.

10. The battery cell according to claim 9, 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.

11. The battery cell according to claim 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.

12. The battery cell according to claim 1, 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.

13. The battery cell according to claim 1, characterized in that: The conductivity of the electrolyte at room temperature is 9 mS / cm to 18 mS / cm.

14. The battery cell according to claim 1, characterized in that: The mass content of the carboxylic acid ester solvent in the electrolyte is 5% to 30%.

15. The battery cell according to claim 1, 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.

16. The battery cell according to claim 1, 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.

17. The battery cell according to claim 1, 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.

18. The battery cell according to claim 17, 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%.

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

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

21. The battery cell according to claim 19, 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 The mass content of the vinylene carbonate is 0.1% to 3% based on the mass of the electrolyte.

22. The battery cell according to claim 19, 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%.

23. The battery cell according to claim 19, 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%.

24. The battery cell according to claim 1, characterized in that The carbon-containing material is coated on the surface of the lithium-containing phosphate.

25. The battery cell according to claim 24, characterized in that: The mass content of carbon elements in the carbon-containing material coated on the surface of the lithium-containing phosphate in the positive electrode film layer is 0.5% to 2.0%.

26. The battery cell according to claim 1, characterized in that: The lithium-containing phosphate includes lithium iron phosphate.

27. The battery cell according to claim 1, characterized in that: The tubular carbon material includes carbon nanotubes.

28. The battery cell according to claim 27, characterized in that: The mass content of the carbon nanotubes in the positive electrode film layer is 0.1% to 2%.

29. The battery cell according to claim 27, characterized in that: The diameter of the carbon nanotubes is 0.5 nm to 20 nm.

30. The battery cell according to claim 27, characterized in that: The specific surface area of ​​the carbon nanotubes is 500 m 2 / g to 2500m 2 / g.

31. A battery device, characterized in that: The invention comprises the battery cell according to any one of claims 1 to 30.

32. An electrical device, characterized in that: Comprising a battery device as claimed in claim 31.

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