Battery cells, battery devices, and power-consuming devices

Abstract

The present application relates to a battery cell, a battery device and an electrical device. The battery cell includes a negative electrode plate and an electrolyte. The negative electrode plate includes a negative electrode current collector and a negative electrode film layer provided on at least one side of the negative electrode current collector. The negative electrode film layer includes a negative electrode active material. The negative electrode active material includes a silicon-based material and a carbon-based material. The mass content of silicon element of the silicon-based material in the negative electrode active material is 0.3% to 15%. The single-side coating weight of the negative electrode film layer is 80mg / 1540.25mm 2 Up to 150mg / 1540.25mm 2 The electrolyte includes an organic solvent, which includes a carboxylic acid ester solvent, and the mass content of the carboxylic acid ester solvent in the electrolyte is 3% to 70%. The high-temperature storage performance and cycle performance of the battery cell of the present application can be further improved.

Description

[0001] This application claims priority to international patent application PCT / CN2025 / 071105, filed on January 7, 2025, entitled “Battery Cell, Battery Device, and Electrical Device,” the entire contents of which are incorporated herein by reference. Technical Field

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

[0003] Battery cells, with their high capacity and long lifespan, are widely used in electronic devices such as mobile phones, laptops, electric bicycles, electric cars, electric airplanes, electric boats, electric toy cars, electric toy boats, electric toy planes, and power tools. With the rapid advancements in battery technology, higher performance requirements are being placed on them. However, the high-temperature storage and cycling performance of battery cells need to be further improved. Summary of the Invention

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

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

[0006] Therefore, the embodiment of the present application can alleviate the interfacial side reactions between the negative electrode active material and the electrolyte, reduce the high-temperature gas production, and improve the high-temperature storage performance through the coordination of the mass content of the silicon element, the coating weight of the negative electrode film layer, and the components in the electrolyte; moreover, the migration rate of the active ions in the negative electrode film layer and the electrolyte is relatively fast, and the side reactions on the negative electrode side are alleviated, which is beneficial to improving the cycle performance of the battery cell under fast charging.

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

[0008] In some embodiments, the silicon-based material is in granular form with an average particle size of 4 μm to 12 μm. When the average particle size of the silicon-based material is within this range, side reactions between the silicon-based material and the electrolyte can be mitigated, reducing high-temperature gas production and improving the high-temperature storage performance and cycle performance of the battery cell.

[0009] In some embodiments, the silicon-based material includes one or more of silicon, silicon-carbon composites, and silicon oxides. These materials can increase the capacity of the negative electrode active material, help reduce the coating thickness of the negative electrode film, shorten the migration path of lithium ions, and facilitate rapid charging.

[0010] In some embodiments, the negative electrode film layer includes a first region and a second region, the first region 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; 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, wherein, in the cross-section of the negative electrode film layer parallel to the thickness direction, the void proportion of a single carbon-based material located in the first region is less than the void proportion of a single carbon-based material located in the second region.

[0011] Therefore, in the embodiment 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, improves the transmission rate, and is beneficial to the rapid charging of the battery cell; under rapid charging, lithium ions diffuse rapidly into the negative electrode active material, which can reduce the risk of lithium ion side plating at the negative electrode, thereby improving the cycle life of the battery cell.

[0012] In some embodiments, the average particle size of the carbon-based material in the first region is greater than or equal to the average particle size of the carbon-based material in the second region.

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

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

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

[0016] In some embodiments, when the average particle size of the carbon-based material in the first region is greater than or equal to the average particle size of the carbon-based material in the second region, the carbon-based material in the first region includes artificial graphite and / or natural graphite. The above configuration is conducive to improving the cycle performance of the battery cell.

[0017] In some embodiments, when the average particle size of the carbon-based material in the first region is greater than or equal to the average particle size of the carbon-based material in the second region, the carbon-based material in the second region comprises artificial graphite. The above configuration is conducive to improving the cycle performance of the battery cell.

[0018] In some embodiments, the average particle size of the carbon-based material in the second region is greater than the average particle size of the carbon-based material in the first region. The relatively larger average particle size of the carbon-based material in the second region provides a higher pressure resistance during the film preparation process, and the film layer is more stable, which is beneficial for improving the high-temperature storage performance and cycle performance of the battery cell.

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

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

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

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

[0023] In some embodiments, the negative electrode film layer includes a first negative electrode film layer and a second negative electrode film layer. The first negative electrode film layer is disposed on the surface of the negative electrode current collector, and the negative electrode active material of the first negative electrode film layer includes a carbon-based material. The second negative electrode film layer is connected to the side of the first negative electrode film layer facing away from the negative electrode current collector, and the negative electrode active material of the second negative electrode film layer includes a carbon-based material. At least one of the first negative electrode film layer and the second negative electrode film layer includes a silicon-based material. This dual-layer configuration facilitates improving both the fast charging capability and energy density of the battery cell; silicon-based materials can further enhance energy density.

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

[0025] In some embodiments, the mass content of the carboxylate ester solvent in the electrolyte is 5% to 30%. When the mass content of the carboxylate ester solvent is within the above range, the conductivity of the electrolyte can be increased, improving the fast charging capability of the battery cell. In addition, the side reactions of the electrolyte on the negative electrode side can be alleviated, which can effectively reduce the gas production of the battery cell, thereby improving the high-temperature storage performance and cycle performance of the battery cell.

[0026] In some embodiments, the carboxylate solvent includes a cyclic carboxylate, which includes one or more of γ-butyrolactone, γ-valerolactone, and δ-valerolactone. These materials have low viscosity, which can enhance the wettability of the electrode and improve cycling performance under fast charging.

[0027] In some embodiments, the carboxylate solvent includes a linear carboxylate, which includes one or more of methyl acetate, ethyl acetate, propyl acetate, butyl acetate, propyl propionate, and butyl propionate. These materials have low viscosity, which can enhance the wettability of the electrode and improve the cycling performance under fast charge.

[0028] In some embodiments, the organic solvent further comprises a carbonate solvent, including one or more of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate. The combination of carbonate and carboxylate solvents can enhance electrolyte stability and reduce high-temperature gas production, thereby improving the high-temperature storage and cycling performance of the battery cells.

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

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

[0031] In some embodiments, the mass content of lithium bis(fluorosulfonyl)imide is 2% to 11% based on the mass of the electrolyte. When the mass content of lithium bis(fluorosulfonyl)imide is within this range, the hydrofluoric acid content can be reduced, which slows down negative electrode interface side reactions, reduces gas production during high-temperature storage, and helps improve the cycle life of the battery cells.

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

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

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

[0035] In some embodiments, the mass content of the fluorinated cyclic carbonate is 0.5% to 20% based on the mass of the electrolyte. When the mass content of the fluorinated cyclic carbonate is within the above range, it can form an excellent interfacial film, provide excellent protection for the negative electrode, and help improve the high-temperature storage performance and cycle performance of the battery cell.

[0036] In some embodiments, the weight content of vinylene carbonate is 0.1% to 3% based on the weight of the electrolyte. Vinylene carbonate participates in the formation of the negative electrode interface film, forming an excellent interface film that provides excellent protection for the negative electrode, thereby improving the high-temperature storage performance and cycle performance of the battery cell.

[0037] In some embodiments, the mass content of the fluorinated cyclic carbonate is 0.5% to 10% based on the mass of the electrolyte; the mass content of silicon 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 silicon meet the above conditions, the volume expansion of silicon can be more effectively mitigated, the lifespan of the silicon-containing system can be improved, and high-temperature gas production can be reduced, which is beneficial for improving the high-temperature storage performance and cycle performance of the battery cell.

[0038] In some embodiments, the mass content of the fluorinated cyclic carbonate is greater than 10% and less than 20% based on the mass of the electrolyte; and the mass content of silicon in the silicon-based material in the negative electrode active material is greater than 7.5% and less than 15%. When the mass content of the fluorinated cyclic carbonate and the mass content of silicon meet the above conditions, the volume expansion of silicon can be more effectively mitigated, the lifespan of the silicon-containing system can be improved, and high-temperature gas production can be reduced.

[0039] In some embodiments, the battery cell further includes a positive electrode sheet, the positive electrode sheet includes a positive electrode current collector and a positive electrode film layer disposed on at least one side of the positive electrode current collector, the positive electrode film layer includes a positive electrode active material, and the single-side coating weight of the positive electrode film layer is 250 mg / 1540.25 mm 2 Up to 300mg / 1540.25mm 2 .

[0040] When the single-sided coating weight of the positive electrode film layer is within the above range, the heat generated per unit area of ​​the positive electrode sheet will not be too large, so that too much heat will not accumulate in the battery cell system, reducing the risk of high-temperature decomposition of the electrolyte and improving the cycle performance of the battery cell.

[0041] In some embodiments, the positive electrode active material includes one or more of a lithium-containing transition metal oxide and a lithium-containing phosphate.

[0042] In a second aspect, an embodiment of the present application further provides a battery device, comprising a battery cell according to any embodiment of the first aspect of the present application.

[0043] In a third aspect, an embodiment of the present application further proposes an electrical device, which includes a battery device as in any embodiment of the second aspect or the third aspect of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following is a brief introduction to the drawings required for use in the embodiments of the present application. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on the drawings without creative work.

[0045] Figure 1 It is a schematic diagram of the structure of an electrical device provided in some embodiments of the present application.

[0046] Figure 2 is a schematic structural diagram of a battery pack provided in some embodiments of the present application;

[0047] Figure 3 is a schematic structural diagram of a battery module provided in some embodiments of the present application;

[0048] Figure 4 is a schematic structural diagram of a battery cell provided in some embodiments of the present application;

[0049] Figure 5 is a schematic structural diagram of an electrode assembly of a battery cell provided in some embodiments of the present application;

[0050] Figure 6 It is a schematic structural diagram of the negative electrode sheet of a battery cell provided in some embodiments of the present application.

[0051] The drawings are not necessarily drawn to scale.

[0052] The following are the descriptions of the reference numerals:

[0053] X, thickness direction; 1, electrical device; 2, battery pack; 3, controller; 4, motor; 5, casing; 5a, first casing part; 5b, second casing part; 5c, accommodating space; 6, battery module; 7, battery cell; 10, electrode assembly; 11, positive electrode sheet; 12, negative electrode sheet; 121, negative electrode film layer; 122, negative electrode current collector; 1211, first negative electrode film layer; 1212, second negative electrode film layer; 121a, first region; 121b, second region; 121c, third region; 13, separator; 20, outer shell assembly; 21, shell; 22, end cover; 23, electrode terminal. DETAILED DESCRIPTION

[0054] Below, the embodiments of the battery cells, battery devices, and electrical devices of the present application are described in detail with appropriate reference to the accompanying drawings. However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repeated descriptions of substantially the same structures may be omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate understanding by those skilled in the art. In addition, the drawings and the following description are provided to enable those skilled in the art to fully understand the present application and are not intended to limit the subject matter described in the claims.

[0055] " Range " disclosed in this application is limited in the form of lower limit and upper limit, and given range is limited by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundary of special range. The scope limited in this way can be inclusive or exclusive of end values, and can be arbitrarily combined, that is, any lower limit can form a range with any upper limit combination. For example, if the range of 60 to 120 and 80 to 110 is listed for a particular parameter, it is understood that the range of 60 to 110 and 80 to 120 is also expected. 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 can all be expected: 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 abbreviation of any real number combination between a and b, wherein a and b are real numbers. For example, a numerical range of "0 to 5" indicates that all real numbers between "0 and 5" are listed herein, and "0 to 5" is merely an abbreviation for a combination of these values. Furthermore, when a parameter is expressed as an integer ≥ 2, this is equivalent to disclosing that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0056] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution. Unless otherwise specified, all technical features and optional technical features of the present application can be combined with each other to form a new technical solution. Unless otherwise specified, all steps of the present application can be performed sequentially or randomly, preferably sequentially. For example, a method includes steps (a) and (b), which means that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially. For example, it is mentioned that the method may also include step (c), which means that step (c) can be added to the method in any order, for example, the method may include steps (a), (b) and (c), or may include steps (a), (c) and (b), or may include steps (c), (a) and (b), etc.

[0057] The term "plurality" used in this application refers to two or more (including two).

[0058] With the rapid development of the battery field, the performance requirements for battery cells are gradually increasing. For example, with the improvement of fast charging performance requirements, this can be achieved in related technologies by increasing the conductivity of the electrolyte. However, the increase in conductivity may cause the electrolyte to decompose at high temperatures, resulting in an increase in the high-temperature gas production of the battery cell, an increase in the volume expansion rate of the battery cell, and may worsen the cycle performance of the battery cell.

[0059] In view of the above problems, the embodiments of the present application improve the cycling performance and fast charging performance of the battery cell by synergistically regulating the negative electrode plate and the electrolyte. Specifically, the negative electrode plate of the battery cell includes a negative electrode active material containing silicon, which, combined with a relatively small coating weight, facilitates the rapid migration of active ions and improves the fast charging capability of the battery cell.

[0060] Under fast charging conditions, negative electrode active materials containing silicon elements are more likely to undergo side reactions with the electrolyte, resulting in an increase in high-temperature gas production. The embodiments of the present application are also combined with an electrolyte containing an appropriate content of carboxylic acid ester, which can enable the rapid migration of active ions such as lithium ions, while alleviating the side reactions of the negative electrode active materials and the electrolyte, reducing high-temperature gas production, reducing the volume expansion rate of the battery cell, and improving the high-temperature storage performance of the battery cell. In addition, since the side reactions on the negative electrode side interface are alleviated, it is beneficial to improve the cycle performance of the battery cell.

[0061] The battery cell of the present application is applicable to various battery devices and electrical devices using the battery cell.

[0062] For example, the power-consuming device may be a mobile phone, portable device, laptop computer, electric vehicle, electric toy, electric tool, vehicle, ship, spacecraft, etc. Alternatively, for example, the power-consuming device may be a spacecraft, including an airplane, rocket, space shuttle, and spacecraft.

[0063] Figure 1 1 is a schematic diagram of an exemplary electric device 1. The electric device 1 is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the high power and high energy density requirements of the electric device 1, a battery pack or battery module may be used.

[0064] A battery device is disposed within the electrical device 1, and the battery device can be disposed at the bottom, head, or tail of the electrical device 1. The battery device can be used to power the electrical device 1. For example, the battery device can serve as an operating power source for the electrical device 1, and can also serve as a driving power source for 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 FIG. 1 is a battery pack 2 .

[0065] The electric 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, to meet the power requirements of the electric device 1 during startup, navigation, and driving.

[0066] A battery device may include one or more battery cell assemblies to provide voltage and capacity. A battery cell assembly may include multiple battery cells connected in series, parallel, or in series via a busbar.

[0067] In some embodiments, a battery cell assembly is generally formed by arranging a plurality of battery cells.

[0068] As an example, the battery cell assembly may be a battery module, which is formed by arranging and fixing multiple battery cells to form an independent module. As an example, the battery module may be formed by bundling multiple battery cells with a cable tie.

[0069] like Figure 2 As shown, in some embodiments, the battery device may be a battery pack 2, which includes a housing 5 and one or more battery cell assemblies housed in the housing 5. As an example, the battery cell assemblies may also be housed in the housing 5 by directly securing multiple battery cells to the housing 5.

[0070] As an example, the housing 5 includes a first housing portion 5a and a second housing portion 5b, which define a storage space 5c. The first housing portion 5a and the second housing portion 5b engage to form a closed space within the housing 5 for accommodating the battery cell assembly. "Enclosed" here means covered or closed, and can be either sealed or unsealed. The first housing portion 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 5 can be used as a part of the chassis structure of the vehicle. For example, part of the box 5 can become at least a part of the floor of the vehicle, or part of the box 5 can become at least a part of the crossbeam and longitudinal beam of the vehicle.

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

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

[0075] like Figure 4 and Figure 5As 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 outer shell can be made of steel, aluminum, plastic (e.g., polypropylene), a composite metal shell (e.g., a copper-aluminum composite shell), or an aluminum-plastic film. In some embodiments, the outer shell can be either sealed or non-sealed. For example, in a non-sealed outer shell, the outer shell protects the electrode assembly 10 and includes a sealed bag between the outer shell and the electrode assembly 10, which encapsulates the electrode assembly 10 and the electrolyte. Specifically, the sealed bag can be a bag-shaped insulating member or an aluminum-plastic film. In a sealed outer shell, the sealed bag encapsulates the electrode assembly 10 and other components, such as 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 polygonal battery, and a polygonal battery such as a hexagonal battery. There is no special limitation in this application.

[0080] In some embodiments, the housing includes an end cap 22 and a shell 21. The shell 21 has an opening, and the end cap 22 covers the opening. The shell 21 may have one or more openings. One or more end caps 22 may also be provided.

[0081] The shape of the housing 21 can be determined based on the specific shape of the electrode assembly 10. For example, if the electrode assembly 10 has a cylindrical structure, a cylindrical housing 21 can be selected; if the electrode assembly 10 has a rectangular parallelepiped structure, a rectangular parallelepiped housing 21 can be selected. Optionally, both the electrode assembly 10 and the housing 21 have rectangular parallelepiped structures.

[0082] The electrode terminal 23 can be provided on the housing 21 or on the end cap 22. The electrode terminal 23 is electrically connected to the tab of the electrode sheet. The electrode terminal 23 can be directly connected to the tab or indirectly connected to the tab through a current collecting member.

[0083] The electrode assembly 10 may be a wound structure, a laminated structure, or a mixed structure of wound and laminated structures.

[0084] In some embodiments, the electrode assembly 10 is a wound structure in which the positive electrode sheet 11 and the negative electrode sheet 12 are wound into a wound structure.

[0085] In some embodiments, the electrode assembly 10 is a laminated structure.

[0086] As an example, a plurality of positive electrode sheets 11 and a plurality of negative electrode sheets 12 may be provided, and the plurality of positive electrode sheets 11 and the plurality of negative electrode sheets 12 may be alternately stacked.

[0087] As an example, a plurality of positive electrode sheets 11 may be provided, and the negative electrode sheet 12 may be folded to form a plurality of stacked folded segments, with one positive electrode sheet 11 being sandwiched between adjacent folded segments.

[0088] As an example, the positive electrode tab 11 and the negative electrode tab 12 are both folded to form a plurality of stacked folded segments.

[0089] As an example, a plurality of separators 13 may be provided, each of which is disposed between any adjacent positive electrode sheets 11 or negative electrode sheets 12 .

[0090] As an example, the separator 13 may be provided continuously, and may be provided between any adjacent positive electrode sheets 11 or negative electrode sheets 12 by folding or winding.

[0091] In some embodiments, the shape of the electrode assembly 10 can be cylindrical, flat, or polygonal.

[0092] In some embodiments, the electrode assembly 10 is provided with tabs that conduct current from the electrode assembly 10. The tabs include positive tabs and negative tabs. The electrode assembly 10 can have a wound structure or a laminated structure. The laminated structure is preferably selected to improve the energy density of the battery cell 7.

[0093] In some embodiments, the battery cell 7 includes a negative electrode plate 12 and an electrolyte, the negative electrode plate 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 silicon-based material and a carbon-based material, the silicon content of the silicon-based material in the negative electrode active material is 0.3% to 15% by mass, and the single-sided coating weight of the negative electrode film layer is 80 mg / 1540.25 mm 2 Up to 150mg / 1540.25mm 2 The electrolyte includes an organic solvent, the organic solvent includes a carboxylic acid ester solvent, and the mass content of the carboxylic acid ester solvent in the electrolyte is 3% to 70%.

[0094] During the charging process of the battery cell 7, active ions such as lithium ions migrate from the positive electrode plate 11 to the negative electrode plate 12 through the electrolyte. The mass content of the carboxylic acid ester solvent in the electrolyte is greater than or equal to 3%, so that the migration rate of the active ions in the electrolyte is relatively fast.

[0095] The negative electrode sheet 12 includes a silicon-based material. The mass content of silicon in the negative electrode active material is greater than or equal to 0.3%, which is beneficial to reducing the coating thickness. The coating weight of the negative electrode film layer is 80mg / 1540.25mm 2 Up to 150mg / 1540.25mm 2 , which is beneficial to shorten the migration path of lithium ions and increase the migration rate of lithium ions;

[0096] The fast charging capability of the battery cell 7 is enhanced by adjusting the coating weight of the negative electrode film layer and the components in the electrolyte.

[0097] The increase in the mass content of silicon is conducive to the improvement of energy density, and the increase in the addition amount of carboxylate solvents is conducive to improving the migration rate of lithium ions. However, with the increase in the mass content of silicon and the mass content of carboxylate solvents, the interfacial reaction between silicon-based materials and electrolytes intensifies, and the high-temperature gas production increases. Therefore, the embodiment of the present application further regulates the mass content of silicon to be less than or equal to 15%, and the mass content of carboxylate solvents in the electrolyte to be less than or equal to 70%, thereby alleviating the interfacial side reactions between the negative electrode active material and the electrolyte, reducing the high-temperature gas production, and improving the high-temperature storage performance of the battery cell. Moreover, since the interfacial side reactions on the negative electrode side are alleviated, it is beneficial to improve the cycle performance of the battery cell 7, especially the cycle performance under fast charging conditions.

[0098] Negative electrode

[0099] The negative electrode sheet 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 comprising a negative electrode active material. For example, the negative electrode current collector has two opposing surfaces in the thickness direction of the negative electrode current collector, and the negative electrode film layer is disposed on either or both of the two opposing surfaces of the negative electrode current collector.

[0100] The upper limit voltage for charging and the cut-off voltage for discharging of the battery cell vary depending on the different positive electrode active materials. For example, when the phosphate material includes lithium iron phosphate, the upper limit voltage for charging may be 3.65V and the cut-off voltage for discharging may be 2.0V, or the upper limit voltage for charging may be 3.8V and the cut-off voltage for discharging may be 2.0V. For another example, when the phosphate material includes lithium manganese iron phosphate, the upper limit voltage for charging may be 4.3V and the cut-off voltage for discharging may be 2.0V. Next, taking the upper limit voltage for charging of 3.8V and the cut-off voltage for discharging of 2.0V as an example, the state of the battery cell is described: In the embodiment 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:

[0101] The battery cell is charged at a constant current charge rate of 0.33C to the upper limit of the charge 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.

[0102] In some embodiments, the negative electrode layer has a compaction density of 1.1 g / cm2 at 0% state of charge (SOC). 3 to 1.7g / cm 3 For example, the compaction density of the negative electrode film layer of the battery cell at 0% state of charge is 1.10g / cm³, 1.12g / cm³, 1.14g / cm³, 1.16g / cm³, 1.18g / cm³, 1.20g / cm³, 1.22g / cm³, 1.24g / cm³, 1.26g / cm³, 1.28g / cm³, 1.3g / cm 3 , 1.32g / cm 3 , 1.35g / cm 3 , 1.40g / cm 3 , 1.45g / cm 3 , 1.50g / cm 3 , 1.55g / cm 3 , 1.60g / cm 3 , 1.65g / cm 3 , 1.66g / cm³, 1.68g / cm³, 1.70g / cm³ or a range consisting of any two of the above values.

[0103] When the compaction density of the negative electrode film layer is within the above range, the thickness of the negative electrode film layer will not be too thick, which is conducive to the rapid charging of the battery cell; and the particles of the negative electrode active material will not be stacked too densely, reducing the risk of particle crushing, which is conducive to improving the cycle performance of the battery cell.

[0104] In some embodiments, the single-side coating weight of the negative electrode film layer is 80 mg / 1540.25 mm 2 Up to 150mg / 1540.25mm 2 For example, the single-sided coating weight of the negative electrode film layer is 80mg / 1540.25mm², 85mg / 1540.25mm², 90mg / 1540.25mm², 95mg / 1540.25mm², 100mg / 1540.25mm², 105mg / 1540.25mm², 110mg / 1540.25mm², 115mg / 1540.25mm², 120mg / 1540.25mm², 120mg / 1540.25mm², 2 、122mg / 1540.25mm2 、125mg / 1540.25mm 2 、128mg / 1540.25mm 2 、130mg / 1540.25mm 2 、132mg / 1540.25mm 2 、135mg / 1540.25mm 2 、137mg / 1540.25mm 2 、140mg / 1540.25mm 2 、145mg / 1540.25mm 2 、150mg / 1540.25mm 2 、155mg / 1540.25mm 2 、160mg / 1540.25mm 2 、165mg / 1540.25mm 2 、170mg / 1540.25mm 2 、175mg / 1540.25mm 2 、180mg / 1540.25mm 2 Or a range consisting of any two of the above values.

[0105] When the single-sided coating weight of the negative electrode film layer meets the above range, it is combined with an appropriate mass content of silicon elements to help improve the energy density of the battery cell. The migration rate of active ions in the negative electrode film layer is faster, which is beneficial to improving the fast charging capability of the battery cell.

[0106] In the embodiments of the present application, the compaction density of the negative electrode film layer of a battery cell at 0% state of charge (SOC) has a meaning well known in the art. Specifically, the negative electrode sheet of a battery cell at 0% state of charge (SOC) is disassembled and the compaction density of the negative electrode film layer is measured. For example, a single-sided coated negative electrode sheet (if a double-sided coated sheet, the negative electrode film layer on one side can be wiped off first) is punched into small discs with an area of ​​S1. The discs are weighed and recorded as M1, and their thickness H1 is measured. The negative electrode film layer of the weighed negative electrode sheet is then wiped off, and 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 = (weight of the negative electrode sheet M1 - weight of the negative electrode current collector M0) / S1. The thickness of the negative electrode film layer = thickness of the negative electrode sheet H1 - thickness of the negative electrode current collector H0. The compaction density of the negative electrode film layer = single-sided coating weight of the negative electrode film layer / thickness of the negative electrode film layer.

[0107] In some embodiments, the negative electrode active material includes a silicon-based material. Alternatively, the silicon-based material may include elemental silicon, a silicon-carbon composite, silicon oxide SiO x(0<x≤2) At least one of 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.

[0108] In some embodiments, the specific surface area of ​​the silicon-based material is 1 m 2 / g to 4m 2 / g, for example, 1m² / g, 1.2m² / g, 1.4m² / g, 1.5m² / g, 1.6m² / g, 1.8m² / g, 2m² / g, 2.2m² / g, 2.4m² / g, 2.5m² / g, 2.6m² / g, 2.8m² / g, 3m² / g, 3.2m² / g, 3.4m² / g, 3.5m² / g, 3.6m² / g, 3.8m² / g, 4m² / g or a range consisting of any two of the above values.

[0109] When the specific surface area of ​​the silicon-based material is within the above range, it can provide appropriate embedding sites for lithium ions and improve the fast charging capability; it can also alleviate the side reactions between the silicon-based material and the electrolyte, reduce high-temperature gas production, and improve the cycle performance of the battery cell under fast charging conditions.

[0110] In the embodiments of the present application, the specific surface area of ​​the material has a meaning well known in the art and can be tested using equipment and methods well known in the art. For example, according to the test standard GB / T 19587-2017, the negative electrode sheet in the battery cell can be disassembled to obtain relevant materials as samples, and the specific surface area can be tested using a Tri-Star 3020 specific surface area pore size analyzer from Micromeritics, USA.

[0111] In some embodiments, the silicon-based material is granular and has an average particle size of 4 μm to 12 μm, for example, 4 μm, 4.5 μm, 5 μm, 5.5 μm, 6 μm, 6.5 μm, 7 μm, 7.5 μm, 8 μm, 8.5 μm, 9 μm, 9.5 μm, 10 μm, 10.5 μm, 11 μm, 11.5 μm, 12 μm, or a range consisting of any two of the above values.

[0112] When the average particle size of the silicon-based material is within the above range, it can alleviate the side reactions between the silicon-based material and the electrolyte, reduce high-temperature gas production, and improve the cycle performance of the battery cell; and it can provide appropriate embedding sites for lithium ions and enhance the fast charging capability.

[0113] In some embodiments, the negative electrode active material includes a carbon-based material. The carbon-based material has high cycle stability and can improve the cycle performance of the battery cell.

[0114] Optionally, the carbon-based material includes at least one of artificial graphite and natural graphite.

[0115] In some embodiments, the negative electrode active material may include at least one of a tin-based material and lithium titanate in addition to the aforementioned carbon-based material and optionally a silicon-based material. The tin-based material may include at least one of elemental tin, tin oxide, and a tin alloy.

[0116] The qualitative and quantitative properties of each substance or element in this application can be detected using appropriate equipment and methods known to those skilled in the art. The relevant detection methods can refer to domestic and international detection standards, domestic and international enterprise standards, etc., and those skilled in the art can also adapt certain detection steps / instrument parameters, etc. from the perspective of detection accuracy to obtain more accurate detection results. A single detection method can be used for qualitative or quantitative determination, or several detection methods can be used in combination for qualitative or quantitative determination.

[0117] For example, the present application may combine JIS / K0131-1996 General Rules for X-ray Diffraction Analysis Methods to perform X-ray powder diffraction testing and qualitative analysis on the negative electrode sheet or negative electrode active material.

[0118] Artificial graphite and natural graphite can be distinguished by the SEM cross-section taken by a scanning electron microscope (SEM). The SEM cross-section of natural graphite shows gaps between the flake structures, while the SEM cross-section of artificial graphite is dense and has no obvious gaps. They can also be distinguished by the XRD spectrum obtained by the X-ray diffraction method. The XRD spectrum of natural graphite shows obvious 2H phase and 3R phase, while the XRD spectrum of artificial graphite only shows 2H phase.

[0119] like Figure 6 As shown, the negative electrode film layer 121 of the negative electrode plate 12 in the embodiment of the present application 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.

[0120] In the case where the negative electrode film layer 121 is a single-layer 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.

[0121] When the negative electrode film layer 121 comprises at least two layers, the negative electrode active material in the negative electrode film layer 121 includes carbon-based materials and silicon-based materials. The negative electrode film layer 121 may include two layers, three layers, four layers, or even more layers.

[0122] 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. 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. 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 may be regular or irregular, or may be irregular; alternatively, there may be no distinct interface between the first negative electrode film layer 1211 and the second negative electrode film layer 1212.

[0123] The negative electrode film layer 121 includes at least two film layers, and layered coating is beneficial to improving both the fast charging performance and the cycle life of the battery cell.

[0124] 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.

[0125] Optionally, the first negative electrode film layer 1211 further includes a silicon-based material.

[0126] Optionally, the second negative electrode film layer 1212 further includes a silicon-based material.

[0127] Illustratively, 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. Alternatively, 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. Alternatively, 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.

[0128] When both the first negative electrode film layer 1211 and the second negative electrode film layer 1212 comprise silicon-based materials, this further improves the energy density of the battery cell. When the first negative electrode film layer 1211 comprises silicon-based materials, while the second negative electrode film layer 1212 does not, the second negative electrode film layer 1212 can mitigate the volume expansion of the first negative electrode film layer 1211, reduce side reactions between the negative electrode film layer 121 and the electrolyte, and improve cycle performance.

[0129] In the case where the negative electrode film layer 121 comprises at least two film layers, the cross-sectional shapes of the negative electrode film layer 121 along the thickness direction X of the negative electrode film layer 121 may be the same or similar, or may be different.

[0130] 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.

[0131] The cross-sectional morphologies of the first region 121a and the second region 121b may be the same or similar, or they may be different. The cross-sectional morphologies of the first region 121a and the third region 121c may be the same or similar, or they may be different. The cross-sectional morphologies of the second region 121b and the third region 121c may be the same or similar, or they may be different.

[0132] There may or may not be a distinct interface between the first region 121a, the second region 121b, and the third region 121c. For example, the first negative electrode film 1211 includes the first region 121a, the second negative electrode film 1212 includes the second region 121b, and the third region 121c may be a portion of the first negative electrode film 1211, or the third region 121c may be a portion of the second negative electrode film 1212, or the third region 121c may be a portion of the first negative electrode film 1211 and the second negative electrode film 1212.

[0133] In some embodiments, in a cross section of the negative electrode film layer 121 parallel to the thickness direction X, the void ratio of the single carbon-based material located in the first region 121 a is greater than or equal to the void ratio of the single carbon-based material located in the second region 121 b. Alternatively, the void ratio of the single carbon-based material located in the first region 121 a is less than the void ratio of the single carbon-based material located in the second region 121 b.

[0134] 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 to the total cross-sectional area of ​​the carbon-based material is the void ratio of a single carbon-based material.

[0135] During the charging process of the battery cell, lithium ions diffuse to the first region 121a through the second region 121b. 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, improves the transmission rate, and is beneficial to the rapid charging of the battery cell.

[0136] 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. This facilitates the rapid migration of lithium ions from the second region 121b to the first region 121a, thereby improving the fast charging capability of the battery cell. Of course, the average particle size of the carbon-based material in the first region 121a can be smaller than the average particle size of the carbon-based material in the second region 121b.

[0137] Optionally, the average particle size of the carbon-based material of the first negative electrode film layer 1211 can be greater than or equal to the average particle size of the carbon-based material of the second negative electrode film layer 1212. Further optionally, the average particle size of the carbon-based material of the first negative electrode film layer 1211 can be greater than the average particle size of the carbon-based material of the second negative electrode film layer 1212.

[0138] There is a difference in the particle size of the first negative electrode film layer 1211 and the second negative electrode film layer 1212, which can improve the fast charging performance of the battery cell. Specifically, during the fast charging process, the overpotential of the second negative electrode film layer 1212 is usually higher, 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 improve the problem of lithium plating on the surface of the negative electrode plate 12.

[0139] Optionally, the average particle size of the carbon-based material in the first region 121a is 12 μm to 21 μm, for example, 12 μm, 12.5 μm, 13 μm, 13.5 μm, 14 μm, 14.5 μm, 15 μm, 15.5 μm, 16 μm, 16.5 μm, 17 μm, 17.5 μm, 18 μm, 18.5 μm, 19 μm, 19.5 μm, 20 μm, 20.5 μm, 21 μm, or a range consisting of any two of the above values. When the average particle size of the carbon-based material in the first region 121a is within the above range, the cycle life can be improved without substantially adversely affecting the fast charging performance.

[0140] Optionally, the average particle size of the carbon-based material in the first negative electrode film layer 1211 is 12 μm to 21 μm. When the average particle size of the carbon-based material in the first negative electrode film layer 1211 is within the above range, the cycle life can be improved without adversely affecting the fast charging performance.

[0141] Optionally, the average particle size of the carbon-based material in the second region 121b is 9 μm to 17 μm, for example, 9 μm, 9.5 μm, 10 μm, 10.5 μm, 11 μm, 11.5 μm, 12 μm, 12.5 μm, 13 μm, 13.5 μm, 14 μm, 14.5 μm, 15 μm, 15.5 μm, 16 μm, 16.5 μm, 17 μm, or a range consisting of any two of the foregoing values. When the average particle size of the carbon-based material in the second negative electrode film layer 1212 is within the above range, it is beneficial to improve the fast charging capability of the battery cell and enhance the stability of the material.

[0142] Optionally, the average particle size of the carbon-based material in the second negative electrode film layer 1212 is 9 μm to 17 μm. When the average particle size of the carbon-based material in the second negative electrode film layer 1212 is within the above range, the solid-phase transmission path of lithium ions can be shortened, thereby improving fast charging performance and material stability.

[0143] For example, the carbon-based material of the first region 121a includes artificial graphite and natural graphite, and the carbon-based material of the second region 121b includes artificial graphite. For example, the negative electrode active material of the first region 121a includes silicon-based material, artificial graphite, and natural graphite, and the negative electrode active material of the second region 121b includes silicon-based material and artificial graphite.

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

[0145] In other embodiments, in a cross section of the negative electrode film layer 121 parallel to the thickness direction X, the void ratio of the single carbon-based material in the first region 121 a is smaller than the void ratio of the single carbon-based material in the second region 121 b .

[0146] During the charging process of the battery cell, lithium ions diffuse to the first region 121a through the second region 121b. The voids of the single carbon-based material in the second region 121b account for a larger proportion, which is conducive to the rapid transmission of lithium ions in the second region 121b to the first region 121a, thereby facilitating the rapid charging of the battery cell.

[0147] 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 carbon-based material in the second region 121b has a relatively larger average particle size, which provides higher pressure resistance during film preparation and helps improve particle density. The carbon-based material in the first region 121a has a relatively smaller average particle size, which enables faster lithium ion migration and improves the fast charging capability of the battery cell. Of course, the average particle size of the carbon-based material in the first region 121a can be greater than or equal to the average particle size of the carbon-based material in the second region 121b.

[0148] Optionally, the average particle size of the carbon-based material in the first region 121a is 9 μm to 17 μm, for example, 9 μm, 9.5 μm, 10 μm, 10.5 μm, 11 μm, 11.5 μm, 12 μm, 12.5 μm, 13 μm, 13.5 μm, 14 μm, 14.5 μm, 15 μm, 15.5 μm, 16 μm, 16.5 μm, 17 μm or a range consisting of any two of the above values.

[0149] Optionally, the average particle size of the carbon-based material of the first negative electrode film layer 1211 is 9 μm to 17 μm.

[0150] Optionally, the average particle size of the carbon-based material in the second region 121b is 12μm to 21μm, for example, 12μm, 12.5μm, 13μm, 13.5μm, 14μm, 14.5μm, 15μm, 15.5μm, 16μm, 16.5μm, 17μm, 17.5μm, 18μm, 18.5μm, 19μm, 19.5μm, 20μm, 20.5μm, 21μm or a range consisting of any two of the above values.

[0151] Optionally, the average particle size of the carbon-based material of the second negative electrode film layer 1212 is 12 μm to 21 μm.

[0152] Illustratively, 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.

[0153] Illustratively, 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.

[0154] In the embodiment 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: the negative electrode plate 12 is used as a sample, and a scanning electron microscope SEM is used to photograph along the thickness direction X of the negative electrode film layer 121 to obtain a SEM cross-sectional view, and the particle size of the active material in the SEM cross-section is counted, and the average particle size of the active material is calculated based on the counted number.

[0155] In some embodiments, the negative electrode film layer may further optionally include a negative electrode conductive agent. The present application does not particularly limit the type of negative electrode conductive agent. For 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, the weight content of the negative electrode conductive agent is ≤5% based on the total weight of the negative electrode film layer.

[0156] In some embodiments, the negative electrode film layer may further include a negative electrode binder. In some embodiments, the negative electrode binder has a mass content of ≤5% based on the total weight of the negative electrode film layer.

[0157] In some embodiments, the negative electrode film layer may also optionally include other additives. Examples of these additives include thickeners, dispersants, and the like, such as sodium carboxymethylcellulose (CMC-Na) and PTC thermistor materials. In some embodiments, the weight content of these additives is ≤ 2% based on the total weight of the negative electrode film layer.

[0158] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. Examples of metal foils include at least one of copper, copper alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys. The composite current collector may include a polymer base layer and a metal layer formed on at least one surface of the polymer base layer. For example, the metal layer may include at least one of copper, copper alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys. For example, the polymer base layer may include at least one of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0159] The negative electrode film layer is typically formed by coating the negative electrode slurry onto the negative electrode current collector, drying it, and cold pressing it. The negative electrode slurry is typically formed by dispersing the negative electrode active material, optional conductive agent, optional binder, and other optional additives in a solvent and stirring them uniformly. The solvent can be, but is not limited to, N-methylpyrrolidone (NMP) or deionized water.

[0160] The negative electrode sheet does not exclude other additional functional layers in addition to the negative electrode film layer. For example, in some embodiments, the negative electrode sheet of the embodiments of the present application further includes a negative conductive layer sandwiched between the negative electrode current collector and the negative electrode film layer and disposed on the surface of the negative electrode current collector. In other embodiments, the negative electrode sheet of the embodiments of the present application further includes a protective layer covering the surface of the negative electrode film layer.

[0161] Positive electrode

[0162] In some embodiments, the battery cell further includes a positive electrode tab.

[0163] The positive electrode sheet includes a positive electrode current collector and a positive electrode film layer disposed on at least one side of the positive electrode current collector and comprising a positive electrode active material. For example, the positive electrode current collector may have two opposing surfaces in its thickness direction, and the positive electrode film layer may be disposed on either or both of the two opposing surfaces of the positive electrode current collector.

[0164] In some embodiments, the dimension of the positive electrode film layer along the length direction of the positive electrode sheet is 200 mm to 600 mm, for example, 200 mm, 250 mm, 300 mm, 350 mm, 400 mm, 450 mm, 500 mm, 550 mm, 600 mm or a range consisting of any two of the above values.

[0165] In the case of a laminated electrode assembly, the length of the positive electrode sheet is parallel to the length of the battery cell, and the length of the positive electrode film layer can be understood as the length of the positive electrode film layer. The width of the positive electrode sheet is parallel to the width of the battery cell, and the width of the positive electrode film layer can be understood as the width of the positive electrode film layer.

[0166] Exemplarily, the positive electrode film layer has a length dimension of 200 mm to 600 mm; the electrolyte includes an organic solvent, including a carboxylic acid ester solvent, and the electrolyte has a room temperature conductivity of 9 mS / cm to 18 mS / cm. The length of the positive electrode film layer, combined with the electrolyte's conductivity, helps increase the liquid-phase transport rate of lithium ions, improves kinetic performance, and enhances the rapid charging capability of the battery cells. Furthermore, due to the low viscosity of the carboxylic acid ester solvent, it can evenly infiltrate the entire positive electrode film layer, resulting in a uniform charge level throughout the positive electrode film layer. The lithium ions released through 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 cycling performance under rapid charging.

[0167] 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 is 2.20 g / cm3 , 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.

[0168] 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 because the positive electrode active material of the positive electrode film layer is stacked relatively densely, the contact resistance between particles is small, which can further reduce the resistance of the electrode sheet, thereby reducing heat generation under fast charging, reducing high-temperature gas production, and improving the cycle performance of the battery cell.

[0169] In some embodiments, the single-sided coating weight of the positive electrode film layer is 250 mg / 1540.25 mm 2 Up to 300mg / 1540.25mm 2 For example, the coating weight of the positive electrode film on one side is 250 mg / 1540.25 mm 2 、260mg / 1540.25mm 2 、270mg / 1540.25mm 2 、280mg / 1540.25mm 2 、290mg / 1540.25mm 2 、300mg / 1540.25mm 2 Or a range consisting of any two of the above values.

[0170] When the single-sided coating weight of the positive electrode film layer is within the above range, the heat generated per unit area of ​​the positive electrode sheet will not be too large, and it can take into account the improvement of the energy density and charging rate performance of the battery cell, and prevent excessive heat accumulation in the battery cell system, thereby reducing the risk of high-temperature decomposition of the electrolyte and improving the cycle performance of the battery cell.

[0171] In the embodiments of the present application, the compacted density of the positive electrode film layer of a battery cell at 0% state of charge (SOC) has a meaning well known in the art. Specifically, the positive electrode sheet of a battery cell at 0% state of charge (SOC) is disassembled and the compacted density of the positive electrode film layer is measured. For example, a single-sided coated positive electrode sheet (if a double-sided coated sheet, the positive electrode film layer on one side can be wiped off first) is punched into small discs with an area of ​​S1. The discs are weighed and recorded as M1, and their thickness H1 is measured. The positive electrode film layer of the weighed positive electrode sheet is then wiped off, and the weight of the positive current collector is weighed and recorded as M0, and its thickness H0 is measured. The single-sided coating weight of the positive electrode film layer = (weight of the positive electrode sheet M1 - weight of the positive current collector M0) / S1. The thickness of the positive electrode film layer = thickness of the positive electrode sheet H1 - thickness of the positive current collector H0. The compacted density of the positive electrode film layer = single-sided coating weight of the positive electrode film layer / thickness of the positive electrode film layer.

[0172] In some embodiments, the positive electrode active material includes one or more of a lithium-containing transition metal oxide and a lithium-containing phosphate. Optionally, the positive electrode active material includes a lithium-containing phosphate. The lithium-containing phosphate may have an olivine structure, which is structurally stable during charge and discharge, thereby improving the cycle life of the battery cell.

[0173] Examples of 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 modified compounds thereof.

[0174] In some embodiments, the positive electrode film layer further includes a carbon-containing material, which is a carbon-containing conductive material. The above material can enhance the conductivity of the positive electrode film layer, which is beneficial to improving the fast charging performance of the battery cell.

[0175] Optionally, the mass content of the carbon element in the positive electrode film layer is 0.8% to 3.5%, for example, 0.8%, 0.9%, 1.0%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2.0%, 2.1%, 2.2%, 2.3%, 2.4%, 2.5%, 2.6%, 2.7%, 2.8%, 2.9%, 3.0%, 3.1%, 3.2%, 3.3%, 3.4%, 3.5%, or a range consisting of any two of the above values. Optionally, the mass content of the carbon element in the positive electrode film layer is 1.3% to 3.0%.

[0176] For example, the carbon-containing material may include carbon nanotubes, which may serve as a conductive agent in the positive electrode film layer to improve the conductivity of the positive electrode film layer.

[0177] For another 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, the surface of the lithium-containing phosphate is provided with a carbon-containing material, and the carbon-containing material can be coated on the surface of the lithium-containing phosphate as a coating layer, 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, improving the fast charging capability of the battery cell, and reducing the heat generation of the battery cell.

[0178] In some embodiments, the lithium-containing phosphate comprises a general formula of Li x1 A y1 Me a M b P 1-c X c Y z A compound wherein 0.5≤x1≤1.3, 0≤y1≤1.3, and 0.9≤x1+y1≤1.3, 0.9≤a≤1.5, 0≤b≤0.5, and 0.9≤a+b≤1.5, 0≤c≤0.5, 3≤z≤5, A comprises one or more of Na, K, and Mg, Me comprises one or more of Mn, Fe, Co, and Ni, M comprises one or more of B, Mg, Al, Si, P, S, Ca, Sc, Ti, V, Cr, Cu, Zn, Sr, Y, Zr, Nb, Mo, Cd, Sn, Sb, Te, Ba, Ta, W, Yb, La, and Ce, X comprises one or more of Cl, C, and N, and Y comprises one or more of O and F. The lithium-containing phosphate has excellent cycle stability, which is beneficial for improving the cycle performance of battery cells.

[0179] Exemplarily, the lithium-containing phosphate includes one or more of LiFePO4, LiMnPO4, LiNiPO4, and LiCoPO4. The battery cell is accompanied by the deintercalation and consumption of active ions such as Li during the charge and discharge process, and the molar content of Li in the battery cell is different when discharged to different states. In the enumeration of positive electrode active materials LiFePO4, LiMnPO4, LiNiPO4, LiCoPO4, etc., the molar content of Li is the initial state of the material, that is, the state before feeding. The positive electrode active material is used in the battery system, and the molar content of Li may change after charge and discharge cycles. In the enumeration of positive electrode active materials LiFePO4, LiMnPO4, LiNiPO4, LiCoPO4, etc. in the embodiment of the present application, the molar content of oxygen O is only a theoretical state value. The release of oxygen from the lattice will cause the molar content of oxygen O to change. In practice, the molar content of oxygen O will fluctuate. The above situations are all within the scope of protection of the present application.

[0180] In the embodiments of this application, the element content in the positive electrode active material has a meaning well known in the art and can be measured using equipment and methods well known in the art. For example, in accordance with EPA 6010D-2014, it can be measured by inductively coupled plasma atomic emission spectrometry (ICP-OES, instrument model: Thermo ICAP7400). After discharging the battery cell to 0% state of charge (SOC), the positive electrode sheet is disassembled, cleaned with dimethyl carbonate (DMC), dried, and calcined at high temperature to remove impurities. Then, 0.4g of the positive electrode active material is weighed and 10ml (50% concentration) of aqua regia is added. The sample is then placed on a plate at 180°C for 30 minutes. After digestion on the plate, the volume is adjusted to 100ml, and quantitative analysis is performed using a standard curve method.

[0181] In some embodiments, the lithium-containing phosphate is in a granular form, and the lithium-containing phosphate includes a plurality of first phosphate particles and a plurality of second phosphate particles. The longest diameter of the first phosphate particles is greater than or equal to a preset longest diameter, for example, 1 μm, and the longest diameter of the second phosphate particles is less than 1 μm. It can be understood that particles with a longest diameter greater than or equal to 1 μm are all first phosphate particles, and particles with a longest diameter less than 1 μm are all second phosphate particles.

[0182] The longest diameter of the first phosphate particles is greater than the longest diameter of the second phosphate particles. The average longest diameter of the first phosphate particles is 1 μm to 5 μm, and the average longest diameter of the second phosphate particles is 0.1 μm to 0.5 μm.

[0183] Illustratively, the average longest diameter of the first phosphate particles is 1 μm to 5 μm, such as 1 μm, 1.5 μm, 2 μm, 2.5 μm, 3 μm, 3.5 μm, 4 μm, 4.5 μm, 5 μm, or a range consisting of any two of the above values.

[0184] Illustratively, the average longest diameter of the second phosphate particles is 0.1 μm to 0.5 μm, such as 0.1 μm, 0.15 μm, 0.2 μm, 0.25 μm, 0.3 μm, 0.35 μm, 0.4 μm, 0.45 μm, 0.5 μm, or a range consisting of any two of the above values.

[0185] When the lithium-containing phosphate meets the above conditions, its longest diameter is relatively small, the lithium ion deintercalation path in the lithium-containing phosphate is short, and the heat generation is less; moreover, the particle size of the above lithium-containing phosphate is not too small, and basically no agglomeration occurs during the processing and preparation process, making the performance of the lithium-containing phosphate stable; thus, it is beneficial to improve the high-temperature cycle performance of the battery cell.

[0186] In some embodiments, the mass content of the second phosphate particles in the lithium-containing phosphate is 80% to 95%, for example, 80%, 82%, 84%, 85%, 86%, 88%, 90%, 92%, 94%, 95%, or a range consisting of any two of the foregoing values. A mass content of the second phosphate particles within an appropriate range, for example, 80% to 95%, can further reduce heat generation within the battery cell system, reduce the risk of electrolyte component decomposition due to heat accumulation, and improve the high-temperature cycling performance of the battery cell.

[0187] In some embodiments, the positive electrode film layer also includes a lithium supplement, which includes lithium elements and can release lithium ions during the charging process of the battery cell to compensate for lithium loss, which is beneficial to improving the capacity characteristics and high-temperature cycle performance of the battery cell.

[0188] In some embodiments, the lithium supplement comprises at least one of lithium ferrite, lithium nickelate, and lithium cobaltate.

[0189] In some embodiments, the lithium supplement is in granular form, and its average longest diameter is 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 a range consisting of any two of the above.

[0190] In some embodiments, the lithium supplement is in granular form, and its average shortest diameter is 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 a range consisting of any two of the above.

[0191] In the embodiments of the present application, the positive electrode sheet is cut along the thickness direction of the sheet to expose the cross-section of the positive electrode film layer, which can also be understood as a cross-section of the positive electrode film layer along its own thickness direction. The cross-section of the positive electrode film layer is tested by scanning electron microscopy (SEM) to determine the longest and shortest diameters of the lithium supplement particles and the longest diameter of the lithium-containing phosphate. For example, the "longest diameter" of a particle refers to the longest straight line passing through the center point of the particle and extending to the periphery of the particle. The "shortest diameter" of a particle refers to the shortest straight line passing through the center point of the particle and extending to the periphery of the particle.

[0192] In the cross section of the positive electrode film along its own thickness direction, the longest diameters of multiple, for example, 10 lithium supplements are counted and their average value is calculated as the average longest diameter; the shortest diameters of multiple, for example, 10 lithium supplements are counted and their average value is calculated as the average shortest diameter.

[0193] In a cross section of the positive electrode film layer along its own thickness direction, the longest diameters of a plurality of, for example, 50, lithium-containing phosphate particles are counted, particles having a longest diameter greater than or equal to 1 μm are classified as first phosphate particles, particles having a longest diameter less than 1 μm are classified as second phosphate particles, the average of the longest diameters of all first phosphate particles is calculated as the average longest diameter of the first phosphate particles, and the average of the longest diameters of all second phosphate particles is calculated as the average longest diameter of the second phosphate particles;

[0194] The number of all first phosphate particles and the number of all second phosphate particles are counted, and the ratio of the number of the second phosphate particles is calculated, which is the mass content of the second phosphate particles in the lithium-containing phosphate.

[0195] In some embodiments, the mass percentage of the lithium supplement agent is 0.5% to 3% based on the total mass of the positive electrode film layer, for example, 0.5%, 0.6%, 0.8%, 1.0%, 1.2%, 1.4%, 1.6%, 1.8%, 2.0%, 2.5%, 3.0%, or any combination thereof. When a lithium supplement agent within the above mass range is used, the stability of the lithium supplement agent can be effectively improved while also achieving a good oxygen release effect.

[0196] In some embodiments, the positive electrode film layer may further optionally include a positive electrode conductive agent. For example, the positive 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, the weight content of the positive electrode conductive agent is ≤5% based on the weight of the positive electrode film layer.

[0197] 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%, for example, 0.1%, 0.3%, 0.5%, 0.7%, 0.9%, 1.1%, 1.3%, 1.5%, 1.7%, 1.9%, 2%, or a range composed of any two of the foregoing. Optionally, the mass content of the carbon nanotubes in the positive electrode film layer is 0.15% to 1.2%.

[0198] When the mass content of carbon nanotubes is within the above range, it is beneficial to enhance the conductivity of the positive electrode film layer and improve the fast charging performance of the battery cell.

[0199] Optionally, the specific surface area of ​​the carbon nanotubes is 500 m 2 / g to 2500m 2 / g, for example, 500m² / g, 700m² / g, 900m² / g, 1100m² / g, 1300m² / g, 1500m² / g, 1700m² / g, 1900m² / g, 2100m² / g, 2300m² / g, 2500m² / g or a range consisting of any two of the above.

[0200] When the specific surface area of ​​carbon nanotubes is within the above range, it is beneficial to improve the electron conductivity; and adding an appropriate content of carbon nanotubes can reduce the degree of side reactions and improve high-temperature gas production.

[0201] Optionally, the carbon nanotubes have a diameter of 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 consisting of any two of the foregoing. Optionally, the carbon nanotubes have a diameter of 0.5 nm to 7.5 nm.

[0202] When the diameter of the carbon nanotubes is within the above range, the structure is relatively stable and has relatively excellent electron conduction ability.

[0203] Carbon nanotubes can generally be considered to be two-dimensional carbon materials coiled together. When the coiled material has a single layer, it is a single-walled carbon nanotube; when it has multiple layers, it is a multi-walled carbon nanotube. The diameter of a carbon nanotube is the outer diameter of the carbon nanotube along a cross section perpendicular to its central axis.

[0204] In some embodiments, the positive electrode film layer may further optionally include a positive electrode binder. The embodiments of the present application do not particularly limit the type of positive electrode binder. 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 fluorine-containing acrylic resin. In some embodiments, based on the mass of the positive electrode film layer, the mass content of the positive electrode binder is ≤5%.

[0205] In some embodiments, the positive electrode current collector may be a metal foil or a composite current collector. Examples of metal foils include at least one of aluminum, aluminum alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys. The composite current collector may include a polymer base layer and a metal layer formed on at least one surface of the polymer base layer. For example, the metal material of the metal layer may include at least one of aluminum, aluminum alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys. For example, the polymer base layer may include at least one of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0206] The positive electrode film layer is typically formed by coating a positive electrode slurry onto a positive electrode current collector, drying it, and cold pressing it. The positive electrode slurry is typically formed by dispersing the positive electrode active material, an optional conductive agent, an optional binder, and any other components in a solvent and stirring them uniformly. The solvent can be, but is not limited to, N-methylpyrrolidone (NMP).

[0207] The positive electrode sheet does not exclude other additional functional layers in addition to the positive electrode film layer. For example, in some embodiments, the positive electrode sheet of the embodiments of the present application further includes a positive electrode conductive layer sandwiched between the positive electrode current collector and the positive electrode film layer and disposed on the surface of the positive electrode current collector. In other embodiments, the positive electrode sheet of the embodiments of the present application further includes a protective layer covering the surface of the positive electrode film layer.

[0208] [Electrolyte]

[0209] During the charge and discharge process of a battery cell, active ions, such as lithium ions, are intercalated and released back and forth between the positive and negative electrodes. The electrolyte, which consists of an organic solvent and an electrolyte salt, conducts the active ions between the positive and negative electrodes.

[0210] In some embodiments, the electrolyte has a conductivity of 9 mS / cm to 18 mS / cm at room temperature. For example, the electrolyte has a conductivity of 9 mS / cm, 9.5 mS / cm, 10 mS / cm, 10.5 mS / cm, 11 mS / cm, 11.5 mS / cm, 12 mS / cm, 12.5 mS / cm, 13 mS / cm, 13.5 mS / cm, 14 mS / cm, 14.5 mS / cm, 15 mS / cm, 15.5 mS / cm, 16 mS / cm, 16.5 mS / cm, 17 mS / cm, 17.5 mS / cm, 18 mS / cm, or a range consisting of any two of the foregoing values.

[0211] 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, reducing the amount of high-temperature gas production caused by heat accumulation, and improving the cycle performance of the battery cell under rapid charging.

[0212] In the embodiment of the present application, the conductivity of the electrolyte at room temperature, for example, 25° C., is ionic conductivity, which can be tested using equipment and methods known in the art, for example, by referring to the industry standard HG-T 4067-2015.

[0213] In some embodiments, the organic solvent includes a carboxylate solvent.

[0214] Optionally, the mass content of the carboxylate solvent in the electrolyte is 3% to 70%. Exemplarily, the mass content of the carboxylate 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 consisting of any two of the above values. Optionally, the mass content of the carboxylate solvent in the electrolyte is 5% to 30%.

[0215] When the mass content of the carboxylic acid 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 high-temperature gas production of the battery cell, and improve the cycle performance of the battery cell under fast charging.

[0216] Exemplarily, the carboxylate solvent includes cyclic carboxylate, which includes one or more of γ-butyrolactone, γ-valerolactone, and δ-valerolactone. These materials have low viscosity, which can enhance the wettability of the electrode and improve cycling performance under fast charging.

[0217] Illustratively, the carboxylate solvent includes a linear carboxylate, which includes one or more of methyl acetate, ethyl acetate, propyl acetate, butyl acetate, propyl propionate, and butyl propionate. These materials have low viscosity, which can enhance the wettability of the electrode and improve cycling performance under fast charging.

[0218] In some embodiments, the organic solvent includes a carbonate solvent. A mixture of a carbonate solvent and a carboxylate solvent can enhance the stability of the electrolyte, reduce its high-temperature gas production, and improve the cycle performance of the battery cell.

[0219] Illustratively, the carbonate solvent includes one or more of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate. Alternatively, the carbonate solvent includes one or more of ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate.

[0220] In some embodiments, the electrolyte salt includes a lithium salt, and the lithium salt includes one or more of lithium bis(fluorosulfonyl)imide and lithium hexafluorophosphate. Alternatively, the lithium salt includes lithium bis(fluorosulfonyl)imide and lithium hexafluorophosphate.

[0221] 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 increased gas production during high-temperature storage. 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, reduce the gas production during high-temperature storage, and help improve the cycle life of the battery cell.

[0222] In some embodiments, based on the mass of the electrolyte, the ratio of the mass content of lithium bis(fluorosulfonyl)imide to the mass content of lithium hexafluorophosphate is 0.3 to 1.2, for example, 0.3, 0.5, 0.7, 0.9, 1.1, 1.2, or a range consisting of any two of the above values.

[0223] When the ratio of the mass contents of lithium hexafluorophosphate and lithium bis(fluorosulfonyl)imide meets the above range, on the one hand, the content of hydrofluoric acid can be reduced, the side reactions at the negative electrode interface can be slowed down, and the gas production during high-temperature storage can be reduced; on the other hand, the organic component content of the SEI film formed at the negative electrode interface is appropriate, which can also reduce the gas production during high-temperature storage and is beneficial to improving the cycle life of the battery cell.

[0224] Illustratively, based on the mass of the electrolyte, the mass content of lithium bis(fluorosulfonyl)imide is 2% to 11%, for example, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 8%, 8.5%, 9%, 9.5%, 10%, 10.5%, 11%, or a range consisting of any two of the foregoing values. When the mass content of lithium bis(fluorosulfonyl)imide is within the above range, the content of hydrofluoric acid can be reduced, side reactions at the negative electrode interface can be slowed down, gas generation during high-temperature storage can be reduced, and the cycle life of the battery cell can be improved.

[0225] Illustratively, based on the mass of the electrolyte, the mass content of lithium hexafluorophosphate is 3% to 14%, for example, 3%, 3.5%, 4%, 4.5%, 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 8%, 8.5%, 9%, 9.5%, 10%, 10.5%, 11%, 11.5%, 12%, 12.5%, 13%, 13.5%, 14%, or a range consisting of any two of the foregoing values. When the mass content of lithium hexafluorophosphate is within the above range, the conductivity of the electrolyte is relatively high, which is conducive to the migration of lithium ions and improves the fast charging performance of the battery cell.

[0226] In some embodiments, the electrolyte further contains additives, which may include negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain battery properties, such as additives that improve battery overcharge performance, additives that improve battery high temperature performance, additives that improve battery low temperature power performance, etc.

[0227] In some embodiments, the additive comprises a cyclic carbonate additive, for example, one or more of fluorinated cyclic carbonate and vinylene carbonate. Alternatively, the additive comprises fluorinated cyclic carbonate and vinylene carbonate.

[0228] Fluorinated cyclic carbonates can form an interfacial film rich in lithium fluoride (LiF) on the surface of the negative electrode, which can alleviate the volume expansion of silicon, improve the life of the silicon-containing system, and reduce high-temperature gas production.

[0229] The combined use of fluorinated cyclic carbonate and vinylene carbonate makes the interface film on the negative electrode surface more compact, which can more effectively protect the silicon-containing negative electrode, reduce the degree of side reactions at the negative electrode interface, and reduce high-temperature gas production.

[0230] Optionally, the fluorinated cyclic carbonate includes at least one of monofluoroethylene carbonate, bisfluoroethylene carbonate, and trifluoropropylene carbonate.

[0231] Optionally, based on the mass of the electrolyte, the mass content of the fluorinated cyclic carbonate is 0.5% to 20%, for example, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 8%, 8.5%, 9%, 9.5%, 10%, 10.5%, 11%, 11.5%, 12%, 12.5%, 13%, 13.5%, 14%, 14.5%, 15%, 15.5%, 16%, 16.5%, 17%, 17.5%, 18%, 18.5%, 19%, 19.5%, 20%, or a range consisting 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 cycle performance.

[0232] As an example, based on the mass of the electrolyte, the mass content of the fluorinated cyclic carbonate is 0.5% to 10%; the mass content of the silicon element of the silicon-based material in the negative electrode active material is 0.3% to 7.5%.

[0233] The mass content of silicon is relatively high, and the volume expansion is relatively larger. When the mass content of fluorinated cyclic carbonate and the mass content of silicon meet the above conditions, the volume expansion of silicon can be more effectively alleviated, the life of the silicon-containing system can be improved, and the high-temperature gas production can be reduced.

[0234] 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 of the silicon-based material in the negative electrode active material is greater than 7.5% and less than or equal to 15%.

[0235] When the mass content of the fluorinated cyclic carbonate and the mass content of the silicon element meet the above conditions, the volume expansion of silicon can be more effectively alleviated, the life of the silicon-containing system can be improved, and the high-temperature gas production can be reduced.

[0236] Optionally, based on the mass of the electrolyte, the mass content of vinylene carbonate is 0.1% to 3%, for example, 0.1%, 0.5%, 0.6%, 1.0%, 1.1%, 1.5%, 1.6%, 2.0%, 2.1%, 2.5%, 2.6%, 3%, or a range consisting of any two of the foregoing values. The above mass content of vinylene carbonate improves the density of the SEI film on the negative electrode surface, more effectively protects the negative electrode active material, reduces the degree of negative electrode interface side reactions, and improves cycle performance.

[0237] The combination of vinylene carbonate and fluorinated cyclic carbonate in the above mass content further optimizes the performance of the SEI film on the negative electrode surface, with excellent density and low impedance, which can more effectively protect the negative electrode active material, reduce the degree of negative electrode interface side reactions, and improve cycle performance.

[0238] In the embodiments of the present application, the types and contents of the inorganic components / lithium salts in the electrolyte are well known in the art and can be detected using equipment and methods well known in the art. For example, the inorganic components / lithium salts in the electrolyte can be qualitatively or quantitatively analyzed by ion chromatography analysis method with reference to standard JY / T020-1996 "General Rules for Ion Chromatography Analysis Methods". In the embodiments of the present application, a freshly prepared electrolyte can be taken as a sample, the 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 battery's state of charge is approximately 0% SOC) can be reversely disassembled, and the free electrolyte obtained from the battery can be used as a sample for detection using ion chromatography analysis method.

[0239] In the embodiment of the present application, the types and contents of the organic components in the electrolyte are well known in the art and can be detected using equipment and methods well known in the art. For example, reference can be made to GB / T9722-2006 "General Rules for Gas Chromatography of Chemical Reagents" to perform qualitative and quantitative analysis of the organic components in the electrolyte by gas chromatography.

[0240] In the embodiment of the present application, after quantitative and qualitative detection of each component in the electrolyte, the components are classified, and the carboxylate solvent and the carbonate solvent are taken as the components of the organic solvent. The mass content of each component is calculated based on the mass of the electrolyte as 100%.

[0241] Fluorinated cyclic carbonate and vinylene carbonate were used as additives to the electrolyte. The mass content of each component was calculated based on the mass of the electrolyte being 100%.

[0242] Isolators

[0243] In some embodiments, the electrode assembly further includes a separator disposed between the positive electrode sheet and the negative electrode sheet.

[0244] In some embodiments, the separator is a separator. The present application has no particular limitation on the type of separator, and any known separator with a porous structure having good chemical and mechanical stability can be selected.

[0245] As an example, the primary material of the separator can be selected from at least one of glass fiber, non-woven fabric, polyethylene, polypropylene, polyvinylidene fluoride, and ceramic. The separator can be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation. The separator can be a separate component located between the positive and negative electrodes, or it can be attached to the surfaces of the positive and negative electrodes. The surface of the separator can also be coated with an inorganic particle coating, an organic particle coating, or an organic / inorganic composite coating.

[0246] In some embodiments, the separator is a solid electrolyte, which is disposed between the positive electrode and the negative electrode and serves to transport ions and isolate the positive and negative electrodes.

[0247] Example

[0248] The following examples describe the disclosure of the present invention in more detail. These examples are intended for illustrative purposes only, as various modifications and variations within the scope of the disclosure of the present invention will be apparent to those skilled in the art. Unless otherwise stated, all parts, percentages, and ratios reported in the following examples are by mass, and all reagents used in the examples are commercially available or synthesized according to conventional methods and can be used directly without further processing, and the instruments used in the examples are commercially available.

[0249] Example 1

[0250] 1. Preparation of positive electrode sheet

[0251] The positive electrode plate includes a positive electrode current collector and a positive electrode film layer arranged on both sides of the positive electrode current collector, and the positive electrode current collector is aluminum foil.

[0252] The positive electrode film layer includes lithium iron phosphate, binder polyvinylidene fluoride (PVDF) and conductive agent superP in a mass ratio of 97:2:1. The positive electrode film layer is formed by evenly coating the positive electrode slurry (solvent is N-methylpyrrolidone NMP) on both sides of the positive electrode current collector, and then drying and cold pressing.

[0253] Lithium iron phosphate comes from Hunan Yuneng New Energy Battery Materials Co., Ltd.

[0254] 2. Preparation of negative electrode sheet

[0255] The negative electrode plate includes a negative electrode current collector and a negative electrode film layer arranged on both sides of the negative electrode current collector, and the negative electrode current collector is copper foil.

[0256] The negative electrode film layer is formed by evenly coating the negative electrode slurry (the solvent is deionized water) on the surface of the negative electrode current collector, drying it, and cold pressing it.

[0257] 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.

[0258] 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%. The average particle size of the carbon-based material is 18μm, and the void ratio of a single carbon-based material is 20%.

[0259] 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. The average particle size of the carbon-based material is 15 μm, and the void ratio of a single carbon-based material is 25%.

[0260] The carbon-based materials come from Guangdong Kaijin New Energy Technology Co., Ltd.

[0261] 3. Isolation film

[0262] The isolation film includes a base film and a coating provided on both sides of the base film. The base film is a 7μm polyethylene film layer and the coating is polyvinylidene fluoride with a surface density of 1.2g / m 2 .

[0263] The isolation membrane comes from Shanghai Enjie New Material Technology Co., Ltd.

[0264] 4. Preparation of electrolyte

[0265] The electrolyte comprises an organic solvent, a lithium salt and an additive. After the components of the organic solvent are evenly mixed, the lithium salt and the additive are added to prepare the electrolyte.

[0266] The organic solvent includes 25% chain carboxylic acid ester solvent ethyl acetate EA and 57% carbonate solvent (27% ethylene carbonate EC, 30% dimethyl carbonate DMC). The mass content of each component in the organic solvent is calculated based on the mass of the electrolyte.

[0267] The lithium salt includes 8% lithium hexafluorophosphate LiPF6 and 6% lithium bis(fluorosulfonyl)imide.

[0268] The additives include 2% fluorocyclic carbonate monofluoroethylene carbonate FEC and 2% vinylene carbonate VC;

[0269] The conductivity of the electrolyte is 14.2 mS / cm.

[0270] 5. Preparation of battery cells

[0271] The positive electrode sheet, separator, and negative electrode sheet are stacked in order, with the separator placed between the positive electrode sheet and the negative electrode sheet to serve as an isolation to obtain an electrode assembly. The electrode assembly is placed in an outer packaging shell, dried, and then injected with electrolyte. After vacuum packaging, standing, forming, and shaping, a battery cell is obtained. The compaction density of the positive electrode film layer of the battery cell at 0% SOC is 2.7 g / cm 3 The compaction density of the negative electrode film at 0% SOC is 1.45g / cm 3 .

[0272] Comparative Example 1-1 and Comparative Example 1-2

[0273] A battery cell was prepared using a method similar to that of Example 1, except that the mass content of silicon was adjusted.

[0274] Comparative Examples 1-3 and 1-4

[0275] A battery cell was prepared using a method similar to that of Example 1. The difference from Example 1 was that the coating weight of the negative electrode film layer was adjusted.

[0276] Example 2-1 to Example 2-3

[0277] A battery cell was prepared using a method similar to that of Example 1. The difference from Example 1 was that the mass content of silicon and the coating weight of the negative electrode film layer were adjusted.

[0278] Examples 2-4

[0279] A battery cell was prepared using a method similar to that of Example 1. The difference from Example 1 was that the coating weights of the positive and negative electrode film layers were adjusted.

[0280] Example 3-1 and Example 3-2

[0281] A battery cell was prepared using a method similar to that of Example 1. The difference from Example 1 was that the average particle size and specific surface area of ​​the silicon-based material were adjusted.

[0282] Example 4

[0283] A battery cell was prepared using a method similar to that of Example 1. The difference from Example 1 was that the material of the silicon-based material was adjusted.

[0284] Performance Testing

[0285] 1. Room temperature cycle performance test of battery cells

[0286] At 25°C, a fully charged battery cell is charged at a constant current of 0.33C to 10% SOC, then from 10% SOC to 80% SOC, then charged at 0.33C to the upper limit of the charge voltage, left to rest for 30 minutes, and then discharged at 1C to the discharge cutoff voltage. This constitutes one charge-discharge cycle. The battery cell is cycled multiple times until the discharge capacity decays to 90% (i.e., the battery health status reaches 90% SOH). The more cycles, the better the cycle performance of the battery cell.

[0287] The charging steps from 10% SOC to 80% SOC include:

[0288] Charge from 10% SOC to 45% SOC at 3.7 C;

[0289] Charge from 45% SOC to 50% SOC at 3.4 C;

[0290] Charge from 50% SOC to 55% SOC at 3.2 C;

[0291] Charged from 55% SOC to 60% SOC at 2.9 C;

[0292] Charge from 60% SOC to 65% SOC at 2.6 C;

[0293] Charge from 65% SOC to 70% SOC at 2.4 C;

[0294] Charge from 70% SOC to 75% SOC at 2.1 C;

[0295] Charged from 75% SOC to 80% SOC at 1.9 C.

[0296] 2. High temperature storage gas generation test of battery cells

[0297] At 25°C, charge the battery cells at a constant current of 0.5C to the upper charging voltage limit. Then, charge them at a constant voltage to a current of 0.05C. Use the water displacement method to measure the initial volume of the battery cells at this point, and record it as V0. Then, store the battery cells in a 60°C constant temperature chamber for 90 days. After storage, remove them from the chamber and measure their volume again using the water displacement method, and record it as V1. Ten battery cells were tested in each group, and the average value was taken.

[0298] The volume expansion ratio (%) of the battery cell after storage at 60° C. for 90 days = (V1-V0) / V0×100%.

[0299] The test results are shown in Table 1.

[0300] Table 1

[0301]

[0302] In Comparative Example 1-1, due to the relatively low mass content of silicon, the coating weight of the negative electrode film layer is relatively high, and the higher coating weight is not conducive to the migration of lithium ions and is not conducive to fast charging; in Comparative Example 1-2, the mass content of silicon is too high, which makes the risk of side reactions at the negative electrode side interface higher, gas production is aggravated, and high-temperature storage performance and cycle performance deteriorate.

[0303] In the embodiment of the present application, by setting the mass content of silicon element within an appropriate range, the coating weight of the negative electrode film layer will not be too high, which is conducive to the rapid migration of lithium ions and improves the fast charging capability of the battery cell; and the mass content of silicon element will not be too high, which can alleviate the side reactions on the negative electrode side, reduce the high-temperature gas production, and improve the high-temperature storage performance; since the side reactions on the negative electrode side are alleviated, the cycle performance of the battery cell can be improved, especially the cycle performance under fast charging conditions.

[0304] In Comparative Examples 1-3, the coating weight of the negative electrode film layer is too small, making the electrode too thin, prone to breakage, and worsening the cycle; in Comparative Examples 1-4, the coating weight of the negative electrode film layer is too large, resulting in a large lithium ion transmission resistance, which is not conducive to fast charging.

[0305] In Examples 2-1 to 2-4, the coating weight of the negative electrode film layer and the coating weight of the positive electrode film layer cooperate with each other, which is beneficial to improving the migration rate of lithium ions in the positive and negative electrode film layers, so that the resistance of the battery cell under rapid charging is smaller; and the total amount of active materials participating in the side reactions is less, which is beneficial to improving the high-temperature storage performance and cycle life of the battery cell.

[0306] The embodiments of this application are applicable to various silicon-based materials, such as silicon-oxygen materials and silicon-carbon materials (e.g., silicon carbide). By setting the average particle size and specific surface area of ​​the silicon-based material within appropriate ranges, and thus ensuring that the active area of ​​the silicon-based material is within an appropriate range, side reactions on the negative electrode side can be further mitigated, reducing high-temperature gas production and improving the high-temperature storage performance and cycling performance of the battery cell.

[0307] The embodiments of the present application are applicable to different positive electrode active materials, such as lithium iron phosphate material, lithium manganese iron ferrite material, or lithium iron phosphate material mixed with transition metal oxide.

[0308] Example 5-1 and Example 5-2

[0309] A battery cell was prepared using a method similar to that of Example 1. The difference from Example 1 was that the average particle size of the carbon-based material was adjusted.

[0310] Example 6

[0311] A battery cell was prepared using a method similar to that of Example 1. The difference from Example 1 was that the setting of the negative electrode film layer was adjusted. Specifically, the negative electrode film layer included a first negative electrode film layer and a second negative electrode film layer, the first negative electrode film layer was located on the surface of the negative electrode current collector, and the second negative electrode film layer was located on the surface of the first negative electrode film layer.

[0312] The first negative electrode film layer includes a carbon-based material, a silicon-based material silicon oxide, a conductive agent acetylene black, a negative electrode binder styrene-butadiene rubber, and a thickener 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 includes artificial graphite, and the average particle size of the carbon-based material is 15 μm.

[0313] 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 natural graphite with a mass ratio of 80%:20%, and the average particle size of the carbon-based material is 18 μm.

[0314] The mass content of silicon element in the negative electrode active material of the negative electrode film layer is 5%.

[0315] The test results are shown in Table 2.

[0316] Table 2

[0317]

[0318] By regulating the average particle size of the carbon-based material and / or the void ratio of a single carbon-based material, or making the average particle size of the carbon-based material of the first negative electrode film layer larger than the average particle size of the carbon-based material of the second negative electrode film layer, the solid-phase transmission path of lithium ions can be shortened, thereby improving the fast charging capability; and reducing the risk of lithium plating on the negative electrode side surface, thereby improving the cycle performance and storage performance.

[0319] When the average particle size of the carbon-based material of the first negative electrode film layer is smaller than the average particle size of the carbon-based material of the second negative electrode film layer, it is possible to construct a pore difference in the negative electrode film layer, improve the fast charging capability, and improve the cycle performance under fast charging conditions.

[0320] Comparative Examples 1-5 and 1-6

[0321] A battery cell was prepared using a method similar to that of Example 1. The difference from Example 1 was that the components and content of the electrolyte were adjusted.

[0322] Example 7-1 to Example 11

[0323] A battery cell was prepared using a method similar to that of Example 1. The difference from Example 1 was that the components and content of the electrolyte were adjusted.

[0324] The test results are shown in Table 3.

[0325] Table 3

[0326]

[0327] In Table 3,

[0328] EA stands for ethyl acetate; MA stands for methyl acetate; EC stands for ethylene carbonate; DMC stands for dimethyl carbonate; EMC stands for ethyl methyl carbonate; FEC stands for monofluoroethylene carbonate; DFEC stands for difluoroethylene carbonate;

[0329] EA: 25 means the mass content of EA is 25%; EC: 27 means the mass content of EC is 27%.

[0330] The mass ratio of lithium bis(fluorosulfonyl)imide to lithium hexafluorophosphate refers to the ratio of the mass content of lithium bis(fluorosulfonyl)imide to the mass content of lithium hexafluorophosphate. The meanings of other examples are the same as explained above and will not be repeated here.

[0331] The conductivity of the electrolyte in Example 7-1 was 9 mS / cm, and the conductivity of the electrolyte in Example 7-2 was 18 mS / cm.

[0332] By regulating the components of the electrolyte so that the components of the electrolyte are within an appropriate range, the side reactions on the negative electrode side can be effectively improved, the high-temperature gas production can be reduced, and the cycle performance and fast charging performance can be improved.

[0333] The carboxylate solvent in the embodiment of the present application has a mass content of 3% to 70%, which can effectively improve the side reaction on the negative electrode side, reduce the gas production during high-temperature storage, improve the high-temperature storage performance, and improve the cycle performance of the battery cell under fast charging;

[0334] In the embodiment of the present application, lithium hexafluorophosphate and lithium bis(fluorosulfonyl)imide are compounded for use, 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, which can reduce the content of hydrofluoric acid, slow down the side reaction at the negative electrode interface, reduce the gas production during high-temperature storage, and help improve the cycle life of the battery cell.

[0335] 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 alleviate the volume expansion of the negative electrode side, improve the life of the negative electrode system, and improve the cycle performance.

[0336] In Example 10, the mass content of silicon element is 12.5%, which is combined with 15% of monofluoroethylene carbonate to effectively protect the surface of the negative electrode active material, further reduce the side reactions on the negative electrode side, and improve high-temperature storage performance and cycle performance.

[0337] Although illustrative embodiments have been demonstrated and described, those skilled in the art should understand that the above embodiments should not be construed as limitations on the embodiments of the present application, and that changes, substitutions, and modifications may be made to the embodiments without departing from the spirit, principles, and scope of the embodiments of the present application.

Claims

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

2.

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

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

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

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

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

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

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

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

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

11. The battery cell according to any one of claims 1 to 2, characterized in that: The negative electrode film layer comprises: A first negative electrode film layer is provided 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 that is away from the negative electrode current collector, wherein the negative electrode active material of the second negative electrode film layer includes a carbon-based material. Wherein, at least one of the first negative electrode film layer and the second negative electrode film layer comprises a silicon-based material.

12. The battery cell according to any one of claims 1 to 2, characterized in that: The conductivity of the electrolyte at room temperature is 9 mS / cm to 18 mS / cm.

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

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

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

16. The battery cell according to any one of claims 1 to 2, characterized in that: 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%.

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

18. The battery cell according to claim 17, characterized in that The fluorinated cyclic carbonate includes at least one of monofluoroethylene carbonate, bisfluoroethylene carbonate and trifluoropropylene carbonate.

19. The battery cell according to claim 17, characterized in that The mass content of the fluorinated cyclic carbonate is 0.5% to 20% based on the mass of the electrolyte; and / or The mass content of the vinylene carbonate is 0.1% to 3% based on the mass of the electrolyte.

20. 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 in the silicon-based material in the negative electrode active material is 0.3% to 7.5%.

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 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%.

22. The battery cell according to any one of claims 1 to 2, characterized in that: The single-sided coating weight of the positive electrode film layer is 250 mg / 1540.25 mm 2 Up to 300mg / 1540.25mm 2 .

23. A battery device, characterized in that: The invention comprises the battery cell according to any one of claims 1 to 22.

24. An electrical device, characterized in that: Comprising the battery device of claim 23.

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