Battery cell, battery device, and electrical device

Abstract

The present application relates to a battery cell, a battery device and an electrical device. The battery cell includes a positive electrode plate, a negative electrode plate and an electrolyte. The positive electrode plate includes a positive current collector and a positive electrode film layer provided on at least one side of the positive current collector. The positive electrode film layer includes a positive active material, and the positive active material includes lithium iron phosphate. The single-sided coating weight of the positive electrode film layer is 250 mg / 1540.25 mm 2 to 300 mg / 1540.25 mm 2 ; the negative electrode plate includes a negative current collector and a negative electrode film layer provided on at least one side of the negative current collector. The negative electrode film layer includes a negative active material, and the negative active material includes a carbon-based material. The single-sided coating weight of the negative electrode film layer is 80 mg / 1540.25 mm 2 to 150 mg / 1540.25 mm 2 ; the electrolyte includes an organic solvent, the organic solvent includes a carboxylic acid ester solvent, and the mass content of the carboxylic acid ester solvent in the electrolyte is 3% to 70%.

Description

[0001] This application claims the priority of the patent application PCT / CN2025 / 071126 titled "Battery Cell, Battery Device and Electric Appliance" filed on January 7, 2025, and the entire content of this application is incorporated herein by reference. Technical Field

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

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

[0004] This application provides a battery cell, a battery device and an electric appliance, and the cycling performance of the battery cell of this application can be further improved.

[0005] In a first aspect, an embodiment of this application provides a battery cell. The battery cell includes a positive electrode plate, a negative electrode plate and an electrolyte. The positive electrode plate includes a positive current collector and a positive electrode film layer provided on at least one side of the positive current collector. The positive electrode film layer includes a positive electrode active material, and the positive electrode active material includes lithium iron phosphate. The single-sided coating weight of the positive electrode film layer is 250 mg / 1540.25 mm 2 to 300 mg / 1540.25 mm 2 ; the negative electrode plate includes a negative current collector and a negative electrode film layer provided on at least one side of the negative current collector. The negative electrode film layer includes a negative electrode active material, and the negative electrode active material includes a carbon-based material. The single-sided coating weight of the negative electrode film layer is 80 mg / 1540.25 mm 2 to 150 mg / 1540.25 mm 2 ; the electrolyte includes an organic solvent, and the organic solvent includes a carboxylic acid ester solvent. The mass content of the carboxylic acid ester solvent in the electrolyte is 3% to 70%.

[0006] Thus, the single-sided coating weight of the positive electrode film layer and the single-sided coating weight of the negative electrode film layer in the embodiments of the present application, in combination with the electrolyte, enable lithium ions to have a relatively fast migration rate in the positive and negative electrodes and the electrolyte, which is conducive to improving the rapid charging ability of the battery cell. The embodiments of the present application further regulate the mass content of the carboxylic ester solvent to be 3% to 70%. In combination with the carbon-containing negative electrode, it can alleviate the side reactions at the negative electrode interface. Moreover, the carbon-containing negative electrode and the lithium-containing phosphate lithium iron phosphate have excellent cycle stability, which can further improve the cycle performance of the battery cell under rapid charging.

[0007] In some embodiments, the conductivity of the electrolyte at room temperature is 9 mS / cm to 18 mS / cm. The migration rate of lithium ions in this electrolyte is relatively high, which can further reduce the internal resistance of the battery cell, thereby reducing heat generation and improving the cycle performance of the battery cell under rapid charging.

[0008] In some embodiments, the mass content of the carboxylic ester solvent in the electrolyte is 5% to 30%. When the mass content of the carboxylic ester solvent is within the above range, it can improve the conductivity of the electrolyte; and the electrolyte is adapted to the silicon-containing negative electrode, which can effectively reduce the gas generation amount of the battery cell and improve the cycle performance of the battery cell under rapid charging.

[0009] In some embodiments, the carboxylic ester solvent includes cyclic carboxylic esters, and the cyclic carboxylic esters include one or more of γ-butyrolactone, γ-valerolactone, and δ-valerolactone. The viscosity of the above materials is relatively low, which can improve the wetting ability of the electrode sheet and improve the cycle performance of the battery cell under rapid charging.

[0010] In some embodiments, the carboxylic ester solvent includes linear carboxylic esters, and the linear carboxylic esters include one or more of methyl acetate, ethyl acetate, propyl acetate, butyl acetate, propyl propionate, and butyl propionate. The viscosity of the above materials is relatively low, which can improve the wetting ability of the electrode sheet and improve the cycle performance of the battery cell under rapid charging.

[0011] In some embodiments, the organic solvent further includes carbonate solvents, and the carbonate solvents include one or more of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate.

[0012] The carbonate solvents and the carboxylic ester solvents are used in combination, which can improve the stability of the electrolyte and is conducive to improving the cycle life of the battery cell.

[0013] In some embodiments, the electrolyte further includes a lithium salt, and the lithium salt includes lithium bis(fluorosulfonyl)imide and lithium hexafluorophosphate. Based on the mass of the electrolyte, the ratio of the mass content of lithium bis(fluorosulfonyl)imide to the mass content of lithium hexafluorophosphate is 0.3 to 1.2.

[0014] Therefore, when the ratio of the mass contents of lithium hexafluorophosphate and lithium bis(fluorosulfonyl)imide in the embodiments of the present application satisfies the above range, the compound use of lithium hexafluorophosphate and lithium bis(fluorosulfonyl)imide can reduce the content of hydrofluoric acid, slow down the side reaction at the negative electrode interface, and is beneficial to improving the cycle life of the battery cell.

[0015] In some embodiments, based on the mass of the electrolyte, the mass content of lithium bis(fluorosulfonyl)imide is 2% to 11%. When the mass content of lithium bis(fluorosulfonyl)imide is within the above range, the content of hydrofluoric acid can be reduced, the side reaction at the negative electrode interface can be slowed down, and it is beneficial to improving the cycle performance of the battery cell under fast charging.

[0016] In some embodiments, based on the mass of the electrolyte, the mass content of lithium hexafluorophosphate is 3% to 14%. When the mass content of lithium hexafluorophosphate is within the above range, the conductivity of the electrolyte is relatively high, which is beneficial to the migration of lithium ions and is beneficial to improving the cycle performance of the battery cell under fast charging.

[0017] In some embodiments, the electrolyte further includes one or more of fluorinated cyclic carbonates and vinylene carbonate. The fluorinated cyclic carbonate can form an interfacial film rich in lithium fluoride (LiF) on the surface of the negative electrode, which can relieve the volume expansion of silicon and improve the life of the silicon-containing system; the combined use of the fluorinated cyclic carbonate and vinylene carbonate makes the interfacial film on the surface of the negative electrode denser, can more effectively protect the silicon-containing negative electrode, reduce the degree of side reaction at the negative electrode interface, and can improve the cycle performance of the battery cell under fast charging.

[0018] In some embodiments, the fluorinated cyclic carbonate includes at least one of fluoroethylene carbonate, difluoroethylene carbonate, and trifluoropropylene carbonate.

[0019] In some embodiments, based on the mass of the electrolyte, the mass content of the fluorinated cyclic carbonate is 0.5% to 20%. When the mass content of the fluorinated cyclic carbonate is within the above range, an excellent interfacial film can be formed, which can provide excellent protection for the negative electrode and improve the cycle performance of the battery cell under fast charging.

[0020] In some embodiments, based on the mass of the electrolyte, the mass content of vinylene carbonate is 0.1% to 3%. Vinylene carbonate participates in the formation of the negative electrode interfacial film, which can form an excellent interfacial film and provide excellent protection for the negative electrode.

[0021] In some embodiments, when the battery cell is in a 0% state of charge, the tap density of the positive electrode film layer is 2.2 g / cm 3 to 2.85 g / cm 3When the compaction density of the positive electrode film layer is within the above range, the thickness of the positive electrode film layer will not be too thick, which is beneficial to the rapid migration of lithium ions and can improve the cycle performance of the battery cell under fast charging.

[0022] In some embodiments, when the battery cell is in a 0% state of charge, the compaction density of the negative electrode film layer is 1.1 g / cm 3 to 1.7 g / cm 3 When the compaction density of the negative electrode film layer is within the above range, the thickness of the negative electrode film layer will not be too thick, which is beneficial to the rapid migration of lithium ions and can improve the cycle performance of the battery cell under fast charging.

[0023] In some embodiments, the negative electrode film layer includes a first region and a second region. The first region is the region of the negative electrode film layer close to the negative electrode current collector along its own thickness direction, and the thickness of the first region is 1 / 3 of the thickness of the negative electrode film layer; the second region is the region of the negative electrode film layer away from the negative electrode current collector along the thickness direction, and the thickness of the second region is 1 / 3 of the thickness of the negative electrode film layer. Wherein, in the cross-section of the negative electrode film layer parallel to the thickness direction, the void ratio of a single carbon-based material in the first region is less than the void ratio of a single carbon-based material in the second region.

[0024] Thus, in the embodiments of the present application, the void ratio of a single carbon-based material in the first region is less than or equal to the void ratio of a single carbon-based material in the second region, which is more conducive to the diffusion of lithium ions in the first region, improves the transmission rate, and thus is beneficial to the improvement of the cycle performance of the battery cell under fast charging.

[0025] 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.

[0026] Thus, in the embodiments of the present application, the particle size of the second region is relatively small, which can shorten the solid-phase transmission path of lithium ions, improve the fast charging performance, and can improve the problem of lithium deposition on the surface layer of the negative electrode sheet, which is beneficial to the improvement of the cycle performance of the battery cell under fast charging.

[0027] 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 performance of the battery cell under fast charging can be improved.

[0028] 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, the cycle performance of the battery cell under fast charging can be improved.

[0029] 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.

[0030] In some embodiments, when the average particle size of the carbon-based material in the first region is greater than or equal to the average particle size of the carbon-based material in the second region, the carbon-based material in the second region includes artificial graphite.

[0031] 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 smaller average particle size of the carbon-based material in the first region enables the rapid migration of lithium ions, improves the rapid charging ability of the battery cell, and is beneficial to enhancing the cycle life under rapid charging.

[0032] 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.

[0033] 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.

[0034] 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.

[0035] In some embodiments, when the average particle size of the carbon-based material in the second region is greater than the average particle size of the carbon-based material in the first region, the carbon-based material in the first region includes artificial graphite.

[0036] 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. The double-layer setting is beneficial to taking into account the improvement of the cycle life of the battery cell under rapid charging.

[0037] In some embodiments, the negative electrode active material further includes a silicon-based material, which can improve the energy density; and is beneficial to thinning the negative electrode film layer, enhancing the migration rate of lithium ions, and improving the cycle life of the battery cell under rapid charging.

[0038] In some embodiments, the silicon-based material includes one or more of silicon, silicon-carbon composites, and silicon oxides. These silicon-based materials can increase energy density, facilitate thinning of the negative electrode film, increase lithium ion migration rate, and improve the cycle life of the battery cell under rapid charging.

[0039] In some embodiments, the silicon content of the silicon-based material in the negative electrode active material is 0.3% to 15% by weight. Within this range, the silicon-based material can increase energy density, facilitate thinning the negative electrode film layer, increase the migration rate of lithium ions, and improve the cycle life of the battery cell under rapid charging.

[0040] 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.

[0041] 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

[0042] 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.

[0043] Figure 1 It is a schematic diagram of the structure of an electrical device provided in some embodiments of the present application.

[0044] Figure 2 is a schematic structural diagram of a battery pack provided in some embodiments of the present application;

[0045] Figure 3 is a schematic structural diagram of a battery module provided in some embodiments of the present application;

[0046] Figure 4 is a schematic structural diagram of a battery cell provided in some embodiments of the present application;

[0047] Figure 5 is a schematic structural diagram of an electrode assembly of a battery cell provided in some embodiments of the present application;

[0048] 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.

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

[0050] The following are the descriptions of the reference numerals:

[0051] X, thickness direction;

[0052] 1, electrical device; 2, battery pack; 3, controller; 4, motor; 5, housing; 5a, first housing portion; 5b, second housing portion; 5c, accommodation space; 6, battery module;

[0053] 7, battery cell; 10, electrode assembly; 11, positive electrode tab; 12, negative electrode tab; 121, negative electrode film layer; 122, negative electrode current collector; 1211, first negative electrode film layer; 1212, second negative electrode film layer; 121a, first region; 121b, second region; 121c, third region; 13, separator; 20, outer shell assembly; 21, housing; 22, end cap; 23, electrode terminal. Detailed implementation manners

[0054] Hereinafter, embodiments of the battery cell, battery device, and electrical device of the present application will be specifically disclosed in detail with appropriate reference to the drawings. However, there may be cases where unnecessary detailed descriptions are omitted. For example, there may be cases where detailed descriptions of well-known matters and repeated descriptions of actually identical structures are omitted. This is to prevent the following description from becoming unnecessarily lengthy and to facilitate the understanding of those skilled in the art. In addition, the drawings and the following description are provided for those skilled in the art to fully understand the present application and are not intended to limit the subject matter recited in the claims.

[0055] The "range" disclosed in the present application is defined in the form of a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundary of a specific range. The ranges defined in this way can include the end values or not include the end values, and can be combined arbitrarily, that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60 to 120 and 80 to 110 are listed for a specific parameter, ranges of 60 to 110 and 80 to 120 are also contemplated. In addition, if the minimum range values 1 and 2 are listed, and if the maximum range values 3, 4, and 5 are listed, the following ranges are all contemplated: 1 to 3, 1 to 4, 1 to 5, 2 to 3, 2 to 4, and 2 to 5. In the present application, unless otherwise specified, the numerical range "a to b" represents an abbreviated representation of any real number combination between a and b, where a and b are both real numbers. For example, the numerical range "0 to 5" means that all real numbers between "0 to 5" have been fully listed herein, and "0 to 5" is only an abbreviated representation of these numerical combinations. In addition, when it is stated that a certain parameter is an integer ≥2, it is equivalent to disclosing that the parameter is, for example, the integer 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 new technical solutions.

[0057] Unless otherwise specified, all technical features and optional technical features of the present application can be combined with each other to form new technical solutions.

[0058] Unless otherwise specified, all steps of the present application can be carried out in sequence or randomly, preferably in sequence. For example, if the method includes steps (a) and (b), it means that the method can include steps (a) and (b) carried out in sequence, or steps (b) and (a) carried out in sequence. For example, if it is mentioned that the method may further include step (c), it means that step (c) can be added to the method in any order. For example, the method can include steps (a), (b) and (c), or steps (a), (c) and (b), or steps (c), (a) and (b), etc.

[0059] The term "a plurality of" as used in the present application means two or more (including two).

[0060] In the embodiments of the present application, the battery cell can be a secondary battery, which refers to a battery cell that can be activated by charging after discharging to continue to be used.

[0061] With the rapid development of the battery field, the performance requirements for battery cells are gradually increasing. For example, the requirements for the cycling performance of battery cells are gradually increasing, especially the requirements for the cycling performance under fast charging.

[0062] In view of the above problems, the embodiments of the present application can effectively improve the transport ability of active ions such as lithium ions by regulating the coating weights of the positive electrode film layer and the negative electrode film layer, as well as the components of the electrolyte, which is beneficial to the rapid migration of active ions and is beneficial to improving the cycling performance of the battery cell under fast charging.

[0063] The battery cell of the present application is applicable to various battery devices and electrical devices that use battery cells.

[0064] Exemplarily, the electrical device can be a mobile phone, a portable device, a laptop computer, an electric vehicle, an electric toy, an electric tool, a vehicle, a ship, a spacecraft, etc. Or, exemplarily, the electrical device is a spacecraft, and the spacecraft includes an airplane, a rocket, a space shuttle, a spaceship, etc.

[0065] Figure 1 It is a schematic diagram of an electrical device 1 as an example. The electrical device 1 is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. In order to meet the requirements of the electrical device 1 for high power and high energy density, a battery pack or a battery module can be used.

[0066] Inside the electrical device 1, a battery device is provided, and the battery device can be arranged at the bottom, head or tail of the electrical device 1. The battery device can be used to supply power to the electrical device 1. For example, the battery device can serve as the operating power source of the electrical device 1 and can also serve as the driving power source of the electrical device 1, replacing or partially replacing fuel or natural gas to provide driving power for the electrical device 1. Figure 1 The battery device shown is the battery pack 2.

[0067] The electrical device 1 may further include a controller 3 and a motor 4. The controller 3 is used to control the battery device to supply power to the motor 4. For example, it is used for the working power requirements during the startup, navigation and driving of the electrical device 1.

[0068] The battery apparatus may include one or more battery cell assemblies for providing voltage and capacity. The battery cell assembly may include a plurality of battery cells, and the plurality of battery cells are connected in series, parallel or in a hybrid connection through a bus bar component.

[0069] In some embodiments, the battery cell assembly is generally formed by arranging a plurality of battery cells.

[0070] As an example, the battery cell assembly can be a battery module, and the battery module is formed by arranging and fixing a plurality of battery cells into an independent module. As an example, the battery module can be formed by bundling a plurality of battery cells with cable ties.

[0071] As Figure 2 shown, in some embodiments, the battery device can be a battery pack 2, and the battery pack 2 includes a box body 5 and one or more battery cell assemblies, and the battery cell assemblies are accommodated in the box body 5.

[0072] As an example, the battery cell assembly can also be accommodated in the box body 5 by directly fixing a plurality of battery cells to the box body 5.

[0073] As an example, the box body 5 includes a first box body part 5a and a second box body part 5b. The box body 5 has an accommodation space 5c. The first box body part 5a and the second box body part 5b are snapped together so that a closed space is formed inside the box body 5 to accommodate the battery cell assembly. The "closed" here means covering or closing, which can be sealed or non-sealed. The first box body part 5a can be a top cover or a bottom plate.

[0074] As an example, the housing 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 as to form a closed space inside the housing 5 for accommodating the battery cell assembly.

[0075] In some embodiments, the housing 5 may be part of the chassis structure of a vehicle. For example, a part of the housing 5 may form at least a part of the floor of the vehicle, or a part of the housing 5 may form at least a part of the cross beams and longitudinal beams of the vehicle.

[0076] As an example, the battery cell assembly may be a battery module 6, and the battery cell assembly may be accommodated in the housing 5 by fixing the battery module 6 in the housing 5.

[0077] As Figure 3 shown, the battery module 6 includes a plurality of battery cells 7.

[0078] As Figure 4 and Figure 5 shown, in some embodiments, the battery cell 7 includes an electrode assembly 10 and a housing assembly 20.

[0079] The housing assembly 20 has a receiving cavity for receiving the electrode assembly 10 and the electrolyte.

[0080] In some embodiments, the housing assembly 20 includes a housing and electrode terminals 23, and the electrode terminals 23 are disposed on the housing.

[0081] The housing may be a steel shell, an aluminum shell, a plastic shell (such as polypropylene), a composite metal shell (such as a copper-aluminum composite shell), or an aluminum plastic film, etc. In some embodiments, the housing may be a sealed structure or a non-sealed structure. As an example, when the housing is a non-sealed structure, the housing plays a role in protecting the electrode assembly 10, and a sealing bag is further included between the housing and the electrode assembly 10, and the sealing bag is used for encapsulating the electrode assembly 10 and the electrolyte. Specifically, the sealing bag may be a bag-shaped insulating member or an aluminum plastic film. When the housing is a sealed structure, it is used for encapsulating components such as the electrode assembly 10 and the electrolyte.

[0082] As an example, the battery cell 7 may be a cylindrical battery cell, a prismatic battery cell, a pouch battery cell, or a battery cell of other shapes. The prismatic battery cell includes a square shell battery cell, a blade-shaped battery cell, a multi-prismatic battery, and the multi-prismatic battery is, for example, a hexagonal prism battery, etc., and there is no particular limitation in this application.

[0083] In some embodiments, the housing includes an end cap 22 and a housing body 21. The housing body 21 is provided with an opening, and the end cap 22 covers the opening. The housing body 21 may be provided with one or more openings. The end cap 22 may also be provided with one or more.

[0084] The shape of the housing 21 can be determined according to the specific shape of the electrode assembly 10. For example, if the electrode assembly 10 is a cylindrical structure, the housing 21 can be selected as a cylindrical structure; if the electrode assembly 10 is a cuboid structure, the housing 21 can be selected as a cuboid structure. Optionally, both the electrode assembly 10 and the housing 21 are cuboid structures.

[0085] The electrode terminal 23 can be disposed on the housing 21, or the electrode terminal 23 is disposed on the end cap 22. The electrode terminal 23 is electrically connected to the tab of the electrode plate. The electrode terminal 23 can be directly connected to the tab, or indirectly connected to the tab through a current collecting member.

[0086] The electrode assembly 10 can be a wound structure, a stacked structure, or a hybrid structure of winding and stacking.

[0087] In some embodiments, the electrode assembly 10 is a wound structure. The positive electrode plate 11 and the negative electrode plate 12 are wound into a wound structure.

[0088] In some embodiments, the electrode assembly 10 is a stacked structure.

[0089] As an example, a plurality of positive electrode plates 11 and negative electrode plates 12 can be respectively provided, and the plurality of positive electrode plates 11 and the plurality of negative electrode plates 12 are alternately stacked.

[0090] As an example, a plurality of positive electrode plates 11 can be provided, and the negative electrode plate 12 is folded to form a plurality of stacked folding segments, and a positive electrode plate 11 is clamped between adjacent folding segments.

[0091] As an example, both the positive electrode plate 11 and the negative electrode plate 12 are folded to form a plurality of stacked folding segments.

[0092] As an example, a plurality of separators 13 can be provided and are respectively disposed between any adjacent positive electrode plates 11 or negative electrode plates 12.

[0093] As an example, the separator 13 can be continuously provided and is disposed between any adjacent positive electrode plates 11 or negative electrode plates 12 by folding or winding.

[0094] In some embodiments, the shape of the electrode assembly 10 can be cylindrical, flat, prismatic, etc.

[0095] In some embodiments, the electrode assembly 10 is provided with tabs, and the tabs can conduct current out of the electrode assembly 10. The tabs include a positive tab and a negative tab. The electrode assembly 10 can adopt a wound structure or a stacked structure, and the stacked structure is optional, which is beneficial to improving the energy density of the battery cell 7.

[0096] In some embodiments, the battery cell 7 includes a positive electrode plate 11, a negative electrode plate 12, and an electrolyte. The positive electrode plate 11 includes a positive electrode current collector and a positive electrode film layer provided on at least one side of the positive electrode current collector. The positive electrode film layer includes a positive electrode active material, the positive electrode active material includes a lithium-containing phosphate, and the single-sided coating weight of the positive electrode film layer is 250 mg / 1540.25 mm 2 to 300 mg / 1540.25 mm 2 ; 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 carbon-based material, and the single-sided coating weight of the negative electrode film layer is 80 mg / 1540.25 mm 2 to 150 mg / 1540.25 mm 2 ; the electrolyte includes an organic solvent, the organic solvent includes a carboxylic ester solvent, and the mass content of the carboxylic ester solvent in the electrolyte is 3% to 70%.

[0097] The single-sided coating weight of the positive electrode film layer is greater than or equal to 250 mg / 1540.25 mm 2 and, in combination with the single-sided coating weight of the negative electrode film layer being greater than or equal to 80 mg / 1540.25 mm 2 results in a relatively high energy density of the battery cell 7;

[0098] As the single-sided coating weights of the positive electrode film layer and the negative electrode film layer increase, the energy density of the battery cell 7 increases, but the migration path of lithium ions grows and the migration resistance increases; in the embodiments of the present application, however, the single-sided coating weight of the positive electrode film layer is also less than or equal to 300 mg / 1540.25 mm 2 and the single-sided coating weight of the negative electrode film layer is less than or equal to 150 mg / 1540.25 mm 2 and, in combination with the mass content of the carboxylic ester solvent in the electrolyte being greater than or equal to 3%, enables lithium ions to have a relatively fast liquid-phase migration rate in the positive and negative electrodes and the electrolyte, which is beneficial to improving the fast charging ability of the battery cell 7;

[0099] As the mass content of the carboxylic ester solvent increases, the migration rate of lithium ions in the electrolyte accelerates, but if its mass content further increases, side reactions at the negative electrode interface may occur. Therefore, in the embodiments of the present application, the mass content of the carboxylic ester solvent is further regulated to be less than or equal to 70%. In combination with a carbon-containing negative electrode, it can alleviate side reactions at the negative electrode interface; moreover, the carbon-containing negative electrode and the lithium-containing phosphate have relatively excellent cycle stability, which can further improve the cycle performance of the battery cell 7 under fast charging.

[0100] Negative electrode plate

[0101] The negative electrode plate includes a negative electrode current collector and a negative electrode film layer provided on at least one side of the negative electrode current collector and including a negative electrode active material. For example, the negative electrode current collector has two opposite surfaces in its own thickness direction, and the negative electrode film layer is provided on any one or both of the two opposite surfaces of the negative electrode current collector.

[0102] The upper charge limit voltage and the discharge cut-off voltage of the battery cell are different according to the different positive electrode active materials. For example, when the phosphate material includes lithium iron phosphate, the upper charge limit voltage can be 3.65V and the discharge cut-off voltage can be 2.0V, or the upper charge limit voltage can be 3.8V and the discharge cut-off voltage can be 2.0V; another example is that when the phosphate material includes lithium manganese iron phosphate, the upper charge limit voltage can be 4.3V and the discharge cut-off voltage can be 2.0V. Next, taking the upper charge limit voltage of 3.8V and the discharge cut-off voltage of 2.0V as an example, the state of the battery cell is described as follows: 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.

[0103] The battery cell is charged at a constant current charging rate of 0.33C to the upper charge limit voltage, and then charged at a constant voltage to 0.05C, corresponding to the state of 100% SOC of the battery cell. The battery cell is discharged at a constant current discharge rate of 0.33C to the cut-off voltage, corresponding to the state of 0% SOC of the battery cell.

[0104] In some embodiments, when the battery cell is in the 0% state of charge (SOC), the compaction density of the negative electrode film layer is 1.1 g / cm 3 to 1.7 g / cm 3 . Exemplarily, the compaction density of the negative electrode film layer of the battery cell in the 0% state of charge is 1.10 g / cm³, 1.12 g / cm³, 1.14 g / cm³, 1.16 g / cm³, 1.18 g / cm³, 1.20 g / cm³, 1.22 g / cm³, 1.24 g / cm³, 1.26 g / cm³, 1.28 g / cm³, 1.3 g / cm 3 , 1.32 g / cm 3 , 1.35 g / cm 3 , 1.40 g / cm 3 , 1.45 g / cm 3 , 1.50 g / cm 3 , 1.55 g / cm 3 , 1.60 g / cm 3 , 1.65 g / cm 3 , 1.66 g / cm³, 1.68 g / cm³, 1.70 g / cm³ or the range composed of any two of the above values.

[0105] When the compaction density of the negative electrode film layer is within the above range, the thickness of the negative electrode film layer will not be too thick, the migration path of lithium ions is short, which is beneficial to the improvement of the cycle performance of the battery cell under fast charging.

[0106] In some embodiments, the single-sided coating weight of the negative electrode film layer is 80 mg / 1540.25 mm 2 to 150 mg / 1540.25 mm 2 . Exemplarily, the single-sided coating weight of the negative electrode film layer is 80 mg / 1540.25 mm², 85 mg / 1540.25 mm², 90 mg / 1540.25 mm², 95 mg / 1540.25 mm², 100 mg / 1540.25 mm², 105 mg / 1540.25 mm², 110 mg / 1540.25 mm², 115 mg / 1540.25 mm², 120 mg / 1540.25 mm², 120 mg / 1540.25 mm 2 、122 mg / 1540.25 mm 2 、125 mg / 1540.25 mm 2 、128 mg / 1540.25 mm 2 、130 mg / 1540.25 mm 2 、132 mg / 1540.25 mm 2 、135 mg / 1540.25 mm 2 、137 mg / 1540.25 mm 2 、140 mg / 1540.25 mm 2 、145 mg / 1540.25 mm 2 、150 mg / 1540.25 mm 2 、155 mg / 1540.25 mm 2 、160 mg / 1540.25 mm 2 、165 mg / 1540.25 mm 2 、170 mg / 1540.25 mm 2 、175 mg / 1540.25 mm 2 、180 mg / 1540.25 mm 2 or the range composed of any two of the above values.

[0107] When the single-sided coating weight of the negative electrode film layer meets the above range, in combination with an appropriate mass content of silicon element, it is beneficial to improve the energy density of the battery cell, and the migration rate of active ions in the negative electrode film layer is relatively fast, which is beneficial to the improvement of the cycle performance of the battery cell under fast charging.

[0108] In the embodiments of the present application, the tap density of the negative electrode film layer of the battery cell at 0% state of charge (SOC) has the meaning well known in the art, that is, the negative electrode plate is disassembled from the battery cell at 0% SOC, and the tap density of the negative electrode film layer is measured. For example, for a single-sided coated negative electrode plate (if it is a double-sided coated plate, the negative electrode film layer on one side can be wiped off first), it is punched into small round pieces with an area of S1, weighed, and recorded as M1, and its thickness H1 is measured. Then, the negative electrode film layer of the weighed negative electrode plate is wiped off, the weight of the negative electrode current collector is weighed, and recorded as M0, and its thickness H0 is measured. The single-sided coating weight of the negative electrode film layer = (the weight M1 of the negative electrode plate - the weight M0 of the negative electrode current collector) / S1, the thickness of the negative electrode film layer = the thickness H1 of the negative electrode plate - the thickness H0 of the negative electrode current collector, and the tap density of the negative electrode film layer = the single-sided coating weight of the negative electrode film layer / the thickness of the negative electrode film layer.

[0109] In some embodiments, the negative electrode active material includes a silicon-based material. Optionally, the silicon-based material may include elemental silicon, silicon-carbon composite, silicon oxide SiO x (where 0 < x ≤ 2), or at least one of them. The above materials can improve the capacity of the negative electrode active material, which is beneficial to reducing the coating thickness of the negative electrode film layer and shortening the migration path of lithium ions.

[0110] In some embodiments, the specific surface area of the silicon-based material is 1 m 2 ² / g to 4 m 2 ² / g, such as 1 m² / g, 1.2 m² / g, 1.4 m² / g, 1.5 m² / g, 1.6 m² / g, 1.8 m² / g, 2 m² / g, 2.2 m² / g, 2.4 m² / g, 2.5 m² / g, 2.6 m² / g, 2.8 m² / g, 3 m² / g, 3.2 m² / g, 3.4 m² / g, 3.5 m² / g, 3.6 m² / g, 3.8 m² / g, 4 m² / g, or the range composed of any two of the above values.

[0111] When the specific surface area of the silicon-based material is within the above range, it can provide appropriate embedding sites for lithium ions, improve the fast charging ability, and can alleviate the side reaction between the silicon-based material and the electrolyte, and improve the cycle performance under fast charging.

[0112] In the embodiments of the present application, the specific surface area of the material has the meaning well known in the art, and can be detected by using the equipment and methods well known in the art. For example, it can be detected according to the test standard GB / T 19587-2017. The negative electrode plate in the battery cell can be disassembled to obtain the relevant material as a sample, and the specific surface area is tested by a Tri-Star 3020 specific surface area and pore size analyzer produced by Micromeritics Company of the United States.

[0113] In some embodiments, the silicon-based material is granular, and its average particle size is from 4 μm to 12 μm, such as 4 μm, 4.5 μm, 5 μm, 5.5 μm, 6 μm, 6.5 μm, 7 μm, 7.5 μm, 8 μm, 8.5 μm, 9 μm, 9.5 μm, 10 μm, 10.5 μm, 11 μm, 11.5 μm, 12 μm or a range composed of any two of the above values.

[0114] When the average particle size of the silicon-based material is within the above range, it can provide appropriate insertion sites for lithium ions, improve the fast charging ability, and can alleviate the side reaction between the silicon-based material and the electrolyte, improving the cycle performance under fast charging.

[0115] In some embodiments, the negative electrode active material includes a carbon-based material, and the carbon-based material has high cycle stability and can improve the cycle performance of the battery cell.

[0116] Optionally, the carbon-based material includes at least one of artificial graphite and natural graphite.

[0117] In some embodiments, in addition to the above-mentioned carbon-based material and optional silicon-based material, the negative electrode active material may further include at least one of a tin-based material and lithium titanate. The tin-based material may include at least one of elemental tin, tin oxide, and tin alloy material.

[0118] In the present application, the qualitative and quantitative determination of each substance or each element can be detected by suitable equipment and methods known to those skilled in the art. The relevant detection methods can refer to domestic and foreign detection standards, domestic and foreign enterprise standards, etc. And those skilled in the art can also adaptively change some detection steps / instrument parameters, etc. from the perspective of detection accuracy to obtain more accurate detection results. One detection method can be used for qualitative or quantitative determination, or several detection methods can be used in combination for qualitative or quantitative determination.

[0119] For example, the present application can combine the General Rules for X-ray Diffraction Analysis of JIS / K0131-1996 to perform X-ray powder diffraction testing and qualitative analysis on the negative electrode sheet or the negative electrode active material.

[0120] Artificial graphite and natural graphite can be distinguished by the SEM cross-section taken by scanning electron microscope (SEM). There are voids between flaky structures in the SEM cross-section of natural graphite, and the SEM cross-section of artificial graphite is dense and has no obvious gaps, or can be distinguished by the XRD spectrum obtained by X-ray diffraction method. There are obvious 2H phase and 3R phase in the XRD spectrum of natural graphite, and only 2H phase exists in the XRD spectrum of artificial graphite.

[0121] Such as Figure 6As shown, in the embodiments of the present application, the negative electrode film layer 121 of the negative electrode tab 12 includes at least one layer of film layer, which can be a single-layer film layer or at least two-layer film layers. Optionally, the negative electrode film layer 121 includes at least two-layer film layers.

[0122] When 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.

[0123] When the negative electrode film layer 121 includes at least two-layer film layers, the negative electrode active material in the negative electrode film layer 121 includes a carbon-based material and an optional silicon-based material. The negative electrode film layer 121 can include two-layer film layers, three-layer film layers, four-layer film layers, or even more film layers.

[0124] In some embodiments, the negative electrode film layer 121 includes a first negative electrode film layer 1211 and a second negative electrode film layer 1212. The first negative electrode film layer 1211 is disposed on the surface of the negative electrode current collector 122, and the negative electrode active material of the first negative electrode film layer 1211 includes a carbon-based material. The second negative electrode film layer 1212 is connected to the side of the first negative electrode film layer 1211 facing away from the negative electrode current collector 122, and the negative electrode active material of the second negative electrode film layer 1212 includes a carbon-based material. The interface between the first negative electrode film layer 1211 and the second negative electrode film layer 1212 can be regular or irregular, optionally irregular; or there is no obvious interface between the first negative electrode film layer 1211 and the second negative electrode film layer 1212.

[0125] The negative electrode film layer 121 includes at least two-layer film layers, and layer-by-layer coating is beneficial to improving the cycle life of the battery cell under fast charging.

[0126] 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.

[0127] Optionally, the first negative electrode film layer 1211 further includes a silicon-based material.

[0128] Optionally, the second negative electrode film layer 1212 further includes a silicon-based material.

[0129] Exemplarily, the first negative electrode film layer 1211 includes a carbon-based material and a silicon-based material, and the second negative electrode film layer 1212 includes a carbon-based material and a silicon-based material. Or, the first negative electrode film layer 1211 includes a carbon-based material and a silicon-based material, and the second negative electrode film layer 1212 includes a carbon-based material. Or, the first negative electrode film layer 1211 includes a carbon-based material, and the second negative electrode film layer 1212 includes a carbon-based material and a silicon-based material.

[0130] When both the first negative electrode film layer 1211 and the second negative electrode film layer 1212 include silicon-based materials, it is more conducive to improving the energy density of the battery cell. When the first negative electrode film layer 1211 includes silicon-based materials and the second negative electrode film layer 1212 does not include silicon-based materials, the second negative electrode film layer 1212 can alleviate the volume expansion of the first negative electrode film layer 1211, reduce the side reaction between the negative electrode film layer 121 and the electrolyte, and improve the cycling performance under fast charging.

[0131] When the negative electrode film layer 121 adopts at least two film layers, along the thickness direction X of the negative electrode film layer 121, the cross-sectional morphology of the negative electrode film layer 121 can be the same or similar, and of course, it can also be different.

[0132] Along the thickness direction X of the negative electrode film layer 121, the negative electrode film layer 121 is divided into three regions, namely the first region 121a, the third region 121c, and the second region 121b in sequence. The first region 121a is the region of the negative electrode film layer 121 close to the negative electrode current collector 122 along the thickness direction X, and the thickness of the first region 121a is 1 / 3 of the thickness of the negative electrode film layer 121; the second region 121b is the region of the negative electrode film layer 121 away from the negative electrode current collector 122 along the thickness direction X, and the thickness of the second region 121b is 1 / 3 of the thickness of the negative electrode film layer 121.

[0133] The cross-sectional morphology of the first region 121a and the second region 121b can be the same or similar, and of course, it can also be different. The cross-sectional morphology of the first region 121a and the third region 121c can be the same or similar, and of course, it can also be different. The cross-sectional morphology of the second region 121b and the third region 121c can be the same or similar, and of course, it can also be different.

[0134] There can be an obvious layer interface between the first region 121a, the second region 121b, and the third region 121c, or there can be no obvious layer interface. For example, the first negative electrode film layer 1211 includes the first region 121a, the second negative electrode film layer 1212 includes the second region 121b, the third region 121c can be a part of the first negative electrode film layer 1211, or the third region 121c can be a part of the second negative electrode film layer 1212, or the third region 121c can be a part of both the first negative electrode film layer 1211 and the second negative electrode film layer 1212.

[0135] In some embodiments, in the cross-section of the negative electrode film layer 121 parallel to the thickness direction X, the void ratio of a single carbon-based material in the first region 121a is greater than or equal to the void ratio of a single carbon-based material in the second region 121b. Optionally, the void ratio of a single carbon-based material in the first region 121a is less than the void ratio of a single carbon-based material in the second region 121b.

[0136] The carbon-based material is granular and has voids inside. On the cross-section of the negative electrode film layer 121 parallel to the thickness direction X, the percentage of the void area in the total cross-sectional area of the carbon-based material is the void ratio of a single carbon-based material.

[0137] During the charging process of the battery cell, lithium ions diffuse through the second region 121b to the first region 121a. The void ratio of a single carbon-based material in the first region 121a is less than or equal to the void ratio of a single carbon-based material in the second region 121b, which is more conducive to the diffusion of lithium ions in the first region 121a, improving the transmission rate, and thus conducive to the improvement of the cycle life of the battery cell under fast charging.

[0138] Optionally, the average particle size of the carbon-based material in the first region 121a can be greater than or equal to the average particle size of the carbon-based material in the second region 121b. Further optionally, the average particle size of the carbon-based material in the first region 121a can be greater than the average particle size of the carbon-based material in the second region 121b, which is conducive to the rapid migration of lithium ions from the second region 121b to the first region 121a, improving the fast charging ability of the battery cell. Of course, the average particle size of the carbon-based material in the first region 121a can be less than the average particle size of the carbon-based material in the second region 121b.

[0139] Optionally, the average particle size of the carbon-based material in the first negative electrode film layer 1211 can be greater than or equal to the average particle size of the carbon-based material in the second negative electrode film layer 1212. Further optionally, the average particle size of the carbon-based material in the first negative electrode film layer 1211 can be greater than the average particle size of the carbon-based material in the second negative electrode film layer 1212.

[0140] There is a difference in the particle sizes of the first negative electrode film layer 1211 and the second negative electrode film layer 1212, which can improve the fast charging performance of the battery cell. Specifically, during fast charging, the overpotential of the second negative electrode film layer 1212 is usually relatively high, and the bottleneck of fast charging mainly lies in the second negative electrode film layer 1212. In the embodiment of the present application, the particle size of the second negative electrode film layer 1212 is relatively small, which can shorten the solid-phase transmission path of lithium ions, improve the fast charging performance, and can also improve the problem of lithium plating on the surface layer of the negative electrode sheet 12, improving the cycle life under fast charging.

[0141] Optionally, the average particle size of the carbon-based material in the first region 121a is 12 μm to 21 μm, such as 12 μm, 12.5 μm, 13 μm, 13.5 μm, 14 μm, 14.5 μm, 15 μm, 15.5 μm, 16 μm, 16.5 μm, 17 μm, 17.5 μm, 18 μm, 18.5 μm, 19 μm, 19.5 μm, 20 μm, 20.5 μm, 21 μm, or a range composed of any two of the above values. When the average particle size of the carbon-based material in the first region 121a is within the above range, the cycle life under fast charging can be improved.

[0142] 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 under fast charging can be improved.

[0143] Optionally, the average particle size of the carbon-based material in the second region 121b is 9 μm to 17 μm, such as 9 μm, 9.5 μm, 10 μm, 10.5 μm, 11 μm, 11.5 μm, 12 μm, 12.5 μm, 13 μm, 13.5 μm, 14 μm, 14.5 μm, 15 μm, 15.5 μm, 16 μm, 16.5 μm, 17 μm, or a range composed of any two of the above values. When the average particle size of the carbon-based material in the second negative electrode film layer 1212 is within the above range, it is beneficial to improve the fast charging ability of the battery cell and improve the stability of the material.

[0144] 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, the fast charging performance and the stability of the material can be improved, and the cycle life under fast charging can be improved.

[0145] Exemplarily, the carbon-based material in the first region 121a includes artificial graphite and natural graphite, and the carbon-based material in the second region 121b includes artificial graphite. For example, the negative electrode active material in the first region 121a includes a silicon-based material, artificial graphite, and natural graphite, and the negative electrode active material in the second region 121b includes a silicon-based material and artificial graphite.

[0146] Exemplarily, the carbon-based material in the first negative electrode film layer 1211 includes artificial graphite and natural graphite, and the carbon-based material in the second negative electrode film layer 1212 includes artificial graphite. For example, the negative electrode active material in the first negative electrode film layer 1211 includes a silicon-based material, artificial graphite, and natural graphite, and the negative electrode active material in the second negative electrode film layer 1212 includes a silicon-based material and artificial graphite.

[0147] In some other embodiments, in a cross-section of the negative electrode film layer 121 parallel to the thickness direction X, the void ratio of a single carbon-based material in the first region 121a is less than that of a single carbon-based material in the second region 121b.

[0148] During the charging process of the battery cell, lithium ions diffuse from the second region 121b to the first region 121a. The larger void ratio of a single carbon-based material in the second region 121b is conducive to the rapid transport of lithium ions from the second region 121b to the first region 121a, thus facilitating the rapid charging of the battery cell.

[0149] Optionally, the average particle size of the carbon-based material in the first region 121a can be smaller than that of the carbon-based material in the second region 121b. The relatively larger average particle size of the carbon-based material in the second region 121b results in higher pressure resistance during the preparation of the film layer, which is conducive to improving the particle compactness; the relatively smaller average particle size of the carbon-based material in the first region 121a enables the rapid migration of lithium ions, improves the rapid charging ability of the battery cell, and enhances the cycle life under rapid charging.

[0150] Of course, the average particle size of the carbon-based material in the first region 121a can be greater than or equal to that of the carbon-based material in the second region 121b.

[0151] Optionally, the average particle size of the carbon-based material in the first region 121a is 9 μm to 17 μm, such as 9 μm, 9.5 μm, 10 μm, 10.5 μm, 11 μm, 11.5 μm, 12 μm, 12.5 μm, 13 μm, 13.5 μm, 14 μm, 14.5 μm, 15 μm, 15.5 μm, 16 μm, 16.5 μm, 17 μm or the range composed of any two of the above values.

[0152] Optionally, the average particle size of the carbon-based material in the first negative electrode film layer 1211 is 9 μm to 17 μm.

[0153] Optionally, the average particle size of the carbon-based material in the second region 121b is 12 μm to 21 μm, such as 12 μm, 12.5 μm, 13 μm, 13.5 μm, 14 μm, 14.5 μm, 15 μm, 15.5 μm, 16 μm, 16.5 μm, 17 μm, 17.5 μm, 18 μm, 18.5 μm, 19 μm, 19.5 μm, 20 μm, 20.5 μm, 21 μm or the range composed of any two of the above values. <000042 < /

[0154] Optionally, the average particle size of the carbon-based material in the second negative electrode film layer 1212 is 12 μm to 21 μm.

[0155] Exemplarily, the carbon-based material of the second region 121b includes artificial graphite and natural graphite, and the carbon-based material of the first region 121a includes artificial graphite. Optionally, the negative electrode active material further includes a silicon-based material. For example, the negative electrode active material of the second region 121b includes a silicon-based material, artificial graphite, and natural graphite, and the negative electrode active material of the first region 121a includes a silicon-based material and artificial graphite.

[0156] Exemplarily, the carbon-based material of the second negative electrode film layer 1212 includes artificial graphite and natural graphite, and the carbon-based material of the first negative electrode film layer 1211 includes artificial graphite. Optionally, the negative electrode active material further includes a silicon-based material. For example, the negative electrode active material of the second negative electrode film layer 1212 includes a silicon-based material, artificial graphite, and natural graphite, and the negative electrode active material of the first negative electrode film layer 1211 includes a silicon-based material and artificial graphite.

[0157] In the embodiments of the present application, the average particle size of the active material in the first region 121a and the second region 121b can be detected by the following equipment and method: taking the negative electrode sheet 12 as a sample, and taking a scanning electron microscope (SEM) photograph along the thickness direction X of the negative electrode film layer 121 to obtain an SEM cross-sectional view, counting the particle size of the active material in the SEM cross-section, and calculating the average particle size of the active material according to the counted quantity.

[0158] In some embodiments, the negative electrode film layer may optionally further include a negative electrode conductive agent. The embodiments of the present application do not particularly limit the type of the negative electrode conductive agent. As an example, the negative electrode conductive agent may include at least one of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. In some embodiments, based on the total weight of the negative electrode film layer, the mass content of the negative electrode conductive agent is ≤5%.

[0159] In some embodiments, the negative electrode film layer may optionally further include a negative electrode binder. In some embodiments, based on the total weight of the negative electrode film layer, the mass content of the negative electrode binder is ≤5%.

[0160] In some embodiments, the negative electrode film layer may optionally further include other additives. As an example, the other additives may include thickeners, dispersants, etc. For example, sodium carboxymethyl cellulose (CMC-Na), PTC thermistor materials, etc. In some embodiments, based on the total weight of the negative electrode film layer, the mass content of the other additives is ≤2%.

[0161] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. As an example of the metal foil, at least one foil of copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy may be used. The composite current collector may include a polymer material base layer and a metal material layer formed on at least one surface of the polymer material base layer. As an example, the metal material in the metal material layer may include at least one of copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy. As an example, the polymer material base layer may include at least one of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0162] The negative electrode film layer is generally formed by coating a negative electrode slurry on a negative electrode current collector and then drying and cold pressing. The negative electrode slurry is generally formed by dispersing a negative electrode active material, an optional conductive agent, an optional binder, and other optional additives in a solvent and stirring evenly. The solvent may be N-methylpyrrolidone (NMP) or deionized water, but is not limited thereto.

[0163] 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 electrode conductive layer disposed on the surface of the negative electrode current collector and sandwiched between the negative electrode current collector and the negative electrode film layer. In 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.

[0164] Positive electrode plate

[0165] In some embodiments, the battery cell further includes a positive electrode sheet.

[0166] 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 including a positive electrode active material. For example, the positive electrode current collector has two opposite surfaces in its own thickness direction, and the positive electrode film layer is disposed on any one or both of the two opposite surfaces of the positive electrode current collector.

[0167] In some embodiments, the size of the positive electrode film layer in the length direction of the positive electrode sheet is 200 mm to 600 mm, such as 200 mm, 250 mm, 300 mm, 350 mm, 400 mm, 450 mm, 500 mm, 550 mm, 600 mm, or a range composed of any two of the above values.

[0168] 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.

[0169] 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.

[0170] 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 / cm 3 , 2.25g / cm 3 , 2.30g / cm 3 , 2.32g / cm 3 , 2.35g / cm 3 , 2.38g / cm 3 , 2.40g / cm 3 , 2.42g / cm 3 , 2.45g / cm 3 , 2.48g / cm 3 , 2.50g / cm 3 , 2.52g / cm 3 , 2.55g / cm 3 , 2.56g / cm 3 , 2.57g / cm 3 , 2.58g / cm 3 , 2.60g / cm 3 , 2.62g / cm 3 , 2.65g / cm 3 , 2.68g / cm 3 , 2.70g / cm 3 , 2.75g / cm 3 , 2.80g / cm3 、 2.85 g / cm 3 or a range composed of any two of the above values.

[0171] When the compaction density of the positive electrode film layer is within the above range, it is beneficial to improve the energy density of the battery cell; and since the positive electrode active materials in the positive electrode film layer are stacked relatively closely, the contact resistance between particles is small, which can further reduce the resistance of the electrode sheet, thereby reducing heat generation during rapid charging and improving the cycling performance of the battery cell under rapid charging.

[0172] In some embodiments, the single-sided coating weight of the positive electrode film layer is 250 mg / 1540.25 mm 2 to 300 mg / 1540.25 mm 2 . Exemplarily, the single-sided coating weight of the positive electrode film layer is 250 mg / 1540.25 mm 2 、 260 mg / 1540.25 mm 2 、 270 mg / 1540.25 mm 2 、 280 mg / 1540.25 mm 2 、 290 mg / 1540.25 mm 2 、 300 mg / 1540.25 mm 2 or a range composed of any two of the above values.

[0173] When the single-sided coating weight of the positive electrode film layer is within the above range, the heat generation per unit area of the positive electrode sheet will not be too large, improving the cycling performance of the battery cell under rapid charging.

[0174] In the embodiments of the present application, the compaction density of the positive electrode film layer of the battery cell at 0% state of charge (SOC) has the meaning well known in the art, that is, disassembling the positive electrode sheet of the battery cell at 0% SOC and measuring the compaction density of the positive electrode film layer. For example, taking a single-sided coated positive electrode sheet (if it is a double-sided coated sheet, one side of the positive electrode film layer can be wiped off first), punching it into small circular pieces with an area of S1, weighing it, recording it as M1, and measuring its thickness H1. Then wipe off the positive electrode film layer of the above-mentioned weighed positive electrode sheet, weigh the weight of the positive electrode current collector, record it as M0, and measure its thickness H0. The single-sided coating weight of the positive electrode film layer = (the weight M1 of the positive electrode sheet - the weight M0 of the positive electrode current collector) / S1, the thickness of the positive electrode film layer = the thickness H1 of the positive electrode sheet - the thickness H0 of the positive electrode current collector, and the compaction density of the positive electrode film layer = the single-sided coating weight of the positive electrode film layer / the thickness of the positive electrode film layer.

[0175] In some embodiments, the positive electrode active material includes one or more of a lithium-containing transition metal oxide and a lithium-containing phosphate. Optionally, the positive electrode active material includes a lithium-containing phosphate. The lithium-containing phosphate may have an olivine structure, which is stable during charge and discharge and can improve the cycle life of the battery cell.

[0176] Examples of the lithium-containing transition metal oxide may include, but are not limited to, at least one of lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, and their respective modified compounds.

[0177] In some embodiments, the positive electrode film layer further includes a carbon-containing material, and the carbon-containing material is a carbon-containing conductive material. The above materials can improve the conductivity of the positive electrode film layer and are beneficial to improving the cycle performance of the battery cell under fast charging.

[0178] Optionally, the mass content of carbon element in the positive electrode film layer is 0.8% to 3.5%, such as 0.8%, 0.9%, 1.0%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2.0%, 2.1%, 2.2%, 2.3%, 2.4%, 2.5%, 2.6%, 2.7%, 2.8%, 2.9%, 3.0%, 3.1%, 3.2%, 3.3%, 3.4%, 3.5% or the range composed of any two of the above values. Optionally, the mass content of carbon element in the positive electrode film layer is 1.3% to 3.0%.

[0179] For example, the carbon-containing material may include carbon materials with a tubular structure, such as carbon nanotubes, carbon nanofibers, etc., and carbon nanotubes may be selected. Carbon nanotubes can be used as a conductive agent in the positive electrode film layer to improve the conductivity of the positive electrode film layer.

[0180] For another example, the lithium-containing phosphate with an olivine structure may be an unmodified lithium-containing phosphate such as lithium iron phosphate, or a material obtained by coating and modifying it. For example, a carbon-containing material is provided on the surface of the lithium-containing phosphate, and the carbon-containing material can be used as a coating layer to coat the surface of the lithium-containing phosphate, thereby improving the conductivity of the lithium-containing phosphate, reducing the powder resistivity of the material, and being beneficial to the migration rate of lithium ions, and improving the cycle performance of the battery cell under fast charging conditions.

[0181] In some embodiments, the lithium-containing phosphate includes a general formula of Li x1 A y1 Me a M b '' P 1-c X c Y zCompounds, where 0.5 ≤ x1 ≤ 1.3, 0 ≤ y1 ≤ 1.3, and 0.9 ≤ x1 + y1 ≤ 1.3, 0.9 ≤ a ≤ 1.5, 0 ≤ b ≤ 0.5, and 0.9 ≤ a + b ≤ 1.5, 0 ≤ c ≤ 0.5, 3 ≤ z ≤ 5, A includes one or more of Na, K, Mg, Me includes one or more of Mn, Fe, Co, Ni, M includes one or more of B, Mg, Al, Si, P, S, Ca, Sc, Ti, V, Cr, Cu, Zn, Sr, Y, Zr, Nb, Mo, Cd, Sn, Sb, Te, Ba, Ta, W, Yb, La, Ce, X includes one or more of Cl, C, N, and Y includes one or more of O, F. The lithium-containing phosphate has excellent cycle stability, which is beneficial to improving the cycle performance of the battery cell.

[0182] Exemplarily, the lithium-containing phosphate includes one or more of LiFePO4, LiMnPO4, LiNiPO4, LiCoPO4. During the charge and discharge process of the battery cell, the insertion and extraction and consumption of active ions such as Li will occur. The molar content of Li is different when the battery cell is discharged to different states. In the enumeration of the cathode active materials such as LiFePO4, LiMnPO4, LiNiPO4, LiCoPO4, etc., the molar content of Li is the initial state of the material, that is, the state before feeding. When the cathode active material is applied to the battery system and undergoes charge and discharge cycles, the molar content of Li may change. In the embodiments of the present application, in the enumeration of the cathode active materials such as LiFePO4, LiMnPO4, LiNiPO4, LiCoPO4, etc., the molar content of oxygen O is only the theoretical state value. The release of oxygen from the lattice will cause the molar content of oxygen O to change. Actually, the molar content of oxygen O will fluctuate. The above situations are all within the protection scope of the present application.

[0183] In the embodiments of the present application, the content of elements in the cathode active material has the meaning well-known in the art and can be detected by equipment and methods well-known in the art. For example, referring to EPA 6010D-2014, it is tested by inductively coupled plasma atomic emission spectrometry and determined by inductively coupled plasma optical emission spectrometry (ICP-OES, instrument model: Thermo ICAP7400). After the battery cell is discharged to 0% state of charge (SOC) and the cathode electrode is disassembled, it is cleaned with dimethyl carbonate (DMC) and dried, and then after removing impurities by high-temperature calcination, 0.4 g of the cathode active material is weighed and 10 ml (50% concentration) of aqua regia is added thereto. Then it is placed on a flat plate at 180 °C for 30 min. After digestion on the flat plate, it is fixed to a volume of 100 mL, and quantitative testing is carried out by the standard curve method.

[0184] In some embodiments, the positive electrode film layer further includes a lithium supplement agent. The lithium supplement agent contains lithium element and can release lithium ions during the charging process of the battery cell to make up for lithium loss, which is beneficial to improving the capacity characteristics and high-temperature cycle performance of the battery cell.

[0185] In some embodiments, the lithium supplement agent includes at least one of lithium ferrite, lithium nickelate, and lithium cobaltate.

[0186] In some embodiments, the lithium supplement agent is granular, 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 the range composed of any two of the above.

[0187] In some embodiments, the lithium supplement agent is granular, 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 the range composed of any two of the above.

[0188] In the embodiments of the present application, the positive electrode plate is cut along the thickness direction of the plate to expose the cut surface of the positive electrode film layer, which can also be understood as the cross-section of the positive electrode film layer along its own thickness direction. By performing a scanning electron microscope (SEM) test on the cut surface of the positive electrode film layer, the longest diameter and the shortest diameter of the lithium supplement agent particles are determined. For example, the "longest diameter" of the particle refers to the longest straight line passing through the center point of the particle and extending to the outer periphery of the particle. The "shortest diameter" of the particle refers to the shortest straight line passing through the center point of the particle and extending to the outer periphery of the particle.

[0189] In the cross-section of the positive electrode film layer along its own thickness direction, the longest diameters of multiple, for example, 10 lithium supplement agents are statistically counted, and the average value calculated is the average longest diameter; the shortest diameters of multiple, for example, 10 lithium supplement agents are statistically counted, and the average value calculated is the average shortest diameter.

[0190] In some embodiments, based on the total mass of the positive electrode film layer, the mass ratio of the lithium supplement agent is 0.5% to 3%, such as 0.5%, 0.6%, 0.8%, 1.0%, 1.2%, 1.4%, 1.6%, 1.8%, 2.0%, 2.5%, 3.0% or the range composed of any two of the above. When using the lithium supplement agent within the above mass range, it can effectively improve the stability of the lithium supplement agent while having a good oxygen release effect.

[0191] In some embodiments, the positive electrode film layer may further optionally include a positive electrode conductive agent. As an example, the positive electrode conductive agent includes at least one of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. In some embodiments, based on the mass of the positive electrode film layer, the mass content of the positive electrode conductive agent is ≤5%.

[0192] Optionally, the positive electrode conductive agent includes carbon nanotubes, and the mass content of the carbon nanotubes in the positive electrode film layer is 0.1% to 2%, such as 0.1%, 0.3%, 0.5%, 0.7%, 0.9%, 1.1%, 1.3%, 1.5%, 1.7%, 1.9%, 2% or the range composed of any two of the above. Optionally, the mass content of the carbon nanotubes in the positive electrode film layer is 0.15% to 1.2%.

[0193] When the mass content of the carbon nanotubes is within the above range, it is beneficial to improve the conductivity of the positive electrode film layer and improve the cycling performance of the battery cell under fast charging conditions.

[0194] Optionally, the specific surface area of the carbon nanotubes is 500 m 2 / g to 2500 m 2 / g, such as 500 m² / g, 700 m² / g, 900 m² / g, 1100 m² / g, 1300 m² / g, 1500 m² / g, 1700 m² / g, 1900 m² / g, 2100 m² / g, 2300 m² / g, 2500 m² / g or the range composed of any two of the above.

[0195] When the specific surface area of the carbon nanotubes is within the above range, it is beneficial to improve the electron conduction ability; and cooperating with an appropriate content of carbon nanotubes can reduce the degree of side reaction between the carbon nanotubes and the electrolyte, and can improve the cycling performance of the battery cell under fast charging conditions.

[0196] Optionally, the tube diameter of the carbon nanotubes is 0.5 nm to 20 nm, 0.5 nm, 1.5 nm, 2.5 nm, 3.5 nm, 4.5 nm, 5.5 nm, 6.5 nm, 7.5 nm, 8.5 nm, 9.5 nm, 10.5 nm, 11.5 nm, 12.5 nm, 13.5 nm, 14.5 nm, 15.5 nm, 16.5 nm, 17.5 nm, 18.5 nm, 19.5 nm, 20 nm or the range composed of any two of the above. Optionally, the tube diameter of the carbon nanotubes is 0.5 nm to 7.5 nm.

[0197] When the tube diameter of the carbon nanotubes is within the above range, the structure is relatively stable, and it has relatively excellent electron conduction ability, and can improve the cycling performance of the battery cell under fast charging conditions.

[0198] Carbon nanotubes can generally be considered to be formed by curling two-dimensional carbon materials. When the number of curled layers is single layer, it is single-walled carbon nanotubes; when curled into multiple layers, it is multi-walled carbon nanotubes. The tube diameter of the carbon nanotubes is the outer diameter of the carbon nanotubes on the cross-section perpendicular to its own central axis.

[0199] In some embodiments, the positive electrode film layer may optionally further include a positive electrode binder. There is no particular limitation on the type of the positive electrode binder in the embodiments of the present application. As an example, the positive electrode binder may include at least one of polyvinylidene fluoride, polytetrafluoroethylene, vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, polyacrylic acid, and fluorinated acrylate resins. In some embodiments, based on the mass of the positive electrode film layer, the mass content of the positive electrode binder is ≤5%.

[0200] In some embodiments, the positive electrode current collector may be a metal foil or a composite current collector. As an example of the metal foil, at least one of foils of aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy may be used. The composite current collector may include a polymer material base layer and a metal material layer formed on at least one surface of the polymer material base layer. As an example, the metal material of the metal material layer may include at least one of aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy. As an example, the polymer material base layer may include at least one of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0201] The positive electrode film layer is generally formed by coating a positive electrode slurry on a positive electrode current collector and then drying and cold pressing. The positive electrode slurry is generally formed by dispersing a positive electrode active material, an optional conductive agent, an optional binder, and any other components in a solvent and stirring evenly. The solvent may be N-methylpyrrolidone (NMP), but is not limited thereto.

[0202] The positive electrode tab does not exclude other additional functional layers other than the positive electrode film layer. For example, in some embodiments, the positive electrode tab of the embodiments of the present application further includes a positive electrode conductive layer sandwiched between the positive electrode current collector and the positive electrode film layer and disposed on the surface of the positive electrode current collector. In some other embodiments, the positive electrode tab of the embodiments of the present application further includes a protective layer covering the surface of the positive electrode film layer.

[0203] [Electrolyte]

[0204] During the charge and discharge process of the battery cell, active ions such as lithium ions are embedded and extracted back and forth between the positive electrode tab and the negative electrode tab, and the electrolyte plays a role in conducting the active ions between the positive electrode tab and the negative electrode tab. The electrolyte includes an organic solvent and an electrolyte salt.

[0205] In some embodiments, the conductivity of the electrolyte at room temperature is from 9 mS / cm to 18 mS / cm. Exemplarily, the conductivity of the electrolyte at room temperature is 9 mS / cm, 9.5 mS / cm, 10 mS / cm, 10.5 mS / cm, 11 mS / cm, 11.5 mS / cm, 12 mS / cm, 12.5 mS / cm, 13 mS / cm, 13.5 mS / cm, 14 mS / cm, 14.5 mS / cm, 15 mS / cm, 15.5 mS / cm, 16 mS / cm, 16.5 mS / cm, 17 mS / cm, 17.5 mS / cm, 18 mS / cm or a range composed of any two of the above values.

[0206] When the conductivity of the electrolyte at room temperature, such as 25 °C, is within the above range, the migration rate of lithium ions in the electrolyte is relatively high, which can further reduce the internal resistance of the battery cell, thereby reducing heat generation and the gas generation caused by heat accumulation, and can improve the cycle life of the battery cell under fast charging.

[0207] In the embodiments of the present application, the conductivity of the electrolyte at room temperature, such as 25 °C, is the ionic conductivity, and it can be detected by using the equipment and methods well-known in the art. For example, it can be tested with reference to the industry standard HG-T 4067-2015.

[0208] In some embodiments, the organic solvent includes carboxylic ester solvents.

[0209] Optionally, the mass content of the carboxylic ester solvent in the electrolyte is from 3% to 70%. Exemplarily, the mass content of the carboxylic ester solvent is 3%, 5%, 8%, 10%, 13%, 15%, 18%, 20%, 23%, 25%, 28%, 30%, 33%, 35%, 38%, 40%, 43%, 45%, 48%, 50%, 53%, 55%, 58%, 60%, 63%, 65%, 68%, 70% or a range composed of any two of the above values. Optionally, the mass content of the carboxylic ester solvent in the electrolyte is from 5% to 30%.

[0210] When the mass content of the carboxylic ester solvent is within the above range, it can improve the conductivity of the electrolyte; and the electrolyte is compatible with the silicon-containing negative electrode, which can effectively alleviate the side reactions on the negative electrode side, reduce the gas generation of the battery cell, and improve the cycle performance of the battery cell under fast charging. The carboxylic ester solvent with the above mass content can also quickly infiltrate the positive electrode film layer, making the charging state of the positive electrode film layer more uniform, reducing the risk of local side reactions on the negative electrode side, and further improving the cycle performance of the battery cell under fast charging.

[0211] Exemplarily, the carboxylate ester solvents include cyclic carboxylate esters, and the cyclic carboxylate esters include one or more of γ-butyrolactone, γ-valerolactone, and δ-valerolactone. The viscosity of the above materials is relatively low, which can improve the wetting ability of the electrode sheet and improve the cycle performance under fast charging.

[0212] Exemplarily, the carboxylate ester solvents include linear carboxylate esters, and the linear carboxylate esters include one or more of methyl acetate, ethyl acetate, propyl acetate, butyl acetate, propyl propionate, and butyl propionate. The viscosity of the above materials is relatively low, which can improve the wetting ability of the electrode sheet and improve the cycle performance under fast charging.

[0213] In some embodiments, the organic solvent includes carbonate solvents.

[0214] When the carbonate solvents and the carboxylate ester solvents are used in combination, the stability of the electrolyte can be improved and the gas generation amount at high temperature can be reduced.

[0215] Exemplarily, the carbonate solvents include one or more of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate. Optionally, the carbonate solvents include one or more of ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate.

[0216] In some embodiments, the electrolyte salt includes lithium salts, and the lithium salts include one or more of lithium bis(fluorosulfonyl)imide and lithium hexafluorophosphate. Optionally, the lithium salts include lithium bis(fluorosulfonyl)imide and lithium hexafluorophosphate.

[0217] Lithium hexafluorophosphate may decompose to produce hydrofluoric acid HF. The side reaction between hydrofluoric acid and the negative electrode, especially the silicon-containing negative electrode, may lead to an increase in gas generation during high-temperature storage. When lithium hexafluorophosphate and lithium bis(fluorosulfonyl)imide are used in combination, the content of hydrofluoric acid can be reduced, the side reaction at the negative electrode interface can be slowed down, which is beneficial to improving the cycle life of the battery cell.

[0218] In some embodiments, based on the mass of the electrolyte, the ratio of the mass content of lithium bis(fluorosulfonyl)imide to the mass content of lithium hexafluorophosphate is from 0.3 to 1.2, such as 0.3, 0.5, 0.7, 0.9, 1.1, 1.2 or the range composed of any two of the above values.

[0219] When the ratio of the mass content of lithium hexafluorophosphate to the mass content of lithium bis(fluorosulfonyl)imide meets the above range, the content of hydrofluoric acid can be reduced, the side reaction at the negative electrode interface can be slowed down, which is beneficial to improving the cycle performance of the battery cell under fast charging.

[0220] Exemplarily, based on the mass of the electrolyte, the mass content of lithium bis(fluorosulfonyl)imide is 2% to 11%, such as 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 8%, 8.5%, 9%, 9.5%, 10%, 10.5%, 11% or a range composed of any two of the above values. When the mass content of lithium bis(fluorosulfonyl)imide is within the above range, the content of hydrofluoric acid can be reduced, the side reaction at the negative electrode interface can be slowed down, which is beneficial to improving the cycling performance of the battery cell under fast charging.

[0221] Exemplarily, based on the mass of the electrolyte, the mass content of lithium hexafluorophosphate is 3% to 14%, such as 3%, 3.5%, 4%, 4.5%, 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 8%, 8.5%, 9%, 9.5%, 10%, 10.5%, 11%, 11.5%, 12%, 12.5%, 13%, 13.5%, 14% or a range composed of any two of the above values. When the mass content of lithium hexafluorophosphate is within the above range, the conductivity of the electrolyte is relatively high, which is beneficial to the migration of lithium ions and is beneficial to improving the cycling performance of the battery cell under fast charging.

[0222] In some embodiments, the electrolyte further includes additives. The additives can include negative electrode film-forming additives, can also include positive electrode film-forming additives, and can also include additives that can improve certain battery performances, such as additives for improving the overcharge performance of the battery, additives for improving the high-temperature performance of the battery, additives for improving the low-temperature power performance of the battery, etc.

[0223] In some embodiments, the additives include cyclic carbonate additives, such as including one or more of fluorinated cyclic carbonates and vinylene carbonate. Optionally, the additives include fluorinated cyclic carbonates and vinylene carbonate.

[0224] The fluorinated cyclic carbonate can form a SEI film rich in lithium fluoride LiF on the surface of the negative electrode, which can relieve the volume expansion of silicon, improve the life of the silicon-containing system, and improve the cycling performance.

[0225] The fluorinated cyclic carbonate and vinylene carbonate are used in combination, making the SEI film on the surface of the negative electrode denser, which can more effectively protect the silicon-containing negative electrode, reduce the degree of side reaction at the negative electrode interface, and improve the cycling performance.

[0226] Optionally, the fluorinated cyclic carbonate includes at least one of fluoroethylene carbonate, difluoroethylene carbonate, and trifluoropropylene carbonate.

[0227] Optionally, based on the mass of the electrolyte, the mass content of the fluorinated cyclic carbonate is 0.5% to 20%, for example, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 8%, 8.5%, 9%, 9.5%, 10%, 10.5%, 11%, 11.5%, 12%, 12.5%, 13%, 13.5%, 14%, 14.5%, 15%, 15.5%, 16%, 16.5%, 17%, 17.5%, 18%, 18.5%, 19%, 19.5%, 20% or a range composed of any two of the above values. When the mass content of the fluorinated cyclic carbonate is within the above range, it is beneficial to improve the cycling performance.

[0228] As an example, based on the mass of the electrolyte, the mass content of the fluorinated cyclic carbonate is 0.5% to 10%; the mass content of silicon element in the silicon-based material in the negative electrode active material is 0.3% to 7.5%.

[0229] When the mass content of the fluorinated cyclic carbonate and the mass content of the silicon element meet the above conditions, the volume expansion of silicon can be more effectively alleviated, the lifespan of the silicon-containing system can be improved, and the cycling performance can be improved.

[0230] As another example, based on the mass of the electrolyte, the mass content of the fluorinated cyclic carbonate is greater than 10% and less than or equal to 20%, and the mass content of silicon element in the silicon-based material in the negative electrode active material is greater than 7.5% and less than or equal to 15%.

[0231] The mass content of the silicon element is relatively high and the volume expansion is relatively larger. When the mass content of the fluorinated cyclic carbonate and the mass content of the silicon element meet the above conditions, the volume expansion of silicon can be more effectively alleviated, the lifespan of the silicon-containing system can be improved, and the cycling performance can be improved.

[0232] Optionally, based on the mass of the electrolyte, the mass content of vinylene carbonate is 0.1% to 3%, for example, 0.1%, 0.5%, 0.6%, 1.0%, 1.1%, 1.5%, 1.6%, 2.0%, 2.1%, 2.5%, 2.6%, 3% or a range composed of any two of the above values.

[0233] When the vinylene carbonate with the above mass content is used in combination with the fluorinated cyclic carbonate, the compactness of the interfacial film on the negative electrode surface is better, which can more effectively protect the silicon-containing negative electrode, reduce the degree of side reactions at the negative electrode interface, and improve the cycling performance.

[0234] In the embodiments of the present application, the types and contents of inorganic components / lithium salts in the electrolyte have meanings well-known in the art, and can be detected by devices and methods well-known in the art. For example, reference can be made to the General Rules for Ion Chromatography Analysis (JY / T 020-1996) to qualitatively or quantitatively analyze the inorganic components / lithium salts in the electrolyte by ion chromatography analysis method. In the embodiments of the present application, newly prepared electrolyte can be taken as a sample, free electrolyte of a fresh battery can be taken as a sample, or a discharged battery (discharged to the lower cut-off voltage so that the charged state of the battery is about 0% SOC) can be disassembled in reverse, and the free electrolyte obtained from the battery can be taken as a sample for detection by ion chromatography analysis method.

[0235] In the embodiments of the present application, the types and contents of organic components in the electrolyte have meanings well-known in the art, and can be detected by devices and methods well-known in the art. For example, reference can be made to the General Rules for Gas Chromatography of Chemical Reagents (GB / T 9722-2006) to qualitatively and quantitatively analyze the organic components in the electrolyte by gas chromatography method.

[0236] In the embodiments of the present application, after quantitatively and qualitatively detecting each component in the electrolyte, each component is classified, and carboxylic acid ester solvents and carbonate solvents are used as the constituent components of organic solvents. Based on the mass of the electrolyte being 100%, the mass content of each component is calculated.

[0237] Fluorinated cyclic carbonates and vinylene carbonate are used as additives in the electrolyte. Based on the mass of the electrolyte being 100%, the mass content of each component is calculated.

[0238] Separator

[0239] In some embodiments, the electrode assembly further includes a separator disposed between the positive electrode sheet and the negative electrode sheet.

[0240] In some embodiments, the separator is a separator membrane. The present application does not particularly limit the type of the separator membrane, and any well-known porous structure separator membrane with good chemical stability and mechanical stability can be selected.

[0241] As an example, the main material of the separator membrane can be selected from at least one of glass fiber, non-woven fabric, polyethylene, polypropylene, polyvinylidene fluoride, and ceramics. The separator membrane can be a single-layer film or a multi-layer composite film, without particular limitation. When the separator membrane is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation. The separator can be a single component located between the positive and negative electrodes, or can be attached to the surfaces of the positive and negative electrodes. An inorganic particle coating, an organic particle coating, or an organic / inorganic composite coating can also be coated on the surface of the separator membrane.

[0242] In some embodiments, the separator is a solid electrolyte. The solid electrolyte is disposed between the positive electrode and the negative electrode, and functions to transport ions and isolate the positive and negative electrodes simultaneously.

[0243] Embodiment

[0244] The following examples more specifically describe the content disclosed in the embodiments of the present application. These examples are only for illustrative purposes, because various modifications and changes within the scope of the content disclosed in the embodiments of the present application are obvious to those skilled in the art. Unless otherwise stated, all parts, percentages, and ratios reported in the following examples are based on mass, and all reagents used in the examples are commercially available or synthesized according to conventional methods, and can be used directly without further treatment, and all instruments used in the examples are commercially available.

[0245] Example 1

[0246] 1. Preparation of the positive electrode sheet

[0247] The positive electrode sheet includes a positive electrode current collector and positive electrode film layers provided on both sides of the positive electrode current collector. The positive electrode current collector is aluminum foil.

[0248] The positive electrode film layer includes lithium-containing phosphate lithium iron phosphate, binder polyvinylidene fluoride (PVDF), and conductive agent acetylene black with a mass ratio of 97:1.8:1.2. The positive electrode film layer is a film layer formed by uniformly coating the positive electrode slurry (solvent is N-methylpyrrolidone NMP) on both sides of the positive electrode current collector and then drying and cold pressing.

[0249] The lithium-containing phosphate is sourced from Ningbo Ronbay New Energy Technology Co., Ltd.

[0250] 2. Preparation of the negative electrode sheet

[0251] The negative electrode sheet includes a negative electrode current collector and negative electrode film layers provided on both sides of the negative electrode current collector. The negative electrode current collector is copper foil.

[0252] The negative electrode film layer is a film layer formed by uniformly coating the negative electrode slurry (solvent is deionized water) on the surface of the negative electrode current collector and then drying and cold pressing.

[0253] 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.

[0254] The first negative electrode film layer includes a carbon-based material, conductive agent acetylene black, negative electrode binder styrene-butadiene rubber, and thickening agent sodium carboxymethylcellulose with a mass ratio of 97.2:0.8:1:1. The carbon-based material of the first negative electrode film layer includes artificial graphite and natural graphite with a mass ratio of 80%:20%, and the average particle size of the carbon-based material is 15 μm.

[0255] The second negative electrode film layer comprises a carbon-based material, conductive agent acetylene black, negative electrode binder styrene-butadiene rubber, and thickening agent sodium carboxymethyl cellulose with a mass ratio of 96.5:0.5:2:1. The carbon-based material of the second negative electrode film layer includes artificial graphite, and the average particle size of the carbon-based material is 12 μm.

[0256] In the cross-section along the thickness direction of the negative electrode film layer, the void ratio of a single carbon-based material in the second negative electrode film layer is greater than that of a single carbon-based material in the first negative electrode film layer.

[0257] The negative electrode active material is sourced from Shanghai Xiangfenghua Technology Co., Ltd.

[0258] 3. Separator

[0259] The separator includes a base film, which is a 7-μm polyethylene film layer with a porosity of 38%.

[0260] The separator is sourced from Yunnan Enjie New Materials Co., Ltd.

[0261] 4. Preparation of electrolyte

[0262] The electrolyte includes an organic solvent, a lithium salt, and an additive.

[0263] The organic solvent includes 25% chain carboxylic 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.

[0264] The lithium salt includes 8% lithium hexafluorophosphate LiPF6 and 6% lithium bis(fluorosulfonyl)imide.

[0265] The additive includes 2% fluorinated cyclic carbonate fluoroethylene carbonate FEC and 2% vinylene carbonate VC;

[0266] The conductivity of the electrolyte is 14.2 mS / cm.

[0267] 5. Preparation of battery cell

[0268] Stack the above-mentioned positive electrode sheet, separator, and negative electrode sheet in sequence, with the separator placed between the positive electrode sheet and the negative electrode sheet to play an isolation role, obtaining an electrode assembly. Place the electrode assembly in an outer packaging shell, inject the electrolyte after drying, and go through processes such as vacuum packaging, standing, formation, and shaping to obtain the battery cell.

[0269] Comparative Examples 1-1 to 1-3

[0270] Battery cells were prepared using a method similar to that of Example 1. Different from Example 1, the single-sided coating weight of the positive and negative electrode film layers was adjusted.

[0271] Examples 2-1 to 2-3

[0272] The battery single cells were prepared by a method similar to that of Example 1. Different from Example 1, the single-sided coating weight and compaction density of the positive and negative electrode film layers were adjusted.

[0273] Performance test

[0274] 1. Room temperature cycle performance test of the battery single cell

[0275] Under the environment of 25°C, the fully discharged battery single cell was charged at a constant current of 0.33C from 0 to 10% SOC, then charged from 10% SOC to 80% SOC, and then charged at 0.33C to the cut-off upper voltage. After standing for 30 minutes, it was discharged at 1C to the discharge cut-off voltage. This was one charge-discharge cycle. The initial discharge capacity D0 was recorded. The battery was cycled 1500 times, and the discharge capacity D1 after cycling was recorded. The cycle capacity retention rate at the 1500th cycle was (D1 - D0) / D0.

[0276] Among them, the charging step from 10% SOC to 80% SOC includes:

[0277] Charging from 10% SOC to 45% SOC at 3.7C;

[0278] Charging from 45% SOC to 50% SOC at 3.4C;

[0279] Charging from 50% SOC to 55% SOC at 3.2C;

[0280] Charging from 55% SOC to 60% SOC at 2.9C;

[0281] Charging from 60% SOC to 65% SOC at 2.6C;

[0282] Charging from 65% SOC to 70% SOC at 2.4C;

[0283] Charging from 70% SOC to 75% SOC at 2.1C;

[0284] Charging from 75% SOC to 80% SOC at 1.9C.

[0285] The test results are shown in Table 1.

[0286] Table 1

[0287]

[0288] The positive and negative electrode capacity ratios of Example 1 and Comparative Example 1-1 are comparable. However, in Comparative Example 1-1, the single-sided coating weight of the positive electrode film layer is less, and the cycle life is relatively short. In Comparative Example 1-2, the single-sided coating weight of the positive electrode film layer is more, resulting in a greater lithium-ion transport resistance under fast charging conditions and deteriorating the cycle performance. In Comparative Example 1-3, the positive-negative electrode capacity ratio is small, with a risk of lithium deposition, deteriorating the cycle performance.

[0289] For the positive and negative electrode film layers of the embodiments of the present application, the coating weights are within an appropriate range, which can effectively improve the lithium-ion transport ability in the positive and negative electrode film layers, facilitate the rapid migration of lithium ions, and enhance the fast charging ability of the battery cell. Moreover, in combination with an electrolyte with appropriate content and components, it can further improve the liquid-phase transport ability of lithium ions and reduce side reactions on the negative electrode side, improving the cycle performance of the battery cell under fast charging conditions.

[0290] Comparative Example 2-1 and Comparative Example 2-2

[0291] Battery cells were prepared using a method similar to that of Example 1. Different from Example 1, the components and content of the electrolyte were adjusted.

[0292] Examples 3-1 to 3-8

[0293] Battery cells were prepared using a method similar to that of Example 1. Different from Example 1, the components and content of the electrolyte were adjusted.

[0294] The test results are shown in Table 2.

[0295] Table 2

[0296]

[0297] In Table 2, EA represents ethyl acetate; MA represents methyl acetate; EC represents ethylene carbonate;

[0298] DMC represents dimethyl carbonate; EMC represents ethyl methyl carbonate; FEC represents fluoroethylene carbonate;

[0299] EA: 25 means that the mass content of EA is 25%; EC: 27 means that the mass content of EC is 27%.

[0300] The mass ratio of lithium bis(fluorosulfonyl)imide / lithium hexafluorophosphate refers to the ratio of the mass content of lithium bis(fluorosulfonyl)imide to the mass content of lithium hexafluorophosphate.

[0301] The meanings of other examples are as explained above and will not be elaborated here.

[0302] The conductivity of the electrolyte in Example 3-1 is 9 mS / cm, and the conductivity of the electrolyte in Example 3-2 is 18 mS / cm.

[0303] In Comparative Example 2-1, when the mass content of the carboxylic acid ester solvent is too low, the conductivity of the electrolyte may be too low, which is not conducive to the rapid transmission of lithium ions; in Comparative Example 2-2, when the mass content of the carboxylic acid ester solvent is too high, the side reactions on the negative electrode side increase, deteriorating the cycle performance.

[0304] In the embodiment of the present application, the mass content of the carboxylic acid ester solvent is 3% to 70%. The electrolyte can quickly infiltrate the electrode sheet, improve the transmission rate of lithium ions, and is beneficial to the improvement of the cycle performance of the battery monomer under rapid charging;

[0305] In the embodiment of the present application, by using lithium hexafluorophosphate and lithium bis(fluorosulfonyl)imide in combination, for example, the ratio of the mass content of lithium bis(fluorosulfonyl)imide to the mass content of lithium hexafluorophosphate is 0.3 to 1.2, the content of hydrofluoric acid can be reduced, the side reactions at the negative electrode interface can be slowed down, and it is beneficial to improve the cycle life of the battery monomer under rapid charging conditions.

[0306] The mass content of the fluorinated cyclic carbonate is 0.5% to 20%. The fluorinated cyclic carbonate can form a SEI film rich in lithium fluoride (LiF) on the surface of the negative electrode, which can relieve the volume expansion on the negative electrode side, improve the life of the negative electrode system, and improve the cycle life under rapid charging conditions.

[0307] Example 4

[0308] A battery monomer was prepared by a method similar to that of Example 1. Different from Example 1, the particle size of the carbon-based material was adjusted. Specifically:

[0309] The negative electrode sheet includes a negative electrode current collector and negative electrode film layers provided on both sides of the negative electrode current collector. The negative electrode current collector is a copper foil.

[0310] The negative electrode film layer is a film layer formed by uniformly coating a negative electrode slurry (with deionized water as the solvent) on the surface of the negative electrode current collector and then drying and cold pressing.

[0311] 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.

[0312] The first negative electrode film layer includes a carbon-based material, conductive agent acetylene black, negative electrode binder styrene-butadiene rubber, and thickening agent sodium carboxymethylcellulose with a mass ratio of 97.2:0.8:1:1. The carbon-based material in the first negative electrode film layer includes artificial graphite and natural graphite with a mass ratio of 80%:20%, and the average particle size of the carbon-based material is 18 μm.

[0313] The second negative electrode film layer comprises a carbon-based material, conductive agent acetylene black, negative electrode binder styrene-butadiene rubber, and thickening agent sodium carboxymethyl cellulose at a mass ratio of 96.5:0.5:2:1. The carbon-based material of the second negative electrode film layer includes artificial graphite, and the average particle size of the carbon-based material is 15 μm.

[0314] Example 5

[0315] A battery monomer was prepared using a method similar to that of Example 1. Different from Example 1, the negative electrode active material further includes a silicon-based material. Specifically:

[0316] 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.

[0317] The first negative electrode film layer comprises a negative electrode active material, conductive agent acetylene black, negative electrode binder styrene-butadiene rubber, and thickening agent sodium carboxymethyl cellulose at a mass ratio of 97.2:0.8:1:1. The negative electrode active material includes a carbon-based material and silicon-based material silicon oxide, and the mass content of silicon element in the negative electrode active material is 3%. The carbon-based material of the first negative electrode film layer includes artificial graphite and natural graphite at a mass ratio of 80%:20%, and the average particle size of the carbon-based material is 15 μm.

[0318] The second negative electrode film layer comprises a negative electrode active material, conductive agent acetylene black, negative electrode binder styrene-butadiene rubber, and thickening agent sodium carboxymethyl cellulose at a mass ratio of 96.5:0.5:2:1. The negative electrode active material includes a carbon-based material and silicon-based material silicon oxide, and the mass content of silicon element in the negative electrode active material is 3%. The carbon-based material of the second negative electrode film layer includes artificial graphite, and the average particle size of the carbon-based material is 12 μm.

[0319] The single-sided coating weight of the negative electrode film layer is 140 mg / 1540.25 mm 2 。

[0320] Example 6

[0321] A battery monomer was prepared using a method similar to that of Example 1. Different from Example 1, the setting method of the negative electrode film layer was adjusted. Specifically:

[0322] The negative electrode plate includes a negative electrode current collector and negative electrode film layers provided on both sides of the negative electrode current collector. The negative electrode current collector is a copper foil.

[0323] The negative electrode film layer is a film layer formed by uniformly coating a negative electrode slurry (solvent is deionized water) on the surface of the negative electrode current collector and then drying and cold pressing.

[0324] 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.

[0325] The first negative electrode film layer comprises a carbon-based material, conductive agent acetylene black, negative electrode binder styrene-butadiene rubber, and thickener sodium carboxymethyl cellulose with a mass ratio of 96.5:0.5:2:1. The carbon-based material of the first negative electrode film layer comprises artificial graphite, and the average particle size of the carbon-based material is 12 μm.

[0326] The second negative electrode film layer comprises a carbon-based material, conductive agent acetylene black, negative electrode binder styrene-butadiene rubber, and thickener sodium carboxymethyl cellulose with a mass ratio of 97.2:0.8:1:1. The carbon-based material of the second negative electrode film layer comprises artificial graphite and natural graphite with a mass ratio of 80%:20%, and the average particle size of the carbon-based material is 15 μm.

[0327] In the cross-section along the thickness direction of the negative electrode film layer, the void ratio of a single carbon-based material in the second negative electrode film layer is greater than that of a single carbon-based material in the first negative electrode film layer.

[0328] The single-sided coating weight of the negative electrode film layer is 140 mg / 1540.25 mm 2 。

[0329] Example 7

[0330] A battery cell was prepared using a method similar to that of Example 1. Different from Example 1, the setting method of the negative electrode film layer was adjusted. Specifically:

[0331] The negative electrode plate comprises a negative electrode current collector and negative electrode film layers disposed on both sides of the negative electrode current collector. The negative electrode current collector is a copper foil.

[0332] The negative electrode film layer is a film layer formed by uniformly coating a negative electrode slurry (with deionized water as the solvent) on the surface of the negative electrode current collector and then drying and cold pressing.

[0333] The negative electrode film layer comprises a carbon-based material, conductive agent acetylene black, negative electrode binder styrene-butadiene rubber, and thickener sodium carboxymethyl cellulose with a mass ratio of 96.5:0.5:2:1. The carbon-based material of the negative electrode film layer comprises artificial graphite, and the average particle size of the carbon-based material is 12 μm.

[0334] The test results are shown in Table 3.

[0335] Table 3

[0336] [[ID=3-eight]]

[0337] In Example 4, by regulating the average particle size of the carbon-based material, the average particle size of the carbon-based material in the first negative electrode film layer is greater than that in the second negative electrode film layer, which can shorten the solid-phase transmission path of lithium ions, improve the fast charging ability; and reduce the risk of lithium deposition on the negative electrode side surface, and improve the cycle performance of the battery cell under fast charging.

[0338] Example 5 also includes a silicon-based material, which is beneficial to improving the energy density of a battery cell. Silicon-based materials of different materials are applicable to this solution, such as silicon oxide materials, silicon carbide materials, etc.

[0339] In the case where the average particle size of the carbon-based material of the first negative electrode film layer in Example 6 is smaller than the average particle size of the carbon-based material of the second negative electrode film layer, the pore difference of the negative electrode film layer can be constructed, and the cycle performance of the battery cell under fast charging can be improved.

[0340] Example 7 uses a single-layer negative electrode film layer. When its coating weight and the like meet the requirements, the cycle performance of the battery cell under fast charging can also be improved to a certain extent.

[0341] Although the illustrative embodiments have been demonstrated and described, those skilled in the art should understand that the above embodiments cannot be construed as limiting the implementation manners of the present application, and the embodiments can be changed, substituted, and modified without departing from the spirit, principle, and scope of the implementation manners of the present application.

Claims

1. A battery cell, characterized in that, The battery cell comprises: Positive electrode sheet, comprising a positive current collector and a positive electrode film layer provided on at least one side of the positive current collector, the positive electrode film layer comprising a positive active material, the positive active material comprising lithium iron phosphate, and the single-sided coating weight of the positive electrode film layer being 250 mg / 1540.25 mm 2 to 300 mg / 1540.25 mm 2 ; 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 carbon-based material, and the single-sided coating weight of the negative electrode film layer is 80 mg / 1540.25 mm 2 to 150 mg / 1540.25 mm 2 ; and An electrolyte comprising an organic solvent, wherein the organic solvent comprises a carboxylate solvent, and the mass content of the carboxylate solvent in the electrolyte is 3% to 70%; The electrolyte further includes a lithium salt, and the lithium salt includes lithium bis(fluorosulfonyl)imide. The mass content of the lithium bis(fluorosulfonyl)imide is 2% to 11% based on the mass of the electrolyte.

2. The battery cell according to claim 1, wherein The conductivity of the electrolyte at room temperature is 9 mS / cm to 18 mS / cm.

3. The battery cell according to claim 1 or 2, characterized in that, The mass content of the carboxylic acid ester solvent in the electrolyte is 5% to 30%.

4. The battery cell according to claim 1, 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.

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

6. The battery cell according to claim 1, characterized in that, 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.

7. The battery cell according to claim 6, characterized in that, Based on the mass of the electrolyte, the mass content of the lithium hexafluorophosphate is 3% to 14%.

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

9. The battery cell according to claim 8, characterized in that, The fluorinated cyclic carbonate includes at least one of monofluoroethylene carbonate, bisfluoroethylene carbonate and trifluoropropylene carbonate.

10. The battery cell according to claim 8 or 9, 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.

11. The battery cell according to claim 1, wherein, When the battery cell is in a 0% state of charge, the tap density of the positive electrode film layer is 2.2 g / cm 3 to 2.85 g / cm 3 .

12. The battery cell according to claim 1, wherein, When the battery cell is at 0% state of charge, the compaction density of the negative electrode film layer is 1.1 g / cm 3 to 1.7 g / cm 3 .

13. The battery cell according to claim 1, wherein 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.

14. The battery cell according to claim 13, 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.

15. The battery cell according to claim 13 or 14, 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.

16. The battery cell according to claim 13, characterized in that The carbon-based material of the first region includes artificial graphite and / or natural graphite; and / or The carbon-based material of the second region includes artificial graphite.

17. The battery cell according to claim 13, wherein, 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.

18. The battery cell according to claim 17, 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.

19. The battery cell according to any one of claims 17 or 18, characterized in that: The carbon-based material of the second region includes artificial graphite and / or natural graphite; and / or; The carbon-based material of the first region includes artificial graphite.

20. The battery cell according to claim 1, 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; and The 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.

21. The battery cell according to claim 1, characterized in that, The negative electrode active material further includes a silicon-based material.

22. The battery cell according to claim 21, wherein, The silicon-based material includes one or more of silicon element, silicon-carbon composite and silicon oxide.

23. The battery cell according to claim 21 or 22, characterized in that, The mass content of silicon element in the silicon-based material in the negative electrode active material is 0.3% to 15%.

24. A battery device, characterized in that, The battery device includes the battery cell according to any one of claims 1 to 23.

25. An electrical device, characterized in that, The electrical device comprises the battery device as claimed in claim 24.

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