Battery cell, battery device and electric device

Abstract

The invention relates to a battery monomer, a battery device and a power utilization device, the battery monomer comprises a positive pole piece, a negative pole piece and an electrolyte, the positive pole piece comprises a positive current collector and a positive film layer arranged on at least one side of the positive current collector, the positive film layer comprises a positive active material, the positive active material comprises lithium iron phosphate, and the negative electrode film layer comprises a negative electrode. The single-side 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 piece comprises a negative electrode current collector and a negative electrode film layer arranged on at least one side of the negative electrode current collector, the negative electrode film layer comprises a negative electrode active material, the negative electrode active material comprises a carbon-based material, and the single-side coating weight of the negative electrode film layer is 80 mg / 1540.25 mm < 2 > to 150 mg / 1540.25 mm < 2 >; the electrolyte comprises an organic solvent, the organic solvent comprises a carboxylic ester solvent, and the mass content of the carboxylic ester solvent in the electrolyte is 3%-70%.

Description

[0001] This application claims the priority of the patent application PCT / CN2025 / 071126 entitled "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 thus are widely used in electronic devices, such as mobile phones, laptops, battery cars, electric vehicles, electric airplanes, electric ships, electric toy cars, electric toy ships, electric toy airplanes and electric tools, etc. Due to the great progress of batteries, higher requirements are put forward for the performance of batteries. However, the cycle 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 cycle 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 beneficial to improving the fast 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 fast 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 fast 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 compatible with 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 fast 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 fast 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 fast 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 beneficial to improving the cycle life of the battery cell.

[0013] In some embodiments, the electrolyte further includes lithium salts, and the lithium salts include 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 reactions 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 reactions 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 reactions 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 interfacial film at the negative electrode, and can form an excellent interfacial film, which can 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 rapid charging.

[0022] In some embodiments, the compaction density of the negative electrode film layer of the battery cell at 0% state of charge is 1.1 g / cm 3 Up to 1.7g / 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 rapid charging.

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

[0024] Therefore, in the embodiment of the present application, the void ratio of a single carbon-based material in the first region is less than or equal to the void ratio of a single carbon-based material in the second region, which is more conducive to the diffusion of lithium ions in the first region and improves the transmission rate, thereby facilitating 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] Therefore, in the embodiment 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 improve the problem of lithium plating on the surface of the negative electrode plate, 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, it can improve the cycle performance of the battery cell under fast charging.

[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 and improving 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 elemental silicon, silicon-carbon composite, and silicon oxide. The above silicon-based material can improve the energy density; and is beneficial to thinning the negative electrode film layer, enhancing the migration rate of lithium ions, and can improve the cycle life of the battery cell under rapid charging.

[0039] In some embodiments, the mass content of silicon element in the silicon-based material in the negative electrode active material is 0.3% to 15%. Within the above mass content, the silicon-based material can improve the energy density; and is beneficial to thinning the negative electrode film layer, enhancing the migration rate of lithium ions, and can 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, including the battery cell of any one of the embodiments in the first aspect of the present application.

[0041] In a third aspect, an embodiment of the present application further provides an electrical device, and the electrical device includes the battery device of any one of the embodiments in the second or third aspect of the present application. Description of the Drawings

[0042] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings required to be used in the embodiments of the present application will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For those of ordinary skill in the art, other drawings can be obtained according to the drawings without creative efforts.

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

[0044] Figure 2 It is a schematic structural diagram of a battery pack provided by some embodiments of the present application; Figure 3 It is a schematic structural diagram of a battery module provided by some embodiments of the present application; Figure 4 It is a schematic structural diagram of a battery cell provided by some embodiments of the present application; Figure 5 It is a schematic structural diagram of an electrode assembly of a battery cell provided by some embodiments of the present application; Figure 6 It is a schematic structural diagram of a negative electrode tab of a battery cell provided by some embodiments of the present application.

[0045] The drawings are not necessarily drawn to actual scale.

[0046] The description of the reference numerals is as follows: X, the thickness direction; 1. Electrical device; 2. Battery pack; 3. Controller; 4. Motor; 5. Housing; 5a. First housing part; 5b. Second housing part; 5c. Accommodation space; 6. Battery module; 7. Battery cell; 10. Electrode assembly; 11. Positive electrode tab; 12. Negative electrode tab; 121. Negative electrode film layer; 122. Negative electrode current collector; 1211. First negative electrode film layer; 1212. Second negative electrode film layer; 121a. First region; 121b. Second region; 121c. Third region; 13. Separator; 20. Outer shell assembly; 21. Shell; 22. End cap; 23. Electrode terminal. Detailed implementation manners

[0047] Hereinafter, embodiments of the battery cell, battery device, and electrical device of the present application are specifically disclosed in detail with appropriate reference to the drawings. However, there may be cases where unnecessary detailed descriptions are omitted. For example, there are cases where detailed descriptions of well-known matters and repeated descriptions of actually identical structures are omitted. This is to avoid 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.

[0048] 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 range 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.

[0049] If there is no special description, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0050] Unless otherwise specified, all technical features and optional technical features of the present application can be combined with each other to form a new technical solution.

[0051] 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 can also include 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 can also include steps (a), (c) and (b), or can also include steps (c), (a) and (b), etc.

[0052] The term "plurality" as used in the present application means two or more (including two).

[0053] In the embodiments of the present application, the battery cell can be a secondary battery, and a secondary battery refers to a battery cell that can be activated by charging after discharging to continue to be used.

[0054] With the rapid development of the battery field, the performance requirements for battery cells are gradually increasing. For example, the requirements for the cycle performance of battery cells are gradually increasing, especially the requirements for the cycle performance under fast charging.

[0055] In view of the above problems, in the embodiments of the present application, 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, the transmission ability of active ions such as lithium ions can be effectively improved, which is beneficial to the rapid migration of active ions and is beneficial to improving the cycle performance of the battery cell under fast charging.

[0056] The battery cell of the present application is applicable to various battery devices and electrical devices using the battery cell.

[0057] 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.

[0058] Figure 1 It is a schematic diagram of an electrical device 1 as an example. The electrical device 1 is a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, etc. In order to meet the requirements of the electrical device 1 for high power and high energy density, a battery pack or a battery module can be adopted.

[0059] Inside the electrical device 1, a battery device is provided. 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 also as the driving power source of the electrical device 1, replacing or partially replacing fuel or natural gas to provide driving power for the electrical device 1. Figure 1 The battery device shown in

[0060] 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.

[0061] 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 busbar component.

[0062] In some embodiments, the battery cell assembly is generally formed by arranging a plurality of battery cells.

[0063] As an example, the battery cell assembly can be a battery module, which is formed by arranging and fixing a plurality of battery cells into an independent module. As an example, the battery module can be formed by bundling a plurality of battery cells with cable ties.

[0064] As shown in Figure 2 In some embodiments, the battery device can be a battery pack 2, which includes a box body 5 and one or more battery cell assemblies. The battery cell assemblies are accommodated in the box body 5.

[0065] As an example, the battery cell assemblies can also be accommodated in the box body 5 by directly fixing a plurality of battery cells to the box body 5.

[0066] 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 assemblies. Here, "closed" means covered or closed, which can be sealed or non - sealed. The first box body part 5a can be a top cover or a bottom plate.

[0067] As an example, the box body 5 may include a top cover, a frame, and a bottom plate. The top cover and the bottom plate are respectively connected to the frame so that a closed space is formed inside the box body 5 to accommodate the battery cell assemblies.

[0068] In some embodiments, the box body 5 can be part of the chassis structure of a vehicle. For example, a part of the box body 5 can become at least part of the floor of the vehicle, or a part of the box body 5 can become at least part of the cross beams and longitudinal beams of the vehicle.

[0069] As an example, the battery cell assembly can be a battery module 6, and the battery cell assembly can be accommodated in the box body 5 by fixing the battery module 6 in the box body 5.

[0070] As Figure 3 shown, the battery module 6 includes a plurality of battery cells 7.

[0071] As Figure 4 and Figure 5 shown, in some embodiments, the battery cell 7 includes an electrode assembly 10 and a housing assembly 20.

[0072] The housing assembly 20 has a receiving cavity for receiving the electrode assembly 10 and the electrolyte.

[0073] In some embodiments, the housing assembly 20 includes a housing and electrode terminals 23, and the electrode terminals 23 are provided on the housing.

[0074] The housing can be a steel shell, an aluminum shell, a plastic shell (such as polypropylene), a composite metal shell (such as a copper-aluminum composite shell), or an aluminum plastic film, etc. In some embodiments, the housing can be a sealed structure or a non-sealed structure. As an example, when the housing is a non-sealed structure, the housing serves to protect the electrode assembly 10, and a sealing bag is further included between the housing and the electrode assembly 10 for encapsulating the electrode assembly 10 and the electrolyte. Specifically, the sealing bag can be a bag-shaped insulating part or an aluminum plastic film. When the housing is a sealed structure, it is used to encapsulate components such as the electrode assembly 10 and the electrolyte.

[0075] As an example, the battery cell 7 can be a cylindrical battery cell, a prismatic battery cell, a soft-pack battery cell, or a battery cell of other shapes. The prismatic battery cell includes a square shell battery cell, a blade-shaped battery cell, a multi-prismatic battery, and the multi-prismatic battery is, for example, a hexagonal prism battery, etc. There is no particular limitation in this application.

[0076] In some embodiments, the housing includes an end cap 22 and a housing body 21. The housing body 21 is provided with an opening, and the end cap 22 covers the opening. The housing body 21 can be provided with one or more openings. The end cap 22 can also be provided with one or more.

[0077] The shape of the housing 21 can be determined according to the specific shape of the electrode assembly 10. For example, if the electrode assembly 10 is a cylindrical structure, the housing 21 of a cylindrical structure can be selected; if the electrode assembly 10 is a cuboid structure, the housing 21 of a cuboid structure can be selected. Optionally, both the electrode assembly 10 and the housing 21 are of cuboid structure.

[0078] 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. The electrode assembly 10 can be a wound structure, a stacked structure, or a hybrid structure of winding and stacking.

[0079] 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.

[0080] In some embodiments, the electrode assembly 10 is a stacked structure.

[0081] 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.

[0082] 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.

[0083] 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.

[0084] 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.

[0085] 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.

[0086] In some embodiments, the shape of the electrode assembly 10 can be cylindrical, flat, prismatic, etc.

[0087] In some embodiments, the electrode assembly 10 is provided with tabs, and the tabs can conduct current out of the electrode assembly 10. The tabs include positive tabs and negative tabs. The electrode assembly 10 can adopt a wound structure or a stacked structure, and a stacked structure is optional, which is beneficial to improving the energy density of the battery cell 7.

[0088] 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 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 a lithium-containing 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 12 includes a negative current collector and a negative electrode film layer provided on at least one side of the negative current collector. The negative electrode film layer includes a negative electrode active material, 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%.

[0089] 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; 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 acid 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; As the mass content of the carboxylic acid ester solvent increases, the migration rate of lithium ions in the electrolyte accelerates, but a further increase in its mass content may lead to side reactions at the negative electrode interface. Therefore, in the embodiments of the present application, the mass content of the carboxylic acid ester solvent is further regulated to be less than or equal to 70%. In combination with the 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.

[0090] Negative electrode sheet 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 and including a negative electrode active material. For example, the negative current collector has two surfaces opposite to each other in its own thickness direction, and the negative electrode film layer is provided on any one or both of the two opposite surfaces of the negative current collector.

[0091] The upper charge cut-off voltage and the lower discharge cut-off voltage of the battery cell vary depending on the positive electrode active material. For example, when the phosphate material includes lithium iron phosphate, the upper charge cut-off voltage can be 3.65V and the lower discharge cut-off voltage can be 2.0V, or the upper charge cut-off voltage can be 3.8V and the lower discharge cut-off voltage can be 2.0V; also for example, when the phosphate material includes lithium manganese iron phosphate, the upper charge cut-off voltage can be 4.3V and the lower discharge cut-off voltage can be 2.0V. Next, taking the upper charge cut-off voltage of 3.8V and the lower discharge cut-off voltage of 2.0V as an example, the state of the battery cell will be described: In the embodiments of the present application, the 100% state of charge (SOC) and the 0% state of charge (SOC) of the battery cell are defined as follows. The battery cell is charged at a constant current charging rate of 0.33C to the upper charge cut-off 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.

[0092] In some embodiments, when the battery cell is in the 0% state of charge (SOC), the tap density of the negative electrode film layer is 1.1 g / cm 3 to 1.7 g / cm 3 . Exemplarily, the tap density of the negative electrode film layer 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.

[0093] 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, and the migration path of lithium ions is short, which is beneficial to improving the cycling performance of the battery cell under fast charging.

[0094] 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 a range composed of any two of the above values.

[0095] When the single-sided coating weight of the negative electrode film layer meets the above range and is combined with an appropriate mass content of silicon element, it is beneficial to improve the energy density of the battery cell, and the migration rate of active ions in the negative electrode film layer is relatively fast, which is beneficial to improving the cycling performance of the battery cell under fast charging.

[0096] 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, disassembling the negative electrode plate of the battery cell at 0% SOC, and measuring the tap density of the negative electrode film layer. For example, taking a negative electrode plate with single-sided coating (if it is a double-sided coated electrode plate, the negative electrode film layer on one side can be wiped off first), punching it into small round pieces with an area of S1, weighing it, recording it as M1, and measuring its thickness H1. Then wipe off the negative electrode film layer of the above-mentioned weighed negative electrode plate, weigh the weight of the negative electrode current collector, record it as M0, and measure its thickness H0. The single-sided coating weight of the negative electrode film layer = (the weight M1 of the negative electrode 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.

[0097] 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.

[0098] 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.

[0099] 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.

[0100] 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 can be tested by the Tri-Star3020 specific surface area and pore size analyzer of Micromeritics Company, USA.

[0101] 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.

[0102] 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 cycling performance under fast charging.

[0103] In some embodiments, the negative electrode active material includes a carbon-based material, and the carbon-based material has high cycling stability and can improve the cycling performance of the battery cell.

[0104] Optionally, the carbon-based material includes at least one of artificial graphite and natural graphite.

[0105] 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.

[0106] In this application, the qualitative and quantitative determination of each substance or each element can be detected by suitable equipment and methods known to those skilled in the art. The relevant detection methods can refer to domestic and foreign detection standards, domestic and foreign enterprise standards, etc. And those skilled in the art can also adaptively change some detection steps / instrument parameters, etc. from the perspective of detection accuracy to obtain more accurate detection results. One detection method can be used for qualitative or quantitative determination, or several detection methods can be used in combination for qualitative or quantitative determination.

[0107] For example, this application can combine the general rules of X-ray diffraction analysis method of JIS / K0131-1996 to perform X-ray powder diffraction test and qualitative analysis on the negative electrode sheet or the negative electrode active material.

[0108] Artificial graphite and natural graphite can be distinguished by the SEM cross-sectional view taken by scanning electron microscope (SEM). There are voids between flake structures in the SEM cross-sectional view of natural graphite, and the SEM cross-sectional view 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.

[0109] Such as Figure 6As shown, the negative electrode film layer 121 of the negative electrode plate 12 in the embodiment of the present application includes at least one film layer, which may be a single film layer or at least two film layers. Optionally, the negative electrode film layer 121 includes at least two film layers.

[0110] In the case where the negative electrode film layer 121 is a single-layer film layer, the negative electrode active material in the negative electrode film layer 121 includes a carbon-based material and an optional silicon-based material.

[0111] When the negative electrode film layer 121 has at least two layers, the negative electrode active material in the negative electrode film layer 121 includes carbon-based materials and optional silicon-based materials. The negative electrode film layer 121 may include two layers, three layers, four layers, or even more layers.

[0112] In some embodiments, the negative electrode film layer 121 includes a first negative electrode film layer 1211 and a second negative electrode film layer 1212, the first negative electrode film layer 1211 is disposed on the surface of the negative electrode current collector 122, the negative electrode active material of the first negative electrode film layer 1211 includes a carbon-based material, the second negative electrode film layer 1212 is connected to the side of the first negative electrode film layer 1211 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 is 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.

[0113] The negative electrode film layer 121 includes at least two film layers, and layered coating is beneficial to improving the cycle life of the battery cell under fast charging.

[0114] 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.

[0115] Optionally, the first negative electrode film layer 1211 also includes a silicon-based material.

[0116] Optionally, the second negative electrode film layer 1212 further includes a silicon-based material.

[0117] 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. Alternatively, the first negative electrode film layer 1211 includes a carbon-based material and a silicon-based material, and the second negative electrode film layer 1212 includes a carbon-based material. Alternatively, the first negative electrode film layer 1211 includes a carbon-based material, and the second negative electrode film layer 1212 includes a carbon-based material and a silicon-based material.

[0118] When both the first negative electrode film layer 1211 and the second negative electrode film layer 1212 include silicon-based materials, it is more conducive to improving the energy density of the battery cell. When the first negative electrode film layer 1211 includes silicon-based materials and the second negative electrode film layer 1212 does not include silicon-based materials, the second negative electrode film layer 1212 can relieve the volume expansion of the first negative electrode film layer 1211, reduce the side reaction between the negative electrode film layer 121 and the electrolyte, and improve the cycling performance under fast charging.

[0119] 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, or of course, different.

[0120] 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.

[0121] The cross-sectional morphologies of the first region 121a and the second region 121b can be the same or similar, or of course, different. The cross-sectional morphologies of the first region 121a and the third region 121c can be the same or similar, or of course, different. The cross-sectional morphologies of the second region 121b and the third region 121c can be the same or similar, or of course, different.

[0122] There may be an obvious layer interface between the first region 121a, the second region 121b, and the third region 121c, or there may be no obvious layer interface. For example, the first negative electrode film layer 1211 includes the first region 121a, the second negative electrode film layer 1212 includes the second region 121b, and the third region 121c can be a part of the first negative electrode film layer 1211, or the third region 121c can be a part of the second negative electrode film layer 1212, or the third region 121c can be a part of both the first negative electrode film layer 1211 and the second negative electrode film layer 1212.

[0123] 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.

[0124] 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.

[0125] 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.

[0126] Optionally, the average particle size of the carbon-based material in the first region 121a can be greater than or equal to the average particle size of the carbon-based material in the second region 121b. Further optionally, the average particle size of the carbon-based material in the first region 121a can be greater than the average particle size of the carbon-based material in the second region 121b, which is conducive to the rapid migration of lithium ions from the second region 121b to the first region 121a and improves the fast charging ability of the battery cell. Of course, the average particle size of the carbon-based material in the first region 121a can be less than the average particle size of the carbon-based material in the second region 121b.

[0127] 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.

[0128] The difference in the particle sizes of the first negative electrode film layer 1211 and the second negative electrode film layer 1212 can improve the fast charging performance of the battery cell. Specifically, during fast charging, the overpotential of the second negative electrode film layer 1212 is usually relatively high, and the bottleneck of fast charging mainly lies in the second negative electrode film layer 1212. In the embodiment of the present application, the particle size of the second negative electrode film layer 1212 is relatively small, which can shorten the solid-phase transmission path of lithium ions, improve the fast charging performance, and can also improve the problem of lithium plating on the surface of the negative electrode sheet 12 and improve the cycle life under fast charging.

[0129] Optionally, the average particle size of the carbon-based material in the first region 121a is from 12 μm to 21 μm, such as 12 μm, 12.5 μm, 13 μm, 13.5 μm, 14 μm, 14.5 μm, 15 μm, 15.5 μm, 16 μm, 16.5 μm, 17 μm, 17.5 μm, 18 μm, 18.5 μm, 19 μm, 19.5 μm, 20 μm, 20.5 μm, 21 μm, or a range composed of any two of the above values. When the average particle size of the carbon-based material in the first region 121a is within the above range, the cycle life under fast charging can be improved.

[0130] Optionally, the average particle size of the carbon-based material in the first negative electrode film layer 1211 is from 12 μm to 21 μm. When the average particle size of the carbon-based material in the first negative electrode film layer 1211 is within the above range, the cycle life under fast charging can be improved.

[0131] Optionally, the average particle size of the carbon-based material in the second region 121b is from 9 μm to 17 μm, such as 9 μm, 9.5 μm, 10 μm, 10.5 μm, 11 μm, 11.5 μm, 12 μm, 12.5 μm, 13 μm, 13.5 μm, 14 μm, 14.5 μm, 15 μm, 15.5 μm, 16 μm, 16.5 μm, 17 μm, or a range composed of any two of the above values. When the average particle size of the carbon-based material in the second negative electrode film layer 1212 is within the above range, it is beneficial to improve the fast charging ability of the battery cell and the stability of the material.

[0132] Optionally, the average particle size of the carbon-based material in the second negative electrode film layer 1212 is from 9 μm to 17 μm. When the average particle size of the carbon-based material in the second negative electrode film layer 1212 is within the above range, the solid-phase transport 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.

[0133] 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.

[0134] 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.

[0135] In some other 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 smaller than that of a single carbon-based material in the second region 121b.

[0136] During the charging process of the battery cell, lithium ions diffuse from the second region 121b to the first region 121a. The larger void ratio of a single carbon-based material in the second region 121b is conducive to the rapid transmission of lithium ions from the second region 121b to the first region 121a, thereby facilitating the rapid charging of the battery cell.

[0137] Optionally, the average particle size of the carbon-based material in the first region 121a can be smaller than that of the carbon-based material in the second region 121b. The relatively larger average particle size of the carbon-based material in the second region 121b results in a higher pressure resistance during the preparation of the film layer, which is conducive to improving the particle compactness; the relatively smaller average particle size of the carbon-based material in the first region 121a enables the rapid migration of lithium ions, improves the rapid charging ability of the battery cell, and enhances the cycle life under rapid charging.

[0138] 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.

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

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

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

[0142] Optionally, the average particle size of the carbon-based material in the second negative electrode film layer 1212 is from 12 μm to 21 μm.

[0143] 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.

[0144] 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.

[0145] 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 plate 12 as a sample, photographing along the thickness direction X of the negative electrode film layer 121 by a scanning electron microscope (SEM) 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.

[0146] 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%.

[0147] 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%.

[0148] In some embodiments, the negative electrode film layer may optionally further include other additives. As an example, the other additives may include thickeners, dispersants, etc., such as sodium carboxymethyl cellulose (CMC-Na), PTC thermistor materials, etc. In some embodiments, based on the total weight of the negative electrode film layer, the mass content of the other additives is ≤2%.

[0149] 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).

[0150] The negative electrode film layer is usually formed by coating a negative electrode paste on the negative electrode current collector and then drying and cold pressing. The negative electrode paste is usually formed by dispersing a negative electrode active material, an optional conductive agent, an optional binder, and other optional additives in a solvent and stirring evenly. The solvent may be N-methylpyrrolidone (NMP) or deionized water, but is not limited thereto.

[0151] 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 embodiment of the present application further includes a negative electrode conductive layer disposed on the surface of the negative electrode current collector and sandwiched between the negative electrode current collector and the negative electrode film layer. In some other embodiments, the negative electrode sheet of the embodiment of the present application further includes a protective layer covering the surface of the negative electrode film layer.

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

[0153] 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 surfaces opposite to each other in its own thickness direction, and the positive electrode film layer is disposed on either or both of the two opposite surfaces of the positive electrode current collector.

[0154] 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.

[0155] In the case where the electrode assembly is a stacked structure, the length direction of the positive electrode sheet is parallel to the length direction of the battery cell, and the size of the positive electrode film layer in the length direction can be understood as the length of the positive electrode film layer. The width direction of the positive electrode sheet is parallel to the width direction of the battery cell, and the size of the positive electrode film layer in the width direction can be understood as the width of the positive electrode film layer.

[0156] Exemplarily, the dimension of the positive electrode film layer along the length direction is 200mm to 600mm; the electrolyte includes an organic solvent, the organic solvent includes a carboxylic acid ester solvent, and the conductivity of the electrolyte at room temperature is 9mS / cm to 18mS / cm. The length of the positive electrode film layer is matched with the electrolyte of the above conductivity, which is conducive to improving the liquid phase transmission rate of lithium ions, improving the kinetic performance, and improving the fast charging ability of the battery cell; and because the viscosity of the carboxylic acid ester solvent is relatively low, it can evenly infiltrate the positive electrode film layer, so that the charging degree of the positive electrode film layer is uniform, and the lithium ions released from the positive electrode film layer are evenly distributed on the negative electrode side, reducing the risk of local side reactions on the negative electrode side, and improving the cycle performance under fast charging.

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

[0158] 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 and the contact resistance between particles is small, the resistance of the electrode sheet can be further reduced, thereby reducing heat generation during fast charging and improving the cycle performance of the battery cell under fast charging.

[0159] 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.

[0160] When the single-sided coating weight of the positive electrode film layer is within the above range, the heat generation per unit area of the positive electrode sheet will not be too large, improving the cycle performance of the battery cell under fast charging.

[0161] 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 the 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 round 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 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.

[0162] In some embodiments, the positive electrode active material includes one or more of lithium-containing transition metal oxides and lithium-containing phosphates. Optionally, the positive electrode active material includes lithium-containing phosphates. The lithium-containing phosphate can be in an olivine structure, which is stable in structure during charge and discharge and can improve the cycle life of the battery cell.

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

[0164] In some embodiments, the positive electrode film layer further includes a carbon-containing material, and the carbon-containing material is a carbon-containing conductive material. The above materials can improve the conductivity of the positive electrode film layer, which is beneficial to improving the cycling performance of the battery cell under fast charging.

[0165] 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%.

[0166] For example, the carbon-containing material may include carbon materials with a tubular structure, such as carbon nanotubes, carbon nanofibers, etc., and carbon nanotubes can be selected. Carbon nanotubes can be used as a conductive agent in the positive electrode film layer to improve the conductivity of the positive electrode film layer.

[0167] Also, for example, the lithium-containing phosphate with an olivine structure can be an unmodified lithium-containing phosphate such as lithium iron phosphate, or a material obtained by coating and modifying it. For example, a carbon-containing material is provided on the surface of the lithium-containing phosphate, and the carbon-containing material can be used as a coating layer to coat the surface of the lithium-containing phosphate, thereby improving the conductivity of the lithium-containing phosphate, reducing the powder resistivity of the material, and being beneficial to the migration rate of lithium ions, and improving the cycling performance of the battery cell under fast charging conditions.

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

[0169] Exemplarily, the lithium-containing phosphate includes LiFePO 4 , LiMnPO 4 , LiNiPO 4 , LiCoPO 4 or one or more thereof. During the charge and discharge process of the battery cell, the insertion and extraction and consumption of active ions such as Li will occur, and the molar content of Li is different when the battery cell is discharged to different states. Regarding the positive electrode active materials LiFePO 4 , LiMnPO 4 , LiNiPO 4 , LiCoPO 4 etc., the molar content of Li is the initial state of the material, that is, the state before feeding. When the positive electrode active material is applied to the battery system and undergoes charge and discharge cycles, the molar content of Li may change. In the embodiments of the present application, regarding the positive electrode active materials LiFePO 4 , LiMnPO 4 , LiNiPO 4 , LiCoPO 4 etc., the molar content of oxygen O is only the theoretical state value, and the release of oxygen from the lattice will cause the molar content of oxygen O to change. Actually, the molar content of oxygen O will fluctuate, and the above situations are all within the protection scope of the present application.

[0170] In the embodiments of the present application, the content of elements in the positive electrode active material has the meaning well-known in the art, and can be detected by equipment and methods well-known in the art. For example, referring to EPA 6010D-2014, it is tested by inductively coupled plasma atomic emission spectrometry, and determined by inductively coupled plasma optical emission spectrometry (ICP-OES, instrument model: Thermo ICAP7400). After discharging the battery cell to 0% state of charge (SOC) and disassembling the positive electrode plate, it is cleaned with dimethyl carbonate (DMC) and dried, and then after removing impurities by high-temperature calcination, 0.4 g of the positive electrode active material is weighed, and 10 ml (50% concentration) of aqua regia is added thereto. Then it is placed on a flat plate at 180 °C for 30 min. After digestion on the flat plate, it is fixed to a volume of 100 mL, and quantitative testing is carried out by the standard curve method.

[0171] In some embodiments, the positive electrode film layer further includes a lithium supplement agent, and the lithium supplement agent includes lithium element and can release lithium ions during the charging process of the battery cell to make up for lithium loss, which is beneficial to improving the capacity characteristics and high-temperature cycle performance of the battery cell.

[0172] In some embodiments, the lithium supplement agent includes at least one of lithium ferrite, lithium nickelate, and lithium cobaltate.

[0173] In some embodiments, the lithium supplement agent is granular, and its average longest diameter is from 9 μm to 13 μm, such as 9 μm, 9.5 μm, 10 μm, 10.5 μm, 11 μm, 11.5 μm, 12 μm, 12.5 μm, 13 μm or the range composed of any two of the above.

[0174] In some embodiments, the lithium supplement agent is granular, and its average shortest diameter is from 5 μm to 9 μm, such as 5 μm, 5.5 μm, 6 μm, 6.5 μm, 7 μm, 7.5 μm, 8 μm, 8.5 μm, 9 μm or the range composed of any two of the above.

[0175] In the embodiments of the present application, the positive electrode plate is cut along the thickness direction of the plate to expose the cross-section of the positive electrode film layer, which can also be understood as the cross-section of the positive electrode film layer along its own thickness direction. By performing scanning electron microscope (SEM) testing on the cross-section 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.

[0176] 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 analyzed, and the average value calculated is the average longest diameter; the shortest diameters of multiple, for example, 10 lithium supplement agents are statistically analyzed, and the average value calculated is the average shortest diameter.

[0177] In some embodiments, based on the total mass of the positive electrode film layer, the mass proportion 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 the lithium supplement agent within the above mass range is adopted, it can effectively improve the stability of the lithium supplement agent while having a good oxygen release effect.

[0178] 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%.

[0179] 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%.

[0180] 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.

[0181] 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.

[0182] When the specific surface area of the carbon nanotubes is within the above range, it is beneficial to improve the electron conduction ability; and in combination with an appropriate content of carbon nanotubes, the side reaction degree between the carbon nanotubes and the electrolyte can be reduced, and the cycling performance of the battery cell under fast charging conditions can be improved.

[0183] Optionally, the diameter of the carbon nanotubes is from 0.5 nm to 20 nm, such as 0.5 nm, 1.5 nm, 2.5 nm, 3.5 nm, 4.5 nm, 5.5 nm, 6.5 nm, 7.5 nm, 8.5 nm, 9.5 nm, 10.5 nm, 11.5 nm, 12.5 nm, 13.5 nm, 14.5 nm, 15.5 nm, 16.5 nm, 17.5 nm, 18.5 nm, 19.5 nm, 20 nm, or a range composed of any two of the above. Optionally, the diameter of the carbon nanotubes is from 0.5 nm to 7.5 nm.

[0184] When the diameter of the carbon nanotubes is within the above range, the structure is relatively stable, and it has relatively excellent electron conduction ability, which can improve the cycling performance of the battery cell under fast charging conditions.

[0185] Carbon nanotubes can generally be considered to be formed by curling two-dimensional carbon materials. When the number of curled layers is a single layer, it is a single-walled carbon nanotube; when curled into multiple layers, it is a multi-walled carbon nanotube. The diameter of the carbon nanotubes is the outer diameter of the carbon nanotubes on the cross-section perpendicular to its own central axis.

[0186] In some embodiments, the positive electrode film layer may further optionally include a positive electrode binder. The types of the positive electrode binder are not particularly limited in the embodiments of the present application. As an example, the positive electrode binder may include at least one of polyvinylidene fluoride, polytetrafluoroethylene, vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, polyacrylic acid, and fluorinated acrylate resins. In some embodiments, based on the mass of the positive electrode film layer, the mass content of the positive electrode binder is ≤5%.

[0187] In some embodiments, the positive electrode current collector may be a metal foil or a composite current collector. As an example of the metal foil, at least one foil of aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy may be used. The composite current collector may include a polymer material base layer and a metal material layer formed on at least one surface of the polymer material base layer. As an example, the metal material of the metal material layer may include at least one of aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy. As an example, the polymer material base layer may include at least one of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0188] The positive electrode film layer is usually formed by coating a positive electrode slurry on a positive electrode current collector and then drying and cold pressing. The positive electrode slurry is usually formed by dispersing a positive electrode active material, an optional conductive agent, an optional binder, and any other components in a solvent and stirring evenly. The solvent can be N-methylpyrrolidone (NMP), but is not limited thereto.

[0189] The positive electrode tab does not exclude other additional functional layers besides the positive electrode film layer. For example, in some embodiments, the positive electrode tab of the embodiment of the present application further includes a positive electrode conductive layer disposed on the surface of the positive electrode current collector and sandwiched between the positive electrode current collector and the positive electrode film layer. In some other embodiments, the positive electrode tab of the embodiment of the present application further includes a protective layer covering the surface of the positive electrode film layer.

[0190] [Electrolyte] During the charge and discharge process of the battery cell, active ions such as lithium ions shuttle 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.

[0191] 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.

[0192] 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.

[0193] In the embodiment of the present application, the conductivity of the electrolyte at room temperature, such as 25 °C, is the ionic conductivity, and it can be detected by using the equipment and methods well known in the art. For example, it can be tested with reference to the industry standard HG-T 4067-2015.

[0194] In some embodiments, the organic solvent includes carboxylic ester solvents.

[0195] Optionally, the mass content of the carboxylic acid ester solvent in the electrolyte is 3% to 70%. Exemplarily, the mass content of the carboxylic acid ester solvent is 3%, 5%, 8%, 10%, 13%, 15%, 18%, 20%, 23%, 25%, 28%, 30%, 33%, 35%, 38%, 40%, 43%, 45%, 48%, 50%, 53%, 55%, 58%, 60%, 63%, 65%, 68%, 70% or a range composed of any two of the above values. Optionally, the mass content of the carboxylic acid ester solvent in the electrolyte is 5% to 30%.

[0196] When the mass content of the carboxylic acid ester solvent is within the above range, the conductivity of the electrolyte can be improved; and the electrolyte is compatible with the silicon-containing negative electrode, which can effectively alleviate the side reactions on the negative electrode side, reduce the gas generation amount of the battery cell, and improve the cycle performance of the battery cell under fast charging. The carboxylic acid 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.

[0197] Exemplarily, the carboxylic acid ester solvent includes cyclic carboxylic acid esters, and the cyclic carboxylic acid esters include one or more of γ-butyrolactone, γ-valerolactone, and δ-valerolactone. The viscosity of the above materials is relatively low, which can improve the infiltration ability of the electrode sheet and improve the cycle performance under fast charging.

[0198] Exemplarily, the carboxylic acid ester solvent includes chain carboxylic acid esters, and the chain carboxylic acid esters include one or more of methyl acetate, ethyl acetate, propyl acetate, butyl acetate, propyl propionate, and butyl propionate. The viscosity of the above materials is relatively low, which can improve the infiltration ability of the electrode sheet and improve the cycle performance under fast charging.

[0199] In some embodiments, the organic solvent includes a carbonate solvent.

[0200] The carbonate solvent and the carboxylic acid ester solvent are used in combination, which can improve the stability of the electrolyte and reduce its gas generation amount at high temperature.

[0201] Exemplarily, the carbonate solvent includes one or more of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate. Optionally, the carbonate solvent includes one or more of ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate.

[0202] In some embodiments, the electrolyte salt includes a lithium salt, and the lithium salt includes one or more of lithium bis(fluorosulfonyl)imide and lithium hexafluorophosphate. Optionally, the lithium salt includes lithium bis(fluorosulfonyl)imide and lithium hexafluorophosphate.

[0203] 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.

[0204] 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.

[0205] When the ratio of the mass contents of lithium hexafluorophosphate and 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.

[0206] Exemplarily, based on the mass of the electrolyte, the mass content of lithium bis(fluorosulfonyl)imide is from 2% to 11%, such as 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 8%, 8.5%, 9%, 9.5%, 10%, 10.5%, 11% or the range composed of any two of the above values. When the mass content of lithium bis(fluorosulfonyl)imide is within the above range, the content of hydrofluoric acid can be reduced, the side reaction at the negative electrode interface can be slowed down, which is beneficial to improving the cycle performance of the battery cell under fast charging.

[0207] Exemplarily, based on the mass of the electrolyte, the mass content of lithium hexafluorophosphate is from 3% to 14%, such as 3%, 3.5%, 4%, 4.5%, 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 8%, 8.5%, 9%, 9.5%, 10%, 10.5%, 11%, 11.5%, 12%, 12.5%, 13%, 13.5%, 14% or the range composed of any two of the above values. When the mass content of lithium hexafluorophosphate is within the above range, the conductivity of the electrolyte is relatively high, which is beneficial to the migration of lithium ions and is beneficial to improving the cycle performance of the battery cell under fast charging.

[0208] In some embodiments, the electrolyte further comprises additives. The additives may include negative electrode film-forming additives, or may include positive electrode film-forming additives, or may also include additives that can improve certain performance of the battery, such as additives for improving the overcharge performance of the battery, additives for improving the high-temperature performance of the battery, additives for improving the low-temperature power performance of the battery, etc.

[0209] In some embodiments, the additive comprises a cyclic carbonate additive, such as one or more of a fluorinated cyclic carbonate and vinylene carbonate. Optionally, the additive comprises a fluorinated cyclic carbonate and vinylene carbonate.

[0210] The fluorinated cyclic carbonate can form a SEI film rich in lithium fluoride (LiF) on the surface of the negative electrode, which can alleviate the volume expansion of silicon, improve the lifespan of the silicon-containing system, and improve the cycling performance. When the fluorinated cyclic carbonate and vinylene carbonate are used in combination, the SEI film on the surface of the negative electrode has better denseness, 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.

[0211] Optionally, the fluorinated cyclic carbonate includes at least one of ethylene fluorocarbonate, difluoroethylene carbonate, and propylene trifluorocarbonate.

[0212] Optionally, based on the mass of the electrolyte, the mass content of the fluorinated cyclic carbonate is from 0.5% to 20%, for example, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 8%, 8.5%, 9%, 9.5%, 10%, 10.5%, 11%, 11.5%, 12%, 12.5%, 13%, 13.5%, 14%, 14.5%, 15%, 15.5%, 16%, 16.5%, 17%, 17.5%, 18%, 18.5%, 19%, 19.5%, 20% or a range composed of any two of the above values. When the mass content of the fluorinated cyclic carbonate is within the above range, it is beneficial to improve the cycling performance.

[0213] As an example, based on the mass of the electrolyte, the mass content of the fluorinated cyclic carbonate is from 0.5% to 10%; the mass content of silicon element in the silicon-based material in the negative electrode active material is from 0.3% to 7.5%.

[0214] When the mass content of the fluorinated cyclic carbonate and the mass content of silicon element meet the above conditions, it can more effectively alleviate the volume expansion of silicon, improve the lifespan of the silicon-containing system, and improve the cycling performance. As another example, based on the mass of the electrolyte, the mass content of the fluorinated cyclic carbonate is greater than 10% and less than or equal to 20%, and the mass content of silicon element in the silicon-based material in the negative electrode active material is greater than 7.5% and less than or equal to 15%.

[0215] The mass content of silicon element is relatively high and the volume expansion is relatively larger. When the mass content of the fluorinated cyclic carbonate and the mass content of silicon element meet the above conditions, it can more effectively alleviate the volume expansion of silicon, improve the lifespan of the silicon-containing system, and improve the cycling performance. Optionally, based on the mass of the electrolyte, the mass content of vinylene carbonate is 0.1% to 3%, such as 0.1%, 0.5%, 0.6%, 1.0%, 1.1%, 1.5%, 1.6%, 2.0%, 2.1%, 2.5%, 2.6%, 3% or a range composed of any two of the above values.

[0216] The above-mentioned mass content of vinylene carbonate and fluorinated cyclic carbonate are used in combination, making the interfacial film on the negative electrode surface denser, capable of more effectively protecting the silicon-containing negative electrode, reducing the degree of side reactions at the negative electrode interface, and improving the cycling performance.

[0217] In the embodiments of the present application, the types and contents of inorganic components / lithium salts in the electrolyte have the meanings well-known in the art, and can be detected by devices and methods well-known in the art. For example, reference can be made to the standard JY / T 020-1996 "General Rules for Ion Chromatography Analysis Methods" 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, freshly 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 reverse disassembled, and the free electrolyte obtained from the battery can be taken as a sample and detected by ion chromatography analysis method.

[0218] In the embodiments of the present application, the types and contents of organic components in the electrolyte have the meanings well-known in the art, and can be detected by devices and methods well-known in the art. For example, reference can be made to GB / T 9722-2006 "General Rules for Gas Chromatography of Chemical Reagents" to qualitatively and quantitatively analyze the organic components in the electrolyte by gas chromatography.

[0219] In the embodiments of the present application, after quantitatively and qualitatively detecting each component in the electrolyte, each component is classified, and carboxylic ester solvents and carbonate solvents are used as the constituent components of organic solvents. Based on the mass of the electrolyte being 100%, the mass content of each component is calculated. Fluorinated cyclic carbonate and vinylene carbonate are used as additives in the electrolyte. Based on the mass of the electrolyte being 100%, the mass content of each component is calculated.

[0220] Separator In some embodiments, the electrode assembly further includes a separator disposed between the positive electrode plate and the negative electrode plate.

[0221] 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.

[0222] As an example, the main material of the separator can be selected from at least one of glass fiber, non-woven fabric, polyethylene, polypropylene, polyvinylidene fluoride, and ceramics. The separator can be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation. The separator can be a 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.

[0223] In some embodiments, the separator is a solid electrolyte. The solid electrolyte is disposed between the positive electrode and the negative electrode, and simultaneously functions to transport ions and isolate the positive and negative electrodes.

[0224] Embodiment The following examples more specifically describe the content disclosed in the embodiments of the present application. These examples are only for illustrative purposes, because various modifications and changes within the scope of the content disclosed in the embodiments of the present application are obvious to those skilled in the art. Unless otherwise stated, all parts, percentages, and ratios reported in the following examples are based on mass, and all reagents used in the examples are commercially available or synthesized according to conventional methods and can be used directly without further treatment, and the instruments used in the examples are all commercially available.

[0225] Example 1 1. Preparation of the positive electrode sheet The positive electrode sheet includes a positive electrode current collector and positive electrode film layers provided on both sides of the positive electrode current collector. The positive electrode current collector is aluminum foil.

[0226] The positive electrode film layers include 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 layers are 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.

[0227] The lithium-containing phosphate is sourced from Ningbo Ronbay New Energy Technology Co., Ltd.

[0228] 2. Preparation of the negative electrode sheet The negative electrode sheet includes a negative electrode current collector and negative electrode film layers provided on both sides of the negative electrode current collector. The negative electrode current collector is copper foil.

[0229] The negative electrode film layers are 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.

[0230] 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.

[0231] 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 carboxymethyl cellulose 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.

[0232] The second negative electrode film layer includes 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. 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.

[0233] The negative electrode active material is sourced from Shanghai Xiangfenghua Technology Co., Ltd.

[0234] 3. Separator The separator includes a base film, which is a 7-μm polyethylene film layer with a porosity of 38%.

[0235] The separator is sourced from Yunnan Enjie New Materials Co., Ltd.

[0236] 4. Preparation of electrolyte The electrolyte includes an organic solvent, a lithium salt, and an additive.

[0237] The organic solvent includes 25% linear carboxylic acid ester solvent ethyl acetate EA and 57% carbonate solvent (27% ethylene carbonate EC, 30% dimethyl carbonate DMC). The mass content of each component in the organic solvent is calculated based on the mass of the electrolyte.

[0238] The lithium salt includes 8% lithium hexafluorophosphate LiPF 6 and 6% lithium bis(fluorosulfonyl)imide.

[0239] The additive includes 2% fluorinated cyclic carbonate fluoroethylene carbonate FEC and 2% vinylene carbonate VC; The conductivity of the electrolyte is 14.2 mS / cm.

[0240] 5. Preparation of battery cell 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 electrolyte after drying, and go through processes such as vacuum packaging, standing, forming, and shaping to obtain a battery cell.

[0241] Comparative Examples 1-1 to 1-3 Prepare a battery cell using a method similar to that of Example 1. The difference from Example 1 is that the single-sided coating weight of the positive and negative electrode layers is adjusted.

[0242] Examples 2-1 to 2-3 Prepare a battery cell using a method similar to that of Example 1. The difference from Example 1 is that the single-sided coating weight and compaction density of the positive and negative electrode layers are adjusted.

[0243] Performance test 1. Room temperature cycle performance test of the battery cell Under a 25°C environment, charge the fully discharged battery cell at a constant current of 0.33C from 0 to 10% SOC, then charge from 10% SOC to 80% SOC, and then charge at 0.33C to the cut-off upper voltage. After standing for 30 minutes, discharge at 1C to the discharge cut-off voltage. This is one charge-discharge cycle. Record the initial discharge capacity D0. Cycle the battery 1500 times and record the discharge capacity D1 after cycling. The cycle capacity retention rate at the 1500th cycle is (D1 - D0) / D0.

[0244] Among them, the charging step from 10% SOC to 80% SOC includes: Charge from 10% SOC to 45% SOC at 3.7C; Charge from 45% SOC to 50% SOC at 3.4C; Charge from 50% SOC to 55% SOC at 3.2C; Charge from 55% SOC to 60% SOC at 2.9C; Charge from 60% SOC to 65% SOC at 2.6C; Charge from 65% SOC to 70% SOC at 2.4C; Charge from 70% SOC to 75% SOC at 2.1C; Charge from 75% SOC to 80% SOC at 1.9C.

[0245] The test results are shown in Table 1.

[0246] Table 1

[0247] 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 larger 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 plating and deteriorating the cycle performance.

[0248] For the positive and negative electrode film layers of the examples 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 the side reactions on the negative electrode side, thereby improving the cycle performance of the battery cell under fast charging conditions.

[0249] Comparative Example 2-1 and Comparative Example 2-2 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.

[0250] Examples 3-1 to 3-8 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.

[0251] The test results are shown in Table 2.

[0252] Table 2

[0253] In Table 2, EA represents ethyl acetate; MA represents methyl acetate; EC represents ethylene carbonate; DMC represents dimethyl carbonate; EMC represents ethyl methyl carbonate; FEC represents fluoroethylene carbonate; EA: 25 means that the mass content of EA is 25%; EC: 27 means that the mass content of EC is 27%.

[0254] 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.

[0255] The meanings of other examples are the same as the above explanations and will not be elaborated here.

[0256] 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.

[0257] 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.

[0258] 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 improving the cycle performance of the battery cell under fast charging; 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 improving the cycle life of the battery cell under fast charging conditions.

[0259] 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 fast charging conditions. Example 4 A battery cell 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: 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.

[0260] 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.

[0261] 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.

[0262] 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 18 μm.

[0263] The second 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 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.

[0264] Example 5 The battery monomer was prepared by a method similar to that of Example 1. Different from Example 1, the negative electrode active material further includes a silicon-based material. Specifically: The negative electrode film layer includes a first negative electrode film layer and a second negative electrode film layer. The first negative electrode film layer is located on the surface of the negative electrode current collector, and the second negative electrode film layer is located on the surface of the first negative electrode film layer.

[0265] The first negative electrode film layer includes a negative electrode active material, conductive agent acetylene black, negative electrode binder styrene-butadiene rubber, and thickening agent sodium carboxymethyl cellulose with 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. 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 with a mass ratio of 80%:20%, and the average particle size of the carbon-based material is 15 μm.

[0266] The second negative electrode film layer includes a negative electrode active 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 negative electrode active material includes a carbon-based material and silicon-based material silicon oxide. 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. The single-sided coating weight of the negative electrode film layer is 140 mg / 1540.25 mm 2 。

[0267] Example 6 The battery monomer was prepared by a method similar to that of Example 1. Different from Example 1, the setting method of the negative electrode film layer was adjusted. Specifically: The negative electrode plate includes a negative electrode current collector and negative electrode film layers arranged on both sides of the negative electrode current collector. The negative electrode current collector is a copper foil.

[0268] 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.

[0269] 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.

[0270] 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 carboxymethyl cellulose with a mass ratio of 96.5:0.5:2:1. The carbon-based material of the first negative electrode film layer includes artificial graphite, and the average particle size of the carbon-based material is 12 μm.

[0271] 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 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. 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.

[0272] The single-sided coating weight of the negative electrode film layer is 140 mg / 1540.25 mm 2 。

[0273] Example 7 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: 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.

[0274] 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.

[0275] The 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 negative electrode film layer comprises artificial graphite, and the average particle size of the carbon-based material is 12 μm.

[0276] The test results are shown in Table 3.

[0277] Table 3

[0278] 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, reduce the risk of lithium deposition on the negative electrode side surface, and improve the cycling performance of the battery cell under fast charging.

[0279] Example 5 also includes a silicon-based material, which is beneficial to improving the energy density of the battery cell. Different silicon-based materials are applicable to this solution, such as silicon oxide materials, silicon carbon materials, etc.

[0280] In Example 6, when the average particle size of the carbon-based material in the first negative electrode film layer is smaller than that in the second negative electrode film layer, the pore difference of the negative electrode film layer can be constructed, and the cycling performance of the battery cell under fast charging can be improved.

[0281] In Example 7, a single-layer negative electrode film layer is used. When its coating weight and other requirements are met, the cycle performance of the battery cell under fast charging can also be improved to a certain extent.

[0282] Although the illustrative embodiments have been demonstrated and described, those skilled in the art should understand that the above embodiments should not be construed as limitations on the implementation modes of the present application, and the embodiments can be changed, substituted, and modified without departing from the spirit, principle, and scope of the implementation modes of the present application.

Claims

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

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

2.

7. The battery cell according to claim 6, characterized in that: Based on the mass of the electrolyte, the mass content of the lithium bis(fluorosulfonyl)imide is 2% to 11%; and / or Based on the mass of the electrolyte, the mass content of the lithium hexafluorophosphate is 3% to 14%.

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: Based on the mass of the electrolyte, the mass content of the fluorinated cyclic carbonate is 0.5% to 20%; and / or The mass content of the vinylene carbonate is 0.1% to 3% based on the mass of the electrolyte.

11. The battery cell according to claim 1, characterized in that: The compaction density of the positive electrode film layer of the battery cell at 0% charge state is 2.2g / cm 3 Up to 2.85g / cm 3 .

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

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

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, characterized in that: An average particle size of the carbon-based material in the second region is greater than an average particle size of the carbon-based material in the first region.

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 disposed 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 also includes a silicon-based material.

22. The battery cell according to claim 21, characterized in that: The silicon-based material includes one or more of silicon alone, silicon-carbon composites and silicon oxides.

23. The battery cell according to claim 21 or 22, characterized in that: The mass content of silicon element of 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 comprises 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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