Battery cell, battery device, and electrical device

Abstract

The present application relates to a battery cell, a battery device and an electrical device. The battery cell includes a negative electrode plate, a positive electrode plate and an electrolyte. The negative electrode plate includes a negative current collector and a negative electrode film layer disposed 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 positive electrode plate includes a positive current collector and a positive electrode film layer disposed on at least one side of the positive current collector. The positive electrode film layer includes a positive electrode active material and a positive electrode additive. The positive electrode active material includes at least one of a lithium-containing iron oxide and a lithium-containing cobalt oxide. 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%. The high-temperature cycle performance of the battery cell of the present application can be further improved.

Description

[0001] This application claims the priority of the PCT international application PCT / CN2025 / 071032, titled "Battery Cell, Battery Device and Electrical Device", filed on January 7, 2025, the entire content of which is incorporated herein by reference. Technical Field

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

[0003] Battery cells have characteristics such as high capacity and long life, and are therefore widely used in electronic devices, such as mobile phones, laptop computers, battery cars, electric vehicles, electric airplanes, electric ships, electric toy cars, electric toy ships, electric toy airplanes and power tools, etc. Due to the great progress of batteries, higher requirements are put forward for the performance of batteries. However, the high-temperature 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 electrical device, and the high-temperature 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 negative electrode plate, a positive electrode plate and an electrolyte. The negative electrode plate includes a negative electrode current collector and a negative electrode film layer provided on at least one side of the negative electrode current collector. The negative electrode film layer includes a negative electrode active material, and the negative electrode active material includes a carbon-based material; the positive electrode plate includes a positive electrode current collector and a positive electrode film layer provided on at least one side of the positive electrode current collector. The positive electrode film layer includes a positive electrode active material and a positive electrode additive. The positive electrode active material includes a lithium-containing phosphate, and the positive electrode additive includes at least one of a lithium-containing iron oxide and a lithium-containing cobalt oxide; the electrolyte includes an organic solvent, and the organic solvent includes a carboxylic acid ester solvent, and the mass content of the carboxylic acid ester solvent in the electrolyte is 3% to 70%.

[0006] Thus, when the mass content of the carboxylic acid ester solvent in the electrolyte in the embodiment of this application satisfies the above range, the migration rate of active ions such as lithium ions in the electrolyte is relatively fast, which is beneficial to improving the fast charging ability of the battery cell; a positive electrode additive is added to the positive electrode plate, and the oxygen element released by the positive electrode additive can participate in the formation of the negative electrode film, which can repair the solid electrolyte film and improve the high-temperature cycle performance; further, the positive electrode active material in the embodiment of this application includes a lithium-containing phosphate, and the negative electrode active material includes a carbon-based material, and the cycle stability of the positive and negative electrode active materials is relatively high, which is beneficial to further improving the high-temperature cycle performance; therefore, the embodiment of this application can effectively improve the high-temperature cycle performance of the battery cell.

[0007] In some embodiments, the lithium-containing iron oxide includes lithium ferrite; and / or the lithium-containing cobalt oxide includes lithium cobaltate. The above materials can participate in film formation on the negative electrode side and improve the cycling performance of the battery cell.

[0008] In some embodiments, the lithium-containing iron oxide includes Li e FeO f , where 0 < e ≤ 5 and 0 < f ≤ 4. The above materials can participate in film formation on the negative electrode side and improve the cycling performance of the battery cell.

[0009] In some embodiments, the lithium-containing iron oxide includes at least one of Li5FeO4, Li3FeO 3.5 , LiFeO2. The above materials can participate in film formation on the negative electrode side and improve the cycling performance of the battery cell.

[0010] In some embodiments, the lithium-containing cobalt oxide includes Li g CoO h , where 0 < g ≤ 6 and 0 < h ≤ 4. The above materials can participate in film formation on the negative electrode side and improve the cycling performance of the battery cell.

[0011] In some embodiments, the lithium-containing cobalt oxide includes one or more of Li6CoO4, Li3CoO2, LiCoO2. The above materials can participate in film formation on the negative electrode side and improve the cycling performance of the battery cell.

[0012] In some embodiments, based on the mass of the positive electrode film layer, the mass content of the positive electrode additive is 0.5% to 3%. When using the positive electrode additive within the above mass range, the stability of the positive electrode additive can be effectively improved while having a good oxygen release effect.

[0013] In some embodiments, a carbon coating layer is further provided on the surface of the positive electrode additive. After being coated with the carbon coating layer, the structure of the positive electrode additive is more stable, which can alleviate the side reaction between the electrolyte and the positive electrode additive, thereby further improving the cycling performance of the battery cell.

[0014] In some embodiments, the mass content of the carbon coating layer in the positive electrode additive is 1% to 5%. When the mass content of the carbon coating layer is within the above range, the positive electrode additive can be more effectively protected, which is beneficial to the gradual release of oxygen.

[0015] In some embodiments, the positive electrode additive is granular. In the cross-section of the positive electrode film layer along its own thickness direction, the ratio of the longest diameter to the shortest diameter of the positive electrode additive in the same particle is 1.2 to 2.5. When using the positive electrode additive with the above particle size, the stability of the positive electrode additive can be effectively improved while having a good oxygen release effect.

[0016] In some embodiments, in the cross-section of the positive electrode film layer along its own thickness direction, there are multiple positive electrode additives, and the average longest diameter of the multiple positive electrode additives is 9 μm to 13 μm; when using the positive electrode additives with the above particle sizes, while effectively improving the stability of the positive electrode additives, it also has a good oxygen evolution effect.

[0017] In some embodiments, in the cross-section of the positive electrode film layer along its own thickness direction, there are multiple positive electrode additives, and the average shortest diameter of the multiple positive electrode additives is 5 μm to 9 μm. When using the positive electrode additives with the above particle sizes, while effectively improving the stability of the positive electrode additives, it also has a good oxygen evolution effect.

[0018] In some embodiments, both the lithium-containing phosphate and the positive electrode additives are multiple and granular. In the cross-section of the positive electrode film layer along its own thickness direction, the average longest diameter of the multiple lithium-containing phosphates is smaller than the average shortest diameter of the multiple positive electrode additives. When using the positive electrode additives with the above particle sizes, while effectively improving the stability of the positive electrode additives, it also has a good oxygen evolution effect; the migration path of lithium ions in the lithium-containing phosphate is shorter, which can reduce the heat generation amount, reduce the heat accumulation in the system, and reduce the risk of electrolyte decomposition, further improving the cycle performance.

[0019] In some embodiments, the lithium-containing phosphate includes multiple first phosphate particles and multiple second phosphate particles. The longest diameter of the first phosphate particles is greater than that of the second phosphate particles. The average longest diameter of the multiple first phosphate particles is 1 μm to 5 μm, and the average longest diameter of the multiple second phosphate particles is 0.1 μm to 0.5 μm. When the lithium-containing phosphate meets the above conditions, its longest diameter is relatively small, the lithium deintercalation / insertion path of lithium ions in the lithium-containing phosphate is short, and the heat generation amount is small; moreover, the particle size of the above lithium-containing phosphate is not too small, and basically no agglomeration occurs during the processing and preparation process, making the performance of the lithium-containing phosphate stable.

[0020] In some embodiments, the mass content of the second phosphate particles in the lithium-containing phosphate is 80% to 95%. When the mass content of the second phosphate particles is within an appropriate range, such as 80% to 95%, it can further reduce the heat generation amount, reduce the heat generation amount in the battery cell system, reduce the risk of decomposition of electrolyte components due to heat accumulation, and improve the cycle performance of the battery cell.

[0021] In some embodiments, the lithium-containing phosphate includes lithium iron phosphate, and the lithium iron phosphate has excellent cycle stability and can improve the cycle performance of the battery cell.

[0022] In some embodiments, the conductivity of the electrolyte at room temperature is from 9 mS / cm to 18 mS / cm. The migration rate of lithium ions in this electrolyte is relatively high, which can further reduce the internal resistance of the battery cell, thereby reducing heat generation and improving the fast charging performance of the battery cell.

[0023] In some embodiments, the mass content of the carboxylic ester solvent in the electrolyte is from 5% to 30%. When the mass content of the carboxylic ester solvent is within the above range, the conductivity of the electrolyte can be improved; and the electrolyte is compatible with the silicon-containing negative electrode, which can effectively reduce the gas generation amount of the battery cell and improve the fast charging ability of the battery cell.

[0024] 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.

[0025] 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.

[0026] 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.

[0027] When the carbonate solvent and the carboxylic ester solvent are used in combination, the stability of the electrolyte can be improved and its gas generation amount at high temperature can be reduced.

[0028] In some embodiments, the electrolyte further includes a lithium salt, and the lithium salt includes lithium bis(fluorosulfonyl)imide and lithium hexafluorophosphate. Based on the mass of the electrolyte, the ratio of the mass content of lithium bis(fluorosulfonyl)imide to the mass content of lithium hexafluorophosphate is from 0.3 to 1.2.

[0029] Thus, when the ratio of the mass content of lithium hexafluorophosphate and lithium bis(fluorosulfonyl)imide in the embodiments of the present application satisfies the above range, on the one hand, the content of hydrofluoric acid can be reduced, the side reaction at the negative electrode interface can be slowed down, and the gas generation amount during high-temperature storage can be reduced; on the other hand, the content of the organic components in the interface film formed at the negative electrode interface is appropriate, which can also reduce the gas generation amount during high-temperature storage.

[0030] In some embodiments, based on the mass of the electrolyte, the mass content of lithium bis(fluorosulfonyl)imide is from 2% to 11%. When the mass content of lithium bis(fluorosulfonyl)imide is within the above range, the content of hydrofluoric acid can be reduced, the side reaction at the negative electrode interface can be slowed down, the gas generation amount during high-temperature storage can be reduced, which is beneficial to improving the high-temperature cycle life of the battery cell.

[0031] 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 improves the fast charging performance of the battery cell.

[0032] 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 lifespan of the silicon-containing system; when the fluorinated cyclic carbonate and vinylene carbonate are used in combination, the interfacial film on the surface of the negative electrode has better denseness, can more effectively protect the silicon-containing negative electrode, reduce the degree of side reactions at the negative electrode interface, and improve the cycle performance.

[0033] In some embodiments, the fluorinated cyclic carbonate includes at least one of fluoroethylene carbonate, difluoroethylene carbonate, and trifluoropropylene carbonate.

[0034] 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 has an excellent protective effect on the negative electrode.

[0035] In some embodiments, based on the mass of the electrolyte, the mass content of vinylene carbonate is 0.1% to 3%. Vinylene carbonate participates in the formation of the negative electrode interfacial film, can form an excellent interfacial film, and has an excellent protective effect on the negative electrode.

[0036] In some embodiments, based on the mass of the electrolyte, the mass content of the fluorinated cyclic carbonate is 0.5% to 10%; the mass content of silicon element in the silicon-based material in the negative electrode active material is 0.3% to 7.5%. When the mass content of the fluorinated cyclic carbonate and the mass content of the silicon element meet the above conditions, the volume expansion of silicon can be more effectively relieved, the lifespan of the silicon-containing system can be improved, and the cycle performance can be improved.

[0037] In some embodiments, based on the mass of the electrolyte, the mass content of the fluorinated cyclic carbonate is greater than 10% and less than or equal to 20%; the mass content of silicon element in the silicon-based material in the negative electrode active material is greater than 7.5% and less than or equal to 15%. When the mass content of the fluorinated cyclic carbonate and the mass content of the silicon element meet the above conditions, the volume expansion of silicon can be more effectively relieved, the lifespan of the silicon-containing system can be improved, and the cycle performance can be improved.

[0038] In some embodiments, the carbon-based material includes at least one of artificial graphite and natural graphite. The cycle stability of the above structure is relatively excellent, which can further improve the cycle performance of the battery cell.

[0039] 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.

[0040] In a third aspect, an embodiment of the present application further provides an electrical device, which includes the battery device of any one of the embodiments in the second or third aspect of the present application. Description of the Drawings

[0041] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings required for use 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 based on the drawings without creative efforts.

[0042] Figure 1 It is a schematic structural diagram of an electrical device provided by some embodiments of the present application.

[0043] Figure 2 It is a schematic structural diagram of a battery pack provided by some embodiments of the present application;

[0044] Figure 3 It is a schematic structural diagram of a battery module provided by some embodiments of the present application;

[0045] Figure 4 It is a schematic structural diagram of a battery cell provided by some embodiments of the present application;

[0046] Figure 5 It is a schematic structural diagram of an electrode assembly of a battery cell provided by some embodiments of the present application;

[0047] 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.

[0048] The drawings are not necessarily drawn to actual scale.

[0049] The description of the reference numerals is as follows:

[0050] X, thickness direction; 1, electrical device; 2, battery pack; 3, controller; 4, motor; 5, box body; 5a, first box body part; 5b, second box body part; 5c, accommodation space; 6, battery module; 7, battery cell; 10, electrode assembly.

[0051] 11. Positive electrode sheet; 12. Negative electrode sheet; 121. Negative electrode film layer; 122. Negative electrode current collector; 1211. First negative electrode film layer; 1212. Second negative electrode film layer; 121a. First region; 121b. Second region; 121c. Third region; 13. Separator; 20. Outer shell assembly; 21. Housing; 22. End cap; 23. Electrode terminal. Detailed implementation manners

[0052] Hereinafter, embodiments of the battery cell, battery device, and electrical device of the present application will be specifically disclosed with appropriate reference to the accompanying drawings. However, there may be cases where unnecessary details are omitted. For example, there may be cases where details of well-known matters are omitted and repeated descriptions of actually identical structures are omitted. This is to prevent the following description from becoming unnecessarily lengthy and to facilitate understanding by those skilled in the art. In addition, the accompanying 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.

[0053] The "range" disclosed in the present application is defined in the form of a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundary of a specific range. The ranges defined in this way can include the end values or not include the end values, and can be combined arbitrarily, that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60 to 120 and 80 to 110 are listed for a specific parameter, it is understood that ranges of 60 to 110 and 80 to 120 are also contemplated. In addition, if the minimum range values 1 and 2 are listed, and if the maximum range values 3, 4, and 5 are listed, then the following ranges are all contemplated: 1 to 3, 1 to 4, 1 to 5, 2 to 3, 2 to 4, and 2 to 5. In 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.

[0054] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form new technical solutions. Unless otherwise specified, all technical features and optional technical features of the present application can be combined with each other to form new technical solutions. Unless otherwise specified, all steps of the present application can be carried out in sequence or randomly, and preferably in sequence. For example, the method includes steps (a) and (b), which 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, it is mentioned that the method may further include step (c), which 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.

[0055] The term "plurality" as used in the present application means two or more (including two).

[0056] With the rapid development of the battery field, the performance requirements for battery cells are gradually increasing. For example, with the improvement of the fast charging performance requirements, in the related art, it can be achieved by increasing the conductivity of the electrolyte. However, the increase in conductivity may cause the decomposition of the electrolyte at high temperatures, resulting in an increase in the gas generation of the battery cell at high temperatures and may deteriorate the high-temperature cycle performance of the battery cell.

[0057] In view of the above problems, the embodiments of the present application improve the high-temperature cycle performance of the battery cell by coordinately regulating the positive electrode sheet and the electrolyte. Specifically, the electrolyte of the battery cell includes a carboxylic acid ester solvent, and the carboxylic acid ester solvent can improve the conductivity of the electrolyte, enabling the rapid migration of active ions such as lithium ions, thereby improving the fast charging ability of the battery cell. However, too high a content of the carboxylic acid ester solvent is prone to interfacial side reactions on the negative electrode surface, generating acidic substances and damaging the solid electrolyte interface film (SEI film) on the negative electrode surface, which may deteriorate the high-temperature cycle life. In the embodiments of the present application, a positive electrode additive is added to the positive electrode sheet, and the oxygen element released by the positive electrode additive can participate in the film formation on the negative electrode, capable of repairing the SEI film and reducing the influence of the carboxylic acid ester solvent on the cycle performance of the battery cell.

[0058] The battery cell of the present application is applicable to various battery devices and electrical devices that use battery cells.

[0059] 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.

[0060] Figure 1It is a schematic diagram of the 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.

[0061] A battery device is provided inside the electrical device 1, and the battery device can be arranged at the bottom, the head or the tail of the electrical device 1. The battery device can be used for power supply of the electrical device 1. For example, the battery device can be used as the operating power source of the electrical device 1, and can also be used as the driving power source of the electrical device 1, replacing or partially replacing fuel or natural gas to provide driving power for the electrical device 1. Figure 1 The battery device shown in it is the battery pack 2.

[0062] The electrical device 1 may further include a controller 3 and a motor 4. The controller 3 is used to control the battery device to supply power to the motor 4. For example, it is used for the working power requirements during the start-up, navigation and driving of the electrical device 1.

[0063] The battery device (Battery Apparatus) may include one or more battery cell assemblies for providing voltage and capacity. The battery cell assembly (Battery Cell Assembly) may include a plurality of battery cells, and the plurality of battery cells are connected in series, parallel or in a hybrid connection through a busbar component.

[0064] In some embodiments, the battery cell assembly (Battery Cell Assembly) is generally formed by arranging a plurality of battery cells. As an example, the battery cell assembly can be a battery module (Battery Module), and the battery module is formed by arranging and fixing a plurality of battery cells to form an independent module. As an example, the battery module can be formed by bundling a plurality of battery cells with cable ties.

[0065] As shown in Figure 2 In some embodiments, the battery device can be a battery pack 2 (battery Pack), and the battery pack 2 includes a box body 5 and one or more battery cell assemblies, and the battery cell assemblies are accommodated in the box body 5.

[0066] As an example, the battery cell assembly can also be accommodated in the box body 5 by directly fixing a plurality of battery cells to the box body 5.

[0067] 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 buckled so that a closed space is formed inside the box body 5 to accommodate the battery cell assembly. The term "closed" here means covering or closing, which can be sealed or non-sealed. The first box body part 5a can be a top cover or a bottom plate.

[0068] As an example, the box body 5 may include a top cover, a frame, and a bottom plate. The top cover and the bottom plate are respectively connected to the frame, so that a closed space is formed inside the box body 5 to accommodate the battery cell assembly.

[0069] In some embodiments, the box body 5 can be part of the chassis structure of a vehicle.

[0070] For example, a part of the box body 5 can be at least part of the floor of the vehicle, or a part of the box body 5 can be at least part of the cross beam and longitudinal beam of the vehicle.

[0071] 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.

[0072] As Figure 3 shown, the battery module 6 includes a plurality of battery cells 7.

[0073] As Figure 4 and Figure 5 shown, in some embodiments, the battery cell 7 includes an electrode assembly 10 and a housing assembly 20.

[0074] The housing assembly 20 has a receiving cavity for receiving the electrode assembly 10 and the electrolyte.

[0075] In some embodiments, the housing assembly 20 includes a housing and an electrode terminal 23, and the electrode terminal 23 is disposed on the housing.

[0076] The housing can be a steel shell, an aluminum shell, a plastic shell (such as polypropylene), a composite metal shell (such as a copper-aluminum composite shell), or an aluminum plastic film, etc. In some embodiments, the housing can be a sealed structure or a non-sealed structure. As an example, when the housing is a non-sealed structure, the housing plays a role in protecting the electrode assembly 10, and a sealing bag is further included between the housing and the electrode assembly 10, and the sealing bag is used 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 for encapsulating components such as the electrode assembly 10 and the electrolyte.

[0077] 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-prismatic battery, etc., and there is no special limitation in this application.

[0078] 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.

[0079] The shape of the housing 21 can be determined according to the specific shape of the electrode assembly 10. For example, if the electrode assembly 10 is a cylindrical structure, the housing 21 can be selected as a cylindrical structure; if the electrode assembly 10 is a cuboid structure, the housing 21 can be selected as a cuboid structure. Optionally, both the electrode assembly 10 and the housing 21 are cuboid structures.

[0080] The electrode terminal 23 can be arranged on the housing 21, or the electrode terminal 23 is arranged 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.

[0081] The electrode assembly 10 can be a wound structure, a stacked structure, or a hybrid structure of winding and stacking.

[0082] 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.

[0083] In some embodiments, the electrode assembly 10 is a stacked structure.

[0084] 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.

[0085] 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.

[0086] 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.

[0087] As an example, a plurality of separators 13 can be provided and are respectively arranged between any adjacent positive electrode plates 11 or negative electrode plates 12.

[0088] As an example, the separator 13 can be continuously arranged and is arranged between any adjacent positive electrode plates 11 or negative electrode plates 12 by folding or winding.

[0089] In some embodiments, the shape of the electrode assembly 10 can be cylindrical, flat, prismatic, etc.

[0090] In some embodiments, the electrode assembly 10 is provided with tabs, and the tabs can conduct current out of the electrode assembly 10. The tabs include positive tabs and negative tabs. The electrode assembly 10 can adopt a wound structure or a stacked structure, and the stacked structure is optionally selected, which is beneficial to improving the energy density of the battery cell 7.

[0091] In some embodiments, the battery cell 7 includes a positive electrode plate 11 and an electrolyte. The positive electrode plate 11 includes a positive electrode current collector and a positive electrode film layer provided on at least one side of the positive electrode current collector. The positive electrode film layer includes a positive electrode active material and a positive electrode additive. The positive electrode active material includes a lithium-containing phosphate, and the positive electrode additive includes at least one of a lithium-containing iron oxide and a lithium-containing cobalt oxide; the electrolyte includes an organic solvent, and the organic solvent includes a carboxylic acid ester solvent, and the mass content of the carboxylic acid ester solvent in the electrolyte is 3% to 70%.

[0092] The mass content of the carboxylic acid ester solvent in the electrolyte is greater than or equal to 3%, so that the migration rate of active ions such as lithium ions in the electrolyte is relatively fast, which is beneficial to improving the fast charging ability of the battery cell 7;

[0093] As the mass content of the carboxylic acid ester solvent increases, the migration rate of the active ions increases; however, the carboxylic acid ester solvent is prone to interface side reactions on the negative electrode surface, generating acidic substances, destroying the SEI film on the negative electrode surface, and reducing the high-temperature cycle life of the battery cell 7; and in one aspect of the embodiments of the present application, by limiting the upper limit of the addition of the carboxylic acid ester solvent, the mass content of the carboxylic acid ester solvent is less than or equal to 70%, and on the other hand, a positive electrode additive is added to the positive electrode plate. During the charging process, the lithium ions of the positive electrode additive migrate to the negative electrode side through the electrolyte. The positive electrode additive forms a negatively charged group due to the migration of lithium ions, and the negatively charged group can release oxygen into the electrolyte, and the oxygen element can participate in the formation of the negative electrode film and can repair the SEI film, improving the influence of the carboxylic acid ester solvent on the high-temperature cycle life of the battery cell;

[0094] Furthermore, the positive electrode active material of the embodiments of the present application includes a lithium-containing phosphate, the negative electrode active material includes a carbon-based material, and the cycle stability of the positive and negative electrode active materials is relatively high, which is beneficial to further improving the high-temperature cycle performance;

[0095] Thus, the embodiments of the present application can effectively improve the high-temperature cycle performance of the battery cell 7 under fast charging.

[0096] Negative electrode plate

[0097] The negative electrode plate includes a negative electrode current collector and a negative electrode film layer provided on at least one side of the negative electrode current collector and including a negative electrode active material. For example, the negative electrode current collector has two opposite surfaces in its own thickness direction, and the negative electrode film layer is provided on any one or both of the two opposite surfaces of the negative electrode current collector.

[0098] The upper charging limit voltage and the lower discharging cut-off voltage of the battery cell vary depending on the cathode active material. For example, when the phosphate material includes lithium iron phosphate, the upper charging limit voltage can be 3.65V and the lower discharging cut-off voltage can be 2.0V, or the upper charging limit voltage can be 3.8V and the lower discharging cut-off voltage can be 2.0V; another example is when the phosphate material includes lithium manganese iron phosphate, the upper charging limit voltage can be 4.3V and the lower discharging cut-off voltage can be 2.0V. Next, taking the upper charging limit voltage of 3.8V and the lower discharging cut-off voltage of 2.0V as an example, the state of the battery cell is described as follows: In the embodiments of the present application, the 100% state of charge (SOC) and the 0% SOC of the battery cell are defined as follows.

[0099] Charge the battery cell at a constant current charging rate of 0.33C to the upper charging limit voltage, and then charge at a constant voltage until 0.05C, corresponding to the state of 100% SOC of the battery cell. Discharge the battery cell at a constant current discharging rate of 0.33C to the cut-off voltage, corresponding to the state of 0% SOC of the battery cell.

[0100] In some embodiments, when the battery cell is in the 0% SOC state, the compaction density of the negative electrode film layer is 1.1 g / cm 3 to 1.7 g / cm 3 . Exemplarily, the compaction density of the negative electrode film layer of the battery cell in the 0% SOC state 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.

[0101] 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 fast charging of the battery cell; moreover, the particle packing of the negative electrode active material will not be too tight, reducing the risk of particle crushing and being beneficial to improving the cycling performance of the battery cell.

[0102] 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.

[0103] When the single-sided coating weight of the negative electrode film layer meets the above range, in combination with an appropriate mass content of silicon element, it is beneficial to improve the energy density of the battery cell, and the migration rate of active ions in the negative electrode film layer is relatively fast, which is beneficial to improving the fast charging ability of the battery cell.

[0104] 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 from the battery cell at 0% SOC and measuring the tap density of the negative electrode film layer. For example, taking a single-sided coated negative electrode plate (if it is a double-sided coated plate, the negative electrode film layer on one side can be wiped off first), 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 weighed negative electrode plate above, 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.

[0105] In some embodiments, the negative electrode active material includes a silicon-based material. Optionally, the silicon-based material may include elemental silicon, silicon-carbon composite, silicon oxide SiO x (where 0 < x ≤ 2), or at least one of them. The above materials can improve the capacity of the negative electrode active material, help reduce the coating thickness of the negative electrode film layer, and shorten the migration path of lithium ions.

[0106] In some embodiments, the specific surface area of the silicon-based material is 1 m 2 ² / g to 4 m 2 ² / g, such as 1 m² / g, 1.2 m² / g, 1.4 m² / g, 1.5 m² / g, 1.6 m² / g, 1.8 m² / g, 2 m² / g, 2.2 m² / g, 2.4 m² / g, 2.5 m² / g, 2.6 m² / g, 2.8 m² / g, 3 m² / g, 3.2 m² / g, 3.4 m² / g, 3.5 m² / g, 3.6 m² / g, 3.8 m² / g, 4 m² / g or a range composed of any two of the above values.

[0107] When the specific surface area of the silicon-based material is within the above range, it can alleviate the side reaction between the silicon-based material and the electrolyte, improve the cycle performance; and can provide appropriate embedding sites for lithium ions, enhancing the fast charging ability.

[0108] In the embodiments of the present application, the specific surface area of the material has the meaning well-known in the art and can be detected by using the equipment and methods well-known in the art. For example, it can be detected according to the test standard GB / T 19587-2017. The negative electrode plate in the battery cell can be disassembled to obtain the relevant material as a sample, and the specific surface area is measured by a Tri-Star 3020 specific surface area and pore size analyzer of Micromeritics Company, USA.

[0109] 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.

[0110] When the specific surface area of the silicon-based material is within the above range, it can provide appropriate embedding sites for lithium ions, improving the fast charging ability; under fast charging conditions, it can also alleviate the side reaction between the silicon-based material and the electrolyte, reduce the gas generation at high temperature, and improve the cycling performance of the battery cell.

[0111] 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.

[0112] Optionally, the carbon-based material includes at least one of artificial graphite and natural graphite.

[0113] 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.

[0114] In this application, the qualitative and quantitative determination of each substance or element can be detected by suitable equipment and methods known to those skilled in the art. Relevant detection methods can refer to domestic and foreign detection standards, domestic and foreign enterprise standards, etc. And those skilled in the art can also adaptively change some detection steps / instrument parameters from the perspective of detection accuracy to obtain more accurate detection results. One detection method can be used for qualitative or quantitative determination, or several detection methods can be used in combination for qualitative or quantitative determination.

[0115] For example, this application can combine the General Rules of X-ray Diffraction Analysis Method of JIS / K0131-1996 to conduct X-ray powder diffraction testing and qualitative analysis on the negative electrode sheet or the negative electrode active material.

[0116] Artificial graphite and natural graphite can be distinguished by the SEM cross-section taken by scanning electron microscope (SEM). There are voids between flake structures in the SEM cross-section of natural graphite, while the SEM cross-section of artificial graphite is dense and has no obvious gaps, or can be distinguished by the XRD spectrum obtained by X-ray diffraction method. There are obvious 2H phase and 3R phase in the XRD spectrum of natural graphite, while only the 2H phase exists in the XRD spectrum of artificial graphite.

[0117] Such as Figure 6As shown, in the embodiment of the present application, the negative electrode film layer 121 of the negative electrode tab 12 includes at least one film layer, which can be a single film layer or at least two film layers. Optionally, the negative electrode film layer 121 includes at least two film layers.

[0118] When the negative electrode film layer 121 is a single film layer, the negative electrode active material in the negative electrode film layer 121 includes a carbon-based material and an optional silicon-based material.

[0119] When the negative electrode film layer 121 includes at least two film layers, the negative electrode active material in the negative electrode film layer 121 includes a carbon-based material and an optional silicon-based material. The negative electrode film layer 121 can include two film layers, three film layers, four film layers, or even more film layers.

[0120] In some embodiments, the negative electrode film layer 121 includes a first negative electrode film layer 1211 and a second negative electrode film layer 1212. The first negative electrode film layer 1211 is disposed on the surface of the negative electrode current collector 122, and the negative electrode active material of the first negative electrode film layer 1211 includes a carbon-based material. The second negative electrode film layer 1212 is connected to the side of the first negative electrode film layer 1211 facing away from the negative electrode current collector 122, and the negative electrode active material of the second negative electrode film layer 1212 includes a carbon-based material. The interface between the first negative electrode film layer 1211 and the second negative electrode film layer 1212 can be regular or irregular, optionally irregular; or there is no obvious interface between the first negative electrode film layer 1211 and the second negative electrode film layer 1212.

[0121] The negative electrode film layer 121 includes at least two film layers, and layer-by-layer coating is beneficial to taking into account the improvement of the fast charging performance and cycle life of the battery cell.

[0122] 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.

[0123] Optionally, the first negative electrode film layer 1211 further includes a silicon-based material.

[0124] Optionally, the second negative electrode film layer 1212 further includes a silicon-based material.

[0125] Exemplarily, the first negative electrode film layer 1211 includes a carbon-based material and a silicon-based material, and the second negative electrode film layer 1212 includes a carbon-based material and a silicon-based material. Or, the first negative electrode film layer 1211 includes a carbon-based material and a silicon-based material, and the second negative electrode film layer 1212 includes a carbon-based material. Or, the first negative electrode film layer 1211 includes a carbon-based material, and the second negative electrode film layer 1212 includes a carbon-based material and a silicon-based material.

[0126] 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 cycle performance.

[0127] When the negative electrode film layer 121 adopts at least two film layers, along the thickness direction X of the negative electrode film layer 121, the cross-sectional morphology of the negative electrode film layer 121 can be the same or similar, and of course, it can also be different.

[0128] Along the thickness direction X of the negative electrode film layer 121, the negative electrode film layer 121 is divided into three regions, namely the first region 121a, the third region 121c, and the second region 121b. The first region 121a is the region of the negative electrode film layer 121 close to the negative electrode current collector 122 along the thickness direction X, and the thickness of the first region 121a is 1 / 3 of the thickness of the negative electrode film layer 121; the second region 121b is the region of the negative electrode film layer 121 away from the negative electrode current collector 122 along the thickness direction X, and the thickness of the second region 121b is 1 / 3 of the thickness of the negative electrode film layer 121.

[0129] The cross-sectional morphology of the first region 121a and the second region 121b can be the same or similar, and of course, it can also be different. The cross-sectional morphology of the first region 121a and the third region 121c can be the same or similar, and of course, it can also be different. The cross-sectional morphology of the second region 121b and the third region 121c can be the same or similar, and of course, it can also be different.

[0130] 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.

[0131] 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 located in the first region 121a is greater than or equal to the void ratio of a single carbon-based material located in the second region 121b. Optionally, the void ratio of a single carbon-based material located in the first region 121a is less than the void ratio of a single carbon-based material located in the second region 121b.

[0132] 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.

[0133] 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 facilitating the rapid charging of the battery cell.

[0134] 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 rapid 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.

[0135] 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.

[0136] There is a difference in the particle sizes of the first negative electrode film layer 1211 and the second negative electrode film layer 1212, which can improve the rapid charging performance of the battery cell. Specifically, during the rapid charging process, the overpotential of the second negative electrode film layer 1212 is usually relatively high, and the bottleneck of rapid 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 rapid charging performance, and can improve the problem of lithium deposition on the surface of the negative electrode sheet 12.

[0137] Optionally, the average particle size of the carbon-based material in the first region 121a is 12 μm to 21 μm, such as 12 μm, 12.5 μm, 13 μm, 13.5 μm, 14 μm, 14.5 μm, 15 μm, 15.5 μm, 16 μm, 16.5 μm, 17 μm, 17.5 μm, 18 μm, 18.5 μm, 19 μm, 19.5 μm, 20 μm, 20.5 μm, 21 μm or the range composed of any two of the above values. When the average particle size of the carbon-based material in the first region 121a is within the above range, the cycle life can be improved, and it will basically not have an adverse impact on the fast charging performance.

[0138] Optionally, the average particle size of the carbon-based material of the first negative electrode film layer 1211 is 12 μm to 21 μm. When the average particle size of the carbon-based material in the first negative electrode film layer 1211 is within the above range, the cycle life can be improved, and the fast charging performance is basically not adversely affected.

[0139] Optionally, the average particle size of the carbon-based material in the second region 121b is 9 μm to 17 μm, such as 9 μm, 9.5 μm, 10 μm, 10.5 μm, 11 μm, 11.5 μm, 12 μm, 12.5 μm, 13 μm, 13.5 μm, 14 μm, 14.5 μm, 15 μm, 15.5 μm, 16 μm, 16.5 μm, 17 μm or the range composed of any two of the above values. When the average particle size of the carbon-based material in the second negative electrode film layer 1212 is within the above range, it is beneficial to improve the fast charging ability of the battery cell and the stability of the material.

[0140] Optionally, the average particle size of the carbon-based material of the second negative electrode film layer 1212 is 9 μm to 17 μm. When the average particle size of the carbon-based material in the second negative electrode film layer 1212 is within the above range, the solid-phase transmission path of lithium ions can be shortened, and the fast charging performance and the stability of the material can be improved.

[0141] 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.

[0142] Exemplarily, the carbon-based material of the first negative electrode film layer 1211 includes artificial graphite and natural graphite, and the carbon-based material of the second negative electrode film layer 1212 includes artificial graphite. For example, the negative electrode active material of the first negative electrode film layer 1211 includes a silicon-based material, artificial graphite and natural graphite, and the negative electrode active material of the second negative electrode film layer 1212 includes a silicon-based material and artificial graphite.

[0143] 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 located in the first region 121a is smaller than the void ratio of a single carbon-based material located in the second region 121b.

[0144] During the charging process of the battery cell, lithium ions diffuse from the second region 121b to the first region 121a. The larger void ratio of a single carbon-based material in the second region 121b is beneficial to the rapid transmission of lithium ions from the second region 121b to the first region 121a, thus being beneficial to the fast charging of the battery cell.

[0145] Optionally, the average particle size of the carbon-based material in the first region 121a may be smaller than that of the carbon-based material in the second region 121b. The carbon-based material in the second region 121b has a relatively larger average particle size and higher pressure resistance during the preparation of the film layer, which is beneficial to improving the particle compactness. The carbon-based material in the first region 121a has a relatively smaller average particle size, which can enable the rapid migration of lithium ions and improve the rapid charging ability of the battery cell. Of course, the average particle size of the carbon-based material in the first region 121a may be greater than or equal to that of the carbon-based material in the second region 121b.

[0146] Optionally, the average particle size of the carbon-based material in the first region 121a is 9 μm to 17 μm, such as 9 μm, 9.5 μm, 10 μm, 10.5 μm, 11 μm, 11.5 μm, 12 μm, 12.5 μm, 13 μm, 13.5 μm, 14 μm, 14.5 μm, 15 μm, 15.5 μm, 16 μm, 16.5 μm, 17 μm or the range composed of any two of the above values.

[0147] Optionally, the average particle size of the carbon-based material in the first negative electrode film layer 1211 is 9 μm to 17 μm.

[0148] Optionally, the average particle size of the carbon-based material in the second region 121b is 12 μm to 21 μm, such as 12 μm, 12.5 μm, 13 μm, 13.5 μm, 14 μm, 14.5 μm, 15 μm, 15.5 μm, 16 μm, 16.5 μm, 17 μm, 17.5 μm, 18 μm, 18.5 μm, 19 μm, 19.5 μm, 20 μm, 20.5 μm, 21 μm or the range composed of any two of the above values.

[0149] Optionally, the average particle size of the carbon-based material in the second negative electrode film layer 1212 is 12 μm to 21 μm.

[0150] Exemplarily, the carbon-based material in the second region 121b includes artificial graphite and natural graphite, and the carbon-based material in the first region 121a includes artificial graphite. Optionally, the negative electrode active material further includes a silicon-based material. For example, the negative electrode active material in the second region 121b includes a silicon-based material, artificial graphite and natural graphite, and the negative electrode active material in the first region 121a includes a silicon-based material and artificial graphite.

[0151] Exemplarily, the carbon-based material in the second negative electrode film layer 1212 includes artificial graphite and natural graphite, and the carbon-based material in the first negative electrode film layer 1211 includes artificial graphite. Optionally, the negative electrode active material further includes a silicon-based material. For example, the negative electrode active material in the second negative electrode film layer 1212 includes a silicon-based material, artificial graphite and natural graphite, and the negative electrode active material in the first negative electrode film layer 1211 includes a silicon-based material and artificial graphite.

[0152] In the embodiments of the present application, for the average particle size of the active material in the first region 121a and the second region 121b, the following equipment and method can be used for detection: taking the negative electrode sheet 12 as a sample, and taking a scanning electron microscope (SEM) photograph along the thickness direction X of the negative electrode film layer 121 to obtain an SEM sectional view, counting the particle sizes of the active material in the SEM section, and calculating the average particle size of the active material according to the counted quantity.

[0153] In some embodiments, the negative electrode film layer may further optionally 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%.

[0154] In some embodiments, the negative electrode film layer may further optionally 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%.

[0155] In some embodiments, the negative electrode film layer may further optionally 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%.

[0156] 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 can be used. The composite current collector may include a polymer material base layer and a metal material layer formed on at least one surface of the polymer material base layer. As an example, the metal material 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).

[0157] The negative electrode film layer is usually formed by coating a negative electrode slurry on the negative electrode current collector and then drying and cold pressing. The negative electrode slurry is usually formed by dispersing a negative electrode active material, an optional conductive agent, an optional binder, and other optional additives in a solvent and stirring evenly. The solvent can be N-methylpyrrolidone (NMP) or deionized water, but is not limited thereto.

[0158] The negative electrode sheet does not exclude other additional functional layers in addition to the negative electrode film layer. For example, in some embodiments, the negative electrode sheet of the embodiments of the present application further includes a negative conductive layer sandwiched between the negative electrode current collector and the negative electrode film layer and disposed on the surface of the negative electrode current collector. In other embodiments, the negative electrode sheet of the embodiments of the present application further includes a protective layer covering the surface of the negative electrode film layer.

[0159] Positive electrode plate

[0160] In some embodiments, the battery cell further includes a positive electrode tab.

[0161] The positive electrode sheet includes a positive electrode current collector and a positive electrode film layer disposed on at least one side of the positive electrode current collector and comprising a positive electrode active material. For example, the positive electrode current collector may have two opposing surfaces in its thickness direction, and the positive electrode film layer may be disposed on either or both of the two opposing surfaces of the positive electrode current collector.

[0162] In some embodiments, the dimension of the positive electrode film layer along the length direction of the positive electrode sheet is 200 mm to 600 mm, for example, 200 mm, 250 mm, 300 mm, 350 mm, 400 mm, 450 mm, 500 mm, 550 mm, 600 mm or a range consisting of any two of the above values.

[0163] In the case of a laminated electrode assembly, the length of the positive electrode sheet is parallel to the length of the battery cell, and the length of the positive electrode film layer can be understood as the length of the positive electrode film layer. The width of the positive electrode sheet is parallel to the width of the battery cell, and the width of the positive electrode film layer can be understood as the width of the positive electrode film layer.

[0164] Exemplarily, the positive electrode film layer has a length dimension of 200 mm to 600 mm; the electrolyte includes an organic solvent, including a carboxylic acid ester solvent, and the electrolyte has a room temperature conductivity of 9 mS / cm to 18 mS / cm. The length of the positive electrode film layer, combined with the electrolyte's conductivity, helps increase the liquid-phase transport rate of lithium ions, improves kinetic performance, and enhances the rapid charging capability of the battery cells. Furthermore, due to the low viscosity of the carboxylic acid ester solvent, it can evenly infiltrate the entire positive electrode film layer, resulting in a uniform charge level throughout the positive electrode film layer. The lithium ions released through the positive electrode film layer are evenly distributed on the negative electrode side, reducing the risk of local side reactions on the negative electrode side and improving high-temperature cycling performance under rapid charging.

[0165] Optionally, the length of the positive electrode film is 200mm to 600mm; the electrolyte includes an organic solvent, which includes a carboxylate solvent, and the mass content of the carboxylate solvent in the electrolyte is 3% to 70%, optionally 5% to 30%. The above mass content of the carboxylate solvent makes the viscosity of the electrolyte relatively low, which is conducive to rapid infiltration of the positive electrode film layer, resulting in uniform charge and discharge performance throughout the positive electrode film layer, reducing the risk of lateral lithium deposition at the negative electrode, and improving the cycle life of the battery cell.

[0166] In some embodiments, the compaction density of the positive electrode film layer of the battery cell at 0% state of charge SOC is 2.20 g / cm 3 Up to 2.85g / cm 3 For example, when the battery cell is at 0% state of charge (SOC), the compaction density of the positive electrode film is 2.20 g / cm 3 , 2.25g / cm 3 , 2.30g / cm 3 , 2.32g / cm 3 , 2.35g / cm 3 , 2.38g / cm 3 , 2.40g / cm 3 , 2.42g / cm 3 , 2.45g / cm 3 , 2.48g / cm 3 , 2.50g / cm 3 , 2.52g / cm 3 , 2.55g / cm 3 , 2.56g / cm 3 , 2.57g / cm 3 , 2.58g / cm 3 , 2.60g / cm 3 , 2.62g / cm 3 , 2.65g / cm 3 , 2.68g / cm 3 , 2.70g / cm 3 , 2.75g / cm 3 , 2.80g / cm 3 , 2.85g / cm 3 Or a range consisting of any two of the above values.

[0167] When the compaction density of the positive electrode film layer is within the above range, it is beneficial to improve the energy density of the battery cell; and because the positive electrode active material of the positive electrode film layer is stacked relatively densely, the contact resistance between particles is small, which can further reduce the resistance of the electrode sheet, thereby reducing heat generation under fast charging, reducing high-temperature gas production, and improving high-temperature cycle performance, especially the high-temperature cycle performance under the fast charging system is improved.

[0168] 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.

[0169] 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 tab will not be excessive, and it can take into account improving the energy density and charge rate performance of the battery cell, and prevent excessive heat accumulation in the battery cell system, reduce the risk of high-temperature decomposition of the electrolyte, and improve the cycle performance of the battery cell.

[0170] In the embodiments of the present application, the tap 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, the positive electrode tab of the battery cell at 0% SOC is disassembled, and the tap density of the positive electrode film layer is measured. For example, a single-sided coated positive electrode tab (if it is a double-sided coated tab, one side of the positive electrode film layer can be wiped off first) is punched into small round pieces with an area of S1, weighed, recorded as M1, and its thickness H1 is measured. Then, the positive electrode film layer of the above-mentioned weighed positive electrode tab is wiped off, the weight of the positive electrode current collector is weighed, recorded as M0, and its thickness H0 is measured. The single-sided coating weight of the positive electrode film layer = (weight of the positive electrode tab M1 - weight of the positive electrode current collector M0) / S1, the thickness of the positive electrode film layer = thickness of the positive electrode tab H1 - thickness of the positive electrode current collector H0, and the tap density of the positive electrode film layer = single-sided coating weight of the positive electrode film layer / thickness of the positive electrode film layer.

[0171] 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 has a stable structure during charge and discharge and can improve the cycle life of the battery cell.

[0172] 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.

[0173] 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 fast charging performance of the battery cell.

[0174] 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%.

[0175] For example, the carbon-containing material may include carbon nanotubes, and the carbon nanotubes can be used as a conductive agent in the positive electrode film layer to improve the conductivity of the positive electrode film layer.

[0176] For another example, the lithium-containing phosphate in the olivine structure may be an unmodified lithium-containing phosphate such as lithium iron phosphate, or a material obtained by coating and modifying it. For example, a carbon-containing material is provided on the surface of the lithium-containing phosphate, and the carbon-containing material can be used as a coating layer to coat the surface of the lithium-containing phosphate, thereby improving the conductivity of the lithium-containing phosphate, reducing the powder resistivity of the material, and being beneficial to the migration rate of lithium ions, improving the fast charging ability of the battery cell, and reducing the heat generation of the battery cell.

[0177] In some embodiments, the lithium-containing phosphate includes a general formula of Li x1 A y1 Me a M b P 1-c X c Y zCompounds, where 0.5 ≤ x1 ≤ 1.3, 0 ≤ y1 ≤ 1.3, and 0.9 ≤ x1 + y1 ≤ 1.3, 0.9 ≤ a ≤ 1.5, 0 ≤ b ≤ 0.5, and 0.9 ≤ a + b ≤ 1.5, 0 ≤ c ≤ 0.5, 3 ≤ z ≤ 5, A includes one or more of Na, K, Mg, Me includes one or more of Mn, Fe, Co, Ni, M includes one or more of B, Mg, Al, Si, P, S, Ca, Sc, Ti, V, Cr, Cu, Zn, Sr, Y, Zr, Nb, Mo, Cd, Sn, Sb, Te, Ba, Ta, W, Yb, La, Ce, X includes one or more of Cl, C, N, and Y includes one or more of O, F. The lithium-containing phosphate has excellent cycle stability, which is beneficial to improving the cycle performance of the battery cell.

[0178] Exemplarily, the lithium-containing phosphate includes one or more of LiFePO4, LiMnPO4, LiNiPO4, LiCoPO4. During the charge and discharge process of the battery cell, the insertion and extraction and consumption of active ions such as Li will occur. The molar content of Li is different when the battery cell is discharged to different states. In the listing of the cathode active materials such as LiFePO4, LiMnPO4, LiNiPO4, LiCoPO4, etc., the molar content of Li is the initial state of the material, that is, the state before feeding. When the cathode active material is applied to the battery system, after charge and discharge cycles, the molar content of Li may change. In the embodiments of the present application, in the listing of the cathode active materials such as LiFePO4, LiMnPO4, LiNiPO4, LiCoPO4, 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.

[0179] In the embodiments of the present application, the content of elements in the cathode active material has the meaning well-known in the art and can be detected by equipment and methods well-known in the art. For example, referring to EPA 6010D-2014, it is tested by inductively coupled plasma atomic emission spectrometry, and determined by inductively coupled plasma optical emission spectrometry (ICP-OES, instrument model: Thermo ICAP7400). After discharging the battery cell to 0% state of charge (SOC) and disassembling the cathode electrode sheet, it is cleaned with dimethyl carbonate (DMC) and dried, and then after high-temperature calcination to remove impurities, 0.4 g of the cathode active material is weighed, and 10 ml (50% concentration) of aqua regia is added thereto. Then it is placed on a flat plate at 180 °C for 30 min. After digestion on the flat plate, it is fixed to a volume of 100 mL, and quantitative testing is carried out by the standard curve method.

[0180] In some embodiments, the lithium-containing phosphate is granular. The lithium-containing phosphate includes a plurality of first phosphate particles and a plurality of second phosphate particles. The longest diameter of the first phosphate particles is greater than or equal to a preset longest diameter, such as 1 μm, and the longest diameter of the second phosphate particles is less than 1 μm. It can be understood that the particles with a longest diameter greater than or equal to 1 μm all belong to the first phosphate particles, and the particles with a longest diameter less than 1 μm all belong to the second phosphate particles;

[0181] The longest diameter of the first phosphate particles is greater than that of the second phosphate particles. The average longest diameter of the first phosphate particles is 1 μm to 5 μm, and the average longest diameter of the second phosphate particles is 0.1 μm to 0.5 μm.

[0182] Exemplarily, the average longest diameter of the first phosphate particles is 1 μm to 5 μm, such as 1 μm, 1.5 μm, 2 μm, 2.5 μm, 3 μm, 3.5 μm, 4 μm, 4.5 μm, 5 μm or a range composed of any two of the above values.

[0183] Exemplarily, the average longest diameter of the second phosphate particles is 0.1 μm to 0.5 μm, such as 0.1 μm, 0.15 μm, 0.2 μm, 0.25 μm, 0.3 μm, 0.35 μm, 0.4 μm, 0.45 μm, 0.5 μm or a range composed of any two of the above values.

[0184] When the lithium-containing phosphate meets the above conditions, its longest diameter is relatively small, the lithium deintercalation / insertion path of lithium ions in the lithium-containing phosphate is short, and the heat generation is less; moreover, the particle size of the above lithium-containing phosphate is not too small, and basically no agglomeration occurs during the processing and preparation process, so that the performance of the lithium-containing phosphate is stable; thus, it is beneficial to improve the high-temperature cycling performance of the battery cell.

[0185] In some embodiments, the mass content of the second phosphate particles in the lithium-containing phosphate is 80% to 95%, such as 80%, 82%, 84%, 85%, 86%, 88%, 90%, 92%, 94%, 95% or a range composed of any two of the above values. When the mass content of the second phosphate particles is within an appropriate range, such as 80% to 95%, the heat generation can be further reduced, the heat generation in the battery cell system can be reduced, the risk of decomposition of the electrolyte components due to heat accumulation can be reduced, and the cycling performance of the battery cell can be improved.

[0186] In some embodiments, the positive electrode film layer includes a positive electrode additive, and the positive electrode additive includes at least one of a lithium-containing iron oxide and a lithium-containing cobalt oxide. During charging, lithium ions of the positive electrode additive migrate to the negative electrode side through the electrolyte. The positive electrode additive forms a negatively charged group due to the migration of lithium ions, and the negatively charged group can release oxygen into the electrolyte. The oxygen element can participate in the formation of the negative electrode film, can repair the SEI film, improve the influence of carboxylic ester solvents on the high-temperature cycle life of the battery cell, and enhance the high-temperature cycle performance of the battery cell.

[0187] The positive electrode additive contains lithium element and can release lithium ions during the charging process of the battery cell, compensating for lithium loss, which is beneficial to improving the capacity characteristics and cycle performance of the battery cell.

[0188] In some embodiments, the lithium-containing iron oxide includes lithium ferrite. On the one hand, lithium ferrite can supplement the lithium loss in the system, and on the other hand, it can release oxygen to the negative electrode side to participate in the formation of the SEI film, improving the cycle performance of the battery cell.

[0189] Optionally, the lithium-containing iron oxide includes Li e FeO f , 0 < e ≤ 5, 0 < f ≤ 4.

[0190] Exemplarily, the lithium-containing iron oxide includes at least one of Li5FeO4, Li3FeO 3.5 , LiFeO2.

[0191] In some embodiments, the lithium-containing cobalt oxide includes lithium cobaltate. On the one hand, lithium cobaltate can supplement the lithium loss in the system, and on the other hand, it can release oxygen to the negative electrode side to participate in the formation of the SEI film, improving the cycle performance of the battery cell.

[0192] Optionally, the lithium-containing cobalt oxide includes Li g CoO h , 0 < g ≤ 6, 0 < h ≤ 4.

[0193] Exemplarily, the lithium-containing cobalt oxide includes one or more of Li6CoO4, Li3CoO2, LiCoO2.

[0194] In some embodiments, a carbon coating layer is further provided on the surface of the positive electrode additive. It can be understood that the positive electrode additive has a core-shell structure, and the positive electrode additive includes a core part and a carbon coating layer. The core part includes at least one of lithium ferrite particles and lithium cobaltate particles, and the carbon coating layer is disposed on at least a part of the surface of the core part. The positive electrode additive includes a carbon coating layer, which can effectively protect the core part. After being coated with the carbon coating layer, the structure of the positive electrode additive is more stable, and the side reaction between the electrolyte and the positive electrode additive can be alleviated, thereby further improving the cycle performance of the battery cell; moreover, the carbon coating layer can slowly release the oxygen released from the core part, so that the oxygen is gradually released into the electrolyte and gradually participates in the construction and repair of the SEI film, which is more conducive to forming an SEI film with excellent performance and reducing the SEI film impedance. Exemplarily, the core part includes lithium ferrite particles, and the carbon coating layer is coated on the surface of the lithium ferrite particles.

[0195] Optionally, the mass content of the carbon coating layer in the positive electrode additive is 1% to 5%, such as 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5% or the range composed of any two of the above.

[0196] When the mass content of the carbon coating layer is within the above range, the core part can be protected more effectively, which is beneficial to the gradual release of oxygen.

[0197] In some embodiments, both the lithium-containing phosphate and the positive electrode additive are granular, and both the lithium-containing phosphate and the positive electrode additive are multiple particles. The average longest diameter of the multiple lithium-containing phosphates is less than the average shortest diameter of the multiple positive electrode additives. When using the positive electrode additive with the above particle size, the stability of the positive electrode additive can be effectively improved while having a good oxygen release effect.

[0198] In some embodiments, the ratio of the longest diameter to the shortest diameter of the positive electrode additive in the same particle is 1.2 to 2.5, such as 1.2, 1.4, 1.5, 1.6, 1.8, 2.0, 2.2, 2.4, 2.5 or the range composed of any two of the above. When using the positive electrode additive with the above particle size, the stability of the positive electrode additive can be effectively improved while having a good oxygen release effect.

[0199] In some embodiments, the average longest diameter of the multiple positive electrode additives is 9 μm to 13 μm, such as 9 μm, 9.5 μm, 10 μm, 10.5 μm, 11 μm, 11.5 μm, 12 μm, 12.5 μm, 13 μm or the range composed of any two of the above. When using the positive electrode additive with the above particle size, the stability of the positive electrode additive can be effectively improved while having a good oxygen release effect.

[0200] In some embodiments, the average shortest diameter of the plurality of positive electrode additives 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 a range composed of any two of the above. When the positive electrode additives with the above particle sizes are used, the stability of the positive electrode additives can be effectively improved while having a good oxygen release effect.

[0201] In the embodiments of the present application, the positive electrode sheet is cut along the thickness direction of the sheet to expose the cut surface of the positive electrode film layer, which can also be understood as the cross-section of the positive electrode film layer along its own thickness direction. By performing a scanning electron microscope (SEM) test on the cut surface of the positive electrode film layer, the longest diameter and the shortest diameter of the positive electrode additive particles and the longest diameter of the lithium-containing phosphate are determined. For example, the "longest diameter" of a particle refers to the longest straight line passing through the center point of the particle and extending to the outer periphery of the particle. The "shortest diameter" of a particle refers to the shortest straight line passing through the center point of the particle and extending to the outer periphery of the particle.

[0202] In the cross-section of the positive electrode film layer along its own thickness direction, the longest diameters of a plurality of, for example, 10 positive electrode additives are statistically counted, and the average value thereof is calculated as the average longest diameter; the shortest diameters of a plurality of, for example, 10 positive electrode additives are statistically counted, and the average value thereof is calculated as the average shortest diameter.

[0203] In the cross-section of the positive electrode film layer along its own thickness direction, the longest diameters of a plurality of, for example, 50 lithium-containing phosphate particles are statistically counted. The particles with the longest diameter greater than or equal to 1 μm belong to the first phosphate particles, and the particles with the longest diameter less than 1 μm belong to the second phosphate particles. The average value of the longest diameters of all the first phosphate particles is calculated as the average longest diameter of the first phosphate particles, and the average value of the longest diameters of all the second phosphate particles is calculated as the average longest diameter of the second phosphate particles.

[0204] In some embodiments, based on the total mass of the positive electrode film layer, the mass ratio of the positive electrode additive is from 0.5% to 3%, such as 0.5%, 0.6%, 0.8%, 1.0%, 1.2%, 1.4%, 1.6%, 1.8%, 2.0%, 2.5%, 3.0% or a range composed of any two of the above. When the positive electrode additives with the above mass range are used, the stability of the positive electrode additives can be effectively improved while having a good oxygen release effect.

[0205] 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%.

[0206] 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%.

[0207] When the mass content of the carbon nanotubes is within the above range, it is beneficial to improve the conductivity of the positive electrode film layer and improve the fast charging performance of the battery cell.

[0208] Optionally, the specific surface area of the carbon nanotubes is 500m 2 / g to 2500m 2 / g, such as 500m² / g, 700m² / g, 900m² / g, 1100m² / g, 1300m² / g, 1500m² / g, 1700m² / g, 1900m² / g, 2100m² / g, 2300m² / g, 2500m² / g or the range composed of any two of the above.

[0209] When the specific surface area of the carbon nanotubes is within the above range, it is beneficial to improve the electron conduction ability; and with an appropriate content of carbon nanotubes, the degree of side reactions can be reduced and the cycle performance can be improved.

[0210] Optionally, the tube diameter of the carbon nanotubes is 0.5nm to 20nm, 0.5nm, 1.5nm, 2.5nm, 3.5nm, 4.5nm, 5.5nm, 6.5nm, 7.5nm, 8.5nm, 9.5nm, 10.5nm, 11.5nm, 12.5nm, 13.5nm, 14.5nm, 15.5nm, 16.5nm, 17.5nm, 18.5nm, 19.5nm, 20nm or the range composed of any two of the above. Optionally, the tube diameter of the carbon nanotubes is 0.5nm to 7.5nm.

[0211] When the tube diameter of the carbon nanotubes is within the above range, the structure is relatively stable and has relatively excellent electron conduction ability.

[0212] Carbon nanotubes can generally be considered to be formed by curling two-dimensional carbon materials. When the number of curled layers is single layer, it is single-walled carbon nanotubes; when curled into multiple layers, it is multi-walled carbon nanotubes. The tube diameter of the carbon nanotubes is the outer diameter of the carbon nanotubes on the cross-section perpendicular to its own central axis.

[0213] In some embodiments, the positive electrode film layer may further optionally include a positive electrode binder. There is no particular limitation on the type of the positive electrode binder in the embodiments of the present application. As an example, the positive electrode binder may include at least one of polyvinylidene fluoride, polytetrafluoroethylene, vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, polyacrylic acid, and fluorinated acrylate resins. In some embodiments, based on the mass of the positive electrode film layer, the mass content of the positive electrode binder is ≤5%.

[0214] In some embodiments, the positive electrode current collector may be a metal foil or a composite current collector. As an example of the metal foil, at least one of foils of aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy may be used. The composite current collector may include a polymer material base layer and a metal material layer formed on at least one surface of the polymer material base layer. As an example, the metal material of the metal material layer may include at least one of aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy. As an example, the polymer material base layer may include at least one of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0215] The positive electrode film layer is generally formed by coating a positive electrode paste on the positive electrode current collector and then drying and cold pressing. The positive electrode paste is generally formed by dispersing a positive electrode active material, an optional conductive agent, an optional binder, and any other components in a solvent and stirring evenly. The solvent may be N-methylpyrrolidone (NMP), but is not limited thereto.

[0216] The positive electrode tab does not exclude other additional functional layers other than the positive electrode film layer. For example, in some embodiments, the positive electrode tab of the embodiments of the present application further includes a positive electrode conductive layer sandwiched between the positive electrode current collector and the positive electrode film layer and disposed on the surface of the positive electrode current collector. In some other embodiments, the positive electrode tab of the embodiments of the present application further includes a protective layer covering the surface of the positive electrode film layer.

[0217] Electrolyte

[0218] During the charge and discharge process of the battery cell, active ions such as lithium ions are embedded and extracted back and forth between the positive electrode tab and the negative electrode tab, and the electrolyte plays a role in conducting the active ions between the positive electrode tab and the negative electrode tab. The electrolyte includes an organic solvent and an electrolyte salt.

[0219] 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.

[0220] When the conductivity of the electrolyte at room temperature, such as 25 °C, is within the above range, the migration rate of lithium ions in the electrolyte is relatively high, which can further reduce the internal resistance of the battery cell, thereby reducing heat generation and the high-temperature gas generation caused by heat accumulation, and can improve the high-temperature cycling performance of the battery cell during fast charging.

[0221] In the embodiments of the present application, the conductivity of the electrolyte at room temperature, such as 25 °C, is the ionic conductivity, and it can be detected by using the equipment and methods well-known in the art. For example, it can be tested with reference to the industry standard HG-T 4067-2015.

[0222] In some embodiments, the organic solvent includes carboxylic ester solvents.

[0223] Optionally, the mass content of the carboxylic ester solvent in the electrolyte is from 3% to 70%. Exemplarily, the mass content of the carboxylic ester solvent is 3%, 5%, 8%, 10%, 13%, 15%, 18%, 20%, 23%, 25%, 28%, 30%, 33%, 35%, 38%, 40%, 43%, 45%, 48%, 50%, 53%, 55%, 58%, 60%, 63%, 65%, 68%, 70% or a range composed of any two of the above values. Optionally, the mass content of the carboxylic ester solvent in the electrolyte is from 5% to 30%.

[0224] When the mass content of the carboxylic ester solvent is within the above range, it can improve the conductivity of the electrolyte; and the electrolyte is compatible with the silicon-containing negative electrode, which can effectively alleviate the side reactions on the negative electrode side, reduce the gas generation of the battery cell, and improve the fast charging ability of the battery cell.

[0225] Exemplarily, the carboxylic ester solvent includes cyclic carboxylic esters, and the cyclic carboxylic esters include one or more of γ-butyrolactone, γ-valerolactone, and δ-valerolactone. The conductivity of the above materials is relatively high, which can improve the conductivity of the electrolyte.

[0226] Exemplarily, the carboxylic ester solvents include chain carboxylic esters, and the chain carboxylic esters include one or more of methyl acetate, ethyl acetate, propyl acetate, butyl acetate, propyl propionate, and butyl propionate. The above materials have a relatively high conductivity and can improve the conductivity of the electrolyte.

[0227] In some embodiments, the organic solvent includes carbonate solvents.

[0228] When carbonate solvents and carboxylic ester solvents are used in combination, the stability of the electrolyte can be improved, the gas generation amount at high temperature can be reduced, which is beneficial to improving the high-temperature cycle life of the battery cell.

[0229] Exemplarily, the carbonate solvents include one or more of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate. Optionally, the carbonate solvents include one or more of ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate.

[0230] In some embodiments, the electrolyte salt includes lithium salts, and the lithium salts include one or more of lithium bis(fluorosulfonyl)imide and lithium hexafluorophosphate. Optionally, the lithium salts include lithium bis(fluorosulfonyl)imide and lithium hexafluorophosphate.

[0231] Lithium hexafluorophosphate may decompose to produce hydrofluoric acid HF, and the side reaction between hydrofluoric acid and the negative electrode, especially the silicon-containing negative electrode, may lead to an increase in gas generation during high-temperature storage; 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, the gas generation amount during high-temperature storage can be reduced, which is beneficial to improving the high-temperature cycle life of the battery cell.

[0232] In some embodiments, based on the mass of the electrolyte, the ratio of the mass content of lithium bis(fluorosulfonyl)imide to the mass content of lithium hexafluorophosphate is 0.3 to 1.2, such as 0.3, 0.5, 0.7, 0.9, 1.1, 1.2 or the range composed of any two of the above values.

[0233] When the ratio of the mass content of lithium hexafluorophosphate to lithium bis(fluorosulfonyl)imide satisfies the above range, on the one hand, the content of hydrofluoric acid can be reduced, the side reaction at the negative electrode interface can be slowed down, and the gas generation amount during high-temperature storage can be reduced; on the other hand, the content of the organic components in the SEI film formed at the negative electrode interface is appropriate, which can also reduce the gas generation amount during high-temperature storage, which is beneficial to improving the high-temperature cycle life of the battery cell.

[0234] Exemplarily, based on the mass of the electrolyte, the mass content of lithium bis(fluorosulfonyl)imide is 2% to 11%, such as 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 8%, 8.5%, 9%, 9.5%, 10%, 10.5%, 11% or a range composed of any two of the above values. When the mass content of lithium bis(fluorosulfonyl)imide is within the above range, the content of hydrofluoric acid can be reduced, the side reaction at the negative electrode interface can be slowed down, the gas generation during high-temperature storage can be reduced, which is beneficial to improving the high-temperature cycle life of the battery cell.

[0235] Exemplarily, based on the mass of the electrolyte, the mass content of lithium hexafluorophosphate is 3% to 14%, such as 3%, 3.5%, 4%, 4.5%, 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 8%, 8.5%, 9%, 9.5%, 10%, 10.5%, 11%, 11.5%, 12%, 12.5%, 13%, 13.5%, 14% or a range composed of any two of the above values. When the mass content of lithium hexafluorophosphate is within the above range, the conductivity of the electrolyte is relatively high, which is beneficial to the migration of lithium ions and improves the fast charging performance of the battery cell.

[0236] In some embodiments, the electrolyte further comprises additives. The additives can include negative electrode film-forming additives, or can include positive electrode film-forming additives, or can also include additives that can improve certain performance of the battery, such as additives for improving the overcharge performance of the battery, additives for improving the high-temperature performance of the battery, additives for improving the low-temperature power performance of the battery, etc.

[0237] In some embodiments, the additives include cyclic carbonate additives, such as including one or more of fluorinated cyclic carbonates and vinylene carbonate. Optionally, the additives include fluorinated cyclic carbonates and vinylene carbonate.

[0238] The fluorinated cyclic carbonate can form a SEI film rich in lithium fluoride LiF on the surface of the negative electrode, which can relieve the volume expansion of silicon, improve the life of the silicon-containing system, and improve the cycle performance.

[0239] The fluorinated cyclic carbonate and vinylene carbonate are used in combination, making the SEI film on the surface of the negative electrode denser, which can more effectively protect the silicon-containing negative electrode, reduce the degree of side reaction at the negative electrode interface, and improve the cycle performance.

[0240] Optionally, the fluorinated cyclic carbonate includes at least one of fluoroethylene carbonate, difluoroethylene carbonate, and trifluoropropylene carbonate.

[0241] Optionally, based on the mass of the electrolyte, the mass content of the fluorinated cyclic carbonate is 0.5% to 20%, for example, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 8%, 8.5%, 9%, 9.5%, 10%, 10.5%, 11%, 11.5%, 12%, 12.5%, 13%, 13.5%, 14%, 14.5%, 15%, 15.5%, 16%, 16.5%, 17%, 17.5%, 18%, 18.5%, 19%, 19.5%, 20% or a range composed of any two of the above values. When the mass content of the fluorinated cyclic carbonate is within the above range, it is beneficial to improve the cycling performance.

[0242] As an example, based on the mass of the electrolyte, the mass content of the fluorinated cyclic carbonate is 0.5% to 10%; the mass content of silicon element in the silicon-based material in the negative electrode active material is 0.3% to 7.5%.

[0243] The mass content of silicon element is relatively high and the volume expansion is relatively larger. When the mass content of the fluorinated cyclic carbonate and the mass content of silicon element meet the above conditions, the volume expansion of silicon can be more effectively alleviated, the life of the silicon-containing system can be improved, and the cycling performance can be improved.

[0244] 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%.

[0245] When the mass content of the fluorinated cyclic carbonate and the mass content of silicon element meet the above conditions, the volume expansion of silicon can be more effectively alleviated, the life of the silicon-containing system can be improved, and the cycling performance can be improved.

[0246] Optionally, based on the mass of the electrolyte, the mass content of vinylene carbonate is 0.1% to 3%, for example, 0.1%, 0.5%, 0.6%, 1.0%, 1.1%, 1.5%, 1.6%, 2.0%, 2.1%, 2.5%, 2.6%, 3% or a range composed of any two of the above values. The vinylene carbonate with the above mass content makes the SEI film on the 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 improve the cycling performance.

[0247] When the vinylene carbonate with the above mass content and the fluorinated cyclic carbonate are used in combination, the performance of the SEI film on the surface of the negative electrode is further optimized, with excellent denseness and low impedance, 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.

[0248] In the embodiments of the present application, the types and contents of the inorganic components / lithium salts in the electrolyte have meanings well-known in the art, and can be detected by devices and methods well-known in the art. For example, reference can be made to the General Rules for Ion Chromatographic Analysis (JY / T 020-1996) to qualitatively or quantitatively analyze the inorganic components / lithium salts in the electrolyte by ion chromatography. In the embodiments of the present application, newly prepared electrolyte can be taken as a sample, the free electrolyte of a fresh battery can be taken as a sample, or a battery that has been fully discharged (discharged to the lower cut-off voltage so that the charged state of the battery is about 0% SOC) can be disassembled in reverse, and the free electrolyte obtained from the battery can be taken as a sample for detection by ion chromatography.

[0249] In the embodiments of the present application, the types and contents of the organic components in the electrolyte have meanings well-known in the art, and can be detected by devices and methods well-known in the art. For example, reference can be made to the General Rules for Gas Chromatography of Chemical Reagents (GB / T 9722-2006) to qualitatively and quantitatively analyze the organic components in the electrolyte by gas chromatography.

[0250] In the embodiments of the present application, after quantitatively and qualitatively detecting each component in the electrolyte, each component is classified, and carboxylic acid ester solvents and carbonate solvents are used as the constituent components of organic solvents. Based on the mass of the electrolyte being 100%, the mass content of each component is calculated.

[0251] Fluorinated cyclic carbonates and vinylene carbonate are used as additives in the electrolyte. Based on the mass of the electrolyte being 100%, the mass content of each component is calculated.

[0252] Separator

[0253] In some embodiments, the electrode assembly further includes a separator disposed between the positive electrode plate and the negative electrode plate.

[0254] 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.

[0255] As an example, the main material of the separator membrane can be selected from at least one of glass fiber, non-woven fabric, polyethylene, polypropylene, polyvinylidene fluoride, and ceramics. The separator membrane can be a single-layer film or a multi-layer composite film, without particular limitation. When the separator membrane is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation. The separator can be a single component located between the positive and negative electrodes, or can be attached to the surfaces of the positive and negative electrodes. An inorganic particle coating, an organic particle coating, or an organic / inorganic composite coating can also be coated on the surface of the separator membrane.

[0256] In some embodiments, the separator is a solid electrolyte. The solid electrolyte is disposed between the positive electrode and the negative electrode, and functions to transport ions and isolate the positive and negative electrodes simultaneously.

[0257] Example

[0258] 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.

[0259] Example 1

[0260] 1. Preparation of the positive electrode sheet

[0261] The positive electrode sheet includes a positive electrode current collector and positive electrode film layers disposed on both sides of the positive electrode current collector. The positive electrode current collector is aluminum foil.

[0262] The positive electrode film layer includes a lithium-containing phosphate, a positive electrode additive, a binder polyvinylidene fluoride (PVDF), and a conductive agent acetylene black in a mass ratio of 96:1.5:1.5:1. The positive electrode film layer is a film layer formed by uniformly coating a positive electrode slurry (solvent: N-methylpyrrolidone NMP) on both sides of the positive electrode current collector and then drying and cold pressing.

[0263] The lithium-containing phosphate includes a plurality of first phosphate particles and a plurality of second phosphate particles, and the mass content of the second phosphate particles in the lithium-containing phosphate is 90%;

[0264] In a cross-section along the thickness direction of the positive electrode film layer, the average longest diameter of the plurality of first phosphate particles is 2 μm, the average longest diameter of the plurality of second phosphate particles is 0.3 μm, and the mass content of the second phosphate particles in the lithium-containing phosphate is 90%.

[0265] The positive electrode additive is a plurality of particles, each particle includes a core part and a carbon coating layer disposed on the surface of the core part. The core part is lithium ferrite, and the mass content of the carbon coating layer in the positive electrode additive is 2%. In a cross-section along the thickness direction of the positive electrode film layer, the average longest diameter of the plurality of positive electrode additives is 11 μm, and the average shortest diameter of the plurality of positive electrode additives is 7 μm.

[0266] The single-sided coating weight of the positive electrode film layer is 280 mg / 1540.25 mm 2 。

[0267] Lithium iron phosphate is sourced from Xiamen Tungsten Co., Ltd.

[0268] 2. Preparation of the negative electrode plate

[0269] The negative electrode plate includes a negative current collector and negative electrode film layers provided on both sides of the negative current collector. The negative current collector is a copper foil.

[0270] The negative electrode film layer includes artificial graphite of carbon-based material, conductive agent acetylene black, negative electrode binder styrene-butadiene rubber, and thickening agent sodium carboxymethyl cellulose with a mass ratio of 96.5:1:1.5:1. The negative electrode film layer is a film layer formed by uniformly coating the negative electrode slurry (solvent is deionized water) on the surface of the negative current collector and then drying and cold pressing.

[0271] The single-sided coating weight of the negative electrode film layer is 135 mg / 1540.25 mm 2 。

[0272] The artificial graphite is sourced from BETRAY New Energy Materials Co., Ltd.

[0273] 3. Separator

[0274] The separator includes a base film, which is a 7-μm polyethylene film layer with a porosity of 35%.

[0275] The separator is sourced from Shenzhen Xingyuan Material Technology Co., Ltd.

[0276] 4. Preparation of the electrolyte

[0277] The electrolyte includes organic solvents, lithium salts, and additives.

[0278] After mixing the components of the organic solvents evenly, lithium salts and additives are added to prepare the electrolyte.

[0279] The organic solvents include 25% chain carboxylic ester solvents (ethyl acetate EA) and 57% carbonate solvents (27% ethylene carbonate EC, 30% dimethyl carbonate DMC). The mass content of each component in the organic solvents is calculated based on the mass of the electrolyte.

[0280] The lithium salts include 8% lithium hexafluorophosphate LiPF6 and 6% lithium bis(fluorosulfonyl)imide.

[0281] The additives include 2% fluorinated cyclic carbonate fluoroethylene carbonate FEC and 2% vinylene carbonate VC;

[0282] The conductivity of the electrolyte is 14.2 mS / cm.

[0283] 5. Preparation of the battery cell

[0284] The positive electrode sheet, separator, and negative electrode sheet are stacked in order, with the separator placed between the positive electrode sheet and the negative electrode sheet to serve as an isolation to obtain an electrode assembly. The electrode assembly is placed in an outer packaging shell, dried, and then injected with electrolyte. After vacuum packaging, standing, forming, and shaping, a battery cell is obtained. The compaction density of the positive electrode film layer of the battery cell at 0% SOC is 2.65 g / cm 3 The compaction density of the negative electrode film at 0% SOC is 1.56 g / cm 3 .

[0285] Comparative Example 1-1

[0286] A battery cell was prepared using a method similar to that of Example 1. The difference from Example 1 was that no positive electrode additive was added to the positive electrode film layer.

[0287] Example 2

[0288] A battery cell was prepared using a method similar to that of Example 1. The difference from Example 1 was that the type of the positive electrode additive was adjusted.

[0289] Example 3-1 and Example 3-2

[0290] A battery cell was prepared using a method similar to that of Example 1. The difference from Example 1 was that the mass content of the carbon coating layer in the positive electrode additive was adjusted.

[0291] Example 4-1 and Example 4-2

[0292] A battery cell was prepared using a method similar to that of Example 1. The difference from Example 1 was that the mass content of the positive electrode additive was adjusted.

[0293] Example 5-1 to Example 5-3

[0294] A battery cell was prepared using a method similar to that of Example 1. The difference from Example 1 was that the particle size of the positive electrode additive was adjusted.

[0295] Example 6-1 to Example 6-3

[0296] A battery cell was prepared using a method similar to that of Example 1. The difference from Example 1 was that the particle size of the positive electrode active material was adjusted.

[0297] Example 7-1 and Example 7-2

[0298] A battery cell was prepared using a method similar to that of Example 1. The difference from Example 1 was that the mass content of the second phosphate particles in the positive electrode active material was adjusted.

[0299] Performance test

[0300] 1. High-temperature cycling performance test of battery cells

[0301] Under the environment of 45 ± 5 °C, the battery cell is charged at a constant current of 2C to 3.65V, then charged at a constant voltage until the cut-off current of 0.05C, and then discharged at a constant current of 2C to 2.5V. This is one charge-discharge cycle. The discharge capacity of this time is recorded as the discharge capacity C1 of the first cycle of the battery cell.

[0302] Repeat the cycling steps for the same battery cell until the cycling capacity retention rate of the battery cell = Cn / C1×100% = 80%. Record the number of cycling turns n. For accuracy, take the average value of 5 parallel samples as the test result.

[0303] The test results are shown in Table 1.

[0304] Table 1

[0305]

[0306] The organic components of the electrolyte may undergo side reactions on the negative electrode side, deteriorating the high-temperature cycling. In Comparative Example 1-1, no positive electrode additive was added, and the high-temperature cycling performance was relatively poor.

[0307] In the examples of the present application, by adding a positive electrode additive to the positive electrode film layer, the positive electrode additive can release oxygen element, and the oxygen element can participate in the formation of the film on the negative electrode, repair the SEI film on the negative electrode side, reduce the side reaction on the negative electrode side, and improve the high-temperature cycling performance.

[0308] Positive electrode additives of different materials, such as lithium ferrite, lithium cobaltate, etc., can release oxygen during the charging process of the battery cell, repair the negative electrode interface film, and improve the high-temperature cycling performance.

[0309] The surface of lithium ferrite can be coated with a carbon coating layer, and the mass content of the carbon coating layer in the positive electrode additive is 1% to 5%. The carbon coating layer can effectively protect lithium ferrite, alleviate the side reaction between lithium ferrite and the electrolyte, enable lithium ferrite to stably release oxygen, gradually repair the SEI film, and improve the high-temperature cycling performance of the battery cell.

[0310] When the ratio of the longest diameter to the shortest diameter of the positive electrode additive in the same particle satisfies an appropriate ratio, for example, when the ratio of the longest diameter to the shortest diameter is 1.2 to 2.5, while effectively improving the stability of the positive electrode additive, it also has a good oxygen release effect.

[0311] The average longest diameter of the lithium-containing phosphate is smaller than the average shortest diameter of the positive electrode additive. When using the positive electrode additive with the above particle size, it has a good oxygen release effect and improves the high-temperature cycling performance of the battery cell.

[0312] The lithium-containing phosphate includes a plurality of first phosphate particles and a plurality of second phosphate particles. The longest diameter of the first phosphate particles is relatively long, and the longest diameter of the second phosphate particles is relatively short. However, the average longest diameter of the plurality of first phosphate particles is still shorter than the average shortest diameter of the plurality of cathode additives, so that the lithium deintercalation / insertion path in the lithium-containing phosphate is short, the heat generation is less, the heat generation in the battery cell system can be reduced, the risk of decomposition of the electrolyte components due to heat accumulation can be reduced, and the cycle performance of the battery cell can be improved.

[0313] When the mass content of the second phosphate particles is within an appropriate range, such as 80% to 95%, the heat generation can be further reduced, the heat generation in the battery cell system can be reduced, the risk of decomposition of the electrolyte components due to heat accumulation can be reduced, and the cycle performance of the battery cell can be improved.

[0314] Comparative Example 2-1 and Comparative Example 2-2

[0315] The battery cell was prepared by a method similar to that of Example 1. Different from Example 1, the components and contents of the electrolyte were adjusted.

[0316] Examples 8-1 to 8-7

[0317] The battery cell was prepared by a method similar to that of Example 1. Different from Example 1, the components and contents of the electrolyte were adjusted.

[0318] The test results are shown in Table 2.

[0319] Table 2

[0320]

[0321] In Table 3,

[0322] EA represents ethyl acetate; MA represents methyl acetate; EC represents ethylene carbonate; DMC represents dimethyl carbonate;

[0323] EMC represents ethyl methyl carbonate; FEC represents fluoroethylene carbonate;

[0324] EA: 25 means that the mass content of EA is 25%;

[0325] EC: 27 means that the mass content of EC is 27%.

[0326] 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.

[0327] The meanings of other examples are explained as above and will not be elaborated here.

[0328] The conductivity of the electrolyte in Example 8-1 was 9 mS / cm, and the conductivity of the electrolyte in Example 8-2 was 18 mS / cm.

[0329] In Comparative Example 2-1, the mass content of the carboxylic ester solvent was too low, resulting in too low conductivity of the electrolyte and a relatively high internal resistance of the battery cell, leading to more energy loss and deteriorating the cycle life.

[0330] In Comparative Example 2-2, the mass content of the carboxylic ester solvent was too high, resulting in increased gas generation at high temperature on the negative electrode side and poor high-temperature cycle performance.

[0331] In the embodiments of the present application, by regulating the components of the electrolyte, the mass content of the carboxylic ester solvent is 3% to 70%, optionally 5% to 30%. While improving the conductivity of the electrolyte, it can also reduce the gas generation amount at high temperature on the negative electrode side, and can improve the cycle performance and fast charging performance.

[0332] In the embodiments of the present application, by compounding lithium hexafluorophosphate and lithium bis(fluorosulfonyl)imide, 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 reaction at the negative electrode interface can be slowed down, the gas generation amount during high-temperature storage can be reduced, which is beneficial to improving the high-temperature cycle life of the battery cell.

[0333] 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 of silicon, improve the life of the silicon-containing system, and improve the cycle performance.

[0334] 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 limiting the embodiments of the present application, and the embodiments can be changed, substituted, and modified without departing from the spirit, principle, and scope of the embodiments of the present application.

Claims

1. A battery cell, characterized in that, Comprising: A negative electrode plate, including a negative electrode current collector and a negative electrode film layer provided on at least one side of the negative electrode current collector, the negative electrode film layer including a negative electrode active material, and the negative electrode active material including a carbon-based material; A positive electrode plate, including a positive electrode current collector and a positive electrode film layer provided on at least one side of the positive electrode current collector, the positive electrode film layer including a positive electrode active material and a positive electrode additive, the positive electrode active material including a lithium-containing phosphate, and the positive electrode additive including at least one of a lithium-containing iron oxide and a lithium-containing cobalt oxide; and An electrolyte, including an organic solvent, the organic solvent including a carboxylic acid ester solvent, and the mass content of the carboxylic acid ester solvent in the electrolyte being 3% to 70%.

2. The battery cell according to claim 1, wherein The lithium-containing iron oxide includes lithium ferrite; and / or The lithium-containing cobalt oxide includes lithium cobaltate.

3. The battery cell according to claim 1, characterized in that, The lithium-containing iron oxide includes Li e FeO f , where 0 < e ≤ 5 and 0 < f ≤ 4.

4. The battery cell according to claim 3, wherein The lithium-containing iron oxide includes at least one of Li5FeO4, Li3FeO 3.5 , and LiFeO2.

5. The battery cell according to claim 1, wherein The lithium-containing cobalt oxide includes Li g CoO h , where 0 < g ≤ 6 and 0 < h ≤ 4.

6. The battery cell according to claim 5, characterized in that, The lithium-containing cobalt oxide includes one or more of Li6CoO4, Li3CoO2, and LiCoO2.

7. The battery cell according to claim 1, wherein Based on the mass of the positive electrode film layer, the mass content of the positive electrode additive is 0.5% to 3%.

8. The battery cell according to claim 1, wherein, A carbon coating layer is further provided on the surface of the positive electrode additive.

9. The battery cell according to claim 8, wherein, The mass content of the carbon coating layer in the positive electrode additive is 1% to 5%.

10. The battery cell according to claim 1, characterized in that, The positive electrode additive is granular, and in a cross-section of the positive electrode film layer along its own thickness direction, the ratio of the longest diameter to the shortest diameter of the positive electrode additive in the same particle is 1.2 to 2.

5.

11. The battery cell according to claim 1, wherein in a cross-section of the positive electrode film layer along its own thickness direction, there are multiple positive electrode additives, and the average longest diameter of the multiple positive electrode additives is 9 μm to 13 μm; and / or in a cross-section of the positive electrode film layer along its own thickness direction, there are multiple positive electrode additives, and the average shortest diameter of the multiple positive electrode additives is 5 μm to 9 μm.

12. The battery cell according to claim 1, wherein, Both the lithium-containing phosphate and the positive electrode additive are multiple and granular, and in a cross-section of the positive electrode film layer along its own thickness direction, the average longest diameter of the multiple lithium-containing phosphates is less than the average shortest diameter of the multiple positive electrode additives.

13. The battery cell according to claim 1, characterized in that, The lithium-containing phosphate includes multiple first phosphate particles and multiple second phosphate particles, the longest diameter of the first phosphate particles is greater than the longest diameter of the second phosphate particles, the average longest diameter of the multiple first phosphate particles is 1 μm to 5 μm, and the average longest diameter of the multiple second phosphate particles is 0.1 μm to 0.5 μm.

14. The battery cell according to claim 13, characterized in that, The mass content of the second phosphate particles in the lithium-containing phosphate is 80% to 95%.

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

16. 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.

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

18. The battery cell according to claim 17, wherein, The carboxylic acid ester solvent includes a cyclic carboxylic acid ester, and the cyclic carboxylic acid ester includes one or more of γ-butyrolactone, γ-valerolactone, and δ-valerolactone; and / or The carboxylic acid ester solvent includes a chain-like carboxylic acid ester, and the chain-like carboxylic acid ester includes one or more of methyl acetate, ethyl acetate, propyl acetate, butyl acetate, propyl propionate, and butyl propionate.

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

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

2.

21. The battery cell according to claim 20, wherein Based on the mass of the electrolyte, the mass content of lithium bis(fluorosulfonyl)imide is 2% to 11%; and / or Based on the mass of the electrolyte, the mass content of lithium hexafluorophosphate is 3% to 14%.

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

23. The battery cell according to claim 22, characterized in that, The fluorinated cyclic carbonate includes at least one of fluoroethylene carbonate, difluoroethylene carbonate, and trifluoropropylene carbonate.

24. The battery cell according to claim 22, wherein Based on the mass of the electrolyte, the mass content of the fluorinated cyclic carbonate is 0.5% to 20%; and / or Based on the mass of the electrolyte, the mass content of vinylene carbonate is 0.1% to 3%.

25. The battery cell according to claim 1, characterized in that, The carbon-based material includes at least one of artificial graphite and natural graphite.

26. A battery device, characterized in that, Comprising the battery cell according to any one of claims 1 to 25.

27. An electrical device, characterized in that, Comprising the battery device according to claim 26.

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