Battery cell and method for producing the same, battery device, electric device

Abstract

The application provides a battery monomer, a preparation method thereof, and an electric device. The battery monomer comprises an electrode assembly formed by folding and winding a laminated body of a positive electrode sheet, a separator, and a negative electrode sheet. The negative electrode sheet comprises a negative electrode current collector and a negative electrode film layer on the surface of the negative electrode current collector. The negative electrode current collector comprises a first convex surface and a first concave surface. The negative electrode film layer comprises a first negative electrode active material layer on the side of the first convex surface, a first lithium film on the surface of the first negative electrode active material layer, and a second negative electrode active material layer on the side of the first concave surface. The first lithium film is in a stripe shape. The battery monomer has improved cycle performance.

Description

Technical Field

[0001] This application relates to the field of battery technology, and in particular to a battery cell and its preparation method, a battery device, and an electrical device. Background Technology

[0002] In recent years, with the increasingly wide application of rechargeable batteries, they have been widely used in energy storage power systems such as hydropower, thermal power, wind power, and solar power plants, as well as in power tools, electric bicycles, electric motorcycles, electric cars, aerospace, and many other fields. With the application and promotion of rechargeable batteries, people have increasingly higher requirements for their cycle performance.

[0003] Therefore, improving the cycle performance of secondary batteries has become an urgent technical problem to be solved. Summary of the Invention

[0004] This application is made in view of the above-mentioned issues, and its purpose is to provide a battery cell and a method for preparing the same, a battery device, and an electrical device, wherein the battery cell has improved cycle performance.

[0005] To achieve the above objectives, a first aspect of this application provides a battery cell comprising an electrode assembly formed by bending and winding a stack of a positive electrode, a separator, and a negative electrode along a winding axis. The negative electrode includes a negative current collector and a negative electrode film layer located on the surface of the negative current collector. The negative current collector includes a first convex surface and a first concave surface. The negative electrode film layer includes a first negative active material layer located on one side of the first convex surface, a first lithium film located on the surface of the first negative active layer, and a second negative active material layer located on one side of the first concave surface. The first lithium film is striped.

[0006] In this application, a first lithium film is disposed on the surface of the first negative electrode active material layer on the first convex side of the negative electrode current collector. The first lithium film increases the hardness of the convex surface of the negative electrode sheet, thereby suppressing the outward expansion of the corner region through the convex surface of the negative electrode sheet. This reduces the gap between the electrodes in the corner region, which is beneficial to improving the cycle performance of the battery cell. In addition, the first lithium film is striped, which on the one hand allows the lithium film to participate more fully in the reaction, which is beneficial to improving the lithium utilization rate and lithium replenishment efficiency, thus benefiting the cycle performance of the battery cell. On the other hand, the area between adjacent stripes can serve as a wetting channel for the electrolyte and a gas transport channel during high-temperature aging and formation, further benefiting the cycle performance of the battery cell.

[0007] In some embodiments, the negative electrode film layer further includes a second lithium film located on the surface of the second negative electrode active material layer and arranged in a stripe pattern; based on the total mass of the first lithium film and the second lithium film, the mass percentage of the first lithium film in the total mass is greater than the mass percentage of the second lithium film in the total mass.

[0008] In this application, by setting a first lithium film and a second lithium film with different mass ratios on both sides of the negative electrode sheet, and making the mass of the first lithium film located on the convex surface of the negative electrode current collector greater than that of the second lithium film located on the concave surface of the negative electrode current collector, compared with the lithium film being evenly distributed on the convex and concave surfaces, this arrangement has the lithium film mainly located on the convex surface of the negative electrode current collector. Therefore, the concave surface of the negative electrode sheet has lower hardness and better flexibility, which makes the adjacent electrode sheets in the corner area fit more tightly during the hot pressing process, thereby making the gap between the electrode sheets at the corner smaller. In addition, the convex surface of the negative electrode sheet has high hardness, which can suppress the outward expansion of the corner area. Thus, it is beneficial to further improve the cycle performance of the battery cell.

[0009] In some embodiments, the first lithium film accounts for more than or equal to 70% and less than 100% of the total mass. This results in the convex negative electrode being harder than the concave negative electrode, which is more conducive to improving the cycle life of the battery cell.

[0010] In some embodiments, the second lithium film accounts for a mass percentage of more than 0 and less than or equal to 30% of the total mass. This results in the concave surface of the negative electrode sheet having less hardness and greater flexibility than the convex surface, leading to a tighter fit between adjacent electrodes in the corner area. This, in turn, is more conducive to improving the cycle performance of the battery cell.

[0011] In some embodiments, the content of the first lithium film in the negative electrode film layer is 0.5 mg / 1540.25 mm. 2 ~12mg / 1540.25mm 2 This is more beneficial to the cycle performance of individual battery cells.

[0012] In some embodiments, the content of the second lithium film in the negative electrode film layer is 0.05 mg / 1540.25 mm. 2 ~0.2mg / 1540.25mm 2 This is more beneficial to the cycle performance of individual battery cells.

[0013] In some embodiments, both the first lithium film and the second lithium film include multiple wavy lithium metal strips, which are spaced apart in a first direction and a second direction. The first direction is the extension direction of the winding shaft, and the second direction is a direction perpendicular to the first direction within the plane containing the negative electrode sheet. Thus, the area between adjacent lithium metal strips can serve as a wetting channel for the electrolyte, which helps to improve the wetting rate of the negative electrode sheet to the electrolyte, thereby further improving the cycle performance of the battery cell.

[0014] In some embodiments, the thickness of the lithium metal strip is 2 μm to 8 μm. This is beneficial for improving the capacity and cycle performance of the battery cell.

[0015] In some embodiments, the spacing between adjacent lithium metal strips along the first or second direction is 1000 μm to 2000 μm. This provides sufficient channels for high-temperature aging and formation gas generation, and allows for the formation of an electrolyte wetting network, further improving the charge / discharge efficiency and cycle performance of the battery cells.

[0016] In some embodiments, the lithium metal strip has a dimension of 2 mm to 20 mm along the first direction; and / or, the lithium metal strip has a dimension of 200 μm to 2000 μm along the second direction. This is more beneficial to the charge / discharge efficiency and cycle performance of the battery cell.

[0017] In some embodiments, the area of ​​the lithium metal strip on the surface of the first negative electrode active material layer accounts for 10% to 50% of the total area of ​​the first negative electrode active material layer. This is beneficial for achieving both excellent lithium replenishment effect and cycle performance.

[0018] In some embodiments, the area of ​​the lithium metal strip on the surface of the second negative electrode active material layer accounts for 0.5% to 10% of the total area of ​​the second negative electrode active material layer. This is more conducive to achieving both excellent lithium replenishment effect and cycle performance.

[0019] In some embodiments, the coating weight of the first negative electrode active material layer is greater than that of the second negative electrode active material layer. This allows sufficient space for the insertion of lithium cathode material, thereby improving the cycle performance of the battery cell.

[0020] In some embodiments, the coating weight CW1 of the first negative electrode active material and the coating weight CW2 of the second negative electrode active material layer satisfy the condition: 1 < CW1 / CW2 ≤ 3.4. This is more conducive to further improving the cycle performance of the battery cell.

[0021] In some embodiments, the coating weight of the first negative electrode active material layer is 50 mg / 1540.25 mm. 2 ~170mg / 1540.25mm 2 This helps to balance the cycle performance and energy density of individual battery cells.

[0022] In some embodiments, the coating weight of the second negative electrode active material layer is 45 mg / 1540.25 mm. 2 ~140mg / 1540.25mm 2 This helps to balance the cycle performance and energy density of individual battery cells.

[0023] In some embodiments, the compaction density of the negative electrode sheet is 1.45 g / cm³. 3 ~1.7g / cm 3 This is beneficial for increasing the energy density of individual battery cells.

[0024] In some embodiments, both the first negative electrode active material layer and the second negative electrode active material layer include a negative electrode material, which includes a carbon material.

[0025] In some embodiments, the positive electrode sheet includes a positive current collector and a positive electrode film layer located on the surface of the positive current collector. The positive current collector includes a second convex surface and a second concave surface. The positive electrode film layer includes a first positive active material layer located on one side of the second convex surface and a second positive active material layer located on one side of the second concave surface. The coating weight of the second positive active material layer is greater than the coating weight of the first positive active material layer. This can further improve the lithium replenishment effect and is more beneficial to the energy density and cycle performance of the battery cell.

[0026] In some embodiments, the coating weight of the second positive electrode active material layer is 100 mg / 1540.25 mm. 2 ~340mg / 1540.25mm 2 This helps to balance the energy density and cycle performance of individual battery cells.

[0027] In some embodiments, the coating weight of the first positive electrode active material layer is 100 mg / 1540.25 mm. 2 ~260mg / 1540.25mm 2 This makes it easier to balance the energy density and cycle performance of individual battery cells.

[0028] The second aspect of this application provides a method for preparing a battery cell, comprising the following steps: S1, forming a first negative electrode active material layer and a second negative electrode active material layer on two opposing surfaces of a negative electrode current collector; S2, forming a first lithium film by pressing molten lithium metal; S3, transferring the first lithium film to the surface of the first negative electrode active material layer by transfer coating, and forming a negative electrode sheet by roll forming; S4, forming an electrode assembly by bending and winding a laminate of a positive electrode sheet, a separator, and the negative electrode sheet along a winding axis, wherein the negative electrode current collector includes a first convex surface and a first concave surface, the first negative electrode active material layer is located on one side of the first convex surface, and the second negative electrode active material layer is located on one side of the first concave surface; wherein the first lithium film is striped.

[0029] In the battery cell formed in this application, the first lithium film on the convex surface of the negative electrode sheet increases the hardness of the convex surface, thereby suppressing the outward expansion of the corner region. This reduces the gap between the electrodes in the corner region, which is beneficial to improving the cycle performance of the battery cell. The first lithium film is striped, which allows the lithium film to participate more fully in the reaction, improving lithium utilization and replenishment efficiency, thus benefiting the cycle performance of the battery cell. Furthermore, the area between adjacent stripes can serve as a wetting channel for the electrolyte and a gas transport channel during high-temperature aging and formation, further improving the cycle performance of the battery cell.

[0030] In some embodiments, step S2 further includes forming a second lithium film; step S3 further includes transferring the second lithium film onto the surface of the second negative electrode active material layer by means of transfer coating; the second lithium film is striped.

[0031] In some embodiments, based on the total mass of the first lithium film and the second lithium film, the mass percentage of the first lithium film in the total mass is greater than the mass percentage of the second lithium film in the total mass. This is more beneficial to the cycle performance of the battery cell.

[0032] In some embodiments, both the first lithium film and the second lithium film include multiple wavy lithium metal strips, and the multiple lithium metal strips are spaced apart on the surfaces of the first negative electrode active material layer and the second negative electrode active material layer along a first direction and a second direction; the first direction is the extension direction of the winding shaft, and the second direction is a direction perpendicular to the first direction in the plane where the negative electrode sheet is located. This is beneficial for improving the charge / discharge efficiency and cycle performance of the battery cell.

[0033] In some embodiments, the pressure of the rolling process in step S3 is 60T to 100T. This is beneficial for forming a lithium metal strip with suitable thickness and uniformity.

[0034] In some embodiments, the rolling speed in step S3 is 20 m / min to 100 m / min. This facilitates the formation of a lithium metal strip with suitable thickness and uniformity.

[0035] In some embodiments, the coating weight CW1 of the first negative electrode active material and the coating weight CW2 of the second negative electrode active material layer satisfy the condition: 1 < CW1 / CW2 ≤ 3.4. Therefore, both the first and second negative electrode active material layers can provide adequate space for lithium insertion into the cathode, which is beneficial for further improving the cycle performance of the battery cell.

[0036] In some embodiments, the coating weight of the first negative electrode active material layer is 50 mg / 1540.25 mm. 2 ~170mg / 1540.25mm 2 .

[0037] In some embodiments, the coating weight of the second negative electrode active material layer is 45 mg / 1540.25 mm. 2 ~140mg / 1540.25mm 2 .

[0038] In some embodiments, the positive current collector includes a second convex surface and a second concave surface, and before step S4, a first positive active material layer located on one side of the second convex surface and a second positive active material layer located on one side of the second convex surface are formed on both sides of the positive current collector.

[0039] In some embodiments, the coating weight of the second positive electrode active material layer is 100 mg / 1540.25 mm. 2 ~340mg / 1540.25mm 2 .

[0040] In some embodiments, the coating weight of the first positive electrode active material layer is 100 mg / 1540.25 mm. 2 ~260mg / 1540.25mm 2 .

[0041] A third aspect of this application provides a battery device comprising the battery cell described in the first aspect, or comprising a battery cell prepared according to the preparation method described in the second aspect.

[0042] The fourth aspect of this application provides an electrical device, including the battery device provided in the third aspect above. Attached Figure Description

[0043] Figure 1 This is a schematic diagram of the structure of an electrode assembly according to one embodiment of this application.

[0044] Figure 2 yes Figure 1 Schematic diagram of the structure of a corner region of the negative electrode sheet. Figure 1 .

[0045] Figure 3 yes Figure 1 Schematic diagram of the structure of a corner region of the negative electrode sheet. Figure 2 .

[0046] Figure 4 This is a schematic diagram of the negative electrode sheet according to one embodiment of this application.

[0047] Figure 5 yes Figure 1 An enlarged view of a corner area of ​​the positive electrode sheet.

[0048] Figure 6 This is a schematic diagram of a battery cell according to one embodiment of this application.

[0049] Figure 7 yes Figure 6 An exploded view of a battery cell according to one embodiment of this application is shown.

[0050] Figure 8 This is a schematic diagram of a battery module according to one embodiment of this application.

[0051] Figure 9 This is a schematic diagram of a battery pack according to one embodiment of this application.

[0052] Figure 10 yes Figure 9 An exploded view of a battery pack according to one embodiment of this application is shown.

[0053] Figure 11 This is a schematic diagram of a battery device used as a power source according to an embodiment of this application.

[0054] Figure 12 This is a schematic diagram of the negative electrode sheet in Embodiment 1 of this application before formation.

[0055] Figure 13 This is a schematic diagram of the negative electrode sheet in the fully charged state after formation in Embodiment 1 of this application.

[0056] Explanation of reference numerals in the attached figures:

[0057] Positive electrode 10; separator 20; negative electrode 30; positive electrode corner region 10a; negative electrode corner region 30a; negative electrode current collector 301; first convex surface 302; first concave surface 303; first negative electrode active material layer 304; second negative electrode active material layer 305; first lithium film 306; second lithium film 307; positive electrode current collector 101; second convex surface 102; second concave surface 103; first positive electrode active material layer 104; second positive electrode active material layer 105; 1 battery pack; 2 first housing; 3 second housing; 4 battery module; 5 battery cell; 51 casing; 52 electrode assembly; 53 top cover assembly. Detailed Implementation

[0058] The following detailed description, with appropriate reference to the accompanying drawings, discloses embodiments of the battery cell, its preparation method, battery device, and power-consuming device of this application. However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of practically identical structures may be omitted. This is to avoid unnecessarily lengthy descriptions and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided for the purpose of enabling those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0059] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a specific parameter, it is expected that ranges of 60-110 and 80-120 are also included. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, unless otherwise stated, the numerical range "ab" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been listed in this article; "0-5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0060] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0061] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0062] Unless otherwise specified, all steps of this application may be performed sequentially or randomly, preferably sequentially. For example, if the method includes steps (a) and (b), it means that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, if the method may also include step (c), it means that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0063] Unless otherwise specified, the terms used in this application have the common meanings as commonly understood by those skilled in the art.

[0064] Unless otherwise specified, the values ​​of the parameters mentioned in this application can be determined using various testing methods commonly used in the art, for example, according to the testing methods given in this application.

[0065] With the application and promotion of rechargeable batteries, people have increasingly higher requirements for their cycle performance. Currently, to improve the cycle performance of rechargeable batteries, a double-sided lithium-filled negative electrode scheme is commonly used. The surface hardness of the double-sided lithium-filled negative electrode sheet is increased on both sides compared to the unfilled negative electrode sheet. For wound cells, during hot pressing and shaping, the outer side of the negative electrode sheet in the corner area (i.e.,...) Figure 2 The first convex surface 302 in the middle will be subjected to an outward expansion force. At this time, the outer side of the negative electrode sheet has high hardness, which can suppress the outward expansion and is conducive to reducing the gap between the electrodes. However, during hot pressing and shaping, the inner side of the negative electrode sheet in the corner area (i.e., Figure 2 The first concave surface 303 in the middle will be subjected to a force that shrinks into the electrode assembly. If the hardness of the inner side of the negative electrode in the corner area increases, it will hinder the adhesion between adjacent electrodes, resulting in a larger gap between electrodes.

[0066] Furthermore, during charging, the wound cell expands along its width, subjecting the negative electrode at the corners to significant tensile force. Due to the increased hardness of the double-sided lithium-filled negative electrode, significant plastic deformation easily occurs at the corners. During discharge, this deformation cannot be fully recovered, leading to increasingly larger gaps between the electrodes at the corners, with the gaps widening further towards the outer ring of the wound cell. This increased gap causes lithium ions to accumulate at the tangents of the large surfaces and corners, resulting in lithium plating. Additionally, as cycling progresses, a large amount of electrolyte is consumed, and later, the electrolyte cannot fill areas with large gaps, leading to ion bridging at the outer corners of the wound cell. This results in substantial lithium plating at the corners, negatively impacting the cycle performance of the secondary battery.

[0067] In related technologies, the problem of excessively large gaps at the corners of negative electrode sheets in double-sided lithium replenishment is improved by reducing the gaps between each layer of electrode sheets. However, this will also reduce the gaps in the large areas of the cell. The reduction in gaps in the large areas will lead to uneven stress distribution inside the cell, affecting battery performance and lifespan.

[0068] Based on this, this application proposes a novel battery cell and its preparation method, battery device, and power-consuming device. The battery cell in this application has improved cycle performance. The following provides a more detailed description of this application and its optional embodiments.

[0069] battery cell

[0070] The first aspect of this application provides a battery cell, which includes an electrode assembly formed by bending and winding a stack of positive electrode, separator, and negative electrode along a winding axis. The negative electrode includes a negative current collector and a negative electrode film layer located on the surface of the negative current collector. The negative current collector includes a first convex surface and a first concave surface. The negative electrode film layer includes a first negative active material layer located on one side of the first convex surface, a first lithium film located on the surface of the first negative active layer, and a second negative active material layer located on one side of the first concave surface. The first lithium film is striped.

[0071] In this application, a first lithium film is disposed on the surface of the first negative electrode active material layer on the first convex side of the negative electrode current collector. The first lithium film increases the hardness of the convex surface of the negative electrode sheet, thereby suppressing the outward expansion of the corner region through the convex surface of the negative electrode sheet. This reduces the gap between the electrodes in the corner region, which is beneficial to improving the cycle performance of the battery cell. In addition, the first lithium film is striped, which on the one hand allows the lithium film to participate more fully in the reaction, which is beneficial to improving the lithium utilization rate and lithium replenishment efficiency, thus benefiting the cycle performance of the battery cell. On the other hand, the area between adjacent stripes can serve as a wetting channel for the electrolyte and a gas transport channel during high-temperature aging and formation, further benefiting the cycle performance of the battery cell.

[0072] In this application, a laminate of a positive electrode, a separator, and a negative electrode is bent and wound along a winding axis to form an electrode assembly. The first convex surface of the negative electrode current collector refers to the side of the negative electrode current collector facing away from the winding axis in the electrode assembly, and the first concave surface of the negative electrode current collector refers to the side of the negative electrode current collector close to the winding axis in the electrode assembly. That is, the first negative electrode active material layer is located on the side of the negative electrode current collector facing away from the winding axis, and the second negative electrode active material layer is located on the side of the negative electrode current collector close to the winding axis.

[0073] In some embodiments, the negative electrode film layer further includes a striped second lithium film located on the surface of the second negative electrode active material layer; based on the total mass of the first lithium film and the second lithium film, the mass ratio of the first lithium film in the total mass is greater than that of the second lithium film. In this application, by setting the first lithium film and the second lithium film with different mass ratios on both sides of the negative electrode sheet, and making the mass of the first lithium film located on the convex surface of the negative electrode current collector greater than that of the second lithium film located on the concave surface of the negative electrode current collector, compared with the lithium film being evenly distributed on the convex and concave surfaces, this arrangement has the lithium film mainly located on the convex surface of the negative electrode current collector. Therefore, the concave surface of the negative electrode sheet has lower hardness and better flexibility, making the adjacent electrode sheets in the corner area fit more tightly during the hot pressing process, thereby making the gap between the electrode sheets at the corner smaller. In addition, the convex surface of the negative electrode sheet has higher hardness, which can suppress the outward expansion of the corner area, thus helping to further improve the cycle performance of the battery cell.

[0074] Figure 1 This is a schematic diagram of the structure of an electrode assembly provided in one embodiment of this application, as shown below. Figure 1 As shown, the electrode assembly 52 is formed by bending and winding a laminate of a positive electrode 10, a separator 20, and a negative electrode 30. Figure 1 The negative electrode corner region 30a and the positive electrode corner region 10a are also shown. Figure 2 and Figure 3 for Figure 1 An enlarged structural diagram of the negative electrode corner region 30a is shown below. Figure 2 and 3 As shown, the negative electrode sheet includes a negative current collector 301 and a negative electrode film layer on the surface of the negative current collector 301; the negative current collector 301 includes a first convex surface 302 and a first concave surface 303, and the negative electrode film layer includes a first negative electrode active material layer 304 located on one side of the first convex surface 302, a first lithium film 306 located on the surface of the first negative electrode active material layer 304, and a second negative electrode active material layer 305 located on the first concave surface 303. The first lithium film 306 is striped on the surface of the first negative electrode active material layer 304, such as... Figure 3 As shown, the negative electrode film layer also includes a second lithium film 307 located on the surface of the second negative electrode active material layer 305, and the second lithium film 307 is striped on the surface of the second negative electrode active material layer 305.

[0075] In some embodiments, the first lithium film accounts for more than 50% of the total mass, and the second lithium film accounts for less than 50% of the total mass.

[0076] In some embodiments, the first lithium film accounts for 70% or more and less than 100% of the total mass. Optionally, the first lithium film accounts for 70% to 97.4% of the total mass. When the first lithium film accounts for a mass percentage within this range, the convex negative electrode sheet is harder than the concave negative electrode sheet, which is more beneficial for improving the cycle life of the battery cell. For example, the first lithium film accounts for 70%, 75%, 80%, 85%, 90%, 95%, 97.4%, 98%, 99%, or any value within a range of two such values.

[0077] In some embodiments, the second lithium film accounts for a mass percentage of greater than 0 and less than or equal to 30% of the total mass. Optionally, the mass percentage of the second lithium film in the total mass is 2.6% to 30%. When the mass percentage of the second lithium film in the total mass is within the above range, the concave surface of the negative electrode sheet has less hardness and greater flexibility than the convex surface, resulting in a tighter fit between adjacent electrodes in the corner area. This is more conducive to improving the cycle performance of the battery cell. For example, the mass percentage of the second lithium film in the total mass is 1%, 2%, 2.6%, 3%, 5%, 10%, 15%, 20%, 25%, 30%, or a value within a range of any two values.

[0078] In some embodiments, the content of the first lithium film in the negative electrode film layer is 0.5 mg / 1540.25 mm. 2 ~12mg / 1540.25mm 2 Optionally, it is 3.0 mg / 1540.25 mm. 2 ~4.0mg / 1540.25mm 2 The content of the first lithium film is within the aforementioned range, ensuring that the hardness of the convex surface of the negative electrode sheet is within a suitable range. This, in turn, keeps the plastic deformation of the electrode assembly within a suitable range during hot pressing, preventing the gap between the electrodes at the corners from widening, thus benefiting the cycle performance of the battery cell. For example, in the negative electrode film layer, the content of the first lithium film is 0.5 mg / 1540.25 mm. 2 1.0mg / 1540.25mm 2 2.0mg / 1540.25mm 2 3.0mg / 1540.25mm 2 4.0mg / 1540.25mm 2 5.0mg / 1540.25mm 2 6.0mg / 1540.25mm 2 8.0mg / 1540.25mm 2 10.0mg / 1540.25mm 2 12.0mg / 1540.25mm 2 Or the value between any two values ​​within a range.

[0079] In some embodiments, the content of the second lithium film in the negative electrode film layer is 0.05 mg / 1540.25 mm. 2 ~0.2mg / 1540.25mm 2 Optionally, it is 0.05 mg / 1540.25 mm. 2 ~0.1mg / 1540.25mm 2The content of the second lithium film within the aforementioned range ensures that the hardness of the concave surface of the negative electrode is within a suitable range. This facilitates the hot-pressing process of the electrode assembly, resulting in tighter electrode adhesion and smaller electrode gaps, which is beneficial to the cycle performance of the battery cell. For example, in the negative electrode film layer, the content of the second lithium film is 0.05 mg / 1540.25 mm. 2 0.06mg / 1540.25mm 2 0.07mg / 1540.25mm 2 0.08mg / 1540.25mm 2 0.09mg / 1540.25mm 2 0.1mg / 1540.25mm 2 0.12mg / 1540.25mm 2 0.15mg / 1540.25mm 2 0.18mg / 1540.25mm 2 0.2mg / 1540.25mm 2 Or the value between any two values ​​within a range.

[0080] In some embodiments, both the first lithium film and the second lithium film comprise multiple wavy lithium metal strips. Here, "wavy" lithium metal strips refer to lithium metal strips that resemble an S-shape.

[0081] In some embodiments, multiple lithium metal strips are arranged at intervals in both a first direction and a second direction; the first direction is the extension direction of the winding shaft, and the second direction is a direction perpendicular to the first direction within the plane containing the negative electrode sheet. Because the lithium metal strips are arranged at intervals in both the first and second directions, the area between adjacent lithium metal strips can serve as a wetting channel for the electrolyte, which is beneficial for improving the wetting rate of the negative electrode sheet to the electrolyte, thereby further improving the cycle performance of the battery cell. In addition, the area between adjacent lithium metal strips can also serve as a gas transport channel during high-temperature aging and formation processes, i.e., it can serve as a heat diffusion channel, which is beneficial for improving the charge-discharge efficiency and cycle performance of the battery cell.

[0082] Figure 4 This is a schematic diagram of the negative electrode sheet according to one embodiment of this application, as shown below. Figure 4 As shown, lithium metal strips are arranged at intervals along the first and second directions in the negative electrode sheet.

[0083] In some embodiments, the thickness of the lithium metal strip is 2 μm to 8 μm, optionally 3 μm to 5 μm. Setting the thickness of the lithium metal strip within this range is beneficial for improving the capacity and cycle performance of the battery cell. For example, the thickness of the lithium metal strip is 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, or any value within a range of two such values.

[0084] In some embodiments, the spacing between adjacent lithium metal strips along the first or second direction is 1000 μm to 2000 μm, optionally 1000 μm to 1500 μm. A spacing within this range allows sufficient channels for high-temperature aging and formation gas generation, and facilitates the formation of an electrolyte wetting network, further improving the charge-discharge efficiency and cycle performance of the battery cell. For example, the spacing between adjacent lithium metal strips can be 1000 μm, 1200 μm, 1400 μm, 1500 μm, 1600 μm, 1800 μm, 2000 μm, or any value within a range of two such values.

[0085] In some embodiments, the lithium metal strip has a dimension of 2 mm to 20 mm along the first direction; and / or, the lithium metal strip has a dimension of 200 μm to 2000 μm along the second direction. Dimensions of the lithium metal strip along the second or first direction within the aforementioned ranges can further provide sufficient channels for high-temperature aging and formation gas generation, and can form an electrolyte wetting network, further benefiting the charge-discharge efficiency and cycle performance of the battery cell. For example, the dimension of the lithium metal strip along the first direction is 2 mm, 4 mm, 6 mm, 8 mm, 10 mm, 12 mm, 14 mm, 16 mm, 18 mm, 20 mm, or any value within a range of two such values. For example, the dimension of the lithium metal strip along the second direction is 200 μm, 400 μm, 600 μm, 800 μm, 1000 μm, 1200 μm, 1400 μm, 1600 μm, 1800 μm, 2000 μm, or any value within a range of two such values.

[0086] In some embodiments, the area of ​​the lithium metal strip on the surface of the first negative electrode active material layer accounts for 10% to 50% of the total area of ​​the first negative electrode active material layer. This ensures that the content of the first lithium film is within a suitable range, thereby ensuring that the lithium replenishment amount and the hardness of the negative electrode convex surface are within a suitable range, which is beneficial for achieving both excellent lithium replenishment effect and cycle performance. For example, the area of ​​the lithium metal strip on the surface of the first negative electrode active material layer accounts for 10%, 20%, 30%, 40%, 50% of the total area of ​​the first negative electrode active material layer, or a value within a range consisting of any two of these values.

[0087] In some embodiments, the area of ​​the lithium metal strip on the surface of the second negative electrode active material layer accounts for 0.5% to 10% of the total area of ​​the second negative electrode active material layer. This ensures that the content of the second lithium film is within a suitable range, thereby ensuring that the lithium replenishment amount and the hardness of the concave surface of the negative electrode are within a suitable range, which is beneficial for achieving both excellent lithium replenishment effect and cycle performance. For example, the area of ​​the lithium metal strip on the surface of the second negative electrode active material layer accounts for 0.5%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10% of the total area of ​​the second negative electrode active material layer, or a value within a range of any two values.

[0088] In this application, since the lithium metal strips are arranged at intervals in both the first and second directions, the first and second lithium films can be reversed by the morphology of the interval arrangement. In addition, during the charging and discharging process, the lithium metal strips are oxidized to lithium oxide. Therefore, the first and second lithium films can be reversed by measuring the lithium oxide through XRD testing.

[0089] In some embodiments, the coating weight of the first negative electrode active material layer is greater than the coating weight of the second negative electrode active material layer. In this application, since the mass percentage of the first lithium film on the surface of the first negative electrode active material layer is greater than the mass percentage of the second lithium film on the surface of the second active material layer, the first active material layer requires a larger lithium intercalation space. By setting the coating weight of the first negative electrode active material layer to be greater than the coating weight of the second negative electrode active material layer, sufficient space can be provided for the intercalation of cathode lithium, thereby benefiting the cycle performance of the battery cell.

[0090] In some embodiments, the coating weight CW1 of the first negative electrode active material and the coating weight CW2 of the second negative electrode active material layer satisfy the condition: 1 < CW1 / CW2 ≤ 3.4. By controlling CW1 / CW2 within the above range, both the first and second negative electrode active material layers can provide a suitable space for lithium insertion into the cathode, which is beneficial to further improve the cycle performance of the battery cell. For example, CW1 / CW2 is a value between 1.1, 1.2, 1.4, 1.6, 1.8, 2.0, 2.2, 2.4, 2.6, 2.8, 3, 3.2, 3.4, or any two of these values.

[0091] In some embodiments, the coating weight of the first negative electrode active material layer is 50 mg / 1540.25 mm. 2 ~170mg / 1540.25mm 2 Optionally, it is 140mg / 1540.25mm. 2 ~160mg / 1540.25mm 2The coating weight of the first negative electrode active material layer is within the aforementioned range, which allows for complete lithium insertion into the cathode opposite the first negative electrode active material layer, thus balancing the cycle performance and energy density of the battery cell. For example, the coating weight of the first negative electrode active material layer is 50 mg / 1540.25 mm². 2 80mg / 1540.25mm 2 100mg / 1540.25mm 2 120mg / 1540.25mm 2 150mg / 1540.25mm 2 160mg / 1540.25mm 2 170mg / 1540.25mm 2 Or the value between any two values ​​within a range.

[0092] In some embodiments, the coating weight of the second negative electrode active material layer is 45 mg / 1540.25 mm. 2 ~140mg / 1540.25mm 2 The coating weight of the second negative electrode active material layer is within the aforementioned range, which allows for complete lithium insertion into the cathode opposite the second negative electrode active material layer, thus balancing the cycle performance and energy density of the battery cell. For example, the coating weight of the second negative electrode active material layer is 45 mg / 1540.25 mm². 2 50mg / 1540.25mm 2 60mg / 1540.25mm 2 70mg / 1540.25mm 2 80mg / 1540.25mm 2 90mg / 1540.25mm 2 100mg / 1540.25mm 2 110mg / 1540.25mm 2 120mg / 1540.25mm 2 140mg / 1540.25mm 2 Or the value between any two values ​​within a range.

[0093] In some embodiments, since the first lithium film is consumed during charging and discharging, the amount of lithium oxide remaining on the surface of the first negative electrode active material layer is small. Therefore, the coating weight of the first negative electrode active material layer can be reversed in the following way: disassemble the battery cell, obtain the negative electrode sheet, wipe off the second negative electrode active material layer, and then measure the weight W1 of the negative electrode sheet. The weight of the first negative electrode active material layer is W1 minus the weight of the negative electrode current collector.

[0094] In some embodiments, the compaction density of the negative electrode sheet is 1.45 g / cm³. 3 ~1.7g / cm 3 This is beneficial for improving the energy density of individual battery cells. For example, the compaction density of the negative electrode sheet is 1.45 g / cm³. 3 1.5g / cm 3 1.55g / cm 3 1.6g / cm 3 1.65g / cm 3 1.7g / cm 3 Or the value between any two values ​​within a range.

[0095] In some embodiments, both the first and second negative electrode active material layers include a negative electrode material, which includes a carbon material, optionally including graphite. Graphite material has isotropic characteristics, which is beneficial for the rapid insertion of lithium ions, can reduce lithium plating, and is conducive to improving the cycle performance of the battery cell.

[0096] In some embodiments, since the second lithium film is consumed during charging and discharging, the amount of lithium oxide remaining on the surface of the second negative electrode active material layer is small. Therefore, the coating weight of the second negative electrode active material layer can be reversed in the following way: disassemble the battery cell, obtain the negative electrode sheet, wipe off the first negative electrode active material layer, and then measure the weight W2 of the negative electrode sheet. The weight of the first negative electrode active material layer is W2 minus the weight of the negative electrode current collector.

[0097] In some embodiments, the positive electrode sheet includes a positive current collector and a positive electrode film layer located on the surface of the positive current collector. The positive current collector includes a second convex surface and a second concave surface. The positive electrode film layer includes a first positive active material layer located on one side of the second convex surface and a second positive active material layer located on one side of the second concave surface. In this application, in the electrode assembly, the second positive active material layer is opposite to the first negative active material layer, and the first positive active material layer is opposite to the second negative active material layer. Since the coating weight of the first negative active material layer is greater than the coating weight of the second negative active material layer, by taking into account the relationship between the coating weights of the first and second negative active material layers, setting the coating weight of the second positive active material layer to be greater than that of the first positive active material layer can further improve the lithium replenishment effect, which is beneficial to the energy density and cycle performance of the battery cell.

[0098] Figure 5 for Figure 1 An enlarged structural diagram of the positive electrode corner region 10a is shown below. Figure 5As shown, the positive electrode includes a positive current collector 101 and a positive electrode film layer located on the surface of the positive current collector 101. The positive current collector 101 has a second convex surface 102 and a second concave surface 103 at the bend of the electrode assembly. The positive electrode film layer includes a first positive electrode active material layer 104 located on the second convex surface 102 and a second positive electrode active material layer 105 located on the second concave surface 103.

[0099] In some embodiments, the coating weight of the second positive electrode active material layer is 100 mg / 1540.25 mm. 2 ~340mg / 1540.25mm 2 The coating weight of the second positive electrode active material layer within the above-mentioned range can improve the lithium replenishment effect, which is beneficial to the energy density and cycle performance of the battery cell. For example, the coating weight of the second positive electrode active material layer is 100 mg / 1540.25 mm². 2 120mg / 1540.25mm 2 150mg / 1540.25mm 2 180mg / 1540.25mm 2 200mg / 1540.25mm 2 250mg / 1540.25mm 2 300mg / 1540.25mm 2 340mg / 1540.25mm 2 The value between any two values, or the range between any two values.

[0100] In some embodiments, the coating weight of the first positive electrode active material layer is 100 mg / 1540.25 mm. 2 ~260mg / 1540.25mm 2 The coating weight of the first positive electrode active material layer within the above-mentioned range can improve the lithium replenishment effect, which is beneficial to the energy density and cycle performance of the battery cell. For example, the coating weight of the first positive electrode active material layer is 100 mg / 1540.25 mm². 2 120mg / 1540.25mm 2 150mg / 1540.25mm 2 180mg / 1540.25mm 2 200mg / 1540.25mm 2 220mg / 1540.25mm 2 240mg / 1540.25mm 2 260mg / 1540.25mm 2 Or the value between any two values ​​within a range.

[0101] In some implementations, the coating weight of the first positive electrode active material layer can be reversed by disassembling the battery cell, obtaining the positive electrode sheet, wiping away the second positive electrode active material layer, and then measuring the weight W3 of the positive electrode sheet. The weight of the first positive electrode active material layer is W3 minus the weight of the positive electrode current collector.

[0102] In some embodiments, the coating weight of the second positive electrode active material layer can be reversed by disassembling the battery cell, obtaining the positive electrode sheet, wiping away the first positive electrode active material layer, and then measuring the weight W4 of the positive electrode sheet. The weight of the second positive electrode active material layer is W4 minus the weight of the positive electrode current collector.

[0103] In some embodiments, the compaction density of the positive electrode sheet is 2.4 g / cm³. 3 ~2.8g / cm 3 This is beneficial for improving the energy density of individual battery cells. For example, the compaction density of the positive electrode sheet is 2.4 g / cm³. 3 2.5g / cm 3 2.6g / cm 3 2.7g / cm 3 2.8g / cm 3 Or the value between any two values ​​within a range.

[0104] In some implementations, the battery cell can be a secondary battery. A battery cell refers to a battery cell that can be recharged after being discharged to activate the active materials and continue to be used.

[0105] For example, the battery cell can be a lithium-ion battery, sodium-ion battery, sodium-lithium-ion battery, lithium metal battery, sodium metal battery, lithium-sulfur battery, magnesium-ion battery, nickel-metal hydride battery, nickel-cadmium battery, lead-acid battery, etc., and the embodiments of this application are not limited to this.

[0106] In some embodiments, a battery cell includes a casing and electrode assemblies. The casing is the outer protective shell of the battery cell, and has an internal cavity for encapsulating components such as the electrode assemblies and electrolyte. The casing can be made of steel, aluminum, plastic (such as polypropylene), composite metal (such as copper-aluminum composite shell), or aluminum-plastic film, etc.

[0107] In some embodiments, the electrode assembly is the component within the battery cell where electrochemical reactions occur. The electrode assembly is typically stacked along the thickness direction (stack direction) of the battery cell. The electrode assembly includes a positive electrode, a negative electrode, and a separator. During the charging and discharging process of the battery cell, active ions (e.g., lithium ions) repeatedly insert and extract between the positive and negative electrode plates. The separator, positioned between the positive and negative electrode plates, prevents short circuits while allowing active ions to pass through.

[0108] In some embodiments, the positive electrode sheet may include a positive current collector and a positive active material disposed on at least one surface of the positive current collector.

[0109] As an example, the positive current collector has two surfaces opposite each other in its own thickness direction, and the positive active material is disposed on either or both of the two opposite surfaces of the positive current collector.

[0110] As an example, the positive electrode current collector can be a metal foil or a composite current collector. For example, as a metal foil, silver-treated aluminum or stainless steel, copper, nickel, or titanium can be used. The composite current collector may include a polymer material base layer and a metal layer. The composite current collector can be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene, polyethylene terephthalate, polybutylene terephthalate, polystyrene, polyethylene, etc.).

[0111] As an example, the positive electrode active material may include at least one of the following materials: lithium phosphate, lithium transition metal oxide, and their respective modified compounds. However, this disclosure is not limited to these materials, and other conventional materials that can be used as positive electrode active materials for batteries may also be used. These positive electrode active materials may be used alone or in combination of two or more. Examples of lithium phosphate include, but are not limited to, at least one of lithium iron phosphate (such as LiFePO4 (also referred to as LFP)), lithium iron phosphate and carbon composites, lithium manganese phosphate (such as LiMnPO4), lithium manganese phosphate and carbon composites, lithium manganese iron phosphate, and lithium manganese iron phosphate and carbon composites.

[0112] In this application, the battery undergoes Li insertion / extraction and consumption during charging and discharging, resulting in different molar Li content at different discharge states. In the examples of positive electrode active materials in this application, the molar Li content refers to the initial state of the material, i.e., the state before material addition. When the positive electrode active material is applied to the battery system, the molar Li content changes after charge-discharge cycles.

[0113] In the examples of positive electrode active materials in this application, the molar content of O is only a theoretical value. Oxygen release from the crystal lattice will cause changes in the molar content of oxygen, and the actual molar content of O will fluctuate.

[0114] In some embodiments, the negative electrode sheet may include a negative current collector and a negative active material disposed on at least one surface of the negative current collector.

[0115] As an example, the negative electrode current collector has two surfaces opposite each other in its own thickness direction, and the negative electrode active material is disposed on either or both of the two opposite surfaces of the negative electrode current collector.

[0116] In some embodiments, the negative electrode active material may be a negative electrode active material known in the art for use in batteries. As examples, the negative electrode active material includes one or more of graphite, soft carbon, hard carbon, silicon-based materials, selenium-based materials, and lithium titanate. Silicon-based materials may be selected from at least one of elemental silicon, silicon oxides, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. Selenium-based materials may be selected from at least one of elemental selenium, selenium oxides, and selenium alloys. However, this application is not limited to these materials, and other conventional materials that can be used as negative electrode active materials for batteries may also be used. These negative electrode active materials may be used alone or in combination of two or more.

[0117] In some implementations, the negative electrode may include a negative current collector.

[0118] As an example, the negative electrode current collector can be a metal foil, a foamed metal, or a composite current collector. For example, as a metal foil, it can be silver-treated aluminum or stainless steel, copper, nickel, carbon, or titanium. The composite current collector may include a polymer base layer and a metal layer. The foamed metal can be foamed nickel, foamed copper, foamed aluminum, or foamed alloys. The composite current collector can be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy, etc.) on a polymer base material (such as a base material of polypropylene, polyethylene terephthalate, polybutylene terephthalate, polystyrene, polyethylene, etc.). In some embodiments, the positive electrode current collector can be made of aluminum, and the negative electrode current collector can be made of copper.

[0119] In some embodiments, the electrode assembly is a wound structure. The positive electrode and the negative electrode are wound into a wound structure.

[0120] In some implementations, the electrode assembly is a stacked structure.

[0121] As an example, multiple positive and negative electrode plates can be set, and multiple positive and multiple negative electrode plates can be stacked alternately.

[0122] As an example, multiple positive electrode sheets can be set, and negative electrode sheets are folded to form multiple stacked folded segments, with a positive electrode sheet sandwiched between adjacent folded segments.

[0123] As an example, both the positive and negative electrode sheets are folded to form multiple stacked folded segments.

[0124] As an example, multiple separators can be provided, each positioned between any adjacent positive or negative electrode plates.

[0125] As an example, the separator can be continuously installed between any adjacent positive or negative electrode plates by folding or rolling.

[0126] In some embodiments, the electrode assembly is provided with tabs that can either draw current from or introduce current into the electrode assembly. The tabs include positive and negative tabs.

[0127] In some embodiments, the battery cell may include an outer packaging. This outer packaging can be used to encapsulate the electrode assembly and electrolyte described above.

[0128] In some embodiments, the outer packaging of the battery cell can be a rigid shell, such as a hard plastic shell, an aluminum shell, or a steel shell. The outer packaging of the battery cell can also be a flexible package, such as a pouch. The material of the flexible package can be plastic; examples of plastics include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0129] This application does not impose any particular limitation on the shape of the battery cell; it can be cylindrical, square, or any other arbitrary shape. For example, Figure 6 The example shown is a square-structured battery cell 5.

[0130] In some implementations, refer to Figure 7 The outer packaging may include a housing 51 and a top cover assembly 53. The housing 51 may include a base plate and side plates connected to the base plate, the base plate and side plates forming a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the top cover assembly 53 can be placed over the opening to close the receiving cavity. The positive electrode sheet, negative electrode sheet, and separator may be formed into an electrode assembly 52 by a winding process or a stacking process. The electrode assembly 52 is encapsulated within the receiving cavity. Electrolyte is immersed in the electrode assembly 52. ​​The number of electrode assemblies 52 contained in the battery cell 5 may be one or more, which can be selected by those skilled in the art according to specific practical needs.

[0131] Preparation method of battery cell

[0132] The second aspect of this application provides a method for preparing a battery cell, comprising the following steps: S1, forming a first negative electrode active material layer and a second negative electrode active material layer on two opposing surfaces of a negative electrode current collector; S2, forming a first lithium film by pressing molten lithium metal; S3, transferring the first lithium film to the surface of the first negative electrode active material layer by transfer coating, and forming a negative electrode sheet by roll forming; S4, forming an electrode assembly by bending and winding a laminate of a positive electrode sheet, a separator, and a negative electrode sheet along a winding axis, wherein the negative electrode current collector includes a first convex surface and a first concave surface, the first negative electrode active material layer is located on one side of the first convex surface, and the second negative electrode active material layer is located on one side of the first concave surface, wherein the first lithium film is striped.

[0133] In the battery cell formed in this application, the first lithium film on the convex surface of the negative electrode sheet increases the hardness of the convex surface, thereby suppressing the outward expansion of the corner region. This reduces the gap between the electrodes in the corner region, which is beneficial to improving the cycle performance of the battery cell. The first lithium film is striped, which allows the lithium film to participate more fully in the reaction, improving lithium utilization and replenishment efficiency, thus benefiting the cycle performance of the battery cell. Furthermore, the area between adjacent stripes can serve as a wetting channel for the electrolyte and a gas transport channel during high-temperature aging and formation, further improving the cycle performance of the battery cell.

[0134] In some embodiments, step S2 further includes forming a second lithium film, and step S3 further includes transferring the second lithium film onto the surface of the second negative electrode active material layer by means of transfer coating; the second lithium film is striped.

[0135] In some embodiments, based on the total mass of the first lithium film and the second lithium film, the mass percentage of the first lithium film in the total mass is greater than that of the second lithium film. By making the mass percentage of the first lithium film located on the convex surface of the negative electrode current collector greater than that of the second lithium film located on the concave surface of the negative electrode current collector, the hardness of the convex surface of the negative electrode sheet can be increased, and the hardness of the concave surface can be decreased. This results in a tighter fit between adjacent electrodes in the corner area during hot pressing and shaping, and also suppresses the outward expansion of the corner area during cycling, which is beneficial to the cycle performance of the battery cell.

[0136] In some embodiments, both the first lithium film and the second lithium film include multiple wavy lithium metal strips, which are spaced apart along a first direction and a second direction on the surfaces of the first and second negative electrode active material layers. The first direction is the extension direction of the winding shaft, and the second direction is a direction perpendicular to the first direction within the plane of the negative electrode sheet. Thus, the area between adjacent lithium metal strips can serve as a wetting channel for the electrolyte, which is beneficial for increasing the wetting rate of the negative electrode sheet to the electrolyte, thereby further improving the cycle performance of the battery cell. In addition, the area between adjacent lithium metal strips can also serve as a gas transport channel during high-temperature aging and formation processes, i.e., a heat diffusion channel, which is beneficial for improving the charge-discharge efficiency and cycle performance of the battery cell.

[0137] In some embodiments, the rolling pressure in step S3 is 60T to 100T, optionally 70T to 90T. Forming a lithium metal strip under these conditions is beneficial for creating a lithium metal strip with suitable thickness and uniformity, thereby facilitating the acquisition of battery cells with excellent cycle performance. For example, the rolling pressure in step S2 is 60T, 70T, 80T, 90T, 100T, or a value within a range of any two of these values.

[0138] In some embodiments, in step S3, the rolling speed is 20 m / min to 100 m / min, optionally 30 m / min to 50 m / min. Forming the lithium metal strip under these conditions is beneficial for forming a lithium metal strip with suitable thickness and uniformity, thereby facilitating the acquisition of battery cells with excellent cycle performance. Exemplarily, the rolling speed in step S2 is 20 m / min, 30 m / min, 40 m / min, 50 m / min, 60 m / min, 70 m / min, 8 m / min, 90 m / min, 100 m / min, or a value within a range of any two of these values.

[0139] In some embodiments, the coating weight CW1 of the first negative electrode active material and the coating weight CW2 of the second negative electrode active material layer satisfy the condition: 1 < CW1 / CW2 ≤ 3.4. Therefore, both the first and second negative electrode active material layers can provide adequate space for lithium insertion into the cathode, which is beneficial for further improving the cycle performance of the battery cell.

[0140] In some embodiments, the coating weight of the first negative electrode active material layer is 50 mg / 1540.25 mm. 2 ~170mg / 1540.25mm 2 Optionally, it is 140mg / 1540.25mm. 2 ~160mg / 1540.25mm 2This allows for the complete insertion of lithium into the cathode opposite the first negative electrode active material layer, which is beneficial for balancing the cycle performance and energy density of the battery cell.

[0141] In some embodiments, the coating weight of the second negative electrode active material layer is 45 mg / 1540.25 mm. 2 ~140mg / 1540.25mm 2 This allows for the complete embedding of lithium in the cathode opposite the second negative electrode active material layer, which is beneficial for balancing the cycle performance and energy density of the battery cell.

[0142] In some embodiments, the positive current collector includes a second convex surface and a second concave surface. Before step S4, a first positive active material layer located on one side of the second convex surface and a second positive active material layer located on one side of the second convex surface are formed on both sides of the positive current collector. In the electrode assembly, the first positive active material layer is located on the side of the positive current collector away from the winding shaft, and the second positive active material layer is located on the side of the positive current collector close to the winding shaft.

[0143] In some embodiments, the coating weight of the second positive electrode active material layer is greater than that of the first positive electrode active material layer. This can further improve the lithium replenishment effect, which is beneficial to the energy density and cycle performance of the battery cell.

[0144] In some embodiments, the coating weight of the second positive electrode active material layer is 100 mg / 1540.25 mm. 2 ~340mg / 1540.25mm 2 This can improve the lithium replenishment effect, which is beneficial to the energy density and cycle performance of the battery cells.

[0145] In some embodiments, the coating weight of the first positive electrode active material layer is 100 mg / 1540.25 mm. 2 ~260mg / 1540.25mm 2 This can improve the lithium replenishment effect, which is beneficial to the energy density and cycle performance of the battery cells.

[0146] Battery device

[0147] A third aspect of this application provides a battery device. The battery device in this application may include one or more battery cell assemblies for providing voltage and capacity. The battery cell assembly may include multiple battery cells provided in the first aspect, and the multiple battery cells are connected in series, parallel, or mixed connections via a busbar.

[0148] In some implementations, a battery cell assembly is typically formed by arranging multiple battery cells.

[0149] As an example, a battery cell assembly can be a battery module, which is formed by arranging and fixing multiple battery cells together to form an independent module. As another example, a battery module can be formed by bundling multiple battery cells together with cable ties.

[0150] As an example, the battery cell assembly can be a battery module, which can be housed in a housing by fixing the battery module in the housing.

[0151] As an example, battery cell assemblies can also be housed in a housing by directly fixing multiple battery cells to the housing.

[0152] As an example, the enclosure may include a first enclosure and a second enclosure. The first enclosure and the second enclosure are fastened together to form a closed space inside the enclosure to house the individual battery cells. Here, "closed" refers to covering or closing, and can be either sealed or unsealed. The first enclosure may be a top cover or a bottom plate.

[0153] As an example, the enclosure may include a top cover, a frame, and a bottom plate. The top cover and bottom plate are connected to the frame, creating an enclosed space inside the enclosure to house the individual battery cells.

[0154] In some implementations, the housing may be part of the vehicle's chassis structure. For example, a portion of the housing may be at least a part of the vehicle's floor, or a portion of the housing may be at least a part of the vehicle's crossbeams and longitudinal beams.

[0155] In some implementations, the battery device may be a battery pack, which includes a housing and one or more individual battery cells housed within the housing.

[0156] The technical solutions described in the embodiments of this application are applicable to various electrical devices that use individual battery cells, such as mobile phones, portable devices, laptops, electric vehicles, electric toys, power tools, vehicles, ships, and spacecraft. For example, spacecraft include airplanes, rockets, space shuttles, and spacecraft.

[0157] Figure 8 This is battery module 4 as an example. (See reference...) Figure 8 In the battery module 4, multiple battery cells 5 can be arranged sequentially along the length of the battery module 4. Of course, they can also be arranged in any other way. Furthermore, these multiple battery cells 5 can be fixed in place using fasteners.

[0158] Optionally, the battery module 4 may also include a housing with a receiving space in which multiple battery cells 5 are received.

[0159] Figure 9 and Figure 10 This is battery pack 1 as an example. (See reference...) Figure 9 and Figure 10 The battery pack 1 may include a battery box and multiple battery modules 4 disposed within the battery box. The battery box includes a first housing 2 and a second housing 3. The first housing 2 can cover the second housing 3 to form a closed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery box.

[0160] Electrical appliances

[0161] A fourth aspect of the embodiments of this application also provides an electrical device, which will be described below with appropriate reference to the accompanying drawings.

[0162] The electrical device mentioned in the embodiments of this application includes the battery device provided in the second aspect of this application. The battery device can be the power source of the electrical device or the energy storage unit of the electrical device. The electrical device may include, but is not limited to, mobile devices (e.g., mobile phones, laptops, etc.), electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc.

[0163] Figure 11 This is an example of an electrical device. The device could be a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the device's requirements for high power and high energy density, a battery pack or battery module can be used.

[0164] Another example device could be a mobile phone, tablet, or laptop. These devices typically require a slim and lightweight design and can use a single battery cell as their power source.

[0165] Example

[0166] The following describes embodiments of this application. The embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all conventional products that can be obtained commercially.

[0167] Example 1

[0168] Preparation of battery cells:

[0169] 1) Preparation of negative electrode sheet

[0170] S1, graphite (negative electrode active material), conductive carbon black (conductive agent), styrene-butadiene rubber (binder), and sodium carboxymethyl cellulose (dispersant) are uniformly mixed in a weight ratio of 96:1:2:1 and dissolved in deionized water to obtain a negative electrode slurry with a solid content of 70%. The negative electrode slurry is coated onto the surface of a 6 μm thick copper foil current collector, and after drying, a first negative electrode active material layer and a second negative electrode active material layer are formed. The first and second negative electrode active material layers constitute the negative electrode film layer; wherein, the coating weight CW1 of the first negative electrode active material layer is 150 mg / 1540.25 mm. 2 The coating weight (CW2) of the second negative electrode active material layer is 120 mg / 1540.25 mm. 2 .

[0171] S2, molten lithium metal is shaped using pressing technology to form a first lithium film composed of multiple lithium metal strips;

[0172] S3, the first lithium film is transferred to the surface of the first negative electrode active material layer by transfer coating, and then rolled and slit to form a negative electrode sheet. The compaction density of the negative electrode sheet at 70t is 1.5g / cm³. 3 The content of the first lithium film in the negative electrode film layer is 3.8 mg / 1540.25 mm. 2 The lithium metal strips in the first lithium film are evenly spaced along the direction of the negative electrode tab and in a direction perpendicular to the direction of the negative electrode tab. The spacing between adjacent lithium metal strips is 1000 μm. The size of the lithium metal strip in the direction of the negative electrode tab (first direction) is 10 mm, and the size of the lithium metal strip in the direction perpendicular to the direction of the negative electrode tab (second direction) is 1200 μm. The thickness of the lithium metal strips is 3 μm. The ratio (σ1) of the area of ​​the lithium metal strips on the surface of the first negative electrode active material layer to the total area of ​​the first negative electrode active material layer is 50%.

[0173] 2) Preparation of positive electrode sheet

[0174] Lithium iron phosphate (LiFePO4), conductive carbon black (COP), and PVDF (PVDF) binder were uniformly mixed in a weight ratio of 97:1:2 and dissolved in N-methylpyrrolidone (NMP) to obtain a positive electrode slurry with a solid content of 53%. This slurry was then coated onto both sides of the positive electrode current collector to form a first and a second positive electrode active material layer. After drying and cold pressing, the positive electrode sheet was obtained. The compacted density of the positive electrode sheet at 80t was 2.55 g / cm³. 3 The coating mass (CW3) of the first positive electrode active material layer is 240 mg / 1540.25 mm. 2The coating mass (CW4) of the second positive electrode active material layer is 310 mg / 1540.25 mm. 2 .

[0175] 3) Separating membrane

[0176] A 5μm thick polypropylene-polypropylene composite membrane was used as the separator.

[0177] 4) Preparation of electrolyte

[0178] Ethylene carbonate, ethyl methyl carbonate, and dimethyl carbonate were mixed in a volume ratio of 1:1:1 to form an organic solvent. Lithium hexafluorophosphate was dissolved in the organic solvent to prepare an electrolyte with a LiPF6 concentration of 1 mol / L.

[0179] S4, an electrode assembly is formed by winding the stack of positive electrode sheet, separator and negative electrode sheet along the winding shaft. In the electrode assembly, the first negative electrode active material layer is located on the convex surface of the negative electrode current collector bending part, the second negative electrode active material layer is located on the concave surface of the negative electrode current collector bending part, the first positive electrode active material layer is located on the convex surface of the positive electrode current collector bending part, and the second positive electrode active material layer is located on the concave surface of the positive electrode current collector bending part.

[0180] Comparative Example 1

[0181] The battery cell was prepared using the same method as in Example 1, except that the first lithium film in the prepared negative electrode sheet was located on the surface of the second negative electrode active material layer, that is, the first lithium film was located on the concave surface of the negative electrode sheet. Please refer to Table 1 below for details.

[0182] Comparative Example 2

[0183] The battery cells were prepared using the same method as in Example 1, except that the first lithium film in the prepared negative electrode was in sheet form, as detailed in Table 1 below.

[0184] Table 1 below shows the relevant parameters of the negative electrode in Example 1 and Comparative Examples 1 and 2.

[0185] Table 1

[0186]

[0187] Negative electrode morphology test

[0188] Figure 12 This is a schematic diagram of the negative electrode sheet in Example 1 before formation, as shown below. Figure 12 As shown, the black layer on the negative electrode sheet is the first negative electrode active material layer, and the white layer is the first lithium film. It can be seen that the first lithium film is striped.

[0189] Figure 13This is a schematic diagram of the negative electrode sheet in Example 1 under the fully charged state after formation. The first lithium film reacts to form lithium ions after formation, but slight striped traces can still be seen in the negative electrode sheet. If observed with a microscope, the stripes will be more obvious.

[0190] Battery cell performance testing

[0191] 1. Cyclic performance test

[0192] At 25°C, the battery cells prepared in Example 1 and Comparative Examples 1 and 2 were subjected to charge-discharge tests according to the following test procedure.

[0193] ① Charge to 3.65V using a 1 / 3C constant current method;

[0194] ② Charge at a constant voltage of 3.65V until the current reaches 0.05C.

[0195] ③ Let it stand for 5 minutes;

[0196] ④ Discharge to 2.5V at 1 / 3C constant current, and record the resulting capacitance as the initial capacitance D0.

[0197] ⑤ Repeat steps ① to ④ above, and record the discharge capacity Dn on the 5000th cycle;

[0198] Capacity retention rate after 5000 cycles (%) = Capacity Dn at the 5000th cycle / Initial capacity D0 * 100%. The test results are shown in Table 2.

[0199] 2. Loop testing

[0200] a. Obtaining the charging window: The battery cells of Example 1 and Comparative Examples 1 and 2 were charged and discharged for the first time at a current of 1C. Specifically, at 25°C, the battery cells were charged at a constant current rate of 0.8C to a voltage of 3.65V, then charged at a constant voltage rate to a current of 0.05C, left to stand for 5 minutes, and then discharged at a constant current rate of 0.33C to a voltage of 2.5V. The actual capacity was recorded as C0.

[0201] b. Charge each battery cell sequentially at constant current rates of 1.0C0, 1.3C0, 1.5C0, 1.8C0, 2.0C0, 2.3C0, 2.5C0, 3.0C0, 3.5C0, 4C0, 4.5C0, and 5C0 until the full battery charging cutoff voltage of 3.65V or the negative terminal cutoff potential of 0V (whichever comes first). After each charge, discharge at 1C0 until the full battery discharge cutoff voltage of 2.5V. Record the corresponding values ​​when charging to 10%, 20%, 30%, ..., 80% SOC at different charging rates. By plotting the charging rate-negative electrode potential curves under different SOC states, and then linearly fitting the curves, we can obtain the charging rate corresponding to the negative electrode potential being 0V under different SOC states. This charging rate is the charging window under that SOC state, denoted as C(10% SOC), C(20% SOC), C(30% SOC), C(40% SOC), C(50% SOC), C(60% SOC), C(70% SOC), and C(80% SOC). This yields the maximum charging rate under the corresponding state of charge, i.e., the fast charging window.

[0202] c. Using the obtained fast charging window, perform step-by-step charging: charge at a constant current rate of C (10% SOC) to 10% SOC, then charge at a constant current rate of C (20% SOC) to 20% SOC, then charge at a constant current rate of C (30% SOC) to 30% SOC, then charge at a constant current rate of C (40% SOC) to 40% SOC, then charge at a constant current rate of C (50% SOC) to 50% SOC, and then... Charge at a constant current rate of C (60% SOC) to 60% SOC, then charge at a constant current rate of C (70% SOC) to 70% SOC, then charge at a constant current rate of C (80% SOC) to 80% SOC, then charge at a constant current rate of 0.33C to 100% SOC. Rest for 10 minutes, then discharge at a rate of 0.33C to 2.5V. Repeat this process and record the number of cycles when the voltage decays to 80% SOC.

[0203] The number of cycles when decaying to 80% SOH is calculated as follows: divide the discharge capacity of the nth cycle by the discharge capacity of the first cycle from smallest to largest, and record the ratios respectively; when the ratio first appears to be equal to or less than 80% SOH, this number of cycles is the number of cycles when decaying to 80% SOH.

[0204] Table 2 below shows the performance parameters of the negative electrode sheet and the cycle performance parameters of the battery cells in Example 1 and Comparative Examples 1 and 2.

[0205] Table 2

[0206]

[0207] As can be seen from Tables 1 and 2, compared with Comparative Example 1 (the lithium strip is disposed on the first concave surface of the negative electrode current collector) and Comparative Example 2 (the lithium strip is sheet-like), the battery cell in Example 1 has a striped lithium strip disposed on one side of the first convex surface of the negative electrode current collector, which significantly improves the cycle performance of the battery cell.

[0208] Example 2

[0209] The battery cell was prepared using the same method as in Example 1, except that the negative electrode sheet was prepared with a striped second lithium film in addition to the lithium film. Step S3 further included transferring the second lithium film onto the surface of the second negative electrode active material layer using a transfer coating method, followed by rolling and slitting to form the negative electrode sheet. The content of the second lithium film in the negative electrode film layer was 0.1 mg / 1540.25 mm. 2 The lithium metal strips in the second lithium film are evenly spaced along the direction of the negative electrode tab and in a direction perpendicular to the direction of the negative electrode tab. The spacing between adjacent lithium metal strips is 1000 μm. The size of the lithium metal strip in the direction of the negative electrode tab (first direction) is 10 mm, and the size of the lithium metal strip in the direction perpendicular to the direction of the negative electrode tab (second direction) is 1200 μm. The thickness of the lithium metal strips is 3 μm. The second lithium film is located on the concave surface of the negative electrode sheet. The ratio (σ2) of the area of ​​the lithium metal strips on the surface of the second negative electrode active material layer to the total area of ​​the second negative electrode active material layer is 5%. The first lithium film accounts for 97.4% of the total mass of the first lithium film and the second lithium film, and the second lithium film accounts for 2.6% of the total mass of the first lithium film and the second lithium film.

[0210] Examples 3 and 4

[0211] The battery cells were prepared using the same method as in Example 1, except that the mass ratio of the first lithium film and the second lithium film in the prepared negative electrode sheet was adjusted according to Table 3 below. For ease of comparison, the relevant parameters from Example 1 are also shown here.

[0212] Table 3

[0213]

[0214] The cycle performance of the battery cells in Examples 2 to 4 was tested using the same test method as in Example 1, and the test results are shown in Table 4 below. For ease of comparison, the relevant parameters from Example 1 are also shown here.

[0215] Table 4

[0216]

[0217] As can be seen from Tables 3 and 4, when the mass percentage of the first lithium film in the lithium film is greater than or equal to 70%, and the mass percentage of the second lithium film in the lithium film is less than or equal to 30%, the cycle performance of the battery cell can be significantly improved.

[0218] Examples 5 and 6

[0219] The battery cells were prepared using the same method as in Example 1, except that the spacing between adjacent lithium metal strips and the dimensions of the lithium metal strips along the first and second directions were adjusted according to Table 5 below. For ease of comparison, the relevant parameters from Example 1 are also shown here.

[0220] Table 5

[0221]

[0222] The cycle performance of the battery cells in Examples 5 and 6 was tested using the same test method as in Example 1, and the test results are shown in Table 6 below. For ease of comparison, the relevant parameters from Example 1 are also shown here.

[0223] Table 6

[0224]

[0225] As can be seen from Tables 5 and 6, by setting the spacing between adjacent lithium metal strips to 1000μm to 2000μm, the size of the lithium metal strip along the first direction to 2mm to 20mm, and the size of the lithium metal strip along the second direction to 200μm to 2000μm, the cycle performance of the battery cell is significantly improved.

[0226] Examples 7 and 8

[0227] The battery cell was prepared using the same method as in Example 1, except that the ratio of the coating weights of the first negative electrode active material and the second negative electrode active material in the negative electrode sheet, CW1 / CW2, was adjusted according to Table 7 below.

[0228] Table 7

[0229]

[0230] The cycle performance of the battery cells in Examples 7 and 8 was tested using the same test method as in Example 1, and the test results are shown in Table 8 below. For ease of comparison, the cycle performance parameters of the battery cells prepared in Example 1 are also shown in Table 8.

[0231] Table 8

[0232]

[0233]

[0234] As can be seen from Tables 7 and 8, by controlling the coating weight CW1 of the first negative electrode active material layer and the coating weight CW2 of the second negative electrode active layer to satisfy: 1 ​​< CW1 / CW2 ≤ 3.4, the cycle performance of the battery cell can be significantly improved.

[0235] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

Claims

1. A battery cell, characterized in that, The electrode assembly comprises a laminate of a positive electrode, a separator, and a negative electrode, which is bent and wound along a winding axis. The negative electrode includes a negative current collector and a negative electrode film layer located on the surface of the negative current collector. The negative current collector includes a first convex surface and a first concave surface. The negative electrode film layer includes a first negative electrode active material layer located on the first convex side, a first lithium film located on the surface of the first negative electrode active layer, and a second negative electrode active material layer located on the first concave side. The first lithium film is striped.

2. The battery cell according to claim 1, characterized in that, The negative electrode film layer also includes a second lithium film located on the surface of the second negative electrode active material layer and in the form of stripes; Based on the total mass of the first lithium film and the second lithium film, the mass percentage of the first lithium film in the total mass is greater than the mass percentage of the second lithium film in the total mass.

3. The battery cell according to claim 2, characterized in that, The first lithium film accounts for more than or equal to 70% and less than 100% of the total mass.

4. The battery cell according to claim 2 or 3, characterized in that, The second lithium film accounts for a mass percentage of the total mass that is greater than 0 and less than or equal to 30%.

5. The battery cell according to any one of claims 2 to 4, characterized in that, In the negative electrode film layer, the content of the first lithium film is 0.5 mg / 1540.25 mm. 2 ~12mg / 1540.25mm 2 .

6. The battery cell according to any one of claims 2 to 5, characterized in that, In the negative electrode film layer, the content of the second lithium film is 0.05 mg / 1540.25 mm. 2 ~0.2mg / 1540.25mm 2 .

7. The battery cell according to any one of claims 2 to 6, characterized in that, Both the first lithium film and the second lithium film include multiple wavy lithium metal strips, and the multiple lithium metal strips are arranged at intervals in the first direction and the second direction. The first direction is the extension direction of the winding shaft, and the second direction is the direction perpendicular to the first direction in the plane where the negative electrode sheet is located.

8. The battery cell according to claim 7, characterized in that, The thickness of the lithium metal strip is 2μm to 8μm.

9. The battery cell according to claim 8, characterized in that, Along the first direction or the second direction, the spacing between adjacent lithium metal strips is 1000μm to 2000μm.

10. The battery cell according to any one of claims 7 to 9, characterized in that, The lithium metal strip has a dimension of 2 mm to 20 mm along the first direction; and / or, the lithium metal strip has a dimension of 200 μm to 2000 μm along the second direction.

11. The battery cell according to any one of claims 7 to 10, characterized in that, The area of ​​the lithium metal strip on the surface of the first negative electrode active material layer accounts for 10% to 50% of the total area of ​​the first negative electrode active material layer.

12. The battery cell according to any one of claims 7 to 11, characterized in that, The area of ​​the lithium metal strip on the surface of the second negative electrode active material layer accounts for 0.5% to 10% of the total area of ​​the second negative electrode active material layer.

13. The battery cell according to any one of claims 1 to 12, characterized in that, The coating weight of the first negative electrode active material layer is greater than the coating weight of the second negative electrode active material layer.

14. The battery cell according to any one of claims 1 to 13, characterized in that, The coating weight CW1 of the first negative electrode active material and the coating weight CW2 of the second negative electrode active material layer satisfy: 1 ​​< CW1 / CW2 ≤ 3.

4.

15. The battery cell according to any one of claims 1 to 14, characterized in that, The coating weight of the first negative electrode active material layer is 50 mg / 1540.25 mm. 2 ~170mg / 1540.25mm 2 .

16. The battery cell according to any one of claims 1 to 15, characterized in that, The coating weight of the second negative electrode active material layer is 45 mg / 1540.25 mm. 2 ~140mg / 1540.25mm 2 .

17. The battery cell according to any one of claims 1 to 16, characterized in that, The compaction density of the negative electrode sheet is 1.45 g / cm³. 3 ~1.7g / cm 3 .

18. The battery cell according to any one of claims 1 to 17, characterized in that, Both the first negative electrode active material layer and the second negative electrode active material layer include a negative electrode material, which includes carbon material.

19. The battery cell according to any one of claims 1 to 18, characterized in that, The positive electrode sheet includes a positive current collector and a positive electrode film layer located on the surface of the positive current collector. The positive current collector includes a second convex surface and a second concave surface. The positive electrode film layer includes a first positive electrode active material layer located on one side of the second convex surface and a second positive electrode active material layer located on one side of the second concave surface. The coating weight of the second positive electrode active material layer is greater than the coating weight of the first positive electrode active material layer.

20. The battery cell according to claim 19, characterized in that, The coating weight of the second positive electrode active material layer is 100 mg / 1540.25 mm. 2 ~340mg / 1540.25mm 2 .

21. The battery cell according to claim 19 or 20, characterized in that, The coating weight of the first positive electrode active material layer is 100 mg / 1540.25 mm. 2 ~260mg / 1540.25mm 2 .

22. A method for preparing a single battery cell, characterized in that, Includes the following steps: S1, a first negative electrode active material layer and a second negative electrode active material layer are formed on the two opposite surfaces of the negative electrode current collector, respectively; S2, Molten lithium metal is shaped using pressing technology to form the first lithium film; S3, the first lithium film is transferred to the surface of the first negative electrode active material layer by transfer coating, and then formed into a negative electrode sheet by roll forming. S4, an electrode assembly is formed by bending and winding the stack of the positive electrode sheet, the separator, and the negative electrode sheet along the winding axis. The negative current collector includes a first convex surface and a first concave surface. The first negative electrode active material layer is located on one side of the first convex surface, and the second negative electrode active material layer is located on one side of the first concave surface. The first lithium film is striped.

23. The preparation method according to claim 22, characterized in that, Step S2 also includes forming a second lithium film; Step S3 further includes transferring the second lithium film onto the surface of the second negative electrode active material layer using a transfer coating method; The second lithium film is striped.

24. The preparation method according to claim 23, characterized in that, Based on the total mass of the first lithium film and the second lithium film, the mass percentage of the first lithium film in the total mass is greater than the mass percentage of the second lithium film in the total mass.

25. The preparation method according to claim 23 or 24, characterized in that, Both the first lithium film and the second lithium film include a plurality of wavy lithium metal strips, and the plurality of lithium metal strips are arranged at intervals along a first direction and a second direction on the surfaces of the first negative electrode active material layer and the second negative electrode active material layer. The first direction is the extension direction of the winding shaft, and the second direction is the direction perpendicular to the first direction in the plane where the negative electrode sheet is located.

26. The preparation method according to any one of claims 22 to 25, characterized in that, In step S3, the pressure of the roller pressing process is 60T to 100T.

27. The preparation method according to any one of claims 22 to 26, characterized in that, In step S3, the speed of the rolling process is 20m / min to 100m / min.

28. The preparation method according to any one of claims 22 to 27, characterized in that, The coating weight CW1 of the first negative electrode active material and the coating weight CW2 of the second negative electrode active material layer satisfy: 1 ​​< CW1 / CW2 ≤ 3.

4.

29. The preparation method according to any one of claims 22 to 28, characterized in that, The coating weight of the first negative electrode active material layer is 50 mg / 1540.25 mm. 2 ~170mg / 1540.25mm 2 .

30. The preparation method according to any one of claims 22 to 29, characterized in that, The coating weight of the second negative electrode active material layer is 45 mg / 1540.25 mm. 2 ~140mg / 1540.25mm 2 .

31. The preparation method according to any one of claims 22 to 30, characterized in that, The positive current collector includes a second convex surface and a second concave surface. Before step S4, a first positive active material layer located on one side of the second convex surface and a second positive active material layer located on one side of the second convex surface are formed on both sides of the positive current collector.

32. The preparation method according to claim 31, characterized in that, The coating weight of the second positive electrode active material layer is 100 mg / 1540.25 mm. 2 ~340mg / 1540.25mm 2 .

33. The preparation method according to claim 31 or 32, characterized in that, The coating weight of the first positive electrode active material layer is 100 mg / 1540.25 mm. 2 ~260mg / 1540.25mm 2 .

34. A battery device, characterized in that, It includes the battery cell according to any one of claims 1 to 21, or the battery cell prepared by the preparation method according to any one of claims 22 to 33.

35. An electrical appliance, characterized in that, Includes the battery device as described in claim 34.

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