Negative pole piece, secondary battery and electronic device

Abstract

The invention provides a negative pole piece, a secondary battery and an electronic device, the negative pole piece comprises a negative current collector and a negative material layer, along the length direction of the unfolded negative pole piece, the negative pole piece comprises an empty foil area and a single-sided negative material layer area connected with the empty foil area based on the length of the negative pole piece, the length ratio of the empty foil area is A, the length ratio of the single-sided negative electrode material layer region is B, 1 / 60 < = A < = 1 / 11, and 1 / 20 < = B < = 1 / 5. And grooves are formed in the negative electrode material layer of the single-sided negative electrode material layer region, extend along the width direction of the unfolded negative electrode plate and are arranged at intervals along the length direction of the unfolded negative electrode plate. By means of the arrangement, the risks of belt breaking and feeding folding in the actual machining process of the negative pole piece in the single-face area can be reduced.

Description

[0001] This invention is a divisional application of application number 202510111763.1, filed on January 23, 2025, entitled "A negative electrode sheet, a secondary battery and an electronic device". Technical Field

[0002] This application relates to the field of electrochemical technology, and in particular to a negative electrode, a secondary battery, and an electronic device. Background Technology

[0003] Secondary batteries, such as lithium-ion batteries, are characterized by high energy density, high operating voltage, low self-discharge rate, small size, and light weight, making them widely used in consumer electronics. With the widespread application of lithium-ion batteries, the market is placing increasingly higher demands on their performance.

[0004] Currently, the wound structure is the most mature structural technology for lithium-ion batteries. Typically, a single-sided negative electrode layer is used as the initial winding to increase the proportion of active material and improve the energy density of the secondary battery. However, the single-sided negative electrode layer exhibits significant stress concentration after cold pressing, leading to noticeable negative electrode curling. This curled single-sided negative electrode structure affects the electrode assembly structure and adhesive bonding during the winding process, and can even cause tape breakage at the interface between the double-sided and single-sided areas. Summary of the Invention

[0005] The purpose of this application is to provide a negative electrode sheet, a secondary battery, and an electronic device that improves the curling of the single-sided negative electrode sheet, reduces the risk of folding and breakage of the single-sided negative electrode sheet during processing, and improves the wettability of the electrolyte on the single-sided negative electrode sheet, thereby improving the dynamic performance and safety performance of the secondary battery.

[0006] It should be noted that while this application uses lithium-ion batteries as an example of secondary batteries to explain the invention, the secondary batteries in this application are not limited to lithium-ion batteries. The specific technical solution is as follows:

[0007] The first aspect of this application provides a negative electrode sheet, which includes a negative electrode current collector and a negative electrode material layer. Along the length of the unfolded negative electrode sheet, the negative electrode sheet includes an empty foil region and a single-sided negative electrode material layer region connecting the empty foil region. Based on the length of the negative electrode sheet, the length ratio of the empty foil region is A, and the length ratio of the single-sided negative electrode material layer region is B, where 1 / 60≤A≤1 / 11, preferably 1 / 30≤A≤1 / 11; 1 / 20≤B≤1 / 5, preferably 1 / 14≤B≤1 / 5. Multiple grooves are provided on the negative electrode material layer in the single-sided negative electrode material layer region, and the grooves are spaced apart along the length of the negative electrode sheet. By providing grooves on the single-sided negative electrode material layer region and applying it to a secondary battery, the curling of the single-sided negative electrode material layer region can be improved, reducing the risk of kinking and breakage of the single-sided negative electrode material layer region during processing. Simultaneously, it improves the wettability of the electrolyte to the single-sided negative electrode material layer region, thereby improving the dynamic performance and safety performance of the secondary battery.

[0008] In some embodiments of this application, along the thickness direction of the negative electrode sheet, a single groove has an orthographic projection on the negative electrode material layer. Along the length direction of the negative electrode sheet, the length of the single-sided negative electrode material layer region is L mm. The negative electrode sheet also includes a double-sided negative electrode material layer region. The single-sided and double-sided negative electrode material layer regions have a boundary line. The shortest distance between the outer contour of the orthographic projection of a single groove and the boundary line is L1 mm, where 1 / 2 ≤ (L-L1) / L ≤ 1. In some embodiments of this application, along the width direction of the unfolded negative electrode sheet, the single-sided negative electrode material layer region includes a central region and two edge regions connected to the central region. Grooves are spaced apart in the two edge regions and penetrate both edge regions. Based on the width of the negative electrode material layer of the single-sided negative electrode material layer region, the length ratio of the central region is C, where 0% ≤ C ≤ 30%. The above settings help to improve the curling problem of the single-sided negative electrode material layer, thereby reducing the risk of strip breakage and material folding during the actual processing of the single-sided negative electrode sheet. At the same time, it also helps to improve the wetting performance of the electrolyte on the single-sided negative electrode sheet and improve the liquid retention performance of the single-sided negative electrode material layer, thereby improving the dynamic performance and safety performance of the secondary battery. In addition, it takes into account the actual production efficiency and facilitates processing.

[0009] In some embodiments of this application, at least one of the following features is satisfied: (1) the negative electrode current collector comprises copper foil with a thickness of H μm, 4≤H≤8; (2) the unit area coating weight of the negative electrode material layer in the single-sided negative electrode material layer region is mg / 1540.25mm. 2 100≤m≤200. This setting helps to improve the curling problem in the single-sided negative electrode material layer region, thereby further reducing the risk of strip breakage and material bending during the actual processing of the single-sided negative electrode sheet.

[0010] In some embodiments of this application, the width of the negative electrode sheet is D mm along its width direction, and the length of the single-sided negative electrode material layer is L mm along its length direction, where 1 ≤ L / D ≤ ​​2 and 50 ≤ D ≤ 130. By adjusting the values ​​of L / D and D within the above ranges, it is beneficial to improve the curling problem of the single-sided negative electrode material layer, thereby further reducing the risk of strip breakage and material folding during the actual processing of the single-sided negative electrode sheet. In addition, the width of the negative electrode sheet and the length of the single-sided negative electrode material layer are related to the shape of the electrode assembly formed after winding. Adjusting the shape of the electrode assembly is beneficial to balancing actual production efficiency and processing performance.

[0011] In some embodiments of this application, the negative electrode sheet further includes a double-sided negative electrode material layer region, the negative electrode material layer comprising a negative electrode active material, the negative electrode active material comprising at least one of graphite or silicon-carbon composite material, and the compaction density of the negative electrode material layer in the single-sided negative electrode material layer region being PD1 g / cm³. 3 The compaction density of the negative electrode material layer in the double-sided negative electrode material layer region is PD2 g / cm³. 3 0.95≤PD1 / PD2≤1. In some embodiments of this application, 1.5≤PD2≤1.8. With the above settings, while taking into account the energy density of the secondary battery, the effect of reducing the deformation caused by the residual stress of cold pressing in the single-sided negative electrode material layer is more obvious, improving the curling problem of the single-sided negative electrode material layer, thereby further reducing the risk of strip breakage and material bending during the actual processing of the single-sided negative electrode sheet.

[0012] In some embodiments of this application, the average depth of multiple grooves along the thickness direction of the negative electrode sheet is h μm, where 5 ≤ h ≤ 30. By adjusting the value of h within the above range, it is beneficial to improve the curling problem of the single-sided negative electrode material layer, thereby reducing the risk of strip breakage and material bending during the actual processing of the single-sided negative electrode sheet. In addition, it reduces the problem of excessive groove depth, thus balancing actual production efficiency and facilitating processing.

[0013] In some embodiments of this application, multiple grooves are distributed in a strip shape along the thickness direction of the negative electrode sheet. Each groove has an orthographic projection on the negative electrode material layer, satisfying at least one of the following conditions: (1) the average width of the orthographic projection of the multiple grooves is d μm, 50≤d≤110; (2) the shortest distance between the outer contours of the orthographic projections of two adjacent grooves is L2mm, 0.5≤L2≤1.5. In some embodiments of this application, the angle between the centerline of a single groove and the length direction of the negative electrode sheet is α°, 20≤α≤75. The above settings help to improve the curling problem of the single-sided negative electrode material layer area, thereby reducing the risk of strip breakage and material bending during the actual processing of the single-sided negative electrode sheet. At the same time, it helps to improve the wetting performance of the electrolyte on the single-sided negative electrode sheet and improve the liquid retention performance of the single-sided negative electrode material layer area, thereby improving the dynamic performance and safety performance of the secondary battery. In addition, it takes into account the actual production efficiency and is conducive to processing.

[0014] In some embodiments of this application, the total area of ​​the orthographic projection of the plurality of grooves along the thickness direction of the negative electrode sheet is S1 mm. 2 The projected area of ​​the single-sided negative electrode material layer is S² mm. 2 2%≤S1 / S2≤10%. By adjusting the value of S1 / S2 within the above range, it is beneficial to improve the overall stiffness of the single-sided material layer area, thereby helping to improve the curling problem of the single-sided negative electrode material layer area, and thus reducing the risk of strip breakage and material bending during the actual processing of the single-sided negative electrode sheet.

[0015] A second aspect of this application provides a secondary battery comprising the negative electrode sheet of any of the above embodiments. Applying the negative electrode sheet of this application to a secondary battery improves the curling of the single-sided negative electrode sheet, reduces the risk of kinking or breakage of the single-sided negative electrode sheet during processing, and improves the wettability of the electrolyte on the single-sided negative electrode sheet, thereby enhancing the kinetic and safety performance of the secondary battery.

[0016] In some embodiments of this application, the secondary battery is a wound structure, with the empty foil region and the single-sided negative electrode material layer region located at the beginning of the wound structure.

[0017] A third aspect of this application provides an electronic device that includes a secondary battery as described in any of the above embodiments. Therefore, the electronic device provided by this application has good performance.

[0018] The beneficial effects of this application are:

[0019] This application provides a negative electrode sheet, a secondary battery, and an electronic device. The negative electrode sheet includes a negative electrode current collector and a negative electrode material layer. Along the length of the negative electrode sheet, it includes an empty foil region and a single-sided negative electrode material layer region connecting the empty foil region. Based on the length of the negative electrode sheet, the length ratio of the empty foil region is A, and the length ratio of the single-sided negative electrode material layer region is B, where 1 / 60 ≤ A ≤ 1 / 11, and 1 / 20 ≤ B ≤ 1 / 5. Multiple grooves are provided on the negative electrode material layer in the single-sided negative electrode material layer region, and the grooves are spaced apart along the length of the negative electrode sheet. By providing grooves on the single-sided negative electrode sheet, the curling of the single-sided negative electrode sheet can be improved, reducing the risk of kinking and breakage during processing. Simultaneously, it improves the wettability of the electrolyte on the single-sided negative electrode sheet, thereby improving the dynamic performance and safety performance of the secondary battery.

[0020] Of course, implementing any product or method of this application does not necessarily require achieving all of the advantages described above at the same time. Attached Figure Description

[0021] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other embodiments can be obtained based on these drawings.

[0022] Figure 1 This is a schematic diagram of the winding structure formed by the electrode assembly in one embodiment of this application;

[0023] Figure 2 for Figure 1 A partial front view of the negative electrode sheet after the middle electrode assembly has been unfolded;

[0024] Figure 3 for Figure 2 A schematic diagram of the longitudinal cross-section along the thickness direction of the negative electrode sheet.

[0025] The attached figures are labeled as follows:

[0026] Electrode assembly 001; positive electrode 10; negative electrode 20; separator 30; positive current collector 11; positive electrode material layer 12; negative electrode current collector 21; negative electrode material layer 22; empty foil area 210; single-sided negative electrode material layer area 220; double-sided negative electrode material layer area 230; groove 2201. Detailed Implementation

[0027] The technical solutions of this application will be clearly and completely described below with reference to the embodiments and accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. All other embodiments obtained by those skilled in the art based on this application are within the scope of protection of this application.

[0028] It should be noted that, in the specific embodiments of this application, a lithium-ion battery is used as an example of a secondary battery to explain this application; however, the secondary battery in this application is not limited to lithium-ion batteries. The specific technical solution is as follows:

[0029] The first aspect of this application provides a negative electrode sheet, which includes a negative electrode current collector and a negative electrode material layer. Along the length direction of the unfolded negative electrode sheet, the negative electrode sheet includes an empty foil region and a single-sided negative electrode material layer region connecting the empty foil region. Based on the length of the negative electrode sheet, the length ratio of the empty foil region is A, and the length ratio of the single-sided negative electrode material layer region is B. 1 / 60≤A≤1 / 11, preferably, 1 / 30≤A≤1 / 11; 1 / 20≤B≤1 / 5, preferably, 1 / 14≤B≤1 / 5. For example, the value of A can be 1 / 60, 1 / 50, 1 / 40, 1 / 30, 1 / 29, 1 / 28, 1 / 27, 1 / 26, 1 / 25, 1 / 24, 1 / 23, 1 / 22, 1 / 21, 1 / 20, 1 / 19, 1 / 18, 1 / 17, 1 / 16, 1 / 15, 1 / 14, 1 / 13, 1 / 12, 1 / 11, or a range of any two of these values; the value of B can be 1 / 20, 1 / 19, 1 / 18, 1 / 17, 1 / 16, 1 / 15, 1 / 14, 1 / 13, 1 / 12, 1 / 11, 1 / 10, 1 / 9, 1 / 8, 1 / 7, 1 / 6, 1 / 5, or a range of any two of these values. Multiple grooves are provided on the negative electrode material layer in the single-sided negative electrode material layer region, and the grooves are spaced apart along the length of the negative electrode sheet.

[0030] This application, by adjusting the values ​​of A and B within the aforementioned range and setting grooves on the negative electrode material layer in the single-sided negative electrode material layer region, helps to disperse the residual stress from cold pressing in the single-sided negative electrode material layer region, improving the stress concentration problem in the single-sided negative electrode material layer region. Applying this to secondary batteries improves the curling of the single-sided negative electrode sheet, thereby reducing the risk of strip breakage and material folding during actual processing, increasing the winding yield of the secondary battery, and reducing the capacity loss and short-circuit safety risk caused by folding. Simultaneously, by setting grooves on the negative electrode material layer in the single-sided negative electrode material layer region, the wetting performance of the electrolyte on the single-sided negative electrode sheet is improved, enhancing the liquid retention performance of the single-sided negative electrode material layer region, thereby improving the kinetic and safety performance of the secondary battery.

[0031] In some embodiments of this application, along the thickness direction of the negative electrode sheet, a single groove has an orthographic projection on the negative electrode material layer. Along the length direction of the negative electrode sheet, the length of the single-sided negative electrode material layer region is L mm. The negative electrode sheet also includes a double-sided negative electrode material layer region. The single-sided and double-sided negative electrode material layer regions have a boundary line. The shortest distance between the outer contour of the orthographic projection of a single groove and the boundary line is L1 mm, where 1 / 2 ≤ (L-L1) / L ≤ 1. For example, the value of (L-L1) / L can be 1 / 2, 11 / 20, 3 / 5, 13 / 20, 7 / 10, 3 / 4, 4 / 5, 19 / 20, 1, or a range consisting of any two of these values.

[0032] For ease of understanding, in this application, the negative electrode sheet is applied to a wound electrode assembly. The length direction of the electrode assembly in its unfolded state is defined as the X direction, its width direction as the Y direction, and its thickness direction as the Z direction. It can be understood that the length, width, and thickness directions of the negative electrode sheet, positive electrode sheet, and separator in their unfolded state are the same as those of the electrode assembly, and the winding direction of the electrode assembly is the W direction. The above directional limitations are only for understanding the technical solution of this application and do not limit the scope of protection of this application.

[0033] For example, such as Figures 1 to 2 As shown, the electrode assembly 001 includes a positive electrode 10, a negative electrode 20, and a separator 30. The negative electrode 20 includes a negative current collector 21 and a negative electrode material layer 22. Along the length direction (X direction) of the unfolded negative electrode 20 and along the winding direction (W direction) of the electrode assembly 001, the negative electrode 20 includes an empty foil area 210, a single-sided negative electrode material layer area 220, and a double-sided negative electrode material layer area 230. The single-sided negative electrode material layer area 220 is close to the winding center of the electrode assembly 001, and the negative electrode material layer 22 of the single-sided negative electrode material layer area 220 is disposed on the side of the negative current collector 21 away from the winding center of the electrode assembly 001. A plurality of grooves 2201 are provided on the negative electrode material layer 22 of the single-sided negative electrode material layer area 220. The plurality of grooves 2201 extend along the width direction (Y direction) of the unfolded negative electrode 20 and are spaced apart along the length direction (X direction) of the unfolded negative electrode 20. Along the length direction (X direction) of the unfolded negative electrode sheet 20 and along the winding direction (W direction) of the electrode assembly 001, the length of the single-sided negative electrode material layer region 220 is L mm. The single-sided negative electrode material layer region 220 and the double-sided negative electrode material layer region 230 have a boundary line PQ. The shortest distance between the outer contour of the orthographic projection of a single groove 2201 and the boundary line PQ is L1 mm.

[0034] By adjusting the value of (L-L1) / L within the above range, it is beneficial to improve the curling problem of the single-sided negative electrode material layer, thereby reducing the risk of strip breakage and material folding during the actual processing of the single-sided negative electrode sheet. At the same time, it is also beneficial to improve the wetting performance of the electrolyte on the single-sided negative electrode sheet and improve the liquid retention performance of the single-sided negative electrode material layer, thereby improving the dynamic performance and safety performance of the secondary battery. In addition, it takes into account the actual production efficiency and is conducive to processing.

[0035] In some embodiments of this application, along the width direction of the negative electrode sheet, the single-sided negative electrode material layer region includes a central region and two edge regions connected to the central region. Grooves are spaced apart in the two edge regions and penetrate both edge regions. Based on the width of the negative electrode material layer of the single-sided negative electrode material layer region, the length ratio of the central region is C, where 0% ≤ C ≤ 30%. For example, the value of C can be 0%, 2%, 5%, 8%, 10%, 12%, 15%, 18%, 20%, 22%, 25%, 28%, 30%, or a range of any two of these values. For example, as shown... Figure 2 As shown, along the width direction (Y direction) of the unfolded negative electrode sheet 20, the single-sided negative electrode material layer region 220 includes a central region and two edge regions connected to the central region, wherein the two edge regions are the portions within the dashed boxes in the single-sided negative electrode material layer region 220. Grooves 2201 are spaced apart in the two edge regions and penetrate both edge regions respectively. By adjusting the value of C within the above range, it is beneficial to improve the curling problem of the single-sided negative electrode material layer region, thereby reducing the risk of strip breakage and material bending during the actual processing of the single-sided negative electrode sheet. At the same time, it is also beneficial to improve the wetting performance of the electrolyte on the single-sided negative electrode sheet, improve the liquid retention performance of the single-sided negative electrode material layer region, thereby improving the dynamic performance and safety performance of the secondary battery. In addition, it takes into account the actual production efficiency and is conducive to processing.

[0036] In some embodiments of this application, the negative current collector comprises a copper foil with a thickness of H μm, where 4 ≤ H ≤ 8. For example, the value of H can be 4, 4.5, 5, 5.5, 6, 6.5, 7, 7.5, 8, or a range of any two of these values. For example, as... Figure 3As shown, the thickness of the negative electrode current collector 21 is H μm. By adjusting the value of H within the above range, it is beneficial to improve the curling problem of the single-sided negative electrode material layer region. While taking into account the energy density, this further reduces the risk of strip breakage and material bending during the actual processing of the single-sided negative electrode sheet. At the same time, it is also beneficial to improve the wetting performance of the electrolyte on the single-sided negative electrode sheet and improve the liquid retention performance of the single-sided negative electrode material layer region, thereby improving the dynamic performance and safety performance of the secondary battery. This application does not have any particular restrictions on the method of adjusting the thickness of the negative electrode current collector, as long as it can achieve the purpose of this application. For example, commercially available current collectors with different thicknesses can be selected, and the thickness of the negative electrode current collector can be determined by combining the test method of "L, A, B, L1, C, H, D, h, d, L2, α, S1 / S2 test" in this application, and then the negative electrode current collector with the required thickness can be selected.

[0037] In some embodiments of this application, the coating weight per unit area of ​​the negative electrode material layer in the single-sided negative electrode material layer region is mg / 1540.25mm. 2 The value of m is 100 ≤ m ≤ 200. For example, the value of m can be 100, 110, 120, 130, 140, 150, 160, 170, 180, 190, 200, or any two of these values. By adjusting the value of m within the above range, it is beneficial to improve the curling problem of the single-sided negative electrode material layer while ensuring energy density. This further reduces the risk of strip breakage and material bending during the actual processing of the single-sided negative electrode sheet. At the same time, it also helps to improve the wetting performance of the electrolyte on the single-sided negative electrode sheet and improve the liquid retention performance of the single-sided negative electrode material layer, thereby improving the kinetic performance and safety performance of the secondary battery.

[0038] In some embodiments of this application, the negative electrode current collector includes a copper foil with a thickness of H μm, where 4 ≤ H ≤ 8. For example, the value of H can be 4, 4.5, 5, 5.5, 6, 6.5, 7, 7.5, 8, or a range consisting of any two of these values; and the unit area coating weight of the negative electrode material layer in the single-sided negative electrode material layer region is mg / 1540.25 mm. 2 The values ​​of H and m are 100 ≤ m ≤ 200. For example, the value of m can be 100, 110, 120, 130, 140, 150, 160, 170, 180, 190, 200, or any two of these values. By adjusting the values ​​of H and m within the above ranges, it is beneficial to improve the curling problem of the single-sided negative electrode material layer while ensuring energy density. This further reduces the risk of strip breakage and material bending during the actual processing of the single-sided negative electrode sheet. At the same time, it also helps to improve the wetting performance of the electrolyte on the single-sided negative electrode sheet and improve the liquid retention performance of the single-sided negative electrode material layer, thereby improving the kinetic performance and safety performance of the secondary battery.

[0039] In some embodiments of this application, the width of the negative electrode sheet is D mm along its width direction, and the length of the single-sided negative electrode material layer region is L mm along its length direction, where 1 ≤ L / D ≤ ​​2 and 50 ≤ D ≤ 130. For example, the value of L / D can be 1, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2, or a range of any two of these values; the value of D can be 50, 60, 70, 80, 90, 100, 110, 120, 130, or a range of any two of these values. For example, as shown... Figure 2 As shown, along the width direction (Y direction) of the unfolded negative electrode sheet 20, the width of the negative electrode sheet 20 is D mm, and along the length direction (Y direction) of the unfolded negative electrode sheet 20, the length of the single-sided negative electrode material layer region 220 is L mm. By adjusting the values ​​of L / D and D within the above range, the larger the ratio of the length L of the single-sided negative electrode material layer region to the width D of the negative electrode sheet, the smaller the constraint of the double-sided negative electrode material layer region on the single-sided negative electrode material layer region, and the greater the corner curling amplitude. By adjusting the values ​​of L / D and D within the above range, it is beneficial to improve the curling problem of the single-sided negative electrode material layer region, thereby further reducing the risk of strip breakage and material folding during the actual processing of the single-sided negative electrode sheet. At the same time, it is also beneficial to improve the wetting performance of the electrolyte on the single-sided negative electrode sheet and improve the liquid retention performance of the single-sided negative electrode material layer region, thereby improving the dynamic performance and safety performance of the secondary battery. Furthermore, the width of the negative electrode sheet and the length of the single-sided negative electrode material layer are related to the shape of the electrode assembly formed after winding. Adjusting the shape of the electrode assembly is beneficial to balancing actual production efficiency and processing performance.

[0040] In some embodiments of this application, the negative electrode sheet further includes a double-sided negative electrode material layer region, the negative electrode material layer comprising a negative electrode active material, the negative electrode active material comprising at least one of graphite or silicon-carbon composite material, and the compaction density of the negative electrode material layer in the single-sided negative electrode material layer region being PD1 g / cm³. 3 The compaction density of the negative electrode material layer in the double-sided negative electrode material layer region is PD2 g / cm³. 3 0.95 ≤ PD1 / PD2 ≤ 1. For example, the value of PD1 / PD2 can be 0.95, 0.955, 0.96, 0.965, 0.97, 0.975, 0.98, 0.985, 0.99, 0.995, 1, or any range of two of these values. By selecting the above-mentioned types of negative electrode active materials and controlling the value of PD1 / PD2 within the above range, while taking into account the energy density of the secondary battery, the effect of reducing the deformation caused by the residual stress of cold pressing in the single-sided negative electrode material layer is more obvious, improving the curling problem of the single-sided negative electrode material layer, thereby further reducing the risk of strip breakage and material bending during the actual processing of the single-sided negative electrode sheet.

[0041] In some embodiments of this application, 1.5 ≤ PD2 ≤ 1.8. For example, the value of PD2 can be 1.5, 1.52, 1.55, 1.58, 1.6, 1.62, 1.65, 1.68, 1.7, 1.72, 1.75, 1.78, 1.8, or a range consisting of any two of these values. By adjusting the value of PD2 within the above range, while maintaining the energy density of the secondary battery, the effect of reducing the deformation caused by residual stress from cold pressing in the single-sided negative electrode material layer is more significant, improving the curling problem in the single-sided negative electrode material layer, thereby further reducing the risk of strip breakage and material bending during the actual processing of the single-sided negative electrode sheet.

[0042] In some embodiments of this application, the average depth of the plurality of grooves along the thickness direction of the negative electrode sheet is h μm, where 5 ≤ h ≤ 30. For example, the value of h can be 5, 8, 10, 12, 15, 18, 20, 22, 25, 28, 30, or a range of any two of these values. For example, as shown... Figure 3 As shown, along the thickness direction (Z direction) of the negative electrode sheet 20, the average depth of the multiple grooves 2201 is h μm. By adjusting the value of h within the above range, it is beneficial to improve the curling problem of the single-sided negative electrode material layer region, thereby reducing the risk of strip breakage and material folding during the actual processing of the single-sided negative electrode sheet. At the same time, it is beneficial to improve the wetting performance of the electrolyte on the single-sided negative electrode sheet and improve the liquid retention performance of the single-sided negative electrode material layer region, thereby improving the dynamic performance and safety performance of the secondary battery. In addition, it reduces the problem of excessive groove depth, thus balancing actual production efficiency and facilitating processing.

[0043] In some embodiments of this application, multiple grooves are distributed in a strip shape along the thickness direction of the negative electrode sheet. Each groove has an orthographic projection on the negative electrode material layer, and the average width of the orthographic projection of the multiple grooves is d μm, where 50 ≤ d ≤ 110. For example, the value of d can be 50, 60, 70, 80, 90, 100, 110, or a range of any two of these values. For example, as shown... Figure 2 As shown, multiple grooves 2201 are distributed in a strip shape along the thickness direction (Z direction) of the negative electrode sheet 20. Each groove 2201 has an orthographic projection on the negative electrode material layer 22, and the average width of the orthographic projection of the multiple grooves 2201 is d μm. By adjusting the value of d within the above range, it is beneficial to improve the curling problem of the single-sided negative electrode material layer region, thereby reducing the risk of strip breakage and material bending during the actual processing of the single-sided negative electrode sheet. At the same time, it is beneficial to improve the wetting performance of the electrolyte on the single-sided negative electrode sheet and improve the liquid retention performance of the single-sided negative electrode material layer region, thereby improving the dynamic performance and safety performance of the secondary battery. In addition, it takes into account the actual production efficiency and is conducive to processing.

[0044] In some embodiments of this application, multiple grooves are distributed in a strip shape along the thickness direction of the negative electrode sheet. Each groove has an orthographic projection on the negative electrode material layer, and the shortest distance between the outer contours of the orthographic projections of two adjacent grooves is L2 mm, where 0.5 ≤ L2 ≤ 1.5. For example, the value of L2 can be 0.5, 0.6, 0.7, 0.8, 0.9, 1, 1.1, 1.2, 1.3, 1.4, 1.5, or a range of any two values ​​therein. For example, as shown... Figure 2 As shown, multiple grooves 2201 are distributed in a strip shape along the thickness direction (Z direction) of the negative electrode sheet 20. Each groove 2201 has an orthographic projection on the negative electrode material layer 22, and the shortest distance between the outer contours of the orthographic projections of two adjacent grooves 2201 is L2 mm. By adjusting the value of L2 within the above range, it is beneficial to improve the curling problem of the single-sided negative electrode material layer region, thereby reducing the risk of strip breakage and material bending during the actual processing of the single-sided negative electrode sheet. At the same time, it is beneficial to improve the wetting performance of the electrolyte on the single-sided negative electrode sheet and improve the liquid retention performance of the single-sided negative electrode material layer region, thereby improving the dynamic performance and safety performance of the secondary battery. In addition, it takes into account the actual production efficiency and is conducive to processing.

[0045] In some embodiments of this application, multiple grooves are distributed in a strip shape along the thickness direction of the negative electrode sheet. Each groove has an orthographic projection on the negative electrode material layer. The average width of the orthographic projection of the multiple grooves is d μm, 50≤d≤110. For example, the value of d can be 50, 60, 70, 80, 90, 100, 110 or any range of two such values. The shortest distance between the outer contours of the orthographic projections of two adjacent grooves is L2 mm, 0.5≤L2≤1.5. For example, the value of L2 can be 0.5, 0.6, 0.7, 0.8, 0.9, 1, 1.1, 1.2, 1.3, 1.4, 1.5 or any range of two such values. By adjusting the values ​​of L2 and d within the aforementioned ranges, it is beneficial to improve the curling problem of the single-sided negative electrode material layer, thereby reducing the risk of strip breakage and material folding during the actual processing of the single-sided negative electrode sheet. Simultaneously, it helps improve the wetting performance of the electrolyte on the single-sided negative electrode sheet, enhancing the electrolyte retention performance of the single-sided negative electrode material layer, thus improving the kinetic and safety performance of the secondary battery. Furthermore, it balances actual production efficiency and energy density while facilitating processing, resulting in a uniform pore distribution in the negative electrode sheet.

[0046] In some embodiments of this application, the angle between the centerline of a single groove and the length direction of the negative electrode sheet is α°, where 20 ≤ α ≤ 75°. For example, the value of α can be 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75°, or a range of any two of these values. For example, as... Figure 2As shown, the angle between the centerline of a single groove 2201 and the length direction (X direction) of the unfolded negative electrode sheet 20 is α°. By adjusting the value of α within the above range, it is beneficial to improve the curling problem of the single-sided negative electrode material layer region, thereby reducing the risk of strip breakage and material folding during the actual processing of the single-sided negative electrode sheet. At the same time, it is beneficial to improve the wetting performance of the electrolyte on the single-sided negative electrode sheet and improve the liquid retention performance of the single-sided negative electrode material layer region, thereby improving the dynamic performance of the secondary battery. In addition, it takes into account both actual production efficiency and energy density, and is also conducive to processing.

[0047] In some embodiments of this application, the angle between the centerline of a single groove and the length direction of the negative electrode sheet is α°, where 40 ≤ α ≤ 50. For example, the value of α can be 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, or a range of any two of these values. By adjusting the value of α within the above range, and by setting the groove at an angle, stress dispersion is more pronounced, which helps to further improve the curling problem of the single-sided negative electrode material layer region. This reduces the risk of strip breakage and material bending during the actual processing of the single-sided negative electrode sheet. Simultaneously, it helps to improve the wetting performance of the electrolyte on the single-sided negative electrode sheet, enhances the liquid retention performance of the single-sided negative electrode material layer region, and thus improves the kinetic performance of the secondary battery. Furthermore, it balances actual production efficiency and energy density, and is beneficial for processing.

[0048] In some embodiments of this application, the total area of ​​the orthographic projection of the plurality of grooves along the thickness direction of the negative electrode sheet is S1 mm. 2 The projected area of ​​the single-sided negative electrode material layer is S² mm. 2 2% ≤ S1 / S2 ≤ 10%. For example, the value of S1 / S2 can be 2%, 2.2%, 2.5%, 2.8%, 3%, 3.2%, 3.5%, 3.8%, 4%, 4.2%, 4.5%, 4.8%, 5%, 5.2%, 5.5%, 5.8%, 6%, 6.2%, 6.5%, 6.8%, 7%, 7.2%, 7.5%, 7.8%, 8%, 8.2%, 8.5%, 8.8%, 9%, 9.2%, 9.5%, 9.8%, 10%, or a range of any two of these values. For example, such as... Figure 2As shown, the total area of ​​the orthographic projection of multiple grooves 2201 is S1, which is the sum of the areas of the orthographic projection of all grooves 2201 within the edge region of the dashed box in the figure. The area of ​​the single-sided negative electrode material layer region 220 is S2 = L × D. By adjusting the values ​​of S1 / S2 within the above range, it is beneficial to improve the overall stiffness of the single-sided material layer region, thereby improving the curling problem of the single-sided negative electrode material layer region. This reduces the risk of strip breakage and material bending during the actual processing of the single-sided negative electrode sheet. At the same time, it is beneficial to improve the wetting performance of the electrolyte on the single-sided negative electrode sheet and improve the liquid retention performance of the single-sided negative electrode material layer region, thereby improving the dynamic performance and safety performance of the secondary battery.

[0049] In this application, the negative electrode material layer may further include a conductive agent and a binder. This application does not impose any particular limitation on the type of conductive agent in the negative electrode material layer, as long as it achieves the purpose of this application. For example, the conductive agent may include, but is not limited to, at least one of conductive carbon black (Super P), carbon nanotubes (CNTs), carbon fibers, flake graphite, Ketjen black, graphene, metallic materials, or conductive polymers. The aforementioned carbon nanotubes may include, but are not limited to, single-walled carbon nanotubes and / or multi-walled carbon nanotubes. The aforementioned carbon fibers may include, but are not limited to, vapor-grown carbon fibers (VGCF) and / or carbon nanofibers. The aforementioned metallic materials may include, but are not limited to, metal powders and / or metal fibers; specifically, the metal may include, but is not limited to, at least one of copper, nickel, aluminum, or silver. The aforementioned conductive polymers may include, but are not limited to, at least one of polyphenylene derivatives, polyaniline, polythiophene, polyacetylene, or polypyrrole. This application does not impose any particular limitation on the type of binder in the negative electrode material layer, as long as it achieves the purpose of this application. For example, the binder may include, but is not limited to, at least one of polyvinylidene fluoride, a copolymer of polyvinylidene fluoride and hexafluoropropylene, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinyl ether, polymethyl methacrylate, polytetrafluoroethylene, or polyhexafluoropropylene. This application does not impose any particular limitation on the mass ratio of the negative electrode active material, conductive agent, and binder in the negative electrode material layer, as long as the purpose of this application is achieved.

[0050] This application does not impose any particular restrictions on the preparation method of the negative electrode sheet, as long as it can achieve the purpose of this application. For example, the preparation method of the negative electrode sheet includes, but is not limited to, the following steps: (1) preparing a negative electrode slurry; (2) pre-determining the area on the negative electrode current collector where a single-sided negative electrode material layer is set, the area where a double-sided negative electrode material layer is set, and the area where no negative electrode material layer is set; (3) according to the area determined on the negative electrode current collector in step (2), coating a negative electrode slurry on one surface of the negative electrode current collector, and drying it to form a negative electrode sheet including a single-sided negative electrode material layer; (4) according to the area determined on the negative electrode current collector in step (2), coating a slurry on the other surface of the negative electrode current collector, and drying it to obtain a negative electrode sheet including a double-sided negative electrode material layer; (5) after cold pressing and cutting into strips, a groove is set in the single-sided negative electrode material layer area to obtain the negative electrode sheet of this application.

[0051] In some implementations, after step (4), an intermediate region is determined in the single-sided negative electrode material layer region, and two edge regions connected to the intermediate region are defined; and when a groove is set in the single-sided negative electrode material layer region, the groove is set in the two edge regions and penetrates the two edge regions respectively.

[0052] This application does not impose any particular limitation on the solid content of the aforementioned slurry, as long as the purpose of this application can be achieved. This application does not impose any particular limitation on the aforementioned drying temperature and time, as long as the purpose of this application can be achieved. This application does not impose any particular limitation on the aforementioned process parameters for cold pressing, cutting, slitting, etc., as long as the purpose of this application can be achieved.

[0053] This application does not impose any particular restrictions on the method of setting the groove. Those skilled in the art can choose according to actual needs, as long as the purpose of this application can be achieved. For example, the groove can be set by pulsed laser etching. The value of (L-L1) / L can be controlled by adjusting the length L of the single-sided negative electrode material layer region and the speed of the pulsed laser emitter and the etching tape; the value of C can be controlled by adjusting the width of the negative electrode material layer in the single-sided negative electrode material layer region, the power of the pulsed laser emitter, and the defocusing amount; the average depth h of multiple grooves and the average width d of the orthographic projection of multiple grooves can be controlled by adjusting the power of the pulsed laser emitter and the defocusing amount; the shortest distance L2 between the outer contours of the orthographic projection of two adjacent grooves can be controlled by adjusting the spacing between the pulsed laser emitters or the laser emission frequency; the angle α between the centerline of a single groove and the length direction of the unfolded negative electrode sheet can be controlled by adjusting the position, power, and defocusing amount of the pulsed laser emitter; the ratio S1 / S2 of the total area S1 of the orthographic projection of multiple grooves to the projected area S2 of the single-sided negative electrode material layer region can be controlled by adjusting the projected area of ​​the single-sided negative electrode material layer region, the power of the pulsed laser emitter, the defocusing amount, and the number of grooves set in the single-sided negative electrode material layer region.

[0054] In this application, the different features of the grooves included in the single-sided negative electrode material layer region can be combined arbitrarily, and the implementation methods or embodiments covered by the above combinations are all within the protection scope of this application.

[0055] A second aspect of this application provides a secondary battery comprising a positive electrode, a separator, and a negative electrode as described in any of the above embodiments. Applying the negative electrode of this application to a secondary battery improves the curling of the single-sided negative electrode, reducing the risk of kinking or breakage during processing, and simultaneously improving the wettability of the electrolyte on the single-sided negative electrode, thereby enhancing the kinetic and safety performance of the secondary battery.

[0056] In some embodiments of this application, the secondary battery has a wound structure, with the empty foil area and the single-sided negative electrode material layer area located at the starting end of the wound structure. This can more effectively address the significant stress concentration that occurs in the negative electrode sheet of the single-sided negative electrode material layer area at the starting end of the winding after cold pressing, reduce the risk of kinking and breakage of the single-sided negative electrode sheet during processing, and improve the wettability of the electrolyte to the single-sided negative electrode sheet, thereby improving the dynamic performance and safety performance of the secondary battery.

[0057] This application does not impose any particular limitation on the diaphragm, as long as it can achieve the purpose of this application. For example, the diaphragm material may include, but is not limited to, at least one of polyethylene (PE), polyolefins (PO) mainly composed of polypropylene (PP), polyester (e.g., polyethylene terephthalate (PET) film), cellulose, polyimide (PI), polyamide (PA), spandex, or aramid. The type of diaphragm may include at least one of woven membrane, nonwoven membrane, microporous membrane, composite membrane, rolled membrane, or spun membrane.

[0058] In some embodiments of this application, the diaphragm may include a substrate layer and a surface treatment layer. The substrate layer may be a nonwoven fabric, membrane, or composite membrane with a porous structure, and the material of the substrate layer may include at least one of polyethylene, polypropylene, polyethylene terephthalate, or polyimide. Optionally, a polypropylene porous membrane, a polyethylene porous membrane, a polypropylene nonwoven fabric, a polyethylene nonwoven fabric, or a polypropylene-polyethylene-polypropylene porous composite membrane may be used. Optionally, a surface treatment layer is provided on at least one surface of the substrate layer, and the surface treatment layer may be a polymer layer or an inorganic layer, or a layer formed by mixing polymers and inorganic materials. In some embodiments of this application, the inorganic layer includes inorganic particles and a binder. This application does not have particular limitations on the inorganic particles; for example, the inorganic particles may include at least one of alumina, silicon oxide, magnesium oxide, titanium oxide, hafnium dioxide, tin oxide, cerium dioxide, nickel oxide, zinc oxide, calcium oxide, zirconium oxide, yttrium oxide, silicon carbide, boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide, or barium sulfate. This application does not impose any particular limitation on the adhesive; for example, the adhesive can be at least one of the adhesives mentioned above. In some embodiments of this application, the polymer layer comprises a polymer, and the polymer material includes at least one of polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinyl ether, or polyvinylidene fluoride or poly(vinylidene fluoride-hexafluoropropylene). In this application, the thickness of the diaphragm is not particularly limited, as long as it achieves the purpose of this application; for example, the thickness of the diaphragm can be from 3 μm to 30 μm.

[0059] This application does not impose any particular limitation on the positive electrode sheet, as long as the purpose of this application can be achieved. For example, the positive electrode sheet includes a positive current collector and a positive electrode material layer disposed on at least one surface of the positive current collector. The aforementioned "positive electrode material layer disposed on at least one surface of the positive current collector" means that the positive electrode material layer can be disposed on one surface of the positive current collector along its own thickness direction, or it can be disposed on two surfaces of the positive current collector along its own thickness direction. It should be noted that the "surface" here can be the entire area of ​​the surface of the positive current collector, or it can be a partial area of ​​the surface of the positive current collector; this application does not impose any particular limitation, as long as the purpose of this application can be achieved. For example, as shown... Figure 1 As shown, the positive electrode material layer 12 is disposed on two surfaces of the positive electrode current collector 11 along its thickness direction. This application does not impose any particular limitation on the positive electrode current collector, as long as it achieves the purpose of this application. For example, the positive electrode current collector may include aluminum foil, aluminum alloy foil, or a composite current collector (e.g., an aluminum-carbon composite current collector). The positive electrode material layer of this application includes a positive electrode active material. This application does not impose any particular limitation on the type of positive electrode active material, as long as it achieves the purpose of this application. For example, the positive electrode active material may include lithium nickel cobalt manganese oxide (LiNi). 0.90 Co 0.05 Mn0.05 At least one of the following: O2 (NCM955), NCM811, NCM622, NCM523, NCM111, lithium nickel cobalt aluminum oxide, lithium iron phosphate, lithium-rich manganese-based materials, lithium cobalt oxide (LiCoO2), lithium manganese oxide, lithium manganese iron phosphate, or lithium titanate. In this application, the positive electrode active material may also contain non-metallic elements, such as at least one of fluorine, phosphorus, boron, chlorine, silicon, or sulfur. In this application, there are no particular limitations on the thickness of the positive electrode current collector and the positive electrode material layer, as long as the purpose of this application is achieved. In this application, the positive electrode material layer may also include a positive electrode binder and a conductive agent. In this application, there are no particular limitations on the type of positive electrode binder in the positive electrode material layer, as long as the purpose of this application is achieved; for example, the positive electrode binder may be the same type as the binder in the aforementioned negative electrode material layer. In this application, there are no particular limitations on the type of conductive agent in the positive electrode material layer, as long as the purpose of this application is achieved; for example, the conductive agent may be the same type as the conductive agent in the aforementioned negative electrode material layer. This application does not impose any particular restrictions on the mass ratio of positive electrode active material, conductive agent, and binder in the positive electrode material layer. Those skilled in the art can choose according to actual needs, as long as the purpose of this application can be achieved.

[0060] In this application, the secondary battery also includes an electrolyte, which comprises lithium salts and non-aqueous solvents. This application does not impose any particular limitation on the lithium salt, as long as it achieves the purpose of this application. For example, the lithium salt may include, but is not limited to, at least one of LiPF6, LiBF4, LiAsF6, LiClO4, LiB(C6H5)4, LiCH3SO3, LiCF3SO3, LiN(SO2CF3)2, LiC(SO2CF3)3, Li2SiF6, lithium bis(oxalato)borate (LiBOB), or lithium difluoroborate. This application does not impose any particular limitation on the content of lithium salts in the electrolyte, as long as it achieves the purpose of this application. This application does not impose any particular limitation on the non-aqueous solvent, as long as it achieves the purpose of this application. For example, the non-aqueous solvent may include, but is not limited to, at least one of carbonate compounds, carboxylic acid ester compounds, ether compounds, or other organic solvents. The aforementioned carbonate compounds may include, but are not limited to, at least one of chain carbonate compounds, cyclic carbonate compounds, or fluorocarbonate compounds. The aforementioned chain carbonate compounds may include, but are not limited to, at least one of dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), or methyl ethyl carbonate (MEC). The aforementioned cyclic carbonates may include, but are not limited to, at least one of ethylene carbonate (EC), propylene carbonate (PC), butyl carbonate (BC), or vinyl ethylene carbonate (VEC). Fluorinated carbonate compounds may include, but are not limited to, at least one of fluoroethylene carbonate (FEC), 1,2-difluoroethylene carbonate, 1,1-difluoroethylene carbonate, 1,1,2-trifluoroethylene carbonate, 1,1,2,2-tetrafluoroethylene carbonate, 1-fluoro-2-methylethylene carbonate, 1-fluoro-1-methylethylene carbonate, 1,2-difluoro-1-methylethylene carbonate, 1,1,2-trifluoro-2-methylethylene carbonate, or trifluoromethylethylene carbonate. The aforementioned carboxylic acid ester compounds may include, but are not limited to, at least one of methyl formate, methyl acetate, ethyl acetate, n-propyl acetate, tert-butyl acetate, methyl propionate, ethyl propionate, propyl propionate, γ-butyrolactone, decanolactone, valproic acid lactone, or caprolactone. The aforementioned ether compounds may include, but are not limited to, at least one of dibutyl ether, tetraethylene glycol dimethyl ether, diethylene glycol dimethyl ether, 1,2-dimethoxyethane, 1,2-diethoxyethane, 1-ethoxy-1-methoxyethane, 2-methyltetrahydrofuran, or tetrahydrofuran. The aforementioned other organic solvents may include, but are not limited to, at least one of dimethyl sulfoxide, 1,2-dioxolane, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolium ketone, N-methyl-2-pyrrolidone, dimethylformamide, acetonitrile, trimethyl phosphate, triethyl phosphate, or trioctyl phosphate. This application does not impose any particular limitation on the content of non-aqueous solvents in the electrolyte, as long as the purpose of this application is achieved.This application does not impose any particular restrictions on the content of non-aqueous solvents in the electrolyte, as long as the purpose of this application can be achieved.

[0061] The secondary battery also includes a casing for housing the positive electrode, separator, negative electrode, and electrolyte, as well as other components known in the field of secondary batteries. This application does not limit the scope of these other components. This application does not impose any particular limitation on the casing; it can be a casing known in the art, as long as it achieves the purpose of this application. For example, the casing can be a rigid casing or a flexible casing. The material of the rigid casing can be metal; this application does not limit the type of metal and can use known metal rigid casings, as long as they achieve the purpose of this application. The flexible casing can be a metal plastic film, such as aluminum-plastic film, steel-plastic film, etc.

[0062] The fabrication process of the secondary battery described in this application is well known to those skilled in the art, and this application does not impose any particular limitations. For example, the fabrication process of the secondary battery may include, but is not limited to, the following steps: stacking the positive electrode, separator, and negative electrode in sequence, and performing operations such as winding and folding as needed to obtain a wound electrode assembly; placing the electrode assembly into a housing; injecting electrolyte into the housing and sealing it to obtain the secondary battery. Alternatively, stacking the positive electrode, separator, and negative electrode in sequence, and then fixing the four corners of the entire stacked structure with tape to obtain a stacked electrode assembly; placing the electrode assembly into a housing; injecting electrolyte into the housing and sealing it to obtain the secondary battery. In addition, overcurrent protection elements, conductive plates, etc., may be placed in the housing as needed to prevent pressure rise and overcharging / discharging inside the secondary battery.

[0063] A third aspect of this application provides an electronic device that includes a secondary battery as described in any of the above embodiments, thereby providing the electronic device with good performance.

[0064] The electronic device described in this application is not particularly limited and can be any electronic device known in the prior art. For example, the electronic device may include, but is not limited to, laptops, pen input computers, mobile computers, e-book players, portable telephones, portable fax machines, portable copiers, portable printers, stereo headphones, video recorders, LCD TVs, portable cleaners, portable CD players, mini CDs, transceivers, electronic notebooks, calculators, memory cards, portable recorders, radios, backup power supplies, motors, automobiles, motorcycles, electric bicycles, bicycles, lighting fixtures, toys, game consoles, clocks, power tools, flashlights, cameras, household large-capacity batteries, and lithium-ion capacitors.

[0065] Example

[0066] The embodiments and comparative examples provided below illustrate the implementation of this application in more detail. Various tests and evaluations were conducted according to the methods described below. Furthermore, unless otherwise specified, "parts" and "%" are quality standards.

[0067] Test methods and equipment:

[0068] Tests for L, A, B, L1, C, H, D, h, d, L2, α, and S1 / S2:

[0069] At an ambient temperature of 25°C, the lithium-ion batteries of each embodiment and comparative example were discharged to 2.5V at 0.5C and then disassembled to obtain electrode assemblies. The negative electrode sheets were taken out from the electrode assemblies and soaked in dimethyl carbonate (DMC) for 20 minutes. Then, the negative electrode sheets were placed in an oven and dried at 80°C for 12 hours to obtain test samples of the negative electrode sheets.

[0070] Unfold the negative electrode sheet and visually identify the empty foil area, single-sided negative electrode material layer area, and double-sided negative electrode material layer area along its unfolded length. Measure the length L of the single-sided negative electrode material layer area, the length of the empty foil area, and the length of the negative electrode sheet using a measuring tape. Then, based on the length of the negative electrode sheet, calculate the length ratio A of the empty foil area and the length ratio B of the single-sided negative electrode material layer area. Observe the planes along the length and width directions of the unfolded negative electrode sheet to identify the boundary line between the single-sided and double-sided negative electrode material layer areas. Measure the shortest distance L1 between the outer contour of a single groove on the surface of the negative electrode sheet and the boundary line along its unfolded length, and calculate the value of (L-L1) / L. Observe the plane containing the length and width directions of the unfolded negative electrode sheet. Along the width direction of the unfolded negative electrode sheet, observe the location of the groove. If the groove extends through the width direction of the unfolded negative electrode sheet, the proportion of the middle area of ​​the single-sided negative electrode material layer is 0. Based on the width of the negative electrode material layer in the single-sided negative electrode material layer, the length proportion C of the middle area is 0. If the groove does not extend through the width direction of the unfolded negative electrode sheet, measure the length of the single-sided negative electrode material layer without a groove and the width of the negative electrode material layer in the single-sided negative electrode material layer along the width direction of the unfolded negative electrode sheet. Then the length proportion C of the middle area is equal to the length of the single-sided negative electrode material layer without a groove and the width of the negative electrode material layer in the single-sided negative electrode material layer.

[0071] A scanning electron microscope is used to photograph each groove in the single-sided negative electrode material layer region. The projected area of ​​a single groove is calculated by image recognition. Then, the images are summed to obtain the total projected area S1 of multiple grooves. The measured length L of the single-sided negative electrode material layer region is multiplied by the measured width of the single-sided negative electrode material layer region to obtain the projected area S2 of the single-sided negative electrode material layer region. Then, S1 / S2 is calculated.

[0072] Five grooves are randomly selected from the single-sided negative electrode material layer area. Five positions are randomly selected on each groove, and the width of the groove at each of these five positions is measured. The average of these five widths is the width of the orthographic projection of the single groove onto the negative electrode material layer. The average width d of the orthographic projections of the five grooves is then obtained. The shortest distance L2 between the outer contours of the orthographic projections of two adjacent grooves on the negative electrode material layer is measured. Five grooves are randomly selected, and the centerline of each groove is determined. The angle between the centerline of each groove and the unfolded length direction of the negative electrode sheet is measured, and the average of these angles is taken as the angle α between the centerline of each groove and the unfolded length direction of the negative electrode sheet.

[0073] The negative electrode sheet is cut along its thickness direction and its unfolded length direction to obtain a longitudinal section. The longitudinal section of the negative electrode sheet is then ion-polished and observed using an electron scanning microscope. A clear boundary line between the negative electrode material layer and the negative electrode current collector can be observed. The thickness H of the negative electrode current collector is measured using a micrometer along the thickness direction of the negative electrode sheet. Five grooves are randomly selected, and the distance from the surface of the negative electrode material layer to the bottom surface of each groove is measured using a micrometer along the thickness direction of the negative electrode sheet. The average value is taken as the average depth h of the multiple grooves.

[0074] Test of coating weight per unit area of ​​negative electrode material layer:

[0075] At an ambient temperature of 25℃, the lithium-ion battery was disassembled to obtain the wound electrode assembly. The negative electrode sheet was taken out and soaked in dimethyl carbonate (DMC) for 20 minutes. Then, the negative electrode sheet was placed in an oven and dried at 80℃ for 12 hours to obtain a test sample of the negative electrode sheet. The empty foil area, single-sided negative electrode material layer area and double-sided negative electrode material layer area of ​​the negative electrode sheet were confirmed.

[0076] The negative electrode sample with a single-sided negative electrode material layer was stamped and broken into two small circular pieces with a radius of 22.14 mm (area 1540.25 mm²). 2 The negative electrode material layer on the small discs was removed by wiping them off with deionized water, and the average weight was recorded as a1. The negative electrode sample with the double-sided negative electrode material layer was then punched and broken into four small discs with a radius of 22.14 mm (area 1540.25 mm²). 2 After weighing each of the two surfaces of the small disc sequentially, the average value is recorded as b; the negative electrode material layer on both surfaces is wiped off with deionized water, and the average value is recorded as b1. Then,

[0077] The coating weight per unit area of ​​the negative electrode material layer in the single-sided negative electrode material layer region is M = a - a1;

[0078] The coating weight per unit area of ​​the negative electrode material layer in the double-sided negative electrode material layer region = (b-b1) / 2.

[0079] Testing of PD1 and PD2:

[0080] Referring to the "Test of Coating Weight per Unit Area of ​​Negative Electrode Material Layer", the coating weight per unit area of ​​the negative electrode material layer in the single-sided negative electrode material layer region and the coating weight per unit area of ​​the negative electrode material layer region are obtained. Following the test procedures in the "Test of L, A, B, L1, C, H, D, h, d, L2, α, S1 / S2", the thickness of the single-sided negative electrode material layer is measured using a micrometer. Then, PD1 and PD2 are calculated using the following formula:

[0081] The compaction density PD1 of the negative electrode material layer in the single-sided negative electrode material layer region is equal to the coating weight per unit area of ​​the negative electrode material layer in the single-sided negative electrode material layer region / the thickness of the single-sided negative electrode material layer.

[0082] The compaction density PD2 of the negative electrode material layer in the double-sided negative electrode material layer region = the coating weight per unit area of ​​the negative electrode material layer in the double-sided negative electrode material layer region / the thickness of the single-sided negative electrode material layer.

[0083] Low-temperature kinetic rate 0°C lithium plating test of the innermost single-sided negative electrode material layer:

[0084] The lithium-ion battery was placed in an environment of 0°C and charged at a constant current rate of 0.5C, 0.7C, 1.0C, 1.2C, 1.5C, 1.7C, 2.0C, 2.2C, 2.4C, 2.6C, 2.8C, 3.0C, 3.2C, 3.4C, 3.6C, 3.8C, 4.0C, 4.2C, 4.4C, 4.6C, 4.8C, and 5.0C until the voltage reached 4.5V. Then, it was charged at a constant voltage of 4.5V until the cutoff current reached 0.05C, allowed to rest for 5 minutes, and then discharged at a constant current of 0.5C until the voltage reached 3.0V, allowed to rest for 5 minutes. This constitutes one charge-discharge cycle. Then, the same steps were repeated for 10 charge-discharge cycles.

[0085] Then, charge at a constant current rate to 4.5V, followed by constant voltage charging at 4.5V until the cutoff current reaches 0.05C, and let stand for 5 minutes. Next, disassemble the lithium-ion battery and confirm the interface of the single-sided negative electrode material layer. Disassemble at rates ranging from low to high until slight white lithium metal deposition occurs. This rate is recorded as the maximum low-temperature kinetic rate of the single-sided negative electrode material layer. For example, if slight lithium deposition occurs when disassembling the single-sided negative electrode at 1.5C, this is recorded as the low-temperature kinetic rate of 1.5C.

[0086] Energy density testing:

[0087] (1) Place the lithium-ion battery in an environment of 25°C, charge it with a constant current of 1C to a voltage of 4.5V, then charge it with a constant voltage of 4.5V to a cutoff current of 0.05C, let it stand for 5 minutes, discharge it with a constant current of 0.2C to a voltage of 3.0V, let it stand for 5 minutes, and record the discharge capacity at this time as C.

[0088] (2) Use a micrometer to measure three sets of actual thicknesses Da, Db, and Dc in the electrode assembly, 3 mm from the edge of the head, 3 mm from the edge of the tail, and in the middle region. For example, if the first data point of the head is recorded as Da1, and so on, then the average thickness D is:

[0089] D=(1 / 3×(Da1+Da2+Da3)+1 / 3×(Db1+Db2+Db3)+1 / 3×(Dc1+Dc2+Dc3)) / 3;

[0090] (3) Then use a laser measuring instrument to scan and measure the length L and width M of the lithium-ion battery.

[0091] (4) The actual energy density X of the lithium-ion battery is: X = C / (D × L × M);

[0092] (5) The energy density X0 of Comparative Example 1 is set as the "low" level standard. Each 0.2% increase represents a gradient in energy density, and the order is: high > upper-middle > middle > lower-middle > low. The energy density in Comparative Example 1 is 654.1 Wh / L.

[0093] Testing of winding yield related to feed folding / single-sided negative electrode material layer discontinuity:

[0094] (1) Take several rolls of negative electrode sheets prepared in each embodiment and comparative example, totaling N rolls (N=1000).

[0095] (2) Take a sufficient amount of the separator and positive electrode corresponding to the negative electrode sheet prepared in each embodiment and comparative example in step (1), the quantity of which is much greater than N;

[0096] (3) Using the negative electrode, separator and positive electrode from steps (1) and (2), assemble and produce lithium-ion batteries according to the winding method of each embodiment and comparative example;

[0097] (4) Record the total scrap amount M of the negative electrode sheet during the winding process due to folding or single-sided breakage of the feed strip;

[0098] (5) The winding yield of the negative electrode sheet (%) = (1-M / N)×100%.

[0099] Interface characteristics of a 500-cycle single-sided region;

[0100] The lithium-ion batteries prepared in the examples and comparative examples were placed in a 25°C constant temperature test chamber and left to stand for 30 minutes to allow them to reach a constant temperature. They were then charged at a constant current of 0.5C to 4.5V, and then charged at a constant voltage of 4.5V to a current of 0.025C. After standing for 5 minutes, they were discharged at a constant current of 0.5C to 3.0V, and this was recorded as the initial discharge capacity C0. This process was repeated for 500 cycles, and the discharge capacity C1 after 500 cycles was recorded. The 500-cycle capacity retention rate of the lithium-ion battery was calculated as: Cycle Capacity Retention Rate (%) = C1 / C0 × 100%. Simultaneously, the cycled lithium-ion batteries were fully charged (charged at a constant current of 0.5C to 4.5V) and disassembled for analysis to confirm the interface condition of the single-sided negative electrode material layer region after 500 cycles and to identify any differences.

[0101] The electrochemical performance of lithium-ion batteries is characterized by cycle capacity retention and the interface condition of the single-sided negative electrode region. Specifically, a normal interface condition and a higher capacity retention indicate better electrochemical performance of the lithium-ion battery; conversely, an abnormal interface condition and a lower capacity retention indicate poorer electrochemical performance. "Interface condition" refers to the condition of the negative electrode surface after disassembly from a fully charged state following cycling. "No abnormal interface condition" means the absence of black spots, lithium plating, or purple spots on the negative electrode surface; "Abnormal interface condition" means the presence of at least one of the following phenomena on the negative electrode surface: black spots, lithium plating, or purple spots.

[0102] Example 1-1

[0103] <Preparation of Negative Electrode Sheets>

[0104] Artificial graphite, styrene-butadiene rubber, and sodium carboxymethyl cellulose were mixed in a mass ratio of 96:2:2, with deionized water added as a solvent. The mixture was stirred until homogeneous, yielding a negative electrode slurry with a solid content of 40 wt%. The negative electrode slurry was uniformly coated onto one surface of a 6 μm thick copper foil used as a negative electrode current collector. Coating was intermittently applied to the copper foil according to the electrode assembly dimensions, and then dried at 85°C to obtain a negative electrode sheet with a single-sided coating of 100 μm. The above steps were repeated on the other surface of the copper foil to obtain a negative electrode sheet with a double-sided coating of negative electrode material. After cold pressing (at a pressure of 80T), the negative electrode sheet was obtained. The negative electrode sheet was cut to a fixed size. Two edge regions with grooves were pre-determined for the single-sided negative electrode material layer area. The middle region of the single-sided negative electrode material layer area without grooves had a length ratio C of 15% based on the width of the negative electrode material layer. The orthographic projection of a single groove along the thickness direction of the negative electrode sheet is rectangular. After vacuum drying at 120℃ for 12 hours, a negative electrode sheet with dimensions of 78mm × 875mm is obtained for use, meaning the width D of the negative electrode sheet is 78mm. The unit area coating weight m of the negative electrode material layer in the single-sided negative electrode material layer region is 150mg / 1540.25mm. 2 The coating weight per unit area of ​​the negative electrode material layer in the double-sided negative electrode material layer region is 150 mg / 1540.25 mm. 2 The compaction density PD1 of the negative electrode material layer in the single-sided negative electrode material layer region is 1.70 g / cm³. 3 The compaction density PD2 of the anode material layer in the double-sided anode material layer region is 1.73 g / cm³. 3 Based on the length of the negative electrode sheet, the length ratio A of the empty foil area is 1 / 20, the length ratio B of the single-sided negative electrode material layer area is 1 / 10, and the length L of the single-sided negative electrode material layer area is 87.5mm.

[0105] Grooves were created on the two edge regions of the single-sided negative electrode material layer area of ​​the negative electrode sheet using pulsed laser etching. Specific parameters are shown in Table 1. The shortest distance L1 between the outer contour of the orthographic projection of a single groove and the boundary line is 17.5 mm. Along the thickness direction of the negative electrode sheet, the average depth h of multiple grooves is 20 μm, the average width d of the orthographic projection of multiple grooves is 80 μm, the shortest distance L2 between the outer contours of the orthographic projection of two adjacent grooves is 1 mm, the angle α between the center line of a single groove and the length direction of the unfolded negative electrode sheet is 45°, and the ratio S1 / S2 of the total area of ​​the orthographic projection of multiple grooves to the projected area of ​​the single-sided negative electrode material layer area is 5.04%.

[0106] <Preparation of the positive electrode>

[0107] Conductive agent (conductive carbon black) and binder (polyvinylidene fluoride) were mixed in a certain proportion, and N-methylpyrrolidone (NMP) was added to prepare a conductive adhesive with a solid content of 7w%. After mixing, lithium cobalt oxide was added, and the mixture was stirred under vacuum until the system was homogeneous, obtaining a positive electrode slurry with a solid content of 75w. The mass ratio of lithium cobalt oxide:conductive agent:binder was 97:1:2. The positive electrode slurry was uniformly coated on one surface of an 8μm thick aluminum foil, intermittently coated according to the cell size, and then dried at 85℃ to obtain a positive electrode sheet with a single-sided coating of positive electrode material layer with a coating thickness of 100μm. After cold pressing (cold pressing pressure of 85T), a compacted positive electrode sheet was obtained. The positive electrode sheet was cut into fixed sizes and then vacuum dried at 85℃ for 4h to obtain a positive electrode sheet with a specification of 74mm×867mm for later use. The coating weight per unit area of ​​the positive electrode material layer is 300 mg / 1540.25 mm. 2 The compaction density of the positive electrode material layer is 4.20 g / cm³. 3 .

[0108] <Preparation of Electrolyte>

[0109] In a dry argon atmosphere, non-aqueous solvents ethylene carbonate (EC), propylene carbonate (PC), and diethyl carbonate (DEC) were mixed in a weight ratio of 1:1:1. Lithium salt LiPF6 was then added to the non-aqueous solvent and mixed thoroughly to obtain the electrolyte. The molar concentration of lithium salt LiPF6 was 1.15 mol / L.

[0110] <Preparation of the diaphragm>

[0111] A porous polyethylene film with a thickness of 7μm (provided by Celgard) was used as the separator.

[0112] <Preparation of Lithium-ion Batteries>

[0113] The positive electrode, separator, and negative electrode are stacked in sequence, with the separator acting as a separator between the positive and negative electrodes. The electrode assembly is then wound to obtain the electrode assembly. The electrode assembly is placed in an outer packaging foil and dehydrated at 80°C. The prepared electrolyte is then injected, and the battery undergoes vacuum sealing, settling, formation, shaping, and capacity testing to obtain a soft-pack lithium-ion battery.

[0114] Examples 1-2 to 1-28

[0115] Except for adjusting the relevant preparation parameters according to Table 1, the rest is the same as in Example 1-1.

[0116] Examples 2-1 to 2-11

[0117] Except for adjusting the relevant preparation parameters according to Table 2, the rest is the same as in Examples 1-1.

[0118] Comparative Example 1

[0119] Except for not setting grooves on the single-sided negative electrode material layer area in the <Preparation of Negative Electrode Sheet>, the rest is the same as in Example 1-1.

[0120] Comparative Examples 2 to 6

[0121] Except for adjusting the relevant preparation parameters according to Table 1, the rest is the same as in Example 1-1.

[0122] The preparation parameters and performance parameters of each embodiment and comparative example are shown in Table 1 and Table 2.

[0123] Table 1

[0124] Note: In Table 1, " / " indicates that there are no relevant preparation parameters.

[0125] As can be seen from Examples 1-1 to 1-28 and Comparative Examples 1 to 6, by adjusting the values ​​of A and B within the above range and setting multiple grooves on the negative electrode material layer in the single-sided negative electrode material layer region, the low-temperature kinetic maximum rate of the single-sided negative electrode material layer region of the lithium-ion battery is larger, the winding efficiency related to feed breakage / single-sided negative electrode material layer region breakage is improved, the 500-cycle capacity retention rate is larger, and the interface characteristics of the single-sided negative electrode material layer region are improved. This indicates that the above-mentioned setting of the single-sided negative electrode sheet improves the curling of the single-sided negative electrode sheet, thereby reducing the risk of feed breakage and feed breakage during the actual processing of the single-sided negative electrode sheet, improving the winding efficiency of the secondary battery, and while taking into account the energy density of the lithium-ion battery, the lithium-ion battery has good kinetic performance and safety performance. In Comparative Example 1, no grooves are provided on the negative electrode material layer in the single-sided negative electrode material layer region; in Comparative Examples 2 to 6, the values ​​of A and / or B are not within the scope of this application, resulting in a lower maximum low-temperature kinetic rate of the single-sided negative electrode material layer region of the lithium-ion battery, a lower winding efficiency related to feed folding / single-sided negative electrode material layer region breakage, and a lower 500-cycle capacity retention rate, while also exhibiting poor interface characteristics in the single-sided negative electrode material layer region. In contrast, the lithium-ion batteries of Examples 1-1 to 1-28 exhibit a higher maximum low-temperature kinetic rate of the single-sided negative electrode material layer region, improved winding efficiency related to feed folding / single-sided negative electrode material layer region breakage, a higher 500-cycle capacity retention rate, and improved interface characteristics in the single-sided negative electrode material layer region, demonstrating good safety and kinetic performance.

[0126] The value of (L-L1) / L typically affects the safety and kinetic performance of lithium-ion batteries. As can be seen from Examples 1-1, 1-6, and 1-7, when the value of (L-L1) / L is within the range of this application, the maximum low-temperature kinetic rate of the single-sided negative electrode material layer is larger, the winding efficiency related to feed breakage / single-sided negative electrode material layer breakage is larger, the 500-cycle capacity retention rate is larger, and the interface characteristics of the single-sided negative electrode material layer are better. This indicates that the curling of the single-sided negative electrode sheet is improved, thereby reducing the risk of feed breakage and feed breakage during actual processing of the single-sided negative electrode sheet, improving the winding efficiency of the secondary battery, and resulting in good kinetic and safety performance of the lithium-ion battery.

[0127] The value of C typically affects the safety and kinetic performance of lithium-ion batteries. As can be seen from Examples 1-1, 1-6 to 1-7, 1-18, and 1-27 to 1-28, when the value of C is within the range of this application, the maximum low-temperature kinetic rate of the single-sided negative electrode material layer is larger, the winding efficiency related to feed breakage / single-sided negative electrode material layer breakage is larger, the 500-cycle capacity retention rate is larger, and the interface characteristics of the single-sided negative electrode material layer are better. This indicates that the curling of the single-sided negative electrode sheet is improved, thereby reducing the risk of feed breakage and feed breakage during the actual processing of the single-sided negative electrode sheet, improving the winding efficiency of the secondary battery, and demonstrating good kinetic and safety performance of the lithium-ion battery.

[0128] The value of D typically affects the safety and kinetic performance of lithium-ion batteries. As can be seen from Examples 1-1, 1-2 to 1-5, 1-8 to 1-9, and 1-18, when the value of D is within the range of this application, the maximum low-temperature kinetic rate of the single-sided negative electrode material layer is larger, the winding efficiency related to feed breakage / single-sided negative electrode material layer breakage is larger, the 500-cycle capacity retention rate is larger, and the interface characteristics of the single-sided negative electrode material layer are better. This indicates that the curling of the single-sided negative electrode sheet is improved, thereby reducing the risk of feed breakage and feed breakage during actual processing of the single-sided negative electrode sheet, improving the winding efficiency of the secondary battery, and resulting in good kinetic and safety performance of the lithium-ion battery.

[0129] The value of h typically affects the safety and kinetic performance of lithium-ion batteries. As can be seen from Examples 1-1, 1-10 to 1-11, and 1-19 to 1-20, when the value of h is within the range of this application, the maximum low-temperature kinetic rate of the single-sided negative electrode material layer is larger, the winding efficiency related to feed breakage / single-sided negative electrode material layer breakage is larger, the 500-cycle capacity retention rate is larger, and the interface characteristics of the single-sided negative electrode material layer are better. This indicates that the curling of the single-sided negative electrode sheet is improved, thereby reducing the risk of feed breakage and feed breakage during the actual processing of the single-sided negative electrode sheet, improving the winding efficiency of the secondary battery, and improving the wetting performance of the electrolyte on the single-sided negative electrode sheet. Therefore, the lithium-ion battery exhibits good kinetic and safety performance.

[0130] The value of d typically affects the safety and kinetic performance of lithium-ion batteries. As can be seen from Examples 1-1, 1-12 to 1-13, and 1-21 to 1-22, when the value of d is within the range of this application, the maximum low-temperature kinetic rate of the single-sided negative electrode material layer is larger, the winding efficiency related to feed breakage / single-sided negative electrode material layer breakage is larger, the 500-cycle capacity retention rate is larger, and the interface characteristics of the single-sided negative electrode material layer are better. This indicates that the curling of the single-sided negative electrode sheet is improved, thereby reducing the risk of feed breakage and feed breakage during actual processing of the single-sided negative electrode sheet, improving the wetting performance of the electrolyte on the single-sided negative electrode sheet, increasing the winding efficiency of the secondary battery, and resulting in good kinetic and safety performance of the lithium-ion battery.

[0131] The value of L2 typically affects the safety and kinetic performance of lithium-ion batteries. As can be seen from Examples 1-1, 1-14 to 1-15, and 1-23 to 1-24, when the value of L2 is within the range of this application, the maximum low-temperature kinetic rate of the single-sided negative electrode material layer is larger, the winding efficiency related to feed breakage / single-sided negative electrode material layer breakage is larger, the 500-cycle capacity retention rate is larger, and the interface characteristics of the single-sided negative electrode material layer are better. This indicates that the curling of the single-sided negative electrode sheet is improved, thereby reducing the risk of feed breakage and feed breakage during the actual processing of the single-sided negative electrode sheet, improving the winding efficiency of the secondary battery, and resulting in good kinetic and safety performance of the lithium-ion battery.

[0132] The value of α typically affects the safety and kinetic performance of lithium-ion batteries. As can be seen from Examples 1-1, 1-16 to 1-17, and 1-25 to 1-26, when the value of α is within the range of this application, the maximum low-temperature kinetic rate of the single-sided negative electrode material layer is larger, the winding efficiency related to feed breakage / single-sided negative electrode material layer breakage is larger, the 500-cycle capacity retention rate is larger, and the interface characteristics of the single-sided negative electrode material layer are better. This indicates that the curling of the single-sided negative electrode sheet is improved, thereby reducing the risk of feed breakage and feed breakage during the actual processing of the single-sided negative electrode sheet, improving the winding efficiency of the secondary battery, and demonstrating good kinetic and safety performance of the lithium-ion battery.

[0133] The value of S1 / S2 typically affects the safety and kinetic performance of lithium-ion batteries. Examples 1-1, 1-6 to 1-7, 1-12 to 1-15, 1-18, 1-21 to 1-24, and 1-27 to 1-28 show that when the value of S1 / S2 is within the range of this application, the maximum low-temperature kinetic rate of the single-sided negative electrode material layer is larger, the winding efficiency related to feed breakage / single-sided negative electrode material layer breakage is larger, the 500-cycle capacity retention rate is larger, and the interface characteristics of the single-sided negative electrode material layer are better. This indicates that the curling of the single-sided negative electrode sheet is improved, thereby reducing the risk of feed breakage and feed breakage during actual processing of the single-sided negative electrode sheet, improving the winding efficiency of the secondary battery, and resulting in good kinetic and safety performance of the lithium-ion battery.

[0134] Table 2

[0135] Note: In Table 2, " / " indicates that there are no related effect parameters.

[0136] The value of H typically affects the safety performance, energy density, and kinetic performance of lithium-ion batteries. As seen in Examples 1-1, 2-1 to 2-2, and 2-7 to 2-8, when the value of H falls within the range specified in this application, the maximum low-temperature kinetic rate of the single-sided negative electrode material layer is higher, the winding efficiency related to feed breakage / single-sided negative electrode material layer breakage is higher, the energy density is higher, the 500-cycle capacity retention is higher, and the interface characteristics of the single-sided negative electrode material layer are better. This indicates that the curling of the single-sided negative electrode sheet is improved, thereby reducing the risk of feed breakage and feed breakage during actual processing of the single-sided negative electrode sheet, improving the winding efficiency of the secondary battery, and achieving good kinetic and safety performance while maintaining the energy density of the lithium-ion battery. In Examples 2-8, the value of H is relatively high, resulting in a relatively low energy density compared to other lithium-ion batteries of the same volume.

[0137] The value of m typically affects the safety performance, energy density, and kinetic performance of lithium-ion batteries. As can be seen from Examples 1-1, 2-3 to 2-4, and 2-9 to 2-10, when the value of m is within the range of this application, the maximum low-temperature kinetic rate of the single-sided negative electrode material layer is larger, the winding efficiency related to feed breakage / single-sided negative electrode material layer breakage is larger, the energy density is higher, the 500-cycle capacity retention rate is larger, and the interface characteristics of the single-sided negative electrode material layer are better. This indicates that the curling of the single-sided negative electrode sheet is improved, thereby reducing the risk of feed breakage and feed breakage during the actual processing of the single-sided negative electrode sheet, improving the winding efficiency of the secondary battery, and achieving good kinetic and safety performance while maintaining the energy density of the lithium-ion battery. In Examples 2-9, the value of m is relatively small, resulting in a relatively low energy density among lithium-ion batteries of the same volume.

[0138] The values ​​of PD1 / PD2 and PD2 typically affect the safety performance, energy density, and kinetic performance of lithium-ion batteries. As can be seen from Examples 1-1, 2-5 to 2-6, and 2-11, when the values ​​of PD1 / PD2 and PD2 are within the range of this application, the maximum low-temperature kinetic rate of the single-sided negative electrode material layer is larger, the winding efficiency related to feed breakage / single-sided negative electrode material layer breakage is larger, the energy density is higher, the 500-cycle capacity retention rate is larger, and the interface characteristics of the single-sided negative electrode material layer are better. This indicates that the curling of the single-sided negative electrode sheet is improved, thereby reducing the risk of feed breakage and feed breakage during actual processing of the single-sided negative electrode sheet, improving the winding efficiency of the secondary battery, and achieving good kinetic and safety performance while maintaining the energy density of the lithium-ion battery.

[0139] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, or article that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, or article.

[0140] The various embodiments in this specification are described in a related manner. The same or similar parts between the various embodiments can be referred to each other. Each embodiment focuses on describing the differences from other embodiments.

[0141] The above description is only a preferred embodiment of this application and is not intended to limit this application. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the scope of protection of this application.

Claims

1. A negative electrode sheet, comprising a negative electrode current collector and a negative electrode material layer, wherein along the length direction of the negative electrode sheet, the negative electrode sheet includes an empty foil region and a single-sided negative electrode material layer region connecting the empty foil region, wherein based on the length of the negative electrode sheet, the length ratio of the empty foil region is A, the length ratio of the single-sided negative electrode material layer region is B, 1 / 60≤A≤1 / 11, 1 / 20≤B≤1 / 5; Multiple grooves are provided on the negative electrode material layer in the single-sided negative electrode material layer region. The negative electrode current collector includes copper foil with a thickness of H μm and 4≤H≤8.

2. The negative electrode sheet according to claim 1, wherein, 1 / 30 ≤ A ≤ 1 / 11; and / or, 1 / 14 ≤ B ≤ 1 / 5.

3. The negative electrode sheet according to claim 1, wherein, Along the thickness direction of the negative electrode sheet, a single groove has an orthographic projection on the negative electrode material layer. Along the length direction of the negative electrode sheet, the length of the single-sided negative electrode material layer region is L mm. The negative electrode sheet also includes a double-sided negative electrode material layer region. The single-sided negative electrode material layer region and the double-sided negative electrode material layer region have a boundary line. The shortest distance between the outer contour of the orthographic projection of a single groove and the boundary line is L1 mm, and 1 / 2≤(L-L1) / L≤1.

4. The negative electrode sheet according to claim 3, wherein, Along the width direction of the negative electrode sheet, the single-sided negative electrode material layer region includes a middle region and two edge regions connected to the middle region. The grooves are distributed at intervals in the two edge regions and penetrate the two edge regions respectively. Based on the width of the negative electrode material layer of the single-sided negative electrode material layer region, the length ratio of the middle region is C, where 0%≤C≤30%.

5. The negative electrode sheet according to claim 1, wherein it satisfies at least one of the following characteristics: (1) The grooves are spaced apart along the length of the negative electrode sheet; (2) The coating weight per unit area of ​​the negative electrode material layer in the single-sided negative electrode material layer region is mg / 1540.25mm. 2 , 100≤m≤200.

6. The negative electrode sheet according to claim 1, wherein, Along the width direction of the negative electrode sheet, the width of the negative electrode sheet is D mm, and along the length direction of the negative electrode sheet, the length of the single-sided negative electrode material layer region is L mm, 1≤L / D≤2, 50≤D≤130.

7. The negative electrode sheet according to claim 1, wherein, The negative electrode sheet further includes a double-sided negative electrode material layer region, wherein the negative electrode material layer includes a negative electrode active material, which includes at least one of graphite or silicon-carbon composite materials, and the compaction density of the negative electrode material layer in the single-sided negative electrode material layer region is PD1 g / cm³. 3 The compaction density of the negative electrode material layer in the double-sided negative electrode material layer region is PD2 g / cm³. 3 , 0.95≤PD1 / PD2≤1.

8. The negative electrode sheet according to claim 7, wherein, 1.5≤PD2≤1.

8.

9. The negative electrode sheet according to claim 1, wherein, Along the thickness direction of the negative electrode sheet, the average depth of the plurality of grooves is h μm, where 5≤h≤30.

10. The negative electrode sheet according to any one of claims 1 to 9, wherein the plurality of grooves are distributed in a strip shape, and each groove has an orthographic projection onto the negative electrode material layer along the thickness direction of the negative electrode sheet, and satisfies at least one of the following conditions: (1) The average width of the orthographic projection of the plurality of grooves is d μm, 50≤d≤110; (2) The shortest distance between the outer contours of the orthographic projections of two adjacent grooves is L2 mm, 0.5≤L2≤1.

5.

11. The negative electrode sheet according to claim 10, wherein, The angle between the centerline of a single groove and the length direction of the negative electrode sheet is α°, where 20 ≤ α ≤ 75°.

12. The negative electrode sheet according to claim 11, wherein, Along the thickness direction of the negative electrode sheet, the total area of ​​the orthographic projection of the plurality of grooves is S1 mm. 2 The projected area of ​​the single-sided negative electrode material layer region is S² mm. 2 , 2%≤S1 / S2≤10%.

13. A secondary battery comprising a negative electrode sheet according to any one of claims 1 to 12.

14. The secondary battery according to claim 13, wherein, The secondary battery has a wound structure, and the empty foil area is located at the starting end of the wound structure.

15. An electronic device comprising the secondary battery of claim 13 or claim 14.

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