A negative electrode sheet, a secondary battery, and an electronic device

Abstract

The application provides a negative electrode sheet, a secondary battery and an electronic device. The negative electrode sheet comprises a negative electrode current collector and a negative electrode material layer. In the length direction of the negative electrode sheet after being unfolded, the negative electrode sheet comprises an empty foil area and a single-sided negative electrode material layer area connected with the empty foil area. The length proportion of the empty foil area is A, and the length proportion of the single-sided negative electrode material layer area is B, based on the length of the negative electrode sheet. 1 / 60≤A≤1 / 11, and 1 / 20≤B≤1 / 5. A groove is arranged on the negative electrode material layer of the single-sided negative electrode material layer area, the groove extends in the width direction of the negative electrode sheet after being unfolded and is arranged at intervals in the length direction of the negative electrode sheet after being unfolded. Through the above arrangement, the risk of belt breaking and material folding during actual processing of the single-sided negative electrode sheet can be reduced.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of electrochemistry, in particular to a negative electrode sheet, a secondary battery and an electronic device. BACKGROUND

[0002] Secondary batteries, such as lithium ion batteries, have characteristics of high specific energy, high working voltage, low self-discharge rate, small volume, light weight, etc., and have a wide range of applications in the consumer electronics field. With the wide application of lithium ion batteries, the market has put forward higher and higher requirements for the performance of lithium ion batteries.

[0003] At present, the winding structure is the most mature structure process of lithium ion batteries. The negative electrode sheet with a single-layer negative electrode material layer is usually used as the initial winding to improve the proportion of active materials and increase the energy density of the secondary battery. However, the negative electrode sheet with a single-layer negative electrode material layer region will have obvious stress concentration after cold pressing, which will cause obvious negative electrode sheet curling problems. The curled single-layer negative electrode sheet structure will affect the electrode assembly structure and the adhesive during the winding process, and even the belt breakage is prone to occur at the junction between the double-layer and single-layer regions. SUMMARY

[0004] The purpose of the present application is to provide a negative electrode sheet, a secondary battery and an electronic device, so that the curling of the single-layer region negative electrode sheet is improved, the risk of material folding and belt breakage of the single-layer region negative electrode sheet during processing is reduced, and the wettability of the electrolyte to the single-layer region negative electrode sheet is improved, thereby improving the kinetic performance and safety performance of the secondary battery.

[0005] It should be noted that the present application uses lithium ion batteries as an example of a secondary battery to explain the present application, but the secondary battery of the present application is not limited to lithium ion batteries. The specific technical solutions are as follows:

[0006] The first aspect of the present application provides a negative electrode sheet, which comprises a negative electrode current collector and a negative electrode material layer. Along the length direction of the negative electrode sheet after being unfolded, the negative electrode sheet comprises a hollow foil region and a single-layer negative electrode material layer region connected to the hollow foil region. Based on the length of the negative electrode sheet, the length ratio of the hollow foil region is A, and the length ratio of the single-layer 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. A plurality of grooves are arranged on the negative electrode material layer of the single-layer negative electrode material layer region, and the grooves are arranged at intervals along the length direction of the negative electrode sheet. By arranging grooves on the single-layer negative electrode material layer region and applying it to a secondary battery, the curling of the single-layer negative electrode material layer region can be improved, the risk of material folding and belt breakage of the single-layer negative electrode material layer region during processing can be reduced, and the wettability of the electrolyte to the single-layer negative electrode material layer region can be improved, thereby improving the kinetic performance and safety performance of the secondary battery.

[0007] In some embodiments of the present application, along the thickness direction of the negative electrode tab, a single groove has a positive projection on the negative material layer, along the length direction of the negative electrode tab, the length of the single-sided negative material layer region is L mm, the negative electrode tab further comprises a double-sided negative material layer region, the single-sided negative material layer region and the double-sided negative material layer region have a boundary line, the shortest distance between the outer contour of the positive projection of the single groove and the boundary line is L1 mm, 1 / 2≤(L-L1) / L≤1. In some embodiments of the present application, along the width direction of the negative electrode tab after being developed, the single-sided negative material layer region comprises a middle region and two edge regions connected with the middle region, the grooves are spaced apart and respectively penetrate through the two edge regions. Based on the width of the negative material layer of the single-sided negative material layer region, the length proportion of the middle region is C, 0%≤C≤30%. Through the above setting, the curling problem of the single-sided negative material layer region is improved, thereby reducing the risk of belt breakage and material folding in the actual processing of the single-sided region negative electrode tab, and at the same time, the wettability of the electrolyte to the single-sided region negative electrode tab is improved, the liquid retention performance of the single-sided negative material layer region is improved, thereby improving the kinetic performance and safety performance of the secondary battery, and in addition, the actual production efficiency is taken into account and the processing is facilitated.

[0008] In some embodiments of the present application, at least one of the following characteristics is satisfied: (1) the negative current collector comprises a copper foil, the thickness of the copper foil is H μm, 4≤H≤8; (2) the unit area coating weight of the negative material layer of the single-sided negative material layer region is m mg / 1540.25mm 2 , 100≤m≤200. Through the above setting, the curling problem of the single-sided negative material layer region is improved, thereby further reducing the risk of belt breakage and material folding in the actual processing of the single-sided region negative electrode tab.

[0009] In some embodiments of the present application, along the width direction of the negative electrode tab, the width of the negative electrode tab is D mm, along the length direction of the negative electrode tab, the length of the single-sided negative material layer region is L mm, 1≤L / D≤2, 50≤D≤130. By adjusting the values of L / D and D within the above range, the curling problem of the single-sided negative material layer region is improved, thereby further reducing the risk of belt breakage and material folding in the actual processing of the single-sided region negative electrode tab, and in addition, the width of the negative electrode tab and the length of the single-sided negative material layer region are related to the shape of the electrode assembly formed after winding, and adjusting the shape of the electrode assembly is conducive to taking into account the actual production efficiency and processing performance.

[0010] In some embodiments of the present application, the negative electrode sheet further comprises a double-sided negative material layer region, the negative material layer comprises a negative active material, the negative active material comprises at least one of graphite or silicon-carbon composite material, the compaction density of the negative material layer of the single-sided negative material layer region is PD1 g / cm 3 , the compaction density of the negative material layer of the double-sided negative material layer region is PD2 g / cm 3 , and 0.95≤PD1 / PD2≤1. In some embodiments of the present application, 1.5≤PD2≤1.8. Through the above setting, the effect of reducing the deformation of the single-sided negative material layer region caused by the cold pressing residual stress is more obvious while the energy density of the secondary battery is taken into account, the curling problem of the single-sided negative material layer region is improved, and the risk of belt breakage and material folding during actual processing of the single-sided region negative electrode sheet is further reduced.

[0011] In some embodiments of the present application, along the thickness direction of the negative electrode sheet, the average depth of the plurality of grooves is h μm, and 5≤h≤30. By adjusting the value of h within the above range, the curling problem of the single-sided negative material layer region is improved, thereby reducing the risk of belt breakage and material folding during actual processing of the single-sided region negative electrode sheet, and in addition, reducing the groove depth too large leads to taking into account the actual production efficiency and being beneficial to processing.

[0012] In some embodiments of the present application, the plurality of grooves are distributed in a strip shape, and along the thickness direction of the negative electrode sheet, a single groove has a projection on the negative material layer, which satisfies at least one of the following conditions: (1) the average width of the projection of the plurality of grooves is d μm, and 50≤d≤110; (2) the shortest distance between the outer contours of the projections of two adjacent grooves is L2 mm, and 0.5≤L2≤1.5. In some embodiments of the present application, the included angle between the center line of a single groove and the length direction of the negative electrode sheet is α°, and 20≤α≤75. Through the above setting, the curling problem of the single-sided negative material layer region is improved, thereby reducing the risk of belt breakage and material folding during actual processing of the single-sided region negative electrode sheet, and at the same time, the wettability of the electrolyte to the single-sided region negative electrode sheet is improved, the liquid retention performance of the single-sided negative material layer region is improved, thereby improving the kinetic performance and safety performance of the secondary battery. In addition, the actual production efficiency is taken into account and is beneficial to processing.

[0013] In some embodiments of the present application, along the thickness direction of the negative electrode sheet, the total area of the projections of the plurality of grooves is S1 mm 2 , and the projection area of the single-sided negative material layer region is S2 mm 2, 2%≤S1 / S2≤10%. By regulating the value of S1 / S2 within the above range, the overall stiffness of the single-face material layer region is improved, thereby the curling problem of the single-face negative material layer region is improved, and the risk of strip breakage and material folding of the single-face region negative electrode sheet in the actual processing process is reduced.

[0014] The second aspect of the present application provides a secondary battery comprising the negative electrode sheet in any of the above embodiments. The application of the negative electrode sheet of the present application to the secondary battery improves the curling of the single-face region negative electrode sheet, reduces the risk of strip breakage and material folding of the single-face region negative electrode sheet in the processing process, and improves the wettability of the electrolyte to the single-face region negative electrode sheet, thereby improving the kinetic performance and safety performance of the secondary battery.

[0015] In some embodiments of the present application, the secondary battery is of a winding structure, and the empty foil region and the single-face negative material layer region are located at the starting end of the winding structure.

[0016] The third aspect of the present application provides an electronic device comprising the secondary battery in any of the above embodiments. Thus, the electronic device provided by the present application has good use performance.

[0017] The beneficial effects of the present application are:

[0018] The present application provides a negative electrode sheet, a secondary battery and an electronic device. The negative electrode sheet comprises a negative electrode current collector and a negative material layer. Along the length direction of the negative electrode sheet, the negative electrode sheet comprises an empty foil region and a single-face negative material layer region connected to the empty foil region. The length ratio of the empty foil region is A, and the length ratio of the single-face negative material layer region is B, based on the length of the negative electrode sheet, 1 / 60≤A≤1 / 11, and 1 / 20≤B≤1 / 5. A plurality of grooves are arranged on the negative material layer of the single-face negative material layer region, and the grooves are arranged at intervals along the length direction of the negative electrode sheet. By arranging grooves on the single-face region negative electrode sheet, the curling of the single-face region negative electrode sheet is improved, the risk of strip breakage and material folding of the single-face region negative electrode sheet in the processing process is reduced, and the wettability of the electrolyte to the single-face region negative electrode sheet is improved, thereby improving the kinetic performance and safety performance of the secondary battery.

[0019] Of course, implementing any product or method of the present application does not necessarily require all the advantages described above to be achieved at the same time. BRIEF DESCRIPTION OF DRAWINGS

[0020] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the drawings needed to be used in the embodiments or prior art description will be briefly introduced below. Obviously, the drawings in the following description are only some embodiments of the present application, and other embodiments can also be obtained by those skilled in the art based on these drawings.

[0021] Figure 1 A schematic view of a winding structure formed for an electrode assembly in an embodiment of the present application;

[0022] Figure 2 A schematic view of a winding structure formed for an electrode assembly in an embodiment of the present application; Figure 1 A partial front view of a negative electrode tab after the electrode assembly is unfolded;

[0023] Figure 3 A schematic view of a winding structure formed for an electrode assembly in an embodiment of the present application; Figure 2 A schematic view of a longitudinal cross-sectional structure in the thickness direction of the negative electrode tab.

[0024] Reference signs are as follows:

[0025] Electrode assembly 001; positive electrode tab 10; negative electrode tab 20; separator 30; positive current collector 11; positive electrode material layer 12; negative 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 DESCRIPTION

[0026] The technical solutions in the present application will be described clearly and completely below in combination with the embodiments and drawings of the present application. Obviously, the described embodiments are only some of the embodiments of the present application, but not all the embodiments. All other embodiments obtained by those skilled in the art based on the present application belong to the scope of protection of the present application.

[0027] It should be noted that in the specific embodiments of the present application, the present application is explained by taking lithium ion batteries as examples of secondary batteries, but the secondary batteries of the present application are not limited to lithium ion batteries. The specific technical solutions are as follows:

[0028] The first aspect of the present application provides a negative electrode tab, which comprises a negative electrode current collector and a negative electrode material layer. Along the length direction of the negative electrode tab after being spread out, the negative electrode tab comprises an empty foil area and a single-sided negative electrode material layer area connected to the empty foil area. Based on the length of the negative electrode tab, the length ratio of the empty foil area is A, and the length ratio of the single-sided negative electrode material layer area 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 formed by any two of the above 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 formed by any two of the above values. A plurality of grooves are arranged on the negative electrode material layer of the single-sided negative electrode material layer area, and the grooves are arranged at intervals along the length direction of the negative electrode tab.

[0029] By adjusting the values of A and B within the above range and arranging grooves on the negative electrode material layer of the single-sided negative electrode material layer area, the present application is beneficial to dispersing the cold-pressing residual stress received by the single-sided negative electrode material layer area, improving the stress concentration problem of the single-sided negative electrode material layer area, and improving the curling of the single-sided area negative electrode tab when applied to a secondary battery, thereby reducing the risk of belt breakage and material folding during the actual processing of the single-sided area negative electrode tab, improving the winding rate of the secondary battery, reducing the capacity loss and safety risk of short circuit caused by folding, and improving the wettability of the electrolyte to the single-sided area negative electrode tab by arranging grooves on the negative electrode material layer of the single-sided negative electrode material layer area, thereby improving the liquid retention performance of the single-sided negative electrode material layer area and improving the dynamic performance and safety performance of the secondary battery.

[0030] In some embodiments of the present application, along the thickness direction of the negative electrode tab, a single groove has a positive projection on the negative electrode material layer, the length of the single-sided negative electrode material layer area is L mm along the length direction of the negative electrode tab, and the negative electrode tab further comprises a double-sided negative electrode material layer area. The single-sided negative electrode material layer area and the double-sided negative electrode material layer area have a boundary line, the shortest distance between the outer contour of the positive projection of the single groove and the boundary line is L1 mm, and 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 formed by any two of the above values.

[0031] 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.

[0032] 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.

[0033] 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.

[0034] In some embodiments of the present application, along the width direction of the negative electrode tab, the single-sided negative electrode material layer region comprises a middle region and two edge regions connected with the middle region, the grooves are arranged at intervals in the two edge regions and respectively pass through the two edge regions, and the length ratio of the middle region to the negative electrode material layer of the single-sided negative electrode material layer region is C, 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 formed by any two of them. Illustratively, as shown in Figure 2 the width direction (Y direction) of the negative electrode tab 20, the single-sided negative electrode material layer region 220 comprises a middle region and two edge regions connected with the middle region, wherein the two edge regions are the part in the dashed box in the single-sided negative electrode material layer region 220. The grooves 2201 are arranged at intervals in the two edge regions and respectively pass through the two edge regions. By adjusting the value of C within the above range, the curling problem of the single-sided negative electrode material layer region is improved, thereby reducing the risk of breaking the belt and folding the material during the actual processing of the single-sided region negative electrode tab, and also improving the wettability of the electrolyte to the single-sided region negative electrode tab, improving the liquid retention performance of the single-sided negative electrode material layer region, thereby improving the kinetic performance and safety performance of the secondary battery, and in addition, the actual production efficiency is taken into account and the processing is facilitated.

[0035] In some embodiments of the present application, the negative electrode current collector comprises a copper foil, and the thickness of the copper foil is H μm, 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 formed by any two of them. Illustratively, as shown in Figure 3 the thickness of the negative electrode current collector 21 is H μm. By adjusting the value of H within the above range, the curling problem of the single-sided negative electrode material layer region is improved, thereby further reducing the risk of breaking the belt and folding the material during the actual processing of the single-sided region negative electrode tab, while taking into account the energy density, and also improving the wettability of the electrolyte to the single-sided region negative electrode tab, improving the liquid retention performance of the single-sided negative electrode material layer region, thereby improving the kinetic performance and safety performance of the secondary battery. The adjustment method of the thickness of the negative electrode current collector in the present application is not particularly limited as long as the purpose of the present application can be achieved, for example, a commercially available current collector with different thicknesses can be selected, and the thickness of the negative electrode current collector is determined by combining the test method of "L, A, B, L1, C, H, D, h, d, L2, α, S1 / S2 test" in the present application, and then the negative electrode current collector with the required thickness is selected.

[0036] In some embodiments of the present application, the unit area coating weight of the negative electrode material layer of the single-sided negative electrode material layer region is m mg / 1540.25mm 2, 100≤m≤200. For example, m can be 100, 110, 120, 130, 140, 150, 160, 170, 180, 190, 200, or a range defined by any two of them. By regulating the value of m within the above range, the curling problem of the single-face negative material layer region is improved while the energy density is ensured, thereby further reducing the risk of breaking the belt and folding the material during the actual processing of the single-face negative electrode sheet, and also improving the wettability of the electrolyte on the single-face negative electrode sheet and improving the liquid retention performance of the single-face negative material layer region, thereby improving the kinetic performance and safety performance of the secondary battery.

[0037] In some embodiments of the present application, the negative current collector comprises a copper foil, the thickness of the copper foil is H μm, 4≤H≤8, for example, H can be 4, 4.5, 5, 5.5, 6, 6.5, 7, 7.5, 8, or a range defined by any two of them; and the unit area coating weight of the negative material layer of the single-face negative material layer region is m mg / 1540.25mm 2 , 100≤m≤200, for example, m can be 100, 110, 120, 130, 140, 150, 160, 170, 180, 190, 200, or a range defined by any two of them. By regulating the value of H and the value of m within the above range, the curling problem of the single-face negative material layer region is improved while the energy density is ensured, thereby further reducing the risk of breaking the belt and folding the material during the actual processing of the single-face negative electrode sheet, and also improving the wettability of the electrolyte on the single-face negative electrode sheet and improving the liquid retention performance of the single-face negative material layer region, thereby improving the kinetic performance and safety performance of the secondary battery.

[0038] In some embodiments of the present application, along the width direction of the negative electrode sheet, the width of the negative electrode sheet is D mm, along the length direction of the negative electrode sheet, the length of the single-face negative material layer region is L mm, 1≤L / D≤2, 50≤D≤130. For example, 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 defined by any two of them; D can be 50, 60, 70, 80, 90, 100, 110, 120, 130, or a range defined by any two of them. For example, as shown in Figure 2As shown, the width of the negative electrode tab 20 along the width direction (Y direction) after being unfolded is D mm, and the length of the single-sided negative material layer region 220 along the length direction (Y direction) after being unfolded is L mm. By adjusting the values of L / D and D within the above ranges, the greater the ratio of the length L of the single-sided negative material layer region to the width D of the negative electrode tab, the smaller the constraint of the double-sided negative material layer region on the single-sided negative material layer region, and the greater the amplitude of the corner curling. By adjusting the values of L / D and D within the above ranges, the curling problem of the single-sided negative material layer region is improved, thereby further reducing the risk of belt breaking and material folding during the actual processing of the single-sided region negative electrode tab. In addition, it is also beneficial to improve the wettability of the electrolyte on the single-sided region negative electrode tab and improve the liquid retention performance of the single-sided negative material layer region, thereby improving the kinetic performance and safety performance of the secondary battery. In addition, the width of the negative electrode tab and the length of the single-sided negative material layer region are related to the shape of the electrode assembly formed after winding. Adjusting the shape of the electrode assembly is beneficial to balance the actual production efficiency and processing performance.

[0039] In some embodiments of the present application, the negative electrode tab further comprises a double-sided negative material layer region, the negative material layer comprises a negative active material, the negative active material comprises at least one of graphite or silicon-carbon composite material, the compaction density of the negative material layer of the single-sided negative material layer region is PD1 g / cm 3 , the compaction density of the negative material layer of the double-sided negative material layer region is PD2 g / cm 3 , and 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 a range composed of any two of the above values. By selecting the above types of negative active materials and adjusting the value of PD1 / PD2 within the above range, the effect of reducing the deformation of the single-sided negative material layer region caused by cold pressing residual stress is more obvious while the energy density of the secondary battery is considered, and the curling problem of the single-sided negative material layer region is improved, thereby further reducing the risk of belt breaking and material folding during the actual processing of the single-sided region negative electrode tab.

[0040] 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.

[0041] 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.

[0042] 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.

[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 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.

[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. 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.

[0045] 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 included angle between the center line of the single groove 2201 and the length direction (X direction) of the developed negative pole piece 20 is a°. By adjusting the value of a within the above range, the curling problem of the single-face negative material layer area is improved, thereby reducing the risk of breaking the belt and folding the material during the actual processing of the single-face area negative pole piece. At the same time, the wettability of the electrolyte to the single-face area negative pole piece is improved, the liquid retention performance of the single-face negative material layer area is improved, and the kinetic performance of the secondary battery is improved. In addition, the actual production efficiency and energy density are considered, and the processing is facilitated.

[0046] In some embodiments of the present application, the included angle between the center line of the single groove and the length direction of the negative pole piece is a°, 40≤a≤50. For example, the value of a can be 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, or a range composed of any two of them. By adjusting the value of a within the above range, the stress dispersion is more obvious by setting the groove obliquely, which is beneficial to further improve the curling problem of the single-face negative material layer area, thereby reducing the risk of breaking the belt and folding the material during the actual processing of the single-face area negative pole piece. At the same time, the wettability of the electrolyte to the single-face area negative pole piece is improved, the liquid retention performance of the single-face negative material layer area is improved, and the kinetic performance of the secondary battery is improved. In addition, the actual production efficiency and energy density are considered, and the processing is facilitated.

[0047] In some embodiments of the present application, along the thickness direction of the negative pole piece, the total area of the orthographic projection of the plurality of grooves is S1 mm 2 , the projection area of the single-face negative material layer area is S2 mm 2 , and 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 composed of any two of them. For example, as shown in FIG. 2B, the total area of the orthographic projection of the plurality of grooves is S1 mm Figure 2As shown, the total area of the front projection of the plurality of grooves 2201 is S1, which is the sum of the areas of the front projections of all the grooves 2201 in the edge area in the dashed box in the figure, and the area S2 of the single-face negative material layer region 220 is LxD. By adjusting the value of S1 / S2 within the above range, the overall rigidity of the single-face material layer region is improved, thereby improving the curling problem of the single-face negative material layer region, thereby reducing the risk of belt breaking and material folding during actual processing of the single-face negative electrode sheet, and at the same time, improving the wettability of the electrolyte to the single-face negative electrode sheet and improving the liquid retention performance of the single-face negative material layer region, thereby improving the kinetic performance and safety performance of the secondary battery.

[0048] In the present application, the negative material layer can further include a conductive agent and a binder. The present application does not have a particular limitation on the type of conductive agent in the negative material layer as long as the purpose of the present application can be achieved. For example, the conductive agent can 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, a metal material, or a conductive polymer. The above-mentioned carbon nanotubes can include, but are not limited to, single-walled carbon nanotubes and / or multi-walled carbon nanotubes. The above-mentioned carbon fibers can include, but are not limited to, vapor-grown carbon fibers (VGCF) and / or nanocarbon fibers. The above-mentioned metal material can include, but is not limited to, metal powder and / or metal fibers, and specifically, the metal can include, but is not limited to, at least one of copper, nickel, aluminum, or silver. The above-mentioned conductive polymer can include, but is not limited to, at least one of polyphenylene derivative, polyaniline, polythiophene, polyacetylene, or polypyrrole. The present application does not have a particular limitation on the type of binder in the negative material layer as long as the purpose of the present application can be achieved. For example, the binder can include, but is not limited to, at least one of polyvinylidene fluoride, a copolymer of vinylidene fluoride-hexafluoropropylene, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinyl ether, polymethyl methacrylate, polytetrafluoroethylene, or polyhexafluoropropylene. The present application does not have a particular limitation on the mass ratio of the negative active material, the conductive agent, and the binder in the negative material layer as long as the purpose of the present application can be achieved.

[0049] The preparation method of the negative electrode sheet is not particularly limited in the present application, as long as the purpose of the present application can be achieved. 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) determining the area where the single-sided negative electrode material layer is arranged, the area where the double-sided negative electrode material layer is arranged, and the area where no negative electrode material layer is arranged on the negative electrode current collector in advance; (3) coating the negative electrode slurry on one surface of the negative electrode current collector according to the area determined on the negative electrode current collector in step (2), and forming a negative electrode sheet including a single-sided negative electrode material layer after drying; (4) coating the slurry on the other surface of the negative electrode current collector according to the area determined on the negative electrode current collector in step (2), and obtaining a negative electrode sheet including a double-sided negative electrode material layer after drying; (5) after cold pressing, cutting and striping, etc., grooves are arranged in the single-sided negative electrode material layer area to obtain the negative electrode sheet of the present application.

[0050] In some embodiments, after step (4), the intermediate area and the two edge areas connected to the intermediate area are determined in the single-sided negative electrode material layer area; and when the grooves are arranged in the single-sided negative electrode material layer area, the grooves are arranged in the two edge areas and respectively pass through the two edge areas.

[0051] The solid content of the above-mentioned slurry is not particularly limited in the present application, as long as the purpose of the present application can be achieved. The temperature and time of the above-mentioned drying are not particularly limited in the present application, as long as the purpose of the present application can be achieved. The process parameters of the above-mentioned cold pressing, cutting, striping, etc. are not particularly limited in the present application, as long as the purpose of the present application can be achieved.

[0052] The method of arranging the grooves is not particularly limited in the present application, and those skilled in the art can choose according to actual needs, as long as the purpose of the present application can be achieved. For example, the grooves can be arranged by means of pulse laser etching. The value of (L-L1) / L can be controlled by adjusting the length L of the single-sided negative electrode material layer area, the speed of the pulse laser emitter and the etching track; 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 area, the power and defocusing amount of the pulse laser emitter; the average depth h of the plurality of grooves, the average width d of the orthographic projection of the plurality of grooves can be controlled by adjusting the power and defocusing amount of the pulse laser emitter; the shortest distance L2 between the orthographic projection of the outer contour of the orthographic projection of the adjacent two grooves can be controlled by adjusting the distance between the pulse laser emitters or the laser emission frequency; the angle a between the center line of a single groove and the length direction after the negative electrode sheet is unfolded can be controlled by adjusting the position, power and defocusing amount of the pulse laser emitter; the ratio S1 / S2 of the total area S1 of the orthographic projection of the plurality of grooves to the projection area S2 of the single-sided negative electrode material layer area can be controlled by adjusting the projection area of the single-sided negative electrode material layer area, the power of the pulse laser emitter, the defocusing amount and the number of grooves arranged in the single-sided negative electrode material layer area.

[0053] In the present application, the different features of the single-sided negative material layer region described above can be combined in any manner, and the combinations encompassed by the embodiments or examples are within the scope of the present application.

[0054] The second aspect of the present application provides a secondary battery including a positive electrode sheet, a separator, and the negative electrode sheet of any of the embodiments described above. The application of the negative electrode sheet of the present application to a secondary battery improves the curling of the single-sided region negative electrode sheet, reduces the risk of material folding and belt breaking of the single-sided region negative electrode sheet during processing, and improves the wettability of the electrolyte to the single-sided region negative electrode sheet, thereby improving the kinetic performance and safety performance of the secondary battery.

[0055] In some embodiments of the present application, the secondary battery is a winding structure, and the empty foil region and the single-sided negative material layer region are arranged at the starting end of the winding structure. This can more specifically address the stress concentration of the negative electrode sheet of the single-sided negative material layer region at the starting end of the winding after cold pressing, reduce the risk of material folding and belt breaking of the single-sided region negative electrode sheet during processing, and improve the wettability of the electrolyte to the single-sided region negative electrode sheet, thereby improving the kinetic performance and safety performance of the secondary battery.

[0056] The separator of the present application is not particularly limited as long as it can achieve the purpose of the present application. For example, the material of the separator can include, but is not limited to, at least one of polyethylene (PE), polyolefin (PO) based on polypropylene (PP), polyester (e.g., polyethylene terephthalate (PET) film), cellulose, polyimide (PI), polyamide (PA), spandex, or aramid. The type of the separator can include at least one of a woven film, a non-woven film, a microporous film, a composite film, a calendered film, or a spunlaid film.

[0057] 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.

[0058] 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 O2 (NCM955), NCM811, NCM622, NCM523, NCM111), lithium nickel cobalt aluminate, lithium iron phosphate, lithium-rich manganese-based material, lithium cobaltate (LiCoO2), lithium manganate, lithium manganese iron phosphate, or lithium titanate, etc. In the present application, the positive active material can also contain a non-metallic element, for example, the non-metallic element includes at least one of fluorine, phosphorus, boron, chlorine, silicon, or sulfur. In the present application, the thickness of the positive current collector and the positive material layer is not particularly limited, as long as the purpose of the present application can be achieved. In the present application, the positive material layer can also include a positive binder and a conductive agent. The present application does not particularly limit the type of positive binder in the positive material layer, as long as the purpose of the present application can be achieved, for example, the positive binder can be the same as the type of binder in the negative material layer described above. The present application does not particularly limit the type of conductive agent in the positive material layer, as long as the purpose of the present application can be achieved, for example, the conductive agent can be the same as the type of conductive agent in the negative material layer described above. The present application does not particularly limit the mass ratio of the positive active material, the conductive agent, and the binder in the positive material layer, and those skilled in the art can select according to actual needs, as long as the purpose of the present application can be achieved.

[0059] In the present application, the secondary battery further includes an electrolyte including a lithium salt and a non-aqueous solvent. The lithium salt is not particularly limited in the present application as long as the object of the present application is achieved. For example, the lithium salt can 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. The content of the lithium salt in the electrolyte is not particularly limited in the present application as long as the object of the present application is achieved. The non-aqueous solvent is not particularly limited in the present application as long as the object of the present application is achieved, for example, the non-aqueous solvent can include, but is not limited to, at least one of a carbonate compound, a carboxylic acid ester compound, an ether compound, or another organic solvent. The carbonate compound can include, but is not limited to, at least one of a chain carbonate compound, a cyclic carbonate compound, or a fluoro-carbonate compound. The chain carbonate compound can include, but is 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 cyclic carbonate can include, but is not limited to, at least one of ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), or vinyl ethylene carbonate (VEC). The fluoro-carbonate compound can include, but is 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-methyl ethylene carbonate, 1-fluoro-1-methyl ethylene carbonate, 1,2-difluoro-1-methyl ethylene carbonate, 1,1,2-trifluoro-2-methyl ethylene carbonate, or trifluoromethyl ethylene carbonate. The carboxylic acid ester compound can include, but is not limited to, at least one of methyl formate, methyl acetate, ethyl acetate, n-propyl acetate, t-butyl acetate, methyl propionate, ethyl propionate, propyl propionate, γ-butyrolactone, decanolactone, valerolactone, or caprolactone. The ether compound can include, but is not limited to, at least one of dibutyl ether, tetraglyme, diglyme, 1,2-dimethoxyethane, 1,2-diethoxyethane, 1-ethoxy-1-methoxyethane, 2-methyl tetrahydrofuran, or tetrahydrofuran. The other organic solvent can include, but is not limited to, at least one of dimethyl sulfoxide, 1,2-dioxolane, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, N-methyl-2-pyrrolidinone, dimethylformamide, acetonitrile, trimethyl phosphate, triethyl phosphate, or trioctyl phosphate. The content of the non-aqueous solvent in the electrolyte is not particularly limited in the present application as long as the object of the present application is achieved.The content of the non-aqueous solvent in the electrolyte is not particularly limited in the present application, as long as the object of the present application can be achieved.

[0060] The secondary battery further comprises a case for accommodating the positive electrode sheet, the separator, the negative electrode sheet, and the electrolyte, and other components known in the art of secondary batteries, and the present application does not limit the above-mentioned other components. The case is not particularly limited in the present application, and can be a case known in the art, as long as the object of the present application can be achieved. For example, the case can be a hard case or a flexible case. The material of the hard case can be metal, and the type of the metal is not particularly limited in the present application, and a metal hard case known in the art can be used, as long as the object of the present application can be achieved. The flexible case can be a metal plastic film, such as an aluminum plastic film, a steel plastic film, and the like.

[0061] The preparation process of the secondary battery of the present application is well known to those skilled in the art, and the present application is not particularly limited. For example, the preparation process of the secondary battery can include, but is not limited to, the following steps: stacking the positive electrode sheet, the separator, and the negative electrode sheet in order, and performing operations such as winding, folding, and the like as needed to obtain an electrode assembly with a wound structure, placing the electrode assembly into the case, injecting the electrolyte into the case and sealing it to obtain the secondary battery. Alternatively, the positive electrode sheet, the separator, and the negative electrode sheet are stacked in order, and then the four corners of the entire stack structure are fixed with adhesive tape to obtain an electrode assembly with a stack structure, the electrode assembly is placed into the case, the electrolyte is injected into the case and sealed to obtain the secondary battery. In addition, the overcurrent prevention element, the guide plate, and the like can also be placed in the case as needed to prevent the pressure inside the secondary battery from rising and overcharging and discharging.

[0062] The third aspect of the present application provides an electronic device comprising the secondary battery of any of the above embodiments, so that the electronic device provided by the present application has good use performance.

[0063] The electronic device of the present application is not particularly limited, and it can be any electronic device known in the art. For example, the electronic device can include, but is not limited to, a notebook computer, a pen input computer, a mobile computer, an electronic book player, a portable telephone, a portable facsimile machine, a portable copying machine, a portable printer, a head-mounted stereo headset, a video recorder, a liquid crystal television, a portable cleaner, a portable CD player, a mini disc, a transceiver, an electronic organizer, a calculator, a memory card, a portable recorder, a radio, a backup power supply, an electric motor, an automobile, a motorcycle, a power-assisted bicycle, a bicycle, an illuminating appliance, a toy, a game machine, a clock, an electric tool, a flashlight, a camera, a household large storage battery, and a lithium ion capacitor.

[0064] Examples

[0065] The following examples and comparative examples are presented to more specifically explain the embodiments of the present application. Various tests and evaluations were performed according to the following methods. In addition, unless otherwise specified, "parts" and "%" are on a mass basis.

[0066] Test methods and apparatuses:

[0067] Test of L, A, B, L1, C, H, D, h, d, L2, a, S1 / S2:

[0068] The lithium ion battery of each example and comparative example was disassembled after being discharged at 0.5C to 2.5V at an ambient temperature of 25°C to obtain an electrode assembly. The negative electrode sheet was taken out from the electrode assembly, soaked in dimethyl carbonate (DMC) for 20 min, and then placed in an oven for drying at 80°C for 12 h to obtain a test sample of the negative electrode sheet.

[0069] The negative electrode sheet was unfolded, and the length L of the single-sided negative electrode material layer region, the length of the empty foil region, and the length of the negative electrode sheet were measured along the length direction of the unfolded negative electrode sheet using a tape measure. Then, based on the length of the negative electrode sheet, the length ratio A of the empty foil region and the length ratio B of the single-sided negative electrode material layer region were calculated. The boundary line between the single-sided negative electrode material layer region and the double-sided negative electrode material layer region was observed on the plane in which the length direction and the width direction of the unfolded negative electrode sheet were located. The shortest distance L1 between the outer contour of a single groove on the surface of the negative electrode sheet and the boundary line was measured along the length direction of the unfolded negative electrode sheet, and the value of (L-L1) / L was calculated. The setting position of the groove was observed along the width direction of the unfolded negative electrode sheet on the plane in which the length direction and the width direction of the unfolded negative electrode sheet were located. If the groove penetrated through along the width direction of the unfolded negative electrode sheet, the middle region ratio of the single-sided negative electrode material layer region was 0, and the length ratio C of the middle region was 0 based on the width of the negative electrode material layer of the single-sided negative electrode material layer region. If the groove did not penetrate through along the width direction of the unfolded negative electrode sheet, the length of the single-sided negative electrode material layer region without the groove and the width of the negative electrode material layer of the single-sided negative electrode material layer region were measured along the width direction of the unfolded negative electrode sheet, and then the length ratio C of the middle region = the length of the single-sided negative electrode material layer region without the groove / the width of the negative electrode material layer of the single-sided negative electrode material layer region.

[0070] Each groove in the single-sided negative electrode material layer region was photographed using a scanning electron microscope, and the projected area of a single groove was calculated using image recognition. Then, the total area S1 of the orthographic projection of multiple grooves was obtained by summation, and the projected area S2 of the single-sided negative electrode material layer region was obtained by multiplying the measured length L of the single-sided negative electrode material layer region by the measured width of the single-sided negative electrode material layer region. Then, S1 / S2 was calculated.

[0071] Optionally, 5 grooves are located in the single-face negative material layer area, 5 positions are optionally located on a single groove, the width of 5 positions out of the groove is measured, and the average value is taken as the width of the orthographic projection of a single groove on the negative material layer. The average value of the widths of 5 grooves is taken as the average width d of the orthographic projection of multiple grooves on the negative material layer. The shortest distance between the outer contour of a single groove on the negative material layer and the outer contour of the adjacent groove on the negative material layer is measured, which is the shortest distance L2 between the outer contours of the orthographic projections of two adjacent grooves. Optionally, 5 grooves are determined to have a center line respectively, and the included angle between the center line of a single groove and the length direction of the negative electrode sheet after unfolding is measured respectively, and the average value is taken as the included angle a between the center line of a single groove and the length direction of the negative electrode sheet after unfolding.

[0072] The negative electrode sheet is cut along the thickness direction and the length direction after unfolding to obtain the longitudinal section of the negative electrode sheet, and the ion polishing treatment is performed on the longitudinal section of the negative electrode sheet. The clear boundary line between the negative material layer and the negative current collector can be observed by using an electron scanning microscope. The thickness H of the negative current collector is measured by using a micrometer along the thickness direction of the negative electrode sheet. Optionally, 5 grooves are measured by using a micrometer to measure the distance between the surface of the negative material layer and the bottom surface of a single groove along the thickness direction of the negative electrode sheet, and the average value is taken as the average depth h of multiple grooves.

[0073] Test of the coating weight per unit area of the negative material layer:

[0074] At an ambient temperature of 25°C, the lithium ion battery is disassembled to obtain an electrode assembly with a winding structure, and the negative electrode sheet is taken out, soaked in dimethyl carbonate (DMC) for 20 min, and then placed in an oven for drying at 80°C for 12 h to obtain a test sample of the negative electrode sheet. The empty foil area, the single-face negative material layer area and the double-face negative material layer area of the negative electrode sheet are confirmed.

[0075] The negative electrode sheet sample of the single-face negative material layer area is punched into 2 small circular sheets with a radius of 22.14 mm (an area of 1540.25 mm 2 ), and the average value is taken after weighing sequentially, which is a. The negative material layer on the small circular sheet is wiped off with deionized water, and the average value is taken after weighing sequentially, which is a1. The negative electrode sheet sample of the double-face negative material layer area is punched into 4 small circular sheets with a radius of 22.14 mm (an area of 1540.25 mm 2 ), and the average value is taken after weighing sequentially, which is b. The negative material layer on two surfaces of the small circular sheet is wiped off with deionized water, and the average value is taken after weighing sequentially, which is b1. Then,

[0076] The coating weight per unit area of the negative material layer in the single-face negative material layer area is M=a-a1.

[0077] The unit area coating weight of the negative electrode material layer of the single-sided negative electrode material layer region = (b - b1) / 2.

[0078] Test of PD1 and PD2:

[0079] The unit area coating weight of the negative electrode material layer of the single-sided negative electrode material layer region and the unit area coating weight of the negative electrode material layer of the double-sided negative electrode material layer region are obtained according to the test of the unit area coating weight of the negative electrode material layer, and the thickness of the single-sided negative electrode material layer is measured by using a micrometer according to the test steps of the test of L, A, B, L1, C, H, D, h, d, L2, a, S1 / S2, and PD1 and PD2 are calculated according to the following formula:

[0080] The compaction density PD1 of the negative electrode material layer of the single-sided negative electrode material layer region = the unit area coating weight of the negative electrode material layer of the single-sided negative electrode material layer region / the thickness of the single-sided negative electrode material layer;

[0081] The compaction density PD2 of the negative electrode material layer of the double-sided negative electrode material layer region = the unit area coating weight of the negative electrode material layer of the double-sided negative electrode material layer region / the thickness of the single-sided negative electrode material layer.

[0082] Test of the low-temperature kinetic rate of the innermost single-sided negative electrode material layer region:

[0083] The lithium ion battery is charged at a 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, 5.0C to a voltage of 4.5V in a 0℃ environment, and then charged at 4.5V to a cutoff current of 0.05C, and then left for 5 minutes; and then discharged at 0.5C to a voltage of 3.0V, and then left for 5 minutes, which is one charge-discharge cycle. Then, the same steps are performed for 10 cycles of charge and discharge cycles.

[0084] Then, the lithium ion battery is charged at the same rate to 4.5V, and then charged at 4.5V to a cutoff current of 0.05C, and then left for 5 minutes; and then the lithium ion battery is disassembled, the interface of the single-sided negative electrode material layer region is confirmed, and the rate from low rate to high rate is disassembled until there is slight white lithium metal precipitation, and then the rate is recorded as the low-temperature kinetic maximum rate of the single-sided negative electrode material layer region. For example, the single-sided negative electrode is disassembled at 1.5C with slight lithium precipitation, and the low-temperature kinetic rate is recorded as 1.5C.

[0085] Test of energy density:

[0086] (1) The lithium ion battery is placed in an environment of 25°C, charged at 1C constant current to a voltage of 4.5V, then charged at 4.5V constant voltage to a cutoff current of 0.05C, left for 5 min, discharged at 0.2C constant current to a voltage of 3.0V, left for 5 min, and the discharge capacity at this time is recorded as C.

[0087] (2) The actual thickness Da, Db, Dc of the electrode assembly head near the edge 3mm, tail near the edge 3mm, and middle region is measured by micrometer, and 3 groups of data are obtained, such as the first data of the head is recorded as Da1, and the thickness average D is:

[0088] D=(1 / 3×(Da1+Da2+Da3)+1 / 3×(Db1+Db2+Db3)+1 / 3×(Dc1+Dc2+Dc3)) / 3;

[0089] (3) The length L and width M of the lithium ion battery are scanned and measured by laser measuring instrument.

[0090] (4) Then the actual energy density X of the lithium ion battery is: X=C / (D×L×M);

[0091] (5) Wherein the energy density X0 of the comparative example 1 is set as the "low" grade standard, and each increase of 0.2% is one gradient of energy density, and the order is: high>medium high>medium>medium low>low. The energy density in the comparative example 1 is 654.1 Wh / L.

[0092] Test of winding yield related to entry folding / single-sided negative electrode material layer zone breakage:

[0093] (1) Take several rolls of negative electrode sheets prepared in each example and comparative example, a total of N (N=1000);

[0094] (2) Take enough amount of separators and positive electrode sheets corresponding to the negative electrode sheets prepared in each example and comparative example in step (1), the amount is much larger than N;

[0095] (3) Use the negative electrode sheets, separators and positive electrode sheets in step (1) and step (2) to assemble and produce according to the winding mode of the lithium ion battery of each example and comparative example;

[0096] (4) Record the total scrap amount M of the negative electrode sheets related to entry folding or single-sided zone breakage in the winding process;

[0097] (5) The winding yield of the negative electrode sheet (%)=(1-M / N)×100%.

[0098] Interface characteristics of 500 cycle (circle) cycles of single-sided zone;

[0099] The lithium ion battery prepared from the example and the comparative example was placed in a 25℃ constant temperature test box, and was allowed to stand for 30 min to make the lithium ion battery reach a constant temperature. The lithium ion battery was charged at 0.5C constant current to 4.5V, and was charged at 4.5V constant voltage until the current was 0.025C, was allowed to stand for 5 min, was discharged at 0.5C constant current to 3.0V, and was recorded as an initial discharge capacity Co. The above step was repeated for 500 cycles, and a discharge capacity C1 after 500 cycles was recorded. The cycle capacity retention rate of the lithium ion battery was calculated, and the cycle capacity retention rate (%) = C1 / C0 x 100%. Meanwhile, the lithium ion battery after the cycle was disassembled and analyzed under full charge (charged at 0.5C constant current to 4.5V), the interface condition of the single-sided negative electrode material layer region after 500 cycles was confirmed, and the difference was confirmed.

[0100] The cycle capacity retention rate and the interface condition of the single-sided negative electrode region were used to characterize the electrochemical performance of the lithium ion battery. Specifically, the higher the cycle capacity retention rate and the better the interface condition, the better the electrochemical performance of the lithium ion battery; the lower the cycle capacity retention rate and the worse the interface condition, the worse the electrochemical performance of the lithium ion battery. The "interface condition" refers to the condition of the surface of the negative electrode sheet after the lithium ion battery is disassembled under full charge after the cycle; the "interface condition without abnormality" refers to that the surface of the negative electrode sheet is free of black spots, lithium precipitation, purple spots and the like; and the "interface condition with abnormality" refers to that the surface of the negative electrode sheet has at least one of black spots, lithium precipitation or purple spots.

[0101] Example 1-1

[0102] <Preparation of the negative electrode sheet>

[0103] The artificial graphite, styrene-butadiene rubber and sodium carboxymethyl cellulose are mixed in a mass ratio of 96:2:2, deionized water is added as a solvent, and stirring is performed to obtain a negative electrode slurry with a solid content of 40wt%. The negative electrode slurry is uniformly coated on one surface of a negative electrode current collector copper foil with a thickness H of 6μm, intermittent coating is performed on the copper foil according to the size of the electrode assembly, and then drying is performed at 85℃ to obtain a negative electrode sheet with a single-side coated negative electrode material layer with a coating thickness of 100μm. Then the above steps are repeated on the other surface of the copper foil to obtain a negative electrode sheet with a double-side coated negative electrode material layer. After cold pressing (cold pressing pressure is 80T), a negative electrode sheet is obtained, the negative electrode sheet is cut into a fixed size, the two edge regions of the single-side negative electrode material layer region of the negative electrode sheet are pre-determined for groove setting, and the middle region of the single-side negative electrode material layer region which is not provided with grooves is based on the width of the negative electrode material layer, and the length ratio C is 15%. The orthographic projection shape of a single groove along the thickness direction of the negative electrode sheet is a rectangle, and then vacuum drying is performed at 120℃ for 12h to obtain a negative electrode sheet with a specification of 78mm×875mm, i.e. the width D of the negative electrode sheet is 78mm. Among them, the unit area coating weight m of the negative electrode material layer of the single-side negative electrode material layer region is 150mg / 1540.25mm 2 , the unit area coating weight of the negative electrode material layer of the double-side negative electrode material layer region is 150mg / 1540.25mm 2 , the compacted density PD1 of the negative electrode material layer of the single-side negative electrode material layer region is 1.70g / cm 3 , the compacted density PD2 of the negative electrode material layer of the double-side negative electrode material layer region is 1.73g / cm 3 , based on the length of the negative electrode sheet, the length ratio A of the empty foil region is 1 / 20, the length ratio B of the single-side negative electrode material layer region is 1 / 10, and the length L of the single-side negative electrode material layer region is 87.5mm.

[0104] Grooves are set in the two edge regions of the single-side negative electrode material layer region of the negative electrode sheet by means of pulse laser etching, and the specific parameters are shown in Table 1. The shortest distance L1 between the orthographic projection outer contour of a single groove and the boundary line is 17.5mm, the average depth h of the multiple grooves along the thickness direction of the negative electrode sheet is 20μm, the average width d of the orthographic projection of the multiple grooves is 80μm, the shortest distance L2 between the orthographic projection outer contours of two adjacent grooves is 1mm, the included angle α between the center line of a single groove and the length direction of the negative electrode sheet after unfolding is 45°, and the ratio S1 / S2 of the total area of the orthographic projection of the multiple grooves to the projection area of the single-side negative electrode material layer region is 5.04%.

[0105] <Preparation of a positive electrode sheet>

[0106] The conductive agent (conductive carbon black), the binder (polyvinylidene fluoride) are mixed according to a certain proportion, N-methyl pyrrolidone (NMP) is added to prepare a conductive glue solution with a solid content of 7w%. After mixing, lithium cobaltate is added, and the system is continuously stirred under the action of a vacuum stirrer until it is uniform, obtaining a positive electrode slurry with a solid content of 75w%. Among them, the mass ratio of lithium cobaltate: conductive agent: binder is 97:1:2. The positive electrode slurry is uniformly coated on one surface of an aluminum foil with a thickness of 8μm, and is intermittently coated on the aluminum foil according to the size of the battery cell, and then is dried at 85℃ to obtain a positive electrode sheet with a positive electrode material layer coated on one side, and the thickness of the coating is 100μm. After cold pressing (cold pressing pressure is 85T), a positive electrode compact sheet is obtained. The positive electrode sheet is cut into a fixed size, and then is vacuum dried at 85℃ for 4h to obtain a positive electrode sheet with a size of 74mm×867mm for use. The unit area coating weight of the positive electrode material layer is 300mg / 1540.25mm 2 , and the compaction density of the positive electrode material layer is 4.20g / cm 3 .

[0107] <Preparation of electrolyte>

[0108] In a dry argon environment, non-aqueous solvents ethylene carbonate (EC), propylene carbonate (PC), and diethyl carbonate (DEC) are mixed in a weight ratio of 1:1:1, and then lithium salt LiPF6 is added to the non-aqueous solvent and mixed uniformly to obtain an electrolyte. The molar concentration of lithium salt LiPF6 is 1.15mol / L.

[0109] <Preparation of separator>

[0110] A porous polyethylene film (provided by Celgard) with a thickness of 7μm is used as the separator.

[0111] <Preparation of lithium ion battery>

[0112] The positive electrode sheet, the separator, and the negative electrode sheet are stacked in order, with the separator between the positive electrode sheet and the negative electrode sheet to play a separating role, and then the electrode assembly is obtained by winding. The electrode assembly is placed in an outer packaging foil, and the water is removed at 80℃. The electrolyte prepared above is injected, and after vacuum packaging, standing, formation, shaping, capacity testing and other processes, a soft package lithium ion battery is obtained.

[0113] Examples 1-2 to 1-28

[0114] Except for adjusting the relevant preparation parameters according to Table 1, the rest is the same as Example 1-1.

[0115] Examples 2-1 to 2-11

[0116] The rest is the same as Example 1-1 except that the relevant preparation parameters are adjusted according to Table 2.

[0117] Comparative Example 1

[0118] The rest is the same as Example 1-1 except that no groove is set on the single-sided negative material layer area in the preparation of the negative electrode tab.

[0119] Comparative Examples 2 to 6

[0120] The rest is the same as Example 1-1 except that the relevant preparation parameters are adjusted according to Table 1.

[0121] The preparation parameters and performance parameters of each example and comparative example are shown in Tables 1 and 2.

[0122] Table 1

[0123]

[0124] Note: " / " in Table 1 means no relevant preparation parameter.

[0125] As can be seen from Example 1-1 to Example 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 material layer of the single-sided negative material layer area, the maximum rate of the low-temperature kinetics of the single-sided negative material layer area of the lithium ion battery is larger, the winding probability related to the material folding / single-sided negative material layer area breakage is improved, the 500 Cycle cycle capacity retention rate is larger and the interface characteristics of the single-sided negative material layer area are improved, indicating that the winding of the single-sided area negative electrode tab is improved, thereby reducing the risk of breakage and material folding of the single-sided area negative electrode tab in the actual processing process, improving the winding probability of the secondary battery, 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 groove is set on the negative material layer of the single-sided negative material layer area; in Comparative Examples 2 to 6, the values of A and / or B are not within the scope of the present application, the maximum rate of the low-temperature kinetics of the single-sided negative material layer area of the ion battery is smaller, the winding probability related to the material folding / single-sided negative material layer area breakage is lower, and the 500 Cycle cycle capacity retention rate is smaller, and the interface characteristics of the single-sided negative material layer area are poorer. While the lithium ion batteries of Examples 1-1 to 1-28 have larger maximum rates of low-temperature kinetics of the single-sided negative material layer area, improved winding probability related to material folding / single-sided negative material layer area breakage, larger 500 Cycle cycle capacity retention rate and improved interface characteristics of the single-sided negative material layer area, the lithium ion batteries have good safety performance and kinetic performance.

[0126] The value of (L-L1) / L generally affects the safety performance and kinetic performance of the lithium ion battery. As can be seen from Example 1-1, Example 1-6 to Example 1-7, when the value of (L-L1) / L is within the range of the present application, the maximum rate of low-temperature kinetics of the single-face negative electrode material layer region is larger, the winding optimization rate related to the material folding / single-face negative electrode material layer region belt breaking is larger, the 500 Cycle cycle capacity retention rate is larger, and the interface characteristics of the single-face negative electrode material layer region are better, indicating that the curling of the single-face region negative electrode sheet is improved, thereby reducing the risk of belt breaking and material folding of the single-face region negative electrode sheet in the actual processing process, improving the winding optimization rate of the secondary battery, and the lithium ion battery has good kinetic performance and safety performance.

[0127] The value of C generally affects the safety performance and kinetic performance of the lithium ion battery. As can be seen from Example 1-1, Example 1-6 to Example 1-7, Example 1-18, Example 1-27 to Example 1-28, when the value of C is within the range of the present application, the maximum rate of low-temperature kinetics of the single-face negative electrode material layer region is larger, the winding optimization rate related to the material folding / single-face negative electrode material layer region belt breaking is larger, the 500 Cycle cycle capacity retention rate is larger, and the interface characteristics of the single-face negative electrode material layer region are better, indicating that the curling of the single-face region negative electrode sheet is improved, thereby reducing the risk of belt breaking and material folding of the single-face region negative electrode sheet in the actual processing process, improving the winding optimization rate of the secondary battery, and the lithium ion battery has good kinetic performance and safety performance.

[0128] The value of D generally affects the safety performance and kinetic performance of the lithium ion battery. As can be seen from Example 1-1, Example 1-2 to Example 1-5, Example 1-8 to Example 1-9, Example 1-18, when the value of D is within the range of the present application, the maximum rate of low-temperature kinetics of the single-face negative electrode material layer region is larger, the winding optimization rate related to the material folding / single-face negative electrode material layer region belt breaking is larger, the 500 Cycle cycle capacity retention rate is larger, and the interface characteristics of the single-face negative electrode material layer region are better, indicating that the curling of the single-face region negative electrode sheet is improved, thereby reducing the risk of belt breaking and material folding of the single-face region negative electrode sheet in the actual processing process, improving the winding optimization rate of the secondary battery, and the lithium ion battery has good kinetic performance and safety performance.

[0129] The value of h generally affects the safety performance and kinetic performance of the lithium ion battery. As can be seen from Example 1-1, Example 1-10 to Example 1-11, Example 1-19 to Example 1-20, when the value of h is within the range of the present application, the maximum rate of low-temperature kinetics of the single-face negative electrode material layer region is larger, the winding optimization rate related to the material folding / single-face negative electrode material layer region belt breaking is larger, the 500 Cycle cycle capacity retention rate is larger, and the interface characteristics of the single-face negative electrode material layer region are better, indicating that the curling of the single-face region negative electrode sheet is improved, thereby reducing the risk of belt breaking and material folding of the single-face region negative electrode sheet in the actual processing process, improving the winding optimization rate of the secondary battery, improving the infiltration performance of the electrolyte on the single-face region negative electrode sheet, and the lithium ion battery has good kinetic performance and safety performance.

[0130] The value of d generally affects the safety performance and kinetic performance of the lithium ion battery. As can be seen from Example 1-1, Example 1-12 to Example 1-13, Example 1-21 to Example 1-22, when the value of d is within the range of the present application, the maximum rate of low-temperature kinetics of the single-face negative electrode material layer region is larger, the winding optimization rate related to the material folding / single-face negative electrode material layer region belt breaking is larger, the 500 Cycle cycle capacity retention rate is larger, and the interface characteristics of the single-face negative electrode material layer region are better, indicating that the curling of the single-face region negative electrode sheet is improved, thereby reducing the risk of belt breaking and material folding of the single-face region negative electrode sheet in the actual processing process, improving the infiltration performance of the electrolyte on the single-face region negative electrode sheet, and the lithium ion battery has good kinetic performance and safety performance.

[0131] The value of L2 generally affects the safety performance and kinetic performance of the lithium ion battery. As can be seen from Example 1-1, Example 1-14 to Example 1-15, Example 1-23 to Example 1-24, when the value of L2 is within the range of the present application, the maximum rate of low-temperature kinetics of the single-face negative electrode material layer region is larger, the winding optimization rate related to the material folding / single-face negative electrode material layer region belt breaking is larger, the 500 Cycle cycle capacity retention rate is larger, and the interface characteristics of the single-face negative electrode material layer region are better, indicating that the curling of the single-face region negative electrode sheet is improved, thereby reducing the risk of belt breaking and material folding of the single-face region negative electrode sheet in the actual processing process, improving the infiltration performance of the electrolyte on the single-face region negative electrode sheet, and the lithium ion battery has good kinetic performance and safety performance.

[0132] The value of a generally affects the safety performance and kinetic performance of the lithium ion battery. As can be seen from Example 1-1, Example 1-16 to Example 1-17, Example 1-25 to Example 1-26, when the value of a is within the range of the present application, the maximum rate of low-temperature kinetics of the single-face negative electrode material layer region is larger, the winding optimization rate related to the material folding / single-face negative electrode material layer region belt breaking is larger, the 500 Cycle cycle capacity retention rate is larger, and the single-face negative electrode material layer region interface characteristics are better, indicating that the winding of the single-face region negative electrode sheet is improved, thereby reducing the risk of belt breaking and material folding of the single-face region negative electrode sheet in the actual processing process, improving the winding optimization rate of the secondary battery, and the lithium ion battery has good kinetic performance and safety performance.

[0133] The value of S1 / S2 generally affects the safety performance and kinetic performance of the lithium ion battery. As can be seen from Example 1-1, Example 1-6 to Example 1-7, Example 1-12 to Example 1-15, Example 1-18, Example 1-21 to Example 1-24, Example 1-27 to Example 1-28, when the value of S1 / S2 is within the range of the present application, the maximum rate of low-temperature kinetics of the single-face negative electrode material layer region is larger, the winding optimization rate related to the material folding / single-face negative electrode material layer region belt breaking is larger, the 500 Cycle cycle capacity retention rate is larger, and the single-face negative electrode material layer region interface characteristics are better, indicating that the winding of the single-face region negative electrode sheet is improved, thereby reducing the risk of belt breaking and material folding of the single-face region negative electrode sheet in the actual processing process, improving the winding optimization rate of the secondary battery, and the lithium ion battery has good kinetic performance and safety performance.

[0134] Table 2

[0135]

[0136] Note: " / " in Table 2 represents no related effect parameters.

[0137] The value of H generally affects the safety performance, energy density, and kinetic performance of the lithium ion battery. As can be seen from Example 1-1, Example 2-1 to Example 2-2, Example 2-7 to Example 2-8, when the value of H is within the range of the present application, the maximum rate of low-temperature kinetics of the single-face negative electrode material layer region is larger, the winding optimization rate related to the material folding / single-face negative electrode material layer region belt breaking is larger, the energy density is higher, the 500 Cycle cycle capacity retention rate is larger, and the single-face negative electrode material layer region interface characteristics are better, indicating that the winding of the single-face region negative electrode sheet is improved, thereby reducing the risk of belt breaking and material folding of the single-face region negative electrode sheet in the actual processing process, improving the winding optimization rate of the secondary battery, and the lithium ion battery has good kinetic performance and safety performance while taking into account the energy density of the lithium ion battery. In Example 2-8, the value of H is larger, and at this time, the energy density is relatively lower in the lithium ion battery of the same volume specification.

[0138] The value of m generally affects the safety performance, energy density and kinetic performance of the lithium ion battery. As can be seen from Example 1-1, Example 2-3 to Example 2-4, Example 2-9 to Example 2-10, when the value of m is within the range of the present application, the low-temperature kinetic maximum rate of the single-face negative electrode material layer region is larger, the winding probability related to the material folding / single-face negative electrode material layer region breakage is larger, the energy density is higher, the 500 Cycle cycle capacity retention rate is larger and the single-face negative electrode material layer region interface characteristics are better, indicating that the winding of the single-face region negative electrode sheet is improved, thereby reducing the risk of breakage, material folding in the actual processing of the single-face region negative electrode sheet, improving the winding probability of the secondary battery, while taking into account the energy density of the lithium ion battery, the lithium ion battery has good kinetic performance and safety performance. Among them, the value of m in Example 2-9 is smaller, at this time in the lithium ion battery of the same volume specification, the energy density is relatively low.

[0139] The value of PD1 / PD2 and the value of PD2 generally affect the safety performance, energy density and kinetic performance of the lithium ion battery. As can be seen from Example 1-1, Example 2-5 to Example 2-6, Example 2-11, when the value of PD1 / PD2 and the value of PD2 are within the range of the present application, the low-temperature kinetic maximum rate of the single-face negative electrode material layer region is larger, the winding probability related to the material folding / single-face negative electrode material layer region breakage is larger, the energy density is higher, the 500 Cycle cycle capacity retention rate is larger and the single-face negative electrode material layer region interface characteristics are better, indicating that the winding of the single-face region negative electrode sheet is improved, thereby reducing the risk of breakage, material folding in the actual processing of the single-face region negative electrode sheet, improving the winding probability of the secondary battery, while taking into account the energy density of the lithium ion battery, the lithium ion battery has good kinetic performance and safety performance.

[0140] It should be noted that in this document, relational terms such as first and second and the like can be used solely to distinguish one entity or action from another entity or action without necessarily requiring or implying any actual such relationship or order between such entities or actions. Moreover, the terms "comprises", "comprising", or any other variations thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but can include other elements not expressly listed or inherent to such process, method, article, or apparatus.

[0141] Each of the embodiments in the specification is described in a relevant manner, and the same and similar parts between the embodiments can be referred to each other, and each embodiment focuses on the difference from other embodiments.

[0142] The above description is only the preferred embodiment of the present application, and is not used to limit the present application, any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application should be included in the scope of protection of the present application.

Claims

1. A negative electrode sheet, comprising a negative electrode current collector and a negative electrode material layer, along a length direction of the negative electrode sheet, the negative electrode sheet comprises an empty foil region and a single-sided negative electrode material layer region connecting the empty foil region, a length ratio of the empty foil region is A, and a length ratio of the single-sided negative electrode material layer region is B, based on a length of the negative electrode sheet, 1 / 60≤A≤1 / 11, and 1 / 20≤B≤1 / 5. A plurality of grooves are arranged on the negative electrode material layer in the single-sided negative electrode material layer region, and the grooves are arranged at intervals along the length direction of the negative electrode sheet.

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 a thickness direction of the negative electrode sheet, a single groove has a projection on the negative electrode material layer, along the length direction of the negative electrode sheet, a length of the single-sided negative electrode material layer region is L mm, the negative electrode sheet further comprises 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, a shortest distance between an outer contour of the projection of the 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 a width direction of the negative electrode sheet, the single-sided negative electrode material layer region comprises a middle region and two edge regions connected with the middle region, the grooves are distributed at intervals in the two edge regions and respectively pass through the two edge regions, and a length ratio of the middle region is C, based on a width of the negative electrode material layer in the single-sided negative electrode material layer region, 0%≤C≤30%. 5.The negative electrode sheet according to claim 1, which satisfies at least one of the following characteristics: (1) the negative electrode current collector comprises a copper foil, a thickness of the copper foil is H μm, and 4≤H≤8; (2) the unit area coating weight of the negative electrode material layer of the single-sided negative electrode material layer region is m mg / 1540.25 mm 2 , 100≤m≤200.

6. The negative electrode sheet according to claim 1, wherein Along a width direction of the negative electrode sheet, a width of the negative electrode sheet is D mm, 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, and 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, the negative electrode material layer including a negative electrode active material, the negative electrode active material including at least one of graphite or a silicon-carbon composite material, a compaction density of the negative electrode material layer of the single-sided negative electrode material layer region being PD1 g / cm 3 , a compaction density of the negative electrode material layer of the double-sided negative electrode material layer region being PD2 g / cm 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 a thickness direction of the negative electrode sheet, an average depth of the plurality of grooves is h μm, and 5≤h≤30. 10.The negative electrode sheet according to any one of claims 1 to 9, the plurality of grooves are distributed in a strip shape, along a thickness direction of the negative electrode sheet, a single groove has a projection on the negative electrode material layer, and at least one of the following conditions is satisfied: (1) an average width of the projections of the plurality of grooves is d μm, and 50≤d≤110; (2) a shortest distance between outer contours of the projections of two adjacent grooves is L2 mm, and 0.5≤L2≤1.

5.

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

12. The negative electrode sheet according to claim 11, wherein The total area of the orthographic projection of the plurality of grooves in the thickness direction of the negative electrode tab 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 the negative electrode sheet according to any one of claims 1 to 12.

14. The secondary battery according to claim 13, wherein The secondary battery is in a wound structure, and the empty foil region is located at a starting end of the wound structure. 15.An electronic device comprising the secondary battery according to claim 13 or claim 14.

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