Negative pole piece, secondary battery and electronic device

Abstract

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

Description

Technical Field

[0001] The present application relates to the field of electrochemical technology, and in particular to a negative electrode sheet, a secondary battery and an electronic device. Background Art

[0002] Secondary batteries, such as lithium-ion batteries, have the characteristics of high specific energy, high operating voltage, low self-discharge rate, small size, and light weight, and are widely used in the field of consumer electronics. With the widespread application of lithium-ion batteries, the market has put forward higher and higher requirements on the performance of lithium-ion batteries.

[0003] At present, the winding structure is the most mature structural process for lithium-ion batteries. Usually, the negative electrode sheet with a single-sided material layer is used for initial winding in the winding structure to increase the proportion of active materials and improve the energy density of the secondary battery. However, the negative electrode sheet in the single-sided negative electrode material layer area will have obvious stress concentration after cold pressing, which will lead to obvious curling of the negative electrode sheet. The curled single-sided negative electrode sheet structure affects the electrode assembly structure and glue bonding during the winding process, and even the belt breakage problem is prone to occur at the junction of the double-sided and single-sided areas. Summary of the invention

[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 negative electrode sheet in the single-sided area is improved, the risk of bending and breaking of the negative electrode sheet in the single-sided area during processing is reduced, and at the same time, the wettability of the electrolyte to the negative electrode sheet in the single-sided area is improved, thereby improving the dynamic performance and safety performance of the secondary battery.

[0005] It should be noted that in the invention content of this application, lithium-ion batteries are used as an example of secondary batteries to explain this application, but the secondary batteries of this application are 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 includes a negative electrode current collector and a negative electrode material layer. Along the length direction of the unfolded negative electrode sheet, the negative electrode sheet includes an empty foil area and a single-sided negative electrode material layer area connected to the empty foil area. Based on the length of the negative electrode sheet, the length of the empty foil area accounts for A, and the length of the single-sided negative electrode material layer area accounts for 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 provided on the negative electrode material layer in the single-sided negative electrode material layer area, and the grooves are arranged at intervals along the length direction of the negative electrode sheet. By providing grooves on the single-sided negative electrode material layer area and applying it to a secondary battery, the curling of the single-sided negative electrode material layer area can be improved, and the risk of material folding and belt breaking in the single-sided negative electrode material layer area during processing is reduced. At the same time, the wettability of the electrolyte to the single-sided negative electrode material layer area is improved, thereby improving the dynamic performance and safety performance of the secondary battery.

[0007] In some embodiments of the present application, along the thickness direction of the negative electrode sheet, a single groove has an orthographic projection on the negative electrode material layer, and along the length direction of the negative electrode sheet, the length of the single-sided negative electrode material layer area is L mm, and the negative electrode sheet also includes a double-sided negative electrode material layer area, and the single-sided negative electrode material layer area and the double-sided negative electrode material layer area have a dividing line, and the shortest distance between the outer contour of the orthographic projection of a single groove and the dividing line is L1 mm, 1 / 2≤(L-L1) / L≤1. In some embodiments of the present application, along the width direction of the unfolded negative electrode sheet, the single-sided negative electrode material layer area includes a middle area and two edge areas connected to the middle area, and the grooves are spaced and distributed in the two edge areas, and respectively pass through the two edge areas. Based on the width of the negative electrode material layer in the single-sided negative electrode material layer area, the length of the middle area accounts for C, 0%≤C≤30%. The above arrangement is conducive to improving the curling problem of the single-sided negative electrode material layer area, thereby reducing the risk of broken tape and material folding during the actual processing of the single-sided negative electrode sheet. At the same time, it is also conducive to improving the wetting performance of the electrolyte on the single-sided negative electrode sheet and improving the liquid retention performance of the single-sided negative electrode material layer area, thereby improving the kinetic performance and safety performance of the secondary battery. In addition, it takes into account the actual production efficiency and is conducive to processing.

[0008] In some embodiments of the present application, at least one of the following characteristics is met: (1) the negative electrode current collector includes a copper foil, the thickness of the copper foil is H μm, 4≤H≤8; (2) the coating weight per unit area of ​​the negative electrode material layer in the single-sided negative electrode material layer area is m mg / 1540.25 mm 2 , 100≤m≤200. The above arrangement is helpful to improve the curling problem of the single-sided negative electrode material layer area, thereby further reducing the risk of tape breakage and material folding during the actual processing of the single-sided negative electrode sheet.

[0009] 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-sided negative electrode material layer area is L mm, 1≤L / D≤2, 50≤D≤130. By regulating the values ​​of L / D and D within the above range, it is helpful to improve the curling problem of the single-sided negative electrode material layer area, thereby further reducing the risk of broken tape and feed folding during the actual processing of the single-sided negative electrode sheet. In addition, the width of the negative electrode sheet and the length of the single-sided negative electrode material layer area are related to the shape of the electrode assembly formed after winding. Regulating the shape of the electrode assembly is beneficial to taking into account both actual production efficiency and processing performance.

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

[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, 5≤h≤30. By regulating the value of h within the above range, it is helpful to improve the curling problem of the single-sided negative electrode material layer area, thereby reducing the risk of tape breakage and material folding during the actual processing of the single-sided negative electrode sheet. In addition, the groove depth is reduced to a large extent, which takes into account the actual production efficiency and facilitates processing.

[0012] In some embodiments of the present application, a plurality of grooves are distributed in strips, and along the thickness direction of the negative electrode sheet, a single groove has an orthographic projection on the negative electrode material layer, which satisfies at least one of the following conditions: (1) the average width of the orthographic projections of the plurality of grooves is d μm, 50≤d≤110; (2) the shortest distance between the outer contours of the orthographic projections of two adjacent grooves is L2mm, 0.5≤L2≤1.5. In some embodiments of the present application, the angle between the center line of a single groove and the length direction of the negative electrode sheet is α°, 20≤α≤75. The above arrangement is conducive to improving the curling problem of the single-sided negative electrode material layer area, thereby reducing the risk of broken tape and feed folding during the actual processing of the single-sided negative electrode sheet. At the same time, it is conducive to improving the wetting performance of the electrolyte on the single-sided negative electrode sheet, improving the liquid retention performance of the single-sided negative electrode material layer area, thereby improving the dynamic performance and safety performance of the secondary battery. In addition, it takes into account the actual production efficiency and is conducive to processing.

[0013] In some embodiments of the present application, along the thickness direction of the negative electrode sheet, the total area of ​​the positive projection of the plurality of grooves is S1 mm 2 The projected area of ​​the single-sided negative electrode material layer is S2 mm 2, 2%≤S1 / S2≤10%. By adjusting the value of S1 / S2 within the above range, it is beneficial to improve the overall stiffness of the single-sided material layer area, thereby improving the curling problem of the single-sided negative electrode material layer area, thereby reducing the risk of broken tape and material folding during the actual processing of the single-sided negative electrode sheet.

[0014] The second aspect of the present application provides a secondary battery, which includes the negative electrode sheet in any of the above embodiments. The negative electrode sheet of the present application is applied to the secondary battery, so that the curling of the negative electrode sheet in the single-sided area is improved, and the risk of the negative electrode sheet in the single-sided area being folded and broken during processing is reduced, and the wettability of the electrolyte to the negative electrode sheet in the single-sided area is improved, thereby improving the dynamic performance and safety performance of the secondary battery.

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

[0016] The third aspect of the present application provides an electronic device, which includes the secondary battery in any one of the above embodiments. Therefore, the electronic device provided by the present application has good performance.

[0017] Beneficial effects of this application:

[0018] The present application provides a negative electrode plate, a secondary battery and an electronic device, wherein the negative electrode plate includes a negative electrode current collector and a negative electrode material layer. Along the length direction of the negative electrode plate, the negative electrode plate includes 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 plate, the length of the empty foil area accounts for A, and the length of the single-sided negative electrode material layer area accounts for B, 1 / 60≤A≤1 / 11, 1 / 20≤B≤1 / 5. A plurality of grooves are provided on the negative electrode material layer in the single-sided negative electrode material layer area, and the grooves are arranged at intervals along the length direction of the negative electrode plate. By providing grooves on the negative electrode plate in the single-sided area, the curling of the negative electrode plate in the single-sided area can be improved, and the risk of material folding and belt breaking of the negative electrode plate in the single-sided area during processing is reduced. At the same time, the wettability of the electrolyte to the negative electrode plate in the single-sided area is improved, thereby improving the dynamic performance and safety performance of the secondary battery.

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

[0020] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application, and for ordinary technicians in this field, other embodiments can also be obtained based on these drawings.

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

[0022] Figure 2 for Figure 1 A partial front view of the negative electrode sheet after the middle electrode assembly is unfolded;

[0023] Figure 3 for Figure 2 Schematic diagram of the longitudinal cross-section structure along the thickness direction of the negative electrode sheet.

[0024] The reference numerals are as follows:

[0025] Electrode assembly 001; positive electrode plate 10; negative electrode plate 20; separator 30; positive electrode current collector 11; positive electrode material layer 12; negative electrode current collector 21; negative electrode material layer 22; empty foil area 210; single-sided negative electrode material layer area 220; double-sided negative electrode material layer area 230; groove 2201. DETAILED DESCRIPTION

[0026] The following will be combined with the embodiments of the present application and the accompanying drawings to clearly and completely describe the technical solutions in the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than 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 implementation of the present application, lithium-ion batteries are used as an example of secondary batteries to explain the present application, but the secondary batteries of the present application are not limited to lithium-ion batteries. The specific technical solutions are as follows:

[0028] A first aspect of the present application provides a negative electrode sheet, which includes a negative electrode current collector and a negative electrode material layer. Along the length direction of the unfolded negative electrode sheet, the negative electrode sheet includes a hollow foil area and a single-sided negative electrode material layer area connected to the hollow foil area. Based on the length of the negative electrode sheet, the length of the hollow foil area accounts for A, and the length of the single-sided negative electrode material layer area accounts for 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 consisting of any two of the 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 consisting of any two of the values. A plurality of grooves are provided on the negative electrode material layer in the single-sided negative electrode material layer region, and the grooves are spaced apart along the length direction of the negative electrode sheet.

[0029] The present application adjusts the values ​​of A and B within the above range and sets grooves on the negative electrode material layer in the single-sided negative electrode material layer area, which is beneficial to dispersing the cold pressing residual stress of the single-sided negative electrode material layer area and improving the stress concentration problem in the single-sided negative electrode material layer area. It is applied to secondary batteries, thereby improving the curling of the negative electrode pole piece in the single-sided area, thereby reducing the risk of broken tape and material folding during the actual processing of the negative electrode pole piece in the single-sided area, improving the winding rate of the secondary battery, and reducing the capacity loss of the secondary battery caused by folding and the safety risk of short circuit. At the same time, by setting grooves on the negative electrode material layer in the single-sided negative electrode material layer area, the wetting performance of the electrolyte on the negative electrode pole piece in the single-sided area is improved, and the liquid retention performance of the single-sided negative electrode material layer area is improved, thereby 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 sheet, a single groove has an orthographic projection on the negative electrode material layer, along the length direction of the negative electrode sheet, the length of the single-sided negative electrode material layer area is L mm, the negative electrode sheet also includes 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 dividing line, the shortest distance between the outer contour of the orthographic projection of a single groove and the dividing line is L1 mm, 1 / 2≤(L-L1) / L≤1. For example, the value of (L-L1) / L can be 1 / 2, 11 / 20, 3 / 5, 13 / 20, 7 / 10, 3 / 4, 4 / 5, 19 / 20, 1 or a range consisting of any two of these values.

[0031] For ease of understanding, in this application, the negative electrode sheet is applied to the electrode assembly of the winding structure, and the electrode assembly is defined as having its own length direction as the X direction, its own width direction as the Y direction, and its own thickness direction as the Z direction in the unfolded state. It is understandable that the negative electrode sheet, the positive electrode sheet, and the separator have the same length direction, width direction, and thickness direction as the electrode assembly in the unfolded state, and the winding direction of the electrode assembly is the W direction. The above direction limitations are only used to understand the technical solution of this application and do not limit the scope of protection of this application.

[0032] For example, Figure 1 to Figure 2 As shown, the electrode assembly 001 includes a positive electrode sheet 10, a negative electrode sheet 20 and a separator 30. The negative electrode sheet 20 includes a negative electrode current collector 21 and a negative electrode material layer 22. 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 negative electrode sheet 20 includes a hollow 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 arranged on the side of the negative electrode current collector 21 away from the winding center of the electrode assembly 001. A plurality of grooves 2201 are arranged 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 sheet 20 and are arranged at intervals along the length direction (X direction) of the unfolded negative electrode sheet 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 area 220 is L mm, the single-sided negative electrode material layer area 220 and the double-sided negative electrode material layer area 230 have a dividing line PQ, and the shortest distance between the outer contour of the positive projection of a single groove 2201 and the dividing 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 broken tape 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, improve the liquid retention performance of the single-sided negative electrode material layer, thereby improving the kinetic performance and safety performance of the secondary battery. 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 sheet, the single-sided negative electrode material layer area includes a middle area and two edge areas connected to the middle area, and the grooves are spaced apart in the two edge areas and respectively penetrate the two edge areas. Based on the width of the negative electrode material layer in the single-sided negative electrode material layer area, the length of the middle area accounts for 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 consisting of any two of these values. For example, Figure 2 As shown, along the width direction (Y direction) after the negative electrode sheet 20 is unfolded, the single-sided negative electrode material layer area 220 includes a middle area and two edge areas connected to the middle area, wherein the two edge areas are the parts in the dotted frame of the single-sided negative electrode material layer area 220. The grooves 2201 are spaced apart in the two edge areas and respectively penetrate the two edge areas. By adjusting the value of C within the above range, it is beneficial to improve the curling problem of the single-sided negative electrode material layer area, thereby reducing the risk of broken tape and feed 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, improve the liquid retention performance of the single-sided negative electrode material layer area, thereby improving the dynamic performance and safety performance of the secondary battery. In addition, it takes into account the actual production efficiency and is conducive to processing.

[0035] In some embodiments of the present application, the negative electrode current collector includes a copper foil having a thickness of H μm, 4≤H≤8. For example, the value of H may be 4, 4.5, 5, 5.5, 6, 6.5, 7, 7.5, 8, or a range consisting of any two of these values. For example, Figure 3 As shown, the thickness of the negative electrode current collector 21 is H μm. By adjusting the value of H within the above range, it is beneficial to improve the curling problem of the single-sided negative electrode material layer area. On the basis of taking into account the energy density, the risk of broken tape and material folding during the actual processing of the single-sided negative electrode sheet is further reduced. At the same time, it is also beneficial to improve the electrolyte's wetting performance on the single-sided negative electrode sheet, improve the liquid retention performance of the single-sided negative electrode material layer area, and thus improve the dynamic performance and safety performance of the secondary battery. The present application has no special restrictions on the regulation method of the thickness of the negative electrode current collector, as long as the purpose of the present application can be achieved. For example, commercially available current collectors of different thicknesses can be selected, and the thickness of the negative electrode current collector can be determined in combination with 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 of the required thickness is selected.

[0036] In some embodiments of the present application, the coating weight per unit area of ​​the negative electrode material layer in the single-sided negative electrode material layer region is m mg / 1540.25 mm 2, 100≤m≤200. For example, the value of m can be 100, 110, 120, 130, 140, 150, 160, 170, 180, 190, 200 or a range consisting of any two of these values. By regulating the value of m within the above range, it is beneficial to improve the curling problem of the single-sided negative electrode material layer while ensuring the energy density, thereby further reducing the risk of broken tape and feed 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, 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.

[0037] In some embodiments of the present application, the negative electrode current collector includes a copper foil, 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 consisting of any two values ​​thereof; and the coating weight per unit area of ​​the negative electrode material layer in the single-sided negative electrode material layer region is m mg / 1540.25 mm 2 , 100≤m≤200, for example, the value of m can be 100, 110, 120, 130, 140, 150, 160, 170, 180, 190, 200 or a range consisting of any two of these values. By regulating the values ​​of H and m within the above range, it is beneficial to improve the curling problem of the single-sided negative electrode material layer while ensuring the energy density, thereby further reducing the risk of broken tape and feed 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, 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.

[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-sided negative electrode material layer region is L mm, 1≤L / D≤2, 50≤D≤130. For example, the value of L / D can be 1, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2 or a range consisting of any two of the values; the value of D can be 50, 60, 70, 80, 90, 100, 110, 120, 130 or a range consisting of any two of the values. For example, Figure 2As shown, along the width direction (Y direction) of the unfolded negative electrode sheet 20, the width of the negative electrode sheet 20 is D mm, and along the length direction (Y direction) of the unfolded negative electrode sheet 20, the length of the single-sided negative electrode material layer area 220 is L mm. By regulating the value of L / D and the value of D within the above range, the larger the ratio of the length L of the single-sided negative electrode material layer area to the width D of the negative electrode sheet, the smaller the constraint of the double-sided negative electrode material layer area on the single-sided negative electrode material layer area, and the larger the amplitude of the angular curling. By regulating the values ​​of L / D and D within the above range, it is beneficial to improve the curling problem of the single-sided negative electrode material layer area, thereby further reducing the risk of broken tape 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, improve the liquid retention performance of the single-sided negative electrode material layer area, and thus improve the dynamic performance and safety performance of the secondary battery. In addition, the width of the negative electrode sheet and the length of the single-sided negative electrode material layer are related to the shape of the electrode assembly formed after winding. Adjusting the shape of the electrode assembly is beneficial to balancing actual production efficiency and processing performance.

[0039] In some embodiments of the present application, the negative electrode sheet further comprises a double-sided negative electrode material layer region, the negative electrode material layer comprises a negative electrode active material, the negative electrode active material comprises at least one of graphite or a silicon-carbon composite material, and the compaction density of the negative electrode material layer in the single-sided negative electrode material layer region is PD1 g / cm 3 The compaction density of the negative electrode material layer in the double-sided negative electrode material layer area is PD2 g / cm 3 , 0.95≤PD1 / PD2≤1. For example, the value of PD1 / PD2 can be 0.95, 0.955, 0.96, 0.965, 0.97, 0.975, 0.98, 0.985, 0.99, 0.995, 1 or a range consisting of any two of these values. By selecting the above-mentioned types of negative electrode active materials and adjusting the value of PD1 / PD2 within the above-mentioned range, while taking into account the energy density of the secondary battery, the effect of reducing the deformation of the single-sided negative electrode material layer due to the cold pressing residual stress is more obvious, and the curling problem of the single-sided negative electrode material layer is improved, thereby further reducing the risk of broken tape and material folding during the actual processing of the single-sided negative electrode sheet.

[0040] In some embodiments of the present 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 regulating the value of PD2 within the above range, while taking into account the energy density of the secondary battery, the effect of reducing the deformation of the single-sided negative electrode material layer due to the cold pressing residual stress is more obvious, and the curling problem of the single-sided negative electrode material layer is improved, thereby further reducing the risk of broken tape and material folding during the actual processing of the single-sided negative electrode sheet.

[0041] 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, 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 consisting of any two of these values. For example, Figure 3 As shown, along the thickness direction (Z direction) of the negative electrode sheet 20, the average depth of the plurality of grooves 2201 is h μm. By adjusting the value of h within the above range, it is helpful to improve the curling problem of the single-sided negative electrode material layer area, thereby reducing the risk of broken tape and material folding during the actual processing of the single-sided negative electrode sheet. At the same time, it is helpful to improve the wetting performance of the electrolyte on the single-sided negative electrode sheet, improve the liquid retention performance of the single-sided negative electrode material layer area, thereby improving the dynamic performance and safety performance of the secondary battery. In addition, reducing the excessive depth of the grooves takes into account the actual production efficiency and is conducive to processing.

[0042] In some embodiments of the present application, the plurality of grooves are distributed in strips, and along the thickness direction of the negative electrode sheet, a single groove has an orthographic projection on the negative electrode material layer, and the average width of the orthographic projections of the plurality of grooves is d μm, 50≤d≤110. For example, the value of d can be 50, 60, 70, 80, 90, 100, 110, or a range consisting of any two of these values. For example, Figure 2 As shown, multiple grooves 2201 are distributed in strips, along the thickness direction (Z direction) of the negative electrode sheet 20, a single groove 2201 has an orthographic projection on the negative electrode material layer 22, and the average width of the orthographic projections 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 area, thereby reducing the risk of broken belts 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, improve the liquid retention performance of the single-sided negative electrode material layer area, thereby improving the dynamic performance and safety performance of the secondary battery. In addition, it takes into account the actual production efficiency and is conducive to processing.

[0043] In some embodiments of the present application, a plurality of grooves are distributed in strips, and along the thickness direction of the negative electrode sheet, a single 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, 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 consisting of any two of these values. For example, Figure 2 As shown, multiple grooves 2201 are distributed in strips, along the thickness direction (Z direction) of the negative electrode sheet 20, a single 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 helpful to improve the curling problem of the single-sided negative electrode material layer area, thereby reducing the risk of broken belts and material folding during the actual processing of the single-sided negative electrode sheet. At the same time, it is helpful to improve the wetting performance of the electrolyte on the single-sided negative electrode sheet, improve the liquid retention performance of the single-sided negative electrode material layer area, thereby improving the dynamic performance and safety performance of the secondary battery. In addition, it takes into account the actual production efficiency and is conducive to processing.

[0044] In some embodiments of the present application, a plurality of grooves are distributed in strips, and along the thickness direction of the negative electrode sheet, a single groove has an orthographic projection on the negative electrode material layer, and the average width of the orthographic projections of the plurality of grooves is d μm, 50≤d≤110, for example, the value of d can be 50, 60, 70, 80, 90, 100, 110 or a range consisting of any two of the values ​​therein; and, 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 a range consisting of any two of the values ​​therein. By adjusting the value of L2 and the value of d within the above range, it is helpful to improve the curling problem of the single-sided negative electrode material layer area, thereby reducing the risk of broken belts and material folding during the actual processing of the single-sided negative electrode sheet. At the same time, it is helpful to improve the electrolyte wetting performance of the single-sided negative electrode sheet, improve the liquid retention performance of the single-sided negative electrode material layer area, thereby improving the dynamic performance and safety performance of the secondary battery. In addition, it takes into account the actual production efficiency and energy density and is conducive to processing, so that the pore distribution of the negative electrode sheet is uniform.

[0045] In some embodiments of the present application, the angle between the center line of a single groove and the length direction of the negative electrode sheet is α°, 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 consisting of any two of these values. For example, Figure 2As shown, the angle between the center line of a single groove 2201 and the length direction (X direction) of the unfolded negative electrode sheet 20 is α°. By adjusting the value of α within the above range, it is helpful to improve the curling problem of the single-sided negative electrode material layer area, thereby reducing the risk of broken tape and material folding during the actual processing of the single-sided negative electrode sheet. At the same time, it is helpful to improve the wetting performance of the electrolyte on the single-sided negative electrode sheet, improve the liquid retention performance of the single-sided negative electrode material layer area, and thus improve the dynamic performance of the secondary battery. In addition, it takes into account both the actual production efficiency and energy density, and is conducive to processing.

[0046] In some embodiments of the present application, the angle between the center line of a single groove and the length direction of the negative electrode sheet is α°, 40≤α≤50. For example, the value of α can be 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50 or a range consisting of any two of these values. By regulating the value of α within the above range and setting the grooves obliquely, the stress dispersion is more obvious, which is conducive to further improving the curling problem of the single-sided negative electrode material layer area, thereby reducing the risk of broken tape and feed folding during the actual processing of the single-sided negative electrode sheet. At the same time, it is conducive to improving the wetting performance of the electrolyte on the single-sided negative electrode sheet, improving the liquid retention performance of the single-sided negative electrode material layer area, thereby improving the dynamic performance of the secondary battery. In addition, both actual production efficiency and energy density are taken into account, and processing is conducive.

[0047] In some embodiments of the present application, along the thickness direction of the negative electrode sheet, the total area of ​​the positive projection of the plurality of grooves is S1 mm 2 The projected area of ​​the single-sided negative electrode material layer is S2 mm 2 , 2%≤S1 / S2≤10%. For example, the value of S1 / S2 can be 2%, 2.2%, 2.5%, 2.8%, 3%, 3.2%, 3.5%, 3.8%, 4%, 4.2%, 4.5%, 4.8%, 5%, 5.2%, 5.5%, 5.8%, 6%, 6.2%, 6.5%, 6.8%, 7%, 7.2%, 7.5%, 7.8%, 8%, 8.2%, 8.5%, 8.8%, 9%, 9.2%, 9.5%, 9.8%, 10%, or a range consisting of any two of the values. For example, Figure 2As shown, the total area of ​​the orthographic projection of the plurality of grooves 2201 is S1, which is the sum of the areas of the orthographic projections of all the grooves 2201 in the edge region in the dashed box in the figure, and the area of ​​the single-sided negative electrode material layer region 220 is S2=L×D. By adjusting the value of S1 / S2 within the above range, it is beneficial to improve the overall stiffness of the single-sided material layer region, thereby improving the curling problem of the single-sided negative electrode material layer region, thereby reducing the risk of broken tape and material folding during the actual processing of the single-sided negative electrode sheet, and at the same time, it is beneficial to improve the wetting performance of the electrolyte on the single-sided negative electrode sheet, improve the liquid retention performance of the single-sided negative electrode material layer region, thereby improving the dynamic performance and safety performance of the secondary battery.

[0048] In the present application, the negative electrode material layer may also include a conductive agent and a binder. The present application does not particularly limit the type of conductive agent in the negative electrode material layer, as long as the purpose of the present application can be achieved. For example, the conductive agent may include but is not limited to at least one of conductive carbon black (Super P), carbon nanotubes (CNTs), carbon fibers, flake graphite, Ketjen black, graphene, metal materials or conductive polymers. The above-mentioned carbon nanotubes may include but are not limited to single-walled carbon nanotubes and / or multi-walled carbon nanotubes. The above-mentioned carbon fibers may include but are not limited to vapor-grown carbon fibers (VGCF) and / or nano-carbon fibers. The above-mentioned metal materials may include but are not limited to metal powders and / or metal fibers, specifically, the metal may include but are not limited to at least one of copper, nickel, aluminum or silver. The above-mentioned conductive polymers may include but are not limited to at least one of polyphenylene derivatives, polyaniline, polythiophene, polyacetylene or polypyrrole. The present application does not particularly limit the type of binder in the negative electrode material layer, as long as the purpose of the present application can be achieved. For example, the binder may include, but is not limited to, at least one of polyvinylidene fluoride, a copolymer of vinylidene fluoride and hexafluoropropylene, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, polyvinyl pyrrolidone, polyvinyl ether, polymethyl methacrylate, polytetrafluoroethylene or polyhexafluoropropylene. The present application has no particular restrictions on the mass ratio of the negative electrode active material, the conductive agent and the binder in the negative electrode material layer, as long as the purpose of the present application can be achieved.

[0049] The present application has no particular restrictions on the preparation method of the negative electrode sheet, 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) predetermining the area on the negative electrode current collector where a single-sided negative electrode material layer is set, the area where a double-sided negative electrode material layer is set, and the area where no negative electrode material layer is set; (3) 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 drying to form a negative electrode sheet including a single-sided negative electrode material layer; (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 drying to obtain a negative electrode sheet including a double-sided negative electrode material layer; (5) after cold pressing and cutting into strips, a groove is set in the single-sided negative electrode material layer area to obtain the negative electrode sheet of the present application.

[0050] In some embodiments, after step (4), a middle region and two edge regions connected to the middle region are determined in the single-sided negative electrode material layer region; and when a groove is set in the single-sided negative electrode material layer region, the groove is set in the two edge regions and passes through the two edge regions respectively.

[0051] The present application has no particular restrictions on the solid content of the above-mentioned slurry, as long as the purpose of the present application can be achieved. The present application has no particular restrictions on the temperature and time of the above-mentioned drying, as long as the purpose of the present application can be achieved. The present application has no particular restrictions on the process parameters of the above-mentioned cold pressing, cutting, stripping, etc., as long as the purpose of the present application can be achieved.

[0052] The present application has no particular limitation on the method for setting the grooves, and those skilled in the art can select one according to actual needs, as long as the purpose of the present application can be achieved. For example, the grooves can be set by pulsed laser etching. The value of (L-L1) / L can be controlled by regulating the length L of the single-sided negative electrode material layer area, the speed of the pulse laser emitter and the etching tape; the value of C can be controlled by regulating the width of the negative electrode material layer in the single-sided negative electrode material layer area, the power and defocus of the pulse laser emitter; the average depth h of the multiple grooves and the average width d of the orthographic projections of the multiple grooves can be controlled by the power and defocus of the pulse laser emitter; the shortest distance L2 between the outer contours of the orthographic projections of two adjacent grooves can be controlled by adjusting the spacing between the pulse laser emitters or the laser emission frequency; the angle α between the center line of a single groove and the length direction of the negative electrode plate after unfolding can be controlled by adjusting the position, power and defocus of the pulse laser emitter; the ratio S1 / S2 of the total area S1 of the orthographic projections of the multiple grooves to the projection area S2 of the single-sided negative electrode material layer area can be controlled by regulating the projection area of ​​the single-sided negative electrode material layer area, the power of the pulse laser emitter, the defocus and the number of grooves set in the single-sided negative electrode material layer area.

[0053] In the present application, the different features of the grooves provided in the above-mentioned single-sided negative electrode material layer area can be arbitrarily combined, and the implementation methods or embodiments covered by the above-mentioned combination are all within the protection scope of the present application.

[0054] The second aspect of the present application provides a secondary battery, which includes a positive electrode sheet, a separator, and a negative electrode sheet in any of the above embodiments. The negative electrode sheet of the present application is applied to the secondary battery, so that the curling of the negative electrode sheet in the single-sided area is improved, and the risk of the single-sided negative electrode sheet being folded and broken during processing is reduced, and the wettability of the electrolyte to the negative electrode sheet in the single-sided area is improved, thereby improving the dynamic 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 area and the single-sided negative electrode material layer area are arranged at the starting end of the winding structure. This can more specifically solve the problem that the negative electrode sheet in the single-sided negative electrode material layer area at the starting end of the winding will have obvious stress concentration after cold pressing, reduce the risk of material folding and breaking of the negative electrode sheet in the single-sided area during processing, and at the same time improve the wettability of the electrolyte to the negative electrode sheet in the single-sided area, thereby improving the dynamic performance and safety performance of the secondary battery.

[0056] The present application has no particular restrictions on the diaphragm, as long as the purpose of the present application can be achieved. For example, the material of the diaphragm may include, but is not limited to, polyethylene (PE), polypropylene (PP)-based polyolefins (PO), polyesters (e.g., polyethylene terephthalate (PET) films), cellulose, polyimide (PI), polyamide (PA), spandex, or aramid. The type of diaphragm may include at least one of a woven membrane, a nonwoven membrane, a microporous membrane, a composite membrane, a rolled membrane, or a spun membrane.

[0057] In some embodiments of the present application, the diaphragm may include a substrate layer and a surface treatment layer. The substrate layer may be a non-woven fabric, a film or a composite film having 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 film, a polyethylene porous film, a polypropylene non-woven fabric, a polyethylene non-woven fabric or a polypropylene-polyethylene-polypropylene porous composite film 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 a mixed polymer and an inorganic substance. In some embodiments of the present application, the inorganic layer includes inorganic particles and a binder. The present application has no particular restrictions on inorganic particles, for example, inorganic particles may include at least one of aluminum oxide, 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. The present application has no particular restrictions on the binder, for example, the binder can be at least one of the above-mentioned binders. In some embodiments of the present application, the polymer layer includes a polymer, and the material of the polymer includes at least one of polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyacrylate, polyvinyl pyrrolidone, polyvinyl ether or polyvinylidene fluoride or poly (vinylidene fluoride-hexafluoropropylene). In the present application, the thickness of the diaphragm is not particularly limited, as long as the purpose of the present application can be achieved, for example, the thickness of the diaphragm can be 3μm to 30μm.

[0058] The present application has no special restrictions on the positive electrode plate, as long as the purpose of the present application can be achieved. For example, the positive electrode plate includes a positive current collector and a positive electrode material layer disposed on at least one surface of the positive current collector. The above-mentioned "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 the thickness direction of itself, or it can be disposed on two surfaces of the positive current collector along the thickness direction of itself. 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. The present application has no special restrictions, as long as the purpose of the present application can be achieved. For example, such as Figure 1 As shown, the positive electrode material layer 12 is arranged on the two surfaces of the positive electrode collector 11 along its own thickness direction. The present application has no special restrictions on the positive electrode collector, as long as the purpose of the present application can be achieved. For example, the positive electrode collector may include aluminum foil, aluminum alloy foil or a composite collector (such as an aluminum-carbon composite collector). The positive electrode material layer of the present application contains positive electrode active materials. The present application has no special restrictions on the type of positive electrode active materials, as long as the purpose of the present application can be achieved. 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 aluminum oxide, lithium iron phosphate, lithium-rich manganese-based materials, lithium cobalt oxide (LiCoO2), lithium manganate, lithium iron manganese phosphate or lithium titanate, etc. In the present application, the positive electrode active material may also contain non-metallic elements, for example, the non-metallic elements include at least one of fluorine, phosphorus, boron, chlorine, silicon or sulfur. In the present application, there is no particular restriction on the thickness of the positive electrode current collector and the positive electrode material layer, as long as the purpose of the present application can be achieved. In the present application, the positive electrode material layer may also include a positive electrode binder and a conductive agent. The present application does not particularly limit the type of the positive electrode binder in the positive electrode material layer, as long as the purpose of the present application can be achieved. For example, the positive electrode binder may be the same as the type of the binder in the above-mentioned negative electrode material layer. The present application does not particularly limit the type of the conductive agent in the positive electrode material layer, as long as the purpose of the present application can be achieved. For example, the conductive agent may be the same as the type of the conductive agent in the above-mentioned negative electrode material layer. The present application has no particular restriction on the mass ratio of the positive electrode active material, the conductive agent, and the binder in the positive electrode material layer. Those skilled in the art can select the ratio according to actual needs as long as the purpose of the present application can be achieved.

[0059] In the present application, the secondary battery also includes an electrolyte, and the electrolyte includes a lithium salt and a non-aqueous solvent. The present application has no special restrictions on lithium salts, as long as the purpose of the present application can be achieved. For example, the lithium salt may include but is not limited to at least one of LiPF6, LiBF4, LiAsF6, LiClO4, LiB(C6H5)4, LiCH3SO3, LiCF3SO3, LiN(SO2CF3)2, LiC(SO2CF3)3, Li2SiF6, lithium bis(oxalate borate) (LiBOB) or lithium difluoroborate. The present application has no special restrictions on the content of lithium salt in the electrolyte, as long as the purpose of the present application can be achieved. The present application has no special restrictions on non-aqueous solvents, as long as the purpose of the present application can be achieved. For example, non-aqueous solvents may include but are not limited to at least one of carbonate compounds, carboxylate compounds, ether compounds or other organic solvents. The above-mentioned carbonate compounds may include but are not limited to at least one of chain carbonate compounds, cyclic carbonate compounds or fluorinated carbonate compounds. The above-mentioned linear carbonate compound may include but is not limited to at least one of dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methylpropyl carbonate (MPC), ethylpropyl carbonate (EPC) or methylethyl carbonate (MEC). The above-mentioned cyclic carbonate may include but is not limited to at least one of ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC) or vinylethylene carbonate (VEC). The fluorinated carbonate compound may 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-tetrafluoroethylene carbonate, 1-fluoro-2-methylethylene carbonate, 1-fluoro-1-methylethylene carbonate, 1,2-difluoro-1-methylethylene carbonate, 1,1,2-trifluoro-2-methylethylene carbonate or trifluoromethylethylene carbonate. The above-mentioned carboxylate compounds may include but are not limited to at least one of methyl formate, methyl acetate, ethyl acetate, n-propyl acetate, tert-butyl acetate, methyl propionate, ethyl propionate, propyl propionate, γ-butyrolactone, decanolactone, valerolactone or caprolactone. The above-mentioned ether compounds may include but are not limited to at least one of dibutyl ether, tetraethylene glycol dimethyl ether, diethylene glycol dimethyl ether, 1,2-dimethoxyethane, 1,2-diethoxyethane, 1-ethoxy-1-methoxyethane, 2-methyltetrahydrofuran or tetrahydrofuran. The above-mentioned other organic solvents may include but are not limited to at least one of dimethyl sulfoxide, 1,2-dioxolane, cyclopentane, methylcyclopentane, 1,3-dimethyl-2-imidazolidinone, N-methyl-2-pyrrolidone, dimethylformamide, acetonitrile, trimethyl phosphate, triethyl phosphate or trioctyl phosphate. The present application does not particularly limit the content of the non-aqueous solvent in the electrolyte, as long as the purpose of the present application can be achieved.The present application has no particular limitation on the content of the non-aqueous solvent in the electrolyte, as long as the purpose of the present application can be achieved.

[0060] The secondary battery also includes a shell for accommodating a positive electrode plate, a separator, a negative electrode plate and an electrolyte, as well as other components known in the field of secondary batteries, and this application does not limit the above-mentioned other components. This application does not particularly limit the shell, and it can be a shell known in the art, as long as the purpose of this application can be achieved. For example, the shell can be a hard shell or a flexible shell. The material of the hard shell can be metal, and this application does not limit the type of metal. A metal hard shell known in the art can be used, as long as the purpose of this application can be achieved. The flexible shell can be a metal plastic film, such as an aluminum plastic film, a steel plastic film, etc.

[0061] The preparation process of the secondary battery of the present application is well known to those skilled in the art, and there is no particular limitation in the present application. For example, the preparation process of the secondary battery may include but is not limited to the following steps: stacking the positive electrode sheet, the separator and the negative electrode sheet in order, and winding, folding and other operations as needed to obtain an electrode assembly of a winding structure, placing the electrode assembly in a shell, injecting the electrolyte into the shell and sealing it to obtain a secondary battery. Alternatively, stacking the positive electrode sheet, the separator and the negative electrode sheet in order, and then fixing the four corners of the entire laminated structure with tape to obtain an electrode assembly of a laminated structure, placing the electrode assembly in a shell, injecting the electrolyte into the shell and sealing it to obtain a secondary battery. In addition, overcurrent protection elements, guide plates, etc. may also be placed in the shell as needed to prevent the pressure inside the secondary battery from rising and overcharging and discharging.

[0062] A third aspect of the present application provides an electronic device, which includes the secondary battery in any of the above embodiments, so that the electronic device provided by the present application has good performance.

[0063] The electronic device of the present application is not particularly limited, and it can be used for any electronic device known in the prior art. For example, the electronic device can include but is not limited to a laptop computer, a pen-input computer, a mobile computer, an electronic book player, a portable phone, a portable fax machine, a portable copier, 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 notepad, a calculator, a memory card, a portable recorder, a radio, a backup power supply, a motor, a car, a motorcycle, a power-assisted bicycle, a bicycle, a lighting fixture, a toy, a game console, a clock, an electric tool, a flashlight, a camera, a large household battery, and a lithium-ion capacitor.

[0064] Example

[0065] Hereinafter, the embodiments of the present application will be described in more detail with reference to Examples and Comparative Examples. Various tests and evaluations were performed according to the following methods. In addition, unless otherwise specified, "parts" and "%" are by mass.

[0066] Test methods and equipment:

[0067] Tests for L, A, B, L1, C, H, D, h, d, L2, α, S1 / S2:

[0068] At an ambient temperature of 25°C, the lithium-ion batteries of the embodiments and comparative examples were discharged at 0.5C to 2.5V and then disassembled to obtain electrode assemblies. The negative electrode sheets were taken out from the electrode assemblies, soaked in dimethyl carbonate (DMC) for 20 minutes, and then placed in an oven and dried at 80°C for 12 hours to obtain test samples of the negative electrode sheets.

[0069] The negative electrode sheet is unfolded, and the empty foil area, the single-sided negative electrode material layer area and the double-sided negative electrode material layer area of ​​the negative electrode sheet are confirmed by naked eye observation along the length direction of the unfolded negative electrode sheet, and the length L of the single-sided negative electrode material layer area, the length of the empty foil area and the length of the negative electrode sheet are respectively measured with a tape measure, and then, based on the length of the negative electrode sheet, the length proportion A of the empty foil area and the length proportion B of the single-sided negative electrode material layer area are calculated. Observe the plane where the length direction and the width direction of the unfolded negative electrode sheet are located, confirm the dividing line between the single-sided negative electrode material layer area and the double-sided negative electrode material layer area, and measure the shortest distance L1 between the outer contour of a single groove on the surface of the negative electrode sheet and the dividing line along the length direction of the unfolded negative electrode sheet, and calculate the value of (L-L1) / L. Observe the plane where the length and width directions of the unfolded negative electrode pole piece are located, and observe the setting position of the groove along the width direction of the unfolded negative electrode pole piece. If the groove runs through along the width direction of the unfolded negative electrode pole piece, the middle area of ​​the single-sided negative electrode material layer area accounts for 0, and based on the width of the negative electrode material layer in the single-sided negative electrode material layer area, the length proportion C of the middle area is 0; if the groove does not run through along the width direction of the unfolded negative electrode pole piece, then measure the length of the single-sided negative electrode material layer area without the groove and the width of the negative electrode material layer in the single-sided negative electrode material layer area along the width direction of the unfolded negative electrode pole piece, then the length proportion C of the middle area = the length of the single-sided negative electrode material layer area without the groove / the width of the negative electrode material layer in the single-sided negative electrode material layer area.

[0070] A scanning electron microscope is used to photograph each groove of the single-sided negative electrode material layer area, and image recognition is used to calculate the projection area of ​​a single groove, which is then added together to obtain the total area S1 of the positive projections of multiple grooves. The measured length L of the single-sided negative electrode material layer area is multiplied by the measured width of the single-sided negative electrode material layer area to obtain the projection area S2 of the single-sided negative electrode material layer area, and then S1 / S2 is calculated.

[0071] Select any 5 grooves located in the single-sided negative electrode material layer area, select any 5 positions on a single groove, measure the width of the grooves at the 5 positions, take the average value, which is the width of the positive projection of the single groove on the negative electrode material layer, and take the average value of the width of the 5 grooves to obtain the average width d of the positive projections of multiple grooves on the negative electrode material layer. Measure the shortest distance between the outer contour of a single groove on the negative electrode material layer and the outer contour of an adjacent groove on the negative electrode material layer, which is the shortest distance L2 between the outer contours of the positive projections of two adjacent grooves. Select any 5 grooves, determine the center line of each groove, measure the angle between the center line of each groove and the length direction of the negative electrode sheet after unfolding, and take the average value, which is the angle α between the center line of each 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 longitudinal section of the negative electrode sheet is ion polished and observed by electron scanning microscope. A clearer boundary line between the negative electrode material layer and the negative electrode collector can be observed, and the thickness H of the negative electrode collector is measured by using a micrometer along the thickness direction of the negative electrode sheet; 5 grooves are selected at random, and the distances from the surface of the negative electrode material layer to the bottom of each groove are measured by using a micrometer along the thickness direction of the negative electrode sheet, and the average value is taken as the average depth h of the multiple grooves.

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

[0074] At an ambient temperature of 25°C, the lithium-ion battery was disassembled to obtain an electrode assembly with a wound structure. The negative electrode sheet was taken out and soaked in dimethyl carbonate (DMC) for 20 minutes. The negative electrode sheet was then placed in an oven and dried at 80°C for 12 hours to obtain a test sample of the negative electrode sheet. The empty foil area, single-sided negative electrode material layer area and double-sided negative electrode material layer area of ​​the negative electrode sheet were confirmed.

[0075] The negative electrode sheet sample of the single-sided negative electrode material layer area was punched and broken into two small discs with a radius of 22.14 mm (area of ​​1540.25 mm 2 ), weigh them one by one and take the average value, which is recorded as a; wipe the negative electrode material layer on the small disc with deionized water, weigh them one by one and take the average value, which is recorded as a1. Punch the negative electrode sheet sample in the double-sided negative electrode material layer area into 4 small discs with a radius of 22.14mm (area of ​​1540.25mm 2 ), weigh them one by one and take the average value, which is recorded as b; wipe the negative electrode material layer on both surfaces of the small disc with deionized water, weigh them one by one and take the average value, which is recorded as b1, then,

[0076] The coating weight per unit area of ​​the negative electrode material layer in the single-sided negative electrode material layer area is M=a-a1;

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

[0078] PD1 and PD2 tests:

[0079] Refer to the "Test of coating weight per unit area of ​​negative electrode material layer" to obtain the coating weight per unit area of ​​negative electrode material layer in single-sided negative electrode material layer area and the coating weight per unit area of ​​negative electrode material layer in double-sided negative electrode material layer area, and refer to the test steps of "Test of L, A, B, L1, C, H, D, h, d, L2, α, S1 / S2" to measure the thickness of single-sided negative electrode material layer with micrometer, and calculate PD1 and PD2 according to the following formula:

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

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

[0082] Low temperature kinetic rate 0℃ lithium precipitation test of the innermost single-sided negative electrode material layer:

[0083] Place the lithium-ion battery in an environment of 0°C, and charge it at a constant current rate of 0.5C, 0.7C, 1.0C, 1.2C, 1.5C, 1.7C, 2.0C, 2.2C, 2.4C, 2.6C, 2.8C, 3.0C, 3.2C, 3.4C, 3.6C, 3.8C, 4.0C, 4.2C, 4.4C, 4.6C, 4.8C, 5.0C until the voltage reaches 4.5V, then charge it at a constant voltage of 4.5V until the cut-off current reaches 0.05C, let it stand for 5 minutes, and discharge it at a constant current of 0.5C until the voltage reaches 3.0V, let it stand for 5 minutes. This is one charge and discharge cycle. Then perform 10 cycles of charge and discharge in the same steps.

[0084] Then charge at the same rate to 4.5V, then charge at 4.5V to a cut-off current of 0.05C, and let stand for 5 minutes; then disassemble the lithium-ion battery to confirm the interface of the single-sided negative electrode material layer, disassemble from low rate to high rate until there is slight white lithium metal precipitation, and this rate is recorded as the low-temperature kinetic maximum rate of the single-sided negative electrode material layer. For example, if there is slight lithium precipitation when disassembling the single-sided negative electrode at 1.5C, it is recorded as the low-temperature kinetic rate of 1.5C.

[0085] Energy density test:

[0086] (1) Place the lithium-ion battery in an environment of 25°C, charge it at a constant current of 1C to a voltage of 4.5V, then charge it at a constant voltage of 4.5V to a cut-off current of 0.05C, let it stand for 5 minutes, discharge it at a constant current of 0.2C to a voltage of 3.0V, let it stand for 5 minutes, and record the discharge capacity at this time as C.

[0087] (2) Use a micrometer to measure the actual thickness Da, Db, and Dc of the electrode assembly at 3 mm near the edge of the head, 3 mm near the edge of the tail, and the middle area. For example, the first data of the head is recorded as Da1, and so on. The average thickness D is:

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

[0089] (3) Use a laser measuring instrument to scan and measure the length L and width M of the lithium-ion battery.

[0090] (4) The actual energy density X of lithium-ion batteries is: X = C / (D × L × M);

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

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

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

[0094] (2) taking a sufficient amount of separators and positive electrode sheets corresponding to the negative electrode sheets prepared in each embodiment and comparative example in step (1), the amount being much greater than N;

[0095] (3) using the negative electrode sheet, separator and positive electrode sheet in step (1) and step (2), assembling and producing the lithium-ion battery according to the winding method of each embodiment and comparative example;

[0096] (4) Record the total scrap quantity M of negative electrode sheets due to feed material folding or single-sided tape breakage during the winding process;

[0097] (5) Winding efficiency of negative electrode sheet (%) = (1-M / N) × 100%.

[0098] 500 Cycle (circle) cycle single-sided area interface characteristics;

[0099] The lithium-ion battery prepared in the embodiment and comparative example was placed in a 25°C constant temperature test box and allowed to stand for 30 minutes to allow the lithium-ion battery to reach a constant temperature. Charge to 4.5V at a constant current of 0.5C, charge to a current of 0.025 C at a constant voltage of 4.5V, let stand for 5 minutes, and discharge to 3.0V at a constant current of 0.5C, which was recorded as the initial discharge capacity C0. This step was cycled for 500 cycles, and the discharge capacity C1 after 500 cycles was recorded. The capacity retention rate of the lithium-ion battery after 500 cycles was calculated, and the cycle capacity retention rate (%) = C1 / C0×100%. At the same time, the lithium-ion battery after the cycle was fully charged (charged to 4.5V at a constant current of 0.5C) and disassembled for analysis to confirm the interface of the single-sided negative electrode material layer after 500 cycles and confirm the difference points.

[0100] The electrochemical performance of lithium-ion batteries is characterized by the cycle capacity retention rate and the interface condition of the single-sided negative electrode area. Specifically, the higher the capacity retention rate when there is no abnormality in the interface, the better the electrochemical performance of the lithium-ion battery; the lower the capacity retention rate when there is an abnormality in the interface, the worse the electrochemical performance of the lithium-ion battery. Among them, "interface condition" refers to the condition of the surface of the negative electrode plate after the lithium-ion battery is disassembled under full charge after cycling; "no abnormality in the interface condition" means that there are no black spots, lithium precipitation, purple spots and other phenomena on the surface of the negative electrode plate; "abnormality in the interface condition" means that at least one of the following phenomena, such as black spots, lithium precipitation or purple spots, appears on the surface of the negative electrode plate.

[0101] Example 1-1

[0102] <Preparation of negative electrode sheet>

[0103] Artificial graphite, styrene-butadiene rubber and sodium carboxymethyl cellulose were mixed in a mass ratio of 96:2:2, deionized water was added as a solvent, and stirred evenly to obtain a negative electrode slurry with a solid content of 40wt%. The negative electrode slurry was evenly coated on one surface of the negative electrode current collector copper foil with a thickness H of 6μm, and intermittently coated on the copper foil according to the size of the electrode assembly, and then dried at 85°C to obtain a negative electrode sheet with a single-sided negative electrode material layer coated with a coating thickness of 100μm. Then repeat the above steps on the other surface of the copper foil to obtain a negative electrode sheet with a double-sided negative electrode material layer coated. After cold pressing (cold pressing pressure of 80T), a negative electrode sheet was obtained, and the negative electrode sheet was cut into a fixed size, and the two edge areas of the single-sided negative electrode material layer area of ​​the negative electrode sheet were predetermined to set the groove. The middle area of ​​the single-sided negative electrode material layer area where the groove was not set was based on the width of the negative electrode material layer, and the length accounted for C of 15%. The positive projection shape of a single groove along the thickness direction of the negative electrode sheet is a rectangle, and then vacuum dried at 120°C for 12 hours to obtain a negative electrode sheet with a specification of 78mm×875mm for standby use, that is, the width D of the negative electrode sheet is 78mm. Among them, the unit area coating weight m of the negative electrode material layer in the single-sided negative electrode material layer area is 150mg / 1540.25mm 2 The coating weight per unit area of ​​the negative electrode material layer in the double-sided negative electrode material layer area is 150mg / 1540.25mm 2 The compaction density PD1 of the negative electrode material layer in the single-sided negative electrode material layer area is 1.70 g / cm 3 The compaction density PD2 of the negative electrode material layer in the double-sided negative electrode material layer area is 1.73 g / cm 3 Based on the length of the negative electrode sheet, the length of the empty foil area accounts for A which is 1 / 20, the length of the single-sided negative electrode material layer area accounts for B which is 1 / 10, and the length L of the single-sided negative electrode material layer area is 87.5 mm.

[0104] Pulse laser etching is used to set grooves on two edge areas of the single-sided negative electrode material layer of the negative electrode sheet. The specific parameters are shown in Table 1. The shortest distance L1 between the outer contour of the orthographic projection of a single groove and the dividing line is 17.5 mm. Along the thickness direction of the negative electrode sheet, the average depth h of the multiple grooves is 20 μm, the average width d of the orthographic projection of the multiple grooves is 80 μm, the shortest distance L2 between the outer contours of the orthographic projections of two adjacent grooves is 1 mm, the angle α between the center line of the single groove and the length direction of the unfolded negative electrode sheet is 45°, and the ratio S1 / S2 of the total area of ​​the orthographic projection of the multiple grooves to the projection area of ​​the single-sided negative electrode material layer is 5.04%.

[0105] <Preparation of positive electrode sheet>

[0106] Conductive agent (conductive carbon black) and binder (polyvinylidene fluoride) are mixed in a certain proportion, and N-methylpyrrolidone (NMP) is added to make a conductive glue with a solid content of 7w%. After mixing, lithium cobalt oxide is added, and the system is stirred under the action of a vacuum mixer until the system is uniform, and a positive electrode slurry with a solid content of 75w% is obtained. Among them, lithium cobalt oxide: conductive agent: binder (mass ratio) is 97:1:2. The positive electrode slurry is evenly coated on one surface of an aluminum foil with a thickness of 8μm, and intermittently coated on the aluminum foil according to the size of the battery cell, and then dried at 85°C to obtain a positive electrode sheet with a single-sided positive electrode material layer coated with a coating thickness of 100μm. After cold pressing (cold pressing pressure of 85T), a positive electrode compaction sheet is obtained. The positive electrode sheet is cut into a fixed size, and then vacuum dried at 85°C for 4h to obtain a positive electrode sheet with a specification of 74mm×867mm for standby use. The coating weight per unit area of ​​the positive electrode material layer is 300 mg / 1540.25 mm 2 The compaction density of the positive electrode material layer is 4.20g / 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 at a weight ratio of 1:1:1, and then lithium salt LiPF6 is added to the non-aqueous solvent and mixed evenly to obtain an electrolyte. The molar concentration of the lithium salt LiPF6 is 1.15 mol / L.

[0109] <Preparation of Separator>

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

[0111] <Preparation of lithium-ion batteries>

[0112] The positive electrode sheet, the separator and the negative electrode sheet are stacked in order, the separator is placed between the positive electrode sheet and the negative electrode sheet to play an isolating role, and then they are wound to obtain an electrode assembly; the electrode assembly is placed in an outer packaging foil, and moisture is removed at 80°C, and the prepared electrolyte is injected, and a soft-pack lithium-ion battery is obtained after vacuum packaging, standing, formation, shaping, capacity testing and other processes.

[0113] Example 1-2 to Example 1-28

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

[0115] Example 2-1 to Example 2-11

[0116] Except for adjusting the relevant preparation parameters according to Table 2, the rest is the same as Example 1-1.

[0117] Comparative Example 1

[0118] Except that no groove is provided on the single-sided negative electrode material layer area in <Preparation of Negative Electrode Sheet>, the rest is the same as Example 1-1.

[0119] Comparative Examples 2 to 6

[0120] Except for adjusting the relevant preparation parameters according to Table 1, the rest is the same as Example 1-1.

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

[0122] Table 1

[0123] Note: “ / ” in Table 1 indicates no relevant preparation parameters.

[0124] It can be seen from Examples 1-1 to 1-28 and Comparative Examples 1 to 6 that by regulating the values ​​of A and B within the above ranges and setting a plurality of grooves on the negative electrode material layer in the single-sided negative electrode material layer area, the low-temperature kinetic maximum rate of the single-sided negative electrode material layer area of ​​the lithium-ion battery is larger, the winding excellence related to feed discounting / single-sided negative electrode material layer area breaking is improved, the 500Cycle cycle capacity retention rate is larger and the interface characteristics of the single-sided negative electrode material layer area are improved, indicating that the curling of the single-sided negative electrode pole sheet is improved by the above-mentioned setting, thereby reducing the risk of breaking and feed discounting in the actual processing of the single-sided negative electrode pole sheet, improving the winding excellence of the secondary battery, and taking into account the energy density of the lithium-ion battery, the lithium-ion battery has good dynamic performance and safety performance. In Comparative Example 1, no groove is provided on the negative electrode material layer of the single-sided negative electrode material layer area; the values ​​of A and / or B in Comparative Examples 2 to 6 are not within the scope of the present application, the low-temperature kinetic maximum rate of the single-sided negative electrode material layer area of ​​the ion battery is small, the winding superiority rate related to the feed folding / single-sided negative electrode material layer area breaking is low, and the 500Cycle cycle capacity retention rate is small, and the interface characteristics of the single-sided negative electrode material layer area are poor. The low-temperature kinetic maximum rate of the single-sided negative electrode material layer area of ​​the lithium-ion battery of Examples 1-1 to 1-28 is large, the winding superiority rate related to the feed folding / single-sided negative electrode material layer area breaking is improved, the 500Cycle cycle capacity retention rate is large, and the interface characteristics of the single-sided negative electrode material layer area are improved, and the lithium-ion battery has good safety performance and kinetic performance.

[0125] The value of (L-L1) / L usually affects the safety and kinetic performance of lithium-ion batteries. It can be seen from Examples 1-1, 1-6 and 1-7 that when the value of (L-L1) / L is within the scope of this application, the low-temperature kinetic maximum rate of the single-sided negative electrode material layer is large, the winding excellence rate related to the feed folding / single-sided negative electrode material layer breaking is large, the 500Cycle cycle capacity retention rate is large, and the interface characteristics of the single-sided negative electrode material layer are good, indicating that the curling of the single-sided negative electrode pole piece is improved, thereby reducing the risk of breaking and feed folding during the actual processing of the single-sided negative electrode pole piece, improving the winding excellence rate of the secondary battery, and the lithium-ion battery has good kinetic performance and safety performance.

[0126] The value of C usually affects the safety and kinetic performance of lithium-ion batteries. It can be seen from Example 1-1, Example 1-6 to Example 1-7, Example 1-18, Example 1-27 to Example 1-28 that when the value of C is within the scope of this application, the low-temperature kinetic maximum rate of the single-sided negative electrode material layer area is large, the winding excellence rate related to the feed folding / single-sided negative electrode material layer area is large, the 500Cycle cycle capacity retention rate is large, and the interface characteristics of the single-sided negative electrode material layer area are good, indicating that the curling of the single-sided negative electrode pole piece is improved, thereby reducing the risk of breaking and feeding folding during the actual processing of the single-sided negative electrode pole piece, improving the winding excellence rate of the secondary battery, and the lithium-ion battery has good kinetic performance and safety performance.

[0127] The value of D usually affects the safety and kinetic performance of lithium-ion batteries. It can be seen from Example 1-1, Example 1-2 to Example 1-5, Example 1-8 to Example 1-9, and Example 1-18 that when the value of D is within the scope of this application, the low-temperature kinetic maximum rate of the single-sided negative electrode material layer is large, the winding excellence rate related to the feed folding / single-sided negative electrode material layer breaking is large, the 500Cycle cycle capacity retention rate is large, and the interface characteristics of the single-sided negative electrode material layer are good, indicating that the curling of the single-sided negative electrode pole piece is improved, thereby reducing the risk of breaking and feeding folding during the actual processing of the single-sided negative electrode pole piece, improving the winding excellence rate of the secondary battery, and the lithium-ion battery has good kinetic performance and safety performance.

[0128] The value of h usually affects the safety and kinetic performance of lithium-ion batteries. It can be seen from Example 1-1, Example 1-10 to Example 1-11, and Example 1-19 to Example 1-20 that when the value of h is within the scope of this application, the low-temperature kinetic maximum rate of the single-sided negative electrode material layer is large, the winding superiority related to the feed folding / single-sided negative electrode material layer breaking is large, the 500Cycle cycle capacity retention rate is large, and the interface characteristics of the single-sided negative electrode material layer are good, indicating that the curling of the single-sided negative electrode pole piece is improved, thereby reducing the risk of breaking and feeding folding during the actual processing of the single-sided negative electrode pole piece, improving the winding superiority of the secondary battery, and improving the wetting performance of the electrolyte on the single-sided negative electrode pole piece, and the lithium-ion battery has good kinetic performance and safety performance.

[0129] The value of d usually affects the safety and kinetic performance of lithium-ion batteries. It can be seen from Example 1-1, Example 1-12 to Example 1-13, and Example 1-21 to Example 1-22 that when the value of d is within the scope of this application, the low-temperature kinetic maximum rate of the single-sided negative electrode material layer is large, the winding excellence rate related to the feed folding / single-sided negative electrode material layer breaking is large, the 500Cycle cycle capacity retention rate is large, and the interface characteristics of the single-sided negative electrode material layer are good, indicating that the curling of the single-sided negative electrode pole piece is improved, thereby reducing the risk of breaking and feeding folding during the actual processing of the single-sided negative electrode pole piece, improving the wetting performance of the electrolyte on the single-sided negative electrode pole piece, and improving the winding excellence rate of the secondary battery. The lithium-ion battery has good kinetic performance and safety performance.

[0130] The value of L2 usually affects the safety and kinetic performance of lithium-ion batteries. It can be seen from Example 1-1, Example 1-14 to Example 1-15, and Example 1-23 to Example 1-24 that when the value of L2 is within the scope of this application, the low-temperature kinetic maximum rate of the single-sided negative electrode material layer is large, the winding excellence rate related to the feed folding / single-sided negative electrode material layer breaking is large, the 500Cycle cycle capacity retention rate is large, and the interface characteristics of the single-sided negative electrode material layer are good, indicating that the curling of the single-sided negative electrode pole piece is improved, thereby reducing the risk of breaking and feeding folding during the actual processing of the single-sided negative electrode pole piece, improving the winding excellence rate of the secondary battery, and the lithium-ion battery has good kinetic performance and safety performance.

[0131] The value of α usually affects the safety and kinetic performance of lithium-ion batteries. It can be seen from Example 1-1, Example 1-16 to Example 1-17, and Example 1-25 to Example 1-26 that when the value of α is within the scope of this application, the low-temperature kinetic maximum rate of the single-sided negative electrode material layer is large, the winding excellence rate related to the feed folding / single-sided negative electrode material layer breaking is large, the 500Cycle cycle capacity retention rate is large, and the interface characteristics of the single-sided negative electrode material layer are good, indicating that the curling of the single-sided negative electrode pole piece is improved, thereby reducing the risk of breaking and feeding folding during the actual processing of the single-sided negative electrode pole piece, improving the winding excellence rate of the secondary battery, and the lithium-ion battery has good kinetic performance and safety performance.

[0132] The value of S1 / S2 usually affects the safety and kinetic performance of lithium-ion batteries. It 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 that when the value of S1 / S2 is within the scope of this application, the low-temperature kinetic maximum rate of the single-sided negative electrode material layer area is large, the winding superiority rate related to the feed folding / single-sided negative electrode material layer area is large, the 500Cycle cycle capacity retention rate is large and the interface characteristics of the single-sided negative electrode material layer area are good, indicating that the curling of the single-sided negative electrode pole piece is improved, thereby reducing the risk of breaking and feeding folding during the actual processing of the single-sided negative electrode pole piece, improving the winding superiority rate of the secondary battery, and the lithium-ion battery has good kinetic performance and safety performance.

[0133] Table 2

[0134] Note: “ / ” in Table 2 indicates no relevant effect parameter.

[0135] The value of H usually affects the safety performance, energy density and kinetic performance of lithium-ion batteries. It can be seen from Example 1-1, Example 2-1 to Example 2-2, and Example 2-7 to Example 2-8 that when the value of H is within the scope of this application, the low-temperature kinetic maximum rate of the single-sided negative electrode material layer is larger, the winding advantage related to the feed discount / single-sided negative electrode material layer is larger, the energy density is higher, the 500Cycle cycle capacity retention rate is larger, and the interface characteristics of the single-sided negative electrode material layer are better, indicating that the curling of the single-sided negative electrode pole piece is improved, thereby reducing the risk of breaking the belt and feeding discount during the actual processing of the single-sided negative electrode pole piece, and improving the winding advantage 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 H in Example 2-8 is larger, and at this time, in lithium-ion batteries of the same volume specifications, the energy density is relatively low.

[0136] The value of m usually affects the safety performance, energy density and kinetic performance of lithium-ion batteries. It can be seen from Example 1-1, Example 2-3 to Example 2-4, and Example 2-9 to Example 2-10 that when the value of m is within the scope of this application, the low-temperature kinetic maximum rate of the single-sided negative electrode material layer is large, the winding advantage related to the feed discount / single-sided negative electrode material layer is large, the energy density is high, the 500Cycle cycle capacity retention rate is large, and the interface characteristics of the single-sided negative electrode material layer are good, indicating that the curling of the single-sided negative electrode pole piece is improved, thereby reducing the risk of breaking the belt and feeding discount during the actual processing of the single-sided negative electrode pole piece, and improving the winding advantage 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 small, and at this time, in lithium-ion batteries of the same volume specification, the energy density is relatively low.

[0137] The value of PD1 / PD2 and the value of PD2 usually affect the safety performance, energy density and kinetic performance of lithium-ion batteries. It can be seen from Example 1-1, Example 2-5 to Example 2-6, and Example 2-11 that when the value of PD1 / PD2 and the value of PD2 are within the scope of this application, the low-temperature kinetic maximum rate of the single-sided negative electrode material layer is large, the winding superiority related to the feed folding / single-sided negative electrode material layer breaking is large, the energy density is high, the 500Cycle cycle capacity retention rate is large, and the interface characteristics of the single-sided negative electrode material layer are good, indicating that the curling of the single-sided negative electrode pole piece is improved, thereby reducing the risk of breaking and feeding folding during the actual processing of the single-sided negative electrode pole piece, and improving the winding superiority 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.

[0138] It should be noted that, in this article, relational terms such as first and second, etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprises" or any other variations thereof are intended to cover non-exclusive inclusion, so that a process, method or article including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method or article.

[0139] Each embodiment in this specification is described in a related manner, and the same or similar parts between the embodiments can be referenced to each other, and each embodiment focuses on the differences from other embodiments.

[0140] The above description is only a preferred embodiment of the present application and is not intended to limit the present application. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present application shall 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, wherein along the length direction of the negative electrode sheet, the negative electrode sheet comprises a hollow foil area and a single-sided negative electrode material layer area connected to the hollow foil area, based on the length of the negative electrode sheet, the length proportion of the hollow foil area is A, the length proportion of the single-sided negative electrode material layer area is B, 1 / 60≤A≤1 / 11, 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 area, and the grooves are arranged at intervals along the length direction of the negative electrode plate.

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

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

4. The negative electrode sheet according to claim 3, wherein: Along the width direction of the negative electrode plate, the single-sided negative electrode material layer area includes a middle area and two edge areas connected to the middle area, the grooves are spaced apart in the two edge areas and respectively penetrate the two edge areas, based on the width of the negative electrode material layer in the single-sided negative electrode material layer area, the length of the middle area accounts for C, 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 includes a copper foil, and the thickness of the copper foil is H μm, 4≤H≤8; (2) The coating weight per unit area of ​​the negative electrode material layer in the single-sided negative electrode material layer area is m mg / 1540.25 mm 2 , 100≤m≤200.

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

7. The negative electrode sheet according to claim 1, wherein: The negative electrode plate also includes a double-sided negative electrode material layer area, the negative electrode material layer includes a negative electrode active material, the negative electrode active material includes at least one of graphite or a silicon-carbon composite material, and the compaction density of the negative electrode material layer in the single-sided negative electrode material layer area is PD1 g / cm 3 The compaction density of the negative electrode material layer in the double-sided negative electrode material layer area is 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 the thickness direction of the negative electrode plate, the average depth of the plurality of grooves is h μm, 5≤h≤30.

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

5.

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

12. The negative electrode sheet according to claim 11, wherein: Along the thickness direction of the negative electrode sheet, the total area of ​​the orthographic projections of the plurality of grooves is S1 mm 2 The projected area of ​​the single-sided negative electrode material layer is S2 mm 2 , 2%≤S1 / S2≤10%. 13 . A secondary battery comprising the negative electrode sheet according to claim 1 .

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

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