Secondary battery and electronic device

Abstract

The invention provides a secondary battery and an electronic device, the secondary battery comprises an electrode assembly of a lamination structure, and a negative pole piece comprises a double-sided negative pole piece and a single-sided negative pole piece; the single-sided negative pole piece comprises a first negative current collector and a first material layer arranged on one surface of the first negative current collector, and the first material layer faces the positive pole piece; the first negative electrode current collector comprises an empty foil area and a coating area, the coating area is provided with a plurality of first strip-shaped concave parts, and the plurality of first strip-shaped concave parts extend along the direction from the coating area to the empty foil area; the depth of the first strip-shaped concave part is h1, and h1 is larger than or equal to 4 and smaller than or equal to 21; the thickness of the first negative current collector is x1, the unit is [mu] m, and x1 is greater than or equal to 9 and less than or equal to 22; the double-sided negative pole piece comprises a second negative current collector, the thickness of the second negative current collector is x2 microns, and x1 / x2 is larger than or equal to 2 and smaller than or equal to 6. The secondary battery provided by the invention has relatively good production process yield and cycle performance.

Description

Technical Field

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

[0002] Secondary batteries are widely used because of their advantages such as high energy density, low self-discharge rate, and no memory effect. Among them, laminated secondary batteries have attracted attention due to their high current consistency, fast charging rate, and uniform heat distribution. Laminated secondary batteries can balance their energy density, safety, and manufacturing costs by setting a single-sided negative electrode sheet on the outermost side and a double-sided positive electrode sheet and a double-sided negative electrode sheet in the middle. However, after the outermost single-sided negative electrode sheet is cold-pressed, due to the different stresses on both sides, the single-sided negative electrode sheet will curl significantly, making it difficult to adjust the machine, increasing the difficulty of production, and reducing the production process quality rate of secondary batteries.

[0003] In order to solve the above problems, the curling problem of the single-sided negative electrode sheet is usually alleviated by increasing the thickness of the current collector. However, when the thickness of the current collector is too large, the energy density of the secondary battery will be reduced. In addition, the current density will be too large, and the electrode sheet will easily precipitate lithium, resulting in a poor interface between the electrode sheet and the electrolyte, and the cycle performance of the secondary battery will deteriorate. In addition, during the charge and discharge cycle of the secondary battery, the negative electrode material layer of the single-sided negative electrode sheet will also expand and shrink in volume, resulting in poor contact between the single-sided negative electrode sheet and the diaphragm of the secondary battery, affecting the interface stability, and then affecting the cycle performance of the secondary battery. Therefore, it is urgent to find a method that can both alleviate the curling of the single-sided negative electrode sheet and improve the interface stability between the single-sided negative electrode sheet and the diaphragm, so as to improve the production process efficiency and cycle performance of the secondary battery. Summary of the invention

[0004] The purpose of this application is to provide a secondary battery and an electronic device to improve the production process efficiency and cycle performance of the secondary battery. The specific technical solution is as follows:

[0005] The first aspect of the present application provides a secondary battery and an electronic device, wherein the secondary battery comprises an electrode assembly of a laminate structure, the electrode assembly comprises a positive electrode sheet, a separator and a negative electrode sheet, the negative electrode sheet comprises a double-sided negative electrode sheet and a single-sided negative electrode sheet located at the outermost side of the electrode assembly in the direction of the laminate; the single-sided negative electrode sheet comprises a first negative electrode collector and a first material layer arranged on one surface of the first negative electrode collector, the first material layer faces the positive electrode sheet; the first negative electrode collector comprises an empty foil area and a coating area, the coating area has a plurality of first strip-shaped recesses, and the plurality of first strip-shaped recesses extend from the coating area to the empty foil area; the depth of the first strip-shaped recess is h1, satisfying: 4≤h1≤21; the thickness of the first negative electrode collector is x1, in μm, satisfying: 9≤x1≤22; the double-sided negative electrode sheet comprises a second negative electrode collector, the thickness of the second negative electrode collector is x2μm, 2≤x1 / x2≤6. In some embodiments of the present application, 9≤x1≤16. In some embodiments of the present application, 4≤h1≤16. In some embodiments of the present application, 2≤x1 / x2≤4. The applicant has found that when the depth h1 of the recess and the thickness x1 of the negative electrode current collector and the thickness x2 of the second negative electrode current collector satisfy the above relationship setting, and x1 is within the range limited by the present application, it is not only conducive to alleviating the curling degree of the single-sided negative electrode sheet during the cold pressing process, improving the production process optimization rate of the single-sided negative electrode sheet, thereby improving the production process optimization rate of the secondary battery and taking into account the energy density, but also conducive to improving the cycle performance and dynamic performance of the secondary battery.

[0006] In some embodiments of the present application, 4≤x2≤6. By adjusting the thickness x2 of the second negative electrode current collector within the above range, the secondary battery obtained has high energy density and high production process efficiency, which is conducive to industrialization.

[0007] In some embodiments of the present application, the minimum set depth of the first strip-shaped recess is y μm, y=0.0071x1 3 -0.3527x1 2 +4.4031x1. The inventors of the present application have found that when the depth y and x1 of the concave portion meet the range limited by the present application, it can help alleviate the curling degree of the single-sided negative electrode sheet during the cold pressing process, improve the production process optimization rate of the single-sided negative electrode sheet, further improve the production process optimization rate of the secondary battery while taking into account the energy density, and also help further improve the cycle performance and dynamic performance of the secondary battery.

[0008] In some embodiments of the present application, the depth of the first strip-shaped recess is h1, 0≤h1-y≤5. The above arrangement is conducive to alleviating the curling degree of the single-sided negative electrode sheet during the cold pressing process, improving the production process optimization rate of the single-sided negative electrode sheet, thereby improving the production process optimization rate of the secondary battery and taking into account the energy density, which is more conducive to improving the cycle performance and dynamic performance of the battery.

[0009] In some embodiments of the present application, the double-sided negative electrode sheet includes a second negative electrode current collector and a second material layer disposed on both surfaces of the second negative electrode current collector, and the coating weight per unit area of ​​the first material layer and the second material layer is independently 5.5 mg / cm 2 ≤CW≤13mg / cm 2 By regulating the CW of the first material layer and the second material layer within the above ranges, the secondary battery has a higher energy density and better dynamic performance.

[0010] In some embodiments of the present application, the coating weight per unit area of ​​the first material layer is CW1 mg / cm 2 The coating weight per unit area of ​​the second material layer is CW2mg / cm 2 , 1.01≤CW1 / CW2≤1.04. By adjusting CW1 / CW2 within the above range, it is beneficial to improve the dynamic matching of the single-sided negative electrode sheet and the double-sided negative electrode sheet in the secondary battery, extend the cycle life of the secondary battery, and reduce the risk of damage to the secondary battery due to deep discharge and overcharging.

[0011] In some embodiments of the present application, the compacted density of the first material layer is PD1g / cm 3 The compaction density of the second material layer is PD2g / cm 3 , 0.95≤PD1 / PD2≤1. The above range of PD1 / PD2 cooperates with the first strip-shaped recessed portion provided in the single-sided negative electrode plate coating area, which is conducive to alleviating the volume expansion of the first material layer, and further improving the dynamic performance and cycle performance of the secondary battery, and reducing the risk of low-temperature lithium precipitation.

[0012] In some embodiments of the present application, along the thickness direction of the single-sided negative electrode sheet, the total area of ​​the positive projections of the plurality of first strip-shaped recesses is S1 mm 2 , the area of ​​the coating area is S2mm 2 , 0.2≤S1 / S2≤0.4. By adjusting the ratio of S1 / S2 within the above range, not only can the kinetic matching of the single-sided negative electrode sheet and the double-sided positive electrode sheet in the secondary battery be further improved, but it is also beneficial to improve the cycle interface stability of the first material layer, thereby improving the cycle performance of the secondary battery.

[0013] In some embodiments of the present application, the first material layer has a plurality of second strip-shaped recesses, which correspond to the first strip-shaped recesses one by one. The distance between the orthographic projections of two adjacent first strip-shaped recesses and two adjacent second strip-shaped recesses is such that 0.3 mm ≤ L ≤ 3 mm. By adjusting L within the above range, the curling phenomenon is alleviated, thereby improving the production process yield of the secondary battery, and it is also beneficial to improve the cycling performance of the secondary battery. Moreover, by adjusting L within the above range, it is beneficial to improve the problem of mismatch in kinetic performance between the outermost single-sided negative electrode sheet and the adjacent positive electrode sheet in the secondary battery with a stacked structure, and further improve the cycling performance of the secondary battery.

[0014] In some embodiments of the present application, the width of the orthographic projection of a single first strip-shaped recess is D1 mm, and the width of the orthographic projection of a single second strip-shaped recess is D2 mm, where 0.1 ≤ D2 < D1 ≤ D2 + 0.38. By adjusting D1 and D2 to satisfy the above relationship, the cycling performance of the secondary battery can be improved while taking into account the kinetic performance.

[0015] In some embodiments of the present application, the depth of the first strip-shaped recess is h1 μm, and the depth of the second strip-shaped recess is h2 μm, where h2 ≥ h1. Through the above settings, it is not only beneficial to alleviate the volume expansion of the first material layer, but also beneficial to further improve the kinetic performance and cycling performance of the secondary battery.

[0016] In some embodiments of the present application, 0 ≤ h2 - h1 ≤ 3. By adjusting the value of h2 - h1 within the above range, it is beneficial to improve the cycling performance of the secondary battery, and it can also improve the kinetic performance and production process yield of the secondary battery.

[0017] In some embodiments of the present application, 4 ≤ h2 ≤ 25. By adjusting the value of h2 within the above range, it is beneficial to alleviate the volume expansion of the first material layer, and it is also beneficial to improve the kinetic performance and cycling performance of the secondary battery.

[0018] In some embodiments of the present application, a single first strip-shaped recess includes a first side wall and a first bottom wall, and the angle between the first side wall and the first bottom wall is α1; a single second strip-shaped recess includes a second side wall and a second bottom wall, and the angle between the second side wall and the second bottom wall is α2; α1 and α2 are each independently 85° to 95°. By adjusting α1 and α2 within the above range respectively, it is not only beneficial to improve the production process yield of the secondary battery, but also can further improve the cycling performance of the secondary battery. Moreover, it is also beneficial to improve the drop performance.

[0019] In some embodiments of the present application, α1 = α2. α1 = α2 is beneficial to improve the production process yield of the secondary battery and enhance the cycling performance of the secondary battery.

[0020] In some embodiments of the present application, the double-sided negative electrode plate includes a second negative electrode current collector and a second material layer arranged on both surfaces of the second negative electrode current collector, and the first material layer and / or the second material layer include at least one of graphite, silicon or hard carbon. By selecting the first material layer and / or the second material layer of the above-mentioned negative electrode material, it is beneficial to improve the energy density of the secondary battery and take into account the dynamic performance, and it is also beneficial to further improve the rate performance of the secondary battery and improve the thermal stability of the secondary battery. The second aspect of the present application provides an electronic device, which includes the secondary battery in any of the aforementioned embodiments.

[0021] Beneficial effects of this application:

[0022] The present application provides a secondary battery and an electronic device, wherein the first current collector of the outermost single-sided negative electrode sheet is provided with a first strip-shaped recess, and 4≤h1≤21, 9≤x1≤22, 2≤x1 / x2≤6 are satisfied, wherein x1 is the thickness of the first negative electrode collector, in μm, x2 is the thickness of the second negative electrode collector, in μm, and the depth of the first strip-shaped recess is h1μm. Such a setting can not only improve the rigidity of the single-sided negative electrode sheet, reduce the curling of the single-sided negative electrode sheet, and improve the production process excellence rate of the secondary battery, but also alleviate the volume expansion of the single-sided negative electrode sheet, stabilize the interface between the single-sided negative electrode sheet and the diaphragm, and improve the cycle performance of the secondary battery. At the same time, it is also beneficial to improve the dynamic matching of the single-sided negative electrode sheet and the double-sided negative electrode sheet in the secondary battery, thereby improving the cycle performance of the lithium-ion battery.

[0023] 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

[0024] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application, and a person skilled in the art can also obtain other embodiments based on these drawings.

[0025] Figure 1 A schematic diagram of a partial cross-sectional structure of a secondary battery along the thickness direction in one embodiment of the present application;

[0026] Figure 2 A schematic diagram of the cross-sectional structure of a single-sided negative electrode sheet along the thickness direction according to an embodiment of the present application;

[0027] Figure 3 A schematic diagram of the structure of a single-sided negative electrode sheet according to an embodiment of the present application;

[0028] Figure 4A schematic diagram of a partial cross-sectional structure of a single-sided negative electrode sheet along the thickness direction according to an embodiment of the present application;

[0029] Figure 5 This is a schematic diagram of the structure of a lithium-ion battery in one embodiment of the present application. DETAILED DESCRIPTION

[0030] 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.

[0031] It should be noted that in the specific implementation manner of the present application, the present application is explained by taking a lithium-ion battery as an example of a secondary battery, but the secondary battery of the present application is not limited to a lithium-ion battery.

[0032] The existing stacking structure design can set a single-sided negative electrode sheet on the outermost side of the secondary battery. However, after cold pressing, due to the different stresses on both sides, the single-sided negative electrode sheet will curl significantly, making it difficult to adjust the machine, increasing the difficulty of production, and reducing the production process efficiency of the secondary battery. At present, the main method to alleviate the above problems and improve the production process efficiency of secondary batteries is to increase the thickness of the negative electrode collector, but this will not only reduce the energy density of the secondary battery, but also affect the dynamic matching between the single-sided negative electrode sheet and the double-sided negative electrode sheet, affecting the long cycle performance of the secondary battery. At the same time, during the charge and discharge cycle of the secondary battery, the problem of the deterioration of the cycle performance of the secondary battery caused by the volume change of the single-sided negative electrode sheet has not been solved.

[0033] Based on the above problems, the present application provides a secondary battery and an electronic device, which can solve the curling of the single-sided negative electrode sheet, improve the production process efficiency of the secondary battery, alleviate the volume expansion of the single-sided negative electrode sheet, improve the cycle performance of the secondary battery, and take into account the energy density.

[0034] The first aspect of the present application provides a secondary battery, which includes an electrode assembly of a laminated structure, wherein the electrode assembly includes a positive electrode sheet, a separator and a negative electrode sheet. Specifically, Figure 1 and Figure 2As shown, the secondary battery includes a shell 100 and an electrode assembly 200 of a laminated structure, the outermost side of the electrode assembly 200 adjacent to the shell 100 is a single-sided negative electrode sheet 210, and the electrode assembly 200 also includes a double-sided negative electrode sheet 220, a separator 230 and a double-sided positive electrode sheet 240. The single-sided negative electrode sheet 210 includes a first negative electrode collector 211 and a first material layer 212 arranged on one surface of the first negative electrode collector 211, the first negative electrode collector 211 has a plurality of first strip-shaped recesses 213, the first material layer 212 has a plurality of second strip-shaped recesses 214, and the first strip-shaped recesses 213 and the second strip-shaped recesses 214 correspond one to one. Specifically, the second strip-shaped recesses 214 are formed on a surface of the first material layer 212 away from the first negative electrode collector 211, and the second strip-shaped recesses 214 and the first strip-shaped recesses 213 are mutually nested and correspond one to one. The first material layer 212 faces the double-sided positive electrode sheet 240; the double-sided positive electrode sheet 240 includes a positive electrode current collector 241 and positive electrode material layers 242 disposed on both surfaces of the positive electrode current collector 241. Figure 3 As shown, the first negative electrode current collector 211 includes an empty foil area 215 and a coating area 216. The empty foil area 215 in this application refers to an area where both sides of the current collector do not contain an active material layer. The coating area 216 has a plurality of first strip-shaped recesses 213, which extend from the coating area 216 to the empty foil area 215. Figure 3 Through the above arrangement, the convex structure formed between adjacent first strip-shaped concave portions can play a supporting role in contact with the diaphragm, provide a channel for the transmission of the electrolyte, and be beneficial to improving the dynamic performance and cycle performance of the secondary battery.

[0035] Wherein, x1 is the thickness of the first negative electrode current collector, in μm, 9≤x1≤22. In some embodiments of the present application, 9≤x1≤16. For example, x1 can be 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22 or a range consisting of any two of the values. When x1 is too small, for example, x1<9, the thickness of the first negative electrode current collector is too small, and the residual stress inside the first negative electrode current collector after cold pressing is too large, which easily leads to severe curling of the single-sided negative electrode pole piece and the occurrence of broken and broken belts, making the production of the single-sided negative electrode pole piece difficult, and thus resulting in a low production process rate of the secondary battery. Although x1 is too large, it is beneficial to improve the stiffness of the first negative electrode current collector, but it will reduce the energy density of the secondary battery. Therefore, by regulating the thickness x1 of the first positive electrode current collector within the above range, the thickness of the first positive electrode current collector is appropriate, the energy density of the secondary battery obtained is high, and the production process rate is high, which is conducive to industrialization.

[0036] like Figure 2As shown, the depth of the first strip-shaped recess 213 is h1 μm. In some embodiments of the present application, 4≤h1≤21. In some embodiments of the present application, 4≤h1≤16. For example, h1 can be 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21 or a range consisting of any two of these values. When h1 is too large, for example, greater than 21, the processing difficulty of the single-sided negative electrode sheet will be increased, and the distance between the negative electrode sheet area where the first strip-shaped recess is set and the adjacent positive electrode sheet is too large, thereby affecting the production process optimization rate and cycle performance of the secondary battery. When h1 is too small, for example, less than 4, the curling rate of the first negative electrode collector is high, and it is not conducive to alleviating the volume change of the first material layer during the cycle, thereby affecting the production process optimization rate and cycle performance of the secondary battery. Therefore, by adjusting the value of h1 within the above range, it is helpful to alleviate the curling of the single-sided negative electrode sheet during the cold pressing process, thereby improving the processing performance of the single-sided negative electrode sheet and improving the production process efficiency of the secondary battery. In addition, in the obtained secondary battery, the matching of the dynamic performance of the single-sided negative electrode sheet and the adjacent positive electrode sheet is improved; at the same time, h1 within the above range can also provide a channel for the transmission of the electrolyte, which is beneficial to further improve the dynamic performance and cycle performance of the secondary battery.

[0037] like Figure 1As shown, the double-sided negative electrode sheet 220 includes a second negative current collector 221 and a second material layer 222 disposed on both surfaces of the second negative current collector 221. The thickness of the second negative current collector is x2μm, 2≤x1 / x2≤6. In some embodiments of the present application, 2≤x1 / x2≤4. For example, x1 / x2 can be 2, 2.1, 2.3, 2.5, 2.8, 3, 3.2, 3.4, 3.5, 3.7, 3.9, 4, 4.2, 4.4, 4.6, 4.8, 5.0, 5.2, 5.4, 5.6, 5.8, 6.0 or a range consisting of any two ratios thereof. When x1 / x2 is too large, for example, greater than 6, that is, x1 is too large or x2 is too small, when x1 is too large, the proportion of negative electrode current collector in the secondary battery will increase, thereby affecting the energy density of the secondary battery; when x2 is too small, it will increase the difficulty of processing the double-sided negative electrode sheet, thereby affecting the production process optimization rate of the secondary battery. At the same time, the kinetic matching between the first negative electrode collector and the second negative electrode collector decreases, affecting the cycle performance of the secondary battery. When x1 / x2 is too small, for example, less than 2, that is, x1 is too small or x2 is too large, when x1 is too small, the production of single-sided negative electrode sheets is difficult, resulting in a low production process optimization rate of the secondary battery; when x2 is too large, it will increase the proportion of negative electrode current collector in the secondary battery, thereby affecting the energy density of the secondary battery, and it is impossible to take into account both the production process optimization rate and the cycle performance of the secondary battery. Therefore, by regulating x1 / x2 within the above range, it is helpful to improve the problem of mismatching the kinetic performance of the outermost single-sided negative electrode sheet and the double-sided negative electrode sheet in the laminated structure secondary battery, improve the kinetic matching of the single-sided negative electrode sheet and the double-sided negative electrode sheet in the secondary battery, and thus improve the cycle performance of the lithium-ion battery. In addition, x1 / x2 within the above range is also beneficial to balance the processing difficulty and energy density of the single-sided negative electrode sheet, so as to achieve the purpose of taking into account the production process excellence rate and energy density of the secondary battery. Further preferably, 2≤x1 / x2≤4 can be regulated, which is conducive to achieving better cycle performance of lithium-ion batteries and further balancing the processing difficulty and energy density of the single-sided negative electrode sheet.

[0038] Therefore, through the above arrangement, it is not only beneficial for the first negative electrode current collector to have a suitable thickness and rigidity, but also to alleviate the curling degree of the single-sided negative electrode sheet during the cold pressing process, improve the production process efficiency of the secondary battery and take into account the energy density; it can also improve the problem of deterioration of the circulation interface caused by the volume expansion of the first material layer during the cycle, thereby improving the cycle performance of the secondary battery. The first strip-shaped recess in the single-sided negative electrode sheet is also beneficial to improve the infiltration of the electrolyte into the first material layer, thereby improving the cycle performance of the secondary battery. At the same time, it is also beneficial to improve the dynamic matching of the single-sided negative electrode sheet and the double-sided negative electrode sheet in the secondary battery, and further improve the cycle performance of the lithium-ion battery.

[0039] In some embodiments of the present application, the minimum set depth of the first strip-shaped recess is y μm, y=0.0071x1 3 -0.3527x1 2 +4.4031x1. The inventors of the present application have found that when the depth y and x1 of the concave portion meet the range limited by the present application, it can help alleviate the curling degree of the single-sided negative electrode sheet during the cold pressing process, improve the production process optimization rate of the single-sided negative electrode sheet, further improve the production process optimization rate of the secondary battery while taking into account the energy density, and also help further improve the cycle performance and dynamic performance of the secondary battery.

[0040] In some embodiments of the present application, 0≤h1-y≤5. The inventors found that the minimum setting depth of the first strip-shaped recess is y, that is, the minimum value of the depth of the first strip-shaped recess that can be taken to improve the curling problem of the single-sided negative electrode sheet, and the size of y varies with the thickness of the first negative electrode collector, and according to the formula y=0.0071x1 3 -0.3527x1 2 +4.4031x1 is calculated. In the first negative electrode current collector of the laminated structure secondary battery, the depth h1 of the first strip-shaped recess should be greater than or equal to the theoretical minimum depth y, and satisfy 0≤h1-y≤5. For example, h1-y can be 0, 0.2, 0.5, 0.7, 1, 1.3, 1.5, 1.8, 2, 2.3, 2.5, 2.7, 3, 3.2, 3.5, 3.8, 4, 4.2, 4.5, 4.8, 5 or a range consisting of any two of these values. Adjusting h1-y within the scope of this application, on the one hand, is conducive to the single-sided negative electrode sheet having a suitable stiffness, alleviating its internal stress during the cold pressing process, reducing its curling degree, and improving the processing stability of the first negative electrode current collector, thereby helping to improve the production process excellence rate of the secondary battery; on the other hand, a suitable depth is conducive to improving the problem of deterioration of the circulation interface caused by the volume expansion of the first material layer during the cycle, thereby improving the cycle performance of the secondary battery. In the present application, h1 generally refers to the actual depth of the first strip-shaped recess.

[0041] The present application has no particular restriction on the type of the above-mentioned first negative electrode current collector, as long as the purpose of the present application can be achieved. For example, it may include copper foil, copper alloy foil, nickel foil, stainless steel foil, titanium foil, foam nickel, foam copper or a composite current collector. For example, the composite current collector can be a lithium-copper composite current collector, a carbon-copper composite current collector, a nickel-copper composite current collector, a titanium-copper composite current collector, etc.

[0042] The present application has no particular restriction on the type of the second negative electrode current collector as long as the purpose of the present application can be achieved. For example, it may include copper foil, copper alloy foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam or a composite current collector. For example, the composite current collector may be a lithium-copper composite current collector, a carbon-copper composite current collector, a nickel-copper composite current collector, a titanium-copper composite current collector, etc.

[0043] In some embodiments of the present application, 4≤x2≤6. For example, x2 can be 4, 4.2, 4.5, 4.7, 5, 5.2, 5.5, 5.8, 6, or a range consisting of any two of these values. By adjusting the thickness x2 of the second negative electrode current collector within the above range, the thickness of the second negative electrode current collector is appropriate, the energy density of the secondary battery obtained is high, and the production process is high in efficiency, which is conducive to industrialization.

[0044] In some embodiments of the present application, the double-sided negative electrode sheet includes a second negative electrode current collector and a second material layer disposed on both surfaces of the second negative electrode current collector, and the coating weight per unit area of ​​the first material layer and the second material layer is independently 5.5 mg / cm 2 ≤CW≤13mg / cm 2 For example, CW can be independently 5.5, 6, 6.5, 7, 7.5, 8, 8.5, 9, 9.5, 10, 10.5, 11, 11.5, 12, 12.5, 13, or a range consisting of any two of these values. By regulating the CW of the first material layer and the second material layer within the above ranges, the secondary battery has a higher energy density and better dynamic performance.

[0045] In some embodiments of the present application, the coating weight per unit area of ​​the first material layer is CW1 mg / cm 2 The coating weight per unit area of ​​the second material layer is CW2mg / cm 2 , 1.01≤CW1 / CW2≤1.04. For example, CW1 / CW2 can be 1.01, 1.012, 1.015, 1.018, 1.02, 1.022, 1.025, 1.028, 1.03, 1.032, 1.035, 1.038, 1.04 or a range consisting of any two ratios thereof. By adjusting CW1 to be larger than CW2, and CW1 / CW2 being within the above range, it is beneficial to increase the lithium storage space of the single-sided negative electrode sheet, thereby improving its lithium precipitation level, and is beneficial to improving the kinetic matching of the single-sided negative electrode sheet and the double-sided negative electrode sheet in the secondary battery, and promoting the single-sided negative electrode sheet and the double-sided negative electrode sheet to maintain a good battery state of charge (SOC), thereby extending the cycle life of the secondary battery and reducing the risk of damage to the secondary battery due to deep discharge and overcharging.

[0046] In some embodiments of the present application, 5.64≤CW1≤13. In some embodiments of the present application, 5.5 mg / cm 2 ≤CW2≤12.6. For example, CW1 may be 5.64, 5.8, 6, 6.5, 7, 7.5, 8, 8.5, 9, 9.5, 10, 10.5, 11, 11.5, 12, 12.5, 13, or a range consisting of any two values ​​thereof, and CW2 may be 5.5, 5.8, 6, 6.5, 7, 7.5, 8, 8.5, 9, 9.5, 10, 10.5, 11, 11.5, 12, 12.5, 12.6, or a range consisting of any two ratios thereof.

[0047] In some embodiments of the present application, the compacted density of the first material layer is PD1g / cm 3 , the compaction density of the second material layer is PD2g / cm 3 , 0.95≤PD1 / PD2≤1. For example, 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 ratios thereof. By regulating PD1 / PD2 within the above range, it is beneficial to improve the problem of mismatching the dynamic performance of the outermost single-sided negative electrode sheet and the double-sided negative electrode sheet in the laminated structure secondary battery, improve the dynamic matching of the single-sided negative electrode sheet and the double-sided negative electrode sheet in the secondary battery, and thus improve the cycle performance of the lithium-ion battery. In addition, the PD1 / PD2 in the above range cooperates with the first strip-shaped recess set in the coating area of ​​the single-sided negative electrode sheet, which is beneficial to further reduce the internal stress in the single-sided negative electrode sheet during processing, alleviate the volume expansion of the first material layer, and is also beneficial to the transmission of the electrolyte, which is beneficial to further improve the dynamic performance and cycle performance of the secondary battery, and reduce the risk of low-temperature lithium precipitation.

[0048] In some embodiments of the present application, 1.65≤PD1≤1.78. In some embodiments of the present application, 1.65≤PD2≤1.78. For example, PD1 can be 1.65, 1.66, 1.67, 1.68, 1.69, 1.7, 1.71, 1.72, 1.73, 1.74, 1.75, 1.76, 1.77, 1.78, or a range consisting of any two of the values, and PD2 can be 1.65, 1.66, 1.67, 1.68, 1.69, 1.7, 1.71, 1.72, 1.73, 1.74, 1.75, 1.76, 1.77, 1.78, or a range consisting of any two ratios thereof.

[0049] In some embodiments of the present application, along the thickness direction of the single-sided negative electrode sheet, the total area of ​​the positive projections of the plurality of first strip-shaped recesses is S1 mm2 , the area of ​​the coating area is S2cm 2 , 0.2≤S1 / S2≤0.4. For example, S1 / S2 can be 0.2, 0.23, 0.25, 0.27, 0.3, 0.33, 0.35, 0.37, 0.4 or a range consisting of any two ratios thereof. By adjusting the ratio of S1 / S2 within the above range, the distribution density of the first strip-shaped recess on the coating area of ​​the single-sided negative electrode sheet is appropriate, which can not only better improve the problem of mismatch in dynamic performance between the outermost single-sided negative electrode sheet and the adjacent positive electrode sheet in the laminated structure secondary battery, but also further improve the dynamic matching of the single-sided negative electrode sheet and the double-sided positive electrode sheet in the secondary battery; and S1 / S2 within the above range is also conducive to providing a buffer space for the volume expansion and contraction of the first material layer during the cycle, improving the cycle interface stability of the first material layer, and thus improving the cycle performance of the secondary battery.

[0050] In some embodiments of the present application, the first material layer has a plurality of second strip-shaped recesses, the second strip-shaped recesses correspond to the first strip-shaped recesses one by one, and the spacing between the positive projections of two adjacent first strip-shaped recesses and two adjacent second strip-shaped recesses is 0.3mm≤L≤3mm. For example, L can be 0.3, 0.5, 0.7, 1, 1.2, 1.5, 1.8, 2, 2.2, 2.5, 2.8, 3 or a range consisting of any two of these values. By regulating L within the above range, it is beneficial for the first material layer to be better arranged on the first negative electrode current collector, which can not only improve the processing performance and alleviate the curling phenomenon, but also help alleviate the change in volume of the first material layer during the cycle process that affects the stability of the cycle interface, thereby improving the production process efficiency and cycle performance of the secondary battery. Moreover, regulating L within the above range is beneficial to improving the problem of the mismatch between the dynamic performance of the outermost single-sided negative electrode sheet and the adjacent positive electrode sheet in the laminated structure secondary battery, and can also better provide a channel for the infiltration and diffusion of the electrolyte, further improving the dynamic performance and cycle performance of the secondary battery.

[0051] Specifically, Figure 3 As shown, a plurality of first strip-shaped recesses 213 are distributed in stripes, and the two sides of the positive projection of a single first strip-shaped recess 213 are parallel to the direction from the coating area to the empty foil area of ​​the single-sided negative electrode sheet 210, that is, the direction of the arrow in the figure, and the shape of the positive projection of a single first strip-shaped recess 213 is a narrow and long rectangle, the width of the rectangle is D1, and the minimum spacing between two adjacent rectangles is L. It can be understood that, correspondingly, the shape of the positive projection of the second strip-shaped recess of the first material layer is also a narrow and long rectangle, the width of the rectangle of the positive projection of the second strip-shaped recess is D2, and the minimum spacing between two adjacent rectangles is also L. In the present application, the above-mentioned rectangle refers to a shape close to or similar to a standard rectangular shape.

[0052] In some embodiments of the present application, the width of the positive projection of a single first strip-shaped recess is D1 mm, and the width of the positive projection of a single second strip-shaped recess is D2 mm, where 0.1 ≤ D2 < D1 ≤ D2 + 0.38. In some embodiments of the present application, 0.1 < D1 ≤ 1.38; for example, D1 can be 0.11, 0.15, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 1.1, 1.2, 1.3, 1.38 or a range composed of any two of these values. In some embodiments of the present application, 0.1 ≤ D2 ≤ 1; for example, D2 can be 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1 or a range composed of any two of these values. By regulating D1 and D2 to satisfy the above relationship, it is possible to better provide a buffer space for the volume change generated by the first material layer during the cycling process of the secondary battery, thereby improving the cycling performance of the secondary battery. Moreover, the deformation zones of the first strip-shaped recess and the second strip-shaped recess can be better controlled, so as to more precisely control the range of the compaction density of the single-sided negative electrode sheet, and further improve the kinetic matching between the single-sided negative electrode sheet and the adjacent positive electrode sheet in the secondary battery.

[0053] In some embodiments of the present application, as Figure 2 shown, the depth of the first strip-shaped recess 213 is h1 μm, and the depth of the second strip-shaped recess 214 is h2 μm, where h2 ≥ h1. The depth of the second strip-shaped recess being greater than or equal to the depth of the first strip-shaped recess can reduce the overall thickness of the single-sided negative electrode sheet to increase the overall compaction density of the single-sided negative electrode sheet. This is not only beneficial for reducing the internal stress in the first negative electrode sheet during the processing, alleviating the volume expansion of the first material layer, but also beneficial for the transmission of the electrolyte, improving the problem of the kinetic performance mismatch between the outermost single-sided negative electrode sheet and the adjacent positive electrode sheet in the laminated structure secondary battery, thereby being beneficial for further improving the kinetic performance and cycling performance of the secondary battery. At the same time, through the above settings, it is also beneficial for improving the bonding strength between the first material layer and the first negative electrode current collector, and reducing the risk of the first material layer peeling off when the single-sided negative electrode sheet undergoes slight curling.

[0054] In some embodiments of the present application, 0≤h2-h1≤3. For example, h2-h1 can be 0, 0.2, 0.5, 0.8, 1, 1.2, 1.5, 1.8, 2, 2.2, 2.5, 2.8, 3 or a range consisting of any two of these values. By regulating the value of h2-h1 within the above range, it is beneficial to improve the cycle interface stability of the single-sided negative electrode sheet, reduce the risk of the first material layer being peeled off from the first negative electrode during the charging and discharging process of the secondary battery, and improve the cycle performance of the secondary battery. It is also beneficial to provide a channel for the transmission of the electrolyte, improve the processing performance of the single-sided negative electrode sheet, thereby improving the cycle performance, kinetic performance and production process excellence of the secondary battery.

[0055] In some embodiments of the present application, 4≤h2≤25. For example, h2 can be 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25 or a range consisting of any two of the values. By regulating the value of h2 within the above range, it is beneficial to reduce the internal stress in the first negative electrode sheet during processing, alleviate the volume expansion of the first material layer, and also facilitate the transmission of the electrolyte, improve the problem of mismatching the dynamic performance of the outermost single-sided negative electrode sheet and the adjacent positive electrode sheet in the laminated structure secondary battery, thereby helping to improve the dynamic performance and cycle performance of the secondary battery.

[0056] In some embodiments of the present application, Figure 4 As shown, a single first strip-shaped recess 213 includes a first side wall 2111 and a first bottom wall 2112, and the angle between the first side wall 2111 and the first bottom wall 2112 is α1; a single second strip-shaped recess 214 includes a second side wall 2121 and a second bottom wall 2122, and the angle between the second side wall 2121 and the second bottom wall 2122 is α2; α1 and α2 are independently 85° to 95°. For example, α1 and α2 are independently 85°, 86°, 87°, 88°, 89°, 90°, 91°, 92°, 93°, 94°, 95°, or a range consisting of any two of these values. By regulating α1 and α2 within the above range, it is not only beneficial for the first negative electrode plate to have a suitable thickness and rigidity, alleviate its curling degree during the cold pressing process, improve its processing stability, and improve the production process quality rate of the secondary battery; it can also further improve the problem of deterioration of the cycle interface caused by the volume expansion of the first material layer during the cycle, thereby improving the cycle performance of the secondary battery. In addition, suitable α1 and α2 are also beneficial to increase the friction between the shell and the first negative electrode collector in the single-sided negative electrode plate, thereby improving the drop performance; at the same time, it can also provide a channel for the transmission of the electrolyte, further improving the dynamic performance and cycle performance of the secondary battery.

[0057] In some embodiments of the present application, α1=α2. α1=α2 is conducive to improving the processing accuracy of the single-sided negative electrode sheet, improving its processing stability, and thus improving the production process efficiency of the secondary battery. At the same time, it can also further improve the problem of cycle interface deterioration caused by the volume expansion of the first material layer during the cycle, thereby improving the cycle performance of the secondary battery.

[0058] In some embodiments of the present application, the double-sided negative electrode sheet includes a second negative electrode current collector and a second material layer disposed on both surfaces of the second negative electrode current collector, and the first material layer and / or the second material layer include at least one of graphite, silicon or hard carbon. By selecting the first material layer and / or the second material layer of the above-mentioned negative electrode material, it is beneficial to improve the energy density of the secondary battery and take into account the dynamic performance, and it is also beneficial to improve the rate performance of the secondary battery and improve the thermal stability.

[0059] The negative electrode material layer may also include a conductive agent and a binder. The present application does not particularly limit the types of conductive agents and binders, 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 (SuperP), carbon nanotubes (CNTs), carbon fibers, flake graphite, graphene, metal materials or conductive polymers, and the conductive carbon black may include but is not limited to at least one of acetylene black or Ketjen black. 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, and specifically, the metal may include but is 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 binder may include, but is not limited to, at least one of polyacrylic acid, sodium polyacrylate, potassium polyacrylate, lithium polyacrylate, polyimide, polyvinyl alcohol, carboxymethyl cellulose, sodium carboxymethyl cellulose, lithium carboxymethyl cellulose, polyimide, polyamide-imide, styrene-butadiene rubber, or polyvinylidene fluoride. The present application does not particularly limit the mass ratio of the positive electrode active material, the conductive agent, and the binder in the negative electrode material layer. Those skilled in the art may select according to actual needs, as long as the purpose of the present application can be achieved.

[0060] The present application has no particular restrictions on the preparation method of the single-sided negative electrode sheet, as long as the purpose of the present application can be achieved. For example, the preparation method of the single-sided negative electrode sheet may include but is not limited to the following steps: a first material layer is arranged on one surface of the first negative electrode current collector, and then a first cold pressing treatment is performed on the first material layer using a pressure roller, and then a second cold pressing treatment is performed on the first material layer using a pressure roller with strip-shaped protrusions to obtain a single-sided negative electrode sheet. The present application has no particular restrictions on the pressure P1 of the first cold pressing treatment and the pressure P2 of the second cold pressing treatment, as long as the purpose of the present application can be achieved. For example, P1 can be 30t to 100t, and P2 can be 200 to 500kgf. The purpose of the second cold pressing treatment is to produce the first strip-shaped recess and the second strip-shaped recess in the single-sided negative electrode sheet. The cold pressing pressure applied in this process is relatively small relative to the pressure in the first cold pressing treatment. Therefore, the compaction density of the first material layer before and after the second cold pressing treatment is basically unchanged. At the same time, the second cold pressing treatment has basically no effect on the thickness of the first material layer. In the present application, the thickness of the convex structure area formed between adjacent first strip-shaped recesses is measured.

[0061] In the present application, after the first cold pressing process, the compaction density of the first negative electrode material layer can be 1.65 g / cm 3 Up to 1.78g / cm 3 .

[0062] The present application has no particular restrictions on the method of regulating h1, h2, D1, D2, L, α1, α2, CW1, CW2, PD1 and PD2, as long as the purpose of the present application can be achieved. For example, the size of h1, h2, D1, D2, L, α1, α2 can be regulated by selecting the size of the strip protrusions, arranging different pressure rollers, or by the coating amount; CW1 and CW2 can be regulated by adjusting the viscosity and solid content of the slurry; PD1 and PD2 can be regulated by changing P1 and P2.

[0063] The present application has no particular restrictions on the method for preparing the double-sided negative electrode sheet, as long as the purpose of the present application can be achieved. For example, the method for preparing the double-sided negative electrode sheet may include but is not limited to the following steps: a second material layer is arranged on one surface of the second negative electrode current collector, and then the second material layer is further arranged on the other surface of the second negative electrode current collector, and then a third cold pressing process is performed using a pressure roller to obtain a double-sided negative electrode sheet. The present application has no particular restrictions on the pressure P3 of the third cold pressing process, as long as the purpose of the present application can be achieved. For example, P3 can be 30t to 120t.

[0064] In the present application, after the third cold pressing process, the compaction density of the second negative electrode material layer can be 1.65 g / cm 3 Up to 1.78g / cm 3 .

[0065] In the present application, the first negative electrode current collector and the second negative electrode current collector of different thicknesses can be purchased, and their thicknesses can be confirmed using a micrometer, and the first negative electrode current collector and the second negative electrode current collector of the required thickness can be selected.

[0066] In the present application, the secondary battery also includes a positive electrode plate, which includes a positive electrode collector and a positive electrode material layer disposed on at least one surface of the positive electrode collector. The above-mentioned "positive electrode material layer disposed on at least one surface of the positive electrode collector" means that the positive electrode material layer can be disposed on one surface of the positive electrode collector along its own thickness direction, or on two surfaces of the positive electrode collector along its own thickness direction. It should be noted that the "surface" here can be the entire area of ​​the surface of the positive electrode collector, or it can be a partial area of ​​the surface of the positive electrode collector. This application has no special restrictions, as long as the purpose of this application can be achieved.

[0067] The present application has no particular limitation on the positive electrode current collector, as long as the purpose of the present application can be achieved. For example, it may include aluminum foil, aluminum alloy foil or a composite current collector (such as an aluminum-carbon composite current collector).

[0068] The positive electrode material layer includes a positive electrode active material. The present application has no particular limitation on the positive electrode active material as long as the purpose of the present application can be achieved. For example, the positive electrode active material may include but is not limited to at least one of lithium nickel cobalt manganese oxide (such as NCM811, NCM622, NCM523, NCM111), lithium nickel cobalt aluminum oxide, lithium iron phosphate, lithium-rich manganese-based materials, lithium cobalt oxide (LiCoO2), lithium manganese oxide, lithium iron manganese phosphate or lithium titanate.

[0069] In some embodiments of the present application, the positive electrode material layer may further include a conductive agent and a binder. The present application does not particularly limit the types of the conductive agent and the binder, as long as the purpose of the present application can be achieved. For example, it may be at least one of the above conductive agent and the above binder. The present application does not particularly limit 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 may select according to actual needs, as long as the purpose of the present application can be achieved.

[0070] The present application has no particular limitation 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. For example, the thickness of the positive electrode current collector is 5 μm to 20 μm, and the thickness of the positive electrode material layer is 30 μm to 120 μm.

[0071] Optionally, the positive electrode sheet may further include a conductive layer, which is located between the positive electrode current collector and the positive electrode material layer. The composition of the conductive layer is not particularly limited, and it can be a conductive layer commonly used in the art. The conductive layer includes a conductive agent and a binder. The present application has no particular restrictions on the conductive agent and the binder in the conductive layer, for example, it can be at least one of the above conductive agent and the above binder.

[0072] 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.

[0073] 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 nonwoven 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 nonwoven fabric, a polyethylene nonwoven fabric or a polypropylene-polyethylene-polypropylene porous composite film may be used.

[0074] Optionally, a surface treatment layer is disposed on at least one surface of the substrate layer. The surface treatment layer may be a polymer layer or an inorganic layer, or a layer formed by mixing a polymer and an inorganic layer.

[0075] In some embodiments of the present application, the inorganic layer includes inorganic particles and a binder. The present application is not particularly limited to inorganic particles, such as inorganic particles can 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 is not particularly limited to binders, such as binders can be at least one of the above-mentioned binders. In some embodiments of the present application, the polymer layer includes polymers, and the material of the polymer includes at least one of polyamide, polyacrylonitrile, acrylate polymers, polyacrylic acid, polyacrylates, polyvinyl pyrrolidone, polyvinyl ether or polyvinylidene fluoride or poly (vinylidene fluoride-hexafluoropropylene).

[0076] In the present application, there is no particular limitation on the thickness of the separator as long as the purpose of the present application can be achieved. For example, the thickness of the separator may be 3 μm to 30 μm.

[0077] In the present application, the secondary battery further includes an electrolyte, and the electrolyte includes a lithium salt and a non-aqueous solvent.

[0078] The present application has no particular 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(oxalatoborate) (LiBOB) or lithium difluoroborate. The present application has no particular restrictions on the content of lithium salts in the electrolyte, as long as the purpose of the present application can be achieved.

[0079] The present application has no particular limitation on the non-aqueous solvent as long as the purpose of the present application can be achieved. For example, the non-aqueous solvent may include but is not limited to at least one of carbonate compounds, carboxylate compounds, ether compounds or other organic solvents.

[0080] The carbonate compound may include but is not limited to at least one of a linear carbonate compound, a cyclic carbonate compound or a fluorinated carbonate compound. The linear carbonate compound may include but is not limited to at least one of dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC) or methyl ethyl carbonate (MEC). The cyclic carbonate may include but is not limited to at least one of ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC) or vinyl ethylene carbonate (VEC). The 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, 1,1,2,2-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 compound may include, but is 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, decalactone, valerolactone, or caprolactone. The above-mentioned ether compound may include but is 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, methyl cyclopentane, 1,3-dimethyl-2-imidazolidinone, N-methyl-2-pyrrolidone, dimethylformamide, acetonitrile, trimethyl phosphate, triethyl phosphate or trioctyl phosphate. The present application has no particular restrictions on the content of the non-aqueous solvent in the electrolyte, as long as the purpose of the present application can be achieved.

[0081] The preparation process of the secondary battery of the present application is well known to those skilled in the art, and there is no special 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 diaphragm, the single-sided negative electrode sheet, the diaphragm, the positive electrode sheet, the diaphragm, the double-sided negative electrode sheet, and the diaphragm in order, and setting the single-sided negative electrode sheet on the outermost sides with the first material layer facing the negative electrode sheet, and then fixing the four corners of the entire stacked structure with tape to obtain the electrode assembly of the stacked structure, placing the electrode assembly in the shell, injecting the electrolyte into the shell and sealing it to obtain the secondary battery. In addition, as needed, overcurrent protection elements, guide plates, etc. can also be placed in the shell to prevent the pressure inside the secondary battery from rising and overcharging and discharging.

[0082] The second aspect of the present application provides an electronic device, which includes the secondary battery in any of the above embodiments. Therefore, the electronic device provided by the present application has good performance.

[0083] The present application does not particularly limit the type of electronic device, and it can be used for any electronic device known in the prior art. In some embodiments of the present application, the electronic device may 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, etc.

[0084] Example

[0085] The following examples and comparative examples are given to more specifically describe the embodiments of the present application. Various tests and evaluations were performed according to the following methods. In addition, unless otherwise specified, "parts" and "%" are based on mass.

[0086] Test methods and equipment:

[0087] Production process quality test:

[0088] (1) preparing several rolls of single-sided negative electrode sheets according to the preparation methods of the single-sided negative electrode sheets in the embodiments and comparative examples;

[0089] (2) taking sufficient amounts of the single-sided negative electrode sheets and corresponding separators, positive electrode sheets, and double-sided negative electrode sheets prepared in each embodiment and comparative example in step (1);

[0090] (3) using the single-sided negative electrode sheet, separator, positive electrode sheet, and double-sided negative electrode sheet in step (1) and step (2), assembling and producing the lithium-ion battery in accordance with the stacking method of each embodiment and comparative example;

[0091] (4) Record the number of electrode assemblies that can be produced by the stack as N;

[0092] (5) The total number of times that the negative electrode sheets cannot be normally prepared into electrode assemblies or the obtained electrode assemblies cannot work normally due to curling, wrinkling, etc. during the lamination process is recorded as M;

[0093] (6) Production process excellence (%) = (1-M / N) × 100%.

[0094] Energy density test:

[0095] (1) Test of discharge capacity: At an ambient temperature of 25°C, charge the lithium-ion battery at a constant current of 1C to a voltage of 4.5V, then charge at a constant voltage of 4.5V to a cut-off current of 0.05C, let stand for 5 minutes, then discharge at a constant current of 0.2C to a voltage of 3.0V, let stand for 5 minutes, and record the discharge capacity at this time as C, in Wh.

[0096] (2) Lithium-ion battery size test: Figure 5 , along the extension direction of the positive pole ear 70, i.e., the direction of the arrow in the figure, the lithium-ion battery 02 includes a fifth edge 401 and a sixth edge 601 opposite to each other, the edge of the positive pole ear 70 is set as the fifth edge 401, the area within 3 mm extending from the fifth edge 401 in the opposite direction of the extension direction of the positive pole ear 70 is the head area 40, the area within 3 mm extending from the sixth edge 601 in the extension direction of the positive pole ear 70 is the tail area 60, and the remaining area between the head area 40 and the tail area 60 is the middle area 50. The distance between the fifth edge 401 and the sixth edge 601 is the length L of the lithium-ion battery 02, the length of the fifth edge 401 is the width M of the lithium-ion battery 02, and the size of the lithium-ion battery 02 in the lamination direction is its thickness D. The length L and width M of the lithium-ion battery are respectively scanned and measured using a laser measuring instrument. The thickness Da of the head area 40, the thickness Db of the middle area 50, and the thickness Dc of the tail area 60 are measured with a micrometer, and the thickness of each area is measured 3 times. The average value of the 3 tests is taken as the thickness of the corresponding area. The thickness D of the lithium-ion battery is calculated by the following formula: D = 1 / 3 × (Da + Db + Dc). The units of D, L, and M are dm.

[0097] (3) Calculation of lithium-ion battery energy density X: X = C / (D × L × M);

[0098] The energy density X0 of comparative example 2 is recorded as "low", X0 = 748Wh / L. Each increase of 0.2% is a gradient of energy density, and the energy density of the obtained lithium-ion battery is ranked from low to high as follows: high>upper middle>middle>lower middle>low> / . Among them, energy density less than X0 is recorded as " / ", energy density greater than X0 and less than or equal to 1.002X0 is recorded as "low", energy density greater than 1.002X0 and less than or equal to 1.004X0 is recorded as "lower middle", energy density greater than 1.004X0 and less than or equal to 1.006X0 is recorded as "middle", energy density greater than 1.006X0 and less than or equal to 1.008X0 is recorded as "upper middle", and energy density greater than 1.008X0 and less than or equal to 1.010X0 is recorded as "high".

[0099] Cycle performance test:

[0100] Place the lithium-ion battery in an environment of 25°C, charge it at a constant current of 0.5C 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 0.5C to a voltage of 3.0V, let it stand for 5 minutes, this is a charge and discharge cycle, record the discharge capacity of the first cycle. Then perform 200 cycles of charge and discharge cycles in the same steps, and record the discharge capacity of the 200th cycle.

[0101] 200 cycle capacity retention rate (%) = (discharge capacity at the 200th cycle / discharge capacity at the first cycle) × 100%.

[0102] Single-sided negative electrode curling test:

[0103] 1. Take a single-sided negative electrode sheet, and then cut the single-sided negative electrode sheet into a rectangular sheet of 91.5 mm × 55 mm, which only includes the coating area;

[0104] 2. Lay the rectangular pole piece flat on a flat marble table with the first material layer facing downward in a naturally stretched state. Measure the dimensions of the rectangular pole piece in the transverse TD and longitudinal MD directions in the stretched state, and record them as T1 and M1;

[0105] 3. Use a glass plate to flatten the rectangular electrode until it is flush with the desktop, and measure the actual transverse TD and longitudinal MD dimensions of the rectangular electrode, which are recorded as T2 and M2;

[0106] 4. Calculate the curvature of the single-sided negative electrode sheet:

[0107] TD curling rate = (T2-T1) / T2×100%;

[0108] MD curling rate = (M2-M1) / M2×100%;

[0109] The larger of the TD curling rate and the MD curling rate is taken as the final result. When the curling rate is less than or equal to 3%, it means that the curling rate of the single-sided negative electrode sheet is low and the production process quality rate is high; when the curling rate is greater than 3% and less than 4%, it means that the curling rate of the single-sided negative electrode sheet is good and has little impact on the production process quality rate; when the curling rate is greater than or equal to 4%, it means that the curling of the single-sided negative electrode sheet is serious, the risk in the processing process is high, and the production process quality rate is seriously affected.

[0110] Interface observation:

[0111] (1) According to the steps in the cycle performance test, the lithium-ion battery was cycled for 200 cycles, then charged to 4.5 V, and then charged at a constant voltage of 4.5 V to a cut-off current of 0.05 C, and then left to stand for 5 minutes.

[0112] (2) The lithium-ion battery is disassembled and the first material layer of the single-sided negative electrode sheet is confirmed to be the outermost interface.

[0113] (3) Observe whether the outermost interface is "golden" and uniform. If there are black spots, record it as "black spots". If there are silver spots, record it as "lithium deposition". If there are no black spots or lithium deposition, record it as "normal".

[0114] CW1, CW2, PD1, PD2 testing:

[0115] CW1, PD1: compaction density of the first material layer PD1 = mass of the first material layer per unit area (in g / cm 2 ) / thickness of the first material layer (in cm). The mass of the first material layer per unit area is weighed by a balance, and the measured mass is CW1. The thickness of the first material layer is measured by a micrometer.

[0116] CW2, PD2: compacted density of the second material layer PD2 = mass of the second material layer per unit area (in g / cm 2 ) / thickness of the second material layer (in cm). The mass of the second material layer per unit area is weighed by a balance, and the measured mass is CW2. The thickness of the second material layer is measured by a micrometer.

[0117] Size Measurements:

[0118] x1, h1, h2: The cross section of the single-sided negative electrode sheet along the thickness direction is ion polished and the cross section of the electrode sheet is observed and measured under a scanning electron microscope to obtain x1, h1, h2.

[0119] x2: The cross section of the double-sided negative electrode sheet along the thickness direction is ion polished and the cross section of the electrode sheet is observed and measured under a scanning electron microscope x2.

[0120] D2, L, S2: Place the first material layer of the single-sided negative electrode sheet face up under a VHX5000 microscope with the magnification set to 50 to 200 times; take a photo of the surface of the first material layer, and use the microscope software to measure D2, L, S2 = coating area length × coating area width.

[0121] D1, S1: Place the first negative electrode current collector of the single-sided negative electrode sheet facing upward under a VHX5000 microscope, with the magnification set to 50 to 200 times; take a photo of the surface of the first negative electrode current collector, use the microscope software to measure D1 and the length b mm of the first strip-shaped recess, and calculate S1 = D1 × b. Then calculate S1 / S2.

[0122] The above dimensions were measured at 10 points and the average value was taken as the final result.

[0123] Example 1-1

[0124] <Preparation of single-sided negative electrode sheet>

[0125] 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 45%wt. The negative electrode slurry was evenly coated on one surface of a negative electrode current collector copper foil with a thickness of 15μm, and dried at 85°C to obtain a negative electrode sheet with a single-sided negative electrode material layer coated with a coating thickness of 97μm. After the first cold pressing treatment, a pressing roller with strip-shaped protrusions was used to perform a second cold pressing treatment on the surface of the first material layer to press out the first strip-shaped concave portion and the second strip-shaped concave portion, and then the sheet was cut and the pole ear was welded, and then vacuum dried at 120°C for 12h to obtain a single-sided negative electrode sheet with a specification of 78mm×88mm for standby use. The cold pressure of the above second cold pressing is 300kgf. The specific parameters are shown in Tables 1 to 4.

[0126] <Preparation of double-sided negative electrode sheet>

[0127] 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 45%wt. The negative electrode slurry was evenly coated on one surface of a negative electrode current collector copper foil with a thickness of 6μm, and 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 the above steps were repeated 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, cutting, and welding the pole ears, vacuum drying was performed at 120°C for 12h to obtain a negative electrode sheet with a specification of 78mm×88mm for standby use. The specific parameters of the double-sided negative electrode sheet are shown in Tables 2 to 4.

[0128] <Preparation of positive electrode sheet>

[0129] Conductive carbon black, a conductive agent, and polyvinylidene fluoride, a binder, are mixed in a certain proportion, and N-methylpyrrolidone (NMP) is added to prepare a conductive glue with a solid content of 7%wt. After mixing, lithium cobalt oxide, a positive active material, 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 75%wt is obtained. Among them, the mass ratio of positive electrode active material: conductive agent: binder is 97%: 1%: 2%. The positive electrode slurry is evenly coated on one surface of an aluminum foil with a thickness of 10μm, and dried at 85°C to obtain a positive electrode sheet coated with a single-sided positive electrode material layer. The positive electrode material then repeats the above steps on the other surface of the aluminum foil to obtain a positive electrode sheet coated with a double-sided positive electrode material layer. The above positive electrode sheet is then cold pressed, and the cold pressing pressure is 90T. The 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×84mm for standby use. The coating weight per unit area of ​​the positive electrode material layer in the positive electrode sheet is 16 mg / cm 2 , compacted density is 4.23g / cm 3 .

[0130] <Preparation of Electrolyte>

[0131] 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 LiPF6 is added to the non-aqueous solvent and mixed evenly to obtain an electrolyte, wherein the molar concentration of LiPF6 is 1.15 mol / L.

[0132] <Preparation of Separator>

[0133] A porous polyethylene film with a thickness of 7 μm (provided by Celgard Company) was used as a separator.

[0134] <Preparation of lithium-ion batteries>

[0135] The prepared single-sided negative electrode sheet, separator, positive electrode sheet, separator, and double-sided negative electrode sheet are stacked in order, and the single-sided negative electrode sheet is arranged on the outermost sides of both sides with the first material layer facing the positive electrode sheet, so that the separator is between the positive electrode sheet and the negative electrode sheet to play an isolating role, and then the four corners of the entire stacking structure are fixed with tape to obtain the stacking structure and hot press to obtain the electrode assembly; the electrode assembly is placed in an aluminum-plastic film packaging bag, and the moisture is removed at 80°C, and the prepared electrolyte is injected, and the soft-pack lithium-ion battery is obtained after vacuum packaging, standing, forming, shaping, capacity testing and other processes. Among them, the formation temperature is 80°C and the formation standing time is 2h.

[0136] Example 1-2 to Example 1-18

[0137] Except for adjusting the relevant preparation parameters according to Table 1, the rest is the same as Example 1-1.

[0138] Example 2-1 to Example 2-10

[0139] Except for adjusting the relevant preparation parameters according to Table 2, the rest is the same as Example 1-2.

[0140] Example 3-1 to Example 3-10

[0141] Except for adjusting the relevant preparation parameters according to Table 3, the rest is the same as Example 1-2.

[0142] Example 4-1 to Example 4-10

[0143] Except for adjusting the relevant preparation parameters according to Table 4, the rest is the same as Example 1-9.

[0144] Comparative Examples 1 to 2, Comparative Examples 4 to 9

[0145] Except for adjusting the relevant preparation parameters according to Table 1, the rest is the same as Example 1-1.

[0146] Comparative Example 3

[0147] Except that the relevant preparation parameters are adjusted according to Table 1 and the first strip-shaped recess is not provided on the negative electrode current collector, the rest is the same as Example 1-1.

[0148] The preparation parameters and performance tests in each embodiment and comparative example are shown in Tables 1 to 4.

[0149] Table 1

[0150]

[0151]

[0152] Note: For the reference standard of energy density in the table, please refer to the test method; "—" in Table 1 means there is no relevant parameter

[0153] It can be seen from Examples 1-1 to 1-18 and Comparative Examples 1 to 9 that the first negative electrode collector x of the single-sided negative electrode sheet in the embodiments has a first strip-shaped recess within the scope of the present application, and its depth h1 satisfies 4≤h1≤21, and the thickness of the first negative electrode collector is x1 that satisfies: 9≤x1≤22; the double-sided negative electrode sheet includes a second negative electrode collector, and the thickness of the second negative electrode collector is x2 that satisfies: 2≤x1 / x2≤6, then the curling rate of the single-sided negative electrode sheet is smaller, the production process optimization rate is higher, the capacity retention rate is higher, and the energy density can be taken into account, and there are no obvious black spots on the surface of the single-sided negative electrode sheet. Although the energy density of the lithium-ion battery in Comparative Example 1 is slightly higher, its capacity retention rate is low, and there are black spots on the surface of the single-sided negative electrode sheet; the energy density of the lithium-ion battery in Comparative Example 2 is low, and the curling rate of the single-sided negative electrode sheet in Comparative Example 3 is high, the production process optimization rate is low, and the circulation interface is poor. When no groove is set on the negative electrode collector, as shown in the effect of Comparative Example 3, it can be seen that the curling rate of the single-sided negative electrode sheet is high, the production process optimization rate is low, and the circulation interface is poor. This shows that the curling problem of the single-sided negative electrode sheet of the present application is improved, and the circulation performance, energy density and kinetic performance can be taken into account when the production process optimization rate of the lithium-ion battery is high.

[0154] The depth h1 of the first strip-shaped recess usually affects the curling rate and production process excellence of the single-sided negative electrode sheet, and also affects the cycle performance of the lithium-ion battery. It can be seen from Examples 1-1 to 1-18 that when the depth h1 of the first strip-shaped recess is within the scope of this application, the curling rate of the single-sided negative electrode sheet is small, the obtained lithium-ion battery has a good capacity retention rate and a high energy density, and the production process excellence rate is high. After the cycle, the single-sided negative electrode sheet of the lithium-ion battery has no black spots, lithium precipitation and other problems. This shows that the curling rate of the single-sided negative electrode sheet that meets the present application is small, the production process excellence rate is high, and the obtained lithium-ion battery has good cycle performance and kinetic performance, as well as a high energy density.

[0155] The thickness x2 of the second negative electrode current collector usually affects the energy density, cycle performance and production process excellence of the lithium-ion battery. It can be seen from Examples 1-1 to 1-18 that when the thickness x2 of the second negative electrode current collector is within the scope of this application, the obtained lithium-ion battery has both high energy density and capacity retention rate. When x2 is small, the processing difficulty of the second negative electrode current collector is large, which will reduce the production process excellence of the lithium-ion battery, such as Example 1-15. This shows that when x2 is within the scope of this application, the obtained lithium-ion battery can better balance the cycle performance, energy density and production process excellence of the lithium-ion battery.

[0156] The difference between the depth h1 of the first strip-shaped recess and the minimum set depth y usually affects the production process excellence and cycle performance of the lithium-ion battery. It can be seen from Example 1-1 to Example 1-17 that when h1-y is within the scope of this application, the curling rate of the single-sided negative electrode sheet is small, the obtained lithium-ion battery production process excellence rate is high, and the capacity retention rate is high. When h1-y is too large, although the curling rate of the positive electrode sheet is small, the processing is difficult and creases are easily generated, which affects the production process excellence rate of the lithium-ion battery, such as Example 1-17. Therefore, by adjusting h1-y within the scope of this application, it is beneficial to take into account both the production process excellence rate and the cycle performance of the lithium-ion battery.

[0157] Table 2

[0158]

[0159] The coating weight per unit area CW1 of the first material layer, the coating weight per unit area CW2 of the second material layer, and CW1 / CW2 usually affect the energy density, cycle performance and kinetic performance of the lithium-ion battery, as well as the production process excellence rate of the single-sided negative electrode sheet. It can be seen from Example 1-1, Example 2-1 to Example 2-6 that when CW1, CW2 and CW1 / CW2 are within the scope of this application, the obtained lithium-ion battery has both high energy density and capacity retention rate, and there are no obvious black spots or lithium precipitation problems on the single-sided negative electrode sheet, and the curling rate of the single-sided negative electrode sheet is small, and the production process excellence rate is large. The capacity retention rate of the lithium-ion battery in Example 2-3 is slightly lower than that of other embodiments. It is speculated that this is because its CW1 / CW2 is too large, resulting in insufficient lithium embedding in the single-sided negative electrode sheet, affecting its cycle performance. This shows that the lithium-ion battery within the scope of this application can better take into account the cycle performance and energy density of the lithium-ion battery, and take into account good kinetic performance.

[0160] The compaction density PD1 of the first material layer, the compaction density PD2 of the second material layer, and PD1 / PD2 usually affect the energy density, cycle performance and kinetic performance of the lithium-ion battery, as well as the production process excellence rate of the single-sided negative electrode sheet. It can be seen from Example 1-1, Example 2-7 to Example 2-10 that when PD1, PD2 and PD1 / PD2 are within the scope of this application, the obtained lithium-ion battery has both high energy density and capacity retention rate, and there are no obvious black spots or lithium precipitation problems on the single-sided negative electrode sheet, and the curling rate of the single-sided negative electrode sheet is small, and the production process excellence rate is large. This shows that when PD1, PD2 and PD1 / PD2 are within the scope of this application, the lithium-ion battery can take into account the cycle performance and energy density of the lithium-ion battery, and take into account the kinetic performance.

[0161] Table 3

[0162]

[0163] The spacing L1 between the orthographic projections of two adjacent first strip-shaped recesses and the spacing L2 between the orthographic projections of two adjacent second strip-shaped recesses usually affect the production process yield of the single-sided negative electrode sheet, as well as the cycle performance and kinetic performance of the lithium-ion battery. It can be seen from Examples 1-1, 3-1 to 3-4 that when L1 and L2 are within the scope of this application, the single-sided negative electrode sheet has a lower curling rate and a higher production process yield, and the obtained lithium-ion battery has a higher capacity retention rate. After cycling, there are no obvious black spots or lithium deposition problems on the single-sided negative electrode sheet. This shows that the single-sided negative electrode sheet within the scope of this application has a higher production process yield, and at the same time, the obtained lithium-ion battery can take into account better cycle performance and kinetic performance.

[0164] The relationship between the width D1 of the orthographic projection of a single first strip-shaped recess and the width D2 of the orthographic projection of a single second strip-shaped recess usually affects the production process yield of the single-sided negative electrode sheet, as well as the cycle performance and kinetic performance of the lithium-ion battery. It can be seen from Examples 1-1, 3-5 to 3-7 that when the relationship between D1 and D2 satisfies 0.1 ≤ D2 < D1 ≤ D2 + 0.38, the single-sided negative electrode sheet has a lower curling rate and a higher production process yield, and the obtained lithium-ion battery has a higher capacity retention rate. After cycling, there are no obvious black spots or lithium deposition problems on the single-sided negative electrode sheet. This shows that the single-sided negative electrode sheet within the scope of this application has a higher production process yield, and at the same time, the obtained lithium-ion battery can take into account better cycle performance and kinetic performance.

[0165] The spacing L1 between the orthographic projections of two adjacent first strip-shaped recesses and the width D1 of the orthographic projection of a single first strip-shaped recess affect the ratio of the total area S1 of the orthographic projection of the first strip-shaped recess to the area S2 of the coating area, and there is the following relationship: S1 / S2 = D1 / (D1 + L1). S1 / S2 usually affects the production process yield of the single-sided negative electrode sheet, as well as the cycle performance and kinetic performance of the lithium-ion battery. It can be seen from Examples 1-1, 3-1 to 3-10 that when S1 / S2 is within the scope of this application, the single-sided negative electrode sheet has a lower curling rate and a higher production process yield, and the obtained lithium-ion battery has a higher capacity retention rate. After cycling, there are no obvious black spots or lithium deposition problems on the single-sided negative electrode sheet. This shows that the single-sided negative electrode sheet within the scope of this application has a higher production process yield, and at the same time, the obtained lithium-ion battery can take into account better cycle performance and kinetic performance.

[0166] Table 4

[0167]

[0168] The depth h2 of the second strip-shaped recess and the difference between the depth h2 of the second strip-shaped recess and the depth h1 of the first strip-shaped recess usually affect the production process excellence, energy density, cycle performance and kinetic performance of the lithium-ion battery. It can be seen from Examples 1-1, 4-1 to 4-10 that when h2 and h2-h1 are within the scope of this application, the positive electrode sheet has a smaller curling rate and a higher production process excellence rate, and the obtained lithium-ion battery has both a higher energy density and a capacity retention rate. This shows that the lithium-ion battery within the scope of this application can better balance the cycle performance and energy density of the lithium-ion battery.

[0169] The angle α1 between the first side wall and the first bottom wall, and the angle α2 between the second side wall and the second bottom wall usually affect the production process excellence rate and the dynamic performance of the lithium-ion battery. It can be seen from Example 1-1, Example 4-4 to Example 4-6 that when α1 and α2 are within the scope of this application, the positive electrode sheet has a smaller curling rate and a higher production process excellence rate, and there is no obvious black spot or lithium precipitation problem on the single-sided negative electrode sheet after cycling. This shows that the positive electrode sheet within the scope of this application has a good production process excellence rate, and the obtained lithium-ion battery has good dynamic performance.

[0170] 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.

[0171] 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 secondary battery, comprising an electrode assembly of a stacked structure, the electrode assembly comprising a positive electrode sheet, a separator and a negative electrode sheet, the negative electrode sheet comprising a double-sided negative electrode sheet and a single-sided negative electrode sheet located at the outermost side of the electrode assembly in the stacking direction; The single-sided negative electrode sheet comprises a first negative electrode current collector and a first material layer arranged on one surface of the first negative electrode current collector, the first material layer faces the positive electrode sheet; the first negative electrode current collector comprises a hollow foil area and a coating area, the coating area has a plurality of first strip-shaped recesses, and the plurality of first strip-shaped recesses extend from the coating area to the hollow foil area; The depth of the first strip-shaped recess is h1, which satisfies: 4≤h1≤21; in, The thickness of the first negative electrode current collector is x1, in μm, satisfying: 9≤x1≤22; The double-sided negative electrode sheet includes a second negative electrode current collector, and the thickness of the second negative electrode current collector is x2 μm, 2≤x1 / x2≤6.

2. The secondary battery according to claim 1, characterized in that: 9≤x1≤16, and / or, 2≤x1 / x2≤4.

3. The secondary battery according to claim 1, wherein 4≤h1≤16。 4. The secondary battery according to claim 1, wherein 4≤x2≤6。 5. The secondary battery according to claim 4, wherein The minimum set depth of the first strip-shaped concave portion is y μm, y=0.0071x1 3 -0.3527x1 2 +4.4031x1.

6. The secondary battery according to claim 5, wherein 0≤h1-y≤5.

7. The secondary battery according to claim 1, wherein The double-sided negative electrode sheet includes a second negative electrode current collector and a second material layer disposed on both surfaces of the second negative electrode current collector. The coating weight per unit area of ​​the first material layer and the second material layer is independently 5.5 mg / cm 2 ≤CW≤13mg / cm 2 .

8. The secondary battery according to claim 7, wherein The coating weight per unit area of ​​the first material layer is CW1 mg / cm 2 The coating weight per unit area of ​​the second material layer is CW2 mg / cm 2 , 1.01≤CW1 / CW2≤1.

04.

9. The secondary battery according to claim 7, wherein The compacted density of the first material layer is PD1 g / cm 3 The compaction density of the second material layer is PD2 g / cm 3 , 0.95≤PD1 / PD2≤1.

10. The secondary battery according to claim 1, wherein Along the thickness direction of the single-sided negative electrode sheet, the total area of ​​the orthographic projections of the plurality of first strip-shaped recesses is S1 mm 2 The area of ​​the coating area is S2 mm 2 , 0.2≤S1 / S2≤0.

4.

11. The secondary battery according to any one of claims 1 to 10, wherein The first material layer has a plurality of second strip-shaped recesses, the second strip-shaped recesses correspond to the first strip-shaped recesses one by one, and the spacing between the orthographic projections of two adjacent first strip-shaped recesses and two adjacent second strip-shaped recesses is 0.3 mm≤L≤3 mm.

12. The secondary battery according to claim 11, wherein The width of the orthographic projection of a single first strip-shaped concave portion is D1 mm, the width of the orthographic projection of a single second strip-shaped concave portion is D2 mm, 0.1≤D2 <D1≤D2+0.38。 13. The secondary battery according to claim 11, wherein The depth of the second strip-shaped recess is h2 μm, and h2 ≥ h1.

14. The secondary battery according to claim 13, wherein 0≤h2-h1≤3.

15. The secondary battery according to claim 14, wherein 4≤h2≤25。 16. The secondary battery according to claim 11, wherein A single first strip-shaped recess includes a first side wall and a first bottom wall, and the angle between the first side wall and the first bottom wall is α1; a single second strip-shaped recess includes a second side wall and a second bottom wall, and the angle between the second side wall and the second bottom wall is α2; α1 and α2 are each independently 85° to 95°.

17. The secondary battery according to claim 16, wherein α1＝α2。 18. The secondary battery according to any one of claims 1 to 10, wherein The double-sided negative electrode sheet includes a second negative electrode current collector and second material layers arranged on both surfaces of the second negative electrode current collector, and the first material layer and / or the second material layer includes at least one of graphite, silicon or hard carbon. 19 . An electronic device comprising the secondary battery according to claim 1 .

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