Secondary battery and electronic apparatus

Abstract

A secondary battery and an electronic apparatus. The secondary battery comprises an electrode assembly (200) of a stacked structure, wherein the electrode assembly (200) comprises a positive electrode sheet, separators and negative electrode sheets; the negative electrode sheets comprise a double-sided negative electrode sheet (220) and a single-sided negative electrode sheet (210); the single-sided negative electrode sheet (210) comprises a first negative electrode current collector (211) and a first material layer (212) arranged on a surface of the first negative electrode current collector (211); the first material layer (212) faces the positive electrode sheet; the first negative electrode current collector (211) comprises a bare foil region (215) and a coated region (216), the coating region (216) has a plurality of first strip-shaped recesses (213), and the plurality of first strip-shaped recesses (213) extend in the direction from the coated region (216) to the bare foil region (215); the depth of each first strip-shaped recess (213) is h1, with the unit thereof being μm, and satisfies 4≤h1≤21; the thickness of the first negative electrode current collector (211) is x1, with the unit thereof being μm, and satisfies 9≤x1≤22; and the double-sided negative electrode sheet (220) comprises a second negative electrode current collector (221), and the thickness of the second negative electrode current collector (221) is x2, with the unit thereof being μm, and satisfies 2≤x1 / x2≤6.

Description

Secondary battery and electronic device

[0001] The present application claims priority to the Chinese patent application No. 202510120654.6 filed on January 24, 2025, and entitled "Secondary battery and electronic device", the content of which is incorporated herein by reference in its entirety. TECHNICAL FIELD

[0002] The present application relates to the technical field of electrochemistry, in particular to a secondary battery and an electronic device. BACKGROUND

[0003] Secondary batteries are widely used due to their high energy density, low self-discharge rate, and no memory effect. Among them, the laminated structure secondary battery is concerned due to its high current consistency, fast charging rate, and uniform heat distribution. The laminated structure secondary battery can use a structure of setting a single-face negative electrode tab on the outermost side and setting double-face positive electrode tabs and double-face negative electrode tabs in the middle to balance its energy density, safety, and manufacturing cost. However, when the single-face negative electrode tab on the outermost side is cold-pressed, the single-face negative electrode tab will be obviously curled due to the different stresses on both sides, which leads to difficult adjustment and increased production difficulty, and reduces the production process yield of the secondary battery.

[0004] To solve the above problems, the thickness of the current collector is usually increased to alleviate the curling problem of the single-face negative electrode tab. However, when the thickness of the current collector is too large, it will also lead to a decrease in the energy density of the secondary battery, and in addition, it will also cause a large current density, and the electrode tab is prone to lithium precipitation, which leads to poor interface between the electrode tab and the electrolyte, and deteriorates the cycle performance of the secondary battery. In addition, during the charging and discharging cycle of the secondary battery, the negative electrode material layer of the single-face negative electrode tab will also expand and shrink, which leads to poor contact between the single-face negative electrode tab and the separator of the secondary battery, affects the interface stability, and further affects the cycle performance of the secondary battery. Therefore, it is urgent to seek a method that can both alleviate the curling of the single-face negative electrode tab and improve the interface stability between the single-face negative electrode tab and the separator, to improve the production process yield and cycle performance of the secondary battery. SUMMARY

[0005] The present application aims to provide a secondary battery and an electronic device to improve the production process yield and cycle performance of the secondary battery. The specific technical solutions are as follows:

[0006] The first aspect of the present application provides a secondary battery and an electronic device, the secondary battery comprising an electrode assembly of a stacked structure, the electrode assembly comprising a positive electrode tab, a separator, and a negative electrode tab, the negative electrode tab comprising a double-sided negative electrode tab and a single-sided negative electrode tab located at the outermost side of the electrode assembly in a stacking direction; the single-sided negative electrode tab comprising a first negative current collector and a first material layer disposed on one surface of the first negative current collector, the first material layer facing the positive electrode tab; the first negative current collector comprising a blank foil region and a coated region, the coated region having a plurality of first strip-shaped recesses, the plurality of first strip-shaped recesses extending in a direction from the coated region to the blank foil region; the depth of the first strip-shaped recess being h1, satisfying: 4≤h1≤21; the thickness of the first negative current collector being x1, in units of μm, satisfying: 9≤x1≤22; the double-sided negative electrode tab comprising a second negative current collector, the thickness of the second negative current collector being x2 μm, 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 found that when the depth h1 of the recess and the thickness x1 of the negative current collector and the thickness x2 of the second negative current collector satisfy the above relationship setting, and x1 is within the range limited by the present application, not only is it beneficial to alleviate the degree of curling of the single-sided negative electrode tab during cold pressing, improve the production process yield of the single-sided negative electrode tab, and thus improve the production process yield of the secondary battery while taking into account the energy density, but it is also beneficial to improve the cycle performance and kinetic performance of the secondary battery.

[0007] In some embodiments of the present application, 4≤x2≤6. By adjusting the thickness x2 of the second negative current collector within the above range, the energy density of the secondary battery obtained is high, and the production process yield is high, which is beneficial to industrialization.

[0008] 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 applicant found that when the depth y of the recess and x1 satisfy the range limited by the present application, it can be beneficial to alleviate the degree of curling of the single-sided negative electrode tab during cold pressing, improve the production process yield of the single-sided negative electrode tab, and further improve the production process yield of the secondary battery while taking into account the energy density, and it is also beneficial to further improve the cycle performance and kinetic performance of the secondary battery.

[0009] In some embodiments of the present application, the depth of the first strip-shaped recess is h1, 0≤h1-y≤5. Through the above setting, it is beneficial to alleviate the degree of curling of the single-sided negative electrode tab during cold pressing, improve the production process yield of the single-sided negative electrode tab, and thus improve the production process yield of the secondary battery while taking into account the energy density, and it is also beneficial to improve the cycle performance and kinetic performance of the battery.

[0010] In some embodiments of the present application, the double-sided negative electrode tab comprises a second negative current collector and a second material layer arranged on both surfaces of the second negative current collector, the unit area coating weight of the first material layer and the second material layer is independently CW, 5.5 mg / cm 2 ≤ CW≤ 13 mg / cm 2 By adjusting the CW of the first material layer and the second material layer in the above range respectively, the secondary battery has a higher energy density and better kinetic performance.

[0011] In some embodiments of the present application, the unit area coating weight of the first material layer is CW1mg / cm 2 , the unit area coating weight of the second material layer is CW2mg / cm 2 , 1.01≤ CW1 / CW2≤ 1.04. By adjusting CW1 / CW2 in the above range, the kinetic matching of the single-sided negative electrode tab and the double-sided negative electrode tab in the secondary battery is improved, the cycle life of the secondary battery is prolonged, and the risk of damage of the secondary battery due to deep discharge and overcharge is reduced.

[0012] In some embodiments of the present application, the compaction 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 PD1 / PD2 in the above range cooperates with the first strip-shaped recess arranged in the coating area of the single-sided negative electrode tab, which is conducive to relieving the volume expansion of the first material layer, and further improving the kinetic performance and cycle performance of the secondary battery, and reducing the risk of lithium precipitation at low temperature.

[0013] In some embodiments of the present application, along the thickness direction of the single-sided negative electrode tab, the total area of the orthogonal projection of the plurality of first strip-shaped recesses is S1mm 2 , the area of the coating area is S2mm 2 , 0.2≤ S1 / S2≤ 0.4. By adjusting the ratio of S1 / S2 in the above range, not only the kinetic matching of the single-sided negative electrode tab and the double-sided positive electrode tab in the secondary battery can be further improved, but also the cycle interface stability of the first material layer is improved, and the cycle performance of the secondary battery is improved.

[0014] In some embodiments of the present application, the first material layer has a plurality of second strip-shaped recesses, each of the second strip-shaped recesses corresponds to one of the first strip-shaped recesses, and the spacing between the projections of any two adjacent first strip-shaped recesses and any two adjacent second strip-shaped recesses is L, 0.3 mm≤L≤3 mm. By regulating L within the above range, the curling phenomenon is alleviated, thereby improving the production process yield of the secondary battery, and also helping to improve the cycle performance of the secondary battery. Moreover, by regulating L within the above range, it is beneficial to improve the problem of mismatch between the kinetic performance of the outermost single-sided negative electrode sheet and the adjacent positive electrode sheet in the jelly-roll structure secondary battery, further improving the cycle performance of the secondary battery.

[0015] In some embodiments of the present application, the projection of a single first strip-shaped recess has a width of D1 mm, the projection of a single second strip-shaped recess has a width of D2 mm, and 0.1≤D2<D1≤D2+0.38. By regulating D1 and D2 to satisfy the above relationship, the cycle performance of the secondary battery can be improved, and the kinetic performance is also taken into account.

[0016] 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, and h2≥h1. By the above arrangement, it is not only beneficial to alleviate the volume expansion of the first material layer, but also helps to further improve the kinetic performance and cycle performance of the secondary battery.

[0017] In some embodiments of the present application, 0≤h2-h1≤3. By regulating the value of h2-h1 within the above range, it is beneficial to improve the cycle performance of the secondary battery, and also helps to improve the kinetic performance and production process yield of the secondary battery.

[0018] In some embodiments of the present application, 4≤h2≤25. By regulating the value of h2 within the above range, it is beneficial to alleviate the volume expansion of the first material layer, and also helps to improve the kinetic performance and cycle performance of the secondary battery.

[0019] 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 included 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 included angle between the second side wall and the second bottom wall is α2; and α1 and α2 are each independently 85° to 95°. By regulating α1 and α2 each within the above range, not only is it beneficial to improve the production process yield of the secondary battery, but also the cycle performance of the secondary battery can be further improved. Moreover, it is also beneficial to improve the drop performance.

[0020] In some embodiments of the present application, α1=α2. α1=α2 is beneficial to improve the production process yield of the secondary battery and improve the cycle performance of the secondary battery.

[0021] In some embodiments of this application, the double-sided negative electrode includes a second negative current collector and a second material layer disposed on both surfaces of the second negative current collector. The first material layer and / or the second material layer includes at least one of graphite, silicon, or hard carbon. By selecting the aforementioned negative electrode material for the first material layer and / or the second material layer, it is beneficial to improve the energy density of the secondary battery while maintaining kinetic performance. It also helps to further improve the rate performance and thermal stability of the secondary battery. A second aspect of this application provides an electronic device comprising the secondary battery of any of the foregoing embodiments.

[0022] The beneficial effects of this application are:

[0023] This application provides a secondary battery and electronic device. A first strip-shaped recess is formed in the first current collector of the outermost single-sided negative electrode sheet, satisfying 4≤h1≤21, 9≤x1≤22, and 2≤x1 / x2≤6, where x1 is the thickness of the first negative current collector in μm, x2 is the thickness of the second negative current collector in μm, and the depth of the first strip-shaped recess is h1μm. This configuration not only improves the stiffness of the single-sided negative electrode sheet, reduces its curling, and improves the manufacturing yield of the secondary battery, but also alleviates the volume expansion of the single-sided negative electrode sheet, stabilizes the interface between the single-sided negative electrode sheet and the separator, and improves the cycle performance of the secondary battery. Simultaneously, it also helps improve the kinetic matching between the single-sided and double-sided negative electrode sheets in the secondary battery, thereby improving the cycle performance of the lithium-ion battery.

[0024] Of course, implementing any product or method of this application does not necessarily require achieving all of the advantages described above at the same time. Attached Figure Description

[0025] The accompanying drawings, which are provided to further illustrate this application and form part of this application, illustrate exemplary embodiments of this application and are used to explain this application, but do not constitute an undue limitation of this application.

[0026] Figure 1 is a partial cross-sectional view of the secondary battery along the thickness direction in one embodiment of this application;

[0027] Figure 2 is a schematic cross-sectional view of a single-sided negative electrode sheet along the thickness direction according to one embodiment of this application.

[0028] Figure 3 is a schematic diagram of the structure of a single-sided negative electrode sheet according to one embodiment of this application;

[0029] Figure 4 is a schematic diagram of a partial cross-sectional structure of a single-sided negative electrode sheet along the thickness direction according to one embodiment of this application.

[0030] Figure 5 is a schematic diagram of a lithium-ion battery structure according to one embodiment of this application. DETAILED DESCRIPTION

[0031] For the purpose of making the purpose, technical solutions, and advantages of the present application more clear, the present application is further described in detail below with reference to the accompanying drawings and examples. Obviously, the described examples are only some of the embodiments of the present application, but not all the embodiments. All other embodiments obtained by those skilled in the art based on the present application are within the scope of protection of the present application.

[0032] It should be noted that in the specific embodiments of the present application, the present application is explained by taking lithium-ion batteries as examples of secondary batteries, but the secondary batteries of the present application are not limited to lithium-ion batteries.

[0033] The existing lamination structure design can be provided with a single-face negative electrode tab at the outermost side of the secondary battery, and when it is cold-pressed, the single-face negative electrode tab will be obviously curled due to the different stresses borne by the two sides, resulting in difficult adjustment and increased production difficulty, and the production process yield of the secondary battery is reduced. At present, the thickness of the negative current collector is mainly increased to alleviate the above problems and improve the production process yield of the secondary battery, but this not only reduces the energy density of the secondary battery, but also affects the kinetic matching of the single-face negative electrode tab and the double-face negative electrode tab, and affects the long cycle performance of the secondary battery. At the same time, the problem of poor cycle performance of the secondary battery caused by the volume change of the single-face negative electrode tab during the charging and discharging cycle of the secondary battery still cannot be solved.

[0034] Based on the above problems, the present application provides a secondary battery and an electronic device, which can solve the curling of the single-face negative electrode tab, improve the production process yield of the secondary battery, alleviate the volume expansion of the single-face negative electrode tab, improve the cycle performance of the secondary battery, and take into account the energy density.

[0035] The first aspect of this application provides a secondary battery including a stacked electrode assembly. The electrode assembly includes a positive electrode, a separator, and a negative electrode. Specifically, as shown in Figures 1 and 2, the secondary battery includes a housing 100 and a stacked electrode assembly 200. The outermost part of the electrode assembly 200 adjacent to the housing 100 is a single-sided negative electrode 210. The electrode assembly 200 also includes a double-sided negative electrode 220, a separator 230, and a double-sided positive electrode 240. The single-sided negative electrode 210 includes a first negative current collector 211 and a first material layer 212 disposed on one surface of the first negative current collector 211. The first negative current collector 211 has a plurality of first strip-shaped recesses 213, and the first material layer 212 has a plurality of second strip-shaped recesses 214. The first strip-shaped recesses 213 and the second strip-shaped recesses 214 correspond one-to-one. Specifically, a second strip-shaped recess 214 is formed on a surface of the first material layer 212 away from the first negative current collector 211. This second strip-shaped recess 214 is nested with and corresponds to the first strip-shaped recess 213. The first material layer 212 faces the double-sided positive electrode sheet 240; the double-sided positive electrode sheet 240 includes a positive current collector 241 and positive material layers 242 disposed on both surfaces of the positive current collector 241. As shown in FIG3, the first negative current collector 211 includes an empty foil region 215 and a coating region 216. In this application, the empty foil region 215 refers to a region on both sides of the current collector that does not contain an active material layer. The coating region 216 has a plurality of first strip-shaped recesses 213, which extend along the direction from the coating region 216 to the empty foil region 215, i.e., the direction indicated by the arrow in FIG3. With the above configuration, the protruding structure formed between adjacent first strip-shaped recesses can provide support when in contact with the diaphragm, providing a channel for electrolyte transport and improving the kinetic and cycle performance of the secondary battery.

[0036] Where x1 represents the thickness of the first negative electrode current collector in μm, and 9 ≤ x1 ≤ 22. In some embodiments of this application, 9 ≤ x1 ≤ 16. For example, x1 can be 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, or a range of any two of these values. When x1 is too small, for example, x1 < 9, the thickness of the first negative electrode current collector is too small, resulting in excessive residual stress inside the first negative electrode current collector after cold pressing. This can easily lead to severe curling and breakage of the single-sided negative electrode sheet, making the production of the single-sided negative electrode sheet difficult and resulting in a low yield rate in the secondary battery manufacturing process. While an excessively large x1 can improve the rigidity of the first negative electrode current collector, it will reduce the energy density of the secondary battery. Therefore, by controlling the thickness x1 of the first positive electrode current collector within the above range, a suitable thickness of the first positive electrode current collector results in a secondary battery with high energy density and a high yield rate in the manufacturing process, which is beneficial for industrialization.

[0037] As shown in FIG. 2, the first strip-shaped recess 213 has a depth of 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 between any two of them. When h1 is too large, for example, greater than 21, it will increase the processing difficulty of the single-sided negative electrode tab, and the distance between the negative electrode tab area provided with the first strip-shaped recess and the adjacent positive electrode tab is too large, thereby affecting the production process yield and cycle performance of the secondary battery. When h1 is too small, for example, less than 4, the curling rate of the first negative current collector is high, and it is not conducive to alleviating the volume change of the first material layer during the cycle process, thereby affecting the production process yield and cycle performance of the secondary battery. Therefore, by adjusting the value of h1 within the above range, it is beneficial to alleviate the curling of the single-sided negative electrode tab during the cold pressing process, thereby improving the processing performance of the single-sided negative electrode tab and improving the production process yield of the secondary battery. Moreover, in the obtained secondary battery, the matching of the kinetic performance of the single-sided negative electrode tab and the adjacent positive electrode tab is improved; at the same time, h1 within the above range can also provide a channel for the transmission of electrolyte, which is beneficial to further improve the kinetic performance and cycle performance of the secondary battery.

[0038] As shown in Figure 1, the double-sided negative electrode 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, and 2≤x1 / x2≤6. In some embodiments of this 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 of these ratios. When x1 / x2 is too large, for example, greater than 6, meaning either x1 is too large or x2 is too small, an excessively large x1 increases the proportion of the negative electrode current collector in the secondary battery, thus affecting the energy density of the secondary battery. Conversely, an excessively small x2 increases the processing difficulty of the double-sided negative electrode sheet, thus affecting the production yield of the secondary battery. Simultaneously, the kinetic matching between the first and second negative electrode current collectors decreases, affecting the cycle performance of the secondary battery. Conversely, when x1 / x2 is too small, for example, less than 2, meaning either x1 is too small or x2 is too large, an excessively small x1 makes the production difficulty of the single-sided negative electrode sheet high, leading to a low production yield of the secondary battery. An excessively large x2 increases the proportion of the negative electrode current collector in the secondary battery, thus affecting the energy density of the secondary battery, making it impossible to simultaneously achieve both production yield and cycle performance. Therefore, by adjusting x1 / x2 within the aforementioned range, it is beneficial to improve the mismatch in kinetic performance between the outermost single-sided and double-sided negative electrode sheets in stacked secondary batteries, thereby enhancing the kinetic matching between the single-sided and double-sided negative electrode sheets and improving the cycle performance of lithium-ion batteries. Furthermore, x1 / x2 within the aforementioned range also helps to balance the processing difficulty and energy density of single-sided negative electrode sheets, achieving a balance between the manufacturing process yield and energy density of secondary batteries. More preferably, adjusting 2 ≤ x1 / x2 ≤ 4 can further improve the cycle performance of lithium-ion batteries and further balance the processing difficulty and energy density of single-sided negative electrode sheets.

[0039] Therefore, the above-mentioned design not only helps the first negative electrode current collector to have suitable thickness and rigidity, alleviating the curling of the single-sided negative electrode sheet during cold pressing, improving the production process yield of the secondary battery while maintaining energy density, but also mitigates the problem of deteriorated cycle interface caused by the volume expansion of the first material layer during cycling, thereby improving the cycle performance of the secondary battery. The first strip-shaped recess in the single-sided negative electrode sheet also helps improve the wetting of the first material layer by the electrolyte, thus further improving the cycle performance of the secondary battery. Simultaneously, it also helps improve the kinetic matching between the single-sided and double-sided negative electrode sheets in the secondary battery, further enhancing the cycle performance of the lithium-ion battery.

[0040] In some embodiments of this application, the minimum set depth of the first strip-shaped recess is y μm, where y = 0.0071 x 1 3 -0.3527x1 2 +4.4031x1. The inventors of this application have discovered that when the depths y and x1 of the recess meet the limits of this application, it can help alleviate the curling of the single-sided negative electrode sheet during the cold pressing process, improve the production process yield of the single-sided negative electrode sheet, further improve the production process yield of the secondary battery while taking into account the energy density, and also help to further improve the cycle performance and dynamic performance of the secondary battery.

[0041] In some embodiments of this application, 0 ≤ h1 - y ≤ 5. The inventors discovered that the minimum set depth of the first strip-shaped recess is y, which is the minimum acceptable depth of the first strip-shaped recess to improve the aforementioned problem of curling of the single-sided negative electrode sheet. The magnitude of y varies with the thickness of the first negative current collector, and is determined according to the formula y = 0.0071x1. 3 -0.3527x1 2 The result is calculated as +4.4031x1. In the first negative electrode current collector of the stacked 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, helps the single-sided negative electrode sheet to have suitable stiffness, alleviates its internal stress during cold pressing, reduces its curling degree, and improves the processing stability of the first negative electrode current collector, thereby improving the production process yield of the secondary battery; on the other hand, a suitable depth helps to improve the problem of deterioration of the cycle interface caused by the volume expansion of the first material layer during cycling, thereby improving the cycle performance of the secondary battery. In this application, h1 typically refers to the actual depth of the first strip-shaped recess.

[0042] This application does not impose any particular limitation on the type of the first negative electrode current collector, as long as it can achieve the purpose of this application. For example, it may include copper foil, copper alloy foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, or composite current collector. For example, the composite current collector may be lithium copper composite current collector, carbon copper composite current collector, nickel copper composite current collector, titanium copper composite current collector, etc.

[0043] This application does not impose any particular limitation on the type of the second negative electrode current collector, as long as it can achieve the purpose of this application. For example, it may include copper foil, copper alloy foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, or composite current collector. For example, the composite current collector may be lithium copper composite current collector, carbon copper composite current collector, nickel copper composite current collector, titanium copper composite current collector, etc.

[0044] In some embodiments of this 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 of any two of these values. By adjusting the thickness x2 of the second negative electrode current collector within the above range, a suitable thickness of the second negative electrode current collector results in a secondary battery with high energy density and high production process efficiency, which is beneficial for industrialization.

[0045] In some embodiments of this application, the double-sided negative electrode includes a second negative current collector and a second material layer disposed on both surfaces of the second negative current collector. The coating weight per unit area of ​​the first material layer and the second material layer is independently CW, 5.5 mg / cm³. 2 ≤CW≤13mg / cm 2 For example, the 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 any combination of two of these values. By adjusting the CW of the first and second material layers within the above ranges, the secondary battery exhibits high energy density while also achieving good kinetic performance.

[0046] In some embodiments of this application, the coating weight per unit area of ​​the first material layer is CW1 mg / cm³. 2 The coating weight per unit area of ​​the second material layer is CW2 mg / cm³. 2 The ratio CW1 / CW2 should be 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 any two of these ratios. By adjusting CW1 to be slightly larger than CW2, and ensuring that CW1 / CW2 is within the above range, it is beneficial to increase the lithium storage space of the single-sided negative electrode, thereby improving its lithium plating level. This also helps to improve the kinetic matching between the single-sided and double-sided negative electrodes in the secondary battery, promoting good state of charge (SOC) for both electrodes, thus extending the cycle life of the secondary battery and reducing the risk of damage due to deep discharge and overcharging.

[0047] In some embodiments of this application, 5.64 ≤ CW1 ≤ 13. In some embodiments of this application, 5.5 ≤ CW2 ≤ 12.6. For example, CW1 can 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 of these values, and CW2 can 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, 13, or a range consisting of any two of these ratios.

[0048] In some embodiments of this application, the compaction density of the first material layer is PD1 g / cm³. 3 The compaction density of the second material layer is PD2 g / cm³. 3 The ratio PD1 / PD2 should be 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 any two of these ratios. By adjusting PD1 / PD2 within the above range, it is beneficial to improve the mismatch in kinetic performance between the outermost single-sided negative electrode and the double-sided negative electrode in the stacked secondary battery structure, improve the kinetic matching between the single-sided and double-sided negative electrode in the secondary battery, and thus improve the cycle performance of the lithium-ion battery. In addition, the PD1 / PD2 within the above range, combined with the first strip-shaped recess in the coating area of ​​the single-sided negative electrode, helps to further reduce the internal stress in the single-sided negative electrode during processing, alleviate the volume expansion of the first material layer, and also facilitates electrolyte transport, further improving the kinetic and cycle performance of the secondary battery, and reducing the risk of low-temperature lithium plating.

[0049] In some embodiments of this application, 1.65 ≤ PD1 ≤ 1.78. In some embodiments of this 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 these values; 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 of these ratios.

[0050] In some embodiments of this application, along the thickness direction of the single-sided negative electrode sheet, the total area of ​​the orthographic projection of the plurality of first strip-shaped recesses is S1mm. 2The area of ​​the coated region is S2cm 2 The ratio S1 / S2 is 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 any two of these ratios. By adjusting the ratio of S1 / S2 within the above range, the distribution density of the first strip-shaped recess on the single-sided negative electrode coating area is appropriate. This not only better improves the problem of the mismatch in kinetic performance between the outermost single-sided negative electrode and the adjacent positive electrode in the stacked secondary battery, further improving the kinetic matching between the single-sided negative electrode and the double-sided positive electrode in the secondary battery; but also, the S1 / S2 within the above range helps to provide buffer space for the volume expansion and contraction of the first material layer during cycling, improving the cycle interface stability of the first material layer, and thus improving the cycle performance of the secondary battery.

[0051] In some embodiments of this application, the first material layer has a plurality of second strip-shaped recesses, each corresponding to a first strip-shaped recess. The distance between the orthographic projections of two adjacent first strip-shaped recesses and two adjacent second strip-shaped recesses is L, where 0.3 mm ≤ L ≤ 3 mm. 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 any combination of two of these values. By adjusting L within the above range, the first material layer is better positioned on the first negative electrode current collector, which not only improves processing performance and alleviates edge curling, but also helps to mitigate the impact of volume changes in the first material layer during cycling on the stability of the cycling interface, thereby improving the production process yield and cycle performance of the secondary battery. Moreover, adjusting L within the above range helps to improve the problem of mismatch in kinetic performance between the outermost single-sided negative electrode and the adjacent positive electrode in a stacked secondary battery, while also providing better channels for electrolyte wetting and diffusion, further improving the kinetic and cycle performance of the secondary battery.

[0052] Specifically, as shown in Figure 3, multiple first strip-shaped recesses 213 are distributed in a stripe pattern. The two sides of the orthographic 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, i.e., the direction of the arrow in the figure. The orthographic projection of a single first strip-shaped recess 213 is a narrow, elongated rectangle with a width of D1 and a minimum spacing of L between two adjacent rectangles. Correspondingly, the orthographic projection of the second strip-shaped recess in the first material layer is also a narrow, elongated rectangle with a width of D2 and a minimum spacing of L between two adjacent rectangles. In this application, the aforementioned rectangle refers to a shape close to or similar to a standard rectangle.

[0053] 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 controlling 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, it is also possible to better control the deformation zones of the first strip-shaped recess and the second strip-shaped recess, 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.

[0054] In some embodiments of the present application, as shown in FIG. 2, 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.

[0055] 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 composed of any two of these values. By controlling the value of h2 - h1 within the above range, it is beneficial for improving the cycling interface stability of the single-sided negative electrode sheet, reducing the risk of the first material layer peeling off from the first negative electrode during the charge and discharge process of the secondary battery, and improving the cycling performance of the secondary battery. Moreover, it is beneficial for providing a channel for the transmission of the electrolyte, improving the processing performance of the single-sided negative electrode sheet, and thus improving the cycling performance, kinetic performance and production process yield of the secondary battery.

[0056] In some embodiments of this 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 of any two of these values. By adjusting 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 electrolyte transport. This improves the problem of mismatch in kinetic performance between the outermost single-sided negative electrode sheet and the adjacent positive electrode sheet in the stacked secondary battery structure, thereby improving the kinetic and cycle performance of the secondary battery.

[0057] In some embodiments of this application, as shown in FIG4, a single first strip-shaped recess 213 includes a first sidewall 2111 and a first bottom wall 2112, with an included angle α1 between the first sidewall 2111 and the first bottom wall 2112; a single second strip-shaped recess 214 includes a second sidewall 2121 and a second bottom wall 2122, with an included angle α2 between the second sidewall 2121 and the second bottom wall 2122; α1 and α2 are each independently between 85° and 95°. For example, α1 and α2 are each independently 85°, 86°, 87°, 88°, 89°, 90°, 91°, 92°, 93°, 94°, 95°, or a range consisting of any two of these values. By adjusting α1 and α2 within the aforementioned ranges, it is not only beneficial for the first negative electrode sheet to have suitable thickness and rigidity, alleviating its curling during cold pressing, improving its processing stability, and increasing the production yield of the secondary battery; it can also further improve the problem of deteriorated cycle interface caused by the volume expansion of the first material layer during cycling, thereby improving the cycle performance of the secondary battery. Moreover, suitable α1 and α2 also help increase the frictional force between the casing and the first negative electrode current collector in the single-sided negative electrode sheet, thus improving drop performance; at the same time, it can also provide channels for electrolyte transport, further improving the kinetic and cycle performance of the secondary battery.

[0058] In some embodiments of this application, α1 = α2. α1 = α2 is beneficial for improving the processing precision and stability of the single-sided negative electrode sheet, thereby increasing the yield rate of the secondary battery production process. Simultaneously, it can further mitigate the problem of deteriorated cycle interface caused by the volume expansion of the first material layer during cycling, thereby improving the cycle performance of the secondary battery.

[0059] In some embodiments of this application, the double-sided negative electrode sheet includes a second negative current collector and a second material layer disposed on both surfaces of the second negative current collector. The first material layer and / or the second material layer includes at least one of graphite, silicon, or hard carbon. By selecting the aforementioned negative electrode material for the first material layer and / or the second material layer, it is beneficial to improve the energy density of the secondary battery while maintaining kinetic performance, and also to improve the rate performance and thermal stability of the secondary battery.

[0060] The negative electrode material layer may also include a conductive agent and a binder. This application does not impose any particular limitation on the types of conductive agents and binders, as long as they achieve the purpose of this application. For example, the conductive agent may include, but is not limited to, at least one of conductive carbon black (Super P), carbon nanotubes (CNTs), carbon fibers, flake graphite, graphene, metallic materials, or conductive polymers. The conductive carbon black may include, but is not limited to, at least one of acetylene black or Ketjen black. The aforementioned carbon nanotubes may include, but are not limited to, single-walled carbon nanotubes and / or multi-walled carbon nanotubes. The aforementioned carbon fibers may include, but are not limited to, vapor-grown carbon fibers (VGCF) and / or carbon nanofibers. The aforementioned metallic materials may include, but are not limited to, metal powders and / or metal fibers; specifically, the metal may include, but is not limited to, at least one of copper, nickel, aluminum, or silver. The aforementioned conductive polymers may include, but are not limited to, at least one of polyphenylene derivatives, polyaniline, polythiophene, polyacetylene, or polypyrrole. 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. This application does not impose any particular limitation on the mass ratio of the positive electrode active material, conductive agent, and binder in the negative electrode material layer; those skilled in the art can select according to actual needs, as long as the purpose of this application is achieved.

[0061] This application does not impose any particular limitation on the preparation method of the single-sided negative electrode sheet, as long as it achieves the purpose of this application. For example, the preparation method of the single-sided negative electrode sheet may include, but is not limited to, the following steps: setting a first material layer on one surface of the first negative current collector, then performing a first cold pressing treatment on the first material layer using a pressure roller, and then performing a second cold pressing treatment on the first material layer using a pressure roller with strip-shaped protrusions to obtain the single-sided negative electrode sheet. This application does not impose any particular limitation on the pressure P1 of the first cold pressing treatment and the pressure P2 of the second cold pressing treatment, as long as it achieves the purpose of this application. For example, P1 can be 30t to 100t, and P2 can be 200 to 500 kgf. The purpose of the second cold pressing treatment is to create 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 compared to the pressure in the first cold pressing treatment. Therefore, the compaction density of the first material layer remains essentially unchanged before and after the second cold pressing treatment. At the same time, the second cold pressing treatment has virtually no effect on the thickness of the first material layer. In this application, the thickness is measured by the thickness of the protruding structural region formed between adjacent first strip-shaped recesses.

[0062] In this application, after the first cold pressing treatment, the compaction density of the first negative electrode material layer can be 1.65 g / cm³. 3 Up to 1.78 g / cm 3 .

[0063] This application does not impose any particular restrictions on the methods of adjusting h1, h2, D1, D2, L, α1, α2, CW1, CW2, PD1, and PD2, as long as the purpose of this application can be achieved. For example, the sizes of h1, h2, D1, D2, L, α1, and α2 can be adjusted by selecting the size of the strip protrusions and arranging different pressure rollers, or by adjusting the coating amount; CW1 and CW2 can be adjusted by adjusting the viscosity and solid content of the slurry; PD1 and PD2 can be adjusted by changing P1 and P2.

[0064] This application does not impose any particular limitation on the preparation method of the double-sided negative electrode sheet, as long as it achieves the purpose of this application. For example, the preparation method of the double-sided negative electrode sheet may include, but is not limited to, the following steps: depositing a second material layer on one surface of the second negative current collector, then depositing another second material layer on the other surface of the second negative current collector, and then performing a third cold pressing treatment using a pressure roller to obtain the double-sided negative electrode sheet. This application does not impose any particular limitation on the pressure P3 of the third cold pressing treatment, as long as it achieves the purpose of this application. For example, P3 can be from 30t to 120t.

[0065] In this application, after the third cold pressing treatment, the compaction density of the second negative electrode material layer can be 1.65 g / cm³. 3 Up to 1.78 g / cm 3 .

[0066] In this application, the first negative electrode current collector and the second negative electrode current collector of different thicknesses can be purchased, and their thickness can be confirmed using a micrometer. The desired thickness of the first negative electrode current collector and the second negative electrode current collector can then be selected.

[0067] In this application, the secondary battery further includes a positive electrode sheet, which includes a positive current collector and a positive electrode material layer disposed on at least one surface of the positive current collector. The phrase "positive electrode material layer disposed on at least one surface of the positive current collector" means that the positive electrode material layer can be disposed on one surface of the positive current collector along its thickness direction, or on two surfaces of the positive current collector along its thickness direction. It should be noted that the term "surface" here can refer to the entire surface area of ​​the positive current collector, or only a portion thereof; this application does not impose any particular limitation, as long as the purpose of this application is achieved.

[0068] This application does not impose any particular restrictions on the positive electrode current collector, as long as it can achieve the purpose of this application. For example, it may include aluminum foil, aluminum alloy foil, or composite current collector (such as aluminum-carbon composite current collector).

[0069] The positive electrode material layer includes a positive electrode active material. This application does not impose any particular limitation on the positive electrode active material, as long as it can achieve the purpose of this application. For example, the positive electrode active material may include, but is not limited to, lithium nickel cobalt manganese oxide (e.g., NCM811, NCM622, NCM523, NCM111), lithium nickel cobalt aluminum oxide, lithium iron phosphate, lithium-rich manganese-based materials, lithium cobalt oxide (LiCoO2), lithium manganese oxide, lithium manganese iron phosphate, or lithium titanate.

[0070] In some embodiments of this application, the positive electrode material layer may further include a conductive agent and a binder. This application does not impose any particular restrictions on the types of conductive agents and binders, as long as they achieve the purpose of this application. For example, it may be at least one of the aforementioned conductive agents and binders. This application does not impose any particular restrictions on the mass ratio of the positive electrode active material, conductive agent, and binder in the positive electrode material layer. Those skilled in the art can select according to actual needs, as long as the purpose of this application is achieved.

[0071] This application does not impose any particular limitations on the thickness of the positive electrode current collector and the positive electrode material layer, as long as the purpose of this application can be achieved. For example, the thickness of the positive electrode current collector can be 5 μm to 20 μm, and the thickness of the positive electrode material layer can be 30 μm to 120 μm.

[0072] Optionally, the positive electrode may further include a conductive layer located between the positive current collector and the positive electrode material layer. The composition of the conductive layer is not particularly limited and can be any conductive layer commonly used in the art. The conductive layer includes a conductive agent and a binder. This application does not impose any particular limitation on the conductive agent and binder in the conductive layer; for example, it can be at least one of the aforementioned conductive agents and binders.

[0073] This application does not impose any particular limitation on the diaphragm, as long as it can achieve the purpose of this application. For example, the diaphragm material may include, but is not limited to, at least one of polyethylene (PE), polyolefin (PO) based on polypropylene (PP), polyester (e.g., polyethylene terephthalate (PET) film), cellulose, polyimide (PI), polyamide (PA), spandex, or aramid. The type of diaphragm may include at least one of woven membrane, nonwoven membrane, microporous membrane, composite membrane, rolled membrane, or spun membrane.

[0074] In some embodiments of this application, the diaphragm may include a substrate layer and a surface treatment layer. The substrate layer may be a nonwoven fabric, membrane, or composite membrane with a porous structure, and the material of the substrate layer may include at least one of polyethylene, polypropylene, polyethylene terephthalate, or polyimide. Optionally, a polypropylene porous membrane, a polyethylene porous membrane, a polypropylene nonwoven fabric, a polyethylene nonwoven fabric, or a polypropylene-polyethylene-polypropylene porous composite membrane may be used.

[0075] Optionally, a surface treatment layer is provided 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 polymers and inorganic substances.

[0076] In some embodiments of this application, the inorganic layer comprises inorganic particles and a binder. This application does not particularly limit the inorganic particles; for example, the inorganic particles may include at least one selected from alumina, silicon oxide, magnesium oxide, titanium oxide, hafnium dioxide, tin oxide, cerium dioxide, nickel oxide, zinc oxide, calcium oxide, zirconium oxide, yttrium oxide, silicon carbide, boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide, or barium sulfate. This application does not particularly limit the binder; for example, the binder may be at least one of the binders described above. In some embodiments of this application, the polymer layer comprises a polymer, the polymer material of which includes at least one selected from polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinyl ether, or polyvinylidene fluoride or poly(vinylidene fluoride-hexafluoropropylene).

[0077] In this application, there is no particular limitation on the thickness of the diaphragm, as long as it can achieve the purpose of this application. For example, the thickness of the diaphragm can be from 3 μm to 30 μm.

[0078] In this application, the secondary battery also includes an electrolyte, which includes lithium salts and non-aqueous solvents.

[0079] This application does not impose any particular limitation on the lithium salt, as long as it achieves the purpose of this application. For example, the lithium salt may include, but is not limited to, at least one of LiPF6, LiBF4, LiAsF6, LiClO4, LiB(C6H5)4, LiCH3SO3, LiCF3SO3, LiN(SO2CF3)2, LiC(SO2CF3)3, Li2SiF6, lithium bis(oxalato)borate (LiBOB), or lithium difluoroborate. This application does not impose any particular limitation on the content of the lithium salt in the electrolyte, as long as it achieves the purpose of this application.

[0080] This application does not impose any particular restrictions on non-aqueous solvents, as long as they can achieve the purpose of this application. For example, non-aqueous solvents may include, but are not limited to, at least one of carbonate compounds, carboxylic acid ester compounds, ether compounds, or other organic solvents.

[0081] The aforementioned carbonate compounds may include, but are not limited to, at least one of chain carbonate compounds, cyclic carbonate compounds, or fluorocarbonate compounds. The aforementioned chain carbonate compounds may include, but are not limited to, at least one of dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), or methyl ethyl carbonate (MEC). The aforementioned cyclic carbonates may include, but are not limited to, at least one of ethylene carbonate (EC), propylene carbonate (PC), butyl carbonate (BC), or vinyl ethylene carbonate (VEC). Fluorocarbonate compounds may include, but are not limited to, at least one of fluoroethylene carbonate (FEC), 1,2-difluoroethylene carbonate, 1,1-difluoroethylene carbonate, 1,1,2-trifluoroethylene carbonate, 1,1,2,2-tetrafluoroethylene carbonate, 1-fluoro-2-methylethylene carbonate, 1-fluoro-1-methylethylene carbonate, 1,2-difluoro-1-methylethylene carbonate, 1,1,2-trifluoro-2-methylethylene carbonate, or trifluoromethylethylene carbonate. The aforementioned carboxylic acid ester compounds may include, but are not limited to, at least one of methyl formate, methyl acetate, ethyl acetate, n-propyl acetate, tert-butyl acetate, methyl propionate, ethyl propionate, propyl propionate, γ-butyrolactone, decanolactone, valproic acid lactone, or caprolactone. The aforementioned ether compounds may include, but are not limited to, at least one of dibutyl ether, tetraethylene glycol dimethyl ether, diethylene glycol dimethyl ether, 1,2-dimethoxyethane, 1,2-diethoxyethane, 1-ethoxy-1-methoxyethane, 2-methyltetrahydrofuran, or tetrahydrofuran. Other organic solvents may include, but are not limited to, at least one of dimethyl sulfoxide, 1,2-dioxolane, sulfolane, methylsulfolane, 1,3-dimethyl-2-imidazolium ketone, N-methyl-2-pyrrolidone, dimethylformamide, acetonitrile, trimethyl phosphate, triethyl phosphate, or trioctyl phosphate. This application does not impose any particular limitation on the content of non-aqueous solvents in the electrolyte, as long as the purpose of this application is achieved.

[0082] The fabrication process of the secondary battery described in this application is well known to those skilled in the art, and this application does not impose any particular limitations. For example, the fabrication process of the secondary battery may include, but is not limited to, the following steps: stacking a separator, a single-sided negative electrode sheet, a separator, a positive electrode sheet, a separator, a double-sided negative electrode sheet, and a separator in sequence, and placing a single-sided negative electrode sheet on the outermost side with the first material layer facing the negative electrode sheet; 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 into the housing; injecting electrolyte into the housing and sealing it to obtain the secondary battery. In addition, overcurrent protection elements, conductive plates, etc., may be placed in the housing as needed to prevent the internal pressure of the secondary battery from rising and overcharging / discharging.

[0083] A second aspect of this application provides an electronic device that includes a secondary battery as described in any of the foregoing embodiments. Therefore, the electronic device provided by this application has good performance in use.

[0084] This application does not specifically limit the type of electronic device; it can be any electronic device known in the prior art. In some embodiments of this application, the electronic device may include, but is not limited to, laptops, pen input computers, mobile computers, e-book players, portable telephones, portable fax machines, portable copiers, portable printers, stereo headphones, video recorders, LCD TVs, portable cleaners, portable CD players, mini CDs, transceivers, electronic notebooks, calculators, memory cards, portable recorders, radios, backup power supplies, motors, automobiles, motorcycles, electric bicycles, bicycles, lighting fixtures, toys, game consoles, clocks, power tools, flashlights, cameras, large household batteries, and lithium-ion capacitors, etc.

[0085] Example

[0086] The embodiments and comparative examples provided below illustrate the implementation of this application in more detail. Various tests and evaluations were conducted according to the methods described below. Furthermore, unless otherwise specified, "parts" and "%" are quality standards.

[0087] Test methods and equipment:

[0088] Production process yield testing:

[0089] (1) Several rolls of single-sided negative electrode sheets were prepared according to the preparation methods of single-sided negative electrode sheets in each embodiment and comparative example;

[0090] (2) Take sufficient amounts of the single-sided negative electrode sheet and corresponding separator, positive electrode sheet and double-sided negative electrode sheet prepared in each of the embodiments and comparative examples in step (1);

[0091] (3) Using the single-sided negative electrode, separator, positive electrode, and double-sided negative electrode from steps (1) and (2), assemble and produce lithium-ion batteries according to the stacking method of each embodiment and comparative example.

[0092] (4) Record the number of electrode assemblies that can be produced by the stacking process as N;

[0093] (5) Record the total number of negative electrode sheets that cannot be properly prepared or that cannot work properly during the stacking process due to reasons such as curling and wrinkling.

[0094] (6) Production process efficiency (%) = (1-M / N)×100%.

[0095] Energy density test:

[0096] (1) Test of discharge capacity: At an ambient temperature of 25°C, the lithium-ion battery was charged at a constant current of 1C to a voltage of 4.5V, then charged at a constant voltage of 4.5V to a cutoff current of 0.05C, left to stand for 5 minutes, and then discharged at a constant current of 0.2C to a voltage of 3.0V, left to stand for 5 minutes. The discharge capacity at this time was recorded as C, and the unit was Wh.

[0097] (2) Lithium-ion battery size test: As shown in Figure 5, along the extension direction of the positive electrode tab 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. The edge of the positive electrode tab 70 is designated as the fifth edge 401. The region extending 3mm from the fifth edge 401 in the opposite direction to the extension direction of the positive electrode tab 70 is designated as the head region 40. The region extending 3mm from the sixth edge 601 in the extension direction of the positive electrode tab 70 is designated as the tail region 60. The remaining region between the head region 40 and the tail region 60 is designated as the middle region 50. The distance between the fifth edge 401 and the sixth edge 601 is the length L of the lithium-ion battery 02, and the length of the fifth edge 401 is the width M of the lithium-ion battery 02. The dimension of the lithium-ion battery 02 in the stacking direction is its thickness D. The length L and width M of the lithium-ion battery are measured using a laser measuring instrument. The thickness of the head region (40), the middle region (50), and the tail region (60) were measured using a micrometer. Each region was measured three times, and the average of the three measurements was taken as the thickness of the corresponding region. The thickness D of the lithium-ion battery was calculated using the following formula: D = 1 / 3 × (Da + Db + Dc). Where D, L, and M are in dm.

[0098] (3) Calculation of energy density X of lithium-ion battery: X=C / (D×L×M);

[0099] In this study, the energy density X0 of Comparative Example 2 is designated as "Low," with X0 = 748 Wh / L. Each 0.2% increase represents a gradient in energy density, and the resulting lithium-ion batteries are ranked from low to high as follows: High > Upper-Medium > Medium > Lower-Medium > Low > / . Specifically, energy densities less than X0 are designated as " / ," energy densities greater than X0 and less than or equal to 1.002X0 are designated as "Low," energy densities greater than 1.002X0 and less than or equal to 1.004X0 are designated as "Lower-Medium," energy densities greater than 1.004X0 and less than or equal to 1.006X0 are designated as "Medium," energy densities greater than 1.006X0 and less than or equal to 1.008X0 are designated as "Upper-Medium," and energy densities greater than 1.008X0 and less than or equal to 1.010X0 are designated as "High."

[0100] Cyclic performance test:

[0101] The lithium-ion battery was placed in an environment of 25°C and charged at a constant current of 0.5C to a voltage of 4.5V. Then, it was charged at a constant voltage of 4.5V to a cutoff current of 0.05C, allowed to rest for 5 minutes, and then discharged at a constant current of 0.5C to a voltage of 3.0V, allowed to rest for 5 minutes. This constitutes one charge-discharge cycle. The discharge capacity of the first cycle was recorded. Then, the same steps were repeated for 200 charge-discharge cycles, and the discharge capacity of the 200th cycle was recorded.

[0102] 200-cycle capacity retention rate (%) = (discharge capacity of the 200th cycle / discharge capacity of the first cycle) × 100%.

[0103] Single-sided negative electrode sheet curling test:

[0104] 1. Take a single-sided negative electrode sheet, and then cut the single-sided negative electrode sheet into a rectangular electrode sheet of 91.5mm×55mm. The rectangular electrode sheet only includes the coating area.

[0105] 2. Lay the rectangular electrode sheet flat on a flat marble countertop, with the first material layer facing down and in its natural, extended state. Measure the dimensions of the rectangular electrode sheet in the horizontal TD and vertical MD directions in its extended state, and record them as T1 and M1.

[0106] 3. Use a glass plate to flatten the rectangular electrode sheet until it is flush with the table. Measure the actual dimensions of the rectangular electrode sheet in the transverse TD and longitudinal MD directions, and record them as T2 and M2.

[0107] 4. Calculate the curl rate of a single-sided negative electrode sheet:

[0108] TD curl rate = (T2-T1) / T2×100%;

[0109] MD curl rate = (M2-M1) / M2×100%;

[0110] The larger of the TD curl rate and the MD curl rate is taken as the final result. When the curl rate is less than or equal to 3%, it indicates that the curl rate of the single-sided negative electrode is low and the production process yield is high; when the curl rate is greater than 3% and less than 4%, it indicates that the curl rate of the single-sided negative electrode is good and has little impact on the production process yield; when the curl rate is greater than or equal to 4%, it indicates that the curl of the single-sided negative electrode is severe, the risk in the processing is high, and it seriously affects the production process yield.

[0111] Interface observation:

[0112] (1) Cycle the lithium-ion battery 200 times according to the steps in the cycle performance test, then charge it to 4.5V, and then charge it at a constant voltage of 4.5V to the cutoff current of 0.05C, and let it stand for 5 minutes.

[0113] (2) Disassemble the lithium-ion battery and confirm that the first material layer of the single-sided negative electrode sheet is the outermost interface.

[0114] (3) Observe whether the outermost interface is uniformly "golden yellow". If there are black spots, mark them as "black spots". If there are silver bright spots, mark them as "lithium plating". If there are no black spots or lithium plating, mark them as "normal".

[0115] Testing of CW1, CW2, PD1, and PD2:

[0116] CW1, PD1: Compacted density of the first material layer PD1 = Mass of the first material layer per unit area (unit: g / cm³) 2 The mass of the first material layer per unit area is measured by weighing with a balance, and the measured mass is CW1. The thickness of the first material layer is measured by a micrometer.

[0117] CW2, PD2: Compacted density of the second material layer. PD2 = Mass of the second material layer per unit area (unit: g / cm³). 2 The second material layer thickness (in cm) is calculated as follows: The mass of the second material layer per unit area is measured using a balance, and the measured mass is CW2. The thickness of the second material layer is measured using a micrometer.

[0118] Dimension measurement:

[0119] x1, h1, h2: The cross-section of the single-sided negative electrode sheet along the thickness direction is obtained by ion polishing and then observed and measured under a scanning electron microscope. x1, h1, h2 are the cross-sections of the electrode sheet.

[0120] x2: The cross-section of the double-sided negative electrode sheet along the thickness direction is obtained by ion polishing and then observed and measured under a scanning electron microscope.

[0121] D2, L, S2: Place the first material layer of the single-sided negative electrode sheet facing upwards under a VHX5000 microscope with the magnification set to 50 to 200 times; take a picture of the surface of the first material layer, and use microscope software to measure D2, L, S2 = coating area length × coating area width.

[0122] D1, S1: Place the single-sided negative electrode sheet with the first negative current collector facing upwards under a VHX5000 microscope, with the magnification set to 50 to 200x; take a photograph of the surface of the first negative current collector, and use microscope software to measure D1 and the length bmm of the first strip-shaped recess, and calculate S1 = D1 × b. Then calculate S1 / S2.

[0123] For each of the above dimensions, 10 points were measured and the average value was taken as the final result.

[0124] Example 1-1

[0125] <Preparation of Single-Sided Negative Electrode>

[0126] Artificial graphite, styrene-butadiene rubber, and sodium carboxymethyl cellulose were mixed in a mass ratio of 96:2:2, with deionized water added as a solvent. The mixture was stirred until homogeneous, yielding a negative electrode slurry with a solid content of 45% wt. This slurry was uniformly coated onto one surface of a 15 μm thick copper foil used as a negative electrode current collector. The foil was then dried at 85°C to obtain a single-sided coated negative electrode sheet with a 97 μm thick coating. After a first cold pressing treatment, a second cold pressing treatment was performed on the surface of the first material layer using a roller with raised stripes, pressing out the first and second strip-shaped recesses. The sheet was then cut, tabs were welded, and it was vacuum dried at 120°C for 12 hours to obtain a single-sided negative electrode sheet with dimensions of 78 mm × 88 mm. The cold pressing pressure was 300 kgf. Specific parameters are shown in Tables 1 to 4.

[0127] <Preparation of double-sided negative electrode>

[0128] Artificial graphite, styrene-butadiene rubber, and sodium carboxymethyl cellulose were mixed in a mass ratio of 96:2:2, with deionized water added as a solvent. The mixture was stirred until homogeneous, yielding a negative electrode slurry with a solid content of 45% wt. This slurry was uniformly coated onto one surface of a 6 μm thick copper foil used as a negative electrode current collector. The foil was then dried at 85°C to obtain a single-sided coated negative electrode sheet with a 100 μm thick coating. The above steps were repeated on the other surface of the copper foil to obtain a double-sided coated negative electrode sheet. After cold pressing, cutting, and welding of tabs, the sheet was vacuum dried at 120°C for 12 hours to obtain a negative electrode sheet with dimensions of 78 mm × 88 mm for later use. Specific parameters of the double-sided negative electrode sheet are shown in Tables 2 to 4.

[0129] <Preparation of the positive electrode>

[0130] Conductive carbon black (a conductive agent) and polyvinylidene fluoride (PVDF) (a binder) were mixed in a specific ratio, and N-methylpyrrolidone (NMP) was added to prepare a conductive adhesive with a solid content of 7% wt. After mixing, lithium cobalt oxide (the positive electrode active material) was added, and the mixture was stirred under vacuum until homogeneous, yielding a positive electrode slurry with a solid content of 75% wt. The mass ratio of positive electrode active material: conductive agent: binder was 97%:1%:2%. The positive electrode slurry was uniformly coated onto one surface of a 10 μm thick aluminum foil and dried at 85°C to obtain a positive electrode sheet with a single-sided coating of positive electrode material. The above steps were then repeated on the other surface of the aluminum foil to obtain a positive electrode sheet with a double-sided coating of positive electrode material. The positive electrode sheet was then cold-pressed at a pressure of 90T. The electrode sheet was cut into fixed sizes and then vacuum-dried at 85°C for 4 hours to obtain a positive electrode sheet with a specification of 74 mm × 84 mm for later use. The coating weight per unit area of ​​the positive electrode material layer in the positive electrode sheet is 16 mg / cm². 2 The compacted density is 4.23 g / cm³. 3 .

[0131] <Preparation of Electrolyte>

[0132] In a dry argon atmosphere, non-aqueous solvents ethylene carbonate (EC), propylene carbonate (PC), and diethyl carbonate (DEC) were mixed in a weight ratio of 1:1:1. LiPF6 was then added to the non-aqueous solvent and mixed thoroughly to obtain the electrolyte. The molar concentration of LiPF6 was 1.15 mol / L.

[0133] <Preparation of the diaphragm>

[0134] A porous polyethylene film with a thickness of 7μm (provided by Celgard) was used as the separator.

[0135] <Preparation of Lithium-ion Batteries>

[0136] The single-sided negative electrode, separator, positive electrode, separator, and double-sided negative electrode prepared above are stacked in sequence, with the single-sided negative electrode placed on the outermost side of both sides and the first material layer facing the positive electrode. The separator is positioned between the positive and negative electrode to act as an separator. Then, the four corners of the entire stacked structure are fixed with tape to obtain the stacked structure, and the electrode assembly is obtained by hot pressing. The electrode assembly is placed in an aluminum-plastic film packaging bag and dehydrated at 80°C. The prepared electrolyte is then injected, and after vacuum sealing, settling, formation, shaping, and capacity testing, a soft-pack lithium-ion battery is obtained. The formation temperature is 80°C, and the settling time is 2 hours.

[0137] Examples 1-2 to Examples 1-18

[0138] Except for adjusting the relevant preparation parameters according to Table 1, the rest is the same as in Example 1-1.

[0139] Examples 2-1 to 2-10

[0140] Except for adjusting the relevant preparation parameters according to Table 2, the rest is the same as in Examples 1-2.

[0141] Examples 3-1 to 3-11

[0142] Except for adjusting the relevant preparation parameters according to Table 3, the rest is the same as in Examples 1-2.

[0143] Examples 4-1 to 4-10

[0144] Except for adjusting the relevant preparation parameters according to Table 4, the rest is the same as in Examples 1-9.

[0145] Comparative Examples 1 to 2, and Comparative Examples 4 to 9

[0146] Except for adjusting the relevant preparation parameters according to Table 1, the rest is the same as in Example 1-1.

[0147] Comparative Example 3

[0148] Except for adjusting the relevant preparation parameters according to Table 1, and without setting the first strip-shaped recess on the negative electrode current collector, the rest is the same as in Example 1-1.

[0149] The preparation parameters and performance tests in each embodiment and comparative example are shown in Tables 1 to 4.

[0150] Table 1

[0151] Note: Please refer to the test method for the energy density reference standards in the table; "—" in Table 1 indicates that the relevant parameters do not exist.

[0152] As can be seen from Examples 1-1 to 1-18 and Comparative Examples 1 to 9, the first negative current collector x of the single-sided negative electrode sheet in the examples has a first strip-shaped recess within the scope of this application, and its depth h1 satisfies 4≤h1≤21, and the thickness of the first negative current collector x1 satisfies: 9≤x1≤22; the double-sided negative electrode sheet includes a second negative current collector, and the thickness of the second negative current collector x2 satisfies: 2≤x1 / x2≤6. Therefore, the single-sided negative electrode sheet has a smaller curling rate, higher production process efficiency, higher capacity retention rate, and can also take into account energy density. Moreover, the surface of the single-sided negative electrode sheet has no obvious black spots. While the lithium-ion battery in Comparative Example 1 has a slightly higher energy density, its capacity retention is low, and black spots appear on the surface of the single-sided negative electrode. The lithium-ion battery in Comparative Example 2 has a low energy density, and the single-sided negative electrode in Comparative Example 3 has a high curling rate, low manufacturing yield, and poor cycle interface. When no groove is provided on the negative electrode current collector, as seen in Comparative Example 3, the high curling rate, low manufacturing yield, and poor cycle interface of the single-sided negative electrode are evident. This demonstrates that the single-sided negative electrode curling problem in this application is improved, achieving a high manufacturing yield for lithium-ion batteries while balancing cycle performance, energy density, and kinetic performance.

[0153] The depth h1 of the first strip-shaped recess typically affects the curling rate and manufacturing process yield of the single-sided negative electrode sheet, and also influences the cycle performance of the lithium-ion battery. As can be seen from Examples 1-1 to 1-18, when the depth h1 of the first strip-shaped recess is within the range of this application, the curling rate of the single-sided negative electrode sheet is smaller, resulting in a lithium-ion battery with better capacity retention and higher energy density, a higher manufacturing process yield, and no black spots or lithium plating issues on the single-sided negative electrode sheet after cycling. This demonstrates that the single-sided negative electrode sheet satisfying this application has a smaller curling rate, a higher manufacturing process yield, and the resulting lithium-ion battery exhibits good cycle performance, kinetic performance, and a higher energy density.

[0154] The thickness x2 of the second negative electrode current collector typically affects the energy density, cycle performance, and manufacturing process yield of lithium-ion batteries. As seen in Examples 1-1 to 1-18, when the thickness x2 of the second negative electrode current collector is within the range specified in this application, the resulting lithium-ion battery exhibits both high energy density and capacity retention. Conversely, when x2 is smaller, the processing difficulty of the second negative electrode current collector increases, reducing the manufacturing process yield of the lithium-ion battery, as shown in Examples 1-15. This demonstrates that when x2 is within the range specified in this application, the resulting lithium-ion battery can effectively balance cycle performance, energy density, and manufacturing process yield.

[0155] The difference between the depth h1 of the first recessed section and the minimum set depth y typically affects the production process yield and cycle performance of lithium-ion batteries. As can be seen from Examples 1-1 to 1-17, when h1-y is within the scope of this application, the curling rate of the single-sided negative electrode sheet is small, resulting in a higher production process yield and capacity retention rate for the lithium-ion battery. When h1-y is too large, although the curling rate of the positive electrode sheet is small, the processing difficulty is high, and creases are easily generated, affecting the production process yield of the lithium-ion battery, as in Examples 1-17. Therefore, by adjusting h1-y within the scope of this application, it is beneficial to balance the production process yield and cycle performance of lithium-ion batteries.

[0156] Table 2

[0157] The coating weight per unit area of ​​the first material layer (CW1), the coating weight per unit area of ​​the second material layer (CW2), and the ratio of CW1 to CW2 typically affect the energy density, cycle performance, and kinetic performance of lithium-ion batteries, as well as the production process yield of the single-sided negative electrode sheet. As can be seen from Examples 1-1, 2-1 to 2-6, when CW1, CW2, and CW1 / CW2 are within the scope of this application, the resulting lithium-ion battery simultaneously exhibits high energy density and capacity retention, with no obvious black spots or lithium plating issues on the single-sided negative electrode sheet, and a low curling rate, resulting in a high production process yield. However, the capacity retention rate of the lithium-ion battery in Example 2-3 is slightly lower than in other examples, presumably due to its larger CW1 / CW2 ratio, leading to insufficient lithium intercalation on the single-sided negative electrode sheet and affecting its cycle performance. This demonstrates that the lithium-ion battery within the scope of this application can effectively balance the cycle performance and energy density of lithium-ion batteries while also maintaining good kinetic performance.

[0158] The compaction density PD1 of the first material layer, the compaction density PD2 of the second material layer, and the PD1 / PD2 ratio typically affect the energy density, cycle performance, and kinetic performance of lithium-ion batteries, as well as the manufacturing process yield of the single-sided negative electrode sheet. As can be seen from Examples 1-1, 2-7 to 2-10, when PD1, PD2, and PD1 / PD2 are within the scope of this application, the resulting lithium-ion battery simultaneously exhibits high energy density and capacity retention, the single-sided negative electrode sheet does not show obvious black spots or lithium plating problems, and the single-sided negative electrode sheet has a low curling rate, resulting in a high manufacturing process yield. This demonstrates that when PD1, PD2, and PD1 / PD2 are within the scope of this application, the lithium-ion battery can balance the cycle performance and energy density of the lithium-ion battery, while also considering kinetic performance.

[0159] Table 3

[0160] 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. As can be seen from Examples 1-1, 3-1 to 3-4, when L1 and L2 are within the scope of the present 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 the present application has a higher production process yield, and at the same time, the obtained lithium-ion battery can balance good cycle performance and kinetic performance.

[0161] 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. As can be seen from Examples 1-1, 3-5 to 3-7, 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 the present application has a higher production process yield, and at the same time, the obtained lithium-ion battery can balance good cycle performance and kinetic performance.

[0162] 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. As can be seen from Examples 1-1, 3-1 to 3-11, when S1 / S2 is within the scope of the present 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 the present application has a higher production process yield, and at the same time, the obtained lithium-ion battery can balance good cycle performance and kinetic performance.

[0163] Table 4

[0164] The depth h2 of the second strip-shaped recess and the difference between the depth h2 and the depth h1 of the first strip-shaped recess typically affect the manufacturing process yield, energy density, cycle performance, and kinetic performance of lithium-ion batteries. As can be seen from Examples 1-1, 4-1 to 4-10, when h2 and h2-h1 are within the scope of this application, the positive electrode sheet has a smaller curling rate and a higher manufacturing process yield, while the resulting lithium-ion battery also exhibits higher energy density and capacity retention. This demonstrates that the lithium-ion battery within the scope of this application can effectively balance the cycle performance and energy density of lithium-ion batteries.

[0165] The included angle α1 between the first sidewall and the first bottom wall, and the included angle α2 between the second sidewall and the second bottom wall, typically affect the manufacturing yield and the kinetic performance of the lithium-ion battery. As can be seen from Examples 1-1, 4-4 to 4-6, when α1 and α2 are within the scope of this application, the positive electrode has a smaller curling rate and a higher manufacturing yield, and the single-sided negative electrode after cycling does not exhibit obvious black spots or lithium plating problems. This demonstrates that the positive electrode within the scope of this application has good manufacturing yield, and the resulting lithium-ion battery exhibits good kinetic performance.

[0166] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, or article that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, or article.

[0167] The above description is only a preferred embodiment of this application and is not intended to limit this application. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the scope of protection of this application.

Claims

1. A secondary battery comprising an electrode assembly with a stacked structure, the electrode assembly comprising a positive electrode, a separator, and a negative electrode, the negative electrode comprising a double-sided negative electrode and a single-sided negative electrode located on the outermost side of the electrode assembly in the stacking direction; The single-sided negative electrode sheet includes a first negative current collector and a first material layer disposed on one surface of the first negative current collector, the first material layer facing the positive electrode sheet; the first negative current collector includes an empty foil area and a coating area, the coating area having a plurality of first strip-shaped recesses, the plurality of first strip-shaped recesses extending along the direction from the coating area to the empty 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, which satisfies: 9≤x1≤22; The double-sided negative electrode sheet includes a second negative current collector, the thickness of which is x2μm, and 2≤x1 / x2≤6.

2. The secondary battery according to claim 1, wherein, 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 recess is y μm, where y = 0.0071 x 1 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 current collector and a second material layer disposed on both surfaces of the second negative current collector. The coating weight per unit area of ​​the first material layer and the second material layer is independently CW, 5.5 mg / cm³. 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 / cm³. 2 The coating weight per unit area of ​​the second material layer is CW2 mg / cm³. 2 , 1.01≤CW1 / CW2≤1.

04.

9. The secondary battery according to claim 7, wherein, The compaction density of the first material layer is PD1 g / cm³ 3 The compaction density of the second material layer is PD2 g / cm³. 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 projection of the plurality of first strip-shaped recesses is S1 mm. 2 The area of ​​the coated region 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, and the second strip-shaped recesses correspond one-to-one with the first strip-shaped recesses. The distance between the orthographic projections of two adjacent first strip-shaped recesses and two adjacent second strip-shaped recesses is L, where 0.3mm≤L≤3mm.

12. The secondary battery according to claim 11, wherein, 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。 13. The secondary battery according to claim 11, wherein, The depth of the second strip-shaped recess is h2μm, where 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, Each of the first strip-shaped recesses includes a first sidewall and a first bottom wall, with an angle α1 between the first sidewall and the first bottom wall; each of the second strip-shaped recesses includes a second sidewall and a second bottom wall, with an angle α2 between the second sidewall and the second bottom wall; α1 and α2 are each independently between 85° and 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 current collector and a second material layer disposed on both surfaces of the second negative current collector, wherein 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 a secondary battery as claimed in any one of claims 1 to 18.

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