Secondary battery and electronic apparatus

Abstract

Provided are a secondary battery and an electronic apparatus. The secondary battery can ameliorate the problem of dynamic-performance mismatch between an outermost single-sided positive electrode sheet and a negative electrode sheet adjacent thereto in a secondary battery of a laminated structure, and improve the dynamic matching performance between the single-sided positive electrode sheet and the double-sided negative electrode sheet in the secondary battery, thereby improving the dynamic performance of a lithium ion battery. In addition, protrusions and recesses in the single-sided positive electrode sheet correspond to each other on a one-to-one basis, thereby further enhancing the dynamic performance of the secondary battery, and also improving the drop performance of the secondary battery and the yield and efficiency thereof in a production process.

Description

Secondary batteries and electronic devices Technical Field

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

[0002] Secondary batteries, such as lithium-ion batteries, are widely used in consumer applications, power generation, energy storage, and other fields due to their high energy density, high dynamics, and long lifespan. They are currently the focus of much attention in the new energy sector. With the continuous advancement and innovation of technology, the demand for energy density and rate capability is becoming increasingly urgent. As a technological innovation, laminated lithium-ion batteries are becoming the future direction of lithium-ion battery technology development.

[0003] To reduce active material waste and maximize energy density, laminated lithium-ion batteries typically have a single-sided positive or negative electrode sheet on the outermost side of the electrode assembly, with a double-sided positive or negative electrode sheet in the middle. When the outermost single-sided positive electrode sheet is used, the higher current density of the single-sided positive electrode sheet prevents the adjacent double-sided positive electrode sheet from matching the higher charge and discharge rate, thus affecting the kinetic performance of the lithium-ion battery.

[0004] Summary of the Invention

[0005] The purpose of the present application is to provide a secondary battery and an electronic device to improve the kinetic matching of single-sided positive electrode sheets and double-sided positive electrode sheets in the secondary battery, thereby improving the kinetic performance of the lithium-ion battery.

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

[0007] The first aspect of the present application provides a secondary battery comprising an electrode assembly of a laminated structure, the electrode assembly comprising a positive electrode sheet, a separator and a negative electrode sheet, the positive electrode sheet comprising a double-sided positive electrode sheet and a single-sided positive electrode sheet located on the outermost side of the electrode assembly in the direction of the laminate. The single-sided positive electrode sheet comprises a first positive current collector and a first material layer disposed on one surface of the first positive current collector. The first positive current collector has a plurality of protrusions, and the first material layer has a plurality of concave portions, with the protrusions and concave portions corresponding one to one. The double-sided positive electrode sheet comprises a second positive current collector and a second material layer disposed on both surfaces of the second positive current collector. The first material layer faces the negative electrode sheet. The thickness of the first positive current collector is H1, and the thickness of the second positive current collector is H2, where 1≤H1 / H2≤2.5. The compaction density of the concave portion is PD1, the compaction density of the second material layer is PD2, and the compaction density of the non-concave region of the first material layer excluding the concave portion is PD3, where PD1 / PD2≥0.929, and PD3+0.05g / cm 3 <PD1.

[0008] By adjusting H1 / H2 and PD1 / PD2 within the above range, and meeting PD3+0.05g / cm 3 <PD1, which can improve the kinetic performance mismatch between the outermost single-sided positive electrode sheet and the adjacent negative electrode sheet in stacked secondary batteries. This improves the kinetic matching between the single-sided positive electrode sheet and the double-sided negative electrode sheet in the secondary battery, thereby enhancing the kinetic performance of the lithium-ion battery. Furthermore, the one-to-one correspondence between the convex and concave portions of the single-sided positive electrode sheet further enhances the kinetic performance of the secondary battery, as well as improving the drop resistance, yield rate, and efficiency of the secondary battery production process.

[0009] In some embodiments of the present application, 1≤H1 / H2≤2.

[0010] In some embodiments of the present application, 1≤H1 / H2≤1.5.

[0011] In some embodiments of the present application, 0.929≤PD1 / PD2≤1.

[0012] In some embodiments of the present application, the first positive electrode current collector is an aluminum foil, with a thickness of 10 μm ≤ H1 ≤ 20 μm.

[0013] In some embodiments of the present application, the second positive electrode current collector is an aluminum foil, 8 μm≤H2≤12 μm.

[0014] With such a design, the thickness of the first positive electrode current collector and / or the second positive electrode current collector is appropriate, the energy density of the obtained secondary battery is high, and the production process is highly efficient, which is conducive to industrialization.

[0015] In some embodiments of the present application, 2.3 g / cm3 ≤PD1≤4.35g / cm 3 , 2.4g / cm 3 ≤PD2≤4.35g / cm 3 By regulating PD1 and PD2 within the above range, the secondary battery has a higher energy density and can improve the problem of mismatch in kinetic performance between the outermost single-sided positive electrode sheet and the adjacent negative electrode sheet in the laminated structure secondary battery, thereby improving the kinetic matching between the single-sided positive electrode sheet and the double-sided negative electrode sheet in the secondary battery, thereby improving the kinetic performance of the lithium-ion battery.

[0016] In some embodiments of the present application, the first material layer and / or the second material layer includes lithium cobalt oxide, 3.93 g / cm 3 ≤PD1≤4.35g / cm 3 , 4.03g / cm 3 ≤PD2≤4.35g / cm 3 When the first material layer and / or the second material layer includes lithium cobalt oxide, PD1 and PD2 are regulated within the above range. While improving the problem of mismatch in dynamic performance between the outermost single-sided positive electrode sheet and the adjacent negative electrode sheet in the laminated structure secondary battery, the overall dynamic performance of the secondary battery can also be further improved, and the secondary battery has a higher energy density.

[0017] In some embodiments of the present application, the compaction density of the first material layer in the area other than the concave portion is PD3, PD3+0.05 g / cm 3 <PD1≤PD3+0.15g / cm 3 By adjusting PD1 and PD3 to meet the above relationship, the problem of mismatch in dynamic performance between the outermost single-sided positive electrode sheet and the adjacent negative electrode sheet in the laminated structure secondary battery can be improved, and the dynamic matching of the single-sided positive electrode sheet and the double-sided negative electrode sheet in the secondary battery can be improved, and the production process has a high rate of excellence.

[0018] In some embodiments of the present application, the depth of the concave portion is h1, the height of the convex portion is h2, and h1 ≥ h2. The depth of the concave portion is greater than or equal to the height of the convex portion, which can reduce the overall thickness of the single-sided positive electrode sheet, thereby improving the overall compaction of the single-sided positive electrode sheet, improving the problem of mismatching the dynamic performance of the outermost single-sided positive electrode sheet and the adjacent negative electrode sheet in a laminated secondary battery, and improving the dynamic matching between the single-sided positive electrode sheet and the double-sided negative electrode sheet in the secondary battery.

[0019] In some embodiments of the present application, the compaction density of the first material layer in the area other than the concave portion is PD3, and the secondary battery satisfies: 0 g / cm 3 ≤PD2-PD3≤0.43g / cm 3, 0 μm ≤ h1 - h2 ≤ 3 μm. By controlling the values of PD2 - PD3 and h1 - h2 within the above ranges, the obtained secondary battery has a high matching degree of kinetic performance between the single-sided positive electrode plate and the adjacent negative electrode plate and can further improve the kinetic performance of the secondary battery.

[0020] In some embodiments of the present application, 3 μm ≤ h1 ≤ 50 μm, 2.64 μm ≤ h2 ≤ 48 μm. By controlling the values of h1 and h2 within the above ranges, the obtained secondary battery has a high matching degree of kinetic performance between the single-sided positive electrode plate and the adjacent negative electrode plate. Moreover, the friction force between the housing and the first positive current collector in the single-sided positive electrode plate is large, which can improve the drop performance; at the same time, it provides a channel for the transmission of the electrolyte, further improving the kinetic performance of the secondary battery.

[0021] In some embodiments of the present application, the plurality of recesses are distributed in a dot pattern. Along the thickness direction of the single-sided positive electrode plate, the shape of the orthographic projection of a single recess includes at least one of a circle, an ellipse, and a polygon. The diameter D1 of the largest circumscribed circle of the outer contour of the orthographic projection of a single recess is 0.3 mm to 4 mm, and the minimum distance L1 between the outer contours of the orthographic projections of two adjacent recesses is 0.5 mm to 5 mm. The plurality of recesses are distributed in a dot pattern and by controlling D1 and L1 within the above ranges, the distribution density of the recesses on the first material layer is appropriate, which can better improve the problem of non-matching kinetic performance between the outermost single-sided positive electrode plate and the adjacent negative electrode plate in the laminated structure secondary battery, and further improve the kinetic matching degree between the single-sided positive electrode plate and the double-sided negative electrode plate in the secondary battery.

[0022] In some embodiments of the present application, along the thickness direction of the single-sided positive electrode plate, the diameter of the largest circumscribed circle of the outer contour of the orthographic projection of a single protrusion is D2, D2 - 0.2 mm < D1 < D2, preferably, D2 - 0.18 mm < D1 < D2. By controlling D1 and D2 to satisfy the above relationship, the deformation zones of the protrusion and the recess can be better controlled, so as to more precisely control the range of the compaction density of the single-sided positive electrode plate, and further improve the kinetic matching degree between the single-sided positive electrode plate and the double-sided negative electrode plate in the secondary battery.

[0023] In some embodiments of the present application, the plurality of recesses are distributed in a stripe-like pattern. Along the thickness direction of the single-sided positive electrode sheet, the orthographic projection of a single recess comprises a stripe shape. The width D1' of the orthographic projection of a single recess is between 0.2 mm and 4 mm, and the minimum spacing L1' between the outer contours of the orthographic projections of two adjacent recesses is between 0.5 mm and 5 mm. The plurality of recesses are distributed in a stripe-like pattern, and by regulating D1' and L1' within the above-mentioned ranges, while improving the problem of kinetic performance mismatch between the outermost single-sided positive electrode sheet and the adjacent negative electrode sheet in a laminated secondary battery, a better channel can be provided for electrolyte infiltration and diffusion, further improving the kinetic performance of the secondary battery.

[0024] In some embodiments of the present application, along the thickness direction of the single-sided positive electrode sheet, the total area of ​​the orthographic projections of the multiple recesses is S1, the area of ​​the single-sided positive electrode sheet is S2, and 0.02≤S1 / S2≤0.44. By regulating the value of S1 / S2 within the above range, the distribution density of the recesses on the first material layer is appropriately adjusted, which can better improve the problem of mismatching the dynamic performance of the outermost single-sided positive electrode sheet and the adjacent negative electrode sheet in a laminated structure secondary battery, and further improve the dynamic matching of the single-sided positive electrode sheet and the double-sided negative electrode sheet in the secondary battery.

[0025] In some embodiments of the present application, the thickness H3 of the first material layer, excluding the concave portion, is between 25 μm and 70 μm. By adjusting H3 within this range, the deformation amplitude of the single-sided positive electrode sheet within different coating weight ranges can be better achieved. The resulting single-sided positive electrode sheet can not only improve the dynamic compatibility with the double-sided negative electrode sheet, but also be less prone to breakage that affects production yield.

[0026] A second aspect of the present application provides an electronic device comprising the secondary battery according to any one of the aforementioned embodiments.

[0027] Beneficial effects of this application:

[0028] The present application provides a secondary battery and an electronic device. The secondary battery includes an electrode assembly of a laminated structure, the electrode assembly includes a positive electrode sheet, a separator and a negative electrode sheet, the positive electrode sheet includes a double-sided positive electrode sheet and a single-sided positive electrode sheet located on the outermost side of the electrode assembly. The single-sided positive electrode sheet includes a first positive current collector and a first material layer arranged on one surface of the first positive current collector, the first positive current collector has a plurality of protrusions, and the first material layer has a plurality of concave portions, and the protrusions and concave portions correspond one to one; the double-sided positive electrode sheet includes a second positive current collector and a second material layer arranged on both surfaces of the second positive current collector, and the first material layer faces the negative electrode sheet. The thickness of the first positive current collector is H1, and the thickness of the second positive current collector is H2, 1≤H1 / H2≤2.5. The compaction density of the concave portion is PD1, the compaction density of the second material layer is PD2, and the compaction density of the non-concave area of ​​the first material layer other than the concave portion is PD3, PD1 / PD2≥0.925, PD3+0.05g / cm 3 <PD1; In some embodiments of the present application, 0.925≤PD1 / PD2≤1. By regulating H1 / H2 and PD1 / PD2 within the above ranges and satisfying PD3+0.05g / cm 3 <PD1, which can improve the kinetic performance mismatch between the outermost single-sided positive electrode sheet and the adjacent negative electrode sheet in laminated secondary batteries, enhancing the kinetic matching between the single-sided positive electrode sheet and the double-sided negative electrode sheet in the secondary battery, thereby improving the kinetic performance of the lithium-ion battery. Furthermore, the one-to-one correspondence between the convex and concave portions of the single-sided positive electrode sheet can further enhance the kinetic performance of the secondary battery, as well as improve the drop resistance of the secondary battery and the yield rate and efficiency of the production process. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] The drawings described herein are used to provide further understanding of the present application and constitute a part of the present application. The illustrative embodiments of the present application and their descriptions are used to explain the present application and do not constitute improper limitations on the present application.

[0030] FIG1 is a schematic diagram of a partial cross-sectional structure of a secondary battery along the thickness direction in one embodiment of the present application;

[0031] FIG2 is a schematic diagram of a cross-sectional structure of a single-sided positive electrode sheet along the thickness direction according to an embodiment of the present application;

[0032] FIG3 is a schematic structural diagram of a single-sided positive electrode sheet according to an embodiment of the present application;

[0033] FIG4 is a schematic structural diagram of a single-sided positive electrode sheet according to another embodiment of the present application;

[0034] FIG5 is a schematic structural diagram of a single-sided positive electrode sheet according to another embodiment of the present application;

[0035] FIG6 is a schematic diagram of a partial cross-sectional structure of a single-sided positive electrode sheet along the thickness direction according to another embodiment of the present application. DETAILED DESCRIPTION

[0036] To make the objectives, technical solutions, and advantages of this application more clearly understood, the present application is further described in detail below with reference to the accompanying drawings and examples. It is apparent that the described examples are only a portion of the embodiments of this application, rather than all of them. All other embodiments obtained by those skilled in the art based on this application are within the scope of protection of this application.

[0037] It should be noted that, in the specific embodiments of the present application, lithium-ion batteries are used as an example of secondary batteries to explain the present application, but the secondary batteries of the present application are not limited to lithium-ion batteries.

[0038] Currently, the following methods are commonly used to address the kinetic performance mismatch between the outermost single-sided positive electrode sheet and the adjacent negative electrode sheet in laminated secondary batteries: coating the single-sided positive electrode sheet with an adhesive, or using a low-kinetic positive electrode formulation to balance the kinetics of the outermost single-sided positive electrode sheet. However, these methods change the formulation of the positive electrode material layer, increasing production complexity and limiting versatility.

[0039] Based on the above problems, the present application provides a secondary battery and an electronic device, which improves the problem of mismatch in dynamic performance between the outermost single-sided positive electrode sheet and the adjacent negative electrode sheet in a laminated structure secondary battery without changing the formula of the positive electrode material layer, improves the dynamic matching of the single-sided positive electrode sheet and the double-sided negative electrode sheet in the secondary battery, and thereby improves the dynamic performance of the lithium-ion battery.

[0040] The first aspect of the present application provides a secondary battery, which includes an electrode assembly of a laminated structure, the electrode assembly including a positive electrode sheet, a separator and a negative electrode sheet, the positive electrode sheet including a double-sided positive electrode sheet and a single-sided positive electrode sheet located on the outermost side of the electrode assembly. Specifically, as shown in Figures 1 and 2, the secondary battery includes a shell 100 and an electrode assembly 200 of a laminated structure, the outermost side of the electrode assembly 200 adjacent to the shell 100 is a single-sided positive electrode sheet 210, and the electrode assembly 200 also includes a double-sided positive electrode sheet 220, a separator 230 and a double-sided negative electrode sheet 240. The single-sided positive electrode sheet 210 includes a first positive electrode collector 211 and a first material layer 212 provided on one surface of the first positive electrode collector 211, the first positive electrode collector 211 having a plurality of protrusions 213, and the first material layer 212 having a plurality of recesses 214, and the protrusions 213 and the recesses 214 correspond one to one. Specifically, a recess 214 is formed on one surface of the first material layer 212, and correspondingly, a protrusion 215 is formed on the other surface of the first material layer 212. The protrusion 215 and the protrusion 213 are nested with each other and correspond one-to-one with the recess 214. The double-sided positive electrode sheet 220 includes a second positive electrode current collector 221 and a second material layer 222 disposed on both surfaces of the second positive electrode current collector 221. The first material layer 212 faces the negative electrode sheet 240. The negative electrode sheet is a double-sided negative electrode sheet 240, which includes a negative electrode current collector 241 and a negative electrode material layer 242 disposed on both surfaces of the negative electrode current collector 241.

[0041] In the present application, the thickness of the first positive electrode current collector is H1, the thickness of the second positive electrode current collector is H2, and 1≤H1 / H2≤2.5. In some embodiments of the present application, 1≤H1 / H2≤2. In some embodiments of the present application, 1≤H1 / H2≤1.5. In some embodiments of the present application, 1≤H1 / H2≤1.3. For example, H1 / H2 can be 1, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2, 2.1, 2.2, 2.3, 2.4, 2.5 or a range consisting of any two values ​​therein. When H1 / H2 is too small, for example, less than 1, H1 is too small or H2 is too large. When H1 is too small, the single-sided positive electrode sheet is prone to curling. When H2 is too large, the energy density of the secondary battery is affected. When H1 / H2 is too large, H1 is too large or H2 is too small. When H1 is too large, the energy density of the secondary battery is affected. When H2 is too small, the preparation cost increases. In this application, the compaction density of the concave portion is PD1, the compaction density of the second material layer is PD2, and the compaction density of the non-concave portion area of ​​the first material layer excluding the concave portion is PD3. PD1 / PD2 ≥ 0.929, PD3 + 0.05 g / cm 3<PD1. In some embodiments of the present application, 0.925≤PD1 / PD2≤1. For example, PD1 / PD2 can be 0.929, 0.935, 0.945, 0.955, 0.965, 0.975, 0.976, 0.977, 0.978, 0.979, 0.980, 0.982, 0.985, 0.987, 0.990, 0.992, 0.995, 0.997, 0.999, 1, or a range consisting of any two values ​​therein. When PD1 / PD2 is too large, PD1 is too large to exceed the upper limit of compaction density processing and cannot be processed, or PD2 is too small to affect the energy density of the secondary battery; when PD1 / PD2 is too small, PD1 is too small to cause a large kinetic difference between the double-sided negative electrode sheets, or PD2 is too large to exceed the upper limit of compaction density processing and cannot be processed. For example, PD1 and PD3 meet PD3+0.01g / cm 3 <PD1, PD3+0.02g / cm 3 <PD1, PD3+0.03g / cm 3 <PD1, PD3+0.04g / cm 3 <PD1 or PD3 + 0.05g / cm 3 <PD1. The compaction density of the concave portions of the first material layer is greater than the compaction density of the non-concave areas, making the dynamic performance of the concave portions slightly worse than that of the non-concave areas, thereby weakening the overall dynamic performance of the first material layer to match the dynamic performance of the negative electrode material layer. At the same time, by regulating PD1 / PD2 within the above range, it is possible to match the dynamic performance of the negative electrode material layer with minimal impact on the energy density of the secondary battery. Secondly, the one-to-one correspondence between the convex and concave portions of the single-sided positive electrode sheet can improve the curling and wrinkling problems caused by the different internal stresses on both sides of the single-sided positive electrode sheet, thereby improving the yield and efficiency of the production process. It also increases the electrolyte retention in the first material layer, allowing for more complete infiltration and diffusion of the electrode liquid, which is beneficial for improving the cycle performance of the secondary battery. Thirdly, the convex portions on the surface of the first positive electrode current collector can increase or decrease the friction between the shell and the shell, which can improve the problem of secondary battery failure caused by insufficient friction between the shell and the single-sided positive electrode sheet during a drop. Thirdly, the convex structure formed between adjacent concave portions can play a supporting role in contact with the diaphragm, providing a channel for the transmission of the electrolyte, which is beneficial to improving the dynamic performance of the secondary battery.

[0042] Therefore, by adjusting H1 / H2 and PD1 / PD2 within the above range and satisfying PD3+0.05g / cm 3<PD1, which can improve the kinetic performance mismatch between the outermost single-sided positive electrode sheet and the adjacent negative electrode sheet in laminated secondary batteries, enhancing the kinetic matching between the single-sided positive electrode sheet and the double-sided negative electrode sheet in the secondary battery, thereby improving the kinetic performance of the lithium-ion battery. Furthermore, the one-to-one correspondence between the convex and concave portions of the single-sided positive electrode sheet can further enhance the kinetic performance of the secondary battery, as well as improve the drop resistance of the secondary battery and the yield rate and efficiency of the production process.

[0043] In some embodiments of the present application, the first positive electrode current collector is aluminum foil, and 8μm ≤ H1 ≤ 20μm; for example, H1 can be 8μm, 9μm, 10μm, 11μm, 12μm, 13μm, 14μm, 15μm, 16μm, 17μm, 18μm, 19μm, 20μm, or a range consisting of any two of these values. When the first positive electrode current collector is aluminum foil, by adjusting the thickness H1 of the first positive electrode current collector within the above range, the first positive electrode current collector has an appropriate thickness, the resulting secondary battery has a high energy density, and the production process has a high yield, which is conducive to industrialization.

[0044] In some embodiments of the present application, the second positive electrode current collector is aluminum foil, and 8μm ≤ H2 ≤ 12μm. For example, H2 can be 8μm, 9μm, 10μm, 11μm, 12μm, or a range consisting of any two of these values. When the second positive electrode current collector is aluminum foil, by regulating the thickness H2 of the second positive electrode current collector within the above range, the second positive electrode current collector has an appropriate thickness, the resulting secondary battery has a high energy density, and the production process has a high yield, which is conducive to industrialization.

[0045] In the present application, first positive electrode current collectors and second positive electrode current collectors of different thicknesses can be purchased and measured with a micrometer to select first positive electrode current collectors and second positive electrode current collectors of desired thicknesses.

[0046] In some embodiments of the present application, the first and second positive electrode current collectors are aluminum foils, and 8μm ≤ H1 ≤ 20μm, and 8μm ≤ H2 ≤ 12μm. When the first and second positive electrode current collectors are aluminum foils, and the thickness H1 of the first positive electrode current collector and the thickness H2 of the second positive electrode current collector are within the above ranges, the thickness of the first and second positive electrode current collectors are appropriate, the resulting secondary battery has a high energy density, and the production process has a high yield, which is conducive to industrialization.

[0047] In some embodiments of the present application, 2.3 g / cm 3 ≤PD1≤4.35g / cm 3 , 2.4g / cm 3 ≤PD2≤4.35g / cm 3 For example, PD1 can be 2.3 g / cm3 , 2.5g / cm 3 , 2.8g / cm 3 , 3g / cm 3 、3.2g / cm 3 、3.5g / cm 3 、3.8g / cm 3 , 4g / cm 3 , 4.1g / cm 3 , 4.2g / cm 3 , 4.23g / cm 3 , 4.28g / cm 3 , 4.35g / cm 3 Or a range consisting of any two values. For example, PD2 can be 2.4 g / cm 3 , 2.5g / cm 3 , 2.8g / cm 3 , 3g / cm 3 、3.2g / cm 3 、3.5g / cm 3 、3.8g / cm 3 , 4g / cm 3 , 4.1g / cm 3 , 4.2g / cm 3 , 4.23g / cm 3 , 4.28g / cm 3 , 4.35g / cm 3 Or a range consisting of any two of these values. By regulating PD1 and PD2 within the above range, the secondary battery has a higher energy density and can improve the kinetic performance mismatch between the outermost single-sided positive electrode sheet and the adjacent negative electrode sheet in a laminated secondary battery, thereby improving the kinetic matching between the single-sided positive electrode sheet and the double-sided negative electrode sheet in the secondary battery, thereby improving the kinetic performance of the lithium-ion battery.

[0048] In some embodiments of the present application, the first material layer includes lithium cobalt oxide. In some embodiments of the present application, the second material layer includes lithium cobalt oxide. In some embodiments of the present application, the first material layer and the second material layer include lithium cobalt oxide. 3.93 g / cm 3 ≤PD1≤4.35g / cm 3 , 4.03g / cm 3 ≤PD2≤4.35g / cm 3 For example, PD1 can be 3.93 g / cm 3 、3.94g / cm 3 、3.95g / cm 3 、3.97g / cm 3 、3.99g / cm3 , 4.00g / cm 3 , 4.02g / cm 3 , 4.05g / cm 3 , 4.07g / cm 3 、 4.09g / cm 3 , 4.10g / cm 3 , 4.12g / cm 3 , 4.15g / cm 3 , 4.17g / cm 3 , 4.19g / cm 3 , 4.20g / cm 3 , 4.21g / cm 3 , 4.22g / cm 3 , 4.23g / cm 3 , 4.28g / cm 3 , 4.35g / cm 3 Or a range consisting of any two values. For example, PD2 can be 4.03 g / cm 3 , 4.05g / cm 3 , 4.07g / cm 3 , 4.09g / cm 3 , 4.10g / cm 3 , 4.12g / cm 3 , 4.15g / cm 3 , 4.17g / cm 3 , 4.19g / cm 3 , 4.20g / cm 3 , 4.21g / cm 3 , 4.22g / cm 3 , 4.23g / cm 3 , 4.28g / cm 3 , 4.35g / cm 3 Or a range consisting of any two of these values. When the first material layer and / or the second material layer includes lithium cobalt oxide, regulating PD1 and PD2 within the above range can improve the kinetic performance mismatch between the outermost single-sided positive electrode sheet and the adjacent negative electrode sheet in a laminated secondary battery while further improving the overall kinetic performance of the secondary battery, and at the same time, the secondary battery has a higher energy density.

[0049] In some embodiments of the present application, the compaction density of the first material layer in the area other than the concave portion is PD3, PD3+0.05 g / cm 3 ≤PD1≤PD3+0.15g / cm 3 For example, the relationship between PD1 and PD3 can satisfy -, PD3 + 0.05g / cm3 <PD1≤PD3+0.07g / cm 3 、PD3+0.05g / cm 3 <PD1≤PD3+0.09g / cm 3 、PD3+0.05g / cm 3 <PD1≤PD3+0.10g / cm 3 、PD3+0.05g / cm 3 <PD1≤PD3+0.11g / cm 3 、PD3+0.05g / cm 3 <PD1≤PD3+0.12g / cm 3 、PD3+0.05g / cm 3 <PD1≤PD3+0.13g / cm 3 、PD3+0.05g / cm 3 <PD1≤PD3+0.14g / cm 3 or PD3+0.05g / cm 3 <PD1≤PD3+0.15g / cm 3 By adjusting PD1 and PD3 to meet the above relationship, the problem of mismatch in dynamic performance between the outermost single-sided positive electrode sheet and the adjacent negative electrode sheet in the laminated structure secondary battery can be improved, and the dynamic matching of the single-sided positive electrode sheet and the double-sided negative electrode sheet in the secondary battery can be improved, and the production process has a high rate of excellence.

[0050] In some embodiments of the present application, 3.8 g / cm 3 ≤PD3≤4.15g / cm 3 For example, PD3 can be 3.8 g / cm 3 、3.85g / cm 3 、3.9g / cm 3 、3.95g / cm 3 , 4g / cm 3 , 4.05g / cm 3 , 4.1g / cm 3 , 4.15g / cm 3 Or a range consisting of any two values.

[0051] In some embodiments of the present application, as shown in FIG2 , the depth of the recess 214 is h1, the height of the protrusion 213 is h2, and h1 ≥ h2. In some embodiments of the present application, h1>h2. When the depth of the recess is greater than or equal to the height of the protrusion, the overall thickness of the single-sided positive electrode sheet can be reduced to improve the overall compaction of the single-sided positive electrode sheet, improve the problem of mismatching the dynamic performance of the outermost single-sided positive electrode sheet and the adjacent negative electrode sheet in the laminated structure secondary battery, and improve the dynamic matching of the single-sided positive electrode sheet and the double-sided negative electrode sheet in the secondary battery.

[0052] In some embodiments of the present application, 0 g / cm 3 ≤PD2-PD3≤0.43g / cm 3 , 0μm≤h1-h2≤3μm. For example, PD2-PD3 can be 0g / cm 3 , 0.11g / cm 3 , 0.12g / cm 3 , 0.13g / cm 3 , 0.14g / cm 3 , 0.15g / cm 3 , 0.16g / cm 3 , 0.17g / cm 3 , 0.18g / cm 3 , 0.19g / cm 3 , 0.2g / cm 3 , 0.3g / cm 3 , 0.4g / cm 3 , 0.43g / cm 3 , or a range consisting of any two of the values. For example, h1-h2 can be 0μm, 0.2μm, 0.5μm, 0.8μm, 1μm, 1.2μm, 1.5μm, 1.7μm, 1.9μm, 2μm, 2.2μm, 2.5μm, 2.7μm, 2.9μm, 3μm, or a range consisting of any two of the values. By regulating the values ​​of PD2-PD3 and h1-h2 within the above ranges, the resulting secondary battery has a high matching of the kinetic performance of the single-sided positive electrode sheet and the adjacent negative electrode sheet, better consistency of the cycle interface, and a better low-temperature lithium precipitation window, which can further improve the kinetic performance of the secondary battery.

[0053] In some embodiments of the present application, 3μm≤h1≤50μm, 2.64μm≤h2≤48μm. For example, h1 can be 3μm, 5μm, 10μm, 15μm, 20μm, 25μm, 30μm, 35μm, 40μm, 45μm, 50μm, or a range consisting of any two of the values ​​therein. For example, h2 can be 2.64μm, 5μm, 10μm, 15μm, 20μm, 24μm, 30μm, 34μm, 40μm, 41μm, 42μm, 43μm, 45μm, 48μm, or a range consisting of any two of the values ​​therein. By regulating the values ​​of h1 and h2 within the above range, the secondary battery obtained has a high matching of the dynamic performance of the single-sided positive electrode sheet and the adjacent negative electrode sheet. Moreover, the friction between the shell and the first positive electrode current collector in the single-sided positive electrode sheet is relatively large, which can improve the drop performance; at the same time, it provides a channel for the transmission of the electrolyte, further improving the dynamic performance of the secondary battery.

[0054] In some embodiments of the present application, a plurality of recesses are distributed in a point-like manner. Along the thickness direction of the single-sided positive electrode sheet, the shape of the orthographic projection of a single recess includes at least one of a circle, an ellipse, and a polygon. The diameter D1 of the maximum circumscribed circle of the outer contour of the orthographic projection of a single recess is 0.3 mm to 4 mm, and the minimum spacing L1 between the outer contours of the orthographic projections of two adjacent recesses is 0.5 mm to 5 mm. For example, D1 can be 0.3 mm, 0.5 mm, 0.8 mm, 1 mm, 1.2 mm, 1.5 mm, 1.7 mm, 1.9 mm, 2 mm, 2.2 mm, 2.5 mm, 2.7 mm, 2.9 mm, 3 mm, 3.2 mm, 3.5 mm, 3.7 mm, 4 mm, or a range consisting of any two of these values. For example, L1 can be 0.5 mm, 1 mm, 1.5 mm, 2 mm, 2.5 mm, 3 mm, 3.5 mm, 4 mm, 4.5 mm, 5 mm, or a range consisting of any two of these values. Multiple recesses are distributed in a point-like manner and by regulating D1 and L1 within the above-mentioned range, the distribution density of the recesses on the first material layer is appropriate, which can better improve the problem of mismatch in dynamic performance between the outermost single-sided positive electrode sheet and the adjacent negative electrode sheet in the laminated structure secondary battery, and further improve the dynamic matching of the single-sided positive electrode sheet and the double-sided negative electrode sheet in the secondary battery.

[0055] Specifically, as shown in FIG. 3, the concave portions 214 are distributed in a dot-like array. The shape of the orthographic projection of the concave portions 214 includes a circle and a triangle. The diameter D1 of the largest circumscribed circle of the circle is the diameter of the circle, and the diameter D1 of the circumscribed circle of the triangle is the diameter of the circumscribed circle. The minimum distance between two adjacent circles or triangles is L1. It can be understood that when the concave portions are distributed in a dot-like pattern, they can also be distributed in a scattered dot-like pattern. The diameter D1 of the largest circumscribed circle of the outer contour of the orthographic projection of a single concave portion and the minimum distance L1 between the outer contours of the orthographic projections of two adjacent concave portions both satisfy the above range. It can be understood that the dimensions, the number, and the shape of the concave portions in FIG. 3 are only examples and do not limit the scope of protection of the present application.

[0056] In the present application, the shape of the orthographic projection of the concave portion is a polygon. Exemplarily, the polygon can be a triangle, a square, a rectangle, a pentagon, a hexagon, an octagon, etc. When multiple concave portions are distributed in a dot-like pattern, the shapes of the orthographic projections of two adjacent concave portions can be the same or different, and D1 and L1 can also be the same or different, as long as the object of the present application can be achieved.

[0057] In some embodiments of the present application, along the thickness direction of the single-sided positive electrode sheet, the diameter of the largest circumscribed circle of the outer contour of the orthographic projection of a single convex portion is D2, and D2 - 0.2 mm < D1 < D2. Preferably, D2 - 0.18 mm < D1 < D2. For example, the relationship between D1 and D2 can satisfy D2 - 0.18 mm < D1 < D2, D2 - 0.15 mm < D1 < D2, D2 - 0.14 mm < D1 < D2, D2 - 0.13 mm < D1 < D2, D2 - 0.12 mm < D1 < D2, D2 - 0.11 mm < D1 < D2, D2 - 0.10 mm < D1 < D2, D2 - 0.09 mm < D1 < D2, D2 - 0.07 mm < D! < D2 or D2 - 0.03 mm < D1 < D2. By controlling D1 and D2 to satisfy the above relationship, the deformation zones of the convex and concave portions can be better controlled, so as to more precisely control the range of the compaction density of the single-sided positive electrode sheet, and further improve the kinetic matching between the single-sided positive electrode sheet and the double-sided negative electrode sheet in the secondary battery.

[0058] In some embodiments of the present application, 0.44 mm ≤ D2 ≤ 4.14 mm. For example, D2 can be 0.440 mm, 0.450 mm, 0.480 mm, 0.50 mm, 1 mm, 1.5 mm, 2 mm, 2.5 mm, 3 mm, 3.5 mm, 4 mm, 4.14 mm or a range composed of any two of these values.

[0059] In some embodiments of the present application, a plurality of recesses are distributed in stripes, that is, the stripes are distributed in parallel. Along the thickness direction of the single-sided positive electrode sheet, the shape of the orthographic projection of a single recess includes a stripe, the width D1' of the orthographic projection of a single recess is 0.2mm to 4mm, and the minimum spacing L1' between the outer contours of the orthographic projections of two adjacent recesses is 0.5mm to 5mm. For example, D1' can be 0.2mm, 0.5mm, 0.8mm, 1mm, 1.2mm, 1.5mm, 1.7mm, 1.9mm, 2mm, 2.2mm, 2.5mm, 2.7mm, 2.9mm, 3mm, 3.2mm, 3.5mm, 3.7mm, 4mm or a range consisting of any two of the values ​​therein. For example, L1' can be 0.5mm, 1mm, 1.5mm, 2mm, 2.5mm, 3mm, 3.5mm, 4mm, 4.5mm, 5mm or a range consisting of any two of the values ​​therein. The multiple recesses are distributed in a stripe shape and by regulating D1' and L1' within the above range, while improving the problem of mismatch in dynamic performance between the outermost single-sided positive electrode sheet and the adjacent negative electrode sheet in the laminated structure secondary battery, it can better provide channels for the infiltration and diffusion of the electrolyte, further improving the dynamic performance of the secondary battery.

[0060] Specifically, as shown in FIG4 , multiple recesses 214 are distributed in a stripe-like pattern, and one side of the orthographic projection of a single recess 214 is parallel to one side of the single-sided positive electrode sheet 210 . The orthographic projection of a single recess 214 is in the shape of a narrow, long rectangle, with a width of D1′, and the minimum spacing between adjacent rectangles is L1′. It is understood that, as shown in FIG5 , multiple recesses 214 are distributed in a stripe-like pattern, and an angle is formed between one side of the orthographic projection of a single recess 214 and one side of the single-sided positive electrode sheet 210 . The orthographic projection of a single recess 214 is in the shape of a narrow, long rectangle, with a width of D1′, and the minimum spacing between adjacent rectangles is L1′, with adjacent rectangles having different lengths. This application does not particularly limit the size of the aforementioned angle, as long as it can achieve the purpose of this application. For example, the angle is 25° to 65°. The dimensions, number, and shape of the recesses in FIG4 and FIG5 are merely examples and do not limit the scope of protection of this application.

[0061] In some embodiments of the present application, multiple recesses are distributed in a stripe shape. Multiple recesses can be set along the width direction of the single-sided positive electrode sheet, multiple recesses can be set along the length direction of the single-sided positive electrode sheet, or multiple recesses can be set along the width and length directions of the single-sided positive electrode sheet at the same time.

[0062] In this application, the width D1' of the orthographic projection of a single recess is the maximum width of the orthographic projection. When multiple recesses are distributed in a stripe shape, the width D1' of the orthographic projection of two adjacent recesses can be the same or different, the length of the strips can be the same or different, and L1 can also be the same or different, as long as the purpose of this application can be achieved. This application has no special restrictions on the length of the strips, and can be designed according to the size of the single-sided positive electrode sheet, as long as the purpose of this application can be achieved.

[0063] In some embodiments of the present application, along the thickness direction of the single-sided positive electrode sheet, the total area of ​​the orthographic projections of the plurality of recesses is S1, the area of ​​the single-sided positive electrode sheet is S2, and 0.02≤S1 / S2≤0.44. For example, S1 / S2 can be 0.02, 0.05, 0.07, 0.09, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.44 or a range consisting of any two of these values. By regulating the value of S1 / S2 within the above range, the distribution density of the recesses on the first material layer is appropriate, which can better improve the problem of mismatch in dynamic performance between the outermost single-sided positive electrode sheet and the adjacent negative electrode sheet in the laminated structure secondary battery, and further improve the dynamic matching of the single-sided positive electrode sheet and the double-sided negative electrode sheet in the secondary battery.

[0064] In some embodiments of the present application, the thickness H3 of the first material layer in the area other than the concave portion is 25 μm to 70 μm. For example, H3 can be 25 μm, 30 μm, 35 μm, 40 μm, 45 μm, 50 μm, 55 μm, 60 μm, 65 μm, 70 μm, or a range consisting of any two of these values. By regulating H3 within the above range, the deformation amplitude of the single-sided positive electrode sheet within different coating weight ranges can be better achieved. The resulting single-sided positive electrode sheet can not only improve the dynamic matching with the double-sided negative electrode sheet, but also is not easily damaged and affects the production rate.

[0065] In some embodiments of the present application, the thickness H4 of the second material layer is 25 μm to 70 μm. For example, H4 can be 25 μm, 30 μm, 35 μm, 40 μm, 45 μm, 50 μm, 55 μm, 60 μm, 65 μm, 70 μm, or a range consisting of any two of these values.

[0066] This application does not specifically limit the method for preparing a single-sided positive electrode sheet, as long as the objectives of this application can be achieved. For example, the method for preparing a single-sided positive electrode sheet may include, but is not limited to, the following steps: providing a first positive electrode material layer on one surface of a first positive electrode current collector, then performing a first cold pressing process using a press roller, and then performing a second cold pressing process on the surface of the first material layer using a press roller with a protrusion to obtain a single-sided positive electrode sheet. This application does not specifically limit the pressure P1 of the first cold pressing process and the pressure P2 of the second cold pressing process, as long as the objectives of this application can be achieved. For example, P1 can be 30t to 100t, and P2 can be 5t to 50t.

[0067] In the present application, before the first cold pressing process, the compaction density of the first positive electrode material layer can be 2.05 g / cm 3 Up to 4.2g / cm 3 When the first material layer includes lithium cobalt oxide, before the first cold pressing process, the compaction density of the first positive electrode material layer can be 3.15 / cm 3 Up to 4.2g / cm 3 .

[0068] The present application does not specifically limit the method for adjusting h1, h2, D1, D1', L1, L1', PD1, and PD3, as long as the objectives of the present application can be achieved. For example, the sizes of h1, h2, D1, D1', L1, and L1' can be adjusted by selecting rollers with different protrusion sizes, shapes, and arrangements, or by adjusting the coating amount; PD1 and PD3 can be adjusted by varying P1 and P2.

[0069] In the present application, a single-sided positive electrode sheet is obtained through a first cold pressing process and a second cold pressing process, and the first material layer is deformed in the direction of the first positive current collector to form convex and concave portions. For example, as shown in FIG6 , the formed concave portion 214 is "bathtub-shaped", and the angle between the bottom and the side wall of the "bathtub" is α. The compaction density PD1 of the concave portion refers to the compaction density of the bottom area of ​​the "bathtub", and the compaction density PD3 of the non-concave area of ​​the first material layer other than the concave portion is the compaction density of the area between two adjacent "bathtubs". The compaction density of the side wall of the "bathtub" is PD4, and under normal circumstances, PD3<PD4<PD1. The present application has no special restrictions on the size of the above-mentioned angle α, as long as the purpose of the present application can be achieved. For example, 90°≤α≤135°.

[0070] In the present application, the first positive electrode current collector of the single-sided positive electrode sheet has a convex portion, which contacts the inner surface of the shell, and the friction coefficient between the two is greater than 0.2, which is conducive to improving the drop performance of the secondary battery. The concave and convex portions are obtained by secondary cold pressing, so that the compaction density of the concave portion is PD1, which is greater than the compaction density of the non-concave area of ​​the first material layer excluding the concave portion, which is PD3. In addition, the ionic resistance R1 of the concave portion is greater than the ionic resistance R2 of the non-concave area, the porosity K1 of the concave portion is less than the porosity K2 of the non-concave area, and the DC impedance IMP1 of the concave portion is equal to the DC impedance IMP2 of the non-concave area, so as to weaken the overall dynamic performance of the first material layer and match the dynamic performance of the negative electrode material layer, and improve the problem of mismatch in dynamic performance between the outermost single-sided positive electrode sheet and the adjacent negative electrode sheet in the laminated structure secondary battery.

[0071] This application does not specifically limit the method for preparing a double-sided positive electrode sheet, as long as the objectives of this application can be achieved. For example, the method for preparing a double-sided positive electrode sheet may include, but is not limited to, the following steps: disposing a second positive electrode material layer on one surface of a second positive electrode current collector, then disposing a second positive electrode material layer on the other surface of the second positive electrode current collector, and then cold-pressing the sheet using a roller to obtain the double-sided positive electrode sheet. This application does not specifically limit the pressure P3 of the cold pressing process, as long as the objectives of this application can be achieved. For example, P3 may be 30t to 120t.

[0072] In the present application, before the cold pressing process, the compaction density of the second positive electrode material layer can be 2.05 g / cm 3 Up to 4.2g / cm 3 When the first material layer includes lithium cobalt oxide, the compaction density of the first positive electrode material layer can be 3.15 g / cm before cold pressing. 3 Up to 4.2g / cm 3 .

[0073] The present application has no particular limitation on the method of regulating PD2, as long as the purpose of the present application can be achieved. For example, PD2 can be regulated by changing P3.

[0074] In the present application, the secondary battery further includes a positive electrode sheet, which includes a positive electrode current collector and a positive electrode material layer disposed on at least one surface of the positive electrode current collector. The "surface" in the above-mentioned "first material layer disposed on one surface of the first positive electrode current collector" and "second material layer disposed on both surfaces of the second positive electrode current collector" can refer to the entire surface area of ​​the first positive electrode current collector and the second positive electrode current collector, or it can refer to a partial surface area of ​​the first positive electrode current collector and the second positive electrode current collector. This application is not particularly limited, as long as the purpose of this application can be achieved.

[0075] The present application has no particular limitation on the first positive electrode current collector and the second positive electrode current collector, as long as the purpose of the present application can be achieved. For example, they may include aluminum foil, aluminum alloy foil or a composite current collector (such as an aluminum-carbon composite current collector).

[0076] The first material layer and the second material layer each independently include a positive electrode active material. The present application has no particular limitation on the positive electrode active material as long as the purpose of the present application can be achieved. For example, the positive electrode active material may include but is not limited to at least one of lithium nickel cobalt manganese oxide (such as NCM811, NCM622, NCM523, NCM111), lithium nickel cobalt aluminum oxide, lithium iron phosphate, lithium-rich manganese-based material, lithium cobalt oxide (LiCoO2), lithium manganese oxide, lithium iron manganese phosphate or lithium titanate.

[0077] The positive electrode material layer may also include a conductive agent and a binder. The present application does not particularly limit the types of the conductive agent and the binder, as long as the purpose of the present application can be achieved. For example, 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, metal materials or conductive polymers, and the conductive carbon black may include but is not limited to at least one of acetylene black or Ketjen black. The above-mentioned carbon nanotubes may include but are not limited to single-walled carbon nanotubes and / or multi-walled carbon nanotubes. The above-mentioned carbon fibers may include but are not limited to vapor-grown carbon fibers (VGCF) and / or nano-carbon fibers. The above-mentioned metal materials may include but are not limited to metal powder and / or metal fibers, and specifically, the metal may include but is not limited to at least one of copper, nickel, aluminum or silver. The above-mentioned conductive polymers may include but are not limited to at least one of polyphenylene derivatives, polyaniline, polythiophene, polyacetylene or polypyrrole. The binder may include, but is not limited to, at least one of polyacrylic acid, sodium polyacrylate, potassium polyacrylate, lithium polyacrylate, polyimide, polyvinyl alcohol, carboxymethyl cellulose, sodium carboxymethyl cellulose, lithium carboxymethyl cellulose, polyimide, polyamide-imide, styrene-butadiene rubber, or polyvinylidene fluoride. The present application does not particularly limit the mass ratio of the positive electrode active material, conductive agent, and binder in the positive electrode material layer. Those skilled in the art may select the binder according to actual needs, as long as the purpose of the present application can be achieved.

[0078] Optionally, the positive electrode sheet may further include a conductive layer positioned between the positive electrode current collector and the positive electrode material layer. The composition of the conductive layer is not particularly limited and may be any commonly used conductive layer in the art. The conductive layer includes a conductive agent and a binder. The present application does not particularly limit the conductive agent and binder in the conductive layer; for example, the conductive layer may be at least one of the aforementioned conductive agents and binders.

[0079] The present application has no particular restrictions on the negative electrode current collector, as long as the purpose of the present application can be achieved. For example, it may include copper foil, copper alloy foil, nickel foil, stainless steel foil, titanium foil, foam nickel, foam copper or a composite current collector. For example, the composite current collector can be a lithium-copper composite current collector, a carbon-copper composite current collector, a nickel-copper composite current collector, a titanium-copper composite current collector, etc.

[0080] The negative electrode material layer includes a negative electrode active material. The present application has no particular limitation on the negative electrode active material, as long as the purpose of the present application can be achieved. For example, the negative electrode active material may include but is not limited to natural graphite, artificial graphite, mesophase microcarbon beads, hard carbon, soft carbon, silicon, silicon-carbon composite, Li-Sn alloy, Li-Sn-O alloy, Sn, SnO, SnO2, spinel structured lithiated TiO2-Li4Ti5O 12 or at least one of Li-Al alloys.

[0081] In some embodiments of the present application, the negative electrode material layer may further include a conductive agent and a binder. The present application does not particularly limit the types of the conductive agent and binder, as long as they can achieve the purpose of the present application. For example, they can be at least one of the above-mentioned conductive agents and binders. The present application does not particularly limit the mass ratio of the negative 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 they can achieve the purpose of the present application.

[0082] The present application does not particularly limit the thickness of the negative electrode material layer, as long as it can achieve the purpose of the present application. For example, the thickness of the negative electrode material layer is 30 μm to 120 μm. The present application does not particularly limit the thickness of the negative electrode current collector, as long as it can achieve the purpose of the present application. For example, the thickness of the negative electrode current collector is 4 μm to 15 μm.

[0083] Optionally, the negative electrode sheet may further include a conductive layer positioned between the negative electrode current collector and the negative electrode material layer. The present application does not particularly limit the composition of the conductive layer, and it may be any conductive layer commonly used in the art. For example, the conductive layer may include a conductive agent and a binder. The present application does not particularly limit the conductive agent and binder in the conductive layer, and for example, it may be at least one of the above-mentioned conductive agents and binders.

[0084] The present application does not particularly limit the separator, as long as it can achieve the purpose of the present application. For example, the material of the separator may include, but is not limited to, at least one of polyethylene (PE), polypropylene (PP)-based polyolefins (PO), polyesters (e.g., polyethylene terephthalate (PET) film), cellulose, polyimide (PI), polyamide (PA), spandex, or aramid. The type of separator may include at least one of a woven membrane, a non-woven membrane, a microporous membrane, a composite membrane, a rolled membrane, or a spun membrane.

[0085] In some embodiments of the present application, the separator may include a substrate layer and a surface treatment layer. The substrate layer may be a non-woven fabric, a film, or a composite film having a porous structure, and the material of the substrate layer may include at least one of polyethylene, polypropylene, polyethylene terephthalate, or polyimide. Optionally, a polypropylene porous film, a polyethylene porous film, a polypropylene non-woven fabric, a polyethylene non-woven fabric, or a polypropylene-polyethylene-polypropylene porous composite film may be used.

[0086] 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 a polymer and an inorganic layer.

[0087] In some embodiments of the present application, the inorganic layer includes inorganic particles and a binder. The application is not particularly limited to inorganic particles. For example, inorganic particles can include at least one of aluminum oxide, silicon oxide, magnesium oxide, titanium oxide, hafnium dioxide, tin oxide, cerium dioxide, nickel oxide, zinc oxide, calcium oxide, zirconium oxide, yttrium oxide, silicon carbide, boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide or barium sulfate. The application is not particularly limited to the binder. For example, the binder can be at least one of the above-mentioned binders. In some embodiments of the present application, the polymer layer includes polymer, and the material of the polymer includes at least one of polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyacrylate, polyvinyl pyrrolidone, polyvinyl ether or polyvinylidene fluoride or poly (vinylidene fluoride-hexafluoropropylene).

[0088] In the present application, the thickness of the separator is not particularly limited as long as the purpose of the present application can be achieved. For example, the thickness of the separator may be 3 μm to 30 μm.

[0089] In the present application, the secondary battery further includes an electrolyte, and the electrolyte includes a lithium salt and a non-aqueous solvent.

[0090] The present application does not specifically limit the lithium salt, as long as the objectives of the present application can be achieved. For example, the lithium salt may include, but is not limited to, at least one of LiPF6, LiBF4, LiAsF6, LiClO4, LiB(C6H5)4, LiCH3SO3, LiCF3SO3, LiN(SO2CF3)2, LiC(SO2CF3)3, Li2SiF6, lithium bis(oxalatoborate) (LiBOB), or lithium difluoroborate. The present application does not specifically limit the content of the lithium salt in the electrolyte, as long as the objectives of the present application can be achieved.

[0091] The present application has no particular limitation on the non-aqueous solvent, as long as the purpose of the present application can be achieved. For example, the non-aqueous solvent may include but is not limited to at least one of carbonate compounds, carboxylate compounds, ether compounds or other organic solvents.

[0092] Above-mentioned carbonate compound can include but not limited to at least one in linear carbonate compound, cyclic carbonate compound or fluorinated carbonate compound.Above-mentioned linear carbonate compound can include but not limited to at least one in dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methylpropyl carbonate (MPC), ethylpropyl carbonate (EPC) or methyl ethyl carbonate (MEC).Above-mentioned cyclic carbonate can include but not limited to at least one in ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC) or vinyl ethylene carbonate (VEC). The fluorinated carbonate compound may include, but is not limited to, at least one of fluoroethylene carbonate (FEC), 1,2-difluoroethylene carbonate, 1,1-difluoroethylene carbonate, 1,1,2-trifluoroethylene carbonate, 1,1,2,2-tetrafluoroethylene carbonate, 1-fluoro-2-methylethylene carbonate, 1-fluoro-1-methylethylene carbonate, 1,2-difluoro-1-methylethylene carbonate, 1,1,2-trifluoro-2-methylethylene carbonate, or trifluoromethylethylene carbonate. The above-mentioned carboxylate compound may include, but is not limited to, at least one of methyl formate, methyl acetate, ethyl acetate, n-propyl acetate, tert-butyl acetate, methyl propionate, ethyl propionate, propyl propionate, γ-butyrolactone, decanoic acid lactone, valerolactone, or caprolactone. The above-mentioned ether compound may include but is not limited to at least one of dibutyl ether, tetraglyme, diglyme, 1,2-dimethoxyethane, 1,2-diethoxyethane, 1-ethoxy-1-methoxyethane, 2-methyltetrahydrofuran or tetrahydrofuran. The above-mentioned other organic solvents may include but are not limited to at least one of dimethyl sulfoxide, 1,2-dioxolane, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, N-methyl-2-pyrrolidone, dimethylformamide, acetonitrile, trimethyl phosphate, triethyl phosphate or trioctyl phosphate. The present application does not particularly limit the content of the non-aqueous solvent in the electrolyte, as long as the purpose of the present application can be achieved.

[0093] The preparation process of the secondary battery of the present application is well known to those skilled in the art and is not particularly limited in the present application. For example, the preparation process of the secondary battery may include, but is not limited to, the following steps: stacking a diaphragm, a negative electrode sheet, a diaphragm, a double-sided positive electrode sheet, a diaphragm, a negative electrode sheet, and a diaphragm in order, and setting a single-sided positive electrode sheet on the outermost sides with the first material layer facing the negative electrode sheet, and then fixing the four corners of the entire stacked structure with tape to obtain an electrode assembly of the stacked structure, placing the electrode assembly in a shell, injecting the electrolyte into the shell and sealing it to obtain a secondary battery. In addition, as needed, overcurrent protection elements, guide plates, etc. can also be placed in the shell to prevent pressure rise and overcharge and discharge inside the secondary battery.

[0094] The second aspect of the present application provides an electronic device, which includes the secondary battery in any of the aforementioned embodiments. Therefore, the electronic device provided by the present application has good performance.

[0095] The present application does not particularly limit the type of electronic device, and it can be any electronic device known in the prior art. In some embodiments of the present application, the electronic device can include, but is not limited to, a laptop computer, a pen-type computer, a mobile computer, an electronic book player, a portable phone, a portable fax machine, a portable copier, a portable printer, a head-mounted stereo headset, a video recorder, an LCD television, a portable cleaner, a portable CD player, a mini-disc, a transceiver, an electronic notepad, a calculator, a memory card, a portable recorder, a radio, a backup power supply, a motor, a car, a motorcycle, a power-assisted bicycle, a bicycle, a lighting fixture, a toy, a game console, a clock, a power tool, a flashlight, a camera, a large household battery, and a lithium-ion capacitor.

[0096] Example

[0097] The following examples and comparative examples are provided to more specifically illustrate the embodiments of the present invention. Various tests and evaluations were performed according to the following methods. In addition, unless otherwise specified, "parts" and "%" are based on mass.

[0098] Test methods and equipment:

[0099] Drop performance test:

[0100] The lithium-ion battery to be tested was placed in an environment of 25°C, charged at a constant current of 0.5C to a voltage of 4.5V, then charged at a constant voltage of 4.5V to a cut-off current of 0.05C, and left to stand for 5 minutes to reach a fully charged state;

[0101] Place the lithium-ion battery in a fixed fixture, inspect its appearance and take photos before and after the test;

[0102] Use a metal drop floor and drop the device from a height of 1.8m once along the head and tail, and once at each of the four corners. Perform 7 rounds of testing, with 6 drops per round. The drop order is: head -> tail -> right corner of the head -> right corner of the tail -> left corner of the head -> left corner of the tail (angle: 45±15 degrees).

[0103] The voltage and internal resistance of the lithium-ion batteries were measured after the drop test and 24 hours after the test. The criteria for passing the drop test were: no fire, no explosion, no smoke, no leakage, and a voltage drop of less than 50 mV. For each example or comparative example, 10 lithium-ion batteries were tested and the number of passing batteries was recorded. This was expressed as: number of passing batteries / number of experiments. For example, 9 / 10 means 9 out of 10 lithium-ion batteries passed the test.

[0104] Single-sided positive electrode curling test:

[0105] 1. Take the single-sided positive electrode sheet, and then cut the single-sided positive electrode sheet into a rectangular electrode sheet of 91.5mm×55mm;

[0106] 2. Lay the rectangular electrode flat on a smooth marble table with the first material layer facing downward in a naturally stretched state. Measure the dimensions of the rectangular electrode in the transverse TD and longitudinal MD directions in the stretched state, and record them as T1 and M1;

[0107] 3. Use a glass plate to flatten the rectangular electrode until it is flush with the tabletop, and measure the actual transverse TD and longitudinal MD dimensions of the rectangular electrode, which are recorded as T2 and M2;

[0108] 4. Calculate the curvature of the single-sided positive electrode sheet:

[0109] TD curling rate = (T2-T1) / T2×100%;

[0110] MD curl = (M2-M1) / M2×100%;

[0111] The larger of the TD and MD curling ratios is used as the final result. A curling ratio greater than or equal to 2% indicates that the single-sided positive electrode sheet is severely curled, posing a high risk during processing. A curling ratio less than 2% indicates that the single-sided positive electrode sheet is not severely curled, posing little risk during processing.

[0112] Cyclic performance test:

[0113] Place the lithium-ion battery in a 25°C environment and charge it at a constant current of 0.5C to a voltage of 4.5V. Then, charge it at a constant voltage of 4.5V to a cutoff current of 0.05C, let it rest for 5 minutes, and discharge it at a constant current of 0.5C to a voltage of 3.0V. Let it rest for 5 minutes. This is one charge and discharge cycle. Record the discharge capacity of the first cycle. Then, perform 500 charge and discharge cycles using the same steps and record the discharge capacity of the 500th cycle.

[0114] 500-cycle capacity retention rate (%)=(discharge capacity at the 500th cycle / discharge capacity at the first cycle)×100%.

[0115] Interface observation:

[0116] (1) The lithium-ion battery was cycled for 500 cycles according to the steps in the cycle performance test, then charged to 4.5 V, and then charged at a constant voltage of 4.5 V to a cutoff current of 0.05 C, and allowed to stand for 5 minutes.

[0117] (2) The lithium-ion battery is disassembled and the surface of the negative electrode sheet adjacent to the single-sided positive electrode sheet is confirmed to be the outermost interface.

[0118] (3) Observe whether the outermost interface is uniformly golden. If there are black spots, mark it as “black spots”; if there are no black spots, mark it as “normal”.

[0119] 0℃_1.5C_lithium deposition test:

[0120] Place the lithium-ion battery in a 0°C environment and charge it at a constant current of 1.5C to a voltage of 4.5V. Then charge it at a constant voltage of 4.5V to a cutoff current of 0.05C, let it rest for 5 minutes, and discharge it at a constant current of 0.5C to a voltage of 3.0V, let it rest for 5 minutes. This is one charge and discharge cycle. Repeat the same steps for 10 cycles of charge and discharge.

[0121] Then charge at a constant current of 1.5C to 4.5V, and then charge at a constant voltage of 4.5V to a cutoff current of 0.05C, and let it stand for 5 minutes; then disassemble the lithium-ion battery and confirm that the surface of the negative electrode sheet adjacent to the single-sided positive electrode sheet is the outermost interface.

[0122] The outermost interface is observed. If there is no white lithium metal precipitation, it is recorded as no lithium precipitation; if there is white lithium metal precipitation and the lithium precipitation area accounts for less than 5%, it is recorded as slight lithium precipitation; if there is white lithium metal precipitation and the lithium precipitation area accounts for greater than or equal to 5%, it is recorded as significant lithium precipitation. The lithium precipitation area ratio is the percentage of the lithium precipitation area to the outermost interface area.

[0123] The 0℃_1.5C_lithium deposition test is used to characterize the kinetic performance of lithium-ion batteries.

[0124] PD1, PD2, PD3 testing:

[0125] PD2: Compacted density of the second material layer = mass of the second material layer per unit area (in g / cm 2 ) / thickness of the second material layer (in cm). The mass of the second material layer per unit area was measured using a balance, and the thickness of the second material layer was measured using a micrometer.

[0126] The average compacted density of the first material layer PD = the mass of the first material layer per unit area (unit: g / cm 2 ) / thickness of the first material layer (in cm). The mass of the first material layer per unit area is measured by a balance, and the thickness of the first material layer is measured by a micrometer.

[0127] PD1 and PD3 can be calculated from the measured average compaction density PD, S1, S2, and h1-h2.

[0128] PD=(PD1×S1+PD3(S2-S1)) / S2 Formula A

[0129] PD1×(H3-(h1-h2))=PD3×H3 Formula B

[0130] The values ​​of PD1 and PD3 are obtained by the above-mentioned equations A and B.

[0131] Size Measurements:

[0132] H1, h1, h2, H3: The cross section of the single-sided positive electrode sheet along the thickness direction is ion polished and the cross section of the sheet is observed and measured under a scanning electron microscope H1, h1, h2, H3.

[0133] H2, H4: The cross section of the double-sided positive electrode sheet along the thickness direction is ion polished to obtain the cross section of the electrode sheet and observed and measured under a scanning electron microscope H2, H4.

[0134] D1, L1, D1', L1', S1: Place the first material layer of the single-sided positive electrode face up under a VHX5000 microscope with the magnification set to 50 to 200 times; take a photo of the surface of the first material layer, use the microscope software to measure D1, L1, D1', L1', and calculate S1. S2 = 55 × 91.5 = 5032.5 mm 2 , and then calculate S1 / S2.

[0135] D2: Place the first positive electrode current collector of the single-sided positive electrode sheet facing upward under a VHX5000 microscope with the magnification set to 50 to 200 times; take a photo of the surface of the first positive electrode current collector and measure D2 using the microscope software.

[0136] The above dimensions were measured at 10 points and the average value was taken as the final result.

[0137] Example 1

[0138] <Preparation of positive electrode slurry>

[0139] The positive electrode active material LiCoO2, the conductive agent acetylene black, and the binder polyvinylidene fluoride were mixed in a mass ratio of 97:1:2, and N-methylpyrrolidone (NMP) was added as a solvent to prepare a slurry with a solid content of 75wt%. The positive electrode slurry was obtained after vacuum stirring.

[0140] <Preparation of single-sided positive electrode sheet>

[0141] The positive electrode slurry was evenly coated on one surface of a first positive electrode current collector aluminum foil with a thickness H1 of 10 μm and dried at 85°C to obtain a positive electrode sheet coated on one side with a 120 μm thick positive electrode material layer. A first cold pressing process was then performed using a press roller, followed by a second cold pressing process using a press roller with projections to obtain a single-sided positive electrode sheet. Concave portions were formed on the surface of the first material layer, and convex portions were formed on the surface of the first current collector. The convex and concave portions corresponded to each other and were distributed in an array of dots. The orthographic projections of the convex and concave portions were both circular. The pressure of the first cold pressing process was P1 = 80t, and the pressure of the second cold pressing process was P2 = 20t. The sheet was vacuum dried at 85°C for 8 hours, and then cut into pieces and welded to the tabs to obtain a single-sided positive electrode sheet with a size of 55 mm × 91.5 mm for later use. Where h1 = 20 μm, h2 = 18.91 μm, D1 = 0.5 mm, D2 = 0.65 mm, L1 = 1.5 mm, PD1 = 4.13 g / cm 3 , PD3=4.05g / cm 3 , H3=53.7μm.

[0142] <Preparation of double-sided positive electrode sheet>

[0143] The positive electrode slurry is evenly coated on one surface of the second positive electrode current collector aluminum foil with a thickness H2 of 10μm, and dried at 85℃ to obtain a positive electrode sheet with a single-sided positive electrode material layer coated with 120μm thick. Then repeat the above steps on the other surface of the aluminum foil to obtain a positive electrode sheet with a double-sided positive electrode material layer coated. Then cold pressing is carried out, and the pressure of the cold pressing treatment P3 = 95t; then vacuum drying is carried out at 85℃ for 8h, and after cutting and welding the tabs, a double-sided positive electrode sheet with a specification of 55mm×91.5mm is obtained for standby use. Among them, PD2 = 4.23g / cm 3 The thickness of the single-sided second material layer is 53.2 μm.

[0144] <Preparation of negative electrode sheet>

[0145] The negative electrode active material, artificial graphite, the binder, styrene-butadiene rubber, and the conductive agent, acetylene black, were mixed in a mass ratio of 96:2:2. Deionized water was added as a solvent to form a slurry with a solid content of 45 wt%. The mixture was then stirred evenly in a vacuum mixer to obtain a negative electrode slurry. The negative electrode slurry was evenly coated on one surface of a 6 μm thick copper foil, a negative electrode current collector, and dried at 85°C to obtain a negative electrode sheet coated on one side with a 100 μm thick negative electrode material layer. The above steps were repeated on the other surface of the copper foil to obtain a negative electrode sheet coated on both sides with a negative electrode material layer. After cold pressing, cutting, and welding the tabs, the sheet was vacuum dried at 120°C for 12 hours to obtain a negative electrode sheet measuring 56 mm x 93 mm for use. The thickness of the negative electrode material layer on one side was 66.5 μm.

[0146] <Preparation of Electrolyte>

[0147] In an environment with a water content of less than 10 ppm, ethylene carbonate, propylene carbonate, and diethyl carbonate are mixed in a mass ratio of 1:1:1 to obtain an organic solvent. An electrolyte salt, LiPF6, is then added to the organic solvent and mixed thoroughly to obtain an electrolyte solution. The molar concentration of the electrolyte salt is 1.15 mol / L based on the mass of the electrolyte solution.

[0148] <Diaphragm>

[0149] A porous polyethylene film with a thickness of 7 μm (supplied by Celgard) was used as the separator.

[0150] <Preparation of lithium-ion batteries>

[0151] The above-prepared separator, negative electrode sheet, separator, double-sided positive electrode sheet, separator, negative electrode sheet, and separator are stacked in order, and single-sided positive electrode sheets are placed on the outermost sides with the first material layer facing the negative electrode sheet. The four corners of the entire stack are then secured with tape to obtain a stacked electrode assembly. The electrode assembly is placed in an aluminum-plastic film packaging bag and dehydrated at 80°C. The above-prepared electrolyte is then injected. The lithium-ion battery is produced through vacuum packaging, standing, formation, shaping, capacity measurement, degassing, and trimming. The formation temperature is 80°C and the formation standing time is 2 hours.

[0152] Examples 2 to 34

[0153] Except for adjusting the relevant preparation parameters according to Table 1, the rest is the same as Example 1. The "dot pattern" in Table 1 refers to the distribution of the concave portions in an array of dot patterns, "horizontal pattern" refers to the distribution of the concave portions in a stripe pattern and the stripes are perpendicular to the short side of the single-sided positive electrode sheet, "vertical pattern" refers to the distribution of the concave portions in a stripe pattern and the stripes are perpendicular to the long side of the single-sided positive electrode sheet, and "grid pattern" refers to the simultaneous provision of horizontal and vertical patterns. The positive electrode active material in Example 9 is lithium iron phosphate, and the positive electrode active material in Example 34 is LiNi 0.8 Co 0.1 Mn 0.1 O2, the rest of the embodiments are the same as Example 1.

[0154] Comparative Example 1

[0155] Except that the second cold pressing process is not performed when preparing the single-sided positive electrode sheet and P1=95t, the rest is the same as Example 1.

[0156] Comparative Examples 2 to 5

[0157] Except for adjusting the relevant preparation parameters according to Table 1, the rest is the same as Example 1. The "dot pattern" in Table 1 refers to the concave portions being distributed in an array of dots.

[0158] The relevant preparation parameters and performance tests of each embodiment and comparative example are shown in Table 1 and Table 2.

[0159] Table 2

[0160] Note: “ / ” in Table 2 indicates that there is no relevant performance.

[0161] From Examples 1 to 34 and Comparative Examples 1 to 5, it can be seen that the first current collector of the single-sided positive electrode sheet in the embodiment has a convex portion, the first material layer has a concave portion, and 1≤H1 / H2≤2.5, PD1 / PD2≥0.925, PD3+0.05g / cm 3 <PD1, the curling rate of the single-sided positive electrode sheet is smaller, the number of lithium-ion batteries that pass the drop test is large, the cycle capacity retention rate is high, and there are no black spots on the surface of the negative electrode sheet adjacent to the single-sided positive electrode sheet. However, the lithium-ion batteries in Comparative Examples 1 and 5 both have black spots and lithium plating problems, the curling rate of the single-sided positive electrode sheet in Comparative Examples 2 and 4 is high, and the single-sided positive electrode sheet in Comparative Example 3 is damaged, and the lithium-ion battery cannot be prepared. This shows that the kinetic performance of the lithium-ion battery that meets the requirements of this application is improved, while the curling problem of the single-sided positive electrode sheet is improved, and the lithium-ion battery also has good cycle performance.

[0162] The thickness H1 of the first positive electrode collector usually affects the curling rate of the single-sided positive electrode sheet, and H1 and the thickness H2 of the second positive electrode collector usually affect the cycle performance of the lithium-ion battery. It can be seen from Examples 1 to 8 that when the thickness H1 of the first positive electrode collector and the thickness H2 of the second positive electrode collector are within the scope of this application, the curling rate of the single-sided positive electrode sheet is small, the number of lithium-ion batteries passing the drop test is large, the cycle capacity retention rate is high, and the surface of the negative electrode sheet adjacent to the single-sided positive electrode sheet is free of black spots and lithium deposition. This shows that the lithium-ion battery of the above embodiment has good dynamic performance, while the curling problem of the single-sided positive electrode sheet is improved and the lithium-ion battery also has good cycle performance.

[0163] The compaction density PD1 of the concave portion, the compaction density PD2 of the second material layer, the compaction density PD3 of the non-concave portion, and PD2-PD3 usually affect the dynamic performance, cycle performance, and curling rate of the single-sided positive electrode sheet of the lithium-ion battery. It can be seen from Example 2, Example 9 to Example 13 that when PD1, PD2, PD3, and PD2-PD3 are within the scope of this application, the curling rate of the single-sided positive electrode sheet is small, the number of passes in the drop test of the obtained lithium-ion battery is large, the cycle capacity retention rate is high, and the surface of the negative electrode sheet adjacent to the single-sided positive electrode sheet is free of black spots and lithium deposition. This shows that the lithium-ion battery of the above embodiment has good dynamic performance, while the curling problem of the single-sided positive electrode sheet is improved and the lithium-ion battery also has good cycle performance.

[0164] The size and distribution of the concave and convex portions usually affect the dynamic performance, cycle performance, and curling rate of the single-sided positive electrode sheet of the lithium-ion battery. It can be seen from Examples 2, 14 to 34 that when the concave portions are distributed in a dotted or striped manner, and the depth h1 of the concave portions, the height h2 of the convex portions, h1-h2, D1, L1, D2, D1', L1', and S1 / S2 are within the scope of this application, the curling rate of the single-sided positive electrode sheet is small, the number of passes in the drop test of the obtained lithium-ion battery is large, the cycle capacity retention rate is high, and the surface of the negative electrode sheet adjacent to the single-sided positive electrode sheet is free of black spots and lithium deposition. This shows that the lithium-ion battery of the above embodiment has good dynamic performance, while the curling problem of the single-sided positive electrode sheet is improved and the lithium-ion battery also has good cycle performance.

[0165] The above description is only a preferred embodiment of the present application and is not intended to limit the present application. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present application shall be included in the scope of protection of the present application.

Claims

1. A secondary battery, comprising a laminated electrode assembly, the electrode assembly including a positive electrode tab, a separator, and a negative electrode tab, the positive electrode tab including a double-sided positive electrode tab and a single-sided positive electrode tab located on the outermost side of the electrode assembly in the lamination direction; The single-sided positive electrode tab includes a first positive current collector and a first material layer provided on one surface of the first positive current collector, the first positive current collector having a plurality of protrusions, the first material layer having a plurality of recesses, the protrusions and the recesses corresponding to each other one by one; the double-sided positive electrode tab includes a second positive current collector and second material layers provided on two surfaces of the second positive current collector, the first material layer facing the negative electrode tab; The thickness of the first positive current collector is H1, the thickness of the second positive current collector is H2, and 1 ≤ H1 / H2 ≤ 2.5; The compaction density of the concave portion is PD1, the compaction density of the second material layer is PD2, and the compaction density of the first material layer other than the concave portion is PD3, PD1 / PD2≥0.929, PD3+0.05g / cm 3 <PD1.

2. The secondary battery according to claim 1, which satisfies at least one of the following features: (1) 1 ≤ H1 / H2 ≤ 2; (2) 0.929 ≤ PD1 / PD2 ≤ 1.

3. The secondary battery according to claim 1, which satisfies at least one of the following features: (1) The first positive current collector is aluminum foil, and 8 μm ≤ H1 ≤ 20 μm; (2) The second positive current collector is aluminum foil, and 8 μm ≤ H2 ≤ 12 μm.

4. The secondary battery according to claim 1, wherein 2.3g / cm 3 ≤PD1≤4.35g / cm 3 ,2.4g / cm 3 ≤PD2≤4.35g / cm 3 。 5. The secondary battery according to claim 1, wherein The first material layer and / or the second material layer includes lithium cobalt oxide, 3.93 g / cm 3 ≤PD1≤4.35g / cm 3 , 4.03g / cm 3 ≤PD2≤4.35g / cm 3 .

6. The secondary battery according to claim 1, wherein PD3+0.05g / cm 3 <PD1≤PD3+0.15g / cm 3 。 7. The secondary battery according to claim 1, wherein The depth of the recess is h1, the height of the protrusion is h2, and h1 ≥ h2.

8. The secondary battery according to claim 7, which satisfies: 0 g / cm 3 ≤PD2-PD3≤0.43g / cm 3 , 0μm≤h1-h2≤3μm.

9. The secondary battery according to claim 7, wherein 3 μm ≤ h1 ≤ 50 μm, 2.64 μm ≤ h2 ≤ 48 μm.

10. The secondary battery according to any one of claims 1 to 9, wherein The plurality of recesses are distributed in a dot pattern. Along the thickness direction of the single-sided positive electrode tab, the shape of the orthographic projection of a single recess includes at least one of a circle, an ellipse, and a polygon. The diameter D1 of the largest circumscribed circle of the outer contour of the orthographic projection of a single recess is 0.3 mm to 4 mm, and the minimum distance L1 between the outer contours of the orthographic projections of two adjacent recesses is 1 mm to 5 mm.

11. The secondary battery according to claim 10, wherein [[ID=\\(8\\)]]Along the thickness direction of the single-sided positive electrode tab, the diameter of the largest circumscribed circle of the outer contour of the orthographic projection of a single protrusion is D2, D2 - 0.2 mm < D1 < D2, preferably, D2 - 0.18 mm < D1 < D2.

12. The secondary battery according to any one of claims 1 to 9, wherein The plurality of recesses are distributed in a stripe pattern. Along the thickness direction of the single-sided positive electrode tab, the shape of the orthographic projection of a single recess includes a strip shape, the width D1' of the orthographic projection of a single recess is 0.2 mm to 4 mm, and the minimum distance L1' between the outer contours of the orthographic projections of two adjacent recesses is 0.5 mm to 5 mm.

13. The secondary battery according to any one of claims 1 to 9, wherein Along the thickness direction of the single-sided positive electrode tab, the total area of the orthographic projections of the plurality of recesses is S1, the area of the single-sided positive electrode tab is S2, and 0.02 ≤ S1 / S2 ≤ 0.

44.

14. The secondary battery according to any one of claims 1 to 9, which satisfies at least one of the following features: (1) 1 ≤ H1 / H2 ≤ 1.5; (2) The thickness H3 of the region of the first material layer except for the recesses is 25 μm to 70 μm.

15. An electronic device, comprising the secondary battery according to any one of claims 1 to 14.

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