Secondary battery and electronic device

Abstract

A secondary battery and an electronic device. The secondary battery comprises an electrode assembly having a wound structure; the electrode assembly comprises a positive electrode sheet, a negative electrode sheet and a separator; the positive electrode sheet comprises a positive electrode current collector and a positive electrode material layer; the positive electrode sheet comprises a corner area of a first turn starting from the winding center; the corner area is provided with a plurality of stripe-shaped protrusions located between the current collector and the positive electrode material layer, and the plurality of stripe-shaped protrusions are arranged at intervals; the included angle α between a single stripe-shaped protrusion and the length direction of the positive electrode sheet is 20°-70°. By providing the stripe-shaped protrusions and configuring the included angle α to be within the above range, the strength and the compaction window of the positive electrode sheet can be improved, the brittleness of the high-compaction positive electrode sheet is reduced, and therefore the energy density and the safety performance of the secondary battery are both improved.

Description

Secondary battery and electronic device

[0001] This application claims priority to the Chinese patent application filed with the China Patent Office on March 31, 2024, with application number 202410383479.5 and invention name “A Secondary Battery and Electronic Device”, the entire contents of which are incorporated by reference into this application. Technical Field

[0002] The present application relates to the field of electrochemical technology, and in particular to a secondary battery and an electronic device. Background Art

[0003] Secondary batteries, such as lithium-ion batteries, are widely used in consumer electronics, power generation, energy storage, and other fields due to their high energy density, high dynamics, and long life. They are currently the focus of attention in the new energy sector. With the continuous advancement and innovation of technology, people's demand for higher energy density is becoming more and more urgent.

[0004] High-energy-density lithium-ion batteries inevitably require higher electrode density. However, for electrode assemblies with winding technology, when the pressure reaches a certain level, the positive electrode density is slightly improved. This is mainly because after the compaction density reaches a certain level, the positive electrode is brittle and the unit fracture strength drops sharply, affecting the safety performance of the secondary battery. Considering the subsequent process optimization of electrode routing, bending, cutting, etc., it is usually difficult to achieve both high density and brittle fracture resistance of the positive electrode, and it is also difficult to take into account the energy density and safety performance of the secondary battery. Summary of the Invention

[0005] The purpose of the present application is to provide a secondary battery and an electronic device to reduce the brittle fracture of a high-pressure dense positive electrode plate, while taking into account both the energy density and safety performance of the secondary 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, which includes an electrode assembly of a wound structure, the electrode assembly including a positive electrode sheet, a negative electrode sheet and a separator, the positive electrode sheet including a positive electrode current collector and a positive electrode material layer; the positive electrode sheet includes a corner area of ​​the first circle starting from the winding center, the corner area is provided with a plurality of striped protrusions located between the current collector and the positive electrode material layer, and the plurality of striped protrusions are arranged at intervals; the angle α between a single striped protrusion and the length direction of the positive electrode sheet is 20° to 70°. In some embodiments of the present application, 40°≤α≤50°. By setting the striped protrusions and the angle α within the above range, the strength of the positive electrode sheet can be improved and the brittle fracture of the high-pressure positive electrode sheet can be reduced, thereby taking into account both the energy density and safety performance of the secondary battery.

[0008] In some embodiments of the present application, the spacing d between two adjacent stripe protrusions is 50μm to 500μm, the width L of a single stripe protrusion is 10μm to 300μm, and the height h1 is 0.5μm to 10μm. In some embodiments of the present application, 50μm≤d≤200μm, 20μm≤L≤50μm, and 1μm≤h1≤4μm. By regulating d, L, and h1 within the above ranges, the distribution density of the stripe protrusions on the positive electrode current collector is appropriate, which can enhance the strength of the positive electrode sheet and improve the compaction window of the positive electrode sheet. When preparing a high-pressure compaction positive electrode sheet, it is less likely to have a brittle fracture problem, thereby reducing the brittle fracture of the high-pressure compaction positive electrode sheet and taking into account the energy density and safety performance of the secondary battery.

[0009] In some embodiments of the present application, the total area of ​​the orthographic projections of the plurality of striped protrusions on the surface of the positive electrode current collector is S1, the area of ​​the positive electrode current collector in the corner region is S2, and 0.057≤S1 / S2≤0.500. By regulating S1 / S2 within the above range, the distribution density of the striped protrusions on the positive electrode current collector is appropriate, which can enhance the strength of the positive electrode sheet and improve the compaction window of the positive electrode sheet. When preparing a high-pressure positive electrode sheet, it is less likely to have brittle fracture problems, thereby reducing the brittle fracture of the high-pressure positive electrode sheet and taking into account both the energy density and safety performance of the secondary battery.

[0010] In some embodiments of the present application, the height of a single stripe protrusion is h1, the thickness of the positive electrode material layer is h2, and 0.01≤h1 / h2≤0.21. By regulating the value of h1 / h2 within the above range, the compaction density can be increased at different coating surface densities, avoiding excessive space occupation and resulting in insufficient benefits due to overdesign, while also avoiding a narrow window for compaction density improvement due to insufficient design.

[0011] In some embodiments of the present application, the plurality of striped protrusions include a plurality of first stripes and a plurality of second stripes, the plurality of first stripes are arranged on one surface of the positive electrode current collector, the plurality of second stripes are arranged on the other surface of the positive electrode current collector, and the angle β formed by a single first stripe and a single second stripe is 40° to 140°. By simultaneously arranging the first stripes and the second stripes on both surfaces of the positive electrode current collector, the strength of the positive electrode pole piece can be further improved, and the compression window of the positive electrode pole piece can be enhanced, so that when preparing a high-pressure-density positive electrode pole piece, it is less likely to have a brittle fracture problem. At the same time, by regulating the angle β within the above range, the force on both sides of the positive electrode current collector can be made more uniform, and the strength improvement can be more ideal. Combining the strength advantages of both sides, a better compression window improvement effect can be achieved. This further reduces the brittle fracture of the high-pressure-density positive electrode pole piece, while taking into account the energy density and safety performance of the secondary battery.

[0012] In some embodiments of the present application, the striped convex portion includes an organic material and a conductive material, the organic material includes at least one of polyacrylonitrile, polyethylene glycol, styrene-butadiene rubber, nylon, water-based polyamide resin, dimethyl silicone rubber, polyacrylic acid, polymethyl methacrylate or polyvinylidene fluoride, the conductive material includes at least one of graphite and conductive fiber, and the mass ratio of the organic material to the conductive material is (4 to 49): 1. The striped convex portion includes an organic material and a conductive material and regulates the mass ratio X within the above range. While improving the problem of easy brittle fracture of the high-pressure dense positive electrode sheet, it also has little effect on the conductivity of the positive electrode sheet, and can take into account the strength and conductivity of the positive electrode sheet. In addition, the above-mentioned organic materials and conductive materials have a high spectrum, which is conducive to broadening the scope of application.

[0013] In some embodiments of the present application, the thickness h3 of the positive electrode current collector is 8 μm to 10 μm. By adjusting the thickness h3 of the positive electrode current collector within the above range, the positive electrode current collector thickness is appropriate, the resulting secondary battery has a high energy density, and the production process has a high efficiency, which is conducive to industrialization.

[0014] In some embodiments of the present application, the compaction density PD of the positive electrode material layer is greater than or equal to 4.24 g / cm 3 The compaction density PD of the positive electrode material layer is within the above range, indicating that the positive electrode material layer is highly compacted, thereby facilitating the production of a secondary battery with high energy density.

[0015] In some embodiments of the present application, the secondary battery satisfies at least one of the following characteristics:

[0016] (1) The coating area density of the positive electrode material layer is 240 mg / 1540.25 mm 2 Up to 400mg / 1540.25mm 2 ;

[0017] (2) The unit fracture strength of the positive electrode plate is 150 MPa to 270 MPa;

[0018] (3) The thickness h2 of the positive electrode material layer is 36 μm to 61 μm.

[0019] A secondary battery satisfying at least one of the above characteristics can achieve both energy density and safety performance.

[0020] A second aspect of the present application provides an electronic device comprising the secondary battery according to any one of the aforementioned embodiments.

[0021] Beneficial effects of this application:

[0022] The present application provides a secondary battery and an electronic device, wherein the secondary battery includes an electrode assembly of a wound structure, the electrode assembly includes a positive electrode sheet, a negative electrode sheet and a separator, the positive electrode sheet includes a positive current collector and a positive electrode material layer; the positive electrode sheet includes a corner area of ​​the first corner starting from the winding center, the corner area is provided with a plurality of striped protrusions located between the current collector and the positive electrode material layer, and the plurality of striped protrusions are arranged at intervals; the angle α between a single striped protrusion and the length direction of the positive electrode sheet is 20° to 70°. In some embodiments of the present application, 40°≤α≤50°. By setting the striped protrusions and the angle α within the above range, the strength and compaction window of the positive electrode sheet can be improved, and the brittle fracture of the high-pressure compaction positive electrode sheet can be reduced, thereby taking into account both the energy density and safety performance of the secondary battery.

[0023] Of course, it is not necessary to achieve all the advantages described above at the same time when implementing any product or method of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] 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.

[0025] FIG1 is a schematic diagram of a cross-sectional structure of an electrode assembly along its thickness direction in some embodiments of the present application;

[0026] FIG2 is a schematic diagram of a partial structure of a positive electrode sheet in some embodiments of the present application;

[0027] FIG3 is a schematic structural diagram of a positive electrode current collector provided with striped convex portions in some embodiments of the present application;

[0028] FIG4 is a schematic structural diagram of a positive electrode current collector provided with striped convex portions in some other embodiments of the present application. DETAILED DESCRIPTION

[0029] 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.

[0030] 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.

[0031] Currently, the following methods are commonly used to address the brittle fracture of high-density cathode plates: adding additives to the cathode material layer to soften it, or using a high-strength cathode current collector. Adding additives such as paraffin wax, glycerol, and flake graphite to the material layer can soften the cathode material layer and improve its compaction to a certain extent, but this often leads to binder failure, affecting the safety performance of the secondary battery. High-strength cathode current collectors have limited effectiveness in improving compaction and remedying the brittle fracture problem, and are typically thick, which affects the energy density of the secondary battery.

[0032] Based on the above problems, the present application provides a secondary battery and an electronic device to reduce the brittle fracture of the high-voltage dense positive electrode plate, while taking into account the energy density and safety performance of the secondary battery.

[0033] The first aspect of the present application provides a secondary battery comprising a wound electrode assembly, as shown in Figures 1 and 2. The electrode assembly includes a positive electrode sheet 10, a negative electrode sheet 20, and a separator 30. The positive electrode sheet 10 includes a positive current collector 11 and a positive electrode material layer 12, with the positive electrode material layer 12 disposed on both surfaces of the positive electrode collector 11. The positive electrode sheet 10 includes a corner region 13 at the corner of the first turn from the winding center. The corner region 13 is provided with a plurality of striped protrusions 14 located between the positive electrode collector 11 and the positive electrode material layer 12, with the plurality of striped protrusions 14 spaced apart. The positive electrode sheet 10 is wound from the winding center, i.e., the first turn, i.e., the region between line segment A-A'. The corner region 13 of the first turn is also the region between line segment B-B'. As shown in Figure 3, the angle α formed between a single striped protrusion 14 and the length direction of the positive electrode sheet is 20° to 70°. In some embodiments of the present application, 40°≤α≤50°. For example, the angle α can be 20°, 25°, 30°, 35°, 40°, 45°, 50°, 55°, 60°, 65°, 70°, or a range consisting of any two values ​​therebetween. The striped protrusions are arranged on the positive electrode current collector and have an angle α, which can enhance the strength of the positive electrode sheet and improve the compaction window of the positive electrode sheet, so that when preparing a high-pressure compaction positive electrode sheet, it is less likely to have a brittle fracture problem. When the angle α is too small, for example, less than 20°, the angle difference between the striped protrusion and the longitudinal direction is small, and the positive electrode sheet is easily broken in the fixed area during the winding process; when the angle α is too large, for example, greater than 70°, the angle difference between the striped protrusion and the longitudinal direction is too large. After the compaction density is increased, when the wound positive electrode sheet is bent, the striped protrusion layer cannot share the bending deformation force of the positive electrode current collector, resulting in the positive electrode sheet bending and breaking, so that the compaction density window cannot be improved. Therefore, by setting the stripe protrusions and the angle α within the above range, the strength and compaction window of the positive electrode sheet can be improved, and the brittle fracture of the high-pressure compaction positive electrode sheet can be reduced, thereby taking into account both the energy density and safety performance of the secondary battery.

[0034] In the present application, in the first turn of the wound electrode assembly starting from the winding center, the area where the positive electrode sheet has a fold is recorded as the corner area, specifically the area where the fold extends 2 mm to both sides.

[0035] In some embodiments of the present application, multiple striped coatings can be provided in areas other than the corners of the first circle of the positive electrode sheet, which is more conducive to industrial production. In some embodiments of the present application, multiple striped coatings are provided in the corners of both the first and second circles of the positive electrode sheet, which can further reduce the brittle fracture of the high-pressure positive electrode sheet, while ensuring both the energy density and safety performance of the secondary battery.

[0036] In this application, multiple stripe protrusions are parallel to each other; the length direction of the positive electrode sheet is the direction of the longer side of the positive electrode sheet; the high-density positive electrode sheet refers to a positive electrode material layer with a compaction density greater than 4.24g / cm 3 The positive electrode.

[0037] In some embodiments of the present application, the spacing d between two adjacent stripe convex portions is 50 μm to 500 μm, the width L of a single stripe convex portion is 10 μm to 300 μm, and the height h1 is 0.5 μm to 10 μm. In some embodiments of the present application, 50 μm ≤ d ≤ 200 μm, 20 μm ≤ L ≤ 50 μm, and 1 μm ≤ h1 ≤ 4 μm. For example, d can be 50 μm, 60 μm, 70 μm, 80 μm, 90 μm, 100 μm, 120 μm, 140 μm, 150 μm, 170 μm, 190 μm, 200 μm, 250 μm, 300 μm, 350 μm, 400 μm, 450 μm, or a range consisting of any two values ​​therebetween. For example, L may be 10 μm, 15 μm, 20 μm, 25 μm, 30 μm, 35 μm, 40 μm, 45 μm, 50 μm, 60 μm, 70 μm, 80 μm, 90 μm, 100 μm, 125 μm, 150 μm, 175 μm, 200 μm, 225 μm, 250 μm, 275 μm, 300 μm, or a range consisting of any two values ​​therebetween. For example, h1 may be 0.5 μm, 1 μm, 1.5 μm, 2 μm, 2.5 μm, 3 μm, 3.5 μm, 4 μm, 4.5 μm, 5 μm, 5.5 μm, 6 μm, 6.5 μm, 7 μm, 7.5 μm, 8 μm, 8.5 μm, 9 μm, 9.5 μm, 10 μm, or a range consisting of any two values ​​therebetween. By regulating d, L, and h1 within the above ranges, the distribution density of the stripe protrusions on the positive electrode current collector is appropriate, which can enhance the strength of the positive electrode sheet and improve the compression window of the positive electrode sheet. When preparing high-pressure-density positive electrode sheets, it is less likely to have brittle fracture problems, thereby reducing the brittle fracture of high-pressure-density positive electrode sheets and taking into account the energy density and safety performance of the secondary battery.

[0038] In some embodiments of the present application, the total area of ​​the positive projection of the plurality of stripe protrusions on the surface of the positive electrode current collector is S1, the area of ​​the positive electrode current collector in the corner area is S2, and 0.057≤S1 / S2≤0.500. For example, S1 / S2 can be 0.057, 0.060, 0.070, 0.080, 0.090, 0.100, 0.150, 0.200, 0.250, 0.300, 0.350, 0.400, 0.450, 0.500 or a range consisting of any two values ​​therebetween. By regulating S1 / S2 within the above range, the distribution density of the stripe protrusions on the positive electrode current collector is appropriate, the strength of the positive electrode sheet can be enhanced, the compaction window of the positive electrode sheet is improved, and when preparing a high-pressure compaction positive electrode sheet, it is not easy to have a brittle fracture problem, thereby reducing the brittle fracture of the high-pressure compaction positive electrode sheet, taking into account the energy density and safety performance of the secondary battery.

[0039] In some embodiments of the present application, the height of a single stripe convex portion is h1, the thickness of the positive electrode material layer is h2, and 0.01≤h1 / h2≤0.21. For example, h1 / h2 can be 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, 0.11, 0.12, 0.13, 0.14, 0.15, 0.16, 0.17, 0.18, 0.19, 0.20, 0.21, or a range consisting of any two values ​​therebetween. By regulating the value of h1 / h2 within the above range, the compaction density under different coating surface densities can be improved, without overdesigning and taking up too much space to cause too little benefit, and without insufficient compaction density improvement window due to insufficient design.

[0040] In some embodiments of the present application, the thickness h2 of the positive electrode material layer is 36 μm to 61 μm. For example, h2 can be 36 μm, 37 μm, 38 μm, 39 μm, 40 μm, 42 μm, 44 μm, 45 μm, 46 μm, 48 μm, 50 μm, 52 μm, 54 μm, 55 μm, 56 μm, 58 μm, 60 μm, 61 μm, or a range consisting of any two values ​​therebetween. By regulating the thickness h2 of the positive electrode material layer within the above range, the striped convex portion design can be used to maximize the energy density, while taking into account the energy density and safety performance of the secondary battery.

[0041] In some embodiments of the present application, as shown in FIG4 , the plurality of striped protrusions 14 include a plurality of first stripes 141 and a plurality of second stripes 142. The plurality of first stripes 141 are disposed on one surface of the positive electrode current collector 11, and the plurality of second stripes 142 are disposed on the other surface of the positive electrode current collector 11. The angle β formed by each first stripe and each second stripe is between 40° and 140°. For example, the angle β can be 40°, 50°, 60°, 70°, 80°, 90°, 100°, 110°, 120°, 130°, 140°, or a range consisting of any two values ​​therebetween. Providing both first and second stripes on both surfaces of the positive electrode current collector can further enhance the strength of the positive electrode sheet and increase the compression window of the positive electrode sheet, thereby reducing the risk of brittle fracture when producing a high-pressure-density positive electrode sheet. Simultaneously regulating the angle β within the above range can ensure more uniform force distribution on both sides of the positive electrode current collector, resulting in a more ideal strength increase. Combining the strength advantages of both surfaces can achieve a better compression window improvement. This further reduces the brittle fracture of the high-pressure, high-density positive electrode sheet, while taking into account both the energy density and safety performance of the secondary battery. In this application, the angle β refers to the angle between the orthographic projection of a single first stripe and the orthographic projection of a single second stripe along the thickness direction of the positive electrode sheet.

[0042] In some embodiments of the present application, the striped convex portion includes an organic material and a conductive material, the organic material includes at least one of polyacrylonitrile, polyethylene glycol, styrene-butadiene rubber, nylon, water-based polyamide resin, dimethyl silicone rubber, polyacrylic acid, polymethyl methacrylate or polyvinylidene fluoride, the conductive material includes at least one of graphite and conductive fiber, and the mass ratio X of the organic material and the conductive material is (4 to 49): 1. For example, the mass ratio X can be 4: 1, 5: 1, 10: 1, 15: 1, 20: 1, 25: 1, 30: 1, 35: 1, 40: 1, 45: 1, 49: 1 or a range consisting of any two ratios therebetween. The striped convex portion includes an organic material and a conductive material and regulates the mass ratio X within the above range. While improving the problem of easy brittle fracture of the high-pressure dense positive electrode sheet, it also has little effect on the conductivity of the positive electrode sheet, and can take into account both the strength and conductivity of the positive electrode sheet. In addition, the above-mentioned organic materials and conductive materials have a high spectrum, which is conducive to broadening the scope of application.

[0043] In some embodiments of the present application, the conductive fibers may include but are not limited to at least one of carbon nanotubes (CNTs), carbon fibers, or conductive polymer fibers. The carbon nanotubes may include but are not limited to single-walled carbon nanotubes and / or multi-walled carbon nanotubes. The carbon fibers may include but are not limited to vapor-grown carbon fibers (VGCFs) and / or nanofiber fibers. The conductive polymer fibers may include but are not limited to fibers formed from at least one of the following compounds: polyphenylene derivatives, polyaniline, polythiophene, polyacetylene, or polypyrrole.

[0044] In some embodiments of the present application, the thickness h3 of the positive electrode current collector is between 8 μm and 10 μm. For example, h3 can be 8 μm, 9 μm, 10 μm, or a range consisting of any two values ​​therebetween. By regulating the thickness h3 of the positive electrode current collector within the above range, the positive electrode current collector has an appropriate thickness, resulting in a secondary battery with high energy density and a high production process efficiency, which is conducive to industrialization.

[0045] In some embodiments of the present application, the compaction density PD of the positive electrode material layer is greater than or equal to 4.24 g / cm 3 In some embodiments of the present application, the compacted density PD of the positive electrode material layer is 4.24 g / cm 3 to 4.38g / cm 3 For example, the compacted density PD can be 4.24 g / cm 3 , 4.25g / cm 3 , 4.26g / cm 3 , 4.27g / cm 3 , 4.28g / cm 3 , 4.29g / cm 3 , 4.3g / cm 3 , 4.31g / cm 3 , 4.32g / cm 3 , 4.33g / cm 3 , 4.34g / cm 3 , 4.35g / cm 3 , 4.36g / cm 3 , 4.37g / cm 3 , 4.38g / cm 3 The positive electrode material layer compaction density PD is within the above range, indicating that the positive electrode material layer is highly compacted, thereby facilitating the production of a secondary battery with high energy density.

[0046] In some embodiments of the present application, the coating area density CW of the positive electrode material layer is 240 mg / 1540.25 mm 2 Up to 400mg / 1540.25mm 2 For example, the coating area density CW can be 240mg / 1540.25mm 2 、250mg / 1540.25mm 2 、260mg / 1540.25mm 2 、270mg / 1540.25mm 2 、280mg / 1540.25mm 2 、290mg / 1540.25mm 2、300mg / 1540.25mm 2 、310mg / 1540.25mm 2 、320mg / 1540.25mm 2 、330mg / 1540.25mm 2 、340mg / 1540.25mm 2 、350mg / 1540.25mm 2 、360mg / 1540.25mm 2 、370mg / 1540.25mm 2 、380mg / 1540.25mm 2 、390mg / 1540.25mm 2 , 400mg / 1540.25mm 2 The coating area density CW of the positive electrode material layer is within the above range, which indicates that the coating area density of the positive electrode material layer is high, thereby being conducive to obtaining a secondary battery with high energy density.

[0047] In some embodiments of the present application, the unit fracture strength F of the positive electrode sheet is 150 MPa to 270 MPa. For example, the unit fracture strength F can be 150 MPa, 160 MPa, 170 MPa, 180 MPa, 190 MPa, 210 MPa, 220 MPa, 230 MPa, 240 MPa, 250 MPa, 260 MPa, 270 MPa, or a range consisting of any two values ​​therebetween. The unit fracture strength of the positive electrode sheet within the above range indicates that it has high strength, which is beneficial to improving the safety performance of the secondary battery.

[0048] The present application does not impose any particular restrictions on the method for preparing the positive electrode sheet, as long as the objectives of the present application can be achieved. For example, the method for preparing the positive electrode sheet may include, but is not limited to, the following steps: adding an organic material and a conductive material to a solvent and mixing them to obtain a protrusion slurry; applying the protrusion slurry to one or both surfaces of the positive electrode current collector; and drying to form striped protrusions; and further providing a positive electrode material layer to obtain a positive electrode sheet. The above-mentioned solvent may include, but is not limited to, at least one of N-methylpyrrolidone and deionized water. The present application does not impose any particular restrictions on the solid content W of the protrusion slurry, as long as the objectives of the present application can be achieved. For example, the solid content W of the protrusion slurry may be 10% to 40%. It is understood that the striped protrusions may be fully or partially covered by the positive electrode material layer, and the selection can be made as required.

[0049] The present application does not particularly limit the method for regulating d, L, h1, α, and β, as long as the purpose of the present application can be achieved. For example, the size of d, L, and h1 can be regulated by controlling the solid content and coating amount of the protrusion slurry during the coating process, and α and β can be regulated by the coating angle and method.

[0050] The present application has no particular limitation on the positive electrode current collector, as long as the purpose of the present application can be achieved. For example, it may include aluminum foil, aluminum alloy foil or a composite current collector (such as an aluminum-carbon composite current collector).

[0051] The positive electrode material layer includes a positive electrode active material. The present application has no particular limitation on the positive electrode active material as long as the purpose of the present application can be achieved. For example, the positive electrode active material may include but is not limited to at least one of lithium nickel cobalt manganese oxide (such as NCM811, NCM622, NCM523, NCM111), lithium nickel cobalt aluminum oxide, lithium iron phosphate, lithium-rich manganese-based material, lithium cobalt oxide (LiCoO2), lithium manganese oxide, lithium iron manganese phosphate or lithium titanate.

[0052] 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.

[0053] In the present application, the negative electrode sheet includes a negative electrode current collector and a negative electrode material layer disposed on at least one surface of the negative electrode current collector. The phrase "the negative electrode material layer is disposed on at least one surface of the negative electrode current collector" means that the negative electrode material layer can be disposed on one surface of the negative electrode current collector along its thickness direction, or on both surfaces of the negative electrode current collector along its thickness direction. It should be noted that the "surface" here can refer to the entire surface of the negative electrode current collector or a portion of the surface of the negative electrode current collector. This is not particularly limited in the present application, as long as the purpose of this application can be achieved.

[0054] 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.

[0055] 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.

[0056] 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.

[0057] 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.

[0058] 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.

[0059] 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.

[0060] 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.

[0061] 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.

[0062] 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).

[0063] 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.

[0064] In the present application, the secondary battery further includes an electrolyte, and the electrolyte includes a lithium salt and a non-aqueous solvent.

[0065] 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.

[0066] The application has no particular restrictions on non-aqueous solvents, as long as the purpose of the application can be achieved, for example, non-aqueous solvents can include but are not limited to at least one of carbonate compounds, carboxylate compounds, ether compounds or other organic solvents. Above-mentioned carbonate compounds can include but are not limited to at least one of linear carbonate compounds, cyclic carbonate compounds or fluorinated carbonate compounds. Above-mentioned linear carbonate compounds can include but are not limited to at least one of dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC) or methyl ethyl carbonate (MEC). Above-mentioned cyclic carbonates can include but are not limited to at least one of ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC) or vinyl ethylene carbonate (VEC). The fluorinated carbonate compound may include, but is not limited to, at least one of fluoroethylene carbonate (FEC), 1,2-difluoroethylene carbonate, 1,1-difluoroethylene carbonate, 1,1,2-trifluoroethylene carbonate, 1,1,2,2-tetrafluoroethylene carbonate, 1-fluoro-2-methylethylene carbonate, 1-fluoro-1-methylethylene carbonate, 1,2-difluoro-1-methylethylene carbonate, 1,1,2-trifluoro-2-methylethylene carbonate, or trifluoromethylethylene carbonate. The above-mentioned carboxylate compound may include, but is not limited to, at least one of methyl formate, methyl acetate, ethyl acetate, n-propyl acetate, tert-butyl acetate, methyl propionate, ethyl propionate, propyl propionate, γ-butyrolactone, 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.

[0067] The secondary battery also includes a shell for accommodating the positive electrode sheet, the separator, the negative electrode sheet and the electrolyte, as well as other components known in the field of secondary batteries. This application does not limit the above-mentioned other components. This application does not particularly limit the shell, and it can be a shell known in the art, as long as it can achieve the purpose of this application. For example, the shell can be a hard shell or a flexible shell. The material of the hard shell can be metal. This application does not limit the type of metal. A metal hard shell known in the art can be used, as long as it can achieve the purpose of this application. The flexible shell can be a metal plastic film, such as an aluminum plastic film, a steel plastic film, etc.

[0068] 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 the positive electrode sheets, the separator and the negative electrode sheets in order, and winding, folding and other operations as needed to obtain an electrode assembly with a wound structure, placing the electrode assembly in a shell, injecting the electrolyte into the shell and sealing it to obtain a secondary battery. Alternatively, stacking the positive electrode sheets, the separator and the negative electrode sheets in order, and then fixing the four corners of the entire laminated structure with tape to obtain an electrode assembly with a laminated structure, placing the electrode assembly in a shell, injecting the electrolyte into the shell and sealing it to obtain a secondary battery. In addition, as needed, overcurrent protection elements, guide plates, etc. may be placed in the shell to prevent pressure rise and overcharge and discharge inside the secondary battery.

[0069] 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.

[0070] 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.

[0071] Example

[0072] 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.

[0073] Test methods and equipment:

[0074] Unit fracture strength test of positive electrode:

[0075] (1) Cut the positive electrode to be tested into strips with a width of 20 mm x 200 mm using a blade, and make sure there are no obvious burrs on the edges;

[0076] (2) Turn on the power of the Sansi tensile testing machine, the indicator light will light up, and adjust the limit block to the appropriate position;

[0077] (3) Clamp the two ends of the cut positive electrode sheet on the two clamps of the tensile testing machine;

[0078] (4) Set the speed to 10 mm / min, the test range to 0 mm to 100 mm, and start pulling the positive electrode straight at 180 degrees until it breaks. The test is over.

[0079] (5) Save the unit breaking strength test data according to the software prompts.

[0080] Processing performance test:

[0081] Winding performance: At a conveying speed of 35m / min and a tension of 3MPa, the positive electrode sheet is rolled onto a reel with a diameter of 100mm through a roller until the reel diameter reaches 500mm. If there is no bulging, breakage or damage to the electrode sheet during the process, the winding is normal. Otherwise, the winding is abnormal and the problems are recorded.

[0082] Winding inner ring breaks:

[0083] 1) After the separator, positive electrode sheet, separator and negative electrode sheet are stacked and wound to form a dry battery cell, they are compacted under a surface pressure of 0.5 MPa for 5 seconds.

[0084] 2) Then disassemble the dry cell to the innermost circle where the positive electrode material layer is bent. Confirm the innermost fold of the positive electrode sheet under strong light. The light-transmitting hole >200μm is recorded as 1 light-transmitting point. The grading judgment standard is:

[0085] a. There are 1 to 3 light transmission points that are critically light transmission, which is recorded as critical brittle fracture of the inner circle;

[0086] b. If the number of translucent points is greater than 3 or a single translucent point is greater than 2 mm, it is recorded as brittle fracture of the inner ring;

[0087] c. If there is no light-transmitting point, the inner circle is considered normal;

[0088] If both the winding performance and the winding inner ring fracture performance are normal, it is recorded as normal processing performance; if one of them is abnormal, it is recorded as risky processing performance.

[0089] DC internal resistance test:

[0090] The lithium-ion battery was placed in a 25°C high and low temperature chamber for 4 hours; it was charged at a constant current of 0.1C to a voltage of 4.5V, then charged at a constant voltage of 4.5V to a cut-off current of 0.05C and allowed to rest for 10 minutes; it was then discharged at a current of 0.2C for 10 seconds, at which point the voltage was recorded as V1 and the current as I1; it was then discharged at a constant current of 1C for 1 second, at which point the voltage was recorded as V2 and the current as I2; R = (V1-V2) / (I1-I2) was recorded as the DC internal resistance of the lithium-ion battery. When the DC internal resistance was less than 80mΩ, it was recorded as normal resistance; when the DC internal resistance was greater than or equal to 80mΩ, it was recorded as excessive internal resistance.

[0091] Positive electrode compaction density PD test:

[0092] Positive electrode sheet compaction density = mass of positive electrode material layer per unit area (unit: g / cm 2 ) / thickness of the positive electrode material layer (in cm). The mass of the positive electrode material layer per unit area can be weighed using a balance, and the thickness of the positive electrode material layer can be measured using a micrometer.

[0093] The highest compaction density that can be processed for the positive electrode sheets of each embodiment and comparative example is the maximum compaction density at which the positive electrode sheets do not have bulging edges, fractures, breakages, or light-transmitting spots.

[0094] Energy density test:

[0095] Place the lithium-ion battery in an environment of 25°C, charge it at a constant current of 1C to a voltage of 4.5V, then charge it at a constant voltage of 4.5V to a cutoff current of 0.2C, let it stand for 5 minutes, discharge it at a constant current of 0.2C to a voltage of 3.0V, let it stand for 5 minutes, record the discharge capacity at this time as C, and record the constant current value as I.

[0096] The lithium-ion battery was pressed along the thickness direction with a 600g flat plate, and the actual thickness D of the battery cell was measured with a micrometer; the length L' and width M of the lithium-ion battery were scanned and measured using a laser measuring instrument.

[0097] Then the actual energy density of lithium-ion battery is: X = C × I / (D × L' × M);

[0098] Energy density yield is recorded as Y: Y = (X-X0) / X0×100%

[0099] Wherein, X0 is the energy density of the lithium ion battery in Comparative Example 3, and X is the energy density of the lithium ion battery in each embodiment or comparative example.

[0100] Extrusion safety performance test:

[0101] (1) Place the lithium-ion battery under test in an environment of 25°C, charge it at a constant current of 0.5C to a voltage of 4.5V, then charge it at a constant voltage of 4.5V to a cut-off current of 0.05C, and let it stand for 5 minutes to reach a fully charged state;

[0102] (2) Check the appearance and take photos before and after the test;

[0103] (3) In a test environment of 20±5℃, place the lithium-ion battery on the test table, use a 25mm round rod to place it in the center of the lithium-ion battery, squeeze with a force of 5±0.78kN and a speed of 0.1mm / s, and maintain the squeeze force at the set value for 10s. The test ends when one of the following conditions is met: explosion, smoke, or fire.

[0104] (4) During the test, the voltage and internal resistance of the lithium-ion battery are monitored and measured using the 1KHZ specification;

[0105] (5) Judgment criteria: no explosion, no smoke, no fire, voltage drop <1.5V;

[0106] For each example or comparative example, 10 lithium-ion batteries were tested, and the number of batteries that passed was recorded, which was expressed as: number of passed batteries / number of experiments. For example, 9 / 10 means that 9 out of 10 lithium-ion batteries were tested and passed.

[0107] Measurement of d, L, h1, α, β:

[0108] Disassemble the lithium-ion battery and ion-polish the cross-section of the positive electrode along its thickness. Observe the protrusions and select one to measure its d, L, and h1. Soak the positive electrode in an NMP solution for 4 hours. Then, use ultrasound to remove the positive active layer, leaving only the positive current collector and the surface protrusions or traces of these protrusions. The protrusions or traces of these protrusions can be used to measure α, β, and the length of the protrusions. Ten measurements are performed on each of these dimensions, and the average value is used as the final result.

[0109] In the first turn of the wound electrode assembly, starting from the center of the winding, the area where the positive electrode sheet has a crease is marked as the corner area, specifically the area extending 2 mm to either side of the crease. S1 can be calculated using the above d, L, and the length of the convex portion of the stripe. S2 = 4 mm × the width of the positive electrode material layer, and then S1 / S2 is calculated.

[0110] Example 1

[0111] <Preparation of positive electrode sheet>

[0112] The organic material polyacrylic acid (PAA) and the conductive material graphite were mixed at a mass ratio X of 19:1, added into N-methylpyrrolidone and mixed evenly to obtain a convex portion slurry with a solid content W of 15% and a viscosity of 15000 mPa.s.

[0113] The positive electrode active material LiCoO2, the conductive agent Super P, and the binder polyvinylidene fluoride were mixed in a mass ratio of 97.9:0.9:1.2, and N-methylpyrrolidone (NMP) was added as a solvent to prepare a slurry with a solid content of 75wt%. After vacuum stirring, the positive electrode slurry was obtained.

[0114] The convex slurry was coated using a micro-gravure process onto one surface of an 8μm thick aluminum foil for the positive electrode current collector and dried at 100°C to produce multiple striped convex features on one surface of the foil. The slurry had d = 100μm, L = 30μm, h1 = 2μm, and α = 45°. The multiple striped convex features were applied only to the surface of the positive electrode current collector corresponding to the first circle of the positive electrode sheet.

[0115] Then, the positive electrode slurry is coated on the surface of the aluminum foil with multiple striped protrusions, dried at 120°C, and then coated on the other surface of the aluminum foil. After drying at 120°C, it is cold pressed, cut into pieces, and the tabs are welded to obtain a positive electrode sheet with a size of 74mm×867mm for use. The coating weight CW of the positive electrode material layer is 320mg / 1540mm 2 , the thickness h2 of the positive electrode material layer is 48 μm.

[0116] <Preparation of negative electrode sheet>

[0117] The negative electrode active material, artificial graphite, the binder, styrene-butadiene rubber, and sodium carboxymethyl cellulose 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 negative electrode current collector copper foil and dried at 120°C to obtain a negative electrode sheet coated on one side with a 100 μm thick layer of negative electrode active material. 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 active material layer. After drying at 120°C, the sheet was cold pressed, cut into pieces, and the tabs were welded to obtain a negative electrode sheet measuring 78 mm x 875 mm for future use. The thickness of the negative electrode material layer on one side was 54.5 μm.

[0118] <Preparation of Electrolyte>

[0119] In an environment with a water content of less than 10 ppm, ethylene carbonate (EC), propylene carbonate (PC), and diethyl carbonate (DEC) are mixed in a mass ratio of 1:1:1 to obtain an organic solvent. The electrolyte salt LiPF6 is then added to the organic solvent and mixed thoroughly to obtain an electrolyte solution. The electrolyte salt concentration is 1.15 mol / L based on the mass of the electrolyte solution, with the remainder being the organic solvent.

[0120] <Diaphragm>

[0121] A porous polyethylene film with a thickness of 5 μm (supplied by Celgard) was used as the separator.

[0122] <Preparation of lithium-ion batteries>

[0123] The positive electrode sheet, separator, and negative electrode sheet prepared above are stacked in order, with the separator positioned between the positive and negative electrode sheets to act as a separator, and then wound to form an electrode assembly. The electrode assembly is placed in an aluminum-plastic film packaging bag, dehydrated at 80°C, and then injected with the electrolyte prepared above. The lithium-ion battery is produced through vacuum packaging, standing, forming, degassing, and trimming. The forming temperature is 80°C, and the forming standing time is 2 hours.

[0124] Examples 2 to 35, Examples 43 to 46

[0125] Except for adjusting the relevant preparation parameters according to Table 1, the rest is the same as Example 1. When the mass ratio X of the organic material to the conductive material changes, the total mass of the organic material and the conductive material remains unchanged, and the mass ratio changes as shown in Table 1.

[0126] Example 36

[0127] Except for the following steps to prepare the positive electrode sheet, the rest is the same as Example 1:

[0128] <Preparation of positive electrode sheet>

[0129] The organic material polyacrylic acid (PAA) and the conductive material graphite were mixed at a mass ratio X of 19:1, added into N-methylpyrrolidone and mixed evenly to obtain a convex portion slurry with a solid content W of 15% and a viscosity of 15000 mPa.s.

[0130] The positive electrode active material LiCoO2, the conductive agent Super P, and the binder polyvinylidene fluoride were mixed in a mass ratio of 97.9:0.9:1.2, and N-methylpyrrolidone (NMP) was added as a solvent to prepare a slurry with a solid content of 75wt%. After vacuum stirring, the positive electrode slurry was obtained.

[0131] The convex slurry was coated using a micro-gravure process on one surface of an 8μm thick aluminum foil for the positive electrode current collector. The process was then dried at 100°C. The above steps were repeated on the other surface of the foil to form multiple striped convex features on both surfaces of the foil. The slurry has a d = 50μm, L = 40μm, h1 = 2μm, α = 45°, and β = 40° angles. The multiple striped convex features were applied to both surfaces of the positive electrode current collector corresponding to the first circle of the positive electrode sheet.

[0132] Then, the positive electrode slurry is continuously coated on the surface of the aluminum foil with multiple striped convex portions, dried at 120°C, and then the above steps are repeated on the other surface of the aluminum foil with multiple striped convex portions. After cutting and welding the tabs, a positive electrode sheet with a specification of 74mm×867mm is obtained for use. Among them, the coating weight CW of the positive electrode material layer is 400mg / 1540mm 2 , the thickness h2 of the positive electrode material layer is 60 μm.

[0133] Example 37 to Example 42

[0134] Except for adjusting the relevant preparation parameters according to Table 1, the rest is the same as Example 1.

[0135] Example 47

[0136] Except that when preparing the positive electrode sheet, the plurality of striped protrusions are only provided on one surface of the positive electrode collector corresponding to the first circle and the second circle of the positive electrode sheet, the rest is the same as that of Example 1.

[0137] Comparative Example 1 to Comparative Example 2

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

[0139] Comparative Example 3

[0140] Except that the striped protrusions are not provided when preparing the positive electrode plate, the rest is the same as that of Example 1.

[0141] Comparative Example 4

[0142] The process is the same as in Example 1 except that the positive electrode slurry is prepared according to the following steps when preparing the positive electrode sheet and no striped protrusions are provided:

[0143] The positive electrode active material LiCoO2, the conductive agent Super P, the binder polyvinylidene fluoride, and the lubricating additive glycerol were mixed in a mass ratio of 96.9:0.9:1.2:1, and N-methylpyrrolidone was added as a solvent to prepare a slurry with a solid content of 75wt%. After vacuum stirring, the positive electrode slurry was obtained.

[0144] The preparation parameters and performance tests of each embodiment and comparative example are shown in Table 1.

[0145] As can be seen from Examples 1 to 47 and Comparative Examples 1 to 4, the positive electrode sheets in the examples are all provided with striped protrusions, and the angle α is within the scope of the present application. The angle α of Comparative Examples 1 and 2 is not within the scope of the present application. Comparative Example 3 does not provide striped protrusions. Glycerol is added to the positive electrode sheet in Comparative Example 4 during preparation to improve the flexibility of the material layer and improve the problem of brittle fracture of the high-pressure density positive electrode sheet. The positive electrode sheet obtained in Comparative Example 1 has the problem of broken strips on the drum edge, which cannot be produced normally and therefore does not have the corresponding lithium-ion battery performance. The positive electrode sheet in Comparative Example 2 has the problem of brittle fracture of the inner ring and the maximum processable pressure density is low, the energy density yield of the lithium-ion battery is negative, and the energy density and safety of the lithium-ion battery cannot be achieved at the same time. The positive electrode sheet in Comparative Example 3 has the problem of brittle fracture of the inner ring and the maximum processable pressure density is low, and the safety performance of the lithium-ion battery is poor. The lithium-ion battery in Comparative Example 4 has a negative energy density yield, and both the energy density and safety performance of the lithium-ion battery are poor. The positive electrode plate in the embodiment does not have the problems of bulging edge, broken belt, and brittle fracture of the inner ring, and the unit fracture strength F and the highest processable pressure density are high, which means that the positive electrode plate is not easy to be brittle fractured under high pressure density, and the energy density and safety performance of the obtained lithium-ion battery can also be achieved.

[0146] The size and arrangement of the striped protrusions usually affect the energy density of the lithium-ion battery. It can be seen from Examples 15 to 35 that when d, L, h1, h1 / h2, and S1 / S2 are within the scope of this application, the inner circle of the obtained positive electrode plate is normal and the unit fracture strength F and the maximum machinable pressure density are high, which means that the positive electrode plate is not easy to break brittlely under high pressure density, and the energy density and safety performance of the obtained lithium-ion battery can also be achieved.

[0147] The material in the convex portion of the stripe usually affects the energy density and internal resistance of the lithium-ion battery. It can be seen from Examples 8 to 11 and Examples 43 to 46 that when the type of organic material and the mass ratio X of the organic material to the conductive material are within the scope of this application, the inner circle of the obtained positive electrode plate is normal and the unit fracture strength F and the maximum machinable pressure density are high, which means that the positive electrode plate is not easy to break brittlely under high pressure density, the internal resistance of the obtained lithium-ion battery is normal, and energy density and safety performance can also be achieved.

[0148] The arrangement of the striped protrusions on both surfaces of the positive electrode current collector usually affects the energy density of the lithium-ion battery. It can be seen from Examples 36 to 42 that when the striped protrusions are arranged on both surfaces of the positive electrode current collector and the angle β is within the scope of this application, the inner circle of the obtained positive electrode plate is normal and the unit fracture strength F and the maximum processable pressure density are high, which means that the positive electrode plate is not easy to break brittlely under high pressure density, and the energy density and safety performance of the obtained lithium-ion battery can also be achieved.

[0149] 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 wound electrode assembly, the electrode assembly comprising a positive electrode sheet, a negative electrode sheet, and a separator, the positive electrode sheet comprising a positive electrode current collector and a positive electrode material layer; The positive electrode sheet includes a corner area of ​​the first turn starting from the winding center, and the corner area is provided with a plurality of striped protrusions located between the current collector and the positive electrode material layer, and the plurality of striped protrusions are arranged at intervals; the angle α between a single striped protrusion and the length direction of the positive electrode sheet is 20° to 70°.

2. The secondary battery according to claim 1, wherein 40°≤α≤50°。 3. The secondary battery according to claim 1, wherein The distance d between two adjacent stripe convex portions is 50 μm to 500 μm, the width L of a single stripe convex portion is 10 μm to 300 μm, and the height h1 is 0.5 μm to 10 μm.

4. The secondary battery according to claim 3, wherein 50μm≤d≤200μm, 20μm≤L≤50μm, 1μm≤h1≤4μm.

5. The secondary battery according to any one of claims 1 to 4, wherein The total area of ​​the orthographic projections of the plurality of stripe protrusions on the surface of the positive electrode current collector is S1, the area of ​​the positive electrode current collector in the corner region is S2, and 0.057≤S1 / S2≤0.

500.

6. The secondary battery according to any one of claims 1 to 4, wherein The height of a single stripe convex portion is h1, the thickness of the positive electrode material layer is h2, and 0.01≤h1 / h2≤0.

21.

7. The secondary battery according to any one of claims 1 to 4, wherein The multiple striped protrusions include multiple first stripes and multiple second stripes, the multiple first stripes are arranged on one surface of the positive electrode collector, and the multiple second stripes are arranged on the other surface of the positive electrode collector, and the angle β formed by a single first stripe and a single second stripe is 40° to 140°.

8. The secondary battery according to any one of claims 1 to 4, wherein The striped protrusion includes an organic material and a conductive material, the organic material includes at least one of polyacrylonitrile, polyethylene glycol, styrene-butadiene rubber, nylon, water-based polyamide resin, dimethyl silicone rubber, polyacrylic acid, polymethyl methacrylate or polyvinylidene fluoride, and the conductive material includes at least one of graphite and conductive fiber. The mass ratio of the organic material to the conductive material is (4 to 49):

1.

9. The secondary battery according to any one of claims 1 to 4, wherein The thickness h3 of the positive electrode current collector is 8 μm to 10 μm.

10. The secondary battery according to any one of claims 1 to 4, wherein The compaction density PD of the positive electrode material layer is greater than or equal to 4.24 g / cm 3 .

11. The secondary battery according to any one of claims 1 to 4, which satisfies at least one of the following characteristics: (1) The coating area density of the positive electrode material layer is 240 mg / 1540.25 mm 2 Up to 400mg / 1540.25mm 2 ; (2) The unit fracture strength of the positive electrode plate is 150 MPa to 270 MPa; (3) The thickness h2 of the positive electrode material layer is 36 μm to 61 μm. 12 . An electronic device comprising the secondary battery according to claim 1 .

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