Secondary battery and electronic device

Abstract

Provided are a secondary battery and an electronic device. The secondary battery comprises an electrode assembly (100); the electrode assembly (100) comprises a positive electrode sheet (10), a negative electrode sheet (20) and a separator (30); the positive electrode sheet (10) comprises a positive electrode current collector and a positive electrode material layer located on at least one surface of the positive electrode current collector; a plurality of protrusions (11) are provided on the positive electrode sheet (10); in the thickness direction of the positive electrode sheet (10), the maximum height of a single protrusion (11) is h mm; the separator comprises a base film and a bonding layer; the coating weight of the bonding layer is X g / m 2, wherein h=-0.0044X2-0.0206X+0.1195, and 0.02≤h≤0.1195. By means of the arrangement, the weight of the secondary battery can be reduced, the hardness of the secondary battery can be increased, the wettability of an electrolyte can be enhanced, the cycle performance of the secondary battery can be improved, and the cost of the secondary battery can be reduced.

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] Lithium-ion batteries have the advantages of good rate performance, light weight, long cycle life, no memory effect and good stability. They are the most widely used energy storage and power products under current technical conditions.

[0003] Currently, the cost of lithium-ion batteries continues to rise, and cost advantages can easily become product competitiveness. Among them, the separators in lithium-ion batteries generally include an adhesive layer. Reducing the cost of the separator means reducing the coating weight of the adhesive layer, which can easily lead to a decrease in the hardness of the electrode assembly in the lithium-ion battery. The lithium-ion battery is prone to deformation, which seriously affects the assembly of the lithium-ion battery. In the existing technology, increasing the bonding force during assembly to reduce the risk of lithium-ion battery deformation is often used, but this will lead to an increase in the production cost of lithium-ion batteries.

[0004] Summary of the Invention

[0005] The purpose of this application is to provide a secondary battery and electronic device that reduces the weight of the secondary battery while increasing its hardness, further enhancing the electrolyte's wettability, improving the secondary battery's cycle performance, and reducing the cost of the secondary battery. The specific technical solution is as follows:

[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.

[0007] A first aspect of the present application provides a secondary battery, comprising an 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 located on at least one surface of the positive electrode current collector, the positive electrode sheet being provided with a plurality of protrusions, wherein the maximum height of a single protrusion along the thickness direction of the positive electrode sheet is h mm, the separator comprising a base film and an adhesive layer, the coating weight of the adhesive layer being X g / m 2 , h=-0.0044X 2-0.0206X+0.1195, 0.02≤h≤0.1195, preferably, 0.05≤h≤0.1. Through the above-mentioned setting, the present application can reduce the coating weight of the adhesive layer in the diaphragm under the same secondary battery specifications, thereby reducing the weight of the secondary battery. During the formation stage of the secondary battery, the positive electrode sheet, the diaphragm and the negative electrode sheet are tightly fitted through mechanical riveting, which is beneficial to the transmission of lithium ions. At the same time, when the coating weight of the diaphragm adhesive layer is reduced or even when the diaphragm has no adhesive layer, the hardness of the secondary battery is improved, and the protection cost during the assembly of the secondary battery is reduced. In addition, providing a protrusion on the positive electrode sheet can improve the wetting performance of the electrolyte to the secondary battery, thereby improving the cycle performance of the secondary battery.

[0008] In one or more embodiments of the present application, 0≤X≤2.9594. By regulating the coating weight of the adhesive layer within the above range, the weight of a secondary battery of the same specification is reduced. During the secondary battery formation stage, the positive electrode sheet, separator, and negative electrode sheet are tightly attached through mechanical riveting, which facilitates the transmission of lithium ions while also taking into account the hardness of the secondary battery and reducing the protective cost during the secondary battery assembly process.

[0009] In one or more embodiments of the present application, adjacent protrusions are located on the same side of the positive electrode sheet along the thickness direction of the positive electrode sheet. This arrangement facilitates the operability of providing protrusions on the positive electrode sheet, reduces the production cost of the secondary battery while meeting mass production manufacturability, improves the cycle performance of the secondary battery, and achieves the goal of reducing costs and increasing efficiency.

[0010] In one or more embodiments of the present application, the electrode assembly has a wound structure, a length of the electrode assembly is a mm, a width of the electrode assembly is b mm, 0.5 ≤ a / b ≤ 4, and 30 ≤ b ≤ 200. By regulating the values ​​of a / b and b within the above ranges, the secondary battery can have good dynamic performance while meeting mass production manufacturability.

[0011] In one or more embodiments of the present application, when 0≤X≤1.5, 1.5≤a / b≤4, 30mm≤b≤130mm, and / or when 1.5<X≤2.9594, 0.5≤a / b<1.5, 130mm<b≤200mm. By regulating the values ​​of a / b within different ranges of X and the value of b within the above ranges, the specifications of the electrode assembly are matched with the coating weight of the adhesive layer in the separator, so that the secondary battery has good dynamic performance while meeting mass production manufacturability.

[0012] In one or more embodiments of the present application, the protrusions are distributed in a dotted pattern on the positive electrode sheet. Along the thickness direction of the positive electrode sheet, the orthographic projection of the protrusions on the positive electrode sheet is at least one of a circle, an ellipse or a polygon. The density of the protrusions is 5000 / m 2 Up to 10,000 pieces / m 2 By regulating the shape of the projection of the protrusion on the positive electrode sheet and the density of the protrusion within the above range, it is beneficial to improve the mass production manufacturability of the secondary battery, while reducing the production cost of the secondary battery, improving the cycle performance of the secondary battery, and achieving the goal of reducing costs and increasing efficiency.

[0013] In one or more embodiments of the present application, the diameter of the maximum circumscribed circle of the outer contour of the orthographic projection is between 1 mm and 4 mm. By regulating the diameter of the maximum circumscribed circle of the outer contour of the orthographic projection within the above range, the production cost of the secondary battery is reduced while the cycle performance of the secondary battery is improved, thereby achieving the goal of reducing costs and increasing efficiency.

[0014] In one or more embodiments of the present application, the orthographic projection of the protrusion on the positive electrode sheet is a strip shape along the thickness direction of the positive electrode sheet, multiple protrusions extend along the width direction of the positive electrode sheet and are spaced apart along the length direction of the positive electrode sheet, and the density of the protrusions is 50 to 300 per meter. By regulating the shape of the orthographic projection of the protrusions on the positive electrode sheet and the density of the protrusions within the above ranges, the production cost of the secondary battery is reduced while the cycle performance of the secondary battery is improved, thereby achieving the goal of reducing costs and increasing efficiency.

[0015] In one or more embodiments of the present application, the width of the orthographic projection along the length of the positive electrode sheet is 1 mm to 5 mm. By regulating the width of the orthographic projection within the above range, the production cost of the secondary battery is reduced while the cycle performance of the secondary battery is improved, thereby achieving the goal of reducing costs and increasing efficiency.

[0016] In one or more embodiments of the present application, the adhesive layer includes a binder, and the binder includes at least one of polyvinylidene fluoride, polyacrylonitrile, polyethylene oxide, or polyimide. By regulating the type of the binder within the above range, the bonding strength of the adhesive layer in the separator is improved, the hardness of the secondary battery is increased, and thus the cycling performance of the secondary battery is improved.

[0017] A second aspect of the present application provides an electronic device comprising the secondary battery of any of the aforementioned embodiments. The secondary battery of the present application is capable of maintaining high hardness while reducing its own weight. Furthermore, the electrolyte has good wettability in the secondary battery, and the secondary battery has good cycle performance. Therefore, the electronic device of the present application has a long service life.

[0018] Beneficial effects of this application:

[0019] The present application provides a secondary battery and an electronic device. The secondary battery includes an electrode assembly, the electrode assembly includes a positive electrode sheet, a negative electrode sheet, and a separator. The positive electrode sheet includes a positive electrode current collector and a positive electrode material layer located on at least one surface of the positive electrode current collector. The positive electrode sheet is provided with a plurality of protrusions. Along the thickness direction of the positive electrode sheet, the maximum height of a single protrusion is h mm. The separator includes a base film and an adhesive layer. The coating weight of the adhesive layer is X g / m 2 , h=-0.0044X 2 -0.0206X+0.1195, 0.02≤h≤0.1195. The present application provides a protrusion on the positive electrode sheet so that X and h satisfy the above relationship and the value of h is regulated within the above range. Under the same secondary battery specifications, the coating weight of the adhesive layer in the diaphragm can be reduced, thereby reducing the weight of the secondary battery. During the formation stage of the secondary battery, the positive electrode sheet, the diaphragm and the negative electrode sheet are tightly fitted by mechanical riveting, which is beneficial to the transmission of lithium ions. At the same time, when the coating weight of the diaphragm adhesive layer is reduced or even when the diaphragm has no adhesive layer, the hardness of the secondary battery is improved, and the protection cost during the assembly of the secondary battery is reduced. In addition, providing a protrusion on the positive electrode sheet can improve the wetting performance of the electrolyte on the secondary battery, thereby improving the cycle performance of the secondary battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] 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.

[0021] FIG1 is an electrode assembly and a partially enlarged schematic diagram thereof in one embodiment of the present application;

[0022] FIG2 is a partial schematic diagram of an electrode assembly in another embodiment of the present application;

[0023] FIG3 is a schematic structural diagram of an electrode assembly in another embodiment of the present application;

[0024] FIG4 is a schematic diagram of the process of providing protrusions on the positive electrode sheet and preparing a wound electrode assembly in this application;

[0025] FIG5 is a schematic diagram of the hardness performance test of the lithium-ion battery of the present application.

[0026] Reference numerals: electrode assembly 100 ; positive electrode sheet 10 ; negative electrode sheet 20 ; separator 30 ; protrusion 11 ; rubber roller 41 ; embossing roller 42 ; winding core 43 . DETAILED DESCRIPTION

[0027] 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.

[0028] 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.

[0029] In order to reduce the risk of deformation of lithium-ion batteries, a diaphragm including an adhesive layer is currently used to bond the layers of the electrode assembly so that the electrode assembly has a certain hardness, and / or, pressure is applied to restrain it when assembling the lithium-ion battery. However, when using a diaphragm including an adhesive layer, the coating weight of the adhesive layer needs to reach a large value to achieve the purpose of reducing the deformation of the lithium-ion battery, resulting in an increase in the production cost of the diaphragm; at the same time, the coating weight of the diaphragm adhesive layer is too large, which affects the replenishment of the electrolyte during the cycle of the lithium-ion battery, resulting in a decrease in the cycle performance of the lithium-ion battery. The electrode assembly is easily generated by the pressurized design. When the electrode assembly is a winding structure, the gap between the layers in the corner area of ​​the electrode assembly increases, affecting the cycle performance of the lithium-ion battery. Based on this, the present application provides a secondary battery and an electronic device, which can increase the hardness of the secondary battery while reducing the weight of the secondary battery, and also improve the wettability of the electrolyte, improve the cycle performance of the secondary battery, reduce the cost of the secondary battery, and achieve the purpose of reducing costs and increasing efficiency.

[0030] A first aspect of the present application provides a secondary battery, comprising an 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 located on at least one surface of the positive electrode current collector, the positive electrode sheet being provided with a plurality of protrusions, wherein the maximum height of a single protrusion along the thickness direction of the positive electrode sheet is h mm, the separator comprising a base film and an adhesive layer, the coating weight of the adhesive layer being X g / m 2 , h=-0.0044X 2 -0.0206X+0.1195, 0.02≤h≤0.1195, preferably, 0.05≤h≤0.1, for example, the value of h can be 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, 0.11, 0.115, 0.118, 0.1195 or a range consisting of any two values ​​therein.

[0031] In this application, for ease of understanding, the electrode assembly in the unfolded state is defined as having its own length direction as the x-direction, its own width direction as the y-direction, and its own thickness direction as the z-direction. It is understood that the positive electrode sheet, positive electrode material layer, positive electrode current collector, negative electrode sheet, negative electrode material layer, negative electrode current collector, and separator in the unfolded state have their own length direction, width direction, and thickness direction the same as the electrode assembly. As shown in Figures 1 and 2, the electrode assembly 100 includes a positive electrode sheet 10, a negative electrode sheet 20, and a separator 30. The positive electrode sheet 10 is provided with a plurality of protrusions 11. Along the thickness direction z of the positive electrode sheet 10, the maximum height of a single protrusion 11 is h mm.

[0032] When the height h of the protrusion on the positive electrode plate and the coating weight X of the adhesive layer in the diaphragm do not satisfy the relationship of the present application, the height of the protrusion on the positive electrode plate does not match the coating weight of the adhesive layer in the diaphragm, which can easily cause the hardness of the secondary battery to decrease, thereby affecting the assembly of the secondary battery, and / or, the electrolyte has a poor wetting effect on the secondary battery, resulting in a decrease in the cycle performance of the secondary battery. The present application provides a protrusion on the positive electrode plate so that X and h meet the above relationship and regulates the value of h within the above range. Under the same secondary battery specifications, the coating weight of the adhesive layer in the diaphragm can be reduced, thereby reducing the weight of the secondary battery. During the secondary battery formation stage, the positive electrode plate, the diaphragm and the negative electrode plate are tightly fitted by mechanical riveting, which is conducive to the transmission of lithium ions. At the same time, when the coating weight of the diaphragm adhesive layer is reduced or even when the diaphragm has no adhesive layer, the hardness of the secondary battery is improved, and the protection cost during the assembly of the secondary battery is reduced. In addition, providing a protrusion on the positive electrode plate can improve the wetting performance of the electrolyte on the secondary battery, thereby improving the cycle performance of the secondary battery. The above configuration can reduce the production cost of the secondary battery, improve the cycle performance of the secondary battery, and achieve the goal of reducing costs and increasing efficiency. In this application, when the value of X is 0, the coating weight of the adhesive layer is 0, that is, there is no adhesive layer in the separator.

[0033] In one or more embodiments of the present application, 0≤X≤2.9594. For example, the value of X can be 0, 0.2, 0.5, 0.8, 1, 1.2, 1.5, 1.8, 2, 2.2, 2.5, 2.8, 2.9, 2.9594 or a range consisting of any two of these values. By regulating the coating weight of the adhesive layer within the above range, the weight of the secondary battery of the same specification is lower. During the formation stage of the secondary battery, the positive electrode sheet, the diaphragm and the negative electrode sheet are tightly fitted by mechanical riveting, which is beneficial to the transmission of lithium ions, while taking into account the hardness of the secondary battery and reducing the protection cost during the assembly of the secondary battery. In one or more embodiments of the present application, along the thickness direction of the positive electrode sheet, adjacent protrusions are located on the same side of the positive electrode sheet. Through the above arrangement, it is beneficial to improve the operability of setting the protrusions on the positive electrode sheet, reduce the coating weight of the adhesive layer in the diaphragm, and thus reduce the weight of the secondary battery. At the same time, it is beneficial to increase the hardness of the secondary battery, improve the wetting performance of the electrolyte to the secondary battery, reduce the production cost of the secondary battery while meeting the mass production and manufacturability, improve the cycle performance of the secondary battery, and achieve the goal of reducing costs and increasing efficiency.

[0034] In one or more embodiments of the present application, the electrode assembly is a wound structure, as shown in FIG3 , wherein the length of the electrode assembly 100 is a mm, the width of the electrode assembly 100 is b mm, 0.5≤a / b≤4, and 30≤b≤200. For example, the value of a / b may be 0.5, 0.8, 1, 1.2, 1.5, 1.8, 2, 2.2, 2.5, 2.8, 3, 3.2, 3.5, 3.8, 4, or a range consisting of any two values ​​thereof, and the value of b may be 30 mm, 40 mm, 50 mm, 60 mm, 70 mm, 80 mm, 90 mm, 100 mm, 110 mm, 120 mm, 130 mm, 140 mm, 150 mm, 160 mm, 170 mm, 180 mm, 190 mm, 200 mm, or a range consisting of any two values ​​thereof. By regulating the value of a / b and the value of b within the above range, it is beneficial to reduce the coating weight of the adhesive layer in the diaphragm and the height of the protrusion on the positive electrode sheet while the secondary battery can still maintain a certain hardness and is not prone to deformation, so that the secondary battery has good dynamic performance while meeting mass production manufacturability.

[0035] In one or more embodiments of the present application, when 0≤X≤1.5, 1.5≤a / b≤4, 30mm≤b≤130mm. For example, when 0≤X≤1.5, the value of a / b can be 1.5, 1.8, 2, 2.2, 2.5, 2.8, 3, 3.2, 3.5, 3.8, 4 or a range consisting of any two of the values ​​therein, and the value of b can be 30mm, 40mm, 50mm, 60mm, 70mm, 80mm, 90mm, 100mm, 110mm, 120mm, 130mm or a range consisting of any two of the values ​​therein. And / or; when 1.5<X≤2.9594, 0.5≤a / b<1.5, 130mm<b≤200mm, for example, when 1.5<X≤2.9594, the value of a / b can be 0.5, 0.6, 0.7, 0.8, 0.9, 1, 1.1, 1.2, 1.3, 1.4, 1.45, 1.49 or a range consisting of any two of these values, and the value of b can be 131mm, 135mm, 138mm, 140mm, 150mm, 160mm, 170mm, 180mm, 190mm, 200mm or a range consisting of any two of these values. By regulating the value of a / b within different ranges of X and the value of b within the above range, it is beneficial to match the specifications of the electrode assembly with the coating weight of the adhesive layer in the separator, and the secondary battery can still maintain a certain hardness under different specifications and is not easily deformed, so that the secondary battery has good dynamic performance while meeting mass production manufacturability.

[0036] In one or more embodiments of the present application, the protrusions are distributed in a dotted pattern on the positive electrode sheet. Along the thickness direction of the positive electrode sheet, the orthographic projection of the protrusions on the positive electrode sheet is at least one of a circle, an ellipse or a polygon. The density ρ1 of the protrusions is 5000 / m 2 Up to 10,000 pieces / m 2 For example, the density of the protrusions ρ1 can be 5000 / m 2 5200 pieces / m 2 5500 pieces / m 2 5800 pieces / m 2 , 6000 pieces / m 2 , 6200 pieces / m 2 , 6500 pieces / m 2 , 6800 pieces / m 2 7000 pieces / m 2 7200 pieces / m 2 7500 pieces / m 2 7800 pieces / m 2 , 8000 pieces / m 2 , 8200 pieces / m 2 , 8500 pieces / m 2, 8800 pieces / m 2 9000 pieces / m 2 9200 pieces / m 2 9500 pieces / m 2 9800 pieces / m 2 10,000 pieces / m 2 Or a range consisting of any two of the values. By regulating the shape of the orthographic projection of the protrusion on the positive electrode sheet and the density of the protrusion within the above range, it is beneficial to improve the mass production manufacturability of the secondary battery, reduce the coating weight of the adhesive layer in the diaphragm, reduce the weight of the secondary battery while increasing the hardness of the secondary battery, and at the same time help improve the wetting performance of the electrolyte to the secondary battery, thereby improving the cycle performance of the secondary battery. Therefore, while reducing the production cost of the secondary battery, the cycle performance of the secondary battery is improved, achieving the purpose of reducing costs and increasing efficiency. In the present application, polygons include but are not limited to at least one of a positive direction, a rectangle, a rhombus, a pentagon or a hexagon. In one embodiment of the present application, when the protrusions are distributed in a dotted manner on the positive electrode sheet, the protrusions are arranged in a matrix on the positive electrode sheet.

[0037] In one or more embodiments of the present application, the diameter d1 of the maximum circumscribed circle of the outer contour of the orthographic projection is 1 mm to 4 mm. For example, the diameter d1 of the maximum circumscribed circle of the outer contour of the orthographic projection can be 1 mm, 1.2 mm, 1.5 mm, 1.8 mm, 2 mm, 2.2 mm, 2.5 mm, 2.8 mm, 3 mm, 3.2 mm, 3.5 mm, 3.8 mm, 4 mm or a range consisting of any two of these values. By regulating the diameter of the maximum circumscribed circle of the outer contour of the orthographic projection within the above range, it is beneficial to reduce the coating weight of the adhesive layer in the diaphragm, reduce the weight of the secondary battery while increasing the hardness of the secondary battery, and at the same time help improve the wettability of the electrolyte to the secondary battery, thereby improving the cycle performance of the secondary battery. Therefore, while reducing the production cost of the secondary battery, the cycle performance of the secondary battery is improved, achieving the purpose of reducing costs and increasing efficiency.

[0038] In one or more embodiments of the present application, along the thickness direction of the positive electrode sheet, the orthographic projection of the protrusion on the positive electrode sheet is a strip shape, and the plurality of protrusions extend along the width direction of the positive electrode sheet and are spaced apart along the length direction of the positive electrode sheet, and the density ρ2 of the protrusions is 50 to 300. For example, the density ρ2 of the protrusions can be 50, 80, 100, 120, 150, 180, 200, 220, 250, 280, 300, or a range consisting of any two of these values. By regulating the shape of the orthographic projection of the protrusions on the positive electrode sheet and the density of the protrusions within the above range, it is beneficial to improve the mass production manufacturability of the secondary battery, reduce the coating weight of the adhesive layer in the diaphragm, reduce the weight of the secondary battery, and increase the hardness of the secondary battery, thereby reducing the production cost of the secondary battery. At the same time, it is beneficial to the infiltration performance of the electrolyte on the secondary battery, thereby improving the cycle performance of the secondary battery. Therefore, while reducing the production cost of the secondary battery, the cycle performance of the secondary battery is improved, achieving the purpose of reducing costs and increasing efficiency. In the present application, along the thickness direction of the positive electrode sheet, when the orthographic projection of the protrusion on the positive electrode sheet is a strip, the spacing between adjacent protrusions along the length direction of the positive electrode sheet is equal. This application does not particularly limit the spacing between adjacent protrusions, and those skilled in the art can control the spacing between adjacent protrusions by the density of the protrusions.

[0039] In one or more embodiments of the present application, along the length direction of the positive electrode sheet, the width d2 of the orthographic projection is 1mm to 5mm. For example, the width d2 of the orthographic projection can be 1mm, 1.2mm, 1.5mm, 1.8mm, 2mm, 2.2mm, 2.5mm, 2.8mm, 3mm, 3.2mm, 3.5mm, 3.8mm, 4mm, 4.2mm, 4.5mm, 4.8mm, 5mm or a range consisting of any two of these values. By regulating the width of the orthographic projection within the above range, it is beneficial to reduce the coating weight of the adhesive layer in the diaphragm, reduce the weight of the secondary battery while increasing the hardness of the secondary battery, and at the same time help to improve the wetting performance of the electrolyte on the secondary battery, thereby improving the cycle performance of the secondary battery. Therefore, while reducing the production cost of the secondary battery, the cycle performance of the secondary battery is improved, achieving the purpose of reducing costs and increasing efficiency. In this application, the cross section of a single orthographic projection refers to the plane formed by the protrusion with an orthographic projection being a strip along the length direction and the thickness direction of the electrode assembly after it is unfolded (or the cross section obtained by sectioning the protrusion with an orthographic projection being a strip along the length direction and the thickness direction after the electrode assembly is unfolded). This application does not particularly limit the cross-sectional shape of the protrusion with an orthographic projection being a strip, as long as it can achieve the purpose of this application. For example, the cross section of the protrusion with an orthographic projection being a strip can be independently selected from at least one of a triangle, an arc (the area is smaller than a semicircle with the same radius), a semicircle, a rectangle, a trapezoid, or a square.

[0040] In one or more embodiments of the present application, the bonding layer includes a binder, and the binder includes at least one of polyvinylidene fluoride (PVDF), polyacrylonitrile (PAN), polyethylene oxide (PEO), or polyimide (PI). By regulating the type of the binder within the above range, it is beneficial to improve the bonding strength of the bonding layer in the separator, so that the positive electrode sheet, the separator, and the negative electrode sheet are more closely attached, which is beneficial to the transmission of lithium ions and increases the hardness of the secondary battery, thereby improving the cycle performance of the secondary battery.

[0041] In one or more embodiments of the present application, the base film in the separator includes at least one of polyethylene (PE), polypropylene (PP), or polyethylene terephthalate (PET), and the thickness of the base film is 5 μm to 25 μm. By regulating the type and thickness of the base film within the above range, the base film has good mechanical strength, and the transmission distance of lithium ions during the secondary battery cycle is moderate, thereby achieving good cycle performance of the secondary battery.

[0042] In one or more embodiments of the present application, the bonding layer in the diaphragm may further include a thickener. Applying the thickener to the bonding layer is beneficial to increasing the stability of the bonding layer slurry and preventing the sedimentation of the components in the bonding layer slurry. The present application does not particularly limit the type of thickener, as long as the purpose of the present application can be achieved. For example, the thickener includes at least one of hydroxyethyl cellulose, methyl hydroxyethyl cellulose, sodium carboxymethyl cellulose, polyacrylamide or sodium alginate. The present application does not particularly limit the content of the thickener in the bonding layer, and those skilled in the art can make a selection according to actual needs, as long as the purpose of the present application can be achieved.

[0043] The present application does not particularly limit the method for preparing the diaphragm, as long as the purpose of the present application can be achieved. For example, the method for preparing the diaphragm may include, but is not limited to, the following steps: (1) uniformly mixing a binder and a thickener to obtain a bonding layer slurry; (2) coating the bonding layer slurry on one surface of a base film and drying it to obtain a diaphragm coated with a bonding layer on one side; (4) repeating the above steps on the other surface of the base film to obtain the diaphragm.

[0044] In one or more embodiments of the present application, the separator further includes a ceramic coating disposed between the base film and the adhesive layer. The ceramic coating has excellent hardness and heat resistance. Disposing the ceramic coating in the separator prevents shrinkage of the separator at high temperatures, thereby improving the hardness and heat resistance of the secondary battery. This improves the mechanical reliability and high-temperature stability of the secondary battery while maintaining good cycle performance.

[0045] In one or more embodiments of the present application, the ceramic coating includes inorganic particles and a ceramic coating binder. The present application has no particular restrictions on the types of inorganic particles and ceramic coating binders, as long as the purpose of the present application can be achieved. For example, inorganic particles include but are not limited to at least one of aluminum oxide, boehmite, titanium dioxide, silicon dioxide, zirconium dioxide, tin dioxide, magnesium hydroxide, magnesium oxide, zinc oxide, barium sulfate, boron nitride, aluminum nitride or silicon nitride. The ceramic coating binder includes but is not limited to at least one of polyvinylidene fluoride, polyacrylic acid, polymethyl methacrylate, polybutyl acrylate or polyacrylonitrile. The present application has no particular restrictions on the content of ceramic particles and ceramic coating binder in the ceramic coating, as long as the purpose of the present application can be achieved.

[0046] In the present application, “the positive electrode material layer located on at least one surface of the positive electrode current collector” means that the positive electrode material layer can be located on one surface of the positive electrode current collector along the thickness direction of itself, or on two surfaces of the positive electrode current collector along the thickness direction of itself. It should be noted that the “surface” here can be the entire area of ​​the surface of the positive electrode current collector, or it can be a partial area of ​​the surface of the positive electrode current collector. This application has no special restrictions, as long as the purpose of this application can be achieved. This application has no special restrictions on the positive electrode current collector, as long as the purpose of this application can be achieved. For example, the positive electrode current collector may include aluminum foil, aluminum alloy foil or a composite current collector (such as an aluminum-carbon composite current collector). The positive electrode material layer of this application contains positive electrode active materials. This application has no special restrictions on the type of positive electrode active materials, as long as the purpose of this application can be achieved. For example, the positive electrode active material may include lithium nickel cobalt manganese oxide (LiNi 0.90 Co 0.05 Mn 0.05O2 (NCM955), NCM811, NCM622, NCM523, NCM111), lithium nickel cobalt aluminum oxide, lithium iron phosphate, lithium-rich manganese-based materials, lithium cobalt oxide (LiCoO2), lithium manganese oxide, lithium iron manganese phosphate or lithium titanate, etc. In the present application, the positive electrode active material may also contain non-metallic elements, for example, the non-metallic elements include at least one of fluorine, phosphorus, boron, chlorine, silicon or sulfur. In the present application, there is no particular restriction on the thickness of the positive electrode current collector, as long as the purpose of the present application can be achieved. For example, the thickness of the positive electrode current collector is 10μm to 20μm. In the present application, the positive electrode material layer may also include a positive electrode binder and a conductive agent. The present application has no particular restrictions on the type of positive electrode binder in the positive electrode material layer, as long as the purpose of the present application can be achieved. For example, the positive electrode binder may include but is not limited to polyvinylidene fluoride, a copolymer of vinylidene fluoride and hexafluoropropylene, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, polyvinyl pyrrolidone, polyvinyl ether, polymethyl methacrylate, polytetrafluoroethylene or polyhexafluoropropylene. The present application has no particular restrictions on the type of conductive agent in the positive electrode material layer, as long as the purpose of the present application can be achieved. For example, the conductive agent may include but is not limited to at least one of conductive carbon black (Super P), carbon nanotubes (CNTs), carbon fibers, flake graphite, Ketjen black, graphene, metal materials or conductive polymers. The above-mentioned carbon nanotubes may include but are not limited to single-walled carbon nanotubes and / or multi-walled carbon nanotubes. The above-mentioned carbon fibers may include but are not limited to vapor-grown carbon fibers (VGCF) and / or nano-carbon fibers. The above-mentioned metal materials may include but are not limited to metal powder and / or metal fibers. Specifically, the metal may include but is not limited to at least one of copper, nickel, aluminum or silver. The conductive polymer may include, but is not limited to, at least one of a polyphenylene derivative, polyaniline, polythiophene, polyacetylene, or polypyrrole. The present application does not particularly limit the mass ratio of the positive electrode active material, conductive agent, and positive electrode binder in the positive electrode material layer. Those skilled in the art may select the ratio based on actual needs, as long as the objectives of the present application are achieved.

[0047] This application places no particular restrictions on the negative electrode sheet, as long as the objectives of this application can be achieved. For example, the negative electrode sheet includes a negative electrode current collector and a negative electrode material layer located on at least one surface of the negative electrode current collector. The above "negative electrode material layer located on at least one surface of the negative electrode current collector" means that the negative electrode material layer can be located on one surface of the negative electrode current collector along its thickness direction, or on two surfaces of the negative electrode current collector along its thickness direction. It should be noted that the "surface" here can be the entire area of the surface of the negative electrode current collector, or a partial area of the surface of the negative electrode current collector. This application places no particular restrictions, as long as the objectives of this application can be achieved. This application places no particular restrictions on the negative electrode current collector, as long as the objectives of this application can be achieved. For example, the negative electrode current collector can include copper foil, copper alloy foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, or a composite current collector (such as 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.). The negative electrode material layer of this application includes a negative electrode active material. This application places no particular restrictions on the type of the negative electrode active material, as long as the objectives of this application can be achieved. For example, the negative electrode active material can include natural graphite, artificial graphite, mesophase microcarbon microbeads (MCMB), hard carbon, soft carbon, silicon, silicon-carbon composite, SiO x (0 < x < 2), Li-Sn alloy, Li-Sn-O alloy, Sn, SnO, SnO2, spinel-structured lithium titanate Li4Ti5O 12 , Li-Al alloy, or at least one of metallic lithium. In this application, there are no particular restrictions on the thickness of the negative electrode current collector, as long as the objectives of this application can be achieved. For example, the thickness of the negative electrode current collector is 4 μm to 15 μm. Optionally, the negative electrode material layer can further include a conductive agent and a negative electrode binder. This application places no particular restrictions on the type of the conductive agent in the negative electrode material layer, as long as the objectives of this application can be achieved. For example, the conductive agent can be of the same type as the conductive agent in the above positive electrode material layer. This application places no particular restrictions on the type of the negative electrode binder in the negative electrode material layer, as long as the objectives of this application can be achieved. For example, the negative electrode binder can be of the same type as the positive electrode binder in the above positive electrode material layer. This application places no particular restrictions on the mass ratio of the negative electrode active material, the conductive agent, and the negative electrode binder in the negative electrode material layer, as long as the objectives of this application can be achieved.

[0048] The secondary battery of the present application includes an electrolyte, and the electrolyte includes a lithium salt and a non-aqueous solvent. The lithium salt may include at least one of LiPF6, LiNO3, LiBF4, LiClO4, LiB(C6H5)4, LiCH3SO3, LiCF3SO3, LiN(SO2CF3)2, LiC(SO2CF3)3, Li2SiF6, lithium bis(oxalatoborate) (LiBOB), lithium bis(trifluoromethanesulfonyl imide) (LiTFSI) or lithium difluoroborate. The present application does not limit the content of the lithium salt in the electrolyte, as long as the purpose of the present application can be achieved. The present application has no special restrictions on 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 a carbonate compound, a carboxylate compound, an ether compound or other organic solvents. The above-mentioned carbonate compound may include but is not limited to at least one of a chain carbonate compound, a cyclic carbonate compound or a fluorinated carbonate compound. Above-mentioned linear carbonate compound can include but not limited to at least one of dimethyl carbonate, diethyl carbonate, dipropyl carbonate, methylpropyl carbonate, ethylpropyl carbonate or methyl ethyl carbonate.Above-mentioned cyclic carbonate can include but not limited to at least one of ethylene carbonate, propylene carbonate (PC), butylene carbonate or vinyl ethylene carbonate.Fluorinated carbonate compound can include but not limited to at least one of fluoroethylene carbonate, 1,2-difluoro ethylene carbonate, 1,1-difluoro ethylene carbonate, 1,1,2-trifluoro ethylene carbonate, 1,1,2,2-tetrafluoro ethylene carbonate, 1-fluoro-2-methyl ethylene carbonate, 1-fluoro-1-methyl ethylene carbonate, 1,2-difluoro-1-methyl ethylene carbonate, 1,1,2-trifluoro-2-methyl ethylene carbonate or trifluoromethyl ethylene carbonate. The 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, valerolactone or caprolactone. The ether compound may include but is not limited to at least one of dibutyl ether, tetraethylene glycol dimethyl ether, diethylene glycol dimethyl ether, 1,2-dimethoxyethane, 1,2-diethoxyethane, 1-ethoxy-1-methoxyethane, 2-methyltetrahydrofuran or tetrahydrofuran. The 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.

[0049] The secondary battery of this application also includes a packaging bag for containing the positive electrode sheet, the negative electrode sheet, the separator, and the electrolyte, as well as other components of the electrochemical device known in the art. This application does not limit these other components. This application does not specifically limit the packaging bag and can be any packaging bag known in the art, as long as it can achieve the purpose of this application.

[0050] The present application does not particularly limit the secondary battery, which may include any device that generates an electrochemical reaction. In one embodiment of the present application, the secondary battery may include but is not limited to: a lithium ion secondary battery (lithium ion battery), a lithium polymer secondary battery or a lithium ion polymer secondary battery, etc.

[0051] The present application does not impose any particular restrictions on the method for preparing a secondary battery, as long as the purpose of the present application can be achieved. For example, the method for preparing a secondary battery includes but is not limited to the following steps: placing the prepared positive electrode sheet, diaphragm, negative electrode sheet, and diaphragm in order, providing a protrusion on the positive electrode sheet, and then winding to obtain an electrode assembly. The electrode assembly is placed in a packaging bag, the electrolyte is injected into the packaging bag and sealed to obtain a secondary battery. Alternatively, a protrusion is provided on the positive electrode sheet, the positive electrode sheet, diaphragm, negative electrode sheet, and diaphragm are stacked in order, the four corners of the entire stacked structure are fixed to obtain an electrode assembly of a stacked structure, the electrode assembly is placed in a packaging bag, the electrolyte is injected into the packaging bag and sealed to obtain a secondary battery. The present application does not impose any particular restrictions on the method for providing a protrusion on the positive electrode sheet, and those skilled in the art can select it according to actual needs, as long as the purpose of the present application can be achieved. For example, an embossing process can be used, that is, an embossing roller and a rubber roller are used and a certain pressure value is set to provide a protrusion on the positive electrode sheet. As shown in Figure 4, the prepared positive electrode sheet 10, separator 30, negative electrode sheet 20, and separator 30 are placed in order. A rubber roller 41 and an embossing roller 42 are used to create a protrusion on the positive electrode sheet 10, and the electrode assembly is wound around a winding core 43. The shape of the protrusion's orthographic projection on the positive electrode sheet can be controlled by the shape of the stainless steel needles on the embossing roller, and the protrusion density ρ1 or ρ2 can be controlled by the number of stainless steel needles on the embossing roller and the number of roller turns. The height h of the protrusion can be controlled by the pressure value set by the embossing roller and the rubber roller, or the specifications of the stainless steel needles on the embossing roller. This application does not specifically limit the pressure value set by the embossing roller and the rubber roller, as long as it can achieve the purpose of this application. For example, the pressure value set by the embossing roller and the rubber roller can be 0.02 MPa to 0.9 MPa. The diameter d1 of the maximum circumscribed circle of the outer contour of the orthographic projection of the protrusion on the positive electrode sheet or the width d2 of the orthographic projection can be controlled by the specifications of the stainless steel needles on the embossing roller.

[0052] In one embodiment of the present application, when preparing a secondary battery, a pressure of 0.1 MPa to 1.2 MPa is applied to the secondary battery during assembly. This configuration is beneficial for improving the mechanical riveting effect between the layers of the electrode assembly, thereby increasing the hardness of the secondary battery.

[0053] A second aspect of the present application provides an electronic device comprising the secondary battery of any of the aforementioned embodiments. The secondary battery of the present application is capable of maintaining high hardness while reducing its own weight. Furthermore, the electrolyte has good wettability in the secondary battery, and the secondary battery has good cycle performance. Therefore, the electronic device of the present application has a long service life.

[0054] The electronic device of the present application is not particularly limited and can be any electronic device known in the art. For example, 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 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, an automobile, 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.

[0055] Example

[0056] 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.

[0057] Test methods and equipment:

[0058] Tests for a, b, h, ρ1, d1, ρ2, d2:

[0059] At an ambient temperature of 25°C, the lithium-ion batteries of each embodiment and comparative example were discharged at 0.5C to 2.5V and then disassembled to obtain electrode assemblies. The length a and width b of the electrode assemblies were measured using a tape measure. The positive electrode sheets were removed and soaked in dimethyl carbonate (DMC) for 20 minutes. The positive electrode sheets were then dried in an oven at 80°C for 12 hours to obtain test samples of the positive electrode sheets.

[0060] The positive electrode sheet is ion polished along the length and thickness directions of the electrode assembly after it is unfolded to obtain a cross-section of the positive electrode sheet, and the cross-section of the positive electrode sheet is measured using a scanning electron microscope. Five protrusions are randomly selected, and the maximum height from the surface of the positive electrode sheet to a single protrusion is measured, and the average value is taken as the maximum height h of a single protrusion. The length and width of the positive electrode sheet after it is unfolded are measured along the length and width directions after it is unfolded, and the number of protrusions is counted. If the protrusions are distributed in a point-like manner on the positive electrode sheet, the density ρ1 of the protrusions is calculated based on the number of protrusions and the length and width of the positive electrode sheet after it is unfolded; five protrusions are randomly selected, and the maximum circumscribed circle diameter of the outer contour of the orthographic projection of a single protrusion on the positive electrode sheet is measured, and the average value is taken as the diameter d1 of the maximum circumscribed circle of the outer contour of the orthographic projection. If the orthographic projection of the protrusion on the positive electrode sheet is in the shape of a strip, the density ρ2 of the protrusion is calculated based on the number of protrusions and the length of the positive electrode sheet after unfolding; select any 5 protrusions, measure the maximum distance between the cross-sections of individual protrusions along the length direction of the unfolded positive electrode sheet, and take the average value, which is the width d2 of the orthographic projection.

[0061] Coating weight test for adhesive layer:

[0062] At an ambient temperature of 25°C, the lithium-ion batteries of the examples and comparative examples were discharged at 0.5C to 2.5V, and then the diaphragms were disassembled and soaked in dimethyl carbonate (DMC) for 20 minutes. The diaphragms were then dried in an oven at 80°C for 12 hours to obtain test samples of the diaphragms. An area of ​​S mm was punched out on the test samples of the diaphragms. 2 The small disc is weighed and recorded as m1, and then the adhesive layer on one side of the small disc is peeled off to obtain the mass of the small disc after peeling off the adhesive layer on one side, which is recorded as m2. The coating weight of the single-sided adhesive layer = (m1-m2) / S.

[0063] Hardness performance test:

[0064] Place two support points on a horizontal table with a distance of 20 mm between the support points. Place the wide side of the lithium-ion battery upward and horizontally above the two support points, wherein the length direction of the lithium-ion battery is the same as the direction of the straight line where the two support points are located, and the center position of the wide side of the lithium-ion battery (relative to one of the two planes along the thickness direction of the lithium-ion battery) coincides with the midpoint between the two support points. As shown in Figure 5, a universal tensile testing machine is used to apply a certain load downward to the midpoint position from above the lithium-ion battery along the thickness direction of the lithium-ion battery (i.e., the z direction). The state after the load is applied is shown in the dotted line in Figure 5. Along the thickness direction of the lithium-ion battery (i.e., the z direction), the force corresponding to the downward displacement of the midpoint position by 5 mm is obtained. The same method is used to measure three lithium battery samples made by the same method, and the average value is taken as the hardness value of the lithium-ion battery.

[0065] Cyclic performance test:

[0066] The lithium-ion batteries in the examples and comparative examples were subjected to charge and discharge cycle tests in a 25°C constant temperature box. The lithium-ion batteries were charged to 3.6V at a constant current of 1C, charged to 0.05V at a constant voltage of 3.6V, and allowed to stand for 5 minutes before being discharged to 2.5V at a constant current of 1C. This was the first cycle, and the first cycle discharge capacity C1 was recorded. After 600 cycles according to the above cycle process, the lithium-ion battery discharge capacity C 600 The 600th cycle capacity retention rate is calculated as an indicator for evaluating the electrolyte's wetting effect on the lithium-ion battery and the cycle performance of the lithium-ion battery, as shown in formula (I). A lower 600cls capacity retention rate indicates a poorer electrolyte wetting effect on the lithium-ion battery, a poorer electrolyte wetting performance, and a poorer lithium-ion battery cycle performance. A higher 600cls capacity retention rate indicates a better electrolyte wetting effect on the lithium-ion battery, a better electrolyte wetting performance, and a better lithium-ion battery cycle performance.

[0067] 600cls capacity retention rate (%) = C 600 / C1×100%. (I)

[0068] Example 1-1

[0069] <Preparation of Separator>

[0070] A porous polypropylene (PP) film with a thickness of 16 μm was used as the base film. The binder polyvinylidene fluoride (PVDF, Mw = 8.5 × 10 6 ) and thickener sodium carboxymethyl cellulose (Mw = 8 × 10 5 ) were mixed in a mass ratio of 98.5:1.5, deionized water was added as a solvent, and the mixture was stirred evenly to form a bonding layer slurry with a solid content of 75 wt%.

[0071] The adhesive layer slurry was coated on one surface of the base film and dried at 60°C to obtain a diaphragm coated with an adhesive layer on one side; the above steps were repeated on the other surface of the base film to obtain a diaphragm. The coating weight X of the adhesive layer was 2.9594 g / m 2 .

[0072] <Preparation of positive electrode sheet>

[0073] The positive electrode active material lithium iron phosphate (LiFePO4), conductive agent conductive carbon black, and binder polyvinylidene fluoride were mixed in a mass ratio of 96.7:1.7:1.6, and N-methylpyrrolidone (NMP) was added as a solvent. The mixture was stirred and mixed to obtain a positive electrode slurry with a solid content of 76 wt%. The positive electrode slurry was evenly coated on one surface of a positive electrode current collector aluminum foil with a thickness of 12 μm and dried at 120 ° C to obtain a coating weight of 300 mg / 1540.25 mm 2 A single-sided positive electrode sheet coated with a positive electrode material layer is produced. The above steps are then repeated on the other surface of the positive electrode current collector aluminum foil to obtain a double-sided positive electrode sheet coated with a positive electrode material layer. After cold pressing, cutting, and slitting, a 4000mm x 185mm positive electrode sheet is obtained.

[0074] <Preparation of negative electrode sheet>

[0075] The negative electrode active materials, artificial graphite, sodium carboxymethyl cellulose (CMC-Na), and styrene-butadiene rubber (SBR), were mixed in a mass ratio of 97.3:1.7:1.0. Deionized water was then added as a solvent and stirred to obtain a negative electrode slurry with a solid content of 50 wt%. The negative electrode slurry was evenly coated on one surface of an 8 μm thick negative electrode current collector copper foil and dried at 80°C to obtain a coating weight of 100.1 mg / 1540.25 mm 2 A negative electrode sheet coated on one side with a negative electrode material layer is produced. The above steps are then repeated on the other surface of the negative electrode current collector copper foil to obtain a negative electrode sheet coated on both sides with a negative electrode material layer. After cold pressing, cutting, and slitting, a negative electrode sheet with a size of 4010 mm x 190 mm is obtained.

[0076] <Preparation of Electrolyte>

[0077] In a dry argon atmosphere glove box, the organic solvents ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) were mixed in a mass ratio of 30:50:20 to create a base solvent. Lithium hexafluorophosphate (LiPF6) was then added to the base solvent and thoroughly mixed to create an electrolyte. The mass percentage of LiPF6 in the electrolyte was 12.5%, with the remainder being the base solvent.

[0078] <Preparation of lithium-ion batteries>

[0079] The positive electrode sheet, diaphragm, negative electrode sheet and diaphragm prepared above are placed in order, and a rubber roller and an embossing roller are used to make a protrusion on the positive electrode sheet. The applied pressure value is 0.1MPa, and the electrode assembly is obtained by winding the core, wherein the length of the electrode assembly is 200mm and the width is 100mm. The electrode assembly is placed in an aluminum-plastic film packaging bag, and the moisture is removed at 80°C, and the above-prepared electrolyte is injected. After vacuum packaging, standing, forming, shaping and other processes, a lithium-ion battery is obtained. Among them, the assembly forming pressure is 0.5MPa. The maximum height h of a single protrusion is 0.02mm, the shape of the protrusion's positive projection on the positive electrode sheet is circular, and the density ρ1 of the protrusion is 8000 / m 2 The diameter d1 of the maximum circumscribed circle of the outer contour of the positive projection of the protrusion on the positive electrode sheet is 2 mm.

[0080] Example 1-2 to Example 1-6

[0081] The process is the same as Example 1-1 except that the coating weight X of the adhesive layer in the separator is adjusted according to Table 1. The coating weight X of the adhesive layer in the separator is 0, that is, the separator only contains the base film.

[0082] Examples 1-7

[0083] Except that the specifications of the positive electrode sheet prepared in <Preparation of Positive Electrode Sheet> are 100mm×30mm, the specifications of the negative electrode sheet prepared in <Preparation of Negative Electrode Sheet> are 105mm×33mm, the length a of the electrode assembly in <Preparation of Lithium-ion Battery> is 45mm, the width b of the electrode assembly is 30mm, and the value of a / b is 1.5, the rest are the same as Examples 1-4.

[0084] Examples 1-8

[0085] Except that the specifications of the positive electrode sheet prepared in <Preparation of Positive Electrode Sheet> are 4000mm×500mm, the specifications of the negative electrode sheet prepared in <Preparation of Negative Electrode Sheet> are 4015mm×505mm, the length a of the electrode assembly in <Preparation of Lithium-ion Battery> is 520mm, the width b of the electrode assembly is 130mm, and the value of a / b is 4, the rest is the same as Examples 1-4.

[0086] Examples 1-9

[0087] Except that the specifications of the positive electrode sheet prepared in <Preparation of Positive Electrode Sheet> are 2000mm×130mm, the specifications of the negative electrode sheet prepared in <Preparation of Negative Electrode Sheet> are 2010mm×135mm, the length a of the electrode assembly in <Preparation of Lithium-ion Battery> is 150mm, the width b of the electrode assembly is 150mm, and the value of a / b is 1, the rest is the same as Example 1-2.

[0088] Examples 1-10

[0089] Except that the specifications of the positive electrode sheet prepared in <Preparation of Positive Electrode Sheet> are 1000mm×50mm, the specifications of the negative electrode sheet prepared in <Preparation of Negative Electrode Sheet> are 1010mm×55mm, the length a of the electrode assembly in <Preparation of Lithium-ion Battery> is 70mm, the width b of the electrode assembly is 140mm, and the value of a / b is 0.5, the rest is the same as Example 1-2.

[0090] Examples 1-11

[0091] Except that the specifications of the positive electrode sheet prepared in <Preparation of Positive Electrode Sheet> are 4000mm×260mm, the specifications of the negative electrode sheet prepared in <Preparation of Negative Electrode Sheet> are 4010mm×265mm, the length a of the electrode assembly in <Preparation of Lithium-ion Battery> is 280mm, the width b of the electrode assembly is 200mm, and the value of a / b is 1.4, the rest is the same as Example 1-2.

[0092] Example 2-1 to Example 2-17

[0093] Except for adjusting the relevant preparation parameters according to Table 2, the rest is the same as Example 1-5.

[0094] Comparative Example 1

[0095] Except that no protrusion is provided on the positive electrode sheet and the coating weight of the adhesive layer in the separator is adjusted as shown in Table 1, the rest is the same as Example 1-1.

[0096] Comparative Example 2 to Comparative Example 3

[0097] The preparation parameters were adjusted according to Table 1, and the rest were the same as Example 1-1. The coating weight X of the adhesive layer in the separator was 0, that is, the separator contained only the base film.

[0098] The preparation parameters and performance parameters of each embodiment and comparative example are shown in Tables 1 and 2.

[0099] Table 1 Note: “ / ” in Table 1 indicates no relevant preparation parameters.

[0100] As can be seen from Examples 1-1 to 1-11 and Comparative Examples 1 to 3, by providing protrusions on the positive electrode sheet, the coating weight of the adhesive layer in the separator is reduced for the same lithium-ion battery specifications, thereby reducing the weight of the lithium-ion battery. This allows X and h to satisfy the relationship of the present application, and by regulating the value of h within the range of the present application, the hardness value and 600cls capacity retention rate of the lithium-ion battery are improved, indicating that the lithium-ion battery has high hardness, good electrolyte wettability in the lithium-ion battery, and good cycling performance. In Comparative Example 1, no protrusions are provided on the positive electrode sheet, and the hardness value of the lithium-ion battery is low, indicating that the hardness of the lithium-ion battery is poor. In Comparative Example 2, the separator only has a base film, and the protrusion height is not within the range of the present application. The hardness value of the lithium-ion battery is low, indicating that the hardness of the lithium-ion battery is poor. In Comparative Example 3, the relationship between the protrusion height and the coating weight of the adhesive layer does not satisfy the relationship within the range of the present application, and the hardness value of the lithium-ion battery is low, indicating that the hardness of the lithium-ion battery is poor. In Examples 1-1 to 1-11, the coating weight of the adhesive layer in the diaphragm is low under the same lithium-ion battery specifications, the weight of the lithium-ion battery is lighter, and the hardness value and 600cls capacity retention rate of the lithium-ion battery are higher, indicating that the lithium-ion battery of the present application has higher hardness and good cycle performance.

[0101] When X is within different ranges, the values ​​of a / b and b generally affect the hardness and cycle performance of lithium-ion batteries. As can be seen from Examples 1-2, 1-4, 1-7, and 1-11, when X is within different ranges and the values ​​of a / b and b are within the ranges of this application, the lithium-ion batteries have high hardness values ​​and 600cls capacity retention rates, indicating that the electrolyte in the examples of this application has a good infiltration effect on the lithium-ion batteries, resulting in the lithium-ion batteries having high hardness and good cycle performance.

[0102] Table 2 Note: “ / ” in Table 2 indicates no relevant preparation parameters.

[0103] When the protrusions are distributed in a dotted pattern on the positive electrode sheet, the shape of the orthographic projection and the density ρ1 of the protrusions usually affect the hardness and cycle performance of the lithium-ion battery. From Examples 1-5, 2-1 to 2-5, it can be seen that when the protrusions are distributed in a dotted pattern on the positive electrode sheet, when the shape of the orthographic projection and the density ρ1 of the protrusions are within the scope of this application, the hardness value and 600cls capacity retention rate of the lithium-ion battery are high, indicating that the electrolyte in the embodiment of this application has a good infiltration effect on the lithium-ion battery, and the lithium-ion battery has a high hardness and good cycle performance. Among them, in the lithium-ion battery of Example 2-5, the protrusions are distributed in a dotted pattern on the positive electrode sheet, and the density ρ1 of the protrusions is large, which will affect the bonding force between the positive electrode sheet and the diaphragm, while reducing the processing efficiency of the positive electrode sheet, thereby affecting the processing performance and assembly performance of the lithium-ion battery.

[0104] The diameter d1 of the maximum circumscribed circle of the orthographic projection's outer contour typically affects the hardness and cycling performance of lithium-ion batteries. As can be seen from Examples 1-5, 2-6, and 2-8, when the diameter d1 of the maximum circumscribed circle of the orthographic projection's outer contour falls within the range of this application, the lithium-ion batteries exhibit high hardness and 600 cls capacity retention, indicating that the electrolyte in the examples of this application effectively wets the lithium-ion batteries, resulting in high hardness and good cycling performance.

[0105] When the orthographic projection of the protrusion on the positive electrode sheet is a bar, the density ρ2 of the protrusion usually affects the hardness and cycle performance of the lithium-ion battery. From Example 2-9 to Example 2-13, it can be seen that when the orthographic projection of the protrusion on the positive electrode sheet is a bar, when the density ρ2 of the protrusion is within the scope of this application, the hardness value and 600cls capacity retention rate of the lithium-ion battery are high, indicating that the electrolyte in the embodiment of this application has a good infiltration effect on the lithium-ion battery, and the lithium-ion battery has a high hardness and good cycle performance. Among them, in the lithium-ion battery of Example 2-13, the orthographic projection of the protrusion on the positive electrode sheet is a bar, and the density ρ2 of the protrusion is large, which will affect the bonding force between the positive electrode sheet and the diaphragm, and at the same time reduce the processing efficiency of the positive electrode sheet, thereby affecting the processing performance and assembly performance of the lithium-ion battery.

[0106] The width d2 of the orthographic projection typically affects the hardness and cycling performance of lithium-ion batteries. Examples 2-9, 2-14, and 2-16 show that when the width d2 of the orthographic projection falls within the range of this application, the lithium-ion batteries exhibit high hardness and 600 cls capacity retention, indicating that the electrolyte in the examples of this application effectively wets the lithium-ion batteries, resulting in high hardness and good cycling performance.

[0107] The type of binder generally affects the hardness and cycle performance of lithium-ion batteries. As can be seen from Examples 1-5 and 2-17, when the binder type is within the scope of this application, the hardness value and 600cls capacity retention rate of the lithium-ion battery are relatively high, indicating that the electrolyte in the examples of this application has a good infiltration effect on the lithium-ion battery, and the lithium-ion battery has high hardness and good cycle performance.

[0108] The terms "comprises," "comprising," or any other variations thereof are intended to cover non-exclusive inclusion such that a process, method, or article that comprises a list of elements includes not only those elements but also other elements not expressly listed or inherent to such process, method, or article.

[0109] Each embodiment in this specification is described in a related manner. The same or similar parts between the embodiments can be referred to each other. Each embodiment focuses on the differences from other embodiments.

[0110] 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 an 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 located on at least one surface of the positive electrode current collector, the positive electrode sheet being provided with a plurality of protrusions, wherein the maximum height of a single protrusion along the thickness direction of the positive electrode sheet is h mm, the separator comprising a base film and an adhesive layer, wherein the coating weight of the adhesive layer is X g / m 2 , h=-0.0044X 2 -0.0206X+0.1195, 0.02≤h≤0.1195.

2. The secondary battery according to claim 1, wherein 0≤X≤2.9594。 3. The secondary battery according to claim 1 or 2, wherein Along the thickness direction of the positive electrode sheet, adjacent protrusions are located on the same side of the positive electrode sheet.

4. The secondary battery according to claim 1, wherein 0.05≤h≤0.1。 5. The secondary battery according to any one of claims 1 to 4, wherein The electrode assembly is a wound structure, the length of the electrode assembly is a mm, the width of the electrode assembly is b mm, 0.5≤a / b≤4, 30≤b≤200.

6. The secondary battery according to claim 5, wherein When 0≤X≤1.5, 1.5≤a / b≤4, 30mm≤b≤130mm, and / or; When 1.5<X≤2.9594, 0.5≤a / b<1.5, 130mm<b≤200mm.

7. The secondary battery according to any one of claims 1 to 6, wherein The protrusions are distributed in a dotted pattern on the positive electrode sheet. Along the thickness direction of the positive electrode sheet, the orthographic projection of the protrusions on the positive electrode sheet is at least one of a circle, an ellipse or a polygon. The density of the protrusions is 5000 / m 2 Up to 10,000 pieces / m 2 .

8. The secondary battery according to claim 7, wherein The diameter of the maximum circumscribed circle of the outer contour of the orthographic projection is 1 mm to 4 mm.

9. The secondary battery according to any one of claims 1 to 8, wherein Along the thickness direction of the positive electrode sheet, the projection of the protrusion on the positive electrode sheet is a strip shape, and multiple protrusions extend along the width direction of the positive electrode sheet and are arranged at intervals along the length direction of the positive electrode sheet. The density of the protrusions is 50 / m to 300 / m.

10. The secondary battery according to claim 9, wherein Along the length direction of the positive electrode sheet, the width of the orthographic projection is 1 mm to 5 mm.

11. The secondary battery according to any one of claims 1 to 10, wherein The bonding layer includes a bonding agent, and the bonding agent includes at least one of polyvinylidene fluoride, polyacrylonitrile, polyethylene oxide, or polyimide. 12 . An electronic device comprising the secondary battery according to claim 1 .

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