Secondary battery and electronic device

Abstract

A secondary battery and an electronic device. The secondary battery includes an electrode assembly and a tab. The electrode assembly comprises a first pole piece, a second pole piece and an isolating membrane, wherein the isolating membrane is arranged between the first pole piece and the second pole piece. The first pole piece comprises a first current collector and a first active material layer arranged on at least part of the first current collector. The first current collector includes a first surface and a second surface, the second surface facing away from a center of the electrode assembly in a thickness direction. The second surface comprises a first area, a third area and a second area which are sequentially connected along the extending direction of the tab; the first pole piece comprises a first part, a first active material layer is arranged on the first surface of the first part, and the first active material layer is not arranged on the second surface of the first part. The first portion includes a first portion forming an outermost side of the electrode assembly in the first direction. A first coating part is arranged in the first area of the first part;

Description

Technical Field

[0001] This application relates to the technical field of energy storage, and particularly to a secondary battery and an electronic device having the secondary battery. Background Art

[0002] With the popularization of consumer electronic products such as laptop computers, mobile phones, handheld game consoles, tablet computers, mobile power supplies, and drones, people's requirements for the safety performance and cycle life of secondary batteries are becoming increasingly strict.

[0003] The secondary battery includes an electrode assembly. In related technologies, due to reasons such as energy density and safety, the outermost electrode sheet in the thickness direction is usually a single-sided coated electrode sheet. However, such electrode assemblies are prone to lithium deposition during cycling, reducing the safety and cycle life of the secondary battery. Summary of the Invention

[0004] The inventors of this application found that since one side of the outermost electrode sheet is provided with an active material layer while the other side is not, the edge region of the outermost electrode sheet may warp outward under stress, thereby forming a gap between the outermost electrode sheet and the separator, deteriorating the transmission interface. Taking the outermost electrode sheet as the positive electrode sheet as an example, during charge and discharge, the impedance of the active ions released from the warped region of the outermost electrode sheet to be transmitted to the edge region of the negative electrode sheet through the above gap becomes larger. Therefore, the active ions will preferentially be transmitted to the inner region of the negative electrode sheet, causing lithium deposition to easily occur at the junction of the edge region and the edge region of the negative electrode sheet, reducing the safety and cycle life of the secondary battery.

[0005] In view of this, it is necessary to propose a secondary battery that can improve the lithium deposition situation of the negative electrode sheet. In addition, it is also necessary to provide an electronic device having the secondary battery.

[0006] The first aspect of the present application provides a secondary battery, including an electrode assembly and a tab. The electrode assembly includes a first electrode plate, a second electrode plate, and a separator, and the separator is disposed between the first electrode plate and the second electrode plate. The first electrode plate includes a first current collector and a first active material layer provided on at least a part of the first current collector. The first current collector includes a first surface and a second surface oppositely arranged along the thickness direction of the first current collector, and the second surface faces away from the center of the electrode assembly in a first direction, and the first direction is the thickness direction of the electrode assembly. The tab is electrically connected to the electrode assembly, and a second direction is the direction in which the tab protrudes from the electrode assembly, and the second direction is perpendicular to the first direction. The second surface includes a first region, a third region, and a second region sequentially connected along the second direction. The second surface further includes a first edge and a second edge oppositely arranged along the second direction, one edge of the first region in the second direction coincides with the first edge, and one edge of the second region in the second direction coincides with the second edge. The width of the first electrode plate in the second direction is W, the width of the first region in the second direction is W1, the width of the second region in the second direction is W2, and W1 = 0.4W, W2 = 0.4W. The first electrode plate includes a first part, and a first active material layer is provided on the first surface of the first part, and no active material layer is provided on the second surface of the first part. The first part includes a first portion, and the first portion constitutes the outermost side of the electrode assembly in the first direction. A first coating portion is provided in the first region of the first portion, and no first coating portion is provided in the third region.

[0007] In the present application, a first coating portion is provided on the first region of the first portion. The first coating portion can improve the mechanical strength and anti-deformation ability of the first region of the first portion, reduce the risk of the first region of the first portion warping outward under the action of stress, thereby reducing the risk of lithium plating caused by the outward warping of the first region of the first portion, and improving the safety and cycle life of the secondary battery.

[0008] Based on the first aspect, in some possible implementation manners, the orthographic projection of the first coating portion in the first direction is located within the orthographic projection of the first portion in the first direction. The first coating portion includes a third edge and a fourth edge oppositely arranged along the second direction, and the third edge is closer to the first edge than the fourth edge. The distance between the third edge and the first edge in the second direction is W3, and 0 ≤ W3 ≤ 3 mm. Therefore, the first coating portion can fully cover the first region of the first portion, further improve the mechanical strength and anti-deformation ability of the first region of the first portion, and reduce the risk of the first region of the first portion warping outward under the action of stress.

[0009] Based on the first aspect, in some possible implementation manners, 0 ≤ W3 ≤ 1 mm, so as to further reduce the risk of the first region of the first portion warping outward under the action of stress.

[0010] Based on the first aspect, in some possible implementation manners, the maximum width of the first coating portion in the second direction is W4, and 0.10W ≤ W4 ≤ 0.30W. Therefore, it is beneficial to increase the area of the first coating portion, so that the first coating portion fully covers the first region in the first portion along the first direction (especially the portion in the first region that is more likely to warp outwards), further improving the mechanical strength and anti-deformation ability of the first region of the first portion, and reducing the risk of the first region of the first portion warping outwards under the action of stress.

[0011] Based on the first aspect, in some possible implementation manners, 0.12W ≤ W4 ≤ 0.20W, so as to further increase the area of the first coating portion while making the first coating portion fully cover the first region in the first portion along the first direction, and reducing the influence of the first coating portion on the energy density of the secondary battery.

[0012] Based on the first aspect, in some possible implementation manners, 0.14W ≤ W4 ≤ 0.17W, so as to further increase the area of the first coating portion while making the first coating portion fully cover the first region in the first portion along the first direction, and reducing the influence of the first coating portion on the energy density of the secondary battery.

[0013] Based on the first aspect, in some possible implementation manners, the orthographic projection of the first coating portion in the first direction is located within the orthographic projection of the first portion in the first direction. The width of the first portion in the third direction is L, and the maximum length of the first coating portion in the third direction is L1, and 0.50L ≤ L1 ≤ L. Among them, the third direction, the first direction, and the second direction are perpendicular to each other pairwise. Therefore, it is beneficial to increase the area of the first coating portion, so that the first coating portion fully covers the first region of the first portion along the third direction, further improving the mechanical strength and anti-deformation ability of the first region of the first portion, and reducing the risk of the first region of the first portion warping outwards under the action of stress.

[0014] Based on the first aspect, in some possible implementation manners, 0.70L ≤ L1 ≤ 0.90L. By further limiting the lower limit of L1, the area of the first coating portion can be further increased, so that the first coating portion fully covers the first region in the first portion along the first direction. By further limiting the upper limit of L1, it is beneficial to make the first coating portion cover the position in the first region of the first portion that is more likely to warp (i.e., the position far from the corner area of the electrode assembly in the third direction), while further reducing the risk of the first region of the first portion warping outwards and reducing the influence of the first coating portion on the energy density of the secondary battery.

[0015] Based on the first aspect, in some possible implementation manners, the first part includes a fifth edge and a sixth edge oppositely arranged along a third direction, the first coating part includes a seventh edge and an eighth edge oppositely arranged along the third direction, and the seventh edge is closer to the fifth edge than the eighth edge. Along the third direction, the distance between the seventh edge and the fifth edge is L2, the distance between the eighth edge and the sixth edge is L3, L′ = |L2 - L3|, and 0 ≤ L′ ≤ 0.15L. Therefore, along the third direction, the first coating part can be arranged approximately in the middle of the first area of the first part, which is beneficial for the first coating part to cover the position where warping is more likely to occur in the first area of the first part (i.e., the position far from the corner area of the electrode assembly in the third direction), and further reduces the risk of the first area of the first part warping outwards.

[0016] Based on the first aspect, in some possible implementation manners, 0 ≤ L′ ≤ 0.10L, which is further beneficial for the first coating part to cover the position where warping is more likely to occur in the first area of the first part, and further reduces the risk of the first area of the first part warping outwards.

[0017] Based on the first aspect, in some possible implementation manners, along the direction from the first edge to the second edge, the length of the first coating part gradually decreases in the third direction. Among them, the third direction, the first direction, and the second direction are perpendicular to each other in pairs.

[0018] Based on the first aspect, in some possible implementation manners, the first coating part is also provided in the second area of the first part. Therefore, the first coating part can also improve the mechanical strength and anti-deformation ability of the second area of the first part, reduce the risk of the second area of the first part warping outwards under the action of stress, thereby reducing the risk of lithium deposition caused by the warping outwards of the second area of the first part, and further improving the safety and cycle life of the secondary battery.

[0019] Based on the first aspect, in some possible implementation manners, the material of the first coating part includes an adhesive and inorganic ceramic particles, so that the first coating part can effectively improve the mechanical strength and anti-deformation ability of the first area of the first part, and reduce the risk of the first area of the first part warping outwards under the action of stress.

[0020] Based on the first aspect, in some possible implementation manners, the material of the inorganic ceramic particles is selected from at least one of hafnium dioxide, strontium titanate, tin dioxide, cesium oxide, magnesium oxide, nickel oxide, calcium oxide, barium oxide, zinc oxide, zirconium oxide, yttrium oxide, aluminum oxide, titanium oxide, silicon dioxide, boehmite, magnesium hydroxide or aluminum hydroxide. Based on the first aspect, in some possible implementation manners, the material of the binder is selected from at least one of a copolymer of difluoroethylene and hexafluoropropylene, a copolymer of vinylidene fluoride and trichloroethylene, polymethyl methacrylate, polyacrylic acid, polyacrylate, polyacrylate salt, polyacrylonitrile, polyvinylpyrrolidone, polyvinyl acetate, a copolymer of ethylene and vinyl acetate, polyimide, polyethylene oxide, cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, cyanoethylated amylose, cyanoethylated polyvinyl alcohol, cyanoethylated cellulose, cyanoethylated sucrose, amylopectin, sodium carboxymethyl cellulose, lithium carboxymethyl cellulose, a copolymer of acrylonitrile, styrene and butadiene, polyvinyl alcohol, polyvinyl ether, polytetrafluoroethylene, polyhexafluoropropylene, a copolymer of styrene and butadiene or polyvinylidene fluoride. The components of the above inorganic ceramic particles and the binder are the same as those of the ceramic coating used to reduce the risk of burr piercing in the single-sided area of the secondary battery in the related art, that is, the first coating part can adopt the existing ceramic coating components with stable properties and low reactivity, so that while effectively improving the mechanical strength and anti-deformation ability of the first region in the first part, the influence of the first coating part on the electrochemical performance of the secondary battery is reduced.

[0021] Based on the first aspect, in some possible implementation manners, the coating weight per unit area of the first coating part is 11 mg / 1540.25 mm 2 to 13 mg / 1540.25 mm 2 . Therefore, the first coating part can effectively improve the mechanical strength and anti-deformation ability of the first region in the first part, and reduce the risk of the first region in the first part warping outward under the action of stress. At the same time, it can also reduce the risk of reducing the energy density of the secondary battery due to a large coating weight per unit area.

[0022] Based on the first aspect, in some possible implementation manners, the thickness of the first coating part is 7 μm to 9 μm. Therefore, the first coating part can effectively improve the mechanical strength and anti-deformation ability of the first region in the first part, and reduce the risk of the first region in the first part warping outward under the action of stress. At the same time, it can also reduce the risk of reducing the energy density of the secondary battery due to a large thickness.

[0023] Based on the first aspect, in some possible implementation manners, the electrode assembly is of a wound structure. The first electrode tab includes a second portion, a first portion, and a third portion that are sequentially connected along the winding direction of the electrode assembly. The first active material layer is provided on both the first surface and the second surface of the second portion, and the first active material layer is not provided on both the first surface and the second surface of the third portion. The outermost winding of the electrode assembly includes the third portion and a part of the first portion, and the other part of the first portion is located in the second outermost winding of the first electrode tab. For the wound electrode assembly, the flat region in the first portion is less restricted than the corner region, so that the flat region is more likely to warp outward under the action of stress. Therefore, by disposing the first coating portion on the flat region of the first portion, such as on the first region of the first portion, the mechanical strength and deformation resistance of the first region of the first portion, which is more likely to warp outward under the action of stress, are improved, thereby effectively reducing the risk of the first portion warping outward under the action of stress.

[0024] Based on the first aspect, in some possible implementation manners, the first portion further includes a second portion, and the second portion constitutes the other outermost side of the electrode assembly opposite to the first surface in the first direction. The second coating portion is provided on the first region of the second portion. The second coating portion can improve the mechanical strength and deformation resistance of the first region of the second portion, reduce the risk of the first region of the second portion warping outward under the action of stress, thereby reducing the risk of lithium plating caused by the outward warping of the first region of the second portion, and further improving the safety and cycle life of the secondary battery.

[0025] Based on the first aspect, in some possible implementation manners, the electrode assembly includes a first corner region and a second corner region that are oppositely disposed in the third direction, and the third direction, the first direction, and the second direction are perpendicular to each other in pairs. The first portion further includes a third portion, the first portion, the third portion, and the second portion are sequentially connected along the winding direction of the electrode assembly, and the third portion constitutes the outermost side of the first corner region or the second corner region. The third coating portion is provided on the first region of the third portion. The third coating portion can improve the mechanical strength and deformation resistance of the first region of the third portion, reduce the risk of the first region of the third portion warping outward under the action of stress, thereby reducing the risk of lithium plating caused by the outward warping of the first region of the third portion, and further improving the safety and cycle life of the secondary battery. In addition, the third coating portion can also reduce the risk of the first region of the third portion being torn.

[0026] Based on the first aspect, in some possible implementation manners, the first coating portion, the third coating portion, and the second coating portion are sequentially connected along the winding direction of the electrode assembly. Therefore, the first coating portion, the third coating portion, and the second coating portion are connected as a whole, which can further improve the mechanical strength and deformation resistance of the first region of the first portion, and is also convenient for printing the coating on the first region of the first portion at one time, simplifying the process.

[0027] Based on the first aspect, in some possible implementation manners, the first part includes a fourth part which is located in the second outermost layer of the winding of the electrode assembly, and the fourth part and the first part are sequentially connected along the winding direction of the electrode assembly. A first region of the fourth part is provided with a fourth coating part. The fourth coating part can improve the mechanical strength and anti-deformation ability of the first region of the fourth part, reduce the risk of the first region of the fourth part warping outwards under the action of stress, thereby reducing the risk of lithium plating caused by the warping outwards of the first region of the fourth part, and further improving the safety and cycle life of the secondary battery. In addition, the fourth coating part can have a relatively high porosity, especially when the fourth coating part also has inorganic ceramic particles, which is beneficial to increasing the space for electrolyte storage and circulation in the electrode assembly, thereby further improving the cycle life of the secondary battery.

[0028] Based on the first aspect, in some possible implementation manners, the first active material layer on the second surface includes a finishing area in the winding direction. Observed from the first direction, the fourth coating part overlaps with a part of the finishing area. For example, the fourth coating part can cover this part of the finishing area, so that the fourth coating part can reduce the risk of micro-short circuit caused by the shedding of the first active material at the finishing area, and further improve the safety and cycle life of the secondary battery. Another example is that this part of the finishing area can cover the fourth coating part, so that this part of the finishing area can also play the role of capacity.

[0029] Based on the first aspect, in some possible implementation manners, along the winding direction of the electrode assembly, the width of the overlapping area between the fourth coating part and a part of the finishing area is 2 mm to 4 mm. Therefore, when the fourth coating part covers this part of the finishing area, setting the above width can further reduce the risk of micro-short circuit caused by the shedding of the first active material at the finishing area, and at the same time can also reduce the risk that more first active materials cannot play the role of capacity due to the relatively large width of the covering area.

[0030] Based on the first aspect, in some possible implementation manners, the second region and the third region of the fourth part are also provided with the fourth coating part. Therefore, the fourth coating part can enhance the strength of the fourth part and improve the ability of the electrode assembly to resist mechanical shock.

[0031] Based on the first aspect, in some possible implementation manners, the first region and / or the second region of the third part are provided with a fifth coating part. Therefore, the fifth coating part can enhance the strength of the first region or the second region of the third part and further improve the ability of the electrode assembly to resist mechanical shock.

[0032] Based on the first aspect, in some possible implementation manners, the electrode assembly is a laminated structure. The first part is the first electrode sheet located in the outermost layer of the electrode assembly along the first direction. The second surface of the first part includes, along the third direction, a fourth region, a third region, and a fifth region that are sequentially connected. The third direction is perpendicular to the first direction and the second direction respectively. The first coating portion is also disposed on the fourth region and / or the fifth region. Therefore, the first coating portion can also improve the mechanical strength and anti-deformation ability of the fourth region and / or the fifth region located in the first part, reduce the risk of the fourth region or the fifth region of the first part warping outward under the action of stress, thereby reducing the risk of lithium plating caused by the outward warping of the fourth region or the fifth region of the first part, and further improving the safety and cycle life of the secondary battery.

[0033] Based on the first aspect, in some possible implementation manners, the first electrode sheet is a positive electrode sheet, the first active material layer includes a first active material, and the first active material includes lithium nickel cobalt manganese oxide. Using lithium nickel cobalt manganese oxide as the first active material can improve the energy density of the secondary battery and reduce costs. At the same time, even if there are alkaline substances remaining in the lithium nickel cobalt manganese oxide resulting in a low bonding strength between the first electrode sheet and the separator, the first coating portion can also reduce the risk of the first region of the first part warping outward under the action of stress.

[0034] The second aspect of the present application provides an electronic device, including the above secondary battery. The electronic device is powered by the above secondary battery, and the lithium plating situation of the electrode assembly is improved. Therefore, the secondary battery has high safety and cycle life. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 It is a cross-sectional schematic view of a secondary battery provided by an embodiment of the present application.

[0036] Figure 2 is Figure 1 A side view of the first electrode sheet of the secondary battery shown after being unfolded.

[0037] Figure 3 is Figure 1 A front view of the first electrode sheet of the secondary battery shown after being unfolded.

[0038] Figure 4 It is a cross-sectional schematic view of a secondary battery in other embodiments.

[0039] Figure 5 is Figure 4 A side view of the first electrode sheet of the secondary battery shown after being unfolded.

[0040] Figure 6 is Figure 4 A front view of the first electrode sheet of the secondary battery shown after being unfolded.

[0041] Figure 7 It is the official diagram of the first pole piece after unfolding in some other embodiments.

[0042] Figure 8 It is the official diagram of the first pole piece after unfolding in some other embodiments.

[0043] Figure 9 It is the official diagram of the first pole piece after unfolding in some other embodiments.

[0044] Figure 10 It is a schematic cross-sectional view of a secondary battery provided in another embodiment of the present application.

[0045] Figure 11 It is Figure 10 a front view of the first pole piece of the secondary battery shown.

[0046] Figure 12 It is a schematic structural view of an electronic device provided in an embodiment of the present application.

[0047] The following specific embodiments will further illustrate the present application in conjunction with the above-mentioned drawings. Specific Embodiments

[0048] The technical solutions in the embodiments of the present application will be clearly and detailedly described below. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all of the embodiments. Unless otherwise defined, all the technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the technical field to which the present application belongs. The terms used in the specification of the present application are only for the purpose of describing specific embodiments, and are not intended to limit the present application.

[0049] Hereinafter, the embodiments of the present application will be described in detail. However, the present application can be embodied in many different forms and should not be construed as limited to the exemplary embodiments set forth herein. Instead, these exemplary embodiments are provided so that the present application will be thorough and detailed and will convey to those skilled in the art.

[0050] In addition, for the sake of brevity and clarity, in the drawings, the sizes or thicknesses of various components and layers may be enlarged. Throughout the text, the same numerical values refer to the same elements. As used herein, the terms "and / or", "and / or" include any and all combinations of one or more of the related listed items. In addition, it should be understood that when element A is referred to as being "connected" to element B, element A may be directly connected to element B, or there may be an intermediate element C and elements A and B may be indirectly connected to each other.

[0051] Furthermore, when describing the embodiments of the present application, the use of "may" means "one or more embodiments of the present application".

[0052] The technical terms used herein are for the purpose of describing specific embodiments and are not intended to limit the present application. As used herein, the singular forms are also intended to include the plural forms unless the context clearly indicates otherwise. It should be further understood that the term "comprising", when used in this specification, refers to the presence of the recited features, values, steps, operations, elements, and / or components, but does not preclude the presence or addition of one or more other features, values, steps, operations, elements, components, and / or combinations thereof.

[0053] Spatial relative terms, such as "upper" and the like, may be used herein for convenience of description to describe the relationship of one element or feature to another element(s) or feature(s) as illustrated in the figures. It should be understood that, in addition to the directions described in the figures, the spatial relative terms are intended to include different directions of the device or apparatus during use or operation. For example, if the device in the figures is turned over, an element described as "above" or "on" another element or feature will be oriented "below" or "beneath" the other element or feature. Thus, the exemplary term "upper" can include both upward and downward directions. It should be understood that although the terms first, second, third, etc. may be used herein to describe various elements, components, regions, layers, and / or parts, these elements, components, regions, layers, and / or parts should not be limited by these terms. These terms are used to distinguish one element, component, region, layer, or part from another element, component, region, layer, or part. Thus, a first element, component, region, layer, or part discussed below may be referred to as a second element, component, region, layer, or part without departing from the teachings of the exemplary embodiments.

[0054] Please refer to Figure 1 , an embodiment of the present application provides a secondary battery 100, including a housing 10, an electrode assembly 20, an electrolyte (not shown in the figure), and tabs. The electrode assembly 20 and the electrolyte are located within the housing 10.

[0055] The electrode assembly 20 includes a first electrode tab 21, a second electrode tab 22, and a separator 23 disposed between the first electrode tab 21 and the second electrode tab 22. The first electrode tab 21 includes a first current collector 210 and a first active material layer 211 provided on at least a portion of the first current collector 210. The first current collector 210 includes a first surface 210A and a second surface 210B oppositely disposed along the thickness direction of the first current collector 210. The first active material layer 211 is provided on at least a portion of the first surface 210A and at least a portion of the second surface 210B, wherein the second surface 210B faces away from the center of the electrode assembly 20 in the first direction X and faces the housing 10. The second electrode tab 22 includes a second current collector 220 and a second active material layer 221 provided on at least a portion of the second current collector 220. The second current collector 220 includes a third surface 220A and a fourth surface 220B oppositely disposed along the thickness direction of the second current collector 220. The second active material layer 221 is provided on at least a portion of the third surface 220A and at least a portion of the fourth surface 220B, wherein the fourth surface 220B faces away from the center of the electrode assembly 20 in the first direction X and faces the housing 10. The electrode tabs may include a first electrode tab 30 and a second electrode tab 40. The first electrode tab 30 and the second electrode tab 40 are respectively electrically connected to the first current collector 210 and the second current collector 220, and the first electrode tab 30 and the second electrode tab 40 can be connected to external components (not shown in the figure).

[0056] This embodiment is illustrated by taking the electrode assembly 20 as a winding structure, that is, the first pole piece 21, the isolation film 23 and the second pole piece 22 are stacked and wound. At this time, the first surface 210A of the first current collector 210 and the third surface 220A of the second current collector 220 are both arranged facing the winding center axis O, and the second surface 210B of the first current collector 210 and the fourth surface 220B of the second current collector 220 are both arranged away from the winding center axis O. The center of the electrode assembly 20 in the first direction X is the position of the winding center axis O. Among them, the three-dimensional coordinate system is defined by the first direction X, the second direction Y and the third direction Z that are perpendicular to each other. The first direction X is the thickness direction of the electrode assembly 20, the second direction Y is the width direction of the first pole piece 21 or the second pole piece 22 in the direction where the first pole ear 30 or the second pole ear 40 protrudes from the electrode assembly 20, and the second direction Y is also the width direction of the first pole piece 21 or the second pole piece 22. The electrode assembly 20 can be divided into a first straight area 201, a first corner area 202, a second straight area 203 and a second corner area 204 which are sequentially connected in the winding direction D. The first straight area 201 and the second straight area 203 are arranged opposite to each other in the first direction X, and the first corner area 202 and the second corner area 204 are arranged opposite to each other in the third direction Z. The corner area is a bending portion of the electrode assembly 20, and the corner area is a concept opposite to the straight area. When viewed from the second direction Y, the first corner area 202 and the second corner area 204 can be arranged in an arc shape.

[0057] Among them, Figure 1As shown, the first flat region 201 has a first outer surface 201A, and the second flat region 203 has a second outer surface 203A. The connection between the first flat region 201 located on the outermost side of the electrode assembly 20 and the first corner region 202 located on the outermost side of the electrode assembly 20 is the first connection end 205. The first connection end 205 is the starting part of the leftmost bent edge of the first corner region 202 in the winding direction D, and the first connection end 205 is also the part where the dotted line A-A formed by the leftmost bent edge located inside the electrode assembly 20 and extending in the first direction X intersects the first outer surface 201a. The connection between the first corner region 202 located on the outermost side of the electrode assembly 20 and the second flat region 203 located on the outermost side of the electrode assembly 20 is the second connection end 206. The second connection end 206 is the ending part of the leftmost bent edge of the first corner region 202 in the winding direction D, and the second connection end 206 is also the part where the dotted line A-A intersects the second outer surface 203A. The connection between the second flat region 203 located on the outermost side of the electrode assembly 2020 and the second corner region 204 located on the outermost side of the electrode assembly 2020 is the third connection end 207. The third connection end 207 is the starting part of the leftmost and rightmost curve of the second corner region 204 in the winding direction D, and the third connection end 207 is also the part where the dotted line B-B formed by the rightmost bent edge located inside the electrode assembly 20 and extending in the first direction X intersects the second outer surface 203A. The connection between the second corner region 204 located on the outermost side of the electrode assembly 2020 and the first flat region 201 located on the outermost side of the electrode assembly 2020 is the fourth connection end 208. The fourth connection end 208 is the ending part of the rightmost curve of the second corner region 204 in the winding direction D, and the fourth connection end 208 is also the part where the dotted line B-B intersects the first outer surface 201A. In the first direction X, the first connection end 205 and the second connection end 206 are aligned, and the third connection end 207 and the fourth connection end 208 are aligned.

[0058] Among them, the first electrode tab 21 can be a positive electrode tab, and the second electrode tab 22 can be a negative electrode tab. Correspondingly, the first current collector 210 is a positive current collector, the first active material layer 211 includes a first active material, and the first active material is a positive electrode active material; the second current collector 220 is a negative current collector, the second active material layer 221 includes a second active material, and the second active material is a negative electrode active material. In some other embodiments, it is also possible to set the first electrode tab 21 as a negative electrode tab and the second electrode tab 22 as a positive electrode tab. As Figure 2 and Figure 3 shown, where Figure 2 and Figure 3 is Figure 1 the schematic structural diagram of the unfolded first electrode tab 21 shown. Figure 2 and Figure 3A three-dimensional coordinate system is established with a fourth direction X', a second direction Y, and a fifth direction Z'. The fourth direction X' is the thickness direction of the first electrode 21, and the fifth direction Z' is the length direction of the first electrode 21.

[0059] Among them, the positive current collector can be made of aluminum foil or nickel foil, and the negative current collector can be made of at least one of copper foil, nickel foil, or a carbon-based current collector.

[0060] The positive electrode active material includes a compound (i.e., a lithiated intercalation compound) that can reversibly insert and extract metal ions (such as lithium ions, sodium ions, etc., hereinafter taking lithium ions as an example). In some embodiments, the positive electrode active material may include a lithium transition metal composite oxide. The lithium transition metal composite oxide contains lithium and at least one element selected from cobalt, manganese, and nickel. In some embodiments, the positive electrode active material is selected from at least one of lithium cobalt oxide (LiCoO2), nickel cobalt manganese ternary material (NCM), nickel cobalt aluminum ternary material (NCA), lithium manganese oxide (LiMn2O4), lithium nickel 0.5 Mn 1.5 O4), or lithium iron phosphate (LiFePO4).

[0061] The negative electrode active material uses a negative electrode active substance known in the art that can reversibly insert and extract active ions, and this application does not limit it. For example, it may include, but is not limited to, one or a combination of graphite, soft carbon, hard carbon, carbon fiber, mesophase carbon microspheres, silicon-based materials, tin-based materials, lithium titanate, or other metals that can form alloys with lithium. Among them, graphite can be selected from one or a combination of artificial graphite, natural graphite, and modified graphite; silicon-based materials can be selected from one or a combination of elemental silicon, silicon oxide compounds, silicon-carbon composites, and silicon alloys; tin-based materials can be selected from one or a combination of elemental tin, tin oxide compounds, and tin alloys.

[0062] The separator 23 includes at least one of polyethylene, polypropylene, polyvinylidene fluoride, polyethylene terephthalate, polyimide, or aramid. For example, polyethylene includes at least one selected from high-density polyethylene, low-density polyethylene, or ultra-high molecular weight polyethylene.

[0063] Such as Figure 3As shown, the second surface 210B includes a first region 2101, a third region 2103, and a second region 2102 that are sequentially connected along the second direction Y. Among them, the second surface 210B further includes a first edge 210B1 and a second edge 210B2 that are oppositely arranged along the second direction Y. When observed from the fourth direction X’, there is an overlap between the first tab 30 and the first edge 210B1. One edge of the first region 2101 in the second direction Y coincides with the first edge 210B1, and one edge of the second region 2102 in the second direction Y coincides with the second edge 210B2. That is, the first region 2101 and the second region 2102 are respectively two edge regions of the second surface 210B along the second direction Y. Define the width of the first pole piece 21 in the second direction Y as W, the width of the first region 2101 in the second direction Y as W1, and the width of the second region 2102 in the second direction Y as W2. W1 = 0.4W and W2 = 0.4W.

[0064] As Figures 1 to 3 shown, the first pole piece 21 includes a first part 212, and the first part 212 can be a single-sided coating area. A first active material layer 211 is provided on the first surface 210A of the first part 212, and no active material layer is provided on the second surface 210B of the first part 212. When the electrode assembly 20 is a wound structure, the first pole piece 21 includes a second part 213, a first part 212, and a third part 214 that are sequentially connected along the winding direction D. The second part 213 is a double-sided coating area, and the first active material layer 211 is provided on both the first surface 210A and the second surface 210B of the second part 213. The third part 214 is an empty foil area, and no active material layer is provided on both the first surface 210A and the second surface 210B of the third part 214. Along the winding direction D (or, Figure 2 and Figure 3 the fifth direction Z’), the length of the first region 2101 is greater than the length of the second region 2102 and also greater than the length of the third region 2103, thereby improving the energy density of the secondary battery 100. The outermost winding of the electrode assembly 20 includes the third part 214 and a part of the first part 212, and the other part of the first part 212 is located in the second outermost winding of the first pole piece 21. Therefore, the outer surface of the outermost winding is the second surface 210B of the first current collector 210. On the one hand, the first current collector 210 can improve the hardness of the electrode assembly 20 and play a role in protecting the electrode assembly 20. On the other hand, when the first pole piece 21 is a positive electrode pole piece and the second pole piece 22 is a negative electrode pole piece, the risk that the electrolyte easily corrodes the second current collector 220 (such as a copper foil) when the second pole piece 22 ends is reduced.

[0065] Among them, the first part 212 includes a fourth part 2124, a first part 2121, a third part 2123, and a second part 2122 that are sequentially connected along the winding direction D. The first part 2121 constitutes the outermost side of the electrode assembly 20 in the first direction X. For example, the first part 2121 can be the outermost side of the first flat area 201 in the first direction X. The second part 2122 constitutes the other outermost side of the electrode assembly 20 that is oppositely arranged to the first part 2121 in the first direction X. For example, the second part 2122 can be the outermost side of the second flat area 203 in the first direction X. The third part 2123 constitutes the outermost side of the first corner area 202. The fourth part 2124 is located in the second outermost layer of the winding of the electrode assembly 20 and is also the second outermost layer of the second corner area 204.

[0066] A first coating part 51 is provided in the first area 2101 of the first part 2121, and the first coating part 51 covers the first area 2101 of the first part 2121. Among them, the orthographic projection of the first coating part 51 in the first direction X is located within the orthographic projection of the first part 2121 in the first direction X. The third area 2103 is not provided with the first coating part 51. In some embodiments, the first coating part 51 is a ceramic coating, and the material of the first coating part 51 includes an adhesive and inorganic ceramic particles. Among them, the material of the inorganic ceramic particles can be selected from at least one of hafnium dioxide, strontium titanate, tin dioxide, cesium oxide, magnesium oxide, nickel oxide, calcium oxide, barium oxide, zinc oxide, zirconium oxide, yttrium oxide, aluminum oxide, titanium oxide, silicon dioxide, boehmite, magnesium hydroxide, or aluminum hydroxide. The material of the adhesive can be selected from at least one of a copolymer of difluoroethylene - hexafluoropropylene, a copolymer of vinylidene fluoride - trichloroethylene, polymethyl methacrylate, polyacrylic acid, polyacrylate, polyacrylate salt, polyacrylonitrile, polyvinylpyrrolidone, polyvinyl acetate, a copolymer of ethylene - vinyl acetate, polyimide, polyethylene oxide, cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, cyanoethylated amylose, cyanoethylated polyvinyl alcohol, cyanoethylated cellulose, cyanoethylated sucrose, amylose, sodium carboxymethyl cellulose, lithium carboxymethyl cellulose, a copolymer of acrylonitrile - styrene - butadiene, polyvinyl alcohol, polyvinyl ether, polytetrafluoroethylene, polyhexafluoropropylene, a copolymer of styrene - butadiene, or polyvinylidene fluoride. During production, the first coating part 51 can be provided on the first area 2101 of the first part 2121 by intaglio printing.

[0067] In this application, considering that the first surface 210A of the first part 212 is provided with the first active material layer 211 while the second surface 210B of the first part 212 is not provided with the active material layer, by disposing the first coating part 51 on the first area 2101 of the first part 2121, the first coating part 51 can improve the mechanical strength and anti-deformation ability of the first area 2101 of the first part 2121, reduce the risk of the first area 2101 of the first part 2121 warping outward under the action of stress, thereby reducing the risk of lithium plating caused by the outward warping of the first area 2101 of the first part 2121, and enhancing the safety and cycle life of the secondary battery 100. For example, when the first electrode sheet 21 is the positive electrode sheet and the second electrode sheet 22 is the negative electrode sheet, since the risk of increasing the transfer impedance due to the outward warping of the first area 2101 of the first part 2121 is reduced, the active ions (such as lithium ions) released from the first active material layer 211 corresponding to the first area 2101 in the first part 2121 can be transmitted along the first direction X towards the corresponding area of the second electrode sheet 22, reducing the risk of the active ions in this part preferentially transmitting towards other areas of the second electrode sheet 22 due to the increase in transfer impedance, thereby reducing the risk of lithium plating caused by the inability of too many active ions to be embedded in the local area of the second electrode sheet 22. Another example is when the first electrode sheet 21 is the negative electrode sheet and the second electrode sheet 22 is the positive electrode sheet. Since the risk of increasing the transfer impedance due to the outward warping of the first area 2101 of the first part 2121 is reduced, the active ions released from the corresponding area of the second electrode sheet 22 can be transmitted along the first direction X towards the first active material layer 211 corresponding to the first area 2101 in the first part 2121, reducing the risk of the active ions in this part preferentially transmitting towards other areas of the first active material layer 211 in the first part, thereby reducing the risk of lithium plating caused by the inability of too many active ions to be embedded in the local area of the first electrode sheet 21.

[0068] In particular, when the electrode assembly 20 has a wound structure, considering that the flat region in the first part 212 is less restricted than the corner region, making the flat region more likely to warp outward under stress, the first coating portion 51 is provided on the first region 2101 of the first part 2121 in this application (the first part 2121 constitutes the outermost side of the electrode assembly 20 in the first direction X, that is, the first part 2121 is located in the flat region), so that the mechanical strength and deformation resistance of the first region 2101 of the first part 2121, which is more likely to warp outward under stress, are improved, thereby effectively reducing the risk of the first part 212 warping outward under stress. It should be noted that the ranges of the first region 2101 and the second region 2102 are defined by limiting the width relationship between the first region 2101 and the second region 2102 relative to the first pole piece 21. This is not to illustrate that the position where the first part 212 warps outward in the case of omitting the first coating portion 51 is the entire first region 2101 or the entire second region 2102 of the first part 212. In fact, the position where the first part 212 is likely to warp outward may be smaller than the first region 2101 or smaller than the second region 2102. For example, the position where the first part 212 is likely to warp outward may be the part of the first region 2101 closer to the edge of the first pole piece 21 along the second direction Y.

[0069] Moreover, in order to improve the energy density and reduce the cost, when the first active material is provided to include ternary materials such as lithium nickel cobalt manganate, since nickel salts, cobalt salts, and manganese salts are usually used as raw materials in the preparation process of the first active material, and in order to control the pH value, these salts may introduce alkaline substances such as sodium hydroxide (NaOH) or potassium hydroxide (KOH) during the synthesis process. These alkaline substances may remain in the final ternary material, resulting in a relatively low bonding strength between the first pole piece 21 and the separator 23, which makes the first region 2101 of the first part 2121 more likely to warp outward under stress. In this application, the first coating portion 51 is provided on the first region 2101 of the first part 2121. Even when using ternary materials such as lithium nickel cobalt manganate as the positive electrode active material, the risk of the first region 2101 of the first part warping outward under stress can be reduced, thereby reducing the risk of lithium plating caused by the warping of the first region 2101 of the first part 2121, and improving the safety and cycle life of the secondary battery 100.

[0070] Such as Figure 3As shown, in some embodiments, in order to further reduce the risk of the first part 212 warping outward under stress, the second region 2102 of the first part 2121 may also be provided with a first coating part 51. Since the first coating part 51 is not provided on the third region 2103, the first coating part 51 provided on the first region 2101 of the first part and the first coating part 51 provided on the second region 2102 of the first part 2121 are separated from each other along the second direction Y. By providing the first coating part 51 on the second region 2102 of the first part 2121, the first coating part 51 can also improve the mechanical strength and deformation resistance of the second region 2102 of the first part 2121, reduce the risk of the second region 2102 of the first part 2121 warping outward under stress, thereby reducing the risk of lithium plating caused by the outward warping of the second region 2102 of the first part 2121, and further improving the safety and cycle life of the secondary battery 100.

[0071] Please refer to Figures 4 to 6 , in order to further reduce the risk of the first part 212 warping outward under stress, a second coating part 52 may also be provided on the first region 2101 of the second part 2122. The second coating part 52 can improve the mechanical strength and deformation resistance of the first region 2101 of the second part 2122, reduce the risk of the first region 2101 of the second part 2122 warping outward under stress, thereby reducing the risk of lithium plating caused by the outward warping of the first region 2101 of the second part 2122, and further improving the safety and cycle life of the secondary battery 100. Further, a third coating part 53 may also be provided on the first region 2101 of the third part 2123, or a fourth coating part 54 may be provided on the first region 2101 of the fourth part 2124. The materials of the second coating part 52, the third coating part 53, and the fourth coating part 54 may be the same as that of the first coating part 51. Among them, the fourth coating part 54 may have a relatively high porosity. Especially when the fourth coating part 54 has inorganic ceramic particles, this is conducive to increasing the space for electrolyte storage and circulation inside the electrode assembly 20, thereby further improving the cycle life of the secondary battery 100. In some embodiments, the fourth coating part 54, the first coating part 51, the third coating part 53, and the second coating part 52 are sequentially connected along the winding direction D, so that the fourth coating part 54, the first coating part 51, the third coating part 53, and the second coating part 52 are connected as a whole, further improving the mechanical strength and deformation resistance of the first region 2101 of the first part 212, and also facilitating printing the coating on the first region 2101 of the first part 212 at one time, thereby simplifying the process. It can be understood that corresponding coating parts may also be provided on the second region 2102 of the second part 2122, the second region 2102 of the third part 2123, and the second region 2102 of the fourth part 2124, which will not be elaborated here.

[0072] As shown Figure 3 In some embodiments, as shown, the first coating portion 51 includes a third edge 51A and a fourth edge 51B that are oppositely disposed along the second direction Y. Along the second direction Y, the third edge 51A is closer to the first edge 210B1 than the fourth edge 51B. The distance between the third edge 51A and the first edge 210B1 in the second direction Y is W3, where 0 ≤ W3 ≤ 3 mm. That is, when viewed from the first direction X, the third edge 51A may coincide with the first edge 210B1, or be sufficiently close to the first edge 210B1 in the second direction Y. In this way, the first coating portion 51 can sufficiently cover the first region 2101 of the first part 2121, further improving the mechanical strength and anti-deformation ability of the first region 2101 of the first part 2121, reducing the risk of the first region 2101 of the first part 2121 warping outward under stress, thereby reducing the risk of lithium plating caused by the outward warping of the first region 2101 of the first part 2121, and further enhancing the safety and cycle life of the secondary battery 100.

[0073] Optionally, it can be set that 0 ≤ W3 ≤ 1 mm, thereby further reducing the risk of the first region 2101 of the first part 2121 warping outward under stress. As an example, W3 can be 0 mm, 0.2 mm, 0.4 mm, 0.6 mm, 0.8 mm, 1 mm, or any value within the range formed by any two of the above values.

[0074] In some embodiments, the maximum width of the first coating portion 51 in the second direction Y is W4, where 0.10W ≤ W4 ≤ 0.30W. As shown Figure 3 When viewed from the first direction X, the first coating portion 51 can be generally rectangular in shape, and W4 is the width of the first coating portion 51 in the second direction Y. It can be understood that the shape of the first coating portion 51 is not limited to a rectangle, and can also be oval, polygonal, or other irregular shapes. Therefore, the width of the first coating portion 51 in the second direction Y is not a fixed value, and there is a maximum width W4 among the above widths. By limiting the range of W4, it is beneficial to increase the area of the first coating portion 51, so that the first coating portion 51 sufficiently covers the first region 2101 in the first part 2121 along the first direction X (especially the part in the first region 2101 that is more likely to warp outward), further improving the mechanical strength and anti-deformation ability of the first region 2101 of the first part 2121, reducing the risk of the first region 2101 of the first part 2121 warping outward under stress, thereby reducing the risk of lithium plating caused by the outward warping of the first region 2101 of the first part 2121, and further enhancing the safety and cycle life of the secondary battery 100.

[0075] Optionally, it can be set that 0.12W≤W4≤0.20W, so as to further increase the area of the first coating portion 51, which is beneficial to making the first coating portion 51 fully cover the first region 2101 in the first portion 2121 along the first direction X, while reducing the influence of the first coating portion 51 on the energy density of the secondary battery 100. Further, it can be set that 0.14W≤W4≤0.17W, so as to further be beneficial to the first coating portion 51 fully covering the first region 2101 in the first portion 2121 along the first direction X, while reducing the influence of the first coating portion 51 on the energy density of the secondary battery 100.

[0076] As Figure 1 shown, in some embodiments, the width of the first portion 2121 in the third direction Z is L, and the maximum length of the first coating portion 51 in the third direction Z is L1, where 0.50L≤L1≤L. Therefore, it is beneficial to increase the area of the first coating portion 51, so that the first coating portion 51 fully covers the first region 2101 of the first portion 2121 along the third direction Z, further improving the mechanical strength and anti-deformation ability of the first region 2101 located in the first portion, and reducing the risk of the first region 2101 of the first portion 2121 warping outwards under the action of stress. Thus, the risk of lithium plating caused by the outward warping of the first region 2101 of the first portion 2121 can be reduced, and the safety and cycle life of the secondary battery 100 are further improved. Wherein, the first portion 2121 includes a fifth edge 2121A and a sixth edge 2121B oppositely arranged along the third direction Z. The fifth edge 2121A is the first connection end 205, and the sixth edge 2121B is the edge of the first portion 2121 aligned with the fourth connection end 208 in the first direction X. The distance between the fifth edge 2121A and the sixth edge 2121B is the width L.

[0077] Optionally, it can be set that 0.70L ≤ L1 ≤ 0.90L. In this way, by further defining the lower limit of L1, the area of the first coating portion 51 can be further increased, so that the first coating portion 51 fully covers the first region 2101 in the first portion 2121 along the first direction X. At the same time, considering the third direction Z, in the first region 2101 of the first portion 2121, the position closer to the first corner region 202 or the second corner region 204 is less likely to warp due to the restraint of the first corner region 202 or the second corner region 204; on the contrary, the position in the first region 2101 of the first portion 2121 farther away from the first corner region 202 and the second corner region 204 is more likely to warp. Therefore, by further defining the upper limit of L1, it is beneficial to make the first coating portion 51 cover the position in the first region 2101 of the first portion 2121 that is more likely to warp (i.e., the position farther away from the first corner region 202 and the second corner region 204 in the third direction Z), while further reducing the risk of the first region 2101 of the first portion 2121 warping outward and reducing the impact of the first coating portion 51 on the energy density of the secondary battery 100.

[0078] As Figure 1 shown, the first coating portion 51 includes a seventh edge 51C and an eighth edge 51D oppositely arranged along the third direction Z, and the seventh edge 51C is closer to the fifth edge 2121A than the eighth edge 51D. Along the third direction Z, the fifth edge 2121A, the seventh edge 51C, the eighth edge 51D, and the sixth edge 2121B are arranged in sequence. Along the third direction Z, the distance between the seventh edge 51C and the fifth edge 2121A is L2, the distance between the eighth edge 51D and the sixth edge 2121B is L3, L′ = |L2 - L3|, and 0 ≤ L′ ≤ 0.15L. In this way, along the third direction Z, the first coating portion 51 can be arranged approximately in the middle of the first region 2101 of the first portion 2121, which is beneficial to the first coating portion 51 covering the position in the first region 2101 of the first portion 2121 that is more likely to warp (i.e., the position farther away from the first corner region 202 and the second corner region 204 in the third direction Z), and further reducing the risk of the first region 2101 of the first portion 2121 warping outward.

[0079] Optionally, it can be set that 0≤L′≤0.10L, which further facilitates the first coating portion 51 to cover the positions in the first region 2101 of the first part 2121 where warping is more likely to occur (i.e., the positions farther away from the first corner region 202 and the second corner region 204 in the third direction Z), and further reduces the risk of the first region 2101 of the first part 2121 warping outward. Among them, the values of W, W1, W3, W4, L, L1 - L3, etc. can be measured in the following way: 1) At a test temperature of 25°C, discharge the secondary battery 100 to 0% SOC, disassemble to obtain the first electrode sheet 21; 2) Use a suitable measuring tool to measure the corresponding dimensions.

[0080] In some embodiments, the coating weight per unit area of the first coating portion 51 can be set to 11 mg / 1540.25 mm 2 to 13 mg / 1540.25 mm 2 . By setting the coating weight per unit area of the first coating portion 51, the first coating portion 51 can effectively improve the mechanical strength and anti - deformation ability of the first region 2101 of the first part 2121, and reduce the risk of the first region 2101 of the first part 2121 warping outward under stress. At the same time, it can also reduce the risk of the energy density of the secondary battery 100 decreasing due to a relatively large coating weight per unit area. Among them, the coating weight per unit area of the first coating portion 51 can be measured in the following way: 1) At a test temperature of 25°C, discharge the secondary battery 100 to 0% SOC, disassemble to obtain the first electrode sheet 21, clean it with dimethyl carbonate (DMC) and then dry it; 2) Punch out a first part 2121 with an area of S and covered by the first coating portion 51 from the first part 212 of the first electrode sheet 21 as a sample, and weigh it using a balance, and record the weight as G1; 3) Scrape off the first coating portion 51 with a scraper, weigh the remaining sample, and record it as G0; calculate the coating weight per unit area of the first coating portion 51 through the following formula: G2=(G1 - G0) / S.

[0081] Moreover, the thickness H of the first coating portion 51 (marked in Figure 2 ) can be set to 7 μm to 9 μm. By setting the thickness of the first coating portion 51, the first coating portion 51 can effectively improve the mechanical strength and anti - deformation ability of the first region 2101 of the first part 2121, and reduce the risk of the first region 2101 of the first part 2121 warping outward under stress. At the same time, it can also reduce the risk of the energy density of the secondary battery 100 decreasing due to a relatively large thickness.

[0082] Such as Figures 4 to 6As shown, in some embodiments, the first active material layer 211 located on the second surface 210B includes a tail region 2110 in the winding direction D. When the fourth coating portion 54 is provided on the first region 2101 of the fourth portion 2124, when viewed from the first direction X, the fourth coating portion 54 overlaps with this part of the tail region 2110. For example, the fourth coating portion 54 may also cover a part of the tail region 2110. In this way, the fourth coating portion 54 can reduce the risk of micro-short circuit caused by the shedding of the first active material at the tail region 2110. Further, along the winding direction D, the width of the overlapping region between the fourth coating portion 54 and this part of the tail region 2110 can be set to be 2 mm to 4 mm. In this way, the fourth coating portion 54 can fully cover a part of the tail region 2110, further reducing the risk of micro-short circuit caused by the shedding of the first active material at the tail region 2110, and at the same time, it can also reduce the risk that a large amount of the first active material fails to play a capacity role when the width of the covered area is large. Of course, in other embodiments, it is also possible to set this part of the tail region 2110 to cover the fourth coating portion 54, so that the first active material in the tail region 2110 can fully play its capacity role.

[0083] As Figure 7 shown, in some other embodiments, the fourth coating portion 54 may also be provided on the second region 2102 and the third region 2103 of the fourth portion 2124. In this way, the fourth coating portion 54 can enhance the strength of the fourth portion 2124, improve the ability of the electrode assembly 20 to resist mechanical shock, and reduce the risk of the edge of the fourth portion 2124 being torn. Among them, the fourth coating portions 54 provided on the first region 2101, the third region 2103, and the second region 2102 of the fourth portion 2124 can be connected together along the second direction Y.

[0084] As Figure 8 shown, in some other embodiments, the fifth coating portion 55 is provided on the first region 2101 of the third part 214, i.e., the empty foil region. Alternatively, the fifth coating portion 55 is provided on the second region 2102 of the third part 214. In this way, the fifth coating portion 55 can enhance the strength of the first region 2101 or the second region 2102 of the third part 214, further improve the ability of the electrode assembly 20 to resist mechanical shock, and reduce the risk of the edge of the third part 214 being torn. Among them, the material of the fifth coating portion 55 can be the same as that of the first coating portion 51. The fourth coating portion 54, the first coating portion 51, the third coating portion 53, the second coating portion 52, and the fifth coating portion 55 are connected in sequence along the winding direction D ( Figure 8 in which is the fifth direction Z') so that the fourth coating portion 54, the first coating portion 51, the third coating portion 53, the second coating portion 52, and the fifth coating portion 55 are connected together.

[0085] As Figure 9As shown, in some other embodiments, the shape of the first coating portion 51 is not limited to a rectangle. For example, considering that in the region closer to the first edge 210B1 along the second direction Y, the risk of the first region 2101 warping outward may be higher. Therefore, it can be set that along the direction from the first edge 210B1 to the second edge 210B2, the length of the first coating portion 51 in the third direction Z gradually decreases. In this way, the first coating portion 51 fully covers the more easily warped portion of the first region 2101 in the first part 2121 along the first direction X, further improving the mechanical strength and anti-deformation ability of the first region 2101 of the first part 2121, reducing the risk of the first region 2101 of the first part 2121 warping outward under stress, and thus reducing the risk of lithium plating caused by the outward warping of the first region 2101 of the first part 2121, further enhancing the safety and cycle life of the secondary battery 100. Wherein, the length of the edge of the first coating portion 51 closest to the first edge 210B1 along the second direction Y is the above-mentioned maximum length L1.

[0086] Please refer to Figure 10 , another embodiment of the present application further provides a secondary battery 200. The difference from the above-mentioned secondary battery 100 is that the electrode assembly 20 is a stacked structure, which includes a plurality of first electrode plates 21, a plurality of second electrode plates 22, and a separator 23. In the stacked structure, the first electrode plates 21 and the second electrode plates 22 are alternately stacked in sequence. One second electrode plate 22 is provided between every two adjacent first electrode plates 21, and one first electrode plate 21 is provided between every two adjacent second electrode plates 22. The separator 23 is disposed between the adjacent first electrode plate 21 and the second electrode plate 22. At this time, the first part 2121 is the first electrode plate 21 located at the outermost layer of the electrode assembly 20 along the first direction X among the plurality of first electrode plates 21, and the first part 2121 constitutes one outermost side of the electrode assembly 20 along the first direction X. The second part 2122 constitutes the other outermost side of the electrode assembly 20 opposite to the first part 2121 along the first direction X.

[0087] By providing the first coating portion 51 on the first region 2101 of the first part 2121, the first coating portion 51 can also improve the mechanical strength and anti-deformation ability of the first region 2101 of the first part 2121, reduce the risk of the first region 2101 of the first part 2121 warping outward under stress, and thus reduce the risk of lithium plating caused by the outward warping of the first region 2101 of the first part 2121, enhancing the safety and cycle life of the secondary battery 200.

[0088] Such as Figure 11As shown, in some embodiments, the first part 212 includes a fourth region 2104, a third region 2103, and a fifth region 2105 that are sequentially connected along the third direction Z. Among them, the first region 2101, the fourth region 2104, the third region 2103, and the fifth region 2105 can be sequentially connected and jointly surround the outer periphery of the first region 2101. The first coating portion 51 can also be provided on the fourth region 2104 or the fifth region 2105. By providing the first coating portion 51 on the fourth region 2104 or the fifth region 2105 of the first part 2121, the first coating portion 51 can also improve the mechanical strength and anti-deformation ability of the fourth region 2104 or the fifth region 2105 of the first part 2121, reduce the risk of the fourth region 2104 or the fifth region 2105 of the first part 2121 warping outward under stress, thereby reducing the risk of lithium plating caused by the outward warping of the fourth region 2104 or the fifth region 2105 of the first part 2121, and further improving the safety and cycle life of the secondary battery 200.

[0089] Among them, the secondary batteries 100 and 200 of the present application can be lithium secondary batteries, including lithium metal secondary batteries, lithium ion secondary batteries, lithium polymer secondary batteries, or lithium ion polymer secondary batteries.

[0090] Please refer to Figure 12 , an embodiment of the present application further provides an electronic device 1. The electronic device 1 includes a battery compartment 101 and the above-mentioned secondary battery 100 (or secondary battery 200) provided in the battery compartment 101. Among them, the secondary battery 100 of the present application is applicable to electronic devices 1 in various fields. The electronic device 1 is powered by the above-mentioned secondary battery 100, and the lithium plating condition of the electrode assembly 20 is improved. Therefore, the secondary battery 100 has high safety and cycle life. In one embodiment, the electronic device 1 of the present application can be, but is not limited to, a notebook computer, a pen input computer, a mobile computer, an e-book player, a portable phone, a portable fax machine, a portable copier, a portable printer, a head-mounted stereo headset, a video recorder, a liquid crystal TV, a portable cleaner, a portable C machine, 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 flash, a camera, a large household battery, and a lithium ion capacitor, etc.

[0091] The present application will be described in detail below through specific examples and comparative examples. Among them, taking the secondary battery 100 as a wound lithium-ion secondary battery, the first electrode sheet 21 as the positive electrode sheet, and the second electrode sheet 22 as the negative electrode sheet as examples, and combining with the specific preparation process and testing method to describe the present application. Those skilled in the art should understand that the preparation methods described in the present application are only examples, and any other suitable preparation methods are within the scope of the present application.

[0092] Example 1

[0093] (1) Preparation of the first electrode sheet, i.e., the positive electrode sheet: Mix the positive electrode active material lithium cobalt oxide (LiCoO2), conductive carbon black (Super P), and polyvinylidene fluoride (PVDF) in a weight ratio of 96.5:1.5:2, add N-methylpyrrolidone (NMP) as a solvent, and formulate a slurry with a solid content of 75 wt%. Stir evenly. Pre-stick foaming glue on a part of the surface of the positive electrode current collector, i.e., aluminum foil with a thickness of 9 μm, evenly coat the slurry on the first surface of the aluminum foil, heat to make the foaming glue fall off to expose a part of the surface of the aluminum foil, and then dry it at 90 °C. Repeat the above coating steps on the second surface of the aluminum foil to obtain a double-sided coated positive electrode sheet. Cold press the initial positive electrode sheet to obtain a positive electrode active material layer with a single-layer coating thickness of 50 μm, and then obtain the positive electrode sheet through processes such as cutting. Weld the first electrode tab on the exposed aluminum foil, and the material of the first electrode tab is aluminum. Then, coat the first coating part on the second surface of the positive electrode current collector through a gravure coating process. The first coating part is located in the first region and the second region of the first part (single-sided coating area) of the first part respectively, and the material of the first coating part is aluminum oxide (Al2O3) ceramic and polyacrylate (PAA).

[0094] (2) Preparation of the second electrode sheet, i.e., the negative electrode sheet: Mix the negative electrode active material artificial graphite, silicon-carbon material, conductive carbon black (Super P), polyacrylic acid binder (PAA), and lithium difluorophosphate (LDPF) in a weight ratio of 69:5:6:19:1, add deionized water as a solvent, and formulate a slurry with a weight percentage of 55 wt%. Stir evenly. Pre-stick foaming glue on a part of the surface of the negative electrode current collector, i.e., copper foil with a thickness of 5 μm, evenly coat the slurry on the third surface of the copper foil, heat to make the foaming glue fall off to expose a part of the surface of the copper foil, and then dry it at 90 °C. Repeat the above coating steps on the fourth surface of the copper foil to obtain a double-sided coated negative electrode sheet. Roll press the initial negative electrode sheet to obtain a negative electrode active material layer with a coating thickness of 70 μm. Then, weld the second electrode tab on the exposed copper foil, and the material of the second electrode tab is nickel.

[0095] (3) Preparation of electrolyte: In a dry argon atmosphere, first, organic solvents ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) were mixed at a mass ratio of EC:EMC:DEC = 30:50:20. Then, lithium salt lithium hexafluorophosphate (LiPF6) was added to the organic solvents and dissolved and mixed evenly to obtain an electrolyte with a lithium salt concentration of 1.15 mol / L.

[0096] (4) Preparation of separator: A polyethylene (PE) membrane with a thickness of 9 μm was selected.

[0097] (5) Preparation of secondary battery: The first electrode sheet, the separator, and the second electrode sheet were stacked and wound in sequence to obtain Figure 1 the electrode assembly shown. An aluminum-plastic film (with a thickness of 150 μm) formed with a pit was placed in an assembly fixture with the pit surface facing up, and the electrode assembly was placed in the pit. Then, the electrolyte was injected into the pit of the aluminum-plastic film, and the first pole ear and the second pole ear were led out of the aluminum-plastic film and then encapsulated and formed to obtain a secondary battery.

[0098] Example 2

[0099] The difference from Example 1 lies in the preparation process of the first electrode sheet. In addition to coating the first coating portion on the second surface of the positive current collector through a gravure coating process, the second coating portion, the third coating portion, and the fourth coating portion were also simultaneously coated and formed. The second coating portion was respectively located in the first region and the second region of the second part of the first part, the third coating portion was respectively located in the first region and the second region of the third part of the first part, and the fourth coating portion was respectively located in the first region and the second region of the fourth part of the first part. The materials of the second to fourth coating portions were the same as the material of the first coating portion. After winding, the Figure 4 electrode assembly shown was obtained.

[0100] Comparative Example 1

[0101] The difference from Example 1 is that the first coating portion is omitted in the positive electrode sheet.

[0102] Then, 20 secondary batteries of each example and comparative example were respectively taken for cyclic performance tests, which included cyclic capacity retention rate tests and thickness expansion rate tests. The thickness expansion rate test can indirectly ensure whether lithium is deposited on the negative electrode sheet after cycling. The test results are recorded in Table 1.

[0103] Among them, the test steps for the cycle capacity retention rate are as follows: 1) At a test temperature of 25°C, let the secondary battery stand for 50 min, and charge it according to the following charging steps: (a) Constant current charge at 1.1C to 4.1V, and set the cut-off capacity of this step to C1; (b) Constant current charge at 0.5C to 4.4V, and then constant voltage charge to 0.05C, and set the cut-off capacity of this step to C2; (c) Stand for 5 min, and constant current discharge at 1.1C to 3.5V, and set the cut-off capacity of this step to C3; (d) Constant current discharge at 0.5C to 3V, and set the cut-off capacity of this step to C4; (e) Stand for 5 min; (f) If (C1 + C2) / (C3 + C4) > 1.02, then suspend charging; (g) If (C1 + C2) / (C3 + C4) ≤ 1.02, then stand for 5 min, and then cycle steps (a) to (g) until 1500 cycles are completed. 2) Take the discharge capacity of the third cycle as the reference capacity, and the ratio of the discharge capacity of the 1000th cycle to the reference capacity multiplied by 100% is the capacity retention rate after 1000 cycles. Take the average value of the capacity retention rates of 20 samples.

[0104] The test steps for the thickness expansion rate are as follows: Record the thickness h0 of the secondary battery before cycling and the thickness h after the 1000th cycle, and then calculate the thickness expansion rate of the secondary battery = (h / h0 - 1) × 100%. The results are recorded in Table 1.

[0105] Table 1

[0106] Coating part setting Capacity retention rate Thickness swelling rate Example 1 First coating part 93％ 10％ Example 2 First to fourth coating parts 96％ 8％ Comparative example 1 None 86％ 16％

[0107] It can be seen from the data in Table 1 that compared with Comparative Example 1, in Example 1, a first coating portion is provided on the first region of the first part. Therefore, the risk of the first region of the first part warping outward under stress is reduced, and the risk of lithium deposition caused by the outward warping of the first region of the first part is also reduced. Therefore, the secondary battery of Example 1 has a smaller thickness expansion rate and a higher cycle capacity retention rate. Compared with Example 1, in Example 2, a second coating portion, a third coating portion, and a fourth coating portion are further provided on the second part, the third part, and the fourth part respectively. Therefore, the risk of the first regions of the second part, the third part, and the fourth part warping outward under stress can be further reduced, and the risk of lithium deposition caused by the outward warping of the first region of the first part is also reduced. Therefore, the secondary battery of Example 2 has a smaller thickness expansion rate and a higher cycle capacity retention rate.

[0108] Examples 3 to 29

[0109] The differences from Example 1 lie in the values of W3, W4, L1, etc., which are specifically recorded in Tables 2 and 3. Among them, in Example 28, the material of the binder is replaced with polyvinylidene fluoride, and in Example 29, the material of the inorganic ceramic particles is replaced with boehmite.

[0110] Then, 20 secondary batteries of each embodiment were respectively subjected to the first debonding length test, cycle performance test, and volume energy density test, and the test results were recorded in Tables 2 and 3.

[0111] Among them, the steps of the first debonding length test are as follows:

[0112] At a test temperature of 25°C, the secondary battery was charged to 100% SOC. By means of CT (Computed Tomography) of the side structure of the battery, the middle region of the first coating part of the battery in the third direction (i.e., the region with the most severe warping) was taken to measure the debonding length. The starting point was set at the non-debonded edge of the positive electrode tab, and the end point was set at the starting point of debonding (i.e., the overhang edge), and the actual length value was marked and defined as the debonding length.

[0113] The judgment criteria for the severity of warping in the first part are as follows: debonding length < 0.5 mm, slight warping; debonding length 0.5 mm - 1 mm, medium warping; debonding length > 1 mm, severe warping.

[0114] The steps of the volume energy density test are as follows: 1) Under the environmental conditions of 25°C, the secondary battery was left standing for 10 min, charged at a constant current of 0.2C to 4.5V, charged at a constant voltage to 0.02C, and left standing for 5 min; then discharged at a constant current of 0.2C to 3V and left standing for 5 min, and the discharge capacity C0 was recorded; 2) The length, width, and thickness of the secondary battery were measured by a PPG battery thickness measuring instrument, and calculated by the following formula: volume energy density = platform voltage × C0 / (length × width × thickness).

[0115] The steps of the weight energy density test are as follows: 1) Under the environmental conditions of 25°C, the secondary battery was left standing for 10 min, charged at a constant current of 0.2C to 4.5V, charged at a constant voltage to 0.02C, and left standing for 5 min; then discharged at a constant current of 0.2C to 3V and left standing for 5 min, and the discharge capacity C0 was recorded; 2) The weight of the secondary battery was measured using a high-precision electronic balance, and calculated by the following formula: weight energy density = platform voltage × C0 / weight of the secondary battery.

[0116] Table 2

[0117]

[0118] As can be seen from Table 2, the distance W3 between the third edge and the first edge of the first coating portion in Examples 1, 3 to 5 in the second direction satisfies: 0 ≤ W3 ≤ 3 mm. Compared with Example 6, the distance W3 in Examples 1, 3 to 5 is smaller. Therefore, the first coating portion can fully cover the first region of the first part, reducing the risk of lithium plating caused by the outward warping of the first region of the first part under stress. As a result, the thickness expansion rate of the secondary battery is smaller and the cycle capacity retention rate is higher. In Examples 1 and 3, 0 ≤ W3 ≤ 1 mm, so the thickness expansion rate of the secondary battery is further smaller and the cycle capacity retention rate is further improved.

[0119] In Examples 1, 7 to 12, the maximum width W4 of the first coating in the second direction satisfies: 0.10W ≤ W4 ≤ 0.30W. Compared with Example 13, the area of the first coating portion in Examples 1, 7 to 12 is larger, so that the first coating portion fully covers the first region in the first part (especially the part that is more likely to warp outward in the first region) along the first direction. Therefore, the risk of lithium plating caused by warping is reduced, the thickness expansion rate of the secondary battery is smaller, and the cycle capacity retention rate is higher. Compared with Example 14, the secondary batteries in Examples 1, 7 to 12 can also take into account a relatively high weight energy density. Among them, in Examples 1 and 8 to 11, 0.12W ≤ W4 ≤ 0.20W, so the thickness expansion rate of the secondary battery is further smaller, the cycle capacity retention rate is further improved, and a relatively high weight energy density is taken into account at the same time. Further, in Examples 1, 9 and 10, 0.14W ≤ W4 ≤ 0.17W, so the thickness expansion rate of the secondary battery is further smaller, the cycle capacity retention rate is further improved, and a relatively high weight energy density is taken into account at the same time.

[0120] Table 3

[0121]

[0122] As can be seen from Table 3, the maximum length L1 of the first coating portion in the third direction in Examples 1, 15 to 18 satisfies: 0.50L ≤ L1 ≤ L. Compared with Example 19, the area of the first coating portion in Examples 1, 15 to 18 is larger, so that the first coating portion fully covers the first region of the first part along the third direction. Therefore, the thickness expansion rate of the secondary battery is smaller and the cycle capacity retention rate is higher. Among them, Examples 1, 16 and 17 satisfy 0.70L ≤ L1 ≤ 0.90L, which not only further increases the area of the first coating portion, but also makes the first coating portion cover the position where warping is more likely to occur in the first region of the first part (that is, the position in the middle of the first region of the first part in the third direction). Therefore, the risk of lithium plating caused by warping is reduced, the thickness expansion rate of the secondary battery is smaller, the cycle capacity retention rate is higher, and at the same time, due to the decrease of L1, the secondary battery can also take into account a higher weight energy density.

[0123] The absolute difference between the distance L2 between the seventh edge of the first coating and the fifth edge of the first part and the distance L3 between the eighth edge of the first coating and the sixth edge of the first part in Examples 1, 20 to 22 satisfies: 0 ≤ L′ ≤ 0.15L. Compared with Example 23, Examples 1, 20 to 22 can make the first coating portion be disposed substantially in the middle of the first region of the first part along the third direction, which is beneficial to the first coating portion covering the position where warping is more likely to occur in the first region of the first part (that is, the position in the middle of the first region of the first part in the third direction). Therefore, the risk of lithium plating caused by warping is reduced, the thickness expansion rate of the secondary battery is smaller, and the cycle capacity retention rate is higher. Among them, Examples 1, 20 and 21 satisfy 0 ≤ L′ ≤ 0.10L, so the thickness expansion rate of the secondary battery is further reduced and the cycle capacity retention rate is further improved.

[0124] The thickness H of the first coating portion in Examples 1, 24 and 25 satisfies: 7μm ≤ H ≤ 9μm. Compared with Example 26, the first coating portion in Examples 1, 24 and 25 is thicker, which can effectively improve the mechanical strength and anti-deformation ability of the first region of the first part, and reduce the risk of lithium plating caused by the outward warping of the first region of the first part under stress. Therefore, the thickness expansion rate of the secondary battery is smaller and the cycle capacity retention rate is higher. Compared with Example 27, the secondary batteries in Examples 1, 24 and 25 can also take into account a higher volume energy density and weight energy density.

[0125] In Example 1, Example 28, and Example 29, the materials of the inorganic ceramic particles or the binder are different. By comparing the experimental data of Example 1 and Example 28, it can be seen that using PAA as the binder material can better reduce the warping degree of the first part compared to using PVDF, in order to obtain a higher capacity retention rate and a lower thickness expansion rate. This is because PVDF belongs to an oily polymer and is easily dissolved in the electrolyte, which will lead to a decrease in the adhesion of the first coating part, resulting in a reduction in the inhibitory effect of the first coating part on the warping of the first part. By comparing the experimental data of Example 1 and Example 29, it can be seen that when the material of the inorganic ceramic particles is replaced from Al2O3 to boehmite, the difference in the warping degree, capacity retention rate, and thickness expansion rate of the first part is not significant.

[0126] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application and not to limit them. Although the present application has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that the technical solutions of the present application can be modified or equivalently replaced without departing from the spirit and scope of the technical solutions of the present application.

Claims

1. A secondary battery, comprising an electrode assembly and a tab, wherein the electrode assembly comprises a first pole piece, a second pole piece and a separator, wherein the separator is disposed between the first pole piece and the second pole piece; wherein: The first electrode sheet includes a first current collector and a first active material layer disposed on at least a portion of the first current collector; the first current collector includes a first surface and a second surface disposed opposite to each other along a thickness direction of the first current collector, the second surface is away from the center of the electrode assembly in a first direction, and the first direction is a thickness direction of the electrode assembly; The pole tab is electrically connected to the electrode assembly, the second direction is the direction in which the pole tab protrudes from the electrode assembly, and the second direction is perpendicular to the first direction; the second surface includes a first region, a third region, and a second region sequentially connected along the second direction, and the second surface also includes a first edge and a second edge arranged opposite to each other along the second direction, an edge of the first region in the second direction coincides with the first edge, and an edge of the second region in the second direction coincides with the second edge; the width of the first pole piece in the second direction is W, the width of the first region in the second direction is W1, and the width of the second region in the second direction is W2, W1=0.4W, W2=0.4W; The first electrode sheet includes a first part, the first surface of the first part is provided with the first active material layer, and the second surface of the first part is not provided with the active material layer; the first part includes a first portion, and the first portion constitutes an outermost side of the electrode assembly in the first direction; the first area of ​​the first portion is provided with a first coating portion, and the third area is not provided with the first coating portion.

2. The secondary battery according to claim 1, wherein The orthographic projection of the first coating portion in the first direction is located within the orthographic projection of the first portion in the first direction, the first coating portion includes a third edge and a fourth edge arranged relatively to each other along the second direction, the third edge is closer to the first edge relative to the fourth edge, and the distance between the third edge and the first edge in the second direction is W3, 0≤W3≤3mm.

3. The secondary battery according to claim 2, wherein: 0≤W3≤1mm.

4. The secondary battery according to claim 2, wherein: The maximum width of the first coating portion in the second direction is W4, and 0.10W≤W4≤0.30W.

5. The secondary battery according to claim 4, wherein: 0.12W≤W4≤0.20W.

6. The secondary battery according to claim 5, wherein: 0.14W≤W4≤0.17W.

7. The secondary battery according to claim 1, wherein The orthographic projection of the first coating portion in the first direction is located within the orthographic projection of the first portion in the first direction, the width of the first portion in the third direction is L, the maximum length of the first coating portion in the third direction is L1, 0.50L≤L1≤L; the third direction, the first direction and the second direction are perpendicular to each other.

8. The secondary battery according to claim 7, wherein: 0.70L≤L1≤0.90L.

9. The secondary battery according to claim 7, wherein: The first portion includes a fifth edge and a sixth edge arranged opposite to each other along the third direction, and the first coating portion includes a seventh edge and an eighth edge arranged opposite to each other along the third direction, and the seventh edge is closer to the fifth edge than the eighth edge; along the third direction, the distance between the seventh edge and the fifth edge is L2, and the distance between the eighth edge and the sixth edge is L3, L′=|L2-L3|, 0≤L′≤0.15L.

10. The secondary battery according to claim 9, wherein 0≤L′≤0.10L.

11. The secondary battery according to claim 1, wherein Along the direction from the first edge to the second edge, the length of the first coating portion in the third direction gradually decreases; the third direction, the first direction and the second direction are perpendicular to each other.

12. The secondary battery according to claim 1, wherein The second region located in the first portion is also provided with the first coating portion.

13. The secondary battery according to claim 1, wherein The material of the first coating layer includes a binder and inorganic ceramic particles.

14. The secondary battery according to claim 13, wherein The material of the first coating portion satisfies at least one of the following conditions: (1) The material of the inorganic ceramic particles is at least one selected from hafnium dioxide, strontium titanate, tin dioxide, cesium oxide, magnesium oxide, nickel oxide, calcium oxide, barium oxide, zinc oxide, zirconium oxide, yttrium oxide, aluminum oxide, titanium oxide, silicon dioxide, boehmite, magnesium hydroxide or aluminum hydroxide; (2) The material of the adhesive is selected from at least one of a copolymer of difluoroethylene and hexafluoropropylene, a copolymer of vinylidene fluoride and trichloroethylene, polymethyl methacrylate, polyacrylic acid, polyacrylate, polyacrylate, polyacrylonitrile, polyvinyl pyrrolidone, polyvinyl acetate, a copolymer of ethylene-vinyl acetate, polyimide, polyethylene oxide, cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, cyanoethyl pullulan, cyanoethyl polyvinyl alcohol, cyanoethyl cellulose, cyanoethyl sucrose, pullulan, sodium carboxymethyl cellulose, lithium carboxymethyl cellulose, a copolymer of acrylonitrile-styrene-butadiene, polyvinyl alcohol, polyvinyl ether, polytetrafluoroethylene, polyhexafluoropropylene, a copolymer of styrene-butadiene or polyvinylidene fluoride.

15. The secondary battery according to claim 13, wherein The coating weight per unit area of ​​the first coating portion is 11 mg / 1540.25 mm 2 Up to 13mg / 1540.25mm 2 .

16. The secondary battery according to claim 1, wherein The first coating portion has a thickness of 7 μm to 9 μm.

17. The secondary battery according to any one of claims 1 to 16, wherein: The electrode assembly is a wound structure, the first pole sheet includes a second part, the first part and a third part connected in sequence along the winding direction of the electrode assembly, the first surface and the second surface of the second part are both provided with the first active material layer, and the first surface and the second surface of the third part are not provided with the first active material layer; the outermost winding circle of the electrode assembly includes the third part and part of the first part, and the other part of the first part is located in the secondary winding outer circle of the first pole sheet.

18. The secondary battery according to claim 17, wherein The first portion further includes a second portion, which constitutes another outermost side of the electrode assembly disposed opposite to the first portion in the first direction; and a second coating portion is disposed in the first region of the second portion.

19. The secondary battery according to claim 18, wherein The electrode assembly includes a first corner area and a second corner area arranged relatively along a third direction, and the third direction, the first direction and the second direction are perpendicular to each other; the first part also includes a third portion, the first portion, the third portion and the second portion are sequentially connected along the winding direction of the electrode assembly, and the third portion constitutes the outermost side of the first corner area or the second corner area; the first area located in the third portion is provided with a third coating portion.

20. The secondary battery according to claim 19, wherein The first coating portion, the third coating portion, and the second coating portion are sequentially connected along a winding direction of the electrode assembly.

21. The secondary battery according to claim 17, wherein The first part includes a fourth part, the fourth part is located in the secondary outer circle of the winding of the electrode assembly, the fourth part and the first part are sequentially connected along the winding direction of the electrode assembly, and the first area located in the fourth part is provided with a fourth coating part.

22. The secondary battery according to claim 21, wherein The first active material layer located on the second surface includes an end region in the winding direction, and the fourth coating portion overlaps a portion of the end region when viewed from the first direction.

23. The secondary battery according to claim 22, wherein: Along the winding direction of the electrode assembly, a width of an overlapping area between the fourth coating portion and a portion of the finishing area is 2 mm to 4 mm.

24. The secondary battery according to claim 21, wherein The second region located in the fourth portion and the third region located in the fourth portion are also provided with the fourth coating portion.

25. The secondary battery according to claim 17, wherein The first region of the third portion and / or the second region of the third portion is provided with a fifth coating portion.

26. The secondary battery according to any one of claims 1 to 16, wherein: The electrode assembly is a stacked structure, the first part is the first pole piece among the multiple first pole pieces located at the outermost side of the electrode assembly along the first direction, the second surface of the first part includes a fourth region, a third region and a fifth region connected in sequence along a third direction, the third direction is perpendicular to the first direction and the second direction respectively, and the first coating part is also arranged in the fourth region and / or the fifth region.

27. The secondary battery according to claim 1, wherein The first electrode sheet is a positive electrode sheet, the first active material layer includes a first active material, and the first active material includes lithium nickel cobalt manganese oxide.

28. An electronic device, wherein: The electronic device includes the secondary battery according to any one of claims 1 to 27.

Images