Secondary battery and electronic device

Abstract

The invention discloses a secondary battery and electronic equipment, the secondary battery comprises an electrode assembly and a tab, and the electrode assembly comprises a first pole piece, an isolating membrane and a second pole piece. The first current collector 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 second surface is divided into a first region, a second region, and a third region. The second surface comprises a first edge and a second edge which are oppositely arranged, one edge of the first area coincides with the first edge, and one edge of the second area coincides with the second edge. The first part comprises a first section, and in the first direction, the outermost layer pole piece of the electrode assembly comprises the first section. The first area of the first section is provided with the first adhesive layer, and the third area is not provided with the first adhesive layer. The lithium precipitation risk caused by outward warping of the first region of the first section can be reduced, and the safety and cycle life of the secondary battery are improved.

Description

Technical Field

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

[0002] With the rapid development of modern technology, the demand for high-performance energy storage devices in fields such as portable electronic devices and electric vehicles is increasing day by day. As an efficient and environmentally friendly energy storage device, secondary batteries have been widely used in many fields.

[0003] The secondary battery includes an electrode assembly. Due to reasons such as energy density and safety, the outermost electrode sheet in the thickness direction of the electrode assembly 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 present application provides a secondary battery and an electronic device, aiming to reduce the technical problem of easy lithium deposition in the secondary battery.

[0005] In a first aspect, the present application provides a secondary battery, including an electrode assembly and a tab. The electrode assembly includes a first electrode sheet, a separator, and a second electrode sheet, and the separator is disposed between the first electrode sheet and the second electrode sheet. One end of the tab is connected to the electrode assembly, and the other end of the tab extends out of the electrode assembly. The first electrode sheet includes a first current collector and a first active material layer stacked on the first current collector. The first current collector includes a first surface and a second surface disposed opposite to each other, and the second surface faces away from the center of the electrode assembly in a first direction. Here, the first direction is the thickness direction of the electrode assembly, the direction from the electrode assembly to the tab is the second direction, and the second direction is perpendicular to the first direction. The first current collector includes a first portion, and a first active material layer is disposed on the first surface of the first portion, and no first active material layer is disposed on the second surface of the first portion. The second surface is divided into a first region, a second region, and a third region. Along the second direction, the third region is located between the first region and the second region. Along the second direction, the second surface includes a first edge and a second edge disposed opposite to each other. One edge of the first region coincides with the first edge, and one edge of the second region coincides with the second edge. Along the second direction, the width of the first current collector is W, the width of the first region is W1, the width of the second region is W2, and W1 = 0.4W, W2 = 0.4W. The first portion includes a first section, and along the first direction, the outermost electrode sheet of the electrode assembly includes the first section; a first adhesive layer is disposed in the first region of the first section, and no first adhesive layer is disposed in the third region.

[0006] In the above technical solution, a first adhesive layer is provided on the first region of the first section. The first adhesive layer can improve the mechanical strength and anti-deformation ability of the first region of the first section, reduce the risk of the first region of the first section warping outwards under stress, thereby reducing the risk of lithium deposition caused by the warping outwards of the first region of the first section, and improving the safety and cycle life of the secondary battery. Moreover, the adhesive application process is simple and convenient, conducive to mass production, and has a low cost.

[0007] In some embodiments, the orthographic projection of the first adhesive layer in the first direction is located within the orthographic projection of the first section in the first direction. Along the second direction, the first adhesive layer includes a relatively arranged third edge and a fourth edge. Compared with the fourth edge, the third edge is closer to the first edge. Along the second direction, the distance between the third edge and the first edge is W3, and 0mm ≤ W3 ≤ 3mm. The first adhesive layer can fully cover the first region of the first section, further improving the mechanical strength and anti-deformation ability of the first region of the first section, and reducing the risk of the first region of the first section warping outwards under stress.

[0008] In some embodiments, 0mm ≤ W3 ≤ 1mm, so as to further reduce the risk of the first region of the first section warping outwards under stress.

[0009] In some embodiments, along the second direction, the maximum width of the first adhesive layer is W4, and 0.1W ≤ W4 ≤ 0.3W, which is beneficial to increasing the area of the first adhesive layer, enabling the first adhesive layer to fully cover the first region in the first section (especially the part in the first region that is more likely to warp outwards) along the first direction, further improving the mechanical strength and anti-deformation ability of the first region of the first section, and reducing the risk of the first region of the first section warping outwards under stress.

[0010] In some embodiments, 0.12W ≤ W4 ≤ 0.2W, further increasing the area of the first adhesive layer, enabling the first adhesive layer to fully cover the first region in the first section along the first direction while reducing the impact of the first adhesive layer on the energy density of the secondary battery.

[0011] In some embodiments, 0.14W ≤ W4 ≤ 0.17W, further increasing the area of the first adhesive layer, enabling the first adhesive layer to fully cover the first region in the first section along the first direction while reducing the impact of the first adhesive layer on the energy density of the secondary battery.

[0012] In some embodiments, the orthographic projection of the first adhesive layer in the first direction is located within the orthographic projection of the first section in the first direction. The length of the first section in the third direction is L, and the maximum length of the first adhesive layer in the third direction is L1, where 0.5L ≤ L1 ≤ L. Herein, the first direction, the second direction, and the third direction are perpendicular to each other pairwise. This is conducive to increasing the area of the first adhesive layer, enabling the first adhesive layer to fully cover the first region of the first section along the third direction, further enhancing the mechanical strength and anti-deformation ability of the first region of the first section, and reducing the risk of the first region of the first section warping outward under stress.

[0013] In some embodiments, 0.7L ≤ L1 ≤ 0.9L. By further defining the lower limit of L1 as 0.7L, the area of the first adhesive layer can be further increased, enabling the first adhesive layer to fully cover the first region in the first section along the first direction. By further defining the upper limit of L1 as 0.9L, it is conducive to the first adhesive layer covering the position in the first region of the first section that is more prone to warping (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 section warping outward and reducing the impact of the first adhesive layer on the energy density of the secondary battery.

[0014] In some embodiments, the orthographic projection of the first section in the first direction includes a fifth edge and a sixth edge that are oppositely arranged along the third direction. The first adhesive layer includes a seventh edge and an eighth edge that are oppositely arranged along the third direction. Compared with the eighth edge, the seventh edge is closer to the fifth 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, and L′ = |L2 - L3|, where 0 ≤ L′ ≤ 0.15L. This enables the first adhesive layer to be disposed approximately in the middle of the first region of the first section along the third direction, which is conducive to the first adhesive layer covering the position in the first region of the first section that is more prone to warping (i.e., the position far from the corner area of the electrode assembly in the third direction), further reducing the risk of the first region of the first section warping outward, and thus reducing the occurrence of lithium plating.

[0015] In some embodiments, 0 ≤ L′ ≤ 0.1L, which is further conducive to the first adhesive layer covering the position in the first region of the first section that is more prone to warping, further reducing the risk of the first region of the first section warping outward, and thus reducing the occurrence of lithium plating.

[0016] In some embodiments, along the direction from the first edge to the second edge, the length of the first adhesive layer in the third direction gradually decreases. Herein, the first direction, the second direction, and the third direction are perpendicular to each other pairwise. The shape adjusted according to the stress distribution is conducive to reducing the outward warping of the first region of the first section while reducing the impact of the first adhesive layer on the energy density of the secondary battery.

[0017] In some embodiments, a first adhesive layer is provided in the second region of the first segment. The first adhesive layer can also improve the mechanical strength and anti-deformation ability of the second region of the first segment, reduce the risk of the second region of the first segment warping outward under stress, thereby reducing the risk of lithium plating caused by the outward warping of the second region of the first segment, and further improving the safety and cycle life of the secondary battery.

[0018] In some embodiments, the first adhesive layer includes a substrate layer and an adhesive layer. The adhesive layer is bonded between the first part and the substrate layer. The substrate layer can provide support, which is more conducive to maintaining the shape integrity of the first adhesive layer and reducing the risk of the first region of the first segment warping outward. The adhesive layer provides adhesive force, enabling the first adhesive layer to adhere to the first region of the first segment.

[0019] In some embodiments, the material of the substrate layer includes one or more of polyethylene terephthalate, polyimide, polyethylene, polypropylene, polyvinyl chloride, kraft paper, cotton cloth, synthetic fiber cloth, metal foil, and glass fiber. The material of the adhesive layer includes one or more of rubber-based adhesives, silicone-based adhesives, hot melt adhesives, water-based adhesives, polyurethane-based adhesives, epoxy-based adhesives, and polyimide-based adhesives.

[0020] In some embodiments, the thickness of the first adhesive layer is T, where 7μm ≤ T ≤ 9μm, such that the first adhesive layer can effectively improve the mechanical strength and anti-deformation ability of the first region of the first segment, reduce the risk of the first region of the first segment warping outward under stress. At the same time, it can also reduce the risk of reducing the energy density of the secondary battery due to a relatively large thickness.

[0021] In some embodiments, 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 relatively low bonding strength between the first electrode sheet and the separator, the first adhesive layer can still reduce the risk of the first region of the first segment warping outward under stress.

[0022] In some embodiments, the electrode assembly has a wound structure. Along the winding direction, the first electrode tab includes a second portion, a first portion, and a third portion connected in sequence. 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 electrode tab 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 layer of the first electrode tab. For the wound electrode assembly, the flat region in the first portion is less restricted than the corner region, making it easier for the flat region to warp outward under stress. Therefore, by disposing the first adhesive layer on the flat region of the first portion, such as on the first region of the first segment, the mechanical strength and deformation resistance of the first region of the first segment, which is more likely to warp outward under stress, are improved, thereby effectively reducing the risk of the first portion warping outward under stress.

[0023] In some embodiments, the outermost electrode tab of the electrode assembly further includes a second segment, the second segment is disposed opposite to the first segment along a first direction, and a second adhesive layer is provided on the first region of the second segment. The second adhesive layer can improve the mechanical strength and deformation resistance of the first region of the second segment, reduce the risk of the first region of the second segment warping outward under stress, thereby reducing the risk of lithium plating caused by the outward warping of the first region of the second segment, and further improving the safety and cycle life of the secondary battery.

[0024] In some embodiments, along a third direction, the electrode assembly further includes a first corner region and a second corner region disposed opposite to each other. The first portion further includes a third segment, and along the winding direction, the first segment, the third segment, and the second segment are connected in sequence, and the third segment constitutes the outermost electrode tab of the first corner region. A third adhesive layer is provided on the first region of the third segment. The third adhesive layer can improve the mechanical strength and deformation resistance of the first region of the third segment, reduce the risk of the first region of the third segment warping outward under stress, thereby reducing the risk of lithium plating caused by the outward warping of the first region of the third segment, and further improving the safety and cycle life of the secondary battery. In addition, the third adhesive layer can also reduce the risk of the first region of the third segment being torn.

[0025] In some embodiments, along the winding direction, the first adhesive layer, the third adhesive layer, and the second adhesive layer are connected in sequence, and the first adhesive layer, the third adhesive layer, and the second adhesive layer 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 applying the adhesive at one time on the first region of the first portion, simplifying the process.

[0026] In some embodiments, the first part further includes a fourth section located in the second outermost layer of the electrode assembly. Along the winding direction, the fourth section and the first section are arranged in sequence, and a fourth adhesive layer is provided in a first area of the fourth section. The fourth adhesive layer can improve the mechanical strength and anti-deformation ability of the first area of the fourth section, reduce the risk of the first area of the fourth section warping outwards under the action of stress, thereby reducing the risk of lithium plating caused by the outward warping of the first area of the fourth section, and further improving the safety and cycle life of the secondary battery. In addition, the fourth adhesive layer can have a relatively high porosity, especially when the fourth adhesive layer also has inorganic ceramic particles, which is conducive to increasing the space for electrolyte storage and circulation in the electrode assembly, thereby further improving the cycle life of the secondary battery.

[0027] In some embodiments, along the winding direction, the first active material layer located on the second surface includes a finishing area. Along the winding direction, the fourth adhesive layer overlaps with a part of the finishing area. This enables the fourth adhesive layer to reduce the risk of micro-short circuit caused by the shedding of the first active material at the finishing area, and further improves the safety and cycle life of the secondary battery.

[0028] In some embodiments, along the winding direction, the length of the overlapping area between the fourth adhesive layer and a part of the finishing area is L4, where 2 mm ≤ L4 ≤ 4 mm. When the fourth adhesive layer 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 capacity role due to the relatively large width of the covering area.

[0029] In some embodiments, a fifth adhesive layer is provided in the first area and / or the second area of the third part. The fifth adhesive layer can enhance the strength of the first area or the second area of the third part, and further improve the mechanical shock resistance of the electrode assembly.

[0030] In some embodiments, the electrode assembly is a stacked structure. Along the first direction, the first section is the first electrode sheet located in the outermost layer of the electrode assembly among a plurality of first electrode sheets. Along the third direction, the first section includes a fourth area, a third area, and a fifth area connected in sequence, and a first adhesive layer is provided in the fourth area and / or the fifth area. Among them, the third direction is perpendicular to the first direction and the second direction in pairs. The first adhesive layer can also improve the mechanical strength and anti-deformation ability of the fourth area and / or the fifth area of the first section, reduce the risk of the fourth area or the fifth area of the first section warping outwards under the action of stress, thereby reducing the risk of lithium plating caused by the outward warping of the fourth area or the fifth area of the first section, and further improving the safety and cycle life of the secondary battery.

[0031] In a second aspect, the present application also proposes an electronic device, including the secondary battery according to any one of the embodiments in the first aspect above.

[0032] Additional aspects and advantages of the embodiments of the present application will be described, shown, or elucidated in part in the following description, or by the implementation of the embodiments of the present application. Description of the Drawings

[0033] One or more embodiments are exemplarily illustrated by pictures in the corresponding drawings. These exemplary illustrations are not intended to limit the embodiments. Elements with the same reference numerals in the drawings represent similar elements.

[0034] Figure 1 Schematic cross-sectional view of a secondary battery according to some embodiments of the present application;

[0035] Figure 2 Side view of the first electrode tab after being unfolded according to some embodiments of the present application;

[0036] Figure 3 Front view of the opening of the first electrode tab according to some embodiments of the present application;

[0037] Figure 4 Schematic structural view of an electrode assembly according to some embodiments of the present application;

[0038] Figure 5 Schematic cross-sectional view of a secondary battery according to some embodiments of the present application;

[0039] Figure 6 Side view of the first electrode tab after being unfolded according to some embodiments of the present application;

[0040] Figure 7 Front view of the opening of the first electrode tab according to some embodiments of the present application;

[0041] Figure 8 Front view of the opening of the first electrode tab according to some embodiments of the present application;

[0042] Figure 9 Front view of the opening of the first electrode tab according to some embodiments of the present application;

[0043] Figure 10 Front view of the opening of the first electrode tab according to some embodiments of the present application;

[0044] Figure 11 Schematic cross-sectional view of a secondary battery according to some embodiments of the present application;

[0045] Figure 12 is Figure 10 Front view of the first electrode tab of the secondary battery shown.

[0046] Description of the Reference Numerals:

[0047] 100, secondary battery;

[0048] 10. Housing;

[0049] 20. Electrode assembly;

[0050] 201. First flat region; 201a. First outer surface; 202. First corner region; 203. Second flat region; 204. Second corner region; 203a. Second outer surface; 205. First connection end; 206. Second connection end; 207. Third connection end; 208. Fourth connection end;

[0051] 21. First pole piece; 210. First current collector; 210a. First surface; 210b. Second surface; 210b1. First edge; 210b2. Second edge; 212. First part; 2121. First section; 2121a. Fifth edge; 2121b. Sixth edge; 2122. Second section; 2123. Third section; 2124. Fourth section; 213. Second part; 214. Third part; 2101. First region; 2102. Second region; 2103. Third region; 2104. Fourth region; 2105. Fifth region; 2110. Ending region; 211. First active material layer;

[0052] 22. Second pole piece; 220. Second current collector; 220a. Third surface; 220b. Fourth surface; 221. Second active material layer; 23. Separator;

[0053] 30. First tab;

[0054] 40. Second tab;

[0055] 51. First adhesive layer; 51a. Third edge; 51b. Fourth edge; 51c. Fifth and seventh edges; 51d. Eighth edge; 52. Second adhesive layer; 53. Third adhesive layer; 54. Fourth adhesive layer; 55. Fifth adhesive layer;

[0056] O. Winding central axis; X. First direction; Y. Second direction; Z. Third direction; X’ 、 Fourth direction; Z’ 、 Fifth direction. Detailed implementation manners

[0057] To make the objectives, technical solutions, and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be clearly described below with reference to the accompanying drawings in the embodiments of the present application. Apparently, the described embodiments are some, but not all, of the embodiments of the present application.

[0058] References to "embodiments" in this application mean that the specific features, structures, or characteristics described in connection with the embodiments can be included in at least one embodiment of this application. The phrase appears in various places in the specification and does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment mutually exclusive with other embodiments.

[0059] In the description of the embodiments of this application, technical terms such as "first" and "second" are only used to distinguish different objects, and cannot be understood as indicating or implying relative importance or implicitly specifying the quantity, specific order, or primary-secondary relationship of the indicated technical features. In the description of the embodiments of this application, the meaning of "a plurality" is more than two, unless otherwise clearly and specifically defined.

[0060] In the description of the embodiments of this application, the term "and / or" is merely a description of the association relationship of associated objects, indicating that there can be three relationships. For example, A and / or B can represent: A exists alone, A and B exist simultaneously, and B exists alone. In addition, the character " / " in this article generally represents an "or" relationship between the associated objects before and after.

[0061] The technical features involved in different embodiments of this application described below can be combined with each other as long as they do not conflict with each other.

[0062] In a first aspect, this application provides a secondary battery 100. Please refer to Figure 1 , the secondary battery 100 includes a housing 10, an electrode assembly 20, an electrolyte (not labeled in the figure), and tabs (including a first tab 30 and / or a second tab 40). The electrode assembly 20 and the electrolyte are disposed inside the housing 10, and one end of the tab is electrically connected to the electrode assembly 20, and the other end can extend out of the housing 10.

[0063] The electrode assembly 20 includes a first electrode plate 21, a second electrode plate 22, and a separator 23. The polarities of the first electrode plate 21 and the second electrode plate 22 are opposite. For example, the first electrode plate 21 is a positive electrode plate and the second electrode plate 22 is a negative electrode plate. In some other embodiments, the first electrode plate 21 may also be a negative electrode plate, and the second electrode plate 22 is a positive electrode plate. The separator 23 is disposed between the first electrode plate 21 and the second electrode plate 22 for insulating and separating the first electrode plate 21 and the second electrode plate 22.

[0064] Please further refer to Figure 2 , Figure 2 shows the unfolded structure of the first electrode plate 21. The first electrode plate 21 includes a first current collector 210 and a first active material layer 211 stacked on at least a part of the first current collector 210. Along the thickness direction of the first current collector 210 (for example, along Figure 2The fourth direction X' (the fourth direction X is the thickness of the first current collector 210), the first current collector 210 includes a first surface 210a and a second surface 210b which are oppositely arranged, and the first active material layer 211 is respectively arranged on at least part of the first surface 210a and at least part of the second surface 210b. Among them, the second surface 210b faces away from the center of the electrode assembly 20 in the first direction X, and the second surface 210b faces the housing 10.

[0065] The second electrode tab 22 includes a second current collector 220 and a second active material layer 221 stacked on at least part of the second current collector 220. Along the thickness direction of the second current collector 220, the second current collector 220 includes a third surface 220a and a fourth surface 220b which are oppositely arranged, and the second active material layer 221 is respectively arranged on at least part of the third surface 220a and at least part of the fourth surface 220b. Among them, the fourth surface 220b faces away from the center of the electrode assembly 20 in the first direction X, and the fourth surface 220b faces the housing 10.

[0066] The electrode tabs may include a first electrode tab 30 and a second electrode tab 40. One end of the first electrode tab 30 is electrically connected to the first electrode tab 21, and the other end of the first electrode tab 30 extends out of the first electrode tab 21. One end of the second electrode tab 40 is electrically connected to the second electrode tab 22, and the other end of the second electrode tab 40 extends out of the second electrode tab 22. The first electrode tab 30 and the second electrode tab 40 can be connected to external components, and then charge and discharge the secondary battery 100. Among them, the first electrode tab 30 can be electrically connected to the first current collector 210 by means of welding or conductive adhesive bonding, etc., or directly cut out the first electrode tab 30 on the first current collector 210 by die-cutting. The second electrode tab 40 can be arranged similarly to the first electrode tab 30.

[0067] The electrode assembly 20 can adopt a wound structure, that is, the first electrode tab 21, the separator 23 and the second electrode tab 22 are laminated 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 both face the winding central axis O, and the second surface 210b of the first current collector 210 and the fourth surface 220b of the second current collector 220 both face away from the winding central axis O. The center of the electrode assembly 20 in the first direction X is the position of the winding central axis O. Among them, taking the three-dimensional coordinate system defined by the first direction X, the second direction Y and the third direction Z which are perpendicular to each other in pairs as an example, the first direction X is the thickness direction of the electrode assembly 20, the second direction Y is the direction in which the first electrode tab 30 or the second electrode tab 40 protrudes from the electrode assembly 20, the second direction Y is also the width direction of the first electrode tab 21 or the second electrode tab 22, and the third direction Z is the width direction of the secondary battery 100.

[0068] The electrode assembly 20 can be divided into a first straight region 201, a first corner region 202, a second straight region 203, and a second corner region 204 that are sequentially connected in the winding direction S. The first straight region 201 and the second straight region 203 are oppositely arranged in the first direction X, and the first corner region 202 and the second corner region 204 are oppositely arranged in the third direction Z. Among them, the corner region is the bent portion of the electrode assembly 20. The corner region is a concept opposite to the straight region. When observed along the second direction Y, the first corner region 202 and the second corner region 204 can be arranged in an arc shape.

[0069] Please refer to Figure 1 , the first straight region 201 has a first outer surface 201a, and the second straight region 203 has a second outer surface 203a. The connection between the first straight 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 S. The first connection end 205 is also the part where the dotted line A-A formed by the extension of the leftmost bent edge located inside and on the left side of the electrode assembly 20 in the first direction X intersects the first outer surface 201a.

[0070] The connection between the first corner region 202 located on the outermost side of the electrode assembly 20 and the second straight 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 S. The second connection end 206 is also the part where the dotted line A-A intersects the second outer surface 203a.

[0071] The connection between the second straight region 203 located on the outermost side of the electrode assembly 20 and the second corner region 204 located on the outermost side of the electrode assembly 20 is the third connection end 207. The third connection end 207 is the starting part of the rightmost curve of the second corner region 204 in the winding direction S. The third connection end 207 is also the part where the dotted line B-B formed by the extension of the rightmost bent edge located inside and on the right side of the electrode assembly 20 in the first direction X intersects the second outer surface 203a.

[0072] The connection between the second corner region 204 located on the outermost side of the electrode assembly 20 and the first straight region 201 located on the outermost side of the electrode assembly 20 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 S. 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.

[0073] In the embodiments of the present application, the first electrode sheet 21 is taken as the positive electrode sheet, and the second electrode sheet 22 is taken as the negative electrode sheet as an example. Correspondingly, the first current collector 210 is the positive current collector, the first active material layer 211 includes the first active material, and the first active material is the positive active material. The second current collector 220 is the negative current collector, the second active material layer 221 includes the second active material, and the second active material is the negative active material. In some other embodiments, the first electrode sheet 21 may also be set as the negative electrode sheet, and the second electrode sheet 22 may be set as the positive electrode sheet.

[0074] Please refer to Figures 2 to 4 , in which Figure 2 and Figure 3 is Figure 1 the schematic structural diagram of the first electrode sheet 21 after being unfolded as shown, Figure 4 and Figure 2 is Figure 3 the schematic structural diagram of the overall electrode assembly 20. A three-dimensional coordinate system is established in

[0075] and 0.5 Mn 1.5 O4) or lithium iron phosphate (LiFePO4).

[0076] The negative active material uses a negative active substance known in the art that can reversibly deintercalate and intercalate active ions, and the present 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 oxides, silicon-carbon composites, and silicon alloys; tin-based materials can be selected from one or a combination of elemental tin, tin oxides, and tin alloys.

[0077] Please refer to Figure 3, the second surface 210b is divided into a first region 2101, a second region 2102, and a third region 2103. Along the second direction Y, the third region 2103 is located between the first region 2101 and the second region 2102, that is, the first region 2101, the third region 2103, and the second region 2102 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', the first tab 3030 and the first edge 210b1 overlap, and the first tab 30 extends from the edge out of the first electrode tab 21. 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 electrode tab 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, where W1 = 0.4W and W2 = 0.4W.

[0078] Please refer to Figures 1 to 4 , the first current collector 210 includes a first portion 212, and the first portion 212 can be a single-sided coating area. A first active material layer 211 is provided on the first surface 210a of the first portion 212, and the first active material layer 211 is not provided on the second surface 210b of the first portion 212. When the electrode assembly 20 is a wound structure, the first electrode tab 21 includes a second portion 213, a first portion 212, and a third portion 214 that are sequentially connected along the winding direction S. The second portion 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 portion 213. The third portion 214 is an empty foil area, and the first active material layer 211 is not provided on both the first surface 210a and the second surface 210b of the third portion 214.

[0079] Along the winding direction S (or, Figure 2 and Figure 3In 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 wound pole piece of the electrode assembly 20 includes a 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 layer of the winding of the first pole piece 21. Therefore, the outer surface of the outermost wound pole piece is the second surface 210b of the first current collector 210. On the one hand, the first current collector 210 can improve the strength 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 pole piece and the second pole piece 22 is a negative pole piece, the risk that the electrolyte easily corrodes the second current collector 220 (such as copper foil) when the second pole piece 22 ends is reduced.

[0080] The first part 212 includes a fourth section 2124, a first section 2121, a third section 2123, and a second section 2122 that are sequentially connected along the winding direction S. The outermost pole piece of the electrode assembly 20 includes the first section 2121, and the first section 2121 constitutes one outermost pole piece of the electrode assembly 20 in the first direction X. For example, the first section 2121 can be the outermost pole piece of the first flat region 201 in the first direction X. The second section 2122 constitutes the other outermost pole piece of the electrode assembly 20 that is oppositely arranged with the first section 2121 in the first direction X. For example, the second section 2122 can be the outermost pole piece of the second flat region 203 in the first direction X. The third section 2123 constitutes the outermost pole piece of the first corner region 202. The fourth section 2124 is located in the second outermost wound pole piece of the electrode assembly 20 and is also the second outermost pole piece of the second corner region 204.

[0081] To improve the energy density, the outermost pole piece is usually a single-sided pole piece, that is, the active material layer is provided only on one side of the outermost pole piece. The inventors of the present application have found that since the active material layer is provided on one side of the outermost pole piece and not on the other side, the edge region of the outermost pole piece may warp outward under the action of stress, thereby forming a gap between the outermost pole piece and the separator, deteriorating the transmission interface. Taking the outermost pole piece as the positive pole piece as an example, during charging and discharging, the impedance of the active ions escaping from the warped region of the outermost pole piece to the edge region of the negative pole piece through the above gap becomes larger. Therefore, the active ions will preferentially transmit to the inner region of the negative pole piece, causing lithium deposition to easily occur at the junction of the edge region and the edge region of the negative pole piece, reducing the safety and cycle life of the secondary battery.

[0082] To reduce the above problems, in the embodiments of the present application, a first adhesive layer 51 is provided in the first region 2101 of the first segment 2121. The first adhesive layer 51 covers the first region 2101 of the first segment 2121, while the first adhesive layer 51 is not provided in the third region 2103. In some embodiments, the first adhesive layer 51 includes a substrate layer and an adhesive layer, and the adhesive layer is bonded between the first part 212 and the substrate layer. The material of the substrate layer includes one or more of polyethylene terephthalate, polyimide, polyethylene, polypropylene, polyvinyl chloride, kraft paper, cotton cloth, synthetic fiber cloth, metal foil, and glass fiber. The material of the adhesive layer includes one or more of rubber-based adhesives, silicone-based adhesives, hot melt adhesives, water-based adhesives, polyurethane-based adhesives, epoxy-based adhesives, and polyimide-based adhesives.

[0083] In the present application, considering that the first active material layer 211 is provided on the first surface 210a of the first part 212 while the first active material layer 211 is not provided on the second surface 210b of the first part 212, by providing the first adhesive layer 51 in the first region 2101 of the first segment 2121, the first adhesive layer 51 can improve the mechanical strength and anti-deformation ability of the first region 2101 of the first segment 2121, reduce the risk of the first region 2101 of the first segment 2121 warping outward under stress, and thus can reduce the risk of lithium plating caused by the outward warping of the first region 2101 of the first segment 2121, improving the safety and cycle life of the secondary battery 100.

[0084] Moreover, in the present application, the first adhesive layer 51 is not provided in the second region 2102, which is beneficial for the second region 2102 to be closer to the separator 23, and thus is beneficial for reducing the impedance near the second region 2102.

[0085] For example, when the first electrode sheet 21 is a positive electrode sheet and the second electrode sheet 22 is a negative electrode sheet, since the risk of the first region 2101 of the first segment 2121 warping outward is reduced, the risk of an increase in the transfer impedance is reduced. Therefore, the active ions (such as lithium ions) released from the first active material layer 211 corresponding to the first region 2101 in the first segment 2121 can be transmitted along the first direction X towards the corresponding region of the second electrode sheet 22, reducing the risk that the active ions in this part preferentially transmit to other regions of the second electrode sheet 22 due to an increase in the transfer impedance, and thus reducing the risk of lithium plating caused by the inability of too many active ions to be embedded in a local region of the second electrode sheet 22.

[0086] For another example, when the first electrode tab 21 is a negative electrode tab and the second electrode tab 22 is a positive electrode tab, since the risk of the first region 2101 of the first segment 2121 warping outward is reduced, the risk of an increase in the transfer impedance is reduced. Therefore, the active ions escaping from the corresponding region of the second electrode tab 22 can travel along the first direction X towards the first active material layer 211 corresponding to the first region 2101 in the first segment 2121, reducing the risk that these active ions preferentially travel towards other regions of the first active material layer 211 in the first segment 2121 due to an increase in the transfer impedance, thereby reducing the risk of lithium plating caused by an inability to embed too many active ions in a local area of the first electrode tab 21.

[0087] When the electrode assembly 20 has a wound structure, considering that the flat region in the first part 212 is subject to less restraint force than the corner region, making the flat region more likely to warp outward under stress, the present application disposes the first adhesive layer 51 on the first region 2101 of the first segment 2121 (the first segment 2121 constitutes the outermost electrode tab of the electrode assembly 20 in the first direction X, that is, the first segment 2121 is located in the flat region), so that the mechanical strength and anti-deformation ability of the first region 2101 of the first segment 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.

[0088] It should be noted that the present application defines the ranges where the first region 2101 and the second region 2102 are located by limiting the width relationship between the first region 2101 and the second region 2102 with respect to the first electrode tab 21. This is not to illustrate that the position where the first part 212 warps outward in the case of omitting the first adhesive layer 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 may be smaller than the second region 2102. For example, the position where the first part 212 is likely to warp outward can be the part of the first region 2101 closer to the edge of the first electrode tab 21 along the second direction Y.

[0089] Moreover, in order to improve the energy density and reduce the cost, when the first active material is set to include ternary materials such as lithium nickel cobalt manganese oxide, 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 themselves may introduce alkaline substances during the synthesis process, such as sodium hydroxide (NaOH) or potassium hydroxide (KOH). These alkaline substances may remain in the final ternary material, resulting in a relatively low adhesion strength between the first electrode sheet 21 and the separator 23, which makes the first region 2101 of the first section 2121 more likely to warp outward under stress. In the present application, a first adhesive layer 51 is provided on the first region 2101 of the first section 2121. Even when using ternary materials such as lithium nickel cobalt manganese oxide as the positive electrode active material, the risk of the first region 2101 of the first section 2121 warping outward under stress can be reduced, thereby reducing the risk of lithium plating caused by the outward warping of the first region 2101 of the first section 2121, and improving the safety and cycle life of the secondary battery 100.

[0090] Please refer to Figure 3 , 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 section 2121 may also be provided with a first adhesive layer 51. Since the first adhesive layer 51 is not provided on the third region 2103, the first adhesive layer 51 provided on the first region 2101 of the first section 2121 and the first adhesive layer 51 provided on the second region 2102 of the first section 2121 are separated from each other along the second direction Y. By providing the first adhesive layer 51 on the second region 2102 of the first section 2121, the first adhesive layer 51 can also improve the mechanical strength and deformation resistance of the second region 2102 of the first section 2121, reduce the risk of the second region 2102 of the first section 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 section 2121, and further improving the safety and cycle life of the secondary battery 100.

[0091] Please refer to Figures 5 to 7 , in order to further reduce the risk of the first part 212 warping outward under stress, a second adhesive layer 52 may also be provided on the first region 2101 of the second section 2122. The second adhesive layer 52 can improve the mechanical strength and deformation resistance of the first region 2101 of the second section 2122, reduce the risk of the first region 2101 of the second section 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 section 2122, and further improving the safety and cycle life of the secondary battery 100.

[0092] Further, a third adhesive layer 53 may be provided on the first region 2101 of the third section 2123, or a fourth adhesive layer 54 may be provided on the first region 2101 of the fourth section 2124. The materials of the second adhesive layer 52, the third adhesive layer 53, and the fourth adhesive layer 54 may be the same as that of the first adhesive layer 51. Among them, the fourth adhesive layer 54 may have a relatively high porosity, which 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.

[0093] In some embodiments, the fourth adhesive layer 54, the first adhesive layer 51, the third adhesive layer 53, and the second adhesive layer 52 are sequentially connected along the winding direction S, so that the fourth adhesive layer 54, the first adhesive layer 51, the third adhesive layer 53, and the second adhesive layer 52 are connected as a whole, further improving the mechanical strength and anti-deformation ability of the first region 2101 of the first part 212, and also facilitating one-time bonding on the first region 2101 of the first part 212, thereby simplifying the process. It can be understood that corresponding adhesive layers may also be provided on the second region 2102 of the second section 2122, the second region 2102 of the third section 2123, and the second region 2102 of the fourth section 2124, which will not be elaborated here.

[0094] Please refer to Figure 3 , in some embodiments, the orthographic projection of the first adhesive layer 51 in the first direction X is located within the orthographic projection of the first section 2121 in the first direction X. The first adhesive layer 51 includes a third edge 51a and a fourth edge 51b that are oppositely arranged 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, and any value between 0 mm and 3 mm can be selected, such as 0 mm, 0.2 mm, 0.4 mm, 0.6 mm, 0.8 mm, 1 mm, 1.2 mm, 1.4 mm, 1.6 mm, 1.8 mm, 2 mm, 2.2 mm, 2.4 mm, 2.6 mm, 2.8 mm, or 3 mm, etc.

[0095] 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 adhesive layer 51 can fully cover the first region 2101 of the first section 2121, further improving the mechanical strength and anti-deformation ability of the first region 2101 of the first section 2121, reducing the risk of the first region 2101 of the first section 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 section 2121, and further improving the safety and cycle life of the secondary battery 100.

[0096] Optionally, it can be set that 0≤W3≤1mm, so that the risk of the first region 2101 of the first segment 2121 warping outwards under the action of stress can be further reduced. As an example, W3 can be 0mm, 0.2mm, 0.4mm, 0.6mm, 0.8mm, 1mm or any value within the range formed by any two of the above values.

[0097] In some embodiments, the maximum width of the first adhesive layer 51 in the second direction Y is W4, and 0.1W≤W4≤0.3W. Among them, please refer to Figure 3 , when viewed from the first direction X, the first adhesive layer 51 can be generally rectangular in shape, and W4 is the width of the first adhesive layer 51 in the second direction Y. It can be understood that the shape of the first adhesive layer 51 is not limited to rectangular, and can also be oval, polygonal or other irregular shapes. Therefore, the width of the first adhesive layer 51 in the second direction Y is not a fixed value, and there is a maximum width W4 among the above widths.

[0098] By limiting the range of W4, it is beneficial to increase the area of the first adhesive layer 51, so that the first adhesive layer 51 fully covers the first region 2101 in the first segment 2121 along the first direction X (especially the part of the first region 2101 that is more likely to warp outwards), further improving the mechanical strength and anti-deformation ability of the first region 2101 of the first segment 2121, reducing the risk of the first region 2101 of the first segment 2121 warping outwards under the action of stress, and thus reducing the risk of lithium plating caused by the outward warping of the first region 2101 of the first segment 2121, further enhancing the safety and cycle life of the secondary battery 100.

[0099] Optionally, it can be set that 0.12W≤W4≤0.2W, so that while further increasing the area of the first adhesive layer 51 and facilitating the first adhesive layer 51 to fully cover the first region 2101 in the first segment 2121 along the first direction X, the influence of the first adhesive layer 51 on the energy density of the secondary battery 100 is reduced. Further, it can be set that 0.14W≤W4≤0.17W, which is beneficial for the first adhesive layer 51 to fully cover the first region 2101 in the first segment 2121 along the first direction X and can reduce the influence of the first adhesive layer 51 on the energy density of the secondary battery 100.

[0100] Please refer to Figure 1, in some embodiments, the positive projection of the first adhesive layer 51 in the first direction X is located within the positive projection of the first section 2121 in the first direction X. The width of the first section 2121 in the third direction Z is L, and the maximum length of the first adhesive layer 51 in the third direction Z is L1, where 0.5L ≤ L1 ≤ L. Therefore, it is beneficial to increase the area of the first adhesive layer 51, so that the first adhesive layer 51 fully covers the first region 2101 of the first section 2121 along the third direction Z, further improving the mechanical strength and anti-deformation ability of the first region 2101 of the first section 2121, reducing the risk of the first region 2101 of the first section 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 section 2121, and further improving the safety and cycle life of the secondary battery 100.

[0101] Among them, the positive projection of the first section 2121 in the first direction X includes a fifth edge 2121a and a sixth edge 2121b that are 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 section 2121 that is 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.

[0102] Furthermore, it can be set that 0.7L ≤ L1 ≤ 0.9L. In this way, by further limiting the lower limit of L1, the area of the first adhesive layer 51 can be further increased, so that the first adhesive layer 51 fully covers the first region 2101 in the first section 2121 along the first direction X. At the same time, considering that along the third direction Z, the position in the first region 2101 of the first section 2121 that is closer to the first corner area 202 or the second corner area 204 is less likely to warp due to the restraint of the first corner area 202 or the second corner area 204; on the contrary, the position in the first region 2101 of the first section 2121 that is farther away from the first corner area 202 and the second corner area 204 is more likely to warp. Therefore, by further limiting the upper limit of L1, it is beneficial to make the first adhesive layer 51 cover the position in the first region 2101 of the first section 2121 that is more likely to warp (i.e., the position that is farther away from the first corner area 202 and the second corner area 204 in the third direction Z), while further reducing the risk of the first region 2101 of the first section 2121 warping outward, and reducing the impact of the first adhesive layer 51 on the energy density of the secondary battery 100.

[0103] Please refer to Figure 1, the first adhesive layer 51 includes a seventh edge 51c and an eighth edge 51d that are oppositely arranged along the third direction Z. 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, and 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 adhesive layer 51 can be disposed substantially in the middle of the first region 2101 of the first section 2121, which is beneficial for the first adhesive layer 51 to cover the positions in the first region 2101 of the first section 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), further reducing the risk of the first region 2101 of the first section 2121 warping outward.

[0104] Furthermore, 0 ≤ L′ ≤ 0.1L can be set, which is further beneficial for the first adhesive layer 51 to cover the positions in the first region 2101 of the first section 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), further reducing the risk of the first region 2101 of the first section 2121 warping outward. Among them, the values of W, W1, W3, W4, L, L1 to 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 and disassemble to obtain the first electrode sheet 21; 2) Use a suitable measuring tool to measure the corresponding dimensions.

[0105] In some embodiments, the thickness T of the first adhesive layer 51 (marked in Figure 2 ) is 7 μm to 9 μm. By setting the thickness of the first adhesive layer 51, the first adhesive layer 51 can effectively improve the mechanical strength and anti-deformation ability of the first region 2101 of the first section 2121, reducing the risk of the first region 2101 of the first section 2121 warping outward under stress. At the same time, the risk of reducing the energy density of the secondary battery 100 due to a large thickness can also be reduced.

[0106] Please refer to Figures 5 to 7 , in some embodiments, the first active material layer 211 on the second surface 210b includes a finishing area 2110 in the winding direction S. When the fourth adhesive layer 54 is disposed on the first region 2101 of the fourth section 2124, when viewed from the first direction X, the fourth adhesive layer 54 overlaps with this part of the finishing area 2110. For example, the fourth adhesive layer 54 can also cover part of the finishing area 2110. In this way, the fourth adhesive layer 54 can reduce the risk of micro-short circuit caused by the detachment of the first active material at the finishing area 2110.

[0107] Furthermore, along the winding direction S, the width of the overlapping area between the fourth adhesive layer 54 and the part of the tail region 2110 can be set to L4, 2mm≤L4≤4mm. In this way, the fourth adhesive layer 54 can fully cover the part of the tail region 2110, further reducing the risk of the first active material at the tail region 2110 falling off and causing a micro short circuit, and at the same time, it can also reduce the risk of more first active materials failing to play a capacity role when the width of the covering area is large. Of course, in some other embodiments, the part of the tail region 2110 can also be set to cover the fourth adhesive layer 54, so that the first active material in the tail region 2110 can fully play a capacity role.

[0108] Please refer to Figure 8 In other embodiments, the second region 2102 of the fourth segment 2124 and the third region 2103 of the fourth segment 2124 may also be provided with a fourth adhesive layer 54. In this way, the fourth adhesive layer 54 can enhance the strength of the fourth segment 2124, improve the mechanical impact resistance of the electrode assembly 20, and reduce the risk of the edge of the fourth segment 2124 being torn. The fourth adhesive layer 54 respectively provided in the first region 2101, the third region 2103, and the second region 2102 of the fourth segment 2124 can be connected as a whole along the second direction Y.

[0109] Please refer to Figure 9 In other embodiments, a fifth adhesive layer 55 is provided on the first area 2101 of the third part 214, i.e., the empty foil area. Alternatively, a fifth adhesive layer 55 is provided on the second area 2102 of the third part 214. In this way, the fifth adhesive layer 55 can enhance the strength of the first area 2101 or the second area 2102 of the third part 214, further improve the ability of the electrode assembly 20 to withstand mechanical shock, and reduce the risk of the edge of the third part 214 being torn. The material of the fifth adhesive layer 55 can be the same as that of the first adhesive layer 51. The fourth adhesive layer 54, the first adhesive layer 51, the third adhesive layer 53, the second adhesive layer 52, and the fifth adhesive layer 55 are arranged along the winding direction S( Figure 9 The fourth adhesive layer 54, the first adhesive layer 51, the third adhesive layer 53, the second adhesive layer 52 and the fifth adhesive layer 55 are connected in sequence in the fifth direction (Z′).

[0110] Please refer to Figure 10, in some other embodiments, the shape of the first adhesive layer 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 adhesive layer 51 in the third direction Z gradually decreases. In this way, the first adhesive layer 51 fully covers the more easily warped part of the first region 2101 in the first segment 2121 along the first direction X, further improving the mechanical strength and anti-deformation ability of the first region 2101 located in the first segment 2121, reducing the risk of the first region 2101 of the first segment 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 segment 2121, and further enhancing the safety and cycle life of the secondary battery 100. Among them, the length of the edge of the first adhesive layer 51 closest to the first edge 210b1 along the second direction Y is the above-mentioned maximum length L1.

[0111] Please refer to Figure 11 , 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 segment 2121 is the outermost first electrode plate 21 among the plurality of first electrode plates 21 along the first direction X of the electrode assembly 20, that is, the first segment 2121 constitutes an outermost electrode plate of the electrode assembly 20 along the first direction X. The second segment 2122 constitutes the other outermost electrode plate of the electrode assembly 20 along the first direction X opposite to the first segment 2121.

[0112] By providing the first adhesive layer 51 on the first region 2101 located in the first segment 2121, the first adhesive layer 51 can also improve the mechanical strength and anti-deformation ability of the first region 2101 located in the first segment 2121, reduce the risk of the first region 2101 of the first segment 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 segment 2121, and enhancing the safety and cycle life of the secondary battery 100.

[0113] Please refer to Figure 12, in some embodiments, the first section 2121 includes, along a third direction Z, a fourth region 2104, a third region 2103, and a fifth region 2105 that are connected in sequence. Among them, the first region 2101, the fourth region 2104, the third region 2103, and the fifth region 2105 can be connected in sequence and jointly surround the outer periphery of the first region 2101. The first adhesive layer 51 can also be disposed in the fourth region 2104 or in the fifth region 2105. By disposing the first adhesive layer 51 on the fourth region 2104 or the fifth region 2105 of the first section 2121, the first adhesive layer 51 can also improve the mechanical strength and anti-deformation ability of the fourth region 2104 or the fifth region 2105 of the first section 2121, reduce the risk of the fourth region 2104 or the fifth region 2105 of the first section 2121 warping outward under the action of 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 section 2121, and further improving the safety and cycle life of the secondary battery 200.

[0114] Among them, the secondary batteries 100, 200 of the present application can be lithium secondary batteries 100, including lithium metal secondary batteries 100, lithium ion secondary batteries 100, lithium polymer secondary batteries 100, or lithium ion polymer secondary batteries 100.

[0115] In a second aspect, an embodiment of the present application further provides an electronic device, which includes the secondary battery 100 (or secondary battery 200) of any one of the embodiments in the first aspect above. Among them, the secondary battery 100 of the present application is applicable to electronic devices in various fields. The electronic device is powered by the secondary battery 100 above, 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 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.

[0116] 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 100, 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 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.

[0117] Example 1

[0118] Preparation of the adhesive layer: Polyethylene terephthalate was selected as the base material layer, and a polyurethane-based adhesive was selected as the adhesive layer. The adhesive layer was laminated on the base material layer to form a first adhesive layer with a thickness of 10 μm. The second adhesive layer, the third adhesive layer, the fourth adhesive layer, etc. can be prepared similarly.

[0119] Preparation of the first electrode sheet, i.e., the positive electrode sheet: The positive electrode active material lithium cobaltate (LiCO2), conductive carbon black (SuperP), and polyvinylidene fluoride (PVDF) were mixed in a weight ratio of 96.5:1.5:2, and N-methylpyrrolidone (NMP) was added as a solvent to prepare a slurry with a solid content of 75 wt%. The slurry was stirred evenly. Foaming glue was pre-pasted on a part of the surface of the positive electrode current collector aluminum foil with a thickness of 9 μm. The slurry was evenly coated on the first surface of the aluminum foil, and heated to make the foaming glue fall off to expose a part of the surface of the aluminum foil, and then dried at 90 °C. The above coating steps were repeated on the second surface of the aluminum foil to obtain a double-sided coated positive electrode sheet. The initial positive electrode sheet was cold-pressed to obtain a positive electrode active material layer with a single-layer coating thickness of 50 μm, and then obtained the positive electrode sheet through processes such as cutting. A first pole ear was welded on the exposed aluminum foil, and the material of the first pole ear was aluminum. Then, the first adhesive layer was bonded on the second surface of the positive electrode current collector, and the first adhesive layer was located in the first region and the second region of the first section of the first part (single-sided coating area) respectively.

[0120] Preparation of the second electrode sheet, i.e., the negative electrode sheet: The negative electrode active material artificial graphite, silicon-carbon material, conductive carbon black (Super P), polyacrylic acid binder (PAA), and lithium difluorophosphate (LDPF) were mixed in a weight ratio of 69:5:6:19:1, and deionized water was added as a solvent to prepare a slurry with a weight percentage of 55 wt%. The slurry was stirred evenly. Foaming glue was pre-pasted on a part of the surface of the negative electrode current collector, i.e., copper foil with a thickness of 5 μm. The slurry was evenly coated on the third surface of the copper foil, and heated to make the foaming glue fall off to expose a part of the surface of the copper foil, and then dried at 90 °C. The above coating steps were repeated on the fourth surface of the copper foil to obtain a double-sided coated negative electrode sheet. The initial negative electrode sheet was roll-pressed to obtain a negative electrode active material layer with a coating thickness of 70 μm. Then, a second pole ear was welded on the exposed copper foil, and the material of the second pole ear was nickel.

[0121] Preparation of electrolyte: In a dry argon atmosphere, first, ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) as organic solvents were mixed at a mass ratio of EC:EMC:DEC = 30:50:20. Then, lithium hexafluorophosphate (LiPF6) as a lithium salt 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.

[0122] Preparation of separator: A polyethylene (PE) film with a thickness of 9 μm was selected.

[0123] 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 as 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 electrode tab and the second electrode tab were led out of the aluminum-plastic film and then encapsulated and formed to obtain a secondary battery.

[0124] Example 2

[0125] The difference from Example 1 lies in the preparation process of the first electrode sheet. In addition to bonding the first adhesive layer on the second surface of the positive current collector, the second adhesive layer, the third adhesive layer, and the fourth adhesive layer were also bonded simultaneously. The second adhesive layer was located in the first region and the second region of the second segment of the first part, the third adhesive layer was located in the first region and the second region of the third segment of the first part, and the fourth adhesive layer was located in the first region and the second region of the fourth segment of the first part. The materials of the second to fourth adhesive layers were the same as that of the first adhesive layer. After winding, the Figure 5 electrode assembly as shown was obtained.

[0126] Comparative Example 1

[0127] The difference from Example 1 is that the first adhesive layer was not provided in the positive electrode sheet.

[0128] Then, 20 secondary batteries of each of the examples and comparative examples were taken respectively for cyclic performance tests, which included cyclic capacity retention rate tests and thickness expansion rate tests. The thickness expansion rate test can indirectly characterize whether lithium is deposited on the negative electrode sheet after cycling. The test results were recorded in Table 1.

[0129] Among them, the test steps for the cycle capacity retention rate are as follows: 1) At a test temperature of 25°C, the secondary battery is left standing for 50 min and then charged according to the following charging steps: (a) Constant current charging at 1.1C until 4.1V, and the cut-off capacity for this step is set as C1; (b) Constant current charging at 0.5C until 4.4V, followed by constant voltage charging until 0.05C, and the cut-off capacity for this step is set as C2; (c) Leave standing for 5 min, then constant current discharge at 1.1C until 3.5V, and the cut-off capacity for this step is set as C3; (d) Constant current discharge at 0.5C until 3V, and the cut-off capacity for this step is set as C4; (e) Leave standing for 5 min; (f) If (C1 + C2) / (C3 + C4) > 1.02, then suspend charging; (g) If (C1 + C2) / (C3 + C4) ≤ 1.02, then leave standing for 5 min, and then repeat steps (a) to (g) until 1000 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. The average values of the capacity retention rates of 20 samples are recorded in Table 1.

[0130] The test steps for the thickness expansion rate are as follows: Record the thickness T0 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 = (T / T0 - 1) × 100%. The results are recorded in Table 1.

[0131] Table 1

[0132] Adhesive layer setting Capacity retention rate Thickness swelling rate Comparative Example 1 None 82％ 19％ Example 1 First adhesive layer 92％ 11％ Example 2 First to fourth adhesive layers 94％ 8％

[0133] According to Table 1 above, in combination with Examples 1 to 2 and Comparative Example 1, compared with Comparative Example 1, in Example 1, a first adhesive layer is provided on the first region of the first segment. Therefore, the risk of the first region of the first segment warping outward under stress is reduced, and the risk of lithium plating caused by the outward warping of the first region of the first segment 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 adhesive layer, a third adhesive layer, and a fourth adhesive layer are further provided on the second segment, the third segment, and the fourth segment respectively. Therefore, the risk of the first regions of the second segment, the third segment, and the fourth segment warping outward under stress can be further reduced, and the risk of lithium plating caused by the outward warping of the first region of the first segment is also reduced. Therefore, the secondary battery of Example 2 has a smaller thickness expansion rate and a higher cycle capacity retention rate.

[0134] The differences between Examples 3 to 27 and Example 1 lie in the values of W3, W4, L1, etc., which are specifically recorded in Table 2. Then, for each of the secondary batteries of the examples, 20 samples are taken respectively for the first segment debonding length test, the cycle performance test, and the volume energy density test, and the average values of the test results are recorded in Table 2.

[0135] Among them, the test steps for the debonding length of the first section are as follows:

[0136] At a test temperature of 25°C, charge the secondary battery 100 to 100% SOC. Through the side structure of the CT (Computed Tomography) battery, take the middle area of the first adhesive layer of the battery in the third direction (i.e., the area with the most severe warping) to measure the debonding length. The starting point is set at the non-debonded edge of the positive electrode plate, and the end point is set at the debonding starting point (i.e., the overhang edge), and mark the actual length value, which is defined as the debonding length.

[0137] The judgment criteria for the warping severity of the first section 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.

[0138] The test steps for the volumetric energy density are as follows: 1) Under the environmental conditions of 25°C, let the secondary battery stand for 10 min, charge it at a constant current of 0.2C to 4.5V, charge it at a constant voltage to 0.02C, and let it stand for 5 min; then discharge it at a constant current of 0.2C to 3V, and let it stand for 5 min, and record the discharge capacity C0; 2) Measure the length, width, and thickness of the secondary battery through a PPG battery thickness measuring instrument, and calculate through the following formula: Volumetric energy density = plateau voltage × C0 / (length × width × thickness).

[0139] The test steps for the gravimetric energy density are as follows: 1) Under the environmental conditions of 25°C, let the secondary battery stand for 10 min, charge it at a constant current of 0.2C to 4.5V, charge it at a constant voltage to 0.02C, and let it stand for 5 min; then discharge it at a constant current of 0.2C to 3V, and let it stand for 5 min, and record the discharge capacity C0; 2) Measure the weight of the secondary battery using a high-precision electronic balance, and calculate through the following formula: Gravimetric energy density = plateau voltage × C0 / weight of the secondary battery.

[0140] Table 2

[0141]

[0142]

[0143] As can be seen from Table 2, the distance W3 between the third edge and the first edge of the first adhesive layer 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 adhesive layer can fully cover the first region of the first segment, reducing the risk of lithium deposition caused by the outward warping of the first region of the first segment 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, the thickness expansion rate of the secondary battery is further smaller and the cycle capacity retention rate is further improved.

[0144] In Examples 1, 7 to 12, the maximum width W4 of the first coating in the second direction satisfies: 0.1W ≤ W4 ≤ 0.3W. Compared with Example 13, the area of the first adhesive layer in Examples 1, 7 to 12 is larger, so that the first adhesive layer fully covers the first region in the first segment along the first direction (especially the part in the first region that is more likely to warp outward). The risk of lithium deposition 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 higher weight energy density. Among them, in Examples 1 and 8 to 11, 0.12W ≤ W4 ≤ 0.2W, so the thickness expansion rate of the secondary battery is further smaller, the cycle capacity retention rate is further improved, and a higher 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 higher weight energy density is taken into account at the same time.

[0145] In Examples 1, 15 to 18, the maximum length L1 of the first adhesive layer in the third direction satisfies: 0.5L ≤ L1 ≤ L. Compared with Example 19, the area of the first adhesive layer in Examples 1, 15 to 18 is larger, so that the first adhesive layer fully covers the first region of the first segment along the third direction, the thickness expansion rate of the secondary battery is smaller, and the cycle capacity retention rate is higher. Among them, in Examples 1, 16 and 17, 0.7L ≤ L1 ≤ 0.9L, which not only further increases the area of the first adhesive layer, but also makes the first adhesive layer cover the position in the first region of the first segment that is more likely to warp (i.e., the position in the middle of the first region of the first segment in the third direction). Therefore, the risk of lithium deposition 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.

[0146] In Embodiment 1, Embodiments 20 to 22, the absolute difference between the distance L2 between the seventh edge of the first adhesive layer and the fifth edge of the first section, and the distance L3 between the eighth edge of the first adhesive layer and the sixth edge of the first section satisfies: 0 ≤ L′ ≤ 0.15L. Compared with Embodiment 23, in Embodiment 1, Embodiments 20 to 22, along the third direction, the first adhesive layer is disposed substantially centered on the first region of the first section, which is conducive to the first adhesive layer covering the position where warping is more likely to occur in the first region of the first section (i.e., the position centered in the third direction of the first region of the first section). Therefore, the risk of lithium deposition due to warping is reduced, the thickness expansion rate of the secondary battery is small, and the cycle capacity retention rate is high. Among them, in Embodiment 1, Embodiment 20, and Embodiment 21, 0 ≤ L′ ≤ 0.1L, so the thickness expansion rate of the secondary battery is further reduced, and the cycle capacity retention rate is further improved.

[0147] In Embodiment 1, Embodiment 24, and Embodiment 25, the thickness T of the first adhesive layer satisfies: 7 μm ≤ T ≤ 9 μm. Compared with Embodiment 26, the first adhesive layer in Embodiment 1, Embodiment 24, and Embodiment 25 is thicker, which can effectively improve the mechanical strength and anti-deformation ability of the first region of the first section, and reduce the risk of lithium deposition caused by the outward warping of the first region of the first section under stress. Therefore, the thickness expansion rate of the secondary battery is small, and the cycle capacity retention rate is high. Compared with Embodiment 27, the secondary batteries in Embodiment 1, Embodiment 24, and Embodiment 25 can also achieve a relatively high volume energy density and weight energy density.

[0148] The difference between Embodiments 28 to 31 and Embodiment 2 lies in the value of L4, which is specifically recorded in Table 3. For each of the secondary batteries of each embodiment, 20 were taken respectively for volume energy density testing and Hi-pot pass rate testing, and the test results were averaged and recorded in Table 3.

[0149] Among them, the Hi-pot pass rate testing steps are as follows: 1) Detect the leakage current generated by the secondary battery prepared in the embodiment or comparative example under the 100V test voltage output by the high-voltage machine, and then calculate the resistance value = test voltage / leakage current; 2) Compare the calculated resistance value with the set determination resistance. In this application, the preset value of the determination resistance is 5 mΩ. If the detected resistance value is greater than or equal to the preset value of 5 mΩ, it is determined that the tested product passes the test (OK); if the detected resistance value is less than the preset value of 5 mΩ, the test voltage is instantly cut off and the tested product is determined to fail the test (NG); 3) For each group of embodiments or comparative examples, 100 secondary batteries were tested. The number of lithium-ion batteries passing the test is X1, and the test pass rate is X1 / 100 × 100%, that is, the Hi-pot pass rate.

[0150] Table 3 <![CDATA[L4(mm)]]> Volume energy density (Wh / L) Hi-pot excellent rate Example 2 3 695 90％ Example 28 2 698 88％ Example 29 4 693 92％ Example 30 1 699 85％ Example 31 5 692 93％

[0151] As can be seen from the data in Table 3, in Example 2, Example 28, and Example 29, 2 mm ≤ L4 ≤ 4 mm. Compared with Example 30, L4 is not too small, so that the width of the overlapping region between the fourth adhesive layer and the finishing region is not too small, reducing the risk of micro short circuit caused by the shedding of the first active material at the finishing region and improving the Hi-pot excellent rate of the secondary battery. Compared with Example 31, L4 is not too large, so that the width of the overlapping region between the fourth adhesive layer and the finishing region is not too large, reducing the risk that more first active materials cannot play a capacity role when the width of the covering region is large and reducing the loss of the volume energy density of the secondary battery.

[0152] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application and are not intended to limit them; under the idea of the present application, the technical features in the above embodiments or different embodiments can also be combined, and the steps can be implemented in any order, and there are many other changes in different aspects of the present application as described above. For the sake of brevity, they are not provided in detail; although the present application has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions described in the foregoing embodiments or equivalently replace some of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present application.

Claims

1. A secondary battery, comprising an electrode assembly and a pole tab, wherein the electrode assembly comprises a first pole sheet, a separator and a second pole sheet, wherein the separator is disposed between the first pole sheet and the second pole sheet; one end of the pole tab is connected to the electrode assembly, and the other end of the pole tab extends out of the electrode assembly; the first pole sheet comprises a first current collector and a first active material layer stacked on the first current collector; The first current collector comprises a first surface and a second surface arranged opposite to each other, the second surface is away from the center of the electrode assembly in the first direction; the first direction is the thickness direction of the electrode assembly, the direction of the electrode assembly pointing to the electrode ear is the second direction, and the second direction is perpendicular to the first direction, characterized in that: The first current collector includes a first portion, the first surface of the first portion is provided with the first active material layer, and the second surface of the first portion is not provided with the first active material layer; The second surface is divided into a first area, a second area and a third area, and along the second direction, the third area is located between the first area and the second area; Along the second direction, the second surface includes a first edge and a second edge that are oppositely disposed, an edge of the first region coincides with the first edge, and an edge of the second region coincides with the second edge; Along the second direction, the width of the first current collector is W, the width of the first region is W1, and the width of the second region is W2, W1=0.4W, W2=0.4W; The first part includes a first section. Along the first direction, the outermost electrode sheet of the electrode assembly includes the first section. The first region of the first section is provided with a first glue layer, and the first glue layer is not provided in the third region.

2. The secondary battery according to claim 1, characterized in that: The orthographic projection of the first adhesive layer in the first direction is located within the orthographic projection of the first segment in the first direction; Along the second direction, the first adhesive layer includes a third edge and a fourth edge that are arranged opposite to each other, and compared with the fourth edge, the third edge is closer to the first edge; Along the second direction, a distance between the third edge and the first edge is W3, 0mm≤W3≤3mm.

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

4. The secondary battery according to claim 2, characterized in that: Along the second direction, the maximum width of the first adhesive layer is W4, 0.1W≤W4≤0.3W.

5. The secondary battery according to claim 4, characterized in that: 0.12W≤W4≤0.2W.

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

7. The secondary battery according to claim 1, characterized in that: The orthographic projection of the first adhesive layer in the first direction is located within the orthographic projection of the first segment in the first direction; The length of the first section in the third direction is L, the maximum length of the first adhesive layer in the third direction is L1, 0.5L≤L1≤L; The first direction, the second direction and the third direction are perpendicular to each other.

8. The secondary battery according to claim 7, characterized in that: 0.7L≤L1≤0.9L.

9. The secondary battery according to claim 7, characterized in that: The orthographic projection of the first section in the first direction includes a fifth edge and a sixth edge disposed opposite to each other along the third direction, and the first adhesive layer includes a seventh edge and an eighth edge disposed 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, 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, characterized in that: 0≤L′≤0.1L.

11. The secondary battery according to claim 1, characterized in that: Along the direction from the first edge to the second edge, the length of the first adhesive layer in the third direction gradually decreases; The first direction, the second direction and the third direction are perpendicular to each other.

12. The secondary battery according to claim 1, characterized in that: The second area of ​​the first section is provided with the first adhesive layer.

13. The secondary battery according to claim 12, characterized in that: The first adhesive layer includes a base material layer and an adhesive layer, and the adhesive layer is bonded between the first portion and the base material layer.

14. The secondary battery according to claim 13, characterized in that: The material of the substrate layer includes one or more of polyethylene terephthalate, polyimide, polyethylene, polypropylene, polyvinyl chloride, kraft paper, cotton cloth, synthetic fiber cloth, metal foil, and glass fiber; The material of the adhesive layer includes one or more of a rubber-based adhesive, a silicone-based adhesive, a hot melt adhesive, a water-based adhesive, a polyurethane-based adhesive, an epoxy-based adhesive, and a polyimide-based adhesive.

15. The secondary battery according to claim 1, characterized in that: The thickness of the first adhesive layer is T, 7 μm≤T≤9 μm.

16. The secondary battery according to claim 1, characterized in that: 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.

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

18. The secondary battery according to claim 17, characterized in that: The outermost electrode sheet of the electrode assembly further includes a second section, the second section is arranged opposite to the first section along the first direction, and the first region of the second section is provided with a second glue layer.

19. The secondary battery according to claim 18, characterized in that: Along the third direction, the electrode assembly further includes a first corner region and a second corner region that are oppositely disposed. The first part further includes a third section, and along the winding direction, the first section, the third section and the second section are sequentially connected, and the third section constitutes the outermost pole piece of the first corner area; The first region of the third section is provided with a third adhesive layer.

20. The secondary battery according to claim 19, characterized in that: Along the winding direction, the first adhesive layer, the third adhesive layer and the second adhesive layer are connected in sequence.

21. The secondary battery according to claim 17, characterized in that: The first portion further includes a fourth section, and the fourth section is located at the secondary outer circle of the electrode assembly. Along the winding direction, the fourth section and the first section are arranged in sequence, and the first area of ​​the fourth section is provided with a fourth adhesive layer.

22. The secondary battery according to claim 21, characterized in that: Along the winding direction, the first active material layer located on the second surface includes a tailing region; Along the winding direction, the fourth adhesive layer overlaps a portion of the finishing area.

23. The secondary battery according to claim 22, characterized in that: Along the winding direction, the length of the overlapping area between the fourth adhesive layer and a portion of the finishing area is L4, 2mm≤L4≤4mm.

24. The secondary battery according to claim 17, characterized in that: The first region of the third portion and / or the second region of the third portion is provided with a fifth adhesive layer.

25. The secondary battery according to any one of claims 1 to 16, characterized in that: The electrode assembly is a laminated structure, and along the first direction, the first section is a first electrode sheet located at an outermost layer of the electrode assembly among a plurality of first electrode sheets; Along the third direction, the first section includes a fourth region, the third region and a fifth region which are connected in sequence, and the first adhesive layer is provided on the fourth region and / or the fifth region; The third direction is perpendicular to the first direction and the second direction.

26. An electronic device, characterized in that: The electronic device includes the secondary battery according to any one of claims 1 to 25.

Images