Secondary battery and electronic device

Abstract

The present application discloses a secondary battery and an electronic device. The secondary battery comprises a housing, an electrode assembly, and a first bonding member. The electrode assembly comprises a first electrode plate, a second electrode plate, and a separator disposed between the first electrode plate and the second electrode plate. The first electrode plate, the second electrode plate, and the separator are wound to form a wound structure. The outermost electrode plate of the electrode assembly is the first electrode plate. The outermost ring of the first electrode plate is sequentially provided with a first coating area and a first empty foil area. A part of the first electrode plate is recessed to form a first recess. The first bonding member is bonded to the outermost ring of the first electrode plate. The first bonding member bonds a part of a first active material layer in the first coating area and a part of a first current collector in the first empty foil area. The first bonding member covers the first recess along a thickness direction of the first electrode plate. In the secondary battery, the provision of the first recess facilitates the release of stress generated at least in part by the expansion of the first electrode plate or the second electrode plate. The first bonding member can maintain the structure of the first recess during winding.

Description

Secondary batteries and electronic devices Technical Field

[0001] This application belongs to the field of energy storage technology, and specifically relates to a secondary battery and electronic device. Background Technology

[0002] Currently, silicon-based lithium-ion batteries, as a promising energy storage device, possess advantages such as high capacity and low cost. With continuous technological advancements and improvements, silicon-based lithium-ion batteries are expected to become one of the mainstream batteries in the field of mobile electronic devices in the future, providing efficient and reliable energy solutions. A silicon-based lithium-ion battery includes a positive electrode, a negative electrode, and a separator, with the separator positioned between the positive and negative electrodes.

[0003] Summary of the Invention

[0004] In existing silicon-based lithium-ion batteries, the volume change of silicon during charging and discharging causes the negative electrode to expand and contract, resulting in a greater expansion and contraction rate compared to graphite batteries. This volume change leads to instability in silicon-based lithium-ion batteries, making them prone to side reactions and electrode breakage, significantly reducing battery performance and potentially posing safety risks. When the silicon content of the negative electrode exceeds 5%, the effect of volume change becomes even more pronounced, with severe electrode expansion leading to stress concentration at the corners and ultimately electrode breakage.

[0005] In view of the above situation, it is necessary to provide a secondary battery and electronic device that can reduce stress concentration on the electrode due to expansion.

[0006] A first aspect of this application provides a secondary battery, including a housing, an electrode assembly, and a first adhesive member. The electrode assembly is disposed within the housing and includes a first electrode, a second electrode, and a separator. The first electrode, separator, and second electrode are stacked and wound to form a wound structure, with the outermost electrode of the electrode assembly being the first electrode. The first electrode includes a first current collector and a first active material layer stacked together. Along the winding direction of the electrode assembly, the first electrode has a first coating area and a first empty foil area sequentially disposed, with at least a portion of the first coating area located at the outermost edge of the first electrode. Along the thickness direction of the first electrode, the first active material layer is disposed on one side of the first coating area facing the second electrode, and not on the other side. No first active material layer is disposed on either side of the first empty foil area. The second electrode includes a second current collector and a second active material layer stacked together. The first active material layer includes silicon, with a silicon content of 5% or more based on the mass of the first active material layer; or the second active material layer contains silicon, with a silicon content of 5% or more based on the mass of the second active material layer. Along the winding direction of the electrode assembly, the electrode assembly has a first curved portion, a first straight portion, a second curved portion, and a second straight portion arranged sequentially. Along the thickness direction of the first electrode sheet, a partial depression of the first electrode sheet forms a first recess. A first adhesive is bonded to the outermost ring of the first electrode sheet. The first adhesive adheres to a portion of the first active material layer in the first coating area and a portion of the first current collector in the first empty foil area. Along the thickness direction of the first electrode sheet, the first adhesive covers the first recess.

[0007] In this secondary battery, the first recess helps to release at least part of the stress caused by the expansion of the first or second electrode, reducing the possibility of damage to the first and second electrodes. The first adhesive covering the first recess reduces the possibility of the first recess being flattened due to stress on the first electrode during the winding of the electrode assembly. Furthermore, the first electrode at the first recess can overcome the adhesive force of the first adhesive and stretch under stress, thereby releasing stress. In addition, the first adhesive also serves to cover burrs and the positive electrode to reduce the area of ​​lithium removal.

[0008] In one alternative embodiment of this application, the first recess is located in the second curved portion. When the electrode assembly generates stress due to the expansion of the first or second electrode, the stress on the first and second curved portions is more concentrated than that on the first and second straight portions. Placing the first recess in the second curved portion helps to release the stress at the stress concentration point of the electrode assembly and reduces the possibility of damage to the first and second electrode.

[0009] In one optional embodiment of this application, along the winding direction of the electrode assembly, the minimum distance between the boundary between the first coated area and the first empty foil area and the first recess is L1, where 0.5mm ≤ L1. L1 is greater than or equal to 0.5mm, ensuring that there is a certain distance between the first recess and the boundary between the first coated area and the first empty foil area, thereby reducing the possibility of damage to the first electrode sheet due to the provision of the first recess.

[0010] In one optional embodiment of this application, the minimum distance between the edge of the first adhesive and the first recess along the winding direction of the electrode assembly is D1, where 1mm ≤ D1. The edge of the first adhesive extends more than 1mm beyond the edge of the first recess along the winding direction of the electrode assembly, which helps to maintain the structural stability of the first recess during the winding process of the electrode assembly.

[0011] In one optional embodiment of this application, the number of first recesses is N, and the N first recesses are sequentially arranged along the winding direction of the electrode assembly, where N is a positive integer, 2≤N≤10. If N is greater than or equal to 2, the number of first recesses will not be too small, which helps to increase the stress relief of the electrode assembly and further reduce the possibility of damage to the first and second electrode sheets. If N is less than or equal to 10, the number of first recesses will not be too large, which helps to reduce the possibility of damage to the first electrode sheet due to the arrangement of the first recesses.

[0012] In one optional embodiment of this application, along a first direction, the first recess extends from one side of the first electrode to the other side of the first electrode. The first direction is parallel to the winding center axis of the electrode assembly. Along the winding direction of the electrode assembly, the width of the first recess is W1, where 0.5mm ≤ W1 ≤ 5mm. W1 ≥ 0.5mm is beneficial for allowing the first electrode at the first recess to release stress through deformation, reducing the possibility of breakage of the first and second electrodes. W1 ≤ 5mm is beneficial for reducing the possibility of damage to the first electrode during the processing of the first recess.

[0013] In one optional embodiment of this application, along a first direction, the first recess extends from one side of the first electrode to the other side of the first electrode. The first direction is parallel to the winding center axis of the electrode assembly. The depth of the first recess is H1, where 0.1mm ≤ H1 ≤ 1.5mm. H1 ≥ 0.1mm is beneficial for allowing the first electrode at the first recess to release stress through deformation, reducing the possibility of damage to the first and second electrodes. H1 ≤ 1.5mm is beneficial for reducing the possibility of damage to the first electrode during the processing of the first recess.

[0014] In one optional embodiment of this application, when viewed along a first direction, the outline of the first recess is arc-shaped, and the radius of the first recess is R, where 0.2mm ≤ R ≤ 15mm. Setting the outline of the first recess to be arc-shaped facilitates manufacturing by locally pressing the first electrode sheet during processing; R ≥ 0.2mm allows the first electrode sheet at the first recess to release stress through deformation, reducing the possibility of damage to the first and second electrodes; R ≤ 15mm further reduces the possibility of damage to the first electrode sheet during processing to form the first recess.

[0015] In one optional embodiment of this application, an electrolyte is provided inside the housing, and the peel strength between the first adhesive and the first electrode is F1, where 0.02 N / mm ≤ F1 ≤ 0.1 N / mm. F1 ≤ 0.1 N / mm is beneficial for the first electrode at the first recess to overcome the adhesiveness of the first adhesive and unfold when subjected to stress, thereby releasing the stress; F1 ≥ 0.02 N / mm is beneficial for maintaining the structural stability of the first recess when the first adhesive is not wetted by the electrolyte, as its peel strength is higher than this value.

[0016] In one optional embodiment of this application, the first electrode has a second coating area. The second coating area and the first coating area are sequentially arranged along the winding direction of the electrode assembly. Both the first and second coating areas are partially located on the second outer ring of the first electrode. A first active material layer is provided on each side of the second coating area along the thickness direction of the first electrode. A second recess is formed in a localized area of ​​the first electrode along the thickness direction of the first electrode. The second recess is located in a second bend. The secondary battery includes a second adhesive member, which is bonded to the second outer ring of the first electrode. The second adhesive member bonds a portion of the first active material layer in the second coating area and a portion of the first current collector in the first coating area. The second adhesive member covers the second recess along the thickness direction of the first electrode. Providing the second recess helps increase the stress value that the first electrode can release, further reducing the risk of damage to both the first and second electrodes. The second adhesive covers the second recess, which can reduce the possibility that the second recess will be flattened due to the force on the first electrode during the winding of the electrode assembly. Furthermore, the first electrode at the second recess can overcome the adhesive tension of the second adhesive under stress, thereby releasing the stress.

[0017] In one optional embodiment of this application, a third recess is formed in a partial depression of the first electrode along the thickness direction of the first electrode. The third recess is located in the first curved portion. The secondary battery includes a third adhesive member, which is bonded to the first current collector on the outermost ring of the first electrode. At least a portion of the third adhesive member is located in the first curved portion, and the third adhesive member covers the third recess along the thickness direction of the first electrode. Providing the third recess increases the stress value that the first electrode can release through deformation, further reducing the risk of damage to the first and second electrodes. Furthermore, the stress is more concentrated in the first curved portion compared to the first and second straight portions; placing the third recess in the first curved portion further reduces the possibility of damage to the first and second electrodes. The third adhesive member covering the third recess reduces the possibility that the third recess will be flattened due to the force on the first electrode during the winding of the electrode assembly. Additionally, the first electrode at the third recess can overcome the adhesive force of the third adhesive member and stretch under stress, thereby releasing stress.

[0018] In one alternative embodiment of this application, the first curved portion and the second curved portion are arranged along a second direction, and a third adhesive member covers the first curved portion along the second direction. This helps to reduce the possibility of corner corrosion.

[0019] In one optional embodiment of this application, the first electrode is a positive electrode, the second electrode is a negative electrode, and the material of the second active material layer includes silicon. Based on the mass of the second active material layer, the mass content of silicon is less than 50%. Silicon-based active materials have the advantage of high capacity. The inclusion of silicon in the second active material layer is beneficial for improving the energy density of the secondary battery. A silicon mass content of less than 50% helps reduce the stress generated during silicon expansion, thus reducing the possibility of damage to the first and second electrodes.

[0020] In one optional embodiment of this application, the first straight portion and the second straight portion are arranged along a third direction. Along this third direction, the projection of the outermost edge of the second electrode is located within the projection of the first adhesive. The third direction is the thickness direction of the electrode assembly. Having the projection of the outermost edge of the second electrode located within the projection of the first adhesive helps reduce the possibility of lithium plating during secondary battery cycling.

[0021] A second aspect of the embodiments of this application provides an electronic device including a secondary battery as described in any of the foregoing embodiments. Attached Figure Description

[0022] Figure 1 is a schematic diagram of the overall structure of the secondary battery in one embodiment of this application.

[0023] Figure 2 is a partial structural schematic diagram of the secondary battery in one embodiment of this application.

[0024] Figure 3 is a schematic diagram of the structure of the first electrode in a flattened state in one embodiment of this application.

[0025] Figure 4 is a schematic diagram of the structure of the first electrode in a flattened state in another embodiment of this application.

[0026] Figure 5 is a schematic diagram showing the relative positions of the first adhesive member and the first recess in one embodiment of this application.

[0027] Figure 6 is a schematic diagram showing the relative positions of the first adhesive member and the second recess in another embodiment of this application.

[0028] Figure 7 is a schematic diagram of the structure of an electronic device in one embodiment of this application.

[0029] Explanation of main component symbols

[0030] Secondary battery 100

[0031] Casing 10

[0032] Electrode assembly 20

[0033] First film 21

[0034] First current collector 211

[0035] First active material layer 212

[0036] First coating area 21a

[0037] First empty foil area 21b

[0038] Second coating area 21c

[0039] first recess 201

[0040] Second recess 202

[0041] Third recess 203

[0042] Second pole piece 22

[0043] Second current collector 221

[0044] Second active material layer 222

[0045] Separator 23

[0046] First straight section 20a

[0047] Second straight section 20b

[0048] First bend 20c

[0049] Second bend 20d

[0050] First adhesive component 30

[0051] Second adhesive component 40

[0052] Third adhesive component 50

[0053] Electronic devices 1000

[0054] First direction X

[0055] Second direction Y

[0056] Third direction Z

[0057] The following detailed description, in conjunction with the accompanying drawings, will further illustrate this application. Detailed Implementation

[0058] The technical solutions of the embodiments of this application will be described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments.

[0059] It should be noted that when a component is considered to be "connected" to another component, it can be directly connected to the other component or may also have a component that is centrally located. When a component is considered to be "set" on another component, it can be directly set on the other component or may also have a component that is centrally located.

[0060] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application.

[0061] In the description of the embodiments of this application, technical terms such as "first" and "second" are used only to distinguish different objects and should not be construed as indicating or implying relative importance or implicitly specifying the number, specific order, or primary and secondary relationship of the indicated technical features. In the description of the embodiments of this application, "multiple" means two or more, unless otherwise explicitly defined.

[0062] The term "parallel" is used to describe an ideal state between two components. In actual production or use, two components can exist in a state that is approximately parallel. The two components described as "parallel" do not have to be absolute straight lines or planes, but can be approximately straight lines or planes. From a macroscopic perspective, if the overall direction of extension is a straight line or plane, the component can be considered a "straight line" or "plane".

[0063] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a mutually exclusive, independent, or alternative embodiment. Where there is no conflict, the various embodiments in this application can be combined with each other.

[0064] It should be noted that the thickness, length, width, and other dimensions of various components in the embodiments of this application shown in the accompanying drawings, as well as the overall thickness, length, width, and other dimensions of the integrated device, are merely illustrative examples and should not constitute any limitation on this application.

[0065] In existing silicon-based lithium-ion batteries, the volume change of silicon during charging and discharging causes the negative electrode to expand and contract. This results in silicon-carbon-silicon-based lithium-ion batteries exhibiting greater expansion and contraction rates during charging and discharging compared to graphite batteries. This volume change leads to instability in silicon-based lithium-ion batteries, making them prone to side reactions and electrode breakage, significantly reducing battery performance and potentially posing safety risks. When the silicon content of the negative electrode exceeds 5%, the effects of volume change become even more pronounced, with severe electrode expansion leading to stress concentration at the corners and ultimately electrode breakage.

[0066] This application provides a secondary battery, including a casing, an electrode assembly, and a first adhesive member. The electrode assembly is disposed within the casing and includes a first electrode, a second electrode, and a separator disposed between the first and second electrodes. The first electrode, separator, and second electrode are stacked and wound to form a wound structure, with the outermost electrode of the electrode assembly being the first electrode. The first electrode includes a first current collector and a first active material layer stacked together. Along the winding direction of the electrode assembly, the first electrode has a first coated area and a first empty foil area sequentially disposed, with at least a portion of the first coated area located at the outermost edge of the first electrode. Along the thickness direction of the first electrode, the first active material layer is disposed on one side of the first coated area facing the second electrode, while no first active material layer is disposed on the other side. No first active material layer is disposed on either side of the first empty foil area. The second electrode includes a second current collector and a second active material layer stacked together. The first active material layer includes silicon, and the mass content of silicon is 5% or more based on the mass of the first active material layer; or, the second active material layer includes silicon, and the mass content of silicon is 5% or more based on the mass of the second active material layer. Along the winding direction of the electrode assembly, the electrode assembly has a first curved portion, a first straight portion, a second curved portion, and a second straight portion arranged sequentially. Along the thickness direction of the first electrode sheet, a partial recess in the first electrode sheet forms a first recess. A first adhesive is bonded to the outermost ring of the first electrode sheet. The first adhesive adheres to a portion of the first active material layer in the first coating area and a portion of the first current collector in the first empty foil area. Along the thickness direction of the first electrode sheet, the first adhesive covers the first recess.

[0067] In this secondary battery, the first recess helps to release at least part of the stress caused by the expansion of the first or second electrode, reducing the possibility of damage to the first and second electrodes. The first adhesive covering the first recess reduces the possibility of the first recess being flattened due to stress on the first electrode during the winding of the electrode assembly. Furthermore, the first electrode at the first recess can overcome the adhesive force of the first adhesive and stretch under stress, thereby releasing stress. In addition, the first adhesive also serves to cover burrs and the positive electrode to reduce the area affected by lithium removal.

[0068] The embodiments of this application will be further described below with reference to the accompanying drawings.

[0069] As shown in Figures 1 and 2, an embodiment of this application provides a secondary battery 100, including a housing 10 and an electrode assembly 20, the electrode assembly 20 being disposed within the housing 10. The electrode assembly 20 includes a first electrode 21, a second electrode 22, and a separator 23, the separator 23 being disposed between the first electrode 21 and the second electrode 22. The first electrode 21, the second electrode 22, and the separator 23 are stacked and wound to form a wound structure. The wound electrode assembly 20 has a first curved portion 20c, a first straight portion 20a, a second curved portion 20d, and a second straight portion 20b arranged sequentially, and the outermost electrode of the electrode assembly 20 is the first electrode 21.

[0070] In some embodiments, as shown in FIG2, the first electrode 21 includes a first current collector 211 and a first active material layer 212 stacked together. Along the winding direction of the electrode assembly 20, the outermost ring of the first current collector 211 has a first coating area 21a and a first empty foil area 21b sequentially disposed. Along the thickness direction of the first electrode 21, the first coating area 21a has the first active material layer 212 disposed on the side facing the second electrode 22, and the other side does not have the first active material layer 212 disposed. The first empty foil area 21b does not have the first active material layer 212 disposed on either side. At least a portion of the first empty foil area 21b is located in the second bend 20d.

[0071] In some embodiments, as shown in FIG2, the second electrode 22 includes a second current collector 221 and a second active material layer 222 stacked together.

[0072] In some embodiments, one of the first active material layer 212 and the second active material layer 222 includes silicon, and the mass content of silicon is 5% or more based on the mass of the first active material layer 212 or the second active material layer 222.

[0073] In some embodiments, as shown in Figures 2 to 4, a first recess 201 is formed by a partial depression in the first electrode 21 along the thickness direction of the first electrode 21.

[0074] The first recess 201 releases stress in the following two types of embodiments, depending on its shape. It should be noted that the two methods are compatible.

[0075] In some embodiments, as shown in FIG3, a first recess 201 extends from one side of the first electrode 21 to the other side along a first direction X, the first direction X being parallel to the central axis around which the electrode assembly 20 is wound. When the first electrode 21 or the second electrode 22, which has a silicon content of more than 5%, expands during charging and discharging, the interaction between the first electrode 21, the second electrode 22, and the separator 23 generates stress in the entire electrode assembly 20. The first electrode 21 at the first recess 201 can be stretched and deformed under stress, thereby releasing at least part of the stress and reducing the possibility of damage to the first electrode 21 and the second electrode 22 due to stress concentration. In this embodiment, when the first recess 201 protrudes toward the separator 23, the first recess 201 can also support a gap between the separator 23 and the first electrode 21 to provide space for the overall deformation of the electrode assembly 20, thereby releasing stress and reducing stress accumulation.

[0076] In some embodiments, as shown in FIG4, the dimension of the first recess 201 along the first direction X is smaller than the dimension of the first electrode 21 along the first direction X. The first recess 201 protrudes toward the separator 23, creating a gap between the first electrode 21 and the separator 23. The first direction X is parallel to the central axis of the electrode assembly 20. When the first electrode 21 or the second electrode 22, which has a silicon content of 5% or more, expands during charging and discharging, the gap between the first electrode 21 and the separator 23 provides space for the overall deformation of the electrode assembly 20, which helps to release stress, reduce stress accumulation, and thus reduce the possibility of damage to the first electrode 21 and the second electrode 22 due to stress concentration. As an exemplary example, the first recess 201 is a hemispherical shape protruding from the surface of the first electrode 21.

[0077] In some embodiments, a first recess 201 is provided in a first coating area 21a. In this case, the first active material layer 212 and the first current collector 211 deform together to form the first recess 201. Providing the first recess 201 helps to release at least part of the stress generated by the expansion of the first electrode 21 or the second electrode 22, and reduces the possibility of damage to the first electrode 21 and the second electrode 22.

[0078] In some embodiments, as shown in Figures 3 and 4, a first recess 201 is provided in a first empty foil region 21b. In this case, the first recess 201 is formed by deformation of a first current collector 211. The first recess 201 being provided in the empty foil region can prevent partial shedding of the active material in the first active material layer 212 that may occur due to the manufacture of the first recess 201.

[0079] In some embodiments, as shown in FIG2, the first recess 201 is located in the second curved portion 20d. When the electrode assembly 20 is stressed due to the expansion of the first electrode 21 or the second electrode 22, the stress on the first curved portion 20c and the second curved portion 20d is more concentrated than that on the first straight portion 20a and the second straight portion 20b. Placing the first recess 201 in the second curved portion 20d helps to release the stress at the stress concentration point of the electrode assembly 20 and reduces the possibility of damage to the first electrode 21 and the second electrode 22.

[0080] In some embodiments, as shown in Figures 3 and 5, along the first direction X, the first recess 201 extends from one side of the first electrode 21 to the other side of the first electrode 21. Along the winding direction of the electrode assembly 20, the width of the first recess 201 is W1, where 0.5mm ≤ W1 ≤ 5mm. W1 ≥ 0.5mm is beneficial for allowing the first electrode 21 at the first recess 201 to release stress through deformation, reducing the possibility of damage to the first electrode 21 and the second electrode 22. W1 ≤ 5mm is beneficial for reducing the possibility of damage to the first electrode 21 during the processing of the first recess 201.

[0081] As an example, W1 can be any one of 1mm, 1.5mm, 2mm, 2.5mm, 3mm, 3.5mm, 4mm, or 4.5mm.

[0082] In some embodiments, as shown in Figures 3 and 5, the depth of the first recess 201 along the thickness direction of the first electrode 21 is H1, where 0.1 mm ≤ H1 ≤ 1.5 mm. H1 ≥ 0.1 mm helps the first electrode 21 at the first recess 201 to release stress through deformation, reducing the possibility of damage to the first electrode 21 and the second electrode 22. H1 ≤ 1.5 mm helps reduce the possibility of damage to the first electrode 21 during the processing of the first recess 201. Here, the depth H1 of the first recess 201 refers to the depth of the groove formed by the first recess 201. During measurement, in the unfolded state of the first electrode 21, along the thickness direction of the first electrode 21, H1 is the distance from the surface of the unrecessed portion of the first electrode 21 on the same side as the opening of the groove to the bottom wall of the groove.

[0083] As an example, H1 is any one of 0.2mm, 0.4mm, 0.6mm, 0.8mm, 1.0mm, 1.2mm, and 1.4mm.

[0084] In some embodiments, as shown in FIG2, the secondary battery 100 further includes a first adhesive member 30. The first adhesive member 30 is bonded to the outermost ring of the first electrode 21 and to a portion of the first active material layer 212 of the first coating area 21a and a portion of the first current collector 211 of the first empty foil area 21b. Along the thickness direction of the first electrode 21, the first adhesive member 30 covers the first recess 201. The first adhesive member 30 covering the first recess 201 can reduce the possibility that the first recess 201 will be flattened due to the force on the first electrode 21 during the winding of the electrode assembly 20. Furthermore, after the first adhesive member 30 is wetted by the electrolyte, its adhesiveness will decrease, so that the first electrode 21 at the first recess 201 can be stretched under stress, thereby releasing stress. Furthermore, in the prior art, the electrode assembly 20 usually requires the first adhesive 30 to cover burrs and the positive electrode to reduce the area of ​​lithium removal. Based on the solution of setting the first recess 201 on the first electrode 21 provided in the embodiments of this application, the first adhesive 30 is used to cover the first recess 201. Compared with setting an additional adhesive to cover the first recess 201, the processing cost and material cost can be reduced.

[0085] In some embodiments, as shown in Figures 2 and 5, the first recess 201 encloses a groove. Here, the groove refers to the space formed by the deformation of the first electrode 21 at the first recess 201. The first adhesive 30 is adhered to the side of the first recess 201 facing away from the groove opening to cover the first recess 201. In this case, the first recess 201 protrudes towards the separator 23. In other embodiments, as shown in Figures 2 and 6, the first adhesive 30 is adhered to the side of the first recess 201 with the groove opening to cover the first recess 201. In this case, the first recess 201 protrudes away from the separator 23.

[0086] In some embodiments, as shown in Figures 2 and 5, along the winding direction of the electrode assembly 20, the minimum distance between the junction of the first coating area 21a and the first empty foil area 21b and the first recess 201 is L1, where 0.5mm ≤ L1. During the manufacturing process of the electrode assembly 20, the first electrode 21 needs to be cold-pressed. During the cold-pressing process, since the first coating area 21a has a first active material layer 212, the pressure on the first current collector 211 in the first coating area 21a is greater than that on the first current collector 211 in the empty foil area. Therefore, the structure of the first current collector 211 at the junction of the first coating area 21a and the first empty foil area 21b is relatively weak, and L1 is greater than or equal to 0.5mm. This ensures that there is a certain distance between the first recess 201 and the junction of the first coating area 21a and the first empty foil area 21b, which can reduce the possibility of damage to the first electrode 21 caused by the first recess 201.

[0087] It should be noted that, in this embodiment, when measuring the distance from the first recess 201 to the boundary between the first coating area 21a and the first empty foil area 21b, the minimum distance from a point on the edge of the first recess 201 to the boundary between the first coating area 21a and the first empty foil area 21b is taken as the distance from the first recess 201 to the boundary between the first coating area 21a and the first empty foil area 21b. When the first active material layer 212 at the first coating area 21a has uneven edges due to flowing towards the empty foil area 21b, the distance from the point on the edge of the first active material layer 212 closest to the first recess 201 towards the empty foil area 21b to the first recess 201 is taken as the distance from the boundary between the first coating area 21a and the first empty foil area 21b to the first recess 201. When there are multiple first recesses 201, the distance from a point on the edge of the first recess 201 to the junction of the first coating area 21a and the first empty foil area 21b is measured, and the minimum value is taken. That is, for any one first recess 201, the minimum distance between it and the junction of the first coating area 21a and the first empty foil area 21b should be greater than 0.5mm.

[0088] In some embodiments, as shown in Figures 2 and 5, the minimum distance between the edge of the first adhesive member 30 and the first recess 201 along the winding direction of the electrode assembly 20 is D1, where 1 mm ≤ D1. The winding direction of the electrode assembly 20 corresponds to the length direction of the first electrode sheet 21 in its flattened state. Along the winding direction of the electrode assembly, the edge of the first adhesive member 30 extends more than 1 mm beyond the edge of the first recess 201, which helps maintain the structural stability of the first recess 201 during the winding process of the electrode assembly 20. It should be noted that in this embodiment, when measuring the distance from the first recess 201 to the edge of the first adhesive member 30, the points on the edges of the first recess 201 and the first adhesive member 30 are used as the measurement endpoints.

[0089] In some embodiments, as shown in Figures 2 and 3, a plurality of first recesses 201 are sequentially arranged along the winding direction of the electrode assembly 20. Providing a plurality of first recesses 201 helps to enhance stress relief on the electrode assembly 20, further reducing the possibility of damage to the first electrode 21 and the second electrode 22.

[0090] In some embodiments, the number of first recesses 201 is N, where N is a positive integer, 2≤N≤10. If N is greater than or equal to 2, the number of first recesses 201 will not be too small, which helps to increase the amount of stress released on the electrode assembly 20 and further reduce the possibility of damage to the first electrode 21 and the second electrode 22. If N is less than or equal to 10, the number of first recesses 201 will not be too large, which helps to reduce the possibility of damage to the first electrode 21 due to the provision of the first recesses 201.

[0091] In some embodiments, as shown in FIG5 or FIG6, when viewed along the first direction X, the outline of the first recess 201 is arc-shaped. By setting the outline of the first recess 201 to be arc-shaped, the first recess 201 can be formed by locally pressing the first electrode 21 during processing, which facilitates manufacturing.

[0092] In some embodiments, as shown in FIG5 or FIG6, the radius of the first recess 201 is R, where 0.2mm≤R≤15mm. R≥0.2mm is beneficial to allow the first electrode 21 at the first recess 201 to release stress through deformation, thereby reducing the possibility of damage to the first electrode 21 and the second electrode 22. R≤15mm is beneficial to reduce the possibility of damage to the first electrode 21 during the processing of the first recess 201.

[0093] As an example, R is any one of 1mm, 2mm, 3mm, 4mm, 5mm, 6mm, 7mm, 8mm, 9mm, 10mm, 11mm, 12mm, 13mm, and 14mm.

[0094] In some embodiments, the housing 10 contains an electrolyte.

[0095] In some embodiments, the electrolyte comprises an electrolyte salt. The electrolyte salt comprises at least one of an organic lithium salt or an inorganic lithium salt.

[0096] In some embodiments, the electrolyte salts include, but are not limited to, lithium hexafluorophosphate (LiPF6), lithium bis(fluorosulfonyl)imide LiN(CF3SO2)2 (LiTFSI), and lithium bis(fluorosulfonyl)imide L... i (N(SO2F)2)(LiFSI), lithium hexafluorocesium oxide (LiCsF6), lithium perchlorate (LiC) l At least one of O4 or lithium trifluoromethanesulfonate (LiCF3SO3).

[0097] In some embodiments, the peel strength between the first adhesive 30 and the first electrode 21 is F1, where 0.02 N / mm ≤ F1 ≤ 0.1 N / mm. F1 ≤ 0.1 N / mm is beneficial for the first electrode 21 at the first recess 201 to overcome the adhesiveness of the first adhesive 30 and unfold when subjected to stress, thereby releasing the stress; F1 ≥ 0.02 N / mm is a higher peel strength than this value when the first adhesive 30 is not wetted by electrolyte, which is beneficial for maintaining the structural stability of the first recess 201 during the winding process of the electrode assembly 20.

[0098] As an example, F1 is any one of 0.03 N / mm, 0.04 N / mm, 0.05 N / mm, 0.06 N / mm, 0.07 N / mm, 0.08 N / mm, and 0.09 N / mm.

[0099] In some embodiments, the first adhesive 30 includes a substrate layer and an adhesive layer.

[0100] In some embodiments, the substrate layer may be selected from polyethylene terephthalate, co-extruded polypropylene, oriented polystyrene, thermoplastic polyurethane, polylactic acid, polyolefin, and polyimide.

[0101] In some embodiments, the adhesive layer is made of one or more of the following: natural rubber, styrene-butadiene rubber, isoprene rubber, styrene-polybutadiene-styrene block copolymer, hydrogenated styrene-polybutadiene-styrene block copolymer, styrene-isoprene-styrene block copolymer, hydrogenated styrene-polyisoprene-styrene block copolymer, polyisobutylene, amorphous α-olefin copolymer, petroleum resin, terpene resin, and rosin resin.

[0102] For the first adhesive 30, its peel strength F1 is adjusted by selecting different types and / or qualities of adhesive layer materials.

[0103] The embodiments of this application, according to GB / T 2792-2014 "Test Method for Peel Strength of Adhesive Tapes", use a high-speed rail tensile testing machine to test the peel strength between the first adhesive component 3050 and the first electrode 21. The test process is as follows:

[0104] Discharge the secondary battery 100 to 3.0V, then disassemble the secondary battery 100. Remove the first electrode 21 and the first adhesive component 30 bonded to it as a whole, and wipe the electrolyte off the surface with lint-free paper. Then cut the first adhesive component 30 and the first electrode 21 into strip-shaped samples. Along the length of the sample, adhere the side of the first electrode 21 without the first adhesive component 30 to the steel plate using double-sided adhesive (Nitto 5000NS), with an adhesion length of not less than 15mm. Fix the steel plate in the corresponding position on the high-speed rail tensile testing machine, pull up one end of the first adhesive component 30 on the other side of the sample, and clamp it in the clamp. The angle between the pulled-up part of the first adhesive component 30 and the steel plate in space is 180°. Pull the sample at a speed of 5±0.2mm / s. The average tensile force in the final measured stable area is recorded as the peel strength between the first adhesive component 30 and the first electrode 21, expressed in N / mm. The stable region refers to the area in which the tension of the clamp pulling the first adhesive component 30 does not change significantly over time when a line graph is plotted on the graph.

[0105] In some embodiments, as shown in FIG2, the first electrode 21 has a second coating area 21c. Along the winding direction of the electrode assembly 20, the second coating area 21c and the first coating area 21a are sequentially arranged. Both the first coating area 21a and the second coating area 21c are partially located on the outermost ring of the first electrode 21. Along the thickness direction of the first electrode 21, a first active material layer 212 is provided on both opposite sides of the second coating area 21c. Along the thickness direction of the first electrode 21, a partial recess in the first electrode 21 forms a second recess 202, located in the second bend 20d. Providing the second recess 202 helps increase the stress value that the first electrode 21 can release, further reducing the risk of damage to the first electrode 21 and the second electrode 22.

[0106] In some embodiments, the dimension of the second recess 202 along the first direction X is smaller than the dimension of the first electrode 21 along the first direction X. The second recess 202 protrudes towards the separator 23, creating a gap between the first electrode 21 and the separator 23. When the first electrode 21 or the second electrode 22, which has a silicon content of 5% or more, expands during charging and discharging, the gap between the first electrode 21 and the separator 23 provides space for the overall deformation of the electrode assembly 20, which helps to release stress, reduce stress accumulation, and thus reduce the possibility of damage to the first electrode 21 and the second electrode 22 due to stress concentration.

[0107] In some embodiments, along a first direction X, the second recess 202 extends from one side of the first electrode 21 to the other side of the first electrode 21, the first direction X being parallel to the central axis around which the electrode assembly 20 is wound. When the first electrode 21 or the second electrode 22, which has a silicon content of 5% or more, expands during charging and discharging, the interaction between the first electrode 21, the second electrode 22, and the separator 23 generates stress in the entire electrode assembly 20. The first electrode 21 at the first recess 201 can be stretched and deformed under stress, thereby releasing at least part of the stress and reducing the possibility of damage to the first electrode 21 and the second electrode 22 due to stress concentration. In this embodiment, the second recess 202 can also support a gap between the separator 23 and the first electrode 21 to provide space for the overall deformation of the electrode assembly 20, thereby releasing stress and reducing stress accumulation.

[0108] In some embodiments, as shown in FIG2, the secondary battery 100 includes a second adhesive member 40, which is bonded to the outermost ring of the first electrode 21. The second adhesive member 40 also bonds a portion of the first active material layer 212 of the second coating region 21c and a portion of the first current collector 211 of the first coating region 21a. Along the thickness direction of the first electrode 21, the second adhesive member 40 covers the second recess 202. The second adhesive member 40 covering the second recess 202 reduces the possibility that the second recess 202 will be flattened due to the force on the first electrode 21 during the winding of the electrode assembly 20. Furthermore, the first electrode 21 at the second recess 202 can overcome the adhesive tension of the second adhesive member 40 under stress, thereby releasing stress.

[0109] In some embodiments, as shown in FIG2, a third recess 203 is formed in a localized depression of the first electrode 21 along the thickness direction of the first electrode 21. The third recess 203 is located in the first curved portion 20c. Providing the third recess 203 helps to increase the stress value that the first electrode 21 can release through deformation, further reducing the risk of damage to the first electrode 21 and the second electrode 22. Furthermore, the stress is more concentrated in the first curved portion 20c compared to the first straight portion 20a and the second straight portion 20b. Providing the third recess 203 in the first curved portion 20c helps to further reduce the possibility of damage to the first electrode 21 and the second electrode 22.

[0110] In some embodiments, the dimension of the third recess 203 along the first direction X is smaller than the dimension of the first electrode 21 along the first direction X. The first recess 201 protrudes towards the separator 23, creating a gap between the first electrode 21 and the separator 23. The first direction X is parallel to the central axis of the electrode assembly 20. When the first electrode 21 or the second electrode 22, which has a silicon content of 5% or more, expands during charging and discharging, the gap between the first electrode 21 and the separator 23 provides space for the overall deformation of the electrode assembly 20, which helps to release stress, reduce stress accumulation, and thus reduce the possibility of damage to the first electrode 21 and the second electrode 22 due to stress concentration.

[0111] In some embodiments, along a first direction X, a third recess 203 extends from one side of the first electrode 21 to the other side of the first electrode 21, the first direction X being parallel to the central axis around which the electrode assembly 20 is wound. When the first electrode 21 or the second electrode 22, which has a silicon content of 5% or more, expands during charging and discharging, the interaction between the first electrode 21, the second electrode 22, and the separator 23 generates stress in the entire electrode assembly 20. The first electrode 21 at the third recess 203 can be stretched and deformed under stress, thereby releasing at least part of the stress and reducing the possibility of damage to the first electrode 21 and the second electrode 22 due to stress concentration. In this embodiment, when the third recess 203 protrudes toward the separator 23, the first recess 201 can also support a gap between the separator 23 and the first electrode 21 to provide space for the overall deformation of the electrode assembly 20, thereby releasing stress and reducing stress accumulation.

[0112] In some embodiments, as shown in FIG2, the secondary battery 100 includes a third adhesive member 50, which is bonded to a first current collector 211 on the outermost ring of the first electrode 21. At least a portion of the third adhesive member 50 is located at the first bend 20c, and along the thickness direction of the first electrode 21, the third adhesive member 50 covers the third recess 203. The third adhesive member 50 covering the third recess 203 reduces the possibility that the third recess 203 will be flattened due to the force exerted on the first electrode 21 during the winding of the electrode assembly 20. Furthermore, the first electrode 21 at the third recess 203 can overcome the adhesive force of the third adhesive member 50 and stretch under stress, thereby releasing stress.

[0113] In some embodiments, as shown in FIG2, the first curved portion 20c and the second curved portion 20d are arranged along the second direction Y. Along the second direction Y, the third adhesive 50 covers the first curved portion 20c, which helps to reduce the possibility of corner corrosion.

[0114] In some embodiments, the first electrode 21 is a positive electrode, the second electrode 22 is a negative electrode, and the material of the second active material layer 222 includes silicon, with the silicon content being less than 50% based on the mass of the second active material layer 222. Silicon-based active materials have the advantage of high capacity, and the inclusion of silicon in the second active material layer 222 is beneficial for improving the energy density of the secondary battery 100; the silicon content being less than 50% helps reduce the stress generated during silicon expansion, thus reducing the possibility of damage to the first electrode 21 and the second electrode 22.

[0115] In the embodiments of this application, the silicon content in the secondary battery 100 can be measured by the following method: the secondary battery 100 is discharged at a constant current of 0.1C to 3.0V, and the secondary battery 100 is disassembled to obtain the negative electrode sheet. The negative electrode sheet is cleaned with dimethyl carbonate (DMC) for 10 minutes, and then baked at 100°C for 2 hours before use. The negative electrode active material layer on the negative electrode sheet is scraped off, and the powder of the negative electrode active material layer is collected. The silicon and lithium content in the powder of the negative electrode material layer is tested using an inductively coupled plasma atomic emission spectrometer (ICP, model Agilent 5800, provided by Agilent Technologies); the carbon content in the powder of the negative electrode active material layer is tested using a high-frequency carbon-sulfur analyzer (model DK-606).

[0116] In some embodiments, as shown in FIG2, the first straight portion 20a and the second straight portion 20b are arranged along a third direction Z. Along the third direction Z, the projection of the outermost end of the second electrode 22 is located within the projection of the first adhesive 30. The third direction Z is the thickness direction of the electrode assembly 20. The fact that the projection of the outermost end of the second electrode 22 is located within the projection of the first adhesive 30 helps to reduce the possibility of lithium plating during the cycling process of the secondary battery 100.

[0117] In some implementations, the first adhesive 30, the second adhesive 40, and the third adhesive 50 can all be selected from acrylic adhesives, epoxy resin adhesives, and polyurethane adhesives.

[0118] As shown in FIG7, an embodiment of this application also provides an electronic device 1000, including a secondary battery 100 as described in any of the foregoing embodiments.

[0119] In some embodiments, the electronic device 1000 includes, but is not limited to, mobile phones, laptops, electric toys, power tools, and electronic cigarettes.

[0120] To investigate the impact of the arrangement of the first recess 201 and its related dimensions on the damage to the first electrode 21 and the second electrode 22, the inventors conducted the following experiments, which included two sets of comparative examples and 26 sets of embodiments. Each set of comparative examples and each set of embodiments included 20 secondary batteries. The difference between the secondary batteries used in Comparative Example 1 and those used in the embodiments is that the positive electrode of the secondary battery used in the embodiments has the first recess 201, while the positive electrode of the secondary battery in the comparative examples does not have the first recess 201. The difference between the secondary batteries used in Comparative Example 2 and those used in the experimental examples is that although the secondary battery in Comparative Example 2 has the first recess 201, the first adhesive does not cover the first recess 201. Apart from the aforementioned conditions, the only difference between the secondary batteries used in the comparative examples and embodiments between different groups is the difference in the parameters listed in Table 1 below. Parameters not mentioned in the table are the same, and the secondary batteries in the embodiments within the same group are all the same.

[0121] The preparation of the secondary battery used in the experiment includes the following steps:

[0122] 1. Preparation of the positive electrode sheet:

[0123] The positive electrode active material is lithium iron phosphate, the positive electrode conductive agent is acetylene black, and the positive electrode binder is polyvinylidene fluoride (PVDF, with a weight average molecular weight of 5×10⁻⁶). 5 The materials were mixed at a mass ratio of 94:3:3, with N-methylpyrrolidone (NMP) added as a solvent. The mixture was stirred under vacuum until a homogeneous positive electrode slurry with a solid content of 75 wt% was obtained. An 8 μm thick aluminum foil was selected as the positive electrode current collector, and the foil was cut to create the inner electrode tabs. The positive electrode slurry was uniformly coated onto one surface of the aluminum foil and dried at 110°C to obtain a positive electrode sheet with a single-sided coating of positive active material (80 μm thick). The above steps were then repeated on the other surface of the aluminum foil to obtain a positive electrode sheet with a double-sided coating of positive active material.

[0124] In addition to the steps described above, the positive electrode used in this embodiment also includes the step of pressing a first recess 201 into the positive electrode. The first recess 201 extends from one side of the first electrode 21 to the other side of the first electrode 21 along the first direction X.

[0125] 2. Preparation of negative electrode sheet

[0126] A mixture of graphite powder (negative electrode active material), silicon powder, conductive carbon black (Super P) as a conductive agent, and styrene-butadiene rubber (SBR) as a binder was prepared in a weight ratio of 87:10.5:1.5. Deionized water was then added as a solvent to form a negative electrode slurry with a solid content of 50 wt%, and the mixture was stirred thoroughly. A 5 μm thick copper foil was selected as the negative electrode current collector, and the inner tabs of the copper foil were cut out. The negative electrode slurry was uniformly coated onto one surface of the copper foil and dried at 90°C to obtain a single-sided negative electrode sheet. This completes the single-sided coating of the negative electrode sheet. The above steps were then repeated on the other surface of the negative electrode sheet to obtain a double-sided coated negative electrode sheet.

[0127] 3. Preparation of the separating membrane

[0128] A porous polyethylene (PE) film with a thickness of 8 μm was used as the separator.

[0129] 4. Electrolyte preparation

[0130] In a dry argon atmosphere, ethylene carbonate, methyl ethyl carbonate and diethyl carbonate are mixed in a mass ratio of 30:50:20 to obtain an organic solution. Then, lithium hexafluorophosphate is added to the organic solvent to dissolve and mix evenly to obtain an electrolyte with a lithium salt concentration of 1.15 mol / L.

[0131] 5. Preparation of lithium-ion batteries

[0132] The separator, positive electrode, separator, and negative electrode prepared above are wound sequentially to obtain an electrode assembly. In the electrode assembly, the first recess 213 is located at the first bend. The electrode assembly is hot-pressed at a pressure of 5 MPa and a temperature of 65°C for 10 seconds. The electrode assembly is placed in an aluminum-plastic film packaging bag, with both the positive and negative electrode tabs extending from the top seal edge of the packaging bag. After removing moisture at 80°C, electrolyte is injected and the bag is sealed.

[0133] After the secondary battery was prepared, the following experimental steps were performed on both the comparative and example samples:

[0134] Charge-discharge cycle test: The prepared secondary battery was charged at 25°C with a constant current of 0.5C, then charged at a constant voltage of 0.05C CV to the upper limit cutoff voltage, allowed to stand for 30 minutes, and then discharged at 1C to the lower limit cutoff voltage. The charge-discharge cycle was repeated 500 times. The secondary battery was disassembled, and the tearing condition of the first electrode 21 and the second electrode 22 was observed. F1 was measured using the method described above.

[0135] The parameters and observation results involved in the experiment are recorded in Table 1 below. In Table 1, L1 represents the minimum distance between the boundary of the first coated area 21a and the first empty foil area 21b and the first recess 201; D1 represents the minimum distance between the edge of the first adhesive 30 and the first recess 201; N represents the number of first recesses 201; W1 represents the width of the first recess 201; H1 represents the depth of the first recess 201; R represents the radius of the first recess 201; and F1 represents the peel strength between the first adhesive 30 and the first electrode 21. L1, D1, W1, H1, and R are measured after the positive electrode is manufactured. The units of L1, D1, W1, H1, and R are mm, and the unit of F1 is N / mm. The electrode tearing rate is the ratio of the number of secondary batteries in a group where either the first electrode 21 or the second electrode 22 tears to the total number of secondary batteries in that group.

[0136] Table 1

[0137] As shown in Table 1, compared with Comparative Examples 1 and 2, the secondary battery 100 in Examples 1-26 has a first recess 201 at the first electrode 21, and the first adhesive 30 is used to bond the first recess 201. Since the first adhesive 30 can reduce the possibility that the first recess 201 will be flattened during the winding of the electrode assembly 20, the first recess 201 can play a role in releasing stress during the long cycle of the secondary battery 100, thereby effectively reducing the possibility of tearing of the first electrode 21 and the second electrode 22.

[0138] Compared to Embodiments 1 and 2, the secondary battery 100 in Embodiments 3 and 4 satisfies L1≥0.5mm, and the distance between the first recess 201 and the junction of the first coating area 21a and the first empty foil area 21b is not too close, which helps to reduce the possibility of damage to the first electrode 21 due to the provision of the first recess 201. Therefore, the electrode tear rate in Embodiments 3 and 4 is less than that in Embodiments 1 and 2.

[0139] Compared to Embodiment 6, the secondary battery 100 in Embodiments 4 and 5 satisfies D1≥1mm. The distance between the edge of the first adhesive 30 and the edge of the first recess 201 along the winding direction of the electrode assembly 20 is not too small, which helps to maintain the structural stability of the first recess 201 during the winding process of the electrode assembly 20, thereby reducing the probability of tearing of the first electrode 21 and the second electrode 22.

[0140] Compared to Examples 7 and 13, the secondary batteries in Examples 4 and 8-12 satisfy the condition 0.5mm ≤ W1 ≤ 5mm. Under this condition, W1 is not too small, which helps the first electrode 21 at the first recess 201 to release stress through deformation, reducing the possibility of breakage of the first electrode 21 and the second electrode 22. Conversely, W1 is not too large, which helps reduce the possibility of damage to the first electrode 21 during the processing of the first recess 201, thereby reducing the probability of tearing of the first electrode 21 and the second electrode 22 during long-term cycling of the secondary battery 100. Therefore, the electrode tearing rate in Examples 4 and 8-12 is lower than that in Examples 7 and 13.

[0141] Compared to Examples 14 and 19, the secondary battery 100 in Examples 4 and 15-18 satisfies 0.1mm ≤ H1 ≤ 1.5mm. Under this condition, the value of H1 is not too small, which is beneficial for the first electrode 21 at the first recess 201 to release stress through deformation, reducing the possibility of breakage of the first electrode 21 and the second electrode 22. Furthermore, the value of H1 is not too large, which is beneficial for reducing the possibility of damage to the first electrode 21 during the processing of the first recess 201, thereby reducing the probability of tearing of the first electrode 21 and the second electrode 22 during long-term cycling of the secondary battery 100. Therefore, the electrode tearing rate in Examples 4 and 15-18 is lower than that in Examples 14 and 19.

[0142] Compared to Examples 20 and 26, the secondary batteries in Examples 4 and 20-26 satisfy 0.2mm ≤ R ≤ 15mm. Under this condition, the value of R is not too small, which is beneficial for the first electrode 21 at the first recess 201 to release stress through deformation, reducing the possibility of damage to the first electrode 21 and the second electrode 22. Furthermore, the value of R is not too large, which is beneficial for reducing the possibility of damage to the first electrode 21 during the processing of the first recess 201. Therefore, the electrode tearing rate in Examples 4 and 21-25 is lower than that in Examples 20 and 26.

[0143] It should be noted that, limited by the time, effort, and economic costs required for experiments, the value ranges of L1, D1, N, W1, H1, R, and F1 in the embodiments of this application are numerical ranges derived by the inventors from a limited number of experiments and practical experience. This does not preclude the possibility that values ​​outside this range but close to it can achieve substantially the same technical effect as values ​​within this range. When a value outside this range but close to it can achieve substantially the same technical effect as a value within this range, it should be considered that the value is still disclosed in the embodiments of this application.

[0144] Furthermore, those skilled in the art should recognize that the above embodiments are merely illustrative of this application and are not intended to limit this application. Any appropriate changes and variations made to the above embodiments within the essential spirit and scope of this application fall within the scope of this application's disclosure.

Claims

1. A secondary battery characterized by comprising: The application relates to a battery, which comprises: a shell; an electrode assembly arranged in the shell, the electrode assembly comprising a first tab, a second tab and a separator, the first tab, the separator and the second tab being stacked and wound to form a winding structure, and the outermost tab of the electrode assembly being the first tab; the first tab comprises a first current collector and a first active material layer arranged in a stack, and the first tab has a first coating area and a first empty foil area arranged in sequence in the winding direction of the electrode assembly, and at least part of the first coating area is located at the outermost position of the first tab; in the thickness direction of the first tab, the side of the first coating area facing the second tab is provided with the first active material layer, and the other side is not provided with the first active material layer, and the opposite sides of the first empty foil area are not provided with the first active material layer; the second tab comprises a second current collector and a second active material layer arranged in a stack, the first active material layer comprises silicon elements, and the mass content of the silicon elements is greater than 5% based on the mass of the first active material layer; or the second active material layer contains silicon elements, and the mass content of the silicon elements is greater than 5% based on the mass of the second active material layer; in the winding direction of the electrode assembly, the electrode assembly has a first bending part, a first straight part, a second bending part and a second straight part arranged in sequence; in the thickness direction of the first tab, the local concave part of the first tab forms a first concave part; and a first adhesive is bonded to the outermost position of the first tab, the first adhesive bonds part of the first active material layer of the first coating area and part of the first current collector of the first empty foil area, and the first adhesive covers the first concave part in the thickness direction of the first tab.

2. The secondary battery according to claim 1, characterized by The first concave part is located in the second bending part.

3. The secondary battery according to claim 1, characterized by In the winding direction of the electrode assembly, the minimum distance between the junction of the first coating area and the first empty foil area and the first concave part is L1, and 0.5mm<=L1.

4. The secondary battery according to claim 1, characterized by In the winding direction of the electrode assembly, the minimum distance between the edge of the first adhesive and the first concave part is D1, and 1mm<=D1.

5. The secondary battery according to claim 1, characterized by The number of the first concave parts is N, the N first concave parts are arranged in sequence in the winding direction of the electrode assembly, N is a positive integer, and 2<=N<=10.

6. The secondary battery according to claim 1, characterized by In the first direction, the first concave part extends from one side of the first tab to the other side of the first tab, and the first direction is parallel to the winding central axis of the electrode assembly; In the winding direction of the electrode assembly, the width of the first concave part is W1, and 0.5mm<=W1<=5mm; and / or, in the thickness direction of the first tab, the depth of the first concave part is H1, and 0.1mm<=H1<=1.5mm.

7. The secondary battery according to claim 6, characterized by In the first direction, the profile of the first concave part is in the shape of a circular arc, the radius of the first concave part is R, and 0.2mm<=R<=15mm.

8. The secondary battery according to claim 1, characterized by The shell is provided with an electrolyte, and the peeling strength between the first adhesive and the first tab is F1, and 0.02N / mm<=F1<=0.1N / mm.

9. The secondary battery according to any one of claims 1 to 8, characterized by, The first tab has a second coating region, the second coating region and the first coating region are arranged in sequence along a winding direction of the electrode assembly, and the first coating region and the second coating region are both partially located in the secondary outer ring of the first tab, and opposite sides of the second coating region along a thickness direction of the first tab are both provided with the first active material layer; The local recess of the first tab forms a second recess along the thickness direction of the first tab, and the second recess is located in the second bending part; The secondary battery comprises a second adhesive member, the second adhesive member is attached to the secondary outer ring of the first tab, and the second adhesive member attaches part of the first active material layer of the second coating region and part of the first current collector of the first coating region, and the second adhesive member covers the second recess along the thickness direction of the first tab.

10. The secondary battery according to any one of claims 1 to 9, characterized by The local recess of the first tab forms a third recess along the thickness direction of the first tab, and the third recess is located in the first bending part; The secondary battery comprises a third adhesive member, the third adhesive member is attached to the first current collector of the outermost ring of the first tab, at least part of the third adhesive member is located in the first bending part, and the third adhesive member covers the third recess along the thickness direction of the first tab.

11. The secondary battery according to claim 10, characterized by The first bending part and the second bending part are arranged along a second direction, and the third adhesive member covers the first bending part along the second direction.

12. The secondary battery according to any one of claims 1 to 11, characterized by The first tab is a positive tab, and the second tab is a negative tab; The material of the second active material layer comprises silicon, and the mass content of the silicon is 50% or less based on the mass of the second active material layer.

13. The secondary battery according to claim 12, characterized by The first flat part and the second flat part are arranged along a third direction, and a projection of an end of the outermost ring of the second tab is located within a projection of the first adhesive member along the third direction; The third direction is a thickness direction of the electrode assembly.

14. An electronic device, comprising: The secondary battery comprises the secondary battery as claimed in any one of claims 1 to 13.

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