Secondary battery and electronic device

Abstract

The invention relates to a secondary battery and electronic equipment, the secondary battery comprises a first tab and a first pole piece, the first pole piece comprises a first current collector and a first active substance layer, the first active substance layer is stacked on the surface of the first current collector along a first direction, the first current collector is provided with a first empty foil area, and the first tab is partially arranged in the first empty foil area. The secondary battery further comprises a first adhesive layer, and the first adhesive layer is bonded between the first tab and the first empty foil area in the first direction. The first tab comprises a first surface facing the first current collector, a plurality of first convex parts are convexly arranged on the first surface, the width of the first convex parts in the second direction is reduced along the direction from the first tab to the first empty foil region, and at least part of the first convex parts are in contact with the first empty foil region. The short circuit of the secondary battery can be reduced, and the first lug boss is more beneficial to piercing the first adhesive layer so as to be directly contacted and electrically connected with the first current collector, so that the charging and discharging efficiency of the secondary battery can be improved.

Description

Technical Field

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

[0002] The tab serves as a bridge for electrically connecting the secondary battery to the external circuit. It is usually made of metal material. The tab is welded to the current collector inside the secondary battery, which allows the tab to be conductive with the electrode assembly inside the secondary battery, thereby achieving the purpose of transmitting current.

[0003] In order to facilitate the welding of the tabs, double-sided empty foil areas are usually required on the current collector. The welding seat supports the current collector on one side of the empty foil area, and the welding head welds the tabs and the current collector on the other side of the empty foil area. However, the welding of the tabs and the empty foil area of ​​the current collector usually produces some welding burrs, which can easily pierce the isolation film and cause the positive and negative electrodes inside the secondary battery to short-circuit and fail. Summary of the invention

[0004] The purpose of the present application is to provide a secondary battery and an electronic device, aiming to reduce the technical problem that the secondary battery is prone to short circuit.

[0005] According to the first aspect of the present application, a secondary battery is provided, comprising a first pole ear and a first pole piece, the first pole piece comprising a first current collector and a first active material layer, the first active material layer is stacked on the surface of the first current collector along a first direction, the first current collector is provided with a first empty foil area, and the first pole ear is partially provided in the first empty foil area. The secondary battery also comprises a first adhesive layer, and the first adhesive layer is bonded between the first pole ear and the first empty foil area along the first direction. The first pole ear comprises a first surface facing the first current collector, and a plurality of first protrusions are convexly provided on the first surface. Along the direction from the first pole ear to the first empty foil area, the width of the first protrusion in the second direction decreases, and at least part of the first protrusion is in contact with the first empty foil area. The first direction is the thickness direction of the first pole piece, and the second direction is the length or width direction of the first pole piece.

[0006] In the above technical solution, the first pole ear is bonded and fixed to the first empty foil area through the first adhesive layer, and there is no welding burr, which can reduce the short circuit of the secondary battery and improve the safety performance of the secondary battery. In addition, there is no need to set a protective adhesive layer on the first pole ear or the first empty foil area to cover the burrs, which saves the space occupied by the protective adhesive layer, and can reduce the cost while improving the energy density of the secondary battery. At the same time, the gluing process is relatively simple, and does not require complex welding equipment and professional welding technicians. Compared with the traditional welding process, the gluing process can save the preparation work, equipment debugging and strict control of welding quality in the welding process, which is conducive to improving the production efficiency of secondary batteries and reducing production costs.

[0007] Moreover, the provision of the first protrusion can increase the bonding area between the first adhesive layer and the first pole ear, and the first adhesive layer can effectively fill the tiny gap between the first pole ear and the first empty foil area, which can improve the connection strength between the first pole ear and the first empty foil area. In addition, the width of the first protrusion is reduced, so that the first protrusion forms a structure that is wide at the top and narrow at the bottom, which is more conducive to piercing the first adhesive layer and then directly contacting and electrically connecting with the first current collector, forming a more stable metal-metal electrical connection channel, which can effectively reduce the problem of unstable electrical connection caused by factors such as aging and deformation of the first adhesive layer, and is conducive to reducing the contact resistance between the first pole ear and the first current collector, and improving the charge and discharge efficiency of the secondary battery.

[0008] In some embodiments, along the first direction, the height of the first protrusion is H, 10μm≤H≤30μm, which is conducive to the first protrusion piercing the first adhesive layer to form a stable metal-metal electrical connection channel, reduce the contact resistance between the first pole ear and the first current collector, and improve the connection strength between the first pole ear and the first current collector while improving the charge and discharge rate of the secondary battery.

[0009] In some embodiments, at least part of the first protrusion penetrates the first current collector, so that an anchor point can be formed between the first pole ear and the first current collector, providing a more secure mechanical interlock, and effectively reducing the separation of the first pole ear from the first current collector caused by the secondary battery being subjected to vibration, impact, etc. At the same time, it can provide a more direct conductive path, form a more stable electrical connection, reduce current fluctuations and energy losses caused by poor contact, and reduce the contact resistance between the first pole ear and the first current collector, which is beneficial to improving the charge and discharge rate of the secondary battery.

[0010] In some embodiments, along the first direction, at least a portion of the first protrusion penetrates the first current collector, and a more secure interlocking structure can be constructed between the first pole ear and the first current collector, further improving the bonding strength between the first pole ear and the first current collector, and being able to effectively resist strong vibrations, impacts, and extreme acceleration changes, etc., and reduce loosening or detachment between the first pole ear and the first current collector.

[0011] In some embodiments, the first surface is in direct contact with the first empty foil area, which can further increase the electrical connection area between the first electrode tab and the first current collector and reduce the contact resistance.

[0012] In some embodiments, along the first direction, the first protrusion penetrates the first current collector to a depth of H1, 2 μm ≤ H1 ≤ 10 μm, which can improve the mechanical anchoring force between the first protrusion and the first current collector, thereby improving the connection strength between the first electrode tab and the first current collector, forming a more stable electrical connection, and reducing damage to the first current collector and reducing the occurrence of damage and tearing of the first current collector.

[0013] In some embodiments, along the second direction, the maximum width of the first protrusion is W, 5μm≤W≤10μm, which can improve the strength of the first protrusion, reduce damage to the first protrusion due to external force, and improve the connection strength between the first electrode ear and the first current collector, reducing the tearing of the first current collector caused by the first protrusion penetrating the first current collector.

[0014] In some embodiments, the first surface is further provided with a plurality of first recessed portions, and the first adhesive layer is partially embedded in the first recessed portions. The first recessed portions can serve as storage space for the first adhesive layer, so that the first adhesive layer can be better retained between the first electrode tab and the first current collector, thereby increasing the bonding area between the first electrode tab and the first adhesive layer, and thereby improving the connection strength between the first electrode tab and the first current collector.

[0015] In some embodiments, a plurality of first protrusions are disposed between two adjacent first recesses, part of the first adhesive layer may be embedded in the first recess, and the first protrusions are in direct contact and electrical connection with the first current collector, thereby increasing the connection strength between the first electrode tab and the first current collector and reducing contact resistance.

[0016] In some embodiments, the first adhesive layer is partially embedded between two adjacent first protrusions, which can also increase the bonding area between the first adhesive layer and the first electrode tab, and improve the connection strength between the first electrode tab and the first current collector.

[0017] In some embodiments, when observed along the first direction, the diameter of the first recessed portion is L1, and the distance between two adjacent first recessed portions is L2. 30μm≤L1≤500μm, and / or, 30μm≤L2≤500μm. It is beneficial to increase the bonding area between the first pole ear and the first adhesive layer, thereby improving the connection stability between the first pole ear and the first current collector, and reducing the damage and tearing of the first pole ear. Preferably, 50μm≤L1≤100μm, and / or, 50μm≤L2≤100μm, further improve the connection stability between the first pole ear and the first current collector, while making the first pole ear have a higher strength.

[0018] In some embodiments, along the first direction, the depth of the first recess is D, 20μm≤D≤60μm, which can facilitate the first adhesive layer to fill the first recess, increase the bonding area between the first electrode tab and the first adhesive, and further improve the connection stability between the first electrode tab and the first current collector.

[0019] In some embodiments, the first adhesive layer includes a hot melt adhesive, a thermosetting adhesive, or a pressure-sensitive adhesive. For example, the first adhesive layer is a hot melt adhesive, which is heated and melted and then coated on the first pole ear, and can fill the concave-convex structure on the first pole ear, and can be cooled and solidified in a short time to achieve bonding with the first current collector. Alternatively, the first adhesive layer is a thermosetting adhesive, and the cured first adhesive layer has high strength and hardness, which can reduce the damage and tearing of the first pole ear and can adapt to the high temperature environment at the first pole ear. Alternatively, the first adhesive layer is a pressure-sensitive adhesive, which does not require heating, solvent activation or a complicated curing process, and can achieve bonding by applying light pressure. The operation is simple and quick, and is suitable for bonding the concave-convex structure of the first pole ear.

[0020] In some embodiments, the first active material layer is provided with a first groove, the first current collector forms a first empty foil area in the first groove, and the first pole ear is partially provided in the first groove. The first pole piece also includes a second active material layer, and the second active material layer is superimposed on the surface of the first current collector away from the first active material layer. Along the first direction, the first groove is located within the projection of the second active material layer. Because the first pole ear and the first current collector are bonded by the first adhesive layer, no welding head and welding seat are required, that is, no groove is required in the second active material layer to place the welding seat, so that the structure of the second active material layer is more complete, and the powder shedding of part of the second active material layer caused by the groove is reduced, so that the second active material layer can be fully utilized, and the energy density of the secondary battery is improved.

[0021] In some embodiments, the secondary battery further includes an isolating membrane and a second pole piece, and the isolating membrane is disposed between the first pole piece and the second pole piece along the first direction. The second active material layer includes a first region, and along the first direction, the projection of the first region coincides with the first groove, and the surface of the first region facing away from the first current collector is at least partially in contact with the isolating membrane. The first region of the second active material layer does not need to be provided with a corresponding groove, nor does it need to be provided with a protective adhesive layer to cover the burrs. Therefore, the first region of the second active material layer can directly contact the isolating membrane, that is, the first region can participate in the electrochemical reaction, thereby improving the energy density of the secondary battery.

[0022] In some embodiments, the secondary battery further includes a separator and a second pole piece. Along the first direction, the separator is arranged between the first pole piece and the second pole piece. The first pole piece is a positive pole piece, and the second pole piece is a negative pole piece. The second pole piece includes a second current collector and a third active material layer. The third active material layer is stacked on the surface of the second current collector facing the first active material layer. The third active material layer includes a second region. Along the first direction, the projection of the second region coincides with the first groove, and the surface of the second region facing the first groove is at least partially in direct contact with the separator. The second region of the third active material layer does not need to be provided with a protective adhesive layer, so that the second region can participate in the electrochemical reaction normally, thereby improving the energy density of the secondary battery. In addition, because the second pole piece is a negative pole piece, the second pole piece can have sufficient margin to embed the lithium ions released from the first pole piece, which can reduce the occurrence of lithium plating.

[0023] In some embodiments, the third active material layer is provided with a second groove, the second current collector forms a second empty foil area in the second groove, the second pole ear is partially provided in the second groove, and the second adhesive layer is bonded between the second pole ear and the second empty foil area. The second pole ear includes a second surface facing the second current collector, and a plurality of second protrusions are convexly provided on the second surface. Along the direction from the second pole ear to the second empty foil area, the width of the second protrusion in the second direction is reduced, and at least part of the second protrusion is in contact with the second empty foil area. There is no welding burr, which can reduce the short circuit of the secondary battery and improve the safety performance of the secondary battery. In addition, there is no need to set a protective adhesive layer in the second pole ear or the second empty foil area to cover the burr, which saves the space occupied by the protective adhesive layer, and can reduce the cost while improving the energy density of the secondary battery.

[0024] In a second aspect, the present application further proposes an electronic device, comprising a secondary battery as in any embodiment of the first aspect above.

[0025] Additional aspects and advantages of the embodiments of the present application will be described, shown, or explained in part in the subsequent description through implementation of the embodiments of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] One or more embodiments are exemplarily described by corresponding drawings, which do not constitute limitations on the embodiments. Elements with the same reference numerals in the drawings represent similar elements, and unless otherwise stated, the dimensions in the drawings do not constitute proportional limitations.

[0027] Figure 1 A schematic diagram of the structure of a secondary battery in some embodiments of the present application;

[0028] Figure 2 A schematic diagram of stacking a first pole piece, an isolation film, and a second pole piece in some embodiments of the present application;

[0029] Figure 3This is a schematic structural diagram of a first pole piece in some embodiments of the present application;

[0030] Figure 4 for Figure 3 A partial enlarged view of the middle A;

[0031] Figure 5 This is a schematic structural diagram of a first pole piece in some embodiments of the present application;

[0032] Figure 6 This is a schematic structural diagram of a first pole piece in some embodiments of the present application;

[0033] Figure 7 An exploded schematic diagram of a first pole piece of some embodiments of the present application;

[0034] Figure 8 This is a schematic structural diagram of a first pole piece in some embodiments of the present application;

[0035] Fig. 9 for Figure 8 A partial enlarged view of point B in the middle;

[0036] Fig.10 This is a schematic structural diagram of a first pole piece in some embodiments of the present application;

[0037] Fig.11 for Fig.10 A partial enlarged view of point C in the middle;

[0038] Fig.12 A schematic diagram of the structure of a first electrode tab in some embodiments of the present application;

[0039] Fig.13 This is a schematic diagram of the structure of the second pole piece of some embodiments of the present application.

[0040] Description of reference numerals:

[0041] 100. Secondary battery;

[0042] 10. Shell;

[0043] 20. Electrode assembly;

[0044] 21, first pole piece; 211, first current collector; 212, first active material layer; 213, second active material layer; 211a, first empty foil area; 211b, first groove; 2131, first region;

[0045] 22, second pole piece; 221, second current collector; 221a, second empty foil area; 221b, second groove; 222, third active material layer; 2221, second area; 223, fourth active material layer;

[0046] 23. Isolation film;

[0047] 30, first pole ear; 31, first surface; 30a, first protrusion; 30b, first depression;

[0048] 40, second pole ear; 41, second surface; 40a, second protrusion;

[0049] 50. First adhesive layer;

[0050] 60, second adhesive layer;

[0051] Z, first direction; X, second direction; Y, third direction. DETAILED DESCRIPTION

[0052] In order to make the purpose, 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 in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments.

[0053] Reference to "embodiment" in this application means that a particular feature, structure, or characteristic described in conjunction with the embodiment may be included in at least one embodiment of the present application. The appearance of the phrase in various places in the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment that is mutually exclusive with other embodiments.

[0054] In the description of the embodiments of the present application, the technical terms "first", "second", etc. are only used to distinguish different objects, and cannot be understood as indicating or implying relative importance or implicitly indicating the number, specific order or primary and secondary relationship of the indicated technical features. In the description of the embodiments of the present application, the meaning of "multiple" is more than two, unless otherwise clearly and specifically defined.

[0055] In the description of the embodiments of the present application, the term "and / or" is only a description of the association relationship of the associated objects, indicating that there may be three relationships. For example, A and / or B can represent: A exists alone, A and B exist at the same time, and B exists alone. In addition, the character " / " in this article generally indicates that the associated objects before and after are in an "or" relationship.

[0056] The technical features involved in the different embodiments of the present application described below can be combined with each other as long as they do not conflict with each other.

[0057] In the first aspect, the present application proposes a secondary battery 100, please refer to Figure 1The secondary battery 100 includes a housing 10, an electrode assembly 20, a first pole tab 30, and a second pole tab 40. The housing 10 can accommodate the electrode assembly 20 and an electrolyte (not shown in the figure). The electrolyte infiltrates the electrode assembly 20 in the housing 10, thereby generating an electrochemical reaction. One end of the first pole tab 30 is connected to the electrode assembly 20 in the housing 10, and the other end of the first pole tab 30 extends out of the housing 10. One end of the second pole tab 40 is connected to the electrode assembly 20 in the housing 10, and the other end of the second pole tab 40 extends out of the housing 10. The first pole tab 30 and the second pole tab 40 have opposite polarities and are used to lead out the positive and negative electrodes of the secondary battery 100.

[0058] For the electrode assembly 20, please refer to Figure 1 and Figure 2 The electrode assembly 20 includes a first electrode sheet 21, a second electrode sheet 22 and a separator 23. The first electrode sheet 21, the separator 23 and the second electrode sheet 22 are stacked and wound, for example, stacked along the thickness direction (first direction Z) of the first electrode sheet 21 and wound along its length direction (second direction X) to form a wound electrode assembly 20. The separator 23 is disposed between the first electrode sheet 21 and the second electrode sheet 22 to insulate and separate the first electrode sheet 21 and the second electrode sheet 22.

[0059] In some other embodiments, a plurality of first pole pieces 21 and a plurality of second pole pieces 22 are alternately stacked, and an isolation film 23 is disposed between adjacent first pole pieces 21 and second pole pieces 22 , thereby forming a stacked electrode assembly 20 .

[0060] The polarity of the first pole piece 21 is opposite to that of the second pole piece 22, for example, the first pole piece 21 is a positive pole piece and the second pole piece 22 is a negative pole piece, or in some other embodiments, the first pole piece 21 is a negative pole piece and the second pole piece 22 is a positive pole piece. The first pole tab 30 is connected to the first pole piece 21, and the current of the first pole piece 21 is collected and transmitted through the first pole tab 30, and the second pole tab 40 is connected to the second pole piece 22, and the current of the second pole piece 22 is collected and transmitted through the second pole tab 40, thereby leading out the positive and negative poles of the secondary battery 100.

[0061] Please refer to Figure 2 The first pole piece 21 includes a first current collector 211 and a first active material layer 212. The first current collector 211 serves as a conductive substrate of the first pole piece 21 and may be an overall flat aluminum foil. Aluminum foil has high electrical conductivity and low resistance, and can improve the maximum charge and discharge rate of the secondary battery 100. In addition, aluminum foil has certain strength and ductility. In the production process such as winding or lamination, the aluminum foil is not easy to break or deform, so as to ensure the structural integrity of the first pole piece 21. In some other embodiments, the first current collector 211 may also be made of titanium foil, nickel foil or stainless steel foil.

[0062] The first active material layer 212 can be stacked on one surface of the first current collector 211 in the thickness direction (first direction Z), and the first active material layer 212 includes a positive electrode active material, a conductive agent, and an adhesive, etc. The above-mentioned material components are mixed and stirred evenly and coated on the surface of the first current collector 211, thereby obtaining the first active material layer 212. Among them, the positive electrode active material includes one or more of lithium nickel cobalt manganese oxide, lithium cobalt oxide, lithium iron phosphate, lithium nickel cobalt manganese oxide, lithium manganese oxide, or lithium manganese iron phosphate. Optionally, the first pole piece 21 also includes a second active material layer 213, which is stacked on the other surface of the first current collector 211 in the thickness direction (first direction Z) to form a double-sided coating structure, and the second active material layer 213 can be set similarly to the first active material layer 212.

[0063] Please refer to Figure 2 The second pole piece 22 includes a second current collector 221 and a third active material layer 222. The second current collector 221 serves as a conductive substrate of the second pole piece 22 and may be a flat copper foil. The copper foil has high electrical conductivity and low resistance, and can improve the maximum charge and discharge rate of the secondary battery 100. In addition, the copper foil has certain strength and ductility. In the production process such as winding or lamination, the copper foil is not easy to break or deform, so as to ensure the structural integrity of the second pole piece 22. In some other embodiments, the second current collector 221 may also be made of titanium foil, nickel foil, stainless steel foil or silver foil.

[0064] The third active material layer 222 can be stacked on one surface of the second current collector 221 in the thickness direction (first direction Z), and the third active material layer 222 includes negative electrode active materials, conductive agents, and adhesives, etc. These materials are mixed and stirred evenly and applied to the surface of the second current collector 221 to obtain the third active material layer 222. Among them, the negative electrode active material includes one or more of graphite, soft carbon, hard carbon, elemental silicon, silicon oxides, silicon alloys, etc. Optionally, the second pole piece 22 also includes a fourth active material layer 223, which is stacked on the other surface of the second current collector 221 in the thickness direction (first direction Z) to form a double-sided coating structure. The fourth active material layer 223 can be set similarly to the third active material layer 222.

[0065] For the first tab 30, please refer to Figure 2 The first current collector 211 is provided with a first empty foil area 211a (the first active material layer 212 is not provided), and the first pole ear 30 is partially provided in the first empty foil area 211a. For example, a part of the first pole ear 30 is electrically connected to the first empty foil area 211a, and the other part extends out of the first pole sheet 21 along the width direction (third direction Y) of the first pole sheet 21.

[0066] Please refer to Figures 2 to 4In some embodiments, the secondary battery 100 further includes a first adhesive layer 50, and the first adhesive layer 50 is bonded between the first pole tab 30 and the first empty foil area 211a along the first direction Z. The first pole tab 30 includes a first surface 31 facing the first current collector 211, and the first surface 31 is provided with a plurality of first protrusions 30a. Along the direction from the first pole tab 30 to the first empty foil area 211a (the first direction Z), the first protrusions 30a are arranged with a reduced width in the second direction X, and at least part of the first protrusions 30a is in contact with the first empty foil area 211a. The first direction Z is the thickness direction of the first pole sheet 21, and the second direction X is the length or width direction of the first pole sheet 21. In this application, the second direction X is taken as the length direction of the first pole sheet 21 as an example.

[0067] In the embodiment of the present application, the first pole tab 30 is bonded and fixed to the first empty foil area 211a through the first adhesive layer 50, and there is no welding burr, which can reduce the short circuit of the secondary battery 100 and improve the safety performance of the secondary battery 100. In addition, it is not necessary to set a protective adhesive layer on the first pole tab 30 or the first empty foil area 211a to cover the burr, which saves the space occupied by the protective adhesive layer, and can reduce the cost while improving the energy density of the secondary battery 100.

[0068] At the same time, the gluing process is relatively simple and does not require complicated welding equipment and professional welding technicians. Compared with the traditional welding process, the gluing process can save the preparation work, equipment debugging and strict control of welding quality during the welding process, which is beneficial to improve the production efficiency of the secondary battery 100 and reduce production costs.

[0069] Furthermore, the provision of the first protrusion 30a can increase the bonding area between the first adhesive layer 50 and the first electrode tab 30, and the first adhesive layer 50 can effectively fill the tiny gap between the first electrode tab 30 and the first empty foil area 211a, thereby increasing the connection strength between the first electrode tab 30 and the first empty foil area 211a.

[0070] In addition, the width of the first protrusion 30a is reduced, so that the first protrusion 30a forms a structure that is wide at the top and narrow at the bottom, which is more conducive to piercing the first adhesive layer 50 and then directly contacting and electrically connecting with the first current collector 211, forming a more stable metal-to-metal electrical connection channel, which can effectively reduce the problem of unstable electrical connection caused by factors such as aging and deformation of the first adhesive layer 50, and is beneficial to reducing the contact resistance between the first electrode 30 and the first current collector 211, thereby improving the charge and discharge efficiency of the secondary battery 100.

[0071] As for the height of the first protrusion 30a, the inventor of the present application has found that if the height of the first protrusion 30a is too small, it may be difficult to effectively pierce the first adhesive layer 50, resulting in the first protrusion 30a being difficult to form a good direct contact with the first current collector 211, and may cause the contact area between the first adhesive layer 50 and the first pole tab 30 to be too small, resulting in a loose connection between the first pole tab 30 and the first current collector 211. If the height of the first protrusion 30a is too large, it may be difficult for the first adhesive layer 50 to be completely embedded between adjacent first protrusions 30a, resulting in bubbles formed between the first adhesive layer 50 and the first pole tab 30, affecting the bonding strength between the first pole tab 30 and the first current collector 211.

[0072] In the embodiments of this application, please refer to Figure 3 and Figure 4 , along the first direction Z, the height of the first protrusion 30a is H, 10μm≤H≤30μm, which is conducive to the first protrusion 30a piercing the first adhesive layer 50 to form a stable metal-metal electrical connection channel, reduce the contact resistance between the first electrode tab 30 and the first current collector 211, and improve the connection strength between the first electrode tab 30 and the first current collector 211 while improving the charge and discharge rate of the secondary battery 100.

[0073] For the maximum width of the first protrusion 30a, if the maximum width is too small, the strength of the first protrusion 30a may be insufficient, and the first protrusion 30a may be damaged by a small external force, such as breaking, bending, etc., which may affect the electrical connection between the first electrode tab 30 and the first current collector 211, resulting in unstable electrical connection. If the width is too large, when piercing the first adhesive layer 50, a large area of ​​the first adhesive layer 50 may be damaged, and it may be difficult to penetrate the first adhesive layer 50, affecting the bonding strength, and a single first protrusion 30a occupies too much space, resulting in a small number of first protrusions 30a, so that the bonding area between the first adhesive layer 50 and the first electrode tab 30 is insufficient.

[0074] In the embodiment of the present application, along the second direction X, the maximum width of the first protrusion 30a is W, 10μm≤W≤30μm, which can improve the strength of the first protrusion 30a, reduce the damage of the first protrusion 30a due to external force, and improve the connection strength between the first electrode tab 30 and the first current collector 211.

[0075] In some embodiments, please refer to Figure 5At least part of the first protrusion 30a penetrates the first current collector 211, so that an anchor point can be formed between the first pole ear 30 and the first current collector 211, providing a more secure mechanical interlocking, and effectively reducing the separation of the first pole ear 30 from the first current collector 211 caused by the first pole ear 30 when the secondary battery 100 is subjected to vibration, impact, etc. At the same time, it can provide a more direct conductive path, form a more stable electrical connection, reduce current fluctuations and energy losses caused by poor contact, and reduce the contact resistance between the first pole ear 30 and the first current collector 211, which is conducive to improving the charge and discharge rate of the secondary battery 100.

[0076] Regarding the penetration depth of the first protrusion 30a in the first current collector 211, if the penetration depth is too small, it may be difficult to provide sufficient mechanical anchoring force, so that the connection between the first protrusion 30a and the first current collector 211 is not strong enough, and when the secondary battery 100 is subjected to collision and impact, the first protrusion 30a and the first current collector 211 are easily separated, resulting in unstable electrical connection. If the penetration depth is too large, mechanical damage will be caused to the first current collector 211, which may easily cause the first current collector 211 to be damaged, torn, or torn.

[0077] In the embodiments of this application, please refer to Figure 5 , along the first direction Z, the depth of the first protrusion 30a penetrating the first current collector 211 is H1, 2μm≤H1≤10μm, which can improve the mechanical anchoring force between the first protrusion 30a and the first current collector 211, thereby improving the connection strength between the first electrode tab 30 and the first current collector 211, and forming a more stable electrical connection. It can also reduce the damage to the first current collector 211 and reduce the damage and tearing of the first current collector 211. Among them, when the first protrusion 30a penetrates the first current collector 211, along the second direction X, the maximum width of the first protrusion 30a is W, 5μm≤W≤10μm, which can make the first protrusion 30a have a higher structural strength, and can facilitate the first protrusion 30a to penetrate the first current collector 211, reduce the damage to the first current collector 211, and then the first current collector 211 will tear.

[0078] In some other embodiments, please refer to Figure 6, in the thickness direction (first direction Z) of the first pole piece 21, at least part of the first protrusion 30a penetrates the first current collector 211, and a more solid interlocking structure can be constructed between the first pole tab 30 and the first current collector 211, further improving the bonding strength between the first pole tab 30 and the first current collector 211, and can effectively resist strong vibration, impact and extreme acceleration changes, etc., and reduce the loosening or separation between the first pole tab 30 and the first current collector 211. It can also further reduce the contact resistance between the first pole tab 30 and the first current collector 211, which helps to improve the uniformity of current distribution on the first current collector 211 and effectively reduce local overheating.

[0079] When the first protrusion 30a penetrates the first current collector 211, the first surface 31 can be in direct contact with the first empty foil area 211a. For example, part of the first surface 31 is bonded to the first current collector 211 through the first adhesive layer 50, and the other part is in direct contact with the first current collector 211. This can further increase the electrical connection area between the first pole ear 30 and the first current collector 211 and reduce the contact resistance, which is beneficial to improving the charge and discharge rate of the secondary battery 100 while improving the connection strength between the first pole ear 30 and the first current collector 211.

[0080] In some embodiments, please refer to Figures 7 to 9 The first surface 31 is also provided with a plurality of first recessed portions 30b, the first protruding portions 30a protrude relative to the first surface 31, the first recessed portions 30b are recessed relative to the first surface 31, and the first adhesive layer 50 is partially embedded in the first recessed portions 30b. This can increase the bonding area between the first electrode tab 30 and the first adhesive layer 50, thereby improving the connection strength between the first electrode tab 30 and the first current collector 211.

[0081] At the same time, the first recessed portion 30b can be used as a storage space for the first adhesive layer 50, so that the first adhesive layer 50 is better retained between the first pole tab 30 and the first current collector 211. For example, during the thermal runaway of the secondary battery 100, the temperature at the first pole tab 30 rises sharply, and the first adhesive layer 50 may be melted, so that the first pole tab 30 is separated from the first current collector 211, and then the electrical connection between the first pole tab 30 and the first current collector 211 is disconnected, thereby alleviating thermal runaway. The first recessed portion 30b can reduce the loss of the melted first adhesive layer 50. After solidification, sufficient first adhesive layer 50 can be again between the first pole tab 30 and the first current collector 211 to achieve a good bonding effect, which is conducive to maintaining the connection stability of the first pole tab 30 and the first current collector 211 for a long time.

[0082] In some embodiments, a plurality of first protrusions 30a are provided between two adjacent first recesses 30b, and part of the first adhesive layer 50 can be embedded in the first recesses 30b, and the first protrusions 30a are directly in electrical contact with the first current collector 211, which can improve the connection strength between the first pole tab 30 and the first current collector 211 and reduce the contact resistance. For example, the first recesses 30b are formed on the surface of the first pole tab 30 by laser processing, and the slag generated by the laser processing is accumulated around the first recesses 30b to form the first protrusions 30a beyond the first surface 31. The process is simple and convenient, and the first recesses 30b and the first protrusions 30a can be formed by one laser processing. In some other embodiments, the first recesses 30b and / or the first protrusions 30a can also be formed on the first surface 31 by stamping, etching and / or cold heading.

[0083] In some embodiments, the first adhesive layer 50 may also be partially embedded between two adjacent first protrusions 30 a , which can also increase the bonding area between the first adhesive layer 50 and the first electrode tab 30 , and improve the connection strength between the first electrode tab 30 and the first current collector 211 .

[0084] Please refer to Fig.10 and Fig.11 When the first protrusion 30a penetrates the first current collector 211, the first recessed portion 30b can accommodate part of the first adhesive layer 50, and the first surface 31 can directly contact and electrically connect with the first current collector 211, which is more conducive to reducing the contact resistance, and the first adhesive layer 50 in the first recessed portion 30b can directly bond the first electrode tab 30 and the first current collector 211, thereby improving the connection strength between the first electrode tab 30 and the first current collector 211.

[0085] For the diameter of the first recessed portion 30b, if the diameter is too small, the bonding area that can be increased is relatively small, and the effect on improving the connection stability between the first pole tab 30 and the first current collector 211 is not obvious. If the diameter is too large, the strength of the first pole tab 30 may be affected, and it is easy to cause the first pole tab 30 to be damaged or torn. In addition, the distance between two adjacent first recessed portions 30b is similar. If the distance is too large, the bonding area increased is limited. If the distance is too small, the first recessed portions 30b are too dense, which affects the strength of the first pole tab 30.

[0086] In the embodiment of the present application, please refer to the figure, and when observed along the first direction Z, the diameter of the first recessed portion 30b is L1, and the distance between two adjacent first recessed portions 30b is L2, 30μm≤L1≤500μm, and / or, 30μm≤L2≤500μm. This is conducive to increasing the bonding area between the first pole tab 30 and the first adhesive layer 50, thereby improving the connection stability between the first pole tab 30 and the first current collector 211, and reducing the damage and tearing of the first pole tab 30. Preferably, 50μm≤L1≤100μm, and / or, 50μm≤L2≤100μm, further improving the connection stability between the first pole tab 30 and the first current collector 211, while making the first pole tab 30 have a higher strength.

[0087] As for the depth of the first recessed portion 30b, in the embodiment of the present application, along the first direction Z, the depth of the first recessed portion 30b is D, 20μm≤D≤60μm, which can facilitate the first adhesive layer 50 to fill the first recessed portion 30b, increase the bonding area between the first electrode tab 30 and the first adhesive, and further improve the connection stability between the first electrode tab 30 and the first current collector 211.

[0088] Among them, the first adhesive layer 50 can be made of hot melt adhesive, thermosetting adhesive or pressure-sensitive adhesive. For example, the first adhesive layer 50 is a hot melt adhesive, which is heated and melted and then coated on the first pole ear 30, and can fill the concave-convex structure on the first pole ear 30, and can be cooled and solidified in a short time to achieve bonding with the first current collector 211. Alternatively, the first adhesive layer 50 is a thermosetting adhesive, and the first adhesive layer 50 after solidification has high strength and hardness, which can reduce the damage and tearing of the first pole ear 30 and can adapt to the high temperature environment at the first pole ear 30. Alternatively, the first adhesive layer 50 is a pressure-sensitive adhesive, which does not require heating, solvent activation or a complicated curing process, and can achieve bonding by applying light pressure. The operation is simple and quick, and is suitable for bonding the concave-convex structure of the first pole ear 30.

[0089] In some other embodiments, the first adhesive layer 50 may also be made of conductive adhesive. For example, conductive particles such as silver, copper, nickel, aluminum, graphite or carbon nanotubes may be added to the first adhesive layer 50 to achieve electrical connection between the first electrode tab 30 and the first current collector 211 .

[0090] In some embodiments, please refer to Figure 2, the first active material layer 212 is provided with a first groove 211b, and the first current collector 211 forms a first empty foil area 211a at the first groove 211b, for example, a part of the first active material layer 212 is removed by laser cleaning or foaming glue, so that the first current collector 211 is partially exposed, thereby forming the first empty foil area 211a. The first pole piece 21 also includes a second active material layer 213, and the second active material layer 213 is superimposed on the surface of the first current collector 211 away from the first active material layer 212. Along the thickness direction (first direction Z) of the first pole piece 21, the first groove 211b is located within the projection of the second active material layer 213.

[0091] In the embodiment of the present application, since the first electrode tab 30 is bonded to the first current collector 211 by the first adhesive layer 50, there is no need for a welding head and a welding seat, that is, there is no need to open a groove in the second active material layer 213 to place the welding seat, so that the structure of the second active material layer 213 is more complete, and the powder shedding of part of the second active material layer 213 caused by the grooving is reduced, so that the second active material layer 213 can be fully utilized, thereby improving the energy density of the secondary battery 100.

[0092] In addition, when the above-mentioned first protrusion 30a penetrates the first current collector 211, please refer to the figure further, the first protrusion 30a can be in direct contact with the second active material layer 213, which can shorten the conductive path, help improve the current distribution inside the second active material layer 213, promote the full reaction of the active material, improve the utilization rate of the second active material layer 213, and thus improve the energy density of the secondary battery 100.

[0093] In some embodiments, please refer to Figure 2 The second active material layer 213 includes a first region 2131. Along the thickness direction (first direction Z) of the first electrode 21, the projection of the first region 2131 coincides with the first groove 211b, and the surface of the first region 2131 facing away from the first current collector 211 is at least partially in contact with the isolation film 23.

[0094] In the embodiment of the present application, since the first electrode tab 30 is bonded to the first current collector 211 through the first adhesive layer 50, there are no welding burrs. The first region 2131 of the second active material layer 213 does not need to have a corresponding groove, nor does it need to have a protective adhesive layer to cover the burrs. Therefore, the first region 2131 of the second active material layer 213 can directly contact the isolation membrane 23, that is, the first region 2131 can participate in the electrochemical reaction, thereby improving the energy density of the secondary battery 100.

[0095] Regarding the second pole tab 40, the second pole tab 40 may also be configured similarly to the first pole tab 30. Please refer to Figure 2, the second current collector 221 is provided with a second empty foil area 221a, for example, by opening a second groove 221b on the third active material layer 222 so that the second current collector 221 is partially exposed, thereby forming the second empty foil area 221a. The secondary battery 100 also includes a second adhesive layer 60, and the second pole tab 40 is partially provided in the second groove 221b, and the second adhesive layer 60 is bonded between the second pole tab 40 and the second empty foil area 221a. The second pole tab 40 includes a second surface 41 facing the second current collector 221, and the second surface 41 is convexly provided with a plurality of second protrusions 40a. Along the direction from the second pole tab 40 to the second empty foil area 221a, the width of the second protrusion 40a in the second direction X is reduced, and at least part of the second protrusion 40a is in contact with the second empty foil area 221a.

[0096] The second pole tab 40 is bonded and fixed to the second empty foil area 221a through the second adhesive layer 60, and there is no welding burr, which can reduce the short circuit of the secondary battery 100 and improve the safety performance of the secondary battery 100. In addition, there is no need to set a protective adhesive layer on the second pole tab 40 or the second empty foil area 221a to cover the burr, which saves the space occupied by the protective adhesive layer, and can reduce the cost while improving the energy density of the secondary battery 100.

[0097] At the same time, the gluing process is relatively simple and does not require complicated welding equipment and professional welding technicians. Compared with the traditional welding process, the gluing process can save the preparation work, equipment debugging and strict control of welding quality during the welding process, which is beneficial to improve the production efficiency of the secondary battery 100 and reduce production costs.

[0098] Furthermore, the second protrusion 40a can increase the bonding area between the second adhesive layer 60 and the second electrode tab 40, and the second adhesive layer 60 can effectively fill the small gap between the second electrode tab 40 and the second empty foil area 221a, thereby increasing the connection strength between the second electrode tab 40 and the second empty foil area 221a.

[0099] In addition, the width of the second protrusion 40a is reduced, so that the second protrusion 40a forms a structure that is wide at the top and narrow at the bottom, which is more conducive to piercing the second adhesive layer 60 and directly contacting and electrically connecting with the second current collector 221, forming a more stable metal-to-metal electrical connection channel, which can effectively reduce the problem of unstable electrical connection caused by factors such as aging and deformation of the second adhesive layer 60, and is beneficial to reducing the contact resistance between the second electrode tab 40 and the second current collector 221, thereby improving the charge and discharge efficiency of the secondary battery 100.

[0100] The specific connection structure of the second electrode tab 40, the second current collector 221 and the second adhesive layer 60 can refer to the first electrode tab 30, the first current collector 211 and the first adhesive layer 50, which have similar structures and are not described one by one in this application.

[0101] In some embodiments, taking the first electrode sheet 21 as a positive electrode sheet and the second electrode sheet 22 as a negative electrode sheet as an example, the second electrode sheet 22 includes a second current collector 221 and a third active material layer 222, and the third active material layer 222 is superimposed on the surface of the second current collector 221 facing the first active material layer 212. The third active material layer 222 includes a second region 2221, and along the thickness direction (first direction Z) of the first electrode sheet 21, the projection of the second region 2221 coincides with the first groove 211b, and the surface of the second region 2221 facing the first groove 211b is at least partially in contact with the isolation film 23.

[0102] In the embodiment of the present application, since the first pole tab 30 is bonded to the first current collector 211 through the adhesive layer, there is no welding burr, and the risk of piercing the separator 23 is low. Therefore, the second region 2221 of the third active material layer 222 does not need to be provided with a protective adhesive layer, so that the second region 2221 can participate in the electrochemical reaction normally, thereby improving the energy density of the secondary battery 100. In addition, since the second pole piece 22 is a negative pole piece, the second pole piece 22 can have enough margin to embed the lithium ions released from the first pole piece 21, thereby reducing the occurrence of lithium plating.

[0103] In the second aspect, the present application also proposes an electronic device, including a secondary battery 100 as described in any embodiment of the first aspect above. The electronic device of the embodiment of the present application is not particularly limited, and it can be any electronic device known in the prior art. For example, electronic devices include but are not limited to Bluetooth headsets, mobile phones, tablets, laptops, electric toys, electric tools, battery cars, electric cars, ships, spacecraft, etc. Among them, electric toys can include fixed or mobile electric toys, such as game consoles, electric car toys, electric ship toys, and electric airplane toys, etc., and spacecraft can include airplanes, rockets, space shuttles, and spacecrafts, etc.

[0104] Example 1

[0105] Preparation of positive electrode:

[0106] The positive electrode active material is lithium cobalt oxide, 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 5 ) were mixed in a mass ratio of 94:3:3, N-methylpyrrolidone (NMP) was added as a solvent, and a positive electrode slurry with a solid content of 75wt% was prepared, and the mixture was stirred evenly in a vacuum mixer. A 12μm thick aluminum foil was selected as the positive electrode current collector, and the positive electrode slurry was evenly coated on one surface of the positive electrode current collector aluminum foil, and dried at 110°C to obtain a positive electrode sheet with a single-sided positive electrode active material layer. Afterwards, the above steps were repeated on the other surface of the aluminum foil to obtain a positive electrode sheet with a double-sided positive electrode active material layer.

[0107] A first groove is reserved on a positive electrode active material layer on one surface by using a foaming glue process, so that the positive electrode current collector is partially exposed, thereby forming a first empty foil area. The first empty foil area has a width of 10 mm and a length of 20 mm.

[0108] An aluminum sheet with a thickness of 80 μm is used as the positive electrode tab. A first protrusion is formed on the first surface of the positive electrode tab by mechanical crimping, and the width of the first protrusion is reduced along the width direction of the positive electrode sheet. The height H of the first protrusion is 8 μm, the maximum width W of the first protrusion is 5 μm, the spacing between two adjacent first protrusions is 50 μm, and each first protrusion forms a protruding area.

[0109] The first adhesive layer of epoxy resin is bonded to the first surface of the positive electrode tab, and the thickness of the first adhesive layer is 15μm. The positive electrode tab and the first empty foil area of ​​the positive current collector are fixed by hot pressing. During the hot pressing, the first protrusion is squeezed and embedded in the first adhesive layer, and the first adhesive layer fills the gap between two adjacent first protrusions. The bonding width of the first adhesive layer in the first empty foil area is 8mm, and a gap of 1mm is reserved on both sides with the positive electrode active material layer. The bonding length is 18mm, and a gap of 1mm is reserved with the positive electrode active material layer in the length direction. The length of the protruding area on the first empty foil area is 18mm, and the length of the protruding area is less than the length of the first adhesive layer, and the difference is 3mm.

[0110] Preparation of negative electrode sheet:

[0111] The negative electrode active material graphite powder, conductive agent conductive carbon black (Super P), and binder styrene butadiene rubber (SBR) were mixed in a weight ratio of 97.5:1:1.5, and then deionized water was added as a solvent to prepare a slurry with a solid content of 50wt%, and stirred evenly. The slurry was evenly coated on one surface of a negative electrode current collector copper foil with a thickness of 6μm, and dried at 110℃ to obtain a negative electrode active material with a weight of 9.1mg / cm 2 Single-sided negative electrode sheet. After the above steps are completed, the single-sided coating of the negative electrode sheet has been completed. After that, the above steps are repeated on the other surface of the negative electrode sheet to obtain a negative electrode sheet with a double-sided coating of the negative electrode active material layer. A second empty foil area is reserved on the negative electrode sheet through the foaming glue process, and the second empty foil area has a width of 10 mm and a length of 20 mm.

[0112] A 80μm nickel sheet is used as the negative electrode tab, and a second protrusion is formed on the negative electrode tab by mechanical crimping. A second glue layer of epoxy resin is bonded to the surface of the negative electrode tab, and the thickness of the second glue layer is 15μm. The negative electrode tab is bonded to the second empty foil area, and the bonding width of the second glue layer in the second empty foil area is 8mm. A gap of 1mm is reserved on both sides with the negative electrode active material layer. The bonding length is 18mm, and a gap of 1mm is reserved with the negative electrode active material layer in the length direction. The second protrusion is set similarly to the first protrusion, and its parameters are consistent.

[0113] Preparation of isolation membrane:

[0114] A polyethylene (PE) porous film with a thickness of 8 μm was used as the isolation membrane.

[0115] Preparation of electrolyte:

[0116] In a dry argon atmosphere, ethylene carbonate, ethyl methyl carbonate and diethyl carbonate were mixed in a mass ratio of 30:50:20 to obtain an organic solution, and then lithium salt lithium hexafluorophosphate was added to the organic solvent to dissolve and mix evenly to obtain an electrolyte with a lithium salt concentration of 1.15 mol / L.

[0117] Preparation of lithium-ion batteries:

[0118] The prepared separator, positive electrode sheet, separator, and negative electrode sheet are stacked in order, wound to obtain an electrode assembly, and the electrode assembly is hot pressed at a pressure of 5 MPa, a temperature of 65°C, and a holding time of 10 seconds. The electrode assembly is placed in an aluminum-plastic film packaging bag, and the positive electrode tab and the negative electrode tab are both extended from the top seal of the packaging bag. After dehydration at 80°C, the electrolyte is injected and packaged.

[0119] Different from Example 1, the relevant parameters in Examples 2 to 24 are shown in Table 1 below, wherein in Examples 8 to 24, the depth to which the first protrusion penetrates into the positive electrode current collector is H1. In Examples 18 to 24, a first recessed portion is formed on the positive electrode tab by laser treatment, the depth of the first recessed portion is D, and the laser-treated slag is deposited on the positive electrode tab to form a first protrusion.

[0120] Drop test method: pre-treat the lithium-ion battery at 25°C, let it stand for 60 minutes at room temperature, and then test the voltage of the lithium-ion battery before the drop test; load the lithium-ion battery into the fixture, and use the drop device to drop freely from a position 1.5m above the ground in the following order: head-tail-head right corner-tail right corner-head left corner-tail left corner (angle: 45±15°), and repeat 10 rounds. After the drop, let it stand for 24 hours at room temperature, measure and record the voltage of the lithium-ion battery, and check the appearance of the lithium-ion battery before and after the test and take pictures. The judgment criteria for passing the drop test: no smoke, no leakage, no tabs or current collectors torn, no disconnection between the tabs and the current collector, and the voltage drop <30mV. 50 lithium-ion batteries were tested, and the number of batteries that failed the test was X, and the test failure rate was X / 50. The test results are shown in Table 1 below.

[0121] Table 1

[0122]

[0123]

[0124] According to the above Table 1, combined with Examples 1 to 25 and Comparative Examples 1 to 2, it can be known that when the first protrusion is set on the first adhesive layer, and the width of the first protrusion is reduced, the drop failure rate of the lithium-ion battery can be effectively reduced. This is because the positive electrode tab is bonded and fixed to the first empty foil area through the first adhesive layer, and there are no welding burrs, which can reduce the short circuit of the lithium-ion battery, reduce the drop voltage drop failure of the lithium-ion battery, and improve the safety performance of the lithium-ion battery. In addition, the setting of the first protrusion is conducive to the first protrusion to penetrate into the first adhesive layer, which can increase the bonding area between the first adhesive layer and the positive electrode tab. The first adhesive layer can effectively fill the small gap between the positive electrode tab and the first empty foil area, which can improve the connection strength between the positive electrode tab and the first empty foil area.

[0125] Combined with Examples 1 to 7, the drop failure rate of Examples 2 to 6 is less than that of Examples 1 and 7. In Example 1, the height H of the first protrusion is small, which has little effect on increasing the bonding area between the positive electrode tab and the first glue layer, is not conducive to forming an anchoring structure, and thus has low connection strength. When the lithium-ion battery falls, it may cause the positive electrode tab to separate from the positive electrode collector. In Example 7, the height H of the first protrusion is large, which may form a gap between the positive electrode tab and the positive electrode collector, affecting the bonding effect of the first glue layer and the positive electrode tab, affecting the bonding strength, and may also cause bonding separation. In Examples 2 to 6, the height H of the first protrusion is better, which can effectively form an anchoring mechanism, improve the connection strength between the positive electrode tab and the positive electrode collector, and facilitate the first glue layer to fill the gap between the positive electrode tab and the positive electrode collector, increase the bonding area, and further improve the connection strength. Therefore, in the embodiment of the present application, the height of the first protrusion can be selected to be 10μm≤H≤30μm.

[0126] Combined with Examples 8 to 13, the drop failure rate of Examples 9 to 12 is less than that of Examples 8 and 13. In Example 8, the depth of penetration of the first protrusion into the positive electrode current collector is small, and the effect on improving the connection strength is not obvious. In Example 13, the depth of penetration of the first protrusion into the positive electrode current collector is large, causing mechanical damage to the positive electrode current collector, which can easily lead to damage and tearing of the positive electrode current collector. In Examples 9 to 12, the penetration depth is better, which can increase the mechanical anchoring force between the first protrusion and the positive electrode current collector, form a more stable electrical connection, and reduce damage to the positive electrode current collector, reducing the damage and tearing of the positive electrode current collector. Therefore, in the embodiments of the present application, the depth of penetration of the first protrusion into the positive electrode current collector is 2μm≤H1≤10μm.

[0127] In combination with Examples 14 to 18 and Example 10, in Examples 16 to 17 and Example 10, the drop failure rate is less than that in Examples 14 and 18. In Example 14, the maximum width of the first protrusion is small, which may lead to insufficient strength of the first protrusion, and the first protrusion may be damaged due to a small external force, such as breaking, bending, etc. In Example 18, the width is large, and when piercing the first glue layer and the positive current collector, it may cause large-scale damage to the first glue layer and the positive current collector, which may cause the positive current collector to tear and may affect the bonding strength. In Examples 16 to 17 and Example 10, the strength of the first protrusion is high, which can reduce the damage of the first protrusion due to external force, and can improve the connection strength between the positive electrode tab and the positive current collector, and reduce the tearing of the positive current collector. Therefore, in the embodiment of the present application, the maximum width of the first protrusion can be selected to be 5μm≤W≤10μm.

[0128] In combination with Examples 19 to 25, in Examples 20 to 24, the drop failure rate is less than that in Examples 19 and 25. In Example 19, the depth of the first recessed portion is small, it is difficult to form the first protrusion, and the effect on increasing the bonding area between the positive electrode tabs is small. In Example 24, the depth of the first recessed portion is large, which affects the strength of the positive electrode tab itself and easily causes the positive electrode tab to break and tear. In combination with Examples 20 to 24, in the embodiments of the present application, the depth of the first recessed portion can be selected to be 20μm≤D≤60μm.

[0129] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit them. Under the concept of the present application, the technical features in the above embodiments or different embodiments may also be combined, the steps may be implemented in any order, and there are many other changes in different aspects of the present application as described above, which are not provided in detail for the sake of simplicity. Although the present application has been described in detail with reference to the aforementioned embodiments, a person of ordinary skill in the art should understand that the technical solutions described in the aforementioned embodiments may still be modified, or some of the technical features may be replaced by equivalents. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the scope of the technical solutions of the embodiments of the present application.

Claims

1. A secondary battery, comprising a first pole ear and a first pole sheet, wherein the first pole sheet comprises a first current collector and a first active material layer, wherein the first active material layer is stacked on the surface of the first current collector along a first direction, the first current collector is provided with a first empty foil area, and the first pole ear portion is provided in the first empty foil area, characterized in that: The secondary battery further comprises a first adhesive layer, and along the first direction, the first adhesive layer is bonded between the first electrode tab and the first empty foil area; The first electrode tab comprises a first surface facing the first current collector, the first surface is provided with a plurality of first protrusions, and the width of the first protrusions in a second direction decreases along the direction from the first electrode tab to the first empty foil area, and at least part of the first protrusions is in contact with the first empty foil area; The first direction is the thickness direction of the first pole piece, and the second direction is the length or width direction of the first pole piece.

2. The secondary battery according to claim 1, characterized in that: Along the first direction, the height of the first protrusion is H, and 10 μm≤H≤30 μm.

3. The secondary battery according to claim 1, characterized in that: At least a portion of the first protrusions penetrate the first current collector.

4. The secondary battery according to claim 1, characterized in that: Along the first direction, at least a portion of the first protrusions penetrate the first current collector.

5. The secondary battery according to claim 3 or 4, characterized in that: The first surface is in direct contact with the first empty foil area.

6. The secondary battery according to claim 3 or 4, characterized in that: Along the first direction, the first protrusion penetrates into the first current collector to a depth H1, 2 μm≤H1≤10 μm.

7. The secondary battery according to claim 3 or 4, characterized in that: Along the second direction, the maximum width of the first protrusion is W, 5 μm≤W≤10 μm.

8. The secondary battery according to claim 1, characterized in that: The first surface is also provided with a plurality of first recessed portions, and the first adhesive layer is partially embedded in the first recessed portions.

9. The secondary battery according to claim 8, characterized in that: A plurality of first protrusions are arranged between two adjacent first recesses.

10. The secondary battery according to claim 9, characterized in that: The first adhesive layer is partially embedded between two adjacent first protrusions.

11. The secondary battery according to any one of claims 8 to 10, characterized in that: When viewed along the first direction, the diameter of the first recessed portion is L1, and the distance between two adjacent first recessed portions is L2; 30μm≤L1≤500μm, and / or, 30μm≤L2≤500μm.

12. The secondary battery according to any one of claims 11, characterized in that: 50μm≤L1≤100μm, and / or, 50μm≤L2≤100μm.

13. The secondary battery according to any one of claims 8 to 10, characterized in that: Along the first direction, the depth of the first recessed portion is D, 20 μm≤D≤60 μm.

14. The secondary battery according to claim 1, characterized in that: The first adhesive layer includes hot melt adhesive, thermosetting adhesive or pressure sensitive adhesive.

15. The secondary battery according to claim 1, characterized in that: The first active material layer is provided with a first groove, the first current collector forms a first empty foil area in the first groove, and the first electrode tab portion is provided in the first groove; The first pole piece further includes a second active material layer, and the second active material layer is stacked on a surface of the first current collector away from the first active material layer; Along the first direction, the first groove is located within a projection of the second active material layer.

16. The secondary battery according to claim 15, characterized in that: The secondary battery further includes a separator and a second pole piece, and along the first direction, the separator is arranged between the first pole piece and the second pole piece; The second active material layer includes a first region, a projection of the first region coincides with the first groove along the first direction, and a surface of the first region facing away from the first current collector is at least partially in contact with the isolation film.

17. The secondary battery according to claim 15, characterized in that: The secondary battery further includes a separator and a second pole piece. Along the first direction, the separator is disposed between the first pole piece and the second pole piece. The first pole piece is a positive pole piece, and the second pole piece is a negative pole piece. The second pole piece includes a second current collector and a third active material layer, wherein the third active material layer is stacked on a surface of the second current collector facing the first active material layer; The third active material layer includes a second region, a projection of the second region coincides with the first groove along the first direction, and a surface of the second region facing the first groove is at least partially in direct contact with the isolation film.

18. The secondary battery according to claim 17, characterized in that: The secondary battery further includes a second electrode tab and a second glue layer; The third active material layer is provided with a second groove, the second current collector forms a second empty foil area in the second groove, the second electrode tab is partially provided in the second groove, and the second adhesive layer is bonded between the second electrode tab and the second empty foil area; The second electrode tab includes a second surface facing the second current collector, and a plurality of second protrusions are protruding from the second surface. Along the direction from the second electrode tab to the second empty foil area, the width of the second protrusions in the second direction is reduced, and at least part of the second protrusions is in contact with the second empty foil area.

19. An electronic device, characterized in that: The invention comprises the secondary battery according to any one of claims 1 to 18.

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