Secondary battery and electronic device

Abstract

The invention discloses 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 material layer, and the first active material layer is stacked on the surface of the first current collector along the thickness direction of the first pole piece. The first current collector comprises a first empty foil area, and the first tab is electrically connected with 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 thickness direction of the first pole piece. And the first adhesive layer is configured to reduce the adhesive force when the temperature rises to a first threshold value, so that the first tab is at least partially separated from the first empty foil region. The occurrence of short circuit can be reduced, thermal runaway of the secondary battery can be reduced, and the safety performance of the secondary battery is 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, there are welding burrs in the welding of the tabs and the empty foil area of ​​the current collector, which may cause the burrs to pierce the isolation film and cause a short circuit, thereby causing thermal runaway of the secondary battery. Summary of the invention

[0004] The present application aims to provide a secondary battery and an electronic device, aiming to reduce the technical problem that the secondary battery is prone to thermal runaway.

[0005] In the first aspect, the present application proposes a secondary battery, 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, and the first active material layer is stacked on the surface of the first current collector along the thickness direction of the first pole piece. The first current collector comprises a first empty foil area, and the first pole ear is electrically connected to the first empty foil area. The secondary battery also includes a first adhesive layer, and the first adhesive layer is bonded between the first pole ear and the first empty foil area along the thickness direction of the first pole piece. The first adhesive layer is constructed so that the adhesive force decreases when the temperature rises to a first threshold value, so that the first pole ear is at least partially separated from the first empty foil area.

[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, and there is no risk of welding burr piercing the isolation film, which can reduce the short circuit of the secondary battery, thereby reducing the thermal runaway of the secondary battery and improving 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 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.

[0007] 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. In addition, 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.

[0008] In addition, when the temperature rises to the first threshold value, for example, when the secondary battery is short-circuited or in a high-temperature environment, the viscosity of the first adhesive layer weakens, causing the first pole ear to be at least partially separated from the first empty foil area, thereby increasing the resistance of the first pole ear and the first current collector, and even directly disconnecting the electrical connection, which can effectively reduce the further development of thermal runaway and the continuous rise in the temperature of the secondary battery, thereby reducing serious safety accidents such as fire and explosion of the secondary battery.

[0009] In some embodiments, the first threshold is T, 100°C ≤ T ≤ 150°C ， Within the normal operating temperature range of the secondary battery (usually below 80°C), the first adhesive layer can withstand certain temperature changes and maintain good viscosity, so that a reliable connection is formed between the first pole ear and the first current collector. When an abnormal situation such as a short circuit occurs inside the secondary battery, causing the temperature to rise to 100°C to 150°C, the first adhesive layer reduces viscosity, so that the first pole ear is partially separated from the first current collector, thereby increasing resistance or cutting off the short-circuit current path, which can effectively reduce the sharp rise in temperature and reduce the occurrence of thermal runaway.

[0010] In some embodiments, the first pole ear includes a first surface facing the first current collector, the first surface is provided with a plurality of first protrusions, and the first adhesive layer is partially embedded between two adjacent first protrusions. This can increase the bonding area between the first pole ear and the first adhesive layer, thereby increasing the connection strength between the first pole ear and the first current collector, and can increase the strength of the first pole ear, thereby reducing the damage and tearing of the first pole ear.

[0011] In some embodiments, at least a portion of the first protrusion is in contact with the first empty foil area, which can provide a more direct conductive path. Compared with conducting current only by adding conductive particles, under normal operating conditions, direct contact can significantly reduce the contact resistance between the first electrode and the first current collector, which is beneficial to improving the charge and discharge efficiency of the secondary battery.

[0012] In some embodiments, along the direction from the first electrode tab to the first current collector, the width of the first protrusion in the second direction is reduced. The second direction is perpendicular to the direction from the first electrode tab to the first current collector. The first protrusion can be formed into 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.

[0013] In some embodiments, the first electrode tab includes a first surface facing the first current collector, the first surface is provided with a plurality of first recessed portions, and the first adhesive layer is partially embedded in the first recessed portions, which can increase the bonding area between the first electrode tab and the first adhesive layer, thereby improving the connection strength between the first electrode tab and the first current collector.

[0014] In some embodiments, the first surface contacts the first empty foil area, so that the first pole ear is directly in contact with the first current collector and is electrically connected, which is more conducive to reducing contact resistance, and the first adhesive layer in the first recessed portion can directly bond the first pole ear and the first current collector, thereby improving the connection strength between the first pole ear and the first current collector.

[0015] In some embodiments, the first adhesive layer includes a plurality of conductive particles, and the conductive particles include at least one of silver, copper, nickel, aluminum, graphite or carbon nanotubes, which can realize electrical connection between the first electrode tab and the first current collector and reduce the resistance between the first electrode tab and the first current collector under normal operating conditions.

[0016] In some embodiments, the first adhesive layer includes a thermosetting adhesive, which includes at least one of epoxy resin, phenolic resin or polyurethane resin; or, the first adhesive layer includes a hot melt adhesive, which includes at least one of polyolefin, polyurethane, polyamide or ethylene-vinyl acetate copolymer; or, the first adhesive layer includes a metal adhesive, which includes at least one of tin, lead, zinc or aluminum. Each material can make the first pole ear and the first current collector have a high connection strength under normal working conditions, and each material can lose adhesion at abnormally high temperatures, so that the first pole ear and the first current collector are at least partially separated, thereby increasing resistance or cutting off the short-circuit current path, which can effectively reduce the sharp rise in temperature and reduce the occurrence of thermal runaway.

[0017] In some embodiments, along the thickness direction of the first pole piece, the thickness of the first adhesive layer is H, 5μm≤H≤10μm, which can provide sufficient adhesion, improve the connection strength between the first pole ear and the first current collector, and facilitate direct contact and electrical connection between the first pole ear and the first current collector, as well as facilitate the timely separation of the first pole ear and the first current collector under abnormal circumstances, thereby improving the safety performance of the secondary battery.

[0018] In some embodiments, the first active material layer is provided with a first groove, and the first current collector forms a first empty foil area 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 facing away from the first active material layer. Along the thickness direction of the first pole piece, 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, there is no need to open a groove 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 grooving is reduced, so that the second active material layer can be fully utilized, and the energy density of the secondary battery is improved.

[0019] In some embodiments, the secondary battery further includes an isolating membrane and a second pole piece, and an isolating membrane is disposed between the first pole piece and the second pole piece along the thickness direction of the first pole piece. The second active material layer includes a first region, and along the thickness direction of the first pole piece, 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.

[0020] In some embodiments, the secondary battery further includes a separator and a second pole piece. Along the thickness direction of the first pole piece, a 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 thickness direction of the first pole piece, 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 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.

[0021] In some embodiments, the secondary battery further includes a second pole ear 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, and the second pole ear portion is provided in the second groove and is electrically connected to the second empty foil area. Along the thickness direction of the second pole piece, the second glue layer is bonded between the second pole ear and the second empty foil area. The second glue layer is configured so that the bonding force decreases when the temperature rises to a first threshold value, so that the second pole ear is at least partially separated from the second empty foil area. The absence of welding burrs can reduce the occurrence of short circuits in the secondary battery and improve the safety performance of the secondary battery. In addition, there is no need to provide a protective glue layer on the second pole ear or the second empty foil area to cover the burrs, which saves the space occupied by the protective glue layer, and can reduce costs while increasing the energy density of the secondary battery.

[0022] In addition, when the temperature rises to the first threshold value, the viscosity of the second adhesive layer weakens, so that the second pole ear and the second empty foil area are at least partially separated, thereby increasing the resistance of the second pole ear and the second current collector, and even directly disconnecting the electrical connection, which can effectively reduce the further development of thermal runaway and the continuous rise in the temperature of the secondary battery, thereby reducing serious safety accidents such as fire and explosion of the secondary battery.

[0023] In some embodiments, the thermal expansion coefficient of the first adhesive layer is 50 ppm to 5000 ppm. The thermal expansion coefficient of the first adhesive layer is greater than 50 ppm, which can cause the first adhesive layer to thermally expand at high temperatures, thereby reducing the bonding force and pushing open the electrical contact point, so that the first electrode and the first current collector are disconnected. When the thermal expansion coefficient is greater than 5000 ppm, the manufacturing difficulty is greater.

[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 the implementation of the embodiments of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] One or more embodiments are exemplarily described by the figures in the corresponding drawings, and these exemplary descriptions are not intended to limit the embodiments. Elements with the same reference numerals in the drawings represent similar elements.

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

[0030] Figure 4 This is a schematic structural diagram of a first pole piece in some embodiments of the present application;

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

[0034] Figure 8 An exploded schematic diagram of a first pole piece of some embodiments of the present application;

[0035] Fig. 9 A schematic diagram of the structure of a first pole piece in some embodiments of the present application;

[0036] Fig.10 This is a schematic diagram of the structure of the second pole piece of some embodiments of the present application.

[0037] Description of reference numerals:

[0038] 100. Secondary battery;

[0039] 10. Shell;

[0040] 20. Electrode assembly;

[0041] 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;

[0042] 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;

[0043] 23. Isolation film;

[0044] 30, first pole ear; 31, first surface; 30a, first protrusion; 30b, first depression;

[0045] 40. Second pole lug;

[0046] 50. First adhesive layer;

[0047] 60, second adhesive layer;

[0048] Z, first direction; X, second direction; Y, third direction. DETAILED DESCRIPTION

[0049] 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.

[0050] 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.

[0051] 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.

[0052] 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.

[0053] 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.

[0054] In the first aspect, the present application proposes a secondary battery 100, please refer to Figure 1 The 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.

[0055] 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.

[0056] 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 .

[0057] 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.

[0058] 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.

[0059] 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.

[0060] 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.

[0061] 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.

[0062] For the first tab 30, please refer to Figure 2 and Figure 3 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.

[0063] Please refer to Figure 3 In some embodiments, the secondary battery 100 further includes a first adhesive layer 50, which is bonded between the first electrode tab 30 and the first empty foil area 211a along the first direction Z. Moreover, the first adhesive layer 50 is configured to reduce the adhesive force when the temperature rises to a first threshold value, so that the first electrode tab 30 is at least partially separated from the first empty foil area 211a.

[0064] 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, and there is no risk of the welding burr piercing the isolation film 23, which can reduce the short circuit of the secondary battery 100, thereby reducing the thermal runaway of the secondary battery 100, and improving the safety performance of the secondary battery 100. In addition, there is no need 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.

[0065] 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 the secondary battery 100 and reducing the production cost. In addition, the first adhesive layer 50 can effectively fill the small gap between the first pole tab 30 and the first empty foil area 211a, which can improve the connection strength between the first pole tab 30 and the first empty foil area 211a.

[0066] In addition, when the temperature rises to the first threshold value, for example, when the secondary battery 100 is short-circuited or in a high-temperature environment, the viscosity of the first adhesive layer 50 is weakened, so that the first pole ear 30 is at least partially separated from the first empty foil area 211a, thereby increasing the resistance of the first pole ear 30 and the first current collector 211, and even directly disconnecting the electrical connection, which can effectively reduce the further development of thermal runaway and reduce the continuous rise in the temperature of the secondary battery 100, thereby reducing the occurrence of serious safety accidents such as fire and explosion of the secondary battery 100.

[0067] Adhesion test method of the first adhesive layer 50: According to GB / T 2792-2014 "Test method for adhesion of adhesive tape", the adhesion strength between the first pole ear 30 and the first current collector 211 is tested using a high-speed rail tensile machine. The adhesion strength is the adhesion of the first adhesive layer 50. The test process is as follows: discharge the secondary battery to 0V, then disassemble the secondary battery, remove the first pole ear 30 and the first current collector 211 bonded thereto, and wipe the electrolyte on the surface with dust-free paper. Then cut a 20mm×60mm strip sample (including the part bonded to the first pole ear 30) on the first current collector 211. The side of the sample facing away from the first pole ear 30 is adhered to the steel plate with a double-sided tape (Nito 5000NS), and the adhesion length is not less than 40mm. The steel plate is fixed at the corresponding position of the high-speed rail tensile machine, the first pole ear 30 is clamped by the chuck, and the first pole ear 30 is pulled up, wherein the pulled up part and the steel plate have a spatial angle of 180°, and the chuck pulls the sample at a speed of 5±0.2 mm / s, and the average tensile force in the stable area is finally measured and recorded as the bonding strength between the first pole ear 30 and the first current collector 211, that is, the bonding strength of the first adhesive layer 50. The test can be carried out under different temperature environments to obtain the bonding strength of the first adhesive layer 50 at different temperatures.

[0068] In some embodiments, the first threshold is T, 100°C≤T≤150°C. Within the normal operating temperature range of the secondary battery 100 (usually below 80°C), the first adhesive layer 50 can withstand certain temperature changes and maintain good viscosity, so that a reliable connection is formed between the first pole ear 30 and the first current collector 211. When an abnormal situation such as a short circuit occurs inside the secondary battery 100, causing the temperature to rise to 100°C to 150°C, the first adhesive layer 50 reduces the viscosity, so that the first pole ear 30 is partially separated from the first current collector 211, thereby increasing the resistance or cutting off the short-circuit current path, which can effectively reduce the sharp rise in temperature and reduce the occurrence of thermal runaway.

[0069] As for the material of the first adhesive layer 50, the first adhesive layer 50 includes hot melt adhesive, and the hot melt adhesive includes at least one of polyolefin, polyurethane, polyamide or ethylene-vinyl acetate copolymer. The hot melt adhesive can be heated and melted and then coated on the first pole ear 30. After heating and melting, the hot melt adhesive has good fluidity and can quickly fill the small gap between the first pole ear 30 and the first current collector 211. After being solidified, the connection strength between the first pole ear 30 and the first current collector 211 can be improved. In addition, the debonding temperature of the hot melt adhesive is close to 100°C to 150°C. Under normal operating temperature, the hot melt adhesive can maintain solid state and good viscosity. Due to the thermoplasticity of the hot melt adhesive itself, when the temperature rises to the debonding temperature range due to the internal short circuit of the secondary battery 100, the hot melt adhesive will gradually soften and reduce viscosity, so that the first pole ear 30 and the first current collector 211 are at least partially separated. This temperature response characteristic is consistent with the essential properties of the hot melt adhesive, and can effectively realize the safety protection mechanism of the secondary battery 100 at abnormally high temperatures.

[0070] In some embodiments, the first adhesive layer 50 includes a thermosetting adhesive, and the thermosetting adhesive includes at least one of epoxy resin, phenolic resin or polyurethane resin. The thermosetting adhesive undergoes a chemical reaction during the curing process to form a three-dimensional network cross-linked structure, which gives the thermosetting adhesive a high cohesive strength and can provide a strong adhesive force for the first pole ear 30 and the first current collector 211. When the temperature rises to 100°C to 150°C due to an internal short circuit in the secondary battery 100, the van der Waals force and chemical bonds (such as covalent bonds) of the three-dimensional network cross-linked structure of the thermosetting adhesive may be destroyed at high temperatures, causing the cross-linked structure to gradually disintegrate, thereby reducing the viscosity of the first adhesive layer 50, and then separating the first pole ear 30 from the first current collector 211, which can alleviate thermal runaway.

[0071] In some other embodiments, the first adhesive layer 50 includes a metal adhesive, and the metal adhesive includes at least one of tin (tin paste), lead (lead paste), zinc (zinc paste) or aluminum (aluminum paste). The metal adhesive itself has good conductivity and can form an effective conductive path between the first pole ear 30 and the first current collector 211. Under normal working conditions, it can reduce the contact resistance between the first pole ear 30 and the first current collector 211, which is beneficial to improve the charge and discharge rate of the secondary battery 100. When the temperature rises to 100°C to 150°C due to the internal short circuit of the secondary battery 100, the metal adhesive loses adhesion, causing the first pole ear 30 to be partially separated from the first current collector 211, which can effectively cut off the main path of the short-circuit current, reduce the continuous rise in the temperature of the secondary battery 100, and thus reduce the occurrence of serious safety accidents such as fire and explosion of the secondary battery 100. It is understandable that the first adhesive layer 50 can also use other types of high-temperature loss-adhesive adhesives.

[0072] For adjusting the debonding temperature of the first adhesive layer 50, the hot melt adhesive can change its viscosity, hardness, heat resistance and other properties by adding different tackifiers, fillers, etc. For example, adding inorganic fillers such as silicon dioxide (SiO), aluminum oxide (AlO), calcium carbonate (CaCO), etc. can improve the thermal stability of the hot melt adhesive, thereby increasing the debonding temperature; or, the debonding temperature can be adjusted by a polymer modification method. The debonding temperature of the thermosetting adhesive can be adjusted by the resin composition and the curing agent system. For example, the debonding temperature can be adjusted by selecting epoxy resins with different epoxy values. The higher the epoxy value, the more reactive points on the molecular chain, the greater the crosslinking density after curing, and the higher the debonding temperature; or by adding fillers and curing agent types, appropriately increasing or decreasing the amount of curing agent to change the crosslinking density, thereby adjusting the debonding temperature. As for metal adhesives, different metals have different melting points and thermal expansion coefficients. The debonding temperature can be adjusted by changing the metal component ratio; or, ceramic materials (boron nitride, silicon carbide, etc.) or metal oxides (titanium dioxide, zinc oxide, etc.) can be added to adjust its high-temperature debonding temperature.

[0073] In some embodiments, when the first adhesive layer 50 is made of hot melt adhesive or thermosetting adhesive, a number of conductive particles can also be added to the first adhesive layer 50. For example, the conductive particles include at least one of silver, copper, nickel, aluminum, graphite or carbon nanotubes, which can realize the electrical connection between the first electrode tab 30 and the first current collector 211 and reduce the resistance between the first electrode tab 30 and the first current collector 211 under normal operating conditions.

[0074] In some embodiments, please refer to Figure 4 The first pole tab 30 includes a first surface 31 facing the first current collector 211, and a plurality of first protrusions 30a are convexly provided on the first surface 31. The first protrusions 30a protrude relative to the first surface 31, and the first adhesive layer 50 is partially embedded between two adjacent first protrusions 30a. The bonding area between the first pole tab 30 and the first adhesive layer 50 can be increased, thereby improving the connection strength between the first pole tab 30 and the first current collector 211. At the same time, the provision of the first protrusions 30a can improve the strength of the first pole tab 30 and reduce the damage and tearing of the first pole tab 30.

[0075] In some embodiments, please refer to Figure 5 , at least part of the first protrusion 30a is in contact with the first empty foil area 211a, which can provide a more direct conductive path. Compared with conducting current only by adding conductive particles, under normal working conditions, direct contact can significantly reduce the contact resistance between the first pole ear 30 and the first current collector 211, which is beneficial to improving the charge and discharge efficiency of the secondary battery 100. It can be understood that when the first protrusion 30a is in direct contact with the first empty foil area 211a, the first pole ear 30 is directly connected to the first current collector 211, and there is no need to add conductive particles in the first part, which is beneficial to simplifying the manufacturing process and reducing production costs.

[0076] In some embodiments, please refer to Figure 6 , along the direction from the first electrode tab 30 to the first current collector 211 (first direction Z), the width of the first protrusion 30a in the second direction X is reduced, and the second direction X is perpendicular to the direction from the first electrode tab 30 to the first current collector 211. The first protrusion 30a can be formed into 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-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. In some other embodiments, the width of the first protrusion 30a in the third direction Y is reduced.

[0077] In some embodiments, please refer to Figure 7 and Figure 8 The first surface 31 is also provided with a plurality of first recessed portions 30b, which 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.

[0078] 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 may cause the first adhesive layer 50 to melt, thereby partially separating the first pole tab 30 from the first current collector 211, increasing the resistance of the first pole tab 30 and the first current collector 211 or disconnecting the electrical connection, 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.

[0079] In some embodiments, please refer to Fig. 9 The first surface 31 contacts the first empty foil area 211a, so that the first electrode tab 30 is directly in contact with the first current collector 211 and is electrically connected, 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.

[0080] In some other embodiments, the first electrode tab 30 is also provided with a first protrusion 30a and a first depression 30b, and the width of the first protrusion 30a in the second direction X is reduced, which can further increase the bonding area between the first electrode tab 30 and the first adhesive layer 50, thereby improving the bonding strength between the first electrode tab 30 and the first current collector 211.

[0081] As for the thickness of the first adhesive layer 50, the inventors of the present application have found that if the thickness of the first adhesive layer 50 is too small, it may not provide sufficient bonding force. For example, when the first pole tab 30 is bonded to the first current collector 211, the first adhesive layer 50 is too thin to fully fill the small gap between the two, resulting in insufficient bonding area and insufficient bonding force. When the secondary battery 100 is used, the first pole tab 30 is easily separated from the first current collector 211 when subjected to external forces such as vibration and electrode expansion, affecting the normal operation of the secondary battery 100. If the thickness of the first adhesive layer 50 is too large, it is difficult to directly connect the first pole tab 30 with the first current collector 211 under normal working conditions, which may cause the resistance between the first pole tab 30 and the first current collector 211 to be too large. Moreover, when the secondary battery 100 has an abnormal situation such as a short circuit, even if the first adhesive layer 50 loses adhesion, too much first adhesive layer 50 may cause the first pole tab 30 and the first current collector 211 to be difficult to separate in time, thereby further deteriorating the thermal runaway and affecting the safety performance of the secondary battery 100.

[0082] In the embodiments of this application, please refer to Figure 3 Along the thickness direction of the first pole piece 21 (the first direction Z), the thickness of the first adhesive layer 50 is H, 5μm≤H≤10μm, which can provide sufficient adhesion, improve the connection strength between the first pole ear 30 and the first current collector 211, and facilitate the direct contact and electrical connection between the first pole ear 30 and the first current collector 211, as well as facilitate the timely separation of the first pole ear 30 and the first current collector 211 under abnormal circumstances, thereby improving the safety performance of the secondary battery 100.

[0083] 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.

[0084] 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.

[0085] 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.

[0086] 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.

[0087] 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 and Fig.10 , 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, 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. In addition, the second adhesive layer 60 is configured such that the adhesive force decreases when the temperature rises to the first threshold value, so that the second pole tab 40 is at least partially separated from the second empty foil area 221a.

[0088] In the embodiment of the present application, 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, and there is no risk of the welding burr piercing the isolation film 23, 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.

[0089] 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 the secondary battery 100 and reducing the production cost. In addition, the second adhesive layer 60 can effectively fill the small gap between the second pole tab 40 and the second empty foil area 221a, which can improve the connection strength between the second pole tab 40 and the second empty foil area 221a.

[0090] In addition, when the temperature rises to the first threshold, for example, when the secondary battery 100 is short-circuited or in a high-temperature environment, the viscosity of the second adhesive layer 60 is weakened, so that the second pole ear 40 and the second empty foil area 221a are at least partially separated, thereby increasing the resistance of the second pole ear 40 and the second current collector 221, and even directly disconnecting the electrical connection, which can effectively reduce the further development of thermal runaway and reduce the continuous rise in the temperature of the secondary battery 100, thereby reducing the occurrence of serious safety accidents such as fire and explosion of the secondary battery 100.

[0091] 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.

[0092] In some embodiments, the thermal expansion coefficients of the first adhesive layer 50 and the second adhesive layer 60 are 50 ppm to 5000 ppm. The thermal expansion coefficient of the first adhesive layer 50 is greater than 50 ppm, which can cause the first adhesive layer 50 to thermally expand at high temperatures, thereby reducing the bonding force and pushing open the electrical contact point, so that the first electrode 30 and the first current collector 211 are disconnected. When the thermal expansion coefficient is greater than 5000 ppm, the manufacturing difficulty is greater. The second adhesive layer 60 is similar.

[0093] In some embodiments, the first electrode 21 is a positive electrode and the second electrode 22 is a negative electrode. Figure 2 The second pole piece 22 includes a second current collector 221 and a third active material layer 222, and the third active material layer 222 is stacked 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 pole piece 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.

[0094] 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.

[0095] 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.

[0096] Example 1

[0097] Preparation of positive electrode:

[0098] 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.

[0099] 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.

[0100] An aluminum sheet with a thickness of 80 μm is used as the positive electrode tab, and a first adhesive layer of ethylene-vinyl acetate copolymer is bonded to the first surface of the positive electrode tab, and the first adhesive layer has a debonding temperature T of 100°C. The positive electrode tab and the first empty foil area of ​​the positive electrode current collector are hot pressed, and the positive electrode tab and the first empty foil area are bonded after the first adhesive layer is cured. The bonding width of the first adhesive layer in the first empty foil area is 8 mm, and a gap of 1 mm is reserved on both sides with the positive electrode active material layer. The bonding length is 18 mm, and a gap of 1 mm is reserved with the positive electrode active material layer in the length direction. The thickness of the first adhesive layer is 8 μm.

[0101] Preparation of negative electrode sheet:

[0102] 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.

[0103] A 80 μm nickel sheet is used as the negative electrode tab, and a second adhesive layer of ethylene-vinyl acetate copolymer is bonded to the surface of the negative electrode tab, and the debonding temperature of the second adhesive layer is 100° C. The negative electrode tab is bonded to the second empty foil area, and the bonding width of the second adhesive layer in the second empty foil area is 8 mm, and a gap of 1 mm is reserved on both sides with the negative electrode active material layer. The bonding length is 18 mm, and a gap of 1 mm is reserved with the negative electrode active material layer in the length direction, and the thickness of the second adhesive layer is 8 μm.

[0104] Preparation of isolation membrane:

[0105] A polyethylene (PE) porous film with a thickness of 8 μm was used as the isolation membrane.

[0106] Preparation of electrolyte:

[0107] 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.

[0108] Preparation of lithium-ion batteries:

[0109] 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.

[0110] Different from Example 1, the relevant parameters in Examples 2 to 15 and Comparative Example 1 are shown in Table 1 below.

[0111] Short circuit test method: Charge and discharge the lithium-ion battery for 20 cycles in a 70±5℃ environment, observe the current change, and if the current drops suddenly, it is considered to be a failure. If it is not a failure, place the fully charged lithium-ion battery sample in a 20±5℃ test environment, use a load resistor of 80±20mΩ to short-circuit the positive and negative poles of the sample, and test until the voltage is lower than 0.2V. The test ends when one of the following conditions is met: 1) The surface temperature of the lithium-ion battery tends to be stable (the temperature change is less than 10℃ within 30 minutes); 2) The surface temperature of the lithium-ion battery drops to the same as the ambient temperature. Measurement frequency: The voltage internal resistance measurement uses the 1KHz specification, and is measured after pretreatment and testing. Failure criteria: The lithium-ion battery explodes, leaks, or catches fire. The test results are shown in Table 1 below.

[0112] Table 1

[0113]

[0114]

[0115] According to the above Table 1, combined with Examples 1 to 15 and Comparative Example 1, it can be seen that when the positive electrode tab and the positive electrode current collector are bonded through the first adhesive layer, and the first adhesive layer is a high-temperature loss adhesive layer, the short-circuit test failure rate can be effectively reduced. This is because when the lithium-ion battery is short-circuited or in a high-temperature environment, the viscosity of the first adhesive layer is weakened, so that the positive electrode tab and the first empty foil area are at least partially separated, thereby increasing the resistance of the positive electrode tab and the positive electrode current collector, and even directly disconnecting the electrical connection, which can effectively reduce the further development of thermal runaway, reduce the continuous rise in the temperature of the lithium-ion battery, and thus reduce the occurrence of serious safety accidents such as fire and explosion of the lithium-ion battery.

[0116] In combination with Examples 1 to 8, in Examples 1 to 3 and Examples 5 to 7, the test failure rate is less than that in Example 4. In Example 4, the thickness of the first adhesive layer is relatively large, and it may be difficult to melt in time at high temperatures, resulting in separation of the positive electrode tab and the positive electrode collector, posing a safety risk. In Example 8, the thickness of the first adhesive layer is relatively small, which may result in insufficient connection strength between the positive electrode tab and the positive electrode collector, which may affect the normal operating conditions of the lithium-ion battery. In Examples 1 to 3 and Examples 5 to 7, the first adhesive layer has sufficient thickness, so that the positive electrode tab and the positive electrode collector have a high connection strength, and the short-circuit test failure rate is low. Therefore, in the embodiments of the present application, the thickness of the first adhesive layer can be selected to be 5μm≤H≤10μm.

[0117] In combination with Examples 9 to 15, in Examples 10 to 14, the test failure rate is less than that in Examples 9 and 15. In Example 9, the debonding temperature of the first adhesive layer is relatively low, which may cause the first adhesive layer to debond under normal working conditions, affecting the normal operation of the lithium-ion battery. In Example 15, the debonding temperature of the first adhesive layer is relatively high, which may cause the first adhesive layer to be difficult to debond in time, and further cause the positive electrode tab and the positive electrode current collector to be difficult to separate in time, posing a safety risk. Therefore, in the embodiments of the present application, the debonding temperature of the first adhesive layer can be selected to be 100°C to 150°C, that is, 100°C≤T≤150°C.

[0118] 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 the thickness direction of the first pole sheet; the first current collector comprises a first empty foil area, and the first pole ear is electrically connected to the first empty foil area, wherein: The secondary battery further includes a first adhesive layer, and along the thickness direction of the first electrode sheet, the first adhesive layer is bonded between the first electrode tab and the first empty foil area; The first glue layer is configured such that the adhesive force thereof decreases when the temperature rises to a first threshold value, so that the first electrode tab is at least partially separated from the first empty foil area.

2. The secondary battery according to claim 1, characterized in that: The first threshold is T, 100°C≤T≤150°C.

3. The secondary battery according to claim 1, characterized in that: The first electrode tab includes a first surface facing the first current collector, a plurality of first protrusions are protruding from the first surface, and the first glue layer is partially embedded between two adjacent first protrusions.

4. The secondary battery according to claim 3, characterized in that: At least a portion of the first protrusion is in contact with the first empty foil area.

5. The secondary battery according to claim 3 or 4, characterized in that: Along the direction from the first electrode tab to the first current collector, the first protrusion is arranged with a reduced width in the second direction; The second direction is perpendicular to a direction from the first electrode tab to the first current collector.

6. The secondary battery according to claim 1, characterized in that: The first electrode tab includes a first surface facing the first current collector, the first surface is provided with a plurality of first recessed portions, and the first glue layer is partially embedded in the first recessed portions.

7. The secondary battery according to claim 6, characterized in that: The first surface is in contact with the first empty foil area.

8. The secondary battery according to claim 1, characterized in that: The first adhesive layer includes a plurality of conductive particles, and the conductive particles include at least one of silver, copper, nickel, aluminum, graphite or carbon nanotubes.

9. The secondary battery according to claim 1, characterized in that: The first adhesive layer includes a thermosetting adhesive, and the thermosetting adhesive includes at least one of epoxy resin, phenolic resin or polyurethane resin; or The first adhesive layer includes a hot melt adhesive, and the hot melt adhesive includes at least one of polyolefin, polyurethane, polyamide or ethylene-vinyl acetate copolymer; or The first adhesive layer includes a metal adhesive, and the metal adhesive includes at least one of tin, lead, zinc or aluminum.

10. The secondary battery according to claim 1, characterized in that: Along the thickness direction of the first pole piece, the thickness of the first adhesive layer is H, 5 μm≤H≤10 μm.

11. The secondary battery according to claim 1, characterized in that: The first active material layer is provided with a first groove, and the first current collector forms the first empty foil area 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 thickness direction of the first pole piece, the first groove is located within the projection of the second active material layer.

12. The secondary battery according to claim 11, characterized in that: The secondary battery further comprises a separator and a second pole piece, wherein the separator is arranged between the first pole piece and the second pole piece along the thickness direction of the first pole piece; The second active material layer includes a first region, a projection of the first region coincides with the first groove along the thickness direction of the first pole piece, and a surface of the first region facing away from the first current collector is at least partially in contact with the isolation film.

13. The secondary battery according to claim 11, characterized in that: The secondary battery further comprises a separator and a second pole piece, wherein the separator is disposed between the first pole piece and the second pole piece along the thickness direction of the first 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 thickness direction of the first pole piece, and a surface of the second region facing the first groove at least partially contacts the isolation film.

14. The secondary battery according to claim 13, 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, and the second electrode tab portion is provided in the second groove and electrically connected to the second empty foil area; Along the thickness direction of the second pole piece, the second adhesive layer is bonded between the second pole tab and the second empty foil area; The second glue layer is configured such that the adhesive force decreases when the temperature rises to a first threshold value, so that the second electrode tab is at least partially separated from the second empty foil area.

15. The secondary battery according to claim 1, characterized in that: The thermal expansion coefficient of the first adhesive layer is 50 ppm to 5000 ppm.

16. An electronic device, characterized in that: The invention comprises the secondary battery according to any one of claims 1 to 15.

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