Secondary battery and electronic device

Abstract

A secondary battery and an electronic device. The second battery comprises a first tab and a first electrode sheet. The first electrode sheet comprises a first current collector and a first active material layer. In the thickness direction of the first electrode sheet, the first active material layer is stacked on the surface of the first current collector. The first current collector comprises a first uncoated area. The first tab is electrically connected to the first uncoated area. The secondary battery further comprises a first adhesive layer. In the thickness direction of the first electrode sheet, the first adhesive layer is bonded between the first tab and the first uncoated area. The first adhesive layer is configured so that adhesive strength is reduced when the temperature rises to a first threshold, enabling the first tab to be at least partially separated from the first uncoated area. The occurrence of short circuits can be reduced, and thermal runaway in the secondary battery can be reduced, thereby improving the safety performance of the secondary battery.

Description

Secondary batteries and electronic devices

[0001] Cross-reference of related applications

[0002] This application claims priority to Chinese Patent Application No. 202411985627.7, filed with the Chinese Patent Office on December 31, 2024, entitled “Secondary Battery and Electronic Device”, the entire contents of which are incorporated herein by reference. Technical Field

[0003] This application relates to the field of battery technology, and in particular to a secondary battery and electronic device. Background Technology

[0004] The tabs, which serve as a bridge connecting the secondary battery to the external circuit, are usually made of metal. The welding of the tabs to the current collector inside the secondary battery allows the tabs to conduct electricity with the electrode components inside the secondary battery, thereby achieving the purpose of transmitting current.

[0005] To facilitate the welding of the tabs, a double-sided empty foil area is usually required on the current collector. The welding socket supports the current collector in one empty foil area, and the welding head welds the tab to the current collector in the other empty foil area. However, the welding of the tab to the empty foil area of ​​the current collector can produce welding burrs, which may puncture the separator and cause a short circuit, leading to thermal runaway of the secondary battery. Summary of the Invention

[0006] This application aims to provide a secondary battery and electronic device that reduces the technical problem of thermal runaway in secondary batteries.

[0007] In a first aspect, this application proposes a secondary battery, including a first tab and a first electrode. The first electrode includes a first current collector and a first active material layer, with the first active material layer stacked on the surface of the first current collector along the thickness direction of the first electrode. The first current collector includes a first empty foil region, and the first tab is electrically connected to the first empty foil region. The secondary battery also includes a first adhesive layer, which is bonded between the first tab and the first empty foil region along the thickness direction of the first electrode. The first adhesive layer is configured such that the adhesive force decreases when the temperature rises to a first threshold, causing the first tab to separate at least partially from the first empty foil region.

[0008] In the above technical solution, the first tab is bonded and fixed to the first empty foil area by the first adhesive layer, eliminating the risk of welding burrs piercing the separator. This reduces the risk of short circuits in the secondary battery, thereby reducing thermal runaway and improving the safety performance of the secondary battery. Furthermore, it eliminates the need for a protective adhesive layer to cover burrs in the first tab or the first empty foil area, saving space and increasing the energy density of the secondary battery while reducing costs.

[0009] Meanwhile, the adhesive bonding process is relatively simple, requiring no complex welding equipment or professional welding technicians. Compared with traditional welding processes, adhesive bonding eliminates preparation work, equipment debugging, and strict quality control during welding, which helps improve the production efficiency of secondary batteries and reduce production costs. Furthermore, the first adhesive layer can effectively fill the tiny gaps between the first tab and the first empty foil area, improving the connection strength between them.

[0010] In addition, when the temperature rises to the first threshold, for example, when the secondary battery is short-circuited or in a high-temperature environment, the adhesiveness of the first adhesive layer weakens, causing the first tab to separate from the first empty foil area at least partially, thereby increasing the resistance between the first tab and the first current collector, or even directly breaking the electrical connection. This can effectively reduce the further development of thermal runaway, reduce the continuous rise in the temperature of the secondary battery, and thus reduce serious safety accidents such as fires and explosions of the secondary battery.

[0011] In some embodiments, the first threshold is T, where 100℃≤T≤150℃. Within the normal operating temperature range of the secondary battery (typically below 80℃), the first adhesive layer can withstand certain temperature changes and maintain good adhesion, enabling a reliable connection between the first tab 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℃ to 150℃, the adhesion of the first adhesive layer decreases, causing the first tab to partially separate from the first current collector. This increases the resistance or cuts off the short-circuit current path, effectively reducing the rapid temperature rise and the occurrence of thermal runaway.

[0012] In some embodiments, the first tab includes a first surface facing the first current collector, the first surface having a plurality of first protrusions, and a first adhesive layer partially embedded between two adjacent first protrusions. This increases the bonding area between the first tab and the first adhesive layer, thereby improving the connection strength between the first tab and the first current collector, and also improves the strength of the first tab, reducing the likelihood of breakage or tearing of the first tab.

[0013] In some embodiments, at least a portion of the first protrusion contacts the first empty foil area, which can provide a more direct conductive path. Compared to simply adding conductive particles to conduct current, direct contact can significantly reduce the contact resistance between the first tab and the first current collector under normal operating conditions, which is beneficial to improving the charging and discharging efficiency of the secondary battery.

[0014] In some embodiments, the width of the first protrusion is reduced in a second direction along the direction from the first tab to the first current collector. The second direction is perpendicular to the direction from the first tab to the first current collector. This allows the first protrusion to form a structure that is wider at the top and narrower at the bottom, which is more conducive to piercing the first adhesive layer and making direct contact with the first current collector for electrical connection, forming a more stable metal-to-metal electrical connection channel, and effectively reducing the problem of unstable electrical connection caused by factors such as aging and deformation of the first adhesive layer.

[0015] In some embodiments, the first tab includes a first surface facing the first current collector, the first surface is provided with a plurality of first recesses, and the first adhesive layer is partially embedded in the first recesses, which can increase the bonding area between the first tab and the first adhesive layer, thereby improving the connection strength between the first tab and the first current collector.

[0016] In some embodiments, the first surface contacts the first empty foil area, so that the first electrode tab is directly connected to the first current collector, which is more conducive to reducing contact resistance. Furthermore, the first adhesive layer in the first recess can directly bond the first electrode tab and the first current collector, thereby improving the connection strength between the first electrode tab and the first current collector.

[0017] In some embodiments, the first adhesive layer includes a plurality of conductive particles, which include at least one of silver, copper, nickel, aluminum, graphite or carbon nanotubes, enabling electrical connection between the first tab and the first current collector and reducing the resistance between the first tab and the first current collector under normal operating conditions.

[0018] In some embodiments, the first adhesive layer comprises a thermosetting adhesive, which includes at least one of epoxy resin, phenolic resin, or polyurethane resin; or, the first adhesive layer comprises a hot melt adhesive, which includes at least one of polyolefin, polyurethane, polyamide, or ethylene-vinyl acetate copolymer; or, the first adhesive layer comprises a metal adhesive, which includes at least one of tin, lead, zinc, or aluminum. Each material can provide a high bonding strength between the first tab and the first current collector under normal operating conditions, and each material can lose adhesion at abnormally high temperatures, causing the first tab and the first current collector to separate at least partially, thereby increasing resistance or interrupting the short-circuit current path, effectively reducing the rapid temperature rise and the occurrence of thermal runaway.

[0019] In some embodiments, the thickness of the first adhesive layer along the thickness direction of the first electrode is H, where 5μm≤H≤10μm. This provides sufficient adhesive force, improves the connection strength between the first electrode tab and the first current collector, facilitates direct contact electrical connection between the first electrode tab and the first current collector, and facilitates timely separation of the first electrode tab and the first current collector under abnormal conditions, thereby improving the safety performance of the secondary battery.

[0020] 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 electrode also includes a second active material layer, which is stacked on the surface of the first current collector opposite to the first active material layer. Along the thickness direction of the first electrode, the first groove is located within the projection of the second active material layer. Because the first tab and the first current collector are bonded by the first adhesive layer, no solder head or solder pad is required, that is, there is no need to open a groove in the second active material layer to place the solder pad. This makes the structure of the second active material layer more complete, reduces the shedding of powder from the second active material layer caused by slotting, and allows the second active material layer to be fully utilized, thereby improving the energy density of the secondary battery.

[0021] In some embodiments, the secondary battery further includes a separator and a second electrode. A separator is disposed between the first electrode and the second electrode along the thickness direction of the first electrode. The second active material layer includes a first region. Along the thickness direction of the first electrode, the projection of the first region coincides with the first groove, and at least part of the surface of the first region facing away from the first current collector is in contact with the separator. The first region of the second active material layer does not require a corresponding groove or a protective adhesive layer to cover burrs; therefore, the first region of the second active material layer can directly contact the separator, meaning it can participate in electrochemical reactions, thereby improving the energy density of the secondary battery.

[0022] In some embodiments, the secondary battery further includes a separator and a second electrode. A separator is disposed between the first electrode and the second electrode along the thickness direction of the first electrode. The first electrode is a positive electrode, and the second electrode is a negative electrode. The second electrode includes a second current collector and a third active material layer, which 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 electrode, 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 require a protective adhesive layer, allowing it to participate normally in the electrochemical reaction and improving the energy density of the secondary battery. Furthermore, because the second electrode is a negative electrode, it has sufficient margin to embed lithium ions extracted from the first electrode, reducing lithium plating.

[0023] In some embodiments, the secondary battery further includes a second tab and a second adhesive layer. A third active material layer is provided with a second groove, a second current collector forms a second empty foil region in the second groove, and the second tab is partially disposed in the second groove and electrically connected to the second empty foil region. Along the thickness direction of the second electrode, the second adhesive layer is bonded between the second tab and the second empty foil region. The second adhesive layer is configured such that the adhesive force decreases when the temperature rises to a first threshold, causing the second tab and the second empty foil region to separate at least partially. The absence of welding burrs reduces the risk of short circuits in the secondary battery, improving its safety performance. Furthermore, the elimination of the need for a protective adhesive layer to cover burrs in the second tab or the second empty foil region saves space and increases the energy density of the secondary battery while reducing costs.

[0024] In addition, when the temperature rises to the first threshold, the adhesiveness of the second adhesive layer weakens, causing the second tab to separate from the second empty foil area at least partially, thereby increasing the resistance between the second tab and the second current collector, or even directly breaking the electrical connection. This can effectively reduce the further development of thermal runaway, reduce the continuous rise in the temperature of the secondary battery, and thus reduce serious safety accidents such as fires and explosions of the secondary battery.

[0025] In some embodiments, the coefficient of thermal expansion of the first adhesive layer is between 50 ppm and 5000 ppm. A coefficient of thermal expansion greater than 50 ppm allows the first adhesive layer to expand thermally at high temperatures, reducing adhesion and potentially opening the electrical contact points, thus breaking the circuit between the first tab and the first current collector. A coefficient of thermal expansion greater than 5000 ppm presents greater manufacturing challenges.

[0026] Secondly, this application also proposes an electronic device including a secondary battery as described in any of the embodiments of the first aspect above.

[0027] Additional aspects and advantages of the embodiments of this application will be described, shown, or illustrated in part by way of implementation of the embodiments of this application in the following description. Attached Figure Description

[0028] One or more embodiments are illustrated by way of example with reference to the accompanying drawings, which are not intended to limit the embodiments, and elements having the same reference numerals in the drawings are designated as similar elements.

[0029] Figure 1 is a schematic diagram of the structure of a secondary battery according to some embodiments of this application;

[0030] Figure 2 is a schematic diagram of the stacking of the first electrode, the separator, and the second electrode in some embodiments of this application;

[0031] Figure 3 is a schematic diagram of the structure of the first electrode sheet in some embodiments of this application;

[0032] Figure 4 is a schematic diagram of the structure of the first electrode sheet in some embodiments of this application;

[0033] Figure 5 is a schematic diagram of the structure of the first electrode sheet in some embodiments of this application;

[0034] Figure 6 is a schematic diagram of the structure of the first electrode sheet in some embodiments of this application;

[0035] Figure 7 is a schematic diagram of the structure of the first electrode sheet in some embodiments of this application;

[0036] Figure 8 is an exploded schematic diagram of the first electrode sheet in some embodiments of this application;

[0037] Figure 9 is a schematic diagram of the structure of the first electrode sheet in some embodiments of this application;

[0038] Figure 10 is a schematic diagram of the structure of the second electrode sheet in some embodiments of this application.

[0039] Explanation of reference numerals in the attached figures:

[0040] 100. Secondary batteries;

[0041] 10. Shell;

[0042] 20. Electrode assembly;

[0043] 21. First electrode; 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;

[0044] 22. Second electrode; 221. Second current collector; 221a. Second empty foil region; 221b. Second groove; 222. Third active material layer; 2221. Second region; 223. Fourth active material layer;

[0045] 23. Separating membrane;

[0046] 30. First electrode tab; 31. First surface; 30a. First protrusion; 30b. First recess;

[0047] 40. Second pole ear;

[0048] 50. First adhesive layer;

[0049] 60. Second adhesive layer;

[0050] Z, first direction; X, second direction; Y, third direction. Embodiments of the present invention

[0051] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly described below with reference to the accompanying drawings. Obviously, the described embodiments are some embodiments of this application, but not all embodiments.

[0052] In this application, the reference to "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places in the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment that is mutually exclusive with other embodiments.

[0053] In the description of the embodiments of this application, technical terms such as "first" and "second" are used only to distinguish different objects and should not be construed as indicating or implying relative importance or implicitly specifying the number, specific order, or primary and secondary relationship of the indicated technical features. In the description of the embodiments of this application, "multiple" means two or more, unless otherwise explicitly defined.

[0054] In the description of the embodiments in this application, the term "and / or" is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, and B existing alone. Additionally, the character " / " in this document generally indicates that the preceding and following related objects have an "or" relationship.

[0055] The technical features involved in the different embodiments of this application described below can be combined with each other as long as they do not conflict with each other.

[0056] In one aspect, this application proposes a secondary battery 100. Referring to Figure 1, the secondary battery 100 includes a casing 10, an electrode assembly 20, a first tab 30, and a second tab 40. The casing 10 can accommodate the electrode assembly 20 and an electrolyte (not shown in the figure). The electrolyte wets the electrode assembly 20 within the casing 10, thereby causing an electrochemical reaction. One end of the first tab 30 is connected to the electrode assembly 20 inside the casing 10, and the other end of the first tab 30 extends outside the casing 10. One end of the second tab 40 is connected to the electrode assembly 20 inside the casing 10, and the other end of the second tab 40 extends outside the casing 10. The first tab 30 and the second tab 40 have opposite polarities and are used to lead out the positive and negative electrodes of the secondary battery 100.

[0057] Referring to Figures 1 and 2, the electrode assembly 20 includes a first electrode 21, a second electrode 22, and a separator 23. The first electrode 21, the separator 23, and the second electrode 22 are stacked and wound together, for example, stacked along the thickness direction (first direction Z) of the first electrode 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 21 and the second electrode 22 to provide insulation between them.

[0058] In some other embodiments, a plurality of first electrode plates 21 and a plurality of second electrode plates 22 are alternately stacked, and an isolation film 23 is provided between adjacent first electrode plates 21 and second electrode plates 22, thereby forming a stacked electrode assembly 20.

[0059] The first electrode 21 and the second electrode 22 have opposite polarities. For example, the first electrode 21 is the positive electrode and the second electrode 22 is the negative electrode. Alternatively, in some other embodiments, the first electrode 21 is the negative electrode and the second electrode 22 is the positive electrode. The first tab 30 is connected to the first electrode 21, and the current of the first electrode 21 is collected and transmitted through the first tab 30. The second tab 40 is connected to the second electrode 22, and the current of the second electrode 22 is collected and transmitted through the second tab 40, thereby leading out the positive and negative electrodes of the secondary battery 100.

[0060] Referring to Figure 2, the first electrode 21 includes a first current collector 211 and a first active material layer 212. The first current collector 211 serves as the conductive substrate of the first electrode 21 and can be made of a flat aluminum foil. Aluminum foil has high conductivity and low resistance, which can improve the maximum charge / discharge rate of the secondary battery 100. Furthermore, aluminum foil has certain strength and ductility, making it less prone to breakage or deformation during winding or stacking processes, thus ensuring the structural integrity of the first electrode 21. In other embodiments, the first current collector 211 can also be made of titanium foil, nickel foil, or stainless steel foil.

[0061] 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). The first active material layer 212 includes a positive electrode active material, a conductive agent, and a binder. The above-mentioned material components are mixed, stirred evenly, and coated on the surface of the first current collector 211 to obtain the first active material layer 212. 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 electrode 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. The second active material layer 213 can be similarly configured to the first active material layer 212.

[0062] Referring to Figure 2, the second electrode 22 includes a second current collector 221 and a third active material layer 222. The second current collector 221 serves as the conductive substrate of the second electrode 22 and can be a flat copper foil. Copper foil has high conductivity and low resistance, which can improve the maximum charge-discharge rate of the secondary battery 100. Furthermore, copper foil has certain strength and ductility, making it less prone to breakage or deformation during winding or stacking processes, thus ensuring the structural integrity of the second electrode 22. In other embodiments, the second current collector 221 can also be made of titanium foil, nickel foil, stainless steel foil, or silver foil.

[0063] 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). The third active material layer 222 includes a negative electrode active material, a conductive agent, and a binder, etc. These materials are mixed, stirred evenly, and coated on the surface of the second current collector 221 to obtain the third active material layer 222. The negative electrode active material includes one or more of graphite, soft carbon, hard carbon, elemental silicon, silicon oxide, silicon alloy, etc. Optionally, the second electrode 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 configured similarly to the third active material layer 222.

[0064] Regarding the first tab 30 mentioned above, please refer to Figures 2 and 3. The first current collector 211 is provided with a first empty foil area 211a (without a first active material layer 212). The first tab 30 is partially disposed in the first empty foil area 211a. For example, a part of the first tab 30 is electrically connected to the first empty foil area 211a, and the other part extends out of the first electrode 21 along the width direction (third direction Y) of the first electrode 21.

[0065] Referring to Figure 3, in some embodiments, the secondary battery 100 further includes a first adhesive layer 50, which is bonded between the first tab 30 and the first empty foil region 211a along a first direction Z. Furthermore, the first adhesive layer 50 is configured such that the adhesive force decreases when the temperature rises to a first threshold, causing the first tab 30 to separate at least partially from the first empty foil region 211a.

[0066] In the embodiments of this application, the first tab 30 is bonded and fixed to the first empty foil area 211a by the first adhesive layer 50. There are no welding burrs, eliminating the risk of welding burrs piercing the separator 23. This reduces the risk of short circuits in the secondary battery 100, thereby reducing the risk of thermal runaway and improving the safety performance of the secondary battery 100. Furthermore, there is no need to provide a protective adhesive layer to cover burrs on the first tab 30 or the first empty foil area 211a, saving the space occupied by the protective adhesive layer and increasing the energy density of the secondary battery 100 while reducing costs.

[0067] Meanwhile, the adhesive bonding process is relatively simple, requiring no complex welding equipment or professional welding technicians. Compared with traditional welding processes, adhesive bonding eliminates preparation work, equipment debugging, and strict quality control during welding, which helps improve the production efficiency of the secondary battery 100 and reduce production costs. Furthermore, the first adhesive layer 50 can effectively fill the tiny gaps between the first tab 30 and the first empty foil area 211a, thereby improving the connection strength between the first tab 30 and the first empty foil area 211a.

[0068] 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 adhesiveness of the first adhesive layer 50 weakens, causing the first tab 30 to separate from the first empty foil area 211a at least partially, thereby increasing the resistance between the first tab 30 and the first current collector 211, or even directly breaking the electrical connection. This can effectively reduce the further development of thermal runaway, 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.

[0069] The adhesive strength test method for the first adhesive layer 50 is as follows: According to GB / T 2792-2014 "Test Method for Adhesive Tape Adhesion Strength", a high-speed rail tensile testing machine is used to test the adhesive strength between the first tab 30 and the first current collector 211. The adhesive strength is the adhesive strength of the first adhesive layer 50. The test procedure is as follows: Discharge the secondary battery to 0V, then disassemble the secondary battery, remove the first tab 30 and the first current collector 211 bonded to it, and wipe the electrolyte off the surface with lint-free paper. Then, cut a 20mm × 60mm strip sample (including the part bonded to the first tab 30) from the first current collector 211. Adhere the side of the sample away from the first tab 30 to the steel plate using double-sided adhesive (Nitto 5000NS), with an adhesion length of not less than 40mm. The steel plate is fixed in the corresponding position on the high-speed rail tensile testing machine. The first tab 30 is clamped by the clamps, and the first tab 30 is pulled up, with the pulled-up part forming a spatial angle of 180° with the steel plate. The clamps pull the sample at a speed of 5±0.2 mm / s. The average tensile force in the stable region is recorded as the bonding strength between the first tab 30 and the first current collector 211, which is also the bonding force of the first adhesive layer 50. Testing can be conducted under different temperature environments to obtain the bonding force of the first adhesive layer 50 at different temperatures.

[0070] In some embodiments, the first threshold is T, where 100℃≤T≤150℃. Within the normal operating temperature range of the secondary battery 100 (typically below 80℃), the first adhesive layer 50 can withstand certain temperature changes and maintain good adhesion, enabling a reliable connection between the first tab 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℃ to 150℃, the adhesion of the first adhesive layer 50 decreases, causing the first tab 30 to partially separate from the first current collector 211. This increases the resistance or cuts off the short-circuit current path, effectively reducing the rapid temperature rise and the occurrence of thermal runaway.

[0071] The material of the first adhesive layer 50 includes a hot melt adhesive, which includes at least one of polyolefin, polyurethane, polyamide, or ethylene-vinyl acetate copolymer. The hot melt adhesive can be heated and melted before being applied to the first tab 30. After melting, the hot melt adhesive has good fluidity, enabling it to quickly fill the tiny gaps between the first tab 30 and the first current collector 211. After curing, it can improve the connection strength between the first tab 30 and the first current collector 211. Furthermore, the detack temperature of the hot melt adhesive is close to 100°C to 150°C. Under normal operating temperatures, the hot melt adhesive can maintain a solid state and good adhesion. Due to the thermoplasticity of the hot melt adhesive itself, when a short circuit occurs inside the secondary battery 100, causing the temperature to rise to the detack temperature range, the hot melt adhesive will gradually soften and reduce its viscosity, causing the first tab 30 and the first current collector 211 to separate at least partially. This temperature response characteristic is consistent with the inherent properties of the hot melt adhesive, effectively realizing a safety protection mechanism for the secondary battery 100 under abnormally high temperatures.

[0072] In some embodiments, the first adhesive layer 50 comprises a thermosetting adhesive, which includes at least one of epoxy resin, phenolic resin, or polyurethane resin. During curing, the thermosetting adhesive undergoes a chemical reaction to form a three-dimensional network cross-linked structure. This structure gives the thermosetting adhesive high cohesive strength, providing strong adhesion between the first tab 30 and the first current collector 211. However, when a short circuit occurs inside the secondary battery 100, causing the temperature to rise to 100°C to 150°C, the van der Waals forces and chemical bonds (such as covalent bonds) of the thermosetting adhesive's three-dimensional network cross-linked structure may be destroyed at high temperatures, leading to the gradual disintegration of the cross-linked structure. This reduces the tackiness of the first adhesive layer 50, thereby causing the first tab 30 to separate from the first current collector 211, mitigating thermal runaway.

[0073] In some other embodiments, the first adhesive layer 50 includes a metal adhesive, which may include at least one of tin (solder paste), lead (lead paste), zinc (zinc paste), or aluminum (aluminum paste). The metal adhesive itself has good conductivity, enabling it to form an effective conductive path between the first tab 30 and the first current collector 211. Under normal operating conditions, this reduces the contact resistance between the first tab 30 and the first current collector 211, which is beneficial for improving the charge / discharge rate of the secondary battery 100. However, when a short circuit occurs inside the secondary battery 100, causing the temperature to rise to 100°C to 150°C, the metal adhesive loses its adhesion, causing the first tab 30 to partially separate from the first current collector 211. This effectively cuts off the main path of the short-circuit current, reducing the continuous rise in the temperature of the secondary battery 100, and thus reducing the risk of serious safety accidents such as fire or explosion. It is understood that the first adhesive layer 50 may also use other types of high-temperature-dead-adhesion adhesives.

[0074] To adjust the tack-free temperature of the first adhesive layer (50°C), hot melt adhesives can have their properties such as tack, hardness, and heat resistance altered by adding different tackifiers and fillers. For example, adding inorganic fillers such as silica (SiO₂), alumina (Al₂O₃), and calcium carbonate (CaCO₃) can improve the thermal stability of the hot melt adhesive, thereby increasing the tack-free temperature. Alternatively, the tack-free temperature can be adjusted through polymer modification. Thermosetting adhesives can have their tack-free temperature adjusted by modifying the resin composition and curing agent system. For instance, the tack-free temperature can be adjusted by selecting epoxy resins with different epoxy values. Higher epoxy values ​​result in more reactive sites on the molecular chain, greater crosslinking density after curing, and a relatively higher tack-free temperature. Alternatively, the crosslinking density can be altered by adding fillers and adjusting the type of curing agent, appropriately increasing or decreasing the amount of curing agent, thereby adjusting the tack-free temperature. For metal adhesives, different metals have different melting points and coefficients of thermal expansion. The debonding temperature can be adjusted by changing the metal composition 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.

[0075] In some embodiments, when the first adhesive layer 50 is a hot melt adhesive or a thermosetting adhesive, a number of conductive particles may 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 tab 30 and the first current collector 211 and reduce the resistance between the first tab 30 and the first current collector 211 under normal operating conditions.

[0076] In some embodiments, referring to FIG4, the first tab 30 includes a first surface 31 facing the first current collector 211. The first surface 31 is provided with a plurality of first protrusions 30a, which protrude relative to the first surface 31. The first adhesive layer 50 is partially embedded between two adjacent first protrusions 30a. This increases the bonding area between the first tab 30 and the first adhesive layer 50, thereby improving the connection strength between the first 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 tab 30 and reduce the risk of breakage or tearing of the first tab 30.

[0077] In some embodiments, referring to Figure 5, at least a portion of the first protrusion 30a contacts the first empty foil region 211a, providing a more direct conductive path. Compared to simply adding conductive particles to conduct current, direct contact under normal operating conditions can significantly reduce the contact resistance between the first tab 30 and the first current collector 211, which is beneficial for improving the charging and discharging efficiency of the secondary battery 100. It is understood that when the first protrusion 30a directly contacts the first empty foil region 211a, the first tab 30 and the first current collector 211 are directly connected, eliminating the need to add conductive particles in the first portion. This simplifies the manufacturing process and reduces production costs.

[0078] In some embodiments, referring to Figure 6, along the direction from the first tab 30 to the first current collector 211 (first direction Z), the width of the first protrusion 30a is reduced in the second direction X, which is perpendicular to the direction from the first tab 30 to the first current collector 211. This allows the first protrusion 30a to form a structure that is wider at the top and narrower at the bottom, which is more conducive to piercing the first adhesive layer 50 and directly contacting and connecting with the first current collector 211, forming a more stable metal-to-metal electrical connection channel. This effectively reduces the problem of unstable electrical connection caused by factors such as aging and deformation of the first adhesive layer 50. In other embodiments, the width of the first protrusion 30a is reduced in the third direction Y.

[0079] In some embodiments, referring to Figures 7 and 8, the first surface 31 is further provided with a plurality of first recesses 30b, which are recessed relative to the first surface 31, and the first adhesive layer 50 is partially embedded in the first recesses 30b. This can increase the bonding area between the first tab 30 and the first adhesive layer 50, thereby improving the connection strength between the first tab 30 and the first current collector 211.

[0080] Meanwhile, the first recess 30b can serve as a storage space for the first adhesive layer 50, allowing the first adhesive layer 50 to be better retained between the first tab 30 and the first current collector 211. For example, during thermal runaway of the secondary battery 100, the temperature at the first tab 30 rises sharply, which may cause the first adhesive layer 50 to melt, resulting in partial separation between the first tab 30 and the first current collector 211. This increases the resistance between the first tab 30 and the first current collector 211 or breaks the electrical connection, thereby mitigating thermal runaway. The first recess 30b can reduce the loss of the molten first adhesive layer 50. After curing, it can again provide sufficient first adhesive layer 50 between the first tab 30 and the first current collector 211 to achieve a good bonding effect, which is beneficial for maintaining the connection stability between the first tab 30 and the first current collector 211 in the long term.

[0081] In some embodiments, referring to FIG9, the first surface 31 contacts the first empty foil area 211a, so that the first tab 30 directly contacts and is electrically connected to the first current collector 211, which is more conducive to reducing contact resistance. Furthermore, the first adhesive layer 50 in the first recess 30b can directly bond the first tab 30 and the first current collector 211, thereby improving the connection strength between the first tab 30 and the first current collector 211.

[0082] In some other embodiments, the first tab 30 is also provided with a first protrusion 30a and a first recess 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 tab 30 and the first adhesive layer 50, thereby improving the bonding strength between the first tab 30 and the first current collector 211.

[0083] Regarding the thickness of the first adhesive layer 50, the inventors of this application have discovered that if the thickness of the first adhesive layer 50 is too small, it may not provide sufficient adhesive force. For example, when bonding the first tab 30 to the first current collector 211, if the first adhesive layer 50 is too thin, it cannot fully fill the tiny gap between them, resulting in insufficient bonding area and insufficient adhesive force. During the use of the secondary battery 100, when subjected to external forces such as vibration or electrode expansion, the first tab 30 is prone to separating from the first current collector 211, affecting the normal operation of the secondary battery 100. On the other hand, if the thickness of the first adhesive layer 50 is too large, under normal operating conditions, it is difficult to directly connect the first tab 30 to the first current collector 211, which may lead to excessive resistance between the first tab 30 and the first current collector 211. Furthermore, in the event of an abnormal situation such as a short circuit in the secondary battery 100, even if the first adhesive layer 50 loses its adhesion, the excessive thickness of the first adhesive layer 50 may still make it difficult for the first tab 30 to separate from the first current collector 211 in time, thereby further aggravating thermal runaway and affecting the safety performance of the secondary battery 100.

[0084] In the embodiments of this application, please refer to FIG3. Along the thickness direction (first direction Z) of the first electrode 21, the thickness of the first adhesive layer 50 is H, 5μm≤H≤10μm, which can provide sufficient adhesive force, improve the connection strength between the first tab 30 and the first current collector 211, facilitate the direct contact electrical connection between the first tab 30 and the first current collector 211, and facilitate the timely separation of the first tab 30 and the first current collector 211 under abnormal conditions, thereby improving the safety performance of the secondary battery 100.

[0085] In some embodiments, referring to FIG2, 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 portion of the first active material layer 212 is removed by laser cleaning or foaming adhesive processes, thereby exposing part of the first current collector 211 and forming the first empty foil area 211a. The first electrode 21 also includes a second active material layer 213, which is stacked on the surface of the first current collector 211 facing away from the first active material layer 212. Along the thickness direction (first direction Z) of the first electrode 21, the first groove 211b is located within the projection of the second active material layer 213.

[0086] In the embodiments of this application, since the first tab 30 and the first current collector 211 are bonded together by the first adhesive layer 50, there is no need for a welding head and a welding base, that is, there is no need to open a groove in the second active material layer 213 to place the welding base. This makes the structure of the second active material layer 213 more complete, reduces the powder shedding and falling off of the second active material layer 213 caused by the groove, and allows the second active material layer 213 to be fully utilized, thereby improving the energy density of the secondary battery 100.

[0087] In some embodiments, referring to FIG2, 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 separator 23.

[0088] In the embodiments of this application, since the first tab 30 and the first current collector 211 are bonded together by 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 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 2131 of the second active material layer 213 can directly contact the separator 23, that is, the first region 2131 can participate in the electrochemical reaction, thereby improving the energy density of the secondary battery 100.

[0089] The second tab 40 described above can also be configured similarly to the first tab 30. Referring to Figures 2 and 10, the second current collector 221 is provided with a second empty foil region 221a. For example, a second groove 221b is formed on the third active material layer 222 to expose part of the second current collector 221, thereby forming the second empty foil region 221a. The secondary battery 100 also includes a second adhesive layer 60. The second tab 40 is partially disposed in the second groove 221b, and the second adhesive layer 60 is bonded between the second tab 40 and the second empty foil region 221a. Furthermore, the second adhesive layer 60 is configured such that the adhesive force decreases when the temperature rises to a first threshold, causing the second tab 40 to separate from the second empty foil region 221a at least partially.

[0090] In the embodiments of this application, the second tab 40 is bonded and fixed to the second empty foil area 221a by the second adhesive layer 60, eliminating the risk of welding burrs piercing the separator 23 and reducing the risk of short circuits in the secondary battery 100, thus improving its safety performance. Furthermore, it eliminates the need for a protective adhesive layer to cover burrs on the second tab 40 or the second empty foil area 221a, saving space and increasing the energy density of the secondary battery 100 while reducing costs.

[0091] Meanwhile, the adhesive bonding process is relatively simple, requiring no complex welding equipment or professional welding technicians. Compared with traditional welding processes, adhesive bonding eliminates preparation work, equipment debugging, and strict quality control during welding, which helps improve the production efficiency of the secondary battery 100 and reduce production costs. Furthermore, the second adhesive layer 60 can effectively fill the tiny gaps between the second tab 40 and the second empty foil area 221a, thereby improving the connection strength between the second tab 40 and the second empty foil area 221a.

[0092] 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 adhesion of the second adhesive layer 60 weakens, causing the second tab 40 to separate from the second empty foil region 221a at least partially, thereby increasing the resistance between the second tab 40 and the second current collector 221, or even directly breaking the electrical connection. This can effectively reduce the further development of thermal runaway, 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.

[0093] The specific connection structure of the second tab 40, the second current collector 221 and the second adhesive layer 60 can be referred to the first tab 30, the first current collector 211 and the first adhesive layer 50 mentioned above. Their structures are similar and will not be described one by one in this application.

[0094] In some embodiments, the coefficients of thermal expansion of the first adhesive layer 50 and the second adhesive layer 60 are between 50 ppm and 5000 ppm. The coefficient of thermal expansion of the first adhesive layer 50 is greater than 50 ppm, which allows it to thermally expand at high temperatures. This reduces the adhesive strength and simultaneously opens the electrical contact points, causing a break in the circuit between the first tab 30 and the first current collector 211. A coefficient of thermal expansion greater than 5000 ppm presents greater manufacturing challenges. The second adhesive layer 60 is similar.

[0095] In some embodiments, taking the first electrode 21 as the positive electrode and the second electrode 22 as the negative electrode as an example, referring to Figure 2, the second electrode 22 includes a second current collector 221 and a third active material layer 222. 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. Along the thickness direction (first direction Z) of the first electrode 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 separator 23.

[0096] In the embodiments of this application, since the first tab 30 is bonded to the first current collector 211 through an adhesive layer, there are no welding burrs, and the risk of puncturing 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, allowing the second region 2221 to participate normally in the electrochemical reaction and improve the energy density of the secondary battery 100. Furthermore, since the second electrode 22 is a negative electrode, it has sufficient margin to embed the lithium ions extracted from the first electrode 21, which can reduce lithium plating.

[0097] Secondly, this application also proposes an electronic device, including a secondary battery 100 as described in any embodiment of the first aspect above. The electronic device in this application is not particularly limited and 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, power tools, electric vehicles, electric cars, ships, spacecraft, etc. Electric toys can include stationary or mobile electric toys, such as game consoles, electric car toys, electric ship toys, and electric airplane toys, etc., while spacecraft can include airplanes, rockets, space shuttles, and spacecraft, etc.

[0098] Example 1

[0099] Preparation of the positive electrode sheet:

[0100] 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 5×10⁻⁶). 5 The materials were mixed at a mass ratio of 94:3:3, with N-methylpyrrolidone (NMP) added as a solvent to prepare a positive electrode slurry with a solid content of 75 wt%. The slurry was then stirred evenly under a vacuum mixer. A 12 μm thick aluminum foil was selected as the positive electrode current collector. The positive electrode slurry was uniformly coated on one surface of the aluminum foil and dried at 110°C to obtain a positive electrode sheet with a single-sided coating of positive active material. The above steps were then repeated on the other surface of the aluminum foil to obtain a positive electrode sheet with a double-sided coating of positive active material.

[0101] A first groove is pre-drilled on the positive electrode active material layer on one surface using a foaming adhesive process, exposing the positive electrode current collector portion and thus forming a first empty foil area. The first empty foil area has a width of 10 mm and a length of 20 mm.

[0102] An 80μm thick aluminum sheet is used as the positive electrode tab. A first adhesive layer of ethylene-vinyl acetate copolymer is bonded to the first surface of the positive electrode tab. The debonding temperature T of the first adhesive layer is 100℃. The positive electrode tab and the first empty foil area of ​​the positive current collector are bonded by hot pressing. After the first adhesive layer cures, the positive electrode tab and the first empty foil area are bonded. The bonding width of the first adhesive layer in the first empty foil area is 8mm, with a 1mm gap between each side and the positive active material layer. The bonding length is 18mm, with a 1mm gap between the first adhesive layer and the positive active material layer in the length direction. The thickness of the first adhesive layer is 8μm.

[0103] Preparation of negative electrode sheet:

[0104] Graphite powder (negative electrode active material), conductive carbon black (Super P) (conductive agent), and styrene-butadiene rubber (SBR) (binder) were mixed in a weight ratio of 97.5:1:1.5. Deionized water was then added as a solvent to prepare a slurry with a solid content of 50 wt%, and the mixture was stirred thoroughly. The slurry was then uniformly coated onto one surface of a 6 μm thick copper foil negative electrode current collector and dried at 110 °C to obtain a negative electrode active material with a weight of 9.1 mg / cm³. 2 Single-sided negative electrode sheet. After completing the above steps, the single-sided coating of the negative electrode sheet is finished. Then, repeat the above steps 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 pre-reserved on the negative electrode sheet using a foaming adhesive process. The second empty foil area is 10mm wide and 20mm long.

[0105] An 80μm nickel sheet is used as the negative electrode tab. A second adhesive layer of ethylene-vinyl acetate copolymer is bonded to the surface of the negative electrode tab. The debonding temperature of the second adhesive layer is 100℃. The negative electrode tab is then bonded to the second empty foil area. The bonding width of the second adhesive layer in the second empty foil area is 8mm, with a 1mm gap reserved on each side from the negative electrode active material layer. The bonding length is 18mm, with a 1mm gap reserved in the length direction from the negative electrode active material layer. The thickness of the second adhesive layer is 8μm.

[0106] Preparation of the separating membrane:

[0107] A porous polyethylene (PE) film with a thickness of 8 μm was used as the separator.

[0108] Electrolyte preparation:

[0109] In a dry argon atmosphere, ethylene carbonate, methyl ethyl carbonate and diethyl carbonate were mixed in a mass ratio of 30:50:20 to obtain an organic solution. Then, 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.

[0110] Preparation of lithium-ion batteries:

[0111] The separator, positive electrode, separator, and negative electrode prepared above are stacked in sequence and wound to obtain an electrode assembly. The electrode assembly is then hot-pressed at a pressure of 5 MPa and a temperature of 65°C for 10 seconds. The electrode assembly is placed in an aluminum-plastic film packaging bag, with both the positive and negative electrode tabs extending from the top seal edge of the bag. After dehydration at 80°C, electrolyte is injected and the bag is sealed.

[0112] Unlike Example 1, the relevant parameters in Examples 2 to 15 and Comparative Example 1 are shown in Table 1 below.

[0113] Short-circuit test method: The lithium-ion battery is charged and discharged 20 times at 70±5°C. The current change is observed; a sudden drop in current indicates failure. If not failed, the fully charged lithium-ion battery sample is placed in a 20±5°C test environment. An 80±20mΩ load resistor is short-circuited between the positive and negative terminals of the sample. The test continues until the voltage drops below 0.2V. The test ends when one of the following conditions is met: 1) The surface temperature of the lithium-ion battery stabilizes (temperature change less than 10°C within 30 minutes); 2) The surface temperature of the lithium-ion battery drops to the same as the ambient temperature. Measurement frequency: Voltage and internal resistance measurements are performed using a 1kHz specification after pretreatment and post-testing. Failure criteria: The lithium-ion battery explodes, leaks, or catches fire. Test results are shown in Table 1 below.

[0114] Table 1

[0115] Connection Method H(μm) T(°C) Test Failure Rate Comparison Example 1 Welding / / 18 / 20 Example 1 Adhesion 8 1000 / 20 Example 2 Adhesion 9 1000 / 20 Example 3 Adhesion 10 100 2 / 20 Example 4 Adhesion 11 100 4 / 20 Example 5 Adhesion 7 100 1 / 20 Example 6 Adhesion 6 100 2 / 20 Example 7 Adhesion 5 100 4 / 20 Example 8 Adhesion 4 100 5 / 20 Example 9 Adhesion 10 90 5 / 20 Example 10 Adhesion 10 110 2 / 20 Example 11 Adhesion 10 120 2 / 20 Example 12 Adhesion 10 130 3 / 20 Example 13 Adhesion 10 140 3 / 20 Example 14 Adhesion 10 150 4 / 20 Example 15 Adhesion 10 160 7 / 20

[0116] According to Table 1 above, and in conjunction 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 together through a first adhesive layer, and the first adhesive layer is a high-temperature non-adhesive adhesive layer, the short-circuit test failure rate can be effectively reduced. This is because when a lithium-ion battery experiences a short circuit or is in a high-temperature environment, the adhesiveness of the first adhesive layer weakens, causing the positive electrode tab to separate from the first empty foil area at least partially. This increases the resistance between the positive electrode tab and the positive electrode current collector, and may even cause the electrical connection to break directly. This effectively reduces the further development of thermal runaway, reduces the continuous rise in lithium-ion battery temperature, and thus reduces the occurrence of serious safety accidents such as fires and explosions in lithium-ion batteries.

[0117] In conjunction with Examples 1 to 8, Examples 1 to 3, and Examples 5 to 7, the failure rate in the tests is lower than that in Example 4. In Example 4, the thickness of the first adhesive layer is relatively large, which may make it difficult to melt in time at high temperatures, leading to separation of the positive electrode tab from the positive current 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 current collector, potentially affecting 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, resulting in high connection strength between the positive electrode tab and the positive current collector, and a low short-circuit test failure rate. Therefore, in the embodiments of this application, the thickness of the first adhesive layer can be selected as 5μm≤H≤10μm.

[0118] In conjunction with Examples 9 to 15, and Examples 10 to 14, the failure rates were lower than those in Examples 9 and 15. In Example 9, the debonding temperature of the first adhesive layer was relatively low, which could lead to debonding under normal operating conditions, affecting the normal operation of the lithium-ion battery. In Example 15, the debonding temperature of the first adhesive layer was relatively high, which could make it difficult for the first adhesive layer to debond in time, thus making it difficult for the positive electrode tab and the positive current collector to separate in time, posing a safety risk. Therefore, in the embodiments of this application, the debonding temperature of the first adhesive layer can be selected to be 100℃ to 150℃, that is, 100℃≤T≤150℃.

[0119] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and not to limit them; under the concept of this application, the technical features of the above embodiments or different embodiments can also be combined, the steps can be implemented in any order, and there are many other variations of different aspects of this application as described above, which are not provided in detail for the sake of brevity; although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the foregoing embodiments, or make equivalent substitutions for some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application.

Claims

1. A secondary battery, comprising a first tab and a first electrode, the first electrode comprising 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 electrode; the first current collector comprising a first empty foil region, the first tab being electrically connected to the first empty foil region, characterized in that, The secondary battery further includes a first adhesive layer, which is bonded between the first electrode tab and the first empty foil area along the thickness direction of the first electrode sheet. The first adhesive layer is configured such that the adhesive strength decreases when the temperature rises to a first threshold, causing the first tab to separate at least partially from the first empty foil region.

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

3. The secondary battery according to claim 1, characterized in that, The first electrode tab includes a first surface facing the first current collector, and the first surface is provided with a plurality of first protrusions, and the first adhesive 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 contacts 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 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.

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

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 any one of claims 1 to 7, characterized in that, The first adhesive layer includes a plurality of conductive particles, wherein the conductive particles include at least one of silver, copper, nickel, aluminum, graphite or carbon nanotubes.

9. The secondary battery according to any one of claims 1 to 8, characterized in that, The first adhesive layer comprises a thermosetting adhesive, wherein the thermosetting adhesive comprises at least one of epoxy resin, phenolic resin, or polyurethane resin; or, The first adhesive layer comprises a hot melt adhesive, which includes at least one selected from 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.

10. The secondary battery according to any one of claims 1 to 9, characterized in that, Along the thickness direction of the first electrode, the thickness of the first adhesive layer is H, where 5μm≤H≤10μm.

11. The secondary battery according to any one of claims 1 to 10, 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 electrode further includes a second active material layer, which is stacked on the surface of the first current collector opposite to the first active material layer. Along the thickness direction of the first electrode, 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 also includes a separator and a second electrode. The separator is disposed between the first electrode and the second electrode along the thickness direction of the first electrode. The second active material layer includes a first region along the thickness direction of the first electrode, 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 separator membrane.

13. The secondary battery according to claim 11, characterized in that, The secondary battery also includes a separator and a second electrode. The separator is disposed between the first electrode and the second electrode along the thickness direction of the first electrode. The first electrode is a positive electrode and the second electrode is a negative electrode. The second electrode includes a second current collector and a third active material layer, wherein 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 electrode, 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.

14. The secondary battery according to claim 13, characterized in that, The secondary battery also includes a second tab and a second adhesive 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 is disposed in the second groove and electrically connected to the second empty foil area. Along the thickness direction of the second electrode sheet, the second adhesive layer is bonded between the second electrode tab and the second empty foil area; The second adhesive layer is configured such that the adhesive strength decreases when the temperature rises to a first threshold, causing the second tab to separate at least partially from the second empty foil region.

15. The secondary battery according to any one of claims 1 to 14, characterized in that, The coefficient of thermal expansion of the first adhesive layer is 50 ppm to 5000 ppm.

16. An electronic device, characterized in that, Includes the secondary battery as described in any one of claims 1 to 15.

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