Secondary battery and electronic device

Abstract

The invention relates to a secondary battery and electronic equipment, the secondary battery comprises a first pole piece and a second pole piece which are opposite in polarity, the first pole piece comprises a first current collector and a first active layer arranged on the surface of the first current collector, the first current collector comprises a first polymer layer, a first metal layer and a second metal layer, a first metal layer and a second metal layer are arranged on the two opposite surfaces of the first polymer layer respectively. A first tab is arranged on the surface, deviating from the first polymer layer, of the first metal layer and comprises a first connecting part electrically connected with the first metal layer, a first heat insulation part is arranged on the surface, deviating from the first metal layer, of the first tab, and the projection of the first heat insulation part is at least partially overlapped with the first connecting part in the thickness direction of the first tab. According to the secondary battery and the electronic equipment, the thermal runaway risk of the secondary battery can be improved.

Description

Technical Field

[0001] This application relates to the technical field of batteries, and particularly to a secondary battery and an electronic device. Background Art

[0002] As the power source of an electronic device, a secondary battery is crucial for ensuring the normal use of the electronic device. During the high-current charge and discharge process of a secondary battery, there is a risk of thermal runaway. The composite metal current collector (MPF) uses a metal-polymer-metal structure, which can reduce the weight of the battery. Moreover, the metal layer is relatively thin, which can reduce the burrs during the mechanical damage of the electrode assembly, reduce the probability of short circuit, and enhance the safety of the secondary battery, showing broad prospects in the field of secondary battery safety. However, the metal layer of the composite current collector is relatively thin. After the current collector and the tab are electrically connected by ultrasonic welding or riveting, the contact area between the metal layer on the current collector and the tab is small, resulting in an increase in the electrical connection resistance. In this case, during the high-current charge and discharge process, the joule heat generated at the connection between the metal layer and the tab increases significantly, leading to an increase in the temperature of the secondary battery, and further triggering the risk of thermal runaway. Summary of the Invention

[0003] The purpose of this application is to provide a secondary battery and an electronic device, aiming to improve the risk of thermal runaway of the secondary battery.

[0004] According to the first aspect of this application, a secondary battery is provided, which includes a first electrode plate and a second electrode plate with opposite polarities. The first electrode plate includes a first current collector and a first active layer provided on the surface of the first current collector. The first current collector includes a first polymer layer, a first metal layer, and a second metal layer, and the first metal layer and the second metal layer are respectively provided on the opposite surfaces of the first polymer layer. A first tab is provided on the surface of the first metal layer facing away from the first polymer layer. The first tab includes a first connection portion electrically connected to the first metal layer, and a first heat insulation member is provided on the surface of the first tab facing away from the first metal layer. Along the thickness direction of the first tab, the projection of the first heat insulation member overlaps at least a part of the first connection portion.

[0005] In the above technical solution, by providing that the first current collector includes a first polymer layer, a first metal layer, and a second metal layer, with the first metal layer and the second metal layer respectively disposed on the opposite two surfaces of the first polymer layer, the safety of the secondary battery can be enhanced. By providing that a first tab is disposed on the surface of the first metal layer facing away from the first polymer layer, and the first tab includes a first connecting portion electrically connected to the first metal layer, the current of the first metal layer can be transmitted to the first tab. By providing that a first heat insulating member is disposed on the surface of the first tab facing away from the first metal layer, and in the thickness direction of the first tab, the projection of the first heat insulating member overlaps at least a part of the first connecting portion, the first heat insulating member can isolate the heat of the first connecting portion, reduce the possibility of the heat of the first connecting portion diffusing to the surrounding positive and negative active materials and other structures, maintain the temperature stability of other regions inside the secondary battery, improve the problems of battery performance degradation and safety hazards caused by overheating of the positive and negative active materials, and thus improve the problem of thermal runaway caused by overheating during high-current discharge of the secondary battery.

[0006] In some preferred embodiments, in the thickness direction of the first tab, the first heat insulating member covers the first connecting portion, and the first heat insulating member can better isolate the heat of the first connecting portion.

[0007] In some preferred embodiments, in the thickness direction of the first tab, the first heat insulating member covers the first tab, and the first heat insulating member can better isolate the heat of the first tab.

[0008] In some preferred embodiments, the surface of the first metal layer facing away from the first polymer layer includes a connected coating area and an empty foil area, a first active layer is disposed in the coating area, and the first tab is disposed in the empty foil area, which can reduce the possibility of the first active layer and the first tab overlapping in the thickness direction of the first current collector, and further reduce the thickness of the secondary battery and improve the energy density of the secondary battery.

[0009] In some preferred embodiments, the thermal conductivity of the first heat insulating member ≤ 0.15 W / (m·K). The smaller the thermal conductivity of the first heat insulating member, the stronger the ability of the first heat insulating member to isolate the heat of the first connecting portion, and the better the effect of improving the diffusion of the heat of the first connecting portion to the surrounding positive and negative active materials and other structures. When the thermal conductivity of the first heat insulating member is greater than 0.15 W / (m·K), the ability of the first heat insulating member to isolate the heat of the first connecting portion is not obvious. By providing that the thermal conductivity of the first heat insulating member ≤ 0.15 W / (m·K), the ability to isolate the heat of the first connecting portion can be improved, and further the problem of the heat of the first connecting portion diffusing to the surrounding positive and negative active materials and other structures can be improved.

[0010] In some preferred embodiments, the first heat-insulating member includes at least one of ceramic fibers and ceramic particles. The ceramic fibers and ceramic particles have a low thermal conductivity, high-temperature stability, and excellent heat-insulating properties, which can reduce the possibility of heat from the first connecting portion being conducted to the second pole piece.

[0011] In some preferred embodiments, the porosity of the first heat-insulating member is ≥25%. Porosity characterizes the percentage of the pore volume in the material to its total volume in its natural state. The pore structure is filled with tiny air bubbles, and the air inside these bubbles is an excellent thermal insulator, which can prevent heat conduction, reduce the heat transfer efficiency, and thus isolate heat. The larger the porosity of the first heat-insulating member, the larger the proportion of the pore volume of the first heat-insulating member, the stronger the ability of the first heat-insulating member to isolate the heat of the first connecting portion, and the better the effect of improving the diffusion of the heat of the first connecting portion to the surrounding positive and negative electrode active materials and other structures. When the porosity of the first heat-insulating member is less than 25%, the ability of the first heat-insulating member to isolate the heat of the first connecting portion is not obvious. By setting the porosity of the first heat-insulating member to be ≥25%, the ability of the first heat-insulating member to isolate the heat of the first connecting portion can be improved, and thus the problem of the heat of the first connecting portion diffusing to the surrounding positive and negative electrode active materials and other structures can be improved.

[0012] In some preferred embodiments, the first heat-insulating member includes at least one of foam silicone rubber, aerogel, and glass fiber. Foam silicone rubber, aerogel, and glass fiber have a high porosity, which can improve the ability of the first heat-insulating member to isolate the heat of the first connecting portion.

[0013] In some preferred embodiments, the coefficient of thermal expansion of the first heat-insulating member is ≥50×10 -6 / K. The coefficient of thermal expansion characterizes the degree of expansion of the material when heated. When the material expands when heated, tiny cracks or air bubbles will be generated inside the material. These structures can hinder the rapid transfer of heat. In addition, the deformation caused by thermal expansion can increase the complexity of the heat conduction path, reduce the efficiency of heat passing through the material, and thus isolate heat. The larger the coefficient of thermal expansion of the first heat-insulating member, the greater the degree of expansion of the first heat-insulating member when heated, the stronger the ability of the first heat-insulating member to isolate the heat of the first connecting portion, and the better the effect of improving the diffusion of the heat of the first connecting portion to the surrounding positive and negative electrode active materials and other structures. When the coefficient of thermal expansion of the first heat-insulating member is less than 50×10 -6 / K, the ability of the first heat-insulating member to isolate the heat of the first connecting portion is not obvious. By setting the coefficient of thermal expansion of the first heat-insulating member to be ≥50×10 -6 / K, the ability of the first heat-insulating member to isolate the heat of the first connecting portion can be improved, and thus the problem of the heat of the first connecting portion diffusing to the surrounding positive and negative electrode active materials and other structures can be improved.

[0014] In some preferred embodiments, the first heat insulating member includes at least one of graphite-based expandable materials, thermoplastic elastomers, ceramic-based foaming materials, vermiculite / mineral fiber-based foaming materials, and ammonium polyphosphate-based foaming materials. Graphite-based expandable materials, thermoplastic elastomers, ceramic-based foaming materials, vermiculite / mineral fiber-based foaming materials, and ammonium polyphosphate-based foaming materials have a relatively high coefficient of thermal expansion, which can enhance the ability of the first heat insulating member to isolate the heat of the first connection portion.

[0015] In some preferred embodiments, the thickness of the first heat insulating member is 10 μm to 50 μm. The greater the thickness of the first heat insulating member, the stronger the ability of the first heat insulating member to isolate the heat of the first connection portion, and the better the effect of improving the diffusion of the heat of the first connection portion to the surrounding positive and negative active materials and other structures. When the thickness of the first heat insulating member is less than 10 μm, the ability of the first heat insulating member to isolate the heat of the first connection portion is not obvious. By setting the thickness of the first heat insulating member ≥10 μm, the ability of the first heat insulating member to isolate the heat of the first connection portion can be enhanced, and further the problem of the heat of the first connection portion diffusing to the surrounding positive and negative active materials and other structures can be improved. When the thickness of the first heat insulating member is greater than 50 μm, continuing to increase the thickness of the first heat insulating member, the improvement of the ability of the first heat insulating member to isolate the heat of the first connection portion is not obvious, and it is easy to consume more energy density of the secondary battery. By setting the thickness of the first heat insulating member ≤50 μm, the energy density of the secondary battery can be increased.

[0016] In some preferred embodiments, the first connection portion, the first metal layer, and the second metal layer are connected by riveting or roll welding, so that the first tab, the first metal layer, and the second metal layer can be electrically connected and conducted, and the energy utilization rate of the first electrode sheet can be improved.

[0017] In some preferred embodiments, a second tab is provided on the surface of the second metal layer facing away from the first polymer layer. The second tab is connected to the first tab. The second tab includes a second connection portion electrically connected to the second metal layer. The current of the second metal layer can be sequentially transmitted to the second tab and the first tab. A second heat insulating member is provided on the surface of the second tab facing away from the second metal layer. Along the thickness direction of the second tab, the projection of the second heat insulating member overlaps at least a part of the second connection portion. The second heat insulating member can isolate the heat of the second connection portion, can reduce the possibility of the heat of the second connection portion diffusing to the surrounding positive and negative active materials and other structures, can keep the temperature of other regions inside the secondary battery stable, and can improve the problems of battery performance degradation and safety hazards caused by overheating of the positive and negative active materials. Thus, the problem of thermal runaway caused by overheating during high-current discharge of the secondary battery can be improved.

[0018] In some preferred embodiments, the second electrode tab includes a second current collector and a second active layer disposed on the surface of the second current collector. The second current collector includes a second polymer layer, a third metal layer, and a fourth metal layer. The third metal layer and the fourth metal layer are respectively disposed on the opposite surfaces of the second polymer layer, which can enhance the safety of the secondary battery. A third tab is disposed on the surface of the third metal layer facing away from the second polymer layer. The third tab includes a third connecting portion electrically connected to the third metal layer, and the current of the third metal layer can be transmitted to the third tab. A third heat insulator is disposed on the surface of the third tab facing away from the third metal layer. Along the thickness direction of the third tab, the projection of the third heat insulator on the third tab overlaps at least a part of the third connecting portion. The third heat insulator can isolate the heat of the third connecting portion, reduce the possibility of the heat of the third connecting portion diffusing to the surrounding positive and negative active materials and other structures, maintain the temperature stability of other regions inside the secondary battery, improve the degradation of battery performance and potential safety hazards caused by overheating of the positive and negative active materials, and thus improve the problem of thermal runaway caused by overheating during high-current discharge of the secondary battery.

[0019] In a second aspect, the present application also provides an electronic device, including the secondary battery according to any one of the embodiments in the first aspect above.

[0020] Additional aspects and advantages of the embodiments of the present application will be described, shown, or elucidated in part in the subsequent description, or through the implementation of the embodiments of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] One or more embodiments are illustrated by corresponding drawings. These illustrative descriptions do not constitute a limitation on the embodiments. Elements with the same reference numerals in the drawings are represented as similar elements, unless otherwise stated, and the dimensions in the drawings do not constitute a proportional limitation.

[0022] Figure 1 Schematic diagram of the structure of the secondary battery according to some embodiments of the present application;

[0023] Figure 2 Schematic diagram of the structure of the electrode assembly according to some embodiments of the present application;

[0024] Figure 3 Schematic diagram of the structure of the electrode assembly and the first heat insulator according to some embodiments of the present application;

[0025] Figure 4 Schematic diagram of the structure of the electrode assembly, the first heat insulator, and the second heat insulator according to some embodiments of the present application;

[0026] Figure 5 Schematic diagram of the structure of the electrode assembly, the first heat insulator, and the third heat insulator according to some embodiments of the present application.

[0027] Description of the reference numerals in the drawings:

[0028] 100. Secondary battery; 10. Case; 20. Electrode assembly; 21. First electrode tab; 211. First current collector; 2111. First polymer layer; 2112. First metal layer; 211a. Coated area; 211b. Uncoated foil area; 2113. Second metal layer; 212. First active layer; 22. Second electrode tab; 221. Second current collector; 2211. Second polymer layer; 2212. Third metal layer; 2213. Fourth metal layer; 222. Second active layer; 23. Separator; 241. First tab; 2411. First connection part; 242. Second tab; 2421. Second connection part; 243. Third tab; 2431. Third connection part; 251. First heat insulator; 252. Second heat insulator; 253. Third heat insulator; X. First direction. Detailed implementation manners

[0029] To make the objectives, technical solutions, and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be clearly described below with reference to the accompanying drawings in the embodiments of the present application. Obviously, the described embodiments are some, but not all, of the embodiments of the present application.

[0030] Referring to "embodiments" in the present application means that specific features, structures, or characteristics described in connection with the embodiments can be included in at least one embodiment of the present application. The phrase appears in various places in the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment mutually exclusive with other embodiments.

[0031] In the description of the embodiments of the present application, technical terms such as "first" and "second" are only used to distinguish different objects, and cannot be understood as indicating or implying relative importance or implicitly specifying the quantity, specific order, or primary-secondary relationship of the indicated technical features. In the description of the embodiments of the present application, "a plurality of" means two or more, unless otherwise specifically defined.

[0032] In the description of the embodiments of the present application, the term "and / or" is only a description of the association relationship of associated objects, indicating that three relationships may exist. For example, A and / or B may represent: A exists alone, A and B exist simultaneously, and B exists alone. In addition, the character " / " in this article generally represents an "or" relationship between the associated objects before and after.

[0033] The term "vertical" is used to describe the ideal state between two components. In the actual production or use state, there can be a state approximately vertical between two components. For example, in combination with numerical description, vertical can refer to the included angle range between two straight lines being between 90 ± 10°, vertical can also refer to the dihedral angle range between two planes being between 90 ± 10°, and vertical can further refer to the included angle range between a straight line and a plane being between 90 ± 10°. The two components described as "vertical" may not be absolute straight lines or planes, and can also be approximately straight lines or planes. From a macroscopic perspective, as long as the overall extension direction is a straight line or a plane, the components can be considered "straight lines" or "planes".

[0034] In different embodiments of the present application described below, the technical features involved can be combined with each other as long as they do not conflict with each other.

[0035] In a first aspect, an embodiment of the present application provides a secondary battery 100. Please refer to Figure 1 , the secondary battery 100 includes a housing 10 and an electrode assembly 20. The housing 10 can accommodate the electrode assembly 20 and an electrolyte (not shown in the figure), and the electrolyte infiltrates the electrode assembly 20 within the housing 10.

[0036] Regarding the above electrode assembly 20, please refer to Figure 2 , Figure 2 shows the winding structure of the electrode assembly 20. The electrode assembly 20 includes a first electrode tab 21, a separator 23, and a second electrode tab 22. The polarities of the first electrode tab 21 and the second electrode tab 22 are opposite, and a separator 23 is disposed between the adjacent second electrode tab 22 and the first electrode tab 21. The first electrode tab 21, the separator 23, and the second electrode tab 22 are stacked and wound. Exemplarily, along the thickness direction of the first electrode tab 21 and / or the second electrode tab 22, after the first electrode tab 21, the separator 23, and the second electrode tab 22 are stacked in sequence, they are wound to form a wound electrode assembly 20. In the embodiment of the present application, the electrode assembly 20 is taken as an example of a winding structure for illustration. In some other embodiments, the electrode assembly 20 can also be a stacked structure. For example, along the thickness direction of the first electrode tab 21 and / or the second electrode tab 22, the first electrode tab 21, the separator 23, and the second electrode tab 22 are stacked in sequence to form a stacked electrode assembly 20.

[0037] In some embodiments, please refer to Figure 3 , the first electrode tab 21 includes a first current collector 211 and a first active layer 212, and the first active layer 212 is disposed on the surface of the first current collector 211. In some embodiments, the first electrode tab 21 can be a positive electrode tab, and in some other embodiments, the first electrode tab 21 can be a negative electrode tab.

[0038] In some embodiments, the first current collector 211 includes a first metal layer 2112, a first polymer layer 2111, and a second metal layer 2113. Along the thickness direction (the first direction X) of the first current collector 211, the first metal layer 2112 and the second metal layer 2113 are respectively disposed on opposite surfaces of the first polymer layer 2111. The first polymer layer 2111 serves as the main mechanical support layer of the first current collector 211 and may include at least one of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), polyimide, polytetrafluoroethylene, and polyester. The first metal layer 2112 may include at least one of aluminum, copper, nickel, titanium, silver, and zirconium. The second metal layer 2113 may include at least one of aluminum, copper, nickel, titanium, silver, and zirconium. By using the first polymer layer 2111 as the main mechanical support layer, the first current collector 211 can reduce the thickness of the metal layer, thereby reducing the metal burrs generated during mechanical damage of the secondary battery 100 and reducing the mass of the first current collector 211, thus improving the mass energy density of the secondary battery 100. In some other embodiments, the first current collector 211 may be a single-layer metal foil, and the single-layer metal foil may include at least one of aluminum, copper, nickel, titanium, and silver.

[0039] In some embodiments, the first metal layer 2112 and the second metal layer 2113 are respectively disposed on opposite surfaces of the first polymer layer 2111 by electroplating. In some embodiments, the first metal layer 2112 and the second metal layer 2113 are respectively disposed on opposite surfaces of the first polymer layer 2111 by evaporation coating.

[0040] In some embodiments, a first active layer 212 is disposed on the surface of the first metal layer 2112 facing away from the first polymer layer 2111. In some embodiments, a first active layer 212 is disposed on the surface of the second metal layer 2113 facing away from the first polymer layer 2111, which can reduce the number of layers of the first electrode sheet 21 in the secondary battery 100, thereby improving the energy density.

[0041] In some embodiments, the first active layer 212 is infiltrated by the above-mentioned electrolyte in the housing 10 to undergo an electrochemical reaction. The first active layer 212 includes a positive electrode active material, a conductive agent, a binder, etc. The above-mentioned materials are mixed and stirred evenly and then coated on the surface of the first metal layer 2112 facing away from the first polymer layer 2111 to obtain the first active layer 212. The positive electrode active material may include at least one of lithium nickel cobalt manganate, lithium cobaltate, lithium iron phosphate, lithium nickel cobalt aluminate, lithium manganate, and lithium manganese iron phosphate.

[0042] In some embodiments, a first tab 241 is provided on the surface of the first metal layer 2112 facing away from the first polymer layer 2111. The first tab 241 includes a first connecting portion 2411 electrically connected to the first metal layer 2112, and the current of the first metal layer 2112 can be transmitted to the first tab 241. Since the first metal layer 2112 is relatively thin and the contact area between the first connecting portion 2411 and the first tab 241 is small, the electrical connection resistance between the first connecting portion 2411 and the first tab 241 increases. In this case, during the large current charge and discharge process, the Joule heat generated at the connection between the first connecting portion 2411 and the first tab 241 increases significantly, resulting in an increase in the temperature of the secondary battery 100, and further leading to the risk of thermal runaway.

[0043] To improve the above problems, in the embodiments of the present application, a first heat insulating member 251 is provided on the surface of the first tab 241 facing away from the first metal layer 2112. Along the thickness direction of the first tab 241, the projection of the first heat insulating member 251 overlaps at least a part of the first connecting portion 2411. The first heat insulating member 251 can isolate the heat of the first connecting portion 2411, reduce the possibility of the heat of the first connecting portion 2411 diffusing to the surrounding positive and negative active materials and other structures, keep the temperature of other areas inside the secondary battery 100 stable, improve the battery performance degradation and safety hazards caused by overheating of the positive and negative active materials, and thus can improve the problem of thermal runaway of the secondary battery 100 due to overheating during large current discharge.

[0044] In some embodiments, along the thickness direction of the first tab 241, the first heat insulating member 251 covers the first connecting portion 2411, and the first heat insulating member 251 can better isolate the heat of the first connecting portion 2411.

[0045] In some embodiments, along the thickness direction of the first tab 241, the first heat insulating member 251 covers the first tab 241, and the first heat insulating member 251 can better isolate the heat of the first tab 241.

[0046] In some embodiments, the surface of the first metal layer 2112 facing away from the first polymer layer 2111 includes a connected coating area 211a and a bare foil area 211b. The first active layer 212 is provided in the coating area 211a, and the first tab 241 is provided in the bare foil area 211b, which can reduce the possibility of the first active layer 212 and the first tab 241 overlapping in the thickness direction of the first current collector 211, and further can reduce the thickness of the secondary battery 100 and improve the energy density of the secondary battery 100.

[0047] In some embodiments, the thermal conductivity of the first heat insulation member 251 is ≤ 0.15 W / (m·K). The smaller the thermal conductivity of the first heat insulation member 251, the stronger the ability of the first heat insulation member 251 to isolate the heat of the first connection portion 2411, and the better the effect of improving the diffusion of the heat of the first connection portion 2411 to the surrounding positive and negative electrode active materials and other structures. When the thermal conductivity of the first heat insulation member 251 is greater than 0.15 W / (m·K), the ability of the first heat insulation member 251 to isolate the heat of the first connection portion 2411 is not obvious. By setting the thermal conductivity of the first heat insulation member 251 to ≤ 0.15 W / (m·K), the ability to isolate the heat of the first connection portion 2411 can be improved, and thus the problem of the heat of the first connection portion 2411 diffusing to the surrounding positive and negative electrode active materials and other structures can be improved.

[0048] In some embodiments, the first heat insulation member 251 includes at least one of ceramic fiber and ceramic particles. Ceramic fiber and ceramic particles have low thermal conductivity, and have high-temperature stability and excellent heat insulation performance, which can reduce the possibility of the heat of the first connection portion 2411 being conducted to the second pole piece 22. The first heat insulation member 251 can also be a glue film filled with ceramic fiber or ceramic particles.

[0049] In some embodiments, the porosity of the first heat insulation member 251 is ≥ 25%. Porosity characterizes the percentage of the pore volume in the material to its total volume in its natural state. The pore structure is filled with tiny air bubbles, and the air in these bubbles is an excellent thermal insulator, which can prevent heat conduction, reduce the heat transfer efficiency, and thus isolate heat. The larger the porosity of the first heat insulation member 251, the larger the proportion of the pore volume of the first heat insulation member 251, and the stronger the ability of the first heat insulation member 251 to isolate the heat of the first connection portion 2411, and the better the effect of improving the diffusion of the heat of the first connection portion 2411 to the surrounding positive and negative electrode active materials and other structures. When the porosity of the first heat insulation member 251 is less than 25%, the ability of the first heat insulation member 251 to isolate the heat of the first connection portion 2411 is not obvious. By setting the porosity of the first heat insulation member 251 to ≥ 25%, the ability of the first heat insulation member 251 to isolate the heat of the first connection portion 2411 can be improved, and thus the problem of the heat of the first connection portion 2411 diffusing to the surrounding positive and negative electrode active materials and other structures can be improved.

[0050] In some embodiments, the first heat insulation member 251 includes at least one of foamed silicone rubber, aerogel, and glass fiber. Foamed silicone rubber, aerogel, and glass fiber have high porosity, which can improve the ability of the first heat insulation member 251 to isolate the heat of the first connection portion 2411.

[0051] In some embodiments, the coefficient of thermal expansion of the first heat insulation member 251 is ≥ 50×10 -6 / K. The coefficient of thermal expansion characterizes the degree of expansion of a material when heated. When the material expands upon heating, tiny cracks or bubbles will be generated inside the material, and these structures can impede the rapid transfer of heat. In addition, the deformation caused by thermal expansion can increase the complexity of the heat conduction path, reduce the efficiency of heat passing through the material, and thus insulate heat. The greater the coefficient of thermal expansion of the first heat insulation member 251, the greater the degree of expansion of the first heat insulation member 251 when heated, and the stronger the ability of the first heat insulation member 251 to insulate the heat of the first connection portion 2411, and the better the effect of improving the diffusion of the heat of the first connection portion 2411 to the surrounding positive and negative active materials and other structures. When the coefficient of thermal expansion of the first heat insulation member 251 is less than 50×10 -6 / K, the ability of the first heat insulation member 251 to insulate the heat of the first connection portion 2411 is not obvious. By setting the coefficient of thermal expansion of the first heat insulation member 251 ≥ 50×10 -6 / K, the ability of the first heat insulation member 251 to insulate the heat of the first connection portion 2411 can be improved, and thus the problem of the diffusion of the heat of the first connection portion 2411 to the surrounding positive and negative active materials and other structures can be improved.

[0052] In some embodiments, the first heat insulation member 251 includes at least one of graphite-based expandable materials, thermoplastic elastomers, ceramic-based foaming materials, vermiculite / mineral fiber-based foaming materials, and ammonium polyphosphate-based foaming materials. Graphite-based expandable materials, thermoplastic elastomers, ceramic-based foaming materials, vermiculite / mineral fiber-based foaming materials, and ammonium polyphosphate-based foaming materials have relatively high coefficients of thermal expansion, and can improve the ability of the first heat insulation member 251 to insulate the heat of the first connection portion 2411.

[0053] In some embodiments, the thickness H of the first heat insulation member 251 is 10 μm to 50 μm. The greater the thickness of the first heat insulation member 251, the stronger the ability of the first heat insulation member 251 to insulate the heat of the first connection portion 2411, and the better the effect of improving the diffusion of the heat of the first connection portion 2411 to the surrounding positive and negative active materials and other structures. When the thickness of the first heat insulation member 251 is less than 10 μm, the ability of the first heat insulation member 251 to insulate the heat of the first connection portion 2411 is not obvious. By setting the thickness of the first heat insulation member 251 ≥ 10 μm, the ability of the first heat insulation member 251 to insulate the heat of the first connection portion 2411 can be improved, and thus the problem of the diffusion of the heat of the first connection portion 2411 to the surrounding positive and negative active materials and other structures can be improved. When the thickness of the first heat insulation member 251 is greater than 50 μm, continuing to increase the thickness of the first heat insulation member 251, the improvement of the ability of the first heat insulation member 251 to insulate the heat of the first connection portion 2411 is not obvious, and it is easy to consume more energy density of the secondary battery 100. By setting the thickness of the first heat insulation member 251 ≤ 50 μm, the energy density of the secondary battery 100 can be improved.

[0054] In some embodiments, the first connecting portion 2411, the first metal layer 2112, and the second metal layer 2113 are connected by riveting or roll welding, so that the first tab 241, the first metal layer 2112, and the second metal layer 2113 can be electrically connected and conducted, which can improve the energy utilization rate of the first electrode sheet 21.

[0055] In some embodiments, please refer to Figure 4 , on the surface of the second metal layer 2113 facing away from the first polymer layer 2111, a second tab 242 is provided. The second tab 242 is connected to the first tab 241. The second tab 242 includes a second connecting portion 2421 electrically connected to the second metal layer 2113. The current of the second metal layer 2113 can be sequentially transmitted to the second tab 242 and the first tab 241. On the surface of the second tab 242 facing away from the second metal layer 2113, a second heat insulation member 252 is provided. Along the thickness direction of the second tab 242, the projection of the second heat insulation member 252 overlaps at least part of the second connecting portion 2421. The second heat insulation member 252 can isolate the heat of the second connecting portion 2421, can reduce the possibility of the heat of the second connecting portion 2421 diffusing to the surrounding positive and negative active materials and other structures, can maintain the temperature stability of other regions inside the secondary battery 100, and can improve the degradation of battery performance and safety hazards caused by overheating of the positive and negative active materials, thereby improving the problem of thermal runaway caused by overheating during high-current discharge of the secondary battery 100.

[0056] In some embodiments, please refer to Figure 5, the second electrode sheet 22 includes a second current collector 221 and a second active layer 222 provided on the surface of the second current collector 221. The second current collector 221 includes a second polymer layer 2211, a third metal layer 2212, and a fourth metal layer 2213. The third metal layer 2212 and the fourth metal layer 2213 are respectively provided on the opposite two surfaces of the second polymer layer 2211. This can reduce the thickness of the metal layer of the second current collector 221, improve the energy density of the secondary battery 100, and enhance the safety of the secondary battery 100. A third tab 243 is provided on the surface of the third metal layer 2212 facing away from the second polymer layer 2211. The third tab 243 includes a third connecting portion 2431 electrically connected to the third metal layer 2212, and the current of the third metal layer 2212 can be transmitted to the third tab 243. A third heat insulator 253 is provided on the surface of the third tab 243 facing away from the third metal layer 2212. Along the thickness direction of the third tab 243, the projection of the third heat insulator 253 on the third tab 243 overlaps at least a part of the third connecting portion 2431. The third heat insulator 253 can isolate the heat of the third connecting portion 2431, reduce the possibility of the heat of the third connecting portion 2431 diffusing to the surrounding positive and negative active materials and other structures, maintain the temperature stability of other regions inside the secondary battery 100, improve the battery performance degradation and safety hazards caused by overheating of the positive and negative active materials, and thus improve the problem of thermal runaway of the secondary battery 100 due to overheating during high-current discharge.

[0057] In some embodiments, the second polymer layer 2211 may include at least one of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE). The third metal layer 2212 may include at least one of aluminum, copper, nickel, titanium, and silver. The second current collector 221 uses the second polymer layer 2211 as the main mechanical support layer, which can thin the metal layer, thereby reducing the metal burrs generated during mechanical damage of the secondary battery 100 and reducing the mass of the second current collector 221, thus improving the mass energy density of the secondary battery 100.

[0058] In some embodiments, the second active layer 222 is infiltrated by the above-mentioned electrolyte inside the housing 10 to undergo an electrochemical reaction. The second active layer 222 includes a negative electrode active material, a conductive agent, a binder, etc. The above-mentioned materials are mixed and stirred evenly and then coated on the surface of the second current collector 221 to obtain the second active layer 222. The negative electrode active material may include at least one of graphite, silicon, hard carbon, and carbon fiber.

[0059] In the second aspect of the present application, an electronic device is further proposed, which includes the secondary battery 100 as described in any embodiment of the first aspect above. The electronic device in the embodiments of the present application is not particularly limited, and it can be any electronic device known in the prior art. For example, the electronic device includes but is not limited to Bluetooth headsets, mobile phones, tablets, laptop computers, electric toys, electric tools, battery cars, electric vehicles, ships, spacecraft, and so on. Among them, the electric toy can include fixed or mobile electric toys, such as game consoles, electric vehicle toys, electric ship toys, and electric aircraft toys, etc., and the spacecraft can include airplanes, rockets, space shuttles, and spaceships, etc.

[0060] Test part:

[0061] 1. External short-circuit test of the secondary battery:

[0062] Place the secondary battery sample in a test environment of 25±2°C, and short-circuit the positive and negative electrodes of the sample with a load resistor of 40±20 mΩ until one of the following conditions is reached to end the test: 1) Stop when the sample voltage is lower than 0.1 V and the surface temperature drops to the test environment temperature ±10°C; 2) If the sample voltage cannot drop to 0.1 V, stop when the surface temperature drops to the test environment temperature.

[0063] Passing standard: After the above steps, the secondary battery sample does not explode, the surface temperature of the sample does not exceed 150°C, and it does not catch fire to pass.

[0064] Example 1

[0065] <Preparation of the first electrode sheet>:

[0066] The first electrode sheet is a positive electrode sheet. Mix the positive active material lithium cobalt oxide (LiCoO2), carbon black (Super P), and polyvinylidene fluoride (PVDF) according to a weight ratio of 97.5:1.0:1.5, add N-methylpyrrolidone (NMP) as a solvent, and formulate a slurry with a solid content of 75 wt%, and stir evenly.

[0067] Select polyethylene terephthalate as the first polymer layer, the thickness of the first polymer layer is 6 μm, and a first metal layer and a second metal layer made of aluminum with a thickness of 1.5 μm are provided on both surfaces of the first polymer layer to obtain a first current collector. Coat the above slurry in the coating area on the surface of the first current collector and leave an empty foil area. Dry the slurry to obtain a first electrode sheet with a first active layer coated on the surface.

[0068] <Preparation of the second electrode sheet>:

[0069] The second electrode is the negative electrode. Graphite is used as the negative active material. The negative active material graphite, binder styrene-butadiene rubber (SBR), and thickener sodium carboxymethyl cellulose (CMC) are mixed in a weight ratio of 96:2:2. Deionized water is added as a solvent to prepare a slurry with a solid content of 70 wt%, and it is stirred evenly.

[0070] Copper foil is selected as the second current collector. The above slurry is coated on the surface of the second current collector and an empty foil area is reserved. The slurry is dried to obtain the second electrode with the second active layer coated on the surface.

[0071] <Preparation of separator>:

[0072] Using a polyethylene porous membrane as the base layer, a ceramic layer containing alumina ceramic and PVDF binder is coated on one side surface of the base layer as the separator (CCS). Among them, the mass percentage content of alumina ceramic in the ceramic layer is 95%.

[0073] <Preparation of electrolyte>:

[0074] In a dry argon atmosphere, first, ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) are mixed in a mass ratio of EC:EMC:DEC = 30:50:20 to form a basic organic solvent. Then, lithium salt lithium hexafluorophosphate (LiPF6) is added to the basic organic solvent and dissolved and mixed evenly to obtain an electrolyte with a LiPF6 mass concentration of 12.5%.

[0075] <Preparation of secondary battery>:

[0076] Aluminum foil with a length of 38 mm, a width of 6 mm, and a thickness of 80 μm is selected as the first tab. The first tab is provided in the empty foil area of the first metal layer. The first tab includes a first connecting portion electrically connected to the first metal layer. A first heat insulation member is provided on the surface of the first tab facing away from the first metal layer. The first heat insulation member is a ceramic fiber with a thickness of 20 μm, and the thermal conductivity of the first heat insulation member is 0.15 W / (m·K). Along the thickness direction of the first tab, the first heat insulation member covers the first connecting portion. The first electrode, separator, and second electrode are stacked in sequence and then wound to obtain an electrode assembly. The electrode assembly is placed in an aluminum-plastic film packaging bag, dried, and then injected with electrolyte. After processes such as vacuum packaging, standing, formation, capacity measurement, degassing, and trimming, a secondary battery is obtained.

[0077] The relevant parameters in Comparative Example 1 and Examples 1 to 7 are shown in Table 1 below.

[0078] Among them, the thermal conductivities of the first heat insulation members in Examples 1 to 3 are different, and the thicknesses of the first heat insulation members in Example 1 and Examples 4 to 7 are different.

[0079] Table 1

[0080]

[0081]

[0082] Note: In Table 1, "\ " means that the parameter is not included.

[0083] According to the above Table 1, combined with Comparative Example 1 and Examples 1 to 7, it can be seen that by providing a first heat insulating member on the surface of the first tab away from the first metal layer, in the thickness direction of the first tab, the projection of the first heat insulating member overlaps at least a part of the first connecting portion. The first heat insulating member can isolate the heat of the first connecting portion, reduce the possibility of the heat of the first connecting portion diffusing to the surrounding positive and negative active materials and other structures, keep the temperature of other areas inside the secondary battery stable, improve the problems of battery performance degradation and safety hazards caused by overheating of the positive and negative active materials, and thus can improve the problem of thermal runaway caused by overheating during high-current discharge of the secondary battery. Therefore, the passing rate of the external short-circuit test of the secondary battery can be improved.

[0084] Combined with Examples 1 to 3, it can be seen that the smaller the thermal conductivity of the first heat insulating member, the stronger the ability of the first heat insulating member to isolate the heat of the first connecting portion, and the better the effect of improving the diffusion of the heat of the first connecting portion to the surrounding positive and negative active materials and other structures. Therefore, the higher the passing rate of the external short-circuit test of the secondary battery. When the thermal conductivity of the first heat insulating member is greater than 0.15 W / (m·K), the ability of the first heat insulating member to isolate the heat of the first connecting portion is not obvious. By setting the thermal conductivity of the first heat insulating member ≤ 0.15 W / (m·K), the ability to isolate the heat of the first connecting portion can be improved, and further the problem of the heat of the first connecting portion diffusing to the surrounding positive and negative active materials and other structures can be improved, and the passing rate of the external short-circuit test of the secondary battery can be improved.

[0085] Combined with Examples 4 to 7, it can be seen that the larger the thickness of the first heat insulating member, the stronger the ability of the first heat insulating member to isolate the heat of the first connecting portion, and the better the effect of improving the diffusion of the heat of the first connecting portion to the surrounding positive and negative active materials and other structures. Therefore, the higher the passing rate of the external short-circuit test of the secondary battery. When the thickness of the first heat insulating member is less than 10 μm, the ability of the first heat insulating member to isolate the heat of the first connecting portion is not obvious. By setting the thickness of the first heat insulating member ≥ 10 μm, the ability of the first heat insulating member to isolate the heat of the first connecting portion can be improved, and further the problem of the heat of the first connecting portion diffusing to the surrounding positive and negative active materials and other structures can be improved, and the passing rate of the external short-circuit test of the secondary battery can be improved. When the thickness of the first heat insulating member is greater than 50 μm, continuing to increase the thickness of the first heat insulating member, the improvement of the ability of the first heat insulating member to isolate the heat of the first connecting portion is not obvious, and it is easy to consume more energy density of the secondary battery. By setting the thickness of the first heat insulating member ≤ 50 μm, the energy density of the secondary battery can be improved.

[0086] The relevant parameters in Comparative Example 1 and Examples 8 to 10 are shown in Table 2 below.

[0087] Among them, the material of the first heat insulation member in Examples 8 to 10 is foam silicone rubber, and the porosity of the first heat insulation member in Examples 8 to 10 is different.

[0088] Table 2

[0089]

[0090] Note: In Table 2, "\ " means that the parameter is not included.

[0091] According to Table 2 above, in combination with Comparative Example 1 and Examples 8 to 10, it can be seen that the porosity characterizes the percentage of the pore volume in the material to the total volume in its natural state. The pore structure is filled with tiny air bubbles, and the air in these bubbles is an excellent thermal insulator, which can prevent heat conduction, reduce the heat transfer efficiency, and thus isolate heat. The larger the porosity of the first heat insulation member, the larger the proportion of the pore volume of the first heat insulation member, the stronger the ability of the first heat insulation member to isolate the heat of the first connection part, and the better the effect of improving the diffusion of the heat of the first connection part to the surrounding positive and negative active materials and other structures. Therefore, the passing rate of the external short-circuit test of the secondary battery is higher. When the porosity of the first heat insulation member is less than 25%, the ability of the first heat insulation member to isolate the heat of the first connection part is not obvious. By setting the porosity of the first heat insulation member ≥ 25%, the ability of the first heat insulation member to isolate the heat of the first connection part can be improved, and then the problem of the diffusion of the heat of the first connection part to the surrounding positive and negative active materials and other structures can be improved, and the passing rate of the external short-circuit test of the secondary battery can be increased.

[0092] The relevant parameters in Comparative Example 1 and Examples 11 to 13 are shown in Table 3 below.

[0093] Among them, the material of the first heat insulation member in Examples 11 to 13 is expanded graphite, and the thermal expansion coefficients of the first heat insulation members in Examples 11 to 13 are different.

[0094] Table 3

[0095]

[0096]

[0097] Note: In Table 3, "\ " means that the parameter is not included.

[0098] According to Table 3 above, in combination with Comparative Example 1 and Examples 11 to 13, it can be seen that the coefficient of thermal expansion characterizes the degree of expansion of a material when heated. When the material expands upon heating, tiny cracks or bubbles will be generated inside the material, and these structures can impede the rapid transfer of heat. In addition, the deformation caused by thermal expansion can increase the complexity of the heat conduction path and reduce the efficiency of heat passing through the material, thereby insulating heat. The greater the coefficient of thermal expansion of the first heat insulation member, the greater the degree of expansion of the first heat insulation member when heated, the stronger the ability of the first heat insulation member to insulate the heat of the first connection portion, and the better the effect of improving the diffusion of the heat of the first connection portion to the surrounding positive and negative active materials and other structures. Therefore, the passing rate of the external short-circuit test of the secondary battery is higher. When the coefficient of thermal expansion of the first heat insulation member is less than 50×10 -6 / K, the ability of the first heat insulation member to insulate the heat of the first connection portion is not obvious. By setting the coefficient of thermal expansion of the first heat insulation member ≥50×10 -6 / K, the ability of the first heat insulation member to insulate the heat of the first connection portion can be improved, and further, the problem of the heat of the first connection portion diffusing to the surrounding positive and negative active materials and other structures can be improved, and the passing rate of the external short-circuit test of the secondary battery can be increased.

[0099] The above are only the embodiments of the present application, and do not limit the patent scope of the present application accordingly. Any equivalent structure or equivalent process transformation made by using the content of the specification and drawings of the present application, or directly or indirectly applied in other related technical fields, shall be equally included in the patent protection scope of the present application.

Claims

1. A secondary battery, comprising a first pole piece and a second pole piece with opposite polarities, wherein the first pole piece comprises a first current collector and a first active layer disposed on a surface of the first current collector, the first current collector comprises a first polymer layer, a first metal layer and a second metal layer, and the first metal layer and the second metal layer are disposed on opposite surfaces of the first polymer layer, respectively; It is characterized in that A first pole lug is arranged on a surface of the first metal layer facing away from the first polymer layer, the first pole lug includes a first connecting portion electrically connected to the first metal layer, a first thermal insulation member is arranged on a surface of the first pole lug facing away from the first metal layer, and along the thickness direction of the first pole lug, a projection of the first thermal insulation member overlaps with at least part of the first connecting portion.

2. The secondary battery according to claim 1, characterized in that: The first heat insulating member covers the first connecting portion along a thickness direction of the first electrode tab.

3. The secondary battery according to claim 2, characterized in that: The first thermal insulation member covers the first electrode tab along a thickness direction of the first electrode tab.

4. The secondary battery according to claim 1, characterized in that: The surface of the first metal layer facing away from the first polymer layer includes a connected coating area and a hollow foil area, the coating area is provided with the first active layer, and the first electrode tab is provided in the hollow foil area.

5. The secondary battery according to claim 1, characterized in that: The thermal conductivity of the first thermal insulation member is ≤0.15 W / (m·K).

6. The secondary battery according to claim 5, characterized in that: The first thermal insulation component includes at least one of ceramic fibers and ceramic particles.

7. The secondary battery according to claim 1, characterized in that: The porosity of the first thermal insulation component is ≥25%.

8. The secondary battery according to claim 7, characterized in that: The first thermal insulation member includes at least one of foam silicone rubber, aerogel and glass fiber.

9. The secondary battery according to claim 1, characterized in that: The thermal expansion coefficient of the first thermal insulation member is ≥50×10 -6 / K.

10. The secondary battery according to claim 9, characterized in that: The first thermal insulation member includes at least one of a graphite-based intumescent material, a thermoplastic elastomer, a ceramic-based intumescent material, a vermiculite / mineral fiber-based intumescent material, and an ammonium polyphosphate-based intumescent material.

11. The secondary battery according to any one of claims 5 to 10, characterized in that: The first thermal insulation member has a thickness of 10 μm to 50 μm.

12. The secondary battery according to claim 1, characterized in that: The first connecting portion, the first metal layer and the second metal layer are connected by riveting or roller welding.

13. The secondary battery according to claim 1, characterized in that: A second pole lug is provided on the surface of the second metal layer facing away from the first polymer layer, the second pole lug is connected to the first pole lug, the second pole lug includes a second connecting portion electrically connected to the second metal layer, and a second thermal insulation member is provided on the surface of the second pole lug facing away from the second metal layer, and along the thickness direction of the second pole lug, the projection of the second thermal insulation member overlaps with at least part of the second connecting portion.

14. The secondary battery according to any one of claims 1 to 4, characterized in that: The second pole piece includes a second current collector and a second active layer disposed on the surface of the second current collector, the second current collector includes a second polymer layer, a third metal layer and a fourth metal layer, and the third metal layer and the fourth metal layer are disposed on two opposite surfaces of the second polymer layer respectively; A third pole lug is arranged on a surface of the third metal layer facing away from the second polymer layer, and the third pole lug includes a third connecting portion electrically connected to the third metal layer. A third thermal insulation member is arranged on a surface of the third pole lug facing away from the third metal layer, and along the thickness direction of the third pole lug, a projection of the third pole lug of the third thermal insulation member overlaps with at least part of the third connecting portion.

15. An electronic device, characterized in that: The invention comprises the secondary battery according to any one of claims 1 to 14.

Images