Secondary battery and electronic device

Abstract

The present application discloses a secondary battery and an electronic device. In the thickness direction of a second bare foil section, a first bare foil section is located on the side of the second bare foil section facing away from a winding center; the first bare foil section is a portion of an electrode sheet adjacent to the second bare foil section; a first tab is connected to the first bare foil section; and a second tab is connected to the second bare foil section. The first tab and the second tab are respectively located on two adjacent electrode sheets; the first bare foil section located between the first tab and the second tab is a first portion; and a winding start end of a first electrode sheet is located at the first portion. In the thickness direction of the secondary battery, a first insulating layer is provided between the first portion and the second bare foil section; and the melting point of the first insulating layer is T1, wherein T1≥300℃. Melting or deformation of the first insulating layer caused by temperature rise can be reduced, and the physical properties and insulating performance of the first insulating layer can be maintained at a high temperature, such that a better insulating effect is achieved between the first portion and the second bare foil section, and short circuits caused by direct contact between the first electrode sheet and a second electrode sheet can be reduced.

Description

Secondary batteries and electronic devices Technical Field

[0001] This application relates to the field of battery technology, and in particular to a secondary battery and electronic device. Background Technology

[0002] Lithium-ion batteries are widely used in consumer electronics due to their advantages such as high energy density, light weight, small size, and long cycle life. With commercial development, the market demands increasingly higher safety standards for lithium-ion batteries. However, lithium-ion batteries generate heat during use, especially during external short circuits. This heat buildup at the tabs, where heat can accumulate between the positive and negative electrodes, potentially causing the separator between them to melt and leading to a short circuit. Summary of the Invention

[0003] This application aims to provide a secondary battery and electronic device that reduces the technical problem of short circuits in secondary batteries.

[0004] The embodiments of this application adopt the following technical solutions:

[0005] In a first aspect, this application proposes a secondary battery, including a first tab, a second tab, and an electrode assembly. The electrode assembly includes a first electrode sheet, a separator, and a second electrode sheet stacked and wound together. The first electrode sheet includes a first empty foil segment, and the second electrode sheet includes a second empty foil segment. Along the winding direction, the first empty foil segment is the winding start segment of the first electrode sheet, and the second empty foil segment is the winding start segment of the second electrode sheet. Along the thickness direction of the second empty foil segment, the first empty foil segment is located on the side of the second empty foil segment opposite to the winding center, and the first empty foil segment is an adjacent electrode sheet to the second empty foil segment. The first tab is connected to the first empty foil segment, and the second tab is connected to the second empty foil segment. Along the thickness direction of the secondary battery, the first tab and the second tab are respectively located on two adjacent electrode sheets. The first tab and the second tab are arranged along a first direction. The first empty foil segment includes a first portion. Along the first direction, the first empty foil segment located between the first tab and the second tab is the first portion, and the winding start end of the first electrode sheet is located in the first portion. Along the thickness direction of the secondary battery, a first insulating layer is provided between the first part and the second empty foil segment. The melting point of the first insulating layer is T1, and T1≥300℃.

[0006] In the above technical solution, by providing a first insulating layer between the first part and the second empty foil segment, the first part and the second empty foil segment can be insulated and separated, reducing the risk of short circuits caused by contact between the first electrode and the second electrode. Furthermore, the high melting point of the first insulating layer reduces melting or deformation due to temperature increases, maintaining its physical and insulating properties at higher temperatures, resulting in better insulation between the first part and the second empty foil segment. Simultaneously, the high melting point of the first insulating layer reduces the transfer of heat generated by the first and second electrodes to the first part and the second empty foil segment. Even in extreme situations such as thermal runaway of the secondary battery, the high melting point of the first insulating layer can, to some extent, delay the spread of the fault, improving the safety performance of the secondary battery.

[0007] For example, when the resistance of the first tab is less than that of the second tab, the heat source is mainly concentrated in the second tab. The first insulating layer can isolate the heat of the second tab from being transferred between the first part and the second empty foil segment, reducing the melting and damage of the isolation film between the first part and the second empty foil segment, thereby reducing the direct contact between the first part and the second empty foil segment and the occurrence of a short circuit.

[0008] When the resistance of the first tab is greater than that of the second tab, the heat source is mainly concentrated in the first tab. The first insulating layer can directly isolate the first part from the second empty foil segment, which can reduce the melting and damage of the isolation film between the first part and the second empty foil segment, thereby reducing the direct contact between the first part and the second empty foil segment and the occurrence of short circuit.

[0009] In some embodiments, the second electrode further includes a second coating section, and along the thickness direction of the first empty foil section, the electrode adjacent to the first empty foil section is respectively the second empty foil section and the second coating section. The secondary battery also includes a second insulating layer, which is disposed between the first portion and the second coating section along the thickness direction of the secondary battery. The melting point of the second insulating layer is T2, where T2 ≥ 300°C. The high melting point of the second insulating layer reduces melting or deformation caused by temperature increases, and maintains its physical and insulating properties at higher temperatures. Simultaneously, the high melting point of the second insulating layer reduces the heat generated by the first and second tabs from being transferred between the first portion and the second coating section, further reducing the risk of short circuits in the secondary battery and improving its safety performance.

[0010] In some embodiments, along the thickness direction of the secondary battery, a first insulating layer covers the winding start end. Covering the winding start end with a high-melting-point first insulating layer can reduce short circuits between the winding start end and the second empty foil segment, thereby improving the safety performance of the secondary battery.

[0011] In some embodiments, along the thickness direction of the secondary battery, the second insulating layer covers the winding start end. The high melting point of the second insulating layer covering the winding start end can reduce short circuits between the winding start end and the second coated section, thereby improving the safety performance of the secondary battery.

[0012] In some embodiments, the second tab and the first tab are arranged sequentially along the winding direction, the resistance of the first tab is R1, the resistance of the second tab is R2, and R1 < R2.

[0013] In some embodiments, the first electrode is a positive electrode, and the second electrode is a negative electrode. The first electrode is made of aluminum, aluminum alloy, nickel-plated aluminum, or silver-plated aluminum. The second electrode is made of nickel or stainless steel.

[0014] In some embodiments, the first insulating layer is an adhesive layer, disposed on the second empty foil segment along the thickness direction of the secondary battery. Within the projection range of the second empty foil segment, the projection of the second tab lies within the projection of the first insulating layer. The second tab, as the primary heat source, is covered by the high-melting-point first insulating layer, which prevents the heat generated by the second tab from diffusing to other areas. This helps maintain the uniformity of the internal temperature of the secondary battery, reduces local overheating and side reactions, and reduces the melting and breakage of the separator corresponding to the second tab, thereby reducing the occurrence of short circuits.

[0015] In some embodiments, a first insulating layer is disposed on a first portion. The first insulating layer is an insulating coating, which includes a ceramic material, comprising at least one of alumina, magnesium oxide, boehmite, or zirconium oxide. Alumina, magnesium oxide, boehmite, and zirconium oxide all have high melting points and thermal stability, and can maintain their insulating properties even at high temperatures. They can adapt to the high-temperature environment at the edge of the tab, enabling the secondary battery to adapt to higher charge and discharge rates.

[0016] In some embodiments, the secondary battery further includes a first adhesive layer disposed on a first empty foil segment and located between the first empty foil segment and a second empty foil segment. Along the thickness direction of the secondary battery, within the projection range of the first empty foil segment, the projection of the first electrode tab lies within the projection of the first adhesive layer, and the first adhesive layer covers at least a portion of the first portion. The first adhesive layer can also insulate against some heat and isolate the first portion from the separator, thereby reducing the risk of melting and breakage of the separator.

[0017] In some embodiments, along the thickness direction of the secondary battery, the projection of the first insulating layer and the projection of the first adhesive layer partially overlap, which allows the first adhesive layer and the first insulating layer to cover the first part, reducing the exposure of the first part and thus reducing the direct contact between the first part and the second empty foil segment, which could lead to a short circuit.

[0018] In some embodiments, the second tab and the first tab are arranged sequentially along the winding direction, the resistance of the first tab is R1, the resistance of the second tab is R2, and R1 > R2.

[0019] In some embodiments, the first electrode is a positive electrode, and the second electrode is a negative electrode. The first electrode is made of aluminum, aluminum alloy, nickel, or nickel-plated aluminum. The second electrode is made of copper, copper-nickel alloy, nickel-plated copper, copper-plated nickel, or silver-plated copper.

[0020] In some embodiments, the first tab is made of aluminum and the second tab is made of nickel-plated copper. T1 ≥ 330°C can reduce the melting or deformation of the first insulating layer caused by temperature rise, so that the first insulating layer can maintain its physical and insulating properties at higher temperatures.

[0021] In some embodiments, the first insulating layer is an adhesive layer, and the first insulating layer is disposed in the first empty foil segment. Along the thickness direction of the secondary battery, within the projection range of the first empty foil segment, the projection of the first tab lies within the projection of the first insulating layer. As the main heat source, the first tab is covered by the high-melting-point first insulating layer, which can prevent the heat generated by the first tab from diffusing to other areas, helping to maintain the uniformity of the internal temperature of the secondary battery, reducing the occurrence of side reactions due to local overheating, and reducing the melting and damage of the separator corresponding to the first tab, thereby reducing the occurrence of short circuits.

[0022] In some embodiments, the secondary battery further includes a third adhesive layer disposed on the second empty foil segment and located between the first empty foil segment and the second empty foil segment. Along the thickness direction of the secondary battery, within the projection range of the second empty foil segment, the third adhesive layer covers the second tab, and the third adhesive layer covers at least a portion of the first portion. The second adhesive layer can also prevent heat from the first tab and the second tab from diffusing to the first portion, thereby isolating the first portion from the separator and reducing the risk of melting and breakage of the separator.

[0023] In some embodiments, along the thickness direction of the secondary battery, the third adhesive layer partially overlaps with the first insulating layer, such that the third adhesive layer and the first insulating layer cover the first portion, which can reduce the exposure of the first portion and thus reduce the direct contact between the first portion and the first empty foil segment, thus reducing the occurrence of short circuits.

[0024] In some embodiments, a first insulating layer is disposed on the second empty foil segment and located between the first and second empty foil segments. The first insulating layer is an insulating coating and includes a ceramic material, which includes at least one of alumina, magnesium oxide, boehmite, or zirconium oxide. Alumina, magnesium oxide, boehmite, and zirconium oxide all have high melting points and thermal stability, and can maintain their insulating properties even at high temperatures. They can adapt to the high-temperature environment at the edge of the electrode, enabling the secondary battery to adapt to higher charge and discharge rates.

[0025] In some embodiments, along the thickness direction of the secondary battery, within the projection range of the first empty foil segment, the projection of the first tab lies within the projection of the first insulating layer. The first tab, as the primary heat source, is covered by the high-melting-point first insulating layer, which prevents the heat generated by the first tab from diffusing to other areas. This helps maintain the uniformity of the internal temperature of the secondary battery, reduces local overheating and side reactions, and reduces the melting and breakage of the separator corresponding to the first tab, thereby reducing the occurrence of short circuits.

[0026] In some embodiments, the projection of the first empty foil segment lies within the projection of the first insulating layer along its thickness direction. The first insulating layer can isolate the first and second empty foil segments, reducing foil exposure and minimizing the risk of short circuits due to direct contact between the first and second empty foil segments. Furthermore, when the first insulating layer employs an insulating coating, such as alumina, magnesium oxide, boehmite, or zirconium oxide, its thickness is smaller, reducing the space occupied by the first insulating layer and thus reducing energy density loss in the secondary battery.

[0027] In some embodiments, the second electrode further includes a second coating section. Along the thickness direction of the secondary battery, the electrode adjacent to the first empty foil section is the second empty foil section and the second coating section, respectively. A first active material layer is disposed on the surface of the second coating section away from the winding center. Along the winding direction, the length of the first insulating layer covering the first active material layer is L1, where 0.5mm ≤ L1 ≤ 2mm. Limiting L1 ≥ 0.5mm reduces the exposure of the second empty foil section, reducing the risk of short circuits due to direct contact between the second and first empty foil sections. Furthermore, limiting L1 ≤ 2mm reduces the amount of the second active material layer covered by the first insulating layer, thus reducing energy density loss in the secondary battery.

[0028] In some embodiments, the distance between the first tab and the second tab along the width direction of the secondary battery is D, where 2mm≤D≤35mm.

[0029] In some embodiments, the width of the secondary battery is W along the width direction, where 11mm ≤ W ≤ 70mm.

[0030] In some embodiments, the first insulating layer is an adhesive layer, which includes a substrate layer and an adhesive layer. The substrate layer includes at least one of polyetheretherketone, polyimide, polyetherimide, or polytetrafluoroethylene, and the adhesive layer includes at least one of rubber, silicone, or acrylic resin.

[0031] In some embodiments, the second insulating layer is an adhesive layer, which includes a substrate layer and an adhesive layer. The substrate layer includes at least one of polyetheretherketone, polyimide, polyetherimide, or polytetrafluoroethylene, and the adhesive layer includes at least one of rubber, silicone, or acrylic resin.

[0032] Secondly, this application also proposes an electronic device including a secondary battery as described in any of the embodiments of the first aspect above.

[0033] 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

[0034] One or more embodiments are illustrated by way of example with reference to the accompanying drawings. These illustrations do not constitute a limitation on the embodiments. Elements having the same reference numerals in the drawings are denoted as similar elements. Unless otherwise stated, the figures in the drawings are not to be limited by scale.

[0035] Figure 1 is a schematic diagram of the structure of a secondary battery according to some embodiments of this application;

[0036] Figure 2 is a schematic diagram of the stacked structure of the first electrode, the separator, and the second electrode in some embodiments of this application;

[0037] Figure 3 is a schematic diagram of the winding structure of the electrode assembly in some embodiments of this application;

[0038] Figure 4 is a schematic diagram of the winding structure of the electrode assembly in some embodiments of this application;

[0039] Figure 5 is a schematic diagram of the winding structure of the electrode assembly in some embodiments of this application;

[0040] Figure 6 is a schematic diagram of the winding structure of the electrode assembly in some embodiments of this application;

[0041] Figure 7 is a schematic diagram of the winding structure of the electrode assembly in some embodiments of this application;

[0042] Figure 8 is a schematic diagram of the winding structure of the electrode assembly in some embodiments of this application;

[0043] Figure 9 is a schematic diagram of the winding structure of the electrode assembly in some embodiments of this application;

[0044] Figure 10 is a schematic diagram of the winding structure of an electrode assembly according to some embodiments of this application;

[0045] Figure 11 is a schematic diagram of the winding structure of an electrode assembly according to some embodiments of this application.

[0046] Explanation of reference numerals in the attached drawings: 100, secondary battery; 10, casing; 20, electrode assembly; 21, first electrode; 211, first current collector; 212, first active material layer; 21a, first empty foil segment; 21a1, first part; 21a2, winding start end; 21b, first coated segment; 22, second electrode; 221, second current collector; 222, second active material layer; 22a, second empty foil segment; 22b, second coated segment; 23, separator; 30, first tab; 40, second tab; 51, first insulating layer; 52, second insulating layer; 61, first adhesive layer; 62, second adhesive layer; 63, third adhesive layer; 64, fourth adhesive layer; 65, fifth adhesive layer; 66, sixth adhesive layer; H, first direction; X, second direction; T, third direction; Z, fourth direction; S, winding direction; G, winding center. Detailed Implementation

[0047] 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.

[0048] 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.

[0049] 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.

[0050] 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.

[0051] 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.

[0052] 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.

[0053] 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 (fourth 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.

[0054] 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.

[0055] 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.

[0056] The first active material layer 212 can be disposed on at least one surface of the first current collector 211 in the thickness direction (fourth direction Z). The first active material layer 212 includes a positive electrode active material, a conductive agent, and a binder, etc. 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. Among them, the positive electrode active material includes one or more of lithium nickel cobalt manganese oxide, lithium cobalt oxide, lithium iron phosphate, lithium nickel cobalt manganese oxide, lithium manganese oxide, or lithium manganese iron phosphate.

[0057] Referring to Figure 2, the second electrode 22 includes a second current collector 221 and a second active material layer 222. The second current collector 221 serves as the conductive substrate of the second electrode 22 and can be made of 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.

[0058] The second active material layer 222 can be disposed on at least one surface of the second current collector 221 in the thickness direction (fourth direction Z). The second 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 second active material layer 222. The negative electrode active material includes one or more of graphite, soft carbon, hard carbon, carbon fiber, elemental silicon, silicon oxide, silicon alloy, etc.

[0059] Referring to Figures 2 and 3, the first electrode 21 includes a first empty foil segment 21a and a first coated segment 21b connected together. Along the winding direction S, the first empty foil segment 21a is the starting segment of the winding of the first electrode 21, meaning that the first empty foil segment 21a can form at least a portion of the innermost ring of the first electrode 21. The first tab 30 is connected to the first empty foil segment 21a, and the connection method includes, but is not limited to, welding or conductive adhesive bonding. In the embodiments of this application, the first empty foil segment 21a does not have an active material layer. The first empty foil segment 21a is provided on the innermost ring of the first electrode 21, which provides a clean, flat surface free from active material interference for the connection of the first tab 30. This not only facilitates the connection between the first tab 30 and the first electrode 21 but also helps to reduce the connection resistance between the first tab 30 and the first electrode 21.

[0060] The second electrode 22 includes a second empty foil segment 22a and a second coated segment 22b connected to each other. Along the winding direction S, the second empty foil segment 22a is the starting segment of the winding of the second electrode 22, that is, the second empty foil segment 22a can form at least a portion of the innermost ring of the second electrode 22. The second coated segment 22b can be single-sided coated, that is, only one side is provided with the second active material layer 222, for example, only the side away from the winding center G is provided with the second active material layer 222, which can make full use of space and is beneficial to improving the energy density of the secondary battery 100. In some other embodiments, the second coated segment 22b can also be double-sided coated. The second tab 40 is connected to the second empty foil segment 22a. Along the width direction (first direction H) of the secondary battery 100, the first tab 30 and the second tab 40 are arranged in sequence, and along the winding direction S, the second tab 40 and the first tab 30 are arranged in sequence. Along the thickness direction of the first empty foil segment 21a, the electrode adjacent to the first empty foil segment 21a are the second empty foil segment 22a and the second coated segment 22b, respectively.

[0061] In the embodiments of this application, the first tab 30 is connected to the innermost ring of the first electrode 21, and the second tab 40 is connected to the innermost ring of the second electrode 22. This optimizes the space utilization of the secondary battery 100. Preferably, the first tab 30 is a positive tab, and the second tab 40 is a negative tab. The gap space at the winding center G provides additional space for the first tab 30 and the second tab 40, making the layout of the lead-out lines of the first tab 30 and the second tab 40 more compact. Furthermore, the shorter length of the inner ring empty foil section allows for increasing the size of the first electrode 21 and the second electrode 22 or increasing the content of the active material layer without increasing the volume of the secondary battery 100, thereby improving the energy density of the secondary battery 100. Additionally, the inner ring structure is more stable, and the tabs connected to the inner ring improve the stability of the electrical connection between the tabs and the electrode.

[0062] The inventors of this application have discovered that the first tab 30 and the second tab 40, as locations where current accumulates, generate significant heat. This heat radiates outwards, potentially causing partial melting of the surrounding insulating film 23, thus increasing the risk of short circuits. For example, the first electrode 21 includes a winding start end 21a2 located between the first tab 30 and the second tab 40. The heat generated by the first tab 30 and / or the second tab 40 may even radiate to the winding start end 21a2. The winding start end 21a2 is the cutting position of the first current collector 211. To facilitate the cutting of the first current collector 211, the part near the winding start end 21a2 is usually empty foil (no active material layer or insulating layer is provided). Heat radiates to the winding start end 21a2, and the isolation membrane 23 corresponding to the part between the winding start end 21a2 and the first electrode tab 30 (the first part 21a1) may melt and break, which will directly cause the first electrode 21 and the second electrode 22 to come into contact and short circuit.

[0063] To mitigate the aforementioned issues, please refer to Figure 3. The first empty foil segment 21a includes a first portion 21a1. Along the width direction (first direction H) of the secondary battery 100, the first empty foil segment 21a located between the first electrode tab 30 and the second electrode tab 40 is the first portion 21a1, and the winding start end 21a2 of the first electrode sheet 21 is located in the first portion 21a1. In the embodiments of this application, along the thickness direction (third direction T) of the secondary battery 100, a first insulating layer 51 is provided between the first portion 21a1 and the second empty foil segment 22a. The melting point of the first insulating layer 51 is T1, where T1 ≥ 300°C.

[0064] By providing a first insulating layer 51 between the first portion 21a1 and the second empty foil segment 22a, the first portion 21a1 and the second empty foil segment 22a can be insulated and separated, reducing the risk of short circuits caused by contact between the first electrode 21 and the second electrode 22. Furthermore, the high melting point of the first insulating layer 51 reduces the melting or deformation of the first insulating layer 51 due to temperature increases, maintaining its physical and insulating properties at higher temperatures, resulting in better insulation between the first portion 21a1 and the second empty foil segment 22a. Simultaneously, the high melting point of the first insulating layer 51 reduces the transfer of heat generated by the first tab 30 and the second tab 40 to the first portion 21a1 and the second empty foil segment 22a. Even in extreme situations such as thermal runaway of the secondary battery 100, the high melting point of the first insulating layer 51 can, to some extent, delay the spread of the fault, improving the safety performance of the secondary battery 100.

[0065] For example, when the resistance of the first tab 30 is less than that of the second tab 40, the heat source is mainly concentrated in the second tab 40. The first insulating layer 51 can isolate the heat of the second tab 40 from being transferred between the first part 21a1 and the second empty foil segment 22a, reducing the melting and damage of the isolation film 23 between the first part 21a1 and the second empty foil segment 22a, thereby reducing the direct contact between the first part 21a1 and the second empty foil segment 22a and the occurrence of a short circuit.

[0066] When the resistance of the first tab 30 is greater than the resistance of the second tab 40, the heat source is mainly concentrated in the first tab 30. The first insulating layer 51 can directly isolate the first part 21a1 from the second empty foil segment 22a, which can reduce the melting and damage of the isolation film 23 between the first part 21a1 and the second empty foil segment 22a, thereby reducing the direct contact between the first part 21a1 and the second empty foil segment 22a and the occurrence of a short circuit.

[0067] In some embodiments, referring to FIG3, along the thickness direction (third direction T) of the secondary battery 100, the first insulating layer 51 covers the winding start end 21a2. The heat sources of the first tab 30 and the second tab 40 may radiate to the winding start end 21a2, which may cause the separator 23 corresponding to the winding start end 21a2 to melt and break. The high melting point of the first insulating layer 51 covering the winding start end 21a2 can reduce the short circuit between the winding start end 21a2 and the second empty foil segment 22a, thereby improving the safety performance of the secondary battery 100.

[0068] In addition, when the secondary battery 100 falls, the electrode may become misaligned and cause the winding start end 21a2 to move, which may also cause the winding start end 21a2 to puncture the separator 23. Covering the winding start end 21a2 with the first insulating layer 51 can reduce the risk of the winding start end 21a2 puncturing the separator 23.

[0069] Based on the same inventive concept, please refer to FIG3. The secondary battery 100 also includes a second insulating layer 52. Along the thickness direction (third direction T) of the secondary battery 100, the second insulating layer 52 is disposed between the first part 21a1 and the second coating section 22b. The melting point of the second insulating layer 52 is T2, and T2≥300℃.

[0070] In the embodiments of this application, the energy density of the secondary battery 100 can be improved by providing a second active material layer 222 in the second coating section 22b. However, the inventors of this application have discovered that the second active material layer 222 is relatively close to the first electrode 30 and the second electrode 40, that is, the second active material layer 222 is near the heat source. If the second coating section is the negative electrode, the risk of combustion of the second active material layer 222 is relatively high. If the second active material layer 222 is the positive electrode, the second active material layer 222 is prone to decomposition at high temperatures and is prone to side reactions, resulting in severe gas production in the secondary battery 100.

[0071] In the embodiments of this application, by providing a second insulating layer 52 between the first portion 21a1 and the second coating section 22b, the first portion 21a1 and the second coating section 22b can be insulated and separated, reducing the risk of short circuits caused by contact between the first electrode 21 and the second electrode 22. Furthermore, the high-melting-point second insulating layer 52 can reduce melting or deformation of the second insulating layer 52 due to temperature increases, maintaining its physical and insulating properties at higher temperatures, resulting in better insulation between both sides of the first portion 21a1 in the thickness direction and the second electrode 22. Simultaneously, the high-melting-point second insulating layer 52 can reduce heat transfer to the second active material layer 222, reducing the risk of combustion and decomposition of the second active material layer 222 due to heat, reducing side reactions, and reducing gas production in the secondary battery 100. Additionally, the high-melting-point second insulating layer 52 can also reduce the heat generated by the first tab 30 and the second tab 40 transferred between the first portion 21a1 and the second coating section 22b, further reducing the risk of short circuits in the secondary battery 100 and improving its safety performance.

[0072] In some embodiments, referring to FIG3, along the thickness direction (third direction T) of the secondary battery 100, the second insulating layer 52 covers the winding start end 21a2. The high melting point of the second insulating layer 52 covering the winding start end 21a2 can reduce the short circuit between the winding start end 21a2 and the second coated section 22b, thereby improving the safety performance of the secondary battery 100.

[0073] In the embodiments of this application, the first tab 30 and the second tab 40 may be made of different materials. The resistance of the first tab 30 and the second tab 40 may differ. The greater the resistance, the more severe the heat generation, and the more likely the separator 23 will melt.

[0074] The resistance value of the first tab 30 can be measured using the following method: Based on the direction of current flow on the first tab 30 when the secondary battery 100 is working, connect one end of the first tab 30 to one electrode of a measuring device (e.g., a multimeter), and connect the other end of the first tab 30 to the other electrode of the measuring device. The resistance value of the first tab 30 is then obtained based on the measured value provided by the measuring device. If the first tab 30 is welded to the first current collector 211 to form a solder mark, the first tab 30 can be cut off from the edge of the solder mark to separate it from the first current collector 211. The first tab 30 can then be electrically connected to the measuring device (e.g., a multimeter) to measure its resistance. The resistance of the second tab 40 can be measured similarly.

[0075] When the resistance of the first tab 30 is less than the resistance of the second tab 40, in some embodiments, referring to 3, the second tab 40 and the first tab 30 are arranged sequentially along the winding direction G. The resistance of the first tab 30 is R1, and the resistance of the second tab 40 is R2, where R1 < R2. For example, the first tab 30 is the positive tab, and the second tab 40 is the negative tab. The material of the first tab 30 is aluminum, aluminum alloy, nickel-plated aluminum, or silver-plated aluminum, etc. The material of the second tab 40 is nickel or stainless steel, etc.

[0076] Alternatively, the first tab 30 can be the negative tab, and the second tab 40 can be the positive tab. The first tab 30 can be made of copper, copper-nickel alloy, nickel-plated copper, copper-plated nickel, or silver-plated copper, etc. The second tab 40 can be made of aluminum, aluminum alloy, nickel, or nickel-plated aluminum, etc.

[0077] The second tab 40 has a higher resistance, and the heat source is mainly concentrated at the second tab 40. In the embodiments of this application, the first insulating layer 51 may be an adhesive layer, which includes a substrate layer and an adhesive layer. The substrate layer includes at least one of polyetheretherketone (melting point around 343°C), polyimide (melting point varies depending on the specific type and structure, usually between 300°C and 400°C), polyetherimide (melting point usually between 343°C and 393°C, the specific value depends on the grade and structure), or polytetrafluoroethylene (melting point around 327°C). The adhesive layer includes at least one of rubber, silicone, or acrylic resin.

[0078] Referring to Figure 3, the first insulating layer 51 is disposed on the second empty foil segment 22a along the thickness direction (third direction T) of the secondary battery 100. Within the projection range of the second empty foil segment 22a, the projection of the second electrode 40 is located within the projection of the first insulating layer 51. The second insulating layer 52 can serve as a protective adhesive layer for the second electrode 40, reducing the puncture of the separator 23 by burrs (welding burrs and cutting burrs, etc.) at the second electrode 40, and reducing the occurrence of short circuits.

[0079] Furthermore, the second tab 40, as the main heat source, is covered by the high-melting-point first insulating layer 51, which can prevent the heat generated by the second tab 40 from spreading to other areas. This helps to maintain the uniformity of the internal temperature of the secondary battery 100, reduce the occurrence of side reactions due to local overheating, and reduce the melting and damage of the separator 23 corresponding to the second tab 40, thereby reducing the occurrence of short circuits.

[0080] In some embodiments, referring to FIG4, the first insulating layer 51 may also be disposed on the first portion 21a1, and the first insulating layer 21a1 is located between the first portion 21a1 and the second empty foil segment 22a. The first insulating layer 51 is an insulating coating, and the first insulating layer 51 includes a ceramic material, including at least one of alumina, magnesium oxide, boehmite, or zirconium oxide. The insulating coating makes it easier for the first insulating layer 51 to be flush with the end of the first electrode 21, and can reduce the misalignment between the first insulating layer 51 and the first electrode 21 compared to an adhesive layer.

[0081] Alumina, magnesium oxide, boehmite, and zirconium oxide all possess excellent chemical stability, making them suitable for the electrolyte environment inside the secondary battery 100. They also exhibit good insulation properties, effectively isolating the first portion 21a1 from the second empty foil segment 22a, reducing the risk of short circuits due to direct contact between the two materials. Furthermore, alumina, magnesium oxide, boehmite, and zirconium oxide all have high melting points (alumina melting point: 2054℃, magnesium oxide melting point: 2852℃, boehmite melting point: 350℃, zirconium oxide melting point: 2715℃) and thermal stability, maintaining their insulation properties even at high temperatures. This allows them to withstand the high-temperature environment at the edge of the electrode tabs, enabling the secondary battery 100 to handle higher charge / discharge rates.

[0082] In some embodiments, referring to Figures 3 and 4, the secondary battery 100 further includes a first adhesive layer 61, which is disposed on the first empty foil segment 21a and located between the first empty foil segment 21a and the second empty foil segment 22a. Along the thickness direction (third direction T) of the secondary battery 100, within the projection range of the first empty foil segment 21a, the projection of the first tab 30 is located within the projection of the first adhesive layer 61. The first adhesive layer 61 serves as a protective adhesive layer for the first tab 30, reducing the puncture of the separator 23 by burrs (welding burrs and cutting burrs, etc.) at the first tab 30, thus reducing the occurrence of short circuits. Furthermore, along the thickness direction (third direction T) of the secondary battery 100, the first adhesive layer 61 covers at least a portion of the first portion 21a1, and can also insulate some heat and isolate the first portion 21a1 from the separator 23, reducing the risk of melting and breakage of the separator 23.

[0083] Regardless of whether the first insulating layer 51 is disposed on the second empty foil segment 22a or on the first portion 21a1, in the embodiments of this application, please refer to Figures 5 and 6. Along the thickness direction (third direction T) of the secondary battery 100, the projection of the first insulating layer 51 partially overlaps with the projection of the first adhesive layer 61. This allows the first adhesive layer 61 and the first insulating layer 51 to cover the first portion 21a1, reducing the exposure of the first portion 21a1 and thus reducing the direct contact between the first portion 21a1 and the second empty foil segment 22a, which could lead to a short circuit.

[0084] As for the second insulating layer 52, referring to Figure 3, the second insulating layer 52 is disposed in the second coating section 22b and located between the second coating section 22b and the first portion 21a1. The second insulating layer 52 is an adhesive layer, which includes a substrate layer and an adhesive layer. The substrate layer includes at least one of polyetheretherketone, polyimide, polyetherimide, or polytetrafluoroethylene, and the adhesive layer includes at least one of rubber, silicone, or acrylic resin. The second insulating layer 52 can insulatingly separate the first portion 21a1 and the second coating section 22b, so that both sides of the first portion 21a1 in the thickness direction are provided with a high melting point insulating layer, which can reduce the heat diffusion from the first tab 30 and the second tab 40 to the first portion 21a1, thereby reducing the risk of short circuit due to contact between the first electrode 21 and the second electrode 22.

[0085] In some other embodiments, referring to FIG4, the second insulating layer 52 may also be disposed on the first portion 21a1, and the second insulating layer 52 is located between the first portion 21a1 and the second coating section 22b. The second insulating layer 52 may be made of at least one of alumina, magnesium oxide, boehmite, or zirconium oxide, and can insulatingly separate the first portion 21a1 and the second coating section 22b. The second insulating layer 52 can still maintain its insulating performance in high-temperature environments, and can adapt to the high-temperature environment of the tab edge region, so that the secondary battery 100 can adapt to a larger charge and discharge rate.

[0086] In some embodiments, referring to Figures 3 and 4, the secondary battery 100 further includes a second adhesive layer 62, which is disposed on the first empty foil segment 21a and located between the first empty foil segment 21a and the second coated segment 22b. Along the thickness direction (third direction T) of the secondary battery 100, within the projection range of the first empty foil segment 21a, the projection of the first tab 30 lies within the projection of the second adhesive layer 62. The first adhesive layer 61 serves as a protective adhesive layer for the first tab 30, reducing the puncture of the separator 23 by burrs (welding burrs and cutting burrs, etc.) at the first tab 30, thus reducing the occurrence of short circuits. Furthermore, along the thickness direction (third direction T) of the secondary battery 100, the second adhesive layer 62 covers at least a portion of the first portion 21a1. The second adhesive layer 62 can also isolate part of the heat generated by the first tab 30 and the second tab 40, reducing heat diffusion to the first portion 21a1, thereby isolating the first portion 21a1 from the separator 23 and reducing the possibility of melting and breakage of the separator 23.

[0087] Regardless of whether the second insulating layer 52 is disposed in the second empty foil segment 22a or the second coating segment 22b, in the embodiments of this application, referring to Figures 5 and 6, along the thickness direction (third direction T) of the secondary battery 100, the projection of the second insulating layer 52 partially overlaps with the projection of the second adhesive layer 62, so that the second adhesive layer 62 and the second insulating layer 52 cover the first part 21a1, which can reduce the exposure of the first part 21a1, thereby reducing the direct contact between the first part 21a1 and the second coating segment 22b and the occurrence of a short circuit.

[0088] It should be noted that the thickness of the first insulating layer 51 is H1. When the material of the first insulating layer 51 is a polymer adhesive layer, 10μm ≤ H1 ≤ 25μm. When the material of the first insulating layer 51 is at least one of alumina, magnesium oxide, boehmite, or zirconium oxide, the thickness of the first insulating layer 51 can be set to be smaller, which is beneficial to improving the energy density of the secondary battery 100. For example, 10μm ≤ H1 ≤ 16μm.

[0089] The thickness H2 of the second insulating layer 52 is similar; when the material of the second insulating layer 52 is a polymer adhesive layer, 10 μm ≤ H2 ≤ 25 μm. When the material of the second insulating layer 52 is at least one of alumina, magnesium oxide, boehmite, or zirconium oxide, the thickness of the second insulating layer 52 can be set smaller, which is beneficial to improving the energy density of the secondary battery 100. For example, 10 μm ≤ H2 ≤ 16 μm.

[0090] Regarding the materials of the first adhesive layer 61 and the second adhesive layer 62, in the embodiments of this application, the first adhesive layer 61 and the second adhesive layer 62 can be made of conventional adhesive layer materials, or they can be made of high-melting-point materials. For example, the adhesive layer includes a substrate layer and an adhesive layer. The substrate layer is made of at least one of polyetheretherketone, polyimide, polyetherimide, or polytetrafluoroethylene, and the adhesive layer includes at least one of rubber, silicone, or acrylic resin. The third adhesive layer 63, the fourth adhesive layer 64, the fifth adhesive layer 65, and the sixth adhesive layer 66 can also be made of similar materials.

[0091] When the resistance of the first tab 30 is greater than the resistance of the second tab 40, in some embodiments, the resistance of the first tab 30 is R1, and the resistance of the second tab 40 is R2, where R1 > R2. For example, the first tab 30 is the positive tab, and the second tab 40 is the negative tab. The material of the first tab 30 is aluminum, aluminum alloy, nickel, or nickel-plated aluminum, etc. The material of the second tab 40 is copper, copper-nickel alloy, nickel-plated copper, copper-plated nickel, or silver-plated copper, etc.

[0092] Alternatively, the first tab 30 can be the negative tab, and the second tab 40 can be the positive tab. The first tab 30 can be made of nickel or stainless steel, etc. The second tab 40 can be made of aluminum, aluminum alloy, nickel-plated aluminum, or silver-plated aluminum, etc.

[0093] For example, the first tab 30 is made of aluminum, while the second tab 40 is made of nickel-plated copper. The first tab 30 has a higher resistance, and the heat source is mainly concentrated at the first tab 30. In the embodiments of this application, T1 can be limited to ≥330℃, which can reduce the melting or deformation of the first insulating layer 51 due to temperature rise, so that the first insulating layer 51 can maintain its physical and insulating properties at higher temperatures.

[0094] In some embodiments, referring to FIG7, the first insulating layer 51 is an adhesive layer, comprising a substrate layer and an adhesive layer. The substrate layer comprises at least one of polyetheretherketone, polyimide, polyetherimide, or polytetrafluoroethylene, and the adhesive layer comprises at least one of rubber, silicone, or acrylic resin. The first insulating layer 51 is disposed on the first empty foil segment 21a along the thickness direction (third direction T) of the secondary battery 100. Within the projection range of the first empty foil segment 21a, the projection of the first electrode 30 is located within the projection of the first insulating layer 51. The first insulating layer 51 can serve as a protective adhesive layer for the first electrode 30, reducing the puncture of the separator 23 by burrs at the first electrode 30 and reducing the occurrence of short circuits.

[0095] Furthermore, the first tab 30, as the main heat source, is covered by the high-melting-point first insulating layer 51, which can prevent the heat generated by the first tab 30 from spreading to other areas. This helps to maintain the uniformity of the internal temperature of the secondary battery 100, reduce the occurrence of side reactions due to local overheating, and reduce the melting and damage of the separator 23 corresponding to the first tab 30, thereby reducing the occurrence of short circuits.

[0096] In some embodiments, the secondary battery 100 further includes a third adhesive layer 63. Referring to FIG7, the third adhesive layer 63 is disposed on the second empty foil segment 22a and located between the first empty foil segment 21a and the second empty foil segment 22a. Along the thickness direction (third direction T) of the secondary battery 100, within the projection range of the second empty foil segment 22a, the third adhesive layer 63 covers the second tab 40. The third adhesive layer 63 serves as a protective adhesive layer for the second tab 40, which can reduce the puncture of the separator 23 by burrs at the second tab 40 and reduce the occurrence of short circuits.

[0097] Furthermore, along the thickness direction (third direction T) of the secondary battery 100, the third adhesive layer 63 covers at least part of the first portion 21a1, and the second adhesive layer 62 can also isolate the heat of the first tab 30 and the second tab 40 from spreading to the first portion 21a1, so as to isolate the first portion 21a1 from the separator 23 and reduce the melting and damage of the separator 23.

[0098] In some embodiments, referring to FIG8, along the thickness direction (third direction T) of the secondary battery 100, the third adhesive layer 63 partially overlaps with the first insulating layer 51, such that the third adhesive layer 63 and the first insulating layer 51 cover the first portion 21a1, which can reduce the exposure of the first portion 21a1, thereby reducing the direct contact between the first portion 21a1 and the first empty foil segment 21a and the short circuit.

[0099] For the second insulating layer 52, T2 can be limited to ≥330℃ to reduce the melting or deformation of the second insulating layer 52 due to temperature rise, so that the second insulating layer 52 can maintain its physical and insulating properties at higher temperatures.

[0100] In some embodiments, referring to FIG7, the second insulating layer 52 is an adhesive layer, comprising a substrate layer and an adhesive layer. The substrate layer comprises at least one of polyetheretherketone, polyimide, polyetherimide, or polytetrafluoroethylene, and the adhesive layer comprises at least one of rubber, silicone, or acrylic resin. The second insulating layer 52 is disposed on the first empty foil segment 21a, along the thickness direction (third direction T) of the secondary battery 100. Within the projection range of the first empty foil segment 21a, the projection of the first electrode 30 is located within the projection of the second insulating layer 52. The second insulating layer 52 can also serve as a protective adhesive layer for the first electrode 30, ensuring that both sides of the first electrode 30 in the thickness direction are covered by a high-melting-point insulating layer, reducing the puncture of the separator 23 by burrs at the first electrode 30 and reducing the occurrence of short circuits.

[0101] In some embodiments, the secondary battery 100 further includes a fourth adhesive layer 64, which is disposed in the second coating section 22b and located between the first empty foil section 21a and the second coating section 22b. Along the thickness direction (third direction T) of the secondary battery 100, the fourth adhesive layer 64 covers at least a portion of the first portion 21a1. The fourth adhesive layer 64 can also prevent the heat from the first tab 30 and the second tab 40 from diffusing to the first portion 21a1, thereby isolating the first portion 21a1 from the separator 23, reducing the risk of melting and breakage of the separator 23, and isolating the first portion 21a1 from the second coating section 22b, thereby reducing the occurrence of short circuits.

[0102] In some embodiments, referring to FIG8, along the thickness direction (third direction T) of the secondary battery 100, the fourth adhesive layer 64 partially overlaps with the first insulating layer 51, such that the fourth adhesive layer 64 and the second insulating layer 52 cover the first portion 21a1, which can reduce the exposure of the first portion 21a1, thereby reducing the direct contact between the first portion 21a1 and the second coated section 22b and the occurrence of a short circuit.

[0103] In some embodiments, referring to FIG9, a first insulating layer 51 may also be disposed on the second empty foil segment 22a, and the first insulating layer 51 is located between the first empty foil segment 21a and the second empty foil segment 22a. The first insulating layer 51 includes at least one of alumina, magnesium oxide, boehmite, or zirconium oxide. It can adapt to the electrolyte environment inside the secondary battery 100, isolate the first portion 21a1 from the second empty foil segment 22a, and reduce the direct contact between the first portion 21a1 and the second empty foil segment 22a to prevent short circuits.

[0104] Along the thickness direction (third direction T) of the secondary battery 100, within the projection range of the first empty foil segment 21a, the projection of the first tab 30 lies within the projection of the first insulating layer 51. The first tab 30, as the main heat source, is covered by the high-melting-point first insulating layer 51, which prevents the heat generated by the first tab 30 from diffusing to other areas. This helps maintain the uniformity of the internal temperature of the secondary battery 100, reduces the occurrence of side reactions due to localized overheating, and reduces the melting and breakage of the separator 23 corresponding to the first tab 30, thereby reducing the occurrence of short circuits.

[0105] Regarding the second insulating layer 52, referring to Figure 9, the second insulating layer 52 can be disposed in the second coating section 22b, and the second insulating layer 52 is located between the first empty foil section 21a and the second coating section 22b. The second insulating layer 52 is an insulating coating, and the second insulating layer 52 includes a ceramic material, including at least one of alumina, magnesium oxide, boehmite, or zirconium oxide. It can adapt to the electrolyte environment inside the secondary battery 100, isolate the first part 21a1 from the second coating section 22b, and reduce the direct contact between the first part 21a1 and the second coating section 22b to prevent short circuits.

[0106] Along the thickness direction (third direction T) of the secondary battery 100, within the projection range of the first empty foil segment 21a, the projection of the first tab 30 lies within the projection of the second insulating layer 52. The first tab 30, as the main heat source, is covered by the high-melting-point second insulating layer 52, which prevents the heat generated by the first tab 30 from diffusing to other areas. This helps maintain the uniformity of the internal temperature of the secondary battery 100, reduces local overheating and side reactions, and reduces the melting and breakage of the separator 23 corresponding to the first tab 30, thereby reducing the occurrence of short circuits.

[0107] In some embodiments, referring to FIG10, the secondary battery 100 further includes a fifth adhesive layer 65, which is disposed on the first empty foil segment 21a and located between the first empty foil segment 21a and the second empty foil segment 22a. Along the winding direction S, the fifth adhesive layer 65 is located between the first tab 30 and the first coated segment 21b. Along the thickness direction of the first empty foil segment 21a, the projection of the fifth adhesive layer 65 partially overlaps with the first insulating layer 51. This isolates the first empty foil segment 21a from the second empty foil segment 22a, reducing empty foil exposure and thus reducing the risk of short circuits caused by contact between the first empty foil segment 21a and the second empty foil segment 22a.

[0108] Similarly, the secondary battery 100 also includes a sixth adhesive layer 66, which has a first empty foil segment 21a disposed thereon and is located between the first empty foil segment 21a and the second coated segment 22b. Along the winding direction S, the sixth adhesive layer 66 is located between the first tab 30 and the first coated segment 21b. Along the thickness direction of the first empty foil segment 21a, the projection of the sixth adhesive layer 66 partially overlaps with the second insulating layer 52. This isolates the first empty foil segment 21a from the second empty foil segment 22a, reducing the exposure of the empty foil and thus reducing the risk of short circuits caused by contact between the first empty foil segment 21a and the second empty foil segment 22a.

[0109] In some embodiments, the first empty foil segment 21a and the second empty foil segment 22a can also be directly isolated by the first insulating layer 51. Referring to FIG11, the first insulating layer 51 is disposed on the second empty foil segment 22a and located between the second empty foil segment 22a and the first empty foil segment 21a. Along the thickness direction of the first empty foil segment 21a, the projection of the first empty foil segment 21a is located within the projection of the first insulating layer 51. By isolating the first empty foil segment 21a and the second empty foil segment 22a by the first insulating layer 51, the exposure of the empty foil can be reduced, and the direct contact between the first empty foil segment 21a and the second empty foil segment 22a can be reduced to prevent short circuits. Furthermore, when the first insulating layer 51 is made of alumina, magnesium oxide, boehmite, or zirconium oxide, its thickness is smaller, which can reduce the space occupied by the first insulating layer 51, thereby reducing the energy density loss of the secondary battery 100.

[0110] The second insulating layer 52 can also be similarly configured, with the second insulating layer 52 disposed between the second coated section 22b and the first empty foil section 21a. Along the thickness direction of the first empty foil section 21a, the projection of the first empty foil section 21a lies within the projection of the second insulating layer 51, which can isolate the first empty foil section 21a from the second coated section 22b, reducing the direct contact between the first empty foil section 21a and the second coated section 22b and thus preventing short circuits.

[0111] In some embodiments, referring to Figures 2 and 11, a second active material layer 222 is disposed on the surface of the second coated section 22b facing away from the winding center G, and a first insulating layer 51 is disposed on the surface of the second empty foil section 22a facing away from the winding center G. Along the winding direction S, the length of the first insulating layer 51 covering the second active material layer 222 is L1, 0.5mm ≤ L1 ≤ 2mm. Limiting L1 ≥ 0.5mm reduces the exposure of the second empty foil section 22a, reducing the risk of short circuits caused by direct contact between the second empty foil section 22a and the first empty foil section 21a. Furthermore, limiting L1 ≤ 2mm reduces the amount of the second active material layer 222 covered by the first insulating layer 51, reducing the energy density loss of the secondary battery 100. The second insulating layer 52 can also be disposed similarly.

[0112] Regarding the distance between the first tab 30 and the second tab 40, a smaller distance results in more concentrated heat, increasing the risk of a short circuit between the first portion 21a1 and the second empty foil segment 22a. In the embodiments of this application, because the high-melting-point first insulating layer 51 is disposed between the first portion 21a1 and the second empty foil segment 22a, the melting or deformation of the first insulating layer 51 and the separator 23 due to temperature rise can be reduced. This allows the first insulating layer 51 and the separator 23 to maintain their physical and insulating properties at higher temperatures, resulting in better insulation between the first portion 21a1 and the second empty foil segment 22a. For secondary batteries 100 with smaller widths, the reduction in the risk of short circuits is even more significant, and the distance between the first tab 30 and the second tab 40 can be further reduced. For example, referring to Figure 1, along the width direction (first direction H) of the secondary battery 100, the distance between the first tab 30 and the second tab 40 is D, where 2mm ≤ D ≤ 35mm. This saves space, optimizes the structure of the secondary battery 100, and improves energy density. The overall width of the secondary battery 100 can be set to be smaller. For example, the width of the secondary battery 100 is W, 11mm≤W≤70mm, which can be adapted to electronic devices such as Bluetooth headsets, small radios, and power tools.

[0113] Furthermore, the secondary battery 100 can be adapted to higher tab temperatures. For example, increasing the capacity of the secondary battery 100 increases the current flowing through the tabs, and lengthening the secondary battery 100 can increase its capacity, making it suitable for narrow and elongated secondary batteries 100. In some embodiments, the length of the secondary battery 100 is L (excluding the length of the tabs extending out of the casing), and the width of the secondary battery 100 is W, where 2.5 ≤ L / W ≤ 6, resulting in a higher capacity for the secondary battery 100 and improved battery life.

[0114] 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.

[0115] Example 1-1

[0116] <Preparation of the positive electrode>

[0117] The positive electrode active material lithium cobalt oxide (LiCoO2), conductive agent conductive carbon black (Super P), and binder polyvinylidene fluoride were mixed in a mass ratio of 97.9:0.9:1.2. N-methylpyrrolidone (NMP) was added as a solvent to prepare a slurry with a solid content of 75wt%. After vacuum stirring, the positive electrode slurry was obtained.

[0118] A 9μm 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, with a coating weight of 0.166 mg / mm². 2 A first empty foil area is reserved in the positive current collector. The foil is dried at 110°C to obtain a positive electrode sheet with a single-sided coating of positive active material. Then, the above steps are repeated on the other surface of the aluminum foil, and a second empty foil area is reserved on that surface. The first and second empty foil areas are partially opposite each other in the thickness direction of the positive current collector, thus forming a first empty foil segment. The positive electrode sheet has dimensions of 120mm × 618.5mm, and the thickness of the single-layer positive active material is 39.1μm. Aluminum sheet positive electrode tabs with a width of 6mm, a length of 20mm, and a thickness of 80μm are selected and welded to the first empty foil segment.

[0119] <Preparation of Negative Electrode Sheets>

[0120] Artificial graphite, styrene-butadiene rubber (SBR) binder, and acetylene black (HBL) conductive agent were mixed in a mass ratio of 97.7:0.8:1.5. Deionized water was added as a solvent to prepare a slurry with a solid content of 50 wt%. The slurry was then stirred evenly in a vacuum mixer to obtain the negative electrode slurry.

[0121] A 5μm thick copper foil was selected as the negative electrode current collector. The negative electrode slurry was uniformly coated on one surface of the copper foil, with a coating weight of 0.087 mg / mm². 2 A third empty foil area is reserved on the copper foil. The electrode is dried at 120℃ to obtain a single-sided negative electrode sheet. After completing the above steps, the single-sided coating of the negative electrode sheet is complete. Then, the above steps are repeated on the other surface of the negative electrode sheet, and a fourth empty foil area is reserved on this surface. The third and fourth empty foil areas are positioned opposite each other in the thickness direction of the negative current collector, thus forming the second empty foil segment of the negative electrode sheet. The third and fourth empty foil areas have different lengths in the length direction of the negative current collector, forming a single-sided coated segment (second coated segment) with a negative active material layer on one side and an empty foil on the other. A nickel sheet negative electrode tab with a width of 6mm, a length of 20mm, and a thickness of 80μm is selected and welded to the second empty foil segment. The resistance R2 of the negative electrode tab is greater than the resistance R1 of the positive electrode tab. The negative electrode sheet has dimensions of 121.1mm × 622mm, and the thickness of the single-layer negative active material layer is 50μm.

[0122] <Preparation of the separating membrane>

[0123] A porous polyethylene (PE) film with a thickness of 5 μm was used as the separator.

[0124] <Electrolyte Preparation>

[0125] In a dry argon atmosphere, ethylene carbonate, methyl ethyl carbonate and diethyl carbonate are mixed in a mass ratio of 30:50:20 to obtain an organic solvent. Then, lithium hexafluorophosphate is added to the organic solvent to dissolve and mix evenly to obtain an electrolyte with a lithium salt concentration of 1.15 mol / L.

[0126] <Preparation of Insulating Layer>

[0127] Polyimide is selected as the substrate layer, and acrylic resin is selected as the adhesive layer. The adhesive layer is laminated to the substrate layer to form a first insulating layer with a thickness of 20 μm and a melting point T1 of 300 °C. The first insulating layer is disposed on the second empty foil segment. A second insulating layer with a melting point T2 of 300 °C and a thickness of 20 μm is prepared in a similar manner. The second insulating layer is disposed on the empty foil surface of the second coating segment. A first adhesive layer and a second adhesive layer made of polyimide are respectively disposed on the two surfaces of the first empty foil segment in the thickness direction and cover the first tab.

[0128] <Preparation of Lithium-ion Batteries>

[0129] The separator, negative electrode, separator, and positive electrode prepared above are stacked in sequence and wound to obtain an electrode assembly. The first empty foil segment forms the innermost portion of the positive electrode, and the first empty foil segment between the winding start end of the positive electrode and the positive electrode tab forms the first part. The second empty foil segment forms the innermost portion of the negative electrode. After winding, the first insulating layer is located between the first part and the second empty foil segment, and the second insulating layer is located between the first part and the second coated segment. The first insulating layer does not cover the winding start end of the positive electrode and does not overlap with the first adhesive layer. Similarly, the second insulating layer does not cover the winding start end of the positive electrode and does not overlap with the second adhesive layer.

[0130] The perforated aluminum-plastic film is placed in an assembly fixture with the perforated side facing down. The electrode assembly is then placed inside the perforation and pressed firmly. Next, the other perforated side of the aluminum-plastic film is placed over the electrode assembly with the perforated side facing up. The two edges of the aluminum-plastic film are then heat-sealed using a hot-pressing method. One heat-sealed edge is the side where the negative and positive electrode tabs extend from the casing. Electrolyte is then injected through the unsealed edge. After vacuum sealing, settling, hot-pressing formation, and shaping, a lithium-ion battery is obtained.

[0131] Unlike Example 1-1, the relevant parameters in Examples 1-2 to 1-18 and Comparative Examples 1-1 to 1-4 are shown in Table 1 below. In Comparative Examples 1-1 and 1-2, the first insulating layer is polypropylene; in Comparative Examples 1-3 and 1-4, the first insulating layer is polyethylene terephthalate. In Examples 1-4 to 1-6, the first insulating layer is polytetrafluoroethylene. In Examples 1-7 to 1-9, the first insulating layer is polyetherimide. Wherein, if the first insulating layer covers the winding start end, the second insulating layer also covers the winding start end; if the first insulating layer overlaps with the first adhesive layer, the second insulating layer overlaps with the second adhesive layer. In Examples 1-10 to 1-12, alumina is used as the first insulating layer, with a thickness of 12 μm. The first insulating layer is disposed in the first part, and the second insulating layer is similarly disposed. In Examples 1-13 to 1-15, zirconium oxide was used as the first insulating layer with a thickness of 12 μm. The first insulating layer was disposed in the first part, and the second insulating layer was disposed similarly. In Examples 1-16 to 1-18, magnesium oxide was used as the first insulating layer with a thickness of 12 μm. The first insulating layer was disposed in the first part, and the second insulating layer was disposed similarly.

[0132] Regarding the adjustment of the melting point of the first insulating layer:

[0133] (1) Substituents can be introduced. Introducing different substituents into the monomer molecules of the first insulating layer will change the intermolecular interactions and the spatial structure of the molecules, thereby affecting the melting point of the first insulating layer. For example, introducing a substituent with a larger volume may increase the steric hindrance between molecules, reduce the intermolecular interactions, and lower the melting point; while introducing a substituent with strong polarity or that can form hydrogen bonds may enhance the intermolecular interactions and increase the melting point.

[0134] (2) Changing the polymerization reaction conditions, such as changing the reaction temperature, may increase the molecular weight of the polymer and make its molecular structure more regular, thereby increasing the melting point. Alternatively, extending the reaction time is beneficial for the full progress of the polymerization reaction, which may increase the molecular weight of the first insulating layer and make its structure more complete, which may also increase the melting point.

[0135] (3) Adding fillers with high melting points, such as ceramic particles and carbon fibers, can increase the melting point of the first insulating layer.

[0136] (4) By controlling the conditions of the polymerization reaction or by adopting appropriate post-processing methods, the molecular weight of the first insulating layer can be adjusted, thereby adjusting its melting point.

[0137] Short-circuit test method: Place the fully charged lithium-ion battery sample in a test environment of 20±5℃, and short-circuit the positive and negative terminals of the sample with a load resistor of 80±20mΩ. 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 tends to stabilize (temperature change is less than 10℃ within 30 minutes); 2) The surface temperature of the lithium-ion battery drops to the same as the ambient temperature.

[0138] Measurement frequency: Voltage internal resistance measurement uses 1KHz specification, after preprocessing, and measurement is performed after testing;

[0139] Failure criteria: The lithium-ion battery explodes, leaks, or catches fire;

[0140] Each group tested 20 lithium-ion batteries, and the failure rates are shown in Table 1 below.

[0141] Table 1

[0142] Based on Table 1 above, and in conjunction with Comparative Examples 1-1 to 1-4 and Examples 1-1 to 1-9, the short-circuit test failure rate in Examples 1-1 to 1-9 is significantly lower than that in Comparative Examples 1-1 to 1-4. This is because when the negative electrode tab resistance R2 is greater than the positive electrode tab resistance R1, the high-melting-point first insulating layer between the first part and the second empty foil segment reduces the melting or deformation of the first insulating layer due to temperature rise, maintaining its physical and insulating properties at higher temperatures, resulting in better insulation between the first part and the second empty foil segment. Simultaneously, the high-melting-point first insulating layer reduces the heat generated by the first and second tabs from being transferred between the first part and the second empty foil segment. Even in extreme cases such as thermal runaway of the secondary battery, the high-melting-point first insulating layer can, to some extent, delay the spread of the fault and improve the safety performance of the secondary battery.

[0143] In conjunction with Examples 1-10 to 1-18, setting a high-melting-point first insulating layer in the first part can also reduce the short-circuit test failure rate. This is because alumina, magnesium oxide, and zirconium oxide all have good chemical stability and can adapt to the electrolyte environment inside the secondary battery. They also have good insulating properties, isolating the first part from the second empty foil segment and reducing the risk of short circuits due to direct contact between the first part and the second empty foil segment. Simultaneously, alumina, magnesium oxide, and zirconium oxide all have high melting points and thermal stability, maintaining their insulating properties even at high temperatures. Therefore, in the embodiments of this application, the melting point of the first insulating layer can be selected as T1 ≥ 300℃.

[0144] In Examples 1-2 to 1-3, the short-circuit test failure rate is lower than that in Example 1-1; in Examples 1-5 to 1-6, the short-circuit test failure rate is lower than that in Example 1-4; in Examples 1-8 to 1-9, the short-circuit test failure rate is lower than that in Example 1-7; in Examples 1-11 to 1-12, the short-circuit test failure rate is lower than that in Example 1-10; and in Examples 1-17 to 1-18, the short-circuit test failure rate is lower than that in Example 1-16. This is because the first insulating layer covers the winding start end and / or overlaps with the first adhesive layer, which reduces the exposure of the empty foil in the first part, thereby reducing the risk of short circuits caused by the first part contacting the second empty foil segment. Therefore, in this application, the first insulating layer can be selected to cover the winding start end and / or overlap with the first adhesive layer. Preferably, the first insulating layer covers the winding start end and overlaps with the first adhesive layer.

[0145] Unlike Example 1-1, in Comparative Examples 2-1 to 2-2 and Examples 2-1 to 2-19, the positive electrode tab is made of aluminum, the negative electrode tab is made of nickel-plated copper, and the resistance R2 of the negative electrode tab is less than the resistance R1 of the positive electrode tab. In Examples 2-1 to 2-4, the first insulating layer is polyimide, which covers the first electrode tab, and polyimide is used as the third adhesive layer, which is disposed in the second empty foil segment and covers the second electrode tab. In Examples 2-5 to 2-8, the first insulating layer is polytetrafluoroethylene. In Examples 2-9 to 2-12, alumina is used as the first insulating layer, which is disposed in the second empty foil segment and covers the first electrode tab. In Examples 2-13 to 2-16, zirconium oxide is used as the first insulating layer, which is disposed in the second empty foil segment and covers the first electrode tab. In Examples 2-17 to 2-20, magnesium oxide is used as the first insulating layer. The first insulating layer is disposed in the second empty foil segment and covers the first electrode tab. The second insulating layer is disposed similarly to the first insulating layer, only the placement is different, as shown in Table 1 above. The relevant parameters in Examples 2-1 to 2-19 are shown in Table 2 below.

[0146] Table 2

[0147] Based on Table 2 above, and in conjunction with Comparative Examples 2-1 to 2-2 and Examples 2-1 to 2-8, the short-circuit test failure rate in Examples 2-1 to 2-8 is significantly lower than that in Comparative Examples 2-1 to 2-2. This is because when the negative electrode tab resistance R2 is less than the positive electrode tab resistance R1, the high-melting-point first insulating layer between the first part and the second empty foil segment reduces the melting or deformation of the first insulating layer due to temperature rise, maintaining its physical and insulating properties at higher temperatures, resulting in better insulation between the first part and the second empty foil segment. Simultaneously, the high-melting-point first insulating layer reduces the heat generated by the first and second tabs from being transferred between the first part and the second empty foil segment. Even in extreme cases such as thermal runaway of the secondary battery, the high-melting-point first insulating layer can, to some extent, delay the spread of the fault and improve the safety performance of the secondary battery.

[0148] Furthermore, in conjunction with Examples 2-9 to 2-20, placing a high-melting-point first insulating layer in the second empty foil segment can also reduce the short-circuit test failure rate. This is because alumina, magnesium oxide, and zirconium oxide all possess excellent chemical stability, adaptable to the electrolyte environment inside the secondary battery. They also have good insulating properties, isolating the first part from the second empty foil segment and reducing the risk of short circuits due to direct contact between the two. Simultaneously, alumina, magnesium oxide, and zirconium oxide all have high melting points and thermal stability, maintaining their insulating properties even at high temperatures. Therefore, in the embodiments of this application, the melting point of the first insulating layer can be selected as T1 ≥ 300℃.

[0149] Furthermore, the short-circuit failure rate in Examples 2-5 is lower than that in Example 2-1, the short-circuit failure rate in Example 2-6 is lower than that in Example 2-2, the short-circuit failure rate in Example 2-7 is lower than that in Example 2-3, and the short-circuit failure rate in Example 2-8 is lower than that in Example 2-4. This is because in Examples 2-5 to 2-8, a first insulating layer with a higher melting point is used, which further ensures that the first insulating layer can maintain its insulation performance integrity under high-temperature environments, further reducing the occurrence of short circuits. Therefore, in the embodiments of this application, T1 ≥ 330℃ is preferred.

[0150] In Examples 2-2 to 2-4, the short-circuit test failure rate is lower than that in Example 2-1; in Examples 2-6 to 2-8, the short-circuit test failure rate is lower than that in Example 2-5; in Examples 2-10 to 2-12, the short-circuit test failure rate is lower than that in Example 2-9; in Examples 2-14 to 2-16, the short-circuit test failure rate is lower than that in Example 2-13; and in Examples 2-18 to 2-20, the short-circuit test failure rate is lower than that in Example 2-17. This is because the first insulating layer covers the winding start end and / or overlaps with the third adhesive layer, which reduces the exposure of the empty foil in the first part, thereby reducing the risk of short circuits caused by the first part contacting the second empty foil segment. Therefore, in this application, the first insulating layer can be selected to cover the winding start end and / or overlap with the third adhesive layer. Preferably, the first insulating layer covers the winding start end and overlaps with the third adhesive layer.

[0151] 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, a second tab, and an electrode assembly, wherein the electrode assembly comprises a first electrode sheet, a separator, and a second electrode sheet stacked and wound together, the first electrode sheet comprising a first empty foil segment, the second electrode sheet comprising a second empty foil segment, wherein along the winding direction, the first empty foil segment is the winding start segment of the first electrode sheet, and the second empty foil segment is the winding start segment of the second electrode sheet; along the thickness direction of the second empty foil segment, the first empty foil segment is located on the side of the second empty foil segment opposite to the winding center, the first empty foil segment is an electrode sheet adjacent to the second empty foil segment, the first tab is connected to the first empty foil segment, and the second tab is connected to the second empty foil segment; along the thickness direction of the secondary battery, the first tab and the second tab are respectively located on two adjacent electrode sheets; characterized in that, The secondary battery also includes a first insulating layer; The first electrode tab and the second electrode tab are arranged along a first direction. The first empty foil segment includes a first part. Along the first direction, the first empty foil segment located between the first electrode tab and the second electrode tab is the first part, and the winding start end of the first electrode sheet is located in the first part. Along the thickness direction of the secondary battery, a first insulating layer is provided between the first portion and the second empty foil segment, and the melting point of the first insulating layer is T1, where T1 ≥ 300℃.

2. The secondary battery according to claim 1, characterized by The second electrode also includes a second coating section, and along the thickness direction of the first empty foil section, the electrode adjacent to the first empty foil section is the second empty foil section and the second coating section, respectively; The secondary battery further includes a second insulating layer. Along the thickness direction of the secondary battery, the second insulating layer is disposed between the first part and the second coated section. The melting point of the second insulating layer is T2, and T2≥300℃.

3. The secondary battery according to claim 1 or 2, characterized by Along the thickness direction of the secondary battery, the first insulating layer covers the winding start end.

4. The secondary battery according to claim 2, characterized by Along the thickness direction of the secondary battery, the second insulating layer covers the winding start end.

5. The secondary battery according to any one of claims 1 to 4, characterized in that, Along the winding direction, the second electrode and the first electrode are arranged sequentially, the resistance of the first electrode is R1, the resistance of the second electrode is R2, and R1 < R2.

6. The secondary battery according to claim 5, characterized in that, The first electrode tab is the positive electrode tab, and the second electrode tab is the negative electrode tab; The material of the first electrode tab is aluminum, aluminum alloy, nickel-plated aluminum, or silver-plated aluminum; The second electrode tab is made of nickel or stainless steel.

7. The secondary battery according to claim 5 or 6, characterized by The first insulating layer is an adhesive layer. The first insulating layer is disposed on the second empty foil segment. Along the thickness direction of the secondary battery, within the projection range of the second empty foil segment, the projection of the second electrode is located within the projection of the first insulating layer.

8. The secondary battery according to claim 5 or 6, characterized by The first insulating layer is disposed on the first portion, and the first insulating layer is an insulating coating, comprising a ceramic material.

9. The secondary battery according to any one of claims 5 to 8, characterized by, The secondary battery further includes a first adhesive layer, which is disposed on the first empty foil segment and located between the first empty foil segment and the second empty foil segment; Along the thickness direction of the secondary battery, within the projection range of the first empty foil segment, the projection of the first tab is located within the projection of the first adhesive layer, and the first adhesive layer covers at least part of the first portion.

10. The secondary battery according to claims 1 to 9, characterized by Along the thickness direction of the secondary battery, the projection of the first insulating layer partially overlaps with the projection of the first adhesive layer.

11. The secondary battery according to any one of claims 1 to 4, characterized by Along the winding direction, the second electrode and the first electrode are arranged sequentially, the resistance of the first electrode is R1, the resistance of the second electrode is R2, and R1 > R2.

12. The secondary battery according to claim 11, characterized by The first electrode tab is the positive electrode tab, and the second electrode tab is the negative electrode tab; The material of the first electrode tab is aluminum, aluminum alloy, nickel, or nickel-plated aluminum; The material of the second electrode is copper, copper-nickel alloy, nickel-plated copper, copper-plated nickel, or silver-plated copper.

13. The secondary battery according to claim 11 or 12, characterized by The first electrode is made of aluminum, and the second electrode is made of copper plated with nickel, with T1 ≥ 330℃.

14. The secondary battery according to any one of claims 11 to 13, characterized in that, The first insulating layer is an adhesive layer, and the first insulating layer is disposed on the first empty foil segment; Along the thickness direction of the secondary battery, within the projection range of the first empty foil segment, the projection of the first electrode is located within the projection of the first insulating layer.

15. The secondary battery according to claim 14, characterized in that, The secondary battery further includes a third adhesive layer, which is disposed on the second empty foil segment and located between the first empty foil segment and the second empty foil segment; Along the thickness direction of the secondary battery, within the projection range of the second empty foil segment, the third adhesive layer covers the second tab, and the third adhesive layer covers at least a portion of the first portion.

16. The secondary battery according to claim 15, characterized by Along the thickness direction of the secondary battery, the third adhesive layer partially overlaps with the first insulating layer.

17. The secondary battery according to any one of claims 11 to 13, characterized by The first insulating layer is disposed on the second empty foil segment and located between the first empty foil segment and the second empty foil segment. The first insulating layer is an insulating coating and includes a ceramic material.

18. The secondary battery according to claim 17, characterized by Along the thickness direction of the secondary battery, within the projection range of the first empty foil segment, the projection of the first electrode is located within the projection of the first insulating layer.

19. The secondary battery according to claim 17 or 18, characterized by Along the thickness direction of the first empty foil segment, the projection of the first empty foil segment lies within the projection of the first insulating layer.

20. The secondary battery according to claim 19, characterized by The second electrode also includes a second coating section. Along the thickness direction of the secondary battery, the electrode adjacent to the first empty foil section is the second empty foil section and the second coating section, respectively. The second coating section has a first active material layer on its surface away from the winding center. Along the winding direction, the length of the first insulating layer covering the first active material layer is L1, where 0.5mm≤L1≤2mm.

21. The secondary battery according to any one of claims 1 to 20, characterized by Along the width direction of the secondary battery, the distance between the first tab and the second tab is D, where 2mm≤D≤35mm.

22. The secondary battery according to any one of claims 1 to 21, characterized by Along the width direction of the secondary battery, the width of the secondary battery is W, where 11mm≤W≤70mm.

23. The secondary battery according to claim 2, characterized in that, The first insulating layer and / or the second insulating layer are adhesive layers, the adhesive layer comprising a substrate layer and an adhesive layer, the substrate layer comprising at least one of polyetheretherketone, polyimide, polyetherimide or polytetrafluoroethylene, and the adhesive layer comprising at least one of rubber, silicone or acrylic resin.

24. An electronic device, characterized in that, Includes the secondary battery as described in any one of claims 1 to 23.

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