Secondary battery and electronic device

Abstract

Disclosed in the present application are a secondary battery and an electronic device. A first tab is connected to a first bare foil segment, and a second tab is connected to a second bare foil segment. A second insulating layer is provided on the surface of the second bare foil segment facing away from a winding center, and a fourth insulating layer is provided on the surface of a single-sided coated segment facing the winding center. A first electrode sheet comprises a winding start end. In the direction of thickness of the secondary battery, within the projection range of the first bare foil segment, the projection of the first tab and the projection of the winding start end are located within the projection of the second insulating layer, and the projection of the first tab and the projection of the winding start end are located within the projection of the fourth insulating layer. A first insulating layer is provided on the surface of the first bare foil segment facing the winding center, and in the direction of thickness of the secondary battery, the first insulating layer partially overlaps the second insulating layer. A third insulating layer is provided on the surface of the first bare foil segment facing away from the winding center, and in the direction of thickness of the secondary battery, the third insulating layer partially overlaps the fourth insulating layer. The occurrence of a short circuit in the secondary battery 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] With the technological development of electronic products, miniaturization is becoming increasingly important. For example, small electronic devices such as smartwatches, smart glasses, and Bluetooth headsets require narrow-width rechargeable batteries. However, with narrow-width rechargeable batteries, the distance between the positive and negative electrodes is small. During charging and discharging, the electrodes generate significant heat, which can easily cause the separator between them to melt and break, leading to short circuits due to contact between the positive and negative electrodes.

[0003] Summary of the Invention

[0004] This application aims to provide a secondary battery and electronic device that reduces the technical problem of short circuits in secondary batteries.

[0005] The embodiments of this application adopt the following technical solutions:

[0006] 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, which is the starting segment for winding the first electrode sheet, and the first tab is connected to the first empty foil segment. The second electrode sheet includes a second empty foil segment and a single-sided coated segment connected together, with the second empty foil segment being the starting segment for winding the second electrode sheet. The second tab is connected to the second empty foil segment. Along the winding direction, the second tab and the first tab are arranged sequentially. Along the thickness direction of the first empty foil segment, the electrode sheets adjacent to the first empty foil segment are the second empty foil segment and the single-sided coated segment, respectively. A second insulating layer is disposed on the surface of the second empty foil segment facing away from the winding center, and a fourth insulating layer is disposed on the surface of the single-sided coated segment facing the winding center. The first electrode includes a winding start end. Along the thickness direction of the secondary battery, within the projection range of the first empty foil segment, the projections of the first electrode tab and the winding start end are located within the projection of the second insulating layer, and the projections of the first electrode tab and the winding start end are located within the projection of the fourth insulating layer. A first insulating layer is disposed on the surface of the first empty foil segment facing the winding center, and along the thickness direction of the secondary battery, the first insulating layer partially overlaps with the second insulating layer. A third insulating layer is disposed on the surface of the first empty foil segment away from the winding center, and along the thickness direction of the secondary battery, the third insulating layer partially overlaps with the fourth insulating layer.

[0007] In the above technical solution, the projections of the first electrode tab and the winding start end are located within the projection of the second insulating layer. This allows the second insulating layer to isolate the portion between the first electrode tab and the winding start end from the second empty foil segment, reducing the risk of melting and breakage of the separator film between this portion and the second empty foil segment, thereby reducing the risk of short circuits between the first electrode and the second empty foil segment. Furthermore, the second insulating layer also isolates this portion from the second empty foil segment, further reducing the occurrence of short circuits. Simultaneously, the second insulating layer can cover some of the burrs at the first electrode tab, reducing the risk of burrs piercing the separator film and further reducing the risk of short circuits between the first electrode and the second empty foil segment.

[0008] The projections of the first tab and the winding start end are located within the projection of the fourth insulating layer. This allows the fourth insulating layer to isolate the portion between the first tab and the winding start end from the single-sided coated section, reducing the risk of melting and breakage of the separator film between this portion and the single-sided coated section, thereby reducing the risk of short circuits between the first electrode and the single-sided coated section. Furthermore, the fourth insulating layer also isolates this portion from the single-sided coated section, further reducing the occurrence of short circuits. Simultaneously, the fourth insulating layer isolates the burrs on the side of the first tab away from the winding center, reducing the risk of burrs piercing the separator film and further reducing the risk of short circuits between the first electrode and the single-sided coated section.

[0009] In addition, by partially overlapping the first insulating layer and the second insulating layer, the first insulating layer and the second insulating layer can isolate the area of ​​heat radiation from the first electrode tab from the second empty foil segment, which can reduce the melting and breakage of the isolation film between the first electrode and the first empty foil segment. The first insulating layer and the second insulating layer can also isolate the first electrode and the second empty foil segment, which can reduce the contact between the first electrode and the second empty foil segment and the occurrence of short circuit.

[0010] The third and fourth insulating layers partially overlap, which allows the third and fourth insulating layers to isolate the area of ​​heat radiation from the first electrode tab from the single-sided coated section. This reduces the melting and breakage of the isolation film between the first electrode and the single-sided coated section. The third and fourth insulating layers can also isolate the first electrode from the single-sided coated section, reducing the risk of short circuits caused by contact between the first electrode and the second empty foil section.

[0011] In some embodiments, the resistance of the first tab is R1, and the resistance of the second tab is R2, where R1 < R2. Along the thickness direction of the first empty foil segment, the first insulating layer does not overlap with the first tab, that is, the first insulating layer does not need to cover the first tab, which can reduce the amount of the first insulating layer and reduce the thickness of the first electrode sheet occupied by the first insulating layer, thereby improving the energy density of the secondary battery.

[0012] In some embodiments, the first electrode tab is a positive electrode tab, and the second electrode tab is a negative electrode tab. The first electrode tab is made of aluminum, aluminum alloy, nickel-plated aluminum, or silver-plated aluminum. The second electrode tab is made of nickel or stainless steel.

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

[0014] In some other embodiments, the third insulating layer does not overlap with the first electrode tab along the thickness direction of the first empty foil segment, which can reduce the amount of the third insulating layer and reduce the thickness of the first electrode sheet occupied by the third insulating layer, thereby further improving the energy density of the secondary battery.

[0015] In some embodiments, the first electrode includes a first portion. Along the winding direction, the portion of the first electrode located between the winding start end and the first tab forms the first portion. The length of the first portion is L1, where 1mm ≤ L1 ≤ 3.2mm. This reduces the occurrence of short circuits, facilitates welding of the first tab, and reduces cutting to the first seal, thus minimizing the impact on the sealing performance of the secondary battery. Preferably, 1.3mm ≤ L1 ≤ 1.7mm.

[0016] In some embodiments, the first electrode includes a coated section connected to a first empty foil segment. The first empty foil segment includes a second portion, the portion of the first empty foil segment located between the first electrode tab and the coated section forming the second portion. Both the first insulating layer and the third insulating layer are disposed in the second portion. Along the winding direction, the distance between the first insulating layer and the first electrode tab is L2, 1mm ≤ L2 ≤ 2mm. This reduces the bending portion of the second insulating layer extending to the electrode assembly, facilitates the adhesion of the first insulating layer, reduces adhesion of the first insulating layer to the first electrode tab, and reduces direct exposure of the surface of the first empty foil segment facing the winding center, thereby reducing the occurrence of short circuits. The distance between the third insulating layer and the first electrode tab is L3, 1mm ≤ L3 ≤ 2mm. ， This reduces the extension of the fourth insulating layer to the curved portion, which is beneficial for the adhesion of the third insulating layer, reduces the adhesion of the third insulating layer to the first tab, and reduces the direct exposure of the surface of the first empty foil segment away from the winding center, thereby reducing the occurrence of short circuits.

[0017] In some embodiments, along the winding direction, the projected overlap length of the first insulating layer and the second insulating layer in the thickness direction of the first empty foil segment is L4, where 1mm ≤ L4 ≤ 6mm. This reduces the exposure of the first empty foil segment, reduces the occurrence of short circuits, and reduces the bending portion of the second insulating layer extending into the electrode assembly. The projected overlap length of the second insulating layer and the fourth insulating layer in the thickness direction of the first empty foil segment is L5, where 1mm ≤ L5 ≤ 6mm. ， This can reduce the exposure of the first empty foil segment, reduce the occurrence of short circuits, and reduce the bending portion of the fourth insulating layer extending to the electrode assembly.

[0018] In some embodiments, 1mm ≤ L4 ≤ 2mm, and / or 1mm ≤ L5 ≤ 2mm. This can further reduce the exposure of the first empty foil segment, reduce the occurrence of short circuits, and further reduce the extension of the second and / or fourth insulating layers to the bent portions of the electrode assembly.

[0019] In some embodiments, along the thickness direction of the secondary battery, the electrode assembly includes a first flat portion and a second flat portion disposed opposite to each other; along the width direction of the secondary battery, the electrode assembly includes a first curved portion and a second curved portion disposed opposite to each other, the first curved portion and the second curved portion being connected between the first flat portion and the second flat portion. Both the second insulating layer and the fourth insulating layer are disposed on the first flat portion or the second flat portion. Disposing of them on the flat portion allows for better resistance to external mechanical stress, reducing damage to the second and fourth insulating layers caused by mechanical stress.

[0020] In some embodiments, the resistance of the first tab is R1, and the resistance of the second tab is R2, where R1 > R2. Along the thickness direction of the first empty foil segment, 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. This ensures that there are two insulating layers and one insulating film between the first tab and the second empty foil segment, reducing the risk of short circuits due to contact between the first tab and the second empty foil segment. Furthermore, the projection of the first tab lies within the projection of the third insulating layer, ensuring that there are two insulating layers and one insulating film between the first tab and the single-sided coated segment, further reducing the risk of short circuits due to contact between the first tab and the single-sided coated segment.

[0021] 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.

[0022] In some embodiments, the first electrode is a negative electrode, and the second electrode is a positive electrode. The first electrode is made of either nickel or stainless steel. The second electrode is made of either aluminum, aluminum alloy, nickel-plated aluminum, or silver-plated aluminum.

[0023] In some embodiments, the first empty foil segment includes a winding start end. Along the winding direction, the length between the first insulating layer and the winding start end is L6, where 1mm ≤ L6 ≤ 2mm. This reduces the exposure of the first empty foil segment, decreases the occurrence of short circuits, and facilitates the cutting operation of the first current collector. The length between the third insulating layer and the winding start end is L7, where 1mm ≤ L7 ≤ 2mm. This also reduces the exposure of the first empty foil segment, decreases the occurrence of short circuits, and facilitates the cutting operation of the first current collector.

[0024] In some embodiments, the first empty foil segment includes a first portion, the portion of the first empty foil segment located between the winding start end and the first tab forming the first portion. Along the winding direction, the first insulating layer and the first portion overlap by a length L8 in the thickness direction of the first portion, where 1mm ≤ L8 ≤ 1.5mm, which reduces the exposure of the first tab, reduces the occurrence of short circuits, and facilitates the cutting operation of the first current collector. The third insulating layer and the first portion overlap by a length L9 in the thickness direction of the first portion, where 1mm ≤ L9 ≤ 1.5mm, which also reduces the exposure of the first tab, reduces the occurrence of short circuits, and facilitates the cutting operation of the first current collector.

[0025] In some embodiments, the first electrode includes a coated section connected to a first empty foil segment, the first empty foil segment including a second portion, the portion of the first empty foil segment located between the first electrode tab and the coated section forming the second portion. In the second portion, along the winding direction, the first insulating layer and the second insulating layer overlap by a length L in the thickness direction of the second portion. 10 ,1mm≤L 10 ≤1.5mm, which reduces the occurrence of short circuits while minimizing the extension of the second section to the bend. The overlap length between the third and fourth insulating layers in the thickness direction of the second section is L. 11 ,1mm≤L 11 With a diameter of ≤1.5mm, the second part can be reduced from extending to the bend while minimizing the occurrence of short circuits.

[0026] In some embodiments, the first insulating layer, the second insulating layer, the third insulating layer, and the fourth insulating layer are all adhesive layers.

[0027] 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 ≤ 10mm. By adopting the above scheme, the occurrence of short circuits due to heat generation between the first tab and the second tab can be reduced. Therefore, the distance between the first tab and the second tab can be set smaller, saving space and optimizing the secondary battery structure, thus reducing the overall width of the secondary battery.

[0028] In some embodiments, the width of the secondary battery is W, where 10mm ≤ W ≤ 35mm.

[0029] In some embodiments, the length of the secondary battery is L, the width of the secondary battery is W, and 2.5≤L / W≤6, so that the secondary battery has a higher capacity and improves the battery's endurance.

[0030] In some embodiments, the first electrode is a positive electrode and the second electrode is a negative electrode.

[0031] Secondly, this application also proposes an electronic device including a secondary battery as described in any of the embodiments of the first aspect above.

[0032] 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

[0033] 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.

[0034] Figure 1 is a schematic diagram of the structure of a secondary battery according to some embodiments of this application;

[0035] Figure 2 is a schematic diagram of the stacking of the first electrode, the separator, and the second electrode in some embodiments of this application;

[0036] Figure 3 is a schematic diagram of the winding structure of the electrode assembly in some embodiments of this application;

[0037] Figure 4 is a schematic diagram of the winding structure of the electrode assembly in some embodiments of this application;

[0038] Figure 5 is a schematic diagram of the winding structure of the electrode assembly in some embodiments of this application;

[0039] Figure 6 is a schematic diagram of the winding structure of the electrode assembly in some embodiments of this application;

[0040] Figure 7 is a schematic diagram of the winding structure of the electrode assembly in some embodiments of this application.

[0041] 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, second part; 21b, coated segment; 211a, winding start end; 22, second electrode; 221, second current collector; 222, second active material layer; 22a, second empty foil segment; 22b, single-sided coated segment; 23, separator; 30, first tab; 40, second tab; 51, first insulating layer; 52, second insulating layer; 53, third insulating layer; 54, fourth insulating layer; 60, first seal; 70, second seal; Z, first direction; X, second direction; T, third direction; H, fourth direction; G, winding center. Detailed Implementation

[0042] 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.

[0043] 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.

[0044] 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.

[0045] 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.

[0046] 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.

[0047] 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.

[0048] Referring to Figures 2 and 3, the electrode assembly 20 includes a first electrode 21, a second electrode 22, and a separator 23. The first electrode 21, the separator 23, and the second electrode 22 are stacked and wound together, for example, stacked along the thickness direction (first direction Z) of the first electrode 21 and wound along its length direction (second direction X) to form a wound electrode assembly 20. The separator 23 is disposed between the first electrode 21 and the second electrode 22 to provide insulation between them.

[0049] 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.

[0050] 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 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.

[0051] The first active material layer 212 can be disposed on at least one surface of the first current collector 211 in the thickness direction. 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.

[0052] 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 a flat copper foil. Copper foil has high conductivity and low resistance, which can improve the 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.

[0053] The second active material layer 222 can be disposed on at least one surface of the second current collector 221 in the thickness direction. 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.

[0054] Referring to Figures 2 and 3, the first electrode 21 includes a first empty foil segment 21a. Along the winding direction, the first empty foil segment 21a is the starting segment of the winding of the first electrode 21, that is, the first empty foil segment 21a forms 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 is not provided with an active material layer. The first empty foil segment 21a is provided on the innermost ring of the first electrode 21, which can provide 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.

[0055] The second electrode 22 includes a second empty foil segment 22a and a single-sided coated segment 22b connected to each other. Along the winding direction, 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 forms at least part of the innermost ring of the second electrode 22. The single-sided coated segment 22b has a second active material layer 222 on only one side, for example, only on the side opposite to the winding center G, which can make full use of space and is beneficial to improving the energy density of the secondary battery 100. The second tab 40 is connected to the second empty foil segment 22a, and along the winding direction, the second tab 40 and the first tab 30 are arranged sequentially. Along the thickness direction of the first empty foil segment 21a, the electrodes adjacent to the first empty foil segment 21a are the second empty foil segment 22a and the single-sided coated segment 22b, respectively.

[0056] 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.

[0057] Referring to Figure 3, a second insulating layer 52 is provided on the surface of the second empty foil segment 22a facing away from the winding center G. Along the thickness direction of the second empty foil segment 22a, the projection of the second insulating layer 52 covers the second tab 40. The second insulating layer 52 serves as a protective adhesive layer for the second tab 40, reducing the likelihood of burrs (welding burrs and cutting burrs, etc.) piercing the separator 23 at the second tab 40 and thus reducing the occurrence of short circuits. A fourth insulating layer 54 is provided on the surface of the single-sided coated segment 22b facing the winding center G. Along the thickness direction of the second empty foil segment 22a, the projection of the fourth insulating layer 54 covers the second tab 40. The fourth insulating layer 54 also serves as a protective adhesive layer for the second tab 40, reducing direct contact between the electrode layers and further reducing the occurrence of short circuits.

[0058] Optionally, in some embodiments, referring to FIG4, along the thickness direction (third direction T) of the secondary battery 100, the electrode assembly 20 includes a first straight portion 20a and a second straight portion 20b disposed opposite to each other. Along the width direction (fourth direction H) of the secondary battery 100, the electrode assembly 20 includes a first curved portion 20c and a second curved portion 20d disposed opposite to each other, the first curved portion 20c and the second curved portion 20d being connected between the first straight portion 20a and the second straight portion 20b. The second insulating layer 52 and the fourth insulating layer 54 are both disposed on the first straight portion 20a or the second straight portion 20b. The curved portion is subjected to greater mechanical stress. If disposed on the curved portion, it may result in an excessively thick curved portion, which not only affects the width of the secondary battery 100 but may also cause the second insulating layer 52 and the fourth insulating layer 54 to be crushed and damaged. Disposing on the straight portion can better withstand external mechanical stress and reduce the damage of the second insulating layer 52 and the fourth insulating layer 54 caused by mechanical stress.

[0059] 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 can easily cause the insulating membrane 23 at the first tab 30 and the second tab 40 to melt and break, leading to a short circuit between the first electrode 21 and the second electrode 22. Furthermore, the heat from the first tab 30 and the second tab 40 radiates outwards, potentially causing partial melting of the insulating membrane 23 around them, further increasing the risk of a short circuit. For example, the first electrode 21 includes a winding start end 211a 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 211a. In the traditional scheme, the winding start end 211a is the cutting position of the first current collector 211. In order to facilitate the cutting of the first current collector 211, the part near the winding start end 211a is usually empty foil (no active material layer or insulating layer is provided). Heat radiation to the winding start end 211a may cause the separator 23 at that place to melt and break, which will directly cause the winding start end 211a to come into contact with the second electrode 22 and cause a short circuit.

[0060] To mitigate the aforementioned problems, in the embodiments of this application, referring to Figure 3, along the thickness direction (third direction T) of the secondary battery 100, within the projection range of the first empty foil segment 21a, the projections of the first tab 30 and the winding start end 211a are located within the projection of the second insulating layer 52. This allows the second insulating layer 52 to isolate the portion between the first tab 30 and the winding start end 211a from the second empty foil segment 22a, reducing the risk of melting and breakage of the separator 23 between this portion and the second empty foil segment 22a, thereby reducing the risk of short circuits between the first electrode 21 and the second empty foil segment 22a. Furthermore, even if the separator 23 melts and breaks, the second insulating layer 52 can still isolate this portion from the second empty foil segment 22a, further reducing the occurrence of short circuits. Simultaneously, the second insulating layer 52 can cover some burrs (cutting burrs and welding burrs, etc.) at the first tab 30, reducing the risk of burrs piercing the separator 23, further reducing the risk of short circuits between the first electrode 21 and the second empty foil segment 22a.

[0061] Based on the same inventive concept, along the thickness direction (third direction T) of the secondary battery 100, within the projection range of the first empty foil segment 21a, the projections of the first tab 30 and the winding start end 211a are located within the projection of the fourth insulating layer 54. This allows the fourth insulating layer 54 to isolate the portion between the first tab 30 and the winding start end 211a from the single-sided coated segment 22b, reducing the risk of melting and breakage of the separator 23 between this portion and the single-sided coated segment 22b, thereby reducing the risk of short circuits between the first electrode 21 and the single-sided coated segment 22b. Furthermore, even if the separator 23 melts and breaks, the fourth insulating layer 54 can still isolate this portion from the single-sided coated segment 22b, further reducing the occurrence of short circuits. Simultaneously, the fourth insulating layer 54 can isolate the burrs on the side of the first tab 30 away from the winding center G, reducing the risk of burrs piercing the separator 23, further reducing the risk of short circuits between the first electrode 21 and the single-sided coated segment 22b.

[0062] Referring to Figure 3, a first insulating layer 51 is provided on the surface of the first empty foil segment 21a facing the winding center G. Along the thickness direction (third direction T) of the secondary battery 100, the first insulating layer 51 and the second insulating layer 52 partially overlap. The portion of the first empty foil segment 21a on the side of the first tab 30 away from the winding start end 211a is also affected by the heat radiation from the first tab 30, and the separator 23 located in this portion is also at risk of melting and breaking. In the embodiments of this application, the first insulating layer 51 and the second insulating layer 52 partially overlap, which allows the first insulating layer 51 and the second insulating layer 52 to isolate the area of ​​heat radiation from the first tab 30 from the second empty foil segment 22a, reducing the risk of melting and breaking of the separator 23 between the first electrode 21 and the first empty foil segment 21a. The first insulating layer 51 and the second insulating layer 52 also isolate the first electrode 21 from the second empty foil segment 22a, reducing the risk of short circuits caused by contact between the first electrode 21 and the second empty foil segment 22a.

[0063] Similarly, a third insulating layer 53 is disposed on the surface of the first empty foil segment 21a away from the winding center G. Along the thickness direction (third direction T) of the secondary battery 100, the third insulating layer 53 and the fourth insulating layer 54 partially overlap, which allows the third insulating layer 53 and the fourth insulating layer 54 to isolate the area of ​​heat radiation from the first electrode tab 30 from the single-sided coated segment 22b, thereby reducing the melting and breakage of the separator 23 between the first electrode 21 and the single-sided coated segment 22b. The third insulating layer 53 and the fourth insulating layer 54 can also isolate the first electrode 21 from the single-sided coated segment 22b, thereby reducing the risk of short circuits caused by contact between the first electrode 21 and the second empty foil segment 22a. In some embodiments, the first insulating layer 51 and the third insulating layer 53 are both adhesive layers.

[0064] Regarding the material of the first insulating layer 51, in the embodiments of this application, the first insulating layer 51 includes a first substrate layer (not shown in the figure) and a first adhesive layer (not shown in the figure), the first adhesive layer being disposed on the surface of the first substrate layer facing the first electrode 21. The first substrate layer includes at least one of polyethylene terephthalate, polyimide, polypropylene, or polyethylene. The first adhesive layer includes at least one of acrylic resin, polypropylene, rubber, or polyurethane. The second insulating layer 52, the third insulating layer 53, and the fourth insulating layer 54, etc., can all be similarly disposed.

[0065] 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.

[0066] When the resistance of the first tab 30 is less 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 one of aluminum, aluminum alloy, nickel-plated aluminum, or silver-plated aluminum. The material of the second tab 40 is one of nickel or stainless steel.

[0067] Alternatively, the first tab 30 may be the negative tab, and the second tab 40 may be the positive tab. The first tab 30 may be made of one of the following materials: copper, copper-nickel alloy, nickel-plated copper, copper-plated nickel, or silver-plated copper. The second tab 40 may be made of one of the following materials: aluminum, aluminum alloy, nickel, or nickel-plated aluminum.

[0068] The second tab 40 has a higher resistance, and the heat source is mainly concentrated at the second tab 40. Therefore, in the embodiments of this application, referring to FIG3, along the thickness direction of the first empty foil segment 21a, the first insulating layer 51 does not overlap with the first tab 30, that is, the first insulating layer 51 does not need to cover the first tab 30, which can reduce the amount of the first insulating layer 51 and reduce the thickness of the first electrode 21 occupied by the first insulating layer 51, thereby improving the energy density of the secondary battery 100.

[0069] Based on the same inventive concept, along the thickness direction of the first empty foil segment 21a, the third insulating layer 53 does not overlap with the first electrode tab 30, which can reduce the amount of the third insulating layer 53 and reduce the thickness of the first electrode 21 occupied by the third insulating layer 53, thereby further improving the energy density of the secondary battery 100.

[0070] In some embodiments, the first electrode 21 includes a first portion 21a1, which is formed along the winding direction by the portion of the first electrode 21 located between the winding start end 211a and the first tab 30. Since the first insulating layer 51 and the third insulating layer 53 do not overlap with the first tab 30, the first portion 21a1 is not provided with an insulating layer. During the cutting process of the first current collector 211, since there is no insulating layer, there is no need to reserve cutting space, and the length of the first portion 21a1 can be set to be smaller. This reduces the area where the first portion 21a1 can contact the second electrode 22, that is, increases the distance between the winding start end 211a and the main heat source (second tab 40), which can reduce the melting and breakage of the isolation film 23 located at the first portion 21a1, thereby reducing the risk of short circuit due to contact between the first portion 21a1 and the second electrode 22.

[0071] The inventors of this application have discovered that if the length of the first portion 21a1 is too small, it will affect the welding between the first tab 30 and the first empty foil segment 21a, impacting the welding quality and potentially increasing the welding resistance. Increased resistance leads to more severe heat generation, further increasing the risk of the separator melting and breaking. Furthermore, referring to Figures 1 and 5, a first sealing element 60 is provided on the first tab 30. When the first tab 30 extends out of the housing 10, the first sealing element 60 seals the gap between the first tab 30 and the housing 10. If the length of the first portion 21a1 is too small, the first sealing element 60 may also be cut when the first current collector 211 is cut, affecting the sealing performance of the secondary battery 100. Conversely, if the length of the first portion 21a1 is too large, the distance between the winding starting end 211a and the main heat source (second tab 40) will be too close, increasing the risk of a short circuit.

[0072] In the embodiments of this application, please refer to FIG5. Along the winding direction, the length of the first part 21a1 is L1, 1mm≤L1≤3.2m. This can reduce the occurrence of short circuits, facilitate the welding of the first tab 30, and reduce the cutting to the first sealing member 60, thereby reducing the impact on the sealing performance of the secondary battery 100.

[0073] Furthermore, 1.3mm≤L1≤1.7mm can further reduce the occurrence of short circuits and the impact on the welding of the first tab 30, while also reducing the impact on the sealing performance of the secondary battery 100.

[0074] In some embodiments, referring to Figures 2 and 3, the first electrode 21 includes a coating section 21b connected to the first empty foil section 21a. The coating section 21b may be a portion on both sides of the first electrode 21 in the thickness direction where the first active material layer 212 is disposed, or it may be a portion on one surface of the first electrode 21 in the thickness direction where the first active material layer 212 is disposed. The first empty foil section 21a includes a second portion 21a2, which is formed by the portion of the first empty foil section 21a located between the first electrode tab 30 and the coating section 21b. The first insulating layer 51 and the third insulating layer 53 are both disposed in the second portion 21a2. In the embodiments of this application, since both the second insulating layer 52 and the fourth insulating layer 54 extend to the side of the first tab 30 away from the winding start end 211a, the second insulating layer 52 and the fourth insulating layer 54 cover the portion of the first tab 30 located on the first empty foil segment 21a. Therefore, the first insulating layer 51 and the third insulating layer 53 do not need to cover the first tab 30, which can reduce the amount of the first insulating layer 51 and the third insulating layer 53 used.

[0075] Regarding the distance between the first insulating layer 51 and the third insulating layer 53 and the first electrode tab 30, if the distance is too small, the first insulating layer 51 and the third insulating layer 53 may adhere to the first electrode tab 30 during the bonding process, affecting the thickness of the first electrode sheet 21. If the distance is too large, the first empty foil segment 21a will be exposed too much, posing a risk of short circuit. Furthermore, if the distance is too large, the second insulating layer 52 and the fourth insulating layer 54 will need to be extended too much, which may cause the second insulating layer 52 and the fourth insulating layer 54 to extend into the winding and bending portion, resulting in an excessively thick bending portion that affects the thickness of the battery. This will also cause the empty foil of the first electrode tab 30 to lengthen away from the winding start end 211a, affecting the energy density.

[0076] In the embodiments of this application, please refer to FIG5. Along the winding direction, the distance between the first insulating layer 51 and the first tab 30 is L2, 1mm≤L2≤2mm. This can reduce the extension of the second insulating layer 52 to the bent portion, which is beneficial to the adhesion of the first insulating layer 51, reduces the adhesion of the first insulating layer 51 to the first tab 30, and reduces the direct exposure of the surface of the first empty foil segment 21a facing the winding center G, thereby reducing the occurrence of short circuits.

[0077] Similarly, the distance between the third insulating layer 53 and the first tab 30 is L3, 1mm≤L3≤2mm, which can reduce the extension of the fourth insulating layer 54 to the curved part, which is beneficial to the adhesion of the third insulating layer 53, reduces the adhesion of the third insulating layer 53 to the first tab 30, and reduces the direct exposure of the surface of the first empty foil segment 21a away from the winding center G, thereby reducing the occurrence of short circuits.

[0078] Regarding the overlap length between the first insulating layer 51 and the second insulating layer 52, if the overlap length is too small, due to the expansion of the electrode sheet and impacts to the secondary battery 100, a portion of the first empty foil segment 21a between the first insulating layer 51 and the first tab 30 may be exposed, posing a short circuit risk. If the overlap length is too large, the second insulating layer 52 may extend to the curved portion of the electrode assembly 20, resulting in an excessively thick curved portion, affecting the thickness of the secondary battery 100 and the winding of the electrode assembly 20.

[0079] In the embodiments of this application, referring to FIG5, along the winding direction, the projected overlap length of the first insulating layer 51 and the second insulating layer 52 in the thickness direction of the first empty foil segment 21a is L4, where 1mm≤L4≤6mm. This reduces the exposure of the first empty foil segment 21a, reduces the occurrence of short circuits, and reduces the bending portion of the second insulating layer 52 extending into the electrode assembly 20. Based on the same inventive concept, along the winding direction, the projected overlap length of the second insulating layer 52 and the fourth insulating layer 54 in the thickness direction of the first empty foil segment 21a is L5, where 1mm≤L5≤6mm. This reduces the exposure of the first empty foil segment 21a, reduces the occurrence of short circuits, and reduces the bending portion of the fourth insulating layer 52 extending into the electrode assembly 20.

[0080] Furthermore, 1mm≤L4≤2mm, and / or 1mm≤L5≤2mm. This can further reduce the exposure of the first empty foil segment 21a, reduce the occurrence of short circuits, and further reduce the bending portion of the second insulating layer 52 and / or the fourth insulating layer 54 extending into the electrode assembly 20.

[0081] In some embodiments, the first insulating layer 51 and the third insulating layer 53 may also extend to a portion of the first active material layer 212 in the coating section 21b, which can reduce the amount of empty foil exposed between the first insulating layer 51 and the third insulating layer 53 and the coating section 21b, thereby reducing the occurrence of short circuits. Furthermore, by covering the edges of the first active material layer 212 with the first insulating layer 51 and the third insulating layer 53, the shedding of the first active material layer 212 at the edges can be reduced.

[0082] To measure the resistance of the first tab 30 and the second tab 40, the first tab 30 and the second tab 40 can be cut to the same size and connected to the same voltage. The current flowing through the first tab 30 and the second tab 40 can be detected, and the resistance of the first tab 30 and the second tab 40 can be obtained according to the resistance calculation formula.

[0083] 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 first tab 30 is made of aluminum, aluminum alloy, nickel, or nickel-plated aluminum. The second tab 40 is made of copper, copper-nickel alloy, nickel-plated copper, copper-plated nickel, or silver-plated copper.

[0084] Alternatively, the first tab 30 may be the negative tab, and the second tab 40 may be the positive tab. The first tab 30 may be made of either nickel or stainless steel. The second tab 40 may be made of either aluminum, aluminum alloy, nickel-plated aluminum, or silver-plated aluminum.

[0085] For example, the first tab 30 is made of aluminum, while the second tab 40 is made of copper plated with nickel. The first tab 30 has a higher resistance, and the heat source is mainly concentrated at the first tab 30.

[0086] In the embodiments of this application, please refer to FIG6. Along the thickness direction of the first empty foil segment 21a, 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 covers the portion of the first electrode 30 located on the first empty foil segment 21a, which allows two insulating layers (first insulating layer 51 and second insulating layer 52) and a separating film 23 to exist between the first electrode 30 and the second empty foil segment 22a, thereby reducing the risk of short circuits caused by contact between the first electrode 30 and the second empty foil segment 22a.

[0087] Based on the same inventive concept, along the thickness direction of the first empty foil segment 21a, 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 third insulating layer 53. The third insulating layer 53 covers the portion of the first electrode 30 located on the first empty foil segment 21a, which allows two insulating layers (the third insulating layer 53 and the fourth insulating layer 54) and a separating film 23 to exist between the first electrode 30 and the single-sided coated segment 22b, thereby reducing the risk of short circuits caused by contact between the first electrode 30 and the single-sided coated segment 22b.

[0088] Referring to Figure 6, the first insulating layer 51 extends to the first portion 21a1 to completely cover the portion of the first tab 30 located on the first empty foil segment 21a. However, if the length between the first insulating layer 51 and the winding start end 211a is too large, the exposed length of the first empty foil segment 21a will be excessive, increasing the risk of a short circuit. If the length is too small, it will affect the cutting of the first current collector 211. In the embodiments of this application, the length between the first insulating layer 51 and the winding start end 211a along the winding direction is L6, where 1mm ≤ L6 ≤ 2mm. This reduces the exposure of the first empty foil segment 21a, decreases the occurrence of short circuits, and facilitates the cutting operation of the first current collector 211.

[0089] Based on the same inventive concept, along the winding direction, the length between the third insulating layer 53 and the winding start end 211a is L7, 1mm≤L7≤2mm, which can reduce the exposure of the first empty foil segment 21a, reduce the occurrence of short circuits, and facilitate the cutting operation of the first current collector 211.

[0090] Regarding the overlap length between the first insulating layer 51 and the first portion 21a1, if the overlap length is too short, the first tab 30 may be exposed, causing the first tab 30 to melt the insulating film 23 or even the second insulating layer 52, resulting in a high risk of short circuit. If the overlap length is too long, the amount of insulating layer used will be too large, and it may affect the cutting of the first current collector 211. In the embodiments of this application, along the winding direction, the overlap length between the first insulating layer 51 and the first portion 21a1 in the thickness direction of the first portion 21a1 is L8, where 1mm≤L8≤1.5mm. This reduces the exposure of the first tab 30, reduces the occurrence of short circuits, and facilitates the cutting operation of the first current collector 211.

[0091] Based on the same inventive concept, along the winding direction, the third insulating layer 53 overlaps with the first part 21a1 by a length L9 in the thickness direction of the first part 21a1, where 1mm≤L9≤1.5mm. This reduces the exposure of the first electrode tab 30, reduces the occurrence of short circuits, and facilitates the cutting operation of the first current collector 211.

[0092] If the overlap length between the first insulating layer 51 and the second insulating layer 52 is too short, and the heat radiation range of the first electrode tab 30 is large, there may be only one insulating layer and one separator 23 within the heat radiation range, posing a risk of short circuit due to melting and breakage of the insulating layer and separator 23. If the overlap length is too long, the second insulating layer 52 may extend to the curved portion of the electrode assembly 20, resulting in an excessively thick curved portion, affecting the width of the secondary battery 100 and the winding of the electrode assembly 20.

[0093] In the embodiments of this application, please refer to FIG7. In the second part 21a2, along the winding direction, the first insulating layer 51 and the second insulating layer 52 overlap by a length L in the thickness direction of the second part 21a2. 10 ,1mm≤L 10 ≤1.5mm, which can reduce the occurrence of short circuits while reducing the extension of the second part 21a2 to the bending part.

[0094] Based on the same inventive concept, in the second part 21a2, along the winding direction, the third insulating layer 53 and the fourth insulating layer 54 overlap by a length L in the thickness direction of the second part 21a2. 11 ,1mm≤L 11 ≤1.5mm, which can reduce the occurrence of short circuits while reducing the extension of the second part 21a2 to the bending part.

[0095] By adopting the above solution, the occurrence of short circuits due to heat generation in the first tab 30 and the second tab 40 can be reduced. Therefore, the distance between the first tab 30 and the second tab 40 can be made smaller. For example, referring to Figure 1, along the width direction (fourth direction H) of the secondary battery 100, the distance between the first tab 30 and the second tab 40 is D, where 2mm ≤ D ≤ 10mm. This saves space and optimizes the structure of the secondary battery 100, reducing the overall width of the secondary battery 100. For example, if the width of the secondary battery 100 is W, where 10mm ≤ W ≤ 35mm, it can be adapted to electronic devices such as Bluetooth headsets, small radios, and small power tools.

[0096] 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.

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

[0098] Example 1-1

[0099] <Preparation of the positive electrode>

[0100] 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.

[0101] An 8μm 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 0.135 mg / mm². 2A 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 first and second empty foil areas have different lengths in the length direction of the positive current collector, forming a first single-sided empty foil segment with a positive active material layer on one side and an empty foil on the other. The positive electrode sheet has dimensions of 40.7mm × 403.5mm, and the thickness of the single-layer positive active material layer is 39.1μm. A 2mm wide aluminum sheet positive electrode tab is selected and welded to the first empty foil segment.

[0102] <Preparation of Negative Electrode Sheets>

[0103] 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.

[0104] A 6μm 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 0.075 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 lengths of the third and fourth empty foil areas are different in the length direction of the negative current collector, forming a single-sided coated segment with a negative active material layer on one side and an empty foil on the other. A 2mm wide nickel sheet negative electrode tab is selected and welded to the second empty foil segment. The resistance R2 of the negative electrode sheet is greater than the resistance R1 of the positive electrode tab. The specifications of the negative electrode sheet are 42.2mm × 391.6mm, and the thickness of the single-layer negative active material layer is 38.6μm.

[0105] <Preparation of the separating membrane>

[0106] A porous polyethylene (PE) film with a thickness of 5 μm was used as the separator.

[0107] <Electrolyte Preparation>

[0108] 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.

[0109] <Preparation of Insulating Layer>

[0110] Polyethylene terephthalate (PET) was selected as the first substrate layer, and acrylic resin was selected as the first adhesive layer. The first adhesive layer was laminated onto the first substrate layer to form a first insulating layer with a thickness of 20 μm. The first insulating layer was then bonded to one surface of the first empty foil segment. Following a similar method, second, third, and fourth insulating layers with a thickness of 20 μm were prepared. The third insulating layer was bonded to the other surface of the first empty foil segment, the second insulating layer was bonded to one surface of the second empty foil segment, and the fourth insulating layer was bonded to one surface of the single-sided coated segment.

[0111] <Preparation of Lithium-ion Batteries>

[0112] The separator, negative electrode, separator, and positive electrode prepared above are stacked in sequence and wound to obtain an electrode assembly. After winding, the first insulating layer faces the winding center, the third insulating layer faces away from the winding center, and the first empty foil segment forms the innermost ring of the positive electrode. The second insulating layer faces away from the winding center, the fourth insulating layer faces the winding center, and the second empty foil segment forms the innermost ring of the negative electrode. Along the thickness direction of the first empty foil segment, within the projection range of the first empty foil segment, the projection of the positive electrode tab and the projection of the starting end of the positive electrode winding are located within the projection of the second insulating layer, and the projection of the positive electrode tab and the projection of the starting end of the winding are located within the projection of the fourth insulating layer. Along the thickness direction of the first empty foil segment, the first insulating layer partially overlaps with the second insulating layer, and the third insulating layer partially overlaps with the fourth insulating layer. Furthermore, the length L1 between the positive electrode tab and the starting segment of the winding (the first part) is 1 mm, and the first and third insulating layers do not cover the positive electrode tab.

[0113] 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.

[0114] Unlike Example 1-1, the relevant parameters in Examples 1-2 to 1-11 and Comparative Examples 1-1 to 1-3 are shown in Table 1 below. In Comparative Examples 1-1 to 1-3, both the first insulating layer and the third insulating layer cover the positive electrode tab.

[0115] 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.

[0116] Measurement frequency: Voltage internal resistance measurement uses 1KHz specification, after preprocessing, and measurement is performed after testing;

[0117] Failure criteria: The lithium-ion battery explodes, leaks, or catches fire;

[0118] Each group tested 20 lithium-ion batteries, and the failure rates are shown in Table 1 below.

[0119] Table 1

[0120] According to Table 1 above, and in conjunction with Examples 1-11 and Comparative Examples 1-1 to 1-3, when the negative electrode tab resistance R2 is greater than the positive electrode tab resistance R1, the risk of short-circuit failure in lithium-ion batteries can be effectively reduced when the positive electrode tab overlaps with the second and fourth insulating layers, and the first and second insulating layers partially overlap, and the third and fourth insulating layers partially overlap. The portion between the positive electrode tab and the winding start end is isolated from the negative electrode sheet by the insulating layers, which not only reduces burrs piercing the separator but also reduces short circuits caused by contact between the positive and negative electrode sheets.

[0121] In Example 1-1, the length L1 between the positive electrode tab and the winding start section is relatively small, making the welding operation of the positive electrode tab more complicated and unfavorable. In Examples 1-2 to 1-10, the risk of short-circuit failure is lower than in Example 1-11. Compared to Example 1-11, in Examples 1-2 to 1-10, the length L1 between the positive electrode tab and the winding start end is smaller, resulting in less potential contact between the positive and negative electrode sheets and a lower risk of short circuit. Furthermore, compared to Example 1-1, L1 is larger in Examples 1-2 to 1-10, facilitating the welding operation of the positive electrode tab. Therefore, in the embodiments of this application, 1mm ≤ L1 ≤ 3.2mm can be selected.

[0122] In Examples 1-2 to 1-5, the risk of short-circuit failure is further reduced. In the examples of this application, it is preferred that 1.3mm≤L1≤1.7mm.

[0123] Unlike Example 1-1, in Examples 2-1 to 2-7 and Comparative Examples 2-1 to 2-2, the negative electrode tab is made of nickel-plated copper. The resistance R2 of the negative electrode tab is less than the resistance R1 of the positive electrode tab. The main heat source is located on the positive electrode tab. Furthermore, the first insulating layer covers the positive electrode tab and extends to the first portion, with a length of 1.5 mm covering the first portion. The length between the first insulating layer and the winding start end is L6. The third insulating layer covers the positive electrode tab and extends to the first portion, with a length of 1.5 mm covering the first portion. The length between the third insulating layer and the winding start end is L7. The relevant parameters in Examples 2-1 to 2-7 and Comparative Examples 2-1 to 2-2 are shown in Table 2 below.

[0124] Table 2

[0125] According to Table 2 above, and in conjunction with Examples 2-4 and Comparative Examples 2-1 to 2-2, when the resistance R2 of the negative electrode tab is less than the resistance R1 of the positive electrode tab, the risk of short-circuit failure of the lithium-ion battery can be effectively reduced when the positive electrode tab overlaps with the second and fourth insulating layers, and the first and second insulating layers partially overlap, and the third and fourth insulating layers partially overlap. This is because there are two insulating layers and one separator film between the first electrode tab and the second empty foil segment, which reduces the risk of short circuits caused by contact between the first electrode tab and the second empty foil segment. Similarly, there are two insulating layers and one separator film between the first electrode tab and the single-sided coated segment, which also reduces the risk of short circuits caused by contact between the first electrode tab and the single-sided coated segment.

[0126] In Example 2-1, the lengths of L6 and L7 are too small, making it easy to cut into the insulating layer when cutting the current collector, which is detrimental to the current collector cutting operation. In Examples 2-2 to 2-6, the short-circuit test failure rate is lower than that in Example 2-7. The lengths L6 between the first insulating layer and the winding start end, and L7 between the third insulating layer and the winding start end are smaller, resulting in a lower risk of short circuits. Furthermore, compared to Example 2-1, L6 and L7 are larger in Examples 2-2 to 2-6, which reduces the risk of cutting into the first and third insulating layers. Therefore, in the embodiments of this application, 1mm≤L6≤2mm and 1mm≤L7≤2mm can be selected.

[0127] 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 first empty foil segment being the winding start segment of the first electrode sheet, and the first tab being connected to the first empty foil segment; the second electrode sheet comprising a second empty foil segment and a single-sided coated segment connected together, the second empty foil segment being the winding start segment of the second electrode sheet, the second tab being connected to the second empty foil segment, the second tab and the first tab being arranged sequentially along the winding direction, and the electrode sheet adjacent to the first empty foil segment being the second empty foil segment and the single-sided coated segment, respectively, characterized in that: The second empty foil segment has a second insulating layer on its surface away from the winding center, and the single-sided coated segment has a fourth insulating layer on its surface facing the winding center; the first electrode includes a winding start end, and 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 and the projection of the winding start end are located within the projection of the second insulating layer, and the projection of the first electrode tab and the projection of the winding start end are located within the projection of the fourth insulating layer; A first insulating layer is provided on the surface of the first empty foil segment facing the winding center, and the first insulating layer and the second insulating layer partially overlap along the thickness direction of the secondary battery; A third insulating layer is provided on the surface of the first empty foil segment away from the winding center, and the third insulating layer partially overlaps with the fourth insulating layer along the thickness direction of the secondary battery.

2. The secondary battery according to claim 1, characterized in that, The resistance of the first tab is R1, and the resistance of the second tab is R2, where R1 < R2; Along the thickness direction of the first empty foil segment, the first insulating layer does not overlap with the first tab, and / or the third insulating layer does not overlap with the first tab.

3. The secondary battery according to claim 2, 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 one of aluminum, aluminum alloy, nickel-plated aluminum, or silver-plated aluminum; The second electrode is made of either nickel or stainless steel.

4. The secondary battery according to claim 2, characterized in that, The first electrode tab is a negative electrode tab, and the second electrode tab is a positive electrode tab; The material of the first electrode tab is one of copper, copper-nickel alloy, nickel-plated copper, copper-plated nickel, or silver-plated copper; The material of the second electrode tab is one of aluminum, aluminum alloy, nickel, or nickel-plated aluminum.

5. The secondary battery according to claim 2, characterized in that, The first electrode includes a first portion. Along the winding direction, the portion of the first electrode located between the winding start end and the first electrode tab forms the first portion. The length of the first portion is L1, where 1mm ≤ L1 ≤ 3.2mm.

6. The secondary battery according to claim 5, characterized in that, 1.3mm≤L1≤1.7mm.

7. The secondary battery according to any one of claims 2 to 6, characterized in that, The first electrode includes a coated section connected to the first empty foil section. The first empty foil section includes a second part, and the portion of the first empty foil section located between the first electrode tab and the coated section forms the second part. The first insulating layer and the third insulating layer are both disposed in the second part. Along the winding direction, the distance between the first insulating layer and the first tab is L2, and the distance between the third insulating layer and the first tab is L3; 1mm≤L2≤2mm, and / or, 1mm≤L3≤2mm.

8. The secondary battery according to any one of claims 2 to 7, characterized in that, Along the winding direction, the length of the overlap between the projections of the first insulating layer and the second insulating layer in the thickness direction of the first empty foil segment is L4, and the length of the overlap between the projections of the second insulating layer and the fourth insulating layer in the thickness direction of the first empty foil segment is L5. 1mm≤L4≤6mm, and / or, 1mm≤L5≤6mm.

9. The secondary battery according to claim 8, characterized in that, 1mm≤L4≤2mm, and / or 1mm≤L5≤2mm.

10. The secondary battery according to any one of claims 2 to 9, characterized in that, Along the thickness direction of the secondary battery, the electrode assembly includes a first straight portion and a second straight portion disposed opposite to each other. Along the width direction of the secondary battery, the electrode assembly includes a first curved portion and a second curved portion disposed opposite to each other. The first curved portion and the second curved portion are connected between the first straight portion and the second straight portion. Both the second insulating layer and the fourth insulating layer are disposed on the first straight portion or the second straight portion.

11. The secondary battery according to claim 1, characterized in that, The resistance of the first tab is R1, and the resistance of the second tab is R2, where R1 > R2; Along the thickness direction of the first empty foil segment, 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, and the projection of the first electrode is located within the projection of the third insulating layer.

12. The secondary battery according to claim 11, 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 one of aluminum, aluminum alloy, nickel, or nickel-plated aluminum; The material of the second electrode tab is one of copper, copper-nickel alloy, nickel-plated copper, copper-plated nickel, or silver-plated copper.

13. The secondary battery according to claim 11, characterized in that, The first electrode tab is a negative electrode tab, and the second electrode tab is a positive electrode tab; The material of the first electrode tab is either nickel or stainless steel; The material of the second electrode is one of aluminum, aluminum alloy, nickel-plated aluminum, or silver-plated aluminum.

14. The secondary battery according to claim 11, characterized in that, The first empty foil segment includes a winding start end, and along the winding direction, the length between the first insulating layer and the winding start end is L6, and the length between the third insulating layer and the winding start end is L7; 1mm≤L6≤2mm, and / or, 1mm≤L7≤2mm.

15. The secondary battery according to any one of claims 11 to 14, characterized in that, The first empty foil segment includes a first portion, which is formed by the portion of the first empty foil segment located between the winding start end and the first electrode tab; Along the winding direction, the first insulating layer overlaps with the first portion by a length L8 in the thickness direction of the first portion, and the third insulating layer overlaps with the first portion by a length L9 in the thickness direction of the first portion; 1mm≤L8≤1.5mm, and / or, 1mm≤L9≤1.5mm.

16. The secondary battery according to any one of claims 11 to 15, characterized in that, The first electrode includes a coated section connected to the first empty foil section, the first empty foil section including a second portion, the portion of the first empty foil section located between the first electrode tab and the coated section forming the second portion; In the second portion, along the winding direction, the length by which the first insulating layer and the second insulating layer overlap in the thickness direction of the second portion is L. 10 The overlap length between the third insulating layer and the fourth insulating layer in the thickness direction of the second portion is L. 11 ; 1mm≤L 10 ≤1.5mm, and / or, 1mm≤L 11 ≤1.5mm.

17. The secondary battery according to any one of claims 1 to 16, characterized in that, The first insulating layer, the second insulating layer, the third insulating layer, and the fourth insulating layer are all adhesive layers.

18. The secondary battery according to any one of claims 1 to 17, characterized in that, Along the width direction of the secondary battery, the distance between the first tab and the second tab is D, where 2mm≤D≤10mm.

19. The secondary battery according to any one of claims 1 to 18, characterized in that, The width of the secondary battery is W, where 10mm ≤ W ≤ 35mm.

20. The secondary battery according to any one of claims 1 to 19, characterized in that, The secondary battery has a length of L and a width of W, where 2.5 ≤ L / W ≤ 6.

21. The secondary battery according to claim 1, characterized in that, The first electrode is the positive electrode, and the second electrode is the negative electrode.

22. An electronic device, characterized in that, Includes the secondary battery as described in any one of claims 1 to 21.

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