Secondary battery and electronic device

Abstract

A secondary battery and an electronic device. The secondary battery comprises an electrode assembly, wherein the electrode assembly comprises a first electrode sheet, a separator, and a second electrode sheet that are stacked and wound. In a winding direction, the first electrode sheet comprises a first starting end. In the thickness direction of the first electrode sheet, the second electrode sheet is an electrode sheet adjacent to the first starting end. The secondary battery further comprises a first adhesive layer. In the thickness direction of the first electrode sheet, the first adhesive layer is disposed on the separator between the first starting end and the second electrode sheet, and the first adhesive layer covers the first starting end. In a direction opposite to the winding direction, the first adhesive layer extends beyond the first electrode sheet from the first starting end. The risk of burrs at the first starting end piercing the separator can be reduced, and exposure of the first starting end caused by slipping of the first starting end can be reduced, thereby reducing the occurrence of short circuits caused by the burrs at the first starting end piercing the separator, and improving the safety performance of the secondary battery.

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 rapid development of modern technology, the demand for high-performance energy storage devices is increasing in fields such as portable electronic devices and electric vehicles. Lithium-ion batteries, as a highly efficient and environmentally friendly energy storage device, have been widely used in many fields due to their advantages such as high energy density, long cycle life, and low self-discharge rate. As lithium-ion batteries continue to develop, the requirements for battery safety performance are becoming increasingly stringent. Summary of the Invention

[0003] This application aims to provide a secondary battery and electronic device that improves the safety performance of the battery.

[0004] In a first aspect, embodiments of this application propose a secondary battery, including an electrode assembly comprising a first electrode, a separator, and a second electrode stacked and wound together. Along the winding direction, the first electrode includes a first starting end, and along the thickness direction of the first electrode, a second electrode is adjacent to the first starting end. The secondary battery also includes a first adhesive layer. Along the thickness direction of the first electrode, the first adhesive layer is disposed on the separator between the first starting end and the second electrode, covering the first starting end. In the opposite direction of the winding direction, the first adhesive layer extends from the first starting end of the first electrode.

[0005] In the above technical solution, placing the first adhesive layer on the separator and covering the first starting end of the first current collector reduces the risk of burrs from the first starting end piercing the separator, thereby reducing the risk of short circuits caused by direct contact between the first starting end and the second electrode. Furthermore, since the first starting end is not affected, the first adhesive layer can be pre-positioned and adhered to the separator. When the separator and the first current collector are stacked, the first adhesive layer can accurately cover and extend beyond the first starting end, making the operation simple and convenient. This not only helps improve the accuracy and stability of the secondary battery during assembly but also reduces the risk of the first starting end being exposed due to slippage, thus reducing the risk of burrs from the first starting end piercing the separator and causing short circuits, and improving the safety performance of the secondary battery.

[0006] In some embodiments, the first starting end is located on the secondary inner ring electrode of the electrode assembly. The secondary inner ring electrode has a higher risk of puncturing the separator. Placing the first adhesive layer on the separator and covering the first starting end of the secondary inner ring has a more significant effect on reducing the risk of puncturing the separator.

[0007] In some embodiments, the secondary battery is cylindrical. ，In the embodiments of this application, the first adhesive layer is disposed on the separator, which makes it easier for the first adhesive layer to cover and extend beyond the first starting end, thereby reducing the slippage of the first starting end and the occurrence of short circuit, which is especially suitable for cylindrical secondary batteries.

[0008] In some embodiments, the secondary battery further includes a housing, an electrode assembly disposed within the housing, the inner diameter of the housing being D1, and the outer diameter of the electrode assembly being D2. The first adhesive layer includes a first portion and a second portion. Along the thickness direction of the first electrode sheet, the first portion overlaps with the first electrode sheet. Along the opposite direction of the winding direction, the second portion extends beyond the first starting end. Along the winding direction, the length of the first portion is L1, where L1 ≥ π(D1 - D2). As the first starting end slides outwards along the winding direction, even if the electrode assembly occupies the internal space of the housing, the first portion can still cover the first starting end, reducing the exposure of the first starting end.

[0009] Optionally, the length of the second part is L2, where L2≥π(D1-D2). When the first starting end slides in the opposite direction of the winding direction toward the inner circle, even if the electrode assembly occupies the internal space of the housing, the second part can still cover the first starting end, further reducing the exposure of the first starting end.

[0010] In some embodiments, 0.47mm≤L1≤5mm is beneficial for the first portion to fully cover the first starting end, reducing short circuits caused by slippage of the first starting end, and also reducing the impact on the energy density of the secondary battery, as well as ensuring a high adhesive strength between the first portion and the separator. Preferably, 1mm≤L1≤3mm further reduces the exposure of the first starting end, reduces the impact on the energy density of the secondary battery, and improves the adhesive strength.

[0011] In some embodiments, 0.47mm ≤ L2 ≤ 7mm is beneficial for the second portion to fully cover the first starting end, reducing short circuits caused by slippage of the first starting end, minimizing the impact on the energy density of the secondary battery, and ensuring high adhesive strength between the second portion and the separator. Preferably, 1mm ≤ L2 ≤ 4mm further reduces the exposure of the first starting end, minimizing the impact on the energy density of the secondary battery, and improving adhesive strength.

[0012] In some embodiments, along the width direction of the first electrode, the width of the first adhesive layer is W1, the width of the first electrode is W2, and the width of the separator is W, where W2 < W1 ≤ W. This facilitates the first adhesive layer completely covering the first starting end, reduces the first adhesive layer extending beyond the separator, and thus reduces the impact of the first adhesive layer on the energy density of the secondary battery.

[0013] In some embodiments, the first adhesive layer is located between the first starting end and the separator. ，The first adhesive layer can directly isolate the first starting end from the separator, thereby reducing the burrs at the first starting end from piercing the separator, reducing the occurrence of short circuits, and helping to ensure that the separator has high integrity.

[0014] In some embodiments, the separator includes a substrate layer and a ceramic layer. Along the thickness direction of the separator, the substrate layer includes a first surface and a second surface disposed opposite to each other. The ceramic layer is disposed on the first surface, and the first adhesive layer is bonded to the second surface. The substrate layer and the first adhesive layer of the separator have good compatibility. When the first adhesive layer is bonded to the substrate layer, problems such as deterioration and detachment caused by chemical interactions can be reduced. Furthermore, the substrate layer of the separator has a certain degree of flexibility and strength, which can provide stable support for the first adhesive layer and help maintain the integrity of the first adhesive layer structure.

[0015] In some embodiments, the substrate layer comprises at least one of polyethylene, polypropylene, polytetrafluoroethylene, cellulose acetate, or cellulose nanofibers. Each material exhibits excellent chemical stability, maintaining its structural and performance stability in an electrolyte environment, thereby effectively reducing the risk of membrane failure due to chemical reactions with the electrolyte.

[0016] In some embodiments, the ceramic layer comprises at least one of boehmite, alumina, or silica. This reduces heat dissipation, thereby reducing thermal runaway in the secondary battery and effectively improving its safety performance.

[0017] In some embodiments, a second electrode is disposed on the side of the first starting end opposite to the winding center, and a first adhesive layer is disposed on the separator film on the side of the first starting end opposite to the winding center. Due to the outward tension of the first electrode, it is easier for the first starting end to puncture the separator film on the side opposite to the winding center. Preferably, the first adhesive layer is disposed on the separator film on the side of the first starting end opposite to the winding center, which can effectively reduce burrs puncturing the separator film between the first starting end and the second electrode, thereby reducing the direct contact between the first starting end and the second electrode and the resulting short circuit.

[0018] In some embodiments, the second electrode extends from the first starting end toward the winding center in the opposite direction to the winding direction. The secondary battery also includes a second adhesive layer disposed on the separator on the side of the first starting end facing the winding center. The second adhesive layer covers the first starting end along the thickness direction of the first electrode. In the opposite direction to the winding direction, the second adhesive layer extends from the first starting end of the first electrode. This allows both the first and second adhesive layers to cover the first starting end, protecting the separator on both sides of the first starting end and further reducing the risk of short circuits caused by burrs piercing the separator.

[0019] In some embodiments, bonding the first adhesive layer to the second adhesive layer can improve the fixation effect of the separator, reduce separator displacement during secondary battery assembly, and thus reduce misalignment between the first and second adhesive layers, making it easier to fully isolate the first starting end. Furthermore, the bonding between the first and second adhesive layers can, to some extent, limit the slippage of the first starting end, reducing exposure of the first starting end and thus reducing the occurrence of short circuits.

[0020] In some embodiments, along the thickness direction of the first electrode, the first electrode includes a first current collector and a first active material layer stacked together. The first adhesive layer and the first active material layer do not overlap, which can reduce the influence of the first adhesive layer on the thickness of the first electrode and facilitate the winding of the first electrode.

[0021] In some embodiments, the first adhesive layer has through holes, and the first adhesive layer covers a portion of the first active material layer. Since the first adhesive layer is directly disposed on the separator, it has no effect on the first current collector. Therefore, the first current collector does not need to have too many empty foil areas for bonding the first adhesive layer, which can increase the first active material layer. Furthermore, the through holes are used for ion conduction, which is beneficial to improving the kinetics of the secondary battery and increasing the energy density of the secondary battery.

[0022] In some embodiments, the first electrode includes a first terminal end, and a second electrode is adjacent to the first terminal end along the thickness direction of the first electrode. The secondary battery also includes a third adhesive layer, which is disposed on the separator between the first terminal end and the second electrode along the thickness direction of the first electrode, covering the first terminal end. Furthermore, the third adhesive layer extends out of the first electrode from the first terminal end along the winding direction.

[0023] By placing the third adhesive layer on the separator and covering the first end of the first current collector, the burrs from the first end can be reduced from piercing the separator, thereby reducing the risk of a short circuit due to direct contact between the first end and the second electrode. Furthermore, since the first end is not affected, the third adhesive layer can be pre-positioned and adhered to the separator. When the separator and the first current collector are stacked, the third adhesive layer can accurately cover and extend beyond the first end. This not only improves the accuracy and stability of the secondary battery during assembly but also reduces the risk of the first end being exposed due to slippage, thus reducing the risk of a short circuit caused by burrs from the first end piercing the separator.

[0024] In some embodiments, the first termination end is located on the secondary outer ring electrode of the electrode assembly. The secondary outer ring electrode has a higher risk of puncturing the separator. Placing the third adhesive layer on the separator and covering the first termination end of the secondary outer ring has a more significant effect on reducing the risk of puncturing the separator.

[0025] In some embodiments, a third adhesive layer is disposed on the separator film on the side of the first terminal end facing away from the winding center. The secondary battery also includes a fourth adhesive layer disposed on the separator film on the side of the first terminal end facing the winding center. The fourth adhesive layer covers the first terminal end along the thickness direction of the first electrode sheet. Furthermore, the fourth adhesive layer extends from the first terminal end of the first electrode sheet along the winding direction. This allows both the third and fourth adhesive layers to cover the first terminal end, protecting the separator film on both sides of the first terminal end and further reducing the risk of short circuits caused by burrs piercing the separator film.

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

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

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

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

[0030] Figure 2 is a schematic diagram of the explosion of a secondary battery according to some embodiments of this application;

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

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

[0033] Figure 5 is a partial structural schematic diagram of the electrode assembly located at the first starting end in some embodiments of this application;

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

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

[0036] Figure 8 is a schematic diagram of the stacked structure of the first electrode and the separator in some embodiments of this application;

[0037] Figure 9 is a partial structural schematic diagram of the electrode assembly located at the first starting end in some embodiments of this application;

[0038] Figure 10 is a schematic diagram of the structure of the isolation membrane and the first adhesive layer in some embodiments of this application;

[0039] Figure 11 is a partial structural diagram of the electrode assembly located at the first terminal end in some embodiments of this application.

[0040] Explanation of reference numerals in the attached figures:

[0041] 100. Secondary batteries;

[0042] 10. Shell; 11. First wall portion; 12. Second wall portion; 13. Main body portion; 14. Opening;

[0043] 20. Electrode assembly;

[0044] 21. First electrode; 211. First current collector; 2111. First starting end; 2112. First ending end; 212. First active material layer;

[0045] 22. Second electrode; 221. Second inner circle electrode; 222. Second inner circle electrode;

[0046] 23. Separating membrane; 231. Substrate layer; 232. Ceramic layer;

[0047] 30. First adhesive layer; 30a. First substrate layer; 30b. First bonding layer; 31. First part; 32. Second part;

[0048] 40. Second adhesive layer; 50. Third adhesive layer; 60. Fourth adhesive layer;

[0049] Z, first direction; X, second direction; Y, third direction; S, winding direction; G, winding center; K, axial direction. Detailed Implementation

[0050] 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.

[0051] 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.

[0052] 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" and "several" mean two or more, unless otherwise explicitly defined.

[0053] 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.

[0054] In a first aspect, embodiments of this application provide a secondary battery 100. Referring to Figures 1 and 2, the secondary battery 100 includes a housing 10 and an electrode assembly 20 and an electrolyte (not shown in the figures) housed within the housing 10. The electrolyte wets the electrode assembly 20 within the housing 10, thereby causing an electrochemical reaction.

[0055] The housing 10 described above can be square, trapezoidal, or cylindrical. In this embodiment, a cylindrical housing 10 is used as an example. Referring to Figures 1 and 2, the housing 10 includes a first wall portion 11, a second wall portion 12, and a main body portion 13. Along the axial direction K of the secondary battery 100, the first wall portion 11 and the second wall portion 12 can be respectively connected to both ends of the main body portion 13. The second wall portion 12 can be integrally formed with the main body portion 13 or separately formed. An opening 14 is provided at the end of the main body portion 13 opposite to the second wall portion 12. The electrode assembly 20 can be placed inside the housing 10 through the opening 14. The housing 10 can be sealed by covering the opening 14 with the first wall portion 11.

[0056] The casing 10 can be made of conductive metal materials such as aluminum, aluminum alloy, steel, stainless steel, nickel, copper, or magnesium alloy. This allows the casing 10 to lead out a certain polarity of the secondary battery 100, for example, the casing 10 itself can be used as the positive or negative electrode of the secondary battery 100. In some other embodiments, the casing 10 can also be made of a soft-pack material, such as an aluminum-plastic film or a copper-plastic film.

[0057] The electrode assembly 20 described above is housed within the housing 10. Referring to Figures 3 and 4, the electrode assembly 20 includes a first electrode 21, a second electrode 22, and a separating membrane 23. The first electrode 21, the separating membrane 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). The separating membrane 23 is disposed between the first electrode 21 and the second electrode 22 to insulate and separate them.

[0058] 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, the first electrode 21 is the negative electrode and the second electrode 22 is the positive electrode. For example, when a cylindrical housing 10 is used, the first electrode 21 can be electrically connected to the first wall portion 11, so that the first wall portion 11 leads out one polarity of the secondary battery 100, and the second electrode 22 can be electrically connected to the second wall portion 12, so that the second wall portion 12 leads out the other polarity of the secondary battery 100. By insulating the first wall portion 11 and the second wall portion 12, the occurrence of short circuits can be reduced.

[0059] Referring to Figure 4, the first electrode 21 includes a first current collector 211 and a first active material layer 212. Along the thickness direction (first direction Z) of the first current collector 211, the first active material layer 212 is stacked on at least one surface of the first current collector 211. The first current collector 211 can be made of aluminum foil, copper foil, titanium foil, or nickel foil, etc., which has high strength and high conductivity, can reduce tearing of the first current collector 211, and is beneficial to improving the charge-discharge rate of the secondary battery 100.

[0060] When the first electrode 21 is a positive electrode, the first active material layer 212 includes a positive active material, a conductive agent, and a binder, etc., wherein the positive 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.

[0061] In some other embodiments, when the first electrode 21 is a negative electrode, the first active material layer 212 includes a negative electrode active material, a conductive agent, and a binder, wherein the negative electrode active material includes one or more of graphite, soft carbon, hard carbon, elemental silicon, silicon oxide, and silicon alloy.

[0062] Referring to Figures 3 and 5, along the winding direction S, the first electrode 21 includes a first starting end 2111 and a first ending end 2112. In the preparation process of the first current collector 211, the large roll of current collector needs to be cut to form multiple first current collectors 211. The first starting end 2111 is the cutting position of the first current collector 211, and the first ending end 2112 is another cutting position of the first current collector 211.

[0063] The burrs from the first starting end 2111 pose a risk of puncturing the separator 23, potentially causing the first starting end 2111 to directly contact the second electrode 22 and result in a short circuit. Before cutting out the first current collector 211, it is necessary to apply adhesive to the first current collector 211, and then cut the adhesive layer and the first current collector 211 together. This allows the adhesive layer to cover the first starting end 2111, thereby reducing the risk of the burrs from the first starting end 2111 puncturing the separator 23 and causing a short circuit.

[0064] However, the inventors of this application have discovered that during long-term charge and discharge cycles, the first electrode 21 of the secondary battery 100 may expand, which may cause the first starting end 2111 to slip along the winding direction S or in the opposite direction of the winding direction S. This may cause the first starting end 2111 to misalign with the adhesive layer, which may expose the first starting end 2111. Consequently, the burrs on the first starting end 2111 may pierce the separator 23 and cause a short circuit.

[0065] The inventors of this application employ a method of first cutting out two first current collectors 211, separating the two first current collectors 211 by a certain distance, then bonding the two first current collectors 211 together with an adhesive layer, and finally cutting the adhesive layer between the two current collectors so that the adhesive layer covers and extends beyond the first starting end 2111. However, this method requires multiple adhesive application and cutting operations, making the process complex and affecting the production efficiency of the secondary battery 100. Furthermore, after the two first current collectors 211 are separated by a certain distance, the portion of the adhesive layer between the two first current collectors 211 is unsupported, making adhesive application and cutting difficult and prone to low accuracy, potentially resulting in the first starting end 2111 being directly exposed.

[0066] To mitigate the aforementioned problems, in the embodiments of this application, referring to Figures 5 and 6, the secondary battery 100 includes a first adhesive layer 30, a first electrode 21 in the thickness direction (first direction Z), a second electrode 22 adjacent to the first starting end 2111, and a first adhesive layer 30 disposed on a separator 23 between the first starting end 2111 and the second electrode 22, covering the first starting end 2111. Furthermore, in the opposite direction to the winding direction S, the first adhesive layer 30 extends from the first starting end 2111 out of the first electrode 21.

[0067] In the embodiments of this application, the first adhesive layer 30 is disposed on the isolation membrane 23 and covers the first starting end 2111 of the first current collector 211, which can reduce the burrs of the first starting end 2111 from piercing the isolation membrane 23, thereby reducing the direct contact between the first starting end 2111 and the second electrode 22 and the resulting short circuit.

[0068] Furthermore, since there is no influence from the first starting end 2111, the first adhesive layer 30 can be pre-positioned and pasted on the separator 23. When the separator 23 is stacked with the first current collector 211, the first adhesive layer 30 can accurately cover and extend beyond the first starting end 2111. The operation is simple and convenient, which not only helps to improve the accuracy and stability of the secondary battery 100 during the assembly process, but also reduces the exposure of the first starting end 2111 due to slippage, thereby reducing the risk of short circuit caused by burrs from the first starting end 2111 piercing the separator 23, and improving the safety performance of the secondary battery 100.

[0069] In addition, since the first adhesive layer 30 is directly disposed on the separator 23, it has no effect on the first current collector 211. Therefore, the first current collector 211 does not need to have too many empty foil areas for bonding the first adhesive layer 30, and the first active material layer 212 can be increased. For example, as shown in Figure 7, the first active material layer 212 can even extend to the first starting end 2111, which is beneficial to improving the energy density of the secondary battery 100.

[0070] It should be noted that, in the opposite direction of the winding direction S, the first adhesive layer 30 extends from the first starting end 2111 to the first electrode 21. This means that, in the opposite direction of the winding direction S, one side of the first adhesive layer 30 has a portion of the first adhesive layer 30, which can reduce the amount of the first adhesive layer 30 exposed due to the first starting end 2111. The same applies to the second adhesive layer 40, the third adhesive layer 50, and the fourth adhesive layer 60.

[0071] The inventors of this application have also discovered that, for the innermost electrode of the electrode assembly 20, there are electrodes of opposite polarity (second electrodes 22) on both sides of its thickness direction, and the inner ring experiences greater stress, increasing the risk of burrs piercing the separator 23. In the embodiments of this application, the first starting end 2111 is located on the innermost electrode of the electrode assembly 20, and the innermost electrode of the electrode assembly 20 is part of the second electrodes 22. Placing the first adhesive layer 30 on the separator 23 and covering the first starting end 2111 of the innermost ring significantly reduces the risk of piercing the separator 23.

[0072] The first adhesive layer 30 can be provided with a porous structure similar to the separator 23. For example, the first adhesive layer 30 is provided with a number of through holes 33. Along the thickness direction of the first electrode 21 (first direction Z), the first adhesive layer 30 covers part of the first active material layer 212, which allows ions to be transported through the separator 23 and the through holes of the first adhesive layer 30, thereby making full use of the internal space of the secondary battery 100 and improving the energy density of the secondary battery 100.

[0073] In some other embodiments, please refer to FIG6. Along the thickness direction (first direction Z) of the first electrode 21, the first adhesive layer 30 and the first active material layer 212 do not overlap. That is, the first adhesive layer 30 is provided with an empty foil area near the first starting end 2111, which can reduce the influence of the first adhesive layer 30 on the thickness of the first electrode 21 and facilitate the winding of the first electrode 21.

[0074] In the embodiments of this application, the secondary battery 100 is cylindrical. During the winding process of the first electrode 21 and the second electrode 22, the first electrode 21 needs to withstand a certain bending stress. Compared with square batteries or batteries with other structures, the first electrode 21 of the cylindrical battery forms a relatively tight cylindrical shape after winding, which may cause the first electrode 21 to form a centripetal tension, making it easier for the first electrode 21 to loosen locally, thereby causing the first starting end 2111 to slip. In the embodiments of this application, the first adhesive layer 30 is disposed on the separator 23, which makes it easier for the first adhesive layer 30 to cover and extend beyond the first starting end 2111, thereby reducing the slippage of the first starting end 2111 and causing a short circuit, which is especially suitable for cylindrical secondary batteries 100.

[0075] In some embodiments, referring to Figures 2 and 7, the electrode assembly 20 is disposed within the housing 10, the inner diameter of the housing 10 is D1, and the outer diameter of the electrode assembly 20 is D2. The first adhesive layer 30 includes a first portion 31 and a second portion 32. Along the thickness direction (first direction Z) of the first electrode 21, the first portion 31 overlaps with the first electrode 21. Along the opposite direction of the winding direction S, the second portion 32 extends out from the first starting end 2111.

[0076] The inventors of this application have discovered that when the electrode expands and causes the electrode assembly 20 to occupy the internal space of the housing 10, the maximum slippage of the first starting end 2111 is typically π(D1-D2). In the embodiments of this application, the length of the first portion 31 along the winding direction S is L1, where L1 ≥ π(D1-D2). For example, when the first starting end 2111 slides outward along the winding direction S, even if the electrode assembly 20 occupies the internal space of the housing 10, the first portion 31 can still cover the first starting end 2111, reducing the exposure of the first starting end 2111.

[0077] Based on the same inventive concept, along the winding direction S, the length of the second part 32 is L2, where L2≥π(D1-D2). For example, when the first starting end 2111 slides in the opposite direction of the winding direction S toward the inner circle, even if the electrode assembly 20 occupies the internal space of the housing 10, the second part 32 can still cover the first starting end 2111, further reducing the exposure of the first starting end 2111.

[0078] The inventors of this application have discovered that if the length of the first adhesive layer 30 is too short, it may be difficult to effectively cover the first starting end 2111, and may also lead to insufficient adhesion between the first adhesive layer 30 and the separator 23, making it easy for the first adhesive layer 30 to fall off. If the length of the first adhesive layer 30 is too long, it occupies a large amount of space and affects the energy density of the secondary battery 100.

[0079] In the embodiments of this application, selecting 0.47mm≤L1≤5mm, such as 0.47mm, 0.5mm, 1mm, 2mm, 3mm, 4mm, or 5mm, is beneficial for the first portion 31 to fully cover the first starting end 2111, reducing short circuits caused by slippage of the first starting end 2111, reducing the impact on the energy density of the secondary battery 100, and ensuring a high bonding strength between the first portion 31 and the separator 23. Preferably, 1mm≤L1≤3mm further reduces the exposure of the first starting end 2111, reduces the impact on the energy density of the secondary battery 100, and improves the bonding strength.

[0080] Because the inner electrode sheet is easier to slide towards the innermost circle, the length of the second part 32 can be appropriately extended. Based on the same inventive concept, a length of 0.47mm ≤ L2 ≤ 7mm is chosen, such as 0.47mm, 0.5mm, 1mm, 2mm, 3mm, 4mm, 5mm, 6mm, or 7mm. This helps the second part 32 to fully cover the first starting end 2111, reducing short circuits caused by the slippage of the first starting end 2111, reducing the impact on the energy density of the secondary battery 100, and ensuring a higher adhesive strength between the second part 32 and the separator 23. Preferably, 1mm ≤ L2 ≤ 4mm further reduces the exposure of the first starting end 2111, reduces the impact on the energy density of the secondary battery 100, and improves the adhesive strength.

[0081] The inner diameter D1 of the housing 10 and the outer diameter D2 of the electrode assembly 20 can be measured using a Keyence microscope. For example, after disassembling the secondary battery sample, fix the sample on the microscope stage, turn on the Keyence microscope, and start the microscope software. Use the coarse and fine focus knobs on the microscope to focus the sample clearly. During focusing, observe the real-time image in the microscope software to ensure that the edges and details of the sample are clearly visible. In the Keyence microscope software, select the circular measuring tool to measure the diameter. Align the center of the circular measuring tool with the center of the secondary battery, and then adjust the size of the measuring tool so that it just surrounds the edge of the secondary battery. During adjustment, the accuracy of the measurement can be ensured by magnifying the image and fine-tuning the position of the measuring tool. Read the measurement results. The software will automatically display the diameter value of the circular measuring tool.

[0082] It should be noted that the aforementioned diameter D1 can be the diameter of the inner ring of the shell itself or the diameter of the fitted circle containing the inner ring of the shell, and D2 is similar.

[0083] If the width of the first adhesive layer 30 is too small, it may be difficult to completely cover the first starting end 2111. After the first starting end 2111 slips, it may be exposed from the first adhesive layer 30, posing a risk of short circuit. If the width is too large, it may affect ion transport and occupy too much space, affecting the energy density of the secondary battery 100. In the embodiments of this application, referring to FIG8, along the width direction (third direction Y) of the first electrode 21, the width of the first adhesive layer 30 is W1, the width of the first electrode 21 is W2, and the width of the separator 23 is W, where W2 < W1 ≤ W. This facilitates the first adhesive layer 30 to completely cover the first starting end 2111, reduces the first adhesive layer 30 from exceeding the separator 23, and thus reduces the impact of the first adhesive layer 30 on the energy density of the secondary battery 100.

[0084] Referring to Figure 9, the first adhesive layer 30 can be disposed on the surface of the separator 23 opposite to the first starting end 2111. Even if the burrs of the first starting end 2111 pierce the separator 23, the first adhesive layer 30 can isolate the burrs, thereby reducing the direct contact between the first starting end 2111 and the second electrode 22 and the resulting short circuit.

[0085] Referring to Figure 5, the first adhesive layer 30 can also be disposed between the separator 23 and the first starting end 2111. After the separator 23 and the first electrode 21 are stacked, the first adhesive layer 30 can directly isolate the first starting end 2111 from the separator 23, thereby reducing the puncture of the separator 23 by burrs at the first starting end 2111 and reducing the occurrence of short circuits. In the embodiments of this application, it is preferable that the first adhesive layer 30 is disposed between the first starting end 2111 and the separator 23, which can reduce the puncture of the separator 23 by burrs and help to make the separator 23 have higher integrity.

[0086] Regarding the material of the first adhesive layer 30, please refer to Figure 10. The first adhesive layer 30 includes a first substrate layer 30a and a first adhesive layer 30b. The first adhesive layer 30b is disposed on the surface of the first substrate layer 30a and is bonded to the separator 23. The first substrate layer 30a can be made of materials such as polyimide or polyethylene terephthalate, and the first adhesive layer 30b can be made of materials such as polypropylene, polyethylene, polyvinylidene fluoride, acrylic resin, or acrylic. This allows for high bonding strength between the first adhesive layer 30 and the separator 23, and also allows the first adhesive layer 30 to have high resistance to electrolyte, which helps to extend the service life of the first adhesive layer 30.

[0087] For the material of the separator 23, please refer to Figure 10. The separator 23 includes a substrate layer 231 and a ceramic layer 232.

[0088] The substrate layer 231 comprises at least one of polyethylene, polypropylene, polytetrafluoroethylene, cellulose acetate, or cellulose nanofibers. Each material exhibits excellent chemical stability, maintaining its structural and performance stability in the electrolyte environment, thereby effectively reducing chemical reactions with the electrolyte that could lead to the failure of the separator 23. Furthermore, each material possesses good electrical insulation properties, effectively isolating the first electrode 21 from the second electrode 22 and reducing the occurrence of short circuits. Simultaneously, each material possesses a certain degree of flexibility and strength, which helps reduce damage to the separator 23, thereby effectively isolating the first electrode 21 from the second electrode 22.

[0089] The ceramic layer 232 includes at least one of boehmite, alumina, or silicon dioxide. Each material has good insulation and thermal stability. When the internal temperature of the secondary battery 100 rises, it can reduce heat dissipation, thereby reducing the occurrence of thermal runaway in the secondary battery 100 and effectively improving the safety performance of the secondary battery 100.

[0090] Along the thickness direction (first direction Z) of the separator 23, the substrate layer 231 includes a first surface 2311 and a second surface 2312 disposed opposite to each other. A ceramic layer 232 is disposed on the first surface 2311, and a first adhesive layer 30 is bonded to the second surface 2312. The inventors of this application have discovered that the substrate layer 231 of the separator 23 has good compatibility with the first adhesive layer 30. When the first adhesive layer 30 is bonded to the substrate layer 231, problems such as deterioration and detachment caused by chemical interactions can be reduced. Furthermore, the substrate layer 231 of the separator 23 has a certain degree of flexibility and strength, which can provide stable support for the first adhesive layer 30 and help maintain the structural integrity of the first adhesive layer 30.

[0091] In some embodiments, please refer to FIG9, the second electrode 22 includes a second inner ring electrode 221 and a second inner ring electrode 222, wherein the second inner ring electrode 221 is the innermost electrode of the electrode assembly 20, and the electrodes adjacent to the first starting end 2111 along the thickness direction of the first electrode 21 are the second inner ring electrode 221 and the second inner ring electrode 222, respectively.

[0092] The first adhesive layer 30 can be disposed on the separator 23 on the side of the first starting end 2111 facing the winding center G, which can effectively reduce the puncture of the separator 23 between the first starting end 2111 and the second inner ring electrode 221 by burrs, thereby reducing the direct contact between the first starting end 2111 and the second inner ring electrode 221 and the resulting short circuit.

[0093] The inventors of this application have discovered that, due to the outward tension of the first electrode 21, the first starting end 2111 is more likely to puncture the separator 23 on the side away from the winding center G. In the embodiments of this application, a second electrode 22 (second inner ring electrode 222) is provided on the side of the first starting end 2111 away from the winding center G. Preferably, the first adhesive layer 30 is disposed on the separator 23 on the side of the first starting end 2111 away from the winding center G, which can effectively reduce the puncture of the separator 23 between the first starting end 2111 and the second inner ring electrode 222 by burrs, thereby reducing the direct contact between the first starting end 2111 and the second inner ring electrode 222 and the resulting short circuit.

[0094] In some embodiments, referring to FIG9, in the opposite direction to the winding direction S, the second electrode 22 extends on the side of the first starting end 2111 facing the winding center G (i.e., a second inner ring electrode 221 is formed on the side facing the winding center G). The first adhesive layer 30 is disposed on the separator 23 on the side of the first starting end 2111 facing away from the winding center G. The secondary battery 100 also includes a second adhesive layer 40, which is disposed on the separator 23 on the side of the first starting end 2111 facing the winding center G. In the thickness direction of the first electrode 21, the first adhesive layer 30 and the second adhesive layer 40 can cover the first starting end 2111, so that the separator 23 on both sides of the first starting end 2111 can be protected, which can further reduce the short circuit caused by burrs piercing the separator 23.

[0095] In some embodiments, the bonding of the first adhesive layer 30 and the second adhesive layer 40 can improve the fixation effect of the separator 23, reduce the displacement of the separator 23 during the assembly of the secondary battery 100, and thus reduce the misalignment of the first adhesive layer 30 and the second adhesive layer 40, making it easier to fully isolate the first starting end 2111. Furthermore, the bonding of the first adhesive layer 30 and the second adhesive layer 40 can also, to some extent, restrict the slippage of the first starting end 2111, reducing the exposure of the first starting end 2111 and thus reducing the occurrence of short circuits.

[0096] The inventors of this application have discovered that the cutting burrs at the first end 2112 also pose a risk of puncturing the separator 23. To reduce this problem, referring to Figure 11, the secondary battery 100 further includes a third adhesive layer 50. Along the thickness direction of the first electrode 21, the second electrode 22 is adjacent to the first end 2112. The third adhesive layer 50 is disposed on the separator 23 between the first end 2112 and the second electrode 22, covering the first end 2112. Furthermore, along the winding direction S, the third adhesive layer 50 extends from the first end 2112 beyond the first electrode 21.

[0097] In the embodiments of this application, the third adhesive layer 50 is disposed on the separator 23 and covers the first end 2112 of the first current collector 211. This reduces the puncture of the separator 23 by the cutting burrs of the first end 2112, thereby reducing the risk of a short circuit caused by direct contact between the first end 2112 and the second electrode 22. Furthermore, since the first end 2112 is not affected, the third adhesive layer 50 can be pre-positioned and adhered to the separator 23. When the separator 23 and the first current collector 211 are stacked, the third adhesive layer 50 can accurately cover and extend beyond the first end 2112. This not only helps improve the accuracy and stability of the secondary battery 100 during assembly, but also reduces the risk of the first end 2112 being exposed due to slippage, thereby reducing the risk of a short circuit caused by the burrs of the first end 2112 puncturing the separator 23.

[0098] In addition, since the third adhesive layer 50 is directly disposed on the separator 23, it has no effect on the first current collector 211. Therefore, the first current collector 211 does not need to have too many empty foil areas for bonding the third adhesive layer 50, which can increase the first active material layer 212. The first active material layer 212 can even extend to the first end 2112, thereby improving the energy density of the secondary battery 100.

[0099] The inventors of this application have discovered that, for the outermost electrode of the electrode assembly 20, there are opposite polarity electrode sheets (second electrode sheets 22) on both sides of its thickness direction. The risk of burrs piercing the separator 23 and causing short circuits due to contact with the opposite polarity electrode sheets is high. In the embodiments of this application, the first electrode sheet 21 extends along the winding direction S of the outermost electrode of the electrode assembly 20, and the outermost electrode of the electrode assembly 20 is a portion of the second electrode sheet 22. Placing the third adhesive layer 50 on the separator 23 and covering the first end 2112 of the outermost ring significantly reduces the puncture effect on the separator 23.

[0100] In some embodiments, the third adhesive layer 50 is disposed on the separator 23 on the side of the first electrode 21 facing away from the winding center G. The separator 23 facing away from the winding center G has a higher risk of being punctured. In the embodiments of this application, it is preferable that the third adhesive layer 50 is disposed on the separator 23 on the side of the first terminal 2112 facing away from the winding center G. This can effectively reduce the risk of burrs puncturing the separator 23 between the first terminal 2112 and the second inner ring electrode, thereby reducing the risk of short circuits caused by direct contact between the first terminal 2112 and the second inner ring electrode.

[0101] In some embodiments, the secondary battery 100 further includes a fourth adhesive layer 60, which is disposed on the separator 23 on the side of the first terminal end 2112 facing the winding center G. Along the thickness direction of the first electrode 21, the fourth adhesive layer 60 covers the first terminal end 2112. Furthermore, along the winding direction S, the fourth adhesive layer 60 extends from the first terminal end 2112 out of the first electrode 21. In the thickness direction of the first electrode 21, the third adhesive layer 50 and the fourth adhesive layer 60 cover the first terminal end 2112, thus protecting the separator 23 on both sides of the first terminal end 2112 and further reducing the risk of short circuits caused by burrs piercing the separator 23.

[0102] The second adhesive layer 40, the third adhesive layer 50 and the fourth adhesive layer 60 can be configured similarly to the first adhesive layer 30, and will not be described in detail in this application.

[0103] Secondly, this application also proposes an electronic device, including a secondary battery 100 as described in any of the embodiments 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. Among them, electric toys can include stationary or mobile electric toys, such as game consoles, electric car toys, electric ship toys, and electric airplane toys, etc., and spacecraft can include airplanes, rockets, space shuttles, and spacecraft, etc.

[0104] Example 1:

[0105] <Preparation of the positive electrode>

[0106] The positive electrode active material is lithium cobalt oxide, the positive electrode conductive agent is acetylene black, and the positive electrode binder is polyvinylidene fluoride (PVDF, with a weight average molecular weight of 5×10⁻⁶). 5 The materials were mixed at a mass ratio of 94:3:3, with N-methylpyrrolidone (NMP) added as a solvent to prepare a positive electrode slurry with a solid content of 75 wt%, and stirred evenly under vacuum. An aluminum foil with a thickness of 12 μm, a length of 358 mm, and a width of 3.5 mm was used as the positive electrode current collector. The positive electrode slurry was uniformly coated on one surface of the aluminum foil, leaving uncoated areas at both ends. The foil was dried at 110°C to obtain a positive electrode sheet with a single-sided coating of the positive active material layer. The above steps were then repeated on the other surface of the aluminum foil to obtain a positive electrode sheet with a double-sided coating of the positive active material layer. The single-sided coating weight of the positive electrode sheet was 17 mg / cm³. 2 .

[0107] <Preparation of negative electrode sheet>

[0108] A mixture of graphite powder (negative electrode active material), silicon powder, conductive carbon black (Super P) as a conductive agent, and styrene-butadiene rubber (SBR) as a binder was prepared in a weight ratio of 87.5:10:1:1.5. Deionized water was then added as a solvent to prepare a negative electrode slurry with a solid content of 50 wt%, and the mixture was stirred thoroughly. A copper foil with a thickness of 10 μm, a length of 394 mm, and a width of 4.1 mm was selected as the negative electrode current collector. The negative electrode slurry was uniformly coated onto one surface of the copper foil, leaving uncoated areas at both ends. The foil was then dried at 90°C to obtain a single-sided negative electrode sheet. This completes the single-sided coating of the negative electrode sheet. The same steps were then repeated on the other surface of the negative electrode sheet to obtain a double-sided coated negative electrode sheet. The single-sided coating weight of the negative electrode sheet was 8 mg / cm³. 2 .

[0109] <Preparation of the separating membrane>

[0110] A porous membrane with a polyethylene (PE) thickness of 7 μm and an alumina (Al2O3) coating of 2 μm was used as the separator.

[0111] <Preparation of the adhesive layer>

[0112] Polyethylene terephthalate is selected as the first substrate layer, and acrylic resin is selected as the first adhesive layer. The first adhesive layer is laminated onto the first substrate layer to form a first adhesive layer with a thickness of 10 μm.

[0113] <Electrolyte Preparation>

[0114] In a dry argon atmosphere, ethylene carbonate, methyl ethyl carbonate and diethyl carbonate were mixed in a mass ratio of 30:50:20 to obtain an organic solution. Then, lithium hexafluorophosphate was added to the organic solvent to dissolve and mix evenly to obtain an electrolyte with a lithium salt concentration of 1.15 mol / L.

[0115] <Preparation of Lithium-ion Batteries>

[0116] A 3mm wide aluminum sheet is used as the positive electrode tab, which is welded to the empty foil area of ​​the positive electrode sheet. A 3mm wide nickel sheet is used as the negative electrode tab, which is welded to the empty foil area of ​​the negative electrode sheet. A first adhesive layer is bonded to the separator. The separator, positive electrode sheet, separator, and negative electrode sheet prepared above are stacked in sequence and wound to obtain the electrode assembly. The first adhesive layer is located on the side of the positive electrode sheet away from the winding center, and the first adhesive layer covers and extends beyond the first starting end (winding start end) of the positive electrode sheet. The length L1 of the first adhesive layer covering the first electrode sheet is 0.47mm, and the length L2 of the first adhesive layer extending beyond the first starting end is 2mm. The electrode assembly is placed in a cylindrical shell with an inner diameter D1 of 10.5mm and an outer diameter D2 of 10.35mm, where π(D1-D2) = 0.47mm. The electrode assembly is then subjected to hot pressing (pressure 5MPa, temperature 65℃, holding time 10s). The positive electrode tab is welded to the top wall of the casing, and the negative electrode tab is welded to the bottom wall of the casing. After removing moisture at 80°C, electrolyte is injected, and the secondary battery is produced through processes such as encapsulation, electrolyte injection, formation, capacity testing, and voltage and internal resistance testing.

[0117] Unlike Example 1, the relevant parameters in Examples 2 to 22 and Comparative Examples 1 to 2 are shown in Table 1 below. In Comparative Example 1, no first adhesive layer was provided. In Comparative Example 2, the adhesive was applied first, and then the first adhesive layer and the first current collector were cut together, so that the first adhesive layer directly covered the first starting end (cut position), and the first adhesive layer did not extend beyond the first starting end.

[0118] Charge-discharge cycle test: The prepared lithium-ion battery was placed at room temperature (25°C) and left to stand for 30 minutes. Then, it was charged in stages to 4.45V according to the following charging steps:

[0119] (1) Charge at 2.5C constant current to 4.15V, and charge at constant voltage to cut off current at 1.5C;

[0120] (2) Charge at a constant current of 1.5C to 4.18V, and then charge at a constant voltage until the current is cut off at 0.5C;

[0121] (3) Charge at a constant current of 0.5C to 4.45V, and charge at a constant voltage until the cutoff current is 0.02C;

[0122] After letting it stand for 10 minutes, proceed with the following steps to discharge:

[0123] Discharge at a constant current of 1C to 3V, let stand for 10 minutes, this is one cycle.

[0124] The test involves 1000 charge-discharge cycles. An internal short circuit is detected during the test; if one occurs, the sample is considered a failure. Each group consists of 20 samples, with N being the number of failures, resulting in a failure rate of N / 20.

[0125] Determination of internal short circuit: The constant voltage charging is difficult to cut off, resulting in an excessively high charging capacity (above 3%). Upon disassembly and observation, the separator at the first starting end of the electrode sheet shows signs of melting and damage.

[0126] Table 1

[0127] According to Table 1 above, and in conjunction with Examples 1 to 22 and Comparative Examples 1 to 2, it can be seen that when the first adhesive layer is bonded to the separator and extends beyond the first starting end (L2), the test failure rate can be effectively reduced, thus effectively reducing the risk of short circuits in lithium-ion batteries. This is because placing the first adhesive layer on the separator and covering the first starting end of the first current collector reduces the puncture of the separator by the cutting burrs at the first starting end, thereby reducing the direct contact between the first starting end and the second electrode plate, which could lead to a short circuit. Furthermore, since there is no influence from the first starting end, the first adhesive layer can be pre-positioned and adhered to the separator. When the separator and the first current collector are stacked, the first adhesive layer can accurately cover and extend beyond the first starting end, making the operation simple and convenient. This not only helps improve the accuracy and stability of lithium-ion batteries during assembly but also reduces the exposure of the first starting end due to slippage, thereby reducing the puncture of the separator by burrs at the first starting end and the resulting short circuit, thus improving the safety performance of lithium-ion batteries.

[0128] In conjunction with Examples 1 to 10, the failure rate in Examples 1 and 3 to 10 is lower than that in Example 2. In Example 2, the length L1 of the first adhesive layer covering the first electrode is 0.4 mm, which is smaller than the size of the electrode that can expand. The first starting end may slide outward and exceed the first adhesive layer, resulting in the exposure of burrs at the first starting end. In Examples 1 and 3 to 10, L1≥π(D1-D2) is satisfied, which can effectively reduce the exposure of the first starting end and thus reduce the risk of short circuit in the lithium-ion battery. Therefore, in the embodiments of this application, L1≥π(D1-D2) can be selected.

[0129] The failure rate of Example 10 is similar to that of Example 9. However, in Example 10, the first adhesive layer covers too much of the first electrode, occupying a large space. Furthermore, the excessive length of the first adhesive layer may affect the electrode thickness and lithium-ion transport, leading to a loss of energy density in the lithium-ion battery. Therefore, in the embodiments of this application, a thickness of 0.47mm ≤ L1 ≤ 5mm can be selected, which can reduce the occurrence of short circuits while minimizing the impact on the energy density of the lithium-ion battery.

[0130] In Examples 5 to 7, the failure rates were all lower than those in Examples 1 to 4. Furthermore, compared to Examples 8 to 10, the length of the first adhesive layer was shorter in Examples 5 to 7, resulting in a smaller impact on the energy density of the lithium-ion battery. In conjunction with Examples 5 to 7, in the embodiments of this application, preferably 1mm ≤ L1 ≤ 3mm, which can further reduce the impact on the energy density of the lithium-ion battery.

[0131] In conjunction with Examples 11 to 22, the failure rate in Examples 11 and 13 to 22 is lower than that in Example 12. In Example 12, the length L2 of the first adhesive layer extending beyond the first electrode is 0.4 mm, which is less than the size of the electrode that can expand. The first starting end may slide inward and extend beyond the first starting end, resulting in the first starting end being exposed. This increases the risk of short circuits caused by burrs piercing the separator. In Examples 11 and 13 to 22, L2 ≥ π(D1-D2) is satisfied, which can effectively reduce the exposure of the first starting end and thus reduce the risk of short circuits in the lithium-ion battery. Therefore, in the embodiments of this application, L2 ≥ π(D1-D2) can be selected.

[0132] The failure rate of Example 22 is similar to that of Example 21. However, in Example 22, the length of the first adhesive layer extending beyond the first starting end is too large, occupying a significant amount of space. Furthermore, the excessive length of the first adhesive layer may affect the electrode thickness and the winding of the electrode, leading to a loss of energy density in the lithium-ion battery. Therefore, in the embodiments of this application, a length of 0.47mm ≤ L2 ≤ 7mm can be selected, which can reduce the occurrence of short circuits while minimizing the impact on the energy density of the lithium-ion battery.

[0133] In Examples 15 to 18, the test failure rates were all lower than those in Examples 11 to 14. Furthermore, compared to Examples 19 to 22, the length of the first adhesive layer in Examples 15 to 18 was shorter, resulting in a smaller impact on the energy density of the lithium-ion battery. In conjunction with Examples 15 to 18, in the embodiments of this application, it is preferable that 1mm ≤ L2 ≤ 4mm to further reduce the impact on the energy density of the lithium-ion battery.

[0134] 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

A secondary battery includes an electrode assembly comprising a first electrode, a separator, and a second electrode stacked and wound together. Along the winding direction, the first electrode includes a first starting end. Along the thickness direction of the first electrode, the second electrode is adjacent to the first starting end. The battery is characterized in that... The secondary battery also includes a first adhesive layer; Along the thickness direction of the first electrode, the first adhesive layer is disposed on the separator between the first starting end and the second electrode, and the first adhesive layer covers the first starting end; In the opposite direction to the winding direction, the first adhesive layer extends from the first starting end of the first electrode. The secondary battery according to claim 1 is characterized in that, The first starting end is located on the innermost electrode plate of the electrode assembly. The secondary battery according to claim 1 or 2 is characterized in that, The secondary battery is cylindrical. The secondary battery according to claim 3 is characterized in that, The secondary battery also includes a housing, and the electrode assembly is disposed inside the housing. The inner diameter of the housing is D1, and the outer diameter of the electrode assembly is D2. The first adhesive layer includes a first portion and a second portion. Along the thickness direction of the first electrode sheet, the first portion overlaps with the first electrode sheet; and along the opposite direction of the winding direction, the second portion extends beyond the first starting end. Along the winding direction, the length of the first portion is L1, and the length of the second portion is L2; L1≥π(D1-D2), and / or, L2≥π(D1-D2). The secondary battery according to claim 4 is characterized in that, 0.47mm≤L1≤5mm, and / or 0.47mm≤L2≤7mm. The secondary battery according to claim 5 is characterized in that, 1mm≤L1≤3mm and / or, 1mm≤L2≤4mm. The secondary battery according to any one of claims 1 to 6 is characterized in that, Along the width direction of the first electrode, the width of the first adhesive layer is W1, the width of the first electrode is W2, and the width of the separator is W, where W2 < W1 ≤ W. The secondary battery according to claims 1 to 7 is characterized in that, The first adhesive layer is located between the first starting end and the separator membrane. The secondary battery according to any one of claims 1 to 8 is characterized in that, The separator includes a substrate layer and a ceramic layer. Along the thickness direction of the separator, the substrate layer includes a first surface and a second surface disposed opposite to each other. The ceramic layer is disposed on the first surface, and the first adhesive layer is bonded to the second surface. The secondary battery according to claim 9 is characterized in that, The substrate layer comprises at least one of polyethylene, polypropylene, polytetrafluoroethylene, cellulose acetate, or cellulose nanofibers; and / or, the ceramic layer comprises at least one of boehmite, alumina, or silica. The secondary battery according to any one of claims 1 to 10 is characterized in that, The second pole piece is provided on the side of the first starting end that is away from the winding center; The first adhesive layer is disposed on the release film on the side of the first starting end opposite to the winding center. The secondary battery according to claim 11 is characterized in that, In the opposite direction to the winding direction, the second electrode extends on the side of the first starting end facing the winding center; the secondary battery also includes a second adhesive layer, which is disposed on the separator on the side of the first starting end facing the winding center. Along the thickness direction of the first electrode sheet, the second adhesive layer covers the first starting end; In the opposite direction to the winding direction, the second adhesive layer extends from the first starting end of the first electrode. The secondary battery according to claim 12 is characterized in that, The first adhesive layer is bonded to the second adhesive layer. The secondary battery according to any one of claims 1 to 13 is characterized in that, Along the thickness direction of the first electrode, the first electrode includes a first current collector and a first active material layer stacked together; In the thickness direction of the first electrode, the first adhesive layer and the first active material layer do not overlap; or, the first adhesive layer is provided with a plurality of through holes, and the first adhesive layer covers part of the first active material layer. The secondary battery according to any one of claims 1 to 14 is characterized in that, The first electrode includes a first terminal end, and along the thickness direction of the first electrode, the second electrode is adjacent to the first terminal end; The secondary battery further includes a third adhesive layer. Along the thickness direction of the first electrode, the third adhesive layer is disposed on the separator between the first terminal end and the second electrode, and the third adhesive layer covers the first terminal end; and along the winding direction, the third adhesive layer extends out of the first electrode from the first terminal end. The secondary battery according to claim 15 is characterized in that, The first termination end is located on the outermost electrode plate of the electrode assembly. The secondary battery according to claim 16 is characterized in that, The third adhesive layer is disposed on the release film on the side of the first tail end away from the winding center; The secondary battery further includes a fourth adhesive layer, which is disposed on the separator film on the side of the first end facing the winding center. Along the thickness direction of the first electrode sheet, the fourth adhesive layer covers the first end; and along the winding direction, the fourth adhesive layer extends out of the first end of the first electrode sheet. A secondary battery, characterized in that, Includes the secondary battery as described in any one of claims 1 to 17.

Images