Secondary battery and electronic device

Abstract

Disclosed in the present application are a secondary battery and an electronic device. In the winding direction, a first electrode sheet comprises a first starting end. In the direction of thickness of the first electrode plate, an electrode sheet adjacent to the first starting end is a second electrode sheet. A first adhesive layer is disposed on a surface of the first electrode sheet, and the first adhesive layer is arranged between the first starting end and the second electrode sheet in the direction of thickness of the first electrode sheet. The first adhesive layer comprises a first portion, a second portion and a third portion, wherein the second portion comprises a first segment and a second segment, and the first portion, the first segment, the second segment and the third portion are sequentially connected; and the first portion and the third portion are bonded to the first electrode sheet, and in the winding direction, the first portion is close to the first starting end. In the direction of thickness of the first electrode sheet, the first portion, the first segment and the second segment are stacked, and the second portion covers the first starting end; and in the direction opposite the winding direction, the second portion extends beyond the first electrode sheet from the first starting end. The occurrence of short circuits can be reduced, and the safety performance of the secondary battery can be improved.

Description

Secondary batteries and electronic devices

[0001] Cross-reference of related applications

[0002] This application claims priority to Chinese Patent Application No. 202411982980.X, filed with the Chinese Patent Office on December 30, 2024, entitled “Secondary Battery and Electronic Device”, the entire contents of which are incorporated herein by reference. Technical Field

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

[0004] 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

[0005] This application provides a secondary battery and an electronic device, which aims to improve the safety performance of the battery.

[0006] In a first aspect, this application proposes 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. Along the thickness direction of the first electrode, the electrode adjacent to the first starting end is the second electrode. The secondary battery also includes a first adhesive layer disposed on the surface of the first electrode, with the first adhesive layer positioned between the first starting end and the second electrode along the thickness direction of the first electrode. The first adhesive layer includes a first portion, a second portion, and a third portion. The second portion includes a first segment and a second segment, which are sequentially connected. Both the first portion and the third portion are bonded to the first electrode. Along the winding direction, the first portion is closer to the first starting end than the third portion. Along the thickness direction of the first electrode, the first portion, the first segment, and the second segment are stacked, with the second portion covering the first starting end. Along the opposite direction of the winding direction, the second portion extends out of the first starting end from the first electrode.

[0007] In the above technical solution, the first adhesive layer is placed on the first electrode, while the second part covers and extends beyond the first starting end. This 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, the second part covering and extending beyond the first starting end can be formed simply by folding the first adhesive layer, eliminating the need for multiple cutting and positioning operations. This simple and convenient operation not only improves 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 short circuits caused by burrs from the first starting end piercing the separator and improving the safety performance of the secondary battery.

[0008] 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. The first adhesive layer covering the first starting end of the secondary inner ring has a more significant effect on reducing the puncture of the separator.

[0009] In some embodiments, the secondary battery is cylindrical. In the embodiments of this application, the first adhesive layer covers and extends beyond the first starting end, which can reduce the slippage of the first starting end and the occurrence of short circuits, and is especially suitable for cylindrical secondary batteries.

[0010] 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. Along the winding direction, the length of the first portion is L1, and the length of the second portion is L2, where L2 ≥ π(D1 - D2) + L1. When the first starting end slides in the opposite direction of the winding direction towards the innermost ring, the constraint L2 ≥ π(D1 - D2) + L1 ensures that even if the electrode assembly occupies the internal space of the housing, the second portion still covers the first starting end, reducing the exposure of the first starting end.

[0011] In some embodiments, the length of the first portion along the winding direction is 0.5mm≤L1≤5mm, which facilitates stable adhesion of the first adhesive layer to the first electrode, improves the stability of the second portion, reduces the exposure of the first starting end, and can reduce material costs and energy density loss of the secondary battery. Preferably, 2mm≤L1≤3mm can further improve the adhesion stability between the first adhesive layer and the first electrode, and further reduce the energy density loss of the secondary battery.

[0012] In some embodiments, the length of the second portion along the winding direction is 1mm≤L2≤12mm, which can effectively cover the first starting end, reduce the exposure of the first starting end, and reduce the energy density loss of the secondary battery. Preferably, 3mm≤L2≤5mm can further reduce the energy density loss of the secondary battery while reducing the exposure of the first starting end.

[0013] In some embodiments, the length of the third portion along the winding direction is L3, where L3 ≥ π(D1-D2)-L1. When the first starting end slides outward along the winding direction, the limit of L3 ≥ π(D1-D2)-L1 ensures that even if the electrode assembly occupies the internal space of the housing, a portion of the first portion and / or the third portion can adhere to the first electrode 21, thereby effectively covering the first starting end 2111 and reducing the exposure of the first starting end 2111.

[0014] In some embodiments, the length of the third portion along the winding direction S is 0.5mm≤L3≤8mm, which can improve the bonding stability between the third portion and the first electrode, reduce the exposure of the first starting end, and reduce the impact on the first active material layer, thereby reducing the energy density loss of the secondary battery. Preferably, 2mm≤L3≤3mm can further reduce the energy density loss of the secondary battery while improving the bonding stability between the third portion and the first electrode.

[0015] In some embodiments, the first segment and the second segment are bonded together, and the first segment and the second segment do not overlap along the thickness direction of the first electrode. This allows the first segment to be bonded to the separator, and the second segment to be bonded to the first adhesive layer and the separator, forming a three-point fixing structure connecting the separator, the first electrode, and the separator. This can limit the slippage of the first starting end, reduce the exposure of the first starting end, and further improve the safety performance of the secondary battery.

[0016] 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 to completely cover the first starting end, reduces the first adhesive layer from extending beyond the separator, and thus reduces the impact of the first adhesive layer on the energy density of the secondary battery.

[0017] 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, a first adhesive layer is bonded to the first current collector, and the first adhesive layer does not overlap with the first active material layer, that is, the first adhesive layer is provided with an empty foil area near the first starting end, which can reduce the influence of the first adhesive layer on the thickness of the first electrode, reduce the energy density loss of the secondary battery, and facilitate the winding of the first electrode.

[0018] In some embodiments, the first electrode includes a first surface away from the winding center, and both the first portion and the third portion are bonded to the first surface, which can effectively reduce burrs from piercing the separator between the first starting end and the second inner ring electrode, thereby reducing the direct contact between the first starting end and the second inner ring electrode and the resulting short circuit.

[0019] In some embodiments, the secondary battery further includes a second adhesive layer comprising a fourth portion, a fifth portion, and a sixth portion. The fifth portion comprises a third segment and a fourth segment, and the fourth, third, fourth, and sixth portions are sequentially connected. The first electrode also includes a second surface facing the winding center. Both the fourth and sixth portions are bonded to the second surface. Along the winding direction, the fourth portion is closer to the first starting end than the sixth portion. Along the thickness direction of the first electrode, the fourth portion, the third segment, and the sixth segment are stacked, and the fifth portion covers the first starting end; in the opposite direction of the winding direction, the fifth portion extends out of the first electrode from the first starting end.

[0020] By depositing the second adhesive layer on the second surface of the first electrode, and having the fourth portion cover and extend beyond the first starting end, the burrs from the first starting end can be reduced from piercing the separator. This ensures that both sides of the first starting end have adhesive layer covering the burrs, further reducing the risk of short circuits caused by direct contact between the first starting end and the second electrode. Furthermore, the fourth portion covering and extending beyond the first starting end can be formed simply by folding the second adhesive layer, eliminating the need for multiple cutting and positioning operations. This simplifies the process and improves the accuracy and stability of the secondary battery during assembly. It also reduces the risk of the first starting end being exposed due to slippage, thereby reducing the risk of short circuits caused by burrs piercing the separator and improving the safety performance of the secondary battery.

[0021] In some embodiments, along the winding direction, the first electrode further includes a first terminal end, and the electrode adjacent to the first terminal end is a second electrode. The secondary battery also includes a third adhesive layer, which is disposed on the surface of the first electrode. Along the thickness direction of the first electrode, the third adhesive layer is disposed between the first terminal end and the second electrode. The third adhesive layer includes a seventh part, an eighth part, and a ninth part. The eighth part includes a fifth segment and a sixth segment. The seventh part, the fifth segment, the sixth segment, and the ninth part are connected sequentially. Both the seventh part and the ninth part are bonded to the first electrode. Along the winding direction, the seventh part is closer to the first terminal end than the ninth part. Along the thickness direction of the first electrode, the seventh part, the fifth segment, and the sixth segment are stacked, and the eighth part covers the first terminal end. Along the winding direction, the eighth part extends out of the first terminal end of the first electrode.

[0022] By placing the third adhesive layer on the first electrode and having the eighth portion cover and extend beyond the first termination end, the burrs from the first termination end can be reduced from piercing the separator, thereby reducing the risk of short circuits caused by direct contact between the first termination end and the second electrode. Furthermore, by partially folding the third adhesive layer, the eighth portion covering and extending beyond the first termination end can be formed, eliminating the need for multiple cutting and positioning operations. This simple and convenient operation not only improves the accuracy and stability of the secondary battery during assembly but also reduces the risk of the first termination end being exposed due to slippage, thus reducing the risk of short circuits caused by burrs from the first termination end piercing the separator and improving the safety performance of the secondary battery.

[0023] Secondly, this application also proposes an electronic device including a secondary battery as described in any of the embodiments of the first aspect above.

[0024] 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

[0025] 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.

[0026] Figure 1 is a schematic diagram of the structure of a secondary battery according to some embodiments of this application;

[0027] Figure 2 is a schematic diagram of the explosion of a secondary battery according to some embodiments of this application;

[0028] Figure 3 is a schematic diagram of the winding structure of the electrode assembly in some embodiments of this application;

[0029] Figure 4 is a schematic diagram of the structure of the first electrode sheet in some embodiments of this application;

[0030] Figure 5 is a schematic diagram of the bonding structure between the first adhesive layer and the first electrode sheet in some embodiments of this application;

[0031] Figure 6 is a partial structural schematic diagram of the electrode assembly located at the first starting end in some embodiments of this application;

[0032] Figure 7 is a schematic diagram of the bonding structure between the first adhesive layer and the first electrode sheet in some embodiments of this application;

[0033] Figure 8 is a schematic diagram of the misaligned structure of the first and second segments in some embodiments of this application;

[0034] Figure 9 is a schematic diagram of the stacked structure of the first electrode and the separator in some embodiments of this application;

[0035] Figure 10 is a schematic diagram of the structure of the first adhesive layer in some embodiments of this application;

[0036] Figure 11 is a schematic diagram of the bonding structure between the first adhesive layer and the second adhesive layer and the first electrode sheet in some embodiments of this application;

[0037] Figure 12 is a schematic diagram of the bonding structure between the third and fourth adhesive layers and the first electrode sheet in some embodiments of this application;

[0038] Figure 13 is a partial structural diagram of the electrode assembly located at the first terminal end in some embodiments of this application.

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

[0040] 100. Secondary batteries;

[0041] 10. Shell; 11. First wall portion; 12. Second wall portion; 13. Main body portion; 14. Opening;

[0042] 20. Electrode assembly;

[0043] 21. First electrode; 211. First current collector; 2111. First starting end; 2112. First ending end; 212. First active material layer; 21a. First surface; 21b. Second surface;

[0044] 22. Second electrode; 221. Second inner circle electrode; 222. Second inner circle electrode;

[0045] 23. Separating membrane;

[0046] 30. First adhesive layer; 30a. First substrate layer; 30b. First bonding layer; 31. First part; 32. Second part; 331. First segment; 332. Second segment; 33. Third part;

[0047] 40. Second adhesive layer; 41. Fourth part; 42. Fifth part; 421. Third section; 422. Fourth section; 43. Sixth part;

[0048] 50. Third adhesive layer; 51. Seventh part; 52. Eighth part; 521. Fifth section; 522. Sixth section; 53. Ninth part;

[0049] 60. Fourth adhesive layer;

[0050] Z, first direction; X, second direction; Y, third direction; S, winding direction; G, winding center; K, axial direction. Embodiments of the present invention

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

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

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

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

[0055] 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.

[0056] 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.

[0057] 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.

[0058] 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.

[0059] The first electrode 21 and the second electrode 22 have opposite polarities. For example, the first electrode 21 is the positive electrode and the second electrode 22 is the negative electrode. Alternatively, 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.

[0060] 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.

[0061] 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.

[0062] 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.

[0063] Referring to Figures 3 to 5, along the winding direction S, the first electrode 21 includes a first starting end 2111 and a first ending end 2112. During the preparation of the first current collector 211, the large current collector roll 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. During the winding of the first current collector 211, the first starting end 2111 forms the winding starting end of the first current collector 211, and the first ending end 2112 forms the winding ending end of the first current collector 211.

[0064] 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.

[0065] 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.

[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. Along the thickness direction (first direction Z) of the first electrode 21, a second electrode 22 is adjacent to the first starting end 2111. The second electrode 22 is an electrode adjacent to the first starting end 2111. The first adhesive layer 30 is disposed on the surface of the first electrode 21, which may be the surface of the first active material layer 212. When a portion of the first current collector 211 is not provided with the first active material layer 212, this surface is the surface of the first current collector 211. Along the thickness direction (first direction Z) of the first electrode 21, the first adhesive layer 30 is disposed between the first starting end 2111 and the second electrode 22.

[0067] The first adhesive layer 30 includes a first portion 31, a second portion 32, and a third portion 33. The second portion 32 includes a first segment 331 and a second segment 332. The first portion 31, the first segment 331, the second segment 332, and the third portion 33 are connected sequentially. The first portion 31 and the third portion 33 are respectively bonded to the first electrode 21. Along the winding direction S, the first portion 31 is closer to the first starting end 2111 than the third portion 33. Along the thickness direction (first direction Z) of the first electrode 21, the first portion 31, the first segment 331, and the second segment 332 are stacked, and the second portion 32 covers the first starting end 2111. Along the opposite direction of the winding direction S, the second portion 32 extends out of the first electrode 21 from the first starting end 2111.

[0068] For example, firstly, the first part 31 and the third part 33 are bonded to the first electrode 21 respectively. The length of the second part 32 is greater than the distance between the first part 31 and the second part 32, allowing the second part 32 to protrude. Then, the protruding second part 32 is folded with the first part 31 to form a stacked first segment 331 and second segment 332. The second part 32 covers and extends beyond the first starting end 2111. The first part 31 and the third part 33, as the connecting parts between the first adhesive layer 30 and the first electrode 21, provide stable support and fixation for the second part 32, enabling it to reliably cover the first starting end 2111. While the second part 32 performs a protective function, it also enhances the stability of the first part 31 through stacking and other methods, reducing the problem of edge curling and warping of the first electrode 21. The three parts work together to form an adhesive layer structure that provides comprehensive protection for the first starting end 2111.

[0069] In the embodiments of this application, the first adhesive layer 30 is disposed on the first electrode 21 and the second portion 32 covers and extends beyond the first starting end 2111. This reduces the puncture of the separator 23 by the cutting burrs of the first starting end 2111, thereby reducing the direct contact between the first starting end 2111 and the second electrode 22 that could cause a short circuit. Furthermore, by partially folding the first adhesive layer 30, the second portion 32 covering and extending beyond the first starting end 2111 can be formed, eliminating the need for multiple cutting and positioning operations. This simple and convenient operation not only helps improve the accuracy and stability of the secondary battery 100 during assembly but also reduces the exposure of the first starting end 2111 due to slippage, thereby reducing the puncture of the separator 23 by the burrs of the first starting end 2111 and improving the safety performance 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] In this context, along the thickness direction (first direction Z) of the first electrode 21, the first portion 31 may be flush with the first starting end 2111, or, as shown in Figure 7, along the opposite direction of the winding direction S, the first portion 31 may extend beyond the first starting end 2111. For example, when cutting out the first adhesive layer 50 and the first current collector 211, the cutter may be angled to make the first portion 31 extend beyond the first starting end 2111, which may further cover the burrs of the first starting end 2111 and reduce the occurrence of short circuits.

[0072] 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. Covering the first starting end 2111 of the innermost electrode with the first adhesive layer 30 has a more significant effect on reducing the piercing of the separator 23.

[0073] 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 covers and extends beyond the first starting end 2111, which can reduce the slippage of the first starting end 2111 and the occurrence of short circuits, especially suitable for cylindrical secondary batteries 100.

[0074] In some embodiments, referring to Figures 2 and 5, 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. Along the winding direction S, the length of the first portion 31 is L1, the length of the second portion 32 is L2, and L2≥π(D1-D2)+L1.

[0075] 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 approximately π(D1-D2). In the embodiments of this application, the portion of the second part 32 that extends beyond the first starting end 2111 along the winding direction S is approximately L2-L1. In the embodiments of this application, L2-L1 is defined as ≥ π(D1-D2), that is, the length of the second part 32 satisfies L2 ≥ π(D1-D2) + L1. When the first starting end 2111 slides in the opposite direction of the winding direction S towards the inner circle, L2 ≥ π(D1-D2) + L1 is defined. 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, reducing the exposure of the first starting end 2111.

[0076] It should be noted that the aforementioned diameter D1 can be the diameter of the inner ring of the housing 10 itself or the diameter of the fitted circle where the inner ring of the housing 10 is located, and D2 is similar.

[0077] 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 100 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 100, and then adjust the size of the measuring tool so that it just surrounds the edge of the secondary battery 100. 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.

[0078] Regarding the length of the first portion 31, the inventors of this application have found that if the length of the first portion 31 is too small, it is difficult to effectively fix the entire first adhesive layer 30, which can easily lead to a decrease in the stability of the second portion 32 of the adhesive layer. This may cause the first starting end 2111 to slip, resulting in the first adhesive layer 30 failing to accurately cover the first starting end 2111. If the length of the first portion 31 is too large, it increases material costs and occupies too much space, leading to a loss of energy density in the secondary battery 100.

[0079] In the embodiments of this application, along the winding direction S, the length of the first portion 31 is 0.5mm≤L1≤5mm, which facilitates the stable adhesion of the first adhesive layer 30 to the first electrode 21, improves the stability of the second portion 32, reduces the exposure of the first starting end 2111, and reduces material costs and energy density loss of the secondary battery 100. Preferably, 2mm≤L1≤3mm can further improve the adhesion stability between the first adhesive layer 30 and the first electrode 21, and further reduce the energy density loss of the secondary battery 100.

[0080] Regarding the length of the second part 32, the inventors of this application have found that if the length of the second part 32 is too small, it may be difficult to effectively cover the first starting end 2111, especially after the first starting end 2111 has slid, which may cause the first starting end 2111 to be exposed. If the length is too large, it occupies too much space, resulting in a loss of energy density in the secondary battery 100.

[0081] In the embodiments of this application, along the winding direction S, the length of the second portion 32 is 1mm≤L2≤12mm, which can effectively cover the first starting end 2111, reduce the exposure of the first starting end 2111, and reduce the energy density loss of the secondary battery 100. Preferably, 3mm≤L2≤5mm can further reduce the energy density loss of the secondary battery 100 while reducing the exposure of the first starting end 2111.

[0082] In some embodiments, along the winding direction S, the bonding length between the first adhesive layer 30 and the first electrode 21 is L1+L3. In the embodiments of this application, along the winding direction S, the length of the third portion 33 is L3, L1+L3≥π(D1-D2), that is, the length of the third portion 33 satisfies L3≥π(D1-D2)-L1. When the first starting end 2111 slides towards the outer circle in the opposite direction of the winding direction S, L3≥π(D1-D2)-L1 is limited. Even if the electrode assembly 20 occupies the internal space of the housing 10, it is possible to bond part of the first portion 31 and / or the third portion 33 to the first electrode 21, thereby effectively covering the first starting end 2111 and reducing the exposure of the first starting end 2111.

[0083] Regarding the length of the third part 33, the inventors of this application have found that if the length of the third part 33 is too small, the bonding area between the first adhesive layer 30 and the first electrode 21 will be insufficient, making it difficult to effectively fix the first adhesive layer 30. This may result in poor stability of the second part 32, making it easy for the third part 33 to separate from the first electrode 21, and may also make it difficult for the second part 32 to effectively cover the first starting end 2111. If the length of the third part 33 is too large, it will occupy too much space and may affect the coating of the first active material layer 212, causing a loss of energy density in the secondary battery 100.

[0084] In the embodiments of this application, along the winding direction S, the length of the third portion 33 is 0.5mm≤L3≤8mm, which can improve the bonding stability between the third portion 33 and the first electrode 21, reduce the exposure of the first starting end 2111, and reduce the impact on the first active material layer 212, thereby reducing the energy density loss of the secondary battery 100. Preferably, 2mm≤L3≤3mm can further reduce the energy density loss of the secondary battery 100 while improving the bonding stability between the third portion 33 and the first electrode 21.

[0085] In some embodiments, please refer to FIG5, the first adhesive layer 30 is bonded to the first current collector 211, and the first adhesive layer 30 does not overlap with the first active material layer 212. 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, reduce the energy density loss of the secondary battery 100, and facilitate the winding of the first electrode 21.

[0086] Please refer to Figure 8. The first segment 331 and the second segment 332 are bonded together, which can improve the overall stability of the second part 32. When the second part 32 is folded toward the first part 31, a stable three-layer adhesive structure can be formed at the first starting end 2111, which can effectively cover the first starting end 2111 and reduce the problems of curling and lifting of the first starting end 2111.

[0087] In this configuration, along the thickness direction (first direction Z) of the first electrode 21, the first segment 331 and the second segment 332 do not overlap, allowing the first segment 331 to bond with the separator 23, and the second segment 332 to bond with the first adhesive layer 30 and the separator 23, forming a three-point fixing structure connecting the separator 23, the first electrode 21, and the separator 23. This restricts the slippage of the first starting end 2111, reduces the exposure of the first starting end 2111, and further improves the safety performance of the secondary battery 100.

[0088] 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 FIG9, 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.

[0089] 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.

[0090] In some embodiments, please refer to FIG6, 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 (first direction Z) of the first electrode 21 are the second inner ring electrode 221 and the second inner ring electrode 222, respectively.

[0091] 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 pierce the separator 23 on the side opposite to the winding center G, thereby coming into contact with the second inner electrode 222 and causing a short circuit. In the embodiments of this application, the first electrode 21 includes a first surface 21a opposite to the winding center G and a second surface 21b facing the winding center G. Preferably, the first portion 31 and the third portion 33 are both bonded to the first surface 21a, which can effectively reduce the puncture of the separator 23 between the first starting end 2111 and the second inner electrode 222 by burrs, thereby reducing the direct contact between the first starting end 2111 and the second inner electrode 222 and the resulting short circuit.

[0092] In some other embodiments, the secondary battery 100 further includes a second adhesive layer 40, which may be disposed on the second surface 21b. For example, referring to FIG11, the second adhesive layer 40 includes a fourth portion 41, a fifth portion 42, and a sixth portion 43. The fifth portion 42 includes a third segment 421 and a fourth segment 422, and the fourth portion 41, the third segment 421, the fourth segment 422, and the sixth portion 43 are connected sequentially. Both the fourth portion 41 and the sixth portion 43 are bonded to the second surface 21b. Along the winding direction S, the fourth portion 41 is closer to the first starting end 2111 than the sixth portion 43. Along the thickness direction (first direction Z) of the first electrode 21, the fourth portion 41, the third segment 421, and the fourth segment 422 are stacked, and the fifth portion 42 covers the first starting end 2111. Along the opposite direction of the winding direction S, the fifth portion 42 extends out of the first electrode 21 from the first starting end 2111.

[0093] For example, firstly, the fourth part 41 and the sixth part 43 are bonded to the first electrode 21 respectively. The length of the fifth part 42 is greater than the distance between the fourth part 41 and the fifth part 42, so that the fifth part 42 protrudes. Then, the protruding fifth part 42 and the fourth part 41 are folded to form the stacked third segment 421 and the fourth segment 422. The fifth part 42 is covered and extends beyond the first starting end 2111.

[0094] In the embodiments of this application, the second adhesive layer 40 is disposed on the second surface 21b of the first electrode 21, and the fourth portion 41 covers and extends beyond the first starting end 2111. This reduces the puncture of the separator 23 by the cutting burrs of the first starting end 2111, ensuring that both sides of the first starting end 2111 have adhesive layer covering burrs, further reducing the direct contact between the first starting end 2111 and the second electrode 22, thus preventing short circuits. Furthermore, the fourth portion 41 covering and extending beyond the first starting end 2111 can be formed by partially folding the second adhesive layer 40, eliminating the need for multiple cutting and positioning operations. This simple and convenient operation not only helps improve the accuracy and stability of the secondary battery 100 during assembly but also reduces the exposure of the first starting end 2111 due to slippage, thereby reducing the puncture of the separator 23 by the burrs of the first starting end 2111 and improving the safety performance of the secondary battery 100.

[0095] 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 Figures 12 and 13, the secondary battery 100 further includes a third adhesive layer 50. Along the thickness direction (first direction Z) of the first electrode 21, the second electrode 22 is adjacent to the first end 2112, that is, the second electrode 22 is an electrode adjacent to the first end 2112. The third adhesive layer 50 is disposed on the surface of the first electrode 21, and along the thickness direction (first direction Z) of the first electrode 21, the third adhesive layer 50 is disposed between the first end 2112 and the second electrode 22.

[0096] The third adhesive layer 50 includes a seventh part 51, an eighth part 52, and a ninth part 53. The eighth part 52 includes a fifth segment 521 and a sixth segment 522. The seventh part 51, the fifth segment 521, the sixth segment 522, and the ninth part 53 are connected sequentially. Both the seventh part 51 and the ninth part 53 are bonded to the first electrode 21. Along the winding direction S, the seventh part 51 is closer to the first termination end 2112 than the ninth part 53, while the ninth part 53 is further away from the first termination end 2112. Along the thickness direction (first direction Z) of the first electrode 21, the seventh part 51, the fifth segment 521, and the sixth segment 522 are stacked, and the eighth part 52 covers the first termination end 2112. Along the winding direction S, the eighth part 52 extends out of the first electrode 21 from the first termination end 2112.

[0097] In the embodiments of this application, the third adhesive layer 50 is disposed on the first electrode 21 and the eighth portion 52 covers and extends beyond the first end 2112. This reduces the puncture of the separator 23 by the cutting burrs of the first end 2112, thereby reducing the direct contact between the first end 2112 and the second electrode 22 that could cause a short circuit. Furthermore, by partially folding the third adhesive layer 50, the eighth portion 52 covering and extending beyond the first end 2112 can be formed, eliminating the need for multiple cutting and positioning operations. This simple and convenient operation not only helps improve the accuracy and stability of the secondary battery 100 during assembly but also reduces the exposure of the first end 2112 due to slippage, thus reducing the puncture of the separator 23 by the burrs of the first end 2112 and improving the safety performance of the secondary battery 100.

[0098] In some embodiments, the first termination end 2112 is located on the second outermost electrode of the electrode assembly 20, and the outermost electrode of the electrode assembly 20 is a portion of the second electrode 22. Covering the first termination end 2112 of the second outermost electrode with the third adhesive layer 50 has a more significant effect on reducing the puncture of the separator 23.

[0099] In some other embodiments, the secondary battery 100 further includes a fourth adhesive layer 60, which may be similar to the third adhesive layer 50, so that both sides of the first end 2112 in the thickness direction are covered with adhesive layer burrs, which can further reduce the risk of the burrs of the first end 2112 piercing the separator 23, thereby reducing the occurrence of short circuits and improving the safety performance of the secondary battery 100.

[0100] 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.

[0101] Example 1:

[0102] <Preparation of the adhesive layer>

[0103] 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 adhesive layer with a thickness of 10 μm. A second adhesive layer with a thickness of 10 μm was prepared in a similar manner.

[0104] <Preparation of the positive electrode>

[0105] 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 mm, a length of 338.5 mm, and a width of 3.5 mm was used as the positive electrode current collector. A first adhesive layer and a second adhesive layer were respectively bonded to the two surfaces of the positive electrode current collector along its thickness direction. The first adhesive layer included a first part, a second part, and a third part. The second part included a first segment and a second segment. The first part, the first segment, the second segment, and the third part were connected sequentially. Both the first part and the third part were bonded to the positive electrode current collector. The length L1 of the first part was 3 mm, the length L2 of the second part was 5 mm, and the length L3 of the third part was 3 mm. The first part was located near the first starting end. Along the thickness direction of the positive electrode current collector, the first part, the first segment, and the second segment were stacked, with the second part covering the first starting end and extending beyond the first electrode sheet from the first starting end. The second adhesive layer was similarly configured.

[0106] A positive electrode slurry was uniformly coated onto one surface of a positive electrode current collector aluminum foil, leaving uncoated areas at both ends. The foil was then dried at 110°C to obtain a positive electrode sheet with a single-sided coating of the positive electrode active material layer. This process was repeated on the other surface of the aluminum foil to obtain a positive electrode sheet with a double-sided coating of the positive electrode active material layer. The coated electrode sheets were then cold-pressed to obtain a cold-pressed positive electrode sheet with a double-sided coating of the positive electrode active material layer. The single-sided coating weight of the positive electrode sheet was 21 mg / cm³. 2 The thickness of single-sided cold pressing is 62.25mm, and the thickness of double-sided cold pressing is 112.5mm.

[0107] <Preparation of Negative Electrode Sheets>

[0108] A negative electrode active material (graphite powder), silicon powder, conductive agent (super P), and binder (styrene-butadiene rubber (SBR)) were mixed 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 evenly. A copper foil with a thickness of 10 mm, a length of 374 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 dried at 90°C to obtain a single-sided negative electrode sheet. This process 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 coated electrode sheet was then cold-pressed to obtain a cold-pressed double-sided negative electrode sheet. The single-sided coating weight of the negative electrode sheet is 8.6 mg / cm². 2 The thickness of single-sided cold pressing is 61.4 mm, and the thickness of double-sided cold pressing is 112.8 mm.

[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] <Electrolyte Preparation>

[0112] 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.

[0113] <Preparation of Lithium-ion Batteries>

[0114] 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. The separator, positive electrode sheet, separator, and negative electrode sheet prepared above are stacked in sequence and wound to obtain the electrode assembly. The electrode assembly is placed in a cylindrical shell, with the positive electrode tab welded to the top wall of the shell and the negative electrode tab welded to the bottom wall of the shell. After removing moisture at 80℃, electrolyte is injected. After processes such as encapsulation, electrolyte injection, formation, capacity testing, and voltage and internal resistance testing, a lithium-ion secondary battery is obtained. The inner diameter D1 of the shell is 10.5mm, the outer diameter of the electrode assembly is D2=10.35mm, and π(D1-D2)=0.47mm.

[0115] Unlike Example 1, the relevant parameters in Examples 2 to 22 and Comparative Example 1 are shown in Table 1 below. In Comparative Example 1, the first adhesive layer, the second adhesive layer, and the first current collector are cut together after applying the adhesive, so that the first adhesive layer and the second adhesive layer are flush with the first starting end (cutting position). The length of the first adhesive layer and the second adhesive layer is 4.5 mm.

[0116] Charge-discharge cycle test: The battery prepared above was placed at room temperature (25°C) and left to stand for 30 minutes in an environment with a test temperature of 25°C. Then, it was charged to 4.45V in stages according to the following charging steps:

[0117] (1) Charge at a constant current of 2.5C to 4.15V, and then charge at a constant voltage until the current is cut off at 1.5C;

[0118] (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;

[0119] (3) Charge at a constant current of 0.5C to 4.45V, and then charge at a constant voltage until the cutoff current is 0.02C;

[0120] After letting it stand for 10 minutes, proceed with the following steps to discharge:

[0121] Discharge at a constant current of 1C to 3V; this completes one cycle.

[0122] 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.

[0123] Determination of internal short circuit: Constant voltage charging is difficult to cut off, resulting in a higher charging capacity (above 3%). Disassembly and observation show that the separator at the first starting end of the electrode is damaged. If there is damage, it is considered as failure.

[0124] Table 1

[0125] L1(mm) L2(mm) L3(mm) π(D1-D2) / (mm) Test Failure Rate Comparison Example 1 / / / 0.47 18 / 20 Example 1 0.3 0.5 3 0.47 9 / 20 Example 2 0.5 13 0.47 6 / 20 Example 3 0.5 23 0.47 4 / 20 Example 4 12 3 0.47 4 / 20 Example 5 13 3 0.47 2 / 20 Example 6 15 3 0.47 2 / 20 Example 7 18 3 0.47 2 / 20 Example 8 11 0 3 0.47 2 / 20 Example 9 11 2 3 0.47 1 / 20 Example 10 11 4 30.471 / 20 Example 11 28 30.471 / 20 Example 12 38 30.471 / 20 Example 13 48 30.471 / 20 Example 14 58 30.472 / 20 Example 15 68 30.472 / 20 Example 16 38 0.3 0.473 / 20 Example 17 38 0.5 0.472 / 20 Example 18 38 10.472 / 20 Example 19 38 20.471 / 20 Example 20 38 50.471 / 20 Example 21 38 80.470 / 20 Example 22 38 100.470 / 20

[0126] According to Table 1 above, in conjunction with Examples 1 to 22 and Comparative Example 1, the failure rate in Examples 1 to 22 is less than that in Comparative Example 1. In Examples 1 to 22, by folding the first adhesive layer, a second part that covers and extends beyond the first starting end can be formed, which can reduce the exposure of the first starting end due to slippage of the first starting end, thereby reducing the short circuit caused by burrs at the first starting end piercing the separator, and improving the safety performance of the battery.

[0127] In conjunction with Examples 1 to 10, the failure rate in Examples 2 to 10 is lower than that in Example 1. In Example 1, the length of the second part is too small, L2-L1 is less than π(D1-D2), making it difficult to accommodate the expansion of the electrode sheet, which may lead to the exposure of the first starting end and thus cause a short circuit. Therefore, in the embodiments of this application, L2≥π(D1-D2)+L1 can be selected. When the first starting end slides in the opposite direction of the winding direction towards 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, reducing the exposure of the first starting end.

[0128] The failure rates of Example 10 are similar to those of Example 9, but in Example 10, the second part is longer, occupying more space and affecting the energy density of the battery. In Example 1, the length of the second part is too small, and after the electrode expands, it may not be able to effectively cover the first starting end, easily leading to a short circuit. Considering both energy density and reducing short circuits, in the embodiments of this application, the length of the second part can be selected as 1mm≤L2≤12mm. In Examples 5 and 6, the failure rates are similar to those of Examples 7 and 8, but in Examples 5 and 6, the length of the second part is smaller, occupying less space and reducing the energy density loss of the lithium-ion battery. Therefore, in the embodiments of this application, 3mm≤L2≤5mm is preferred.

[0129] In Example 1, the shorter length of the first part results in weaker adhesion between the first part and the positive electrode, potentially leading to misalignment between the first adhesive layer and the first electrode, posing a risk of exposure of the first starting end. The failure rate in Example 14 is similar to that in Example 15, but the shorter length of the first part in Example 14 has a smaller impact on energy density. Combining Examples 2 to 14, in the embodiments of this application, the length of the first part can be selected as 0.5mm ≤ L1 ≤ 5mm. In Examples 11 and 12, the failure rate is lower than that in Example 7, and the failure rate in Examples 11 and 12 is similar to that in Example 13. Considering further reducing short circuit occurrences while reducing energy density loss, in the embodiments of this application, 2mm ≤ L1 ≤ 3mm is preferred.

[0130] In Example 16, the shorter length of the third part may result in weaker adhesion to the positive electrode, potentially causing the first adhesive layer to detach and misalign with the positive electrode, easily exposing the first starting end. In Example 21, the drop failure rate is similar to that of Example 22, but the shorter length of the third part results in less energy density loss. Therefore, in this application's embodiments, 0.5mm ≤ L3 ≤ 8mm can be selected. In Examples 19 and 12, the test failure rate is lower than that of Example 18, and similar to that of Example 20. Considering further reducing short circuit occurrences while minimizing energy density loss, in this application's embodiments, 2mm ≤ L3 ≤ 3mm is preferred.

[0131] 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 an electrode assembly, the electrode assembly comprising a first electrode, a separator, and a second electrode stacked and wound together, wherein along the winding direction, the first electrode includes a first starting end; and along the thickness direction of the first electrode, the electrode adjacent to the first starting end is the second electrode, characterized in that, The secondary battery further includes a first adhesive layer, which is disposed on the surface of the first electrode sheet. Along the thickness direction of the first electrode sheet, the first adhesive layer is disposed between the first starting end and the second electrode sheet. The first adhesive layer includes a first part, a second part, and a third part. The second part includes a first segment and a second segment. The first part, the first segment, the second segment, and the third part are connected in sequence. The first part and the third part are both bonded to the first electrode sheet. Along the winding direction, the first part is closer to the first starting end than the third part. Along the thickness direction of the first electrode, the first portion, the first segment, and the second segment are stacked, and the second portion covers the first starting end; In the opposite direction to the winding direction, the second portion extends out of the first electrode from the first starting end.

2. The secondary battery according to claim 1, characterized in that, The first starting end is located on the innermost electrode plate of the electrode assembly.

3. The secondary battery according to claim 1 or 2, characterized in that, The secondary battery is cylindrical.

4. The secondary battery according to any one of claims 1 to 3, 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. Along the winding direction, the length of the first part is L1, the length of the second part is L2, and L2≥π(D1-D2)+L1.

5. The secondary battery according to claim 4, characterized in that, 1mm≤L2≤12mm.

6. The secondary battery according to claim 5, characterized in that, 3mm≤L2≤5mm.

7. The secondary battery according to claim 4, characterized in that, 0.5mm≤L1≤5mm.

8. The secondary battery according to claim 7, characterized in that, 2mm≤L1≤3mm.

9. The secondary battery according to claim 4, characterized in that, Along the winding direction, the length of the third part is L3, where L3 ≥ π(D1-D2)-L1.

10. The secondary battery according to claim 9, characterized in that, 0.5mm≤L3≤8mm.

11. The secondary battery according to claim 10, characterized in that, 2mm≤L3≤3mm.

12. The secondary battery according to any one of claims 1 to 11, characterized in that, The first segment and the second segment are bonded together, and the first segment and the second segment do not overlap along the thickness direction of the first electrode.

13. The secondary battery according to any one of claims 1 to 12, 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.

14. The secondary battery according to any one of claims 1 to 13, 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, the first adhesive layer is bonded to the first current collector, and the first adhesive layer does not overlap with the first active material layer.

15. The secondary battery according to any one of claims 1 to 14, characterized in that, The first electrode includes a first surface away from the winding center, and both the first portion and the third portion are bonded to the first surface.

16. The secondary battery according to claim 15, characterized in that, The secondary battery further includes a second adhesive layer, which includes a fourth part, a fifth part, and a sixth part. The fifth part includes a third segment and a fourth segment, and the fourth part, the third segment, the fourth segment, and the sixth part are connected in sequence. The first electrode also includes a second surface facing the winding center, and the fourth part and the sixth part are both bonded to the second surface. Along the winding direction, the fourth part is closer to the first starting end than the sixth part. Along the thickness direction of the first electrode, the fourth part, the third segment, and the fourth segment are stacked together, and the fifth part covers the first starting end; In the opposite direction to the winding direction, the fifth portion extends from the first starting end of the first electrode.

17. The secondary battery according to any one of claims 1 to 16, characterized in that, Along the winding direction, the first electrode further includes a first terminal end, and the electrode adjacent to the first terminal end is the second electrode. The secondary battery further includes a third adhesive layer, which is disposed on the surface of the first electrode and along the thickness direction of the first electrode. The third adhesive layer is disposed between the first end and the second electrode. The third adhesive layer includes a seventh part, an eighth part, and a ninth part. The eighth part includes a fifth segment and a sixth segment. The seventh part, the fifth segment, the sixth segment, and the ninth part are connected in sequence. The seventh part and the ninth part are both bonded to the first electrode sheet. Along the winding direction, the seventh part is closer to the first end than the ninth part. Along the thickness direction of the first electrode sheet, the seventh part, the fifth segment, and the sixth segment are stacked, and the eighth part covers the first terminal end; Along the winding direction, the eighth portion extends out of the first electrode sheet from the first terminal end.

18. An electronic device, characterized in that, Includes the secondary battery as described in any one of claims 1 to 17.

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