Secondary battery and electronic device

Abstract

The invention discloses a secondary battery and electronic equipment, and a first pole piece comprises a first starting end along a winding direction. And in the thickness direction of the first pole piece, the pole piece adjacent to the first starting end is the second pole piece. The first adhesive layer is arranged on the surface of the first pole piece, and the first adhesive layer is arranged between the first starting end and the second pole piece in the thickness direction of the first pole piece. The first adhesive layer comprises a first part, a second part and a third part, the second part comprises a first section and a second section, and the first part, the first section, the second section and the third part are sequentially connected; the first part and the third part are both adhered to the first pole piece, and the first part is close to the first starting end along the winding direction. The first part, the first section and the second section are stacked in the thickness direction of the first pole piece, and the second part covers the first starting end; and the second part extends out of the first pole piece from the first starting end along the opposite direction of the winding direction. The occurrence of short circuit can be reduced and the safety performance of the secondary battery is improved.

Description

Technical Field

[0001] The present application relates to the field of battery technology, and in particular to a secondary battery and an electronic device. Background Art

[0002] With the rapid development of modern science and technology, the demand for high-performance energy storage devices in the fields of portable electronic devices, electric vehicles, etc. is growing. As an efficient and environmentally friendly energy storage device, lithium-ion batteries have been widely used in many fields due to their advantages such as high energy density, long cycle life, and low self-discharge rate. In the continuous development of lithium-ion batteries, the safety performance requirements of batteries are getting higher and higher. Summary of the invention

[0003] The present application provides a secondary battery and an electronic device, aiming to improve the safety performance of the battery.

[0004] In the first aspect, the present application proposes a secondary battery, including an electrode assembly, the electrode assembly including a first electrode sheet, a separator and a second electrode sheet which are stacked and wound. Along the winding direction, the first electrode sheet includes a first starting end. In the thickness direction of the first electrode sheet, the electrode sheet adjacent to the first starting end is the second electrode sheet. The secondary battery also includes a first adhesive layer, the first adhesive layer is arranged on the surface of the first electrode sheet, and the first adhesive layer is arranged between the first starting end and the second electrode sheet along the thickness direction of the first electrode sheet. The first adhesive layer includes a first part, a second part and a third part, the second part includes a first section and a second section, the first part, the first section, the second section and the third part are connected in sequence; the first part and the third part are both bonded to the first electrode sheet, and 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 sheet, the first part, the first section and the second section are stacked, and the second part covers the first starting end; along the opposite direction of the winding direction, the second part extends from the first starting end to the first electrode sheet.

[0005] In the above technical solution, the first adhesive layer is arranged on the first pole piece, and the second part covers and exceeds the first starting end, which can reduce the cutting burrs of the first starting end from piercing the isolation membrane, thereby reducing the short circuit caused by direct contact between the first starting end and the second pole piece. In addition, the second part covering and exceeding the first starting end can be formed by folding the first adhesive layer part, without multiple cutting and positioning operations, and the operation is simple and convenient, which not only helps to improve the accuracy and stability of the secondary battery during the assembly process, but also reduces the exposure of the first starting end due to the slippage of the first starting end, thereby reducing the short circuit caused by the burrs of the first starting end piercing the isolation membrane, thereby improving the safety performance of the secondary battery.

[0006] In some embodiments, the first starting end is located at the sub-inner circle pole piece of the electrode assembly. The sub-inner circle pole piece has a higher risk of piercing the isolation membrane. The first adhesive layer covers the first starting end of the sub-inner circle, which is more effective in reducing the piercing of the isolation membrane.

[0007] In some embodiments, the secondary battery is cylindrical. In the embodiments of the present application, the first adhesive layer covers and exceeds the first starting end, which can reduce the short circuit caused by the slip of the first starting end, and is particularly suitable for cylindrical secondary batteries.

[0008] In some embodiments, the secondary battery further includes a shell, the electrode assembly is disposed in the shell, the inner diameter of the shell 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. When the first starting end slides toward the inner circle in the opposite direction of the winding direction, L2≥π(D1-D2)+L1 is defined, so that even if the electrode assembly occupies the internal space of the shell, the second part can still cover the first starting end, reducing the exposure of the first starting end.

[0009] In some embodiments, along the winding direction, the length of the first portion is 0.5mm≤L1≤5mm, which can facilitate the first adhesive layer to be stably bonded to the first pole piece, improve the stability of the second portion, reduce the exposure of the first starting end, and reduce material costs and reduce the energy density loss of the secondary battery. Preferably, 2mm≤L1≤3mm, which can further improve the bonding stability of the first adhesive layer and the first pole piece, and further reduce the energy density loss of the secondary battery.

[0010] In some embodiments, along the winding direction, the length of the second portion 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, which can reduce the exposure of the first starting end and further reduce the energy density loss of the secondary battery.

[0011] In some embodiments, along the winding direction, the length of the third portion is L3, L3≥π(D1-D2)-L1. When the first starting end slides toward the outer circle along the winding direction, L3≥π(D1-D2)-L1 is defined, and even if the electrode assembly occupies the internal space of the shell, part of the first portion and / or the third portion can be bonded to the first electrode sheet 21, thereby effectively covering the first starting end 2111 and reducing the exposure of the first starting end 2111.

[0012] In some embodiments, along the winding direction S, the length of the third portion is 0.5 mm ≤ L3 ≤ 8 mm, which can improve the bonding stability between the third portion and the first pole piece, reduce the exposure of the first starting end, reduce the impact on the first active material layer, and reduce the energy density loss of the secondary battery. Preferably, 2 mm ≤ L3 ≤ 3 mm, which can improve the bonding stability between the third portion and the first pole piece while further reducing the energy density loss of the secondary battery.

[0013] In some embodiments, the first section is bonded to the second section, and along the thickness direction of the first pole piece, the first section and the second section do not overlap partially, so that the first section is bonded to the isolation membrane, and the second section is bonded to the first adhesive layer and the isolation membrane, forming a three-point fixed structure connecting the isolation membrane, the first pole piece, and the isolation membrane, which 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.

[0014] In some embodiments, along the width direction of the first electrode piece, the width of the first adhesive layer is W1, the width of the first electrode piece is W2, the width of the isolation membrane is W, W2<W1≤W, which can facilitate the first adhesive layer to completely cover the first starting end, reduce the first adhesive layer beyond the isolation membrane, and thereby reduce the impact of the first adhesive layer on the energy density of the secondary battery.

[0015] In some embodiments, along the thickness direction of the first pole sheet, the first pole sheet includes a first current collector and a first active material layer that are stacked, the first adhesive layer is bonded to the first current collector, and the first adhesive layer and the first active material layer do not overlap, 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 pole sheet, reduce the energy density loss of the secondary battery, and facilitate the winding of the first pole sheet.

[0016] In some embodiments, the first pole piece includes a first surface facing away from the winding center, and the first part and the third part are both bonded to the first surface, which can effectively reduce the burrs from piercing the isolation membrane between the first starting end and the second inner circle pole piece, thereby reducing the short circuit caused by direct contact between the first starting end and the second inner circle pole piece.

[0017] In some embodiments, the secondary battery further includes a second adhesive layer, the second adhesive layer includes a fourth part, a fifth part and a sixth part, the fifth part includes a third section and a fourth section, and the fourth part, the third section, the fourth section and the sixth part are connected in sequence. The first pole piece further includes a second surface facing the winding center, the fourth part and the sixth part are both bonded to the second surface, and along the winding direction, the fourth part is closer to the first starting end than the second six parts. Along the thickness direction of the first pole piece, the fourth part, the third section and the fourth section are stacked, and the fifth part covers the first starting end; along the opposite direction of the winding direction, the fifth part extends from the first starting end to the first pole piece.

[0018] The second adhesive layer is arranged on the second surface of the first pole piece, and the fourth part covers and exceeds the first starting end, which can reduce the cutting burrs of the first starting end from piercing the isolation membrane, so that both sides of the first starting end in the thickness direction have adhesive layer covering burrs, which can further reduce the short circuit caused by direct contact between the first starting end and the second pole piece. In addition, the fourth part covering and exceeding the first starting end can be formed by folding the second adhesive layer part, without multiple cutting and positioning operations, and the operation is simple and convenient, which not only helps to improve the accuracy and stability of the secondary battery during the assembly process, but also reduces the exposure of the first starting end due to the slippage of the first starting end, thereby reducing the burrs of the first starting end from piercing the isolation membrane and causing short circuits, thereby improving the safety performance of the secondary battery.

[0019] In some embodiments, along the winding direction, the first pole piece also includes a first tail end, and the pole piece adjacent to the first tail end is the second pole piece. The secondary battery also includes a third glue layer, which is arranged on the surface of the first pole piece, and along the thickness direction of the first pole piece, the third glue layer is arranged between the first tail end and the second pole piece. The third glue layer includes a seventh part, an eighth part and a ninth part, and the eighth part includes a fifth section and a sixth section. The seventh part, the fifth section, the sixth section and the ninth section are connected in sequence; the seventh part and the ninth part are both bonded to the first pole piece, and along the winding direction, the seventh part is closer to the first tail end than the ninth part. Along the thickness direction of the first pole piece, the seventh part, the fifth section and the sixth section are stacked, and the eighth part covers the first tail end; along the winding direction, the eighth part extends from the first tail end to the first pole piece.

[0020] The third adhesive layer is arranged on the first pole piece and the eighth part covers and exceeds the first tail end, which can reduce the cutting burrs of the first tail end from piercing the isolation membrane, thereby reducing the short circuit caused by direct contact between the first tail end and the second pole piece. In addition, the eighth part covering and exceeding the first tail end can be formed by folding the third adhesive layer part, without multiple cutting and positioning operations, and the operation is simple and convenient, which not only helps to improve the accuracy and stability of the secondary battery during the assembly process, but also reduces the exposure of the first tail end due to the slippage of the first tail end, thereby reducing the short circuit caused by the burrs of the first tail end piercing the isolation membrane, thereby improving the safety performance of the secondary battery.

[0021] In a second aspect, the present application further proposes an electronic device, comprising a secondary battery as in any embodiment of the first aspect above.

[0022] Additional aspects and advantages of the embodiments of the present application will be described, shown, or explained in part in the subsequent description through implementation of the embodiments of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] One or more embodiments are exemplarily described by the figures in the corresponding drawings, and these exemplary descriptions are not intended to limit the embodiments. Elements with the same reference numerals in the drawings represent similar elements.

[0024] Figure 1 A schematic diagram of the structure of a secondary battery in some embodiments of the present application;

[0025] Figure 2 An exploded schematic diagram of a secondary battery according to some embodiments of the present application;

[0026] Figure 3 A schematic diagram of the winding structure of an electrode assembly in some embodiments of the present application;

[0027] Figure 4 This is a schematic structural diagram of a first pole piece in some embodiments of the present application;

[0028] Figure 5 A schematic diagram of the bonding structure between the first adhesive layer and the first pole piece in some embodiments of the present application;

[0029] Figure 6 This is a partial structural schematic diagram of an electrode assembly located at a first starting end in some embodiments of the present application;

[0030] Figure 7 A schematic diagram of the bonding structure between the first adhesive layer and the first pole piece in some embodiments of the present application;

[0031] Figure 8 A schematic diagram of the staggered structure of the first section and the second section of some embodiments of the present application;

[0032] Fig. 9 A schematic diagram of the stacked structure of the first pole piece and the isolation film in some embodiments of the present application;

[0033] Fig.10 This is a schematic diagram of the structure of the first adhesive layer of some embodiments of the present application;

[0034] Fig.11 This is a schematic diagram of the bonding structure of the first adhesive layer, the second adhesive layer and the first pole piece in some embodiments of the present application;

[0035] Fig.12 A schematic diagram of the bonding structure of the third adhesive layer and the fourth adhesive layer and the first pole piece in some embodiments of the present application;

[0036] Fig.13 This is a schematic diagram of the partial structure of the electrode assembly located at the first tail end of some embodiments of the present application.

[0037] Description of reference numerals:

[0038] 100. Secondary battery;

[0039] 10. Shell; 11. First wall; 12. Second wall; 13. Main body; 14. Opening;

[0040] 20. Electrode assembly;

[0041] 21, first pole piece; 211, first current collector; 2111, first starting end; 2112, first ending end; 212, first active material layer; 21a, first surface; 21b, second surface;

[0042] 22, second pole piece; 221, second inner ring pole piece; 222, second inner ring pole piece;

[0043] 23. Isolation film;

[0044] 30, first adhesive layer; 30a, first substrate layer; 30b, first bonding layer; 31, first portion; 32, second portion; 331, first section; 332, second section; 33, third portion;

[0045] 40, second adhesive layer; 41, fourth section; 42, fifth section; 421, third section; 422, fourth section; 43, sixth section;

[0046] 50, third adhesive layer; 51, seventh section; 52, eighth section; 521, fifth section; 522, sixth section; 53, ninth section;

[0047] 60, fourth adhesive layer;

[0048] Z, first direction; X, second direction; Y, third direction; S, winding direction; G, winding center; K, axial direction. DETAILED DESCRIPTION

[0049] In order to make the purpose, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be clearly described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments.

[0050] Reference to "embodiment" in this application means that a particular feature, structure, or characteristic described in conjunction with the embodiment may be included in at least one embodiment of the present application. The appearance of the phrase in various places in the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment that is mutually exclusive with other embodiments.

[0051] In the description of the embodiments of the present application, the technical terms "first", "second", etc. are only used to distinguish different objects, and cannot be understood as indicating or implying relative importance or implicitly indicating the number, specific order or primary and secondary relationship of the indicated technical features. In the description of the embodiments of the present application, the meaning of "multiple" and "several" is more than two, unless otherwise clearly and specifically defined.

[0052] In the description of the embodiments of the present application, the term "and / or" is only a description of the association relationship of the associated objects, indicating that there may be three relationships. For example, A and / or B can represent: A exists alone, A and B exist at the same time, and B exists alone. In addition, the character " / " in this article generally indicates that the associated objects before and after are in an "or" relationship.

[0053] In the first aspect, the embodiment of the present application provides a secondary battery 100, please refer to Figure 1 and Figure 2 The secondary battery 100 includes a shell 10 and an electrode assembly 20 and an electrolyte (not shown) contained in the shell 10. The electrolyte infiltrates the electrode assembly 20 in the shell 10, thereby generating an electrochemical reaction.

[0054] For the above-mentioned housing 10, the housing 10 may be square, trapezoidal or cylindrical, etc. In the embodiment of the present application, the cylindrical housing 10 is taken as an example, please refer to Figure 1 and Figure 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 connected to both ends of the main body portion 13 respectively. The second wall portion 12 can be integrally provided with the main body portion 13 or separately provided. An opening 14 is provided at one end of the main body portion 13 opposite to the second wall portion 12. The electrode assembly 20 can be placed in the housing 10 through the opening 14. The housing 10 can be sealed by covering the opening 14 with the first wall portion 11.

[0055] The housing 10 may be made of conductive metal materials such as aluminum, aluminum alloy, steel, stainless steel, nickel, copper or magnesium alloy, so that the housing 10 can lead to a certain polarity of the secondary battery 100, for example, the housing 10 itself is used as the positive electrode or negative electrode of the secondary battery 100. In some other embodiments, the housing 10 may also be made of soft packaging materials, such as aluminum plastic film or copper plastic film.

[0056] Regarding the electrode assembly 20, the electrode assembly 20 is accommodated in the housing 10. Please refer to Figure 3 and Figure 4The electrode assembly 20 includes a first pole piece 21, a second pole piece 22 and a separator 23. The first pole piece 21, the separator 23 and the second pole piece 22 are stacked and wound, for example, stacked along the thickness direction (first direction Z) of the first pole piece 21 and wound along its length direction (second direction X), and the separator 23 is arranged between the first pole piece 21 and the second pole piece 22 for insulating and separating the two.

[0057] The first pole piece 21 and the second pole piece 22 have opposite polarities, for example, the first pole piece 21 is a positive pole piece, and the second pole piece 22 is a negative pole piece. Alternatively, the first pole piece 21 is a negative pole piece, and the second pole piece 22 is a positive pole piece. For example, when a cylindrical housing 10 is used, the first pole piece 21 can be electrically connected to the first wall portion 11, so that the first wall portion 11 leads to one polarity of the secondary battery 100, and the second pole piece 22 can be electrically connected to the second wall portion 12, so that the second wall portion 12 leads to the other polarity of the secondary battery 100. By insulating the first wall portion 11 from the second wall portion 12, the occurrence of short circuit can be reduced.

[0058] Please refer to Figure 4 The first electrode sheet 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 the tearing of the first current collector 211, and is conducive to improving the charge and discharge rate of the secondary battery 100.

[0059] When the first electrode plate 21 is a positive electrode plate, the first active material layer 212 includes positive electrode active materials, conductive agents, adhesives, etc., wherein the positive electrode active materials include 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 iron manganese phosphate.

[0060] In some other embodiments, when the first electrode plate 21 is a negative electrode plate, the first active material layer 212 includes a negative electrode active material, a conductive agent, and a binder, etc., wherein the negative electrode active material includes one or more of graphite, soft carbon, hard carbon, elemental silicon, silicon oxides, silicon alloys, etc.

[0061] Please refer to Figures 3 to 5, along the winding direction S, the first pole piece 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 current collector roll needs to be cut to form a plurality of 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. When the first current collector 211 is wound, 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.

[0062] The cutting burrs of the first starting end 2111 have the risk of piercing the isolation film 23, which may cause the first starting end 2111 to directly contact the second pole piece 22 and cause a short circuit. Before cutting out the first current collector 211, the first current collector 211 needs to be glued, and then the glue layer and the first current collector 211 are cut together, so that the glue layer can cover the first starting end 2111, thereby reducing the burrs of the first starting end 2111 from piercing the isolation film 23 and causing a short circuit.

[0063] However, the inventors of the present application have discovered that during a long-term charge and discharge cycle of the secondary battery 100, the first electrode plate 21 will 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, which may easily cause the first starting end 2111 to be misaligned with the glue layer, which may cause the first starting end 2111 to be exposed, and further easily cause the burrs of the first starting end 2111 to pierce the isolation membrane 23 and cause a short circuit.

[0064] To reduce the above problems, in the embodiments of this application, please refer to Figure 5 and Figure 6 , the secondary battery 100 includes a first adhesive layer 30, and along the thickness direction (first direction Z) of the first electrode sheet 21, the second electrode sheet 22 is adjacent to the first starting end 2111, and the second electrode sheet 22 is the electrode sheet adjacent to the first starting end 2111. The first adhesive layer 30 is disposed on the surface of the first electrode sheet 21, and the surface may be the surface of the first active material layer 212, and when the first active material layer 212 is not disposed on a part of the first current collector 211, the surface is the surface of the first current collector 211. Along the thickness direction (first direction Z) of the first electrode sheet 21, the first adhesive layer 30 is disposed between the first starting end 2111 and the second electrode sheet 22.

[0065] 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 section 331 and a second section 332. The first portion 31, the first section 331, the second section 332 and the third portion 33 are connected in sequence. The first portion 31 and the third portion 33 are respectively bonded to the first pole piece 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 pole piece 21, the first portion 31, the first section 331 and the second section 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 from the first starting end 2111 to the first pole piece 21.

[0066] For example, firstly, the first part 31 and the third part 33 are respectively bonded to the first pole piece 21, and the length of the second part 32 is greater than the distance between the first part 31 and the second part 32, so that the second part 32 can be protruded, and then the protruding second part 32 is folded with the first part 31 to form a first section 331 and a second section 332 arranged in a stacked manner, and the second part 32 covers and exceeds the first starting end 2111. The first part 31 and the third part 33 serve as the connecting part between the first adhesive layer 30 and the first pole piece 21, providing stable support and fixation for the second part 32, so that it can reliably cover the first starting end 2111. While the second part 32 plays a protective function, it also enhances the stability of the first part 31 by stacking and other means, which can reduce the problem of edge curling and warping of the first pole piece 21. The three cooperate with each other to form a comprehensive adhesive layer structure for protecting the first starting end 2111.

[0067] In the embodiment of the present application, the first adhesive layer 30 is arranged on the first pole piece 21 and the second part 32 covers and exceeds the first starting end 2111, which can reduce the cutting burrs of the first starting end 2111 from piercing the isolation film 23, thereby reducing the short circuit caused by direct contact between the first starting end 2111 and the second pole piece 22. In addition, the second part 32 covering and exceeding the first starting end 2111 can be formed by folding part of the first adhesive layer 30, without multiple cutting and positioning operations, and 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 the slippage of the first starting end 2111, thereby reducing the short circuit caused by the burrs of the first starting end 2111 piercing the isolation film 23, thereby improving the safety performance of the secondary battery 100.

[0068] It should be noted that, in the opposite direction of the winding direction S, the first adhesive layer 30 extends out of the first pole piece 21 from the first starting end 2111, which 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 exposure of the first adhesive layer 30 due to the first starting end 2111. The second adhesive layer 40, the third adhesive layer 50 and the fourth adhesive layer 60 are similar.

[0069] Wherein, along the thickness direction (first direction Z) of the first pole piece 21, the first portion 31 may be flush with the first starting end 2111, or, please refer to Figure 7 , along the opposite direction of the winding direction S, the first portion 31 exceeds the first starting end 2111. For example, when cutting out the first adhesive layer 50 and the first current collector 211, the cutter cuts at an angle, so that the first portion 31 exceeds the first starting end 2111, and can further cover the burrs of the first starting end 2111, thereby reducing the occurrence of short circuits.

[0070] The inventors of the present application have also found that for the sub-inner circle pole piece of the electrode assembly 20, there are pole pieces of opposite polarity (second pole piece 22) on both sides in the thickness direction, and the stress on the inner circle is relatively large, and the risk of burrs piercing the isolation membrane 23 is relatively high. In the embodiment of the present application, the first starting end 2111 is located at the sub-inner circle pole piece of the electrode assembly 20, and the innermost circle pole piece of the electrode assembly 20 is part of the second pole piece 22. Covering the first starting end 2111 of the sub-inner circle with the first adhesive layer 30 has a more significant effect on reducing the piercing of the isolation membrane 23.

[0071] In the embodiment of the present application, the secondary battery 100 is cylindrical. During the winding process of the first pole piece 21 and the second pole piece 22, the first pole piece 21 needs to bear a certain bending stress. Compared with square batteries or batteries of other structures, the first pole piece 21 of the cylindrical battery forms a relatively tight cylindrical shape after winding, which may cause the first pole piece 21 to form a tension similar to the centripetal force, which is more likely to cause the first pole piece 21 to be partially loose, and then cause the first starting end 2111 to slip. Because in the embodiment of the present application, the first adhesive layer 30 covers and exceeds the first starting end 2111, the first starting end 2111 can be reduced from slipping and short circuiting, which is particularly suitable for cylindrical secondary batteries 100.

[0072] In some embodiments, please refer to Figure 2 and Figure 5 The electrode assembly 20 is disposed in 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, and the length of the second portion 32 is L2, L2 ≥ π (D1-D2) + L1.

[0073] The inventors of the present application have found that when the pole piece expands and causes the electrode assembly 20 to occupy the internal space of the shell 10, the maximum slippage of the first starting end 2111 is generally approximately π(D1-D2). In the embodiment of the present application, along the winding direction S, the portion of the second portion 32 that exceeds the first starting end 2111 is approximately L2-L1. In the embodiment of the present application, L2-L1≥π(D1-D2), that is, the length of the second portion 32 satisfies L2≥π(D1-D2)+L1. When the first starting end 2111 slides toward the inner circle in the opposite direction of the winding direction S, L2≥π(D1-D2)+L1 is defined. Even if the electrode assembly 20 occupies the internal space of the shell 10, the second portion 32 can still cover the first starting end 2111, reducing the exposure of the first starting end 2111.

[0074] It should be noted that the diameter D1 may be the diameter of the inner ring of the housing 10 itself or the diameter of the fitting circle where the inner ring of the housing 10 is located, and D2 is similar.

[0075] The measurement of the inner diameter D1 of the shell 10 and the outer diameter D2 of the electrode assembly 20 can be measured by a Keyence microscope. For example, after disassembling the secondary battery 100 sample, fix the sample on the sample stage of the microscope, turn on the power of the Keyence microscope, and start the microscope software. Use the coarse focus and fine focus knobs of the microscope to focus the sample clearly. During the focusing process, you can 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 measurement tool to measure the diameter. Align the center of the circular measurement tool with the center of the secondary battery 100, and then adjust the size of the measurement tool so that it just surrounds the edge of the secondary battery 100. During the adjustment process, the accuracy of the measurement can be ensured by enlarging the image and fine-tuning the position of the measurement tool. Read the measurement results. The software automatically displays the diameter value of the circular measurement tool.

[0076] As for the length of the first portion 31, the inventors of the present 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 may deteriorate the stability of the second portion 32 of the adhesive layer, and may cause the first starting end 2111 to slip, resulting in the first adhesive layer 30 being unable to accurately cover the first starting end 2111. If the length of the first portion 31 is too large, the material cost is increased, and too much space is occupied, resulting in a loss of energy density of the secondary battery 100.

[0077] In the embodiment of the present application, along the winding direction S, the length of the first portion 31 is 0.5mm≤L1≤5mm, which can facilitate the first adhesive layer 30 to be stably bonded to the first pole piece 21, improve the stability of the second portion 32, reduce the exposure of the first starting end 2111, and reduce the material cost and the energy density loss of the secondary battery 100. Preferably, 2mm≤L1≤3mm, which can further improve the bonding stability of the first adhesive layer 30 and the first pole piece 21, and further reduce the energy density loss of the secondary battery 100.

[0078] As for the length of the second portion 32, the inventors of the present application have found that if the length of the second portion 32 is too small, it may be difficult to effectively cover the first starting end 2111, especially after the first starting end 2111 slides, 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 of the secondary battery 100.

[0079] In the embodiment of the present 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, which can reduce the exposure of the first starting end 2111 and further reduce the energy density loss of the secondary battery 100.

[0080] In some embodiments, along the winding direction S, the bonding length of the first adhesive layer 30 and the first pole piece 21 is L1+L3. In the embodiment of the present 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, and when the first starting end 2111 slides toward the outer circle in the opposite direction of the winding direction S, L3≥π(D1-D2)-L1 is defined, and even if the electrode assembly 20 occupies the internal space of the shell 10, part of the first portion 31 and / or the third portion 33 can be bonded to the first pole piece 21, thereby effectively covering the first starting end 2111 and reducing the exposure of the first starting end 2111.

[0081] Regarding the length of the third portion 33, the inventor of the present application has found that if the length of the third portion 33 is too small, the bonding area between the first adhesive layer 30 and the first pole piece 21 is insufficient, making it difficult to effectively fix the first adhesive layer 30, which may result in poor stability of the second portion 32, and easily cause the third portion 33 to separate from the first pole piece 21, and may cause the second portion 32 to be difficult to effectively cover the first starting end 2111. If the length of the third portion 33 is too large, it occupies too much space and may affect the coating of the first active material layer 212, resulting in a loss of energy density of the secondary battery 100.

[0082] In the embodiment of the present application, along the winding direction S, the length of the third portion 33 is 0.5 mm ≤ L3 ≤ 8 mm, which can improve the bonding stability between the third portion 33 and the first pole piece 21, reduce the exposure of the first starting end 2111, reduce the impact on the first active material layer 212, and reduce the energy density loss of the secondary battery 100. Preferably, 2 mm ≤ L3 ≤ 3 mm, which can improve the bonding stability between the third portion 33 and the first pole piece 21 while further reducing the energy density loss of the secondary battery 100.

[0083] In some embodiments, please refer to Figure 5 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 sheet 21, reduce the energy density loss of the secondary battery 100, and facilitate the winding of the first electrode sheet 21.

[0084] Please refer to Figure 8 The first section 331 is bonded to the second section 332, which can improve the stability of the overall structure 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 curling and warping problems of the first starting end 2111.

[0085] Among them, along the thickness direction of the first pole piece 21 (the first direction Z), the first section 331 and the second section 332 do not overlap partially, so that the first section 331 can be bonded to the isolation membrane 23, and the second section 332 can be bonded to the first adhesive layer 30 and the isolation membrane 23, forming a three-point fixed structure connecting the isolation membrane 23, the first pole piece 21, and the isolation membrane 23, which can limit the slippage of the first starting end 2111, reduce the exposure of the first starting end 2111, and further improve the safety performance of the secondary battery 100.

[0086] 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 slides, the first starting end 2111 may be exposed from the first adhesive layer 30, which may cause a short circuit. If the width is too large, it may affect ion transmission and occupy too much space, affecting the energy density of the secondary battery 100. In the embodiments of this application, please refer to Fig. 9 , along the width direction of the first pole piece 21 (third direction Y), the width of the first adhesive layer 30 is W1, the width of the first pole piece 21 is W2, the width of the isolation film 23 is W, and W2<W1≤W. This can facilitate the first adhesive layer 30 to completely cover the first starting end 2111, reduce the first adhesive layer 30 beyond the isolation film 23, and further reduce the impact of the first adhesive layer 30 on the energy density of the secondary battery 100.

[0087] For the material of the first adhesive layer 30, please refer to Fig.10 The first adhesive layer 30 includes a first substrate layer 30a and a first bonding layer 30b, wherein the first bonding layer 30b is disposed on the surface of the first substrate layer 30a and is bonded to the isolation film 23. The first substrate layer 30a may be made of materials such as polyimide or polyethylene terephthalate, and the first bonding layer 30b may be made of materials such as polypropylene, polyethylene, polyvinylidene fluoride, acrylic resin or acrylic, so that the first adhesive layer 30 and the isolation film 23 have a high bonding strength, and the first adhesive layer 30 has a high tolerance to the electrolyte, which is beneficial to prolonging the service life of the first adhesive layer 30.

[0088] In some embodiments, please refer to Figure 6 The second pole piece 22 includes a second inner circle pole piece 221 and a second inner circle pole piece 222, wherein the second inner circle pole piece 221 is the innermost circle pole piece of the electrode assembly 20, and along the thickness direction (first direction Z) of the first pole piece 21, the pole pieces adjacent to the first starting end 2111 are the second inner circle pole piece 221 and the second inner circle pole piece 222 respectively.

[0089] The inventor of the present application has found that due to the outward tension of the first pole piece 21, it is easier for the first starting end 2111 to pierce the isolation film 23 away from the winding center G, and then contact the second inner circle pole piece 222 to cause a short circuit. In the embodiment of the present application, the first pole piece 21 includes a first surface 21a away from the winding center G and a second surface 21b facing the winding center G. Preferably, the first part 31 and the third part 33 are both bonded to the first surface 21a, which can effectively reduce the burrs from piercing the isolation film 23 between the first starting end 2111 and the second inner circle pole piece 222, thereby reducing the first starting end 2111 and the second inner circle pole piece 222 directly contacting and causing a short circuit.

[0090] In some other embodiments, the secondary battery 100 further includes a second adhesive layer 40, and the second adhesive layer 40 can be disposed on the second surface 21b. Fig.11The 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 section 421 and a fourth section 422. The fourth portion 41, the third section 421, the fourth section 422 and the sixth portion 43 are connected in sequence. The fourth portion 41 and the sixth portion 43 are both 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 pole piece 21, the fourth portion 41, the third section 421 and the fourth section 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 from the first starting end 2111 to the first pole piece 21.

[0091] For example, firstly, the fourth part 41 and the sixth part 43 are respectively bonded to the first pole piece 21, and 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 can protrude, and then the protruding fifth part 42 and the fourth part 41 are folded to form a stacked third section 421 and a fourth section 422, and the fifth part 42 covers and exceeds the first starting end 2111.

[0092] In the embodiment of the present application, the second adhesive layer 40 is disposed on the second surface 21b of the first pole piece 21, and the fourth portion 41 covers and exceeds the first starting end 2111, which can reduce the cutting burrs of the first starting end 2111 from piercing the isolation film 23, so that both sides of the first starting end 2111 in the thickness direction have adhesive layer covering burrs, which can further reduce the short circuit caused by direct contact between the first starting end 2111 and the second pole piece 22. In addition, the fourth portion 41 covering and exceeding the first starting end 2111 can be formed by partially folding the second adhesive layer 40, without multiple cutting and positioning operations, and 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 the slippage of the first starting end 2111, thereby reducing the burrs of the first starting end 2111 from piercing the isolation film 23 and causing short circuits, thereby improving the safety performance of the secondary battery 100.

[0093] The inventor of the present application has found that the cutting burrs of the first tail end 2112 also have the risk of piercing the isolation film 23. To reduce this problem, please refer to Fig.12 and Fig.13 The secondary battery 100 further includes a third adhesive layer 50. Along the thickness direction (first direction Z) of the first electrode sheet 21, the second electrode sheet 22 is adjacent to the first tail end 2112, that is, the second electrode sheet 22 is the electrode sheet adjacent to the first tail end 2112. The third adhesive layer 50 is disposed on the surface of the first electrode sheet 21, and along the thickness direction (first direction Z) of the first electrode sheet 21, the third adhesive layer 50 is disposed between the first tail end 2112 and the second electrode sheet 22.

[0094] The third adhesive layer 50 includes a seventh portion 51, an eighth portion 52 and a ninth portion 53. The eighth portion 52 includes a fifth section 521 and a sixth section 522. The seventh portion 51, the fifth section 521, the sixth section 522 and the ninth portion 53 are connected in sequence. The seventh portion 51 and the ninth portion 53 are both bonded to the first pole piece 21. Along the winding direction S, the seventh portion 51 is closer to the first tail end 2112 than the ninth portion 53, while the ninth portion 53 is farther away from the first tail end 2112. Along the thickness direction (first direction Z) of the first pole piece 21, the seventh portion 51, the fifth section 521 and the sixth section 522 are stacked, and the eighth portion 52 covers the first tail end 2112. Along the winding direction S, the eighth portion 52 extends out of the first pole piece 21 from the first tail end 2112.

[0095] In the embodiment of the present application, the third adhesive layer 50 is arranged on the first pole piece 21 and the eighth portion 52 covers and exceeds the first tail end 2112, which can reduce the cutting burrs of the first tail end 2112 from piercing the isolation film 23, thereby reducing the short circuit caused by direct contact between the first tail end 2112 and the second pole piece 22. In addition, the eighth portion 52 covering and exceeding the first tail end 2112 can be formed by partially folding the third adhesive layer 50, without multiple cutting and positioning operations, and 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 tail end 2112 due to the slippage of the first tail end 2112, thereby reducing the burrs of the first tail end 2112 from piercing the isolation film 23 and causing a short circuit, thereby improving the safety performance of the secondary battery 100.

[0096] In some embodiments, the first end 2112 is located at the secondary outer ring electrode piece of the electrode assembly 20, and the outermost electrode piece of the electrode assembly 20 is part of the second electrode piece 22. Covering the secondary outer ring first end 2112 with the third adhesive layer 50 has a more significant effect on reducing the puncture of the isolation film 23.

[0097] In some other embodiments, the secondary battery 100 also includes a fourth adhesive layer 60, which can be configured similarly to the third adhesive layer 50, so that both sides of the first tail end 2112 in the thickness direction have adhesive layer covering burrs, which can further reduce the risk of the burrs of the first tail end 2112 piercing the isolation membrane 23, thereby reducing the occurrence of short circuits and improving the safety performance of the secondary battery 100.

[0098] In the second aspect, the present application also proposes an electronic device, including a secondary battery 100 as in any embodiment of the first aspect described above. The electronic device of the embodiment of the present application is not particularly limited, and it 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, electric tools, battery cars, electric cars, ships, spacecraft, and the like. Among them, electric toys can include fixed or mobile electric toys, for example, game consoles, electric car toys, electric ship toys, electric airplane toys, and the like, and spacecraft can include airplanes, rockets, space shuttles, and spacecrafts, and the like.

[0099] Embodiment 1:

[0100] <Preparation of Substrate Layer>

[0101] Polyethylene terephthalate was selected as the first substrate layer, and acrylic resin was selected as the first adhesive layer, and the first adhesive layer was compounded on 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.

[0102] <Preparation of positive electrode sheet>

[0103] 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 5 ) are mixed according to a mass ratio of 94:3:3, N-methylpyrrolidone (NMP) is added as a solvent, and a positive electrode slurry with a solid content of 75wt% is prepared, and the mixture is stirred evenly under a vacuum mixer. An aluminum foil with a thickness of 12μm, a length of 338.5mm, and a width of 3.5mm is used as a positive electrode current collector. The first adhesive layer and the second adhesive layer are respectively bonded to the two surfaces in the thickness direction of the positive electrode current collector, wherein the first adhesive layer includes a first part, a second part, and a third part, the second part includes a first section and a second section, the first part, the first section, the second section, and the third section are connected in sequence, the first part and the third part are both bonded to the positive electrode current collector, the length L1 of the first part is 3mm, the length L2 of the second part is 5mm, and the length L3 of the third part is 3mm. The first part is close to the first starting end, and the first part, the first section, and the second section are stacked along the thickness direction of the positive electrode current collector, and the second part covers the first starting end, and the second part extends from the first starting end to the first pole piece. The second adhesive layer is similarly arranged.

[0104] The positive electrode slurry is evenly coated on one surface of the positive electrode current collector aluminum foil, and empty foil areas not coated with the positive electrode slurry are reserved at the beginning and end of the aluminum foil, and dried at 110°C to obtain a positive electrode sheet coated with a positive electrode active material layer on one side. Then, the above steps are repeated on the other surface of the aluminum foil to obtain a positive electrode sheet coated with a positive electrode active material layer on both sides. The coated sheet is cold pressed to obtain a cold pressed positive electrode sheet with a double-sided positive electrode active material layer. The single-sided coating weight of the positive electrode sheet is 21 mg / cm 2 The thickness of single-sided cold pressing is 62.25μm, and the thickness of double-sided cold pressing is 112.5μm.

[0105] <Preparation of negative electrode sheet>

[0106] The negative electrode active material graphite powder, silicon powder, conductive carbon black (Super P), and binder styrene-butadiene rubber (SBR) are mixed in a weight ratio of 87.5:10:1:1.5, and then deionized water is added as a solvent to prepare a negative electrode slurry with a solid content of 50wt%, and stirred evenly. A copper foil with a thickness of 10μm, a length of 374mm, and a width of 4.1mm is selected as the negative electrode current collector, and the negative electrode slurry is evenly coated on one surface of the negative electrode current collector copper foil, and an empty foil area without negative electrode slurry is reserved at the beginning and end of the copper foil, and dried at 90°C to obtain a single-sided negative electrode sheet. After the above steps are completed, the single-sided coating of the negative electrode sheet is completed. After that, the above steps are repeated on the other surface of the negative electrode sheet to obtain a negative electrode sheet with a negative electrode active material layer coated on both sides. The coated sheet is cold pressed to obtain a negative electrode sheet with a cold-pressed double-sided negative electrode active material layer. The single-sided coating weight of the negative electrode sheet is 8.6 mg / cm 2 The thickness of single-sided cold pressing is 61.4μm, and the thickness of double-sided cold pressing is 112.8μm.

[0107] <Preparation of Separator Film>

[0108] Polyethylene (PE) with a thickness of 7 μm and a 2 μm aluminum oxide (Al2O3) coated porous film were used as isolation membranes.

[0109] <Electrolyte Preparation>

[0110] In a dry argon atmosphere, ethylene carbonate, ethyl methyl carbonate and diethyl carbonate were mixed in a mass ratio of 30:50:20 to obtain an organic solution, and then lithium salt 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.

[0111] <Preparation of lithium-ion batteries>

[0112] An aluminum sheet with a width of 3 mm is used as the positive electrode tab, and the positive electrode tab is welded to the empty foil area of ​​the positive electrode sheet. A nickel sheet with a width of 3 mm is used as the negative electrode tab, and the negative electrode tab is welded to the empty foil area of ​​the negative electrode sheet. The isolation membrane, positive electrode sheet, isolation membrane, and negative electrode sheet prepared above are stacked in order and wound to obtain an electrode assembly. The electrode assembly is placed in a cylindrical shell, the positive electrode tab is welded to the top wall of the shell, and the negative electrode tab is welded to the bottom wall of the shell. After removing moisture at 80°C, the electrolyte is injected, and after the processes of packaging and liquid injection, formation, capacity testing, voltage internal resistance testing, etc., a lithium-ion secondary battery is obtained. The inner diameter D1 of the shell is 10.5 mm, the outer diameter of the electrode assembly is D2=10.35 mm, and π(D1-D2)=0.47 mm.

[0113] Different from Example 1, the relevant parameters in Examples 2 to 22 and Comparative Example 1 are shown in Table 1 below, wherein in Comparative Example 1, the glue is first applied and then the first glue layer, the second glue layer and the first current collector are cut together, so that the first glue layer and the second glue layer are directly flush with the first starting end (cutting position), and the lengths of the first glue layer and the second glue layer are both 4.5 mm.

[0114] Charge and 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, and then charged to 4.45V according to the following charging steps:

[0115] (1) 2.5C constant current charging to 4.15V, constant voltage charging cut-off current to 1.5C;

[0116] (2) 1.5C constant current charging to 4.18V, constant voltage charging cut-off current to 0.5C;

[0117] (3) 0.5C constant current charging to 4.45V, constant voltage charging cut-off current to 0.02C;

[0118] After standing for 10 minutes, discharge according to the following steps:

[0119] 1C constant current discharge to 3V, this is one cycle.

[0120] The charge and discharge cycle is 1000 times, and the internal short circuit is tested. If it occurs, it is considered as failure. Each group tests 20 samples, the number of failures is N, and the failure rate is N / 20.

[0121] Determination of internal short circuit: constant voltage charging is difficult to cut off, resulting in a high charging capacity (more than 3%). Disassembly and observation show that the isolation membrane at the first starting end of the electrode is damaged. If damaged, it is considered a failure.

[0122] Table 1

[0123]

[0124]

[0125] According to the above Table 1, in combination with Examples 1 to 22 and Comparative Example 1, the test failure rate in Examples 1 to 22 is lower than that in Comparative Example 1. In Examples 1 to 22, the first adhesive layer is partially folded to form a second portion covering and exceeding the first starting end, which can reduce the exposure of the first starting end due to the slippage of the first starting end, thereby reducing the burrs of the first starting end from piercing the isolation membrane and causing a short circuit, thereby improving the safety performance of the battery.

[0126] In combination with Examples 1 to 10, the test 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), which makes it difficult to adapt to the expansion of the pole piece, which may cause the first starting end to be exposed, thereby causing a short circuit. Therefore, in the embodiment of the present application, L2≥π(D1-D2)+L1 can be selected. When the first starting end slides toward the inner circle in the opposite direction of the winding direction, even if the electrode assembly occupies the internal space of the shell, the second part can still cover the first starting end, reducing the exposure of the first starting end.

[0127] The test failure rate of Example 10 is similar to that of Example 9, but in Example 10, the length of the second part is longer, occupying a larger space, affecting the energy density of the battery. In Example 1, the length of the second part is too small, and after the pole piece expands, it may be difficult to effectively cover the first starting end, which may easily lead to a short circuit. Taking into account the energy density and reducing short circuits, in the embodiments of the present application, the length of the second part can be selected to be 1mm≤L2≤12mm. In Examples 5 and 6, the test failure rate is similar to that of Examples 7 and 8, but in Examples 5 and 6, the length of the second part is smaller, occupying a smaller space, which can reduce the energy density loss of the lithium-ion battery. Therefore, in the embodiments of the present application, 3mm≤L2≤5mm is preferred.

[0128] In Example 1, the length of the first part is relatively small, so that the bonding strength between the first part and the positive electrode plate is relatively small, which may cause the first adhesive layer and the first electrode plate to be misaligned, and there is a risk of the first starting end being exposed. The test failure rate of Example 14 is similar to that of Example 15, but in Example 14, the length of the first part is relatively small, and the impact on the energy density is smaller. In combination with Examples 2 to 14, in the embodiments of the present application, the length of the first part can be selected to be 0.5mm≤L1≤5mm. In Examples 11 to 12, the test failure rate is less than that of Example 7, and in Examples 11 to 12, the test failure rate is similar to that of Example 13. Taking into account the reduction of energy density loss while further reducing the occurrence of short circuits, in the embodiments of the present application, 2mm≤L1≤3mm is preferred.

[0129] In Example 16, the length of the third part is relatively small, which may lead to weaker bonding strength with the positive electrode sheet, which may further cause the first adhesive layer to come off and be misaligned with the positive electrode sheet, easily causing the first starting end to be exposed. In Example 21, the drop failure rate is similar to that in Example 22, but in Example 21, the length of the third part is smaller, and the battery capacity density loss is smaller. Therefore, in the embodiments of the present application, 0.5mm≤L3≤8mm can be selected. In Examples 19 and 12, the test failure rate is less than that in Example 18, and the test failure rate is similar to that in Example 20. Considering the further reduction of short circuits while reducing the loss of energy density, in the embodiments of the present application, 2mm≤L3≤3mm is preferred.

[0130] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit them. Under the concept of the present application, the technical features in the above embodiments or different embodiments may also be combined, the steps may be implemented in any order, and there are many other changes in different aspects of the present application as described above, which are not provided in detail for the sake of simplicity. Although the present application has been described in detail with reference to the aforementioned embodiments, a person of ordinary skill in the art should understand that the technical solutions described in the aforementioned embodiments may still be modified, or some of the technical features may be replaced by equivalents. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the scope of the technical solutions of the embodiments of the present application.

Claims

1. A secondary battery, comprising an electrode assembly, wherein the electrode assembly comprises a first electrode sheet, a separator and a second electrode sheet stacked and wound, wherein along the winding direction, the first electrode sheet comprises a first starting end; along the thickness direction of the first electrode sheet, the electrode sheet adjacent to the first starting end is the second electrode sheet, characterized in that: The secondary battery further includes a first glue layer, which is disposed on a surface of the first pole piece, and along a thickness direction of the first pole piece, the first glue layer is disposed between the first starting end and the second pole piece; The first adhesive layer includes a first part, a second part and a third part, the second part includes a first section and a second section, the first part, the first section, the second section and the third part are connected in sequence; the first part and the third part are both bonded to the first pole piece, and 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 pole piece, the first portion, the first section and the second section are stacked, and the second portion covers the first starting end; Along the opposite direction of the winding direction, the second portion extends out of the first pole piece from the first starting end.

2. The secondary battery according to claim 1, characterized in that: The first starting end is located at the secondary inner circle pole piece of the electrode assembly.

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

4. The secondary battery according to claim 1, characterized in that: The secondary battery further includes a shell, the electrode assembly is disposed in the shell, the inner diameter of the shell is D1, and the outer diameter of the electrode assembly is D2; Along the winding direction, the length of the first portion is L1, the length of the second portion 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 portion is L3, and 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 section is bonded to the second section, and along the thickness direction of the first pole piece, the first section and the second section do not overlap.

13. The secondary battery according to any one of claims 1 to 11, characterized in that: Along the width direction of the first pole piece, the width of the first adhesive layer is W1, the width of the first pole piece is W2, the width of the isolation film is W, and W2<W1≤W.

14. The secondary battery according to any one of claims 1 to 11, characterized in that: Along the thickness direction of the first pole piece, the first pole piece includes a first current collector and a first active material layer that are stacked, 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 11, characterized in that: The first pole piece includes a first surface facing away from a winding center, and the first portion and the third portion are both bonded to the first surface.

16. The secondary battery according to claim 15, characterized in that: The secondary battery further includes a second glue layer, the second glue layer includes a fourth portion, a fifth portion and a sixth portion, the fifth portion includes a third section and a fourth section, and the fourth portion, the third section, the fourth section and the sixth portion are connected in sequence; The first pole piece further includes a second surface facing the winding center, the fourth portion and the sixth portion are both bonded to the second surface, and 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 pole piece, the fourth portion, the third section and the fourth section are stacked, and the fifth portion covers the first starting end; Along the opposite direction of the winding direction, the fifth portion extends out of the first pole piece from the first starting end.

17. The secondary battery according to any one of claims 1 to 11, characterized in that: Along the winding direction, the first pole piece further includes a first tail end, and the pole piece adjacent to the first tail end is the second pole piece; The secondary battery further includes a third adhesive layer, which is disposed on the surface of the first pole piece, and along the thickness direction of the first pole piece, the third adhesive layer is disposed between the first tail end and the second pole piece; The third adhesive layer includes a seventh portion, an eighth portion and a ninth portion, the eighth portion includes a fifth section and a sixth section, the seventh portion, the fifth section, the sixth section and the ninth portion are connected in sequence; the seventh portion and the ninth portion are both bonded to the first pole piece, and along the winding direction, the seventh portion is closer to the first tail end than the ninth portion; Along the thickness direction of the first pole piece, the seventh portion, the fifth section and the sixth section are stacked, and the eighth portion covers the first tail end; Along the winding direction, the eighth portion extends out of the first pole piece from the first tail end.

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

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