Secondary battery and electronic device

Abstract

Disclosed in the present application are a secondary battery and an electronic device. The secondary battery comprises a casing, an electrode assembly, a first bonding piece and a second bonding piece. The electrode assembly is arranged in the casing and comprises a first electrode sheet, a separator and a second electrode sheet which are stacked and wound, wherein the first electrode sheet comprises a first section, and the first section forms the part of the electrode assembly on the outermost circle; the first section has a first surface facing a winding center axis and a second surface facing away from the winding center axis; and in the winding direction of the first section, the first section comprises an ending section, the first and second surfaces of the ending section being empty foil areas. The first bonding piece is at least partially bonded to the first surface of the ending section. The second bonding piece is arranged on the second surface of the ending section and bonds the second surface of the ending section to the casing, and in a direction perpendicular to the first surface, the projection of the second bonding piece partially overlaps with the projection of the first bonding piece. The falling or collision failure risk of the secondary battery of the present application is reduced.

Description

Secondary batteries and electronic devices

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to the Chinese patent application filed with the China Patent Office on June 30, 2023, with application number 202310796380.3, and invention name “Secondary Batteries and Electronic Devices”, the entire contents of which are incorporated by reference into this application. Technical Field

[0003] The embodiments of the present application relate to the field of electrochemical technology, and in particular to a secondary battery and an electronic device. Background Art

[0004] With the development of science and technology, consumer electronic products such as mobile phones and laptops are popular among the general public. Secondary batteries (lithium-ion batteries), as the core components of electronic products, have become an important component that determines the development of electronic products due to their advantages such as high operating voltage and long service life.

[0005] Lithium-ion batteries typically include a casing and an electrode assembly. To reduce the risk of lithium-ion battery failure due to drops, a commonly used method is to bond the electrode assembly to the casing with adhesive to reduce the relative movement between the electrode assembly and the casing, thereby reducing collision failure between the electrode assembly and the casing.

[0006] However, for the outermost electrode of the electrode assembly, there is still a risk of the electrode tearing at the junction of the covered adhesive and the uncovered adhesive; and, for the end of the adhesive, the end of the electrode is still in a semi-constrained state, which can easily cause the electrode to tear when the lithium-ion battery falls, resulting in failure of the lithium-ion battery.

[0007] Summary of the Invention

[0008] The embodiments of the present application aim to provide a secondary battery and an electronic device to improve the problem of easy tearing of the outermost electrode sheet, thereby reducing the failure risk of the lithium-ion battery.

[0009] In order to solve the technical problems, the embodiments of the present application adopt the following technical solutions:

[0010] The present application proposes a secondary battery comprising a housing, an electrode assembly, a first adhesive, and a second adhesive. The electrode assembly is disposed within the housing and comprises a first electrode sheet, a second electrode sheet, and a separator located between the first electrode sheet and the second electrode sheet. The first electrode sheet, the second electrode sheet, and the separator are stacked and wound, with the winding center axis of the electrode assembly oriented in a first direction. The first electrode sheet comprises a first section, which constitutes the outermost portion of the electrode assembly. The first section has a first surface facing the winding center axis and a second surface facing away from the winding center axis. Along the winding direction of the first section, the first section comprises a tail section, and both the first and second surfaces of the tail section are hollow foil areas. The first adhesive is at least partially bonded to the first surface of the tail section. The second adhesive is disposed on the second surface of the tail section and bonds the second surface of the tail section to the housing. The second adhesive partially overlaps the first adhesive along a direction perpendicular to the first surface.

[0011] In the above technical solution, the first adhesive is at least partially bonded to the first surface of the terminal segment, thereby increasing the tensile strength of the terminal segment and reducing the risk of tearing. The second adhesive is disposed on the second surface of the terminal segment and bonds the terminal segment to the housing, thereby reducing relative movement between the electrode assembly and the housing and further increasing the tensile strength of the terminal segment, further reducing the risk of tearing. Furthermore, the projection of the second adhesive partially overlaps with the projection of the first adhesive in a direction perpendicular to the first surface. If the secondary battery is dropped or collides, some of the shear force applied to the second adhesive can be transferred to the first adhesive, thereby reducing shear force concentration and further reducing the risk of tearing in the terminal segment.

[0012] In some preferred embodiments, the portion of the second adhesive that overlaps the first adhesive is the first portion. The projection of the first portion, perpendicular to the first surface, falls within the projection of the first adhesive. The shear force transmission between the first and second adhesives effectively reduces the risk of tearing in the final section.

[0013] In some preferred embodiments, the area of ​​the first portion is S1, the area of ​​the second adhesive is S2, and 15% ≤ S1 / S2 ≤ 50%. Sufficient adhesive coverage of the second adhesive can improve the tensile strength of the tail section while ensuring sufficient overlap between the second adhesive and the first adhesive for shear force transmission, thereby reducing the risk of tail tearing.

[0014] In some preferred embodiments, along the winding direction of the first section, the distance between the first adhesive member and the end of the tail section is a first distance, and the first distance is greater than or equal to 2 mm. Reserving the first distance allows the first adhesive member to fully adhere to the tail section, thereby effectively reducing curling of the first adhesive member.

[0015] In some preferred embodiments, the first section further includes a coating section connected to the finishing section.

[0016] In some preferred embodiments, one end of the first adhesive is bonded to the coating segment and the other end to the tail segment, with the first adhesive covering the junction between the coating segment and the tail segment. Along the first direction, the length of the first adhesive is L1 mm, and the length of the first segment is L2 mm, with 0 ≤ L1 - L2 ≤ 3. The first direction is parallel to the winding center axis of the electrode assembly. This reduces the risk of burrs and other protruding structures piercing the separator, thereby reducing the risk of short circuits and reducing the shedding of active material layers at the interface.

[0017] In some preferred embodiments, the first adhesive member includes a first sub-adhesive member and a second sub-adhesive member. The first sub-adhesive member is disposed on the first surface. The second sub-adhesive member is disposed on the first surface, and the second sub-adhesive member is bonded to the first sub-adhesive member at the end section, with the projection of the second sub-adhesive member on the second surface partially overlapping the projection of the second sub-adhesive member in a direction perpendicular to the first surface.

[0018] In some preferred embodiments, one end of the first sub-adhesive is bonded to the coating segment and the other end to the tail segment, with the first sub-adhesive covering the junction between the coating segment and the tail segment. Along the first direction, the length of the first sub-adhesive is L3 mm, and the length of the first segment is L2 mm, with 0 ≤ L3 - L2 ≤ 3. The first sub-adhesive completely covers the junction in the first direction X, further reducing the risk of burrs and other protruding structures piercing the separator, thereby reducing the risk of short circuits and reducing the shedding of active material layer powder at the junction.

[0019] In some preferred embodiments, the first adhesive includes a plurality of second sub-adhesives. The plurality of second sub-adhesives are arranged in sequence on the first surface along the winding direction of the first section, with adjacent second sub-adhesives bonded to each other. Along the winding direction of the first section, the second sub-adhesive at the starting end of the arrangement is bonded to the first sub-adhesive at the ending section, and along a direction perpendicular to the first surface, the projection of the second sub-adhesive at the end of the arrangement partially overlaps with the projection of the second adhesive. The structural arrangement of the plurality of sub-adhesives can further reduce the occurrence of bubbles during bonding and can further reduce the concentration of shear force, thereby reducing the risk of tearing in the ending section.

[0020] In some preferred embodiments, the first adhesive member and the second adhesive member are adhesive tapes, so as to facilitate the gluing process of the first adhesive member and the second adhesive member and improve production efficiency.

[0021] In some preferred embodiments, the first section includes a first straight section, a first curved section, a second straight section, and a second curved section that are connected to each other. The first straight section and the second straight section are arranged relative to each other in the second direction, the first curved section and the second curved section are both connected between the first straight section and the second straight section, and the first curved section and the second curved section are arranged relative to each other in the third direction. The second adhesive component is partially arranged on the first straight section or the second straight section, and the first direction, the second direction, and the third direction are perpendicular to each other. The straight section is easier for the second adhesive component to adhere to the tail, which can facilitate bonding and improve the bonding effect, thereby facilitating the improvement of the tensile strength of the first section and reducing the risk of tearing of the first section.

[0022] In some preferred embodiments, the peel strength between the separator and the first electrode piece or the second electrode piece is 8 N / m to 12 N / m, thereby effectively improving the bonding strength of the entire electrode assembly.

[0023] In some preferred embodiments, the first adhesive member is a single-sided adhesive tape having adhesiveness on only one side, and the single-sided adhesive tape comprises a first substrate layer and a first adhesive layer coated on one side of the first substrate layer.

[0024] In some preferred embodiments, the second adhesive member is a double-sided tape having adhesiveness on both sides, and the double-sided tape comprises a second substrate layer and a second adhesive layer and / or hot melt adhesive layer coated on both sides of the second substrate layer.

[0025] In some preferred embodiments, the housing is a packaging bag.

[0026] In some preferred embodiments, the first electrode piece is a cathode electrode piece, and the second electrode piece is an anode electrode piece. The active material layer is provided on only the first side of the first section, and the active material layer is provided on the first side of the coating section. Since there is no corresponding anode electrode piece outside the single-sided cathode electrode piece, one active material layer can be eliminated, thereby increasing the energy density of the secondary battery.

[0027] In some preferred embodiments, the second adhesive is used to fix the end section. By directly fixing the end section with the second adhesive, a step of adhesive finishing and adhesive finishing can be eliminated, thereby reducing tearing of the end section and achieving the purpose of reducing costs and increasing efficiency.

[0028] In a second aspect, the present application further proposes an electronic device comprising the secondary battery described in any one of the above embodiments.

[0029] The above description is only an overview of the technical solution of the present application. In order to more clearly understand the technical means of the present application, it can be implemented in accordance with the contents of the specification. In order to make the above and other purposes, features and advantages of the present application more obvious and easy to understand, the specific implementation methods of the present application are listed below. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] One or more embodiments are exemplarily described by corresponding drawings, which do not constitute limitations on the embodiments. Elements with the same reference numerals in the drawings are represented as similar elements, and unless otherwise stated, the figures in the drawings do not constitute proportional limitations.

[0031] FIG1 is an exploded view of a secondary battery according to some embodiments of the present application;

[0032] FIG2 is a schematic diagram of the winding structure of an electrode assembly according to some embodiments of the present application;

[0033] FIG3 a is a schematic diagram of a stacked structure of a first pole piece, an isolation film, and a second pole piece in some embodiments of the present application;

[0034] FIG3 b is a schematic structural diagram of an isolation membrane according to some embodiments of the present application;

[0035] FIG4 is a schematic diagram of the bonding structure of the first section and the first and second adhesive members in some embodiments of the present application (viewed along the X direction);

[0036] FIG5 a is a schematic diagram of the bonding structure of the first section and the first and second adhesive members in some embodiments of the present application (viewed along the M direction);

[0037] FIG5 b is a schematic structural diagram of a first adhesive member and a second adhesive member according to some embodiments of the present application;

[0038] FIG6 is a schematic diagram of the bonding structure of the first section and the first and second adhesive members in some embodiments of the present application (viewed along the X direction);

[0039] FIG7 is a schematic diagram of the bonding structure of the first section and the first and second adhesive members in some embodiments of the present application (viewed along the M direction);

[0040] FIG8 is a schematic diagram of the bonding structure of a first sub-adhesive and a plurality of second sub-adhesives in some embodiments of the present application.

[0041] Description of reference numerals:

[0042] 100. Secondary battery;

[0043] 10. Housing; 11. First housing; 12. Second housing;

[0044] 20. Electrode assembly; 20a. Winding center; 21. First pole piece; 211. First current collector; 212. First active material layer; 213. First segment; 213a. First surface; 213b. Second surface; 2131. Finishing segment; 2132. Coating segment; 22. Second pole piece; 221. Second current collector; 222. Second active material layer; 23. Separator; 231. Base layer; 232. Ceramic bonding layer; 24. First straight segment; 25. First curved segment; 26. Second straight segment; 27. Second curved segment;

[0045] 30, first adhesive member; 30a, first substrate layer; 30b, first adhesive layer; 31, first sub-adhesive member; 32, second sub-adhesive member;

[0046] 40. Second adhesive member; 40a. First portion; 41. Second substrate layer; 42. Second adhesive layer;

[0047] N, winding direction; X, first direction; Y, second direction; Z, third direction; M, direction perpendicular to the first surface. DETAILED DESCRIPTION

[0048] The following embodiments of the technical solution of the present application will be described in detail with reference to the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solution of the present application and are therefore only examples and are not intended to limit the scope of protection of the present application.

[0049] In the description of the embodiments of this application, the technical terms "first," "second," etc. are used only to distinguish different objects and should not be understood to indicate or imply relative importance or to implicitly indicate the quantity, specific order, or primary and secondary relationship of the indicated technical features. In the description of the embodiments of this application, the meaning of "plurality" is more than two, unless otherwise specifically defined.

[0050] In the description of the embodiments of this application, the term "and / or" is simply a description of the association relationship between associated objects, indicating that three relationships can exist. For example, A and / or B can represent the following three situations: A exists alone, A and B exist simultaneously, and B exists alone. In addition, the character " / " in this document generally indicates that the associated objects are in an "or" relationship.

[0051] References to "embodiments" herein mean that a particular feature, structure, or characteristic described in connection with the embodiment may be included in at least one embodiment of the present application. The appearance of this phrase in various places in the specification does not necessarily refer to the same embodiment, nor does it constitute an independent or alternative embodiment that is mutually exclusive with other embodiments. Furthermore, the technical features described below in the different embodiments of the present application may be combined with each other as long as they do not conflict with each other.

[0052] First, the present application provides a secondary battery 100. Referring to Figures 1 and 2, the secondary battery 100 includes a housing 10, an electrode assembly 20, a first adhesive 30, and a second adhesive 40. The electrode assembly 20 is housed within the housing 10, and the second adhesive 40 is used to secure the electrode assembly 20 to a stable structure. The second adhesive 40 can also be used to bond the electrode assembly 20 to the housing 10 to reduce relative movement between the two.

[0053] Regarding the housing 10, please refer to Figure 1. The housing 10 encloses a housing cavity (not shown in the figure), which can accommodate the electrode assembly 20 and the electrolyte (not shown in the figure). In the embodiment of the present application, the housing 10 can be a packaging bag. For example, the housing 10 can be a multi-layer composite film packaging bag including a metal layer. The packaging bag can be an aluminum-plastic film packaging bag including a PP (polypropylene) layer and an aluminum layer. The PP layer can be provided on both surfaces of the aluminum layer in the thickness direction to facilitate insulation and sealing of the packaging bag.

[0054] Optionally, the shell 10 includes a first shell 11 and a second shell 12, and the first shell 11 and / or the second shell 12 are punched with a pit cavity (not shown in the figure), and the electrode assembly 20 can be set in the pit cavity, and then the first shell 11 and the second shell 12 are packaged by hot pressing to form a complete shell 10, wherein the above-mentioned pit cavity forms a accommodating cavity.

[0055] Regarding the electrode assembly 20, please refer to Figures 1 to 3a. The electrode assembly 20 is disposed in the housing 10. The electrode assembly 20 includes a first electrode sheet 21, a second electrode sheet 22, and a separator 23. The first electrode sheet 21, the second electrode sheet 22, and the separator 23 are stacked and wound to form a wound electrode assembly 20. The separator 23 is disposed between the first electrode sheet 21 and the second electrode sheet 22 to separate the two (Figure 2 shows the wound structure of the electrode assembly 20). The first electrode sheet 21 and the second electrode sheet 22 have opposite polarities. For example, the first electrode sheet 21 is a cathode electrode sheet and the second electrode sheet 22 is an anode electrode sheet. The first electrode sheet 21 includes a first current collector 211 and a first active material layer 212. The first active material layer 212 is coated on at least one surface of the first current collector 211. The second electrode sheet 22 includes a second current collector 221 and a second active material layer 222. The second active material layer 222 is coated on at least one surface of the first current collector 211. Alternatively, in some other embodiments, the first pole piece 21 is an anode pole piece, and the second pole piece 22 is a cathode pole piece.

[0056] For the isolation film 23 of the electrode assembly 20, the isolation film 23 can be bonded between the first electrode piece 21 and the second electrode piece 22, so as to improve the overall bonding strength of the electrode assembly 20 and improve the flatness of the interface between the first electrode piece 21 and the second electrode piece 22, thereby reducing the risk of tail tearing and enhancing the cycle performance of the secondary battery.

[0057] Please refer to Figure 3a and Figure 3b. The isolation film 23 includes a base layer and an adhesive layer 232 arranged on at least one surface of the base layer 231. For example, the adhesive layer 232 is provided on both surfaces of the base layer 231 in the thickness direction. When the isolation film 23 is arranged between the first electrode 21 and the second electrode 22, the first electrode 21 and the second electrode 22 can be bonded at the same time.

[0058] The base layer 231 may be made of one or more of polyethylene, polypropylene, polyethylene terephthalate, polybutylene terephthalate, polystyrene, polyparaphenylene, polynaphthalene, polyimide, polyamide, aramid, and polyparaphenylene benzodithiazole. The adhesive layer 232 may be made of at least one of polyvinylidene fluoride and vinyl-polysilsesquioxane.

[0059] In some embodiments, the peel strength between the separator 23 and the first electrode piece 21 or the second electrode piece 22 is 8 N / m to 12 N / m, thereby effectively improving the overall bonding strength of the electrode assembly 20. The peel strength can be controlled by the adhesive content in the adhesive layer 232. When the peel strength is too high, the excess adhesive will clog the pores on the surfaces of the first electrode piece 21 and the second electrode piece 22, causing problems such as lithium deposition black spots. On the other hand, too little adhesive will result in low bonding strength of the electrode assembly 20 and low smoothness of the interface between the first electrode piece 21 and the second electrode piece 22. When dropped, the electrode assembly 20 is more likely to move between the housing 10, increasing the risk of tearing at the end.

[0060] In the embodiment of the present application, the first electrode sheet 21 is a cathode electrode sheet, the second electrode sheet 22 is an anode electrode sheet, and the electrode assembly 20 adopts a wound type as an example. The first electrode sheet 21 includes a first section 213, and the first section 213 constitutes the outermost part of the electrode assembly 20. Referring to Figures 2 and 4, the first section 213 has a first surface 213a facing the winding center 20a of the electrode assembly 20 and a second surface 213b away from the winding center 20a. Along the winding direction N of the first section 213 (winding along the length direction of the first electrode sheet 21), the first section 213 has a tail section 2131, which is also the winding end section of the first section 213. The first surface 213a and the second surface 213b of the tail section 2131 are both empty foil areas. The empty foil area in this embodiment is also the section that is not coated with the active material layer.

[0061] It should be noted that when the first current collector 211 of the first pole piece 21 is coated with the first active material layer 212, the first surface 213a is the surface of the first active material layer 212 facing the winding center 20a; when the first current collector 211 is not coated with the first active material layer 212, the surface of the first current collector 211 facing the winding center 20a is the first surface 213a, and the same applies to the second surface 213b.

[0062] Optionally, the first section 213 further includes a coating section 2132 connected to the above-mentioned finishing section 2131. The coating section 2132 is also the section of the first section 213 coated with the active material layer. Preferably, only the first surface 213a of the first section 213 is provided with the first active material layer 212. The first active material layer 212 is provided on the first surface 213a of the coating section 2132, which is also the single-sided cathode electrode sheet used in the first section 213. In this embodiment, the outermost layer uses a single-sided cathode electrode sheet, and there is no corresponding anode electrode sheet on the outside of the single-sided cathode electrode sheet, which can reduce one layer of active material layer, thereby increasing the energy density of the secondary battery 100.

[0063] Regarding the above-mentioned first adhesive member 30, please refer to Figure 4. The first adhesive member 30 is at least partially bonded to the first surface 213a of the tail section 2131. The first surface 213a of the tail section 2131 is a hollow foil area. The shear force exerted on the hollow foil area can be transmitted to the first adhesive member 30, thereby increasing the tensile strength of the tail section 2131 and reducing the risk of tearing of the tail section 2131.

[0064] Optionally, one end of the first adhesive 30 is bonded to the coating section 2132, that is, the first adhesive 30 is bonded to the first active material layer 212 of the coating section 2132, and the other end is bonded to the tail section 2131, and the first adhesive 30 covers the connection between the coating section 2132 and the tail section 2131. When the first active material layer 212 is coated on the first surface 213a, at the junction of the coating section 2132 and the tail section 2131, the first active material layer 212 is prone to have protruding structures such as tailing burrs. Such protruding structures are likely to interfere with the isolation membrane 23 and easily cause the first active material layer 212 to shed powder. In this embodiment, by bonding and covering with the first adhesive 30, the probability of protruding structures such as burrs piercing the isolation membrane 23 can be reduced, thereby reducing the risk of short circuits and reducing the shedding of powder from the active material layer at the junction.

[0065] When the first adhesive 30 covers the junction between the coating section 2132 and the tail section 2131, the first adhesive 30 can be used to completely cover the junction in the first direction X. For example, further referring to Figure 5a, along the first direction X, the length of the first adhesive 30 is L1 mm, the length of the first section 213 is L2 mm, and 0≤L1-L2≤3; wherein the first direction X is parallel to the winding center axis of the electrode assembly 20, and the first adhesive 30 completely covers the junction in the first direction X, thereby further reducing the risk of protruding structures such as burrs at the junction piercing the separator 23 and causing a short circuit, and reducing the shedding of active material at the junction.

[0066] Continuing with Figures 4 and 5a, along the winding direction N of the first segment 213, the distance between the first adhesive 30 and the end of the tail segment 2131 is a first distance W. The first distance W is greater than or equal to 2 mm to reserve space for cutting the end of the first segment 213. It should be noted that when the first adhesive 30 covers the end of the tail segment 2131, there is no further component for the first adhesive 30 to adhere to. This means that the first adhesive 30 is prone to insufficient adhesion, which may cause the first adhesive 30 to curl at the end. Furthermore, when cutting the first segment 213, there is also a significant risk of cutting into the first adhesive 30, which may also cause the first adhesive 30 to curl at the end. This curling can affect the energy density of the secondary battery 100 and easily interfere with the separator 23. In this embodiment, reserving the first distance allows the first adhesive 30 to fully adhere to the tail segment 2131, effectively reducing the risk of curling the first adhesive 30.

[0067] Optionally, the first adhesive member 30 can be made of adhesive tape. When in use, the adhesive tape can be directly adhered to the first surface 213a of the tail section 2131 and the first active material layer 212 of the coating section 2132. For example, the first adhesive member 30 is a single-sided adhesive tape that is adhesive only on one side. The single-sided adhesive tape includes a first substrate layer 30a and a first adhesive layer 30b coated on one side of the first substrate layer 30a (see Figure 5b). The first adhesive layer 30b can directly adhere to the first active material layer 212 and the tail section 2131. The shear force applied to the hollow foil area of ​​the tail section 2131 can be transferred to the single-sided adhesive tape, thereby reducing the tearing of the tail section 2131. In addition, the single-sided adhesive tape directly covers the junction between the coating section 2132 and the tail section 2131, thereby reducing the risk of protruding structures such as burrs piercing the isolation membrane 23.

[0068] The material of the first substrate layer 30a includes at least one of polyethylene terephthalate (PET), polyimide, or polypropylene. Polyethylene terephthalate has excellent physical and mechanical properties, with a long-term operating temperature of up to 120°C. It has excellent electrical insulation properties, and even at high temperatures and high frequencies, its electrical properties remain good. It also has excellent creep resistance, fatigue resistance, friction resistance, and dimensional stability. The first adhesive member 30 made of polyethylene terephthalate can fully improve the tensile strength of the tail section 2131 to reduce the risk of tearing of the tail section 2131. The material of the first adhesive layer 30b includes at least one of polyacrylic acid (PAA), polymethyl methacrylate, polypropylene, polyethylene, polyamide, styrene-butadiene rubber, nitrile rubber, butadiene rubber, isoprene rubber, ethylene-propylene rubber, or chloroprene rubber.

[0069] Regarding the above-mentioned second adhesive 40, the second adhesive 40 is bonded between the electrode assembly 20 and the shell 10. For example, please refer to Figure 1 as well as Figure 4 and Figure 5a. The second adhesive 40 is arranged on the second surface 213b of the tail section 2131 to further improve the tensile strength of the tail section 2131; and the second adhesive 40 is bonded between the second surface 213b of the tail section 2131 and the shell 10, which can reduce the relative movement between the electrode assembly 20 and the shell 10. When the secondary battery 100 falls or collides, due to the bonding effect of the second adhesive 40, the collision between the electrode assembly 20 and the shell 10 can be effectively reduced, thereby reducing the failure risk of the secondary battery 100.

[0070] The second adhesive member 40 can also be made of adhesive tape, such as double-sided adhesive tape with adhesiveness on both sides. The double-sided adhesive tape includes a second substrate layer 41 and a second adhesive layer 42 and / or a hot melt adhesive layer coated on both sides of the second substrate layer 41. The second adhesive member 40 is bonded to the electrode assembly 20 on one side and to the housing 10 on the other side, thereby reducing relative movement between the electrode assembly 20 and the housing 10. The material of the second substrate layer 41 includes one or more of polyester resin, cellulose derivatives, polyvinyl chloride, polyolefin, polystyrene, polyester, polyimide, polyamide, polycarbonate, polyphenylene sulfide, and polyethylene terephthalate. When the second adhesive layer 42 is an adhesive layer, the material includes one or more of rubber resin, acrylic resin, or silicone resin. When the second adhesive layer 42 is a hot melt adhesive layer, the material includes one or more of styrene-isoprene-styrene block copolymer, ethylene-vinyl acetate copolymer, polyurethane elastomer, polyurethane acrylate, polyisobutylene, or polybutadiene. After the electrode assembly 20 is wound, it can be fastened with the second adhesive 40 , which can reduce one step of the finishing glue and adhesive finishing process, thereby reducing the tearing of the finishing section and improving the energy density of the secondary battery 100 .

[0071] Along a direction M perpendicular to the first surface 213a, the second adhesive 40 partially overlaps the first adhesive 30; that is, along the direction M perpendicular to the first surface 213a, the projection of the second adhesive 40 partially overlaps the projection of the first adhesive 30. When the secondary battery 100 is dropped or collides, the second adhesive 40 adheres to the electrode assembly 20 and the housing 10, reducing relative movement between the electrode assembly 20 and the housing 10. However, the second adhesive 40 is subjected to significant shear force, which can easily cause the end section 2131 bonded by the second adhesive 40 to tear. In this embodiment, since the projections of the first adhesive 30 and the second adhesive 40 overlap, some of the shear force applied to the second adhesive 40 is transferred to the first adhesive 30, thereby reducing shear force concentration and further reducing the risk of tearing in the end section 2131.

[0072] In some embodiments, the portion of the second adhesive 40 that overlaps the projection of the first adhesive 30 is a first portion 40a. Along a direction M perpendicular to the first surface 213a, the projection of the first portion 40a falls within the projection of the first adhesive 30. The shear force transmission between the first adhesive 30 and the second adhesive 40 effectively reduces the risk of tearing of the tail section 2131.

[0073] Preferably, the area of ​​the first portion 40a is S1, the area of ​​the second adhesive member 40 is S2, and 15% ≤ S1 / S2 ≤ 50%. The sufficient adhesive surface area of ​​the second adhesive member 40 not only improves the tensile strength of the tail section 2131 but also ensures sufficient overlap between the second adhesive member 40 and the first adhesive member 30 for shear force transmission, thereby reducing the risk of tail tearing.

[0074] Furthermore, the actual bonding area between the second adhesive member 40 and the first section 213 is S3, and the effective bonding area between the second adhesive member 40 and the first section 213 is S4, where S3>S4. Sufficient actual bonding area can reduce the risk of the first section 213 being torn.

[0075] 6 and 7 , in some embodiments, the first adhesive 30 includes a first sub-adhesive 31 and a second sub-adhesive 32. The first sub-adhesive 31 is disposed on the first surface 213a, and the second sub-adhesive 32 is also disposed on the first surface 213a. Furthermore, the second sub-adhesive 32 is bonded to the first sub-adhesive 31 at the end section 2131. If the length of the first adhesive 30 is too long (30 mm) along the winding direction N of the first section 213, bubbles may form when bonding the first section 213. These bubbles not only affect the energy density of the secondary battery 100 but also result in poor bonding of the first adhesive 30, resulting in poor shear force transmission between the second adhesive 40 and the first adhesive 30. In this regard, in the embodiment of the present application, the first adhesive 30 is configured as a two-line sub-adhesive structure. Specifically, the first adhesive 30 includes a first sub-adhesive 31 and a second sub-adhesive 32 that are bonded to each other. Both the first adhesive 30 and the second adhesive 40 are relatively short, effectively reducing the formation of bubbles during the bonding process. Furthermore, the projection of the second sub-adhesive 32 on the second surface 213b partially overlaps with the second adhesive 40. All shear forces from the second adhesive 40 are transferred to the second sub-adhesive 32, and then to the first sub-adhesive 31, thereby reducing shear force concentration.

[0076] Optionally, one end of the first sub-adhesive member 31 is bonded to the coating section 2132 and the other end is bonded to the tail section 2131, and the first sub-adhesive member 31 covers the junction between the coating section 2132 and the tail section 2131. Because a shorter first sub-adhesive member 31 is used, the bonding of the first sub-adhesive member 31 can reduce the formation of bubbles during bonding and cover protruding structures such as trailing burrs at the junction. This can reduce the risk of these protruding structures piercing the isolation film 23, thereby reducing the risk of short circuits and reducing the shedding of powder from the active material layer at the junction.

[0077] Furthermore, along the first direction X, the length of the first sub-adhesive member 31 is L3 mm, the length of the first section 213 is L2 mm, and 0≤L3-L2≤3. The first sub-adhesive member 31 completely covers the junction in the first direction X, further reducing the risk of protruding structures such as burrs piercing the isolation film 23, thereby reducing the risk of short circuits.

[0078] The first adhesive component 30 may also be composed of a plurality of sub-adhesive components. For example, referring to FIG. 8 , the first adhesive component 30 includes a plurality of second sub-adhesive components 32 .

[0079] Multiple second sub-adhesive components 32 are arranged sequentially on the first surface 213a along the winding direction N of the first section 213, with adjacent second sub-adhesive components 32 bonded to each other. Along the winding direction N of the first section 213, the second sub-adhesive component 32 at the beginning of the arrangement adheres to the first sub-adhesive component 31 on the ending section 2131. Along the direction M perpendicular to the first surface 213a, the projection of the second sub-adhesive component 32 at the end of the arrangement partially overlaps with the projection of the second adhesive component 40. This multiple sub-adhesive component arrangement further reduces the risk of bubbles during bonding and reduces shear force concentration, thereby reducing the risk of tearing in the ending section 2131.

[0080] In some embodiments, referring to FIG. 7 , along the winding direction N of the first segment 213, the length of the first sub-adhesive component 31 is L4 mm, where L4 ≤ 30 mm. When the length of the first sub-adhesive component 31 exceeds 30 mm, bubbles are more likely to form during bonding. Therefore, in the embodiments of the present application, a length of the first sub-adhesive component 31 of less than 30 mm is preferably employed. The second sub-adhesive component 32 can also be configured similarly, that is, along the winding direction N of the first segment 213, the length of the second sub-adhesive component 32 is L5 mm, where L5 ≤ 30 mm, thereby reducing the risk of bubbles forming during bonding.

[0081] Please refer to Figures 2 and 4. Figure 2 shows the winding structure of the electrode assembly 20. The first section 213 includes a first straight section 24, a first curved section 25, a second straight section 26, and a second curved section 27, which are connected to each other. The first straight section 24 and the second straight section 26 are arranged opposite each other in the second direction Y. The first curved section 25 and the second curved section 27 are both connected between the first straight section 24 and the second straight section 26. The first curved section 25 and the second curved section 27 are also arranged opposite each other in the third direction Z. For example, the first section 213 is first wound to form the first curved section 25, then straightened to form the second straight section 26, the second straight section 26 is extended and wound to form the second curved section 27, and finally straightened to form the first straight section 24.

[0082] The second adhesive member 40 is partially disposed on the first straight segment 24 or partially disposed on the second straight segment 26. For example, when the wound end of the first segment 213 is close to the first straight segment 24, the second adhesive member 40 may be partially bonded to the first straight segment 24; or, as shown in FIG2 , when the wound end of the first segment 213 is close to the second straight segment, the second adhesive member 40 may be partially bonded to the second straight segment 26. Partially disposing the second adhesive member 40 on the flat first straight segment 24 or second straight segment 26 facilitates bonding and improves the bonding effect, thereby increasing the tensile strength of the first segment 213 and reducing the risk of tearing of the first segment 213.

[0083] Regarding the thickness of the electrode assembly 20, when the thickness of the electrode assembly 20 is greater than or equal to 6.95 mm (the thickness of the electrode assembly 20 along the second direction Y in FIG. 2 ), the length of the first adhesive 30 should be greater than or equal to 30 mm (in this case, up to the first sub-adhesive 31 can be used). The relationship between the thickness of the electrode assembly 20 and the length L of the corner (first curved segment 25 or second curved segment 27) of the outermost first segment 213 is L = (π*T) / 2. In this application, in order to achieve the anti-collision tearing effect and prevent the generation of bubbles in the adhesive at the same time, the thickness of the electrode assembly 20 satisfies: L+H+W≤25~30 mm. H is the length of the second active material layer 222 exceeding the first active material layer 212 along the winding direction N of the first segment 213, that is, the dimension H in FIG. 2; W is the distance between the first adhesive 30 and the end of the tail segment 2131 (that is, the above-mentioned first distance W).

[0084] In the embodiment of the present application, the first adhesive 30 is at least partially bonded to the first surface 213a of the end section 2131, thereby increasing the tensile strength of the end section 2131 and reducing the risk of tearing of the end section 2131. The second adhesive 40 is disposed on the second surface 213b of the end section 2131 and bonds the end section 2131 to the housing 10, thereby reducing relative movement between the electrode assembly 20 and the housing 10 and further increasing the tensile strength of the end section 2131, further reducing the risk of tearing of the end section 2131. Furthermore, along a direction perpendicular to the first surface 213a, the projection of the second adhesive 40 partially overlaps with the projection of the first adhesive 30. If the secondary battery 100 is dropped or collided, some of the shear force applied to the second adhesive 40 can be transferred to the first adhesive 30, thereby reducing the concentration of shear force and further reducing the risk of tearing of the end section 2131.

[0085] Example

[0086] Hereinafter, the embodiments of the present application will be described in more detail with reference to Examples and Comparative Examples. Various tests and evaluations were performed according to the following methods.

[0087] Example 1

[0088] Preparation of positive electrode (cathode)

[0089] The positive electrode active material, lithium cobalt oxide (LiCoO2), the conductive agent, conductive carbon black, and the binder, polyvinylidene fluoride (PVDF), were mixed in a weight ratio of 97.5:1:1.5. N-methylpyrrolidone (NMP) was added as a solvent to form a slurry with a solid content of 75 wt%, and stirred evenly. The slurry was evenly coated on one surface of a 9 μm thick aluminum foil for the positive electrode current collector and dried at 90°C to obtain a positive electrode sheet with a positive electrode active material layer thickness of 110 μm. After completing the above steps, the positive electrode sheet was coated on one side. The above steps were then repeated on the other side of the positive electrode sheet to obtain a positive electrode sheet coated on both sides with a positive electrode active material layer. After coating, the sheet was cold pressed, cut, and slit, and then dried under vacuum at 85°C for 4 hours to obtain a positive electrode sheet with a size of 74 mm x 867 mm.

[0090] Preparation of negative electrode (anode)

[0091] The negative electrode active material, graphite powder, conductive carbon black (Super P), and binder, styrene-butadiene rubber (SBR), were mixed in a weight ratio of 96:1.5:2.5. Deionized water was then added as a solvent to form a slurry with a solid content of 70 wt%, which was then stirred evenly. The slurry was evenly coated on one surface of a 5 μm thick copper foil for the negative electrode current collector and dried at 110°C to produce a single-sided negative electrode sheet with a 130 μm thick negative electrode active material layer. After completing these steps, the negative electrode sheet was coated on one side. The above steps were then repeated on the other side of the negative electrode sheet to produce a double-sided negative electrode sheet coated with the negative electrode active material layer. After coating, the sheet was cold pressed, cut, and slit, and then dried under vacuum at 120°C for 12 hours to produce a negative electrode sheet measuring 76.6 mm x 875 mm.

[0092] Preparation of isolation membrane

[0093] Polyvinylidene fluoride (adhesive) and alumina ceramics are mixed in a mass ratio of 9:1, deionized water is added as a solvent, and a slurry with a solid content of 25 wt% is prepared and stirred evenly. The slurry is evenly coated on one surface of a 5 μm thick polyethylene porous polymer film, dried, and then the slurry is evenly coated on the other surface of the polyethylene porous polymer film to obtain an isolation membrane coated with a 2 μm alumina ceramic layer on both sides.

[0094] Preparation of electrolyte

[0095] In a dry argon environment, organic solvents 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 (LiPF6) 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.

[0096] Preparation of the first bonding member

[0097] Polyacrylic acid (PAA) was coated on one surface of a first substrate layer of polyethylene terephthalate film (PET) having a thickness of 8 μm, and dried at 80° C. to form a first adhesive layer having a thickness of 4 μm, thereby obtaining a first adhesive member.

[0098] Preparation of the second bonding member

[0099] The styrene-isoprene-styrene block copolymer is heated to 150°C for hot melting, and then coated on one surface of a second substrate layer of polyethylene terephthalate film (PET) with a thickness of 8 μm, and then dried at 120°C to form a second adhesive layer with a thickness of 8 μm.

[0100] Polyacrylic acid (PAA) was coated on the other surface of the second substrate layer and dried at 80° C. to form a second adhesive layer with a thickness of 4 μm, thereby obtaining a second adhesive member comprising a second adhesive layer, a second substrate layer, and a second adhesive layer stacked in sequence.

[0101] Preparation of lithium-ion batteries

[0102] The positive electrode sheet, separator, and negative electrode sheet prepared above are stacked in order, with the separator placed between the positive and negative electrode sheets to serve as an isolation layer, and then wound to obtain an electrode assembly with a wound structure, wherein the outermost layer is a positive electrode sheet coated with an active material layer on one side, and the first adhesive of modified polypropylene is bonded to the coated section and the empty foil section of the outermost positive electrode sheet.

[0103] The second adhesive member prepared above is adhered to the outer surface of the electrode assembly via the second adhesive layer. The electrode assembly is then placed in an aluminum-plastic film packaging bag, and the first adhesive layer is adhered to the inner surface of the casing. The lithium-ion battery is then produced through processes such as top and side sealing, vacuum drying, liquid injection, formation (temperature 85°C, pressure 1.05 MPa, 3.5V), capacity measurement, and air extraction.

[0104] The mass of the lithium-ion battery is 61.5g, and the liquid retention coefficient is 1.75g / Ah. The size of the first adhesive layer is 20mm×30mm, and the orthographic projection size of the electrode assembly along the stacking direction of the electrode assembly, adhesive and shell is 30mm×40mm, that is, S5=600mm 2 , S6=1200mm 2 ;The actual glue area is S=S5=600mm 2 Along the thickness direction of the positive electrode sheet, the area of ​​the overlapped area between the second adhesive and the first adhesive is 100mm. 2 (S1=100mm 2), the distance between the first adhesive and the end of the positive electrode sheet is 3.2 mm (W = 3.2 mm), the length difference (length along the central axis of the electrode assembly) between the first adhesive and the outer single-sided positive electrode sheet (including the empty foil area) is 0.8 mm (L1-L2 = 0.8 mm), and the isolation film peel strength is 10 N / m.

[0105] Example 2

[0106] The difference from Example 1 is: S1 = 60 mm 2 .

[0107] Example 3

[0108] The difference from Example 1 is: S1 = 90 mm 2 .

[0109] Example 4

[0110] The difference from Example 1 is: S1 = 150 mm 2 .

[0111] Example 5

[0112] The difference from Example 1 is: S1 = 240 mm 2 .

[0113] Example 6

[0114] The difference from Example 1 is: S1 = 300 mm 2 .

[0115] Example 7

[0116] The difference from Example 1 is: S1 = 360 mm 2 .

[0117] Example 8

[0118] The difference from Example 1 is that W=2 mm.

[0119] Example 9

[0120] The difference from Example 1 is that: L1-L2=3mm.

[0121] Example 10

[0122] The difference from Example 1 is that: L1-L2=0 mm.

[0123] Example 11

[0124] The difference from Example 1 is: S1 = 150 mm 2 The mass ratio of polyvinylidene fluoride to alumina ceramic is 6:4, and the peel strength between the separator and the positive electrode is 7N / m.

[0125] Example 12

[0126] The difference from Example 1 is: S1 = 150 mm 2 The mass ratio of polyvinylidene fluoride to alumina ceramic is 8:2, and the peel strength between the separator and the positive electrode is 8N / m.

[0127] Example 13

[0128] The difference from Example 1 is: S1 = 150 mm 2 The mass ratio of polyvinylidene fluoride to alumina ceramic is 9.5:0.5, and the peel strength between the separator and the positive electrode is 12N / m.

[0129] Example 14

[0130] The difference from Example 1 is: S1 = 150 mm 2 The mass ratio of polyvinylidene fluoride to alumina ceramic is 9.8:0.2, and the peel strength between the separator and the positive electrode is 13N / m.

[0131] Comparative Example 1

[0132] Different from Example 1, the first adhesive does not cover the empty foil segment, the projections of the first adhesive and the second adhesive in the thickness direction of the positive electrode sheet do not overlap, and S1=0.

[0133] Test methods and equipment:

[0134] Drop aluminum foil tearing rate test:

[0135] Lithium-ion batteries were preconditioned at 25°C and allowed to rest at room temperature for 60 minutes. The voltage of the lithium-ion batteries was then measured before the drop test. The lithium-ion batteries were then placed in a fixture and dropped from a height of 1.5 meters using a drop device in the following sequence: head-to-tail-head right corner-to-tail right corner-to-head left corner-to-tail left corner (angle: 45±15°). This was repeated six times. After the drop, the battery cells were disassembled and the aluminum foil was inspected for tears.

[0136] Drop failure rate test:

[0137] The lithium-ion battery was preconditioned at 25°C and allowed to stand at room temperature for 60 minutes. The voltage of the lithium-ion battery was then measured before the drop test. The lithium-ion battery was then placed in a fixture and dropped from 1.5m above the ground in the following sequence: head-to-tail-head right corner-tail right corner-head left corner-tail left corner (angle: 45±15°), repeated six times. After the drop, the lithium-ion battery voltage was measured and recorded. The appearance of the lithium-ion battery was inspected and photographed before and after the test. Drop test passing criteria: no smoke, no leakage, and a voltage drop of <30mV.

[0138] Peel strength test:

[0139] According to GB / T 2792-2014 "Test method for peel strength of adhesive tape", a high-speed rail tensile tester is used to test the peel strength between the isolation membrane and the positive electrode sheet or the negative electrode sheet (the peel strength between the isolation membrane and the positive electrode sheet is tested as an example in the embodiment of the present application). The test process is as follows: discharge the lithium-ion battery to 0V, then disassemble the lithium-ion battery, remove the isolation membrane and the electrode sheet bonded thereto as a whole, and wipe the electrolyte on the surface with dust-free paper. Then cut into 20mm×60mm strip specimens. Along the length direction of the specimen, the side of the electrode assembly in the specimen is adhered to the steel plate with double-sided tape (Nitto 5000NS), and the adhesion length is not less than 40mm. Fix the steel plate at the corresponding position of the high-speed rail tensile testing machine, pull up the other end of the electrode that is not adhered to the diaphragm, and clamp the sample in the chuck. The angle between the pulled-up sample part and the steel plate in space is 180°. The chuck pulls the sample at a speed of 5±0.2mm / s. The average tensile force in the stable area is finally measured and recorded as the peel strength between the isolation diaphragm and the electrode, which is recorded as F and the unit is N / m.

[0140] The relevant preparation parameters and performance tests of each embodiment and comparative example are shown in Table 1:

[0141] Table 1

[0142] According to Table 1, combined with Comparative Example 1 and Examples 1 to 14, when the first adhesive is used to cover the bare foil segment, and the projections of the first and second adhesives in the thickness direction of the positive electrode sheet overlap, the aluminum foil tear rate and drop failure rate are significantly reduced. This is because some of the shear force applied to the second adhesive is transferred to the first adhesive, reducing shear force concentration and, in turn, foil tearing. Furthermore, because the first adhesive adheres from the coated segment to the bare foil segment, it covers the edge burrs of the active material layer, reducing the risk of burrs piercing the separator and, consequently, lowering the drop failure rate.

[0143] In Example 2, S1 / S2 = 10%, and the area occupied by the first portion is relatively small. In this case, the risk of aluminum foil tearing and the risk of drop failure are both relatively high. In Example 7, S1 / S2 = 60%. The excessively large area occupied by the first portion can easily cause the first adhesive to be cut during cutting, resulting in curling of the edge of the first adhesive. Therefore, Example 7 also has a relatively low aluminum foil tear rate and drop failure risk. In Example 3, S1 / S2 = 15%, and in Example 6, S1 / S2 = 50%, both have relatively low aluminum foil tear rates and drop failure risks. In this application, it is preferred that 15% ≤ S1 / S2 ≤ 50%.

[0144] The length of the first adhesive member in the width direction of the electrode sheet should not be too large or too small. If it is too large, it may easily curl in the width direction of the electrode sheet, entering the top seal area and affecting the energy density of the lithium-ion battery. If it is too small, it will be difficult to cover the burrs on the edge of the active material layer, which may easily pierce the separator and cause a short circuit. In this application, 0≤L1-L2≤3 is preferred.

[0145] Moreover, the first distance W ≥ 2mm can better reduce the curling of the first adhesive in the length direction of the electrode when it is cut. In combination with Example 11, when the peel strength between the isolation membrane and the positive electrode is 7N / m, the bonding strength of the electrode assembly is not high, so that there is still a risk of aluminum foil tearing; in combination with Example 14, when the peel strength between the isolation membrane and the positive electrode is 13N / m, the peel strength is too large, and too much adhesive will clog the pores on the surface of the positive electrode and the negative electrode, causing problems such as lithium plating black spots, thereby causing the lithium-ion battery to still have a risk of falling and failing. In combination with Examples 11 to 14, in this application, the preferred peel strength of the isolation membrane is 8N / m to 12N / m, and its falling aluminum foil tearing rate and falling failure risk are low.

[0146] In a second aspect, the present application further provides an electronic device comprising the secondary battery described in any embodiment of the first aspect. The electronic device may be a portable consumer electronic device, a power tool, a drone, a wearable electronic device, an electric vehicle, or the like.

[0147] 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. Based on the concept of the present application, the technical features in the above embodiments or different embodiments can also be combined, the steps can be implemented in any order, and there are many other variations in different aspects of the present application as described above. For the sake of simplicity, they are not provided in detail. Although the present application has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. 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, characterized in that: include: case; An electrode assembly is disposed in the housing, the electrode assembly comprising a first electrode sheet, a second electrode sheet, and a separator located between the first electrode sheet and the second electrode sheet, the first electrode sheet, the second electrode sheet, and the separator being stacked and wound, with the winding center axis of the electrode assembly directed in a first direction; the first electrode sheet comprises a first section, the first section constituting an outermost portion of the electrode assembly, the first section having a first surface facing the winding center axis and a second surface facing away from the winding center axis; along the winding direction of the first section, the first section comprises a tail section, the first and second surfaces of the tail section being both hollow foil areas; a first adhesive member, at least partially bonded to the first surface of the tail section; The second adhesive member is provided on the second surface of the tail section and bonds the second surface of the tail section and the housing. The second adhesive member partially overlaps with the first adhesive member along a direction perpendicular to the first surface.

2. The secondary battery according to claim 1, wherein The overlapping portion of the second adhesive member and the first adhesive member is a first portion, the area of ​​the first portion is S1, the area of ​​the second adhesive member is S2, and 15%≤S1 / S2≤50%.

3. The secondary battery according to claim 1 or 2, characterized in that Along the winding direction of the first section, the distance between the first adhesive component and the end of the tail section is a first distance, and the first distance is greater than or equal to 2 mm.

4. The secondary battery according to any one of claims 1 to 3, characterized in that The first section further includes a coating section connected to the finishing section.

5. The secondary battery according to claim 4, wherein One end of the first adhesive is bonded to the coating section, and the other end is bonded to the tail section, and the first adhesive covers the connection between the coating section and the tail section; Along the first direction, the length of the first adhesive is L1 mm, and the length of the first section is L2mm, 0≤L1-L2≤3.

6. The secondary battery according to claim 4 or 5, characterized in that: The first adhesive member includes: a first sub-adhesive component, disposed on the first surface; The second sub-adhesive is provided on the first surface and is bonded to the first sub-adhesive at the end section. The projection of the second sub-adhesive on the second surface partially overlaps with the second adhesive along a direction perpendicular to the first surface.

7. The secondary battery according to claim 6, characterized in that One end of the first sub-adhesive is bonded to the coating section, and the other end is bonded to the tail section, and the first sub-adhesive covers the connection between the coating section and the tail section; Along the first direction, the length of the first sub-adhesive component is L3 mm, the length of the first segment is L2 mm, and 0≤L3-L2≤3.

8. The secondary battery according to claim 6 or 7, characterized in that The first adhesive component includes a plurality of second sub-adhesive components; The plurality of second sub-adhesive members are sequentially arranged on the first surface along the winding direction of the first section, and two adjacent second sub-adhesive members are bonded to each other; Along the winding direction of the first section, the second sub-adhesive component at the starting end is bonded to the first sub-adhesive component on the ending section, and along the direction perpendicular to the first surface, the projection of the second sub-adhesive component at the end of the arrangement partially overlaps with the projection of the second adhesive component.

9. The secondary battery according to any one of claims 1 to 8, characterized in that The first adhesive member and the second adhesive member are adhesive tapes.

10. The secondary battery according to any one of claims 1 to 9, characterized in that The first section includes a first straight section, a first curved section, a second straight section and a second curved section connected to each other; The first straight section and the second straight section are arranged opposite to each other in the second direction, and the first curved The first curved segment and the second curved segment are both connected between the first straight segment and the second straight segment, and the first curved segment and the second curved segment are arranged opposite to each other in the third direction; The second adhesive member is disposed on the first straight section or the second straight section, and the first direction, the second direction, and the third direction are perpendicular to each other.

11. The secondary battery according to any one of claims 1 to 10, characterized in that The peel strength between the isolation film and the first pole piece or the second pole piece is 8 N / m to 12 N / m.

12. The secondary battery according to any one of claims 1 to 11, characterized in that: The first adhesive member is a single-sided adhesive tape having adhesiveness on only one side, and the single-sided adhesive tape comprises a first base material layer and a first adhesive layer coated on one side of the first base material layer.

13. The secondary battery according to any one of claims 1 to 11, characterized in that The second adhesive component is a double-sided tape with adhesiveness on both sides, and the double-sided tape includes a second substrate layer and a second adhesive layer coated on both sides of the second substrate layer, and the second adhesive layer is an adhesive layer and / or a hot melt adhesive layer.

14. The secondary battery according to any one of claims 1 to 13, characterized in that The shell is a packaging bag.

15. The secondary battery according to any one of claims 1 to 14, characterized in that The first electrode piece is a cathode electrode piece, and the second electrode piece is an anode electrode piece; only the first surface of the first section is provided with an active material layer, and the active material layer is provided on the first surface of the coating section.

16. The secondary battery according to any one of claims 1 to 15, characterized in that The second adhesive member is used to fix the tail section.

17. An electronic device, characterized in that: The secondary battery according to any one of claims 1 to 16 is included.

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