Secondary battery and electronic device

Abstract

The invention discloses a secondary battery and electronic equipment, a first concave part of a first adhesive layer is bonded with a first concave area of a first surface, the first adhesive layer comprises a second starting end along a winding direction, the second starting end is flush with the first starting end, or the first adhesive layer extends out of a first pole piece from the first starting end along a direction opposite to the winding direction. And / or the first protruding part of the second adhesive layer is bonded with the first protruding area on the second surface, the second adhesive layer comprises a third starting end in the winding direction, and the third starting end is flush with the first starting end or the second adhesive layer extends out of the first pole piece from the first starting end in the direction opposite to the winding direction. Therefore, cutting burrs at the first starting end can be prevented from puncturing the isolating membrane, and short circuit caused by direct contact between the first starting end and the second pole piece is further reduced.

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 requirements for battery safety performance are getting higher and higher. Summary of the invention

[0003] The present application aims to provide 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 stacked and wound, along the winding direction, the first electrode sheet includes 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. Along the thickness direction of the first electrode sheet, the first electrode sheet includes a first surface and a second surface arranged opposite to each other, the first surface has a plurality of first recessed areas, and the first recessed areas form a first raised area on the second surface.

[0005] The secondary battery includes a first adhesive layer disposed on the first surface, the first adhesive layer having a plurality of first recessed portions, the first recessed portions being disposed in the first recessed region, and the first recessed portions being bonded to the first recessed region; along the winding direction, the first adhesive layer includes a second starting end, the second starting end being flush with the first starting end, or the first adhesive layer extending a first pole piece from the first starting end in the opposite direction of the winding direction. And / or, the secondary battery includes a second adhesive layer disposed on the second surface, the second adhesive layer having a plurality of first protruding portions, the first protruding portions being disposed in the first protruding region, and the first protruding portions being bonded to the first protruding region; along the winding direction, the second adhesive layer includes a third starting end, the third starting end being flush with the first starting end, or the second adhesive layer extending a first pole piece from the first starting end in the opposite direction of the winding direction.

[0006] In the above technical solution, the first adhesive layer is arranged on the first surface, and the second starting end of the first adhesive layer is flush with the first starting end or the first adhesive layer exceeds the first starting end, so that the first adhesive layer covers the first starting end, reducing 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 first recessed portion of the first adhesive layer is bonded to the first recessed area, which can form a structure similar to a mechanical anchor, thereby improving the bonding force between the first adhesive layer and the first current collector, and can effectively reduce the exposure of the first starting end caused by the slippage of the first adhesive layer, thereby reducing the occurrence of short circuits. At the same time, the first recessed portion of the first adhesive layer is bonded to the first recessed area, so that the first pole piece forms an uneven structure, and the uneven structure makes the contact area between the first adhesive layer and the adjacent isolation membrane or second pole piece smaller, so that the risk of the isolation membrane or the second pole piece driving the first adhesive layer to slip is reduced, which can further reduce the occurrence of short circuits. In addition, the first concave area and the first convex area of ​​the first electrode piece are arranged so that the first electrode piece forms a retractable elastic structure, which can adapt to the expansion or contraction of the electrode piece, thereby reducing the exposure of the first starting end from the first adhesive layer, further reducing the occurrence of short circuits, and effectively improving the safety performance of the secondary battery. The second adhesive layer is similar.

[0007] In some embodiments, the first starting end is located at the sub-inner pole piece of the electrode assembly. The sub-inner pole piece has a higher risk of piercing the isolation membrane. Setting the first adhesive layer on the sub-inner pole piece has a more significant effect on reducing the piercing of the isolation membrane.

[0008] In some embodiments, the secondary battery is cylindrical. In the embodiments of the present application, the first pole piece is provided with a first recessed area and a first raised area, and a first glue layer and / or a second glue layer are provided correspondingly. This can reduce the slippage of the first glue layer and / or the second glue layer relative to the first pole piece, thereby reducing the exposure of the first starting end, reducing the occurrence of short circuits, and is particularly suitable for cylindrical secondary batteries.

[0009] In some embodiments, the electrode assembly is provided with a cavity, which is arranged at the winding center of the electrode assembly. The setting of the first recessed area and the first raised area provides support for the first pole piece, which can reduce the collapse of the electrode assembly near the inner circle and help improve the structural stability of the electrode assembly.

[0010] In some embodiments, the cylindrical 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 thickness direction of the first pole piece, the depth of the first recessed area is H1. The first recessed area includes a bottom wall, a first side wall, and a second side wall. Along the length direction of the first pole piece, the bottom wall is connected between the first side wall and the second side wall; the angle between the bottom wall and the first side wall is α, and the angle between the bottom wall and the second side wall is β. Along the length direction of the first pole piece, a plurality of first recessed areas are arranged in an array, and the number of the arranged first recessed areas is n.

[0011] Limit n × [H1 / sin(π-α)-H1 / tan(π-α)]+n × [H1 / sin(π-β)-H1 / tan(π-β)]≥π(D1-D2), which can facilitate the maximum stretching of the first pole piece to be greater than the maximum expansion of the first pole piece. When the first pole piece expands, the first recessed area and the first raised area of ​​the first pole piece are preferentially flattened, thereby reducing the slippage of the first adhesive layer and / or the second adhesive layer, thereby reducing the exposure of the first starting end, and further reducing the burrs at the first starting end from piercing the isolation membrane and causing a short circuit.

[0012] In some embodiments, along the winding direction, 10≤n≤30 can improve the bonding strength between the first adhesive layer and the first electrode piece, reduce the slippage of the first adhesive layer, and facilitate the winding and feeding of the first electrode piece, reduce the warping of the first starting end, and further reduce the first starting end piercing the isolation film and causing a short circuit. Preferably, 15≤n≤25 can further reduce the occurrence of short circuits, simplify the process, and reduce the impact on the active material layer.

[0013] In some embodiments, 10μm≤H1≤100μm can reduce the imprint damage of the first pole piece and / or the first adhesive layer, and can reduce the influence of the first recessed area on the thickness of the first pole piece, reduce the energy density loss, and reduce the first adhesive layer from cracking or separation from the first pole piece due to uneven stress distribution. In addition, it can also make the first adhesive layer and the first pole piece have a higher bonding strength, which can reduce the slippage of the first adhesive layer and thus reduce the exposure of the first starting end. Preferably, 30μm≤H1≤80μm can further reduce the occurrence of short circuits and reduce the influence on the thickness of the first pole piece.

[0014] In some embodiments, along the length direction of the first electrode piece, the first electrode piece includes a first empty foil section and a first coated section. In the first empty foil section, along the thickness direction of the first electrode piece, the maximum distance from the first surface to the second surface is T1, the first glue layer is provided in the first empty foil section, and the thickness of the first glue layer is T a In the first coating section, along the thickness direction of the first electrode, the maximum thickness of the first coating section is T2, T1+T a≤T2. The first empty foil section and the first adhesive layer do not occupy the thickness space of the first pole piece, thereby reducing the energy density loss of the secondary battery.

[0015] In some embodiments, along the winding direction, the length of the first recessed area is L1, 0.5mm≤L1≤5mm, which can reduce the separation of the first adhesive layer from the first pole piece due to stress concentration, and can make the first adhesive layer and the first pole piece have a higher bonding strength, reduce the exposure of the first starting end, and thus reduce the occurrence of short circuits.

[0016] In some embodiments, along the winding direction, the distance between two adjacent first recessed areas is L2, 0.5mm≤L2≤5mm, which is beneficial for the first pole piece to maintain a high structural strength and enable the first adhesive layer and the first pole piece to have a high bonding strength, thereby reducing the exposure of the first starting end due to slippage of the first pole piece, thereby reducing the occurrence of short circuits.

[0017] In some embodiments, the second pole piece includes a second inner ring pole piece and a second inner ring pole piece, the second inner ring pole piece is the innermost pole piece of the electrode assembly, and along the thickness direction of the first pole piece, the pole pieces adjacent to the first starting end are the second inner ring pole piece and the second inner ring pole piece respectively. Along the thickness direction of the first pole piece, the distance from the first starting end to the second inner ring pole piece is H2, and the distance from the first starting end to the second inner ring pole piece is H3, H3>H2. The contact between the first starting end and the second inner ring pole piece can be reduced, thereby reducing the burrs from piercing the isolation membrane between the first starting end and the second inner ring pole piece, and reducing the occurrence of short circuits.

[0018] In some embodiments, 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. This can facilitate the first adhesive layer to completely cover the first starting end, reduce the first adhesive layer beyond the isolation film, and further reduce the impact of the first adhesive layer on the energy density of the secondary battery.

[0019] In some embodiments, the first surface further has a plurality of second recessed areas, and the second recessed areas form second raised areas on the second surface. When viewed along the width direction of the first pole piece, the second raised areas are at least partially located between two adjacent first raised areas. The first raised areas and the second raised areas are staggered in the width direction of the first pole piece, which can improve the strength of the first pole piece and reduce the occurrence of tearing of the first pole piece.

[0020] In some embodiments, a first adhesive layer is provided on the first surface, the first adhesive layer has a plurality of second recessed portions, the second recessed portions are provided in the second recessed area, and the second recessed portions are bonded to the second recessed area. A second adhesive layer is provided on the second surface, the second adhesive layer has a plurality of second raised portions, the second raised portions are provided in the second raised area, and the second raised portions are bonded to the second raised area. The provision of multiple recessed portions and raised portions increases the anchoring points between the first adhesive layer and the second adhesive layer and the first pole piece, thereby improving the bonding strength.

[0021] In some embodiments, along the winding direction, the first pole piece further includes a first tail end; along the thickness direction of the first pole piece, the pole piece adjacent to the first tail end is the second pole piece. The first surface also has a plurality of third recessed areas, and the third recessed areas form third raised areas on the second surface.

[0022] The secondary battery also includes a third glue layer, which is arranged on the first surface, and the third glue layer has a plurality of third recessed portions, which are arranged in the third recessed area, and the third recessed portions are bonded to the third recessed area; along the winding direction, the third glue layer includes a second tail end, which is flush with the first tail end, or the third glue layer extends the first pole piece from the first tail end along the winding direction. And / or, the secondary battery also includes a fourth glue layer, which is arranged on the second surface, and the fourth glue layer has a plurality of fourth protrusions, which are arranged in the fourth protrusion area, and the fourth protrusions are bonded to the fourth protrusion area; along the winding direction, the fourth glue layer includes a third tail end, which is flush with the first tail end, or the fourth glue layer extends the first pole piece from the first tail end along the winding direction. It can further 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.

[0023] In some embodiments, the first tail end is located at the secondary outer ring pole piece of the electrode assembly. The secondary outer ring pole piece has a higher risk of piercing the isolation membrane. Covering the first tail end of the secondary outer ring with the third adhesive layer and / or the fourth adhesive layer has a more significant effect on reducing the piercing of the isolation membrane.

[0024] In a second aspect, the present application also proposes a method for preparing a secondary battery, comprising:

[0025] A first current collector is provided. Along the thickness direction of the first current collector, the first current collector includes a first surface and a second surface that are arranged oppositely. A first adhesive layer is bonded to the first surface, and a second adhesive layer is bonded to the second surface. The first current collector, the first adhesive layer and the second adhesive layer are embossed as a whole, so that a plurality of first concave areas are formed on the first surface, and a plurality of first concave parts are formed in the first adhesive layer, and the first concave parts are bonded to the first concave areas; and a plurality of first convex areas are formed on the second surface, and a plurality of first convex parts are formed in the second adhesive layer, and the first convex parts are bonded to the first convex areas. Wherein, along the winding direction, the first current collector includes a first starting end, the first adhesive layer includes a second starting end, and the second adhesive layer includes a third starting end; the second starting end is flush with the first starting end or the second starting end extends out of the first pole piece from the first starting end in the opposite direction of the winding direction; and / or the third starting end is flush with the first starting end or the third starting end extends out of the first pole piece from the first starting end in the opposite direction of the winding direction.

[0026] In the above technical solution, a structure similar to mechanical anchoring can be formed, which improves the bonding force between the first adhesive layer and the first current collector, and can effectively reduce the exposure of the first starting end due to the slippage of the first adhesive layer, thereby reducing the occurrence of short circuits. At the same time, the first recessed portion of the first adhesive layer is bonded to the first recessed area, so that the first pole piece forms an uneven structure. The uneven structure makes the contact area between the first adhesive layer and the adjacent isolation membrane or second pole piece smaller, so that the risk of the isolation membrane or the second pole piece driving the first adhesive layer to slip is reduced, which can further reduce the occurrence of short circuits. In addition, the setting of the first recessed area and the first raised area of ​​the first pole piece allows the first pole piece to form a retractable elastic structure that can adapt to the expansion or contraction of the pole piece, thereby reducing the exposure of the first starting end from the first adhesive layer, further reducing the occurrence of short circuits, and effectively improving the safety performance of the secondary battery. The second adhesive layer is similar.

[0027] In a third aspect, the present application further proposes an electronic device, comprising a secondary battery as in any embodiment of the first aspect above.

[0028] 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

[0029] Figure 1 A schematic diagram of the structure of a secondary battery in some embodiments of the present application;

[0030] Figure 2 An exploded schematic diagram of a secondary battery according to some embodiments of the present application;

[0031] Figure 3 A schematic diagram of the winding structure of an electrode assembly in some embodiments of the present application;

[0032] Figure 4 This is a schematic structural diagram of a first pole piece in some embodiments of the present application;

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

[0034] Figure 6 A partial structural schematic diagram of the first pole piece stamping area of ​​some embodiments of the present application;

[0035] Figure 7 Schematic diagram of bonding the first adhesive layer and the second adhesive layer to the first pole piece in some embodiments of the present application;

[0036] Figure 8 Schematic diagram of bonding the first adhesive layer and the second adhesive layer to the first pole piece in some embodiments of the present application;

[0037] Fig. 9 This is a schematic diagram of the structure of the first adhesive layer of some embodiments of the present application;

[0038] Fig.10 Schematic diagram of bonding the first adhesive layer and the second adhesive layer to the first pole piece in some embodiments of the present application;

[0039] Fig.11 A schematic diagram of the stacked structure of the first pole piece, the second inner circle pole piece and the second inner circle pole piece in some embodiments of the present application;

[0040] Fig.12 A schematic diagram of the stacked structure of the first pole piece and the isolation film in some embodiments of the present application;

[0041] Fig.13 A partial structural schematic diagram of a first pole piece in some embodiments of the present application;

[0042] Fig.14 A partial structural schematic diagram of a first pole piece in some embodiments of the present application;

[0043] Fig.15 A schematic diagram of bonding the first adhesive layer and the first pole piece in some embodiments of the present application;

[0044] Fig.16 A schematic diagram of bonding the second adhesive layer and the first pole piece in some embodiments of the present application;

[0045] Fig.17 This is a partial structural schematic diagram of an electrode assembly located at a first tail end in some embodiments of the present application;

[0046] Fig.18 A schematic diagram of bonding the third adhesive layer and the fourth adhesive layer to the first pole piece in some embodiments of the present application;

[0047] Fig.19 This is a schematic diagram of bonding the third adhesive layer and the fourth adhesive layer to the first pole piece in some embodiments of the present application.

[0048] Description of reference numerals:

[0049] 100. Secondary battery;

[0050] 10. Shell; 11. First wall; 12. Second wall; 13. Main body; 14. Opening;

[0051] 20. Electrode assembly;

[0052] 21, first pole piece; 21a, first surface; 21b, second surface; 2101, first empty foil section; 2102, first coating section; 211, first current collector; 2111, first starting end; 2112, first ending end; 212, first active material layer; 213, first recessed area; 2131, bottom wall; 2132, first side wall; 2133, second side wall; 214, first raised area; 215, second recessed area; 216, second raised area; 217, third recessed area; 218, third raised area;

[0053] 22, second pole piece; 221, second inner ring pole piece; 222, second inner ring pole piece;

[0054] 23. Isolation film;

[0055] 30, first adhesive layer; 30a, first substrate layer; 30b, first bonding layer; 31, first recessed portion; 32, second recessed portion; 33, second starting end;

[0056] 40, second adhesive layer; 41, first raised portion; 42, second raised portion; 43, third starting end;

[0057] 50, third adhesive layer; 51, third recessed portion; 52, second tail end;

[0058] 60, fourth adhesive layer; 61, third raised portion; 62, third tail end;

[0059] Z, first direction; X, second direction; Y, third direction; S, winding direction; G, winding center; G1, cavity; K, axial direction. DETAILED DESCRIPTION

[0060] 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.

[0061] 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.

[0062] 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" is more than two, unless otherwise clearly and specifically defined.

[0063] 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.

[0064] The technical features involved in the different embodiments of the present application described below can be combined with each other as long as they do not conflict with each other.

[0065] In the first aspect, the embodiment of the present application provides a secondary battery 100, please refer to Figure 1 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.

[0066] 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 shell 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 shell 10 through the opening 14. The shell 10 can be sealed by covering the opening 14 with the first wall portion 11.

[0067] 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.

[0068] Regarding the electrode assembly 20, the electrode assembly 20 is accommodated in the housing 10. Please refer to Figure 3 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 separator 23 and the second electrode sheet 22 are stacked and wound. For example, please refer to Figure 4 , stacked along the thickness direction (first direction Z) of the first pole piece 21 and wound along its length direction (second direction X), the isolation film 23 is arranged between the first pole piece 21 and the second pole piece 22 to insulate and separate the two.

[0069] 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. 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.

[0070] 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.

[0071] 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.

[0072] 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.

[0073] Please refer to Figure 3 and Figure 4 , 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. After the first current collector 211 is wound, the first starting end 2111 is the winding starting end of the first current collector 211, and the first ending end 2112 is the winding ending end of the first current collector 211.

[0074] 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.

[0075] 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.

[0076] To reduce the above problems, in the embodiments of this application, please refer to Figures 5 to 7 , along the thickness direction (first direction Z) of the first pole piece 21, the second pole piece 22 is adjacent to the first starting end 2111, that is, the second pole piece 22 is the pole piece adjacent to the first starting end 2111, and the first pole piece 21 includes a first surface 21a and a second surface 21b that are arranged opposite to each other, wherein the first surface 21a may be the surface of the first active material layer 212, and when the first active material layer 212 is not arranged in a part of the first current collector 211, the first surface 21a is the surface of the first current collector 211. The first surface 21a has a plurality of first recessed areas 213, and the first recessed areas 213 form a first raised area 214 on the second surface 21b.

[0077] It should be noted that, when viewed along the first direction Z, the first surface 21a has a first concave area 213, and two adjacent first concave areas 213 form a convex area of ​​the first surface 21a. When viewed along the opposite direction of the first direction Z, the second surface 21b has a first convex area 214, and a concave area of ​​the second surface 21b is formed between two adjacent first convex areas 214.

[0078] Please refer to Figures 5 to 8 The secondary battery 100 further includes a first adhesive layer 30, which is disposed on the first surface 21a. The first adhesive layer 30 has a plurality of first recessed portions 31, which are disposed in the first recessed area 213, and the first recessed portions 31 are bonded to the first recessed area 213. Along the winding direction S, the first adhesive layer 30 includes a second starting end 33, which is flush with the first starting end 2111 or the first adhesive layer 30 extends from the first starting end 211 to the first electrode sheet 21 in the opposite direction of the winding direction S.

[0079] For example, when cutting a large current collector roll (which may or may not be provided with an active material layer), the first surface 21a of the large current collector roll may be firstly subjected to a glue treatment, and then the glued area may be subjected to a stamping treatment, so that the first recessed area 213 and the first raised portion 41 area may be directly formed on the large current collector roll, and the glue layer may directly form a first recessed portion 31, and the first recessed portion 31 is bonded to the first recessed area 213. The large current collector roll and the glue layer may be cut together to form a first current collector 211 and a first glue layer 30, and the second starting end 33 of the first glue layer 30 may be flush with the first starting end 2111, or the first glue layer 30 may exceed the first starting end 2111. Whether flush or exceeding, the first glue layer 30 may directly cover the first starting end 2111 in the thickness direction (first direction Z) of the first electrode sheet 21.

[0080] In the embodiment of the present application, the first adhesive layer 30 is disposed on the first surface 21a, and the second starting end 33 of the first adhesive layer 30 is flush with the first starting end 2111 or the first adhesive layer 30 extends from the first starting end 2111 to the first pole piece 21 in the opposite direction of the winding direction S, 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 first recessed portion 31 of the first adhesive layer 30 is bonded to the first recessed area 213 to form a structure similar to a mechanical anchoring, which improves the bonding force between the first adhesive layer 30 and the first current collector 211, and can effectively reduce the exposure of the first starting end 2111 due to the slippage of the first adhesive layer 30, thereby reducing the occurrence of short circuits.

[0081] At the same time, the first recessed portion 31 of the first adhesive layer 30 is bonded to the first recessed area 213, so that the first pole piece 21 forms an uneven structure. The uneven structure reduces the contact area between the first adhesive layer 30 and the adjacent isolation membrane 23 or the second pole piece 22, thereby reducing the risk of the isolation membrane 23 or the second pole piece 22 driving the first adhesive layer 30 to slip, which can further reduce the occurrence of short circuits.

[0082] In addition, the first recessed area 213 and the first raised area 214 of the first pole piece 21 enable the first pole piece 21 to form a retractable elastic structure that can adapt to the expansion or contraction of the pole piece, thereby reducing the exposure of the first starting end 2111 from the first adhesive layer 30, further reducing the occurrence of short circuits, and effectively improving the safety performance of the secondary battery 100.

[0083] For the material of the first adhesive layer 30, please refer to Fig. 9 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 first pole piece 21. 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 first pole piece 21 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.

[0084] In some other embodiments, please refer to Figures 5 to 8 The secondary battery 100 further includes a second adhesive layer 40. The material of the second adhesive layer 40 can be similar to that of the first adhesive layer 30. The second adhesive layer 40 is disposed on the second surface 21b. The second adhesive layer 40 has a first protrusion 41. The first protrusion 41 is disposed on the first protrusion area 214, and the first protrusion 41 is bonded to the first protrusion area 214. Along the winding direction S, the second adhesive layer 40 includes a third starting end 43. The third starting end 43 is flush with the first starting end 2111, or the second adhesive layer 40 extends from the first starting end 2111 to the first electrode sheet 21 in the opposite direction of the winding direction S.

[0085] For example, when cutting the current collector roll, the second surface 21b of the current collector roll may be firstly subjected to a glue treatment, and after the embossing treatment, the glue layer may directly form a first protrusion 41, and the first protrusion 41 is bonded to the first protrusion area 214. The current collector roll and the glue layer may then be cut together to form a first current collector 211 and a second glue layer 40, and the third starting end 43 of the first glue layer 30 may be flush with the first starting end 2111, or the first glue layer 30 may exceed the first starting end 2111 in the opposite direction of the winding direction S, that is, directly cover the first starting end 2111.

[0086] In the embodiment of the present application, the second adhesive layer 40 is disposed on the second surface 21b, and the third starting end 43 of the second adhesive layer 40 is flush with the first starting end 2111, or the second adhesive layer 40 exceeds the first starting end 2111 in the opposite direction of the winding direction S, so that the second adhesive layer 40 covers 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 first protrusion 41 of the second adhesive layer 40 is bonded to the first protrusion area 214 to form a structure similar to a mechanical anchor, which improves the bonding force between the second adhesive layer 40 and the first current collector 211, and can effectively reduce the exposure of the first starting end 2111 due to the slippage of the second adhesive layer 40, thereby reducing the occurrence of short circuits, and effectively improving the safety performance of the secondary battery 100.

[0087] Furthermore, if the first adhesive layer 30 and the second adhesive layer 40 are provided at the same time, both sides of the first electrode 21 in the thickness direction can have adhesive layers covering the first starting end 2111, which can fully isolate the cutting burrs of the first starting end 2111 and further reduce the occurrence of short circuits.

[0088] The inventors of the present application have also found that for the secondary inner ring pole piece of the electrode assembly 20, there are pole pieces of opposite polarity (second pole pieces 22) on both sides of the thickness direction, and the stress on the inner ring is relatively large, and the risk of burrs piercing the isolation film 23 is relatively high. Figure 3 The first starting end 2111 is located at the sub-inner circle electrode piece of the electrode assembly 20, and the innermost circle electrode piece of the electrode assembly 20 is part of the second electrode piece 22. The first adhesive layer 30 is arranged on the isolation film 23 and covers the first starting end 2111 of the sub-inner circle, which has a more significant effect on reducing the puncture of the isolation film 23.

[0089] In an 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 withstand 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 loosen locally, and then cause the first starting end 2111 to slip.

[0090] In the embodiment of the present application, the first pole piece 21 is provided with a first recessed area 213 and a first raised area 214, and a first adhesive layer 30 and / or a second adhesive layer 40 are provided correspondingly, so that the slippage of the first adhesive layer 30 and / or the second adhesive layer 40 relative to the first pole piece 21 can be reduced, thereby reducing the exposure of the first starting end 2111, reducing the occurrence of short circuits, and is particularly suitable for cylindrical secondary batteries 100.

[0091] In some embodiments, the electrode assembly 20 is provided with a cavity G1, which is provided at the winding center G of the electrode assembly. The provision of the cavity G1 helps the electrode liquid to diffuse from the inside of the electrode assembly 20 to the first pole piece 21 and the second pole piece 22, and can enhance the dynamics of the secondary battery 100. The provision of the first concave area 213 and the first convex area 214 provides support for the first pole piece 21, which can reduce the collapse of the electrode assembly 20 near the inner circle, and help improve the structural stability of the electrode assembly 20.

[0092] In some embodiments, please refer to Figure 2 and Figure 3 , the electrode assembly 20 is arranged in the shell 10, the inner diameter of the shell 10 is D1, and the outer diameter of the electrode assembly 20 is D2. The inventors of the present application have found that when the pole piece expands and the electrode assembly 20 occupies the internal space of the shell 10, the maximum slip amount of the first starting end 2111 is usually π(D1-D2). In the embodiment of the present application, the first pole piece 21 is provided with a first recessed area 213 and a first raised area 214, so that the first pole piece 21 can form a retractable elastic structure similar to that of the pole piece, which can adapt to the expansion or contraction of the pole piece, thereby reducing the misalignment of the first adhesive layer 30 with the first pole piece 21 due to the expansion of the first pole piece 21.

[0093] Please refer to Figure 6, along the thickness direction (first direction Z) of the first pole piece 21, the depth of the first recessed area 213 is H1. The first recessed area 213 includes a bottom wall 2131, a first side wall 2132 and a second side wall 2133. Along the length direction (second direction X) of the first pole piece 21, the bottom wall 2131 is connected between the first side wall 2132 and the second side wall 2133. The angle between the bottom wall 2131 and the first side wall 2132 is α, and the angle between the bottom wall 2131 and the second side wall 2133 is β. For example, a pressing head is used to perform a stamping process on the first pole piece 21, and one chamfer of the pressing head is the angle α, and the other angle is the angle β. Along the length direction (second direction X) of the first pole piece 21, a plurality of first recessed areas 213 are arranged in an array, and the number of the arranged first recessed areas 213 is n. Therefore, in the embodiment of the present application, the maximum stretching amount of the first pole piece 21 is generally n×[H1 / sin(π-α)-H1 / tan(π-α)]+n×[H1 / sin(π-β)-H1 / tan(π-β)].

[0094] Limiting n×[H1 / sin(π-α)-H1 / tan(π-α)]+n×[H1 / sin(π-β)-H1 / tan(π-β)]≥π(D1-D2) can facilitate making the maximum stretching of the first pole piece 21 greater than the maximum expansion of the first pole piece 21. When the first pole piece 21 expands, the first recessed area 213 and the first raised area 214 of the first pole piece 21 are preferentially flattened, thereby reducing the slippage of the first adhesive layer 30 and / or the second adhesive layer 40, thereby reducing the exposure of the first starting end 2111, and further reducing the burrs of the first starting end 2111 from piercing the isolation membrane 23 and causing a short circuit.

[0095] As for the number of the first recessed areas 213, if the number of the first recessed areas 213 is too small, it means that the area where the first adhesive layer 30 and the first pole piece 21 are tightly bonded is limited, which may lead to insufficient bonding strength between the first adhesive layer 30 and the first pole piece 21, and further lead to possible slippage of the first adhesive layer 30. If the number of the first recessed areas 31 is too large, it may increase the difficulty of winding the first pole piece 21, and easily lead to excessive warping of the first pole piece 21 near the starting end of the winding, resulting in an increased risk of piercing the isolation film 23.

[0096] In the embodiment of the present application, the number of the first recessed areas 213 satisfies 10≤n≤30, which can improve the bonding strength between the first adhesive layer 30 and the first pole piece 21, reduce the slippage of the first adhesive layer 30, and facilitate the winding and feeding of the first pole piece 21, reduce the warping of the first starting end 2111, and further reduce the first starting end 2111 piercing the isolation film 23 and causing a short circuit. Preferably, 15≤n≤25 can further reduce the occurrence of short circuits, simplify the process, and reduce the impact on the active material layer.

[0097] For the depth of the first recessed area 213, if the depth is too large, it means that a greater force is required to emboss the first pole piece 21, which may cause damage to the first pole piece 21 and / or the first adhesive layer 30, and the thickness difference between the recessed area and the non-recessed area will become more obvious, which will not only occupy the thickness of the first pole piece 21, resulting in a loss of energy density of the secondary battery 100, but also may cause uneven stress distribution of the first pole piece 21 due to uneven thickness, which may easily cause the first adhesive layer 30 to crack or separate from the first pole piece 21 when subjected to external forces (such as stress changes inside the secondary battery 100 or external impacts). If the depth is too small, the surface of the first pole piece 21 may be too flat, which may easily lead to insufficient bonding strength between the first adhesive layer 30 and the first pole piece 21, and the slippage of the first adhesive layer 30 may cause the first starting end 2111 to be exposed, and the risk of burrs piercing the isolation membrane 23 is high.

[0098] In the embodiment of the present application, 10μm≤H1≤100μm can reduce the embossing damage of the first pole piece 21 and / or the first adhesive layer 30, and can reduce the influence of the first recessed area 213 on the thickness of the first pole piece 21, reduce the energy density loss, and reduce the first adhesive layer 30 from cracking or separation from the first pole piece 21 due to uneven stress distribution. In addition, it can also make the first adhesive layer 30 and the first pole piece 21 have a higher bonding strength, which can reduce the slippage of the first adhesive layer 30, and further reduce the exposure of the first starting end 2111. Preferably, 30μm≤H1≤80μm can further reduce the occurrence of short circuits and reduce the influence on the thickness of the first pole piece 21.

[0099] For the measurement of the depth of the first recessed area 213, a laser confocal microscope can be used to scan and image the surface of the first current collector to obtain three-dimensional morphological information of the first recessed area 213. In the obtained three-dimensional image, the depth data of the first recessed area 213 can be directly measured.

[0100] The angle of the first recessed area 213 can be measured by using a high-resolution microscope or industrial camera to take an image of the first recessed area 213 of the first current collector 211, and then transferring the image to a computer software for analysis. In the software, a coordinate system can be established to determine the boundary line of the first recessed area 213, and the angle of the first recessed area 213 can be calculated using mathematical methods such as trigonometric functions.

[0101] In some embodiments, please refer to Fig.10, along the length direction (second direction Y) of the first pole piece 21, the first pole piece 21 includes a first empty foil segment 2101 and a first coated segment 2102. The area of ​​the first current collector 211 where the first active material layer 212 is not provided forms the first empty foil segment 2101, and the first coated segment 2102 is the area where the first active material layer 212 is provided. In the embodiment of the present application, the first empty foil segment 2101 is embossed to form the first recessed area 213 and the first raised area 214, which has no effect on the first active material layer 212, and is conducive to making the first active material layer 212 have a higher integrity.

[0102] Please refer to Fig.10 , in the first empty foil segment 2101, along the thickness direction (first direction Z) of the first electrode piece 21, the maximum distance from the first surface 21a to the second surface 21b is T1, that is, the maximum distance between the two surfaces in the thickness direction of the first empty foil segment 2101 is T1. The first adhesive layer 30 is provided on the first empty foil segment 2101, along the thickness direction (first direction Z) of the first electrode piece 21, and the thickness of the first adhesive layer 30 is T a In the first coating section 2102, along the thickness direction (first direction Z) of the first pole piece 21, the maximum thickness of the first coating section 2102 is T2, T1+T a ≤T2. The first empty foil segment 2101 and the first adhesive layer 30 do not occupy the thickness space of the first pole piece 21, thereby reducing the energy density loss of the secondary battery 100. For example, 45 μm≤T1≤100 μm.

[0103] In some other embodiments, when the first adhesive layer 30 and the second adhesive layer 40 are provided at the same time, along the thickness direction (first direction Z) of the first pole piece 21, the thickness of the second adhesive layer 40 is T b , T1+T a +T b ≤T2. The first empty foil section 2101, the first adhesive layer 30 and the second adhesive layer 40 do not occupy the thickness space of the first electrode sheet 21, thereby reducing the energy density loss of the secondary battery 100. Optionally, when only the second adhesive layer 40 is provided, T1+T b ≤T2, so that the first empty foil segment 2101 and the second adhesive layer 40 do not occupy the thickness space of the first electrode sheet 21 .

[0104] In some embodiments, along the winding direction S, the length of the first recessed area 213 is L1, wherein the first pole piece 21 is wound along its length direction, that is, along the second direction X, the length of the first recessed area 213 is L1. The inventors of the present application have found that the length of the first recessed area 213 is too large, and when the first adhesive layer 30 is subjected to external force, the deformation range of the first adhesive layer 30 in the first recessed area 213 is large. When stress is generated inside the secondary battery 100 (such as expansion and contraction of the pole piece) or subjected to external impact, the stress of the first adhesive layer 30 in the long recessed area cannot be effectively dispersed, and it is easy to separate from the first pole piece 21 locally. However, the length of the first recessed area 213 is too small, and it is impossible to provide enough effective attachment sites for the first adhesive layer 30, so that the bonding force between the first adhesive layer 30 and the first pole piece 21 is not significantly improved. During the use of the secondary battery 100, the first adhesive layer 30 may still slip, resulting in the exposure of the first starting end 2111.

[0105] In the embodiment of the present application, the length of the first recessed area 213 is 0.5mm≤L1≤5mm, which can reduce the separation of the first adhesive layer 30 from the first pole piece 21 due to stress concentration, and can ensure that the first adhesive layer 30 and the first pole piece 21 have a higher bonding strength, reduce the exposure of the first starting end 2111, and thus reduce the occurrence of short circuits.

[0106] In some embodiments, please refer to Fig.10 , the distance between two adjacent first recessed areas 213 is L2. The inventor of the present application has found that if the distance between two adjacent first recessed areas 213 is too close, the continuous and complete structure of the first pole piece 21 in the length direction will be frequently interrupted, which will reduce the strength of the first pole piece 21. When the secondary battery 100 is subjected to external force, the first pole piece 21 may be torn. If the distance is too large, it means that there are relatively few effective recessed areas on the surface of the first pole piece 21 for increasing the adhesion of the first adhesive layer 30, resulting in insufficient bonding strength between the first adhesive layer 30 and the first pole piece 21, which may easily cause the adhesive layer to slip and expose the first starting end 2111.

[0107] In the embodiment of the present application, the length of the first recessed area 213 is 0.5mm≤L2≤5mm, which is beneficial for the first pole piece 21 to maintain a relatively high structural strength, and can ensure that the first adhesive layer 30 and the first pole piece 21 have a relatively high bonding strength, thereby reducing the exposure of the first starting end 2111 due to the slippage of the first pole piece 21, thereby reducing the occurrence of short circuits.

[0108] The inventor of the present application has found that due to the outward tension of the first pole piece 21, it is easier to cause the first starting end 2111 to pierce the isolation film 23 away from the winding center G. Figure 5 and Fig.11, the second pole piece 22 includes a second inner pole piece 221 and a second inner pole piece 222. The second inner pole piece 221 is the innermost pole piece of the electrode assembly 20. 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 pole piece 221 and the second inner pole piece 222. Along the thickness direction of the first pole piece 21, the distance from the first starting end 2111 to the second inner pole piece 221 is H2, and the distance from the first starting end 2111 to the second inner pole piece 222 is H3, and H3>H2. That is, the distance from the first starting end 2111 to the second inner pole piece 222 is larger, which can reduce the contact between the first starting end 2111 and the second inner pole piece 221, thereby reducing the burrs from piercing the isolation film 23 between the first starting end 2111 and the second inner pole piece 221, and reducing the occurrence of short circuits.

[0109] 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.12 , 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.

[0110] In some embodiments, please refer to Fig.13 and Fig.14 , the first surface 21a also has a plurality of second recessed areas 215, and the second recessed areas 215 form a second raised area 216 on the second surface 21b. Observing along the width direction (third direction Y) of the first pole piece 21, the second raised area 216 is at least partially located between two adjacent first raised areas 214. That is, the first raised area 214 and the second raised area 216 are staggered in the width direction of the first pole piece 21, which can improve the strength of the first pole piece 21 and reduce the occurrence of tearing of the first pole piece 21.

[0111] In some embodiments, please refer to Fig.15 and Fig.16The first surface 21a is provided with a first adhesive layer 30, the first adhesive layer 30 has a plurality of second recessed portions 32, the second recessed portions 32 are provided in the second recessed area 215, and the second recessed portions 32 are bonded to the second recessed area 215. The second surface 21b is provided with a second adhesive layer 40, the second adhesive layer 40 has a plurality of second raised portions 42, the second raised portions 42 are provided in the second raised area 216, and the second raised portions 42 are bonded to the second raised area 216. The provision of multiple recessed portions and raised portions increases the anchoring points between the first adhesive layer 30 and the second adhesive layer 40 and the first pole piece 21, thereby improving the bonding strength.

[0112] 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. In particular, the secondary outer ring pole piece of the electrode assembly 20 has pole pieces of opposite polarity (second pole piece 22) on both sides of its thickness direction, and the risk of burrs piercing the isolation film 23 and contacting with the opposite polarity and the pole piece is high.

[0113] To reduce this problem, refer to Figures 17 to 19 , along the thickness direction of the first pole piece 21, the second pole piece 22 is adjacent to the first tail end 2112. The first surface 21a also has a plurality of third recessed areas 217, and the third recessed areas 217 form a third raised area 218 on the second surface 21b. The secondary battery 100 also includes a third adhesive layer 50, which is disposed on the first surface 21a. The third adhesive layer 50 has a plurality of third recessed portions 51, which are disposed in the third recessed areas 217, and the third recessed portions 51 are bonded to the third recessed areas 217. Along the winding direction S, the third adhesive layer 50 includes a second tail end 52, and the second tail end 52 is flush with the first tail end 2112 or the third adhesive layer 50 extends from the first tail end 2112 to the first pole piece 21 along the winding direction S.

[0114] In the embodiment of the present application, the third adhesive layer 50 is disposed on the first surface 21a, and the second end 52 of the third adhesive layer 50 is flush with the first end 2112 or the third adhesive layer 50 extends from the first end 2112 to the first electrode sheet 21 along the winding direction S, so that the third adhesive layer 50 covers the first end 2112 in the thickness direction (first direction Z) of the first electrode sheet 21, which can reduce the cutting burrs of the first end 2112 from piercing the isolation film 23, thereby reducing the short circuit caused by direct contact between the first end 2112 and the second electrode sheet 22. In addition, the third recessed portion 51 of the third adhesive layer 50 is bonded to the third recessed area 217 to form a structure similar to a mechanical anchoring, which improves the bonding force between the third adhesive layer 50 and the first current collector 211, and can effectively reduce the exposure of the first end 2112 due to the slippage of the third adhesive layer 50, thereby reducing the occurrence of short circuits.

[0115] In some other embodiments, the secondary battery 100 also includes a fourth adhesive layer 60, which is disposed on the second surface 21b. The fourth adhesive layer 60 has a plurality of third protrusions 61, which are disposed in the third protrusion area 218, and the third protrusions 61 are bonded to the third protrusion area 218. Along the winding direction S, the fourth adhesive layer 60 includes a third tail end 62, and the third tail end 62 is flush with the first tail end 2112 or the fourth adhesive layer 60 extends from the first tail end 2112 to the first pole piece 21 along the winding direction S.

[0116] The cutting burrs of the first tail end 2112 can further reduce the piercing of the isolation film 23, thereby reducing the short circuit caused by the direct contact between the first tail end 2112 and the second pole piece 22. In addition, the third recessed portion 61 of the fourth adhesive layer 60 is bonded to the third recessed area 218, which improves the bonding force between the fourth adhesive layer 60 and the first current collector 211, and can effectively reduce the exposure of the first tail end 2112 due to the slippage of the fourth adhesive layer 60, thereby reducing the occurrence of short circuits.

[0117] In some embodiments, the first tail end 2112 is located at the secondary outer ring pole piece of the electrode assembly 20, and the risk of the secondary outer ring pole piece piercing the isolation membrane 23 is higher. Covering the first tail end 2112 of the secondary outer ring with the third adhesive layer 50 and / or the fourth adhesive layer 60 is more effective in reducing the piercing effect of the isolation membrane 23.

[0118] In a second aspect, the present application also proposes a method for preparing a secondary battery 100, comprising:

[0119] A first current collector 211 is provided. Along the thickness direction (first direction Z) of the first current collector 211, the first current collector 211 includes a first surface 21a and a second surface 21b that are oppositely disposed. The first adhesive layer 30 is bonded to the first surface 21a, and the second adhesive layer 40 is bonded to the second surface 21b.

[0120] The first current collector 211, the first glue layer 30 and the second glue layer 40 are embossed together, so that a plurality of first recessed areas 213 are formed on the first surface 21a, and a plurality of first recessed portions 31 are formed in the first glue layer 30, and the first recessed portions 31 are bonded to the first recessed areas 213; and a plurality of first raised areas 214 are formed on the second surface 21b, and a plurality of first raised portions 41 are formed in the second glue layer 40, and the first raised portions 41 are bonded to the first raised areas 214.

[0121] Among them, along the winding direction S, the first current collector 211 includes a first starting end 2111, the first adhesive layer 30 includes a second starting end 33, and the second adhesive layer 40 includes a third starting end 43; the second starting end 33 is flush with the first starting end 2111 or the second starting end 33 extends from the first starting end 2111 to the first pole piece 21 in the opposite direction of the winding direction S; and / or the third starting end 43 is flush with the first starting end 2111 or the third starting end 43 extends from the first starting end 2111 to the first pole piece 21 in the opposite direction of the winding direction S.

[0122] In the above technical solution, a structure similar to mechanical anchoring can be formed, which improves the bonding force between the first adhesive layer 30 and the first current collector 211, and can effectively reduce the exposure of the first starting end 2111 due to the slippage of the first adhesive layer 30, thereby reducing the occurrence of short circuits. At the same time, the first recessed portion 31 of the first adhesive layer 30 is bonded to the first recessed area 213, so that the first pole piece 21 forms an uneven structure, which makes the contact area between the first adhesive layer 30 and the adjacent isolation film 23 or the second pole piece 22 smaller, so that the risk of the isolation film 23 or the second pole piece 22 driving the first adhesive layer 30 to slip is reduced, which can further reduce the occurrence of short circuits. In addition, the first recessed area 213 and the first raised area 214 of the first pole piece 21 are set, so that the first pole piece 21 forms a retractable elastic structure similar to a retractable elastic structure, which can adapt to the expansion or contraction of the pole piece, thereby reducing the exposure of the first starting end 2111 from the first adhesive layer 30, further reducing the occurrence of short circuits, and effectively improving the safety performance of the secondary battery 100. The second adhesive layer 40 is similar.

[0123] In the third 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, spacecraft, and the like.

[0124] Embodiment 1:

[0125] <Preparation of Substrate Layer>

[0126] 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.

[0127] <Preparation of positive electrode sheet>

[0128] 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 in 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 the positive electrode current collector. 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. Dry at 110°C to obtain a positive electrode sheet coated with a single-sided positive electrode active material layer. After that, 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 electrode sheet is cold pressed to obtain a positive electrode sheet with a double-sided positive electrode active material layer after cold pressing. The single-sided coating weight of the positive electrode sheet is 21mg / cm 2 The thickness of single-sided cold pressing is 62.25μm, and the thickness of double-sided cold pressing is 112.5μm.

[0129] The two surfaces of the empty foil area in the thickness direction are respectively provided with a first glue layer and a second glue layer, and the first glue layer and the second glue layer both cover the cutting position of the positive electrode sheet (flush with the first starting end). The first glue layer, the second glue layer and the empty foil area are embossed so that the empty foil area forms a first concave area and a first convex area, the first glue layer is bonded to the first concave area so that the first glue layer forms a first concave portion, and the second glue layer is bonded to the second convex area so that the second glue layer forms a first convex portion. The depth H1 of the first concave area is 8 μm, and along the length direction of the positive electrode sheet, the number n of the first concave areas is 20, and the angles between the bottom wall of the concave area and the two side walls are α=120° and β=120°, respectively.

[0130] <Preparation of negative electrode sheet>

[0131] 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.

[0132] <Preparation of Separator Film>

[0133] Polyethylene (PE) with a thickness of 7 μm and a 2 μm alumina (Al2O3) coated porous film were used as isolation membranes.

[0134] <Electrolyte Preparation>

[0135] 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.

[0136] <Preparation of lithium-ion batteries>

[0137] 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. Among them, 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.

[0138] Different from Example 1, the relevant parameters of Examples 2 to 17 and Comparative Example 1 are shown in Table 1 below, wherein no concave area and convex area are set in Comparative Example 1, and the first adhesive layer, the second adhesive layer and the first current collector are cut at the same time after applying the adhesive first, so that the first adhesive layer and the second adhesive layer directly cover the first starting end (cutting position). Definition A = n × [H1 / sin(π-α)-H1 / tan(π-α)]+n × [H1 / sin(π-β)-H1 / tan(π-β)].

[0139] 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:

[0140] (1) 2.5C constant current charging to 4.15V, constant voltage charging cut-off current to 1.5C;

[0141] (2) 1.5C constant current charging to 4.18V, constant voltage charging cut-off current to 0.5C;

[0142] (3) 0.5C constant current charging to 4.45V, constant voltage charging cut-off current to 0.02C;

[0143] After standing for 10 minutes, discharge according to the following steps:

[0144] 1C constant current discharge to 3V, let stand for 10 minutes, this is one cycle.

[0145] 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.

[0146] 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.

[0147] Table 1

[0148]

[0149]

[0150] According to the above Table 1, combined with Examples 1 to 17 and Comparative Example 1, it can be known that when the first recessed area and the first raised area are set near the first starting end of the positive electrode plate, the glue layer is bonded to the first recessed area and the first raised area respectively, which can reduce the test failure rate. This is because a structure similar to a mechanical anchor can be formed between the glue layer and the pole piece, which improves the bonding force between the glue layer and the pole piece, and can effectively reduce the exposure of the first starting end caused by the slip of the glue layer, thereby reducing the occurrence of short circuits. At the same time, the bonding area between the glue layer and the pole piece is larger, and the contact area with the isolation membrane is smaller, so that the risk of the isolation membrane or the second pole piece driving the glue layer to slip is reduced, which can further reduce the occurrence of short circuits. In addition, the setting of the first recessed area and the first raised area allows the pole piece to form a retractable elastic structure similar to a retractable elastic structure, which can adapt to the expansion or contraction of the pole piece, thereby reducing the exposure of the first starting end and further reducing the occurrence of short circuits.

[0151] In combination with Examples 1 to 10, the test failure rates of Examples 2 to 9 are lower than those of Examples 1 and 10. In Example 1, the depth H1 of the first recessed area is too small, which may cause the surface of the pole piece to be too flat, which may lead to insufficient bonding strength between the adhesive layer and the pole piece, and may cause the first starting end to be exposed, and there is a high risk of burrs piercing the isolation membrane. In Example 10, the depth H1 of the first recessed area is too large, which means that a greater force is required to stamp the pole piece, which may cause damage to the pole piece and / or the adhesive layer. After winding, the pole piece and the adhesive layer may be damaged due to uneven stress, and there is also a risk of short circuit. Therefore, in the embodiments of the present application, 10μm≤H1≤100μm can be selected. Moreover, in Examples 3 to 9, the drop failure rate is further reduced, and n is limited. × [H1 / sin(π-α)-H1 / tan(π-α)]+n × [H1 / sin(π-β)-H1 / tan(π-β)]≥π(D1-D2), which can make the maximum stretchable amount of the pole piece greater than the maximum expansion amount of the pole piece. When the pole piece expands, the first concave area and the first convex area of ​​the pole piece are first flattened, which can reduce the slippage of the glue layer, thereby reducing the exposure of the first starting end, and further reducing the burrs of the first starting end piercing the isolation membrane and causing a short circuit. In addition, in Examples 4 to 8, the test failure rate is further reduced. In the embodiments of the present application, 30μm≤H1≤80μm can be preferably used to further reduce the occurrence of short circuits and reduce the impact on the thickness of the pole piece.

[0152] The test failure rate of Examples 13 to 17 is less than that of Examples 11 to 12. In Examples 13 to 17, n × [H1 / sin(π-α)-H1 / tan(π-α)]+n ×[H1 / sin(π-β)-H1 / tan(π-β)]≥π(D1-D2), which can reduce the occurrence of short circuits, so the test failure rate is reduced. However, in Examples 11 to 12, this is not satisfied, so the test failure rate is relatively high. In Example 17, the test failure rate is similar to that in Example 13. However, in Example 17, the number of the first recessed area and the first raised area is relatively large, which may cause the degree of warping near the first starting end to be too large, which will not only affect the convex part of the active material layer, but also may cause the isolation membrane to be pierced due to the warping, and there is also a risk of short circuit. Therefore, in the embodiments of the present application, 10≤n≤30 can be selected. The test failure rates of Examples 14 to 16 are similar. Compared with Example 16, the number of the first recessed areas in Example 15 is smaller, the process is simpler, and the impact on the active material layer is smaller. Therefore, in the embodiments of the present application, 15≤n≤25 is preferably selected, which can further reduce the occurrence of short circuits, simplify the process, and reduce the impact on the active material layer.

[0153] 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 which are 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: Along the thickness direction of the first pole piece, the first pole piece includes a first surface and a second surface arranged opposite to each other, the first surface has a plurality of first recessed areas, and the first recessed areas form first raised areas on the second surface; The secondary battery comprises a first adhesive layer disposed on the first surface, the first adhesive layer having a plurality of first recessed portions, the first recessed portions being disposed in the first recessed area, and the first recessed portions being bonded to the first recessed area; Along the winding direction, the first adhesive layer includes a second starting end, the second starting end is flush with the first starting end or the first adhesive layer extends from the first starting end to the first pole piece in the opposite direction of the winding direction; and / or, The secondary battery comprises a second adhesive layer disposed on the second surface, the second adhesive layer has a plurality of first protrusions, the first protrusions are disposed in the first protrusion area, and the first protrusions are bonded to the first protrusion area; Along the winding direction, the second adhesive layer includes a third starting end, and the third starting end is flush with the first starting end, or the second adhesive layer extends from the first starting end to the first pole piece in the opposite direction of the winding direction.

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 3, characterized in that: The electrode assembly is provided with a cavity, and the cavity is arranged at the winding center of the electrode assembly.

5. The secondary battery according to claim 3, characterized in that: The cylindrical 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 thickness direction of the first pole piece, the depth of the first recessed area is H1; The first recessed area includes a bottom wall, a first side wall, and a second side wall. Along the length direction of the first pole piece, the bottom wall is connected between the first side wall and the second side wall; the angle between the bottom wall and the first side wall is α, and the angle between the bottom wall and the second side wall is β; Along the length direction of the first pole piece, a plurality of the first recessed areas are arranged in an array, and the number of the arranged first recessed areas is n; n × [H1 / sin(π-α)-H1 / tan(π-α)]+n × [H1 / sin(π-β)-H1 / tan(π-β)]≥π(D1-D2).

6. The secondary battery according to claim 5, characterized in that: Along the winding direction, 10≤n≤30.

7. The secondary battery according to claim 6, characterized in that: 15≤n≤25。 8. The secondary battery according to claim 5, characterized in that: 10μm≤H1≤100μm.

9. The secondary battery according to claim 8, characterized in that: 30μm≤H1≤80μm.

10. The secondary battery according to claim 1, characterized in that: Along the length direction of the first pole piece, the first pole piece includes a first empty foil section and a first coated section; In the first empty foil section, along the thickness direction of the first electrode sheet, the maximum distance from the first surface to the second surface is T1, the first adhesive layer is arranged on the first empty foil section, and the thickness of the first adhesive layer is T a ; In the first coating section, along the thickness direction of the first pole piece, the maximum thickness of the first coating section is T2, T1+T a ≤T2.

11. The secondary battery according to claim 1, characterized in that: Along the winding direction, the length of the first recessed area is L1, and the distance between two adjacent first recessed areas is L2; 0.5mm≤L1≤5mm, and / or, 0.5mm≤L2≤5mm.

12. The secondary battery according to any one of claims 1 to 11, characterized in that: The second pole piece includes a second inner circle pole piece and a second inner circle pole piece, the second inner circle pole piece is the innermost circle pole piece of the electrode assembly, and along the thickness direction of the first pole piece, the pole pieces adjacent to the first starting end are respectively the second inner circle pole piece and the second inner circle pole piece; Along the thickness direction of the first pole piece, the distance from the first starting end to the second inner circle pole piece is H2, and the distance from the first starting end to the second inner circle pole piece is H3, and H3>H2.

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: The first surface also has a plurality of second recessed areas, and the second recessed areas form second raised areas on the second surface; Observing along the width direction of the first pole piece, the second raised area is at least partially located between two adjacent first raised areas.

15. The secondary battery according to claim 14, characterized in that: The first surface is provided with the first adhesive layer, the first adhesive layer has a plurality of second recessed parts, the second recessed parts are provided in the second recessed area, and the second recessed parts are bonded to the second recessed area; The second surface is provided with the second adhesive layer, the second adhesive layer has a plurality of second protrusions, the second protrusions are provided in the second protrusion area, and the second protrusions are bonded to the second protrusion area.

16. 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; along the thickness direction of the first pole piece, the pole piece adjacent to the first tail end is the second pole piece; The first surface also has a plurality of third recessed areas, and the third recessed areas form third raised areas on the second surface; The secondary battery further includes a third adhesive layer, the third adhesive layer is disposed on the first surface, the third adhesive layer has a plurality of third recessed portions, the third recessed portions are disposed in the third recessed area, and the third recessed portions are bonded to the third recessed area; Along the winding direction, the third adhesive layer includes a second tail end, the second tail end is flush with the first tail end, or the third adhesive layer extends from the first tail end to the first pole piece along the winding direction; and / or, The secondary battery further includes a fourth adhesive layer, the fourth adhesive layer is disposed on the second surface, the fourth adhesive layer has a plurality of fourth protrusions, the fourth protrusions are disposed in the fourth protrusion area, and the fourth protrusions are bonded to the fourth protrusion area; Along the winding direction, the fourth adhesive layer includes a third tail end, the third tail end is flush with the first tail end, or the fourth adhesive layer extends from the first tail end to the first pole piece along the winding direction.

17. The secondary battery according to claim 16, characterized in that: The first tail end is located at the secondary outer ring pole piece of the electrode assembly.

18. A method for preparing a secondary battery according to any one of claims 1 to 17, characterized in that: include: Providing a first current collector, wherein along a thickness direction of the first current collector, the first current collector comprises a first surface and a second surface that are oppositely disposed, a first adhesive layer is bonded to the first surface, and a second adhesive layer is bonded to the second surface; Performing embossing treatment on the first current collector, the first glue layer, and the second glue layer as a whole, so that a plurality of first recessed areas are formed on the first surface, and a plurality of first recessed parts are formed on the first glue layer, and the first recessed parts are bonded to the first recessed areas; The second surface is formed with a plurality of first raised areas, and the second adhesive layer is formed with a plurality of first raised portions, wherein the first raised portions are bonded to the first raised areas; Among them, along the winding direction, the first current collector includes a first starting end, the first glue layer includes a second starting end, and the second glue layer includes a third starting end; the second starting end is flush with the first starting end or the second starting end extends from the first starting end to the first pole piece in the opposite direction of the winding direction; and / or the third starting end is flush with the first starting end or the third starting end extends from the first starting end to the first pole piece in the opposite direction of the winding direction.

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

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