Secondary battery and electrochemical device

Abstract

The embodiment of the invention provides a secondary battery and an electrochemical device. The secondary battery comprises an electrode assembly, the electrode assembly is of a flat winding type structure, the electrode assembly comprises a first pole piece, a second pole piece and an isolating membrane, the isolating membrane is arranged between the first pole piece and the second pole piece, and the innermost ring of pole piece of the electrode assembly is the first pole piece; wherein the length of the electrode assembly is L, the width of the electrode assembly is W, the thickness of the electrode assembly is H, and L / W is larger than or equal to 0.9 and smaller than or equal to 1.1, H is smaller than or equal to 3 mm, the electrode assembly further comprises a bonding layer, the innermost ring of the first pole piece comprises a first straight section, a first bent section, a second straight section and a second bent section which are sequentially connected, and the first pole piece is provided with a first surface facing a roll core of the electrode assembly. And at least one part of the bonding layer is arranged on the first surface of the first straight section and / or the first surface of the second straight section. According to the technical scheme provided by the embodiment of the invention, the safety performance and the cycle performance of the secondary battery can be improved.

Description

Technical Field

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

[0002] During the winding manufacturing process of the electrode assembly, the electrode sheet of the electrode assembly is usually required to be kept flat to prevent lithium deposition caused by uneven thickness of the electrode assembly, or uneven stress on the left and right of the wide and thin electrode assembly, which leads to large cycle expansion. However, in actual production, the innermost area of ​​the anode electrode sheet is prone to curling after feeding, and the wide and thin electrode assembly is prone to deformation. This phenomenon not only causes serious appearance problems, but also causes uneven thickness and interface of the electrode assembly, affecting the safety performance and cycle performance of the secondary battery.

[0003] During the narrow surface extrusion test of secondary batteries, it is usually required that the secondary batteries cannot catch fire or explode. However, due to the presence of gaps in the innermost anode pole piece and the isolation membrane in the electrode assembly of the soft-pack winding structure, the innermost anode pole piece and the wrapped cathode pole piece will preferentially short-circuit and fail at the sharp corners of the cathode and cathode during the narrow surface extrusion process of the secondary battery, which will affect the yield rate. Summary of the invention

[0004] The present application provides a secondary battery and an electrochemical device, which can improve the safety performance and cycle performance of the secondary battery.

[0005] This application is achieved through the following technical solutions:

[0006] In a first aspect, an embodiment of the present application provides a secondary battery, which includes an electrode assembly, wherein the electrode assembly is a flat wound structure, the electrode assembly includes a first electrode sheet, a second electrode sheet and a separation membrane, the separation membrane is arranged between the first electrode sheet and the second electrode sheet, and the innermost electrode sheet of the electrode assembly is the first electrode sheet; wherein, the length of the electrode assembly is L, the width of the electrode assembly is W, and the thickness of the electrode assembly is H, satisfying 0.9≤L / W≤1.1, H≤3mm, the electrode assembly also includes an adhesive layer, the innermost circle of the first electrode sheet includes a first straight section, a first bent section, a second straight section and a second bent section connected in sequence, the first electrode sheet has a first surface of the winding core facing the electrode assembly, and at least a portion of the adhesive layer is arranged on the first surface of the first straight section and / or the first surface of the second straight section.

[0007] According to the secondary battery of the embodiment of the present application, the electrode assembly is a flat winding structure, and the length L, width W and thickness H of the electrode assembly satisfy 0.9≤L / W≤1.1, H≤3mm, and the electrode assembly is a wide and thin electrode assembly; the first pole piece is the pole piece of the innermost circle, and the bonding layer is arranged on the straight section of the innermost circle of the first pole piece, which can increase the strength of the innermost circle of the first pole piece, support the electrode assembly, reduce the deformation of the electrode assembly, improve the pass rate of the narrow surface extrusion test of the secondary battery, and improve the safety performance and cycle performance of the secondary battery.

[0008] In one or more of the above optional embodiments, the first pole piece has a second surface arranged opposite to the first surface, and the first pole piece includes a single-sided area and a double-sided area. The single-sided area has active materials only arranged on the second surface, and the double-sided area has active materials arranged on both the first surface and the second surface. Along the winding direction, the single-sided area and the double-sided area are arranged in sequence, the single-sided area includes a first single-sided area, and the first single-sided area is located at the innermost circle of the first pole piece, and at least part of the adhesive layer is arranged on the first surface of the first single-sided area.

[0009] In the above scheme, the first single-sided area is located in the innermost circle of the first pole piece, and the side of the single-sided area where the active material is not set is the first surface. When the bonding layer is set in the first single-sided area, it can not only enhance the anti-deformation energy of the part of the first pole piece in the first single-sided area, but also can be bonded with the isolation film of the inner circle under high temperature conditions, thereby enhancing the strength of the inner circle of the electrode assembly, reducing the probability of deformation of the electrode assembly, and preventing failure caused by sharp-corner short circuits of the positive and negative pole pieces in the inner circle of the electrode assembly due to narrow surface extrusion.

[0010] In one or more of the above optional embodiments, the area of ​​the first single-sided region covered by the adhesive layer is S1, the area of ​​the first single-sided region is S2, and 1 / 2≤S1 / S2≤1.

[0011] In the above scheme, the ratio of the area covered by the adhesive layer to the area of ​​the first single-sided area satisfies the above relationship, so that the adhesive layer and the first single-sided area have a larger connection area, thereby improving the strength of the first single-sided area and reducing the probability of deformation of the electrode assembly.

[0012] In one or more of the above optional embodiments, 2 / 3≤S1 / S2≤1.

[0013] In the above solution, when 2 / 3≤S1 / S2≤1, the strength of the first single-sided area can be improved and the probability of deformation of the electrode assembly can be reduced.

[0014] In one or more of the above embodiments, along the thickness direction of the electrode assembly, the orthographic projection of the adhesive layer covers the entire second straight segment.

[0015] In the above solution, the orthographic projection of the adhesive layer covers the entire second straight section, so that the innermost circle of the first pole piece has a higher strength, which can improve the pass rate of the narrow surface extrusion test.

[0016] In one or more of the above optional embodiments, a portion of the adhesive layer is disposed on the first bending segment and / or the second bending segment.

[0017] In the above scheme, a portion of the adhesive layer is arranged in the first bending section and / or the second bending section, which can further improve the overall strength of the innermost circle of the first pole piece, reduce the risk of brittle fracture of the first pole piece, and further improve the pass rate of the narrow surface extrusion test.

[0018] In one or more of the above optional embodiments, at least part of the adhesive layer is disposed on the first straight section, the first bent section, the second straight section, and the second bent section.

[0019] In the above scheme, the bonding layer is arranged in the first straight section, the first bent section, the second straight section and the second bent section, which can strengthen the innermost part of the first pole piece, effectively reduce the probability of deformation of the electrode assembly, and improve the pass rate of the narrow surface extrusion test.

[0020] In one or more optional embodiments above, the adhesive layer includes a first sub-adhesive layer and a second sub-adhesive layer spaced apart along the winding direction, at least a portion of the first sub-adhesive layer is disposed in the first straight segment, and at least a portion of the second sub-adhesive layer is disposed in the second straight segment.

[0021] In the above scheme, the first sub-adhesive layer and the second sub-adhesive layer are two independent parts, which can reduce the process difficulty when bonding the first sub-adhesive layer and the second sub-adhesive layer to the first surface, so that the first sub-adhesive layer and the second sub-adhesive layer are firmly bonded to the first surface.

[0022] In one or more of the above optional embodiments, along the thickness direction of the electrode assembly, the orthographic projection of the first sub-adhesive layer and the orthographic projection of the second sub-adhesive layer have an overlapping area.

[0023] In the above scheme, the orthographic projection of the first sub-adhesive layer and the orthographic projection of the second sub-adhesive layer have an overlapping area, which can increase the bonding area between the adhesive layer and the isolation film and at the same time, can increase the bonding effect of the wide and thin inner circle of the electrode assembly.

[0024] In one or more of the above optional embodiments, the first sub-adhesive layer includes a first part and a second part connected to each other, the first part is arranged in the first straight section, and the second part is arranged in the second bent section; the second sub-adhesive layer includes a third part and a fourth part connected to each other, the third part is arranged in the second straight section, and the fourth part is arranged in the first bent section.

[0025] In the above scheme, the first part and the second part are connected to each other, the first part is located in the first straight section, and the second part is located in the second bending section, which can reduce the risk of brittle fracture of the first pole piece located in the second bending section; the third part and the fourth part are connected to each other, the third part is located in the second straight section, and the fourth part is located in the first bending section, which can reduce the risk of brittle fracture of the first pole piece located in the first bending section.

[0026] In one or more of the above optional embodiments, the first pole piece includes a single-sided area and a double-sided area. The single-sided area has active material arranged on only one side, and the double-sided area has active material arranged on both sides. Along the winding direction, the single-sided area and the double-sided area are arranged in sequence, the tail end of the adhesive layer is the first end, and the double-sided area includes a second end connected to the single-sided area. When the first pole piece is unfolded, along the length direction of the first pole piece, the distance between the first end and the second end is D1, satisfying 0≤D1≤2mm.

[0027] In the above solution, the distance between the first end and the second end satisfies the above relationship, which can reduce the risk of overlapping between the adhesive layer and the active material in the double-sided area and reduce the risk of lithium deposition.

[0028] In one or more of the above optional embodiments, the thickness of the adhesive layer is 10 μm to 60 μm.

[0029] In the above scheme, the thickness direction of the bonding layer is parallel to the thickness direction of the first pole piece, and the thickness of the bonding layer satisfies the above relationship, which can not only reduce the probability of deformation of the innermost circle of the first pole piece and improve the pass rate of the narrow surface extrusion test, but also occupy a smaller assembly space and reduce the impact on energy density.

[0030] In one or more optional embodiments above, the adhesive layer includes a pressure-sensitive adhesive layer, a substrate layer and a hot-melt adhesive layer sequentially distributed along its thickness direction, the hot-melt adhesive layer is connected to the isolation film, and the pressure-sensitive adhesive layer is connected to the first electrode.

[0031] In the above scheme, the pressure-sensitive adhesive layer is connected to the first electrode piece, and the hot-melt adhesive layer is connected to the isolation membrane, which can firmly connect the first electrode piece and the isolation membrane, improve the inner ring strength of the electrode assembly, and reduce the probability of deformation of the electrode assembly.

[0032] In one or more optional embodiments above, along the winding axis direction of the electrode assembly, the adhesive layer exceeds the edge of the first pole piece, and the dimension C of the adhesive layer exceeding the edge of the first pole piece satisfies 0≤C≤0.75mm.

[0033] In the above scheme, the size of the adhesive layer beyond the edge of the first pole piece meets the above range, which can not only completely cover the first pole piece in the winding axis direction of the electrode assembly to meet the pasting requirements, but also reduce the impact on the assembly of the secondary battery.

[0034] In one or more of the above optional embodiments, when the first pole piece is unfolded, along the length direction of the first pole piece, the distance between the adhesive layer and the winding start end of the first pole piece is D2, satisfying 1mm≤D2≤2mm.

[0035] In the above scheme, the distance between the adhesive layer and the winding starting end of the first pole piece satisfies the above relationship. On the one hand, it is convenient for feeding the first pole piece when the electrode assembly is wound. On the other hand, it can shield the burrs at the winding starting end and improve the safety performance of the secondary battery.

[0036] In one or more of the above optional embodiments, the first pole piece has a second surface arranged opposite to the first surface, the first pole piece includes a single-sided area and a double-sided area, the single-sided area has active material only arranged on the second surface, and the double-sided area has active material arranged on both the first surface and the second surface. Along the winding direction, the single-sided area and the double-sided area are arranged in sequence, the isolation film includes a first isolation film and a second isolation film, the first isolation film is arranged toward the second surface, and the second isolation film is arranged toward the first surface, at least part of the bonding layer is arranged between the single-sided area and the second isolation film, and the single-sided area and the second isolation film are bonded by the bonding layer.

[0037] In the above scheme, at least part of the bonding layer is arranged between the single-sided area and the second isolation film, and the single-sided area and the second isolation film are bonded by the bonding layer so as to improve the strength of the inner circle of the electrode assembly, reduce the probability of deformation of the electrode assembly, and improve the pass rate of the narrow surface extrusion test.

[0038] In one or more of the above optional embodiments, the winding starting end of the first isolation film and the winding starting end of the second isolation film are both bent structures.

[0039] In the above solution, the winding starting end of the first isolation film and the winding starting end of the second isolation film are both bent structures, so as to facilitate clamping by the winding needle when the electrode assembly is wound.

[0040] In one or more of the above optional embodiments, the secondary battery further includes a packaging bag, and the electrode assembly is accommodated in the packaging bag.

[0041] In the above solution, the electrode assembly is contained in the packaging bag, which can protect the electrode assembly, and the wall thickness of the packaging bag can be thinner, so that the secondary battery can have a higher energy density.

[0042] In one or more of the above optional embodiments, L≥65mm, W≥65mm.

[0043] In the above scheme, when L≥65mm and W≥65mm, the electrode assembly is a wide and thin electrode assembly, and the provision of the adhesive layer can effectively reduce the deformation of the electrode assembly and improve the pass rate of the narrow surface extrusion test of the secondary battery.

[0044] In a second aspect, an embodiment of the present application provides an electrochemical device, which includes a secondary battery provided by any of the above embodiments.

[0045] Additional aspects and advantages of the present application will be given in part in the description below, and in part will become apparent from the description below, or will be learned through the practice of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings required for use in the embodiments will be briefly introduced below. It should be understood that the following drawings only show certain embodiments of the present application and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without paying creative work.

[0047] Figure 1 A schematic diagram of the structure of a secondary battery provided in some embodiments of the present application;

[0048] Figure 2 for Figure 1 A bottom view of the secondary battery shown;

[0049] Figure 3 A schematic diagram of the structure of an electrode assembly provided in some embodiments of the present application;

[0050] Figure 4 A schematic diagram of the structure of an electrode assembly provided in some other embodiments of the present application;

[0051] Figure 5 A schematic diagram of the structure of an electrode assembly provided in some other embodiments of the present application;

[0052] Figure 6 A schematic diagram of the structure of an electrode assembly provided in some other embodiments of the present application;

[0053] Figure 7 A schematic diagram of the structure of an electrode assembly provided in some other embodiments of the present application;

[0054] Figure 8 A schematic diagram of the structure of an electrode assembly provided in some other embodiments of the present application;

[0055] Fig. 9 A schematic diagram of the adhesive layer and the single-sided area in the unfolded state of the first pole piece provided in some embodiments of the present application;

[0056] Fig.10 A schematic diagram of the structure of the adhesive layer provided in some embodiments of the present application;

[0057] Fig.11 A schematic diagram of assembling the bonding layer and the first pole piece provided in some embodiments of the present application;

[0058] Fig.12 A schematic structural diagram of the adhesive layer and the winding start end of the first pole piece in the unfolded state provided by other embodiments of the present application;

[0059] Fig.13 for Figure 8 A partial enlarged view of point A.

[0060] Icon: 100-secondary battery; 10-electrode assembly; 10a-straight area; 10b-bending area; 11-first pole piece; 11a-first surface; 11b-second surface; 111-first straight section; 112-first bending section; 113-second straight section; 114-second bending section; 115-single-sided area; 115a-first single-sided area; 116-double-sided area; 116a-second end; 12-second pole piece; 13-isolating film; 131-first isolating film; 132-second isolating film Release film; 20-adhesive layer; 20a-first end; 20b-third end; 21-first sub-adhesive layer; 211-first part; 212-second part; 22-second sub-adhesive layer; 221-third part; 222-fourth part; 23-pressure-sensitive adhesive layer; 24-substrate layer; 25-hot-melt adhesive layer; 30-packaging bag; J-winding direction; P-winding starting end of the first pole piece; X-winding axis direction of the electrode assembly; Y-length direction of the first pole piece; Z-thickness direction of the electrode assembly. DETAILED DESCRIPTION

[0061] 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 and completely described below in combination 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.

[0062] Unless otherwise defined, all technical and scientific terms used in this application have the same meaning as those commonly understood by technicians in the technical field of this application; the terms used in the specification of this application are only for the purpose of describing specific embodiments and are not intended to limit this application; the terms "including" and "having" in the specification and claims of this application and the above-mentioned drawings and any variations thereof are intended to cover non-exclusive inclusions. The terms "first", "second", etc. in the specification and claims of this application or the above-mentioned drawings are used to distinguish different objects, rather than to describe a specific order or a primary and secondary relationship.

[0063] Reference to "embodiments" in this application means that a particular feature, structure, or characteristic described in conjunction with the embodiments may be included in at least one embodiment of the present application. The appearance of the phrase in various locations 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. It is explicitly and implicitly understood by those skilled in the art that the embodiments described in this application may be combined with other embodiments.

[0064] In the description of this application, it should be noted that, unless otherwise clearly specified and limited, the terms "installed", "connected", "connected", and "attached" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a direct connection, or an indirect connection through an intermediate medium, or it can be the internal communication of two elements. For ordinary technicians in this field, the specific meanings of the above terms in this application can be understood according to specific circumstances.

[0065] The term "and / or" in this application is only a description of the association relationship of associated objects, indicating that there can 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 application generally indicates that the associated objects before and after are in an "or" relationship.

[0066] The term "multiple" as used in this application refers to more than two (including two). Similarly, "multiple groups" refers to more than two groups (including two groups), and "multiple sheets" refers to more than two sheets (including two sheets).

[0067] When the electrode assembly is a flat winding structure, the secondary battery needs to be subjected to a narrow surface extrusion test during the manufacturing process of the secondary battery. However, for the wide and thin electrode assembly of the soft-pack secondary battery, the innermost anode electrode piece is easily broken during the narrow surface extrusion process of the secondary battery, resulting in a short circuit between the anode and cathode electrode pieces. The pass rate of the narrow surface extrusion test is low, which affects the safety performance and cycle performance of the secondary battery.

[0068] The structure of the secondary battery provided in the embodiments of the present application will be described below with reference to the accompanying drawings.

[0069] Please refer to Figures 1 to 5 The embodiment of the present application provides a secondary battery 100, which includes an electrode assembly 10, and the electrode assembly 10 is a flat winding structure.

[0070] The flat shape means that the electrode assembly 10 has a straight area 10 a and two bent areas 10 b , and the two bent areas 10 b are located at two ends of the straight area 10 a .

[0071] The electrode assembly 10 includes a first pole piece 11 , a second pole piece 12 and an isolation membrane 13 . The isolation membrane 13 is disposed between the first pole piece 11 and the second pole piece 12 . The innermost pole piece of the electrode assembly 10 is the first pole piece 11 .

[0072] The length of the electrode assembly 10 is L, the width of the electrode assembly 10 is W, and the thickness of the electrode assembly 10 is H, satisfying 0.9≤L / W≤1.1, H≤3mm.

[0073] The electrode assembly 10 also includes an adhesive layer 20. The innermost circle of the first electrode piece 11 includes a first straight section 111, a first bent section 112, a second straight section 113 and a second bent section 114 connected in sequence. The first electrode piece 11 has a first surface 11a of the winding core facing the electrode assembly 10. At least a portion of the adhesive layer 20 is arranged on the first surface 11a of the first straight section 111 and / or the first surface 11a of the second straight section 113.

[0074] The first straight section 111 and the second straight section 113 are the innermost parts of the first pole piece 11 in the straight area 10a, and the first bent section 112 and the second bent section 114 are the innermost parts of the first pole piece 11 in the bent area 10b.

[0075] The innermost electrode sheet of the electrode assembly 10 refers to the electrode sheet closest to the winding core among the electrode sheets constituting the electrode assembly 10 .

[0076] The first pole piece 11 and the second pole piece 12 have opposite polarities. The first pole piece 11 may be an anode pole piece, and correspondingly, the second pole piece 12 may be a cathode pole piece.

[0077] The isolation film 13 is disposed between the first pole piece 11 and the second pole piece 12 so as to insulate and isolate the first pole piece 11 from the second pole piece 12 .

[0078] The length L, width W and thickness H of the electrode assembly 10 satisfy 0.9≤L / W≤1.1, H≤3 mm, so that the electrode assembly 10 is a wide and thin structure, and the secondary battery 100 formed by the electrode assembly 10 is a wide and thin battery.

[0079] In some embodiments, L ≥ 65 mm, W ≥ 65 mm.

[0080] The innermost circle of the first pole piece 11 refers to a structure formed starting from the winding starting end P of the first pole piece and ending along the winding direction J of the first pole piece 11 to a point aligned with the winding starting end.

[0081] Since the electrode assembly 10 is a flat winding structure, the winding starting end P of the first pole piece is in the first straight section 111. The first straight section 111 includes two sections. One end of the first section is the winding starting end, the other end of the first section is connected to the first bending section 112, one end of the second section is connected to the second bending section 114, and the other end of the second section is aligned with the winding starting end P of the first pole piece in the thickness direction Z of the electrode assembly.

[0082] The adhesive layer 20 is disposed on the first surface 11 a and can be bonded to the first surface 11 a so that the adhesive layer 20 and the first electrode sheet 11 are firmly connected.

[0083] “At least a portion of the adhesive layer 20 is disposed on the first surface 11a of the first straight section 111 and / or the first surface 11a of the second straight section 113” means that at least a portion of the adhesive layer 20 can be disposed on the first surface 11a of the first straight section 111, or at least a portion of the adhesive layer 20 can be disposed on the first surface 11a of the second straight section 113, or at least a portion of the adhesive layer 20 is disposed on the first surface 11a of the first straight section 111 and the first surface 11a of the second straight section 113.

[0084] The provision of the adhesive layer 20 can increase the strength of the first straight section 111 and / or the second straight section 113 .

[0085] During the winding process of the electrode assembly 10 , the adhesive layer 20 is firstly laminated on the first electrode sheet 11 , and then the first electrode sheet 11 laminated with the adhesive layer 20 is fed into the material for winding.

[0086] According to the secondary battery 100 of the embodiment of the present application, the first pole piece 11 is the innermost pole piece, and the bonding layer 20 is arranged on the straight section of the innermost circle of the first pole piece 11, which can increase the strength of the innermost circle of the first pole piece 11, support the electrode assembly 10, reduce the deformation of the electrode assembly 10, improve the pass rate of the narrow surface extrusion test of the secondary battery 100, and improve the safety performance and cycle performance of the secondary battery 100.

[0087] Please refer to Figures 3 to 5 In one or more of the above optional embodiments, the first pole piece 11 has a second surface 11b arranged opposite to the first surface 11a, and the first pole piece 11 includes a single-sided area 115 and a double-sided area 116. The single-sided area 115 is only provided with active materials on the second surface 11b, and the double-sided area 116 is provided with active materials on both the first surface 11a and the second surface 11b. Along the winding direction J, the single-sided area 115 and the double-sided area 116 are arranged in sequence, and the single-sided area 115 includes a first single-sided area 115a, which is located at the innermost circle of the first pole piece 11, and at least part of the adhesive layer 20 is arranged on the first surface 11a of the first single-sided area 115a.

[0088] The single-sided region 115 is a region where active materials are disposed on only one side of the first pole piece 11 in the thickness direction, and the double-sided region 116 is a region where active materials are disposed on both sides of the first pole piece 11 in the thickness direction.

[0089] Along the winding direction J, the single-sided area 115 and the double-sided area 116 are arranged in sequence, and the single-sided area 115 is closer to the winding start end than the double-sided area 116.

[0090] The first single-sided region 115 a is located at the innermost circle of the first pole piece 11 . Part of the single-sided region 115 may be located at the innermost circle of the first pole piece 11 , or the entire single-sided region 115 may be located at the innermost circle of the first pole piece 11 .

[0091] A portion of the adhesive layer 20 may be disposed in the first single-sided region 115 a , or the entire adhesive layer 20 may be disposed in the first single-sided region 115 a .

[0092] For example, when the area near the winding start end of the first pole piece 11 includes an empty foil area, the empty foil area, the single-sided area 115 and the double-sided area 116 are sequentially distributed along the winding direction J, a part of the adhesive layer 20 can be located in the empty foil area, and another part can be arranged in the single-sided area 115. Alternatively, when the area near the winding start end of the first pole piece 11 does not have an empty foil area, the entire adhesive layer 20 can be arranged in the single-sided area 115.

[0093] In the above scheme, the first single-sided area 115a is located in the innermost circle of the first pole piece 11, and the side of the single-sided area 115 on which the active material is not set is the first surface 11a. When the bonding layer 20 is set in the first single-sided area 115a, it can not only enhance the anti-deformation energy of the part of the first pole piece 11 in the first single-sided area 115a, but also can be bonded with the isolation film 13 of the inner circle under high temperature conditions, thereby enhancing the strength of the inner circle of the electrode assembly 10, reducing the probability of deformation of the electrode assembly 10, and preventing failure caused by sharp-corner short circuits of the positive and negative pole pieces in the inner circle of the electrode assembly 10 due to narrow surface extrusion.

[0094] In one or more optional embodiments above, the area of ​​the first single-sided region 115 a covered by the adhesive layer 20 is S1, the area of ​​the first single-sided region 115 a is S2, and 1 / 2≤S1 / S2≤1.

[0095] Optionally, S1 / S2 can be but is not limited to 1 / 2, 2 / 3, 3 / 4, 4 / 5, 5 / 6, 6 / 7, 7 / 8, 8 / 9, 9 / 10, 1, etc.

[0096] In the above scheme, the ratio of the area of ​​the first single-sided area 115a covered by the adhesive layer 20 to the area of ​​the first single-sided area 115a satisfies the above relationship, so that the adhesive layer 20 and the first single-sided area 115a have a larger connection area, thereby improving the strength of the first single-sided area and reducing the probability of deformation of the electrode assembly 10. However, when S1>S2, energy density is lost.

[0097] In one or more of the above optional embodiments, 2 / 3≤S1 / S2≤1.

[0098] In the above solution, when 2 / 3≤S1 / S2≤1, the strength of the first single-sided area 115 a can be improved, and the probability of deformation of the electrode assembly 10 can be reduced.

[0099] Please refer to Figure 5 , and further refer to Figure 6 and Figure 7 In one or more of the above optional embodiments, along the thickness direction Z of the electrode assembly, the orthographic projection of the bonding layer 20 covers the entire second straight section 113 .

[0100] The orthographic projection of the adhesive layer 20 covers the entire second straight section 113 . The adhesive layer 20 may be disposed on the second straight section 113 , the first straight section 111 , or the first straight section 111 and the second straight section 113 . When the adhesive layer 20 is disposed on the first straight section 111 and the second straight section 113, the adhesive layer 20 located at the first straight section 111 may cover a portion of the first straight section 111, and the adhesive layer 20 located at the second straight section 113 may cover a portion of the second straight section 113; or, the adhesive layer 20 located at the first straight section 111 may cover the entire first straight section 111, and the adhesive layer 20 located at the second straight section 113 may cover a portion of the second straight section 113; or, the adhesive layer 20 located at the first straight section 111 may cover a portion of the first straight section 111, and the adhesive layer 20 located at the second straight section 113 may cover the entire second straight section 113; or, the adhesive layer 20 located at the first straight section 111 may cover the entire first straight section 111, and the adhesive layer 20 located at the second straight section 113 may cover the entire second straight section 113.

[0101] In the above solution, the orthographic projection of the adhesive layer 20 covers the entire second straight section 113 , so that the innermost circle of the first pole piece 11 has a higher strength, which can improve the pass rate of the narrow surface extrusion test.

[0102] Please refer to Figures 5 to 7 In one or more of the above optional embodiments, a portion of the adhesive layer 20 is disposed on the first bending segment 112 and / or the second bending segment 114 .

[0103] A portion of the adhesive layer 20 may be disposed at the first bending section 112 , which can enhance the strength of the first bending section 112 and reduce the risk of brittle fracture of the first pole piece 11 at the first bending section 112 .

[0104] A portion of the adhesive layer 20 may be disposed at the second bending section 114 , which can enhance the strength of the second bending section 114 and reduce the risk of brittle fracture of the first pole piece 11 at the second bending section 114 .

[0105] A portion of the adhesive layer 20 may be disposed at the first bending section 112 and the second bending section 114 , which can enhance the strength of the first bending section 112 and the second bending section 114 and reduce the risk of brittle fracture of the first pole piece 11 at the first bending section 112 and the second bending section 114 .

[0106] In the above scheme, a portion of the adhesive layer 20 is arranged in the first bending section 112 and / or the second bending section 114, which can further improve the overall strength of the innermost circle of the first pole piece 11, reduce the risk of brittle fracture of the first pole piece 11, and further improve the pass rate of the narrow surface extrusion test.

[0107] Please refer to Figure 5 In one or more of the above optional embodiments, at least part of the adhesive layer 20 is disposed on the first straight section 111 , the first bent section 112 , the second straight section 113 and the second bent section 114 .

[0108] The adhesive layer 20 may be a continuous structure, and may be sequentially disposed on the first straight section 111 , the first bent section 112 , the second straight section 113 , and the second bent section 114 , that is, the adhesive layer 20 may be disposed on the entire innermost circle of the first pole piece 11 .

[0109] In some embodiments, a portion of the adhesive layer 20 may be disposed at the innermost circle of the first pole piece 11 , and another portion of the adhesive layer 20 may be disposed at the second inner circle of the first pole piece 11 .

[0110] In the above scheme, the adhesive layer 20 is arranged in the first straight section 111, the first bent section 112, the second straight section 113 and the second bent section 114, which can strengthen the innermost part of the first pole piece 11, effectively reduce the probability of deformation of the electrode assembly 10, and improve the pass rate of the narrow surface extrusion test.

[0111] Please refer to Figure 6 and Figure 7 In one or more of the above optional embodiments, the adhesive layer 20 includes a first sub-adhesive layer 21 and a second sub-adhesive layer 22 arranged at intervals along the winding direction J, at least a portion of the first sub-adhesive layer 21 is arranged in the first straight section 111, and at least a portion of the second sub-adhesive layer 22 is arranged in the second straight section 113.

[0112] The first sub-adhesive layer 21 and the second sub-adhesive layer 22 are arranged at intervals along the winding direction J. The first sub-adhesive layer 21 and the second sub-adhesive layer 22 are two independent parts.

[0113] At least a portion of the first sub-adhesive layer 21 is disposed on the first straight section 111 . It may be that a portion of the first sub-adhesive layer 21 is disposed on the first straight section 111 , and another portion is disposed on the first bent section 112 and / or the second bent section 114 ; or, the entire first sub-adhesive layer 21 is disposed on the first straight section 111 .

[0114] At least a portion of the second sub-adhesive layer 22 is disposed on the second straight section 113 . It may be that a portion of the second sub-adhesive layer 22 is disposed on the second straight section 113 , and another portion is disposed on the first bending section 112 and / or the second bending section 114 ; or, the entire second sub-adhesive layer 22 is disposed on the second straight section 113 .

[0115] In the above scheme, the first sub-adhesive layer 21 and the second sub-adhesive layer 22 are two independent parts, which can reduce the process difficulty when the first sub-adhesive layer 21 and the second sub-adhesive layer 22 are bonded to the first surface 11a, so that the first sub-adhesive layer 21 and the second sub-adhesive layer 22 are firmly bonded to the first surface 11a.

[0116] Please refer to Figure 7 In one or more of the above optional embodiments, along the thickness direction Z of the electrode assembly, the orthographic projection of the first sub-adhesive layer 21 and the orthographic projection of the second sub-adhesive layer 22 have an overlapping area.

[0117] “The orthographic projection of the first sub-adhesive layer 21 and the orthographic projection of the second sub-adhesive layer 22 have an overlapping area” means that, when observed along the thickness direction Z of the electrode assembly, the first sub-adhesive layer 21 and the second sub-adhesive layer 22 at least partially overlap.

[0118] In the above scheme, the orthographic projection of the first sub-adhesive layer 21 and the orthographic projection of the second sub-adhesive layer 22 have an overlapping area, which can increase the bonding area between the adhesive layer 20 and the isolation film 13, and at the same time, can increase the bonding effect of the inner circle of the wide and thin electrode assembly 10.

[0119] Please refer to Figure 7 In one or more of the above optional embodiments, the first sub-adhesive layer 21 includes a first part 211 and a second part 212 connected to each other, the first part 211 is arranged in the first straight section 111, and the second part 212 is arranged in the second bent section 114; the second sub-adhesive layer 22 includes a third part 221 and a fourth part 222 connected to each other, the third part 221 is arranged in the second straight section 113, and the fourth part 222 is arranged in the first bent section 112.

[0120] The first portion 211 and the second portion 212 are two portions of the first sub-adhesive layer 21 distributed sequentially along the winding direction J.

[0121] The third portion 221 and the fourth portion 222 are two portions of the second sub-adhesive layer 22 distributed in sequence along the winding direction J.

[0122] In the above scheme, the first part 211 and the second part 212 are connected to each other, the first part 211 is located in the first straight section 111, and the second part 212 is located in the second bending section 114, which can reduce the risk of brittle fracture of the first pole piece 11 located in the second bending section 114; the third part 221 and the fourth part 222 are connected to each other, the third part 221 is located in the second straight section 113, and the fourth part 222 is located in the first bending section 112, which can reduce the risk of brittle fracture of the first pole piece 11 located in the first bending section 112.

[0123] Please refer to Figure 8 and Fig. 9 In one or more optional embodiments above, the first pole piece 11 includes a single-sided area 115 and a double-sided area 116. The single-sided area 115 is provided with active material only on one side, and the double-sided area 116 is provided with active material on both sides. Along the winding direction J, the single-sided area 115 and the double-sided area 116 are arranged in sequence, the tail end of the adhesive layer 20 is the first end 20a, and the double-sided area 116 includes a second end 116a connected to the single-sided area 115. When the first pole piece 11 is in the unfolded state, along the length direction Y of the first pole piece, the distance between the first end 20a and the second end 116a is D1, satisfying 0≤D1≤2mm.

[0124] The tail end of the adhesive layer 20 refers to an end of the adhesive layer 20 along the winding direction J away from the winding start end P of the first pole piece.

[0125] The single-sided area 115 and the double-sided area 116 are sequentially arranged along the winding direction J, and the second end 116 a is one end of the double-sided area 116 connected to the single-sided area 115 .

[0126] The adhesive layer 20 is disposed in the single-sided region 115 and extends along the winding direction J toward the double-sided region 116 .

[0127] Optionally, D1 may be, but is not limited to, 0, 0.25 mm, 0.5 mm, 0.75 mm, 1 mm, 1.25 mm, 1.5 mm, 1.75 mm, 2 mm, etc.

[0128] When D1 is 0, the end surface of the first end 20 a of the adhesive layer 20 contacts the end surface of the active material in the double-sided region 116 .

[0129] In the above solution, the distance between the first end 20a and the second end 116a satisfies the above relationship, which can reduce the risk of overlapping between the adhesive layer 20 and the active material in the double-sided area 116 and reduce the risk of lithium deposition.

[0130] In one or more of the above embodiments, the thickness of the adhesive layer 20 is 10 μm to 60 μm.

[0131] When the first pole piece 11 is in an unfolded state, the thickness direction of the adhesive layer 20 is parallel to the thickness direction of the first pole piece 11 .

[0132] Optionally, the thickness of the adhesive layer 20 may be, but is not limited to, 10 μm, 15 μm, 20 μm, 25 μm, 30 μm, 35 μm, 40 μm, 45 μm, 50 μm, 55 μm, 60 μm, etc.

[0133] In the above scheme, the thickness direction of the bonding layer 20 is parallel to the thickness direction of the first pole piece 11, and the thickness of the bonding layer 20 satisfies the above relationship, which can not only reduce the probability of deformation of the innermost circle of the first pole piece 11 and improve the pass rate of the narrow surface extrusion test, but also occupy a smaller assembly space and reduce the impact on energy density.

[0134] Please refer to Fig.10 In one or more optional embodiments above, the adhesive layer 20 includes a pressure-sensitive adhesive layer 23, a substrate layer 24 and a hot-melt adhesive layer 25 sequentially distributed along its thickness direction, the hot-melt adhesive layer 25 is connected to the isolation film 13, and the pressure-sensitive adhesive layer 23 is connected to the first pole piece 11.

[0135] The material of the substrate layer 24 may be polyethylene terephthalate;

[0136] The pressure-sensitive adhesive layer 23 may include hydrogenated styrene block copolymer, modified hydrogenated styrene block copolymer, hydrogenated petroleum resin, plasticizer and antioxidant.

[0137] The hot melt adhesive layer 25 includes hydrogenated styrene block copolymer, modified hydrogenated styrene block copolymer, hydrogenated petroleum resin, plasticizer and antioxidant.

[0138] During the manufacturing process of the electrode assembly 10, the pressure-sensitive adhesive layer 23 of the adhesive layer 20 is laminated on the first electrode piece 11 to connect the pressure-sensitive adhesive layer 23 to the first electrode piece 11, and then the first electrode piece 11 laminated with the adhesive layer 20 is fed into the material for winding. After the winding of the electrode assembly 10 is completed, the hot melt adhesive layer 25 of the adhesive layer 20 is connected to the isolation film 13 of the inner circle under high temperature conditions.

[0139] In the above scheme, the pressure-sensitive adhesive layer 23 is connected to the first pole piece 11, and the hot-melt adhesive layer 25 is connected to the isolation membrane 13, which can firmly connect the first pole piece 11 and the isolation membrane 13, improve the inner ring strength of the electrode assembly 10, and reduce the probability of deformation of the electrode assembly 10.

[0140] Please refer to Fig.11 In one or more of the above optional embodiments, along the winding axis direction X of the electrode assembly, the bonding layer 20 exceeds the edge of the first pole piece 11, and the dimension C of the bonding layer 20 exceeding the edge of the first pole piece 11 satisfies 0≤C≤0.75mm.

[0141] The adhesive layer 20 extends beyond the edge of the first pole piece 11 along the winding axis direction X of the electrode assembly so that the adhesive layer 20 and the first pole piece 11 have a larger connection area, so that the adhesive layer 20 completely covers the first pole piece 11 in the winding axis direction X of the electrode assembly.

[0142] Optionally, C may be, but is not limited to, 0, 0.1 mm, 0.15 mm, 0.2 mm, 0.25 mm, 0.3 mm, 0.35 mm, 0.4 mm, 0.45 mm, 0.5 mm, 0.55 mm, 0.6 mm, 0.65 mm, 0.7 mm, 0.75 mm, etc.

[0143] In the above scheme, the size of the adhesive layer 20 beyond the edge of the first pole piece 11 meets the above range, which can completely cover the first pole piece 11 in the winding axis direction X of the electrode assembly to meet the pasting requirements and reduce the impact on the assembly of the secondary battery 100.

[0144] Please refer to Fig.12 In one or more of the above optional embodiments, when the first pole piece 11 is unfolded, along the length direction Y of the first pole piece, the distance between the adhesive layer 20 and the winding starting end P of the first pole piece is D2, satisfying 1mm≤D2≤2mm.

[0145] Along the winding direction J, the first end of the adhesive layer 20 is the third end 20b. When the first pole piece 11 is unfolded, along the length direction Y of the first pole piece, the distance between the third end 20b and the winding starting end P of the first pole piece is D2.

[0146] Optionally, D2 may be, but is not limited to, 1 mm, 1.1 mm, 1.2 mm, 1.3 mm, 1.4 mm, 1.5 mm, 1.6 mm, 1.7 mm, 1.8 mm, 1.9 mm, 2 mm, etc.

[0147] In the above scheme, the distance between the adhesive layer 20 and the winding starting end P of the first pole piece satisfies the above relationship. On the one hand, it is convenient for feeding the first pole piece 11 when the electrode assembly 10 is wound. On the other hand, it can shield the burrs at the winding starting end and improve the safety performance of the secondary battery 100.

[0148] Please refer to Fig.13 In one or more of the above optional embodiments, the first pole piece 11 has a second surface 11b arranged opposite to the first surface 11a, the first pole piece 11 includes a single-sided area 115 and a double-sided area 116, the single-sided area 115 is only provided with active materials on the second surface 11b, and the double-sided area 116 is provided with active materials on both the first surface 11a and the second surface 11b, along the winding direction J, the single-sided area 115 and the double-sided area 116 are arranged in sequence, the isolation film 13 includes a first isolation film 131 and a second isolation film 132, the first isolation film 131 is arranged toward the second surface 11b, and the second isolation film 132 is arranged toward the first surface 11a, at least a portion of the bonding layer 20 is arranged between the single-sided area 115 and the second isolation film 132, and the single-sided area 115 and the second isolation film 132 are bonded by the bonding layer 20.

[0149] The first isolation film 131 and the second isolation film 132 are respectively arranged on both sides of the thickness direction of the first electrode 11. The first isolation film 131 is located on the side of the single-sided area 115 where the active material is arranged, and the second isolation film 132 is located on the side of the single-sided area 115 where the active material layer is not arranged, and the adhesive layer 20 connects the single-sided area 115 and the second isolation film 132.

[0150] The adhesive layer 20 is a double-sided adhesive tape, and both sides of the adhesive layer 20 in the thickness direction are respectively bonded to the single-sided area 115 and the second isolation film 132 .

[0151] In the above scheme, at least part of the bonding layer 20 is arranged between the single-sided area 115 and the second isolation film 132, and the single-sided area 115 and the second isolation film 132 are bonded by the bonding layer 20, so as to improve the strength of the inner circle of the electrode assembly 10, reduce the probability of deformation of the electrode assembly 10, and improve the pass rate of the narrow surface extrusion test.

[0152] In one or more of the above optional embodiments, the winding starting end of the first isolation film 131 and the winding starting end of the second isolation film 132 are both bent structures.

[0153] like Figure 8 As shown, the winding starting ends of the first isolation film 131 and the second isolation film 132 are both bent toward the winding starting end P of the first pole piece, so that the winding starting ends of the first isolation film 131 and the second isolation film 132 form a bent structure.

[0154] In the above solution, the winding starting end of the first isolation film 131 and the winding starting end of the second isolation film 132 are both bent structures, so as to facilitate clamping by the winding needle when the electrode assembly 10 is wound.

[0155] Please refer to Figure 1 and Figure 2 In one or more of the above optional embodiments, the secondary battery 100 further includes a packaging bag 30 , and the electrode assembly 10 is accommodated in the packaging bag 30 .

[0156] The electrode assembly 10 is housed in the packaging bag 30 so that the second battery is a pouch battery.

[0157] The packaging bag 30 may include but is not limited to aluminum-plastic film, aluminum shell, etc.

[0158] In the above solution, the electrode assembly 10 is contained in the packaging bag 30, which can protect the electrode assembly 10, and the wall thickness of the packaging bag 30 can be thinner, so that the secondary battery 100 can have a higher energy density.

[0159] According to some embodiments of the present application, an electrochemical device is further provided, which includes the secondary battery 100 provided in any of the above embodiments.

[0160] According to some embodiments of the present application, an electrical device is further provided, which includes the electrochemical device provided by any of the above embodiments.

[0161] The electrical equipment may be, but is not limited to, mobile phones, smart wearable devices, etc.

[0162] In the embodiments of the present application, a secondary battery (100) is taken as an example and a narrow surface compression test is performed on it.

[0163] Preparation of Secondary Battery 100:

[0164] Example 1

[0165] (1) Preparation of negative electrode sheet: Using graphite as the negative electrode active material, the negative electrode active material graphite, the binder styrene butadiene rubber (SBR) and the thickener sodium carboxymethyl cellulose (CMC) are mixed in a weight ratio of 96:2:2, deionized water is added as a solvent, and a slurry with a solid content of 70wt% is prepared, and stirred evenly. The slurry is evenly coated on one surface of a copper foil with a thickness of 10μm, dried, and a negative electrode sheet with a negative electrode active layer coated on one side is obtained. On the other surface of the copper foil, the above steps are repeated to obtain a negative electrode sheet with a negative electrode active layer coated on both sides. The single-sided area S2 of the negative electrode sheet is 333.5mm 2 .

[0166] (2) Preparation of positive electrode sheet: Mix the positive electrode active materials lithium cobalt oxide (LiCoO2), conductive carbon black (Super P), and polyvinylidene fluoride (PVDF) in a weight ratio of 97.5:1.0:1.5, add N-methylpyrrolidone (NMP) as a solvent, prepare a slurry with a solid content of 75wt%, and stir evenly. The slurry is evenly coated on one surface of an aluminum foil with a thickness of 12μm, dried, and a positive electrode sheet coated with a positive electrode active layer on one side is obtained. Repeat the above steps on the other surface of the aluminum foil to obtain a positive electrode sheet coated with a positive electrode active layer on both sides.

[0167] (3) Preparation of electrolyte: In a dry argon atmosphere, ethylene carbonate (EC), ethyl methyl carbonate (EMC) and diethyl carbonate (DEC) are first mixed in a mass ratio of EC:EMC:DEC=30:50:20 to form a basic organic solvent, and then lithium salt lithium hexafluorophosphate (LiPF6) is added to the basic organic solvent to dissolve and mix evenly to obtain an electrolyte with a LiPF6 mass concentration of 12.5%.

[0168] (4) Preparation of isolation membrane: A polyethylene porous membrane is used as a substrate layer, and a ceramic layer containing alumina ceramics and a PVDF binder is coated on one surface of the substrate layer as a separator (CCS), wherein the mass percentage of alumina ceramics in the ceramic layer is 95%.

[0169] (5) Preparation of adhesive layer: Styrene-isoprene-styrene block copolymer (SIS, weight average molecular weight 100,000), functional resin ethylene-vinyl acetate copolymer (EVA, weight average molecular weight 120,000), additive titanium dioxide, and antioxidant diphenylamine were mixed in a mass ratio of 70:20:5:5, heated to 150°C for hot melting, and then coated on one surface of a substrate layer polyethylene terephthalate film (PET) with a thickness of 8 μm, and then dried at 120°C to form a first adhesive layer with a thickness of 8 μm. Polyacrylic acid (PAA) was coated on the other surface of the substrate layer and dried at 80°C to form a second adhesive layer with a thickness of 4 μm, thereby obtaining an adhesive member comprising a first adhesive layer, a substrate layer, and a second adhesive layer stacked in sequence.

[0170] (6) Preparation of electrode assembly: A nickel sheet and an aluminum sheet with a thickness T of 0.16 mm were selected as metal strips. The aluminum sheet metal strip was welded to the positive electrode sheet (aluminum foil of the positive electrode sheet), and the nickel sheet metal strip was welded to the negative electrode sheet (copper foil of the negative electrode sheet). The adhesive layer was bonded to the negative electrode sheet, and the single-side area S1 covered was 166.8 mm. 2 The positive electrode sheet, the separator and the negative electrode sheet are stacked and wound to form an electrode assembly for use.

[0171] (7) Electrode assembly: Place the aluminum-plastic film with holes punched and formed in an assembly fixture, with the holes facing upward, place the electrode assembly in the holes, and apply external force to press it. Then, cover the electrode assembly with another aluminum-plastic film with holes punched and formed, with the holes facing downward, and heat-seal the two aluminum-plastic films around by hot pressing to obtain an assembled electrode assembly.

[0172] (8) Liquid injection packaging: The assembled electrode assembly is injected with electrolyte, and after vacuum packaging, static, hot pressing, shaping and other processes, a lithium-ion battery is obtained. The length, thickness and width of the lithium-ion battery are 29.3 mm, 7.65 mm and 15.9 mm.

[0173] Example 2

[0174] The difference from Example 1 is that the bonding area S1 is 222.3 mm 2 .

[0175] Example 3

[0176] The difference from Example 1 is that the bonding area S1 is 250.1 mm 2 .

[0177] Example 4

[0178] The difference from Example 1 is that the bonding area S1 is 266.8 mm 2 .

[0179] Example 5

[0180] The difference from Example 1 is that the bonding area S1 is 300.2 mm 2 .

[0181] Example 6

[0182] The difference from Example 1 is that the bonding area S1 is 333.5 mm 2 .

[0183] Example 7

[0184] The difference from Example 1 is that the bonding area S1 is 111.2 mm 2 .

[0185] The method of the narrow face extrusion test mentioned in this application is: in a test environment of 25±5℃, place the secondary battery 100 between two flat plates, with the narrow face of the secondary battery 100 parallel to the two flat plates, apply an extrusion force of 13±1KN, and the extrusion speed is 15mm / s, and terminate when one of the following conditions is met: 1) the extrusion force reaches the set value of 13±1KN; 2) the voltage drop reaches 100mv; 3) the cell deformation rate>50%. During the test, if the secondary battery 100 does not catch fire or explode, it means that the narrow face extrusion test of the secondary battery 100 has passed.

[0186] The secondary batteries 100 of the above-mentioned embodiments 1 to 7 were subjected to narrow surface compression tests, and specific test data are shown in the following table:

[0187] Table 1

[0188]

[0189]

[0190] According to Table 1 above, combined with Examples 1 to 7, it can be seen that if S1 / S2 is too small, the connection area between the adhesive layer and the first single-sided area is too small, the strength of the first single-sided area is insufficient, and it is difficult to resist the deformation of the electrode assembly; if S1 / S2 is too large, the energy density is lost. Therefore, in the embodiments of the present application, S1 / S2 can be selected to be 1 / 2 to 1, preferably 2 / 3 to 1, so as to reduce the probability of deformation of the electrode assembly and effectively improve the narrow surface extrusion pass rate of the lithium-ion battery.

[0191] Although the present application has been described with reference to preferred embodiments, various modifications may be made thereto and parts thereof may be replaced with equivalents without departing from the scope of the present application. In particular, the various technical features mentioned in the various embodiments may be combined in any manner as long as there are no structural conflicts. The present application is not limited to the specific embodiments disclosed herein, but includes all technical solutions falling within the scope of the claims.

Claims

1. A secondary battery, characterized in that: The invention comprises an electrode assembly, wherein the electrode assembly is a flat winding structure, the electrode assembly comprises a first pole piece, a second pole piece and a separator, the separator is arranged between the first pole piece and the second pole piece, and the innermost pole piece of the electrode assembly is the first pole piece; Among them, the length of the electrode assembly is L, the width of the electrode assembly is W, and the thickness of the electrode assembly is H, satisfying 0.9≤L / W≤1.1, H≤3mm, the electrode assembly also includes an adhesive layer, the innermost circle of the first pole piece includes a first straight section, a first bent section, a second straight section and a second bent section connected in sequence, the first pole piece has a first surface facing the winding core of the electrode assembly, and at least a portion of the adhesive layer is arranged on the first surface of the first straight section and / or the first surface of the second straight section.

2. The secondary battery according to claim 1, characterized in that: The first pole piece has a second surface arranged opposite to the first surface, and the first pole piece includes a single-sided area and a double-sided area. The single-sided area is only provided with active materials on the second surface, and the double-sided area is provided with active materials on both the first surface and the second surface. Along the winding direction, the single-sided area and the double-sided area are arranged in sequence, and the single-sided area includes a first single-sided area, and the first single-sided area is located at the innermost circle of the first pole piece. At least part of the bonding layer is arranged on the first surface of the first single-sided area.

3. The secondary battery according to claim 2, characterized in that: The area of ​​the first single-sided region covered by the adhesive layer is S1, the area of ​​the first single-sided region is S2, and 1 / 2≤S1 / S2≤1.

4. The secondary battery according to claim 3, characterized in that: 2 / 3≤S1 / S2≤1.

5. The secondary battery according to claim 1, characterized in that: Along the thickness direction of the electrode assembly, the orthographic projection of the adhesive layer covers the entire second straight segment.

6. The secondary battery according to claim 5, characterized in that: A portion of the adhesive layer is disposed on the first bending section and / or the second bending section.

7. The secondary battery according to claim 5, characterized in that: At least part of the adhesive layer is disposed on the first straight section, the first bent section, the second straight section, and the second bent section.

8. The secondary battery according to claim 5, characterized in that: The adhesive layer includes a first sub-adhesive layer and a second sub-adhesive layer spaced apart along a winding direction, at least a portion of the first sub-adhesive layer is disposed in the first straight segment, and at least a portion of the second sub-adhesive layer is disposed in the second straight segment.

9. The secondary battery according to claim 8, characterized in that: Along the thickness direction of the electrode assembly, an orthographic projection of the first sub-adhesive layer and an orthographic projection of the second sub-adhesive layer have an overlapping area.

10. The secondary battery according to claim 8, characterized in that: The first sub-adhesive layer comprises a first part and a second part connected to each other, the first part is arranged in the first straight section, and the second part is arranged in the second bending section; The second sub-adhesive layer includes a third portion and a fourth portion connected to each other, the third portion is arranged at the second straight section, and the fourth portion is arranged at the first bending section.

11. The secondary battery according to claim 1, characterized in that: The first pole piece includes a single-sided area and a double-sided area, the single-sided area is provided with active material only on one side, and the double-sided area is provided with active material on both sides, along the winding direction, the single-sided area and the double-sided area are arranged in sequence, the tail end of the adhesive layer is the first end, and the double-sided area includes a second end connected to the single-sided area. In the unfolded state of the first pole piece, along the length direction of the first pole piece, the distance between the first end and the second end is D1, satisfying 0≤D1≤2mm.

12. The secondary battery according to claim 1, characterized in that: The thickness of the adhesive layer is 10 μm to 60 μm.

13. The secondary battery according to claim 1, characterized in that: The adhesive layer includes a pressure-sensitive adhesive layer, a substrate layer and a hot-melt adhesive layer which are sequentially distributed along the thickness direction thereof. The hot-melt adhesive layer is connected to the isolation film, and the pressure-sensitive adhesive layer is connected to the first pole piece.

14. The secondary battery according to claim 1, characterized in that: Along the winding axis direction of the electrode assembly, the adhesive layer exceeds the edge of the first pole piece, and a dimension C of the adhesive layer exceeding the edge of the first pole piece satisfies 0≤C≤0.75mm.

15. The secondary battery according to claim 1, characterized in that: When the first pole piece is unfolded, along the length direction of the first pole piece, the distance between the adhesive layer and the winding start end of the first pole piece is D2, which satisfies 1mm≤D2≤2mm.

16. The secondary battery according to claim 1, characterized in that: The first pole piece has a second surface arranged opposite to the first surface, the first pole piece includes a single-sided area and a double-sided area, the single-sided area is provided with active material only on the second surface, and the double-sided area is provided with active material on both the first surface and the second surface, along the winding direction, the single-sided area and the double-sided area are arranged in sequence, the isolation film includes a first isolation film and a second isolation film, the first isolation film is arranged toward the second surface, and the second isolation film is arranged toward the first surface, at least part of the bonding layer is arranged between the single-sided area and the second isolation film, and the single-sided area and the second isolation film are bonded by the bonding layer.

17. The secondary battery according to claim 16, characterized in that: The winding starting end of the first isolation film and the winding starting end of the second isolation film are both bent structures.

18. The secondary battery according to claim 1, characterized in that: L≥65mm, W≥65mm.

19. An electrochemical device, characterized in that: Comprising the secondary battery according to any one of claims 1 to 18.

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