Secondary battery and electrochemical device

Abstract

Provided in embodiments of the present application are a secondary battery and an electrochemical device. The secondary battery comprises an electrode assembly, the electrode assembly being a flat winding-type structure. The electrode assembly comprises a first electrode sheet, a second electrode sheet and a separator, the separator being arranged between the first electrode sheet and the second electrode sheet, and the innermost electrode sheet of the electrode assembly being the first electrode sheet. The length L of the electrode assembly, the width W of the electrode assembly, and the thickness H of the electrode assembly satisfy 0.9 ≤ L / W ≤ 1.1, H ≤ 3 mm. The electrode assembly further comprises an adhesive layer. The innermost race of the first electrode sheet comprises, successively connected to each other, a first straight section, a first bent section, a second straight section, and a second bent section. The first electrode sheet is provided with a first surface facing a jellyroll core of the electrode assembly. At least part of the adhesive layer is arranged on a first surface of the first straight section and / or a first surface of the second straight section. The technical solution provided in the embodiments of the present application can improve the safety performance and the cycle performance of secondary batteries.

Description

Secondary batteries and electrochemical devices CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to Chinese patent application CN2023115314570, entitled “Secondary Batteries and Electrochemical Devices,” filed on November 16, 2023, the entire contents of which are incorporated herein by reference. Technical Field

[0002] The present application relates to the technical field of secondary batteries, and in particular to a secondary battery and an electrochemical device. Background Art

[0003] During the winding manufacturing process, the electrode assembly's pole pieces are typically required to remain flat to prevent lithium deposition caused by uneven thickness, or uneven stress on the left and right sides of wide, thin electrode assemblies, which can lead to large expansion during cycling. However, in actual production, the innermost area of ​​the anode pole piece is prone to curling after feeding, and wide, thin electrode assemblies are prone to deformation. This phenomenon not only creates serious cosmetic issues but also causes uneven thickness and interface of the electrode assembly, impacting the safety and cycling performance of the secondary battery.

[0004] 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 electrode sheet and the isolation membrane in the electrode assembly with a soft-pack wound structure, short-circuit failures at the sharp corners of the cathode and cathode will occur preferentially at the innermost anode electrode sheet and the wrapped cathode electrode sheet during the narrow-surface extrusion process of the secondary battery, which will affect the yield rate. Summary of the Invention

[0005] The present application provides a secondary battery and an electrochemical device, which can improve the safety performance and cycle performance of the secondary battery.

[0006] This application is achieved through the following technical solutions:

[0007] In a first aspect, an embodiment of the present application provides a secondary battery, which includes an electrode assembly, the electrode assembly is a flat wound structure, the electrode assembly includes a first electrode sheet, a second electrode sheet and a separator, the separator 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.

[0008] 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.

[0009] In one or more optional embodiments above, the first electrode has a second surface arranged opposite to the first surface, and the first electrode 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 electrode, and at least part of the adhesive layer is arranged on the first surface of the first single-sided area.

[0010] In the above scheme, the first single-sided area is located in the innermost circle of the first electrode 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 electrode piece in the first single-sided area, but also be bonded to 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 circuit of the anode and cathode electrodes in the inner circle of the electrode assembly due to narrow surface extrusion.

[0011] In one or more optional embodiments above, 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.

[0012] In the above scheme, the ratio of the area of ​​the first single-sided 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.

[0013] In one or more of the above optional embodiments, 2 / 3≤S1 / S2≤1.

[0014] 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.

[0015] 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.

[0016] 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 higher strength, which can improve the pass rate of the narrow surface extrusion test.

[0017] In one or more of the above optional embodiments, a portion of the adhesive layer is disposed on the first bending section and / or the second bending section.

[0018] 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.

[0019] In one or more of the above optional embodiments, at least part of the adhesive layer is provided on the first straight section, the first bent section, the second straight section and the second bent section.

[0020] In the above scheme, the adhesive 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 electrode, effectively reduce the probability of deformation of the electrode assembly, and improve the pass rate of the narrow surface extrusion test.

[0021] In one or more optional embodiments above, the adhesive layer includes a first sub-adhesive layer and a second sub-adhesive layer arranged at intervals along the winding direction, at least a portion of the first sub-adhesive layer is arranged in the first straight segment, and at least a portion of the second sub-adhesive layer is arranged in the second straight segment.

[0022] 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.

[0023] 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.

[0024] In the above solution, 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.

[0025] In one or more optional embodiments above, 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.

[0026] 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.

[0027] In one or more optional embodiments above, 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. When the first pole piece is unfolded, the distance between the first end and the second end along the length direction of the first pole piece is D1, satisfying 0≤D1≤2mm.

[0028] In the above solution, the distance between the first end and the second end satisfies the above relationship, which can reduce the risk of overlap between the adhesive layer and the active material in the double-sided area and reduce the risk of lithium plating.

[0029] In one or more of the above optional embodiments, the thickness of the adhesive layer is 10 μm to 60 μm.

[0030] 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.

[0031] 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.

[0032] In the above solution, 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.

[0033] In one or more optional embodiments above, along the winding axis direction of the electrode assembly, the adhesive layer extends beyond the edge of the first electrode sheet, and a dimension C of the adhesive layer extending beyond the edge of the first electrode sheet satisfies 0≤C≤0.75mm.

[0034] In the above solution, the size of the adhesive layer exceeding the edge of the first electrode sheet meets the above range, which can completely cover the first electrode sheet in the winding axis direction of the electrode assembly to meet the pasting requirements and reduce the impact on the assembly of the secondary battery.

[0035] In one or more optional embodiments above, 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 starting end of the first pole piece is D2, satisfying 1mm≤D2≤2mm.

[0036] In the above scheme, the distance between the adhesive layer and the winding starting end of the first electrode sheet satisfies the above relationship. On the one hand, it facilitates the feeding of the first electrode sheet 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.

[0037] In one or more optional embodiments above, the first electrode has a second surface arranged opposite to the first surface, the first electrode includes a single-sided area and a double-sided area, the single-sided area has active substances only on the second surface, and the double-sided area has active substances 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 adhesive 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 adhesive layer.

[0038] 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 ring of the electrode assembly, reduce the probability of deformation of the electrode assembly, and improve the pass rate of the narrow surface extrusion test.

[0039] 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.

[0040] In the above solution, the winding starting end of the first separator and the winding starting end of the second separator are both bent structures, so as to facilitate clamping by the winding needle when the electrode assembly is wound.

[0041] 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.

[0042] In the above solution, the electrode assembly is housed in the packaging bag, which can protect the electrode assembly. In addition, the wall thickness of the packaging bag can be thinner, so that the secondary battery can have a higher energy density.

[0043] In one or more of the above optional embodiments, L≥65mm, W≥65mm.

[0044] In the above solution, when L≥65mm and W≥65mm, the electrode assembly is a wide and thin electrode assembly. 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.

[0045] In a second aspect, an embodiment of the present application provides an electrochemical device, which includes the secondary battery provided by any of the above embodiments.

[0046] Additional aspects and advantages of the present application will be given in part in the description below, and in part will become obvious from the description below, or will be learned through practice of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following is a brief introduction to the drawings required for use in the embodiments. 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 relevant drawings can be obtained based on these drawings without creative work.

[0048] FIG1 is a schematic structural diagram of a secondary battery provided in some embodiments of the present application;

[0049] FIG2 is a bottom view of the secondary battery shown in FIG1 ;

[0050] FIG3 is a schematic structural diagram of an electrode assembly provided in some embodiments of the present application;

[0051] FIG4 is a schematic structural diagram of an electrode assembly provided in some other embodiments of the present application;

[0052] FIG5 is a schematic structural diagram of an electrode assembly provided in yet other embodiments of the present application;

[0053] FIG6 is a schematic structural diagram of an electrode assembly provided in yet other embodiments of the present application;

[0054] FIG7 is a schematic structural diagram of an electrode assembly provided in yet other embodiments of the present application;

[0055] FIG8 is a schematic structural diagram of an electrode assembly provided in yet other embodiments of the present application;

[0056] FIG9 is a schematic diagram of the adhesive layer and the single-sided area in the unfolded state of the first pole piece provided by some embodiments of the present application;

[0057] FIG10 is a schematic structural diagram of an adhesive layer provided in some embodiments of the present application;

[0058] FIG11 is a schematic diagram of the assembly of the adhesive layer and the first pole piece provided in some embodiments of the present application;

[0059] FIG12 is a schematic structural diagram of the adhesive layer and the winding starting end of the first electrode sheet in the unfolded state provided by other embodiments of the present application;

[0060] FIG13 is a partial enlarged view of point A in FIG8 .

[0061] Icon: 100-secondary battery; 10-electrode assembly; 10a-flat 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 membrane; 131-first isolating membrane; 132-second isolating membrane 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-base material 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

[0062] 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.

[0063] Unless otherwise defined, all technical and scientific terms used in this application have the same meanings as commonly understood by those skilled in the art to which this application belongs. 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" and any variations thereof in the specification and claims of this application and the above-mentioned drawings are intended to cover non-exclusive inclusions. The terms "first" and "second" 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-secondary relationship.

[0064] References to "embodiments" in this application mean that a particular feature, structure, or characteristic described in connection with the embodiment may be included in at least one embodiment of the application. The appearance of this phrase in various places in the specification does not necessarily refer to the same embodiment, nor does it constitute an independent or alternative embodiment that is mutually exclusive of other embodiments. It is understood, both explicitly and implicitly, by those skilled in the art that the embodiments described in this application may be combined with other embodiments.

[0065] In the description of this application, it should be noted that, unless otherwise expressly specified or limited, the terms "mounted," "connected," "connected," and "attached" should be understood in a broad sense. For example, they may refer to fixed connections, detachable connections, or integral connections; they may refer to direct connections, indirect connections through an intermediate medium, or internal connections between two components. Those skilled in the art will understand the specific meanings of the above terms in this application based on specific circumstances.

[0066] The term "and / or" in this application simply describes an association between related objects, indicating that three possible relationships exist. For example, A and / or B can represent: A exists alone, A and B exist simultaneously, and B exists alone. In addition, the character " / " in this application generally indicates that the related objects are in an "or" relationship.

[0067] The term "multiple" in this application refers to more than two (including two). Similarly, "multiple groups" refers to more than two groups (including two groups), and "multiple pieces" refers to more than two pieces (including two pieces).

[0068] When the electrode assembly has a flat, wound structure, the secondary battery needs to undergo a narrow-surface extrusion test during its manufacturing process. However, for the wide, thin electrode assembly of soft-pack secondary batteries, the innermost anode electrode sheet is prone to brittle fracture during the narrow-surface extrusion process, resulting in a short circuit between the cathode and anode electrodes. This results in a low pass rate for the narrow-surface extrusion test, affecting the safety and cycling performance of the secondary battery.

[0069] The structure of the secondary battery provided by the embodiments of the present application will be described below with reference to the accompanying drawings.

[0070] 1 to 5 , an embodiment of the present application provides a secondary battery 100 , which includes an electrode assembly 10 . The electrode assembly 10 is a flat, wound structure.

[0071] 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 both ends of the straight area 10 a .

[0072] The electrode assembly 10 includes a first electrode piece 11 , a second electrode piece 12 and an isolation membrane 13 . The isolation membrane 13 is disposed between the first electrode piece 11 and the second electrode piece 12 . The innermost electrode piece of the electrode assembly 10 is the first electrode piece 11 .

[0073] 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, and H≤3 mm.

[0074] 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 facing the winding core of the electrode assembly 10, and 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.

[0075] 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.

[0076] The innermost electrode of the electrode assembly 10 refers to the electrode closest to the winding core among the electrode sheets constituting the electrode assembly 10 .

[0077] The first electrode 11 and the second electrode 12 have opposite polarities. The first electrode 11 may be an anode electrode, and correspondingly, the second electrode 12 may be a cathode electrode.

[0078] The isolation film 13 is disposed between the first pole piece 11 and the second pole piece 12 to insulate and isolate the first pole piece 11 from the second pole piece 12 .

[0079] The length L, width W and thickness H of the electrode assembly 10 satisfy 0.9≤L / W≤1.1, and H≤3 mm, so that the electrode assembly 10 has a wide and thin structure. The secondary battery 100 formed by the electrode assembly 10 is a wide and thin battery.

[0080] In some embodiments, L ≥ 65 mm, W ≥ 65 mm.

[0081] The innermost circle of the first pole piece 11 refers to a structure formed from the winding starting end P of the first pole piece and along the winding direction J of the first pole piece 11 to a point aligned with the winding starting end.

[0082] Since the electrode assembly 10 is a flat winding structure, the winding starting end P of the first electrode sheet 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, and 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. The other end of the second section is aligned with the winding starting end P of the first electrode sheet in the thickness direction Z of the electrode assembly.

[0083] 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 piece 11 are firmly connected.

[0084] “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.

[0085] The provision of the adhesive layer 20 can increase the strength of the first straight section 111 and / or the second straight section 113 .

[0086] 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.

[0087] According to the secondary battery 100 of the embodiment of the present application, the first electrode piece 11 is the innermost electrode piece. The bonding layer 20 is arranged on the straight section of the innermost circle of the first electrode piece 11, which can increase the strength of the innermost circle of the first electrode 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.

[0088] Please refer to Figures 3 to 5. In one or more optional embodiments above, the first electrode 11 has a second surface 11b arranged opposite to the first surface 11a. The first electrode 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 single-sided area 115 includes a first single-sided area 115a, and the first single-sided area 115a is located at the innermost circle of the first electrode 11. At least part of the adhesive layer 20 is provided on the first surface 11a of the first single-sided area 115a.

[0089] The single-sided region 115 is a region where active material is provided on only one side of the first electrode sheet 11 in the thickness direction, and the double-sided region 116 is a region where active material is provided on both sides of the first electrode sheet 11 in the thickness direction.

[0090] 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 starting end than the double-sided area 116.

[0091] The first single-sided area 115 a is located at the innermost circle of the first pole piece 11 . Alternatively, a portion of the single-sided area 115 a may be located at the innermost circle of the first pole piece 11 , or the entire single-sided area 115 may be located at the innermost circle of the first pole piece 11 .

[0092] A portion of the adhesive layer 20 may be provided in the first single-sided region 115 a , or the entire adhesive layer 20 may be provided in the first single-sided region 115 a .

[0093] For example, when the area near the winding start end of the first electrode sheet 11 includes a hollow foil area, the hollow foil area, the single-sided area 115, and the double-sided area 116 are sequentially distributed along the winding direction J. A portion of the adhesive layer 20 can be located in the hollow foil area, and another portion can be provided in the single-sided area 115. Alternatively, when the area near the winding start end of the first electrode sheet 11 does not have a hollow foil area, the entire adhesive layer 20 can be provided in the single-sided area 115.

[0094] In the above scheme, the first single-sided area 115a is located in the innermost circle of the first electrode 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 electrode piece 11 in the first single-sided area 115a, but also be bonded to 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 circuit of the anode and cathode electrodes in the inner circle of the electrode assembly 10 due to narrow surface extrusion.

[0095] 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.

[0096] 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.

[0097] 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.

[0098] In one or more of the above optional embodiments, 2 / 3≤S1 / S2≤1.

[0099] In the above solution, when 2 / 3≤S1 / S2≤1, the strength of the first single-sided area 115a can be improved, and the probability of deformation of the electrode assembly 10 can be reduced.

[0100] 5 , and further referring to FIG. 6 and FIG. 7 , in one or more of the above optional embodiments, along the thickness direction Z of the electrode assembly, the orthographic projection of the adhesive layer 20 covers the entire second straight section 113 .

[0101] The orthographic projection of the adhesive layer 20 covers the entire second straight section 113 . The adhesive layer 20 may be arranged in 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 provided on the first straight section 111 and the second straight section 113, the adhesive layer 20 located in the first straight section 111 may cover part of the first straight section 111, and the adhesive layer 20 located in the second straight section 113 may cover part of the second straight section 113; alternatively, the adhesive layer 20 located in the first straight section 111 may cover the entire first straight section 111, and the adhesive layer 20 located in the second straight section 113 may cover part of the second straight section 113; alternatively, the adhesive layer 20 located in the first straight section 111 may cover part of the first straight section 111, and the adhesive layer 20 located in the second straight section 113 may cover the entire second straight section 113; alternatively, the adhesive layer 20 located in the first straight section 111 may cover the entire first straight section 111, and the adhesive layer 20 located in the second straight section 113 may cover the entire second straight section 113.

[0102] 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 higher strength, which can improve the pass rate of the narrow surface extrusion test.

[0103] 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 section 112 and / or the second bending section 114 .

[0104] 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 .

[0105] 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 .

[0106] 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 .

[0107] 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.

[0108] Referring to FIG. 5 , in one or more optional embodiments above, at least a portion 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 .

[0109] The adhesive layer 20 may be a continuous structure, and may be sequentially arranged 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 arranged on the entire innermost circle of the first pole piece 11 .

[0110] In some embodiments, a portion of the adhesive layer 20 may be disposed on the innermost circle of the first pole piece 11 , and another portion of the adhesive layer 20 may be disposed on the second inner circle of the first pole piece 11 .

[0111] 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 electrode piece 11, effectively reduce the probability of deformation of the electrode assembly 10, and improve the pass rate of the narrow surface extrusion test.

[0112] Please refer to Figures 6 and 7. In one or more optional embodiments above, 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.

[0113] The first sub-adhesive layer 21 and the second sub-adhesive layer 22 are spaced apart from each other along the winding direction J. The first sub-adhesive layer 21 and the second sub-adhesive layer 22 are two independent parts.

[0114] At least a portion of the first sub-adhesive layer 21 is arranged in the first straight section 111. It can be that a portion of the first sub-adhesive layer 21 is arranged in the first straight section 111, and another portion is arranged in the first bending section 112 and / or the second bending section 114; or, the entire first sub-adhesive layer 21 is arranged in the first straight section 111.

[0115] At least a portion of the second sub-adhesive layer 22 is arranged in the second straight section 113. It can be that a portion of the second sub-adhesive layer 22 is arranged in the second straight section 113, and another portion is arranged in the first bending section 112 and / or the second bending section 114; or, the entire second sub-adhesive layer 22 is arranged in the second straight section 113.

[0116] 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.

[0117] 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.

[0118] “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 viewed 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.

[0119] 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.

[0120] Please refer to Figure 7. In one or more optional embodiments above, 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.

[0121] 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.

[0122] The third portion 221 and the fourth portion 222 are two portions of the second sub-adhesive layer 22 distributed sequentially along the winding direction J.

[0123] 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.

[0124] Please refer to Figures 8 and 9. In one or more optional embodiments above, the first electrode sheet 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 electrode sheet 11 is in the unfolded state, along the length direction Y of the first electrode sheet, the distance between the first end 20a and the second end 116a is D1, satisfying 0≤D1≤2mm.

[0125] 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 starting end P of the first pole piece.

[0126] 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 .

[0127] 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 .

[0128] 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.

[0129] 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 .

[0130] 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 overlap between the adhesive layer 20 and the active material in the double-sided area 116 and reduce the risk of lithium plating.

[0131] In one or more of the above embodiments, the thickness of the adhesive layer 20 is 10 μm to 60 μm.

[0132] 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 .

[0133] 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.

[0134] In the above scheme, the thickness direction of the adhesive layer 20 is parallel to the thickness direction of the first pole piece 11, and the thickness of the adhesive 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.

[0135] Please refer to Figure 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 distributed in sequence 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 electrode 11.

[0136] The material of the substrate layer 24 can be polyethylene terephthalate;

[0137] The pressure-sensitive adhesive layer 23 may include hydrogenated styrene block copolymer, modified hydrogenated styrene block copolymer, hydrogenated petroleum resin, plasticizer, and antioxidant.

[0138] The hot melt adhesive layer 25 includes hydrogenated styrene block copolymer, modified hydrogenated styrene block copolymer, hydrogenated petroleum resin, plasticizer and antioxidant.

[0139] During the manufacturing process of the electrode assembly 10, the pressure-sensitive adhesive layer 23 of the adhesive layer 20 is coated 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 coated 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.

[0140] In the above scheme, the pressure-sensitive adhesive layer 23 is connected to the first electrode piece 11, and the hot-melt adhesive layer 25 is connected to the isolation membrane 13, which can firmly connect the first electrode 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.

[0141] Please refer to Figure 11. In one or more optional embodiments above, along the winding axis direction X of the electrode assembly, the adhesive layer 20 extends beyond the edge of the first electrode sheet 11, and the dimension C of the adhesive layer 20 extending beyond the edge of the first electrode sheet 11 satisfies 0≤C≤0.75mm.

[0142] The adhesive layer 20 extends beyond the edge of the first electrode sheet 11 along the winding axis direction X of the electrode assembly, so that the adhesive layer 20 and the first electrode sheet 11 have a larger connection area, so that the adhesive layer 20 completely covers the first electrode sheet 11 in the winding axis direction X of the electrode assembly.

[0143] Alternatively, 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.

[0144] In the above solution, the size of the adhesive layer 20 exceeding the edge of the first electrode sheet 11 meets the above range, which can completely cover the first electrode sheet 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.

[0145] 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 1 mm ≤ D2 ≤ 2 mm.

[0146] 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.

[0147] 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.

[0148] In the above scheme, the distance between the adhesive layer 20 and the winding starting end P of the first electrode sheet satisfies the above relationship. On the one hand, it facilitates the feeding of the first electrode sheet 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.

[0149] Please refer to Figure 13. In one or more optional embodiments above, the first electrode 11 has a second surface 11b arranged opposite to the first surface 11a. The first electrode 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 part of the adhesive 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 adhesive layer 20.

[0150] The first isolation film 131 and the second isolation film 132 are respectively disposed 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 region 115 where the active material layer is disposed, and the second isolation film 132 is located on the side of the single-sided region 115 where the active material layer is not disposed. The adhesive layer 20 connects the single-sided region 115 and the second isolation film 132.

[0151] The adhesive layer 20 is a double-sided adhesive tape, and both sides of the adhesive layer 20 in the thickness direction are bonded to the single-sided area 115 and the second isolation film 132 respectively.

[0152] 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 ring 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.

[0153] 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.

[0154] As shown in FIG8 , the winding starting end of the first isolation film 131 and the winding starting end of the second isolation film 132 are both bent toward the winding starting end P of the first pole piece, so that the winding starting end of the first isolation film 131 and the winding starting end of the second isolation film 132 form a bent structure.

[0155] In the above solution, the winding starting ends of the first separator 131 and the second separator 132 are both bent structures, so as to facilitate clamping by the winding needle when the electrode assembly 10 is wound.

[0156] 1 and 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 .

[0157] The electrode assembly 10 is housed in the packaging bag 30 so that the second battery is a pouch battery.

[0158] The packaging bag 30 may include but is not limited to aluminum-plastic film, aluminum shell, etc.

[0159] 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 relatively thin, so that the secondary battery 100 can have a higher energy density.

[0160] 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.

[0161] 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.

[0162] Electrical devices may include but are not limited to mobile phones, smart wearable devices, etc.

[0163] In the embodiments of the present application, a secondary battery (100) is taken as an example and a narrow surface extrusion test is performed on it.

[0164] Preparation of Secondary Battery 100:

[0165] Example 1

[0166] (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 .

[0167] (2) Preparation of positive electrode sheet: The positive electrode active material lithium cobalt oxide (LiCoO2), conductive carbon black (Super P), and polyvinylidene fluoride (PVDF) are mixed in a weight ratio of 97.5:1.0:1.5, and N-methylpyrrolidone (NMP) is added as a solvent to prepare a slurry with a solid content of 75wt%, and stirred evenly. The slurry is evenly coated on one surface of an aluminum foil with a thickness of 12μm and dried to obtain a positive electrode sheet coated with a positive electrode active layer on one side. 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 layer on both sides.

[0168] (3) Preparation of electrolyte: In a dry argon atmosphere, ethylene carbonate (EC), ethyl methyl carbonate (EMC) and diethyl carbonate (DEC) were first mixed in a mass ratio of EC:EMC:DEC = 30:50:20 to form a basic organic solvent. Then, lithium salt lithium hexafluorophosphate (LiPF6) was added to the basic organic solvent to dissolve and mix evenly to obtain an electrolyte with a LiPF6 mass concentration of 12.5%.

[0169] (4) Preparation of isolation membrane: A polyethylene porous membrane is used as a substrate layer, and a ceramic layer containing alumina ceramic and PVDF binder is coated on one surface of the substrate layer as a separator (CCS), wherein the mass percentage of alumina ceramic in the ceramic layer is 95%.

[0170] (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 uniformly 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 component comprising a first adhesive layer, a substrate layer, and a second adhesive layer stacked in sequence.

[0171] (6) Preparation of electrode assembly: nickel sheets and aluminum sheets 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.

[0172] (7) Electrode assembly: Place the aluminum-plastic film with the cavities formed in the assembly fixture with the cavities facing upwards, place the electrode assembly in the cavities, and apply external force to compress. Then, place another aluminum-plastic film with the cavities formed in the cavities facing downwards over the electrode assembly. Heat-seal the two aluminum-plastic films around the edges using hot pressing to obtain an assembled electrode assembly.

[0173] (8) Liquid injection and packaging: The electrolyte is injected into the assembled electrode assembly, and after vacuum packaging, static standing, hot pressing, shaping and other processes, a lithium-ion battery is obtained. The length, thickness and width of the lithium-ion battery are 29.3mm, 7.65mm and 15.9mm.

[0174] Example 2

[0175] The difference from Example 1 is that the bonding area S1 is 222.3 mm 2 .

[0176] Example 3

[0177] The difference from Example 1 is that the bonding area S1 is 250.1 mm 2 .

[0178] Example 4

[0179] The difference from Example 1 is that the bonding area S1 is 266.8 mm 2 .

[0180] Example 5

[0181] The difference from Example 1 is that the bonding area S1 is 300.2 mm 2 .

[0182] Example 6

[0183] The difference from Example 1 is that the bonding area S1 is 333.5 mm 2 .

[0184] Example 7

[0185] The difference from Example 1 is that the bonding area S1 is 111.2 mm 2 .

[0186] The narrow-side squeeze test method mentioned in this application is as follows: In a test environment at 25±5°C, the secondary battery 100 is placed between two flat plates with its narrow side parallel to the plates. A squeeze force of 13±1 kN is applied at a speed of 15 mm / s. The test is terminated when one of the following conditions is met: 1) the squeeze force reaches the set value of 13±1 kN; 2) the voltage drop reaches 100 mV; or 3) the cell deformation rate exceeds 50%. If the secondary battery 100 does not catch fire or explode during the test, it indicates that the secondary battery 100 has passed the narrow-side squeeze test.

[0187] The secondary batteries 100 of Examples 1 to 7 were subjected to narrow surface compression tests. Specific test data are shown in the following table:

[0188] Table 1

[0189] 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 deformation of the electrode assembly; if S1 / S2 is too large, 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, to reduce the probability of electrode assembly deformation and effectively improve the narrow-side extrusion pass rate of lithium-ion batteries.

[0190] Although the present application has been described with reference to preferred embodiments, various modifications may be made thereto and components may be substituted with equivalents without departing from the scope of the present application. In particular, the various technical features described 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 encompasses all technical solutions 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.

Images