Secondary battery and electronic device

Abstract

A secondary battery and an electronic device. The secondary battery includes a packaging bag, an electrode assembly, and a first adhesive. The first pole piece and the second pole piece of the electrode assembly are stacked and wound. The first pole piece comprises a first current collector and a first active material layer. The first current collector includes a first surface and a second surface, the first surface facing the winding center axis. The first active material layer comprises a first sub-layer arranged on the first surface and a second sub-layer arranged on the second surface. The first current collector includes a first ending region in the winding direction. The first ending area is exposed on the first sub-layer and the second sub-layer and located at the last fold in the winding direction. The first ending area comprises a third edge, and the third edge is an ending edge of the electrode assembly. The first bonding piece is bonded with the surface, facing the electrode assembly, of the packaging bag, the surface, facing the packaging bag, of the first ending area and the third edge. Observed along the second direction, the edge, arranged along the width direction, of the first pole piece is overlapped with the first bonding piece.

Description

Technical Field

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

[0002] With the popularity of consumer electronic products such as laptops, mobile phones, handheld game consoles, tablets, mobile power supplies and drones, people have increasingly stringent requirements on the safety performance and service life of secondary batteries.

[0003] Soft-pack secondary batteries usually include a packaging bag and an electrode assembly arranged in the packaging bag. In the related art, the electrode assembly is a winding structure and uses a current collector as the end. In order to reduce the risk of the positive and negative electrodes being in contact and short-circuited due to the wrinkling or shrinkage of the separator due to the action of free electrolyte during mechanical abuse (such as falling, collision, etc.), a glue wrap is usually arranged at the head and tail of the electrode assembly to fix the edge of the separator. However, in some cases, there may not be enough space for the head or tail of the electrode assembly to set the glue wrap. If the glue wrap is omitted, the separator (especially the outer layers of the separator) will wrinkle or shrink during mechanical abuse. The end of the current collector will shake due to the loss of restraint and short-circuit with the inner electrode, thereby reducing the safety performance and service life of the secondary battery. Summary of the invention

[0004] In view of this, it is necessary to provide a secondary battery with improved safety performance and service life.

[0005] In addition, it is also necessary to provide an electronic device having the secondary battery.

[0006] In a first aspect, the present application provides a secondary battery, comprising a packaging bag, an electrode assembly and a first adhesive. The electrode assembly is arranged in the packaging bag. The electrode assembly comprises a first electrode sheet and a second electrode sheet, which are stacked and wound. The first electrode sheet comprises a first current collector and a first active material layer. The first current collector comprises a first surface and a second surface opposite to each other along the thickness direction of the first current collector, the first surface faces the winding center axis, and the second surface faces away from the winding center axis. The first active material layer comprises a first sublayer arranged on the first surface and a second sublayer arranged on the second surface. The first current collector comprises a first tailing region in the winding direction. The first tailing region is exposed to the first sublayer and the second sublayer and is located at the last fold of the first current collector in the winding direction. The first tailing region comprises a third edge, which is the tailing edge of the electrode assembly. The first adhesive adheres to at least a portion of the surface of the first tailing region facing the packaging bag and the third edge, and the first adhesive crosses the third edge in the winding direction and adheres to a portion of the second surface. The width direction of the first pole piece is the first direction, the thickness direction of the electrode assembly is the second direction, the first direction and the second direction are perpendicular to each other, and the third direction is a direction perpendicular to the first direction and the second direction. The first pole piece includes a first edge and a second edge arranged opposite to each other along the first direction, and when viewed along the second direction, the first edge overlaps with the first adhesive.

[0007] In the present application, the first adhesive can act as a finishing glue to fix the first finishing area, thereby reducing the possibility of loose electrode assembly and misalignment of pole pieces, making the electrode assembly more regular as a whole. Moreover, by extending the first adhesive along the first direction, the first edge of the first pole piece overlaps with the first adhesive, so that the first adhesive can be fully fixed to the first finishing area arranged adjacent to the first edge in the first direction. Even if the isolation film is wrinkled or shrunk during mechanical abuse, the first adhesive can reduce the risk of short circuit between the part of the first finishing area and the second pole piece (especially the extension area of ​​the second pole piece) located inside the first finishing area. Therefore, the present application can improve the safety performance and service life of the secondary battery.

[0008] Based on the first aspect, in one or more of the above possible implementations, the first adhesive also adheres to a portion of the surface of the packaging bag facing the electrode assembly; the secondary battery also includes a plurality of conductive plates, the number of conductive plates in the plurality of conductive plates is N, the number of conductive plates extending from one side of the first edge is N1, N≥N1, N1≥3. Therefore, the first adhesive not only serves as a finishing glue to fix the first finishing area, but also can fix the electrode assembly to the packaging bag, reduce the risk of the electrode assembly moving in the packaging bag under mechanical abuse, and improve the mechanical abuse resistance of the secondary battery. At the same time, by setting up a plurality of conductive plates, the demand for high current charging and discharging can be met and the internal resistance of the first pole piece or the second pole piece can be reduced. Moreover, even if there is not enough space for winding glue at the end of the electrode assembly corresponding to the first edge, the risk of contact short circuit caused by the first finishing area contacting the second pole piece due to wrinkling or shrinkage of the isolation film can be reduced, thereby improving the safety performance and service life of the secondary battery.

[0009] Based on the first aspect, in one or more possible implementations above, N=4, N1=4. The plurality of conductive plates include two first conductive plates and two second conductive plates. The second pole piece includes a second current collector. The two first conductive plates are electrically connected to the first current collector, respectively, and the two second conductive plates are electrically connected to the second current collector, respectively. The two first conductive plates and the two second conductive plates are arranged in sequence in the third direction. Therefore, the requirements for large current charging and discharging can be met and the internal resistance of the first pole piece or the second pole piece can be further reduced. Moreover, even if there is not enough space for setting the winding glue at the end of the electrode assembly corresponding to the first edge, the risk of the first tailing area contacting the second pole piece and causing a short circuit after the isolation film is wrinkled or shrunk can be reduced, thereby improving the safety performance and service life of the secondary battery.

[0010] Based on the first aspect, in one or more possible implementations above, the first adhesive includes a fourth edge, and the fourth edge and the first edge are located at the same end of the electrode assembly along the first direction. Observed along the second direction, the distance between the fourth edge and the first edge along the first direction is L1, 0≤L1≤2.0mm. When L1 is greater than zero, the risk of the first adhesive failing to fully fix the first edge due to process errors can be reduced, and the risk of the first tailing area contacting the second pole piece after the isolation film is wrinkled or shrunk, causing a short circuit, can be further reduced. Moreover, by limiting the upper limit value of L1, the risk of the first adhesive pressing against the sealed edge of the packaging bag in the first direction can be reduced, or the risk of the first adhesive entering the area to be packaged of the packaging bag before the packaging bag is packaged can be reduced, thereby reducing the risk of leakage in the packaging bag.

[0011] Based on the first aspect, in one or more of the above possible implementations, 0.2 mm ≤ L1 ≤ 2.0 mm. Therefore, the risk of the first tail region contacting the second pole piece and causing a short circuit after the isolation film is wrinkled or shrunk can be further reduced.

[0012] Based on the first aspect, in one or more of the above possible implementations, 0.2mm≤L1≤1.4mm. Therefore, the first adhesive member does not extend beyond the isolation film along the first direction, reducing the effect of the first adhesive member on the length of the secondary battery, and further reducing the risk of the first adhesive member pressing against the sealed edge of the packaging bag in the first direction or entering the area to be packaged of the packaging bag before packaging, thereby reducing the risk of leakage of the packaging bag.

[0013] Based on the first aspect, in one or more of the above possible implementations, when viewed along the second direction, the extension line of the third edge along the first direction is located between two adjacent conductive plates in the third direction. Therefore, the risk of the third edge opening compared to the electrode assembly is reduced, the compactness of the electrode assembly is improved, and the first adhesive member bonded to the third edge has a suitable position along the third direction, reducing the stress between the packaging bag and the electrode assembly under mechanical abuse, thereby reducing the risk of tearing in the first tailing area, and further improving the mechanical abuse resistance of the secondary battery.

[0014] Based on the first aspect, in one or more possible implementations above, the projection of the electrode assembly in the second direction includes a fifth edge and a sixth edge relatively arranged along the third direction. The first adhesive includes a seventh edge and an eighth edge relatively arranged along the third direction. Along the third direction, the fifth edge, the seventh edge, the eighth edge, and the sixth edge are arranged in sequence. The distance between the fifth edge and the seventh edge along the third direction is L2, and the distance between the sixth edge and the eighth edge along the third direction is L3; 0≤|L2-L3|≤4mm. Therefore, the first adhesive can be arranged roughly in the center along the third direction, further reducing the stress between the packaging bag and the electrode assembly under mechanical abuse, thereby reducing the risk of tearing in the first tailing area, and further improving the mechanical abuse resistance of the secondary battery.

[0015] Based on the first aspect, in one or more of the above possible implementations, the projected area of ​​the electrode assembly along the second direction is S1, the area of ​​the first adhesive is S2, and 0.4≤S2 / S1≤1. By limiting the lower limit of S2 / S1, the bonding force between the electrode assembly and the packaging bag can be increased to further improve the mechanical abuse resistance of the secondary battery, and the risk of local lithium deposition caused by undervoltage at the position of the electrode assembly not covered by the first adhesive during the formation process can also be reduced. By limiting the upper limit of S2 / S1, the risk of the first adhesive being easily bonded to other positions after exceeding the electrode assembly can be reduced, thereby improving the risk of mechanical abuse resistance of the secondary battery, and the risk of bubbles appearing when the first adhesive is pasted can also be reduced, thereby improving the bonding effect of the first adhesive and the appearance of the secondary battery.

[0016] Based on the first aspect, in one or more of the above possible implementations, 0.5≤S2 / S1≤0.7. Therefore, the bonding force between the electrode assembly and the packaging bag can be further improved, and the risk of local lithium deposition caused by undervoltage at the position of the electrode assembly not covered by the first adhesive during the formation process can be reduced. Moreover, the risk of the first adhesive being easily bonded to other positions after extending beyond the electrode assembly can be further reduced, and the risk of bubbles forming when the first adhesive is pasted can be reduced.

[0017] Based on the first aspect, in one or more possible implementations above, when viewed along the first direction, the projection of the first tail region does not overlap with the projections of the plurality of conductive plates, thereby reducing the impact of the first tail region on the thickness and energy density of the secondary battery.

[0018] Based on the first aspect, in one or more of the above possible implementations, the secondary battery also includes a second adhesive. The second adhesive bonds the surface of the packaging bag facing the electrode assembly and a portion of the second surface that is on the same side as the third edge in the second direction. The first adhesive and the second adhesive are arranged sequentially and separated in the third direction. Therefore, the first adhesive and the second adhesive can jointly fix the electrode assembly to the packaging bag, thereby reducing the risk of the electrode assembly moving in the packaging bag due to mechanical abuse. In addition, the second adhesive can improve the thickness flatness of the secondary battery, and can also improve the stress problem between the packaging bag and the electrode assembly when only the first adhesive is provided.

[0019] Based on the first aspect, in one or more possible implementations above, the projection of the electrode assembly in the second direction includes a fifth edge and a sixth edge relatively arranged along the third direction. The first adhesive includes a seventh edge and an eighth edge relatively arranged along the third direction. The second adhesive includes a ninth edge and a tenth edge relatively arranged along the third direction. Along the third direction, the fifth edge, the ninth edge, the tenth edge, the seventh edge, the eighth edge and the sixth edge are arranged in sequence. The straight-line distance between the sixth edge and the eighth edge along the third direction is L3, and the straight-line distance between the fifth edge and the ninth edge along the third direction is L4; 0≤|L3-L4|≤4mm. Therefore, the first adhesive and the second adhesive are arranged roughly centered along the third direction as a whole, further reducing the stress between the packaging bag and the electrode assembly under mechanical abuse, thereby reducing the risk of tearing in the first tailing area, and further improving the mechanical abuse resistance of the secondary battery.

[0020] Based on the first aspect, in one or more of the above possible implementations, the projection area of ​​the electrode assembly along the second direction is S1, the area of ​​the first adhesive is S2, the area of ​​the second adhesive is S3, and 0.4≤(S2+S3) / S1≤1. By limiting the lower limit of (S2+S3) / S1, the bonding force between the electrode assembly and the packaging bag can be increased to further improve the mechanical abuse resistance of the secondary battery, and the risk of local lithium precipitation caused by undervoltage at the position of the electrode assembly not covered by the first adhesive and the second adhesive during the formation process can also be reduced. By limiting the upper limit of (S2+S3) / S1, the risk of the first adhesive or the second adhesive being easily bonded to other positions after exceeding the electrode assembly can be reduced, thereby improving the risk of mechanical abuse resistance of the secondary battery, and the risk of bubbles appearing when the first adhesive or the second adhesive is pasted can also be reduced, thereby improving the bonding effect and the appearance of the secondary battery.

[0021] Based on the first aspect, in one or more of the above possible implementations, 0.5≤(S2+S3) / S1≤0.7. Therefore, the bonding strength between the electrode assembly and the packaging bag can be further improved, and the risk of local lithium deposition caused by undervoltage at the position of the electrode assembly not covered by the first adhesive and the second adhesive during the formation process can be reduced. Moreover, the risk of the first adhesive or the second adhesive being easily bonded to other positions after extending beyond the electrode assembly can be further reduced, and the risk of bubbles appearing when the first adhesive or the second adhesive is pasted can be reduced.

[0022] Based on the first aspect, in one or more possible implementations above, the first sublayer includes a second tail region in the winding direction, and the second sublayer includes a third tail region in the winding direction. The second tail region is located at the outermost winding circle of the first pole piece, and the third tail region is located at the second outer winding circle of the first pole piece. The secondary battery also includes a third adhesive, which is arranged in the second tail region and extends along the winding direction and adheres to the first surface. When viewed from the second direction, the first adhesive and the third adhesive are separated in the third direction. Therefore, the influence of the overlap of the first adhesive and the third adhesive on the thickness and energy density of the secondary battery can be reduced.

[0023] Based on the first aspect, in one or more of the above possible implementations, the secondary battery further includes a fourth adhesive member, which is disposed in the third end region and extends along the winding direction and adheres to the second surface, and when viewed from the second direction, the first adhesive member and the fourth adhesive member are separated in the third direction. Therefore, the influence of the overlap of the first adhesive member and the fourth adhesive member on the thickness and energy density of the secondary battery can be reduced.

[0024] Based on the first aspect, in one or more possible implementations above, the secondary battery further includes a fifth adhesive. The electrode assembly includes a first end and a second end that are arranged opposite to each other in a first direction, the first edge is located at the first end, and the second edge is located at the second end. The fifth adhesive is bonded to the second end. When viewed from the second direction, the first adhesive is separated from the fifth adhesive in the first direction. Therefore, the fifth adhesive can be bonded to the edge of the isolation film, reducing the risk of contact short circuit between the first pole piece and the second pole piece caused by wrinkling or shrinking of the edge of the isolation film during mechanical abuse, and because the first adhesive is separated from the fifth adhesive in the first direction, the impact on the thickness and energy density of the secondary battery can be reduced.

[0025] Based on the first aspect, in one or more possible implementations above, the first adhesive member includes a first adhesive layer, a substrate layer, and a second adhesive layer stacked in sequence along the thickness direction of the first adhesive member. The first adhesive layer is arranged on the surface of the substrate layer facing the packaging bag, and the second adhesive layer is arranged on the surface of the substrate layer facing the first tailing area. The material of the substrate layer includes at least one of polyethylene, polypropylene, polyethylene terephthalate, polyimide, polyamide, spandex, and aramid. The materials of the first adhesive layer and the second adhesive layer independently include at least one of polyethylene, polypropylene, polyurethane, epoxy resin, styrene-butadiene rubber, polyvinylidene fluoride, polyacrylate, polyacrylic acid, and their derivatives.

[0026] Based on the first aspect, in one or more of the above possible implementations, the first pole piece is a positive pole piece, and the second pole piece is a negative pole piece.

[0027] Based on the first aspect, in one or more possible implementations above, the first adhesive extends beyond the edge of the second pole piece in the first direction. Such an arrangement enables the first adhesive to better reduce the risk of contact between the first pole piece and the second pole piece.

[0028] The second aspect of the present application provides an electronic device, comprising the secondary battery. The electronic device is powered by the secondary battery, and the short circuit risk of the secondary battery due to wrinkling or shrinking of the isolation film is reduced, so the secondary battery has higher safety and service life. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 This is a schematic structural diagram of a secondary battery provided in one embodiment of the present application when viewed from a second direction.

[0030] Figure 2 for Figure 1 The illustrated secondary battery is a cross-sectional view taken along the cutting line II-II in some embodiments.

[0031] Figure 3 for Figure 1The schematic diagram of the structure of the secondary battery shown in some embodiments is shown after the packaging bag is removed.

[0032] Figure 4 for Figure 1 The schematic diagram of the structure of the secondary battery without the packaging bag in other embodiments is shown.

[0033] Figure 5 for Figure 1 The schematic diagram of the structure of the secondary battery without the packaging bag in other embodiments is shown.

[0034] Figure 6 for Figure 2 An expanded view of the first electrode sheet of the secondary battery is shown.

[0035] Figure 7 for Figure 2 FIG. 4 is a cross-sectional view of a first bonding member of a secondary battery.

[0036] Figure 8 A schematic diagram of the overall structure of an electronic device provided in one embodiment of the present application.

[0037] Main component symbols

[0038] Electronic device 1 Packaging bag 10

[0039] Main body 11 Electrode assembly 20

[0040] Fifth edge 20A Sixth edge 20B

[0041] First end portion 20C Second end portion 20D

[0042] First pole piece 21 First edges 21A, 22A, 23A

[0043] Second edges 21B, 22B, 23B Second pole piece 22

[0044] Isolation film 23 First conductive plate 31

[0045] Second conductive plate 32 First adhesive member 41

[0046] Fourth edge 41A Seventh edge 41B

[0047] Eighth edge 41C Second adhesive member 42

[0048] Ninth edge 42A Tenth edge 42B

[0049] The third adhesive member 50 and the fourth adhesive member 60

[0050] Fifth adhesive member 70 Secondary battery 100

[0051] Battery compartment 101 First straight section 201

[0052] First bending section 202 Second straight section 203

[0053] Second bending section 204 First current collector 210

[0054] First active material 211 Second current collector 220

[0055] Second active material 221 Base material layer 410

[0056] First adhesive layer 411 Second adhesive layer 412

[0057] First end area 2100 Third edge 2100A

[0058] First surface 2101 Second surface 2102

[0059] Second finishing area 2110 Third finishing area 2110'

[0060] First sublayer 2111 Second sublayer 2112

[0061] Winding center axis O Winding direction D

[0062] Winding center plane P First direction X

[0063] Second direction Y Third direction Z

[0064] Fourth direction Y' Fifth direction Z'

[0065] Straight line distance L1, L2, L3, L4

[0066] The following specific implementation methods will further illustrate the present application in conjunction with the above-mentioned drawings. DETAILED DESCRIPTION

[0067] The technical scheme in the embodiment of the present application is described clearly and in detail below. Obviously, the described embodiment is only a part of the embodiment of the present application, rather than all the embodiments. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those generally understood by those skilled in the art of the present application. The terms used in the specification of the present application are only for the purpose of describing specific embodiments and are not intended to limit the present application.

[0068] Hereinafter, the embodiments of the present application will be described in detail. However, the present application can be embodied in many different forms and should not be construed as being limited to the exemplary embodiments illustrated herein. Rather, these exemplary embodiments are provided so that the present application is thoroughly and in detail communicated to those skilled in the art.

[0069] In addition, for simplicity and clarity, in the accompanying drawings, the size or thickness of various components, layers may be amplified. Throughout the entire text, the same numerical value refers to the same element. As used herein, the term "and / or", "and / or" includes any and all combinations of one or more related enumerated items. In addition, it should be understood that when element A is referred to as "connecting" element B, element A may be directly connected to element B, or there may be an intermediate element C and element A and element B may be indirectly connected to each other.

[0070] Further, the use of “may” when describing embodiments of the present application means “one or more embodiments of the present application”.

[0071] The technical terms used herein are for the purpose of describing specific embodiments and are not intended to limit the present application. As used herein, the singular form is intended to also include the plural form, unless the context clearly indicates otherwise. It should be further understood that the term "comprising", when used in this specification, refers to the presence of narrated features, values, steps, operations, elements and / or components, but does not exclude the presence or increase of one or more other features, values, steps, operations, elements, components and / or combinations thereof.

[0072] Spatial related terms, such as "on" and the like can be used herein for convenient description, to describe the relationship between an element or feature and another element (multiple elements) or feature (multiple features) as illustrated in the figure. It should be understood that, in addition to the directions described in the figure, spatial related terms are intended to include different directions of equipment or devices in use or operation. For example, if the equipment in the figure is turned over, the elements described as "above" or "on" other elements or features will be oriented "below" or "below" other elements or features. Therefore, the exemplary term "on" may include the direction above and below. It should be understood that although the terms first, second, third, etc. can be used herein to describe various elements, components, regions, layers and / or parts, these elements, components, regions, layers and / or parts should not be limited by these terms. These terms are used to distinguish an element, component, region, layer or part from another element, component, region, layer or part. Therefore, the first element, component, region, layer or part discussed below may be referred to as the second element, component, region, layer or part without departing from the teaching of the exemplary embodiment.

[0073] See also Figure 1 and Figure 2In one embodiment of the present application, a secondary battery 100 is provided, comprising a packaging bag 10 , an electrode assembly 20 , and an electrolyte (not shown). The electrode assembly 20 and the electrolyte are located in the packaging bag 10 .

[0074] like Figure 2 As shown, the electrode assembly 20 includes a first pole piece 21, a second pole piece 22 and a separator 23, and the separator 23 is arranged between the first pole piece 21 and the second pole piece 22. The first pole piece 21, the separator 23 and the second pole piece 22 are stacked and wound. The first pole piece 21 includes a first current collector 210 and a first active material layer 211 arranged on the first current collector 210. The first current collector 210 includes a first surface 2101 and a second surface 2102 opposite to each other along the thickness direction of the first current collector 210, the first surface 2101 faces the winding center axis O, and the second surface 2102 faces away from the winding center axis O. The first active material layer 211 includes a first sublayer 2111 arranged on the first surface 2101 and a second sublayer 2112 arranged on the second surface 2102. The second pole piece 22 includes a second current collector 220 and a second active material layer 221 arranged on the second current collector 220. The three-dimensional coordinate system is defined by the first direction X, the second direction Y and the third direction Z which are perpendicular to each other. The width direction of the first pole piece 21 or the second pole piece 22 is the first direction X. In some embodiments, the first direction X is also the extension direction of the winding center axis O. The thickness direction of the electrode assembly 20 is the second direction Y. The electrode assembly 20 can be divided into a first straight section 201, a first bent section 202, a second straight section 203 and a second bent section 204 which are sequentially connected in the winding direction D. The first straight section 201 and the second straight section 203 are arranged relative to each other in the second direction Y, and the first bent section 202 and the second bent section 204 are arranged relative to each other in the third direction Z.

[0075] The first electrode sheet 21 may be a positive electrode sheet, and the second electrode sheet 22 may be a negative electrode sheet. Correspondingly, the first current collector 210 and the first active material layer 211 are respectively a positive electrode current collector and a positive electrode active material layer, and the second current collector 220 and the second active material layer 221 are respectively a negative electrode current collector and a negative electrode active material layer. Figure 3, the first pole piece 21 includes a first edge 21A and a second edge 21B arranged opposite to each other in the first direction X. The second pole piece 22 includes a first edge 22A and a second edge 22B arranged opposite to each other in the first direction X. The isolation film 23 includes a first edge 23A and a second edge 23B arranged opposite to each other in the first direction X. The electrode assembly 20 includes a first end 20C and a second end 20D arranged opposite to each other in the first direction X. The first edges 21A, 22A, and 23A are located at the first end 20C of the electrode assembly 20, and the second edges 21B, 22B, and 23B are located at the second end 20D of the electrode assembly 20. In order to reduce the risk of lithium plating of the second pole piece 22, the first edge 22A of the second pole piece 22 may be arranged to exceed the first edge 21A of the first pole piece 21 along the first direction X, and the second edge 22B of the second pole piece 22 may be arranged to exceed the second edge 21B of the first pole piece 21 along the first direction X, and the portion of the second pole piece 22 exceeding the first pole piece 21 is an overhang area. In order to reduce the risk of contact between the first pole piece 21 and the second pole piece 22, the first edge 23A of the isolation film 23 may be further arranged to extend beyond the first edge 22A of the second pole piece 22 along the first direction X, and the second edge 23B of the isolation film 23 may be arranged to extend beyond the second edge 23B of the second pole piece 22 along the first direction X. In other embodiments, the first pole piece 21 may be arranged to be a negative pole piece, and the second pole piece 22 may be arranged to be a positive pole piece.

[0076] like Figures 1 to 3 As shown, the secondary battery 100 may also include a plurality of conductive plates. The plurality of conductive plates are electrically connected to the electrode assembly 20 and extend out of the packaging bag 10, and the conductive plates can be connected to external elements (not shown). The first direction X is also the direction in which the conductive plate extends out of the electrode assembly 20 (i.e., the direction from the electrode assembly 20 to the conductive plate). Among them, the plurality of conductive plates include at least one first conductive plate 31 and at least one second conductive plate 32. The first conductive plate 31 is electrically connected to the first current collector 210 or is electrically connected to the first current collector 210 through a first pole ear (not shown), and the second conductive plate 32 is electrically connected to the second current collector 220 or is electrically connected to the second current collector 220 through a second pole ear (not shown). Moreover, when viewed from the second direction Y, the first conductive plate 31 may extend out of the electrode assembly 20 from the first edge 21A or the second edge 21B, and the second conductive plate 32 may extend out of the electrode assembly 20 from the first edge 21A or the second edge 21B. In some embodiments, in order to meet the requirements of high current charging and discharging and reduce the internal resistance of the first pole piece 21 or the second pole piece 22, the number of the first conductive plate 31 or the second conductive plate 32 can be increased accordingly. Therefore, the number of conductive plates in the plurality of conductive plates can be set to N, and the number of conductive plates extending from one side of the first edge 21A can be set to N1, N≥N1, and N1≥3. Therefore, the first conductive plate 31 or the second conductive plate 32 can achieve parallel shunting, thereby facilitating the reduction of the internal resistance of the first pole piece 21 or the second pole piece 22 and meeting the requirements of high current charging and discharging.

[0077] Further, in some embodiments, N=4 and N1=4 can be set. The plurality of conductive plates include two first conductive plates 31 and two second conductive plates 32. Therefore, the first conductive plate 31 can realize parallel shunting, thereby facilitating the reduction of the internal resistance of the first electrode 21; the second conductive plate 32 can realize parallel shunting, thereby facilitating the reduction of the internal resistance of the second electrode 22. Moreover, the two first conductive plates 31 and the two second conductive plates 32 are arranged in sequence in the third direction Z, that is, the two conductive plates located on both sides of a first conductive plate 31 in the third direction Z have different polarities, and the two conductive plates located on both sides of a second conductive plate 32 in the third direction Z have different polarities, which is conducive to reducing the risk of short circuit caused by contact between the conductive plates and adjacent conductive plates during mechanical abuse. In some embodiments, the packaging bag 10 includes a main body 11 and an edge seal 12 connected to each other, the main body 11 is used to accommodate the electrode assembly 20 and the electrolyte, and the edge seal 12 is arranged facing the first edge 21A. The two first conductive plates 31 and the two second conductive plates 32 are both extended out of the packaging bag 10 from the sealed edge 12 .

[0078] like Figure 2 As shown, the outermost winding circle of the electrode assembly 20 is the first pole piece 21, and the first pole piece 21 wound on the outermost circle includes a single-sided coating area and a double-sided empty foil area connected in sequence along the winding direction D, that is, the first current collector 210 wound on the outermost circle is provided with a first sublayer 21111 only on a part of the first surface 2101, and the second sublayer 2112 is not provided on the second surface 2102 of the first current collector 210 wound on the outermost circle. Therefore, the outer surface of the outermost winding circle of the electrode assembly 20 is the second surface 2102. This can improve the energy density of the secondary battery 100 and improve the situation that when the outer surface of the electrode assembly 20 is provided with an active material, the active material is easy to fall off after contacting the packaging bag 10. Moreover, the first current collector 210 wound on the outermost circle can increase the hardness of the electrode assembly 20, play a role in protecting the electrode assembly 20, and improve the ability of the electrode assembly 20 to resist mechanical impact.

[0079] The positive electrode current collector may be made of aluminum foil or nickel foil, and the negative electrode current collector may be made of at least one of copper foil, nickel foil or a carbon-based current collector.

[0080] The positive electrode active material layer contains a positive electrode active material, and the positive electrode active material includes a compound (i.e., a lithiated intercalation compound) that can reversibly embed and deintercalate metal ions (such as lithium ions, sodium ions, etc., and lithium ions are taken as an example below). In some embodiments, the first active material may include a lithium transition metal composite oxide. The lithium transition metal composite oxide contains lithium and at least one element selected from cobalt, manganese and nickel. In some embodiments, the positive electrode active material is selected from lithium cobalt oxide (LiCoO2), lithium nickel cobalt manganese ternary material (NCM), lithium nickel cobalt aluminum ternary material (NCA), lithium manganese oxide (LiMn2O4), lithium nickel manganese oxide (LiNi 0.5 Mn 1.5 O4) or at least one of lithium iron phosphate (LiFePO4).

[0081] The negative electrode active material layer contains a negative electrode active material, and a negative electrode active material capable of reversibly deintercalating active ions known in the art is used, and this application does not limit it. For example, it may include but is not limited to a combination of one or more of graphite, soft carbon, hard carbon, carbon fiber, mesophase carbon microspheres, silicon-based materials, tin-based materials, lithium titanate or other metals that can form alloys with lithium. Among them, graphite can be selected from a combination of one or more of artificial graphite, natural graphite and modified graphite; silicon-based materials can be selected from a combination of one or more of elemental silicon, silicon oxide compounds, silicon-carbon composites, and silicon alloys; tin-based materials can be selected from a combination of one or more of elemental tin, tin oxide compounds, tin alloys, etc.

[0082] The isolation film 23 includes at least one of polyethylene, polypropylene, polyvinylidene fluoride, polyethylene terephthalate, polyimide or aramid. For example, the polyethylene includes at least one selected from high-density polyethylene, low-density polyethylene or ultra-high molecular weight polyethylene.

[0083] like Figure 2As shown, the first current collector 210 also includes a first end region 2100 in the winding direction D, and the first end region 2100 is exposed in the first sublayer 21111 and the second sublayer 2112, that is, the first end region 2100 is a double-sided empty foil area. The first end region 2100 is located at the last fold of the first current collector 210 along the winding direction D. The first end region 2100 includes a third edge 2100A in the winding direction D, and the third edge 2100A is the end edge of the electrode assembly 20. The third edge 2100A may be located in the first straight section 201 of the electrode assembly 20, or at the junction of the first straight section 201 and the second bent section 204, or at the second bent section 204. In some embodiments, the first sublayer 2111 includes a second end region 2110 in the winding direction D, and the second end region 2110 is located at the outermost winding circle of the first pole piece 21. The second sublayer 2112 includes a third end region 2110' in the winding direction D, and the third end region 2110' is located at the winding secondary outer circle of the first pole piece 21. The second end region 2110 and the third end region 2110' may both be located at the second straight section 203 of the electrode assembly 20. The first end region 2100 is exposed in the second end region 2110 and the third end region 2110'.

[0084] In the embodiment of the present application, the outermost winding circle of the first pole piece 21 refers to a circle structure located at the outermost side relative to the winding center axis O of the electrode assembly 20 in the multi-layer structure formed by winding the first pole piece 21 along the winding direction D; the second outermost winding circle refers to a circle structure located on the side of the outermost circle facing the winding center axis O and adjacent to the outermost circle in the multi-layer structure formed by winding the first pole piece 21 along the winding direction D. Moreover, one circle refers to starting from a certain point on the first pole piece 21 as the starting end, and reaching another point along the winding direction D as the ending end, the ending end is on a straight line with the starting end and the center of this circle, and the starting end is between the ending end and the center of this circle.

[0085] In the embodiment of the present application, a virtual plane passing through the winding center axis O and perpendicular to the second direction Y is defined as the winding center plane P. The winding center plane P divides the electrode assembly 20 into two parts with approximately the same thickness in the second direction Y. The winding center plane P and each circle of the electrode assembly 20 have two intersections at the first bending section 202 and the second bending section 204, respectively. Each fold of the winding refers to: the intersection of the winding center plane P and one bending section is the starting edge of the fold, and the intersection of the winding center plane P and another bending section along the winding direction D is the ending edge of the fold. Therefore, the last fold refers to the first current collector 210 of the first pole piece 21 of the outermost circle of the winding, with the intersection of the winding center plane P and the second bending section 204 as the starting edge, and extending along the winding direction D to the winding end of the first current collector 210.

[0086] like Figure 2 , Figure 3 and Figure 6 As shown, Figure 6 for Figure 2 The structure schematic diagram of the first pole piece 21 after unfolding is shown. Figure 6 A three-dimensional coordinate system is established with the first direction X, the fourth direction Y' and the fifth direction Z', wherein the fourth direction Y' is the thickness direction of the first electrode sheet 21, and the fifth direction Z' is the length direction of the first electrode sheet 21. The secondary battery 100 further includes a first adhesive 41. The first adhesive 41 is bonded to a portion of the surface of the packaging bag 10 facing the electrode assembly 20, at least a portion of the surface of the first tailing area 2100 facing the packaging bag 10, and the third edge 2100A. Figure 3 As shown, when viewed along the second direction Y, the first edge 21A of the first electrode sheet 21 overlaps with the first adhesive 41. The first adhesive 41 can fix the electrode assembly 20 to the packaging bag 10, thereby reducing the risk of the electrode assembly 20 moving in the packaging bag 10 due to mechanical abuse. Moreover, by setting the first adhesive 41 to bond the third edge 2100A, the first adhesive 41 can also play the role of a finishing glue to fix the first finishing area 2100, reduce the risk of the first finishing area 2100 moving, and thus improve the compactness of the electrode assembly 20.

[0087] When the first pole piece 21 is a positive pole piece and the second pole piece 22 is a negative pole piece, the edge of the first adhesive 41 in the first direction X can be flush with the first edge 21A, or it can extend beyond the first edge 21A and be located between the first pole piece 21 and the second pole piece 22, or extend in the first direction X beyond the edge of the second pole piece 22 in the first direction X.

[0088] When the first electrode sheet 21 is a negative electrode sheet and the second electrode sheet 22 is a positive electrode sheet, the edge of the first adhesive 41 in the first direction X may be flush with the first edge 21A or may extend beyond the first edge 21A.

[0089] like Figure 7As shown, in some embodiments, the first adhesive member 41 includes a first adhesive layer 411, a substrate layer 410, and a second adhesive layer 412 sequentially stacked along the thickness direction of the first adhesive member 41. The first adhesive layer 411 is disposed on the surface of the substrate layer 410 facing the packaging bag 10. The second adhesive layer 412 is disposed on the surface of the substrate layer 410 facing the first tailing area 2100. The material of the substrate layer 410 includes at least one of polyethylene, polypropylene, polyethylene terephthalate, polyimide, polyamide, spandex, and aramid. The materials of the first adhesive layer 411 and the second adhesive layer 412 independently include at least one of polyethylene, polypropylene, polyurethane, epoxy resin, styrene-butadiene rubber, polyvinylidene fluoride, polyacrylate, polyacrylic acid, and derivatives thereof. Among them, the material of the first adhesive layer 411 can be the same as or different from the material of the second adhesive layer 412, and the materials of the first adhesive layer 411 and the second adhesive layer 421 have high bonding properties.

[0090] In the present application, the first adhesive 41 can fix the electrode assembly 20 and the packaging bag 10, thereby reducing the risk of the electrode assembly 20 moving in the packaging bag 10 under mechanical abuse, and can also play the role of a tail glue to fix the first tail area 2100, thereby improving the mechanical abuse resistance of the secondary battery 100. In addition, by extending the first adhesive 41 along the first direction X, the projection of the first edge 21A of the first pole piece 21 falls within the projection range of the first adhesive 41, so the first adhesive 41 can be fully fixed to the first tail area 2100 arranged adjacent to the first edge 21A in the first direction X. In this way, even if the first edge 21A of the isolation film 23 is wrinkled or shrunk during mechanical abuse, the first adhesive 41 can reduce the risk of short circuit between the first tail area 2100 and the second pole piece 22 (especially the extension area of ​​the second pole piece 22) located inside the first tail area 2100. In particular, when the number of conductive plates N1 ≥ 3 extending from one side of the first edge 21A causes insufficient space for setting the glue wrapping at the first end 20C of the electrode assembly 20, even if the head glue wrapping is omitted, the risk of short circuit caused by wrinkling or shrinking of the first edge 21A of the separator 23 can be reduced. Therefore, the present application can improve the safety performance and service life of the secondary battery 100.

[0091] like Figure 3 As shown, in some embodiments, the first adhesive member 41 includes a fourth edge 41A, and the fourth edge 41A and the first edge 21A are located at the same end of the electrode assembly 20. It can be set that the fourth edge 41A is substantially flush with the first edge 21A when viewed along the second direction Y. That is, when viewed along the second direction Y, the straight-line distance between the fourth edge 41A and the first edge 21A along the first direction X is zero. Figure 4As shown, in some other embodiments, the fourth edge 41A may also be set to extend beyond the first edge 21A along the first direction X. When observed along the second direction Y, the linear distance between the fourth edge 41A and the first edge 21A along the first direction X is L1, where 0 < L1 ≤ 2.0 mm. In this way, the risk that the first bonding member 41 fails to fully fix the first edge 21A due to process errors can be reduced, and further, the risk that the first finishing region 2100 disposed adjacent to the first edge 21A contacts the protruding region of the second electrode sheet 22 after the separator film 23 wrinkles or shrinks, causing contact short circuit, can be reduced. Moreover, by defining the upper limit value of L1, the risk that the first bonding member 41 presses against the sealing edge 12 of the packaging bag 10 in the first direction X can be reduced, or the risk that the first bonding member 41 enters the to-be-sealed region of the packaging bag 10 before the packaging bag 10 is sealed can be reduced (wherein, if the first bonding member 41 enters the to-be-sealed region of the packaging bag 10, after the to-be-sealed region is sealed to form the sealing edge 12, the first bonding member 41 that enters the sealing region may cause the packaging bag 10 to be damaged), thereby reducing the risk of liquid leakage from the packaging bag 10.

[0092] Furthermore, 0.2 mm ≤ L1 ≤ 2.0 mm can be set. By defining the lower limit value of L1, the risk that the first finishing region 2100 disposed adjacent to the first edge 21A contacts the protruding region of the second electrode sheet 22 after the separator film 23 wrinkles or shrinks, causing contact short circuit, can be further reduced. Even further, 0.2 mm ≤ L1 ≤ 1.4 mm can be set. By defining the upper limit value of L1, the first bonding member 41 does not extend beyond the first edge 21A of the separator film 23 along the first direction X, reducing the influence of the setting of the first bonding member 41 on the length of the secondary battery 100. Also, the risk that the first bonding member 41 presses against the sealing edge 12 of the packaging bag 10 in the first direction X or enters the to-be-sealed region of the packaging bag 10 before packaging can be further reduced, thereby reducing the risk of liquid leakage from the packaging bag 10.

[0093] As shown in FIGS. 3 and Figure 4 As shown, in some embodiments, when observed along the second direction Y, the extension line of the third edge 2100A along the first direction X is located between two adjacent conductive plates in the third direction Z. Among them, when observed from the second direction Y, the third edge 2100A may be located in the first straight section 201. This helps to reduce the risk that the third edge 2100A opens relative to the electrode assembly 20 and improves the compactness of the electrode assembly 20. Moreover, due to the position of the third edge 2100A, the first bonding member 41 bonding the third edge 2100A has a suitable position along the third direction Z, which can reduce the stress between the packaging bag 10 and the electrode assembly 20 under mechanical abuse, thereby reducing the risk of tearing of the first finishing region 2100 and further improving the anti-mechanical abuse performance of the secondary battery 100.

[0094] In some embodiments, the projection of the electrode assembly 20 in the second direction Y includes a fifth edge 20A and a sixth edge 20B that are relatively arranged along the third direction Z. The first adhesive member 41 also includes a seventh edge 41B and an eighth edge 41C that are relatively arranged along the third direction Z, and the fourth edge 41A connects the seventh edge 41B and the eighth edge 41C, respectively. Along the third direction Z, the fifth edge 20A, the seventh edge 41B, the eighth edge 41C, and the sixth edge 20B are arranged in sequence. Along the third direction Z, the seventh edge 41B is closer to the fifth edge 20A than the eighth edge 41C, and the eighth edge 41C is closer to the sixth edge 20B than the seventh edge 41B. The distance between the fifth edge 20A and the seventh edge 41B along the third direction Z is L2, and the distance between the sixth edge 20B and the eighth edge 41C along the third direction Z is L3, then 0≤|L2-L3|≤4mm. In this way, the first adhesive 41 is arranged roughly in the center along the third direction Z, further reducing the stress between the packaging bag 10 and the electrode assembly 20 under mechanical abuse, thereby reducing the risk of tearing in the first tail area 2100 and further improving the mechanical abuse resistance of the secondary battery 100.

[0095] In some embodiments, the projection area of ​​the electrode assembly 20 along the second direction Y is S1, the area of ​​the first adhesive 41 is S2, and 0.4≤S2 / S1≤1. By limiting the lower limit of S2 / S1, the bonding force between the electrode assembly 20 and the packaging bag 10 can be increased to further improve the mechanical abuse resistance of the secondary battery 100, and the risk of local lithium deposition caused by undervoltage at the position of the electrode assembly 20 not covered by the first adhesive 41 during the formation process can be reduced. By limiting the upper limit of S2 / S1, the risk of the first adhesive layer 411 of the first adhesive 41 being easily bonded to other positions after exceeding the electrode assembly 20 can be reduced, thereby improving the risk of mechanical abuse resistance of the secondary battery 100, and the risk of bubbles appearing when the first adhesive 41 is pasted can be reduced, thereby improving the bonding effect of the first adhesive 41 and the appearance of the secondary battery 100.

[0096] Furthermore, 0.5≤S2 / S1≤0.7 can be set, so as to further improve the bonding strength between the electrode assembly 20 and the packaging bag 10, and reduce the risk of local lithium deposition caused by undervoltage during the formation process at the position of the electrode assembly 20 not covered by the first adhesive member 41. In addition, the risk of the first adhesive layer 411 of the first adhesive member 41 being easily bonded to other positions after exceeding the electrode assembly 20 can be further reduced, and the risk of bubbles appearing when the first adhesive member 41 is attached can be reduced.

[0097] like Figure 5As shown, in other embodiments, when viewed along the second direction Y, the extension line of the third edge 2100A along the first direction X may also be located on the same side of all the conductive plates, and the third edge 2100A may be approximately located at the junction of the first straight section 201 and the second bent section 204. Moreover, when viewed along the first direction X, the projection of the first tailing region 2100 does not overlap with the projections of all the conductive plates. Therefore, the influence of the first tailing region 2100 on the thickness and energy density of the secondary battery 100 can be reduced.

[0098] Further, in this case, in addition to the first adhesive 41, the secondary battery 100 may also include a second adhesive 42. The second adhesive 42 adheres part of the surface of the packaging bag 10 facing the electrode assembly 20 and part of the second surface 2102. The second adhesive 42 is separated from the first adhesive 41 in the third direction Z. The first adhesive 41 and the second adhesive 42 can jointly fix the electrode assembly 20 and the packaging bag 10, thereby reducing the risk of the electrode assembly 20 moving in the packaging bag 10 due to mechanical abuse. Moreover, the second adhesive 42 is additionally provided, which can improve the thickness flatness of the secondary battery 100 and can also improve the stress problem between the packaging bag 10 and the electrode assembly 20 when only the first adhesive 41 is provided. Among them, the second adhesive 42 can have a stacked structure similar to the first adhesive 41, which is not described in detail in this application.

[0099] Among them, the projection of the electrode assembly 20 along the second direction Y includes a fifth edge 20A and a sixth edge 20B arranged relatively along the third direction Z. The first adhesive member 41 also includes a seventh edge 41B and an eighth edge 41C arranged relatively along the third direction Z, and the fourth edge 41A connects the seventh edge 41B and the eighth edge 41C respectively. The second adhesive member 42 includes a ninth edge 42A and a tenth edge 42B arranged relatively along the third direction Z. Along the third direction Z, the fifth edge 20A, the ninth edge 42A, the tenth edge 42B, the seventh edge 41B, the eighth edge 41C, and the sixth edge 20B are arranged in sequence. Among them, the distance between the sixth edge 20B and the eighth edge 41C along the third direction is L3, and the distance between the fifth edge 20A and the ninth edge 42A along the third direction is L4, then 0≤|L3-L4|≤4mm. In this way, the first adhesive 41 and the second adhesive 42 are arranged roughly in the center along the third direction Z, further reducing the stress between the packaging bag 10 and the electrode assembly 20 under mechanical abuse, thereby reducing the risk of tearing in the first finishing area 2100 and further improving the mechanical abuse resistance of the secondary battery 100.

[0100] In some embodiments, the projection area of ​​the electrode assembly 20 along the second direction Y is S1, the area of ​​the first adhesive 41 is S2, the area of ​​the second adhesive 42 is S3, and 0.4≤(S2+S3) / S1≤1. By limiting the lower limit of (S2+S3) / S1, the bonding force between the electrode assembly 20 and the packaging bag 10 can be increased to further improve the mechanical abuse resistance of the secondary battery 100, and the risk of local lithium deposition caused by undervoltage in the formation process at the position of the electrode assembly 20 not covered by the first adhesive 41 and the second adhesive 42 can be reduced. By limiting the upper limit of (S2+S3) / S1, the risk of the first adhesive 41 or the second adhesive 42 being easily bonded to other positions after exceeding the electrode assembly 20 can be reduced, thereby improving the risk of mechanical abuse resistance of the secondary battery 100, and the risk of bubbles appearing when the first adhesive 41 or the second adhesive 42 is pasted can be reduced, thereby improving the bonding effect and the appearance of the secondary battery 100.

[0101] Furthermore, 0.5≤(S2+S3) / S1≤0.7 can be set, so as to further improve the bonding strength between the electrode assembly 20 and the packaging bag 10, and reduce the risk of local lithium deposition caused by undervoltage during the formation process at the position of the electrode assembly 20 not covered by the first adhesive 41 and the second adhesive 42. In addition, the risk of the first adhesive 41 or the second adhesive 42 being easily bonded to other positions after extending beyond the electrode assembly 20 can be further reduced, and the risk of bubbles appearing when the first adhesive 41 or the second adhesive 42 is pasted can be reduced.

[0102] like Figures 2 to 5 As shown, in some embodiments, the secondary battery 100 may further include at least one of a third adhesive member 50 and a fourth adhesive member 60. In some embodiments, the secondary battery 100 includes both the third adhesive member 50 and the fourth adhesive member 60.

[0103] The third adhesive member 50 is disposed in the second end region 2110. Figure 6 In the fifth direction Z' shown in FIG. 1 , part of the third adhesive 50 covers the second end region 2110, and another part of the third adhesive 50 extends along the winding direction D and adheres to and covers the first surface 2101 of the first current collector 210 (i.e., the first surface 2101 located in the first end region 2100). The third adhesive 50 can reduce the risk of micro-short circuit caused by the shedding of active materials in the second end region 2110. At the same time, the third adhesive 50 also plays an insulating and protective role for the first surface 2101 of the first end region 2100, and can absorb part of the impact force during mechanical abuse, reduce the risk of tearing of the first end region 2100, and enhance the strength of the first end region 2100, thereby further improving the ability of the electrode assembly 20 to withstand mechanical impact.

[0104] The fourth adhesive 60 is disposed in the third end region 2110'. Along the winding direction D, part of the fourth adhesive 60 covers the third end region 2110', and another part of the fourth adhesive 60 extends along the winding direction D and adheres to and covers the second surface 2102 of the first current collector 210. The fourth adhesive 60 can reduce the risk of micro-short circuit caused by the active material falling off in the third end region 2110', and at the same time, the fourth adhesive 60 can also enhance the strength of the first current collector 210 wound in the secondary outer circle, thereby further improving the ability of the electrode assembly 20 to resist mechanical impact.

[0105] When viewed from the second direction Y, the first adhesive 41 and the third adhesive 50 are separated in the third direction Z, thereby reducing the influence of the first adhesive 41 and the third adhesive 50 overlapping on the thickness and energy density of the secondary battery 100. When viewed from the second direction Y, the first adhesive 41 and the fourth adhesive 60 are separated in the third direction Z, thereby reducing the influence of the first adhesive 41 and the fourth adhesive 60 overlapping on the thickness and energy density of the secondary battery 100. In some embodiments, the third adhesive 50 and the fourth adhesive 60 may be single-sided adhesives, and the materials of the substrate layer and the adhesive layer thereof may refer to the first adhesive 41.

[0106] like Figures 3 to 5 As shown, in some embodiments, the secondary battery 100 may further include at least one fifth adhesive 70. The fifth adhesive 70 is bonded to the second end 20D of the electrode assembly 20. The fifth adhesive 70 can be bonded to the second edge 21B of the isolation film 23 to reduce the risk of contact short circuit between the first pole piece 21 and the second pole piece 22 caused by wrinkling or shrinking of the second edge 21B during mechanical abuse. Observed from the second direction Y, the first adhesive 41 and the fifth adhesive 70 are separated in the first direction X, thereby reducing the impact of the first adhesive 41 and the fifth adhesive 70 overlapping on the thickness and energy density of the secondary battery 100. In some embodiments, the fifth adhesive 70 can be a single-sided adhesive, and the material of its base material layer and adhesive layer can refer to the first adhesive 41.

[0107] The secondary battery 100 of the present application may be a lithium secondary battery, including a lithium metal secondary battery, a lithium ion secondary battery, a lithium polymer secondary battery or a lithium ion polymer secondary battery.

[0108] See also Figure 8, an embodiment of the present application also provides an electronic device 1, the electronic device 1 includes a battery compartment 101 and the above-mentioned secondary battery 100 disposed in the battery compartment 101. Among them, the secondary battery 100 of the present application is applicable to electronic devices 1 in various fields. The electronic device 1 is powered by the above-mentioned secondary battery 100, and the short circuit risk of the secondary battery 100 due to the wrinkling or shrinkage of the isolation film 23 is reduced, so it has high safety and service life. In one embodiment, the electronic device 1 of the present application can be, but is not limited to, a laptop computer, a pen-input computer, a mobile computer, an e-book player, a portable phone, a portable fax machine, a portable copier, a portable printer, a head-mounted stereo headset, a video recorder, an LCD TV, a portable cleaner, a portable C machine, a mini CD, a transceiver, an electronic notepad, a calculator, a memory card, a portable recorder, a radio, a backup power supply, a motor, a car, a motorcycle, a power bicycle, a bicycle, a lighting fixture, a toy, a game console, a clock, an electric tool, a flashlight, a camera, a large household battery and a lithium ion capacitor, etc.

[0109] The present application is described in detail below through specific embodiments and comparative examples. Among them, the secondary battery is a lithium-ion secondary battery, the first pole piece is a positive pole piece, and the second pole piece is a negative pole piece. The present application is described in combination with a specific preparation process and a test method. Those skilled in the art should understand that the preparation method described in the present application is only an example, and any other suitable preparation method is within the scope of the present application.

[0110] Example 1 to Example 16

[0111] (1) Preparation of the first 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 96.5:1.5:2, and N-methylpyrrolidone (NMP) is added as a solvent to prepare a slurry with a solid content of 75wt%, and stirred evenly. Pre-apply foam glue to a portion of the surface of the positive electrode current collector, i.e., aluminum foil, with a thickness of 9μm, and evenly coat the slurry on one surface of the aluminum foil, heat it to make the foam glue fall off so that a portion of the surface of the aluminum foil is exposed, and then dry it at 90°C, and repeat the above coating steps on the other surface of the aluminum foil to obtain a double-sided coated positive electrode sheet. The initial positive electrode sheet is cold pressed to obtain a single coating thickness of 77μm positive electrode active material layer, and then cut and other processes are performed to obtain a positive electrode sheet. Then, two first conductive plates are welded on the exposed aluminum foil, and the material of the first conductive plates is aluminum. Then, refer to Figure 2 The third adhesive component and the fourth adhesive component are respectively adhered to the third end area of ​​the aluminum foil.

[0112] (2) Preparation of the second electrode sheet: The negative electrode active material artificial graphite, silicon carbon material, conductive carbon black (Super P), polyacrylic acid binder (PAA), and lithium difluorophosphate (LDPF) are mixed in a weight ratio of 69:5:6:19:1, and deionized water is added as a solvent to prepare a slurry with a weight percentage of 55wt%, and stirred evenly. Pre-apply foam glue to a portion of the surface of the negative electrode current collector, i.e., copper foil, with a thickness of 5μm, and evenly coat the slurry on one surface of the copper foil, heat it to make the foam glue fall off so that the copper foil surface is exposed, and then dry it at 90°C, and repeat the above coating steps on the other surface of the copper foil to obtain a double-sided coated negative electrode sheet. The initial negative electrode sheet is rolled to obtain a negative electrode active material layer with a coating thickness of 70μm. Then, two second conductive plates are welded on the exposed copper foil, and the second conductive plates are made of nickel.

[0113] (3) Preparation of electrolyte: In a dry argon atmosphere, first mix the organic solvents ethylene carbonate (EC), ethyl methyl carbonate (EMC) and diethyl carbonate (DEC) in a mass ratio of EC:EMC:DEC=30:50:20, then add lithium salt lithium hexafluorophosphate (LiPF6) to the organic solvent to dissolve and mix evenly to obtain an electrolyte with a lithium salt concentration of 1.15 mol / L.

[0114] (4) Preparation of isolation film: A polyethylene (PE) film with a thickness of 9 μm was selected.

[0115] (5) Preparation of secondary battery: The first electrode sheet, the separator and the second electrode sheet are stacked and wound in sequence to obtain Figure 2 The electrode assembly shown in FIG. 1 , wherein the two second conductive plates and the two first conductive plates are arranged as follows Figure 1 As shown, the two second conductive plates and the two first conductive plates are arranged in sequence along the third direction, and the extension line of the third edge along the first direction is located between the two first conductive plates (such as Figure 3 As shown). A fifth adhesive is provided at the tail of the electrode assembly. Then, the aluminum-plastic film (thickness of 150 μm) with the pits formed is placed in an assembly fixture with the pits facing upward, and the electrode assembly is placed in the pits through the first adhesive, wherein the base material layer of the first adhesive is made of polyimide, and the materials of the first adhesive layer and the second adhesive layer are polypropylene. Then, the electrolyte is injected into the pits of the aluminum-plastic film, and the first conductive plate and the second conductive plate are led out of the aluminum-plastic film and then packaged to obtain a secondary battery. The length of the electrode assembly in Examples 1 to 15 is 70.5 mm, the width is 40.5 mm, and the area of ​​the electrode assembly is 2855.25 mm 2It should be noted that the length, width and area of ​​the electrode assembly are the dimensions of the projection of the electrode assembly along the second direction, measured using a micrometer. The differences between the embodiments are related parameters L1, |L2-L3|, S2, which are specifically recorded in Table 1.

[0116] Embodiment 17

[0117] The difference from Example 1 is that the end position of the first pole piece is different, and when viewed along the first direction, the projection of the first end region does not overlap with the projections of the plurality of conductive plates (eg Figure 5 shown).

[0118] Embodiment 18

[0119] The difference from Embodiment 1 is that the end position of the first pole piece is different, and when viewed along the first direction, the extension line of the third edge along the first direction is located in the middle position of the first conductive plate along the third direction.

[0120] Comparative Example

[0121] The difference from the first embodiment is that the first adhesive member is not extended along the first direction, that is, the projection of the first edge does not fall within the projection range of the first adhesive member.

[0122] Then, the secondary batteries of the embodiments and comparative examples were subjected to a drop test, a volume energy density test, a cycle capacity retention rate test, and a secondary battery expansion rate test, respectively.

[0123] The drop test steps are as follows: 1) Under the environmental conditions of 20±5℃, let the secondary battery stand for 5 minutes, charge to 4.53V at 0.2C constant current, charge to 0.025C at constant voltage, and let stand for 5 minutes; 2) Put the secondary battery into the fixture compartment, and use the automatic drop device to drop the secondary battery from a position of 1m to the cement floor along the four corners and six surfaces in a round, for a total of 5 rounds, i.e. 50 times; 3) After the drop, if the secondary battery does not catch fire, explode, leak, etc., the secondary battery passes the drop test. Take 20 secondary batteries from each group of embodiments and each group of comparative examples for testing, and the corresponding test results are recorded in Table 1.

[0124] The volume energy density test steps are as follows: 1) Under the environmental conditions of 25°C, let the secondary battery stand for 10 minutes, charge to 4.5V at 0.2C constant current, charge to 0.02C at constant voltage, and let stand for 5 minutes; then discharge to 3V at 0.2C constant current, let stand for 5 minutes, and record the discharge capacity C0; 2) Measure the length, width and thickness of the secondary battery by PPG (Parallel Plate Gauge), and calculate the volume energy density by the following formula: Volume energy density = 3.92C0 / (length × width × thickness). The test results are recorded in Table 1.

[0125] The test steps for the cycle capacity retention rate and the secondary battery expansion rate are as follows: at room temperature (25°C), charge the secondary battery to 4.53V at 3C constant current and constant voltage, cut off at 0.02C, let it stand for 5 minutes, and use PPG to measure the thickness of the secondary battery as the thickness of the first full charge and record it; then discharge it to 3V at 1C constant current, and then discharge it to 3V at 0.7C constant current, let it stand for 5 minutes. This process is recorded as 1 cycle, and the discharge capacity of the first cycle is recorded; repeat the charge and discharge according to the above steps 1000 times, and record the thickness of the secondary battery after the 1000th full charge and the discharge capacity of the secondary battery after 1000 cycles.

[0126] Cycle capacity retention rate = (discharge capacity of the secondary battery after 1000 cycles / discharge capacity of the first cycle) × 100% Secondary battery expansion rate = [(thickness of the secondary battery after the 1000th full charge - thickness of the secondary battery after the first full charge) / thickness of the secondary battery after the first full charge] × 100%

[0127] The test results are recorded in Table 1.

[0128] Whether there are bubbles in the first adhesive: Observe the state of the first adhesive on the surface of the electrode assembly with the naked eye to determine whether there are bubbles.

[0129] Table 1

[0130]

[0131]

[0132]

[0133]

[0134]

[0135]

[0136] Note: (1) In Table 1, L1 is “-0.1 mm”, which means that the first edge of the first pole piece exceeds the fourth edge of the first adhesive member along the first direction by a distance of 0.1 mm;

[0137] (2) In Table 1, all values ​​of |L2-L3| within the range of ±0.05 mm can be regarded as corresponding values. For example, all values ​​within the range of -0.05 mm ≤ |L2-L3| ≤ 0.05 mm can be regarded as |L2-L3| = 0 mm, and the same applies to the others.

[0138] (3) In Table 1, the drop test passing rate is n / 20, which means that among the 20 secondary batteries tested, the number of secondary batteries that passed the test is n. The meanings of other ratio values ​​are similar.

[0139] From the comparison of the experimental data of the comparative example and Example 1 in Table 1, it can be seen that the first edge of the first pole piece is flush with the fourth edge of the first adhesive, which can greatly improve the drop pass rate of the secondary battery. By comparing the experimental data of Examples 1 to 7 in Table 1, it can be seen that when 0.2mm≤L1≤2.0mm, the drop test pass rate of the secondary battery is high; when L1>2.0mm, the drop pass rate of the secondary battery does not continue to increase, and it can be imagined that due to the excessive size of L1, it is easy to cause the first adhesive to occupy more space in the first direction, and increase the risk of the first adhesive abutting the sealing edge of the packaging bag in the first direction, and increase the risk of the first adhesive entering the packaging area of ​​the packaging bag. The risk of reduced packaging reliability; in order to take into account the secondary battery has a higher drop safety performance and reduce the related risks caused by the first adhesive exceeding the edge of the first pole piece in the first direction, it is preferred that 0.2mm≤L1≤2.0mm; on this basis, it is further preferred that 0.2mm≤L1≤1.4mm. By comparing the experimental data of Example 1 and Examples 8 to 10 in Table 1, it can be seen that when 0≤|L2-L3|≤4mm, the secondary battery has a higher drop test pass rate. When |L2-L3|>4mm, the first adhesive is more biased toward one of the edges of the electrode assembly in the third direction, which increases the stress between the packaging bag and the electrode assembly during the drop process, resulting in a lower drop test pass rate for the secondary battery. By comparing the experimental data of Example 1 and Examples 11 to 16 in Table 1, it can be seen that the value of S2 / S1 has an impact on the cycle capacity retention rate of the secondary battery, the expansion rate of the secondary battery and whether there are bubbles in the first adhesive. When S2 / S1≥0.4, the area of ​​the electrode assembly covered by the first adhesive is not too small, which can improve the drop resistance of the secondary battery, and can reduce the risk of local lithium precipitation due to undervoltage in the position of the electrode assembly not covered by the first adhesive during the formation process, thereby improving the cycle capacity retention rate of the secondary battery. In addition, the first adhesive has a certain area, which can reduce the expansion of the secondary battery during the cycle process to a certain extent and reduce the expansion rate of the secondary battery. When S2 / S1≤1, it can reduce the risk of the first adhesive being easily bonded to other positions after exceeding the electrode assembly. The risk of adhesion is reduced, thereby improving the anti-drop performance of the secondary battery; therefore, limiting 0≤S2 / S1≤1 can take into account the higher anti-drop risk, higher cycle capacity retention rate and lower expansion rate of the secondary battery; when S2 / S1≥1, bubbles exist on the surface of the first adhesive, which is because the area of ​​the first adhesive is too large, resulting in bubbles in the pasting process; and when S2 / S1>1, the first adhesive is prone to adhesion to other positions after exceeding the electrode assembly, which instead deteriorates the anti-drop performance of the secondary battery; therefore, 0.5≤S2 / S1≤0.7 is preferred, thereby improving the anti-drop performance of the secondary battery, increasing the cycle capacity retention rate of the secondary battery and reducing the expansion rate of the secondary battery, while also improving the bonding effect of the first adhesive and the appearance of the secondary battery.By comparing the experimental data of Example 1 and Example 17 and Example 18 in Table 1, it can be seen that when the projection of the first tail area does not overlap with the projections of the multiple conductive plates, the volume energy density of the secondary battery is the largest. This is because the conductive plate is located at a position where the thickness of the electrode assembly is relatively large, and the first tail area does not overlap with the projection of the conductive plate, thereby avoiding the accumulation of thickness at the conductive plate position; when the extension line of the third edge along the first direction is located between the two first conductive plates, the volume energy density of the secondary battery is centered; when the extension line of the third edge along the first direction is located in the middle position of the first conductive plate along the third direction, that is, the extension line of the third edge overlaps with the first conductive plate, and at this time, there is an accumulation of the thickness of the conductive plate and the thickness of the tail area at the conductive plate position, resulting in the lowest volume energy density of the secondary battery.

[0140] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present application and are not intended to limit it. Although the present application has been described in detail with reference to the preferred embodiments, a person of ordinary skill in the art should understand that the technical solution of the present application may be modified or replaced by equivalents without departing from the spirit and scope of the technical solution of the present application.

Claims

1. A secondary battery, wherein: include: Packaging bags; An electrode assembly is arranged in the packaging bag, the electrode assembly includes a first pole sheet and a second pole sheet, the first pole sheet and the second pole sheet are stacked and wound; the first pole sheet includes a first current collector and a first active material layer, the first current collector includes a first surface and a second surface opposite to each other along the thickness direction of the first current collector, the first surface faces the winding center axis, and the second surface faces away from the winding center axis, the first active material layer includes a first sublayer arranged on the first surface and a second sublayer arranged on the second surface, the first current collector includes a first tail region in the winding direction, the first tail region is exposed to the first sublayer and the second sublayer and is located at the last fold of the first current collector along the winding direction; the first tail region includes a third edge, and the third edge is the tail edge of the electrode assembly; as well as A first adhesive member is bonded to at least a portion of the surface of the first tail area facing the packaging bag and the third edge, and the first adhesive member crosses the third edge along the winding direction and bonds to a portion of the second surface; the width direction of the first pole piece is the first direction, the thickness direction of the electrode assembly is the second direction, the first direction and the second direction are perpendicular to each other, and the third direction is a direction perpendicular to the first direction and the second direction; the first pole piece includes a first edge and a second edge arranged opposite to each other along the first direction, and when viewed along the second direction, the first edge overlaps with the first adhesive member.

2. The secondary battery according to claim 1, wherein The first adhesive also adheres a portion of the surface of the packaging bag facing the electrode assembly; the secondary battery also includes a plurality of conductive plates, the number of the conductive plates in the plurality of conductive plates is N, the number of the conductive plates extending from one side of the first edge is N1, N≥N1, N1≥3.

3. The secondary battery according to claim 2, wherein: N=4, N1=4, the multiple conductive plates include two first conductive plates and two second conductive plates, the second pole piece includes a second current collector, the two first conductive plates are electrically connected to the first current collectors, the two second conductive plates are electrically connected to the second current collectors, and the two first conductive plates and the two second conductive plates are arranged sequentially in the third direction.

4. The secondary battery according to any one of claims 1 to 3, wherein: The first adhesive member includes a fourth edge, and the fourth edge and the first edge are located at the same end of the electrode assembly along the first direction; Observed along the second direction, a distance between the fourth edge and the first edge along the first direction is L1, and 0≤L1≤2.0 mm.

5. The secondary battery according to claim 4, wherein: 0.2mm≤L1≤2.0mm.

6. The secondary battery according to claim 5, wherein: 0.2mm≤L1≤1.4mm.

7. The secondary battery according to claim 2, wherein: When viewed along the second direction, an extension line of the third edge along the first direction is located between two adjacent conductive plates in the third direction.

8. The secondary battery according to claim 7, wherein: The projection of the electrode assembly in the second direction includes a fifth edge and a sixth edge arranged opposite to each other along the third direction, and the first adhesive includes a seventh edge and an eighth edge arranged opposite to each other along the third direction; along the third direction, the fifth edge, the seventh edge, the eighth edge, and the sixth edge are arranged in sequence; the distance between the fifth edge and the seventh edge along the third direction is L2, and the distance between the sixth edge and the eighth edge along the third direction is L3; 0≤|L2-L3|≤4mm.

9. The secondary battery according to claim 7 or 8, wherein: The projection area of ​​the electrode assembly along the second direction is S1, the area of ​​the first adhesive is S2, and 0.4≤S2 / S1≤1.

10. The secondary battery according to claim 9, wherein 0.5≤S2 / S1≤0.

7.

11. The secondary battery according to claim 2, wherein: When viewed along the first direction, a projection of the first termination area does not overlap with projections of the plurality of conductive plates.

12. The secondary battery according to claim 11, wherein The secondary battery also includes a second adhesive, which is bonded to the surface of the packaging bag facing the electrode assembly and a portion of the second surface located on the same side as the third edge in the second direction, and the first adhesive and the second adhesive are arranged in sequence and separated in the third direction.

13. The secondary battery according to claim 12, wherein The projection of the electrode assembly in the second direction includes a fifth edge and a sixth edge arranged opposite to each other along the third direction, the first adhesive includes a seventh edge and an eighth edge arranged opposite to each other along the third direction, and the second adhesive includes a ninth edge and a tenth edge arranged opposite to each other along the third direction; along the third direction, the fifth edge, the ninth edge, the tenth edge, the seventh edge, the eighth edge and the sixth edge are arranged in sequence; the straight-line distance between the sixth edge and the eighth edge along the third direction is L3, and the straight-line distance between the fifth edge and the ninth edge along the third direction is L4; 0≤|L3-L4|≤4mm.

14. The secondary battery according to claim 12 or 13, wherein: The projection area of ​​the electrode assembly along the second direction is S1, the area of ​​the first adhesive is S2, the area of ​​the second adhesive is S3, and 0.4≤(S2+S3) / S1≤1.

15. The secondary battery according to claim 14, wherein 0.5≤(S2+S3) / S1≤0.

7.

16. The secondary battery according to claim 1, wherein The first sublayer includes a second end region in the winding direction, the second sublayer includes a third end region in the winding direction, the second end region is located at the outermost winding circle of the first pole piece, and the third end region is located at the second outer winding circle of the first pole piece; The secondary battery further includes a third adhesive member, the third adhesive member is disposed in the second tail region and extends along the winding direction and adheres to the first surface, and when viewed from the second direction, the first adhesive member and the third adhesive member are separated in the third direction; And / or, the secondary battery further includes a fourth adhesive, which is disposed in the third finishing area and extends along the winding direction and adheres to the second surface, and when viewed from the second direction, the first adhesive and the fourth adhesive are separated in the third direction.

17. The secondary battery according to claim 1, wherein The secondary battery also includes a fifth adhesive, the electrode assembly includes a first end and a second end arranged opposite to each other in the first direction, the first edge is located at the first end, the second edge is located at the second end, the fifth adhesive is bonded to the second end, and when viewed from the second direction, the first adhesive and the fifth adhesive are separated in the first direction.

18. The secondary battery according to claim 1, wherein The first adhesive member comprises a first adhesive layer, a substrate layer and a second adhesive layer sequentially stacked along the thickness direction of the first adhesive member, the first adhesive layer is arranged on a surface of the substrate layer facing the packaging bag, and the second adhesive layer is arranged on a surface of the substrate layer facing the first finishing area; The material of the substrate layer includes at least one of polyethylene, polypropylene, polyethylene terephthalate, polyimide, polyamide, spandex and aramid; The materials of the first adhesive layer and the second adhesive layer independently include at least one of polyethylene, polypropylene, polyurethane, epoxy resin, styrene-butadiene rubber, polyvinylidene fluoride, polyacrylate, polyacrylic acid and derivatives thereof.

19. The secondary battery according to claim 1, wherein The first pole piece is a positive pole piece, and the second pole piece is a negative pole piece.

20. The secondary battery according to claim 19, wherein The first adhesive component exceeds an edge of the second pole piece in the first direction.

21. An electronic device, wherein: The electronic device includes the secondary battery according to any one of claims 1 to 20.

Images