Secondary battery and electric device

Abstract

The invention discloses a secondary battery and electric equipment, the secondary battery comprises an electrode assembly and a first extension part, and the electrode assembly is of a laminated structure. The electrode assembly comprises a first outer-layer pole piece, an isolating membrane and a second outer-layer pole piece which are arranged in the first direction. And the first outer-layer pole piece comprises a first outer-layer current collector. And the second outer-layer pole piece comprises a second outer-layer current collector. The first outer current collector includes a first angular position. And the second outer layer current collector comprises a second angular position. The first angular position and the second angular position are at least partially overlapped when viewed in the first direction. And the first extension part extends out of the first outer-layer current collector from the first angular position and is fixedly connected with the second outer-layer current collector. The first corner position and the second corner position are fixedly connected, so that the problem that the first corner position and the second corner position tilt to influence the performance of the secondary battery is solved; and the risk that the outer-layer current collector is turned over due to the upwarp of the first corner position and / or the second corner position is reduced.

Description

Technical Field

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

[0002] With the continuous updating and development of secondary battery technology, the application fields of secondary batteries are also expanding. The safety issues of secondary batteries that follow are receiving more and more public attention. During the recycling process of secondary batteries with a laminated structure, the corners of the outermost electrodes are prone to warping, causing safety issues for the secondary batteries. Summary of the invention

[0003] In view of this, it is necessary to provide a secondary battery and an electrical device to improve the corner warping problem and enhance the safety of the secondary battery.

[0004] An embodiment of the present application provides a secondary battery, including an electrode assembly, wherein the electrode assembly is in a laminate structure. The electrode assembly includes a first outer electrode sheet, a separator, and a second outer electrode sheet arranged along a first direction. The first outer electrode sheet includes a first outer current collector. The second outer electrode sheet includes a second outer current collector. The first outer current collector includes a first angular position. The second outer current collector includes a second angular position. When viewed along the first direction, the first angular position and the second angular position at least partially overlap. The electrode assembly also includes a first extension portion, the first extension portion extends from the first angular position to the first outer current collector, and the first extension portion is fixedly connected to the second outer current collector. The first corner and the second corner are fixedly connected by the first extension part, so as to reduce the warping of the first corner and the second corner, improve the poor contact between the first outer electrode and the isolation membrane and between the second outer electrode and the isolation membrane in the warping area, which leads to the obstruction of the lithium ion transmission path and the generation of lithium purple spots, thus affecting the performance of the secondary battery; improve the repeated mechanical stress on the warping area during the charging and discharging process, which is beneficial to reduce the risk of cracks in the active material layer on the first outer current collector and / or the second outer current collector; reduce the risk of the first corner and / or the second corner warping scratching the adhesive layer of the packaging bag, causing the adhesive layer to accumulate, hindering the extension of the first outer current collector and / or the second outer current collector, and causing the first outer current collector and / or the second outer current collector to fold.

[0005] In one or more optional embodiments above, the electrode assembly further includes a second extension portion, the second extension portion extends from the second corner position to the second outer current collector, and the first extension portion is fixedly connected to the second extension portion.

[0006] In one or more of the above optional embodiments, the first extension portion is connected to the second corner by welding.

[0007] In one or more optional embodiments above, the first extension portion is connected to the second extension portion by welding.

[0008] In one or more optional embodiments above, the first pole ear is further included, the first outer current collector further includes a second edge, one of the edges at the first corner is a part of the second edge, and the first pole ear is connected to the second edge. This improves the problem that the corner of the head of the secondary battery is warped compared to the bottom.

[0009] In one or more optional embodiments above, along the thickness direction of the first extension portion, the first extension portion includes a first connection surface and a second connection surface relative to each other, and the first connection surface faces the electrode assembly. Along the thickness direction of the second extension portion, the second extension portion includes a third connection surface and a fourth connection surface relative to each other, and the third connection surface faces the electrode assembly. The first connection surface is welded to the fourth connection surface to form a first welding portion, or the second connection surface is welded to the third connection surface to form a first welding portion, or the first connection surface is welded to the third connection surface to form a first welding portion bent along the first direction; along the first direction, the length L1 of the first welding portion is 1mm≤L1≤2mm. By L1≥1mm, the structural strength of the first welding portion is increased, and the risk of separation of the first extension portion and the second extension portion is reduced. The more overlapping parts of the first extension portion and the second extension portion, the larger the space occupied. By L1≤2mm, the space occupied by the first welding portion is reduced.

[0010] In one or more optional embodiments above, the first extension portion is welded to the second corner to form a second weld portion, and along the length extension direction of the first extension portion, the length L2 of the second weld portion is 1mm≤L2≤2mm. By L2≥1mm, the welding strength of the second weld portion is increased, and the risk of the second weld portion falling off from the second corner is reduced. By L2≤2mm, the space occupied by the second weld portion is reduced.

[0011] In one or more optional embodiments above, the width D1 of the first extension portion is 1 mm ≤ D1 ≤ 5 mm; and / or the width D2 of the second extension portion is 1 mm ≤ D2 ≤ 5 mm. This reduces the difficulty of welding the first extension portion and the second extension portion, facilitates welding, reduces the impact on the electrode assembly, and reduces the occupied space.

[0012] In one or more optional embodiments above, the thickness H1 of the first extension portion is 8μm≤H1≤20μm. By H1≥8μm, the risk of the first extension portion and the first pole tab connected to the first outer current collector being too thin and breaking is reduced. By H1≤20μm, the thickness of the first extension portion, the first outer current collector and the first pole tab is controlled to reduce the impact on the energy density of the secondary battery; and / or, the thickness H2 of the second extension portion is 8μm≤H2≤20μm. By H2≥8μm, the risk of the second extension portion and the second pole tab connected to the second outer current collector being too thin and breaking is reduced. By H2≤20μm, the thickness of the second extension portion, the second outer current collector and the second pole tab is controlled to reduce the impact on the energy density of the secondary battery.

[0013] In one or more optional embodiments above, the electrode assembly includes a second pole piece, the second pole piece has a polarity opposite to that of the first outer pole piece, the second pole piece is disposed between adjacent isolation films, and the adjacent isolation films are bonded and disposed in a region beyond the second pole piece and cover the second pole piece, thereby reducing the risk of the first extension portion and the second extension portion contacting the second pole piece and causing a short circuit.

[0014] In one or more optional embodiments above, the first extension portion is bent relative to the first outer current collector and forms a first angle α, 90°≤α≤120°. By α≥90°, the first extension portion is away from the isolation membrane and other pole pieces between the first outer pole piece and the second outer pole piece, reducing the difficulty of welding and facilitating welding. On the basis of facilitating welding, by α≤120°, the space occupied by the first extension portion along the second direction is reduced, and the interference in the subsequent packaging molding process of the secondary battery is reduced. The second extension portion is bent relative to the second outer current collector and forms a second angle β, 90°≤β≤120°, and the first extension portion is welded to the second extension portion. By β≥90°, the second extension portion is away from the isolation membrane and other pole pieces between the first outer pole piece and the second outer pole piece, reducing the difficulty of welding and facilitating welding. On the basis of facilitating welding, by β≤120°, the space occupied by the second extension portion along the second direction is reduced, and the interference in the subsequent packaging molding process of the secondary battery is reduced.

[0015] In one or more optional embodiments above, the first outer current collector includes a third corner, the second outer current collector includes a fourth corner, and when viewed along the first direction, the third corner overlaps with the fourth corner. The electrode assembly includes a third extension portion, the third extension portion extends from the third corner to the first outer current collector, and the third extension portion is welded to the fourth corner; or the electrode assembly further includes a fourth extension portion, the fourth extension portion extends from the fourth corner to the second outer current collector, and the third extension portion is welded to the fourth extension portion, so as to improve the problem caused by the warping of the third corner and the fourth corner.

[0016] In one or more optional embodiments above, the first pole ear and the second pole ear are also included, the first outer current collector includes a second edge, one of the edges at the first corner is a part of the second edge, one of the edges at the third corner is a part of the second edge, and the first pole ear is connected to the second edge; the second outer current collector includes a fourth edge, one of the edges at the second corner is a part of the fourth edge, one of the edges at the fourth corner is a part of the fourth edge, and the second pole ear is connected to the fourth edge. The problem of the corner of the head of the secondary battery being warped compared to the bottom is improved.

[0017] In one or more optional embodiments above, the first outer current collector includes a fifth corner, the second outer current collector includes a sixth corner, and when viewed along the first direction, the fifth corner overlaps the sixth corner. The electrode assembly includes a fifth extension, the fifth extension extends from the fifth corner to the first outer current collector, and the fifth extension is welded to the sixth corner; or the electrode assembly further includes a sixth extension, the sixth extension extends from the sixth corner to the second outer current collector, and the fifth extension is welded to the sixth extension, so as to improve the warping problem of the fifth corner and the sixth corner.

[0018] An embodiment of the present application provides an electrical device, comprising the secondary battery in any one of the above embodiments.

[0019] The above-mentioned electrical equipment reduces the warping of the first corner and the second corner by fixedly connecting the first corner with the second corner, improves the poor contact between the first outer electrode and the isolation membrane and between the second outer electrode and the isolation membrane in the warping area, resulting in obstruction of the lithium ion transmission path and thus the generation of lithium purple spots, which affects the performance of the secondary battery; improves the repeated mechanical stress on the warping area during the charging and discharging process, which is beneficial to reduce the risk of cracks in the active material layer on the first outer current collector and / or the second outer current collector; reduces the risk of the first corner and / or the second corner warping scratching the adhesive layer of the packaging bag, causing the adhesive layer to accumulate, hindering the extension of the first outer current collector and / or the second outer current collector, and causing the first outer current collector and / or the second outer current collector to fold; in addition, compared with the existing method of slowing down the warping of the first corner and / or the second corner by thickening the thickness of the first outer current collector and the second outer current collector, the present application can also reduce the thickness of the first outer current collector and the thickness of the second outer current collector, thereby improving the energy density of the secondary battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 A partial structural schematic diagram of a secondary battery in some embodiments is shown.

[0021] Figure 2 A schematic diagram of the structure of the first outer pole piece in some embodiments is shown.

[0022] Figure 3 A schematic diagram of the structure of the second outer pole piece in some embodiments is shown.

[0023] Figure 4 A partial schematic diagram of a secondary battery from another perspective in some embodiments is shown.

[0024] Figure 5 A partial schematic diagram of a secondary battery from another viewing angle in some other embodiments is shown.

[0025] Figure 6 A partial schematic diagram of a secondary battery from another perspective in some embodiments is shown.

[0026] Figure 7 Schematic diagrams of the structure of the first outer pole piece in other embodiments are shown.

[0027] Figure 8 Partial structural schematic diagrams of secondary batteries in some further embodiments are shown.

[0028] Fig. 9 Schematic diagrams of the structures of the first outer pole pieces in some other embodiments are shown.

[0029] Fig.10 Schematic diagrams of the structures of the second outer pole pieces in other embodiments are shown.

[0030] Fig.11 Shows Figure 8 A partial schematic diagram of a secondary battery from another perspective in an embodiment.

[0031] Fig.12 A schematic diagram of the structure of electrical equipment in some embodiments is shown.

[0032] Description of main component symbols:

[0033] Secondary battery 100

[0034] Electrode assembly 10

[0035] The first outer pole piece 11

[0036] First outer current collector 11a

[0037] First corner 111

[0038] The third corner 112

[0039] Fifth Corner 113

[0040] Seventh corner 114

[0041] First active material layer 11b

[0042] First Edge 101

[0043] Second Edge 102

[0044] Sixth section 102b

[0045] First intersection point A

[0046] First section 101a

[0047] Second section 102a

[0048] First Link 110

[0049] Second Link 120

[0050] Third Link 130

[0051] Fourth Link 140

[0052] Isolation film 12

[0053] The second outer pole piece 13

[0054] Second outer current collector 13a

[0055] Second corner 131

[0056] The fourth corner 132

[0057] Sixth corner 133

[0058] Eighth Corner 134

[0059] Second active material layer 13b

[0060] Third Edge 103

[0061] Fourth Edge 104

[0062] Eighth section 104b

[0063] The third section 103a

[0064] Fourth section 104a

[0065] The second intersection point B

[0066] Fifth Edge 105

[0067] The third intersection point C

[0068] Fifth section 105a

[0069] Sixth Edge 106

[0070] Fourth intersection D

[0071] Seventh section 106a

[0072] Seventh Edge 107

[0073] Eighth Edge 108

[0074] The first extension portion 14

[0075] First welding portion 14a

[0076] The first connecting surface 141

[0077] The second connecting surface 142

[0078] The second extension portion 15

[0079] The third connection surface 151

[0080] Fourth connecting surface 152

[0081] The third extension portion 16

[0082] The third welding portion 16a

[0083] Fourth extension portion 17

[0084] Fifth extension portion 18

[0085] Sixth extension 19

[0086] Seventh extension portion 10A

[0087] Eighth extension portion 10B

[0088] Fifth welding portion 10C

[0089] The second pole piece 10D

[0090] First tab 20

[0091] Second pole ear 30

[0092] Electrical equipment 200

[0093] First direction X

[0094] Second direction Y

[0095] The third direction Z

[0096] The following specific embodiments will further illustrate the present application in conjunction with the above-mentioned drawings. DETAILED DESCRIPTION

[0097] The technical solutions in the embodiments of the present application will be described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all of the embodiments.

[0098] When a component is considered to be “provided on” another component, it can be directly provided on the other component or there may be a component in between. When a component is considered to be “connected to” another component, it can be directly connected to the other component or there may be a component in between.

[0099] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art to which this application belongs. The terms used herein in the specification of this application are only for the purpose of describing specific embodiments and are not intended to limit this application. The term "or / and" used herein includes any and all combinations of one or more related listed items.

[0100] It can be understood that the term "perpendicular" is used to describe an ideal state between two components. In actual production or use, there may be a state that is approximately perpendicular or equal to each other between the two components. For example, in combination with numerical descriptions, perpendicularity can refer to the angle between two straight lines being between 90°±10°, perpendicularity can also refer to the dihedral angle between two planes being between 90°±10°, and perpendicularity can also refer to the angle between a straight line and a plane being between 90°±10°. The two components described as "perpendicular" may not be absolute straight lines or planes, but may be roughly straight lines or planes. From a macroscopic perspective, a component can be considered a "straight line" or a "plane" if the overall extension direction is a straight line or a plane.

[0101] Unless otherwise defined, when the term "plurality" is used to describe the number of components, it specifically means that the components are two or more.

[0102] Some embodiments of the present application are described in detail below in conjunction with the accompanying drawings. In the absence of conflict, the following embodiments and features in the embodiments can be combined with each other.

[0103] See also Figures 1 to 3 An embodiment of the present application provides a secondary battery 100, including an electrode assembly 10, the electrode assembly 10 is a laminate structure, and the electrode assembly 10 includes a first outer electrode sheet 11, a separator 12 and a second outer electrode sheet 13 arranged along a first direction X.

[0104] The first outer electrode piece 11 includes a first outer current collector 11a, the second outer electrode piece 13 includes a second outer current collector 13a, the first outer current collector 11a includes a first angle position 111, and the second outer current collector 13a includes a second angle position 131. When viewed along the first direction X, the first angle position 111 and the second angle position 131 at least partially overlap.

[0105] In some embodiments, the electrode assembly 10 includes a first extension 14, the first extension 14 extends from the first corner 111 to the first outer current collector 11a, and the first extension 14 is fixedly connected to the second outer current collector 13a. In some embodiments, the secondary battery 100 includes a packaging bag (not shown), and the electrode assembly 10 is arranged in the packaging bag. The packaging bag includes an adhesive layer, a metal layer and an outer layer arranged in sequence along its thickness direction. The adhesive layer is the innermost side of the packaging bag. The outer layer can be a nylon layer or a composite layer of polyester resin (PET) and nylon, which has the functions of anti-pollution, corrosion resistance and protection against external damage. The metal layer can include one of aluminum and steel, which has waterproof and barrier effects and shapes the packaging bag. The adhesive layer is a heat-sealing layer, and the adhesive layer can include a polymer, and the polymer includes one of polypropylene and polyethylene, which is used to seal the packaging bag and to separate the metal layer from the electrode assembly 10, thereby reducing the risk of electrolyte leakage in the packaging bag and corrosion of the metal layer.

[0106] The present application fixes the first corner 111 and the second corner 131 through the first extension portion 14, thereby reducing the warping of the first corner 111 and the second corner 131, improving the poor contact between the first outer electrode 11 and the isolation film 12 and between the second outer electrode 13 and the isolation film 12 in the warping area, resulting in the obstruction of the lithium ion transmission path and the generation of lithium purple spots, which affects the performance of the secondary battery 100; improving the warping area to repeatedly withstand mechanical stress during the charging and discharging process, which is beneficial to reducing the risk of cracks in the active material layer on the first outer current collector 11a and / or the second outer current collector 13a; reducing the risk of the first corner 111 and / or the second corner 131 warping and scratching the adhesive layer of the packaging bag, causing the adhesive layer to accumulate, hindering the extension of the first outer current collector 11a and / or the second outer current collector 13a, and causing the first outer current collector 11a and / or the second outer current collector 13a to fold. In addition, compared with the existing method of reducing the warping of the first corner 111 and / or the second corner 131 by thickening the thickness of the first outer current collector 11a and the thickness of the second outer current collector 13a, the present application can also reduce the thickness of the first outer current collector 11a and the thickness of the second outer current collector 13a, so as to improve the energy density of the secondary battery.

[0107] In some embodiments, the first outer electrode sheet 11 includes a first active material layer 11b. Along the first direction X, the first active material layer 11b is provided on the side of the first outer current collector 11a facing the isolation membrane 12, and the first active material layer 11b is not provided on the side of the first outer current collector 11a away from the isolation membrane 12, that is, the first active material layer 11b is not provided on the outermost side of the first outer current collector 11a.

[0108] In some embodiments, the second outer electrode sheet 13 includes a second active material layer 13b, and along the first direction X, the second outer current collector 13a is provided with the second active material layer 13b on the side facing the isolation film 12, and the second outer current collector 13a is not provided with the second active material layer 13b on the side facing away from the isolation film 12, that is, the outermost side of the second outer current collector 13a is not provided with the second active material layer 13b. The first active material layer 11b and the second active material layer 13b are active materials of the same polarity.

[0109] In some embodiments, the present application is described with the first outer electrode sheet 11 being a positive electrode sheet, the second outer electrode sheet 13 being a positive electrode sheet, and the first outer current collector 11a and the second outer current collector 13a can be made of aluminum foil or nickel foil. In other embodiments, the first outer electrode sheet 11 is a negative electrode sheet, the second outer electrode sheet 13 is a negative electrode sheet, and the first outer current collector 11a and the second outer current collector 13a can be made of at least one of copper foil, nickel foil or carbon-based current collector.

[0110] The isolation film 12 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.

[0111] Embodiment 1

[0112] See also Figure 2 In some embodiments, the first outer current collector 11a includes a first edge 101 and a second edge 102, the first edge 101 and the second edge 102 intersect at a first intersection A, a first segment 101a is formed by extending from the first intersection A along the first edge 101, and the length of the first segment 101a is H1, H1≤3mm, and a second segment 102a is formed by extending from the first intersection A along the second edge 102, and the length of the second segment 102a is H2, H2≤3mm, and a first connecting line 110 is defined, and the first connecting line 110 connects one end of the first segment 101a away from the first intersection A and one end of the second segment 102a away from the first intersection A. The first segment 101a, the second segment 102a and the first connecting line 110 enclose a first corner 111.

[0113] See also Figure 3In some embodiments, the second outer current collector 13a includes a third edge 103 and a fourth edge 104, the third edge 103 and the fourth edge 104 intersect at a second intersection B, a third segment 103a is formed by extending from the second intersection B along the third edge 103, and the length of the third segment 103a is H3, H3≤3mm, and a fourth segment 104a is formed by extending from the second intersection B along the fourth edge 104, and the length of the fourth segment 104a is H4, H4≤3mm, and a second connecting line 120 is defined, and the second connecting line 120 connects one end of the third segment 103a away from the second intersection B and one end of the fourth segment 104a away from the second intersection B. The third segment 103a, the fourth segment 104a and the second connecting line 120 enclose a second corner 131.

[0114] In some embodiments, when viewed along the first direction X, the spacing between the first edge 101 and the third edge 103 along the second direction Y is less than 0.5 mm, and the spacing between the second edge 102 and the fourth edge 104 along the third direction Z is less than 0.5 mm, so that the first corner 111 and the second corner 131 at least partially overlap. The second direction Y is one of the length direction and the width direction of the electrode assembly 10, and the third direction Z is the other of the length direction and the width direction of the electrode assembly 10. The first direction X, the second direction Y, and the third direction Z are perpendicular to each other.

[0115] See also Figures 1 to 3 In some embodiments, the electrode assembly 10 includes a second extension portion 15 , the second extension portion 15 extends from the second corner 131 to the second outer current collector 13 a , and the first extension portion 14 and the second extension portion 15 are fixedly connected.

[0116] In some embodiments, the first extension portion 14 and the second extension portion 15 are welded and connected. Specifically, the first extension portion 14 is bent toward the second outer current collector 13a, and the second extension portion 15 is bent toward the first outer current collector 11a, so that a portion of the first extension portion 14 overlaps a portion of the second extension portion 15, and the overlapping portion is welded to form a first welding portion 14a.

[0117] Optionally, the first extension portion 14 extends out of the first outer current collector 11a from the first edge 101 of the area where the first corner position 111 is located, and the second extension portion 15 extends out of the second outer current collector 13a from the third edge 103 of the area where the second corner position 131 is located.

[0118] Optionally, the first extension portion 14 extends out of the first outer current collector 11a from the second edge 102 of the area where the first corner position 111 is located, and the second extension portion 15 extends out of the second outer current collector 13a from the fourth edge 104 of the area where the second corner position 131 is located.

[0119] See also Figure 4In some embodiments, along the thickness direction of the first extension portion 14, the first extension portion 14 includes a first connection surface 141 and a second connection surface 142 opposite to each other, the first connection surface 141 faces the electrode assembly 10, and along the thickness direction of the second extension portion 15, the second extension portion 15 includes a third connection surface 151 and a fourth connection surface 152 opposite to each other, the third connection surface 151 faces the electrode assembly 10. The first connection surface 141 is welded to the fourth connection surface 152 to form a first welding portion 14a. At this time, along the second direction Y, the second connection surface 142 is located at the outermost side.

[0120] In some embodiments, the second connection surface 142 is welded to the third connection surface 151 to form a first welding portion 14a. At this time, the second connection surface 142 is located at the outermost side. At this time, along the second direction Y, the fourth connection surface 152 is located at the outermost side.

[0121] See also Figure 5 In some embodiments, the first connection surface 141 is welded to the third connection surface 151 to form a first welding portion 14a bent along the first direction X.

[0122] In some embodiments, along the first direction X, the length L1 of the first welding portion 14a is 1mm≤L1≤2mm. By L1≥1mm, the structural strength of the first welding portion 14a is increased, and the risk of separation of the first extension portion 14 and the second extension portion 15 is reduced. The more overlapping parts of the first extension portion 14 and the second extension portion 15 are, the larger the space occupied is. By L1≤2mm, the space occupied by the first welding portion 14a is reduced.

[0123] Optionally, L1 can be any value within the range of any one of 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, and 2 mm, or any two of them.

[0124] See also Figure 4 In some embodiments, the first extension portion 14 is bent relative to the first outer current collector 11a and forms a first angle α, 90°≤α≤120°. By α≥90°, the first extension portion 14 is away from the isolation film 12 and other pole pieces between the first outer pole piece 11 and the second outer pole piece 13, reducing the difficulty of welding and facilitating welding. On the basis of facilitating welding, by α≤120°, the space occupied by the first extension portion 14 along the second direction Y is reduced, reducing interference with the subsequent packaging molding process of the secondary battery 100.

[0125] Optionally, α may be any value within the range of any one of 90°, 95°, 100°, 105°, 110°, 115°, and 120°, or any two of them.

[0126] In some embodiments, the second extension portion 15 is bent relative to the second outer current collector 13a and forms a second angle β, 90°≤β≤120°. When β≥90°, the second extension portion 15 is away from the isolation film 12 and other pole pieces between the first outer pole piece 11 and the second outer pole piece 13, reducing the difficulty of welding and facilitating welding. On the basis of facilitating welding, when β≤120°, the space occupied by the second extension portion 15 along the second direction Y is reduced, reducing interference with the subsequent packaging molding process of the secondary battery 100.

[0127] Optionally, β may be any value within the range of any one of 90°, 95°, 100°, 105°, 110°, 115°, 120°, or any two of them.

[0128] In some embodiments, the first extension portion 14 extends from the first intersection A, and the second extension portion 15 extends from the second intersection B, which is further beneficial to improve the problem of warping at the first corner 111 and the second corner 131 .

[0129] See also Figures 4 to 6 The first outer current collector 11a includes a third corner 112, and the second outer current collector 13a includes a fourth corner 132. When viewed along the first direction X, the third corner 112 overlaps with the fourth corner 132, and the third corner 112 is welded to the fourth corner 132. By welding the third corner 112 and the fourth corner 132, the warping of the third corner 112 and the fourth corner 132 is reduced, and the poor contact between the first outer electrode 11 and the isolation film 12 and between the second outer electrode 13 and the isolation film 12 in the warping area of ​​the third corner 112 and the fourth corner 132 is improved, resulting in obstruction of the lithium ion transmission path and the generation of lithium purple spots, which affects the performance of the secondary battery; the warping area is improved to repeatedly withstand mechanical stress during the charge and discharge process, which is beneficial to reduce the risk of cracks in the active material layer on the first outer current collector 11a and / or the second outer current collector 13a, and reduce the risk of the third corner 112 and / or the fourth corner 132 warping and scratching the adhesive layer of the packaging bag, causing the adhesive layer to accumulate, hindering the extension of the first outer current collector 11a and / or the second outer current collector 13a, and causing the risk of the first outer current collector 11a and / or the second outer current collector 13a to fold.

[0130] See also Figure 2In some embodiments, the first outer current collector 11a includes a fifth edge 105, the fifth edge 105 intersects with the second edge 102 at a third intersection C, a fifth segment 105a is formed by extending from the third intersection C along the fifth edge 105, the length of the fifth segment 105a is H5, H5≤3mm, a sixth segment 102b is formed by extending from the third intersection C along the second edge 102, the length of the sixth segment 102b is H6, H6≤3mm, and a third connecting line 130 is defined, the third connecting line 130 connects one end of the fifth segment 105a away from the third intersection C and one end of the sixth segment 102b away from the third intersection C. The fifth segment 105a, the sixth segment 102b and the third connecting line 130 enclose a third corner 112.

[0131] See also Figure 3 In some embodiments, the second outer current collector 13a includes a sixth edge 106, the sixth edge 106 intersects with the fourth edge 104 at a fourth intersection D, and extends from the fourth intersection D along the sixth edge 106 to form a seventh segment 106a, the length of the seventh segment 106a is H7, H7≤3mm, and extends from the fourth intersection D along the fourth edge 104 to form an eighth segment 104b, the length of the eighth segment 104b is H8, H8≤3mm, and a fourth connecting line 140 is defined, and the fourth connecting line 140 connects an end of the seventh segment 106a away from the fourth intersection D and an end of the eighth segment 104b away from the fourth intersection D. The seventh segment 106a, the eighth segment 104b and the fourth connecting line 140 enclose a fourth corner 132.

[0132] See also Figure 4 In some embodiments, the electrode assembly 10 includes a third extension portion 16 and a fourth extension portion 17, the third extension portion 16 extends from the third corner position 112 to the first outer current collector 11a, the fourth extension portion 17 extends from the fourth corner position 132 to the second outer current collector 13a, and the third extension portion 16 is welded to the fourth extension portion 17. Specifically, the third extension portion 16 is bent toward the second outer current collector 13a, and the fourth extension portion 17 is bent toward the first outer current collector 11a, so that a portion of the third extension portion 16 and a portion of the fourth extension portion 17 overlap, and the overlapping portion is welded to form a third welding portion 16a.

[0133] Optionally, the third extension portion 16 extends out of the first outer current collector 11a from the fifth edge 105 of the area where the third corner 112 is located, and the fourth extension portion 17 extends out of the second outer current collector 13a from the sixth edge 106 of the area where the fourth corner 132 is located.

[0134] Optionally, the third extension portion 16 extends from the second edge 102 of the area where the third corner 112 is located to the first outer current collector 11a, and the fourth extension portion 17 extends from the fourth edge 104 of the area where the fourth corner 132 is located to the second outer current collector 13a.

[0135] In some embodiments, the welding method of the third extension portion 16 and the fourth extension portion 17 is the same as the welding method of the first extension portion 14 and the second extension portion 15 , and will not be described in detail herein.

[0136] In some embodiments, the secondary battery 100 includes a first electrode tab 20 , and the first electrode tab 20 extends from the second edge 102 to the first outer current collector 11 a , thereby improving the problem that the top corner of the secondary battery 100 is more likely to be lifted than the bottom corner.

[0137] In some embodiments, the secondary battery 100 includes a second electrode tab 30 , which extends out of the second outer current collector 13 a from the fourth edge 104 , thereby improving the problem that the corner of the head of the secondary battery 100 is more likely to be lifted than the bottom.

[0138] In some embodiments, the width D1 of the first extension portion 14 is 1 mm ≤ D1 ≤ 5 mm. When D1 ≥ 1 mm, the difficulty of welding the first extension portion 14 and the second extension portion 15 is reduced, and welding is facilitated. When D1 ≤ 5 mm, the impact on the electrode assembly 10 is reduced, and the occupied space is reduced.

[0139] Optionally, D1 may be any value within the range of any one of 1 mm, 2 mm, 3 mm, 4 mm, and 5 mm, or any two of them.

[0140] When the first extension portion 14 extends from the first edge 101 along the second direction Y to the first outer current collector 11 a , D1 is the width of the first extension portion 14 along the third direction Z.

[0141] When the first extension portion 14 extends out of the first outer current collector 11 a from the second edge 102 along the third direction Z, D1 is the width of the first extension portion 14 along the second direction Y.

[0142] In some embodiments, the width D2 of the second extension portion 15 is 1 mm ≤ D2 ≤ 5 mm. When D2 ≥ 1 mm, the difficulty of welding the first extension portion 14 and the second extension portion 15 is reduced, and welding is facilitated. When D2 ≤ 5 mm, the impact on the electrode assembly 10 is reduced, and the occupied space is reduced.

[0143] Optionally, D2 may be any value within the range of any one of 1 mm, 2 mm, 3 mm, 4 mm, and 5 mm, or any two of them.

[0144] When the second extension portion 15 extends out of the second outer current collector 13 a from the third edge 103 along the second direction Y, D2 is the width of the second extension portion 15 along the third direction Z.

[0145] When the second extension portion 15 extends out of the second outer current collector 13 a from the fourth edge 104 along the third direction Z, D2 is the width of the second extension portion 15 along the second direction Y.

[0146] In some embodiments, the width D1 of the first extension portion 14 is equal to the width D2 of the second extension portion 15 .

[0147] In some embodiments, the thickness H1 of the first extension portion 14 is 8 μm ≤ H1 ≤ 20 μm. When H1 ≥ 8 μm, the risk of the first extension portion 14 and the first tab 20 being too thin and broken is reduced. When H1 ≤ 20 μm, the thickness of the first extension portion 14, the first outer layer current collector 11a and the first tab 20 is controlled to reduce the impact on the energy density of the secondary battery 100.

[0148] In some embodiments, the thickness H2 of the second extension portion 15 is 8 μm ≤ H2 ≤ 20 μm. 8 μm ≤ H2 ≤ 20 μm. By H2 ≥ 8 μm, the risk of the second extension portion 15 and the second tab 30 being too thin and broken is reduced. By H2 ≤ 20 μm, the thickness of the second extension portion 15, the second outer layer current collector 13a and the second tab 30 is controlled to reduce the impact on the energy density of the secondary battery 100.

[0149] In some embodiments, the thickness H1 of the first extension portion 14 is equal to the thickness H2 of the second extension portion 15 .

[0150] See also Figure 1 , Figure 6 and Figure 7 In some embodiments, the first outer current collector 11a includes a fifth corner 113, and the second outer current collector 13a includes a sixth corner 133. When viewed along the first direction X, the fifth corner 113 overlaps with the sixth corner 133, and the fifth corner 113 is welded to the sixth corner 133. By welding the fifth corner 113 and the sixth corner 133, the warping of the fifth corner 113 and the sixth corner 133 is reduced, and the poor contact between the first outer electrode 11 and the isolation film 12 and between the second outer electrode 13 and the isolation film 12 in the warping area of ​​the fifth corner 113 and the sixth corner 133 is improved, resulting in obstruction of the lithium ion transmission path and the generation of lithium purple spots, which affects the performance of the secondary battery; the warping area is improved to repeatedly withstand mechanical stress during the charge and discharge process, which is beneficial to reduce the risk of cracks in the active material layer on the first outer current collector 11a and / or the second outer current collector 13a, and reduce the risk of the fifth corner 113 and / or the sixth corner 133 warping and scratching the adhesive layer of the packaging bag, causing the adhesive layer to accumulate, hindering the extension of the first outer current collector 11a and / or the second outer current collector 13a, and causing the first outer current collector 11a and / or the second outer current collector 13a to fold.

[0151] In some embodiments, the first outer current collector 11a includes a seventh edge 107, and the seventh edge 107 and the first edge 101 intersect at a fifth corner 113. The fifth corner 113 is defined in the same manner as the first corner 111, and will not be described in detail herein.

[0152] In some embodiments, the second outer current collector 13a includes an eighth edge 108, and the eighth edge 108 and the third edge 103 intersect at a sixth angle 133. The sixth angle 133 is defined in the same manner as the first angle 111, and will not be described in detail herein.

[0153] In some embodiments, the electrode assembly 10 includes a fifth extension portion 18 and a sixth extension portion 19, the fifth extension portion 18 extends from the first outer current collector 11a from the fifth corner 113, the sixth extension portion 19 extends from the second outer current collector 13a from the sixth corner 133, and the fifth extension portion 18 is welded to the sixth extension portion 19. Specifically, the fifth extension portion 18 is bent toward the second outer current collector 13a, and the sixth extension portion 19 is bent toward the first outer current collector 11a, so that a portion of the fifth extension portion 18 and a portion of the sixth extension portion 19 overlap, and the overlapping portion is welded to form a fourth welding portion 18a.

[0154] In some embodiments, the welding method of the fifth extension portion 18 and the sixth extension portion 19 is the same as the welding method of the first extension portion 14 and the second extension portion 15 , and will not be described in detail herein.

[0155] In some embodiments, the first outer current collector 11a includes a seventh corner 114, and the second outer current collector 13a includes an eighth corner 134. When viewed along the first direction X, the seventh corner 114 overlaps with the eighth corner 134, and the seventh corner 114 is welded to the eighth corner 134. By welding the seventh corner 114 and the eighth corner 134, the warping of the seventh corner 114 and the eighth corner 134 is reduced, and the poor contact between the first outer electrode 11 and the isolation film 12 and between the second outer electrode 13 and the isolation film 12 in the warping area of ​​the seventh corner 114 and the eighth corner 134 is improved, resulting in the obstruction of the lithium ion transmission path and the generation of lithium purple spots, which affects the performance of the secondary battery; the warping area is improved to repeatedly withstand mechanical stress during the charging and discharging process, which is beneficial to reduce the risk of cracks in the active material layer on the first outer current collector 11a and / or the second outer current collector 13a, and reduce the risk of the seventh corner 114 and / or the eighth corner 134 warping and scratching the adhesive layer of the packaging bag, causing the adhesive layer to accumulate, hindering the extension of the first outer current collector 11a and / or the second outer current collector 13a, and causing the first outer current collector 11a and / or the second outer current collector 13a to fold.

[0156] In some embodiments, the first outer current collector 11a includes a seventh edge 107, and the seventh edge 107 and the fifth edge 105 intersect at an eighth angle 134. The seventh angle 114 is defined in the same manner as the first angle 111, and will not be described in detail herein.

[0157] In some embodiments, the second outer current collector 13a includes an eighth edge 108, and the eighth edge 108 and the sixth edge 106 intersect at an eighth angle 134. The eighth angle 134 is defined in the same manner as the first angle 111, and will not be described in detail herein.

[0158] In some embodiments, the electrode assembly 10 includes a seventh extension portion 10A and an eighth extension portion 10B, the seventh extension portion 10A extends from the seventh corner 114 to the first outer current collector 11a, the eighth extension portion 10B extends from the eighth corner 134 to the second outer current collector 13a, and the seventh extension portion 10A is welded to the eighth extension portion 10B. Specifically, the seventh extension portion 10A is bent toward the second outer current collector 13a, and the eighth extension portion 10B is bent toward the first outer current collector 11a, so that a portion of the seventh extension portion 10A overlaps a portion of the eighth extension portion 10B, and the overlapping portion is welded to form a fifth welding portion 10C.

[0159] In some embodiments, the welding method of the seventh extension portion 10A and the eighth extension portion 10B is the same as the welding method of the first extension portion 14 and the second extension portion 15 , and will not be described in detail herein.

[0160] In some embodiments, the width and thickness of the third extension portion 16 , the fourth extension portion 17 , the fifth extension portion 18 , the sixth extension portion 19 , the seventh extension portion 10A and the eighth extension portion 10B are the same as those of the first extension portion 14 , and are not further described herein.

[0161] In some embodiments, the electrode assembly 10 includes a second electrode sheet 10D, the second electrode sheet 10D has a polarity opposite to that of the first outer electrode sheet 11, and the second electrode sheet 10D is disposed between adjacent isolation films 12, and the adjacent isolation films 12 are bonded and disposed beyond the area of ​​the second electrode sheet 10D, and cover the second electrode sheet 10D. The risk of short circuit caused by contact between the first welding portion 14a, the third welding portion 16a, the fourth welding portion 18a, and the fifth welding portion 10C and the second electrode sheet 10D is reduced.

[0162] Embodiment 2

[0163] See also Figures 8 to 11In some embodiments, the first extension portion 14 extends from the first corner 111 to the first outer current collector 11a, and the first extension portion 14 is welded to the second corner 131. That is, the first extension portion 14 extends from the first edge 101 or the second edge 102 of the area where the first corner 111 is located, and bends to the side surface of the second outer current collector 13a away from the first outer current collector 11a, and is welded to the area where the second corner 131 is located on the side surface.

[0164] In some embodiments, the first extension portion 14 and the second corner 131 form a second welding portion 14b. Along the length extension direction of the first extension portion 14, the length L2 of the second welding portion 14b is 1mm≤L2≤2mm. By L2≥1mm, the welding strength of the second welding portion 14b is increased and the risk of the second welding portion 14b falling off from the second corner 131 is reduced. By L2≤2mm, the space occupied by the second welding portion 14b is reduced.

[0165] In some embodiments, the first extension portion 14 extends from the first intersection A, and the second welding portion 14 b covers the second intersection B, further improving the warping problem of the second corner 131 .

[0166] In some embodiments, the third extension portion 16 extends out of the first outer current collector 11 a from the third corner 112 , and the third extension portion 16 is welded to the fourth corner 132 .

[0167] In some embodiments, the fifth extension portion 18 extends out of the first outer current collector 11 a from the fifth corner 113 , and the fifth extension portion 18 is welded to the sixth corner 133 .

[0168] In some embodiments, the seventh extension portion 10A extends out of the first outer current collector 11 a from the seventh corner 114 , and the seventh extension portion 10A is welded to the eighth corner 134 .

[0169] The present application is described in detail below through specific embodiments and comparative examples. Among them, the first outer electrode sheet 11 and the second outer electrode sheet 13 are positive electrode sheets, and the second electrode sheet 10D is a negative electrode sheet. 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.

[0170] Example 1

[0171] Preparation of positive electrode sheet: The positive electrode active material lithium cobalt oxide, the conductive agent conductive carbon black, and the binder polyvinylidene fluoride (PVDF) are dissolved in N-methylpyrrolidone (NMP) solution at a weight ratio of 97.5:1:1.5 to form a positive electrode slurry. Aluminum foil is used as the positive electrode current collector, and the positive electrode slurry is coated on the positive electrode current collector. After drying, cold pressing, and cutting, the positive electrode sheet is obtained. The first outer layer sheet and the second outer layer sheet are obtained by cutting. The first outer layer sheet includes a first extension portion, and the second outer layer sheet includes a second extension portion.

[0172] Preparation of negative electrode sheets: Mix the negative electrode active material artificial graphite, thickener sodium carboxymethyl cellulose (CMC), and binder styrene-butadiene rubber (SBR) in a weight ratio of 96:1.5:2.5, add deionized water, and stir evenly under the action of a vacuum mixer to obtain a negative electrode slurry; evenly coat the negative electrode slurry on the negative electrode collector copper foil; dry, and then cold press, cut, and slit to obtain a negative electrode sheet.

[0173] Preparation of isolation film: A polyethylene (PE) film with a thickness of 9 μm was selected.

[0174] Preparation of electrolyte: In a dry argon atmosphere glove box, ethylene carbonate (EC), ethyl methyl carbonate (EMC) and diethyl carbonate (DEC) were mixed in a mass ratio of 3:5:2, lithium salt LiPF6 was added, and the mixture was mixed evenly to obtain an electrolyte, wherein the mass percentage concentration of LiPF6 was 12.5%.

[0175] Preparation of electrode assembly: stack the positive electrode sheet, the isolation membrane and the negative electrode sheet so that the isolation membrane covers the negative electrode sheet, weld the first extension portion and the second extension portion, connect the first corner portion to the second corner portion, gather multiple first pole ears to form a pole ear assembly and weld it to the first adapter, and extend multiple second pole ears out of the isolation membrane, gather to form a pole ear assembly and weld it to the second adapter.

[0176] Electrode assembly assembly: Place the aluminum-plastic film with holes punched and formed in the assembly fixture, with the holes facing upward, place the electrode assembly in the holes, and apply external force to press it. Then, cover the electrode assembly with another aluminum-plastic film with holes punched and formed, with the holes facing downward, and heat-seal the four sides of the two aluminum-plastic films by hot pressing to obtain an assembled electrode assembly.

[0177] Liquid injection packaging: Inject electrolyte into the assembled electrode assembly, and after vacuum packaging, standing, hot pressing, shaping and other processes, the secondary battery is produced.

[0178] Example 2

[0179] The difference from Example 1 is that during the preparation of the electrode assembly, in addition to welding the first corner to connect the second corner, the third corner is also welded to connect the fourth corner.

[0180] Example 3

[0181] The difference from Example 1 is that: during the preparation process of the electrode assembly, in addition to welding the first corner to the second corner, the third corner is welded to the fourth corner, the fifth corner is welded to the sixth corner, and the seventh corner is welded to the eighth corner.

[0182] Example 4

[0183] The difference from Example 1 is that during the preparation of the electrode assembly, the first extension portion is welded to the second corner, thereby achieving welding connection of the first corner to the second corner.

[0184] Comparative Example 1

[0185] The difference from Example 1 is that the outermost positive electrode sheet is not provided with the first extension portion and the second extension portion.

[0186] Then, 50 secondary batteries of each embodiment and comparative example were taken for purple spot lithium precipitation area test and outer current collector folding test. The test results are recorded in Table 1.

[0187] Outer current collector folding test method: (1) Maintain the test temperature at 25°C and let the secondary battery 100 stand for 30 minutes; (2) Charge at 2.5C constant current to 4.25V, then charge at constant voltage to 2C; (3) Charge at 2C constant current to 4.35V, then charge at constant voltage to 1.5C; (4) Charge at 1.5C constant current to 4.3V, then charge at constant voltage to 1C; (5) Charge at 1.0C constant current to 4.53V, then charge at constant voltage to 0.025C; (6) Let stand for 5 minutes, discharge at 1.0C constant current to 3V; (7) Let stand for 5 minutes; (8) Repeat steps 2 to 7 for 800 times.

[0188] Judgment criteria: After the cycle is completed, disassemble the secondary battery and observe whether the first outer current collector and the second outer current collector are folded; the number of test batteries is 50, the number of folded cells is Y, and the occurrence ratio is Y / 50.

[0189] Purple spot / lithium precipitation area test: After 800 cycles, the secondary battery was disassembled to observe the purple spot and lithium precipitation of the negative electrode. The non-lithium precipitation area on the surface of the negative electrode was golden yellow, the purple spot area was dark purple, and the lithium precipitation area was grayish white. The percentage of the purple spot lithium precipitation area was calculated based on the total area of ​​the single-sided negative electrode material layer. High-resolution optical microscopy combined with color threshold segmentation;

[0190] The surface images of the pole piece were taken with an optical microscope, and the significant color differences of different regions (golden non-lithium-deposited area, dark purple spot area, gray-white lithium-deposited area) were used for identification. The color threshold was segmented using image processing software (ImageJ, PythonOpenCV), and the area proportion of each region could be quantitatively calculated.

[0191] The judgment criteria for the purple spot lithium precipitation state on the surface of the negative electrode are as follows: purple spot lithium precipitation area is less than or equal to 2% for no lithium precipitation, purple spot lithium precipitation area is less than or equal to 5% for slight lithium precipitation, purple spot lithium precipitation area is 5% to 10% for moderate lithium precipitation, and purple spot lithium precipitation area is greater than 10% for severe lithium precipitation. The number of tested batteries is 50, the number of cells without lithium precipitation is A, the number of cells with slight lithium precipitation is B, the number of cells with moderate lithium precipitation is C, the number of cells with severe lithium precipitation is D, and the lithium precipitation states are A / 50, B / 50, C / 50, and D / 50.

[0192] It should be noted that, except for the parameters in the table, the other parameters of Comparative Example 1 are the same as those of Example 1.

[0193] Table 1 (Except for the parameters mentioned in Table 1, all other parameters of Examples 1 to 11 are the same as those of Example 1)

[0194]

[0195] From the data in Table 1, it can be seen that compared with Comparative Example 1, Example 1 uses the first extension part and the second extension part to weld the first corner to the second corner, thereby improving the problem of purple lithium deposition in the secondary battery of Example 1 and reducing the risk of folding of the outermost current collector. Example 4 uses the first extension part to weld the first corner to the second corner, thereby improving the problem of purple lithium deposition in the secondary battery of Example 4 and reducing the risk of folding of the outermost current collector.

[0196] Compared with Example 1, Example 2 welds the first corner to the second corner, and welds the third corner to the fourth corner, thereby further improving the purple lithium deposition problem of the secondary battery of Example 2 and reducing the risk of folding the outermost current collector.

[0197] Compared with Example 1, Example 3 welds the first corner to the second corner, the third corner to the fourth corner, the fifth corner to the sixth corner, and the seventh corner to the eighth corner, thereby further improving the problem of purple lithium deposition in the secondary battery of Example 3 and further reducing the risk of folding the outermost current collector.

[0198] Embodiment 4 to Embodiment 20

[0199] The difference from Example 1 is that L 1、, L2, D1, D2, H1, and H2 values ​​are specifically recorded in Table 2.

[0200] Then, 20 secondary batteries of each embodiment were taken for peel strength test and volume energy density test, and the test results are recorded in Table 2.

[0201] Peel strength test method:

[0202] The experimental temperature is 20±5℃, disassemble the secondary battery 100, and take out the first welding part. Then, fix the first extension part of the sample on the upper clamp, and fix the second extension part of the sample (the second outer current collector) on the lower clamp to ensure that the sample will not break or detach from the clamp during the peeling process. Use a load sensor to record the force applied to the sample, and use a displacement sensor to record the deformation of the sample. Set the peeling angle to 180° and the peeling speed to 3mm / min. Stop the test when the sample is stretched to be fully pulled apart, and record the force and displacement data during the peeling process. Peel strength = maximum peeling force (N) / sample width (mm), and take the average value as the test result.

[0203] The volume energy density test steps are as follows:

[0204] 1) Under the environmental condition of 25℃, 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) Calculate by the following formula: volume energy density = platform voltage × C0 / volume of secondary battery.

[0205] It should be noted that, except for the parameters in the table, the other parameters of Examples 4 to 20 are the same as those of Example 1.

[0206] Table 2

[0207]

[0208]

[0209] From Table 2, Example 1 and Examples 5-8, it can be seen that the length L1 of the first welding portion is 1mm≤L1≤2mm, and the first extension portion and the second extension portion have a high peel strength. At the same time, the welding portion occupies a reasonable space and has little impact on the energy density of the secondary battery.

[0210] From Table 2, Example 4 and Examples 9-12, it can be seen that the length L2 of the second welding portion is 1mm≤L2≤2mm, and the peel strength between the first extension portion and the second outer current collector is relatively high. In addition, the space occupied by the welding portion is relatively reasonable, and the impact on the energy density of the secondary battery is relatively small.

[0211] It can be seen from Table 2, Example 1, and Examples 13-16 that when 1mm≤D1≤5mm and 1mm≤D2≤5mm, welding is facilitated, so that the first extension portion and the second extension portion have higher peel strength, and the secondary battery has higher energy density.

[0212] From Table 2, Example 1 and Examples 17-20, it can be seen that when 8μm≤H1≤20μm, the first extension portion has a higher peel strength, reducing the impact on the energy density of the secondary battery; when 8μm≤H2≤20μm, the second extension portion has a higher peel strength, reducing the impact on the energy density of the secondary battery.

[0213] See also Fig.12 The present application also provides an electric device 200 using the secondary battery 100. In one embodiment, the electric device 200 of the present application may be, but is not limited to, electronic equipment, drones, backup power supplies, electric vehicles, electric motorcycles, electric power-assisted bicycles, electric tools, large household battery modules, etc.

[0214] Those skilled in the art should recognize that the above embodiments are only used to illustrate the present application, and are not used as limitations on the present application. As long as they are within the spirit of the present application, appropriate changes and modifications to the above embodiments are within the scope of the present application.

Claims

1. A secondary battery, characterized in that: The electrode assembly includes an electrode assembly having a laminate structure, the electrode assembly including a first outer electrode sheet, a separator, and a second outer electrode sheet arranged along a first direction, the first outer electrode sheet including a first outer current collector, and the second outer electrode sheet including a second outer current collector; the first outer current collector includes a first angle position, and the second outer current collector includes a second angle position, and when viewed along the first direction, the first angle position and the second angle position at least partially overlap; The electrode assembly further includes a first extension portion, the first extension portion extends from the first corner position to the first outer current collector, and the first extension portion is fixedly connected to the second outer current collector.

2. The secondary battery according to claim 1, wherein: The electrode assembly further includes a second extension portion, the second extension portion extends from the second corner position to the second outer current collector, and the first extension portion is fixedly connected to the second extension portion.

3. The secondary battery according to claim 1, wherein: The first extension portion is connected to the second corner by welding.

4. The secondary battery according to claim 2, characterized in that: The first extension portion is connected to the second extension portion by welding.

5. The secondary battery according to claim 1, wherein: It also includes a first pole tab, the first outer current collector also includes a second edge, one of the edges at the first corner is a part of the second edge, and the first pole tab is connected to the second edge.

6. The secondary battery according to claim 4, characterized in that: Along the thickness direction of the first extension portion, the first extension portion includes a first connection surface and a second connection surface opposite to each other, the first connection surface faces the electrode assembly, and along the thickness direction of the second extension portion, the second extension portion includes a third connection surface and a fourth connection surface opposite to each other, the third connection surface faces the electrode assembly; The first connection surface is welded to the fourth connection surface to form a first welding portion, or the second connection surface is welded to the third connection surface to form a first welding portion, or the first connection surface is welded to the third connection surface to form a first welding portion bent along the first direction; Along the first direction, the length L1 of the first welding portion is 1 mm ≤ L1 ≤ 2 mm.

7. The secondary battery according to claim 3, characterized in that: The first extension portion is welded to the second corner to form a second welding portion. Along the length extension direction of the first extension portion, the length of the second welding portion is L2, and 1mm≤L2≤2mm.

8. The secondary battery according to claim 2, wherein: The width D1 of the first extending portion is 1mm≤D1≤5mm; and / or the width D2 of the second extending portion is 1mm≤D2≤5mm.

9. The secondary battery according to claim 2, wherein: The thickness H1 of the first extension portion is 8 μm≤H1≤20 μm; and / or the thickness H2 of the second extension portion is 8 μm≤H2≤20 μm.

10. The secondary battery according to claim 1, wherein: The electrode assembly includes a second pole piece, the second pole piece has a polarity opposite to that of the first outer pole piece, and the second pole piece is arranged between adjacent isolation films. The adjacent isolation films are bonded to the area beyond the second pole piece and cover the second pole piece.

11. The secondary battery according to claim 2, characterized in that: The first extension portion is bent relative to the first outer current collector to form a first angle α, 90°≤α≤120°; The second extension portion is bent relative to the second outer current collector to form a second angle β, 90°≤β≤120°, and the first extension portion is welded to the second extension portion.

12. The secondary battery according to any one of claims 1 to 11, characterized in that: The first outer current collector includes a third angle, the second outer current collector includes a fourth angle, and when viewed along the first direction, the third angle overlaps with the fourth angle, and the electrode assembly further includes a third extension, and the third extension extends from the third angle to the first outer current collector; The third extension portion is welded to the fourth corner; Alternatively, the electrode assembly further includes a fourth extension portion, the fourth extension portion extends out from the fourth corner position to the second outer current collector, and the third extension portion is welded to the fourth extension portion.

13. The secondary battery according to claim 12, characterized in that: Also includes a first pole ear and a second pole ear; the first outer current collector includes a second edge, one of the edges at the first angle is a part of the second edge, one of the edges at the third angle is a part of the second edge, and the first pole ear is connected to the second edge; The second outer current collector includes a fourth edge, one of the edges at the second corner is a part of the fourth edge, one of the edges at the fourth corner is a part of the fourth edge, and the second electrode tab is connected to the fourth edge.

14. The secondary battery according to claim 12, wherein: The first outer current collector includes a fifth angle, the second outer current collector includes a sixth angle, and when viewed along the first direction, the fifth angle overlaps with the sixth angle, and the electrode assembly further includes a fifth extension, the fifth extension extending from the fifth angle to the first outer current collector; The fifth extension portion is welded to the sixth corner; Alternatively, the electrode assembly further includes a sixth extension portion, the sixth extension portion extends out of the second outer current collector from the sixth corner, and the fifth extension portion is welded to the sixth extension portion.

15. An electrical equipment, characterized in that: Comprising the secondary battery as claimed in any one of claims 1 to 14.

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