Secondary battery and electronic device

Abstract

Provided are a secondary battery and an electronic device. The secondary battery comprises a packaging pouch, an electrode assembly and a first conductive plate. The packaging pouch comprises an accommodating part and a first sealing edge. The electrode assembly is disposed in the accommodating part and comprises a first electrode sheet. The first electrode sheet comprises a first current collector and a first active material layer. The first conductive plate is electrically connected to the first current collector and extends out of the packaging pouch from the first sealing edge. The direction in which the first conductive plate extends out of the electrode assembly is a first direction; the first electrode sheet comprises a first edge and a second edge which are arranged opposite each other in the first direction. The first edge is closer to the first sealing edge than the second edge, and the first electrode sheet is provided with at least one first recess at the second edge. The direction of thickness of the electrode assembly is a second direction; the first recess penetrates the first current collector and the first active material layer in the second direction. The projection of the at least one first recess in the second direction forms a projected area; the width of the projected area is W1, and the width of the electrode assembly is W0, where 15%≤W1 / W0≤40%. The secondary battery has relatively high reliability and safety.

Description

Secondary battery and electronic device TECHNICAL FIELD

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

[0002] Secondary batteries are widely used in electronic mobile devices, power tools, electric vehicles and other electronic products, and people have increasingly high requirements for the safety performance of secondary batteries.

[0003] Because the work inside the secondary battery needs to maintain a relatively closed environment with the outside world, the shell of the secondary battery needs to have a certain sealing function. In some cases (such as hot box testing), gas will be generated inside the secondary battery, and the gas will accumulate in the shell. If the gas cannot be effectively discharged to the outside environment, the internal pressure of the shell will continue to increase, affecting the reliability and safety of the secondary battery.

[0004] SUMMARY

[0005] Therefore, it is necessary to provide a secondary battery with high reliability and safety during hot box testing.

[0006] In addition, it is also necessary to provide an electronic device having the secondary battery.

[0007] The first aspect of the present application provides a secondary battery, comprising a packaging bag, an electrode assembly and a first conductive plate. The packaging bag comprises a containing portion and a first sealing edge. The electrode assembly is arranged in the containing portion and comprises a first electrode tab. The first electrode tab comprises a first current collector and a first active material layer arranged on the first current collector. The first conductive plate is electrically connected to the first current collector and extends out of the packaging bag from the first sealing edge. The direction in which the first conductive plate extends out of the electrode assembly is a first direction, and the first electrode tab comprises a first edge and a second edge arranged opposite to each other in the first direction. In the first direction, the first edge is closer to the first sealing edge than the second edge, and the first electrode tab is provided with at least one first recess at the second edge. The thickness direction of the electrode assembly is a second direction, which is perpendicular to the first direction, and the first recess penetrates the first current collector and the first active material layer in the second direction. The projection of the at least one first recess in the second direction forms a projection area. In a third direction perpendicular to both the first direction and the second direction, the width of the projection area is W1, and the width of the electrode assembly is W0, then 15%≤W1 / W0≤40%.

[0008] In the present application, if the internal high-temperature gas accumulation under the heat box test causes the packaging bag to swell and press the electrode assembly, the first recess can form a weak force point, and the electrode assembly tends to bend and deform at the first recess. Therefore, the internal high-temperature gas is easy to accumulate at the bending and deforming position of the electrode assembly and timely break the first sealing edge, thereby reducing the risk of thermal runaway that may be caused by the continuous accumulation of heat in the packaging bag, and improving the reliability and safety of the secondary battery. Moreover, when the electrode assembly bends and deforms at the first recess, since the first current collector and the first active material layer are missing at the first recess, it is beneficial to reduce the risk of direct contact short circuit between the first tab provided with the first recess and the second tab adjacent to the first tab at the bending and deforming position, and to accelerate the gas production, thereby further reducing the risk of thermal runaway of the secondary battery under the heat box test. Furthermore, by setting the width of the projection area composed of the first recess, the first tab can form an effective weak force point, so that the electrode assembly is more likely to bend and deform at the first recess under the heat box test, and the risk that the internal high-temperature gas is difficult to accumulate at the bending and deforming position of the electrode assembly under the heat box test can also be reduced, so that the internal high-temperature gas is more likely to break the first sealing edge.

[0009] Based on the first aspect, in some possible implementation manners, the number of the first recesses is a plurality, and the plurality of first recesses are respectively arranged on the plurality of layers of first tabs arranged adjacent to each other. From the second direction, any two first recesses overlap. Therefore, the electrode assembly is more likely to bend and deform at the first recess under the heat box test, thereby facilitating the internal high-temperature gas to accumulate at the bending and deforming position of the electrode assembly and timely break the first sealing edge, and reducing the risk of thermal runaway that may be caused by the continuous accumulation of heat in the packaging bag.

[0010] Based on the first aspect, in some possible implementation manners, in the third direction, the maximum width of the first recess is W max , W max and W1 are in mm, and W1≤W max +5 mm. Therefore, the plurality of first recesses can have a smaller displacement in the third direction, which is beneficial to reduce the risk that the internal high-temperature gas is difficult to accumulate at the bending and deforming position of the electrode assembly under the heat box test, so that the internal high-temperature gas is more likely to break the first sealing edge.

[0011] Based on the first aspect, in some possible implementation manners, in the first direction, the length of the projection area is L1, and the length of the electrode assembly is L0, and 3%≤L1 / L0≤10%. Therefore, the first tab can form an effective weak force point, so that the electrode assembly is more likely to bend and deform at the first recess under the heat box test. Moreover, the influence of setting the first recess on the energy density of the secondary battery can also be reduced.

[0012] In some possible implementations based on the first aspect, the number of the first recesses is one. In the first direction, the length of the first recess is L2, and the length of the electrode assembly is L0, and 3%≤L2 / L0≤10%. In this way, the first tab can form an effective stress weak point, so that the electrode assembly is more likely to bend and deform at the first recess under a heat chamber test. Moreover, the impact of the first recess on the energy density of the secondary battery can be reduced.

[0013] In some possible implementations based on the first aspect, the first tab is a positive tab. Therefore, the risk of lithium precipitation caused by the absence of negative active material in the second tab after the second tab is provided with the first recess, so that the second active material layer cannot normally embed active ions during the charging and discharging process, can be reduced.

[0014] In some possible implementations based on the first aspect, the outermost layer of the electrode assembly in the second direction is the first tab, and the first tab of the outermost layer is not provided with the first recess. Therefore, when the electrode assembly bends and deforms at the first recess under a heat chamber test, the risk of direct contact and short circuit between the first tab provided with the first recess and the two adjacent second tabs at the bending and deforming position, and the risk of accelerating gas production can be reduced, thereby further reducing the risk of thermal runaway of the secondary battery under a heat chamber test.

[0015] In some possible implementations based on the first aspect, the first tab is a negative tab. The electrode assembly further includes a second tab, and the second tab is a positive tab. The second tab includes a second current collector and a second active material layer provided on the second current collector. The secondary battery further includes a first insulating member, and the first insulating member is bonded to the second active material layer provided facing the first recess. The first insulating member covers the first recess as viewed in the second direction. Therefore, the first insulating member can hinder the active ions in the second active material layer corresponding to the first insulating member in the second direction from moving to the first recess, thereby reducing the risk of excessive active ions accumulating and generating lithium dendrites due to the lack of the first recess capable of embedding these active ions.

[0016] In some possible implementations based on the first aspect, the electrode assembly has a wound structure. The first tab is provided with a first groove at the first edge, the first groove penetrates the first active material layer along the second direction, and the first groove does not penetrate the first current collector. The first conductive plate is arranged in the first groove and is electrically connected with the first current collector. The first conductive plate includes an electrically conductive connection region that overlaps the first current collector as viewed in the second direction. The first recess and the electrically conductive connection region overlap as viewed in the first direction. Therefore, when the electrode assembly bends and deforms at the first recess under a heat chamber test, the risk of the end of the electrode assembly away from the first recess also bending and deforming, so that the first tab and the second tab directly contact and short circuit at the end of the electrode assembly can be reduced, because the first conductive plate is less likely to deform due to its greater hardness.

[0017] In some possible implementation manners based on the first aspect, the electrode assembly is in a roll structure. The first current collector includes a first surface including a first region and a second region connected in a rolling direction. The second region is provided with the first active material layer, and the first region is not provided with the first active material layer. The first conductive plate is electrically connected to the first region. The first recess penetrates the second region and the first active material layer in the second direction. Therefore, by setting the position of the first recess, the electrode assembly is more likely to bend and deform at the first recess under the heat chamber test, thereby facilitating the internal high-temperature gas to gather at the bending and deforming position of the electrode assembly and timely rush out of the first sealing edge, and reducing the risk of thermal runaway that may be caused by the continuous accumulation of heat in the packaging bag.

[0018] In some possible implementation manners based on the first aspect, the electrode assembly is in a roll structure or a stack structure. The secondary battery further includes a plurality of first tabs integrally arranged with the first current collector and extending out of the first current collector from the first edge. The plurality of first tabs are further electrically connected to the first conductive plate. The first tab includes a tab connection area connected to the first edge. A first recess and a tab connection area overlap in the first direction. Therefore, when the electrode assembly bends and deforms at the first recess under the heat chamber test, the risk that the end of the electrode assembly away from the first recess also bends and deforms, causing the first tab and the second tab to directly contact and short circuit at the above-mentioned end of the electrode assembly, can be reduced due to the greater hardness of the first tab which is not easy to deform.

[0019] In some possible implementation manners based on the first aspect, the edge of the first recess includes a first side edge, a bottom edge and a second side edge connected in sequence in the second direction, and the first side edge and the second side edge are respectively connected to the second edge. The first side edge includes a first slope edge away from the second edge in the second direction, and the first slope edge is connected to the bottom edge and is arc-shaped. Therefore, the risk that the edge of the first recess forms a sharp corner can be reduced, and the risk that the above-mentioned sharp corner pierces the separator to cause the first tab and the second tab to directly contact and short circuit when the electrode assembly bends and deforms at the first recess under the heat chamber test can be reduced. Moreover, the risk that the active material of the first active material layer falls off at the above-mentioned sharp corner can also be reduced.

[0020] In some possible implementation manners based on the first aspect, the first side edge includes a second slope edge connected to the second edge in the second direction, and the second slope edge is arc-shaped. Therefore, the risk that the edge of the first recess forms a sharp corner can be reduced, and the risk that the above-mentioned sharp corner pierces the separator to cause the first tab and the second tab to directly contact and short circuit when the electrode assembly bends and deforms at the first recess under the heat chamber test can be reduced. Moreover, the risk that the active material of the first active material layer falls off at the above-mentioned sharp corner can also be reduced.

[0021] In some possible implementation manners based on the first aspect, the edge of the first recess is arc-shaped as viewed from the second direction. Thus, the risk that the edge of the first recess forms a sharp corner can be reduced, and when the electrode assembly is deformed to bend at the first recess under the heat box test, the risk that the sharp corner pierces the separation film to cause the first electrode tab and the second electrode tab to directly contact and short circuit can be reduced. Moreover, the risk that the active material of the first active material layer falls off at the sharp corner can also be reduced.

[0022] The second aspect of the present application provides an electronic device including the secondary battery and a battery compartment. The electronic device is powered by the secondary battery, and the secondary battery can timely release the high-temperature gas in the internal space during the heat box test, thereby maintaining good reliability and safety. BRIEF DESCRIPTION OF DRAWINGS

[0023] FIG. 1A is a schematic structural view of a secondary battery as viewed from a second direction according to an embodiment of the present application.

[0024] FIG. 1B is a schematic structural view of a secondary battery as viewed from the second direction according to another embodiment of the present application.

[0025] FIG. 1C is a schematic structural view of a secondary battery as viewed from the second direction according to another embodiment of the present application.

[0026] FIG. 2 is a sectional view of the secondary battery shown in FIG. 1A along a cutting line II-II according to some embodiments.

[0027] FIG. 3 is a sectional view of the secondary battery shown in FIG. 1A along a cutting line III-III according to some embodiments.

[0028] FIG. 4 is a sectional view of the secondary battery shown in FIG. 1A along the cutting line III-III according to another embodiment.

[0029] FIG. 5 is a sectional view of the secondary battery shown in FIG. 1A along a cutting line IV-IV according to another embodiment.

[0030] FIG. 6 is a schematic structural view of a first electrode tab of the secondary battery shown in FIG. 2 or FIG. 3 after being unfolded according to some embodiments.

[0031] FIG. 7 is a schematic structural view of the first electrode tab of the secondary battery shown in FIG. 2 after being unfolded according to another embodiment.

[0032] FIG. 8 is a schematic structural view of the first electrode tab of the secondary battery shown in FIG. 4 or FIG. 5 after being unfolded.

[0033] FIG. 9A is an enlarged view of a first recess of the first electrode tab shown in FIG. 6, FIG. 7, or FIG. 8 according to some embodiments.

[0034] FIG. 9B is an enlarged view of the first recess of the first tab shown in FIG. 6, FIG. 7, or FIG. 8, in other embodiments.

[0035] FIG. 9C is an enlarged view of the first recess of the first tab shown in FIG. 6, FIG. 7, or FIG. 8, in other embodiments.

[0036] FIG. 10 is a cross-sectional view of the secondary battery shown in FIG. 1A, along the cutting line II-II, in other embodiments.

[0037] FIG. 11 is a cross-sectional view of the secondary battery shown in FIG. 1A, along the cutting line III-III, in other embodiments.

[0038] FIG. 12 is a structural schematic view of a projection area of the first recess of the secondary battery shown in FIG. 10 or FIG. 11.

[0039] FIG. 13 is a cross-sectional view of the secondary battery shown in FIG. 1A, along the cutting line II-II, in other embodiments.

[0040] FIG. 14 is a structural schematic view of an overall structure of an electronic device according to an embodiment of the present application.

[0041] Main element symbol explanation

[0042] Electronic device 1

[0043] Packaging bag 10

[0044] Receptacle 11

[0045] First sealing edge 12

[0046] Second sealing edge 13

[0047] Electrode assembly 20

[0048] First tab 21

[0049] First edge 21A

[0050] Second edge 21B

[0051] Second tab 22

[0052] Separation film 23

[0053] First conductive plate 30

[0054] Conductive connection region 31

[0055] Third conductive plate 32

[0056] Second conductive plate 40

[0057] First tab 50

[0058] Tab connection region 51

[0059] Conductive plate connection region 52

[0060] Second tab 60

[0061] First insulating member 70

[0062] Secondary battery 100

[0063] Battery compartment 101

[0064] First end wall 111

[0065] Second end wall 112

[0066] first flat section 201

[0067] first curved section 202

[0068] second flat section 203

[0069] second curved section 204

[0070] first current collector 210

[0071] first active material layer 211

[0072] first recess 212

[0073] second current collector 220

[0074] second active material layer 221

[0075] first surface 2101

[0076] first region 2101A

[0077] second region 2101B

[0078] second surface 2102

[0079] first groove 2110

[0080] first side 2121

[0081] second side 2122

[0082] bottom edge 2123

[0083] first slope edge 2124

[0084] second slope edge 2125

[0085] second groove 2210

[0086] first direction X

[0087] second direction Y

[0088] third direction Z

[0089] fourth direction Y'

[0090] winding direction D

[0091] winding center axis O

[0092] projection region P

[0093] width W0, W1, W2, W max

[0094] length L0, L1, L2

[0095] The following detailed description will further explain the present application with reference to the above mentioned figures. DETAILED DESCRIPTION

[0096] The technical solutions in the embodiments of the present application will be described clearly and detailed below. Obviously, the described embodiments are only part of the embodiments of the present application, but not all the embodiments. Unless otherwise defined, all the technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which this application belongs. The terms used in the specification of the present application are only for the purpose of describing the specific embodiments and are not intended to limit the present application.

[0097] 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 limited to the exemplary embodiments set forth herein. Rather, these exemplary embodiments are provided so that this disclosure will be thorough and complete, and fully convey the scope of the application to those skilled in the art.

[0098] In addition, for the sake of brevity and clarity, in the drawings, the size or thickness of various components, layers, or regions can be exaggerated. Throughout the specification, like numbers refer to like elements throughout. As used herein, the terms "and / or" and "at least one of" include any and all combinations of one or more of the associated listed items. In addition, it should be understood that if an element A is said to be "connected to" element B, then element A can be directly connected to element B or an intervening element C can be present and element A and element B can be indirectly connected to each other through element C.

[0099] Further, use of "may" when describing embodiments of the present application means that one or more embodiments of the present application.

[0100] The professional terms used herein are for the purpose of describing the specific embodiments and are not intended to limit the present application. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. It should be further understood that the term "comprising" when used in this specification, means that the stated features, numbers, steps, operations, elements, and / or components are present, but does not exclude the presence or addition of one or more other features, numbers, steps, operations, elements, components, and / or combinations thereof.

[0101] Spatially relative terms, such as "on", "above", and the like, can be used herein for ease of description to describe one element or feature's relationship to another element(s) or feature(s) as illustrated in the figures. It will be understood that the spatially relative terms are intended to encompass different orientations of the device or apparatus in use or operation in addition to the orientations depicted in the figures. For example, if a device or apparatus is turned over, elements described as "above" or "up" other elements or features would then be oriented "below" or "down" the other elements or features. Thus, the example term "above" can encompass both an orientation that is above as well as below. The terms "first", "second", "third", etc. can be used herein to describe various elements, components, regions, layers and / or sections but should not be construed as limiting of the example embodiments. The terms are used to distinguish one element, component, region, layer or section from another element, component, region, layer or section. Thus, a first element, component, region, layer or section discussed below could be termed a second element, component, region, layer or section without departing from the teachings of the example embodiments.

[0102] In a hot box test, a large amount of gas is generated inside the secondary battery at high temperature. The gas accumulates in the shell (such as a packaging bag), and if the gas cannot be released to the outside environment in a favorable manner, the internal pressure of the shell will continue to increase. When the high-temperature gas accumulates inside the shell, the middle position of the packaging bag in the width direction will be greatly inflated, thereby pressing the electrode tab, which is prone to bulging or breaking. After the gas continues to accumulate, the entire electrode assembly of the secondary battery may even be broken as a whole under the action of the gas. The positive electrode tab and the negative electrode tab at the broken part are prone to contact short circuit, thereby generating a large amount of heat and further accelerating the gas generation, which may cause a risk of failure such as smoking, fire, or explosion.

[0103] Referring to FIGS. 1A to 3, an embodiment of the present application provides a secondary battery 100 including a packaging bag 10, an electrode assembly 20, an electrolyte (not shown), a first conductive plate 30, and a second conductive plate 40. The electrode assembly 20 and the electrolyte are located in the packaging bag 10. The first conductive plate 30 and the second conductive plate 40 are both electrically connected to the electrode assembly 20 and extend out of the packaging bag 10. The first conductive plate 30 and the second conductive plate 40 can be connected to an external element (not shown). Among them, the direction in which the first conductive plate 30 extends out of the electrode assembly 20 (i.e., the direction from the electrode assembly 20 to the first conductive plate 30) is defined as a first direction X, the thickness direction of the electrode assembly 20 is a second direction Y, and the direction from the first conductive plate 30 to the second conductive plate 40 is a third direction Z, and the first direction X, the second direction Y, and the third direction Z are perpendicular to each other.

[0104] As shown in FIG. 1A and FIG. 3, the packaging bag 10 includes a containing portion 11 and a first sealing edge 12. The electrode assembly 20 and the electrolyte are disposed in the containing portion 11. The first conductive plate 30 extends out of the packaging bag 10 from the first sealing edge 12. In some embodiments, in the first direction X, the containing portion 11 includes a first end wall 111 and a second end wall 112 oppositely disposed. The surface on which the first end wall 111 is located extends in the second direction Y and the third direction Z, and the surface on which the second end wall 112 is located extends in the second direction Y and the third direction Z. The first sealing edge 12 is connected to the first end wall 111, and the first conductive plate 30 and the second conductive plate 40 can both extend out of the packaging bag 10 from the first sealing edge 12.

[0105] As shown in FIG. 2 and FIG. 3, in some embodiments, the electrode assembly 20 is a winding structure, which includes a first electrode tab 21, a second electrode tab 22, and a separator 23. The separator 23 is disposed between the first electrode tab 21 and the second electrode tab 22. The first electrode tab 21 includes a first current collector 210 and a first active material layer 211 disposed on the first current collector 210, and the first conductive plate 30 is electrically connected to the first current collector 210. The second electrode tab 22 includes a second current collector 220 and a second active material layer 221 disposed on the second current collector 220, and the second conductive plate 40 is electrically connected to the second current collector 220. As shown in FIG. 3, the first electrode tab 21 includes a first edge 21A and a second edge 21B oppositely disposed in the first direction X. In the first direction X, the first edge 21A is closer to the first sealing edge 12 than the second edge 21B.

[0106] Further, in combination with reference to FIG. 3 and FIG. 6, wherein FIG. 6 is a structure schematic diagram of the first electrode tab 21 after being unfolded. In some embodiments, the first conductive plate 30 can be disposed to be connected to the first current collector 210 and extend out of the first current collector 210 from the first edge 21A. More specifically, the first electrode tab 21 is provided with a first groove 2110 at the first edge 21A, the first groove 2110 penetrates the first active material layer 211 along the second direction Y, but the first groove 2110 does not penetrate the first current collector 210. The first conductive plate 30 is disposed in the first groove 2110 and electrically connected to the first current collector 210. For example, the first conductive plate 30 is disposed in the first groove 2110 and fixedly welded to the first current collector 210, thereby improving the connection strength of the first conductive plate 30 and the first current collector 210. The connection mode of the second conductive plate 40 and the second current collector 220 can refer to the connection mode of the first conductive plate 30 and the first current collector 210.

[0107] Referring to FIGS. 4 and 5, in some embodiments, when the electrode assembly 20 is in a jelly-roll structure, the secondary battery 100 can further include a plurality of first tabs 50 and a plurality of second tabs 60. The first tabs 50 are integrally connected to the first current collector 210 (e.g., the first tabs 50 can be cut from the first current collector 210) and extend out of the first current collector 210 from the first edge 21A. The plurality of first tabs 50 are welded to the first conductive plate 30 by a transition welding process. The second tabs 60 can be connected to the second current collector 220 in the same manner as the first tabs 50 are connected to the first current collector 210.

[0108] In some embodiments, the electrode assembly 20 shown in FIGS. 4 and 5 can also be in a stack structure including a plurality of first electrode plates 21, a plurality of second electrode plates 22, and a separator 23. The first electrode plates 21 and the second electrode plates 22 are alternately stacked in sequence, with one second electrode plate 22 between every two adjacent first electrode plates 21 and one first electrode plate 21 between every two adjacent second electrode plates 22. The separator 23 is disposed between adjacent first electrode plates 21 and second electrode plates 22.

[0109] In some embodiments, the first electrode plates 21 can be positive electrode plates, and the second electrode plates 22 can be negative electrode plates. Correspondingly, the first current collector 210 and the first active material layer 211 are a positive current collector and a positive active material layer, respectively, and the second current collector 220 and the second active material layer 221 are a negative current collector and a negative active material layer, respectively. As shown in FIGS. 2 to 5, in some embodiments, the outermost layer of the electrode assembly 20 in the second direction Y is a first electrode plate 21. The first current collector 210 includes a first surface 2101 and a second surface 2102 disposed opposite to each other, with the first surface 2101 disposed away from the winding center axis O of the electrode assembly 20 and the second surface 2102 disposed toward the winding center axis O. The outermost first electrode plate 21 is a single-sided coated electrode plate, i.e., the first surface 2101 of the outermost first electrode plate 21 is not provided with the first active material layer 211, and the second surface 2102 of the outermost first electrode plate 21 is provided with the first active material layer 211. Thus, the outer surface of the outermost layer of the electrode assembly 20 is the first surface 2101. By providing the outermost first electrode plate 21 as a single-sided coated electrode plate, the energy density of the secondary battery 100 can be improved, and the problem that the active material on the outer surface of the electrode assembly 20 is easily detached after contacting the packaging bag 10 can be solved. In some other embodiments, the first electrode plates 21 can be negative electrode plates, and the second electrode plates 22 can be positive electrode plates.

[0110] The positive current collector can be an aluminum foil or a nickel foil, and the negative current collector can be at least one of a copper foil, a nickel foil, or a carbon-based current collector.

[0111] The positive electrode active material layer includes a positive electrode active material, which includes a compound that reversibly intercalates and deintercalates metal ions (e.g., lithium ions, sodium ions, etc., hereinafter lithium ions are taken as an example). In some embodiments, the first active material can 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 at least one of lithium cobaltate (LiCoO2), lithium nickel cobalt manganese ternary material (NCM), lithium nickel cobalt aluminum ternary material (NCA), lithium manganate (LiMn2O4), lithium nickel manganate (LiNi 0.5 Mn 1.5 O4), or lithium iron phosphate (LiFePO4).

[0112] The negative electrode active material layer includes a negative electrode active material, which employs a negative electrode active material known in the art capable of reversible deintercalation of active ions, which is not limited in the present application. For example, it can include but is not limited to a combination of one or more of graphite, soft carbon, hard carbon, carbon fiber, mesocarbon microbead, silicon-based material, tin-based material, lithium titanate, or other metals capable of forming alloys with lithium, etc. Among them, the graphite can be selected from a combination of one or more of artificial graphite, natural graphite, and modified graphite; the silicon-based material can be selected from a combination of one or more of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon alloys; the tin-based material can be selected from a combination of one or more of elemental tin, tin oxide compounds, tin alloys, etc.

[0113] The separator 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.

[0114] In other embodiments, in order to meet the demand for large current charging and discharging, reduce the internal resistance of the first tab 21 or the second tab 22, the width of the first tab 50 or the second tab 60 in the third direction Z can be increased accordingly. As shown in FIG. 1B, at this time, the packaging bag 10 can further include a second sealing edge 13 connected to the second end wall 112. The first conductive plate 30 welded to the first tab 50 extends out of the packaging bag 10 from the first sealing edge 12, and the second conductive plate 40 welded to the second tab 60 extends out of the packaging bag 10 from the second sealing edge 13. Therefore, the risk of contact and short circuit of the first tab 50 and the second tab 60 with a larger width can be reduced, and a larger welding operation space can also be provided when welding the first conductive plate 30 and the second conductive plate 40 to the first tab 50 and the second tab 60, respectively.

[0115] In some embodiments, as shown in FIG. 1C, the secondary battery 100 can further include a third conductive plate 32, the first conductive plate 30, the second conductive plate 40, and the third conductive plate 32 all extend from the first sealing edge 12 to the packaging bag 10. The third conductive plate 32 can have the same polarity as the first conductive plate 30. That is, the third conductive plate 32 can be electrically connected to the first current collector 210, or electrically connected to the first current collector 210 through a first tab (not shown in FIG. 1C). By arranging the first conductive plate 30 and the second conductive plate 32 in parallel shunt, it can also help to reduce the internal resistance of the first tab 21, to meet the demand of large current charging and discharging.

[0116] As shown in FIGS. 2-5, the first tab 21 is provided with at least one first recess 212 at the second edge 21B. The first recess 212 penetrates the first current collector 210 and the first active material layer 211 in the second direction Y. The number of the first recess 212 in the first tab 21 is one, as shown in FIGS. 2-5. As shown in FIG. 2, when the electrode assembly 20 is in a wound structure, the electrode assembly 20 can include a first flat section 201, a first curved section 202, a second flat section 203, and a second curved section 204 connected in sequence in the winding direction D. The first flat section 201 and the second flat section 203 are oppositely arranged in the second direction Y, and the first curved section 202 and the second curved section 204 are oppositely arranged in the third direction Z. The first recess 212 can be provided on the first tab 21 of the first flat section 201 or the second flat section 203.

[0117] In some embodiments, when the electrode assembly 20 is in a wound structure and the first conductive plate 30 is connected to the first current collector 210, as shown in FIGS. 2 and 6, the thickness direction of the first tab 21 (i.e., the stacking direction of the first current collector 210 and the first active material layer 211) is the fourth direction Y'. The first surface 2101 of the first current collector 210 includes a first region 2101A and a second region 2101B connected in the winding direction D. When the first tab 21 in FIG. 2 is unfolded, as shown in FIG. 6, the first region 2101A and the second region 2101B are connected along the length direction of the first tab 21. The first region 2101A is provided with the first active material layer 211, and the second region 2101B is exposed to the first active material layer 211. The second region 2101B can be the winding tail of the first current collector 210 or the outer surface of the outermost layer of the electrode assembly 20. The first conductive plate 30 is connected to the first region 2101A. As shown in FIG. 6, the first recess 212 penetrates the first region 2101A and the first active material layer 211 in the fourth direction Y'. When the first tab 21, the separator film 23, and the second tab 22 are stacked and wound, as shown in FIG. 2, the first recess 212 penetrates the first region 2101A and the first active material layer 211 in the second direction Y.

[0118] As shown in FIG. 7, in some other embodiments, when the electrode assembly 20 is in a wound structure, the first region 2101A can be exposed to the first active material layer 211, and the second region 2101B can be provided with the first active material layer 211. For example, the first region 2101A can be a winding head portion of the first current collector 210. The first conductive plate 30 can be connected to the winding head portion of the first current collector 210. The first recess 212 can penetrate the second region 2101B and the first active material layer 211 in the fourth direction Y’ (the second direction Y after winding).

[0119] As shown in FIG. 8, in some other embodiments, when the electrode assembly 20 is in a wound structure, and the first conductive plate 30 is connected to the first current collector 210 through the plurality of first tabs 50, the plurality of first tabs 50 can be connected to the first region 2101A, similar to the structure shown in FIG. 6.

[0120] In the present application, if the internal high-temperature gas accumulation under the heat box test causes the packaging bag 10 to swell and press the electrode assembly 20, the first recess 212 can form a weak stress point, causing the electrode assembly 20 to tend to bend and deform at the first recess 212. Thus, the internal high-temperature gas is more likely to accumulate at the bending and deforming portion of the electrode assembly 20, and the accumulated gas is more likely to burst through the first sealing edge 12, thereby releasing the internal high-temperature gas, reducing the risk of thermal runaway that can be caused by the continuous accumulation of heat in the packaging bag 10, and improving the reliability and safety of the secondary battery 100. When the secondary battery 100 further includes the second sealing edge 13, the accumulated gas can also burst through the second sealing edge 13, thereby more timely releasing the internal high-temperature gas. Moreover, when the electrode assembly 20 bends and deforms at the first recess 212 (the first tab 21 or the second tab 22 at the bending and deforming portion can have a sharp corner, which is easy to pierce the separator 23 to cause the first tab 21 and the second tab 22 to directly contact and short circuit), since the first current collector 210 and the first active material layer 211 are absent at the first recess 212, it is beneficial to reduce the risk of direct contact and short circuit between the first tab 21 provided with the first recess 212 and the second tab 22 adjacent to the first tab 21 at the bending and deforming portion and accelerate gas production, thereby further reducing the risk of thermal runaway of the secondary battery 100 under the heat box test.

[0121] Referring to FIG. 9A, in some embodiments, the edge of the first recess 212 comprises, in sequence, a first side edge 2121, a bottom edge 2123, and a second side edge 2122, which are connected to the second edge 21B respectively, when viewed from the second direction Y. The bottom edge 2123 can be substantially perpendicular to the first side edge 2121 and the second side edge 2122, i.e., the first recess 212 is substantially rectangular, when viewed from the second direction Y. Referring to FIG. 9B, in other embodiments, the first side edge 2121 can comprise a first slope edge 2124 facing away from the second edge 21B, which is connected to the bottom edge 2123 and is arc-shaped, when viewed from the second direction Y. Since the first slope edge 2124 is provided, the risk of the edge of the first recess 212 forming a sharp corner can be reduced, so that the risk of the above-mentioned sharp corner of the first tab 21 piercing the separation film 23 to cause the first tab 21 and the second tab 22 to directly contact and short circuit when the electrode assembly 20 is bent and deformed at the first recess 212 under a hot box test can be reduced. Moreover, the risk of the active material of the first active material layer 211 falling off at the above-mentioned sharp corner of the first tab 21 can also be reduced. Similarly, the second side edge 2122 can also be provided with an arc-shaped slope edge connected to the second edge 21B.

[0122] As shown in FIG. 9B, the first side edge 2121 can also comprise a second slope edge 2125 connected to the second edge 21B and arc-shaped, when viewed from the second direction Y. Since the second slope edge 2125 is provided, the risk of the edge of the first recess 212 forming a sharp corner can be reduced, so that the risk of the above-mentioned sharp corner of the first tab 21 piercing the separation film 23 to cause the first tab 21 and the second tab 22 to directly contact and short circuit when the electrode assembly 20 is bent and deformed at the first recess 212 under a hot box test can be reduced. Moreover, the risk of the active material of the first active material layer 211 falling off at the above-mentioned sharp corner of the first tab 21 can also be reduced. Similarly, the second side edge 2122 can also be provided with an arc-shaped slope edge connected to the second edge 21B.

[0123] Referring to FIG. 9C, in other embodiments, the edge of the first recess 212 is arc-shaped, when viewed from the second direction Y. This can also reduce the risk of the edge of the first recess 212 forming a sharp corner, so that the risk of the above-mentioned sharp corner of the first tab 21 piercing the separation film 23 to cause the first tab 21 and the second tab 22 to directly contact and short circuit when the electrode assembly 20 is bent and deformed at the first recess 212 under a hot box test can be reduced. Moreover, the risk of the active material of the first active material layer 211 falling off at the above-mentioned sharp corner of the first tab 21 can also be reduced.

[0124] As shown in FIG. 2, in the present application, when the number of the first recesses 212 is one, in the third direction Z, the width of the projection area composed of the projection of the first recess 212 in the second direction Y (i.e. the width of the first recess 212 itself) is W2, the width of the electrode assembly 20 is W0, then 15%≤W2 / W0≤40%. In this way, the first tab 21 can form an effective stress weak point, so that the electrode assembly 20 is more likely to bend and deform at the first recess 212 under the heat chamber test. Moreover, it can also reduce the risk that the internal high-temperature gas is difficult to gather at the bending and deforming part of the electrode assembly 20 due to the large width of the first recess 212, so that the internal high-temperature gas is more likely to rush through the first sealing edge 12. At the same time, it can also reduce the impact of the first recess 212 on the energy density of the secondary battery 100. Wherein, as shown in FIG. 9A and FIG. 9B, when the edge of the first recess 212 includes a first side edge 2121, a bottom edge 2123 and a second side edge 2122 connected in turn, the width W2 can be the distance between the first side edge 2121 and the second side edge 2122 in the third direction Z; as shown in FIG. 9C, when the edge of the first recess 212 is arc-shaped, the width W2 can be the length of the line segment (chord) connecting the two endpoints of the arc segment.

[0125] As shown in FIG. 3 to FIG. 5, in some embodiments, in the first direction X, the length of the first recess 212 is L2, the length of the electrode assembly 20 is L0, 3%≤L2 / L0≤10%. In this way, the first tab 21 can form an effective stress weak point, so that the electrode assembly 20 is more likely to bend and deform at the first recess 212 under the heat chamber test. Moreover, it can also reduce the impact of the first recess 212 on the energy density of the secondary battery 100. Wherein, when the edge of the first recess 212 includes a first side edge 2121, a bottom edge 2123 and a second side edge 2122 connected in turn, the length L2 can be the length of the first side edge 2121 or the second side edge 2122 in the second direction Y; when the edge of the first recess 212 is arc-shaped, the length L2 can be the arc height of the arc segment.

[0126] In the present application, the measurement steps of W2, W0, L2, L0 can be: (1) using X-ray to perform two-dimensional projection and scanning test on the secondary battery 100 from the first direction X, the instrument can use the instrument or device known to those skilled in the art (such as GE Phoenix vtomex S device), so as to obtain the CT image; (2) using a caliper or other suitable measuring tool to directly measure the numerical value of W2, W0, L2, L0.

[0127] As shown in FIGS. 2, 3 and 6, in some embodiments, when the electrode assembly 20 is in a jelly-roll structure and the first conductive plate 30 is connected to the first current collector 210, the first conductive plate 30 includes a conductive connection region 31 overlapping the first current collector 210 as viewed from the second direction Y. The first conductive plate 30 can be welded to the first current collector 210 through at least part of the conductive connection region 31. As viewed from the first direction X, a first recess 212 overlaps the conductive connection region 31. When the electrode assembly 20 is bent and deformed at the first recess 212, the top of the electrode assembly 20 (i.e., the end of the electrode assembly 20 facing away from the first recess 212) is less likely to be bent and deformed simultaneously due to the greater rigidity of the first conductive plate 30, thereby reducing the risk of the first tab 21 and the second tab 22 directly contacting and short-circuiting at the top of the electrode assembly 20.

[0128] As shown in FIGS. 4 and 8, when the electrode assembly 20 is in a jelly-roll or stacked structure and the first conductive plate 30 is connected to the first current collector 210 through a plurality of first tabs 50, the first tab 50 includes a tab connection region 51 connected to the first edge 21A and a conductive plate connection region 52 connected to the tab connection region 51. The conductive plate connection region 52 is connected to the first conductive plate 30, and the conductive plate connection region 52 is bent relative to the tab connection region 51. As viewed from the first direction X, a first recess 212 overlaps a tab connection region 51. When the electrode assembly 20 is bent and deformed at the first recess 212, the top of the electrode assembly 20 is less likely to be bent and deformed simultaneously due to the greater rigidity of the first tab 50, thereby reducing the risk of the first tab 21 and the second tab 22 directly contacting and short-circuiting at the top of the electrode assembly 20.

[0129] Referring to FIGS. 10 and 11, in other embodiments, the number of first recesses 212 can also be multiple, and the multiple first recesses 212 are respectively arranged on the multiple layers of first tabs 21 arranged adjacently. FIGS. 10 and 11 show that the number of first recesses 212 is three, but the present application is not limited thereto, for example, the number of first recesses 212 can also be two, four, five, etc. As viewed from the second direction Y, any two first recesses 212 overlap. In this way, the electrode assembly 20 is more likely to be bent and deformed at the first recess 212 under heat box testing. The width W2 of the multiple first recesses 212 in the third direction Z can be the same or different; the length L2 of the multiple first recesses 212 in the first direction X can be the same or different. When the widths W2 of the multiple first recesses 212 are different, there is at least one first recess 212 having a maximum width W2max; when the widths W2 of the multiple first recesses 212 are the same, the maximum width W2max is equal to the width W2. max max

[0130] ​​Please refer to FIG. 12, which shows a schematic view of the plurality of first recesses 212 shown in FIG. 10 or FIG. 11 as viewed along the second direction Y (in FIG. 12, two first recesses 212 are shown as fully overlapping, and another first recess 212 is shown as partially overlapping with the aforementioned first recesses 212). The projections of the plurality of first recesses 212 on the second direction Y together form a projection region P. Taking each first recess 212 as substantially rectangular as an example, one edge of the projection region P on the third direction Z is formed by a first side edge 2121 of the plurality of first recesses 212 closest to one end of the third direction Z, and another edge is formed by a second side edge 2122 of the plurality of first recesses 212 closest to another end of the third direction Z. The two edges can be formed by the first side edge 2121 and the second side edge 2122 of the same first recess 212, or can be formed by the first side edge 2121 and the second side edge 2122 of different first recesses 212. Similarly, one edge of the projection region P on the first direction X is flush with the second edge 21B of the first pole piece 21, and another edge is formed by a bottom edge 2123 of the plurality of first recesses 212 closest to one end of the first direction X.

[0131] In some embodiments, the maximum width of the first recess 212 on the third direction Z is W max (mm), and the width of the projection region P is W1 (mm), W1≤W max +5 mm. In this way, the plurality of first recesses 212 can have a smaller displacement on the third direction Z, reducing the risk of the plurality of first recesses 212 having a large displacement, making it difficult for the internal high-temperature gas to gather at the bending deformation of the electrode assembly 20 during hot box testing, so that the internal high-temperature gas is more easily flushed away by the first sealing edge 12. In combination with FIG. 10 and FIG. 12, when measuring W1, a first side edge 2121 of the plurality of first recesses 212 closest to one end of the third direction Z can be marked on the CT image, and a second side edge 2122 of the plurality of first recesses 212 closest to another end of the third direction Z can be marked on the CT image. Then, the distance between the marked first side edge 2121 and the second side edge 2122 can be directly measured using a caliper or other suitable measuring tool, and this distance is W1. In combination with FIG. 11 and FIG. 12, when measuring L1, an edge of the plurality of first recesses 212 on the first direction X (which is flush with the second edge 21B of the first pole piece 21) can be marked on the CT image, and a bottom edge 2123 of the plurality of first recesses 212 closest to one end of the first direction X can be marked on the CT image. Then, the distance between the marked edge and the bottom edge 2123 can be measured, and this distance is L1.

[0132] As shown in FIGS. 10-12, in some embodiments, in the third direction Z, the width of the projection region P is W1, and the width of the electrode assembly 20 is W0, 15%≤W1 / W0≤40%. In this way, the first tab 21 can form an effective stress weak point, so that the electrode assembly 20 is more likely to bend and deform at the first recess 212 under the heat chamber test. Moreover, it can also reduce the risk that the internal high-temperature gas is difficult to gather at the bending and deforming position of the electrode assembly 20 under the heat chamber test due to the large width of the first recess 212, so that the internal high-temperature gas is more likely to rush through the first sealing edge 12. In some embodiments, in the first direction X, the length of the projection region P is L1, and the length of the electrode assembly 20 is L0, 3%≤L1 / L0≤10%. In this way, the first tab 21 can form an effective stress weak point, so that the electrode assembly 20 is more likely to bend and deform at the first recess 212 under the heat chamber test. Moreover, it can also reduce the impact of the first recess 212 on the energy density of the secondary battery 100.

[0133] As shown in FIGS. 2-5, in some embodiments, the first tab 21 is a positive electrode tab, i.e., the first recess 212 is arranged on the positive electrode tab, thereby reducing the risk of lithium precipitation caused by the absence of negative active material, which causes the second active material layer 221 to be unable to normally intercalate active ions (such as lithium ions) during the charging and discharging process, when the second tab 22 is provided with the first recess 212. Further, when the outermost layer of the electrode assembly 20 in the second direction Y is the first tab 21, the first tab 21 of the outermost layer is not provided with the first recess 212, i.e., the first recess 212 is arranged on at least one layer of the first tab 21 other than the outermost layer. Therefore, when the electrode assembly 20 bends and deforms at the first recess 212 under the heat chamber test, the risk of short circuit and accelerated gas production of the first tab 21 contacting the second tab 22 can be further reduced (the above risk is because when the first recess 212 is arranged on the first tab 21 of the outermost layer, the risk of direct contact between the first tab 21 and the adjacent second tab 22 at the bending and deforming position can be reduced, but the second tab 22 can still directly contact and short circuit with another adjacent first tab 21 at the bending and deforming position). That is, by arranging the first tab 21 of the outermost layer without the first recess 212, it is beneficial to reduce the risk of short circuit and accelerated gas production of the first tab 21 provided with the first recess 212 directly contacting two adjacent second tabs 22 at the bending and deforming position, thereby further reducing the risk of thermal runaway of the secondary battery 100 under the heat chamber test.

[0134] Referring to FIG. 13, in some embodiments, the first tab 21 is a negative electrode tab, and the first recess 212 is disposed on the negative electrode tab. In this case, the secondary battery 100 can further include a first insulating member 70 adhered to the second active material layer 221 disposed facing the first recess 212. The first insulating member 70 covers the first recess 212 as viewed in the second direction Y. In this way, the first insulating member 70 can prevent active ions, which are discharged from the second active material layer 221 corresponding to the first insulating member 70 in the second direction Y, from moving to the first recess 212, thereby reducing the risk of excessive active ions accumulating and lithium dendrites being generated due to the first recess 212 lacking the ability to intercalate these active ions. In the drawings, the number of first insulating members 70 is two, and each is adhered to the two layers of second active material layers 221 disposed facing the first recess 212. In some embodiments, the first insulating member 70 can be a single-sided adhesive or a double-sided adhesive. The material of the adhesive layer in the single-sided adhesive or the double-sided adhesive can be selected from one or more of acrylate, polyurethane, rubber, and silicone.

[0135] In some embodiments, the secondary battery 100 of the present application can 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.

[0136] Referring to FIG. 14, in some embodiments, the present application also provides an electronic device 1 including a battery compartment 101 and the above-mentioned secondary battery 100 disposed in the battery compartment 101. In some embodiments, the secondary battery 100 of the present application is suitable for various electronic devices 1. The electronic device 1 is powered by the above-mentioned secondary battery 100, and the secondary battery 100 can timely release high-temperature gas inside the battery during a hot box test, thereby maintaining good reliability and safety. In some embodiments, the electronic device 1 of the present application can be, but is not limited to, a notebook computer, a pen input computer, a mobile computer, an electronic book player, a portable phone, a portable fax machine, a portable copier, a portable printer, a headset, a video recorder, a liquid crystal television, a portable cleaner, a portable C machine, a mini disc, a transceiver, an electronic organizer, a calculator, a memory card, a portable recorder, a radio, a backup power supply, an electric motor, an automobile, a motorcycle, an electrically assisted bicycle, a bicycle, a lighting appliance, a toy, a game machine, a clock, a power tool, a flashlight, a camera, a household large battery, and a lithium ion capacitor, etc.

[0137] The present application is described in detail below through specific examples and comparative examples. In some embodiments, the secondary battery is a lithium ion secondary battery, the first tab is a positive electrode tab, and the second tab is a negative electrode tab. The preparation method described in the present application is only an example, and any suitable preparation method is within the scope of the present application.

[0138] Examples 1-8

[0139] Preparation of the first electrode tab: the positive electrode active material lithium cobalt oxide (LiCoO2), conductive carbon black (Super P), and polyvinylidene fluoride (PVDF) were mixed in a weight ratio of 97.5:1.0:1.5, N-methyl pyrrolidone (NMP) was added as a solvent, a slurry with a solid content of 75 wt% was prepared, and the slurry was stirred uniformly. The slurry was uniformly coated on one surface of a first current collector, i.e., an aluminum foil, with a thickness of 12 μm, and an empty foil area was reserved at the edge of the aluminum foil. Drying was performed at 90°C to obtain a first electrode tab with a first active material layer having a thickness of 100 μm. On the other surface of the aluminum foil, the above steps were repeated to obtain a first electrode tab coated with a first active material layer on both surfaces. Then, the excess empty foil area was cut off by laser die forming to obtain a plurality of first tabs, and part of the aluminum foil and the first active material layer was cut off from the edge of the first electrode tab away from the first tabs to obtain a first recess.

[0140] Preparation of the second electrode tab: the negative electrode active material artificial graphite, conductive carbon black (Super P), and styrene-butadiene rubber (SBR) were mixed in a weight ratio of 96:1.5:2.5, deionized water was added as a solvent, a slurry with a solid content of 70 wt% was prepared, and the slurry was stirred uniformly. The slurry was uniformly coated on one surface of a second current collector, e.g., a copper foil, with a thickness of 10 μm, and an empty foil area was reserved at the edge of the copper foil. Drying was performed at 110°C to obtain a second electrode tab coated with a second active material layer on one surface with a coating thickness of 150 μm. On the other surface of the second electrode tab, the above steps were repeated to obtain a second electrode tab coated with a second active material layer on both surfaces. Then, the excess empty foil area was cut off by laser die forming to obtain a plurality of second tabs.

[0141] Preparation of the electrolyte: in a dry argon atmosphere, first, the organic solvents ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) were mixed in a mass ratio of EC:EMC:DEC=30:50:20, and then lithium salt lithium hexafluorophosphate (LiPF6) was added to the organic solvents to dissolve and mix uniformly to obtain an electrolyte with a lithium salt concentration of 1.15 mol / L.

[0142] Assembly of the electrode assembly: the second electrode tab, a separator, and the first electrode tab were stacked in sequence to obtain an electrode assembly, the separator was a polyethylene (PE) film with a thickness of 15 μm, and the first tab and the second tab were welded to a first conductive plate and a second conductive plate, respectively, by adapter welding, the first conductive plate was made of aluminum, and the second conductive plate was made of nickel, the width W0 and the length L0 of the obtained electrode assembly were 67.91 mm and 76.11 mm, respectively. An impact pit formed aluminum plastic film (with a thickness of 150 μm) was placed in an assembly jig with the pit facing up, and the electrode assembly was placed in the pit.

[0143] The injection packaging is to inject electrolyte into the pit of the aluminum plastic film, and the first conductive plate and the second conductive plate are led out of the aluminum plastic film. A special-shaped sealing head is used to press at the edge of the aluminum plastic film to form a first sealing edge, thereby obtaining a lithium ion secondary battery.

[0144] Comparative Example 1

[0145] The difference from Example 1 is that the first pole piece is not provided with a first recess.

[0146] Comparative Examples 2-3

[0147] The difference from Example 1 is the width of the first recess.

[0148] Then, the batteries of each example and comparative example were respectively subjected to a hot box test. 10 batteries of each group of examples and each group of comparative examples were tested, and the corresponding test results are recorded in Table 1.

[0149] The hot box test procedure is as follows: 1) discharging the battery, specifically: placing the battery at 23±2℃ for 5min, discharging at 0.2C constant current to 3.0V, and standing for 20min; 2) charging the battery, specifically: 3.5C constant current charging to 4.33V, then constant voltage charging to 2.5C; 2.5C constant current charging to 4.38V, then constant voltage charging to 2.0C; 2.0C constant current charging to 4.50V, then constant voltage charging to 0.02C; 3) placing the battery horizontally in the hot box, heating the hot box to 130±2℃ at a heating rate of 5±2℃, and keeping for 60min, 4) recording the changes of voltage, temperature and hot box temperature of the lithium ion battery. The lithium ion battery is not on fire, explosion or smoke, which is passed the hot box test. The test results are recorded in Table 1.

[0150] Table 1

[0151] In Table 1, the hot box test pass rate is n / 10, indicating that among the 10 batteries tested, the number of batteries that pass the test is n. The meanings of other ratio values are similar.

[0152] From the data in Table 1, compared with Comparative Example 1, because Example 1 sets a first recess at the second edge of the first pole piece, the electrode assembly is prone to bending deformation at the first recess under the hot box test, and the internal high-temperature gas is gathered at the bending deformation of the electrode assembly and bursts through the first sealing edge, reducing the risk of thermal runaway, so the hot box test pass rate of Example 1 is higher.

[0153] Compared with Comparative Example 2-3, the size of the first recess of Example 1-3 satisfies 15%≤W2 / W0≤40%, the electrode assembly is prone to bending deformation at the first recess under the hot box test, and the risk of the internal high-temperature gas being difficult to gather at the bending deformation of the electrode assembly under the hot box test due to the large width of the first recess can be reduced, so that the internal high-temperature gas is more easily to rush open the first sealing edge, and therefore the hot box test pass rate of Example 1-3 is higher. Moreover, compared with Example 3, Example 1-3 can also take into account higher energy density at the same time.

[0154] Compared with Example 7, the size of the first recess of Example 1, 4-5 satisfies 3%≤L2 / L0≤10%, the electrode assembly is more prone to bending deformation at the first recess under the hot box test, and therefore the hot box test pass rate of Example 1, 4-5 is higher. The size of the first recess of Example 8 is large, the electrode assembly is also prone to bending deformation at the first recess under the hot box test, and the hot box test pass rate is higher, and compared with Example 8, Example 1, 4-5 can also take into account higher energy density at the same time.

[0155] Example 9-11

[0156] Different from Example 1, the first tab is provided with a plurality of first recesses.

[0157] Then, the batteries of each example are respectively subjected to hot box test. 10 batteries of each group of examples and each group of comparative examples are tested, and the corresponding test results are recorded in Table 2.

[0158] Table 2

[0159] From the data in Table 2, compared with Example 11, Examples 9-10 satisfy W1≤W max +5mm, so that the displacement of the plurality of first recesses in the third direction is small, the internal high-temperature gas is more easily to gather at the bending deformation of the electrode assembly under the hot box test, so that the internal high-temperature gas is more easily to rush open the first sealing edge, and therefore the hot box test pass rate of Example 9-10 is higher.

[0160] Finally, it should be noted that the above examples are only used to illustrate the technical solutions of the present application and not to limit it. Although the present application has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present application can be modified or replaced equivalently without departing from the spirit and scope of the technical solutions of the present application.

Claims

1. A secondary battery, comprising a packaging bag, an electrode assembly, and a first conductive plate, wherein the packaging bag includes a receiving portion and a first sealing edge, the electrode assembly is disposed within the receiving portion and includes a first electrode sheet, the first electrode sheet including a first current collector and a first active material layer disposed on the first current collector, and the first conductive plate is electrically connected to the first current collector and extends out of the packaging bag from the first sealing edge, wherein... The direction in which the first conductive plate extends out of the electrode assembly is a first direction. The first electrode includes a first edge and a second edge disposed opposite to each other in the first direction. In the first direction, the first edge is closer to the first sealing edge than the second edge. The first electrode has at least one first recess at the second edge. The thickness direction of the electrode assembly is a second direction, which is perpendicular to the first direction. The first recess penetrates the first current collector and the first active material layer along the second direction. The projection of the at least one first recess in the second direction forms a projection area. In a third direction perpendicular to both the first and second directions, the width of the projection area is W1, and the width of the electrode assembly is W0, where 15% ≤ W1 / W0 ≤ 40%.

2. The secondary battery as described in claim 1, wherein, There are multiple first recesses, which are respectively disposed on adjacent layers of first electrode sheets. When viewed from the second direction, any two first recesses overlap.

3. The secondary battery as described in claim 2, wherein, In the third direction, the maximum width of the first recess is W. max W max The units for W1 and W1 are mm, and W1 ≤ W max +5mm.

4. The secondary battery as described in claim 2, wherein, In the first direction, the length of the projection area is L1, the length of the electrode assembly is L0, and 3% ≤ L1 / L0 ≤ 10%.

5. The secondary battery as described in claim 1, wherein, The number of the first recess is one, the length of the first recess in the first direction is L2, the length of the electrode assembly is L0, and 3% ≤ L2 / L0 ≤ 10%.

6. The secondary battery as described in any one of claims 1 to 5, wherein, The first electrode is a positive electrode.

7. The secondary battery as described in claim 6, wherein, The outermost layer of the electrode assembly in the second direction is the first electrode sheet, and the first electrode sheet on the outermost layer does not have the first recess.

8. The secondary battery as described in any one of claims 1 to 5, wherein, The first electrode is a negative electrode, and the electrode assembly further includes a second electrode, which is a positive electrode. The second electrode includes a second current collector and a second active material layer disposed on the second current collector. The secondary battery further includes a first insulating member, which is bonded to the second active material layer disposed facing the first recess. When viewed from the second direction, the first insulating member covers the first recess.

9. The secondary battery according to any one of claims 1 to 8, wherein, The electrode assembly is a wound structure. The first electrode sheet has a first groove at the first edge. The first groove penetrates the first active material layer along the second direction. The first groove does not penetrate the first current collector. The first conductive plate is disposed in the first groove and electrically connected to the first current collector. When viewed from the second direction, the first conductive plate includes a conductive connection area that overlaps with the first current collector. When viewed from the first direction, the first groove and the conductive connection area overlap.

10. The secondary battery according to any one of claims 1 to 8, wherein, The electrode assembly is a wound structure. The first current collector includes a first surface. The first surface includes a first region and a second region connected in the winding direction. The first region is not provided with the first active material layer. The second region is provided with the first active material layer. The first conductive plate is electrically connected to the first region. The first recess penetrates the second region and the first active material layer along the second direction.

11. The secondary battery according to any one of claims 1 to 8, wherein, The secondary battery also includes a plurality of first tabs, which are integrally disposed with the first current collector and extend from the first edge of the first current collector. The plurality of first tabs are also electrically connected to the first conductive plate. The first tab includes a tab connection area connected to the first edge. When viewed from the first direction, a first recess and a tab connection area overlap.

12. The secondary battery according to any one of claims 1 to 11, wherein, Viewed from the second direction, the edge of the first recess includes a first side, a bottom edge, and a second side connected in sequence, with the first side and the second side respectively connected to the second edge. The secondary battery satisfies at least one of the following conditions: (1) When viewed from the second direction, the first side includes a first slope edge that is away from the second edge, the first slope edge being connected to the bottom edge, and the first slope edge being arc-shaped; (2) When viewed from the second direction, the first side includes a second slope edge connected to the second edge, the second slope edge being arc-shaped.

13. The secondary battery according to any one of claims 1 to 11, wherein, Viewed from the second direction, the edge of the first recess is arc-shaped.

14. An electronic device, wherein, It includes a battery compartment and a secondary battery as described in any one of claims 1 to 13 disposed within the battery compartment.

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