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 batteries and electronic devices Technical Field

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

[0002] Secondary batteries are widely used in electronic products such as electronic mobile devices, power tools, and electric vehicles, and people are increasingly demanding higher safety performance from secondary batteries.

[0003] Because the operation of a secondary battery requires a relatively sealed environment, the battery casing needs to have a certain sealing function. In some cases (such as hot chamber testing), gas may be generated inside the secondary battery. If this gas accumulates inside the casing and is not properly released into the external environment, the internal pressure of the casing will continue to increase, affecting the reliability and safety of the secondary battery.

[0004] Summary of the Invention

[0005] In view of this, it is necessary to propose a secondary battery with high reliability and safety during hot box testing.

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

[0007] This application provides a secondary battery, including a packaging bag, an electrode assembly, and a first conductive plate. 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 includes a first current collector and a first active material layer disposed 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. The first electrode sheet 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, and the first electrode sheet 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, then 15% ≤ W1 / W0 ≤ 40%.

[0008] In this application, if the high-temperature gas accumulation inside the hot box test causes the packaging bag to bulge and compress the electrode assembly, the first recess can become a weak point under stress, and the electrode assembly tends to bend and deform at the first recess. Therefore, the high-temperature gas inside easily accumulates at the bending deformation point of the electrode assembly and promptly breaks through the first seal, thereby reducing the risk of thermal runaway that may be caused by the continuous accumulation of heat inside the packaging bag, and improving the reliability and safety of the secondary battery. Furthermore, when the electrode assembly bends and deforms at the first recess, the absence of the first current collector and the first active material layer at the first recess reduces the risk of direct contact and short circuit between the first electrode with the first recess and the adjacent second electrode at the bending deformation point, accelerating gas generation, thereby further reducing the risk of thermal runaway of the secondary battery under hot box testing. Furthermore, by setting the width of the projection area formed by the first recess, the first electrode can form an effective weak point under stress, making it easier for the electrode assembly to bend and deform at the first recess during hot box testing. It can also reduce the risk that the high-temperature gas inside the electrode assembly will have difficulty accumulating at the bending and deformation point of the electrode assembly due to the large width of the first recess, thus making it easier for the high-temperature gas inside to break through the first seal.

[0009] Based on the first aspect, in some possible implementations, there are multiple first recesses, each disposed on an adjacent multilayer of first electrodes. Viewed from the second direction, any two first recesses overlap. Therefore, this makes it easier for the electrode assembly to bend and deform at the first recesses during hot-box testing, thereby facilitating the accumulation of high-temperature gas at the bending deformation point of the electrode assembly and timely breaking through the first seal, reducing the risk of thermal runaway that may result from continuous heat accumulation inside the packaging bag.

[0010] Based on the first aspect, in some possible implementations, 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. Therefore, the misalignment of the multiple first recesses in the third direction is smaller, which helps to reduce the risk that the high-temperature gas inside the chamber will have difficulty accumulating at the bending deformation of the electrode assembly under the hot box test, thus making it easier for the high-temperature gas inside to break through the first seal.

[0011] Based on the first aspect, in some possible implementations, the length of the projection area is L1 in the first direction, and the length of the electrode assembly is L0, where 3% ≤ L1 / L0 ≤ 10%. Therefore, the first electrode can form an effective weak point under stress, making the electrode assembly more prone to bending deformation at the first recess during hot-box testing. Furthermore, the impact of the first recess on the energy density of the secondary battery can also be reduced.

[0012] Based on the first aspect, in some possible implementations, the number of 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, where 3% ≤ L2 / L0 ≤ 10%. This allows the first electrode to form an effective weak point under stress, making the electrode assembly more prone to bending deformation at the first recess during hot-box testing. Furthermore, it can also reduce the impact of the first recess on the energy density of the secondary battery.

[0013] Based on the first aspect, in some possible implementations, the first electrode is a positive electrode. Therefore, the risk of lithium plating caused by the absence of negative active material in the second electrode after the first recess is provided, resulting in the inability of the second active material layer to properly insert active ions during charging and discharging, can be reduced.

[0014] Based on the first aspect, in some possible implementations, the outermost layer of the electrode assembly in the second direction is a first electrode sheet, and the outermost first electrode sheet does not have a first recess. Therefore, when the electrode assembly bends and deforms at the first recess during hot box testing, it helps to reduce the risk of the first electrode sheet with the first recess directly contacting and short-circuiting with the two adjacent second electrode sheets at the bending deformation point and accelerating gas generation, thereby further reducing the risk of thermal runaway of the secondary battery under hot box testing.

[0015] Based on the first aspect, in some possible implementations, the first electrode is a negative electrode. The electrode assembly also 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 also includes a first insulating member, which is bonded to the second active material layer disposed facing the first recess. Viewed from a second direction, the first insulating member covers the first recess. Therefore, the first insulating member can prevent active ions detached from the second active material layer corresponding to the first insulating member in the second direction from moving towards the first recess, thereby reducing the risk of excessive accumulation of active ions and formation of lithium dendrites due to the lack of space for these active ions to be embedded in the first recess.

[0016] Based on the first aspect, in some possible implementations, the electrode assembly is a wound structure. A first electrode has a first groove at its first edge, the first groove penetrating the first active material layer along a second direction, but not penetrating the first current collector. A first conductive plate is disposed in the first groove and electrically connected to the first current collector. Viewed from the second direction, the first conductive plate includes a conductive connection area overlapping with the first current collector. Viewed from the first direction, a first recess and the conductive connection area overlap. Therefore, when the electrode assembly bends and deforms at the first recess during a hot-box test, the high hardness of the first conductive plate reduces the risk of the end of the electrode assembly away from the first recess also bending and deforming simultaneously, leading to a direct short circuit between the first and second electrodes at that end of the electrode assembly.

[0017] Based on the first aspect, in some possible implementations, the electrode assembly is a wound structure. The first current collector includes a first surface, which includes a first region and a second region connected in the winding direction. The first region does not have a first active material layer, while the second region has a first active material layer. A first conductive plate is electrically connected to the first region. A first recess penetrates the second region and the first active material layer along a second direction. Therefore, by setting the position of the first recess, the electrode assembly can more easily bend and deform at the first recess during hot-box testing, thereby facilitating the accumulation of high-temperature gas at the bending deformation point of the electrode assembly and timely breaking through the first seal, reducing the risk of thermal runaway that may be caused by the continuous accumulation of heat inside the packaging bag.

[0018] Based on the first aspect, in some possible implementations, the electrode assembly is a wound structure or a stacked structure. The secondary battery also includes a plurality of first tabs, which are integrally disposed with a first current collector and extend from a first edge of the first current collector. The plurality of first tabs are also electrically connected to a first conductive plate. The first tab includes a tab connection area connected to the first edge. Viewed from a first direction, a first recess and a tab connection area overlap. Therefore, when the electrode assembly bends and deforms at the first recess during a hot box test, the first tab is relatively hard and not easily deformed, thus reducing the risk that the end of the electrode assembly away from the first recess will also bend and deform simultaneously, causing the first and second electrodes to directly contact and short-circuit at the aforementioned end of the electrode assembly.

[0019] Based on the first aspect, in some possible implementations, 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 and second side respectively connected to the second edge. Viewed from the second direction, the first side includes a first sloping edge facing away from the second edge, connected to the bottom edge, and the first sloping edge is arc-shaped. Therefore, the risk of sharp corners forming at the edge of the first recess can be reduced. When the electrode assembly bends and deforms at the first recess during hot-box testing, the risk of the sharp corners piercing the separator and causing a short circuit between the first and second electrodes can be reduced. Furthermore, the risk of active material detachment from the first active material layer at the sharp corners can also be reduced.

[0020] Based on the first aspect, in some possible implementations, viewed from the second direction, the first side includes a second ramp edge connected to the second edge, and the second ramp edge is arc-shaped. Therefore, the risk of sharp corners forming at the edge of the first recess can be reduced. When the electrode assembly bends and deforms at the first recess during hot-box testing, the risk of the sharp corners piercing the separator and causing a short circuit between the first and second electrodes can be reduced. Furthermore, the risk of active material detachment from the first active material layer at the sharp corners can also be reduced.

[0021] Based on the first aspect, in some possible implementations, viewed from the second direction, the edge of the first recess is arc-shaped. Therefore, the risk of the edge of the first recess forming a sharp corner can be reduced. When the electrode assembly bends and deforms at the first recess during hot-box testing, the risk of the sharp corner piercing the separator and causing a short circuit between the first and second electrodes can be reduced. Furthermore, the risk of active material detachment from the first active material layer at the sharp corner can also be reduced.

[0022] A second aspect of this application provides an electronic device including a battery compartment and the aforementioned secondary battery disposed within the battery compartment. The electronic device is powered by the aforementioned secondary battery, and the secondary battery can promptly release internal high-temperature gases during hot-chamber testing, thereby maintaining good reliability and safety. Attached Figure Description

[0023] Figure 1A is a schematic diagram of the structure of a secondary battery provided in an embodiment of this application when viewed from a second direction.

[0024] Figure 1B is a structural schematic diagram of the secondary battery in some other embodiments when viewed from a second direction.

[0025] Figure 1C is a structural schematic diagram of the secondary battery in some other embodiments when viewed from a second direction.

[0026] Figure 2 is a cross-sectional view of the secondary battery shown in Figure 1A along section line II-II in some embodiments.

[0027] Figure 3 is a cross-sectional view of the secondary battery shown in Figure 1A along section line III-III in some embodiments.

[0028] Figure 4 is a cross-sectional view of the secondary battery shown in Figure 1A along section line III-III in some other embodiments.

[0029] Figure 5 is a cross-sectional view of the secondary battery shown in Figure 1A along section line IV-IV in some other embodiments.

[0030] Figure 6 is a schematic diagram of the unfolded structure of the first electrode of the secondary battery shown in Figure 2 or Figure 3 in some embodiments.

[0031] Figure 7 is a schematic diagram of the unfolded structure of the first electrode of the secondary battery shown in Figure 2 in some other embodiments.

[0032] Figure 8 is a schematic diagram of the structure of the first electrode of the secondary battery shown in Figure 4 or Figure 5 after it has been unfolded.

[0033] Figure 9A is an enlarged view of the first recess of the first electrode shown in Figures 6, 7 or 8 in some embodiments.

[0034] Figure 9B is an enlarged view of the first recess of the first electrode shown in Figures 6, 7 or 8 in some other embodiments.

[0035] Figure 9C is an enlarged view of the first recess of the first electrode shown in Figures 6, 7 or 8 in some other embodiments.

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

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

[0038] Figure 12 is a schematic diagram of the projection area of ​​the first concave part of the secondary battery shown in Figure 10 or Figure 11.

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

[0040] Figure 14 is a schematic diagram of the overall structure of an electronic device provided in one embodiment of this application.

[0041] Explanation of main component symbols

[0042] Electronic device 1

[0043] Packaging bag 10

[0044] Reception Section 11

[0045] First edge sealing 12

[0046] Second edge sealing 13

[0047] Electrode assembly 20

[0048] First Extreme Film 21

[0049] First Edge 21A

[0050] Second Edge 21B

[0051] Second pole piece 22

[0052] Separator 23

[0053] First conductive plate 30

[0054] Conductive connection area 31

[0055] Third conductive plate 32

[0056] Second conductive plate 40

[0057] First Pole Ear 50

[0058] Electrode Connection Area 51

[0059] Conductive plate connection area 52

[0060] Second pole ear 60

[0061] First insulating component 70

[0062] Secondary battery 100

[0063] Battery compartment 101

[0064] First end wall 111

[0065] Second end wall 112

[0066] First straight section 201

[0067] First bending section 202

[0068] Second straight section 203

[0069] Second bending 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] Area 1, 2101A

[0077] Area 2101B

[0078] Second surface 2102

[0079] First groove 2110

[0080] First side 2121

[0081] Second side 2122

[0082] Bottom edge 2123

[0083] First slope side 2124

[0084] Second slope side 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 area P

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

[0094] Lengths L0, L1, L2

[0095] The following detailed description, in conjunction with the accompanying drawings, will further illustrate this application. Detailed Implementation

[0096] The technical solutions in the embodiments of this application are described clearly and in detail below. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used in the specification of this application is for the purpose of describing particular embodiments only and is not intended to limit this application.

[0097] The embodiments of this application will be described in detail below. However, this application may 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 to provide a thorough and detailed understanding of this application to those skilled in the art.

[0098] Additionally, for brevity and clarity, the dimensions or thicknesses of various components and layers may be enlarged in the accompanying drawings. Throughout the text, the same numerical values ​​refer to the same elements. As used herein, the terms "and / or" and "and / or" include any and all combinations of one or more of the associated enumerated items. Furthermore, it should be understood that when element A is referred to as "connecting" element B, element A may be directly connected to element B, or there may be an intermediate element C and element A and element B may be indirectly connected to each other.

[0099] Furthermore, when describing the implementation of this application, the word "may" refers to "one or more implementations of this application".

[0100] The technical terms used herein are for the purpose of describing particular embodiments and are not intended to limit this 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," as used in this specification, means the presence of the described features, values, steps, operations, elements, and / or components, but does not exclude the presence or addition of one or more other features, values, steps, operations, elements, components, and / or combinations thereof.

[0101] Spatial terms, such as "above," may be used herein for convenience in describing the relationship between one element or feature and another element (or feature) or feature (or feature) illustrated in the figures. It should be understood that, in addition to the directions depicted in the figures, spatial terms are intended to include different orientations of the device or apparatus during use or operation. For example, if the device in the figure is flipped, an element described as "above" or "on" other elements or features would be oriented "below" or "under" other elements or features. Therefore, the exemplary term "above" can include both above and below orientations. It should be understood that although the terms first, second, third, etc., may be used herein to describe various elements, components, regions, layers, and / or portions, these elements, components, regions, layers, and / or portions should not be limited by these terms. These terms are used to distinguish one element, component, region, layer, or portion from another element, component, region, layer, or portion. Therefore, a first element, component, region, layer, or portion discussed below may be referred to as a second element, component, region, layer, or portion without departing from the teachings of the exemplary embodiments.

[0102] In hotbox testing, a large amount of gas is generated inside the secondary battery at high temperatures. This gas accumulates inside the casing (such as the packaging bag). If the gas is not effectively released to the external environment, the internal pressure will continue to increase. When the high-temperature gas accumulates inside the casing, the middle of the packaging bag will bulge significantly along its width, compressing the electrode plates and making them prone to bulging or breaking. With continued gas accumulation, the entire electrode assembly of the secondary battery may even be broken off entirely by the gas. At the break, the positive and negative electrode plates are prone to short-circuiting, generating a large amount of heat and further accelerating gas production. Additionally, the separator is also prone to shrinkage under the influence of the high-temperature gas inside, which can also cause direct short-circuiting between the positive and negative electrode plates, generating a large amount of heat and further accelerating gas production, leading to risks of smoke, fire, or even explosion.

[0103] Please refer to Figures 1A to 3. One embodiment of this 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 inside 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 external components (not shown). 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 the first direction X, the thickness direction of the electrode assembly 20 is defined as the second direction Y, and the direction from the first conductive plate 30 to the second conductive plate 40 is defined as the third direction Z. The first direction X, the second direction Y, and the third direction Z are all perpendicular to each other.

[0104] As shown in Figures 1A and 3, the packaging bag 10 includes a receiving portion 11 and a first sealing edge 12. An electrode assembly 20 and an electrolyte are disposed within the receiving portion 11. A first conductive plate 30 extends from the first sealing edge 12 into the packaging bag 10. In some embodiments, in the first direction X, the receiving portion 11 includes a first end wall 111 and a second end wall 112 disposed opposite to each other. The surface of the first end wall 111 extends in the second direction Y and the third direction Z, and the surface of the second end wall 112 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 both the first conductive plate 30 and the second conductive plate 40 can extend from the first sealing edge 12 into the packaging bag 10.

[0105] As shown in Figures 2 and 3, in some embodiments, the electrode assembly 20 is a wound structure, comprising a first electrode 21, a second electrode 22, and a separator 23. The separator 23 is disposed between the first electrode 21 and the second electrode 22. The first electrode 21 includes a first current collector 210 and a first active material layer 211 disposed on the first current collector 210, and a first conductive plate 30 is electrically connected to the first current collector 210. The second electrode 22 includes a second current collector 220 and a second active material layer 221 disposed on the second current collector 220, and a second conductive plate 40 is electrically connected to the second current collector 220. As shown in Figure 3, the first electrode 21 includes a first edge 21A and a second edge 21B disposed opposite each other 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, referring to Figures 3 and 6, where Figure 6 is a schematic diagram of the structure of the first electrode 21 after unfolding. In some embodiments, a first conductive plate 30 may be provided connected to the first current collector 210 and extend from the first edge 21A of the first current collector 210. More specifically, the first electrode 21 has a first groove 2110 at the first edge 21A, the first groove 2110 penetrating 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 welded to the first current collector 210, thereby improving the connection strength between the first conductive plate 30 and the first current collector 210. The connection method between the second conductive plate 40 and the second current collector 220 can refer to the connection method between the first conductive plate 30 and the first current collector 210.

[0107] Referring to Figures 4 and 5, in some embodiments, when the electrode assembly 20 is a wound structure, the secondary battery 100 may 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 (for example, the first tabs 50 may be formed by cutting the first current collector 210) and extend from the first edge 21A of the first current collector 210. The plurality of first tabs 50 are welded to the first conductive plate 30 by an adapter welding process. The connection method between the second tabs 60 and the second current collector 220 can refer to the connection method between the first tabs 50 and the first current collector 210.

[0108] In some embodiments, the electrode assembly 20 shown in Figures 4 and 5 may also be a stacked structure, comprising a plurality of first electrodes 21, a plurality of second electrodes 22, and a separator 23. In the stacked structure, the first electrodes 21 and second electrodes 22 are stacked alternately, with one second electrode 22 located between every two adjacent first electrodes 21, and one first electrode 21 located between every two adjacent second electrodes 22. The separator 23 is disposed between adjacent first electrodes 21 and second electrodes 22.

[0109] In this embodiment, the first electrode 21 can be a positive electrode, and the second electrode 22 can be a negative electrode. Correspondingly, the first current collector 210 and the first active material layer 211 are the positive current collector and the positive active material layer, respectively, and the second current collector 220 and the second active material layer 221 are the negative current collector and the negative active material layer, respectively. As shown in Figures 2 to 5, in some embodiments, the outermost layer of the electrode assembly 20 in the second direction Y is the first electrode 21. The first current collector 210 includes a first surface 2101 and a second surface 2102 disposed opposite to each other. The first surface 2101 is disposed away from the winding center axis O of the electrode assembly 20, and the second surface 2102 is disposed towards the winding center axis O. The outermost first electrode 21 is a single-sided coated electrode, that is, the first surface 2101 of the outermost first electrode 21 does not have the first active material layer 211, and the second surface 2102 of the outermost first electrode 21 has the first active material layer 211. Therefore, the outermost surface of the electrode assembly 20 is the first surface 2101. By setting the outermost first electrode 21 to be a single-sided coated electrode, the energy density of the secondary battery 100 can be improved, and the situation where the active material on the outer surface of the electrode assembly 20 is prone to detachment after contact with the packaging bag 10 can be mitigated. In other embodiments, the first electrode 21 can also be set as a negative electrode and the second electrode 22 as a positive electrode.

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

[0111] The positive electrode active material layer comprises a positive electrode active material, which includes a compound that reversibly inserts and de-intercalates metal ions (such as lithium ions, sodium ions, etc., hereinafter taking lithium ions as an example) (i.e., a lithiation intercalation compound). In some embodiments, the first active material may include a lithium transition metal composite oxide. This lithium transition metal composite oxide contains lithium and at least one element selected from cobalt, manganese, and nickel. In some embodiments, the positive electrode active material is selected from lithium cobalt oxide (LiCoO2), lithium nickel cobalt manganese ternary materials (NCM), lithium nickel cobalt aluminum ternary materials (NCA), lithium manganese oxide (LiMn2O4), and lithium nickel manganese oxide (LiNi). 0.5 Mn 1.5 At least one of lithium iron phosphate (LiFePO4) or lithium iron phosphate (LiFePO4).

[0112] The negative electrode active material layer contains a negative electrode active material, which is a known negative electrode active material capable of reversible intercalation and deintercalation of active ions, and this application is not limited to this. For example, it may include, but is not limited to, one or more combinations of graphite, soft carbon, hard carbon, carbon fiber, mesophase carbon microspheres, silicon-based materials, tin-based materials, lithium titanate, or other metals that can form alloys with lithium. Among them, graphite may be selected from one or more combinations of artificial graphite, natural graphite, and modified graphite; silicon-based materials may be selected from one or more combinations of elemental silicon, silicon oxide compounds, silicon-carbon composites, and silicon alloys; tin-based materials may be selected from one or more combinations of elemental tin, tin oxide compounds, and tin alloys.

[0113] The separator 23 comprises at least one of polyethylene, polypropylene, polyvinylidene fluoride, polyethylene terephthalate, polyimide, or aramid. For example, polyethylene comprises at least one selected from high-density polyethylene, low-density polyethylene, or ultra-high molecular weight polyethylene.

[0114] In other embodiments, to meet the requirements of high-current charging and discharging and reduce the internal resistance of the first electrode 21 or the second electrode 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 FIG1B, the packaging bag 10 may also 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 the wider first tab 50 and the second tab 60 coming into contact and causing a short circuit can be reduced, and a larger welding operation space can 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 FIG1C, the secondary battery 100 may further include a third conductive plate 32, wherein the first conductive plate 30, the second conductive plate 40, and the third conductive plate 32 all extend from the first sealing edge 12 of the packaging bag 10. The third conductive plate 32 may have the same polarity as the first conductive plate 30. That is, the third conductive plate 32 may 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 FIG1C). By setting the first conductive plate 30 and the second conductive plate 32 in parallel to shunt the current, it is also beneficial to reduce the internal resistance of the first electrode 21 and meet the requirements of high current charging and discharging.

[0116] As shown in Figures 2 to 5, the first electrode 21 has at least one first recess 212 at its second edge 21B. The first recess 212 penetrates the first current collector 210 and the first active material layer 211 along the second direction Y. Figures 2 to 5 show that the number of first recesses 212 in the first electrode 21 is one. As shown in Figure 2, when the electrode assembly 20 is a wound structure, the electrode assembly 20 may include a first straight section 201, a first curved section 202, a second straight section 203, and a second curved section 204 connected sequentially in the winding direction D. The first straight section 201 and the second straight section 203 are arranged opposite each other in the second direction Y, and the first curved section 202 and the second curved section 204 are arranged opposite each other in the third direction Z. The first recess 212 may be provided on the first electrode 21 of the first straight section 201 or the second straight section 203.

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

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

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

[0120] In this application, if the high-temperature gas accumulates inside the hot box during testing, causing the packaging bag 10 to bulge and compress the electrode assembly 20, the first recess 212 can become a weak point under stress, causing the electrode assembly 20 to tend to bend and deform at the first recess 212. Consequently, the high-temperature gas inside easily accumulates at the bending deformation point of the electrode assembly 20, and the accumulated gas more easily breaks through the first seal 12, thereby releasing the high-temperature gas inside. This reduces the risk of thermal runaway that may be caused by the continuous accumulation of heat inside the packaging bag 10, improving the reliability and safety of the secondary battery 100. When the secondary battery 100 further includes a second seal 13, the accumulated gas can also break through the second seal 13, thereby releasing the high-temperature gas inside more promptly. Moreover, when the electrode assembly 20 bends and deforms at the first recess 212 (the first electrode 21 or the second electrode 22 at the bending and deformation point may generate sharp corners, which can easily pierce the separator 23 and cause the first electrode 21 and the second electrode 22 to directly contact and short-circuit), since the first current collector 210 and the first active material layer 211 are missing at the first recess 212, it is beneficial to reduce the risk of the first electrode 21 with the first recess 212 and the second electrode 22 adjacent to the first electrode 21 directly contacting and short-circuiting at the bending and deformation point and accelerating gas generation, thereby further reducing the risk of thermal runaway of the secondary battery 100 under hot box testing.

[0121] Referring to Figure 9A, in some embodiments, viewed from the second direction Y, the edge of the first recess 212 includes a first side 2121, a bottom edge 2123, and a second side 2122 connected in sequence, with the first side 2121 and the second side 2122 respectively connected to the second edge 21B. Viewed from the second direction Y, the bottom edge 2123 may be approximately perpendicular to the first side 2121 and the second side 2122, meaning the first recess 212 is approximately rectangular. Referring to Figure 9B, in other embodiments, viewed from the second direction Y, the first side 2121 may include a first sloping edge 2124 facing away from the second edge 21B, with the first sloping edge 2124 connected to the bottom edge 2123, and the first sloping edge 2124 being arc-shaped. By providing the first sloping edge 2124, the risk of sharp corners forming at the edge of the first recess 212 can be reduced. Thus, when the electrode assembly 20 bends and deforms at the first recess 212 during hot-box testing, the risk of a short circuit due to direct contact between the first electrode 21 and the second electrode 22 caused by the sharp corner of the first electrode 21 piercing the separator 23 can be reduced. Furthermore, the risk of active material detachment from the first active material layer 211 at the sharp corner of the first electrode 21 can also be reduced. Similarly, the second side 2122 can include an arc-shaped sloping edge connected to the bottom edge 2123.

[0122] As shown in Figure 9B, viewed from the second direction Y, the first side 2121 may also include a second ramp edge 2125 connected to the second edge 21B, and the second ramp edge 2125 is arc-shaped. By providing the second ramp edge 2125, the risk of the edge of the first recess 212 forming a sharp corner can be reduced. Thus, when the electrode assembly 20 undergoes bending deformation at the first recess 212 during hot box testing, the risk of the first electrode 21 and the second electrode 22 directly contacting and short-circuiting due to the sharp corner of the first electrode 21 piercing the separator 23 can be reduced. Furthermore, the risk of the active material of the first active material layer 211 at the sharp corner of the first electrode 21 can also be reduced. Similarly, the second side 2122 may also include an arc-shaped ramp edge connected to the second edge 21B.

[0123] Referring to Figure 9C, in some embodiments, when viewed from the second direction Y, the edge of the first recess 212 is arc-shaped. This also reduces the risk of the edge of the first recess 212 forming a sharp corner. Thus, when the electrode assembly 20 bends and deforms at the first recess 212 during hot box testing, the risk of a direct short circuit between the first electrode 21 and the second electrode 22 due to the sharp corner of the first electrode 21 piercing the separator 23 can be reduced. Furthermore, the risk of the active material of the first active material layer 211 at the sharp corner of the first electrode 21 can also be reduced.

[0124] As shown in Figure 2, in this application, when there is only one first recess 212, the width of the projection area formed by the projection of the first recess 212 in the third direction Z and the second direction Y (i.e., the width of the first recess 212 itself) is W2, and the width of the electrode assembly 20 is W0. Therefore, 15% ≤ W2 / W0 ≤ 40%. This allows the first electrode 21 to form an effective weak point under stress, making it easier for the electrode assembly 20 to bend and deform at the first recess 212 during hot box testing. Furthermore, it reduces the risk that the large width of the first recess 212 makes it difficult for high-temperature gas to accumulate at the bending deformation point of the electrode assembly 20 during hot box testing, thus making it easier for the high-temperature gas to break through the first seal 12. Simultaneously, it also reduces the impact of the first recess 212 on the energy density of the secondary battery 100. As shown in Figures 9A and 9B, when the edge of the first recess 212 includes a first side 2121, a bottom edge 2123, and a second side 2122 connected in sequence, the width W2 can be the distance between the first side 2121 and the second side 2122 in the third direction Z; as shown in Figure 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 Figures 3 to 5, in some embodiments, the length of the first recess 212 in the first direction X is L2, and the length of the electrode assembly 20 is L0, where 3% ≤ L2 / L0 ≤ 10%. This allows the first electrode 21 to form an effective weak point under stress, making the electrode assembly 20 more prone to bending deformation at the first recess 212 during hot-box testing. Furthermore, it can reduce the impact of the first recess 212 on the energy density of the secondary battery 100. Specifically, when the edge of the first recess 212 includes a first side 2121, a bottom edge 2123, and a second side 2122 connected in sequence, the length L2 can be the length of the first side 2121 or the second side 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 that arc segment.

[0126] In this application, the measurement steps of W2, W0, L2, L0 can be: (1) using X-rays to perform two-dimensional projection and scanning tests on the secondary battery 100 from the first direction X, the instrument can be an instrument or device known to those skilled in the art (e.g., GE Phoenix vtomex S device), thereby obtaining a CT image; (2) using calipers or other suitable measuring tools to directly measure the values ​​of W2, W0, L2, L0.

[0127] As shown in Figures 2, 3, and 6, in some embodiments, when the electrode assembly 20 has a wound structure and the first conductive plate 30 is connected to the first current collector 210, viewed from the second direction Y, the first conductive plate 30 includes a conductive connection area 31 that overlaps with the first current collector 210. The first conductive plate 30 can be welded to the first current collector 210 through at least a portion of the conductive connection area 31. Viewed from the first direction X, a first recess 212 and the conductive connection area 31 overlap. When the electrode assembly 20 undergoes bending deformation at the first recess 212, because the first conductive plate 30 has high hardness and is not easily deformed, the risk of the top of the electrode assembly 20 (i.e., the end of the electrode assembly 20 away from the first recess 212) also bending deformation simultaneously, leading to a direct contact and short circuit between the first electrode 21 and the second electrode 22 at the top of the electrode assembly 20, can be reduced.

[0128] As shown in Figures 4 and 8, when the electrode assembly 20 has a wound or stacked structure and the first conductive plate 30 is connected to the first current collector 210 through multiple first tabs 50, the first tab 50 includes a tab connection area 51 connected to the first edge 21A and a conductive plate connection area 52 connected to the tab connection area 51. The conductive plate connection area 52 is connected to the first conductive plate 30, and the conductive plate connection area 52 is bent relative to the tab connection area 51. Viewed from the first direction X, a first recess 212 and a tab connection area 51 overlap. When the electrode assembly 20 is bent and deformed at the first recess 212, the first tab 50 has high hardness and is not easily deformed, thus reducing the risk that the top of the electrode assembly 20 will also be bent and deformed at the same time, causing the first electrode 21 and the second electrode 22 to directly contact and short-circuit at the top of the electrode assembly 20.

[0129] Referring to Figures 10 and 11, in some embodiments, the number of first recesses 212 may also be multiple, and the multiple first recesses 212 are respectively disposed on adjacent multilayer first electrode sheets 21. Figures 10 and 11 show that the number of first recesses 212 is three, but this application is not limited to this. For example, the number of first recesses 212 may also be two, four, five, etc. Viewed from the second direction Y, any two first recesses 212 overlap. In this way, the electrode assembly 20 can more easily bend and deform at the first recesses 212 during hot box testing. The width W2 of the multiple first recesses 212 in the third direction Z may be the same or different; the length L2 of the multiple first recesses 212 in the first direction X may be the same or different. When the widths W2 of the multiple first recesses 212 are different, there is at least one with a maximum width W2. max The first recess 212; when the width W2 of multiple first recesses 212 is the same, the maximum width W max That is, the width W2.

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

[0131] In some embodiments, the maximum width of the first recess 212 on the third direction Z is W. max (Unit: mm), the width of the projection area P is W1 (unit: mm), W1 ≤ W max +5mm. This minimizes the misalignment of the multiple first recesses 212 in the third direction Z, reducing the risk that large misalignment of the multiple first recesses 212 would make it difficult for high-temperature gas to accumulate at the bending deformation of the electrode assembly 20 during hot box testing, thus making it easier for the high-temperature gas to break through the first seal 12. Referring to Figures 10 and 12, when measuring W1, the first side 2121 of the multiple first recesses 212, which is closest to the third direction Z, can be marked on the CT image, and the second side 2122 of the multiple first recesses 212, which is closest to the other end in the third direction Z, can be marked. Then, the distance between the marked first side 2121 and second side 2122 can be directly measured using calipers or other suitable measuring tools. This distance is W1. Referring to Figures 11 and 12, when measuring L1, one edge of the plurality of first recesses 212 in the first direction X (which is flush with the second edge 21B of the first electrode 21) can be marked on the CT image, and the bottom edge 2123 of the plurality of first recesses 2122 that is closest to the end in the first direction X can be marked. Then the distance between the marked edge and the bottom edge 2123 can be measured, and this distance is L1.

[0132] As shown in Figures 10 to 12, in some embodiments, the width of the projection area P in the third direction Z is W1, and the width of the electrode assembly 20 is W0, with 15% ≤ W1 / W0 ≤ 40%. This allows the first electrode 21 to form an effective weak point under stress, making it easier for the electrode assembly 20 to bend and deform at the first recess 212 during hot box testing. Furthermore, it reduces the risk that the large width of the first recess 212 might prevent the accumulation of high-temperature gas at the bending deformation point of the electrode assembly 20 during hot box testing, thus making it easier for the high-temperature gas to break through the first seal 12. In some embodiments, in the first direction X, the length of the projection area P is L1, and the length of the electrode assembly 20 is L0, with 3% ≤ L1 / L0 ≤ 10%. This allows the first electrode 21 to form an effective weak point under stress, making it easier for the electrode assembly 20 to bend and deform at the first recess 212 during hot box testing. Furthermore, it also reduces the impact of the first recess 212 on the energy density of the secondary battery 100.

[0133] As shown in Figures 2 to 5, in some embodiments, the first electrode 21 is a positive electrode, that is, the first recess 212 is provided on the positive electrode, thereby reducing the risk of lithium plating caused by the absence of negative active material after the second electrode 22 is provided with the first recess 212, resulting in the second active material layer 221 being unable to properly embed active ions (such as lithium ions) during charging and discharging. Further, when the outermost layer of the electrode assembly 20 in the second direction Y is the first electrode 21, the first recess 212 is not provided on the outermost first electrode 21, that is, the first recess 212 is provided on at least one other first electrode 21 besides the outermost layer. Therefore, when the electrode assembly 20 bends and deforms at the first recess 212 during the hot box test, the risk of short circuit between the first electrode 21 and the second electrode 22 and accelerated gas production can be further reduced (the above risk is because when the first recess 212 is provided on the outermost first electrode 21, the risk of the first electrode 21 directly contacting the adjacent second electrode 22 at the bending deformation point can be reduced, but the second electrode 22 may still directly contact and short circuit with another adjacent first electrode 21 at the bending deformation point). That is, by setting the outermost first electrode 21 without the first recess 212, the risk of the first electrode 21 with the first recess 212 directly contacting and short-circuiting with the two adjacent second electrode 22 at the bending deformation point and accelerated gas production is reduced, thereby further reducing the risk of thermal runaway of the secondary battery 100 under the hot box test.

[0134] Referring to Figure 13, in some embodiments, the first electrode 21 is a negative electrode, i.e., the first recess 212 is disposed on the negative electrode. In this case, the secondary battery 100 may also include a first insulating member 70, which is bonded to a second active material layer 221 facing the first recess 212. Viewed from the second direction Y, the first insulating member 70 covers the first recess 212. Thus, the first insulating member 70 can prevent active ions detached from the second active material layer 221 corresponding to the first insulating member 70 in the second direction Y from moving towards the first recess 212, thereby reducing the risk of excessive active ion accumulation and lithium dendrite formation due to the lack of space for these active ions to be embedded in the first recess 212. The figure shows two first insulating members 70, which are bonded to the two second active material layers 221 facing the first recess 212, respectively. 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 or double-sided adhesive can be selected from one or more of acrylate, polyurethane, rubber, and silicone.

[0135] The secondary battery 100 of this 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] Please refer to Figure 14. One embodiment of this application also provides an electronic device 1, which includes a battery compartment 101 and the aforementioned secondary battery 100 disposed within the battery compartment 101. The secondary battery 100 of this application is applicable to electronic devices 1 in various fields. The electronic device 1 is powered by the aforementioned secondary battery 100, and the secondary battery 100 can promptly release internal high-temperature gases during hot-box testing, thereby maintaining good reliability and safety. In one embodiment, the electronic device 1 of this application may be, but is not limited to, laptops, pen-based computers, mobile computers, e-book players, portable telephones, portable fax machines, portable copiers, portable printers, stereo headphones, video recorders, LCD TVs, portable cleaners, portable C-type devices, mini CD-ROMs, transceivers, electronic notebooks, calculators, memory cards, portable recorders, radios, backup power supplies, motors, automobiles, motorcycles, electric bicycles, bicycles, lighting fixtures, toys, game consoles, clocks, power tools, flashlights, cameras, household large-capacity batteries, and lithium-ion capacitors, etc.

[0137] The present application will be described in detail below through specific embodiments and comparative examples. Specifically, a lithium-ion secondary battery, a first electrode as a positive electrode, and a second electrode as a negative electrode are used as examples to illustrate the present application, along with specific preparation processes and testing methods. Those skilled in the art should understand that the preparation methods described in this application are merely examples, and any other suitable preparation methods are within the scope of this application.

[0138] Examples 1-8

[0139] Preparation of the first electrode: 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-methylpyrrolidone (NMP) was added as a solvent to prepare a slurry with a solid content of 75 wt%, and the mixture was stirred evenly. The slurry was uniformly coated on one surface of the first current collector, i.e., aluminum foil, with a thickness of 12 μm, leaving an empty foil area at the edge of the aluminum foil. The slurry was dried at 90°C to obtain a first electrode with a first active material layer thickness of 100 μm. The above steps were repeated on the other surface of the aluminum foil to obtain a first electrode with a first active material layer coated on both sides. Then, the excess empty foil area was removed by laser die-cutting to obtain multiple first tabs. Finally, a portion of the aluminum foil and the first active material layer were removed from the edge of the first electrode away from the first tab to obtain a first recess.

[0140] Preparation of the second electrode: Artificial graphite (anode active material), 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 to prepare a slurry with a solid content of 70 wt%, and the mixture was stirred evenly. The slurry was uniformly coated onto one surface of a second current collector, such as a copper foil, with a thickness of 10 μm, leaving an empty foil area at the edge of the copper foil. The slurry was dried at 110 °C to obtain a second electrode with a single-sided coating of the second active material layer, with a coating thickness of 150 μm. The above steps were repeated on the other surface of the second electrode to obtain a second electrode with a double-sided coating of the second active material layer. Then, excess empty foil areas were removed by laser die-cutting to obtain multiple second electrode tabs.

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

[0142] Electrode assembly assembly: The second electrode, the separator, and the first electrode are stacked sequentially to obtain the electrode assembly. The separator is a 15μm thick polyethylene (PE) film. The first and second electrode tabs are welded to the first and second conductive plates respectively using an adapter weld. The first conductive plate is made of aluminum, and the second conductive plate is made of nickel. The width W0 and length L0 of the resulting electrode assembly are 67.91mm and 76.11mm, respectively. A 150μm thick aluminum-plastic film with a dented shape is placed in the assembly fixture with the dented surface facing upwards, and the electrode assembly is placed in the dent.

[0143] Electrolyte injection encapsulation: Electrolyte is injected into the pit of the aluminum-plastic film, and the first and second conductive plates are led out of the aluminum-plastic film. A shaped end cap is used to apply pressure at the edge of the aluminum-plastic film to form the first seal, thus obtaining a lithium-ion secondary battery.

[0144] Comparative Example 1

[0145] The difference from Embodiment 1 is that the first electrode does not have a first recess.

[0146] Comparative Examples 2-3

[0147] The difference from Embodiment 1 lies in the width of the first recess.

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

[0149] The hot chamber test steps are as follows: 1) Discharge the battery: Under an ambient temperature of 23±2℃, let the battery stand for 5 minutes, then discharge it at a constant current of 0.2C to 3.0V, and let it stand for 20 minutes; 2) Charge the battery: Charge it at a constant current of 3.5C to 4.33V, then charge it at a constant voltage to 2.5C; charge it at a constant current of 2.5C to 4.38V, then charge it at a constant voltage to 2.0C; charge it at a constant current of 2.0C to 4.50V, then charge it at a constant voltage to 0.02C; 3) Place the battery horizontally in the hot chamber, raise the temperature of the hot chamber to 130±2℃ at a heating rate of 5±2℃, and maintain the temperature for 60 minutes; 4) Record the changes in the voltage and temperature of the lithium-ion battery and the temperature of the hot chamber. The lithium-ion battery passes the hot chamber test if it does not catch fire, explode, or emit smoke. 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 out of the 10 batteries tested, n batteries passed the test. The meanings of other percentage values ​​are deduced similarly.

[0152] As can be seen from the data in Table 1, compared with Comparative Example 1, because Example 1 has a first recess at the second edge of the first electrode, the electrode assembly is more likely to bend and deform at the first recess during the hot box test. Furthermore, the high-temperature gas inside accumulates at the bending and deformation point of the electrode assembly and breaks through the first seal, reducing the risk of thermal runaway. Therefore, Example 1 has a higher pass rate in the hot box test.

[0153] Compared to Comparative Examples 2-3, the size of the first recess in Examples 1-3 satisfies 15% ≤ W2 / W0 ≤ 40%. Under hot-box testing, the electrode assembly is more prone to bending deformation at the first recess. Furthermore, the larger width of the first recess reduces the risk of high-temperature gas accumulating at the bending deformation point of the electrode assembly during hot-box testing, making it easier for the high-temperature gas to break through the first seal. Therefore, Examples 1-3 have a higher hot-box test pass rate. Moreover, compared to Example 3, Examples 1-3 also achieve a higher energy density.

[0154] Compared to Example 7, the dimensions of the first recess in Examples 1 and 4-5 satisfy 3% ≤ L2 / L0 ≤ 10%, making it easier for the electrode assembly to bend and deform at the first recess during hot box testing. Therefore, Examples 1 and 4-5 have a higher pass rate in hot box testing. In Example 8, the dimensions of the first recess are larger, and the electrode assembly is also more likely to bend and deform at the first recess during hot box testing, resulting in a higher pass rate in hot box testing. Compared to Example 8, Examples 1 and 4-5 can also achieve higher energy density.

[0155] Examples 9-11

[0156] The difference from Embodiment 1 is that the first electrode has a plurality of first recesses.

[0157] Then, the batteries of each embodiment were subjected to a hot box test. Ten batteries from each embodiment and each comparative example were tested, and the corresponding test results are recorded in Table 2.

[0158] Table 2

[0159] As shown in Table 2, compared to Example 11, Examples 9-10 satisfy W1≤W max The +5mm makes the misalignment of the multiple first recesses in the third direction smaller. Under the hot box test, the high temperature gas inside is more likely to accumulate at the bending deformation of the electrode assembly, making it easier for the high temperature gas inside to break through the first seal. Therefore, the hot box test pass rate of Examples 9-10 is higher.

[0160] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application and are not intended to limit it. Although this application has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of this application without departing from the spirit and scope of the technical solutions of this 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 according to 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 according to 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, the first side and the second side being respectively connected to the second edge, and 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 is connected to the bottom edge, and the first slope edge is arc-shaped; (2) When viewed from the second direction, the first side includes a second ramp edge connected to the second edge, the second ramp 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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