Secondary battery and electronic device

Abstract

A secondary battery and an electronic device. An electrode assembly of the secondary battery is of a winding structure, an outermost ring of pole piece is a first pole piece and comprises an ending part with an ending end, and the ending part is not provided with an active material. The first tab is connected to the ending portion. The first tab comprises a first conductive part overlapped with the ending part, and the first conductive part is connected to the ending part through a connecting area. The connecting area comprises a plurality of side edges which are connected end to end, and the side edges comprise a first side edge. In the winding direction, the rest of the side edges are located on the side, close to the ending end, of the first side edge. The extension direction of at least part of the first side deviates from the extension direction of the first tab, and the length of the first side is greater than the size of the first conductive part along the extension direction of the first tab. The secondary battery provided by the invention has relatively high reliability and long service life.

Description

Technical Field

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

[0002] With the popularity of consumer electronic products such as laptops, mobile phones, handheld game consoles, tablets, mobile power supplies and drones, people's requirements for secondary batteries are becoming more and more stringent.

[0003] Secondary batteries typically include a housing, an electrode assembly housed within the housing, and tabs electrically connected to the electrode assembly's pole pieces. During battery use, for example, when the battery expands during cycling, stress concentration may occur at the connection between the tab and the pole piece, leading to fatigue fracture and ultimately battery failure, impacting the battery's reliability and service life. Summary of the Invention

[0004] In view of this, it is necessary to provide a secondary battery and an electronic device having the secondary battery that can solve at least one of the above problems.

[0005] In a first aspect, the present application provides a secondary battery comprising a housing and an electrode assembly disposed within the housing. The electrode assembly is a wound structure 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 outermost electrode sheet of the electrode assembly is the first electrode sheet. The outermost first electrode sheet includes a tail portion, which includes a tail end. The tail portion is not provided with the first active material layer. The secondary battery also includes a first electrode tab connected to the tail portion. The first electrode tab includes a first conductive portion that overlaps with the tail portion in a first direction, where the first direction is the thickness direction of the first electrode sheet. The first conductive portion includes a connection region, the first conductive portion is connected to the tail portion via the connection region, and the first electrode tab extends beyond the tail portion in a second direction, the second direction being perpendicular to the first direction. When viewed from the first direction, the connection region includes a plurality of side edges connected end to end. The plurality of side edges include the first side edge. Along the winding direction, the remaining side edges of the plurality of side edges are located on the side of the first side edge that is closer to the tail end. The extension direction of at least part of the first side deviates from the second direction. The length of the first side along the extension direction is L. The size of the first conductive portion along the second direction is H. <L。

[0006] In this application, by arranging the extension direction of at least a portion of the first side to deviate from the second direction, the length of the first side can be increased while maintaining a constant area of ​​the first conductive portion, compared to the related art solution in which the first side extends along the second direction. When the first electrode sheet expands in volume during cycling, the stress caused by this inward-outward expansion is primarily concentrated in the tail portion. This stress is preferentially dispersed along the first side, reducing the risk of fatigue fracture at the connection between the first tab and the tail portion under stress, thereby reducing the risk of secondary battery failure. Consequently, the reliability and service life of the secondary battery can be improved.

[0007] Based on the first aspect, in some possible implementations, along the length direction of the first pole piece, the size of the first conductive portion is W, H <L≤ Therefore, under the premise that the area of ​​the first conductive portion is constant, the length of the first side can be appropriately increased, so that the stress generated by the volume expansion of the electrode assembly can be dispersed along the first side, further reducing the risk of fatigue fracture at the connection between the first tab and the tail portion under stress.

[0008] Based on the first aspect, in some possible implementations, the first conductive portion includes a first vertex, a second vertex, a third vertex, and a fourth vertex. The third vertex and the first vertex are arranged in sequence along the second direction, and the fourth vertex and the second vertex are arranged in sequence along the second direction. The first vertex and the second vertex are arranged in sequence along the winding direction. The first conductive portion also includes an intersecting first diagonal and a second diagonal. The first diagonal connects the second vertex and the third vertex, and the second diagonal connects the first vertex and the fourth vertex. When viewed from the first direction, at least part of the first side overlaps with the first diagonal. Therefore, under the premise that the area of ​​the first conductive portion is certain, the length of the first side can be appropriately increased, so that the stress generated by the volume expansion of the electrode assembly is dispersed along the first side, further reducing the risk of fatigue fracture at the connection between the first tab and the tail portion under stress.

[0009] Based on the first aspect, in some possible implementations, the first side is a broken line. When viewed from the first direction, at least a portion of the first side also overlaps with the second diagonal line. Therefore, on the one hand, the length of the first side can be appropriately increased under the premise that the area of ​​the first conductive portion is constant, so that the stress generated by the volume expansion of the electrode assembly is dispersed along the first side, further reducing the risk of fatigue fracture at the connection between the first tab and the tail portion under stress. On the other hand, the area of ​​the connection region, that is, the flow area of ​​the first tab, can be increased, and when the secondary battery is charged, the current distribution on the first tab is more dispersed and uniform, thereby making the heat generated at the first tab during high-current charging more dispersed, reducing the risk of local overheating of the first tab.

[0010] Based on the first aspect, in some possible implementations, the first conductive portion includes a first side, a second side, a third side, and a fourth side connected end to end in sequence. The first side connects the first vertex and the second vertex, the second side connects the first vertex and the third vertex, the third side connects the third vertex and the fourth vertex, and the fourth side connects the second vertex and the fourth vertex. The first side includes a first end and a second end, and the first end and the second end are two ends of the first side that are opposite to each other along its extension direction. Along the second direction, the first end is closer to one side than the second end. The first end is located on the first side or the fourth side, and the second end is located on the second side or the third side. Therefore, under the premise that the area of ​​the first conductive portion is constant, the length of the first side can be appropriately increased, so that the stress generated by the volume expansion of the electrode assembly is dispersed along the first side, further reducing the risk of fatigue fracture under stress at the connection between the first tab and the tail portion.

[0011] Based on the first aspect, in some possible implementations, the area of ​​the connection region is S1, the area of ​​the first conductive portion is S2, and 0.4 ≤ S1 / S2 < 1. Therefore, the first tab can have a larger flow area, and when the secondary battery is charging, the current distribution on the first tab is more dispersed and uniform. This further disperses the heat generated at the first tab during high-current charging, reducing the risk of local overheating of the first tab.

[0012] Based on the first aspect, in some possible implementations, the dimension of the first conductive portion along the second direction is equal to the dimension of the first pole piece along the second direction. Therefore, the area of ​​the first conductive portion can be increased, and the length of the first side can be further increased on the larger first conductive portion, thereby further reducing the risk of fatigue fracture at the connection between the first tab and the tail portion under stress.

[0013] Based on the first aspect, in some possible implementations, the connection region is welded to the tail portion. The connection region is provided with a weld mark, the outer edge of which is a region enclosed by smooth straight lines, forming the connection region. The edge of the connection region includes the aforementioned multiple side edges. This provides a high connection strength between the first tab and the first current collector.

[0014] Based on the first aspect, in some possible implementations, the first electrode sheet is a negative electrode sheet, and the first current collector includes copper foil. By setting the extension direction of at least a portion of the first side edge to deviate from the second direction, the risk of the copper foil being more susceptible to fracture under stress due to poor ductility can be reduced.

[0015] Based on the first aspect, in some possible implementations, the secondary battery is a cylindrical secondary battery. The housing is a metal housing and includes a terminal post, and the first electrode tab is electrically connected to the terminal post. Therefore, the electrical polarity of the first electrode sheet can be led out through the terminal post.

[0016] A second aspect of the present application provides an electronic device comprising a storage compartment and the aforementioned secondary battery. The secondary battery is disposed within the storage compartment. The electronic device is powered by the aforementioned electrochemical device, and the secondary battery has high reliability and service life. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 A schematic structural diagram of a secondary battery provided in one embodiment of the present application.

[0018] Figure 2 for Figure 1 The secondary battery is shown as a top view with the top cover removed.

[0019] Figure 3 for Figure 1 The secondary battery is shown in a cross-sectional view along the cutting line III-III.

[0020] Figure 4 for Figure 2 or Figure 3 The diagram shows the structure of the second battery after the first electrode is unfolded.

[0021] Figure 5 for Figure 4 A partially enlarged view of the first pole piece is shown.

[0022] Figure 6 It is a partial enlarged view of the first pole piece in some other embodiments.

[0023] Figure 7 It is a partial enlarged view of the first pole piece in some other embodiments.

[0024] Figure 8 It is a partial enlarged view of the first pole piece in some other embodiments.

[0025] Figure 9 It is a partial enlarged view of the first pole piece in some other embodiments.

[0026] Figure 10 A schematic structural diagram of an electronic device provided in one embodiment of the present application.

[0027] The following specific implementation methods will further illustrate the present application in conjunction with the above-mentioned drawings. DETAILED DESCRIPTION

[0028] The technical solutions in the embodiments of the present application are described clearly and in detail below. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art of the present application. The terms used in the specification of the present application are only for the purpose of describing specific embodiments and are not intended to limit the present application.

[0029] Below, embodiments of the present application will be described in detail. However, the present application may be embodied in many different forms and should not be construed as limited to the exemplary embodiments illustrated herein. Rather, these exemplary embodiments are provided to make the present application thorough and detailed for those skilled in the art.

[0030] In addition, for the sake of brevity and clarity, the size or thickness of various components or layers may be exaggerated in the accompanying drawings. Throughout the text, the same numerical value refers to the same element. As used herein, the terms "and / or" and "and / or" include any and all combinations of one or more related enumerated items. In addition, it should be understood that when element A is referred to as "connecting" element B, element A can be directly connected to element B, or there may be an intermediate element C and element A and element B can be indirectly connected to each other.

[0031] Further, when describing embodiments of the present application, the use of “may” refers to “one or more embodiments of the present application.”

[0032] The technical terms used herein are for the purpose of describing specific embodiments and are not intended to limit this application. As used herein, the singular is intended to include the plural, unless the context clearly indicates otherwise. It should be further understood that the term "comprising", when used in this specification, refers to the presence of 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.

[0033] Spatial related terms, such as "on" etc., can be used herein for convenient description, to describe the relationship between an element or feature and another element (multiple elements) or feature (multiple features) as illustrated in the figure. It should be understood that, in addition to the directions described in the figure, spatial related terms are intended to include different directions of equipment or devices in use or operation. For example, if the equipment in the figure is turned over, the elements described as "above" or "on" other elements or features will be oriented "below" or "below" other elements or features. Therefore, the exemplary term "on" can include the direction above and below. It should be understood that although the terms first, second, third, etc. can be used herein to describe various elements, components, regions, layers and / or parts, these elements, components, regions, layers and / or parts should not be limited by these terms. These terms are used to distinguish an element, component, region, layer or part from another element, component, region, layer or part. Therefore, the first element, component, region, layer or part discussed below can be referred to as the second element, component, region, layer or part, without departing from the teachings of the exemplary embodiments.

[0034] See also Figures 1 to 3In one embodiment of the present application, a secondary battery 100 is provided, including a housing 10 , an electrode assembly 20 , an electrolyte (not shown), a first electrode tab 30 , and a second electrode tab 40 . The electrode assembly 20 and the electrolyte are located in the housing 10 .

[0035] In some embodiments, the shell 10 is a metal shell, which includes a shell body 11, a cover 12 covering the shell body 11, and a pole 13 provided on the cover 12. The pole 13 is electrically isolated from the cover 12. In some embodiments, the secondary battery 100 is a cylindrical secondary battery 100, and the shell body 11 and the cover 12 can be welded and fixed. The shell 10 can be made of steel as a whole. The steel shell includes the elements Fe and C. The steel shell 10 can also include one or more of the elements Ni, Co, Al, Mn, Cr, Cu, Mg, Mo, S, Si, Ti, V, Pb, Sb, N, and P. In other embodiments, the shell 10 can be a packaging bag encapsulated with a packaging film (such as an aluminum-plastic film).

[0036] like Figure 2 and Figure 3 As shown, the electrode assembly 20 has a wound structure and includes a first electrode sheet 21, a second electrode sheet 22, and a separator 23. The separator 23 is disposed between the first electrode sheet 21 and the second electrode sheet 22. The first electrode sheet 21 includes a first current collector 210 and a first active material layer 211 disposed on the first current collector 210. The first current collector 210 includes a first surface 210A facing the winding center axis O and a second surface 210B opposite the first surface 210A. The first active material layer 211 is disposed on the first surface 210A and the second surface 210B, respectively. The second electrode sheet 22 includes a second current collector 220 and a second active material layer 221 disposed on the second current collector 220. The second current collector 220 includes a third surface 220A facing the winding center axis O and opposite to the third surface. The second active material layer 221 is disposed on the third surface 220A and the fourth surface 220B, respectively.

[0037] The first electrode tab 30 and the second electrode tab 40 are connected to the first current collector 210 and the second current collector 220, respectively. The first electrode tab 30 and the second electrode tab 40 can be connected to external components (not shown). When the housing 10 is a steel housing, the first electrode tab 30 extends out of the first current collector 210 and is electrically connected to the electrode post 13. The second electrode tab 40 extends out of the second current collector 220 and is electrically connected to the housing body 11. When the housing 10 is a packaging bag, the first electrode tab 30 and the second electrode tab 40 both extend from the interior of the housing 10.

[0038] The first direction X is defined as the thickness direction of the first electrode sheet 21 or the second electrode sheet 22. The second direction Y is the direction in which the first electrode tab 30 protrudes from the first electrode sheet 21, and is also the width direction of the first electrode sheet 21 or the second electrode sheet 22. It can be understood that when the electrode assembly 20 is a cylindrical wound structure, any direction in a two-dimensional plane perpendicular to the second direction Y can be regarded as the first direction X of the present application. However, for ease of understanding, Figures 1 to 3 In the diagram, the first direction X and the first direction X' are used to distinguish two mutually perpendicular directions in the two-dimensional plane. Therefore, the first direction X, the first direction X', and the second direction Y can constitute a three-dimensional coordinate system. When the electrode assembly 20 has a flat wound structure, the first direction X is the thickness direction of the electrode assembly 20.

[0039] like Figure 2 and Figure 3 As shown, the outermost electrode piece of the electrode assembly 20 is the first electrode piece 21, and the outermost first electrode piece 21 includes a tail portion 2100. The tail portion 2100 is the tail portion of the first current collector 210 along the winding direction D. The tail portion 2100 is not provided with the first active material layer 211, and the tail portion 2100 includes a tail end 2101. Figure 4 ,in Figure 4 for Figure 2 or Figure 3 The structure diagram of the first pole piece 21 after unfolding is shown. Figure 4 A three-dimensional coordinate system is established with a first direction X, a second direction Y and a third direction Z, wherein the third direction Z is the length direction of the first pole piece 21. In the embodiment of the present application, the outermost pole piece of the electrode assembly 20 refers to the multilayer structure formed by winding the first pole piece 21, the isolation film 23 and the second pole piece 22 along the winding direction D, and the outermost pole piece relative to the winding center axis O of the electrode assembly 20 is the first pole piece 21. Moreover, one circle refers to starting from a certain point on the first pole piece 21 as the starting end, and reaching another point along the winding direction D as the ending end. The ending end is on a straight line with the starting end and the center of the circle, and the starting end is between the ending end and the center of the circle. In the embodiment of the present application, the winding direction D refers to the direction of moving from the inside to the outside around the winding center axis O along a certain point of the first pole piece 21, the isolation film 23 or the second pole piece 22 as shown in the figure. In some embodiments, the winding direction D is a counterclockwise direction.

[0040] The first electrode sheet 21 can be a negative electrode sheet, and the second electrode sheet 22 can be a positive electrode sheet. Accordingly, the first current collector 210 is a negative electrode current collector, the first active material layer 211 is a negative electrode active material layer, and the first electrode tab 30 is a negative electrode tab. The second current collector 220 is a positive electrode current collector, the second active material layer 221 is a positive electrode active material layer, and the second electrode tab 40 is a positive electrode tab. In other embodiments, the first electrode sheet 21 can also be a positive electrode sheet, and the second electrode sheet 22 can be a negative electrode sheet.

[0041] The positive electrode current collector may be made of aluminum foil or nickel foil, and the negative electrode current collector may be made of copper foil, nickel foil or a carbon-based current collector.

[0042] The positive active material of the positive active material layer includes a compound (i.e., a lithiated intercalation compound) that can reversibly intercalate and deintercalate metal ions (such as lithium ions, sodium ions, etc., lithium ions are taken as an example below). In some embodiments, the positive active material may include a lithium transition metal composite oxide. The lithium transition metal composite oxide contains lithium and at least one element selected from cobalt, manganese and nickel. In some embodiments, the positive active material is selected from lithium cobalt oxide (LiCoO2), nickel cobalt manganese oxide ternary material (NCM), nickel cobalt aluminum oxide ternary material (NCA), lithium manganese oxide (LiMn2O4), lithium nickel manganese oxide (LiNi 0.5 Mn 1.5 O4) or at least one of lithium iron phosphate (LiFePO4).

[0043] The negative electrode active material of the negative electrode active material layer may be a negative electrode active material capable of reversible deintercalation of active ions, and may include, but is not limited to, a combination of one or more of graphite, soft carbon, hard carbon, carbon fiber, mesophase carbon microbeads, silicon-based materials, tin-based materials, lithium titanate, or other metals capable of forming an alloy with lithium. Graphite may be selected from a combination of one or more of artificial graphite, natural graphite, and modified graphite; silicon-based materials may be selected from a combination of one or more of elemental silicon, silicon oxide compounds, silicon-carbon composites, and silicon alloys; and tin-based materials may be selected from a combination of one or more of elemental tin, tin oxide compounds, and tin alloys.

[0044] The isolation film 23 includes at least one of polyethylene, polypropylene, polyvinylidene fluoride, polyethylene terephthalate, polyimide or aramid. For example, the polyethylene includes at least one selected from high-density polyethylene, low-density polyethylene or ultra-high molecular weight polyethylene.

[0045] like Figure 4As shown, the first tab 30 includes a first conductive portion 31 and a second conductive portion 32 connected to each other. The first conductive portion 31 overlaps with the tail portion 2100 in the first direction X, and the second conductive portion 32 does not overlap with the tail portion 2100 in the first direction X. When the housing 10 is a steel housing, the second conductive portion 32 is electrically connected to the pole 13 (at Figure 3 In some embodiments, the size of the first conductive portion 31 along the second direction Y is H, and the size of the first pole piece 21 along the second direction Y is H0, H <H0。

[0046] like Figure 4 and Figure 5 As shown, the first conductive portion 31 can be generally rectangular when viewed from the first direction X. The first conductive portion 31 includes a connection region 311 and a non-connection region 312 disposed at least partially around the connection region 311. The first conductive portion 31 is connected to the tail portion 2100 via the connection region 311, and the first electrode tab 30 extends beyond the tail portion 2100 along the second direction Y. In some embodiments, the connection region 311 is welded to the tail portion 2100, such as by ultrasonic welding, thereby achieving a high connection strength between the first electrode tab 30 and the first current collector 210. The welding of the connection region 311 and the tail portion 2100 forms a plurality of weld points 3110, which secure the connection region 311 to the tail portion 2100 via the weld points 3110. In other embodiments, the connection region 311 can also be connected to the tail portion 2100 using a conductive adhesive (not shown) or other methods.

[0047] like Figure 5 As shown, when viewed from the first direction X, the connection area 311 includes a plurality of side edges connected end to end. When the connection area 311 and the tail portion 2100 are fixed by welding prints such as solder joints 3110 or welding wires, the weld prints are taken as a whole, and the outer edges of which are surrounded by smooth straight lines constitute the connection area 311, and the edges of the connection area 311 include a plurality of side edges. When the connection area 311 is connected to the tail portion 2100 by conductive adhesive, for example, the conductive adhesive is composed of a plurality of spaced adhesive clumps, then the plurality of adhesive clumps are taken as a whole, and the outer edges of which are surrounded by smooth straight lines constitute the connection area 311, and the edges of the connection area 311 include a plurality of side edges. For another example, when the conductive adhesive is a block-shaped conductive adhesive, the conductive adhesive constitutes the connection area 3111, and the edge of the connection area 311 is the edge of the conductive adhesive. When viewed from the first direction X, the connection area 311 may be a triangle. As Figures 6 to 8 As shown, the connection area 311 can also be in the form of other polygons, which can be convex polygons or concave polygons. Specifically, the connection area 311 can be in the form of a trapezoid, a concave pentagon, a convex pentagon, or the like.

[0048] Among them, Figures 5 to 8As shown, among the multiple side edges, there is a first side edge 3111. The first side edge 3111 can be a straight edge or a broken line edge. Along the winding direction D, the rest of the side edges among the multiple side edges are all located on one side of the first side edge 3111 close to the end part 2101. The extending direction of at least a part of the first side edge 3111 deviates from the second direction Y. The length of the first side edge 3111 along its extending direction is L, and the dimension of the first conductive part 31 along the second direction Y is H, and H < L. In some embodiments, the extending direction of the entire first side edge 3111 deviates from the second direction Y.

[0049] In this application, when the first pole piece 21 expands in volume during the cycling process, the stress caused by the volume expansion from the inside to the outside will be mostly concentrated at the tail part, i.e., the end part 2100, of the outermost pole piece of the electrode assembly 20, thereby pulling the first pole ear 30 and causing a risk of fatigue fracture at the connection between the first pole ear 30 and the end part 2100 of the end part 2100. By setting the extending direction of at least a part of the first side edge 3111 to deviate from the second direction Y, compared with the solution in the related art where the first side edge 3111 extends along the second direction Y, in this application, the length of the first side edge 3111 can be increased on the premise that the area of the first conductive part 31 is certain. Therefore, the stress generated by the expansion will be preferentially dispersed along the first side edge 3111, reducing the risk of fatigue fracture at the connection between the first pole ear 30 and the end part 2100 under the action of stress, and further reducing the risk of failure of the secondary battery 100. Especially when the first pole piece 21 is a negative pole piece and the first current collector 210 includes copper foil, by setting the extending direction of at least a part of the first side edge 3111 to deviate from the second direction Y, the risk of the copper foil being more likely to break under the action of stress due to poor ductility can be reduced. Therefore, the reliability and service life of the secondary battery 100 can be improved.

[0050] Such as Figures 5 to 8As shown, in some embodiments, the first conductive portion 31 includes a first vertex 31A, a second vertex 31B, a third vertex 31C, and a fourth vertex 31D. The third vertex 31C and the first vertex 31A are arranged sequentially along the second direction Y, and the fourth vertex 31D and the second vertex 31B are arranged sequentially along the second direction Y. The first vertex 31A and the second vertex 31B are arranged sequentially along the winding direction D, and the third vertex 31C and the fourth vertex 31D are arranged sequentially along the winding direction D. The first conductive portion 31 includes a first edge 3101, a second edge 3102, a third edge 3103, and a fourth edge 3104 connected end to end. The first edge 3101 is a virtual dividing line between the first conductive portion 31 and the second conductive portion 32. The first side 3101 connects the first vertex 31A and the second vertex 31B, the second side 3102 connects the first vertex 31A and the third vertex 31C, the third side 3103 connects the third vertex 31C and the fourth vertex 31D, and the fourth side 3104 connects the second vertex 31B and the fourth vertex 31D. The first conductive portion 31 also includes an intersecting first diagonal line 31E and a second diagonal line 31F. The first diagonal line 31E connects the second vertex 31B and the third vertex 31C, and the second diagonal line 31F connects the first vertex 31A and the fourth vertex 31D. The dimension of the first vertex 31A and the third vertex 31C along the second direction Y is H, that is, the dimension of the first conductive portion 31 along the second direction Y is H. The distance between the first vertex 31A and the second vertex 31B along the third direction Z is W, that is, the dimension of the first conductive portion 31 along the third direction Z is W. The length L of the first side 3111 satisfies: H <L≤ In this way, under the premise that the area of ​​the first conductive portion 31 is constant, the length of the first side 3111 can be appropriately increased, so that the stress generated by the volume expansion of the electrode assembly 20 is dispersed along the first side 3111, reducing the risk of fatigue fracture at the connection between the first tab 30 and the tail portion 2100 under stress.

[0051] In some embodiments, when viewed from the first direction X, at least a portion of the first side 3111 overlaps with the first diagonal line 31E. Figure 5 and Figure 6 As shown, the entire first side 3111 overlaps with the first diagonal line 31E. It can be understood that when the entire first side 3111 overlaps with the first diagonal line 31E, the length L of the first side 3111 is equal to In this way, under the premise that the area of ​​the first conductive portion 31 is constant, the length of the first side 3111 can be appropriately increased, so that the stress generated by the volume expansion of the electrode assembly 20 is dispersed along the first side 3111, reducing the risk of fatigue fracture at the connection between the first tab 30 and the tail portion 2100 under stress.

[0052] like Figure 7As shown, in some embodiments, the first side 3111 is a broken line. For example, when viewed from the first direction X, the connection area 311 is a concave pentagon. In this case, the first side 3111 is the broken line side corresponding to the inner angle of the concave pentagon that is greater than 180°. When viewed from the first direction X, part of the first side 3111 overlaps with the first diagonal 31E, and part of the first side 3111 overlaps with the second diagonal 31F. In this way, on the one hand, the length of the first side 3111 can also be appropriately increased under the premise that the area of ​​the first conductive part 31 is constant, so that the stress generated by the volume expansion of the electrode assembly 20 is dispersed along the first side 3111, reducing the risk of fatigue fracture under stress at the connection between the first tab 30 and the tail portion 2100. On the other hand, the area of ​​the connection region 311, i.e., the flow area of ​​the first electrode tab 30, can be increased. When the secondary battery 100 is charging, the current distribution on the first electrode tab 30 is more dispersed and uniform, thereby making the heat generated at the first electrode tab 30 during high-current charging more dispersed, reducing the risk of local overheating of the first electrode tab 30. In other embodiments, the first side 3111 can also be formed by connecting more than two line segments, which is conducive to further increasing the flow area of ​​the first electrode tab 30.

[0053] like Figures 5 to 7 As shown, in some embodiments, when viewed from the first direction X, the first side 3111 includes a first end P1 and a second end P2, where the first end P1 and the second end P2 are two ends of the first side 3111 that are opposite to each other along its extension direction. Along the second direction Y, the first end P1 is closer to the side 3101 than the second end P2. The first end P1 is located at the first side 3101 or the fourth side 3104, and the second end P2 is located at the second side 3102 or the third side 3103. For example, Figure 5 and Figure 6 As shown, first end P1 is located on both first side 3101 and fourth side 3104, coinciding with second vertex 31B. Second end P2 is located on both second side 3102 and third side 3103, coinciding with third vertex 31C. Thus, while maintaining the area of ​​first conductive portion 31, the length of first side 3111 can be appropriately increased. This allows the stress generated by the volume expansion of electrode assembly 20 to be dispersed along first side 3111, reducing the risk of fatigue fracture at the connection between first tab 30 and tail portion 2100 under stress.

[0054] In some embodiments, the area of ​​the connection region 311 is S1, the area of ​​the first conductive portion 31 is S2, and 0.4 ≤ S1 / S2 < 1. This allows the first electrode 30 to have a larger flow area, making the current distribution on the first electrode 30 more dispersed and uniform when the secondary battery 100 is charging. This further disperses the heat generated at the first electrode 30 during high-current charging, reducing the risk of localized overheating of the first electrode 30. The above areas are measured when the first electrode sheet 21 is flattened. Area S1 can be calculated based on the specific shape of the connection region 311.

[0055] like Figure 9 As shown, in other embodiments, the dimension of the first conductive portion 31 along the second direction Y (i.e., the distance between the first vertex 31A and the third vertex 31C along the second direction Y) is approximately equal to the dimension of the first pole piece 21 along the second direction Y. That is, H = H0. This increases the area of ​​the first conductive portion 31, and further increases the length of the first side 3111 on the larger first conductive portion 31, thereby further reducing the risk of fatigue fracture at the connection between the first tab 30 and the tail portion 2100 under stress. In the embodiment of the present application, the dimension of the first conductive portion 31 along the second direction Y is equal to the dimension of the first pole piece 21 along the second direction Y, meaning that the dimensions may have a ±5% tolerance.

[0056] The secondary battery 100 of the present application may be a lithium secondary battery, including a lithium metal secondary battery, a lithium ion secondary battery, a lithium polymer secondary battery or a lithium ion polymer secondary battery.

[0057] See also Figure 10One embodiment of the present application further provides an electronic device 1, comprising a storage compartment 101 and the aforementioned secondary battery 100 disposed within the storage compartment 101. The secondary battery 100 of the present application is applicable to electronic devices 1 in various fields. The electronic device 1 supplies power to a load (not shown) via the aforementioned secondary battery 100, and when the first electrode sheet 21 expands in volume during cycling, the risk of fatigue fracture at the connection between the first electrode tab 30 and the tail portion 2100 under stress is reduced, thereby improving the reliability and service life of the secondary battery 100. In one embodiment, the electronic device 1 of the present application can be, but is not limited to, a laptop computer, a pen-input computer, a mobile computer, an e-book player, a portable phone, a portable fax machine, a portable copier, a portable printer, a head-mounted stereo headset, a video recorder, an LCD TV, a portable cleaner, a portable C machine, a mini CD, a transceiver, an electronic notepad, a calculator, a memory card, a portable recorder, a radio, a backup power supply, a motor, a car, a motorcycle, a power-assisted bicycle, a bicycle, a lighting fixture, a toy, a game console, a clock, an electric tool, a flashlight, a camera, a large household battery and a lithium-ion capacitor, etc.

[0058] The present application is described in detail below through specific embodiments and comparative examples. The present application is described using a wound lithium-ion secondary battery 100, a first electrode 21 being a negative electrode, and a second electrode 22 being a positive electrode as an example, 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.

[0059] Example 1 (1) Preparation of the first electrode, i.e., the negative electrode: the negative electrode active materials artificial graphite, silicon carbon material, conductive carbon black (Super P), polyacrylic acid binder (PAA), and lithium difluorophosphate (LDPF) are mixed in a weight ratio of 69:5:6:19:1, deionized water is added as a solvent, and a slurry with a weight percentage of 55 wt% is prepared and stirred evenly. The slurry is evenly coated on the first side of a copper foil with a width of 8 mm and a thickness of 10 μm, dried at 90°C, and the above coating steps are repeated on the second side of the copper foil to obtain a double-sided coated negative electrode. The initial negative electrode is rolled to obtain a negative electrode active material layer. Then, a first electrode tab with a thickness of 60 μm is welded to the tail of the copper foil by ultrasonic welding. The first electrode tab is made of copper. The dimension H of the first conductive part of the first electrode tab along the second direction is 8 mm, and the dimension W of the first conductive part along the length direction of the first electrode is 8 mm. The conductive area is triangular in shape with an area of ​​30 mm. 2The first side of the conductive area overlaps with the first diagonal line of the first conductive portion, and the length of the first side is 8.5 mm.

[0060] (2) Preparation of the second electrode sheet, i.e., the positive electrode sheet: The positive electrode active material lithium cobalt oxide (LiCoO2), conductive carbon black (Super P), and polyvinylidene fluoride (PVDF) are mixed in a weight ratio of 96.5:1.5:2, and N-methylpyrrolidone (NMP) is added as a solvent to prepare a slurry with a solid content of 75 wt%, and stirred evenly. The slurry is evenly coated on the third side of an aluminum foil with a width of 7.5 mm and a thickness of 12 μm, and dried at 90°C. The above coating steps are repeated on the fourth side of the aluminum foil to obtain a double-sided coated positive electrode sheet. The initial positive electrode sheet is cold pressed to obtain a positive electrode active material layer, and then cut and other processes are performed to obtain a positive electrode sheet. A second electrode tab with a thickness of 60 μm is welded to the tail of the aluminum foil by ultrasonic welding. The second electrode tab is made of aluminum. The conductive area of ​​the second electrode tab adopts the existing technology and is rectangular in shape, with the long side of the rectangle extending along the second direction.

[0061] (3) Preparation of electrolyte: In a dry argon atmosphere, organic solvents ethylene carbonate (EC), ethyl methyl carbonate (EMC) and diethyl carbonate (DEC) were first mixed at a mass ratio of EC:EMC:DEC = 30:50:20. Then, lithium salt lithium hexafluorophosphate (LiPF6) was added to the organic solvent, dissolved and mixed evenly to obtain an electrolyte with a lithium salt concentration of 1.15 mol / L.

[0062] (4) Preparation of isolation film: A polyethylene (PE) film with a thickness of 9 μm was selected.

[0063] (5) Preparation of secondary battery: The first electrode sheet, separator, and second electrode sheet are stacked and wound in sequence to obtain an electrode assembly with a diameter of 20 mm. The outermost electrode sheet of the electrode assembly is the first electrode sheet. The electrode assembly is placed in the shell body, and the first and second electrode tabs are welded to the electrode column and the shell body, respectively. Then, the electrolyte is injected into the shell body, and the cover is welded to the shell body. After formation, the secondary battery is obtained.

[0064] Examples 2-9 The difference from Example 1 lies in the values ​​of L, S1 or S2.

[0065] Comparative Examples 1-3 The difference from Example 1 is that the conductive area of ​​the first tab adopts the existing technology and has a rectangular shape, with the long side of the rectangle extending along the second direction.

[0066] Then, 20 samples of the secondary batteries of each embodiment and comparative example were taken for expansion test and temperature rise test, respectively. The test results are recorded in Table 1 and Table 2.

[0067] Among them, the steps of the swelling test may include: 1) At a test temperature of 25°C, charge the secondary battery at a constant current of 0.2C to the cut-off voltage, and then charge it at a constant voltage until 0.02C; then discharge it at 0.2C until the voltage reaches 3.0V. The above charge-discharge process is regarded as one cycle; 2) Conduct a total of 800 cycles. After the cycles are completed, disassemble the secondary battery and observe whether the welding mark of the first tab is cracked or whether the copper foil near the welding mark is torn. If the welding mark is cracked or the copper foil near the welding mark is torn, it is determined that the secondary battery fails the swelling test. Among them, the number of test samples is 20, and the number of samples passing the swelling test is Y. Then the passing rate of the swelling test is Y / 20.

[0068] The steps of the temperature rise test may include: 1) In a test environment with a temperature of 25±1°C and a humidity less than 30%, adjust the initial SOC of the secondary battery to 50%, and detect the temperature t1 at the first tab through a temperature sensor; 2) Referring to GB / T 31485, charge the secondary battery at a constant current of 1C to 4.2V, then charge it at a constant voltage until the current is less than or equal to 0.05C, and then discharge it at a constant current of 1C to 0.5V. This is one charge-discharge cycle. Repeat the above charge-discharge cycle 500 times, and then detect the temperature t2 at the first tab through a temperature sensor. Calculate the temperature rise ΔT = t2 - t1. The average temperature rise of multiple test samples is the final test result.

[0069] Table 1 As can be seen from the data in Table 1, the conductive area of the first tab in Comparative Examples 1-3 is rectangular, and the long side of the conductive area extends along the second direction with a limited length. When the first electrode plate expands in volume during the cycling process, most of the stress is concentrated at the end parts of the first electrode plate, resulting in fatigue fracture at the connection between the first tab and the end parts under the action of stress. Therefore, the passing rate of the swelling test is relatively low.

[0070] Compared with Comparative Examples 1-3, the extension direction of the first side of the conductive area of the first tab in Example 1 deviates from the second direction, and the length of the first side can be appropriately increased to satisfy H < L. Therefore, when the first electrode plate expands in volume during the cycling process, the stress will be preferentially dispersed along the first side. Therefore, the risk of fatigue fracture at the connection between the first tab and the end parts under the action of stress is reduced, and the passing rate of the swelling test is increased.

[0071] Table 2 As can be seen from the data in Table 2, the lengths of the first sides in Examples 1-9 all satisfy H < L ≤ Compared to Example 1, Example 2-7 increases the length of the first side. Therefore, the risk of fatigue fracture at the connection between the first tab and the tail portion under stress is further reduced, thereby further improving the expansion test pass rate. Furthermore, the increase in the length of the first side in Example 2-7 is accompanied by an increase in the flow area. Therefore, the risk of localized overheating of the first conductive portion during high-current charging is reduced, and the temperature rise near the first conductive portion is reduced.

[0072] Compared to Example 7, Examples 8-9 improve the shape of the conductive area from a triangle to a concave polygon, thereby further increasing the flow area of ​​the first tab and further reducing the temperature rise near the first conductive portion. Specifically, Examples 1, 5-9 satisfy the condition: 0.4 ≤ S1 / S2 < 1, resulting in the lowest temperature rise near the first conductive portion.

[0073] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application and are not intended to limit the present application. 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 may be modified or replaced by equivalents without departing from the spirit and scope of the technical solutions of the present application.

Claims

1. A secondary battery comprising a housing and an electrode assembly disposed in the housing, wherein: The electrode assembly has a wound structure and includes a first electrode sheet, the first electrode sheet includes a first current collector and a first active material layer provided on the first current collector, the outermost electrode sheet of the electrode assembly is the first electrode sheet, the outermost first electrode sheet includes a tail portion, the tail portion includes a tail end, and the first active material layer is not provided on the tail portion; The secondary battery further includes a first electrode tab connected to the tail portion, the first electrode tab including a first conductive portion overlapping the tail portion in a first direction, the first direction being the thickness direction of the first electrode sheet; the first conductive portion including a connection area, the first conductive portion being connected to the tail portion via the connection area, and the first electrode tab extending out of the tail portion along a second direction, the second direction being perpendicular to the first direction; When viewed from the first direction, the connection area includes a plurality of side edges connected end to end, the plurality of side edges include a first side edge, and along the winding direction, the remaining side edges of the plurality of side edges are all located on a side of the first side edge close to the tail end; The extension direction of at least part of the first side deviates from the second direction, the length of the first side along the extension direction is L, the size of the first conductive part along the second direction is H, H <L。 2. The secondary battery according to claim 1, wherein Along the length direction of the first pole piece, the size of the first conductive part is W, H <L≤ .

3. The secondary battery according to claim 1 or 2, wherein The first conductive portion includes a first vertex, a second vertex, a third vertex, and a fourth vertex, the third vertex and the first vertex are sequentially arranged along the second direction, the fourth vertex and the second vertex are sequentially arranged along the second direction, and the first vertex and the second vertex are sequentially arranged along the winding direction; The first conductive portion also includes an intersecting first diagonal and a second diagonal, the first diagonal connecting the second vertex and the third vertex, and the second diagonal connecting the first vertex and the fourth vertex; when viewed from the first direction, at least part of the first side overlaps with the first diagonal.

4. The secondary battery according to claim 3, wherein The first side is a fold line, and when viewed from the first direction, at least a portion of the first side overlaps with the second diagonal line.

5. The secondary battery according to claim 3, wherein The first conductive portion includes a first side, a second side, a third side, and a fourth side connected end to end, wherein the first side connects the first vertex and the second vertex, the second side connects the first vertex and the third vertex, the third side connects the third vertex and the fourth vertex, and the fourth side connects the second vertex and the fourth vertex; The first side includes a first end and a second end, the first end and the second end are two ends of the first side that are opposite to each other along the extension direction; along the second direction, the first end is closer to the side than the second end; the first end is located at the first side or the fourth side, and the second end is located at the second side or the third side.

6. The secondary battery according to claim 1, wherein The area of ​​the connection region is S1, the area of ​​the first conductive portion is S2, and 0.4≤S1 / S2<1.

7. The secondary battery according to claim 1, wherein A size of the first conductive portion along the second direction is equal to a size of the first pole piece along the second direction.

8. The secondary battery according to claim 1, wherein The connection area is welded and fixed to the tail portion. The connection area is provided with a weld mark. The outer edge of the weld mark is formed by an area surrounded by smooth straight lines to form the connection area. The edge of the connection area includes the multiple side edges.

9. The secondary battery according to claim 1, wherein The first electrode sheet is a negative electrode sheet, and the first current collector includes copper foil.

10. The secondary battery according to claim 1, wherein The secondary battery is a cylindrical secondary battery, the housing is a metal housing and includes a pole, and the first tab is electrically connected to the pole.

11. An electronic device comprising a battery compartment, wherein: The electronic device further comprises a secondary battery according to any one of claims 1 to 10, wherein the secondary battery is disposed in the battery compartment.

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