Secondary battery and electrical device

Abstract

Provided in the embodiments of the present application are a secondary battery and an electrical device. The secondary battery comprises a housing, an electrode assembly and a first tab. The electrode assembly is arranged in the housing, and the electrode assembly comprises a first electrode plate, a second electrode plate and a separator. The first tab is welded to the first electrode plate. The first tab comprises a first surface and a second surface arranged opposite to each other in the thickness direction of the first tab, wherein a partial surface of the first surface is connected to the first electrode plate, and the second surface faces and makes contact with the separator. The first tab further comprises a third surface and a fourth surface, wherein the third surface and the fourth surface are located on two opposite sides of the first tab in the width direction thereof. The included angle between the second surface and the third surface is defined as α, where 120°≤α≤175°; or the third surface is smoothly connected to the second surface. In the secondary battery, the structure of the first tab facilitates a reduction in the pressure of the first tab on the separator at a connection of the second surface and the third surface, thereby reducing the possibility of damage to the separator caused by the first tab, reducing the possibility of a poor K value of the secondary battery, and improving the cycle life of the secondary battery.

Description

Secondary batteries and electrical equipment Technical Field

[0001] This application relates to the field of energy storage technology, and in particular to a secondary battery and electrical equipment. Background Technology

[0002] Welding the tabs to the electrode sheets is a common connection method in secondary batteries. In this structure, the separator and the tabs in the secondary battery are stacked along the thickness direction of the electrode sheets.

[0003] Summary of the Invention

[0004] The inventors of this application have discovered that during the charging and discharging process of a secondary battery, the electrode assembly expands and generates internal stress, causing the separator to press tightly against the surface of the tab. This can easily lead to the tab cutting the separator. Damage to the separator may cause an internal short circuit in the secondary battery, resulting in a poor K value and the appearance of short-circuit black spots near the internal short circuit location.

[0005] In view of the above situation, it is necessary to provide a secondary battery to reduce the possibility of the tabs cutting the separator.

[0006] A first aspect of this application provides a secondary battery, including a housing, an electrode assembly, and a first tab. The electrode assembly, disposed within the housing, includes a first electrode, a second electrode, and a separator. The first electrode, separator, and second electrode are stacked along the thickness direction of the first electrode and wound to form a wound structure. The separator is located between the first and second electrodes. The first tab is welded to the first electrode and includes a first surface and a second surface disposed opposite each other along the thickness direction of the first tab. A portion of the first surface is connected to the first electrode, and the second surface faces the separator. The first tab also includes a third surface and a fourth surface, located on opposite sides of the first tab along its width direction. The third surface connects to the second surface, and the included angle between the second and third surfaces is α, where 120° ≤ α ≤ 175°.

[0007] In this secondary battery, setting α≥120° helps to reduce the pressure of the first tab on the separator at the connection between the second and third surfaces, thereby reducing the possibility of the first tab damaging the separator, and further reducing the possibility of poor K value and short-circuit black spots on the tab in the secondary battery; setting α≤175° ensures that the cutting angle corresponding to α is not too small, which helps to reduce the difficulty of cutting the first tab to obtain the required α angle, thereby improving processing efficiency.

[0008] In one alternative embodiment of this application, 135°≤α≤165°. Setting α≥135° helps to further reduce the pressure of the first electrode tab on the separator at the connection between the second and third surfaces; setting α≤165° helps to further reduce the difficulty of cutting the first electrode tab to obtain the required α angle.

[0009] A second aspect of the embodiments of this application provides a secondary battery, including a housing, an electrode assembly, and a first tab. The electrode assembly, disposed within the housing, includes a first electrode, a second electrode, and a separator. The first electrode, separator, and second electrode are stacked along the thickness direction of the first electrode and wound to form a wound structure. The separator is located between the first and second electrodes. The first tab is welded to the first electrode and includes a first surface and a second surface disposed opposite each other along the thickness direction of the first tab. A portion of the first surface is connected to the first electrode, and the second surface faces the separator. The first tab also includes a third surface and a fourth surface, located on opposite sides of the first tab along its width direction. The third surface and the second surface are smoothly connected with a rounded chamfered surface; or, the third surface is an arc surface, protruding outwards in the width direction of the first tab, and the third surface is smoothly connected to the second surface.

[0010] In this secondary battery, the third side is smoothly connected to the second side, which helps to reduce the pressure of the first tab on the separator at the connection between the second and third sides, thereby reducing the possibility of the first tab damaging the separator, and further reducing the possibility of the secondary battery having poor K value and short circuit black spots on the tab.

[0011] In one optional embodiment of this application, the fourth surface is connected to the second surface, and the angle between the fourth surface and the second surface is ω, where 120°≤ω≤175°. Setting ω≥120° helps to reduce the pressure of the first tab 23 on the separator 25 at the connection between the second surface 232 and the fourth surface 234, thereby reducing the possibility of the first tab 23 damaging the separator 25, and further reducing the possibility of the secondary battery 100 having poor K value and short-circuit black spots on the tab; setting ω≤175° ensures that the cutting angle corresponding to ω is not too small, which helps to reduce the difficulty of cutting the first tab 23 to obtain the required ω angle, thereby improving processing efficiency.

[0012] In one optional embodiment of this application, the first tab includes a fifth surface connected to the first surface. The fifth surface is a surface of the first tab along its width direction. The fifth surface is connected to the first surface and is set at an angle to the first surface, the angle being β, where 120°≤β≤175°. Setting β≥120° helps to reduce the pressure of the first tab on the separator at the connection between the second and third surfaces, thereby reducing the possibility of the first tab damaging the separator, and further reducing the possibility of poor K-value in the secondary battery and short-circuit black spots on the tab. Setting β≤175° ensures that the cutting angle corresponding to β is not too small, which helps to reduce the difficulty of cutting the first tab to obtain the required β angle, thereby improving processing efficiency.

[0013] In one optional embodiment of this application, 120°≤β≤135°. Setting β≥120° helps to further reduce the difficulty of cutting the first electrode tab to obtain the required β angle; setting β≤135° prevents the angle between the fifth surface and the first surface from being too large, which helps to reduce the amount of cutting during the machining of the first electrode tab, thereby increasing the area of ​​the first surface, increasing the contact area between the first electrode tab and the first electrode plate, and reducing the impedance.

[0014] In one optional embodiment of this application, the first electrode tab includes a first portion. Along the thickness direction of the first electrode tab, the projection of the first portion lies within the projection range of the first current collector. The first portion is welded to the first current collector. The width of the portion of the first surface located in the first portion along the width direction of the first electrode tab is W1. The maximum width of the first portion is W, and 0.7 ≤ W1 / W ≤ 0.9. Setting W1 / W ≥ 0.7 helps to increase the area of ​​the first surface, thereby increasing the contact area between the first electrode tab and the first electrode plate and reducing impedance. Setting W1 / W ≤ 0.9 helps to reduce the difficulty of processing the first electrode tab and improve processing efficiency.

[0015] In one optional embodiment of this application, the first tab includes a fifth surface connected to the first surface, and the fifth surface is a surface of the first tab along its width direction. The fifth surface and the first surface are smoothly connected with a rounded chamfered surface; or, the fifth surface is an arc surface, protruding outward in the width direction of the first tab, and the fifth surface is smoothly connected to the first surface. This helps to reduce the pressure of the first tab on the separator at the connection point between the fifth surface and the first surface, thereby reducing the possibility of the first tab damaging the separator, and further reducing the possibility of poor K-value in the secondary battery and short-circuit black spots on the tab.

[0016] In one alternative embodiment of this application, the third surface intersects the first surface, the fourth surface intersects the first surface, and the first surface is a plane. This increases the contact area between the first tab and the first electrode plate, reducing impedance.

[0017] In one optional embodiment of this application, the first electrode is a positive electrode, the first tab is a positive tab, and the second electrode is a negative electrode. The negative electrode includes a negative current collector and a negative active material layer stacked along the thickness direction of the negative electrode. The negative active material layer includes silicon, and the mass content of silicon is between 3 wt% and 50 wt% based on the mass of the negative active material layer. Applying the structure of the first tab provided by the embodiment of this application to a silicon-based secondary battery helps to reduce the possibility of damage to the separator in the silicon-based secondary battery by the first tab.

[0018] In one optional embodiment of this application, the electrode assembly is flat. For flat electrode assemblies, pressure shaping is required during fabrication. Applying the first tab provided in the embodiments of this application to a flat electrode assembly helps reduce the possibility of the first tab damaging the insulating membrane during the pressure shaping process.

[0019] In one optional embodiment of this application, the electrode assembly includes a first straight section, a first curved section, a second straight section, and a second curved section arranged sequentially along the winding direction. A first electrode tab is disposed on the first straight section. Along the extending direction of the first straight section, the length of the first electrode tab to the boundary between the first straight section and the first curved section is D1, and the length of the first electrode tab to the boundary between the first straight section and the second curved section is D2, where D1 ≥ 3 mm and D2 ≥ 3 mm. Setting D1 ≥ 3 mm and D2 ≥ 3 mm ensures that the distance between the first electrode tab 23 and the boundary between the first straight section 20a and the first curved section 20b is not too small, and the distance between the first electrode tab 23 and the boundary between the first straight section 20b and the second curved section 20d is also not too small. This helps to reduce the pressure of the first electrode tab 23 on the separator 25, thereby reducing the possibility of damage to the separator 25.

[0020] In one optional embodiment of this application, the first electrode includes a first current collector and a first active material layer. Two first active material layers are respectively disposed on two surfaces of the first current collector along the thickness direction of the first electrode. The first current collector includes a first empty foil portion not covered by the first active material layer. The first empty foil portion is located at the end of the winding structure of the first electrode, and a first tab is welded to the first empty foil portion. Welding the first tab to the first empty foil portion helps to keep the first tab as far away as possible from the winding center of the electrode assembly, thereby reducing the pressure between the first tab and the separator and minimizing the possibility of damage to the separator.

[0021] A third aspect of the embodiments of this application provides an electrical device including a secondary battery as described in any of the foregoing embodiments. Attached Figure Description

[0022] Figure 1 is a schematic diagram of the structure of a secondary battery in one embodiment of this application.

[0023] Figure 2 is a cross-sectional view of a secondary battery in one embodiment of this application.

[0024] Figure 3 is a schematic diagram of the structure of the first electrode in a flattened state in one embodiment of this application.

[0025] Figure 4 is a schematic diagram of the structure of the first electrode in a flattened state in one embodiment of this application.

[0026] Figure 5 is a cross-sectional view of the first tab in one embodiment of this application.

[0027] Figure 6 is a cross-sectional view of the first tab in one embodiment of this application.

[0028] Figure 7 is a cross-sectional view of the first tab in one embodiment of this application.

[0029] Figure 8 is a cross-sectional view of the first tab in one embodiment of this application.

[0030] Figure 9 is a cross-sectional view of the first tab in one embodiment of this application.

[0031] Figure 10 is a schematic diagram of the structure of an electrical device in one embodiment of this application.

[0032] Explanation of main component symbols

[0033] Secondary battery 100

[0034] Casing 10

[0035] Electrode assembly 20

[0036] First straight section 20a

[0037] First curved section 20b

[0038] Third bending section 20c

[0039] Fourth bending segment 20d

[0040] First Extreme Film 21

[0041] First current collector 211

[0042] First blank foil section 211a

[0043] First active material layer 212

[0044] First slot 2121

[0045] Second pole piece 22

[0046] Second current collector 221

[0047] Second active material layer 222

[0048] First pole ear 23

[0049] Page 1, page 231

[0050] Page 232

[0051] Page 3, page 233

[0052] Page 4, page 234

[0053] Page 5, page 235

[0054] Page 6, page 236

[0055] Page 7, page 237

[0056] Page 8, 238

[0057] Part 1, page 239

[0058] Second pole ear 24

[0059] 25 Separator

[0060] Insulating component 26

[0061] First dividing line 27

[0062] Second dividing line 28

[0063] 1000 electrical appliances

[0064] The following detailed description, in conjunction with the accompanying drawings, will further illustrate this application. Detailed Implementation

[0065] The technical solutions of the embodiments of this application will be described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments.

[0066] It should be noted that when a component is considered to be "connected" to another component, it can be directly connected to the other component or may also have a component that is centrally located. When a component is considered to be "set" on another component, it can be directly set on the other component or may also have a component that is centrally located.

[0067] 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 herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application.

[0068] In the description of the embodiments of this application, technical terms such as "first" and "second" are used only to distinguish different objects and should not be construed as indicating or implying relative importance or implicitly specifying the number, specific order, or primary and secondary relationship of the indicated technical features. In the description of the embodiments of this application, "multiple" means two or more, unless otherwise explicitly defined.

[0069] In the description of the embodiments of this application, the term "perpendicular" is used to describe the ideal state between two components. In actual production or use, two components may exist in a state that is approximately perpendicular. The two components described as "perpendicular" may not be absolutely straight lines or planes, but may be approximately straight lines or planes. From a macroscopic perspective, if the overall extension direction is a straight line or plane, the component can be considered as a "straight line" or "plane".

[0070] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a mutually exclusive, independent, or alternative embodiment. Where there is no conflict, the various embodiments in this application can be combined with each other.

[0071] It should be noted that the thickness, length, width, and other dimensions of various components in the embodiments of this application shown in the accompanying drawings, as well as the overall thickness, length, width, and other dimensions of the integrated device, are merely illustrative examples and should not constitute any limitation on this application.

[0072] The inventors of this application have discovered that during the charging and discharging process of a secondary battery, the electrode assembly expands and generates internal stress, causing the separator to press tightly against the surface of the tab. This can easily lead to the tab cutting the separator, resulting in poor K value of the secondary battery and short-circuit black spots on the tab.

[0073] In view of this, embodiments of this application provide a secondary battery, including a casing, an electrode assembly, and a first tab. The electrode assembly is disposed within the casing and includes a first electrode, a second electrode, and a separator. The first electrode, the separator, and the second electrode are stacked along the thickness direction of the first electrode, and the separator is located between the first and second electrodes. The first tab is welded to the first electrode. The first tab includes a first surface and a second surface disposed opposite to each other along the thickness direction of the first tab. A portion of the first surface is connected to the first electrode, and the second surface faces and contacts the separator. The first tab also includes a third surface and a fourth surface, which are located on two opposite sides of the first tab along its width direction.

[0074] The third surface connects to the second surface, and the angle between the second and third surfaces is α, where 120°≤α≤175°; or, the third surface and the second surface are smoothly connected with rounded corners; or, the third surface is an arc surface, and the third surface protrudes in a direction away from the center of the first electrode tab, and the third surface is smoothly connected to the second surface.

[0075] In this secondary battery, the structure of the first tab helps to reduce the pressure on the separator at the connection between the first tab and the second and third sides, thereby reducing the possibility of the first tab damaging the separator, and further reducing the possibility of poor K value and short-circuit black spots on the tab in the secondary battery.

[0076] The embodiments of this application will be further described below with reference to the accompanying drawings. In the drawings, for ease of description, the thickness direction of the first electrode tab is defined as the first direction X, the width direction of the first electrode tab is defined as the second direction Y, and the length direction of the first electrode tab is defined as the third direction Z. In the following content, for ease of correspondence with the drawings, the description of directions related to the first electrode tab 23 will all use the first direction X, the second direction Y, and the third direction Z.

[0077] As shown in Figure 1, an embodiment of this application provides a secondary battery 100, including a housing 10, an electrode assembly 20, a first tab 23 and a second tab 24. The electrode assembly 20 is disposed inside the housing 10, and the first tab 23 and the second tab 24 are both electrically connected to the electrode assembly 20 and extend out of the housing 10.

[0078] In some embodiments, as shown in FIG2, the electrode assembly 20 includes a first electrode 21, a second electrode 22 and a separator 25. The first electrode 21, the separator 25 and the second electrode 22 are stacked along the thickness direction of the first electrode 21, and the separator 25 is located between the first electrode 21 and the second electrode 22.

[0079] In some embodiments, as shown in FIG2, the first electrode 21, the separator 25, and the second electrode 22 are stacked and wound to form a wound structure.

[0080] In some embodiments, as shown in FIG2, the first electrode 21 includes a first current collector 211 and a first active material layer 212. The first current collector 211 includes two surfaces disposed opposite to each other along the thickness direction of the first electrode 21, and both surfaces are coated with the first active material layer 212.

[0081] In some embodiments, as shown in FIG2, the second electrode 22 includes a second current collector 221 and a second active material layer 222. The second current collector 221 includes two surfaces disposed opposite to each other along the thickness direction of the second electrode 22, and both surfaces are coated with the second active material layer 222.

[0082] In some embodiments, one of the first electrode 21 and the second electrode 22 is a positive electrode and the other is a negative electrode. One of the first current collector 211 and the second current collector 221 is a positive current collector and the other is a negative current collector. One of the first active material layer 212 and the second active material layer 222 is a positive active material layer and the other is a negative active material layer.

[0083] In some embodiments, both the positive current collector and the negative current collector are metal layers. As an example, the positive current collector may be a metal layer comprising at least one of aluminum, nickel, tantalum, and titanium, such as aluminum foil. The negative current collector may be a metal layer comprising at least one of copper, nickel, tantalum, and titanium, such as copper foil.

[0084] In some embodiments, the positive electrode active material layer includes a positive electrode active material, which includes at least one of lithium cobalt oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium iron phosphate, lithium manganese iron phosphate, or lithium manganese oxide.

[0085] In some embodiments, the negative electrode active material layer includes a negative electrode active material, which includes at least one of graphite, hard carbon, soft carbon, silicon, silicon-oxygen materials, and silicon-carbon materials.

[0086] In some embodiments, the separator 25 is an insulating film material such as a polyethylene film, a polypropylene film, a polyester film, or a polyimide film.

[0087] In some embodiments, the secondary battery 100 further includes an electrolyte (not shown) contained within the housing 10.

[0088] In some embodiments, the electrolyte is any one of gel, solid, and liquid states.

[0089] In some embodiments, the electrolyte comprises a lithium salt and a non-aqueous solvent.

[0090] In some embodiments, the lithium salt includes at least one of LiPF6, LiBF4, LiAsF6, LiClO4, LiB(C6H5)4, LiCH3SO3, LiCF3SO3, LiN(SO2CF3)2, LiC(SO2CF3)3, or LiPO2F2.

[0091] In some embodiments, the non-aqueous solvent includes at least one of carbonate compounds, carboxylic acid ester compounds, ether compounds, nitrile compounds, or other organic solvents. For example, the carbonate compound may include at least one of diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), methyl ethyl carbonate (MEC), ethylene carbonate (EC), propylene carbonate (PC), butyl carbonate (BC), vinyl ethylene carbonate (VEC), fluoroethylene carbonate (FEC), 1,2-difluoroethylene carbonate, 1,1-difluoroethylene carbonate, 1,1,2-trifluoroethylene carbonate, 1,1,2,2-tetrafluoroethylene carbonate, 1-fluoro-2-methylethylene carbonate, 1-fluoro-1-methylethylene carbonate, 1,2-difluoro-1-methylethylene carbonate, 1,1,2-trifluoro-2-methylethylene carbonate, or trifluoromethylethylene carbonate.

[0092] In some embodiments, as shown in FIG3, one of the two first active material layers 212 has a first groove 2121. The first groove 2121 penetrates the first active material layer 212 along the thickness direction of the first electrode 21, so that a portion of the surface of the first current collector 211 is exposed in the first groove 2121, and the first tab 23 is connected to the portion of the first current collector 211 exposed in the first groove 2121.

[0093] In some embodiments, the first tab 23 is welded to the first electrode 21, and the second tab 24 is welded to the second electrode 22. Specifically, the first tab 23 is welded to the first current collector 211, and the second tab 24 is welded to the second current collector 221.

[0094] In some embodiments, as shown in FIG2, FIG3 and FIG5, the first tab 23 includes a first surface 231 and a second surface 232 disposed opposite to each other along a first direction X, a portion of the surface of the first surface 231 is connected to the first electrode 21, and the second surface 232 faces the separator 25.

[0095] In some embodiments, as shown in FIG5, the first tab 23 further includes a third surface 233 and a fourth surface 234, which are located on two opposite sides of the first tab 23 along the second direction Y. The third surface 233 connects to the second surface 232, and the angle between the second surface 232 and the third surface 233 is α, where 120°≤α≤175°. Setting α≥120° helps to reduce the pressure of the first tab 23 on the separator 25 at the connection between the second surface 232 and the third surface 233, thereby reducing the possibility of the first tab 23 damaging the separator 25, and further reducing the possibility of the secondary battery 100 having a poor K value and short-circuit black spots on the tab; setting α≤175° ensures that the cutting angle corresponding to α is not too small, which helps to reduce the difficulty of cutting the first tab 23 to obtain the required α angle, thereby improving processing efficiency.

[0096] Wherein, the cutting angle corresponding to α is the supplementary angle of α, which is represented by the first cutting angle θ in Figure 5. When machining the first tab 23, the cutting equipment removes part of the material of the first tab 23 with the first cutting angle θ to form the third surface 233, and makes the third surface 233 and the second surface 232 form a required angle.

[0097] In some embodiments, 135°≤α≤165°. Setting α≥135° helps to further reduce the pressure of the first tab 23 on the separator 25 at the connection between the second surface 232 and the third surface 233; setting α≤165° helps to further reduce the difficulty of cutting the first tab 23 to obtain the required α angle.

[0098] In some embodiments, as shown in FIG5, the fourth surface 234 is connected to the second surface 232, and the angle between the fourth surface 234 and the second surface 232 is ω, where 120°≤ω≤175°. Setting ω≥120° helps to reduce the pressure of the first tab 23 on the separator 25 at the connection between the second surface 232 and the fourth surface 234, thereby reducing the possibility of the first tab 23 damaging the separator 25, and further reducing the possibility of the secondary battery 100 having poor K value and short-circuit black spots on the tab; setting ω≤175° ensures that the cutting angle corresponding to ω is not too small, which helps to reduce the difficulty of cutting the first tab 23 to obtain the required ω angle, thereby improving processing efficiency.

[0099] Among them, the cutting angle corresponding to ω is the supplementary angle of δ, which is represented by the second cutting angle δ in Figure 5.

[0100] In some embodiments, as shown in FIG6, the third surface 233 and the second surface 232 are smoothly connected with a rounded chamfered surface. This helps to reduce the pressure of the first tab 23 on the separator 25 at the connection between the second surface 232 and the third surface 233, thereby reducing the possibility of the first tab 23 damaging the separator 25, and further reducing the possibility of the secondary battery 100 having poor K value and short-circuit black spots on the tab.

[0101] The meaning of the connection between the third surface 233 and the second surface 232 with a rounded chamfer is that, for the cross section of the electrode assembly 20 perpendicular to its winding center axis, there is a rounded chamfer at the connection between the second surface 232 and the third surface 233.

[0102] In some embodiments, as shown in FIG7, the third surface 233 is an arc surface, and the third surface 233 protrudes outward from the first tab 23 along the second direction Y, and the third surface 233 is smoothly connected to the second surface 232. In this way, it is beneficial to reduce the pressure of the first tab 23 on the separator 25 at the connection between the second surface 232 and the third surface 233, thereby reducing the possibility of the first tab 23 damaging the separator 25, and further reducing the possibility of the secondary battery 100 having poor K value and short circuit black spots on the tab.

[0103] In some embodiments, as shown in FIG5, the first electrode tab 23 includes a fifth surface 235, which is connected to the first surface 231. The fifth surface 235 is a surface of the first electrode tab 23 along the second direction Y.

[0104] In some embodiments, as shown in FIG5, the fifth surface 235 is connected to the first surface 231 and is set at an angle to the first surface 231. The angle between the fifth surface 235 and the first surface 231 is β, where 120°≤β≤175°. Setting β≥120° helps to reduce the pressure of the first tab 23 on the separator 25 at the connection between the second surface 232 and the third surface 233, thereby reducing the possibility of the first tab 23 damaging the separator 25, and further reducing the possibility of the secondary battery 100 having poor K value and short-circuit black spots on the tab. Setting β≤175° ensures that the cutting angle corresponding to β is not too small, which helps to reduce the difficulty of cutting the first tab 23 to obtain the required β angle, thereby improving processing efficiency.

[0105] Wherein, the cutting angle corresponding to β is the supplementary angle of β, which is represented by the third cutting angle γ in Figure 5. When machining the first tab 23, the cutting equipment removes part of the material of the first tab 23 with the third cutting angle γ to form the fifth surface 235, and makes the fifth surface 235 and the first surface 231 form a required angle.

[0106] In some embodiments, 120°≤β≤135°. Setting β≥120° helps to further reduce the difficulty of cutting the first electrode tab 23 to obtain the required β angle; setting β≤135° prevents the angle between the fifth surface 235 and the first surface 231 from being too large, which helps to reduce the amount of cutting of the first electrode tab 23 during the machining process, thereby increasing the area of ​​the first surface 231, increasing the contact area between the first electrode tab 23 and the first electrode plate 21, and reducing the impedance.

[0107] It should be noted that, in the embodiments of this application, an optical measuring machine (OMM) can be used to measure the cross-section of the first electrode 23 in order to obtain various angles and dimensions related to the first electrode 23.

[0108] In some embodiments, as shown in Figures 3 and 4, the first electrode tab 23 includes a first portion 239. Along the first direction X, the projection of the first portion 239 is located within the projection range of the first current collector 211, and the first portion 239 is welded to the first current collector 211.

[0109] In some embodiments, as shown in FIG5, the width of the portion of the first surface 231 located in the first part 239 along the second direction Y is W1, the maximum width of the first part 239 is W, and 0.7≤W1 / W≤0.9. Setting W1 / W≥0.7 is beneficial to increasing the area of ​​the first surface 231, thereby increasing the contact area between the first tab 23 and the first electrode 21 and reducing the impedance; setting W1 / W≤0.9 is beneficial to reducing the difficulty of processing the first tab 23 and improving processing efficiency.

[0110] Here, when measuring the width of the first surface 231 and the maximum width of the first tab 23, the first part 239 can be placed under an optical measuring machine (OMM) for measurement. During the measurement, the measurement can be performed from a perspective that is directly facing the first surface 231.

[0111] In some embodiments, as shown in Figures 2 to 4, the secondary battery 100 further includes an insulating member 26, which is bonded to the first electrode 21 and covers the first portion 239. Along the first direction X, the thickness of the insulating member 26 is 8–12 μm. Providing the insulating member 26 helps to reduce the possibility of the solder joint at the welding point between the first portion 239 and the first current collector 211 puncturing the separator 25, and also helps to reduce the possibility of the edge of the first electrode tab 23 damaging the separator.

[0112] In some embodiments, the insulating element 26 includes a substrate layer and an adhesive layer, wherein the adhesive layer bonds the first electrode 21 to the base layer.

[0113] In some embodiments, the substrate layer may be selected from polyethylene terephthalate, co-extruded polypropylene, oriented polystyrene, thermoplastic polyurethane, polylactic acid, polyolefin, and polyimide.

[0114] In some embodiments, the adhesive layer is made of one or more of the following: natural rubber, styrene-butadiene rubber, isoprene rubber, styrene-polybutadiene-styrene block copolymer, hydrogenated styrene-polybutadiene-styrene block copolymer, styrene-isoprene-styrene block copolymer, hydrogenated styrene-polyisoprene-styrene block copolymer, polyisobutylene, amorphous α-olefin copolymer, petroleum resin, terpene resin, and rosin resin.

[0115] In some embodiments, as shown in FIG6, the fifth surface 235 and the first surface 231 are smoothly connected with a rounded chamfered surface. This helps to reduce the pressure of the first tab 23 on the separator 25 at the connection between the fifth surface 235 and the first surface 231, thereby reducing the possibility of the first tab 23 damaging the separator 25, and further reducing the possibility of the secondary battery 100 having poor K value and short-circuit black spots on the tab.

[0116] In some embodiments, as shown in FIG7, the fifth surface 235 is an arc surface, and the fifth surface 235 protrudes outward from the first tab 23 along the second direction Y, and the fifth surface 235 is smoothly connected to the first surface 231. This helps to reduce the pressure of the first tab 23 on the separator 25 at the connection point of the fifth surface 235 and the first surface 231, thereby reducing the possibility of the first tab 23 damaging the separator 25, and further reducing the possibility of the secondary battery 100 exhibiting poor K-value and short-circuit black spots on the tab.

[0117] In some embodiments, as shown in FIG5, the first electrode tab 23 further includes a sixth surface 236, which is disposed opposite to the fifth surface along the second direction Y. The sixth surface 236 is connected to the first surface 231.

[0118] In some embodiments, the third surface 233 connects to the fifth surface 235, and the fourth surface 234 connects to the sixth surface 236, such that the cross section of the first electrode tab perpendicular to the third direction Z is hexagonal or approximately hexagonal. Approximately hexagonal means that at least one edge of the cross section of the first electrode tab 23 perpendicular to the third direction Z is arc-shaped, i.e., the surface corresponding to this edge is an arc surface.

[0119] In some embodiments, as shown in Figures 5 to 7, the first electrode tab 23 further includes a seventh surface 237 and an eighth surface 238, which are arranged opposite to each other along the second direction Y. The seventh surface connects the third surface 233 and the fifth surface 235, and the eighth surface 238 connects the fourth surface 234 and the sixth surface 236, such that the cross-section of the first electrode tab perpendicular to the third direction Z is octagonal or approximately octagonal. The term "approximately octagonal" means that at least one edge of the cross-section of the first electrode tab 23 perpendicular to the third direction Z is arc-shaped, i.e., the surface corresponding to this edge is an arc surface.

[0120] In some embodiments, as shown in Figures 8 and 9, the third surface 233 intersects the first surface 231, and the fourth surface 234 intersects the first surface 231, where the first surface 231 is a plane. This helps to increase the contact area between the first tab 23 and the first electrode plate 21, thereby reducing the impedance.

[0121] In some embodiments, as shown in FIG2, the electrode assembly 20 is flat. For the flat electrode assembly 20, it needs to be shaped under pressure during the manufacturing process. Applying the first tab 23 provided in the embodiments of this application to the flat electrode assembly 20 helps to reduce the possibility of the first tab 23 damaging the isolation membrane 25 during the pressure shaping process of the electrode assembly 20.

[0122] In some embodiments, as shown in FIG2, the electrode assembly 20 includes a first straight section 20a, a first curved section 20b, a second straight section 20c, and a second curved section 20d arranged sequentially along the winding direction. A first electrode tab 23 is disposed on the first straight section 20a. Along the extending direction of the first straight section 20a, the distance from the first electrode tab 23 to the boundary between the first straight section 20a and the first curved section 20b is D1, and the distance from the first electrode tab 23 to the boundary between the first straight section 20b and the second curved section 20d is D2. D1≥3mm and D2≥3mm. In the electrode assembly 20, the internal stress at the corner of the winding structure is relatively large during the charging and discharging process of the secondary battery 20. Setting D1≥3mm and D2≥3mm ensures that the distance between the first tab 23 and the boundary between the first straight section 20a and the first curved section 20b is not too small, and the distance between the first tab 23 and the boundary between the first straight section 20b and the second curved section 20d is also not too small. This helps to reduce the pressure of the first tab 23 on the separator 25, thereby reducing the possibility of damage to the separator 25.

[0123] The four sections—first straight segment 20a, first curved segment 20b, second straight segment 20c, and second curved segment 20d—are defined as follows: The secondary battery is placed in a computed tomography (CT) scanner, and the electrode assembly 20 is observed from the perspective shown in Figure 2. For the innermost ring of the electrode assembly 20, the boundary points connecting the first straight segment 20a and the first curved segment 20b, and the boundary points connecting the second straight segment 20c and the first curved segment 20b, are extended to obtain the first straight segment 20a and the first curved segment 20d. The boundary line between the curved segment 20b and the second straight segment 20c and the first curved segment 20b is referred to as the first boundary line 27 for ease of description. Connecting the boundary points of the first straight segment 20a and the second curved segment 20d, as well as the boundary points of the second straight segment 20c and the second curved segment 20d, and extending them, we obtain the boundary lines between the first straight segment 20a and the second curved segment 20d, as well as the boundary lines between the second straight segment 20c and the second curved segment 20d. For ease of description, this boundary line is referred to as the second boundary line 28. When measuring the distance between the first electrode tab 23 and the boundary between the first straight segment 20a and the first curved segment 20b, the distance from the outermost edge of the first electrode tab 23 along the second direction Y toward the first boundary line 27 to the first boundary line 27 is measured. When this edge forms an angle with the third direction Z, the minimum distance from the point on this edge to the first boundary line 27 is taken. When measuring the distance between the first electrode tab 23 and the boundary between the first straight segment 20b and the second curved segment 20d, the distance from the outermost edge of the first electrode tab 23 along the second direction Y toward the second boundary line 28 to the second boundary line 28 is measured. When this edge forms an angle with the third direction Z, the minimum distance from the point on this edge to the second boundary line 28 is taken.

[0124] In some embodiments, as shown in FIG4, the first current collector 211 includes a first empty foil portion 211a not covered by the first active material layer 212. The first empty foil portion 211a is located at the end of the winding structure of the first electrode 21, and the first tab 23 is welded to the first empty foil portion 211a. When the electrode assembly 20 expands, the stress on the outer ring of the electrode assembly 20 is less than the stress on the inner ring of the electrode assembly 20. Welding the first tab 23 to the first empty foil portion 211a helps to keep the first tab 23 as far away from the winding center of the electrode assembly 20 as possible, thereby helping to reduce the pressure between the first tab 23 and the separator 25 and reducing the possibility of damage to the separator 25.

[0125] In some embodiments, the first current collector 211 includes a second empty foil portion not covered by the first active material layer 212, the second empty foil portion being located at the beginning section of the first electrode 21 in the winding structure, and the first electrode tab 23 being welded to the second empty foil portion.

[0126] In some embodiments, the first electrode 21 is a positive electrode, the first tab 23 is a positive tab, and the second electrode 22 is a negative electrode. The negative electrode includes a negative current collector and a negative active material layer stacked along the thickness direction of the negative electrode. The negative active material layer includes silicon, and the mass content of silicon is between 3 wt% and 50 wt% based on the mass of the negative active material layer. When the negative active material layer includes silicon, the volume change of the electrode assembly 20 during charging and discharging is greater than that of a graphite battery, resulting in greater internal stress. Applying the structure of the first tab 23 provided in the embodiments of this application to the silicon-based secondary battery 100 helps to reduce the possibility of the separator 25 in the silicon-based secondary battery 100 being damaged by the first tab 23.

[0127] The method for testing the silicon content in the negative electrode is as follows:

[0128] The secondary battery 100 was discharged at a constant current of 0.1C to 3.0V, and then disassembled to obtain the negative electrode sheet. The negative electrode sheet was cleaned with dimethyl carbonate (DMC) for 10 minutes, and then baked at 100°C for 2 hours before use. The negative electrode active material layer on the negative electrode sheet was scraped off, and the powder of the negative electrode active material layer was collected. The silicon content in the powder of the negative electrode material layer was tested using an inductively coupled plasma atomic emission spectrometer (ICP, model Agilent 5800, provided by Agilent Technologies).

[0129] As shown in Figure 10, an embodiment of this application also provides an electrical device 1000, including the secondary battery 100 involved in any of the foregoing embodiments.

[0130] In some embodiments, the electrical device 1000 includes, but is not limited to, mobile phones, laptops, power tools, electric toys, and electronic cigarettes.

[0131] To verify the improvement effect of the embodiments in this application on the K value of the secondary battery 100, the inventors of this application conducted the following experiments, which included two sets of comparative examples and seven sets of embodiments. In Comparative Example 1, the first tab 23 and the second tab 24 of the secondary battery 100 are both quadrangular prism structures. In Comparative Example 2 and Embodiments 1-5, the second surface 232 of the first tab 23 forms an angle α with the third surface 233, and the second surface 232 forms an angle with the fourth surface 234, the fifth surface 235 forms an angle with the first surface 231, and the sixth surface 236 forms an angle with the first surface 231, and the angle values ​​are all equal to α. The structure of the second tab 24 is the same as the structure of the first tab 23. In Example 6, the second surface 232 of the first tab 23 of the secondary battery 100 is smoothly connected to the third surface 233 with rounded corners. The second surface 232 is also smoothly connected to the fourth surface 234, the fifth surface 235 to the first surface 231, and the sixth surface 236 to the first surface 231 with rounded corners. The structure of the second tab 24 is the same as that of the first tab 23. In Example 7, the third surface 233, the fourth surface 234, the fifth surface 235, and the sixth surface 236 of the first tab 23 of the secondary battery 100 are all curved surfaces. The third surface 233, the fourth surface 234, the fifth surface 235, and the sixth surface 236 all protrude outward from the first tab 23 along the second direction Y. The third surface 233 and the fourth surface 234 are smoothly connected to the second surface 232, and the fifth surface 235 and the sixth surface 236 are smoothly connected to the first surface 231. The structure of the second tab 24 is the same as that of the first tab 23. In the comparative examples and embodiments, the first electrode 21 is a positive electrode, the first tab 23 is a positive tab, the second electrode 22 is a negative electrode, and the second tab 24 is a negative tab.

[0132] The preparation process of the secondary battery 100 in Comparative Example 1 includes the following steps:

[0133] (1) Preparation of the positive electrode sheet: Lithium cobalt oxide (LiCoO2), conductive carbon black (Super P), CNTs (carbon nanotubes), and polyvinylidene fluoride (PVDF) were mixed in a weight ratio of 97.5:0.5:0.5:1.5. N-methylpyrrolidone (NMP) was added as a solvent to prepare a positive electrode active material with a solid content of 75 wt%, and the mixture was stirred evenly for later use. A 10 μm thick aluminum foil was used as the positive electrode current collector. The above active material was uniformly coated onto one surface of the positive electrode current collector along its thickness direction using a slit coater, and then dried at 90°C to obtain a positive electrode sheet with a single-sided coating of the positive electrode active material. The coating process was then repeated on the other surface of the positive electrode current collector along its thickness direction to obtain a positive electrode sheet with positive electrode active material layers coated on both sides. At this point, the thickness of each positive electrode active material layer along the thickness direction of the positive electrode sheet was 50 μm. The coated positive electrode sheet is then cold-pressed, resulting in a positive electrode active material layer thickness of 35 μm. The first tab 23 is then welded to the portion of the positive electrode current collector not covered by the positive electrode active material layer, specifically the end of the positive electrode sheet along its length.

[0134] (2) Preparation of the negative electrode sheet: Artificial graphite, conductive carbon black (Super P), styrene-butadiene rubber (SBR), and CMC (sodium carboxymethyl cellulose) were mixed in a weight ratio of 97:0.5:1.3:1.2, with deionized water added as a solvent to prepare a negative electrode active material with a weight percentage of 50 wt%, and stirred evenly for later use. A 10 μm thick copper foil was used as the negative electrode current collector. The above negative electrode active material was uniformly coated onto one surface of the negative electrode current collector along its thickness direction using a slot coater, and then dried at 110°C to obtain a negative electrode sheet with a single-sided coating of the negative electrode active material layer. The above steps were then repeated on the other side of the negative electrode current collector along its thickness direction to obtain a negative electrode sheet with a double-sided coating of the negative electrode active material layer. At this time, the thickness of each negative electrode active material layer along the thickness direction of the negative electrode sheet was 55 μm. The coated negative electrode sheet was then cold-pressed, and the thickness of the negative electrode active material layer after cold pressing was 45 μm. The second tab 24 is then welded to the portion of the negative electrode current collector that is not covered by the negative electrode active material layer, wherein the portion not covered by the negative electrode active material layer is the end of the negative electrode sheet in the length direction.

[0135] (3) Preparation of electrolyte: In a dry argon atmosphere, ethylene carbonate (EC), ethyl methyl carbonate (EMC) and diethyl carbonate (DEC) are first mixed in a mass ratio of EC:EMC:DEC = 30:50:20 to form a basic organic solvent. Then, lithium salt lithium hexafluorophosphate (LiPF6) is added to the basic organic solvent to dissolve and mix evenly to obtain an electrolyte with a lithium salt concentration of 1.15 mol / L.

[0136] (4) Preparation of the isolation membrane 25: A 7 μm thick polyethylene porous polymer film was used as the isolation membrane 2523.

[0137] (5) Preparation of electrode assembly 20: The positive electrode sheet, the separator 25 and the negative electrode sheet are stacked and wound together along the thickness direction of the negative electrode sheet to obtain the electrode assembly 20.

[0138] (6) Assembly of the secondary battery 100: Place the punched aluminum-plastic film in the assembly fixture with the punched surface facing upwards, place the electrode assembly 20 in the punch, and apply external force to press it firmly. Then, cover the electrode assembly 20 with another punched aluminum-plastic film with the punched surface facing downwards, and heat-seal the three edges of the two aluminum-plastic films by hot pressing. The unsealed edge is the negative electrode tab and the positive electrode tab protruding from one side of the housing 10. Then, inject electrolyte through the unsealed edge, and after vacuum sealing, standing, hot pressing formation, shaping and other processes, the secondary battery 100 is obtained.

[0139] The preparation process of the secondary battery 100 in Comparative Example 2 and Examples 1-7 is basically the same as that of the comparative example, the only difference being the different structures of the first tab 23 and the second tab 24 used.

[0140] After the secondary battery 100 in each comparative example and embodiment was prepared, 100 secondary batteries 100 in each comparative example and embodiment were tested for K value, and then 10 secondary batteries 100 in each group were randomly selected for cycle capacity retention rate test.

[0141] The process of K-value testing is as follows:

[0142] 1. Charge the secondary battery to full charge, specifically as follows:

[0143] 1) The test temperature is 25℃;

[0144] 2) Let stand for 30 minutes;

[0145] 3) Charge at a constant current of 5C to 4.25V, then charge at a constant voltage of 3C;

[0146] 4) Charge at 3C constant current to 4.35V, then charge at constant voltage to 1.5C;

[0147] 5) Charge at a constant current of 1.5C to 4.45V, then charge at a constant voltage to 0.05C;

[0148] 2. Measure the initial voltage: Measure the voltage of the secondary battery 100 as the initial voltage OCV1, which serves as a reference value;

[0149] 3. Let stand: The temperature for standing is 25℃, and the standing time is 24 hours;

[0150] 4. Measure the voltage after settling: Immediately after the settling period, measure the voltage OCVB of the secondary battery 100.

[0151] 5. Calculate the self-discharge rate K using the formula: K = (OCV1 - OCVB) / 24.

[0152] In this test, the acceptable specification for secondary battery 100 is defined as a K value between 0 and 0.06 mV / h.

[0153] The test procedure for cycle capacity retention is as follows:

[0154] 1) Maintain the test temperature at 25℃;

[0155] 2) Let the secondary battery 100 stand for 30 minutes;

[0156] 3) Charge at a constant current of 5C to 4.25V, then charge at a constant voltage of 3C;

[0157] 4) Charge at 3C constant current to 4.35V, then charge at constant voltage to 1.5C;

[0158] 5) Charge at a constant current of 1.5C to 4.45V, then charge at a constant voltage to 0.05C;

[0159] 6) Let stand for 5 minutes;

[0160] 7) Discharge at a constant current of 0.7C to 3V and record the first discharge cycle capacity;

[0161] 8) Let stand for 5 minutes;

[0162] 9) Repeat steps 3 to 8 800 times, and record the discharge capacity on the 800th cycle;

[0163] 10) Calculate the capacity retention rate. Capacity retention rate = (discharge capacity of the 800th cycle / discharge capacity of the first cycle) × 100%.

[0164] Calculate the average capacity retention rate of 10 secondary batteries after 100 cycles and 800 cycles.

[0165] After the cycle capacity retention test, the secondary battery 100 was disassembled, and the first tab 23 and the second tab 24 and their vicinity were observed for black spots. The observation locations were the portions of the positive and negative electrodes overlapping with the first tab 23 and the second tab 24 along the thickness direction of the positive electrode, as well as the edges of the tabs. It should be noted that the appearance of black spots on the portions overlapping with the electrodes along the thickness direction or at the edges of the tabs indicates micro-damage to the separator at the edge of the tab, leading to a short circuit between the positive and negative electrodes near the edge. The large current at the moment of the short circuit causes the separator, electrode, or tab to be burned, resulting in internal short-circuit black spots. In Table 1, the ratio in the column for the probability of black spots in the secondary battery is the ratio of the number of secondary batteries 100 with observed black spots to the total number of secondary batteries 100 disassembled in each group.

[0166] After the experiment, the experimental data was recorded in Table 1:

[0167] Table 1

[0168] As shown in Table 1, the first tab 23 of the secondary battery 100 in Examples 1-5 satisfies 120°≤α≤175°. Compared with Comparative Examples 1-2, the pass rate of the K-value test and the pass rate of the cycle capacity retention test of the secondary battery 100 in Examples 2-6 are higher than those of Comparative Examples 1-2. Moreover, the probability of black spots appearing on the tab after 800 charge-discharge cycles is lower than that of the Comparative Examples and Example 1. It can be seen that setting α≥120° is beneficial to reduce the pressure of the first tab 23 on the separator 25 at the connection between the second surface 232 and the third surface 233, thereby reducing the possibility of the first tab 23 damaging the separator 25, and thus reducing the possibility of poor K-value and short-circuit black spots on the tab of the secondary battery 100. Based on this, considering the processing difficulty, setting α≤175° is beneficial to reduce the difficulty of cutting the first tab 23 to obtain the required α angle, thereby improving processing efficiency.

[0169] As shown in Table 1, the first tab 23 of the secondary battery 100 in Example 6 satisfies the requirement that the second surface 232 and the third surface 233 are smoothly connected with rounded chamfered surfaces. Compared with Comparative Example 1, the pass rate of the K value test of the secondary battery 100 in Example 6 is higher than that of Comparative Example 1, and the pass rate of the cycle capacity retention test is also higher than that of Comparative Example 1. Moreover, the probability of black spots appearing on the tab after 800 charge-discharge cycles is lower than that of Comparative Example 1. It can be seen that the smooth connection between the third surface 233 and the second surface 232 with rounded corners is beneficial to reduce the pressure of the first tab 23 on the separator 25 at the connection between the second surface 232 and the third surface 233, thereby reducing the possibility of the first tab 23 damaging the separator 25, and thus reducing the possibility of the secondary battery 100 having poor K value and short-circuit black spots on the tab.

[0170] As shown in Table 1, the first tab 23 of the secondary battery 100 in Example 7 satisfies that the third surface 233 is an arc surface and the third surface 233 is smoothly connected to the second surface 232. Compared with Comparative Example 1, the pass rate of the K value test of the secondary battery 100 in Example 7 is higher than that of Comparative Example 1, the pass rate of the cycle capacity retention test is also higher than that of Comparative Example 1, and the probability of black spots appearing on the tab after 800 charge-discharge cycles is lower than that of Comparative Example 1. It can be seen that the third surface 233 is an arc surface and the third surface 233 protrudes in a direction away from the center of the first tab 23, so that the third surface 233 is smoothly connected to the second surface 232. This helps to reduce the pressure of the first tab 23 on the separator 25 at the connection between the second surface 232 and the third surface 233, thereby reducing the possibility of the first tab 23 damaging the separator 25, and thus reducing the possibility of the secondary battery 100 having poor K value and short-circuit black spots on the tab.

[0171] Those skilled in the art should recognize that the above embodiments are only used to illustrate this application and are not intended to limit this application. Any appropriate changes and variations made to the above embodiments within the essential spirit and scope of this application fall within the scope of this application.

Claims

1. A secondary battery, characterized in that, include: case; An electrode assembly is disposed within the housing. The electrode assembly includes a first electrode, a second electrode, and a separator. The first electrode, the separator, and the second electrode are stacked along the thickness direction of the first electrode and wound to form a wound structure. The separator is located between the first electrode and the second electrode. The first electrode tab is welded to the first electrode plate; and The first electrode tab includes a first surface and a second surface disposed opposite to each other along the thickness direction of the first electrode tab, a portion of the surface of the first surface is connected to the first electrode sheet, and the second surface faces the separator membrane; The first electrode tab also includes a third surface and a fourth surface, which are located on two opposite sides of the first electrode tab along its width direction; The third surface is connected to the second surface, and the angle between the second surface and the third surface is α, where 120°≤α≤175°.

2. The secondary battery as described in claim 1, characterized in that, 135°≤α≤165°。 3. A secondary battery, characterized in that, include: case; An electrode assembly is disposed within the housing. The electrode assembly includes a first electrode, a second electrode, and a separator. The first electrode, the separator, and the second electrode are stacked and wound to form a wound structure. The separator is located between the first electrode and the second electrode. The first electrode tab is connected to the first electrode plate; The first electrode tab includes a first surface and a second surface disposed opposite to each other along the thickness direction of the first electrode tab, a portion of the surface of the first surface is connected to the first electrode sheet, and the second surface faces the separator membrane; The first electrode tab also includes a third surface and a fourth surface, which are located on two opposite sides of the first electrode tab along its width direction; The third surface is smoothly connected to the second surface with a rounded chamfered surface; or The third surface is an arc surface, and the third surface protrudes outward in the width direction of the first electrode tab. The third surface is smoothly connected to the second surface.

4. The secondary battery according to any one of claims 1 to 3, characterized in that, The fourth surface is connected to the second surface, and the angle between the fourth surface and the second surface is ω, where 120°≤ω≤175°.

5. The secondary battery as described in any one of claims 1 to 4, characterized in that, The first electrode tab includes a fifth surface, which is connected to the first surface. The fifth surface is a surface of the first electrode tab along the width direction of the first electrode tab. The fifth surface is connected to the first surface and is set at an angle to the first surface. The angle between the fifth surface and the first surface is β, where 120°≤β≤175°.

6. The secondary battery as described in claim 5, characterized in that, 120°≤β≤135°。 7. The secondary battery as described in claim 5, characterized in that, The first electrode tab includes a first portion. Along the thickness direction of the first electrode tab, the projection of the first portion is located within the projection range of the first current collector. The first portion is welded to the first current collector. The width of the portion of the first surface located in the first portion along the width direction of the first electrode tab is W1. The maximum width of the first portion is W, and 0.7≤W1 / W≤0.

9.

8. The secondary battery as described in any one of claims 1 to 4, characterized in that, The first electrode tab includes a fifth surface, which is connected to the first surface, and the fifth surface is a surface of the first electrode tab along its width direction; The fifth surface is smoothly connected to the first surface with a rounded chamfered surface; or The fifth surface is an arc surface, and the fifth surface protrudes outward in the width direction of the first electrode tab, and the fifth surface is smoothly connected to the first surface.

9. The secondary battery as described in any one of claims 1 to 4, characterized in that, The third surface intersects with the first surface, and the fourth surface intersects with the first surface, wherein the first surface is a plane.

10. The secondary battery according to any one of claims 1 to 4, characterized in that, The first electrode is a positive electrode, the first tab is a positive tab, and the second electrode is a negative electrode. The negative electrode includes a negative current collector and a negative active material layer stacked along the thickness direction of the negative electrode. The negative active material layer includes silicon, and the mass content of the silicon is between 3 wt% and 50 wt% based on the mass of the negative active material layer.

11. The secondary battery as described in any one of claims 1 to 4, characterized in that, The electrode assembly is flat.

12. The secondary battery as described in claim 11, characterized in that, The electrode assembly includes a first straight section, a first curved section, a second straight section, and a second curved section arranged sequentially along the winding direction. The first electrode tab is disposed on the first straight section. Along the extension direction of the first straight section, the length of the first electrode tab to the boundary between the first straight section and the first curved section is D1, and the length of the first electrode tab to the boundary between the first straight section and the second curved section is D2. D1 ≥ 3 mm, and D2 ≥ 3 mm.

13. The secondary battery as described in any one of claims 1 to 4, characterized in that, The first electrode includes a first current collector and a first active material layer. The two first active material layers are respectively disposed on the two surfaces of the first current collector along the thickness direction of the first electrode. The first current collector includes a first empty foil portion not covered by the first active material layer. The first empty foil portion is located at the end of the first electrode in the winding structure. The first electrode tab is welded to the first empty foil portion.

14. The secondary battery according to any one of claims 1 to 4, characterized in that, The first tab includes a first portion, and along the thickness direction of the first tab, the projection of the first portion is located within the projection range of the first current collector. The first portion is welded to the first current collector. The secondary battery also includes an insulating component, which is bonded to the first electrode and covers the first portion. Along the thickness direction of the first tab, the thickness of the insulating component is 8 to 12 μm.

15. An electrical appliance, characterized in that, Includes the secondary battery as described in any one of claims 1 to 14.

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