Secondary battery, power consuming device, and method for manufacturing electrode sheet

Abstract

Embodiments of the present application disclose a secondary battery, a power consumption device and a preparation method of an electrode tab. The secondary battery comprises a first tab, a first electrode tab and a first connecting piece. The first electrode tab comprises a first current collector, a first active material layer and a second active material layer. The first current collector comprises a first surface and a second surface arranged oppositely. The first active material layer is arranged on the first surface, and the second active material layer is arranged on the second surface. The first active material layer is provided with a first groove. Part of the surface of the first surface is exposed to the first groove. At least part of the projection of the first groove along a first direction overlaps the second active material layer. Along the first direction, part of the first tab, the first connecting piece and part of the surface of the first surface exposed to the first groove are sequentially stacked, and the first connecting piece is welded to the first tab and the first current collector. The melting point of the first connecting piece is lower than the melting point of the first tab. The secondary battery is welded to the first tab and the first current collector through the first connecting piece, which is conducive to improving the energy density of the secondary battery.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of energy storage, and particularly relates to a secondary battery, a power utilization device, and a preparation method of an electrode sheet. BACKGROUND

[0002] For the existing secondary battery, the structure (MMT) of welding the tab in the middle of the electrode sheet is a common structure for connecting the current collector and the tab. When welding the current collector and the tab, if the ultrasonic welding method is used, the active material layer on both sides of the current collector along the thickness direction needs to be slotted in order to facilitate the cooperation of the welding head and the welding seat of the ultrasonic welding machine. This slotting method has a large capacity loss for the electrode sheet. If the laser welding method is used, the active material layer on only one surface of the current collector along the thickness direction can be slotted. However, the active material layer on the opposite side of the slot is easy to lose capacity under the influence of the high temperature generated during laser welding. Therefore, compared with ultrasonic welding, although laser welding only needs to slot the active material layer on one side of the current collector, the capacity of the secondary battery is not obviously improved. On this basis, for the secondary battery with multiple tabs connected on the same electrode sheet, the adverse effects of ultrasonic welding and laser welding on the capacity of the secondary battery will be further amplified. SUMMARY

[0003] In view of the above situation, it is necessary to provide a secondary battery, a power utilization device, and a preparation method of an electrode sheet, which can improve the energy density of the secondary battery.

[0004] A first aspect of an embodiment of the present application provides a secondary battery, comprising a first tab, a first electrode sheet, and a first connecting piece. The first electrode sheet comprises a first current collector, a first active material layer, and a second active material layer. The first current collector comprises a first surface and a second surface oppositely arranged along a first direction, the first direction being the thickness direction of the first electrode sheet. The first active material layer is arranged on the first surface, and the second active material layer is arranged on the second surface. The first active material layer is provided with a first slot, which penetrates the first active material layer along the first direction, so that part of the surface of the first surface is exposed to the first slot, and at least part of the projection of the first slot along the first direction overlaps the second active material layer. Along the first direction, part of the first tab, the first connecting piece, and the part of the surface of the first surface exposed to the first slot are sequentially stacked, and the first connecting piece welds the first tab and the first current collector. The melting point of the first connecting piece is lower than the melting point of the first tab.

[0005] In this secondary battery, the melting point of the first connecting piece is lower than the melting point of the first tab. Compared with the scheme of directly welding the first tab to the first current collector, welding the first tab and the first current collector through the first connecting piece is conducive to reducing the energy required in the welding process, thereby reducing the possibility of deactivation of the active material of the part of the second active material layer corresponding to the first slot along the first direction, and further improving the energy density of the secondary battery.

[0006] In an optional embodiment of the present application, the thickness of the first connecting member in the first direction is less than the thickness of the first active material layer in the first direction, so that part of the first tab is accommodated in the first groove. In this way, it is beneficial to reduce the impact of the thickness of the first tab on the thickness of the secondary battery.

[0007] In an optional embodiment of the present application, in the first direction, the thickness of the first connecting member is T1, 5 μm≤T1≤20 μm. T1≥5 μm is set, so that the thickness of the first connecting member is not too thin, which is beneficial to improve the stability of the connection between the first tab and the first current collector; T1≤20 μm is set, so that the thickness of the first connecting member is not too thick, which is beneficial to reduce the impact of the setting of the first connecting member on the thickness of the electrode assembly, so as to reduce the impact on the energy density of the secondary battery.

[0008] In an optional embodiment of the present application, the first tab is provided with a second groove, the opening of the second groove is exposed to part of the surface of the first groove in the first direction towards the first face, and at least part of the first connecting member is accommodated in the second groove. In this way, it is beneficial to reduce the impact of the setting of the first connecting member on the thickness of the electrode assembly.

[0009] In an optional embodiment of the present application, the secondary battery further comprises a second connecting member, which is located between the first tab and the part of the surface of the first face exposed to the first groove in the first direction, the projection of the first connecting member and the second connecting member in the first direction is in contact or apart, and the second connecting member bonds the first tab and the first current collector. In this way, before the first connecting member melts and welds the first tab and the first current collector, the second connecting member bonds the first tab and the first current collector, which can preliminarily fix the relative position of the first tab and the first current collector, reduce the possibility of relative movement of the first tab and the first current collector during welding, and improve the welding quality; and the second connecting member bonds the first tab and the first current collector, which is beneficial to improve the stability of the connection between the first tab and the first current collector.

[0010] In an optional embodiment of the present application, the second connecting member is annular and surrounds the first connecting member. In this way, it is beneficial to isolate the first connecting member from the electrolyte, so as to reduce the possibility of the electrolyte contacting the first connecting member.

[0011] In an optional embodiment of the present application, the secondary battery comprises a first bonding member, which is bonded to the first active material layer, and the first bonding member covers the opening of the first groove in the first direction and part of the first tab. The first bonding member is set, which is beneficial to reduce the possibility of the burr of the first tab piercing the separator and causing internal short circuit of the secondary battery.

[0012] In an optional embodiment of the present application, the thickness of the first adhesive along the first direction is T2, and 5 μm≤T2≤20 μm. T2≥5 μm is provided so that the thickness of the first adhesive along the first direction is not too small, which is conducive to reducing the possibility that the burr of the first tab pierces the separator and causes internal short circuit of the secondary battery; and T2≤20 μm is provided so that the thickness of the first adhesive along the first direction is not too large, which is conducive to reducing the influence of the first adhesive on the thickness of the electrode assembly.

[0013] In an optional embodiment of the present application, the secondary battery further comprises a second tab and a separator, the first tab, the separator and the second tab are sequentially stacked along the first direction, the second tab comprises a second current collector and a third active material layer which are sequentially stacked, and the third active material layer is located on the side of the second current collector which faces the first tab along the first direction. The secondary battery comprises a second adhesive, the second adhesive is bonded to the third active material layer, and the projection of the second adhesive along the first direction covers part of the first tab. On the basis of the first adhesive, the second adhesive is further provided, which is conducive to further reducing the possibility that the edge burr of the first tab pierces the separator and causes internal short circuit of the secondary battery.

[0014] In an optional embodiment of the present application, the thickness of the second adhesive along the first direction is T3, and 5 μm≤T3≤20 μm. T3≥5 μm is provided so that the thickness of the second adhesive along the first direction is not too small, which is conducive to reducing the possibility that the burr of the first tab pierces the separator and causes internal short circuit of the secondary battery; and T3≤20 μm is provided so that the thickness of the second adhesive along the first direction is not too large, which is conducive to reducing the influence of the second adhesive on the thickness of the electrode assembly.

[0015] In an optional embodiment of the present application, the secondary battery further comprises a second tab, the first tab and the second tab are stacked along the first direction, the first tab is a positive tab, the second tab is a negative tab, the width of the first tab along the second direction is smaller than the width of the second tab along the second direction, the second direction is perpendicular to the first direction, and the first tab is arranged on one side of the first tab along the second direction. The edge of the second tab along the second direction and on the same side as the first tab protrudes beyond the first tab; the first tab comprises a first part, the projection of the first part along the first direction is outside the projection area of the first tab and overlaps the projection area of the second tab. The secondary battery further comprises a third adhesive, the third adhesive is bonded to and covers the surface of the first part which faces the second tab. In this way, the possibility that the burr of the first tab pierces the separator and is short-circuited with the negative tab is reduced.

[0016] In an optional embodiment of the present application, the melting point of the first connecting piece is a, 300℃≤a≤400℃. If the melting point is too high, the energy required for welding the first connecting piece is too high, which causes the active material on the back of the tab to be deactivated more seriously. If the melting point is too low, the first connecting piece is easily welded through, which reduces the product yield.

[0017] In an optional embodiment of the present application, the first tab is a positive tab, the melting point of the first connecting piece is a, the melting point of the first tab is b, and 200℃≤b-a≤400℃; and / or, the first tab is a negative tab, the melting point of the first tab is c, and 1000℃≤c-a≤1300℃.

[0018] When the first tab is a positive tab, the melting point of the positive tab is lower, 200℃≤b-a≤400℃, which can make the energy required for welding the first connecting piece relative to the first tab less, and can ensure that the melting point of the first connecting piece is not too small, which causes the welding process to be easily welded through.

[0019] When the first tab is a negative tab, the melting point is higher, 1000℃≤c-a≤1300℃, which can make the energy required for welding the first connecting piece relative to the first tab less, and can ensure that the melting point of the first connecting piece is not too small, which causes the welding process to be easily welded through.

[0020] The second aspect of the embodiments of the present application provides a power utilization device, which comprises the secondary battery according to any one of the preceding embodiments.

[0021] The third aspect of the embodiments of the present application provides a method for preparing an electrode sheet, which comprises the following steps:

[0022] Take a first electrode sheet, the first electrode sheet comprising a first current collector, a first active material layer and a second active material layer, the first current collector comprising a first surface and a second surface oppositely arranged along a first direction, the first active material layer being arranged on the first surface, and the second active material layer being arranged on the second surface, the first active material layer being provided with a first groove, the projection of the first groove being at least partially located within the projection area of the second active material layer along the first direction, the first groove penetrating through the first active material layer along the first direction, so that part of the surface of the first surface is exposed to the first groove; the first direction being the thickness direction of the first electrode sheet;

[0023] Take a metal foil, the melting point of the metal foil being lower than the melting point of the first tab;

[0024] Clamp the metal foil between the first tab and the part of the surface of the first surface exposed to the first groove;

[0025] Heat the metal foil to weld the first tab and the first current collector.

[0026] In one optional embodiment of the present application, the method of manufacturing the tab includes the steps of:

[0027] Before the metal foil is sandwiched between the first tab and the portion of the surface of the first face exposed in the first groove, the second connecting member is attached to the first tab, and the metal foil is attached to the second connecting member. BRIEF DESCRIPTION OF DRAWINGS

[0028] Figure 1 is a structural schematic diagram of a secondary battery in one embodiment of the present application.

[0029] Figure 2 is a cross-sectional structural schematic diagram of II-II in Figure 1

[0030] Figure 3 is a cross-sectional structural schematic diagram of III-III in Figure 2

[0031] Figure 4 is a cross-sectional structural schematic diagram of B in Figure 2

[0032] Figure 5 is a structural schematic diagram of the first tab in a flattened state in one embodiment of the present application.

[0033] Figure 6 is a cross-sectional structural schematic diagram of VI-VI in Figure 5

[0034] Figure 7 is a partial structural schematic diagram of a secondary battery in one embodiment of the present application.

[0035] Figure 8 is a cross-sectional structural schematic diagram of VIII-VIII in Figure 1

[0036] Figure 9 is a structural schematic diagram of the first tab in a flattened state in one embodiment of the present application.

[0037] Figure 10 is a structural schematic diagram of an electrical device in one embodiment of the present application.

[0038] MAIN ELEMENT SYMBOL EXPLANATION

[0039] Secondary battery 1000

[0040] Electrode assembly 100

[0041] First tab 10

[0042] First current collector 11

[0043] First face 111 ​​​​​

[0044] second surface 112

[0045] first active material layer 12

[0046] first groove 121

[0047] second active material layer 13

[0048] second tab 20

[0049] second current collector 21

[0050] third surface 211

[0051] fourth surface 212

[0052] third active material layer 22

[0053] third groove 221

[0054] fourth active material layer 23

[0055] separator film 30

[0056] first tab 40

[0057] second groove 41

[0058] first portion 42

[0059] second tab 50

[0060] first connecting member 60

[0061] second connecting member 70

[0062] first adhesive member 81

[0063] second adhesive member 82

[0064] third adhesive member 83

[0065] third connecting member 90

[0066] housing 200

[0067] electric device 10000

[0068] first direction X

[0069] second direction Y

[0070] The following detailed description will further explain the present application in conjunction with the above-mentioned drawings. DETAILED DESCRIPTION

[0071] The technical solutions in the embodiments of the present application will be described below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only some of the embodiments of the present application, but not all the embodiments of the present application.

[0072] It should be noted that when an element is considered to be "connected" to another element, it can be directly connected to the other element or can exist simultaneously with a middle element. When an element is considered to be "arranged" on another element, it can be directly arranged on the other element or can exist simultaneously with a middle element. The term "and / or" used herein includes any and all combinations of one or more related listed items.

[0073] 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 the present application belongs. 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.

[0074] In the description of the embodiments of the present application, the technical terms "first", "second", and the like are only used to distinguish different objects, and cannot be understood as indicating or implying relative importance or implicitly indicating the number, specific order or primary and secondary relationship of the indicated technical features. In the description of the embodiments of the present application, the meaning of "a plurality of" is two or more, unless otherwise explicitly specified.

[0075] In the description of the embodiments of the present application, the term "vertical" is used to describe the ideal state between two components. In the actual production or use state, there can be an approximate vertical state between the two components. The two components described as "vertical" can not be an absolute straight line, plane, but can be approximately straight or planar, and the overall extension direction is a straight line or a plane from a macroscopic point of view. The components can be considered as "straight line" or "plane".

[0076] Reference to "embodiments" herein means that the specific features, structures, or properties described in conjunction with the embodiments can be included in at least one embodiment of the present application. The phrase appears in various places in the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment to other embodiments. In the case of no conflict, each embodiment in the present application can be combined with each other.

[0077] Embodiments of the present application provide a secondary battery, comprising a first tab, a first tab sheet and a first connecting piece. The first tab sheet comprises a first current collector, a first active material layer and a second active material layer. The first current collector comprises a first surface and a second surface oppositely arranged along a first direction, the first direction being a thickness direction of the first tab sheet, the first active material layer being arranged on the first surface, and the second active material layer being arranged on the second surface. The first active material layer is provided with a first groove, the first groove penetrating the first active material layer along the first direction, so that part of the surface of the first surface is exposed to the first groove, and at least part of the projection of the first groove along the first direction overlaps the second active material layer. Along the first direction, part of the first tab, the first connecting piece and the part of the surface of the first surface exposed to the first groove are sequentially stacked, and the first connecting piece welds the first tab and the first current collector, and the melting point of the first connecting piece is lower than the melting point of the first tab.

[0078] In the secondary battery, the melting point of the first connecting piece is lower than the melting point of the first tab, and compared with the scheme of directly welding the first tab to the first current collector, welding the first tab and the first current collector through the first connecting piece is conducive to reducing the energy required in the welding process, thereby reducing the possibility of deactivation of the active material of the part of the second active material layer corresponding to the first groove along the first direction, and further improving the energy density of the secondary battery.

[0079] The embodiments of the present application will be further described below with reference to the accompanying drawings.

[0080] As shown in Figure 1 and Figure 2 Embodiments of the present application provide a secondary battery 1000, comprising a secondary battery 1000, comprising an electrode assembly 100, a housing 200, a first tab 40 and a second tab 50. The electrode assembly 100 is received in the housing 200, the first tab 40 is electrically connected to the electrode assembly 100 and extends out of the housing 200, and the second tab 50 is electrically connected to the electrode assembly 100 and extends out of the housing 200.

[0081] In some embodiments, as shown in Figure 2 The electrode assembly 100 comprises a first tab sheet 10, a second tab sheet 20 and a separator 30, and the separator 30 is arranged between the first tab sheet 10 and the second tab sheet 20.

[0082] In some embodiments, as shown in Figure 2 The first tab sheet 10, the separator 30 and the second tab sheet 20 are stacked along a first direction X and then wound to form a wound structure. The first direction X is a thickness direction of the first tab sheet 10.

[0083] In some embodiments, as shown in Figure 2 and Figure 3As shown, the first tab 10 includes a first current collector 11, a first active material layer 12, and a second active material layer 13. The first current collector 11 includes a first surface 111 and a second surface 112 oppositely arranged along the first direction X, the first active material layer 12 is disposed on the first surface 111, and the second active material layer 13 is disposed on the second surface 112.

[0084] In some embodiments, as shown in Figure 2 and Figure 4 As shown, the second tab 20 includes a second current collector 21, a third active material layer 22, and a fourth active material layer 23. The second current collector 21 includes a third surface 211 and a fourth surface 212 oppositely arranged along the first direction X, the third active material layer 22 is disposed on the third surface 211, and the fourth active material layer 23 is disposed on the fourth surface 212.

[0085] In some embodiments, one of the first tab 10 and the second tab 20 is a positive tab, and the other is a negative tab. When the first tab 10 is a positive tab, the first current collector 11 is a positive current collector, the first active material layer 12 and the second active material layer 13 are positive active material layers, the first lug 40 is a positive lug, the second current collector 21 is a negative current collector, the third active material layer 22 and the fourth active material layer 23 are negative active material layers, and the second lug 50 is a negative lug; when the first tab 10 is a negative tab, the first current collector 11 is a negative current collector, the first active material layer 12 and the second active material layer 13 are negative active material layers, the first lug 40 is a negative lug, the second current collector 21 is a positive current collector, the third active material layer 22 and the fourth active material layer 23 are positive active material layers, and the second lug 50 is a positive lug.

[0086] In some embodiments, the positive current collector is a metal layer. As an illustrative example, the positive current collector can be a metal layer including at least one of aluminum, nickel, tantalum, titanium, such as an aluminum foil.

[0087] In some embodiments, the positive active material layer includes a positive active material, and the positive active material includes at least one of lithium cobaltate, lithium nickel cobalt manganese acid, lithium nickel cobalt aluminum acid, lithium iron phosphate, lithium manganese iron phosphate, or lithium manganese acid.

[0088] In some embodiments, the negative current collector is a metal layer. As an illustrative example, the negative current collector can be a metal layer including at least one of copper, nickel, tantalum, titanium, such as a copper foil.

[0089] In some embodiments, at least one of the positive current collector and the negative current collector is a composite current collector.

[0090] In some embodiments, the negative active material layer includes a negative active material, and the negative active material includes at least one of graphite, hard carbon, soft carbon, silicon, silicon-oxygen material, silicon-carbon material.

[0091] In some embodiments, the isolation film 30 is a polyethylene film, a polypropylene film, a polyester film, or a polyimide film, or the like, which is capable of insulation.

[0092] In some embodiments, the secondary battery 1000 further includes an electrolyte (not shown in the figure), which is accommodated in the housing 200.

[0093] In some embodiments, the electrolyte includes an electrolyte salt. The electrolyte salt includes at least one of an organic lithium salt or an inorganic lithium salt.

[0094] In some embodiments, the electrolyte salt includes, but is not limited to, at least one of lithium hexafluorophosphate (LiPF6), lithium bis-trifluoromethanesulfonimide LiN(CF3SO2)2 (LiTFSI), lithium bis(fluorosulfonyl)imide Li(N(SO2F)2) (LiFSI), lithium hexafluorocerate (LiCsF6), lithium perchlorate (LiClO4), or lithium trifluoromethanesulfonate (LiCF3SO3).

[0095] In some embodiments, as shown in FIG. 1, the first active material layer 12 is provided with a first groove 121, which penetrates the first active material layer 12 along the first direction X, so that part of the surface of the first face 111 is exposed to the first groove 121, and at least part of the projection of the first groove 121 along the first direction X overlaps the second active material layer 13. The secondary battery 1000 further includes a first connecting piece 60, which is sequentially stacked with part of the first tab 40, the first connecting piece 60, and the part of the surface of the first face 111 exposed to the first groove 121 along the first direction X, and the first connecting piece 60 welds the first tab 40 and the first current collector 11, and the melting point of the first connecting piece 60 is lower than that of the first tab 40. Figure 3 In some embodiments, as shown in FIG. 1, the first active material layer 12 is provided with a first groove 121, which penetrates the first active material layer 12 along the first direction X, so that part of the surface of the first face 111 is exposed to the first groove 121, and at least part of the projection of the first groove 121 along the first direction X overlaps the second active material layer 13. The secondary battery 1000 further includes a first connecting piece 60, which is sequentially stacked with part of the first tab 40, the first connecting piece 60, and the part of the surface of the first face 111 exposed to the first groove 121 along the first direction X, and the first connecting piece 60 welds the first tab 40 and the first current collector 11, and the melting point of the first connecting piece 60 is lower than that of the first tab 40.

[0096] In some embodiments, as shown in FIG. 1, the first active material layer 12 is provided with a first groove 121, which penetrates the first active material layer 12 along the first direction X, so that part of the surface of the first face 111 is exposed to the first groove 121, and at least part of the projection of the first groove 121 along the first direction X overlaps the second active material layer 13. The secondary battery 1000 further includes a first connecting piece 60, which is sequentially stacked with part of the first tab 40, the first connecting piece 60, and the part of the surface of the first face 111 exposed to the first groove 121 along the first direction X, and the first connecting piece 60 welds the first tab 40 and the first current collector 11, and the melting point of the first connecting piece 60 is lower than that of the first tab 40.

[0097] In some embodiments, as shown in FIG. 1, the first active material layer 12 is provided with a first groove 121, which penetrates the first active material layer 12 along the first direction X, so that part of the surface of the first face 111 is exposed to the first groove 121, and at least part of the projection of the first groove 121 along the first direction X overlaps the second active material layer 13. The secondary battery 1000 further includes a first connecting piece 60, which is sequentially stacked with part of the first tab 40, the first connecting piece 60, and the part of the surface of the first face 111 exposed to the first groove 121 along the first direction X, and the first connecting piece 60 welds the first tab 40 and the first current collector 11, and the melting point of the first connecting piece 60 is lower than that of the first tab 40.

[0098] In some embodiments, the material of the first connecting member 60 is a metal material.

[0099] In some embodiments, the material of the first connecting member 60 includes at least one of a tin alloy, a bismuth alloy, or an indium alloy. The tin alloy includes, but is not limited to, at least one of a tin-bismuth alloy or a tin-bismuth-copper alloy.

[0100] In some embodiments, as shown in FIG. 1A, the thickness of the first connecting member 60 along the first direction X is less than the thickness of the first active material layer 12 along the first direction X, so that part of the first tab 40 is accommodated in the first groove 121. In this way, it is beneficial to reduce the impact of the thickness of the first tab 40 on the thickness of the secondary battery 1000. Figure 3

[0101] In some embodiments, as shown in FIG. 1A, the thickness of the first connecting member 60 is T1, and 5 pm ≤ T1 ≤ 20 pm. By setting T1 ≥ 5 pm, the thickness of the first connecting member 60 is not too thin, which is beneficial to improve the stability of the connection between the first tab 40 and the first current collector 11. By setting T1 ≤ 20 pm, the thickness of the first connecting member 60 is not too thick, which is beneficial to reduce the impact of the setting of the first connecting member 60 on the thickness of the electrode assembly 100, so as to reduce the impact on the energy density of the secondary battery 1000. Figure 3

[0102] In some embodiments, the thickness of the first connecting member 60 can be measured by an optical measuring machine (OMM). Specifically, when measuring, a cross section of the first tab 10 and the first tab 40 along the first direction X can be made, and when observing, the observation angle is perpendicular to the cross section. Since part of the first connecting member 60 penetrates into the first tab 40 and part of the first connecting member 60 penetrates into the first current collector 11, the distance between the two surfaces of the first tab 40 and the first current collector 11 facing each other can be measured as the thickness of the first connecting member 60.

[0103] In some embodiments, as shown in FIG. 1A and FIG. 1B, the first tab 40 is provided with a second groove 41, and the opening of the second groove 41 is exposed to the part of the surface of the first tab 40 along the first direction X towards the first surface 111, and at least part of the first connecting member 60 is accommodated in the second groove 41. In this way, it is beneficial to reduce the impact of the setting of the first connecting member 60 on the thickness of the electrode assembly 100. Figure 5 Figure 6

[0104] ​​​​It should be noted that, in the embodiment where the first tab 40 has a second groove 41, when measuring the thickness of the first connector 60, if the first connector 60 contacts the bottom wall of the second groove 41 along the first direction, the distance from the bottom wall of the second groove 41 along the first direction to the first collector 11 can be measured as the thickness of the first connector 60. If the first connector 60 is separated from the bottom wall of the second groove 41 along the first direction, the distance from the outermost edge of the first connector along the first direction to the first collector 11 can be measured as the thickness of the first connector 60.

[0105] In some embodiments, such as Figure 3 As shown, the secondary battery 1000 also includes a second connector 70. Along the first direction X, the second connector 70 is located between the first tab 40 and the portion of the first surface 111 exposed in the first groove 121. The second connector 70 bonds the first tab 40 and the first current collector 11. Thus, before the first connector 60 heat-melts and welds the first tab 40 and the first current collector 11, the second connector 70 bonds the first tab 40 and the first current collector 11, which can initially fix the relative position of the first tab 40 and the first current collector 11, reducing the possibility of relative movement between the first tab 40 and the first current collector 11 during the welding process and improving the welding quality. Furthermore, the second connector 70 bonding the first tab 40 and the first current collector 11 helps to improve the stability of the connection between the first tab 40 and the first current collector 11.

[0106] In some embodiments, the second connector 70 is a hot melt adhesive. Before hot-melting the first connector 60, the hot melt adhesive can be heated to activate it, thereby initially bonding the first tab 40 to the first current collector 11. This reduces the possibility of movement between the first tab 40 and the first current collector 11 during welding, thus improving welding quality. Furthermore, the hot melt adhesive bonding of the first tab 40 and the first current collector 11 improves the stability of their connection.

[0107] In some embodiments, as an example, the hot melt adhesive material includes at least one of styrene-isoprene-styrene block copolymer, ethylene-vinyl acetate copolymer, polyurethane, polypropylene, or polyethylene.

[0108] In some embodiments, the second connector 70 is a hot melt pressure-sensitive adhesive. The hot melt pressure-sensitive adhesive includes a hot melt adhesive layer, a substrate layer, and a pressure-sensitive adhesive layer stacked sequentially. The pressure-sensitive adhesive layer is bonded to the first tab 40, and the hot melt adhesive layer is bonded to the first current collector 11. Before hot melting the first connector 60, the second connector 70 can be heated to activate the hot melt adhesive layer.

[0109] In some embodiments, the hot melt adhesive layer comprises styrene-isoprene-styrene block copolymer; the substrate layer comprises at least one of polyethylene terephthalate, polyimide or polypropylene; and the material of the pressure sensitive adhesive layer comprises at least one of polymethyl methacrylate (PMMA, commonly known as acrylic), polypropylene (PP), polyethylene (PE) or polyamide.

[0110] In some embodiments, the projection of the first connecting member 60 along the first direction X meets (as shown in Figure 3 ) or is separated from the projection of the second connecting member 70 along the first direction X. In this way, the first connecting member 60 and the second connecting member 70 do not overlap in the first direction X, which is conducive to reducing the impact of the arrangement of the second connecting member 70 on the thickness of the secondary battery 1000.

[0111] Contact of the electrolyte with the first connecting member 60 can affect the cycle capacity retention rate of the secondary battery 1000. Specifically, taking tin as the material of the first connecting member 60 as an example, when the first tab 40 is a negative tab, if the electrolyte contacts the first connecting member 60, lithium ions are easily reduced and can easily react with the first connecting member 60 to form an alloy; when the first tab 40 is a positive tab, if the electrolyte contacts the first connecting member 60, the first connecting member 60 is easily oxidized to a divalent ion and enters the electrolyte, both of which can affect the cycle capacity retention rate of the secondary battery 1000. In some embodiments, as shown in Figure 7 , the second connecting member 70 is annular and surrounds the first connecting member 60. In this way, it is conducive to isolating the first connecting member 60 from the electrolyte to reduce the possibility of the electrolyte contacting the first connecting member 60.

[0112] In some embodiments, as shown in Figure 3 , the secondary battery 1000 comprises a first adhesive member 81, the first adhesive member 81 is bonded to the first active material layer 12, and the first adhesive member 81 covers the opening of the first groove 121 facing the first direction X and part of the first tab 40. The arrangement of the first adhesive member 81 is conducive to reducing the possibility of the burr of the first tab 40 piercing the separator 30 to cause internal short circuit of the secondary battery 1000.

[0113] In some embodiments, as shown in Figure 3 , the thickness of the first adhesive member 81 along the first direction X is T2, and 5 μm≤T2≤20 μm. The arrangement of T2≥5 μm is to prevent the thickness of the first adhesive member 81 along the first direction X from being too small, which is conducive to reducing the possibility of the burr of the first tab 40 piercing the separator 30 to cause internal short circuit of the secondary battery 1000; the arrangement of T2≤20 μm is to prevent the thickness of the first adhesive member 81 along the first direction X from being too large, which is conducive to reducing the impact of the arrangement of the first adhesive member 81 on the thickness of the electrode assembly 100.

[0114] The thickness T2 of the first adhesive 81 can be measured by using a micrometer.

[0115] In some embodiments, as shown in FIG. 1, the third active material layer 22 of the second tab 20 is located on a side of the second current collector 21 facing the first tab 10 along the first direction X, and the secondary battery 1000 further comprises a second adhesive 82 adhering the third active material layer 22, a projection of the second adhesive 82 along the first direction X covering part of the first tab 40. Figure 3 In some embodiments, as shown in FIG. 1, the third active material layer 22 of the second tab 20 is located on a side of the second current collector 21 facing the first tab 10 along the first direction X, and the secondary battery 1000 further comprises a second adhesive 82 adhering the third active material layer 22, a projection of the second adhesive 82 along the first direction X covering part of the first tab 40.

[0116] In some embodiments, as shown in FIG. 1, the third active material layer 22 of the second tab 20 is located on a side of the second current collector 21 facing the first tab 10 along the first direction X, and the secondary battery 1000 further comprises a second adhesive 82 adhering the third active material layer 22, a projection of the second adhesive 82 along the first direction X covering part of the first tab 40. Figure 3 In some embodiments, as shown in FIG. 1, the third active material layer 22 of the second tab 20 is located on a side of the second current collector 21 facing the first tab 10 along the first direction X, and the secondary battery 1000 further comprises a second adhesive 82 adhering the third active material layer 22, a projection of the second adhesive 82 along the first direction X covering part of the first tab 40.

[0117] The thickness T3 of the second adhesive 82 can be measured by using a micrometer.

[0118] In some embodiments, the first tab 10 is a negative tab, and the second tab 20 is a positive tab. Along the first direction X, the projection of the second adhesive 82 covers the projection of the first adhesive 81. In this way, the CB (Cell Balance, ratio of the capacity of the unit area of the negative tab to the capacity of the unit area of the positive tab) of the positive and negative tabs can be increased, and the possibility of lithium precipitation of the electrode assembly 100 during the cycle process can be reduced.

[0119] In some embodiments, the first tab 10 is a positive tab, and the second tab 20 is a negative tab. Along the first direction X, the projection of the second adhesive 82 covers the projection of the third adhesive 83. In this way, the CB of the positive and negative tabs can be increased, and the possibility of lithium precipitation of the electrode assembly 100 during the cycle process can be reduced.

[0120] In some embodiments, the melting point of the first connecting piece 60 is a, and 300℃≤a≤400℃. If the melting point is too high, the energy required for welding the first connecting piece 60 is too high, which causes the active material on the back of the tab to be inactivated more seriously. If the melting point is too low, the first connecting piece 60 is easily welded through, which leads to a decrease in product yield.

[0121] In some embodiments, the first tab 40 is a positive tab, the melting point of the first connector 60 is a, the melting point of the first tab 40 is b, and 200℃≤ba≤400℃; and / or, the first tab 40 is a negative tab, and the melting point of the first tab 40 is c, and 1000℃≤ca≤1300℃.

[0122] When the first tab 40 is the positive tab 40, the positive tab 40 has a low melting point, 200℃≤ba≤400℃, which means that the welding energy required for the first connector 60 is less than that required for the first tab, and also ensures that the melting point of the first connector 60 is not too low, which would make it easy to be welded through during the welding process.

[0123] When the first tab 40 is the negative tab, it has a high melting point of 1000℃≤ca≤1300℃. This means that the welding energy required for the first connector 60 is less than that required for the first tab 40, and it also ensures that the melting point of the first connector 60 is not too low, which would make it easy to burn through during the welding process.

[0124] In some embodiments, such as Figure 8 As shown, the first electrode 10 is the positive electrode, and the second electrode 20 is the negative electrode. The width of the first electrode 10 along the second direction Y is smaller than the width of the second electrode 20 along the second direction Y, and the second direction Y is perpendicular to the first direction X. The first tab 40 is disposed on one side of the first electrode 10 along the second direction Y; the edge of the second electrode 20 along the second direction Y and on the same side as the first tab 40 extends beyond the first electrode 10. This is beneficial for increasing the CB of the positive and negative electrodes, and for reducing the possibility of lithium plating occurring in the electrode assembly 100 during cycling.

[0125] In some embodiments, such as Figure 8 and Figure 9 As shown, the first tab 40 includes a first portion 42, the projection of which along the first direction X is outside the projection area of ​​the first electrode 10 and overlaps with the projection area of ​​the second electrode 20. The secondary battery 1000 also includes a third adhesive member 83, which adheres to and covers the surface of the first portion 42 facing the second electrode 20. This helps to reduce the possibility of burrs on the first tab 40 puncturing the separator 30 and short-circuiting with the negative electrode.

[0126] In some embodiments, at least one of the first adhesive 81, the second adhesive 82, and the third adhesive 83 is adhesive tape.

[0127] In some embodiments, the adhesive tape includes a substrate layer and an adhesive layer.

[0128] In some embodiments, the substrate layer may be selected from polyethylene terephthalate, co-extruded polypropylene, oriented polystyrene, thermoplastic polyurethane, polylactic acid, polyolefin, and polyimide.

[0129] 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.

[0130] In some embodiments, such as Figure 4 As shown, the third active material layer 22 has a third groove 221 along the first direction X, which penetrates the fourth active material layer 23, such that a portion of the surface of the fourth surface 212 is exposed in the third groove 221. At least a portion of the projection of the third groove 221 along the first direction X overlaps with the third active material layer 22. The secondary battery 1000 also includes a third connector 90. Along the first direction X, a portion of the second tab 50, the third connector 90, and the portion of the surface of the fourth surface 212 exposed in the third groove 221 are sequentially stacked. The third connector 90 is welded to the second tab 50 and the second current collector 21. The melting point of the third connector 90 is lower than the melting point of the second tab 50. The melting point of the third connector 90 is lower than that of the second tab 50. Compared with the solution of directly welding the second tab 50 to the second current collector 21, welding the second tab 50 and the second current collector 21 through the third connector 90 helps to reduce the energy required for the welding process, thereby reducing the possibility of deactivation of the active material material of the third active material layer 22 along the first direction X and the part corresponding to the third groove 221, and thus improving the energy density of the secondary battery 1000.

[0131] In some embodiments, the third connector 90 is made of metal.

[0132] In some embodiments, the material of the third connector 90 includes at least one of a tin alloy, a bismuth alloy, or an indium alloy. The tin alloy includes, but is not limited to, at least one of a tin-bismuth alloy or a tin-bismuth-copper alloy.

[0133] like Figure 10 As shown, embodiments of this application also provide an electrical device 10000, which includes a secondary battery 1000 as described in any of the foregoing embodiments.

[0134] In some embodiments, the electrical device 10000 includes, but is not limited to, a mobile phone, a laptop computer, a tablet computer, a power tool, an electric toy, and an electronic cigarette.

[0135] Embodiments of this application also provide a method for preparing an electrode sheet, the method comprising the following steps:

[0136] Take a first tab 10, the first tab 10 comprising a first current collector 11, a first active material layer 12 and a second active material layer 13, the first current collector 11 comprising a first surface 111 and a second surface 112 oppositely arranged along a first direction X, the first active material layer 12 being arranged on the first surface 111, and the second active material layer 13 being arranged on the second surface 112, the first active material layer 12 being provided with a first groove 121, along the first direction X, at least part of a projection of the first groove 121 being located within a projection area of the second active material layer 13, the first groove 121 penetrating the first active material layer 12 along the first direction X, so that part of the surface of the first surface 111 is exposed in the first groove 121;

[0137] Take a metal foil, the melting point of the metal foil being lower than the melting point of the first tab 40;

[0138] Clamp the metal foil between the first tab 40 and the part of the surface of the first surface 111 exposed in the first groove 121;

[0139] Thermally fuse the metal foil, so that the first tab 40 is welded to the first current collector 11.

[0140] In some embodiments, the method for preparing the tab further comprises the following steps:

[0141] Before clamping the metal foil between the first tab 40 and the part of the surface of the first surface 111 exposed in the first groove 121, bond the second connecting piece 70 to the first tab 40, and bond the metal foil to the second connecting piece 70.

[0142] In some embodiments, the thickness of the metal foil before thermal fusion is 30 μm to 50 μm.

[0143] In some embodiments, in the step of thermally fusing the metal foil, the metal foil is thermally fused by means of laser or heating block heating.

[0144] To verify the effect of the scheme in the embodiments of the present application, the inventors conducted the following experiments, which included two groups of comparative examples and seven groups of examples, each group of comparative example and each group of example comprising 20 secondary batteries.

[0145] The preparation process of the secondary battery in Example 1 comprises the following steps:

[0146] (1) Preparation of the positive electrode sheet: mix active material lithium cobalt oxide (LiCoO2), conductive carbon black (Super P), CNT (carbon nanotube), and polyvinylidene fluoride (PVDF) in a weight ratio of 97.5:0.5:0.5:1.5, add N-methyl pyrrolidone (NMP) as a solvent, and adjust to a solid content of 75 wt% of the positive electrode active material, and mix uniformly for standby. Use an aluminum foil with a thickness of 8 μm as the positive electrode current collector. Tape the adhesive paper at the position where the groove is to be formed on the positive electrode current collector, uniformly coat the above active material on one side of the positive electrode current collector in the thickness direction using a slot coater, and then dry at 90°C to obtain a positive electrode sheet with a positive electrode active material layer coated on one side. After drying, remove the adhesive paper to form a groove (corresponding to one of the first groove 121 and the third groove 221). Then repeat the coating step on the other side of the positive electrode current collector in the thickness direction without taping the adhesive paper to obtain a positive electrode sheet with positive electrode active material layers coated on both sides. Then, the coated positive electrode sheet is cold-pressed. After cold-pressing, the thickness of each positive electrode active material layer is 40 μm. Take a positive electrode tab and a metal foil (corresponding to one of the first connecting member 60 and the third connecting member 90), attach the metal foil to the surface of the positive electrode tab, and bond a pressure-sensitive adhesive layer of a hot melt pressure-sensitive adhesive to the positive electrode tab and the metal foil to fix the metal foil to the positive electrode tab. Place the positive electrode tab on the surface of the positive electrode current collector exposed to the groove, and activate the hot melt adhesive layer to preliminarily bond the positive electrode tab and the positive electrode current collector. Then, heat the metal foil and cool it again to weld the positive electrode tab to the surface of the positive electrode current collector exposed to the groove.

[0147] (2) Preparation of the negative electrode sheet: The active material 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, deionized water was added as a solvent, and a negative electrode active material with a weight percentage of 50wt% was prepared and stirred uniformly for standby use. A copper foil with a thickness of 4μm was used as the negative electrode current collector. The above-mentioned negative electrode active material was uniformly coated on one side of the negative electrode current collector in the thickness direction using a slot coater, and then dried at 110°C to obtain a negative electrode sheet with a negative electrode active material layer coated on one side. Then the above steps were repeated on the other side of the negative electrode current collector in the thickness direction to obtain a negative electrode sheet with a negative electrode active material layer coated on both sides. Then the coated negative electrode sheet was cold-pressed. After cold-pressing, the thickness of each negative electrode active material layer was 40μm. Then, a groove (equivalent to the other of the first groove 121 and the third groove 221) was made on one negative electrode active material layer of the negative electrode sheet by laser cleaning. A negative electrode tab and a metal foil (equivalent to the other of the first connecting piece 60 and the third connecting piece 90) were taken, the metal foil was attached to the surface of the negative electrode tab, a pressure-sensitive adhesive layer of hot melt pressure-sensitive adhesive was bonded to the negative electrode tab and the metal foil to fix the metal foil to the negative electrode tab, the negative electrode tab was arranged on the surface of the negative electrode current collector exposed to the groove, the hot melt adhesive layer of the hot melt pressure-sensitive adhesive faced the negative electrode current collector, the hot melt adhesive layer was activated to preliminarily bond the negative electrode tab and the negative electrode current collector, and then the hot melt metal foil was cooled to make the negative electrode tab welded to the surface of the negative electrode current collector exposed to the groove. The thickness of the metal foil used in the preparation of the negative electrode sheet was equal to the thickness of the metal foil used in the preparation of the positive electrode sheet.

[0148] (3) Preparation of the electrolyte: In a dry argon atmosphere, first, ethylene carbonate (EC), methyl ethyl carbonate (EMC), and diethyl carbonate (DEC) were mixed in a mass ratio of EC:EMC:DEC=30:50:20 to form a base organic solvent, and then lithium salt lithium hexafluorophosphate (LiPF6) was added to the base organic solvent to dissolve and mix uniformly to obtain an electrolyte with a lithium salt concentration of 1.15mol / L.

[0149] (4) Preparation of the separator film 30: A 7μm thick polyethylene porous polymer film was used as the separator film 30.

[0150] (5) Preparation of the electrode assembly 100: The positive electrode sheet, the separator film, and the negative electrode sheet were stacked and wound in the thickness direction of the negative electrode sheet to obtain the electrode assembly 100.

[0151] (6) Assembly of the secondary battery 1000: Place the punched aluminum plastic film into the assembly jig with the pit surface facing up, and place the electrode assembly 100 into the pit, and apply an external force to press it. Then place another punched aluminum plastic film with the pit surface facing down on the electrode assembly 100, and heat seal the three edges of the two aluminum plastic films by hot pressing, and the unsealed edge is the side where the negative and positive tabs extend out of the shell. Then inject electrolyte through the unsealed edge, and go through the processes of vacuum packaging, standing, hot pressing, and shaping, and the secondary battery 1000 is obtained.

[0152] The preparation process of the secondary battery 1000 in Examples 2-6 is basically the same as that in Example 1, and the difference is that the thickness of the metal foil used in Examples 1-6 is different, and the thickness of the metal foil after hot melting and solidification is T1, which is recorded in Table 1.

[0153] The preparation method of the secondary battery 1000 in Comparative Example 1 is basically the same as that in Example 1, and the difference is that grooves are provided at positions opposite to each other along the first direction X on the two positive active material layers of the positive electrode sheet, and the positive tab is welded to the surface of the positive current collector exposed to the groove by ultrasonic welding; grooves are provided at positions opposite to each other along the first direction X on the two negative active material layers of the negative electrode sheet, and the negative tab is welded to the surface of the negative current collector exposed to the groove by ultrasonic welding.

[0154] The preparation method of the secondary battery 1000 in Comparative Example 2 is basically the same as that in Example 1, and the difference is that the positive tab is directly welded to the surface of the positive current collector exposed to the groove by laser welding; and the negative tab is directly welded to the surface of the negative current collector exposed to the groove by laser welding.

[0155] After the preparation of the secondary battery 1000 in the comparative examples and examples, the discharge capacity of 20 secondary batteries 1000 in each group is tested, and the volume energy density is calculated, and the average value of the volume energy density of 20 secondary batteries in each group is taken as Q. n The average value of the volume energy density of the secondary battery in Comparative Example 1 is taken as the reference value, and the average value of the volume energy density of the secondary battery in each experimental group is calculated relative to the reference value, and recorded as Q.

[0156] The specific process of the discharge capacity test is as follows:

[0157] 1) Maintain the test temperature at 25°C;

[0158] 2) Let the secondary battery 1000 stand for 30 min;

[0159] 3) 5C constant current charging to 4.25V, and then constant voltage charging to 3C;

[0160] 4) 3C constant current charging to 4.35V, then constant voltage charging to 1.5C;

[0161] 5) 1.5C constant current charging to 4.45V, then constant voltage charging to 0.05C;

[0162] 6) standing for 5min;

[0163] 7) 0.7C constant current discharging to 3V, recording the first discharge cycle capacity.

[0164] Volume energy density = first discharge cycle capacity / (length of secondary battery x width of secondary battery x thickness).

[0165] Q = 100% (Q n / M).

[0166] Subsequently, 5 secondary batteries 1000 were randomly selected from each group for tensile test.

[0167] The process of tensile test is as follows:

[0168] Disassembling the secondary battery, taking a slice of the first tab 40, the slice including part of the first current collector 11 and the first tab 40, the first tab 40 being connected with the first current collector 11, and the process of taking the slice does not damage the integrity of the connection between the first tab 40 and the first current collector 11; using the clamping heads of a high-iron or horizontal tensile testing machine to clamp the first tab 40 and the first current collector 11 respectively, and pulling one of the first tab 40 and the first current collector 11 at a test speed of 175mm / min. The tensile test results of the 5 secondary batteries 1000 in each group are averaged.

[0169] The experimental results are recorded in Table 1.

[0170] Table 1

[0171]

[0172]

[0173] Note: In Table 1, " / " means no data.

[0174] From Table 1, it can be seen that in Examples 1-6, the positive and negative tabs of the secondary battery 1000 are welded with the positive and negative current collectors through metal foils, respectively, and the energy density of the secondary battery 1000 in Examples 1-6 is higher than that of Comparative Examples 1 and 2. It can be seen that in the examples of the present application, the first tab 40 is welded with the first current collector 11 through the first connecting piece 60, which is conducive to reducing the energy required in the welding process, thereby reducing the possibility of deactivation of the active material of the part of the second active material layer 13 corresponding to the first slot 121 along the first direction X, and further improving the energy density of the secondary battery 1000.

[0175] In the embodiments 2-5, the thickness T1 of the metal foil meets 5 pm≤T1≤20 pm, compared with the embodiment 1, the average tensile force value measured in the tensile test of the secondary battery 1000 in the embodiments 2-5 is higher; compared with the embodiment 6, the energy density of the secondary battery 1000 in the embodiments 2-5 is higher. It can be seen that, in the embodiments of the present application, T1≥5 pm is set, the thickness of the first connecting piece 60 is not too thin, which is conducive to improving the stability of the connection between the first tab 40 and the first current collector 11; T1≤20 pm is set, the thickness of the first connecting piece 60 is not too thick, which is conducive to reducing the influence of the setting of the first connecting piece 60 on the thickness of the electrode assembly 100, so as to reduce the influence on the energy density of the secondary battery 1000.

[0176] Those skilled in the art of the present technology should recognize that the above embodiments are only used to illustrate the present application, and are not used as a limitation on the present application, and any appropriate changes and variations made to the above embodiments within the spirit and principles of the present application fall within the scope of the present disclosure.

Claims

1. A secondary battery characterized by comprising: The secondary battery comprises: a first tab; a first electrode tab comprising a first current collector, a first active material layer and a second active material layer, the first current collector comprising a first surface and a second surface oppositely arranged along a first direction, the first direction being a thickness direction of the first electrode tab, the first active material layer being arranged on the first surface, and the second active material layer being arranged on the second surface; the first active material layer is provided with a first groove, the first groove penetrating through the first active material layer along the first direction, so that part of the surface of the first surface exposed to the first groove, and a projection of the first groove along the first direction at least partially overlaps with the second active material layer; a first connecting piece, part of the first tab, the first connecting piece and the part of the surface of the first surface exposed to the first groove are sequentially stacked along the first direction, and the first connecting piece is welded to the first tab and the first current collector; the melting point of the first connecting piece is lower than the melting point of the first tab.

2. The secondary battery according to claim 1, wherein The thickness of the first connecting piece along the first direction is less than the thickness of the first active material layer along the first direction, so that part of the first tab is accommodated in the first groove.

3. The secondary battery according to claim 1, wherein The thickness of the first connecting piece along the first direction is T1, and 5 μm≤T1≤20 μm.

4. The secondary battery according to any one of claims 1 to 3, wherein The first tab is provided with a second groove, the opening of the second groove along the first direction is towards the part of the surface of the first surface exposed to the first groove, and at least part of the first connecting piece is accommodated in the second groove.

5. The secondary battery according to claim 1, wherein The secondary battery further comprises a second connecting piece, the second connecting piece is located between the first tab and the part of the surface of the first surface exposed to the first groove along the first direction, the projection of the first connecting piece along the first direction is connected to or separated from the projection of the second connecting piece along the first direction, and the second connecting piece is bonded to the first tab and the first current collector.

6. The secondary battery according to claim 5, wherein The second connecting piece is annular, and the second connecting piece surrounds the first connecting piece.

7. The secondary battery according to claim 1, wherein The secondary battery comprises a first bonding piece, the first bonding piece is bonded to the first active material layer, and the first bonding piece covers the opening of the first groove along the first direction and part of the first tab.

8. The secondary battery according to claim 7, wherein The secondary battery further comprises a second electrode tab and a separator, the first electrode tab, the separator and the second electrode tab are sequentially stacked along the first direction, the second electrode tab comprises a second current collector and a third active material layer stacked, and the third active material layer is located on a side of the second current collector facing the first electrode tab along the first direction; The secondary battery comprises a second bonding piece, the second bonding piece is bonded to the third active material layer, and the projection of the second bonding piece along the first direction covers part of the first tab.

9. The secondary battery according to claim 8, wherein The thickness of the first bonding piece along the first direction is T2, and 5 μm≤T2≤20 μm; and / or The thickness of the second bonding piece along the first direction is T3, and 5 μm≤T3≤20 μm.

10. The secondary battery according to any one of claims 5 to 9, wherein The second connecting piece is a hot melt pressure sensitive adhesive.

11. The secondary battery according to claim 1, wherein The secondary battery further comprises a second tab, the first tab and the second tab are stacked along the first direction, the first tab is a positive tab, the second tab is a negative tab, a width of the first tab along a second direction is less than a width of the second tab along the second direction, the second direction is perpendicular to the first direction, the first tab is provided on one side of the first tab along the second direction; An edge of the second tab along the second direction and on the same side as the first tab exceeds the first tab; The first tab comprises a first portion, a projection of the first portion along the first direction is outside a projection area of the first tab and overlaps a projection area of the second tab; The secondary battery further comprises a third adhesive, the third adhesive adheres and covers a surface of the first portion facing the second tab.

12. The secondary battery according to claim 1, wherein The melting point of the first connecting member is a, 300℃≤a≤400℃.

13. The secondary battery according to claim 1, wherein The first tab is a positive tab, the melting point of the first connecting member is a, the melting point of the first tab is b, 200℃≤b-a≤400℃; And / or, the first tab is a negative tab, the melting point of the first tab is c, 1000℃≤c-a≤1300℃.

14. An electrical device, characterized by The secondary battery comprises any one of claims 1 to 13.

15. A method of manufacturing a pole piece, characterized by, The method comprises the following steps: A first tab is taken, the first tab comprises a first current collector, a first active material layer and a second active material layer, the first current collector comprises a first surface and a second surface oppositely arranged along a first direction, the first active material layer is provided on the first surface, the second active material layer is provided on the second surface, the first active material layer is provided with a first groove, along the first direction, at least part of a projection of the first groove is located in a projection area of the second active material layer, the first groove penetrates the first active material layer along the first direction, so that part of the surface of the first surface is exposed to the first groove; The first direction is a thickness direction of the first tab; A metal foil is taken, the melting point of the metal foil is lower than the melting point of the first tab; The metal foil is clamped between the first tab and the part of the surface of the first surface exposed to the first groove; The metal foil is hot-melted, so that the first tab and the first current collector are welded.

16. The method of producing a pole piece according to claim 15, wherein The method comprises the following steps: Before clamping the metal foil between the first tab and the part of the surface of the first surface exposed to the first groove, a second connecting member is adhered on the first tab, and the metal foil is adhered to the second connecting member.

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