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

Abstract

The application discloses a secondary battery, an electric device and a preparation method of an electrode sheet. The secondary battery comprises a first electrode sheet and a first tab. 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 which are oppositely arranged along a first direction. 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. Along the first direction, at least part of the projection of the first groove is located in the projection area of the second active material layer, and part of the surface of the first surface is exposed to the first groove. The first tab comprises a first main part and a first thinning part in an integrated structure. Along the first direction, the thickness of the first thinning part is smaller than that of the first main part. At least part of the first thinning part is welded to the part of the surface of the first surface which is exposed to the first groove. The secondary battery is provided with the first thinning part, which is beneficial to reducing the energy required during welding and improving the energy density.

Description

TECHNICAL FIELD

[0001] The present 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 of welding the tab in the middle of the electrode sheet (MMT) 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 easily affected by the high temperature generated during laser welding and loses capacity. Therefore, compared with ultrasonic welding, although laser welding only needs to slot the active material layer on one side of the current collector, it does not significantly improve the capacity of the secondary battery. 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 electrode sheet and a first tab. 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 a 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. Along the first direction, at least part of the projection of the first slot is located within the projection area of the second active material layer. The first slot 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. The first tab comprises a first main part and a first thinned part in an integral structure. Along the first direction, the thickness of the first thinned part is less than the thickness of the first main part. At least part of the first thinned part is welded to the part of the surface of the first surface exposed to the first slot.

[0005] In this secondary battery, the thickness of the first thinned part is less than the thickness of the first main part, and the first tab is welded to the first current collector at the first thinned part, which is conducive to reducing the energy required for welding, 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. Moreover, the thickness of the first main part is greater than the first thinned part, which is conducive to balancing the current carrying capacity of the first tab.

[0006] In an optional embodiment of the present application, the thickness of the first main body part in the first direction is T1, and the thickness of the first thinning part in the first direction is T, 0.1T1≤T≤0.5T. T≥0.1T1 is set to prevent the thickness of the first thinning part from being too small, which is conducive to improving the current carrying capacity of the first tab and the strength of the welding of the first tab 40 to the first current collector 11; T≤0.5T is set to prevent the thickness of the first thinning part from being too large, which is conducive to reducing the energy required for welding the first tab and the current collector.

[0007] In an optional embodiment of the present application, 30μm≤T≤120μm. T≥30μm is set to prevent the thickness of the first thinning part from being too small, which is conducive to improving the current carrying capacity of the first tab and the strength of the welding of the first tab to the first current collector; T≤120μm is set to prevent the thickness of the first thinning part from being too large, which is conducive to reducing the energy required for welding the first tab and the first current collector.

[0008] In an optional embodiment of the present application, the secondary battery comprises a first adhesive, the first tab comprises a third surface, the third surface being a surface of the first tab facing the first current collector in the first direction, the third surface comprising a first region, the first region being located in the first thinning part, the first adhesive bonding the first surface and the first thinning part, and the first adhesive being located outside the first region. By bonding the first tab and the first surface with the first adhesive, the first tab and the first surface can be preliminarily fixed relative to each other before welding the first thinning part and the first surface, which is conducive to improving the welding quality; in addition, the first adhesive is located outside the first region, which is conducive to reducing the influence of the setting of the first adhesive on the welding process and improving the welding quality.

[0009] In an optional embodiment of the present application, the thickness of the first adhesive in the first direction is T2, and 5μm≤T2≤50μm. T2≥5μm is set to prevent the thickness of the first adhesive from being too small, which is conducive to reducing the requirements on the production process of the first adhesive and improving the bonding force between the first adhesive and the first surface and the first thinning part; the first adhesive is located between the first thinning part and the first surface, and T2≤50μm is set to prevent the thickness of the first adhesive from being too large, so that the distance between the first thinning part and the first surface is not too large, which is conducive to improving the strength of the welding structure formed by the first thinning part after melting and solidification and the first current collector.

[0010] In an optional embodiment of the present application, the thickness of the first thinning part in the first direction is T, and the thickness of the first adhesive in the first direction is T2, T2≤T. By setting T2≤T, the distance between the first thinning part and the first surface is smaller than the thickness of the first thinning part, which is conducive to improving the strength of the welding structure formed by the first thinning part after melting and solidification and the first current collector.

[0011] In an optional embodiment of the present application, the secondary battery comprises a second adhesive member, the second adhesive member is adhered to the first active material layer, and the second adhesive member covers the opening of the first slot facing the first direction and part of the first tab. The second adhesive member is arranged 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 second adhesive member in the first direction is T3, and 5 μm≤T3≤20 μm. T3≥5 μm is arranged to prevent the thickness of the second adhesive member in the first direction from being too small, which is conducive to reducing the possibility of the burr of the first tab piercing the separator and causing internal short circuit of the secondary battery; and T3≤20 μm is arranged to prevent the thickness of the second adhesive member in the first direction from being too large, which is conducive to reducing the influence of the arrangement of the second adhesive member 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 in 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 facing the first tab in the first direction. The secondary battery comprises a third adhesive member, the third adhesive member is adhered to the third active material layer, and the projection of the third adhesive member in the first direction covers part of the first tab. On the basis of arranging the second adhesive member, the third adhesive member is further arranged to further reduce the possibility of the edge burr of the first tab piercing the separator and causing internal short circuit of the secondary battery.

[0014] In an optional embodiment of the present application, the thickness of the third adhesive member in the first direction is T4, and 5 μm≤T4≤20 μm. T4≥5 μm is arranged to prevent the thickness of the second adhesive member in the first direction from being too small, which is conducive to reducing the possibility of the burr of the first tab piercing the separator and causing internal short circuit of the secondary battery; and T4≤20 μm is arranged to prevent the thickness of the second adhesive member in the first direction from being too large, which is conducive to reducing the influence of the arrangement of the second adhesive member on the thickness of the electrode assembly.

[0015] In an optional embodiment of the present application, the secondary battery further comprises a second electrode tab, the first electrode tab and the second electrode tab are stacked along a first direction, the first electrode tab is a positive electrode tab, the second electrode tab is a negative electrode tab, a width of the first electrode tab along a second direction is less than a width of the second electrode tab along the second direction, the second direction is perpendicular to the first direction, the first electrode tab is provided on one side of the first electrode tab along the second direction; an edge of the second electrode tab along the second direction and on the same side as the first electrode tab protrudes beyond the first electrode tab. The first electrode tab comprises a first portion, a projection of the first portion along the first direction is outside a projection area of the first electrode tab and overlaps a projection area of the second electrode tab. The secondary battery further comprises a fourth adhesive, the fourth adhesive adheres and covers a surface of the first portion facing the second electrode tab. In this way, the possibility of the burr of the first electrode tab piercing the separator and short-circuiting with the negative electrode tab is reduced.

[0016] A second aspect of the embodiments of the present application provides a power-using device comprising the secondary battery according to any one of the preceding aspects.

[0017] A third aspect of the embodiments of the present application provides a method for manufacturing an electrode tab, comprising the following steps:

[0018] A first electrode tab is taken, 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 oppositely arranged along a first direction, 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, a projection of the first groove along the first direction is at least partially located within 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 electrode tab;

[0019] A first electrode tab is taken, and part of the material of the first electrode tab is removed to form a first thinned portion, the thickness of the first thinned portion is less than the thickness of the remaining part of the first electrode tab;

[0020] A surface of the first electrode tab along the thickness direction thereof is attached to the part of the surface of the first surface exposed to the first groove, and at least part of the projection of the first thinned portion along the first direction overlaps the part of the surface of the first surface exposed to the first groove;

[0021] The first thinned portion is melted so that the first thinned portion is welded to the first current collector.

[0022] In an optional embodiment of the present application, the first thinned portion is laser welded to the first current collector, so that the first thinned portion can be more reliably welded to the first current collector when the second active material layer is on the back of the first groove. BRIEF DESCRIPTION OF DRAWINGS

[0023] Figure 1is a cross-sectional structure schematic view of the secondary battery in the embodiment of the present application.

[0024] Figure 2 is Figure 1 is a cross-sectional structure schematic view of the secondary battery in the embodiment of the present application.

[0025] Figure 3 is Figure 2 is an enlarged view of A in FIG. 1.

[0026] Figure 4 is Figure 2 is an enlarged view of B in FIG. 1.

[0027] Figure 5 is a structure schematic view of the first electrode tab in a flattened state in the embodiment of the present application.

[0028] Figure 6 is Figure 5 is a cross-sectional structure schematic view of the secondary battery in the embodiment of the present application.

[0029] Figure 7 is a structure schematic view of the first electrode tab in a flattened state in the embodiment of the present application.

[0030] Figure 8 is Figure 7 is a cross-sectional structure schematic view of the secondary battery in the embodiment of the present application.

[0031] Figure 9 is a cross-sectional structure schematic view of the secondary battery in the embodiment of the present application.

[0032] Figure 10 is Figure 9 is an enlarged view of C in FIG. 1.

[0033] Figure 11 is Figure 1 is a cross-sectional structure schematic view of the secondary battery in the embodiment of the present application.

[0034] Figure 12 is a structure schematic view of the first electrode tab in a flattened state in the embodiment of the present application.

[0035] Figure 13 is a structure schematic view of the electrical device in the embodiment of the present application.

[0036] Main element symbol explanation

[0037] Secondary battery 1000

[0038] Electrode assembly 100

[0039] First electrode tab 10

[0040] First current collector 11

[0041] First surface 111

[0042] Second surface 112

[0043] First active material layer 12

[0044] First groove 121

[0045] Second active material layer 13

[0046] Second tab 20

[0047] Second current collector 21

[0048] Fourth surface 211

[0049] Fifth surface 212

[0050] Third active material layer 22

[0051] Second groove 221

[0052] Fourth active material layer 23

[0053] Separation film 30

[0054] First tab 40

[0055] First main portion 41

[0056] First thinning portion 42

[0057] Groove body 43

[0058] Third surface 44

[0059] First region 441

[0060] First portion 45

[0061] Second tab 50

[0062] Second main portion 51

[0063] Second thinning portion 52

[0064] First adhesive 60

[0065] Second adhesive 70

[0066] Third adhesive 80

[0067] Fourth adhesive 90

[0068] Housing 200

[0069] Electric device 10000

[0070] First direction X

[0071] Second direction Y DETAILED DESCRIPTION

[0072] 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, not all the embodiments of the present application.

[0073] It should be noted that when one 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 one element is considered to be "arranged" in another element, it can be directly arranged in 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.

[0074] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used in the description of the specification of the present application is only for the purpose of describing specific embodiments and is not intended to limit the present application.

[0075] 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.

[0076] 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".

[0077] 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 independent or alternative to other embodiments. In the case of no conflict, each embodiment in the present application can be combined with each other.

[0078] A first aspect of embodiments of the present application provides a secondary battery including a first tab and a first electrode plate. The first electrode plate includes a first current collector, a first active material layer, and a second active material layer. The first current collector includes a first surface and a second surface oppositely arranged along a first direction, the first direction being a thickness direction of the first electrode plate. The first active material layer is disposed on the first surface, and the second active material layer is disposed on the second surface. The first active material layer is provided with a first groove. Along the first direction, at least a portion of a projection of the first groove is located within a projection area of the second active material layer. The first groove penetrates the first active material layer along the first direction, so that a portion of the surface of the first surface is exposed to the first groove. The first tab includes a first main portion and a first thinned portion in an integral structure. Along the first direction, the thickness of the first thinned portion is less than the thickness of the first main portion. At least a portion of the first thinned portion is welded to the portion of the surface of the first surface exposed to the first groove.

[0079] In the secondary battery, the thickness of the first thinned portion is less than the thickness of the first main portion, and the first tab is welded to the first current collector at the first thinned portion. This is advantageous for reducing the energy required for welding, thereby reducing the possibility of deactivation of the active material of the portion of the second active material layer corresponding to the first groove along the first direction, thereby improving the energy density of the secondary battery. Moreover, the thickness of the first main portion is greater than the first thinned portion, which is advantageous for balancing the current-carrying capacity of the first tab.

[0080] Embodiments of the present application will be further described below with reference to the accompanying drawings.

[0081] As shown in Figure 1 and Figure 2 , embodiments of the present application provide a secondary battery 1000 including an electrode assembly 100, a housing 200, a first tab 40, and a second tab 50. The electrode assembly 100 is accommodated 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.

[0082] In some embodiments, as shown in Figure 2 , the electrode assembly 100 includes a first electrode plate 10, a second electrode plate 20, and a separator 30, and the separator 30 is disposed between the first electrode plate 10 and the second electrode plate 20.

[0083] In some embodiments, as shown in Figure 2 , the first electrode plate 10, the separator 30, and the second electrode plate 20 are stacked along a first direction X and then wound to form a jelly-roll structure. The first direction X is a thickness direction of the first electrode plate 10.

[0084] 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.

[0085] 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 fourth surface 211 and a fifth surface 212 oppositely arranged along the first direction X, the third active material layer 22 is disposed on the fourth surface 211, and the fourth active material layer 23 is disposed on the fifth surface 212.

[0086] 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 tab 40 is a positive tab, 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 tab 50 is a negative tab; 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 tab 40 is a negative tab, 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 tab 50 is a positive tab.

[0087] In some embodiments, the positive current collector is a metal layer. As an exemplary example, the positive current collector can be a metal layer including at least one of aluminum, nickel, tantalum, titanium, such as an aluminum foil.

[0088] 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.

[0089] In some embodiments, the negative current collector is a metal layer. As an exemplary example, the negative current collector can be a metal layer including at least one of copper, nickel, tantalum, titanium, such as a copper foil.

[0090] In some embodiments, at least one of the positive current collector and the negative current collector is a composite current collector.

[0091] 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.

[0092] 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 insulating.

[0093] In some embodiments, the secondary battery 1000 further includes an electrolyte (not shown in the figure), which is accommodated in the casing 200.

[0094] 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.

[0095] 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).

[0096] In some embodiments, as shown in Figure 3 , Figure 5 and Figure 6 The first active material layer 12 is provided with a first groove 121, at least part of the projection of the first groove 121 is located within the projection area of the second active material layer 13 along the first direction X, the first groove 121 penetrates the first active material layer 12 along the first direction X, so that part of the surface of the first surface 111 is exposed to the first groove 121. The first tab 40 includes a one-piece structure of a first main body part 41 and a first thinned part 42, the thickness of the first thinned part 42 is less than the thickness of the first main body part 41 along the first direction X, and at least part of the first thinned part 42 is welded to the part of the surface of the first surface 111 exposed to the first groove 121.

[0097] In this embodiment, the thickness of the first thinned part 42 is less than the thickness of the first main body part 41, the first tab 40 is welded to the first current collector 11 at the first thinned part 42, which is conducive to reducing the energy required for welding, thereby reducing the possibility of deactivation of the active material of the part of the second active material layer 13 corresponding to the first groove 121 along the first direction X, and further improving the energy density of the secondary battery 1000; and the thickness of the first main body part 41 is greater than the first thinned part 42, which is conducive to balancing the current carrying capacity of the first tab 40.

[0098] In some embodiments, as shown in Figure 5 and Figure 6 The first thinned part 42 is formed by opening a groove 43 on the first tab 40.

[0099] In some embodiments, as shown in Figure 5 and Figure 6 The first thinned part 42 is formed by opening a groove 43 on the first tab 40.As shown, the position where the first tab 40 is provided with the groove 43 is the surface of the first tab 40 facing away from the first current collector 11 in the first direction X.

[0100] In some embodiments, the position where the first tab 40 is provided with the groove 43 is the surface of the first tab 40 facing the first current collector 11 in the first direction X. It should be noted that when the position where the groove is provided is the surface of the first tab 40 facing the first current collector 11, the depth of the groove 43 needs to be controlled to be within a certain range, so that the distance between the bottom wall of the groove 43 (i.e., the surface of the first thinning area facing the first current collector 11) in the first direction X and the first surface 111 is within the first range, so as to improve the welding quality.

[0101] In some embodiments, the position where the first tab 40 is provided with the groove 43 is the surface of the first tab 40 facing the first current collector 11 in the first direction X, and the surface of the first tab 40 facing away from the first current collector 11 in the first direction X; in other words, the first tab 40 is provided with two grooves 43 opposite in the first direction X.

[0102] In some embodiments, the projections of the two grooves 43 in the first direction X are staggered or overlapped, and / or the projection areas of the two grooves 43 in the first direction X are equal or unequal.

[0103] It should be noted that the depth range of the groove 43 is not specifically limited in the present application, and can be determined as needed in actual production. The shape of the groove 43 is also not specifically limited in the present application. As an exemplary example, the projection of the groove 43 in the first direction X can be one of a circle, an ellipse, and a rectangle.

[0104] In some embodiments, as shown in Figure 7 and Figure 8 The first thinning portion 42 is obtained by removing a layer of material from part of the first tab 40, so that a step structure is formed between the first thinning portion 42 and the first main body portion 41.

[0105] In some embodiments, as shown in Figure 6 The thickness of the first main body portion 41 in the first direction X is T1, and the thickness of the first thinning portion 42 in the first direction X is T, and 0.1T1≤T≤0.5T. By setting T≥0.1T1, the thickness of the first thinning portion 42 is not too thin, which is beneficial to improve the current carrying capacity of the first tab 40 and reduce the processing difficulty; by setting T≤0.5T, the thickness of the first thinning portion 42 is not too thick, which is beneficial to reduce the energy required for welding the first tab 40 and the current collector.

[0106] In some embodiments, 30μm≤T≤120μm. Setting T≥30μm prevents the thickness of the first thinning portion 42 from being too thin, which is beneficial to improving the current carrying capacity of the first tab 40 and the welding strength between the first tab 40 and the first current collector 11; setting T≤120μm prevents the thickness of the first thinning portion 42 from being too thick, which is beneficial to reducing the energy required to weld the first tab 40 and the first current collector.

[0107] In some embodiments, such as Figure 6 , Figure 9 and Figure 10 As shown, the secondary battery 1000 includes a first adhesive member 60, and a first tab 40 includes a third surface 44. The third surface 44 is the surface of the first tab 40 facing the first current collector 11 along the first direction X. The third surface 44 includes a first region 441, which is located in the first thinned portion 42. The first adhesive member 60 bonds the first surface 111 to the first thinned portion 42, and the first adhesive member 60 is located outside the first region 441. By setting the first adhesive member 60 to bond the first tab 40 to the first surface 111, the first tab 40 and the first surface 111 can be initially fixed relative to each other before welding the first thinned portion 42 and the first surface 111, which is beneficial to improving the welding quality. In addition, the first adhesive member 60 is located outside the first region 441, which helps to reduce the impact of the setting of the first adhesive member 60 on the welding process and improve the welding quality.

[0108] In some embodiments, before the first electrode tab 40 is welded to the first current collector 11, the first adhesive 60 creates a gap between the first electrode tab 40 and the first current collector 11. During the welding process, at least a portion of the first thinning portion 42 melts and flows toward the first current collector 11 until it comes into contact with the first current collector 11. After solidification, it forms a welded structure with the first current collector 11.

[0109] In some embodiments, the first tab 40 has a third groove (not shown), the opening of which faces the first current collector 11. At least a portion of the first adhesive member 60 is housed within the third groove, such that the surface of the first adhesive member 60 facing the first current collector 11 is flush with or slightly higher than the third surface 44. This reduces or eliminates the gap between the first thinned portion 42 and the first current collector 11 before welding, improving welding quality.

[0110] In some embodiments, the first adhesive 60 is a hot melt adhesive. Before welding the first tab 40 and the first current collector 11, the hot melt adhesive can be heated to activate it, thereby initially bonding the first tab 40 and the first current collector 11 together. This reduces the possibility of the first tab 40 and the first current collector 11 moving relative to each other 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.

[0111] 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.

[0112] In some embodiments, the first adhesive 60 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 welding the first tab 40 and the first current collector 11, the first adhesive 60 can be heated to activate the hot melt adhesive layer.

[0113] In some embodiments, the hot melt adhesive layer comprises a styrene-isoprene-styrene block copolymer; the substrate layer comprises at least one of polyethylene terephthalate, polyimide, or polypropylene; and the pressure-sensitive adhesive layer comprises at least one of polymethyl methacrylate (PMMA, commonly known as acrylic), polypropylene (PP), polyethylene (PE), or polyamide.

[0114] In some embodiments, such as Figure 6 As shown, the thickness of the first adhesive component 60 along the first direction X is T2, where 5μm≤T2≤50μm. Setting T2≥5μm ensures that the thickness of the first adhesive component 60 is not too small. This reduces the requirements for the manufacturing process of the first adhesive component 60 and improves the adhesion between the first adhesive component 60 and the first surface 111 and the first thinned portion 42. The first adhesive component 60 is located between the first thinned portion 42 and the first surface 111. Setting T2≤50μm ensures that the thickness of the first adhesive component 60 is not too thick. Therefore, the distance between the first thinned portion 42 and the first surface 111 is not too large, which helps to improve the strength of the welded structure formed by the first thinned portion 42 and the first current collector 11 after melting and re-solidification.

[0115] In some embodiments, such as Figure 6As shown, the thickness of the first thinning portion 42 along the first direction X is T, and the thickness of the first adhesive 60 along the first direction X is T2, T2≤T. In the case where the thickness of the first adhesive 60 is constant, the distance between the first thinning portion 42 and the first surface 111 along the first direction X is constant. At this time, if the thickness of the first thinning portion 42 is reduced, the material required to form the first thinning portion 42 is also reduced, and the strength of the welding structure formed between the first thinning portion 42 and the first current collector 11 after the first thinning portion 42 is melted and resolidified is reduced. Therefore, by setting T2≤T, the distance between the first thinning portion 42 and the first surface 111 is smaller than the thickness of the first thinning portion 42, which is conducive to improving the strength of the welding structure formed between the first thinning portion 42 and the first current collector 11 after the first thinning portion 42 is melted and resolidified.

[0116] In some embodiments, as shown in FIG. 1, the secondary battery 1000 includes a first adhesive 60. The first adhesive 60 is attached to the first active material layer 12. The first adhesive 60 covers the opening of the first groove 121 facing the first direction X and part of the first tab 40. Figure 3 As shown, the thickness of the second adhesive 70 along the first direction X is T3, 5 μm≤T3≤20 μm. By setting T3≥5 μm, the thickness of the second adhesive 70 along the first direction X is not too small, which is conducive to reducing the possibility of internal short circuit of the secondary battery 1000 caused by the burr of the first tab 40 piercing the separator 30; by setting T3≤20 μm, the thickness of the second adhesive 70 along the first direction X is not too large, which is conducive to reducing the impact of the setting of the second adhesive 70 on the thickness of the electrode assembly 100.

[0117] In some embodiments, as shown in FIG. 1, the secondary battery 1000 includes a first adhesive 60. The first adhesive 60 is attached to the first active material layer 12. The first adhesive 60 covers the opening of the first groove 121 facing the first direction X and part of the first tab 40. Figure 3 As shown, the thickness of the second adhesive 70 along the first direction X is T3, 5 μm≤T3≤20 μm. By setting T3≥5 μm, the thickness of the second adhesive 70 along the first direction X is not too small, which is conducive to reducing the possibility of internal short circuit of the secondary battery 1000 caused by the burr of the first tab 40 piercing the separator 30; by setting T3≤20 μm, the thickness of the second adhesive 70 along the first direction X is not too large, which is conducive to reducing the impact of the setting of the second adhesive 70 on the thickness of the electrode assembly 100.

[0118] In some embodiments, as shown in FIG. 1, the secondary battery 1000 includes a first adhesive 60. The first adhesive 60 is attached to the first active material layer 12. The first adhesive 60 covers the opening of the first groove 121 facing the first direction X and part of the first tab 40. Figure 3 As shown, the third active material layer 22 of the second tab 20 is located on the side of the second current collector 21 facing the first tab 10 along the first direction X. The secondary battery 1000 further includes a third adhesive 80. The third adhesive 80 is attached to the third active material layer 22. The projection of the third adhesive 80 along the first direction X covers part of the first tab 40. Based on the setting of the second adhesive 70, further setting the third adhesive 80 is conducive to further reducing the possibility of internal short circuit of the secondary battery 1000 caused by the edge burr of the first tab 40 piercing the separator 30.

[0119] In some embodiments, as shown in FIG. 1, the secondary battery 1000 includes a first adhesive 60. The first adhesive 60 is attached to the first active material layer 12. The first adhesive 60 covers the opening of the first groove 121 facing the first direction X and part of the first tab 40. Figure 3As shown, the thickness of the third adhesive 80 along the first direction X is T4, and 5 μm≤T4≤20 μm. T4≥5 μm is set to prevent the thickness of the third adhesive 80 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 and causing internal short circuit of the secondary battery 1000; T4≤20 μm is set to prevent the thickness of the third adhesive 80 along the first direction X from being too large, which is conducive to reducing the influence of the arrangement of the second adhesive 70 on the thickness of the electrode assembly 100.

[0120] 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 third adhesive 80 covers the projection of the second adhesive 70. In this way, it is conducive to increasing the CB (Cell Balance, ratio of unit area negative electrode capacity to unit area positive electrode capacity) of the positive and negative tabs, and reducing the possibility of lithium precipitation of the electrode assembly 100 during the cycle process.

[0121] 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 70 covers the projection of the third adhesive 80. In this way, it is conducive to increasing the CB of the positive and negative tabs, and reducing the possibility of lithium precipitation of the electrode assembly 100 during the cycle process.

[0122] In the embodiments of the present application, T, T1, T2, T3 and T4 can all be measured by a micrometer. When measuring the thickness T of the first thinning portion 42, the first tab 40 can be separated from the first current collector 11 for measurement.

[0123] In some embodiments, as shown in FIG. 1, Figure 11 The first tab 10 is a positive tab, and the second tab 20 is a negative tab. The width of the first tab 10 along the second direction Y is less than the width of the second tab 20 along the second direction Y, and the second direction Y is perpendicular to the first direction X. The first tab 40 is arranged at one side of the first tab 10 along the second direction Y; and the edge of the second tab 20 along the second direction Y and on the same side as the first tab 40 exceeds the first tab 10. In this way, it is conducive to increasing the CB of the positive and negative tabs, and reducing the possibility of lithium precipitation of the electrode assembly 100 during the cycle process.

[0124] In some embodiments, as shown in FIG. 1, Figure 11 and Figure 12As shown, the first tab 40 includes a first portion 45, a projection of the first portion 45 along the first direction X is outside the projection area of the first tab 10 and overlaps with the projection area of the second tab 20. The secondary battery 1000 further includes a fourth adhesive 90, the fourth adhesive 90 adheres and covers a surface of the first portion 45 facing the second tab 20. In this way, it is beneficial to reduce the possibility that burrs of the first tab 40 pierce the separator 30 and short-circuit with the negative tab.

[0125] It should be noted that the division criteria of the first main portion 41 and the first thinning portion 42 is the thickness of different parts of the first tab 40, and the division criteria of the first portion 45 is the positional relationship of the part of the first tab 40 relative to the first tab 10 and the second tab 20, therefore, the first portion 45 is not a part that is exclusive of the first main portion 41 and the first thinning portion 42. As an exemplary example, the first portion 45 can be a part of the first main portion 41, or the first portion 45 includes a part of the first main portion 41 and a part of the first thinning portion 42, or the first portion 45 is a part of the thinning portion.

[0126] In some embodiments, at least one of the second adhesive 70, the third adhesive 80 and the fourth adhesive 90 is adhesive tape.

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

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

[0129] In some embodiments, the glue layer is made of one or a combination of several of 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 alpha-olefin copolymer, petroleum resin, terpene resin, rosin resin.

[0130] In some embodiments, as Figure 4As shown, the fourth active material layer 23 is provided with a second groove 221, a projection of the second groove 221 is at least partially located within a projection area of the third active material layer 22 along the first direction X, the second groove 221 penetrates the fourth active material layer 23 along the first direction X, so that part of the surface of the fifth surface 212 is exposed to the second groove 221. The second tab 50 comprises a second main body part 51 and a second thinning part 52 in an integral structure, the thickness of the second thinning part 52 is less than the thickness of the second main body part 51 along the first direction X; at least part of the second thinning part 52 is welded to the part of the surface of the fifth surface 212 exposed to the second groove 221. The thickness of the second thinning part 52 is less than the thickness of the second main body part 51, the second tab 50 forms a weld between the second thinning part 52 and the second current collector 21, which is conducive to reducing the energy required for welding, thereby reducing the possibility of deactivation of the active material of the part of the third active material layer 22 corresponding to the second groove 221 along the first direction X, thereby improving the energy density of the secondary battery 1000; and the thickness of the second main body part 51 is greater than that of the second thinning part 52, which is conducive to balancing the current carrying capacity of the first tab 40.

[0131] As shown, Figure 13 Embodiments of the present application also provide a use electric device 10000, comprising the secondary battery 1000 according to any one of the preceding embodiments.

[0132] In some embodiments, the use electric device 10000 includes but is not limited to one of a mobile phone, a notebook computer, a tablet computer, a power tool, an electric toy, and an electronic cigarette.

[0133] Embodiments of the present application also provide a method for manufacturing a tab, the method comprising the following steps:

[0134] Take a first tab 10, the first tab 10 comprises a first current collector 11, a first active material layer 12, and a second active material layer 13, the first current collector 11 comprises a first surface 111 and a second surface 112 arranged opposite along a first direction X, the first active material layer 12 is arranged on the first surface 111, and the second active material layer 13 is arranged on the second surface 112, the first active material layer 12 is provided with a first groove 121, a projection of the first groove 121 is at least partially located within a projection area of the second active material layer 13 along the first direction X, and the first groove 121 penetrates the first active material layer 12 along the first direction X, so that part of the surface of the first surface 111 is exposed to the first groove 121;

[0135] Take a first tab 40, remove part of the material of the first tab 40 to form a first thinning part 42, the thickness of the first thinning part 42 is less than the thickness of the remaining part of the first tab 40;

[0136] The first tab 40 is attached to a portion of the first surface 111 exposed to the first groove 121 in a surface direction of the first tab 40, and at least a portion of a projection of the first thinning portion 42 in the first direction X overlaps with a portion of the first surface 111 exposed to the first groove 121.

[0137] The first thinning portion 42 is melted so that the first thinning portion 42 is welded to the first current collector 11.

[0138] In some embodiments, a laser or a heat block is used to heat the first thinning portion 42 when welding the first thinning portion 42 to the first current collector 11.

[0139] To verify the effect of the embodiments of the present application, the inventors of the present application conducted the following experiments, which included two groups of comparative examples and five groups of examples, and each group of comparative examples and each group of examples included 20 secondary batteries 1000.

[0140] In the following examples and comparative examples, the thickness of the tab is taken as 150 μm.

[0141] In Example 1, the preparation process of the secondary battery 1000 includes the following steps:

[0142] (1) Preparation of the positive electrode sheet: active material lithium cobalt oxide (LiCoO2), conductive carbon black (Super P), CNT (carbon nanotube), and polyvinylidene fluoride (PVDF) are mixed in a weight ratio of 97.5:0.5:0.5:1.5, N-methyl pyrrolidone (NMP) is added as a solvent, and a positive electrode active material with a solid content of 75 wt% is prepared and stirred uniformly for standby use. An aluminum foil with a thickness of 8 μm is used as the positive electrode current collector. The positive electrode current collector is pasted with adhesive tape at the position where the groove is to be formed, and a slot coater is used to uniformly coat the active material on one side of the positive electrode current collector in the thickness direction, and then dried at 90°C to obtain a positive electrode sheet with a positive electrode active material layer coated on one side. After drying, the adhesive tape is removed to form a groove (equivalent to one of the first groove 121 and the second groove 221). Then the above coating step is repeated on the other side of the positive electrode current collector in the thickness direction without pasting the adhesive tape 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. A positive tab is taken, and the material of the positive tab is removed to form a thinning portion (equivalent to one of the first thinning portion 42 and the second thinning portion 52), and the thickness of the thinning portion is less than the thickness of the remaining part of the positive tab. The positive tab is arranged on the surface of the positive electrode current collector exposed to the groove, and the surface of the positive tab in the first direction facing the surface of the positive electrode current collector is a plane. The thinning portion of the positive tab is melted so that the positive tab is welded to the surface of the positive electrode current collector exposed to the groove.

[0143] (2) Preparation of the negative electrode sheet: The active material artificial graphite, conductive carbon black (Super P), 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 second groove 221) was made on one negative electrode active material layer of the negative electrode sheet by laser cleaning. A negative tab was taken, and part of the material of the negative tab was removed to form a thinned portion (equivalent to the other of the first thinned portion 42 and the second thinned portion 52), the thickness of the thinned portion being less than the thickness of the remaining part of the negative tab, the negative tab was arranged on the surface of the negative electrode current collector exposed to the groove, the surface of the negative tab in the first direction towards the surface of the negative electrode current collector was a plane, and the thinned portion of the negative tab was fused so that the negative tab was welded to the surface of the negative electrode current collector exposed to the groove. The thickness of the thinned portion of the negative tab was the same as that of the thinned portion of the positive tab, recorded as T in Table 1.

[0144] (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.

[0145] (4) Preparation of the separator film 30: A 7μm thick polyethylene porous polymer film was used as the separator film 30.

[0146] (5) Preparation of the electrode assembly 100: The positive electrode sheet, the separator film, and the negative electrode sheet were stacked in the thickness direction of the negative electrode sheet and wound to obtain the electrode assembly 100.

[0147] (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 compress 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.

[0148] The preparation process of the secondary battery 1000 in Examples 2-5 is basically the same as that in Example 1, and the difference is that the thickness of the thinned portion of the positive and negative tabs used in Examples 2-5 is different from that in Example 1, and the thickness of the thinned portion is recorded in Table 1.

[0149] 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 on the two positive active material layers of the positive electrode sheet at positions opposite to each other along the first direction X, the positive tab is not formed with a thinned portion, and is welded to the surface of the positive current collector exposed in the groove by ultrasonic welding; grooves are provided on the two negative active material layers of the negative electrode sheet at positions opposite to each other along the first direction X, the negative tab is not formed with a thinned portion, and is welded to the surface of the negative current collector exposed in the groove by ultrasonic welding.

[0150] 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 not formed with a thinned portion, and is directly welded to the surface of the positive current collector exposed in the groove by laser welding; the negative tab is not formed with a thinned portion, and is directly welded to the surface of the negative current collector exposed in the groove by laser welding.

[0151] 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 is represented by M, and the percentage of the average value of the volume energy density of the secondary battery in each experimental group relative to the reference value is calculated, and is recorded as Q.

[0152] The specific process of the discharge capacity test is as follows:

[0153] 1) Maintain the test temperature at 25°C;

[0154] 2) Let the secondary battery 1000 stand for 30 min;

[0155] 3) 5C constant current charge to 4.25V, then constant voltage charge to 3C;

[0156] 4) 3C constant current charge to 4.35V, then constant voltage charge to 1.5C;

[0157] 5) 1.5C constant current charge to 4.45V, then constant voltage charge to 0.05C;

[0158] 6) Stand for 5min;

[0159] 7) 0.7C constant current discharge to 3V, record the discharge capacity.

[0160] Volume energy density = Discharge capacity / (length of secondary battery x width of secondary battery x thickness).

[0161] Q = 100% (Qn / M).

[0162] The experimental results are recorded in Table 1.

[0163] Table 1

[0164] Experimental group T (μm) Q Comparative example 1 / 100％ Comparative example 2 / 101％ Example 1 28 102.75％ Example 2 30 102.75％ Example 3 70 102.38％ Example 4 120 101.93％ Example 5 122 101.93％

[0165] Note: In Table 1, " / " means no data.

[0166] From Table 1, it can be seen that in Examples 1-5, the positive and negative tabs are welded to the positive and negative current collectors through the respective thinning portions, and the energy density of the secondary battery in Examples 1-5 is higher than that in Comparative Examples 1 and 2. It can be seen that in the examples of the present application, the first tab 40 is welded to the first current collector 11 at the first thinning portion 42, which is conducive to reducing the energy required for welding, thereby reducing the possibility of deactivation of the active material of the portion of the second active material layer 13 corresponding to the first slot 121 along the first direction X, and improving the energy density of the secondary battery 1000.

[0167] In Examples 1-5, as the thickness of the first thinning portion 42 increases, the energy density of the secondary battery 1000 tends to decrease. It can be seen that in the examples of the present application, T≤120μm is set, so that the thickness of the first thinning portion 42 is not too thick, which is conducive to further reducing the possibility of deactivation of the active material of the portion of the second active material layer 13 corresponding to the first slot 121 along the first direction X due to the energy of welding, thereby improving the energy density of the secondary battery 1000. On this basis, T≥30μm is set, so that the thickness of the first thinning portion 42 is not too small, which on the one hand reduces the processing difficulty, and on the other hand is conducive to improving the strength of the welding structure formed by welding the first tab 40 to the first current collector 11.

[0168] Those skilled in the art should know that the above-mentioned embodiments are only used to explain the present application, but not as a limitation to the present application, as long as the changes and modifications made to the above embodiments are within the scope of the present application.

Claims

1. A secondary battery characterized by comprising: The secondary battery includes: a first electrode sheet including a first current collector, a first active material layer, and a second active material layer, the first current collector including a first surface and a second surface disposed opposite each other in a first direction, the first direction being a thickness direction of the first electrode sheet, the first active material layer being disposed on the first surface, and the second active material layer being disposed on the second surface, the first active material layer including a first groove, a projection of the first groove being at least partially within a projection area of the second active material layer in the first direction, the first groove extending through the first active material layer in the first direction such that a portion of the first surface is exposed in the first groove; and a first tab including a first main portion and a first thinned portion in an integral structure, a thickness of the first thinned portion being less than a thickness of the first main portion in the first direction, and at least a portion of the first thinned portion being welded to the portion of the first surface exposed in the first groove.

2. The secondary battery according to claim 1, wherein The thickness of the first main portion in the first direction is T1, the thickness of the first thinned portion in the first direction is T, 0.1T1≤T≤0.5T; and / or 30μm≤T≤120μm.

3. The secondary battery according to claim 1 or 2, characterized by, The secondary battery includes a first adhesive, the first tab includes a third surface, the third surface being a surface of the first tab facing the first current collector in the first direction, the third surface including a first region, the first region being located in the first thinned portion, the first adhesive adhering the first surface to the first thinned portion, and the first adhesive being located outside the first region.

4. The secondary battery according to claim 3, wherein The thickness of the first adhesive in the first direction is T2, 5μm≤T2≤50μm.

5. The secondary battery according to claim 3, wherein the positive electrode active material layer is formed on the positive electrode current collector, and the negative electrode active material layer is formed on the negative electrode current collector. The thickness of the first thinned portion in the first direction is T, and the thickness of the first adhesive in the first direction is T2, T2≤T.

6. The secondary battery according to claim 1, wherein The secondary battery includes a second adhesive, the second adhesive being adhered to the first active material layer, and the second adhesive covering an opening of the first groove in the first direction and a portion of the first tab.

7. The secondary battery according to claim 6, wherein The secondary battery further includes a second electrode sheet and a separator, the first electrode sheet, the separator, and the second electrode sheet being sequentially stacked in the first direction, the second electrode sheet including a second current collector and a third active material layer stacked, the third active material layer being located on a side of the second current collector facing the first electrode sheet in the first direction; The secondary battery includes a third adhesive, the third adhesive adhering the third active material layer, and a projection of the third adhesive in the first direction covering a portion of the first tab.

8. The secondary battery according to claim 7, wherein The thickness of the second adhesive in the first direction is T3, 5μm≤T3≤20μm; and / or The thickness of the third adhesive in the first direction is T4, 5μm≤T4≤20μm.

9. The secondary battery according to claim 1, wherein The secondary battery further includes a second electrode sheet, the first electrode sheet and the second electrode sheet are stacked along the first direction, the first electrode sheet is a positive electrode sheet, the second electrode sheet is a negative electrode sheet, a width of the first electrode sheet along a second direction is less than a width of the second electrode sheet along the second direction, the second direction is perpendicular to the first direction, the first tab is disposed on one side of the first electrode sheet along the second direction, and an edge of the second electrode sheet along the second direction and on the same side as the first tab exceeds the first electrode sheet. The first tab includes a first portion, a projection of the first portion along the first direction is outside a projection area of the first electrode sheet and overlaps a projection area of the second electrode sheet. The secondary battery further includes a fourth adhesive, the fourth adhesive adheres and covers a surface of the first portion facing the second electrode sheet.

10. An electric device, characterized by A secondary battery including any one of claims 1 to 9.

11. A method of manufacturing a pole piece, characterized by, A method including the following steps: A first electrode sheet is taken, the first electrode sheet includes a first current collector, a first active material layer and a second active material layer, the first current collector includes a first surface and a second surface oppositely disposed along a first direction, the first active material layer is disposed on the first surface, and the second active material layer is disposed 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 within a projection area of the second active material layer, and 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 electrode sheet; A first tab is taken, part of the material of the first tab is removed to form a first thinning portion, a thickness of the first thinning portion is less than a thickness of the remaining part of the first tab; A surface of the first tab along the thickness direction thereof is attached to the part of the surface of the first surface exposed to the first groove, and at least part of a projection of the first thinning portion along the first direction overlaps the part of the surface of the first surface exposed to the first groove; The first thinning portion is melted, so that the first thinning portion is welded to the first current collector.

12. The production method according to claim 11, wherein The first thinning portion is laser welded to the first current collector.

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