Secondary battery, electric device and method for manufacturing pole plate

Abstract

The invention discloses a secondary battery, electric equipment and a manufacturing method of a pole piece, the secondary battery comprises a first pole piece, the first pole piece comprises a first current collector, a first active substance layer, a second active substance layer and a first tab, the first current collector comprises a first main body part and a first connecting part, the first active substance layer is arranged on a first surface of the first main body part, and the second active substance layer is arranged on a second surface of the first main body part; the second active material layer is provided on the second surface of the first body portion. The first active material layer is provided with a first groove, the first connecting part is connected with the first main body part, and at least part of the first connecting part is located in the first groove. The first tab comprises a first part, the first part is welded with the first connecting part, the projection of the first part in the first direction is located in the first groove, and part of the first tab extends out of the first groove in the second direction; the second direction is perpendicular to the first direction. In the secondary battery, the first tab is connected with the first main body part through the first connecting part and does not need to be directly welded to the first surface, so that the energy density of the secondary battery is favorably improved.

Description

Technical Field

[0001] The present application belongs to the field of energy storage technology, and in particular relates to a secondary battery, an electrical device and a method for manufacturing an electrode. Background Art

[0002] For existing secondary batteries, the structure of welding the pole lug in the middle of the pole piece (MMT) is a common structure for connecting the current collector and the pole lug. When welding the current collector and the pole lug, if ultrasonic welding is used, it is necessary to groove the active material layer on both sides of the current collector along its thickness direction, so that the welding head and welding seat of the ultrasonic welding machine can work together. This kind of groove method has a large capacity loss for the pole piece; if laser welding is used, it is only necessary to groove the active material layer on one surface of the current collector along its thickness direction. However, the active material layer on the opposite side of the groove body 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 groove the active material layer on one side of the current collector, its improvement on the capacity of the secondary battery is not obvious. On this basis, for secondary batteries with multiple pole lugs connected to the same pole piece, the adverse effects of ultrasonic welding and laser welding on the capacity of the secondary battery will be further amplified. Summary of the invention

[0003] In view of the above situation, it is necessary to provide a secondary battery, an electrical device and a method for manufacturing an electrode to improve the capacity of the secondary battery.

[0004] The first aspect of the embodiment of the present application provides a secondary battery, comprising a first pole piece, a second pole piece and a separator, wherein the first pole piece, the separator and the second pole piece are stacked along a first direction, and the first direction is the thickness direction of the first pole piece. The first pole piece comprises a first current collector, a first active material layer, a second active material layer and a first pole ear, the first current collector comprises a first main body and a first connecting portion, the first main body comprises a first face and a second face arranged oppositely along the first direction, the first active material layer is arranged on the first face, and the second active material layer is arranged on the second face. The first active material layer is provided with a first groove, and 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, the first groove penetrates the first active material layer along the first direction, and part of the surface of the first face is exposed in the first groove. The first connecting portion is connected to the first main body, and at least part of the first connecting portion is located in the first groove. The first pole ear comprises a first part, the first part is welded with the first connecting portion, the projection of the first part along the first direction is located in the first groove, and part of the first pole ear extends out of the first groove along the second direction, and the second direction is perpendicular to the first direction; the thickness of the first connecting portion along the first direction is less than the thickness of the first pole ear along the first direction.

[0005] In this secondary battery, the first pole tab is connected to the first main body through the first connecting portion, and the first pole tab does not need to be directly welded to the partial surface of the first surface exposed in the first groove, thereby facilitating the reduction of the degree to which the portion of the second active material layer corresponding to the first groove along the first direction is affected by the heat generated during the welding process of the first pole tab during the process of connecting the first pole tab to the first current collector, so as to maintain the capacity of the portion as much as possible and improve the energy density of the secondary battery. In addition, at least part of the first connecting portion and part of the first pole tab are accommodated in the first groove, which is conducive to reducing the occupation of the first connecting portion and the first pole tab in the internal space of the secondary battery shell, thereby facilitating the improvement of the energy density of the secondary battery.

[0006] In an optional embodiment of the present application, the first connecting portion includes a first end portion and a second end portion, the first end portion is integrally connected to the first main body portion, the second end portion is located in the first groove, the second end portion and the first main body portion are stacked along the first direction; the first portion is welded to the second end portion. The first connecting portion and the first main body portion are an integral structure, which is conducive to improving the stability of the connection between the first connecting portion and the first main body portion, and there is no need to weld between the first connecting portion and the first main body portion, further reducing the impact of welding energy on the second active material layer.

[0007] In an optional embodiment of the present application, the length of the first groove along the second direction is L1, and when the first connecting portion is flattened, the length of the first connecting portion along the second direction is L, L1>L, and 0.1mm≤L1-L≤3mm. When L1-L≤3mm is set, the length of the first connecting portion is not too short, which is conducive to reducing the difficulty of connecting the first connecting portion with the first pole ear and improving production efficiency; when 0.1mm≤L1-L is set, the length of the first connecting portion is not too long, and when the first connecting portion is accommodated in the first groove, it is conducive to reducing the thickness of the first connecting portion stacked along the first direction, thereby facilitating improving the energy density of the secondary battery.

[0008] In an optional embodiment of the present application, the width of the first groove along the third direction is W1, the width of the first connecting portion along the third direction is W, 0.1mm≤W1-W≤3mm, and the first direction, the second direction and the third direction are perpendicular to each other. By setting W1-W≤3mm, the width of the first connecting portion is not too small, which is conducive to reducing the difficulty of welding the first connecting portion to the first tab; by setting 0.1mm≤W i -W, the edge of the first connecting portion along the third direction is not too close to the edge of the first groove along the third direction, which is beneficial to reduce the possibility that the first connecting portion squeezes or rubs the first active material layer and causes the active material of the first active material layer to fall off.

[0009] In an optional embodiment of the present application, the first connecting portion includes a first end portion, an intermediate portion, and a second end portion, the second end portion, the first end portion, and the first main body portion are sequentially stacked along the first direction, the first end portion and the second end portion extend along the second direction, the intermediate portion connects the first end portion and the second end portion, the first end portion is welded to the partial surface of the first surface exposed to the first groove, and the first portion is welded to the second end portion; the thickness of the first end portion along the first direction is less than the thickness of the first pole tab along the first direction. The thickness of the first end portion along the first direction is less than the thickness of the first pole tab along the first direction. In the process of welding the first end portion to the first surface, compared with directly welding the first pole tab to the first surface, less energy is required to melt the first end portion. In other words, less heat is generated during the welding of the first end portion to the first surface, which is conducive to maintaining the capacity of the portion of the second active material layer corresponding to the first groove along the first direction, thereby facilitating the improvement of the energy density of the secondary battery.

[0010] In an optional embodiment of the present application, the thickness of the first end portion along the first direction is T,4 μ m≤T≤30 μ m. Set T≥4 μ m, the thickness of the first connection part is not too small, which is beneficial to improve the structural strength of the first connection part; set T≤30 μ m, the thickness of the first connecting portion is not too large, which is beneficial to reducing the energy required for welding the first connecting portion and the first current collector, so as to maintain the capacity of the portion of the second active material layer corresponding to the first groove along the first direction as much as possible.

[0011] In an optional embodiment of the present application, the first connecting portion includes a first end, an intermediate portion, and a second end, the second end, the first end, and the first main body are sequentially stacked along the first direction, the first end and the second end extend along the second direction, the intermediate portion connects the first end and the second end, the first end is bonded to the surface of the first surface exposed to the first groove, and the first portion is welded to the second end. The first end is bonded to the first surface without welding, which is conducive to further reducing the impact of welding energy on the second active material layer.

[0012] In an optional embodiment of the present application, the length of the first groove along the second direction is L1, and when the first connecting portion is flattened, the length of the first connecting portion along the second direction is L, L>L1, and 0.1mm≤L1-L / 2≤3mm. By setting L1-L / 2≤3mm, the length of the first connecting portion is not too short, which is conducive to reducing the difficulty of connecting the first connecting portion with the first pole ear and improving production efficiency; by setting 0.1mm≤L1-L / 2, the length of the first connecting portion is not too long, and when the first connecting portion is accommodated in the first groove, it is conducive to taking into account the thickness of the first connecting portion stacked along the first direction and the amount of the first active material layer removed to form the first groove, thereby facilitating the improvement of the energy density of the secondary battery.

[0013] In an optional embodiment of the present application, the width of the first groove along the third direction is W1, the width of the first connecting portion along the third direction is W, 0.1mm≤W1-W≤3mm, and the first direction, the second direction and the third direction are perpendicular to each other. When W1-W≤3mm is set, the width of the first connecting portion is not too small, which is conducive to reducing the difficulty of welding the first connecting portion to the first pole ear; when 0.1mm≤W1-W is set, the edge of the first connecting portion along the third direction is not too close to the edge of the first groove along the third direction, which is conducive to reducing the possibility that the first connecting portion squeezes or rubs the first active material layer and causes the active material material of the first active material layer to fall off.

[0014] In an optional embodiment of the present application, the secondary battery further comprises a first adhesive member, and the first adhesive member bonds the second end portion to the first end portion, thereby reducing the possibility of the tab shaking during the use of the secondary battery.

[0015] In an optional embodiment of the present application, the secondary battery further includes a first adhesive member, a portion of the second end portion exceeds the first end portion along the second direction, and the first adhesive member bonds the portion of the second end portion that exceeds the first end portion and the first current collector. This is conducive to reducing the possibility of the tab shaking during the use of the secondary battery.

[0016] In an optional embodiment of the present application, the second end is welded to the first end, which is helpful to reduce the possibility of the tab shaking during the use of the secondary battery.

[0017] In an optional embodiment of the present application, the first part extends beyond the first groove along the first direction. The second pole piece includes a second current collector and a third active material layer connected to each other, the third active material layer is arranged on the side of the second current collector facing the first pole piece along the first direction, and the third active material layer is provided with a second groove, and the projection of the second groove along the first direction covers the projection of the first part along the first direction. In this way, the part of the first pole ear extending beyond the first groove along the first direction can be at least partially accommodated in the second groove, which is conducive to reducing the thickness of the secondary battery along the first direction and improving the energy density of the secondary battery.

[0018] In an optional embodiment of the present application, the first groove has a first opening facing the first direction, and the secondary battery includes a second adhesive member, which is bonded to the first active material layer and covers the first portion and the first opening. The second adhesive member covers the first portion, which is conducive to reducing the possibility that the burrs of the first portion pierce the isolation film and cause an internal short circuit in the secondary battery.

[0019] In an optional embodiment of the present application, the second pole piece includes a second current collector and a third active material layer connected to each other, and the third active material layer is arranged on the side of the second current collector facing the first pole piece along the first direction. The secondary battery includes a third adhesive, the third adhesive is bonded to the third active material layer, and the projection of the third adhesive along the first direction overlaps with the projection of the first part along the first direction. Adding a third adhesive on the basis of the second adhesive is conducive to further reducing the possibility of the burrs of the first part piercing the isolation membrane and causing an internal short circuit of the secondary battery.

[0020] In an optional embodiment of the present application, the first electrode sheet is a positive electrode sheet, the second electrode sheet is a negative electrode sheet, the width of the first main body along the second direction is less than the width of the second electrode sheet along the second direction, and the edge of the second electrode sheet along the second direction and on the same side as the first pole ear exceeds the first pole sheet. The first pole ear includes a second part, the first part and the second part are arranged in sequence along the second direction, and the projection of the second part along the first direction coincides with the partial projection of the second electrode sheet along the first direction. The secondary battery also includes a fourth adhesive, and the fourth adhesive is bonded to and covers the surface of the second part facing the second pole sheet.

[0021] A second aspect of the embodiments of the present application provides an electrical device, comprising a secondary battery as described in any of the aforementioned embodiments.

[0022] A third aspect of an embodiment of the present application provides a method for manufacturing a pole piece, comprising the following steps:

[0023] Providing a first current collector, the first current collector comprising a first surface, the first surface being a surface of the first current collector along a first direction, the first direction being a thickness direction of the first current collector;

[0024] Active material is coated on a portion of the surface of the first side to form a first active material layer, and a portion not coated with the first active material layer forms a hollow foil area;

[0025] A first groove is formed in the first active material layer, the first groove penetrates the first active material layer along a first direction, so that a portion of the surface of the first surface is exposed in the first groove;

[0026] cutting the empty foil area to form a first connecting portion;

[0027] Welding the first pole tab and the first connecting portion, wherein the welding position of the first pole tab and the first connecting portion is located outside the first groove;

[0028] The first connecting portion is bent so that a portion of the first connecting portion and a portion of the first electrode tab are received in the first groove.

[0029] A fourth aspect of an embodiment of the present application provides a method for manufacturing a pole piece, comprising the following steps:

[0030] A first current collector is provided, the first current collector comprises a first surface, the first surface is a surface of the first current collector along a first direction, the first direction is a thickness direction of the first current collector, and an active material is coated on at least a portion of the surface of the first surface to form a first active material layer;

[0031] A first groove is formed in the first active material layer, the first groove penetrates the first active material layer along a first direction, so that a portion of the surface of the first surface is exposed in the first groove;

[0032] Taking a long strip of metal foil as a first connecting portion, welding the first electrode tab to the first connecting portion;

[0033] Welding the first connecting portion to the surface of the first surface exposed in the first groove;

[0034] The first connecting portion is bent so that a portion of the first tab is received in the first groove. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 It is a schematic diagram of the overall structure of a secondary battery in one embodiment of the present application.

[0036] Figure 2 yes Figure 1 Schematic diagram of the cross-sectional structure at II-II.

[0037] Figure 3 It is a schematic diagram of the structure of the first pole piece in a flattened state in one embodiment of the present application.

[0038] Figure 4 yes Figure 3 Schematic diagram of the cross-sectional structure at IV-IV in the figure.

[0039] Figure 5It is a schematic diagram of the cross-sectional structure of the first pole piece in an embodiment of the present application.

[0040] Figure 6 yes Figure 2 Enlarged view of point A in the middle.

[0041] Figure 7 yes Figure 1 Schematic diagram of the cross-sectional structure at VII-VII.

[0042] Figure 8 It is a schematic structural diagram of the first pole piece and the fourth adhesive member in one embodiment of the present application.

[0043] Fig. 9 yes Figure 2 Enlarged view of point B in the middle.

[0044] Fig.10 It is a schematic diagram of the structure of the second pole piece in one embodiment of the present application.

[0045] Fig.11 yes Fig.10 Cross-sectional view at XI-XI in the figure.

[0046] Fig.12 It is a schematic diagram of the structure of an electrical device in an embodiment of the present application.

[0047] Fig.13 It is a schematic structural diagram of a first pole piece in a preparation state in an embodiment of the present application.

[0048] Fig.14 It is a schematic structural diagram of a first pole piece in a preparation state in an embodiment of the present application.

[0049] Fig.15 It is a schematic structural diagram of a first pole piece in a preparation state in an embodiment of the present application.

[0050] Main component symbols

[0051] Secondary battery 1000

[0052] Electrode assembly 100

[0053] The first pole piece 10

[0054] The first current collector 11

[0055] The first main body 111

[0056] First 1111

[0057] First edge 1111a

[0058] Second edge 1111b

[0059] Second side 1112

[0060] The third edge 1112a

[0061] Fourth edge 1112b

[0062] First connection portion 112

[0063] First end 1121

[0064] Second end 1122

[0065] Middle part 1123

[0066] First active material layer 12

[0067] First slot 121

[0068] First opening 1211

[0069] Second active material layer 13

[0070] The second pole piece 20

[0071] Second collector 21

[0072] The second main body 211

[0073] The third side

[0074] The fourth side

[0075] The second connection portion 212

[0076] The third active material layer 22

[0077] Second slot 221

[0078] The third slot 222

[0079] Fourth active material layer 23

[0080] Isolation film 30

[0081] First tab 40

[0082] Part 41

[0083] Part 242

[0084] Second adhesive member 50

[0085] The third adhesive member 60

[0086] Fourth adhesive member 70

[0087] Second pole ear 80

[0088] Part III 81

[0089] Housing 200

[0090] Electrical equipment 10000

[0091] First direction X

[0092] Second direction Y

[0093] The third direction Z

[0094] The following specific implementation methods will further illustrate the present application in conjunction with the above-mentioned drawings. DETAILED DESCRIPTION

[0095] The technical solutions in the embodiments of the present application will be described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all of the embodiments.

[0096] It should be noted that when an element is considered to be "connected" to another element, it may be directly connected to the other element or there may be a centrally disposed element at the same time. When an element is considered to be "disposed on" another element, it may be directly disposed on the other element or there may be a centrally disposed element at the same time.

[0097] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art to which this application belongs. The terms used herein in the specification of this application are only for the purpose of describing specific embodiments and are not intended to limit this application.

[0098] In the description of the embodiments of the present application, the technical terms "first", "second", etc. 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 "multiple" is more than two, unless otherwise clearly and specifically defined.

[0099] In the description of the embodiments of the present application, the term "perpendicular" is used to describe an ideal state between two components. In actual production or use, there may be a state that is approximately perpendicular between the two components. The two components described as "perpendicular" may not be absolutely straight lines or planes, but may be roughly straight lines or planes. From a macroscopic point of view, if the overall extension direction is a straight line or a plane, the components can be considered to be "straight lines" or "planes".

[0100] Reference to "embodiment" herein means that a particular feature, structure, or characteristic described in conjunction with the embodiment may be included in at least one embodiment of the present application. The appearance of the phrase in various locations in the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment that is mutually exclusive with other embodiments. The various embodiments in the present application may be combined with each other in the absence of conflict.

[0101] The embodiment of the present application provides a secondary battery, including a first pole piece, a second pole piece and a separator, wherein the first pole piece, the separator and the second pole piece are stacked along a first direction, and the first direction is the thickness direction of the first pole piece. The first pole piece includes a first current collector, a first active material layer, a second active material layer and a first pole ear, and the first current collector includes a first main body and a first connecting portion, and the first main body includes a first surface and a second surface, and the first surface and the second surface are arranged oppositely along the first direction, and 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, and 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 the first groove penetrates the first active material layer along the first direction, and part of the surface of the first surface is exposed in the first groove. The first connecting portion is connected to the first main body, and at least part of the first connecting portion is located in the first groove. The first pole ear includes a first part, the first part is welded to the first connecting portion, the projection of the first part along the first direction is located in the first groove, and part of the first pole ear extends out of the first groove along the second direction; the second direction is perpendicular to the first direction.

[0102] In this secondary battery, the first pole tab is connected to the first main body through the first connecting portion, and the first pole tab does not need to be directly welded to the partial surface of the first surface exposed in the first groove, thereby facilitating the reduction of the degree to which the portion of the second active material layer corresponding to the first groove along the first direction is affected by the heat generated during the welding process of the first pole tab during the process of connecting the first pole tab to the first current collector, so as to maintain the capacity of the portion as much as possible and improve the energy density of the secondary battery. In addition, at least part of the first connecting portion and part of the first pole tab are accommodated in the first groove, which is conducive to reducing the occupation of the first connecting portion and the first pole tab in the internal space of the secondary battery shell, thereby facilitating the improvement of the energy density of the secondary battery.

[0103] The embodiments of the present application are further described below in conjunction with the accompanying drawings.

[0104] like Figure 1 and Figure 2 As shown, an embodiment of the present application provides a secondary battery 1000 , including an electrode assembly 100 and a shell 200 , wherein the electrode assembly 100 is accommodated in the shell 200 .

[0105] In some embodiments, the electrode assembly 100 includes a first electrode sheet 10 , a second electrode sheet 20 and an isolation film 30 . The first electrode sheet 10 , the isolation film 30 and the second electrode sheet 20 are stacked along a first direction X, and the first direction X is the thickness direction of the first electrode sheet 10 .

[0106] In some embodiments, Figure 2 As shown, the first pole piece 10, the isolation film 30 and the second pole piece 20 are stacked along a first direction X and then wound to form a winding structure.

[0107] In some embodiments, a plurality of first pole sheets 10 , a plurality of isolation films 30 , and a plurality of second pole sheets 20 are stacked to form a stacked structure, and for any adjacent positive pole sheet and negative pole sheet, an isolation film 30 is disposed between the two.

[0108] In some embodiments, Figure 2 As shown, the first pole piece 10 includes a first current collector 11, a first active material layer 12, a second active material layer 13 and a first pole tab 40. The first active material layer 12, the first current collector 11 and the second active material layer 13 are sequentially stacked along a first direction μ, and the first pole tab 40 is connected to the first current collector 11. The first direction X is the thickness direction of the first pole piece 10.

[0109] In some embodiments, Figure 2 As shown, the second electrode sheet 20 includes a second current collector 21, a third active material layer 22, a fourth active material layer 23 and a second electrode tab 80. The third active material layer 22, the second current collector 21 and the fourth active material layer 23 are stacked in sequence along the first direction X, and the second electrode tab 80 is connected to the second current collector 21.

[0110] In some embodiments, one of the first electrode sheet 10 and the second electrode sheet 20 is a positive electrode sheet, and the other is a negative electrode sheet. When the first electrode sheet 10 is a positive electrode sheet, the first current collector 11 is a positive electrode current collector, the first active material layer 12 and the second active material layer 13 are positive electrode active material layers, the first electrode tab 40 is a positive electrode tab, the second current collector 21 is a negative electrode current collector, the third active material layer 22 and the fourth active material layer 23 are negative electrode active material layers, and the second electrode tab 80 is a negative electrode tab; when the first electrode sheet 10 is a negative electrode sheet, the first current collector 11 is a negative electrode current collector, the first active material layer 12 and the second active material layer 13 are negative electrode active material layers, the first electrode tab 40 is a negative electrode tab, the second current collector 21 is a positive electrode current collector, the third active material layer 22 and the fourth active material layer 23 are positive electrode active material layers, and the second electrode tab 80 is a positive electrode tab.

[0111] In some embodiments, the positive electrode current collector is a metal layer. As an illustrative example, the positive electrode current collector can be a metal layer including at least one of aluminum, nickel, tantalum, and titanium, such as aluminum foil.

[0112] In some embodiments, the positive electrode active material layer includes a positive electrode active material, and the positive electrode active material includes at least one of lithium cobalt oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium iron phosphate, lithium manganese iron phosphate, or lithium manganese oxide.

[0113] In some embodiments, the negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer, and the negative electrode active material layer is disposed on at least one side of the negative electrode current collector along the thickness direction thereof.

[0114] In some embodiments, the negative electrode current collector is a metal layer. As an illustrative example, the negative electrode current collector may be a metal layer including at least one of copper, nickel, tantalum, and titanium, such as copper foil.

[0115] In some embodiments, at least one of the positive electrode current collector and the negative electrode current collector is a composite current collector.

[0116] In some embodiments, the negative electrode active material layer includes a negative electrode active material, and the negative electrode active material includes at least one of graphite, hard carbon, soft carbon, silicon, silicon-oxygen material, and silicon-carbon material.

[0117] In some embodiments, the isolation film 30 is made of insulating film materials such as polyethylene film, polypropylene film, polyester film or polyimide film.

[0118] In some embodiments, the secondary battery 1000 further includes an electrolyte (not shown), which is contained in the housing.

[0119] 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.

[0120] In some embodiments, the electrolyte salt includes but is not limited to at least one of lithium hexafluorophosphate (LiPF6), lithium bis(trifluoromethanesulfonyl)imide LiN(CF3SO2)2 (LiTFSI), lithium bis(fluorosulfonyl)imide Li(N(SO2F)2) (LiFSI), lithium hexafluorocesium oxide (LiCsF6), lithium perchlorate (LiClO4) or lithium trifluoromethanesulfonate (LiCF3SO3).

[0121] In some embodiments, Figure 3 and Figure 4 As shown, the first current collector 11 includes a first main body 111 and a first connecting portion 112, the first main body 111 includes a first surface 1111 and a second surface 1112, the first surface 1111 and the second surface 1112 are arranged opposite to each other along the first direction X, the first active material layer 12 is arranged on the first surface 1111, and the second active material layer 13 is arranged on the second surface 1112. The first main body 111 is connected to the first connecting portion 112, and the first electrode tab 40 is welded to the first connecting portion 112.

[0122] In some embodiments, Figure 3 and Figure 4 As shown, the first active material layer 12 is provided with a first groove 121, and along the first direction X, at least part of the projection of the first groove 121 is located in the projection area of ​​the second active material layer 13. The first groove 121 penetrates the first active material layer 12 along the first direction X, and part of the surface of the first surface 1111 is exposed in the first groove 121. The first connecting portion 112 is connected to the first main body 111, and at least part of the first connecting portion 112 is located in the first groove 121; the first pole ear 40 includes a first portion 41, the first portion 41 is welded to the first connecting portion 112, and the projection of the first portion 41 along the first direction X is located in the first groove 121, and part of the first pole ear 40 extends out of the first groove 121 along the second direction Y. The thickness of the first connecting portion 112 along the first direction X is less than the thickness of the first pole ear 40 along the first direction X. The second direction Y is perpendicular to the first direction X. Among them, the thickness of the first connecting portion 112 refers to the thickness of the first connecting portion 112 in a flattened state.

[0123] In this embodiment, the first pole tab 40 is connected to the first main body 111 through the first connecting portion 112, and the first pole tab 40 does not need to be directly welded to the surface of the first 1111 exposed in the first groove 121, which is conducive to reducing the degree of influence of the heat generated by the welding process of the first pole tab 40 on the portion of the second active material layer 13 corresponding to the first groove 121 along the first direction X during the connection between the first pole tab 40 and the first current collector 11, so as to maintain the capacity of the portion as much as possible and improve the energy density of the secondary battery 1000. In addition, at least part of the first connecting portion 112 and part of the first pole tab 40 are accommodated in the first groove 121, which is conducive to reducing the occupation of the first connecting portion 112 and the first pole tab 40 on the internal space of the shell of the secondary battery 1000, thereby facilitating the improvement of the energy density of the secondary battery 1000.

[0124] In some embodiments, the first groove 121 is formed by removing a portion of the first active material layer 12 using a laser.

[0125] In some embodiments, before the active material of the first active material layer 12 is coated, adhesive tape is attached to part of the surface of the first surface 1111. After the active material is coated and dried, the adhesive tape and the active material covering the surface of the adhesive tape fall off, thereby forming a first groove 121.

[0126] In some embodiments, Figure 4As shown, the first connection portion 112 includes a first end portion 1121 and a second end portion 1122, the first end portion 1121 is integrally connected to the first main body portion 111, the second end portion 1122 is located in the first groove 121, the second end portion 1122 and the first main body portion 111 are stacked along the first direction X, and the first portion 41 is welded to the second end portion 1122. The first connection portion 112 and the first main body portion 111 are an integral structure, which is conducive to improving the stability of the connection between the first connection portion 112 and the first main body portion 111, and there is no need to weld between the first connection portion 112 and the first main body portion 111, further reducing the influence of welding energy on the second active material layer 13.

[0127] The stacked state of the second end portion 1122 and the first main body portion 111 is formed by bending the first connection portion 112 , and the extension direction of the first connection portion 112 corresponds to the length direction of the first connection portion 111 in the flattened state.

[0128] In order to improve the energy density of the secondary battery 1000, it is usually necessary to accommodate the first connecting portion 112 in the first groove 121 as much as possible to reduce the possibility of the first connecting portion 112 being stacked on the end surface of the electrode assembly 100 along the second direction Y. On this basis, if the energy density of the secondary battery 1000 is to be further improved, it is necessary to reduce the area of ​​the projection of the first groove 121 along the first direction X, that is, to reduce the mass of the removed first active material layer 12. At this time, when the first connecting portion 112 is accommodated in the first groove 121, the thickness of the first connecting portion 112 stacked along the first direction X may increase, affecting the further improvement of the energy density of the secondary battery 1000. If the area of ​​the projection of the first groove 121 along the first direction X is increased to reduce the thickness of the first connecting portion 112 stacked along the first direction X, the mass of the first active material layer 12 to be removed increases, which also affects the further improvement of the energy density of the secondary battery 1000.

[0129] Fig.13 A schematic diagram of the structure of the first pole piece 10 in a preparation state in one embodiment of the present application is shown. Fig.13 In the embodiment, the first end portion 1121 of the first connecting portion 112 is integrally connected to the first current collector 11 , a portion of the first electrode tab 40 has not yet been folded into the first groove 121 , and the first transition portion 112 is in a flattened state.

[0130] In some embodiments, Fig.13As shown, the length of the first groove 121 along the second direction is L1. When the first connection part 112 is flattened, the length of the first connection part 112 along the second direction is L, L1>L, and 0.1mm≤L1-L≤3mm. When L1-L≤3mm is set, the length of the first connection part is not too short, which is conducive to reducing the difficulty of connecting the first connection part with the first pole ear and improving production efficiency; when 0.1mm≤L1-L is set, the length of the first connection part is not too long. When the first connection part is accommodated in the first groove, it is conducive to reducing the thickness of the first connection part stacked along the first direction, thereby facilitating improving the energy density of the secondary battery.

[0131] In some embodiments, Figure 5 As shown, the first connecting portion 112 includes a first end portion 1121, a middle portion 1123 and a second end portion 1122. The second end portion 1122, the first end portion 1121 and the first main body portion 111 are stacked in sequence along the first direction X. The first end portion 1121 and the second end portion 1122 extend along the second direction Y. The middle portion 1123 connects the first end portion 1121 and the second end portion 1122.

[0132] In some embodiments, the first end 1121 is welded to the partial surface of the first surface 1111 exposed to the first groove 121, and the first portion 41 is welded to the second end 1122. The thickness of the first end 1121 along the first direction X is less than the thickness of the first electrode tab 40 along the first direction X. Since the thickness of the first end 1121 along the first direction X is less than the thickness of the first electrode tab 40 along the first direction X, during the welding process of the first end 1121 and the first electrode 1111, compared with the direct welding of the first electrode tab 40 and the first electrode 1111, less energy is required to melt the first end 1121. In other words, less heat is generated during the welding process of the first end 1121 and the first surface 1111, which is conducive to maintaining the capacity of the portion of the second active material layer 13 corresponding to the first groove 121 along the first direction X, thereby facilitating the improvement of the energy density of the secondary battery 1000.

[0133] The stacked state of the first end 1121 and the second end 1122 is formed by bending the first connection portion 112 , and the extending direction of the first connection portion 112 corresponds to the length direction of the first connection portion 112 in the flattened state.

[0134] In some embodiments, Figure 4 and Figure 5As shown, the thickness of the first end portion 1121 along the first direction X is T, 4μm≤T≤30μm. When T≥4μm, the thickness of the first end portion 1121112 is not too small, which is beneficial to improving the structural strength of the first end portion 1121; when T≤30μm, the thickness of the first end portion 1121 is not too large, which is beneficial to reducing the energy required for welding the first end portion 1121 and the first current collector 11, so as to maintain the capacity of the portion of the second active material layer 13 corresponding to the first groove 121 along the first direction X as much as possible.

[0135] In the embodiment of the present application, the thickness of the first end portion 1121 may be measured using a micrometer.

[0136] In some embodiments, the first end 1121 is bonded to the surface of the first surface 1111 exposed in the first groove 121, and the first portion 41 is welded to the second end 1122. The first end 1121 is bonded to the first surface 1111 without welding, which is beneficial to further reduce the impact of welding energy on the second active material layer 13.

[0137] Fig.14 A schematic diagram of the structure of the first pole piece 10 in a preparation state in one embodiment of the present application is shown. Fig.14 In the embodiment, the first end portion 1121 of the first connecting portion 112 is welded to the first current collector 11 , a portion of the first electrode tab 40 has not yet been folded into the first groove 121 , and the first transition portion 112 is in a flattened state.

[0138] In some embodiments, Fig.14 As shown, 0.1mm≤L1-L / 2≤3mm. When L1-L / 2 is set to 3mm, the length of the first connecting portion 112 is not too short, which is conducive to reducing the difficulty of connecting the first connecting portion 112 with the first pole ear 40 and improving production efficiency; when 0.1mm≤L1-L / 2 is set, the length of the first connecting portion 112 is not too long. When the first connecting portion 112 is accommodated in the first groove 121, it is conducive to taking into account the thickness of the first connecting portion 112 stacked along the first direction X and the amount of the first active material layer 12 removed to form the first groove 121, thereby facilitating the improvement of the energy density of the secondary battery 1000.

[0139] In some embodiments, Fig.13 and Fig.14As shown, the width of the first groove 121 along the third direction Z is W1, the width of the first connection part 112 along the third direction Z is W, 0.1mm≤W1-W≤3mm; the first direction X, the second direction Y and the third direction Z are perpendicular to each other. When W1-W≤3mm, the width of the first connection part 112 is not too small, which is conducive to reducing the difficulty of welding the first connection part 112 with the first pole tab 40; when 0.1mm≤W1-W is set, the edge of the first connection part 112 along the third direction Z and the edge of the first groove 121 along the third direction Z are not too close, which is conducive to reducing the possibility that the first connection part 112 squeezes or rubs the first active material layer 12 and causes the active material material of the first active material layer 12 to fall off; it is also conducive to reducing the possibility that the first connection part 112 and the first active material layer 12 are stacked when the first connection part 112 is folded during the production process of the secondary battery 1000, so as to reduce the influence of the thickness of the first connection part on the thickness of the secondary battery.

[0140] In this embodiment of the present application, the length L of the first connecting portion 112 , the width W of the first connecting portion 112 , the length L1 of the first groove 121 , and the width W1 of the first groove 121 may all be measured using a micrometer.

[0141] In some embodiments, as an illustrative example, the first connection portion 112 is one of aluminum, nickel, and copper, or the first connection portion 112 is one of an aluminum alloy, a nickel alloy, or a copper alloy.

[0142] In some embodiments, Figure 3 As shown, the first surface 1111 includes a first edge 1111a and a second edge 1111b arranged oppositely along the second direction Y, and the first active material layer 12 extends to the first edge 1111a and the second edge 1111b along the first direction X; the second surface 1112 includes a third edge 1112a and a fourth edge 1112b arranged oppositely along the second direction Y, and the second active material layer 13 extends to the third edge 1112a and the fourth edge 1112b along the second direction Y. In this way, it is beneficial to fully utilize the width of the first main body 111 of the first current collector 11 along the second direction Y, thereby facilitating the increase of the coating area of ​​the first active material layer 12 and the second active material layer 13, and improving the energy density of the secondary battery 1000.

[0143] In some embodiments, the secondary battery 1000 further includes a first adhesive member (not shown), the first adhesive member bonding the second end 1122 and the first end 1121. This helps to reduce the possibility of the tab shaking during the use of the secondary battery 1000.

[0144] In some embodiments, the secondary battery 1000 further includes a first adhesive member (not shown), a portion of the second end 1122 exceeds the first end 1121 along the second direction Y, and the first adhesive member bonds the portion of the second end 1122 that exceeds the first end 1121 and the first current collector. This helps reduce the possibility of the tab shaking during use of the secondary battery 1000.

[0145] In some embodiments, the first adhesive member is a conductive adhesive or an epoxy resin adhesive.

[0146] In some embodiments, the conductive adhesive includes an adhesive layer matrix and a conductor, and the conductor is dispersed in the adhesive layer matrix.

[0147] In some embodiments, the adhesive layer matrix includes at least one of silicone rubber, polyurethane rubber, chloroprene rubber, hot melt adhesive, and tackifying resin.

[0148] In some embodiments, the conductor includes at least one of gold, silver, copper, aluminum, nickel, and graphite.

[0149] In some embodiments, the first adhesive member is adhesive tape.

[0150] In some embodiments, the second end 1122 is welded to the first end 1121. This helps to reduce the possibility of the tab shaking during the use of the secondary battery 1000.

[0151] In some embodiments, the first portion 41 exceeds the first groove 121 along the first direction X. The third active material layer 22 is disposed on the side of the second current collector 21 facing the first electrode sheet 10 along the first direction X, and the third active material layer 22 is provided with a second groove 221, and the projection of the second groove 221 along the first direction X covers the projection of the first portion 41 along the first direction X. In this way, the portion of the first electrode tab 40 that exceeds the first groove 121 along the first direction X can be at least partially accommodated in the second groove 221, which is conducive to reducing the thickness of the secondary battery 1000 along the first direction X and improving the energy density of the secondary battery 1000.

[0152] In some embodiments, Figure 6 As shown, the first groove 121 has a first opening 1211 facing the first direction μ, and the secondary battery 1000 includes a second adhesive 50, which is bonded to the first active material layer 12 and covers the first portion 41 and the first opening 1211. The second adhesive 50 covers the first portion 41, which is conducive to reducing the possibility that the burrs of the first portion 41 pierce the isolation film 30 and cause an internal short circuit of the secondary battery 1000.

[0153] In some embodiments, Figure 6As shown, the third active material layer 22 is disposed on the side of the second current collector 21 along the first direction μ toward the first pole piece 10. The secondary battery 1000 includes a third adhesive 60, the third adhesive 60 is bonded to the third active material layer 22, and the projection of the third adhesive 60 along the first direction μ overlaps with the projection of the first part 41 along the first direction X. The third adhesive 60 is provided on the basis of the second adhesive 50, which is conducive to further reducing the possibility of the burrs of the first part 41 piercing the isolation film 30 and causing an internal short circuit of the secondary battery 1000.

[0154] In some embodiments, the first electrode sheet 10 is a negative electrode sheet, the second electrode sheet 20 is a positive electrode sheet, and along the first direction X, the projection of the third adhesive member 60 covers the projection of the second adhesive member 50. In this way, it is beneficial to increase the CB (Cell Balance, the ratio of the negative electrode capacity per unit area to the positive electrode capacity per unit area) of the positive and negative electrode sheets, and it is beneficial to reduce the possibility of lithium deposition in the electrode assembly 100 during the cycle process.

[0155] In some embodiments, Figure 6 As shown, the first electrode sheet 10 is a positive electrode sheet, the second electrode sheet 20 is a negative electrode sheet, and along the first direction X, the projection of the second adhesive member 50 covers the projection of the third adhesive member 60. In this way, it is beneficial to increase the CB of the positive and negative electrode sheets, and to reduce the possibility of lithium deposition in the electrode assembly 100 during the cycle.

[0156] In some embodiments, Figure 7 and Figure 8 As shown, the first pole piece 10 is a positive pole piece, the second pole piece 20 is a negative pole piece, the width of the first main body 111 along the second direction Y is less than the width of the second pole piece 20 along the second direction Y, and the edge of the second pole piece 20 along the second direction Y and on the same side as the first pole ear 40 exceeds the first pole piece 10. The first pole ear 40 includes a second part 42, the first part 41 and the second part 42 are arranged in sequence along the second direction Y, and the projection of the second part 42 along the first direction X coincides with the partial projection of the second pole piece 20 along the first direction c. The secondary battery 1000 also includes a fourth adhesive 70, and the fourth adhesive 70 is bonded to and covers the surface of the second part 42 facing the second pole piece 20. In this way, it is helpful to reduce the possibility that the burrs of the second part 42 pierce the isolation film 30 and cause an internal short circuit of the secondary battery 1000.

[0157] In some embodiments, at least one of the second adhesive member 50 , the third adhesive member 60 , and the fourth adhesive member 70 is adhesive tape.

[0158] In some embodiments, the adhesive tape includes a base layer and an adhesive layer.

[0159] In some embodiments, the substrate layer can be selected from one of polyethylene terephthalate, coextruded polypropylene, oriented polystyrene, thermoplastic polyurethane, polylactic acid, polyolefin, and polyimide.

[0160] In some embodiments, the rubber layer is made of one or a combination 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 α-olefin copolymer, petroleum resin, terpene resin, and rosin resin.

[0161] In some embodiments, Figures 9 to 11 As shown, the second current collector 21 includes a second main body 211 and a second connecting portion 212, the second main body 211 includes a third surface 2111 and a fourth surface 2112, the third surface 2111 and the fourth surface 2112 are arranged opposite to each other along the first direction X, the third active material layer 22 is arranged on the third surface 2111, and the fourth active material layer 23 is arranged on the fourth surface 2112. The second main body 211 is connected to the second connecting portion 212, and the second electrode tab 80 is welded to the second connecting portion 212.

[0162] In some embodiments, Figures 9 to 11 As shown, the fourth active material layer 23 is provided with a third groove 222, and along the first direction X, at least part of the projection of the third groove 222 is located in the projection area of ​​the third active material layer 22. The third groove 222 penetrates the fourth active material layer 23 along the first direction X, and part of the surface of the fourth surface 2112 is exposed in the third groove 222. The second connecting portion 212 is connected to the second main body portion 212, and at least part of the second connecting portion 212 is located in the third groove 222; the second pole ear 80 includes a third portion 81, the third portion 81 is welded to the second connecting portion 212, and the projection of the third portion 81 along the first direction X is located in the third groove 222, and part of the second pole ear 80 extends out of the third groove 222 along the second direction Y. The second pole tab 80 is connected to the second main body 211 through the second connecting portion 212. The second pole tab 80 does not need to be directly welded to the partial surface of the fourth surface 2112 exposed in the third groove 222. In the process of connecting the second pole tab 80 to the second current collector 21, the portion of the third active material layer 22 corresponding to the third groove 222 along the first direction X is not affected by the heat generated during the welding process of the second pole tab 80, so that the capacity can be maintained, which is beneficial to improving the energy density of the secondary battery 1000. In addition, at least part of the second connecting portion 212 and part of the second pole tab 80 are accommodated in the third groove 222, which is beneficial to reducing the occupation of the second connecting portion 212 and the second pole tab 80 for the internal space of the shell of the secondary battery 1000, thereby facilitating the improvement of the energy density of the secondary battery 1000.

[0163] like Fig.12 As shown, an embodiment of the present application further provides an electric device 10000, and the electric device 10000 includes the secondary battery 1000 involved in any of the aforementioned embodiments.

[0164] An embodiment of the present application provides a method for manufacturing a pole piece, and the method for manufacturing a pole piece comprises the following steps:

[0165] A first current collector 11 is provided. The first current collector 11 includes a first portion 1111. The first portion 1111 is a surface of the first current collector 11 along a first direction X. The first direction X is a thickness direction of the first current collector 11.

[0166] Active material is coated on a portion of the surface of the first surface 1111 to form a first active material layer 12, and a portion not coated with the first active material layer 12 forms an empty foil area;

[0167] A first groove 121 is formed in the first active material layer 12 . The first groove 121 penetrates the first active material layer 12 along the first direction X, so that a portion of the surface of the first surface 1111 is exposed in the first groove 121 .

[0168] Cutting the empty foil area to form a first connecting portion 112;

[0169] The first electrode tab 40 and the first connecting portion 112 are welded, and the welding position of the first electrode tab 40 and the first connecting portion 112 is located outside the first groove 121;

[0170] The first connection portion 112 is bent so that a portion of the first connection portion 112 and a portion of the first electrode tab 40 are received in the first groove 121 .

[0171] An embodiment of the present application provides another method for manufacturing a pole piece, and the method for manufacturing a pole piece comprises the following steps:

[0172] A first current collector 11 is provided. The first current collector 11 includes a first surface 1111. The first surface 1111 is a surface of the first current collector 11 along a first direction μ. The first direction μ is a thickness direction of the first current collector 11. Active material is coated on at least a portion of the surface of the first surface 1111 to form a first active material layer 12.

[0173] A first groove 121 is formed in the first active material layer 12 , and the first groove 121 penetrates the first active material layer 12 along the first direction μ, so that a portion of the surface of the first surface 1111 is exposed in the first groove 121 ;

[0174] A long strip of metal foil is used as the first connecting portion 112, and the first electrode tab 40 is welded to the first connecting portion 112;

[0175] Welding the first connection portion 112 to the surface of the first 1111 exposed in the first groove 121;

[0176] The first connecting portion 112 is bent so that a portion of the first electrode tab 40 is received in the first groove 121 .

[0177] It should be noted that, in the aforementioned steps, there is no strict time sequence limitation between the step of welding the first electrode tab 40 and the first connecting portion 112 and the step of welding the first connecting portion 112 and the first current collector 11, that is, the first electrode tab 40 and the first connecting portion 112 may be welded first, and then the first connecting portion 112 and the first current collector 11 may be welded, or the first connecting portion 112 and the first current collector 11 may be welded first, and then the first electrode tab 40 and the first connecting portion 112 may be welded.

[0178] In some embodiments, Figures 13 to 15 As shown, when welding the first electrode tab 40 and the first connecting portion 112, the first electrode tab 40 is welded to the surface of the first connecting portion 112 on the same side as the second surface 1112 along the first direction X, and the end of the first electrode tab 40 not welded to the first connecting portion 112 is toward the middle of the first current collector 11 along the second direction Y, and then the first connecting portion 112 is folded ( Fig.15 The arc arrow in the figure indicates the folding direction of the first connecting portion 112 ), so that the first electrode tab 40 and the first 1111 are on the same side of the first current collector 11 .

[0179] Those skilled in the art should recognize that the above embodiments are only used to illustrate the present application and are not intended to be limiting of the present application. As long as they are within the spirit and scope of the present application, appropriate changes and modifications to the above embodiments are within the scope of the present application.

Claims

1. A secondary battery, comprising a first pole piece, a second pole piece and a separator, wherein the first pole piece, the separator and the second pole piece are stacked along a first direction, the first direction being a thickness direction of the first pole piece, characterized in that: The first electrode sheet comprises a first current collector, a first active material layer, a second active material layer and a first electrode tab, the first current collector comprises a first main body and a first connecting portion, the first main body comprises a first surface and a second surface arranged opposite to each other along the 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, and along the first direction, at least part of the projection of the first groove is located within the projection area of ​​the second active material layer, the first groove penetrates the first active material layer along the first direction, and part of the surface of the first surface is exposed in the first groove; The first connecting portion is connected to the first main body portion, and at least a portion of the first connecting portion is located in the first groove; The first pole tab comprises a first portion, the first portion is welded to the first connecting portion, a projection of the first portion along the first direction is located in the first slot, and a portion of the first pole tab extends out of the first slot along a second direction, and the second direction is perpendicular to the first direction; Along the first direction, the thickness of the first connecting portion is smaller than the thickness of the first electrode tab.

2. The secondary battery according to claim 1, wherein: The first connecting portion includes a first end portion and a second end portion, the first end portion is integrally connected to the first main body portion, the second end portion is located in the first groove, and the second end portion and the first main body portion are stacked along the first direction; the first portion is welded to the second end portion.

3. The secondary battery according to claim 2, characterized in that: The first connection portion satisfies at least one of the following conditions a and b: a. The length of the first groove along the second direction is L1. When the first connecting portion is flattened, the length of the first connecting portion along the second direction is L, L1>L, and 0.1mm≤L1-L≤3mm; b. The width of the first groove along the third direction is W1, the width of the first connecting portion along the third direction is W, 0.1mm≤W1-W≤3mm; the first direction, the second direction and the third direction are perpendicular to each other.

4. The secondary battery according to claim 1, wherein: The first connecting portion includes a first end portion, a middle portion, and a second end portion, the second end portion, the first end portion, and the first main portion are sequentially stacked along the first direction, the first end portion and the second end portion extend along the second direction, the middle portion connects the first end portion and the second end portion, the first end portion is welded to a portion of the surface of the first surface exposed to the first groove, and the first portion is welded to the second end portion; A thickness of the first end portion along the first direction is smaller than a thickness of the first electrode tab along the first direction.

5. The secondary battery according to claim 4, characterized in that: A thickness of the first end portion along the first direction is T, and 4 μm≤T≤30 μm.

6. The secondary battery according to claim 1, wherein: The first connecting portion includes a first end portion, a middle portion, and a second end portion. The second end portion, the first end portion, and the first main body portion are stacked in sequence along the first direction. The first end portion and the second end portion extend along the second direction. The middle portion connects the first end portion and the second end portion. The first end portion is bonded to the surface of the first surface exposed to the first groove, and the first portion is welded to the second end portion.

7. The secondary battery according to claim 4 or 6, characterized in that: The first connection portion satisfies at least one of the following conditions c and d: c. The length of the first groove along the second direction is L1. When the first connecting portion is flattened, the length of the first connecting portion along the second direction is L, L>L1, and 0.1mm≤L1-L / 2≤3mm; d. The width of the first groove along the third direction is W1, the width of the first connecting portion along the third direction is W, 0.1 mm ≤ W1 - W ≤ 3 mm; the first direction, the second direction and the third direction are perpendicular to each other.

8. The secondary battery according to claim 2, 4 or 6, characterized in that: The secondary battery satisfies at least one of the conditions e, f, and g: e. The secondary battery further includes a first adhesive member, wherein the first adhesive member bonds the second end portion and the first end portion; f. The secondary battery further includes a first adhesive member, a portion of the second end portion exceeds the first end portion along the second direction, and the first adhesive member bonds a portion of the second end portion exceeding the first end portion and the first current collector; g. The second end is welded to the first end.

9. The secondary battery according to claim 1, wherein: The first portion extends beyond the first slot along the first direction; The second pole piece includes a second current collector and a third active material layer which are connected to each other. The third active material layer is arranged on a side of the second current collector along the first direction facing the first pole piece. The third active material layer is provided with a second groove. The projection of the second groove along the first direction covers the projection of the first part along the first direction.

10. The secondary battery according to claim 1, wherein: The first groove has a first opening facing the first direction. The secondary battery further includes a second adhesive member, which is adhered to the first active material layer and covers the first portion and the first opening.

11. The secondary battery according to claim 10, characterized in that: The second pole piece includes a second current collector and a third active material layer connected to each other, and the third active material layer is arranged on a side of the second current collector along the first direction toward the first pole piece; The secondary battery includes a third adhesive member, the third adhesive member is bonded to the third active material layer, and a projection of the third adhesive member along the first direction overlaps with a projection of the first portion along the first direction.

12. The secondary battery according to claim 1, wherein: The first pole piece is a positive pole piece, the second pole piece is a negative pole piece, the width of the first main body along the second direction is smaller than the width of the second pole piece along the second direction, and the edge of the second pole piece along the second direction and on the same side as the first pole ear exceeds the first pole piece; The first pole lug includes a second portion, the first portion and the second portion are sequentially arranged along the second direction, and a projection of the second portion along the first direction coincides with a partial projection of the second pole piece along the first direction; The secondary battery further includes a fourth adhesive member, and the fourth adhesive member is bonded to and covers a surface of the second portion facing the second pole piece.

13. An electrical equipment, characterized in that: The invention comprises the secondary battery according to any one of claims 1 to 12.

14. A method for manufacturing a pole piece, characterized in that: The following steps are involved: Providing a first current collector, wherein the first current collector comprises a first surface, wherein the first surface is a surface of the first current collector along a first direction, and the first direction is a thickness direction of the first current collector; coating active material on a portion of the surface of the first surface to form a first active material layer, and forming a hollow foil area on a portion not coated with the first active material layer; A first groove is formed in the first active material layer, wherein the first groove penetrates the first active material layer along the first direction so that a portion of the first surface is exposed in the first groove; cutting the empty foil area to form a first connecting portion; Welding the first pole tab and the first connecting portion, wherein the welding position of the first pole tab and the first connecting portion is located outside the first groove; The first connecting portion is bent so that a portion of the first connecting portion and a portion of the first electrode tab are received in the first groove.

15. A method for manufacturing a pole piece, characterized in that: The following steps are involved: Providing a first current collector, the first current collector comprising a first surface, the first surface being a surface of the first current collector along a first direction, the first direction being a thickness direction of the first current collector, and coating at least a portion of the surface of the first surface with an active material to form a first active material layer; A first groove is formed in the first active material layer, wherein the first groove penetrates the first active material layer along the first direction so that a portion of the first surface is exposed in the first groove; Taking a long strip of metal foil as a first connecting portion, welding a first electrode tab to the first connecting portion; welding the first connecting portion to a surface of the first surface exposed in the first groove; The first connecting portion is bent so that a portion of the first electrode tab is received in the first groove.

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