Secondary battery and electronic device

Abstract

A secondary battery (100) comprises an electrode sheet (10). The electrode sheet (10) comprises a current collector (11), which has a first surface (111) and a second surface (112) arranged opposite each other. A first active material layer (12) is disposed on the first surface (111). The first active material layer (12) has a first recess (121) and a first edge (122). A portion of a tab (13) is arranged in the first recess (121), while the other portion thereof extends from the first edge (122). The first recess (121) has a first inner wall (1211), a second inner wall (1212), a third inner wall (1213) and a fourth inner wall (1214). In the direction of length of the current collector (11), the first inner wall (1211) and the second inner wall (1212) are respectively inner walls at two ends of the first recess (121). In the extension direction of the tab (13), the third inner wall (1213) and the fourth inner wall (1214) are respectively inner walls at the ends of the first recess (121). The third inner wall (1213) is away from the first edge (122), whereas the fourth inner wall (1214) is close to the first edge (122). A first connecting wall (123) is provided between the fourth inner wall (1214) and the first inner wall (1211). In the extension direction of the tab (13), the minimum width from the first connecting wall (123) to the first edge (122) is W1, where W1>0 mm. By means of limiting the value of W1, the likelihood of damage and tearing of the current collector can be reduced, the cold-pressing resistance of the electrode sheet can be improved and the collision resistance of the secondary battery can be improved.

Description

Secondary battery and electronic device TECHNICAL FIELD

[0001] The present application relates to the technical field of batteries, in particular to a secondary battery and an electronic device. BACKGROUND

[0002] The tab is usually made of metal material as a bridge for electrical connection between the battery and the external circuit. The tab is welded with the current collector inside the battery, which can make the tab conductive with the electrode assembly inside the battery, so as to achieve the purpose of transmitting current.

[0003] The current collector is provided with an active material layer, and a slot is usually formed in the active material layer to expose the current collector, so as to facilitate the welding of the tab and the current collector. However, in the process of cold pressing of the pole piece or dropping of the battery, the slotted area of the pole piece is easy to be subjected to a large shear force, and the current collector is easy to be damaged and torn, resulting in voltage drop of the battery and failure.

[0004] SUMMARY

[0005] The present application aims to provide a secondary battery and an electronic device, which can improve the damage and tearing of the current collector and reduce the risk of battery failure.

[0006] The embodiments of the present application adopt the following technical solutions:

[0007] In a first aspect, the present application provides a secondary battery, comprising a current collector, a first active material layer and a tab. Along the thickness direction of the current collector, the current collector has a first surface and a second surface arranged oppositely. The first surface is provided with the first active material layer. The first active material layer has a first groove and a first edge. A part of the tab is arranged in the first groove, and another part of the tab extends out of the first edge. The first groove has a first inner wall, a second inner wall, a third inner wall and a fourth inner wall. Along the length direction of the current collector, the first inner wall and the second inner wall are respectively the inner walls at both ends of the first groove. Along the extending direction of the tab, the third inner wall and the fourth inner wall are respectively the inner walls at both ends of the first groove. The third inner wall is away from the first edge, and the fourth inner wall is close to the first edge. The fourth inner wall and the first inner wall have a first connecting wall therebetween. Along the extending direction of the tab, the minimum width of the first connecting wall to the first edge is W1, and W1>0 mm.

[0008] In the above technical solution, the minimum width of the first connecting wall to the first edge is W1, and W1>0 mm, that is, a part of the first active material layer is arranged between the fourth inner wall and the first edge. This part can provide support for the current collector, can disperse the shear force of the current collector in the first groove area, and can resist the damage and tearing of the current collector in the first groove area, thereby reducing the risk of voltage drop and failure of the secondary battery, improving the cold pressing performance of the pole piece, and improving the anti-collision performance of the secondary battery.

[0009] In some preferred embodiments, 0.5mm≤W1≤4mm ， The breaking and tearing resistance of the pole piece can be improved, and the influence of the first part on the energy density of the secondary battery can be reduced.

[0010] In some preferred embodiments, the fourth inner wall comprises a plane and / or a curved surface.

[0011] In some preferred embodiments, the first groove further has a fifth inner wall, the fifth inner wall and the third inner wall are respectively the inner walls at two ends of the first groove along the protruding direction of the tab, one end of the second inner wall is connected to the fifth inner wall, and the other end is connected to the third inner wall. The fifth inner wall and the second inner wall have a second connecting wall therebetween, the minimum width of the second connecting wall to the first edge along the protruding direction of the tab is W2, and W2>0mm. That is, a part of the first active material layer is also arranged between the fifth inner wall and the first edge. This part of the first active material layer can provide support for the current collector, disperse the shear force of the current collector in the first groove area, and limit the breaking and tearing of the current collector in the first groove area, thereby reducing the risk of voltage drop failure of the secondary battery and improving the anti-collision performance of the secondary battery.

[0012] In some preferred embodiments, 0.5mm≤W2≤4mm, which can improve the breaking and tearing resistance of the pole piece while reducing the influence of the third part on the energy density of the secondary battery.

[0013] In some preferred embodiments, the first active material layer further has a sixth inner wall and a seventh inner wall, one end of the sixth inner wall is connected to the first edge, and the other end is connected to the fourth inner wall, one end of the seventh inner wall is connected to the first edge, and the other end is connected to the second inner wall. The sixth inner wall and the seventh inner wall have a first gap space therebetween along the length direction of the current collector, and the tab part is located in the first gap space. The arrangement of the first gap space can further reduce the influence of the first part and / or the third part on the energy density of the secondary battery, and the tab part located in the first gap space can directly protrude from the first edge of the first gap space, which can facilitate the welding of the tab and the current collector and the protrusion of the tab, and is conducive to improving the welding precision of the tab and the current collector.

[0014] In some preferred embodiments, the first active material layer further has a sixth inner wall and a seventh inner wall, one end of the sixth inner wall is connected to the first edge, and the other end is connected to the fourth inner wall, one end of the seventh inner wall is connected to the first edge, and the other end is connected to the fifth inner wall. The sixth inner wall and the seventh inner wall have a first gap space therebetween along the length direction of the current collector, and the tab part is located in the first gap space. The influence of the first part on the energy density of the battery can be further reduced, and the welding of the tab and the current collector and the protrusion of the tab can be facilitated.

[0015] In some preferred embodiments, the length of the fourth inner wall is L1 along the length direction of the current collector, and 0mm

[0016] In some preferred embodiments, the length of the fifth inner wall is L2 along the length direction of the current collector, and 0mm

[0017] In some preferred embodiments, the electrode tab further comprises a second active material layer, and the second active material layer is arranged on the second surface of the current collector. The second active material layer has a second groove, and the first groove and the second groove at least partially overlap along the thickness direction of the current collector. The second active material layer has a second edge along the protruding direction of the tab. The second groove has an eighth inner wall, a ninth inner wall, a tenth inner wall, and an eleventh inner wall. The eighth inner wall and the ninth inner wall are respectively the inner walls at both ends of the second groove along the length direction of the current collector. The eleventh inner wall and the tenth inner wall are respectively the inner walls at both ends of the second groove along the protruding direction of the tab, and the eleventh inner wall is closer to the second edge, and the tenth inner wall is farther away from the second edge. The eleventh inner wall and the eighth inner wall have a third connecting wall therebetween, and the minimum width of the third connecting wall to the second edge along the protruding direction of the tab is W3, and W3>0mm. That is, there is a part of the second active material layer between the eleventh inner wall and the second edge, which can provide support to the current collector, further disperse the shear force of the current collector in the second groove area, limit the damage tearing of the current collector in the second groove area, thereby reducing the risk of voltage drop failure of the secondary battery, and improving the anti-collision performance of the secondary battery.

[0018] In some preferred embodiments, 0.5mm

[0019] In some preferred embodiments, the second groove further has a twelfth inner wall, and the twelfth inner wall and the tenth inner wall are respectively the inner walls at both ends of the second groove along the protruding direction of the tab. One end of the ninth inner wall is connected with the tenth inner wall, and the other end is connected with the twelfth inner wall. The twelfth inner wall and the ninth inner wall have a fourth connecting wall therebetween, and the minimum width of the fourth connecting wall to the second edge along the protruding direction of the tab is W4, and W4>0mm. That is, there is a part of the second active material layer between the twelfth inner wall and the second edge, which can also provide support to the current collector, disperse the shear force of the current collector in the second groove area, and limit the damage tearing of the current collector in the second groove area, thereby reducing the risk of voltage drop failure of the battery, and improving the anti-collision performance of the secondary battery.

[0020] In some preferred embodiments, 0.5mm≤W4≤4mm, which can improve the anti- breakage tearing ability of the pole piece while reducing the impact of the fourth part on the energy density of the secondary battery.

[0021] In some preferred embodiments, the second active material layer further has a thirteenth inner wall and a fourteenth inner wall, one end of the thirteenth inner wall is connected with the second edge, and the other end is connected with the eleventh inner wall, one end of the fourteenth inner wall is connected with the second edge, and the other end is connected with the eighth inner wall. Between the thirteenth inner wall and the fourteenth inner wall in the length direction of the current collector, there is a second gap space. The arrangement of the second gap space can further reduce the impact of the second part and the fourth part on the energy density of the battery.

[0022] In some preferred embodiments, the second active material layer further has a thirteenth inner wall and a fourteenth inner wall, one end of the thirteenth inner wall is connected with the second edge, and the other end is connected with the eleventh inner wall, one end of the fourteenth inner wall is connected with the second edge, and the other end is connected with the twelfth inner wall. Between the thirteenth inner wall and the fourteenth inner wall in the length direction of the current collector, there is a second gap space. In the length direction of the current collector, the length of the eleventh inner wall is L3, 0mm

[0023] In some preferred embodiments, the first inner wall has a first profiled edge facing the second inner wall, the second inner wall has a second profiled edge facing the first inner wall, and the third inner wall has a third profiled edge facing the fourth inner wall, as viewed along the thickness direction of the current collector. The first profiled edge comprises a first point and a second point, the first point being the farthest point from the second profiled edge along the length direction of the current collector, and the second point being the farthest point from the third profiled edge along the protruding direction of the tab. The second profiled edge comprises a third point and a fourth point, the third point being the farthest point from the first profiled edge along the length direction of the current collector, and the fourth point being the farthest point from the third profiled edge along the protruding direction of the tab. The third profiled edge comprises a fifth point, the fifth point being the farthest point from the first edge along the protruding direction of the tab. The tab satisfies 1.2Z0<Z1<2.5Z0. Wherein, D1 is the length from the second point to the fifth point, D2 is the length from the fourth point to the fifth point, and D3 is the length from the first point to the third point, as viewed along the thickness direction of the current collector, along the protruding direction of the tab, and along the length direction of the current collector; Z0=L1+L2+D1+D2+D3; and Z1 is the profiled perimeter of the first groove inner wall. Not only can the damage to the current collector during cold pressing be reduced, but also the interference with the tab welding can be reduced, and the tab welding precision can be improved.

[0024] In some preferred embodiments, the maximum length of the first groove is L5, and the maximum length of the second groove is L6, as viewed along the width direction of the current collector, and L5≥L6. The first groove and the second groove can form empty foil areas on the two surfaces of the current collector, respectively, so as to facilitate the welding of the tab, reduce the active material layer powder falling onto the welding during welding, and improve the welding precision. The first active material layer comprises a first part, and the active material layer between the first inner wall and the first edge forms the first part. The second active material layer comprises a second part, and the active material layer between the eleventh inner wall and the second edge forms the second part. The first part and the second part at least partially overlap along the thickness direction of the current collector, and |W1-W3|≤2mm. The first groove and the second groove are less staggered in the thickness direction of the current collector, the stress distribution can be improved, and the welding of the tab and the current collector can be facilitated, and the welding precision can be improved.

[0025] In a second aspect, the present application further provides an electronic device comprising the secondary battery according to any one of the embodiments of the first aspect.

[0026] Additional aspects and advantages of embodiments of the present application will be described in part in the description that follows, and will in part be apparent to those of ordinary skill in the art from the description, or can be learned by practice of embodiments of the present application. BRIEF DESCRIPTION OF DRAWINGS

[0027] One or more embodiments are illustrated by way of example in the figures that are not intended to be limiting of the embodiments so as to illustrate exemplary principles of the embodiments. The same reference numerals in different figures identify the same element, and these drawings are not intended to be limiting in that regard. The figures are not necessarily to scale.

[0028] FIG. 1 is a schematic diagram of a structure of a secondary battery according to some embodiments of the present application;

[0029] FIG. 2 is a schematic diagram of a structure of an electrode sheet according to some embodiments of the present application;

[0030] FIG. 3 is a schematic diagram of a structure of an electrode sheet according to some embodiments of the present application (stacked structure);

[0031] FIG. 4 is a schematic diagram of a structure of an electrode sheet according to some embodiments of the present application in a first groove portion;

[0032] FIG. 5 is a partial enlarged view of A in FIG. 4;

[0033] FIG. 6 is a schematic diagram of a connection between a fourth wall surface and a first wall surface according to some embodiments of the present application;

[0034] FIG. 7 is a schematic diagram of a connection between a fourth wall surface and a first wall surface according to some embodiments of the present application;

[0035] FIG. 8a is a schematic diagram of various structures of a fourth wall surface according to some embodiments of the present application (the fourth wall surface includes a flat surface);

[0036] FIG. 8b is a schematic diagram of various structures of a fourth wall surface according to some embodiments of the present application (the fourth wall surface includes a curved surface);

[0037] FIG. 8c is a schematic diagram of various structures of a fourth wall surface according to some embodiments of the present application (the fourth wall surface includes a combination of a flat surface and a curved surface);

[0038] FIG. 9 is a schematic diagram of a boundary between a fourth wall surface and a first wall surface according to some embodiments of the present application;

[0039] FIG. 10 is a schematic diagram of a boundary between a fourth wall surface and a first wall surface according to some embodiments of the present application;

[0040] FIG. 11 is a schematic diagram of coverage of a first groove by a first adhesive layer according to some embodiments of the present application;

[0041] FIG. 12 is a schematic diagram of a structure of an electrode sheet according to some embodiments of the present application in a first groove portion;

[0042] FIG. 13 is a schematic diagram of a structure of an electrode sheet according to some embodiments of the present application in a first groove portion;

[0043] FIG. 14 is a schematic diagram of a structure of an electrode sheet according to some embodiments of the present application in a first groove portion;

[0044] FIG. 15 is a structural schematic diagram of a pole piece according to some embodiments of the present application;

[0045] FIG. 16 is a structural schematic diagram of a pole piece located in a first groove portion according to some embodiments of the present application;

[0046] FIG. 17 is an enlarged view of B in FIG. 16;

[0047] FIG. 18 is a structural schematic diagram of a pole piece located in a first groove portion according to some embodiments of the present application.

[0048] BRIEF DESCRIPTION OF DRAWINGS 100, secondary battery; 101, electrode assembly; 10, pole piece; 11, current collector; 111, first surface; 112, second surface; 12, first active material layer; 12a, first portion; 12a1, sixth inner wall; 12b, third portion; 12b1, seventh inner wall; 121, first groove; 1211, first inner wall; 1211a, first profile edge; 1212, second inner wall; 1212a, second profile edge; 1213, third inner wall; 1213a, third profile edge; 1214, fourth inner wall; 1215, fifth inner wall; 122, first edge; 123, first connecting wall; 124, second connecting wall; 125, first gap space; 13, tab; 14, second active material layer; 14a, second portion; 14a1, thirteenth inner wall; 14b, fourth portion; 14b1, fourteenth inner wall; 141, second groove; 1411, eighth inner wall; 1412, ninth inner wall; 1413, tenth inner wall; 1414, eleventh inner wall; 1415, twelfth inner wall; 142, second edge; 143, third connecting wall; 144, fourth connecting wall; 145, second gap space; 20, first adhesive layer; Q1, first point; Q2, second point; Q3, third point; Q4, fourth point; Q5, fifth point; X, first direction; Y, second direction; Z, third direction; K, fitting straight line. DETAILED DESCRIPTION

[0049] In order to make the objects, technical solutions, and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be described clearly below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are some but not all of the embodiments of the present application.

[0050] Reference to "an embodiment" in this application means that a particular feature, structure, or characteristic described in connection with the embodiment can be included in at least one embodiment of the present application. The appearance of the phrase in various places in the specification does not necessarily all refer to the same embodiment, nor does it necessarily refer to a particular alternative embodiment.

[0051] 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 explicitly specified.

[0052] In the description of the embodiments of the present application, the term "and / or" is only used to describe the association relationship of the associated objects, which means that there can be three relationships, for example, A and / or B, which can represent the three cases of A alone, A and B together, and B alone. In addition, the character " / " in this paper generally represents that the front and rear associated objects are in an "or" relationship.

[0053] The technical features involved in the different embodiments of the present application described below can be combined with each other as long as there is no conflict between them.

[0054] In a first aspect, the present application provides a secondary battery 100, which comprises a pole piece 10. Please refer to FIG. 1 and FIG. 2, the pole piece 10 can be divided into a positive pole piece and a negative pole piece. An isolation film (not marked in the figure) is used to separate the positive pole piece and the negative pole piece, and the positive pole piece, the isolation film and the negative pole piece are stacked and wound to form a wound electrode assembly 101. In other embodiments, a laminated electrode assembly 101 can also be used, that is, the positive pole piece and the negative pole piece are alternately stacked in sequence, and the isolation film is arranged between the two. After the electrode assembly 101 is packaged in a shell, the secondary battery 100 can be formed. The pole piece 10 comprises a current collector 11, a first active material layer 12 and a tab 13. The first active material layer 12 is arranged on the current collector 11, and the tab 13 is electrically connected to the current collector 11.

[0055] For the above-mentioned current collector 11, please refer to FIG. 2 and FIG. 3. The current collector 11, as the conductive base material of the pole piece 10, can use a whole flat and strip-shaped metal foil, for example, an aluminum foil or a copper foil, etc. When the pole piece 10 is a positive pole piece, the current collector 11 can use an aluminum foil, which is more stable at high potential. When the pole piece 10 is a negative pole piece, the current collector 11 can use a copper foil, which is chemically stable at low potential and is not easy to be corroded by electrolyte. In addition, the metal foil has high strength, which can provide support for the above-mentioned first active material layer 12, so that the first active material layer 12 can be more uniformly coated on the current collector 11. Along the thickness direction (third direction Z) of the current collector 11, the current collector 11 has a first surface 111 and a second surface 112 arranged oppositely, and the first active material layer 12 can be arranged on the first surface 111.

[0056] For the first active material layer 12, the active material layer is a key component involved in the electrochemical reaction. During the charging process of the secondary battery 100, the active material layer can absorb and store electrical energy. During the discharging process of the secondary battery 100, the active material layer can release electrical energy. The content and properties of the active material layer directly affect the amount of charge that the secondary battery 100 can store, thereby determining the energy density of the secondary battery 100.

[0057] When the tab 10 is a positive electrode tab, the first active material layer 12 includes a positive electrode active material, a conductive agent, and a binder, and the like. After the above-mentioned material components are mixed and stirred uniformly, they are coated on the first surface 111, thereby obtaining the first active material layer 12. The positive electrode active material can be selected from one or more of lithium nickel cobalt manganese oxide, lithium cobalt oxide, lithium iron phosphate, lithium nickel cobalt manganese oxide, lithium manganese oxide, and lithium manganese iron phosphate. When the tab 10 is a negative electrode tab, the first active material layer 12 includes a negative electrode active material, a conductive agent, and a binder, and the like. After the above-mentioned material components are mixed and stirred uniformly, they are coated on the first surface 111, thereby obtaining the first active material layer 12. The negative electrode active material can be selected from one or more of graphite, soft carbon, hard carbon, carbon fiber, elemental silicon, silicon oxide compounds, and silicon alloys.

[0058] For the tab 13, please refer to FIGS. 2 and 3. The tab 13 is a metal conductor that leads out the current from the tab 10. It can be made of aluminum, copper, or nickel, etc. The tab 13 is electrically connected to the current collector 11, and the electrical connection mode includes but is not limited to welding or conductive adhesive bonding, etc. In this application, welding is taken as an example. In order to facilitate the electrical connection between the tab 13 and the current collector 11, the first active material layer 12 is provided with a first recess 121, and the current collector 11 can be exposed from the first recess 121. The tab 13 can be placed in the first recess 121 to perform the welding between the tab 13 and the current collector 11.

[0059] The first active material layer 12 has a first edge 122. A part of the tab 13 is arranged in the first recess 121 and electrically connected to the current collector 11, and another part extends out of the first edge 122. For example, the tab 10 is wound along its length direction (the first direction X), and the first edge 122 is one end of the width direction (the second direction Y) of the tab 10. The tab 13 directly extends out of the width direction (the second direction Y) of the tab 10.

[0060] Please refer to FIG. 4 and FIG. 5, the first recess 121 has a first inner wall 1211, a second inner wall 1212, a third inner wall 1213 and a fourth inner wall 1214, the first inner wall 1211 and the second inner wall 1212 are respectively the inner wall of the two ends of the first recess 121. Optionally, along the length direction (the first direction X) of the current collector 11, the first inner wall 1211 is oppositely arranged with the second inner wall 1212, along the extending direction (the second direction Y) of the tab 13, the third inner wall 1213 is oppositely arranged with the fourth inner wall 1214, the third inner wall 1213 is away from the first edge 122, and the fourth inner wall 1214 is close to the first edge 122. Optionally, the fourth inner wall 1214, the first inner wall 1211, the third inner wall 1213 and the second inner wall 1212 are sequentially connected, and the first recess 121 can be approximately square, which is beneficial to the accommodation and welding of the sheet-shaped square tab 13.

[0061] The first connecting wall 123 between the fourth inner wall 1214 and the first inner wall 1211 has a minimum width W1 to the first edge 122 along the extending direction (the second direction Y) of the tab 13, W1>0mm, that is, a part of the first active material layer 12 is arranged between the fourth inner wall 1214 and the first edge 122. The part of the first active material layer 12 can provide support for the current collector 11, can disperse the shear force of the current collector 11 in the first recess 121 area, and can resist the damage and tearing of the current collector 11 in the first recess 121 area, thereby reducing the risk of voltage drop failure of the secondary battery 100, improving the cold pressure resistance of the tab 10, and improving the anti-collision performance of the secondary battery 100.

[0062] It should be noted that during the cold pressing process of the tab 10, the tab 10 is compacted at room temperature (25℃) or close to room temperature by applying a certain pressure, which can improve the compaction density of the tab 10, so that the active material, conductive agent and binder and other components are more closely combined together, increasing the content of substances in unit volume, thereby improving the energy density of the secondary battery 100. In the embodiments of the present application, the cold pressure resistance of the tab 10 can be higher, so it can adapt to a higher compaction density, thereby improving the energy density of the secondary battery 100.

[0063] For the above-mentioned first connecting wall 123, please refer to FIG. 6 and FIG. 7, the first connecting wall 123 is the connecting place between the fourth inner wall 1214 and the first inner wall 1211, and the first connecting wall 123 can be a straight line, a plane, an uneven curve or an uneven curved surface, etc., as long as the minimum width W1 of the first connecting wall 123 to the first edge 122 is greater than 0mm.

[0064] For the outer shape of the fourth inner wall 1214, the fourth inner wall 1214 includes at least one of a plane or an arc surface.

[0065] For example, referring to FIG. 8a, the fourth inner wall 1214 can include a plane, which can be arranged to be inclined towards the first edge 122, arranged to be inclined away from the first edge 122, arranged to be parallel to the first edge 122, or arranged to be partially inclined and partially parallel. In other embodiments, the fourth inner wall 1214 can also be a combination of multiple planes.

[0066] Referring to FIG. 8b, the fourth inner wall 1214 can include an arc surface, which can better disperse the shear force received by the current collector, and the arc surface can be connected to the first inner wall 1211 at one end and connected to the first edge 122 at the other end, or the fourth inner wall 1214 can include multiple arc surfaces to form a concave-convex fourth inner wall 1214.

[0067] Referring to FIG. 8c, the fourth inner wall 1214 can include a combination of an arc surface and a plane, the plane being connected to the first inner wall 1211, and the arc surface being connected to the first edge 122; or the plane being connected to the first edge 122, and the arc surface being connected to the first inner wall 1211; or the fourth inner wall 1214 can include a combination of multiple planes and multiple arc surfaces to form a concave-convex and tortuous inner wall.

[0068] For the determination of the first inner wall 1211, the first inner wall 1211 can be a plane or a concave-convex and tortuous surface. When the first inner wall 1211 is a plane and the fourth inner wall 1214 is a plane, the connection between the first inner wall 1211 and the fourth inner wall 1214 can be directly determined.

[0069] Referring to FIGS. 9 and 10, when the first inner wall 1211 is a concave-convex and tortuous surface and / or the fourth inner wall 1214 is an arc surface, etc., a straight line can be fitted according to the profile curve of the first inner wall 1211 when viewed in the thickness direction (the third direction Z) of the current collector 11. For example, an image processing library (such as OpenCV, PIL, etc.) can be used to read a picture containing the profile curve of the first inner wall 1211, and the opencv library in python can be used for image processing, including grayscale, binarization, denoising, etc., to enhance the contrast and clarity of the profile curve; an edge detection algorithm (such as Canny edge detection) or a cv2.findcontours function can be used to identify the edge of the profile curve, and a series of data points evenly distributed on the profile curve can be extracted from the profile curve; a linear regression method (such as the least squares method) can be used to fit the extracted data points to obtain a fitting straight line K. As shown in FIGS. 9 and 10, the intersection between the fitting straight line K and the fourth inner wall 1214 is the first connecting wall 123. The fitting straight line K can be parallel to the extension direction of the tab 13, or can form a certain angle with the extension direction of the tab 13.

[0070] Optionally, the first active material layer 12 between the first inner wall 1211 and the first edge 122 forms a first part 12a, and the width of the first part 12a is too small to disperse the shear force. In the embodiments of the present application, the minimum width of the first part 12a is selected to be W1≥0.5mm, which can further improve the ability of the first part 12a to limit the damage tearing of the pole piece 10.

[0071] After the tab 13 is welded to the current collector 11, a welding burr will be generated. When the pole piece 10 is wound or stacked to form the electrode assembly 101, the first adhesive layer 20 will be provided. Please further refer to FIGS. 2, 4 and 11, the first adhesive layer 20 covers the first groove 121 and part of the first active material layer 12, which can reduce the risk of the welding burr piercing the separator. The first part 12a is also covered by the first adhesive layer 20, and the first part 12a and the other part of the first active material layer 12 covered by the first adhesive layer 20 are difficult to participate in the electrochemical reaction. In the present application, the range of 0.5mm≤W1≤4mm is limited, which can improve the damage tearing resistance of the pole piece 10 and reduce the influence of the first part 12a on the energy density of the secondary battery 100.

[0072] In some embodiments, please refer to FIGS. 4 and 5, the first groove 121 also has a fifth inner wall 1215, and the fifth inner wall 1215 and the third inner wall 1213 are the inner walls at both ends of the first groove 121 along the extension direction (second direction Y) of the tab 13. For example, the fifth inner wall 1215 is oppositely arranged with the third inner wall 1213, one end of the second inner wall 1212 is connected with the fifth inner wall 1215, and the other end is connected with the third inner wall 1213. The fifth inner wall 1215 and the second inner wall 1212 have a second connecting wall 124 therebetween, and the minimum width of the second connecting wall 124 to the first edge 122 along the extension direction (second direction Y) of the tab 13 is W2, W2>0mm, that is, part of the first active material layer 12 is also arranged between the fifth inner wall 1215 and the first edge 122. The part of the first active material layer 12 provides support for the current collector 11, forms a two-side support structure in the length direction of the current collector 11, disperses the shear force of the current collector 11 in the first groove 121 area, and limits the damage tearing of the current collector 11 in the first groove 121 area, thereby reducing the risk of voltage drop failure of the secondary battery 100 and improving the crashworthiness of the secondary battery 100.

[0073] Optionally, the portion of the fifth inner wall 1215 to the first edge 122 of the first active material layer 12 forms a third portion 12b, and along the length direction (the first direction X) of the tab 10, the two sides of the first groove 121 are limited by the first portion 12a and the third portion 12b respectively, which can further improve the cold pressing resistance of the tab 10 and improve the crashworthiness of the secondary battery 100. In the embodiments of the present application, similar to the first portion 12a, the minimum width of the third portion 12b is 0.5mm≤W 2≤ 4mm, which can improve the anti-tearing performance of the tab 10 while reducing the impact of the third portion 12b on the energy density of the secondary battery 100.

[0074] Optionally, please refer to FIG. 12, the first portion 12a can be connected with the third portion 12b, which has stronger strength and shear force dispersion ability, thereby improving the anti-tearing performance of the tab 10, and the tab 13 can directly extend from the first edge 122 of the first portion 12a and / or the third portion 12b.

[0075] In some embodiments, the first portion 12a is not connected with the third portion 12b. Please refer to FIG. 4 and FIG. 5, the first portion 12a of the first active material layer 12 further has a sixth inner wall 12a1, one end of the sixth inner wall 12a1 is connected with the first edge 122, and the other end is connected with the fourth inner wall 1214. The third portion 12b of the first active material layer 12 further includes a seventh inner wall 12b1, one end of the seventh inner wall 12b1 is connected with the first edge 122, and the other end is connected with the fifth inner wall 1215. Along the length direction (the first direction X) of the current collector 11, the first portion 12a and the third portion 12b are oppositely arranged, and the sixth inner wall 12a1 and the seventh inner wall 12b1 have a first gap space 125 therebetween. The arrangement of the first gap space 125 can further reduce the impact of the first portion 12a and the third portion 12b on the energy density of the secondary battery 100, and the tab 13 is partially located in the first gap space 125, which can directly extend from the first edge 122 of the first gap space 125, thereby facilitating the welding of the tab 13 and the current collector 11 and the extension of the tab 13, and being conducive to improving the welding precision of the tab 13 and the current collector 11.

[0076] The first gap space 125 can be a part of the first groove 121, or in other embodiments, the first gap space 125 can not belong to the first groove 121.

[0077] In other embodiments, referring to FIG. 13, the first active material layer 12 only includes the first portion 12a, and the first portion 12a of the first active material layer 12 further includes a sixth inner wall 12a1, one end of the sixth inner wall 12a1 is connected with the first edge 122, and the other end is connected with the fourth inner wall 1214. The first active material layer 12 further includes a seventh inner wall 12b1, one end of the seventh inner wall 12b1 is connected with the first edge 122, and the other end is connected with the second inner wall 1212. The sixth inner wall 12a1 and the seventh inner wall 12b1 have a first gap space 125 therebetween, and the first gap space 125 is configured to further reduce the influence of the first portion 12a on the energy density of the secondary battery 100, and the tab 13 is partially located in the first gap space 125, which can directly extend out of the first edge 122 from the first gap space 125, thereby facilitating the welding of the tab 13 and the current collector 11 and the extension of the tab 13.

[0078] Optionally, referring to FIG. 14, the first active material layer 12 also only includes the third portion 12b, and when only including the third portion 12b, the third portion 12b can also be considered as the first portion 12a because the positions of the first portion 12a and the third portion 12b are interchangeable.

[0079] In some embodiments, referring to FIGS. 4 and 5, along the length direction (the first direction X) of the current collector 11, the length of the fourth inner wall 1214 is L1, and 0mm < L1≤ 3mm. It can be understood that the presence of the fourth inner wall 1214 indicates that L1> 0mm, which can reduce the damage and tearing of the pole piece 10. Regardless of whether the fourth inner wall 1214 is a bevel or a curved surface, L1 is the straight-line length of the fourth inner wall 1214 in the length direction of the current collector 11. If the length of the fourth inner wall 1214 is too large, it will interfere with the welding of the tab 13 and the current collector 11, not only affecting the welding precision of the tab 13, but also occupying too much space and affecting the energy density of the secondary battery 100. In the embodiments of the present application, L1≤ 3mm is limited, which can reduce the influence of the first portion 12a on the energy density of the secondary battery 100. If the length of the fourth inner wall 1214 is too small, the anti-damage and tearing capability of the pole piece 10 is insufficient. In the embodiments of the present application, 1mm≤ L1≤ 3mm is preferred, which improves the anti-damage and tearing capability of the pole piece 10.

[0080] Based on the same inventive concept, along the length direction (the first direction X) of the current collector 11, the length of the fifth inner wall 1215 is L2, and 0mm < L2≤ 3mm, which reduces the influence of the third portion 12b on the energy density of the secondary battery 100. Preferably, 1mm≤ L2≤ 3mm, which improves the anti-damage and tearing capability of the pole piece 10.

[0081] In some embodiments, referring to FIG. 3 and FIG. 15, the tab 10 further comprises a second active material layer 14 disposed on the second surface 112 of the current collector 11. The double-sided active material coated tab 10 can improve the energy density of the secondary battery 100. The second active material layer 14 has a second groove 141, and the first groove 121 and the second groove 141 at least partially overlap along the thickness direction (the third direction Z) of the current collector 11. During welding, the welding seat can support the current collector 11 in the second groove 141, and the welding head can weld the tab 13 and the current collector 11 in the first groove 121.

[0082] Referring further to FIG. 16 and FIG. 17, the second active material layer 14 has a second edge 142 along the extension direction (the second direction Y) of the tab 13. The second groove 141 has an eighth inner wall 1411, a ninth inner wall 1412, a tenth inner wall 1413, and an eleventh inner wall 1414. The eighth inner wall 1411 and the ninth inner wall 1412 are respectively the inner walls at both ends of the second groove 141 along the length direction (the first direction X) of the current collector 11. For example, the eighth inner wall 1411 and the ninth inner wall 1412 are oppositely arranged, the eleventh inner wall 1414 and the tenth inner wall 1413 are oppositely arranged along the extension direction (the second direction Y) of the tab 13, and the eleventh inner wall 1414 is close to the second edge 142 and the tenth inner wall 1413 is away from the second edge 142. Optionally, the eleventh inner wall 1414, the eighth inner wall 1411, the tenth inner wall 1413, and the ninth inner wall 1412 are sequentially connected to form a second groove 141 in the shape of a square, which is suitable for the approximately square second groove 141 and the approximately square tab 13.

[0083] The third connecting wall 143 is between the eleventh inner wall 1414 and the eighth inner wall 1411, and the minimum width of the third connecting wall 143 to the second edge 142 along the extension direction (the second direction Y) of the tab 13 is W3, W3>0 mm. That is, there is a part of the second active material layer 14 between the eleventh inner wall 1414 and the second edge 142. This part of the second active material layer 14 can provide support to the current collector 11, disperse the shear force of the current collector 11 in the second groove 141 area, and resist the damage and tearing of the current collector 11 in the second groove 141 area, thereby reducing the risk of voltage drop failure of the secondary battery 100 and improving the crashworthiness of the secondary battery 100.

[0084] Optionally, the part of the second active material layer 14 from the eleventh inner wall 1414 to the second edge 142 forms a second part 14a, and the minimum width of the second part 14a is 0.5 mm≤W3≤4 mm. This can improve the damage and tearing resistance of the tab 10 while reducing the impact of the third part 12b on the energy density of the secondary battery 100.

[0085] In some embodiments, the second groove 141 further has a twelfth inner wall 1415, which is an inner wall of the second groove 141 at one end of the second direction Y along the extension direction of the tab 13, and the tenth inner wall 1413 is an inner wall of the second groove 141 at the other end of the second direction Y. For example, the twelfth inner wall 1415 is opposite to the tenth inner wall 1413. One end of the ninth inner wall 1412 is connected to the tenth inner wall 1413, and the other end is connected to the twelfth inner wall 1415. The fourth connecting wall 144 is between the twelfth inner wall 1415 and the ninth inner wall 1412, and the minimum width of the fourth connecting wall 144 to the second edge 142 along the extension direction of the tab 13 (the second direction Y) is W4, W4>0mm. That is, a part of the second active material layer 14 is arranged between the twelfth inner wall 1415 and the second edge 142, which can provide support for the current collector 11. In combination with the first active material layer 12 between the fourth inner wall 1214 and the first edge 122 and the first active material layer 12 between the fifth inner wall 1215 and the first edge 122, a support structure can be formed on both sides of the current collector 11 in the thickness direction, further dispersing the shear force of the current collector 11 in the second groove 141 region, and resisting the damage and tearing of the current collector 11 in the second groove 141 region, thereby reducing the risk of battery voltage drop failure and improving the impact resistance of the secondary battery 100.

[0086] Optionally, the part of the second active material layer 14 from the twelfth inner wall 1415 to the second edge 142 forms a fourth part 14b, and the minimum width of the fourth part 14b is 0.5mm≤W4≤4mm. This can improve the damage and tearing resistance of the tab 10 while reducing the impact of the fourth part 14b on the energy density of the secondary battery 100. Through the combination of the first part 12a, the second part 14a, the third part 12b, and the fourth part 14b, the first surface 111 and the second surface 112 of the tab 10 can both have an active material layer that resists damage and tearing of the tab 10, further improving the cold pressing performance of the tab 10 and the impact resistance of the secondary battery 100.

[0087] Optionally, the second part 14a can be connected to the fourth part 14b, which has stronger strength and shear force dispersion capability, further dispersing the shear force and improving the damage and tearing resistance of the tab 10.

[0088] In some embodiments, the second portion 14a is not connected with the fourth portion 14b, the second portion 14a of the second active material layer 14 further comprises a thirteenth inner wall 14a1, one end of the thirteenth inner wall 14a1 is connected with the second edge 142, and the other end is connected with the eleventh inner wall 1414, the fourth portion 14b of the second active material layer 14 further comprises a fourteenth inner wall 14b1, one end of the fourteenth inner wall 14b1 is connected with the second edge 142, and the other end is connected with the twelfth inner wall 1415. Along the length direction (the first direction X) of the current collector 11, the second portion 14a is arranged opposite to the fourth portion 14b, and the second gap space 145 is arranged between the thirteenth inner wall 14a1 and the fourteenth inner wall 14b1. The arrangement of the second gap space 145 can further reduce the influence of the second portion 14a and the fourth portion 14b on the energy density of the secondary battery 100.

[0089] Optionally, along the length direction (the first direction X) of the current collector 11, the length of the eleventh inner wall 1414 is L3, and 0 < L3 ≤ 3 mm, which can reduce the influence of the third portion 12b on the energy density of the secondary battery 100. Preferably, 1 mm ≤ L3 ≤ 3 mm, which can further improve the anti-breaking tearing capacity of the pole piece 10. Based on the same inventive concept, along the length direction (the first direction X) of the current collector 11, the length of the twelfth inner wall 1415 is L4, and 0 < L4 ≤ 3 mm, preferably, 1 mm ≤ L4 ≤ 3 mm.

[0090] In some embodiments, the second active material layer 14 only comprises the second portion 14a, which can improve the energy density of the secondary battery 100. The second portion 14a of the second active material layer 14 comprises a thirteenth inner wall 14a1, one end of the thirteenth inner wall 14a1 is connected with the second edge 142, and the other end is connected with the eleventh inner wall 1414. The second active material layer 14 further comprises a fourteenth inner wall 14b1, one end of the fourteenth inner wall 14b1 is connected with the second edge 142, and the other end is connected with the eighth inner wall 1411. Along the length direction (the first direction X) of the current collector 11, the second gap space 145 is arranged between the thirteenth inner wall 14a1 and the fourteenth inner wall 14b1, which can further reduce the influence of the second portion 14a on the energy density of the secondary battery 100.

[0091] In other embodiments, the second active material layer 14 can also only comprise the fourth portion 14b, because the positions of the second portion 14a and the fourth portion 14b can be interchanged. When only comprising the fourth portion 14b, the fourth portion 14b can also be regarded as the second portion 14a.

[0092] For the formation of the first groove 121, the first groove 121 can be directly etched on the first active material layer 12 by laser etching, or the foaming glue process can be used to coat the foaming glue on the first surface 111 of the current collector 11, and then coat the first active material layer 12. When drying, the foaming glue rises and takes part of the first active material layer 12, and the foaming glue and the part of the first active material layer 12 are removed, that is, the first groove 121 is formed. When laser etching is used, each inner wall of the first groove 121 is closer to a flat surface, and when the foaming glue process is used, part of the first active material layer 12 will flow towards each inner wall of the first groove 121, so that each inner wall of the first groove 121 presents an irregular surface.

[0093] For example, taking the foaming glue process, when observed along the thickness direction (the third direction Z) of the current collector 11, the first inner wall 1211 has a first profile edge 1211a facing the second inner wall 1212, the second inner wall 1212 has a second profile edge 1212a facing the first inner wall 1211, and the third inner wall 1213 has a third profile edge 1213a facing the fourth inner wall 1214.

[0094] Please refer to FIG. 18, the first profile edge 1211a includes a first point Q1 and a second point Q2, along the length direction (the first direction X) of the current collector 11, the first point Q1 is the farthest point from the second profile edge 1212a, and along the extending direction (the second direction Y) of the tab 13, the second point Q2 is the farthest point from the third profile edge 1213a.

[0095] The second profile edge 1212a has a third point Q3 and a fourth point Q4, along the length direction (the first direction X) of the current collector 11, the third point Q3 is the farthest point from the first profile edge 1211a, and along the extending direction (the second direction Y) of the tab 13, the fourth point Q4 is the farthest point from the third profile edge 1213a.

[0096] The third profile edge 1213a has a fifth point Q5, and along the extending direction (the second direction Y) of the tab 13, the fifth point Q5 is the farthest point from the first edge 122.

[0097] The tab 10 satisfies: 1.2Z0

[0098] Z1 is too small, the inner wall of the first groove 121 is too flat, and it is difficult to better alleviate the damage to the current collector 11 during the cold pressing process. If Z1 is too large, it will interfere with the welding of the tab 13, affecting the welding precision of the tab 13 and the current collector 11. In the embodiments of the present application, 1.2Z0<Z1<2.5Z0 is limited, which not only reduces the damage to the current collector 11 during the cold pressing process, but also reduces the interference with the welding of the tab 13, and improves the welding precision of the tab 13.

[0099] For the measurement of Z0 and Z1, the opencv library in python language can be used for image processing. First, the color image (for example, the first groove real object image taken by the camera) is converted into a gray image, the threshold value is identified, the rubber area is identified, then the cv2.findcontours function is used to identify the rubber area contour, and finally the cv2.arclength function is called to identify the contour length.

[0100] For the maximum length of the first groove 121 and the maximum length of the second groove 141, in some embodiments, please refer to FIG. 2, FIG. 4, and FIG. 15 and FIG. 16, along the width direction (second direction Y) of the current collector 11, the maximum length of the first groove 121 is L5 (in other embodiments, the maximum length can also be considered as D1 or D2 in FIG. 18, taking D2 as an example, L5=D2), and the maximum length of the second groove 141 is L6. L5 can be selected to be less than or equal to L6. The first groove 121 can be welded with the tab 13, and the glue process can be performed first. In other embodiments, L5 can be greater than or equal to L6, and the first groove 121 and the second groove 141 can form empty foil areas on the two surfaces of the current collector 11, respectively, so as to facilitate the welding of the tab, reduce the falling of the second active material layer 14 during welding, and improve the welding precision.

[0101] When L5 is greater than or equal to L6, the first part 12a and the second part 14a at least partially overlap along the thickness direction (third direction Z) of the current collector 11, and |W1-W3|≤2mm. The first groove 121 and the second groove 141 have less displacement in the thickness direction (third direction Z) of the current collector 11, which can improve the stress distribution and facilitate the welding of the tab 13 and the current collector 11, thereby improving the welding precision. For example, the welding seat supports the current collector 11 in the second groove 141, and the welding head welds the tab 13 and the current collector 11 in the first groove 121. Less displacement is more conducive to the support and welding of the welding head by the welding seat.

[0102] In a second aspect, the present application also provides an electronic device comprising the secondary battery 100 according to any one of the above embodiments of the first aspect. The electronic device according to the embodiments of the present application is not particularly limited and can be any electronic device known in the art. For example, the electronic device includes, but is not limited to, a Bluetooth headset, a mobile phone, a tablet, a notebook computer, an electric toy, an electric tool, an electric vehicle, an electric automobile, a ship, a spacecraft, and the like. Among them, the electric toy can include a fixed or mobile electric toy, such as a game console, an electric automobile toy, an electric ship toy, an electric aircraft toy, and the like, and the spacecraft can include an airplane, a rocket, a space shuttle, a spacecraft, and the like.

[0103] Experiment 1: Drop test of lithium ion battery

[0104] Example A1

[0105] Preparation of positive electrode sheet:

[0106] The positive electrode active material lithium cobaltate, the positive electrode conductive agent acetylene black, and the positive electrode binder polyvinylidene fluoride (PVDF, weight average molecular weight 5 x 10 5 ) in a mass ratio of 94:3:3 were mixed, N-methyl pyrrolidone (NMP) was added as a solvent, and the positive electrode slurry was stirred in a vacuum stirrer until the solid content was 75 wt% and the system was uniform. An aluminum foil with a thickness of 8 um was selected as the positive electrode current collector, and the positive electrode slurry was uniformly coated on one surface of the positive electrode current collector aluminum foil. After drying at 110°C, a positive electrode active material layer was obtained. Then, the above steps were repeated on the other surface of the aluminum foil to obtain a double-sided coated positive electrode active material layer.

[0107] Preparation of negative electrode sheet

[0108] The negative electrode active material graphite powder, silicon powder, conductive agent conductive carbon black (Super P), and binder styrene-butadiene rubber (SBR) were mixed in a weight ratio of 87:10.5:1:1.5, and then deionized water was added as a solvent to prepare a negative electrode slurry with a solid content of 50 wt% and stir uniformly. A copper foil with a thickness of 5 um was selected as the negative electrode current collector, and the negative electrode slurry was uniformly coated on one surface of the negative electrode current collector copper foil. After drying at 90°C, a single-sided negative electrode sheet was obtained. After the above steps were completed, the single-sided coating of the negative electrode sheet was completed. Then, the above steps were repeated on the other surface of the negative electrode sheet to obtain a double-sided coated negative electrode active material layer.

[0109] Preparation of separator film

[0110] A polyethylene (PE) porous film with a thickness of 7 um was used as the separator film.

[0111] Preparation of electrolyte

[0112] In a dry argon atmosphere, ethylene carbonate, methyl ethyl carbonate and diethyl carbonate were mixed in a mass ratio of 30:50:20 to obtain an organic solution, then lithium salt lithium hexafluorophosphate was dissolved and mixed uniformly in the organic solvent to obtain an electrolyte with a lithium salt concentration of 1.15 mol / L.

[0113] Preparation of lithium ion battery

[0114] By laser cleaning, a first groove was cleaned on one side of the positive electrode sheet active material layer, and a second groove was cleaned on the other side. The aluminum sheet positive electrode tab was welded with the positive electrode current collector in the first groove, and the nickel sheet was used as the negative electrode tab. The negative electrode tab was welded with the negative electrode current collector in a similar manner as the positive electrode sheet. When the first groove was cleaned by laser, a first part was left between the first groove and the first edge of the active material layer (the positive electrode tab extends out of the first edge). Along the width direction of the positive electrode sheet, the width W1 of the first part is 0.1 mm, and along the length direction of the positive electrode sheet, the length L1 of the first part facing the inner wall (the fourth inner wall) of the first groove is 1 mm. The above prepared separator, positive electrode sheet, separator, negative electrode sheet were stacked in order, and the electrode assembly was obtained by winding. The electrode assembly was placed in a packaging bag of aluminum plastic film, and the above positive electrode tab and negative electrode tab were stretched out from the top sealing edge of the packaging bag. After removing the water at 80℃, the electrolyte was injected and packaged.

[0115] The related parameters in Comparative Example 1 and Examples A2 to A30 are shown in Table 1. In Examples A10 to A16, a third part is also left between the first groove and the first edge. Along the width direction of the electrode sheet, the first part and the third part are connected to the opposite two inner walls of the first groove respectively, the width W2 of the third part, and the length L2 of the third part facing the inner wall (the fifth inner wall) of the first groove is 1 mm. In Examples A17 to A23, a second part is also left between the second groove and the second edge. The width of the second part is W3, and the length L3 of the second part facing the inner wall (the eleventh inner wall) of the second groove is 1 mm. In Examples A24 to A30, a fourth part is also left between the second groove and the second edge. Along the width direction of the electrode sheet, the second part and the fourth part are connected to the opposite two inner walls of the second groove respectively, the width W4 of the fourth part, and the length L4 of the fourth part facing the inner wall (the twelfth inner wall) of the second groove is 1 mm.

[0116] Drop test method: lithium ion batteries are pre-treated at 25°C, and after standing for 60 min in a normal temperature environment, the voltage of the lithium ion battery before drop test is tested; the lithium ion battery is loaded into a clamp, and the drop equipment is used to drop freely from a position 1.5 m away from the ground in the following order: head-tail-head right corner-tail right corner-head left corner-tail left corner (angle: 45±15°), repeated for 6 rounds. After the drop is completed, the lithium ion battery is allowed to stand at room temperature for 24 h, and the voltage of the lithium ion battery is measured and recorded. The appearance of the lithium ion battery is checked before and after the test and photographed. The pass criteria for the drop test: voltage drop <30 mV, disassemble the lithium ion battery to observe the positive electrode sheet, and the positive electrode sheet is not damaged or torn, which is considered to pass, otherwise it is considered to fail (in other embodiments, when the negative electrode sheet is similarly provided with the first, second, third and / or fourth parts described above, the negative electrode sheet also needs to be observed). Test 50 lithium ion batteries, the number of lithium ion batteries that fail the test is X, and the test failure rate is X / 50.

[0117] Table 1

[0118] According to Table 1 above, in combination with Comparative Example 1 and Examples A1 to A30 described above, it can be seen that when the partial active material layer (first part) is provided between the first groove and the first edge, the risk of drop failure of the lithium ion battery can be effectively reduced. This is because the partial active material layer can reduce the thickness mutation between the first groove and the active material layer, can disperse the shear force of the current collector in the first groove area, and can resist the damage and tearing of the current collector in the first groove area, thereby reducing the risk of voltage drop failure of the lithium ion battery and improving the anti-impact performance of the lithium ion battery. As can be seen from Table 1 above, as long as the first part exists, the drop failure rate can be reduced, and therefore in the present application, W1>0 mm, W2>0 mm, W3>0 mm and W4>0 mm can be selected.

[0119] In combination with Examples A1 to A9, the drop failure rate in Examples A3 to A9 is less than that in Examples A1 and A2, and in Examples A1 and A2, the width of the first part is too small, which is insufficient to disperse the shear force of the current collector, and it is difficult to resist the damage and tearing of the current collector in the first groove area. In Example A9, the width of the first part is too large, resulting in uneven stress distribution on both sides of the current collector, which can also cause the tearing of the electrode sheet when the lithium ion battery is dropped, and occupies a large space, affecting the energy density of the lithium ion battery. Therefore, in the examples of the present application, 0.5 mm≤W1≤4 mm is preferred.

[0120] Similarly, in combination with Embodiment A10 to Embodiment A16, the failure rate of Embodiments A11 to A15 is less than that of Embodiment A10, because in Embodiment A10, the width of the third portion is too small, and the ability to disperse the shear force of the current collector is insufficient, which is difficult to resist the damage and tearing of the current collector in the first groove area. In Embodiment A16, the width of the third portion is too large, which will cause uneven stress distribution on both sides of the thickness direction of the current collector, not only causing the tearing of the pole piece, but also occupying a large space, affecting the energy density of the lithium ion battery. Therefore, in the embodiments of the present application, it is preferred that 0.5mm≤W2≤4mm.

[0121] In combination with Embodiments A17 to A23, the failure rate of Embodiments A18 to A22 is less than that of Embodiment A17, because in Embodiment A17, the width of the second portion is too small, and the ability to disperse the shear force of the current collector is insufficient, which is difficult to resist the damage and tearing of the current collector in the first groove or the second groove area. In Embodiment A23, the width of the second portion is too large, which will cause uneven stress distribution on both sides of the thickness direction of the current collector, not only causing the tearing of the pole piece, but also occupying a large space, affecting the energy density of the lithium ion battery. Therefore, in the embodiments of the present application, it is preferred that 0.5mm≤W3≤4mm.

[0122] In combination with Embodiments A24 to A30, the failure rate of Embodiments A25 to A29 is less than that of Embodiment A24, because in Embodiment A24, the width of the fourth portion is too small, and the ability to disperse the shear force of the current collector is insufficient, which is difficult to resist the damage and tearing of the current collector in the first groove or the second groove area. In Embodiment A30, the width of the fourth portion is too large, which will cause uneven stress distribution on both sides of the thickness direction of the current collector, not only causing the tearing of the pole piece, but also occupying a large space, affecting the energy density of the lithium ion battery. Therefore, in the embodiments of the present application, it is preferred that 0.5mm≤W4≤4mm.

[0123] The related parameters in Embodiments B1 to B23 are shown in Table 2, wherein in Embodiments B1 to B8, the width W1 of the fourth inner wall is 2mm. In Embodiments B9 to B13, the width W1 of the first portion and the width W2 of the third portion are both 2mm. In Embodiments B14 to B18, the width W1 of the first portion, the width W2 of the third portion and the width W3 of the second portion are all 2mm. In Embodiments B19 to B23, the width W1 of the first portion, the width W2 of the third portion, the width W3 of the second portion and the width W4 of the fourth portion are all 2mm.

[0124] Table 2

[0125] According to the above Table 2, in combination with Examples B1 to B23, when the length L1 of the fourth inner wall is greater than 0 mm, the risk of drop failure of the lithium ion battery can be effectively reduced, and when L2 > 0 mm, L3 > 0 mm and / or L4 > 0 mm, the risk of drop failure can be further reduced. In Examples B1 to B8, the drop failure rate in Example B8 is similar to that in Example B7, and in Example B8, the length of the fourth inner wall is too large, which affects the tab welding, and the unfirm welding also causes the tab to tear when the lithium ion battery drops. Therefore, in the present application, 0 mm < L1 ≤ 3 mm can be selected.

[0126] In Examples B4 to B7, the drop failure rate is less than that in Examples B1 to B3, and in the present application, 1 mm ≤ L1 ≤ 3 mm is preferred.

[0127] Similarly, in combination with Examples B9 to B13, the length of the fifth inner wall in Example B13 is too large, which occupies space and affects the energy density, and the drop failure rate is similar to that in Examples B11 and B12, and in the present application, 0 mm < L2 ≤ 3 mm can be selected. The drop failure rates in Examples B11 and B12 are less than those in Examples B9 and B10, and in Examples B9 and B10, the length of the fifth inner wall is small, which has limited effect on resisting tab tearing, and therefore in the present application, 1 mm ≤ L2 ≤ 3 mm is preferred.

[0128] In combination with Examples B14 to B18, the length of the eleventh inner wall in Example B18 is too large, which occupies space and affects the energy density, and in the present application, 0 mm < L3 ≤ 3 mm can be selected. The drop failure rates in Examples B16 and B17 are less than those in Examples B14 and B15, and in Examples B14 and B15, the length of the eleventh inner wall is small, which has limited effect on resisting tearing, and therefore in the present application, 1 mm ≤ L3 ≤ 3 mm is preferred.

[0129] In combination with Examples B19 to B23, the length of the twelfth inner wall in Example B23 is too large, which occupies space and affects the energy density, and in the present application, 0 mm < L4 ≤ 3 mm can be selected. The drop failure rates in Examples B21 to B22 are less than those in Examples B19 and B20, and in Examples B19 and B20, the length of the twelfth inner wall is small, which has limited effect on resisting tearing, and therefore in the present application, 1 mm ≤ L4 ≤ 3 mm is preferred.

[0130] Finally, it should be noted that: the above examples are only used to illustrate the technical solutions of the present application, but not to limit them; under the idea of the present application, the technical features in the above examples or different embodiments can also be combined, the steps can be implemented in any order, and there are many other changes of different aspects of the present application as described above, which are not provided in details for simplicity; although the present application has been described in detail with reference to the foregoing examples, those skilled in the art should understand that: it can still modify the technical solutions recorded in the foregoing examples, or make equivalent replacement for part of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present application.

Claims

1. A secondary battery comprising a tab sheet including a current collector, a first active material layer, and a tab, the current collector having a first surface and a second surface disposed opposite each other in a thickness direction of the current collector, the first surface being provided with the first active material layer, the first active material layer having a first recess and a first edge, a portion of the tab being disposed in the first recess and another portion of the tab protruding beyond the first edge, characterized in that, The first recess has a first inner wall, a second inner wall, a third inner wall and a fourth inner wall; The first inner wall and the second inner wall are respectively the inner walls of the two ends of the first recess along the length direction of the current collector; the third inner wall and the fourth inner wall are respectively the inner walls of the two ends of the first recess along the extending direction of the tab, the third inner wall is away from the first edge, and the fourth inner wall is close to the first edge; The fourth inner wall and the first inner wall have a first connecting wall therebetween, and the minimum width of the first connecting wall to the first edge along the extending direction of the tab is W1, W1>0 mm.

2. The secondary battery according to claim 1, characterized by 0.5 mm≤W1≤4 mm.

3. The secondary battery according to claim 1 or 2, characterized by The fourth inner wall comprises a plane and / or an arc surface.

4. The secondary battery according to any one of claims 1 to 3, characterized by, The first recess further has a fifth inner wall, the fifth inner wall and the third inner wall are respectively the inner walls of the two ends of the first recess along the extending direction of the tab, one end of the second inner wall is connected with the fifth inner wall, and the other end is connected with the third inner wall; The fifth inner wall and the second inner wall have a second connecting wall therebetween, and the minimum width of the second connecting wall to the first edge along the extending direction of the tab is W2, W2>0 mm.

5. The secondary battery according to claim 4, characterized by 0.5 mm≤W2≤4 mm.

6. The secondary battery according to any one of claims 1 to 3, characterized by The first active material layer further has a sixth inner wall and a seventh inner wall, one end of the sixth inner wall is connected with the first edge, and the other end is connected with the fourth inner wall, one end of the seventh inner wall is connected with the first edge, and the other end is connected with the second inner wall; The sixth inner wall and the seventh inner wall have a first gap space therebetween along the length direction of the current collector, and the tab portion is located in the first gap space.

7. The secondary battery according to claim 4 or 5, characterized by The first active material layer further has a sixth inner wall and a seventh inner wall, one end of the sixth inner wall is connected with the first edge, and the other end is connected with the fourth inner wall, one end of the seventh inner wall is connected with the first edge, and the other end is connected with the fifth inner wall; The sixth inner wall and the seventh inner wall have a first gap space therebetween along the length direction of the current collector, and the tab portion is located in the first gap space.

8. The secondary battery according to any one of claims 1 to 7, characterized by, The length of the fourth inner wall along the length direction of the current collector is L1, 0 mm 9. The secondary battery according to claim 8, characterized by 1 mm≤L1≤3 mm.

10. The secondary battery according to any one of claims 4, 5, 7, 8, or 9, characterized by, The length of the fifth inner wall along the length direction of the current collector is L2, 0 mm 11. The secondary battery according to claim 10, characterized by 1 mm≤L2≤3 mm.

12. The secondary battery according to any one of claims 1 to 11, characterized by The tab further comprises a second active material layer, and the second active material layer is arranged on the second surface of the current collector; The second active material layer has a second recess, and the first recess and the second recess at least partially overlap along the thickness direction of the current collector; The second active material layer has a second edge along the extending direction of the tab; The second recess has an eighth inner wall, a ninth inner wall, a tenth inner wall and an eleventh inner wall; The eighth inner wall and the ninth inner wall are respectively inner walls at two ends of the second groove in a length direction of the current collector; the eleventh inner wall and the tenth inner wall are respectively inner walls at two ends of the second groove in an extending direction of the tab, and the eleventh inner wall is close to the second edge and the tenth inner wall is away from the second edge; The eleventh inner wall and the eighth inner wall have a third connecting wall therebetween, and a minimum width of the third connecting wall to the second edge in the extending direction of the tab is W3, W3>0 mm.

13. The secondary battery according to claim 12, characterized by 0.5 mm≤W3≤4 mm.

14. The secondary battery according to claim 12 or 13, characterized by The second groove further has a twelfth inner wall, and the twelfth inner wall and the tenth inner wall are respectively inner walls at two ends of the second groove in the extending direction of the tab; one end of the ninth inner wall is connected with the tenth inner wall and the other end is connected with the twelfth inner wall; The twelfth inner wall and the ninth inner wall have a fourth connecting wall therebetween, and a minimum width of the fourth connecting wall to the second edge in the extending direction of the tab is W4, W4>0 mm.

15. The secondary battery according to claim 14, characterized by 0.5 mm≤W4≤4 mm.

16. The secondary battery according to claim 12 or 13, characterized by The second active material layer further has a thirteenth inner wall and a fourteenth inner wall, one end of the thirteenth inner wall is connected with the second edge and the other end is connected with the eleventh inner wall, and one end of the fourteenth inner wall is connected with the second edge and the other end is connected with the eighth inner wall; The thirteenth inner wall and the fourteenth inner wall have a second gap space therebetween in the length direction of the current collector.

17. The secondary battery according to any one of claims 12 to 15, characterized by The second active material layer further has a thirteenth inner wall and a fourteenth inner wall, one end of the thirteenth inner wall is connected with the second edge and the other end is connected with the eleventh inner wall, and one end of the fourteenth inner wall is connected with the second edge and the other end is connected with the twelfth inner wall; The thirteenth inner wall and the fourteenth inner wall have a second gap space therebetween in the length direction of the current collector. The length of the eleventh inner wall in the length direction of the current collector is L3, 0 mm The length of the twelfth inner wall in the length direction of the current collector is L4, 0 mm 1 mm≤L3≤3 mm, and / or, 1 mm≤L4≤3 mm.

18. The secondary battery according to claim 17, characterized by The first inner wall has a first profiled edge facing the second inner wall, the second inner wall has a second profiled edge facing the first inner wall, and the third inner wall has a third profiled edge facing the fourth inner wall, as viewed in a thickness direction of the current collector; 19. The secondary battery according to any one of claims 12 to 18, characterized by The first profiled edge comprises a first point and a second point, the first point is the farthest point from the second profiled edge in the length direction of the current collector, and the second point is the farthest point from the third profiled edge in the extending direction of the tab; The second profiled edge comprises a third point and a fourth point, the third point is the farthest point from the first profiled edge in the length direction of the current collector, and the fourth point is the farthest point from the third profiled edge in the extending direction of the tab; ​ The third profile edge has a fifth point, which is the farthest point from the first edge in the protruding direction of the tab; The tab satisfies 1.2Z0<Z1<2.5Z0; Wherein, in the thickness direction of the current collector, in the protruding direction of the tab, D1 is the length from the second point to the fifth point, D2 is the length from the fourth point to the fifth point, in the length direction of the current collector, D3 is the length from the first point to the third point; Z0=L1+L2+D1+D2+D3; Z1 is the profile perimeter of the first groove inner wall.

20. The secondary battery according to any one of claims 12 to 19, characterized by In the width direction of the current collector, the maximum length of the first groove is L5, and the maximum length of the second groove is L6, L5≥L6; The first active material layer includes a first part, and the active material layer between the first inner wall and the first edge forms the first part; The second active material layer includes a second part, and the active material layer between the eleventh inner wall and the second edge forms the second part; In the thickness direction of the current collector, the first part and the second part at least partially overlap, and |W1-W3|≤2mm.

21. An electronic device, comprising: A secondary battery including any one of the secondary batteries according to claims 1 to 20.

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