Secondary battery and electronic device

Abstract

Disclosed in the present application are a secondary battery and an electronic device. The secondary battery comprises a packaging bag, an electrode assembly, a first tab and a first electrode terminal, wherein the packaging bag comprises a main body portion configured to accommodate the electrode assembly, and a top sealing portion connected to the main body portion; the electrode assembly comprises a first electrode plate, which comprises a first current collector; the first electrode terminal passes through the top sealing portion in a first direction and extends out of the packaging bag; and the first tab comprises a third extension section, a first bending section, a first extension section, a second bending section and a second extension section, which are connected in sequence, the third extension section being welded to the first current collector, the second extension section being connected to the first electrode terminal, and in a second direction perpendicular to the first direction, the first bending section being bent in a direction away from the top sealing portion, and the second bending section being bent in a direction towards the top sealing portion. In the present application, the first tab can extend from the first current collector to the first electrode terminal along the longest path, such that the drop performance is 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] With the continuous updating and development of lithium ion battery technology, the application field of lithium ion batteries is also expanding, and the resulting safety problems are increasingly attracting public attention. When the soft package battery falls, the electrode assembly jumps in the packaging bag, which causes the packaging bag to be torn open and the risk of liquid leakage; during the movement of the electrode assembly in the packaging bag, the packaging bag exerts a pulling force on the tab, which causes the tab to easily fall off the pole piece. SUMMARY

[0003] One purpose of the present application is to provide a secondary battery and an electronic device that can improve drop performance.

[0004] The first aspect of the present application provides a secondary battery, comprising a packaging bag, an electrode assembly, a first tab and a first electrode terminal. The packaging bag comprises a main body portion for accommodating the electrode assembly and a top sealing portion connected to the main body portion. The electrode assembly comprises a first pole piece, a second pole piece and a separator arranged between the first pole piece and the second pole piece, the first pole piece comprising a first current collector, the first electrode terminal extending out of the packaging bag along a first direction through the top sealing portion. The first tab comprises a third extension section, a first bending section, a first extension section, a second bending section and a second extension section connected in sequence, the third extension section being welded to the first current collector, the second extension section being connected to the first electrode terminal; in a second direction perpendicular to the first direction, the first bending section is bent in a direction away from the top sealing portion, and the second bending section is bent in a direction towards the top sealing portion.

[0005] The present application configures the first bending section and the second bending section, so that the first tab can extend from the first current collector to the first electrode terminal along the longest path, so that the first tab can cover the end surface of the electrode assembly on the side of the top sealing portion in the first direction X to the maximum in the second direction Z, which is beneficial to reduce the space in the first direction X in which the electrode assembly can move relative to the packaging bag during the drop, and the first tab acts like a spring during the drop, which can buffer the impact of the electrode assembly on the top sealing portion and reduce the risk of the packaging bag being torn open; and increasing the length of the first tab is beneficial to reduce the pulling force of the packaging bag on the first tab during the drop, reduce the risk of the first tab falling off the first current collector, and improve the drop performance.

[0006] According to some embodiments of the present application, the secondary battery further includes a second tab having the same polarity as the first tab, the second tab and the first tab are each independently welded to the first current collector, the second tab and the first tab are stacked and welded to the first electrode terminal, and the first tab and the second tab are welded to the first electrode terminal. By configuring the second tab, the impedance of each tab is reduced, the amount of heat generated by a single tab is reduced, and the short circuit problem caused by the melting of the sealing layer of the separator or the packaging bag due to temperature rise is improved.

[0007] According to some embodiments of the present application, in the second direction, the first tab includes a plurality of tab layers, the plurality of tab layers include a first tab layer provided with the first tab and a second tab layer provided with the second tab, the number of the plurality of tab layers is N, the number of tab layers between the first tab layer and the second tab layer is M, and M≥1 / 4N. When M / N is in the above range, the heat accumulation at the welding position of the first tab and the second tab to the first current collector is small, and the risk of short circuit caused by the melting of the first adhesive or the separator is reduced.

[0008] According to some embodiments of the present application, 1 / 3N≤M≤2 / 3N, so that the effect of improving the short circuit problem is better.

[0009] According to some embodiments of the present application, the thickness of the first tab and the thickness of the second tab are each greater than the thickness of the first current collector, and the thickness of the first tab and the thickness of the second tab are each less than the thickness of the first electrode terminal, so that the first tab and the second tab are facilitated to be welded to the first current collector, and the thickness of the first tab and the second tab welded to the current collector is reduced to reduce the influence of the first tab and the second tab on the thickness of the electrode assembly, and the first tab and the second tab are configured to facilitate reducing the impedance of the first electrode terminal.

[0010] According to some embodiments of the present application, the thickness of the first tab ranges from 20μm to 50μm, the thickness of the first current collector ranges from 4μm to 15μm, and the thickness of the first electrode terminal ranges from 60μm to 120μm.

[0011] According to some embodiments of the present application, the electrode assembly has a wound structure, the first tab is arranged at the innermost circle of the first tab, the second tab is arranged at the outermost circle of the first tab, and the first tab and the second tab are located on opposite sides of the winding central axis of the electrode assembly in the second direction.

[0012] According to some embodiments of the present application, the area of the first tab that overlaps the second tab in the second direction is a first area, the width of the first tab in a third direction perpendicular to both the first direction and the second direction is W1, the width of the first area is W2, and 0.8W1≤W2≤W1. When W2 / W1 is within the above range, the welding between the first tab and the second tab is firm, the first tab and the second tab together have a better effect of buffering impact force, and the drop performance is improved.

[0013] According to some embodiments of the present application, 0.92W1≤W2≤W1, so that the effect of improving the drop performance is better.

[0014] According to some embodiments of the present application, the secondary battery further comprises a first adhesive member bonded to the first tab, and the first adhesive member comprises a first section covering the second bending section and located on the side of the second bending section facing the packaging bag. By configuring the first section, the toughness of the second bending section can be increased, the risk of fatigue damage and fracture of the second bending section can be reduced, and the drop performance can be improved. The first section configured between the second bending section and the packaging bag can improve the problem of corrosion at the corner position of the main body during the drop.

[0015] According to some embodiments of the present application, the first adhesive member further comprises a second section covering the first extension section and located on the side of the first extension section facing the electrode assembly. By configuring the second section between the first extension section and the electrode assembly, the risk of short circuit caused by the contact between the first extension section and the second tab during the drop can be reduced.

[0016] According to some embodiments of the present application, the first adhesive member further comprises a third section covering the third extension section. Configuring the third section can reduce the risk of short circuit caused by the contact between the first tab and the second tab due to the puncture of the diaphragm by the welding burr.

[0017] According to some embodiments of the present application, the first adhesive member further comprises a base material and an adhesive layer stacked, the base material comprises at least one of polyethylene terephthalate, polyimide, and polypropylene, and the adhesive layer comprises at least one of rubber, acrylic glue, and styrene-isoprene-styrene.

[0018] According to some embodiments of the present application, the minimum distance between the second bending section and the electrode assembly is L1 mm, the minimum distance between the second bending section and the packaging bag is L2 mm, 0.05≤L1≤0.4, and / or 0.05≤L2≤0.4. When L1 and / or L2 is within the above range, the risk of contact short circuit between the second bending section and the second tab can be reduced, and the energy density is not affected.

[0019] According to some embodiments of the present application, the first electrode terminal is integrally arranged with the first tab.

[0020] According to some embodiments of the present application, as viewed in a third direction perpendicular to both the first direction and the second direction, the third extension is located between the second bend and the top seal in the second direction.

[0021] The second aspect of the present application provides an electronic device including any of the above secondary batteries. BRIEF DESCRIPTION OF DRAWINGS

[0022] FIG. 1 is a schematic view of the structure of a secondary battery as viewed in the thickness direction according to an embodiment.

[0023] FIG. 2 is a schematic view of the cross section of the secondary battery of FIG. 1 along line II-II.

[0024] FIG. 3 is a schematic view of the structure of a first adhesive member according to an embodiment.

[0025] FIG. 4 is a schematic view of the cross section of a secondary battery according to another embodiment.

[0026] FIG. 5 is a schematic view of the structure of an electrode assembly as viewed in the length direction according to an embodiment.

[0027] FIG. 6 is a schematic view of the structure of an electronic device according to an embodiment.

[0028] Main element symbol explanation: secondary battery 100, packaging bag 10, electrode assembly 20, first electrode terminal 31, second electrode terminal 32, main body part 11, top sealing part 12, side sealing part 13, accommodating cavity 110, first pole piece 21, second pole piece 22, separator 23, first current collector 211, first active layer 212, second current collector 221, second active layer 222, first tab 41, second tab 42, third tab 43, first bending section 411, first extending section 412, second bending section 413, second extending section 414, third extending section 415, first adhesive member 50, first section 51, second section 52, third section 53, base material 501, adhesive layer 502, edge 231, side wall 111, third adhesive member60 first region 410 pole piece layer 210 first pole piece layer 2101 second pole piece layer 2102 start end 201 end end 202 start section 21A winding center axis O electronic device 200

[0029] The following detailed embodiments will further illustrate the present application in conjunction with the above-mentioned drawings. DETAILED DESCRIPTION

[0030] The following detailed embodiments are illustrative rather than limiting and are intended to provide further examples of the present application. Thus, the scope of the application is not to be determined by any of the foregoing detailed description but only by the claims, and the equivalents thereto.

[0031] When a component is referred to as being "on" another component, it can be directly on the other component or intervening components can also be present. When a component is referred to as being "connected" or "coupled" to another component, it can be directly connected to the other component or intervening components can also be present.

[0032] Unless otherwise defined, the term "plurality" as used herein, in describing a quantity of components, specifically refers to the components being two or more. In the present application, the term "and / or" is merely an associative relationship between the associated objects, which means that there can be three relationships, for example, A and / or B, which can represent the following three cases: A exists alone, A and B exist together, and B exists alone.

[0033] Some embodiments of the present application will be described below in conjunction with the accompanying drawings. The following embodiments and features in the embodiments can be combined with each other without conflict.

[0034] Referring to FIG. 1, an embodiment of the present application provides a secondary battery 100 including a packaging bag 10, an electrode assembly 20, a first electrode terminal 31, and a second electrode terminal 32. The electrode assembly 20 is accommodated in the packaging bag 10. The first electrode terminal 31 and the second electrode terminal 32 are connected to the electrode assembly 20, respectively, and extend out of the packaging bag 10 in a first direction X to connect external elements. In the present application, the first direction X is a length direction of the electrode assembly 20. The first electrode terminal 31 can be a positive electrode and can include at least one of Ni, Ti, Al, Ag, Au, Pt, Fe, and combinations thereof. The second electrode terminal 32 can be a negative electrode and can include at least one of Ni, Ti, Cu, Ag, Au, Pt, Fe, and combinations thereof.

[0035] The packaging bag 10 includes a main body portion 11, a top seal portion 12, and side seal portions 13, as viewed in a second direction Z perpendicular to the first direction X. The main body portion 11 is provided with an accommodation cavity 110 (see FIG. 2), and the electrode assembly 20 is disposed in the accommodation cavity 110. The top seal portion 12 extends from an edge of the main body portion 11 and is located on one side of the main body portion 11 in the first direction X. The first electrode terminal 31 and the second electrode terminal 32 extend out of the packaging bag 10 through the top seal portion 12 in the first direction X. The side seal portions 13 extend from edges of the main body portion 11 and are located on opposite sides of the main body portion 11 in a third direction Y. The third direction Y is perpendicular to the first direction X and the second direction Z. The top seal portion 12 is connected to the side seal portions 13, and the top seal portion 12 and the side seal portions 13 are disposed around three sides of the main body portion 11. In the present application, the second direction Z is a thickness direction of the electrode assembly 20, and the third direction Y is a width direction of the electrode assembly 20.

[0036] In some embodiments, the packaging bag 10 has a film layer structure. Specifically, the packaging bag 10 includes a packaging layer, a metal layer, and a protection layer, which are disposed in a stack. The packaging layer is disposed close to the electrode assembly 20 and is located inside the secondary battery 100. The protection layer is disposed away from the electrode assembly 20 and is exposed outside the secondary battery 100. The protection layer can be made of a high-molecular resin and is used to protect the metal layer. The metal layer can be made of aluminum, steel, or the like and is used to prevent moisture in the external environment from penetrating and to improve the strength of the packaging bag 10. The packaging layer can be made of a polymer, such as polypropylene or polyamide. The packaging layer can be connected to form the top seal portion 12 and the side seal portions 13 by a hot melting method or by an adhesive method. In the present embodiment, the packaging bag 10 is an aluminum-plastic film or a steel-plastic film, and the main body portion 11, the top seal portion 12, and the side seal portions 13 are formed by punching, folding, hot pressing, and cutting from a whole aluminum-plastic film or steel-plastic film, i.e., the main body portion 11, the top seal portion 12, and the side seal portions 13 are integrally disposed.

[0037] Referring to FIG. 2, the electrode assembly 20 includes a first tab 21, a second tab 22, and a separator 23 disposed between the second tab 22 and the first tab 21. In the present embodiment, the electrode assembly 20 has a jellyroll structure, specifically, the electrode assembly 20 is formed by sequentially stacking the first tab 21, the separator 23, and the second tab 22 along the second direction Z and then winding the stack along the first direction X. In another embodiment, the electrode assembly 20 has a stack structure, specifically, the electrode assembly 20 is formed by sequentially and alternately stacking a plurality of first tabs 21, a plurality of separators 23, and a plurality of second tabs 22 along the second direction Z.

[0038] The first tab 21 includes a first current collector 211 and a first active layer 212 disposed on a surface of the first current collector 211. The first active layer 212 can be disposed on both surfaces of the first current collector 211 or on only one surface of the first current collector 211, without limitation. In the present embodiment, the first tab 21 is a positive electrode. The first current collector 211 includes at least one of Ni, Ti, Ag, Au, Pt, Fe, AL, and combinations thereof. The first active layer 212 includes a positive electrode active material, which can include at least one of lithium cobaltate, lithium manganate, lithium nickelate, lithium nickel cobalt manganate, lithium iron phosphate, lithium manganese iron phosphate, lithium vanadium phosphate, lithium vanadium oxyphosphate, lithium-rich manganese-based material, lithium nickel cobalt aluminum phosphate, and combinations thereof.

[0039] The second tab 22 includes a second current collector 221 and a second active layer 222 disposed on a surface of the second current collector 221. The second active layer 222 can be disposed on both surfaces of the second current collector 221 or on only one surface of the second current collector 221, without limitation. In the present embodiment, the second tab 22 is a negative electrode. The second current collector 221 includes at least one of Ni, Ti, Cu, Ag, Au, Pt, Fe, and combinations thereof. The second active layer 222 includes one or more of soft carbon, hard carbon, artificial graphite, natural graphite, silicon, silicon oxide compounds, silicon-carbon composites, lithium titanate, and metals capable of forming alloys with lithium.

[0040] The secondary battery 100 further comprises a first tab 41. The first tab 41 is welded with the first current collector 211 and connected with the first electrode terminal 31. In the embodiment, the first tab 41 and the first electrode terminal 31 are integrally arranged. In some embodiments, the plurality of current collector layers distributed along the second direction Z formed by bending the first current collector 211 are connected with the first electrode terminal 31 through only one first tab 41. The first tab 41 comprises a third extending section 415, a first bending section 411, a first extending section 412, a second bending section 413 and a second extending section 414 connected in sequence. The third extending section 415 is welded with the first current collector 211, and the second extending section 414 is connected with the first electrode terminal 31. The first bending section 411 is a section of the first tab 41 that is bent for the first time from the end close to the first current collector 211, and the second bending section 413 is a section of the first tab 41 that is bent for the second time from the end close to the first current collector 211. In the third direction Y, the projection of the third extending section 415 along the second direction Z is located within the second current collector 221. In the second direction Z, the first extending section 412, the second extending section 414 and the third extending section 425 are all located between the second bending section 413 and the top sealing part 12, as viewed in the third direction Y. In the first direction X, the first bending section 411 is located between the end surface defined by the plurality of edges of the second current collector 221 located on the side of the first electrode terminal 31 in the first direction X and distributed along the second direction Z and the top sealing part 12, as viewed in the third direction Y. The end surface defined by the plurality of edges of the second current collector 221 located on the side of the first electrode terminal 31 in the first direction X and distributed along the second direction Z can be a flat surface or a curved surface, which is not limited in the application.

[0041] In the second direction Z, the first bending section 411 is bent in a direction away from the top sealing part 12, and the second bending section 413 is bent in a direction toward the top sealing part 12, as viewed in the third direction Y. By configuring the first bending section 411 and the second bending section 413, the first tab 41 can extend from the first current collector 211 to the first electrode terminal 31 along the longest path, so that the first tab 41 can cover the end surface of the electrode assembly 20 located on the side of the top sealing part 12 in the first direction X to the maximum in the second direction Z, which is conducive to reducing the space in the first direction X in which the electrode assembly 20 can move relative to the packaging bag 10 during the drop process, and the first tab 41 can act like a spring during the drop process to buffer the impact of the electrode assembly 20 on the top sealing part 12, reduce the risk of the packaging bag 10 being torn open, and improve the drop performance. By configuring the first bending section 411 and the second bending section 413, the length of the first tab 41 can be increased, which is conducive to reducing the pulling force of the packaging bag 10 on the first tab 41 during the drop process, reducing the risk of the first tab 41 falling off the first current collector 211, and improving the drop performance.

[0042] In some embodiments, the bending direction of the first bending section 411 and the bending direction of the second bending section 413 are opposite. The first bending section 411 is bent along the second direction Z, and the second bending section 413 is bent along a direction opposite to the second direction Z. By configuring the first bending section 411 and the second bending section 413 with opposite bending directions, the space occupied by the first tab 41 can be reduced, and the energy density can be improved.

[0043] In some embodiments, the first extension section 412 and the second extension section 414 are substantially linear sections, which can reduce the space occupied by the first tab 41 and improve the energy density. The first extension section 412 includes a first end connected to the first bending section 411 and a second end connected to the second bending section 413, and the first end and the second end form a first linear section. The angle between the first extension section 412 and the first linear section ranges from 0° to 5°. The second extension section 414 includes a third end connected to the second bending section 413 and a fourth end connected to the first electrode terminal 31, and the third end and the fourth end form a second linear section. The angle between the second extension section 414 and the second linear section ranges from 0° to 5°. In some embodiments, the first extension section 412 extends along the third direction Y, and the second extension section 414 extends along a direction opposite to the third direction Y.

[0044] In some embodiments, the secondary battery 100 further includes a first adhesive member 50 bonded to the first tab 41. The first adhesive member 50 includes a first section 51 bonded to the second bending section 413, and the first section 51 covers the second bending section 413 and is located on the side of the second bending section 413 facing the packaging bag 10. By configuring the first section 51, the toughness of the second bending section 413 can be increased, and the risk of fatigue failure of the second bending section 413 due to stress concentration caused by repeated extrusion of the first tab 41 by the electrode assembly 20 moving in the first direction X relative to the packaging bag 10 can be reduced. The first section 51 configured between the second bending section 413 and the packaging bag 10 can reduce the risk of corrosion caused by contact between the metal layer of the packaging bag 10 and the first tab 41 at the corner position of the main body 11 during the falling process.

[0045] In some embodiments, the first adhesive member 50 further includes a second section 52 bonded to the first extension section 412. The second section 52 is connected to the first section 51 and covers the first extension section 412. The second section 52 is located on the side of the first extension section 412 facing the electrode assembly 20. By configuring the second section 52 between the first extension section 412 and the electrode assembly 20, the risk of short circuit caused by contact between the first extension section 412 and the edge of the second tab 22 on the side of the first tab 41 in the first direction X when the electrode assembly 20 moves in the first direction X relative to the packaging bag 10 can be reduced.

[0046] In some embodiments, the first adhesive 50 further comprises a third section 53 adhered to the third extension 415. The third section 53 is connected to the second section 52 and covers the third extension 415. The third section 53 is located on the side of the third extension 415 facing away from the first current collector 211. The third section 53 is configured to reduce the risk of the first tab 21 and the second tab 22 being short-circuited by a welding burr formed by welding the third extension 415 to the first current collector 211 piercing the separator 23. In some embodiments, the third section 53 is adhered to the first tab 21 to increase the relative fixation between the first tab 41 and the first tab 21 and reduce the risk of the first tab 41 falling off the first current collector 211 due to the pulling force of the packaging bag 10 on the first tab 41 when dropped.

[0047] In some embodiments, the first adhesive 50 further covers the surface of the second extension 414 facing the packaging bag 10 to further reduce the risk of the first tab 41 being broken by repeated extrusion.

[0048] In some embodiments, the secondary battery 100 further comprises a second adhesive disposed on the surface of the first tab 41 facing away from the first adhesive 50. The second adhesive can be adhered to the first adhesive 50. The material of the second adhesive can be the same as that of the first adhesive 50.

[0049] Referring to FIG. 3, in some embodiments, the first adhesive 50 comprises a base material 501 and an adhesive layer 502 stacked and disposed, and the adhesive layer 502 is adhered to the first tab. The base material 501 comprises at least one of polyethylene terephthalate, polyimide, and polypropylene. The adhesive layer 502 comprises at least one of rubber, acrylic glue, and styrene-isoprene-styrene, which has good adhesive properties. In this embodiment, the material of the base material 501 is polyethylene terephthalate, and the material of the adhesive layer 502 is styrene-isoprene-styrene.

[0050] In some embodiments, the separator 23 extends beyond the first and second tabs 21 and 22 in the first direction X to reduce the risk of contact short between the first and second tabs 21 and 22. The separator 23 includes a plurality of edges 231 on the side of the first tab 41 in the first direction X and distributed along the second direction Z, which form an end face that can be planar or curved. In the first direction X, the minimum distance between the second bent section 413 and the electrode assembly 20 is L1 mm. In this application, the minimum distance between the second bent section 413 and the electrode assembly 20 refers to the minimum value of the vertical distance between the second bent section 413 and the end face formed by the plurality of edges 231 in the first direction X. In some embodiments, in the first direction X, 0.05≤L1≤0.4. When L1 is less than 0.05 mm, the gap between the second bent section 413 and the electrode assembly 20 is too small, and the second bent section 413 is easily rubbed against the second tab 22 during the drop process, causing local wear and contact short between the second bent section 413 and the second tab 22. Moreover, the small gap leads to insufficient space for heat generation, which can cause heat accumulation and melting of the separator 23 at the second bent section 413, resulting in contact short between the second bent section 413 and the second tab 22. When L1 is greater than 0.4 mm, the gap between the second bent section 413 and the electrode assembly 20 is too large, resulting in large energy loss in the first direction X. Preferably, 0.15≤L1≤0.3, which improves the effects of short circuit and drop.

[0051] The accommodation cavity 110 includes a side wall 111 on the side of the edge 231 in the first direction X. The side wall 111 can be planar or curved, which is not limited in this application. In the first direction X, the minimum distance between the second bent section 413 and the packaging bag 10 is L2 mm. In this application, the minimum distance between the second bent section 413 and the packaging bag 10 refers to the minimum value of the vertical distance between the second bent section 413 and the side wall 111 in the first direction X. In some embodiments, 0.05≤L2≤0.4. When L2 is less than 0.05 mm, the gap between the second bent section 413 and the packaging bag 10 is too small, and the corners of the main body 11 are easily pressed by the second bent section 413 during the drop process, causing the first tab 41 to contact the metal layer of the packaging bag 10 and corrode. When L2 is greater than 0.4 mm, the gap between the second bent section 413 and the packaging bag 10 is too small, resulting in large energy loss in the first direction X. Preferably, 0.15≤L2≤0.3, which improves the effects of short circuit and drop.

[0052] Referring to FIG. 1, in some embodiments, the secondary battery 100 further comprises a third adhesive 60. The third adhesive 60 covers the first electrode terminal 31 and adheres the first electrode terminal 31 and the packaging bag 10 at the top sealing portion 12. The third adhesive 60 also covers the second electrode terminal 32 and adheres the second electrode terminal 32 and the packaging bag 10 at the top sealing portion 12. By configuring the third adhesive 60, the sealing performance of the top sealing portion 12 at the location of the first electrode terminal 31 and the second electrode terminal 32 is improved. In some embodiments, the third adhesive 60 comprises at least one of polypropylene, polyethylene, polyimide, and polyethylene terephthalate, which have good sealing performance.

[0053] Referring to FIG. 4, the secondary battery 100 further comprises a second tab 42 having the same polarity as the first tab 41. The second tab 42 is welded to the first current collector 211 independently of the first tab 41, and the second tab 42 is welded to the first electrode terminal 31 after being stacked with the first tab 41. By configuring the second tab 42, the impedance of each tab is reduced, the heat generation of a single tab during external short circuit is less, and the short circuit problem caused by the melting of the sealing layer of the packaging bag 10 due to excessive temperature rise is reduced, and the short circuit problem caused by the melting of the separator 23 due to excessive temperature rise is reduced, and the risk of short circuit is reduced.

[0054] In some embodiments, the second tab 42 and the first tab 41 are stacked and welded to form a tab group, and the tab group is welded to the first electrode terminal 31, so that the first tab 41 and the second tab 42 are pressed against each other, and the first tab 41 is easily maintained in a bent shape without being damaged; and the second tab 42 also functions like a spring to enhance the buffering capacity and further improve the drop performance.

[0055] In some embodiments, the thickness of the first tab 41 and the second tab 42 is greater than the thickness of the first current collector 211, so as to facilitate the welding of the first tab 41 and the second tab 42 to the first current collector 211 without affecting the volumetric energy density. In some embodiments, the thickness of the first tab 41 and the second tab 42 is less than the thickness of the first electrode terminal 31. The thicker the thickness of the first electrode terminal 31, the more conducive to reducing impedance. The thickness of the first tab 41 and the thickness of the second tab 42 can be the same or different, which is not limited in the present application. In some embodiments, the thickness of the first current collector 211 is 4-15 μm, for example, 4 μm, 9 μm, 10 μm, 11 μm, 12 μm, 15 μm, or a range formed by any two of the above values. In some embodiments, the thickness of the first tab 41 and the second tab 42 is 20-50 μm, for example, 20 μm, 22 μm, 24 μm, 26 μm, 28 μm, 30 μm, 35 μm, 40 μm, 45 μm, 50 μm, or a range formed by any two of the above values. In some embodiments, the thickness of the first electrode terminal 31 is 60-120 μm, for example, 60 μm, 65 μm, 70 μm, 75 μm, 80 μm, 90 μm, 100 μm, 110 μm, 120 μm, or a range formed by any two of the above values.

[0056] In the second direction Z, the first tab 41 includes a plurality of tab layers 210. In the case where the electrode assembly 20 has a stack structure, the tab layers 210 are sheet-shaped tabs, and each sheet-shaped first tab 21 serves as a tab layer 210. In the case where the electrode assembly 20 has a jelly-roll structure, the plurality of tab layers 210 are formed by the first tab 21 being folded back and forth and stacked, and the first tab 21 includes a plurality of folded portions and a plurality of flat portions, each flat portion serving as a tab layer 210. The plurality of tab layers 210 include a first tab layer 2101 provided with the first tab 41 and a second tab layer 2102 provided with the second tab 42. The number of the plurality of tab layers 210 is N, and the number of the tab layers 210 between the first tab layer 2101 and the second tab layer 2102 is M. In some embodiments, M≥1 / 4N. When M<1 / 4N, the distance between the first tab 41 and the second tab 42 is too small, the local heat generation is too high when short-circuiting, the heat accumulation at the welding position of the first tab 41 and the second tab 42 to the first current collector 211 is large, and the first adhesive 50 or the separator 23 is easily melted, thereby causing a short circuit in a local area; in addition, the welding burr formed by welding is more likely to pierce the first adhesive 50 or the separator 23, causing a short circuit; furthermore, the smaller the distance, the greater the impedance, affecting the electrochemical performance. Preferably, 1 / 3N≤M≤2 / 3N, which improves the effect of short circuiting.

[0057] Referring to FIG. 5, in some embodiments, the region of the first tab 41 that overlaps the second tab 42 in the second direction Z is a first region 410. In this application, the first region 410 is the largest region of the first tab 41 that overlaps the second tab 42 in the second direction Z. In the third direction Y, the width of the first tab 41 is W1, and the width of the first region 410 is W2. In some embodiments, 0.8W1≤W2≤W1. When W2<0.8W1, the overlap between the first tab 41 and the second tab 42 is small, the area that can be welded between the first tab 41 and the second tab 42 is small, which can easily lead to the first tab 41 and the second tab 42 not being welded firmly, and the collision during transportation can easily lead to the tabs being broken; and the smaller the overlap between the first tab 41 and the second tab 42, the lower the buffering effect compared to the case where the overlap is large, and the effect of improving the drop performance is reduced. Preferably, 0.92≤W2 / W2≤1, and the effect of improving the drop performance is better.

[0058] Referring to FIG. 5, in the case where the electrode assembly 20 has a jelly-roll structure, the first tab 21 has a start end 201 and an end end 202 opposite to each other in the winding direction of the electrode assembly 20. The first tab 41 is disposed at the innermost circle of the first tab 21, the second tab 42 is disposed at the outermost circle of the first tab 21, and the first tab 41 and the second tab 42 are located on opposite sides of the winding central axis O of the electrode assembly 20 in the second direction Z, thus improving the drop performance and the effect of short circuit is better. The innermost circle of the first tab 21 refers to a circle counted from the start end 201, and the outermost circle of the first tab 21 refers to a circle counted from the end end 202. The first tab 21 further includes a start section 21A, which refers to a section between the start end 201 of the first tab 21 and the first bending section of the first tab 21. In some embodiments, the first tab 41 is disposed at the start section 21A. Referring to FIG. 5, the secondary battery 100 further includes two third tabs 43 having polarities different from those of the first tab 41 and the second tab 42. The two third tabs 43 are each independently welded to the second current collector 221 and then welded to the second electrode terminal 32 after being stacked. In some embodiments, the thickness of the third tab 43 is greater than the thickness of the second current collector 221 and less than the thickness of the second electrode terminal 32. In some embodiments, the thickness of the second current collector 221 is 4-15 μm, for example, 4 μm, 9 μm, 10 μm, 11 μm, 12 μm, 15 μm, or a range formed by any two of the above values. In some embodiments, the thickness of the third tab 43 is 20-50 μm, for example, 20 μm, 22 μm, 24 μm, 26 μm, 28 μm, 30 μm, 35 μm, 40 μm, 45 μm, 50 μm, or a range formed by any two of the above values. In some embodiments, the thickness of the second electrode terminal 32 is 60-120 μm, for example, 60 μm, 65 μm, 70 μm, 75 μm, 80 μm, 90 μm, 100 μm, 110 μm, 120 μm, or a range formed by any two of the above values.

[0059] Referring to FIG. 6, an embodiment of the present application further provides an electronic device 200 including any one of the secondary batteries 100 described above. The electronic device 200 of the present application can be, but is not limited to, a notebook computer, a pen input computer, a mobile computer, an electronic book player, a portable telephone, a portable facsimile, a portable copier, a portable printer, a headphone, a video recorder, a liquid crystal television, a portable cleaner, a portable CD player, a mini disc, a transceiver, an electronic organizer, a calculator, a memory card, a portable recorder, a radio, a backup power supply, an electric motor, an automobile, a motorcycle, a power-assisted bicycle, a lighting appliance, a toy, a game machine, a clock, an electric tool, a flashlight, a camera, a household large storage battery, and a lithium ion capacitor, etc.

[0060] The performance of the secondary battery provided in the present application is described below through specific examples and comparative examples.

[0061] Example 1

[0062] Preparation of the first electrode tab: the positive electrode active material (lithium cobaltate), the conductive agent (conductive carbon black and carbon nanotube), and the binder (polyvinylidene fluoride) were dissolved in N-methylpyrrolidone solution in a ratio of 97.5:1:1.5 by weight to form a positive electrode slurry with a solid content of 75%. An aluminum foil was used as the current collector, and the positive electrode slurry was coated on the surface of the first current collector to obtain a positive electrode active material layer. Subsequently, cold pressing, cutting, and welding of two positive electrode tabs (the first electrode tab and the second electrode tab) were performed to obtain the first electrode tab. The thickness of the aluminum foil was 10 μm, and the thickness of the first electrode tab and the second electrode tab was 20 μm.

[0063] Preparation of the second electrode tab: the negative electrode active material (graphite), the conductive agent (conductive carbon black), the thickening agent (sodium carboxymethyl cellulose), and the binder (styrene-butadiene rubber) were mixed in a mass ratio of 97.5:1:0.5:1, and then deionized water was added as the solvent to obtain a negative electrode slurry with a solid content of 50 wt%. A copper foil was used as the current collector, and the negative electrode slurry was coated on the surface of the second current collector to obtain a negative electrode active material layer. Subsequently, cold pressing, cutting, and welding of two negative electrode tabs (the third electrode tab) were performed to obtain the second electrode tab. The thickness of the copper foil was 8 μm, and the thickness of the negative electrode tab was 30 μm.

[0064] Preparation of the separator: a polyethylene film was selected as the separator.

[0065] Preparation of the electrolyte: ethylene carbonate (EC), diethyl carbonate (DEC), propylene carbonate (PC), propyl propionate (PP), and vinylene carbonate (VC) were mixed in a weight ratio of 20:30:20:28:2 to obtain an organic solvent, and then fully dried lithium salt LiPF6 and the organic solvent were mixed in a weight ratio of 8:92 to obtain the electrolyte.

[0066] Preparation of the lithium ion battery: the first electrode tab, the separator, and the second electrode tab were sequentially stacked and wound to obtain an electrode assembly, two positive electrode tabs were stacked and welded to the first electrode terminal, two negative electrode tabs were stacked and welded to the second electrode terminal, the electrode assembly was placed in an aluminum-plastic film packaging bag, and hot pressing was performed at a preset pressure to bond the electrode assembly. After liquid injection and formation, the lithium ion battery was obtained. The structure of the lithium ion battery was similar to that of FIGS. 4 and 5, except that the first electrode tab was not provided with the first adhesive. The total number N of electrode tab layers was 24, and the width W1 of the first electrode tab and the second electrode tab was 9 mm. The thickness of the first electrode terminal and the second electrode terminal was 100 μm.

[0067] Example 2

[0068] The difference from Example 1 is that the first tab is provided with a first adhesive, and the structure of the lithium ion battery of Example 2 is shown in FIGS. 4 and 5.

[0069] Example 3

[0070] The difference from Example 2 is that the second tab is not provided, and only the first tab is provided, and the structure of the lithium ion battery of Example 3 is shown in FIG. 2.

[0071] Examples 4-28

[0072] The difference from Example 2 is that at least one of the ratio M / N of the number of the tab layers between the first tab layer and the second tab layer to the number of the tab layers, the ratio W2 / W1 of the width of the first region to the width of the first tab, the minimum distance L1 between the second bending section and the electrode assembly, and the minimum distance L2 between the second bending section and the packaging bag is different.

[0073] Comparative Example 1

[0074] The difference from Example 1 is that the first tab is not provided with the first bending section and the second bending section, and the part of the first tab between the electrode assembly and the first electrode terminal is substantially a straight section.

[0075] The test methods of the various parameters of the present application are described below.

[0076] (1) Determination method of the number N, M of the tab layers:

[0077] The lithium ion battery is discharged at 0.2C constant current to the cut-off voltage. The lithium ion battery is disassembled, the first tab is taken out and unfolded, and the number of the tab layers is counted according to the creases on the first tab (the flat part on one side of the crease is one tab layer), the total number N of the tab layers and the number N of the tab layers between the first tab and the second tab of the first tab are calculated.

[0078] (2) Test method of the width W1, W2 of the first tab:

[0079] The lithium ion battery is discharged at 0.2C constant current to the cut-off voltage. The lithium ion battery is disassembled, the first tab is taken out and unfolded, and the width W1 of the first tab is measured using a steel ruler.

[0080] The lithium ion battery is scanned along the length direction using an electronic computed tomography method, the cross-sectional view of the position of the first tab and the second tab is taken, and the width W2 of the part of the first tab and the second tab overlapping in the width direction is measured.

[0081] (3) Test method of the minimum distance L1, L2 between the second bending section and the electrode assembly and the packaging bag:

[0082] The lithium ion battery is scanned along the width direction by using the computer tomography method, and a cross-sectional view at the first electrode terminal position is taken; an end face is formed by a plurality of edges of the separator in the thickness direction, and a vertical distance in the length direction between the highest point of the end face and the lowest point of the second bending section is L1; a vertical distance in the length direction between the highest point of the second bending section and the lowest point of the side wall of the packaging bag is L2.

[0083] (4) Drop test:

[0084] The lithium ion battery is pretreated at 25°C, and after standing for 60 min in a normal temperature environment, the voltage of the lithium ion battery before the drop test is tested; the lithium ion battery is loaded into a clamp, and a drop device 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, the lithium ion battery is left to stand for 24 h at room temperature, 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 are: no smoke, no leakage, and voltage drop <50 mV. 100 lithium ion batteries are tested, and the number of batteries that pass the test is X, and the test pass rate is X / 100.

[0085] (5) Short circuit test:

[0086] At 25°C, after standing for 5 min, the lithium ion battery is charged to 4.50 V at a constant current of 0.2 C, and then charged to 0.025 C at a constant voltage of 4.50 V, and after standing for 60 min, a positive and negative electrode short circuit test is performed using a resistance of 60±20 mΩ in a test environment of 55±2°C. The test ends when one of the following conditions is met: 1) when the sample voltage is lower than 0.1 V, and the surface temperature drops to the test environment temperature±10°C, stop; 2) if the voltage cannot be lowered to 0.1 V, stop when the surface temperature drops to the test environment temperature. The test pass criteria are that the sample does not catch fire, does not explode, and the sample surface temperature does not exceed 150°C. 100 batteries are tested, and the number of batteries that pass the test is X, and the test pass rate is X / 100.

[0087] Table 1 lists the parameters and evaluation results of each example and comparative example.

[0088] Table 1

[0089] As shown in Table 1, compared with Comparative Example 1, the first tab in Example 1 is configured with the first bending section and the second bending section, so that the first tab can extend from the first current collector to the first electrode terminal along the longest path, and the first tab can cover the end surface of the electrode assembly on the side of the top seal portion in the second direction to the maximum extent, which is conducive to reducing the space in which the electrode assembly can move relative to the packaging bag in the first direction during the drop process, and the first tab can buffer the impact of the electrode assembly on the top seal portion during the drop process, thereby improving the drop test pass rate. In Comparative Example 1, the length of the first tab is short, and when dropped, the impact of the electrode assembly on the welding position of the tab and the current collector is more intense, and the drop test pass rate is smaller.

[0090] As shown in Table 1, compared with Example 1, the first tab in Example 2 is provided with the first adhesive, which is bonded with the first tab, thereby reducing the risk of the first tab being broken due to repeated extrusion during the drop; the first adhesive covers the second bending section and the first extension section, thereby reducing the risk of corrosion occurring between the first tab and the metal layer of the packaging bag located at the corner position, and improving the short circuit test pass rate; and the first adhesive covers the first extension section, thereby reducing the risk of short circuit caused by the contact between the first extension section and the edge of the second tab during the drop, and improving the drop test pass rate.

[0091] As shown in Table 1, compared with Example 3, two positive electrode tabs are provided in Example 2, which reduces the impedance of each tab, so that the heat generated by a single tab is less when an external short circuit occurs, thereby reducing the short circuit problem caused by the melting of the separator due to excessive temperature rise, reducing the short circuit risk, and improving the short circuit test pass rate. In Example 3, only one tab (the first tab) is provided, and the heat generated is large, which is prone to cause the short circuit problem caused by the melting of the separator due to excessive temperature rise, and the short circuit test pass rate is lower.

[0092] As shown in Table 1, compared with Example 5, Examples 2, 4, 6-9 satisfy M≥1 / 4N, the gap between the first tab and the second tab is controlled within a suitable range, which is conducive to the discharge of heat at the welding position of the first tab and the first current collector, thereby reducing the risk of local short circuit caused by the melting of the first adhesive or the separator due to excessive heat accumulation, and improving the short circuit test pass rate. Among them, Examples 2, 6-9 satisfy 1 / 3N≤M≤2 / 3N, and the effect of improving the short circuit is better.

[0093] As shown in Table 1, compared with Example 10, Examples 11-14 satisfy 0.8W1≤W2≤W1, the first tab and the second tab have a larger overlap width, and the buffering effect of the first tab and the second tab is better, thereby improving the drop performance. Among them, Examples 12-14 satisfy 0.92≤W2 / W2≤1, and the effect of improving the drop performance is better.

[0094] As shown in Table 1, compared with Examples 15 and 21, Examples 16-20 satisfy 0.05≤L1≤0.4, the spacing between the second bending section and the electrode assembly is controlled in a proper range, and both the external short circuit test pass rate and the drop test pass rate are high. In Example 15, L1 is too small, the gap between the second bending section and the electrode assembly is too small, the space for heat generation is insufficient, heat accumulation easily occurs, the separator at the second bending section is easily melted, and thus short circuit failure occurs; and due to the small gap, the friction between the second bending section and the second tab is large during the drop, local wear easily occurs, and thus contact short circuit failure occurs. In Example 21, L1 is too large, and the volumetric energy density is lost too much. Examples 17-19 satisfy 0.05≤L1≤0.3, and the effects of improving short circuit and drop are better.

[0095] As shown in Table 1, compared with Examples 22 and 28, Examples 23-27 satisfy 0.05≤L2≤0.4, the spacing between the second bending section and the packaging bag is controlled in a proper range, and both the external short circuit test pass rate and the drop test pass rate are high. In Example 22, L2 is too small, the gap between the second bending section and the packaging bag is too small, the space for heat generation is insufficient, heat accumulation easily occurs, the separator at the second bending section is easily melted, and thus short circuit failure occurs; and due to the small gap, the friction between the second bending section and the corner position of the packaging bag is large during the drop, local wear easily occurs, and thus contact short circuit failure occurs; in Example 28, L2 is too large, and the volumetric energy density is lost too much. Examples 24-26 satisfy 0.05≤L2≤0.3, and the effects of improving short circuit and drop are better.

[0096] Those skilled in the art should recognize that the above examples are only used to illustrate the present application, and are not used as a limitation to the present application. Any suitable changes and variations to the above examples within the scope of the present application are within the scope of the present disclosure.

Claims

1. A secondary battery, comprising a packaging bag, an electrode assembly, a first tab, and a first electrode terminal, wherein the packaging bag includes a main body portion for receiving the electrode assembly and a top seal portion connected to the main body portion, the electrode assembly includes a first electrode plate, a second electrode plate, and a separator disposed between the first electrode plate and the second electrode plate, the first electrode plate including a first current collector, and the first electrode terminal extending out of the packaging bag through the top seal portion in a first direction, characterized in that, The first electrode tab includes a third extension section, a first bending section, a second bending section, and a second extension section connected in sequence. The third extension section is welded to the first current collector, and the second extension section is connected to the first electrode terminal. In a second direction perpendicular to the first direction, the first bending section is bent away from the top seal, and the second bending section is bent toward the top seal.

2. The secondary battery as described in claim 1, characterized in that, The secondary battery also includes a second electrode with the same polarity as the first electrode. The second electrode and the first electrode are each independently welded to the first current collector. The second electrode and the first electrode are stacked and then welded to the first electrode terminal.

3. The secondary battery as described in claim 2, characterized in that, In the second direction, the first electrode includes multiple electrode layers, each of which includes a first electrode layer with a first tab and a second electrode layer with a second tab. The number of the multiple electrode layers is N, and the number of electrode layers located between the first electrode layer and the second electrode layer is M, where M ≥ 1 / 4N.

4. The secondary battery as described in claim 3, characterized in that, 1 / 3N≤M≤2 / 3N.

5. The secondary battery as described in claim 3, characterized in that, The electrode assembly has a winding structure, with the first tab disposed on the innermost ring of the first electrode sheet and the second tab disposed on the outermost ring of the first electrode sheet. The first tab and the second tab are located on opposite sides of the winding center axis of the electrode assembly in the second direction.

6. The secondary battery as described in claim 2, characterized in that, The area on the first electrode that overlaps with the second electrode in the second direction is the first region. In a third direction perpendicular to both the first and second directions, the width of the first electrode is W1, and the width of the first region is W2, where 0.8W1≤W2≤W1.

7. The secondary battery as described in claim 6, characterized in that, 0.92W1≤W2≤W1.

8. The secondary battery as described in claim 2, characterized in that, The thickness of the first electrode tab and the thickness of the second electrode tab are both greater than the thickness of the first current collector, and the thickness of the first electrode tab and the thickness of the second electrode tab are both less than the thickness of the first electrode terminal.

9. The secondary battery as described in claim 8, characterized in that, The thickness of the first tab ranges from 20 μm to 50 μm, the thickness of the first current collector ranges from 4 μm to 15 μm, and the thickness of the first electrode terminal ranges from 60 μm to 120 μm.

10. The secondary battery as described in claim 1, characterized in that, The secondary battery also includes a first adhesive member that is bonded to the first tab. The first adhesive member includes a first section that covers the second bent section and is located on the side of the second bent section facing the packaging bag.

11. The secondary battery as described in claim 10, characterized in that, The first adhesive also includes a second section that covers the first extension and is located on the side of the first extension facing the electrode assembly.

12. The secondary battery as described in claim 10, characterized in that, The first adhesive also includes a third section that covers the third extension.

13. The secondary battery as described in claim 10, characterized in that, The first adhesive further includes a substrate and an adhesive layer stacked together. The substrate includes at least one of polyethylene terephthalate, polyimide, and polypropylene, and the adhesive layer includes at least one of rubber, acrylic adhesive, and styrene-isoprene-styrene.

14. The secondary battery as described in claim 1, characterized in that, In the first direction, the minimum distance between the second bent section and the electrode assembly is L1 mm, the minimum distance between the second bent section and the packaging bag is L2 mm, 0.05≤L1≤0.4, and / or 0.05≤L2≤0.

4.

15. The secondary battery as described in claim 1, characterized in that, The first electrode terminal is integrally formed with the first electrode tab.

16. The secondary battery as described in claim 1, characterized in that, Viewed from a third direction perpendicular to both the first and second directions, in the second direction, the third extension is located between the second bent section and the top sealing portion.

17. An electronic device, characterized in that, Includes the secondary battery as described in any one of claims 1-16.

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