Secondary battery and electronic device

Abstract

A secondary battery and an electronic device are disclosed. The secondary battery includes an electrode assembly. The electrode assembly includes a first electrode, a second electrode, and a separator. The separator includes an integrally formed first extension, a bent section, and a second extension, with the bent section located between the first and second extensions. The electrode assembly is columnar and is formed by sequentially stacking the first extension, the first electrode, the second extension, and the second electrode and winding them around a central axis. Along the winding direction of the electrode assembly, the first electrode includes a starting end, and the bent section covers the starting end.

Description

Secondary battery and electronic device TECHNICAL FIELD

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

[0002] Secondary batteries have the advantages of high energy density, long cycle life, low self-discharge rate, environmental protection and no pollution, and have been widely used in the fields of aviation, aerospace, navigation, electric vehicles, mobile electronic products and the like. The secondary battery includes an electrode assembly, and the electrode assembly with a winding structure usually adopts a double-separator design, that is, a separator, a positive electrode sheet, a separator and a negative electrode sheet are stacked and then wound by a winding needle to form a winding structure. During winding, there is a large friction force between the winding needle and the separator. After winding is completed, when the winding needle is extracted, the winding needle may carry out the separator to cause the separator to be folded or misaligned, so that the separator cannot effectively isolate the positive electrode sheet and the negative electrode sheet in the direction of extraction of the winding needle, thereby causing internal short circuit.

[0003] SUMMARY

[0004] An object of the present application is to provide a secondary battery and an electronic device, which can reduce the short circuit risk caused by extraction of the winding needle.

[0005] The first aspect of the present application provides a secondary battery, including an electrode assembly. The electrode assembly includes a first electrode sheet, a second electrode sheet and a separator. The separator includes a first extension section, a bending section and a second extension section arranged integrally, and the bending section is located between the first extension section and the second extension section. The electrode assembly is in a columnar shape and is formed by sequentially stacking the first extension section, the first electrode sheet, the second extension section and the second electrode sheet and winding around a winding center axis. In the winding direction of the electrode assembly, the first electrode sheet includes a starting end, the bending section is a part of the separator that protrudes beyond the starting end in a direction opposite to the winding direction, the first extension section is a part of the separator extending from one end of the bending section in the winding direction, the second extension section is a part of the separator extending from the other end of the bending section in the winding direction, and the bending section covers the starting end.

[0006] In the present application, the first extension section and the second extension section of the diaphragm are integrally arranged around the first tab, and the first extension section and the second extension section have mutual constraint force. When the winding needle is extracted after winding is completed, the constraint force between the second extension section and the first extension section prevents the diaphragm from being easily taken out and causing folding or mispositioning when the winding needle is extracted. Thus, the diaphragm can effectively isolate the first tab and the second tab in the length direction of the electrode assembly (the direction in which the winding needle is extracted), thereby reducing the risk of contact short circuit of the first tab and the second tab. In addition, the diaphragm arranged integrally around the first tab can bind the electrode assembly, thereby reducing the risk of impact loosening of the electrode assembly in the drop test. The integrally arranged first extension section and second extension section can provide better support, thereby reducing the risk of internal short circuit caused by collapse of the electrode assembly in the cycle process and improving the cycle performance.

[0007] In some embodiments, in the direction opposite to the winding direction, the vertex of the bending section is a bending point, and the bending point is separated from the starting end. In this way, a gap is formed between the bending section and the starting end, which provides a buffer space and reduces the risk of short circuit caused by the starting end piercing the bending section due to impact of the first tab, thereby improving the drop performance. In addition, the gap can serve as a heat buffer zone, thereby reducing the risk of high-temperature short circuit caused by local overheating.

[0008] In some embodiments, in the winding direction, the distance between the bending point and the starting end is 3 mm to 6 mm, so as to provide a suitable gap between the bending point and the starting end.

[0009] In some embodiments, the secondary battery further includes a first tab, and the first tab includes a first current collector. The first tab is welded to the first current collector, and the first tab includes a first region and a second region connected to each other. The first region is an area where the first tab overlaps the first current collector.

[0010] In some embodiments, in the length direction of the electrode assembly, the length of the first region is L1, and the length of the first current collector is L2. 0.5≤L1 / L2≤0.85. When L1 / L2 is within the above range, the first tab and the first current collector have a suitable contact area, which can reduce the resistance to improve the charge-discharge cycle efficiency, and facilitate uniform distribution of current on the first tab to reduce the risk of local overheating. In addition, the welding firmness between the first tab and the first current collector can be improved.

[0011] In some embodiments, the secondary battery further includes a first insulating member arranged on the surface of the second region. By arranging the first insulating member, the risk of contact short circuit between the first tab and the second tab can be reduced.

[0012] In some embodiments, the first tab is welded with the first current collector to form a welding spot, and the secondary battery further comprises a second insulating member arranged on the side of the first current collector away from the first tab and covering the welding spot, so as to reduce the risk of the welding spot formed by welding the second tab with the second current collector piercing the separator.

[0013] In some embodiments, the first tab is arranged on the inner side of the first tab of the innermost circle, which helps to shorten the current path of the first tab, reduce the resistance, and thus reduce the internal resistance of the electrode assembly, thereby improving the charging and discharging rate.

[0014] In some embodiments, the secondary battery further comprises a second tab, and the second tab is welded with the second current collector and arranged on the outer side of the second tab of the outermost circle. Arranging the first tab on the inner side of the first tab of the innermost circle and the second tab on the outer side of the second tab of the outermost circle helps to make the current distribution more uniform, reduce the length of the current path, and thus reduce the internal resistance, and helps to disperse heat and reduce local overheating, thereby prolonging the service life.

[0015] In some embodiments, the secondary battery comprises a third insulating member arranged around the electrode assembly and covering part of the second tab, which can improve the structural stability of the electrode assembly, reduce safety problems such as tab breakage and current collector wrinkling caused by dropping and impact during use, prolong the service life, and reduce problems caused by the welding spot formed by welding the second tab with the second current collector.

[0016] In some embodiments, the ratio of the length of the electrode assembly to the diameter of the electrode assembly is 3:1-10:1.

[0017] In some embodiments, the separator comprises a base material and a ceramic coating arranged on the surface of the base material facing the first tab, and the first tab is a positive electrode. The ceramic coating can reduce heat transfer, thereby reducing the risk of the base material shrinking due to heat, and thus reducing the risk of internal short circuit.

[0018] In some embodiments, the first tab is a positive electrode, the first tab comprises a first current collector, and the first current collector is an aluminum foil; the second tab is a negative electrode, the second tab comprises a second current collector, and the second current collector is a copper foil. The starting end of the first tab is located inside the starting end of the second tab, and the starting end of the first tab is beyond the starting end of the second tab in the winding direction; the first extension section and the second extension section are clamped on both sides of the first tab, and the at least partially bent section is arranged inside the starting end of the first tab. In this way, the bent section can be arranged beyond the first tab and the second tab during stacking, and the at least partially bent section can be arranged inside the starting end of the first tab during needle extraction, so that the first tab and the second tab can be isolated to a greater extent to improve safety performance, and the starting end of the first tab can be supported after needle extraction, so that the risk of bending and folding of the starting end can be reduced, and the support for the winding center can be enhanced.

[0019] The second aspect of the present application provides an electronic device comprising any one of the secondary batteries described above. BRIEF DESCRIPTION OF DRAWINGS

[0020] FIG. 1 is a schematic cross-sectional view of a secondary battery in an embodiment.

[0021] FIG. 2 is a schematic view of a first tab after being unfolded in an embodiment.

[0022] FIG. 3 is a schematic cross-sectional view of a separator and a first tab and a second tab in an embodiment.

[0023] FIG. 4 is a schematic view of a module of an electronic device in an embodiment.

[0024] Main element symbol explanation: secondary battery 200, case 210, electrode assembly 100, first pole piece 10, second pole piece 20, separator 30, first extension section 31, bent section 32, second extension section 33, starting end 10A, bending point 32A, first end 31A, second end 33A, first current collector 11, first active layer 12, second current collector 21, second active layer 22, first tab 41, second tab 42, first empty foil section 101, finishing end 20A, second empty foil section 201, first region 411, second region 412, first insulating member 61, second insulating member 62, welding mark 50, base material 301, ceramic coating 302, winding central axis O, third insulating member 71, first end 71A, second end71B fourth insulating member 72

[0025] The following detailed embodiments will further illustrate the present application with reference to the above drawings. DETAILED DESCRIPTION

[0026] The following detailed embodiments are illustrative and not restrictive, and are intended to provide a basic understanding of the application. The various technical features mentioned in the various embodiments can be combined in any manner, as long as there is no structural conflict.

[0027] When a component is considered to be "provided on" another component, it can be directly provided on the other component or a middle component can be present. When a component is considered to be "connected" or "joined" to another component, it can be directly connected to the other component or a middle component can be present.

[0028] Some embodiments of the present application will be described below with reference to the accompanying drawings. The following embodiments and features of the embodiments can be combined with each other as long as there is no structural conflict.

[0029] Referring to FIG. 1, an embodiment of the present application provides a secondary battery 200 including a housing 210 and an electrode assembly 100 and an electrolyte provided in the housing 210.

[0030] The electrode assembly 100 includes a first electrode tab 10, a second electrode tab 20, and a separator 30. The first electrode tab 10 and the second electrode tab 20 have opposite polarities. The separator 30 includes a first extension 31, a bending section 32, and a second extension 33 provided integrally, the bending section 32 being located between and connected to the first extension 31 and the second extension 33. The electrode assembly 100 is formed by sequentially stacking the first extension 31, the first electrode tab 10, the second extension 33, and the second electrode tab 20 and winding around a winding center axis O. The winding direction R of the winding structure can be a clockwise direction or a counterclockwise direction, and FIG. 1 illustrates a case in which the winding direction R is the counterclockwise direction. When viewed in a length direction Y of the electrode assembly 100, the first extension 31 is closer to the winding center axis O than the second extension 33, the first electrode tab 10 is closer to the winding center axis O than the second electrode tab 20, and the first extension 31 is closer to the winding center axis O than the first electrode tab 10. In the present application, the length direction Y is an extension direction of the winding center axis O, which is perpendicular to the winding direction R.

[0031] The electrode assembly 100 is in a columnar shape. For example, the electrode assembly 100 can be in a cylindrical shape, an elliptical cylindrical shape, or the like. FIG. 1 illustrates a case where the electrode assembly 100 is in a cylindrical shape. In some embodiments, the housing 210 is in a cylindrical shape.

[0032] The first tab 10 includes a starting end 10A in the winding direction R. The starting end 10A refers to an end where the winding of the first tab 10 starts. The bent section 32 is a portion of the separator 30 that extends beyond the starting end 10A in a direction opposite to the winding direction R, the first extension section 31 is a portion of the separator 30 that extends from one end of the bent section 32 in the winding direction R, and the second extension section 33 is a portion of the separator 30 that extends from the other end of the bent section 32 in the winding direction R. In the winding direction R, the bent section 32 covers the starting end 10A, so that the separator 30 is disposed around the first tab 10.

[0033] In some embodiments, the first tab 10, the second tab 20, and the separator 30 are wound to form the electrode assembly 100 in a cylindrical shape by using a cylindrical winding needle. The specific steps are as follows: first, the first tab 10 is placed on the separator 30, and then the separator 30 is folded to dispose the separator 30 around the first tab 10, wherein the separator 30 located on opposite sides of the first tab 10 respectively serves as the first extension section 31 and the second extension section 33; then, the first tab 10 and the separator 30 are stacked together with the second tab 20; then, the first tab 10, the second tab 20, and the separator 30 stacked together are wound on the cylindrical winding needle; and finally, the cylindrical winding needle is extracted to obtain the electrode assembly 100 in a cylindrical shape. When the winding needle is extracted, the separator 30 is not easily brought out by the winding needle to cause folding or misplacement due to the mutual restraining force between the first extension section 31 and the second extension section 33, so that the separator 30 can effectively isolate the first tab 10 and the second tab 20 in the length direction Y (the direction in which the winding needle is extracted) of the electrode assembly 100, and the risk of contact short circuit of the first tab 10 and the second tab 20 is reduced. The winding needle leaves a central hole at the center of the electrode assembly 100 after being extracted. In the cycle process, the tabs of the electrode assembly 100 can swell and collapse into the central hole, and the sharp corners generated by the collapse can pierce the separator 30 to cause the first tab 10 and the second tab 20 to contact and short circuit, which deteriorates the cycle performance. The first extension section 31 and the second extension section 33 integrally provided in the present application can provide better support, reduce the risk of internal short circuit of the tabs of the electrode assembly 100 towards the winding center axis O in the cycle process, and improve the cycle performance. In addition, the separator 30 around the first tab 10 and integrally provided can bind the electrode assembly 100, reduce the risk of impact loosening of the electrode assembly 100 in the drop process, and help to improve the drop performance.

[0034] In the direction opposite to the winding direction R, the vertex of the bending segment 32 is a bending point 32A. In some embodiments, in the winding direction R, the bending point 32A is away from the starting end 10A. In this way, a gap is formed between the bending segment 32 and the starting end 10A, which provides a buffer space to reduce the risk of short circuit caused by the starting end 10A piercing the bending segment 32 in the falling process, and improves the falling performance; and when heat is generated inside the electrode assembly 100, the gap can act as a heat buffer zone to reduce the risk of high-temperature short circuit caused by local overheating.

[0035] In the winding direction R, the distance between the starting end 10A and the bending point 32A is W1. In some embodiments, W1 is 3mm-6mm. When W1 is less than 3mm, the gap is too small, increasing the risk of short circuit caused by the first tab 10 piercing the bending segment 32 in the falling process, affecting the falling performance, and easily causing the problem of local overheating. When W1 is greater than 6mm, the bending segment 32 is too long, reducing the overall proportion of active materials in the electrode assembly 100, affecting the energy density; and the overlong bending segment 32 needs to be folded, which may cause internal short circuit or mechanical damage due to improper folding, affecting the falling performance.

[0036] In some embodiments, the first tab 10 is a positive electrode, the second tab 20 is a negative electrode, and the outermost circle of the electrode assembly 100 is the second tab 20. In the winding direction R, the first extension segment 31 and the second extension segment 33 both extend beyond the first tab 10, so that the first extension segment 31 and the second extension segment 33 can effectively isolate the adjacent first tab 10 and the second tab 20 in the winding direction R, reducing the risk of contact short circuit of the first tab 10 and the second tab 20.

[0037] In some embodiments, the first tab 10 is a positive electrode, the first tab 10 comprises a first current collector 11, and the first current collector 11 is an aluminum foil; the second tab 20 is a negative electrode, the second tab 20 comprises a second current collector 21, and the second current collector 21 is a copper foil. The starting end 10A of the first tab 10 is located inside the starting end of the second tab 20, and the starting end 10A of the first tab 10 exceeds the starting end of the second tab 20 in the winding direction R. The first extension section 31 and the second extension section 33 are clamped on both sides of the first tab 10, i.e., the first extension section 31 and the second extension section 33 clamp the first tab 10 and are wound after being laminated with the second tab. At least part of the bent section 32 is arranged inside the starting end 10A of the first tab 10. In this way, it is beneficial to make the bent section 32 exceed the first tab 10 and the second tab 20 during lamination, and it is beneficial to arrange at least part of the bent section 32 inside the starting end 10A of the first tab 10 during needle extraction, which can greatly isolate the first tab 10 and the second tab 20 to improve safety performance, and it is also beneficial to support the inside of the starting end 10A of the first tab 10 after needle extraction, which can reduce the risk of bending, folding, etc. of the starting end 10A, and can also enhance the support for the winding center.

[0038] In some embodiments, the ratio L / D of the length L of the electrode assembly 100 in the length direction Y to the diameter D of the electrode assembly 100 is 3:1-10:1. When L / D is greater than 10:1, the length of the electrode assembly 100 is too long, which is not conducive to heat dissipation; and the length that is too long can cause uneven distribution of internal pressure or electrolyte at the two opposite ends in the length direction Y, thereby affecting the electrochemical performance. When L / D is less than 3:1, the length of the electrode assembly 100 is too short, which limits the loading amount of the active material and reduces the energy density.

[0039] In some embodiments, the diameter D of the electrode assembly 100 is 6-15 mm, and the length L of the electrode assembly 100 is 20-50 mm. When the size of the electrode assembly 100 satisfies the above relationship, the electrode assembly 100 is suitable for application in a needle-type battery.

[0040] Referring to FIG. 1, the first tab 10 comprises a first current collector 11 and a first active layer 12 arranged on the surface of the first current collector 11. The first active layer 12 can be arranged on both surfaces of the first current collector 11, or only on one surface of the first current collector 11, which is not limited in the present application. In the present embodiment, the first tab 10 is a positive electrode. The first current collector 11 comprises at least one of Ni, Ti, Ag, Au, Pt, Fe, AL, and combinations thereof. The first active layer 12 comprises a positive electrode active material, and the positive electrode active material can comprise 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.

[0041] The second tab 20 includes a second current collector 21 and a second active layer 22 disposed on a surface of the second current collector 21. The second active layer 22 can be disposed on both surfaces of the second current collector 21 or only on one surface of the second current collector 21, which is not limited in the present application. In the present embodiment, the second tab 20 is a negative electrode. The second current collector 21 includes at least one of Ni, Ti, Cu, Ag, Au, Pt, Fe, and combinations thereof. The second active layer 22 includes a negative electrode active material, which 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.

[0042] The secondary battery 200 includes a first tab 41 electrically connected to the first current collector 11. In some embodiments, the first current collector 11 includes a first empty foil segment 101, and the starting end 10A is configured as an edge of the first empty foil segment 101. At least one surface of the first empty foil segment 101 of the first current collector 11 is not provided with an active material. The first tab 41 is welded to the first empty foil segment 101.

[0043] In some embodiments, the first tab 41 is disposed on the inner side of the first tab 10 of the innermost circle. In the present application, the first tab of the innermost circle refers to a circle counted from the starting segment of the first tab. Disposing the first tab 41 on the inner side of the first tab 10 of the innermost circle helps to shorten the current path of the first tab 41, reduce the resistance, thereby reducing the internal resistance of the electrode assembly 100, and further improving the charge and discharge rate.

[0044] The secondary battery 200 includes a second tab 42 electrically connected to the second current collector 21. Along the winding direction R, the second tab 20 includes an ending end 20A. The ending end 20A refers to an end of the second tab 20 winding the end. In some embodiments, the second current collector 21 includes a second empty foil segment 201, and the ending end 20A is configured as an edge of the second empty foil segment 201. At least one surface of the second empty foil segment 201 of the second current collector 21 is not provided with an active material. The second tab 42 is welded to the second empty foil segment 201.

[0045] In some embodiments, the second tab 42 is disposed on the outer side of the second tab 20 of the outermost circle. In the present application, the second tab of the outermost circle refers to a circle counted from the ending end of the second tab. Disposing the first tab 41 on the inner side of the first tab 10 of the innermost circle and disposing the second tab 42 on the outer side of the second tab 20 of the outermost circle helps to make the current distribution more uniform, reduce the length of the current path, thereby reducing the internal resistance; and helps to disperse heat, reduce local overheating, and prolong the service life.

[0046] In some embodiments, the shell 210 is made of a conductive material or an insulating material. The conductive material is not limited to one or more of steel alloy, aluminum alloy, iron alloy, copper alloy, and nickel alloy. The insulating material is not limited to one or more of polystyrene, polypropylene, polyethylene, polyester, polyvinyl chloride, polyimide, polycarbonate, polyamide, and ceramic. In some embodiments, the second tab 42 is welded with the shell 210.

[0047] Referring to FIG. 2, the first tab 41 includes a first region 411 and a second region 412. The first region 411 is a region where the first tab 41 overlaps the first current collector 11, and the second region 412 is a region where the first tab 41 does not overlap the first current collector 11. The first region 411 is welded with the first current collector 11 and is located inside the electrode assembly 100, and the second region 412 is located outside the electrode assembly 100. In the length direction Y, the length of the first region 411 is L1, and the length of the first current collector 11 is L2. In some embodiments, 0.5≤L1 / L2≤0.85. When L1 / L2 is within the above range, the length of the first tab 41 overlapping the first current collector 11 is appropriate, so that the first tab 41 has appropriate welding strength with the first current collector 11, which is beneficial to improve the drop performance; and is beneficial to increase the current contact area, reduce the resistance, and improve the cycle efficiency; and is beneficial to uniformly distribute the current on the tab, avoid local overheating, and improve the service life. When L1 / L2 is less than 0.5, the contact area between the first tab 41 and the first current collector 11 is too small, which leads to an increase in resistance; the small contact area also makes the current not uniformly distributed on the first current collector 11, which leads to an excessive local current density and increases the risk of heating; and the small contact area also makes the welding point between the first tab 41 and the first current collector 11 not strong enough, which is easy to break due to vibration or stress during use, affecting the drop performance. When L1 / L2 is greater than 0.85, the first tab 41 occupies too much space in the electrode assembly 100, which increases the overall thickness of the electrode assembly 100, affects the energy density, and the first region 411 welded with the first current collector 11 is too long, which increases the cost of the welding process, and the long first region 411 is more likely to be physically damaged during assembly, increasing the risk of short circuit and affecting the drop performance.

[0048] In some embodiments, the secondary battery 200 includes a first insulating member 61. The first insulating member 61 is disposed at the second region 412 and covers the surface of the second region 412. By configuring the first insulating member 61, the risk of contact short circuit between the first tab 41 and the second tab 42 can be reduced.

[0049] In some embodiments, the first region 411 of the first tab 41 is welded with the first current collector 11 to form a weld 50 between the first region 411 and the first current collector 11. The secondary battery 200 includes a second insulating member 62. The second insulating member 62 is disposed on a surface of the first current collector 11 facing away from the first tab 41 and covers the weld 50 to reduce the risk of the weld burr piercing the separator 30.

[0050] In some embodiments, the secondary battery 200 includes a third insulating member 71. The third insulating member 71 is disposed around the electrode assembly 100, covers a portion of the electrode assembly 100, and covers a portion of the second tab 42. The third insulating member 71 can improve the structural stability of the electrode assembly 100, reduce safety problems such as tab breakage and current collector wrinkling caused by dropping and impact during use, and prolong the service life. The third insulating member 71 covering the second tab 42 can reduce problems caused by the weld burr formed when the second tab 42 is welded to the second current collector 21.

[0051] The third insulating member 71 includes a first end 71A and a second end 71B disposed opposite each other along the winding direction R. The first end 71A and the second end 71B are located on the same side of the electrode assembly 100 in a direction perpendicular to the length direction Y and are located on the opposite side of the second tab 42 in the direction, which facilitates the arrangement of the third insulating member 71 to secure the electrode assembly 100 and cover the second tab 42. In some embodiments, the first end 71A and the second end 71B are apart from each other.

[0052] In some embodiments, the secondary battery 200 includes a fourth insulating member 72. The fourth insulating member 72 is disposed on a surface of the second current collector 21 facing away from the second tab 42 and covers a portion of the second tab 42 to reduce the risk of the weld burr formed when the second tab 42 is welded to the second current collector 21 piercing the separator 30.

[0053] In some embodiments, the insulating material of the first insulating member 61, the second insulating member 62, the third insulating member 71, and the fourth insulating member 72 each includes, but is not limited to, one or more of ethylene, polypropylene, phenol formaldehyde resin, melamine resin, unsaturated polyester resin, epoxy resin, silicone resin, and polyurethane.

[0054] Referring to FIG. 3, in some embodiments, the separator 30 includes a substrate 301 and a ceramic coating 302 disposed on a surface of the substrate 301. When the first tab 10 is a positive electrode, the ceramic coating 302 is disposed on the surface of the substrate 301 facing the first tab 10. When the first tab 10 is a positive electrode, the first tab 10 has a high potential and is prone to heat generation; by disposing the ceramic coating 302 between the substrate 301 and the first tab 10, the ceramic coating 302 can reduce heat transfer, thereby reducing the risk of shrinkage of the substrate 301 due to heat, and further reducing the risk of internal short circuit caused by shrinkage of the separator 30. In other embodiments, the ceramic coating 302 can also be disposed on the surface of the substrate 301 facing the second tab 20.

[0055] In some embodiments, the substrate 301 includes one or more of polyethylene terephthalate, polyethylene, polypropylene, phenol formaldehyde resin, melamine resin, unsaturated polyester resin, epoxy resin, silicone resin, and polyurethane.

[0056] The ceramic coating 302 includes ceramic particles and a binder. In some embodiments, the ceramic particles are selected from one or more of boehmite, alumina, barium sulfate, magnesium oxide, magnesium hydroxide, silicon dioxide, tin dioxide, titanium oxide, calcium oxide, zinc oxide, zirconium oxide, yttrium oxide, nickel oxide, cerium oxide, zirconium titanate, barium titanate, and magnesium fluoride. In some embodiments, the binder is selected from one or more of polyvinylidene fluoride, polyacrylate, polymethyl methacrylate, polyacrylonitrile, polyimide, polyethylene oxide, and polyvinyl alcohol.

[0057] In some embodiments, the thickness of the separator 30 is 7-13 μm, for example, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, or 13 μm. When the thickness of the separator 30 is within the above range, sufficient insulation barrier effect can be provided without affecting the energy density.

[0058] In some embodiments, the thickness of the ceramic coating 302 is 1-3 μm. When the thickness of the ceramic coating 302 is within the above range, better heat insulation effect can be achieved without affecting the energy density.

[0059] Referring to FIG. 4, the electronic device 1 according to an embodiment of the present application includes any one of the secondary batteries 200 described above. The electronic device according to 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 phone, a portable facsimile, a portable copying machine, 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 audio player, 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 home-use large storage battery, a lithium ion capacitor, and the like.

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

[0061] Example 1

[0062] Preparation of the first electrode sheet: A positive electrode active material (lithium cobaltate), a conductive agent (conductive carbon black and carbon nanotube), and a binder (polyvinylidene fluoride) were mixed in a weight ratio of 97.5:1:1.5, and then dissolved in an N-methylpyrrolidone solution to form a positive electrode slurry having a solid content of 75%. An aluminum foil was used as a 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 and cutting were performed to obtain the first electrode sheet.

[0063] Preparation of the second electrode sheet: A negative electrode active material (graphite), a conductive agent (conductive carbon black), a thickening agent (sodium carboxymethyl cellulose), and a binder (styrene butadiene rubber) were mixed in a mass ratio of 97.5:1:0.5:1, and then deionized water was added as a solvent to obtain a negative electrode slurry having a solid content of 50 wt%. A copper foil was used as a 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 and cutting were performed to obtain the second electrode sheet.

[0064] Preparation of the separator: A polyethylene film was used 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 a 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 tab was welded with the first tab sheet, then the first tab sheet was placed on the separator, the separator was folded to wrap the first tab sheet, then the first tab sheet and the separator were stacked with the second tab sheet, and then the electrode assembly was obtained by winding with the winding needle. Finally, the electrode assembly was placed in the shell to obtain the lithium ion battery. The structure of the lithium ion battery was the same as that of FIG. 1. The diameter of the electrode assembly was 6 mm, and the length was 36 mm.

[0067] Examples 2 to 11

[0068] The difference from Example 1 is that at least one of the distance W1 between the bending point and the starting end, the ratio L1 / L2 of the length L1 of the first region of the first tab to the length L2 of the first current collector is different.

[0069] Comparative Example 1

[0070] The difference from Example 1 is that the bending point of the bending section is disconnected to divide the bending section into two separate parts, that is, the separator is divided into two separate parts.

[0071] The test method of each parameter of the present application is described below.

[0072] High-temperature external short-circuit test:

[0073] The lithium ion battery was charged at 1.5C constant current to 4.25V, then charged at 1.2C constant current to 4.5V, then charged at 0.8C constant current to 4.53V, then charged at constant voltage to 0.14C, and then rested for 5 minutes. The lithium ion battery was charged at 0.8C constant current to 4.5V, then charged at constant voltage to 0.05C, and then placed in an environment of 57℃±4℃. After the surface temperature of the battery reached 57℃±4℃, it was placed for 30 minutes. Then, under this environment temperature, the positive and negative electrodes of the battery were connected by wires, and the total external resistance was ensured to be 80mΩ. During the test, the temperature change of the lithium ion battery was monitored, and the test was terminated when one of the following two conditions occurred: (a) the battery temperature dropped by 20% of the maximum temperature; (b) the short-circuit time reached 24 hours. When there is a dispute, (a) and (b) are selected as the more stringent. The standard for the lithium ion battery to pass the external short-circuit test is: no fire, no explosion. The pass rate of the high-temperature external short-circuit test = the number of lithium ion batteries that pass the high-temperature external short-circuit test / m x 100%, m is the number of lithium ion batteries tested in each example or comparative example, and 100 batteries are tested in each example or comparative example.

[0074] Drop test:

[0075] 1) The test temperature was 20±5℃;

[0076] 2) The appearance was checked before and after the test and photographed;

[0077] 3) In a 20±5 test environment, using marble as the drop floor, lithium ion batteries were dropped from a 1.5 m drop height, a total of 10 rounds of tests were conducted, 100 batteries were tested for each example or comparative example;

[0078] 4) Test pass judgment criteria: no fire, no explosion, no smoke, no liquid leakage.

[0079] Table 1 lists the parameters and evaluation results of each example and comparative example.

[0080] Table 1

[0081] As can be seen from Table 1, compared with Comparative Example 1, the configuration of the separator integrally arranged around the first pole piece in Examples 1-11 can improve the high-temperature short-circuit pass rate and the drop pass rate, because the integrally arranged separator is not easy to be brought out by the needle and folded or misaligned when the needle is extracted, so that the separator can effectively isolate the first pole piece and the second pole piece in the length direction of the electrode assembly, reducing the risk of short circuit; and the integrally arranged separator can play a role in restraining the electrode assembly, reducing the risk of impact loosening of the electrode assembly during the drop process, and improving the drop performance.

[0082] As can be seen from Examples 1-6, when the distance W1 between the bending point and the starting end is 3 mm-6 mm, the high-temperature short-circuit pass rate and the drop pass rate are relatively high. In Examples 1-2, when W1 is less than 3 mm, the gap between the bending point and the starting end is too small, and the high-temperature short-circuit pass rate and the drop pass rate are both relatively small. In Example 6, when W1 is greater than 6 mm, the gap between the bending point and the starting end is too large, and the high-temperature short-circuit pass rate and the drop pass rate are both relatively small.

[0083] As can be seen from Examples 7-11, when the ratio L1 / L2 of the length L1 of the first region of the first tab to the length L2 of the first current collector is 0.5-0.85, the high-temperature short-circuit pass rate and the drop pass rate are relatively high. In Example 7, L1 / L2<0.5, the contact area between the first tab and the first current collector is too small, increasing the resistance and heat generation, affecting the high-temperature short-circuit pass rate; and the welding between the first tab and the first current collector is not firm enough, affecting the drop pass rate. In Example 11, L1 / L2>0.85, the length of the first region is too long, which is easy to be physically damaged during the assembly process, increasing the risk of short circuit and affecting the drop performance.

[0084] 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 on the present application, and as long as the above examples are appropriately changed and changed within the spirit and principles of the present application, they fall within the scope of the present application.

Claims

1. A secondary battery comprising an electrode assembly including a first electrode sheet, a second electrode sheet, and a separator, characterized by, The diaphragm comprises a first extension section, a bending section and a second extension section arranged integrally, the bending section being located between the first extension section and the second extension section, the electrode assembly being cylindrical and being formed by the first extension section, the first tab, the second extension section and the second tab being stacked in sequence and wound around a winding center axis; along the winding direction of the electrode assembly, the first tab comprises a starting end, the bending section is a part of the diaphragm beyond the starting end in a direction opposite to the winding direction, the first extension section is a part of the diaphragm extending from one end of the bending section in the winding direction, the second extension section is a part of the diaphragm extending from the other end of the bending section in the winding direction, and the bending section covers the starting end.

2. The secondary battery according to claim 1, wherein Along the direction opposite to the winding direction, the vertex of the bending section is a bending point, and along the winding direction, the bending point is separated from the starting end.

3. The secondary battery according to claim 2, wherein Along the winding direction, the distance between the bending point and the starting end is 3mm-6mm.

4. The secondary battery according to claim 1, wherein The secondary battery further comprises a first tab, the first tab further comprises a first current collector, the first tab is welded to the first current collector, the first tab comprises a first region and a second region connected to each other, and the first region is a region where the first tab overlaps the first current collector.

5. The secondary battery according to claim 4, wherein the positive electrode is a lithium ion secondary electrode. Along the length direction of the electrode assembly, the length of the first region is L1, the length of the first current collector is L2, and 0.5≤L1 / L2≤0.

85.

6. The secondary battery according to claim 4, wherein The secondary battery further comprises a first insulating member, and the first insulating member is arranged on the surface of the second region.

7. The secondary battery according to claim 4, wherein the positive electrode active material layer is formed on the surface of the positive electrode current collector. The first tab is welded to the first current collector to form a welding mark, the secondary battery further comprises a second insulating member, and the second insulating member is arranged on the side of the first current collector away from the first tab and covers the welding mark.

8. The secondary battery according to claim 4, wherein The first tab is arranged on the inner side of the first tab of the innermost circle.

9. The secondary battery according to claim 8, wherein The secondary battery further comprises a second tab, the second tab comprises a second current collector, the second tab is welded to the second current collector and arranged on the outer side of the second tab of the outermost circle.

10. The secondary battery according to claim 9, wherein The secondary battery comprises a third insulating member, the third insulating member is arranged around the electrode assembly and covers part of the second tab.

11. The secondary battery according to claim 1, wherein The ratio of the length of the electrode assembly to the diameter of the electrode assembly is 3:1-10:

1.

12. The secondary battery according to claim 1, wherein The diaphragm comprises a base material and a ceramic coating, the ceramic coating is arranged on the surface of the base material facing the first tab, and the first tab is a positive electrode.

13. The secondary battery according to claim 1, wherein The first tab is a positive electrode, the first tab comprises a first current collector, the first current collector is an aluminum foil, the second tab is a negative electrode, the second tab comprises a second current collector, the second current collector is a copper foil, the starting end of the first tab is located on the inner side of the starting end of the second tab, along the winding direction, the starting end of the first tab is beyond the starting end of the second tab, the first extension section and the second extension section are clamped on both sides of the first tab, and at least part of the bending section is arranged on the inner side of the starting end of the first tab.

14. An electronic device, wherein, A secondary battery including the positive electrode active material as claimed in any one of claims 1 to 13.

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