Electrode assembly, secondary battery, and electronic device

Abstract

The embodiment of the invention relates to the technical field of energy storage, and discloses an electrode assembly, a secondary battery and electronic equipment, the electrode assembly comprises a first bonding piece, and a first pole piece, a first diaphragm and a second pole piece which are stacked and wound, in the winding direction, the first pole piece comprises a first ending section located at the outermost winding ring of the electrode assembly, and the second ending section comprises a second ending section located at the outermost winding ring of the electrode assembly; at least part of the first ending section exceeds the second pole piece; one side of the first bonding piece is bonded with the first ending section, the first diaphragm comprises a second ending section, the second ending section is provided with a first through hole area, the first through hole area is provided with at least one first through hole, the other side of the first bonding piece is bonded with the second ending section, and the first bonding piece covers at least part of the first through hole area; at least part of the first bonding piece penetrates through the first through hole, and the first bonding piece is bonded with the part, exposed out of the first through hole, of the second pole piece. In this way, the risk of lithium precipitation at the tail of the electrode assembly can be reduced.

Description

Technical Field

[0001] The embodiments of the present application relate to the technical field of energy storage, and in particular, to an electrode assembly, a secondary battery, and an electronic device. Background Art

[0002] With the rapid development of modern technology, the demand for high-performance energy storage devices in fields such as portable electronic devices and electric vehicles is increasing day by day. As an efficient and environmentally friendly energy storage device, lithium-ion batteries have been widely used in many fields due to their high energy density, long cycle life, low self-discharge rate, etc. In the continuous development of lithium-ion batteries, how to reduce lithium plating in the battery has become a research hotspot. Summary of the Invention

[0003] The main technical problem to be solved by the embodiments of the present application is to provide an electrode assembly, a secondary battery, and an electronic device, which can reduce the risk of lithium plating in the electrode assembly.

[0004] To solve the above technical problem, one technical solution adopted by the embodiments of the present application is: to provide an electrode assembly, including a first electrode tab, a first separator, and a second electrode tab that are stacked and wound. Along the winding direction, the first electrode tab includes a first end section, at least a part of the first end section extends beyond the second electrode tab, and the first end section is located at the outermost winding of the electrode assembly; the electrode assembly further includes a first bonding member, one side of the first bonding member in the thickness direction of the first bonding member is bonded to the first end section, the first separator includes a second end section, a first through-hole area is provided in the second end section, at least one first through-hole is provided in the first through-hole area, the other side of the first bonding member in the thickness direction of the first bonding member is bonded to the second end section, the first bonding member covers at least a part of the first through-hole area, at least a part of the first bonding member passes through the first through-hole, and the first bonding member is bonded to the part of the second electrode tab exposed in the first through-hole.

[0005] In this embodiment, by providing the first bonding member, one side of the first bonding member is bonded to the first end section, and at least a part of the other side passes through the first through-hole and is bonded to the part of the second electrode tab exposed in the first through-hole, so that the first bonding member can generate a constraint on the first electrode tab located at the outermost winding, thereby reducing the risk of the first electrode tab at the outermost winding warping outwards, thereby reducing the risk of lithium plating at the warping part of the second electrode tab on the first electrode tab, and reducing the risk of the first electrode tab at the outermost winding generating wrinkles, and reducing the risk of increasing the thickness of the electrode assembly due to wrinkles.

[0006] In some embodiments, the second pole piece includes a second current collector and a second active material layer, the second active material layer is arranged on at least one surface of the second current collector, and at the tail part of the second pole piece, part of the second current collector protrudes from the second active material layer along the winding direction to form a protrusion, and the part of the first adhesive member passing through the first through hole is bonded and fixed to the protrusion.

[0007] In this embodiment, by bonding and fixing the first adhesive member to the protruding portion, the risk of the first end of the first pole piece warping outward can be reduced.

[0008] In some embodiments, along the winding direction, the length of the protrusion is L, 0.5mm≤L≤30mm. Preferably, 10mm≤L≤20mm. If the value of L is too small, it is easy to cause a small bonding area between the first bonding member and the protrusion, which is not conducive to the bonding between the first bonding member and the protrusion; if the value of L is too large, the size of the protrusion is too long, and after winding, the protrusion is easy to extend to the above-mentioned first straight section, resulting in an increase in the thickness of the electrode assembly. Therefore, setting 0.5mm≤L is conducive to increasing the bonding area between the first bonding member and the protrusion and improving the stability of the bonding between the first bonding member and the protrusion; setting L≤30mm can reduce the risk of the protrusion extending to the first straight section, which is conducive to reducing the thickness of the electrode assembly and increasing the energy density of the electrode assembly.

[0009] In some embodiments, the electrode assembly includes a first straight section, a first corner section, a second straight section and a second corner section connected in sequence along the winding direction; along the winding direction, the end position of the second active material layer is located in the first straight section, and the end position of the protrusion is located in the first corner section.

[0010] In this embodiment, since the end position of the protrusion is located at the first corner section, the influence of the protrusion on the thickness of the electrode assembly can be reduced, which is beneficial to improving the energy density of the electrode assembly.

[0011] In some embodiments, the number of the first through holes is multiple, and the multiple first through holes are spaced apart in the first through hole region; along the winding direction, the minimum distance between the first through hole region and the second active material layer is L1, where 0 mm ≤ L1 ≤ 3 mm. Preferably, 1 mm ≤ L1 ≤ 2 mm. If the value of L1 is too small, the risk of the second active material layer being exposed to the first through hole increases, and further the risk of short circuit between the second active material layer and the first pole piece increases; if the value of L1 is too large, it is likely to cause too small an area of the protruding portion being exposed to the first through hole, that is, too small a bonding area between the first bonding member and the protruding portion, resulting in unstable bonding. Therefore, setting 0 mm ≤ L1 can reduce the risk of the second active material layer being exposed to the first through hole, and further reduce the risk of short circuit between the second active material layer and the first pole piece; setting L1 ≤ 3 mm is beneficial to increasing the area of the protruding portion exposed to the first through hole, thereby increasing the bonding area between the first bonding member and the protruding portion, and enhancing the bonding stability between the first bonding member and the protruding portion.

[0012] In some embodiments, the number of the first through holes is multiple, and the multiple first through holes are spaced apart in the first through hole region; along the winding direction, at least a part of the first through hole region protrudes from the protruding portion; the electrode assembly further includes a second separator, the first separator and the second separator are respectively located on two sides of the second pole piece in the thickness direction, the first separator is farther from the winding center of the electrode assembly than the second separator, and the second separator includes a third end section; in the first through hole region protruding from the protruding portion, at least a part of the first bonding member passes through the first through hole and bonds to a part of the third end section exposed in the first through hole.

[0013] In this embodiment, by making at least a part of the first bonding member pass through the first through hole and bond to a part of the third end section exposed in the first through hole, the restriction of the first bonding member on the first end can be enhanced, the risk of the first end tilting outwards can be reduced, thereby reducing the risk of lithium deposition at the position of the first end of the electrode assembly, and the risk of the electrode assembly generating wrinkles at the position of the first end and causing an increase in the thickness of the electrode assembly can also be reduced.

[0014] In some embodiments, along the winding direction, the dimension of the first through hole region protruding from the protruding portion is L2, where L2 ≥ 3 mm. If the value of L2 is too small, the area of the third end section exposed in the first through hole region is too small, resulting in too small a bonding area between the first bonding member and the third end section, which is not conducive to the bonding between the first bonding member and the third end section. Therefore, setting L2 ≥ 3 mm is beneficial to increasing the bonding area between the first bonding member and the third end section, enhancing the bonding force between the first bonding member and the third end section, and further enhancing the restraining ability of the first bonding member on the first end, and reducing the risk of the first end tilting outwards.

[0015] In some embodiments, along the width direction of the first separator, the width of the first separator is W1, the width of the first through-hole region is W2, and 0.2 ≤ W2 / W1 ≤ 1. Preferably, 0.4 ≤ W2 / W1 ≤ 0.8. More preferably, 0.5 ≤ W2 / W1 ≤ 0.7. If the ratio between W2 and W1 is too small, the area of the first through-hole region is too small, which is not conducive to the bonding between the first bonding member and the protruding portion and between the first bonding member and the third end segment; if the ratio between W2 and W1 is too large, the distance between the first through-hole region and the edge in the width direction of the first separator is too small, resulting in too low mechanical strength of the second end segment, and the second end segment is prone to breakage, which in turn causes the first separator to contract inward, leading to a short-circuit situation. Therefore, setting 0.2 ≤ W2 / W1 is beneficial to increasing the area of the first through-hole region, thereby increasing the bonding area between the first bonding member and the protruding portion and between the first bonding member and the third end segment, enhancing the bonding force between the first bonding member and the third end segment and between the first bonding member and the protruding portion, and thus reducing the risk of the first end tilting outward; setting W2 / W1 ≤ 1 can reduce the risk of the third end segment breaking, and further reduce the risk of the third end segment contracting inward.

[0016] In some embodiments, along the width direction of the first separator, the minimum distance between the first through-hole region and the edge of the first separator is D1, and 1 mm ≤ D1 ≤ 15 mm. Preferably, 5 mm ≤ D1 ≤ 10 mm. If the value of D1 is too small, the mechanical strength of the second end segment is too low, and the second end segment is prone to breakage, which in turn causes the first separator to contract inward, leading to a short-circuit situation; if the value of D1 is too large, it is likely to cause the size of the first through-hole region in the width direction of the first separator to be too small, and the area of the first through-hole region is too small, which is not conducive to the bonding between the first bonding member and the protruding portion and between the first bonding member and the third end segment. Therefore, setting 1 mm ≤ D1 can reduce the risk of the third end segment breaking, and further reduce the risk of the third end segment contracting inward; setting D1 ≤ 15 mm is beneficial to increasing the size of the first through-hole region in the width direction of the first separator, increasing the area of the first through-hole region, and is beneficial to enhancing the bonding force between the first bonding member and the protruding portion and between the first bonding member and the third end segment, and further reducing the risk of the first end tilting outward.

[0017] In some embodiments, the first bonding member includes a first base layer, a first bonding layer, and a second bonding layer. The first bonding layer and the second bonding layer are respectively disposed on both sides in the thickness direction of the first base layer. The first bonding layer is bonded to the first end segment, the second bonding layer is bonded to the second end segment, and at least part of the second bonding layer passes through the first through-hole and is bonded to the second pole piece.

[0018] In this embodiment, a first adhesive layer and a second adhesive layer are respectively disposed on both sides of the first base layer. The first adhesive layer is bonded to the first end section, and the second adhesive layer is bonded to the second end section, the third end section, and the protruding portion respectively. Thereby, the first adhesive member can generate a pulling force on the first end through the first end section, and this pulling force can prevent the first end from tilting outwards, thereby reducing the risk of lithium deposition at the position of the first end of the electrode assembly.

[0019] In some embodiments, the thickness of the first base layer is A1, where 5 μm ≤ A1 ≤ 20 μm; and / or, the thickness of the first adhesive layer is A2, where 2 μm ≤ A2 ≤ 10 μm. If the value of A1 is too small, the strength of the first base layer is insufficient, and the first adhesive member is prone to breakage; if the value of A1 is too large, the thickness of the first adhesive member is too large, which easily affects the energy density of the electrode assembly. Therefore, setting 5 μm ≤ A1 can improve the strength of the first base layer and reduce the risk of the first adhesive member being pulled and broken; setting A1 ≤ 20 μm can reduce the influence of the thickness of the first adhesive member on the electrode assembly, thereby reducing the influence of the first adhesive member on the energy density of the electrode assembly. If the value of A2 is too small, the bonding ability of the first adhesive layer is insufficient, and it is difficult to limit the tilting of the first end; if the value of A2 is too large, it easily causes an increase in the size of the electrode assembly and a decrease in the energy density of the electrode assembly. Therefore, setting 2 μm ≤ A2 can improve the bonding force between the first adhesive layer and the first end section and reduce the risk of the first end tilting outwards; setting A2 ≤ 10 μm can reduce the influence of the first adhesive layer on the size of the electrode assembly and reduce the influence on the energy density of the electrode assembly.

[0020] In some embodiments, the thickness of the second adhesive layer is A3, and the thickness of the first separator is A4, where 1 ≤ A3 / A4 ≤ 1.2. If the ratio between A3 and A4 is too small, it is difficult for the second adhesive layer to pass through the first through hole and thus difficult to bond to the protruding portion or the third end section; if the ratio between A3 and A4 is too large, it easily makes the thickness of the adhesive member too thick, affecting the energy density of the electrode assembly. Therefore, setting 1 ≤ A3 / A4 can enable the second adhesive layer to pass through the first through hole and bond to the protruding portion or the third end section, so that the first adhesive member can limit the outward tilting of the first end through the first end section; setting A3 / A4 ≤ 1.2 can reduce the influence of the first adhesive member on the size of the electrode assembly, and further reduce the influence of the first adhesive member on the energy density of the electrode assembly.

[0021] In some embodiments, the bonding tensile force between the first bonding layer and the first end segment is F1, and the bonding tensile force between the second bonding layer and the second pole piece is F2; 100 N / m ≤ F1 ≤ 1000 N / m; and / or, 100 N / m ≤ F2 ≤ 1000 N / m. If the value of F1 is too small, the first bonding layer is likely to peel off from the first end segment; if the value of F1 is too large, the first bonding layer is likely to break or tear the first end segment. Therefore, setting 100 N / m ≤ F1 is beneficial to improving the bonding stability between the first bonding layer and the first end segment and reducing the risk of the first end tilting outwards; setting F1 ≤ 1000 N / m can reduce the risk of the first end segment being torn or broken. If the value of F2 is too small, the second bonding layer is likely to peel off from the second pole piece; if the value of F2 is too large, the second bonding layer is likely to break or tear the protruding portion. Therefore, setting 100 N / m ≤ F2 is beneficial to improving the bonding stability between the second bonding layer and the second pole piece and reducing the risk of the first end tilting outwards; setting F2 ≤ 1000 N / m can reduce the risk of the protruding portion being torn or broken.

[0022] In some embodiments, 0.9 ≤ F1 / F2 ≤ 1.1. If the difference between F1 and F2 is too large, it is likely to cause too large a stress difference on both sides of the first bonding member, and then the side with a large bonding tensile force is likely to be torn or even broken. Therefore, setting 0.9 ≤ F1 / F2 ≤ 1.1 can reduce the stress difference on both sides of the first bonding member and reduce the risk of the first end segment or the protruding portion being torn.

[0023] In some embodiments, along the width direction of the first separator, both ends of the first bonding member protrude from the first through-hole region, and the dimension of both ends of the first bonding member protruding from the first through-hole region is L3, 1 mm ≤ L3 ≤ 10 mm; and / or, along the winding direction, both ends of the first bonding member protrude from the first through-hole region, and the dimension of both ends of the first bonding member protruding from the first through-hole region is L4, 1 mm ≤ L4 ≤ 10 mm.

[0024] Setting 1 mm ≤ L3 can reduce the risk that the first through-hole is not covered by the first bonding member, and further reduce the risk of short circuit between the first pole piece and the second pole piece; setting L3 ≤ 10 mm is beneficial to increasing the area of the first through-hole region, thereby increasing the bonding area between the first bonding member and the protruding portion and between the first bonding member and the third end segment, and further reducing the risk of the first end tilting outwards. Setting 1 mm ≤ L4 can reduce the risk that the first through-hole is not covered by the first bonding member, and further reduce the risk of short circuit between the first pole piece and the second pole piece; setting L4 ≤ 10 mm is beneficial to increasing the area of the first through-hole region, thereby increasing the bonding area between the first bonding member and the protruding portion and between the first bonding member and the third end segment, and further reducing the risk of the first end tilting outwards.

[0025] In some embodiments, when observed in the thickness direction of the first separator, the area of a single first through-hole is B1, 2 mm 2 ≤B1≤100 mm 2 . If the value of B1 is too small, it is difficult for the second adhesive layer to pass through the first through-hole, resulting in poor bonding effects between the second adhesive layer and the third end section and between the second adhesive layer and the protrusion. If the value of B1 is too large, it is likely to cause the second end section to have low strength and be easily pulled and broken. Therefore, setting 2 mm 2 ≤B1 can facilitate the second adhesive layer to pass through the first through-hole, which is beneficial to improving the bonding stability between the second adhesive layer and the third end section and between the second adhesive layer and the protrusion, and reducing the risk of the first end tilting outwards. Setting B1≤100 mm 2 , is beneficial to reducing the influence of the first through-hole on the strength of the second end section and reducing the risk of the second end section being pulled and broken.

[0026] In some embodiments, along the winding direction, the minimum distance between two adjacent first through-holes is D2, 1.5 mm ≤ D2 ≤ 75 mm; and / or, along the width direction of the first separator, the minimum distance between two adjacent first through-holes is D3, 1.5 mm ≤ D3 ≤ 75 mm.

[0027] Setting 1.5 mm ≤ D2 can improve the strength of the second end section in the area of the first through-hole and reduce the risk of the first end section being pulled and broken. Setting D2 ≤ 75 mm is beneficial to increasing the sum of the areas of the first through-holes, thereby improving the bonding stability between the second adhesive layer and the third connecting section and between the second adhesive layer and the protrusion, and reducing the risk of the first end tilting outwards. Setting 1.5 mm ≤ D3 can improve the strength of the second end section in the area of the first through-hole and reduce the risk of the first end section being pulled and broken. Setting D3 ≤ 75 mm is beneficial to increasing the sum of the areas of the first through-holes, thereby improving the bonding stability between the second adhesive layer and the third connecting section and between the second adhesive layer and the protrusion, and reducing the risk of the first end tilting outwards.

[0028] In some embodiments, the first pole piece further includes a first section located in the second outermost layer of the winding of the electrode assembly; the electrode assembly further includes a second bonding member, one side of the second bonding member along the thickness direction of the second bonding member is bonded to the first section, and the other side of the second bonding member along the thickness direction of the second bonding member is bonded to the third end section; the third end section is provided with at least one second through-hole, the second bonding member covers at least part of the second through-hole, and at least part of the second bonding member passes through the second through-hole and is bonded and fixed to the second end section.

[0029] In this embodiment, a second adhesive member is provided, at least a portion of the second adhesive member is passed through the second through hole and is bonded and fixed to the second tail section, so that the second adhesive member can apply a tensile force to the second tail section, and the tensile force is transmitted to the first end in sequence through the second tail section, the first adhesive member and the first tail section, thereby increasing the resistance that needs to be overcome when the first end warps outward, and further reducing the risk of the first section warping outward.

[0030] In some embodiments, the number of the second through holes is multiple, and the orthographic projections of the second through holes along the thickness direction of the third end segment and the orthographic projections of the first through holes along the thickness direction of the second end segment at least partially do not overlap. In this way, the sum of the bonding areas between the first bonding member and the third end segment and between the second bonding member and the second end segment can be increased, which is conducive to further increasing the resistance that needs to be overcome when the first end is warped outward, and further reducing the risk of the first segment warping outward.

[0031] In some embodiments, the first pole piece is a positive pole piece, and the second pole piece is a negative pole piece.

[0032] In some embodiments, the second electrode sheet includes a second active material layer, the second active material layer includes a second active material, and the second active material includes silicon.

[0033] In a second aspect, the present application provides a secondary battery comprising the above-mentioned electrode assembly.

[0034] In a third aspect, the present application provides an electronic device, comprising the above-mentioned secondary battery.

[0035] The beneficial effect of the embodiments of the present application is: different from the prior art, in the embodiments of the present application, a first adhesive is provided, one side of the first adhesive is bonded to the first tail section, and at least a portion of the other side passes through the first through hole and is bonded to the portion of the second pole piece exposed to the first through hole, so that the first adhesive can constrain the first pole piece located at the outermost circle of the winding, thereby reducing the risk of the first pole piece of the outermost circle warping outward, thereby reducing the risk of lithium deposition in the second pole piece at the warped position of the first pole piece, and can reduce the risk of wrinkles in the first pole piece of the outermost circle, and reduce the risk of increasing the thickness of the electrode assembly due to wrinkles. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] In order to more clearly illustrate the specific embodiments of the present application or the technical solutions in the prior art, the following is a brief introduction to the drawings required for the specific embodiments or the prior art description. In all the drawings, similar elements or parts are generally identified by similar reference numerals. In the drawings, the elements or parts are not necessarily drawn according to the actual scale.

[0037] Figure 1 It is a structural schematic diagram of an electrode assembly in the prior art;

[0038] Figure 2 It is a schematic structural diagram of the electrode assembly provided in the embodiment of the present application;

[0039] Figure 3 It is a partial structural schematic diagram after the electrode assembly is unfolded in the embodiment of the present application;

[0040] Figure 4 It is a partial structural schematic diagram of the first separator provided in the embodiment of the present application;

[0041] Figure 5 It is a schematic structural diagram of the first bonding member provided in the embodiment of the present application;

[0042] Figure 6 It is a schematic structural diagram of the first separator and the first bonding member provided in the embodiment of the present application.

[0043] Reference numerals in the drawings

[0044] 100. Electrode assembly;

[0045] 1. First pole piece; 11. First end section; 12. First section; 13. First current collector; 14. First active material layer; 15. First end;

[0046] 2. First separator; 21. Second end section; 211. First through-hole area; 212. First through-hole;

[0047] 3. Second pole piece; 31. Second current collector; 311. Protrusion; 32. Second active material layer; 33. End portion;

[0048] 4. First bonding member; 41. First base layer; 42. First bonding layer; 43. Second bonding layer;

[0049] 5. Second separator; 51. Third end section; 511. Second through-hole;

[0050] 6. First straight section; 7. First corner section; 8. Second straight section;

[0051] 9. Second corner section;

[0052] 10. Second bonding member. Detailed implementation manners

[0053] For the convenience of understanding the present application, the present application will be described in more detail below in conjunction with the accompanying drawings and specific embodiments. It should be noted that when an element is expressed as "fixed to" another element, it can be directly on the other element, or there can be one or more intermediate elements therebetween. When an element is expressed as "connected to" another element, it can be directly connected to the other element, or there can be one or more intermediate elements therebetween. The orientation or positional relationship indicated by the terms "upper", "lower", "inner", "outer", "vertical", "horizontal", etc. used in this specification is based on the orientation or positional relationship shown in the accompanying drawings, and is only for the convenience of describing the present application and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation of the present application. In addition, the terms "first", "second", etc. are only used for descriptive purposes and cannot be understood as indicating or implying relative importance.

[0054] Unless otherwise defined, all technical and scientific terms used in this specification have the same meaning as commonly understood by those skilled in the technical field to which this application belongs. The terms used in the specification of this application are only for the purpose of describing specific embodiments and are not used to limit this application. The term "and / or" used in this specification includes any and all combinations of one or more of the related listed items.

[0055] In addition, the technical features involved in different embodiments of the present application described below can be combined with each other as long as they do not conflict with each other.

[0056] With the rapid development of modern technology, the demand for high-performance energy storage devices in fields such as portable electronic devices and electric vehicles is increasing day by day. As an efficient and environmentally friendly energy storage device, lithium-ion batteries have been widely used in many fields due to their advantages such as high energy density, long cycle life, and low self-discharge rate. In the continuous development process of lithium-ion batteries, how to reduce lithium plating in the battery has become a research hotspot.

[0057] Please refer to Figure 1The existing wound electrode assembly 100' comprises a positive electrode sheet 1', a separator 2' and a negative electrode sheet 3', which are stacked and wound in sequence to form the electrode assembly 100'. In the related art, along the winding direction, the electrode sheet located at the outermost circle of the winding is the positive electrode sheet 1', and the positive electrode sheet 1' comprises a tail section 11', and the tail section 11' at least partially protrudes from the tail end 31' of the negative electrode sheet 3', so as to constrain the tail end 31' of the negative electrode sheet 3', and the part of the tail section 11' protruding from the negative electrode sheet 3' is bonded to the positive electrode sheet 1a' located at the second outer circle by an adhesive 4', so as to prevent the electrode assembly 100' from spreading. However, the inventors have found that, with the above-mentioned method, as the number of charge and discharge times of the battery increases, the negative electrode plate 3' expands, causing the outermost positive electrode plate 1' to easily warp outward, resulting in a gap between the positive electrode plate 1' and the negative electrode plate 3' in this part. It is difficult for lithium ions to be evenly embedded in the negative electrode plate 3' during the charge and discharge process, and lithium deposition is likely to occur on the surface of the negative electrode plate 3'.

[0058] In order to at least partially solve the above problems, in the first aspect, the present application provides an electrode assembly, by setting a first adhesive member at the first tail section of the first pole piece, and setting a first through hole at the second tail section of the first diaphragm, the first adhesive member is bonded and fixed to the first diaphragm on the side away from the first tail section, and at least a portion of the first adhesive member passes through the first through hole and is bonded to the portion of the second pole piece exposed to the first through hole, thereby constraining the movement of the outermost first pole piece, which is beneficial to reducing the risk of warping of the first pole piece, thereby reducing the risk of lithium plating in the electrode assembly.

[0059] The specific structure and functions of the present application are described in detail below.

[0060] See also Figure 2 The electrode assembly 100 includes a first electrode sheet 1, a first diaphragm 2 and a second electrode sheet 3, which are stacked in sequence, the first diaphragm 2 is located between the first electrode sheet 1 and the second electrode sheet 3, and the first electrode sheet 1, the first diaphragm 2 and the second electrode sheet 3 are wound, wherein the polarities of the first electrode sheet 1 and the second electrode sheet 3 are opposite.

[0061] For the first pole piece 1 mentioned above, please refer to Figure 2 The first pole piece 1 includes a first current collector 13 and a first active material layer 14 . The first active material layer 14 is arranged on at least one surface of the first current collector 13 along the thickness direction of the first current collector 13 . The above-mentioned first diaphragm 2 is arranged between the first active material layer 14 and the second pole piece 3 .

[0062] For the second pole piece 3 mentioned above, please refer to Figure 2, the second electrode tab 3 includes a second current collector 31 and a second active material layer 32. Along the thickness direction of the second current collector 31, the second active material layer 32 is disposed on at least one surface of the second current collector 31. The above-mentioned first separator 2 is disposed between the first current collector 13 and the second current collector 31.

[0063] In some embodiments, the second active material layer 32 includes a second active material, and the second active material includes silicon element.

[0064] In some embodiments, the outermost electrode tab is the first electrode tab 1.

[0065] In some embodiments, the first electrode tab 1 is a positive electrode tab and the second electrode tab 3 is a negative electrode tab. It can be understood that, in some alternative embodiments, the first electrode tab 1 can also be a negative electrode tab and the second electrode tab 3 is a positive electrode tab.

[0066] In some embodiments, please refer to Figure 2 , along the winding direction X, the first electrode tab 1 includes a first end section 11, and at least part of the first end section 11 extends beyond the end section 33 of the second electrode tab 3. The end section 33 of the second electrode tab 3 is away from the winding center of the second electrode tab 3. Among them, the first end section 11 is located at the outermost winding of the electrode assembly 100.

[0067] In some embodiments, the electrode assembly 100 includes a first bonding member 4. Along the thickness direction of the first bonding member 4, one side of the first bonding member 4 is bonded and fixed to the first end section 11. Among them, the first bonding member 4 is located on the surface of the first end section 11 facing the winding center. The first separator 2 includes a second end section 21. The second end section 21 is provided with a first through-hole area 211. The first through-hole area 211 is provided with at least one first through-hole 212. At least part of the second electrode tab 3 is exposed to the first through-hole 212. The other side of the first bonding member 4 along the thickness direction of the first bonding member 4 is bonded and fixed to the second end section 21. The first bonding member 4 covers at least part of the first through-hole area 211, and the first bonding member 4 covers the first through-hole 212. At least part of the first bonding member 4 passes through the first through-hole 212 and then is bonded to the part of the second electrode tab 3 exposed to the first through-hole 212. In this embodiment, by providing the first bonding member 4, one side of the first bonding member 4 is bonded to the first end section 11, and at least part of the other side passes through the first through-hole 212 and is bonded to the part of the second electrode tab 3 exposed to the first through-hole 212, so that the first bonding member 4 can generate a constraint on the first electrode tab 1 located at the outermost winding, thereby reducing the risk of the first electrode tab 1 at the outermost winding from warping outwards, thereby reducing the risk of lithium plating at the warping part of the second electrode tab 3 at the first electrode tab 1, and reducing the risk of the first electrode tab 1 at the outermost winding from generating wrinkles, and reducing the risk of increasing the thickness of the electrode assembly 100 due to wrinkles.

[0068] Definition: In the first pole piece 1 at the outermost winding circle, along the winding direction X, the end of the first active material layer 14 away from the winding center is the first end 15. It is worth noting that, please refer to Figure 2 and Figure 3 , Figure 3 This is a schematic diagram of the local structure after the electrode assembly is flattened. Figure 3 The two dotted lines in the figure represent the two boundaries of the first through-hole region 211 in the winding direction X. Along the winding direction X, the second active material layer 32 located at the outermost winding circle at least partially exceeds the first active material layer 14 located at the outermost winding circle, and the portion of the second pole piece 3 protruding from the first end 15 of the first active material layer 14 located at the outermost winding circle constitutes the above-mentioned tail portion 33. Along the winding direction X, the portion of the first current collector 13 in the first pole piece 1 that exceeds the first end 15 of the first active material layer 14 located at the outermost winding circle constitutes the above-mentioned first tail section 11, and the first tail section 11 at least partially exceeds the tail portion 33 of the second pole piece 3.

[0069] It is worth noting that the first pole piece 1 is most likely to warp at the position of the first end 15, which makes it difficult for the lithium ions at the first end 15 to be uniformly embedded in the corresponding second active material layer 32, and then lithium deposition is formed at the first active material layer 14. In the embodiment of the present application, one side of the first adhesive 4 is bonded to the first tail section 11, and the first adhesive 4 is in contact with the first end 15, the other side of the first adhesive 4 is connected to the second tail section 21, and at least part of the first adhesive 4 passes through the first through hole 212 and then bonds to the second pole piece 3, which can reduce the risk of the first diaphragm 2 shrinking inwards on the one hand, and on the other hand, the first adhesive 4 can be close to the first end 15, which can better limit the first end 15 from warping outwards, thereby further reducing the risk of lithium deposition in the second pole piece 3 at the position corresponding to the first end 15.

[0070] In some embodiments, see Figure 2 and Figure 3 , along the winding direction X, the first adhesive member 4 at least partially protrudes from the tail portion 33 of the second pole piece 3. In this way, the length of the first adhesive member 4 can be increased, which is beneficial to increase the bonding area between the first adhesive member 4 and the first tail section 11 and between the first adhesive member 4 and the second tail section 21, and improve the bonding stability between the first adhesive member 4 and the first tail section 11 and between the first adhesive member 4 and the second tail section 21.

[0071] In some embodiments, see Figure 3, at the end portion 33 of the second electrode tab 3, along the winding direction X, the second current collector 31 at least partially protrudes from the second active material layer 32 to form a protruding portion 311. The protruding portion 311 is at least partially exposed in the above-mentioned first through-hole region 211, and the protruding portion 311 is at least partially exposed in the above-mentioned first through-hole 212. At least a part of the first bonding member 4 passes through the first through-hole 212 and is bonded to the part of the protruding portion 311 exposed in the first through-hole 212, thereby reducing the risk of the first end 15 of the first electrode tab 1 tilting outwards.

[0072] It should be noted that along the winding direction X, the second active material layer 32 located in the outermost winding circle is offset from the first through-hole 212. That is to say, the first through-hole 212 is arranged to avoid the second active material layer 32. In this way, the risk of the second active material layer 32 contacting the first end section 11 can be reduced, thereby improving the safety performance of the electrode assembly 100.

[0073] In some embodiments, please refer to Figure 4 , the electrode assembly 100 includes a first straight section 6, a first corner section 7, a second straight section 8, and a second corner section 9 that are sequentially connected end to end along the winding direction X. Among them, the first straight section 6 is opposite to the second straight section 8, the first corner section 7 and the second corner section 9 are opposite, and the first straight section 6 and the second straight section 8 are substantially parallel. Along the winding direction X, the end position of the second active material layer 32 is located in the first straight section 6, and the end position of the protruding portion 311 is located in the first corner section 7. That is to say, the protruding portion 311 does not extend to the second straight section 8, which can reduce the influence of the protruding portion 311 on the thickness of the electrode assembly 100 and is beneficial to improving the energy density of the electrode assembly 100. It should be noted that the thickness of the electrode assembly 100 refers to the dimension of the electrode assembly 100 in the arrangement direction of the first straight section 6 and the second straight section 8.

[0074] In some embodiments, please refer to Figure 3 , along the winding direction X, the length of the protruding portion 311 is L, and 0.5 mm ≤ L ≤ 30 mm is satisfied. If the value of L is too small, it is easy to cause a small bonding area between the first bonding member 4 and the protruding portion 311, which is not conducive to the bonding between the first bonding member 4 and the protruding portion 311; if the value of L is too large, the size of the protruding portion 311 is too long, and after winding, the protruding portion 311 is likely to extend to the above-mentioned first straight section 6, resulting in an increase in the thickness of the electrode assembly 100. Therefore, setting 0.5 mm ≤ L is beneficial to increasing the bonding area between the first bonding member 4 and the protruding portion 311 and improving the bonding stability between the first bonding member 4 and the protruding portion 311; setting L ≤ 30 mm can reduce the risk of the protruding portion 311 extending to the first straight section 6, which is beneficial to reducing the thickness of the electrode assembly 100 and increasing the energy density of the electrode assembly 100.

[0075] Further, 10 mm ≤ L ≤ 20 mm. Setting 10 mm ≤ L is beneficial to further increase the bonding area between the first bonding member 4 and the protruding portion 311, and improve the bonding stability between the first bonding member 4 and the protruding portion 311; setting L ≤ 20 mm can further reduce the risk of the protruding portion 311 extending to the first straight section 6, which is beneficial to reducing the thickness of the electrode assembly 100 and increasing the energy density of the electrode assembly 100.

[0076] In some embodiments, referring to the figure, the number of the first through holes 212 is multiple, and the multiple first through holes 212 are spaced apart in the first through hole area 211. Along the winding direction X, the minimum distance between the first through hole area 211 and the second active material layer 32 is L1, and 0 mm ≤ L1 ≤ 3 mm. If the value of L1 is too small, the risk of the second active material layer 32 being exposed to the first through hole 212 increases, and further the risk of the second active material layer 32 coming into contact short circuit with the first pole piece 1 increases; if the value of L1 is too large, it is easy to cause the area of the protruding portion 311 exposed to the first through hole 212 to be too small, that is, the bonding area between the first bonding member 4 and the protruding portion 311 is too small, and the bonding is unstable. Therefore, setting 0 mm ≤ L1 can reduce the risk of the second active material layer 32 being exposed to the first through hole 212, and further reduce the risk of the second active material layer 32 short circuiting with the first pole piece 1; setting L1 ≤ 3 mm is beneficial to increasing the area of the protruding portion 311 exposed to the first through hole 212, thereby increasing the bonding area between the first bonding member 4 and the protruding portion 311, and improving the bonding stability between the first bonding member 4 and the protruding portion 311.

[0077] Further, 1 mm ≤ L1 ≤ 2 mm. Setting 1 mm ≤ L1 can further reduce the risk of the second active material layer 32 being exposed to the first through hole 212, thereby further reducing the risk of the second active material layer 32 short circuiting with the first pole piece 1; setting L1 ≤ 2 mm is beneficial to further increasing the area of the protruding portion 311 exposed to the first through hole 212, thereby further increasing the bonding area between the first bonding member 4 and the protruding portion 311, and further improving the bonding stability between the first bonding member 4 and the protruding portion 311.

[0078] It should be noted that the minimum distance between the first through hole area 211 and the second active material layer 32 is: along the winding direction X, for a first through hole 212 closest to the second active material layer 32 in the first through hole area 211, the distance between the end of this first through hole 212 close to the second active material layer 32 and the end of the second active material layer 32 away from the winding center.

[0079] In some embodiments, please refer to Figure 2 and Figure 3, the electrode assembly 100 further includes a second separator 5. Along the thickness direction of the second electrode tab 3, the first separator 2 and the second separator 5 are respectively located on both sides of the second electrode tab 3, and the first separator 2 is farther from the winding center of the electrode assembly 100 than the second separator 5. Along the winding direction X, at least a part of the first through-hole region 211 protrudes from the protruding portion 311, that is, along the winding direction X, a part of the first through-holes 212 is located within the protruding portion 311, and another part of the first through-holes 212 is located outside the protruding portion 311. The second separator 5 includes a third end section 51 away from the winding center. The first bonding member 4 covers the first through-hole region 211, and at least a part of the first bonding member 4 passes through a part of the first through-holes 212 protruding from the protruding portion 311 and then bonds to the third end section 51, so as to improve the restriction of the first bonding member 4 on the first end 15, reduce the risk of the first end 15 tilting outwards, thereby reducing the risk of lithium deposition at the position of the first end 15 of the electrode assembly 100, and reducing the risk that the electrode assembly 100 generates wrinkles at the position of the first end 15, resulting in an increase in the thickness of the electrode assembly 100.

[0080] In some embodiments, along the winding direction X, the dimension of the first through-hole region 211 protruding from the protruding portion 311 is L2, and L2 ≥ 3 mm. If the value of L2 is too small, the area of the third end section 51 exposed to the first through-hole region 211 is too small, resulting in too small a bonding area between the first bonding member 4 and the third end section 51, which is not conducive to the bonding between the first bonding member 4 and the third end section 51. Therefore, setting L2 ≥ 3 mm is beneficial to increasing the bonding area between the first bonding member 4 and the third end section 51, enhancing the bonding force between the first bonding member 4 and the third end section 51, and further enhancing the restraining ability of the first bonding member 4 on the first end 15, reducing the risk of the first end 15 tilting outwards.

[0081] Furthermore, 5 mm ≤ L2 ≤ 10 mm. If the value of L2 is too large, the risk of the first through-hole region 211 exceeding the first bonding member 4 along the winding direction X increases, resulting in a risk that a part of the first through-hole region 211 is not covered by the first bonding member 4, thereby increasing the risk of contact short circuit between the first end section 11 and the second electrode tab 3. Therefore, setting 5 mm ≤ L2 can further increase the bonding area between the first bonding member 4 and the third end section 51, increase the bonding force between the first bonding member 4 and the third end section 51, thereby further reducing the risk of the first end 15 tilting outwards; setting L2 ≤ 10 mm can reduce the risk of the first through-hole region exceeding the first bonding member 4 along the winding direction X, and further reduce the risk of contact short circuit between the first end section 11 and the second electrode tab 3 after passing through a part of the first through-holes 212 not covered by the first bonding member 4, which is beneficial to improving the safety performance of the electrode assembly 100.

[0082] In some embodiments, please refer to Figure 3 andFigure 4 Along the width direction of the first diaphragm 2, the width of the first diaphragm 2 is W1, the width of the first through-hole region 211 is W2, and 0.2 ≤ W2 / W1 ≤ 1. If the ratio between W2 and W1 is too small, the area of the first through-hole region 211 is too small, which is not conducive to the bonding between the first bonding member 4 and the protrusion 311 and between the first bonding member 4 and the third end section 51. If the ratio between W2 and W1 is too large, the distance between the first through-hole region 211 and the edge of the first diaphragm 2 in the width direction is too small, resulting in too low mechanical strength of the second end section 21, and the second end section 21 is prone to breakage, which further causes the first diaphragm 2 to contract inward, leading to a short-circuit situation. Therefore, setting 0.2 ≤ W2 / W1 is beneficial to increasing the area of the first through-hole region 211, thereby increasing the bonding area between the first bonding member 4 and the protrusion 311 and between the first bonding member 4 and the third end section 51, enhancing the bonding force between the first bonding member 4 and the third end section 51 and between the first bonding member 4 and the protrusion 311, and thus reducing the risk of the first end 15 tilting outward. Setting W2 / W1 ≤ 1 can reduce the risk of the third end section 51 breaking, and further reduce the risk of the third end section 51 contracting inward.

[0083] Furthermore, 0.4 ≤ W2 / W1 ≤ 0.8. Setting 0.4 ≤ W2 / W1 can further increase the bonding area between the first bonding member 4 and the protrusion 311 and between the first bonding member 4 and the third end section 51, further enhance the bonding force between the first bonding member 4 and the third end section 51 and between the first bonding member 4 and the protrusion 311, and thus further reduce the risk of the first end 15 tilting outward. Setting W2 / W1 ≤ 0.8 can further reduce the risk of the third end section 51 breaking, and further reduce the risk of the third end section 51 contracting inward.

[0084] Furthermore, 0.5 ≤ W2 / W1 ≤ 0.7. Setting 0.5 ≤ W2 / W1 can further increase the bonding area between the first bonding member 4 and the protrusion 311 and between the first bonding member 4 and the third end section 51, further enhance the bonding force between the first bonding member 4 and the third end section 51 and between the first bonding member 4 and the protrusion 311, and thus further reduce the risk of the first end 15 tilting outward. Setting W2 / W1 ≤ 0.7 can further reduce the risk of the third end section 51 breaking, and further reduce the risk of the third end section 51 contracting inward.

[0085] In some embodiments, please refer to Figure 3 and Figure 4, along the width direction of the first diaphragm 2, the minimum distance between the first through-hole region 211 and the edge of the first diaphragm 2 is D1, where 1 mm ≤ D1 ≤ 15 mm. If the value of D1 is too small, the mechanical strength of the second end section 21 is too low, and the second end section 21 is prone to breakage, which may further cause the first diaphragm 2 to contract inward, resulting in a short circuit. If the value of D1 is too large, it is likely to cause the size of the first through-hole region 211 in the width direction of the first diaphragm 2 to be too small, and the area of the first through-hole region 211 is too small, which is not conducive to the bonding between the first bonding member 4 and the protrusion 311 and between the first bonding member 4 and the third end section 51. Therefore, setting 1 mm ≤ D1 can reduce the risk of the third end section 51 breaking, and further reduce the risk of the third end section 51 contracting inward. Setting D1 ≤ 15 mm is beneficial to increasing the size of the first through-hole region 211 in the width direction of the first diaphragm 2, increasing the area of the first through-hole region 211, which is beneficial to enhancing the bonding force between the first bonding member 4 and the protrusion 311 and between the first bonding member 4 and the third end section 51, and further reducing the risk of the first end 15 tilting outward.

[0086] Furthermore, 5 mm ≤ D1 ≤ 10 mm. Setting 5 mm ≤ D1 can further reduce the risk of the third end section 51 breaking, and further reduce the risk of the third end section 51 contracting inward. Setting D1 ≤ 10 mm is beneficial to further increasing the size of the first through-hole region 211 in the width direction of the first diaphragm 2, increasing the area of the first through-hole region 211, which is beneficial to enhancing the bonding force between the first bonding member 4 and the protrusion 311 and between the first bonding member 4 and the third end section 51, and further reducing the risk of the first end 15 tilting outward.

[0087] In some embodiments, please refer to Figure 2 、 Figure 3 and Figure 5, the first bonding member 4 includes a first base layer 41, a first bonding layer 42, and a second bonding layer 43. The first bonding layer 42 and the second bonding layer 43 are respectively disposed on both sides of the first base layer 41 in the thickness direction. The first bonding layer 42 is bonded to the first end section 11, and the second bonding layer 43 is bonded to the second end section 21. At least a part of the second bonding layer 43 passes through a part of the first through hole 212 and is bonded to the protruding portion 311 of the second pole piece 3. At least a part of the second bonding layer 43 passes through another part of the first through hole 212 and is bonded to the third end section 51. In this embodiment, by respectively disposing the first bonding layer 42 and the second bonding layer 43 on both sides of the first base layer 41, the first bonding layer 42 is bonded to the first end section 11, and the second bonding layer 43 is bonded to the second end section 21, the third end section 51, and the protruding portion 311 respectively, so that the first bonding member 4 can generate a pulling force on the first end 15 through the first end section 11, and this pulling force can prevent the first end 15 from tilting outwards, thereby reducing the risk of lithium plating at the position of the first end 15 of the electrode assembly 100.

[0088] In some embodiments, referring to Figure 3 and Figure 5 , the thickness of the first base layer 41 is A1, and 5μm ≤ A1 ≤ 20μm. If the value of A1 is too small, the strength of the first base layer 41 is insufficient, and the first bonding member 4 is prone to breakage; if the value of A1 is too large, the thickness of the first bonding member 4 is too large, which is likely to affect the energy density of the electrode assembly 100. Therefore, setting 5μm ≤ A1 can improve the strength of the first base layer 41 and reduce the risk of the first bonding member 4 being pulled and broken; setting A1 ≤ 20μm can reduce the influence of the thickness of the first bonding member 4 on the electrode assembly 100, thereby reducing the influence of the first bonding member 4 on the energy density of the electrode assembly 100.

[0089] Furthermore, 10μm ≤ A1 ≤ 15μm. Setting 10μm ≤ A1 can further improve the strength of the first base layer 41 and further reduce the risk of the first bonding member 4 being pulled and broken; setting A1 ≤ 15μm can further reduce the influence of the thickness of the first bonding member 4 on the electrode assembly 100, thereby further reducing the influence of the first bonding member 4 on the energy density of the electrode assembly 100.

[0090] In some embodiments, the thickness of the first adhesive layer 42 is A2, 2μm≤A2≤10μm. If the value of A2 is too small, the bonding ability of the first adhesive layer 42 is insufficient, and it is difficult to limit the warping of the first end 15; if the value of A2 is too large, it is easy to increase the size of the electrode assembly 100 and reduce the energy density of the electrode assembly 100. Therefore, setting 2μm≤A2 can improve the bonding force between the first adhesive layer 42 and the first tail section 11 and reduce the risk of the first end 15 warping outward; setting A2≤10μm can reduce the impact of the first adhesive layer 42 on the size of the electrode assembly 100 and reduce the impact on the energy density of the electrode assembly 100.

[0091] Furthermore, 5μm≤A2≤8μm. Setting 5μm≤A2 can further enhance the bonding force between the first bonding layer 42 and the first finishing section 11, further reducing the risk of the first end 15 warping outward; setting A2≤8μm can further reduce the effect of the first bonding layer 42 on the size of the electrode assembly 100, and further reduce the effect on the energy density of the electrode assembly 100.

[0092] In some embodiments, the first adhesive layer 42 and the second adhesive layer 43 are made of the same material.

[0093] In some embodiments, the thickness of the second adhesive layer 43 is A3, the thickness of the first diaphragm 2 is A4, and 1≤A3 / A4≤1.2. If the ratio between A3 and A4 is too small, it is difficult for the second adhesive layer 43 to pass through the first through hole 212, and then it is difficult to bond with the protrusion 311 or the third tail section 51; if the ratio between A3 and A4 is too large, it is easy to make the thickness of the adhesive too thick, affecting the energy density of the electrode assembly 100. Therefore, setting 1≤A3 / A4 can enable the second adhesive layer 43 to pass through the first through hole 212 and bond with the protrusion 311 or the third tail section 51, so that the first adhesive 4 can limit the first end 15 from tilting outward through the first tail section 11; setting A3 / A4≤1.2 can reduce the influence of the first adhesive 4 on the size of the electrode assembly 100, and thus reduce the influence of the first adhesive 4 on the energy density of the electrode assembly 100.

[0094] Furthermore, 1.1≤A3 / A4≤1.15. Setting 1.1≤A3 / A4 can improve the stability of the bonding between the second bonding layer 43 and the third end section 51 and between the second bonding layer 43 and the protrusion 311, thereby reducing the risk of the first end 15 warping outward; setting A3 / A4≤1.15 can further reduce the influence of the first bonding member 4 on the size of the electrode assembly 100, thereby reducing the influence of the first bonding member 4 on the energy density of the electrode assembly 100.

[0095] In some embodiments, the bonding tensile force between the first bonding layer 42 and the first end segment 11 is F1, and 100 N / m ≤ F1 ≤ 1000 N / m. If the value of F1 is too small, the first bonding layer 42 is likely to peel off from the first end segment 11; if the value of F1 is too large, the first bonding layer 42 is likely to break or tear the first end segment 11. Therefore, setting 100 N / m ≤ F1 is conducive to improving the bonding stability between the first bonding layer 42 and the first end segment 11 and reducing the risk of the first end 15 tilting outwards; setting F1 ≤ 1000 N / m can reduce the risk of the first end segment 11 being torn or broken.

[0096] Further, 400 N / m ≤ F1 ≤ 600 N / m. Setting 400 N / m ≤ F1 is conducive to further improving the bonding stability between the first bonding layer 42 and the first end segment 11 and further reducing the risk of the first end 15 tilting outwards; setting F1 ≤ 600 N / m can further reduce the risk of the first end segment 11 being torn or broken.

[0097] In some embodiments, the bonding tensile force between the second bonding layer 43 and the second pole piece 3 is F2, and 100 N / m ≤ F2 ≤ 1000 N / m. If the value of F2 is too small, the second bonding layer 43 is likely to peel off from the second pole piece 3; if the value of F2 is too large, the second bonding layer 43 is likely to break or tear the protrusion 311. Therefore, setting 100 N / m ≤ F2 is conducive to improving the bonding stability between the second bonding layer 43 and the second pole piece 3 and reducing the risk of the first end 15 tilting outwards; setting F2 ≤ 1000 N / m can reduce the risk of the protrusion 311 being torn or broken.

[0098] Further, 400 N / m ≤ F2 ≤ 600 N / m. Setting 400 N / m ≤ F2 is conducive to further improving the bonding stability between the second bonding layer 43 and the second pole piece 3 and further reducing the risk of the first end 15 tilting outwards; setting F2 ≤ 600 N / m can further reduce the risk of the protrusion 311 being torn or broken.

[0099] In some embodiments, the bonding tensile force F1 between the first bonding layer 42 and the first end segment 11 and the bonding tensile force F2 between the second bonding layer 43 and the second pole piece 3 satisfy: 0.9 ≤ F1 / F2 ≤ 1.1. If the difference between F1 and F2 is too large, it is likely to cause too large a stress difference on both sides of the first bonding member 4, and then the side with a large bonding tensile force is likely to be torn or even broken. Therefore, setting 0.9 ≤ F1 / F2 ≤ 1.1 can reduce the stress difference on both sides of the first bonding member 4 and reduce the risk of the first end segment 11 or the protrusion 311 being torn.

[0100] Furthermore, 0.95≤F1 / F2≤1.05. Setting 0.95≤F1 / F2≤1.05 can further reduce the stress difference between the two sides of the first bonding member 4 and further reduce the risk of the first tail section 11 or the protruding portion 311 being torn.

[0101] In some embodiments, see Figure 2 , Figure 3 and Figure 6 , Figure 6 The smaller dotted box represents the edge of the first through hole area, and the larger dotted box represents the edge of the first adhesive. Along the width direction of the first diaphragm 2, both ends of the first adhesive 4 protrude from the first through hole area 211, and the dimensions of both ends of the first adhesive 4 protruding from the first through hole area 211 are both L3, and 1mm≤L3≤10mm. If the value of L3 is too small, it is easy for part of the first through hole 212 to be not covered by the first adhesive 4, which may easily lead to a short circuit between the first pole piece 1 and the second pole piece 3; if the value of L3 is too large, the area of ​​the first through hole area 211 is too small, that is, the number of first through holes 212 set in the first through hole area 211 is small, which may easily lead to a small bonding area between the first adhesive 4 and the protrusion 311 and between the first adhesive 4 and the third tail section 51, resulting in the first adhesive 4 not being effective in limiting the tilting of the first end 15. Therefore, setting 1mm≤L3 can reduce the risk of the first through hole 212 not being covered by the first adhesive 4, thereby reducing the risk of a short circuit between the first pole piece 1 and the second pole piece 3; setting L3≤10mm is beneficial to increasing the area of ​​the first through hole region 211, thereby increasing the bonding area between the first adhesive 4 and the protrusion and between the first adhesive 4 and the third tail section 51, thereby reducing the risk of the first end 15 warping outward.

[0102] Furthermore, 4mm≤L3≤6mm. Setting 4mm≤L3 can further reduce the risk that the first through hole 212 is not covered by the first adhesive member 4, and further reduce the risk of short circuit between the first pole piece 1 and the second pole piece 3; setting L3≤6mm is conducive to further increasing the area of ​​the first through hole region 211, thereby further increasing the bonding area between the first adhesive member 4 and the protrusion and between the first adhesive member 4 and the third tail section 51, and further reducing the risk of the first end 15 warping outward.

[0103] In some embodiments, along the winding direction X, both ends of the first adhesive member 4 protrude from the first through-hole region 211, and the dimension of the two ends of the first adhesive member 4 protruding from the first through-hole region 211 is L4, 1mm≤L4≤10mm. If the value of L4 is too small, it is easy for part of the first through-hole 212 to be not covered by the first adhesive member 4, which may easily lead to a short circuit between the first pole piece 1 and the second pole piece 3; if the value of L3 is too large, the area of ​​the first through-hole region 211 is too small, that is, the number of the first through-holes 212 provided in the first through-hole region 211 is small, which may easily lead to a small bonding area between the first adhesive member 4 and the protruding portion 311 and between the first adhesive member 4 and the third tail section 51, resulting in a poor effect of the first adhesive member 4 in limiting the warping of the first end 15. Therefore, setting 1mm≤L4 can reduce the risk of the first through hole 212 not being covered by the first adhesive 4, thereby reducing the risk of a short circuit between the first pole piece 1 and the second pole piece 3; setting L4≤10mm is beneficial to increasing the area of ​​the first through hole region 211, thereby increasing the bonding area between the first adhesive 4 and the protrusion and between the first adhesive 4 and the third finishing section 51, thereby reducing the risk of the first end 15 warping outward.

[0104] Furthermore, 4mm≤L4≤6mm. Setting 4mm≤L4 can further reduce the risk that the first through hole 212 is not covered by the first adhesive member 4, and further reduce the risk of short circuit between the first pole piece 1 and the second pole piece 3; setting L4≤6mm is conducive to further increasing the area of ​​the first through hole region 211, thereby further increasing the bonding area between the first adhesive member 4 and the protrusion and between the first adhesive member 4 and the third tail section 51, and further reducing the risk of the first end 15 warping outward.

[0105] In some embodiments, please refer to the figure. Observed along the thickness direction of the first diaphragm 2, the area of ​​a single first through hole 212 is B1, and 2mm2≤B1≤100mm2. If the value of B1 is too small, it is difficult for the second adhesive layer 43 to pass through the first through hole 212, resulting in poor bonding between the second adhesive layer 43 and the third end section 51 and between the second adhesive layer 43 and the protrusion 311; if the value of B1 is too large, it is easy to cause the strength of the second end section 21 to be low, and the second end section 21 is easy to be pulled and broken. Therefore, setting 2mm2≤B1 can facilitate the second adhesive layer 43 to pass through the first through hole 212, which is conducive to improving the stability of the bonding between the second adhesive layer 43 and the third end section 51 and between the second adhesive layer 43 and the protrusion 311, and reducing the risk of the first end 15 warping outward; setting B1≤100mm2 is conducive to reducing the influence of the first through hole 212 on the strength of the second end section 21, and reducing the risk of the second end section 21 being pulled and broken.

[0106] In some embodiments, see Figure 2, Figure 3 and Figure 4 , along the winding direction X, the minimum distance D2 between two adjacent first through-holes 212 is 1.5 mm ≤ D2 ≤ 75 mm. If the value of D2 is too small, it is likely to cause insufficient strength of the second end section 21 in the first through-hole area 211, and the first end section 11 is likely to be pulled and broken; if the value of D2 is too large, the sum of the areas of the first through-holes 212 is too small, affecting the bonding effect between the second bonding layer 43 and the third connection section and between the second bonding layer 43 and the protrusion 311. Therefore, setting 1.5 mm ≤ D2 can improve the strength of the second end section 21 in the first through-hole area 211 and reduce the risk of the first end section 11 being pulled and broken; setting D2 ≤ 75 mm is beneficial to increasing the sum of the areas of the first through-holes 212, thereby improving the bonding stability between the second bonding layer 43 and the third connection section and between the second bonding layer 43 and the protrusion 311, and reducing the risk of the first end 15 tilting outwards.

[0107] Furthermore, 20 mm ≤ D2 ≤ 40 mm. Setting 20 mm ≤ D2 can further improve the strength of the second end section 21 in the first through-hole area 211 and further reduce the risk of the first end section 11 being pulled and broken; setting D2 ≤ 40 mm is beneficial to further increasing the sum of the areas of the first through-holes 212, thereby further improving the bonding stability between the second bonding layer 43 and the third connection section and between the second bonding layer 43 and the protrusion 311, and reducing the risk of the first end 15 tilting outwards.

[0108] In some embodiments, referring to the figure, in the width direction of the first diaphragm 2, the minimum distance D3 between two adjacent first through-holes 212 is 1.5 mm ≤ D3 ≤ 75 mm. If the value of D2 is too small, it is likely to cause insufficient strength of the second end section 21 in the first through-hole area 211, and the first end section 11 is likely to be pulled and broken; if the value of D3 is too large, the sum of the areas of the first through-holes 212 is too small, affecting the bonding effect between the second bonding layer 43 and the third connection section and between the second bonding layer 43 and the protrusion 311. Therefore, setting 1.5 mm ≤ D3 can improve the strength of the second end section 21 in the first through-hole area 211 and reduce the risk of the first end section 11 being pulled and broken; setting D3 ≤ 75 mm is beneficial to increasing the sum of the areas of the first through-holes 212, thereby improving the bonding stability between the second bonding layer 43 and the third connection section and between the second bonding layer 43 and the protrusion 311, and reducing the risk of the first end 15 tilting outwards.

[0109] Further, 20 mm ≤ D3 ≤ 40 mm. Setting 20 mm ≤ D3 can further enhance the strength of the second finishing section 21 in the first through-hole region 211 and further reduce the risk of the first finishing section 11 being pulled and broken; setting D3 ≤ 40 mm is conducive to further increasing the sum of the areas of the first through-holes 212, thereby further enhancing the bonding stability between the second bonding layer 43 and the third connecting section and between the second bonding layer 43 and the protrusion 311, and reducing the risk of the first end 15 tilting outwards.

[0110] In some embodiments, referring to Figure 2 and Figure 3 , the first pole piece 1 further includes a first section 12, and the first section 12 is located in the second outermost layer of the winding of the electrode assembly 100. The electrode assembly 100 further includes a second bonding member 10. Along the thickness direction of the second bonding member 10, one side of the second bonding member 10 is bonded to the first section 12, and the other side of the second bonding member 10 is bonded to the third finishing section 51. The second bonding member 10 can be used to bond and fix the third finishing section 51 to the first section 12, thereby reducing the risk of the third finishing section 51 contracting inwards. The third finishing section 51 is provided with at least one second through-hole 511, the second bonding member 10 covers at least part of the second through-hole 511, and at least part of the second bonding member 10 passes through the second through-hole 511 and is bonded to the part of the second finishing section 21 exposed in the second through-hole 511, so that the second bonding member 10 can apply a pulling force to the second finishing section 21, and this pulling force is transmitted to the first end 15 through the second finishing section 21, the first bonding member 4, and the first finishing section 11 in sequence, thereby increasing the resistance that needs to be overcome when the first end 15 tilts outwards and further reducing the risk of the first section 12 tilting outwards.

[0111] In some embodiments, the number of the second through-holes 511 is multiple, the second bonding member 10 covers all the second through-holes 511, and part of the second bonding member 10 passes through each second through-hole 511 and is bonded to the second finishing section 21, thereby increasing the bonding force between the second finishing section 21 and the second bonding member 10.

[0112] In some embodiments, referring to Figure 2 and Figure 3 , the orthographic projections of the second through-holes 511 along the thickness direction of the third finishing section 51 and the orthographic projections of the first through-holes 212 along the thickness direction of the second finishing section 21 at least partially do not overlap. With such a setting, the sum of the bonding areas between the first bonding member 4 and the third finishing section 51 and between the second bonding member 10 and the second finishing section 21 can be increased, which is conducive to further increasing the resistance that needs to be overcome when the first end 15 tilts outwards and further reducing the risk of the first section 12 tilting outwards.

[0113] In an embodiment of the present application, by providing a first bonding member 4, one side of the first bonding member 4 is bonded to the first end section 11, and at least a part of the other side passes through the first through hole 212 and is bonded to the part of the second electrode tab 3 exposed in the first through hole 212, so that the first bonding member 4 can exert a constraint on the first electrode tab 1 located in the outermost winding layer, thereby reducing the risk of the first electrode tab 1 at the outermost winding layer warping outwards, reducing the risk of lithium deposition at the warping part of the first electrode tab 1 on the second electrode tab 3, and reducing the risk of the first electrode tab 1 in the outermost winding layer generating wrinkles, and reducing the risk of increasing the thickness of the electrode assembly 100 due to wrinkles.

[0114] In a second aspect, the present application provides an embodiment of a secondary battery. The secondary battery includes the above-mentioned electrode assembly 100. For the specific structure and function of the electrode assembly 100, reference may be made to the above embodiments, and details will not be repeated here.

[0115] In a third aspect, the present application provides an embodiment of an electrical device. The electrical device includes the above-mentioned secondary battery.

[0116] To enable readers to better understand the concept of the present application, experimental verification is carried out below.

[0117] The preparation process of the electrode assembly in Embodiment 1 is as follows:

[0118] <Preparation of the first electrode tab>

[0119] First, the positive electrode active material lithium cobalt oxide LiCoO2, the conductive agent conductive carbon black, and the binder polyvinylidene fluoride PVDF are dissolved in an N-methylpyrrolidone (NMP) solution in a weight ratio of 97.9:0.9:1.2 to form a positive electrode slurry. An aluminum foil with a thickness of 9 μm is used as the positive electrode current collector, and the positive electrode slurry is coated on the positive electrode current collector. After drying, cold pressing, and cutting, a positive electrode tab is obtained. The compaction density of the positive electrode active material layer of the positive electrode tab is 4.2 g / cm³.

[0120] <Preparation of the second electrode tab>

[0121] The negative electrode active material artificial graphite, silicon carbide compound, acetylene black, styrene-butadiene rubber, and sodium carboxymethyl cellulose are mixed and dissolved in deionized water in a mass ratio of 90:6:1:1.5:1.5 to form a negative electrode slurry. A copper foil with a thickness of 5 μm is used as the negative electrode current collector, and the negative electrode slurry is coated on the negative electrode current collector. After drying, cold pressing, and cutting, a negative electrode tab is obtained. The compaction density of the negative electrode active material layer of the negative electrode tab is 1.78 g / cm³. 2 。

[0122] <Preparation of the first separator>

[0123] The separator substrate is polyethylene (PE) with a thickness of 5 μm. An aluminum oxide ceramic layer with a thickness of 2 μm is coated on one side of the separator substrate. Finally, 2.5 mg / 1540.25 mm 2 of the binder polyvinylidene fluoride (PVDF) is coated on both sides of the separator substrate coated with a single layer of ceramic layer, dried to form a porous layer, and then a plurality of first through holes are cut at the cut of the first through hole area of the first separator.

[0124] <Preparation of the second separator>

[0125] The separator substrate is polyethylene (PE) with a thickness of 5 μm. An aluminum oxide ceramic layer with a thickness of 2 μm is coated on one side of the separator substrate. Finally, 2.5 mg / 1540.25 mm 2 of the binder polyvinylidene fluoride (PVDF) is coated on both sides, dried to form a porous layer.

[0126] <Preparation of the electrode assembly>

[0127] The first double-sided tape is bonded to the first end section of the first electrode tab. After the first electrode tab, the first separator, the second electrode tab, and the second separator are stacked in sequence, they are wound, and a single-sided adhesive tape is used to bond and fix at the end of the winding to form a wound electrode assembly, wherein the first double-sided tape constitutes the first bonding member described in this application.

[0128] <Preparation of the electrolyte>

[0129] In an environment with a water content of less than 10 ppm, ethylene carbonate, propylene carbonate, diethyl carbonate, ethyl propionate, and propyl propionate are mixed evenly according to a mass ratio of 1:1:1:1:1. Then, the electrolyte salt LiPF6 is dissolved in the above non-aqueous solvent, and after mixing evenly, an electrolyte is formed. Among them, based on the mass of the electrolyte, the mass percentage content of LiPF6 is 12.5%.

[0130] <Preparation of the secondary battery>

[0131] The electrode assembly is placed in an aluminum-plastic film packaging bag, the moisture is removed at 80 °C, the prepared electrolyte is injected, and an electrochemical device is obtained through vacuum packaging, standing, forming, and shaping processes. Among them, the upper limit voltage of forming is 4.53 V, the forming temperature is 85 °C, and the forming time is 45 min to 60 min.

[0132] Different from Example 1, the first separator in Comparative Example 1 does not have the first through hole;

[0133] Different from Example 1, the parameters of Examples 2 to 53 are different. The differences in specific parameters are detailed in Table 1. Except for the differences listed in Table 1, the other parameters in Examples 2 to 53 are the same as those in Example 1.

[0134] The test methods are as follows:

[0135] 1. Cyclic test

[0136] The test steps for the cyclic capacity retention rate are as follows: 1) At a test temperature of 25 °C, let the secondary battery stand for 50 min and charge it according to the following charging steps: (a) Constant current charge at 1.1C to 4.1V, and set the cut-off capacity of this step to C1; (b) Constant current charge at 0.5C to 4.4V, and then constant voltage charge to 0.05C, and set the cut-off capacity of this step to C2; (c) Stand for 5 min, and then constant current discharge at 1.1C to 3.5V, and set the cut-off capacity of this step to C3; (d) Constant current discharge at 0.5C to 3V, and set the cut-off capacity of this step to C4; (e) Stand for 5 min; (f) If (C1 + C2) / (C3 + C4)>1.02, then suspend charging; (g) If (C1 + C2) / (C3 + C4)≤1.02, then stand for 5 min, and then cycle steps (a) to (g) until 1000 cycles are completed. 2) Take the discharge capacity of the third cycle as the reference capacity, and the ratio of the discharge capacity of the 1000th cycle to the reference capacity multiplied by 100% is the capacity retention rate after 1000 cycles. The average value of the capacity retention rates of 20 samples in each group of examples and comparative examples is recorded in the table.

[0137] The test steps for the thickness expansion rate are as follows: Record the thickness h0 of the secondary battery before cycling and the thickness h after the 1000th cycle, and then calculate the thickness expansion rate of the secondary battery = (h / h0 - 1)×100%. The average value of the thickness expansion rates of 20 samples in each group of examples and comparative examples is recorded in the table. The judgment criteria for the degree of lithium deposition in the last two cycles: After disassembling the negative electrode sheet after 1000 cycles, the grayish-white part is the part where lithium metal is deposited. Measure the area of the lithium deposition part in the last two turns of the wound battery cell. If there is no white lithium metal deposition, it is recorded as "no lithium deposition"; if there is white lithium metal deposition and the proportion of the lithium deposition area is greater than 0 and less than 5%, it is recorded as "mild lithium deposition"; if there is white lithium metal deposition and the proportion of the lithium deposition area is greater than or equal to 5% and less than or equal to 10%, it is recorded as "moderate lithium deposition"; if there is white lithium metal deposition and the proportion of the lithium deposition area is greater than 10%, it is recorded as "severe lithium deposition". Among them, the proportion of the lithium deposition area is the percentage of the lithium deposition area in the last two turns in the area of the negative electrode active material layer on the two surfaces of the negative electrode sheet in the last two turns. Measure the lithium deposition area of 20 samples in each group of examples and comparative examples, and take the average value as the lithium deposition area in the last two turns of this group of examples or comparative examples.

[0138] Pole piece fracture rate on both sides of the first bonding member: Disassemble the electrode assembly after 1000 cycles, and visually observe whether the pole pieces on both sides of the first bonding member are fractured. Take 20 samples for each group of examples or comparative examples, record the number X1 of fractured pole pieces on both sides of the first bonding member, and the pole piece fracture rate on both sides of the first bonding member is recorded as X1 / 20.

[0139] 2. Hi-pot pass rate test:

[0140] Conduct the Hi-pot test on the secondary battery and calculate the test passing rate.

[0141] The test method is as follows: Detect the leakage current generated by the secondary battery prepared in the example or comparative example under the 100V test voltage output by the high-voltage machine, and then calculate the resistance value = test voltage / leakage current.

[0142] Compare the calculated resistance value with the set judgment resistance. In this application, the preset value of the judgment resistance is 5mΩ.

[0143] If the detected resistance value is greater than or equal to the preset value of 5mΩ, it is determined that the tested product passes the test (OK);

[0144] If the detected resistance value is less than the preset value of 5mΩ, the test voltage is instantaneously cut off and the tested product is determined to fail the test (NG).

[0145] Take 100 secondary batteries for each group of examples or comparative examples for the test. The number of secondary batteries passing the test is X2, and the Hi-pot pass rate is recorded as X2 / 100.

[0146] 3. Volume energy density test:

[0147] The volume energy density test steps are as follows: 1) Under the environmental condition of 25°C, let the secondary battery stand for 10 min, charge it at a constant current of 0.2C to 4.5V, charge it at a constant voltage to 0.02C, and then stand for 5 min; then discharge it at a constant current of 0.2C to 3V and stand for 5 min, and record the discharge capacity C0; 2) Measure the length, width, and thickness of the secondary battery with a PPG battery thickness measuring instrument, and calculate through the following formula: Volume energy density = platform voltage × C0 / (length × width × thickness).

[0148] In Table 1, L is the length of the protruding portion along the winding direction, with the unit of mm; L1 is the minimum distance between the first through-hole region and the second active material layer along the winding direction, with the unit of mm; L2 is the dimension by which the first through-hole region protrudes from the protruding portion along the winding direction, with the unit of mm; L3 is the dimension by which the two ends of the first bonding member protrude from the first through-hole region along the width direction of the first separator, with the unit of mm; L4 is the dimension by which the two ends of the first bonding member protrude from the first through-hole region along the winding direction, with the unit of mm; W1 is the width of the first separator along the width direction of the first separator; W2 is the width of the first through-hole region along the width direction of the first separator; D1 is the minimum distance between the first through-hole region and the edge of the first separator along the width direction of the first separator, with the unit of mm; A3 is the thickness of the second bonding layer, and A4 is the thickness of the first separator; F1 is the bonding tensile force between the first bonding layer and the first ending section; F2 is the bonding tensile force between the second bonding layer and the second pole piece.

[0149] Table 1

[0150]

[0151]

[0152]

[0153]

[0154]

[0155] In Table 1, " / " represents no such data. L1 being -0.1 mm means that there is an overlapping region between the first through-hole region and the second active material layer, and the dimension of the overlapping region along the winding direction is 0.1 mm.

[0156] From the experimental data of Comparative Example 1 and Examples 1 to 54 in Table 1, it can be seen that by providing through-holes on the separator opposite to the first bonding member, and thus using the first bonding member to bond the first ending section and the second pole piece, the lithium deposition situation in the last two turns of the winding structure can be improved, the cyclic expansion rate can be reduced, and the cyclic capacity retention rate can be enhanced. This is because the first bonding member bonds the first ending section and the second pole piece through the through-holes on the first separator, which can reduce the risk of the first pole piece at the outermost turn of the winding tilting outwards, thereby reducing the risk of lithium deposition at the tilting position of the first pole piece on the second pole piece.

[0157] From the experimental data of Examples 1 to 7 in Table 1, it can be seen that as the length of the protrusion increases, the degree of lithium deposition in the last two turns of the winding structure is improved more, the cycle capacity retention rate increases, and the cycle expansion rate decreases; however, as the length of the protrusion increases, the volumetric energy density of the secondary battery decreases. Therefore, to balance the cycle capacity retention rate and the volumetric energy density, 0.5 mm ≤ L ≤ 30 mm is selected; further preferably, 10 mm ≤ L ≤ 20 mm.

[0158] From the experimental data of Examples 1 to 7 and Example 8 in Table 1, it can be seen that when the end position of the protrusion is extended to the second straight section, the loss of the volumetric energy density of the secondary battery is relatively serious. Therefore, the end position of the protrusion is selected to be located in the first corner section.

[0159] From the experimental data of Example 1 and Examples 9 to 14 in Table 1, when L1 is too small or there is an overlapping area between the first through-hole region and the second active material layer, the degree of improvement in the lithium deposition in the last two turns is greater, the cycle capacity retention rate is higher, and the cycle expansion rate is lower; but at the same time, since the distance between the through-hole region and the second active material layer is too close or even overlapping, the risk of the second active material layer being exposed to the through region increases, the risk of contacting the first current collector increases, and the Hi-pot excellent rate decreases. When L1 > 3 mm, the area of the first through-hole region is relatively small, and the bonding area between the first end section and the second pole piece is correspondingly small, resulting in a poor improvement effect on the warping of the first pole piece in the last two turns, thus causing a relatively large degree of lithium deposition in the last two turns, a relatively low cycle capacity retention rate of the secondary battery, and a relatively high cycle expansion rate. To balance a high Hi-pot excellent rate, a high cycle capacity retention rate, and a low cycle expansion rate, 0 mm ≤ L1 ≤ 3 mm is selected; further, preferably, 1 mm ≤ L1 ≤ 2 mm.

[0160] From the experimental data of Example 1 and Examples 15 to 18 in Table 1, when L2 < 3 mm, the improvement effect on the lithium deposition in the last two turns is relatively poor, and the cycle capacity retention rate of the secondary battery is relatively low and the cycle expansion rate is relatively high. As L2 increases, the degree of lithium deposition in the last two turns decreases, and the cycle capacity retention rate of the secondary battery is higher and the cycle expansion rate is lower.

[0161] As can be seen from the experimental data of Example 1 and Examples 19 to 24 in Table 1, when L3 < 1 mm, the size of the first bonding member protruding from the first through-hole region is too small, and the risk of short circuit between the first finishing section and the second pole piece is relatively high, resulting in a low Hi-pot excellent rate; when L3 > 10 mm, the size of the first bonding member protruding from the first through-hole region is too large, resulting in a small area where the first bonding member can pass through the first through-hole region to bond the first finishing section and the second pole piece. As a result, the degree of lithium plating in the last two turns of the tail is relatively serious, the cycle capacity retention rate is low, and the cycle expansion rate is high. To balance a high Hi-pot excellent rate, a high cycle capacity retention rate, and a low cycle expansion rate, 1 mm ≤ L3 ≤ 10 mm is selected.

[0162] As can be seen from the experimental data of Example 1 and Examples 25 to 30 in Table 1, when L4 < 1 mm, the size of the first bonding member protruding from the first through-hole region is too small, and the risk of short circuit between the first finishing section and the second pole piece is relatively high, resulting in a low Hi-pot excellent rate; when L4 > 10 mm, the size of the first bonding member protruding from the first through-hole region is too large, resulting in a small area where the first bonding member can pass through the first through-hole region to bond the first finishing section and the second pole piece. As a result, the degree of lithium plating in the last two turns of the tail is relatively serious, the cycle capacity retention rate is low, and the cycle expansion rate is high. To balance a high Hi-pot excellent rate, a high cycle capacity retention rate, and a low cycle expansion rate, 1 mm ≤ L4 ≤ 10 mm is selected.

[0163] As can be seen from the experimental data of Examples 31 to 37 in Table 1, when W2 / W1 < 0.2, the effective bonding area between the first finishing section and the second pole piece bonded through the first through-hole is too small, and the improvement of the warping of the first pole piece in the last two turns of the tail is small, resulting in a large degree of lithium plating in the last two turns of the tail, a low cycle capacity retention rate of the secondary battery, and a high cycle expansion rate; as W2 / W1 increases, the degree of lithium plating in the last two turns of the tail is improved, the cycle capacity retention rate increases, and the cycle expansion rate decreases. However, at the same time, due to the increase in the area of the first through-hole region, the mechanical strength of the first separator is reduced, and the risk of short circuit between the first pole piece and the second pole piece increases, resulting in a decrease in the Hi-pot excellent rate. To balance a high Hi-pot excellent rate, a high cycle capacity retention rate, and a low cycle expansion rate, 0.2 ≤ W2 / W1 ≤ 1 is selected; preferably, 0.4 ≤ W2 / W1 ≤ 0.8; further preferably, 0.5 ≤ W2 / W1 ≤ 0.7.

[0164] As can be seen from the experimental data of Example 1 and Examples 38 to 43 in Table 1, when D1 < 1 mm, the edge of the first through-hole region is too close to the edge of the first separator, which easily causes the first separator to tear from the edge, thus increasing the risk of short circuit between the first and second electrode sheets and resulting in a low Hi-pot yield; when D1 > 15 mm, the edge of the first through-hole region is too far from the edge of the first separator, making the effective bonding area between the first end section and the second electrode sheet through the first through-hole region too small, leading to deterioration of the lithium deposition degree in the last two turns of the tail, and further affecting the cycle capacity retention rate and cycle expansion rate of the secondary battery. Therefore, to balance a high Hi-pot yield, a high cycle capacity retention rate, and a low cycle expansion rate, 1 mm ≤ D1 ≤ 15 mm is selected; further preferably, 5 mm ≤ D1 ≤ 10 mm.

[0165] As can be seen from the experimental data of Example 1 and Examples 44 to 47 in Table 1, when A3 / A4 < 1, the improvement degree of lithium deposition in the last two turns of the tail is small, the cycle capacity retention rate of the secondary battery is low, and the cycle expansion rate is high. This is because the thickness of the second bonding layer is not enough to penetrate the through-holes of the first separator, resulting in poor bonding effect between the first end section and the second electrode sheet and poor suppression effect on the warping of the first end section; when A3 / A4 > 1.2, due to the excessive thickness of the second bonding layer, the volume energy density loss of the secondary battery is relatively serious. Therefore, to balance a high cycle capacity retention rate, a low cycle expansion rate, and a high volume energy density, 1 ≤ A3 / A4 ≤ 1.2 is selected.

[0166] As can be seen from the experimental data of Example 1 and Examples 48 to 53 in Table 1, when F1 / F2 < 0.9 or F1 / F2 > 1.1, the risk of fracture of the electrode sheets on both sides of the first bonding member is relatively high. This is because the difference between F1 and F2 is too large, which easily causes uneven stress on the electrode sheets on both sides of the first bonding member, and the electrode sheets are torn due to stress pulling. Therefore, to reduce the risk of fracture of the electrode sheets on both sides of the first bonding member, 0.9 ≤ F1 / F2 ≤ 1.1 is selected.

[0167] The above are only the embodiments of the present application, and do not limit the patent scope of the present application accordingly. Any equivalent structure or equivalent process transformation made by using the content of the specification and drawings of the present application, or directly or indirectly applied to other related technical fields, shall be equally included in the patent protection scope of the present application.

Claims

1. An electrode assembly, comprising a first electrode tab, a first separator, and a second electrode tab that are stacked and wound. Along the winding direction, the first electrode tab includes a first end section, and at least a part of the first end section extends beyond the second electrode tab. The first end section is located at the outermost winding layer of the electrode assembly. It is characterized in that the electrode assembly further includes a first bonding member. One side of the first bonding member in the thickness direction of the first bonding member is bonded to the first end section. The first separator includes a second end section. The second end section is provided with a first through-hole area. The first through-hole area is provided with at least one first through-hole. The other side of the first bonding member in the thickness direction of the first bonding member is bonded to the second end section. The first bonding member covers at least a part of the first through-hole area. At least a part of the first bonding member passes through the first through-hole, and the first bonding member is bonded to the part of the second electrode tab exposed in the first through-hole.

2. The electrode assembly according to claim 1, wherein the second electrode tab includes a second current collector and a second active material layer. The second active material layer is disposed on at least one surface of the second current collector. At the end part of the second electrode tab, a part of the second current collector protrudes from the second active material layer along the winding direction to form a protruding part. The part of the first bonding member passing through the first through-hole is bonded and fixed to the protruding part.

3. The electrode assembly according to claim 2, wherein Along the winding direction, the length of the protruding part is L, and 0.5 mm ≤ L ≤ 30 mm.

4. The electrode assembly according to claim 3, characterized in that, 10 mm ≤ L ≤ 20 mm.

5. The electrode assembly according to claim 3 or 4, characterized in that, The electrode assembly includes a first straight section, a first corner section, a second straight section, and a second corner section that are sequentially connected along the winding direction; Along the winding direction, the end position of the second active material layer is located in the first straight section, and the end position of the protruding part is located in the first corner section.

6. The electrode assembly according to claim 2, wherein the number of the first through-holes is multiple, and the multiple first through-holes are spaced apart in the first through-hole area; Along the winding direction, the minimum distance between the first through-hole area and the second active material layer is L1, and 0 mm ≤ L1 ≤ 3 mm.

7. The electrode assembly according to claim 6, characterized in that, 1 mm ≤ L1 ≤ 2 mm.

8. The electrode assembly according to claim 2, wherein the number of the first through-holes is multiple, and the multiple first through-holes are spaced apart in the first through-hole area; Along the winding direction, at least a part of the first through-hole area protrudes from the protruding part; the electrode assembly further includes a second separator. The first separator and the second separator are respectively located on two sides of the second electrode tab in the thickness direction. The first separator is farther from the winding center of the electrode assembly than the second separator. The second separator includes a third end section; In the first through-hole area protruding from the protruding part, at least a part of the first bonding member passes through the first through-hole and is bonded to the part of the third end section exposed in the first through-hole.

9. The electrode assembly according to claim 8, wherein In the winding direction, the size by which the first through-hole region protrudes from the protruding portion is L2, and L2 ≥ 3 mm.

10. The electrode assembly according to claim 1, wherein In the width direction of the first separator, the width of the first separator is W1, the width of the first through-hole region is W2, and 0.2 ≤ W2 / W1 ≤ 1.

11. The electrode assembly according to claim 10, wherein, 0.4 ≤ W2 / W1 ≤ 0.

8.

12. The electrode assembly according to claim 11, wherein, 0.5 ≤ W2 / W1 ≤ 0.

7.

13. The electrode assembly according to claim 1, wherein, In the width direction of the first separator, the minimum distance between the first through-hole region and the edge of the first separator is D1, and 1 mm ≤ D1 ≤ 15 mm.

14. The electrode assembly according to claim 13, wherein 5 mm ≤ D1 ≤ 10 mm.

15. The electrode assembly according to claim 1, wherein The first bonding member includes a first base layer, a first bonding layer, and a second bonding layer. The first bonding layer and the second bonding layer are respectively disposed on two sides in the thickness direction of the first base layer. The first bonding layer is bonded to the first end segment, the second bonding layer is bonded to the second end segment, and at least a part of the second bonding layer passes through the first through-hole and is bonded to the second electrode tab.

16. The electrode assembly according to claim 15, wherein The thickness of the first base layer is A1, and 5 μm ≤ A1 ≤ 20 μm; and / or, the thickness of the first bonding layer is A2, and 2 μm ≤ A2 ≤ 10 μm.

17. The electrode assembly according to claim 15, wherein The thickness of the second bonding layer is A3, the thickness of the first separator is A4, and 1 ≤ A3 / A4 ≤ 1.

2.

18. The electrode assembly according to claim 15, wherein The bonding tensile force between the first bonding layer and the first end segment is F1, and the bonding tensile force between the second bonding layer and the second electrode tab is F2; 100 N / m ≤ F1 ≤ 1000 N / m; and / or 100 N / m ≤ F2 ≤ 1000 N / m.

19. The electrode assembly according to claim 18, characterized in that, 0.9 ≤ F1 / F2 ≤ 1.

1.

20. The electrode assembly according to claim 1, wherein In the width direction of the first separator, both ends of the first bonding member protrude from the first through-hole region, and the size by which both ends of the first bonding member protrude from the first through-hole region is L3, and 1 mm ≤ L3 ≤ 10 mm; and / or In the winding direction, both ends of the first bonding member protrude from the first through-hole region, and the size by which both ends of the first bonding member protrude from the first through-hole region is L4, and 1 mm ≤ L4 ≤ 10 mm.

21. The electrode assembly according to claim 1, wherein When observed in the thickness direction of the first diaphragm, the area of a single first through hole is B1, 2 mm 2 ≤B1≤100 mm 2 .

22. The electrode assembly according to claim 6, wherein In the winding direction, the minimum distance between two adjacent first through-holes is D2, and 1.5 mm ≤ D2 ≤ 75 mm; and / or, In the width direction of the first separator, the minimum distance between two adjacent first through-holes is D3, and 1.5 mm ≤ D3 ≤ 75 mm.

23. The electrode assembly according to claim 8, wherein The first electrode tab further includes a first segment, and the first segment is located in the second outermost layer of the winding of the electrode assembly; The electrode assembly further includes a second bonding member, one side of the second bonding member along the thickness direction of the second bonding member is bonded to the first section, and the other side of the second bonding member along the thickness direction of the second bonding member is bonded to the third end section; At least one second through hole is provided in the third end section, at least part of the second bonding member covers at least part of the second through hole, and at least part of the second bonding member penetrates through the second through hole and is fixedly bonded to the second end section.

24. The electrode assembly according to claim 23, wherein The number of the second through holes is multiple, and the orthographic projections of the second through holes along the thickness direction of the third end section and the orthographic projections of the first through holes along the thickness direction of the second end section at least partially do not overlap.

25. The electrode assembly according to claim 1, wherein The first electrode tab is a positive electrode tab, and the second electrode tab is a negative electrode tab.

26. The electrode assembly according to claim 25, wherein The second electrode tab includes a second active material layer, the second active material layer includes a second active material, and the second active material includes silicon element.

27. A secondary battery, characterized in that, Comprising the electrode assembly according to any one of claims 1-26.

28. An electronic device, characterized in that, Comprising the secondary battery according to claim 27.

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