Secondary battery, preparation method thereof and electronic equipment

Abstract

The invention discloses a secondary battery, a preparation method thereof and electronic equipment, and belongs to the technical field of secondary batteries. The secondary battery comprises an electrode assembly and a tab, the tab extends out of the electrode assembly along a first direction Y, the electrode assembly is of a winding structure, the electrode assembly comprises a pole piece, the pole piece comprises a current collector, a conductive connecting layer and an adhesive layer are arranged between the tab and the current collector, the tab is electrically connected with the current collector through the conductive connecting layer, and the tab and the current collector are bonded by the adhesive layer. The adhesive layer is arranged on one side, close to the winding starting end, of the conductive connecting layer; the adhesive layer is arranged at the front end of the conductive connecting layer between the tab and the current collector, and the adhesive layer has a relatively good bonding effect with the tab and the current collector at the same time, so that a resistance effect on a pulling force towards a winding starting end between the current collector and the tab is generated, and a protection effect on initial damage caused by arranging the conductive connecting layer on the current collector is achieved; and further, the probability of fracture at the joint of the tab and the current collector caused by the pulling force is reduced.

Description

Technical Field

[0001] The present application relates to the technical field of secondary batteries, and more particularly, to a secondary battery, a method for manufacturing the same, and an electronic device. Background Art

[0002] For a secondary battery using a wound electrode assembly, such as certain cylindrical batteries or button batteries, during cycling, due to the expansion of the electrode sheets, the inner electrode sheets exert extrusion on the outer electrode sheets, and the force is transmitted from the inner layer to the outer layer of the wound electrode assembly, resulting in a large extrusion force on the outer layer of the wound electrode assembly. Under the action of this shear force, there is a pulling effect between the current collector and the tab in the outermost electrode sheet. During the connection process of the current collector and the tab, initial damage is likely to occur on the current collector, so fractures are likely to occur at the initial damage site, leading to a large internal resistance and a decrease in capacity of the secondary battery, and even directly rendering the secondary battery unusable. Summary of the Invention

[0003] The present application provides a secondary battery, a method for manufacturing the same, and an electronic device to reduce the probability of fracture at the connection between the tab and the current collector.

[0004] In a first aspect, an embodiment of the present application provides a secondary battery. The secondary battery includes an electrode assembly and a tab. The tab extends out of the electrode assembly in a first direction. The electrode assembly has a wound structure and includes electrode sheets. The electrode sheets include current collectors. A conductive connection layer and an adhesive layer are provided between the tab and the current collector. The tab is electrically connected to the current collector through the conductive connection layer, and the adhesive layer bonds the tab and the current collector. The adhesive layer is provided on a side of the conductive connection layer close to the start end of winding.

[0005] In the above implementation process, by providing the adhesive layer at the front end of the conductive connection layer between the tab and the current collector, the adhesive layer has a good bonding effect with both the tab and the current collector, generating a resistance to the pulling force between the current collector and the tab towards the start end of winding, protecting the initial damage on the current collector caused by the provision of the conductive connection layer, and thus reducing the probability of fracture at the connection between the tab and the current collector caused by the pulling force.

[0006] In one or more of the above optional embodiments, the area of the adhesive layer bonded to the current collector is not less than 3 mm 2 .

[0007] In the above implementation process, the larger the bonding area of the adhesive layer on the current collector, the stronger the resistance to the pulling force between the current collector and the tab towards the start end of winding, and the stronger the protection of the initial damage on the current collector caused by the provision of the conductive connection layer, thus facilitating the reduction of the probability of fracture at the connection between the tab and the current collector. By controlling the area of the adhesive layer bonded to the current collector to be not less than 3 mm 2, which can reduce the probability of breakage at the connection between the tab and the current collector.

[0008] In one or more of the above optional embodiments, along the winding direction of the electrode assembly, the length of the adhesive layer is A, the tab includes a first edge and a second edge arranged opposite to each other, the first edge is closer to the winding center of the electrode assembly compared to the second edge, the conductive connection layer includes a third edge and a fourth edge arranged opposite to each other, the third edge is closer to the winding center of the electrode assembly compared to the fourth edge, the distance between the first edge and the third edge is W3, and 0.25W3 ≤ A ≤ W3.

[0009] In the above implementation process, the longer the length of the adhesive layer in the winding direction of the electrode assembly, the stronger the resistance to the pulling force between the current collector and the tab towards the winding start end, and the stronger the protection against the initial damage caused by the conductive connection layer on the current collector, which is conducive to reducing the probability of breakage at the connection between the tab and the current collector. By controlling the relationship between the length of the adhesive layer and the distance between the first edge and the third edge to satisfy 0.25W3 ≤ A ≤ W3, the probability of breakage at the connection between the tab and the current collector can be reduced.

[0010] In one or more of the above optional embodiments, 0.5mm ≤ A ≤ 2mm.

[0011] In the above implementation process, by controlling the length of the adhesive layer in the winding direction of the electrode assembly to satisfy 0.5mm ≤ A ≤ 2mm, the probability of breakage at the connection between the tab and the current collector can be reduced.

[0012] In one or more of the above optional embodiments, along the winding direction of the electrode assembly, the adhesive layer includes a fifth edge and a sixth edge arranged opposite to each other, the sixth edge is closer to the winding center of the electrode assembly compared to the fifth edge, the distance between the first edge and the fifth edge is A1, the distance between the third edge and the fifth edge is A2, and |A1 - A2| ≤ 2mm.

[0013] In the above implementation process, by controlling the relationship between the distance between the first edge and the fifth edge and the distance between the third edge and the fifth edge to satisfy |A1 - A2| ≤ 2mm, it is more conducive to reducing the probability of breakage at the connection between the tab and the current collector in the middle position of the area between the frontmost edge of the tab and the frontmost edge of the conductive connection layer.

[0014] In one or more of the above optional embodiments, along the first direction, the length of the adhesive layer is B, the length of the conductive connection layer is H1, and the length of the overlapping area between the tab and the current collector is H, and H1 ≤ B ≤ H.

[0015] In the above implementation process, the longer the length of the adhesive layer in the first direction, the stronger the resistance to the pulling force between the current collector and the tab towards the winding start end, and the stronger the protection against the initial damage caused by the conductive connection layer on the current collector. This is conducive to reducing the probability of breakage at the connection between the tab and the current collector. By controlling the length of the adhesive layer in the first direction to satisfy: H1 ≤ B ≤ H, the probability of breakage at the connection between the tab and the current collector can be made relatively low.

[0016] In one or more of the above alternative embodiments, the projection of the adhesive layer in the winding direction of the electrode assembly and the projection of the conductive connection layer in the winding direction of the electrode assembly have an overlapping segment. The length of the overlapping segment in the first direction is C and the length of the conductive connection layer in the first direction is H1, and C ≥ 0.75H1.

[0017] In the above implementation process, by controlling the length of the overlapping segment of the projections of the adhesive layer and the conductive connection layer in the winding direction of the electrode assembly and the length of the conductive connection layer in the first direction to satisfy C ≥ 0.75H1, it is more conducive to reducing the probability of breakage at the connection between the tab and the current collector.

[0018] In one or more of the above alternative embodiments, along the first direction, the distance between the upper edge of the adhesive layer and the upper edge of the current collector is less than the distance between the upper edge of the conductive connection layer and the upper edge of the current collector. The upper edge of the adhesive layer, the upper edge of the current collector, and the upper edge of the conductive connection layer are on the same side of the electrode assembly in the first direction.

[0019] In the above implementation process, by controlling the distance between the upper edge of the adhesive layer and the upper edge of the current collector to be less than the distance between the upper edge of the conductive connection layer and the upper edge of the current collector, the adhesive layer can produce a better resistance to the pulling force between the current collector and the tab, which is more conducive to reducing the probability of breakage at the connection between the tab and the current collector.

[0020] In one or more of the above alternative embodiments, along the thickness direction of the electrode tab, the thickness of the adhesive layer is T2, and 10 μm ≤ T2 ≤ 60 μm.

[0021] In the above implementation process, the thicker the thickness of the adhesive layer, the stronger the resistance to the pulling force between the current collector and the tab towards the winding start end, and the stronger the protection against the initial damage caused by the conductive connection layer on the current collector, thereby reducing the probability of breakage at the connection between the tab and the current collector. The thinner the thickness of the adhesive layer, the more conducive to controlling the volume of the entire electrode assembly, and thus conducive to the energy density of the secondary battery. By controlling the thickness of the adhesive layer to satisfy: 10 μm ≤ T2 ≤ 60 μm, it is possible to balance reducing the probability of breakage at the connection between the tab and the current collector and the energy density of the secondary battery.

[0022] In one or more of the above optional embodiments, the material of the adhesive layer includes at least one of epoxy resin, polyurethane, acrylate, silicone, polyimide, fluorosilicone rubber, or ethylene-vinyl acetate copolymer.

[0023] In the above implementation process, materials such as epoxy resin, polyurethane, acrylate, silicone, polyimide, fluorosilicone rubber, or ethylene-vinyl acetate copolymer have high bonding strength, good chemical resistance, good high-temperature resistance, and good electrical insulation properties. Using them as the adhesive layer material can be applicable to the working environment of secondary batteries and can maintain the resistance to the pulling force between the current collector and the tab for a long time.

[0024] In one or more of the above optional embodiments, the electrode assembly is cylindrical.

[0025] In the above implementation process, the problem of breakage at the connection between the tab and the current collector in the cylindrical electrode assembly is more serious. By providing an adhesive layer at the front end of the conductive connection layer between the tab and the current collector, the problem of breakage at the connection between the tab and the current collector in the cylindrical electrode assembly can be significantly improved.

[0026] In one or more of the above optional embodiments, the tab is welded to the current collector, and the conductive connection layer is a welded metal layer.

[0027] In a second aspect, an embodiment of the present application provides a method for manufacturing a secondary battery provided in the first aspect. The method includes:

[0028] Stack and wind the electrode sheet and the separator to obtain an electrode assembly, where the electrode sheet includes a current collector;

[0029] Weld the tab and the current collector to form a conductive connection layer;

[0030] Use a wedge-shaped fixture to open a first position where the tab and the current collector are not welded. The first position is on the side of the conductive connection layer close to the starting end of winding, and drop glue into the first position to form an adhesive layer.

[0031] In a third aspect, an embodiment of the present application provides a method for manufacturing a secondary battery provided in the first aspect. The method includes:

[0032] Stack and wind the electrode sheet and the separator to obtain an electrode assembly, where the electrode sheet includes a current collector;

[0033] Bond the adhesive tape to the surface of the current collector. The adhesive tape is located between the tab and the current collector to form an adhesive layer;

[0034] Weld the tab and the current collector to form a conductive connection layer, and the adhesive layer is on the side of the conductive connection layer close to the starting end of winding.

[0035] Fourthly, an embodiment of the present application provides an electronic device, which includes the secondary battery provided in the first aspect or the secondary battery prepared by the method provided in the second aspect / the third aspect. Description of the Drawings

[0036] To more clearly illustrate the technical solutions of the embodiments of the present application, the drawings required for use in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present application, and thus should not be regarded as limiting the scope. For those of ordinary skill in the art, other related drawings can be obtained based on these drawings without creative efforts.

[0037] Figure 1 Structural schematic diagram of the electrode assembly and the tab provided in the embodiment of the present application;

[0038] Figure 2 Connection schematic of the current collector and the tab provided in the embodiment of the present application Figure 1 ;

[0039] Figure 3 Connection schematic of the current collector and the tab provided in the embodiment of the present application Figure 2 ;

[0040] Figure 4 Connection schematic of the current collector and the tab provided in the embodiment of the present application Figure 3 。

[0041] Icons: 1000 - electrode assembly; 1100 - electrode tab; 1110 - current collector; 2000 - tab; 2100 - first edge; 2200 - second edge; 3000 - conductive connection layer; 3100 - third edge; 3200 - fourth edge; 4000 - adhesive layer; 4100 - fifth edge; 4200 - sixth edge. Detailed Embodiments

[0042] The embodiments of the technical solutions of the present application will be described in detail below with reference to the drawings. The following embodiments are only used to more clearly illustrate the technical solutions of the present application, and thus are only examples and should not be used to limit the protection scope of the present application.

[0043] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the technical field to which this application belongs; the terms used herein are only for the purpose of describing specific embodiments and are not intended to limit this application; the terms "including" and "having" and any variations thereof in the specification and claims of this application and the above description of the drawings are intended to cover non-exclusive inclusion.

[0044] In the description of the embodiments of the present application, technical terms such as "first" and "second" are only used to distinguish different objects, and cannot be understood as indicating or implying relative importance or implicitly specifying the quantity, specific order, or primary-secondary relationship of the indicated technical features. In the description of the embodiments of the present application, the meaning of "a plurality of" is more than two, unless otherwise specifically defined.

[0045] Reference to "embodiment" herein means that a particular feature, structure, or characteristic described in connection with the embodiment can be included in at least one embodiment of the present application. The phrase appears in various places in the specification and does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment mutually exclusive with other embodiments. Those skilled in the art will explicitly and implicitly understand that the embodiments described herein can be combined with other embodiments.

[0046] In the description of the embodiments of the present application, the term "and / or" is merely a description of the association relationship of associated objects, indicating that there can be three relationships. For example, A and / or B can represent: A exists alone, A and B exist simultaneously, and B exists alone. In addition, the character " / " herein generally represents an "or" relationship between the associated objects before and after.

[0047] In the description of the embodiments of the present application, the orientation or positional relationship indicated by technical terms such as "center", "longitudinal", "lateral", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", "axial", "radial", "circumferential", etc. is based on the orientation or positional relationship shown in the drawings. It is only for the convenience of describing the embodiments of the present application and simplifying the description, rather than indicating or implying that the indicated device or element must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the embodiments of the present application.

[0048] In the description of the embodiments of the present application, unless otherwise clearly specified and limited, technical terms such as "installation", "connection", "connection", "fixation", etc. should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or integrated; it can also be a mechanical connection or an electrical connection; it can be directly connected or indirectly connected through an intermediate medium, and can be the communication inside two elements or the interaction relationship between two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the embodiments of the present application can be understood according to specific circumstances.

[0049] The embodiments of the present application provide an electronic device, which can be any electronic device, such as a mobile phone, a laptop computer, a camera, a digital camera, an electric toy, an electric vehicle, etc. The electronic device is provided with a secondary battery for supplying electric energy.

[0050] Currently, for secondary batteries employing a wound electrode assembly 1000, such as certain cylindrical batteries or button batteries, during cycling, due to the expansion of the electrode tab 1100, the inner electrode tab 1100 exerts extrusion on the outer electrode tab 1100, and the force is transmitted from the inner layer to the outer layer of the wound electrode assembly 1000, resulting in a relatively large extrusion force on the outer layer of the wound electrode assembly 1000. Under the action of this shear force, there is a pulling effect between the current collector 1110 and the tab 2000. During the connection process of the current collector 1110 and the tab 2000, initial damage is likely to occur on the current collector 1110. Therefore, the initial damaged area is prone to fracture, which further leads to a large internal resistance and a decrease in capacity of the secondary battery, and even directly causes the secondary battery to be unusable.

[0051] Some people propose to increase the thickness of the current collector 1110 to improve this problem. However, after the current collector 1110 is thickened, it is disadvantageous to the energy density of the entire secondary battery. Some people also propose to reduce the thickness of the tab 2000. Due to its relatively small structural strength, the tab 2000 deforms during the pulling process to improve the above problem. However, after the tab 2000 is thinned, it is difficult to meet the overcurrent requirement.

[0052] Therefore, the inventor intends to reduce the probability of fracture at the connection between the tab 2000 and the current collector 1110, and provides an electrode assembly 1000 having an adhesive layer 4000 between the current collector 1110 and the tab 2000, specifically as follows:

[0053] An embodiment of the present application provides a secondary battery, which includes an electrode assembly 1000 and a tab 2000. Figure 1 For the structural schematic diagram of the electrode assembly 1000 and the tab 2000 provided by the embodiment of the present application, please refer to Figure 1 , the tab 2000 extends out of the electrode assembly 1000 along the first direction Y. The electrode assembly 1000 is of a wound structure, and the electrode assembly 1000 includes an electrode tab 1100, and the electrode tab 1100 includes a current collector 1110. Figures 2 to 4 For the connection schematic diagram of the current collector 1110 and the tab 2000 provided by the embodiment of the present application, please refer to Figures 2 to 4 , a conductive connection layer 3000 and an adhesive layer 4000 are provided between the tab 2000 and the current collector 1110. The tab 2000 is electrically connected to the current collector 1110 through the conductive connection layer 3000, and the adhesive layer 4000 bonds the tab 2000 and the current collector 1110. The adhesive layer 4000 is provided on the side of the conductive connection layer 3000 close to the starting end of winding.

[0054] The electrode assembly 1000 includes a positive electrode tab 1100, a negative electrode tab 1100, and a separator. The current collector 1110 can be the positive current collector 1110 of the positive electrode tab 1100 or the negative current collector 1110 of the negative electrode tab 1100. The preparation process of the wound electrode assembly 1000 can be as follows: stack the first separator, the positive electrode tab 1100, the second separator, and the negative electrode tab 1100 in sequence, and form the wound electrode assembly 1000 after winding. The wound structure can specifically be a cylindrical winding structure. Among them, the current collector 1110 of the positive current collector 1110 can adopt a metal foil or a composite current collector 1110. For example, as the metal foil, aluminum foil can be used. The composite current collector 1110 can include a polymer material substrate and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector 1110 can be formed by forming a metal material (such as aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.). The current collector 1110 of the negative current collector 1110 can also adopt a metal foil or a composite current collector 1110. For example, as the metal foil, copper foil can be used. The composite current collector 1110 can include a polymer material substrate and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector 1110 can be formed by forming a metal material (such as copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0055] The first direction Y is the winding central axis direction of the electrode assembly 1000.

[0056] The conductive connection layer 3000 that connects the tab 2000 and the current collector 1110 can usually be formed by welding (the corresponding conductive connection layer 3000 is a welded metal layer), or can be formed by a conductive adhesive. When the conductive connection layer 3000 is formed by welding, there are usually welding burrs, and usually, it is necessary to control the thickness of the adhesive layer 4000 not to exceed the height of the welding burrs.

[0057] The adhesive layer 4000 is made of a material having an adhesive force to the tab 2000 and the current collector 1110, such as epoxy resin, silicone-modified epoxy resin, acrylate-modified epoxy resin, polyurethane, acrylate, silicone, polyimide, fluorosilicone rubber, ultraviolet curable adhesive or hot melt adhesive, etc. The adhesive layer 4000 can be formed by coating the above materials in a flowing form after the tab 2000 and the current collector 1110 are connected (such as welded) through the conductive connection layer 3000, or the above materials in the form of a pre-bonded adhesive tape (that is, the above materials are coated on a substrate to form a bonded adhesive tape form) can be pre-bonded, and then the tab 2000 and the current collector 1110 are connected through the conductive connection layer 3000 (such as welded).

[0058] It should be noted that in addition to setting the adhesive layer 4000 at the front end of the conductive connection layer 3000, the adhesive layer 4000 can also be set in the remaining area between the tab 2000 and the current collector 1110 except the conductive connection layer 3000, such as the rear end of the conductive connection layer 3000, the lower end of the conductive connection layer 3000, the lower end of the conductive connection layer 3000, etc. When using an adhesive tape as the adhesive layer 4000, adhesive tapes can be pre-pasted at the front end, the rear end, the lower end and the lower end of the conductive connection layer 3000, and then the conductive connection layer 3000 is set. At this time, the adhesive tape can play a positioning role. Of course, an adhesive tape can also be set only at the front end of the conductive connection layer 3000, or an adhesive tape can be set at the front end of the conductive connection layer 3000 and combined with any one or more positions in the remaining area between the tab 2000 and the current collector 1110 except the conductive connection layer 3000. Similarly, when using the above materials in a flowing form to prepare the adhesive layer 4000, the setting position can refer to the position when using the adhesive tape as described above, and will not be elaborated here one by one.

[0059] In this secondary battery, by setting the adhesive layer 4000 at the front end of the conductive connection layer 3000 between the tab 2000 and the current collector 1110, the adhesive layer 4000 has a good bonding effect with both the tab 2000 and the current collector 1110, generates a resistance to the pulling force between the current collector 1110 and the tab 2000 towards the winding starting end, and plays a protective role for the initial damage caused by setting the conductive connection layer 3000 on the current collector 1110, thereby reducing the probability of the connection between the tab 2000 and the current collector 1110 being broken due to the pulling force.

[0060] According to some embodiments of the present application, the area where the adhesive layer 4000 is bonded to the current collector 1110 is not less than 3mm 2. The larger the bonding area of the adhesive layer 4000 on the current collector 1110, the stronger the resistance to the pulling force between the current collector 1110 and the tab 2000 towards the winding start end, and the stronger the protection against the initial damage caused by the conductive connection layer 3000 on the current collector 1110. This is conducive to reducing the probability of breakage at the connection between the tab 2000 and the current collector 1110. By controlling the area of the adhesive layer 4000 bonded to the current collector 1110 to be not less than 3 mm 2 , the probability of breakage at the connection between the tab 2000 and the current collector 1110 can be made relatively low.

[0061] Exemplarily, the area of the adhesive layer 4000 bonded to the current collector 1110 can be 3 mm 2 , 3.5 mm 2 , 4 mm 2 , 4.5 mm 2 , 5 mm 2 , 5.5 mm 2 , 6 mm 2 , etc. It can also be any value within the range not less than 3 mm 2 .

[0062] It can be understood that when the area of the adhesive layer 4000 bonded to the current collector 1110 satisfies not less than 3 mm 2 , it can produce a good resistance to the pulling force between the current collector 1110 and the tab 2000 towards the winding start end. When the bonding area of the adhesive layer 4000 on the current collector 1110 cannot reach the above range (that is, the area of all regions between the tab 2000 at the front end of the conductive connection layer 3000 and the current collector 1110 cannot satisfy not less than 3 mm 2 ), it can still produce a certain resistance to the pulling force between the current collector 1110 and the tab 2000 on the side of the current collector 1110 near the winding start end where the initial damage occurs, and achieve the effect of reducing the probability of breakage at the connection between the tab 2000 and the current collector 1110 caused by this pulling force. At this time, it is preferable to make the adhesive layer 4000 cover all regions between the tab 2000 at the front end of the entire conductive connection layer 3000 and the current collector 1110.

[0063] Next, when the area of the adhesive layer 4000 bonded to the current collector 1110 can satisfy not less than 3 mm 2 , the size and position settings of the adhesive layer 4000 will be further described.

[0064] Figure 2Schematic diagram of the connection between the current collector 1110 and the tab 2000 provided by the embodiments of the present application. In the figure, X refers to the winding direction of the electrode assembly 1000, A refers to the length of the adhesive layer 4000 in the winding direction X of the electrode assembly 1000, A1 refers to the distance between the first edge 2100 and the fifth edge 4100, A2 refers to the distance between the third edge 3100 and the fifth edge 4100, W refers to the length of the tab 2000 in the winding direction X of the electrode assembly 1000, W1 refers to the length of the conductive connection layer 3000 in the winding direction X of the electrode assembly 1000, W2 refers to the distance between the second edge 2200 and the fourth edge 3200, and W3 refers to the distance between the first edge 2100 and the third edge 3100.

[0065] It should be noted that the position of the conductive connection layer 3000 is usually set in the middle of the overlapping area of the tab 2000 and the current collector 1110, that is, the numerical difference between W2 and W3 is small or the same. For example, the relationship between W2 and W3 satisfies |W1 - W2| ≤ 2 mm.

[0066] Please refer to Figure 2 , according to some embodiments of the present application, along the winding direction X of the electrode assembly 1000, the length of the adhesive layer 4000 is A, the tab 2000 includes a first edge 2100 and a second edge 2200 that are oppositely arranged. Compared with the second edge 2200, the first edge 2100 is closer to the winding center of the electrode assembly 1000. The conductive connection layer 3000 includes a third edge 3100 and a fourth edge 3200 that are oppositely arranged. Compared with the fourth edge 3200, the third edge 3100 is closer to the winding center of the electrode assembly 1000. The distance between the first edge 2100 and the third edge 3100 is W3, and 0.25W3 ≤ A ≤ W3. The longer the length of the adhesive layer 4000 in the winding direction X of the electrode assembly 1000, the stronger the resistance to the pulling force between the current collector 1110 and the tab 2000 towards the winding starting end, and the stronger the protection against the initial damage caused by the setting of the conductive connection layer 3000 on the current collector 1110. Furthermore, it is beneficial to reduce the probability of breakage at the connection between the tab 2000 and the current collector 1110. By controlling the relationship between the length of the adhesive layer 4000 and the distance between the first edge 2100 and the third edge 3100 to satisfy 0.25W3 ≤ A ≤ W3, the probability of breakage at the connection between the tab 2000 and the current collector 1110 can be made relatively low.

[0067] Exemplarily, along the winding direction X of the electrode assembly 1000, the value of the relationship A / W3 between the length of the adhesive layer 4000 and the distance between the first edge 2100 and the third edge 3100 can be 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, 0.55, 0.6, 0.65, 0.7, 0.75, 0.8, 0.85, 0.9, 0.95, 1, etc., and it can also be any value within the range of 0.25 to 1.

[0068] According to some embodiments of the present application, 0.5 mm ≤ A ≤ 2 mm. By controlling the length of the adhesive layer 4000 in the winding direction X of the electrode assembly 1000 to satisfy 0.5 mm ≤ A ≤ 2 mm, the probability of breakage at the connection between the tab 2000 and the current collector 1110 can be made relatively low.

[0069] Exemplarily, the length A of the adhesive layer 4000 can be 0.5 mm, 0.6 mm, 0.7 mm, 0.8 mm, 0.9 mm, 1 mm, 1.1 mm, 1.2 mm, 1.3 mm, 1.4 mm, 1.5 mm, 1.6 mm, 1.7 mm, 1.8 mm, 1.9 mm, 2 mm, etc., and it can also be any value within the range of 0.5 mm ≤ A ≤ 2 mm.

[0070] Please continue to refer to Figure 2 , according to some embodiments of the present application, along the winding direction X of the electrode assembly 1000, the adhesive layer 4000 includes a relatively arranged fifth edge 4100 and a sixth edge 4200. Compared with the fifth edge 4100, the sixth edge 4200 is closer to the winding center of the electrode assembly 1000. The distance between the first edge 2100 and the fifth edge 4100 is A1, and the distance between the third edge 3100 and the fifth edge 4100 is A2, and |A1 - A2| ≤ 2 mm. By controlling the relationship between the distance between the first edge 2100 and the fifth edge 4100 and the distance between the third edge 3100 and the fifth edge 4100 to satisfy |A1 - A2| ≤ 2 mm, it is more conducive to reducing the probability of breakage at the connection between the tab 2000 and the current collector 1110 at the middle position of the area between the frontmost edge of the tab 2000 and the frontmost edge of the conductive connection layer 3000.

[0071] Exemplarily, along the winding direction X from the inside to the outside of the electrode assembly 1000, the value of the relationship |A1 - A2| between the distance between the first edge 2100 and the fifth edge 4100 and the distance between the third edge 3100 and the fifth edge 4100 can be 0 mm, 0.2 mm, 0.4 mm, 0.6 mm, 0.8 mm, 1 mm, 1.2 mm, 1.4 mm, 1.6 mm, 1.8 mm, 2 mm, etc., and it can also be any value within the range of less than or equal to 2 mm.

[0072] Figure 3 A connection schematic diagram of the current collector 1110 and the tab 2000 provided in the embodiment of the present application. In the figure, Y refers to the thickness direction of the electrode assembly 1000, B refers to the length of the adhesive layer 4000 in the thickness direction of the electrode assembly 1000, B1 refers to the distance between the uppermost edge of the overlapping area of the current collector 1110 and the tab 2000 and the adhesive layer 4000, B2 refers to the distance between the lowermost edge of the overlapping area of the current collector 1110 and the tab 2000 and the adhesive layer 4000, H refers to the length of the overlapping area of the current collector 1110 and the tab 2000 in the thickness direction of the electrode assembly 1000, H1 refers to the length of the conductive connection layer 3000 in the thickness direction of the electrode assembly 1000, H2 refers to the distance between the uppermost edge of the overlapping area of the current collector 1110 and the tab 2000 and the conductive connection layer 3000, H3 refers to the distance between the lowermost edge of the overlapping area of the current collector 1110 and the tab 2000 and the conductive connection layer 3000, and C refers to the length in the thickness direction Y of the overlapping segment of the projection of the adhesive layer 4000 in the winding direction X of the electrode assembly 1000 and the projection of the conductive connection layer 3000 in the winding direction X of the electrode assembly 1000.

[0073] According to some embodiments of the present application, in the thickness direction Y of the electrode assembly 1000, the length of the adhesive layer 4000 is B, the length of the conductive connection layer 3000 is H1, and the length of the overlapping area of the tab 2000 and the current collector 1110 is H, where H1 ≤ B ≤ H. The longer the length of the adhesive layer 4000 in the thickness direction Y of the electrode assembly 1000, the stronger the resistance to the pulling force between the current collector 1110 and the tab 2000 towards the winding start end, and the stronger the protection against the initial damage caused by the setting of the conductive connection layer 3000 on the current collector 1110. Furthermore, it is beneficial to reduce the probability of breakage at the connection between the tab 2000 and the current collector 1110. By controlling the length of the adhesive layer 4000 in the thickness direction Y of the electrode assembly 1000 to satisfy H1 ≤ B ≤ H, the probability of breakage at the connection between the tab 2000 and the current collector 1110 can be made relatively low.

[0074] According to some embodiments of the present application, the projection of the adhesive layer 4000 along the winding direction X of the electrode assembly 1000 and the projection of the conductive connection layer 3000 along the winding direction X of the electrode assembly 1000 have an overlapping section. The length of the overlapping section in the thickness direction Y of the electrode assembly 1000 is C, and the length of the conductive connection layer 3000 in the thickness direction Y of the electrode assembly 1000 is H1, and C≥0.75H1. By controlling the length of the overlapping section of the projections of the adhesive layer 4000 and the conductive connection layer 3000 along the winding direction X of the electrode assembly 1000 and the length of the conductive connection layer 3000 in the thickness direction of the electrode assembly 1000 to satisfy C≥0.75H1, it is more beneficial to reduce the probability of breakage at the connection between the tab 2000 and the current collector 1110. It should be noted that, please refer to Figure 3 , in the flattened state of the current collector 1110, the overlapping section is the overlapping area of the positive projections of both the adhesive layer 4000 and the conductive connection layer 3000 in the right direction.

[0075] Exemplarily, the value of the relationship C / H1 between the length of the overlapping section in the thickness direction Y of the electrode assembly 1000 and the length of the conductive connection layer 3000 in the thickness direction Y of the electrode assembly 1000 can be 0.75, 0.77, 0.79, 0.81, 0.83, 0.85, 0.87, 0.89, 0.91, 0.93, 0.95, 0.97, 0.99, 1, etc., and it can also be any value within the range of ≥0.75.

[0076] According to some embodiments of the present application, along the thickness direction Y of the electrode assembly 1000, the distance between the upper edge of the adhesive layer 4000 and the upper edge of the current collector 1110 is less than the distance between the upper edge of the conductive connection layer 3000 and the upper edge of the current collector 1110. The upper edge of the adhesive layer 4000, the upper edge of the current collector 1110, and the upper edge of the conductive connection layer 3000 are located on the same side of the electrode assembly 1000 in the thickness direction Y of the electrode assembly 1000. Please refer to Figure 3 , and this same side is the upper side in the thickness direction Y of the electrode assembly 1000 in the figure. By controlling the distance between the upper edge of the adhesive layer 4000 and the upper edge of the current collector 1110 to be less than the distance between the upper edge of the conductive connection layer 3000 and the upper edge of the current collector 1110, the adhesive layer 4000 can produce a better resistance to the pulling force between the current collector 1110 and the tab 2000, which is more beneficial to reducing the probability of breakage at the connection between the tab 2000 and the current collector 1110.

[0077] Figure 4 This is a schematic diagram of the connection between the current collector 1110 and the tab 2000 provided by the embodiments of the present application. In the figure, T refers to the height of the burr generated by welding, T1 refers to the thickness of the tab 2000, and T2 refers to the thickness of the adhesive layer 4000.

[0078] According to some embodiments of the present application, along the thickness direction Z of the electrode tab 1100, the thickness of the adhesive layer 4000 is T2, and 10 μm ≤ T2 ≤ 60 μm. The thicker the adhesive layer 4000, the stronger the resistance to the pulling force between the current collector 1110 and the electrode tab 2000 towards the winding start end, and the stronger the protection against the initial damage caused by the conductive connection layer 3000 provided on the current collector 1110, thereby reducing the probability of breakage at the connection between the electrode tab 2000 and the current collector 1110. The thinner the adhesive layer 4000, the more beneficial it is to control the volume of the entire electrode assembly 1000, and thus beneficial to the energy density of the secondary battery. By controlling the thickness of the adhesive layer 4000 to satisfy 10 μm ≤ T2 ≤ 60 μm, the probability of breakage at the connection between the electrode tab 2000 and the current collector 1110 and the energy density of the secondary battery can be taken into account.

[0079] Exemplarily, the thickness T2 of the adhesive layer 4000 can be 10 μm, 15 μm, 20 μm, 25 μm, 30 μm, 35 μm, 40 μm, 45 μm, 50 μm, 55 μm, 60 μm, etc., or it can also be any value within the range of 10 μm to 60 μm.

[0080] According to some embodiments of the present application, the adhesive layer 4000 can be formed by selecting an ultraviolet curable adhesive or a hot melt adhesive, etc. The materials of the adhesive layer 4000 include at least one of epoxy resin, polyurethane, acrylate, silicone, polyimide, fluorosilicone rubber, or ethylene-vinyl acetate copolymer. Among them, the epoxy resin can be a modified epoxy resin, such as an organosilicon-modified epoxy resin, an acrylate-modified epoxy resin, etc. Materials such as epoxy resin, polyurethane, acrylate, silicone, polyimide, fluorosilicone rubber, or ethylene-vinyl acetate copolymer have high bonding strength, good chemical resistance, good high-temperature resistance, and good electrical insulation performance. Using them as the materials of the adhesive layer 4000 can be suitable for the working environment of the secondary battery and can maintain the resistance to the pulling force between the current collector 1110 and the electrode tab 2000 for a long time.

[0081] According to some embodiments of the present application, the electrode assembly 1000 is cylindrical. The problem of breakage at the connection between the electrode tab 2000 and the current collector 1110 in the cylindrical electrode assembly 1000 is more serious. By providing the adhesive layer 4000 at the front end of the conductive connection layer 3000 between the electrode tab 2000 and the current collector 1110, the problem of breakage at the connection between the electrode tab 2000 and the current collector 1110 in the cylindrical electrode assembly 1000 can be significantly improved.

[0082] According to some embodiments of the present application, the electrode tab 2000 is welded to the current collector 1110, and the conductive connection layer 3000 is a welded metal layer.

[0083] The above electrode assembly 1000 can be encapsulated in a housing and injected with an electrolyte to form a secondary battery.

[0084] Among them, the housing can be a hard shell or a soft shell. For example, it can be a packaging bag made of aluminum plastic film.

[0085] The electrolyte plays a role in conducting ions between the positive electrode plate 1100 and the negative electrode plate 1100. There is no specific limitation on the type of the electrolyte in this application, and it can be selected according to requirements.

[0086] The electrolyte mainly includes electrolyte salts and solvents. The electrolyte salts can be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalate borate, lithium bis(oxalato)borate, lithium difluoro bis(oxalato)phosphate, and lithium tetrafluorooxalate phosphate. The solvents can be selected from at least one of ethylene carbonate, propylene carbonate, ethyl methyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butylene carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, sulfolane, dimethyl sulfone, methyl ethyl sulfone, and diethyl sulfone.

[0087] The electrolyte may also optionally include additives. For example, the additives can include negative electrode film-forming additives, positive electrode film-forming additives, and can also include additives that can improve certain performance of the battery, such as additives for improving the overcharge performance of the battery, additives for improving the high-temperature or low-temperature performance of the battery, etc.

[0088] The above introduced the structure and other contents of the secondary battery. Next, the preparation method of the secondary battery will be introduced.

[0089] The setting order of the adhesive layer and the conductive connection layer in the secondary battery during the preparation process is not limited. For example, the conductive connection layer can be set first. Specifically, it can be: First, perform metal laser welding to weld the tab and the current collector foil; Secondly, insert a wedge-shaped hollow fixture into the tab and the current collector foil on the side close to the non-terminal to form a certain angle; Then, slowly withdraw the wedge-shaped fixture while dropping glue; Finally, use silicone to press flat so that the glue fully bonds the tab and the current collector foil to obtain a secondary battery. Or the adhesive layer can be set first. Specifically, it can be: Bond the adhesive tape between the tab and the current collector to form an adhesive layer; Weld the tab and the current collector on the side of the adhesive layer away from the starting end of winding to form a conductive connection layer to obtain a secondary battery.

[0090] Next, the present application will be specifically described through examples and comparative examples.

[0091] Example 1

[0092] A secondary battery (cell design: lithium cobalt oxide / graphite, 4.5V system, capacity 50mAh), the assembly process is as follows:

[0093] Prepare the positive current collector 1110 and the negative current collector 1110:

[0094] Weld the tab 2000 to the current collector 1110, and apply glue in the area between the tab 2000 and the current collector 1110 on the side of the formed conductive connection layer 3000 close to the start end of winding (the main substrate of the glue is fluororubber, the mechanical strength is enhanced by adding nano-silica; a phosphate plasticizer is added to improve the interfacial compatibility, and a peroxide crosslinking agent is added to obtain the final glue; the specific mass ratio is as follows: fluororubber( A - 500) 50%, nano - silica (fumed) 13%, triphenyl phosphate (TPP) 6%, dicumyl peroxide (DCP) 2%, TAIC co - crosslinking agent 1.5%, acetone 27.5%, and the viscosity of this glue is 3000 Pa·s to 5000 Pa·s), to form a current collector 1110. This current collector 1110 serves as both the positive - electrode current collector and the negative - electrode current collector respectively. Among them, the current collector 1110 of the negative - electrode current collector uses copper foil, and the current collector 1110 of the positive - electrode current collector uses aluminum foil. The thickness of the current collector 1110 is 10 μm, the width of the current collector 1110 is 8 mm, the thickness (T1) of the tab 2000 is 60 μm, the width of the tab 2000 is 8 mm, the length (H) of the overlapping area of the current collector 1110 and the tab 2000 in the thickness direction of the electrode assembly 1000 is 6 mm, the length (W1) of the conductive connection layer 3000 in the winding direction X of the electrode assembly 1000 is 4 mm, the distance (W3) between the first edge 2100 of the tab 2000 and the third edge 3100 of the conductive connection layer 3000 is 2 mm, the distance (W2) between the second edge 2200 of the tab 2000 and the fourth edge 3200 of the conductive connection layer 3000 is 2 mm, the length (H1) of the conductive connection layer 3000 in the thickness direction of the electrode assembly 1000 is 4 mm, the distance (H2) between the uppermost edge of the overlapping area of the current collector 1110 and the tab 2000 and the conductive connection layer 3000 is 1 mm, the distance (H3) between the lowermost edge of the overlapping area of the current collector 1110 and the tab 2000 and the conductive connection layer 3000 is 1 mm, the height (T) of the burrs generated by welding is 120 μm, the thickness (T2) of the adhesive layer 4000 is 30 μm, the length (A) of the adhesive layer 4000 in the winding direction X of the electrode assembly 1000 is 1 mm, the length of the adhesive layer 4000 in the thickness direction of the electrode assembly 1000 is 6 mm, the distance (A1) between the first edge 2100 and the fifth edge 4100 is equal to the distance (A2) between the third edge 3100 and the fifth edge 4100, and the distance (B1) between the uppermost edge of the overlapping area of the current collector 1110 and the tab 2000 and the adhesive layer 4000 is equal to the distance (B2) between the lowermost edge of the overlapping area of the current collector 1110 and the tab 2000 and the adhesive layer 4000.

[0095] Preparation of the negative - electrode plate 1100:

[0096] Mix 95 wt% of the negative - electrode active - material particles graphite, 2 wt% of the conductive agent acetylene black, 2 wt% of the thickening agent sodium carboxymethyl cellulose, and 1 wt% of the binder styrene - butadiene rubber, add an appropriate amount of deionized water and stir well to obtain a negative - electrode active slurry. The negative - electrode active slurry is applied at 0.2 g / 1540.25 mm 2After the coating amount is coated on the two surfaces of the negative electrode current collector 1110, drying, cold pressing, and cutting are carried out to obtain the negative electrode sheet 1100.

[0097] Preparation of the positive electrode sheet 1100:

[0098] Mix 96 wt% lithium cobaltate, 2 wt% superconducting carbon black, and 2 wt% binder polyvinylidene fluoride, use N-methylpyrrolidone as the solvent, and fully stir and mix to obtain the positive electrode active paste. Coat the positive electrode active paste on the two surfaces of the positive electrode current collector 1110 at a coating amount of 0.3 g / 1540.25 mm 2 After that, drying is carried out to obtain the positive electrode active paste layer; then cold pressing and cutting are carried out to obtain the positive electrode sheet 1100.

[0099] Preparation of the electrode assembly 1000:

[0100] Stack the negative electrode sheet 1100, the first separator, the positive electrode sheet 1100, and the second separator, and then wind them to form a cylindrical electrode assembly 1000.

[0101] Preparation of the secondary battery:

[0102] Place the electrode assembly 1000 into the housing, inject the electrolyte, and then carry out formation to obtain the secondary battery. Among them, the solute in the electrolyte is 2 mol / L lithium hexafluorophosphate, and the solvent in the electrolyte is ethylene carbonate and dimethyl carbonate with a volume ratio of 1:1.

[0103] Example 2

[0104] In this example, except that the length (B) of the adhesive layer 4000 in the thickness direction of the electrode assembly 1000 is adjusted to 5 mm, the rest of the content is the same as that in Example 1.

[0105] Example 3

[0106] In this example, except that the length (B) of the adhesive layer 4000 in the thickness direction of the electrode assembly 1000 is adjusted to 4 mm, the rest of the content is the same as that in Example 1.

[0107] Example 4

[0108] In this example, except that the length (B) of the adhesive layer 4000 in the thickness direction of the electrode assembly 1000 is adjusted to 3 mm, the rest of the content is the same as that in Example 1.

[0109] Example 5

[0110] In this example, except that the length (B) of the adhesive layer 4000 in the thickness direction of the electrode assembly 1000 is adjusted to 2 mm, the rest of the content is the same as that in Example 1.

[0111] Example 6

[0112] In this example, except that the length (A) of the adhesive layer 4000 in the winding direction X of the electrode assembly 1000 is adjusted to 0.4 mm, the rest is the same as in Example 1.

[0113] Example 7

[0114] In this example, except that the length (A) of the adhesive layer 4000 in the winding direction X of the electrode assembly 1000 is adjusted to 0.5 mm, the rest is the same as in Example 1.

[0115] Example 8

[0116] In this example, except that the length (A) of the adhesive layer 4000 in the winding direction X of the electrode assembly 1000 is adjusted to 1.5 mm, the rest is the same as in Example 1.

[0117] Example 9

[0118] In this example, except that the length (A) of the adhesive layer 4000 in the winding direction X of the electrode assembly 1000 is adjusted to 2 mm, the rest is the same as in Example 1.

[0119] Example 10

[0120] In this example, except that an adhesive layer 4000 is provided at the front end of the conductive connection layer 3000, adhesive layers 4000 are also prepared at the rear end, upper end, and lower end of the conductive connection layer 3000 by the same method. The size and corresponding position of the adhesive layer 4000 at the rear end of the conductive connection layer 3000 are the same as those of the adhesive layer 4000 at the front end of the conductive connection layer 3000. At the same time, the adhesive layers 4000 at the upper end and lower end of the conductive connection layer 3000 connect the adhesive layers 4000 at the front end and rear end of the conductive connection layer 3000 to form an overall "square frame" - shaped adhesive layer 4000. The rest is the same as in Example 1.

[0121] Example 11

[0122] In this example, except that the adhesive layer 4000 is prepared using adhesive tape (selecting polytetrafluoroethylene (PTFE) as the base material layer and a modified acrylic adhesive as the first adhesive layer, and laminating the first adhesive layer on the base material layer to form a first adhesive layer with a thickness of 10 μm. A second adhesive layer with a thickness of 10 μm is prepared in a similar manner.), the rest is the same as in Example 1.

[0123] Among them, the process of preparing the adhesive layer 4000 using adhesive tape includes: reserving the position of the conductive connection layer 3000 in the overlapping area of the tab 2000 and the current collector 1110. The overlapping area, the position and size of the conductive connection layer 3000 are the same as those in Embodiment 1. Adhesive tape is adhered to the overlapping area around the reserved position, and then the conductive connection layer 3000 is formed by welding to connect the tab 2000 and the current collector 1110.

[0124] Embodiment 12

[0125] In this embodiment, except that the thickness T2 of the adhesive layer 4000 is adjusted to 5 μm, the rest of the content is the same as that in Embodiment 1.

[0126] Embodiment 13

[0127] In this embodiment, except that the thickness T2 of the adhesive layer 4000 is adjusted to 10 μm, the rest of the content is the same as that in Embodiment 1.

[0128] Embodiment 14

[0129] In this embodiment, except that the thickness T2 of the adhesive layer 4000 is adjusted to 20 μm, the rest of the content is the same as that in Embodiment 1.

[0130] Embodiment 15

[0131] In this embodiment, except that the thickness T2 of the adhesive layer 4000 is adjusted to 40 μm, the rest of the content is the same as that in Embodiment 1.

[0132] Embodiment 16

[0133] In this embodiment, except that the thickness T2 of the adhesive layer 4000 is adjusted to 50 μm, the rest of the content is the same as that in Embodiment 1.

[0134] Embodiment 17

[0135] In this embodiment, except that the thickness T2 of the adhesive layer 4000 is adjusted to 60 μm, the rest of the content is the same as that in Embodiment 1.

[0136] Embodiment 18

[0137] In this embodiment, except that the thickness T2 of the adhesive layer 4000 is adjusted to 70 μm, the rest of the content is the same as that in Embodiment 1.

[0138] Performance tests are conducted on each secondary battery. The specific tests include:

[0139] Probability test for cracks or fractures in the current collector 1110: Place the secondary battery to be tested on the test platform. At room temperature of 25 °C, charge the secondary battery that has reached a constant temperature at a constant current of 0.2C until the voltage reaches the cut-off voltage, then charge it at a constant voltage of the cut-off voltage until the current is 0.02C, and discharge it at 0.2C until the voltage is 3.0V. One charge-discharge cycle is a cycle process; a total of 800 cycles are carried out. After the cycle test is completed, disassemble the electrode assembly 1000, record the occurrence of cracks or fractures in the current collector 1110. A total of 10 battery cells are tested, and the proportion of battery cells with cracks or fractures is calculated and obtained.

[0140] The main parameter control and test results of the adhesive layer 4000 in each example and comparative example are shown in Table 1:

[0141]

[0142]

[0143] It can be seen from the above table that in Example 1, by coating glue in the area between the tab and the current collector on the side of the conductive connection layer close to the starting end of winding to form an adhesive layer, compared with Comparative Example 1, the proportion of cracks or fractures in the current collector can be significantly reduced.

[0144] The adhesive layer area of Examples 1 to 4 satisfies not less than 3 mm 2 , compared with Example 5, has a larger adhesive layer area, has a stronger resistance to the pulling force between the current collector and the tab towards the starting end of winding, has a stronger protective effect on the initial damage caused by the conductive connection layer on the current collector, and thus the probability of fracture at the connection between the tab and the current collector is lower. Similarly, the adhesive layer area of Examples 1 and 7 to 9 satisfies not less than 3 mm 2 , compared with Example 6, has a larger adhesive layer area, has a stronger resistance to the pulling force between the current collector and the tab towards the starting end of winding, has a stronger protective effect on the initial damage caused by the conductive connection layer on the current collector, and thus the probability of fracture at the connection between the tab and the current collector is lower.

[0145] For Examples 1 and 7 to 9, the value of the relationship A / W3 between the length of the adhesive layer in the winding direction X of the electrode assembly and the distance between the first edge of the tab and the third edge of the conductive connection layer satisfies 0.25 to 1. Compared with Example 6, the value of the relationship A / W3 between the length of the adhesive layer in the winding direction X of the electrode assembly and the distance between the first edge of the tab and the third edge of the conductive connection layer is larger, has a stronger resistance to the pulling force between the current collector and the tab towards the starting end of winding, has a stronger protective effect on the initial damage caused by the conductive connection layer on the current collector, and thus the probability of fracture at the connection between the tab and the current collector is lower.

[0146] The length of the adhesive layer in Embodiment 1 and Embodiments 7 to 9 in the winding direction X of the electrode assembly satisfies 0.5 mm to 2 mm. Compared with Embodiment 6, the length of the adhesive layer in the winding direction X of the electrode assembly is longer, the resistance to the pulling force between the current collector and the tab towards the winding starting end is stronger, and the protection effect on the initial damage caused by the conductive connection layer on the current collector is stronger. As a result, the probability of breakage at the connection between the tab and the current collector is lower.

[0147] The length B of the adhesive layer in Embodiments 1 to 3 in the first direction Y, the length of the overlapping region between the current collector and the tab in the first direction Y, and the length of the conductive connection layer in the first direction Y satisfy H1 ≤ B ≤ H. Compared with Embodiments 4 and 5, the length of the adhesive layer in the first direction Y is longer, the resistance to the pulling force between the current collector and the tab towards the winding starting end is stronger, and the protection effect on the initial damage caused by the conductive connection layer on the current collector is stronger. As a result, the probability of breakage at the connection between the tab and the current collector is lower.

[0148] The relationship between the length of the overlapping segment of the projection of the adhesive layer in Embodiments 1 to 4 in the winding direction X of the electrode assembly and the projection of the conductive connection layer in the winding direction X of the electrode assembly in the first direction Y and the length of the conductive connection layer in the first direction Y is that C / H1 satisfies not less than 0.75. Compared with Embodiment 5, the length of the overlapping segment of the projection of the adhesive layer in the winding direction X of the electrode assembly and the projection of the conductive connection layer in the winding direction X of the electrode assembly in the first direction Y is larger, the resistance to the pulling force between the current collector and the tab towards the winding starting end is stronger, and the protection effect on the initial damage caused by the conductive connection layer on the current collector is stronger. As a result, the probability of breakage at the connection between the tab and the current collector is lower.

[0149] Through the data comparison between Embodiment 10 and Embodiment 1, it can be obtained that the method of setting the adhesive layer around the conductive connection layer can also better reduce the proportion of cracks or fractures in the current collector.

[0150] Through the data comparison between Embodiment 11 and Embodiment 1, it can be obtained that using the method of adhesive tape and the method of glue to form the adhesive layer can both significantly reduce the proportion of cracks or fractures in the current collector.

[0151] The thickness of the adhesive layer in Example 1, Example 13, and Example 17 satisfies 10 μm to 60 μm. Compared with Example 12, the adhesive layer is thicker, providing a stronger resistance to the pulling force between the current collector and the tab towards the winding starting end, and a stronger protection against the initial damage caused by the conductive connection layer on the current collector. As a result, the probability of breakage at the connection between the tab and the current collector is lower. Compared with Example 18, the adhesive layer is thinner, which is more conducive to controlling the volume of the entire electrode assembly and thus beneficial to the energy density of the secondary battery.

[0152] The above are only specific embodiments of the present application and are not intended to limit the present application. For those skilled in the art, various changes and modifications can be made to the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A secondary battery, characterized in that: The secondary battery includes an electrode assembly and a pole ear, the pole ear extends out of the electrode assembly along a first direction, the electrode assembly is a winding structure, the electrode assembly includes a pole sheet, the pole sheet includes a current collector, a conductive connecting layer and an adhesive layer are provided between the pole ear and the current collector, the pole ear and the current collector are electrically connected through the conductive connecting layer, the adhesive layer bonds the pole ear and the current collector, and the adhesive layer is provided on one side of the conductive connecting layer close to the starting end of the winding.

2. The secondary battery according to claim 1, characterized in that: The area of ​​the adhesive layer bonding the current collector is not less than 3mm 2 .

3. The secondary battery according to claim 1 or 2, characterized in that: Along the winding direction of the electrode assembly, the length of the adhesive layer is A, the electrode ear includes a first edge and a second edge arranged opposite to each other, compared with the second edge, the first edge is close to the winding center of the electrode assembly, the conductive connection layer includes a third edge and a fourth edge arranged opposite to each other, compared with the fourth edge, the third edge is close to the winding center of the electrode assembly, the distance between the first edge and the third edge is W3, 0.25W3≤A≤W3.

4. The secondary battery according to claim 3, characterized in that: 0.5mm≤A≤2mm.

5. The secondary battery according to claim 3, characterized in that: Along the winding direction of the electrode assembly, the adhesive layer includes a fifth edge and a sixth edge arranged opposite to each other. Compared with the fifth edge, the sixth edge is closer to the winding center of the electrode assembly. The distance between the first edge and the fifth edge is A1, and the distance between the third edge and the fifth edge is A2, and |A1-A2|≤2mm.

6. The secondary battery according to claim 1 or 2, characterized in that: Along the first direction, the length of the adhesive layer is B, the length of the conductive connection layer is H1, the length of the overlapping area between the electrode tab and the current collector is H, and H1≤B≤H.

7. The secondary battery according to claim 1 or 2, characterized in that: The projection of the adhesive layer along the winding direction of the electrode assembly and the projection of the conductive connecting layer along the winding direction of the electrode assembly have an overlapping segment, the length of the overlapping segment in the first direction is C, the length of the conductive connecting layer in the first direction is H1, and C≥0.75H1.

8. The secondary battery according to claim 1 or 2, characterized in that: Along the first direction, the distance between the upper edge of the adhesive layer and the upper edge of the current collector is smaller than the distance between the upper edge of the conductive connection layer and the upper edge of the current collector, and the upper edge of the adhesive layer, the upper edge of the current collector and the upper edge of the conductive connection layer are located on the same side of the electrode assembly in the first direction.

9. The secondary battery according to claim 1 or 2, characterized in that: Along the thickness direction of the pole piece, the thickness of the adhesive layer is T2, 10 μm≤T2≤60 μm.

10. The secondary battery according to claim 1, characterized in that: The material of the adhesive layer includes at least one of epoxy resin, polyurethane, acrylate, silicone, polyimide, fluorosilicone rubber or ethylene-vinyl acetate copolymer.

11. The secondary battery according to claim 1, characterized in that: The electrode assembly is cylindrical.

12. The secondary battery according to claim 1, characterized in that: The electrode tab is connected to the current collector by welding, and the conductive connection layer is a welding metal layer.

13. A method for preparing a secondary battery according to any one of claims 1 to 12, characterized in that: The method comprises: The electrode sheet and the separator are stacked and wound to obtain an electrode assembly, wherein the electrode sheet includes a current collector; Welding the electrode tab and the current collector to form a conductive connection layer; The first position where the electrode tab and the current collector are not welded is opened, the first position is located on the side of the conductive connection layer close to the winding start end, and glue is dripped into the first position to form an adhesive layer.

14. A method for preparing a secondary battery according to any one of claims 1 to 12, characterized in that: The method comprises: The electrode sheet and the separator are stacked and wound to obtain an electrode assembly, wherein the electrode sheet includes a current collector; Adhere adhesive tape to the surface of the current collector, wherein the adhesive tape is located between the electrode tab and the current collector to form an adhesive layer; The electrode tab and the current collector are welded to form a conductive connection layer, and the adhesive layer is located on a side of the conductive connection layer close to the winding start end.

15. An electronic device, characterized in that: The electronic device comprises the secondary battery according to any one of claims 1 to 12 or the secondary battery prepared by the method according to any one of claims 13 to 14.

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