Secondary battery and electronic device
Patent Information
- Authority / Receiving Office
- WO · WO
- Patent Type
- Applications
- Current Assignee / Owner
- Filing Date
- 2024-03-27
- Publication Date
- 2026-08-13
Smart Images
Figure CN2024084046_13082026_PF_FP_ABST
Abstract
Description
Secondary batteries and electronic devices Technical Field
[0001] This application relates to the field of energy storage technology, and in particular to a secondary battery and electronic device. Background Technology
[0002] The tabs of the secondary battery are welded to the current collector of the electrode assembly to serve as the positive and negative leads of the secondary battery. In related technologies, during the cycling process of the secondary battery, the thickness of the electrode sheet of the electrode assembly repeatedly expands, causing the wound electrode assembly to repeatedly contract and expand. During this process, the weld edge formed by the tabs and the current collector is subjected to stress, which can easily lead to damage and breakage of the current collector.
[0003] Summary of the Invention
[0004] In view of this, this application provides a secondary battery and an electronic device that is beneficial to improving the tensile strength of the electrode tab and electrode welding part, and to reducing the risk of electrode damage.
[0005] In a first aspect, this application provides a secondary battery, comprising an electrode assembly and a first tab. The electrode assembly includes a first electrode, a second electrode, and a separator disposed between the first and second electrodes. The first electrode, the second electrode, and the separator are stacked and wound to form a wound structure. The first electrode includes a first current collector and a first active material layer disposed on the first current collector. The first current collector has a first connection region, and the first connection region does not have the first active material layer. The first tab is welded to the first connection region, and the first connection region includes multiple welding areas arranged along the winding direction of the electrode assembly. Each welding area has at least one weld mark formed by welding the first tab to the first connection region. Along the winding direction of the electrode assembly, the weld mark in the welding area closest to the winding center of the electrode assembly has the lowest welding strength.
[0006] In the above embodiments, among the multiple welding zones, the welding strength of the weld mark in the welding zone closest to the winding center of the electrode assembly along the winding direction of the electrode assembly is the smallest. This reduces the damage of the welding to the first current collector in the welding zone closest to the winding center of the electrode assembly, thereby improving the tensile strength of the weld mark in the welding zone closest to the winding center of the electrode assembly. This helps to resist the pulling force on the welding part of the first electrode tab and the first current collector along the winding structure from the outside to the inside when the electrode assembly expands, and helps to reduce the risk of electrode damage.
[0007] In one or more of the above embodiments, along the winding direction of the electrode assembly from the outside to the inside, the welding strength of the solder marks in different welding zones gradually decreases.
[0008] In the above embodiments, in the winding direction of the electrode assembly, the closer the solder mark is to the winding center of the electrode assembly, the lower the welding strength, and the lower the degree of damage to the strength of the first current collector structure caused by the welding. This is beneficial to improving the tensile strength of the solder mark of the first electrode sheet, to resisting the tensile force on the welding part between the first electrode tab and the first current collector along the winding structure from the outside to the inside when the electrode assembly expands, and to reducing the risk of damage to the first electrode sheet.
[0009] In one or more of the above embodiments, there is a welding pull between the first electrode tab and the first current collector at each solder mark, and the welding pull at the solder mark in different welding areas gradually decreases along the winding direction of the electrode assembly from the outside to the inside.
[0010] In the above embodiments, in the winding direction of the electrode assembly, the closer the welding is to the winding center of the electrode assembly, the less damage it causes to the structural strength of the first current collector. This is beneficial for improving the tensile strength of the weld at the first electrode plate, for resisting the tensile force exerted on the welded portion between the first electrode tab and the first current collector along the winding structure from the outside to the inside when the electrode assembly expands, and for reducing the risk of damage to the first electrode plate.
[0011] In one or more of the above embodiments, the welding pull force between the first electrode tab and the first current collector at each solder joint is F, which satisfies 1N≤F≤80N.
[0012] In the above embodiments, when 1N≤F≤80N is satisfied, it is beneficial to reduce the risk of insufficient welding pull and poor welding at the weld with the smallest welding pull, and also beneficial to reduce the risk of excessive welding pull and damage to the first current collector at the weld with the largest welding pull.
[0013] [Amended according to Rule 26, 29.05.2026] In one or more of the above embodiments, the number of welding areas is N. Along the winding direction of the electrode assembly, the i-th welding area is closer to the winding center of the electrode assembly than the (i+1)-th welding area, and the welding pull force of the weld in the i-th welding area is F. i The welding pull force of the weld in the (i+1)th welding zone is F. i+1 , satisfying 1N≤F i+1 -F i ≤5N. N is a positive integer greater than or equal to 2, and i is a positive integer greater than or equal to 1 and less than N.
[0014] In the above embodiments, the difference in welding strength between the weld marks in two adjacent welding areas is between 1N and 5N, which ensures that the structural strength difference between the two adjacent welding areas is not too large. This helps to reduce the risk of incomplete welding due to insufficient welding pull and also helps to reduce the risk of damage to the first current collector due to excessive welding pull.
[0015] In one or more of the above embodiments, the number of solder marks is S, and the average welding pull force of the S solder marks is K, satisfying 5N≤K≤9N. S is a positive integer greater than or equal to 2.
[0016] In the above embodiments, when K satisfies the range of 5N≤K≤9N, it is beneficial to reduce the risk of the first electrode tab falling off due to the overall welding pull force of the first electrode tab and the first electrode sheet being too small. It allows the welding strength of some solder marks to be reduced in order to improve the structural strength of the first electrode sheet. It is also beneficial to realize that the welding pull force at the solder mark in different welding areas gradually decreases along the winding direction of the electrode assembly from the outside to the inside, thereby reducing the risk of electrode sheet damage.
[0017] In one or more of the above embodiments, along the winding direction of the electrode assembly from the outside to the inside, the height of the solder marks in different welding areas gradually decreases in the thickness direction of the first electrode sheet.
[0018] In the above embodiments, the solder height in different welding zones gradually decreases along the winding direction of the electrode assembly from the outside to the inside. This results in a lower degree of damage to the structural strength of the first current collector caused by welding closer to the winding center of the electrode assembly in the winding direction. This is beneficial for improving the tensile strength of the solder joint of the first electrode sheet, resisting the tensile force exerted on the welding portion between the first electrode tab and the first current collector along the winding structure from the outside to the inside when the electrode assembly expands, and reducing the risk of damage to the first electrode sheet.
[0019] In one or more of the above embodiments, the height of the soldered part in the thickness direction of the first electrode is H, which satisfies 1um≤H≤100um.
[0020] In the above embodiments, when 1um≤H≤100um is satisfied, it is beneficial to reduce the risk of poor welding due to insufficient welding pull at the weld with the smallest welding pull, and also beneficial to reduce the risk of damage to the first current collector due to excessive welding pull at the weld with the largest welding pull.
[0021] [Amended according to Rule 26, 29.05.2026] In one or more of the above embodiments, the number of welding areas is N. Along the winding direction of the electrode assembly, the i-th welding area is closer to the winding center of the electrode assembly than the (i+1)-th welding area. The height of the solder mark of the i-th welding area in the thickness direction of the first electrode sheet is H. i The height of the solder mark in the (i+1)th welding area in the thickness direction of the first electrode is H. i+1 , satisfying 1um≤H i+1 -H i ≤10um. N is a positive integer greater than or equal to 2, and i is a positive integer greater than or equal to 1 and less than N.
[0022] In the above embodiments, the difference in the height of the weld stamps in two adjacent welding areas is between 1um and 10um, so that the difference in structural strength between the two adjacent welding areas is not too large. This helps to reduce the risk of incomplete welding due to insufficient welding pull and also helps to reduce the risk of damage to the first current collector due to excessive welding pull.
[0023] In one or more of the above embodiments, the number of solder marks is S, and the average height of the S solder marks is L, satisfying 5um ≤ L ≤ 15um. S is a positive integer greater than or equal to 2.
[0024] In the above embodiments, when L satisfies the range of 5um≤L≤15um, it is beneficial to reduce the risk of the first electrode tab falling off due to the overall welding pull force of the first electrode tab and the first electrode sheet being too small. It allows the welding strength of some solder marks to be reduced in order to improve the structural strength of the first electrode sheet. It is also beneficial to realize that the welding pull force at the solder mark in different welding areas gradually decreases along the winding direction of the electrode assembly from the outside to the inside, thereby reducing the risk of electrode sheet damage.
[0025] In one or more of the above embodiments, the edge of the first tab on the side closer to the winding center of the electrode assembly in the winding direction from the outside to the inside of the electrode assembly is defined as the first edge, the minimum distance of the solder marks in the multiple solder areas from the first edge is A, the total width of the multiple solder marks is W, and the maximum distance of the multiple solder marks from the first edge is B = A + W.
[0026] In one or more of the above embodiments, 0.1mm≤A≤1mm is satisfied.
[0027] In the above embodiments, the distance between the solder mark closest to the first edge and the first edge is between 0.1mm and 1mm, so that the solder mark is not too close to the first edge, which is beneficial to the welding operation, and the solder mark is not too far from the first edge, which is beneficial to increasing the area of the welding area and improving the utilization rate of the first connection area.
[0028] In one or more of the above embodiments, 1mm≤W≤3mm is satisfied.
[0029] In the above embodiments, when 1mm≤W≤3mm is satisfied, the area occupied by multiple solder marks is not too small, which is beneficial to increasing the total area of multiple welding areas, which is beneficial to increasing the connection strength between the first electrode tab and the first electrode sheet, allowing the welding strength of some solder marks to be reduced in order to improve the structural strength of the first electrode sheet, and is beneficial to realizing that the welding pull force at the solder mark in different welding areas gradually decreases along the winding direction of the electrode assembly from the outside to the inside, which is beneficial to reducing the risk of electrode sheet damage.
[0030] In one or more of the above embodiments, 1.1mm≤B≤4mm is satisfied.
[0031] In one or more of the above embodiments, along the winding direction of the electrode assembly from the outside to the inside, the first current collector includes a blank foil segment, a coated segment, and a first active material layer arranged sequentially. The coated segment is provided with a first active material layer, the blank foil segment is not provided with a first active material layer, at least a portion of the blank foil segment is located at the outermost ring of the first electrode, and the first connection area is located in the blank foil segment and at the outermost ring of the first electrode.
[0032] In the above embodiments, among the multiple welding zones, the welding strength of the weld mark in the welding zone closest to the winding center of the electrode assembly along the winding direction of the electrode assembly is the smallest. This reduces the damage of welding to the first current collector in the welding zone closest to the winding center of the electrode assembly, thereby improving the tensile strength of the weld mark in the welding zone closest to the winding center of the electrode assembly and reducing the risk of electrode damage.
[0033] In one or more of the above embodiments, the shape of the solder mark includes at least one of rhombus, square, and circle.
[0034] In a second aspect, this application also provides an electronic device comprising a secondary battery as described in any of the above embodiments.
[0035] In the above embodiments, the probability of damage to the electrodes of the secondary battery is reduced, which helps to improve the reliability of electronic devices.
[0036] The secondary battery of this application includes an electrode assembly and tabs. The electrode assembly includes a first electrode, a second electrode, and a separator disposed between the first and second electrodes, all stacked and wound. The first electrode includes a first current collector and a first active material layer, all stacked. The first current collector has a first connection area without the first active material layer. The tab is welded to the first connection area, which includes multiple welding areas arranged along the winding direction of the electrode assembly. Each welding area has at least one solder mark. Along the winding direction of the electrode assembly, the solder mark in the welding area closest to the winding center of the electrode assembly has the lowest welding strength. This helps reduce the damage to the first current collector caused by welding, thereby improving the tensile strength of the solder mark in the welding area closest to the winding center of the electrode assembly. This helps resist the tensile force exerted on the welded portion between the first tab and the first current collector along the winding structure from the outside to the inside when the electrode assembly expands, thus reducing the risk of damage to the first electrode. Attached Figure Description
[0037] Figure 1 is a schematic diagram of the structure of a secondary battery provided in an embodiment of this application.
[0038] Figure 2 is an exploded view of a secondary battery provided in an embodiment of this application.
[0039] Figure 3 is a side view of an electrode assembly provided in an embodiment of this application.
[0040] Figure 4 is a partial top view of the first electrode and the first electrode tab provided in an embodiment of this application.
[0041] Figure 5 is a partial side view of the first electrode and the first electrode tab provided in an embodiment of this application.
[0042] Figure 6 is a partial top view of the first electrode and the first electrode tab provided in another embodiment of this application.
[0043] Figure 7 is a partial top view of the first electrode and the first electrode tab provided in another embodiment of this application.
[0044] Figure 8 is a schematic diagram of an electronic device provided in an embodiment of this application.
[0045] Key Component Symbols Explanation: Secondary Battery 100 Casing 10 Electrode Assembly 20 First Electrode 21 First Current Collector 211 First Connection Area 2111 Welding Area 211a Coated Section 2112 Empty Foil Section 2113 First Active Material Layer 212 Second Electrode 22 Second Current Collector 221 Second Active Material Layer 222 Separator 23 First Tab 30 Solder Mark 203 Second Tab 40 Electrode Assembly Winding Direction X: Outer-to-inner winding direction of the electrode assembly X': Length direction of the first electrode X”: Width direction of the first electrode Y: Thickness direction of the first electrode Z: Device Body 200 Electronic Device 1000 Detailed Implementation
[0046] The technical solutions of the embodiments of this application will be described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments.
[0047] It should be noted that in this application, the center of the electrode refers to the center of gravity of the layered structure electrode. Understandably, the center of gravity of the layered structure can be determined by the suspension method. The layered structure is suspended by a thin thread, and a straight line is drawn vertically from the starting point of the thin thread. The layered structure is then suspended again from a different endpoint than the first time, and another straight line is drawn in the same way. The intersection of the two straight lines is the center of gravity of the planar shape.
[0048] It should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," and "fixing" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection. When a component is considered to be "connected" to another component, it can be directly connected to the other component or there may be an intervening component present. When a component is considered to be "located" to another component, it can be directly mounted on the other component or there may be an intervening component present.
[0049] Unless otherwise stated, the term "multiple" as used herein refers to two or more.
[0050] The terms “first”, “second”, etc., are used only to distinguish different objects and should not be construed as indicating or implying relative importance or implying the quantity, specific order, or primary and secondary relationship of the indicated technical features.
[0051] It should be noted that when a parameter is greater than, equal to or less than a certain endpoint value, it should be understood that the endpoint value is allowed to have a tolerance of ±5%.
[0052] It should be understood that the dimensions of layers, regions, pillars, or protrusions shown in the accompanying drawings are provided for better understanding and convenience of description, and this application is not limited to the dimensions shown in the drawings. For the sake of clarity, elements unrelated to the description have been omitted from the details of this specification.
[0053] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application.
[0054] In related technologies, during the cycling process of a secondary battery, the thickness of the electrode sheet of the electrode assembly expands repeatedly, causing the wound electrode assembly to repeatedly contract and expand. During this process, the edge of the weld formed by the welding of the electrode tab and the current collector is subjected to stress, which can easily lead to damage and breakage of the current collector.
[0055] This application discloses a secondary battery, which includes an electrode assembly and tabs. The electrode assembly includes a first electrode, a second electrode, and a separator disposed between the first and second electrodes. The first electrode, the second electrode, and the separator are stacked and wound to form a wound structure. The first electrode includes a first current collector and a first active material layer disposed on the first current collector. The first current collector has a first connection region, and the first connection region does not have the first active material layer. The tabs are welded to the first connection region, which includes multiple welding areas arranged along the winding direction of the electrode assembly. Each welding area has at least one weld mark formed by welding the tabs to the first connection region. Along the winding direction of the electrode assembly, the weld mark in the welding area closest to the winding center of the electrode assembly has the lowest welding strength.
[0056] Among the multiple welding zones mentioned above, the welding strength of the weld mark in the welding zone closest to the winding center of the electrode assembly along the winding direction of the electrode assembly is the lowest. When the welding strength is low, it is beneficial to reduce the damage of welding to the first current collector, thereby improving the tensile strength of the weld mark in the welding zone closest to the winding center of the electrode assembly. It is also beneficial to resist the tensile force on the welding part of the first electrode tab and the first current collector along the winding structure from the outside to the inside when the electrode assembly expands, and to reduce the risk of damage to the first electrode sheet.
[0057] Some embodiments of this application will now be described with reference to the accompanying drawings. Unless otherwise specified, the following embodiments and features can be combined with each other.
[0058] Please refer to Figures 1 to 3. This application embodiment provides a secondary battery 100. The secondary battery 100 includes an electrode assembly 20. The electrode assembly 20 includes a first electrode 21, a second electrode 22, and a separator 23 disposed between the first electrode 21 and the second electrode 22. The first electrode 21 and the second electrode 22 have opposite polarities. The separator 23 is used to isolate the first electrode 21 and the second electrode 22. The first electrode 21, the second electrode 22, and the separator 23 are stacked and wound to form a wound structure.
[0059] In some embodiments, please refer to FIG3, the first electrode 21 includes a first current collector 211 and a first active material layer 212 disposed on the first current collector 211, the first active material layer 212 and the first current collector 211 being stacked.
[0060] In some embodiments, please refer to FIG3, the second electrode 22 includes a second current collector 221 and a second active material layer 222 disposed on the second current collector 221, the second active material layer 222 and the second current collector 221 being stacked.
[0061] In some embodiments, the first electrode 21 is an anode electrode and the second electrode 22 is a cathode electrode. In other embodiments, the first electrode 21 is a cathode electrode and the second electrode 22 is an anode electrode.
[0062] In some embodiments, the cathode electrode includes a cathode current collector and a cathode active material layer stacked together, and the anode electrode includes an anode current collector and an anode active material layer stacked together.
[0063] In some embodiments, the cathode current collector may be a metal layer comprising at least one of aluminum, nickel, tantalum, and titanium, such as aluminum foil. The anode current collector may be a metal layer comprising at least one of copper, nickel, tantalum, and titanium, such as copper foil.
[0064] In some embodiments, the cathode active material layer includes a cathode active material, which may include at least one of lithium cobalt oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium iron phosphate, lithium manganese iron phosphate, or lithium manganese oxide. The anode active material layer includes an anode active material, which may include at least one of graphite, hard carbon, soft carbon, silicon, silicon-oxygen materials, and silicon-carbon materials.
[0065] In some embodiments, the separator 23 is an insulating film material such as a polyethylene film, a polypropylene film, a polyester film, or a polyimide film.
[0066] In some embodiments, please refer to FIG3, the first current collector 211 is provided with a first connection region 2111, and the first connection region 2111 is not provided with a first active material layer 212.
[0067] In some embodiments, the first connection region 2111 is formed by the absence of a first active material layer 212 at the winding end of the first current collector 211, resulting in an empty foil segment 2113. The area on the empty foil segment 2113 used for welding with the first electrode 21 is the first connection region 2111.
[0068] In some other embodiments, the first connection region 2111 is a region formed after part of the first active material layer 212 is washed away from the first current collector 211 on which the first active material layer 212 is provided, and the current collector of the first connection region 2111 is exposed.
[0069] In some embodiments, referring to Figures 3 and 4, the secondary battery 100 further includes a first tab 30, which is connected to the electrode assembly 20.
[0070] In some embodiments, the first tab 30 is connected to the first electrode 21, the material of the first tab 30 can be the same as the material used in the first current collector 211, and the polarity of the first tab 30 is the same as that of the first electrode 21.
[0071] In some embodiments, referring to FIG3, the secondary battery 100 further includes a second tab 40, which is connected to the electrode assembly 20.
[0072] In some embodiments, the second tab 40 is connected to the second electrode 22, and the material of the second tab 40 can be the same as the material used in the second current collector 221. The polarity of the second tab 40 is the same as that of the second electrode 22.
[0073] In some embodiments, referring to Figures 1 and 2, the secondary battery 100 further includes a housing 10, which houses an electrode assembly 20. The electrode assembly 20 is connected to a first tab 30 and a second tab 40. A portion of the first tab 30 and the second tab 40 extends out of the housing 10 to bring the polarity of the electrode assembly 20 out of the housing 10.
[0074] In some embodiments, the secondary battery 100 is a pouch battery, and the casing 10 is an aluminum-plastic film. In other embodiments, the secondary battery 100 is a hard-shell battery, and the casing 10 is made of any one or more of plastic, steel, or aluminum.
[0075] In some embodiments, the housing 10 is further provided with an electrolyte (not shown), which contains a lithium salt and a solvent. The lithium salt may include at least one of LiPF6, LiBF6, LiClO, LiB(CH3), LiCHSO4, LiCFSO4LiN(SOCF), LiC(SOCF), or LiBOB. The solvent may be a carbonate compound, a carboxylic acid ester compound, an ether compound, other organic solvents, or a combination thereof.
[0076] In some embodiments, referring to FIG4, the first tab 30 is welded to the first connection area 2111. The first connection area 2111 includes a plurality of welding areas 211a, which are arranged along the winding direction X of the electrode assembly 20 (in the unfolded state of the first electrode 21 as shown in FIG4, the plurality of welding areas 211a are arranged along the length direction X” of the first electrode 21). At least one solder mark 203 is provided in the welding area 211a formed by welding the first tab 30 and the first connection area 2111. Along the winding direction X of the electrode assembly 20, the solder mark 203 in the welding area 211a closest to the winding center of the electrode assembly 20 has the lowest welding strength.
[0077] When the electrode assembly 20 expands, the area where the first tab 30 is welded to the first connection area 2111 is subjected to a tensile force from the outside to the inside along the electrode assembly 20. Among the multiple welding areas 211a, the solder mark 203 in the welding area 211a closest to the winding center of the electrode assembly 20 along the winding direction X of the electrode assembly 20 is subjected to the tensile force first. In this application, the welding strength of the solder mark 203 in the welding area 211a closest to the winding center of the electrode assembly 20 is the smallest among the multiple welding areas 211a. This is beneficial to reducing the damage of the welding to the first current collector 211 in the welding area 211a closest to the winding center of the electrode assembly 20, thereby improving the tensile strength of the solder mark 203 in the welding area 211a closest to the winding center of the electrode assembly 20. This is beneficial to resisting the tensile force exerted on the welded part of the first tab 30 and the first current collector 211 in the direction from the outside to the inside along the winding structure when the electrode assembly 20 expands, and is beneficial to reducing the risk of electrode damage.
[0078] It should be noted that the higher the welding strength, the greater the welding force between the first electrode tab 30 and the first connection area 2111, and the greater the degree of damage to the structural strength of the first current collector 211 caused by the welding. The welding strength can be characterized by the welding tensile force and the height of the weld mark 203. The higher the welding strength, the greater the welding tensile force and the higher the weld mark 203.
[0079] In some embodiments, the welding strength of the weld marks 203 within the same welding zone 211a is substantially the same.
[0080] In some embodiments, please refer to FIG4, each welding area 211a is provided with a plurality of solder marks 203, and the plurality of solder marks 203 in each welding area 211a are arranged along the width Y direction of the first electrode 21.
[0081] In some embodiments, the number of solder marks 203 in different welding zones 211a may be the same or different, and no specific limitation is made here.
[0082] In some embodiments, the multiple solder marks 203 of the first connection area 2111 are arranged discretely, which is beneficial to improving the uniformity of welding of the first connection area 2111, improving the uniformity of stress in the welding area 211a of the first electrode tab 30 and the first electrode 21, reducing the risk of the first electrode tab 30 falling off, and reducing the risk of damage to the first electrode 21.
[0083] In some embodiments, the welding method is ultrasonic welding, and the ultrasonic welding apparatus includes multiple welding heads. Different weld marks 203 with varying weld strengths can be produced by setting different groove depths on different welding heads. Alternatively, weld marks 203 with varying weld strengths can be produced by controlling the energy of different welding heads.
[0084] In some other embodiments, the welding method is laser welding, and weld marks 203 with different welding strengths are produced by adjusting different power.
[0085] In some embodiments, referring to FIG4, along the winding direction X' of the electrode assembly 20 from the outside to the inside, the welding strength of the solder marks 203 in different welding areas 211a gradually decreases. This results in a lower welding strength of the solder marks 203 closer to the winding center of the electrode assembly 20 along the winding direction X, and a lower degree of damage to the structural strength of the first current collector 211 caused by welding. This is beneficial for improving the tensile strength at the solder marks 203 of the first electrode 21, for resisting the tensile force exerted on the welded portion between the first electrode tab 30 and the first current collector 211 along the winding structure from the outside to the inside when the electrode assembly 20 expands, and for reducing the risk of damage to the first electrode 21.
[0086] In some embodiments, there is a welding pull between the first tab 30 and the first current collector 211 at each solder mark 203, and the welding pull at the solder mark 203 in different welding areas 211a gradually decreases along the winding direction X' of the electrode assembly 20 from the outside to the inside.
[0087] The welding pull at the weld mark 203 in different welding zones 211a gradually decreases along the winding direction X' of the electrode assembly 20 from the outside to the inside. This results in a lower degree of damage to the structural strength of the first current collector 211 caused by welding closer to the winding center of the electrode assembly 20 along the winding direction X. This is beneficial for improving the tensile strength of the weld mark 203 of the first electrode 21, resisting the pulling force on the welded part between the first electrode tab 30 and the first current collector 211 along the winding structure from the outside to the inside when the electrode assembly 20 expands, and reducing the risk of damage to the first electrode 21.
[0088] Welding tensile test method: After fully disassembling the finished secondary battery 100, the first electrode 21 to be measured is obtained. Along the width direction Y of the first electrode 21, weld pieces corresponding to different welding areas 211a of the first electrode tab 30 and the first current collector 211 are cut at the first connection area 2111 between the first electrode tab 30 and the first electrode 21. The weld pieces of the first electrode tab 30 and the first current collector 211 of different welding areas 211a are respectively taken to a high-speed rail tensile testing machine and subjected to tensile testing at a speed of 1 mm / s along the width direction Y of the first electrode 21. The maximum tensile force value is recorded as the welding tensile force at the weld mark 203 of the corresponding welding area 211a.
[0089] In the embodiment where the welding pull at the weld mark 203 in different welding zones 211a gradually decreases along the winding direction X' of the electrode assembly 20 from the outside to the inside, the welding pull between the first tab 30 and the first current collector 211 at each weld mark 203 is F, which satisfies 1N≤F≤80N. This helps to reduce the risk of incomplete welding due to insufficient welding pull at the weld mark 203 with the smallest welding pull, and also helps to reduce the risk of the first current collector 211 easily breaking due to excessive welding pull at the weld mark 203 with the largest welding pull.
[0090] [Amended according to Rule 26, 29.05.2026] As an example, the number of welding zones 211a is N. The Nth welding zone 211a is furthest from the winding center of the electrode assembly 20 along the winding direction X of the electrode assembly 20, and the first welding zone 211a is closest to the winding center of the electrode assembly 20 along the winding direction X of the electrode assembly 20. The welding pull at the solder mark 203 in different welding zones 211a gradually decreases along the winding direction X' of the electrode assembly 20 from the outside to the inside, so that the welding pull at the solder mark 203 in the i-th welding zone 211a is F. i And F i <F i+1 , where N is a positive integer greater than or equal to 2, and i is a positive integer greater than or equal to 1 and less than N. Then, F satisfies: N ≤80N, F1≥1N.
[0091] For example, F can specifically be 80N, 78N, 75N, 72N, 70N, 68N, 65N, 62N, 60N, 58N, 55N, 52N, 50N, 48N, 45N, 42N, 40N, 38N, 35N, 32N, 30N, 28N, 25N, 22N, 20N, 18N, 15N, 12N, 10N, 8N, 5N, 4N, 3N, 2N, or 1N.
[0092] [Amended according to Rule 26, 29.05.2026] In some embodiments, the number of welding areas 211a is N, and along the winding direction X of the electrode assembly 20, the i-th welding area 211a is closer to the winding center of the electrode assembly 20 than the (i+1)-th welding area 211a, and the welding pull force of the solder mark 203 of the i-th welding area 211a is F. i The welding pull force of the weld mark 203 in the (i+1)th welding area 211a is F. i+1 , satisfying 1N≤F i+1 -F i ≤5N, so that the difference in welding strength of the weld mark 203 in two adjacent welding areas 211a is between 1N and 5N, so that the difference in structural strength between the two adjacent welding areas 211a is not too large, which helps to reduce the risk of false welding, and also helps to reduce the risk of damage to the first electrode 21 caused by excessive welding tensile force.
[0093] [Amended to Rule 26 on May 29, 2026] As an example, F i+1 -F i Specifically, it can be any one of 5N, 4N, 3N, 2N, or 1N.
[0094] In some embodiments, the number of solder marks 203 is S, and the average welding pull of the S solder marks 203 is K, satisfying 5N≤K≤9N, where S is a positive integer greater than or equal to 2. When K satisfies the range of 5N≤K≤9N, it is beneficial to reduce the risk of the first electrode tab 30 falling off due to the overall welding pull of the first electrode tab 30 and the first electrode 21 being too small. It allows for a reduction in the welding strength of some solder marks 203 to improve the structural strength of the first electrode 21. It is also beneficial to achieve a gradual decrease in the welding pull at the solder marks 203 in different welding areas 211a along the winding direction X' of the electrode assembly 20 from the outside to the inside, thereby reducing the risk of electrode damage.
[0095] As an example, K can be any one of 9N, 8N, 7N, 6N, 5N, 4N, 3N, 2N, or 1N.
[0096] In some embodiments, referring to FIG5, along the winding direction X' from the outside to the inside of the electrode assembly 20, the height of the solder marks 203 in different welding areas 211a in the thickness direction Z of the first electrode 21 gradually decreases.
[0097] The height of the weld marks 203 in different welding zones 211a gradually decreases along the winding direction X' of the electrode assembly 20 from the outside to the inside. This results in a lower degree of damage to the structural strength of the first current collector 211 caused by welding closer to the winding center of the electrode assembly 20 along the winding direction X. This is beneficial for improving the tensile strength at the weld marks 203 of the first electrode 21, for resisting the tensile force exerted on the welded portion between the first electrode tab 30 and the first current collector 211 along the winding structure from the outside to the inside when the electrode assembly 20 expands, and for reducing the risk of damage to the first electrode 21.
[0098] In some embodiments, please refer to FIG5, the height of the solder mark 203 in the thickness direction Z of the first electrode 21 is H, which satisfies 1um≤H≤100um. This is beneficial to reduce the risk of insufficient welding pull and poor soldering at the solder mark 203 where the welding pull is the smallest, and also beneficial to reduce the risk of excessive welding pull and damage to the first current collector 211 at the solder mark 203 where the welding pull is the largest.
[0099] [Amended according to Rule 26, 29.05.2026] As an example, the number of welding areas 211a is N. The Nth welding area 211a is furthest from the winding center of the electrode assembly 20 along the winding direction X of the electrode assembly 20, and the first welding area 211a is closest to the winding center of the electrode assembly 20 along the winding direction X of the electrode assembly 20. The welding pull at the solder mark 203 in different welding areas 211a gradually decreases along the winding direction X' of the electrode assembly 20 from the outside to the inside, so that the height of the solder mark 203 of the i-th welding area 211a in the thickness direction Z of the first electrode sheet 21 is H. i And H i <H i+1 , where N is a positive integer greater than or equal to 2, and i is a positive integer greater than or equal to 1 and less than N. Then H satisfies: N ≤100um, H1≥1um.
[0100] For example, H can specifically be 100um, 98um, 95um, 92um, 90um, 88um, 85um, 82um, 80um, 78um, 75um, 72um, 70um, 68um, 65um, 62um, 60um, 58um, 55um, 52um, 50um, 48um, 45um, 42um, 40um, 38um, 35um, 32um, 30um, 28um, 25um, 22um, 20um, 18um, 15um, 12um, 10um, 8um, 5um, 4um, 3um, 2um, or 1um.
[0101] [Amended according to Rule 26, 29.05.2026] In some embodiments, the number of welding areas 211a is N. Along the winding direction X of the electrode assembly 20, the i-th welding area 211a is closer to the winding center of the electrode assembly 20 than the (i+1)-th welding area 211a. The height of the solder mark 203 of the i-th welding area 211a in the thickness direction Z of the first electrode sheet 21 is H. i The height of the solder mark 203 of the (i+1)th welding area 211a in the thickness direction Z of the first electrode 21 is H. i+1 , satisfying 1um≤H i+1 -H i ≤10um, ensuring the height difference of the weld mark 203 in two adjacent welding areas 211a is between 1um and 10um, preventing excessive differences in structural strength between the two adjacent welding areas 211a. This helps reduce the risk of incomplete welds and also reduces the risk of damage to the first electrode 21 due to excessive welding tensile force. As an example, H i+1 -H i Specifically, it can be any one of 10N, 9N, 8N, 7N, 6N, 5N, 4N, 3N, 2N, or 1N.
[0102] In some embodiments, the number of solder marks 203 is S, and the average height of the S solder marks 203 is L, satisfying 5um≤L≤15um, where S is a positive integer greater than or equal to 2. When L satisfies the range of 5um≤L≤15um, it is beneficial to reduce the risk of the first electrode tab 30 falling off due to insufficient overall welding pull force between the first electrode tab 30 and the first electrode sheet 21. It allows for a reduction in the welding strength of some solder marks 203 to improve the structural strength of the first electrode sheet 21. It is also beneficial to achieve a gradual decrease in welding pull force at the solder marks 203 in different welding areas 211a along the winding direction X' of the electrode assembly 20 from the outside to the inside, thereby reducing the risk of electrode sheet damage.
[0103] As an example, L can be any one of 15um, 14um, 13um, 12um, 11um, 10um, 9um, 8um, 7um, 6um or 5um.
[0104] To verify the effects of welding pull force and height of solder mark 203 on poor solder joints and electrode damage, the following experiment was conducted:
[0105] Cold solder joint test:
[0106] After fully disassembling the finished secondary battery 100, the first electrode 21 to be measured is obtained. Along the width direction Y of the first electrode 21, welded pieces of the first electrode 30 and the first current collector 211 corresponding to different welding areas 211a are cut at the first connection area 2111 between the first electrode tab 30 and the first electrode 21. The welded pieces of the first electrode tab 30 and the first current collector 211 of different welding areas 211a are respectively taken to a high-speed rail tensile testing machine and subjected to tensile testing at a speed of 1mm / s along the width direction Y of the first electrode 21. After the test, it is observed whether there is any residue of the first current collector 211 at the weld mark 203 of the first electrode tab 30. If no residue is observed, the weld mark 203 is a cold weld; otherwise, there is no cold weld.
[0107] Electrode damage test:
[0108] A battery cycle test was conducted on the secondary battery 100: The secondary battery 100 was placed in a 25°C environment and left to stand for 30 minutes, then charged and discharged according to the following steps: Charged at a constant current of 2.5C to 4.2V, then charged at a constant voltage to 0.5C; then charged at a constant current of 0.5C to 4.45V, then charged at a constant voltage to 0.02C; left to stand for 5 minutes, then discharged at a constant current of 1C to 3V, and left to stand for 5 minutes. This constitutes one cycle. The above cycle was repeated 500 times. The secondary battery 100 was then disassembled to observe whether the first electrode 21 was damaged.
[0109] In the above tests, 20 batteries were tested for each embodiment or comparative example. If there was no poor soldering on the first electrode 21 and the first electrode 21 was not damaged, the test was passed; otherwise, it failed. Pass rate = (number of passes / 20) × 100%.
[0110] The specific implementation of the secondary battery 100 in the embodiments and comparative examples will be described below.
[0111] Example:
[0112] The assembly process of a secondary battery 100 is as follows:
[0113] (1) Preparation of the anode electrode: Artificial graphite, conductive carbon black (Super P), and styrene-butadiene rubber (SBR) are mixed in a weight ratio of 96:1.5:2.5, and deionized water is added as a solvent to prepare a slurry with a weight percentage of 70 wt%, which is then stirred evenly. The slurry is uniformly coated on one surface of a copper foil with a thickness of 10 μm for the anode current collector, leaving an empty foil area at the edge of the copper foil. The foil is dried at 110°C to obtain an anode electrode with a coating thickness of 150 μm on one side coated with an anode active material layer. The above steps are repeated on the other surface of the anode electrode to obtain an anode electrode with a double-sided coating of an anode active material layer. Then, the winding end of the anode electrode is not coated with an anode active material layer, and the empty foil section 2113 without the anode active material layer has a first connection area 2111. A copper foil is soldered to the first connection area 2111 to serve as an anode tab. The first connection area 2111 includes multiple welding areas 211a, which are arranged along the winding direction X of the electrode assembly 20. Each welding area 211a contains multiple weld marks 203 formed by welding the anode tab to the first connection area 2111. The weld marks 203 in each welding area 211a are arranged along the width direction Y of the anode sheet. Along the winding direction X' of the electrode assembly 20 from the outside in, the welding strength of the weld marks 203 in different welding areas 211a gradually decreases.
[0114] (2) Preparation of the cathode electrode: Lithium cobalt oxide (LiCoO2), conductive carbon black (Super P), and polyvinylidene fluoride (PVDF) were mixed in a weight ratio of 97.5:1.0:1.5, and N-methylpyrrolidone (NMP) was added as a solvent to prepare a slurry with a solid content of 75 wt%, which was then stirred evenly. The slurry was uniformly coated on one surface of a 12 μm thick aluminum foil for the cathode current collector, leaving an empty foil area at the edge of the foil. The foil was then dried at 90 °C to obtain a cathode electrode with a cathode active material layer thickness of 100 μm. When preparing other first electrodes 21 with double-sided coating, the above coating steps were repeated on the other surface of the aluminum foil. Then, a part of the cathode electrode was left without a cathode active material layer, exposing the current collector. An aluminum foil was welded to the current collector to serve as a cathode tab.
[0115] (3) Preparation of electrolyte: In a dry argon atmosphere, ethylene carbonate (EC), ethyl methyl carbonate (EMC) and diethyl carbonate (DEC) are first mixed in a mass ratio of EC:EMC:DEC = 30:50:20 to form a basic organic solvent. Then, lithium salt lithium hexafluorophosphate (LiPF6) is added to the basic organic solvent to dissolve and mix evenly to obtain an electrolyte with a lithium salt concentration of 1.15 mol / L.
[0116] (4) Preparation of the separator 23: The separator 23 adopts a three-layer structure, which includes a first adhesive layer, a first substrate layer and a first adhesive layer stacked together. The first substrate layer is made of polyethylene (PE), the first adhesive layer contains a first adhesive, and the first adhesive layer also contains inorganic ceramic particles Al2O3.
[0117] (5) Electrode assembly 20 preparation: The cathode electrode, the separator 23 and the anode electrode are stacked. The resulting structure is hot-pressed on a flat plate for 10 seconds at a temperature of 80°C and a pressure of 1.5 MPa to form the electrode assembly 20 for later use.
[0118] (6) Assembly of electrode assembly 20: Place the punched aluminum-plastic film in the assembly fixture with the punched surface facing up, place the electrode assembly 20 in the punch, and apply external force to press it. Then cover the electrode assembly 20 with another punched aluminum-plastic film with the punched surface facing down, and heat seal the two aluminum-plastic films around their perimeter by hot pressing to obtain the assembled electrode assembly 20.
[0119] (7) Electrolyte injection and encapsulation: Electrolyte is injected into the assembled electrode assembly 20, and after vacuum encapsulation, standing, hot pressing formation, shaping and other processes, the secondary battery 100 is obtained.
[0120] Comparative example:
[0121] The difference from the embodiment is that the welding strength of each weld mark 203 formed by welding the anode electrode sheet and the anode tab in Comparative Example 1 is basically the same, while the welding strength of the multiple weld marks 203 formed by welding the anode tab of the anode electrode sheet in Comparative Example 2 gradually increases along the winding direction X' from the outside to the inside of the electrode assembly 20 in different welding areas 211a.
[0122] The main parameter controls and test results for each embodiment and comparative example are shown in Table 1:
[0123] Table 1
[0124] According to Table 1 above, compared with Comparative Examples 1 and 2, Examples 1-12 satisfy the following: along the winding direction X of the electrode assembly 20, the weld strength of the weld mark 203 in the weld area 211a closest to the winding center of the electrode assembly 20 is the smallest. This is beneficial to reduce the damage of the welding to the first current collector 211 in the weld area 211a closest to the winding center of the electrode assembly 20, thereby improving the tensile strength of the weld mark 203 in the weld area 211a closest to the winding center of the electrode assembly 20, and reducing the risk of electrode damage.
[0125] [Revised according to Rule 26, 29.05.2026] As can be seen from Table 1 above, compared with Examples 1 and 12, Examples 2-11 satisfy: 1N≤F i+1 -F i ≤5N ensures that the structural strength difference between two adjacent welding areas 211a is not too large, which helps reduce the risk of incomplete welding and also helps reduce the risk of damage to the first electrode 21 caused by excessive welding tensile force.
[0126] [Revised according to Rule 26, 29.05.2026] As can be seen from Table 1 above, compared with Examples 1 and 12, Examples 2-11 satisfy: 1um≤H i+1 -H i ≤10um, so that the structural strength difference between two adjacent welding areas 211a will not be too large, which helps to reduce the risk of false welding, and also helps to reduce the risk of damage to the first electrode 21 due to excessive welding tensile force.
[0127] According to Table 1 above, compared with Examples 13 and 18, Examples 6 and Examples 14-17 satisfy: 5N≤K≤9N. This is beneficial to reducing the risk of the first electrode tab 30 falling off due to the overall welding pull force between the first electrode tab 30 and the first electrode sheet 21 being too small. It is also beneficial to reduce the possibility of false welding. It also allows the welding strength of some solder marks 203 to be reduced in order to improve the structural strength of the first electrode sheet 21. This is also beneficial to realize that the welding pull force at the solder mark 203 in different welding areas 211a gradually decreases along the winding direction X' of the electrode assembly 20 from the outside to the inside, thereby reducing the risk of electrode sheet damage.
[0128] In some embodiments, referring to FIG4, the edge of the first tab 30 near the winding center of the electrode assembly 20 in the winding direction X' from the outside to the inside of the electrode assembly 20 is defined as the first edge. The minimum distance A between the solder marks 203 in the plurality of soldering areas 211a and the first edge satisfies 0.1mm≤A≤1mm, so that the distance between the solder mark 203 closest to the first edge and the first edge is between 0.1mm and 1mm. This ensures that the solder mark 203 is not too close to the first edge, which is beneficial for the soldering operation, and also prevents the solder mark 203 from being too far from the first edge, which is beneficial for increasing the area of the soldering area 211a and improving the utilization rate of the first connection area 2111.
[0129] As an example, A can be any one of 0.1mm, 0.2mm, 0.3mm, 0.4mm, 0.5mm, 0.6mm, 0.7mm, 0.8mm, 0.9mm or 1mm.
[0130] In some embodiments, referring to FIG4, along the winding direction X of the electrode assembly 20 (the length direction Y of the first electrode 21 in the unfolded state), the total width of the plurality of solder marks 203 is W, satisfying 1mm≤W≤3mm, so that the area occupied by the plurality of solder marks 203 is not too small, thereby helping to increase the total area of the plurality of welding areas 211a, which is beneficial to increasing the connection strength between the first electrode tab 30 and the first electrode 21, allowing the welding strength of some solder marks 203 to be reduced in order to improve the structural strength of the first electrode 21, and helping to achieve the welding pull at the solder marks 203 in different welding areas 211a to gradually decrease along the winding direction X' of the electrode assembly 20 from the outside to the inside, thereby helping to reduce the risk of electrode damage.
[0131] In some embodiments, please refer to Figure 4, the maximum distance of the plurality of solder marks 203 from the first edge is B = A + W.
[0132] In one or more of the above embodiments, please refer to Figures 3 and 4. Along the winding direction X' from the outside to the inside of the electrode assembly 20, the first current collector 211 includes an empty foil segment 2113 and a coated segment 2112 arranged in sequence. The coated segment 2112 is provided with a first active material layer 212. The empty foil segment 2113 is not provided with the first active material layer 212. At least a portion of the empty foil segment 2113 is located at the outermost ring of the first electrode 21. The first connection area 2111 is located in the empty foil segment 2113 and at the outermost ring of the first electrode 21.
[0133] The inventors discovered that during the cycling process, the lithium insertion / extraction of the first electrode 21 in the wound electrode assembly 20 causes repeated expansion and contraction of the first electrode 21 due to lithium insertion / extraction, resulting in repeated expansion and contraction of the electrode assembly 20. The outermost first electrode 21 experiences the greatest tensile force. In this embodiment, by setting multiple welding zones 211a, the welding strength of the solder mark 203 in the welding zone 211a closest to the winding center of the electrode assembly 20 is minimized. This reduces the damage to the first current collector 211 in the welding zone 211a closest to the winding center of the electrode assembly 20, thereby improving the tensile strength of the solder mark 203 in the welding zone 211a closest to the winding center of the electrode assembly 20 and reducing the risk of electrode damage.
[0134] In some embodiments, please refer to Figures 4, 6 and 7, the shape of the solder mark 203 includes at least one of rhombus, square and circle.
[0135] In some embodiments, the connection between the second electrode 40 and the second electrode 22 is basically the same as that between the first electrode 30 and the first electrode 21. The specific implementation of the connection between the second electrode 40 and the second electrode 22 can be referred to the embodiment on the connection between the first electrode 30 and the first electrode 21, and will not be repeated here.
[0136] Please refer to Figure 8. An embodiment of this application also provides an electronic device 1000, which includes the secondary battery 100 from any of the above embodiments. Since this electronic device 1000 adopts the technical solution of the secondary battery 100 from any of the above embodiments, it at least possesses the beneficial effects brought about by the technical solution of the secondary battery 100 from any of the above embodiments, which will not be elaborated further here.
[0137] In some embodiments, referring to FIG8, the electronic device 1000 further includes a device body 200, and a secondary battery 100 is mounted on the device body 200.
[0138] In some embodiments, the electronic device 1000 may be a mobile phone, tablet computer, e-reader, AR glasses or VR glasses, etc., which will not be listed here.
[0139] Furthermore, those skilled in the art should recognize that the above embodiments are merely illustrative of this application and are not intended to limit this application. Any appropriate changes and variations made to the above embodiments within the substantive scope of this application fall within the scope of this application.
Claims
1. A secondary battery, characterized in that, include: An electrode assembly includes a first electrode, a second electrode, and a separator disposed between the first electrode and the second electrode. The first electrode, the second electrode, and the separator are stacked and wound to form a wound structure. The first electrode includes a first current collector and a first active material layer disposed on the first current collector. The first current collector has a first connection area, and the first connection area does not have the first active material layer disposed thereon. A first tab is welded to a first connection area. The first connection area includes multiple welding areas arranged along the winding direction of the electrode assembly. Each welding area has at least one weld mark formed by welding the first tab to the first connection area. Along the winding direction of the electrode assembly, the weld mark in the welding area closest to the winding center of the electrode assembly has the lowest welding strength.
2. The secondary battery according to claim 1, characterized in that, Along the winding direction of the electrode assembly from the outside to the inside, the welding strength of the weld marks in different welding zones gradually decreases.
3. The secondary battery according to claim 2, characterized in that, There is a welding pull between the first electrode tab and the first current collector at each of the solder marks, and the welding pull at the solder marks in different welding areas gradually decreases along the winding direction of the electrode assembly from the outside to the inside.
4. The secondary battery according to claim 3, characterized in that, The welding pull force between the first electrode tab and the first current collector at each of the weld marks is F, which satisfies 1N≤F≤80N.
5. [Amended according to Rule 26, 29.05.2026] The secondary battery according to claim 4 is characterized in that, The number of welding zones is N. Along the winding direction of the electrode assembly, the i-th welding zone is closer to the winding center of the electrode assembly than the (i+1)-th welding zone. The welding pull force of the solder joint in the i-th welding zone is F. i The welding pull force of the weld mark in the (i+1)th welding zone is F. i+1 , satisfying 1N≤F i+1 -F i ≤5N; N is a positive integer greater than or equal to 2, and i is a positive integer greater than or equal to 1 and less than N.
6. The secondary battery according to claim 4, characterized in that, The number of weld marks is S, and the average welding tensile force of the S weld marks is K, which satisfies 5N≤K≤9N; S is a positive integer greater than or equal to 2.
7. The secondary battery according to claim 2, characterized in that, Along the winding direction of the electrode assembly from the outside to the inside, the height of the solder mark in the thickness direction of the first electrode sheet gradually decreases in different soldering areas.
8. The secondary battery according to claim 7, characterized in that, The height of the solder mark on the first electrode sheet in the thickness direction is H, which satisfies 1um≤H≤100um.
9. The secondary battery according to claim 8, characterized in that, The number of welding areas is N. Along the winding direction of the electrode assembly, the i-th welding area is closer to the winding center of the electrode assembly than the (i+1)-th welding area. The height of the solder mark of the i-th welding area in the thickness direction of the first electrode sheet is H. i The height of the solder mark in the (i+1)th welding area in the thickness direction of the first electrode is H. i+1 , satisfying 1um≤H i+1 -H i ≤10um; N is a positive integer greater than or equal to 2, and i is a positive integer greater than or equal to 1 and less than N.
10. The secondary battery according to claim 8, characterized in that, The number of solder marks is S, and the average height of the S solder marks is L, satisfying 5um≤L≤15um; S is a positive integer greater than or equal to 2.
11. The secondary battery according to any one of claims 1 to 10, characterized in that, The first electrode tab is defined as the edge of the electrode assembly near the winding center in the winding direction from the outside to the inside of the electrode assembly as the first edge. The minimum distance of the solder mark in the plurality of solder areas from the first edge is A. The total width of the plurality of solder marks is W. The maximum distance of the plurality of solder marks from the first edge is B = A + W. The secondary battery satisfies at least one of the following conditions (1) to (3): (1) 0.1mm≤A≤1mm; (2) 1mm≤W≤3mm; (3) 1.1mm≤B≤4mm.
12. The secondary battery according to any one of claims 1 to 10, characterized in that, Along the winding direction of the electrode assembly from the outside to the inside, the first current collector includes a blank foil segment and a coated segment arranged sequentially. The coated segment is provided with the first active material layer, while the blank foil segment is not provided with the first active material layer. At least a portion of the blank foil segment is located at the outermost ring of the first electrode sheet, and the first connection area is located at the blank foil segment and at the outermost ring of the first electrode sheet.
13. The secondary battery according to any one of claims 1 to 10, characterized in that, The shape of the solder mark includes at least one of rhombus, square, and circle.
14. An electronic device, characterized in that, Includes the secondary battery as described in any one of claims 1 to 13.