Welding apparatus and welding method

Abstract

The application relates to a welding device and a welding method. The welding device is used for welding a to-be-welded piece and forming a first welding mark. The welding device comprises a welding head and a welding seat which are oppositely arranged in a first direction. The welding head has a first welding surface, and the welding seat has a second welding surface which faces the first welding surface. In a third direction, the welding head is in an elliptical shape, and the welding seat is in an elliptical shape. The first direction, the second direction and the third direction are perpendicular to each other in pairs. In the thickness direction of the to-be-welded piece, the first welding mark extends to a depth S1, and 10 microns <= S1 <= 23 microns. The welding device and the welding method can improve the welding reliability between a first current collector and a first conductive piece.

Description

Technical Field

[0001] This application relates to the field of battery technology, and in particular to a welding apparatus and welding method. Background Technology

[0002] Secondary batteries, as the power source for electronic devices, are crucial for ensuring their normal operation. To improve battery performance, composite current collectors are often used. These composite current collectors typically have a three-layer structure: a metal layer, a polymer layer, and another metal layer. Conductive components are usually welded to the opposite surfaces of the composite current collector to achieve conductivity between the two metal layers and the tabs. The welding method between the composite current collector and the conductive component is primarily roll welding. Current welding equipment has a small welding contact area, resulting in a narrow welding window. This requires high power and energy for welding, which can easily lead to deep weld marks, potentially damaging the current collector. Furthermore, the weld mark depth can fluctuate significantly, increasing the risk of incomplete or over-welded connections between the composite current collector and the conductive component, thus affecting the reliability of the weld between them. Summary of the Invention

[0003] The purpose of this application is to provide a welding apparatus and welding method, which aims to improve the welding reliability between composite current collectors and conductive components.

[0004] According to a first aspect of this application, a secondary battery is provided, comprising a first electrode and a first tab. The first electrode includes a first current collector and a first active layer. Along the thickness direction of the first current collector, the first current collector includes a first polymer layer and a first metal layer disposed on opposite surfaces of the first polymer layer. The first current collector includes a first coated section and a first empty foil section connected together. The surface of the first coated section is provided with the first active layer. A first conductive element is welded to one surface of the first empty foil section, forming a first solder mark. Along the thickness direction of the first empty foil section, the first solder mark extends from the surface of the first conductive element away from the first empty foil section toward the first empty foil section, and the extension depth is S1, 10μm≤S1≤23μm. A second conductive element is disposed on the surface of the first empty foil section away from the first conductive element. The first conductive element, the second conductive element, and the first tab are connected.

[0005] In the above technical solution, along the thickness direction of the first current collector, the first current collector includes a first polymer layer and a first metal layer disposed on the two opposite surfaces of the first polymer layer, which can improve the performance of the secondary battery. A first conductive element is welded to one surface of the first empty foil segment, forming a first solder mark. A second conductive element is disposed on the surface of the first empty foil segment opposite to the first conductive element. The first conductive element, the second conductive element, and the first electrode tab are connected. The first conductive element and the second conductive element can assist the first metal layer on the two opposite surfaces of the first polymer layer in connecting and conducting with the first electrode tab. Along the thickness direction of the first empty foil segment, the first solder mark extends from the surface of the first conductive element opposite to the first empty foil segment towards the first empty foil segment, and the extension depth is S1, 10μm≤S1≤23μm. This can make the extension depth of the first solder mark relatively stable, which can reduce the possibility of poor soldering or over-soldering (poor soldering or over-soldering of the first solder mark) between the first current collector and the first conductive element, and can improve the welding reliability between the first current collector and the first conductive element. When the first solder joint is poorly soldered, the connection strength between the first current collector and the first conductive component is low, which easily reduces the pull-off force between them. Furthermore, the poorly soldered joint has contact resistance, which is much greater than that of a normal solder joint, thus increasing the resistance between them. When the first solder joint is over-soldered, it easily causes stress concentration within the solder joint, reducing its mechanical strength. The first solder joint can also damage the first current collector, reducing its tensile strength and making it prone to breakage. This further reduces the pull-off force between the current collector and the first conductive component. Over-soldering can also lead to oxidation or the formation of an impurity layer on the solder joint surface, and can cause irregular solder joint shapes, resulting in uneven current distribution, thus increasing contact resistance and the overall resistance between them. A solder joint thickness of S1 ≤ 23μm can reduce the likelihood of over-soldering, thereby increasing the pull-off force between the first current collector and the first conductive component while simultaneously reducing their resistance. S1≥10μm can reduce the possibility of poor soldering of the first solder mark, thereby increasing the pull force between the first current collector and the first conductive component, improving the stability of the connection between the first current collector and the first conductive component, and reducing the resistance between the first current collector and the first conductive component.

[0006] It should be noted that the coated section is the part of the current collector with an active layer, while the empty foil section is the part of the current collector without an active layer.

[0007] In some preferred embodiments, the second conductive element is soldered to the surface of the first empty foil segment away from the first conductive element, forming a second solder mark. Along the thickness direction of the first empty foil segment, the second solder mark extends from the surface of the second conductive element away from the first empty foil segment toward the first empty foil segment, which can improve the stability of the connection between the second conductive element and the first current collector.

[0008] In some preferred embodiments, when viewed along the thickness direction of the first empty foil segment, the projections of the first solder mark and the second solder mark are misaligned, which can reduce the possibility of the first solder mark and the second solder mark overlapping and affecting each other.

[0009] In some preferred embodiments, 10μm≤S1≤15μm. S1≤15μm can further reduce the possibility of over-soldering of the first solder mark, thus further increasing the pull-out force between the first current collector and the first conductive element, and further reducing the resistance between the first current collector and the first conductive element.

[0010] In some preferred embodiments, the first metal layer comprises aluminum, the first conductive element is aluminum foil, and the thicknesses of the first and second conductive elements along the thickness direction of the first empty foil segment are H1, where 8μm≤H1≤20μm. H1≥8μm reduces the possibility of damage to the first conductive element during the welding process, thereby increasing the pull-off force between the first current collector and the first conductive element. It also reduces the resistance of the first conductive element (the greater the thickness of the conductive element, the lower its resistance), further reducing the resistance between the first current collector and the first conductive element, and improving the performance of the first conductive element in transmitting electrical energy from the first current collector. A thicker first conductive element makes it more difficult to transfer welding energy from the first conductive element to the first current collector, making it difficult for the first solder joint to extend from the first conductive element to the first current collector, leading to a higher risk of incomplete soldering. H1≤20μm facilitates the transfer of welding energy from the surface of the first conductive element to the first current collector, reducing the possibility of incomplete soldering between the first conductive element and the first current collector, thereby increasing the pull-off force between the first current collector and the first conductive element.

[0011] In some preferred embodiments, the thickness of the first current collector is H2, where 4.5μm≤H2≤14μm and H2≥4.5μm. This reduces the possibility of damage or breakage of the first current collector during the welding process. H2≤14μm facilitates the transfer of welding energy from the first conductive element through the first current collector to the second conductive element, thereby improving the stability of the connection between the first conductive element, the first current collector, and the second conductive element, while also reducing the possibility of the first current collector losing energy density from the secondary battery.

[0012] In some preferred embodiments, the thickness of the first metal layer is H3, where 0.5μm≤H3≤3μm and H3≥0.5μm. This can improve the welding quality between the first metal layer and the first conductive element, thereby improving the stability of the connection between the first metal layer and the first conductive element. H3≤3μm can reduce the thickness of the first current collector, thereby reducing the possibility of the first current collector losing energy density of the secondary battery.

[0013] Secondly, this application also proposes a welding apparatus for welding workpieces and forming a first weld mark. The welding apparatus includes a welding head and a welding base disposed opposite each other in a first direction. The welding head has a first welding surface, and the welding base has a second welding surface facing the first welding surface. Viewed from a third direction, both the welding head and the welding base are elliptical in shape. The first, second, and third directions are mutually perpendicular. Along the thickness direction of the workpiece, the depth of the first weld mark is S1, where 10μm≤S1≤23μm. By setting the shapes of the welding head and the welding base to elliptical, the welding contact area can be increased, thereby reducing welding power and energy, improving welding reliability, and increasing the welding window. Therefore, the depth of the first weld mark S1 can be reduced, thereby reducing the possibility of damaging the first current collector. Furthermore, the depth of the first weld mark can be made more stable, reducing the possibility of incomplete or over-welded welds. A depth of 10μm≤S1≤23μm can make the extension depth of the first solder mark more stable, which can reduce the possibility of incomplete soldering or over-soldering (incomplete soldering or over-soldering of the first solder mark) in the workpiece to be soldered, and can improve the welding reliability of the workpiece to be soldered.

[0014] In some preferred embodiments, in the second direction, the welding head includes a first arc segment, a first flat segment, and a second arc segment connected in sequence, and the welding base includes a third arc segment, a second flat segment, and a fourth arc segment connected in sequence. In the first direction, the projection of the first flat segment overlaps with the second flat segment, which can further increase the welding contact area.

[0015] In some preferred embodiments, the first welding surface is provided with a plurality of first protrusions, and the array of the plurality of first protrusions is distributed on the first welding surface, which can increase the effective welding area of ​​the welding head and thus improve the welding quality.

[0016] In some preferred embodiments, when viewed in a direction perpendicular to the first welding surface, the first protrusion is rectangular in shape, which can increase the contact area between the first protrusion and the workpiece to be welded, thereby dispersing welding energy, reducing damage to the workpiece to be welded, and improving the welding window.

[0017] In some preferred embodiments, in the third direction, the width of the first protrusion is T1, where 0.1mm ≤ T1 ≤ 1mm. T1 ≥ 0.1mm increases the effective welding area of ​​the welding head and the extension depth S1 of the first solder mark, thereby reducing the possibility of poor soldering between the first current collector and the first conductive element. This increases the tensile strength between the first current collector and the first conductive element and reduces their resistance. T1 ≤ 1mm reduces the possibility of the welding head's effective welding area being too large and damaging the first current collector, thus increasing the tensile strength of the first current collector.

[0018] In some preferred embodiments, the length of the first protrusion is T2 in the extension direction of the first welding surface, where 0.1mm ≤ T2 ≤ 1mm, and the extension direction of the first welding surface is perpendicular to a third direction. T2 ≥ 0.1mm increases the effective welding area of ​​the welding head and the extension depth S1 of the first solder mark, thereby reducing the possibility of poor soldering between the first current collector and the first conductive element. This increases the tensile strength between the first current collector and the first conductive element and reduces their resistance. T2 ≤ 1mm reduces the possibility of the welding head's effective welding area being too large and damaging the first current collector, thus increasing the tensile strength of the first current collector.

[0019] In some preferred embodiments, in the third direction, the first welding surface includes opposing first and second sides. The first protrusion includes a first sub-protrusion and a second sub-protrusion, the first sub-protrusion being the first protrusion closest to the first side, and the second sub-protrusion being the first protrusion closest to the second side. In the third direction, the distance between the edge of the first sub-protrusion near the first side and the edge of the second sub-protrusion near the second side is W1, 0.8mm≤W1≤5mm. W1≥0.8mm can increase the welding width of the first current collector and the first conductive element in the extension direction of the first electrode tab, thereby increasing the release pull between the first current collector and the first conductive element. Simultaneously, under a certain welding energy, the extension depth S1 of the first solder mark can be reduced, thereby reducing the possibility of the first solder mark damaging the first current collector. W1≤5mm can reduce the possibility of excessive welding width of the first current collector and the first conductive element in the extension direction of the first electrode tab, resulting in a loss of secondary battery energy density.

[0020] In some preferred embodiments, the welding head includes a first fixed member and a first rotating member. The first rotating member is rotatably disposed around the first fixed member, and the first welding surface is located on the surface of the first rotating member away from the first fixed member. This facilitates the formation of continuous weld marks on the workpiece to be welded and can improve welding efficiency.

[0021] In some preferred embodiments, the second welding surface is provided with a plurality of second protrusions, and the array of the plurality of second protrusions is distributed on the second welding surface, which can increase the effective welding area of ​​the welding seat and thus improve the welding quality.

[0022] In some preferred embodiments, when viewed in a direction perpendicular to the second welding surface, the second protrusion is rectangular in shape, which can increase the contact area between the second protrusion and the workpiece to be welded, thereby dispersing welding energy, reducing damage to the workpiece to be welded, and improving the welding window.

[0023] In some preferred embodiments, in the third direction, the width of the second protrusion is T3, where 0.1mm ≤ T3 ≤ 1mm. T3 ≥ 0.1mm increases the effective welding area of ​​the solder pad and the extension depth of the second solder mark, thereby reducing the possibility of poor soldering between the first current collector and the second conductive element. This increases the tensile strength between the first current collector and the second conductive element and reduces their resistance. T3 ≤ 1mm reduces the possibility of the solder pad's effective welding area being too large and damaging the first current collector, thus improving the tensile strength of the first current collector.

[0024] In some preferred embodiments, the length of the second protrusion is T4 in the extension direction of the second welding surface, where 0.1mm ≤ T4 ≤ 1mm. The extension direction of the second welding surface is perpendicular to a third direction. T4 ≥ 0.1mm increases the effective welding area of ​​the solder pad and the extension depth of the second solder mark, thereby reducing the possibility of poor soldering between the first current collector and the second conductive element. This increases the tensile strength between the first current collector and the second conductive element and reduces the resistance between them. T4 ≤ 1mm reduces the possibility of the solder pad's effective welding area being too large and damaging the first current collector, thus increasing the tensile strength of the first current collector.

[0025] In some preferred embodiments, in the third direction, the second welding surface includes opposing third and fourth sides. The second protrusion includes a third sub-protrusion and a fourth sub-protrusion, wherein the third sub-protrusion is the second protrusion closest to the third side, and the fourth sub-protrusion is the second protrusion closest to the fourth side. In the third direction, the distance between the edge of the third sub-protrusion near the third side and the edge of the fourth sub-protrusion near the fourth side is W2, where 0.8mm ≤ W2 ≤ 5mm. W2 ≥ 0.8mm can increase the welding width between the first current collector and the second conductive element in the extension direction of the first electrode tab, thereby increasing the release tension between the first current collector and the second conductive element. Simultaneously, under a certain welding energy, the extension depth of the second solder mark can be reduced, thereby reducing the possibility of the second solder mark damaging the first current collector. W2 ≤ 5mm can reduce the possibility of excessive welding width between the first current collector and the second conductive element in the extension direction of the first electrode tab, resulting in a loss of secondary battery energy density.

[0026] In some preferred embodiments, the welding base includes a second fixing member and a second rotating member. The second rotating member is rotatably disposed around the second fixing member, and the second welding surface is located on the surface of the second rotating member away from the second fixing member. This facilitates the formation of continuous weld marks on the workpiece to be welded and can improve welding efficiency.

[0027] Thirdly, this application also proposes a welding method, employing a welding apparatus as described in any embodiment of the second aspect above. The welding method includes: providing a first current collector, a first conductive element, and a second conductive element. Along a first direction, the second conductive element, the first current collector, and the first conductive element are sequentially stacked on a second welding surface to form a workpiece to be welded. The welding apparatus is activated to weld the workpiece, and the workpiece is moved in a second direction, thereby forming a first weld mark extending towards the first current collector on the surface of the first conductive element.

[0028] Additional aspects and advantages of the embodiments of this application will be described, shown, or illustrated in part by way of implementation of the embodiments of this application in the following description. Attached Figure Description

[0029] One or more embodiments are illustrated by way of example with reference to the accompanying drawings. These illustrations do not constitute a limitation on the embodiments. Elements having the same reference numerals in the drawings are denoted as similar elements. Unless otherwise stated, the dimensions in the drawings do not constitute a limitation on scale.

[0030] Figure 1 This is a schematic diagram of the structure of a secondary battery according to some embodiments of this application; Figure 2 This is a schematic diagram of the structure of the first electrode sheet in some embodiments of this application; Figure 3 This is a schematic diagram of the structure of the first current collector in some embodiments of this application; Figure 4 This is a schematic diagram of the structure of the first electrode sheet in some embodiments of this application; Figure 5 This is a schematic diagram of the welding apparatus according to some embodiments of this application; Figure 6 This is a schematic diagram of the welding apparatus according to some embodiments of this application; Figure 7 This is a schematic diagram showing the unfolded first welding surface of some embodiments of this application; Figure 8 This is a schematic diagram of the welding apparatus according to some embodiments of this application; Figure 9 This is a schematic diagram of the welding apparatus according to some embodiments of this application; Figure 10 This is a schematic diagram showing the unfolded second welding surface of some embodiments of this application; Figure 11 This is a schematic diagram of the welding apparatus according to some embodiments of this application; Figure 12 This is a schematic diagram of the resistance test between the first current collector and the first conductive element in this application.

[0031] Explanation of reference numerals in the attached figures: 100. Secondary battery; 10. Housing; 20. Electrode assembly; 30. First electrode tab; 21. First electrode; 211. First current collector; 2111. First polymer layer; 2112. First metal layer; 211a. First coated section; 211b. First empty foil section; 212. First active layer; 213. First conductive element; 2131. First solder mark; 214. Second conductive element; 2141. Second solder mark; X. Thickness direction of the first empty foil section; 200. Welding device; 3. Welding head; 31. First welding surface; 311. First protrusion; 3111. First sub-protrusion; 3112. Second sub-protrusion; 312. First side; 313. Second side; 32. First arc segment; 33. First flat segment; 34. Second arc segment; 35. First fixing member; 36. First rotating member; 4. Welding base; 41. Second welding surface; 411. Second protrusion; 4111. Third sub-protrusion; 4112. Fourth sub-protrusion; 412. Third side; 413. Fourth side; 42. Third arc segment; 43. Second flat segment; 44. Fourth arc segment; 45. Second fixing member; 46. Second rotating member; Y, first direction; Z, second direction; M, third direction; N, extension direction of the first welding surface; P, extension direction of the second welding surface; 300. Components to be welded. Detailed Implementation

[0032] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly described below with reference to the accompanying drawings. Obviously, the described embodiments are some embodiments of this application, but not all embodiments.

[0033] In this application, the reference to "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places in the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment that is mutually exclusive with other embodiments.

[0034] In the description of the embodiments of this application, technical terms such as "first" and "second" are used only to distinguish different objects and should not be construed as indicating or implying relative importance or implicitly specifying the number, specific order, or primary and secondary relationship of the indicated technical features. In the description of the embodiments of this application, "multiple" means two or more, unless otherwise explicitly defined.

[0035] In the description of the embodiments in this application, the term "and / or" is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, and B existing alone. Additionally, the character " / " in this document generally indicates that the preceding and following related objects have an "or" relationship.

[0036] The term "perpendicular" is used to describe an ideal state between two components. In actual production or use, two components can exist in a state that is approximately perpendicular. For example, in numerical terms, perpendicularity can refer to the angle between two straight lines within the range of 90 ± 10°, the dihedral angle between two planes within the range of 90 ± 10°, or the angle between a straight line and a plane within the range of 90 ± 10°. The two components described as "perpendicular" do not have to be absolutely straight lines or planes; they can be approximately straight lines or planes. From a macroscopic perspective, if the overall direction of extension is straight or plane, the component can be considered a "straight line" or "plane".

[0037] The technical features involved in the different embodiments of this application described below can be combined with each other as long as they do not conflict with each other.

[0038] In the first aspect, embodiments of this application provide a secondary battery 100, please refer to... Figure 1 The secondary battery 100 includes a housing 10 and an electrode assembly 20. The housing 10 can accommodate the electrode assembly 20 and an electrolyte (not shown in the figure). The electrolyte wets the electrode assembly 20 inside the housing 10.

[0039] In some embodiments, please refer to Figures 1 to 3The electrode assembly 20 includes a first electrode 21 and a first tab 30. The first electrode 21 includes a first current collector 211 and a first active layer 212. Along the thickness direction of the first current collector 211, the first current collector 211 includes a first polymer layer 2111 and a first metal layer 2112 disposed on opposite surfaces of the first polymer layer 2111, which can improve the performance of the secondary battery 100. The first current collector 211 includes a first coated section 211a and a first empty foil section 211b connected together. The surface of the first coated section 211a is provided with the first active layer 212. A first conductive element 213 is welded to one surface of the first empty foil segment 211b, forming a first solder mark 2131. A second conductive element 214 is disposed on the surface of the first empty foil segment 211b opposite to the first conductive element 213. The first conductive element 213, the second conductive element 214, and the first electrode tab 30 are connected. The first conductive element 213 and the second conductive element 214 can assist the first metal layer 2112 on the opposite two surfaces of the first polymer layer 2111 in connecting and conducting with the first electrode tab 30. The first electrode 21 can be a positive electrode or a negative electrode. A large depth of the first solder mark 2131 can easily damage the first current collector 211, and the depth of the first solder mark 2131 fluctuates greatly, which can easily lead to the risk of poor soldering or over-soldering between the first current collector 211 and the first conductive element 213, thereby affecting the welding reliability between the first current collector 211 and the first conductive element 213.

[0040] To solve the above problems, please refer to the following in this application: Figure 2Along the thickness direction X of the first empty foil segment 211b, the first solder mark 2131 extends from the surface of the first conductive element 213 away from the first empty foil segment 211b towards the first empty foil segment 211b, with an extension depth of S1, 10μm≤S1≤23μm. This makes the extension depth of the first solder mark 2131 relatively stable, reducing the possibility of cold solder joints or over-soldering (cold solder joints or over-soldering of the first solder mark 2131) between the first current collector 211 and the first conductive element 213, and improving the welding reliability between the first current collector 211 and the first conductive element 213. When the first solder mark 2131 is cold solder jointed, the connection strength between the first current collector 211 and the first conductive element 213 is low, thus easily reducing the pull-out force between the first current collector 211 and the first conductive element 213. Moreover, the cold solder joint has contact resistance, the resistance of which is much greater than that of a normal solder joint, thus easily increasing the resistance between the first current collector 211 and the first conductive element 213. When the first solder mark 2131 is over-soldered, it can easily cause stress concentration inside the solder joint, reducing the mechanical strength of the solder joint. Furthermore, the first solder mark 2131 can easily damage the first current collector 211, reducing its tensile strength and making it more prone to breakage. This reduces the pull-off force between the first current collector 211 and the first conductive element 213. Over-soldering can also lead to oxidation or the formation of an impurity layer on the solder joint surface, and can cause irregular solder joint shapes, resulting in uneven current distribution and increasing contact resistance. Therefore, it can increase the resistance between the first current collector 211 and the first conductive element 213. S1≤23μm can reduce the likelihood of over-soldering the first solder mark 2131, thus improving the pull-off force between the first current collector 211 and the first conductive element 213 while simultaneously reducing the resistance between them. S1≥10μm can reduce the possibility of poor soldering of the first solder mark 2131, thereby increasing the pull force between the first current collector 211 and the first conductive element 213, improving the stability of the connection between the first current collector 211 and the first conductive element 213, and reducing the resistance between the first current collector 211 and the first conductive element 213.

[0041] It should be noted that the coated section is the part of the current collector with an active layer, while the empty foil section is the part of the current collector without an active layer.

[0042] In some embodiments, 10μm≤S1≤15μm. S1≤15μm can further reduce the possibility of over-soldering of the first solder mark 2131, thereby further increasing the pull-off force between the first current collector 211 and the first conductive element 213, and further reducing the resistance between the first current collector 211 and the first conductive element 213.

[0043] In some embodiments, S1 can be any value among 10μm, 11μm, 12μm, 13μm, 14μm, 15μm, 16μm, 17μm, 18μm, 19μm, 20μm, 21μm, 22μm, and 23μm, and any range between any two.

[0044] In some embodiments, the first metal layer 2112 comprises aluminum, and the first conductive element 213 is an aluminum foil. Along the thickness direction X of the first empty foil segment 211b, the thickness of the first conductive element 213 and the second conductive element 214 is H1, where 8μm ≤ H1 ≤ 20μm. H1 ≥ 8μm reduces the possibility of damage to the first conductive element 213 during the welding process, thereby improving the release tension between the first current collector 211 and the first conductive element 213. Simultaneously, it reduces the resistance of the first conductive element 213 (the greater the thickness of the conductive element, the lower its resistance), further reducing the resistance between the first current collector 211 and the first conductive element 213, and improving the performance of the first conductive element 213 in transmitting electrical energy from the first current collector 211. The thicker the first conductive element 213, the more difficult it is to transfer welding energy from the first conductive element 213 to the first current collector 211, making it difficult for the first solder mark 2131 to extend from the first conductive element 213 to the first current collector 211, easily leading to incomplete soldering. H1≤20μm, which is beneficial for the transfer of welding energy from the surface of the first conductive element 213 to the first current collector 211, can reduce the possibility of poor welding between the first conductive element 213 and the first current collector 211, thereby improving the separation pull force between the first current collector 211 and the first conductive element 213.

[0045] In some embodiments, please refer to Figure 2 and Figure 3 The thickness of the first current collector 211 is H2, where 4.5μm≤H2≤14μm and H2≥4.5μm, which reduces the possibility of damage and breakage of the first current collector 211 during the welding process. H2≤14μm facilitates the transfer of welding energy from the first conductive element 213 through the first current collector 211 to the second conductive element 214, thereby improving the stability of the connection between the first conductive element 213, the first current collector 211, and the second conductive element 214, and reducing the possibility of the first current collector 211 losing energy density of the secondary battery 100.

[0046] In some embodiments, the thickness of the first metal layer 2112 is H3, where 0.5μm≤H3≤3μm and H3≥0.5μm. This can improve the welding quality between the first metal layer 2112 and the first conductive element 213, thereby improving the stability of the connection between the first metal layer 2112 and the first conductive element 213. H3≤3μm can reduce the thickness of the first current collector 211, thereby reducing the possibility of the first current collector 211 losing energy density of the secondary battery 100.

[0047] In some embodiments, please refer to Figure 4 The second conductive element 214 is soldered to the surface of the first empty foil segment 211b away from the first conductive element 213, and forms a second solder mark 2141. Along the thickness direction X of the first empty foil segment 211b, the second solder mark 2141 extends from the surface of the second conductive element 214 away from the first empty foil segment 211b toward the first empty foil segment 211b, which can improve the stability of the connection between the second conductive element 214 and the first current collector 211.

[0048] In some embodiments, when viewed along the thickness direction X of the first empty foil segment 211b, the projections of the first solder mark 2131 and the second solder mark 2141 are misaligned, which can reduce the possibility that the first solder mark 2131 and the second solder mark 2141 overlap and affect each other.

[0049] Secondly, please refer to Figure 5 This application also proposes a welding apparatus 200 for welding a workpiece 300 and forming a first weld mark 2131. The workpiece 300 includes a first empty foil segment 211b, a first conductive element 213, and a second conductive element 214 as described in any embodiment of the first aspect above. The welding apparatus 200 includes a welding head 3 and a welding seat 4 disposed opposite to each other in a first direction Y. The welding head 3 has a first welding surface 31, and the welding seat 4 has a second welding surface 41 facing the first welding surface 31. The welding apparatus 200 is used to weld the workpiece 300. When the welding apparatus 200 welds the workpiece 300, the workpiece 300 is located between the first welding surface 31 and the second welding surface 41, and the workpiece 300 moves in the second direction Z. Viewed in a third direction M, the welding head 3 is elliptical in shape, and the welding seat 4 is elliptical in shape. The first direction Y, the second direction Z, and the third direction M are all perpendicular to each other. Along the thickness direction of the workpiece 300, the first weld mark 2131 extends to a depth of S1, where 10μm ≤ S1 ≤ 23μm. By setting the shapes of the welding head 3 and the welding seat 4 to elliptical, the welding contact area can be increased, thereby reducing welding power and energy, improving welding reliability, and increasing the welding window. This reduces the extension depth S1 of the first weld mark 2131, thus reducing the possibility of damaging the first current collector 211. Furthermore, the extension depth of the first weld mark 2131 can be made more stable, reducing the possibility of incomplete or excessive welding of the first weld mark 2131. The 10μm ≤ S1 ≤ 23μm setting ensures a more stable extension depth of the first weld mark 2131, reducing the possibility of incomplete or excessive welding (incomplete or excessive welding of the first weld mark 2131) in the workpiece 300, and improving the welding reliability of the workpiece 300.

[0050] In some embodiments, in the second direction Z, the welding head 3 includes a first arc segment 32, a first flat segment 33, and a second arc segment 34 connected in sequence, and the welding seat 4 includes a third arc segment 42, a second flat segment 43, and a fourth arc segment 44 connected in sequence. In the first direction Y, the projection of the first flat segment 33 overlaps with the second flat segment 43, which can further increase the welding contact area.

[0051] In some embodiments, please refer to Figure 6 The first welding surface 31 is provided with a plurality of first protrusions 311, and the plurality of first protrusions 311 are arrayed on the first welding surface 31, which can increase the effective welding area of ​​the welding head 3, thereby improving the welding quality.

[0052] In some embodiments, please refer to Figure 7 When viewed in a direction perpendicular to the first welding surface 31, the first protrusion 311 is rectangular in shape, which can increase the contact area between the first protrusion 311 and the workpiece 300 to be welded, thereby dispersing the welding energy, reducing damage to the workpiece 300 to be welded, and improving the welding window.

[0053] In some embodiments, on the third-direction M, the width of the first protrusion 311 is T1, where 0.1mm ≤ T1 ≤ 1mm. T1 ≥ 0.1mm increases the effective welding area of ​​the welding head 3 and the extension depth S1 of the first solder mark 2131, thereby reducing the possibility of poor soldering between the first current collector 211 and the first conductive element 213. This increases the tensile strength between the first current collector 211 and the first conductive element 213 and reduces their resistance. T1 ≤ 1mm reduces the possibility of the welding head 3's effective welding area being too large and damaging the first current collector 211, thus increasing the tensile strength of the first current collector 211.

[0054] In some embodiments, the length of the first protrusion 311 in the extension direction N of the first welding surface 31 is T2, where 0.1mm ≤ T2 ≤ 1mm, and the extension direction N of the first welding surface 31 is perpendicular to the third direction M. T2 ≥ 0.1mm can increase the effective welding area of ​​the welding head 3 and the extension depth S1 of the first solder mark 2131, thereby reducing the possibility of poor soldering between the first current collector 211 and the first conductive element 213. This increases the tensile strength between the first current collector 211 and the first conductive element 213 and reduces the resistance between them. T2 ≤ 1mm can reduce the possibility of the welding head 3's effective welding area being too large and damaging the first current collector 211, thereby increasing the tensile strength of the first current collector 211.

[0055] In some embodiments, in the third direction M, the first welding surface 31 includes opposing first side 312 and second side 313. The first protrusion 311 includes a first sub-protrusion 3111 and a second sub-protrusion 3112, where the first sub-protrusion 3111 is the first protrusion 311 closest to the first side 312, and the second sub-protrusion 3112 is the first protrusion 311 closest to the second side 313. In the third direction M, the distance between the edge of the first sub-protrusion 3111 near the first side 312 and the edge of the second sub-protrusion 3112 near the second side 313 is W1, where 0.8mm ≤ W1 ≤ 5mm. A weld width of W1 ≥ 0.8 mm can increase the welding width between the first current collector 211 and the first conductive element 213 in the extension direction of the first electrode tab 30, thereby increasing the release tension between the first current collector 211 and the first conductive element 213. Simultaneously, under a certain welding energy, it can reduce the extension depth S1 of the first solder mark 2131, thus reducing the possibility of the first solder mark 2131 damaging the first current collector 211. A weld width of W1 ≤ 5 mm can reduce the possibility of excessive welding width between the first current collector 211 and the first conductive element 213 in the extension direction of the first electrode tab 30, which could lead to a loss of energy density in the secondary battery 100.

[0056] In some embodiments, please refer to Figure 8 The welding head 3 includes a first fixing member 35 and a first rotating member 36. The first rotating member 36 is rotatably mounted around the first fixing member 35. The first welding surface 31 is located on the surface of the first rotating member 36 away from the first fixing member 35, which is beneficial for the workpiece 300 to form a continuous weld mark and can improve welding efficiency.

[0057] In some embodiments, please refer to Figure 9 The second welding surface 41 is provided with a plurality of second protrusions 411, and the plurality of second protrusions 411 are arrayed on the second welding surface 41, which can increase the effective welding area of ​​the welding seat 4 and thus improve the welding quality.

[0058] In some embodiments, please refer to Figure 10 When viewed in a direction perpendicular to the second welding surface 41, the second protrusion 411 is rectangular in shape, which can increase the contact area between the second protrusion 411 and the workpiece 300 to be welded, thereby dispersing the welding energy, reducing damage to the workpiece 300 to be welded, and improving the welding window.

[0059] In some embodiments, on the third direction M, the width of the second protrusion 411 is T3, where 0.1mm ≤ T3 ≤ 1mm. T3 ≥ 0.1mm increases the effective welding area of ​​the solder pad 4 and the extension depth of the second solder mark 2141, thereby reducing the possibility of poor soldering between the first current collector 211 and the second conductive element 214. This increases the tensile strength between the first current collector 211 and the second conductive element 214 and reduces the resistance between them. T3 ≤ 1mm reduces the possibility of the solder pad 4's effective welding area being too large and damaging the first current collector 211, thus improving the tensile strength of the first current collector 211.

[0060] In some embodiments, the length of the second protrusion 411 in the extension direction P of the second welding surface 41 is T4, where 0.1mm ≤ T4 ≤ 1mm. The extension direction P of the second welding surface 41 is perpendicular to the third direction M. T4 ≥ 0.1mm can increase the effective welding area of ​​the solder pad 4 and the extension depth of the second solder mark 2141, thereby reducing the possibility of poor soldering between the first current collector 211 and the second conductive element 214. This can increase the tensile strength between the first current collector 211 and the second conductive element 214 and reduce the resistance between them. T4 ≤ 1mm can reduce the possibility of the effective welding area of ​​the solder pad 4 being too large and damaging the first current collector 211, thereby increasing the tensile strength of the first current collector 211.

[0061] In some embodiments, in the third direction M, the second welding surface 41 includes opposing third side 412 and fourth side 413. The second protrusion 411 includes a third sub-protrusion 4111 and a fourth sub-protrusion 4112, wherein the third sub-protrusion 4111 is the second protrusion 411 closest to the third side 412, and the fourth sub-protrusion 4112 is the second protrusion 411 closest to the fourth side 413. In the third direction M, the distance between the edge of the third sub-protrusion 4111 near the third side 412 and the edge of the fourth sub-protrusion 4112 near the fourth side 413 is W2, where 0.8mm ≤ W2 ≤ 5mm. A weld width of W2 ≥ 0.8 mm can increase the welding width between the first current collector 211 and the second conductive element 214 in the extension direction of the first electrode 30, thereby increasing the release tension between the first current collector 211 and the second conductive element 214. Simultaneously, under a given welding energy, it can reduce the extension depth of the second solder mark 2141, thus reducing the possibility of the second solder mark 2141 damaging the first current collector 211. A weld width of W2 ≤ 5 mm can reduce the possibility of excessive welding width between the first current collector 211 and the second conductive element 214 in the extension direction of the first electrode 30, which could lead to a loss of energy density in the secondary battery 100.

[0062] In some embodiments, please refer to Figure 11 The welding base 4 includes a second fixing member 45 and a second rotating member 46. The second rotating member 46 is rotatably mounted around the second fixing member 45. The second welding surface 41 is located on the surface of the second rotating member 46 away from the second fixing member 45, which is beneficial for the workpiece 300 to form a continuous weld mark and can improve welding efficiency.

[0063] Thirdly, this application also proposes a welding method, which employs a welding apparatus 200 as described in any embodiment of the second aspect above. The welding method includes: providing a first current collector 211, a first conductive element 213, and a second conductive element 214. Along a first direction Y, the second conductive element 214, the first current collector 211, and the first conductive element 213 are sequentially stacked on a second welding surface 41 to form a workpiece 300 to be welded. The welding apparatus 200 is activated to weld the workpiece 300, and the workpiece 300 is moved in a second direction Z, thereby forming a first weld mark 2131 extending towards the first current collector 211 on the surface of the first conductive element 213.

[0064] Test section: 1. Depth of extension test of the first solder mark: Testing instrument: micrometer Test method: Take two different locations in the welding area between the first current collector and the first conductive component. The thickness of the first solder mark is measured at the first solder mark location as X1, and the thickness of the junction area between the first solder marks is measured as X2. The difference between the measured thicknesses is the depth of the first solder mark: X2-X1. The test is performed three times and the average value is recorded as the measurement result.

[0065] 2. Tensile test for separation between the first current collector and the first conductive element: Disassemble the secondary battery, remove the first tab, remove the first active layer of the first electrode, and obtain the connected first current collector and first conductive element. Use a tensile testing tool to prepare a 100mm long and 15mm wide test sample. Fix the portion of the first current collector and the first conductive element extending beyond the first current collector onto the test fixture of a high-speed rail tensile testing machine. The tensile speed is 50±0.5mm / min, and the tensile spacing is 50mm. The maximum tensile force after the first conductive element and the first current collector detach is taken as the detachment tensile force.

[0066] 3. Resistance test between the first current collector and the first conductive element: Test instrument: DC resistance tester Test methods: such as Figure 12As shown, the first electrode 21 with the first conductive element 213 welded on it is first cut into a concave shape. The position of the first conductive element 213 welded on is a notch (the first conductive element 213 is separated in the middle). The exposed size of the two first conductive elements 213 is 20mm (L1) × 20mm (L2). The distance between the two first conductive elements 213 is 20mm (L3). The main body size of the first electrode 21 is 60mm (L4) × 40mm (L5). The resistance of the DC resistance meter is measured by placing the test head at the center of the two first conductive parts 213 and measuring the average value of the three samples.

[0067] Example 1 <Preparation of Welding Apparatus>: The welding apparatus includes a welding head and a welding seat disposed opposite each other in a first direction. The welding head has a first welding surface, and the welding seat has a second welding surface facing the first welding surface. Viewed in a third direction, both the welding head and the welding seat are elliptical in shape. The first welding surface is provided with a plurality of first protrusions, and an array of the plurality of first protrusions is distributed on the first welding surface. Viewed in a direction perpendicular to the first welding surface, the first protrusions are rectangular in shape. In a third direction, the width T1 of the first protrusion is 0.2 mm. In the extending direction of the first welding surface, the length T2 of the first protrusion is 0.2 mm, and the extending direction of the first welding surface is perpendicular to the third direction. In the third direction, the first welding surface includes opposing first and second sides; the first protrusions include first sub-protrusions and second sub-protrusions, the first sub-protrusion being the first protrusion closest to the first side, and the second sub-protrusion being the first protrusion closest to the second side. In the third direction, the distance W1 between the edge of the first sub-protrusion near the first side and the edge of the second sub-protrusion near the second side is 2 mm. Multiple rows of first protrusions are arranged along the extending direction of the first welding surface.

[0068] <Preparation of the first electrode>: The first electrode is a positive electrode, and polyethylene terephthalate (PET) is selected as the first polymer layer with a thickness of 6 μm. A first metal layer of aluminum with a thickness H3 of 1 μm is disposed on both surfaces of the first polymer layer to obtain a first current collector with a thickness H2 of 8 μm. The first current collector includes a first coated section and a first empty foil section connected together.

[0069] Along the first direction, the second conductive element, the first current collector, and the first conductive element are sequentially stacked on the second welding surface to form a workpiece to be welded. The first conductive element and the second conductive element are located on opposite surfaces of the first empty foil segment. The welding device is activated to weld the workpiece to be welded, and the workpiece to be welded is moved in the second direction to form a first solder mark on the surface of the first conductive element. Along the thickness direction of the first empty foil segment, the first solder mark extends from the surface of the first conductive element away from the first empty foil segment toward the first empty foil segment, and the depth of extension S1 is 15μm. Both the first conductive element and the second conductive element are aluminum foils with a thickness H1 of 8μm. The first direction, the second direction, and the third direction are mutually perpendicular.

[0070] Lithium cobalt oxide (LiCoO2), carbon black (Super P), and polyvinylidene fluoride (PVDF) were mixed in a weight ratio of 97.5:1.0:1.5. N-methylpyrrolidone (NMP) was added as a solvent to prepare a slurry with a solid content of 75wt%. The mixture was stirred evenly and coated on the surface of the first coating section and dried to obtain the first active layer.

[0071] <Preparation of the Second Electrode>: The second electrode uses a negative electrode, with graphite as the negative electrode active material. The negative electrode active material graphite, the binder styrene-butadiene rubber (SBR) and the thickener sodium carboxymethyl cellulose (CMC) are mixed in a weight ratio of 96:2:2, deionized water is added as a solvent, and a slurry with a solid content of 70wt% is prepared and stirred evenly.

[0072] Copper foil was selected as the negative electrode current collector. The above-mentioned slurry was coated on the surface of the negative electrode current collector, leaving an empty foil area. The slurry was dried to obtain a negative electrode sheet with a negative electrode active layer coated on the surface.

[0073] <Preparation of the diaphragm>: A porous polyethylene membrane is used as the substrate layer, and a ceramic layer containing alumina ceramic and PVDF binder is coated on one side of the substrate layer as a separator (CCS). The mass percentage of alumina ceramic in the ceramic layer is 95%.

[0074] <Electrolyte Preparation>: 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, dissolved, and mixed evenly to obtain an electrolyte with a LiPF6 mass concentration of 12.5%.

[0075] <Preparation of Secondary Batteries>: An electrode assembly is obtained by sequentially stacking a first electrode, a separator, and a second electrode. A first conductive element and a second conductive element are connected to a first tab. The electrode assembly is placed in an aluminum-plastic film housing with the first tab extending out of the housing. After drying, electrolyte is injected. The secondary battery is obtained through processes such as vacuum sealing, settling, formation, capacity testing, degassing, and edge trimming.

[0076] The relevant parameters in Comparative Examples 1 and 2, as well as Examples 1 to 9, are shown in Table 1 below.

[0077] The welding head and welding base of Comparative Example 2 are circular, while the welding head and welding base of Comparative Example 1 and Examples 1 to 9 are elliptical.

[0078] The extension depth S1 of the first solder mark in Comparative Examples 1 and 2 and Examples 1 to 5 is different.

[0079] In Examples 1 and 6 to 9, only the thickness H1 of the first conductive element and the second conductive element are different.

[0080] Table 1

[0081] According to Table 1 above, and in conjunction with Comparative Examples 1 and 2 and Examples 1 to 9, it can be seen that the first empty foil segment of the first current collector and the first conductive element are typically welded together by a welding head and a welding seat to form a first solder mark. Along the thickness direction of the first empty foil segment, the first solder mark extends from the surface of the first conductive element away from the first empty foil segment towards the first empty foil segment, with an extension depth of S1. By setting the shape of the welding head and welding seat to elliptical, the welding contact area can be increased, thereby reducing welding power and energy, improving welding reliability, and increasing the welding window. Therefore, the extension depth S1 of the first solder mark can be reduced, thus reducing the possibility of damaging the first current collector. Furthermore, the extension depth of the first solder mark can be made more stable, reducing the possibility of incomplete or over-welded solder joints. When the first solder mark is incompletely soldered, the connection strength between the first current collector and the first conductive element is low, thus easily reducing the pull-out force between them. Moreover, the incomplete solder joint has contact resistance, the value of which is much greater than that of a normal solder joint, thus easily increasing the resistance between the first current collector and the first conductive element. When the first solder mark is over-soldered, stress concentration easily occurs inside the solder joint, reducing the mechanical strength of the solder joint. The first solder mark can also damage the first current collector, reducing its tensile strength and making it prone to breakage. This reduces the pull-off force between the first current collector and the first conductive element. Over-soldering can also lead to oxidation or the formation of an impurity layer on the solder joint surface, and can cause irregular solder joint shapes, resulting in uneven current distribution and increasing contact resistance. Therefore, it can increase the resistance between the first current collector and the first conductive element. A solder mark depth of 10μm ≤ S1 ≤ 23μm allows for a more stable extension depth of the first solder mark, reducing the possibility of incomplete soldering or over-soldering. This improves the pull-off force between the first current collector and the first conductive element and reduces their resistance, thus improving the energy transfer efficiency of the first electrode. Combining Comparative Examples 1 and 2 and Examples 1 to 5, it is clear that S1 ≤ 23μm reduces the possibility of over-soldering the first solder mark, thereby improving the pull-off force between the first current collector and the first conductive element and reducing their resistance. A solder joint width (S1 ≥ 10 μm) reduces the likelihood of a cold solder joint in the first solder mark, thereby increasing the pull-out force between the first current collector and the first conductive component, improving the stability of the connection between them, and reducing the resistance between them. Therefore, 10 μm ≤ S1 ≤ 23 μm is preferred. Furthermore, a solder joint width (S1 ≤ 15 μm) further reduces the likelihood of an over-soldering in the first solder mark, thus further increasing the pull-out force between the first current collector and the first conductive component, and further reducing the resistance between them. Therefore, 10 μm ≤ S1 ≤ 15 μm is further preferred.

[0082] As can be seen from Examples 1 and 6 to 9, the thickness of the first conductive element and the second conductive element is H1, where H1 ≥ 8 μm. This reduces the possibility of damage to the first conductive element during the welding process, thereby increasing the pull-off force between the first current collector and the first conductive element. Simultaneously, it reduces the resistance of the first conductive element, further reducing the resistance between the first current collector and the first conductive element, thus improving the performance of the first conductive element in transmitting electrical energy from the first current collector. H1 ≤ 20 μm facilitates the transfer of welding energy from the surface of the first conductive element to the first current collector, reducing the possibility of incomplete soldering between the first conductive element and the first current collector, thereby increasing the pull-off force between the first current collector and the first conductive element.

[0083] The relevant parameters in Example 1 and Examples 10 to 17 are shown in Table 2 below.

[0084] The only differences between Embodiment 1 and Embodiments 10 to 13 are the width T1 and the length T2 of the first protrusion.

[0085] In Examples 1 and 14 to 17, the only difference is the distance W1 between the edge of the first sub-protrusion near the first side and the edge of the second sub-protrusion near the second side.

[0086] Table 2

[0087] According to Table 2 above, and in conjunction with Embodiments 1 and 10 to 13, the welding head has a first welding surface, which is provided with a plurality of first protrusions. The dimension of the first protrusion in the third direction is T1, and the dimension of the first protrusion in the extension direction of the first welding surface is T2. T1 and T2 ≥ 0.1 mm, which can increase the effective welding area of ​​the welding head and increase the extension depth S1 of the first solder mark, thereby reducing the possibility of poor soldering between the first current collector and the first conductive component. Therefore, it can increase the tensile strength between the first current collector and the first conductive component and reduce the resistance between the first current collector and the first conductive component. T1 and T2 ≤ 1 mm, which can reduce the possibility of the welding head's effective welding area being too large and damaging the first current collector, thereby increasing the tensile strength of the first current collector.

[0088] Based on Embodiment 1 and Embodiments 14 to 17, in the third direction, the first welding surface includes opposing first and second sides; the first protrusion includes a first sub-protrusion and a second sub-protrusion, the first sub-protrusion being the first protrusion closest to the first side, and the second sub-protrusion being the first protrusion closest to the second side; in the third direction, the distance between the edge of the first sub-protrusion near the first side and the edge of the second sub-protrusion near the second side is W1. W1 ≥ 0.8 mm can increase the welding width of the first current collector and the first conductive element in the extension direction of the first electrode tab, thereby increasing the release tension between the first current collector and the first conductive element. Simultaneously, under a certain welding energy, it can reduce the extension depth S1 of the first solder mark, thereby reducing the possibility of the first solder mark damaging the first current collector. W1 ≤ 5 mm can reduce the possibility of excessive welding width of the first current collector and the first conductive element in the extension direction of the first electrode tab, thus reducing the possibility of loss of secondary battery energy density.

[0089] The above description is merely an embodiment of this application and does not limit the patent scope of this application. Any equivalent structural or procedural transformations made using the content of this application's specification and drawings, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of this application.

Claims

1. A welding apparatus for welding workpieces and forming a first weld mark, characterized in that, The welding apparatus includes a welding head and a welding seat disposed opposite to each other in a first direction, the welding head having a first welding surface and the welding seat having a second welding surface facing the first welding surface; Viewed from a third-party perspective, the welding head is elliptical in shape, and the welding base is also elliptical in shape; the first direction, the second direction, and the third direction are mutually perpendicular. Along the thickness direction of the workpiece to be welded, the depth of the first solder mark is S1, 10μm≤S1≤23μm.

2. The welding apparatus according to claim 1, characterized in that, In the second direction, the welding head includes a first arc segment, a first flat segment, and a second arc segment connected in sequence, and the welding seat includes a third arc segment, a second flat segment, and a fourth arc segment connected in sequence; in the first direction, the projection of the first flat segment overlaps with the second flat segment.

3. The welding apparatus according to claim 1, characterized in that, The first welding surface is provided with a plurality of first protrusions, and the plurality of first protrusions are arrayed on the first welding surface.

4. The welding apparatus according to claim 3, characterized in that, Viewed in a direction perpendicular to the first welding surface, the first protrusion has a rectangular shape.

5. The welding apparatus according to claim 4, characterized in that, In the third direction, the width of the first protrusion is T1, 0.1mm≤T1≤1mm; and / or, in the extension direction of the first welding surface, the length of the first protrusion is T2, 0.1mm≤T2≤1mm, and the extension direction of the first welding surface is perpendicular to the third direction.

6. The welding apparatus according to claim 5, characterized in that, In the third direction, the first welding surface includes a first side and a second side opposite to each other; the first protrusion includes a first sub-protrusion and a second sub-protrusion, the first sub-protrusion being the first protrusion closest to the first side, and the second sub-protrusion being the first protrusion closest to the second side; in the third direction, the distance between the edge of the first sub-protrusion near the first side and the edge of the second sub-protrusion near the second side is W1, 0.8mm≤W1≤5mm.

7. The welding apparatus according to claim 3, characterized in that, The welding head includes a first fixing member and a first rotating member, the first rotating member being rotatably mounted around the first fixing member, and the first welding surface being located on the surface of the first rotating member opposite to the first fixing member.

8. The welding apparatus according to claim 3, characterized in that, The second welding surface is provided with a plurality of second protrusions, and the plurality of second protrusions are arrayed on the second welding surface.

9. The welding apparatus according to claim 8, characterized in that, Viewed in a direction perpendicular to the second welding surface, the second protrusion has a rectangular shape.

10. The welding apparatus according to claim 9, characterized in that, In the third direction, the width of the second protrusion is T3, 0.1mm≤T3≤1mm; and / or, in the extension direction of the second welding surface, the length of the second protrusion is T4, 0.1mm≤T4≤1mm; the extension direction of the second welding surface is perpendicular to the third direction.

11. The welding apparatus according to claim 10, characterized in that, In the third direction, the second welding surface includes a third side and a fourth side; the second protrusion includes a third sub-protrusion and a fourth sub-protrusion, the third sub-protrusion being the second protrusion closest to the third side, and the fourth sub-protrusion being the second protrusion closest to the fourth side; in the third direction, the distance between the edge of the third sub-protrusion near the third side and the edge of the fourth sub-protrusion near the fourth side is W2, 0.8mm≤W2≤5mm.

12. The welding apparatus according to claim 8, characterized in that, The welding base includes a second fixing member and a second rotating member, the second rotating member being rotatably mounted around the second fixing member, and the second welding surface being located on the surface of the second rotating member opposite to the second fixing member.

13. A welding method, characterized in that, Welding is performed using the welding apparatus as described in any one of claims 1 to 12, the welding method comprising: Provides a first current collector, a first conductive element, and a second conductive element; Along the first direction, the second conductive element, the first current collector, and the first conductive element are sequentially stacked on the second welding surface to form a workpiece to be welded; The welding device is activated to weld the workpiece and the workpiece is moved in the second direction.

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