Joining method, power storage device, and method for manufacturing power storage device

Abstract

To provide a joining method in which weld spatter hardly remains.SOLUTION: A joining method disclosed herein includes a laser welding step of irradiating a boundary portion between a first member 30 made of metal and a second member 51 made of metal with a laser to form a welded joint portion J, and an etching step of irradiating a surface and a peripheral edge portion of the welded joint portion J with an energy ray at an output lower than that in the laser welding step to form a plurality of substantially circular recesses in the surface and the peripheral edge portion of the welded joint portion J.SELECTED DRAWING: Figure 8

Description

[Technical Field]

[0001] The present invention relates to a joining method, an electricity storage device, and a method for manufacturing the same. [Background technology]

[0002] Conventionally, in the manufacturing process of an electricity storage device, a first metal member and a second metal member are welded together using a laser. Related prior art documents include Patent Documents 1 to 3. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] International Publication No. 2010 / 131298 [Patent Document 2] Patent No. 6885072 [Patent Document 3] Japanese Patent Application Laid-Open No. 2016-140877 Summary of the Invention [Problem to be solved by the invention]

[0004] According to the inventor's findings, when metal members are welded together using a laser, high-temperature molten metal is generated from the weld as fine particles (so-called weld spatter) that may randomly scatter on the surface and periphery of the welded joint. If the weld spatter remains, it can cause defects such as short circuits, so there is a need to efficiently remove the weld spatter after laser welding.

[0005] The present invention has been made in view of the above circumstances, and its main object is to provide a joining method that is less likely to leave welding spatter. [Means for solving the problem]

[0006] The present invention provides a joining method including a laser welding process in which a laser is irradiated onto the boundary between a first metal member and a second metal member to form a welded joint, and an etching process in which an energy beam is irradiated onto the surface and peripheral edge of the welded joint at a lower output than in the laser welding process to form a plurality of approximately circular recesses on the surface and peripheral edge of the welded joint.

[0007] In the present invention, the surface and peripheral area of ​​the welded joint are irradiated with energy rays in the etching process. This allows for efficient removal of welding spatter that has scattered in random locations during the laser welding process. As a result, the amount of remaining welding spatter can be reduced. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is a perspective view schematically illustrating an electricity storage device according to one embodiment. [Figure 2] FIG. 2 is a schematic vertical cross-sectional view taken along line II-II in FIG. [Figure 3] FIG. 3 is a perspective view that schematically shows a combination of a sealing plate and an electrode assembly. [Figure 4] FIG. 4 is a schematic diagram showing the configuration of a wound electrode body. [Figure 5] FIG. 5 is a perspective view that schematically shows a sealing plate assembly. [Figure 6] FIG. 6 is a perspective view of the sealing plate of FIG. 5 turned upside down. [Figure 7] FIG. 7 is a cross-sectional view taken along line VII-VII in FIG. [Figure 8] FIG. 8 is a partially enlarged plan view schematically showing the vicinity of the welded joint in FIG. [Figure 9] FIG. 9 is a partially enlarged view of the roughened portion of FIG. [Figure 10] FIG. 10 is a cross-sectional view taken along line XX in FIG. [Figure 11] FIG. 11 is a view corresponding to FIG. 8 according to a modified example. [Figure 12]12(A) to 12(D) are observation images of the vicinity of the welded joint according to the example. DETAILED DESCRIPTION OF THE INVENTION

[0009] Preferred embodiments of the technology disclosed herein will be described below with reference to the drawings. It should be noted that matters other than those specifically mentioned in this specification that are necessary for implementing the present invention (for example, the general configuration and manufacturing process of an electricity storage device that do not characterize the present invention) can be understood as design matters for those skilled in the art based on prior art in the relevant field. The present invention can be implemented based on the contents disclosed in this specification and common technical knowledge in the relevant field.

[0010] Note that, as one embodiment of the joining method disclosed herein, a method for manufacturing an electricity storage device that includes a metal first member and a metal second member as components will be described below as an example, but it is not intended that the application of the joining method disclosed herein be limited to electricity storage devices. Furthermore, in this specification, the expression "A to B" indicating a range means not less than A and not more than B, and also includes the meanings of "greater than A (exceeds A)" and "smaller than B (less than B)."

[0011] <Electricity storage device> First, the structure of an electricity storage device manufactured by the manufacturing method disclosed herein will be described. In this specification, the term "electricity storage device" refers to a device in general that can be repeatedly charged and discharged by the movement of charge carriers between a positive electrode and a negative electrode via an electrolyte. The electrolyte may be any of a liquid electrolyte (electrolytic solution), a gel electrolyte, and a solid electrolyte. Electricity storage devices include secondary batteries such as lithium ion batteries and nickel-metal hydride batteries, and capacitors such as lithium ion capacitors and electric double layer capacitors.

[0012] Fig. 1 is a perspective view of the electricity storage device 100. Fig. 2 is a schematic longitudinal cross-sectional view taken along line II-II in Fig. 1. In the following description, the symbols L, R, F, Rr, U, and D in the drawings represent left, right, front, rear, top, and bottom, and the symbols X, Y, and Z in the drawings represent the short side direction of the electricity storage device 100, the long side direction perpendicular to the short side direction, and the up-down direction perpendicular to the short side direction and the long side direction, respectively. However, these directions are merely used for the convenience of description and do not limit the installation form of the electricity storage device 100 in any way.

[0013] As shown in Fig. 2, the electricity storage device 100 includes a case 10, an electrode assembly 20, a positive electrode terminal 30, a negative electrode terminal 40, a positive electrode current collector 50, and a negative electrode current collector 60. Although not shown, the electricity storage device 100 further includes a non-aqueous electrolyte. The electricity storage device 100 is configured by accommodating the electrode assembly 20 and a non-aqueous electrolyte (not shown) in the case 10. The electricity storage device 100 is a non-aqueous electrolyte secondary battery. More specifically, it is a lithium-ion secondary battery.

[0014] The case 10 is a housing that houses the electrode assembly 20 and the non-aqueous electrolyte. Here, the case 10 has a flat, bottomed, rectangular parallelepiped (rectangular) outer shape. The material of the case 10 may be the same as that conventionally used, and is not particularly limited. The case 10 is preferably made of metal, and more preferably made of, for example, aluminum, an aluminum alloy, iron, an iron alloy, or the like. As shown in FIG. 2, the case 10 includes a case main body 12 having an opening 12h, and a sealing plate (lid) 14 that closes the opening 12h.

[0015] As shown in Fig. 1, the case body 12 includes a substantially rectangular bottom wall 12a, a pair of long side walls 12b extending from the long sides of the bottom wall 12a and facing each other, and a pair of short side walls 12c extending from the short sides of the bottom wall 12a and facing each other. The area of ​​the short side walls 12c is smaller than the area of ​​the long side walls 12b. An electrode assembly 20 and a nonaqueous electrolyte are housed inside the case body 12. In this specification, the term "substantially rectangular" is intended to encompass not only a perfect rectangular shape (rectangular shape) but also shapes in which the corners connecting the long and short sides of the rectangle are rounded or have notches at the corners.

[0016] The sealing plate 14 is a plate-like member having a predetermined thickness. The sealing plate 14 is attached to the case body 12 so as to close the opening 12h of the case body 12. The sealing plate 14 faces the bottom wall 12a of the case body 12. The sealing plate 14 has a substantially rectangular shape in a plan view. The case 10 is integrated by joining (for example, welding) the sealing plate 14 to the periphery of the opening 12h of the case body 12. The case 10 is hermetically sealed (sealed).

[0017] As shown in FIG. 2 , the sealing plate 14 is provided with a liquid inlet 15, a gas release valve 17, and two terminal holes 18 and 19. The liquid inlet 15 is for injecting nonaqueous electrolyte into the case 10 after the sealing plate 14 is assembled to the case body 12. The liquid inlet 15 is sealed with a sealing member 16. The gas release valve 17 is configured to break when the pressure inside the case 10 reaches or exceeds a predetermined value, thereby releasing gas inside the case 10 to the outside. The terminal holes 18 and 19 are formed at both ends of the sealing plate 14 in the long side direction Y. The terminal holes 18 and 19 penetrate the sealing plate 14 in the up-down direction Z. Here, the terminal holes 18 and 19 are cylindrical. The terminal pull-out holes 18 and 19 each have an inner diameter large enough to allow insertion of the positive electrode terminal 30 and the negative electrode terminal 40 before they are attached to the sealing plate 14 (before crimping). For example, the terminal pull-out hole 18 is formed smaller than the shaft portion 30a of the positive electrode terminal 30 before crimping, which will be described later.

[0018] FIG. 3 is a perspective view that schematically shows an assembly of the sealing plate 14 (more specifically, the sealing plate assembly described below) and the electrode assembly group 20. In this example, the electrode assembly 20 has three electrode bodies 20a, 20b, and 20c. However, the number of electrode bodies arranged inside one case 10 is not particularly limited, and may be one, or two or more (plural). Furthermore, the configuration of the electrode bodies 20a, 20b, and 20c is not particularly limited, and may be the same as conventional ones.

[0019] FIG. 4 is a schematic diagram showing the configuration of the electrode assembly 20a. While the electrode assembly 20a will be described in detail below as an example, the electrode assemblies 20b and 20c may also have a similar configuration. The electrode assembly 20a has a positive electrode 22 and a negative electrode 24. The positive electrode 22 and the negative electrode 24 are examples of the first electrode and second electrode disclosed herein. The electrode assembly 20a is a flat wound electrode assembly formed by stacking a strip-shaped positive electrode 22 and a strip-shaped negative electrode 24 with two strip-shaped separators 26 interposed therebetween and winding the stack around a winding axis WL. However, the electrode assemblies 20a, 20b, and 20c may also be laminated electrode assemblies formed by stacking a square-shaped (typically rectangular) positive electrode and a square-shaped (typically rectangular) negative electrode in an insulated state.

[0020] 2 and 4, the electrode assembly 20a is disposed inside the case 10 with the winding axis WL oriented parallel to the long side direction Y. In other words, the electrode assembly 20a is disposed inside the case 10 with the winding axis WL oriented parallel to the bottom wall 12a and perpendicular to the short side wall 12c. As shown in FIG. 2, the electricity storage device 100 has a so-called horizontal tab structure in which a positive electrode tab group 23 and a negative electrode tab group 25, which will be described later, are located on the left and right sides of the electrode assembly group 20. However, the electricity storage device 100 may also have a so-called upper tab structure in which the positive electrode tab group 23 and the negative electrode tab group 25, which will be described later, are located above and below the electrode assembly group 20.

[0021] As shown in FIG. 4, the positive electrode 22 includes a positive electrode current collector 22c, a positive electrode active material layer 22a, and a positive electrode protective layer 22p adhered to at least one surface of the positive electrode current collector 22c. However, the positive electrode protective layer 22p is not essential and may be omitted in other embodiments. The positive electrode current collector 22c is strip-shaped. The positive electrode current collector 22c is made of a conductive metal such as aluminum, an aluminum alloy, nickel, or stainless steel. Here, the positive electrode current collector 22c is a metal foil, specifically, an aluminum foil.

[0022] A plurality of positive electrode tabs 22t are provided at one end of the positive electrode current collector 22c in the long side direction Y (the left end in FIG. 4). Each of the plurality of positive electrode tabs 22t is convex and protrudes toward one side in the long side direction Y (the left side in FIG. 4). The plurality of positive electrode tabs 22t are provided at intervals (intermittently) along the longitudinal direction of the positive electrode 22. Here, the positive electrode tabs 22t are part of the positive electrode current collector 22c and are made of metal foil (aluminum foil). The positive electrode tab 22t is a portion of the positive electrode current collector 22c where the positive electrode active material layer 22a and the positive electrode protective layer 22p are not formed (exposed current collector portion). However, the positive electrode tab 22t may be a member separate from the positive electrode current collector 22c. The plurality of positive electrode tabs 22t are stacked at one end of the long side direction Y (the left end in FIG. 4) to form a positive electrode tab group 23, as shown in FIG. 2. The positive electrode tab group 23 is electrically connected to the positive electrode terminal 30 via the positive electrode current collector 50. A positive electrode second current collector 52, which will be described later, is attached to the positive electrode tab group 23.

[0023] 4, the positive electrode active material layer 22a is provided in a strip shape along the longitudinal direction of the strip-shaped positive electrode current collector 22c. The positive electrode active material layer 22a contains a positive electrode active material (e.g., a lithium transition metal composite oxide such as a lithium nickel cobalt manganese composite oxide) that can reversibly store and release charge carriers. The positive electrode active material layer 22a may further contain optional components other than the positive electrode active material, such as a conductive material, a binder, and various additive components.

[0024] As shown in Fig. 4, the positive electrode protective layer 22p is provided at the boundary between the positive electrode current collector 22c and the positive electrode active material layer 22a in the long side direction Y. Here, the positive electrode protective layer 22p is provided at one end of the positive electrode current collector 22c in the long side direction Y (the left end in Fig. 4). The positive electrode protective layer 22p is provided in a strip shape along the positive electrode active material layer 22a. The positive electrode protective layer 22p contains an inorganic filler (e.g., alumina). The positive electrode protective layer 22p may further contain optional components other than the inorganic filler, such as a conductive material, a binder, and various additive components.

[0025] As shown in FIG. 4, the negative electrode 24 includes a negative electrode current collector 24c and a negative electrode active material layer 24a fixed to at least one surface of the negative electrode current collector 24c. The negative electrode current collector 24c is strip-shaped. The negative electrode current collector 24c is made of a conductive metal such as copper, a copper alloy, nickel, or stainless steel. Here, the negative electrode current collector 24c is a metal foil, specifically, a copper foil.

[0026] A plurality of negative electrode tabs 24t are provided at one end of the negative electrode current collector 24c in the long side direction Y (the right end in FIG. 4). Each of the plurality of negative electrode tabs 24t is convex and protrudes toward one side in the long side direction Y (the right side in FIG. 4). The plurality of negative electrode tabs 24t are provided at intervals (intermittently) along the longitudinal direction of the negative electrode 24. Here, the negative electrode tabs 24t are part of the negative electrode current collector 24c and are made of metal foil (copper foil). The negative electrode tab 24t is a portion of the negative electrode current collector 24c where the negative electrode active material layer 24a is not formed (exposed current collector portion). However, the negative electrode tab 24t may be a member separate from the negative electrode current collector 24c. The plurality of negative electrode tabs 24t are stacked at one end of the long side direction Y (the right end in FIG. 4) to form a negative electrode tab group 25 as shown in FIG. 2. The negative electrode tab group 25 is electrically connected to the negative electrode terminal 40 via the negative electrode current collector 60. The negative electrode tab group 25 is provided with a negative electrode second current collector 62, which will be described later.

[0027] As shown in Fig. 4, the negative electrode active material layer 24a is provided in a strip shape along the longitudinal direction of the strip-shaped negative electrode current collector 24c. The negative electrode active material layer 24a contains a negative electrode active material (e.g., a carbon material such as graphite) that can reversibly store and release charge carriers. The negative electrode active material layer 24a may further contain optional components other than the negative electrode active material, such as a binder, a dispersant, and various additive components.

[0028] The separator 26 is a member that insulates the positive electrode active material layer 22a of the positive electrode 22 from the negative electrode active material layer 24a of the negative electrode 24. A porous resin sheet made of a polyolefin resin such as polyethylene (PE) or polypropylene (PP) is suitable as the separator 26. Note that a functional layer, such as an adhesive layer containing a binder or a heat resistance layer (HRL) containing an inorganic filler, may be provided on the surface of the separator 26.

[0029] The non-aqueous electrolyte may be the same as conventional ones and is not particularly limited. The non-aqueous electrolyte typically contains a non-aqueous solvent and a supporting salt. The non-aqueous solvent contains, for example, carbonates such as ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate. The supporting salt is, for example, a fluorine-containing lithium salt such as LiPF6. However, in other embodiments, the electricity storage device 100 may include, as the electrolyte, an aqueous electrolyte, a gel electrolyte, a solid electrolyte (solid electrolyte), or the like, instead of a non-aqueous electrolyte.

[0030] FIG. 5 is a perspective view schematically illustrating a sealing plate assembly. FIG. 6 is a perspective view of the sealing plate 14 of FIG. 5 turned upside down. FIG. 6 shows the surface (inner surface) of the sealing plate 14 facing the case body 12. The sealing plate assembly here is a combination of the sealing plate 14, a positive electrode terminal 30, a negative electrode terminal 40, a first positive electrode current collecting portion 51 of the positive electrode current collecting portion 50, a first negative electrode current collecting portion 61 of the negative electrode current collecting portion 60, two resin members 70, and two gaskets 90. In the sealing plate assembly, the positive electrode terminal 30, the gasket 90, the first positive electrode current collecting portion 51 of the positive electrode current collecting portion 50, and the resin members 70 are integrated with the sealing plate 14 by crimping the positive electrode terminal 30 and welding it to the first positive electrode current collecting portion 51. Similarly, the negative electrode terminal 40, the gasket 90, the negative electrode first current collecting portion 61 of the negative electrode current collecting portion 60, and the resin member 70 are integrated into the sealing plate 14 by crimping the negative electrode terminal 40 and welding it to the negative electrode first current collecting portion 61.

[0031] As shown in Fig. 5, the positive electrode terminal 30 and the negative electrode terminal 40 are each attached to the sealing plate 14. The positive electrode terminal 30 is disposed on one side of the sealing plate 14 in the long side direction Y (the left side in Fig. 5). The negative electrode terminal 40 is disposed on the other side of the sealing plate 14 in the long side direction Y (the right side in Fig. 5). Note that, although the positive electrode terminal 30 side will be described in detail below as an example, the negative electrode terminal 40 side can also have a similar configuration.

[0032] As shown in FIG. 2, the positive electrode terminal 30 is electrically connected to each of the positive electrodes 22 (more specifically, the positive electrode tab group 23) of the electrode bodies 20a, 20b, and 20c inside the case 10 via a positive electrode current collecting portion 50. The positive electrode terminal 30 is electrically connected to the positive electrode first current collecting portion 51 of the positive electrode current collecting portion 50 by crimping (mechanical fastening) and welding. The positive electrode terminal 30 is preferably made of metal, and more preferably made of aluminum or an aluminum alloy, for example. The positive electrode terminal 30 is an example of the metal first member disclosed herein.

[0033] 7 is a cross-sectional view taken along line VII-VII in FIG. 5, and is a partially enlarged cross-sectional view schematically illustrating the vicinity of the positive electrode terminal 30. In FIG. 7, the central axis CL of the positive electrode terminal 30 is indicated by a dashed line. As shown in FIG. 7, the positive electrode terminal 30 is inserted through the terminal lead-out hole 18 of the sealing plate 14 and extends from the inside to the outside of the sealing plate 14. The positive electrode terminal 30 has a shaft portion 30a, a flange portion 30f whose diameter is enlarged from the upper end of the shaft portion 30a, and a crimping portion 30c provided at the lower end of the shaft portion 30a.

[0034] As shown in Fig. 7, the shaft portion 30a extends in the up-down direction Z along the central axis CL. The shaft portion 30a is inserted through the terminal pull-out hole 18 of the sealing plate 14 and a through-hole 51h (see Fig. 6) of the positive electrode first current collecting portion 51, which will be described later. Here, the shaft portion 30a has a cylindrical shape. The lower end of the shaft portion 30a, i.e., the end opposite to the side where the flange portion 30f is located, is hollow.

[0035] As shown in FIG. 7, the flange portion 30f is connected to the upper end of the shaft portion 30a and extends upward. The flange portion 30f has a larger outer shape than the shaft portion 30a. The flange portion 30f has a larger outer shape than the terminal outlet hole 18 of the sealing plate 14. The flange portion 30f protrudes from the terminal outlet hole 18 to the outside of the case 10 (more specifically, to the outer surface of the sealing plate 14). In this case, the flange portion 30f has a circular shape in a plan view. In this case, the outer shape of the flange portion 30f is approximately cylindrical. The axis of the flange portion 30f coincides with the axis of the shaft portion 30a.

[0036] As shown in FIG. 7 , the crimped portion 30c is provided at the end of the shaft portion 30a inside the case 10 (the lower end in FIG. 7 ). The crimped portion 30c is provided on the periphery of the terminal outlet hole 18 of the sealing plate 14. The crimped portion 30c is a portion where the lower end of the shaft portion 30a is expanded by crimping when the positive terminal 30 is attached to the sealing plate 14. The crimped portion 30c is preferably provided symmetrically with respect to the central axis CL of the positive terminal 30. This ensures stable electrical connection between the positive terminal 30 and the positive current collecting portion 50, improving the reliability of electrical continuity of the positive terminal 30, even when vibrations or impacts are applied during use of the power storage device 100. Here, the crimped portion 30c has an annular (e.g., circular) shape in a plan view. The crimped portion 30c is provided around the entire periphery of the terminal outlet hole 18.

[0037] 7, the gasket 90 is an insulating member disposed between the sealing plate 14 and the positive electrode terminal 30. Here, the gasket 90 has the function of insulating the sealing plate 14 from the positive electrode terminal 30 and closing the terminal withdrawal hole 18. The gasket 90 is made of an electrically insulating and elastically deformable resin material, for example, a fluorinated resin such as perfluoroalkoxy fluorine resin (PFA), polyphenylene sulfide resin (PPS), aliphatic polyamide, or the like. Here, the gasket 90 has a tubular portion 90a and a base portion 90b.

[0038] The tubular portion 90a is a portion that prevents direct contact between the sealing plate 14 and the shaft portion 30a of the positive electrode terminal 30. The tubular portion 90a has a hollow cylindrical shape. The tubular portion 90a has a through-hole that penetrates in the up-down direction Z at a position corresponding to the terminal lead-out hole 18 of the sealing plate 14. The through-hole has an inner diameter large enough to allow the shaft portion 30a of the positive electrode terminal 30 to be inserted therethrough before crimping. The tubular portion 90a is inserted into the terminal lead-out hole 18 of the sealing plate 14. The base portion 90b is a portion that prevents direct contact between the sealing plate 14 and the flange portion 30f of the positive electrode terminal 30. The base portion 90b is connected to the upper end of the tubular portion 90a. Here, the base portion 90b is provided in an annular shape so as to surround the terminal lead-out hole 18 of the sealing plate 14. The base portion 90b is sandwiched between the lower surface of the flange portion 30f of the positive electrode terminal 30 and the sealing plate 14, and is compressed in the up-down direction Z by crimping.

[0039] As shown in FIG. 2, the positive electrode current collecting part 50 forms a conductive path that electrically connects the positive electrode tab group 23 (positive electrode 22) consisting of multiple positive electrode tabs 22t to the positive electrode terminal 30. The positive electrode current collecting part 50 may be made of the same metal as the positive electrode current collector 22c, such as a conductive metal such as aluminum, an aluminum alloy, nickel, or stainless steel. The positive electrode current collecting part 50 is more preferably made of aluminum or an aluminum alloy. Here, the positive electrode current collecting part 50 includes a positive electrode first current collecting part 51 (see also FIG. 6) that extends along the inner surface of the sealing plate 14, and a positive electrode second current collecting part 52 (see also FIG. 3) that extends along the short side wall 12c of the case body 12.

[0040] As shown in FIG. 7, the positive electrode first current collecting portion 51 is fixed to the sealing plate 14 by a crimping portion 30c and a welded joint J. As shown in FIG. 6, the positive electrode first current collecting portion 51 is generally L-shaped. The positive electrode first current collecting portion 51 may be formed by bending a single member, for example, by pressing or the like, or by integrating multiple members by welding or the like. The positive electrode first current collecting portion 51 has a first portion 511 that extends horizontally along the inner surface of the sealing plate 14, and a second portion 512 that extends in the up-down direction Z from one end of the first portion 511 in the long side direction Y (the left end in FIG. 6). The positive electrode first current collecting portion 51 is an example of the metallic second member disclosed herein.

[0041] As shown in FIG. 7, the first portion 511 is electrically connected to the positive electrode terminal 30 via the crimped portion 30c and the welded joint J. The first portion 511 is flat. Although not particularly limited, the thickness T of the first portion 511 is typically 0.5 to 5 mm, for example, approximately 1 to 3 mm, or 1.5 to 2 mm. The first portion 511 has an upper surface 51u and a lower surface 51d. A resin member 70 is disposed between the sealing plate 14 and the upper surface 51u of the first portion 511. The first portion 511 is insulated from the sealing plate 14 by the resin member 70. A through-hole 51h penetrating the first portion 511 in the up-down direction Z is provided at a position corresponding to the terminal lead-out hole 18 of the sealing plate 14. As shown in FIG. 6, the positive electrode terminal 30 (specifically, the shaft portion 30a) is inserted through the through-hole 51h.

[0042] As shown in Fig. 7, a welded joint J formed by laser welding is provided at the boundary between the periphery of the through hole 51h of the first portion 511 and the crimped portion 30c of the positive terminal 30. The presence of the welded joint J makes it possible to maintain a stable electrical connection between the positive terminal 30 and the positive current collector 50, thereby improving the reliability of electrical continuity. The welded joint J is formed in a laser welding step (step S4) described below. The welded joint J is an example of a welded joint between a first member and a second member disclosed herein.

[0043] The welded joint J is provided around the central axis CL of the positive electrode terminal 30. The welded joint J is preferably provided symmetrically with respect to the central axis CL of the positive electrode terminal 30. This makes it possible to maintain a stable electrical connection between the positive electrode terminal 30 and the positive electrode current collector 50, even if vibrations or impacts are applied during use of the electricity storage device 100, thereby improving the conduction reliability of the positive electrode terminal 30. The weld depth of the welded joint J (the maximum length in the vertical direction Z, the vertical length from the lower surface 51d of the first portion 511 to the end of the welded joint J on the upper surface 51u side) is typically 0.15 mm or more, for example, approximately 0.15 to 0.5 mm, or 0.3 to 0.4 mm.

[0044] FIG. 8 is a partially enlarged plan view schematically illustrating the vicinity of the welded joint J in FIG. 6, and similarly to FIG. 6, it illustrates the surface (inner surface) of the sealing plate 14 on the side of the case body 12. In plan view, the welded joint J is preferably provided along the crimped portion 30c in a ring-shaped (e.g., circular ring), U-shaped, C-shaped (semi-ring) or other shape, and is particularly preferably provided in a ring-shaped (e.g., circular ring) shape as shown in FIG. 8. That is, it is particularly preferably provided that the welded joint J is provided continuously around the entire periphery of the through hole 51h (see FIG. 7). The diameter D1 of the ring-shaped (e.g., circular ring) welded joint J is, for example, about 10 mm.

[0045] As shown in Figures 7 and 8, a roughened portion Ae is provided on the surface of the welded joint J and its peripheral portion. Note that the "periphery" of the welded joint J here refers to the area where welding spatter may scatter, for example, in the laser welding process (step S4) described below. Therefore, there are no particular limitations as this may vary depending on the laser welding conditions, etc., but in one example, it is a range within approximately 5 mm from the welded joint J. The roughened portion Ae is the area irradiated with energy rays in the etching process (step S5) described below. Note that hereinafter, the area around the roughened portion Ae (i.e., the area not irradiated with energy rays in the etching process (step S5)) may be referred to as the general portion An.

[0046] As shown in FIG. 7, in a cross-sectional view, the roughened portion Ae is formed axially symmetrically with respect to the central axis CL of the positive terminal 30. As shown in FIG. 8, in a plan view, the roughened portion Ae is substantially circular (more specifically, a perfect circle) centered on the central axis CL of the positive terminal 30. The diameter D2 of the roughened portion Ae is larger than the diameter D1 of the welded joint J, and is preferably approximately 1 to 20 mm, for example, approximately 10 mm larger. Here, the diameter D2 of the roughened portion Ae is approximately 20 mm. Note that although the roughened portion Ae is a perfect circle here, it may be another shape, for example, an ellipse or a polygonal shape such as a rectangle.

[0047] FIG. 9 is a partial enlarged view of the front half of the roughened portion Ae in FIG. 8. As shown in FIG. 9, the roughened portion Ae has a plurality of recesses e1 in a substantially circular shape. This makes the roughened portion Ae unevener than its surroundings (for example, a region farther from the central axis CL of the positive electrode terminal 30 than the roughened portion Ae; general area An in FIG. 8). The recesses e1 can be formed by intermittently irradiating energy rays using, for example, a pulsed laser in the etching step (step S5) described below. Note that the term "substantially circular shape" is used to distinguish it from a linear (strip) shape and encompasses both a circle and an ellipse with an aspect ratio of approximately 1:5 to 5:1, preferably 1:2 to 2:1.

[0048] The recesses e1 are preferably arranged regularly. In this embodiment, as shown in Fig. 8, the roughened portion Ae has a substantially circular shape in a plan view, and as shown in Fig. 9, the recesses e1 are arranged in a line in the circumferential direction (arc-shaped). The recesses e1 are evenly arranged around the central axis CL of the positive electrode terminal 30. However, in other embodiments, the recesses e1 may be arranged in a straight line or in other lines.

[0049] 10 is a cross-sectional view taken along line XX in FIG. 9. As shown in FIG. 10, in the roughened portion Ae, a plurality of recesses e1 are regularly arranged in a cross section of any circular arc along the circumferential direction. As a result, the cross section of the roughened portion Ae has an uneven shape, and the unevenness is greater than that of its surroundings (general portion An). In some embodiments, the diameter w of the recesses e1 (average diameter of the plurality of recesses e1, spot diameter) is preferably 5 to 200 μm, more preferably 10 to 150 μm, and even more preferably 20 to 100 μm. The diameter w of the recesses e1 mainly depends on the specifications of the apparatus used in the etching step (step S5) described below, but can also be adjusted by, for example, the heat quantity, output, and irradiation time of an energy beam such as a laser.

[0050] In some embodiments, the depth h of the recess e1 (the average of the maximum depths of the recesses e1) is preferably 0.1 μm or more, more preferably 0.5 μm or more, and even more preferably 1 μm or more. The depth h of the recess e1 can be formed by adjusting the output and heat of an energy beam, such as a laser, in the etching step (step S5) described below. As will be described in detail in the manufacturing method section, applying an energy beam in the etching step so that the depth h of the recess e1 is a predetermined value or more can achieve a high level of the effects of the technology disclosed herein. Furthermore, the depth h of the recess e1 is typically smaller than the weld depth of the welded joint J, preferably 50 μm or less, more preferably 20 μm or less, and even more preferably 10 μm or less. As will be described in detail in the manufacturing method section, applying an energy beam in the etching step so that the depth h of the recess e1 is a predetermined value or less can effectively prevent new welding spatter from occurring. Furthermore, the bonding strength of the welded joint J can be improved.

[0051] As shown in Fig. 2, the positive electrode second current collecting portion 52 extends along the short side wall 12c of the case body 12. One end (the upper end in Fig. 2) of the positive electrode second current collecting portion 52 is electrically connected to the positive electrode first current collecting portion 51 (more specifically, the second portion 512 (see Fig. 6)). The other end (the lower end in Fig. 2) of the positive electrode second current collecting portion 52 is attached to the positive electrode tab group 23 and electrically connected to the plurality of positive electrode tabs 22t. The positive electrode second current collecting portion 52 and the positive electrode tab group 23 are joined by welding, for example, with the plurality of positive electrode tabs 22t overlapping each other.

[0052] As shown in FIG. 7 , the resin member 70 is an insulating member disposed between the lower surface (inner surface) of the sealing plate 14 and the first portion 511 of the positive electrode first current collecting portion 51. The resin member 70 is made of an elastically deformable resin material that is resistant to the nonaqueous electrolyte solution used, has electrical insulating properties, and is, for example, a fluorinated resin such as perfluoroalkoxy fluorine resin (PFA) or polyphenylene sulfide resin (PPS). As shown in FIGS. 7 and 8 , the resin member 70 has a base portion 70a that extends horizontally along the inner surface of the sealing plate 14. As shown in FIG. 7 , the base portion 70a is a portion that prevents direct contact between the sealing plate 14 and the positive electrode first current collecting portion 51. The base portion 70a has a through-hole that penetrates in the up-down direction Z at a position corresponding to the terminal lead-out hole 18 of the sealing plate 14. The shaft portion 30a of the positive electrode terminal 30 and the tubular portion 90a of the gasket 90 are inserted into the through-hole.

[0053] As shown in FIG. 2 , the negative electrode terminal 40 is electrically connected to the negative electrode 24 (more specifically, the negative electrode tab group 25) of the electrode bodies 20a, 20b, and 20c inside the case 10 via the negative electrode current collecting portion 60. The configuration of the negative electrode terminal 40 may be the same as or different from the configuration of the positive electrode terminal 30 described above. Like the positive electrode terminal 30, the negative electrode terminal 40 is electrically connected to the negative electrode first current collecting portion 61 of the negative electrode current collecting portion 60 by crimping (mechanical fastening) and welding. The negative electrode terminal 40 extends from the inside to the outside of the sealing plate 14 through the terminal lead-out hole 19 of the sealing plate 14. The negative electrode terminal 40 is provided symmetrically to the positive electrode terminal 30 and includes a flange portion (reference numeral omitted), a shaft portion 40a, and a crimped portion 40c.

[0054] The negative electrode terminal 40 is preferably made of metal, and more preferably made of copper or a copper alloy, for example. The negative electrode terminal 40 may be configured by joining two conductive members together. For example, the shaft portion 40a or the clamping portion 40c connected to the negative electrode current collecting portion 60 may be made of copper or a copper alloy, and the flange portion protruding from the terminal lead-out hole 19 to the outside of the case 10 (more specifically, to the outer surface of the sealing plate 14) may be made of aluminum or an aluminum alloy. The negative electrode terminal 40 is an example of the first metal member disclosed herein.

[0055] As shown in FIG. 2 , the negative electrode current collector 60 forms a conductive path that electrically connects the negative electrode tab group 25 (negative electrode 24) consisting of multiple negative electrode tabs 24t to the negative electrode terminal 40. The negative electrode current collector 60 may be made of the same metal as the negative electrode current collector 24c, such as a conductive metal such as copper, a copper alloy, nickel, or stainless steel. Here, the negative electrode current collector 60 includes a negative electrode first current collector 61 and a negative electrode second current collector 62. The configurations of the negative electrode first current collector 61 and the negative electrode second current collector 62 may be the same as those of the positive electrode first current collector 51 and the positive electrode second current collector 52 of the positive electrode current collector 50. The negative electrode first current collector 61 is an example of the metallic second member disclosed herein.

[0056] 6, the negative electrode first current collecting portion 61 is welded to the crimped portion 40c of the negative electrode terminal 40. Similar to the positive electrode side, a welded joint J formed by laser welding is provided at the boundary between the negative electrode first current collecting portion 61 and the crimped portion 40c. Similar to the positive electrode side, a roughened portion Ae is provided on the surface and peripheral edge of the welded joint J.

[0057] <Method for manufacturing sealing plate assembly> 5 and 6 can be produced by fixing a positive electrode terminal 30, a positive electrode current collecting portion 50 (specifically, the positive electrode first current collecting portion 51), a negative electrode terminal 40, and a negative electrode current collecting portion 60 (specifically, the negative electrode first current collecting portion 61) to the sealing plate 14 while they are insulated from the sealing plate 14. Although not particularly limited, the sealing plate assembly can be produced by a manufacturing method that includes, for example, a component assembling step (step S1), a crimping step (step S2) of forming a crimped portion at one end of the shank of the terminal, a cover placement step (step S3) of placing a cover on a non-welded portion excluding the boundary between the crimped portion and the current collecting portion, a laser welding step (step S4) of forming a welded joint at the boundary between the crimped portion and the current collecting portion, and an etching step (step S5) of irradiating the surface and peripheral portion of the welded joint with energy rays. The laser welding step (step S4) and the etching step (step S5) are an example of the joining method disclosed herein.

[0058] The crimping step (step S2) and the cover placement step (step S3) are optional and may be omitted in other embodiments. While the positive electrode side will be described in detail below, the negative electrode side may be similarly described. In such cases, the term "positive electrode" may be appropriately read as "negative electrode." The manufacturing method disclosed herein may further include other steps at any stage.

[0059] In the assembly process (step S1), the positive electrode terminal 30, the positive electrode current collector 50, the negative electrode terminal 40, and the negative electrode current collector 60 are each assembled to the sealing plate 14, typically while being insulated from the sealing plate 14. The positive electrode terminal 30 and the positive electrode current collector 50 are assembled by, for example, placing the flange portion 30f of the positive electrode terminal 30 on the outer surface of the sealing plate 14 with a gasket 90 interposed therebetween, and placing the positive electrode current collector 50 on the inner surface of the sealing plate 14 with a resin member 70 interposed therebetween, as shown in FIG. Specifically, the components are assembled by inserting the shaft portion 30a of the positive terminal 30 before crimping through the cylindrical portion 90a of the gasket 90, the terminal lead-out hole 18 of the sealing plate 14, the through hole of the resin member 70, and the through hole 51h of the first portion 511 of the positive current collector 50, in that order, so that the shaft portion 30a protrudes below the lower surface 51d of the through hole 51h. The negative terminal 40 and the negative current collector 60 are similarly assembled to the sealing plate 14.

[0060] In the crimping process (step S2), one end of the shaft portion 30a of the positive electrode terminal 30 attached to the sealing plate 14 is deformed by crimping (riveting) to form the crimped portion 30c as shown in FIG. 7 . Specifically, for example, the lower surface 51d of the first portion 511 is placed on a fixed die, and a compression punch is used to apply a compressive force in the vertical direction Z to the shaft portion 30a from above the flange portion 30f of the positive electrode terminal 30. This causes the tip portion of the shaft portion 30a, which protrudes downward from the lower surface 51d of the first portion 511, to be pressed against the inner surface of the through-hole 51h of the positive electrode current collector 50. This causes the tip portion of the shaft portion 30a to expand, forming the crimped portion 30c. This crimping process fixes the positive electrode terminal 30 and the positive electrode current collector 50 to the sealing plate 14, and seals the terminal lead-out hole 18. Similarly, the negative electrode terminal 40 also has a crimping portion 40c formed thereon, so that the negative electrode terminal 40 and the negative electrode current collecting portion 60 can be fixed to the sealing plate 14.

[0061] In the cover placement step (step S3), prior to the laser welding step (step S4), at least a portion of the area excluding the portion where the welded joint J will be formed is covered with a cover. This reduces the area where welding spatter can scatter during the laser welding step (described later). This reduces the area to be processed in the etching step (step S5) (described later), thereby shortening the time required for the etching step. The cover is made of, for example, resin. To prevent the cover from being burned during the laser welding step, it is preferable to place the cover approximately 5 mm away from the portion where the welded joint J will be formed. In one example, a cover may be applied to the entire general portion An of the positive electrode first current collecting portion 51, excluding the area where the roughened portion Ae in FIG. 8 will be formed (the area of ​​diameter D2 centered on the central axis CL of the positive electrode terminal 30).

[0062] In the laser welding process (step S4), a laser is irradiated onto the boundary between the positive terminal 30 (first metal member) and the positive first current collector 51 (second metal member) to form a welded joint. Here, the laser is irradiated onto the boundary between the crimping portion 30c provided at the tip of the shaft portion 30a of the positive terminal 30 and the periphery of the through-hole 51h in the first portion 511 of the positive current collector 50. This forms a welded joint J at the boundary between the positive terminal 30 and the positive current collector 50. The laser irradiation can be performed in a conventional manner using a known laser welding device. The laser irradiation is preferably performed along the fitting line of the crimping portion 30c. The welded joint J is preferably formed around the entire periphery of the through-hole 51h (in a ring shape). In addition, by similarly welding the crimping portion 40c to the periphery of the through hole of the negative electrode current collector 60, a welded joint J can also be formed at the boundary between the negative electrode terminal 40 and the negative electrode current collector 60.

[0063] The laser welding conditions are preferably varied between the positive electrode side and the negative electrode side, which are made of different metals. While not particularly limited, in some embodiments, laser welding is preferably performed under the conditions shown in Table 1 below. For example, by increasing the laser output to 1000 W or more, or even 2000 W or more, or by increasing the laser heat quantity to 100 J or more, or even 200 J or more, a welded joint J with the above-described weld depth can be suitably formed. Furthermore, the use of a continuous wave laser enables linear welding, improving the joint strength. [Table 1]

[0064] During laser welding, high-temperature molten metal can be generated from the welded area as fine particles (so-called welding spatter). Therefore, after laser welding, welding spatter may be found scattered randomly on the surface of the welded joint J and its periphery.

[0065] In the etching step (step S5), the surface and peripheral portion of the welded joint J are irradiated with energy rays at a lower output than in the laser welding step (step S4). This allows welding spatter that has randomly scattered on the surface and peripheral portion of the welded joint J to be re-melted and removed. Lasers and electron beams are preferred as energy rays, with lasers being more preferred. A low-output device such as a laser marker can be used in this step. However, the laser welding device used in the laser welding step (step S4) can also be used as long as the output can be adjusted. The energy rays in this step are preferably irradiated intermittently and regularly using a pulsed laser. This makes it easier to accurately remove welding spatter with relatively simple device settings. However, in other embodiments, a laser other than a pulsed laser, such as an electron beam or a continuous wave laser, can be used and irradiated in a pulsed manner by changing the output.

[0066] The energy beam is preferably scanned along the welded joint J. Here, since the welded joint J is annular and has curved portions, the energy beam is preferably scanned along the circumferential direction of the welded joint J (in an arc). This forms a plurality of recesses e1 lined up in the circumferential direction. However, the energy beam may also be scanned in a linear or spiral pattern, for example.

[0067] In this step, the output of the energy beam (preferably the output of the laser) is set lower than the output of the laser in the laser welding step (step S4). This prevents new welding spatter from being generated in this step. From this perspective, the inventors have found that the output of the energy beam in this step is preferably approximately 200 W or less, more preferably 100 W or less, even more preferably 50 W or less, and particularly preferably 30 W or less. Furthermore, the output of the energy beam in this step is preferably approximately 5 W or more, more preferably 10 W or more. This makes it easier to remove even relatively large welding spatter in a short period of time.

[0068] Furthermore, in some embodiments, when the laser output in the laser welding step (step S4) is taken as 100, the output ratio of the energy beam in this step is preferably 0.1 or more, more preferably 0.2 or more, and even more preferably, for example, 0.5 or more. This makes it easier to remove welding spatter generated in the laser welding step (step S4) more efficiently in a shorter time. It also makes it easier to suitably form the recess e1 with the depth h (for example, 1 to 10 μm) as described above. The output ratio is preferably approximately 3 or less, more preferably 2 or less, and in one example, even more preferably 1 or less. This effectively prevents new welding spatter from being generated in this step.

[0069] The scanning speed of the energy beam in this step is preferably faster than the scanning speed in the laser welding step (step S4). This improves productivity and work efficiency. It also better suppresses the generation of new welding spatter. Although not particularly limited, the scanning speed in this step is preferably 1000 mm / s or more, more preferably 2000 mm / s or more, and even more preferably 3000 mm / s or more. Furthermore, the scanning speed in this step is preferably approximately 12000 mm / s or less, more preferably 10000 mm / s or less, and even more preferably 5000 mm / s or less. This makes it easier to remove even relatively large welding spatter.

[0070] When a pulsed laser is used, the pulse frequency of the laser in this step adjusts the spacing between the multiple recesses e1 and is preferably determined based on the diameter w of the recesses e1, the scanning speed, etc. Although not particularly limited, the pulse frequency of the laser in this step is preferably 10,000 to 100,000, and more preferably 30,000 to 80,000. This makes it easier to accurately remove randomly scattered welding spatter.

[0071] Since the heat quantity of the energy beam is expressed as output x irradiation time, it is preferable that the heat quantity of the energy beam in this step be typically lower than that in the laser welding step (step S4). This can better prevent new welding spatter from being generated in this step. From this perspective, the heat quantity of the energy beam in this step is preferably approximately 0.01 J or less, more preferably 0.001 J or less, and even more preferably 0.0005 J or less. Furthermore, the heat quantity of the energy beam in this step is preferably approximately 0.00001 J or more, and more preferably 0.0001 J or more. This makes it easier to remove even relatively large welding spatter in a short period of time.

[0072] In some embodiments, when the heat quantity of the laser in the laser welding step (step S4) is taken as 100, the heat quantity ratio of the energy beam in this step is preferably approximately 0.01 or less, more preferably 0.001 or less, and in one example, even more preferably 0.0005 or less. This makes it easier to remove welding spatter generated in the laser welding step (step S4) more efficiently in a shorter time. It also makes it easier to preferably form the recesses e1 with the depth h (e.g., 1 to 10 μm) as described above.

[0073] Although not particularly limited, in some embodiments, etching can be performed using a laser under conditions such as those shown in Table 2 below. [Table 2]

[0074] In this process, a plurality of substantially circular recesses e1 are formed on the surface and peripheral edge of the welded joint J. That is, a roughened portion Ae is formed. As described above, in the technique disclosed herein, by irradiating the surface and peripheral edge of the welded joint with an energy beam (preferably a laser) in the etching process, welding spatter scattered at random positions in the laser welding process can be efficiently removed. As a result, the remaining welding spatter can be appropriately reduced. Ultimately, a highly reliable electricity storage device 100 can be provided.

[0075] Other methods for removing weld spatter include, for example, a method in which a person visually checks for weld spatter and manually removes it, or a method in which a camera detects the location of the weld spatter and pinpoints the weld spatter with an energy beam. However, manual removal is costly. There is also a risk that the weld spatter may be overlooked due to human error. On the other hand, the method of pinpointing the weld spatter with an energy beam has the disadvantages of high camera purchase costs and a long takt time required to read the weld spatter with a camera and then irradiate it with an energy beam. Compared to these methods, the technology disclosed herein can be said to be a method that can remove weld spatter efficiently and accurately at a relatively low cost.

[0076] <Method of manufacturing an electricity storage device> The electricity storage device 100 can be manufactured, for example, by preparing the sealing plate assembly, the electrode group 20, the non-aqueous electrolyte, and the case body 12 as described above, and by a manufacturing method including an attachment process and a construction process.

[0077] In the attachment step, the electrode body group 20 is attached to the sealing plate 14 to produce a combination (sealing plate assembly) of the sealing plate 14 and electrode body group 20 as shown in FIG. 3. Specifically, a positive electrode second current collecting portion 52 is attached to each of the positive electrode tab groups 23 of the electrode bodies 20a, 20b, and 20c, and the positive electrode second current collecting portion 52 is joined (e.g., welded) to the positive electrode first current collecting portion 51 of the sealing plate assembly. This electrically connects the positive electrodes 22 of the electrode bodies 20a, 20b, and 20c to the positive electrode terminal 30. Similarly, a negative electrode second current collecting portion 62 is attached to each of the negative electrode tab groups 25 of the electrode bodies 20a, 20b, and 20c, and the negative electrode second current collecting portion 62 is joined (e.g., welded) to the negative electrode first current collecting portion 61 of the sealing plate assembly. As a result, the negative electrodes 24 of the electrode bodies 20a, 20b, 20c are electrically connected to the negative electrode terminal 40. As a result, the sealing plate assembly and the electrode body group 20 are integrated together.

[0078] In the construction step, as shown in FIGS. 1 and 2, the electrode assembly 20 integrated with the sealing plate 14 is housed in the internal space of the case body 12, and the case body 12 and the sealing plate 14 are sealed together. Sealing can be performed by welding, for example, laser welding. Thereafter, a nonaqueous electrolyte is injected through the liquid injection hole 15 in the sealing plate 14, and the liquid injection hole 15 is closed with a sealing member 16, thereby sealing the electricity storage device 100. In this manner, the electricity storage device 100 can be manufactured.

[0079] <Applications of electricity storage devices> The power storage device 100 can also be suitably used as an assembled battery in which a plurality of power storage devices 100 are electrically connected to one another via a bus bar. In this case, the plurality of power storage devices 100 can be electrically connected by, for example, bridging a conductive member such as a bus bar between the positive electrode terminals 30 and negative electrode terminals 40 of adjacent power storage devices 100. The power storage device 100 can be used for a variety of purposes, and can be suitably used, for example, as a power source (driving power source) for a motor mounted on a vehicle such as a passenger car or truck. The type of vehicle is not particularly limited, and examples thereof include a plug-in hybrid electric vehicle (PHEV), a hybrid electric vehicle (HEV), and a battery electric vehicle (BEV).

[0080] Although several embodiments of the present invention have been described above, the above embodiments are merely examples. The present invention can be implemented in various other forms. The present invention can be implemented based on the contents disclosed in this specification and the common general technical knowledge in the relevant field. The technology described in the claims includes various modifications and alterations of the above-exemplified embodiments. For example, it is possible to replace part of the above-described embodiments with other modified embodiments, and it is also possible to add other modified embodiments to the above-described embodiments. Furthermore, if a technical feature is not described as essential, it may be deleted as appropriate.

[0081] <First Modification> For example, in the above-described embodiment, in the cover placement step (step S3), a cover is placed on the positive terminal 30 except for the area of ​​diameter D2 centered on the central axis CL, and in the etching step (step S5), a roughened portion Ae (see FIG. 8) having a substantially circular shape in plan view is formed. However, this is not limited to this. For example, as can be seen from FIG. 7, the bottom surface of the positive terminal 30 (the inner peripheral side of the annular crimping portion 30c) is recessed. Therefore, it may be difficult to irradiate the energy beam during the etching step. In such a case, it is preferable to place a cover on the recessed portion of the positive terminal 30 in the cover placement step (step S3).

[0082] If a cover is provided on the recessed portion of the positive terminal 30 in the cover placement step (step S3), welding spatter will not scatter on that portion in the laser welding step (step S4). Therefore, in the etching step (step S5), there is no need to irradiate that portion with energy rays, and the time required for the etching step can be shortened. FIG. 11 is a view corresponding to FIG. 8 according to this modification. As shown in FIG. 11, in this modification, a roughened portion Ae1 that is annular (donut-shaped) in plan view is formed on the surface of the welded joint J and its peripheral edge in the etching step.

[0083] As an example, an example of the negative electrode side according to this modification is shown in Figures 12(A) to 12(D). In this example, the negative electrode terminal 40 as the first member and the negative electrode first current collecting portion 61 as the second member are both made of copper (C1020). Figure 12(A) is an observation image of the vicinity of the welded joint J before the etching step (step S5), and Figure 12(B) is a partial enlarged view of Figure 12(A). As shown in Figure 12(A), there are two welded joints J, each of which is approximately C-shaped. As indicated by the circles in Figure 12(B), weld spatter can be seen scattered at random positions near the welded joints J.

[0084] Therefore, in this example, the etching process was carried out using the following equipment: The conditions for laser etching were as shown in Table 2 above. Equipment: Keyence Corporation 3-Axis Hybrid Laser Marker (Model: MD-X2500A) Laser wavelength: 1064nm (IR) Laser power: 90% Fill line type: Contour line Fill line spacing: 0.06mm

[0085] Fig. 12(C) is an observation image of the vicinity of the welded joint J after the etching process (step S5), and Fig. 12(D) is a partially enlarged view of Fig. 12(C). As shown in Fig. 12(C), it can be seen that a plurality of approximately circular recesses are formed on the surface and peripheral edge of the welded joint J, forming an annular roughened portion Ae1. Furthermore, as shown in Fig. 12(D), it can be seen that the welding spatter that was present before the etching process has been removed after the etching process.

[0086] <Second Modification> For example, in the above-described embodiment, the first member is a terminal (positive electrode terminal 30 or negative electrode terminal 40), and the second member is a current collector (positive electrode first current collector 51 or negative electrode first current collector 61). However, this is not limited thereto. For example, in the above-described battery pack, the first member may be a terminal (positive electrode terminal 30 or negative electrode terminal 40), and the second member may be a conductive member such as a bus bar.

[0087] As described above, specific aspects of the technology disclosed herein include those described in the following sections. Item 1: A joining method including a laser welding process in which a laser is irradiated onto the boundary between a first metal member and a second metal member to form a welded joint, and an etching process in which an energy beam is irradiated onto the surface and peripheral edge of the welded joint with a lower output than that of the laser welding process to form a plurality of approximately circular recesses on the surface and peripheral edge of the welded joint. Item 2: The bonding method according to Item 1, wherein in the etching step, the output of the energy beam is set to 50 W or less. Item 3: The joining method according to item 1 or 2, wherein in the etching step, the scanning speed of the energy beam is set to be faster than in the laser welding step. Item 4: The bonding method according to any one of Items 1 to 3, wherein the etching step forms a plurality of recesses each having a diameter of 20 to 100 μm and a depth of 1 to 10 μm. Item 5: The bonding method according to any one of Items 1 to 4, wherein the etching step forms a plurality of the recesses in a regular pattern. Item 6: The joining method according to any one of Items 1 to 5, wherein in the etching step, the energy beam is scanned along the welded joint. Item 7: The joining method according to any one of items 1 to 6, wherein in the etching step, the energy beam is scanned along the circumferential direction of the welded joint having a curved portion, thereby forming a plurality of the recesses aligned in the circumferential direction. Item 8: The joining method according to any one of items 1 to 7, further comprising a cover arrangement step of covering with a cover at least a portion of the area excluding the portion where the welded joint is to be formed, before the laser welding step, and irradiating the energy beam to the area not covered with the cover in the etching step. Item 9: A method for manufacturing an electricity storage device including the first member and the second member as components, the method including the joining method according to any one of items 1 to 8. Item 10: An energy storage device comprising: a first metal member; a second metal member; a welded joint between the first member and the second member; and a roughened portion provided on the surface of the welded joint and its peripheral portion, wherein the roughened portion has a plurality of approximately circular recesses and has larger recesses than the surrounding area. Item 11: The electricity storage device according to Item 10, wherein the recess has a diameter of 20 to 100 μm and a depth of 1 to 10 μm. Item 12: The electricity storage device according to item 10 or 11, wherein the recesses are regularly arranged. Item 13: The electricity storage device according to any one of Items 10 to 12, wherein the roughened portion is provided in a substantially circular or annular shape in a plan view, and the recesses are arranged side by side in the circumferential direction. Item 14: The electricity storage device according to any one of items 10 to 13, comprising: an electrode body including a first electrode and a second electrode; a case that houses the electrode body; a terminal that is electrically connected to the first electrode and attached to the case; and a current collector that is disposed within the case and electrically connects the first electrode and the terminal, wherein the first member is the terminal and the second member is the current collector. [Explanation of symbols]

[0088] 10 cases 20a, 20b, 20c electrode body 22 positive electrode (first electrode) 24 Negative electrode (second electrode) 30 Positive terminal (terminal) 30c Crimping part 40 Negative terminal (terminal) 50 Positive electrode current collector 51 Positive electrode first current collecting part (current collecting part) 60 Negative electrode current collector 61 Negative electrode first current collecting part (current collecting part) 100 Energy storage device J Welded joint Ae roughening part e1 recess An general department

Claims

1. a laser welding process of irradiating a laser to a boundary portion between a first metal member and a second metal member to form a welded joint; an etching process in which an energy beam is irradiated onto the surface and peripheral portion of the welded joint at a lower output than that of the laser welding process, thereby forming a plurality of substantially circular recesses on the surface and peripheral portion of the welded joint; A bonding method comprising:

2. In the etching step, the output of the energy beam is set to 50 W or less. The joining method according to claim 1 .

3. In the etching step, the scanning speed of the energy beam is set to be faster than that in the laser welding step. The joining method according to claim 1 .

4. In the etching step, a plurality of recesses each having a diameter of 20 to 100 μm and a depth of 1 to 10 μm are formed. The joining method according to claim 1 .

5. In the etching step, a plurality of the recesses are formed regularly. The joining method according to claim 1 .

6. In the etching step, the energy beam is scanned along the welded joint. The joining method according to claim 1 .

7. In the etching step, the energy beam is scanned along a circumferential direction of the welded joint having a curved portion, thereby forming a plurality of the recesses aligned in the circumferential direction. The joining method according to claim 1 .

8. The method further includes a cover placement step of covering at least a portion of the area excluding the portion forming the welded joint with a cover before the laser welding step, In the etching step, the energy beam is irradiated onto the region not covered with the cover. The joining method according to claim 1 .

9. A method for manufacturing an electricity storage device including the first member and the second member as components, the method including the joining method according to any one of claims 1 to 8. A method for manufacturing an electricity storage device.

10. The welding device comprises a first member made of metal, a second member made of metal, a welded joint between the first member and the second member, and a roughened portion provided on the surface of the welded joint and on a peripheral portion thereof, The roughened portion has a plurality of substantially circular recesses, and the recesses are larger than the surrounding area. Energy storage device.

11. The recess has a diameter of 20 to 100 μm and a depth of 1 to 10 μm. The electricity storage device according to claim 10.

12. The plurality of recesses are regularly arranged. The electricity storage device according to claim 10.

13. The roughened portion is provided in a substantially circular or annular shape in a plan view, The recesses are arranged in a circumferential direction. The electricity storage device according to claim 10.

14. an electrode assembly including a first electrode and a second electrode; a case for accommodating the electrode assembly; a terminal electrically connected to the first electrode and attached to the case; a current collecting portion disposed within the case and electrically connecting the first electrode and the terminal; Equipped with the first member is the terminal, The second member is the current collecting portion. The electricity storage device according to any one of claims 10 to 13.

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