Laser processing method, laser processing device, and sealed battery

Abstract

The present invention relates to a laser processing method, a laser processing device, and a sealed battery. In the laser processing method, a plurality of plate-like members, including a first plate-like member disposed at one end in a stacking direction and a second plate-like member disposed at the other end, are stacked. A laser beam is split into a first branched laser beam and a second branched laser beam, which are irradiated in parallel with each other. The branched laser beams are moved in a direction intersecting the direction in which the branched laser beams are arranged, thereby forming a linear molten portion in the first plate-like member. In the second plate-like member, the molten portion formed by the first branched laser beam and the molten portion formed by the second branched laser beam are connected, and the molten portion does not penetrate the second plate-like member. In this state, the stacked plate-like members are joined.

Description

Technical Field

[0001] The present disclosure relates to a laser processing method, a laser processing device, and a sealed battery. Background Art

[0002] Various laser processing methods are known in the past. For example, as a laser processing method for welding a plurality of plate-like members to each other, spot welding for welding at a single point and line welding for continuous welding in a straight line or a curved line are known.

[0003] Furthermore, these laser welding techniques are used, for example, in the manufacture of sealed batteries. In recent sealed battery manufacturing, a laser beam is irradiated from the outside of the battery outer can, creating a fusion zone between the outer can and the current collector tabs extending from the battery electrodes (see, for example, Patent Documents 1 and 2). Sealed batteries manufactured in this manner are used in power tools, electric bicycles, electric motorcycles, and the like.

[0004] For example, in Patent Document 1, the battery outer can and the current collecting tab are joined by spot welding. Figure 17A 2 is a cross-sectional view of a conventional laser processing method described in Patent Document 1. Figure 17B This is a detailed cross-sectional view of the vicinity of the molten portion 13, which is magnified and turned upside down for easier understanding. Figure 17A As shown, with the collector tab 12 superimposed on the inner surface of the bottom of the battery outer can 5, the laser beam 21 is irradiated from the outside of the bottom of the battery outer can 5 to form a fusion zone 13. Thus, the battery outer can 5 and the collector tab 12 are joined by spot welding. Figure 17B As shown, the width of the molten zone 13 in the horizontal direction of the drawing is greater than the thickness of the battery outer can 5. Consequently, the energy of the laser beam 21 entering the molten zone 13 increases, and the depth of the molten zone 13 in the vertical direction of the drawing is easily affected by the output of the laser beam 21. When the output of the laser beam 21 is high, the molten zone 13 is more likely to penetrate the current collector 12. If the molten zone 13 penetrates the current collector 12, spatter will enter the interior of the battery outer can 5, potentially causing a battery short circuit.

[0005] In addition, for example, in Patent Document 2, in order to prevent the inclusion of sputtering materials as in Patent Document 1, a fiber laser having enhanced focusing properties is used to reduce the focal spot diameter to a size smaller than the thickness of the battery outer can 5. Figure 18A As shown in FIG, the penetration of the current collecting tab 12 can be prevented by forming a narrow fusion zone 13. However, since the width of the fusion zone 13 at the boundary between the current collecting tab 12 and the battery outer can 5, i.e., the joining width, becomes narrow, the joining strength between the current collecting tab 12 and the battery outer can 5 is reduced. Figure 18BAs shown, the battery outer can 5 and the current collecting tab 12 are welded using three wires to increase the joint strength.

[0006] Prior art literature

[0007] Patent Literature

[0008] Patent Document 1: JP Patent No. 4547855

[0009] Patent Document 2: JP Patent No. 6512474 Summary of the Invention

[0010] A laser processing method according to one embodiment of the present invention is constructed as follows. A plurality of plate-like members including a first plate-like member arranged at one end side in the stacking direction and a second plate-like member arranged at the other end side are stacked. Next, the laser beam is branched into a first branch laser beam and a second branch laser beam. Next, the first branch laser beam and the second branch laser beam are irradiated on the first plate-like member in a parallel state. Next, the first branch laser beam and the second branch laser beam are moved relative to the first plate-like member in a direction intersecting with the direction in which the first branch laser beam and the second branch laser beam are arranged, so as to form a linear molten portion along the surface of the first plate-like member. In the second plate-like member, the molten portion formed by the first branch laser beam and the molten portion formed by the second branch laser beam are connected, and the molten portion does not penetrate the second plate-like member. Thus, the stacked plate-like members are joined via the linear molten portion.

[0011] A laser processing device according to one embodiment of the present invention comprises a laser oscillator, a laser oscillation control unit, a laser branching optical system, a laser processing optical system, a workbench, a workbench control unit, and an overall control unit. The laser oscillator irradiates a laser beam. The laser oscillation control unit controls the output of the laser beam. The laser branching optical system branches the laser beam into a plurality of branched laser beams. The laser processing optical system causes the branched laser beams to irradiate the first plate-like member of the stacked plate-like member as an irradiation object, which includes the first plate-like member arranged at one end side of the stacking direction and the second plate-like member arranged at the other end side, in a state of advancing in parallel with each other. The workbench moves the stacked plate-like member relative to the laser beam. The workbench control unit controls the movement of the workbench. The overall control unit synchronously controls the workbench control unit and the laser oscillation control unit. Therefore, the overall control unit controls the movement of the workbench and the irradiation of the branched laser beams. As a result, the branch laser beam is irradiated and moved relatively in a direction intersecting the direction in which the branch laser beams are arranged, forming a linear melting portion along the first plate-like component. The melting portion formed by one branch laser beam and the melting portion formed by another branch laser beam are connected in the second plate-like component, and the melting portion does not penetrate the second plate-like component.

[0012] A sealed battery according to one embodiment of the present disclosure includes a battery outer can and a current collector tab superimposed on the inner surface of the bottom portion of the battery outer can and joined to the battery outer can at a fusion zone. The current collector tab extends into the outer periphery of the fusion zone in the battery outer can.

[0013] A sealed battery according to one embodiment of the present disclosure comprises: a battery outer can; and a current collector tab superimposed on the inner surface of the bottom portion of the battery outer can and joined to the battery outer can at a fusion zone. The current collector tab extends further into the battery outer can in a peripheral portion surrounding the fusion zone of the battery outer can than in a central portion thereof. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1A This is an explanatory diagram of conventional wire bonding using three wires.

[0015] Figure 1B This is an explanatory diagram of conventional wire bonding using three wires.

[0016] Figure 2 This is a graph showing the correlation between laser output and bonding strength in conventional wire bonding using three wires.

[0017] Figure 3 This is a photo of the appearance of wire bonding using four wires.

[0018] Figure 4 This graph shows the correlation between laser output and joint strength in wire bonding using four wires.

[0019] Figure 5 It is a schematic cross-sectional view showing the structure of a sealed battery according to an embodiment.

[0020] Figure 6 It is a schematic cross-sectional view of a laser welding device according to an embodiment.

[0021] Figure 7 This is a schematic cross-sectional view of a laser processing optical system of a laser welding device according to an embodiment.

[0022] Figure 8 is a schematic diagram of the focal point of the branched laser beam.

[0023] Figure 9A This is a cross-sectional view of the melt after laser welding using a single branched laser beam according to Comparative Example 1.

[0024] Figure 9B This is a cross-sectional view of the melt after laser welding using a single branched laser beam according to Comparative Example 1.

[0025] Figure 10A This is a cross-sectional view of the melt after laser welding using two branched laser beams according to the embodiment.

[0026] Figure 10B This is a cross-sectional view of the melt after laser welding using two branched laser beams according to the embodiment.

[0027] Figure 11A This is a cross-sectional view immediately after the start of irradiation during the laser welding process using two branched laser beams according to the embodiment.

[0028] Figure 11B This is a cross-sectional view of a keyhole formed during laser welding using two branched laser beams according to an embodiment.

[0029] Figure 11C This is a cross-sectional view of the laser welding process using two branched laser beams according to the embodiment when the current collecting tab at the front end of the molten zone reaches the laser welding process.

[0030] Figure 11D This is a cross-sectional view of a keyhole being eliminated during laser welding using two branched laser beams according to an embodiment.

[0031] Figure 12A 4 is a cross-sectional view of a laser welding process using two non-simultaneously branched laser beams according to Comparative Example 2.

[0032] Figure 12B 4 is a cross-sectional view of a laser welding process using two non-simultaneously branched laser beams according to Comparative Example 2.

[0033] Figure 12C 4 is a cross-sectional view of a laser welding process using two non-simultaneously branched laser beams according to Comparative Example 2.

[0034] Figure 12D 4 is a cross-sectional view of a laser welding process using two non-simultaneously branched laser beams according to Comparative Example 2.

[0035] Figure 13A This is a cross-sectional view of the melt after laser welding using a split laser beam.

[0036] Figure 13B This is a cross-sectional view of the melt after laser welding using a split laser beam.

[0037] Figure 13C This is a cross-sectional view of the melt after laser welding using a split laser beam.

[0038] Figure 14A It is an explanatory diagram of a laser welding process using four branched laser beams according to an embodiment.

[0039] Figure 14B It is an explanatory diagram of a laser welding process using four branched laser beams according to an embodiment.

[0040] Figure 14C It is an explanatory diagram of a laser welding process using four branched laser beams according to an embodiment.

[0041] Figure 14D It is an explanatory diagram of a laser welding process using four branched laser beams according to an embodiment.

[0042] Figure 15 This is a correlation diagram between the laser output and the bonding strength using four-branched laser beams in the example.

[0043] Figure 16A This is a cross-sectional view of a current collecting tab suitable for the laser processing method according to the embodiment.

[0044] Figure 16B This is a cross-sectional view of a current collecting tab suitable for the laser processing method according to the embodiment.

[0045] Figure 16C This is a cross-sectional view of a current collecting tab suitable for the laser processing method according to the embodiment.

[0046] Figure 17A This is a diagram showing a conventional laser processing method described in Patent Document 1.

[0047] Figure 17B This is a diagram showing a conventional laser processing method described in Patent Document 1.

[0048] Figure 18A This is a diagram showing a conventional laser processing method described in Patent Document 2.

[0049] Figure 18B This is a diagram showing a conventional laser processing method described in Patent Document 2.

[0050] Description of Reference Signs

[0051] 100 Sealed batteries

[0052] 200 Laser welding device

[0053] 1 positive plate

[0054] 2 negative plates

[0055] 3 partitions

[0056] 4 winding body

[0057] 5. Battery outer can

[0058] 6 washers

[0059] 7 Upper insulation board

[0060] 8 Lower insulation board

[0061] 9 Melting area

[0062] 10 Sealing plate

[0063] 11 Positive electrode collector connector

[0064] 12 Negative electrode collector connector

[0065] 13, 13a~b Melting area

[0066] 14 Laser Oscillator

[0067] 15 Laser oscillation control unit

[0068] 16 Laser processing optical system

[0069] 17 Laser splitting optical system

[0070] 18 Workbench

[0071] 19 Workbench control unit

[0072] 20 Overall Control Department

[0073] 21 Laser Beam

[0074] 21a~d Split laser beam

[0075] 22, 22a~d focal point

[0076] 23 Melt Flow

[0077] 24 Current collector diffuser

[0078] 25a~b keyhole

[0079] 43 Melting area

[0080] 51 Laser Beam

[0081] 52 Spotlight

[0082] 53 Melt Flow DETAILED DESCRIPTION

[0083] (The Process of This Disclosure)

[0084] When conventional wire welding is used in a sealed battery manufacturing method (see Patent Document 2), the joint strength between the battery outer can and the current collecting tab after welding does not meet the target value (the joint strength value at which the battery outer can and the current collecting tab do not become detached).

[0085] Specifically, when a sealed battery or sealed battery assembly (a battery pack composed of multiple sealed batteries) manufactured using existing laser welding is dropped, the battery does not meet the normal state (for example, a state in which a device using the battery can function normally). If the battery is dropped under given conditions in various drop tests, the battery outer can and the collector connector will fall off. In order to prevent such falling off, it is desirable to increase the bonding strength compared to the bonding strength between the battery outer can and the collector connector in existing laser welding. For example, it is better to increase the bonding strength to about 1.5 times the existing one.

[0086] exist Figure 1A as well as Figure 1B : The figure shows the conventional wire bonding method using three wires. Figure 1A As shown, wire welding using three wires is performed as a conventional method. As a result, three linear fusion zones 13 are formed along the surface of the battery outer can 5 .

[0087] like Figure 1B As shown in the cross-sectional view of , the fusion zone 13 penetrates the battery outer can 5 and reaches the current collecting tab 12. The current collecting tab 12 is formed of a three-layer coating (nickel / copper / nickel).

[0088] exist Figure 2 The graph in FIG. 1 shows the correlation between the laser output and the bonding strength in conventional three-wire wire welding. The horizontal axis represents the laser output (W), and the vertical axis represents the bonding strength between the battery outer can 5 and the current collector tab 12. Figure 2 In the figure, for the purpose of explanation, the current value, which is the value of the bonding strength currently being sought, and the target value, which is the value set as the target for further increasing the bonding strength, are shown. Figure 2 The collector tab penetration region is shown in FIG. The collector tab penetration region is the range of laser output where the molten zone 13 formed by irradiation using the laser output penetrates the collector tab 12. Increasing the laser output increases the joint strength, but excessively increasing the laser output will cause the laser output to reach the collector tab penetration region. In this case, the molten zone 13 penetrates the collector tab 12, and sputtering from the melted collector tab 12 can enter the interior of the battery can 5, causing short circuits. Therefore, even with increased laser output, the target joint strength cannot be achieved.

[0089] exist Figure 3 2 shows an external appearance photograph of wire welding using four wires, which was studied as an improvement measure for wire welding using three wires. Four linear fusion zones 13 are formed along the surface of the battery outer can 5 .

[0090] In addition, Figure 4The graph in FIG. 1 shows the correlation between the laser output and the bonding strength when four wires are welded. The horizontal axis represents the laser output (W), and the vertical axis represents the bonding strength between the battery outer can 5 and the current collector tab 12. Figure 4 As shown, even if the number of linear fusion zones 13 is increased to four, the maximum bonding strength increases by only about 5%, and the target bonding strength value cannot be achieved.

[0091] On the other hand, simultaneous wire welding of five wires requires a laser device capable of achieving even higher laser output. Consequently, conventional laser processing methods have made it difficult to achieve the target bond strength between the battery outer can 5 and the current collector tab 12. To address this issue, the inventors of the present invention have developed the laser processing method disclosed herein as a method that could address this issue.

[0092] The present disclosure aims to solve the above-mentioned conventional problems by increasing the joint strength at the molten zone formed by laser irradiation without penetrating the plate-like member farthest from the irradiation surface in overlapping laser welding of two or more plate-like members.

[0093] A laser processing method according to one embodiment of the present invention includes the following steps. A plurality of plate-like members including a first plate-like member arranged at one end side in the stacking direction and a second plate-like member arranged at the other end side are stacked. Next, the laser beam is branched into a first branch laser beam and a second branch laser beam. Next, the first branch laser beam and the second branch laser beam are irradiated on the first plate-like member in a parallel state. Next, the first branch laser beam and the second branch laser beam are moved relative to the first plate-like member in a direction intersecting with the direction in which the first branch laser beam and the second branch laser beam are arranged, so as to form a linear molten portion along the surface of the first plate-like member. In the second plate-like member, the molten portion formed by the first branch laser beam and the molten portion formed by the second branch laser beam are connected, and the molten portion does not penetrate the second plate-like member. Thus, the stacked plate-like members are joined via the linear molten portion.

[0094] Furthermore, the interval between the focal points of the branched laser beams may be greater than the joining width and less than the melting width of the fusion zone formed by one branched laser beam.

[0095] Alternatively, the laser beam may be split into a plurality of branched laser beams, each comprising a plurality of groups of first branched laser beams and second branched laser beams. Alternatively, the respective branched laser beams may be caused to irradiate the first plate-shaped member while traveling in parallel. Alternatively, in the first plate-shaped member, the interval between the branched laser beams in one group and the branched laser beams in another adjacent group may be greater than the interval between the first branched laser beam and the second branched laser beam.

[0096] The interval between adjacent focal points of the branched laser beams is greater than the joining width and less than the melting width of the fusion zone formed by the branched laser beam. Alternatively, it may be greater than the melting width of the fusion zone formed by the branched laser beam.

[0097] Alternatively, the split laser beams may be irradiated so that the molten portions formed by the split laser beams are point-symmetrical or line-symmetrical with respect to the center position of the surface of the first plate-shaped member.

[0098] Alternatively, the second plate-shaped member may be made of a copper-based material that suppresses absorption of the laser beam.

[0099] A laser processing device according to one embodiment of the present invention comprises a laser oscillator, a laser oscillation control unit, a laser branching optical system, a laser processing optical system, a workbench, a workbench control unit, and an overall control unit. The laser oscillator irradiates a laser beam. The laser oscillation control unit controls the output of the laser beam. The laser branching optical system branches the laser beam into a plurality of branched laser beams. The laser processing optical system causes the branched laser beams to irradiate the first plate-like member of the stacked plate-like members as the irradiation object in a mutually parallel state. The stacked plate-like members as the irradiation object include the first plate-like member arranged on one end side of the stacking direction and the second plate-like member arranged on the other end side. The workbench moves the stacked plate-like members relative to the laser beam. The workbench control unit controls the movement of the workbench. The overall control unit synchronously controls the workbench control unit and the laser oscillation control unit. Therefore, the overall control unit controls the movement of the workbench and the irradiation of the branched laser beams. As a result, the branch laser beam is irradiated and moved relatively in a direction intersecting with the direction in which the branch laser beams are arranged, forming a linear melting portion along the first plate-like component. The melting portion formed by one branch laser beam and the melting portion formed by another branch laser beam are connected in the second plate-like component, and the melting portion does not penetrate the second plate-like component.

[0100] Furthermore, the laser beam branching optical system may include a diffraction optical element (DOE) that branches the laser beam into a plurality of branched laser beams.

[0101] A sealed battery according to one embodiment of the present disclosure includes a battery outer can and a current collector tab superimposed on the inner surface of the bottom portion of the battery outer can and joined to the battery outer can at a fusion zone. The current collector tab extends into the outer periphery of the fusion zone in the battery outer can.

[0102] A sealed battery according to one embodiment of the present disclosure comprises: a battery outer can; and a current collector tab superimposed on the inner surface of the bottom portion of the battery outer can and joined to the battery outer can at a fusion zone. The current collector tab extends further into the battery outer can in a peripheral portion surrounding the fusion zone of the battery outer can than in a central portion thereof.

[0103] According to the laser processing method and laser processing apparatus of the present disclosure, in overlapping laser welding of two or more plate-like members, the joining strength of the molten zone formed by laser irradiation can be increased without penetrating the plate-like member farthest from the irradiation surface.

[0104] Hereinafter, a laser processing method and a laser processing device in a method for manufacturing a sealed battery according to an embodiment will be described in detail with reference to the drawings.

[0105] Furthermore, the laser processing method of this embodiment is not limited to the sealed batteries described in the following embodiments. Specifically, the following description uses a method for manufacturing a sealed battery as an example of a laser processing method and laser processing apparatus. Furthermore, modifications may be made as appropriate without departing from the scope of the present disclosure. Furthermore, combinations with other embodiments are also possible.

[0106] (Sealed Battery According to Embodiment)

[0107] First, the sealed battery 100 according to the embodiment will be described in detail.

[0108] exist Figure 5 : A schematic cross-sectional view of the structure of a sealed battery 100 according to an embodiment is shown in FIG. The sealed battery 100 includes a battery outer can 5, a gasket 6, a sealing plate 10, an insulating plate 7, an insulating plate 8, a wound body 4, a positive electrode plate 1, a negative electrode plate 2, a separator 3, a positive electrode collector tab 11, and a negative electrode collector tab 12. The battery outer can 5 includes an opening. The opening is sealed by the sealing plate 10. A gasket 6 is arranged between the opening and the sealing plate 10, and the sealing plate 10 is fixed to the opening by compressing the gasket 6. A plurality of wound bodies 4, insulating plates 7, insulating plates 8, and an electrolyte are accommodated in the battery outer can 5. The wound body 4 is sandwiched by the insulating plates 7 and 8 in the battery outer can 5. The wound body 4 includes a positive electrode plate 1, a negative electrode plate 2, and a separator 3, and the positive electrode plate 1 and the negative electrode plate 2 are wound with the separator 3 interposed therebetween. A positive electrode current collector tab 11 is extended from one electrode plate (e.g., the positive electrode plate 1) of the wound body 4. A negative electrode current collector tab 12 is extended from the other electrode plate (e.g., the negative electrode plate 2). A fusion zone 9 is provided between the positive electrode current collector tab 11 and the sealing plate 10. The positive electrode current collector tab 11 and the sealing plate 10 are joined together by the fusion zone 9. A fusion zone 13 is provided between the negative electrode current collector tab 12 and the battery outer can 5. The negative electrode current collector tab 12 and the battery outer can 5 are joined together by the fusion zone 13.

[0109] Next, laser welding in the method of manufacturing the sealed battery 100 will be described.

[0110] First, the positive electrode plate 1 and the negative electrode plate 2 are wound or stacked with the separator 3 to form a wound body 4. Then, one end of each current collector tab 11, 12 is connected to each electrode plate 1, 2 of the wound body 4. Then, the wound body 4 is housed in the battery outer can 5. Then, the other end of the current collector tab 12 is overlapped with the inner surface bottom portion of the battery outer can 5. Figure 5 Although not shown, the laser beam is branched into a plurality of branch laser beams. Next, the branch laser beam is irradiated onto the approximate center of the outer bottom surface of the battery outer can 5 with a focal spot diameter smaller than the plate thickness of the battery outer can 5, and the branch laser beam is scanned on the battery outer can 5. As a result, a linear molten portion 13 is formed on the battery outer can 5, and the battery outer can 5 and the current collector 12 located therein can be joined by laser welding. On the other hand, the other end of the current collector 11 is superimposed on the sealing plate 10, and the sealing plate 1 is irradiated in the same manner as the battery outer can 5. As a result, a linear molten portion 9 is formed on the sealing plate 10, and the sealing plate 10 and the current collector 11 can be joined by laser welding.

[0111] (Laser processing device according to embodiment)

[0112] Next, a laser welding device 200 will be described in detail as an example of the laser processing device according to the embodiment.

[0113] exist Figure 6 A laser welding device 200 according to an embodiment is shown. Figure 6 The X and Y directions are respectively directions along the bottom surface of the battery outer can 5 and are orthogonal to each other. The Z direction is the direction in which the battery outer can 5 and the current collecting tab 12 are superimposed and is orthogonal to the X and Y directions.

[0114] like Figure 6 As shown, the laser welding device 200 includes a laser oscillator 14 , a laser oscillation control unit 15 , a laser beam splitting optical system 17 , a laser processing optical system 16 , a stage 18 , a stage control unit 19 , and an overall control unit 20 .

[0115] The laser oscillator 14 irradiates the laser beam 21. The laser oscillator 14 is, for example, a fiber laser oscillator. The laser oscillator 14 oscillates laser light having, for example, a laser output of 1 kW and a laser wavelength of 1070 nm. The laser oscillator 14 is not limited to such specifications.

[0116] The laser oscillation control unit 15 controls the irradiation (on / off) of the laser beam 21 emitted from the laser oscillator 14 and the output of the laser beam 21. By performing output control, the laser beam 21 with the output required to melt the battery outer can 5 and the current collector tab 12 can be irradiated. For example, by controlling the output of the laser oscillation control unit 15, irradiation can be performed so that the battery outer can 5 and the current collector tab 12 are melted, and the formed molten portion 13 does not penetrate the current collector tab 12.

[0117] The laser beam 21 emitted from the laser oscillator 14 is incident on the laser branching optical system 17, and the laser beam 21 is branched into two or more branched laser beams by the optical system. Figure 6 2 shows a case where the laser beam 21 is split into two split laser beams 21a and 21b by the laser splitting optical system 17. The split laser beams 21a and 21b are arranged in the Y direction. A diffractive optical element (DOE) can also be used in the laser splitting optical system 17 to split the laser beam 21. Furthermore, for example, by designing the splitting pattern of the DOE (diffractive optical element), the laser beam 21 can be split at any position and with any intensity. The laser splitting optical system 17 is built into the laser processing optical system 16.

[0118] The laser beam 21 emitted from the laser oscillator 14 passes through the optical fiber and enters the laser processing optical system 16. The laser beam 21 is split into split laser beams 21a and 21b by the laser splitting optical system 17 built into the laser processing optical system 16. The laser processing optical system 16 focuses the split laser beams 21a and 21b so that the split laser beams 21a and 21b irradiate the battery outer can 5 in a parallel state. Figure 6 In the embodiment, the branched laser beams 21a and 21b are aligned in the Y direction and irradiated in the Z direction. Furthermore, the focal points 22a and 22b formed on the bottom surface of the battery outer can 5 by the branched laser beams 21a and 21b are also aligned in the Y direction. For example, the laser processing optical system 16 can focus the focal points of the branched laser beams 21a and 21b to a position less than the plate thickness of the battery outer can 5 (the thickness of the cross section in the Z direction). Furthermore, for example, the laser processing optical system 16 can irradiate the branched laser beams 21a and 21b at a position approximately at the center of the outer bottom surface of the battery outer can 5. Furthermore, when the laser beam 21 is branched into three or more branched laser beams by the laser branching optical system 17, the laser processing optical system 16 can irradiate the laser beams so that the focal points of each branched laser beam are located on the same straight line in the Y direction.

[0119] The workbench 18 is moved while carrying the irradiation object. Figure 6 As shown, the stage 18 carries, for example, the battery exterior can 5 and the current collecting tab 12 and moves the battery exterior can 5 and the current collecting tab 12 in the X direction.

[0120] The stage control unit 19 controls the movement of the stage 18. For example, the moving distance, moving speed, and movement start timing of the stage 18 can be controlled by the stage control unit 19.

[0121] The overall control unit 20 synchronously controls the workbench control unit 19 and the laser oscillation control unit 15, thereby controlling the movement of the workbench 18 and the output of the branched laser beams 21a and 21b. The branched laser beams 21a and 21b can be irradiated, and the battery outer can 5 and the collector terminal 12 can be moved relative to the laser processing optical system 16 in a direction that intersects and is orthogonal to the direction in which the branched laser beams 21a and 21b are arranged. The so-called direction in which the branched laser beams 21a and 21b are arranged refers to the direction on the straight line connecting the focal points 22a and 22b formed on the bottom surface of the battery outer can 5. Figure 6 As shown, in this embodiment, the branched laser beams 21a and 21b are aligned in the Y direction, and the sealed battery 100 is moved in the X direction by the stage 18. As a result, the branched laser beams 21a and 21b form linear molten zones 13 along the X direction of the battery outer can 5. The molten zones 13 are connected to each other at the current collecting tab 12, and the molten zones 13 do not penetrate the current collecting tab 12. The battery outer can 5 and the current collecting tab 12 are joined by the linear molten zones 13.

[0122] In addition, in the above description, the laser welding device 200 is described as irradiating the battery outer can 5 and the collector tab 12 of the sealed battery 100. However, the irradiation target is not limited to this. For example, a plurality of plate-like components can be stacked as the irradiation target. In addition, the shape of the plate-like component is not limited to a flat surface as a whole. As long as the component extends in a surface direction perpendicular to the thickness direction of the component and the components can be stacked on each other in the irradiation target area, it can be used. For example, the plate-like components can be stacked on the disc-shaped end surface of the cylinder, and the cylinder and the plate-like components can be used as the irradiation target. In addition, a single plate-like component can have multiple layers, such as a covering or a laminated material.

[0123] In the above description, the laser beam 21 is split into two split laser beams 21a and 21b by the laser splitting optical system 17, but the present invention is not limited to this. The laser beam 21 may be split into two or more, for example, four, split laser beams.

[0124] Furthermore, the moving element in the laser welding apparatus 200 is not limited to the worktable 18. For example, the laser processing optical system 16 may be moved relative to the stationary worktable 18. Furthermore, for example, the worktable 18 and the laser processing optical system 16 may be moved relative to each other. Furthermore, the movement is not limited to movement in a single axis direction; for example, movement within the XY plane may be possible.

[0125] In the above description, the direction in which the branched laser beams 21a and 21b are arranged is perpendicular to the direction in which the battery outer can 5 and the current collecting tab 12 are moved. However, this is not the only limitation. The branched laser beams 21a and 21b may be moved relative to the battery outer can 5 and the current collecting tab 12 in a direction intersecting the direction in which the branched laser beams 21a and 21b are arranged. For example, the battery outer can 5 and the like may be moved in a direction having an angle other than 90° with respect to the Y direction, which is the direction in which the branched laser beams 21a and 21b are arranged.

[0126] (Laser processing method according to embodiment)

[0127] Next, the laser processing method according to the embodiment will be described in detail.

[0128] The laser processing method involved in this embodiment includes the following steps. A plurality of plate-like members including a first plate-like member arranged on one end side of the stacking direction and a second plate-like member arranged on the other end side are stacked. Then, the laser beam is branched into a first branch laser beam and a second branch laser beam. Then, the first branch laser beam and the second branch laser beam are irradiated on the first plate-like member in a parallel state. Then, the first branch laser beam and the second branch laser beam are relatively moved relative to the first plate-like member in a direction intersecting with the direction in which the first branch laser beam and the second branch laser beam are arranged, so as to form a linear molten portion along the surface of the first plate-like member. In the second plate-like member, the molten portion formed by the first branch laser beam and the molten portion formed by the second branch laser beam are connected, and the molten portion does not penetrate the second plate-like member. Therefore, the stacked plate-like members are joined through the linear molten portion.

[0129] In this embodiment, the bottom of the battery outer can 5 corresponds to the first plate-shaped member, and the current collector tab 12 corresponds to the second plate-shaped member. Furthermore, a laser processing method is performed using a laser welding device 200. Furthermore, a laser beam 21 is split by a laser splitting optical system 17, and irradiated onto the battery outer can 5 by a laser processing optical system 16. The overall control unit 20 moves the battery outer can 5 and the current collector tab 12 relative to the laser beam 21. This embodiment is described below.

[0130] (Laser beam splitting)

[0131] First, refer to Figure 7 as well as Figure 8 To explain the laser beam splitting in detail. Figure 7 1 is a schematic cross-sectional view of the laser processing optical system 16 of the laser welding device 200 according to the embodiment. Figure 8 A schematic diagram showing the focal points of the branched laser beams 21a to 21d.

[0132] exist Figure 7 Detailed diagram of the vicinity of the laser processing optical system 16 in the laser welding device 200 is shown. Figure 7 In the process, the laser beam 21 enters the laser processing optical system 16 and is branched into four branched laser beams 21a to 21d by the laser branching optical system 17. The branched laser beams 21a to 21d irradiate the battery outer can 5 in the Z direction while being aligned in the Y direction.

[0133] exist Figure 8 The branched laser beams 21a to 21d are focused at points 22a to 22d. The branched laser beams 21a to 21d are focused by the laser processing optical system 16 to have a focusing point diameter of Four focal points 22a to 22d are formed. These focal points 22a to 22d are located on the same straight line in the Y direction. The laser beam intensity at each of these focal points 22a to 22d is equal. In this embodiment, the battery outer can 5 and the current collector 12 are moved relative to the branched laser beams 21a to 21d in the X direction, which is perpendicular to the Y direction in which the focal points 22a to 22d are arranged.

[0134] like Figure 8 As shown, the pitch between light-converging points 22a and 22b is P1, the pitch between light-converging points 22b and 22c is P2, and the pitch between light-converging points 22c and 22d is P3. P1 and P3 are equal. On the other hand, P1 and P3 are smaller than P2. In this embodiment, P1 and P3 are 100 μm, P2 is 800 μm, and the total width (P1 + P2 + P3) is 1 mm.

[0135] The branch laser beams 21a and 21b, which are adjacent to each other at a narrow point spacing P1, form one group of branch laser beams. Similarly, the branch laser beams 21c and 21d, which are adjacent to each other at a narrow point spacing P3, form another group of branch laser beams. That is, the four branch laser beams form two groups (a group of 21a and 21b, and a group of 21c and 21d). In addition, the interval between one group and another group, that is, the point spacing P2, is set to be larger than the point spacing between the branch laser beams in one group (for example, the point spacing P1 or P3). In addition, the so-called interval between one group and another group is the minimum distance between the branch laser beams of one group and the branch laser beams of another group.

[0136] The following describes a pair of branched laser beams 21a and 21b in detail. In the following description, a pair of branched laser beams may be referred to as the first branched laser beam 21a and the second branched laser beam 21b. The description of a pair of branched laser beams 21a and 21b also applies to the other pair of branched laser beams 21c and 21d.

[0137] (Laser welding using two split laser beams)

[0138] The laser beam 21 is split at a spot pitch P1, and laser welding is performed simultaneously using a pair of the first split laser beam 21a and the second split laser beam 21b. Figure 9A 、 Figure 9B 、 Figure 10A as well as Figure 10B To explain in detail the method of laser welding. Figure 9A In FIG. 1 , a cross-sectional view of the melt after laser welding using a single laser beam 51 is shown as Comparative Example 1. Figure 9B Shown in Figure 9A The actual cross-sectional view of the photo. Figure 10A FIG shows a cross-sectional view of the melt after laser welding using two branched laser beams 21a and 21b in this embodiment. Figure 10B Shown in Figure 10A A photo of the actual cross section.

[0139] exist Figure 9A as well as Figure 9B In the comparative example 1 shown, the thickness of the battery outer can 5 is 300 μm, and the thickness of the collector tab 12 is 100 μm. The laser beam 51 is focused at the focal point 52 to a focal point diameter of The upper surface of the battery outer can 5 in the accompanying drawings is used as the irradiation surface of the laser beam 51, and the laser beam 51 is irradiated in the Z direction. By keyhole laser welding, the battery outer can 5 and the collector tab 12 are melted, and a molten portion 43 is formed between the battery outer can 5 and the collector tab 12. A molten flow 53 in the negative direction of the Z direction is generated in the molten portion 43, and the melted battery outer can 5 and the melted collector tab 12 are mixed together. Under appropriate laser conditions, laser welding can be performed without the molten portion 43 penetrating the collector tab 12. The width of the molten portion 43 in the irradiation surface of the battery outer can 5 (hereinafter referred to as the molten width) is 120 μm. In addition, the width of the molten portion 43 at the boundary between the collector tab 12 and the battery outer can 5 adjacent to the collector tab 12 (hereinafter referred to as the joining width) is 50 μm.

[0140] exist Figure 10A In the embodiment shown, as in Comparative Example 1, the thickness of the battery outer can 5 is 300 μm, and the thickness of the collector tab 12 is 100 μm. On the other hand, the laser beam 21 is branched into a first branched laser beam 21a and a second branched laser beam 21b arranged in the Y direction, and is focused at each focusing point 22a and focusing point 22b to a focusing point diameter of Spot diameter This is smaller than the 300 μm thickness of the battery outer can 5. The spot pitch P1 between the light-converging points 22a and 22b is 100 μm.

[0141] By irradiating the battery outer can 5 in the Z direction with the two branched laser beams 21a and 21b aligned in the Y direction, the battery outer can 5 and the current collecting tab 12 are melted. A continuous molten portion 13 is formed at the current collecting tab 12 and the boundary between the current collecting tab 12 and the battery outer can 5. By irradiating the branched laser beams 21a and 21b simultaneously, the temperature of the molten portion 13 becomes higher than Figure 9A The temperature of the melting portion 43 is higher. In addition, the melting volume of the melting portion 13 becomes larger than Figure 9A The melting volume of the melting portion 43 is large. The so-called melting volume is the volume of the melting portion 13 or the melting portion 43. In the melting portion 13, a melt flow 23 is generated that is disordered in the negative direction of the Z direction, the positive or negative direction of the Y direction, and the positive or negative direction of the X direction. Since the temperature of the melting portion 13 is high and the melting volume of the melting portion 13 is large, the melt flow 23 is larger than Figure 9A The melt flow 53 is large, and the area where the melt flow 23 appears is also larger. Through the melt flow 23, the melted battery outer can 5 and the melted collector tab 12 are mixed together. Therefore, the joint width of the melt portion 13 in the collector tab 12 is expanded. The joint width of the melt portion 13 is 150 μm, which is three times the joint width of Comparative Example 1. If the joint width is increased, the joint strength between the battery outer can 5 and the collector tab 12 will increase. Therefore, by irradiating with two branched laser beams 21a and 21b using one laser beam 21, the joint strength is increased.

[0142] On the other hand, similar to Comparative Example 1, the molten portion 13 does not penetrate the current collector tab 12. This prevents spatter from the melted current collector tab 12 from entering the space inside the battery can 5. Consequently, short circuit failures in the sealed battery 100 can be suppressed.

[0143] In addition, if Figure 10B As shown, as a result of the molten flow 23 , a portion of the current collecting tab 12 diffuses toward the battery exterior can 5 , forming a current collecting tab diffusion portion 24 .

[0144] By forming the collector tab diffusion portion 24, the material constituting the collector tab 12 flows from the collector tab 12 into the area of the battery outer can 5 at the outer peripheral portion of the molten portion 13. For example, the collector tab 12 may be a three-layer coating of nickel, copper, and nickel. In this case, the nickel and / or copper of the collector tab 12 is melted by laser irradiation and enters the area of the battery outer can 5 through the molten flow 23. As a result, a collector tab diffusion portion 24 comprising nickel and / or copper is formed in the area of the battery outer can 5. Since the material constituting the collector tab 12 has high electrical conductivity, the conductivity of the battery outer can 5 in the molten portion 13 is increased. Therefore, in the sealed battery 100, the flow of current from the collector tab 12 to the battery outer can 5 becomes good.

[0145] Furthermore, when the material constituting the current collector tab 12 enters the region of the battery outer can 5 from the current collector tab 12 due to the formation of the current collector tab diffusion portion 24, more material constituting the current collector tab 12 enters the outer peripheral portion of the fusion zone 13 than the central portion of the fusion zone 13. As a result, the current collector tab diffusion portion 24 reaches a higher height in the Z direction opposite to the fusion zone 13 at the outer peripheral portion of the fusion zone 13 than at the central portion of the fusion zone 13. With this structure, the flow of current from the current collector tab 12 to the battery outer can 5 in the sealed battery 100 is further improved.

[0146] Next reference Figures 11A to 11D To explain the laser welding method in detail. Figures 11A to 11D 2 shows a cross-sectional view of a laser welding process using a set of 2 branched laser beams 21 a , 21 b with a spot pitch P1 .

[0147] exist Figure 11A The figure shows the melting cross section immediately after the irradiation of the first branch laser beam 21a and the second branch laser beam 21b. The first branch laser beam 21a and the second branch laser beam 21b are irradiated in parallel with a narrow spot pitch P1. Therefore, elongated holes called keyholes 25a and 25b are opened inside the molten portions 13a and 13b. The first branched laser beam 21a and the second branched laser beam 21b propagate through the holes, and the molten portions 13a and 13b grow elongated in the Z direction.

[0148] exist Figure 11B The figure further illustrates a cross-sectional view of the melt, with keyholes 25a and 25b growing in the Z direction. Heat of melting accumulates between melt zone 13a and melt zone 13b, increasing melting efficiency. Consequently, melt zone 13a expands toward melt zone 13b, and melt zone 13b expands toward melt zone 13a. Near the upper surface of the battery can 5 in the figure, melt zones 13a and 13b are connected. "Connected" means that melt zone 13a formed by branched laser beam 21a and melt zone 13b formed by branched laser beam 21b are continuous, with no boundary between them.

[0149] exist Figure 11C The molten cross-sectional view shows a state where the tips of the molten portions 13a and 13b have reached the current collector tab 12. At the tips of the molten portions 13a and 13b, a molten flow 23 is generated that is disrupted in the negative Z direction and the positive or negative Y direction, mixing the melted battery outer can 5 and the melted current collector tab 12. As a result, the molten portions 13a and 13b are connected.

[0150] exist Figure 11D The figure shows a cross-sectional view of the melt process with keyholes 25a and 25b shallowed. After laser irradiation ends, keyholes 25a and 25b become shallower and disappear. Furthermore, upon completion of laser irradiation, the upper surface of the battery outer can 5 (in the figure) cools, increasing the temperature gradient in the melted portions 13a and 13b. Consequently, the melt flow 23 in the negative Z direction becomes stronger, further intermixing the battery outer can 5 and the current collector tab 12. This increases the width of the bond between the melted portions 13a and 13b in the current collector tab 12. Consequently, the bond strength between the battery outer can 5 and the current collector tab 12 is enhanced.

[0151] Next, as a comparative example 2 of the embodiment, referring to the cross-sectional view showing the laser welding process, Figure 12A as well as Figure 12B The case where the molten portion is formed by irradiating the laser beam not simultaneously but sequentially will be described in detail.

[0152] exist Figure 12A The figure shows the melted cross section after irradiation with the first laser beam 21a (identified by the same reference numeral 21a as the first branched laser beam). The laser beam 21a irradiates the battery outer can 5 alone, forming a melted portion 13a between the battery outer can 5 and the current collecting tab 12.

[0153] Then, if Figure 12B As shown, the battery outer can 5 is irradiated with the second laser beam 21b (denoted by the same reference numeral 21b as the second branched laser beam for clarity) at the position of the focal point 22b, which is offset by 100 μm in the Y direction from the first laser beam 21a. The melted portion 13a has already solidified when the laser beam 21b is irradiated. Therefore, the melted portion 13b formed by the laser beam 21b is formed independently of the melted portion 13a formed by the first laser beam 21a.

[0154] like Figure 12C As shown, the individual fusion zones 13a and 13b are not connected, forming two separate fusion zones 13a and 13b. Since two welds are performed with a joint width of 50 μm, the total joint width is 100 μm. Consequently, the joint strength between the battery outer can 5 and the current collector tab 12 is not increased. Therefore, to increase the joint strength between the battery outer can 5 and the current collector tab 12, it is preferable to irradiate the laser beams 21a and 21b simultaneously.

[0155] In addition, if Figure 12D As shown in the molten cross section, the respective molten portions 13a and 13b formed by the laser beams 21a and 21b are not connected, but are divided into two molten portions 13a and 13b.

[0156] As described above, it is better to irradiate the two branched laser beams 21a and 21b branched at the spot pitch P1 at the same time. Figures 13A to 13C Let's explain the dot pitch P1 in detail. Figures 13A to 13C FIG. 3 shows a cross-sectional view of the melt after laser welding using a split laser beam.

[0157] exist Figure 13A The figure shows the individual joining width JW (Joining Width) and the individual melting width MW (Melting Width) of the molten portion 13 formed by one laser beam 21. The individual joining width JW of the molten portion 13 refers to the width of the molten portion 13 at the boundary between the collector connector 12 and the battery outer can 5 adjacent to the collector connector 12 in a direction perpendicular to the laser scanning direction. The individual melting width MW of the molten portion 13 refers to the width of the molten portion 13 at the irradiated surface in a direction perpendicular to the laser scanning direction, i.e., the upper surface of the battery outer can 5 in the accompanying drawing. Figure 13A In the example, the individual joint width JW is 50 μm and the individual fusion width MW is 120 μm.

[0158] By irradiating the single laser beam 21 with two branched laser beams 21a and 21b, the width of the joint based on the molten zone 13 and the joint strength between the battery outer can 5 and the current collecting tab 12 can be increased. Figure 13B As shown, the split laser beams 21a and 21b form a continuous molten zone 13 at a spot pitch P1 (eg, 30 μm) equal to or smaller than the individual joint width JW. The joint width due to the molten zone 13 is 80 μm.

[0159] In addition, for example, Figure 13C As shown, with a point pitch P1 (e.g., 150 μm) greater than the individual melting width MW, two molten portions 13a and 13b are formed that are not connected but remain separate. Furthermore, since the joining widths of the molten portions 13a and 13b are each 50 μm, the total joining width becomes 100 μm.

[0160] Therefore, by setting the point pitch P1 to be greater than the individual joint width JW and less than the individual melt width MW, the fusion zone 13 is connected, and the joint width based on the fusion zone 13 and the joint strength between the battery outer can 5 and the current collecting tab 12 can be further increased. Figure 10A As shown, the joining width due to the fusion zone 13 is 150 μm.

[0161] (Laser welding using 4-branch laser beams)

[0162] Next, the laser welding of the four branched laser beams 21a to 21d will be described in detail. Figure 8As shown in FIG, the branched laser beams 21a to 21d are irradiated while being parallel to each other. Figures 14A to 14D 2 is an explanatory diagram of a laser welding process using four branched laser beams.

[0163] exist Figure 14A Figure 2 shows a melt cross-section model using these four beams. The four split laser beams 21a to 21d form two groups with a narrow inter-point spacing, with the spacing between the two groups greater than this narrow inter-point spacing. Consequently, two connected melt zones 13 are formed at separate locations, laser welding the battery outer can 5 and current collector tab 12 at two locations. This increases the joint strength.

[0164] exist Figure 14B ] shows an external appearance melt pattern viewed from the bottom of the battery outer can 5. By welding at positions symmetrical or line-symmetrical with respect to the center position of the surface of the battery outer can 5 and separating the two positions, the joint torque strength can also be increased.

[0165] exist Figure 14C The actual melting cross-section photo is shown in Figure 14D The actual appearance photograph is shown in FIG. It can be seen that the above-mentioned model estimates the results. Specifically, the laser processing method according to this embodiment can form a continuous molten zone 13 using a single branched laser beam set without penetrating the current collector tab 12, thereby increasing the joint width at the boundary between the current collector tab 12 and the battery outer can 5.

[0166] As described above, irradiation may be performed by applying four branched laser beams 21a to 21d having narrow point spacings P1 and P3 and wide point spacings P2. In addition, the point spacings P1 and P3 may be set to be greater than the individual joining width JW of the molten portion 13 formed by one laser beam 21 and less than the individual melting width MW formed under the same conditions. In this case, the formation of the connected molten portion 13 can increase the joining strength between the battery outer can 5 and the collector terminal 12. In addition, the point spacing P2 may also be set to be less than the individual melting width MW. Therefore, as Figure 14A As shown, two connected fusion zones 13 are obtained at positions separated from each other, and the bonding strength between the battery outer can 5 and the current collecting tab 12 can be further increased.

[0167] (Example)

[0168] The sealed battery 100 welded using the laser processing method according to the embodiment was evaluated for bonding strength. Figure 15 The graph shows the correlation between laser output and bonding strength. The horizontal axis represents the laser output (W), and the vertical axis represents the bonding strength between the battery outer can 5 and the current collecting tab 12. Figure 15, without penetrating the current collector tab 12, the target joint strength value was achieved, confirming the effectiveness of the laser processing method of this embodiment. Furthermore, the laser processing method of this embodiment was actually used to produce sealed batteries 100. A predetermined drop test was performed on the sealed battery 100 units and the sealed battery assembly. The results showed that the welded portions did not fall off and remained in a normal state, confirming the effectiveness of the laser processing method of this embodiment.

[0169] (Material of current collector connector)

[0170] The material of the current collector tab 12 in the laser processing method according to this embodiment will be described. Current collector tabs 12 are typically made of nickel, which has good absorption of the laser beam 21 and easily melts. However, in the laser processing method according to this embodiment, it is difficult to irradiate the current collector tab 12 so that the melted portion 13 does not penetrate the absorptive current collector tab 12. Therefore, it is preferable to use a material that suppresses absorption of the laser beam 21, such as a copper-based material.

[0171] For example, use Figures 16A to 16C The collector tab 12 shown is preferred. Figure 16A The collector connector is made of copper. Figure 16B The collector joint is a two-layer coating of nickel and copper. Figure 16C The collector tab is a three-layer coating of nickel, copper, and nickel. Regardless of the type, the laser stops at the copper portion of the collector tab 12, preventing penetration.

[0172] In addition, in the description of the laser processing method above, the case where the objects to be irradiated by the laser beam are the battery outer can 5 (an example of the first plate-shaped member) and the collector tab 12 (an example of the second plate-shaped member) in the sealed battery 100 is used as an example, but the present invention is not limited to this. For example, three or more plate-shaped members can be stacked together to serve as the irradiation object. In addition, the shape of the plate-shaped member is not limited to being a plane as a whole. As long as it is a member that extends in a surface direction perpendicular to the thickness direction of the member and can overlap each other in the area of the irradiation object, it can be used. For example, plate-shaped members can be arranged in an overlapping manner on the disc-shaped end face of a cylinder, and the cylinder and the plate-shaped members can be used as the irradiation objects. In addition, other plate-shaped members can be arranged between the first plate-shaped member and the second plate-shaped member. In addition, a plate-shaped member can have multiple layers, such as a covering or a laminated material. In addition, a plate-shaped member can have multiple layers, such as a covering or a laminated material.

[0173] (Effect)

[0174] According to the laser processing method of the embodiment, the branched laser beams 21a and 21b are irradiated while moving in parallel. Furthermore, the battery outer can 5 is moved relative to the branched laser beams 21a and 21b in a direction intersecting the direction in which the branched laser beams 21a and 21b are aligned. As a result, linear fusion zones 13a and 13b are formed along the surface of the battery outer can 5. Thus, the fusion zone 13 can be formed by laser welding, achieving the joining of the battery outer can 5 and the current collector tab 12.

[0175] Furthermore, the fused portions 13a and 13b formed by the two branched laser beams are connected in the current collector tab 12. Forming these connected fused portions 13a and 13b in the current collector tab 12 increases the melt volume compared to irradiation with a single laser beam 21, forming a large melt flow 23. This melt flow 23 mixes the melted battery outer can 5 and the current collector tab 12, thereby increasing the width of the weld at the boundary between the current collector tab 12 and the adjacent battery outer can 5. Consequently, the strength of the bond between the battery outer can 5 and the current collector tab 12 can be increased.

[0176] Furthermore, by irradiation with the branched laser beams 21a and 21b, molten portions 13a and 13b are formed respectively, which do not penetrate the current collecting tab 12. Therefore, it is possible to prevent spatter from entering the battery outer can 5.

[0177] It is preferred to perform irradiation so that the spot pitch P1 between the first branched laser beam 21a and the second branched laser beam 21b is greater than the individual joint width JW and less than the individual melt width MW. As a result, the molten portions 13a and 13b formed by the two branched laser beams 21a and 21b are connected in the current collector tab 12, further increasing the joint width in the current collector tab 12 and further increasing the joint strength between the battery outer can 5 and the current collector tab 12.

[0178] The laser beam 21 can be split into multiple branched laser beams, each consisting of a group of branched laser beams 21a and 21b. The spacing between the groups can be larger than the spot pitch P1 between the first branched laser beam 21a and the second branched laser beam 21b. For example, the spacing can be such that the linear fusion zones 13 formed by the groups are not continuous, as in the spot pitch P2. Thus, forming multiple linear fusion zones 13 can increase the bonding strength between the battery outer can 5 and the current collector tab 12.

[0179] Alternatively, the point pitch P1 may be greater than the individual joint width JW and less than the individual melt width MW, and the point pitch P2 may be greater than the individual melt width MW. For example, a continuous melt portion 13 can be formed in the current collector tab 12 using two branched laser beams 21a and 21b, and a continuous melt portion 13 can be similarly formed in the current collector tab 12 at other separate locations using branched laser beams 21c and 21d. Two continuous melt portions 13 can be obtained at mutually separate locations. Consequently, the total joint width in the current collector tab 12 is further increased, further enhancing the joint strength between the battery outer can 5 and the current collector tab 12.

[0180] Alternatively, the center of the surface of the battery outer can 5 may be irradiated with the split laser beams 21a to 21d so that the multiple melted portions 13 formed by the irradiation are point-symmetrical or line-symmetrical with each other. Alternatively, the individual melted portions 13 may be separated. This can increase the joining torque strength.

[0181] The material of the current collector tab 12 can be a copper-based material that suppresses absorption of the laser beam 21. The current collector tab 12 does not absorb the energy of the laser beam 21, which suppresses melting, and the molten portion 13 does not penetrate the current collector tab 12. This prevents spatter from entering the battery outer can 5.

[0182] According to the laser welding device 200 involved in the embodiment, the movement of the workbench 18 and the irradiation of the branched laser beams 21a to 21d can be controlled by the overall control unit 20. Specifically, the branched laser beams 21a to 21d can be irradiated, and the sealed battery 100 can be moved in a direction intersecting with the direction in which the branched laser beams 21a to 21d are arranged. As a result, a linear molten portion 13 is formed along the battery outer can 5. The molten portion 13 is connected to the collector tab 12, and the molten portion 13 does not penetrate the collector tab 12. Therefore, the joint width in the collector tab 12 is expanded, the joint strength between the battery outer can 5 and the collector tab 12 is increased, and spatter can be prevented from mixing into the battery outer can 5.

[0183] Furthermore, a diffraction optical element (DOE) may be used in the laser beam branching optical system 17 to branch the laser beam 21. This configuration enables branching pattern design, and the laser beam 21 can be branched at any position and with any intensity.

[0184] In the sealed battery 100 according to the embodiment, the formation of the current collector tab diffusion portion 24 allows the material constituting the current collector tab 12 to flow from the current collector tab 12 into the battery outer can 5 at the periphery of the fusion zone 13. Since the material constituting the current collector tab 12 has high conductivity, the conductivity of the battery outer can 5 in the fusion zone 13 is increased. This structure improves the flow of current from the current collector tab 12 to the battery outer can 5.

[0185] Furthermore, the material constituting the current collector tab 12 penetrates further from the current collector tab 12 into the battery outer can 5 at the outer periphery of the fusion zone 13 than at the central portion of the fusion zone 13. This structure further improves the flow of current from the current collector tab 12 to the battery outer can 5.

[0186] In addition, this embodiment uses the example of a sealed battery to illustrate that, in overlapping laser welding of two or more plate-like materials, it is effective to further increase the joint strength by welding in which the molten zone formed by welding does not penetrate.

[0187] The wound body 4 is not limited to a structure in which the positive electrode plate and the negative electrode plate are wound with a separator interposed therebetween, and may also be a stacked structure.

[0188] Furthermore, by appropriately combining any of the various embodiments described above, the effects possessed by each can be achieved.

[0189] Industrial applicability

[0190] The present disclosure is not limited to any particular type of sealed battery and can be applied to lithium-ion secondary batteries, nickel-metal hydride batteries, nickel-cadmium batteries, etc. Furthermore, the disclosure is not limited to cylindrical secondary batteries and can also be applied to square secondary batteries or primary batteries.

Claims

1. A laser processing method, A plurality of plate-like members including a first plate-like member disposed at one end side in a stacking direction and a second plate-like member disposed at the other end side are stacked, The laser beam is split into a plurality of branched laser beams including a plurality of groups of first branched laser beams and second branched laser beams, The respective branched laser beams are made to irradiate the first plate-shaped member in a parallel state, The first branched laser beam and the second branched laser beam are moved relative to the first plate-shaped member in a direction intersecting the direction in which the first branched laser beam and the second branched laser beam are arranged, thereby forming a linear molten portion along the surface of the first plate-shaped member. In the second plate-like member, the molten portion formed by the first branched laser beam and the molten portion formed by the second branched laser beam are connected and the molten portion does not penetrate the second plate-like member, and the superimposed plate-like members are joined through the linear molten portion. In the first plate-shaped member, a distance between the branched laser beams in one group and the branched laser beams in another adjacent group is larger than a distance between the first branched laser beam and the second branched laser beam.

2. The laser processing method according to claim 1, wherein: The branched laser beams are irradiated so that the molten portions formed by the branched laser beams are point-symmetrical or line-symmetrical with respect to the center position of the surface of the first plate-shaped member.

3. The laser processing method according to claim 1 or 2, wherein: The second plate-shaped member is made of a copper-based material that suppresses absorption of the laser beam.

4. A laser processing device comprising: a laser oscillator for irradiating a laser beam; a laser oscillation control unit for controlling output of the laser beam; a laser splitting optical system for splitting the laser beam into a plurality of split laser beams; a laser processing optical system for causing the branched laser beams to irradiate a first plate-like member of a stack of plate-like members as an irradiation target while advancing in parallel with each other, wherein the stacked plate-like members include the first plate-like member disposed at one end in a stacking direction and a second plate-like member disposed at the other end; a workbench for moving the laminated plate-like member relative to the laser beam; A workbench control unit for controlling the movement of the workbench; and an overall control unit for synchronously controlling the stage control unit and the laser oscillation control unit, The overall control unit controls the movement of the workbench and the irradiation of the branch laser beam, so that the branch laser beam is irradiated and relatively moved in a direction intersecting the direction in which the branch laser beams are arranged, forming a linear molten portion along the first plate-like member, the molten portion formed by one branch laser beam and the molten portion formed by another branch laser beam are connected in the second plate-like member, and the molten portion does not penetrate the second plate-like member. The laser branching optical system branches the laser beam into a plurality of branched laser beams including a first branched laser beam and a second branched laser beam. The laser processing optical system causes each of the branched laser beams to irradiate the first plate-shaped member in a parallel state. In the first plate-shaped member, a distance between the branched laser beams in one group and the branched laser beams in another adjacent group is larger than a distance between the first branched laser beam and the second branched laser beam.

5. The laser processing device according to claim 4, wherein: The laser beam splitting optical system includes a diffraction optical element (DOE) that splits the laser beam into a plurality of split laser beams.

6. A sealed battery manufactured by the laser processing method according to any one of claims 1 to 3, wherein the sealed battery comprises: Battery outer cans; and a current collecting tab superimposed on the inner surface of the bottom portion of the battery outer can and joined to the battery outer can via a fusion zone; The current collecting tab enters the outer peripheral portion of the molten portion in the battery outer can.

7. A sealed battery manufactured by the laser processing method according to any one of claims 1 to 3, wherein the sealed battery comprises: Battery outer cans; and a current collecting tab superimposed on the inner surface of the bottom portion of the battery outer can and joined to the battery outer can via a fusion zone; The current collecting tab enters the battery outer can higher in the outer peripheral portion surrounding the central portion than in the central portion of the fusion zone in the battery outer can.

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