Method for welding metal member, resin-metal composite, and battery module

Abstract

A first busbar 21 having a first joining surface 21a and a second busbar 22 having a second joining surface 22a are welded as a result of an abutting step for abutting and bringing the first joining surface 21a and the second joining surface 22a into surface contact with each other, and a welding step for welding the first joining surface 21a and the second joining surface 22a by emitting a laser beam 90. The first metal member 21 has a first end face 21b forming a corner 212 with the first joining surface 21a. The second metal member 22 has a step surface 22c which is continuous with the second joining surface 22a and which forms a step 220 with the first end face 21b. In the welding step, the laser beam 90 is emitted toward the corner 212 from the first busbar 21 side relative to the step surface 22c.

Description

Welding method for metal members, resin-metal composite, and battery module

[0001] The present invention relates to a method for welding metal members, a resin-metal composite, and a battery module.

[0002] Patent Literature 1 describes a battery pack in which a plurality of unit cells, each of which is a secondary battery such as a lithium-ion secondary battery or a nickel-metal hydride battery, or a storage element such as a capacitor, are connected in series by a plurality of bus bars. Each bus bar has a base portion formed with a terminal insertion hole through which an electrode terminal of each unit cell is inserted, and a joint protrusion extending from an area of ​​the base portion adjacent to the terminal insertion hole along the electrode terminal, and the joint protrusion is welded to the electrode terminal. Specifically, the joint protrusion and the electrode terminal, which are in surface contact with each other, are laser-welded to their respective tip portions, and a weld is formed so as to straddle the tip portion of the joint protrusion and the tip portion of the electrode terminal.

[0003] Japanese Patent Application Laid-Open No. 2019-153555

[0004] When a battery pack configured as described above is installed in, for example, a vehicle, it is subjected to continuous vibrations as the vehicle travels, requiring high joint strength at the welded portions between the busbars and the electrode terminals. One possible way to increase the joint strength between the busbars and the electrode terminals is to irradiate a laser beam toward and along the contact surfaces between the busbars and the electrode terminals, thereby welding the busbars and the electrode terminals in a planar shape with a predetermined width. However, in this case, if a step is formed between the tip of the busbar and the tip of the electrode terminal due to dimensional errors or assembly errors of the single cells or busbars, the width of the welded portion may become shorter than the intended dimension depending on the size of the step, and the joint strength may become lower than the designed value.

[0005] Therefore, the present invention provides a method for welding metal members that can stably increase the joining strength between metal members, and a resin-metal composite and a battery module that include a structure that can stably increase the joining strength between metal members.

[0006] In order to solve the above-mentioned problems, the present invention provides a method for welding metal members, which welds a first joining surface of a plate-shaped first metal member and a second joining surface of a plate-shaped second metal member, wherein the first metal member has a first end face that forms a corner between the first joining surface and the second metal member, and the second metal member has a step face that is continuous with the second joining surface and forms a step between the first end face and the first joining surface, the method comprising: a butting process for butting the first joining surface and the second joining surface to bring them into surface contact; and a welding process for welding the first joining surface and the second joining surface by irradiating laser light from the first metal member side toward the corner rather than the step face.

[0007] In addition, in order to solve the above-mentioned problems, the present invention provides a resin-metal composite comprising a resin member, a first joint surface and a plate-shaped first metal member having a first end surface forming a corner between the first joint surface and the first joint surface, and a second metal member having a step surface that is continuous with the second joint surface and forms a step portion between the first end surface, wherein the resin member is molded integrally with the first metal member, the second metal member is inserted into a through hole formed in the resin member, and the first joint surface of the first metal member and the second joint surface of the second metal member are joined by welding. A resin-metal composite is provided.

[0008] In order to solve the above-mentioned problems, the present invention provides a battery module including: a first case member that houses an assembled battery formed by combining a plurality of pouch-type battery cells; a second case member that is arranged so as to cover an opening of the first case member; a first bus bar that is insert-molded into the second case member; and a second bus bar that is inserted into a through-hole formed in the second case member and welded to the first bus bar, wherein the first bus bar has a first joint surface and a first end surface that forms a corner between the first joint surface and the first end surface, and the second bus bar has a second joint surface and a stepped surface that is continuous with the second joint surface and forms a stepped portion between the first end surface and the first end surface, and the first joint surface of the first bus bar and the second joint surface of the second bus bar are joined by welding.

[0009] According to the present invention, it is possible to stably increase the bonding strength between metal members.

[0010] FIG. 1 is an external view showing a battery module including a resin-metal composite having a portion welded by a welding method according to an embodiment of the present invention. FIG. 2 is a structural diagram showing the top surface of the battery module. FIG. 3 is a cross-sectional view taken along line A-A in FIG. 1. FIG. 4 is a cross-sectional view taken along line B-B in FIG. 1. FIG. 5 is an exploded perspective view of a portion of the battery module. FIG. 6 is a structural diagram showing the interior of a second case member of a battery module with a third case member removed. FIG. 7A is an explanatory diagram showing the second case member and the second and sixth bus bars. FIG. 7B is a structural diagram showing a portion of the second case member before welding the second and sixth bus bars. FIG. 7C is an explanatory diagram showing the state when welding the second and sixth bus bars. FIG. 8A is an explanatory diagram showing an example of the state when the first and second bus bars are welded. FIG. 8B is an explanatory diagram showing an example of the state when the sixth and seventh bus bars are welded. FIG. 8C is a schematic diagram showing an example of the structure of a laser apparatus used for welding. Fig. 9A shows the first bus bar and the second bus bar before laser light is emitted from the emission portion of the laser device. Fig. 9B shows a state in which welding is being performed by emitting laser light from the emission portion of the laser device. Fig. 9C shows a state in which welding is being performed by emitting laser light from the emission portion of the laser device. Fig. 9D shows the first bus bar and the second bus bar as viewed from an oblique direction during welding. Fig. 10A is a configuration diagram showing a welding method according to a comparative example. Fig. 10B is a configuration diagram showing a welding method according to a comparative example. Fig. 10C is a configuration diagram showing a welding method according to a comparative example.

[0011] [Embodiments] The following describes embodiments of the present invention. Note that the embodiments described below are shown as preferred specific examples for carrying out the present invention, and while some of them specifically exemplify various technically preferred aspects, the technical scope of the present invention is not limited to these specific embodiments.

[0012] FIG. 1 is an external view showing a battery module 1 including a resin-metal composite 1A having a portion welded by a welding method according to an embodiment of the present invention. FIG. 2 is a configuration diagram showing the top surface of the battery module 1. FIG. 3 is a cross-sectional view of the battery module 1 taken along line A-A in FIG. 1. FIG. 4 is a cross-sectional view of the battery module 1 taken along line B-B in FIG. 1. FIG. 5 is an exploded perspective view of some components of the battery module 1. This battery module 1 is used, for example, as a power source for a vehicle having an electric motor as a driving source for traveling.

[0013] The battery module 1 includes a resin case 10, a battery pack 100 housed in the case 10, first to seventh bus bars 21 to 27, and a control circuit 3. The battery pack 100 is made up of a combination of multiple pouch-type battery cells 4, which are electrically connected in series. The first to seventh bus bars 21 to 27 are plate-shaped metal members with high conductivity, such as copper or a copper alloy.

[0014] 2, the first bus bar 21 and the seventh bus bar 27 serve as output terminals 211, 271, portions of which are exposed to the outside of the case 10. The output terminal 211, which is part of the first bus bar 21, is a positive output terminal, and the output terminal 271, which is part of the seventh bus bar 27, is a negative output terminal. A connection terminal 52 attached to an end of a positive power supply line 51 abuts against the output terminal 211 with a bolt 53. A connection terminal 62 attached to an end of a negative power supply line 61 abuts against the output terminal 271 with a bolt 63. The positive power supply line 51 and the negative power supply line 61 are connected to, for example, an inverter that generates alternating current to be supplied to an electric motor.

[0015] The case 10 is constructed by combining first to third case members 11 to 13. The first to third case members 11 to 13 are resin members made of a thermoplastic resin such as PBT (polybutylene terephthalate). The first case member 11 and the second case member 12, and the second case member 12 and the third case member 13 are hermetically welded together by laser welding. As an example, the battery module 1 is mounted in a vehicle with the first case member 11 positioned vertically downward. Hereinafter, the arrangement direction of the first case member 11, the second case member 12, and the third case member 13 may be referred to as the up-down direction.

[0016] 3, a through-hole 130 is provided in the center of the third case member 13, and the through-hole 130 is closed by a cap 14. The cap 14 is configured to prevent foreign matter from entering the inside of the case 10 through the through-hole 130, and to allow air to circulate through the through-hole 130 when the difference in air pressure between the inside and outside of the case 10 becomes large.

[0017] The first case member 11 houses the battery pack 100. In FIG. 1 , the first case member 11 is indicated by a two-dot chain line, and the battery pack 100 inside is indicated by a solid line. The second case member 12 is arranged to cover the opening of the first case member 11. The second case member 12 is molded integrally with the first bus bar 21 and the seventh bus bar 27. More specifically, the first bus bar 21 and the seventh bus bar 27 are insert-molded into the second case member 12. The second case member 12 houses the control circuit 3.

[0018] The control circuit 3 monitors the voltage of each pouch-type battery cell 4 and communicates with a higher-level control device via a communication line connected to a connector 129 provided on the second case member 12. As shown in Figure 3, the control circuit 3 has a circuit board 31 fixed to the second case member 12 with multiple bolts 15, and multiple electronic components 32 mounted on the circuit board 31, such as ICs, resistors, and capacitors.

[0019] In this embodiment, the battery pack 100 has four pouch-type battery cells 4. The pouch-type battery cells 4 are secondary batteries that house a power storage unit made up of multiple positive electrode plates and multiple negative electrode plates alternately arranged in a laminate film as an exterior material, and an electrolytic solution containing an organic solvent and an electrolyte, and more specifically, are lithium-ion batteries or lithium-ion capacitors.

[0020] Each pouch-type battery cell 4 has a positive electrode tab 401 and a negative electrode tab 402. When each of the four pouch-type battery cells 4 is specifically described below, the four pouch-type battery cells 4 will be referred to as the first to fourth pouch-type battery cells 41 to 44. The positive electrode tabs 401 and negative electrode tabs 402 of the first to fourth pouch-type battery cells 41 to 44 are electrically connected in series.

[0021] The positive electrode tab 401 of the first pouch-type battery cell 41 is connected to the second bus bar 22. A third bus bar 23 is connected to the connection portion 4a between the negative electrode tab 402 of the first pouch-type battery cell 41 and the positive electrode tab 401 of the second pouch-type battery cell 42. A fourth bus bar 24 is connected to the connection portion 4b between the negative electrode tab 402 of the second pouch-type battery cell 42 and the positive electrode tab 401 of the third pouch-type battery cell 43. A fifth bus bar 25 is connected to the connection portion 4c between the negative electrode tab 402 of the third pouch-type battery cell 43 and the positive electrode tab 401 of the fourth pouch-type battery cell 44. The negative electrode tab 402 of the fourth pouch-type battery cell 44 is connected to the sixth bus bar 26.

[0022] The potentials of the second to sixth bus bars 22 to 26 are input to the control circuit 3. The control circuit 3 measures the output voltages of the first to fourth pouch-type battery cells 41 to 44 based on the potentials of the second to sixth bus bars 22 to 26. Note that the third to fifth bus bars 23 to 25 do not carry large currents, so they are formed as thinner plates than the first and second bus bars 21, 22 and the sixth and seventh bus bars 26, 27.

[0023] Resin interposing plates 40 are disposed between the first pouch-type battery cell 41 and the second pouch-type battery cell 42, and between the third pouch-type battery cell 43 and the second pouch-type battery cell 44. The interposing plate 40 between the first pouch-type battery cell 41 and the second pouch-type battery cell 42 is fixed to the first pouch-type battery cell 41 with double-sided tape 451. The interposing plate 40 between the third pouch-type battery cell 43 and the second pouch-type battery cell 44 is fixed to the third pouch-type battery cell 43 with double-sided tape 452.

[0024] Sheet-shaped spacers 453 are arranged between the first pouch-shaped battery cell 41 and the first case member 11, between one of the intervening plates 40 and the second pouch-shaped battery cell 42, between the second pouch-shaped battery cell 42 and the third pouch-shaped battery cell 43, between the other intervening plate 40 and the fourth pouch-shaped battery cell 44, and between the fourth pouch-shaped battery cell 44 and the first case member 11. These spacers 453 and the intervening plate 40 define the positions of the first to fourth pouch-shaped battery cells 41 to 44 within the case 10.

[0025] Figure 6 is a structural diagram showing the interior of the second case member 12 with the third case member 13 removed. In Figure 6, the outline of the circuit board 31 is indicated by a two-dot chain line, and the rear side is indicated by a solid line. The second case member 12 has a bottom plate portion 121 and a wall portion 122 that are integral with each other, and the third case member 13 is attached to the tip of the wall portion 122. The wall portion 122 has a rectangular shape when viewed from above. The output terminals 211 and 271 are exposed on the upper surface of the second case member 12 outside the wall portion 122.

[0026] The bottom plate portion 121 has a plurality of recesses 123 formed therein to reduce weight. The recesses 123 are recessed downward from an upper surface 121a, which is the bottom surface of the bottom plate portion 121, but as shown in FIG. 3 , they do not penetrate the bottom plate portion 121 and do not reach a lower surface 121b of the bottom plate portion 121. However, the recesses 123 may penetrate the bottom plate portion 121. Hereinafter, the space surrounded by the wall portion 122 on the upper surface 121a side of the bottom plate portion 121 will be referred to as the storage space 120 of the second case member 12.

[0027] The second case member 12 also has a plurality of pedestals 124-128 for mounting the substrate 31. The pedestals 124-128 are provided so as to protrude upward from the upper surface 121a of the bottom plate portion 121. Electrodes 281-285 are disposed at the tips of the pedestals 124-128, respectively. Nuts are also disposed on the pedestals 124-128 in the areas corresponding to the backsides of the electrodes 281-285.

[0028] The electrodes 281 to 285 and nuts are insert-molded into the second case member 12 together with the first bus bar 21 and the seventh bus bar 27. The substrate 31 is fixed to the second case member 12 by a plurality of bolts 15 that screw into nuts embedded in the base portions 124 to 128, respectively. The electrodes 281 to 285 are each connected to a substrate electrode provided on the bottom plate portion 121 side of the substrate 31. The electrode 281 is connected to the first bus bar 21 inside the second case member 12, and the electrode 285 is connected to the seventh bus bar 27 inside the second case member 12.

[0029] A plurality of through holes 121c to 121g are formed in the bottom plate portion 121 of the second case member 12, penetrating the bottom plate portion 121 in the vertical direction. These through holes 121c to 121g are open to the upper surface 121a and the lower surface 121b of the bottom plate portion 121.

[0030] A portion of the second bus bar 22 is inserted into the through hole 121c from the lower surface 121b side, and the second bus bar 22 is connected to the first bus bar 21 within the accommodation space 120. A portion of the sixth bus bar 26 is inserted into the through hole 121g from the lower surface 121b side, and the sixth bus bar 26 is connected to the seventh bus bar 27 within the accommodation space 120. The second case member 12, the first bus bar 21, the second bus bar 22, the sixth bus bar 26, and the seventh bus bar 27 constitute the resin-metal composite body 1A.

[0031] The wall portion 122 is formed to surround the first bus bar 21, the second bus bar 22, the sixth bus bar 26, and the seventh bus bar 27 protruding from the bottom plate portion 121. The first bus bar 21 and the second bus bar 22, and the sixth bus bar 26 and the seventh bus bar 27 are connected by welding. A specific welding method will be described later.

[0032] The third bus bar 23, the fourth bus bar 24, and the fifth bus bar 25 are inserted into the through holes 121d, 121e, and 121f, respectively. The third bus bar 23, the fourth bus bar 24, and the fifth bus bar 25 are connected to electrodes 282, 283, and 284, respectively, within the accommodation space 120. These connections may be made by welding, but because no large current flows through the third to fifth bus bars 23 to 25 as described above, these connections may also be made by, for example, soldering.

[0033] On the other hand, since a large current flows through the first bus bar 21 and the second bus bar 22, and the sixth bus bar 26 and the seventh bus bar 27 to be supplied to a power supply target such as an inverter, these bus bars must be welded accurately with high welding strength. Next, a method for welding the first bus bar 21 and the second bus bar 22, and the sixth bus bar 26 and the seventh bus bar 27 will be described in detail.

[0034] Figure 7A is an explanatory diagram showing the second case member 12 in which the first bus bar 21 and the seventh bus bar 27 are insert-molded, the second bus bar 22 welded to the first bus bar 21, and the sixth bus bar 26 welded to the seventh bus bar 27.

[0035] The first bus bar 21 has a joint surface 21a joined to the second bus bar 22. The second bus bar 22 has a joint surface 22a joined to the first bus bar 21. The sixth bus bar 26 has a joint surface 26a joined to the seventh bus bar 27. The seventh bus bar 27 has a joint surface 27a joined to the sixth bus bar 26. The joint surface 21a of the first bus bar 21, the joint surface 22a of the second bus bar 22, the joint surface 26a of the sixth bus bar 26, and the joint surface 27a of the seventh bus bar 27 protrude from the second case member 12.

[0036] The second bus bar 22 is welded to the first bus bar 21 while connected to the positive electrode tab 401 of the first pouch-type battery cell 41, and the sixth bus bar 26 is connected to the seventh bus bar 27 while connected to the negative electrode tab 402 of the fourth pouch-type battery cell 44, but the first pouch-type battery cell 41 and the fourth pouch-type battery cell 44 are not shown in Figure 7A.

[0037] 7B is a configuration diagram showing the first bus bar 21 and the seventh bus bar 27 and a portion of the second case member 12 before the second bus bar 22 and the sixth bus bar 26 are connected. FIG. 7C is an explanatory diagram showing the state when the first bus bar 21 and the second bus bar 22 are welded together and the sixth bus bar 26 and the seventh bus bar 27 are welded together. A portion of the second bus bar 22 in the longitudinal direction is inserted into a through hole 121c formed in the bottom plate portion 121 of the second case member 12 and welded to the first bus bar 21. A portion of the sixth bus bar 26 in the longitudinal direction is inserted into a through hole 121g formed in the bottom plate portion 121 of the second case member 12 and welded to the seventh bus bar 27.

[0038] The welding of the first bus bar 21 and the second bus bar 22 is performed by clamping the first bus bar 21 and the second bus bar 22 with a clip 71 serving as a clamping jig, with the joint surface 21 a of the first bus bar 21 and the joint surface 22 a of the second bus bar 22 butted against each other and in surface contact. The clip 71 presses a portion of the longitudinal direction of the second bus bar 22, which is inserted into the through hole 121 c of the second case member 12, against the first bus bar 21, so that the joint surface 21 a of the first bus bar 21 and the joint surface 22 a of the second bus bar 22 are in surface contact.

[0039] Similarly, the sixth bus bar 26 and the seventh bus bar 27 are welded together by clamping the sixth bus bar 26 and the seventh bus bar 27 with a clip 72 serving as a clamping jig, with the joint surface 26a of the sixth bus bar 26 and the joint surface 27a of the seventh bus bar 27 butted against each other in surface contact. The clip 72 presses a portion of the longitudinal direction of the sixth bus bar 26 inserted through the through hole 121g of the second case member 12 toward the seventh bus bar 27, thereby bringing the joint surface 26a of the sixth bus bar 26 and the joint surface 27a of the seventh bus bar 27 into surface contact.

[0040] The clamping jig that clamps the first bus bar 21 and the second bus bar 22 to bring the joining surfaces 21 a, 22 a into surface contact with each other is not limited to the clip 71, and various other configurations can be used. The same applies to the clamping jig that clamps the sixth bus bar 26 and the seventh bus bar 27; it is not limited to the clip 72, and various other configurations can be used as long as it can clamp the sixth bus bar 26 and the seventh bus bar 27 to bring the joining surfaces 26 a, 27 a into surface contact with each other.

[0041] Fig. 8A is an explanatory diagram showing an example of a state when the first bus bar 21 and the second bus bar 22 are welded together. Fig. 8B is an explanatory diagram showing an example of a state when the sixth bus bar 26 and the seventh bus bar 27 are welded together. Fig. 8C is a schematic diagram showing an example of the configuration of a laser device 9 used to weld the first bus bar 21 and the second bus bar 22, and the sixth bus bar 26 and the seventh bus bar 27. Clips 71 and 72 are not shown in Figs. 8A and 8B.

[0042] The welding of the first bus bar 21 and the second bus bar 22, and the welding of the sixth bus bar 26 and the seventh bus bar 27 are performed by emitting laser light 90 from an emission part 91 of a laser device 9 while the second case member 12 and the emission part 91 are positioned relative to each other using a fixing jig 8, and irradiating the laser light 90 toward the welded portions between the first bus bar 21 and the second bus bar 22, and the welded portions between the sixth bus bar 26 and the seventh bus bar 27. The laser device 9 irradiates the laser light 90 while avoiding the wall part 122 of the second case member 12 so that the laser light 90 does not hit the wall part 122. Note that, as with FIG. 7A , the first pouch-type battery cell 41, the fourth pouch-type battery cell 44, etc. are not shown in FIGS. 8A and 8B .

[0043] The fixing jig 8 has a rod-shaped support 81, a lower arm 82 that grips the second case member 12, and an upper arm 83 that supports the emission portion 91 of the laser device 9. The lower arm 82 is fixed to the support 81 by a lower mounting portion 811, and the upper arm 83 is fixed to the support 81 by an upper mounting portion 812. The lower arm 82 grips the second case member 12 by fastening a pair of gripping members 821, 822 with a thumbscrew 823. Note that the configuration of the fixing jig 8 shown in Figures 8A and 8B is shown as an example, and various configurations can be used as the fixing jig as long as it is possible to position the second case member 12 and the emission portion 91 of the laser device 9 relative to each other.

[0044] 8C , the laser device 9 includes a laser oscillator 92, an emission unit 91 that emits laser light 90 toward the welding site, and a control unit 93 that controls the laser oscillator 92 and the emission unit 91. The output of the laser oscillator 92 and the emission direction of the laser light 90 from the emission unit 91 are controlled by the control unit 93. In this embodiment, the emission unit 91 functions as an angle variable unit that changes the emission direction of the laser light 90. More specifically, the emission unit 91 has the configuration of a galvanometer scanner.

[0045] The emission unit 91 includes a first servo motor 911, a second servo motor 912, a first mirror 913, a second mirror 914, and a housing 915 that accommodates these components. The first servo motor 911 can adjust the angle of the first mirror 913. The second servo motor 912 can adjust the angle of the second mirror 914. The laser beam 90 generated by the laser oscillator 92 is reflected by the first mirror 913 and then further reflected by the second mirror 914 before being emitted from the emission unit 91. That is, the first mirror 913 is an incident-side mirror, and the second mirror 914 is an exit-side mirror. The control unit 93 adjusts the angles of the first mirror 913 and the second mirror 914 by controlling the first servo motor 911 and the second servo motor 912. The housing 915 is supported by the upper arm 83 of the fixing jig 8.

[0046] 9A, 9B, 9C, and 9D, the method for welding the first bus bar 21 and the second bus bar 22 includes a butt-jointing step of butting the joint surface 21a of the first bus bar 21 and the joint surface 22a of the second bus bar 22 together to bring them into surface contact, and a welding step of welding the joint surface 21a of the first bus bar 21 and the joint surface 22a of the second bus bar 22 together by irradiating them with laser light 90 from an emission unit 91 of a laser device 9.

[0047] 7C , in the butting process, the first bus bar 21 and the second bus bar 22 are clamped by clips 71, so that the joint surface 21 a of the first bus bar 21 and the joint surface 22 a of the second bus bar 22 are butted against each other and brought into surface contact. Specifically, a portion of the longitudinal direction of the second bus bar 22, including the joint surface 22 a, of the second bus bar 22 inserted into the through hole 121 c of the second case member 12 is pressed against the first bus bar 21.

[0048] The first bus bar 21 corresponds to the first metal member of the present invention, and the second bus bar 22 corresponds to the second metal member of the present invention. The second case member 12 corresponds to the resin member of the present invention. Hereinafter, the joining surface 21a of the first bus bar 21 will be referred to as the first joining surface 21a, and the joining surface 22a of the second bus bar 22 will be referred to as the second joining surface 22a. Note that the welding process is performed with the first bus bar 21 and the second bus bar 22 clamped by clips 71, but the clips 71 are not shown in Figures 9A, 9B, 9C, and 9D.

[0049] The welding step is performed by positioning an emission portion 91 of a laser device 9 that emits laser light 90 with respect to the first bus bar 21 side of the first bus bar 21 and the second bus bar 22 to be welded to each other as a reference. In the present embodiment, in the welding step, the second case member 12 and the emission portion 91 are positioned relative to each other using a fixing jig 8 as shown in FIG. 8A , thereby positioning the emission portion 91 with respect to the first bus bar 21 side.

[0050] Because the first bus bar 21 is insert-molded into the second case member 12, it has high positional accuracy relative to the second case member 12. By positioning the second case member 12 and the emission portion 91 relative to each other, laser welding can be performed with high relative positional accuracy between the first bus bar 21 and the emission portion 91. That is, in this embodiment, of the first bus bar 21 and the second bus bar 22, the emission portion 91 is positioned based on the first bus bar 21 side, which has relatively high positional accuracy relative to the second case member 12 fixed to the fixing jig 8.

[0051] Fig. 9A shows the first bus bar 21 and the second bus bar 22 before the laser beam 90 is emitted from the emission portion 91 of the laser device 9. Figs. 9B, 9C, and 9D show a state in which welding is being performed by emitting the laser beam 90 from the emission portion 91. Figs. 9A and 9B show the first bus bar 21 and the second bus bar 22 as viewed from a direction perpendicular to the arrangement direction of the first bus bar 21 and the second bus bar 22. Fig. 9C shows the first bus bar 21 and the second bus bar 22 as viewed from the first bus bar 21 side. Fig. 9D shows the first bus bar 21 and the second bus bar 22 as viewed from an oblique direction.

[0052] Second bus bar 22 is positioned relative to first bus bar 21 by second joint surface 22 a being in surface contact with first joint surface 21 a. Second bus bar 22 is also positioned such that longitudinal tip surface 22 b of the portion welded to first bus bar 21 protrudes further in the longitudinal direction than first bus bar 21, and this position is fixed by clip 71.

[0053] The first bus bar 21 has a first end surface 21b that forms a corner 212 between itself and the first joint surface 21a. The first end surface 21b is the tip surface of the first bus bar 21 in the longitudinal direction of the portion that protrudes from the second case member 12 and is welded to the second bus bar 22, and is formed perpendicular to the longitudinal direction. The width of the first end surface 21b corresponds to the thickness of the first bus bar 21. The corner 212 is formed at a substantially right angle by the first joint surface 21a and the first end surface 21b.

[0054] The second bus bar 22 has a step surface 22c that forms a step portion 220 between itself and the first end surface 21b of the first bus bar 21. The step surface 22c is formed continuously with the second joint surface 22a. That is, the second joint surface 22a and the step surface 22c are part of the flat surface of the second bus bar 22 that faces the first bus bar 21. In this embodiment, the dimensional tolerances of the various portions are set so that the step portion 220 is formed between the first bus bar 21 and the second bus bar 22 when the first case member 11 and the second case member 12 that house the battery pack 100 are combined.

[0055] In the welding process, the first bonding surface 21a and the second bonding surface 22a are welded together by irradiating the laser beam 90 from a position closer to the first bus bar 21 than the step surface 22c of the second bus bar 22 toward the corner 212 of the first bus bar 21. More specifically, as shown in Figures 9A and 9B , the emitter 91 is positioned so that a reflection point 914a on the second mirror 914 of the emitter 91 is located closer to the first bus bar 21 than an imaginary plane 20 including the first bonding surface 21a. The reflection point 914a is the portion where the laser beam 90 reflected by the first mirror 913 hits the second mirror 914. In Figures 9A and 9B , this imaginary plane 20 is indicated by a two-dot chain line.

[0056] In the welding process, the laser beam 90 is irradiated with the optical axis 900 of the laser beam 90 inclined at a predetermined inclination angle θ with respect to the imaginary plane 20. This inclination angle θ is the angle of the optical axis 900 of the laser beam 90 irradiated toward the corner 212 when viewed from a direction parallel to the first end surface 21b and the first joining surface 21a of the first bus bar 21 with respect to the imaginary plane 20. If the inclination angle θ is too large, the portion where the first bus bar 21 and the second bus bar 22 are fused together will bite into the second bus bar 22, which is undesirable. The desirable range of the inclination angle θ is greater than 0°, for example, 10° or less. More preferably, the inclination angle θ is in the range of 5°±2°. FIG. 9B shows, as an example, a case where the inclination angle θ is 5°.

[0057] It is desirable that the inclination angle θ is always constant from the start to the end of welding the first bus bar 21 and the second bus bar 22, but it does not necessarily have to be constant at all times and may vary, for example, within a range of ±1° or less.

[0058] In the welding process, the first servo motor 911 and the second servo motor 912 of the emission unit 91 are controlled to move the area irradiated with the laser beam 90 along the length direction (left-right direction in FIG. 9C ) of the portion where the first bus bar 21 and the second bus bar 22 are welded, while irradiating the corner portion 212 of the first bus bar 21 with the laser beam 90. In FIGS. 9B , 9C , and 9D , the compatible portion 200 where the first bus bar 21 and the second bus bar 22 are fused together is illustrated with hatching. The compatible portion 200 is formed to extend from the corner portion 212 of the first bus bar 21 along the first joining surface 21 a and the second joining surface 22 a, and the first bus bar 21 and the second bus bar 22 are welded in a planar manner. This increases the joining strength between the first bus bar 21 and the second bus bar 22 compared to, for example, welding the tips of the first bus bar 21 and the second bus bar 22 together in a block.

[0059] Furthermore, in this embodiment, welding is performed with a step portion 220 formed between the first end surface 21b of the first bus bar 21 and the step surface 22c of the second bus bar 22. Therefore, even if the positional accuracy of the second bus bar 22 relative to the first bus bar 21 is low, the area of ​​the portion where the first bus bar 21 and the second bus bar 22 are fused together is not affected. The size of the step portion 220, i.e., the distance D between the first end surface 21b of the first bus bar 21 and the tip surface 22b of the second bus bar 22 shown in FIG. 9A , is, for example, 0.2 mm or more and 0.8 mm or less. However, even if the size of the step portion 220 is larger than this, the area of ​​the portion where the first bus bar 21 and the second bus bar 22 are fused together remains constant. In other words, this embodiment stabilizes the joint strength between the first bus bar 21 and the second bus bar 22.

[0060] The sixth bus bar 26 and the seventh bus bar 27 are welded together in the same manner as the first bus bar 21 and the second bus bar 22 are welded together.

[0061] 10A, 10B, and 10C are diagrams illustrating a welding method according to a comparative example. In this welding method, plate-shaped first and second metal members 291 and 292 are welded by irradiating them with laser light 90 from a direction along the mating surfaces of the first and second metal members 291 and 292. FIG. 10A illustrates a case in which an end face 291a of the first metal member 291 and an end face 292a of the second metal member 292 are at the same position in the irradiation direction of the laser light 90. FIG. 10B illustrates a case in which the first metal member 291 protrudes so that the end face 291a of the first metal member 291 is closer to the emission part 91 of the laser device 9 than the end face 292a of the second metal member 292. FIG. 10C shows a case where the second metal member 292 protrudes so that the end face 292 a of the second metal member 292 is closer to the emission part 91 of the laser device 9 than the end face 291 a of the first metal member 291 .

[0062] In this comparative example, a portion of the laser light 90 hits the end face 291a of the first metal member 291, and another portion of the laser light 90 hits the end face 292a of the second metal member 292. Therefore, if there is a step between the first metal member 291 and the second metal member 292 as shown in Figures 10B and 10C, the depth of the portion where the first metal member 291 and the second metal member 292 melt together will be shallower depending on the size of this step, and the area of ​​the portion where the first metal member 291 and the second metal member 292 melt together will be smaller.

[0063] In contrast, in this embodiment, even if the size of the step portion 220 varies, the area of ​​the portion where the first bus bar 21 and the second bus bar 22 are fused together remains constant, so the joining strength between the first bus bar 21 and the second bus bar 22 is stable.

[0064] (Note) While the present invention has been described above based on the embodiments, the invention according to the claims is not limited to these embodiments. It should be noted that not all of the combinations of features described in the embodiments are necessarily essential to the means for solving the problems of the invention.

[0065] Furthermore, the present invention can be appropriately modified and implemented by omitting some components or adding or substituting components without departing from the spirit of the present invention. For example, in the above embodiment, the welding method of the first bus bar 21 and the second bus bar 22 of the battery module 1 has been mainly described, but the welding method of the present invention is not limited to welding bus bars together, and can be applied to welding various metal members together.

[0066] In the above embodiment, the laser device 9 emits the laser light 90 from the emission unit 91 configured as a galvanometer scanner, but the emission unit of the laser device that emits the laser light may be, for example, a fiber laser torch. In this case, the irradiation location and irradiation angle of the laser light are adjusted by changing the angle of the torch.

[0067] DESCRIPTION OF SYMBOLS 1... Battery module 100... Assembled battery 11... First case member 12... Second case member (resin member) 121... Bottom plate portion 122... Wall portion 1A... Resin-metal composite 21... First bus bar (first metal member) 212... Corner portion 21a... First bonding surface 21b... First end surface 22... Second bus bar (second metal member) 220... Step portion 22a... Second bonding surface 22c... Step surface 4... Pouch-type battery cell 90... Laser light

Claims

1. A method for welding a first joining surface of a plate-shaped first metal member and a second joining surface of a plate-shaped second metal member, wherein the first metal member has a first end face that forms a corner between the first joining surface and the first joining surface, and the second metal member has a stepped surface that is continuous with the second joining surface and forms a step between the first end face and the first joining surface, the method comprising: a butting step in which the first joining surface and the second joining surface are butted together to bring them into surface contact; and a welding step in which a laser beam is irradiated from the first metal member side relative to the stepped surface toward the corner, thereby welding the first joining surface and the second joining surface.

2. The method for welding metal members according to claim 1, wherein the welding step is performed by positioning the emission part of a laser device that emits the laser light based on the first metal member side of the first metal member or the second metal member.

3. The method for welding metal members according to claim 2, wherein a resin member is integrally molded with the first metal member, the first joining surface protrudes from the resin member, and the welding process is performed with the resin member and the emission part of the laser device positioned relative to each other.

4. A method for welding metal members according to claim 3, wherein a through hole is formed in the resin member, and a part of the second metal member is inserted therethrough, and the butting step presses the second metal member inserted into the through hole against the first metal member, so that the first joining surface and the second joining surface are butted against each other and brought into surface contact.

5. A method for welding metal members according to claim 4, wherein the resin member has a bottom plate portion in which the through hole is formed and a wall portion formed so as to surround the first metal member and the second metal member protruding from the bottom plate portion, and in the welding process, the laser light is irradiated while avoiding the wall portion.

6. A method for welding metal members according to any one of claims 1 to 5, wherein the laser beam is irradiated with the optical axis of the laser beam inclined at a predetermined inclination angle with respect to an imaginary plane including the first joining surface.

7. The method for welding metal members according to claim 6, wherein the inclination angle is greater than 0° and not more than 10°.

8. A resin-metal composite comprising a resin member, a plate-like first metal member having a first bonding surface and a first end surface forming a corner between the first bonding surface and the first bonding surface, and a second metal member having a second bonding surface and a stepped surface that is continuous with the second bonding surface and forms a stepped portion between the second end surface and the second bonding surface, wherein the resin member is molded integrally with the first metal member, the second metal member is inserted into a through hole formed in the resin member, and the first bonding surface of the first metal member and the second bonding surface of the second metal member are joined by welding.

9. A battery module comprising: a first case member that houses an assembled battery formed by combining a plurality of pouch-type battery cells; a second case member that is arranged to cover the opening of the first case member; a first bus bar that is insert-molded into the second case member; and a second bus bar that is inserted into a through-hole formed in the second case member and welded to the first bus bar, wherein the first bus bar has a first joint surface and a first end surface that forms a corner between the first joint surface and the first end surface; the second bus bar has a second joint surface and a stepped surface that is continuous with the second joint surface and forms a stepped portion between the first end surface and the first end surface; and the first joint surface of the first bus bar and the second joint surface of the second bus bar are joined by welding.

Images