JP6885072B2 - Laser welding method - Google Patents

Description

The present invention relates to a laser welding method in which tabs of electrodes or tabs and conductive members are laser welded to each other.

Vehicles such as EV (Electric Vehicle) and PHV (Plug in Hybrid Vehicle) are equipped with a secondary battery as a power storage device for storing the power supplied to the traveling motor. Generally, the secondary battery includes a case for accommodating the electrode assembly, and the electrode assembly is housed in the case. As the electrode assembly, for example, there is a laminated electrode assembly in which a separator is interposed between a plurality of positive electrode electrodes and a plurality of negative electrode electrodes. Then, the electric power is taken out from the secondary battery through the electrode terminals electrically connected to the electrode assembly.

For example, in the secondary battery of Patent Document 1, the electrode assembly has a welded portion in which one end (for example, a tab) of a gathered positive electrode and a part of a positive electrode terminal (for example, a conductive member) are joined by laser welding. Be prepared. Each positive electrode is electrically connected to the positive electrode terminal by a welded portion. The same applies to the negative electrode and the negative electrode terminal.

Further, as another secondary battery, the electrode assembly includes a first welded portion in which one end portions (for example, tabs) of a plurality of positive electrode electrodes in a gathered state are joined by laser welding. The positive electrodes are electrically connected to each other by the first welded portion. Further, the electrode assembly includes a second welded portion in which one end (tab group) of a plurality of positive electrode electrodes joined by the first welded portion and a part of the positive electrode terminal (for example, a conductive member) are joined by laser welding. .. The positive electrode is electrically connected to the positive terminal by the second weld. The same applies to the negative electrode and the negative electrode terminal.

Japanese Unexamined Patent Publication No. 2016-30280

When the tabs or the tabs and the conductive member are laser welded in this way, spatter (metal dust) may be generated from the molten tab or the conductive member and adhere to the electrode assembly or the conductive member. If the secondary battery is manufactured with the spatter still attached to the electrode assembly and the conductive member, the spatter becomes a foreign substance in the secondary battery. Foreign matter can cause an internal short circuit of the secondary battery, for example, and is therefore desired to be removed.

The present invention has been made to solve the above problems, and an object of the present invention is to provide a laser welding method capable of suppressing spatter from adhering to a component of a power storage device.

The laser welding method for solving the above problems is to transfer electricity to and from an electrode assembly in which a plurality of electrodes having a current collector and a tab protruding from one side of the current collector are laminated and the electrode assembly. Laser welding in which the tabs or the tabs and the conductive member are laser welded together for the production of a power storage device including the terminals and a conductive member that electrically connects the electrode assembly and the terminals. In the method, the first gas is applied in the projecting direction of the tab from the electrode assembly toward the weld target portion to be laser-welded later in the portion where the tabs overlap each other or the tab and the conductive member overlap. A laser light irradiation step of irradiating the welding target portion with laser light during the first gas injection step of jetting and the first gas injection step, and laser welding the tabs or the tabs and the conductive member. A second gas injection step of injecting a second gas toward the welding target portion in the direction of protrusion of the tab from the electrode assembly after the laser beam irradiation step. The gist is that the air volume of the second gas is equal to or greater than the air volume of the first gas.

According to this, when the laser beam irradiation step is performed during the first gas injection step, the first gas jetted in the protruding direction of the tab from the electrode assembly generates the tab or the conductive member at the time of laser welding. A part of the spatter is blown away from the electrode assembly. Further, in the second gas injection step after the laser light irradiation step, since the second gas having an air volume equal to or higher than that of the first gas is jetted, the spatter that could not be removed by the first gas is separated from the electrode assembly. You can skip it. Therefore, it is possible to prevent spatter from adhering to the components of the electrode assembly.

Further, regarding the laser welding method, it is preferable that the first gas and the second gas are the same gas.
According to this, when shifting from the first gas injection step to the second gas injection step, it is only necessary to increase the air volume of the first gas. Therefore, it is not necessary to switch the type of gas, and the process can be quickly shifted from the first gas injection process to the second gas injection process. As a result, the spatter can be removed before it is cooled and adheres to the tabs or conductive members.

Further, regarding the laser welding method, in the second gas injection step, it is preferable to recover the second gas after passing through the tab or the conductive member with a dust collector.
According to this, since the spatter blown by the second gas is collected by the dust collector together with the second gas, it is possible to further suppress the spatter from adhering to the components of the power storage device.

Further, regarding the laser welding method, in the first gas injection step, it is preferable to recover the first gas after passing through the tab or the conductive member with a dust collector.
According to this, since the spatter blown by the first gas is collected by the dust collector together with the first gas, it is possible to further suppress the spatter from adhering to the components of the power storage device.

According to the present invention, it is possible to prevent spatter from adhering to the components of the power storage device.

An exploded perspective view of the power storage device of the embodiment. (A) is a plan view showing the arrangement of the positive electrode tab, the positive electrode conductive member, and the welding apparatus of the embodiment, and (b) and (c) are side views thereof. The graph which shows the air volume of the gas in each step of the welding method of embodiment. (A) is a plan view showing another example of the arrangement of the positive electrode tab, the positive electrode conductive member, and the welding apparatus, and (b) and (c) are side views thereof.

Hereinafter, embodiments embodying the present invention will be described with reference to FIGS. 1 to 3.
As shown in FIG. 1, in the secondary battery 10 as a power storage device, the electrode assembly 12 is housed in the case 11. The case 11 has a rectangular parallelepiped case body 13 and a rectangular flat plate-shaped lid 14. The case body 13 has an accommodating portion inside, and an insertion port 13a communicating with the accommodating portion is open. The lid 14 closes the insertion port 13a. The case body 13 and the lid 14 constituting the case 11 are both made of metal (for example, stainless steel or aluminum). Further, the secondary battery 10 of the present embodiment is a square battery having a square appearance. Further, the secondary battery 10 of the present embodiment is a lithium ion battery.

As shown in FIG. 2C, the electrode assembly 12 includes a positive electrode 20 and a negative electrode 30 as electrodes, and a separator 40 formed of a porous film. The electrode assembly 12 is configured by alternately stacking a plurality of positive electrode 20s and a plurality of negative electrode electrodes 30 via a separator 40.

The positive electrode electrode 20 has a positive electrode metal foil (for example, aluminum foil) 21 as a rectangular sheet-shaped current collector, and a positive electrode active material layer 22 as an active material layer existing on both sides of the positive electrode metal foil 21. The positive electrode metal leaf 21 is not covered by the positive electrode active material layer 22, and includes a positive electrode tab 23 as a rectangular tab composed of the positive electrode metal leaf 21 itself. The positive electrode tab 23 projects from a part of one of the edges along the pair of long sides of the positive electrode metal foil 21.

The negative electrode electrode 30 has a negative electrode metal foil (for example, copper foil) 31 as a rectangular sheet-shaped current collector, and a negative electrode active material layer 32 as an active material layer existing on both sides of the negative electrode metal foil 31. The negative electrode metal foil 31 is not covered by the negative electrode active material layer 32, and includes a negative electrode tab 33 as a rectangular tab composed of the negative electrode metal foil 31 itself. The negative electrode tab 33 projects from a part of one of the edges along the pair of long sides of the negative electrode metal foil 31.

In the positive electrode 20 and the negative electrode 30, the positive electrode tabs 23 are arranged in a row along the stacking direction, and the negative electrode tabs 33 are arranged in a row along the stacking direction at positions where they do not overlap with the positive electrode tab 23. It is laminated on. The positive electrode tabs 23 are collected (bunched) at one end side of the electrode assembly 12 in the stacking direction and bent toward the other end side. Similarly, the negative electrode tabs 33 are collected (bunched) on one end side of the electrode assembly 12 in the stacking direction and bent toward the other end side.

As shown in FIG. 1, the secondary battery 10 includes a positive electrode terminal 15 and a negative electrode terminal 16 as terminals for extracting electricity from the electrode assembly 12. The positive electrode terminal 15 and the negative electrode terminal 16 penetrate the through hole 14a of the lid 14 and project to the outside of the case 11. A ring-shaped insulating ring 17 for insulating the case 11 is attached to the positive electrode terminal 15 and the negative electrode terminal 16, respectively. The positive electrode terminal 15 has a positive electrode conductive member 15a as a rectangular plate-shaped conductive member in the case 11. The positive electrode terminal 15 is electrically connected to the positive electrode conductive member 15a. The negative electrode terminal 16 has a negative electrode conductive member 16a as a rectangular plate-shaped conductive member in the case 11. The negative electrode terminal 16 is electrically connected to the negative electrode conductive member 16a.

The secondary battery 10 has a first welded portion 18 as a welded portion in which the positive electrode tab 23 and the positive electrode conductive member 15a are joined by laser welding. The first welded portion 18 is formed by welding the welded target portion A, which is a portion where the gathered positive electrode tabs 23 and the positive electrode conductive member 15a overlap. That is, the welding target portion A is a portion of the portion where the positive electrode tab 23 and the positive electrode conductive member 15a overlap, which is later laser welded. The positive electrode tab 23 is electrically connected to the positive electrode conductive member 15a by the first welded portion 18. The secondary battery 10 has a second welded portion 19 as a welded portion in which the negative electrode tab 33 and the negative electrode conductive member 16a are joined by laser welding. The second welded portion 19 is formed by welding the welded target portion A, which is a portion where the gathered negative electrode tabs 33 and the negative electrode conductive member 16a overlap. The negative electrode tab 33 is electrically connected to the negative electrode conductive member 16a by the second welded portion 19.

Hereinafter, a welding device 50 for joining the positive electrode tab 23 and the positive electrode conductive member 15a by laser welding, and a welding method using the welding device 50 will be described. In this embodiment, each positive electrode tab 23 and the positive electrode conductive member 15a are welded. Since laser welding of the negative electrode tab 33 and the negative electrode conductive member 16a is performed by the same method as laser welding of the positive electrode tab 23 and the positive electrode conductive member 15a, detailed description and illustration will be omitted.

As shown in FIGS. 2A to 2C, the welding device 50 includes a laser device 51 that irradiates the laser beam L, a gas injection device 52 that injects gas, and a dust collector 53. The electrode assembly 12 is placed on a jig (not shown) so that one end side in the stacking direction faces upward and the other end side in the stacking direction faces downward. Then, welding is performed with the positive electrode tab 23 located on one end side in the stacking direction placed on the positive electrode conductive member 15a. Hereinafter, one end side in the stacking direction of the electrode assembly 12 is the lower side, and the other end side in the stacking direction of the electrode assembly 12 is the upper side.

The laser device 51 is arranged diagonally above the positive electrode tabs 23 that are gathered together. The laser device 51 irradiates the welding target portion A with the laser beam L. Since the laser device 51 can move in the stacking direction of the electrode assembly 12 and the protruding direction of the positive electrode tab 23, the irradiation position of the laser beam L moves on the welding target portion A.

The gas injection device 52 is arranged on the side of the electrode assembly 12 so that the gas injection direction coincides with the protruding direction of the positive electrode tab 23 from the electrode assembly 12. The gas injection device 52 injects gas toward the irradiation position of the laser beam L. The gas injection device 52 includes an air volume adjusting unit (not shown) for adjusting the air volume of the assist gas. The gas injection device 52 can move as the irradiation position of the laser beam L moves.

The dust collector 53 is arranged so as to face the injection port 52a of the gas injection device 52. That is, the dust collector 53 is arranged on the downstream side of the positive electrode tab 23 in the injection direction of the assist gas from the gas injection device 52.

The welding method of the present embodiment includes an arrangement step of arranging the electrode assembly 12 and the positive electrode conductive member 15a, and a joining step of joining the positive electrode tab 23 and the positive electrode conductive member 15a by laser welding. The joining step includes a first gas injection step of injecting an assist gas as the first gas, and a laser beam irradiation step of irradiating the laser beam L and laser welding the positive electrode tab 23 and the positive electrode conductive member 15a. The welding method also includes a second gas injection step of injecting a removal gas as the second gas. The assist gas and the removal gas of the present embodiment are the same type of gas, and are inert gases such as nitrogen gas and argon gas.

As shown in FIG. 3, the arrangement step is performed between the time t0 and the time t1. In the arranging step, the electrode assembly 12 and the positive electrode conductive member 15a are arranged so that the positive electrode tab 23 located on one end side in the stacking direction and a part of the positive electrode conductive member 15a overlap.

The joining step is performed between time t1 and time t3. In the first gas injection step of the joining step, the gas injection device 52 continues to inject the assist gas toward the welding target portion A from the time t1 to the time t3. The air volume Q of the gas (assist gas) in the first gas injection step is Q1. This air volume Q1 is set to an air volume suitable for laser welding.

The laser light irradiation step of the joining step is performed from time t2 to time t3 during the first gas injection step. The time t2 is a time when a predetermined time has elapsed from the time t1 when the first gas injection process is started. That is, the laser light irradiation step is started in a state where the vicinity of the irradiation position is filled with the assist gas. In the laser light irradiation step, the laser device 51 irradiates the welding target portion A with the laser beam L, and the welding target portion A is laser-welded to form the first welding portion 18. At this time, sputtering occurs in the positive electrode conductive member 15a irradiated with the laser beam L. A part of the generated spatter is blown by the assist gas in the direction of protrusion of the positive electrode tab 23 from the electrode assembly 12, and then sucked into the dust collector 53 and recovered. At this time, there is also sputtering that is not blown by the assist gas and adheres to the positive electrode conductive member 15a.

The second gas injection step is performed between the time t3 and the time t4. In the second gas injection step, the gas injection device 52 injects the removal gas toward the first welded portion 18. The air volume Q of the gas (removed gas) in the second gas injection step is Q2, which is 10 times larger than the air volume Q1 of the gas in the first gas injection step. As described above, since the assist gas and the removal gas of the present embodiment are the same type of gas, the change from the air volume Q1 to the air volume Q2 is performed by increasing the air volume by the air volume adjusting unit of the gas injection device 52. .. Therefore, the transition from the first gas injection step to the second gas injection step is continuously performed. In the second gas injection step, the spatter on the positive electrode conductive member 15a is not blown in the first gas injection step, but is blown in the protruding direction of the positive electrode tab 23 from the electrode assembly 12 by the assist gas, and then the dust collector 53. It is sucked into and collected. The other positive electrode tab 23 and the positive electrode conductive member 15a are joined by the same welding method.

Next, the effects of this embodiment will be described together with the actions.
(1) In the second gas injection step after the laser beam irradiation step, the gas injection device 52 injects the removal gas at an air volume Q2 larger than the air volume Q1 of the assist gas injected at the time of laser welding, so that the assist gas is injected at the time of laser welding. It is possible to remove the spatter that could not be removed by.

(2) Since the gas injection device 52 injects gas in the direction in which the positive electrode tab 23 protrudes from the electrode assembly 12, spatter can be skipped in the direction away from the electrode assembly 12. Therefore, it is possible to prevent spatter from adhering to the electrode assembly 12.

(3) Since the assist gas and the removal gas are the same type of gas, it is only necessary to increase the air volume Q1 of the gas to the air volume Q2 when shifting from the first gas injection step to the second gas injection step. Therefore, it is not necessary to switch the type of gas, and the process can be quickly shifted from the first gas injection process to the second gas injection process. As a result, the spatter can be removed before it is cooled and adheres to the positive electrode conductive member 15a.

(4) The welding device 50 includes a dust collector 53. Therefore, the spatter that is blown off by the assist gas or the removal gas is sucked by the dust collector 53 together with the gas, so that it can be further suppressed from adhering to the positive electrode conductive member 15a.

The above embodiment may be changed as follows.
○ The current collector is not limited to the positive electrode metal foil 21 and the negative electrode metal foil 31 as long as the positive electrode active material layer 22 and the negative electrode active material layer 32 can be formed. For example, a woven or net-like sheet may be used.

○ The positive electrode electrode 20 may have a structure in which the positive electrode active material layer 22 exists on one side of the positive electrode metal foil 21. Similarly, the negative electrode electrode 30 may have a configuration in which the negative electrode active material layer 32 is present on one side of the negative electrode metal foil 31.

○ The positive electrode tab 23 does not have to be rectangular. Further, the positive electrode tab 23 may protrude from a part of one edge portion of the edge portions along the pair of short sides of the positive electrode metal foil 21. Similarly, the negative electrode tab 33 does not have to be rectangular. Further, the negative electrode tab 33 may protrude from a part of one edge portion of the edge portions along the pair of short sides of the negative electrode metal foil 31.

○ The position where the positive electrode tab 23 and the negative electrode tab 33 are gathered together may be on the other end side or the center in the stacking direction.
○ The position of the laser device 51 may be changed as appropriate. In the above embodiment, the laser device 51 is arranged diagonally above the gathered positive electrode tabs 23. For example, as shown in FIGS. 4A to 4C, the gathered positive electrode tabs 23 are arranged. The laser device 51 may be arranged diagonally downward.

○ In the above embodiment, the positive electrode tab 23 and the positive electrode conductive member 15a are laser welded, but the positive electrode tabs 23 may be welded to each other, and the welding target portion A is a portion where the positive electrode tabs 23 overlap each other. It will be the part that will be laser welded later. In this case, the positive electrode tabs 23 are welded to each other to form the positive electrode tabs 23 group, and then the positive electrode tabs 23 group and the positive electrode conductive member 15a are welded. Further, the positions where the positive electrode tabs 23 are welded to each other and the positions where the positive electrode tabs 23 group and the positive electrode conductive member 15a are welded may be the same or different.

○ In the joining process, the end time of the first gas injection process and the end time of the laser light irradiation process do not have to coincide. However, the end time of the first gas injection step is made later than the end time of the laser beam irradiation step so that the laser beam L can be irradiated in a state where the vicinity of the irradiation position of the laser beam L is filled with the assist gas.

○ The gas air volume Q1 in the first gas injection process and the gas air volume Q2 in the second gas injection process may be the same. Further, the air volume Q2 of the gas in the second gas injection step may be appropriately changed as long as it is equal to or higher than the air volume Q1.

○ The assist gas and the removal gas may be different types of gas. Air can be used as the removal gas. When different types of gases are used for the assist gas and the removal gas, the gas injection device 52 is provided with a valve for the assist gas and a valve for the removal gas. Then, at the time of transition from the first gas injection process to the second gas injection process, the valve for the assist gas is closed and the valve for the removal gas is opened to switch the gas type and the adjustment unit. Adjust the air volume Q of the gas to make the air volume Q2. Further, after the first gas injection step, the removal gas may be added to the assist gas to obtain the air volume Q2 by opening the valve for the removal gas in addition to the valve for the assist gas. In this case, the removal gas is in a state in which two types of gases are mixed.

○ The dust collector 53 does not necessarily have to be installed.
○ In the above embodiment, the dust collector 53 is operated in both the laser light irradiation step and the second gas injection step, but it may be operated only in the laser light irradiation step or only in the second gas injection step. You may.

-In the above embodiment, the positive electrode terminal 15 and the positive electrode conductive member 15a are integrated, but may be configured differently. Similarly, although the negative electrode terminal 16 and the negative electrode conductive member 16a are integrated, they may have different configurations.

○ The secondary battery 10 may be a lithium ion secondary battery or another secondary battery. In short, it suffices as long as the ions move between the active material for the positive electrode and the active material for the negative electrode and transfer charges.

○ The power storage device can also be applied to a power storage device other than a secondary battery, such as a capacitor.

10 ... Secondary battery as a power storage device, 12 ... Electrode assembly, 15 ... Positive electrode terminal as a terminal, 15a ... Positive electrode conductive member as a conductive member, 16 ... Negative electrode terminal as a terminal, 16a ... Negative electrode conductivity as a conductive member Member, 18 ... 1st welded part as welded part, 19 ... 2nd welded part as welded part, 20 ... positive electrode electrode as electrode, 21 ... current collector as positive electrode metal foil, 23 ... positive electrode tab as tab , 30 ... Negative electrode as an electrode, 31 ... Current collector as a negative electrode metal foil, 33 ... Negative tab as a tab, 53 ... Dust collector, A ... Welding target, L ... Laser light, Q, Q1, Q2 ... Air volume ..

Claims (4)

An electrode assembly in which a plurality of electrodes having a current collector and a tab protruding from one side of the current collector are laminated, a terminal for transmitting and receiving electricity to and from the electrode assembly, and the electrode assembly and the terminal are electrically connected to each other. A laser welding method in which the tabs are laser-welded to each other or the tabs and the conductive member are laser-welded in order to manufacture a power storage device including the conductive members that are specifically connected to each other.
A first gas that injects a first gas in the projecting direction of the tab from the electrode assembly toward the weld target portion to be laser-welded later in the portion where the tabs overlap each other or the tab and the conductive member A joining step including a laser beam irradiation step of irradiating the welding target portion with a laser beam during the injection step and the first gas injection step and laser welding the tabs or the tab and the conductive member with each other. ,
After the laser beam irradiation step, the second gas injection step of injecting the second gas toward the welding target portion in the protruding direction of the tab from the electrode assembly is included.
A laser welding method characterized in that the air volume of the second gas is larger than the air volume of the first gas. The laser welding method according to claim 1, wherein the first gas and the second gas are the same gas. The laser welding method according to claim 1 or 2, wherein in the second gas injection step, the second gas after passing through the tab or the conductive member is recovered by a dust collector. The laser welding method according to any one of claims 1 to 3, wherein in the first gas injection step, the first gas after passing through the tab or the conductive member is recovered by a dust collector.

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