JP2003181666A - Method of welding container for rectangular battery and method of manufacturing rectangular battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve the welding quality of the laser welding machine for a container for a rectangular battery and to provide a method of welding a container for a rectangular battery, the method being capable of preventing damage to a laser welding machine, and a method of manufacturing a rectangular battery. <P>SOLUTION: The method of welding a container for a rectangular battery constituted of a metal case 4 for battery and a lid 2 both to be laser-welded comprises such an arrangement that a laser beam of light 21 is set to enter the surface of a portion 30 to be welded at an incident angle of θ<SB>2</SB>from inside the periphery of the lid as the laser beam is viewed from a plane S2 that is normal to the scanning direction of a laser welding machine, and is set to enter the surface of a portion to be welded from the side where scanning has ended at an incident angle of θ<SB>1</SB>, with respect to a plane S1, as is made a reference, which is normal to the scanning direction of the laser welding machine. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for welding a rectangular battery container, which is preferably used as a battery container for a sealed secondary battery such as a lithium secondary battery, and a manufacturing method for the rectangular battery.

[0002]

2. Description of the Related Art As a technique for sealing a case and a lid of a prismatic battery by laser welding, a technique of starting welding from a side portion of the lid and ending welding at the side portion has been reported (Japanese Patent Laid-Open Publication No. Hei 8). -250079). In order to prevent welding defects that occur when welding is completed at the corners of the lid (having a specified radius of curvature), this technique uses the sides of the lid as the starting (end) points for welding as described above. It is what

[0003]

However, the above-mentioned prior art has the following problems. The first problem is that damage to the laser welder occurs.
This is remarkable when the laser beam is incident on the sample at a substantially right angle, and the incident light is reflected on the sample surface and returns to the laser light source side to damage the lens, the laser oscillator, and the like. In particular, when the sample is aluminum (or aluminum alloy), since the light reflectance is high, it is necessary to increase the laser output in order to ensure sufficient heat input, but the laser welder is severely damaged by that amount. Become.

The second problem is that defective welding still occurs. This is considered to be due to the mechanism shown in FIG. That is, the sample irradiated with the laser beam is melted and becomes a melting region, but when the melting region is further irradiated with the laser beam, the molten metal is scattered to the periphery, and the formation of the welding bead becomes insufficient. This problem also
It occurs remarkably when the laser beam is incident on the sample almost vertically.

By the way, the conventional prismatic battery is mainly a small battery for a mobile phone or a personal computer, and since the thickness of the case and the lid is thin, the laser output is also small, and the above-mentioned problems have not been revealed. However, in recent years, plans are being made to increase the size of lithium secondary batteries and use them for backup power supplies, power storage, and the like, and when welding large rectangular battery containers, the above problems become particularly important.

The present invention has been made to solve the above problems, and it is possible to improve the welding quality of laser welding of a rectangular battery container and prevent the damage of the laser welding machine. And a method for manufacturing a prismatic battery.

[0007]

In order to achieve the above object, the method for welding a rectangular battery container according to claim 1 is a rectangular battery container formed by laser welding a metallic battery case and a lid. Welding method, wherein the incident angle of the laser light is a predetermined angle that is not perpendicular to the surface of the welded portion.

It is preferable that the incident angle is set so that the laser light is incident on the surface of the welded portion from inside the peripheral edge of the lid when viewed from a plane perpendicular to the scanning direction of the laser welding machine.

[0009] It is preferable that the incident angle is set so that the surface of the laser welder is incident on the surface of the welded portion from the side where the scanning is completed, with reference to the surface perpendicular to the scanning direction.

When a protrusion is formed on the outer surface of the lid, it is preferable that the incident angle is set so that the laser beam does not interfere with the protrusion.

According to a fifth aspect of the present invention, there is provided a method for welding a rectangular battery container, wherein when the lid is a quadrangle, the torch angle of the laser welding machine with respect to the surface of the welded portion is kept constant, and the lid is fixed. Start laser welding from the starting point on one side of
A first step of performing laser welding along the one side, a second step of performing laser welding along the adjacent side of the one side, and a side adjacent to the adjacent side and facing the one side from the adjacent side The step of performing laser welding until the end of the one side is substantially the same as the unwelded length of the one side, and the fourth step of reversing the relative position of the object to be welded and the laser welder by 180 degrees. A fifth step of starting laser welding from the vicinity of the end point and performing laser welding along the facing side on the object to be welded that has undergone the fourth step; and laser welding along the side adjacent to the facing side. And a seventh step of performing laser welding on the one side adjacent to the adjacent side until reaching the vicinity of the start point.

In the method for welding a rectangular battery container according to claim 6, when the incident angle with respect to the one side is a plane perpendicular to the scanning direction of the laser welding machine as a reference, the incident angle is measured from the side where the scanning is completed. It is set to be incident on the surface of the welded portion, and the incident angle of the one side with respect to the adjacent side is
When viewed from a plane perpendicular to the scanning direction of the laser welding machine, the laser light is set so as to enter the surface of the welded portion from inside the peripheral edge of the lid.

In the method for welding a prismatic battery container according to claim 7, when a protrusion is formed on the outer surface of the lid, the incident angle with respect to the one side causes the laser light to interfere with the protrusion. The feature is that it is set not to.

In the method for welding a rectangular battery container according to the present invention, the laser welding machine sends a shield gas near the irradiation position of the laser light.

The method for manufacturing a prismatic battery of the present invention is characterized by using the method for welding the prismatic battery container.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION A method for welding a rectangular battery container and a method for manufacturing a rectangular battery according to the present invention will be described below with reference to the drawings. A lithium secondary battery (can) will be described as an example. FIG. 1 is a perspective view of a rectangular battery container. FIG. 2 is a perspective view in which a part of a rectangular battery (secondary battery) using the rectangular battery container is cut away.

In FIG. 1, a rectangular battery container 6 is constructed by laser-welding the lid 2 to the battery case 4, and the outer shape of the rectangular battery container 6 is about 70 mm in width and 160 m in height.
It has a substantially rectangular parallelepiped shape with m × depth of about 30 mm. In this embodiment, the battery case 4 is integrally formed by pressing an aluminum alloy plate or the like to perform deep drawing or ironing. And the battery case 4
The lid 2 is laser-welded to the peripheral edge of the opening. Further, the lid 2 is provided with a safety valve 12, a positive electrode terminal 13, a negative electrode terminal 14, and a liquid injection port (sealing) 15.

FIG. 2 is a perspective view in which a part of the secondary battery is cut away. Reference numeral 16 is a positive electrode plate (electrode plate) made of, for example, lithium manganate-based material, and 17 is made of a carbon-based material, for example. A negative electrode plate (electrode plate) 18 is a separator. As shown in the figure, the positive electrode plate 16 and the negative electrode plate 17 are arranged in a substantially upright state, and the separator 18
A plurality of positive electrode plates 16, separators 18, negative electrode plates 17, separators 18, positive electrode plates 16, ... Are laminated in this order to form an electrode group 19. Each positive electrode plate 16 is connected to the positive electrode terminal 13, and each negative electrode plate 17 is connected to the negative electrode terminal 14.

Further, an electrolytic solution made of an organic material such as ethylene carbonate + dimethyl carbonate is enclosed inside the battery container. Although the amount of the electrolytic solution is arbitrarily set, it is 20 with respect to the internal volume of the rectangular battery container.
It is set to about 50% (the liquid level is about 90% of the can height), and the positive electrode 16, the negative electrode 17, and the separator 18 are immersed in the electrolytic solution.

In this secondary battery, after the electrode group 19 is housed in the battery case 4, the lid 2 is laser-welded to the battery case 4, and the electrolytic solution is injected from the injection port 15 and then sealed. It is manufactured by doing.

FIG. 3 is a plan view showing the surface on which the safety valve 12 is provided, and is a plan view showing the lid 2 in the secondary battery of FIG. The safety valve 12 is provided in the container 1 from the stacking direction of the positive electrode plate 16 (electrode plate) and the negative electrode plate 17 (electrode plate).
Are arranged at two opposite corners of the lid 2 which is the upper side when viewed from. Further, the positive electrode terminal 13 and the negative electrode terminal 14 are arranged on the left and right sides of the central portion of the lid 2, respectively.

The secondary battery is a unit cell having a predetermined rating, and a plurality of (four) unit cells are connected in series to form a module. Then, depending on the application, one or more modules are combined and the capacity is adjusted appropriately before use. Also,
Depending on the space of the installation location, as shown in FIG. 1, the case in which the positive electrode terminal 13 and the negative electrode terminal 14 are installed vertically so that the surface provided with the positive electrode terminal 13 and the negative electrode terminal 14 is the upper surface, the positive electrode terminal 13, the negative electrode terminal 1
There is a case where it is installed sideways so that the surface on which 4 is provided becomes the side surface.

Next, an embodiment of the method for welding the rectangular battery container of the present invention will be described with reference to FIG.

In FIG. 4, the lid 2 is fitted in the upper end opening of the battery case 4, and the joints (welded portion) 30 are welded by the laser welding machine 20 in a state where both are flush with each other.
Both the lid 2 and the battery case 4 are made of aluminum alloy. The lid 2 has a rectangular shape with a thickness of 3 mm, and its corners have a predetermined radius of curvature.

The laser welder 20 is installed with a torch angle θ inclined with respect to the surface of the welded portion 30. Here, the torch angle is an angle formed by the irradiation direction of the laser beam 21 and the surface of the welded portion 30. Also, the laser welding machine 20
Is designed to send an inert shield gas to a region 23 substantially along the irradiation direction of the laser light 21 to prevent the oxidation of the welded portion. The surface of the welded part 30 means
The surface of the joint between the lid 2 and the battery case 4 described above.
Further, when the seam of both is stepped, it means the surface of the lid 2.

The laser welding machine 20 is moved in parallel in the direction shown in the figure, that is, along two adjacent sides of the lid 2 and on the surface of the lid 2 without changing the arm angle of the robot, and is scanned. The part 30 is irradiated with laser light. in this case,
The incident direction of the laser light 21 differs depending on the positional relationship between the laser welder 20 and the welded portion 30.

First, the welded portion 30 extending in the left-right direction in the drawing.
Considering the case of a, the laser beam 21 is emitted by the laser welding machine 2
With reference to the surface S1 perpendicular to the scanning direction of 0 (left-right direction in the figure), the incident angle θ1 is set so that the surface of the welded portion 30 is incident from the side where scanning is completed (left side in the figure). There is. Such an incident angle is hereinafter referred to as "advancing angle". When the advancing angle is set, the laser light appears to be incident perpendicularly to the welded part when viewed from the surface S1.

Next, the welded portion 30 extending in the vertical direction in the figure.
Consider the case of b. The extending direction of the welded portion 30b is perpendicular to the extending direction of the welded portion 30a. In this case, the laser beam 21 is incident on the surface of the welded portion 30 from the inside of the peripheral edge of the lid 2 when viewed from the surface S2 perpendicular to the scanning direction of the laser welding machine 20 (the vertical direction in the drawing). It is set to θ2. Such an angle of incidence is referred to below as the "outward angle".
Called. When the outward angle is set, the laser light is incident parallel to the surface S2.

Since the above-mentioned outward angle and advancing angle can be applied by welding the laser light at a predetermined angle which is not perpendicular to the surface of the welded portion 30, laser welding by reflected light of the laser light is possible. This has the effect of preventing damage to the machine. On the other hand, the outward angle is preferable from the viewpoint of preventing defective formation of the weld beads caused by the irradiation of the beam to the molten region and scattering of the molten metal. This will be described with reference to FIGS.

FIG. 5 shows the state of incidence of laser light and the shape of the welded portion in the case of an outward angle. In this figure, laser light is incident at an outward angle of θ2 and a molten region is formed in the welded part. When laser light is further incident in this state, the laser light scatters the edge of the melted region and then escapes to the outside to prevent further scattering of the melted region. Then, the welded portion has a completely rounded and sagging shape without edges.

FIG. 6 shows the incident state of the laser beam and the shape of the welded portion when the advancing angle is set. In this figure, laser light (from the back side of the paper surface) is incident at an advancing angle θ1 and a molten region is formed in the welded portion. When laser light is further incident in this state, the laser light scatters a part of the melted region, and then is reflected and escapes to the front side of the paper surface, and further scattering of the melted region is prevented. Then, the welded portion has a shape with a slightly rounded edge.

Thus, in terms of welding quality, the outward angle is most preferable, but the outward angle may not be applicable depending on the spatial positional relationship with the welded part. For example, when a protrusion such as an electrode terminal is formed on the outer surface of the lid, the laser beam may interfere with the protrusion at the outward angle. This will be described with reference to FIGS. 7 to 9.

In FIG. 7, electrode terminals 13 and 14 are provided on the outer surface of the lid 2.
Is illustrated as an example. Electrode terminals 13, 1
The positional relationship between 4 and the lid is shown by various dimensions (mm) in the figure, but the present invention is not limited to this.

FIG. 8 shows a case where the welded portion 30A in the short side (vertical side of FIG. 7) direction is welded to the lid 2 of FIG. 7 at an outward angle θ2. Here, the electrode terminals 13 and 14 project from the surface of the lid 2 to a height of about 10 mm. Welded part 3
Since 0A is spatially sufficiently separated from the electrode terminals 13 and 14 that interfere with the laser beam, welding can be performed at the outward angle θ2.

FIG. 9 shows a case where the welded portion 30B in the long side (horizontal side of FIG. 7) direction is to be welded to the lid 2 of FIG. 7 at an outward angle θ2. The welded portion 30B has electrode terminals 13 and 1
4, the laser light interferes with the electrode terminal when welding is attempted at the outward angle θ2. Therefore,
In this case, welding is performed at an advancing angle perpendicularly incident on the lid 2 when viewed from the front direction of FIG.

By the way, using both the outward angle and the forward angle,
When performing the welding with the laser welding machine shown in FIG. 10, it is not preferable to weld with the “single stroke” shown in FIG. That is, in this figure, when the laser welding machine 20 is scanned counterclockwise along the peripheral edge of the lid 2, the horizontal side on the front side of the figure is the advance angle,
The right vertical side adjacent to it becomes the outward angle.

Here, it may be difficult to control the direction of the laser welder 20 (arm angle of the robot equipped with the welder) during the welding process, and in view of simplification of the process, the laser should be used as much as possible. It is better to move the welding machine in parallel with the surface of the welded part. Therefore, when the laser welding machine is moved in parallel to advance welding, the horizontal side on the back side has a receding angle (the advancing angle and the incident direction of laser light are opposite), and the vertical side on the left side has an inward angle (outward angle). The incident direction is opposite). In the case of the receding angle, the shield gas is less likely to stay in the traveling direction of the laser welding machine and is inferior to the advancing angle in terms of welding quality. In the case of the inward angle, the laser beam is less likely to escape from the outer angle, which is inferior to the outward angle in terms of welding quality.

Therefore, as a preferred embodiment of the present invention, the two adjacent sides are welded at the advancing angle and the outward angle, and then the lid 2 is inverted, so that the remaining two sides are not changed in the direction of the laser welding machine. With respect to the above, welding is also possible at an advancing angle and an outward angle. This will be described with reference to FIG.

FIG. 11 shows a welding process for welding the lid 2 of FIG. 7 with an outward angle and an advancing angle, and the laser welding machine (YAG laser) shown in FIG. 4 is used. Figure 11
Shows the steps seen from the upper surface of the lid 2, and the torch angle θ is kept constant in all steps. Also, La
1, La2 is the side of the lid 2 (about 71.9 mm), L
b1 and Lb2 are vertical sides (about 28.9 mm).

First, laser welding is started from the starting point on the lower lateral side La1 of the lid 2 and laser welding is performed at an advancing angle along La1 (first step). This starting point is separated from the left end of La1 by a distance Lc (about 10 mm). Next, after laser welding the lower right corner of the lid 2, laser welding is performed at an outward angle along the vertical side Lb1 on the right side which is the adjacent side of La1 (second step). Then, after laser welding the upper right corner of the lid 2, laser welding is performed on the upper lateral side La2 adjacent to Lb1 and facing La1 at a receding angle up to an end point separated by a distance Ld from the right end of La2. (Third step). The distance Ld may be the same as the distance Lc (the unwelded length of La1), but if it is larger than Lc, the welded portion after reversal and the welding end portion before reversal described later partially overlap. Therefore, welding can be performed more reliably. Therefore, Ld is preferably set to about 15 mm.

Next, the relative positions of the object to be welded (battery case 4 and lid 2) and the laser welder 20 are reversed by 180 degrees (fourth step). Usually, the laser welding machine 20 may be left as it is and the battery container may be inverted together with its fixed stage. Then, laser welding is started from this end point to this battery container, and laser welding is performed along La2 (fifth step). In the fifth step, since the lid 2 is inverted, welding can be performed at the same advancing angle as in the first step, instead of the receding angle shown in FIG. Further, after laser welding the upper left corner of the lid 2, laser welding is performed along the adjacent side Lb2 of the LA2 (sixth step). Also in this sixth step, since the lid 2 is inverted, welding can be performed not at the inward angle in FIG. 10 but at the same outward angle as in the second step. Next, laser welding is performed on La1 adjacent to Lb2 at a receding angle until reaching the starting point (seventh step).

When welding is performed in this manner, when the outward angle is applied, the protruding portion of the lid interferes with the laser light (FIG. 10).
The horizontal direction) and the forward angle and the outward angle can be used together to perform good welding. Further, by performing the reversing operation during welding, it is possible to perform good welding at the advancing angle and the outward angle without the remaining portion being welded at the receding angle or the inward angle. The torch angle θ, the forward angle θ1, and the outward angle θ2 are the same angle. Further, in the above-described embodiment, although the third step and the seventh step are welded at the receding angle, since the shield gas stays at the welding site to some extent due to the short distance, the welding quality does not significantly deteriorate.

FIG. 12 shows the bead shape of the welded portion when laser welding is performed at the above-mentioned advance angle or outward angle. It can be seen that good beads are formed.

As described above, in the present invention, laser light is incident at a predetermined angle that is not perpendicular to the surface of the welded portion to perform welding, thereby preventing damage to the laser welding machine due to reflected light of the laser light. To prevent. In order to exert such an effect, the incident angle (torch angle) is preferably in the range of 10 to 30 degrees, more preferably about 20 degrees. If the incident angle exceeds this range, the energy of the laser beam that can be injected into the welded portion will be low, which is not preferable. Further, if the incident angle is less than this range, the effect of preventing damage to the laser welding machine is insufficient.

Then, after accommodating the electrode group in the battery case 4 in advance, the lid 2 is fitted into the battery case 4, the above-mentioned welding is performed, and then the electrolytic solution is injected from the liquid injection port 15 opened in the lid 2. A rectangular battery can be manufactured by injecting and sealing the solution.

The present invention is not limited to the above embodiment. For example, if the orientation of the laser welder is changed during welding, it is possible to weld all of the welded parts at an outward angle or at an advancing angle. Further, the incident angle may be a predetermined angle for each of the outward angle and the forward angle.

Further, in the case of FIG. 11 described above, the long side of the lid is welded at the advancing angle and the short side is welded at the outward angle. However, the invention is not limited to this. The sides may be welded at the advancing angle. Which method is used depends on the shape and position of the protruding portion of the lid. Further, a CO ₂ gas laser may be used for laser welding.

The object to be welded may be any metal to which laser welding can be applied, but the present invention is particularly effective for a metal having a high reflectance, such as aluminum or its alloy. The present invention is effective when the lid has a large thickness (2 mm or more for an aluminum alloy) and the energy of the applied laser is large.

[0049]

According to the present invention, the incident angle of laser light can be
Since the predetermined angle is not perpendicular to the surface of the welded portion, it is possible to prevent the laser welder from being damaged by the reflected light of the laser light. Further, it is possible to prevent defective formation of the weld beads due to the vertical irradiation of the beam to the melting region and the scattering of the molten metal, and the welding quality is improved. The present invention is particularly effective when airtightness is required, such as in a Li-ion secondary battery melting vessel.

According to the second aspect of the present invention, when the shield gas is delivered in the vicinity of the irradiation position of the laser beam, the shielding effect of the welded portion is improved, so that the welding quality is further improved.

According to the present invention as set forth in claim 3, since the laser beam is emitted to the outside, the welding quality is prevented by preventing the defective formation of the welding bead, which is caused by the irradiation of the beam on the melting region and the scattering of the molten metal. It is even more effective in improving.

According to the fifth aspect of the present invention, the two adjacent sides of the lid are welded at a predetermined incident angle, and then the lid is inverted, so that the remaining two portions can be welded without changing the direction of the laser welding machine. It is also possible to weld the sides with a preset incident angle. Therefore, the welding quality of each side of the lid is improved without changing the direction of the laser welding machine.

According to the present invention described in claim 6, since the incident angle for welding the two adjacent sides of the lid can be set to the incident angle in the present invention described in claim 2 or 3, the welding quality is improved. Further improve.

[Brief description of drawings]

FIG. 1 is a perspective view of a rectangular battery container to which a welding method of the present invention is applied.

FIG. 2 is a perspective view in which a part of the prismatic battery container is cut away.

FIG. 3 is a plan view showing a surface on which a safety valve 12 is provided.

FIG. 4 is a diagram showing an embodiment of a method for welding a rectangular battery container of the present invention.

FIG. 5 is a diagram showing a laser beam incident state and a shape of a welded portion in the case of an outward angle.

FIG. 6 is a diagram showing a laser light incident state and a welded portion shape in the case of an advance angle.

FIG. 7 is a diagram showing a configuration of a lid when the electrode terminals are projected to the outside.

8 is a diagram showing a case where a welded portion in the short side direction is welded to the lid of FIG. 7 at an outward angle.

9 is a diagram showing a case where a welded portion in the long side direction is welded to the lid of FIG. 7 at an outward angle or an advancing angle.

10 is a diagram showing a case where the laser welding machine shown in FIG. 4 is used for welding by using both an outward angle and an advance angle.

11 is a diagram showing a case where the lid is inverted and welded by the laser welding machine shown in FIG. 4. FIG.

FIG. 12 is a view showing a weld bead shape when welding is performed at an outward angle or an advancing angle.

FIG. 13 is a diagram showing a conventional method for welding a rectangular battery container.

[Explanation of symbols]

2 Lid 4 Battery Case 6 Rectangular Battery Containers 13 and 14 Lid Projection (Electrode Terminal) 20 Laser Welder 21 Laser Light 23 Shield Gas 30 Welding Part θ1 Laser Light Incident Angle (Advancing Angle) θ2 Laser Light Incident Angle (outward angle) S1, S2 Surface La1 perpendicular to the scanning direction of the laser welding machine One side Lb of the lid One side adjacent to one side La2 One side opposite side Lb2 One side to the opposite side Lc Unwelded length Ld of one side The opposite side Of the length from the adjacent side of one side to the end point

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Hidehiko Tajima             1-1 Satinoura Town, Nagasaki City, Nagasaki Prefecture Mitsubishi Heavy Industries             Nagasaki Shipyard Co., Ltd. (72) Inventor Koichi Ide             Nagasaki Prefecture Nagasaki City Fukahori Town 5 chome 717 1             Ryo Engineering Co., Ltd. F-term (reference) 4E068 BA00 CA08 DA07                 5H011 AA09 BB03 DD13 DD26 FF03                       GG09 JJ29 KK00

Claims (9)

[Claims] 1. A method for welding a rectangular battery container, which comprises laser-welding a metal battery case and a lid, wherein an incident angle of laser light is a predetermined angle which is not perpendicular to a surface of a welded portion. A method for welding a rectangular battery container, comprising: 2. The incident angle is set so that the laser light is incident on the surface of the welded portion from inside the peripheral edge of the lid when viewed from a plane perpendicular to the scanning direction of the laser welding machine. The method for welding a rectangular battery container according to claim 1, wherein the method is for welding a rectangular battery container. 3. The incident angle is set so that when the surface perpendicular to the scanning direction of the laser welding machine is used as a reference, the incident angle is incident on the surface of the welded portion from the side where the scanning is completed. The method for welding a rectangular battery container according to claim 1 or 2. 4. The incident angle is set so that the laser beam does not interfere with the protruding portion when a protruding portion is formed on the outer surface of the lid.
4. The method for welding a rectangular battery container according to any one of 1 to 3. 5. When the lid has a quadrilateral shape, the laser welding is started from a starting point on one side of the lid with the torch angle of the laser welding machine with respect to the surface of the welded portion kept constant. A first step of performing laser welding along the one side, a second step of performing laser welding along the adjacent side of the one side, and the adjacent side to the side adjacent to the adjacent side and facing the one side. The third step of performing the laser welding until the end of the one side, which is substantially the same as the unwelded length of the one side, and the fourth step of reversing the relative position of the object to be welded and the laser welding machine by 180 degrees A fifth step of performing laser welding on the object to be welded that has undergone the fourth step from the vicinity of the end point and performing laser welding along the facing side, and laser along the side adjacent to the facing side. A sixth step of performing welding, and the step of adjoining the adjacent side To the sides, the prismatic battery vessel welding method according to claim 1, characterized in that it comprises a seventh step of performing laser welding up to the vicinity of the starting point. 6. The incident angle with respect to the one side is set so as to be incident on the surface of the welded portion from the side where scanning is completed, with reference to a plane perpendicular to the scanning direction of the laser welding machine. The incident angle with respect to the adjacent side of the one side is set so that the laser light is incident on the surface of the welded portion from the inside from the peripheral edge of the lid when viewed from a plane perpendicular to the scanning direction of the laser welding machine. The method for welding a rectangular battery container according to claim 5, wherein 7. The incident angle with respect to the one side is set so that the laser light does not interfere with the protrusion when the protrusion is formed on the outer surface of the lid. 7. The method for welding the rectangular battery container according to 5 or 6. 8. The method for welding a rectangular battery container according to claim 1, wherein the laser welding machine sends a shield gas near an irradiation position of the laser light. 9. A method for manufacturing a prismatic battery, which comprises using the method for welding a prismatic battery container according to claim 1.