JP2021106096A - Secondary battery and welding method - Google Patents

Abstract

To solve such a problem that, in conventional secondary batteries, there are portions where welding accuracy cannot be increased.SOLUTION: One aspect of a secondary battery of the present invention includes: a case; a pole column 24 that extracts power from a power generating body stored inside the case; a lid 25 that seals the case; a terminal 28 that is provided outside the lid 25; and a buffer washer 31 that is formed so that a filler metal is a porous body. The pole column 24 has a caulked part 32 pressed against the terminal 28 while the member of the pole column 24 is caulked on an outside of the lid 25. The buffer washer 31 has a cross-linked structure 34 where, while the caulked part 32 is welded to the terminal 28, the filler metal solidifies along an outer peripheral edge of the caulked part 32 after melting and thereby the caulked part 32 and the terminal 28 are joined.SELECTED DRAWING: Figure 3

Description

The present invention relates to a secondary battery and a welding method, for example, to a secondary battery having a structure in which a pole column and a terminal are welded via a caulking portion.

In recent years, the use of secondary batteries has been expanding. Among these secondary batteries, the secondary battery for automobiles is formed by sealing a metal case containing a generator. At this time, in the secondary battery, the internal pressure may increase due to use, and various measures have been taken for the sealing structure of the case in order to prevent damage due to the internal pressure. One of the ingenuity is to improve the pressure resistance of the case by improving the accuracy of welding between the opening and the stopper that seals the opening. Therefore, Patent Document 1 discloses an example of a technique for improving welding accuracy.

In the welding line detection method described in Patent Document 1, the weld line portion is irradiated with slit light having a predetermined line width, and the slit light is imaged from an angle forming a constant angle with respect to the irradiation light, and the slit light is obtained by imaging. The shading projection values in the horizontal and vertical directions are calculated based on the obtained image signal, and the shading projection values are set values determined by the maximum and minimum values of the variation points of the horizontal and vertical shading projection values. Is cut out, the center of gravity is calculated for the cut out horizontal shading projection value and the vertical shading projection value, and the pixel positions corresponding to the horizontal and vertical center of gravity positions obtained from the result are obtained. , The position of the welding line is calculated by performing coordinate conversion corresponding to the pixel position.

Japanese Unexamined Patent Publication No. 10-71470

However, in a secondary battery, the position accuracy of the welded part is simply improved, such as a part where welding of dissimilar metals is required or one member must be melted so as to fill a gap between parts. There are some places where the welding accuracy cannot be improved just by using it.

The present invention has been made in view of the above circumstances, and an object of the present invention is to improve welding accuracy of a portion having a complicated structure.

One aspect of the secondary battery of the present invention includes a case, a pole column for extracting electric power from a generator housed inside the case, a lid for sealing the case, and a terminal provided outside the lid. It has a buffer washer formed so that the filler metal is a porous body, and the pole pillar is a caulked portion pressed against the terminal in a state where the member of the pole pillar is crimped on the outside of the lid. In the buffer washer, the filler metal is melted and solidified along the outer peripheral edge of the crimped portion in a state where the crimped portion is welded to the terminal, and the crimped portion and the terminal are joined. It has a cross-linked structure.

In the secondary battery of the present invention, a buffer washer that easily melts against heat input caused by welding is provided between the caulked portion and the terminal to provide a buffer between the outer peripheral portion of the caulked portion to be welded and the terminal. There is a filler material that forms the washer. Then, the caulked portion and the terminal are welded by melting this filler metal by the heat input of welding.

According to the secondary battery of the present invention, it is possible to improve the welding accuracy of a welded portion having a complicated structure such as an irregular outer shape or a gap between parts to be welded.

It is the schematic of the structure of the secondary battery which concerns on Embodiment 1. FIG. It is a figure explaining the welding process of the caulking part and Z terminal of the secondary battery which concerns on Embodiment 1. FIG. FIG. 5 is a cross-sectional view of a welded portion for explaining the structure of the caulked portion of the secondary battery and the Z terminal after the welding step according to the first embodiment. It is a table explaining the material of the pole pillar, the buffer washer and the Z terminal of the secondary battery which concerns on Embodiment 1. FIG. It is a figure explaining the irradiation point of the welding laser in the welding process of the caulking part of the secondary battery and the Z terminal which concerns on Embodiment 1. FIG. It is the schematic of the configuration example of the buffer washer of the secondary battery which concerns on Embodiment 2. FIG. It is a table explaining the material of the pole pillar, the caulking part, the cushioning washer and the Z terminal of the secondary battery which concerns on Embodiment 3. FIG. It is a figure explaining the setting method of the irradiation point of the welding laser in the welding process of the caulking part and Z terminal of the secondary battery which concerns on Embodiment 4. FIG.

Embodiment 1
Hereinafter, embodiments of the present invention will be described with reference to the drawings. In order to clarify the explanation, the following description and drawings have been omitted or simplified as appropriate. In each drawing, the same elements are designated by the same reference numerals, and duplicate explanations are omitted as necessary.

First, FIG. 1 shows a schematic view of the structure of the secondary battery 1 according to the first embodiment. As shown in FIG. 1, the secondary battery 1 according to the first embodiment includes a winding body 10, a case 20, current collector parts 21, 23, a lid 25, and terminals (hereinafter, referred to as Z terminals 26 and 28). Have. As the terminal, a terminal component other than the terminal having a Z shape can also be used.

The wound body 10 is wound in a state where the positive electrode sheet, the negative electrode sheet, and the separator sheet are laminated for three or more turns, and the cross section is formed into a flat shape. The winding body 10 has a power generation body 11, a first current collecting unit 12, and a second current collecting unit 13. The power generator 11 is a region in which a positive electrode active material is coated, a negative electrode active material is coated, and a separator sheet are laminated in the positive electrode sheet. The generator 11 has a function of storing the electric energy of the secondary battery. The first current collecting unit 12 is a portion in which one of the positive electrode sheet and the negative electrode sheet is wound among the sheets included in the wound body. The second current collector 13 is a portion of the sheet included in the wound body in which the other sheet of the positive electrode sheet and the negative electrode sheet is wound. No active material is applied to the sheet provided as the first current collector 12 or the second current collector 13.

Here, the active material coated on the positive electrode sheet and the negative electrode sheet will be described. The positive electrode sheet is coated with, for example, LiCoO2, LiMn2O4, LiNiO2 or the like as an active material. Further, the negative electrode sheet is coated with, for example, graphite (LiC6), titanate (Li4Ti5O12) or the like as an active material. Then, in the laminated body, the active material region on which the active material is coated on the positive electrode sheet and the active material region on which the active material is coated on the negative electrode sheet are laminated so as to be overlapped with each other, and the separator sheet is this. It is provided so as to be sandwiched between positive and negative active material regions. In the following description, the electrode sheet is used as a term including the positive electrode sheet and the negative electrode sheet.

In the case 20, the current collector component 21, the current collector component 21, and the current collector component 23 are housed in a state where the current collector component 21 and the current collector component 23 are attached to the winding body 10. Then, the lid 25 and the case 20 are joined in a state where the winding body 10, the current collecting component 21 and the current collecting component 23 are housed in the case 20.

Here, the current collecting component 21 is joined to the first current collecting unit 12 by using welding technology or the like. A current collecting component 23 is joined to the second current collecting unit 13 by using welding technology or the like. Then, the current collecting component 21 is provided with the pole pillar 22 so as to project toward the lid 25 side. The current collector component 23 is provided with a pole pillar 24 so as to project toward the lid 25 side. Then, with the case 20 covered with the lid 25, the pole pillars 22 and the pole pillars 24 are in a state of protruding from the lid 25 through the electrode take-out holes provided in the case 20.

Then, the Z terminal 26 is joined to the pole pillar 22 protruding from the lid 25. The Z terminal 26 is provided with a bus bar connection terminal 27, and the secondary battery 1 is connected to another secondary battery by the bus bar connected to the bus bar connection terminal 27. Further, the Z terminal 28 is joined to the pole pillar 24 protruding from the lid 25. The Z terminal 28 is provided with a bus bar connection terminal 29, and the secondary battery 1 is connected to another secondary battery by the bus bar connected to the bus bar connection terminal 29.

The secondary battery 1 according to the first embodiment has one of the features in the welded structure of the pole column and the Z terminal. Therefore, FIG. 2 shows a diagram illustrating a welding process of the caulked portion and the Z terminal of the secondary battery according to the first embodiment. In the secondary battery 1 according to the first embodiment, the insulator 30 and the buffer washer 31 are used when joining the Z terminal to the pole column. Further, in the secondary battery 1 according to the first embodiment, the welding method of the pole pillar 22 and the Z terminal 26 and the welding method of the pole pillar 24 and the Z terminal 28 are the same. The welding process for welding the Z terminal 28 is shown. Further, in FIG. 2, the step of joining the pole pillar 22 and the pole pillar 24 is described by being decomposed from the first step to the fourth step.

In the first step shown in FIG. 2, the Z terminal 28 is arranged on the upper portion of the lid 25 (the surface of the lid that is the outer side of the case) via the insulator 30. In this first step, the Z terminal 28 is arranged on the upper surface of the lid 25 so that the pole pillar 24 penetrates the hole provided in the Z terminal 28.

Subsequently, in the second step, the buffer washer 31 is arranged above the Z terminal 28 so that the pole pillar 24 penetrates the buffer washer 31. Here, the buffer washer 31 will be described. The buffer washer 31 is cut out in a donut shape from a plate-shaped member formed so that the filler metal becomes a porous body. Examples of the porous body include a non-woven fabric formed by compressing a metal fiber and a foam formed by foaming a metal body. Further, a copper compound or aluminum is used as the filler material. Whether a copper compound or aluminum is used as the filler material is determined by the material of the pole column (particularly, the caulked portion 32) to be welded and the material of the Z terminal 28. The details of the relationship between the materials of the pole column, the Z terminal and the buffer washer will be described later. Then, in the second step, a caulking force is applied to the end of the portion of the pole column 24 that protrudes from the lid 25. By this caulking step, the end portion of the pole column is crimped to form the caulked portion 32. The surface of the crimped portion 32 facing the Z terminal 28 has a convex shape toward the Z terminal side. At this time, the buffer washer 31 is compressed and deformed following the deformation of the caulking portion 32. That is, in the second child step, the presence of the buffer washer 31 provides a buffer layer that prevents the force of caulking on the caulking portion 32 from being excessively applied to the insulator.

Subsequently, in the third step, the welding laser beam 33 is irradiated along the outer peripheral edge of the crimped portion 32, and the filler metal of the buffer washer 31 melts the outer peripheral portion of the crimped portion 32. As a result, as shown in the fourth step, the outer peripheral edge of the caulked portion 32 and the Z terminal 28 are welded by the crosslinked structure 34 in which the buffer washer 31 is melted and solidified.

In FIG. 2, a caulking force is applied to the end portion of the pole pillar 24 to form the crimped portion 32, but the Z terminal and the pole pillar 24 may be joined separately by using a caulking member. Further, the Z terminal is provided at a position irrelevant to the position of the pole pillar 24, not at a position where the pole pillar 24 penetrates, and is collected in the case via a lid or a case using a caulking member. It can also be joined to electrical components. Even in such a case, the secondary battery can be manufactured by the welding process as shown in FIG. 2 by inserting the buffer washer 31 between the caulking member and the Z terminal (or simply the terminal).

Subsequently, the structure of the welded portion in the fourth step (after the welding step) will be described in detail. Therefore, FIG. 3 shows a cross-sectional view of a welded portion for explaining the structure of the caulked portion and the Z terminal of the secondary battery 1 according to the first embodiment after the welding step.

As shown in FIG. 3, the caulking portion 32 is a portion located on the Z terminal 28 side of the buffer washer 31 so as to crush the buffer washer 31 by being crimped in the caulking step (for example, the second step of FIG. 2). Enters. Then, in the welding step (for example, the step of FIG. 3), the portion of the buffer washer 31 along the outer peripheral portion of the caulked portion 32 is melted by the welding laser beam 33 and then solidified to form a bridge structure 34. The crosslinked structure 34 connects the crimped portion 32 and the Z terminal 28 by melting with the outer peripheral portion of the crimped portion 32 and melting with the Z terminal 28.

Further, in the first embodiment, since the filler metal constituting the buffer washer 31 is porous, the crosslinked structure 34 is formed by the welding laser light 33 having a small amount of heat input. Further, in the first embodiment, only the outer peripheral portion of the crimped portion 32 is irradiated with the weak welding laser light 33. As a result, the buffer washer 31 is maintained in a porous state for the inner peripheral portion of the crimped portion 32. Further, since the buffer washer 31 is a porous body, the energy generated by the welding laser beam 33 is weakened by the porous body, so that the insulator 30 is less likely to be damaged by heat.

Subsequently, the materials of the pole pillar, the buffer washer, and the Z terminal of the secondary battery 1 according to the first embodiment will be described. Therefore, FIG. 4 shows a table for explaining the materials of the pole pillar, the buffer washer, and the Z terminal of the secondary battery 1 according to the first embodiment.

As shown in FIG. 4, the material used as the pole pillar is different in the secondary battery 1. This is because the material of the positive electrode sheet and the material of the negative electrode sheet are different. For example, when a lithium ion battery is configured as the secondary battery 1, aluminum is used as the positive electrode sheet and copper is used as the negative electrode sheet. Therefore, on the positive electrode side, the component is made of aluminum or a material containing aluminum. On the other hand, on the negative electrode side, the component is made of copper or a material containing copper.

Specifically, the following materials are used for the components on the positive electrode side. Aluminum-based materials, especially 1000-based aluminum, are used as the pole columns. Aluminum-based materials, especially 5000-based aluminum, are used as the buffer washers and Z terminals. Here, when 1000-series aluminum and 5000-series aluminum are welded, the alloy components of each other are mixed due to the heat input during welding, and cracks occur during solidification depending on the degree of mixing. However, by using the buffer washer 31 according to the first embodiment, the crosslinked structure 34 can be formed while reducing the amount of heat input to the crimped portion and the Z terminal, so that the above-mentioned cracking can be prevented. can.

The following materials are used for the components on the negative electrode side. Copper is used as the pole column and Z terminal. On the other hand, as the buffer washer, an alloy material of copper and silicon (hereinafter referred to as CuSi) is used. Here, CuSi is characterized by having a lower melting point than copper. Therefore, by using the buffer washer 31 according to the first embodiment, the crosslinked structure 34 can be formed while reducing the amount of heat input to the crimped portion and the Z terminal on the negative electrode side.

Subsequently, the relationship between the outer peripheral edge of the caulked portion and the irradiation point of the welding laser beam 33 will be described. Therefore, FIG. 5 shows a diagram illustrating an irradiation point of the welding laser in the welding process of the caulked portion and the Z terminal of the secondary battery according to the first embodiment.

As shown in FIG. 5, the caulking portion 32 has a distorted outer peripheral edge shape due to the caulking process. In the manufacturing process of the secondary battery 1 according to the first embodiment, the laser irradiation point is moved along the shape of the outer peripheral edge of the original caulking portion 32. At this time, due to the distortion of the caulking portion 32, the welding laser light 33 irradiating the outer peripheral portion of the caulking portion 32 is small at the point A in FIG. 5, and the welding laser light 33 irradiating the outer peripheral portion of the caulking portion 32 at the point B. The amount of irradiation of the welding laser light 33 becomes non-uniform. However, in the secondary battery 1 according to the first embodiment, by providing the buffer washer 31, even if the irradiation amount of the welding laser light 33 is uneven, it is formed by melting and solidifying the buffer washer 31. The crimped portion 32 and the Z terminal 28 are welded with uniform strength by the crosslinked structure 34.

From the above description, in the secondary battery 1 according to the first embodiment, by providing the buffer washer 31, the crosslinked structure 34 can be formed with a low heat input amount and the caulked portion and the Z terminal can be welded to each other.

On the negative electrode terminal side, an insulator 30 is provided below the Z terminal, but the insulator 30 is made of resin, and deformation or deformation due to heat becomes a problem. However, in the secondary battery 1 according to the first embodiment, by providing the buffer washer 31 formed of the filler material of the porous body, the air layer contained in the porous body is heated by the welding laser light 33. Since it functions as a heat insulating material that shields the insulator 30, it is possible to suppress the amount of heat input to the insulator 30 and suppress the deformation or deformation of the insulator 30.

Further, although a gap is formed between the Z terminal and the outer peripheral portion of the caulking portion, it is conceivable to lower the caulking height in order to reduce the gap height. However, if the caulking height is lowered, the Z terminal is scratched, excessive pressure is applied to the insulator 30, and problems such as deformation of the insulator 30 occur. Such scratches on the Z terminal or deformation of the insulator 30 cause a decrease in the sealing performance of the case and the expected life. However, in the secondary battery 1 according to the first embodiment, by providing the buffer washer 31, a large gap can be joined by the crosslinked structure 34 even with a low heat input amount, so that the above problem occurs. do not have.

On the positive electrode terminal side, when the amount of heat input to the crimped portion and the Z terminal becomes large, cracks that become a problem in welding different types of aluminum materials occur. However, in the secondary battery 1 according to the first embodiment, since the caulking portion and the Z terminal are joined by the crosslinked structure 34 while reducing the amount of heat input during welding by providing the buffer washer 31, different types of aluminum are used. Welding can prevent problematic cracking.

Further, by forming the buffer washer 31 with a porous body, the heat generated by the welding laser light 33 irradiated from above is less likely to be transmitted to the Z terminal side. This is because the buffer washer 31 formed of the porous body acts as a heat insulating material. Further, the buffer washer 31 functions as a buffer layer for preventing excessive pressure from being applied to the insulator 30 in the caulking step of crimping the caulking portion 32.

Embodiment 2
In the second embodiment, another embodiment of the buffer washer 31 will be described. Specifically, in the second embodiment, the buffer washer 31a which is a first modification of the buffer washer 31 and the buffer washer 31b which is a second modification of the buffer washer 31 will be described.

Therefore, FIG. 6 shows a schematic view of a configuration example of the buffer washer of the secondary battery according to the second embodiment. In FIG. 6, the buffer washer 31a is shown in the upper figure, and the buffer washer 31b is shown in the lower figure. In the buffer washer 31a, a dense region having a high density of filler material is formed on the outer peripheral portion, and a rough region having a density of the filler material lower than that on the outer peripheral portion is formed on the inner peripheral portion. In the buffer washer 31a, the air layer is increased by lowering the density of the filler metal in the inner peripheral portion, and the heat insulating performance is improved. Further, the buffer washer 31a can form the crosslinked structure 34 with a lower amount of heat input by increasing the density of the filler metal on the outer peripheral portion. As another example of the buffer washer 31a, a low-density region can be formed by a single-layer filler sheet, and a high-density region can be formed by a two-layer filler sheet.

Further, the buffer washer 31b shown in FIG. 6 has a two-layer structure of a first layer 41 on the caulking portion side and a second layer 42 on the Z terminal side in a state of being fitted in the secondary battery 1. .. The first layer 41 is formed of a filler material containing at least a material for a crimped portion. The second layer has at least a second layer formed of a filler material of the same material as the material of the Z terminal. As a result, since the buffer washer 31b is melted with the facing parts with a low heat input amount, the crosslinked structure 34 can be formed with a lower heat input amount than the buffer washer 31 according to the first embodiment.

Embodiment 3
In the third embodiment, another form of the material of the pole column, the caulked portion, the buffer washer, and the Z terminal will be described. Therefore, FIG. 7 shows a table for explaining the materials of the pole pillar, the caulked portion, the buffer washer, and the Z terminal of the secondary battery according to the third embodiment.

As shown in FIG. 7, in the secondary battery according to the third embodiment, the material of the Z terminal on the negative electrode side is aluminum. In recent years, reduction of the amount of copper used in order to reduce the cost of members has been promoted, and it is being studied to use aluminum (particularly 5000 series aluminum) for the Z terminal. In such a case, the following effects are obtained by using CuSi as the buffer washer 31.

When the buffer washer 31 made of CuSi is irradiated with the welding laser beam 33, the copper and silicon of the buffer washer 31 are separated, and silicon oxide (SiO) and CuAl are generated. As a result, the aluminum oxide film on the surface of the crosslinked structure 34 is removed, the silicon oxide film is formed on the surface, and the CuAl layer having excellent corrosion resistance is formed inside. That is, by using aluminum as the Z terminal, a crosslinked structure 34 having high corrosion resistance can be formed.

Embodiment 4
In the fourth embodiment, another embodiment of the method of setting the welding line in laser welding will be described. Therefore, FIG. 8 shows a diagram illustrating a method of setting a welding laser irradiation point in the welding process of the caulked portion and the Z terminal of the secondary battery according to the fourth embodiment.

In the welding line setting method according to the fourth embodiment, welding is performed by acquiring an image around the caulked portion 32 to be welded and using image processing to specify the coordinates of the welding line. Use the device. In the example shown in FIG. 4, first, the welding apparatus acquires an image around the crimped portion 32, and sets a plurality of band-shaped edge detection regions WD in a region including the outer peripheral edge of the crimped portion with respect to the acquired image. .. Subsequently, the welding apparatus generates an image that changes from light to dark according to the height in the height direction with the surface of the lid 25 as the bottom with respect to the image obtained from the edge detection region WD. Then, the welding apparatus sets the welding center line along the boundary line between the bright portion and the dark portion for each edge detection region WD with respect to the generated bright / dark image.

Then, in the welding apparatus according to the fourth embodiment, the set welding center line is set as the welding center line, and the welding laser beam 33 is moved along the welding center line. As a result, in the secondary battery manufactured by using the welding line setting method according to the fourth embodiment, the uniformity of the crosslinked structure 34 formed with respect to the distorted caulking portion 32 is applied to the second embodiment. It can be higher than that of the next battery 1.

The present invention is not limited to the above embodiment, and can be appropriately modified without departing from the spirit. In the description of the above embodiment, the viewpoints described in the following appendices can also be considered.

1 Rechargeable battery 10 Winder 11 Generator 12 1st current collector 13 2nd current collector 20 Case 21 Current collector parts 22 Polar poles 23 Current collectors parts 24 Polar poles 25 Lid 26 Z terminal 27 Busbar connection terminal 28 Z terminal 29 Bus bar connection terminal 30 Insulator 31 Buffer washer 32 Caulking part 33 Welding laser light 34 Bridge structure WD edge detection area

Claims (8)

With the case
A pole pillar that extracts electric power from the generator housed inside the case,
A lid that seals the case and
Terminals provided on the outside of the lid and
It has a buffer washer, which is formed so that the filler metal becomes a porous body.
The pole pillar has a crimped portion pressed against the terminal in a state where the member of the pole pillar is crimped on the outside of the lid.
The buffer washer has a crosslinked structure in which the filler metal is melted and solidified along the outer peripheral edge of the crimped portion while the crimped portion is welded to the terminal, and the crimped portion and the terminal are joined. Secondary battery to have. The secondary battery according to claim 1, wherein the buffer washer is in a state in which the caulked portion is welded to the terminal, the outer peripheral portion is melted, and the inner peripheral portion is maintained in the state of the porous body. .. The buffer washer
A first layer formed of a filler material containing at least the material of the crimped portion on the crimped portion side, and
The secondary battery according to claim 1 or 2, further comprising a second layer formed of a filler material of the same material as the material of the terminal on the terminal side. The secondary battery according to claim 1 or 2, wherein the buffer washer is formed so that the porous body on the outer peripheral side has a higher density than the porous body on the inner peripheral side. The pole column, the buffer washer, and the terminal are provided on the positive electrode side and the negative electrode side, respectively.
The pole column on the positive electrode side has the buffer washer and the terminal on the positive electrode side made of different types of aluminum.
The pole column and the terminal on the negative electrode side are made of copper.
The secondary battery according to claim 1 or 2, wherein the buffer washer on the positive electrode side is a copper compound containing copper and another kind of substance. The pole column, the buffer washer, and the terminal are provided on the positive electrode side and the negative electrode side, respectively.
The pole column on the positive electrode side and the buffer washer and the terminal on the positive electrode side are made of different types of aluminum.
The pole column on the negative electrode side is copper and
The terminal on the negative electrode side is made of the same type of aluminum as the buffer washer on the positive electrode side.
The secondary battery according to claim 1 or 2, wherein the buffer washer on the positive electrode side is a copper compound containing copper and another kind of substance. The secondary battery according to any one of claims 1 to 6, wherein the crimped portion has a shape in which a surface facing the terminal has a convex shape toward the terminal in a state of being attached to the pole pillar. .. With the case
A pole pillar that extracts electric power from the generator housed inside the case,
A lid that seals the case and
Terminals provided on the outside of the lid and
A crimped portion provided at the end of the pole pillar and pressed against the terminal in a state where the member of the pole pillar is crimped on the outside of the lid.
A welding method for the caulked portion of a secondary battery having a buffer washer provided between the caulked portion and the terminal and formed so that the filler metal is a porous body.
A band-shaped edge detection region is set in the region including the outer peripheral edge of the crimped portion, and the band-shaped edge detection region is set.
With respect to the image obtained from the edge detection region, an image that changes from light to dark according to the height in the height direction with the surface of the lid as the bottom is generated.
Based on the boundary line between the bright part and the dark part of the image obtained from the edge detection region, the welding center line is set along the edge of the crimped part.
A welding method for a caulked portion of a secondary battery that irradiates a welding laser along the welding center line.

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