Welding method capable of improving welding reliability by precisely setting welding portions of the electrode taps

1. A method for welding electrode tabs protruding from a plurality of electrode plates, comprising:

forming a tab arrangement by arranging the electrode tabs vertically so that at least parts of the electrode tabs overlap each other;

irradiating light to at least two side surfaces among side surfaces of the tab arrangement excluding surfaces on which the electrode tabs overlap and surfaces facing the overlapped surfaces;

scanning a planar shape of a step on which the electrode tabs do not overlap each other using light reflected from an end portion of each of the electrode tabs;

scanning only an overlapped portion of the electrode tabs excluding the step based on the scanned result;

setting a welding range within the overlapped portion; and

performing welding only within the welding range.

2. The method of claim 1 , wherein scanning the planar shape of the step comprises:

(i) recognizing a first boundary shape between the electrode tabs on a first side surface while light which is incident on the first side surface is being reflected at the end portion of each of the electrode tabs on the first side surface; and

(ii) recognizing n (n being one or more) boundary shapes between the electrode tabs on n side surfaces while light which is incident on the n side surfaces, which are located in directions different from the first side surface, is being reflected at the end portion of the electrode tab located on each of the n side surfaces,

and based on any one of the boundary shapes, the remaining boundary shapes are combined in a planar manner so that a planar shape formed by the steps is scanned, and the overlapped portion of the electrode tabs are further scanned.

3. The method of claim 2 , wherein in the planar shape of the scanned steps, the widest planar portion among the planar shapes which is formed by the steps, are scanned as the overlapped portion of the electrode tabs.

4. The method of claim 2 , wherein when the value of n is 2, the first side surface and the second side surface extend with respect to each other, and the third side surface and the first or second side surface extend with respect to each other.

5. The method of claim 2 , wherein the boundary shape is a shape in which straight lines are positioned in parallel in a vertical direction, and while the straight lines are connected to straight lines of the adjacent boundary shape, the shape of the step is scanned.

6. The method of claim 1 , wherein the light is irradiated perpendicularly with respect to a vertical section of the electrode tab arrangement in the process of light irradiation.

7. The method of claim 1 , wherein the light is irradiated at an angle of 1 to 10 degrees with respect to the vertical section of the electrode tab arrangement in the process of light irradiation.

8. The method of claim 1 , wherein the welding range is set at 50% to 100% of the total area of the overlapped portion.

9. The method of claim 8 , wherein a welding start point is additionally set within the set welding range.

10. The method of claim 1 , wherein the type of welding is laser welding.

11. The method of claim 1 , wherein the tab arrangement is scanned in a state of being fixed to a laser welding jig configured to fix an arrangement structure of the electrode tabs.

12. The method of claim 11 , wherein the jig comprises a light source configured to irradiate light to the tab arrangement.