Sealed secondary battery, and method for manufacturing the battery
An electrode group 4 formed by stacking or winding a positive electrode plate 1 and a negative electrode plate 2 with a separator 3 interposed therebetween, is housed in a battery case 5 . An opening of the battery case 5 is sealed with a sealing plate 10 . A lead 11 extending from one of the positive and negative electrode plates in the electrode group 4 is laser-welded to the sealing plate 10 by application of a laser beam 12 having a spot diameter smaller than a thickness of the lead 11.
1. A sealed secondary battery in which an electrode group formed by stacking or winding a positive electrode plate and a negative electrode plate with a separator interposed therebetween is housed in a battery case, and an opening of the battery case is sealed with a sealing plate, wherein
a lead extending from one of the positive and negative electrode plates in the electrode group is welded to the sealing plate by keyhole welding with application of a fiber laser beam having a spot diameter smaller than a thickness of the lead.
2. The sealed secondary battery of claim 1 , wherein a welded portion formed by parts of the lead and the sealing plate has a penetration depth greater than a bead diameter of the welded portion.
3. The sealed secondary battery of claim 1 , wherein a welded portion formed by parts of the lead and the sealing plate has a linear shape.
4. The sealed secondary battery of claim 1 , wherein each of the lead and the sealing plate contains aluminium as a main component.
5. The sealed secondary battery of claim 1 , wherein the spot diameter of the laser beam is less than or equal to ½ of the thickness of the lead.
6. The sealed secondary battery of claim 3 , wherein the welded portion has at least two separate linear or curved portions.
7. The sealed secondary battery of claim 3 , wherein the welded portion forms one of a continuous closed line and a continuous closed curve.
8. The sealed secondary battery of claim 3 , wherein the welded portion has a continuous zigzag pattern.
9. The sealed secondary battery of claim 3 , wherein the welded portion has at least a linear portion extending perpendicularly to a longitudinal direction of the lead.
10. The sealed secondary battery of claim 3 , wherein a ratio of a welding length to a welding width in the welded portion is at least four.
11. The sealed secondary battery of claim 3 , wherein the welded portion is formed along a width of the lead, and
a welding length of the welded portion is at least ⅓ of the width of the lead.
12. A method for fabricating a sealed secondary battery of claim 1 , the method comprising the steps of
(a) preparing an electrode group formed by stacking or winding a positive electrode plate and a negative electrode plate with a separator interposed therebetween;
(b) connecting one end of a lead to one of the positive and negative electrode plates in the electrode group;
(c) housing the electrode group in a battery case;
(d) applying, to the lead, a fiber laser beam having a spot diameter smaller than a thickness of the lead, with another end of the lead brought into contact with a sealing plate, thereby welding the another end of the lead to the sealing plate by keyhole welding; and
(e) sealing an opening of the battery case with the sealing plate.
13. The method of claim 12 , wherein in step (d), the lead is irradiated with the laser beam, while being continuously scanned with a fiber laser.
14. The method of claim 13 , wherein the laser beam is applied in such a manner that power of the laser beam is increased for a period after start of the scanning and is reduced for a period before stop of the scanning.
15. The method of claim 14 , wherein the laser beam is applied in such a manner that power of the laser beam is kept constant in an interval after a lapse of the period after the start of the scanning and before the period before the stop of the scanning.
16. The method of claim 14 , wherein a welded portion formed by parts of the lead and the sealing plate has a uniform penetration depth along a direction of the scanning with the laser beam.
17. The method of claim 14 , wherein a welded portion formed by parts of the lead and the sealing plate has a linear shape.
18. The method of claim 14 , wherein the increase and the reduction of the power of the laser beam are performed with a focal point of the laser beam moved relative to a surface of the lead.
19. The method of claim 12 , wherein in step (d), the laser beam has a spot, diameter less than or equal to ½ of a thickness of the lead.
20. The method of claim 12 , wherein each of the lead and the sealing plate contains aluminium as a main component.