Secondary battery

1. A secondary battery, comprising:

an electrode assembly;

a can having an upper opening to receive the electrode assembly and two facing wide walls, the wide walls being asymmetrical to each other; and

a cap assembly sealing the upper opening of the can,

wherein the wide walls include a first wide wall and a second wide wall welded with the cap assembly, the second wide wall having an upper part, the upper part including a weak welding part at a middle part thereof and the weak welding part having a weld between the second wide wall and the cap assembly that is weaker than a weld between remaining portions of the upper part of the second wide wall and the cap assembly.

2. The secondary battery as claimed in claim 1 , wherein the second wide wall is thinner than the first wide wall.

3. The secondary battery as claimed in claim 2 , wherein thicknesses of the first wide wall and the second wide wall are each about 0.18 mm to about 0.4 mm.

4. The secondary battery as claimed in claim 3 , wherein a thickness difference between the first wide wall and the second wide wall is about 0.05 mm to about 0.10 mm.

5. The secondary battery as claimed in claim 2 , wherein the can includes a narrow wall connected to the first wide wall and the second wide wall and the narrow wall has a rounded shape.

6. The secondary battery as claimed in claim 5 , wherein the narrow wall has a thickness and the thickness gradually decreases from the first wide wall toward the second wide wall.

7. The secondary battery as claimed in claim 6 , wherein the narrow wall includes a first and a second narrow wall and the first and second narrow walls are symmetrical to each other.

8. The secondary battery as claimed in claim 2 , wherein the upper part includes a stepped part therein.