Secondary battery

1. A secondary battery comprising:

an electrode assembly; and

a case accommodating the electrode assembly, the case comprising:

a bottom surface;

a first pair of parallel sidewalls having a first width and being connected with the bottom surface, the electrode assembly being located between the first pair of parallel sidewalls;

a second pair of parallel sidewalls having a second width smaller than the first width and being connected with the bottom surface, the electrode assembly being located between the second pair of parallel sidewalls, each sidewall of the second pair of parallel sidewalls being connected to each sidewall of the first pair of parallel sidewalls; and

a corner portion formed by an intersection of each of the first pair of parallel sidewalls and the bottom surface, the corner portion having a first radius of curvature at a first region along an edge of the corner portion, and a second radius of curvature different from the first radius of curvature at a second region adjacent the first region along the edge of the corner portion.

2. The secondary battery of claim 1 ,

wherein the corner portion comprises an inner corner portion formed at an interior of the case and an outer corner portion formed at an exterior of the case, and

wherein a radius of curvature of the inner corner portion at the first region is different from a radius of curvature of the outer corner portion at the first region.

3. The secondary battery of claim 2 , wherein the radius of curvature of the inner corner portion is greater than the radius of curvature of the outer corner portion.

4. The secondary battery of claim 2 , wherein the radius of curvature of the inner corner portion is less than the radius of curvature of the outer corner portion.

5. The secondary battery of claim 2 , wherein the inner corner portion forms a recessed portion in the bottom surface at the first region.

6. The secondary battery of claim 5 , wherein the recessed portion comprises a stepped surface.

7. The secondary battery of claim 1 , wherein the first radius of curvature is greater than the second radius of curvature, and forms a groove at the first region.

8. The secondary battery of claim 1 , wherein a thickness of the bottom surface at the first region is about 65% to about 95% of a thickness of the bottom surface at the second region.

9. The secondary battery of claim 1 , wherein the corner portion comprises two second regions and wherein the first region is located between the two second regions.

10. The secondary battery of claim 1 , wherein the first region extends along about 1% to about 35% of the first width.

11. The secondary battery of claim 1 ,

wherein the corner portion comprises an inner corner portion formed at an interior of the case and an outer corner portion formed at an exterior of the case, and

wherein the radius of curvature of the inner corner portion at the first region is substantially equal to the radius of curvature of the outer corner portion at the first region.

12. The secondary battery of claim 1 ,

wherein the corner portion comprises an inner corner portion formed at an interior of the case and an outer corner portion formed at an exterior of the case, and

wherein the radius of curvature of the outer corner portion at the first and the second region is substantially equal to the radius of curvature of the inner corner portion at the second region.

13. The secondary battery of claim 1 ,

wherein the corner portion comprises an inner corner portion formed at an interior of the case and an outer corner portion formed at an exterior of the case, and

wherein the radius of curvature of the inner corner portion at the first and the second region is substantially equal to the radius of curvature of the outer corner portion at the second region.

14. A secondary battery comprising:

an electrode assembly; and

a case accommodating the electrode assembly, the case comprising:

a pair of longer side surfaces;

a pair of shorter side surfaces; and

a bottom portion connecting the pair of longer side surfaces and the pair of shorter side surfaces;

a cap assembly coupled to a top portion of the case; and

a notched region formed at each corner portion formed where each of the pair of longer side surfaces and the bottom portion are coupled.

15. The secondary battery according to claim 14 , wherein the notched region is formed at a center region of the corner portion along each of the pair of longer side surfaces.

16. The secondary battery according to claim 14 , wherein the corner portion comprises an inner corner portion on an inner surface of the case and an outer corner portion on an outer surface of the case.

17. The secondary battery according to claim 16 , wherein the notched region is formed at the inner corner portion, and forms a groove extending from an inner surface of each of the pair of longer side surfaces to an inner surface of the bottom portion.

18. The secondary battery according to claim 16 , wherein the notched region is formed at the outer corner portion, and forms a groove extending from an outer surface of each of the pair of longer side surfaces to an outer surface of the bottom portion.

19. The secondary battery according to claim 16 ,

wherein the notched region comprises a first notched region and a second notched region, the first notched region being formed at the inner corner portion and the second notched region being formed at the outer corner portion,

wherein the first notched region forms an inner groove extending from an inner surface of each of the pair of longer side surfaces to an inner surface of the bottom portion, and

wherein the second notched region forms an outer groove extending from an outer surface of each of the pair of longer side surfaces to an outer surface of the bottom portion.