Rechargeable battery

1. A rechargeable battery, comprising:

an electrode assembly;

a case accommodating the electrode assembly;

a cap plate sealing the case, the cap plate including a vent hole for discharge of gas and a safety vent at the vent hole,

wherein the safety vent includes:

a main groove at a center thereof;

a sub groove entirely spaced apart from and around the main groove,

a first region at a peripheral part of the safety vent, the first region being coupled to the cap plate; and

a second region at an inner part of the safety vent, and

wherein the main groove and the sub groove are in the second region,

wherein the main groove includes:

a first main groove transversely formed in the center of the safety vent;

a second main groove extending from one end of the first main groove toward a peripheral part of the safety vent; and

a third main groove extending from another end of the first main groove toward the peripheral part of the safety vent, and

wherein the sub groove is substantially parallel with the first main groove.

2. The rechargeable battery as claimed in claim 1 , wherein the second region has an upwardly convex shape.

3. The rechargeable battery as claimed in claim 1 , wherein the second region has a thickness smaller than a thickness of the first region.

4. The rechargeable battery as claimed in claim 1 , wherein the sub groove has a depth smaller than a depth of the main groove.

5. The rechargeable battery as claimed in claim 1 , wherein the second main groove and the third main groove each have a “V” shape.

6. The rechargeable battery as claimed in claim 1 , wherein the safety vent includes a plurality of sub grooves, the sub grooves being spaced from each other.

7. The rechargeable battery as claimed in claim 6 , wherein each sub groove has the configuration of a line in the form of a series of dashes, the sub grooves being aligned symmetrically to one another.

8. The rechargeable battery as claimed in claim 6 , wherein each sub groove has the configuration of a line in the form of a series of dashes, the sub grooves on respective sides of the first main groove being aligned to be offset from one another.

9. The rechargeable battery as claimed in claim 1 , wherein the sub groove is substantially perpendicular to the first main groove.

10. The rechargeable battery as claimed in claim 9 , wherein the safety vent includes a plurality of sub grooves, the sub grooves being spaced from each other.

11. The rechargeable battery as claimed in claim 10 , wherein a set of sub grooves on one side of the first main groove are symmetrical with another set of sub grooves on another side of the first main groove.

12. The rechargeable battery as claimed in claim 11 , wherein each sub groove has the configuration of a line in the form of a series of dashes, the sub grooves being aligned symmetrically to one another.

13. The rechargeable battery as claimed in claim 10 , wherein a set of sub grooves on one side of the first main groove are offset from another set of sub grooves on another side of the first main groove.

14. The rechargeable battery as claimed in claim 13 , wherein each sub groove has the configuration of a line in the form of a series of dashes.