Rechargeable battery

1. A rechargeable battery comprising:

an electrode assembly comprising a first electrode, a second electrode, and a separator between the first electrode and the second electrode;

a case containing the electrode assembly;

a cap plate covering an opening of the case and having a short-circuit opening formed therethrough;

an external short circuit assembly on the cap plate and comprising:

a connection tab on the cap plate and electrically coupled to the first electrode;

a cover on the connection tab and covering the short-circuit opening of the cap plate; and

a terminal plate on the cover and coupled to the cover,

wherein the connection tab, the cover, and the terminal plate are stacked on an outer side of the cap plate facing an outside of the case,

wherein the connection tab is between the cap plate and the cover, and the cover is between the connection tab and the terminal plate, and

wherein the cover comprises a cover body and at least one coupling projection protruding from an end of the cover body; and

a variable plate at the short-circuit opening of the cap plate and electrically coupled to the second electrode, the variable plate configured to contact the connection tab and short circuit the first electrode and the second electrode to each other when an internal pressure of the rechargeable battery exceeds a reference pressure.

2. The rechargeable battery of claim 1 , wherein the terminal plate has at least one coupling groove on a surface facing the connection tab, the at least one coupling groove receiving the at least one coupling projection.

3. The rechargeable battery of claim 1 , wherein the at least one coupling projection comprises a pair of coupling projections protruding from the end of the cover body.

4. The rechargeable battery of claim 1 , wherein the at least one coupling projection extends from a central portion of the end of the cover body.

5. The rechargeable battery of claim 4 , wherein the at least one coupling projection has a fixation hole for receiving a first terminal therein, the first terminal being electrically coupled to the first electrode.

6. The rechargeable battery of claim 4 , wherein a length of the at least one coupling projection is less than a length of the terminal plate.

7. The rechargeable battery of claim 1 , wherein a thickness of the at least one coupling projection extending toward the connection tab is less than a thickness of the cover body.

8. The rechargeable battery of claim 1 , wherein the external short circuit assembly further comprises an insulation member between the cap plate and the connection tab.

9. The rechargeable battery of claim 8 , wherein the insulation member, the connection tab, the cover, and the terminal plate are sequentially stacked on the cap plate.

10. The rechargeable battery of claim 9 , wherein the insulation member comprises a side wall surrounding the connection tab, the cover, and the terminal plate.

11. The rechargeable battery of claim 9 , wherein the insulation member has an opening, the connection tab has an opening, the terminal plate has an opening, and a first terminal is received in the openings of the insulation member, the connection tab, and the terminal plate, the first terminal being electrically coupled to the first electrode.

12. The rechargeable battery of claim 8 , wherein the insulation member comprises a first side contacting the cap plate, and a protrusion extending in a direction away from the cap plate from a second side of the insulation member opposite the first side.

13. The rechargeable battery of claim 12 , wherein the connection tab has an opening receiving the protrusion of the insulation member therein.

14. The rechargeable battery of claim 13 , wherein the terminal plate has a recess receiving the protrusion of the insulation member therein.

15. The rechargeable battery of claim 8 , wherein the insulation member has an opening over the variable plate, and the variable plate protrudes through the opening to contact the connection tab when the internal pressure of the rechargeable battery exceeds the reference pressure.

16. The rechargeable battery of claim 15 , wherein a peripheral portion of the variable plate is attached to the cap plate, and an inner portion of the variable plate inside the peripheral portion is arranged within the short-circuit opening of the cap plate.

17. The rechargeable battery of claim 16 , further comprising a terminal protruding outside the case and electrically connected to the cap plate and the second electrode, wherein the first electrode and the second electrode are short circuited to each other through the cap plate and the terminal when the variable plate contacts the connection tab.

18. The rechargeable battery of claim 1 , wherein the cover comprises an electrically insulative material.