Secondary battery

1. A secondary battery comprising:

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

a case configured to accommodate the electrode assembly; and

a cap assembly configured to seal the case and comprising:

a cap plate having a short-circuit opening;

a reversible plate at the short-circuit opening;

an insulation member on the cap plate and comprising an open part at a side; and

a short-circuit plate configured to be inserted into and coupled to the open part for covering the short-circuit opening,

wherein the open part comprises:

a bottom part contacting the cap plate and coupled to the cap plate; and

first and second sidewall parts extending upward from respective sides of the bottom part, and

wherein the first and second sidewall parts define an inlet opening facing away from the open part and along a direction substantially parallel to a length direction of the insulation member.

2. The secondary battery as claimed in claim 1 , wherein the open part further comprises:

a cover part between the first and second sidewall parts.

3. The secondary battery as claimed in claim 2 , wherein the inlet opening is further defined by the bottom part and the cover part, and

wherein the short-circuit plate is inserted into the inlet opening and housed in the insulation member.

4. The secondary battery as claimed in claim 1 , wherein the insulation member further comprises a receiving recess part at which the short-circuit plate inserted into the open part is at least partially placed.

5. The secondary battery as claimed in claim 4 , wherein the receiving recess part comprises:

a receiving recess bottom part;

a receiving recess first sidewall part;

a receiving recess second sidewall part; and

a receiving recess third sidewall part coupled to the receiving recess bottom part, the receiving recess first sidewall part, and the receiving recess second sidewall part of the receiving recess part,

wherein the receiving recess bottom part, the receiving recess first sidewall part, and the receiving recess second sidewall part of the receiving recess part extend from the bottom part and the first and second sidewall parts of the open part.

6. The secondary battery as claimed in claim 4 , wherein a terminal plate having a terminal penetration hole is coupled to the short-circuit plate on the receiving recess part.

7. The secondary battery as claimed in claim 6 , wherein the bottom part of the open part has a contact hole at a position corresponding to a position of the short-circuit opening.

8. The secondary battery as claimed in claim 7 , wherein the receiving recess part comprises a receiving recess bottom part having a first penetration hole.

9. The secondary battery as claimed in claim 8 , wherein the short-circuit plate has a second penetration hole at a position corresponding to a position of the first penetration hole.

10. The secondary battery as claimed in claim 9 , further comprising first and second collecting terminals electrically coupled to the first and second electrode plates, respectively,

wherein the first collecting terminal penetrates through the terminal penetration hole, the first penetration hole, and the second penetration hole.

11. The secondary battery as claimed in claim 9 , wherein the reversible plate comprises:

a downwardly-convex round part; and

an edge part coupled to the cap plate.

12. The secondary battery as claimed in claim 11 , wherein the reversible plate is configured to be brought into contact with the short-circuit plate by an internal pressure in the secondary battery.

13. The secondary battery as claimed in claim 12 , wherein the reversible plate is electrically coupled to the second electrode plate.

14. The secondary battery as claimed in claim 12 , wherein the short-circuit plate is electrically coupled to the first electrode plate.