Secondary battery

1. A secondary battery, comprising:

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

a case accommodating the electrode assembly; and

a cap assembly coupled to the case, the cap assembly including:

a cap plate sealing the case and having a short-circuit hole,

a short-circuit plate covering the short-circuit hole of the cap plate, the short-circuit plate being spaced apart from an outer surface of the cap plate and including a protrusion inserted through the short-circuit hole,

a reversible plate adjacent the short-circuit hole, and

a sealing member between the cap plate and the short-circuit plate,

wherein the protrusion of the short-circuit plate has a hollow cylindrical shape, a blocking part being disposed inside the protrusion to divide an interior of the protrusion into upper and lower regions.

2. The secondary battery as claimed in claim 1 , wherein the short-circuit plate includes a flat portion above the cap plate, and the protrusion extends from the flat portion into the short-circuit hole, first and second surfaces of the short-circuit plate being surfaces of the flat portion and the protrusion, respectively.

3. The secondary battery as claimed in claim 1 , wherein the protrusion extends toward the reversible plate.

4. The secondary battery as claimed in claim 1 , wherein the sealing member includes a hole therethrough, the protrusion being inserted into the hole.

5. The secondary battery as claimed in claim 4 , wherein the sealing member includes a rubber material, the rubber material being shaped into repeated ridges and furrows on top and bottom surfaces of the sealing member.

6. The secondary battery as claimed in claim 4 , wherein an inner diameter of the sealing member directly contacts and surrounds an outer diameter of the protrusion.

7. The secondary battery as claimed in claim 1 , wherein the reversible plate includes a downwardly-convex round part and a rim part fixed to the cap plate.

8. The secondary battery as claimed in claim 7 , wherein the round part of the reversible plate is configured to reverse and contact the protrusion of the short-circuit plate, when an inside pressure of the secondary battery is greater than a set value.

9. The secondary battery as claimed in claim 1 , wherein the sealing member includes an adhesive material.

10. The secondary battery as claimed in claim 1 , wherein the reversible plate and the sealing member contact opposite surfaces of the cap plate.

11. The secondary battery as claimed in claim 1 , wherein the reversible plate is electrically connected to the second electrode plate.

12. The secondary battery as claimed in claim 1 , wherein the short-circuit plate is electrically connected to the first electrode plate.

13. The secondary battery as claimed in claim 1 , wherein an upper insulation member contacts the sealing member, a first surface of the short-circuit plate, and the cap plate, the sealing member separating a second surface of the short-circuit plate from the upper insulation member.

14. The secondary battery as claimed in claim 13 , wherein the upper insulation member is disposed between the sealing member and the cap plate.

15. The secondary battery as claimed in claim 1 , further comprising a first electrode terminal inserted through a side of the cap plate, the first electrode terminal including:

a first collecting plate electrically connected to the first electrode plate; and

a first terminal column electrically connected to the first collecting plate and inserted through the cap plate and the short-circuit plate.

16. The secondary battery as claimed in claim 15 , further comprising a first terminal plate coupled to the first terminal column, the first terminal plate including:

a terminal coupling part through which the first terminal column is inserted; and

a pressure reinforcement part extending horizontally from the terminal coupling part and disposed on a top surface of the short-circuit plate.

17. The secondary battery as claimed in claim 16 , further comprising an insulation cover configured to cover top and lateral surfaces of the pressure reinforcement part.

18. The secondary battery as claimed in claim 1 , further comprising an upper insulation member between the cap plate and the short-circuit plate, the upper insulation member and the sealing member being separate and different layers.

19. The secondary battery as claimed in claim 16 , wherein the pressure reinforcement part extends horizontally over the protrusion.

20. A secondary battery, comprising:

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

a case accommodating the electrode assembly; and

a cap assembly coupled to the case, the cap assembly including:

a cap plate sealing the case and having a short-circuit hole,

a short-circuit plate covering the short-circuit hole of the cap plate, the short-circuit plate being spaced apart from an outer surface of the cap plate and including a protrusion inserted through the short-circuit hole,

a reversible plate adjacent the short-circuit hole, and

a sealing member between the cap plate and the short-circuit plate,

wherein an edge of the cap plate defining the short circuit-hole has a predetermined inner diameter, the inner diameter of the short-circuit hole directly contacting and surrounding an outer diameter of the protrusion of the short-circuit plate.