Secondary battery

1. A secondary battery comprising:

an electrode assembly comprising a positive electrode, a separator, and a negative electrode;

a case comprising an end plate and at least one wall extending therefrom defining an inner cavity, the case housing the electrode assembly in the inner cavity;

a cap assembly coupled to the case for sealing the case;

a positive current collecting plate comprising a first side connected to the positive electrode in the case and a second side connected to the cap assembly;

an insulator in the case adjacent the end plate; and

a negative current collecting plate comprising a first side connected to the negative electrode and a second side adjacent the insulator and connected to the end plate at a connection portion of the end plate,

wherein the end plate is curved convexly toward the inner cavity of the case from one side of the case to another side of the case in its entirety, and

wherein the end plate comprises at least one notch having a thickness less than a thickness of an adjacent portion of the end plate.

2. The secondary battery of claim 1 , wherein the insulator comprises:

an external circumferential surface portion corresponding to an internal circumferential surface of the at least one wall of the case;

a planar portion adjacent the negative current collecting plate; and

a recessed portion curved concavely toward the inner cavity of the case and contacting the end plate,

wherein an aperture extends between the planar portion and the recessed portion near a center of the insulator, and

wherein the negative current collecting plate is connected to the end plate through the aperture.

3. The secondary battery of claim 2 , wherein the negative current collecting plate further comprises a protruding portion extending toward and connected to the end plate through the aperture of the insulator at the connection portion.

4. The secondary battery of claim 1 , wherein a portion of the insulator faces the end plate and is curved.

5. The secondary battery of claim 4 , wherein the portion of the insulator facing the end plate contacts the end plate and has a curvature corresponding to a curvature of the end plate.

6. The secondary battery of claim 1 , wherein the end plate is invertible convexly away from the inner cavity of the case to provide a separating space between the end plate and the negative current collecting plate.

7. The secondary battery of claim 6 , wherein the end plate is invertible convexly away from the inner cavity of the case to disconnect the negative current collecting plate from the end plate when an internal pressure in the case is greater than a reference operating pressure.

8. The secondary battery of claim 1 , wherein the end plate is collapsible away from the inner cavity of the case at the at least one notch upon an increase of an internal pressure in the case.

9. The secondary battery of claim 8 , wherein the at least one notch comprises at least one outer circumferential notch along at least a portion of an outer circumference of the end plate.

10. The secondary battery of claim 8 , wherein the at least one notch comprises central notches arranged in a cross pattern at the connection portion of the end plate.

11. The secondary battery of claim 10 , wherein the at least one notch further comprises at least one outer circumferential notch along at least a portion of an outer circumference of the end plate.

12. The secondary battery of claim 10 , wherein the end plate is configured to rupture away from the inner cavity at the central notches when the internal pressure in the case is greater than a rupturing pressure.

13. The secondary battery of claim 10 , wherein the at least one notch further comprises at least one inner circumferential notch connecting the central notches in a circumferential direction.

14. The secondary battery of claim 1 , wherein a portion of the insulator faces the end plate and has a polyhedron shape.

15. The secondary battery of claim 14 , wherein a portion of the end plate faces and contacts the insulator and has a polyhedron shape.

16. A secondary battery having a current interrupt device between a negative current collecting plate of the secondary battery and a case of the secondary battery, the secondary battery comprising:

an electrode assembly comprising a positive electrode, a separator, and a negative electrode;

a case comprising an end plate and at least one wall extending therefrom defining an inner cavity, the case housing the electrode assembly in the inner cavity;

a cap assembly coupled to the case for sealing the case;

a positive current collecting plate connecting the positive electrode to the cap assembly;

an insulator adjacent the end plate; and

a negative current collecting plate connected to the negative electrode and connectable to the end plate at a connection portion of the end plate,

wherein the end plate is curved convexly toward the inner cavity of the case from one side of the case to another side of the case in its entirety and the end plate is connected to the negative current collecting plate when an internal pressure in the case is less than a reference operating pressure, and

wherein the end plate is curved away from the inner cavity of the case and is configured to be disconnected from the negative current collecting plate when the internal pressure in the case is greater than the reference operating pressure, and

wherein the end plate comprises at least one notch having a thickness less than a thickness of an adjacent portion of the end plate.

17. The secondary battery of claim 16 , wherein the end plate is collapsible away from the inner cavity of the case at the at least one notch when the internal pressure in the case is greater than the reference operating pressure.