Secondary battery

1. A secondary battery, comprising;

an electrode assembly;

a can accommodating the electrode assembly;

a cap plate coupled to the can;

an electrolyte injection unit including an injection hole penetrating the cap plate and an injection ring protruding from the injection hole; and

a stopper to seal the electrolyte injection unit,

wherein the stopper has a truncated conical shape in which a diameter of an upper end is greater than a diameter of a lower end,

wherein the stopper is coupled to the injection ring by pressure and the injection ring is deformed to an angle corresponding to sides of the stopper, and

wherein the injection ring has a funnel shape in which a diameter of an upper end is greater than a diameter of a lower end.

2. The secondary battery as claimed in claim 1 , wherein:

the injection ring includes an inner circumferential surface and an outer circumferential surface,

the cap plate includes a top surface and a bottom surface, and

a thickness of the injection ring between the inner circumferential surface and the outer circumferential surface is less than a thickness of the cap plate between the top surface and the bottom surface.

3. The secondary battery as claimed in claim 1 , wherein the injection ring is integrally formed with the cap plate.

4. The secondary battery as claimed in claim 3 , wherein the injection ring has an upper end, the upper end being disposed higher than a top surface of the cap plate.

5. The secondary battery as claimed in claim 3 , wherein:

the cap plate includes an external groove disposed at an outer circumferential surface of the injection ring, the injection ring being disposed in the external groove, and

the injection ring has an upper end laying in the same plane as or lower than a top surface of the cap plate.

6. The secondary battery as claimed in claim 5 , wherein:

the cap plate includes top and bottom surfaces,

the injection ring includes an inner circumferential surface, and

the external groove is defined by the outer circumferential surface of the injection ring, a first surface lower than the top surface of the cap plate, and a second surface connecting the first surface to the top surface of the cap plate.

7. The secondary battery as claimed in claim 6 , wherein a thickness of the injection ring between the inner circumferential surface and the outer circumferential surface is less than a thickness of a portion of the cap plate between the first surface and the bottom surface.

8. The secondary battery as claimed in claim 1 , wherein the injection ring is coupled to the cap plate.

9. The secondary battery as claimed in claim 8 , wherein the injection ring has an upper end, the upper end being disposed higher than a top surface of the cap plate.

10. The secondary battery as claimed in claim 8 , wherein:

the cap plate includes an external groove disposed at an outer circumferential surface of the injection ring, the injection ring being disposed in the external groove, and

the injection ring has an upper end laying in the same plane as or lower than a top surface of the cap plate.

11. The secondary battery as claimed in claim 10 , wherein:

the cap plate includes top and bottom surfaces;

the injection ring includes an inner circumferential surface; and

the external groove is defined by the outer circumferential surface of the injection ring, a first surface lower than the top surface of the cap plate, and a second surface connecting the first surface to the top surface of the cap plate.

12. The secondary battery as claimed in claim 11 , wherein a thickness of the injection ring between the inner circumferential surface and the outer circumferential surface is less than a thickness of a portion of the cap plate between the first surface and the bottom surface.

13. The secondary battery as claimed in claim 1 , wherein the injection ring is welded to the stopper.