Cap assembly and secondary battery including the same

1. A cap assembly comprising:

a cap-down, at least a portion of the cap-down configured to open when pressure is applied to the cap-down;

a vent plate comprising a first notch configured to open when pressure is applied to the vent plate, wherein the vent plate is entirely spaced from the cap-down;

a stepped insulator between the vent plate and the cap-down, the insulator being configured to be destroyed by being burned by gas, such that when the insulator burns a space forms between the cap-down and the vent plate for the gas to enter; and

a cap-up electrically connected to the vent plate,

wherein each of the cap-down and the vent plate has a stepped portion that is aligned with the stepped insulator,

wherein the cap-down comprises a peripheral opening configured to let gas enter the space between the cap-down and the vent plate, the peripheral opening being completely sealed by the stepped insulator, and a central opening in a center of the cap-down, and no other openings,

wherein the cap-down further comprises:

a dislocation disk configured to open when pressure is applied to the cap-down; and

a second notch around the dislocation disk, the second notch defining a region of the dislocation disk that opens when pressure is applied to the cap-down, a diameter of the second notch being smaller than a diameter of the first notch,

wherein the cap assembly comprises a sub-disk coupled to each of the cap-down and the vent plate and covering the central opening of the cap-down, the vent plate and the cap-down being connected to each other through the sub-disk, and

wherein the sub-disk, the cap-down, and the vent plate are sequentially arranged in a direction from the sub-disk toward the vent plate, such that an upper surface of the sub-disk contacts a lower surface of each of the cap-down and the vent plate.

2. The cap assembly of claim 1 , wherein the cap-down further comprises a support portion in the second notch and connecting the dislocation disk with another region of the cap-down.

3. The cap assembly of claim 1 , wherein a thickness of the second notch is smaller than a thickness of the dislocation disk.

4. The cap assembly of claim 1 ,

wherein the dislocation disk comprises a plurality of dislocation disks and the second notch comprises a plurality of second notches, the plurality of dislocation disks being spaced from one another, and each of the plurality of second notches being around a respective one of the plurality of dislocation disks.

5. The cap assembly of claim 4 , wherein each of the plurality of dislocation disks forms the same angle with the center of the cap-down.

6. The cap assembly of claim 4 , wherein each of the plurality of dislocation disks is the same distance away from the center of the cap-down.

7. The cap assembly of claim 1 , wherein the dislocation disk and the second notch are circles.

8. The cap assembly of claim 1 , wherein the cap-down comprises the dislocation disk in at least one region of the cap-down.

9. The cap assembly of claim 8 , wherein a thickness of the dislocation disk is smaller than a thickness of the region of the cap-down not comprising the dislocation disk.

10. The cap assembly of claim 8 , wherein the dislocation disk comprises a plurality of dislocation disks, and the plurality of dislocation disks are spaced from one another.

11. The cap assembly of claim 10 , wherein each of the plurality of dislocation disks forms the same angle with the center of the cap-down.

12. The cap assembly of claim 10 , wherein each of the plurality of dislocation disks is the same distance away from the center of the cap-down.

13. The cap assembly of claim 8 , wherein the dislocation disk is a circle.

14. The cap assembly of claim 1 , wherein an edge of the vent plate extends beyond an edge of the cap-up and is bent to cover at least a portion of an upper surface of the cap-up.

15. The cap assembly of claim 1 , wherein the insulator covers an edge of at least one of the cap-down, the vent plate, and the cap-up.

16. The cap assembly of claim 15 , further comprising a cover plate covering the insulator, the cover plate comprising a fluid hole.

17. The cap assembly of claim 16 , wherein an area of the fluid hole is 10 mm 2 or less.

18. The cap assembly of claim 1 , wherein the cap-down comprises:

a lower plate;

an upper plate spaced from the lower plate; and

a plurality of bridge portions connecting the upper plate and the lower plate, the plurality of bridge portions forming the stepped portion of the cap-down,

wherein spaces between adjacent bridge portions comprise the insulator.

19. The cap assembly of claim 1 , wherein

the first notch is configured to open when the gas pressure in the space between the vent plate and the cap-down increases to a first level; and

the dislocation disk of the cap-down is configured to open after the first notch, when the gas pressure in the space between the vent plate and the cap-down further increases to a second level.

20. A secondary battery comprising:

an electrode assembly;

a can accommodating the electrode assembly, the can comprising an opening; and

a cap assembly covering the opening of the can,

wherein the cap assembly comprises

a cap-down, at least a portion of the cap-down configured to open when internal pressure of the can increases;

a vent plate comprising a first notch configured to open when internal pressure of the can increases, wherein the vent plate is entirely spaced from the cap-down;

a stepped insulator between the vent plate and the cap-down, the insulator being configured to be destroyed by being burned by gas, such that when the insulator burns a space forms between the cap-down and the vent plate for the gas to enter; and

a cap-up electrically connected to the vent plate,

wherein each of the cap-down and the vent plate has a stepped portion that is aligned with the stepped insulator,

wherein the cap-down comprises a peripheral opening configured to let gas enter the space between the cap-down and the vent plate, the peripheral opening being completely sealed by the stepped insulator, and a central opening in a center of the cap-down, and no other openings,

wherein the cap-down further comprises:

a dislocation disk configured to open when pressure is applied to the cap-down; and

a second notch around the dislocation disk, the second notch defining a region of the dislocation disk that opens when pressure is applied to the cap-down, a diameter of the second notch being smaller than a diameter of the first notch,

wherein the cap assembly comprises a sub-disk coupled to each of the cap-down and the vent plate and covering the central opening of the cap-down, the vent plate and the cap-down being connected to each other through the sub-disk, and

wherein the sub-disk, the cap-down, and the vent plate are sequentially arranged in a direction from the sub-disk toward the vent plate, such that an upper surface of the sub-disk contacts a lower surface of each of the cap-down and the vent plate.

21. The secondary battery of claim 20 , wherein the cap-down further comprises a support portion in the second notch and connecting the dislocation disk with another region of the cap-down.

22. The secondary battery of claim 20 , wherein a thickness of the second notch is smaller than a thickness of the dislocation disk.

23. The secondary battery of claim 20 ,

wherein the dislocation disk comprises a plurality of dislocation disks and the second notch comprises a plurality of second notches, the plurality of dislocation disks being spaced from one another, and each of the plurality of second notches being around a respective one of the plurality of dislocation disks.

24. The secondary battery of claim 23 , wherein each of the plurality of dislocation disks forms the same angle with the center of the cap-down.

25. The secondary battery of claim 23 , wherein each of the plurality of dislocation disks is the same distance away from the center of the cap-down.

26. The secondary battery of claim 20 , wherein the dislocation disk and the second notch are circles.

27. The secondary battery of claim 20 , wherein at least one region of the cap-down comprises the dislocation disk, the dislocation disk configured to rupture when internal pressure of the can increases.

28. The secondary battery of claim 27 , wherein a thickness of the dislocation disk is smaller than a thickness of the region of the cap-down not comprising the dislocation disk.

29. The secondary battery of claim 27 , wherein the dislocation disk comprises a plurality of dislocation disks, and the plurality of dislocation disks are spaced from one another.

30. The secondary battery of claim 29 , wherein each of the plurality of dislocation disks forms the same angle with the center of the cap-down.

31. The secondary battery of claim 29 , wherein each of the plurality of dislocation disks is the same distance away from the center of the cap-down.

32. The secondary battery of claim 27 , wherein the dislocation disk is a circle.

33. The secondary battery of claim 20 , wherein an edge of the vent plate extends beyond an edge of the cap-up is bent to cover at least a portion of an upper surface of the cap-up.

34. The secondary battery of claim 20 , wherein the insulator covers an edge of at least one of the cap-down, the vent plate, and the cap-up.

35. The secondary battery of claim 34 , further comprising a cover plate covering the insulator, the cover plate comprising a fluid hole.

36. The secondary battery of claim 35 , wherein an area of the fluid hole is 10 mm 2 or less.

37. The secondary battery of claim 20 , wherein the cap-down comprises:

a lower plate;

an upper plate spaced from the lower plate; and

a plurality of bridge portions connecting the upper plate and the lower plate, the plurality of bridge portions forming the stepped portion of the cap-down,

wherein spaces between adjacent bridge portions comprise the insulator.

38. The secondary battery of claim 20 , wherein

the first notch is configured to open when the gas pressure in the space between the vent plate and the cap-down increases to a first level; and

the dislocation disk of the cap-down is configured to open after the first notch, when the gas pressure in the space between the vent plate and the cap-down further increases to a second level.