Cap assembly having improved stability and cylindrical secondary battery including the same

1. A cap assembly for a cylindrical secondary battery, which is mounted on a top end portion of the cylindrical secondary battery having a structure in which an electrode assembly is placed in a cylindrical can, the cap assembly comprising:

a safety vent having a predetermined notch configured to be ruptured by high pressure gas generated in the battery;

a current interrupt device coupled to a lower end of the safety vent and blocking a current when an internal pressure of the battery rises; and

a gasket for the current interrupt device surrounding and directly contacting an outer circumferential surface of the current interrupt device,

wherein the gasket for the current interrupt device comprises a composite of a polymer resin and a ceramic material, the polymer resin having a melting point of 250° C. or more and a heat deflection temperature of 200° C. or more, the polymer resin comprising at least one polymer resin selected from the group consisting of a perfluoroalkoxy resin and a thermoplastic polyester elastomer (TPEE) having a weight-average molecular weight of 10,000 to 500,000, and

wherein the gasket for the current interrupt device has an opening at a center thereof such that the gasket for the current interrupt device does not block through holes of the current interrupt device.

2. The cap assembly for a cylindrical secondary battery of claim 1 , wherein the perfluoroalkoxy resin comprises a copolymer of tetrafluoroethylene and perfluoroalkyl vinyl ether.

3. The cap assembly for a cylindrical secondary battery of claim 2 , wherein the copolymer of tetrafluoroethylene and perfluoroalkyl vinyl ether comprises at least one selected from the group consisting of poly(tetrafluoroethylene-co-perfluoro(methylvinyl ether)), poly(tetrafluoroethylene-co-perfluoro(ethylvinyl ether)), and poly(tetrafluoroethylene-co-perfluoro(propylvinyl ether)).

4. The cap assembly for a cylindrical secondary battery of claim 1 , wherein the cap assembly has a stack structure in which the current interrupt device, the gasket for the current interrupt device, the safety vent, and a top cap having at least one gas outlet formed therein are stacked, and

a crimping gasket is further mounted on an outer circumferential surface of the stack structure.

5. The cap assembly for a cylindrical secondary battery of claim 4 , wherein the safety vent, the current interrupt device, and the gasket for the current interrupt device are disposed to communicate with each other in a straight line.

6. The cap assembly for a cylindrical secondary battery of claim 1 , wherein the safety vent, the current interrupt device, and the gasket for the current interrupt device are disposed to communicate with each other in a straight line.

7. The cap assembly for a cylindrical secondary battery of claim 1 , wherein the ceramic material includes at least one selected from the group consisting of: silicon (Si), aluminum (Al), zirconium (Zr), titanium (Ti), and insulating oxides, nitrides, hydroxides, alkoxides, and ketones of each of such elements.

8. The cap assembly for a cylindrical secondary battery of claim 7 , wherein the ceramic material includes at least one selected from the group consisting of: silica (SiO 2 ), alumina (Al 2 O 3 ), zirconium oxide (ZrO 2 ), and titanium oxide (TiO 2 ).

9. The cap assembly for a cylindrical secondary battery of claim 1 , wherein the ceramic material includes a material in which a thermal expansion coefficient at a temperature of 200° C. is 0.2% or less and in which a thermal expansion coefficient at a temperature of 400° C. in a range of 0.1% to 0.4%.

10. The cap assembly for a cylindrical secondary battery of claim 1 , wherein the polymer resin has a weight ratio to the ceramic material in the composite that is greater than or equal to 80:20.

11. A cylindrical secondary battery comprising:

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

a battery can having an opening at one side thereof and accommodating the electrode assembly and an electrolyte through the opening; and

the cap assembly of claim 1 sealing the opening of the battery can.