Cylindrical secondary battery

A cylindrical secondary battery comprising:

• a cylindrical can having a circular bottom portion, a side portion extending from the bottom portion, a beading part concavely formed inwardly at one end of the side portion, and a crimping part formed by bending a distal end of the side portion;
• an electrode assembly in the can;
• and
• a cap assembly sealing the can, the cap assembly comprising:
• a gasket for insulation from the can, an upper portion of the gasket in a direction away from the electrode assembly having a smaller thickness than a lower portion of the gasket;
• a cap-up between the crimping part and the beading part;
• and
• a safety vent below the cap-up,
• wherein the gasket has an inclined surface that is chamfered on an inner circumferential surface thereof, the inclined surface beginning at an edge of the cap-up, and
• wherein a lower surface of an edge of the safety vent is in contact with an upper surface of the cap-up.