Disclosed herein is a cap assembly loaded on an open upper end of a cylindrical container of a battery configured to have a structure in which an electrode assembly (jelly roll) of a cathode/separator/anode structure is mounted in the cylindrical container, the cap assembly including a safety vent connected to a current interruptive device (CID) for safety, a protruding top cap connected to the safety vent along an outer circumference thereof, and a gasket mounted at an outer circumference of the top cap, wherein a cathode tab is attached to a cathode active material-uncoated portion of the cathode by welding and the gasket is provided with at least one groove depressed upward from an outer circumference of a lower end of the gasket for easy welding between the CID and the cathode tab at the time of manufacturing the battery.