SECONDARY BATTERY

A secondary battery, including an electrode assembly, a case accommodating the electrode assembly, and a cap plate covering an open portion of the case, wherein one of the case and the cap plate includes a vent part on an outer surface thereof, the vent part including a notch, the notch includes a first notch and a second notch, the first notch extends from a central portion of the vent part in a first direction, the second notch includes a first area extending from the central portion in the first direction, and a second area extending from the first area in a direction different from the first direction, and the first notch is inside the first area.