CAP ASSEMBLY, CAP ASSEMBLY MANUFACTURING METHOD AND SECONDARY BATTERY INCLUDING CAP ASSEMBLY

A cap assembly includes a vent deformable in response to a change in pressure, a cap-up on the vent and connected to an external terminal, the vent surrounding a portion of an upper surface and a side surface of an outer edge of the cap-up, a cap-down that is below the vent, and a plurality of welding marks at a plurality of points on a portion of the vent arranged on the portion of the upper surface of the outer edge of the cap-up, wherein each of the plurality of welding marks intersects at least three times with an imaginary straight line in a region where the upper surface of the outer edge of the cap-up and the vent come into contact, and wherein the imaginary straight line is horizontal with respect to a boundary surface between the upper surface of the outer edge of the cap-up and the vent.