SECONDARY BATTERY

A secondary battery according to an embodiment of the present disclosure may include an electrode assembly; an outer packaging formed from a sheet such that the outer packaging has an internal space for accommodating the electrode assembly and an outer packaging opening configured to communicate the internal space with an outside; and a cap configured to cover the outer packaging opening. The cap may include a covering portion coupled to the outer packaging; and a terminal portion disposed to cover the outer packaging opening together with the covering portion, wherein the terminal portion is exposed to each of an outside and an inside of the covering portion, and a part of the terminal portion exposed to the inside of the covering portion is electrically connected to the electrode assembly. The terminal portion may include a material having a lower water vapor transmission rate than a material included in the covering portion. An area in which the terminal portion covers the outer packaging opening may be equal to or greater than 90% of an area in which the cap covers the outer packaging opening.