Secondary battery

A secondary battery for reinforcing rigidity and having an easy venting structure. The secondary battery includes an electrode assembly for charging or discharging a power source; and a case for accommodating the electrode assembly and being sealed, wherein the case comprises: a first cover and a second cover, wherein the electrode assembly is accommodated in a space formed between the first cover and the second cover, wherein the first cover and the second cover are formed of different materials, and wherein the second cover