SECONDARY BATTERY

According to the present disclosure, a secondary battery in which a gas discharge valve has excellent operational stability is provided. A battery case of the secondary battery disclosed herein includes a flat rectangular sealing plate, and a gas discharge valve provided in the sealing plate. In addition, in the secondary battery disclosed herein, a thickness T1 of the sealing plate, a length L1 of a short side of the sealing plate, a length L2 of a long side of the sealing plate, and a length L3 of the gas discharge valve in a short side direction of the sealing plate satisfy expression (1) represented by T1/L1≤0.1, expression (2) represented by L2/L1≥6, and expression (3) represented by L3/L1≥0.4. As a result, when an internal pressure of the case rises to a desired pressure, the sealing plate is easily bent and deformed, so that the gas discharge valve can be stably operated by the bending deformation.