SECONDARY BATTERY

There is proposed a secondary battery with a large capacity that excels in safety by causing a safety valve to reliably operate to immediately discharge gas produced in the battery in a limited battery space for the purpose of increasing the capacity and the energy density of the battery. The present invention provides a secondary battery with a high battery capacity of 100 Ah or more. A cleavage valve 10 is formed with an opening pressure of 0.2 to 1.5 MPa. In addition, the cleavage valve 10 is configured such that the region provided with the cleavage valve 10 (safety valve region) occupies an area of 0.025 to 0.066 cmper 1 Ah of the battery capacity.