SECONDARY BATTERY

PROBLEM TO BE SOLVED: To prevent plating layers provided on inner and outer surfaces of a battery container of a secondary battery from being exfoliated at cleavage grooves.SOLUTION: The secondary battery comprises: a power generation unit 20; and a battery can 2 in which the power generation unit 20 is housed. The battery can 2 has a cleavage groove 210 formed in its bottom 2a. The cleavage groove 210 has an inner groove 211 and an outer groove 212, which are provided for forming thinner portions 215 on inner and outer surface sides of the battery can. The inner and outer grooves 211 and 212 each have a smoothly curved face; the thickness of the bottom 2a of the battery can 2 gradually reduces toward the deepest point of the curve that the cross section of each groove forms. The battery can 2 has plating layers formed on the whole inner and outer surfaces including surfaces of the inner and outer grooves 211 and 212.