A secondary battery includes: a cathode; an anode; an electrolytic solution; and an interlayer provided between the cathode and the anode and including one or more of a polyphosphate salt, a melamine salt, a melamine derivative represented by Formula (1), a metal hydroxide, and a metal hydrate, the interlayer partially entering into the cathode, the anode, or both. (R1 to R6 are each one of a hydrogen group (—H), a monovalent hydrocarbon group, a monovalent hydroxyl-group-containing hydrocarbon group, a monovalent group obtained by bonding one or more monovalent hydrocarbon groups and one or more oxygen bonds (—O—), a monovalent group obtained by bonding one or more monovalent hydroxyl-group-containing hydrocarbon groups and one or more oxygen bonds, and a monovalent group obtained by bonding two or more thereof.)