Disclosed is a secondary battery having high capacity and excellent charge/discharge cycle characteristics, which is obtained by employing a positive electrode that is obtained by covering the surface of a positive electrode material with a polymer solid electrolyte composition using a polyether copolymer and an electrolyte salt compound that is a combination of lithium bisoxalate borate and another lithium salt compound. With respect to the positive electrode, the polymer solid electrolyte and/or the positive electrode material contains a compound that has a phenol structure wherein both of two ortho positions are substituted by a tert-butyl group.