NOVELTY - A secondary battery (10) comprises cathode (11), anode (12) and electrolyte layer including nonaqueous electrolytic solution and polymer compound. The polymer compound includes graft copolymer containing block copolymer as main chain, and homopolymer and/or copolymer as side chain. The block copolymer includes vinylidene fluoride and hexafluoropropylene as polymerization unit. The homopolymer includes vinylidene fluoride, hexafluoropropylene, monomethyl maleate, trifluoroethylene, chlorotrifluoroethylene, acrylic acid and/or methacrylic acid as polymerization unit.    USE - Secondary battery e.g. lithium ion secondary battery is used for battery pack, electric vehicle, electric power storage system and electronic apparatus (all claimed). Uses include but are not limited to electric automobile, home electric power server, electric drill, video camcorder, digital still camera, mobile phone, notebook personal computer, cordless phone, headphone stereo, portable radio, portable television, portable information terminal, etc.    ADVANTAGE - The secondary battery has improved flexibility, mechanical strength, ion conductivity and discharge capacity, and suppressed skewness and swollenness.    DETAILED DESCRIPTION - A secondary battery comprises cathode, anode and electrolyte layer including nonaqueous electrolytic solution and polymer compound. The polymer compound includes graft copolymer containing block copolymer as main chain, and homopolymer and/or copolymer as side chain. The block copolymer includes vinylidene fluoride and hexafluoropropylene as polymerization unit. The homopolymer includes vinylidene fluoride, hexafluoropropylene, monomethyl maleate, trifluoroethylene, chlorotrifluoroethylene, acrylic acid and/or methacrylic acid as polymerization unit. The copolymer includes vinylidene fluoride, hexafluoropropylene, monomethyl maleate, trifluoroethylene, chlorotrifluoroethylene, acrylic acid and/or methacrylic acid as polymerization unit.    DESCRIPTION OF DRAWING(S) - The drawing shows a perspective view of the secondary battery.    Secondary battery (10)    Cathode (11)    Anode (12)    Package components (20)    Close attachment films (21)