There is disclosed a cross-linked polymer solid electrolyte and a method of manufacturing the same. A crosslinking agent is added to a block-graft copolymer composed of a polymer block chain A represented by formula I and a polymer block chain B represented by formula II; a high energy ray is irradiated to the block-graft polymer in order to crosslink the entire system; and an nonaqueous electrolytic solution is added to the block-graft polymer. There is also disclosed a composite solid electrolyte for use in a solid electrochemical element. The composite solid electrolyte includes an electrically insulating material, an alkali metal salt, a block-graft copolymer composed of a polymer block chain A represented by formula I and a polymer block chain B represented by formula II, and an aprotic organic solvent. ##STR1##
展开▼