Use of a composition consisting of: (a) a silyl group-containing compound (A), wherein at least one hydrogen atom of an acid selected from the group consisting of a protonic acid having phosphorus atom and/or boron atom, a sulfonic acid, and a carboxylic acid is substituted with a silyl group represented by following general formula (Al): wherein, R a1 , R a2 , and R a3 each independently represent a hydrocarbon group having 1 to 20 carbon atoms, which may be substituted; and (b) at least one basic compound (B) selected from the group consisting of Lewis base and a compound represented by general formula Q + Y - wherein, Q + represents a quaternary ammonium group, a quaternary phosphonium group, an alkali metal, or an alkaline earth metal, and Y - represents an alkoxy group, or an aryloxy group, and at least one silicon compound (C) represented by following general formula (C): wherein R c1 , R c2 , and R c3 each independently represent a hydrocarbon group having 1 to 20 carbon atoms, which may be substituted, or an alkoxy group having 1 to 20 carbon atoms, which may be substituted, and X 1 is a group represented by general formula OR 1 , wherein R 1 represents a hydrogen atom, a hydrocarbon group having 1 to 20 carbon atoms, which may be substituted, a silyl group having 1 to 20 carbon atoms, SO 2 CH 3 , or SO 2 CF 3 , or a halogen atom; as an additive for an electrolytic solution, wherein the composition consists of 0.1 % by mass or more and 10 % by mass or less of the basic compound (B) and the silicon compound (C), relative to 100 % by mass of the silyl group-containing compound (A). (a) a silyl group-containing compound (A), wherein at least one hydrogen atom of an acid selected from the group consisting of a protonic acid having phosphorus atom and/or boron atom, a sulfonic acid, and a carboxylic acid is substituted with a silyl group represented by following general formula (Al): wherein, R a1 , R a2 , and R a3 each independently represent a hydrocarbon group having 1 to 20 carbon atoms, which may be substituted; and (b) at least one basic compound (B) selected from the group consisting of Lewis base and a compound represented by general formula Q + Y - wherein, Q + represents a quaternary ammonium group, a quaternary phosphonium group, an alkali metal, or an alkaline earth metal, and Y - represents an alkoxy group, or an aryloxy group, and at least one silicon compound (C) represented by following general formula (C): wherein R c1 , R c2 , and R c3 each independently represent a hydrocarbon group having 1 to 20 carbon atoms, which may be substituted, or an alkoxy group having 1 to 20 carbon atoms, which may be substituted, and X 1 is a group represented by general formula OR 1 , wherein R 1 represents a hydrogen atom, a hydrocarbon group having 1 to 20 carbon atoms, which may be substituted, a silyl group having 1 to 20 carbon atoms, SO 2 CH 3 , or SO 2 CF 3 , or a halogen atom; as an additive for an electrolytic solution, wherein the composition consists of 0.1 % by mass or more and 10 % by mass or less of the basic compound (B) and the silicon compound (C), relative to 100 % by mass of the silyl group-containing compound (A). wherein R c1 , R c2 , and R c3 each independently represent a hydrocarbon group having 1 to 20 carbon atoms, which may be substituted, or an alkoxy group having 1 to 20 carbon atoms, which may be substituted, and X 1 is a group represented by general formula OR 1 , wherein R 1 represents a hydrogen atom, a hydrocarbon group having 1 to 20 carbon atoms, which may be substituted, a silyl group having 1 to 20 carbon atoms, SO 2 CH 3 , or SO 2 CF 3 , or a halogen atom; as an additive for an electrolytic solution, wherein the composition consists of 0.1 % by mass or more and 10 % by mass or less of the basic compound (B) and the silicon compound (C), relative to 100 % by mass of the silyl group-containing compound (A). <EOS>