An electrolyte solution comprising: (i) a solvent containing at least one fluorinated acyclic carbonate selected from compounds of the formulae CF 3 -O-C(=O)-O-R 11 wherein R 11 is optionally fluorinated C 1-2 -alkyl, and CH 2 F-O-C(=O)-O-R 12 wherein R 12 is C 1-2 -alkyl; and (ii) a compound of the formula, wherein A a+ is a metal ion, a hydrogen ion, or an onium ion; a is an integer of 1-3; b is an integer of 1-3; p is b/a; n 23 is an integer of 1-4; n 21 is an integer of 0-8; n 22 is 0 or 1; Z 21 is P or B; X 21 is O, S, or C 1-10 -alkylene or C 6-20 -arylene each optionally halogenated and each optionally containing a substituent and/or a hetero atom in its structure, and multiple X 21 may optionally bind to each other; L 21 is halogen, cyano, -Z 23 Y 23, or C 1-10 -alkyl or C 6-20 -aryl each optionally halogenated and each optionally containing a substituent and/or a hetero atom in its structure, and multiple L 21 may optionally bind to each other to form a ring; Y 21, Y 22, and Z 23 each individually are O, S, NY 24, or an optionally fluorinated hydrocarbon group; Y 23 and Y 24 each individually are H, F, or C 1-10 -alkyl or C 6-20 -aryl each optionally halogenated and each optionally containing a substituent and/or a hetero atom in its structure, and multiple Y 23 or multiple Y 24 may optionally bind to each other to form a ring. (i) a solvent containing at least one fluorinated acyclic carbonate selected from compounds of the formulae CF 3 -O-C(=O)-O-R 11 wherein R 11 is optionally fluorinated C 1-2 -alkyl, and CH 2 F-O-C(=O)-O-R 12 wherein R 12 is C 1-2 -alkyl; and (ii) a compound of the formula, wherein A a+ is a metal ion, a hydrogen ion, or an onium ion; a is an integer of 1-3; b is an integer of 1-3; p is b/a; n 23 is an integer of 1-4; n 21 is an integer of 0-8; n 22 is 0 or 1; Z 21 is P or B; X 21 is O, S, or C 1-10 -alkylene or C 6-20 -arylene each optionally halogenated and each optionally containing a substituent and/or a hetero atom in its structure, and multiple X 21 may optionally bind to each other; L 21 is halogen, cyano, -Z 23 Y 23, or C 1-10 -alkyl or C 6-20 -aryl each optionally halogenated and each optionally containing a substituent and/or a hetero atom in its structure, and multiple L 21 may optionally bind to each other to form a ring; Y 21, Y 22, and Z 23 each individually are O, S, NY 24, or an optionally fluorinated hydrocarbon group; Y 23 and Y 24 each individually are H, F, or C 1-10 -alkyl or C 6-20 -aryl each optionally halogenated and each optionally containing a substituent and/or a hetero atom in its structure, and multiple Y 23 or multiple Y 24 may optionally bind to each other to form a ring. A a+ is a metal ion, a hydrogen ion, or an onium ion; a is an integer of 1-3; b is an integer of 1-3; p is b/a; n 23 is an integer of 1-4; n 21 is an integer of 0-8; n 22 is 0 or 1; Z 21 is P or B; X 21 is O, S, or C 1-10 -alkylene or C 6-20 -arylene each optionally halogenated and each optionally containing a substituent and/or a hetero atom in its structure, and multiple X 21 may optionally bind to each other; L 21 is halogen, cyano, -Z 23 Y 23, or C 1-10 -alkyl or C 6-20 -aryl each optionally halogenated and each optionally containing a substituent and/or a hetero atom in its structure, and multiple L 21 may optionally bind to each other to form a ring; Y 21, Y 22, and Z 23 each individually are O, S, NY 24, or an optionally fluorinated hydrocarbon group; Y 23 and Y 24 each individually are H, F, or C 1-10 -alkyl or C 6-20 -aryl each optionally halogenated and each optionally containing a substituent and/or a hetero atom in its structure, and multiple Y 23 or multiple Y 24 may optionally bind to each other to form a ring.