Onium salt, electrolyte for nonaqueous cell containing the novel onium salt for nonaqueous cell and method for optimizing negative electrode using electrolyte containing onium salt

An onium salt illustrated by the general formula (V);

• wherein R1 is selected from the group consisting of a perfluoroalkyl group having 1 to 6 carbon atoms, a perfluoroalkyl group and a perfluoroaralkyl group having 7 to 9 carbon atoms, R2 is selected from the group consisting of a formyl group, a acetyl group, a propionyl group, a butyryl group, a isobutyryl group, a valeryl group, a isovaleryl group, a pivaloyl group, a lauroyl group, a trifluoroacetyl group, a 2,2-difuluoropropionyl group, a perfuluoropropionyl group, a perfluorobutyryl group, a perfluoroisobutyryl group, a perfuluorovaleryl group, a methoxycarbonyl group, a ethoxycarbonyl group, a tert-butoxycarbonyl group, a trifuluoromethoxycabonyl group, a perfluoroethylcarbonyl group, a perfluoro-tert-butoxycarbonyl group, a methanesulfonyl group, a ethanesulfonyl group, a propanesulfonyl group, a tert-butanesulfonyl group, a trifluoromethanesulfonyl group, a pentafluoroethanesulfonyl group, a heptafluoropropanesulfonyl group, a nonafluorobutanesulfonyl group, a heptafluoroisopropanesulfonyl group, a nonafluoroisobutanesulfonyl group, a 2,2,2-trifluoroethanesulfonyl group, a 1,1-difuluoroethanesulfonyl group, a pentafuluorobenzenesulfonyl and a 2,4,6-trifuluorobenzenesulfonyl group, R4 is a hydrogen atom, and R3 and R5 are, independently, selected from the group consisting of a methyl group, a ethyl group, a propyl group, a isopropyl group and a tert-butyl group.