Imidazolium-based ionic liquid is one of attractive candidates for advanced lithium battery electrolyte. However, its cathodic stability is not sufficient for the reversible charge–discharge of negative electrodes. The authors previously proposed a quaternary ammonium-based ionic liquid containing a cyano group (cyano-QA) as a film-forming electrolyte on the negative electrode surface. In the present study, several cyano-QA ionic liquids have been prepared and their electrolyte properties have been estimated. Some ionic liquids based on cyano-containing quaternary ammonium cation provided reversible lithium deposition/dissolution couple when they were used as ‘co-solvent’ of electrolyte with the co-existence of EMITFSI.