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. (c) 2005 Elsevier B.V All rights reserved.