Novel electrolyte materials, room temperature ionic liquids (RTILs) were applied to the Li battery system and their characteristics in Li-metal batteries are discussed, partly reviewing authors work in the past. Quaternary ammonium (QA) cation-imide RTIL was focused on because of the excellent stability in cathodic environment of Li. Li/LiCoO2 cell performance and Li cycling efficiency using the selected QA-imide RTIL was almost satisfactory. In addition, thermal stability of selected QA-imide RTIL with the charged positive electrode and Li was the advantage for Li battery. On the other hand, further improvement in the conducting properties is required with balanced approach for both electrochemical stability and thermal stability in order to use the RTIL electrolyte practically in batteries.