Alkyl carbonates are often employed as solvents for the study of energy-storage devices (ESD), such as lithium secondary batteries (LSB) and electric double-layer capacitors. Some of these solvents, including propylene carbonate (PC) and diethyl carbonate, have already been put to practical use in modern electronics technology, such as in mobile phones and laptop computers. However, all of these organic solvents have potential safety drawbacks related to their flammable and volatile nature that can lead to explosions and/or fire accidents. Furthermore, lithium anodes with a high theoretical discharge capacity (3860 mAh g Γ1 ) cannot be utilized in such solvents owing to dendritic lithium deposition during the charging cycle. However, room-temperature ionic liquids (RTILs) [1][2][3] and RTIL-like solvents [3][4][5][6] are expected to be a new class of solvents for next-generation rechargeable highenergy-density batteries because RTILs possess unique saltlike properties. Some of these properties, such as high electrochemical stability, negligible vapor pressure, and resistance to combustion, are highly advantageous in electrochemical applications. [1-3, 7, 8] Thus, we anticipated that chemically combining an appropriate carbonate and organic salt may remove some of the undesirable properties of alkyl carbonates and provide uniquely functionalized RTILs for ESDs, and particularly LSB systems (Figure 1).