Room Temperature Ionic Liquid-based Electrolytes as an Alternative to Carbonate-based Electrolytes

The issue of the safety of Li-ion batteries is becoming more critical with the increase in their size for applications in large energy storage devices, such as hybrid electric vehicles (HEVs), and energy storage systems (ESSs) for smart grids. The thermal runaway of Li-ion batteries is considered to be caused by their flammable components, such as the volatile carbonate solvents of electrolytes. Room temperature ionic liquids (RTILs) have recently received much attention because of their characteristics of non-flammability and non-volatility. In addition, RTILs show high ionic conductivity and a wide electrochemical stability window. Therefore, RTIL-based electrolytes are considered one of the most promising candidates to improve the safety of Na-ion, as well as Li-ion batteries; indeed, RTIL-based electrolytes have shown excellent improvements in terms of thermal stability and electrochemical performance. This review provides a comprehensive overview of selected RTIL materials, including their physicochemical and electrochemical properties. Moreover, we discuss the failure mechanisms of certain RTIL-based electrolytes with various electrodes to suggest alternative strategies for improving their electrochemical performance.