Ionic liquids for safe, high-energy supercapacitors for transportation

Safety is the main concern for application of electrochemical energy storage/conversion systems in transportation and this is where the ionic liquids (ILs) for their low vapour pressure and high thermal stability come in. The use of ILs in supercapacitors which are systems of high power even permits high cell voltage which is the most powerful strategy for supercapacitor energy increase. Cell configurations of IL-based supercapacitors, with capacitive and pseudocapacitive electrode materials, that allow to reach the high cell voltages permitted by the wide electrochemical stability window of IL electrolytes are described. The performance over several thousand cycles above room temperature of hybrid and asymmetric supercapacitors with pyrrolidinium-based ILs and properly designed electrode materials are given in terms of maximum reached cell voltage, specific capacitance and specific energy.