Ionic Liquids for Supercapacitor Applications

Supercapacitors are electrochemical energy storage devices in which the charge is accumulated through the adsorption of ions from an electrolyte on the surface of the electrode. Because of their large ionic concentrations, ionic liquids have widely been investigated for such applications. The main properties that have to be optimized are the electrochemical window, the electrical conductivity, and the interfacial capacitances. Ionic liquids allow a significant improvement of the former, but they suffer from their high viscosity. In this review, I will discuss the advantages and the inconvenience of using ionic liquids in supercapacitors. Some innovative approaches using mixtures of ionic liquids or redox-active ions will also be critically addressed.