Sweet Ionic Liquids as High-Temperature and High-Voltage Supercapacitor Electrolytes

Journal article, 2024

We here present four new fluorine-free ionic liquids (ILs) based on the non-nutritive sweetener saccharinate (Sac) anion coupled with pyrrolidinium, imidazolium, and phosphonium cations and their thermal, physicochemical, and electrochemical properties. The pyrrolidinium cation-based material is a solid at room temperature, whereas the other three materials are room-temperature ionic liquids (RTILs). By infrared spectroscopy, we find the ionic interactions to be controlled by the distinct conformers of the Sac anion, which in turn are cation-dependent. (P4444)(Sac) shows the lowest glass transition temperature, (Tg), the highest thermal stability and ionic conductivity, and the widest electrochemical stability window, up to 6 V. As an electrolyte in a symmetric supercapacitor, it enabled a specific capacitance of 204 F g-1 at 1 mV s-1, an energy density of 53 Wh kg-1 and a power density of 300 W kg-1 at a current density of 0.1 A g-1, and the capacitor retained 81% of its initial capacitance after 10,000 cycles at 60 °C. Altogether, these fluorine-free electrolytes have electrochemical properties promising for application in supercapacitors operating at elevated temperatures over a wide voltage range.