Investigation of the Electrochemical Behavior and Ion Dynamics in a Protic Ionic Liquid and Pre-Intercalated MXene Supercapacitor

The efficiency of energy-storing devices depends on the fundamental properties of the electrodes and electrolytes. To achieve high power and energy densities in supercapacitors, it is important to use porous electrodes and electrolytes with high operational voltage windows. Aprotic ionic liquids have a large voltage window but are ineffective at stabilizing ions and forming strong solvation shells. On the other hand, protic ionic liquids, which have labile protons and considerable voltage windows, have shown better electrochemical performance than aprotic ionic liquids. In this study, we examined the electrochemical performance of a pre-intercalated Ti₃C₂T_x MXene electrode and a protic ionic liquid formed by combining the ionic liquid 1-butyl imidazole (BuIM) with the Bis(trifluoromethanesulfonyl)imide (HTNf2) salt system. We found that the highest capacitance was achieved at a salt-to-an ionic liquid composition ratio of 0.2:0.8. We will discuss the relationship between ion dynamics and electrochemical behaviors based on concentrations obtained through electrochemical and quasi-elastic neutron scattering measurements.