Molecular Dynamics Study On the Capacitive Performance of Double-Cationic Ionic Liquid Electrolytes

Single-cationic ionic liquids have been extensively studied due to their versatility and outstanding properties. However, the study on double-cationic ionic liquids is rarely reported. In this work, the capacitive performance of double-cationic ionic liquids with different chain lengths was investigated using classical molecular dynamics simulation (MD) for comparison with the single-cationic ionic liquids. Different electrical double layer (EDL) structures formed by double- and single-cationic ionic liquids near an onion-like carbon electrode were observed; the orientation of the cation at the interface was analyzed. The number of the cumulative ions was estimated for both double- and single-cationic ionic liquids. The capacitive performance was evaluated by computing the differential capacitance as a function of electrical potential applied. The effects of the linkage chain length as well as temperature on the capacitance-electrical potential curve were studied. This work rationalizes the different capacitive performances of double- and single-cationic ionic liquids as electrolytes in onion-like carbon-based supercapacitors.