Physicochemical characterizations of novel dicyanamide-based ionic liquids applied as electrolytes for supercapacitors

Abstract

Novel ionic liquids (ILs), containing a dicyanamide anion (DCA−), are synthesized and applied as suitable electrolytes for electrochemical double layer capacitors (EDLCs). The prepared ILs are either composed of triethyl-propargylammonium (N222pr+) or triethyl-butylammonium (N2224+) cations paired with the DCA− anion. The structure of the cation influences its electrostatic interaction with the DCA− anion and highly impacts the physical and electrochemical properties of the as-prepared ILs. The geometry and the length of the alkyl chain of the propargyl group in N222pr+ enhance the ionic conductivity of N222pr-DCA (11.68 mS cm−1) when compared to N2224-DCA (5.26 mS cm−1) at 298 K. It is demonstrated that the Vogel-Tammann-Fulcher model governs the variations of the transport properties investigated over the temperature range of 298-353 K. A maximum potential window of 3.29 V is obtained when N222pr-DCA is used as electrolyte in a graphene based symmetric EDLC system. Cyclic voltammetry and galvanostatic measurements confirm that both electrolytes exhibit an ideal capacitive behavior. The highest specific energy of 55 W h kg−1 is exhibited in the presence of N2224-DCA at a current density of 2.5 A g−1.