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

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 (N(222pr)(+)) or triethyl-butylammonium (N(2224)(+)) 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 N(222pr)(+) enhance the ionic conductivity of N(222pr)–DCA (11.68 mS cm(−1)) when compared to N(2224)–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 N(222pr)–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 N(2224)–DCA at a current density of 2.5 A g(−1).