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 (N_222pr⁺) 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 N_222pr⁺ enhance the ionic conductivity of N_222pr–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 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 N₂₂₂₄–DCA at a current density of 2.5 A g⁻¹.