Azepanium-based ionic liquids as green electrolytes for high voltage supercapacitors

Abstract This work provides a first-time-study of Azepanium-based ionic liquids (ILs) as electrolyte components for electrochemical double layer capacitors (EDLCs). Herein, two Azepanium-based ILs, namely N-methyl, N-butyl-azepanium bis(trifluoromethanesulfonyl)imide (Azp 14 TFSI) and N-methyl, N-hexyl-azepanium bis(trifluoromethanesulfonyl)imide (Azp 16 TFSI) were compared with the established IL N-butyl, N-methylpyrrolidinium bis(trifluoromethanesulfonyl)imide (Pyr 14 TFSI) in terms of viscosity, conductivity, thermal stability and electrochemical behavior in EDLC systems. The ILs' operative potentials were found to be comparable, leading to operative voltages up to 3.5 V without significant electrolyte degradation.