Insight into the Effect of Cationsin Ionic Liquidelectrolytes on Charge Storage Capacity of High-Performance Supercapacitors of N-Doped Graphene Aerogels

Abstract

Even though room temperature ionic liquids (RTILs) have been widely used as electrolytes in electrochemical applications including supercapacitors and batteries, the behavior of RTILs at charged interfaces is still not well understood. The cations are expected to have a significant effect on physical properties (i.e., electrolyte viscosity and conductivity) as well as the electrochemical performance.1, 2 For a fully understanding of the cation-effect, herein, we provide a systematic study of the influence of the physical properties of RTIL electrolytes with different structures of cations on the electrochemical performance of carbon-based supercapacitors along with a molecular dynamics (MD) simulation. N-doped reduced graphene oxide aerogel (N-rGO) supercapacitors are incorporated with RTIL electrolytes consisting of cyclic nitrogen-based cations i.e., imidazolium, which are connected with a variable length of alkyl chains (i.e., ethyl, butyl and hexyl). Changing these cations do not widen the potential window of the ionic liquid; however, they do affect the electrochemical performance in term of specific capacitances and specific energies of the supercapacitor. We found that the heterocycles of RTILs affect ionic conductivity while the alkyl chain plays a role in ion diffusion. In this perspective, we hope that this fundamental study may pave the way to design the structure of RTIL electrolyte for high energy storage performance.