Chloride substitution and hydration effects in [emim][bnz] electrolytes for lightweight supercapacitors

Abstract

We investigate the structural and electrochemical properties of graphene-based supercapacitors using hydrated [emim][bnz] electrolytes, with and without chloride ion substitution. Classical molecular dynamics simulations were used to examine mass density profiles, hydrogen bonding, and electrostatic potentials. Hydration strongly influences the formation of electric double layers (EDLs) and enhances ionic mobility. Partial substitution of [bnz]− with Cl− produced only minor structural changes in the EDL, while modestly reducing device mass (∼4 %) and slightly mitigating the hydration-induced narrowing of the electrochemical window. Under low hydration, total capacitance shows an increase of approximately 11 % relative to the pure IL, while the highly hydrated systems reach the highest gravimetric energy density (4.53 J/g at 2.0 V), representing a modest enhancement within the observed variability range. These findings highlight the role of electrolyte composition in optimizing lightweight, high-performance supercapacitors.