Structural and electrochemical properties of graphene-based supercapacitors with water and methanol-co-solvated ionic liquids: a molecular dynamics study

Abstract

We present a molecular dynamics investigation of graphene-based supercapacitors using the ionic liquid ₄ and its mixtures with water and methanol ( ) as co-solvents. The objective is to elucidate how solvent incorporation modifies the electric double layer (EDL) structure, interfacial dynamics, and overall energy storage performance. Structural analyses, including charge density distributions, hydrogen bonding networks, and species-specific mass density profiles, reveal that both water and significantly reorganize the EDL, with exhibiting a strong interfacial affinity. Electrostatic properties were assessed using the constant charge method under various surface charge densities, allowing the calculation of electrode potentials, capacitances, and gravimetric energy densities. The results indicate that, for the hydrated electrolyte, optimal performance in low-voltage regimes ( V) is achieved at a moderate concentration of 20 % (Mid- ), whereas the highest gravimetric energy density (6.25 J/g) is obtained at 40 % (High- ) under a fixed potential difference of 2.5 V. Furthermore, incorporation reduces the overall device mass by 22 %. These findings highlight the dual advantage of co-solvent strategies, enhancing both energy density and material efficiency, and offer insights for the rational design of supercapacitors.