Impact of Chloride and Bromide Composition in Ionic Liquid/Water Electrolytes on the Electrochemical Performance of Graphene-Based Supercapacitors: A Molecular Dynamics Study

Abstract

The electrochemical performance of supercapacitors (SCs) is significantly influenced by the composition of their electrolytes. In this study, we investigate the effects of chloride ([Cl]⁻) and bromide ([Br]⁻) anion variations in 1-butyl-3-methylimidazolium [bmim]⁺/water mixtures for graphene-based SCs using atomistic molecular dynamics simulations. We analyze the structural and energetic profiles of the electrical double layer (EDL), focusing on ion and water distributions, electrostatic charge profiles, and interaction energies at charged electrode interfaces. The results reveal that [Cl]⁻ and [Br]⁻ variations have a minimal impact on electrostatic charge distributions but play a crucial role in determining the gravimetric energy density of SCs. Notably, increasing [Cl^–] concentration enhances the gravimetric energy density by approximately 9% without compromising electrochemical stability, which is particularly advantageous for weight-sensitive applications such as portable electronics and electric vehicles. Additionally, we examined the influence of hydration levels, showing that higher water content improves the gravimetric efficiency of the electrolyte. These findings provide valuable insights into optimizing ionic liquid (IL)/water-based electrolytes for high-performance SCs.