Revealing capacitive behaviors of graphene in ionic liquids using molecular dynamics simulation

This work reveals the capacitive behaviors of graphene nanomaterials in typical ionic liquids of [BMI + ] [BF 4 − ] using molecular dynamics simulations. It is found that the charging process induces a structural transition from disordered to partially ordered and then ordered multilayer structures of [BMI + ][BF 4 − ] electrolyte, yielding a multiple layer-by-layer packing structure of BMI + cation and BF 4 − anion. Especially, a counterion-adsorption-dominated Helmholtz layer is revealed at a high charge density of 16 μC/cm 2 , which is primarily responsible for the superior capacitance results. Besides, the differential capacitance of [BMI + ][BF 4 − ] exhibits a symmetric convexity-shaped curve, showing a maximal capacitance value of 4.83 μF/cm 2 . The as-obtain simulation results help to understand the microscopic charge storage mechanisms of graphene in ionic liquids.