Normal and water-in-salt Li-bis(trifluoromethane) sulfonimide anion-based electrolytes were modeled using atomistic molecular dynamics simulations. Their acetonitrile (ACN) mixtures, in various concentrations, were also studied to evaluate the impact of a cosolvent on the structural, dynamical, and electrical properties of the electrolytes using liquid electrolyte and supercapacitor models. Our simulations for pure and ACN-based electrolytes revealed a drastic difference that exists between normal electrolytes and water-in-salt electrolytes and a systematic reduction of the diffusion of species by approximately a factor of 2 because of the ACN impact. Electrolytic cells for each electrolyte were built with graphene as the electrode. Our results for capacitance reveal an asymmetry between the electrode capacitances, with negative electrode capacitance systematically higher than those of the positive electrode. The total capacitance of the electrode exhibited negligible variations regardless of the concentration and composition of the electrolyte.