Molecular insights on optimizing nanoporous carbon-based supercapacitors with various electrolytes

Abstract

Molecular dynamics (MD) simulations using the constant potential method (CPM) can provide nanoscale insight to explain and optimize supercapacitor charging dynamics and charge storage. We report CPM MD operando simulations for charging of nanoporous carbide-derived carbon supercapacitors with four distinct electrolytes, including ionic liquid (IL), mixed IL-solvent, and solvent-in-salt electrolytes. Instead of employing a coarse-grained model, we used an all-atom model for the electrolytes, allowing us to uncover the essential effects of solvents on the charging mechanism. We find that the water-in-salt electrolyte, lithium bis(trifluoromethanesulfonyl)imide / water, leads to the greatest charge storage among the studied combinations and exhibits a significantly higher integral and differential capacitance on the negative electrode, associated with a strong cation-driven charging mechanism. Our simulations also demonstrate the varying contributions of the different electrode regions to supercapacitor performance, with an especially high local capacitance (up to ∼250 F/g) within the interfacial region of the electrodes. These molecular insights provide important guidance for optimizing supercapacitor performance by carefully tuning electrode nanostructure and electrolyte composition.