Quantitative Evaluation of Electrochemical Potential Windows of Electrolytes for Electric Double-Layer Capacitors Using Ab Initio Calculations

Abstract

The electrochemical potential windows of seven organic liquid electrolytes for electric double-layer capacitors calculated using ab initio molecular orbital theory are reported. Four types of models were used to investigate the effect of intermolecular interactions: (i) a single-ion in vacuo model, (ii) a single-ion-in-solvent model, (iii) an ion-pair in vacuo model, and (iv) an ion-pair-in-solvent model. For all the calculations, the Hartree–Fock level of theory using the basis set was used. Solute–ion interactions were treated by considering several cation–anion pair confirmations, and solute–solvent interactions were introduced by applying the isodensity polarizable continuum model. The ion-pair-in-solvent model quantitatively reproduced the experimental electrochemical potential windows with high accuracy. This demonstrates that in actual electrolytes intermolecular interactions, particularly cation–anion and solute–solvent, play an important role in determining electrochemical potential windows.