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

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 6-31 + G (d,p) 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. (C) 2010 The Electrochemical Society. [DOI: 10.1149/1.3368694] All rights reserved.