(203g) Effect of Polarization on Ionic Conductivity Predictions in Binary Ionic Liquid Mixtures

Imidazolium-based ionic liquids (ILs) offer various advantages, such as low volatility, non-flammability, exceptional thermal and chemical stability, and a wide electrochemical potential window, which make them promising candidates for various applications, including electrolytic materials in electrochemical devices. While a large number of molecular simulation studies are available for predicting ionic conductivity of pure ILs, little attention has been given to estimating ionic conductivity in ionic liquid-ionic liquid mixtures, especially considering that there is a possibility of observing non-ideal behavior due to differing polarizability of anions. Force fields based on fixed charge models may not be adequate to accurately model ionic liquid-ionic liquid mixtures. In this work, we evaluate two methodologies for assigning partial charges for estimating ionic conductivity of ionic liquid-ionic liquid mixtures: (a) partial charges are fixed as a function of concentration; (2) partial charges vary with concentration. We will present how partial charges can be derived for ionic liquid-ionic liquid systems using electronic structure methods taking into account bulk environment. We perform molecular dynamics simulations on four binary ionic liquid mixtures: 1-ethyl-3-methylimidazolium [C₂mim] tetrafluoroborate [BF₄] dicyanamide [N(CN)₂], [C₂mim] [BF₄] bis(trifluoromethanesulfonyl)imide [NTf₂], [C₂mim][BF₄] trifluorosulfonate [TFO], and [C₂mim][NTf₂][TfO]. Our results indicate that fixed charge model leads to sometimes a qualitatively incorrect trend in the ionic conductivity as a function of concentration necessitating the incorporation of variable charge models while the variable-charge models correctly captures the experimental trend in ionic conductivities as a function of concentration underscoring the role of modeling polarization in such systems.