Random-Alloy Model for the Conductivity of Ionic Liquid–Solvent Mixtures

Abstract

[Abstract] Charge transport in ionic systems is of paramount importance in many areas, but the existing theories provide reliable description only at low electrolyte concentrations. A promising theory is the pseudo-lattice or cell theory of fluids, which describes an ionic solution as a mixture of solvent-rich and ion-rich cells, characterized by different ion mobilities, with ion transport taking place by means of a hopping mechanism. The conventional approach considers ion hops between statistically independent cells and leads to a quadratic dependence of the conductivity on ion concentration. Herein, we derive a new equation for the concentration-dependent conductivity by adopting the random-alloy approximation, which takes into account cell–cell correlations. The derived equation describes remarkably well the conductivities of ionic liquid–solvent mixtures and inorganic electrolytes in the whole range of concentration and brings new insights into their temperature and size dependence.