Alkali ion–cryptand interactions and their effects on electrolyte conductivity

Abstract

Combined theoretical and experimental studies are reported on alkali ion–cryptand interactions which affect charge transport in liquid electrolytes. Encapsulation of the cation by a cryptand cage can significantly improve the ionic conductivity, by reducing the fraction of time in which the cation is bound to its counterion. Comparison between experimental conductivities and NMR measurements of diffusion rates of Li and F in the amorphous LiMPSA electrolyte suggest that in the presence of the C222 cryptand, Li is bound to MPSA about 75% of the time. A hybrid classical/quantum methodology is used to model dynamics and electronic structure of a number of cryptand–alkali ion–MPSA and cryptand–ion–cryptand systems in an effort to extract general features which may be useful in designing electrolytes with improved performance.