Ion Transport in Polymerized Ionic Liquid-Ionic Liquid Blends

Abstract

We used atomistic molecular dynamics simulations to study ion mobilities and the molecular mechanisms of transport in blends of poly(1-butyl-3-vinylimidazolium hexafluorophosphate) electrolytes with 1-butyl-3-methylimidazolium hexafluorophosphate ionic liquids. We characterized the structural and dynamical properties of the blend electrolyte systems through radial distribution functions, diffusivities, conductivities, and different time scales of relaxation and probed the correlations underlying such characteristics. Our results indicate that many features of ion transport in such blend systems mirror those observed in our earlier study of pure polymerized ionic liquids [Mogurampelly et al. J. Am. Chem. Soc. 2017, 139, 9511]. Explicitly, we observe that the anions associated with the polymerized cation move along the polymer backbone via the formation and breakup of ion pairs involving polymerized cationic monomers of different polymer chains. Interestingly, for all blend systems excepting pure polymeric ionic liquids, the anion mobilities were seen to be correlated to the ion-pair relaxation times of the free cation-anion pairs. Both the transference numbers and the deviations from the Nernst-Einstein conductivities exhibited minimal variations when examined as a function of the blend compositions. However, as a result of the influence of mobile cations, an optimal blending composition achieves the highest conductivities at a temperature normalized by the glass transition temperature.