Structure and mechanisms underlying ion transport in ternary polymer electrolytes containing ionic liquids.

We use all atom molecular dynamics simulations to investigate the influence of 1-butyl-3-methylimidazolium hexafluorophosphate (BMIMPF) ionic liquid on the structure and transport properties of poly(ethylene oxide) (PEO) polymer electrolytes doped with LiPF salt. We observe enhanced diffusivities of the Li, PF, and BMIM ions with increasing loading of the ionic liquid. Interplay between the different ion-ion and ion-polymer interactions is seen to lead to a destabilization of the Li-PF coordination and increase in the strength of association between the Li cations and the polymer backbone. As a consequence, the polymer segmental relaxation times are shown to be only moderately affected by the addition of ionic liquids. The ionic-liquid induced changes in the mobilities of Li ions are seen to be correlated to polymer segmental relaxation times. However, the mobilities of BMIM ions are seen to be more strongly correlated to the BMIM-PF ion-pair relaxation times.