Mechanism of ion conduction in alkali metal-polymer complexes

Abstract

Polymer electrolytes have many materials properties which are attractive for applications in advanced electrochemical devices. However the ionic conductivities are still too low for widespread utilization. One avenue for the improvement of the conductivity is the delineation of the factors which influence ion transport in polymers. The most successful models for alkali metal ion transport in polymers are based on the concept that ions are passed between polymer segments by large amplitude polymer motions, and that relatively few interactions between the ion and polar polymer groups are broken in the transition state. Evidence for the contribution of polymer segmental motion to ion transport is obtained from the form of the temperature-dependent conductivity, from the higher conductivity for amorphous than for crystalline polymers, from the decrease in conductivity with increasing pressure, and from doping experiments. Simple energy estimates indicate that the ion motion probably occurs with the breaking of at most one or two cation-polar group interactions, rather than the hop of an ion from one polymer chain to the next.