Self-diffusion versus ion conduction in polymer electrolytes: On the occurrence of pairs, triplets, and higher-order clusters

We show that the ion transport properties previously established for several amorphous polyether-based electrolytes by tracer diffusion and conductivity measurements cannot be exclusively explained by triple ions or higher-order ionic clusters as the most significant mobile species. A combined analysis of the tracer diffusion and conductivity data at different concentrations and temperatures rather indicates that charged single ions and neutral ion pairs play a prominent role. In particular, it is found that the single anion controls the transport of negative charge. Allowing for positive and negative charge carriers of various size, the analysis is based on upper and lower limits derived for the charge diffusivity DσDσ with respect to the cation and anion tracer diffusivity. The derived expressions have a general validity and may be applied to any electrolyte system for which a complete set of mass and charge transport data is available.