Cation-oxygen geometry in polymer electrolytes: interpretation of EXAFS results

Abstract

Two issues are of current interest in the field of ionically conducting polymers (polymer electrolytes): these are ion pairing and possible interference of the polymer-cation interaction by water. EXAFS was chosen as a suitable technique to probe local structure surrounding the cations. The systems studied were PEOn:ZnX2, where n= 6–15 and X = Cl, Br or I. They were chosen in order to ascertain the reliability of information pertaining to oxygen neighbours when the system under investigation contains heavy counterions. The results reveal, as expected, that the information about numbers of oxygen nearest neighbours is qualitative rather than quantitative, and firmer conclusions can be drawn for the lighter counterions. Cations and anions were found to be in close proximity, thus confirming ion pairing in PEO-zinc polymer electrolytes; this is in accord with recent observations of zinc diffusion.