Ionic Interactions in Polymeric Electrolytes Based on Low Molecular Weight Poly(ethylene glycol)s

Abstract

It is shown that ionic conductivity of polymeric electrolytes based on low molecular weight amorphous polyglycols can be modified by the addition of α-Al2O3 fillers containing surface groups of the Lewis acid type. An enhancement of conductivity over pure PEG−LiClO4 electrolyte is observed for PEG−α-Al2O3−LiClO4 composite electrolytes containing from 0.5 to 3 mol/kg of the lithium salt. This increase in conductivity is coupled with the lowering of the viscosity of composite electrolytes and increasing chain flexibility when compared to the PEG−LiClO4 system as shown by rheological and DSC experiments. A decrease in the fraction of ionic aggregates is also seen from the FT-IR experiments for composite electrolyte in this salt concentration range. FT-IR studies of the C−O−C stretching mode has shown reduction in the transient cross-link density obtained after the addition of α-Al2O3 in the salt concentration range corresponding to the conductivity enhancement. The phenomena observed are explained in view of ion−ion and ion-polymer interactions, involving dispersed filler particles, which are of the Lewis acid−base origin.