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.

The effect of filler surface group on the conductivity, ion−ion, ion−polymer interactions, and microstructure of PEG−LiClO4−Al2O3 composite polymer electrolytes is studied. It is shown that the addition of fillers results in an increase in ionic conductivity of polyether electrolytes observed in the narrow lithium salt concentration range. The position of conductivity maximum depends on the type of the surface groups of the filler and results from the Lewis acid−base type interactions between filler surface centers, ions, and ether oxygen base groups. These interactions are reflected by changes in the polymer chain flexibility observed by DSC and rheological experiments as well as microstructural changes due to polymer−filler−Li+ interactions as revealed by FT-IR experiments. Finally, the addition of the filler results in the changes in ionic associations as studied by FT-IR and by applying the Fuoss−Kraus formalism to the salt concentration dependence of the molar conductivity of the composite electrolytes studied.