The effects of AlBr3, AlCl3, and alpha-Al2O3 on the conductivity and ultrastructure of electrolytes based on LiClO4 and polyethers have been studied. The results obtained are analyzed in terms of Lewis acid-base interactions occurring between various chemical moieties within these composite systems. It is shown that aluminum halides form complexes with ClO4- anion acting as plasticizing agents for polyether matrixes, However, aluminum halides interact also with polyethers leading to the formation of polyether-aluminum halide complexes, thus stiffening polymeric electrolytes, It is shown that for low additive concentrations the addition of Lewis acid results in a decrease in the degree of crystallinity of poly(ethylene oxide)-based electrolytes; this is followed by an increase in the conductivity. A significant increase in conductivity was obtained at 0 and 25 degrees C for samples containing up to 25 mass % of aluminum halides or alpha-Al2O3. For samples containing more than 30 mass % of the additive, the effect of the stiffening of polymer hosts dominates(and is confirmed by the increase in T-g values observed from DSC experiments) and the conductivity decreases.