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The effect of salt concentration on the molal conductivity of various composite electrolytes was studied. Conductivity enhancement is achieved for composite electrolytes over the basic poly(ethylene oxide)-LiClO 4 system in the salt concentration range where the filler concentration corresponds to that of LiClO 4 . On the basis of impedance spectroscopy, DSC, and FT-IR studies, it is concluded that changes in the conductivity result from acid-base type interactions involving polyether oxygens, filler acid or base centers, and alkali metal cations. The effect of a filler is to change the fraction of available oxygen sites which in turn results in changes in the formation of ionic aggregates. The region in which the enhancement of ionic conductivity is observed corresponds to a decrease in the fraction of contact-ion pairs and higher aggregates; this is due to the location of filler molecules in the vicinity of the coordination sphere of Li + cations.

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.

The results of detailed studies of the ionic conductivity, ultrastructure, and morpholgy of polyether-poly(N,N-dimethylacrylamide)-LiClO4 electrolytes are presented and discussed. These composite electrolytes have been studied using differential scanning calorimetry (-110-150 °C), with FT-IR spectroscopy (20-85 °C) and impedance analysis (-20-100 °C). Room temperature FT-Raman spectroscopy, SEM, and X-ray energy dispersive studies have also been performed. Highly crystalline poly(ethylene oxide) and amorphous or low-crystalline oxymethylene-linked poly(ethylene oxide) are used as polyether matrices for composite electrolytes. It is shown that interactions of lithium cations with polyether oxygens and the carbonyl oxygens of the "filler" poly(N,N-dimethylacrylamide) lead to the formation of various types of complexes. These interactions can be classified as Lewis acid-base reactions. The formation of different types of complexes modifies the ultrastructure and enhances the subambient and ambient temperature ionic conductivity of these electrolytes in comparison to the pure polyether-LiClO4 electrolyte. The increase in the conductivity is attributed to the presence of a highly flexible uncomplexed polyether phase surrounding filler particles. The temperature dependence of ionic conductivity is Arrhenius at ambient and subambient temperatures and VTF at higher temperatures. The order-disorder transition temperature calculated on the basis of a semiempirical model is found to be equal to the onset temperature of the melting peak of the crystalline poly(ethylene oxide) for these semicrystalline electrolytes or equal to 1.2 times the glass transition temperature of the polyether-LiClO4 electrolyte for the corresponding amorphous systems. Assuming that the enhanced conductivity of these composite polymer electrolytes is associated with interphase phenomena, the conductivity results were analyzed in terms of a model based on effective medium theory.

The effects of AlBr3, AlCl3, and α-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 °C for samples containing up to 25 mass % of aluminum halides or α-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.

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