Organic-inorganic hybrid nanocomposites of poly(ethylene glycol)/siloxane were obtained via the sol-gel approach. In these composites, nanometric siloxane heterogeneity was embedded into a polymer matrix with a covalent bond at the interfaces. The Si-29 magic-angle spinning (MAS) spectrum exhibited a high degree of condensation through the relative abundance of T-0 [RSi(OR)(3)], T-1 [RSi(OR)(2)(OSi)], T-2 [RSi(OR)(OSi)(2)], and T-3 [RSi(OSi)(3)] silicone nuclei. The effect of lithium salt concentration on ionic interaction, conductivity, and thermal properties of these composite electrolytes were investigated by Fourier transform infrared spectroscopy, DSC, thermogravimetric analysis, alternating current impedance, and solid-state Li-7 MAS NMR measurements. These observations indicated that the different types of complexes by the interactions of Li+ and ClO4- ions are formed within a hybrid host, and the formation of transient crosslinks between Li+ ions and the ether oxygens results in an increased glass-transition temperature of the polyether segment and decomposed rate of composite electrolyte. Li-7 MAS NMR measurements revealed the changes in line shape of lithium resonances with different LiClO4 contents, suggesting that a significant degree of ionic association is present in the polymer-salt complexes. The behavior of ion transport in these composite electrolytes was correlated with the interactions between ions and polymer host. (C) 2004 Wiley Periodicals, Inc.