An extensive NMR investigation of filler-free and SiO2 nanoparticle-containing P(EO)(20)LiBETI polymer electrolytes prepared through a solvent-free procedure is reported. Li-7 and F-19 NMR spectra, spin-lattice relaxation times and self-diffusion coefficients were measured in the temperature range extending from 25 to 100degreesC. There was essentially no difference in the D-Li for filler-free and nanosized SiO2-containing P(EO)(20)LiBETI at T greater than or equal to 80degreesC. The D-F showed differences at T less than or equal to 90degreesC, with the SiO2-containing P(EO)(20)LiBETI having the greater D-f. Discrepancies between calculated and measured ionic conductivity are attributed to variable length scale diffusion within heterogeneous media, rather than ion pairing effects, (C) 2003 Elsevier B.V All rights reserved.