The influence of the space charge created by the presence of TiO2 nanoparticles on the lithium and polymer chain mobility have been investigated in solid composite polymer electrolytes (CPE), poly(ethylene oxide) (PEO) LiClO4, by using complex impedance spectroscopy and nuclear magnetic resonance (NMR). Special care was taken with the synthesis and the characterization of the TiO2 particles and with the composite preparation. The conductivity and NMR measurements were undertaken in composite samples nanoparticles having constant total surface area. Proton (H-1) and lithium (Li-7) lineshapes and spin-lattice relaxation times were measured as a function of temperature. Activation energies extracted from the Li-7 relaxation data are in the range 0.20-0.22 eV. The NMR decoupling experiment suggests that the Li-Li interactions are stronger in the composites when compared with those of the ceramic free electrolytes. (C) 2003 Elsevier Science Ltd. All rights reserved.