The effect of fumed TiO2 fillers (pure and modified by H2SO4) on ionic conductivity of composite electrolytes based on poly(ethylene oxide) dimethyl ether (PEODME) oligomer (M-w = 500) doped with lithium bis-(trifluoromethanesulfonyl)imide LiN(CF3SO2)(2) (LiTFSI) are studied by differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy (FT-IR) and complex impedance methods. The electrochemical stability of the electrolytes in the potential range of 4 V versus Li electrode has been confirmed by voltammetric measurements. Li electrode reactions have been followed by means of impedance spectroscopy. The growth in time of the resistance of the interfacial (Li electrode-polymer electrolyte) layers was inhibited upon the addition of fillers. (c) 2006 Elsevier B.V. All rights reserved.