The electrochemical stability behavior of the composite polymer electrolytes obtained by adding a fine Al2O3 powder (activated acidic, neutral, and basic) with a diameter of 5.8 nm to the poly(ethylene oxide) (PEO)-LiClO4 is described. The strong hydrogen bond between the surface group of Al2O3 and lithium salt anion prevents the decomposition of lithium salt anion. An enhancement of the ionic conductivity for the composite polymer electrolytes prepared with Al2O3 and BaTiO3 is described in terms of a reduction of crystallinity and an increase of charge carrier concentration. (C) 2003 Elsevier Science B.V. All rights reserved.