Composite polymeric electrolytes based on PEO complexes and ethyl aluminum alkoxides have been studied. The addition of the aluminum compounds causes a considerable reduction in the PEO crystalline phase content and provides very good mechanical and thermal stability up to 140 degrees C. The glass transition temperatures of blends are low, falling within the - 64 to - 29 degrees C range. The ionic conductivity of such systems reaches the value of 10(-5) S cm(-1) at ambient temperature and that of 10(-3) S cm(-1) at 60-70 degrees C. Impedance studies show that these systems form a passive layer with a lithium electrode, which protects this electrode from corrosion processes. (C) 2000 Elsevier Science Ltd. All rights reserved.