Composite polymer electrolytes based on poly(ethylene oxide) (PEO) with hyperbranched polymer (poly[bis(triethylene glycol)benzoate] capped with an acetyl group) (HBP), ceramic filler (BaTiO3), and lithium salt (LiN(CF3SO2)(2)) were examined as the electrolyte for all solid-state lithium polymer batteries and optimized to achieve high ionic conductivity. The ionic conductivity of the optimized composite polymer electrolyte, [(PEO-20'wt.% HBP)(2)(LiN(CF3SO2)(2))]-10 wt.% BaTiO3, where the PEO with number-average molecular weights (M) of 60 x 104, HBP with M of 15,000 and BaTi03 with a particle size of 0.5 mum were used, was found to be 2.6 x 10(-4) S/cm at 30degreesC and 5.2 x 10(-3) S/cm at 80degreesC, respectively. The optimized composite polymer electrolyte showed an electrochemical stability window of 4.0 V and was stable until 312 C under air. (C) 2003 Published by Elsevier Science B.V.