MoO3 thin films were examined as cathodes for elevated temperature Li thin-film batteries. All solid-state cells incorporating MoO3 cathodes were found to have superior cycle life and specific capacity compared with state-of-art LiCoO2- based Li thin-film cells. At 150 degrees C, the MoO3 cells could be cycled at deep charge and discharge voltages from 3.5 to 1 V over thousands of cycles with no apparent long-term capacity fade, in contrast to LiCoO2 cells which experienced severe capacity fade over a few hundred cycles at this temperature. The practical specific capacity of the MoO3 cathodes, approximately 298 mAh/g, was about twice that of state-of-art LiCoO2 cells cycled from 4.2 to 2.5 V. (c) 2005 The Electrochemical Society.