This work develops a sputter-deposition method to grow cubic-spinel LiMn2O4 of significantly improved thermal stability and electrochemical performance. Thin films, deposited at low working pressure on unheated substrates, contain only LiMn2O4 of variable grain sizes (50 nm to a few nm) which, upon heating, is sequentially decomposed into (i) tetragonal-Li2Mn2O4 /MnO1.88 and (ii) orthorhombic-LiMnO2 /alpha-MnO2. Conversely, the films, deposited at elevated pressure and temperature (2 Pa/300degreesC), comprise LiMn2O4 nano-grains (less than or equal to10 nm) embedded in alpha-MnO2 layers, which are highly stable even after heating at 700degreesC. The phase-transition mechanism and electrochemical behaviors of the films are also presented. (C) 2004 The Electrochemical Society.