Spinel Li4Mn5O12-eta F eta (0 <= eta <= 0.2) oxyfluoride cathodes have been synthesized at 500 and 600 degrees C employing LiF as a fluorine source and characterized by X-ray diffraction, chemical analysis, and electrochemical cycling. Fluorine substitution is found to suppress the disproportionation of Li4Mn5O12 into lithium-rich spinel Li1+xMn2-xO4 and Li2MnO3 during synthesis. The oxyfluoride cathodes exhibit higher initial capacity and improved capacity retention at both 25 and 60 degrees C compared to the corresponding oxide analogs in both the LiClO4- and LiPF(6-)based electrolytes. The improved electrochemical performance is due to a suppression of the Li2MnO3 phase and Mn dissolution. (C) 2007 Elsevier B.V. All rights reserved.