Spinel LiMn2O4 cathode material for rechargeable lithium batteries was prepared by using a hydrothermal process in supercritical water at 400degreesC. The hydrothermal conditions were first optimized to obtain a single phase of spinet LiMn2O4. For preparation of a single phase of LiMn2O4, an addition of H2O2 to the precursor solution was effective, and the prepared sample exhibited 80 mAh g(-1). This discharge capacity was smaller than the theoretical one. A following heat-treatment in air atmosphere was carried out in order to improve electrochemical performance of LiMn2O4. By the heat-treatment at 800degreesC, both particle size and crystallinity of LiMn2O4 were increased. This sample exhibited a discharge capacity of 130 mAh g(-1) and stable charge-discharge cycle behavior. (C) 2005 The Electrochemical Society. All rights reserved.