A new form of LiMnO2, which has recently been shown to reversibly intercalate lithium, has many advantages over other popular lithium-ion battery cathode materials. We describe improvements in the previously reported low temperature(300-450 degrees C) synthesis and report a new synthesis route based on ion exchange which takes place at 100 degrees C. Electrochemical performance is shown to be strongly dependent on synthesis temperature. In situ x-ray diffraction and long time cycling measurements indicate that an irreversible structural transformation to disordered spinel takes place when Li is removed from LiMnO2. Nevertheless, the specific capacity of this material is over 190 mAh/g between 2.5 and 4.2 V.