Orthorhombic LiMnO2 prepared at temperatures near 100 degrees C was evaluated for suitability as a high-capacity cathode for Li-ion cells. Carbon/LiMnO2 test cells showed initial reversible capacities of about 170 mAh/g of LiMnO2. This is much larger than that typically obtained from carbon/LiMn2O4 cells, about 110 mAh/g. The capacity of the LiMnO2 cells is divided approximately equally between 3 and 4 V plateaus. The cells exhibit little capacity loss with cycle number when restricted to either the 3 or the 4 V plateau. The capacity loss is most rapid when the cells are cycled over both plateaus. Using Li/LiMnO2 cells, we investigated the reasons for the cycling behavior and capacity loss with cycle number. We believe that LiMnO2 is an excellent candidate for the cathode of the coming generation of low-cost, high-energy Li-ion cells.