Lithiated manganese oxides (orthorhombic (I)) have been prepared by the heat treatment of MnO2 with LiI at 150-200 degrees C. Highly lithiated MnO2, Li0.50MnO2, is obtained by using LiI as the Li source, in comparison with Li0.33MnO2 obtained from LiNO3/MnO2 mixture heated at 320-360 degrees C. The first theoretical capacities of the orthorhombic (I), Li0.5MnO2, approximately correspond to the experimental values. The structure of the battery active material is essentially the same its Li0.33MnO2. The excellent rechargeable capacity is roughly 250 mA h/g when cycling between 4.5 and 2.0 V. By the chemical and the XRD analysis, it have been found that the orthorhombic phase (II) is formed at the initial molar ratio greater than LiI/MnO2 = 1.3 and Li2MnO3 is formed at the heating temperature greater than 250 degrees C.