The composition of the thermal synthesis products of the LiNO3-MnO2 system has been determined by a continuous variation method in combination with thermal analysis and XRD technique. An optimal 3 V cathode material, a single-phase lithiated MnO2, Li0.33MnO2, was prepared by heating a mixture of LiNO3 and MnO2 with a Li/Mn molar ratio of 1/3 at 260 degrees C, followed by heating at 320-350 degrees C. The electrode material delivers an initial capacity of 210 mA h/g close to the theoretical capacity and shows a good rechargeability with a stable rechargeable capacity of 180 mA h/g at a current rate of 0.4 mA/cm(2) (C/3).