A series of CNT-MnO2 nanocomposites containing different values of MnO2 were prepared and applied as the cathode materials in the Li-O-2 batteries to obtain the optimum rate. The optimum theoretical ratio of MnO2 to the CNT used in synthesis was 60% (w/w(carbon)) but the TGA analysis confirmed that the exact MnO2/CNT ratio in the optimum catalyst was 41% (w/w(total)). The CNT-60% MnO2 nanocomposite was characterized by FE-SEM, TEM, XRD, EDS, TGA, FT-IR, and N-2 adsorption-desorption analyses. The Electrochemical Impedance Spectroscopy (EIS) and discharge-charge cycles were also studied for all the cathodes fabricated using various CNT-MnO2 nanocomposites. The N-2 physisorption analysis showed a lower surface area for the produced composite compared to that of the pristine CNT but it did not negatively affect the battery rate. The synthesized CNT-60% MnO2 compound had a capacity of about 4600 mA h/g(totalcathode) at a current density of 1000 mA/g(totalcathode). The battery fabricated using the optimum nanocatalyst revealed over-voltages equal to 0.20 V and 0.87 V for discharge and charge, respectively, having a cycleability using the current density of 100 mA/g(totalcathode). (C) 2015 Elsevier Ltd. All rights reserved.