An optimization of MnO2 amount in CNT-MnO2 nanocomposite as a high rate cathode catalyst for the rechargeable Li-O2 batteries

• Several CNT-MnO2 nanocomposites were synthesized and applied in Li-O2 batteries.
• The CNT–60% MnO2 nanocomposite was selected as the optimum cathode catalyst.
• The capacity was 4600 mA.h/gtotalcathode at 1000 mA/gtotalcathode for the optimum catalyst.
• The over-voltages for discharge and charge were 0.20 V and 0.87 V, respectively.

A series of CNT–MnO2 nanocomposites containing different values of MnO2 were prepared and applied as the cathode materials in the Li-O2 batteries to obtain the optimum rate. The optimum theoretical ratio of MnO2 to the CNT used in synthesis was 60% (w/wcarbon) but the TGA analysis confirmed that the exact MnO2/CNT ratio in the optimum catalyst was 41% (w/wtotal). The CNT–60% MnO2 nanocomposite was characterized by FE-SEM, TEM, XRD, EDS, TGA, FT-IR, and N2 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 N2 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/gtotalcathode at a current density of 1000 mA/gtotalcathode. 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/gtotalcathode.

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