A Binder-Free Electrocatalytic Cathode for Lithium Oxygen Batteries

Abstract

Lithium oxygen (Li-O2) batteries have promising potential as a next generation energy storage technology due to their high specific energy density of 3500 Wh/kg. However, Li-O2 batteries are still in early development and there are many challenges and problems that need to be solved before commercialization. Two of the most critical issues hindering Li-O2 battery performance are cyclability and round trip efficiency, both of which are dependent on the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). The slow kinetics of these reactions translate to large over potentials during cycling. Adding electrocatalysts to the cathode has shown to significantly enhance the activity for ORR and OER during discharge and charge, significantly increasing the performance of Li-O2 batteries. Thus, the development of a binder free electrocatalytic cathode was proposed for this master thesis. This research investigated the use of a bi-functional α-MnO2 nanowire catalyst with a carbon nanotube (CNT) conductive support as a cathode for sealed Li-O2 batteries. The air cathode was constructed by vacuum filtering a 70/30 wt% α-MnO2/CNT mixture onto glass fiber filter paper. Electrochemical studies were conducted to evaluate the performance of the cathodes. In addition, postmortem analyses were done using scanning electron microscopy and x-ray diffraction. The results of this research showed that the binder free construction proved to be a viable cathode for Li-O2 batteries. Stable cycling was achieved with a capacity of 500 mAh/gcathode on discharge and charge for >50 cycles. Postmortem analyses of the batteries revealed that pore clogging by irreversible and unfavorable discharge products is the most likely mode of failure. Lastly, the facile method developed to construct the cathode is highly tunable, which allows for the future addition of other catalysts.