Cobalt Phthalocyanine Catalyzed Lithium-Air Batteries

Abstract

The full reduction of O2 to Li2O is the ultimate chemistry desired for building a super high energy density Li-air battery. Most investigations to date have identified Li2O2 as the discharge product which limits the specific energy of the Li-air battery to 3500 Wh kg−1, about 67% of the theoretical value. Here, for the first time, we report the full reduction of O2 to Li2O in a Li-air cell using cobalt phthalocyanine catalyzed carbon cathodes. Details of the oxygen reduction reaction mechanism have been discerned through cyclic voltammetry experiments in half cells as well as analysis of discharged Li-air cell cathodes by means of X-ray absorption spectroscopy and X-ray diffraction. The catalyst lowers the activation energy for O2 reduction by forming a complex with superoxide, and enables the reduction of Li2O2 to Li2O. In addition, the catalyst is effective in lowering the gap between the discharge and charge voltage plateaus leading to an increase in the energy efficiency of the Li-air battery. The breakthrough in the discharge chemistry being reported could lead to the realization of the full potential of the Li-air battery.