Role of Defects in Low-Cost Perovskite Catalysts toward ORR and OER in Lithium–Oxygen Batteries

Abstract

Li–O2 batteries are considered as one of the promising beyond Li-ion battery technologies owing to their high energy density. But, their poor cycle life due to sluggish oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) hinder the commercialization of this technology. Hence, fabrication of highly efficient ORR and OER catalysts is of paramount importance in order to improve the cyclic stability and longevity of this device. Herein, we discuss systematically the synthesis and electrochemical analysis of such bifunctional perovskite catalysts, namely, pristine CaMnO3 and its defect induced counterpart. When evaluated as a cathode catalyst in a Li–O2 battery along with a redox mediator LiI, the oxygen deficient CaMnO3 gives an improved cycle life reported at a high current rate of 500 mA g–1 with a capacity of 500 mA h g–1 in comparison with similar catalysts reported in the literature. Introduction of defects in the pristine framework predominantly improves the catalytic activity by lowering the overpotential. The presence of oxygen vacancies creates mixed-valence states of Mn3+/Mn4+ which modify the electronic structure, resulting in the improved catalytic activity. Comprehensive phase and compositional analysis confirm the formation of the desired defect-induced structure with improved catalytic activity toward ORR and OER which is elaborated with electrochemical analysis.