Critically Examining the Role of Nanocatalysts in Li-O2 Batteries: Viability toward Suppression of Recharge Overpotential, Rechargeability, and Cyclability

In lithium-oxygen (Li-O-2) batteries, nano catalysts have been widely employed as a means to suppress the large recharge overpotential and to possibly improve cyclability. However, these studies have consistently been mired with ambiguity relating to the possible exacerbation of side reactions, which in turn has brought into question the role of such catalysts in Li-O-2 cells. Here, we shed light on the viability of nanocatalysts by examining the use of Ru, Pt, Pd, Co3O4, and Au nanoparticles supported on carbon nanotubes in Li-O-2 cells. We show that while there can be noticeable reduction in overpotential with catalysts, the facile decomposition of Li2O2 is not accompanied by a decrease in side reactions, and as a consequence, there is no notable improvement in rechargeability or cyclability. Instead, highly active catalysts can exhibit nonselectivity for all oxidation reactions including Li2O2 and the electrolyte. This work underscores the importance of metrics beyond simple consideration of the recharge overpotential and the necessity of pursuing approaches that can promote reversible Li-O-2 electrochemistry.