Metal/metal oxide–graphene nanocomposites as cathode catalysts for lithium–oxygen batteries

Abstract

As the electrification of society advances, lithium–oxygen batteries (LOBs) are emerging as promising high-energy-density secondary batteries with a wide range of potential applications, including in electric vehicles, aerospace, and portable devices. However, the inherently slow kinetics and complex reaction mechanisms of LOBs result in poor reversibility of Li–O₂ electrochemistry, prompting extensive research into catalytic mechanisms and the development of ideal bifunctional catalysts. With its excellent electrical conductivity, large specific surface area, and high chemical stability, graphene has become a favored carbon material for accelerating the oxygen redox reaction, while metals and metal oxides—with much efficient active sites—can regulate reaction pathways and modify the morphology of discharge products. Consequently, inspired by synergistic effects, metal/metal oxide–graphene nanocomposites have been widely investigated as bifunctional catalysts to enhance the performance of LOBs. This overview first summarizes the categories of discharge products in LOBs and discusses their corresponding conversion mechanisms during discharging and charging for better understanding the Li–O₂ electrocatalytic reaction pathways. Secondly, it classifies the metal/metal oxide–graphene nanocomposites reported previously for LOBs according to the types of metal compounds involved, in which several milestone studies are highlighted. Finally, we discuss the main challenges and opportunities facing metal/metal oxide–graphene nanocomposites for high-performance LOBs and give insights into the critical aspects that deserve more investigations in future research.