MoCl5 as a dual-function redox mediator for Li–O2 batteries

Abstract

Li–O₂ batteries suffer from high polarization and low energy density partly due to the film-like insulating product of Li₂O₂. These problems can be alleviated by a redox mediator, which usually catalyses either the formation or decomposition of solid Li₂O₂. However, few redox mediators have dual functions and catalyse both discharge and charge processes. Here, we propose MoCl₅ as a dual-function redox mediator for Li–O₂ batteries. In the discharge process, with MoCl₅, Li₂O₂ is initially formed in the solution and then deposited on the cathode surface in toroidal morphology, leading to a discharge capacity 2.6 times that without MoCl₅. In the charge process, MoCl₅ could help oxidize Li₂O₂ effectively, resulting in an extremely high coulombic efficiency and long cycling lifespan. Therefore, both oxygen reduction and evolution reactions could be promoted greatly for Li–O₂ batteries with MoCl₅ as the dual-function redox mediator.