High-Rate Long Cycle-Life Li-Air Battery Aided by Bifunctional InX₃ (X = I and Br) Redox Mediators

Redox mediators (RMs) are solution-based additives that have been extensively used to reduce the charge potential and increase the energy efficiency of Li–oxygen (Li–O2) batteries. However, in the presence of RMs, achieving a long cycle-life operation of Li–O2 batteries at a high current rate is still a major challenge. In this study, we discover a novel synergy among InX3 (X = I and Br) bifunctional RMs, molybdenum disulfide (MoS2) nanoflakes as the air electrode, dimethyl sulfoxide/ionic liquid hybrid electrolyte, and LiTFSI as a salt to achieve long cycle-life operations of Li–O2 batteries in a dry air environment at high charge–discharge rates. Our results indicate that batteries with InI3 operate up to 450 cycles with a current density of 0.5 A g–1 and 217 cycles with a current density of 1 A g–1 at a fixed capacity of 1 A h g–1. Batteries with InBr3 operate up to 600 cycles with a current density of 1 A g–1. These batteries can also operate at a higher charge rate of 2 A g–1 up to 200 cycles (for InBr3) and 160 cycles (for InI3). Our experimental and computational results reveal that while X3– is the source of the redox mediator, LiX at the MoS2 cathode, In3+ reacts on the lithium anode side to form a protective layer on the surface, thus acting as an effective bifunctional RM in a dry air environment. This evidence for a simultaneous improvement in the current rates and cycle life of a battery in a dry air atmosphere opens a new direction for research for advanced energy storage systems.