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.