Minimizing the Abnormal High-Potential Discharge Process Related to Redox Mediators in Lithium-Oxygen Batteries.

Nonaqueous lithium-oxygen batteries can achieve a reduced charge potential when an available redox mediator is introduced. However, there are accompanying problems, such as the shuttle effect and the abnormal high-potential discharge process (>2.96 V) after the first cycle. The shuttle effect can be addressed by developing a blocking separator or resistant solid electrolyte interphase on the anode. No attention has been paid to the abnormal discharge process. Here, we unravel the underlying mechanism causing the undesired abnormal phenomenon. Our results show that the slow reaction rate between the discharged lithium peroxide and redox mediator and the low yield of lithium peroxide should take primary responsibility for the abnormal discharge issue. The sluggish reaction kinetics results from the formed byproducts covering lithium peroxide. We propose developing redox mediator-containing hydrate-melt lithium-oxygen batteries. The lithium hydroperoxide intermediator shows high reaction activity with the redox mediator and improves battery charge ability, thus solving the abnormal discharge problem. This work sheds light on the further design of lithium-oxygen batteries using a redox mediator.