Li-O Cell with LiI(3-hydroxypropionitrile) as a Redox Mediator: Insight into the Working Mechanism of I during Charge in Anhydrous Systems.

Redox mediators (RMs) have been widely applied to reduce the charge overpotential of nonaqueous lithium-oxygen (Li-O) batteries. Among the reported RMs, LiI is under hot debate with lots of controversial reports. However, there is a limited understanding of the charge mechanism of I in anhydrous Li-O batteries. Here, we study the chemical reactivity between the oxidized state of I and LiO. We confirm that the LiO particles could be chemically oxidized by I rather than I species. Furthermore, our work demonstrates that the generated I from LiO oxidation would combine with I to give I species, hindering further oxidation of LiO by I. To improve the working efficiency of I RMs, we introduce a compound LiI(3-hydroxypropionitrile) (LiI(HPN)) with a high binding ability of I. Compared with LiI, the cell that contained LiI(HPN) shows a significantly increased amount of I species during charge and enhanced LiO oxidation efficiency under the same working conditions.