Li–O2 Cell with LiI(3-hydroxypropionitrile)2 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–O2) 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–O2 batteries. Here, we study the chemical reactivity between the oxidized state of I– and Li2O2. We confirm that the Li2O2 particles could be chemically oxidized by I2 rather than I3– species. Furthermore, our work demonstrates that the generated I– from Li2O2 oxidation would combine with I2 to give I3– species, hindering further oxidation of Li2O2 by I2. To improve the working efficiency of I– RMs, we introduce a compound LiI(3-hydroxypropionitrile)2 (LiI(HPN)2) with a high binding ability of I–. Compared with LiI, the cell that contained LiI(HPN)2 shows a significantly increased amount of I2 species during charge and enhanced Li2O2 oxidation efficiency under the same working conditions.