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–O 2 ) 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 2 batteries. Here, we study the chemical reactivity between the oxidized state of I – and Li 2 O 2 . We confirm that the Li 2 O 2 particles could be chemically oxidized by I 2 rather than I 3 – species. Furthermore, our work demonstrates that the generated I – from Li 2 O 2 oxidation would combine with I 2 to give I 3 – species, hindering further oxidation of Li 2 O 2 by I 2 . 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 I 2 species during charge and enhanced Li 2 O 2 oxidation efficiency under the same working conditions.