Li-O-2 Cell with Lil(3-hydroxypropionitrile)(2) as a Redox Mediator: Insight into the Working Mechanism of I- during Charge in Anhydrous Systems

摘要

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 Li2O2. We confirm that the Li2O2 particles could be chemically oxidized by I-2 rather than I-3(-) species. Furthermore, our work demonstrates that the generated I- from Li2O2 oxidation would combine with I-2 to give I-3(-) species, hindering further oxidation of Li2O2 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 Li2O2 oxidation efficiency under the same working conditions.