The Origin of Solvent Deprotonation in LiI-added Aprotic Electrolytes for Li-O 2 Batteries.

LiI and LiBr have been employed as soluble redox mediators (RMs) in electrolytes to address the sluggish oxygen evolution reaction kinetics during charging in aprotic Li-O 2 batteries. Compared to LiBr, LiI exhibits a redox potential closer to the theoretical one of discharge products, indicating a higher energy efficiency. However, the reason for the occurrence of solvent deprotonation in LiI-added electrolytes remains unclear. Here, by combining ab initio calculations and experimental validation, we find that it is the nucleophile I O 3 - ${{{\rm I}{\rm O}}_{3}^{-}}$ that triggers the solvent deprotonation and LiOH formation via nucleophilic attack, rather than the increased solvent acidity or the elongated C-H bond as previously suggested. As a comparison, the formation of B r O 3 - ${{{\rm B}{\rm r}{\rm O}}_{3}^{-}}$ in LiBr-added electrolytes is found to be thermodynamically unfavorable, explaining the absence of LiOH formation. These findings provide important insight into the solvent deprotonation and pave the way for the practical application of LiI RM in aprotic Li-O 2 batteries.