Interhalogen of Iodine Chloride Accelerates Charge Transfer for Efficient Li2O2 Oxidation in Lithium–Oxygen Batteries

Abstract

Li–O2 batteries suffer from sluggish Li2O2 oxidation kinetics at electrode/electrolyte interfaces, leading to large charge polarization and low energy efficiency. Soluble redox mediators (RMs) provide a solution-mediated pathway for Li2O2 decomposition and reduce the charge overpotential. However, the chemical oxidation of Li2O2 by oxidized RMs remains kinetically sluggish, resulting in persistent charge polarization. Herein, iodine monochloride (ICl), an interhalogen compound, is electrochemically generated in situ during the charge process to promote the oxidation of Li2O2. The large electronegativity difference between I and Cl promotes intramolecular charge transfer from I to Cl, creating an electrophilic iodine center (Iδ+) that increases the I–Cl bond polarity and strengthens the interaction with Li2O2. This lowers the decomposition barrier of Li2O2 from 2.39 to 0.77 eV, thereby facilitating its chemical oxidation. The Li–O2 battery delivers a low discharge/charge polarization of 0.52 V, effectively mitigating parasitic reactions at high voltages and enabling an extended cycling lifespan exceeding 800 h. This work provides a valuable design principle for developing redox mediators for efficient Li2O2 oxidation.