Oxygen Radical Anion Substituted Iron Phthalocyanine as an Effective Redox Mediator for Li–O<sub>2</sub> Batteries
Yingjie Cheng, Yaying Dou, Xiaoya Zhang, Yuan Song, Siyu Liu, Yizhan Wang, Hao Zhang, Xibang Chen, Jingyi Qiu, Yingjin Wei
Abstract
Transition metal phthalocyanines are potential soluble redox mediators for Li–O 2 batteries. In this work, effective strategies to control the redox potentials and activities of iron phthalocyanine (FePc) based redox mediators are designed by the introduction of electron-withdrawing or electron-donating groups. Substituted electron-donating groups can shift the oxidation potential of FePc to a higher energy level, consequently reducing the charging voltage of Li–O 2 batteries. Especially, oxygen radical anion (−O – ) modified FePc (FePc-O – ) shows the most significant improvement to the oxygen reduction and evolution reactions of Li–O 2 batteries. Electronic analysis indicates that −O – substitution can break the symmetry of electronic structures of FePc which further tunes the reduction of O 2 and the oxidation of Li 2 O 2 . Detailed reaction mechanisms of (FePc-O – )-mediated Li–O 2 batteries are proposed based on first-principles molecular dynamics simulations and thermodynamic free energy calculations.