Distinct Oxygen Redox Activities in Li<sub>2</sub>MO<sub>3</sub> (M = Mn, Ru, Ir)
Zengqing Zhuo, Kehua Dai, Jinpeng Wu, Liang Zhang, Nobumichi Tamura, Yi‐De Chuang, Jun Feng, Jinghua Guo, Zhi‐Xun Shen, Gao Liu, Feng Pan, Wanli Yang
Abstract
Li2MO3 (M = transition metal) systems are parent compounds of Li-rich materials and widely considered to offer oxygen redox for high-energy batteries. However, recent clarifications have revealed that, among the three representative Li2MO3 (M = Mn, Ru, Ir) compounds, no reversible oxygen redox takes place in the Mn and Ir systems. Here, we reevaluate the redox reactions in Li2RuO3 through advanced spectroscopy, which shows both Ru redox and highly reversible O redox (96% initial-cycle reversibility, 80% retained after 10 cycles, and 77% after 50 cycles). This is in sharp contrast with the Li2MnO3 and Li2IrO3 systems and concludes the three distinct oxygen behaviors in the Li2MO3 systems during charging: (i) only irreversible oxygen oxidation in Li2MnO3; (ii) reversible Ru and O redox in Li2RuO3; (iii) only cationic redox in Li2IrO3. This work suggests the critical role of transition metals and their coupling to oxygen for maintaining reversible oxygen redox activities for high-energy batteries.