Enhancing anionic redox stability via oxygen coordination configurations.

Anionic redox in Li-rich cathode materials with disordered crystal structures has potential to increase battery energy density. However, capacity fading due to anionic redox-induced structural transformation hinders practical implementation. To address this challenge, it is crucial to understand the influence of the anion coordination structure on redox reversibility. By comprehensively studying the spinel-like Li 1.7 Mn 1.6 O 3.7 F 0.3 and layered Li 2 MnO 3 model systems, we found that tetrahedral oxygen exhibits higher kinetic and thermodynamic stability than octahedral oxygen in Li 1.7 Mn 1.6 O 3.7 F 0.3 and Li 2 MnO 3 , effectively suppressing aggregation of oxidized anions. Electronic structure analysis showed that the 2p lone-pair states in tetrahedral oxygen lie deeper than those in octahedral oxygen. The Li-O-TM bond angle in a polyhedron is identified as a characteristic parameter to correlate anionic redox stability. TM substitutions using Co 3+ , Ti 4+ and Mo 5+ could effectively regulate the Li-O-Mn bond angle and anionic active electronic state. Our finding that anionic redox stability is influenced by the polyhedral structure offers new opportunities for designing high-energy-density Li-rich cathode materials.