Metal‐Ligand π Interactions in Lithium‐Rich Li2RhO3 Cathode Material Activate Bimodal Anionic Redox

Li‐rich oxide (LRO) cathodes that exhibit anionic redox activity can boost the energy density of Li‐ion batteries. Oxygen redox in LROs can originate from the charge compensation of pure O 2p nonbonding (NB) states; however, the high charging voltages cause much safety concerns in practical applications. Exploiting new anionic redox modes that can be used at low voltages is thus imperative. In view of this, a further understanding of the anionic redox behavior with respect to metal‐ligand interactions in LROs is highly desired. In this study, by analyzing the orbital combinations of transition metals (TMs) and O in LROs, the prevalence of π‐type, σ‐type, and NB states is investigated. Highly covalent Li2RhO3 with strong π‐type interactions is selected as a model material. Owing to the closer energy levels of O and Rh and the orbital vacancy of Rh4+, oxygen acts as a π‐electron donor to central Rh and exhibits high reactivity in the occupied anti‐bonding state, showing a novel low‐voltage O redox which is distinct from high‐voltage NB O redox. This π‐type oxygen redox mode expands the fundamental theories of anionic redox and provides a new design route to achieve high‐capacity Li‐rich cathode materials. π‐type hybridizations in Li‐rich oxide (LROs) stemming from orbital overlap between transition metal (TM) and O 2p states are investigated. In Li2RhO3, O preferentially occupies the hybridized π* states, leading a novel π‐type redox at low voltages that is accompanied by non‐bonding oxygen redox at high voltages, indicating that bimodal O redox can occur in LROs depending on the characteristics of the TM and anions.