Metal‐Ligand π Interactions in Lithium‐Rich Li<sub>2</sub>RhO<sub>3</sub> Cathode Material Activate Bimodal Anionic Redox
Kun Zhang, Zewen Jiang, Fanghua Ning, Biao Li, Huaifang Shang, Song Jin, Yuxuan Zuo, Tonghuan Yang, Guang Feng, Xinping Ai, Dingguo Xia
Abstract
Abstract 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 Li 2 RhO 3 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 Rh 4+ , 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.