Symmetry Breaking Enabled Stable Oxygen Redox in Li-Rich Cathodes via π-Type Interaction.

Effectively stabilizing oxygen redox is the most challenging task for the practical applications of high-energy-density Li-rich cathode materials. However, how to accurately tune the oxygen energy level to achieve reversible redox remains puzzling so far. In this work, we achieve stable oxygen redox in layered Li-rich materials over the whole voltage range without irreversible O release by adjusting the interlayer metal cation environment adjacent to the ligand. Combining synchrotron X-ray absorption spectroscopy and theoretical analysis of metal-ligand orbital combinations, we confirm the obvious charge transfer from O to Ni due to the π-type interaction between Ni 3d spin-down t orbitals and O 2p orbitals. Furthermore, Ab initio molecular dynamics simulations reveal the spontaneous symmetry breaking of the Ni coordination environment after Li extraction under the π-type interaction, which enhances the intrinsic competition between anion and cation oxidation, keeping π* state (from O 2p splitting) below the metal band to avoid over-oxidation. As a result, the modified material shows improved electrochemical performance and stable structural/interface evolution. This work provides new insights into the relationship between the adjacent metal environment and the ligand O redox reactions.