Vacancy-Induced Ligand-Hole Character Redirects Oxygen Redox in Li-Rich Layered Oxides

Li-rich layered oxides access high capacities through the combined participation of transition-metal and oxygen redox, but oxygen oxidation is often coupled with irreversible structural rearrangement and voltage decay. Here, we show that oxygen-vacancy-preconditioning modifies the local Ni–O electronic structure and promotes oxygen-derived ligand-hole character in a Li-rich layered oxide. High-temperature quasi-single-crystal (QSC) formation generates oxygen-deficient local environments while preserving the overall layered framework. Synchrotron spectroscopy combined with density functional theory (DFT) calculations reveals enhanced Ni–O hybridization and redistribution of charge compensation toward oxygen-derived states. Mapping resonant inelastic X-ray scattering further shows earlier oxygen participation during charging, followed by increased delocalization of oxygen-derived holes within hybridized transition-metal–oxygen states. This modified redox pathway suppresses Mn reduction and is coupled to a distinct structural response in which transient lattice environments formed during the initial cycle progressively relax during prolonged cycling, while the layered framework is largely retained. The resulting cathode exhibits reduced voltage hysteresis and voltage decay, together with improved electrochemical reversibility. These results establish a direct connection between vacancy-modified ligand-hole character and oxygen-redox-driven structural relaxation, demonstrating how local electronic structure governs the structural pathway of oxygen-redox-active layered oxides.