Tailoring Intrinsic Oxygen Vacancies in P3‐Type Na0.66Mn0.66Mg0.33O1.93 to Enhance Oxygen Redox Activity

Integrating oxygen redox reactions with transition metal redox reactions offers a promising strategy to double or triple the energy density for large-capacity battery cathodes. In this study, we have introduced intrinsic oxygen vacancies (VO) into a P3 layered cathode to modulate the electronic structure of O atoms and enhance oxygen redox activity. Rietveld-refined X-ray diffraction (XRD), X-ray absorption spectroscopy (XAS), and X-ray photoelectron spectroscopy confirm the successful creation of VO in Na0.66Mn0.66Mg0.33O1.93 (OV-NMM). Density functional theory (DFT) calculations reveal that VO in OV-NMM positively enhances the antibonding interaction between Mn and O, directing excess electrons from O holes toward adjacent Mn t2g and O 2p orbitals. This modification significantly improves the reversibility and accelerates Na+ transport kinetics for O2-/O- redox reactions. Ex situ synthon-based XRD demonstrates that VO effectively eliminates the O3 phase, reduces Mg2+ migration, and suppresses irreversible structural changes. XAS of Mn K-edge and O K-edge further illustrate the advantageous role of oxygen vacancies in facilitating oxygen redox reactions. These findings highlight the potential of defect engineering, particularly VO, to boost anionic redox activity for high-capacity energy storage applications.