Stabilized Oxygen\nVacancy Chemistry toward High-Performance\nLayered Oxide Cathodes for Sodium-Ion Batteries

Anionic redox has emerged as a transformative paradigm\nfor high-energy\nlayered transition-metal (TM) oxide cathodes, but it is usually accompanied\nby the formation of anionic redox-mediated oxygen vacancies (OVs)\ndue to irreversible oxygen release. Additionally, external factor-induced\nOVs (defined as intrinsic OVs) also play a pivotal role in the physicochemical\nproperties of layered TM oxides. However, an in-depth understanding\nof the interplay between intrinsic and anionic redox-mediated OVs\nand the corresponding regulation mechanism of the dynamic evolution\nof OVs is still missing. Herein, we disclose the strong interrelationship\nbetween these OVs and demonstrate that the presence of intrinsic OVs\nin the TMO<sub>2</sub> layers could induce weak integrity of the TM-O\nframeworks and unlock additional diffusion paths to trigger the generation\nand migration of anionic redox-mediated OVs. Accordingly, an OV stabilization\nstrategy is proposed by deliberately introducing high-valence Nb<sup>5+</sup>, which could serve as an important building block in anchoring\nthe oxygen sublattice and preventing the formation of a percolating\nOV migration network, thereby suppressing the formation/diffusion\nof anionic redox-mediated OVs. Consequently, superb structural integrity\nand improved electrochemical performance with reversible anionic redox\nchemistry are achieved. This work advances our understanding of the\nrole of OVs for developing high-performance energy storage systems\nutilizing anionic redox.