A Design Strategy for Durable Anionic Redox via Fluorine-Induced Electronic Structure Modulation in In Situ Formed...

Disordered cathode materials are attractive candidates for next-generation lithium-ion batteries (LIBs), but the intrinsic instability of anionic redox hinders their commercialization. Unlike conventional Li-excess disordered systems limited by compositional constraints of Li_1+xM_1-xO₂, Immm-Li₂NiO₂ offers a platform to access highly lithiated chemistries that enable in situ disorder formation during electrochemical cycling. This allows lattice O to contribute to charge compensation; however, O₂ release at high voltages compromises reversibility and cycling stability. To address this, fluorination generates a quadrupolar Li-O-M-F configuration that lowers the Li─O─Li band energy level and delays the onset of anionic redox. This electronic structure modification suppresses O₂ evolution, enhances structural stability, and improves cycling performance. By coupling electrochemically induced disorder with stabilization through Li-O-M-F units, this work establishes a new framework for engineering durable, high-capacity cathodes, offering a blueprint for material design strategies that transcend stoichiometric restrictions and unlock stable anion redox functionality.