Strategies to Achieve Stable Manganese Oxyfluorides by Tuning the Reactivity of Pure Molecular Fluorine

Thanks to their high initial electrochemical properties and broad compositional flexibility, lithium-rich disordered rocksalt cathode-active materials including high-performance manganese-only materials appear as a potential replacement to the cobalt-based current market leader "NMC" material. The main issue with these materials is their lack of stability. However, recent works have identified bulk fluorination as a potential solution to stabilize these compounds. There is, however, a clear lack of diversity in fluorination agents used to synthesize these disordered rocksalts, as most publications used LiF, a very stable compound. To achieve manganese-only materials, manganese oxyfluorides represent promising precursors, but the literature reports only MnO₃F and Mn₂O₂F₉, which are both unstable and hazardous. The present study develops several strategies for synthesis and a tailored characterization methodology to explore the chemical space of direct fluorination of manganese oxide MnO with molecular fluorine and shows how to tune its reactivity to achieve a range of novel, safe, and finely tunable manganese oxyfluorides of general formula MnOF, with x going from 0 to 1 synthesized via a fluorine insertion mechanism.