Fluorinated Graphite as a Fluorine Source for Mechanochemical Synthesis of Lithium Metal Oxyfluorides

Fluorine incorporation into mixed-anion inorganic solids is often limited by the thermodynamic stability of conventional solid fluorination reagents. LiF, the most used fluorine source in solid-state and mechanochemical synthesis, exhibits strong Li─F bonding that can hinder fluorine transfer and lead to residual LiF and coupled Li/F off-stoichiometry. Here, we investigate fluorinated graphite (CF_x) as an alternative fluorine source for the mechanochemical synthesis of lithium metal oxyfluorides. Owing to the heterogeneous nature of C─F bonding in CF_x, mechanochemical activation enables stepwise defluorination and effective fluorine transfer while decoupling fluorine delivery from lithium stoichiometry. Using disordered rock-salt Li₂VO₂F and Al-substituted Li₂V_{1- x}Al_xO₂F as model systems, we obtain the oxyfluoride active materials with no detectable residual CF_x, as confirmed by combined X-ray and neutron diffraction, atomic pair distribution function analysis, and ^{1 9}F solid-state NMR. Electrochemical measurements indicate improved fluorine incorporation relative to LiF-derived analogues, featured by more symmetric charge-discharge behavior and elevated redox potential. These results demonstrate that fluorinated graphite can serve as an effective fluorine source for mechanochemical oxyfluoride synthesis and provide insight into how heterogeneous C─F bonding environments influence fluorine transfer in the solid state.