Tailoring Solid-State Reaction Pathways for Bulk Fluorination of Mn-Rich Rock-Salt Cathodes

Manganese-based cation-disordered rock-salt (DRX) cathodes offer high capacities without relying on cobalt and nickel, but maintaining that capacity over extended cycling often requires bulk fluorination. The challenge is that incorporating fluorine into Mn-rich DRX host structures is hindered by unfavorable thermodynamics and the stability of LiF, often necessitating elevated synthesis temperatures that promote severe lithium and fluorine volatilization. This study overcomes that limitation by manipulating the solid-state reaction pathway using unconventional Li6MnO4 and MnF2 precursors in a challenging Mn-rich model system (Li1.2Mn0.6Ti0.2O2–xFx). This precursor engineering strategy reshapes the thermodynamic landscape. Computational modeling and in situ X-ray diffraction reveal that by using reactive starting materials, we suppress the crystallization of less reactive intermediates, enabling bulk fluorination at a lower temperature. The resulting DRX retains both a high fluorine content and the lithium excess required for three-dimensional percolation, delivering improved electrochemical performance relative to material synthesized from conventional precursors.