Exploring a new synthesis route to lithium-excess disordered rock salt (DRX) cathode materials

Abstract

Lithium-excess disordered rock salt (DRX) materials are promising candidates for Co/Ni-free Li-ion cathodes due to their high specific energy (800+ W h kg⁻¹) and compositional flexibility. DRX cathodes are typically synthesized using solid-state reactions, which are difficult to scale and provide little-to-no control over particle morphology. To address this bottleneck, the present study reports a two-step, solution-based reaction route to prepare Mn/Ti-based DRX oxyfluoride cathodes with nominal compositions of Li_1.25Mn_0.5Ti_0.3O_1.95F_0.05 and Li_1.35Mn_0.7Ti_0.1O_1.85F_0.15. More specifically, a glycine–nitrate combustion reaction is used to produce a lithiated transition metal oxide, which is further reacted with LiF to produce high-purity DRX powders. Remarkably, this route yields 80–90% pure DRX after annealing for 1 h at 800–1000 °C, and ¹⁹F solid-state nuclear magnetic resonance (ssNMR) spectra demonstrate that F⁻ anions are successfully incorporated into the DRX structure. Cathodes prepared using this approach exhibit promising electrochemical performance, with Li_1.35Mn_0.7Ti_0.1O_1.85F_0.15 attaining reversible capacities ∼210 mA h g⁻¹ and moderate cycling stability in half cells (65% capacity retention over 150 cycles). Overall, these results demonstrate that utilizing novel metal oxide precursors presents a viable and largely unexplored method to produce high-performance Co/Ni-free DRX cathodes.