Disordered rocksalt oxide (DRX) cathodes are promising candidates for next-generation Co- and Ni-free Li-ion batteries. While fluorine substitution for oxygen has been explored as an avenue to enhance their performance, the amount of fluorine incorporated into the DRX structure is particularly challenging to quantify and impedes our ability to relate fluorination to electrochemical performance. Herein, an experimental-computational method combining ⁷Li and ¹⁹F solid-state nuclear magnetic resonance, and ab initio cluster expansion Monte Carlo simulations, is developed to determine the composition of DRX oxyfluorides. Using this method, the synthesis of Mn- and Ti-containing DRX via standard high temperature sintering and microwave heating is optimized. Further, the upper fluorination limit attainable using each of these two synthesis routes is established for various Mn-rich DRX compounds. A comparison of their electrochemical performance reveals that the capacity and capacity retention mostly depend on the Mn content, while fluorination plays a secondary role.

Abstract: Lithium‐rich transition metal oxides with a cation‐disordered rocksalt structure (disordered rocksalt oxides or DRX) are promising candidates for sustainable, next‐generation Li‐ion cathodes due to their high energy densities and compositional flexibility, enabling Co‐ and Ni‐free battery chemistries. However, current methods to synthesize DRX compounds require either high temperature (≈1000 °C) sintering for several hours, or high energy ball milling for several days in an inert atmosphere. Both methods are time‐ and energy‐intensive, limiting the scale up of DRX production. The present study reports the rapid synthesis of various DRX compositions in ambient air via a microwave‐assisted solid‐state technique resulting in reaction times as short as 5 min, which are more than two orders of magnitude faster than current synthesis methods. The DRX compounds synthesized via microwave are phase‐pure and have a similar short‐ and long‐range structure as compared to DRX materials synthesized via a standard solid‐state route, resulting in nearly identical electrochemical performance. In some cases, microwave heating allows for better particle size and morphology control. Overall, the rapid and energy‐efficient microwave technique provides a more sustainable route to produce DRX materials, further incentivizes the development of next‐generation DRX cathodes, and is key to accelerating their optimization via high‐throughput studies.