From synthesis to characterization: Advancing disordered rocksalts for cobalt-free lithium-ion batteries

The expanding market for lithium-ion batteries has intensified the need for cathode materials that combine high energy density with sustainability, cost-effectiveness, and supply-chain security. In this context, disordered rocksalt (DRX) oxides and oxyfluorides have emerged as a compelling class of cobalt-free cathodes, offering compositional flexibility, access to lithium-excess chemistries, and the ability to exploit both cationic and anionic redox processes. This review provides a comprehensive and critical overview of DRX materials. The crystallographic and transport fundamentals of DRX cathodes are discussed, emphasizing the role of cation disorder, short-range order, and lithium percolation through 0-TM diffusion channels as key enablers of reversible lithium transport. The contribution of individual compositional elements—including redox-active and redox-inactive transition metals, fluorine substitution, and oxygen redox activity—is then analysed in terms of voltage response, capacity, stability, and degradation mechanisms. Subsequently, the main synthetic routes to DRX materials are critically compared, including solid-state, mechanochemical, hydrothermal, sol–gel, and microwave-assisted approaches. These methods are evaluated in terms of their ability to stabilize metastable disordered phases, tune short-range order, and control particle morphology and compositional homogeneity. Finally, we review the advanced characterization techniques required to elucidate the multiscale complexity of DRX cathodes.