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.