Understanding the limits to Short-range order Suppression in Many-Component Disordered Rock Salt Lithium-ion Cathode Materials

Abstract

Suppressing unfavourable short-range ordering in disordered rock salt lithium-ion cathode materials is seen as a key research goal on their route to commercialisation. In this study we use cluster-expansion-driven Monte Carlo simulations of a model 3d-transition metal disordered rock salt oxyfluoride system to investigate the effect of many component cation substitution on the suppression of short- range ordering in disordered rock salt cathode materials. We confirm that many-cation substitution is effective in suppressing short-range ordering, but has diminishing returns on increasing the number of component transition metals, or alternatively, increasing the size of the long-range lithium diffusion network as the number of transition metals increases. We particularly emphasize the critical role of lithium excess and fluorine content in the success of the “high-entropy” cation substitution strategy: short-range ordering is strongly influenced by cation-anion bonding preferences, underscoring the need to consider the full composition of the target system when designing high entropy lithium-ion cathode materials.