Origin of enhanced disorder in high entropy rocksalt type Li-ion battery cathodes

Abstract

High entropy disordered rocksalt (HE-DRX) structure has emerged as a new platform for achieving high energy density and high-rate performance while minimizing the use of critical metals, e.g. Co and Ni. Recent studies have shown that high-entropy compositions can reduce detrimental chemical short-range order, making Li more extractable during electrochemical process. However, the factors that control the degree of disorder in HE-DRX remain unknown. In this work, we demonstrate that pronounced cation disorder arises from deviation in lattice distortion and cation charge states. Furthermore, we observe an inverse correlation between the tendency for disorder and the phase stability of specific HE-DRX materials, indicating a trade-off between disordering tendency with structural stability. These design principles are based on data mining 18 810 DFT computed HE-DRX compositions with different orderings, encompassing 28 typical cation species used in cathodes. Experimental comparisons of two materials with the same theoretical redox capacity but different tendencies for disorder further validate our theoretical predictions regarding both phase stability and disordering tendency. The design principles proposed in this work will refine the roadmap for discovering high-rate, earth-abundant Li-ion battery cathodes with optimized short-range order.