Computational design of high-entropy disordered rock salt cathode materials Alexander G. Squires 1, 2 , David O. Scanlon 1, 2 1 Department of Chemistry, University College London UK, 2 Faraday Institution, UK Disordered rock salt oxyfluorid cathode materials are perceived as excellent candidates for application as future lithium-ion cathode materials enabling novel chemistries beyond commercial layered Ni-Mn-Co structures [1] . As with any disordered material, target properties(capacity, rate capability, voltage etc.)are strongly influenced by the presence of any short-range order (SRO). In particular it is found that long-range lithium diffusion is suppressed by the SRO typically observed in disordered rock salt cathode materials [2,3]. Suppressing SRO in disordered oxyfluoride rock salt cathode materials is therefore crucial to maximising their performance. Alloying many transition metals together across the cation sublattice, creating so-called high-entropy rock salts, has been proposed as a method for minimising SRO [4, 5]. This approach has been inspired by the observation that high-entropy oxides are often observed with homogenous cation distribution [6] . While the high-entropy disordered rock salt oxyfluoride cathode concept has been shown to have initial promise, studies on these materials have not gone far beyond “proof-of-concept” stages; a deep understanding of the relationship between compositional chemistry and SRO suppression is lacking. This poses an exciting materials design challenge which requires developing an understanding of the independent effects of cation sublattice configurational entropy and the fluorine content on the anion sublattice and how these variables combine to determine the observed SRO in as-synthesised cathode materials. An understanding of these different concepts will aid in identifying low-cost, high-entropy rock salt compositions which possess excellent electrochemical performance. In this work we have developed a DFT-derived cluster-expansion model to drive Monte Carlo simulations examining the connectivity of the Li percolation network when varying the composition of high-component DRX Li cathode materials.We reveal the relative importance of the specific composition of the system as compared to a general increase in the configurational entropy and generate and explain compositional maps for developing the optimal SRO suppression in many-component disordered rock salt oxyfluoride cathode materials, guiding experimental collaborators to optimal compositions. References 1. Clément, R. J. et al. 2020. “Cation-Disordered Rock salt Transition Metal Oxides and Oxyfluorides for High Energy Lithium- Ion Cathodes.” Energy & Environmental Science 13 (2): 345–73. 2. Lee, Jinhyuk et al. 2014. “Unlocking the Potential of Cation-Disordered Oxides for Rechargeable Lithium Batteries.” Science343 (6170): 519–22. 3. Ji, Huiwen, et al. 2019. “Hidden Structural and Chemical Order Controls Lithium Transport in Cation-Disordered Oxides for Rechargeable Batteries.” Nature Communications 10 (1): 592. 4. Wang, Qingsong, et al. 2019. “Multi-Anionic and-Cationic Compounds: New High Entropy Materials for Advanced Li-Ion Batteries.” Energy & Environmental Science 12 (8): 2433–42. 5. Sarkar, Abhishek, et al. 2018. “High Entropy Oxides for Reversible Energy Storage.” Nature Communications 9 (1): 3400. 6. Lun, Zhengyan, et al. 2021. “Cation-Disordered Rocksalt-Type High-Entropy Cathodes for Li-Ion Batteries.” Nature Materials20 (2): 214–21.
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