Computational Investigation of Short-Range Order Suppression in High-Entropy Disordered Rocksalt Cathode Materials

Disordered rock salt cathode materials are perceived as excellent candidates for application as future lithium-ion cathode materials enabling chemistries beyond commercial Ni-Mn-Cotechnologies [1]. Suppressing short-range order (SRO) in disordered rocksalt cathode materials is crucial to maximizing their performance. Disordered rocksalt cathodes can possess long-range “0-TM” percolation networks, which allow for fast and facile lithium diffusion, ensuring a good rate capability and high capacity [2]. SRO is typically associated with reduced connectivity of these 0-TM networks [3]. Alloying many transition metals together across the cation sublattice in a rocksalt structure, creating so-called high entropy rocksalts, has been proposed as a method for minimizing SRO [4, 5]. This approach is expected to improve Li transport through the bulk by suppressing the formation of a single dominant SRO type by increasing competition between a larger number of transition metal species [6]. While the high-entropy cathode concept has been shown to have initial promise, typically studies on these materials have not gone far beyond “proof of concept” stages, identifying optimal compositions remains an open question. When designing new energy materials which contain many component elements, working within sustainability and cost constraints becomes even more important. Many transition metals with favorable electrochemical properties are subject to high and volatile prices, with supply chain issues, precluding their use of truly sustainable cost-effective energy storage technologies [7]. Taken together, this poses an exciting design challenge in identifying low-cost, high-entropy rocksalt compositions which can remain insensitive to market fluctuations and supply chain issues, while retaining excellent electrochemical performance. In this work, we use cluster-expansion parameterized Monte Carlo simulations to examine the connectivity of the Lipercolation network when varying the number and concentration of different transition metals. We then assess the electrochemical properties and stability of these systems using first-principles approaches. Also included in our cathode design is an analysis of time-series data for the cost and availability of the component elements to ensure that not only are any proposed compositions excellent candidate cathode materials but also should represent cost-effective potential future cathodes.<br/><br/>1. Clément, R. J. et al. 2020. “Cation-Disordered Rocksalt Transition Metal Oxides andOxyfluorides for High Energy Lithium-Ion Cathodes.” Energy & Environmental Science13 (2): 345–73.<br/>2. Lee, Jinhyuk et al. 2014. “Unlocking the Potential of Cation-Disordered Oxides for rechargeable Lithium Batteries.” Science 343 (6170): 519–22.<br/>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.<br/>4. Wang, Qingsong, et al. 2019. “Multi-Anionic and-Cationic Compounds: New High Entropy Materials for Advanced Li-Ion Batteries.” Energy & Environmental Science12 (8): 2433–42.<br/>5. Sarkar, Abhishek, et al. 2018. “High Entropy Oxides for Reversible Energy Storage.”Nature Communications 9 (1): 3400.<br/>6. Lun, Zhengyan, et al. 2021. “Cation-Disordered Rocksalt-Type High-Entropy Cathodes for Li-Ion Batteries.” Nature Materials 20 (2): 214–21.<br/>7. Murdock, Beth E., et al. 2021. “A Perspective on the Sustainability of Cathode Materials Used in Lithium-ion Batteries.” Advanced Energy Materials, September, 2102028