LiNiO2 as a high-entropy functional material
Research Associate
The 2015 discovery of entropy-stabilized transition-metal oxides, such as Mg0.2Co0.2Ni0.2Cu0.2Zn0.2O, [2] has opened a new avenue for synthesizing materials with versatile and highly tunable properties [3]. It only took a few years to realize that such systems can find diverse technological applications, including but not limited to energy storage and catalysis [4]. While the on-going research in the field is currently focused more on exploiting chemical disorder, I will discuss the surprising possibility of high-entropy physics in a prototypical battery cathode material LiNiO2, which is nominally pure in terms of its chemical composition. Based on both experimental evidence and our electronic structure theoretical calculations, I will argue that LiNiO2 presents a rare example of an electronically disordered system, with contributing spin, charge, and orbital degrees of freedom on nickel as well as oxygen ions. In the light of the aforementioned stabilizing effect of entropy in functional materials, our findings explain the outstanding functional characteristics of LiNiO2, as compared to similar cathode materials. The LiNiO2 story showcases how insights from fundamental solid-state physics research can help advance technology.
[1] 鈥淟iNiO2 as a high-entropy charge- and bond-disproportionated glass鈥�, Kateryna Foyevtsova, Ilya Elfimov, Joerg Rottler, and George A. Sawatzky, Phys. Rev. B 100, 165104 (2019).
[2] 鈥淓ntropy-stabilized oxides鈥�, C. M. Rost et al., Nat. Commun. 6, 8485 (2015).
[3] 鈥淥rder emerging from disorder鈥�, Nita Dragoe and David B茅rardan, Science 366, 573-574 (2019).
[4] 鈥淗igh-entropy energy materials: challenges and new opportunities鈥�, Y. Ma et al., Energy Environ. Sci. (2021).