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Li3RuO4 is an intriguing model system for investigating the importance of atomic superstructure in the absence of compositional changes in anion redox active cathode materials. Li3RuO4 exhibits both an ordered structure (O-Li3RuO4) and a disordered rocksalt (DRX) polymorph (D-Li3RuO4). The electrochemical performance of these two phases is very different; D-Li3RuO4 exhibits much larger first cycle capacity, with very significant capacity fade, whereas O-Li3RuO4 delivers much more consistent capacity, but the first cycle first cycle-capacity is significantly lower than in D-Li3RuO4 [1]. Despite these clear differences, experiment shows that the redox processes in the two phases are the same. It was noted that the differences in first cycle capacity could potentially be attributed to the superior kinetics of the DRX phase. Crucially, lithium transport in DRX materials is linked to short-range cation ordering [2], which has been identified but not characterised for D-Li3RuO4, and so the question of whether the lithium percolation networks of the disordered phase are superior to the ordered phase remains open. Additionally, short-range order has implications for oxygen redox with specific local coordination around oxygen ions dictating the nature of anion redox reactions [3]. In this work, we have characterised the short range order D-Li3RuO4 using a cluster expansion, and will present its implications for anion redox and electrochemical performance in comparison to O-Li3RuO4, revealing the role of long-range structure in controlling lithium transport, and the influence of local structure in determining the nature of redox.
[1] Li, H.; Ramakrishnan, S.; Freeland, J. W. et al., J. Am. Chem. Soc. 142, 8160−8173 (2020).
[2] Ji, H.; Urban, A.; Kitchaev, D. A. et al., Nat. Commun. 10, 592 (2019)
[3] Seo, D. H., Lee, J., Urban, A. et al., Nature Chem. 8, 692–697 (2016)
| Speaker Country | UK |
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