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Instruments / Technical Area	Publication Details	Published
B18-Core EXAFS	The role of Ni and Co in suppressing O‐loss in Li‐rich layered cathodes Edouard Boivin , Niccolo Guerrini , Robert A. House , Juan G. Lozano , Liyu Jin , Gregory J. Rees , James W. Somerville , Christian Kuss , Matthew R. Roberts , Peter G. Bruce Advanced Functional Materials DOI: 10.1002/adfm.202003660 Open Access Show Abstract ▼ Abstract: Lithium‐rich transition metal cathodes can deliver higher capacities than stoichiometric materials by exploiting redox reactions on oxygen. However, oxidation of O2− on charging often results in loss of oxygen from the lattice. In the case of Li2MnO3 all the capacity arises from oxygen loss, whereas doping with Ni and/or Co leads to the archetypal O‐redox cathodes Li[Li0.2Ni0.2Mn0.6]O2 and Li[Li0.2Ni0.13Co0.13Mn0.54]O2, which exhibit much reduced oxygen loss. Understanding the factors that determine the degree of reversible O‐redox versus irreversible O‐loss is important if Li‐rich cathodes are to be exploited in next generation lithium‐ion batteries. Here it is shown that the almost complete eradication of O‐loss with Ni substitution is due to the presence of a less Li‐rich, more Ni‐rich (nearer stoichiometric) rocksalt shell at the surface of the particles compared with the bulk, which acts as a self‐protecting layer against O‐loss. In the case of Ni and Co co‐substitution, a thinner rocksalt shell forms, and the O‐loss is more abundant. In contrast, Co doping does not result in a surface shell yet it still suppresses O‐loss, although less so than Ni and Ni/Co doping, indicating that doping without shell formation is effective and that two mechanisms exist for O‐loss suppression.	Aug 2020
I21-Resonant Inelastic X-ray Scattering (RIXS)	Superstructure control of first-cycle voltage hysteresis in O-redox cathodes Robert A. House , Urmimala Maitra , Miguel A. Pérez-Osorio , Juan G. Lozano , Liyu Jin , James W. Somerville , Laurent C. Duda , Abhishek Nag , Andrew Walters , Ke-Jin Zhou , Matthew R. Roberts , Peter G. Bruce Nature DOI: 10.1038/s41586-019-1854-3 Show Abstract ▼ Abstract: Alkali-rich transition metal oxide intercalation cathodes can increase the energy density of Li and Na-ion batteries by storing charge on the oxide and transition metal (TM) ions1–10. The high voltage associated with oxidation of O2- on the first charge is not recovered on discharge, resulting in significantly reduced energy density11. Displacement of TM ions from the TM to alkali metal layers has been proposed to explain the first cycle voltage loss9,12–16. By comparing two closely related intercalation cathodes, Na0.75[Li0.25Mn0.75]O2 and Na0.6[Li0.2Mn0.8]O2, we show that the first cycle voltage hysteresis is determined by the superstructure, specifically the local ordering of Li/TM ions in the TM layers. The honeycomb superstructure of Na0.75[Li0.25Mn0.75]O2, present in almost all O-redox compounds, is lost on charging, driven, in part, by formation of molecular O2 inside the solid. The O2 molecules are cleaved on discharge reforming O2-, but the Mn ions have migrated in the plane changing the coordination around O2- significantly lowering the voltage on discharge (hysteresis). The ribbon superstructure in Na0.6[Li0.2Mn0.8]O2 inhibits Mn disorder and hence O2 formation, suppressing hysteresis and promoting stable electron holes on O2- which are revealed by XAS. The results show that voltage hysteresis can be avoided in O-redox cathodes by forming materials with a superstructure (cation ordering) in the TM layers that suppresses TM migration.	Dec 2019
B18-Core EXAFS I09-Surface and Interface Structural Analysis	What triggers oxygen loss in oxygen redox cathode materials? Robert A. House , Urmimala Maitra , Liyu Jin , Juan G. Lozano , James W. Somerville , Nicholas H. Rees , Andrew J. Naylor , Laurent C. Duda , Felix Massel , Alan V. Chadwick , Silvia Ramos , David M. Pickup , Daniel E. Mcnally , Xingye Lu , Thorsten Schmitt , Matthew R. Roberts , Peter G. Bruce Chemistry Of Materials DOI: 10.1021/acs.chemmater.9b00227 Diamond Proposal Number(s): [14239, 20870] Open Access Show Abstract ▼ Abstract: It is possible to increase the charge capacity of transition metal oxide cathodes in alkali-ion batteries by invoking redox reactions on the oxygen. However, oxygen loss often occurs. To explore what affects oxygen loss in oxygen redox materials, we have compared two analogous Na-ion cathodes, P2-Na0.67Mg0.28Mn0.72O2 and P2-Na0.78Li0.25Mn0.75O2. On charging to 4.5 V, >0.4 e- are removed from the oxide ions of these materials, but neither compound exhibits oxygen loss. Li is retained in P2-Na0.78Li0.25Mn0.75O2 but displaced from the transition metal to the alkali metal layers, showing that vacancies in the transition metal layers, which also occur in other oxygen redox compounds that exhibit oxygen loss such as Li[Li0.2Ni0.2Mn0.6]O2, is not a trigger for oxygen loss. On charging at 5 V, P2-Na0.78Li0.25Mn0.75O2 exhibits oxygen loss whereas P2-Na0.67Mg0.28Mn0.72O2 does not. Under these conditions both Na+ and Li+ are removed from P2-Na0.78Li0.25Mn0.75O2 resulting in underbonded oxygen (fewer than 3 cations coordinating oxygen) and surface localised O loss. In contrast, for P2-Na0.67Mg0.28Mn0.72O2, oxygen remains coordinated by at least 2 Mn4+ and 1 Mg2+ ions, stabilising the oxygen and avoiding oxygen loss.	Apr 2019

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