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Instruments / Technical Area	Publication Details	Published
I21-Resonant Inelastic X-ray Scattering (RIXS)	Covalency does not suppress O2 formation in 4d and 5d Li-rich O-redox cathodes Robert A. House , John-Joseph Marie , Joohyuk Park , Gregory J. Rees , Stefano Agrestini , Abhishek Nag , Mirian Garcia-Fernandez , Ke-Jin Zhou , Peter G. Bruce Nature Communications 12 DOI: 10.1038/s41467-021-23154-4 Diamond Proposal Number(s): [25589] Open Access Show Abstract ▼ Abstract: Layered Li-rich transition metal oxides undergo O-redox, involving the oxidation of the O2− ions charge compensated by extraction of Li+ ions. Recent results have shown that for 3d transition metal oxides the oxidized O2− forms molecular O2 trapped in the bulk particles. Other forms of oxidised O2− such as O22− or (O–O)n− with long bonds have been proposed, based especially on work on 4 and 5d transition metal oxides, where TM–O bonding is more covalent. Here, we show, using high resolution RIXS that molecular O2 is formed in the bulk particles on O2‒ oxidation in the archetypal Li-rich ruthenates and iridate compounds, Li2RuO3, Li2Ru0.5Sn0.5O3 and Li2Ir0.5Sn0.5O3. The results indicate that O-redox occurs across 3, 4, and 5d transition metal oxides, forming O2, i.e. the greater covalency of the 4d and 5d compounds still favours O2. RIXS and XAS data for Li2IrO3 are consistent with a charge compensation mechanism associated primarily with Ir redox up to and beyond the 5+ oxidation state, with no evidence of O–O dimerization.	May 2021
B18-Core EXAFS I21-Resonant Inelastic X-ray Scattering (RIXS)	Redox chemistry and the role of trapped molecular O2 in Li-rich disordered rocksalt oxyfluoride cathodes Ryan Sharpe , Robert A. House , Matt J. Clarke , Dominic Förstermann , John-Joseph Marie , Giannantonio Cibin , Ke-Jin Zhou , Helen Playford , Peter G. Bruce , M. Saiful Islam Journal Of The American Chemical Society DOI: 10.1021/jacs.0c10270 Diamond Proposal Number(s): [20363, 23889] Open Access Show Abstract ▼ Abstract: In the search for high energy density cathodes for next-generation lithium-ion batteries, the disordered rocksalt oxyfluorides are receiving significant attention due to their high capacity and lower voltage hysteresis compared with ordered Li-rich layered compounds. However, a deep understanding of these phenomena and their redox chemistry remains incomplete. Using the archetypal oxyfluoride, Li2MnO2F, we show that the oxygen redox process in such materials involves the formation of molecular O2 trapped in the bulk structure of the charged cathode, which is reduced on discharge. The molecular O2 is trapped rigidly within vacancy clusters and exhibits minimal mobility unlike free gaseous O2, making it more characteristic of a solid-like environment. The Mn redox process occurs between octahedral Mn3+ and Mn4+ with no evidence of tetrahedral Mn5+ or Mn7+. We furthermore derive the relationship between local coordination environment and redox potential; this gives rise to the observed overlap in Mn and O redox couples and reveals that the onset potential of oxide ion oxidation is determined by the degree of ionicity around oxygen, which extends models based on linear Li–O–Li configurations. This study advances our fundamental understanding of redox mechanisms in disordered rocksalt oxyfluorides, highlighting their promise as high capacity cathodes.	Dec 2020
I21-Resonant Inelastic X-ray Scattering (RIXS)	First-cycle voltage hysteresis in Li-rich 3d cathodes associated with molecular O2 trapped in the bulk Robert A. House , Gregory J. Rees , Miguel A. Pérez-Osorio , John-Joseph Marie , Edouard Boivin , Alex W. Robertson , Abhishek Nag , Mirian Garcia-Fernandez , Ke-Jin Zhou , Peter G. Bruce Nature Energy 137 DOI: 10.1038/s41560-020-00697-2 Diamond Proposal Number(s): [23889] Show Abstract ▼ Abstract: Li-rich cathode materials are potential candidates for next-generation Li-ion batteries. However, they exhibit a large voltage hysteresis on the first charge/discharge cycle, which involves a substantial (up to 1 V) loss of voltage and therefore energy density. For Na cathodes, for example Na0.75[Li0.25Mn0.75]O2, voltage hysteresis can be explained by the formation of molecular O2 trapped in voids within the particles. Here we show that this is also the case for Li1.2Ni0.13Co0.13Mn0.54O2. Resonant inelastic X-ray scattering and 17O magic angle spinning NMR spectroscopy show that molecular O2, rather than O22−, forms within the particles on the oxidation of O2− at 4.6 V versus Li+/Li on charge. These O2 molecules are reduced back to O2− on discharge, but at the lower voltage of 3.75 V, which explains the voltage hysteresis in Li-rich cathodes. 17O magic angle spinning NMR spectroscopy indicates a quantity of bulk O2 consistent with the O-redox charge capacity minus the small quantity of O2 loss from the surface. The implication is that O2, trapped in the bulk and lost from the surface, can explain O-redox.	Sep 2020
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
B18-Core EXAFS	Oxygen redox chemistry without excess alkali-metal ions in Na2/3[Mg0.28Mn0.72]O2 Urmimala Maitra , Robert A. House , James W. Somerville , Nuria Tapia-ruiz , Juan G. Lozano , Niccolo Guerrini , Rong Hao , Kun Luo , Liyu Jin , Miguel A. Pérez-osorio , Felix Massel , David M. Pickup , Silvia Ramos , Xingye Lu , Daniel E. Mcnally , Alan V. Chadwick , Feliciano Giustino , Thorsten Schmitt , Laurent C. Duda , Matthew R. Roberts , Peter G. Bruce Nature Chemistry 10, 288 - 295 DOI: 10.1038/nchem.2923 Diamond Proposal Number(s): [12559] Show Abstract ▼ Abstract: The search for improved energy-storage materials has revealed Li- and Na-rich intercalation compounds to have promise as a new class of high-capacity cathodes. They exhibit capacities in excess of what would be expected from alkali-ion removal/reinsertion charge compensated by the transition-metal ions. The additional capacity is provided through charge compensation by oxygen-redox chemistry and some oxygen loss. It has been reported previously that O-redox occurs in O-2p orbitals that interact with alkali-ions in the transition-metal and alkali-ion layers (i.e. O-redox occurs in compounds containing Li+ - O2p - Li+ interactions). Na2/3[Mg0.28Mn0.72]O2 exhibits excess capacity; here we show this is also due to O-redox, despite Mg2+ residing in the transition-metal (TM) layers rather than alkali-metal ions, demonstrating that excess alkali-metal ions are not required to activate O-redox. We also show that unlike the alkali-rich compounds, Na2/3[Mg0.28Mn0.72]O2 does not lose O. Extraction of alkali ions from the alkali and TM layers in the alkali-rich compounds results in severely underbonded oxygen promoting oxygen loss, whereas Mg2+ remains in Na2/3[Mg0.28Mn0.72]O2 stabilising oxygen.	Jan 2018

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