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15 items found (0 items not approved), displaying 1 to 10.[First/Prev] 1, 2 [Next/Last]

Instruments / Technical Area	Publication Details	Published
I21-Resonant Inelastic X-ray Scattering (RIXS)	Transition metal migration and O2 formation underpin voltage hysteresis in oxygen-redox disordered rocksalt cathodes Kit Mccoll , Robert A. House , Gregory J. Rees , Alexander G. Squires , Samuel W. Coles , Peter G. Bruce , Benjamin J. Morgan , M. Saiful Islam Nature Communications 13 DOI: 10.1038/s41467-022-32983-w Diamond Proposal Number(s): [29028] Open Access Show Abstract ▼ Abstract: Lithium-rich disordered rocksalt cathodes display high capacities arising from redox chemistry on both transition-metal ions (TM-redox) and oxygen ions (O-redox), making them promising candidates for next-generation lithium-ion batteries. However, the atomic-scale mechanisms governing O-redox behaviour in disordered structures are not fully understood. Here we show that, at high states of charge in the disordered rocksalt Li2MnO2F, transition metal migration is necessary for the formation of molecular O2 trapped in the bulk. Density functional theory calculations reveal that O2 is thermodynamically favoured over other oxidised O species, which is confirmed by resonant inelastic X-ray scattering data showing only O2 forms. When O-redox involves irreversible Mn migration, this mechanism results in a path-dependent voltage hysteresis between charge and discharge, commensurate with the hysteresis observed electrochemically. The implications are that irreversible transition metal migration should be suppressed to reduce the voltage hysteresis that afflicts O-redox disordered rocksalt cathodes.	Sep 2022
B18-Core EXAFS	Controlling iron versus oxygen redox in the layered cathode Na0.67Fe0.5Mn0.5O2: mitigating voltage and capacity fade by Mg substitution Edouard Boivin , Robert A. House , John-Joseph Marie , Peter G. Bruce Advanced Energy Materials 239 DOI: 10.1002/aenm.202200702 Open Access Show Abstract ▼ Abstract: Layered oxides for Na-ion batteries containing Fe have attracted strong interest mainly due to their low cost. However, full oxidation of Fe3+ to Fe4+ is rarely seen before O-redox sets in and is typically accompanied by voltage and capacity fade on cycling. On charging P2-Na0.67[Fe0.5Mn0.5]O2, Fe3+ is oxidized to only ≈Fe3.3+ before the onset of O-redox. O-redox occurs when the Na content is sufficiently low (Na ≈0.3) to permit the transition from P-type to O-type stacking, thus enabling Fe3+ migration to the Na layer. Fe3+ migration generates cation vacancies in the transition metal layer, forming □-O-□ configurations, which trigger the onset of O-redox. In contrast, doping this material with Mg2+ to form P2-Na0.67[Fe0.25Mn0.6Mg0.15]O2 allows full oxidation of Fe3+ to Fe4+ before the Na content is low enough to favor O-type stacking. During O-redox, Mg2+ is displaced into the Na layers instead of Fe. Mg substitution enables greater reversibility of the Fe3+/Fe4+ redox couple and significantly suppresses Fe migration, which is responsible for the voltage and capacity fade observed for P2-Na0.67Fe0.5Mn0.5O2.	Jun 2022
E02-JEM ARM 300CF	Direct imaging of oxygen shifts associated with the oxygen redox of Li-rich layered oxides Weixin Song , Miguel A. Pérez-Osorio , John-Joseph Marie , Emanuela Liberti , Xiaonan Luo , Colum O'Leary , Robert A. House , Peter G. Bruce , Peter D. Nellist Joule 3 DOI: 10.1016/j.joule.2022.04.008 Diamond Proposal Number(s): [22479] Open Access Show Abstract ▼ Abstract: Li-rich metal oxides, such as Li1.2Ni0.13Mn0.54Co0.13O2, can deliver high specific capacities because of the redox of lattice O2− in addition to the cations. Observing oxygen distortions is key to understand the redox process. Electron ptychography is a phase-reconstruction method in 4D scanning transmission electron microscopy, providing atomic-resolution phase images with high signal-to-noise ratio and dose efficiency. Herein, we use electron ptychography to image the oxygen shift in Li1.2Ni0.13Mn0.54Co0.13O2 during the first cycle. The picometer-scale precision measurement shows distinct oxygen shifts in the bulk and surface after charging and compares with various theoretical anionic redox models. The shift after discharging is not seen to recover in the bulk accounting for voltage hysteresis; however, it recovers close to the surface, although with a phase change. We suggest that Li1.2Ni0.13Mn0.54Co0.13O2 proceeds distinct oxygen redox in the bulk and surface. The altered oxygen sublattice after first cycle potentially explains the changed voltage profiles of following cycles.	May 2022
I21-Resonant Inelastic X-ray Scattering (RIXS)	Detection of trapped molecular O2 in a charged Li-rich cathode by Neutron PDF Robert A. House , Helen Y. Playford , Ronald I. Smith , Jennifer Holter , Ian Griffiths , Ke-Jin Zhou , Peter G. Bruce Energy & Environmental Science 114 DOI: 10.1039/D1EE02237G Diamond Proposal Number(s): [25589] Open Access Show Abstract ▼ Abstract: Oxidation and reduction of the oxide ions in the bulk of cathode materials is a potential route towards increasing the energy density of Li-ion batteries. Here, we present neutron PDF data which demonstrates the presence of short 1.2 Å O–O distances in a charged O-redox cathode material, corresponding to the bond length of molecular O2. This was achieved by collecting our data close to absolute zero (2 K), suppressing thermal motion which may have obscured detection by PDF previously. This direct detection of molecular O2 trapped in the material by diffraction complements the X-ray spectroscopy studies by e.g. RIXS while avoiding issues of possible beam damage as well as being a bulk average technique.	Dec 2021
B18-Core EXAFS	P2–Na2/3Mg1/4Mn7/12Co1/6O2 cathode material based on oxygen redox activity with improved first-cycle voltage hysteresis Nuria Tapia-Ruiz , Cindy Soares , James W. Somerville , Robert A. House , Juliette Billaud , Matthew R. Roberts , Peter G. Bruce Journal Of Power Sources 506 DOI: 10.1016/j.jpowsour.2021.230104 Show Abstract ▼ Abstract: The recent report of P2–Na2/3Mg0.28Mn0.72O2 (P2-NMM) demonstrated the possibility of utilizing the oxygen redox couple in a layered oxide cathode without the need for alkali ions or vacancies in the transition metal layer. In this work, we report the synthesis of a new P2-type compound, Na2/3Mg1/4Mn7/12Co1/6O2 (P2-NMMC), which exhibits reversible specific capacities as high as 173 mAh g−1 and an improvement of the first cycle voltage hysteresis over P2-NMM. The material was characterised using a combination of ex-situ and operando techniques including X-ray diffraction (XRD), differential electrochemical mass spectrometry (DEMS) and X-ray spectroscopy (XAS) to identify potential sources for this improvement.	Sep 2021
B18-Core EXAFS	Li2NiO2F a new oxyfluoride disordered rocksalt cathode material Xiaoyu Xu , John-Joseph Marie , Gregory J Rees , Liquan Pi , Chen Gong , Shengda Pu , Robert A. House , Alexander W. Robertson , Peter G. Bruce Journal Of The Electrochemical Society DOI: 10.1149/1945-7111/ac1be1 Open Access Show Abstract ▼ Abstract: Lithium-rich disordered rocksalts such as Li1.3Nb0.3Mn0.4O2 and Li2MnO2F are being investigated as high energy density cathodes for next generation Li-ion batteries. They can support the (de)intercalation of lithium ions over large compositional ranges while preserving the same overall structure. Here, we present a new Ni-rich oxyfluoride cathode, Li2NiO2F, with a disordered rocksalt structure. Li2NiO2F and can deliver a discharge capacity of 200 mAh g-1 at an average voltage of 3.2 V.	Aug 2021
I21-Resonant Inelastic X-ray Scattering (RIXS)	Trapped oxygen molecules provide an energy storage mechanism in lithium-ion battery cathodes Robert A. House Diamond Proposal Number(s): [23889] Show Abstract ▼ Abstract: Lcation keywords: Li-ion Batteries; Cathode Materials; Resonant Inelastic X-ray Scattering ithium-rich cathode materials exhibit a pronounced drop in voltage between the charging and discharging processes (known as ‘voltage hysteresis’) that limits the available energy density. This needs to be overcome for them to be used in next-generation battery applications. In lithium-rich materials, the charging and discharging processes are accompanied by chemical changes to the oxide ions that form part of the cathode’s crystal structure. The reversibility of these chemical processes is critical in determining how well a cathode material functions. The voltage hysteresis seen in the lithium-rich materials implies the oxide ions undergo chemical changes that are not fully reversible, but the mechanism behind this was not well understood. Researchers used the Resonant Inelastic X-ray Scattering (RIXS) beamline (I21) at Diamond Light Source to study the chemical changes to the oxide ions at different stages of the battery charge-discharge cycle using RIXS. The measurements acquired from this technique offer a direct probe of the electronic structure on oxygen. Using high-resolution RIXS, they detected underlying vibrational fine structure that revealed the identity of the oxidised oxide ions as molecular oxygen. These oxygen molecules are trapped within the charged cathode material, but they can be reduced back to oxide ions on discharge. However, this process takes place at a lower voltage, giving rise to the voltage hysteresis. Researchers can now devise strategies to suppress the release of oxygen, or prevent its formation, in next-generation lithium-ion (Li-ion) batteries with higher energy density. Higher energy density batteries will extend the driving range of electric vehicles and increase the battery life of portable electronics between charges.	Jul 2021
B18-Core EXAFS	Bulk O2 formation and Mg displacement explain O-redox in Na0.67Mn0.72Mg0.28O2 Edouard Boivin , Robert A. House , Miguel A. Pérez-Osorio , John-Joseph Marie , Urmimala Maitra , Gregory J. Rees , Peter G. Bruce Joule 5, 1267 - 1280 DOI: 10.1016/j.joule.2021.04.006 Show Abstract ▼ Abstract: O-redox in compounds with Li on the transition-metal layers (TML) has recently been attributed to the formation of molecular O2 on charge, trapped in the lattice. Here, we show that a similar process occurs for P2-Na0.67[Mn0.72Mg0.28]O2, which contains Mg2+ on the TML. The molecular O2 is identified by high-resolution RIXS and quantified by magnetometry, showing that it equates to the charge passed. This O2 is trapped in voids that are formed by Mg2+ out-of-plane displacement and Mn4+ in-plane disordering and is then reduced on discharge associated with a large voltage hysteresis. In contrast to compounds containing Li+ in the TML, in which the honeycomb ordering and the high-voltage plateau are irreversibly lost after the first cycle, in P2-Na0.67[Mn0.72Mg0.28]O2, the plateau reappears partially on the second charge due to the partial reversibility of Mn in-plane and Mg out-of-plane migration and the local reformation of the honeycomb ordering.	May 2021
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

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