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Instruments / Technical Area	Publication Details	Published
I11-High Resolution Powder Diffraction	Importance of superstructure in stabilizing oxygen redox in P3-Na0.67Li0.2Mn0.8O2 Eun Jeong Kim , Philip A. Maughan , Euan N. Bassey , Raphaële J. Clément , Le Anh Ma , Laurent C. Duda , Divya Sehrawat , Reza Younesi , Neeraj Sharma , Clare P. Grey , Robert Armstrong Advanced Energy Materials DOI: 10.1002/aenm.202102325 Diamond Proposal Number(s): [26699] Open Access Show Abstract ▼ Abstract: Activation of oxygen redox represents a promising strategy to enhance the energy density of positive electrode materials in both lithium and sodium-ion batteries. However, the large voltage hysteresis associated with oxidation of oxygen anions during the first charge represents a significant challenge. Here, P3-type Na0.67Li0.2Mn0.8O2 is reinvestigated and a ribbon superlattice is identified for the first time in P3-type materials. The ribbon superstructure is maintained over cycling with very minor unit cell volume changes in the bulk while Li ions migrate reversibly between the transition metal and Na layers at the atomic scale. In addition, a range of spectroscopic techniques reveal that a strongly hybridized Mn 3d–O 2p favors ligand-to-metal charge transfer, also described as a reductive coupling mechanism, to stabilize reversible oxygen redox. By preparing materials under three different synthetic conditions, the degree of ordering between Li and Mn is varied. The sample with the maximum cation ordering delivers the largest capacity regardless of the voltage windows applied. These findings highlight the importance of cationic ordering in the transition metal layers, which can be tuned by synthetic control to enhance anionic redox and hence energy density in rechargeable batteries.	Dec 2021
B18-Core EXAFS	Activation of anion redox in P3 structure cobalt-doped sodium manganese oxide via introduction of transition metal vacancies Eun Jeong Kim , Kenza Mofredj , David M. Pickup , Alan V. Chadwick , John T. S. Irvine , A. Robert Armstrong Journal Of Power Sources 481 DOI: 10.1016/j.jpowsour.2020.229010 Diamond Proposal Number(s): [14239] Show Abstract ▼ Abstract: Additional capacity delivered by oxygen redox activity may in principle represent a means of enhancing the electrochemical performance of layered sodium transition metal oxides. However, irreversible structural changes occurring during cycling typically cause significant capacity fade with limited reversibility of oxygen redox processes. Here, P3-structure Na0.67Co0.2Mn0.8O2 was synthesised under two different reaction conditions. Both materials exhibit very stable cycling performance in the voltage range 1.8–3.8 V where the redox couples of transition metals entirely dominate the electrochemical reaction. For the compound prepared under more oxidising conditions, anion redox activity is triggered in the wider voltage window 1.8–4.4 V in a reversible manner with exceptionally small voltage hysteresis (20 mV). The presence of vacancies in the transition metal layers is shown to play a critical role not only in generating unpaired O 2p states but also in stabilising the crystal structure in the high voltage region.	Nov 2020
B18-Core EXAFS	Oxygen redox activity through a reductive coupling mechanism in the P3-type nickel-doped sodium manganese oxide Eun Jeong Kim , Le Anh Ma , Laurent C. Duda , David M. Pickup , Alan V. Chadwick , Reza Younesi , John T. S. Irvine , A. Robert Armstrong Acs Applied Energy Materials DOI: 10.1021/acsaem.9b02171 Diamond Proposal Number(s): [14239] Show Abstract ▼ Abstract: Increasing dependence on rechargeable batteries for energy storage calls for the improvement of energy density of batteries. Toward this goal, introduction of positive electrode materials with high voltage and/or high capacity is in high demand. The use of oxygen chemistry in lithium and sodium layered oxides has been of interest to achieve high capacity. Nevertheless, a complete understanding of oxygen-based redox processes remains elusive especially in sodium ion batteries. Herein, a novel P3-type Na0.67Ni0.2Mn0.8O2, synthesized at low temperature, exhibits oxygen redox activity in high potentials. Characterization using a range of spectroscopic techniques reveals the anionic redox activity is stabilized by the reduction of Ni, because of the strong Ni 3d–O 2p hybridization states created during charge. This observation suggests that different route of oxygen redox processes occur in P3 structure materials, which can lead to the exploration of oxygen redox chemistry for further development in rechargeable batteries.	Jan 2020

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