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Instruments / Technical Area	Publication Details	Published
I09-Surface and Interface Structural Analysis	Strategies of mitigating dissolution of solid electrolyte interphases in sodium‐ion batteries Le Anh Ma , Andrew J. Naylor , Leif Nyholm , Reza Younesi Angewandte Chemie International Edition DOI: 10.1002/anie.202013803 Diamond Proposal Number(s): [23159] Open Access Show Abstract ▼ Abstract: With emerging interest in sodium‐ion battery (SIB) technology due to its cost effectiveness and high earth abundance of sodium, the search for an optimised SIB system becomes more and more crucial. It is well known that the formation of a stable solid electrolyte interphase (SEI) at the anode in Na‐based systems is a challenge due to the higher solubility of the SEI components compared to in the lithium‐ion battery case. Our knowledge about the formation and dissolution of the SEI in SIBs is so far based on limited experimental data. The aim of the present research is therefore to enhance the understanding of the behaviour of the SEI in SIBs and shed more light on the influence of the electrolyte chemistry on the dissolution of the SEI. By conducting electrochemical tests including extended open circuit pauses, we study the SEI dissolution in different time domains. With this, it is possible to determine the extent of self‐discharge due to SEI dissolution during a specific time. Instead of using a conventional separator, β‐alumina is employed as a Na‐conductive membrane to avoid crosstalk between the working electrode and Na‐metal counter electrode. The SEI composition is monitored using synchrotron‐based soft X‐ray photoelectron spectroscopy (SOXPES). The electrochemical and XPS results show that the SEIs formed in the studied electrolyte systems have different stabilities. The relative capacity loss after a 50‐hour pause in the tested electrolyte systems can be up to 30%. Among three carbonate‐based solvent systems, NaPF 6 in ethylene carbonate: diethyl carbonate exhibits the most stable SEI. The addition of electrolyte additives improves the SEI stability in PC. The electrolyte is saturated with typical SEI species, NaF and Na 2 CO 3 , in order to oppose the dissolution of the SEI. Furthermore, the solubilities of the latter additives in the different solvent systems are determined by inductively coupled plasma – optical emission spectrometry.	Nov 2020
B18-Core EXAFS	Vacancy enhanced oxygen redox reversibility in P3-type magnesium doped sodium manganese oxide Na0.67Mg0.2Mn0.8O2 Eunjeong Kim , Le Anh Ma , David M. Pickup , Alan V. Chadwick , Reza Younesi , Philip Maughan , John T. S. Irvine , Robert Armstrong Acs Applied Energy Materials DOI: 10.1021/acsaem.0c01352 Diamond Proposal Number(s): [14239] Show Abstract ▼ Abstract: Lithium-rich layered oxides and sodium layered oxides represent attractive positive electrode materials exhibiting excess capacity delivered by additional oxygen redox activity. However, structural degradation in the bulk and detrimental reactions with the electrolyte on the surface often occur, leading to limited reversibility of oxygen redox processes. Here we present the properties of P3-type Na0.67Mg0.2Mn0.8O2 synthesized under both air and oxygen. Both materials exhibit stable cycling performance in the voltage range 1.8-3.8 V where the Mn3+/Mn4+ redox couple entirely dominates the electrochemical reaction. Oxygen redox activity is triggered for both compounds in the wider voltage window 1.8-4.3 V with typical large voltage hysteresis from non-bonding O 2p states generated by substituted Mg. Interestingly, for the compound prepared under oxygen, an additional reversible oxygen redox activity is shown 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 forming unpaired O 2p states independent of substituted elements but also in stabilising the P3 structure during charge with reduced structural transformation to the O’3 phase at the end of discharge. This study reveals the important role of vacancies in P3-type sodium layered oxides to increase energy density using both cationic and anionic redox processes.	Sep 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
I09-Surface and Interface Structural Analysis	Understanding charge compensation mechanisms in Na0.56Mg0.04Ni0.19Mn0.70O2 Le Anh Ma , Felix Massel , Andrew J. Naylor , Laurent-C. Duda , Reza Younesi Communications Chemistry 2 DOI: 10.1038/s42004-019-0227-z Diamond Proposal Number(s): [18974] Open Access Show Abstract ▼ Abstract: Sodium-ion batteries have become a potential alternative to Li-ion batteries due to the abundance of sodium resources. Sodium-ion cathode materials have been widely studied with particular focus on layered oxide lithium analogues. Generally, the capacity is limited by the redox processes of transition metals. Recently, however, the redox participation of oxygen gained a lot of research interest. Here the Mg-doped cathode material P2-Na0.56Mg0.04Ni0.19Mn0.70O2 is studied, which is shown to exhibit a good capacity (ca. 120 mAh/g) and high average operating voltage (ca. 3.5 V vs. Na+/Na). Due to the Mg-doping, the material exhibits a reversible phase transition above 4.3 V, which is attractive in terms of lifetime stability. In this study, we combine X-ray photoelectron spectroscopy, X-ray absorption spectroscopy and resonant inelastic X-ray scattering spectroscopy techniques to shed light on both, cationic and anionic contributions towards charge compensation.	Nov 2019

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