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Acta Cryst. (2014). A70, C354
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Sodium-ion batteries have attracted attention in recent years because of the natural abundance of sodium compared to lithium, making them particularly attractive in applications such as large-scale grid storage where low cost and sustainability, rather than light weight is the key issue [1]. Several materials have been suggested as cathodes but far fewer studies have been done on anode materials and, because of the reluctance of sodium to intercalate into graphite, the anode material of choice in commercial lithium-ion batteries, the anode represents a significant challenge to this technology. Materials which form alloys with sodium, particularly tin and antimony, have been suggested as anode materials; their ability to react with multiple sodium ions per metal-atom give potential for high gravimetric capacities[2]. However, relatively little is known about the reaction mechanism in the battery, primarily due to drastic reduction in crystallinity during (dis)charging conditions, but also because the structures formed on electrochemical cycling may not be alloys known to exist under ambient conditions. In this study, we present a study of antimony as an anode in sodium-ion batteries, using in situ pair distribution function (PDF) analysis combined with ex situ solid-state nuclear magnetic resonance studies. PDF experiments were performed at 11-ID-B, APS using the AMPIX electrochemical cell [3], cycling against sodium metal. Inclusion of diffuse scattering in analysis is able to circumvent some of the issues of crystallinity loss, and gain information about the local structure in all regions, independent of the presence of long-range order in the material. This approach has been used to probe local correlations in previously uncharacterised regions of the electrochemical profile and analyse phase progression over the full charge cycle. This analysis has been linked with ex situ 23Na solid-state NMR experiments to examine the local environment of the sodium; these show evidence of known NaxSb phases but indicate additional metastable phases may be present at partial discharge.

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Acta Cryst. (2014). A70, C357
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A fundamental understanding of an electrode material requires the elucidation of its phase transformation mechanism during charge and discharge. Ex situ methods, which are carried out under equilibrium condition, have been widely used in charactering the thermodynamic phases at different states of charge, from which a thermodynamic phase transformation pathway can be constructed. However, ex situ measurements do not always reflect the process occurred in an operating battery as the non-equilibrium operating condition might result in deviations from the thermodynamic process, especially for high-rate materials, such as LiFePO4, which is predicted to exhibit a fundamentally different phase transformation process at high rates [1,2]. To probe the process at high rate, an in situ method with reasonable temporal resolution must be employed. In this work, the high rate galvanostatic cycling process of LiFePO4 nanoparticle electrode in a customised AMPIX cell [3] was investigated in situ by time-resolved synchrotron X-ray powder diffraction. Formation of continuous non-equilibrium solid solution phases between LiFePO4 and FePO4 was observed at 10 C rate. The in situ diffraction patterns were analysed by a refinement strategy that accounts for the asymmetrical diffraction peak profiles due to Li composition variations.

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Acta Cryst. (2014). A70, C1538
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Carbon capture and storage (CCS) applications offer a plausible solution to the urgent need for a carbon neutral energy source from stationary sources, including power plants and industrial processes. The most mature technology for post-combustion capture currently uses a liquid sorbent, amine scrubbing. However, with the existing technology, a large amount of heat is required for the regeneration of the liquid sorbent, which introduces a substantial energy penalty. Operation at higher temperatures could reduce this energy penalty by allowing the integration of waste heat back into the power cycle. New solid absorbents for use at intermediate to high temperatures, such as CaO, have shown promise in pilot plant studies, but are still far from ideal due to their poor capacity retention upon successive cycling. This presentation will describe our studies aimed at rationally selecting and designing materials for carbon capture and storage applications. We use ab initio calculations of oxide materials from the Materials Project database1 in an effort to screen for novel materials with optimal thermodynamic and kinetic properties for CO2 looping applications. From the determination of a material's optimised structure and ground state energy we have then constructed a screening routine for materials within the database based on simulating their carbonation equilibria and phase stability under differing atmospheric concentrations of CO2. A number of promising materials were identified from the screening, and we are currently investigating their properties experimentally, by using a combination of methods (including thermogravimetric analysis, in situ x-ray diffraction and microscopy). In this way we are able to assess the validity of the screening methodology, and use the insights afforded by experimental studies to iteratively improve the entire process.
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