58 59 D I A M O N D L I G H T S O U R C E A N N U A L R E V I E W 2 0 2 2 / 2 3 D I A M O N D L I G H T S O U R C E A N N U A L R E V I E W 2 0 2 2 / 2 3 Developing a deeper understanding of electrodematerials for sodium-ion batteries Energy Storage – Energy – Physical Chemistry – Energy Materials – Chemistry – Material Science – Nanoscience/Nanotechnology Various materials can be used as electrodes in sodium-ion batteries (SIBs), and a comprehensive understanding of their charge storage mechanisms is essential for SIB development. Researchers from the Christian-Albrecht University of Kiel, in Germany, used X-ray Absorption Spectroscopy (XAS) on Diamond’s B18 beamline as part of a rigorous study of the sodium storage properties of ultra-small Fe 3 S 4 nanoparticles. This material exhibits excellent electrochemical performance as an anode material for SIBs. Previous research using X-ray diffraction and Total Scattering (Pair Distribution Function analysis) had shown different structural phase transformations during the discharge and charge of the anode material. For a more detailed understanding, the researchers needed to analyse the local structure around the elements Fe and S and their oxidation states, in the pristine nanocrystalline material and during charging and discharging. Such element-specific information, combined with other techniques ( e.g. , to determine the crystallographic structure), can yield important insights into the reaction mechanism of a battery material during operation and allow optimisation of battery cells, e.g. , by tailoring materials properties or by adjusting cut-off potentials. B18 provides high-quality XAS data, which allow precise and reliable determination of changes at the K-edges and yield fantastic k space signal with high spectral resolution. During their experiments, the team gathered X-ray Absorption Near Edge Structure (XANES) spectra at the Fe and S K-edges (see figure) and Extended X-ray Absorption Fine Structure (EXAFS) spectra at the Fe K-edge. Their results showed that the Na storage mechanism of this anode material can be attributed to cationic redox chemistry involving Fe. The experiments revealed the oxidation states of both elements at specific discharge/charge voltages. Using this information in combination with findings from other techniques (multi-method analysis), the researchers were able to explain the long-term cycle stabilities of Na/Fe 3 S 4 cells during cycling to different lower cut-off potentials. XANES and EXAFS experiments yield insights into sodium storage mechanisms that are important for understanding and developing other electrode (anode and cathode) materials ex situ and for testing battery cells in operando during galvanostatic or potentiostatic measurements. The investigation of fundamental redox reactions in battery chemistry is a highly relevant topic to understand degradation reactions. Such studies can be used to find root causes for cell failure, precisely adjust battery cell limits and find optimal cycling conditions to improve the electrochemical performances and battery lifetime. Related publication: Hartmann, F. et al. Understanding sodium storage properties of ultra- small Fe 3 S 4 nanoparticles - a combined XRD, PDF, XAS and electrokinetic study. Nanoscale 14,7 : 2696-2710 (2022). DOI:10.1039/D1NR06950K Funding acknowledgement: Financial support by the State of Schleswig-Holstein Corresponding authors: ProfWolfgang Bensch, Christian-Albrechts University,
[email protected] Felix Hartmann, Christian-Albrechts University,
[email protected] Spectroscopy Group Beamline B18 The first electrochemical discharge profile of the anode material nano-Fe 3 S 4 vs Na + /Na in a sodium-ion battery cell is divided into three steps (top). X-Ray Absorption Near Edge Structure (XANES) spectra at the Fe (bottom right) and S K-edges (bottom left) were obtained at Diamond Light Source (beamline B18) after uptake of certain Na amounts into the anode material and reveal the cationic redox chemistry during Na storage, which involves Fe 3+ , Fe 2+ and Fe 0 products, while the oxidation state of Sulphur remains -2. Investigating fungus-plant-soil interactions using synchrotron techniques Plant Science – Life Sciences & Biotech Soil is the largest terrestrial carbon pool, larger than plant and atmospheric pools combined. However, we have very little understanding of what is happening in the soil. Because soil is opaque, it is challenging to unravel intricate plant-soil-microbiome relationships. An increased understanding of these relationships will have profound implications for current agricultural practices. The soil microbiome, which includes fungi, is one of the largest compartments of the soil carbon pool. Phosphorus is essential for plant growth; however, mineral phosphorus resources are sparse and unevenly distributed across the world. Mycorrhizal fungi form symbiotic relationships with plants, acquiring phosphorus from distant sources and providing it to plants in return for carbon. Engaging in these mutualisms increases the total available nutrient pool for plants. However, little is known about how mycorrhizal fungi colonise soil pore-space, and models of phosphorus uptake enhanced by mycorrhizal fungi are poorly validated. A team of researchers imaged soil and fungal structures in 3D and used X-ray Fluorescence Spectroscopy (XRF) coupled with X-ray Absorption Near Edge Structure (XANES) at beamline I18 to study the chemical impacts of the presence of mycorrhizal fungi in the soil. They also used the X-ray Computed Tomography (XCT) beamline at I13 to study how these plant-fungi relationships work in the soil, beyond what can be observed with the naked eye. The XCT results helped them to understand where mycorrhizal fungi are predominantly present. Then they coupled this with XRF and XANES to understand the nature and impacts of mycorrhizal fungus and preferential uptake and mechanisms. Finally, they used advanced image analysis tools to correlate all imaging results and do further quantitative correlative analysis. Using the analysis tool suite, they were able to i) uncover highly detailed subtleties in the preferential presence of mycorrhizal fungi in the soil previously not shown ( e.g. organic matter, ‘clay fraction’, and soil mineralogy), and ii) put tight constraints on mycorrhizal fungus phosphorus uptake models. By employing correlative imaging, they were able to tighten this value down compared to previous macroscopic studies. This study showed for the first time that it is possible to visualise mycorrhizal fungus networks in 3D within soil using synchrotron X-ray Computed Tomography, albeit as yet only in the soil pore-spaces. In order to reduce the need to fertilise crops with phosphorus, there is a requirement to understand and establish alternatives for plant phosphorus acquisition. Symbiotic mycorrhizal fungi are an alternative as a soil treatment, but it is often unclear howmuch and how they can help with plant phosphorus uptake as all processes occur on very small (~1 micron) scales. Thus, it is important to do pore-scale structural and chemical imaging that underpins nutrient uptake and movement models. These models will then allow strategies for the most efficient use of mycorrhizal soil treatments to be found. Related publication: Keyes, S. et al. Multimodal correlative imaging and modelling of phosphorus uptake from soil by hyphae of mycorrhizal fungi. New Phytologist 234 , 688- 703 (2022). DOI: 10.1111/nph.17980 Funding acknowledgement: ERC Consolidator grant DIMR to Tiina Roose Corresponding authors: Prof Tiina Roose, University of Southampton,
[email protected] Dr Arjen van Veelen, Los Alamos National Laboratory,
[email protected] Spectroscopy Group Beamline I18 (and I13-2 from the Imaging andMicroscopy Group) The combination of synchrotron X-ray Computed Tomography (SR-XCT) and synchrotron X-ray Fluorescence (SR-XRF) imaging. By utilizing both SR-XCT and SR-XRF, we were able to elucidate structural- functional relationships and intricacies for mycorrhizal fungi in soils in situ. The figure above is showing the preferential interaction of mycorrhizal hyphae with organic matter rich in both organic phosphorus and sulphur, identified via X-ray Absorption Near Edge Structure (XANES).