Chairs
Dr Stephen Hull, The ISIS Facility, UK
Dr Stephen Hull, The ISIS Facility, UK
Dr Stephen Hull completed his PhD in Physics at the University of Reading in 1985, followed by a Postdoctoral Researcher position held jointly between the Clarendon Laboratory, University of Oxford and the Harwell Laboratory, UK Atomic Energy Authority. In 1988, he joined the Crystallography Group of the ISIS Facility, as Instrument Scientist on the Polaris powder diffractometer. At ISIS, he established a research programme investigating structure-property relationships within ionically conducting solids, focussing on both ‘model’ superionic compounds and more technologically relevant materials for fuel cell and battery applications. In 2012 he became Head of the ISIS Crystallography Group, with responsibility for a suite of 9 diffraction and imaging instruments, which perform experiments across a diverse range of scientific research in the fields of chemistry, physics, earth science, materials science and engineering.
13:30-14:00
Ion migration mechanisms in glassy solid electrolytes at low temperatures
Professor Donald Siegel, University of Michigan, USA
Abstract
Sulphur-based glasses are promising candidates for use as solid electrolytes in Li-based batteries. Nevertheless, due to their amorphous structure, the atomic-scale mechanisms that underlie Li-ion conductivity in these systems are challenging to characterize. The present study employs ab initio molecular dynamics to predict the local structure and migration processes in the prototype Li-ion conducting glass, 75Li2S–25P2S5. A model of the amorphous structure was generated and shown to closely match the measured neutron pair distribution function. Lithium migration is observed to occur via a complex mechanism that combines concerted motion of lithium ions with large, quasi-permanent rotational displacements of the PS43- tetrahedra. This latter effect, commonly referred to as the ‘paddlewheel’ mechanism, is most commonly observed in lower-density crystalline phases that are stable only at elevated-temperatures. Unlike these crystalline analogues, in the glass, the present calculations indicate that paddlewheel dynamics contribute to Li-ion mobility at temperatures as low as 300 K. Paddlewheel contributions are confirmed through analyses of spatial, temporal, vibrational, and energetic correlations with Li motion. Furthermore, the dynamics in the glass are shown to differ from those in the stable crystalline phase (-Li3PS4), where contributions from anion reorientations are negligible and the conductivity is much smaller. These data imply that glasses based on complex anions, and in which covalent network formation is minimized, have the potential to exhibit paddlewheel dynamics at low temperature. Glasses that satisfy these requirements may be fertile ground in the search for new solid electrolytes.
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Professor Donald Siegel, University of Michigan, USA
Professor Donald Siegel, University of Michigan, USA
Don Siegel is Professor and Associate Chair for Graduate Education in the Mechanical Engineering Department at the University of Michigan, with courtesy appointments in Materials Science & Engineering and Applied Physics. His research targets the development of energy storage materials and lightweight alloys, primarily for applications in the transportation sector. Prior to joining UM, he was a Technical Expert at Ford Research and Advanced Engineering. Don has authored more than 85 publications, delivered approximately 105 invited lectures, and has been awarded several patents related to energy storage. He is a recipient of the NSF Career Award, Department of Energy-Secretary of Energy’s Achievement Award, and an NAE Gilbreth Lectureship. Professor Siegel received a PhD in Physics from the University of Illinois at Urbana-Champaign, with postdoctoral training at Sandia National Laboratories and at the U.S. Naval Research Lab. During 2015–2016 year he was a VELUX Visiting Professor in the Department of Energy Conversion and Storage at the Technical University of Denmark.
14:15-14:45
Interplay of site-disorder, interplay and ionic conductivity of superionic conductors: insights from atomistic computer simulations
Professor Karsten Albe, Technische Universität Darmstadt, Germany
Abstract
Glassy, glass–ceramic, and crystalline lithium thiophosphates have attracted interest in their use as solid electrolytes in all-solid-state batteries. Despite similar structural motifs, including PS43–, P2S64–, and P2S74– polyhedra, these materials exhibit a wide range of possible compositions, crystal and amorphous structures, as well as ionic conductivities. Calculations based on density functional theory can be a helpful tool for understanding diffusion pathways and Li+ ionic conductivity and interface stabilities.
This contribution will include a discussion of recent results on the defect chemistry and conductivity of the solid electrolyte Li4P2S6 as well as its interfacial instability with respect to Li. Then, molecular dynamics simulations of crystalline and amorphous Li4PS4I, will be shown, which unravel the diffusion mechanism and can be explained by a rate-equation model based on superbasins. Finally, results on the Lithium argyrodites of the type Li6PS5X (X = Cl, Br, I) are presented, where the influence of S2-/Br- site-disorder was studied. The simulations reveal that local “Li cages” trap Li ions in the ordered material. At higher degrees of site-disorder the cage structures dissolve and long-range low energy pathways are established. The analysis of pair distribution functions (PDF) and Li-density maps elucidates the correlation between structural disorder and ionic conductivity.
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Professor Karsten Albe, Technische Universität Darmstadt, Germany
Professor Karsten Albe, Technische Universität Darmstadt, Germany
Karsten Albe has been a Professor of Materials Modelling at TU Darmstadt since 2002. He is a former Director of the Collaborative Research Centre 595 on Fatigue of Functional Materials (2012–2014) and is currently coordinating a research project on modelling of solid electrolytes funded by BMBF. He was educated in physics at the Universities of Hamburg and Ulm and was a PostDoc at the University of Illinois Urbana-Champaign after he finished is doctoral studies at TU Dresden. His main interests lie in the simulation defect of structures in functional materials using atomic scale models. Much of his work deals with ab-initio calculations of point defects, molecular dynamics simulations of disordered solids, dislocations and diffusional transport as well as the development of computational analysis tools.
15:30-16:00
Paradigms of structural, chemical, and dynamical frustration in superionic conductors
Dr Brandon Wood, Lawrence Livermore National Laboratory, USA
Abstract
Rationally motivated computational discovery and optimization of solid electrolytes require the development of reliable descriptors for fast solid-state ionic conductivity. However, many of the fundamental motivations for superionic behaviour in solids remain enigmatic, which has generally slowed progress in screening new candidates or tuning existing materials to maximize ionic conductivity. Dr Wood will discuss the use of high-performance computer simulations and advanced analytical techniques to unravel various mechanisms of ionic conductivity in model classes of solid electrolytes. Using computational “experiments”, the simulations systematically isolate factors such as stoichiometry, strain, composition, crystal structure, and local environment in the determination of ionic conductivity. Collectively, the results point to the importance of a frustrated energy landscape in promoting ultrafast diffusion. Different types of frustration in model superionic conductors will be discussed, arising from factors such as off-stoichiometry, competition between interstitial site occupancies, symmetry incompatibilities between local bonding character and lattice geometry, and dynamical frustration coupled to anharmonic lattice motion. Dr Wood will explore the physicochemical relevance of these factors for understanding and promoting cation mobility, with a view towards developing design rules for engineering faster ionic conductors. Among the topics to be discussed is the dependence of the different frustration paradigms on the fundamental nature of the lattice-forming ions, which suggests there may be no single universal descriptor for ionic conductivity, but rather classes of superionic conductors with similar underlying motivations. Specific examples will be drawn from recent results on superionic materials based on oxides, halides, and polyatomic anions.
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Dr Brandon Wood, Lawrence Livermore National Laboratory, USA
Dr Brandon Wood, Lawrence Livermore National Laboratory, USA
Brandon Wood is a Staff Scientist in the Materials Science Division at Lawrence Livermore National Laboratory (LLNL), USA. He received his PhD in Materials Science and Engineering from MIT in 2007. His primary research activities lie in the application of first-principles and mesoscale simulation techniques to materials for energy storage and conversion, including solid-state batteries, hydrogen storage media, and electrocatalysts. He is particularly interested in complex dynamics of interfaces and disordered systems. He currently serves as the Deputy Director of the LLNL Laboratory for Energy Applications of the Future (LEAF) and Theory Director of the US Department of Energy Hydrogen Materials--Advanced Research Consortium (HyMARC).
16:15-17:00
Panel discussion