7 research outputs found
Local structure of glassy lithium phosphorus oxynitride thin films: a combined experimental and ab initio approach
Lithium phosphorus oxynitride (LiPON) is an amorphous solid-state lithium ion
conductor displaying exemplary cyclability against lithium metal anodes. There
is no definitive explanation for this stability due to the limited
understanding of the structure of LiPON. We provide a structural model of
RF-sputtered LiPON via experimental and computational spectroscopic methods.
Information about the short-range structure results from 1D and 2D solid-state
nuclear magnetic resonance experiments investigating chemical shift anisotropy
and dipolar interactions. These results are compared with first principles
chemical shielding calculations of Li-P-O/N crystals and ab initio molecular
dynamics-generated amorphous LiPON models to unequivocally identify the glassy
structure as primarily isolated phosphate monomers with N incorporated in both
apical and as bridging sites in phosphate dimers. Structural results suggest
LiPON's stability is a result of its glassy character. Free-standing LiPON
films are produced that exhibit a high degree of flexibility highlighting the
unique mechanical properties of glassy materials
Solid-state NMR spectroscopy
M.H. acknowledges support by National Institutes of Health (NIH) grant GM066976.Solid-state nuclear magnetic resonance (NMR) spectroscopy is an atomic-level method used to determine the chemical structure, three-dimensional structure, and dynamics of solids and semi-solids. This Primer summarizes the basic principles of NMR as applied to the wide range of solid systems. The fundamental nuclear spin interactions and the effects of magnetic fields and radiofrequency pulses on nuclear spins are the same as in liquid-state NMR. However, because of the anisotropy of the interactions in the solid state, the majority of high-resolution solid-state NMR spectra is measured under magic-angle spinning (MAS), which has profound effects on the types of radiofrequency pulse sequences required to extract structural and dynamical information. We describe the most common MAS NMR experiments and data analysis approaches for investigating biological macromolecules, organic materials, and inorganic solids. Continuing development of sensitivity-enhancement approaches, including 1H-detected fast MAS experiments, dynamic nuclear polarization, and experiments tailored to ultrahigh magnetic fields, is described. We highlight recent applications of solid-state NMR to biological and materials chemistry. The Primer ends with a discussion of current limitations of NMR to study solids, and points to future avenues of development to further enhance the capabilities of this sophisticated spectroscopy for new applications.PostprintPeer reviewe
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Atomic and Electronic Structure of Complex Metal Oxides during Electrochemical Reaction with Lithium
Lithium-ion batteries have transformed energy storage and technological applications. They stand poised to convert transportation from combustion to electric engines. The discharge/charge rate is a key parameter that determines battery power output and recharge time; typically, operation is on the timescale of hours but reducing this would improve existing applications and open up new possibilities. Conventionally, the rate at which a battery can operate has been improved by synthetic strategies to decrease the solid-state diffusion length of lithium ions by decreasing particle sizes down to the nanoscale. In this work, a different approach is taken toward next-generation high-power and fast charging lithium-ion battery electrode materials.
The phenomenon of high-rate charge storage without nanostructuring is discovered in niobium oxide and the mechanism is explained in the context of the structure–property relationships of Nb2O5. Three polymorphs, T-Nb2O5, B-Nb2O5, and H-Nb2O5, take bronze-like, rutile-like, and crystallographic shear structures, respectively. The bronze and crystallographic shear compounds, with unique electrochemical properties, can be described as ordered, anion-deficient nonstoichiometric defect structures derived from ReO3. The lessons learned in niobia serve as a platform to identify other compounds with related structural motifs that apparently facilitate high-rate lithium insertion and extraction. This leads to the synthesis, characterisation, and electrochemical evaluation of the even more complicated composition–structure–property relationships in ternary TiO2–Nb2O5 and Nb2O5–WO3 phases. Advanced structural characterisation including multinuclear solid-state nuclear magnetic resonance spectroscopy, density functional theory, X-ray absorption spectroscopy, operando high-rate
X-ray diffraction, and neutron diffraction is conducted throughout to understand the evolution of local and long-range atomic structure and changes in electronic states.Churchill Scholarship - Winston Churchill Foundation of the United States of America
Herchel Smith Scholarship
Cambridge International Trus
Report / Institute fĂĽr Physik
The 2016 Report of the Physics Institutes of the Universität Leipzig presents a hopefully interesting overview of our research activities in the past year. It is also testimony of our scientific interaction with colleagues and partners worldwide. We are grateful to our guests for enriching our academic year with their contributions in the colloquium and within our work groups