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RESEARCH AREAS       The ANSER Center is a |
Kenneth R. Poeppelmeier |
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Biographical SketchKenneth Poeppelmeier is Associate Director of Northwestern University's Science and Technology Center for Superconductivity. He is also Associate Editor of the journal, Inorganic Chemistry, and serves on the editorial boards of the Journal of Alloys and Compounds, CHEMtracks, Chemistry of Materials, and Solid State Sciences.He serves as a lecturer for both the National Science Council of Taiwan and the Natural Science Foundation of China. Research StatementInorganic solid-state chemistry has always had widespread use in industrial applications and in diverse fields such as heterogeneous catalysis and ceramics. Our research emphasizes the connections between the synthesis and structure of new materials, the physical properties of new materials, and the technological advances that can result from these discoveries. One specific example of this is our devlopment of Ag4V2O6F2 (SVOF) as a primary lithium battery material. Presently, Ag2V4O11, or silver vanadium oxide (SVO), is used commercially as a cathode material in primary lithium batteries for high-rate applications, such as those used in implantable cardioverter defibrillators (ICDs). An ICD monitors the heartbeat and, when arrhythmia is detected, interrupts the fibrillation by delivering a shock of 30-35 J to the heart to restore normal rhythm. To deliver the shock, capacitors are rapidly charged to a high voltage and then discharged directly into the heart via electrical leads. SVOF has a higher silver-to-vanadium ratio than SVO, while preserving critical connectivity in the vanadium oxide fluoride framework. The silver ions lie between sheets of alternating vanadium tetrahedra and octahedra chains. This silver interlayer between the vanadium oxide fluoride sheets allows for lithium diffusion into the material and silver diffusion out of the material. An open circuit voltage experiment, which clarifies the voltage plateaus of the electrode, shows the first plateau is at 3.52 V and the second is at 3.25 V. The initial voltage plateau is nearly 300 mV higher than the silver reduction potential of SVO. In addition to the higher reduction potential, the capacity of SVOF above 3 V is 148 mAh/g (892 mAh/cm3), equivalent to 3.7 mol of lithium inserted, while SVO has a capacity of 100 mAh/g (480 mAh/cm3). Thus, it is apparent that the presence of the fluoride increases the reduction potential of the silver and the greater silver content increases the capacity at higher voltages. Inorganic materials that have unusual structures often exhibit interesting chemical and physical characteristics. For example, layered materials exhibit a wide variety of important technological uses because they offer a unique crystalline architecture that can be designed to achieve specific material properties. Most recently, we have begun synthesizing and testing novel mixed metal ferrites as solid oxide fuel cell electrodes, while also studying the fundamental relationship between the structure and its properties. We are also interested in noncentrosymmetric compounds and their technologically important properties such as ferroelectricity and second-order nonlinear behavior. More recently we have begun to study metal oxides that are transparent throughout the visible range yet are metallic conductors. Our research in these areas, ranging from growth of single crystals to the synthesis of new catalysts, is part of an interdisciplinary research program that involves the collaboration of physicists, materials scientists, and chemists. Publications
Most Significant Honors & Awards
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