Zweitveröffentlichungen (grüner Weg)

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Auflistung Zweitveröffentlichungen (grüner Weg) nach Autor:in "Adelhelm, Philipp"

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    Conversion reactions for sodium-ion batteries
    (2013) Klein, Franziska; Jache, Birte; Bhide, Amrtha; Adelhelm, Philipp
    Research on sodium-ion batteries has recently been rediscovered and is currently mainly focused on finding suitable electrode materials that enable cell reactions of high energy densities combined with low cost. Naturally, an assessment of potential electrode materials requires a rational comparison with the analogue reaction in lithium-ion batteries. In this paper, we systematically discuss the broad range of different conversion reactions for sodium-ion batteries based on their basic thermodynamic properties and compare them with their lithium analogues. Capacities, voltages, energy densities and volume expansions are summarized to sketch out the scope for future studies in this research field. We show that for a given conversion electrode material, replacing lithium by sodium leads to a constant shift in cell potential Delta E-(Li-Na)(o) depending on the material class. For chlorides Delta E-(Li-Na)(o) equals nearly zero. The theoretical energy densities of conversion reactions of sodium with fluorides or chlorides as positive electrode materials typically reach values between 700 W h kg(-1) and 1000 W h kg(-1). Next to the thermodynamic assessment, results on several conversion reactions between copper compounds (CuS, CuO, CuCl, CuCl2) and sodium are being discussed. Reactions with CuS and CuO were chosen because these compounds are frequently studied for conversion reactions with lithium. Chlorides are interesting because of Delta E-(Li-Na)(o) approximate to 0 V. As a result of chloride solubility in the electrolyte, the conversion process proceeds at defined potentials under rather small kinetic limitations.
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    The impact of carbon materials on the hydrogen storage properties of light metal hydrides
    (2011) Adelhelm, Philipp; De Jongh, Petra E.
    The safe and efficient storage of hydrogen is still one of the remaining challenges towards fuel cell powered cars. Metal hydrides are a promising class of materials as they allow the storage of large amounts of hydrogen in a small volume at room temperature and low pressures. However, usually the kinetics of hydrogen release and uptake and the thermodynamic properties do not satisfy the requirements for practical applications. Therefore current research focuses on catalysis and the thermodynamic tailoring of metal hydride systems. Surprisingly, carbon materials used as additive or support are very effective to improve the hydrogen storage properties of metal hydrides allowing fast kinetics and even a change in the thermodynamic properties. Even though the underlying mechanisms are not always well understood, the beneficial effect is probably related to the peculiar structure of the carbon materials. This feature article gives an introduction to the different carbon materials, an overview of the preparation strategies to synthesize carbon/hydride nanocomposites, and highlights the beneficial effect of carbon by discussing two important hydrides: MgH(2) and NaAlH(4).
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    Room-temperature sodium-ion batteries : Improving the rate capability of carbon anode materials by templating strategies
    (2011) Wenzel, Sebastian; Hara, Takeshi; Janek, Jürgen; Adelhelm, Philipp
    Current kinetic limitations of carbon anode materials in sodium-ion batteries can be effectively tackled by using tailor-made carbon materials with hierarchical porosity prepared via the nanocasting route. Capacities exceeding 100 mA h g-1 at C/5 are found while exhibiting excellent rate capability and reasonable cycle life.
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    Towards commercial products by nanocasting : characterization and lithium insertion properties of carbons with a macroporous, interconnected pore structure
    (2012) Jache, Birte; Neumann, Christian; Becker, Jorg; Smarsly, Bernd M.; Adelhelm, Philipp
    Carbon materials with defined porosity are prepared using the nanocasting approach. The structural properties of the prepared carbon materials are examined by SEM, XRD, XPS, elemental analysis, nitrogen physisorption and Hg porosimetry. The materials exhibit an interconnected porous network with spherical pores in the macropore range, being a replica of spherical SiO2 particles. The average macropore size (300-700 nm) and surface area (35-470 m2 g-1) can be tailored by the choice of template and carbon precursor. More importantly, based on silica templates prepared by flame pyrolysis, the whole process, including HF etching of the template, can be easily industrialized. Lithium storage measurements are used to demonstrate the beneficial transport properties of the porous carbon materials which are referenced against non-porous carbons. The porous carbon materials exhibit high capacity (550 mA h g-1 at C/5) and excellent rate capability (90 mA h g-1 at 60C). Surprisingly, the excellent lithium storage properties are related to the macroporous framework rather than high surface area and/or micro- and mesoporosity.