Browsing by Author "Quade, A."
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- ItemCarbide-Derived Niobium Pentoxide with Enhanced Charge Storage Capacity for Use as a Lithium-Ion Battery Electrode(Washington, DC : ACS Publications, 2020) Budak, Ö.; Geißler, M.; Becker, D.; Kruth, A.; Quade, A.; Haberkorn, R.; Kickelbick, G.; Etzold, B. J. M.; Presser, V.Nb2O5 has been explored as a promising anode material for use as lithium-ion batteries (LIBs), but depending on the crystal structure, the specific capacity was always reported to be usually around or below 200 mAh/g. For the first time, we present coarse-grained Nb2O5 materials that significantly overcome this capacity limitation with the promise of enabling high power applications. Our work introduces coarse-grained carbide-derived Nb2O5 phases obtained either by a one-step or a two-step bulk conversion process. By in situ production of chlorine gas from metal chloride salt at ambient pressure, we obtain in just one step directly orthorhombic Nb2O5 alongside carbide-derived carbon (o-Nb2O5/CDC). In situ formation of chlorine gas from metal chloride salt under vacuum conditions yields CDC covering the remaining carbide core, which can be transformed into metal oxides covered by a carbon shell upon thermal treatment in CO2 gas. The two-step process yielded a mixed-phase tetragonal and monoclinic Nb2O5 with CDC (m-Nb2O5/CDC). Our combined diffraction and spectroscopic data confirm that carbide-derived Nb2O5 materials show disordering of the crystallographic planes caused by oxygen deficiency in the structural units and, in the case of m-Nb2O5/CDC, severe stacking faults. This defect engineering allows access to a very high specific capacity exceeding the two-electron transfer process of conventional Nb2O5. The charge storage capacities of the resulting m-Nb2O5/CDC and o-Nb2O5/CDC are, in both cases, around 300 mAh/g at a specific current of 10 mA/g, thereby, the values are significantly higher than that of the state-of-the-art for Nb2O5 as a LIB anode. Carbide-derived Nb2O5 materials also show robust cycling stability over 500 cycles with capacity fading only 24% for the sample m-Nb2O5/CDC and 28% for o-Nb2O5/CDC, suggesting low degree of expansion/compaction during lithiation and delithiation.
- ItemPreparation, analysis, and application of coated glass targets for the Wendelstein 7-X laser blow-off system(Melville, NY : American Inst. of Physics, 2020) Wegner, Th.; Geiger, B.; Foest, R.; Jansen van Vuuren, A.; Winters, V. R.; Biedermann, C.; Burhenn, R.; Buttenschön, B.; Cseh, G.; Joda, I.; Kocsis, G.; Kunkel, F.; Quade, A.; Schäfer, J.; Schmitz, O.; Szepesi, T.Coated glass targets are a key component of the Wendelstein 7-X laser blow-off system that is used for impurity transport studies. The preparation and analysis of these glass targets as well as their performance is examined in this paper. The glass targets have a high laser damage threshold and are coated via physical vapor deposition with μm thick films. In addition, nm-thin layers of Ti are used as an interface layer for improved ablation efficiency and reduced coating stress. Hence, the metallic or ceramic coating has a lateral homogeneity within 2% and contaminants less than 5%, being optimal for laser ablation processing. With this method, a short (few ms) and well defined pulse of impurities with about 1017 particles can be injected close to the last closed flux surface of Wendelstein 7-X. In particular, a significant amount of atoms with a velocity of about 1 km/s enters the plasma within 1 ms. The atoms are followed by a negligible concentration of slower clusters and macro-particles. This qualifies the use of the targets and applied laser settings for impurity transport studies with the laser blow-off system in Wendelstein 7-X. © 2020 Author(s).