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Author: Presser, Volker × Author: Tolosa, Aura × End date: 2019 × Start date: 2019 × Type: Text × WGL Institute: INM ×

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Now showing 1 - 5 of 5
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    Carbon onion / sulfur hybrid cathodes via inverse vulcanization for lithium sulfur batteries
    (Cambridge : Royal Society of Chemistry, 2017) Choudhury, Soumyadip; Srimuk, Pattarachai; Raju, Kumar; Tolosa, Aura; Fleischmann, Simon; Zeiger, Marco; Ozoemena, Kenneth I.; Borchardt, Lars; Presser, Volker
    A sulfur–1,3-diisopropenylbenzene copolymer was synthesized by ring-opening radical polymerization and hybridized with carbon onions at different loading levels. The carbon onion mixing was assisted by shear in a two-roll mill to capitalize on the softened state of the copolymer. The sulfur copolymer and the hybrids were thoroughly characterized in structure and chemical composition, and finally tested by electrochemical benchmarking. An enhancement of specific capacity was observed over 140 cycles at higher content of carbon onions in the hybrid electrodes. The copolymer hybrids demonstrate a maximum initial specific capacity of 1150 mA h gsulfur−1 (850 mA h gelectrode−1) and a low decay of capacity to reach 790 mA h gsulfur−1 (585 mA h gelectrode−1) after 140 charge/discharge cycles. All carbon onion/sulfur copolymer hybrid electrodes yielded high chemical stability, stable electrochemical performance superior to conventional melt-infiltrated reference samples having similar sulfur and carbon onion content. The amount of carbon onions embedded in the sulfur copolymer has a strong influence on the specific capacity, as they effectively stabilize the sulfur copolymer and sterically hinder the recombination of sulfur species to the S8 configuration.
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    Vanadia–titania multilayer nanodecoration of carbon onions via atomic layer deposition for high performance electrochemical energy storage
    (Cambridge : Royal Society of Chemistry, 2016) Fleischamann, Simon; Tolosa, Aura; Zieger, Marco; Krüner, Benjamin; Peter, Nicolas J.; Grobelsek, Ingrid; Quade, Antje; Kruth, Angela; Presser, Volker
    Atomic layer deposition has proven to be a particularly attractive approach for ecorating mesoporous carbon substrates with redox active metal oxides for lectrochemical energy storage. This study, for the first time, capitalizes on the cyclic character of atomic layer deposition to obtain highly conformal and atomically controlled decoration of carbon onions with alternating stacks of vanadia and titania. The addition of 25 mass% TiO2 leads to expansion of the VO2 unit cell, thus greatly enhancing lithium intercalation capacity and kinetics. Electrochemical characterization revealed an ultrahigh discharge capacity of up to 382 mA h g^-1 of the composite electrode (554 mA h g^-1 per metal oxide) with an impressive capacity retention of 82 mA h g^-1 (120 mA h g^-1 per metal oxide) at a high discharge rate of 20 A g^-1 or 52C. Stability benchmarking showed stability over 3000 cycles when discharging to a reduced potential of ^-1.8 V vs. carbon. These capacity values are among the highest reported for any metal oxide system, while in addition, upercapacitor-like power performance and longevity are achieved. At a device level, high specific energy and power of up to 110 W h kg^-1 and 6 kW kg^-1, respectively, were achieved when employing the hybrid material as anode versus activated carbon cathode.
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    Electrospinning and electrospraying of silicon oxycarbide-derived nanoporous carbon for supercapacitor electrodes
    (Amsterdam : Elsevier, 2016) Tolosa, Aura; Krüner, Benjamin; Jäckel, Nicolas; Aslan, Mesut; Vakifahmetoglu, Cekdar; Presser, Volker
    In this study, carbide-derived carbon fibers from silicon oxycarbide precursor were synthesized by electrospinning of a commercially available silicone resin without adding a carrier polymer for the electrospinning process. The electrospun fibers were pyrolyzed yielding SiOC. Modifying the synthesis procedure, we were able to obtain electrosprayed SiOC beads instead of fibers. After chlorine treatment, nanoporous carbon with a specific surface area of up to 2394 m2·g-1 was obtained (3089 m2·g-1 BET). Electrochemical characterization of the SiOC-CDC either as free-standing fiber mat electrodes or polymer-bound bead films was performed in 1 M tetraethylammonium tetrafluoroborate in acetonitrile (TEA-BF4 in ACN). The electrospun fibers presented a high gravimetric capacitance of 135 F·g-1 at 10 mV·s-1 and a very high power handling, maintaining 63 % of the capacitance at 100 A·g-1. Comparative data of SiOC-CDC beads and fibers show enhanced power handling for fiber mats only when the fiber network is intact, that is, a lowered performance was observed when using crushed mats that employ polymer binder.
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    Sub-micron novolac-derived carbon beads for high performance supercapacitors and redox electrolyte energy storage
    (Washington D.C. : American Chemical Society, 2016) Krüner, Benjamin; Lee, Juhan; Jäckel, Nicolas; Tolosa, Aura; Presser, Volker
    Carbon beads with sub-micrometer diameter were produced with a self-emulsifying novolac–ethanol–water system. A physical activation with CO2 was carried out to create a high microporosity with a specific surface area varying from 771 (DFT) to 2237 m2/g (DFT) and a total pore volume from 0.28 to 1.71 cm3/g. The carbon particles conserve their spherical shape after the thermal treatments. The controllable porosity of the carbon spheres is attractive for the application in electrochemical double layer capacitors. The electrochemical characterization was carried out in aqueous 1 M Na2SO4 (127 F/g) and organic 1 M tetraethylammonium tetrafluoroborate in propylene carbonate (123 F/g). Furthermore, an aqueous redox electrolyte (6 M KI) was tested with the highly porous carbon and a specific energy of 33 W·h/kg (equivalent to 493 F/g) was obtained. In addition to a high specific capacitance, the carbon beads also provide an excellent rate performance at high current and potential in all tested electrolytes, which leads to a high specific power (>11 kW/kg) with an electrode thickness of ca. 200 μm.
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    Influence of carbon substrate on the electrochemical performance of carbon/manganese oxide hybrids in aqueous and organic electrolytes
    (Cambridge : Royal Society of Chemistry, 2016) Zeiger, Marco; Fleischmann, Simon; Krüner, Benjamin; Tolosa, Aura; Bechtel, Stephan; Baltes, Mathias; Schreiber, Anna; Moroni, Riko; Vierrath, Severin; Thiele, Simon; Presser, Volker
    Manganese oxide presents very promising electrochemical properties as an electrode material in supercapacitors, but there remain important open questions to guide further development of the complex manganese oxide/carbon/electrolyte system. Our work addresses specifically the influence of carbon ordering and the difference between outer and inner porosity of carbon particles for the application in aqueous 1 M Na2SO4 and 1 M LiClO4 in acetonitrile. Birnessite-type manganese oxide was hydrothermally hybridized on two kinds of carbon onions with only outer surface area and different electrical conductivity, and conventional activated carbon with a high inner porosity. Carbon onions with a high degree of carbon ordering, high conductivity, and high outer surface area were identified as the most promising material, yielding 179 F g−1. Pore blocking in activated carbon yields unfavorable electrochemical performances. The highest specific energy of 16.4 W h kg−1 was measured for a symmetric full-cell arrangement of manganese oxide coated high temperature carbon onions in the organic electrolyte. High stability during 10 000 cycles was achieved for asymmetric full-cells, which proved as a facile way to enhance the electrochemical performance stability.