1,720,994 research outputs found
–gC) composite through the hydrothermal process and its application as the anode of lithium ion batteries
No full textA mesostructured TiO2-graphitic carbon (TiO2-gC) composite was synthesized through a simple and scalable hydrothermal method to be employed as an anode material in Li-ion batteries. In a wide voltage range (0.0-2.5 V), the TiO2-gC composite anode possesses a high initial lithiation capacity (598 mA h g(-1)) at 0.1 C (1 C: 150 mA g(-1)), and it still retains 369 mA h g(-1) after 50 cycles at 0.5 C. Furthermore, under a high current density of 2 C, the TiO2-gC anode exhibits stable capacity (252 mA h g(-1)) retention for up to 200 cycles. This excellent electrochemical performance could be ascribed to a synergistic effect of well-developed mesoporosity with a high surface area (345.4 m(2) g(-1)), the conductive graphitic carbon wall, and uniformly dispersed TiO2 nanoparticles, resulting in improved Li+ penetration, fast electron transport and high structural stability during cycling.
Nano-graphite functionalized mesocellular carbon foam with enhanced intra-penetrating electrical percolation networks for high performance electrochemical energy storage electrode materials
No full textMesocellular carbon foam (MSU-F-C) is functionalized with hollow nanographite by a simple solution-phase method to enhance the intrapenetrating electrical percolation network. The electrical conductivity of the resulting material, denoted as MSU-F-C-G, is increased by a factor of 20.5 compared with the pristine MSU-F-C. Hollow graphite nanoparticles are well-dispersed in mesocellular carbon foam, as confirmed by transmission electron microscopy (TEM), and the d spacing of the (002) planes is 0.343 nm, which is only slightly larger than that of pure graphite (0.335 nm), suggesting a random combination of graphitic and turbostratic stacking. After nanographitic functionalization, the BET surface area and total pore volume decreased from 928 m(2) g(-1) and 1.5 cm(3) g(-1) to 394 m(2) g(-1) and 0.7 cm(3) g(-1), respectively. Thermogravimetric analysis in air shows that the thermal stability of MSU-F-C-G is improved relative to that of MSU-F-C, and the one-step weight loss indicates that the nanographite is homogeneously functionalized on the MSU-F-C particles. When the resulting mesocellular carbon materials are used as electrode materials for an electric double layer capacitor (EDLC), the specific capacitances (C-sp) of the MSU-F-C and MSU-F-C-G electrodes at 4 mV s(-1) are 109 F g(-1) and 93 F g(-1), respectively. The MSU-F-C-G electrode exhibited a very high area capacitance (C-area, 23.5 mu F cm(-2)) compared with that of the MSU-F-C electrode (11.7 mu F cm(-2)), which is attributed to the enhanced intraparticle conductivity by the nanographitic functionalization. MSU-F-C-G exhibited high capacity retention (52%) at a very high scan rate of 512 mV s(-1), while only a 23% capacity retention at 512 mV s(-1) was observed in the case of the MSU-F-C electrode. When applied as an anode in a lithium ion battery, a significant increase in the initial efficiency (44%), high reversible discharge capacity (580 mA h g(-1)) in the lower voltage region, and a higher rate capability were observed. The high rate capability of the MSU-F-C-G electrode as charge storage was due to the low resistance derived from the nanographitic functionalization.
Crystallinity-Controlled Titanium Oxide-Carbon Nanocomposites with Enhanced Lithium Storage Performance
No full textNanocomposites of crystalline-controlled TiO2carbon are prepared by a novel one-step approach and applied in anodes of lithium ion batteries. In our nanocomposite anodes, the Li+ capacity contribution from the TiO2 phase was enormous, above 400 mAh?g-1 (Li1+xTiO2, x>0.2), and the volumetric capacity was as high as 877 mAh?cm-3 with full voltage utilization to 0 V versus Li/Li+, which resulted in higher energy density than that of state-of-the-art titania anodes. For the first time, it was clearly revealed that the capacity at 1.2 and 2.0 V corresponded to Li+ storage at amorphous and crystalline TiO2, respectively. Furthermore, improvements in the rate capability and cycle performance were observed; this was attributed to resistance reduction induced by higher electrical/Li+ conduction and faster Li+ diffusion.
TiO2 nanodisks designed for Li-ion batteries: a novel strategy for obtaining an ultrathin and high surface area anode material at the ice interface
No full textA rapid and relatively large-scale production of ultrathin TiO2 nanodisks was achieved under mild conditions by developing a novel and simple sol-gel process occurring at the interface of an organic solvent and ice. Owing to the ultrathin structure and unusually high surface area (>400 m(2) g(-1)), the TiO2 nanodisks exhibited high reversible capacity (191.4 mA h g(-1) at 0.2 C) and excellent rate performance (58% capacity retention at 20 C) as an anode in lithium ion batteries.
Simple fabrication of flexible electrodes with high metal-oxide content: electrospun reduced tungsten oxide/carbon nanofibers for lithium ion battery applications
No full textA one-step and mass-production synthetic route for a flexible reduced tungsten oxide-carbon composite nanofiber (WOx-C-NF) film is demonstrated via an electrospinning technique. The WOx-C-NF film exhibits unprecedented high content of metal-oxides (similar to 80 wt%) and good flexibility (the tensile strength of the specimen was 6.13 MPa) without the use of flexible support materials like CNTs or graphene. The WOx-C-NF film is directly used as an anode in a lithium ion battery (LIB). Compared with previously reported tungsten oxide electrodes, the WOx-C-NF film exhibits high reversible capacity (481 mA h g(total electrode)(-1)), stable cycle, and improved rate performance, without the use of additive carbon, a polymeric binder and a current collector. Moreover, control electrodes fabricated by conventional processes support the positive effects of both the freestanding electrode and metal-oxide embedded carbon 1-D nanofiber structure.
Ordered mesoporous WO3−X possessing electronically conductive framework comparable to carbon framework toward long-term stable cathode supports for fuel cells
No full textWe report on the successful synthesis of ordered mesoporous WO3-X with a high conductivity comparable to a mesoporous carbon framework. Ordered mesoporous WO3-X was prepared using KIT-6 as a hard template. Some WO3-X particles have negative replica structures of KIT-6 template and the other particles are generated by asymmetric incorporation of phosphotungstic acid inside channels of KIT-6 template. The wall of this mesostructured WO3-X has a single crystalline structure, which might be responsible for its high conductivity (1.76 S cm(-1)) comparable to ordered mesoporous carbons (3.0 S cm(-1)). Pt/mesoporous WO3-X exhibits a significant tolerance to cycling between 0.6 and 1.3 V-NHE in 0.5 M H2SO4 solution, preserving 87% of its initial electrochemical surface area (ECSA) after 1000 cycles. On the contrary, the ECSA of the Pt/C decreased significantly with the number of cycles, resulting in loss of 74% of its initial ECSA.
Development of novel mesoporous C–TiO2–SnO2 nanocomposites and their application to anode materials in lithium ion secondary batteries
No full textHerein, we employed the tetra-constituent co-assembly method based on the acid-base pair of Sn and Ti precursors. Using this method, novel mesoporous carbon-TiO2-SnO2 nanocomposite materials were prepared and their structural change with an increase of SnO2 amount was investigated. In low amount of SnO2, an ordered mesoporous structure was observed but it became collapsed at 64 wt.% SnO2, while crystal size of anatase TiO2 embedded within amorphous SnO2 and carbon matrix became larger. When applied to anode materials in lithium ion batteries, an increase of the reaction peaks of Li+ in SnO2 was observed and peak associated with discharging in TiO2 nano-crystal increased in spite of lower amount of TiO2. This indicated that TiO2 was highly utilized for lithium storage (275 mAh g(-1) in 19.9 wt.% TiO2 case). In the nanocomposite electrode with 28.8% TiO2, however, a high rate performance and a very stable cycle performance (95.3% retention at 40th cycles) were observed, which was attributed to the stable nanostructure. (c) 2011 Elsevier Inc. All rights reserved.
An ordered nanocomposite of organic radicalpolymer and mesocellular carbon foam as cathode material in lithium ion batteries
No full textAn ordered nanocomposite of polyethylene glycol-organic radical polymer-mesocellular carbon foam (PEG-ORP-MCF) was prepared by incorporation of ORP into acidified MCF and following PEG coating. The prepared nanocomposite was employed as the cathode material in lithium ion batteries. The nanocomposite electrode exhibited an improvement of high-temperature cycling performance (70% capacity retention after 50 cycles at 50 degrees C) with a high capacity (111 mA h g(-1)), a good rate performance (67% under 20 C current rate) and a smaller polarization under ambient conditions. This improved cathode performance was ascribed to the protective effect of PEG polymer that prevented the ORP from being dissolved in the electrolyte and the high electrical percolation network by the MCF carbon framework.
Investigation of Pseudocapacitive Charge-Storage Behavior in Highly Conductive Ordered Mesoporous Tungsten Oxide Electrodes
No full textHerein, a pseudocapacitive charging behavior of highly conductive ordered mesoporous tungsten oxide (m-WO(3-x)) methods such as cyclic voltammetry (CV), galvanostatic charge-discharge experiment and electrochemical impedance spectroscopy (EIS) were employed. From CV experiment, a relationship analysis between voltammetric charge and scan rate resulted in total (67 C g(-1)), outer (61 C g(-1)) and inner charge (6 C g(-1)), which was related with the well-developed crystalline structure of m-WO(3-x). In galvanostatic charge discharge profiles with change of applied current, a more severe decrease of cathodic capacity than the anodic one was observed, which was attributed to larger cathodic resistance. This resistance dependency on potential was clarified with EIS fitting analysis. Here, the charge transfer resistance and Warburg diffusion resistance became larger with increasing potential, which was relevant to the change of oxidation state during redox reaction. Using these electrochemical analysis results, a schematic illustration of the pseudocapacitive charging mechanism was proposed.
Low-cost electrospun WC/C composite nanofiber as a powerful platinum-free counter electrode for dye sensitized solar cell
No full textTungsten carbide/carbon (WC/C) composite nanofibers were successfully prepared through electro-spinning followed by a one-step heat treatment using in-situ carburization. The WC/C nanofibers were applied to low-cost and platinum-free counter electrodes for dye sensitized solar cells (DSSCs), and their catalytic activities were investigated and compared to platinum (Pt) CEs for triiodide/iodide (I-3(-)/I-) as well as organic disulfide/thiolate (T-2/T-) electrolytes. When WC/C nanofibers are used as the CE catalyst in iodine electrolytes, the DSSCs exhibited a power conversion efficiency (PCE) of 7.77%, corresponding to 96% of that of Pt CEs. In the case of T-2/T- redox couples, the DSSCs based on WC/C nanofibers achieved PCE of 5.85%, which is almost twice that of Pt (3.07%). The high catalytic activities of WC/C nanofibers are attributed to synergetic effects from the combination of catalytically active WC and one-dimensional (1D) conductive carbon acting as an efficient charge transport pathway. In addition, spray-coated WC/C nanofiber CE films have a three-dimensional porous network, enhancing the permeation of the electrolyte into the CE film and the diffusion of redox couples. The electrospinning process used for the synthesis of the WC/C nanofibers is facile and scalable and is therefore promising for the commercialization of DSSCs. (C) 2014 Elsevier Ltd. All rights reserved.
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