; lij4@ornl.gov, Phone: þ01 912 4780850, Fax: þ01 912 4780699Highly porous Si/TiO 2 composite nanofibres were prepared using a unique sulphur-templating method combined with electrospinning. The structure, morphology, surface area, phase and composition of these nanofibres were characterized using Raman spectroscopy, scanning electron microscopy, powder X-ray diffraction, surface area analyser and thermogravimetric analyser. The specific surface area of Si/TiO 2 porous NFs is as large as 387 m 2 g À1, whose silicon capacity can be maintained above 1580 mAh g À1 in 180 cycles.
Asymmetric porous structure formedviaa self-assembly phase inversion method can significantly improve the cycling performance of lithium ion anodes made of micron-size germanium powders.
Alloy electrode material like tin dioxide (SnO2) possesses much higher specific capacity as compared to commercial graphite anode in lithium ion battery (783 vs 372 mAh g(-1)). However, the huge volume change (260%) of SnO2-based anode during the alloying and dealloying process can cause significant electrode pulverization and rapid capacity loss. Herein we report the synthesis of SnO2 asymmetric membranes via a unique combination of phase inversion and sol-gel chemistry to overcome this big challenge. The SnO2 asymmetric membrane electrode demonstrates a specific capacity of 500 mAh g(-1) based on the overall electrode mass at a current density of 280 mA g(-1) (∼0.5C) with >96% capacity retention after 400 cycles. When the current density is increased from 28 to 560 mA g(-1), its overall capacity is only reduced by 36%. Such an outstanding rate and cycling performance is attributed to the existence of networking porous structure in the membrane that can provide high electrical conductivity, multiple diffusion channels, and free volumes for electrode expansion. The carbonization temperature has a dramatic impact on the electrode performance. Membranes carbonized at 500 °C show an excellent cycling performance, whereas the capacity of the membrane carbonized at 800 °C decreases by 51% in 100 cycles. Such a drastic difference in cycle life is caused by the reduction of small SnO2 NPs (∼3.9 nm) into large metallic tin spheres (∼40 nm) at 800 °C. This is the first original report on using asymmetric membrane structure to stabilize an SnO2-based lithium ion battery anode with an excellent electrochemical performance.
Synthetic nanomaterials have many unique chemical and physical properties, mainly due to their high specific surface area and quantum confinement effect. Specifically, titanium dioxide (TiO ) nanomaterial has high stability, anticorrosive, and photocatalytic properties. However, there are concerns over adverse biological effects resulting from bioeffects. This study was to investigate adverse effects associated with acute ingestion of TiO nanofiber (TDNF). TDNF was fabricated via electrospinning method, followed by dissolution in water. Six- to seven-week-old male Sprague Dawley rats were exposed to a total of 0, 40, and 60 ppm of TDNF for 2 weeks via oral gavage. Serum total protein and weight gain during the course of this study displayed marginal concentration-dependent alterations. These findings were followed by a global gene expression analysis to identify which transcripts might be responsive to TNDF toxicity. Differentially expressed mRNA levels were dose-dependently higher in animals exposed to TNDF. The majority of the affected genes were biochemically involved in immune response and inflammation. We believe this is due to the fact that TNDF is unable to penetrate the cell and forms phagocytosis sites that trigger inflammatory and immune response. All results taken together, short-term ingestion of TNDF produced marginal effects indicative of inflammation. Finally, the broad gene expression data were validated through quantification of immunoglobulin heavy chain alpha (Igha). Igha gene was upregulated in treated groups, showing similar expression patterns to the global gene expression data.
V 2 O 5 is deemed as one of the most promising cathode materials for next-generation high-capacity lithium-ion batteries (LIBs). It possesses a theoretical capacity of 294 mAh g À1 , which is much higher than conventional cathodes. However, there are many issues to be solved before its practical use, including poor cycle life and unsatisfactory rate performance, mainly owing to its low electronic conductivity and ionic diffusivity, as well as structural instability. This work reports three types of V 2 O 5 asymmetric membranes synthesized by using an adapted reverse-osmosis membrane technology combined with sol-gel chemistry, aiming to stabilize the cyclability and improve the rate performance. V 2 O 5 asymmetric membrane cathodes prepared using graphene as the conductive additives have a specific capacity of approximately 160 mAh g À1 at a current density of 100 mA g À1 with no capacity degradation after 380 cycles. It is also found that the annealing temperature and the choice of conductive additives can affect the morphology of V 2 O 5 nanoparticles and the overall electrode cyclability. A lower annealing temperature (300 vs. 400 8C) and addition of graphene are beneficial to long-term cycling performance.[a] Dr.
Titanium dioxide nanofiber (TDNF) is widely used in the manufacture of various household products, including cosmetics. As a result, the possibility exists for TDNFs to affect human health. Because the kidneys are responsible for filtering out waste from the blood, the goal of the present study was to investigate the short-term effects of TDNF on kidney function of male Sprague Dawley rats. To achieve study objectives, 6- to 7-wk-old male rats were exposed via oral gavage to a total of 0, 40, and 60 parts per million of TDNF for 2 wk. The TDNF was fabricated by electrospinning and then dissolved in water. We measured serum concentration of lactate dehydrogenase, renal histopathology, identification of TDNF in kidney tissue via scanning electron microscopy, and quantitative amounts of titanium-47 in kidney tissue. We also measured specific gene-expression analysis of transcripts involved in apoptosis, inflammation, cell-division regulation, cell structure, and motility. Results showed a slight dose-dependent reduction in renal weight. In contrast, a concentration-dependent elevation in titanium-47 amounts was noted in kidney tissue. We found no significant differences in histopathological patterns. Gnat3 and Hepacam3 were up-regulated in TDNF-treated groups. Up-regulation of NF-κB likely indicated the involvement of renal-tissue inflammation via an independent mechanism. Similarly, Gadd45-α was significantly overexpressed in kidney tissues. This transcript was previously increased following stressful growth-arrest conditions and treatment with DNA-damaging agents. Our overall results suggest marginal renal toxicity in Sprague Dawley rats after ingesting TDNF.
Silicon is deemed as one of the most promising anode materials for next-generation high capacity lithium ion batteries to power electric vehicles and store intermittent energy sources. However, the large volume change and poor mechanical strength of silicon can cause electrode pulverization, loose contact with conductive additives and thus poor cycling performance. Although there is exciting advancement in cyclability using silicon nanomaterials (nanowires, nanotubes, nano-thin films, and nanoparticles), the cycling performance of silicon micron powders is far away satisfying. Herein, we reported the synthesis of novel asymmetric sandwich membranes containing micron-sized silicon powders (≈1 µm) to accommodate the large volume expansion (≈300%) of silicon during the lithiation and de-lithiation processes. These silicon membranes were prepared using a facile phase-inversion method and systematically characterized using Scanning Electron Microscopy, Transmission Electron Microscopy, Surface Area Analyzer, Thermogravimetric Analyzer, Raman Spectroscopy, and Powder X-Ray Diffraction. Raman spectra shows the characteristic peak of crystalline silicon at a 510 cm-1, as well as broad G and D peaks centered at 1580 cm-1 and 1375 cm-1, respectively. X-Ray Diffraction shows peaks typical of cubic phase silicon. Thermogravimetric analysis confirm that the content of silicon in these sandwich asymmetric membranes is ~35%-45%, depending on whether silicon membranes were coated with carbonaceous asymmetric membranes or not. Scanning Electron Microscopy clearly shows the asymmetric membrane structures with silicon particles embedded within two layers of carbonaceous membranes. The size and size distribution of silicon micron powders are obtained using Transmission Electron Microscopy. As fabricated membranes were glued directly onto copper current collectors and assembled into half-cell lithium ion batteries. An overall capacity of 610 mAh g-1 can be maintained for 100 cycles with an 88% retention rate, applying a current density of 510 mAh g-1. The Coulombic efficiency is around 99.8% on average. It is notable that such a stable cycling performance has rarely been reported for electrodes made from micron-sized silicon particles. The improved cycling performance is believed to be attributed to the unique network of nanopores and micropores where silicon particles are embedded within. By coating silicon asymmetric membranes with one layer or two layers of carbonaceous asymmetric membranes, a stable solid electrolyte interphase can be maintained, leading to a much more stable cycling performance than single-layer membranes alone. In comparison, the overall capacity of pure Si micron-particles showed an initially high capacity of 970 mAh g-1 and then rapidly degraded to 10 mAh g-1 in as few as 30 Cycles. Carbonaceous asymmetric membranes that don’t contain silicon particles demonstrated a high cycling stability with a 98% retention rate after 100 cycles. However their specific capacity is quite low (230 mAh g-1). Single-layer silicon membranes without sandwich structures have a high initial capacity of 936 mAh g-1, but suffer from a 38% capacity loss after 100 cycles. Finally, it shall be pointed out that these membranes can be produced in large scale because the overall process is fully compatible with the conventional roll-to-roll membrane technology. Figure 1
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