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Jiang Z.,Fudan University | Li C.,Shanghai Institute of Space Power Sources | Hao S.,Shanghai Institute of Space Power Sources | Zhu K.,Shanghai Institute of Space Power Sources | Zhang P.,Shanghai Institute of Space Power Sources
Electrochimica Acta

We developed a novel, simple method to prepare porous silicon powder by acid etching Al-Si alloy powder.The morphology and structure of the as-obtained material were investigated using scanning electron microscopy (SEM), X-ray diffraction (XRD), transmission electron microscope (TEM), and BET methods. It was found that the porous silicon powder (size about 15 μm) had a spongy structure, consisting of silicon nanobars with diameter about 50 nm and length of 1.5 μm. Its specific surface area was 102.8 m2 g-1. The electrochemical properties of porous silicon electrode were evaluated by measuring voltammograms and charge and discharge curves. The porous silicon electrode with ratio of porous Si powder:Super P:binder = 1:1:1 was tested in button style lithium/Si cell. It was found that due to its ability to promote the formation of primal SEI film on the surface of electrodes, additive fluoroethylene carbonate (FEC) had an effect to improve the charge and discharge cycle stability of porous silicon electrodes. In solution 1 M LiPF6, EC:DMC = 1:1 (V/V) containing 15% FEC, the first charge and discharge capacities of porous silicon electrode were 3450 mAh g-1 Si and 2072 mAh g-1 Si respectively, at current density 100 mA g-1. The discharge capacity retained 66% as 1368 mAh g-1 Si after 258 charge and discharge cycles. In 1 M LiPF6/EC:DEC = 1:1 (V/V) solution, the charge and discharge capacities of porous silicon electrode in first cycle were 3396 mAh g-1 Si and 2537 mAh g-1 Si respectively. At 69th cycle, the discharge capacity remained 59% as 1497 mAh g-1 Si. The high electrochemical performance of porous silicon powder could be attributed to its porous structure, which provides enough tiny space to buffer the huge volume change of Si anode during charging and discharging processes. The nano-size Si bars benefited the diffusion process of lithium in Li-Si alloy. Moreover, the firm connection between Si nanobars in spongy porous structure prevented the breakdown of porous Si particles. This new advanced method for preparing high performance porous Si material is simple and inexpensive, presenting a promising prospect for practical application.© 2013 Elsevier Ltd. All rights reserved. Source

Zhan Z.,Wuhan University of Technology | Wang C.,Wuhan University of Technology | Wang C.,Shanghai Institute of Space Power Sources | Fu W.,Wuhan University of Technology | Pan M.,Wuhan University of Technology
International Journal of Hydrogen Energy

With a high-speed camera, water transport in the channels of a transparent proton exchange membrane fuel cell (PEMFC) was studied under different operating conditions. The results show that (a) Liquid water production under the banks is much bigger than that in the channels; liquid water close to channel walls can be easily changed into water film due to the hydrophilic capillary force of the walls and the drag force of the flow gas; liquid water on the surface of the gas diffusion layer (GDL) is near sphere drop due to its hydrophobic. (b) When gas velocity is less than 7 m/s, liquid water can not be moved swimmingly through the turns of the serpentine channel, and a part of liquid water will adhere to the walls; when gas velocity is more than 7 m/s, liquid water can be moved cleanlily through the turns. (c) Under the test conditions, when the temperature or the air stoichiometric ratio increases, liquid water production decreases, but cell performance is improved at first due to the increase of the electrochemical activity of the catalyst or the oxygen concentration, however the further increase of the temperature or air stoichiometric ratio will decrease the performance of the cell, because the membrane is dehydrated. These findings will help with the design and operation of the PEMFCs. © 2011, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved. Source

Tang W.,Fudan University | Tang W.,Shanghai Institute of Space Power Sources | Liu L.,Fudan University | Zhu Y.,Fudan University | And 3 more authors.
Energy and Environmental Science

A nanocomposite of MoO3 coated with polypyrrole (PPy) was prepared as an anode material for ARLBs. When nanochain LiMn2O 4 is used as the cathode, the ARLB can deliver an energy density of 45 Wh kg-1 at 350 W kg-1 and even maintain 38 Wh kg -1 at 6 kW kg-1 in 0.5 M Li2SO4 aqueous electrolyte, corresponding to an good rate capability. In addition, its cycling behavior is greatly improved compared with the virginal MoO3. Our findings provide valuable clues to improve the comprehensive performance of ARLBs for practical application. This unique performance demonstrates that this battery will be of great promise as a power source for large power devices such as power loading and the storage of solar and wind energies. © 2012 The Royal Society of Chemistry. Source

Liu W.,Fudan University | Liu W.,Shanghai Institute of Space Power Sources | Sun Q.,Fudan University | Yang Y.,Fudan University | And 2 more authors.
Chemical Communications

Graphene nanosheets (GNS) were employed as an air electrode for a sodium-air battery (SAB). High discharge capacity of 9268 mA h g-1 with low overpotential was achieved, indicating its superiority to a normal carbon film electrode. Our results indicate that GNS as air electrodes could improve the electrochemical performance of rechargeable SABs. © The Royal Society of Chemistry 2013. Source

Tang W.,Fudan University | Tang W.,Shanghai Institute of Space Power Sources | Hou Y.,Fudan University | Wang F.,Fudan University | And 3 more authors.
Nano Letters

LiMn2O4 nanotube with a preferred orientation of (400) planes is prepared by using multiwall carbon nanotubes as a sacrificial template. Because of the nanostructure and preferred orientation, it shows a superfast second-level charge capability as a cathode for aqueous rechargeable lithium battery. At the charging rate of 600C (6 s), 53.9% capacity could be obtained. Its reversible capacity can be 110 mAh/g, and it also presents excellent cycling behavior due to the porous tube structure to buffer the strain and stress from Jahn-Teller effects. © 2013 American Chemical Society. Source

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