Wen-lou Wang

Preparation of nanocrystalline nickel powders through hydrothermal-reduction method

Nanocrystalline nickel powders were prepared in aqueous solution through a thermal-reduction process. The reductive atmosphere was produced from the disproportionation of white phosphorus in basic solution at 100°C. X-ray diffraction (XRD), transmission electron microscopy (TEM), and chemical analysis were employed to characterize the products. XRD revealed that the nickel was single phase. TEM showed that the average particle size was about 26 nm. The purity of the as-prepared nickel was 99.6%, as determined from the spectrophotoscopy. The possible formation mechanism of nanocrystalline nickel is a reduction of nanocrystalline Ni(OH)2.

The preparation and phase transition of nanocrystalline iron sulfides via toluene-thermal process

A series of nanocrystalline iron sulfides have been successfully prepared via the reaction of FeSO4.7H2O and Na2S3 using the toluene-thermal method in the temperature range of 80–170°C. Two single phases of Fe3S4 and FeS2 were obtained. Transmission electron microscopy analyses indicate that Fe3S4 crystallite is about 25 nm and FeS2 is about 50 nm. The iron and sulfur contents are determined by spectrophotometric analysis. The ratios of Fe to S are Fe2.994S4 and Fe0.996S2, respectively. With the change of the reaction condition, the phase transition among iron sulfur was studied.

Ultrafine powder of silver sulfide semiconductor prepared in alcohol solution

Abstract Ultrafine powder of silver sulfide semiconductor was prepared at room temperature between 25 and 35°C in an absolute alcohol solution, with AgNO 3 and CS 2 as the reagents. The final products were characterized by X-ray diffraction and transmission electron microscopy. The average size of the crystallites was about 50 nm. The possible chemical formation process of Ag 2 S is discussed.

A New Way to Prepare Nanocrystalline Dinickel Phosphide

Abstract Nanocrystalline Ni 2 P was successfully prepared through the reaction between anhydrous NiCl 2 and Na 3 P via the solvent–thermal method at 150°C. This method is similar to the well known hydrothermal process, except toluene is substituted for water. X-ray diffraction analysis indicated that the product was Ni 2 P phase, and no Ni–O vibrations were found in infrared spectra. Transmission electron microscopy showed that the average particle size was about 10 nm, and the particle-size distribution was narrow.

Organo-thermal preparation of nanocrystalline cobalt phosphides

Abstract Nanocrystalline cobalt phosphides have been successfully prepared via a benzene-thermal method at 150 °C, which is similar to the well-known hydrothermal process, except that benzene was substituted for water. The yield of cobalt phosphides was about 90%. X-ray diffraction analysis indicated that the product was a mixture of CoP and Co 2 P. Transmission electron microscopy showed two kind of shapes of particles. Electron diffraction confirmed Co 2 P with sphere shape and CoP with spindle shape.

Influence of LiFePO4/C interface on electrochemical properties

LiFePO4/C particles with different LiFePO4–C interface were prepared and investigated with emphasis on the interface property which has been found to be important for the power performance of LiFePO4. Soft-X-ray-absorption (XAS) spectra collected at O and C K-edge show a distinct bonding character between carbon and LiFePO4 in carbon coated LiFePO4/C. Galvanostatic change-discharge at different rates and electrochemical impedance tests demonstrate that the interface action between LiFePO4 and carbon within LiFePO4/C composites has a crucial effect on its electrochemical performance.

Surface phase composition of nanosized LiFePO4 and their enhanced electrochemical properties

Despite the great achievement in understanding the materials properties of LiFePO4, the surface phase composition of nanosized LiFePO4 has been almost ignored. The present study reports the synthesis of nanosized core–shell LiFePO4 with size of about 50 nm by one step solvothermal route using Polyethylene glycol 600 as solvent. The structural characterization of the surface of nanosized core–shell LiFePO4 particles has been investigated using soft X-ray absorption spectroscopy, X-ray photoelectron spectroscopy, Raman spectroscopy and transmission electron microscopy. The nanosized LiFePO4 is well-covered by an amorphous LiFeP2O7 layer containing trace carbon. Density functional theory (DFT) calculation is used to illustrate the origin of amorphous LiFeP2O7 layer. The nanosized core–shell LiFePO4 exhibits excellent charge transfer kinetics and charge/discharge performance. These new investigations shed new insight into the surface phase composition of nano-particles. The synthesis of the nanosized core–shell LiFePO4 paves an effective way to develop cathode materials with high rate capabilities for use in Li-ion batteries.

Preparation and Investigation on Lattice Distortion and Electrochemical Performances of Li0:95Na0:05FePO4/C

Na+ doped sample Li0.95Na0.05FePO4 was prepared through solid state method. Structure characterization shows Na+ is successfully introduced into the LiFePO4 matrix. Scanning electron microscopy shows the particle size mainly ranges in 1–3 μm. X-ray diffraction Rietveld refinement demonstrates lattice distortion with an increased cell volume. As one cathode material, it has a discharge capacity of 150 mAh/g at 0.1 C rate. The material exhibits a capacity of 109 and 107 mAh/g at 5 and 7.5 C respectively. When cycled at 1 and 5 C, the material retains 84% (after 1000 cycles) and 86% (after 350 cycles) of the initial discharge capacity respectively indicating excellent structure stability and cycling performance. Na+ doping enhances the electrochemical activity especially the cycle performance effectively.