Xiang Zhong Ren

Synthesis of LiNi1/3Co1/3Mn1/3O2 Composite Powders by Solid State Reaction

A mixture of Li2CO3, NiO, Co2O3 and MnO2 with a molar ratio was introduced in the mixed high energy ball milling, LiNi1/3Co1/3Mn1/3O2 was prepared by solid state phase using mechanochemical activation which has highly reactive materials. The structure and electrochemical properties of LiNi1/3Co1/3Mn1/3O2 were analisised by employing X-ray diffraction(XRD), scanning electron microscopy(SEM) and galvanotactic charge-discharge test. Charge-discharge test results show that when the the LiNi1/3Co1/3Mn1/3O2 cathode was prepared by wet milling 10h between 2.8 V and 4.4V at a current of 0.5C rate, the initial discharge capacity is 135.1mAh/g, the capacity retention rate of 93.26% after 20 cycles. When nLi: n (Ni + Co + Mn) = 1.1, the samples sintered 20h at 850 °C, the first discharge capacity is 148.5 mAh/g, and the capacity retention rate is 94.88% after 40 cycles.

Synthesis, Characterization and Magnetism of Nanosized Copper Ferrite

Copper ferrite powders were successfully synthesized by sonochemical method. The resultant powders were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), FT-IR, differential thermal analysis-thermal gravimetric (DTA-TG), differential scanning calorimetry (DSC) and VSM. The particle saturation magnetization (Ms) is 66 emu/g and an intrinsic coercive force (iHc) is 2100 Oe when the precursor calcined at 950 °C for 15 h.

Synthesis and Electrochemical Performance of LiV 3 O 8 /MWCNTs Cathode Material for Lithium-Ion Batteries

Layered LiV3O8 cathode material was prepared by sol-gel method using ethylene diamine tetra-acetic acid (EDTA) as chelon, and LiV3O8/MWCNTs composite materials were fabricated by mixing multi-walled carbon nanotubes (MWCNTs) and LiV3O8 particles via ball milling technic. X-ray diffraction (XRD), scanning electron microscopy (SEM), galvanostatic charge-discharge experiments were employed to characterize the material structure, morphology and electrochemical properties respectively. The results show that the layer structure of LiV3O8 did not change after doping MWCNTs, and the LiV3O8/MWCNTs composite showed excellent electrochemical performance. The initial specific discharge capacity of the 2% MWCNTs （mass percent） composites can reach 217.5 mAh/g at 0.1C discharge rate in the potential region 1.8-4.0V, and maintains a stable capacity of 224.9 mAh/g within 30 cycles. Comparing to the LiV3O8/MWCNTs, the capacity of pure LiV3O8 samples can only remain 86% intetial specific capacity at the same test conditions.

Co-Precipitation Synthesis and Optimization Process for LiCo1/3Ni1/3Mn1/3O2

With the acetates of nickel, manganese and cobalt as raw materials and lithium hydroxide as precipitation agent, the precursor Ni1 / 3 Co1 / 3 Mn1 / 3 (OH) 2 was first prepared by chemical coprecipitation method, which was then mixed and ballmilled with certain stoichiometric ratios of LiOH∙H2O, and ultimately obtained LiCo1/3Mn1/3Ni1/3O2 after calcination process. Single-factor experiment method, in conjunction with XRD, SEM, and charge-discharge test, was utilized to study the influence of various factors, including the dispersion way of precursor, pH value of reaction solution, and the content of ballmilling lithium on the electrochemical properties of LiCo1/3Mn1/3Ni1/3O2. The results indicated that: (1) the material dispersed by ultrasonic treatment revealed excellent cycling performance, its ratio of capacity fading decreased at least 34.1% compared to those without ultrasonic process; (2) the optimum conditions of fabricating LiCo1/3Mn1/3Ni1/3O2 may be summarized as the treatment of ultrasonic dispersion, suitable pH value (12~13) and stoichiometric ratio (1.0) of ballmilling lithium.

MgO-Al2O3-SiO2 Glass-Ceramic Prepared by Sol-Gel Method

The crystallization behavior of MgO-Al2O3-SiO2 glass-ceramics by sol-gel technology was investigated by using x-ray diffraction (XRD), differential thermal analysis (DTA), Scanning electron microscopy (SEM). The results showed that: (1)α-cordierite phase was precipitated when the green body was calcined at 1050°C, and α-cordierite of high purity and stability could be formed at 1100°C; (2) Adding an appropriate amount of low melting point glass powder into the green body may provide liquid-phase environment during the sintering process, which will help enhance the tightness density of glass-ceramic, and thus improve its flexural strength.

Preparation and Electrochemical Properties of LiFePO4/PPy Composite Cathode Materials for Lithium-Ion Batteries

LiFePO4/PPy composites with different content of polypyrrole (PPy) were prepared by chemical oxidation reactions. X-ray diffraction (XRD) and scanning electron microscopy (SEM) were employed to characterize the LiFePO4/PPy composite. The results showed that doped PPy did not destroy the olivine structure of LiFePO4 but decreased the intensity of the diffraction peaks, and PPy was found on the surface of LiFePO4 particles. PPy could remarkably increase the conductivity of the composite and improve the electrochemical performance of LiFePO4. The sample with 2.5 % (wt). PPy possessed a high initial discharge capacity of 144.5mAh/g at 0.1C. The results of both cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) proved good cycle performances of the samples doped by PPy.

Modification of LiFePo4 by Citric Acid Coating and Nb5+ Doping

In order to improve the electrochemical performance of LiFePO4, Li0.99Nb0.01FePO4/C composite materials were synthesized with citric acid coating and Nb2O5 doping. The physical chemistry and electrochemical performances of Li0.99Nb0.01FePO4/C were investigated by X-Ray diffraction (XRD) and Transmission electron microscope (TEM). The results show that Li0.99Nb0.01FePO4/C has smooth charge-discharge voltage platform, with first capacity of 151.6 mAh•g-1 (0.1C) and no obvious capacity fading after 16 cycles. The materials have favorable high rate discharge performances, with the first capacity of 131.6 mAh•g-1 at 0.5C, 119.8 mAh•g-1 at 1.0C and 106.2 mAh•g-1 at 2.0C. Equivalent circuits analysis shows that the impedance, especially electrode reaction resistance of Li0.99Nb0.01FePO4/C are significantly reduced compared with the pure LiFePO4 and this helps to improve the electric conductivity, discharge capacity and cycle performance. The diffusion coefficient of Li+ in Li0.99Nb0.01FePO4/C is 2.51×10-12 cm2•s-1 increased two orders of magnitude in comparison with the pure LiFePO4. Carbon-coating makes a more remarkable contribution to lithium diffusion than Nb5+ ion doping.

Application of Au Nanoparticles–AgCl@Polypyrrole Hybrid Material to Amperometric Biosensor

AgCl@polypyrrole(PPy) nanocomposites were synthesized through in situ chemical oxidation polymerization by using poly(vinylpyrrolidane) (PVP) as dispersant, and some Au colloid were prepared by using KBH4 as reductant and sodium citrate as stabilizer, then the Au nanoparticles-AgCl@PPy hybrid material was formed by physical chemical reaction. Fourier transform infrared spectrometer (FTIR) and electron dispersive spectrometer (EDS) data suggested that the hybrid material were composed of Au, AgCl and PPy. An amperometric glucose biosensor was fabricated by adsorbing glucose oxidase (GOx) to an Au nanoparticles-AgCl@PPy hybrid material modified platinum electrode. The biosensor exhibited a super highly sensitive response to H2O2.

Surface Coating of TiO2 Powder

SiO2 nano-scale films were coated on the surface of TiO2 powder by liquid phase deposition. The morphology and the composition of coated TiO2 were studied by transmission electron microscopy (TEM), X-ray photoelectronic spectrscopy (XPS), and X-ray fluorescence (XRF). The study showed that a continuous SiO2 nano-scale film was coated on the TiO2 particles, and the element Si was bonded to the surface of TiO2 in the form of the Ti-O-Si bond. The most suitable conditions for coating are: 0.5 mol•L-1 of C ; pH value of 9.5; 200 g•L-1 of C , reaction time of 5 h at 85 °C.

Synthesis and Characterization of LiFePO4 / PPy Composite Powders

A series of lithium iron phosphate /polypyrrole (LiFePO4/PPy) composite powders were synthesized by chemical oxidation method with different doping agent and oxidation agent. The composite powders were characterized by scanning electron microscopy (SEM), Fourier Transform Infrared Spectrum (FTIR), and X-ray diffraction (XRD). The results showed that the composite powders composed of PPy and LiFePO4. And the doping of polypyrrole in LiFePO4 could weaken the XRD intensity of LiFePO4 , but could not destroy its crystallization. With the increase of pyrrole in LiFePO4/ PPy composite powders, the polypyrrole on the surface of LiFePO4 increased and dispersed more homogeneously. Thermogravimetric analysis (TGA) data indicated the heat-stability of LiFePO4/PPy was very good that the composite powders would not oxidate till 300°C in the air flow.