Papers by Author: Hai Yan Zhang

Abstract: A nanocrystalline LiFePO₄/graphene-carbon nanotubes (LFP-G-CNT) composite has been successfully synthesized by a hydrothermal method followed by heat-treatment. The microstructure and morphology of the LFP-G-CNTs composite were comparatively investigated with LiFePO₄/graphene (LFP-G) and LiFePO₄/carbon nanotubes (LFP-CNT) by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The LFP-G-CNTs nanoparticles were wrapped homogeneously and loosely within a 3D conducting network of graphene-carbon nanotubes. The conducting networks provided highly conductive pathways for electron transfer during the intercalation/deintercalation process, facilitated electron migration throughout the secondary particles, accelerated the penetration of the liquid electrolyte into the LFP-G-CNT composite in all directions and enhanced the diffusion of Li ions. The results indicate that the electrochemical activity of LFP-G-CNT composite may be enhanced significantly. The charge-discharge curves, cyclic voltammograms (CV) and electrochemical impedance spectroscopy (EIS) results demonstrate that LFP-G-CNT composite performes better than LFP-G and LFP-CNT composites. In particular, LFP-G-CNT composite with a low content of graphene and carbon nanotubes exhibites a high initial discharge capacity of 168.4 mAh g⁻¹ at 0.1 C and 103.7 mAh g⁻¹ at 40 C and an excellent cycling stability.

Abstract: Wave-absorbing coating samples are fabricated with ZnO whisker, the absorbent and silicon resin coating as the binder.The influences of the content of ZnO whisker in the absorbing coating and the thickness of the coating on millimeter wave absorbing property are analyzed.With the increasing of the thickness, the absorbing performance of the sample is enhanced significantly , the results show that with a ZnO whisker mass of 50% and coating thickness of 2 mm, excellent absorption (R<-10dB) is observed in the wave band from 66 to 78 GHz (with a bandwidth of 12GHz) . When the ZnO whisker mass is reduced to 30% with the same thickness of 2mm, two absorption bands are obtained from 55 to 67 GHz (with a bandwidth 12GHz) and 100 to 110 GHz (with a bandwidth 10GHz). Maxwell equations and boundary conditions are used to analyze the absorbing mechanism of the coating.

Abstract: In this paper, Ni-Co coatings on Al foil were prepared by electroplating to obtain Al/Ni-Co composite. Phase transformations and magnetic property of Al/Ni-Co composite heated at 823 K for 80 h were investigated. The results showed that obviously exchanged zone in Al matrix exited and the thickness was about 2.5μm. Ni diffused into the Al easilier than Co. β phase (AlNi and AlCo) and γ phase (Al (Ni, Co) solid solution) of Co-Ni-Al formed during the annealing. The Ms of was decreased significantly when Al diffused into the NiCo alloy film and formed Ni-Al and Co-Al intermetallic compounds.

Abstract: The lithium ions transferring into cathode material are similar as nonequilibrium carrier in semiconductor while the cell discharges at constant current small enough. The inpouring Li-ions can be called nonequilibrium Li-ions. The electrochemical diffusion coefficient, named as D, can be worked out approximately in terms of the relationship between the concentration of nonequilibrium Li-ions and the relevant potential difference. The D was found 3.21×10-10cm²/s for LiFePO₄ doped with 10% acetylene black.

Abstract: Hydrogen generation through high temperature solid oxide electrolysis cells (SOEC) has recently received increasingly international interest in the large-scale, highly efficient nuclear hydrogen production field. To achieve cost competitive electrolysis cells that are both high performing i.e. minimum internal resistance of the cell, and long-term stable, it is critical to develop electrode materials that are optimal for steam electrolysis. In this paper, the cathode materials of SOEC are reviewed. Ni-YSZ and Ni-SDC/GDC cermets are promising cathode materials for SOEC working at high temperature. The solid oxide matierials are promising cathode materials for SOEC working in atmospheres with low content of H2,e.g. in smaller scale generators used intermittently without H2 purging. More works, both experimental and theoretical, are needed to further develop SOEC cathode materials.

Abstract: In this paper, the silicone rubber composed of carbon fibers was prepared. The influence of different concentration of carbon fibers on the conductivity, electromagnetic shielding interference effectiveness property of the silicone rubber was discussed from the point of view of condition of carbon fiber and silicone rubber. The results showed that there existed the extreme conductivity and shielding effectiveness (SE) across the tested frequency range from 2.6 GHz to 3.95 GHz of silicone rubber composites filled with carbon fibers. When the content of the carbon fibbers was 50 parts per hundred of rubber (phr), the SE values of composites were typically above 63 dB and close to the extremum. The compact packing structure of carbon fibers does not play an important role in improved the conductivity of composite. The SE of the composite depends on the conductivity of composite.

Abstract: The microwave permittivity and permeability of Carbon Nanotubes (CNTs)/paraffin and CNTs-Co(C)/paraffin were measured respectively and their differences were discussed in detail. Furthermore, the reflection losses for double-layer CNTs (CNTs-Co(C))/epoxy coatings, with the thickness ranged from 1.6-2 mm, were practically tested through Arc Method in 2.6-18 GHz frequence range. The results indicated that the reflection loss peak shifted towards low frequency and the peak value decreased with the coating thickening and possible mechanisms for the phenomena were given.

Abstract: In this paper，electroless Ni-P plating on copper substrate at 50 °C in ultrasonic field was carried out. The frequency of ultrasonic waves was 40 kHz. The effect of ultrasonic on the composition, plating rate and morphology of Ni-P deposite was investigated at the ultrasonic power of 40, 70 and 100 W. The experimental results showed Ni-P deposit could not be obtained without ultrasonic field at 50 °C. The content of nickel and the thickness of Ni-P deposit increased with the ultrasonic waves power increase. Ultrasonic irradiation power remarkably refines the nodule size of Ni-P particles. The collapse of cavities in solution seems to suppress the Z-direction growth of the nodule.

Abstract: With methyl vinyl silicone (MVQ) as the base rubber, filled with self-synthesized carbon coated aluminum nanoparticles, the high thermal conductive composite was prepared by using the method of mechanical blending. The effect of carbon coated aluminum nanoparticles on thermal conductivity and coefficient of thermal expansion (CTE) of the silicone rubber were investigated, and it was found that thermal conductivity of the composite increased with increasing carbon coated aluminum nanoparticles content during the process of thermal conductive network initially formed to throughout the whole composite, the thermal conductivity began to decrease when the filling content reached 250phr,the optimum filling amount of carbon coated nanoparticles was 250phr.The Y-Agrai model was employed to investigate the thermal conductivity of the thermal conductive composite, results indicated that when the filling content was less than 200phr,theoretical value was coincided with measured value. While the filling content was more than 200phr, theoretical value was gradually less than measured value. While the carbon coated aluminum nanoparticles content increased, the coefficient of thermal expansion (CTE) of composite decreased significantly.

Abstract: Aligned carbon nanotubes (ACNTs) array is synthesized by plasma-enhanced hot filament chemical vapor deposition of the stainless steel substrate covered by ferric nitrate. The morphology and structure of the carbon nanotubes array are characterized by Scanning Electron Microscope and Transmission Electron Microscope. Cyclic voltammetry, constant current charge-discharge technique are employed to test the electrochemical performance of the button-like super-capacitor fabricated using the ACNTs array as electrode. The specific capacitance of the ACNTs array electrode reached 160.9F/g in the potential range of -0.2~+0.8V, at a scan rate of 1mV/s in 1mol/L Na2SO4 aqueous electrolyte.