Papers by Author: Ling Long Kong

Abstract: In this paper the fractures appeared in the surface of nanoparticle silicon anode for lithium-ion batteries was explored. The changes of nanoparticle silicon anode before and after cycling were charactered using SEM, XRD,Cyclic voltammograms (CV) and electrochemical impedance spectroscopy (EIS). The result indicates that the electrode cracking occured in the cycling process , the CV, EIS and discharge specific capacity curves proved the fractures could lead to the degradation of the electrochemical performance.

Abstract: Silicon/carbon anode materials of different proportions for lithium ion battery were prepared by high energy ball milling. The composites were characterized using X-ray diffraction (XRD), and scanning electron microscope (SEM). The electrochemical performance of the composites was tested by means of galvanostatic testing system. The results indicated that the initial reversible capacity reached to 2162 mAh•g^-1, which was much larger than the theoretical capacity of carbon negative materials at the ratio of 6:4 (Si: C). The capacity maintained to 1042 mAh•g^-1 after 50 cycles. High capacity and good cycle property of the Si/C composites revealed that they were potential to take the place of the traditional carbon anode materials.

Abstract: To develop novel cathode materials with high electrical performances for intermediate temperature solid oxide fuel cells (IT-SOFCs) and optimize the preparation process, perovskite-type oxides Pr_1-x-ySr_xCa_yCo_1-zFe_zO_3-δ (x=0.1, 0.2; y=0.1, 0.2; z=0.2, 0.3, 0.4; denoted as PSCCF-81182, PSCCF-72173 and PSCCF-62264) were prepared by solid state reaction. The formation process, phase structure and microstructure of the prepared samples were measured using TG-DTA, FT/IR, XRD and SEM techniques. The mixed conductivity of the samples was measured using DC four-terminal method in the range of 150-950 °C. Chemical state of the elements was measured by XPS experiments. The results show that the prepared samples PSCCF-81182, PSCCF-72173 and PSCCF-62264 exhibit a single phase with cubic perovskite structure after sintered at 1200 °C for 6 h. The mixed conductivity of the samples increases with temperature up to a maximum value, and then decreases. At lower temperature, the conductivity follows small polaron hopping mechanism. The negative temperature dependence occurring at higher temperature is due to the creation of oxygen vacancies for charge balance. At intermediate temperature (600-800 °C), the mixed conductivity values of the prepared samples are all much higher than 100 S•cm^-1，and can meet the demand of cathode materials for IT-SOFC. XPS tests show that Co and Fe elements in PSCCF-72173 are all of + 3 and + 4 valence. Absorbed oxygen can also be found from the XPS patterns, which is related to the concentration of oxygen vacancies in the perovskite-type oxides.

Abstract: Si/Al/C composites were synthesized by the method of doping aluminum and glucose-modified. The samples were characterized by XRD, SEM, and the capacity and cycling stability of the composites were tested by electrochemical charge/discharge test system. After glucose was pyrolyzed, the first discharge and charge capacity of Si/Al/C composites were 1312 and 956.7mAh/g, and the first coulombic efficiency was 72.9%. After 50 cycles, the capacity of Si/Al/C composites was 440mAh /g and the coulombic efficiency remained over 98.1%

Abstract: Perovskite-type cathode materials La_0.6Sr_0.2Ca_0.2Co_1-yFe_yO_3-δ (0.2≤y≤0.5, marked as LSCCF62282, LSCCF62273, LSCCF62264 and LSCCF62255) for intermediate-temperature solid oxide fuel cells (IT-SOFCs) were prepared by solid state reaction. The establishment process and phase transformation were measured by TG-DTA, FT/IR and XRD techniques. Single hexagonal perovskite phase can be achieved after sintered at 1100 °C for 3 h. Mixed conductivity, thermal expansion behavior and chemical stability of sintered samples at 1100 °C for 3 h have been investigated. At intermediate temperature (600-800 °C), the mixed conductivity characterized by DC four-probe technique is higher than 100 S/cm. LSCCF62282 has the highest conductivity of 297.3 S/cm at 700 °C among the four samples. At lower temperatures, the conductivity follows small polaron hopping mechanism. Thermal expansion coefficients (TECs) of the samples from 50 °C to 850 °C exhibit a reducing tendency with increasing amount of doped Fe³⁺. Thermal expansion behavior can be improved by doping with Ca²⁺ and Fe³⁺ commonly. XRD pattern for LSCCF62282 and YSZ mixture sintered at 800 °C for 6h indicates that cathode material LSCCF62282 is chemically stable against YSZ electrolyte at operating temperature.

Abstract: Si/C composites were synthesized by using graphite and glucose as carbon source. The samples were characterized by X-ray diffractometer (XRD) and field emission scanning electron microscope(SEM). The electrochemical charge/discharge test was used to evaluate capacity and cycling stability of the composites. The first discharge and charge capacity of SGC composite using graphite and glucose as carbon source were 1661mAh/g and 1259.1 mAh/g, and the first coulombic efficiency was 75.8%. After 20 cycles, the capacity of SGC composite was 380 mAh/g and the coulombic efficiency remained over 98%.