Papers by Author: Takashi Ogihara

Abstract: Spherical C/LiMn1-XMXPO4 (M=Mg, Zn) cathode materials were successfully prepared by spray pyrolysis. An olivine structure was obtained by heating at 973 K under argon/hydrogen (5%) atmosphere. Citric acid was used as the carbon source. Scanning electron microscopy (SEM) showed that the materials had spherical morphology. The electrochemical properties of the cathode were also estimated by the rechargeable capacity and cycle performance. The first discharge capacity of C/LiMn1-XZnXPO4 (X = 0.1) was approximately 60 mAh/g　at 0.1 C.

Abstract: Spherical LiAl0.05Mn1.95O4 precursor powders were successfully prepared by spray pyrolysis. LiAl0.05Mn1.95O4 precursor powders were calcined by 800°C for 10hrs. The particles size, morphology, microstructure, crystal phases of the calcined powders were characterized by X-ray diffraction (XRD) and a scanning electron microscope (SEM). The XRD patterns showed that the crystal phases of the calcined powders were the same as spinel phase (space group: Fd3m). The particles exhibited a spherical morphology with a porous microstructure. The particle size of the primary particles was approximately 200nm. LiAl0.05Mn1.95O4 cathodes exhibited higher rechargeable capacity and cycle stability at high rates. The particle microstructure of LiAl0.05Mn1.95O4 powders was effective for the rechargeable capacity at high rates.

Abstract: La0.8Sr0.2Ga0.8Mg0.2O3-δ (LSGM) precursor particles were successfully prepared by ultrasonic spray pyrolysis. LSGM thin films were prepared by the electrophoretic deposition (EPD) technique using ethanol containing iodine. The LSGM films were obtained by sintering at 1300 °C for 10 h. The X-ray diffraction patterns revealed that the diffraction peak of LSGM thin films was in agreement with the perovskite structure. The LSGM films attained a uniform thickness of 10 μm.

Abstract: Spherical La0.8Sr0.2Ga0.8Mg0.2O3-δ (LSGM) precursor powders were synthesized by aerosol plasma pyrolysis using an aqueous solution of metal nitrate. As-prepared powders obtained by this method were found to have a spherical morphology with a bimodal size distribution of nanosized (primary) and submicron-sized (secondary) particles. The average size of the primary particles was less than 100 nm. X-ray diffraction (XRD) patterns showed that as-prepared powders crystallized to LSGM and other phases. XRD revealed that LSGM pellets were crystallized to a perovskite structure after sintering at 1300 °C for 10 h.

Abstract: Ag and Ni spherical fine powders were continuously produced by carrying out an aerosol process in a mass nanopowder production apparatus. The particles size, particle morphology, crystal phases and crystallinity of the as-prepared powders were characterized by a scanning electron microscope (SEM) and X-ray diffraction (XRD). The particles were nonaggregated and they exhibited a spherical morphology with a narrow size distribution. The average sizes of Ag and Ni particles were 500 nm and 700 nm, respectively. The crystallinity of the as-prepared powders was high. The XRD patterns showed that the crystal phases of the as-prepared powders were the same as those of their respective metals.

Abstract: Spherical Ce0.8Sm0.2O1.9 precursor powders were synthesized by Aerosol Plasma pyrolysis using aqueous solution of metal nitrate. As-prepared powders obtained by this method have a spherical morphology with a nano size and submicron size. They had bimodal size distribution. The average size of primary particles was less than 100 nm. The concentrations of starting solution influenced to average particle size. The relative density of SDC pellet was highest when it was sintered at 1623 K. The relative density was 86 %. XRD, SEM, DTA-TG and BET analysis were used for determination of the composition, morphology, particle size and surface area.

Abstract: Spherical C/LiFePO4 cathode materials were successfully prepared by spray pyrolysis. The saccharides such as monosaccharide and disaccharide or organic acid were used as carbon source. SEM observation showed that they had spherical morphology with particle size of about 1m. XRD analysis revealed that the olivine phase was obtained by heating at 700 °C under the atmosphere of argon/hydrogen (5 %). Electrochemical measurement revealed that the rechargeable capacity of LiFePO4 was significantly improved by the addition of carbon. The use of sucrose was most effective for the high rechargeable capacity and cycle stability.

Abstract: Spherical porous Mn2O3 powders were prepared by spray pyrolysis. Li and Al nitrate solution were immersed to porous Mn2O3 powders to obtain LiAlXMn2-XO4. Homogeneous LiAlXMn2-XO4 powders were formed by the calcination at 800°C. SEM observation showed that they had spherical morphology with particle size of about 1m. XRD revealed that the spinel phase was obtained by heating at 800°C. LiAlXMn2-XO4 cathode obtained by this method exhibited higher rechargeable capacity and cycle stability than that obtained by spray pyrolysis. The doping of Al ion was effective for the cycle stability at elevated temperature.

Abstract: Conductive SnO2 powder was synthesized by ultrasonic spray pyrolysis and was blended with TiO2 nano particles in order to improve the conductivity of TiO2 porous films used in dye-sensitized solar cells. However, the conductivity of the films decreased because of the exposure of SnO2 to high temperature during synthesis and calcination.

Abstract: Silver nanoparticles produced with a solid-phase thermal decomposition method were used for the preparation of a conductive paste supporting curing at low temperatures. The conducting paste was prepared by blending fine spherical silver powder and silver nanoparticles with a diameter of 20nm in order to reduce the electric resistivity of the electrodes. Although the viscosity of the conducting paste increased by about 25% after 60 days, it exhibited superior stability to dispersion in comparison to commercial paste. The electric resistivity of the electrode was of the order of 10-6Ωcm at a curing temperature of 200°C. Using this conducting paste, it is possible to print at widths of 20m. The resistivity was further reduced by 1% in the high temperature test at 120°C, by 5% in the high humidity and high temperature test, and by 5% during the thermal shock test at temperatures ranging from -45 to 80°C.