Papers by Author: Kiyoshi Kanamura

Abstract: A polymer wall was developed between interdigitated comb-type current collectors on a SiO₂/Si substrate as the support for three-dimensionally (3D) accurate deposition of electrode materials by electrophoretic deposition (EPD) method. As anode and cathode materials, Li₄Ti₅O₁₂ and LiCoO₂ with a particle size of ~ 200 nm were synthesized, respectively, and their dispersibility in the suspensions including Ketjen Black and poly (vinylidene fluoride) was investigated. Consequently, N-methylpyrrolidone provided their good suspensions, and an electrode aspect ratio of 1:1, which can provide a high capacity and good rate performance to micro lithium-ion batteries, was successfully achieved in both Li₄Ti₅O₁₂ composite anode and LiCoO₂ composite cathode.

Abstract: Anode for direct methanol fuel cell (DMFC) was fabricated on Nafion 117 membrane by electrophoretic deposition (EPD) method. An ethanol suspension containing Pt-Ru/C and Nafion ionomer was utilized, in which Pt-Ru/C and Nafion ionomer formed composite particles. The prepared electrode was tightly attached to the membrane without mechanical pressing and heat treatment. The electrode composition, i.e., the ratio between Pt-Ru/C and ionomer in the electrode, was controllable by Nafion content in the suspension, and strongly influenced on the DMFC performance. Accordingly, the anode with ionomer fraction of 26% exhibited the highest performance, which was more than twice as high as the performance attained in a standard electrode fabrication (hot press method).

Abstract: Macroporous LiCoO2 was prepared by a colloidal crystal templating method. Colloidal crystal consisting of monodisperse polystyrene particles was used as the template for the synthesis of macroporous LiCoO2. A Li-Co-O sol was injected into the template, and it was calcined at high temperatures. A porous membrane of LiCoO2 with three dimensionally ordered macroporous (3DOM) structure was obtained. The prepared material had a rock-salt type crystallographic structure with R3m space group. The interconnected macropores with relative uniform size (0.8~0.9 ;m) were observed on entire part of the membrane. The electrochemical properties of the 3DOM LiCoO2 were characterized with galvanostatic charge-discharge measurements in an organic electrolyte containing a lithium salt. The 3DOM LiCoO2 exhibited charge and discharge capacities of 136 and 107 mA h g-1, respectively, at around 3.9 V vs. Li/Li+, indicating that 3DOM LiCoO2 electrode had solid state redox reaction accompanying with Li+ ion insertion and extraction to CoO2 frameworks.

Abstract: Three dimensionally ordered macroporous (3DOM) Li4Ti5O12 was successfully prepared by a colloidal crystal templating process. Colloidal crystal consisting of monodisperse polystyrene particles (1 9m diameter) was used as a template for the synthesis of macroporous Li4Ti5O12. A precursor sol consisting of titanium isopropoxide and lithium acetate was injected into the template, and it was calcined at high temperatures. A macroporous membrane of Li4Ti5O12 with inverse-opal structure was obtained. The prepared material had a spinel-related crystallographic structure. The interconnected pores with uniform size (0.8 9m) were clearly observed on entire part of the membrane. The electrochemical properties of the 3DOM Li4Ti5O12
were characterized with cyclic voltammetry and glavanostatic charge-discharge in an organic electrolyte containing a lithium salt. 3DOM Li4Ti5O12 exhibited a discharge capacity of 160 mA h g-1 at the electrode potential of 1.55 V vs. Li/Li+ due to the solid state redox of Ti3+/4+ accompanying with Li+ ion insertion and extraction. The discharge capacity was close to the theoretical capacity (167 mA h g-1). This means that the Li+ insertion and extraction took place at all part of the 3DOM Li4Ti5O12 membrane.

Abstract: A novel micropatterning process for a particle assembly has been performed by using an electrophoretic deposition (EPD) method with a local electric field in a colloidal suspension generated by a three-electrode system. Monodisperse silica colloidal spheres with a diameter of 300 nm were used to fabricate micropattern of colloidal crystal. An interdigitated gold-microarray electrode with a 10 μm of width and a gold plate electrode were used as the working and the counter electrodes, respectively. After optimization of the EPD processing parameters, a micropattern was constructed from silica colloidal spheres. It had a relatively close-packed structure formed onto the interdigitated microarray electrode. This micropattern showed a characteristic optical reflectance peak due to Bragg’s law.

Abstract: A novel micro-fabrication technique for particle assembly has been performed by an electrophoretic deposition (EPD) method using a local electric field in a colloidal suspension generated by a microelectrode. This unique EPD technique was called a “μ-EPD process”. Monodispersed polystyrene microspheres with diameters of 204, 290, and 320 nm were used in this study. A 50 μm Pt wire embedded into a polytetrafluoroethylene tube and an ITO glass slide were employed as the micro-counter electrode and the substrate, respectively. A slow deposition rate in the μ-EPD process was preferable to form a high quality micro-deposit consisting of a three-dimensional periodic polystyrene array. Under the optimized μ-EPD conditions, three-dimensionally ordered polystyrene particles were deposited in front of the micro-counter electrode. This micro-deposit constructed from polystyrene particles with a close-packed structure showed a characteristic optical absorption peak due to Bragg’s law.

Abstract: Micrometer wire consisting of microbeads was successfully fabricated onto a patterned conductive electrode substrate by an electrophoretic deposition (EPD) process with precise control of electric field distribution generated in the colloidal suspension. Monodisperse polystyrene microspheres with 320 nm in diameter and an interdigitated microarray Au electrode having 10 μm in width and 5 μm in spacing were used in this EPD system. A micropattern of polystyrene particles with two dimensional arrays was formed onto the patterned electrode by the EPD process with two electrode system using an electrostatic interaction between the electrodes and the charged particles in the suspension.

Abstract: A new proton-conducting membrane was prepared consisting of uniformly macroporous silica matrix and a proton-conducting gel polymer, 2-acrylamido-2-methyl-1-propanesulfonic acid (AMPS). Three-dimensionally ordered macroporous silica membrane was fabricated by use of a colloidal template method with mono-dispersed polystyrene beads. Surface sulfonation of the pores in the silica matrix was performed by using 1,3-propanesultone. The sulfonated silica matrix exhibited about 400 times higher proton conductivity than unmodified one. The proton conductivity of the composite membrane was also successfully enhanced by using the sulfonated silica matrix.

Abstract: Thin films of lithium ion conductive ceramic Li4+xAlxSi1-xO4 were fabricated on Au substrate using sol-gel process. The sol of Li-Al-Si-O was spread on Au substrate using a spin coater, and it was gelated at room temperature. The gel was calcinated at 400 °C and heat-treated at high temperatures between 500 °C and 800 °C in air. The addition of poly(vinylpyrrolidone) (PVP) was effective in stabilizing the sol. Furthermore, the morphology of the obtained thin film was changed by the PVP additive. Li4+xAlxSi1-xO4 thin film prepared at 800 °C exhibited a Li+ ion conductivity of 10-8 S cm-1 at room temperature.