Koichi Kobayakawa

Self-sterilizing and self-cleaning of silicone catheters coated with TiO2 photocatalyst thin films: A preclinical work

TiO(2) photocatalysts were successfully coated on silicone catheters or medical tubes by pretreatment of the silicone surface with a sulfuric acid solution (5 M) for 3 h. The TiO(2) film adhered to the silicone substrate strongly against tensile and bending stresses. On the TiO(2)-coated silicone-catheters under UV illumination, both the bleaching of methylene blue dye and the photocatalytic bactericidal effect on Escherichia coli (E. coli) cells were confirmed. Thus, this type of catheter can be sterilized and cleaned simply by irradiation with low-intensity UV light and can, therefore, be useful in the protection from catheter-related bacterial infections.

Cause of the memory effect observed in alkaline secondary batteries using nickel electrode

Abstract The cause of the memory effect observed in alkaline-type rechargeable batteries such as nickel–cadmium and nickel–hydrogen batteries was studied using a positive capacity-limited nickel–cadmium cell and AAA-type commercially available nickel–cadmium and nickel–hydrogen batteries. From the X-ray diffraction (XRD) analysis, γ-NiOOH was observed on the nickel electrode in a charged state after repeating shallow discharge cycling of the cells or overcharging. This γ-NiOOH is initially formed at the collector side of the electrode and it then grows to the solution side during shallow discharge cycling. When the amount of γ-NiOOH formed is small, only β-NiOOH can be detected by conventional XRD, even when the memory effect is observed. In this case, γ-NiOOH can be detected by shaving the surface of the electrode, using an emery paper to remove the β-NiOOH covering. This γ-NiOOH disappeared within a few cycles of the normal charge–discharge cycling and the memory effect disappeared. It is concluded that the cause of the memory effect is mainly due to the formation of γ-NiOOH.

Observation of structure change due to discharge/charge process of V2O5 prepared by ozone oxidation method, using in situ X-ray diffraction technique

Abstract The change in structure of vanadium pentoxide due to the discharge/charge process of V 2 O 5 prepared by the ozone oxidation method (O 3− V 2 O 5 ) was studied using an in situ X-ray diffraction technique. The diffraction peaks of (600), (020), (420) and (710) shifted to lower angles as Li + intercalation progressed until about x = 0.8. Then they disappeared and a new broad peak appeared at 47°, which means that lattice extension and structure change occurred. When the O 3− V 2 O 5 was discharged to x = 1.8 and then charged, the XRD pattern recovered to almost its initial pattern. The change in the chemical diffusion coefficient ( D ) for O 3− V 2 O 5 measured using the GIT and the AC techniques closely corresponded to the behavior observed using the in situ XRD technique, i.e. the change in diffusion coefficient levelled at about x = 0.8, but after that the value of D decreased. The changes in the chemical diffusion coefficients of other types of V 2 O 5 (orthorhombic, electrochemically prepared and amorphous V 2 O 5 ) were also measured and their changes due to Li + intercalation are discussed.

Synthesis of nano-crystalline LiFeO2 material with advanced battery performance

LiFeO2 has been synthesized at low temperature (150 °C) using the solid-state method. It was composed of orthorhombic LiFeO2 and small amount of spinel LiFe5O8 phases. A Li/LiFeO2 cell showed not only a fairly high initial discharge capacity of over 150 mAh/g, but also a good cycle retention rate at room temperature. During the cycling test, the Li/LiFeO2 cell exhibited a unique abrupt capacity drop near the 13th cycle and continuously showed an excellent cycling performance of over 99% for 25 cycles. We found that the orthorhombic LiFeO2 underwent a structural change to the spinel phase during the charge/discharge process which resulted in the capacity decline during the long-term cycling.

Gas evolution behavior of Zn alloy powder in KOH solution

Abstract To reduce the mercury content in an alkaline manganese battery, a Zn alloy is used. In the absence or presence of small amounts of mercury, hydrogen gas evolution from the Zn alloy in KOH solution was found to be accelerated by the addition of ZnO or Zn(OH)2 which is the discharge product of Zn. Partly discharged Zn alloy also evolved hydrogen more vigorously compared to undischarged Zn alloy. An optimum quantity of In2O3 added to the Zn reduced hydrogen evolution. Indium metal deposited on Zn by the reduction of In2O3 by Zn will suppress hydrogen evolution because of its large overpotential for the hydrogen evolution reaction. Indium metal was detected by X-ray diffraction analysis of the Zn alloy containing In2O3.

Structural change and capacity loss mechanism in orthorhombic Li/LiFeO2 system during cycling

Abstract Orthorhombic LiFeO 2 was synthesized at low temperature (150 °C) using a solid-state method. The Li/LiFeO 2 cell presented not only a high initial capacity of over 150 mAh/g, but also fairly good cycle retention of 73% after 50 cycles within a voltage range between 1.5 and 4.5 V. It was found that the orthorhombic phase of the LiFeO 2 material underwent a structural change to the spinel phase during cycling. Especially it showed severe structural changes during the first charge/discharge process, which might be the main reason to induce the capacity loss of the Li/LiFeO 2 system. We reported a new observation about the structural change mechanism of the orthorhombic Li/LiFeO 2 cell during cycling using in situ XRD and TEM analyses.

Particle-size effect of carbon powders on the discharge capacity of lithium ion batteries

To improve the performance of the negative electrodes for lithium-ion batteries, a study has been made of the particle-size effect of carbon powder on discharge capacity and the optimum mixing ratio between large (average diameter: 25.8 μm) and small (average diameter: 4.2 μm) powder particle size has been found. The largest capacity is obtained when the large particle size fraction is about 70 wt.%. The smaller the particle size ratio, the larger the capacity, where the particle size ratio is the ratio of the average diameter of the smaller component to that of the larger one. These results indicate that discharge capacity is closely related to carbon powder packing, which is controlled by the mixing weight and particle-size ratios.

Photocatalytic activity of CuInS2 and CuIn5S8

Abstract The photocatalytic activity of CuInS 2 and CuIn 5 S 8 , prepared by chemical precipitation, for the hydrogen evolution from aqueous sulfite solution was investigated. The photocatalytic activity of CuIn 5 S 8 was about twice that of CuInS 2 and was improved remarkably by the addition of silver sulfide.

Characteristics of coke carbon modified with mesophase-pitch as a negative electrode for lithium ion batteries

Abstract To increase the charge–discharge capacity of carbon electrodes for lithium ion secondary batteries, coke carbon, a relatively cheap material, was modified with mesophase-pitch carbon by a heat treatment. While coke carbon powder, mesophase-pitch, and a mixture thereof (4:1 by weight) supplied between 0 and 1.5 V vs. Li/Li+ an initial discharge capacity of about 295 mAh/g, 310 mAh/g, and 310 mAh/g, respectively, the modified coke deintercalated 400 mA h/g of lithium with a high degree of reversibility. The difference in capacity between the modified carbon and mixture are discussed based on the shape of their current–potential curves and their galvanostatic charge–discharge curves.

Possible cause of the memory effect observed in nickel-cadmium secondary batteries

After repeated shallow discharging and overcharging of nickel or cadmium capacity-limited cells, a working voltage lowering of the discharge curve was observed. The magnitude of the lowering was higher in the nickel capacity-limited cells. The X-ray diffraction pattern of the charged-state normal nickel electrode contained diffraction peaks due only to {beta}-NiOOH. A charges-state nickel electrode showing a lowered discharge voltage and diffraction peaks due to {gamma}-NiOOH, in addition to those due to {beta}-NiOOH. This may be a cause of the memory effect observed in practical nickel-cadmium batteries.