Mamoru Kimoto

Development of hydrogen-absorbing alloys for nickel-metal hydride secondary batteries

Abstract The effect of the stoichiometry of Mm(Ni 0.64 Co 0.2 Mn 0.12 Al 0.04 ) x alloy on the hydrogen absorption capacity, and the reactivity of two-phase alloys in alkaline solution, were investigated. Furthermore, the electrochemical characteristics of non-stoichiometric hydrogen-absorbing alloys with a second phase were investigated. Nonstoichiometric hydrogen-absorbing alloys ( x =4.5–4.8) with boron added were found to have higher electrochemical capacities and superior electrochemical reactivities than those of stoichiometric alloys without boron added.

Potentiodynamic reactivation of a passivated lead negative electrode in sulphuric acid solution

Abstract When a fully charged lead negative electrode stood for one month in 1.0 M H 2 SO 4 solution at a temperature of 298.15 K, it was passivated through so-called “sulfation” as indicated by a decrease in the redox peak currents on cyclic voltammograms. As a method of reactivating the passivated lead negative electrode, we proposed the electrochemical redox potentiodynamic method in the potential range from 0.6 V vs. she to the potential of oxygen evolution at a positive electrode. It is recognized that the activity of the passivated lead negative electrode recovered completely after several cycles of such electrochemical treatment.

Hydrogen-absorbing alloy electrode for metal hydride alkaline batteries and process for producing the same

A hydrogen-absorbing alloy electrode for metal hydride alkaline batteries uses as hydrogen-absorbing material a powder of a rare earth element-nickel hydrogen-absorbing alloy obtained by pulverizing thin strips of said alloy prepared by single roll process and having an average thickness of 0.08 to 0.35 mm and a minimum size of crystal grains present in the roll-surface size of at least 0.2 μm and a maximum size of crystal grains in the open-surface side of not more than 20 μm. A process for producing the above electrode is also provided. The electrode can provide, when used as negative electrode, metal hydride alkaline batteries which are excellent in both high-rate discharge characteristics at an initial period of charge-discharge cycles and charge-discharge cycle characteristics.

Direct Synthesis of Carbon Nanotubes on Ti-Coated Metal Substrates and Its Application to Electrochemical Double Layer Capacitors

We have successfully developed a method of direct synthesis of carbon nanotubes on catalytic metal substrates, which uses the predeposition of Ti thin layers by thermal chemical vapor deposition. It was found that the amount of carbon nanotubes was dependent on the thickness of the Ti thin layers. We have fabricated a test device of electrochemical double layer capacitors incorporating the grown carbon nanotubes as electrodes, which exhibited stable charge/discharge characteristics.

Influence of surface treatment by HCl aqueous solution on electrochemical characteristics of a Mm(Ni–Co–Al–Mn)4.76 alloy for nickel–metal hydride batteries

Abstract Surface treatment of a Mm(Ni0.64Co0.20Al0.04Mn0.12)4.76 alloy used as negative electrode material was examined to improve the performance of nickel–metal hydride secondary batteries. The surface treatment was conducted by dipping and stirring the alloy into an HCl aqueous solution of pH 1.0 at room temperature. Initial discharge characteristics and charge–discharge cycle performance of the surface-treated alloy were evaluated by an electrochemical half cell and a sealed test cell. The surface structure of the surface-treated alloy was analyzed by X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) with an energy disperse X-ray spectrometer (EDX). In this paper, the influence of the surface treatment on the charge–discharge characteristics, particularly on the initial discharge characteristics, and surface structure of the alloy are discussed.

Microstructure and electrochemical characteristics of surface-treated Mm(Ni-Co-Al-Mn)4.76 alloys for nickel–metal hydride batteries

Abstract The microstructure and electrochemical characteristics of surface-treated Mm(Ni 0.64 Co 0.20 Al 0.04 Mn 0.12 ) 4.76 alloys, (a) induction-melted and subsequently annealed alloy and (b) rapidly quenched and subsequently annealed alloy were examined to clarify the influence of the microstructure on the surface treatment effects. The surface treatment was conducted by dipping and stirring the alloys into an HCl aqueous solution of pH 1.0 at room temperature. Their initial discharge characteristics and charge–discharge cycle performance were evaluated by an electrochemical half cell and a sealed test cell. The surface structure was analyzed by using X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) with an energy disperse X-ray spectrometer (EDX). It was found that a more homogeneous microstructure present before the surface treatment leads to an increase of the specific surface area and to an enrichment of Ni and Co metal on the surface layer of the surface-treated alloy. This leads to an enhancement of the initial electrochemical activity.

Hydrogen-absorbing alloy electrode for metal hydride alkaline battery

A hydrogen-absorbing alloy electrode for metal hydride alkaline batteries is obtained by coating or filling a collector with a hydrogen-absorbing alloy powder consisting essentially of spherical particles and/or nearly spherical particles and then sintering the powder, the powder having an average particle diameter of 30 to 70 μm and containing 5 to 30% by volume of particles having a diameter of at least 2 times the average diameter and 10 to 40% by volume of particles having a diameter of not more than 1/2 of the average diameter. This electrode can give metal hydride alkaline batteries having excellent high-rate discharge characteristics and a long life.