Tadashi Ise

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.

The surface structure and the electrochemical properties of hydrogen-absorbing alloys treated with an HCl aqueous solution

The surface structure and the electrochemical properties of hydrogen-absorbing alloys treated with an HCl aqueous solution were investigated. This process was observed to form a porous layer rich in nickel on the alloy surface because HCl partially dissolved some of the other elements from the alloy. Therefore, the discharge capacity increased by increasing the reaction surface area. However, the overvoltage of an excessively treated alloy increased along with the depth of discharge as the surface layer of the alloy oxidized and thickened. The effects of treatment on alloys were found to be determined by the hydrogen ion amounts in the acid solution per unit mass of the alloy, regardless of the concentration and volume of the solution. The optimal hydrogen ion amount for a treatment solution was found to be 0.1 mol/kg.

The effect of particle size on the electrochemical properties of hydrogen absorbing alloy electrodes

Abstract The investigation of the effect of the particle size of hydrogen-absorbing-alloys on the electrochemical properties of electrodes revealed that the electrochemical reactivity of small-particle electrodes containing conductive powder was excellent, but that the discharge capacity of the alloy electrodes composed of small particles containing no conductive powder was small. A possible reason for this reduced capacity is the existence of particles that cannot be discharged due to weak contact between the particles as the volume of the alloy changed. Thus, batteries made from electrodes composed of particles larger than 25 μm were found to have superior charge–discharge cycle characteristics.