Mitsuzo Nogami

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.

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.