Shinsuke Nakahori

Nickel electrode active material; a nickel electrode and a nickel alkali storage cell using such nickel electrode active material; and production methods of such material, electrode, and cell

Fine-grained nickel electrode active material, each of which contributing to electrode reaction; production method of the fine-grained nickel electrode active material; and a nickel alkali storage cell of high capacity which is excellent in over discharge characteristics. In order to produce the fine-grained nickel electrode active material, fine-grained nickel hydroxide is precipitated by adding a given amount of alkali to solution in which at least a nickel compound is dissolved while the solution is stirred. Each of the fine-grained nickel hydroxide has pores with 20 vol % or more of a combined volume of the pores being composed of pores of diameter 60 Å or greater. Next, a given amount of alkali is gradually added to suspension including the fine-grained nickel hydroxide and dissolved cobalt compound so that cobalt hydroxide is precipitated on the external surface of the fine-grained nickel hydroxide. The fine-grained nickel electrode active material is produced in the above mentioned way. Each of the fine-grained nickel electrode active material comprises a nickel hydroxide and cobalt oxide having distorted crystal structure and oxidation number higher than +2. The nickel hydroxide has pores whose diameters are 60 Å or greater. And the volume of such pores amounts to 20 vol % or more of the combined volume of all of the pores.

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.