HYDROGEN STORAGE ALLOY CONTAINING RARE EARTH ELEMENT, ITS PRODUCTION, ALKALI STORAGE BATTERY CATHODE USING THE ALLOY, AND ALKALI STORAGE BATTERY

摘要

PROBLEM TO BE SOLVED: To provide a metal-hydrogen alkali storage battery, excellent in various characteristics including low temp. characteristic, and a cathode for it and also to provide a hydrogen storage alloy, suitable for the cathode, and its production. SOLUTION: The hydrogen storage alloy containing rare earth elements has at least one required condition selected from among the following (1) and (2):(1) as impurities, this alloy contains, by weight, =1,200ppm nonmetallic elements, =10ppm, in total, of alkali metal elements, =100ppm, in total, alkaline earth metal elements, =80ppm Mg, and =100ppm Pb; (2) oxygen concentration is abruptly decreased from the surface and the average oxygen concentration in the range between the surface and a position at a depth of 20nm from the surface is regulated to =10wt.%, and further, among the Ni elements constituting the hydrogen storage alloy, the Ni atoms combined with oxygen are abruptly decreased from the surface in the surface layer between the surface and a position at a depth of 20nm from the surface and also the ratio of these Ni atoms combined with oxygen to Ni atoms is regulated to 5wt.% on the average in the range between the surface and a position at a depth of 20nm from the surface.