Method for production of hydrogen storage alloy for use in alkaline storage batteries

Abstract

A method of producing a hydrogen storage alloy, for use in alkaline storage batteries, includes two steps. A first step involves preparing alloy particles having a CaCu5-type crystal structure and the compositional formula MmNixCoyMnzM1−z, wherein M represents at least one element selected from the group consisting of aluminum (Al) and copper (Cu), 3.0≦x≦5.2, 0≦y≦1.2, 0.1≦z≦0.9, and 4.4≦x+y+z≦5.4. A second step involves immersing the alloy particles in an acid treating solution containing a cobalt compound and a copper compound, each in the amount of 0.1 to 5.0% by weight based on the weight of the alloy particles, and an organic additive to remove oxide films from and to reductively deposit cobalt and copper on a surface of each alloy particle to form a surface region surrounding a bulk region and having a graded composition. When the sum in percentage of numbers of cobalt (Co) atoms and copper (Cu) atoms present in the surface region is given by a and that in the bulk region by b, the relationship a/b≧1.3 is satisfied.

Dependencies are inferred from the claim text.