Patent ID: 6576367
Filing Date: 2003-06-10
Classification: C01B,H01M,Y02E,Y02P,Y10S

Abstract:
A hydrogen storage alloy, for use in alkaline storage batteries, having a CaCu5-type crystal structure and represented by the compositional formula MmNixCoyMnzMl-z, wherein M represents at least one element selected from the group consisting of aluminum (Al) and copper (Cu); x is a nickel (Ni) stoichiometry and satisfies 3.0&lE;x&lE;5.2; y is a cobalt (Co) stoichiometry and satisfies 0&lE;y&lE;1.2; z is a manganese (Mn) stoichiometry and satisfies 0.1&lE;z&lE;0.9; and the sum of x, y and z satisfies 4.4&lE;x+y+z&lE;5.4;wherein said hydrogen storage alloy includes a bulk region having a CaCu5-type crystal structure, and a surface region surrounding said bulk region and having a graded composition; wherein said surface region is formed by immersing said hydrogen storage alloy in an acid treating solution containing a cobalt compound, a copper compound and an organic additive so that said surface region receives additional copper deposited from said acid treating solution as a result of said immersing in said acid treating solution; and wherein, when the sum of percentages by number of cobalt (Co) atoms and copper (Cu) atoms present in said surface region is given by a and the sum of percentages by number of cobalt (Co) atoms and copper (Cu) atoms present in said bulk region is given by b, the relationship a/b&gE;1.3 for said graded composition is satisfied.