Hydrogen storage alloy for use in alkaline storage batteries and method for production thereof
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). The hydrogen storage alloy includes a bulk region having a CaCu5-type crystal structure and a substantially uniform composition and a surface region surrounding said 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&gE;1.3 is satisfied.
Sanyo Electric Co., Ltd.
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Masutaka Nobuyuki Shin Yohei Teruhiko Koji Kikuko Mamoru
Ouchi Higashiyama Fujitani Hirota Imoto Nishio Kato Kimoto