Hydrogen-absorbing alloy for batteries, process for their production and nickel-metal hydride secondary battery

摘要

A hydrogen-absorbing alloy for battery according to the present invention comprises an alloy having the composition represented by a general formula A Nia Mnb Mc [where, A is at least one kind of element selected from rare earth elements including Y (yttrium), M is a metal mainly composed of at least one kind of element selected from Co, Al, Fe, Si, Cr, Cu, Ti, Zr, Zn, Hf, V, Nb, Ta, Mo, W, Ag, Pd, B, Ga, In, Ge and Sn, 3.5/= a/= 5, 0.1 /= b /= 1, 0 /= c /= 1, 4.5/= a + b + c/= 6], wherein the alloy has columnar structures in which the area ratio of the columnar structures having the ratio of a minor diameter to a major diameter (aspect ratio) of 1 : 2 or higher is 50 % or more. Further, an average minor diameter of the columnar structures is set to 30 microns or less. With this arrangement, there can be provided a nickel-metal hydride battery capable of satisfying the three leading characteristics of a high electrode capacity, long life and good rising-up all together.