Rare earth metal-nickel hydrogen storage alloy and negative electrode for nickel metal hydride secondary battery

摘要

PROBLEM TO BE SOLVED: To provide a hydrogen storage alloy having superior characteristics by subjecting a molten alloy, having a specific composition consisting of rare earth element and Ni alloy, to rapid solidification under specific conditions and then to heat treatment in vacuum or in an inert gas atmosphere. SOLUTION: A molten alloy, having a composition represented by general formula [where R and L are lathanoide series rare earth elements from La to Nd and from Gd to Lu, respectively, or Y, Sc, Mg, Ca, Ti, Zr, etc., and M represents Co, Al, Mn, Fe, Cu, Zr, Ti, Mo, Si, V, Cr, Nb, Hf, Ta, W, B, and C, and the symbols (x), (y), and (z) are 0.2=X=0.6, 0=Y=0.5 and 1.8=Z=3.0, respectively] is used. This molten alloy is uniformly cooled and solidified under the cooling conditions of 50-500 deg.C degree of supercooling and (1000 to 10000) deg.C/sec cooling rate, and the resulting ingot is heated in vacuum or in an inert atmosphere at 600-750 deg.C for 0.1-12hr. By this method, the (rare earth metal)-Ni based hydrogen storage alloy, which contains the crystal, containing antiphase boundaries perpendicular to the crystalline C axis by 20-40 pieces for 20nm in a C-axial direction, by 50-95vol.% and is excellent as a cathode for Ni-H2 secondary battery, can be produced.