Hydrogen storage alloy and nickel-metal hydride storage battery using the same

A hydrogen storage alloy represented by the general formula MmNi.sub.a Al.sub.b Mn.sub.c Cu.sub.d Co.sub.e, wherein Mm is a misch metal or a mixture of rare earth elements, and wherein 0.2.gtoreq.b.gtoreq.0.8, 0.2.gtoreq.c.gtoreq.0.8, 0.8.gtoreq.b+c.gtoreq.1.4, 0.gtoreq.d.gtoreq.0.8, 0.gtoreq.e.gtoreq.0.3, and 5.2.gtoreq.a+b+c+d+e.gtoreq.5.5, and an amount of La contained in said Mm is in a range between 40 wt % and 70 wt %, said alloy having a microstructure comprising:

• a phase which is composed of a crystal structure of CaCu.sub.5 type, and is capable of absorbing and desorbing hydrogen in a reversible manner, and
• at least one phase which consists mainly of an element or elements other than Mm, and is incapable of storing hydrogen.

A hydrogen storage alloy represented by the general formula MmNi.sub.a Al.sub.b Mn.sub.c Cu.sub.d Co.sub.e Fe.sub.f, wherein Mm is a misch metal or a mixture of rare earth elements, and wherein 0.2.gtoreq.b.gtoreq.0.8, 0.2.gtoreq.c.gtoreq.0.8, 0.8.gtoreq.b+c.gtoreq.1.4, 0.gtoreq.d.gtoreq.0.8, 0.gtoreq.e.gtoreq.0.3, 0<f.gtoreq.0.3, and 5.2.gtoreq.a+b+c+d +e+f.gtoreq.5.5, and an amount of La contained in said Mm is in a range between 40 wt % and 70 wt %, said alloy having a microstructure comprising:

• a phase which is composed of a crystal structure of CaCu.sub.5 type, and is capable of absorbing and desorbing hydrogen in a reversible manner, and
• at least one phase which consists mainly of an element or elements other than Mm, and is incapable of storing hydrogen.

A hydrogen storage alloy represented by the general formula MmNi.sub.a Al.sub.b Mn.sub.c Cu.sub.d Co.sub.e Fe.sub.f Cr.sub.g, where Mm is a misch metal or a mixture of rare earth elements, and wherein 0.2.gtoreq.b.gtoreq.0.8, 0.2.gtoreq.c.gtoreq.0.8, 0.8.gtoreq.b+c.gtoreq.1.4, 0.gtoreq.d.gtoreq.0.8, 0.gtoreq.e.gtoreq.0.3, 0<f.gtoreq.0.3, 0<g.gtoreq.0.1, and 5.2.gtoreq.a+b +c+d+e+f+g.gtoreq.5.5, and an amount of La contained in said Mm is in a range between 40 wt % and 70 wt %, said alloy having a microstructure comprising:

• a phase which is composed of a crystal structure of CaCu.sub.5 type, and is capable of absorbing and desorbing hydrogen in a reversible manner, and
• at least one phase which consists mainly of an element or elements other than Mm, and is incapable of storing hydrogen.

A hydrogen storage alloy represented by the general formula MmNi.sub.h Al.sub.i Mn.sub.j Fe.sub.k Cr.sub.l, wherein Mm is a misch metal or a mixture of rare earth elements, and wherein 0.2.gtoreq.i.gtoreq.0.8, 0.2.gtoreq.j.gtoreq.0.8, 0.8.gtoreq.i+j.gtoreq.1.4, 0.gtoreq.k.gtoreq.0.8, 0.gtoreq.l.gtoreq.0.1, 5.2.gtoreq.h+i+j+k+l.gtoreq.5.5, and an amount of La contained in said Mm is in a range between 40 wt % and 70 wt %, said alloy having a microstructure comprising:

• a phase which is composed of a crystal structure of CaCu.sub.5 type, and is capable of absorbing and desorbing hydrogen in a reversible manner, and
• at least one phase which consists mainly of an element or elements other than Mm, and is incapable of storing hydrogen.

The hydrogen storage alloy in accordance with claim i, wherein said phase incapable of storing hydrogen is dispersed in said phase capable of absorbing and desorbing hydrogen in a reversible manner, and a total area of said phase incapable of storing hydrogen is 100.times.10.sup.-6 cm.sup.2 or smaller per 500.times.10.sup.-6 cm.sup.2 of arbitrary cross-sectional area of the alloy ingot.