Hydrogen storage alloy
An ABs-type hydrogen storage alloy is provided that has a low Co amount and uses Mm composed of La and Ce, which is capable of preventing a decrease in lifetime characteristics. The hydrogen storage alloy has an ABx composition constituted with an A-site composed of an Mm and a B-site composed of Ni, Co, Mn, and Al, or Ni, Mn, and Al, wherein Mm is composed of La and Ce; the molar ratio of Co is 0.0 or more and 0.11 or less when the molar ratio of Mm is 1.00; the ratio (Al/Mn) of the molar ratio of Al to the molar ratio of Mn is 0.35 to 1.10; and the ratio of the c-axis length to the a-axis length in the CaCu 5 -type crystal structure is 0.8092 or more.
1 . A hydrogen storage alloy comprising a parent phase having a CaCu 5 -type, that is, an AB 5 -type crystal structure, the hydrogen storage alloy comprising an ABx composition constituted with an A-site consisting of a misch metal (referred to as “Mm”) and a B-site consisting of Ni, Co, Mn, and Al, or Ni, Mn, and Al,
wherein Mm consists of La and Ce;
a molar ratio of Co is 0.0 or more and 0.11 or less when a molar ratio of Mm is 1.00;
a ratio (Al/Mn) of a molar ratio of Al to a molar ratio of Mn is 0.35 to 1.10;
a ratio of a c-axis length to an a-axis length in the CaCu 5 -type crystal structure is 0.8092 or more; and
the hydrogen storage alloy is allowed to contain impurities at an amount of 0.05% by mass or less.
2 . The hydrogen storage alloy according to claim 1 , having a magnetization of 1.60 emu/g or less after performing a surface treatment, the surface treatment being performed by immersing a hydrogen storage alloy powder having a particle diameter adjusted such that a 50% volume cumulative particle diameter (D50) is 21 μm±2 μm, into a 31% by mass KOH aqueous solution having a liquid temperature of 120° C. for 3 hours.
3 . The hydrogen storage alloy according to claim 1 , wherein in the ABx composition, a total molar ratio (ABx) of elements constituting the B-site is 5.28 or more and 5.46 or less when the molar ratio of Mm constituting the A-site is 1.00.
4 . A negative electrode active material for a nickel-hydrogen battery comprising the hydrogen storage alloy according to claim 1 .
5 . A nickel-hydrogen battery using the negative electrode active material according to claim 4 .
6 . A nickel-hydrogen battery being mounted on an electric vehicle or a hybrid electric vehicle, the battery using the negative electrode active material according to claim 4 .