Metal treatment – Process of modifying or maintaining internal physical... – With casting or solidifying from melt
Patent
1997-04-25
1999-10-12
Andrews, Melvyn
Metal treatment
Process of modifying or maintaining internal physical...
With casting or solidifying from melt
75255, 164463, 164479, 4292182, H01M 402
Patent
active
059649682
DESCRIPTION:
BRIEF SUMMARY
FIELD OF ART
The present invention relates to a rare earth metal-nickel hydrogen storage alloy exhibiting high capacity and long life when it is used as a hydrogen storage vessel, a heat pump, or an anode material for a nickel-hydrogen rechargeable battery, a method for producing the same, and an anode for a nickel-hydrogen rechargeable battery.
An alloy used for an anode of a nickel-hydrogen rechargeable battery which is currently produced in a large amount is mainly an AB.sub.5 type alloy containing light rare earth elements such as La, Ce, Pr, Nd, or mixtures thereof, or Mm (misch metal) in A site, and Ni, Co, Mn, and/or Al in B site thereof. This alloy has larger hydrogen storage capacity than other alloy, and a usable hydrogen absorption-desorption pressure of 1 to 5 atm. at an ordinary temperature.
A conventional rare earth metal-nickel alloy of the AB.sub.5 type structure, however, exhibits low initial activity in absorbing hydrogen, so that several to a dozen of cycles of hydrogen absorption and desorption are required at the initial stage in order to achieve 100% hydrogen storage capacity. Further, this alloy expands and contracts upon absorbing and desorbing hydrogen, thereby generating cracks and being decrepitated to deteriorate the properties of the battery.
There has been a recent demand for an electrode exhibiting still higher battery capacity, and an alloy has been developed having a composition wherein the content of transition metals consisting mainly of nickel is decreased relative to that of rare earth metals in order to increase the battery capacity. For example, Japanese Laid-open Patent Application No. 6-145851 discloses a hydrogen storage alloy obtained by rapidly cooling and solidifying an alloy melt composed mainly of La and Ni with the atomic ratio of Ni to La being not higher than 4.9, which alloy is finely crystallized to have alloy crystals having the length along the short axis of not more than 10 .mu.m. This publication also discloses that capacity and life of a nickel-hydrogen rechargeable battery can be improved by utilizing this hydrogen storage alloy.
This hydrogen storage alloy exhibits the effects expected from its finely crystallized structure, but does not achieve as much increase in battery capacity as is expected theoretically, in spite of its composition rich in rare earths wherein the content of Ni is decreased from the composition of LaNi.sub.5 type. It is believed that this is because in the composition rich in La, which has particularly strong affinity to hydrogen among other rare earth elements, the absorbed hydrogen is trapped, thereby decreasing the substantial capacity which contributes to absorption and desorption of hydrogen. The above referenced publication also discloses that a portion of La may be substituted by other rare earth elements than La, with no specific elements to be employed and no concrete effects resulting therefrom.
As discussed above, a rare earth metal-nickel hydrogen storage alloy for use as an anode material of a nickel-hydrogen rechargeable battery is conventionally expected to have higher capacity and longer life.
In order to prolong life, there are proposed, for example, a method of increasing the content of Co and the like, and a method of subjecting the alloy to a heat treatment to clear compositional segregation for relieving strain occurred in casting, but either with decrease of battery capacity. On the other hand, if the content of Mn is increased to enhance the capacity, prolongation of the life is sacrificed. Accordingly, an alloy has not yet known which satisfies both high initial activity and long life at the same time, and which also achieves high battery capacity when it is used for an anode of a nickel-hydrogen rechargeable battery.
As discussed above, discussion on the conventional nickel-hydrogen rechargeable battery of the AB.sub.5 type structure has mainly been focused on its composition. However, properties of an alloy also depend on a crystal state and crystal distribution from more detailed point of view. The
REFERENCES:
patent: 4660622 (1987-04-01), Reutler et al.
patent: 5470404 (1995-11-01), Yamamoto et al.
patent: 5496424 (1996-03-01), Fujitani et al.
patent: 5512385 (1996-04-01), Komori et al.
patent: 5629000 (1997-05-01), Matsuura et al.
patent: 5654115 (1997-08-01), Hasebe et al.
patent: 5817222 (1998-10-01), Kaneko
Andrews Melvyn
Santoku Metal Industry Co., Ltd
LandOfFree
Rare earth metal-nickel hydrogen storage alloy, method for produ does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Rare earth metal-nickel hydrogen storage alloy, method for produ, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Rare earth metal-nickel hydrogen storage alloy, method for produ will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-648556