Chemistry: electrical and wave energy – Apparatus – Electrolytic
Patent
1996-11-27
1998-10-06
Phipps, Margery
Chemistry: electrical and wave energy
Apparatus
Electrolytic
148403, 148426, 148427, 148428, 148429, 148538, 148442, 148555, 148561, 164463, 164479, 164480, 429 59, 429223, H01M 438, C22C 1903
Patent
active
058172220
DESCRIPTION:
BRIEF SUMMARY
SPECIFICATION
1. Field of Art
This invention relates to a rare earth metal-nickel hydrogen storage alloy which achieves high capacity and long battery life when it is used for a hydrogen storage vessel, a heat pump, or as an anode material for a nickel-hydrogen rechargeable battery, a process for producing the same, and an anode for a nickel-hydrogen rechargeable battery.
2. Background of the Invention
An anode for a nickel-hydrogen rechargeable battery which is currently produced in a large amount is mainly produced with an AB.sub.5 type alloy which has La, Ce, Pr, Nd, or a mixture of these elements (misch metal) in A-site, and Ni, Co, Mn, and/or Al in B-site (referred to as "LaNi.sub.5 type" in the present specification). This alloy has the properties of larger hydrogen storage capacity than other alloy, and a usable hydrogen absorption-desorption pressure of 1 to 5 atmosphere at ordinary temperature.
The conventional rare earth metal-nickel alloy of LaNi.sub.5 type structure, however, exhibits low initial activity in absorbing hydrogen, so that several cycles to several ten cycles of hydrogen absorption and desorption are required at the initial stage for achieving 100 % hydrogen storage capacity. Further, this alloy has drawbacks of expanding and contracting due to the absorption and desorption of hydrogen, thereby generating cracks and being decrepitated to deteriorate the properties of the battery.
Alternatively, electrodes for achieving still larger battery capacity are recently demanded, and an alloy has been developed having a composition wherein the ratio of transition metals containing nickel as a main component to rare earth metals is decreased in order to increase the capacity of the battery. However, this alloy achieves an increased battery capacity at a sacrifice of long battery life.
As mentioned above, the rare earth metal-nickel hydrogen storage alloy used as an anode material for a nickel-hydrogen rechargeable battery has hitherto been required to have more capacity and longer life.
In order to prolong the life, for example, there is proposed a method of increasing the content of Co or the like, or a method of subjecting the alloy itself to a heat treatment to clear compositional segregation and to relieve strain generated in casting, but either of the methods result in decreased battery capacity. On the other hand, when the content of Mn is increased to enhance the capacity, the long life is sacrificed. Therefore, an alloy which achieves high initial activity and long life at the same time, and further high battery capacity when it is used as an anode for a nickel-hydrogen rechargeable battery, is not known.
As stated above, with the conventional nickel-hydrogen rechargeable battery of LaNi.sub.5 type structure, composition has mainly been discussed. However, the properties of an alloy also depend on a crystal state, a crystal distribution, or the like from more detailed point of view. Thus, the effects of the crystal state or the like on the properties of an alloy has recently been attracting attention.
It is hitherto known that an alloy having Ce.sub.2 Ni.sub.7 or CeNi.sub.3 structure contains antiphase boundaries. The antiphase boundary is a boundary face between a normal phase and an antiphase area wherein the arrangement of atoms on a sublattice is inverted, in a superlattice structure with incomplete regularity in the arrangement of the component atoms (Dictionary of Physics, small edition, published by Kabushiki Kaisha Baifukan, Oct., 20, 1986, pp.439-440).
However, it is not known that the antiphase boundaries exist in a LaNi.sub.5 type structure, nor is known the effect of such antiphase boundaries. Therefore, it is not at all known to apply this structure for improving the properties of a hydrogen storage alloy.
As a method for producing a rare earth metal-containing alloy, there is conventionally known a method utilizing a roll casting device having s single roll or double rolls, wherein a rare earth metal-containing alloy melt is supplied on the surface of the roll, and rap
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Phipps Margery
Santoku Metal Industry Co. Ltd.
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