JP2002317256A - Production method for hydrogen storage alloy - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a production method for a hydrogen storage alloy which has a homogeneous structure in all parts, and enables the improvement of the service life of a battery. SOLUTION: The raw material of a hydrogen storage alloy is heated and melted, and the molten alloy is cast, and is thereafter heat-treated in an inert gas atmosphere to produce the hydrogen storage alloy. In this production method, in a temperature region of 500 to 1,000 deg.C on the heat treatment, the calorie of >=26 W per ml of the alloy is applied thereto to increase its temperature, and the alloy is heat-treated.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a hydrogen storage alloy, and more particularly to a method for producing a hydrogen storage alloy having a homogenized alloy structure and improved battery life.

[0002]

2. Description of the Related Art In recent years,
As a high-capacity alkaline storage battery that replaces a nickel-cadmium storage battery, a nickel-hydrogen storage battery (secondary battery) using a hydrogen storage alloy for a negative electrode has attracted attention.

[0003] This hydrogen storage alloy is prepared by heating and melting a hydrogen storage alloy raw material to form a molten alloy, casting it into a mold, casting it, quenching it to obtain a hydrogen storage alloy, and then heat-treating the hydrogen storage alloy. It was homogenized.
Conventionally, in this heat treatment, the temperature region, which is a two-phase separation region, is spending 1 to 3 hours to raise the temperature. At this time, the two-phase separation is promoted, and the existence ratio of the deviated phase increases. The temperature was maintained in the region, and the alloy structure was promoted to have a single phase.

[0004] However, in homogenization by heat treatment, strictly speaking, at a certain site, there is a considerable amount of a dislodged phase, which cannot be said to be homogenous. Was the cause.

Accordingly, it is an object of the present invention to provide a method for producing a hydrogen storage alloy having a homogeneous structure in all parts and improving the battery life.

[0006]

As a result of investigations, the present inventors have found that heat treatment conditions are important in order to make alloys almost completely homogenous.
It has been found that when the temperature range of 00 to 1000 ° C. is rapidly heated and passed as quickly as possible to reach the optimal heat treatment temperature, the degree of homogenization increases, and the above object can be achieved.

The present invention has been made on the basis of the above-mentioned findings, and a method for producing a hydrogen storage alloy in which a hydrogen storage alloy material is heated and melted, cast, and then heat-treated in an inert gas atmosphere. 500-1000
An object of the present invention is to provide a method for producing a hydrogen storage alloy, in which a heat amount of 26 W or more per mol of an alloy is applied in a temperature range of ° C. to raise the temperature and heat treatment.

[0008]

Embodiments of the present invention will be described below. In the present invention, the hydrogen storage alloy raw material is weighed and mixed so as to have a predetermined alloy composition, for example, by using a high-frequency heating melting furnace by induction heating, melting the hydrogen storage alloy raw material to form a molten metal. The hydrogen storage alloy is poured into a mold, for example, a water-cooled mold, at 1350 to 1550 ° C.
Cast in. In addition, the casting temperature at this time is 1200 to 14
50 ° C. Here, the casting temperature is the temperature of the molten metal in the crucible at the start of casting, and the temperature of the casting metal is the temperature of the mold pouring port (the temperature before the mold).

Next, the obtained hydrogen storage alloy is heat-treated in an inert gas atmosphere, for example, in an argon gas. The heat treatment is performed at 1000 to 1100 ° C. for 1 to 10 hours.

According to the present invention, in this heat treatment, 500
In the temperature range of ~ 1000 ° C, 2 per mole of alloy
It is necessary to input a heat amount of 6 W or more, preferably 26 to 52 W, to raise the temperature and heat treatment. By rapidly heating and passing through such a temperature range as short as possible, the obtained hydrogen storage alloy can be homogenized.

FIG. 1 is a graph showing the relationship between the alloy composition and the heat treatment temperature.
Generally, 700-1000 ° C. is a two-phase separation region, and it is preferable to pass through this region as soon as possible.

[0012] In this manner, a homogenized hydrogen storage alloy can be obtained at any position. Then, by using this hydrogen storage alloy as a negative electrode of a nickel-hydrogen storage battery, the battery life can be improved.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be specifically described below based on embodiments and the like.

Experimental Example 1 (Evaluation of Dependence on Heating Rate) A hydrogen storage alloy having a composition of Mm (La 20% by weight) Al _0.3 Mn _0.5 Co _0.3 Ni _4.20 (AB _5.30 ) was produced by a casting method.

The hydrogen storage alloy was heat-treated in an argon gas atmosphere under the following conditions. The processing amount was 20 g, and the temperature of the thermocouple and the measured temperature of the alloy were the same.

Example 1: 26 W / mol of input heat at 500 to 1050 ° C., and then hold at 1060 ° C. for 3 hours Example 2: 52 W of input heat at 500 to 1050 ° C.
/ Mol, then maintained at 1060 ° C. for 3 hours Comparative Example 1: Heat input at 500 to 1050 ° C. 5 W /
Mol, then maintained at 1060 ° C. for 3 hours Comparative Example 2: Heat input 1W / 500 to 1050 ° C.
Mol, then hold at 1060 ° C for 3 hours

With respect to the hydrogen storage alloys of Examples 1 and 2 and Comparative Examples 1 and 2 thus heat-treated, PCT characteristics, microstructure observation (micrograph), and physical properties (a-axis length, b-axis) were obtained by the following methods. Length, fine powder residual ratio, corrosion characteristics) were evaluated. Fig. 2 shows PCT characteristics and Fig. 3 shows composition observations (micrographs).
Table 6 shows the physical properties of each of Tables 1 to 6.

<PCT capacity> Determined from the storage characteristics measured at 45 ° C.

<Lattice length> Measured by a powder X-ray diffraction method using CuKα radiation.

<Residual rate of pulverization>
30 bar for hydrogen storage alloy adjusted to ~ 53 microns
After the process of introducing hydrogen gas to occlude hydrogen and then evacuating and evacuating hydrogen was repeated 10 times, the ratio was calculated by the ratio of the average particle size after the cycle test to the average particle size before the cycle test.

<Storage Corrosion> In order to evaluate the corrosion behavior during storage, the classified hydrogen storage alloy powder was activated once by storing hydrogen once in a PCT evaluation cell, and the activated hydrogen storage alloy powder was placed in an argon inert gas. Into a KOH aqueous solution having a specific gravity of 1.30, and allowed to stand at 80 ° C. for 4 hours to perform an elution test to determine the amount of surface precipitation and the amount of elution, which are the amounts of corrosion of the alloy components. It was indicated by an index with the value being 100.

[0022]

[Table 1]

In FIG. 2, comparing the plateau regions of the PCT curves, Comparative Examples 1 and 2 are not good in flatness,
In comparison, Examples 1 and 2 have good flatness. This suggests that the alloy is homogeneous and has good crystallinity.

FIGS. 3 to 6 show the comparison of the structure of the alloy at the position farthest from the cooling surface, that is, the structure at the center of the alloy. In FIGS. 3 and 4) and Comparative Examples 1 and 2, a manganese-nickel rich phase was observed, and it was difficult to say that the composition was homogeneous depending on the site (see FIGS. 5 and 6).

As is clear from Table 1, with respect to the crystal structure, Examples 1 and 2 have a shorter a-axis and a longer c-axis than Comparative Examples 1 and 2. That is, the “dumbbell structure” in the non-stoichiometric composition is more suitably formed. This suggests that the homogeneity of the alloy composition has been improved.

As described above, in Examples 1 and 2 having a suitable dumbbell structure, improvement in pulverization characteristics and corrosion characteristics is recognized as compared with Comparative Examples 1 and 2. This is considered to lead to an improvement in battery life.

[0027]

According to the manufacturing method of the present invention, since the material passes through the two-phase separation region in as short a time as possible, it is extremely effective to maintain the temperature in the single-phase region and to homogenize the alloy structure.
As a result, the battery life is improved.

[Brief description of the drawings]

FIG. 1 is a graph showing a relationship between a hydrogen storage alloy composition and a heat treatment temperature.

FIG. 2 shows PCs of Examples 1 and 2 and Comparative Examples 1 and 2.
It is a T curve.

FIG. 3 is a micrograph of Example 1 (× 20
0).

FIG. 4 is a photomicrograph of Example 2 (× 20).
0).

FIG. 5 is a micrograph of Comparative Example 1 (× 20).
0).

FIG. 6 is a micrograph of Comparative Example 2 (× 20).
0).

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Claims (2)

[Claims] 1. A method for producing a hydrogen storage alloy in which a hydrogen storage alloy raw material is heated and melted, cast, and then heat-treated in an inert gas atmosphere. A method for producing a hydrogen storage alloy, wherein a heat quantity of 26 W or more per mol is supplied to heat and heat-treat. 2. After the temperature is raised, 1000-1100 ° C.,
The method for producing a hydrogen storage alloy according to claim 1, wherein the method is held for 10 to 10 hours.