JPH07118711A - Hydrogen storage alloy powder, nickel-hydrogen battery having the powder in negative-electrode active material and production of the powder - Google Patents

Abstract

PURPOSE:To produce an inexpensive and durable hydrogen storage alloy powder by carrying out pulverization to alkali treatment in one step. CONSTITUTION:A hydrogen storage alloy is firstly melted in a high-frequency melting furnace 11 to form the molten melt 12, which is poured into a holding furnace 10. The melt 12, is then injected from an injection nozzle 16 into an alkali-resistant collecting tank 15 filled with gaseous nitrogen supplied from a nitrogen cylinder 14. At this time, aq. alkali is injected from around the nozzle with a high-pressure pump 17 to atomize the melt 12, and a hydrogen storage alloy powder 18 is produced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hydrogen storage alloy powder used in nickel hydrogen batteries and the like and a method for producing the same.

[0002]

2. Description of the Related Art In recent years, a nickel-hydrogen battery using a hydrogen-absorbing alloy powder that reversibly absorbs and desorbs hydrogen as a negative electrode has a long charge-discharge cycle life because there is no generation of dendrite that causes a short circuit in principle. , Has attracted attention as a secondary battery with high energy density.

The typical manufacturing process of the hydrogen storage alloy powder is as follows. First, a predetermined amount of each component metal of the hydrogen storage alloy is weighed, melted in a high frequency melting furnace or the like, and the molten metal is poured into a water-cooled mold to produce a hydrogen storage alloy ingot. Next, after performing annealing treatment (hereinafter referred to as annealing treatment) in vacuum or argon, mechanical pulverization is performed by a pulverizer until the average particle size becomes about 20 μm to 30 μm, and then for activation of the alloy surface. The alloy powder was immersed in a high temperature alkaline solution for several hours to prepare a hydrogen storage alloy powder for a nickel hydrogen battery.

[0004]

However, in the manufacturing process of this hydrogen storage alloy powder, the takt time of the casting process is long, and further the crushing process and the alkali treatment process are required, so that the manufacturing cost is high. Further, the fine powder having a particle size of 7 μm to 8 μm or less, which hardly functions as an active material during the pulverizing step, is very active on the surface and forms a strong oxide film, which is inactive and cannot absorb and desorb hydrogen. Since a considerable amount is generated, the yield of raw materials is poor, and there is a problem that leads to cost increase.

Further, as a cause of deterioration in a charge / discharge cycle life test of a nickel-hydrogen battery using this, pulverization of the hydrogen-absorbing alloy powder can be mentioned, but the crushed product has a mechanical fracture surface and forms a polygonal body. However, there is a drawback that the corners are likely to be pulverized due to expansion and contraction of the volume during charge and discharge.

In order to solve these drawbacks, a pulverizing method such as a gas atomizing method has been considered in the past. For example, JP-A-2-253558 and JP-A-3-116 are available.
No. 655, etc.

However, in the case of the gas atomizing method, an expensive inert gas such as argon (Ar) gas is used, and since the grain size of the alloy powder is only finely down to about 50 μm, a fine pulverization step is required, which is costly. Is not expected to drop significantly. Further, since the alloy powder has a sharp fracture surface because it is mechanically pulverized, there is a problem that the pulverization occurs due to charge / discharge cycles, and the battery using this has a short life. In the case of alloy powder having a large particle size, the high rate discharge characteristics are extremely deteriorated.

[0008] The water atomizing method can be performed at once in a fine powder,
Although it is an excellent manufacturing method because it has high productivity and does not use expensive inert gas, it has a drawback that the produced alloy surface is easily oxidized and requires complicated activation treatment.

The present invention solves the above-mentioned conventional problems, and provides a hydrogen storage alloy powder capable of obtaining a battery having excellent charge / discharge cycle life characteristics and a method of producing a low cost hydrogen storage alloy powder having excellent productivity. The purpose is to do.

[0010]

In order to achieve the above object, the hydrogen storage alloy powder of the present invention and a method for producing the same are
Hydrogen storage alloy powder used as a negative electrode active material for a nickel-hydrogen battery, and as a method for producing the same, a hydrogen storage alloy powder or a hydrogen storage alloy powder finely pulverized at a stretch to about 20 μm to 50 μm by a water atomization method using an alkaline aqueous solution. The present invention provides a hydrogen storage alloy powder obtained by annealing the alloy powder in vacuum or in argon gas, and a method for producing the same. The alkaline solution is KO
The pH is 10 to 13 with H or NaOH, and after pulverization, the hydrogen storage alloy powder is taken out from the aqueous alkali solution within 5 minutes or more and within 1 hour and washed with water to remove the alkali.

As described above, by pulverizing the hydrogen-absorbing alloy at once by the water atomizing method using the alkaline aqueous solution, a surface-active spherical body having no mechanical fracture surface and a hydrogen-absorbing alloy powder having a similar shape are obtained. By using this as a negative electrode active material, a nickel hydrogen battery with low cost and long life is provided.

[0012]

The present invention has the following features which are not present in the conventional casting, crushing method and gas atomizing method by atomizing the molten metal of the hydrogen storage alloy by the water atomizing method using the alkaline aqueous solution as described above. . Firstly, the ability to pulverize the molten metal is higher than that of the gas atomizing method, and it is possible to atomize up to about 20 μm at once, simplifying the pulverization process and the alkali treatment process, and significantly reducing the cost.
In addition, almost no inactive powder having a particle size of 7 μm to 8 μm is produced, and moreover, an expensive inert gas such as argon gas is not used as compared with the gas atomization method, so that the manufacturing cost is reduced. Secondly, since there is no crushing process, the hydrogen storage alloy powder does not have a mechanical fracture surface like conventional powder and has a spherical shape and similar shape, so it is difficult to reduce the size during charge / discharge cycles. It will be the end of life. Thirdly, there is an advantage that the discharge capacity can be increased because the alloy surface can be activated with an alkaline aqueous solution at the time of pulverization.

In the conventional gas atomizing method, the ability to grind molten metal
Only small force and average particle size of 50μm or more can be produced.
Absent. On the other hand, in the water atomizing method, the water pressure is 1500 kg /
cm ²The average particle size is about several μm
It is possible to make even fine things. Generally for nickel metal hydride batteries
The average particle size of the negative electrode active material is about 20 μm to 30 μm.
Is preferred, but the water atomization method should be used.
By adjusting the water pressure to fine powder without crushing process
There is an advantage that you can take it.

However, in the case of the usual water atomizing method, an oxide film is formed on the surface of the alloy powder, and the hydrogen storage capacity is significantly reduced. Therefore, it was possible to reduce the formation of an oxide film and make it surface active by atomizing with an alkaline aqueous solution of KOH or NaOH having a pH of about 10 to 13. A treatment time of 5 minutes or more and 1 hour or less is suitable, and if it is immersed in an alkaline aqueous solution for a too long time, the surface is oxidized and the discharge capacity is rather lowered.
Conventionally, alkali treatment has been carried out at a high temperature of 80 ° C. for several hours, but by spraying an alkaline aqueous solution directly onto a very high temperature molten metal as in the present invention, the alkali treatment time can be greatly shortened. The average particle size of the alloy powder is 20 μm
50 μm is suitable from the viewpoint of the discharge capacity and high rate discharge characteristics of the battery.

Then, the alloy powder is annealed in vacuum or in an argon gas in order to increase the discharge capacity, so that the alloy powder is crystallized and the hydrogen storage capacity is improved, resulting in a high capacity.

[0016]

【Example】

(Embodiment 1) Hereinafter, a hydrogen storage alloy powder of Embodiment 1 of the present invention and a method for producing the same will be described with reference to the drawings.

Hydrogen storage alloys include misch metal (Mm) containing 30% by weight of lanthanum (La), nickel (N).
i), manganese (Mn), aluminum (Al), and cobalt (Co) are mixed at a predetermined ratio and melted in a high frequency melting furnace 11 as shown in FIG. 1 to obtain MmNi _3.55 Mn _0.4 A
First, a melt 12 of a hydrogen storage alloy having a composition of _0.3 Co _0.75 is prepared, and the melt 12 of the hydrogen storage alloy is poured into a holding furnace 13. Next, a collection tank 15 filled with nitrogen gas supplied from the nitrogen gas cylinder 14 and having excellent alkali resistance
From the jet nozzle 16 toward the molten metal 12 of hydrogen storage alloy
Squirt out. At this time, the high pressure pump 17 was used to eject KO of pH 13 at a jet pressure of 800 kg / cm ² as shown in FIG.
An alkaline aqueous solution 21 of H is jetted from around the jet nozzle 22, and the molten metal 23 of the hydrogen storage alloy is atomized (atomized).
Then, the hydrogen storage alloy powder 24 (18 in FIG. 1) was produced.

The hydrogen-absorbing alloy powder thus produced was taken out of the collecting tank 15 after 5 minutes, washed thoroughly with water, and then dried. This hydrogen storage alloy powder 1
The shapes of 8, 24 were various, such as a shape close to a sphere to a shape of a gourd, but each of them had a curved surface without corners. The surface was covered with needle-shaped oxides of Mm and Ni. As a result of particle size distribution measurement, the average particle size is 2
At 2 μm, the particle size is distributed from 8 μm to 60 μm, 10 μm
It was found that the content of the following particles was 0.5 wt% or less.

Next, 100 parts by weight of the hydrogen storage alloy powder, 0.5 parts by weight of synthetic rubber particles (binder), 0.2 parts by weight of carboxymethyl cellulose (CMC: thickener),
Water is added to 0.2 parts by weight of carbon black (conductive material).
By adding parts by weight, a negative electrode paste was prepared. 3 g of this paste was filled in a nickel current collector (core material) having innumerable holes to which leads were attached, dried, and then pressure-integrated by a roller press method to prepare a negative electrode plate. On the other hand, for the positive electrode, 2.2 g of a conventional positive electrode mixture containing nickel hydroxide as a main component
Was filled in a collector made of foamed nickel to produce a positive electrode plate.

One negative electrode plate and four positive electrode plates prepared as described above are inserted into a polypropylene (PP) bag-shaped separator having a thickness of 0.2 mm, and the negative electrode plate is sandwiched between two positive electrodes. As shown in the figure, after sandwiching it with an acrylic plate and welding the lead part to a pole that is connected to a PP lid with pores, it is placed in a cylindrical acrylic battery case and an aqueous potassium hydroxide solution (density 1.30 g A large amount (300 g) of an electrolytic solution containing / cm ³ ) as the main component was poured from the pores, and then vacuumed to defoam to prepare an electrolytic solution-rich negative electrode regulation evaluation battery.

(Embodiment 2) The hydrogen absorption and storage of Embodiment 2 will be described below.
Gold powder and its manufacturing method are explained with reference to the drawings.
Reveal First, the water outlet shown in FIGS. 1 and 2 similar to the first embodiment.
Use a pH 10 NaOH solution in Mize's equipment
A little lower the ejection pressure (700 kg / cm ²) Atomai
I went out. This alloy powder from the collection tank after 1 hour
Take out, wash with water, dry and store hydrogen with an average particle size of 48 μm
A fine alloy powder was prepared. Next, this alloy powder is vacuum annealed.
Place in a furnace for 10^-6Evacuate below torr to 1
After heating at 000 ℃ for 3 hours, slowly cool to room temperature over 8 hours.
It was cooled and annealed. The annealing conditions
Holding temperature 800 ℃ to 1000 ℃, holding time 2 hours
The above is necessary from the isotherm measurement (hereinafter referred to as PCT measurement)
I found out. Alloy particles are welded above 1000 ° C
have done. The hydrogen absorption annealed in this way
By using the same alloy powder as the negative electrode active material in the same manner as in Example 1.
An evaluation battery was produced.

As a comparative example, a hydrogen storage alloy having the same composition as in Example 1 was produced in a high frequency melting furnace, vacuum annealed at 1100 ° C. for 3 hours, coarsely pulverized with a stamp mill, and further finely pulverized with a jet mill to an average particle size of 25 μm. Crushed. The hydrogen storage alloy powder thus produced was used as a negative electrode active material, and an evaluation battery was produced in the same manner and configuration as in Example 1. From the result of particle size distribution measurement of this hydrogen storage alloy powder, 1
It was found that the content of particles of 0 μm or less was about 12 wt%.

FIG. 3 shows changes in the negative electrode discharge capacity when a charge / discharge cycle test was conducted on the liquid-rich negative electrode regulation evaluation battery. The charging condition during the charge / discharge cycle test is 2C (about 1.7A) from the amount of electricity calculated by PCT measurement, the amount of electricity charged is 100% of the amount of electricity discharged, and the discharge condition is 2C.
It was performed at a 0.9 V cut depth of discharge (DOD) of 100%.
On the other hand, the capacity is confirmed by charging condition 0.1 every 100 cycles.
C, 12 hours charge electricity 120%, discharge condition 0.1
C, 0.9 V cut was performed.

From FIG. 3, the initial discharge capacity of the negative electrode was 280 mAh / g in Example 1 and 290 mA in Example 2.
h / g, that of the comparative example was 285 mAh / g, which was not so different. As a result of the charge / discharge cycle test, it was found that the initial capacity was reduced to 80% at 1800 cycles in Example 1, 1500 cycles in Example 2 and 1100 cycles in Comparative Example. In the comparative battery, a large amount (about 12 wt%) of 7 μm to 8 μm or less of fine powder that does not contribute to the battery reaction is generated in the crushing process, and thus the initial capacity (negative electrode utilization rate) is not so high, and It is considered that this is because the shape is a polygonal body and has corners, so that it is easily cracked and pulverized during a charge / discharge cycle. On the other hand, the powder of this example has the advantage that the amount of fine powder of 8 μm or less is small, but on the other hand, the surface is slightly covered with an oxide film, so the capacity is almost the same as that of the comparative example. Is close to a sphere and has no mechanical fracture surface, so pulverization is unlikely to occur, and it is thought that it is excellent in charge-discharge cycle characteristics.

In terms of cost, the conventional product of the comparative example requires casting, cooling and crushing steps, but in the present embodiment, the cooling rate is fast and it is possible to continuously atomize until pulverization. It was found that the value of 1 can reduce the cost by about 60% as compared with the comparative example.

The alkaline aqueous solution has a pH of 10 to 10.
The range of pH 13 is effective, and the effect of surface activation is not obtained at pH 9 or lower, and the oxide film is formed at pH 14 or higher to cause the capacity decrease. Also, the immersion treatment time is 5 minutes ~
The optimum time is about one hour, but it takes a few hours for the conventional alkali treatment, but the time can be greatly shortened. Further, the particle size of the alloy powder is preferably 20 μm to 50 μm from the viewpoint of charge / discharge cycle characteristics and high rate discharge characteristics. Conventionally, a powder having a particle size of 10 μm or less is produced by the water atomizing method, but in this example, a powder having a large particle size was produced by reducing the water pressure during spraying.

As the hydrogen storage alloy, Zr, Mn,
A battery manufactured in the same manner as in Example 2 using an AB2 type alloy composed of V, Cr, and Ni also has a high discharge capacity and excellent charge / discharge cycle characteristics, and like the present example, the pulverization step was omitted and cost reduction was achieved. .

[0028]

As is apparent from the above description, according to the hydrogen storage alloy powder and the method for producing the same of the present invention, the ability of the molten metal to be pulverized is high, and the pulverization process up to about 20 μm can be performed at once in the fine pulverization step and the alkali. The treatment process can be simplified and the cost can be significantly reduced. In addition, an inert powder having a particle size of 7 μm to 8 μm is hardly generated, and an inert gas such as argon gas, which is more expensive than the gas atomization method, is not used. Manufacturing cost is reduced. Furthermore, since there is no crushing step, the hydrogen-absorbing alloy powder does not have the mechanical fracture surface unlike conventional powders, and because it has a spherical body and similar shape, it is unlikely to be miniaturized during charge and discharge cycles and has a long life. Become. Further, when finely pulverized, activation of the alloy surface can be performed at once with an alkaline aqueous solution, which has an advantage that a high discharge capacity can be achieved.

As described above, the hydrogen storage alloy powder and the method for producing the same according to the present invention can provide a low cost and long life nickel hydrogen battery.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view of a water atomizing apparatus used in a method for producing a hydrogen storage alloy powder according to an embodiment of the present invention.

FIG. 2 is a schematic view showing a cutout of the ejection nozzle and showing a section thereof.

FIG. 3 is a graph showing changes in the negative electrode discharge capacity in a charge / discharge cycle test of an evaluation battery using the hydrogen storage alloy powders of Examples and Comparative Examples of the present invention as a negative electrode.

[Explanation of symbols]

 11 High Frequency Melting Furnace 12,23 Molten Metal 13 Holding Furnace 14 Nitrogen Gas Cylinder 15 Collection Tank 16,22 Jet Nozzle 17 High Pressure Pump 18,24 Hydrogen Storage Alloy Powder 21 Alkaline Aqueous Solution

Front page continuation (72) Inventor Seiji Yamaguchi 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. (72) Inventor Tadao Kimura 1006 Kadoma, Kadoma City Osaka Prefecture Toyoguchi Yoshinori 1006 Kadoma, Kadoma, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. (72) Inventor Munehisa Ikoma, 1006 Kadoma, Kadoma City, Osaka Matsushita Electric Industrial Co., Ltd.

Claims (8)

[Claims] 1. A hydrogen storage alloy having a surface-activated spherical body or a shape similar to that obtained by pulverizing a molten metal made of a hydrogen storage alloy by a water atomizing method using an alkaline aqueous solution and having no mechanical fracture surface. Powder. 2. A hydrogen storage alloy having a surface-activated spherical body or a shape similar to that obtained by atomizing a molten metal made of a hydrogen storage alloy by a water atomizing method using an alkaline aqueous solution and having no mechanical fracture surface. Hydrogen storage alloy powder obtained by annealing the powder in vacuum or in argon gas. 3. A nickel hydrogen battery having the hydrogen storage alloy powder according to claim 1 or 2 as a negative electrode active material. 4. A method for producing a hydrogen storage alloy powder, which comprises pulverizing a molten metal comprising a hydrogen storage alloy by a water atomizing method using an alkaline aqueous solution. 5. A method for producing a hydrogen storage alloy powder, which comprises subjecting a hydrogen storage alloy powder obtained by pulverizing a molten metal made of a hydrogen storage alloy by a water atomizing method using an alkaline aqueous solution to an annealing treatment in vacuum or in an argon gas. 6. The method for producing a hydrogen storage alloy powder according to claim 4, wherein the alkaline aqueous solution is an aqueous solution containing caustic potash or caustic soda in the range of pH 10 to pH 13. 7. The hydrogen storage according to claim 4, wherein the hydrogen storage alloy powder is taken out from the aqueous alkali solution within 5 minutes to 1 hour after pulverization and washed with water to remove the alkali. Method for producing alloy powder. 8. The method for producing a hydrogen storage alloy powder according to claim 4, wherein the particle size of the hydrogen storage alloy powder is in the range of 20 μm to 50 μm.