JPH0748602A - Production of hydrogen storage alloy powder - Google Patents

Abstract

PURPOSE:To obtain a hydrogen storage alloy powder of high service capacity excellent in cycle life characteristics at a low cost by atomizing a molten hydrogen storage alloy with water, reducing an oxide layer on the surface of the obtained powder and cleaning the powder surface. CONSTITUTION:A hydrogen storage alloy 13 melted in a high-frequency melting furnace 11 is supplied to a holding furnace 14 and injected against a collecting tank 17 filled with gaseous nitrogen supplied from a cylinder 19 from an injection nozzle 16 at the lower end of the furnace 14. At that time, water is injected from around the nozzle 16 by means of a high-pressure water pump 18 to atomize the molten alloy, and the hydrogen storage alloy powder is obtained. The powder is dried, Ca and CaCl2, for example, are added to the powder as a reducing agent. The powder is compacted, and the compact is heated in Ar to reduce an oxide film on the powder surface. The powder surface is cleaned with water, etc., to remove the CaO remaining on the surface, and the desired hydrogen storage alloy powder is obtained.

Description

Detailed Description of the Invention

[0001]

The present invention relates to the reversible storage and storage of hydrogen.
The present invention relates to a method for producing released hydrogen storage alloy powder, particularly hydrogen storage alloy powder used for a negative electrode of a battery.

[0002]

2. Description of the Related Art In recent years, nickel-hydrogen batteries using a hydrogen storage alloy powder that reversibly stores and releases hydrogen as a negative electrode have been developed.
In principle, it has been attracting attention as a secondary battery that has a long cycle life and a high energy density because it does not generate dendrites that cause a short circuit. A typical manufacturing process of the hydrogen storage alloy fine powder is as follows. First, an appropriate amount of component metal is weighed and made into a hydrogen storage alloy ingot by using a high frequency melting furnace or the like, annealed (annealed), and then a pulverizer until the average particle diameter becomes about 20 to 30 μm. Mechanical pulverization is performed to produce fine powder of hydrogen storage alloy. The particle size of the hydrogen storage alloy powder affects the hydrogen storage capacity (discharge capacity) and the speed of absorption / desorption (high rate discharge characteristics). The larger the particle size is, the better the hydrogen storage capacity is, and the smaller the particle size is, the better the absorption / desorption rate is. However, when the particle diameter is 7 to 8 μm or less, the influence of surface oxidation becomes large, the storage capacity is extremely reduced, and the particle does not function as an active material.

In the manufacturing process of the above-mentioned fine powder of hydrogen storage alloy, a grain size of 7 to 8 μm which does not have a hydrogen storage capacity when the alloy is pulverized.
A considerable amount of fine powder of m or less is produced, and this loss is a considerable burden in terms of cost. Further, as a cause of deterioration in the cycle life test of the nickel-hydrogen battery, pulverization of the hydrogen-absorbing alloy powder can be mentioned, but the conventional crushed product has a polygonal body with many corners, and the volume expansion at the time of charging and discharging. However, it has a drawback that it tends to become finer than the corners due to shrinkage and has a short cycle life. In order to solve these drawbacks, a fine atomization method such as a gas atomization method or a centrifugal atomization method or a direct production method from nickel fine particles by a reduction diffusion method has been conventionally devised (for example, JP-A-2-2535).
58, JP-A-3-216958, JP-A-3
-170601 publication).

[0004]

The hydrogen-absorbing alloy fine powder produced by the gas atomizing method or centrifugal atomizing method as described above is rapidly cooled during its production, so that it approaches an amorphous state and the ductility and corrosion resistance are increased, and the powder shape is further improved. The spherical shape has an advantage that resistance to pulverization increases and cycle life can be improved. However, in either method, the grain size of the alloy is reduced to about 50 μm,
A classifying process and a pulverizing process are required to obtain a battery material having a particle size of 20 to 30 μm, which causes a significant increase in cost and spherical shape destruction. On the other hand, the reduction diffusion method
It is easy to adjust the particle size because the particle size of the finished hydrogen-absorbing alloy fine powder is determined by the size of the nickel powder of the starting material, but it is possible to adjust the particle size by using multiple metal and metal oxide powders as the starting material. The composition of the alloy fine powder lacks uniformity and has a drawback that the hydrogen storage capacity is low and the discharge capacity is low. Also, a large amount of calcium (Ca)
There is also a problem that requires a reducing agent such as the above, leading to an increase in cost.

Further, conventionally, a filling metal, a metal oxide and Ca are press-molded to form a block, which is reacted at a high temperature in an inert gas to carry out reduction diffusion. However, when the reaction starts, the temperature near the center rises excessively due to the exothermic reaction, and there is a risk that the particles will dissolve, so there is a constraint that the block cannot be made too large, and there was a problem in mass productivity. In view of the above problems, the present invention provides a method for producing a hydrogen storage alloy powder that provides a negative electrode having a high discharge capacity at low cost and excellent cycle life characteristics.

[0006]

[Means for Solving the Problems] In order to solve the above problems, the present invention pulverizes a molten metal of a hydrogen storage alloy to a size of about 10 to 50 μm by a water atomizing method, dries the water content, and then uses a reducing agent to form a powder on the surface. The hydrogen storage alloy powder is manufactured by reducing the oxide layer and further washing and removing the remaining reducing agent and the like. Here, it is preferable that, in the reducing step, Ca and CaCl ₂ are used as reducing agents to perform reduction at a temperature of 700 ° C. or more and 1100 ° C. or less in an argon atmosphere. In this case, CaO remaining on the powder surface
Is preferably removed with an aqueous solution of ammonium chloride, and washed with water.

Further, according to the present invention, fine powder of a hydrogen storage alloy produced by a water atomizing method is mixed with a reducing agent and compression molded into a hollow shape, and the molded body is heated in an inert gas atmosphere, It is characterized by reducing the oxide layer on the powder surface. According to this method, the reduction reaction can be carried out uniformly, and a hydrogen storage alloy powder having stable performance can be obtained. Thus, the present invention provides a method for producing a hydrogen storage alloy fine powder having a spherical and uniform composition.

[0008]

The present invention has the following features, which are not provided by the conventional pulverization method and gas atomization method, due to the above-described structure. First, the quenching rate in the water atomizing method is several tens of times higher than that in the gas atomizing method, and it is possible to pulverize particles up to a particle size of about 10 μm at once, omitting the pulverizing step and reducing the cost. Secondly, since there is no pulverization step, a hydrogen storage alloy having a particle size of 7 to 8 μm or less that does not work as an active material is hardly generated, and an electrode having a high discharge capacity is provided. Third
In addition, since the fine particles after reduction have a spherical shape and do not have a polygonal shape like a conventional crushed product, pulverization is less likely to occur during charge / discharge cycles, and an electrode having a long cycle life is provided. Fourth
In addition, when the surface is reduced, the hydrogen storage alloy is annealed and crystallization progresses, which has the advantages that the discharge capacity can be increased and the annealing step can be eliminated. Further, since the water atomization method is used, fine irregularities are generated on the surface of the obtained particles, which has the advantage of improving the hydrogen absorption / desorption ability and omitting the alkali treatment step.

On the other hand, as compared with the conventional hydrogen storage alloy of the reduction diffusion method, the alloy having a uniform composition is first produced by the water atomization method, so that the hydrogen storage capacity is high and the discharge capacity is high. Furthermore, there is an advantage that the quality is stable. The particle size of the powder obtained by the atomizing method is proportional to the quenching rate, and according to the conventional gas atomizing method, the quenching rate on the order of 10 ⁵ ° C / sec is the limit,
Only spherical particles having an average particle size of 50 μm or more can be produced. On the other hand, according to the water atomizing method, the quenching rate is 10 ⁶
Large as to 10 ⁷ ° C. / sec, the average particle size of the resulting powder 1
It is possible to manufacture a fine one of about 0 μm. Generally, as the negative electrode active material of a nickel-hydrogen battery, the average particle size is 20 to
It is said that about 30 μm is desirable, but the use of the water atomizing method has an advantage that fine pulverization can be performed without a pulverizing step. However, according to the water atomizing method, the surface of the obtained powder was heavily oxidized, and the produced alloy powder lacked the ability to adsorb and desorb hydrogen. Therefore, Ca and CaC
l ₂ or the like in an argon atmosphere at 700 ° C. or higher 11
The surface oxide film is reduced and metallized by holding it at a temperature of 00 ° C. or lower for several hours. At this time, as the reduction reaction progresses, heat is generated, temperature unevenness occurs depending on the location of the alloy, and the hydrogen storage capacity varies. To prevent this, a fine powder produced by the water atomizing method is mixed with a reducing agent and compression molded into a hollow shape such as a tubular shape, and this is subjected to a reduction reaction in a high temperature atmosphere to produce a hydrogen storage alloy with a fairly uniform temperature distribution. Fine powders can be produced. In the production method of the present invention, since only the oxide film of the powder surface layer is reduced with a reducing agent such as Ca or CaCl _2, there is an advantage that the amount of the reducing agent is small and the reaction time is short as compared with the conventional reduction diffusion method. is there.

[0010]

EXAMPLES Examples of the present invention will be described below. FIG. 1 shows a schematic configuration of an apparatus used for the water atomizing method in the example, and FIG. 2 shows a configuration of its ejection nozzle. In these figures, 11 is a high-frequency melting furnace in which a coil 12 for passing a high-frequency current is wound, and the hydrogen storage alloy 13 melted therein is supplied to a holding furnace 14 having an electric heating coil 15. The jet nozzle 16 provided at the lower end of the holding furnace 14 is opened in the alloy powder collecting tank 17, and the nozzle body 20 is supplied with water supplied from the high-pressure pump 18 toward the molten alloy 22 to be jetted. Water passage 21 for ejecting water
Is provided. Reference numeral 19 is a cylinder of nitrogen gas supplied into the collection tank 17. Reference numeral 23 is a hydrogen-absorbing alloy powder that is pulverized by the molten metal being scattered by the water jetted from the end of the passage 21.

[Example] As a hydrogen storage alloy, misch metal (Mm) containing 20% by weight of lanthanum (La), nickel (Ni), manganese (Mn), aluminum (A).
l) and cobalt (Co) in a predetermined ratio,
And melted by high-frequency melting furnace 11 MmNi3 _.9 Mn _0.4 A
First, a hydrogen storage alloy 13 having a composition of _0.5 Co _0.2 is prepared, and this alloy is poured into a holding furnace 14. Next, the cylinder 1
Collection tank 1 filled with nitrogen gas supplied from 9
From the jet nozzle 16 toward 7 the molten metal 2 of hydrogen storage alloy
Eject 2. At this time, the high pressure water pump 18 is used to jet water from the periphery of the jet nozzle to atomize the molten metal of the hydrogen storage alloy to produce the hydrogen storage alloy powder 23.

The hydrogen-absorbing alloy powders produced in this manner ranged from those having a nearly spherical shape to those having a gourd shape, but each of them has a curved surface with no corners, and the surface has a thickness of about 40 nm. It was covered with an oxide film. As a result of particle size distribution measurement, it was found that the average particle size was 22 μm and the particle size was distributed from 8 μm to 60 μm. Then, 1 part by weight of Ca to the hydrogen storage alloy powder 100 parts by weight having the oxide film on the thus obtained surface, the CaCl ₂ 0.
Add 1 part by weight, mix well, and use a hydraulic press to get an inner diameter of 30.
mm, an outer diameter of 50 mm, and a length of 20 mm.
At this time, the space area of the central portion is preferably about 10 to 50% of the total cross-sectional area. It is necessary to increase the space area as the amount of hydrogen storage alloy powder increases. The cross-sectional shape of the hollow portion may be square, triangular, star-shaped, polygonal, etc., in addition to the circular shape.

The hollow block thus produced was heated at 900 ° C. for 2 hours in an argon gas atmosphere,
The oxide film on the surface of the hydrogen storage alloy powder is reduced. As the atmosphere for the reduction, other than argon gas, hydrogen gas, nitrogen gas, or vacuum may be used. Moreover, 700-1100 degreeC is suitable as a reduction temperature. If the temperature is 700 ° C. or lower, the reaction takes about one day, and if the temperature is 1100 ° C. or higher, the hydrogen storage alloy powder is melted and integrated, and the effect of pulverizing by the water atomizing method in advance disappears. Although aluminum or magnesium can be used as the reducing agent, the reducing ability is weak and it takes time to remove the oxide film.

Next, in order to remove CaO remaining on the surface of the hydrogen storage alloy powder thus produced, it is washed thoroughly with an aqueous ammonium chloride solution and distilled water. After drying, to 100 parts by weight of this hydrogen storage alloy powder, 0.5 parts by weight of synthetic rubber particles as a binder, 0.2 parts by weight of carboxymethyl cellulose as a thickening agent, and carbon black of 0.
A negative electrode paste is prepared by adding 2 parts by weight and 16 parts by weight of water. 3 g of this negative electrode paste is filled in a foamed nickel current collector, dried and then pressure-integrated by a roller press method, and a lead is connected to the upper end of the current collector by spot welding to produce a negative electrode plate. On the other hand, the positive electrode plate is manufactured by filling 3.2 g of a conventional positive electrode mixture containing nickel hydroxide as a main component in a foamed nickel current collector, and drying and pressing.

One negative electrode plate produced as described above is placed in the center, and two positive electrode plates are set on both sides of the negative electrode plate. The positive electrode plates are wrapped with a polypropylene bag separator having a thickness of 0.2 mm. And lay them on top of each other, apply acrylic resin plates to both ends, and tighten the outer periphery with bolts and nuts to assemble the electrode plate group. Next, this electrode plate group was put into an acrylic resin battery case, and an aqueous potassium hydroxide solution (density 1.30 g / cm 3
^After pouring an electrolytic solution containing ³ ) as a main component and sealing with a polypropylene lid having pores, it is once evacuated to defoam to prepare a liquid-rich negative electrode regulation evaluation battery. Figure 3
Shows a schematic configuration of this evaluation battery. 31 is a battery case, 32 is a negative electrode plate, 33 is a positive electrode plate, 34 is a separator, 35 is an electrolytic solution, 36 is an acrylic resin plate, 37 is a bolt, 38 is a nut, 39 is a lid, 40 is a positive electrode terminal, 41 is a negative electrode. It is a terminal.

[Comparative Example] A hydrogen storage alloy having the same composition as that of the example was produced in a high frequency melting furnace and was placed in argon gas to
After annealing at 100 ° C. for 6 hours, it is roughly pulverized by a stamp mill and then finely pulverized by a jet mill pulverizer. next,
Particles of 37 μm or more are removed with a 400 mesh sieve to obtain a hydrogen storage alloy powder having an average particle diameter of 22 μm. After that, as an alkali treatment, it is immersed in an aqueous potassium hydroxide solution having a density of 1.3 g / cm ³ at 70 ° C. for 20 minutes while stirring well, and then washed with water 6 times to remove the alkali. Using the hydrogen storage alloy powder thus produced as the negative electrode active material, an evaluation battery is produced in the same manner as in the examples.

FIG. 4 shows the change in discharge capacity when a cycle test was conducted on the evaluation batteries of the above-mentioned Examples and Comparative Examples. The discharge condition during the cycle test is P (hydrogen pressure) -C.
Based on the amount of electricity calculated from (composition) -T (temperature) measurement, the discharge depth is 100% at 0.9V cut at 2C (about 1.7A), and the charge depth is 1 at the discharge electricity amount at 2C.
It was set to 10% (both were 25 ° C.). On the other hand, capacity confirmation is
It is charged at 0.1C for 11 hours every 100 cycles, and then charged to 0.
It was performed under the condition of discharging to 0.9V at 1C. As shown in FIG. 4, the initial discharge capacity of the example was 295 mAh / g, which was higher than the 285 mAh / g of the comparative example by 10 mAh / g, and the cycle characteristic of the comparative example was less than 80% of the initial discharge capacity at 400 cycles. It was found that the examples had up to 1200 cycles.

Since the hydrogen storage alloys of the examples were pulverized by the water atomizing method, the hydrogen storage alloy composition was uniformly crystallized in the powder and then annealed at a high temperature to improve the crystallinity of the microcrystals. Therefore, it is considered that the electrode has a high capacity and a long life. In terms of cost, the conventional product of the comparative example requires a crushing step and an alkali treatment, but in the example, even fine pulverization can be done at once, and the alkali treatment step can be omitted. Therefore, a cost reduction of about 5% compared to the comparative example can be achieved. I found that I could achieve it. As a hydrogen storage alloy, ZrM
Similar effects can be obtained by using an AB ₂ type alloy made of nNi or the like or another hydrogen storage alloy. In the case of AB ₂ type, the particle size when prepared by the water atomizing method is 10 to 20 μm.
m was excellent in terms of initial activity. From the viewpoint of battery characteristics, it was possible to use particles having a particle size of about 50 μm.

[0019]

As described above, according to the production method of the present invention, a fine powder of hydrogen storage alloy can be obtained at a stretch by finely pulverizing by a water atomizing method. Therefore, the conventional pulverizing method or gas atomizing method is used. The crushing step, the classification step, and the alkali treatment step, which are necessary, can be omitted, and the cost can be reduced. In addition, the alloy composition in the particles becomes more uniform than in the reduction diffusion method, and a high discharge capacity can be achieved. Further, since the fine powder has a spherical shape without corners, it is difficult for the fine powder to be miniaturized during a charge / discharge cycle, and the life is long. As described above, according to the method for producing a hydrogen storage alloy powder of the present invention, it is possible to provide a nickel-hydrogen battery having a low cost, a high discharge capacity, and a long life.

[Brief description of drawings]

FIG. 1 is a diagram showing a schematic configuration of an apparatus used for a water atomizing method in an example of the present invention.

FIG. 2 is a perspective view showing a cross section of a main part of an ejection nozzle of the same device.

FIG. 3 is a schematic vertical cross-sectional view of a battery used for evaluation of a hydrogen electrode in Examples.

FIG. 4 is a diagram comparing changes in discharge capacity in a cycle test of negative electrodes of an example of the present invention and a comparative example.

[Explanation of symbols]

 11 High Frequency Melting Furnace 12 Coil 13 Hydrogen Storage Alloy 14 Holding Furnace 15 Electric Heating Coil 16 Jet Nozzle 17 Collection Tank 18 High Pressure Water Pump 19 Nitrogen Gas Cylinder 20 Nozzle Body 21 Water Passage 22 Molten Metal 23 Hydrogen Storage Alloy Powder

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 (72) Person Ikukoma Munehisa 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. (72) Inventor Toyoguchi ▲ Yoshi ▼ Tokoku 1006 Kadoma, Kadoma City, Osaka Pref.

Claims (3)

[Claims] 1. A step of atomizing a molten metal of a hydrogen storage alloy by a water atomizing method, a step of drying the obtained powder after reducing the oxide layer on the surface with a reducing agent, and a step of cleaning the powder surface after the reduction. A method for producing a hydrogen storage alloy powder, comprising the steps of: 2. The reducing step uses Ca and CaCl ₂ as reducing agents and is performed in argon at 700 ° C. or higher and 110 ° C. or higher.
The method for producing a hydrogen storage alloy powder according to claim 1, which comprises reducing at a temperature of 0 ° C or lower. 3. A step of pulverizing a molten metal of a hydrogen storage alloy by a water atomizing method, a step of mixing the obtained fine powder with a reducing agent and compression-molding it into a hollow shape, and an inert gas atmosphere of the molded body. A method for producing a hydrogen storage alloy powder, which comprises a step of heating in an atmosphere to reduce the oxide layer on the surface of the fine powder.