JP3417980B2 - Hydrogen storage alloy powder for electrode and method for producing the same - Google Patents

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 a hydrogen storage alloy powder for an electrode to be released and a nickel-hydrogen battery using the alloy powder.

[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. Hydrogen storage alloys include AB ₅ type mainly composed of rare earth element / nickel (Ni) and AB ₂ type mainly composed of zirconium (Zr) / manganese (Mn). Conventionally, the former AB ₅ type, which is well balanced in battery characteristics such as discharge capacity, internal pressure, charge storage characteristics and cycle life, has been used for batteries. The alloy composition used for this is mainly composed of misch metal (Mm) made of a mixture of rare earths such as lanthanum, nickel, cobalt (Co), manganese, and aluminum (Al).

The typical manufacturing process of a negative electrode using the alloy is as follows. First, a hydrogen storage alloy ingot is once produced from the above component metals using a high-frequency melting furnace or the like, and then annealed in vacuum or in argon, and then an average particle size of 20-
Mechanical pulverization is performed until the size becomes about 30 μm. Next, the surface of this powder is subjected to alkali treatment. The hydrogen-absorbing alloy powder thus prepared is mixed with water together with a thickener made of carboxymethyl cellulose or polyvinyl alcohol and a rubber binder, and a conductive agent such as carbon is added if necessary to form a negative electrode paste. Next, this paste is applied to a negative electrode current collector (core material) made of a porous metal substrate or the like, dried, and pressed to strengthen the binding between the constituent elements of the electrode, and this is used as the negative electrode.

[0004]

In the above negative electrode manufacturing process, a considerable amount of fine powder of 7 to 8 μm or less, which hardly functions as an active material when the alloy is pulverized, is produced. This fine powder cannot absorb and desorb hydrogen because the surface thereof is very active and a strong oxide film is formed. However, since Mm and Co are expensive, this loss is a considerable burden in terms of cost. On the other hand, in the AB ₂ type, since the alloy is hard, it takes time to finely pulverize, which leads to an increase in cost over the AB ₅ type. Further, as a cause of the deterioration of the negative electrode in the cycle life test, there is a refinement of the hydrogen storage alloy powder, but the crushed product as described above has a polygonal body with a mechanical fracture surface, and the volume at the time of charging / discharging Inflation,
It has a defect that the shrinkage easily causes miniaturization from the corners.

In order to solve these drawbacks, conventional fine atomization methods such as a gas atomizing method and a centrifugal atomizing method have been devised (for example, JP-A-2-253558, JP-A-3-216958). The hydrogen storage alloy powder produced by such atomization method or centrifugal atomization method has a uniform composition because it is ultra-quenched during its production, and it is possible to lower the equilibrium pressure of hydrogen absorption / desorption characteristics and increase the capacity. There are advantages. However, all of these methods use an inert gas such as expensive argon (Ar) gas, and the grain size of the alloy is reduced to only about 50 μm, which requires a fine pulverization step, which significantly reduces the cost. Cannot be expected.
Further, the finely divided powder needs to be handled with care because it is active, and if left in the air, the surface thereof is gradually oxidized and it is difficult to store.

In view of the above problems, it is an object of the present invention to provide a method for producing a hydrogen storage alloy powder for electrodes, which has excellent hydrogen absorption / desorption characteristics and is easy to store at low cost. The present invention also provides a nickel-hydrogen battery including a hydrogen electrode using such a hydrogen storage alloy powder as an active material.

[0007]

In order to solve the above problems, the present invention pulverizes a hydrogen storage alloy in a nitrogen gas atmosphere by a water atomizing method to about 20 μm at a stretch ,
The present invention is characterized in that a hydrogen storage alloy powder for electrodes having a relatively thin oxide film on the surface thereof is obtained. Here, the water used in the water atomizing method is an aqueous solution of hypophosphorous acid, particularly a concentration of 0.
An aqueous solution of 2N to 5N can considerably suppress the formation of an oxide film on the surface of the hydrogen storage alloy powder.

In the present invention, the hydrogen-absorbing alloy powder finely pulverized by the water atomizing method is used as an active material as it is, and it is annealed, preferably annealed in hydrogen gas, or an oxide film formed on the surface is treated with an acid. This is used as the active material of the hydrogen electrode, which is obtained by removing more than half of it immediately before the electrode is produced by treatment or vibration. As a method of removing the oxide film on the surface of the finely divided hydrogen-absorbing alloy powder, a method of once immersing the surface in a dilute solution of a strong acid containing hydrochloric acid or nitric acid and etching the surface, and then rinsing with water, or nitrogen is used. A method of mechanically destroying and removing the oxide film by vibrating a closed container in which the alloy is placed on a mesh having a sieve of about 10 μm in which an inert gas such as gas or argon gas is injected is effective.

The hydrogen storage alloy powder produced as described above has no mechanical fracture surface and has a thickness of 80 nm or less on the surface.
A spherical electrode having an oxide film or a shape similar thereto is used, and by using this hydrogen storage alloy powder as an active material, a low cost and long life hydrogen electrode is provided.

[0010]

The present invention has the following features, which are not present in the conventional pulverization method and gas atomization method, by finely pulverizing the hydrogen storage alloy by the water atomization method as described above. First,
The quenching rate is several tens of times higher than that of the gas atomizing method. 2
Since the pulverization up to about 0 μm can be performed at once, the pulverization step which was conventionally required can be omitted, and the cost can be significantly reduced. Further, the cost of manufacturing the alloy powder is reduced because the atomization is performed using water without using an expensive inert gas such as argon gas as compared with the gas atomization method.
Secondly, since there is no crushing step, the resulting hydrogen storage alloy powder does not have a mechanical fracture surface unlike conventional powders, and has a spherical body or similar shape, so it is made fine during charge / discharge cycles. Gives a long-life electrode.
Thirdly, since the alloy surface is lightly oxidized during pulverization, the obtained alloy powder is stable and has the advantage that there is no need to store the alloy powder in an inert gas, vacuum, or water as in the past. .

The particle size of the powder obtained by the atomizing method is proportional to the quenching rate. And in the conventional gas atomization 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, in the water atomizing method, the quenching rate is large at 10 ⁶ to 10 ⁷ ° C / sec and the average particle size is 20 µm.
It is possible to manufacture fine things. Generally, as the active material of the hydrogen electrode, one having an average particle size of about 20 to 30 μm is desirable, but by using the water atomizing method, it is possible to finely pulverize to such a desired particle size without a crushing step. There are advantages. There is an oil atomizing method as a similar method, but in this case, it is difficult and costly to remove the oil adhering to the hydrogen storage alloy powder, and further, carbon is mixed in the alloy.

According to the conventional water atomization method, it has been considered that the surface of the obtained powder is severely oxidized and the produced alloy powder lacks the ability to absorb and desorb hydrogen. However, the present inventors have found that an oxide, such as nickel oxide, becomes a passive film,
Furthermore, it was found that the cooling rate was so fast that only the surface was covered with the oxide film, and the oxidation did not proceed to the inside much. In particular, if the collection tank is filled with nitrogen gas, nitrogen
Water atomization in a gas atmosphere was done in the air
In case of exceeding 200 nm, it is about 80 nm or less
A powder with a thin oxide film on the surface is obtained. In addition, if at the time of water atomization Ru using a strong reducing power next phosphorous acid aqueous solution,
There is an advantage that the oxide film of the powder surface is thinner. The use of hypophosphorous acid has the advantage that the alloy powder can be easily washed by neutralization with an alkali and washing with water. Further, since the oxide film is Ru can be removed to an extent less than half the post-treatment such as annealing and acid treatment of the hydrogen gas, such a post-processing to improve the hydrogen absorption and desorption capacity of the alloy powder it can.

As a result of earnest studies, the present inventors have found that the acid treatment can etch oxides on the surface of the alloy powder, for example, rare earth oxides and nickel oxides in Mm-Ni alloys, but if they are overdone. It was found that the oxide film can be removed to less than half by strictly adjusting the etching amount with the acid concentration, the etching time and the liquid temperature because the underlying metal layer is oxidized and is covered with the oxide film. On the other hand, even in the conventional method of finely pulverizing by a jet mill method or the like in an inert gas, the surface of the obtained powder has a small particle size and is active due to contact with air at the time of taking out, so that it is not oxidized. Cage,
The discharge capacity is not so different from that according to the present invention.

It is known that annealing (annealing) the fine powder improves the crystallinity in the microcrystals, increases the hydrogen absorption / desorption ability, and improves the discharge capacity of the electrode, but it is annealed in hydrogen gas. When the treatment is carried out, the oxide film on the powder surface can be reduced at the same time, so that there is an advantage that the internal resistance and the capacity of the electrode using the same can be reduced. When a battery is constructed by producing electrodes from the hydrogen storage alloy powder produced by the water atomizing method without removing the oxide film, the capacity does not appear in the initial characteristics, but by charging and discharging about a dozen or more cycles, It has almost the same discharge capacity as the crushed product.
It is considered that this is because the oxide film on the surface of the hydrogen storage alloy powder is reduced by the hydrogen generated during charging. On the other hand, those obtained by removing the oxide film to some extent with an acid treatment or a vibrator show a slightly higher discharge capacity from the initial stage.

[0015]

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 1 As a hydrogen storage alloy, a lanta
Metal (Mm) containing 20% by weight of metal (La),
Nickel (Ni), manganese (Mn), aluminum
(Al) and cobalt (Co) are mixed in a predetermined ratio
Then, it is melted in the high frequency melting furnace 11 and MmNi 3_.7 Mn
_0.4 Al_0.3 Co_0.6First, the hydrogen storage alloy 13 with the composition
It is produced and this alloy is poured into the holding furnace 14. Then Bon
Collection tank filled with nitrogen gas supplied from
From the jet nozzle 16 to melt the hydrogen storage alloy.
The hot water 22 is spouted. At this time, the high pressure water pump 18 is used.
Water from the passage 21 is sprayed from around the jet nozzle,
Hydrogen absorption by atomizing molten metal of elemental storage alloy (atomize)
The alloy powder 23 is prepared.

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 80 nm. It was covered with an oxide film. As a result of measuring the particle size distribution of this alloy powder, the average particle size is 22 μm.
Then, the particle size was distributed from 8 μm to 60 μm, and the particles of 10 μm or less were 0.5 wt% or less. When the collection tank is not filled with nitrogen gas and water atomization is performed in air, the thickness of the oxide film on the surface of the obtained alloy powder is 2
When the thickness exceeds 00 nm, removal of the oxide film became considerably difficult.

Next, 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 0.2 parts by weight of carbon black as a conductive material. Parts and 16 parts by weight of water are added to prepare a negative electrode paste. 3 g of this paste was filled in a nickel foam current collector (core material) with leads attached,
After drying, pressure integration is performed by a roller press method to produce a negative electrode plate. On the other hand, the positive electrode plate is prepared by filling 2.2 g of the conventional positive electrode mixture paste containing nickel hydroxide as a main component in the same foamed nickel current collector as described above, and drying and pressing.

One negative electrode plate produced as described above is placed in the center, two positive electrode plates are arranged on both sides thereof, and the positive electrode plates are wrapped with a bag-shaped separator made of polypropylene 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.

[Embodiment 2] First, in a water atomizing apparatus similar to that of Embodiment 1, hydrogen storage alloy fine powder is prepared by using 2N aqueous solution of hypophosphorous acid instead of water. The thickness of the oxide film on the surface of the alloy powder obtained by this method is 4
It is about 0 nm, which is about 1/2 of that when using only water.
It becomes the thickness of. This is considered to be due to the reducing action of hypophosphorous acid. FIG. 4 shows the relationship between the concentration of the used hypophosphorous acid aqueous solution and the thickness of the oxide film on the surface of the obtained alloy powder. When the concentration of hypophosphorous acid is 0.2N or less, the antioxidant effect is small, and when it is 5N or more, the oxide film becomes thicker. A suitable concentration of hypophosphorous acid is 0.2N to 5N.

Next, the hydrogen-absorbing alloy powder obtained above was put into an annealing furnace, the vacuum was once drawn, and then hydrogen gas was introduced until it became a slightly pressurized state (0.1 kg / c).
m ² ), heating at 1000 ° C. for 3 hours, then gradually cooling to room temperature over 8 hours, then applying high vacuum again to remove hydrogen absorbed in the alloy powder, and then returning to atmospheric pressure. In this way, hydrogen storage alloy powder is produced. As a result, the thickness of the oxide film is reduced to about 20 nm on average. Annealing conditions are as follows: holding temperature 800 ° C or higher, cooling time 5
It was found from the measurement of the P (hydrogen pressure) -C (composition) -T (temperature) characteristics that time or more was required. The hydrogen storage alloy powder thus annealed was used as the negative electrode active material in Example 1
A negative electrode plate is manufactured in the same manner as in 1. and is combined with a conventional positive electrode plate to manufacture an evaluation battery having the same configuration as in Example 1. It should be noted that although the annealing treatment was performed in vacuum, an increase in discharge capacity was recognized as compared with the case without annealing treatment, but the extent of the increase was larger in the annealing treatment in hydrogen gas. This is probably because the oxide film on the powder surface is reduced by hydrogen and partially removed. At this time, the purity of hydrogen is 99.9.
% Or more was particularly effective.

[Embodiment 3] First, in the same manner as in Embodiment 1, a hydrogen absorbing alloy fine powder is prepared by a water atomizing method, and then this alloy powder is immersed in 0.2N nitric acid at 40 ° C. and ultrasonically vibrated. After being shaken for 1 minute with a machine, it is washed twice with water, then immersed in an aqueous potassium hydroxide solution having a density of 1.3 g / cm ³ at 70 ° C., well stirred for 20 minutes, and then washed with water 6 times. Figure 5
It shows the relationship between the nitric acid concentration and the thickness of the oxide film on the surface of the alloy powder when the solution temperature is 40 ° C. and the etching time is 1 minute. It can be seen that when the nitric acid concentration is lower than 0.1 N, the etching effect is weak, and when it is higher than 1 N, the underlying metal layer is attacked and the oxide film becomes thicker. A negative electrode plate was prepared in the same manner as in Example 1 using the hydrogen storage alloy powder having an oxide film thickness of 20 nm thus produced as a negative electrode active material, and was combined with a conventional positive electrode plate to have the same configuration as in Example 1. A liquid-rich negative electrode regulation evaluation battery is manufactured.

Example 4 First, a hydrogen storage alloy powder was prepared by the same water atomizing method as in Example 1, and then the hydrogen storage alloy fine powder was annealed at 1100 ° C. in hydrogen gas by the same method as in Example 2. To do. Next, 30 parts of this alloy powder
After dipping in 0.2 N hydrochloric acid at 0 ° C. for 2 minutes with an ultrasonic shaker, washing with water is performed 6 times. A negative electrode plate was produced in the same manner as in Example 1 using the hydrogen storage alloy powder having an oxide film thickness of 15 nm thus produced as the negative electrode active material, and combined with a conventional positive electrode plate to obtain the same configuration as in Example 1. An evaluation battery is produced.

[Embodiment 5] First, like Embodiment 2, 0.5
A hydrogen-absorbing alloy fine powder is prepared by a water atomizing method using an aqueous solution of N hypophosphorous acid, and then this alloy powder is placed on a mesh made of stainless steel wire having a sieve size of 8 μm as in the case of a normal classification work, and an upper lid is provided. Then, place on a saucer, fill with nitrogen gas, and vibrate for 20 minutes. By this operation, a part of the surface oxide film of the hydrogen storage alloy powder is peeled off due to the collision between the powders, passes through the mesh and is deposited on the saucer. Then, the hydrogen storage alloy powder remaining on the mesh is used as a negative electrode active material to prepare a negative electrode plate in the same manner as in Example 1, and in combination with a conventional positive electrode plate, an evaluation battery having the same configuration as in Example 1 is prepared. The amount of hydrogen storage alloy oxide that passed through the sieve was about 1 wt%, and the thickness of the surface oxide film of the hydrogen storage alloy powder was 20 nm.

[Comparative Example 1] A hydrogen storage alloy having the same composition as that of Example 1 was produced in a high frequency melting furnace, vacuum annealed at 1100 ° C, coarsely pulverized by a stamp mill, and further averaged by a jet mill pulverizer to an average particle size of 25 µm. Finely pulverize. Then 400
Remove particles of 37 μm or larger with a sieve of mesh. The hydrogen storage alloy powder thus produced has an average particle size of 2
2 μm, and the thickness of the oxide film on the surface is 10 nm. Using this alloy powder as a negative electrode active material, an evaluation battery is manufactured in the same manner as in Example 1. From the result of particle size distribution measurement of this hydrogen storage alloy powder, particles of 10 μm or less are about 12
It was found to be wt%.

[Comparative Example 2] A hydrogen storage alloy powder is produced by an Ar gas atomizing method. The obtained powder has an average particle size of about 65 μm and has a substantially spherical shape, and the surface is also hardly oxidized. Next, by the same method as in Comparative Example 1, annealing treatment is performed in vacuum, and in order to further reduce the average particle diameter, the particles are pulverized and finely divided by a jet mill. After that, classify with a sieve of 400 mesh, average particle size 22μ
m. The oxidation coating thickness of this hydrogen storage alloy powder is 10
As a result of particle size distribution measurement, it was found that about 6 wt% of particles having a particle size of 15 μm or less was measured. An evaluation battery is manufactured in the same manner as in Example 1 using the hydrogen storage alloy powder manufactured as described above as a negative electrode active material.

FIG. 6 shows changes in the discharge capacity of the negative electrode when a cycle test was conducted on the evaluation batteries of the above-mentioned Examples and Comparative Examples. The charging condition during the cycle test is based on the amount of electricity calculated from the PCT measurement, and is 2C (about 1.7A).
Then, the depth of charge was 100% with respect to the amount of electricity discharged, and the discharge condition was a discharge depth of 100% at 0.9 V cut at 2C. On the other hand, the capacity is confirmed by 0.1C every 12 cycles at 12
Time charge (charge depth 120%), 0.9V at 0.1C
It was performed under the condition of discharging up to.

From FIG. 6, the initial discharge capacity of the negative electrode is shown in Comparative Example 1
And those of Comparative Example 2 are 290 mAh / g and 2 respectively.
It can be seen that the value is 85 mAh / g, which is slightly higher than the 262 mAh / g of Example 1, but is not so different from the value of about 280 mAh / g of the other Examples. However, after 100 times of charging and discharging, the battery of Example 1 was 280 mAh /
g up to 285 to 293 mAh in other examples
The discharge capacity increases up to / g. As a result of detailed examination of the initial cycles up to 100 cycles, it was found that the capacity of these batteries increased by the 15th cycle. The result of the cycle test is 90 in the case of the comparative example.
It was found that 80% of the capacity at the peak was cut off at about 0 cycles, but in the case of Example, about 80% of the capacity was cut at about 1300 cycles, which was excellent in life characteristics. This is because the battery of the comparative example produces a large amount (about 12 wt%) of fine powder that does not contribute to the battery reaction and has a particle size of 7 to 8 μm or less in the crushing process, so the initial capacity (negative electrode utilization rate) does not become so high. ,
In addition, it is considered that the powder shape is polygonal and has corners, so that it easily breaks into fine particles during charge / discharge cycles.
On the other hand, in the case of the present example, the capacity is low because the surface is covered with the oxide film at the beginning, but the oxide film on the surface is reduced by the generated hydrogen during repeated cycles to increase the hydrogen storage capacity. It is considered that pulverization is unlikely to occur because the body has a spherical body having no mechanical fracture surface or a similar shape by the water atomizing method.

On the other hand, in terms of cost, according to the comparative example, crushing was carried out.
Although a process is required, in this example, even fine powder is output at once.
Since it comes, man-hours can be saved. Comparing Example 2 with Comparative Example 1
Cost reduction of about 20%, about 30% compared to Comparative Example 2
I can plan. As a hydrogen storage alloy, ZrMn_0.5 
V_0.1 Cr_0.2 Ni_1.2 AB consisting of Type 2 is used
It was made by using finely pulverized water atomizing method
Battery has excellent cycle characteristics,
As in the example, the crushing process can be omitted and cost can be reduced.
Be done.

[0030]

As described above, according to the present invention, a fine powder of hydrogen storage alloy can be obtained at a stretch by pulverizing by a water atomizing method having a large quenching rate. Therefore, the conventional pulverizing method or gas atomizing method was adopted. The pulverization process which is performed in some cases can be omitted, and the manufacturing cost can be reduced because an expensive inert gas such as argon gas is not used as compared with the gas atomizing method. Further, since there is no pulverization step, the powder obtained according to the present invention has a spherical shape without corners, which makes it difficult for the powder to be miniaturized when the electrode is configured and charged and discharged, and has a long life. further,
Stable because the alloy surface is lightly oxidized when pulverized.
There is no need to store the alloy powder in an inert gas, vacuum, or water as in the conventional case, and there is an advantage that storage is easy.
As described above, according to the production method of the present invention, it is possible to provide a hydrogen storage alloy powder that provides a hydrogen electrode having a low cost 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 showing the relationship between the concentration of the aqueous solution of hypophosphorous acid used in the water atomizing method and the thickness of the oxide film on the surface of the obtained alloy powder.

FIG. 5 is a diagram showing the relationship between the nitric acid concentration used for etching and the thickness of the oxide film on the surface of the alloy powder after etching.

FIG. 6 is a diagram comparing changes in discharge capacity in cycle tests of various negative electrodes.

[Explanation of symbols]

11 High frequency melting furnace 12 coils 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

─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Seiji Yamaguchi 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. (72) Tadao Kimura 1006 Kadoma, Kadoma City, Osaka Matsushita Electric Industrial Co., Ltd. (72) Inventor Munehisa Ikoma, 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. (56) References Japanese Patent Laid-Open No. 4-179055 (JP, A) Japanese Patent Laid-Open No. 4-106872 (JP, A) JP-A-63-178447 (JP, A) JP-A-3-93160 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01M 4/38 B22F 9/08

Claims (5)

(57) [Claims] 1. A method for producing a hydrogen storage alloy powder for an electrode, comprising a step of pulverizing the hydrogen storage alloy by a water atomizing method in a nitrogen gas atmosphere. 2. The method for producing a hydrogen storage alloy powder for an electrode according to claim 1, wherein the water used in the water atomizing method is an aqueous solution of hypophosphorous acid. 3. The method for producing a hydrogen storage alloy powder for an electrode according to claim 1, comprising a step of annealing the finely divided hydrogen storage alloy powder in hydrogen gas. 4. The method for producing a hydrogen storage alloy powder for an electrode according to claim 1, further comprising a step of partially removing an oxide film formed on the surface of the hydrogen storage alloy powder. 5. A surface having no mechanical fracture surface and a thickness of 80 n.
A hydrogen storage alloy powder for an electrode , which has a spherical shape having an oxide film of m or less or a shape similar thereto.