JP2920343B2 - Hydrogen storage alloy powder, nickel-metal hydride battery having the hydrogen storage alloy powder as negative electrode active material, and method for producing hydrogen storage alloy powder - Google Patents

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 for nickel-metal hydride batteries and the like and a method for producing the same.

[0002]

2. Description of the Related Art In recent years, nickel-metal hydride batteries using a hydrogen storage alloy powder, which reversibly stores and releases hydrogen, as a negative electrode have a long charge-discharge cycle life because there is no generation of dendrite which causes a short circuit in principle. Has attracted attention as a secondary battery having a high energy density.

[0003] The typical hydrogen storage alloy powder production process is as follows. First, a predetermined amount of each metal component of the hydrogen storage alloy is weighed and 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 annealing treatment (hereinafter referred to as annealing treatment) in a vacuum or argon, mechanical grinding is performed by a grinder until the average particle size becomes about 20 μm to 30 μm. The alloy powder was immersed in a high-temperature alkaline solution for several hours to prepare a hydrogen storage alloy powder for a nickel-metal hydride battery.

[0004]

However, in the production process of this hydrogen storage alloy powder, the tact time of the casting process is long, and the pulverization process and the alkali treatment process are required, so that the production cost is high. The fine powder having a particle size of 7 μm to 8 μm or less, which hardly functions as an active material during the pulverization process, has a very active surface and a strong oxide film is formed thereon, so that it is inactive and cannot absorb or desorb hydrogen. Is produced in a considerable amount, so that the yield of the raw material is poor and there is a problem that leads to an increase in cost.

[0005] Further, as a cause of deterioration in a charge / discharge cycle life test of a nickel-metal hydride battery using the same, pulverization of a hydrogen storage alloy powder can be cited. However, a pulverized product has a mechanically fractured surface and has a polygonal shape. In addition, there is a disadvantage that pulverization is likely to occur from corners due to volume expansion and contraction during charge and discharge.

In order to solve these drawbacks, a pulverization method using a gas atomizing method or the like has conventionally been considered. For example, JP-A-2-253558 and JP-A-3-116.
No. 655, for example.

However, in the gas atomization method, an inert gas such as an expensive argon (Ar) gas is used, and the particle size of the alloy powder is reduced to only about 50 μm. Is not expected to drop significantly. Further, since the alloy powder is mechanically pulverized, the alloy powder has a sharp fractured surface, and is pulverized during a charge / discharge cycle, and a battery using the same has a problem of shortening the life. In the case of alloy powder having a large particle size, high-rate discharge characteristics are extremely deteriorated.

[0008] The water atomization method can be performed at a stretch until pulverization,
Although this is an excellent production method because it has high productivity and does not use expensive inert gas, it has a disadvantage that the produced alloy surface is easily oxidized and a complicated activation treatment is required.

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 for producing a low-cost hydrogen storage alloy powder excellent in productivity. The purpose is to do.

[0010]

In order to achieve the above object, the present invention provides a hydrogen storage alloy powder and a method for producing the same.
Hydrogen storage alloy powder used as negative electrode active material of nickel-metal hydride battery and method for producing the same containing nickel as a component
It pH10 not the molten metal consisting of a hydrogen storage alloy that pH13
A hydrogen atomizing alloy powder obtained by pulverizing to about 20 μm to 50 μm at a stroke by a water atomizing method using an alkaline aqueous solution of the range described above, or a hydrogen absorbing alloy powder obtained by annealing this alloy powder in vacuum or in argon gas, and a method for producing the same. To provide. The alkaline aqueous solution is K
The pH is 10 to 13 with OH or NaOH. After pulverization, the hydrogen storage alloy powder is taken out of the aqueous alkali solution within 5 minutes to 1 hour, and washed with water to remove the alkali.

[0011] As described above , the surface is covered with an oxide containing nickel without a mechanical fracture surface by rapidly pulverizing the hydrogen storage alloy by the water atomization method using an alkaline aqueous solution.
A covered spherical body and a hydrogen storage alloy powder having a similar shape can be obtained, and by using this as a negative electrode active material, a low-cost, long-life nickel-metal hydride battery is provided.

[0012]

The present invention has the following features not found in the conventional casting, pulverizing and gas atomizing methods by pulverizing the molten metal of the hydrogen storage alloy by the water atomizing method using an alkaline aqueous solution as described above. . First, compared to the gas atomization method, the ability to pulverize the molten metal is high, and pulverization up to about 20 μm can be performed at a stroke, and the pulverization step and the alkali treatment step can be simplified, resulting in significant cost reduction.
In addition, an inert powder having a particle size of 7 μm to 8 μm is hardly generated, and the production cost is reduced because an inert gas such as argon gas, which is more expensive than the gas atomization method, is not used. Second, since there is no pulverizing step, the hydrogen storage alloy powder has no mechanical fracture surface unlike conventional powders and has a spherical shape and a similar shape. It is life. Third, since the activation of the alloy surface can be performed with an alkaline aqueous solution during pulverization, there is an advantage that a high discharge capacity can be achieved.

In the conventional gas atomizing method, the crushing ability of molten metal
Only those with small force and average particle size of 50μm or more can be manufactured
Absent. On the other hand, in the water atomization method, the water pressure is 1500 kg /
cm ^TwoAbout several μm average particle size
It is possible to make even small items. Generally, nickel-metal hydride batteries
The average particle size of the negative electrode active material is about 20 to 30 μm
It is considered desirable to use the water atomization method.
With water pressure adjustment to pulverization without grinding process
There is an advantage that can be brought.

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

The alloy powder is annealed in a vacuum or argon gas to increase the discharge capacity, whereby the crystallization of the alloy powder progresses, the hydrogen storage capacity is improved, and the capacity is increased.

[0016]

【Example】

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

As the hydrogen storage alloy, 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 molten metal 12 of a hydrogen storage alloy having a composition of l _0.3 Co _0.75 is prepared, and the molten metal 12 of the hydrogen storage alloy is poured into a holding furnace 13. Next, a collection tank 15 having excellent alkali resistance filled with nitrogen gas supplied from a nitrogen gas cylinder 14.
From the jet nozzle 16 toward the molten hydrogen storage alloy 12
Squirt. When this, KO of using a high-pressure pump 17 in the ejection pressure of 800 kg / cm ² as shown in FIG. 2 pH 13
An alkaline aqueous solution 21 of H is jetted from around the jet nozzle 22 to pulverize the molten metal 23 of the hydrogen storage alloy (atomizing).
Thus, a hydrogen storage alloy powder 24 (18 in FIG. 1) was produced.

The hydrogen-absorbing alloy powder thus completed was taken out from the collecting tank 15 after a lapse of 5 minutes, washed sufficiently with water, and dried. This hydrogen storage alloy powder 1
There were various shapes such as 8, 24, such as a shape close to a spherical shape and a gourd shape, but each of them had a curved surface without a corner. The surface was covered with needle oxides of Mm and Ni. As a result of the particle size distribution measurement, the average particle size was 2
At 2 μm, the particle size is distributed from 8 μm to 60 μm, and 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)
A negative electrode paste was prepared in addition to parts by weight. 3 g of this paste was filled into a nickel current collector (core material) having countless holes to which leads were attached, dried, and then pressure-integrated by a roller press method to produce a negative electrode plate. On the other hand, as a positive electrode, 2.2 g of a conventional positive electrode mixture containing nickel hydroxide as a main component was used.
Was filled in a current collector made of foamed nickel to produce a positive electrode plate.

One negative electrode plate and four positive electrode plates manufactured as described above are inserted into a bag-shaped separator made of polypropylene (PP) having a thickness of 0.2 mm, and the negative electrode plate is sandwiched between two positive electrodes. And the lead portion is welded to a pole connected to a PP lid having pores, and then placed in a cylindrical acrylic battery case, and a potassium hydroxide aqueous solution (density: 1.30 g) / Cm ³ ) as a main component was injected into a large amount (300 g) from the pores, and then evacuated and defoamed to prepare an electrolyte-rich negative electrode regulation battery.

(Example 2) The hydrogen absorption of Example 2 is described below.
The gold powder and its manufacturing method are explained with reference to the drawings.
I will tell. First, the water inlet shown in FIGS.
Using a pH 10 NaOH aqueous solution in the Mize apparatus
And lower the jet pressure slightly (700 kg / cm ^Two) Atmai
Went. One hour later, this alloy powder was removed from the collection tank.
Is taken out, washed with water and dried to absorb hydrogen with an average particle size of 48 μm
An alloy fine powder was produced. Next, this alloy powder is vacuum
Into the furnace for 10 minutes.^-6evacuate to below torr, 1
After heating at 000 ° C for 3 hours, slowly cool to room temperature over 8 hours
It was cooled and annealed. As annealing conditions
Holding temperature 800 ° C or higher and 1000 ° C or lower, holding time 2 hours
The above is necessary from isotherm diagram measurement (hereinafter referred to as PCT measurement)
I knew that. Above 1000 ° C, alloy particles are deposited
have done. The hydrogen absorption thus annealed
Using a storage 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 prepared in a high-frequency melting furnace, vacuum-annealed at 1100 ° C. for 3 hours, coarsely pulverized by a stamp mill, and finely pulverized by a jet mill to an average particle size of 25 μm. Crushed. An evaluation battery was produced in the same manner and in the same manner as in Example 1 using the hydrogen storage alloy powder produced in this manner as a negative electrode active material. In addition, from the result of the particle size distribution measurement of this hydrogen storage alloy powder, 1
It was found that the content of particles having a particle size of 0 μm or less was about 12 wt%.

FIG. 3 shows a change in the discharge capacity of the negative electrode when a charge / discharge cycle test was performed on the battery evaluated for the liquid-rich negative electrode regulation. The charge condition at the time of the charge / discharge cycle test was 2C (approximately 1.7A) from the amount of electricity calculated from the PCT measurement, the charge amount was 100% of the discharge amount, and the discharge condition was 2C.
The test was performed at 0.9 V cut discharge depth (DOD) 100%.
On the other hand, the capacity check is performed every 100 cycles under the charging condition of 0.1.
C, charge amount of electricity for 12 hours is 120%, discharge condition is 0.1
C, 0.9V cut.

From FIG. 3, the initial discharge capacity of the negative electrode was 280 mAh / g in Example 1, and 290 mAh 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 less than 80% in 1800 cycles in Example 1, 1500 cycles in Example 2, and 1100 cycles in Comparative Example. This is because, in the battery of the comparative example, a large amount (about 12 wt%) of fine powder of 7 μm to 8 μm or less that does not contribute to the battery reaction is generated in the pulverization step, so that the initial capacity (negative electrode utilization rate) is not so high, and This is probably because the shape is polygonal and has corners, so that it is easily broken and pulverized during the charge / discharge cycle. On the other hand, this example has the advantage that the amount of fine powder of 8 μm or less is small, but the initial capacity is almost the same as that of the comparative example because the surface is slightly covered with an oxide film. Is close to a spherical shape and does not have a mechanical fracture surface, so that pulverization hardly occurs, which is considered to be excellent in terms of charge / discharge cycle characteristics.

In terms of cost, the conventional product of the comparative example requires a casting, cooling step and a pulverizing step. However, in the present embodiment, the cooling rate is high and the process to pulverization can be continuously performed at once, so that the number of man-hours can be greatly reduced. It was found that in Example 1, the cost could be reduced by about 60% compared to the comparative example.

The alkaline aqueous solution has a pH of 10 to 10.
The range of pH 13 is effective. At pH 9 or lower, the effect of surface activation is not obtained. At pH 14 or higher, an oxide film is formed to cause a reduction in capacity. Also, the immersion time is 5 minutes or more.
Approximately one hour is optimal, but the conventional alkali treatment requires several hours, whereas the time can be greatly reduced. Further, as the particle size of the alloy powder, 20 μm to 50 μm was suitable from the viewpoints of charge / discharge cycle characteristics and high-rate discharge characteristics. Conventionally, a powder having a particle size of 10 μm or less has been produced by the water atomization method. In the present embodiment, a powder having a large particle size was produced by reducing the water pressure at the time of spraying.

As the hydrogen storage alloy, Zr, Mn,
A battery manufactured in the same manner as in Example 2 using an AB2 type alloy made of V, Cr, and Ni also had a high discharge capacity and excellent charge / discharge cycle characteristics, and a pulverizing step was omitted as in this example, thereby reducing costs. .

[0028]

As is apparent from the above description, according to the hydrogen storage alloy powder and the method for producing the same according to the present invention, the ability to pulverize the molten metal is high, the pulverization to about 20 μm can be performed at once, and the pulverization step and the alkali Since the processing step can be simplified and the cost can be significantly reduced, an inert powder having a particle diameter 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 costs are reduced. Furthermore, since there is no pulverizing process, the hydrogen storage alloy powder does not have a mechanical fracture surface like conventional powders, and has a long life due to the fact that it has a spherical body and a similar shape, so that miniaturization during charge / discharge cycles does not easily occur. Become. In addition, when pulverization is performed, activation of the alloy surface can be performed at once using an alkaline aqueous solution, so that there is an advantage that a high discharge capacity can be achieved.

As described above, a low-cost and long-life nickel-metal hydride battery can be provided by the hydrogen storage alloy powder and the method for producing the same according to the present invention.

[Brief description of the 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 cross section of the ejection nozzle cut away.

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

[Explanation of symbols]

 DESCRIPTION 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

──────────────────────────────────────────────────の Continued on the front page (72) Inventor Seiji Yamaguchi 1006 Kadoma Kadoma, Osaka Prefecture Inside Matsushita Electric Industrial Co., Ltd. (72) Inventor Yoshinori Toyoguchi 1006 Kadoma, Kadoma, Osaka Prefecture Inside Matsushita Electric Industrial Co., Ltd. (72) Inventor Munehisa 1006 Odaka, Kazuma, Kadoma, Osaka Pref. JP-A-5-156322 (JP, A) JP-A-5-195024 (JP, A) JP-A-63-100109 (JP, A) Japan Society of Powder Metallurgy Technology “Powder Metallurgy Technical Course 3 Metal Powder Production ”(September 25, 1964), Nikkan Kogyo Shimbun, PP. 35-37 (58) Field surveyed (Int.Cl. ⁶ , DB name) B22F 9/08 B22F 1/00 H01M 4/38 H01M 10/30

Claims (8)

(57) [Claims] 1. An oxide containing nickel, which has no mechanical fracture surface and is finely pulverized by a water atomization method using an aqueous alkali solution having a pH of 10 to 13 and comprising a hydrogen storage alloy having nickel as a component. A hydrogen-absorbing alloy powder having a surface-coated spherical body or a shape similar thereto. Wherein the finely divided water atomizing method using an alkaline aqueous solution ranging from pH10 not a melt consisting of hydrogen absorbing alloy having a nickel component pH 13, no mechanical fracture surface, an oxide having a nickel A hydrogen-absorbing alloy powder obtained by annealing a hydrogen-absorbing alloy powder having a surface-coated spherical body or a shape similar thereto in a vacuum or in argon gas. 3. A nickel-metal hydride battery comprising the hydrogen storage alloy powder according to claim 1 as a negative electrode active material. 4. A metal melt comprising a hydrogen storage alloy containing nickel as a component is pulverized by a water atomization method using an aqueous alkaline solution having a pH in the range of 10 to 13 to mechanically break the molten metal.
A sphere whose surface is coated with an oxide containing nickel without a cross section
Method for producing a hydrogen-absorbing alloy powder to have a shaped body or shape Ruishi thereto. 5. A molten metal made of a hydrogen storage alloy containing nickel as a component is pulverized by a water atomization method using an aqueous alkaline solution having a pH of 10 to 13 to mechanically break the molten metal.
No cross-section, surface coated with nickel-containing oxide
A method for producing a hydrogen storage alloy powder in which a hydrogen storage alloy powder having a spherical shape or a shape similar thereto is annealed in a vacuum or in 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 of 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 the pulverization, and washed with water to remove the alkali. Manufacturing method of alloy powder. 8. The method for producing a hydrogen storage alloy powder according to claim 4, wherein the particle diameter of the hydrogen storage alloy powder is in the range of 20 μm to 50 μm.