JP2010255104A - Method for producing hydrogen storage alloy powder - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a new method for producing hydrogen storage alloy powder which can remove impurities causing a short circuit. <P>SOLUTION: Hydrogen storage alloy powder is produced by performing a magnetic separation step of exhausting magnetically attractable substances using magnets. Namely, a hydrogen storage alloy raw material is melted to be a molten metal, the molten metal is cooled to obtain a hydrogen storage alloy ingot, the ingot is pulverized, and thereafter, the magnetically attractable substances are magnetically separated using magnets, thus impurities causing a short circuit can be removed. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a method for producing a hydrogen storage alloy powder.

  A hydrogen storage alloy is an alloy that reacts with hydrogen to form a metal hydride, and can reversibly store and release a large amount of hydrogen near room temperature. Therefore, the hydrogen storage alloy is also referred to as an electric vehicle (EV). It is used as a negative electrode material for nickel-hydrogen batteries and fuel cells mounted on hybrid electric vehicles (also referred to as “HEV”) and digital still cameras.

Examples of hydrogen storage alloys include AB ₅ type alloys typified by LaNi ₅ , AB ₂ type alloys typified by ZrV _0.4 Ni _1.5 , and other various alloys such as AB type alloys and A ₂ B type alloys. It has been known. Many of them have a high affinity with hydrogen and have an element group (Ca, Mg, rare earth elements, Ti, Zr, V, Nb, Pt, Pd, etc.) that plays a role in increasing the hydrogen storage capacity, and the affinity with hydrogen. Although it is relatively low and has a small amount of occlusion, it is composed of a combination with element groups (Ni, Mn, Cr, Fe, etc.) that promote the hydrogenation reaction and lower the reaction temperature.

  Such a hydrogen storage alloy is prepared by, for example, mixing and melting raw metal at a predetermined ratio and casting it into a mold, then subjecting the ingot to heat treatment, and crushing the ingot. Then, it is manufactured by pulverizing in order to obtain a predetermined particle size.

  By the way, if the hydrogen storage alloy powder contains impurities that do not constitute an alloy, the hydrogen storage amount may decrease (see Patent Document 1), for example, while charging and discharging are repeated under normal conditions. Even if there is no problem, impurities may elute into the electrolytic solution (alkaline solution) while being repeatedly charged and discharged under severe conditions such as overdischarge, and may cause a short circuit (voltage drop) through the separator.

  Thus, conventionally, a method for reducing the amount of impurities in the hydrogen storage alloy has been disclosed. For example, Patent Document 2 discloses that an alloy containing an impurity element is melted by an apparatus that generates an arc or a plasma arc, the molten metal is received by a rotating body, and the molten metal is scattered by the rotation of the rotating body. A manufacturing method has been proposed in which the amount of impurities in the hydrogen storage alloy is reduced by solidifying the inner surface of a rotating cylindrical mold.

JP-A-2005-272906 JP 2003-1389 A

By the way, in a large battery mounted on an EV or HEV, a plurality of (for example, 200 to 300) battery cells are connected in series to form one large battery. A short circuit will occur. Therefore, a high degree of reliability is required for the negative electrode active material used in this type of battery, and it is desirable to remove impurities that cause a short circuit as much as possible.
In the past, even if some impurities were included, the hydrogen storage alloy powder could be treated with an alkali to suppress the effect of impurities on short-circuiting. In order to obtain it, it is desirable to remove impurities that cause a short circuit as much as possible from the hydrogen storage alloy powder.

  Therefore, the present invention proposes a new method for producing a hydrogen storage alloy powder capable of removing impurities that cause a short circuit.

The present invention relates to a method for producing a hydrogen storage alloy powder comprising a magnetic separation step of eliminating magnetic deposits using a magnet, and more preferably, a hydrogen storage alloy raw material is melted to form a molten metal and cooled to obtain a hydrogen obtained The present invention proposes a method for producing a hydrogen-absorbing alloy powder characterized in that after the occlusion alloy ingot is pulverized, a magnetic separation process is performed in which magnetized materials are removed using a magnet.
Here, “pulverization” means to include roughing or fine grinding described later.

As a result of studying the impurities that cause the short circuit, not all the impurities contained in the hydrogen storage alloy powder cause the short circuit, but part of them, especially the magnetic deposits attached to the magnet by magnetic force, that is, Fe and Cr It was found to affect. Therefore, the present invention has succeeded in effectively removing impurities that cause a short circuit by effectively eliminating these magnetic deposits using a magnet based on such knowledge.
The elements constituting the hydrogen storage alloy such as Ni and Co have a magnetic force and adhere to the magnet by the magnetic force, so the hydrogen storage alloy itself also adheres to the magnet. Therefore, conventionally, it has been unexpected for those skilled in the art to sort impurities using a magnet, but it has been found that sorting by a magnet is possible by controlling the strength of the magnet.

  Embodiments of the present invention will be described in detail below, but the scope of the present invention is not limited to the embodiments described below.

  The method for producing a hydrogen storage alloy powder according to the present embodiment (referred to as “the present production method”) involves melting a hydrogen storage alloy raw material to form a molten metal, and then cooling to form a hydrogen storage alloy ingot (“casting process”). Heat treatment (“heat treatment step”), and then mechanically crushing the hydrogen storage alloy ingot (“crushing step”), followed by magnetic separation using a magnet to eliminate magnetic deposits (“magnetic separation step”). ”), And thereafter, mechanically pulverizing (“ fine pulverization step ”) as necessary to obtain a hydrogen storage alloy powder (referred to as“ the present hydrogen storage alloy powder ”). Details will be described below.

(Composition of hydrogen storage alloy)
The composition of the hydrogen storage alloy powder produced by this production method is not particularly limited. It can be expected that the hydrogen storage alloy powder having any composition can enjoy the same result at least with respect to the short-circuit suppressing effect of the present invention.

However, as a negative electrode active material for a battery mounted on an EV or HEV, an ABx type hydrogen storage alloy having a matrix phase of a crystal structure such as CaCu ₅ type is preferable.
In this case, examples of the metal at the A site of the ABx-type hydrogen storage alloy include La or Mm containing La (Misch metal, which is a rare earth-based mixture). Examples of the B site metal include Ni, Any of Al, Mn, Co, Fe, Ti, V, Zn, and Zr, or a combination of two or more thereof can be given.

  The ratio of the total number of moles of elements constituting the B site to the total number of moles of elements constituting the A site in the ABx composition (this ratio is also referred to as “ABx” and “B / A”) is 5.00 ≦ It is preferable that ABx ≦ 5.50. In particular, 5.15 ≦ ABx ≦ 5.45 is preferable, and it is particularly preferable that 5.30 ≦ ABx ≦ 5.40.

Above all, the general formula _{(1) ·· MmNi a Mn b} Al c Co d or MmNi _a Mn _b Al _c Co _d hydrogen storage alloy that can be represented by Fe _e are preferred.
Therefore, in consideration of the use as a negative electrode active material of a battery mounted on an electric vehicle or a hybrid vehicle, the following is expressed by the general formula MmNi _a Mn _b Al _c Co _d or MmNi _a Mn _b Al _c Co _d Fe _e An example of a preferable elemental composition of the parent phase of the hydrogen storage alloy capable of forming the above will be described.

“Mm” in the general formula (1) may be any rare earth-based mixture (Misch metal) containing at least La and Ce. Normal Mm contains rare earths such as Pr, Nd, and Sm in addition to La and Ce. For example, a rare earth mixture having Ce (40 to 50%), La (20 to 40%), Pr, and Nd as main constituent elements can be mentioned. In this hydrogen storage alloy, La, Ce, and Nd in Mm can be mentioned. And Pr (mass%) are 56.8 ≦ La (in Mm) ≦ 88.4, 8.1 ≦ Ce (in Mm) ≦ 30.4, 0 ≦ Nd (in Mm) ≦ 9.7 0 ≦ Pr (in Mm) ≦ 3.1 is preferable.
Especially, it is preferable that La occupies 63.1-88.4 mass% in Mm, and it is more preferable that it occupies 78.9-88.4 mass%. Ce preferably occupies 8.1 to 25.9 mass% in Mm, and more preferably occupies 8.1 to 20.1 mass%.
Nd preferably occupies 0 to 8.3 mass% in Mm, and more preferably 0 to 4.7 mass%.
Pr preferably occupies 0 to 2.7% by mass in Mm, and more preferably occupies 0 to 1.5% by mass.

  Co can be provided at low cost if its amount is reduced, but it is difficult to maintain its life characteristics, so the ratio of Co (d) is preferably set to 0 <d ≦ 0.80, More preferably, 0 <d ≦ 0.30, and particularly preferably 0.05 ≦ d ≦ 0.30.

  The ratio (e) of Fe is preferably 0 <e <0.30, more preferably 0 <e <0.25, and particularly preferably within the range of 0 <e ≦ 0.20.

  The proportion (a) of Ni is 4.0 ≦ a ≦ 4.7, preferably 4.1 ≦ a ≦ 4.6, particularly preferably 4.3 ≦ a ≦ 4.6, and even more preferably 4.4. <= A <= 4.6. If it is within the range of 4.0 ≦ a ≦ 4.7, the output characteristics can be easily maintained, and the pulverization characteristics and the life characteristics are not particularly deteriorated.

  The ratio (b) of Mn is 0.3 ≦ b ≦ 0.7, preferably 0.3 ≦ b ≦ 0.6, and more preferably 0.3 ≦ b ≦ 0.5. When the ratio of Mn is in the range of 0.3 ≦ b ≦ 0.7, the pulverization residual rate can be easily maintained.

  The proportion (c) of Al is 0.20 ≦ c ≦ 0.50, preferably 0.20 ≦ c ≦ 0.45, and more preferably 0.25 ≦ c ≦ 0.45. If the Al ratio is in the range of 0.20 ≦ c ≦ 0.50, the plateau pressure becomes higher than necessary, and it is possible to suppress the deterioration of the energy efficiency of charge / discharge, and the hydrogen storage amount decreases. Can also be suppressed.

  In addition, this hydrogen storage alloy may contain the impurity in any one of Ti, Mo, W, Si, Ca, Pb, Cd, and Mg, if it is about 0.05 mass% or less.

(Casting process)
The mixture obtained by weighing and mixing the alloy raw materials of the present hydrogen storage alloy powder is melted into a molten metal using, for example, a high-frequency heating melting furnace by induction heating. Then, the molten metal is poured into a mold, for example, a water-cooled mold, cast at a casting temperature of, for example, 1350 to 1550 ° C., and cooled at a predetermined cooling rate (a predetermined amount of cooling water).
The casting method is preferably a mold casting method, but other casting methods such as a twin roll method (specifically, refer to paragraphs [0013] to [0016] of Japanese Patent Application No. 2002-299136), an as-cast method (specifically In other words, other casting methods such as Japanese Patent Application No. 2002-299136, paragraphs [0019] to [0020]) may be employed.

(Heat treatment process)
Next, if necessary, that is, if necessary to homogenize the crystal structure and components, heat treatment is performed, for example, in an inert gas atmosphere such as argon gas, for example, at 1000 to 1200 ° C. for 3 to 6 hours. do it.

(Crushing process)
The hydrogen storage alloy ingot is preferably crushed to a particle size (−500 μm) passing through a 500 μm sieve, for example. However, the degree of coarse crushing may be pulverized to a particle size passing through a 1000 μm sieve (−1000 μm) as required, or up to a particle size passing through a 850 μm sieve (−850 μm). It may be pulverized.
In other words, the crushing of the hydrogen storage alloy ingot is such that the repose angle of the powder after pulverization is 24 to 44 °, particularly 26 to 42 °, and particularly 29 to 39 °. It is preferable to grind as follows.
In addition, since the magnetic separation efficiency is reduced if it is too finely pulverized at this stage, it may be finely pulverized to some extent.

The crushing of the hydrogen storage alloy ingot can be performed by using a crushing device or a crushing device in which the crushing portion that comes into contact with the powder, that is, the crushing means is made of iron or an iron alloy. Examples of such a pulverizer or pulverizer include a roll crusher, a double roll crusher, and a jaw crusher.
If it is roughly crushed with an apparatus equipped with a pulverizing means containing iron or an iron alloy, the iron or iron alloy will be mixed into the crushed material, but the magnetic deposit will affect at least a short circuit in the next magnetic separation process. Can be removed, and can be roughly crushed with such a pulverizer. However, the meaning here does not mean that it is preferable to coarsely pulverize with an apparatus equipped with a pulverizing means containing iron or an iron alloy, but means that the effects of the present invention can be enjoyed more.
The rough crushing of the hydrogen storage alloy ingot may be performed either dry or wet.

(Magnetic separation process)
The crushed hydrogen storage alloy is then sent to a magnetic separation process. At this time, stress is present immediately after pulverization, and magnetized substances tend to adhere to the magnet, which is not preferable. Therefore, a magnetic separation apparatus is provided with a time of 20 seconds or longer, more preferably 30 seconds or longer, and particularly preferably 40 seconds or longer after rough crushed. It is preferable to put in
However, since there is a possibility of deterioration if left too long after crushing, it is preferably within 48 hours, especially within 24 hours, and especially within 12 hours.

In the magnetic separation process, the magnetized material is adhered to the magnet using a magnet, and the adhered magnetized material is removed, that is, the non-magnetized material is recovered to obtain a hydrogen storage alloy powder.
Magnetic separation can be performed either dry or wet.

At this time, the magnet used preferably has a magnetic force of 100 mT ± 10% to 600 mT ± 10%.
Since the hydrogen storage alloy has a magnetic force, if a strong magnet is used, the hydrogen storage alloy that does not affect the short circuit is also removed, resulting in a poor yield. This is the reason why, conventionally, selection by magnetic force has not been performed in the manufacturing process of the hydrogen storage alloy. On the other hand, when a magnet having a magnetic force of 100 mT ± 10% to 600 mT ± 10% is used, a substance causing a short circuit can be removed while maintaining the yield of the hydrogen storage alloy.
From this point of view, the magnetic force of the magnet used is more preferably 100 mT ± 10% to 500 mT ± 10%, more preferably 150 mT ± 10% to 450 mT ± 10%, and particularly preferably 150 mT ± 10% to 400 mT ± 10. % Is more preferable.
In addition, even if the magnet has the same magnetic force of 100 mT, the magnetic force changes by about 20% depending on the environment, and hence is described as “± 10%”.

The magnet used may be a permanent magnet or an electromagnet. Further, the shape, size, surface area, distance between magnets, and the like of the magnet can be appropriately selected, and an optimal one may be selected.
As a guideline, (the total surface area in the case of plurality) surface area of the magnet is preferably 50cm ² ~3000cm ^2, especially 50cm ² ~2000cm ² preferred.
Further, the size of the magnet is preferably determined according to the viscosity of the powder to be magnetically selected, but as a guideline, a magnet having a diameter of φ1 mm to 100 mm is preferable, in particular, a diameter of φ10 mm to 80 mm, and especially among them, φ20 mm to Those having 50 mm are preferred.

The rate at which the hydrogen storage alloy is charged into the magnetic separator is preferably 150 g / min to 15000 g / min, particularly preferably 200 g / min to 10000 g / min, and more preferably 200 g / min to 8500 g / min.
In addition, 150 ((g / min) / cm ² ) among them so that the charging speed with respect to the surface area of the magnet (the total surface area in the case of plural magnets) is 300 ((g / min) / cm ² ) or less. In the following, it is particularly preferable to adjust so as to be 75 ((g / min) / cm ² ) or less. Further, in a bar-shaped magnet, when the magnetic force and the direction (N · S) change depending on the position in the length direction, the maximum absolute value of the magnetic force is usually shown.

As an example of a preferable magnetic separator, there can be mentioned a magnetic separator having a configuration in which rod-shaped magnets having a predetermined magnetic force are arranged side by side at intervals, and a plurality of them are vertically stacked. In such a device, when a plurality of magnets are stacked in the vertical direction, the magnets can be arranged so that the directions of the magnets are staggered in the vertical direction.
As another example of a preferable magnetic separator, a rod-shaped magnet having a predetermined magnetic force, in particular, a round bar-shaped magnet is arranged on the circumference at an interval to form a cylindrical shape, and the cylinder is centered on a horizontal axis. And a magnetic separator having a configuration in which the hydrogen storage alloy is dropped from above the cylinder. The rotation speed of the magnet (cylindrical body) in this case is 100 rotations / minute or less, particularly 60 rotations / minute or less, especially 40 rotations / minute, because the magnetized magnetic material is peeled off by centrifugal force when the rotation speed is increased. It is preferable to adjust to the following.

Regarding the magnetic separation apparatus, the ratio of the magnetic separation tank volume (the volume of the space in which the magnetic storage is performed by introducing the hydrogen storage alloy) with respect to the charging speed is 0.5 to 100 (cm ³ / (g / min)). preferable. This is because a magnetic separation apparatus defined in this range can effectively remove magnetic deposits.
From this viewpoint, the ratio of the magnetic separation tank volume to the charging speed is particularly preferably 0.5 to 90 (cm ³ / (g / min)), and more preferably 0.5 to 80 (cm ³ / (g / min). Is more preferable.

(Fine grinding process)
The hydrogen storage alloy powder obtained by magnetic separation is preferably finely pulverized to a particle size (−150 μm) passing through a 150 μm sieve, for example, depending on the application.
However, the degree of pulverization was pulverization up to a particle size passing through a 150 μm sieve (−150 μm) even if pulverization was performed up to a particle size passing through a 250 μm sieve (−250 μm). Alternatively, it may be pulverization up to a particle size passing through a 70 μm sieve (−70 μm) or pulverization up to a particle size passing through a 35 μm sieve (−35 μm).
From the viewpoint of yield, it is preferable to grind to a particle size (−150 μm) that passes through a 150 μm sieve mesh.

The fine pulverization can be performed using a pulverization device or a pulverization device in which the pulverized portion that comes into contact with the powder, that is, the pulverizing means is made of iron or iron alloy. Examples of such a crushing device or crushing device include a pin mill and a hammer mill.
Note that if pulverization is performed with an apparatus equipped with pulverization means containing iron or an iron alloy, the iron or iron alloy is mixed in the crushed material. The present inventor has confirmed that the amount of kimono hardly increases (see Comparative Examples 1 and 2 described later). The cause can be considered that the magnetized material hardly increases because the hydrogen storage alloy is fixed and the contact portion is coated in the fine pulverizer.

  In addition, it is preferable that the magnetic separation is performed not after fine pulverization but after coarse pulverization. The reason is that the amount of magnetic deposits caused by the pulverizer is larger than the pulverization step because the hydrogen storage alloy is fixed and the powder contact part is covered in the pulverization pulverizer. This is because there are more processes for coarse crushing, and further, if magnetic separation is performed after fine pulverization, the surface area of the powder particles is large, so that the fine powder is easily clogged inside the magnetic separation apparatus.

(Other processing)
After that, if necessary, the surface of the alloy is coated with a metal material or polymer resin, or the surface is treated with an acid or alkali, and used as a negative electrode active material for various batteries. it can.

(Evaluation)
As a result of research on impurities that cause short circuits, iron (Fe), Ni, Cr, SUS, and other metal compounds that are mixed in the manufacturing process, such as during pulverization, have a relatively large particle size and a large magnetic force (magnetized material). Has been found to have an effect on Therefore, by performing magnetic separation as in the present invention, it is possible to remove such magnetic deposits that affect the short circuit. In addition, by appropriately adjusting the magnetic separation conditions (mainly the magnetic force of the magnet), impurities that cause a short circuit can be selectively removed while maintaining the yield of the hydrogen storage alloy powder.

The hydrogen storage alloy produced by this production method can have a magnetic deposit amount of less than 0.15 ppm, more preferably less than 0.12 ppm, and particularly preferably less than the measurement limit by the measurement method performed in the following Examples.
On the other hand, if the magnetic separation as in the present manufacturing method is not performed, the amount of magnetic deposit cannot be reduced below 0.15 ppm, so the hydrogen storage alloy having a magnetic deposit amount of less than 0.15 ppm is magnetically selected. It can be estimated.

(Use of this hydrogen storage alloy powder)
The hydrogen storage alloy powder can prepare a negative electrode for a battery by a known method. That is, a hydrogen storage alloy negative electrode can be produced by mixing and forming a binder, a conductive additive and the like by a known method.

The hydrogen storage alloy negative electrode thus obtained can be used not only for secondary batteries but also for primary batteries (including fuel cells). For example, a nickel-MH (Metal Hydride) secondary battery can be composed of a positive electrode using nickel hydroxide as an active material, an electrolytic solution made of an alkaline aqueous solution, and a separator. It can be suitably used for power supply applications such as tools, electric vehicles, hybrid vehicles, and fuel cells (including hybrid fuel cells used in combination with other batteries such as lithium batteries).
This hydrogen storage alloy powder removes impurities that cause short circuits as much as possible, and can meet a high degree of reliability. Therefore, the negative electrode active for large batteries such as those mounted on electric vehicles and hybrid vehicles is particularly important. It can be particularly suitably used as a substance.
“Hybrid vehicle” means a vehicle that uses two power sources, an electric motor and an internal combustion engine. In this case, “internal combustion engine” includes not only a gasoline engine but also a diesel engine and other engines. Is also included.
It can also be used for hydrogen storage alloys used in heat pumps, storage of natural energy such as solar and wind power, hydrogen storage, and actuators.

(Explanation of words)
In the present specification, when expressed as “X to Y” (X and Y are arbitrary numbers), “X is preferably greater than X” or “preferably more than Y” with the meaning of “X to Y” unless otherwise specified. The meaning of “small” is also included.
In addition, when expressed as “X or more” (X is an arbitrary number) or “Y or less” (Y is an arbitrary number), it is “preferably greater than X” or “preferably less than Y”. Includes intentions.

  EXAMPLES Hereinafter, although this invention is demonstrated concretely based on an Example, the scope of the present invention is not limited to the following Example.

<Overdischarge short circuit test>
The present inventors have confirmed from the results of various tests so far that the causative substances of the short circuit in the overdischarge state are iron and Cr. Here, Fe or SUS is added to the hydrogen storage alloy, and the cause of the short circuit in the overdischarged state is iron and Cr.

(Production of electrode cell)
1-1) Only hydrogen storage alloy (standard):
1 g of hydrogen storage alloy is mixed with 3 g of nickel powder as a conductive material and 0.12 g of polyethylene powder as a binder, and 1.24 g of the obtained powder (containing 0.3 g of hydrogen storage alloy) is placed on the foamed Ni. Press-molded into a pellet type with a diameter of 18 mm and a thickness of 1.8 mm, and vacuum-baked at 150 ° C. for 1 hour to produce a pellet electrode. This pellet electrode was used as the negative electrode, which was at least twice the calculated negative electrode capacity A positive electrode (sintered nickel hydroxide) having a capacity of 5 mm was sandwiched between separators and immersed in a 30 wt% KOH aqueous solution to produce an open type test cell.

1-2) Fe additive:
0.95 g of a hydrogen storage alloy and Fe powder (Masuda Rika Kogyo Co., Ltd., iron powder 60 mesh 4N8%) 0.05 g were mixed with 3 g of nickel powder as a conductive material and 0.12 g of polyethylene powder as a binder, 1.24 g of the obtained powder (containing 0.29 g of a hydrogen storage alloy) was pressure-molded on foamed Ni to form a pellet type having a diameter of 18 mm and a thickness of 1.8 mm, and then subjected to vacuum firing at 150 ° C. for 1 hour to form a pellet An electrode was produced. This pellet electrode is used as a negative electrode, which is sandwiched by a positive electrode (sintered nickel hydroxide) having a capacity more than twice the calculated negative electrode capacity through a separator, and immersed in a 30 wt% KOH aqueous solution to be an open type test cell. Was made.

1-3) SUS304 additive:
0.95 g of a hydrogen storage alloy and 0.05 g of SUS304 powder (Masuda Rika Kogyo Co., Ltd., stainless steel SUS304 powder—100 mesh) are mixed with 3 g of nickel powder as a conductive material and 0.12 g of polyethylene powder as a binder, 1.24 g of the obtained powder (containing 0.29 g of a hydrogen storage alloy) was pressure-molded on foamed Ni to form a pellet type having a diameter of 18 mm and a thickness of 1.8 mm, and then subjected to vacuum firing at 150 ° C. for 1 hour to form a pellet An electrode was produced. This pellet electrode is used as a negative electrode, which is sandwiched through a separator with a positive electrode (sintered nickel hydroxide) having a capacity more than twice the calculated negative electrode capacity, and immersed in a 30 wt% aqueous KOH solution to open test cell. Was made.

(Charge / discharge conditions before voltage drop measurement and overdischarge short-circuit test method)
Connect the above open-type test cell to a charge / discharge device (Toyo System Co., Ltd. charge / discharge tester: Toscat3000), put it in a thermostat (YAMATO) with adjustable temperature, and perform it at a temperature of 20 ° C. It was.
First, 10 cycles were performed with charge: 0.2 C × 6 hours, discharge 0.2 C, and 0.7 V cut. Thereafter, the battery was discharged to 0.2 C / 0.1 V in the CC / CV (constant current / constant voltage) mode, held at 0.1 V for 24 hours, and then rested (left) for 12 hours. Then, it started from charge, and also it carried out by charge: 0.2Cx6 hours, discharge 0.2C, and 0.7V cut until 3 cycle charge. After that, it was paused (left) and the voltage was observed.
In all cases, the standing time was 250 hours.

  Also from such a test result, it has confirmed that the causative substance of the short circuit in an overdischarge state was iron and Cr.

<Examples and comparative examples>
Next, examples and comparative examples relating to the present invention will be described. First, evaluation methods of the examples and comparative examples will be described.

(Measurement of magnetic deposit)
Samples (powder) obtained in Examples and Comparative Examples were slurried, and a magnet coated with tetrafluoroethylene was put into the slurry to attach the magnetized material to the magnet, and then JIS G 1258: 1999 was used. In consideration, a method of quantifying the magnetic deposit by dissolving the magnetic deposit adhering to the magnet with an acid was employed. Next, this will be described in detail.
In addition, since the magnetized material adhering to the magnet is a very small amount, it is necessary to immerse the magnet together in an acidic solution to dissolve the magnetized material in acid. Therefore, a magnet coated with tetrafluoroethylene was used as the magnet, and the strength of each magnet was measured before the measurement. The strength of the magnet was measured using a TESLA METER model TM-601 manufactured by KANETEC.

That is, 100 g of hydrogen storage alloy powder (sample) was put into a 500 cc polypropylene pot, 100 cc of ion exchange water and one 150 mT magnet covered with tetrafluoroethylene were put on a ball mill rotating base and adjusted in advance. It rotated for 30 minutes at 60 rpm. Next, take out the magnet, put it in a 300 mL tall beaker, soak it in ion-exchanged water, wash it with an ultrasonic cleaner (model US-205, manufactured by SND Co., Ltd.) for 3 minutes at the setting of output switching 2 frequency, and adhere to the magnet The excess powder was removed. The exchange of ion-exchanged water soaking the magnet and washing with ultrasonic waves were repeated 8 times. After that, the magnet is taken out, put into a 100 mL measuring cylinder, immersed in aqua regia (a liquid in which concentrated hydrochloric acid and concentrated nitric acid are mixed at a volume ratio of 3: 1) so that the magnet is completely submerged, and is 80 ° C. in aqua regia. For 30 minutes to dissolve the magnetic deposit.
The magnet was taken out from the aqua regia, and the aqua regia in which the magnetic deposit was dissolved was diluted with ion exchange water. The diluted aqua regia was analyzed for elements of La, Fe, and Cr with an ICP emission spectrometer.
This magnetized material also contains a part of the hydrogen storage alloy. Therefore, the amount of Fe contained as a composition component in the hydrogen storage alloy is calculated from the La amount in the analysis value, and is subtracted from the analysis value of Fe. The amount of Fe obtained was calculated as the amount of Fe as an impurity.
The total amount of Fe and Cr as impurities obtained as described above was calculated as the amount of magnetic deposits per sample mass.

(Measurement of particle size after crushing: measurement of ratio of 150 μm over (+150 μm))
The coarsely crushed hydrogen storage alloy powder 100 g was subjected to particle size classification for 10 minutes using IIDA SIEVE SHAKER manufactured by IIDA SEISAKUSHO Co., Ltd. with a sieve having a sieve size of 150 μm. Then, the mass above and below the sieve was measured, and the ratio of +150 μm was calculated using the following formula.
+150 μm ratio (mass%) = mass on sieve / (mass on sieve + mass below sieve) × 100

(Measurement of repose angle)
The repose angle of the hydrogen storage alloy powder was measured as follows as an index of the fluidity of the hydrogen storage alloy powder after coarse crushing.

  The angle of repose of the hydrogen storage alloy powder of the hydrogen storage alloy powder after coarse crushing was measured using a powder tester manufactured by Hosokawa Micron. That is, the sample was put in from the funnel attached to the powder tester, the sample was supplied until a sufficient mountain was formed on the tray, and the angle of the mountain formed was measured.

(Measurement of average particle size of finely pulverized hydrogen storage alloy powder)
The average particle size (D50) of the hydrogen storage alloy powder after pulverization was measured under the following condition settings using a microtrack (manufactured by Nikkiso Co., Ltd., HRA9320-X100).
(Transp): Reflect
(Sphere): No
(RefInx): 1.51
(Flow): 60 ml / sec

Example 1
The mass ratio of each element is Mm: 31.70%, Ni: 59.45%, Mn: 5.20%, Al: 2.10%, Co: 1.30%, Fe: 0.25%. Thus, raw materials (pure metals were used as raw materials for Ni, Mn, Al, Co, and Fe) were weighed and mixed.
Mm is a misch metal which is a rare earth mixture of La and Ce, and the content ratio of each component in Mm is La: 79.9% and Ce: 20.1% with respect to the total mass of Mm. The prepared material was used as a raw material.

The mixture obtained above is placed in a crucible and fixed in a high-frequency melting furnace, and after reducing the pressure to 10 ⁻⁴ to 10 ⁻⁵ Torr, argon gas is introduced and heated to 1450 ° C. in an argon gas atmosphere, 10 kg of molten metal was poured into a water-cooled copper mold having a total mass of 200 kg at a rate of 4 kg / second to obtain a hydrogen storage alloy ingot. Further, the obtained hydrogen storage alloy ingot was put in a stainless steel container and set in a vacuum heat treatment apparatus, and heat treatment was performed at 1080 ° C. for 3 hours in an argon gas atmosphere.

Next, using a jaw crusher (model 1021-B) manufactured by Fuji Paudl and a brown mill (model 1025-HBG) manufactured by Yoshida Seisakusho, the particle size (−500 μm) passing through the 500 μm sieve of the hydrogen storage alloy ingot The obtained hydrogen storage mixed powder was transferred to a magnetic separator over 60 seconds and subjected to a magnetic separation process.
In the magnetic separation process, by using a magnetic separator as described below, the magnetic absorption is performed by introducing the hydrogen occlusion mixed powder so that the charging speed with respect to the total surface area of the magnet is 35 ((g / min) / cm ² ). Sorting (ratio of magnetic separation tank volume to charging speed 1.3 cm ³ / (g / min)) was performed.

  Next, the hydrogen storage mixed powder as a non-magnetized product recovered in the magnetic separation process is passed through a 106 μm sieve through a hydrogen storage alloy ingot using a bantam mill (model TAP-1WZ type) manufactured by Tokyo Atomizer Manufacturing Co., Ltd. Finely pulverized to a size (−106 μm) to obtain a hydrogen storage powder (sample).

Incidentally, magnetic separator used is juxtaposed magnets section round bar-like having a magnetic force of 300 mT (± 30 mT), and having a structure in which stacked two stages it up and down (the total surface area 200 cm ² of the magnet) A magnetic separator was used.

The obtained hydrogen storage alloy was confirmed to be MmNi _4.46 Al _0.35 Mn _0.42 Co _0.10 Fe _0.020 (ABx = 5.35) using an ICP emission spectrometer.

(Example 2)
After roughly crushing in the same manner as in Example 1, the obtained hydrogen storage mixed powder was transferred to a magnetic separation device over 60 seconds and subjected to a magnetic separation step.
In the magnetic separation process, using a magnetic separator described below, the hydrogen occlusion mixed powder is charged so that the charging speed with respect to the total surface area of the magnet is 0.75 ((g / min) / cm ² ). Magnetic separation (ratio of magnetic separation tank volume to charging speed 40 cm ³ / (g / min)) was performed.

  Next, the hydrogen storage mixed powder as a non-magnetized product recovered in the magnetic separation process is passed through a 106 μm sieve through a hydrogen storage alloy ingot using a bantam mill (model TAP-1WZ type) manufactured by Tokyo Atomizer Manufacturing Co., Ltd. Finely pulverized to a size (−106 μm) to obtain a hydrogen storage powder (sample).

The magnetic separator used had a configuration in which round-shaped bar-shaped magnets having a magnetic force of 200 mT (± 20 mT) were juxtaposed, and the upper and lower layers of the magnets were stacked vertically (total surface area of the magnet 400 cm ² ). A magnetic separator was used.

(Comparative Example 1)
A hydrogen storage powder (sample) was obtained in the same manner as in Example 1 except that magnetic separation and fine pulverization were not performed.

(Comparative Example 2)
A hydrogen storage powder (sample) was obtained in the same manner as in Example 1 except that magnetic separation was not performed.

(Example 3)
Raw materials (Ni, Mn) so that the mass ratio of each element is Mm: 31.57%, Ni: 58.43%, Mn: 5.20%, Al: 2.10%, Co: 2.70% Pure metal was used as a raw material for Al and Co.) and weighed and mixed.
Mm is a misch metal which is a rare earth mixture of La and Ce, and the content ratio of each component in Mm is La: 79.2% and Ce: 20.8% with respect to the total mass of Mm. The prepared material was used as a raw material.
Thereafter, a hydrogen storage alloy was obtained in the same manner as in Example 1.

The obtained hydrogen storage alloy was confirmed to be MmNi _4.39 Al _0.34 Mn _0.42 Co _0.20 (ABx = 5.35) using an ICP emission spectrometer.

Example 4
The same procedure as in Example 3 was performed except for the magnetic separation process.

In the magnetic separation process, by using a magnetic separator described below, the magnetic absorption magnetic powder is introduced so that the charging speed with respect to the total surface area of the magnet is 54 ((g / min) / cm ² ). Sorting (ratio of magnetic separation tank volume to charging speed: 1.4 cm ³ / (g / min)) was performed.
The magnetic separator used was a circular cylinder with five round bar-shaped magnets having a magnetic force of 450 mT (± 45 mT) arranged at intervals on the circumference, and the cylinder was centered on the horizontal axis. A magnetic separator equipped with a configuration (total surface area of magnet 130 cm ² ) rotating at 40 (rotation / min) was used.

(Example 5)
Raw materials (Ni, Mn) so that the mass ratio of each element is Mm: 31.70%, Ni: 59.70%, Mn: 5.20%, Al: 2.10%, Co: 1.30% Pure metal was used as a raw material for Al, Co, and Co.) and weighed and mixed.
Mm is a misch metal which is a rare earth mixture of La and Ce, and the content ratio of each component in Mm is La: 78.9%, Ce: 14.9%, Nd: What adjusted 4.7% and Pr: 1.5% was used as a raw material.
Thereafter, a hydrogen storage alloy was obtained in the same manner as in Example 4.

The obtained hydrogen storage alloy was confirmed to be MmNi _4.48 Al _0.35 Mn _0.42 Co _0.10 (ABx = 5.35) using an ICP emission spectrometer.

(Example 6)
The mass ratio of each element is Mm: 31.70%, Ni: 59.60%, Mn: 5.20%, Al: 2.10%, Co: 1.30%, Fe: 0.10%. Thus, raw materials (pure metals were used as raw materials for Ni, Mn, Al, Co, and Fe) were weighed and mixed.
Mm is a misch metal which is a rare earth mixture of La and Ce, and the content ratio of each component in Mm is La: 88.4%, Ce: 8.1%, Nd: Those adjusted to 2.6% and Pr: 0.9% were used as raw materials.
Thereafter, a hydrogen storage alloy was obtained in the same manner as in Example 4.

The obtained hydrogen storage alloy was confirmed to be MmNi _4.47 Al _0.35 Mn _0.42 Co _0.10 Fe _0.008 (ABx = 5.35) by an ICP emission spectrometer.

(Example 7)
The mass ratio of each element is Mm: 31.70%, Ni: 59.30%, Mn: 5.20%, Al: 2.10%, Co: 1.30%, Fe: 0.40%. Thus, raw materials (pure metals were used as raw materials for Ni, Mn, Al, Co, and Fe) were weighed and mixed.
Mm is a misch metal which is a rare earth mixture of La and Ce, and the content ratio of each component in Mm is La: 56.8%, Ce: 30.4%, Nd: What was adjusted so that it might become 9.7% and Pr: 3.1% was used as a raw material.
Thereafter, a hydrogen storage alloy was obtained in the same manner as in Example 4.

The obtained hydrogen storage alloy was confirmed to be MmNi _4.45 Al _0.35 Mn _0.42 Co _0.10 Fe _0.032 (ABx = 5.35) using an ICP emission spectrometer.

(Example 8)
By mass ratio of each element, Mm: 31.44%, Ni: 60.68%, Mn: 4.94%, Al: 1.98%, Co: 0.66%, Fe: 0.30% Thus, raw materials (pure metals were used as raw materials for Ni, Mn, Al, Co, and Fe) were weighed and mixed.
Mm is a misch metal that is a rare earth mixture of La and Ce, and the content ratio of each component in Mm is La: 63.6%, Ce: 25.7%, Nd: Materials adjusted to 8.0% and Pr: 2.7% were used as raw materials.
Thereafter, a hydrogen storage alloy was obtained in the same manner as in Example 4.

The obtained hydrogen storage alloy was confirmed to be MmNi _4.60 Al _0.33 Mn _0.40 Co _0.05 Fe _0.024 (ABx = 5.40) using an ICP emission spectrometer.

Example 9
The mass ratio of each element is Mm: 31.78%, Ni: 57.32%, Mn: 4.74%, Al: 1.84%, Co: 4.02%, Fe: 0.30%. Thus, raw materials (pure metals were used as raw materials for Ni, Mn, Al, Co, and Fe) were weighed and mixed.
Mm is a misch metal which is a rare earth mixture of La and Ce, and the content ratio of each component in Mm is La: 63.0%, Ce: 26.2%, Nd: The raw materials were adjusted to 8.1% and Pr: 2.7%.
Thereafter, a hydrogen storage alloy was obtained in the same manner as in Example 4.

The obtained hydrogen storage alloy was confirmed to be MmNi _4.30 Al _0.30 Mn _0.38 Co _0.30 Fe _0.020 (ABx = 5.30) by an ICP emission spectrometer.

(Example 10)
By mass ratio of each element, Mm: 31.51%, Ni: 59.82%, Mn: 6.19%, Al: 1.52%, Co: 0.66%, Fe: 0.30% Thus, raw materials (pure metals were used as raw materials for Ni, Mn, Al, Co, and Fe) were weighed and mixed.
Mm is a misch metal which is a rare earth mixture of La and Ce, and the content ratio of each component in Mm is La: 63.5%, Ce: 25.8%, Nd: Materials adjusted to 8.0% and Pr: 2.7% were used as raw materials.
Thereafter, a hydrogen storage alloy was obtained in the same manner as in Example 4.

The obtained hydrogen storage alloy was confirmed to be MmNi _4.53 Al _0.25 Mn _0.50 Co _0.05 Fe _0.024 (ABx = 5.35) using an ICP emission spectrometer.

(Example 11)
The mass ratio of each element is Mm: 31.91%, Ni: 60.59%, Mn: 3.76%, Al: 2.77%, Co: 0.67%, Fe: 0.30% Thus, raw materials (pure metals were used as raw materials for Ni, Mn, Al, Co, and Fe) were weighed and mixed.
Mm is a misch metal which is a rare earth mixture of La and Ce, and the content ratio of each component in Mm is La: 62.7%, Ce: 26.4%, Nd: Materials adjusted to 8.2% and Pr: 2.7% were used as raw materials.
Thereafter, a hydrogen storage alloy was obtained in the same manner as in Example 4.

The obtained hydrogen storage alloy was confirmed to be MmNi _4.53 Al _0.45 Mn _0.30 Co _0.05 Fe _0.024 (ABx = 5.35) by an ICP emission spectrometer.

(Example 12)
The mass ratio of each element is Mm: 31.53%, Ni: 58.21%, Mn: 4.95%, Al: 2.13%, Co: 0.66%, Fe: 2.52%. Thus, raw materials (pure metals were used as raw materials for Ni, Mn, Al, Co, and Fe) were weighed and mixed.
Mm is a misch metal that is a rare earth mixture of La and Ce, and the content ratio of each component in Mm is La: 63.5%, Ce: 25.9%, Nd: Materials adjusted to 8.0% and Pr: 2.6% were used as raw materials.
Thereafter, a hydrogen storage alloy was obtained in the same manner as in Example 4.

The obtained hydrogen storage alloy was confirmed to be MmNi _4.40 Al _0.35 Mn _0.40 Co _0.05 Fe _0.200 (ABx = 5.40) using an ICP emission spectrometer.

(Example 13)
Raw materials (Ni, Mn) so that the mass ratio of each element is Mm: 31.45%, Ni: 52.78%, Mn: 8.65%, Al: 1.82%, Co: 5.30% Pure metal was used as a raw material for Al, Co, and Co.) and weighed and mixed.
Mm is a misch metal that is a rare earth mixture of La and Ce, and the content ratio of each component in Mm is La: 79.5%, Ce: 14.5%, Nd: What adjusted 4.5% and Pr: 1.5% was used as a raw material.
Thereafter, a hydrogen storage alloy was obtained in the same manner as in Example 4.

The obtained hydrogen storage alloy was confirmed to be MmNi _4.00 Al _0.30 Mn _0.70 Co _0.40 (ABx = 5.40) by ICP emission spectrometer.

(Example 14)
Raw materials (Ni, Mn) so that the mass ratio of each element is Mm: 33.60%, Ni: 56.37%, Mn: 3.96%, Al: 3.24%, Co: 2.83% Pure metal was used as a raw material for Al, Co, and Co.) and weighed and mixed.
Mm is a misch metal which is a rare earth mixture of La and Ce, and the content ratio of each component in Mm is La: 59.6%, Ce: 28.7%, Nd: What was adjusted so that it might become 8.8% and Pr: 2.9% was used as a raw material.
Thereafter, a hydrogen storage alloy was obtained in the same manner as in Example 4.

The obtained hydrogen storage alloy was confirmed to be MmNi _4.00 Al _0.50 Mn _0.30 Co _0.20 (ABx = 5.00) using an ICP emission spectrometer.

(Example 15)
Raw materials (Ni, Mn) so that the mass ratio of each element is Mm: 31.53%, Ni: 52.91%, Mn: 3.71%, Al: 1.22%, Co: 10.63% Pure metal was used as a raw material for Al, Co, and Co.) and weighed and mixed.
Mm is a misch metal that is a rare earth mixture of La and Ce, and the content ratio of each component in Mm is La: 63.5%, Ce: 25.9%, Nd: Materials adjusted to 8.0% and Pr: 2.6% were used as raw materials.
Thereafter, a hydrogen storage alloy was obtained in the same manner as in Example 4.

The obtained hydrogen storage alloy was confirmed to be MmNi _4.00 Al _0.20 Mn _0.30 Co _0.80 (ABx = 5.30) using an ICP emission spectrometer.

(Example 16)
Raw materials (Ni, Mn) so that the mass ratio of each element is Mm: 30.79%, Ni: 60.70%, Mn: 3.63%, Al: 1.19%, Fe: 3.69% Pure metal was used as a raw material for Al, Al, and Fe.) Was weighed and mixed.
Mm is a misch metal which is a rare earth mixture of La and Ce, and the content ratio of each component in Mm is La: 81.2%, Ce: 13.3%, Nd: The material adjusted to 4.1% and Pr: 1.4% was used as a raw material.
Thereafter, a hydrogen storage alloy was obtained in the same manner as in Example 4.

The obtained hydrogen storage alloy was confirmed to be MmNi _4.70 Al _0.20 Mn _0.20 Fe _0.30 (ABx = 5.50) using an ICP emission spectrometer.

(Discussion)
From this result, by performing a magnetic separation process that eliminates magnetic deposits using a magnet, preferably, after the hydrogen storage alloy raw material is melted to form a molten metal and cooled, the hydrogen storage alloy ingot obtained is pulverized. It has been found that impurities (iron and Cr) that cause a short circuit can be effectively removed without reducing the yield by performing a magnetic separation process that eliminates magnetic deposits using a magnet.
Further, when Comparative Example 1 and Comparative Example 2 are compared, it is recognized that the amount of magnetic deposits does not increase even when finely pulverized with an apparatus equipped with pulverizing means containing iron or an iron alloy.

  If magnetic separation is not performed, the amount of magnetic deposits does not drop below 0.15 ppm. Conversely, it can be estimated that a hydrogen storage alloy having a magnetic deposit amount of less than 0.15 ppm is performing magnetic separation.

Claims (10)

  A method for producing a hydrogen-absorbing alloy powder, comprising a magnetic separation step of eliminating magnetized matter using a magnet.   A hydrogen-absorbing alloy powder characterized by melting a hydrogen-absorbing alloy raw material to form a molten metal, pulverizing a hydrogen-absorbing alloy ingot obtained by cooling the raw material, and then performing a magnetic separation step of removing magnetic deposits using a magnet Manufacturing method.   The method for producing a hydrogen-absorbing alloy powder according to claim 1 or 2, wherein the magnetic separation step is performed using a magnet having a magnetic force of 100mT ± 10% to 600mT ± 10%. Force a 100mT ± 10% ~600mT ± 10% , the hydrogen storage according to any one of claims 1 to 3, characterized in that the magnetic separation process using a magnet surface area of 50cm ² ~3000cm ² Method for producing alloy powder.   The method for producing a hydrogen storage alloy powder according to any one of claims 1 to 4, wherein the magnetic storage step is performed after the hydrogen storage alloy ingot is pulverized to a particle size passing through a 500 µm sieve.   The method for producing a hydrogen-absorbing alloy powder according to any one of claims 1 to 5, wherein the crushing of the hydrogen-occlusion alloy ingot is performed using an apparatus equipped with a crushing means containing iron or an iron alloy. 7. The hydrogen storage process according to claim 1, wherein the magnetic separation step is performed such that the charging speed of the hydrogen storage alloy powder with respect to the surface area of the magnet is 300 ((g / min) / cm ² ) or less. Method for producing alloy powder.   The method for producing a hydrogen-absorbing alloy powder according to any one of claims 1 to 7, wherein the magnetic separation step is performed after the pulverization for a period of 20 seconds to 48 hours.   The method for producing a hydrogen storage alloy powder according to any one of claims 1 to 8, which is a method for producing a hydrogen storage alloy powder used as a negative electrode active material of a battery mounted on an electric vehicle or a hybrid vehicle.   The hydrogen storage alloy powder manufactured by the manufacturing method in any one of Claims 1-9.