JP3136961B2 - Method of treating hydrogen storage alloy for batteries - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for treating a hydrogen storage alloy for a battery containing Ni, and more particularly to a method for obtaining a hydrogen storage alloy for a Ni-hydrogen battery having high initial activity and low self-discharge. Regarding the processing method.

[0002]

2. Description of the Related Art At present, secondary batteries used for power supply of portable AV equipment and memory backup of computers are:
Ni-Cd batteries are the mainstream. However, from the viewpoints of pollution of Cd, resource limitation of Cd as a by-product of zinc refining, and development of secondary batteries with higher capacity, hydrogen storage alloys are replaced with hydrogen storage alloys as anode materials (strictly speaking, the activity of anodes). A secondary battery called a Ni-hydrogen battery was developed.

[0003] Ni-hydrogen batteries have the advantage that they have higher capacities than Ni-Cd batteries and Ni-Zn batteries and do not contain harmful elements in their electrodes. For this reason, Ni-hydrogen batteries are beginning to be used in portable AV equipment and computers, and are also being considered for use as secondary batteries for electric vehicles, which are increasingly used as pollution-free and energy-saving vehicles due to global environmental issues. Has already started mass production.

[0004] The major alloy systems that have been studied as a hydrogen-absorbing alloy for a Ni- MH batteries, LaNi ₅ type or MmNi ₅ system (Mm is misch metal is a rare earth metal mixture) A represented by
Intermetallic compound has a crystalline structure type ₅ B, ZnV _0.4 Ni _1.6
In which is an intermetallic compound takes a Laves phase structure of AB ₂ type represented. That is, each contains Ni as a main component. Although the AB ₅ type hydrogen storage alloy is more advanced for practical use, the AB ₂ type hydrogen storage alloy is also promising because it shows a high capacity.

However, when mass production of these hydrogen storage alloys for Ni-hydrogen batteries has started, some new problems have arisen. One is that the initial activation process (the process of increasing the discharge capacity of the battery to a predetermined steady-state value) after constructing the Ni-hydrogen battery takes a very long time, and productivity is significantly impaired. .

The initial activation process currently performed is a process of discharging after charging for a long time at a low current (charging for 15 to 20 hours and discharging for several hours) until a predetermined discharge capacity is obtained. It consists of repeating several times. For this reason, it was necessary to repeat charging / discharging in a factory for several days as an initial activation process from assembling the battery to shipping.

As a means for solving this problem, attempts have been made to improve the initial activity by controlling the grain boundaries of the hydrogen storage alloy. For example, JP-A-3-219036 proposes that boron is added to a hydrogen storage alloy to generate a boron-rich phase that is easy to be powdered, and that the initial activation efficiency is improved by increasing the specific surface area by powdering. I have. However, since this involves powdering of the alloy, the battery life (repetitive charge / discharge cycle life) of the Ni-hydrogen battery is significantly reduced. Therefore, it is difficult to achieve both the initial activity and the battery life by such means.

As another activation means, there is known a method of immersing a hydrogen storage alloy in an aqueous solution containing an acid, an alkali or a salt before producing an electrode. For example, JP
Japanese Patent Application Laid-Open No. 3-328252 discloses a dip treatment using an aqueous solution of hypophosphite.
An immersion treatment using arsenate, chromate, hypophosphite, tetrahydroborate or the like has been proposed. However, in such an immersion treatment using an aqueous solution of a salt, the chemical components used for the treatment remain on the powder surface, and the electrochemical characteristics (positive electrode characteristics) on the positive electrode side deteriorate, and the battery capacity decreases early. There is.

On the other hand, Japanese Patent Application Laid-Open Nos.
JP-A-223827 discloses an immersion treatment using an acid aqueous solution for the purpose of removing oxides on an alloy surface, and JP-A-5-195007 discloses coating an alloy surface with a hydroxide layer having a large specific surface area. For this purpose, Japanese Patent Application Laid-Open Nos. 3-152868 and 4-98760 propose an immersion treatment using an aqueous alkali solution first, followed by an aqueous acid solution and then an aqueous alkali solution.

[0010]

When the hydrogen storage alloy powder treated with the aqueous acid solution and / or the aqueous alkali solution as described above is used for the negative electrode of a Ni-hydrogen battery, the initial activity is certainly improved, but the self-discharge is improved. It has been found that the characteristics are adversely affected, and there is a problem that the capacity decreases when stored for a long time after charging. This problem significantly lowers the practicality of the Ni-hydrogen battery because it is not uncommon for the Ni-Hydrogen battery to be left unused after being charged after use.

An object of the present invention is to provide a method for treating a hydrogen-absorbing alloy capable of producing a battery having a high initial activity when used in a Ni-hydrogen battery and having a small self-discharge and excellent long-term storage properties. It is to be.

[0012]

Means for Solving the Problems The present invention relates to a battery for a battery, characterized by immersing a hydrogen storage alloy containing Ni in a non-oxidizing acid aqueous solution having a dissolved oxygen content of 1 mg / L or less. This is a method for treating a hydrogen storage alloy.

The present inventors have developed a hydrogen storage alloy containing Ni.
When a hydrogen storage alloy (hereinafter simply referred to as hydrogen storage alloy) is used for the negative electrode of a Ni-hydrogen battery, the initial activity of the battery depends on the amount of oxide on the surface of the alloy powder, and the amount of self-discharge depends on the amount of hydroxide on the surface of the alloy powder. Make sure you do. That is, the smaller the oxide, the higher the initial activity, and the smaller the hydroxide, the smaller the amount of self-discharge.

Of these, oxides are formed by the reaction of the metal on the alloy surface with oxygen in the atmosphere or oxygen in the processing atmosphere in each of the melting, heat treatment, and pulverization steps performed in the production of the hydrogen storage alloy powder. Things. Oxides have poor conductivity and therefore reduce the initial activity of the battery. However, as is known in the art, oxides can be removed with an aqueous acid solution, so that treatment with an aqueous acid solution significantly improves initial activity.

On the other hand, hydroxides are formed on the surface of the hydrogen storage alloy when the hydrogen storage alloy is treated with an aqueous alkali solution.
₂ generates a lot. Although it was thought that hydroxide was not generated by the treatment with the acid aqueous solution, the present inventors have found that Ni (OH) ₂ is also present on the surface of the acid-treated hydrogen storage alloy.

Ni (OH) ₂ is a substance used for the positive electrode of a Ni-hydrogen battery, and when this adheres to a hydrogen storage alloy, which is a negative electrode active material, a self-discharge reaction occurs at that part (the electricity stored in the negative electrode becomes (A reaction that is consumed by a chemical reaction other than the discharge reaction). For this reason, when the amount of hydroxide is large, self-discharge occurs during long-term storage after charging, the amount of charged electricity decreases, and the discharge capacity of the battery decreases.

From the above, to achieve the object of the present invention,
It has been found that it is necessary to treat the hydrogen storage alloy with an aqueous acid solution to remove oxides on the surface of the alloy and to suppress the formation of hydroxides at that time. This is because the removal of oxides by acid treatment improves the initial activity of the battery, and in this case, if the amount of hydroxide generated is small, it is possible to prevent a decrease in long-term storage properties of the battery due to self-discharge. The treatment with an alkaline aqueous solution generates a large amount of hydroxide on the alloy surface,
This is disadvantageous for long-term storage of a hydrogen battery.

Based on this finding, the present inventors have investigated the reason why hydroxides, particularly Ni (OH) _2, are formed on the alloy surface by the treatment with an aqueous acid solution, and have found the following points. That is, when the hydrogen storage alloy is immersed in an aqueous acid solution, as a result of anodic reaction, the component metals on the alloy surface dissolve together with the oxides, thereby generating metal ions in the liquid, and the metal ions eluted in the liquid are close to the alloy surface. Are present in higher concentrations.
On the other hand, as a cathode reaction that is a counterpart to this anode reaction, a reduction reaction of oxygen dissolved in the liquid occurs near the alloy surface, thereby generating hydroxyl (OH) ions, which are also close to the alloy surface Are present in higher concentrations. Therefore,
In the vicinity of the alloy, Ni ions combine with hydroxide ions and precipitate on the surface of the alloy as hydroxide [Ni (OH) ₂ ]. That is, the larger the amount of dissolved oxygen in the liquid, the more
Ni (OH) ₂ tends to precipitate on the alloy surface.

Therefore, in order to reduce the self-discharge of a Ni-hydrogen battery and improve its long-term storage properties, the amount of dissolved oxygen in the acid aqueous solution used for the acid treatment is reduced to 1 mg / L or less to reduce the Ni (O
H) It was found that the formation of ₂ should be prevented, and the present invention described above was completed.

When the amount of dissolved oxygen in the aqueous acid solution is large,
The metal that appeared on the alloy surface due to the acid treatment is directly bonded to the dissolved oxygen in the liquid, and the metal oxide is regenerated on the alloy surface, reducing the oxide removal effect of the acid treatment and reducing the initial activity. There is also the problem of adverse effects. Therefore, when an acid aqueous solution having a small amount of dissolved oxygen is used, the initial activity can be further improved.

[0021]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in more detail. Hydrogen storage alloy to be in a processed method of the present invention, AB ₅ type used for Ni- hydrogen secondary battery or A
B is a ₂ type alloys, in particular those containing as a constituent element Ni. The effect of the present invention is not affected by the alloy composition,
If containing Ni in any of AB ₅ type and AB ₂ type can be carried out using a treatment method of the present invention.

Examples of AB ₅ type alloys are LaNi _x or MmNi _x
(x is 4.7 to 5.2) as the basic composition, and in some cases, a part of Ni
Co, Mn, Al, Fe, Cr, Cu, V, Be, Zr, Ti, Mo, etc.
It has been replaced with one or more elements. LaNi
_x is expensive and has a short life, so practically Mm
Ni _x is preferred.

Examples of AB type ₂ alloys include ZrNi _y (y is 1.9 to 2.
25) as the basic composition, and in some cases, Ni, V, Mn, C
It is substituted with one or more elements such as r, Co, Fe, Al, Mo, Cu, Be and the like. Zr _1.0 V as a specific example
_0.4 Ni _1.6 , Zr _1.0 Mn _0.4 Cr _0.2 Ni _1.2 , Zr _1.0 Ni _1.2 Mn _0.6 V
_0.2 Co _0.1 , Zr _1.0 Ni _1.2 Mn _0.6 V _0.2 Fe _0.1 , Zr _1.0 V _0.4 Ni _1.6
and so on. Note that these are merely examples, and those having other compositions can also be used.

As a method for producing the hydrogen storage alloy, in addition to the usual ingot method (a method in which an ingot obtained by casting a molten alloy is crushed), rapid solidification such as a rotating electrode method, a roll quenching method, and an atomizing method is used. Various methods used are known. The method of the present invention can be applied to a hydrogen storage alloy produced by any of these methods. Since the hydrogen storage alloy is used in the form of a powder in the production of the electrode, it is generally necessary to pulverize the hydrogen storage alloy produced by a method other than the atomization method in which the powder is directly obtained. An oxide is generated on the surface of the alloy powder during this pulverization process,
Since the initial activity is reduced, the treatment method of the present invention is desirably applied to a powdery hydrogen storage alloy pulverized to the final particle size. In addition, it is preferable that the hydrogen storage alloy produced by the rapid solidification method be subjected to a heat treatment in a non-oxidizing atmosphere before the treatment of the present invention in order to remove the strain generated during the rapid cooling.

In the treatment of the hydrogen storage alloy according to the present invention, an aqueous solution of a non-oxidizing acid is used. Oxides generated on the alloy surface in the manufacturing and grinding process of the hydrogen storage alloy is mainly (in the case of AB ₅ type) Ni oxide and a rare earth oxide or Zr oxide
(In the case of AB ₂ type). Non-oxidizing acids are effective in removing these oxides from the alloy surface, thereby significantly improving the initial activity of the cell.

Examples of non-oxidizing acids suitable for use in the present invention are hydrochloric acid, hydrofluoric acid, and mixed acids of hydrochloric acid and hydrofluoric acid. If non-oxidizing, other acids can be used alone or in admixture with hydrochloric acid and / or hydrofluoric acid. If an oxidizing acid such as nitric acid or sulfuric acid is used, an oxidizing power easily forms a new oxide film,
The initial activity of the alloy cannot be improved sufficiently.

The aqueous acid solution used in the treatment of the present invention is a stock solution of a non-oxidizing acid having a concentration of a commercially available special grade or a primary grade or a similar concentration (concentration is generally 35 to 36% with hydrochloric acid and hydrofluoric acid). 44-46%) with water (preferably deionized water). The acid concentration in the acid solution is calculated as the content (% by weight) of this stock solution with hydrochloric acid.
The range is preferably 0.1 to 15%, 0.01 to 10% for hydrofluoric acid, and 0.01 to 15% for a mixed acid of hydrochloric acid and hydrofluoric acid. When the acid concentration is lower than the lower limit, the reactivity between the oxide and the aqueous acid solution is low, and it is difficult to sufficiently improve the initial activity even by performing the immersion treatment. On the other hand, when the acid concentration exceeds the upper limit, the dissolution reaction occurs rapidly, not only removing the oxide film on the surface of the alloy, but also the dissolution of the alloy itself progresses, and the loss increases.

Pure water in the air at room temperature (25 ° C.)
mg / L oxygen is dissolved. Therefore, the aqueous acid solution prepared by the above method contains this amount of dissolved oxygen as it is. As a result, metal hydroxides, particularly Ni (OH) _2, are generated during the acid treatment and the self-discharge characteristics are deteriorated during the acid treatment, as described above. The effect of improving activity is also reduced. Therefore, in the present invention, this problem is solved by using an acid aqueous solution in which the amount of dissolved oxygen is reduced to 1 mg / L or less. That is, when the amount of dissolved oxygen in the aqueous acid solution exceeds 1 mg / L, the above problem becomes significant. Preferably, the amount of dissolved oxygen in the aqueous acid solution is set to 0.5 mg / L or less.

As is well known to those skilled in the art, the amount of dissolved oxygen in the aqueous acid solution can be reduced by degassing by blowing gas into the aqueous solution. Inert gas (He, Ne, Ar, Kr, Xe gas) is generally used as the blowing gas used for degassing the liquid. In the present invention, an acid aqueous solution, particularly an aqueous solution of hydrohalic acid is degassed. From the fact that halogen gas
(F ₂ gas and / or Cl ₂ gas) can be used alone or mixed with an inert gas as the blowing gas. Thereby, it can be suppressed that the acid component volatilizes during the degassing and the concentration of the acid aqueous solution decreases. Degassing conditions
(Blowing amount of gas, blowing time, etc.) are selected so that the dissolved oxygen amount in the liquid becomes a desired value of 1 mg / L or less.

If the degassed acid aqueous solution is allowed to stand, oxygen in the air is absorbed and the amount of dissolved oxygen increases, so the degassed acid aqueous solution is used for immersion treatment of the hydrogen storage alloy as soon as possible. Is preferred. When storing the degassed liquid, an increase in dissolved oxygen can be prevented by storing the liquid in an inert gas atmosphere. In short, it is sufficient that the dissolved oxygen amount of the aqueous acid solution immediately before immersion is 1 mg / L or less.

Instead of applying degassing to the aqueous acid solution, water used for preparing the aqueous acid solution (dilution of the undiluted acid solution) may be degassed. This can avoid problems such as volatilization of acid during degassing. Since the amount of water used for dilution is larger than the stock solution of acid, the dissolved oxygen content of the water used for dilution should be reduced to a level sufficiently lower than 1 mg / L (eg, 0.5 mg / L or less). An aqueous acid solution having a dissolved oxygen content of 1 mg / L or less can be obtained. Note that the treatment with the ion exchange resin to obtain deionized water does not reduce the amount of dissolved oxygen in the water.

The dissolved oxygen content of the aqueous acid solution or water is
This can also be reduced by heating or boiling. That is, as the temperature increases, the solubility of oxygen decreases, so that the oxygen is expelled and the dissolved oxygen decreases. Cooling after heating is preferably performed in an inert gas atmosphere to suppress dissolution of oxygen.

The hydrogen storage alloy is immersed in the aqueous acid solution in which the amount of dissolved oxygen is reduced to 1 mg / L or less.
Other conditions of the immersion treatment are not particularly limited, but the temperature is
A range of 10 to 80 ° C is desirable. When the temperature is lower than 10 ° C., the oxide removal reaction does not sufficiently proceed, and the treatment takes too much time. On the other hand, if the temperature is higher than 80 ° C., the alloy will be melted inside.

Although the immersion time in the aqueous acid solution varies depending on the temperature and the type and concentration of the aqueous acid solution, it is generally several minutes to several hours, and in most cases, one hour or less is sufficient. Hydrofluoric acid requires less processing time than hydrochloric acid.
Further, it is effective to achieve the object of the present invention to continue the deaeration treatment while blowing the above-mentioned deaeration gas into the liquid or the liquid during the immersion treatment.

After immersion treatment in an acid aqueous solution, the hydrogen absorbing alloy is sufficiently washed with water (by repeating washing with water if necessary) in accordance with a conventional method to remove the attached acid, and is preferably dried in a vacuum or an inert gas. In this water washing, the amount of dissolved oxygen in the water used for the first washing is reduced by degassing or heating.
(Preferably 1 mg / L or less). This is because the Ni ions attached to the surface of the alloy may melt until the first water washing, and the concentration of Ni ions near the surface may increase. However, if the amount of water used for washing is very large (eg, 5 times or more in weight) with respect to the amount of alloy, the possibility is small. Need not be reduced.

An electrode is produced from the thus treated hydrogen storage alloy by a method well known to those skilled in the art and used as a negative electrode of a Ni-hydrogen battery. The electrode is made of a hydrogen storage alloy powder with a suitable binder
(A resin such as polyvinyl alcohol) and water (or another liquid) to form a paste, fill a porous nickel body, dry, and then press-mold into a desired electrode shape.

[0037]

The following examples illustrate the structure and effect of the present invention. In the examples,% is% by weight unless otherwise specified.
It is. Hydrogen-absorbing alloy powder used in the examples was a AB ₅ type or AB ₂ type alloy having a composition shown in Table 1. The raw materials used for casting these alloys were 99.9% pure flake Ni, 99.8% pure electrolytic Co, and 99.9% pure shot.
Al, plate-like Mn with 99.8% purity, Ni-56.9% V mother alloy, purity 9
Sponge-like Zr of 9.5% or more, misch metal (Mm) with rare earth metal purity of 99.8% or more (La = 28%, Ce = 48%, Nd = 18
%, Pr = 6%).

[0038]

[Table 1]

These raw materials are mixed so as to have a predetermined composition, and then a 75 kg / ch Ar gas atomizing method (cooling rate from molten liquid = 1) is performed using an alloy melt produced by high-frequency induction heating in vacuum. × 10 ³ -1 × 10 ⁴ ° C / sec) or 100
kg / ch ingot method (cooling rate from melt = 1.0 ℃
/ sec) to produce a hydrogen storage alloy powder. The hydrogen storage alloy obtained by the ingot method is then mechanically pulverized in a stainless steel ball mill in an Ar atmosphere to have an average particle size of 40 μm.
m in powder form. The hydrogen storage alloy powder (average particle size 40 μm) obtained by the atomization method is purified to remove cooling strain.
Heat treatment was performed at 900 ° C. for 10 hours in a 99.99% Ar atmosphere.

500 g of the hydrogen storage alloy powder was immersed for 10 minutes in 3 kg of an aqueous acid solution in which the amount of dissolved oxygen was reduced. The acid solution used was prepared by diluting a stock solution of reagent grade hydrochloric acid (HCl, 35% concentration) and / or hydrofluoric acid (HF, 46% concentration) with deionized water (= ion exchanged water). did. At this time, deionized water for dilution is
Degassing was performed by blowing gas. The degassing treatment was performed by blowing Ar gas at a flow rate of 1.5 L / min per liter of an aqueous solution into deionized water maintained at a predetermined immersion temperature shown in Table 2, and using the degassed deionized water. Immediately, the acid aqueous solution was diluted and the hydrogen storage alloy was immersed in the obtained acid aqueous solution. During the immersion process,
Ar gas was circulated over the liquid to prevent the amount of dissolved oxygen from increasing after the immersion treatment.

Table 2 shows the composition of the hydrogen storage alloy (symbol in Table 1), its production method, the dissolved oxygen amount at the start of the immersion treatment of the acid aqueous solution used, the immersion treatment temperature, the hydrochloric acid and the fluoride in the acid aqueous solution. Shows the concentration of the stock solution of hydroacid. The amount of dissolved oxygen in the acid aqueous solution was adjusted by changing the blowing time of Ar gas into the deionized water for dilution, and the amount of dissolved oxygen in the solution was measured using a commercially available dissolved oxygen meter (diaphragm galvanic cell type measurement). Device).

Of the comparative examples shown in Table 2, Test Nos. 20 to
21 is a case where the blowing time of Ar gas is short, and the dissolved oxygen amount of the acid aqueous solution exceeds 1 mg / L, and the remaining cases are those in which the undiluted acid solution was diluted with deionized water which was not degassed. It is.
In the comparative example, except for these points, the immersion treatment of the hydrogen storage alloy was performed in the same manner as described above.

The hydrogen-absorbing alloy powder immersed as described above was washed with a large amount of water, 10 times the weight thereof, and then dried in vacuum. When this alloy powder is
classify to a size of at least μm, and use a binder (polyvinyl alcohol 5%
Aqueous solution) was added and kneaded. The resulting alloy powder paste was filled into a nickel foamed metal porous body (product of Sumitomo Electric Industries, Ltd. CELMET), dried pressurized with a pressure of 1.5 ton / cm ² after, is supported alloy powder of Ni porous body The negative electrode of the battery was produced. At this time, the supported amount of the hydrogen storage alloy powder is
It was 12 g.

A commercially available nominally 2000 mA Ni electrode was used for the positive electrode, and a nylon nonwoven fabric impregnated with 6N-KOH alkaline electrolyte was sandwiched between the positive and negative electrodes as a separator.
A 2000 mA Ni-hydrogen battery was fabricated. This battery was sealed in a C2 case to obtain a battery to be tested. This battery is a positive electrode regulation type battery having a large negative electrode capacity.

The results of the following battery performance studies using this battery are also shown in Table 2. Initial activity The prepared positive-electrode capacity regulated Ni-hydrogen battery was charged at 25 mA at 80 mA / g (current for 1 g of the hydrogen storage alloy supported on the negative electrode) for 3 hours, and then the terminal voltage was 160 mA / g.
Discharge to 0.9 V, repeat charge / discharge 10 times,
Measure the first discharge capacity and the tenth discharge capacity, and calculate the ratio.
The initial activity was determined by (first discharge capacity / 10th discharge capacity × 100%). If the initial activity is 95% or more, it can be evaluated as passing.

Self-discharge characteristics (capacity after storage) Using the prepared Ni-hydrogen battery, the battery was repeatedly charged and discharged 10 times under the same conditions as described above, then charged at 80 mA / g for 3 hours, and then charged at 50 ° C. After 10 days at 160 mA / g, measure the capacity when discharging to a terminal voltage of 0.9 V, and compare it with the discharging capacity after performing the above repeated charging and discharging 10 times (discharging capacity after storage / The discharge capacity after storage was determined by the tenth discharge capacity × 100%). If this value is 85% or more, it can be evaluated as passing.

[0047]

[Table 2]

As can be seen from Table 2, when the hydrogen storage alloy is immersed in an acid aqueous solution having a dissolved oxygen content of 1 mg / L or less according to the present invention, the initial activity is 95% or more, and the capacity after storage is not less than 95%. At 85% or more, Ni-Hydrogen batteries which all passed the acceptance criteria could be obtained. In contrast, in Comparative Examples (Nos. 22 to 25) in which the hydrogen storage alloy was immersed in an acid aqueous solution prepared using deionized water that had not been degassed, the dissolved oxygen content of the acid aqueous solution was 7 mg / L. Due to the high activity, the initial activity of the Ni-hydrogen battery was slightly low at around 90%, and the capacity after storage was extremely low, particularly in the 70% range. In addition, the deaeration of deionized water for dilution was insufficient, and the dissolved oxygen content of the acid aqueous solution was 3 mg / L.
In Comparative Examples (Nos. 20 to 21), the initial activity and the capacity after storage were not sufficiently improved.

[0049]

According to the present invention, a hydrogen storage alloy used for a negative electrode of a Ni-hydrogen battery is immersed in a non-oxidizing acid aqueous solution with a reduced amount of dissolved oxygen, so that the initial activity is high and It is possible to manufacture a Ni-hydrogen battery with a low self-discharge and excellent long-term storage properties.

────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Yukiteru Takeshita 4-5-33 Kitahama, Chuo-ku, Osaka City Sumitomo Metal Industries, Ltd. (56) References JP-A 7-153460 (JP, A) (58) Fields surveyed (Int.Cl. ⁷ , DB name) H01M 4/24-4/26 H01M 4/38

Claims (1)

(57) [Claims] 1. A method for treating a hydrogen storage alloy for a battery, comprising immersing a hydrogen storage alloy containing Ni in a non-oxidizing acid aqueous solution having a dissolved oxygen content of 1 mg / L or less.