JP3317099B2 - Hydrogen storage alloy powder for alkaline storage battery, method for producing the same, and method for producing hydrogen storage electrode - 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 and a method for producing the same, and a method for producing a hydrogen storage electrode using the hydrogen storage alloy powder.

[0002]

2. Description of the Related Art A hydrogen storage alloy is mainly used as a material for an electrode of a nickel-hydrogen storage battery, mainly for a system having nickel (hereinafter referred to as Ni) as a constituent element capable of electrochemically storing and releasing hydrogen. Used. Usually, a hydrogen storage alloy powder having a size of about 100 μm or less is used as an electrode material. As a manufacturing method for obtaining such a hydrogen storage alloy powder, a molten metal of a hydrogen storage alloy is prepared by a high-frequency melting furnace and cast. The method of mechanically pulverizing this alloy ingot after it is made into an alloy ingot (hereinafter referred to as a casting pulverization method) is the most frequently used method for producing a large amount of alloy powder having stable characteristics. I have. The hydrogen storage alloy powder kneaded with a binder, a thickener and the like is filled in a conductive three-dimensional porous body, or is coated on a two-dimensional porous body such as a punching metal to form a hydrogen storage electrode. The nickel-hydrogen storage battery is constructed by combining the electrode and the conventional negative electrode as a positive electrode.

[0003] The capacity of this nickel-hydrogen storage battery gradually decreases due to repetition of charge / discharge cycles. One of the causes is that the electrolyte solution and oxygen gas generated from the positive electrode at the time of overcharging oxidize and elute the surface of the hydrogen storage alloy powder, thereby lowering the charge acceptability of the negative electrode. In order to suppress the oxidation and elution, for example, a method of forming a battery by coating the surface of a hydrogen storage alloy powder with Ni, copper (hereinafter, referred to as Cu) or the like by plating or the like has been proposed.

[0004]

However, this method is expensive, it is difficult to control the coating conditions, and the coating amount effective for suppressing oxidation and elution is 10% by weight or more based on the alloy powder. It was poor in industrial practicality, for example, the energy density per hit was greatly reduced. Therefore, there has been no practical method for suppressing oxidation and elution of the hydrogen storage alloy powder and extending the life of the nickel-hydrogen storage battery.

The present invention provides a long-life nickel-hydrogen storage battery, a method for producing a hydrogen-absorbing alloy powder capable of suppressing oxidation and elution of an alloy powder, which is a main cause of capacity reduction, by a practical method, and hydrogen storage. An object of the present invention is to provide a method for manufacturing an electrode.

[0006]

According to the present invention, in order to achieve the above object, the surface layer of the hydrogen storage alloy is at least partially formed of at least one of scandium (hereinafter referred to as Sc ) oxide or hydroxide. It is a configuration covered with.

The coating amount of the oxide or hydroxide is preferably 0.1 to 1% by weight in terms of metal, and the average particle size of the alloy powder is preferably 10 to 75 μm.

As a method for coating the surface layer of the hydrogen storage alloy powder with the oxides or hydroxides of Sc and Y, any of the following three methods is preferable.

The first is a method in which at least one of Sc and Y is coated on an alloy surface in a metal state, and the alloy powder is immersed in an alkaline aqueous solution (hereinafter referred to as alkaline immersion). Here, a reduction-diffusion reaction is preferable as a method of coating Sc and Y. The temperature, specific gravity, and immersion time of the alkaline aqueous solution to be immersed were 45 to 90 ° C. and 1.1, respectively.
As described above, 10 minutes to 24 hours are preferable.

A second method is to thermally diffuse at least one of oxides and hydroxides of Sc and Y to the surface of the hydrogen storage alloy powder.

A third method is to prepare a hydrogen-absorbing alloy powder coated with at least one of Sc and Y, form an electrode using the alloy powder, and immerse in an alkali. The temperature, specific gravity, and immersion time of the alkaline aqueous solution to be immersed here are preferably 45 to 90 ° C, 1.1 or more, and 10 minutes to 24 hours, respectively.

[0012]

According to the present invention, the oxides or hydroxides of Sc and Y coated on the surface layer of the alloy powder act as a protective coating for the alloy powder, and the oxidation resistance and elution of the alloy are improved. Characteristics such as cycle life are improved.

The control of the amount of oxide or hydroxide of Sc and Y coated on the alloy powder has been proposed in the prior art.
It is easier and more practical than plating of i, Cu or the like. The oxide or hydroxide effective as a protective coating is 0.1 to 1% by weight of the alloy and is relatively inexpensive as compared with plating or the like.

[0014] The Y ₂ O ₃ as a method of coexisting with the hydrogen storage alloy powder, a method of impregnating the mixed or Y salt solution alloy paste. Compared with this, the present invention is considered to be more effective as a method for uniformly coating the required minimum amount of the oxide or hydroxide of Y on the surface of the alloy powder.

[0015]

Embodiments of the present invention will be described below.

Example 1 Mish metal (Mm: mixture of light rare earth elements), Ni, Al, Mn, and Co were mixed at a predetermined ratio, and MmNi _3.55 Al _{0.3 was} obtained by a high frequency melting method.
An Mn _0.4 Co _0.75 alloy lump was prepared and pulverized to obtain a hydrogen storage alloy powder having an average particle diameter of 30 μm. This alloy powder is placed in an aqueous potassium hydroxide solution (specific gravity: 1.25) at 80 ° C. for 1 hour.
After immersion for a time (ie, alkali immersion), washing and drying, 0.7% by weight of styrene-butadiene copolymerizable rubber (SBR) as a binder and carboxymethylcellulose (CMC) as a thickener are added to the alloy powder. 0.
1% by weight was added and kneaded with water to obtain an alloy paste.
Punching metal as a current collector using this alloy paste (iron plate with perforated nickel plate on its surface)
Then, drying and pressurization were performed to produce a hydrogen storage electrode (negative electrode). This negative electrode was combined with a known nickel positive electrode (corresponding to 1.5 Ah) via a separator to obtain a specific gravity of 1.2.
Using a potassium hydroxide aqueous solution of No. 5 as an electrolytic solution, a cylindrical sealed nickel-hydrogen storage battery with positive electrode capacity regulation was assembled. This is called battery A.

With respect to the hydrogen storage alloy powder (average particle size 30 μm) obtained in the same manner as the battery A, 0.5% by weight (Sc
This and Sc ₂ O ₃ in terms of a metal) were mixed Ca powder a sufficient amount capable of reducing the metal, and press-molded into a cylindrical shape. This molded product was heated to 900 ° C. in an Ar atmosphere, allowed to undergo a reduction diffusion reaction, gradually cooled to room temperature, crushed and repeatedly washed with water. The battery was immersed to form a similar battery. This is called battery B. In addition, a battery constituted by using Y ₂ O ₃ instead of Sc ₂ O ₃
And

Subsequently, 0.5% by weight (in terms of Y metal) of Y ₂ O ₃ was mixed with the hydrogen-absorbing alloy powder (average particle size 30 μm) obtained in the same manner as the battery A, and the mixture was formed into a cylindrical shape. Press molded. The temperature of the molded product was increased to 900 ° C. in an Ar atmosphere, then gradually cooled to room temperature, and the molded product was crushed to form a battery similar to Battery A. This is called battery D.

Further, 0.5% by weight (in terms of Y metal) of Y ₂ O ₃ and Ca powder were mixed with the hydrogen storage alloy powder (average particle diameter 30 μm) obtained in the same manner as in the battery A, and Press molded into a shape. This molded product is 900
After the temperature was raised to ℃, the mixture was gradually cooled to room temperature, and the molded product was crushed and washed repeatedly with water. Using this alloy powder, a hydrogen storage electrode similar to that of the battery A was first produced, and then a battery E constituted by subjecting the hydrogen storage electrode to alkali immersion under the same conditions as the battery A was designated as E.

Each of the batteries A to E was charged at 1.5 A for 1.5 hours, paused for 1 hour, and discharged at 1.5 A.
(End voltage: 1 V) Charge / discharge was repeated. FIG. 1 shows the cycle change (up to 500 cycles) of the discharge capacity of these batteries.

[0021] The capacity of the battery A significantly decreased every time charge and discharge were repeated. As a result of analyzing the battery A after 500 cycles, Al oxide was detected from the positive electrode, Mn oxide was detected from the separator, and La · Ce oxide was detected from the negative electrode. That is, the elution of the alloy progresses with the repetition of charge and discharge, and Al (AlO ₂ ⁻ ) with high solubility precipitates on the positive electrode and Mn with low solubility precipitates on the separator, and the electrolyte and oxygen generated from the positive electrode during overcharge It is considered that the oxidation of the alloy powder (particularly La and Ce) proceeded by the gas. As a result, the alteration of the alloy components reduces the amount of hydrogen storage, and excessive oxidation of the alloy surface inhibits the hydrogen storage reaction (a small amount of surface oxide is considered to work as a protective film), and the charge acceptability of the negative electrode Is considered to have decreased, and the capacity has decreased.

On the other hand, the batteries B to E had a longer life than the battery A. As a result of similarly analyzing the batteries B to E after 500 cycles, the positive electrode Al oxide and the separator M
Both the n oxide and the La / Ce oxide of the negative electrode had significantly lower detection amounts than the battery A. Also from the secondary electron image (SEM) and X-ray fluorescence analysis, the surface of the hydrogen storage alloy of the battery B to E, Sc ₂ O ₃ and Y ₂ O ₃ was confirmed to be partially covered. Accordingly, Sc ₂ O ₃ and Y ₂ O ₃ coated with the alloy powder act as protective coatings of the alloy powder, thereby inhibiting the corrosion reaction of the alloy and suppressing the elution of Al · Mn and the oxidation of La · Ce. . As described above, according to the present embodiment, the life of the nickel-metal hydride storage battery can be extended as compared with the related art.

In this embodiment, as a method of coating Sc or Y on the surface of the alloy powder, a reduction diffusion reaction (battery B,
C and E), the same effect was obtained by a method in which a phase rich in Sc or Y was revealed on the surface of the hydrogen storage alloy by a casting and pulverizing method or the like. In the batteries B to E, Y ₂
O ₃ , Y (OH) ₃ , Sc ₂ O ₃ , or Sc (OH) ₃
In any case, the same effect as in the present embodiment was obtained. Further, in the batteries B, C, and E, the same effect was obtained when the form of Y and Sc coated on the alloy surface under the alkali immersion condition was changed to hydroxide.

(Example 2) According to the conditions shown in Table 1, batteries F to BB produced by the same method as Battery C were charged at 1.5 A for 1.5 hours, paused for 1 hour, and discharged for 1. 5
Charge and discharge were repeated at A (final voltage 1 V). The change in the discharge capacity of these batteries (up to 500 cycles) is shown in FIGS.

[0025]

[Table 1]

The amount of Y to be coated was short in the case of 0.05% by weight (battery F), and was low from the beginning in the case of 1.5% by weight (battery H). The reason for this is that in the case of 0.05% by weight, the amount of Y oxide or hydroxide formed after immersion in alkali was insufficient, so that the effect as a protective coating was insufficient. It is considered that the conductivity of the electrode was lowered due to the excessive amount of Y oxide or hydroxide produced. From the above results, the amount of Y to be coated is preferably 0.1 to 1% by weight based on the alloy.

Regarding the average particle size of the alloy powder, 7 μm
(Battery J) has a short life and 100 μm (Battery N)
In the first case, the capacity was low from the beginning. The cause is 7μ
In the case of m, the oxidation / elution reaction is likely to proceed due to the large surface area of the alloy powder, and in the case of 100 μm, the electrode reaction is unlikely to proceed due to the small surface area of the alloy powder. As a result, the average particle size of the alloy powder is 10 to 7
5 μm is preferred.

With respect to the alkaline immersion conditions, the temperature of the KOH aqueous solution was 30 ° C. (battery O) and 95 ° C. (battery S).
Specific gravity 1.05 (battery T), immersion time 5 minutes (battery X)
And 30 hours (battery BB).
The cause was that the corrosion reaction of the alloy progressed due to insufficient formation reaction of the Y oxide or hydroxide on the alloy surface in the batteries O, T, and X, and the Y oxide or hydroxide in the batteries S, BB. It is considered that the elution of the alloy components occurred excessively in addition to the product formation reaction. As a result, the liquid temperature of the alkali immersion is preferably 45 to 90 ° C., the specific gravity is 1.1 or more, and the immersion time is preferably 10 minutes to 24 hours.

In this embodiment, the case where the hydrogen-absorbing alloy powder coated on the surface with Y is immersed in alkali is shown.
Even when the oxide or hydroxide of c and Y is thermally diffused to the surface of the hydrogen storage alloy powder, or when the electrode is molded using the hydrogen storage alloy powder coated on the surface of Sc or Y, and then alkali-immersed. The preferred ranges of the coating amount of the oxide or hydroxide, the average particle size of the alloy powder, and the conditions of alkali immersion were the same.

[0030]

As described above, according to the present invention, it is possible to provide a hydrogen storage alloy powder for a nickel-hydrogen storage battery having excellent characteristics such as cycle life. Further, it is possible to provide a manufacturing method capable of inexpensively manufacturing a hydrogen storage electrode having excellent characteristics such as cycle life.

[Brief description of the drawings]

FIG. 1 is a diagram showing a relationship between life characteristics of an embodiment of the present invention and a hydrogen storage electrode of a comparative example.

FIG. 2 is a diagram showing the relationship between the amount of Y to be coated and the life characteristics.

FIG. 3 is a diagram showing the relationship between the average particle size of the alloy powder and the life characteristics.

FIG. 4 Same alkaline immersion conditions (liquid temperature of KOH aqueous solution)
Diagram showing the relationship between the characteristics and the life characteristics

FIG. 5: Alkaline immersion conditions (specific gravity of KOH aqueous solution)
Diagram showing the relationship between the characteristics and the life characteristics

FIG. 6 is a diagram showing a relationship between alkaline immersion conditions (immersion time) and life characteristics.

──────────────────────────────────────────────────の Continued on the front page (72) Inventor Seiji Yamaguchi 1006 Kadoma Kadoma, Osaka Prefecture Inside Matsushita Electric Industrial Co., Ltd. In-company (72) Inventor Munehisa Ikoma 1006, Kazuma, Kadoma, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. (56) References JP-A-6-215765 (JP, A) JP-A 64-24001 (JP, A (58) Fields surveyed (Int. Cl. ⁷ , DB name) H01M 4/24-4/38

Claims (9)

(57) [Claims] 1. A S c hydrogen absorbing alloy powder surface layer by at least one oxide or hydroxide is at least partially covered in. 2. The coating amount of said oxide or hydroxide is 0.1 to 1% by weight in terms of metal based on the alloy.
The hydrogen storage alloy powder as described in the above. 3. An average particle size of 10 to 75 μm.
The hydrogen storage alloy powder as described in the above. 4. A method for producing a hydrogen storage alloy powder comprising the steps of: coating at least one of Sc and Y on the surface of a hydrogen storage alloy in a metallic state; and immersing the alloy powder in an alkaline aqueous solution. 5. The coating of Sc and Y on the alloy surface is reduced.
The method for producing a hydrogen storage alloy powder according to claim 4, wherein the method is carried out by a diffusion reaction. 6. The solution temperature of the alkaline aqueous solution to be immersed is 45-9.
The method for producing a hydrogen storage alloy powder according to claim 4, wherein the immersion time is 0 ° C, the specific gravity is 1.1 or more, and the immersion time is 10 minutes to 24 hours. 7. A method for producing a hydrogen storage alloy powder, wherein at least one of oxides and hydroxides of Sc and Y is thermally diffused to the surface of the hydrogen storage alloy powder. 8. A step of coating at least one of Sc and Y on the surface of the hydrogen storage alloy in a metal state, a step of molding an electrode using the alloy powder, and a step of immersing the electrode in an aqueous alkaline solution. A method for producing a hydrogen storage electrode comprising: 9. The liquid temperature of the alkaline aqueous solution to be immersed is 45-9.
9. The method for producing a hydrogen storage electrode according to claim 8, wherein the immersion time is 10 minutes to 24 hours.