JPH10172552A - Hydrogen storage alloy powder and its manufacture - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a hydrogen storage alloy powder excellent in electrochemical activity and in particular, having a high initial activity and to establish a method for manufacturing such alloy powder. SOLUTION: In hydrogen storage alloy powder, an oxide layer 2 prepared to an oxygen concentration effective to enhancement of the activity of hydrogen storage alloy is formed at the facial part of each hydrogen storage alloy particle 1. The mean oxygen concentration of the oxide layer 2 is 0.1-2.0wt.% of the total alloy particles. In manufacturing this hydrogen storage alloy powder, the fabricated alloy powder is subjected to a heating process at a temp. over 600 deg.C and below its melting point in an atmosphere with the oxygen partial pressure being over 0.01 Pa, and thereby the oxide layer 2 is formed at the facial part of each hydrogen storage alloy particle 1.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention
The present invention relates to a hydrogen storage alloy powder used as a material of an electrode (negative electrode) of a hydrogen battery, and a hydrogen storage alloy electrode manufactured using the powder.

[0002]

2. Description of the Related Art In general, a hydrogen-absorbing alloy electrode used as a negative electrode of a nickel-hydrogen battery is prepared by pulverizing a hydrogen-absorbing alloy lump having a predetermined component, adding a binder to the powder obtained thereby, and forming the electrode into a shape. It is produced by molding. Here, in order to homogenize the hydrogen storage alloy, the alloy powder is heated to 800 ° C. to 1 ° C. in a vacuum or in an inert gas.
A heat treatment at 000 ° C. is performed. Further, in order to achieve initial activation, a chemical conversion treatment in which charging and discharging are repeated at a high temperature of 50 ° C. or more is performed after the battery is sealed.

[0003]

SUMMARY OF THE INVENTION By the way, nickel
In the case of hydrogen batteries, AB
Type ₅ or AB ₂ type rare earth hydrogen storage alloys such as M
2. Description of the Related Art A negative electrode is manufactured from an m-Ni-based or La-containing Zr-Ni-based hydrogen storage alloy.

However, it is generally difficult to activate a rare-earth hydrogen storage alloy, and there has been a problem that a large number of times of charge and discharge are required for the chemical conversion treatment in the production of a nickel-hydrogen battery. Then, an object of the present invention is to provide a hydrogen storage alloy powder and a hydrogen storage alloy electrode which are excellent in electrochemical activity and particularly high in initial activation degree, and a method for producing them.

[0005]

The hydrogen-absorbing alloy powder according to the present invention comprises an oxide layer having a specified oxygen concentration effective for improving the activity of the hydrogen-absorbing alloy, on the surface layer of the hydrogen-absorbing alloy particles (1).
(2) is formed. Specifically, the average oxygen concentration of the oxide layer (2) is 0.1% of the whole hydrogen storage alloy particles.
When the content is at least 2.0% by weight, the activity of the hydrogen storage alloy is improved. Further, the hydrogen storage alloy electrode according to the present invention is a hydrogen storage alloy particle on which the oxide layer (2) is formed.
It is produced by filling the conductive substrate with the hydrogen storage alloy powder of (1).

Generally, in an alkaline secondary battery using a hydrogen storage alloy electrode as a negative electrode, a gas phase reaction and an electrochemical reaction proceed simultaneously on the alloy surface when the surface of the hydrogen storage alloy comes into contact with an alkaline electrolyte. I do. That is, in the relationship between the hydrogen pressure and the temperature, hydrogen is stored in the hydrogen storage alloy, or hydrogen is released from the hydrogen storage alloy (gas phase reaction). On the other hand, in the relationship between voltage and current, by application of voltage (charging), hydrogen generated by electrolysis of water is occluded in the hydrogen storage alloy, and by taking out current (discharging), hydrogen is oxidized to water ( Electrochemical reaction).

As described above, in an alkaline secondary battery, the gas phase reaction and the electrochemical reaction on the surface of the hydrogen storage alloy cause the absorption and release of hydrogen, and thus the charging and discharging, and thus the properties of the alloy surface Is important. In the alkaline secondary battery using the hydrogen storage alloy electrode of the present invention as a negative electrode, the oxide layer (2) formed on the surface layer of the hydrogen storage alloy particles (1) comes into contact with the alkaline electrolyte, Is transmitted through the oxide layer (2) and comes into contact with the surface of the hydrogen storage alloy particles (1). Here, the oxide layer (2) is porous and hydrogen can be freely absorbed and released through the oxide layer (2).

In general, an oxide layer (2) obtained by oxidizing a hydrogen storage alloy not only has a high affinity for hydrogen, but also has a high affinity for hydrogen.
Since the surface tension at the interface between the oxide layer (2) and the electrolyte is small, the effect of improving the wettability of the electrolyte on the surface of the hydrogen storage alloy particles (1) is exhibited. As a result, the contact area of the surface of the hydrogen storage alloy particles (1) with the electrolytic solution is substantially increased. Further, the oxide layer (2) has a high affinity not only for hydrogen but also for oxygen, and exhibits a high catalytic effect on these gases.

[0009] By the above-mentioned expansion of the contact surface property and the catalytic effect, the gas phase reaction and the electrochemical reaction in the alkaline secondary battery are promoted, and the activity of the hydrogen storage alloy is improved.

In the production of the hydrogen storage alloy powder according to the present invention, after the hydrogen storage alloy powder is produced, the hydrogen storage alloy powder is applied to the hydrogen storage alloy powder in an atmosphere having an oxygen partial pressure of 0.01 Pa or more.
Heat treatment is performed at a temperature of 600 ° C. or higher and not exceeding the melting point of the hydrogen storage alloy powder. In the production of the hydrogen storage alloy electrode according to the present invention, an alloy powder containing the hydrogen storage alloy particles (1) obtained by the above method is filled in a conductive substrate and formed into an electrode.

If the oxygen partial pressure is set lower than 0.01 Pa in the production of the hydrogen storage alloy powder according to the present invention, oxygen atoms do not sufficiently penetrate into the surface layer of the hydrogen storage alloy particles (1). An oxide layer (2) having the desired oxygen concentration cannot be obtained. Also, even if the ambient temperature is set lower than 600 ° C., the oxygen atoms do not sufficiently penetrate into the surface layer of the hydrogen storage alloy particles (1), and the oxide layer having the target oxygen concentration
(2) cannot be obtained. Therefore, by setting the oxygen partial pressure to 0.01 Pa or more, the atmosphere temperature to 600 ° C. or more, and the temperature not exceeding the melting point of the hydrogen storage alloy powder, the surface layer of the hydrogen storage alloy particles (1) has the hydrogen storage alloy particles. An oxide layer (2) whose effective oxygen concentration for improving the activity of the hydrogen storage alloy particles is defined to be 0.1% by weight or more and 2.0% by weight or less of the whole hydrogen storage alloy particles. Become.

[0012]

According to the hydrogen storage alloy powder and the method for producing the same according to the present invention, it is possible to obtain a hydrogen storage alloy powder and a hydrogen storage alloy electrode having excellent electrochemical activity and particularly high initial activation degree.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be specifically described below with reference to the drawings. The hydrogen storage alloy powder according to the present invention comprises hydrogen storage alloy particles (1) as shown in FIG.
The oxide layer (2) is formed on the surface layer portion of (1). Wherein the hydrogen storage alloy particles _{(1), ZrNi 1.2 V 0.2 Mn 0.6 MmNi} 3.2 CoMn 0.5 Al 0.3 is AB ₅ type rare earth hydrogen storage alloy is AB ₅ type rare earth hydrogen storage alloy
Or ZrLa _0.05 Ni _1.2 V _0.2 Mn _0.6 or the like, and the surface layer has an oxide layer (2) having a thickness of 100 to 1000 °.
Are formed. The oxide film formed naturally when the surface of the hydrogen storage alloy particles comes into contact with air or an electrolytic solution has a thickness of about 20 ° to 30 °, and is different from the oxide layer (2) in thickness. Different.

As shown in FIG. 2, the oxide layer (2) is capable of passing oxygen within the range of its thickness T and has an oxygen concentration of 1 at the center of the hydrogen storage alloy particles (1). In this case, the relative oxygen concentration at the interface with the hydrogen storage alloy particles (1) is about 2, and the relative oxygen concentration increases toward the surface within the thickness range of the oxide layer (2). The average oxygen concentration in the thickness range of the oxide layer (2) is set in the range of 0.1% by weight to 2.0% by weight of the whole hydrogen storage alloy particles.

FIG. 3 shows the structure of a nickel-hydrogen secondary battery using the above-mentioned hydrogen storage alloy powder as a negative electrode material. The positive electrode (11), the negative electrode (12), the separator (13), and the positive electrode lead ( 14), negative electrode lead (15), positive external terminal (16), negative electrode can
(17) A nickel-hydrogen secondary battery having a sealed structure is constituted by the sealing lid (18) and the like. The positive electrode (11) and the negative electrode (12) are housed in a negative electrode can (17) in a state of being spirally wound via a separator (13), and the positive electrode (11) is a positive electrode lead (1).
4) to the sealing lid (18), and the negative electrode (12) to the negative electrode lead (15).
Is connected to the negative electrode can (17). An insulating packing (20) is attached to the joint between the negative electrode can (17) and the sealing lid (18) to hermetically seal the battery. Positive external terminal (1
A coil spring (19) is provided between 6) and the sealing lid (18). The coil spring (19) is compressed when the internal pressure of the battery rises abnormally, and releases the gas inside the battery to the atmosphere.

In the manufacture of the nickel-hydrogen secondary battery, as shown in FIG. 4, first, an ingot of a hydrogen storage alloy having the above-mentioned composition is prepared, and then this is ingoted to a particle size of 5 μm.
Pulverized to ~ 500 μm to produce hydrogen storage alloy powder
(Step P1). Next, the hydrogen storage alloy powder was placed in an atmosphere having an oxygen partial pressure of 0.01 Pa to 12 Pa at 600 ° C. to 100 ° C.
A heat treatment is performed at a temperature of 0 ° C. for 4 to 8 hours (step P
2). As a result, the surface element of the hydrogen storage alloy particles (1) has an average elemental concentration of 0.1% by weight of the entire hydrogen storage alloy particles.
２．０2.0% by weight and the thickness is 100Å-1000Å
The oxide layer (2) is formed.

Thereafter, the nickel-hydrogen secondary battery shown in FIG. 3 is assembled (step P3). First, a paste is prepared by mixing the hydrogen storage alloy powder obtained through the step P2 with an aqueous solution of a binder such as PTFE, and the paste is applied to both surfaces of a base made of punching metal plated with nickel. After being applied and dried at room temperature, it is cut into predetermined dimensions to produce a hydrogen storage alloy electrode. Then, using the hydrogen storage alloy electrode as a negative electrode, a positive electrode-dominated nickel-hydrogen battery (for example, a battery capacity of 1000 mAh) having a structure shown in FIG. 3 is manufactured. Incidentally, a sintered nickel electrode can be used as the positive electrode, an alkali-resistant nonwoven fabric can be used as the separator, and a 30% by weight aqueous solution of potassium hydroxide can be used as the electrolytic solution.

In the above nickel-hydrogen secondary battery,
The oxide layer (2) of the hydrogen storage alloy particles (1) comes into contact with the electrolyte, and the electrolyte penetrates the oxide layer (2), and the hydrogen storage alloy particles
The surface of (1) will be wetted. Here, the oxide layer (2)
Has not only a high affinity for hydrogen but also an oxide layer (2)
Since the surface tension at the interface between the electrolyte and the electrolyte is small, the effect of improving the wettability of the electrolyte to the surface of the hydrogen storage alloy particles (1) is exhibited. With this, the hydrogen storage alloy particles
(1) The contact area of the surface with the electrolytic solution is substantially increased. Further, the oxide layer (2) has a high affinity not only for hydrogen but also for oxygen, and exhibits a high catalytic effect on these gases. As a result, as shown in FIG. 2, the gas phase reaction and the electrochemical reaction occurring in the battery are promoted, and the initial activation degree of the hydrogen storage alloy is improved.

FIGS. 5 to 7 show the results of experiments performed to confirm the effects of the present invention. In the experiment, the hydrogen storage alloy powder having each composition shown in FIGS. 5 to 7 was subjected to heat treatment under various heating conditions shown in FIGS. 5 to 7, and the obtained hydrogen storage alloy was obtained. A test electrode was prepared using the powder, and a test cell using the test electrode as a negative electrode was assembled. Then, charge and discharge were repeated using the test cell, and the discharge capacity was measured. The alloy oxygen concentration in each figure represents the weight ratio of oxygen contained in the oxide layer to the whole particles, that is, the average value (% by weight) of the oxygen concentration in the oxide layer. The initial capacity is the discharge capacity of the first cycle obtained during the repetition of charge and discharge, and the maximum capacity is the maximum discharge capacity obtained during the repetition of charge and discharge. or,
The degree of activation indicates the ratio (%) of the discharge capacity in the first cycle to the maximum capacity, that is, the initial degree of activation.

FIG. 5 shows three types of hydrogen storage alloys (composition: M
mNi _3.2 CoMn _0.5 Al _0.3 , ZrNi _1.2 V _0.2 Mn
_0.6 and ZrLa _0.05 Ni _1.2 V _0.2 Mn _0.6 ) comparing the properties of hydrogen storage alloys obtained by heat treatment at various oxygen partial pressures. Samples A-5, B-5, and C-5 without heat treatment in the figure were obtained by leaving the hydrogen storage alloy powder in air for a time sufficient for the surface to be oxidized. Has an oxide layer formed by natural oxidation. Each sample has a particle size of 50 μm, a heating temperature of 800 ° C., and a heating time of 4 hours.

In each sample, the alloy oxygen concentration increases in accordance with the oxygen partial pressure. For example, with respect to the composition MmNi _3.2 CoMn _0.5 Al _0.3 , a large degree of activation was obtained at an alloy oxygen concentration of 0.1 to 2.0% from the comparison between Samples A-1 to A-3 and Sample A-4. I have. However, when the alloy oxygen concentration exceeded 2.0%, the degree of activation tended to decrease. When the alloy oxygen concentration is less than 0.1%, the activation degree of sample A-4 heat-treated at an oxygen partial pressure of 0.005 Pa is 0.06%, and the activation of sample A-5 without heat treatment is performed. Degree is 0.05%,
There is no significant difference between the two, and the electrode characteristics are comparable.

With respect to the hydrogen storage alloy having the composition ZrNi _1.2 V _0.2 Mn _{0.6 and} the hydrogen storage alloy having the composition ZrLa _0.05 Ni _1.2 V _0.2 Mn _0.6 , Samples B-1 to B-3, Samples B-4 and B-5 are respectively provided. And sample C-1
From the comparison between C-3 and Samples C-4 and C-5, it can be seen that the same tendency as that of the hydrogen storage alloy having the composition MmNi _3.2 CoMn _0.5 Al _0.3 is apparent.

When the alloy oxygen concentration is less than 0.1%, the oxide layer does not exhibit a sufficient surface area enlargement effect and catalytic effect, and when the alloy oxygen concentration exceeds 2.0%, the oxide layer As a result, the insulating properties are increased, and the function as an electrode is impaired. Therefore, regardless of the composition of the hydrogen storage alloy, it can be said that setting the alloy oxygen concentration of the oxide layer in the range of 0.1% to 2.0% is preferable from the viewpoint of improving the activation.

FIG. 6A shows MmNi _3.2 CoMn _0.5 Al
_{For 0.3} alloy, the oxygen partial pressure during heat treatment is 0.002 Pa
Is a comparison of characteristics when the pressure is changed from to 12 Pa. Although the alloy oxygen concentration increases from 0.09% to 2% according to the oxygen partial pressure, the initial activation degree is within the range of 0.1% to 2% for the conventional hydrogen storage alloy. A value exceeding the degree of activation of the particles was obtained, and 0.23% to
Higher values are obtained in the range of 0.98%, and the maximum value is obtained at 0.98%. Therefore, MmNi _3.2 CoMn _0.5
For the _Al0.3 alloy, the alloy oxygen concentration of the oxide layer was set to 0.
It is set in the range of 1% to 2.0%, and further, 0.23% to 0.2%.
It can be said that it is preferable to set the range to 98%.

FIG. 6 (b) shows MmNi _3.2 CoMn _0.5 Al
_{For the 0.3} alloy, the characteristics are compared when the heating time is changed to three types of 2 hours, 8 hours, and 24 hours.
Alloy oxygen concentration from 0.26% to 2.14 depending on heating time
%, The initial activation degree is higher than the activation degree of the conventional hydrogen storage alloy particles in any case, and the maximum value is obtained particularly in the case of 8 hours. I have. Therefore, the heating time may be set to 2 hours to 24 hours, and it is particularly preferable to set the heating time to 8 hours.

FIG. 7A shows MmNi _3.2 CoMn _0.5
For Al _0.3 alloy, the particle size of the hydrogen storage alloy particles 50
This is a comparison of the characteristics when changing from 0 μm to 5 μm and changing the oxygen partial pressure during heating between 0.1 Pa and 0.005 Pa. Regardless of the particle size of the hydrogen storage alloy particles, a sufficient degree of activation is obtained when the oxygen partial pressure is 0.1 Pa. As is evident from the results, regardless of the particle size of the hydrogen storage alloy particles, by setting the oxygen partial pressure to an appropriate value (for example, 0.1 Pa), the activation is higher than that of the conventional hydrogen storage alloy particles. You can get a degree.

FIG. 7B shows MmNi _3.2 CoMn _0.5
For Al _0.3 alloy, the heating time is 400 ° C to 100 ° C.
This is a comparison of characteristics when the temperature is changed to 0 ° C.
When the heating temperature is 400 ° C, the alloy oxygen concentration is 0.09%
And less than 0.1%, the improvement of the degree of activation is slight, but when the heating temperature is in the range of 600 ° C to 1000 ° C,
The desired alloy oxygen concentration (0.1% to 2%) is obtained, and the degree of activation can be greatly improved.
When the heating temperature exceeds 1000 ° C. and approaches the melting point of the hydrogen storage alloy (about 1200 ° C.), the effect of the heat treatment for forming the oxide layer decreases.

From the above results, the average oxygen concentration of the oxide layer (2) of the hydrogen storage alloy particles (1) was adjusted to 0.1% or more and 2.0% or more.
The setting within the following range supports that the activity can be improved. The oxygen partial pressure at the time of forming the oxide layer (2) on the surface layer of the hydrogen storage alloy particles (1) was set at 0.0.
It is set to 1 Pa or more, and the heating temperature is 600 ° C. to 10 ° C.
By setting the temperature in the range of 00 ° C., an oxide layer (2) having the above-mentioned oxygen concentration is formed, which confirms that the activity can be improved.

The description of the above embodiment is for the purpose of describing the present invention, and should not be construed as limiting the invention described in the claims or reducing the scope thereof.
In addition, the configuration of each part of the present invention is not limited to the above-described embodiment, and it goes without saying that various modifications can be made within the technical scope described in the claims.

[Brief description of the drawings]

FIG. 1 is an enlarged cross-sectional view showing a state in which an oxide layer is formed on a surface portion of a hydrogen storage alloy particle in a hydrogen storage alloy powder according to the present invention.

FIG. 2 is a diagram illustrating a distribution of a relative oxygen concentration of an oxide layer.

FIG. 3 is a sectional view of a nickel-hydrogen secondary battery.

FIG. 4 is a process chart showing a method for manufacturing a hydrogen storage alloy electrode according to the present invention.

FIG. 5 is a table showing the results of experiments performed to demonstrate the effects of the present invention.

FIG. 6 is another chart of the above.

FIG. 7 is still another chart of the above.

[Explanation of symbols]

 (1) Hydrogen storage alloy particles (2) Oxide layer (11) Positive electrode (12) Negative electrode (13) Separator

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Shin Fujitani 2-5-5 Keihanhondori, Moriguchi-shi, Osaka Sanyo Electric Co., Ltd. (72) Inventor Ikuro Yonezu 2-chome Keihanhondori, Moriguchi-shi, Osaka No. 5 Sanyo Electric Co., Ltd. (72) Inventor Koji Nishio 2-5-5 Keihan Hondori, Moriguchi-shi, Osaka Sanyo Electric Co., Ltd.

Claims (6)

[Claims] 1. A hydrogen storage alloy powder in which an oxide layer (2) having a specified oxygen concentration effective for improving the activity of the hydrogen storage alloy is formed on the surface layer of the hydrogen storage alloy particles (1). 2. The hydrogen storage alloy according to claim 1, wherein the average concentration of oxygen contained in the oxide layer (2) is 0.1% by weight or more and 2.0% by weight or less of the whole hydrogen storage alloy particles. Powder. 3. After preparing the hydrogen storage alloy powder, the hydrogen storage alloy powder is heated in an atmosphere having an oxygen partial pressure of 0.01 Pa or higher at a temperature of 600 ° C. or higher and not exceeding the melting point of the hydrogen storage alloy powder. A method for producing a hydrogen-absorbing alloy powder, characterized by performing a treatment. 4. A hydrogen storage alloy electrode comprising a conductive substrate filled with an alloy powder containing hydrogen storage alloy particles (1),
A hydrogen storage alloy electrode, characterized in that an oxide layer (2) having an oxygen concentration specified to be effective for improving the activity of the hydrogen storage alloy is formed on the surface layer of the hydrogen storage alloy particles (1). 5. The hydrogen storage alloy according to claim 4, wherein the average concentration of oxygen contained in the oxide layer (2) is 0.1% by weight or more and 2.0% by weight or less of the whole hydrogen storage alloy particles. electrode. 6. A first step of preparing a hydrogen storage alloy powder, and applying a hydrogen storage alloy powder obtained at 600 ° C. or higher in an atmosphere having an oxygen partial pressure of 0.01 Pa or higher to a hydrogen storage alloy powder. A hydrogen storage alloy having a second step of performing a heat treatment at a temperature not exceeding the melting point of the storage alloy powder and a third step of filling the conductive base with the heat-treated hydrogen storage alloy powder and forming the same into an electrode shape Manufacturing method of electrode.