JP3235228B2 - Hydrogen storage alloy electrode and method for producing the same - 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 electrode for a nickel-metal hydride battery using a hydrogen storage alloy as a negative electrode active material, and a method for producing the same.

[0002]

2. Description of the Related Art Hydrogen storage alloy electrodes of nickel-metal hydride batteries are prepared by mixing a powdery hydrogen storage alloy with a solution in which a binder is dissolved to form a slurry. After filling in a net or the like, the obtained electrode is dried and formed by pressure molding.

[0003] Hydrogen storage alloy powder is divided into two types: "hydrogenation pulverization" in which powder is formed by using expansion and contraction caused by hydrogen absorption and release of hydrogen in a hydrogen storage alloy, and "mechanical pulverization" using a pulverizer such as a ball mill. Made by the method.

[0004] Since "hydrogenation" is performed in a hydrogen atmosphere, a highly active hydrogen storage alloy powder can be obtained. In order to produce an electrode while maintaining this highly active state, it is necessary to work in a hydrogen atmosphere or a high-purity inert gas atmosphere, and the work equipment or work process becomes large and complicated. I will.

[0005] In addition, since "mechanical pulverization" is performed in an inert gas atmosphere such as high-purity argon to maintain the activity of the hydrogen-absorbing alloy powder, the subsequent steps are also performed in a hydrogen atmosphere or a high-purity inert gas. You need to work in an atmosphere.

In order to solve this problem, for example, in Japanese Patent Application Laid-Open No. 4-79159, a hydrogen storage alloy powder is treated with an inert gas containing a trace amount of oxygen, and the surface of the hydrogen storage alloy powder is coated with a very thin oxide film. Covering makes it possible to work in the air.

[0007]

SUMMARY OF THE INVENTION However, Japanese Patent Application Laid-Open No.
Although the process proposed in No. 9159 enables work in air, the performance is reduced due to the formation of an oxide film, so that an activation process such as charging and discharging after assembling the battery becomes necessary. There is a problem. In addition, when the alloy powder subjected to this treatment is exposed in air for a long time, oxidation proceeds further,
There is a problem that the electrode performance is extremely reduced.

[0008] Therefore, the hydrogen-absorbing alloy powder subjected to the above-mentioned treatment is used as a binder by using a polymer material such as cellulosic or PVA (polyvinyl alcohol) as a binder and mixed with an aqueous solution in which the binder is dissolved to form a slurry. After coating or filling the electrode substrate, it is dried, and is compressed under pressure using a rolling mill to produce a hydrogen storage alloy electrode.

Due to the stress at the time of pressurization and compression, the hydrogen storage alloy powder itself is further finely crushed, or cracks are generated on the surface even if not crushed. This cracked portion or broken portion becomes an active new surface.

[0010] In order to confirm the effect of the activation treatment by pressurization and compression, LaNi5 powder of 200 mesh or less treated in an argon gas containing a trace amount of oxygen was stored in air for 20 days, and then produced by the above procedure. The activation characteristics of the hydrogen-absorbing alloy electrode thus prepared and the hydrogen-absorbing alloy electrode without pressure and compression treatment up to the drying treatment after filling were measured.

FIG. 2 shows the results. This activation characteristic refers to the hydrogen storage rate of a hydrogen storage alloy when a sample is placed in a pressure vessel, degassed with a vacuum pump for several minutes, and then hydrogen is introduced into the pressure vessel at a pressure of 3 MPa. The faster, the more active.

As apparent from FIG. 2, the hydrogen-absorbing alloy electrode pressed and compressed by the rolling mill absorbs hydrogen in a few minutes, while the hydrogen-absorbing alloy electrode without pressure compression does not absorb hydrogen even after 160 minutes. Do not occlude.

As described above, the new surface generated at the time of pressurizing and compression is active and has excellent performance as an electrode.

However, this new surface is also oxidized when stored in air, and its effect is lost if the storage period is long. Therefore, after pressurizing and compressing, it is necessary to immediately incorporate it into a battery case, or if it is left for a certain period of time, store it in an inert gas atmosphere.

[0015] It is an object of the present invention to prevent oxidation after pressurized compression, to enable the handling of hydrogen storage alloy electrodes in air,
Another object of the present invention is to obtain a high-performance hydrogen storage alloy electrode and a method for manufacturing the same without performing an activation treatment as a battery.

[0016]

Means of the present invention for achieving the above object will be described as follows.

According to the first aspect of the present invention, there is provided a hydrogen storage alloy electrode in which the surface of the hydrogen storage alloy electrode body is coated with a coating material.
A is, the covering material, the hydrogen storage alloy electrode body
It has ductility to pressurize and compress the surface, and alkali electrolysis
It is characterized by being soluble in liquid .

Production of the hydrogen storage alloy electrode according to claim 2
The method uses an aqueous solution of a hydrogen storage alloy powder dissolved in a binder.
To form a slurry and apply the slurry to the electrode substrate.
Or after filling to obtain a hydrogen storage alloy electrode body,
The surface of the storage alloy electrode body has ductility against pressure compression
And coated with a coating material that dissolves in an alkaline electrolyte.
And pressurizing and compressing the hydrogen storage alloy electrode .

[0019]

When the surface of the hydrogen-absorbing alloy electrode body is coated with a ductile coating material, the new surface generated during pressurization and compression does not come into direct contact with air, so that oxidation of the new surface can be prevented. . Therefore, the activity is maintained even if the operation is continued in the air. In addition, a high performance hydrogen storage alloy electrode can be obtained without performing an activation process as a battery.

Further, when the coating material of the hydrogen storage alloy electrode body is a coating material that dissolves in the alkaline electrolyte, the coating material is dissolved by the alkali as the electrolyte, and the hydrogen storage alloy of the hydrogen storage alloy electrode body becomes Since the active new surface is exposed to the electrolytic solution, it is possible to obtain a high performance hydrogen storage alloy electrode capable of expressing the original performance of the hydrogen storage alloy.

According to a second aspect of the present invention, the hydrogen storage alloy powder is
The slurry is mixed with an aqueous solution in which the
Apply or fill the electrode base to the hydrogen storage alloy electrode
After obtaining the body, the surface of the hydrogen storage alloy electrode body is
A material having ductility to shrinkage and soluble in an alkaline electrolyte
Covered with a covering material and pressurized and compressed the obtained hydrogen storage alloy electrode.
When manufacturing a hydrogen storage alloy electrode by
Since the new surface generated during shrinkage does not directly contact air,
Oxidation can be prevented, so that subsequent operations can be performed in air.
However, the activity of the new surface can be maintained and the workability is improved.
I can do better.

[0022]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an embodiment of a hydrogen storage alloy electrode and a method for producing the same according to the present invention will be described in detail.

In this embodiment, as the hydrogen storage alloy, MmNiMnCo (1: 4.5: 0.
2: 0.3) was used. This MmNiMnCo (1: 4.
5: 0.2: 0.3) was coarsely pulverized with a stamp mill, and then hydropulverized to a fine particle size of 200 mesh or less.

The conditions for hydrogrinding are as follows. At the time of storing hydrogen, the ambient temperature of the pressure vessel is set at 0 ° C. and the pressure of introducing hydrogen is set at 3 MPa. At the time of releasing hydrogen, the ambient temperature of the pressure vessel is set at 80 ° C. and the pressure is reduced by a vacuum pump.

After one cycle of storing and releasing hydrogen under the above conditions, an argon gas having a purity of 95% is introduced into the pressure vessel, and oxygen as an impurity contained in the argon gas is used to convert the hydrogen storage alloy powder. A small amount of oxide film was formed, enabling work in air.

The hydrogen-absorbing alloy powder subjected to the above treatment was
The mixture was mixed with a wt% aqueous solution of hydroxylmethylcellulose to form a slurry, filled in foamed nickel as an electrode substrate, and then dried at 60 ° C. to obtain a hydrogen storage alloy electrode body.

Next, an alkali-soluble PVA (Kuraray R-2130) was added to a 3 wt% KOH solution in an amount of 10 wt.
It melt | dissolved so that it might become wt%. This solution was applied to the hydrogen storage alloy electrode body and dried at 100 ° C. to obtain a hydrogen storage alloy electrode in which the surface of the hydrogen storage alloy electrode body was coated with a coating material soluble in alkali.

The hydrogen-absorbing alloy electrode was then rolled with a roll diameter of 300
It was pressed and compressed by a rolling mill of mm. Thus, the hydrogen storage alloy powder is further finely crushed in a state of being covered with the coating material, or a crack is generated on the surface even if not crushed, and a new active surface is formed in the hydrogen storage alloy powder. This new surface is not oxidized by the presence of the coating material, and its state is maintained.

FIG. 1 shows the change in the utilization of the hydrogen storage alloy electrode produced by the above-described method with respect to the storage period after pressing. As is apparent from the figure, the utilization rate of the hydrogen storage alloy electrode according to the present invention (the product of the present invention) was maintained in air for 60 days (1440 days).
Even after storage, there is almost no drop in utilization. On the other hand, the utilization of the hydrogen storage alloy electrode (conventional product) not coated with the coating material decreased with the elapse of the storage period.

The present invention can be applied regardless of the above hydrogen storage alloy as long as it can be mechanically pulverized.

The material to be coated may be any material as long as it has ductility that follows the displacement of the degree of deformation during compression and compression.

The means for removing the coating material not only dissolves in the electrolytic solution in the battery, but also performs the treatment before assembling in the battery case, and the effect is sufficiently exhibited if incorporated promptly into the battery case.

[0033]

As described above, according to the hydrogen storage alloy electrode and the method of manufacturing the same according to the present invention, the following effects can be obtained.

In the hydrogen storage alloy electrode according to the first aspect, since the surface of the hydrogen storage alloy electrode body is coated with a ductile coating material, a new surface generated at the time of pressurization and compression does not directly contact air. Oxidation of the new surface can be prevented.
Therefore, the activity can be maintained even if the operation is continued in the air. Further, a high-performance hydrogen storage alloy electrode can be obtained without performing an activation process as a battery.

Further, since the coating material of the hydrogen storage alloy electrode body is a coating material that dissolves in an alkaline electrolyte, the coating material is dissolved by the alkali as the electrolyte, and the hydrogen storage alloy of the hydrogen storage alloy electrode body becomes The active new surface is exposed to the electrolytic solution, so that it is possible to obtain a high performance hydrogen storage alloy electrode capable of expressing the original performance of the hydrogen storage alloy.

Production of the hydrogen storage alloy electrode according to claim 2
In the method, the hydrogen storage alloy powder is
Slurry by mixing with liquid and apply the slurry to electrode substrate
Or after filling to obtain a hydrogen storage alloy electrode body,
The surface of the storage alloy electrode body has ductility against pressure compression.
And coated with a coating material that dissolves in the alkaline electrolyte.
The compressed hydrogen storage alloy electrode is pressurized and compressed to
New surface created during pressurization and compression due to the production of storage alloy electrodes
Is no longer in direct contact with air, thus oxidizing the new surface.
Therefore, even if subsequent work is performed in air, the new
Improve workability by maintaining surface activity
Can be.

[Brief description of the drawings]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a comparison diagram showing a change in utilization of a hydrogen storage alloy electrode with a coating according to the present invention (product of the present invention) and a hydrogen storage alloy electrode without a coating (conventional product) with respect to a storage period after pressing.

FIG. 2 is a comparison diagram showing changes in the activation characteristics of a hydrogen storage alloy electrode that is compressed under pressure and a hydrogen storage alloy electrode that is not compressed under pressure.

Claims (2)

(57) [Claims] The surface of a hydrogen storage alloy electrode body is coated with a coating material.
A hydrogen storage alloy electrode coated with hydrogen, wherein the coating material pressurizes the surface of the hydrogen storage alloy electrode body.
Has ductility for compression and dissolves in alkaline electrolyte
Hydrogen storage alloy electrode which is a shall. 2. A hydrogen storage alloy powder obtained by dissolving a binder.
Mix with an aqueous solution to form a slurry, and use the slurry as an electrode substrate
After coating or filling to obtain a hydrogen storage alloy electrode body,
The surface of the hydrogen storage alloy electrode body is made ductile to compress
And coated with a coating material soluble in an alkaline electrolyte,
The obtained hydrogen storage alloy electrode is compressed and compressed.
Of manufacturing hydrogen storage alloy electrode .