JP2699136B2 - Activation method of hydrogen storage alloy - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

Conventionally, nickel cadmium batteries have been widely used as rechargeable energy sources for various devices that require miniaturization. However, nickel cadmium batteries have been replaced with nickel cadmium batteries in view of environmental issues and high energy consumption. The use of nickel-metal hydride batteries using a hydrogen storage alloy for the negative electrode is expected. The present invention provides a negative electrode for such a nickel-metal hydride battery,
In addition, the present invention relates to a method for activating a hydrogen storage alloy used for a hydrogen tank, a heat pump, or the like.

[0002]

2. Description of the Related Art A hydrogen storage alloy requires a treatment step called activation prior to use. By performing this activation treatment step, a large number of cracks are generated on the surface of the hydrogen storage alloy, and the activated hydrogen storage alloy exhibits practical hydrogen storage characteristics. By the way, in the conventional ordinary activation method, a hydrogen storage alloy is put into a high-pressure vessel and the activation is performed.
After evacuating while maintaining the temperature at about 200 ° C. to about 200 ° C., a hydrogen pressure of a maximum of 50 atm is applied, and then returned to 1 atm. This high-pressure / normal-pressure hydrogen pressurizing / depressurizing cycle was activated by repeating as necessary.

[0003] In this conventional activation method, the higher the hydrogen pressure to be pressurized, the smaller the number of pressurization and decompression cycles, but it is difficult to apply a pressure of 50 atm or more from the viewpoint of leakage and safety. . Therefore, in order to activate the hydrogen storage alloy so as to have a sufficient hydrogen storage capacity, it is necessary to increase the number of repetitions of the hydrogen pressurization / decompression cycle, which requires a long time. In addition, in the case of an alloy that is inherently difficult to activate, even if the number of repetitions of the hydrogen pressurization / decompression cycle is increased, it may not be possible to achieve a sufficient hydrogen storage capacity.

Furthermore, in order to obtain a conventional hydrogen storage alloy powder, it is necessary to grind a cast hydrogen storage alloy ingot, and the ingot is liable to segregate during solidification, and therefore has excellent quality efficiently. It was difficult to produce a hydrogen storage alloy powder. On the other hand, the hydrogen storage alloy powder can be obtained by gas spraying. In this case, since the obtained individual powder corresponds to an ingot in casting, the segregation is extremely small in the whole hydrogen storage alloy powder and the hydrogen storage characteristics are stabilized. However, an extremely thin oxide film is formed on the surface of the hydrogen storage alloy powder obtained by gas atomization, and does not exhibit sufficient characteristics because the reaction with hydrogen is not promoted at a hydrogen pressure in a normal use range, For this reason, activation was more difficult than the powder obtained by grinding the ingot by casting.

[0005]

A first object is to provide a quicker and more reliable activation method than in the prior art.
A second object is to provide an activation treatment method which is particularly effective for atomizing powder which has been difficult to activate in the conventional method.

[0006]

Means for achieving the above object is to fill a hydrogen isolating alloy powder to be activated together with hydrogen gas in a plastic container, and to perform cold isostatic pressing (CI).
P) is an activation treatment method in which the pressure is increased to 100 atmospheres or more.
Enables use of gas atomized powder.

[0007]

According to the present invention, the hydrogen storage alloy powder is activated at a high pressure of 100 atm or more because the hydrogen storage alloy powder is activated at a high pressure of 100 atm or more. The powder can be activated, and the high-pressure activation can be performed with a cold isostatic press to safely apply high pressure without using high-pressure hydrogen piping, and at high pressure. Therefore, usually only one pressurizing and depressurizing step can be efficiently and quickly performed, and it can be effectively activated even for gas atomized powder which has a very thin oxide film on the surface and is difficult to activate by the conventional method. By using the gas atomizing method and the high-pressure activation method of the present method together, a hydrogen storage alloy powder can be efficiently and rapidly produced.

[0008] The present invention relates to a Mm-Ni-based, Fe-Ti-based, Mg-based, Zr-based
The present invention is applicable to many hydrogen storage alloys including a base hydrogen alloy.

[0009]

[Example] A hydrogen-absorbing alloy powder having a chemical composition of MmNi _3.2 CoMn _0.6 Al _0.2 as a misch metal-nickel (Mm-Ni) -based hydrogen absorbing alloy powder was dissolved in a reduced-pressure argon atmosphere.
Powder was produced by an argon gas atomizing method. FIG. 1 shows the particle size distribution of the produced powder. 10 g of the powder was sealed in a polyethylene bag together with 500 cc of pure hydrogen gas, and inserted into a cold isostatic press (CIP). As shown in FIG. After the pressure was increased to the seven types of maximum hydrostatic pressures, and maintained at the maximum hydrostatic pressure for one minute, the pressure was reduced, and after four minutes, the activation treatment was performed to return to the original pressure of 1 atm.

The results of PCT measurement of the powders activated under the respective conditions are summarized in Table 1. As shown in Table 1, when the cold isostatic pressing was performed at a maximum holding pressure of 100 atm or more, excellent activation characteristics were obtained despite the extremely short activation processing time of 15 minutes. You can see that. Here, H / M indicates a ratio of the number of hydrogen atoms stored in one atom of the hydrogen storage alloy.

[0011] PCT of powder by a conventional activation method
FIGS. 3 and 4 show the PCT curves of the 4000-atmosphere-treated powder that showed the best characteristics in the above experiment as compared with the curves.

[0012]

[Table 1]

[0013] The hydrogen storage alloy powder as sprayed before the activation treatment by the cold isostatic press at a hydrogen pressure of 4000 atm and the scanning electron beam of the hydrogen storage alloy powder after the activation treatment are performed. The micrographs are shown in FIG.
And (B). From FIG. 3B, the hydrogen-absorbing alloy powder that has been activated by a cold isostatic press at a hydrogen pressure of 4000 atm has fine cracks throughout the powder, indicating that the excellent activation treatment has been performed. I understand.

[0014]

As described above, the method for activating a hydrogen storage alloy according to the present invention is performed in a cold isostatic press at a hydrogen pressure of 100 atm or more, so that the pressurizing and depressurizing steps are usually performed in one step. It is efficient because it can be activated in a very short time and the high pressure is applied by a hydrostatic press, so there is no hydrogen pipe, so there is no danger of hydrogen leakage from the pipe and the high pressure can be applied very safely. In addition, hydrogen storage alloy powder by gas spraying has an oxide film formed on its surface and it is usually difficult to activate it. However, such hydrogen storage alloy powder can be activated efficiently and well. Can be processed.

[Brief description of the drawings]

FIG. 1 is a graph showing a particle size distribution of a hydrogen storage alloy powder produced by a gas atomization method.

FIG. 2 is a view showing an activation treatment step by a cold isostatic press according to the present invention.

FIG. 3 is a graph showing PCT characteristics of a hydrogen storage alloy powder activated by a conventional method.

FIG. 4 shows the maximum cold isostatic pressing pressure 4 according to the method of the present invention.
It is a graph which shows the PCT characteristic of the hydrogen storage alloy powder activated at the hydrogen pressure of 000 atm.

FIG. 5 (A) is a scanning electron micrograph of the hydrogen storage alloy powder by gas spraying before the activation treatment of the present invention. (B)
FIG. 3 is a scanning electron micrograph of a hydrogen storage alloy powder by gas spraying activated by a maximum cold isostatic press hydrogen pressure of 4000 atm by the activation treatment method of the present invention.

Claims (1)

(57) [Claims] 1. A hydrogen storage alloy is sealed together with hydrogen gas in a plastic container, and the container is cooled to 100% by a cold isostatic press.
A method for activating a hydrogen storage alloy, comprising pressurizing to a pressure of at least atmospheric pressure.