JPH05247568A - Hydrogen storage alloy electrode and battery using them - Google Patents

Abstract

PURPOSE:To develop a hydrogen strage alloy small in hydrogen equilibrium pressure at ordinary temp. and having excellent characteristics by adding Ni, rare earth metals and specified elements to at least two kinds of metals among Ti, Zr and V. CONSTITUTION:The hydrogen storage alloy of Ti-Zr-Ni base, Ti-V-Ni base, Ti-Zr-V-Ni base or the like obtd. by adding Ni to at least >= two kinds of elements among Ti, Zr and V is manufactured by melting respective raw material metals. Then misch metal contg. rare earth metallic elements is added to the same alloy at a ratio of 0.1 to 11atomic%. At this time, the quantity of the misch metal is regulated to <20atomic% to Ni. Or, for improving the corrosion resistance reactivity, activating physical properties of the hydrogen storage aklloy, one or more kinds among Al, Ba, Ca, Co, Cr, Fe, Mg, Mn, Sn and Si are added thereto in such a manner that their total content is regulated to the ratio of 1 to 30atomic% to the total content of Ti, Zr, V and Ni in the hydrogen storage alloy, and it may be used as an electrode material.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention stores hydrogen in high density,
The present invention also relates to a hydrogen storage alloy, an electrode and a battery using the same, which can store and release hydrogen at high speed.

[0002]

2. Description of the Related Art Hydrogen storage alloys have been drawing attention in recent years because they can store hydrogen at a density equivalent to that of liquid hydrogen per unit volume, and can be used for hydrogen storage containers and electrodes of batteries, and also for storing hydrogen. -Since a large amount of heat can be taken in and out at the time of release, its use as a heat storage material has been studied.

To put hydrogen storage alloy into practical use,
In addition to having a large hydrogen storage capacity, the following properties are required. That is, 1. Easy to activate. 2.
Can be used at room temperature. 3. The hydrogen storage / release reaction is reversible. 4. The reaction rate with hydrogen is high. 5. The hydrogen storage capacity is not easily deteriorated by oxygen or methane gas. 6. That is, pulverization is less likely to occur when hydrogen is repeatedly stored and released.

Among hydrogen storage alloys, Ti-Zr-Ni
System, Ti-V-Ni system, Zr-V-Ni system, Ti-Zr
Since the -V-Ni-based alloys are excellent in the above properties 1 to 6, research into electrode materials and the like has been conducted. When the alloys of these systems are applied to batteries and the like, it is required to reduce the hydrogen equilibrium pressure of the alloys at room temperature for safety reasons.

However, in order to reduce the hydrogen equilibrium pressure,
If the composition of these systems is changed indiscriminately, the above 1-5
Will deteriorate in nature. Therefore, as a method of reducing the hydrogen equilibrium pressure of the alloy without deteriorating such properties, for example, JP-A-55-149102 has been proposed. This is because the Ti-based alloy, which originally has a high hydrogen equilibrium pressure, is mixed with the powder of La-Ni-based alloy, which has a low hydrogen equilibrium pressure in the first place.
This is to lower the hydrogen equilibrium pressure of the Ti-based alloy.

However, the effect of reducing the hydrogen equilibrium pressure is naturally limited only by mixing the two hydrogen storage alloy powders in this way. For example, Ti-Zr-V-Ni-based hydrogen storage alloy and Mm-Ni-based (Mm is misch metal)
FIG. 1 shows a pressure-composition-isothermal line diagram (PC line diagram) when the hydrogen storage alloy is mixed in a powder state.

It can be seen from FIG. 1 that the ability of the powder mixture to reduce the hydrogen equilibrium pressure is determined by the alloy having the lower hydrogen equilibrium pressure. Therefore, in order to sufficiently reduce the hydrogen equilibrium pressure, a large amount of an alloy having a low hydrogen equilibrium pressure is required with respect to the total amount of metals corresponding to Ti, Zr, V, and Ni. From this point of view, it is uneconomical and Ti-Zr-V-as an alloy
It can be said that this method is disadvantageous because it is difficult to exhibit the peculiar properties of the Ni-based alloy.

[0008]

The present invention is directed to Ti-Zr.
-Ni system, Ti-V-Ni system, Zr-V-Ni system, Ti
-Zr-V-Ni-based hydrogen storage alloy, the above-mentioned 1 to 6
The object of the present invention is to develop an alloy system capable of sufficiently reducing the hydrogen equilibrium pressure while maintaining the above properties.

[0009]

The inventors of the present invention have conducted various studies based on the above-mentioned object, and as a result, Ti-Zr-Ni
System, Ti-V-Ni system, Zr-V-Ni system, Ti-Zr
With respect to -V-Ni-based hydrogen storage alloys, firstly, it is necessary to incorporate into the crystal lattice of the alloy a metal having a strong bonding force with hydrogen in a simple substance, and secondly, as such a metal. Furthermore, it has been thought that it is necessary to use a metal that has a larger atomic radius than Ti, Zr, V, and Ni and can increase the gap of the crystal lattice. Therefore, Ti-Zr-Ni
System, Ti-V-Ni system, Zr-V-Ni system, Ti-Zr
It has been clarified that the hydrogen equilibrium pressure can be sufficiently reduced by dissolving and adding the rare earth element to the -V-Ni-based hydrogen storage alloy.

If the rare earth element is used, the hydrogen equilibrium pressure of the above alloy system can be reduced, but it is economically advantageous to use misch metal which is a mixture of various rare earth metal elements. For this misch metal, La, Ce,
Metals such as Pd and Sm are contained, and these elements exert their respective effects in reducing the hydrogen equilibrium pressure.

The rare earth metal in the form of a simple substance or a mixture is preferably added in an amount of 0.1 at% or more with respect to the total amount of the metals corresponding to any of Ti, Zr, V and Ni. Is preferably 11 at% or less. Among them, it is more preferable that the content of Ni is less than 20 at%. In addition, Ti, Zr,
It is most preferable to add 0.2 at% to 4 at% of the total amount of metals corresponding to V or Ni.

Although various known melting methods can be applied to the melting of the alloy, it is preferable to use an arc melting furnace or a high-frequency heating furnace with a large stirring force. Also A
l, Ba, Ca, Co, Cr, Fe, Mg, Mn, S
By further adding at least one element selected from n and Si, the corrosion resistance, reaction rate, activation characteristics and the like can be further improved.

[0013]

EXAMPLES The present invention will now be described by way of examples. Example 1 In Example 1 of the present invention, La is a rare earth element having a relatively large atomic radius and a large Clark number.
I chose.

(Preparation of Alloy) As a raw material of the alloy, commercially available Ti having a purity of 99.9%, Ni of 99.5% and Z of 99% are commercially available.
r, 99.9% V, 99.9% Cr metal was used.
The respective raw materials metal and weighing, put into a water-cooled copper crucible of an arc furnace, where the dissolved repeated 10 times at a temperature of about 2000 ° C., was analyzed composition of the obtained alloy, Ti _17.20
Zr _17.20 V _23.66 Ni _41.94 Cr _7.53 was obtained. This alloy is referred to as Sample 1.

The composition of the obtained alloy was obtained by adding 5.11 at% of La to the total amount of Ti, Zr, V and Ni of Sample 1 and melting it again at a temperature of about 2000 ° C. for 10 times. _Was analyzed to find that Ti _17.20 Zr _17.20 V
_23.66 Ni _41.94 Cr _7.53 La _5.11 was obtained (Sample 2
And).

When hydrogen gas having a purity of 7N was added to the alloy thus produced at a pressure of 3 atm, activation started in about 10 minutes and hydrogen was occluded.

After the absorption of hydrogen was stopped, vacuuming was performed at room temperature for 1 hour, and then the operation of absorbing hydrogen again was repeated until the activation was completed. After completion of activation, dehydrogenation was performed under a vacuum of 10 Pa at a temperature of 300 ° C., and then the relationship between the hydrogen storage amount and the hydrogen equilibrium pressure was examined by the Sibelts method. The result is shown by the curve a in FIG.

According to FIG. 2, the alloy of Sample 1 has 5.11 with respect to the total amount of Ti, Zr, V and Ni in this alloy.
At% La is added (for Ni, La is 12.
It can be read that the hydrogen equilibrium pressure decreases to ⅙ or less with only 18 at%), and it is understood that the effect of the present invention is obtained.

From the observation with an optical microscope, it was found that when La was added, a new phase different from the original Ti-Zr-V-Ni alloy was generated. It seems that this new phase has some effect on the decrease in hydrogen equilibrium pressure. Sample 1 includes Misch metal (Mm) manufactured by Santoku Metal Co., Ltd. (composition: La23at%, Ce46at%, P
r11at%, Nd19at%, Sm1at%) was added to the alloy samples 3 to 6 by changing the addition amount. The compositions and sample numbers (circled numbers) are shown below. 1. Ti _17.20 Zr _17.20 V _23.66 Ni _41.94 Cr _7.53 2. La _5.11 Ti _17.20 Zr _17.20 V _23.66 Ni _41.94 Cr
_7.53 3. Mm _1.42 Ti _17.20 Zr _17.20 V _23.66 Ni _41.94 Cr
_7.53 4. Mm _5.11 Ti _17.20 Zr _17.20 V _23.66 Ni _41.94 Cr
_7.53 5. Mm _11.51 Ti _17.20 Zr _17.20 V _23.66 Ni _41.94 C
r _7.53 6. Mm _19.68 Ti _17.20 Zr _17.20 V _23.66 Ni _41.94 C
r _7.53

The method for producing the alloy and the method for activating the alloy are the same as those for sample 1. FIG. 3 shows the results of examining the relationship between the hydrogen storage amount and the hydrogen equilibrium pressure after completion of activation. From FIG. 3, it can be seen that the addition of Mm is effective in reducing the hydrogen equilibrium pressure of the Ti-Zr-V-Ni-based alloy. In particular, when the hydrogen storage alloy is applied to a battery, it is desirable that the hydrogen pressure be 1 atm or less from the viewpoint of safety, and 0.01 atm or more from the viewpoint of electrical characteristics. It can be seen from FIG. 3 that the amount is preferably 0 to 5.11 at%.

From the observation with an optical microscope, it was found that when Mm was added, a new phase different from the original Ti-Zr-V-Ni alloy was generated. To reduce the hydrogen equilibrium pressure,
This new phase seems to have some influence. From the result of X-ray crystal analysis, it was found that the lattice constant of the crystal of the alloy increased with the addition amount of Mm. The hydrogen equilibrium pressure decreased because the rare earth element was Ti
It is considered that this is because hydrogen easily enters the crystal because the lattice constant is increased due to the solid solution in the -Zr-V-Ni alloy.

Example 2 In Example 2, Ti-Z containing Co and Fe was used.
Mm was added to the r-V-Ni based alloy. In preparing the alloy, Co and Fe used as raw materials had a purity of 99.9%. The method for producing the other alloys is the same as in Example 1.

The compositions of the produced alloy samples 7 to 11 are shown below. 7. _{Ti 15 Zr 15 V 21 Ni 31} Cr 6 Co 6 Fe 6 8. Mm _1.3 Ti ₁₅ Zr ₁₅ V ₂₁ Ni ₃₁ Cr ₆ Co ₆ Fe ₆ 9. Mm _2.7 Ti ₁₅ Zr ₁₅ V ₂₁ Ni ₃₁ Cr ₆ Co ₆ Fe ₆ 10. Mm _4.7 Ti ₁₅ Zr ₁₅ V ₂₁ Ni ₃₁ Cr ₆ Co ₆ Fe ₆ 11. Mm ₁₈ Ti ₁₅ Zr ₁₅ V ₂₁ Ni ₃₁ Cr ₆ Co ₆ Fe ₆

After activating these alloys by the same method as in Example 1, the relationship between the hydrogen storage amount and the hydrogen equilibrium pressure was examined, and the results are shown in FIG. According to FIG. 4, the addition of Mm is Cr, C
It can be seen that it is effective in reducing the hydrogen equilibrium pressure of the Ti-Zr-V-Ni-based alloy containing o and Fe. In particular, when the hydrogen storage alloy is applied to a battery, it is desirable that the hydrogen pressure be 1 atm or less from the viewpoint of safety, and 0.01 atm or more from the viewpoint of electrical characteristics. It can be seen from FIG. 4 that the amount is preferably 0.5 at%.

Observation with an optical microscope revealed that when Mm was added, a new phase similar to that of the original Ti-Zr-V-Ni-based alloy similar to that of Example 1 was observed.

[0026]

[Brief description of drawings]

FIG. 1 is a pressure-composition-isothermal diagram when a Ti-Zr-V-Ni-based hydrogen storage alloy as a conventional example and an Mm-Ni-based (Mm is Misch metal) hydrogen storage alloy are mixed in a powder state. (P-C diagram), FIG. 2, FIG. 3, and FIG.
It is a figure which shows the hydrogen equilibrium pressure-hydrogen storage amount characteristic in 0 degreeC.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Toshio Doi 1-88, Tora, Ibaraki, Osaka Prefecture Hitachi Maxell, Ltd.

Claims (8)

[Claims] 1. A hydrogen storage alloy comprising at least two kinds of elements selected from Ti, Zr and V, and Ni and a rare earth element. 2. The hydrogen storage alloy according to claim 1, wherein the amount of rare earth element is at least 0.1a based on the total amount of metals corresponding to any one of Ti, Zr, V and Ni.
A hydrogen storage alloy characterized by being at least t%. 3. The hydrogen storage alloy according to claim 1, wherein
A hydrogen storage alloy, wherein the amount of rare earth element is 11 at% or less with respect to the total amount of metals corresponding to Ti, Zr, V, and Ni. 4. The hydrogen storage alloy according to claim 1, wherein
A hydrogen storage alloy, wherein the amount of rare earth element is less than 20 at% with respect to Ni. 5. The hydrogen storage alloy according to claim 1, wherein
Furthermore, Al, Ba, Ca, Co, Cr, Fe, Mg, M
A hydrogen storage alloy, wherein at least one element selected from n, Sn, and Si is added. 6. The hydrogen storage alloy according to claim 5, wherein
Al, Ba, Ca, Co, Cr, Fe, Mg, Mn, S
Hydrogen in which the total amount of at least one element selected from n and Si is 1 at% to 30 at% with respect to the total amount of metals corresponding to any one of Ti, Zr, V, and Ni. Storage alloy. 7. An electrode comprising an alloy of the hydrogen storage alloy according to claim 1 as a main component. 8. A battery using the hydrogen storage alloy according to claim 1.