JPH0987781A - Hydrogen storage alloy and hydrogen storage alloy electrode - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce a hydrogen storage alloy having high capacity and excellent in cycle characteristics by adding rare earth elements to a Ti-V-Ni base bcc type hydrogen storage alloy and to produce an electrode using the same. SOLUTION: In hydrogen storage alloy having a body-centered cubic structure mainly composed of Ti, V, Cr and Ni, this hydrogen storage alloy contain one kind of La and Ce or a mixture (misch metal) of rare earth elements including La and Ce is contained in the alloy by 1 to 10 atomic %, or, is expressed by the general formula Tix (Va Cr1-a )1-x Mb Nic (0.5<=a<=0.95, 0.05<=b<=0.2, 0.1<=c<=0.6 and 0.2<=x<=0.4 are satisfied, and M denotes one kind of La and Ce or a mixture (Mischmetal) of rare earth elements including La and Ce, and the main components of the alloy phases have a body-centered cubic structure, or it is characterized by using the hydride thereof and has secondary phases mainly composed of rare earth elements in the alloy phases.

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 capable of reversibly electrochemically storing and releasing hydrogen, and a method for producing the same.

[0002]

2. Description of the Related Art In recent years, with the development of portable equipment and cordless equipment, a battery as a power source thereof is required to have a higher energy density. In order to achieve this requirement, a nickel-hydrogen storage battery using a metal hydride, that is, a hydrogen storage alloy electrode has attracted attention, and many proposals have been made for a manufacturing method and the like.

A hydrogen storage alloy electrode of an alkaline storage battery, which uses a hydrogen storage alloy capable of reversibly absorbing and releasing hydrogen as a negative electrode, has a theoretical capacity density larger than that of a cadmium electrode and causes deformation such as a zinc electrode and formation of dendrite. Therefore, future development is expected as a negative electrode for alkaline storage batteries that has a long life, is pollution-free, and has a high energy density.

The alloy used for such a hydrogen storage alloy electrode is usually produced by an arc melting method, a high frequency induction heating melting method, or the like.
There are (or Mm) -Ni based multi-component alloys. AB ₅ type La (A: elements such as La, Zr, and Ti that have a high affinity for hydrogen, B: transition elements such as Ni, Mn, and Cr)
(Or Mm) -Ni-based multi-component alloys have reached a ceiling in capacity, and a new hydrogen storage alloy material having a large discharge capacity is desired.

On the other hand, as an alloy having a larger hydrogen storage capacity, there is a Ti-V type hydrogen storage alloy. Regarding this alloy system, for example, a Ti _x V _y Ni _z alloy (Japanese Patent Laid-Open No. 6-228699), a Ti _x V _y Fe _z alloy (Japanese Patent Laid-Open No. 6-93366), and the like have been proposed.

[0006]

However, when these Ti-V-based hydrogen storage alloys are used for the electrodes, La
Although the discharge capacity is higher than that of the (or Mm) -Ni-based multi-component alloy, it is considered that there is room for further improvement in terms of ease of handling as an alloy and other battery characteristics.

For example, in such a solid solution alloy,
It has great malleability and is very difficult to mechanically grind. In such a case, in a hydrogen storage alloy, absorption and release of hydrogen can be repeated to pulverize by hydrogenation, but Ti-V type alloys are difficult to activate initially, and a high temperature atmosphere is required for hydrogenation. Will be needed. In addition to these industrially disadvantageous conditions, when considered as an electrode for batteries,
Cycle characteristics and high rate discharge characteristics are issues.

[0008] As a result of repeated studies aimed at improving the alloy composition and the manufacturing method, the above-mentioned conventional problems could be solved. That is, by improving the composition and manufacturing method of the hydrogen storage alloy, we have developed a hydrogen storage alloy that is easy to handle as an electrode alloy, has little cycle deterioration, and improves high-rate discharge characteristics.

[0009]

The hydrogen storage alloy of the present invention is a hydrogen storage alloy having a body-centered cubic structure mainly composed of Ti, V, Cr and Ni, and is one of La and Ce in the alloy. Alternatively, the hydrogen storage alloy is characterized by containing a rare earth element mixture (Misch metal) containing La and Ce in an amount of 1 to 10 atom%.

[0010] The hydrogen storage alloy of the present invention have the general formula _{is, Ti x (V a Cr 1} -a) 1-x M b Ni c (0.5 ≦ a ≦
0.95, 0.05 ≦ b ≦ 0.2, 0.1 ≦ c ≦ 0.
6, 0.2 ≦ x ≦ 0.4, M is one kind of La and Ce or a mixture of rare earth elements containing La and Ce (Misch metal), and the main component of the alloy phase is body-centered cubic It is a structural alloy.

The hydrogen storage alloy of the present invention is an alloy characterized in that the alloy phase contains a second phase mainly composed of a rare earth element.

The method for producing a hydrogen storage alloy of the present invention is
After melting the alloy material, it is characterized by being rapidly cooled at a cooling rate of 10 ³ to 10 ⁷ ° C / sec. Further, it is preferably produced as a fine powder by a quench granulation method.

Further, the hydrogen storage alloy electrode of the present invention comprises the above hydrogen storage alloy or a hydride thereof.

[0014]

The electrode using the hydrogen storage alloy or the hydride thereof of the present invention is an improvement of the conventional Ti-V-Ni alloy, and the conventional alloy composition contains at least one of La and Ce or these. Addition of a mixture of rare earth elements (Misch metal) improves the discharge capacity and cycle characteristics of the electrode, and addition of Cr facilitates hydrogenation of the alloy. La and Ce are slightly superior in characteristics when used alone or as a mixture of two kinds, but if it is desired to further reduce the cost, it can be made cheaper by using a misch metal which is a mixture of rare earth elements.

Although the effect of adding rare earth elements such as La and Ce is not clearly known at present, they are hydroxides in an alkaline solution to act as a catalyst for the electrode reaction and segregation of these elements. It is considered that the phases are scattered and suppress the pulverization of the alloy. According to the results of our study, most of these elements are segregated alone or with some Ni, and they are hardly contained in the matrix. Therefore, there is no decrease in the equilibrium pressure due to the addition of the rare earth element as disclosed in JP-A-6-228699, and the effect is completely different.

The addition amount of these rare earth elements is not effective unless added in an amount of 1 atom% or more with respect to the mother alloy, and even if added in an amount of 10 atom% or more, the capacity decreases. Therefore, the addition amount c
Is preferably in the range of 0.01 ≦ b ≦ 0.1.

Cr is added to facilitate activation. Usually, in order to perform hydrogenation in a Ti-Ni based alloy, a high pressure hydrogen atmosphere at several hundreds of degrees Celsius must be used. This requires special equipment and is uncommon for industrial applications. However, when Cr is added, hydrogen can be easily hydrogenated at room temperature by introducing hydrogen at several tens of atmospheric pressure. In addition, mechanical brittleness also increases, which facilitates crushing.

Actually, even when fine pulverization is carried out by hydrogenation, it is necessary to mechanically pulverize it to a certain extent.
Ease of crushing by adding Cr is an important characteristic.

The larger the Cr content, the easier the pulverization and the easier the activation, but conversely the hydrogen storage amount tends to decrease and the hydrogen equilibrium pressure tends to rise. In order to satisfy these contradictory characteristics, the Cr content (1-a) is 0.05 ≦ 1 with respect to the V content a.
It is desirable to be in the range of −a ≦ 0.5.

Next, Ni is an essential element for the hydrogen storage alloy to store and release hydrogen electrochemically. But,
Since the hydrogen storage amount decreases as Ni increases, it is necessary to adjust so that the hydrogen storage amount and the discharge capacity are balanced and the discharge capacity becomes the largest. N for that
The i amount c is 0.1 ≦ c ≦ 0.6.

If the ratio x of Ti to V and Cr is too large, the number of elements having a strong affinity for hydrogen increases, and hydrogen is stabilized in the alloy and cannot be released. Further, when the amount is small, the storage amount decreases. The optimum range is 0.2 ≦ x ≦ 0.4
It is.

Next, regarding the effect of the second phase of the rare earth element, the effect of adding the rare earth element is considered to be the effect as a catalytic point and the prevention of pulverization, as described above. Therefore, it is considered that the distribution of this phase affects the electrode characteristics, and the finer the distribution, the greater the effect. we,
Second, by setting the alloy cooling rate to 10 ³ to 10 ⁷ ° C / sec.
The phase was finely distributed, and the electrode characteristics could be improved.
Further, as an alloy production method having such a cooling rate, there are gas atomization, water atomization, roll quenching method, etc., but if a production method capable of producing such fine powder is used, it is mechanically pulverized as in the present invention. Hard alloys can be handled easily and have great industrial value.

From the above, it is understood that in order to obtain a hydrogen storage alloy electrode having a high capacity, it is important to satisfy the alloy composition conditions and the manufacturing method of the present invention.

[0024]

EXAMPLES The present invention will be described in more detail with reference to the examples.

(Example 1) First, the effect of adding a rare earth element
About. As an example, Ti_0.4(V_0.7Cr _0.3)
_0.6Ni_0.1La_cIn the composition, c = 0,0.0
Changed to 1, 0.03, 0.05, 0.1, 0.2
In the case of c = 0.05, La is Ce, Mm (Misch
The characteristics when changing to metal) were investigated.

The alloys are commercially available Ti, V, Cr, Ni, L
It was prepared by arc melting using a, Ce, and Mm metals as raw materials.

A part of this alloy sample is used for alloy analysis such as X-ray diffraction and hydrogen absorption-desorption amount measurement (normal P (hydrogen pressure) -C (composition) -T (temperature) measurement) in a hydrogen gas atmosphere. The rest was used for electrode characteristic evaluation.

First, X-ray diffraction measurement was performed on each alloy sample. As a result, it was confirmed that the main component of the alloy phase had a body-centered cubic structure in all the alloy samples.

From the results of PCT measurement, the hydrogen storage amount slightly decreased in proportion to the amount of the rare earth element added, but the hydrogen equilibrium pressure did not change.

The above alloys were subjected to a single cell test in order to evaluate the electrode characteristics as a negative electrode for an alkaline storage battery by an electrochemical charge / discharge reaction.

The alloy was crushed by occluding and releasing hydrogen and classified to 75 μm or less. 3 g of Ni powder as a conductive material and 0.12 g of polyethylene powder as a binder were mixed with 1 g of this alloy powder, and the mixture was pressure-molded into pellets, and the binder was melted at 130 ° C. to form an electrode. did. These are used as the negative electrode, a nickel oxide electrode having an excessive electric capacity is arranged on the counter electrode, and an aqueous solution of potassium hydroxide having a specific gravity of 1.30 is used as the electrolytic solution. Charging and discharging were performed in the open system. Charging is 100 mA x 5.5 per gram of hydrogen storage alloy.
The discharge time is 50 mA per gram of alloy and the terminal voltage is 0.
Up to 8V.

FIG. 1 shows the cycle characteristics when the amount of La added was changed, and FIG. 2 shows the case where the rare earth element was changed. As the amount of La added increased, the capacity decrease due to the cycle decreased, and at c = 0.05, there was almost no capacity deterioration and the maximum capacity was exhibited. After that, the capacity decreased with the addition amount.

Regarding the types of rare earth elements, there was almost no difference between La and Ce, and the capacity was slightly reduced in the case of Mm.
It is considered that this is an influence of elements other than La and Ce. It was also confirmed that there was no difference in effect even when a mixture of La and Ce was added.

(Example 2) Next, an example in which the ranges of Ti, V, Cr and Ni were examined will be shown. The alloy was prepared in the same manner as in Example 1.

A part of this alloy sample is used for alloy analysis such as X-ray diffraction and hydrogen absorption-desorption amount measurement (normal P (hydrogen pressure) -C (composition) -T (temperature) measurement) in a hydrogen gas atmosphere. The rest was used for electrode characteristic evaluation.

For the evaluation of the electrode characteristics, a unipolar test was conducted in the same manner as in Example 1. Ratio of V and Cr a, Ti amount x, N
3 to 5 show changes in the maximum discharge capacity when the i amount c is changed.

When the alloy composition is within the range of the present invention, the discharge capacity is 300 mAh / g or more, and the electrode has a high capacity.

Cr does not have a good effect on the capacity, but when the Cr amount is 0 (a = 1), it cannot be activated even if a hydrogen pressure of about 50 atm is applied at 200 ° C., and it is mechanically crushed. I couldn't.

However, the alloy of a = 0.95 can be activated under the above conditions, and if a = 0.7 or less,
It can be mechanically crushed up to about 5 mm or less by using a tool such as a cemented carbide eryth motor punch. Therefore, the amount of Cr needs to be within the range of the present invention in order to satisfy both industrial handling and capacity.

Further, in the alloys in which Ti, V, Cr and Ni were out of the scope of the claims, the capacity was low, but the cycle characteristics were excellent. Therefore, the effect of adding the rare earth element is not limited to this alloy composition range,
The alloy having a body-centered cubic structure with this peripheral composition is also similarly exhibited. Further, even when a new element is added, the rare earth element alone contributes to the improvement of cycle characteristics as segregation, so that the same effect can be obtained.

(Embodiment 3) As is clear from the above embodiment, by adding a rare earth element, a high capacity can be obtained.
It was found that a hydrogen storage alloy electrode having excellent cycleability can be obtained. This rare earth element, as described in the section of action,
It exists separately from the parent phase together with some Ni. We examined how this distribution condition affects the electrode characteristics.

Ti _0.4 (V _0.5 Cr _0.5 ) _0.6 Ni _0.1 La
An alloy having a composition of _0.07 was melted by high frequency and then cast in an iron mold, powdered by a gas atomizing method, and ribbon-shaped by a water-cooled twin roll method.

When these alloys were analyzed by EPMA, the second phase of the rare earth was sparsely distributed as a large lump of 5 to 10 μm in the cast product, whereas it was several μm in the alloy by the gas atomization or twin roll method. It becomes the following and is dispersed finely. Further, the electrode characteristics of these alloys were evaluated in the same manner as in Example 1.

The results are shown in FIG. 6. In the cast product having a large segregation phase, the effect of rare earth addition was small and the cycle deterioration was large, whereas the gas atomized and twin roll alloys showed good cycle characteristics. Therefore, the cooling rate is 10 ³ ~10 ⁵ ℃ / s about gas atomization, the cooling rate of the twin roll method is 10 ⁵ ~10 ⁷ ℃ / s or so, the cooling rate of more than 10 ³ ° C. / s in the alloy produced Cooling improves the dispersion of rare earth elements and improves cycle characteristics. It is considered that the characteristics do not change so much even if it is cooled at a cooling rate higher than this, but it is considered that it is not suitable for practical use in view of cost etc. because such a super-quenching method is not so common. . Therefore, in order to produce an alloy that can be mass-produced at a practical cost and has excellent electrode characteristics, it is necessary to set the cooling rate to about 10 ³ to 10 ⁷ ° C / s.

[0045]

As is apparent from the above embodiments, the hydrogen storage alloy electrode of the present invention has at least one of La and Ce as the alloy composition of the conventional hydrogen storage alloy electrode, or La and Ce.
By adding a mixture of rare earth elements containing Ce (Misch metal), it has a high discharge capacity and excellent cycle characteristics.

[Brief description of drawings]

FIG. 1 is a diagram showing the amount of La added and the cycle characteristics of electrodes in an example of the present invention.

FIG. 2 is a diagram showing changes in cycle characteristics due to the rare earth element added in the present invention.

FIG. 3 is a diagram showing the relationship between the atomic ratio a of V and Cr and the maximum discharge capacity of the present invention.

FIG. 4 is a diagram showing the relationship between the Ti amount x and the maximum discharge capacity of the present invention.

FIG. 5 is a diagram showing the relationship between the Ni amount c and the maximum discharge capacity of the present invention.

FIG. 6 is a diagram comparing the cycle characteristics according to the manufacturing method of the alloy of the present invention.

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Toshihiro Yamada 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd.

Claims (6)

[Claims] 1. A hydrogen storage alloy having a body-centered cubic structure mainly composed of Ti, V, Cr and Ni, wherein La,
A hydrogen storage alloy, characterized by containing 1 to 10 atom% of a mixture of rare earth elements (Misch metal) containing at least one of Ce. 2. The general formula is Ti _x (V _a Cr _1-a ) _1-x M _b N
i _c (0.5 ≦ a ≦ 0.95, 0.01 ≦ b ≦ 0.1,
0.1 ≦ c ≦ 0.6, 0.2 ≦ x ≦ 0.4, M is L
A hydrogen storage alloy which is represented by a mixture of at least one of a and Ce or a rare earth element containing La and Ce (Misch metal), and whose main component of the alloy phase is a body-centered cubic structure. 3. The hydrogen storage alloy according to claim 1, wherein the alloy phase contains a second phase mainly composed of a rare earth element. 4. After dissolving the alloy material, according to claim 1 or 2, characterized in that quenching at a cooling rate of 10 ³ ~10 ⁷ ℃ / sec
A method for producing the hydrogen storage alloy described. 5. The method for producing a hydrogen storage alloy according to claim 1, wherein the alloy material is produced as fine powder by a quench granulation method after melting. 6. A hydrogen storage alloy electrode comprising the hydrogen storage alloy according to any one of claims 1 to 4 or the hydrogen storage alloy according to claim 4 or 5 or a hydride thereof as a constituent element.