JP2719542B2 - Hydrogen storage alloy powder for battery electrode and method for producing hydrogen storage electrode - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a hydrogen storage alloy powder and a hydrogen storage electrode used for a negative electrode of an alkaline storage battery.

Conventional technology and its problems The hydrogen storage electrode uses a hydrogen storage alloy capable of reversibly storing and releasing hydrogen for the electrode, and the electrochemical oxidation-reduction reaction of the hydrogen is used to raise the negative electrode of the alkaline storage battery. It is used for electric reaction. The hydrogen storage alloy used in the hydrogen storage electrode, TiNi, Ti ₂ Ni, and the intermetallic compound such as LaNi ₅ and TiMn _2, there is a constituent element of the intermetallic compound was replaced by another element. If the composition of these hydrogen storage alloys is different, properties such as hydrogen storage capacity, equilibrium hydrogen pressure, and storage capacity characteristics when charging and discharging are repeated in an alkaline electrolyte change, so the alloy composition is changed. Attempts have been made to improve the performance of hydrogen storage electrodes.

In conventional hydrogen storage electrodes for batteries, when the powder of a hydrogen storage alloy such as LaNi ₅ or TiMn ₂ alloy is brittle, the alloy is mechanically pulverized to prepare a powder, and this powder is prepared. It has been manufactured by bonding with an alkali-resistant polymer and holding it on a conductive core, filling foam metal, or sintering this powder at a high temperature. In this way, the method using the powder of the hydrogen storage alloy allows the electrodes to be manufactured in a short time,
There was a feature that the hydrogen storage electrode was excellent in mass productivity.

The alloy powder used in the production of these hydrogen storage electrodes is produced by melting the metal using an arc melting furnace or high-frequency induction furnace and then cooling to produce an alloy, which is then mechanically pulverized. Had been prepared.

However, in the case of an alloy having a particularly high hardness, such as the intermetallic compound TiNi, it is not easy to mechanically pulverize the alloy, and it was necessary to pulverize for a long time using a special high-energy pulverizer. Therefore, this kind of hydrogen storage alloy powder prepared by mechanical pulverization was extremely expensive. In addition, when such a hydrogen storage alloy powder that is mechanically pulverized and adjusted as described above is used for a hydrogen storage electrode, its discharge capacity is such that the hydrogen storage alloy is mechanically pulverized as described later. There is also a disadvantage that the discharge capacity is smaller than that of an electrode which is made to react at a high temperature without using a porous material. Therefore, even if the alloy has an excellent performance such as a long charge / discharge cycle life when used as a hydrogen storage electrode, such as TiNi, if the hardness of the alloy is particularly high, the alloy may be used. The powder was not mechanically crushed and the powder was not used industrially in large quantities.

Conventionally, when a hydrogen storage alloy having such a particularly high hardness is used, instead of using the powder of the alloy, for example, a mixture of a powder of nickel metal and titanium hydride is reacted at a high temperature in a hydrogen atmosphere. Then, a hydrogen absorbing electrode has been manufactured by a method of obtaining the porous body (Japanese Patent Publication No. 49-25135). However, in this method, in order to obtain an alloy having a uniform composition, it was necessary to react at a high temperature for a long time. Therefore, this method was inferior in mass productivity as compared with a method of manufacturing an electrode using a powder of a hydrogen storage alloy.

As described above, even when a hydrogen storage alloy having high hardness is used, a hydrogen storage electrode that is inexpensive, has excellent mass productivity, and has a large discharge capacity has been desired.

Means for Solving the Problems The present invention uses a gas atomized powder as a hydrogen storage alloy for a battery electrode, and further manufactures a hydrogen storage electrode by bonding a hydrogen storage alloy powder produced by a gas atomization method with an alkali-resistant polymer. This aims to solve the above problem.

Action The gas atomized powder of the present invention is produced by the following method called gas atomization. That is, the hydrogen storage alloy itself or a mixture of constituent metals of the hydrogen storage alloy is melted in an inert atmosphere such as argon gas or xenon gas using a high-frequency induction furnace or the like. Then, the melted alloy is pressurized with these gases and sprayed into the above-mentioned gases. By doing so, the hydrogen storage alloy scattered as droplets is cooled in the gas of the atmosphere, and a powder of the hydrogen storage alloy is obtained.

In this method, the gas in the atmosphere is desirably an inert gas such as a rare gas which does not easily react with the hydrogen storage alloy. This is because, for example, in an atmosphere containing oxygen or nitrogen, at high temperatures, oxides or nitrides of the constituent metals of the hydrogen storage alloy are generated, and the amount of the alloy involved in the hydrogen storage / release reaction is reduced. This is because there is a disadvantage of reduction.

According to this gas atomizing method, a powder of the hydrogen storage alloy can be obtained at a lower cost than in the case of manufacturing by mechanical pulverization for the following reasons. That is, in the gas atomizing method, a metal mixture having a desired composition is melted and sprayed as it is to obtain a hydrogen storage alloy powder. Therefore, as in the method of preparing a powder of a hydrogen storage alloy by mechanically pulverizing, first, an alloy ingot is produced by an operation of melting and cooling a metal mixture, and then the complicated process of mechanically pulverizing this alloy ingot is performed. The powder of the hydrogen storage alloy can be prepared in a short time without going through a complicated process.

The effect of simplifying the manufacturing process of the hydrogen storage alloy powder can be obtained in the case of an alloy having a low hardness, but in the case of an alloy having a high hardness, a long mechanical pulverizing process can be omitted. The effect is more remarkable.

In addition, when the gas atomized powder of the present invention, that is, the hydrogen storage alloy manufactured by the gas atomization method is used, the discharge capacity of the hydrogen storage electrode is significantly larger than the case where the powder of the hydrogen storage alloy manufactured by mechanical pulverization is used.

Although the reason is not clear, it is considered as follows from the remarkable difference in X-ray diffraction patterns of these powders. That is, the shape of the X-ray diffraction peak of the hydrogen storage alloy manufactured by the gas atomization method is remarkably clear as compared with the one manufactured by mechanical pulverization. This means that the hydrogen storage alloy powder produced by the gas atomization method has higher crystallinity than the powder produced by mechanical pulverization. In the case of a TiNi alloy, when a liquid alloy is rapidly cooled to become amorphous, a flat portion of an isothermal line of hydrogen equilibrium pressure-hydrogen storage amount (so-called PCT curve) is not recognized, and is reversibly stored and released. It has been reported that the amount of hydrogen gas reduced. From these facts, since the hydrogen storage alloy powder prepared by the gas atomization method has higher crystallinity than the hydrogen storage alloy powder prepared by mechanical pulverization,
It is assumed that the amount of hydrogen reversibly stored and released increases, and the discharge capacity of the hydrogen storage electrode using the alloy powder prepared by the gas atomization method increases.

As described above, the hydrogen storage electrode according to the present invention is capable of holding a gas atomized powder obtained by turning a hydrogen storage alloy into a powder by a gas atomization method in a conductive core or filling a sintered body of a foamed metal or a metal fiber to withstand. These are linked by an alkaline polymer. Therefore, this hydrogen storage electrode is excellent in mass productivity. In particular, this effect is remarkable in the case of a hydrogen storage alloy having a very high hardness in a solid state and difficult to mechanically pulverize.

Further, as described above, gas atomized powder of a hydrogen storage alloy manufactured by a gas atomization method is significantly less expensive than powder of a hydrogen storage alloy manufactured mechanically. Therefore, a hydrogen storage electrode using this powder is less expensive than an electrode using a powder of a hydrogen storage alloy manufactured mechanically.

It should be noted that the shape of the hydrogen storage alloy powder, which is a gas atomized powder produced by the gas atomization method, is also characteristically spherical. On the other hand, the shape of the powder of the hydrogen storage alloy manufactured by mechanical pulverization is irregular. Therefore, the hydrogen storage alloy powder, which is a gas atomized powder, is also advantageous in that the powder has better fluidity than a hydrogen storage alloy manufactured by mechanical pulverization.

Examples Hereinafter, the present invention will be described in detail using preferred examples.

In this example, in order to clarify the features of the present invention,
In particular, a case where an intermetallic compound TiNi alloy which is a hydrogen storage alloy having high hardness is used will be described.

[Hydrogen Storage Electrode A] (Example of the Present Invention) The TiNi alloy powder used for the hydrogen storage electrode of the present invention was manufactured by the following argon gas atomizing method. That is, commercially available electrolytic nickel and sponge titanium were weighed and mixed so as to be equimolar, and the mixture was melted in a high-frequency induction furnace lined with calcium oxide and maintained in an argon atmosphere. This melt was pressurized and sprayed into argon gas to obtain a gas atomized powder a of a TiNi alloy.

Next, 100 parts by weight of the powder a passed through a standard sieve having an opening of 180 μm defined by JIS Z8801 and 100 parts of carbonyl nickel powder (manufactured by INCO, trade name: TYPE 255) 100 Parts by weight and 1 part by weight of a vinyl chloride-acrylic copolymer short fiber as a reinforcing agent were mixed and wetted with water, and then an acrylic-styrene copolymer as an alkali-resistant polymer binder was mixed. The polymer latex (10 parts by weight in solid content) in which the union was dispersed was added,
A paste-like mixture was prepared. Then, the paste-like mixture was applied to a conductive core body plated with nickel on a perforated steel sheet having a thickness of 0.09 mm, dried with hot air at 80 ° C., and pressed with a roll at room temperature to obtain a hydrogen storage electrode A according to the present invention. Made.
The dimensions of this electrode were about 40 mm × 20 mm × 1.4 mm, and one piece of this electrode contained about 3.4 g of a hydrogen storage alloy.

[Hydrogen Storage Electrode B] (Comparative Example) On the other hand, for comparison, a TiNi alloy pulverized powder b prepared by mechanical pulverization instead of the hydrogen storage alloy a of the hydrogen storage electrode A (New Metal End Chemicals Corporation, USA) A hydrogen storage electrode B was produced in the same manner as the hydrogen storage electrode A except that powder passed through a standard sieve having an opening of 180 μm was used.

[Hydrogen Storage Electrode C] (Comparative Example) Further, for comparison, a hydrogen storage electrode was manufactured by the following method according to the prescription described in JP-B-49-25135. That is, powders of titanium hydride and nickel metal were mixed such that the atomic ratio of titanium to nickel was 1: 1. Then, this mixture is dispersed in an aqueous solution of sodium salt of carboxymethylcellulose which functions as a binder in a process up to a heat treatment at 900 ° C., and the resultant is applied to the same conductive core as electrode A, and then dispersed. ° C
And dried with hot air. And at 900 ° C in a hydrogen atmosphere,
After reacting for a time, a porous body of TiNi alloy was obtained. Then, the porous body is cut to obtain a hydrogen storage electrode C containing about 3.4 g of TiNi.
Was made.

In order to clarify the difference in the properties of the TiNi alloy powder used for these electrodes, scanning line electron micrographs of powders a and b are shown in FIG. Magnification is 100x. First, (a) and (b) represent hydrogen storage alloy powders a and b, respectively. Most of the hydrogen storage alloy powder a, that is, the gas atomized powder used for the hydrogen storage electrode A according to the present invention is spherical, while the conventional hydrogen storage electrode B
It can be seen that the hydrogen storage alloy powder b used in the above, that is, the pulverized powder is amorphous.

FIG. 2 shows a comparison of X-ray diffraction patterns of the hydrogen storage alloy powders a and b. In FIG. 2, (a) and (b) represent hydrogen storage alloy powders a (gas atomized powder) and b (crushed powder), respectively. In these X-ray diffraction analyses, Kα radiation of copper is used. In FIG. 2, curve (a) shows clear diffraction peaks of (110), (200) and (211) planes of TiNi, while curve (b) shows small and broad diffraction peaks. , 2θ = 42.5deg.
It was only found nearby. Therefore, it is clear that the powder a of the gas atomized powder has significantly higher crystallinity than the powder b of the pulverized powder.

Next, in order to clarify the discharge performance when the hydrogen storage electrodes A, B, and C were used in an alkaline storage battery, the discharge of the battery was performed using the hydrogen storage electrodes A, B, and C as the negative electrodes. Test open-type alkaline storage batteries A, B, and C, which were configured to be regulated by the above, were manufactured.

These batteries were manufactured as follows. That is,
One hydrogen-absorbing electrode was placed at the center to form a negative electrode, and two sintered nickel hydroxide electrodes were placed on both sides of a separator made of a nonwoven fabric made of nylon to form a positive electrode.

And the nickel hydroxide electrode used for these batteries was produced as follows. That is, the porosity is 85%
Using a sintered nickel substrate of the above, the vacuum impregnation is repeated six times by a normal vacuum impregnation method to cause nickel hydroxide and cobalt hydroxide to co-precipitate in the pores of the sintered substrate, thereby obtaining a sintered nickel electrode. Was made. The size of this electrode is 40mm × 40mm ×
0.85 mm, and the total amount of nickel hydroxide and cobalt hydroxide charged in one electrode was about 2.4 g. The content of cobalt hydroxide was about 95% by molar ratio based on the total amount of nickel hydroxide and cobalt hydroxide. The discharge capacity of the two nickel hydroxide electrodes is 1.39 Ah when the discharge follows a one-electron reaction process. The electrolyte is
A 5.8M KOH aqueous solution was used. Battery case is 45mm × 40mm ×
A 3 mm acrylic resin was used.

Then, the batteries A, B and C were charged at 25 ° C. at a current of 0.25 A for 3 hours and discharged at a current of 0.25 A to 1.0 V in the third cycle in a charge / discharge test. Table 1 shows the discharge capacity of the battery.

In these batteries, as described above, the discharge capacity of the positive electrode plate is significantly larger than that of the negative electrode plate including the hydrogen storage electrode, and thus the discharge capacity of the battery corresponds to the discharge capacity of the hydrogen storage electrode. Therefore, Table 1 shows that the powder was produced by the argon gas atomizing method, that is, the gas atomized powder.
The discharge capacity of the hydrogen storage electrode using TiNi alloy powder is significantly larger than the discharge capacity of the hydrogen storage electrode manufactured by mechanically pulverizing, that is, using the TiNi alloy powder that is a pulverized powder. It can be seen that these are almost the same as electrodes manufactured by reacting at a high temperature.

Instead of applying the paste-like mixture containing the hydrogen storage alloy to the conductive core, the paste-like mixture was filled in foamed nickel (trade name: Celmet, manufactured by Sumitomo Electric Industries, Ltd.). Even when a hydrogen storage electrode was manufactured in the same manner as the electrodes A and B of the example and a charge / discharge test was performed, the discharge capacity of the electrode manufactured using the argon gas atomization method, that is, the electrode using a TiNi alloy powder that is a gas atomized powder was The discharge capacity of the electrode was significantly larger than the discharge capacity of the electrode manufactured using mechanically pulverized TiNi alloy powder. The same effect was obtained when a sintered body of metallic nickel fibers was used instead of foamed nickel.

As a hydrogen storage alloy, LaNi is used instead of TiNi alloy.
₄ addition using a Co alloy having a composition of, by fabricating a hydrogen absorbing alloy powder and the hydrogen storage alloy electrode in the same manner as described above for electrodes A and B, when performing the charge and discharge test, when using a TiNi alloy Although not so remarkable, the discharge capacity of an electrode manufactured using an argon gas atomizing method, that is, using a hydrogen storage alloy powder, which is a gas atomized powder, is the discharge capacity of an electrode using a hydrogen storage alloy powder, which is a crushed powder manufactured by mechanical pulverization. It was bigger than the capacity. Also in the case of this alloy, as a result of X-ray diffraction analysis, it was found that the gas atomized powder produced by the gas atomizing method had higher crystallinity than the pulverized powder produced by mechanical pulverization.

From the above results, the hydrogen storage electrode manufactured using the gas atomizing method, that is, the hydrogen storage electrode using the hydrogen storage alloy powder that is a gas atomized powder has a significantly larger discharge capacity than the case where the hydrogen storage alloy powder manufactured by mechanical pulverization is used. Further, it is clear that the mass productivity is excellent.

Effect of the Invention According to the present invention, when a gas atomized powder is used as a hydrogen storage alloy powder for a battery electrode, a hydrogen storage electrode having a remarkably large discharge capacity and excellent mass productivity can be obtained.

[Brief description of the drawings]

1 (A) and 1 (B) are diagrams (scanning electron micrograph) showing the particle structure of a powder of a hydrogen storage alloy TiNi. FIG. 2 is a view showing an X-ray folding figure of the powder of the hydrogen storage alloy TiNi.

Claims (2)

(57) [Claims] 1. A hydrogen storage alloy powder for a battery electrode, which is a gas atomized powder. 2. A method of manufacturing a hydrogen storage electrode, comprising bonding a hydrogen storage alloy powder produced by a gas atomization method with an alkali-resistant polymer.