JPS6040668B2 - Manufacturing method of hydrogen storage electrode - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a method for producing a hydrogen storage electrode used as the cathode of a storage battery, which generates electrical energy through an electrochemical reaction between hydrogen stored in the cathode and, for example, oxygen at the anode. Regarding.

Conventionally, this type of hydrogen storage electrode has been manufactured using powder of an alloy that stores hydrogen, which is an active substance, such as a Ti2Ni alloy, in the following manner.

First, single metals, such as titanium and nickel, are weighed to form an alloy composition, heated and melted in an arc melting furnace or vacuum electric furnace to create an alloy, and then this alloy is pulverized in an inert air stream. This method is used to make powder. However, this type of alloy is difficult to mechanically grind into fine particles and requires a long time, so the particle size of the alloy powder used in the electrode is 1.
It was about 0-60#. When an electrode made of such an alloy powder is bonded with a binder or bonded with a binder, the alloy powder breaks down and becomes even finer particles when it is repeatedly charged (hydrogen absorption) and discharged (hydrogen release). As a result, the bonding force between particles becomes weaker, causing expansion and cracking of the electrode, and the alloy powder falling off. As the number of charge/discharge cycles increases, the above phenomenon becomes more noticeable. When this happens, the internal resistance of the electrode increases significantly and the discharge capacity decreases. The above phenomenon is due to the primary particles of the alloy being destroyed by the hydrogen absorption and release of the alloy, and changing into secondary particles. Therefore, it is necessary to make the alloy powder finer by allowing it to absorb and release hydrogen in advance. In this case, the occurrence of secondary particles in the alloy is eliminated. The present invention focuses on this point, and
This is an attempt to solve the above-mentioned conventional drawbacks.

That is, the present invention is a method for manufacturing a hydrogen storage electrode, which is characterized in that the electrode is made of a fine powder obtained by making a hydrogen storage alloy powder alternately store and release hydrogen. According to the method of the present invention, since the hydrogen activation treatment is repeated on the alloy powder, there is an advantage that the capacity can be increased. Hereinafter, the present invention will be explained with reference to examples thereof.

Commercially available titanium powder (purity 99.5% 2Kugami) 629 and commercially available nickel powder (purity 99.5% or higher) Shiyu are mixed, pressure molded, and then melted in an arc melting furnace to form Ti2Ni.
Manufacture alloys. This alloy is then ground in an inert air stream,
The powder that passed through a 300 mesh (46〃) sieve was put into a reaction container of an electric furnace, and the inside of the container was heated to 10-5 Tom. After reducing the pressure to
1 Fill the container with hydrogen at an aphobic pressure. In this way, the alloy absorbs hydrogen, and after reaching saturation, the temperature inside the container is lowered to about room temperature by water cooling, and the hydrogen in the container is removed by suction using a vacuum pump, thereby releasing the hydrogen stored in the alloy. After the hydrogen is completely released, the inside of the container is again filled with hydrogen at a pressure of 1 pressure or more, and the pressure is increased to about 100 oo to store hydrogen. Such hydrogen storage and release operations are repeated five times, and finally, deaeration is performed. The fine alloy powder obtained in this way was mixed with 1% by weight of fluororesin, filled into a nickel foam metal, and after pressurized, in an argon gas stream *at a temperature slightly higher than the melting point of the base resin at 300 pm. Heat treat for 1 hour.

An alkaline storage battery was constructed using the electrode of the present invention obtained as described above as a negative electrode and a known nickel oxide electrode having a larger capacity as a positive electrode, and a charge/discharge test was conducted. The charging/discharging current is 50 mA per night for the negative electrode alloy, and the charging/discharging rate is 0. The charging volume is equivalent to 130% of the negative electrode capacity.
Curve A in FIG. 1 shows the change in discharge capacity accompanying charging and discharging of this battery.

The discharge capacity was expressed as a value per hour of negative electrode alloy. curve B
shows the characteristics of a battery using a negative electrode constructed using an alloy powder that does not absorb or release hydrogen. As is clear from the figure, the life of the battery using the electrode of the present invention is more than twice as long as that of the battery using the conventional electrode.
In conventional electrodes, it has been observed using an electron microscope that the alloy particles are broken down and refined into secondary and tertiary particles, and this miniaturization of alloy particles increases the internal resistance of the electrode. It is clear that this caused a decrease in capacity.

On the other hand, since the electrode of the present invention is composed of alloy particles that have been refined in advance through several hydrogen activation treatments, the alloy particles are less likely to be destroyed into secondary and tertiary particles by charging and discharging.
Binder fluororesin particles (approximately 0.5 degrees) and several to 20 particles
It was confirmed that the particles were strongly bonded to the initial alloy particles of France. Next, conditions for the initial hydrogen activation treatment when a Ti2Ni alloy is used as the alloy will be explained.

First, in the case of hydrogen storage, the temperature is preferably room temperature to 10,000 ℃. That is, at temperatures below room temperature, the hydrogen storage reaction does not proceed easily and requires a long time. Further, when the pressure exceeds 100q0, hydrogenation progresses initially, but a high pressure of about 1 pi atmosphere or more is required, which is disadvantageous in terms of equipment. It is more effective to perform the first hydrogen activation at a relatively high temperature and pressure (about 1 atm or higher), but after the second or third time, hydrogenation proceeds easily even if the temperature is lower than that. do. The degassing process is 1
0-ITon. Sufficient degassing will not occur unless the pressure is reduced to below.

Even if hydrogen is absorbed and released in a state where degassing is insufficient, the efficiency of refining the alloy is poor, and relatively large particles remain.
After being formed into an electrode, the particles become microscopic, leading to the collapse of the electrode. Therefore, the average grain size of the alloy obtained by hydrogen storage and release operations is preferably 0.1 to 20 mm. 0.
When the following fine particles become the main elements, No. 1 becomes very easily oxidized and becomes difficult to handle.

Furthermore, if particles larger than 20 mm become the main element, they will break down into secondary particles and tertiary particles after being formed into an electrode. Figure 2 shows the relationship between the number of hydrogen storage and desorption treatments performed under the conditions shown in the example above and the life of a battery similar to the one described above using an electrode made of the treated powder. shows.
The lifespan was expressed as the number of charge/discharge cycles until the discharge capacity reached 0.1 hours. As is clear from the figure, the life span increases as the number of treatments increases up to about 5 times, but there is no effect even if the treatments are repeated beyond that point. Such hydrogenation treatment not only turns the alloy powder into fine particles, but also facilitates the absorption and release of hydrogen, which has the effect of improving properties.

This is believed to be due to the effect of a kind of electrochemical catalysis that facilitates the ionization of gaseous hydrogen on the surface of the alloy particles and vice versa. As described above, according to the present invention, a hydrogen storage electrode with excellent cycle life can be obtained. In the above example, an electrode was explained in which alloy powder was bonded with a binder, but the same applies to an electrode constructed by sintering the alloy powder together with an electrode support, such as foamed metal or punched methyl, at a temperature below the melting point of the alloy. It can be applied to

The electrode according to the invention can also be used as a hydrogen electrode for fuel cells.

[Brief explanation of drawings]

Figure 1 is a diagram comparing the changes in discharge capacity during charging and discharging of an alkaline battery that combines the electrode of the present invention and a nickel oxide electrode, and a battery that uses a conventional electrode. Figure 2 shows the hydrogen occlusion according to the present invention. , shows the relationship between the number of discharge treatments and the charge/discharge cycle life. Figure 1 Figure 2

Claims (1)

[Claims] 1. A method for manufacturing a hydrogen storage electrode, which uses a powder obtained by alternately performing a process of storing hydrogen and a process of degassing hydrogen in an alloy powder that stores hydrogen.