JPH0812777B2 - Manufacturing method of hydrogen storage electrode - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for manufacturing a hydrogen storage electrode using a hydrogen storage alloy that stores and releases hydrogen reversibly.

2. Description of the Related Art Lead storage batteries and alkaline storage batteries are widely used as secondary batteries among various power sources.

Of these, nickel-cadmium storage batteries accounted for the majority of alkaline storage batteries, and the practical application of sintered nickel electrodes greatly expanded the range of applications.

This battery is excellent in discharge characteristics, and its voltage and capacity do not decrease much even if it is discharged at a high rate. It also has a long life, withstands harsh conditions such as overcharging, and has excellent low-temperature performance.

However, considerable effort is still needed to deal with high energy densities. With respect to the positive electrode, for example, a foamed nickel electrode has been put into practical use, but with respect to the cadmium electrode of the negative electrode, no significant progress has been made so far.

For example, zinc is taken up in place of cadmium in the negative electrode. Although it has been successfully used as a primary battery, it is not out of the special range because it has a problem of life due to deformation during charging and discharging, dendritic deposition, etc., as is well known.

Therefore, what has recently attracted attention is the reversible storage of hydrogen.
It is a hydrogen electrode using a hydrogen storage alloy that releases. Unlike the hydrogen gas diffusion electrode method adopted for space, in this case, a battery can be constructed with the same handling such as cadmium and zinc, the actual dischargeable capacity density can be made larger than that of cadmium, and that of dendrite such as zinc. Since there is no formation or change in the shape of the electrodes, it is promising as a non-polluting alkaline storage battery with high energy density, long life and pollution.

As a method for manufacturing a hydrogen storage electrode using this hydrogen storage alloy, conventionally, a hydrogen storage alloy is sintered together with a porous conductor to obtain an electrode by a sintering method or foam metal or metal fiber, punching metal or expanded metal, A method in which a porous conductor such as a metal net is filled with a hydrogen storage alloy together with a binder and the like is often used. The hydrogen storage alloys used for these are in powder form and are generally pulverized by mechanical pulverization. On the other hand, an example in which this pulverization is carried out by hydrogenation and dehydrogenation with hydrogen gas is also known from JP-A-53-103910.

Problems to be Solved by the Invention Although a hydrogen storage electrode using a hydrogen storage alloy is effective in improving high energy density as described above, so far, when it is used for a hydrogen storage alloy negative electrode of an alkaline storage battery, There were the following problems. That is, when hydrogen is occluded and released, that is, charging and discharging are repeated, the alloy powder is pulverized, the electrodes are deformed, and the powder is dropped. This may lead to a decrease in electrode performance. Further, the crushed alloy powder contains a considerable amount of an impurity phase other than the alloy phase which effectively acts as an electrode, which may be dissolved in the electrolytic solution to deteriorate the performance.

The present invention solves the problems such as pulverization and dissolution which have been problems so far when using this hydrogen storage alloy for a hydrogen storage alloy negative electrode of an alkaline storage battery, and aims at extending the service life, and at the same time, simple production of the hydrogen storage electrode. The purpose is to provide a method.

Means for Solving the Problems The present invention is to store a hydrogen storage alloy in a pressure vessel, perform hydrogenation with hydrogen gas and dehydrogenation, and carry out the hydrogenation and impurities not pulverized by dehydrogenation. A method for producing a hydrogen storage electrode, characterized in that a portion containing a phase is separated and the rest is thereafter used for a hydrogen storage electrode.

Furthermore, it is preferable to use only particles having a particle size of 100 μm or less separated by sieving. In addition, hydrogenation with hydrogen gas and dehydrogenation are performed twice or more in order to perform sufficient pulverization, and in the pressure vessel where the hydrogenation was performed to further suppress oxidation, a portion that has not been pulverized thereafter Only good to separate.

Action Hydrogenation with hydrogen gas and dehydrogenation are performed, hydrogenation and the portion containing the impurity phase in the alloy that has not been pulverized by dehydrogenation are separated and removed, and the rest is used for hydrogen storage electrodes thereafter. This solves the problem of pulverization. That is, hydrogenation with hydrogen gas, compared to mechanical grinding,
A finer powder can be easily obtained, and as a result, even if the hydrogen storage electrode is repeatedly charged and discharged, further pulverization is less likely to proceed. With respect to dissolution, only the effective alloy phase is selectively finely divided and the impurity phase in the alloy is not sufficiently finely divided. Therefore, only that portion can be separated by sieving or the like to prevent the impurities from being dissolved.

In this way, only the effective alloy phase selectively pulverized by sieving can be used, and the impurity phase in the alloy that is easily dissolved in the electrolyte can be separated as coarse particles, which is effective for extending the life of the hydrogen storage electrode. I found out.

Examples Hereinafter, examples of the present invention will be described.

Commercially available Mm (Misch metal), Ni, as hydrogen storage alloy
The raw materials of Co, Mn, and Al were weighed to a constant composition ratio, and the production of an alloy having a composition of MmNi _3.8 Co _0.5 Mn _0.4 A _10.3 was aimed at by an argon arc melting furnace. Then, this alloy was heat-treated in a vacuum heat-treatment furnace according to a known method, and then stored in an apparatus as shown in the figure. The figure shows one manufacturing apparatus of the hydrogen storage electrode of the present invention. The block-shaped hydrogen storage alloy 1 of about 1 to 10 cm square was stored on the coarse metal mesh 3 on the upper part of the pressure vessel 2. This pressure vessel 2 has a gas valve 4 and has a structure in which a mesh sieve 5 for sieving is housed inside the vessel and can be sealed. The gas valve 4 is used for evacuation, introduction of hydrogen gas, and introduction of an inert gas.

A procedure of the present invention will be described with reference to the drawings. First, the inside of the pressure vessel 2 accommodating the hydrogen storage alloy 1 was degassed by the vacuum pump via the gas valve 4. And then the same valve 4
A commercially available hydrogen gas was introduced and the pressure was increased to about 30 atm.
As a result, the hydrogen storage alloy 1 soon started the hydrogen storage reaction. After sufficient hydrogenation was performed, hydrogen gas was released from the valve 4, and degassing was performed by a vacuum pump in order to sufficiently release the hydrogen gas. After repeating this hydrogenation and dehydrogenation three times, the pressure vessel 2 was vibrated to finely pulverize the hydrogen-absorbing alloy powder with a 200-mesh mesh sieve 5. The powder that passed through the mesh sieve 5 was left in the argon gas introduced from the valve 4 for a while, and then taken out of the pressure vessel 2. At this time, the amount of hydrogen storage alloy powder recovered after passing through a 200-mesh mesh screen was about 96% of the amount of alloy initially charged. On the other hand, as a result of examining powders and particles that could not pass through the remaining mesh sieve of about 4%, it was confirmed by X-ray diffraction that these were somewhat different from the effective alloy phase for hydrogen storage. . When this coarse powder and particles were subsequently hydrogenated with hydrogen gas, the hydrogenation characteristics were considerably worse than those of the hydrogen storage alloy powder recovered after passing through the 200 mesh screen.

Next, a description will be given of the results of evaluation by using the hydrogen storage alloy powder that has passed through the 200-mesh mesh screen and recovered as a hydrogen storage electrode, and configuring a sealed nickel-hydrogen secondary battery.

First, a hydrogen-absorbing alloy powder that passed through 200 mesh was added to a 5% (by weight) solution of polyvinyl alcohol in ethylene glycol, 0.8% by weight of polyethylene fine powder, and 0.5% of vinyl chloride-acrylonitrile short fibers to form a paste. Thoroughly kneading, thickness 0.15mm, hole diameter 1.8m
It was coated on a punching metal plate made of iron and having a porosity of 50% and plated with nickel, smoothed through a slit having a width of 0.6 mm, and then dried at 120 ° C. for 1 hour to obtain a hydrogen storage electrode. The hydrogen storage electrode thus obtained is referred to as an electrode A.

For comparison, hydrogenation with hydrogen gas and dehydrogenation are carried out in the same manner, but the hydrogen storage alloy powder is similarly used as a hydrogen storage electrode without sieving with a 200-mesh mesh sieve 5 as electrode B. To do. Furthermore, the hydrogen storage alloy powder obtained by pulverizing the hydrogen storage alloy without passing through hydrogenation and dehydrogenation with hydrogen gas until it passes through a 200-mesh mesh sieve by a mechanical pulverization method using a ball mill is also used for hydrogen storage. What was made into an electrode was added as an electrode C.

The hydrogen storage electrodes A to C obtained in this manner were then evaluated as a sealed nickel-hydrogen secondary battery in a C1 type.

That is, each of the hydrogen storage electrodes was 3.9 cm wide and 26 cm long.
Then, the lead plate was attached to two predetermined places by spot welding. A well-known foamed nickel electrode was selected as a counter electrode and used with a width of 3.9 cm and a length of 22 cm. Also in this case, the lead plates were attached at two places.

As the separator, a polyamide nonwoven fabric, and as the electrolyte, 30% lithium hydroxide was added to a caustic potash aqueous solution with a specific gravity of 1.20.
g / dissolved and used. The nominal capacity is 3.0 Ah.

These batteries were subjected to 20
The results evaluated at ° C will be described.

Charge up to 150% at 0.2C (5-hour rate), discharge at 0.5C
The final voltage was set to 0.8 V (at a rate of 2 hours), and the charge / discharge cycle was repeated.

As a result, the AA sealed nickel-hydrogen secondary battery constructed using the electrode A has a discharge capacity of 3.15 A at 100 cycles.
The life performance was extremely excellent as it was 3.14 Ah at 300 cycles for h and 300 cycles and 3.13 Ah at 600 cycles.

On the other hand, the battery composed of the electrode B had a capacity of 3.08 Ah at 100 cycles, but fell below the nominal capacity of 3.0 Ah at 2.95 Ah at 300 cycles, and then the discharge capacity dropped sharply.
The discharge voltage of the battery composed of the electrode B was lower than that of the battery composed of the electrode A as a whole. Furthermore, although the battery composed of electrode C initially met the nominal capacity of 3.0 Ah,
In the 00 cycle, only a discharge capacity of 2.81 Ah was obtained, and thereafter, the discharge capacity decreased sharply like the battery composed of the electrode B.

Based on the results of charge and discharge tests that constituted such a battery, after hydrogen storage and release with hydrogen gas, hydrogen storage electrode powder A was made into only an effective alloy phase by sieving, and hydrogen storage electrode A had a long life performance. It was confirmed that it was excellent.

As a result of various studies on the present invention other than the above explanation, the following were important.

First, the steps of hydrogenating with hydrogen gas and dehydrogenating were performed three times in the examples, but it is preferable to perform the steps twice or more in terms of battery performance. In addition, the particle size of 200 mesh, or 74 microns, was used in the step of separating the particles with a constant particle size by sieving.
It is preferably 00 microns or less. Furthermore, since the hydrogen storage alloy powder that has been hydrogenated with hydrogen gas and dehydrogenated has a very high activity, the surface is covered with a liquid that does not react with the hydrogen storage alloy powder in addition to the inert gas of the example. ,
Not proceeding with oxidation is also an effective means.

EFFECTS OF THE INVENTION As described above, the method for manufacturing a hydrogen storage electrode of the present invention stores the hydrogen storage alloy in a pressure vessel, performs hydrogenation with hydrogen gas and dehydrogenation, and performs the hydrogenation and dehydrogenation. Is used to separate the part containing the impurity phase that has not been pulverized, and the rest is then used as a hydrogen storage electrode.When a hydrogen storage alloy is used for the negative electrode of a hydrogen storage alloy in an alkaline storage battery, the pulverization that has been a problem until now It is possible to solve problems such as melting and melting and to prolong the service life and simplify the hydrogen storage electrode.

[Brief description of drawings]

FIG. 1 is a sectional view of a hydrogen storage electrode manufacturing apparatus according to an embodiment of the present invention. 1 ... Hydrogen storage alloy, 2 ... Pressure vessel, 3 ... Coarse metal mesh, 4 ... Gas valve, 5 ... Mesh sieve.

Claims (5)

[Claims] 1. A hydrogen storage alloy is housed in a pressure vessel, hydrogenated with hydrogen gas and dehydrogenated to separate a portion containing an impurity phase which is not pulverized by the hydrogenation and dehydrogenation. A method for producing a hydrogen storage electrode, characterized in that the electrode is formed of the remaining finely divided hydrogen storage alloy. 2. A part containing an impurity phase which is not pulverized is separated in a pressure vessel which has been subjected to hydrogenation with hydrogen gas and dehydrogenation. Manufacturing method of hydrogen storage electrode. 3. The method for producing a hydrogen storage electrode according to claim 1 or 2, wherein the steps of hydrogenation and dehydrogenation are performed twice or more. 4. The method according to claim 1, wherein the method of separating the portion containing the non-micronized impurity phase is a sieving method with a constant particle size. Manufacturing method of hydrogen storage electrode. 5. The production of a hydrogen storage electrode according to any one of claims 1 to 4, wherein the particle size in the step of separating the particles with a constant particle size by sieving is 100 microns or less. Law.