JPH07101607B2 - 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 use of sintered nickel electrodes greatly expanded the range of applications.

This battery has excellent discharge characteristics, and the voltage and capacity are not significantly reduced even when 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 successful for primary batteries,
As is well known, there is a problem of life due to deformation during charging / discharging, dendritic precipitation, etc., so it is not beyond the special range.

Therefore, what has recently attracted attention is a hydrogen electrode using a hydrogen storage alloy that stores and releases hydrogen reversibly. Unlike the hydrogen gas diffusion electrode method used for space, in this case, a battery can be constructed in the same way as cadmium and zinc, and the actual dischargeable capacity density can be made larger than that of cadmium, and dendrites such as zinc. Since it does not cause the formation of electrodes and changes in the shape of electrodes, it is promising as a high energy density, long-life, pollution-free alkaline storage battery.

As a method for producing a hydrogen storage electrode using this hydrogen storage alloy, conventionally, a sintered body to obtain an electrode by sintering a hydrogen storage alloy together with a porous conductor or a 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 alloy used for these is in powder form, and is 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. While it is effective to carry out pulverization by hydrogenation and dehydrogenation with hydrogen gas, the hydrogen storage alloy is in a chemically active state, which makes it vulnerable to oxidation and hydrogen There has been a problem that the storage capacity is lowered and the performance of the hydrogen storage electrode is likely to be lowered as before.

The present invention, when using this hydrogen storage alloy in a hydrogen storage alloy negative electrode of an alkaline storage battery, solves problems such as pulverization and electrode oxidation, which have been problems so far, and realizes a high-performance and long-life hydrogen storage electrode with a simple structure. It is intended to provide a manufacturing 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 dehydrogenate to obtain fine powder, and then
A method for producing a hydrogen storage electrode, characterized in that a paste solution is directly introduced into this hydrogen storage alloy powder to form a paste, and the obtained paste is filled in a porous conductor.

Further, the step of performing hydrogenation with hydrogen gas and dehydrogenation, and removing only the portion where the fine powder is insufficient due to the hydrogenation and dehydrogenation is a sieving method, and the particle size is 100 microns or less. Be good.

Action Hydrogenation with hydrogen gas and dehydrogenation lead to pulverization, but pulverization by this method produces finer powder than mechanical pulverization, which results in hydrogen storage electrodes. Even if charging and discharging are repeated, it is difficult to further reduce the pulverization. After pulverizing by repeating hydrogenation and dehydrogenation with hydrogen gas in a pressure vessel, the paste solution is directly introduced into this pressure vessel to make a hydrogen storage alloy powder into a paste, and the obtained paste is made into a porous conductor. Since it is filled, it can be used as an electrode material without accelerating the oxidation of the hydrogen storage alloy, so that the life can be extended.

Examples Examples of the present invention will be described below.

Commercially available Mm (Misch metal), Ni, C as hydrogen storage alloy
Raw materials of o, Mn, and Al were weighed to a constant composition ratio, and an MmNl _3.7 Co _0.6 Mn _0.4 Al _0.3 alloy was manufactured 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 housed in an apparatus as shown in FIG. FIG. 1 shows an apparatus for producing a 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. The pressure vessel 2 has a gas valve 4, a solution valve 5 and a paste valve 6 and has a structure capable of being hermetically sealed. Gas valve 4
Is used for evacuation and hydrogen gas introduction, and the solution valve 5 is
A nozzle 8 for introducing the paste solution and for ejecting the paste solution is provided ahead of this. The paste valve 6 is for taking out the paste. A mesh sieve 7 for sieving was provided in the pressure vessel 2.

An embodiment of the present invention will be described with reference to FIG. 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. Then, commercially available hydrogen gas was introduced from the same valve 4 and pressurized 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. By repeating this hydrogenation and dehydrogenation three times, most of the hydrogen storage alloy 1 passed through the coarse metal mesh 3 and collected in the lower part of the pressure vessel 2. Then, the solution valve 5 is opened, and a small amount of a 5% (weight) solution of ethylene glycol as a paste solution is sprayed from the nozzle 8 to make the hydrogen storage alloy powder into a paste, and finally the paste valve 6 is opened to apply pressure. Container 2
I took it out from inside. In this case, the pressure vessel 2 is not provided with a mesh sieve 7 for sieving.

The paste thus obtained is further mixed in a weight ratio of 0.8
% Polyethylene fine powder, also 0.5% vinyl chloride-
Add acrylonitrile short fibers and knead to a thickness of 0.15 mm,
It was applied to a nickel-made punching metal plate made of iron having a hole diameter of 1.8 mm and a porosity of 50%, 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.

Then, after repeating hydrogenation and dehydrogenation three times as before,
As shown in FIG. 1, the pressure vessel 2 was vibrated and the finely divided hydrogen storage alloy powder was sieved with a 200-mesh mesh sieve 7. The powder that has passed through the mesh sieve 7 is sprayed with a 5% (by weight) ethylene glycol solution of polyvinyl alcohol from the nozzle 8 to make the hydrogen storage alloy powder into a paste, and finally the paste valve 6 is opened to press the powder. It was taken out of the container 2. The paste thus obtained was treated in the same manner to obtain a hydrogen storage electrode. The hydrogen storage electrode thus obtained is designated as electrode B.

For comparison, after hydrogenation and dehydrogenation, the sieve and the paste solution were replaced with argon gas without being sprayed and left for 20 hours, then the hydrogen storage alloy powder was taken out and then the paste solution or polyethylene fine powder was used. Was added and kneaded to obtain a hydrogen storage electrode 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 above-mentioned hydrogen storage electrodes was cut into a width of 3.9 cm and a length of 26 cm, and lead plates were attached to two predetermined places with a spot solution. 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 electrolytic solution, 30 g of lithium hydroxide in a caustic potash aqueous solution having a specific gravity of 1.30 /
1 was used after dissolution. The nominal capacity is 3.0 Ah.

These batteries are tested at 20 ° C by a normal charge / discharge cycle test.
The results evaluated in Section 2 will be explained.

Charge up to 130% 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-metal hydride rechargeable battery constructed by using the electrode A has a discharge capacity of 3.12 A at 100 cycles.
h, 300 cycles 3.11Ah, 600 cycles 3.10Ah, excellent life performance.

The battery composed of electrode B is 3.16Ah, 3 in 100 cycles.
The battery had superior performance to the battery composed of electrode A with 3.15 Ah at 00 cycles and 3.15 Ah at 600 cycles. Further, although the battery constituted by the electrode C initially satisfied the nominal capacity of 3.0 Ah, the discharge capacity of 2.81 Ah was only obtained in 100 cycles, and thereafter, the discharge capacity drastically decreased with the progress of the cycle. It was also found that the battery composed of the electrode C had a lower discharge voltage than the battery composed of the electrodes A and B.

The hydrogen storage electrode A and the hydrogen storage electrode A obtained by directly introducing the solution for paste and forming the hydrogen storage alloy powder into a paste after hydrogen storage and hydrogen release with hydrogen gas based on the charge and discharge test results that constituted such a battery were performed. After occluding and desorbing hydrogen with gas, the hydrogen-absorbing alloy powder is separated by sieving to separate only the effective alloy phase, and then the solution for paste is directly introduced to make the hydrogen-absorbing alloy powder into a paste. It was confirmed that the electrode B had excellent life performance.

That is, at this time, after hydrogenation and dehydrogenation, there is a step of separating only a portion where the fine powdering is insufficient, for example, by a sieving method or the like with a constant particle size of 100 microns or less Is preferred. That is, only the effective alloy phase selectively pulverized by sieving can be used, and the impurity phase in the alloy which is easily dissolved in the electrolytic solution can be separated as coarse particles. By the combination of both, that is, by introducing the paste solution directly into the sieve and this pressure vessel to make the hydrogen storage alloy powder into a paste, even a highly active hydrogen storage alloy powder is not poisoned by oxygen at all. It was found that it can be made into a paste, and the safety is improved as the performance is secured and the manufacturing method is rationalized.

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

First, the steps of hydrogenating and dehydrogenating hydrogen gas were three times in the examples, but it is preferable to perform the steps twice or more in terms of battery performance. As the paste solution to be used, ethylene glycol, ethylene glycol aqueous solution, carboxymethyl cellulose aqueous solution, polyvinyl alcohol aqueous solution, etc. are suitable. The particle size in the step of separating the particles with a constant particle size by sieving is preferably 100 μm or less.

Effects of the Invention As described above, the hydrogen storage alloy according to the production method of the present invention,
For example, when it is used for a hydrogen storage alloy negative electrode of an alkaline storage battery, it is possible to solve problems such as pulverization and oxidation, which have been problems so far, and prolong the service life.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a hydrogen storage electrode manufacturing apparatus using the hydrogen storage electrode manufacturing method of one embodiment of the present invention. 1 ... Hydrogen storage alloy, 2 ... Pressure vessel, 3 ... Coarse metal mesh, 4 ... Gas valve, 5 ... Solution valve, 6 ...
... paste valve, 7 ... mesh sieve, 8 ... nozzle.

Claims (5)

[Claims] 1. A hydrogen storage alloy is housed in a pressure vessel, hydrogenated with hydrogen gas and dehydrogenated to obtain fine powder, and then a paste solution is directly introduced into this pressure vessel to paste the hydrogen storage alloy powder. A method for producing a hydrogen storage electrode, characterized in that the obtained paste is filled in a porous conductor. 2. A hydrogen storage alloy is housed in a pressure vessel, hydrogenated with hydrogen gas, and dehydrogenated, and the fine powder is insufficiently removed by the hydrogenation and dehydrogenation. The method for producing a hydrogen storage electrode according to claim 1, wherein the hydrogen storage alloy powder is made into a paste by directly introducing the paste solution into the pressure vessel. 3. The method for producing a hydrogen storage electrode according to claim 1 or 2, wherein the steps of hydrogenation with hydrogen gas and dehydrogenation are performed twice or more. 4. A paste solution containing ethylene glycol,
The method for producing a hydrogen storage electrode according to claim 1 or 2, further comprising at least one selected from an ethylene glycol aqueous solution, a carboxymethyl cellulose aqueous solution, and a polyvinyl alcohol aqueous solution. 5. The step of removing only the part in which the fine powder is insufficient by hydrogenation and dehydrogenation is separated by a sieving method with a constant particle size, and the particle size of the powder used is 100 μm or less. The method for producing a hydrogen storage electrode according to claim 2, which is characterized in that.