JPH0763008B2 - 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 represented by nickel-cadmium storage batteries are widely used as secondary batteries among various power sources.

In recent years, expectations for high energy density have increased,
Therefore, what has recently attracted attention is a secondary battery such as nickel-hydrogen using a hydrogen storage alloy that stores and releases hydrogen reversibly.

This hydrogen storage electrode can be configured in the same way as cadmium and zinc to form a battery, and the actual dischargeable capacity density can be made larger than that of cadmium, and there is no formation of dendrite like zinc or change in electrode shape. It is promising as a non-polluting alkaline storage battery with high energy density and long life. Therefore, a sealed nickel-hydrogen secondary battery using this hydrogen storage electrode as a negative electrode and a nickel electrode used in a nickel-cadmium storage battery as a positive electrode has been actively researched and developed.

By the way, one of the problems of this sealed nickel-hydrogen secondary battery is that the capacity of the negative electrode is low in the initial discharge, and the discharge capacity gradually increases by repeating the charge and discharge cycle,
After that, it will be constant. This phenomenon was a general phenomenon although there were some differences depending on the type of alloy used for the hydrogen storage electrode.

It is considered that this phenomenon occurs because the charging efficiency of the negative electrode is insufficient at the beginning of the charge / discharge cycle. This phenomenon changes the capacity balance in the battery and impedes the high energy density and long life characteristics that the battery originally has.

Until now, there is no effective way to solve this phenomenon. Generally, it is conceivable that the hydrogen storage electrode is subjected to electrochemical charging / discharging in advance in an electrode plate state (generally referred to as electrode plate formation), and then a battery is constituted by the electrode plate. However, in this method, since the hydrogen storage electrode is very active, the hydrogen storage alloy easily oxidizes during battery construction, leading to a decrease in capacity, and the hydrogen storage alloy repeatedly expands and contracts due to charge and discharge. Problems such as falling off from the electrode plate, causing a decrease in capacity, high risk of ignition, etc., and performing treatments such as charging / discharging, washing, and drying complicate the manufacturing process. It is problematic and not always effective.

Also, Japanese Patent Publication No. 60-40668 has already proposed to use a fine powder obtained by hydrogenating and dehydrogenating a hydrogen storage alloy for a hydrogen storage electrode.

Problems to be Solved by the Invention However, if this hydrogenation and dehydrogenation is performed only with the hydrogen storage alloy before it was made into the electrode together with the binder and the conductive agent, the electrode becomes chemically active. Since it was too much, problems such as powder handling and manufacturing complexity remained in the subsequent electrode manufacturing.

It is an object of the present invention to provide a hydrogen storage electrode which does not cause such a phenomenon and can obtain a stable discharge capacity from the initial charge / discharge cycle.

Means for Solving the Problems The present invention provides a method for producing a hydrogen storage electrode, which comprises producing an electrode using a hydrogen storage alloy and then storing and releasing hydrogen at least once in hydrogen gas. is there. And the electrode using the hydrogen storage alloy is preferably a paste type.

Action As a measure to improve the initial charging efficiency of electrodes using hydrogen storage alloys, it was found that hydrogen storage by hydrogen gas and hydrogen release are effective as chemical conversion treatment of electrodes as well as electrochemical charging and discharging. In that case, the acceptability for charging can be improved by producing an electrode using a normal hydrogen storage alloy and then storing and releasing hydrogen in the hydrogen gas at least once, if possible, by repeating the electrode. As a result, when a battery is constructed using this electrode thereafter, a stable discharge capacity can be obtained from the initial stage. And the electrode using the hydrogen storage alloy is preferably the paste type as compared with the sintering type.

Examples Examples of the present invention will be described below.

Commercially available raw materials of Zr, Mn, Cr, Co, and Ni as hydrogen storage alloys were weighed to a constant composition ratio, and were measured by an argon arc melting furnace.
An alloy having a composition of ZrMn _0.6 Cr _0.2 Co _0.2 Ni _1.0 was produced. Then, this alloy was heat-treated in a vacuum heat-treatment furnace according to a known method, and further powdered to 100 μm or less by usual mechanical pulverization.

This hydrogen-absorbing alloy powder was made into a paste with a 3% by weight aqueous solution of polyvinyl alcohol, filled into a foamed nickel porous body having an average pore size of 150 microns and a porosity of 95%, then dried, and pressed to have an average thickness of 0.55 mm. An electrode was obtained.

Then, this hydrogen storage electrode was placed in a pressure-tight container made of stainless steel that was capable of being sealed, and the inside of the container was vacuum degassed, and then hydrogen gas was introduced to maintain the pressure at about 30 atm. It was possible to observe that after a while in this state, the hydrogen storage alloy causes a hydrogen storage reaction, and the hydrogen gas pressure in the container decreases. Next, when the hydrogen gas pressure in the container was forcibly reduced, it was confirmed that hydrogen was being released by the hydrogen releasing reaction. After repeating hydrogen absorption and desorption by pressurization and depressurization four times, the surrounding atmosphere was replaced with argon gas.

Next, the hydrogen storage electrode thus obtained was actually configured as a sealed nickel-hydrogen secondary battery, and the evaluation results will be described.

First, the hydrogen storage electrode was cut into a width of 3.9 cm and a length of 26 cm, and lead plates were attached to two predetermined places by spot welding.
Then, it was stored in a C-sized battery case in combination with the positive electrode and the splatter. As the positive electrode at this time, a known foaming nickel electrode was selected 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. A polyamide non-woven fabric was used for the separator.

Then, add lithium hydroxide to a caustic potash solution with a specific gravity of 1.20.
30 g / L of the dissolved electrolyte was injected. Next, the battery was completely sealed with a cap for sealing. The nominal capacity is 3.0 Ah. A battery using this electrode according to the present invention is designated as A.

For comparison, as a conventional example, a battery obtained by omitting only the steps of storing and releasing hydrogen with hydrogen gas in the previous steps was used as B, and hydrogen was replaced with hydrogen instead of the steps of storing and releasing hydrogen with hydrogen gas. The occlusion electrode was electrochemically charged and discharged 4 times in an aqueous caustic potash solution having a specific gravity of 1.20, and then a battery, which was similarly sealed as a positive electrode, a separator and an electrolytic solution, was added as C.

The results of a charge / discharge test performed on these batteries at 20 ° C. will be described.

Charging was carried out at 0.1 C (10 hour rate) for 15 hours, discharging was 0.2 C (5 hour rate) at a final voltage of 0.9 V, charging / discharging was continued, and the relationship between the charge / discharge cycle and the discharge capacity was obtained. The results are shown in the figure.

From the figure, in the battery B shown in the conventional example, in the initial stage, the discharge capacity gradually increases with the lapse of cycles, becomes saturated in about 30 cycles, and then becomes constant at about 3.0 Ah. It can be seen that the battery A according to the manufacturing method of the present invention has a stable discharge capacity from the initial stage, and the problems thus far solved. In addition, although the initial discharge capacity of Battery C has improved considerably,
Due to the dropout and oxidation of the alloy, the capacity did not reach the nominal capacity of 3 Ah, and the capacity decreased from around 15 cycles as the cycle progressed. It is expected that Battery C probably lacked the capacity of the negative electrode.

Regarding the service life, Battery A maintained a stable discharge capacity even after 300 cycles, but Battery B showed a decrease in discharge capacity from around 220 cycles.

In addition to the pasted electrode, the same evaluation was performed for the sintering type. In this case, the result was almost the same as the paste formula, but the difference was more remarkable in the paste formula.
Further, the hydrogen storage alloy was previously hydrogenated and dehydrogenated with hydrogen gas to obtain fine powder, which was then similarly used as an electrode, and a battery was constructed and evaluated. In this case, in C of the previous example, The result was almost the same as that of the battery.

Effects of the Invention As described above, according to the method for manufacturing a hydrogen storage electrode of the present invention,
The initial discharge capacity, which has been a problem up to now, is improved by a relatively easy method by absorption / desorption of hydrogen gas, and it is possible to obtain a stable discharge capacity from the initial charge / discharge cycle and to extend the life. .

[Brief description of drawings]

The figure is a comparison diagram of the battery discharge capacities in the initial charge / discharge cycle of the sealed nickel-hydrogen secondary battery composed of the hydrogen storage electrodes by various manufacturing methods. A: batteries according to the embodiments of the present invention, B, C ... batteries according to conventional examples.

Claims (2)

[Claims] 1. After forming an electrode using a hydrogen storage alloy,
A method for producing a hydrogen storage electrode, which comprises storing and releasing hydrogen at least once in hydrogen gas. 2. The method for producing a hydrogen storage electrode according to claim 1, wherein the electrode using the hydrogen storage alloy is of a paste type.