JPH04319258A - Hydrogen storage alloy electrode - Google Patents

Abstract

PURPOSE:To obtain a hydrogen storage alloy electrode which can give the stable and high capacity even in a charge-discharge initial stage and is able to lessen the number of charge-discharge cycles necessary to activate initially. CONSTITUTION:Hydrogen storage alloy powder is immersed in and treated with hypophosphorus acid in the stage of either being powder or being formed in an electrode and thus an electrode formed.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hydrogen storage alloy electrode capable of electrochemically storing and desorbing hydrogen for use as a negative electrode of a secondary battery or the like.

0002

2. Description of the Related Art Conventionally, nickel-cadmium batteries and lead batteries have been well known as secondary batteries, but these batteries have the drawback of relatively low energy density per unit weight or unit volume. Therefore, we used an electrode made of a hydrogen storage alloy that can electrochemically absorb and release a large amount of hydrogen as the negative electrode, a nickel oxide as the positive electrode, and an alkaline aqueous solution as the electrolyte. Hydrogen batteries were proposed. The negative electrode here is L
In addition to aNi5, as an improved version, part of the Ni in LaNi5 was replaced with Co, Al, Mn, etc. to make it more diversified, and from an economical point of view, La was replaced with Mn (misch metal), which is a mixture of rare earth elements. Alloys are used. or,
Recently, the application of Laves phase AB2 type hydrogen storage alloys such as Zr-V-Ni has been proposed.

0003

Problems to be Solved by the Invention The improved hydrogen storage alloy described above has a relatively long cycle life, and the effects of improvement are recognized. However, these alloys generally have initial activation,
That is, charging and discharging must be repeated many times before a stable capacity can be obtained. Therefore, when a sealed nickel-metal hydride battery is manufactured by incorporating a hydrogen storage alloy electrode made of these alloys as a negative electrode, the battery capacity decreases because almost no capacity can be extracted from the hydrogen storage alloy electrode at the beginning of the charge/discharge cycle. There were problems such as the capacity being significantly lower than the rated capacity. Therefore, a hydrogen storage alloy electrode is desired that requires fewer charging/discharging times for initial activation and can provide high capacity from the beginning of the charging/discharging cycle.

0004

[Means for Solving the Problems] The present invention relates to a hydrogen storage alloy electrode that satisfies the above-mentioned requirements, and involves immersing a hydrogen storage alloy electrode prepared by a conventional method in hypophosphorous acid, or by immersing a hydrogen storage alloy electrode prepared by a conventional method. The electrode is constructed using hydrogen storage alloy powder that has been immersed in hypophosphorous acid.

[0005]

[Function] Although the function of the present invention is not clear, since the hypophosphorous acid is a reducing agent, it removes the oxide film formed on the surface of the alloy particles, increases the activity of the alloy, and uses the phosphorous acid to prevent oxidation. This is thought to be because it forms a film.

[0006]

[Example] Next, an example of the present invention will be described. Commercially available misch metal, nickel, cobalt, and aluminum powders were mixed at a predetermined composition ratio, for example, MmNi4.0Co0.5A.
They were weighed and mixed to give a total of 0.5 liters, and then heated and melted using an arc melting method to coarsely crush a hydrogen storage alloy ingot, which was then crushed in a ball mill or the like in an inert gas atmosphere to obtain a 250 mm It was made into a powder with a size smaller than mesh. Add 1 portion of carbonyl nickel powder as a conductive agent to this powder.
5wt. %, 5w of tetrafluoroethylene powder as a binder
t. % was added and mixed, and this was pressed onto a nickel wire gauze to produce a hydrogen storage alloy electrode. Add this electrode to hypophosphorous acid (
A hydrogen storage alloy electrode of the present invention was prepared by immersing it in a solution (concentration: 30%) for 1 hour at room temperature. Hereinafter, this will be referred to as the electrode of the present invention. For comparison, a hydrogen storage alloy electrode that was not immersed in hypophosphorous acid was prepared. This is called a reference electrode. The weight of the hydrogen storage alloy powder in each electrode is approximately 1
It is g. The above-mentioned electrode of the present invention and reference electrode were combined as working electrodes and a nickel plate as a counter electrode, and 30 wt. % potassium hydroxide aqueous solution was used to prepare open-type test cells. Using each of these test cells, the capacity that could be taken out during the first charge and discharge was confirmed. Further, charging and discharging were repeated, and the number of charging and discharging cycles required for the capacity to become stable was determined. Charging and discharging were carried out by charging each test cell at a current density of 6 mA/cm2 to 130% of the electrochemical hydrogen storage capacity of each hydrogen storage alloy electrode, and then at a current density of 10 mA.
At a current density of /cm2, the voltage of each hydrogen storage alloy electrode is -0
．． 75V vs. This was done by discharging until Hg/HgO. The above test results are summarized in Table 1 below.

[0007]

[Table 1]

As can be seen from the results in Table 1, the electrode of the present invention which is immersed in hypophosphorous acid has an increased initial discharge capacity and a lower initial activation cycle number than the untreated comparative electrode. Decrease. Such an effect is thought to be due to the fact that the alloy particles in the electrode are reduced and become highly active by the treatment with hypophosphorous acid of the present invention. Next, the polarization characteristics of the electrode of the present invention and the comparative electrode were measured. The measurement was performed using the potential scanning method at a scanning rate of 10 mV/Sec, and the range was -0.75 to -0.90.
V vs. It was carried out in the range of Hg/H/O. The relationship between potential and current at this time is shown in FIG. As can be seen from FIG. 1, the electrode of the present invention treated with hypophosphorous acid has significantly improved polarization characteristics compared to the comparative electrode not treated with hypophosphorous acid. In the above examples, the immersion pulverization treatment with hypophosphorous acid was performed at room temperature, but increasing the treatment temperature of the hypophosphorous acid is effective in shortening the treatment time. Furthermore, if the oxide on the alloy surface is easily reduced, hypophosphorous acid can be used diluted with water. When a secondary battery of AA size 1000 mAh was produced using the above electrode of the present invention, a capacity satisfying the rating could be obtained from the first charge/discharge. In the above example, a hydrogen storage alloy electrode was prepared by a conventional method, and then the electrode plate was immersed in hypophosphorous acid. At the stage of hydrogen-absorbing alloy powder obtained by pulverizing coarse powder of alloy ingot, it is immersed in hypophosphorous acid, washed with water, and after drying, this hypophosphorous acid-treated alloy powder is used. When the hydrogen storage alloy electrode was prepared using a conventional method in the same manner as above, the same effect as above was obtained. Although this drying step was carried out at 60° C. for several hours, the alloy powder remained stable without oxidation or ignition. The reason for this is thought to be that a nickel-phosphoric acid anti-oxidation film is formed on the surface of the alloy powder. In addition to the above-mentioned Mm-Ni alloy, hydrogen storage alloys to be treated by the present invention include Zr-Ni, Ti-Ni,
La-Ni, a part of Ni in La-Ni is Co, Al, M
Multi-component alloys made by substituting n, etc., Ti-Zr-Ni, Zr
-V-Ni type, Ti-Fe, etc. are mentioned.

[0009]

[Effect of the invention] Manufactured using a hydrogen storage alloy electrode manufactured by a conventional method and immersed in hypophosphorous acid, or a hydrogen storage alloy powder manufactured by a conventional method and immersed in hypophosphorous acid. The hydrogen-absorbing alloy electrode has high activity and oxidation resistance, so it can reduce the number of charge/discharge cycles required for initial activation, and has the effect of obtaining stable high capacity from the initial stage of charge/discharge. .

[Brief explanation of drawings]

FIG. 1 shows a comparison graph of polarization characteristics between an electrode of the present invention and a comparison electrode.

Claims (2)

[Claims] Claim: 1. A hydrogen storage alloy electrode obtained by immersion treatment in hypophosphorous acid. 2. A hydrogen storage alloy electrode constructed using hydrogen storage alloy powder immersed in hypophosphorous acid.