JPS63239771A - Paste-type hydrogen occluded electrode - Google Patents

Abstract

PURPOSE:To obtain a high capacity and to improve a high rate discharge property by making a hydrogen occluded alloy holding body with a foamy metallic porous body of copper, an alloy mainly of copper, or, nickel, iron, or the like coated with copper over its surface, and filling a paste mainly of a hydrogen storage alloy powder in this active material holding body. CONSTITUTION:This hydrogen occluded alloy holding body is formed of a foamy metallic porous body of copper, an alloy mainly of copper, or nickel, iron, or the like coated with copper, and an alloy powder or an alloy powder hydrogenated partially is filled in the hydrogen occluded alloy holding body. By applying an alloy powder holding body of a foamy copper, an alloy mainly of copper, or a metal coated with copper, the electron conductibility of the metal and in the three-dimensional directions is improved, and by contacting the copper and the hydrogen occluded alloy directly, a catalystic function to promote smoothly the hydrogen dissociation reaction to absorb and discharge in the alloy in an electrochemical reaction is improved. A nickel-hydrogen storage battery of a high capacity and an excellent high rate discharge property can be obtained consequently.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a paste-type hydrogen storage electrode for alkaline storage batteries that has a high capacity and is excellent in high-rate discharge customization by completely improving the current collector and active material of the hydrogen storage electrode. It is something.

Conventional technology Conventionally, this type of paste-type hydrogen storage electrode has been produced by placing a porous nickel material in the center and integrating it with alloy powder under pressure, or by making a paste and applying or filling both sides of the porous nickel material. A method is used in which electrodes are constructed using According to these methods, it is possible to pack the alloy powder at a high density, but they have the disadvantage of causing a decrease in discharge voltage due to large current discharge or a decrease in the active material utilization rate.

In order to solve this problem, methods have been proposed in which electronically conductive powders that are not directly involved in the reaction are mixed or a metal layer is formed on the surface of alloy powders (Japanese Patent Laid-Open No. 6F-1384
No. 59, JP-A-81-64069, JP-A-59-11
No. 4767).

However, such a configuration has a limit when filling the hydrogen storage alloy powder with high density. Therefore, in a hydrogen storage electrode filled only with a hydrogen storage alloy, it is desirable to lower the overvoltage during charging and discharging and to improve the active material utilization rate in order to increase the capacity.

Problem to be Solved by the Invention With such a conventional structure, there is a limit to the ability to form a paste-type hydrogen storage electrode that is capable of high-density packing of hydrogen storage alloy powder and has excellent high-rate discharge characteristics.

The present invention is intended to solve this problem, and aims to improve the high capacity and high rate discharge characteristics of a paste type hydrogen storage electrode.

Means for Solving Interlayer Points In order to solve all the interlayer points, the present invention proposes that the hydrogen storage alloy support is made of copper, an alloy mainly composed of copper, or a foamed material made of nickel, iron, etc. with copper plating on the surface. It is a porous metal body,
A hydrogen storage electrode is constructed by filling this hydrogen storage alloy support with alloy powder or partially hydrogenated alloy powder.

By applying foamed copper, copper-based alloys, or copper-plated alloy powder supports to metals, the electronic conductivity of metals and three-dimensional directions can be improved, and copper and hydrogen storage alloys can be improved. Direct contact with the alloy improves the catalytic action of the hydrogen dissociation reaction that is absorbed and released by electrochemical reactions in the alloy.

On the other hand, in the case of a completely sealed battery, in a nickel-cadmium storage battery, there is a difference in high rate discharge characteristics between the positive electrode and the negative electrode, so a discharge reserve is provided at the negative electrode, which has poor high rate discharge characteristics, that is, the cadmium electrode. . This configuration is designed to prevent a drop in battery voltage from occurring in the cadmium electrode, which has a large capacity drop when over-discharge is repeated. For this purpose, the cadmium electrode is usually chemically charged to transform it into a partially charged active material (discharge reserve).
It consists of a nickel electrode in a fully discharged state. In this chemical charging process, metal cadmium is formed by anodically polarizing the metal in an alkaline aqueous solution, followed by washing with water and drying. As a result, the copper comes into contact with the alkaline aqueous solution, and then the copper is corroded by washing and drying, which adversely affects battery characteristics? I'm going to call you.

Further, since the above-mentioned problems also exist in sealed nickel-metal hydride storage batteries, it is necessary to provide a discharge reserve. However, due to its high rate discharge characteristics, the capacity decrease is less than that of a cadmium negative electrode. Furthermore, a discharge reserve is formed by applying a positive electrode containing metallic cobalt to the nickel electrode. In other words, by mixing cobalt metal into the positive electrode, the cobalt metal changes into cobalt oxide and cobalt hydroxide during initial charging, and has the characteristic that it does not contribute to discharge, so only the amount of electricity that oxidizes the cobalt metal. The negative electrode will be charged in excess, and as a result, a discharge reserve will be formed. Therefore, from the above two viewpoints, it is possible to create a battery configuration in which chemical charging can be completely omitted in a sealed nickel-metal hydride storage battery. As a result, immersion in alkaline aqueous solution, washing with water,
This prevents the copper metal from being corroded by drying, thereby preventing any adverse effects on battery characteristics, and making it possible to use copper or a copper-based alloy as the support material for the alloy powder. Next, in Examples, the structure and effects of the present invention will be fully explained in detail.

Examples: Lanthanum (La) and nickel (Ni) with a purity of 99.6 cm or higher are used as alloy materials that completely absorb and release hydrogen.

Using cobalt (Go), manganese (Mn), and mischmetal (Mm) with a rare earth element content of cas, s 4 or more, the alloy composition is La (1,5Mm (1,5Ni)
Each gold gt was weighed to give 5,5Go + and 2Mnoj, and the entire alloy was prepared using an arc melting furnace.

This alloy was heat-treated at 1050° C. for 6 hours while keeping the vacuum level at 10 Torr or less.

After cooling, this alloy was mechanically pulverized into an alloy powder of 38 μm or less. In addition, two types of alloy powder were created by storing the alloy in a sealed container without pulverizing it, and occluding and releasing gaseous hydrogen. . A colored powder in which the former powder is used alone as a negative electrode material, a powder b in which 95 wt% of the former powder and Swt% of the latter powder are mixed are prepared, and alloy powder a which occludes no hydrogen at all and alloy powder a which occludes some hydrogen are prepared. Two types of B powder were prepared. Then, 25 f of a 1.5 wt % polyvinyl alcohol aqueous solution was mixed with 100 g of the powders a and b to form a slurry paste.

On the other hand, as an active material support that also serves as a current collector, a punched metal plate with holes of 2+1 ff in diameter and a center-to-center pitch of 2.6 H is coated on both sides of a 0.1 mm nickel plate and a copper plate. After wearing, it was passed through a slit, adjusted to a constant thickness, and dried. After that, pressure pressing is performed to obtain a thickness of 0.6
I made it my pole plate. In addition, an electrode plate having a thickness of 0.6 mm was prepared in the same manner using an active material support obtained by expanding a nickel plate and a copper plate. Further, a foamed porous body of nickel and copper is placed all around and press-fitted into the paster porous body, and after drying, pressure pressing is performed, and the thickness is 0%.
・I made it to 6 friends. The average pore diameter of the nickel, copper, and copper-plated foamed porous material used at this time was 150 μm.
The porosity is 94-96 inches, the average pore diameter is 7゜μ, and the porosity is 93-96 inches.
It was 94chi. Paste-type hydrogen absorption R electrodes were created using the nine types of active material supports and alloy powders shown above. These electrodes were cut into 260 x 38 pieces for evaluation in AA size sealed nickel-metal hydride storage batteries.

Next, a foamed nickel positive electrode obtained by a known method (theoretical photovoltaic capacity 2980~
3090mAh') and a polyamide nonwoven fabric as Separator L'-1 were arranged in the center and wound in a spiral shape with the hydrogen storage electrode. After inserting this into the metal case, as an electrolyte,
After injecting a 30 wt% potassium hydroxide aqueous solution containing 3 oy/1 lithium hydroxide, the cap was sealed and the nominal capacity was 2.8.
It formed a battery of people.

The type of active material support used in the hydrogen storage electrode of these batteries, the type of alloy powder, and the battery characteristics under the evaluation conditions described below were first evaluated.
Shown in the table.

(Hereinafter referred to as gold and white) Comparison of battery characteristics is at 20℃, under constant temperature, first cycle charging 6o, 1c for 16 hours, second cycle and subsequent cycles are all 0.
．． At 2C for 7.6 hours, the discharge continues until the 7th point with a current of 0.20 until the final voltage is 0.9V, and the 8th point is 30 discharges.
From the 9th point onward, all discharges were performed at 0.6C until the final voltage was 0.9V. At this time, the ratio of the intermediate voltage of the 7th and 8th points and the discharge capacity up to 1 V is shown in Table 1.

From these results, regarding the discharge voltage at 0-20,
The material of the active material support used in the hydrogen storage electrode.

No significant differences were observed depending on the morphology. However, 3C
There are significant differences in material and form in the discharge current,
The three-dimensional porous metal material had a higher discharge voltage than the planar porous metal material. Regarding the material, higher discharge voltage was shown when copper was used compared to nickel. Also, if it is actually used as a power source, it will be difficult to use it if it is less than 1V, so the final voltage should be set to 1V and the discharge capacity? 0.2
When comparing 0 and 3C, there was a large difference depending on the active material support. From the above results, the battery using the foamed porous material of the present invention, which is formed by copper plating on copper metal or nickel, as the active material support of the hydrogen storage electrode has little voltage drop during large current discharge, and is suitable for practical use. It can be said that it is effective as a power source.

On the other hand, one of the reasons why copper has not been put to practical use as an active material support material for alkaline storage batteries is said to be that dissolution and precipitation of copper during charging and discharging has a large adverse effect on battery characteristics. In order to investigate this negative effect, the changes in discharge capacity due to repeated charge/discharge cycles were calculated using F, H, and I in Table 1.
, J batteries and the results are shown in the figure. As is clear from the results, almost no adverse effects were observed compared to nickel, which is normally used as an active material support for alkaline storage batteries. H, J with decreased initial discharge capacity
The battery showed a negative potential rather than the normal hydrogen potential in a short period of time after the electrolyte was injected and before the first full charge, which is thought to be due to the dissolution of a small amount of copper. but,
The battery using partially hydrogenated alloy powder did not suffer from such problems and exhibited a stable cycle life. In the examples, foamed porous bodies made of copper metal and nickel plated with copper are shown, but foamed porous bodies made of copper-based alloys such as copper-chromium, copper-zinc, and copper-tin can also be used. Similar results were obtained. Therefore, the present invention is considered to be effective if the alloy is made mainly of wire mesh.

Effects of the Invention As described above, according to the present invention, copper has better electronic conductivity than nickel and has superior catalytic ability for the dissociation reaction with hydrogen stored in the hydrogen storage alloy, so high rate discharge characteristics are improved. It is thought that it was done. In addition, the effect was remarkable when the porous material was made into a foamed material. Furthermore, by mixing partially hydrogenated powder into the alloy powder, no deterioration in battery characteristics is observed during charging and discharging, making it possible to create a nickel-metal hydride storage battery with high capacity and excellent high-rate discharge characteristics. Effects can be obtained.

[Brief explanation of drawings]

The figure shows the cycle life characteristics of a sealed nickel-metal hydride storage battery using a pasted water storage electrode according to an embodiment of the present invention and a conventional method.

Claims (2)

[Claims] (1) The hydrogen storage alloy support has copper, a copper-based alloy, or a foamed metal porous body made of nickel, iron, etc. whose surface is plated with copper, and the hydrogen storage alloy powder is incorporated into the active material support. A paste-type hydrogen storage electrode characterized by being filled with a paste mainly composed of. (2) The paste-type hydrogen storage electrode according to claim 1, wherein a portion of the hydrogen storage alloy powder is an alloy powder that stores hydrogen.