JPS63175340A - Manufacture of hydrogen absorption electrode - Google Patents

Abstract

PURPOSE:To improve an absorptivity of an oxygen gas and make a long time stabilisation by applying an alkali treatment process, formation of a metal layer, and subsequent pressure press process to a hydrogen absorption electrode. CONSTITUTION:An electrode having a hydrogen absorption alloy layer is formed by filling hydrogen absorption alloy powders into a metal porous body, or applying them to both surfaces of the metal body. Next the electrode is submerged into an alkaline water solution, water washed, dried, and subsequently a metal layer is formed on the electrode plate surface. Then the electrode is composed by a pressure pressing. This allows first the alloy powder surface to be oxidized, and a thin oxide membrane formed. This results in a constraint of the oxidation progress to an alloy inside. Then an electronic conductivity can be improved and a gas absorption reaction of oxygen promoted by forming the metal layer on the electrode plate surface.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a method for producing a hydrogen storage electrode using a hydrogen storage alloy that reversibly stores and releases hydrogen in an electrolytic solution as a negative electrode material. This invention relates to a sealed nickel-metal hydride storage battery configured in combination with a positive electrode.

BACKGROUND ART Hydrogen storage alloys can be used as negative electrode materials for secondary batteries by electrochemically storing and releasing hydrogen. Among these, by selecting an alloy that is capable of absorbing and desorbing hydrogen at around room temperature and has a large amount of hydrogen storage and release, and using it as the negative electrode material, a hydrogen storage electrode that can discharge a large amount of electricity becomes possible. Therefore, by combining it with a nickel oxide positive electrode, for example, an alkaline storage battery with high energy density can be expected. Against this background, high-capacity storage batteries using hydrogen storage electrodes are attracting attention.

In this type of electrode, the corrosion resistance of the hydrogen storage alloy, the reduction in discharge capacity due to atomization during charging and discharging, and furthermore, in a sealed battery system combined with a nickel oxide positive electrode, the ability to absorb oxygen generated from the positive electrode during overcharging increases. There were problems such as a drop in battery pressure and an increase in battery internal pressure, which hindered its practical application.

Problems to be Solved by the Invention Since the above-mentioned problems remain in such conventional configurations, phenomena such as a decrease in cycle life and electrolyte leakage in sealed batteries have appeared. In order to solve these problems, the present invention improves the corrosion resistance of the alloy surface and further improves the oxygen gas absorption characteristics by forming a metal layer on the alloy surface with improved corrosion resistance. The purpose of this invention is to provide a battery that exhibits stable characteristics over a long period of time.

Means for Solving the Problem In order to solve this problem, in the present invention, a hydrogen storage alloy powder formed by filling a porous metal body with a hydrogen storage alloy powder or coating both sides of a porous metal body. The electrode is constructed by immersing the electrode with a storage alloy layer in an alkaline aqueous solution, washing with water, and drying it, then forming a metal layer on the surface of the electrode plate, and then pressurizing it. be.

Function: With this configuration, the surface of the alloy powder is first oxidized to form a thin oxide film. As a result, the alloy in the electrode is inhibited from being repeatedly charged and discharged, or from progressing into the interior of the alloy due to oxidation caused by oxygen generated from the positive electrode during overcharging.

Therefore, the decrease in discharge voltage and discharge capacity is reduced.

Next, by forming a metal layer on the surface of the electrode plate, the electron conductivity of the surface of the electrode plate is improved, the oxygen gas absorption reaction is promoted, and at the same time, direct contact between the alloy and oxygen is prevented. However, oxidation of the alloy is suppressed. Furthermore, by performing pressure pressing after forming the metal layer, it is possible to improve the binding force between the alloy layer and the metal layer, and at the same time, it is possible to increase the strength of the alloy layer and the metal layer, respectively.

Due to the above-described effects, the life of the negative electrode can be improved, and problems with the battery can be solved, thereby making it possible to create a battery with a long life.

Examples Lanthanum (La), nickel (N) with a purity of 99.6% or more
i) Mitsushi metal (Mm) with cobalt (Co), manganese (Mn), and rare earth element content of 98.5% or more
was used, and the alloy composition was La0.3 Mmo, 7Ni3.
Each metal was weighed to give 5 Co1.2 Mn0.3, and an alloy was produced using an arc melting furnace.

This alloy was heated in a vacuum heat treatment furnace at a temperature of 1 o 60° C. and a vacuum of 10 Torr or less, and heat treated for 6 hours. After cooling, it was ground into a powder of 400 mesh or less.

26 g of a 1.5% by weight aqueous solution of polyvinyl alcohol was mixed with 100 g of this powder to form a slurry paste. This paste was uniformly filled into a foamed nickel porous body (dimensions: 260 x 38 JIII, thickness: 0.97 IB) with a porosity of 94 to 96% and dried.

Thereafter, these electrode plates were heated to 60°C, washed with water, and dried. An electrode plate is manufactured with the above configuration, and then a metal layer of nickel, copper, and silver is applied to the surface of the electrode plate using a chemical plating method, a plating method, or a paste kneaded with an aqueous solution of metal powder and polyvinyl alcohol. Formed. Thereafter, pressure pressing was performed to obtain a negative electrode. For comparison, negative electrodes with no metal layer formed, negative electrodes with a metal layer formed after pressure pressing, negative electrodes with a metal layer formed without alkali treatment and pressure pressing, etc. were constructed. did. Detailed configuration conditions are shown in Table 1.

Table 1 Detailed configuration conditions of negative electrode Negative electrode Metal layer Metal Negative electrode configuration process Symbol Formation method
Type a -- Alkali treatment → Pressure breath b Electroplating Ni Alka Miri → 'M3U key pressure breath c
Ag d Cu e Cu Air plating → Pressure press f Ibi ≠ plating Ni Next, as a nickel oxide positive electrode, a foamed nickel positive electrode obtained by a known method (theoretical charging electricity amount 2970-30
The separator is made of polyamide non-woven fabric,
A 30% by weight caustic potassium aqueous solution containing 30 I/β of lithium hydroxide dissolved in the electrolyte was used, and in combination with the negative electrode AWK, a sealed nickel-sized AA size (C size) with a nominal capacity of 2.8 Ah was produced. Hydrogen storage batteries A to K were constructed.

These batteries were charged at a constant temperature of 20'C for the first cycle at 0.1C for 16 hours, and from the second cycle onwards
．． The cycle life of the battery was examined under charging conditions of 20 and 5 hours, and discharging was continued at a current of 0.20 until the final voltage o, sV. At the same time, a hole with a diameter of 1.5 mm was made in the bottom of the battery, a pressure sensor was attached, and pressure changes inside the battery were measured. The results are shown in Table 2.

Table 2 Negative electrode configuration conditions and battery characteristics The results show that in battery A using a negative electrode on which no metal layer was formed, the internal pressure of the battery increased by 15.7 KP/d i after 30 o cycles. Discharge capacity also decreased. In this test, the internal pressure was measured without the safety valve operating, but in an actual battery, the safety valve operates at around 1 ol'lP/d for safety reasons, and if the pressure reaches higher than this, the internal pressure is It is designed to emit. Therefore, in an actual battery system, it is thought that the capacity decrease will be even greater. On the other hand, B,
C.

In battery D, no increase in battery internal pressure was observed, and there was almost no decrease in capacity. Also, even when the type of metal formed was changed, there was no significant difference.
Forming a metal layer is considered to be effective in absorbing oxygen gas generated from the positive electrode during overcharging and preventing corrosion of the hydrogen storage alloy material.

On the other hand, in battery E using a negative electrode that omitted the alkali treatment step, an increase in battery internal pressure and a decrease in discharge capacity were observed, similar to the battery A described above, and the alkali treatment step is an important step in the present invention. I can say it.

F by changing the metal formation method and the type of metal formed
, G, H, I, and I also exhibited good charge-discharge characteristics, with almost no difference observed depending on the formation method or type of metal.

In the case of the battery K, in which the manufacturing process for the negative electrode was changed, as is clear from the comparison with the battery ①, there were differences in charging and discharging characteristics when a metal layer was formed after the pressure pressing process. . The reason for this is that the adhesion between the alloy layer and the metal layer is poor and the metal layer is not dense, which leads to a decrease in electronic conductivity and a decrease in the protective effect of the alloy, resulting in deterioration of gas absorption properties and a decrease in discharge capacity. This is thought to have led to the decline.

As described above in the Examples, the present invention provides a long-life hydrogen storage electrode.

Effects of the Invention As described above, according to the present invention, the hydrogen storage electrode is subjected to an alkali treatment process, the formation of a metal layer, and a subsequent pressure pressing process, thereby improving oxygen gas absorption characteristics and making it stable for a long period of time. At the same time, oxidation of the hydrogen storage alloy by oxygen can be suppressed, and an electrode with a long life can be provided.

In addition, in the example, an electrode was shown in which a foamed disokel porous body was used as the metal porous body and the inside thereof was filled with hydrogen-absorbing alloy powder, but an iron punching metal plated with nickel was used as the metal porous body. A similar effect was obtained with an electrode obtained by applying a paste mainly composed of alloy powder to both sides of the electrode.

Claims (3)

[Claims] (1) In a hydrogen storage electrode that uses a hydrogen storage alloy that reversibly stores and releases hydrogen as a negative electrode material, the electrode is constructed by filling the alloy powder into a porous metal body or coating both sides of the porous metal body. A method for producing a hydrogen storage electrode, which includes the steps of: immersing the electrode in an alkaline aqueous solution, washing with water, and drying; forming a metal layer on the surface of the electrode; and then pressing under pressure. (2) The method for manufacturing a hydrogen storage electrode according to claim 1, wherein the metal layer is one metal selected from the group of nickel, copper, and silver. (3) Claim 1 in which the metal layer is formed by chemical plating, electrolytic plating, or by applying a paste obtained by kneading metal powder, a binder, and a solvent.
The method for manufacturing the hydrogen storage electrode described in Section 1.