JPS61233968A - Manufacture of hydrogen occlusion electrode - Google Patents

Abstract

PURPOSE:To provide steady performance over a lengthy period by applying a chemical plating to hydrogen occlusion alloy in which hydrogen is somewhat occluded to form an alkali resistant protective layer, then producing an electrode with this alloy powder. CONSTITUTION:Hydrogen occlusion alloy is held in a hydrogen atmosphere having higher pressure than its dissociation equilibrium pressure to allow to occlude 0.1 or more of hydrogen in H/M. The H/M shows a ratio of the number of hydrogen atoms to the number of metal atoms constituting one mole of hydrogen occlusion alloy. Then plating film is formed on the alloy by chemical plating. By applying chemical plating to the alloy in which hydrogen is occluded, not only Ti-Ni type alloy having relatively high corrosion resistance in acid and alkaline solutions but also LaNi4.7Al0.3 alloy having relatively low corrosion resistance in acid solution provides steady discharge performance over a lengthy period compared with conventional hydrogen occlusion alloy to which chemical copper plating is applied.

Description

[Detailed Description of the Invention] , Technical Field The present invention relates to a hydrogen storage alloy electrode used as a negative electrode of an alkaline secondary battery, and in particular to a hydrogen storage alloy electrode whose characteristics are stabilized by coating the hydrogen storage alloy with a highly corrosion resistant metal. The present invention relates to a method for manufacturing an electrode.

<Prior Art> A MeOx-Me'HY type blue battery using a metal oxide as a positive electrode active material and a hydrogen storage alloy as a negative electrode active material has been proposed and is being put into practical use. As a positive electrode active material,
Ni is used as the positive electrode of conventional alkaline storage batteries.
00H, Ag2O, etc. are considered suitable, and qLaNi5. Hydrogen storage alloys such as Ti2Ni whose hydrogen equilibrium dissociation pressure at room temperature is lPa73n or IMPa have been studied.

In order to create an electrode using a hydrogen storage alloy as an active material,
The following steps are required.

+11 Production of hydrogen storage alloy with arbitrary composition (21
Mechanical pulverization of alloy ingots (31) Micronization of hydrogen storage alloys by hydrogen activation treatment (4)
) Coating the hydrogen storage alloy with a metal having hydrogen permeability and excellent alkali resistance (5) Supporting on the current collector Among these series of steps, the operation step (4) is shown in more detail below. Divided into operations.

(i) Sensitization of the surface of alloy powder particles (iil Activation of alloy powder particles) Electroless plating operation (fil) involves reacting hydrogen-absorbing alloy powder in an acidic solution of tin chloride!Il + hydrochloric acid. Palladium chloride (Il + reacted in an acidic solution of hydrochloric acid).

However, when the hydrogen storage alloy is subjected to the above operations (i) and (11), the corrosion resistance against acids or alkalis becomes better.

There is a risk that a part of the alloy will corrode and the hydrogen storage and release properties inherent to the alloy will be significantly impaired. Further, a situation may occur in which electroless plating is not completely performed.

Furthermore, since palladium chloride, which is extremely expensive, is used, there are problems in terms of cost and the like when putting it into practical use.

<Purpose of the Invention> The present invention provides a manufacturing technology for a hydrogen storage electrode that prevents a decrease in discharge capacity due to repeated charging and discharging processes of an electrode using a hydrogen storage alloy, and provides stable characteristics over a long period of time as an alkaline secondary battery. The purpose is to provide

<Summary of the Invention> In order to achieve the above object, the present invention is made by placing a hydrogen storage alloy that has been pulverized and has a uniform particle size in a pressure-resistant reaction vessel, and performing an activation treatment by introducing high-pressure hydrogen gas and evacuation. The alloy powder is immediately immersed in a pre-prepared electroless plating solution and stirred to form a protective layer with excellent alkali resistance and coated with the alloy powder. A feature of this method is that the electrodes are made using alloy powder. Examples of substances used as hydrogen storage alloys include Ca, Mg, Ti, and Zr.

Elements that easily bond with hydrogen, such as Hf, V, Nb, Ta, Y, or lanthanide elements, and A, Cr, and Fe.

Generally, materials are alloyed with elements that are difficult to bond with hydrogen, such as Ni, Co, Cu, Mn, and Si.

According to the present invention, the hydrogen stored in the activated hydrogen storage alloy acts as a reducing agent, and the corrosion-resistant metal ions in the electroless plating can be easily reduced and bent into the alloy surface. This reaction is thought to be as shown in the following equation.

xCu”+Me t a 1 :Hy+xCu+Me
ta 1+yl ("Here, Me t a l represents a hydrogen storage alloy.

By the way, conventionally, even if vacuum degassing is performed at high temperature after hydrogen activation treatment, hydrogen is not completely released from the hydrogen storage alloy, and a very small amount remains as a very stable hydride. ing. (It is thought that H/M' is less than 50.1.) However, even if electroless plating was performed in this state, no plating was performed. Experiments have confirmed that in order to form a plating film, it is necessary to use a hydride having a hydrogen content of at least H/M-0.1 or more. The present invention maintains a hydrogen storage alloy in a high-pressure hydrogen atmosphere higher than its equilibrium dissociation pressure, so that the hydrogen storage alloy has a VM of 0.
It is possible to cover with a plating film by absorbing at least one amount of hydrogen and then performing an electroless plating treatment.

Here, the ratio between the number of H/Mri hydrogen atoms and the number of metal atoms constituting one mole of the hydrogen storage alloy is expressed.

<Example> Below, as an example of the present invention, hydrogen storage alloys L, a
Ni,. , /IJ. , 3 alloys will be explained in detail.

Commercially available lanthanum (purity 99.5%), nickel (purity 9
9.51) and aluminum (purity 99.5%) were weighed so that the stoichiometric ratio was 1:4.7:0.3,
Mix evenly. This mixed powder is pressed into a single granule, which is arc melted in an argon atmosphere to obtain an alloy ingot. This dissolution operation is performed three times from the front and back screens to measure the uniformity of the sample. This alloy ingot was placed in a stainless steel pressure-resistant reaction vessel, evacuated at room temperature using a vacuum evacuation device, and heated to 200°C using an electric furnace while high-pressure hydrogen (purity 99.9999)
9%) was introduced to create a hydrogen atmosphere in one reaction vessel to remove the oxide film etc. adhering to the alloy surface, and then the vacuum was evacuated again to perform degassing.

Next, 3 MPa of hydrogen is introduced at that temperature, and hydrogen is occluded by allowing it to cool to room temperature. After the hydrogen storage process is completed, vacuum degassing is performed again at high temperature. By repeating this hydrogen storage/release operation 5 to 6 times, a hydrogen storage alloy powder is obtained.

This is further mechanically pulverized to obtain an alloy powder with a particle size of 75 μm or less. When used as an electrode coated with a corrosion-resistant material, the particle size is desirably 75 μm or less.

The alloy powder obtained as described above is put into the reaction vessel again and subjected to hydrogen activation treatment by repeating the hydrogen storage and release operation 2.3 times. After being kept in a high pressure hydrogen atmosphere,
Open to the atmosphere at 200℃.

Immediately after occluding a certain amount of hydrogen, the powder is immersed in an electroless plating bath prepared in advance, and electroless copper plating is applied to the alloy powder No. 1. In this case, the thickness of copper plating on one alloy is approximately 0.5 μm. The copper plating layer has hydrogen permeability and has excellent alkali resistance.
When used as an electrode, it forms a protective layer for the hydrogen storage alloy powder. These two protective layers are made of copper (Cu).
other than.

Nickel (Ni), silver (Ag), etc. may also be used.

LaNi47A with copper plating! A punched nickel plate is filled with 03 alloy and compression molded at 2.5 t/m'' to produce a hydrogen storage electrode.

The hydrogen storage electrode produced as described above was repeatedly charged and discharged at a current of 0.2 C using a two-electrode method in an electrolytic cell.

The change in discharge capacity at this time is shown in the drawing by curve aA. It is recognized that the discharge capacity did not decrease at all even after 50 cycles.

For comparison, hydrogen was released after pulverization by repeated hydrogen storage and release operations.

A punched nickel plate was filled with alloy powder coated with copper by a method of sensitization treatment in an acidic solution and activation treatment followed by immersion in an electroless plating bath.
/(to) 2 to produce a hydrogen storage electrode. Curve B in the drawing shows the change in discharge capacity when this hydrogen storage electrode was repeatedly subjected to charging and discharging operations similar to those in the above example. In addition, in the same manner, a punched nickel plate was filled with the alloy powder before the step (4) of the above manufacturing process, that is, before electroless plating was applied, and compression molded at 2.517 am'' to produce a hydrogen storage electrode. The same charging and discharging operation as in the above embodiment was repeated for the hydrogen storage electrode, and the change in discharge capacity at that time is shown by curve C in the drawing.

The discharge capacity of curve B was % or less compared to curve A, and this is thought to be because a portion of the hydrogen storage alloy corroded due to the use of an acidic solution as a pretreatment for electroless copper plating. Further, curve 1 C#: tThe capacity gradually decreases after about 30 charging and discharging operations. On the other hand, the hydrogen storage electrode obtained in the above example has a high curve 1:I discharge capacity and exhibits stable characteristics with no decrease in discharge capacity with repeated cycles.

<Effects of the Invention> The electroless plated hydrogen storage electrode obtained by the manufacturing method of the present invention has T1-N which is relatively corrosion resistant to acids and alkalis.
LaNi47A, which has a corrosive power of 5, especially when used with acids, etc. Even when 3 is used, the electrode characteristics are the same or better than the conventional hydrogen storage electrode with electroless copper plating, and it shows much better I/I characteristics, and can be charged for a long time. Even if the discharge operation is repeated, the discharge capacity does not decrease, and stable discharge characteristics can be obtained.

Since it can be applied to hydrogen storage alloys that are corrosive to acids and alkalis, it can be used for all hydrogen storage alloys, and the hydrogen storage electrode produced by the present invention can be used for all hydrogen storage alloys. It is effective as a negative electrode for alkaline storage batteries, and can maintain stable battery characteristics over a long period of time.

[Brief explanation of the drawing]

The drawing is a characteristic diagram showing the discharge characteristics of hydrogen storage electrodes produced under various conditions as the charge/discharge cycle dependence of the discharge capacity per hydrogen storage alloy IP.

Claims (1)

[Claims] 1.Hydrogen storage alloy is held in a high-pressure hydrogen atmosphere above its equilibrium dissociation pressure, and the hydrogen storage alloy is heated such that the number of hydrogen atoms absorbed is 0.1 or more per mole of metal atoms constituting 1 mole of hydrogen storage alloy. 1. A method for manufacturing a hydrogen storage electrode, which comprises, after occluding atoms, coating the hydrogen storage alloy with a plating protective layer to form an electrode.