JPS61233966A - Manufacture of sealed nickel-hydrogen storage battery - Google Patents

Abstract

PURPOSE:To prevent dissolution into electrolyte and decrease change of alloy composition and short circuit even after repeating charge-discharge by using an electrode obtained by forming a thin oxide film on the surface of hydrogen absorbing electrode as a negative electrode of sealed-hydrogen storage battery. CONSTITUTION:The surface of hydrogen absorbing alloy powder is converted into a metal compound which is stable in alkaline electrolyte, then this alloy is used as a negative electrode. Practically, by oxidizing the surface of the hydrogen alloy, its corrosion resistance is increased even after repeating charge- discharge in alkaline electrolyte. The oxide film is formed in a condition by which characteristics of hydrogen absorbing negative electrode is not decreased.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a sealed nickel-hydrogen storage battery comprising a hydrogen storage electrode that reversibly stores and desorbs hydrogen in an electrolytic solution and a nickel oxide positive electrode. This relates to a manufacturing method.

BACKGROUND ART Hydrogen storage alloys can be used as negative electrode materials for secondary batteries by electrochemically absorbing and desorbing hydrogen. Among these, by obtaining an alloy with a large amount of hydrogen storage and using it as a negative electrode material, a hydrogen storage electrode that can discharge a large amount of electricity becomes possible. Therefore, by combining it with a known nickel oxide positive electrode, an alkaline storage battery with high energy density can be expected. Furthermore, considering the market for alkaline storage batteries, it is desirable to use a completely sealed type, and the market for this is large. Against this background, sealed nickel-hydrogen storage batteries that use hydrogen storage electrodes and have a large discharge capacity are attracting attention. In this battery system, the corrosion resistance of the hydrogen storage alloy and the decrease in discharge capacity due to atomization during charging and discharging, and in the case of a sealed battery system, the ability to absorb oxygen generated from the positive electrode during overcharging decreases, resulting in an increase in battery internal pressure. There are problems such as causing problems, which are hindering practical application.

As a means to solve these problems, as a hydrogen storage alloy material, LnNi5. C! Alloys represented by LNi5 and alloys in which other metals are substituted for these alloys have been proposed, and hydrogen storage electrodes with excellent initial properties have become possible.

Problems to be Solved by the Invention A sealed nickel-hydrogen plate using the above-mentioned alloy or its substituted material as the negative electrode material of a hydrogen storage electrode.
Although a storage battery has satisfactory charging and discharging characteristics in the initial stage, repeated charging and discharging causes an increase in battery internal pressure and a decrease in discharge capacity during charging, resulting in a decrease in cycle life. Moreover, a short circuit of the battery may occur at the same time as this phenomenon is observed. These causes include a portion of the hydrogen storage alloy being eluted into the electrolyte, a change in the alloy composition, and precipitation of eluted metal within the separator.

The present invention addresses deterioration of battery characteristics caused by such causes, that is, a decrease in discharge capacity due to repeated charging and discharging.
This is an attempt to solve problems such as increases in battery internal pressure and short circuit phenomena.

Furthermore, the capacity of sealed nickel-hydrogen storage batteries is greater than that of normal sealed nickel-cadmium storage batteries during storage. One of the reasons for this is that the hydrogen storage electrode has a more active electrode surface than a cadmium electrode in a charged state, and the present invention aims to suppress this problem, that is, the decrease in storage capacity. It is something.

Means for Solving the Problems The present invention aims to improve the cycle life of sealed nickel-metal hydride storage batteries, prevent the occurrence of short circuits, and improve storage characteristics. By doing so, the purpose is to improve corrosion resistance even in an alkaline electrolyte during repeated charging and discharging, and to form an oxide film under mild oxidation conditions that do not impair the characteristics as a negative electrode material of a hydrogen storage electrode. Possible methods for forming this oxide film include a method of oxidizing the alloy powder, or a method of oxidizing the powder in the form of a paste when forming the powder into an electrode plate.

By using the electrode with a thin oxide film formed on the surface of the hydrogen storage electrode as the negative electrode of a fully sealed nickel-metal hydride storage battery, the negative electrode alloy becomes a stable substance and prevents dissolution into the electrolyte even after repeated charging and discharging. This reduces changes in alloy composition and short circuit phenomena. Further, by reducing the activity of the negative electrode surface, a reduction in storage capacity can be suppressed.

Examples Lanthanum (La) with Mi99.6% or more, nickel (Ni), =rbalt (Go), Mygan (Mn), mischmetal (Mm) with rare earth element content of 98.5% or more
, the alloy composition is 14.3M”0.71La
The metals were each weighed to give 5Mmo, 5Ni3, 5Go 1.5 , and alloys were prepared using an arc melting furnace.These alloys were ground into powder of 400 mesh or less. A portion of each alloy powder was then protected under the conditions shown in Table 1, and then dried to provide a negative electrode material. Other alloy powders were stored in an argon atmosphere. 25 g of a 1.5% by weight polyvinyl alcohol aqueous liquid was added to each of the 100.9 powders of these two types of hydrogen storage alloys having different holding conditions in total to form a slurry-like paste. These pastera foamed nickel porous bodies with a porosity of 93 to 96% (dimensions 260X38jffF thickness 1.0 g
) and dried. Thereafter, pressure pressing was performed to obtain a negative electrode.

In addition, using two types of hydrogen-absorbing alloy powders that had been stored in an argon atmosphere after pulverization, 2 sJ of a 1.6% by weight polyvinyl alcohol aqueous solution and 25.9 sJ of water were added to each 1001i to form a paste with a lower viscosity. Star 2
The alloy was oxidized by blowing air into it while stirring. Thereafter, it was uniformly filled into the above-described foamed nickel porous body and pressed under pressure to form a negative electrode.

Table 1 shows the types of alloys mixed above, the storage conditions of the powder, the manufacturing conditions of the negative electrode, the filling amount of the 9 alloys, etc.

(Left below) Next, as a nickel monoxide positive electrode, a foamed nickel electrode (dimensions: 214 x 38 iw, thickness: 0.2 mm) obtained by a known method is used.
64-0.68fl, theoretical light capacity 2310-2470
mAh ) i was used, the separator was a polyamide non-woven fabric, and the electrolyte was a 9M aqueous solution of potassium hydroxide with a specific gravity of 1.3 and lithium hydroxide 'k 20 ! A sealed nickel-metal hydride storage battery of AA size (C size) with a nominal capacity of 2.2 μm was used for the negative electrode using 1 to g6 shown in Table 1 for the negative electrode. fr was configured.

These batteries were charged at a constant temperature of 20°C under the first cycle charging conditions 'io, 16 hours at 1 G current, 7 hours at 0.2 G current from the second cycle, and all discharges at 0.20
Discharging was continued at a current of 0.9 V until the final voltage reached 0.9 V, and the cycle life of the battery was examined. Further, after the 10th cycle of charging was completed, the battery was left at a constant temperature of 45°C for 6 days, and its storage characteristics were examined. These results are shown in Table 2.

(Left below) From the results in Table 2, the following can be said. First, in the case of B, in which a battery was constructed with a negative electrode obtained by filling a foamed metal with powder that had been stored in an argon atmosphere after crushing a hydrogen storage alloy, there were slight differences depending on the type of alloy, but the storage Characteristics and charge/discharge cycle life are significantly reduced.

Capacity decreases after storage due to repeated charging and discharging, resulting in the formation of a battery system similar to when an alloy or metal is dissolved in an electrolytic solution and an impurity is mixed in. In addition, it is thought that storage characteristics deteriorate, that is, self-discharge becomes large due to factors such as increased activity on the surface of the negative electrode due to dissolution of alloys and metals.

The decrease in cycle life is due to changes in alloy composition due to metal melting,
A slight short circuit or even a complete short circuit due to precipitation of molten metal within the separator.

When deposited on the positive electrode, a decrease in discharge capacity was observed due to factors such as a decrease in charging efficiency and utilization rate of the positive electrode active material.

On the other hand, after pulverizing the alloy, in the powder state, Table 1 C~ was observed, and E-J has a storage property that is more effective in a short period of time than charging and discharging, and is also industrially advantageous. However, 100'
When the temperature is raised to a temperature higher than C, oxidation does not accumulate only on the surface, but also oxidizes the inside, and the alloy becomes an oxide. Therefore, the temperature may be adjusted within the range of 40 to 90°C and relative humidity of 30 to 90% for a time appropriate to the amount of powder.

Furthermore, after filling the alloy powder into the foamed nickel porous body and blowing air between the process of making the powder into a paste form, the battery was constructed from a negative electrode. Although the battery was stored in an argon atmosphere at room temperature, no deterioration in characteristics like that of batteries A and B was observed.

Based on the above, by holding the alloy powder under mild oxidation conditions, it is possible to form a highly corrosion-resistant inert layer on the surface of the alloy powder, that is, a thin film that does not inhibit the hydrogen storage electrode characteristics such as oxides and hydroxides. The melting of the alloy or metal that occurs due to repeated charging and discharging can be suppressed, and changes in the alloy composition can be suppressed.

It was found that the negative effect on the positive electrode active material was reduced, and the battery characteristics were improved.

In the example, as a manufacturing method of the negative electrode, an electrode in which a foamed nickel porous body is filled with a base if mainly composed of hydrogen-absorbing alloy powder is shown. Similar results were obtained with electrodes obtained by applying base coat to the base plate.

Effects of the Invention As described above, the present invention relates to a method for manufacturing a sealed nickel-hydrogen storage battery using a hydrogen storage alloy as a negative electrode material. It is expected that storage characteristics and cycle life will be improved, making it possible to provide highly reliable batteries.

Claims (4)

[Claims] (1) A method for manufacturing a sealed nickel-hydrogen storage battery using a hydrogen storage alloy as the negative electrode material and nickel oxide as the positive electrode material, in which the surface of the hydrogen storage alloy powder, which is the negative electrode material, is soaked in an alkaline electrolyte in advance. A method for manufacturing a sealed nickel-metal hydride storage battery, which comprises converting the negative electrode into a stable metal compound. (2) The method for manufacturing a sealed nickel-hydrogen storage battery according to claim 1, wherein the negative electrode is made of powder that is kept in an atmosphere containing at least oxygen and water vapor after pulverizing the hydrogen storage alloy. (3) Claim 1, wherein the negative electrode is made of powder held in air at a temperature of 40 to 90°C and a relative humidity of 30 to 90%.
A method for manufacturing a sealed nickel-metal hydride storage battery as described in . (4) The closed type nickel-hydrogen according to claim 1, wherein the negative electrode is manufactured by forming a paste with hydrogen storage alloy powder and an aqueous binder solution and blowing a gas containing at least oxygen into the paste. Method of manufacturing storage batteries.