JPS609059A - Manufacture of positive pole plate for alkaline storage battery - Google Patents

Abstract

PURPOSE:To generate efficiently the reducing reaction of cadmium for checking the generation of hydrogen even when a battery reaches an overdischarge state by impregnating independently cadmium salt in addition to the impregnation of nickel salt. CONSTITUTION:The impregnating operation of nickel salt to become a positive pole active substance and the impregnation of cadmium salt as the overdischarge countermeasures are independently performed. For instance, a cadmium nitrate water solution is firstly impregnated into a sintering type substrate having a porosity degree of about 80% when sintering nickel powder while being neutralized in a sodium hydroxide water solution after being dried for performing the impregnating operation to be dried again and secondly for being impregnated in the water solution mainly composed of nickel nitrate followed by being neutralized in the sodium hydroxide water solution after being dried for being dried again, that is to say that the impregnating operation of nickel salt is repeated five times.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing a positive electrode plate for an alkaline storage battery, which is made by impregnating a nickel salt into a so-called sintered substrate made of sintered nickel powder. However, by impregnating cadmium salt alone in addition to impregnating nickel, even if the battery reaches an overdischarge state,
The purpose is to make it possible for the 37-element reaction of cadmium to occur efficiently and to prevent the generation of hydrogen. Among alkaline storage batteries, sealed alkaline storage batteries are designed to prevent negative effects such as overcharging (such as an increase in battery internal pressure) by using an excessive amount of active material on the positive electrode to terminate charging of the positive electrode. The negative electrode absorbs the oxygen generated later, preventing the internal pressure of the battery from rising, and also eliminating the consumption of the electrolyte.On the other hand, when the battery reaches an overdischarge state, hydrogen is removed from the positive electrode. However, oxygen is generated from the negative electrode.In particular, when hydrogen is generated from the positive electrode, it is hardly absorbed within the battery, so as over-discharge progresses, the internal pressure of the battery rises abnormally and battery 1 (It is known to impair one's ability.

In order to prevent harmful overdischarge, a method has conventionally been adopted in which when the discharge voltage drops to a certain level, the voltage is detected and the discharge is automatically stopped. However, this method requires complicated equipment.

In addition to being expensive, when a large number of cells are connected in series, there is inevitably a difference in capacity between the cells, and there is a risk that batteries with relatively small capacities will over-discharge. No matter what methods we tried, it was unavoidable.

From the above points, the ideal sealed alkaline storage battery is:
All you have to do is create a battery that will not malfunction even if it is over-discharged (and will return to normal after being recharged again.There are several ways to do this, but to make it happen, please use the following method). I was in trouble.

One method is to provide a gas absorption electrode inside the battery and recover oxygen and hydrogen generated during over-release.

However, this method uses expensive precious metals as catalysts,
(It is complicated, wasteful, and not common.

The other method is to mix cadmium hydroxide into the positive electrode active material, so that even if the battery is over-discharged, the cadmium hydroxide in the positive electrode active material undergoes a reaction to become metallic cadmium, and hydrogen is generated. This is a way to prevent this. The positive electrode used in this method is made using the hemlock method, which involves repeating an impregnation process in which cadmium salt is mixed into an aqueous nickel salt solution that serves as the positive electrode active material, impregnated into a sintered substrate, dried, and neutralized. However, in this method, the utilization rate of cadmium was very poor during overdischarge, and it was necessary to mix a large amount of cadmium in order to make it work effectively.For this reason, the content of nickel salt had to be reduced. As a result, the discharge capacity (2) as a positive electrode slightly decreased, making it impractical.

The present invention relates to a cadmium impregnation method for preventing hydrogen generation in a positive electrode as a countermeasure against overdischarge, as explained above.
This invention relates to a manufacturing method for obtaining a positive electrode plate for an alkaline storage battery that eliminates the drawbacks caused by the above method and has the desired performance as a countermeasure against overdischarge.

That is, instead of the conventional method of adding cadmium salt to an aqueous nickel salt solution as an impregnation liquid and impregnating it into the positive electrode substrate at the same time, an operation of impregnating nickel salt, which will become the positive electrode active material, is performed.
It is characterized by separately impregnating with cadmium salt as a countermeasure against overdischarge. A detailed explanation will be given below based on the examples.

Sintered nickel powder, porosity approximately 80%, thickness 0.7
For the sintering type J of mn+, an impregnation operation is performed in which the material is first impregnated with a cadmium nitrate aqueous solution, dried, neutralized in a 1-lium hydroxide aqueous solution, and dried again, and then nickel nitrate is used as the main component. The positive electrode plate A according to the present invention was obtained by repeating the nickel salt impregnation operation five times, in which the positive electrode plate A was impregnated with a nickel salt aqueous solution, dried, neutralized in a sodium hydroxide aqueous solution, and dried again. Next, the same substrate as A was impregnated with 78 liquid mixed water of nickel nitrate and cadmium nitrate containing 20% of cadmium nitrate to nickel nitrate, dried at 1 g/water, then neutralized in an aqueous sodium hydroxide solution, and dried again. A positive electrode plate B was produced by the manufacturing method d1 of sub)K obtained by repeating the impregnation operation 6 times, and the positive electrode plate B was tested under the following conditions and the performance was compared. The content of nickel hydroxide and cadmium hydroxide in these A and B electrode plates was adjusted to be the same.

First, in a 6moj potassium hydroxide aqueous solution, add a 2 liter domium electrode to the other electrode to a sufficient capacity.
After charging between cut XlGll, 4m△/c
When discharging at IIT, the results shown in Table 1 were obtained.

Possible overdischarge amount due to the reaction of cadmium in the overdischarge area (
01 (01-1) 2 'When H2 is generated by the reaction of α, J
The positive electrode plate manufactured by the manufacturing method of the present invention has a positive capacity of 6 mΔ11/cot b, but the positive electrode plate manufactured by the conventional manufacturing method has a positive capacity of only 1.5 mA h/a.
n? It can be seen that the utilization rate of cadmium is very small. Note that the capacity of the positive electrode was almost the same as that of the positive electrode according to the present invention or the conventional method.

Table 1. Results of Discharge Test M Next, cylindrical 1.8 At+ batteries were made using positive electrode A according to the present invention and positive electrode B according to the conventional method, and their performance during overdischarge was compared. The test is 0. FIG. 1 shows the results of comparing overdischarge characteristics obtained by charging with a current of IOA for 1 G hours and then discharging with a current of 0.2 CA. In the normal discharge region up to OV, both △ and B have almost the same characteristics, but the polarity reversal (OV
(Below) When the overdischarge condition begins, B has some cadmium effect, but the voltage immediately drops to -0.2 Vl, which indicates hydrogen generation, and at the same time the internal pressure rises abnormally. - It is clear that in Battery No. 8 using the positive electrode manufactured by Rikiki's invention, cadmium acts effectively for more than one minute after polarity reversal, delaying hydrogen generation in the overdischarge region.

In the previous example, the method of impregnating with cadmium salt for the first time and then repeating the impregnation with nickel salt was described, but impregnation with domium salt is not limited to the first time, and even after impregnating with nickel salt. , or impregnated with nickel salt several times, even in the middle of the process, the same effect as f1 was obtained.

Compared to the conventional method of adding cadmium to the nickel salt of the impregnating solution to impregnate nickel and cadmium at the same time, the method of adding cadmium to the positive electrode is based on the present invention, in which cadmium Ju is impregnated separately from the nickel salt. The reason why the positive electrode has a much greater effect on J3 during overdischarge is not known, but it is thought to be due to the close arrangement of Jj4 nickel hydroxide and cadmium hydroxide in the substrate.

As explained above, in the positive electrode plate for an Alno J storage battery according to the present invention, impregnation with cadmium salt for overdischarge protection U↓ and C is performed independently from impregnation with nickel salt.
Under overdischarge conditions, the added cadmium can effectively act to delay the generation of hydrogen, which is of great industrial value.

[Brief explanation of the drawing]

FIG. 1 is a diagram comparing the terminal voltage 63 J: and battery internal pressure during discharging of the battery Δ according to the present invention and the battery B according to the conventional method.

Claims (1)

[Claims] 1. In addition to the process of repeatedly impregnating the porous parts of the sintered substrate with an aqueous solution mainly composed of nickel salts, drying, and neutralizing, impregnating with an aqueous cadmium salt solution, drying, and neutralizing. 4. A method for producing a positive electrode plate for an alkaline storage battery, characterized in that it includes a step.