JPH07101617B2 - Open type alkaline storage battery - Google Patents

Description

TECHNICAL FIELD OF THE INVENTION The present invention relates to an open-type alkaline storage battery, particularly an open-type nickel battery.
It concerns a cadmium storage battery.

2. Description of the Related Art A constant voltage floating charging system is one of the usage conditions of open nickel-cadmium storage batteries that have been used in the field of emergency power sources. This system is based on the following principle. That is, it is well known that if a charged nickel-cadmium storage battery is left in an open circuit state, the capacity gradually decreases due to self-discharge. Since this self-discharge is, so to speak, an electrochemical reaction similar to the local battery mechanism in the metal corrosion reaction, it is possible to prevent self-discharge by the same principle as electrocorrosion. That is, in the positive electrode plate, the charge product Ni
Hold at a noble potential where OOH is reduced and does not discharge,
On the other hand, in the negative electrode plate, it may be maintained at a base potential such that Cd which is a charge product is oxidized and is not discharged. To do this accurately, it is sufficient to set the positive electrode plate and the negative electrode plate to their preferred constant potentials using potentiostats, but it is expensive to carry out such a method with a practical battery. However, in reality, another method is adopted. That is, since a large amount of metallic nickel having a low hydrogen overvoltage is present as a sintered body in the sintered cadmium negative electrode plate, the hydrogen overvoltage of the negative electrode plate is low. Therefore, if a constant voltage of, for example, 1.40 V / cell is applied to a charged open-type sintered nickel-cadmium storage battery,
Since the hydrogen overvoltage of the negative electrode plate is low, the polarization of the negative electrode plate is extremely small, and the potential of the negative electrode plate remains a constant potential very close to the equilibrium potential of the hydrogen generation reaction. As a result, the potential of the positive electrode plate becomes a value close to +1.40 V based on the equilibrium potential of the hydrogen generation reaction. Since NiOOH, which is the positive electrode active material in the charged state, does not discharge at this potential, the positive electrode plate escapes self-discharge. Further, the equilibrium potential of Cd, which is the negative electrode active material in the charged state, is about 20 mV higher than the equilibrium potential of the hydrogen generation reaction.Therefore, self-discharge of the negative electrode plate does not occur at the potential at which the negative electrode plate can cause the hydrogen generation reaction. Absent.

By such a principle, self-discharge of the open alkaline storage battery can be prevented. When a constant voltage is applied for such a purpose, a current flows in the battery in the charging direction, and the current fluctuates depending on the battery temperature and the like. Therefore, the applied voltage is called a floating charging voltage.

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention However, as a result of detailed investigation by the present inventor, the floating charging system as described above is subjected to severe conditions such as a long period of 10 years or more, or a high temperature of 50 ° C. or more, for example. It has been found that when operated under the condition, there is a case where only the capacity of the positive electrode plate decreases, which has not been reported previously. According to the research conducted by the inventor, this phenomenon is considered to result from an increase in the direct hydrogen voltage of the negative electrode plate when the floating charging is continued for a long period of time at a high temperature. The reason why the hydrogen overvoltage rises is that the electrocatalytic activity for the hydrogen generation reaction of the metal nickel sintered body of the negative electrode plate decreases, or the surface of the metal nickel is covered with metal cadmium having a high hydrogen overvoltage and the hydrogen generation reaction occurs. It is thought that there is less. As a result, the negative electrode plate cannot maintain a constant potential during floating charging,
It gradually polarizes to a base potential. At this time, if a constant floating charging voltage is still applied, the potential of the positive electrode plate gradually shifts to the base as the polarization of the negative plate increases, and as a result, it becomes base to the equilibrium potential of NiOOH, and the positive electrode plate becomes It will self-discharge.

In order to prevent such inconvenience, if the floating charging voltage is set high, the hydrogen overvoltage of the negative electrode plate rises after long-term use at high temperature, and even if the negative electrode plate is polarized negatively, the potential of the positive electrode plate will increase. Can be kept nobler than the equilibrium potential of NiOOH. However, in this case, since the polarization of the negative electrode plate is extremely small before the hydrogen overvoltage of the negative electrode plate increases, the potential of the positive electrode plate becomes more noble than necessary. Therefore, the current flowing through the battery becomes excessively large, the rate of oxygen generation from the positive electrode plate and the rate of hydrogen generation from the negative electrode plate are significantly increased, the rate of decrease in the amount of electrolyte is increased, and replenishment of water to the battery is frequently The required inconvenience occurs.

For the above reasons, there has been a demand for an open-type alkaline storage battery in which the capacity of the positive electrode plate does not decrease even when it is floating-charged at a high temperature for a long time.

The present invention is intended to solve the above-mentioned problems of the prior art.

Means for Solving the Problems That is, according to the present invention, an electrode formed by mainly supporting nickel hydroxide on a non-sintered conductive porous body having a nickel layer on the surface of a skeleton is immersed in an electrolytic solution. At the same time, the above-mentioned object is achieved by electrically connecting to the sintered cadmium negative electrode plate and setting the volume of the electrode to 1/100 or more of the total volume of the sintered cadmium negative electrode plate.

For example, nickel hydroxide is mainly supported on a non-sintered conductive porous body that has a nickel layer on the surface of the skeleton, such as a felt made of foamed nickel plate or nickel-plated iron fiber. A new fact has been found that when an electrode (hereinafter referred to as a hydrogen generation electrode) is negatively polarized in an alkaline electrolyte to generate hydrogen, the hydrogen overvoltage is significantly lower than that of a sintered cadmium negative electrode plate having the same volume. . Then, comparing the polarization characteristics of the hydrogen generation electrode and the sintered cadmium negative electrode plate in the present invention regarding the hydrogen generation reaction in 5M KOH electrolyte, when the polarization values are the same, the former is about 100 of the latter. It turned out that a double current flows. That is, regarding the hydrogen generation reaction, the minimum volume of the hydrogen generation electrode required to obtain the same polarization characteristics as that of the sintered cadmium negative electrode plate is 1/100 of the total volume of the sintered cadmium negative electrode plate. Means that.

Next, a sintering type cadmium negative electrode plate and a hydrogen generating electrode having a volume of 1/100 of the total volume of the sintering type cadmium negative electrode plate, each of cadmium contained in the cadmium negative electrode plate in 5M KOH electrolyte solution. It was negatively polarized at 50 ° C. for 1 year using a current of 1000 hours based on the theoretical capacity. As a result, both of them showed the same hydrogen overvoltage at the start of energization, but one year later, the former hydrogen overvoltage increased by about 150 mV, whereas the latter hydrogen overvoltage increased by only about 30 mV.

As described above, the reason why the hydrogen overvoltage of the hydrogen generating electrode in the present invention is significantly lower than that of the sintered cadmium negative electrode plate is not clear, but nickel hydroxide which is considered to have an electrode-catalyzing activity with respect to the hydrogen generating reaction is not clear. However, it seems that the former is abundant in the former. In addition, the hydrogen overvoltage does not easily rise when the hydrogen generation electrode is kept negatively polarized at a high temperature for a long period of time. Since cadmium does not exist in the immediate vicinity, it is considered that the nickel hydroxide is not covered with cadmium and is not reduced to nickel in a metallic state, and therefore the electrocatalytic activity is maintained. Therefore, the hydrogen generation electrode in the present invention,
In an open alkaline storage battery, which is immersed in an electrolytic solution and electrically connected to a sintered cadmium negative electrode plate, and the volume of the electrode is 1/100 or more of the total volume of the sintered cadmium negative electrode plate, Even if the hydrogen overvoltage of the sintered cadmium negative electrode plate is increased by floating charging for a long period of time, the hydrogen overvoltage of the hydrogen generating electrode is kept low. Therefore, since the polarization of the whole negative electrode does not increase, the potential of the positive electrode is maintained noble,
Battery capacity does not decrease. By the way, when nickel hydroxide is mixed with cadmium hydroxide, which is the active material in the sintered cadmium negative electrode plate, nickel hydroxide is reduced after a long period of negative polarization, and the intermetallic compounds in the γ-Ni ₅ Cd ₂₁ phase are reduced. The compound was formed, and the hydrogen overvoltage increased significantly.

EXAMPLES Next, the present invention will be described based on examples.

First, as the product of the present invention, the size is 120 mm × 120 mm × 0.1 mm
Using 10 pieces of sintered nickel hydroxide positive electrode plate of as a positive electrode,
Using 10 pieces of sintered cadmium negative electrode plates of the same size as the negative electrode, 2 sheets of polypropylene non-woven fabric having a thickness of 0.2 mm and a separator in which 1 sheet of cellophane is interposed,
Further, 1/1000 to the total volume of the sintered cadmium negative electrode plate
A hydrogen generating electrode having a double volume was used, and the hydrogen generating electrode was electrically connected to a negative electrode of a sintered cadmium negative electrode, which was a nickel plate, to prepare an open-type battery having a nominal capacity of 60 Ah. The electrolyte of this battery has a specific gravity of 1.220 (2
(0 ° C.) KOH aqueous solution was used. The above-mentioned hydrogen generating electrode was manufactured as follows. That is, a foamed nickel sheet manufactured by Sumitomo Electric Industries, Ltd. is used as a non-sintered conductive porous body having a nickel layer on the surface of the skeleton, and nickel hydroxide powder is kneaded with a 2% CMC aqueous solution to prepare. The slurry was filled in the pores of the foamed nickel sheet,
After drying, nickel hydroxide was carried by pressing to form an electrode.

For comparison, as a conventional product, an electrode for hydrogen generation that is electrically connected to the sintered cadmium negative electrode plate in the product of the present invention is not installed, and the other configuration is the same as that of the product of the present invention. A battery was made.

Next, these batteries were charged at 20 ° C for 10 hours at a current of 10 hours, then at 1.50V / cell constant voltage floating charge at 50 ° C for 1 year, and then at 20 ° C for 1 hour. It was discharged with an electric current. The relationship between the discharge capacity obtained at this time, the volume of the hydrogen generating electrode connected to the sintered cadmium negative electrode plate and the ratio of the total volume of the sintered cadmium negative electrode plate is shown in the figure.

As is clear from the figure, the discharge capacity of the conventional product has been reduced to about 42 Ah, while the product of the present invention has a volume of the hydrogen generating electrode connected to the negative electrode plate and the total volume of the sintered cadmium negative electrode plate. It can be seen that when the ratio of the discharge capacity is 1/100 or more, a discharge capacity larger than the nominal capacity of 60 Ah is obtained, and the capacity is less likely to decrease.

Effects of the Invention As described above, according to the present invention, it is possible to prevent a decrease in the capacity of an open-type alkaline storage battery that is floating-charged at high temperature for a long time.

[Brief description of drawings]

The figure is a characteristic diagram showing a comparison of the discharge capacities of the open alkaline storage battery according to the present invention and the conventional open alkaline storage battery of this kind after floating charging at a high temperature for a long time.

Claims (1)

[Claims] 1. A non-sintered conductive porous body having a nickel layer on the surface of a skeleton, and an electrode mainly comprising nickel hydroxide supported thereon is immersed in an electrolytic solution, and at the same time, a sintered cadmium negative electrode plate is provided. An open-type alkaline storage battery, which is electrically connected and in which the volume of the electrode is set to 1/100 or more of the total volume of the sintered cadmium negative electrode plate.