JPS6240173A - Vent-type sintered alkaline storage battery - Google Patents

Abstract

PURPOSE:To prevent the hydrogen overvoltage of a negative electrode plate of cadmium from rising when floating charge is performed at a high temperature for a long period of time, by causing an alkaline electrolytic solution to contain platinum, or depositing platinum on the negative electrode plate. CONSTITUTION:An alkaline electrolytic solution is caused to contain 1X10<-5>mol/l or more of platinum in the form of a compound such as chloroplatinic acid and an ammine complex to much drop the hydrogen overvoltage of a negative electrode plate of cadmium. It is presumed that metal lic platinum is deposited on the negative electrode plate by the substitutive reaction of the metallic cadmium or nickel of the plate of cadmium and the plastinum compound and then acts as a hydrogen generation site to much drop the hydrogen overvoltage. For that reason, the hydrogen voltage can be much dropped by depositing platinum on the negative electrode plate of cadmium beforehand as well.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to alkaline storage batteries, and in particular to vented sintered nickel-cadmium alkaline FA batteries.

BACKGROUND OF THE INVENTION Conventionally, one of the conditions for using vented sintered nickel-cadmium storage batteries, which have been used in fields such as emergency power sources, is a constant voltage floating charging system. This system is based on the following principle: It is well known that if a charged nickel-cadmium storage battery is left in an open circuit state, its capacity will gradually decrease due to self-discharge. Since this self-discharge is an electrochemical reaction similar to a local battery mechanism in a metal corrosion reaction, self-discharge can be prevented using the same principle as cathodic protection. The charge product Ni OOH is kept at a noble potential so that it is not discharged due to reduction, and the charge product C in the negative electrode plate is
It is sufficient to maintain the potential at a base level such that d is not oxidized and discharged. To do this accurately, it is possible to use a potentiostat to set the positive electrode plate and the fish seed plate to the desired constant potential, but the equipment is expensive to use in practical batteries. In reality, a different method is used, as there are drawbacks such as:

That is, in the sintered cadmium negative electrode plate, a large amount of metal nickel, which has a low hydrogen overvoltage, is present as a sintered body, so the hydrogen overvoltage of the negative electrode plate is low. Therefore, for example, a charged vented sintered nickel-cadmium storage battery has a charge of 1.40μ/
When a constant voltage similar to that of a cell is applied, since the hydrogen overvoltage of the negative plate is low, the polarization of the negative plate is extremely small, and the potential of the zero plate is the constant potential that is 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 the positive electrode active material "NiO1" in a charged state does not discharge at this potential, the positive electrode plate can avoid self-discharge.

In addition, the equilibrium potential of Cd, which is an n-type oil substance in a charged state, is about 20 mVfi higher than the equilibrium potential of the hydrogen generation reaction, so self-discharge of the negative electrode plate will naturally not occur at a potential where the negative electrode plate can cause the hydrogen generation reaction. do not have.

This principle prevents self-strike of vented sintered alkaline storage batteries. When a constant voltage is applied for this purpose, a current flows into the battery in the direction of charging.
Furthermore, since the current varies depending on the battery temperature, etc., the applied voltage is called a floating charging voltage.

Problems to be Solved by the Invention However, when a floating charging system as described above is operated for a long period of time, for example, 10 years or more, or under severe conditions, such as at a high temperature of 50 degrees Celsius or more,
A disadvantage may arise in that only the capacity of the positive electrode plate is reduced. This is because if floating charging is continued for a long period of time, the electrocatalytic activity for the hydrogen generation reaction of the metal nickel in the sintered body, which is the site where the water and N generation reaction occurs in the negative electrode plate, decreases.
This is because the hydrogen overvoltage of the negative electrode plate increases because the surface of the metal nickel is coated with metal cadmium, which has a high hydrogen overvoltage, and the number of sites where hydrogen generation reactions occur decreases. As a result, the oral plate is unable to maintain a constant potential during floating charging and becomes increasingly polarized to a less noble potential. At this time, if a constant floating charging voltage remains applied, the potential of the positive plate will gradually shift to a lower value as the polarization of the negative plate increases, and eventually the Ni
001'', and the positive electrode plate self-discharges.

To prevent such inconveniences, if the floating charge voltage is set high, the hydrogen overvoltage of the negative plate will increase after long-term use at high temperatures, and even if the negative plate is polarized to the base, the potential of the positive plate will decrease. truer than the equilibrium potential of Ni OOH. However, in this case, before the hydrogen overvoltage of the negative electrode plate increases, the decentralization of the negative electrode plate is extremely small.
The potential of the positive electrode plate becomes higher than necessary. Therefore, the rate of oxygen generation from the positive electrode plate and the rate of hydrogen generation from the negative electrode plate increases significantly, and the rate of decrease in the amount of electrolyte increases, resulting in the inconvenience that water replenishment to the battery is frequently required.

For the above reasons, there has been a desire for a vented sintered alkaline storage battery in which the hydrogen overvoltage of the negative electrode plate does not increase even when floating charging at high temperatures for a long period of time.

The present invention aims to solve the problems of the prior art as described above.

Means for solving the problem, that is, the present invention provides an alkaline solution of 1 x 10-5 m
ol/9. The above object is achieved by containing the above platinum or by depositing platinum on the cadmium negative electrode plate. Furthermore, the platinum contained in the alkaline electrolyte is tetraammineplatinum (ff) ion [P
t(NH3)4 ]”Siyahexammine platinum (■v)
The ammine complex, such as the ion [Pt(NH3)6]4+, allows -II to quickly solve the problem.

Action of the above alkali N? Add platinum as a compound such as chloroplatinic acid or ammine complex to the alkaline electrolyte of the Fi pond.
When the content is 10-glol/1 or more, it becomes possible to significantly reduce the water'fA overvoltage of the cadmium negative electrode plate. This is because metal platinum is deposited on the surface of the cadmium negative electrode plate due to a substitution reaction between the metal cadmium or metal nickel contained in the cadmium negative electrode plate and the platinum compound. As a result, the precipitated metal platinum becomes a hydrogen generation site, resulting in a significant hydrogen overvoltage. This is thought to be due to a decrease in If the platinum content in the alkaline electrolyte is lower than 1 x 10-'mol/λ, the equilibrium potential of the dissolution precipitation reaction of metallic platinum becomes extremely base according to the Nernst relation, making it difficult to deposit on the cadmium negative electrode plate. As a result, the hydrogen overvoltage of the cadmium negative electrode plate becomes difficult to decrease. Based on this principle, instead of including platinum in the alkaline electrolyte of an alkaline storage battery, by depositing platinum on the cadmium A electrode plate in advance, a cadmium negative electrode plate with a similarly low hydrogen overvoltage can be obtained.

When platinum is added to the alkaline electrolyte of an alkaline storage battery as described above, the platinum compound to be added is tetraammineplatinum(II) ion [Pt(NH3)a
120 or hexaammine platinum <rv> ion [P
When an ammine complex such as t(NH3)13]'+ is used, the hydrogen overvoltage of the cadmium negative electrode plate decreases quickly. This can be attributed to the fact that ammine 11 of platinum has a high fJ solubility in an alkaline electrolyte, so that the concentration of platinum dissolved in the alkaline electrolyte becomes high. If chloroplatinic acid is used in place of the above ammine complex, the time required for the hydrogen overvoltage to decrease is improved even when using the same concentration, due to its lower solubility in the alkaline electrolyte.

When the hydrogen overvoltage of the cadmium negative electrode plate is reduced as described above, even if an alkaline storage battery using this is floating-charged at high temperatures for a long period of time, the hydrogen overvoltage of the cadmium negative electrode plate remains low, so that the capacity decreases. It won't happen. Furthermore, among conventional alkaline storage batteries, even in batteries where the capacity of the positive electrode plate has decreased due to an increase in the hydrogen overvoltage of the cadmium negative electrode plate due to long-term floating charging at high temperatures, platinum of 1 x 10 = mol 72 or more is added to the alkaline electrolyte. By adding , the hydrogen overvoltage of the cadmium negative electrode plate decreases, the polarization of the f4 electrode plate becomes smaller, the potential of the positive electrode plate increases, and the positive electrode plate is charged again, making it possible to recover the capacity.

In addition, some of the platinum contained in the alkaline electrolyte is deposited on the positive electrode plate, but even in that case, platinum has a significantly high oxygen overvoltage, so it is said that it actually increases the charging efficiency of the positive electrode plate. This has favorable effects. In addition, when platinum ammine complex is used, platinum is cadmium negative (
The ammonia in the ligand that remains in the deposits deposited on the rolling plate is finally electrolytically oxidized on the positive electrode plate and becomes nitrogen gas.
Since it leaves the battery system, it does not have any negative impact on alkaline storage batteries.

Example Next, the present invention will be explained based on examples.

Example 1 First, in order to confirm the effect of the present invention, a conventional product with dimensions of 120 mm x 12 on + m x 1. Ten Omm sintered nickel hydroxide electrode plates were used as positive electrodes, ten sintered cadmium hydroxide electrode plates of the same size were used as negative electrodes, and two 0.2 mm thick polypropylene non-container plates were used. A vented alkaline storage battery with a nominal capacity of 60A h was fabricated using a separator with one sheet of cellophane interposed between 11 and 11cm, and a ratio of fi 1,220 (20℃>KO+-1 aqueous solution was used as an alkaline ff1l solution.Also, the present invention As for the product, instead of the alkaline electrolyte in the conventional product mentioned above, 1
Specific gravity 1.220 (20
℃> A vented alkaline M'FI pond was manufactured using KOH aqueous solution as the alkaline electrolyte and having the other configurations the same as the conventional product. Furthermore, as product B of the present invention, instead of the sintered cadmium hydroxide electrode plate in the conventional product,
Hexaammineplatinum (IV
) A sintered cadmium hydroxide electrode plate was immersed in an aqueous ion solution, and then 1% sodium borohydride (Na BHa
) Platinum is deposited on a sintered cadmium hydroxide electrode plate by adding an aqueous solution♂, which is then washed with water and dried to be used as the negative electrode plate, with other configurations being the same as the conventional product above. I made an alkaline M battery.

Next, the alkaline storage battery produced as described above was heated to 20°C.
After charging for 16 hours at a current rate of 10 hours at 50° C., constant voltage floating charging at 1.40 V/l at 50° C. was performed for one year, and then discharging at a current rate of 1 hour at 20° C. The discharge capacity obtained at this time is shown in FIG.

From FIG. 1, it can be seen that the platinum concentration in the alkaline electrolyte is 1X 1
Product A of the present invention with a diameter of 0-”mal/mm or more has a nominal capacity of 60A.
It can be seen that h or more is maintained. In addition, product B of the present invention, which has a cadmium negative electrode plate on which platinum has been deposited in advance and does not contain platinum in the alkaline Ti solution, also has a nominal capacity of 60△
It can also be seen that the discharge capacity is greater than h. In addition,
Similar results were obtained when hexaammineplatinum (IV) ions were used in place of the tetraammineplatinum (I[> ions) in the product Δ of the present invention.

Example 2 Eleven batteries identical to the conventional products in Example 1 were manufactured, and 2
After charging for 1G hours at a current rate of 10 hours at 0°C, 5
Constant voltage floating charging at 1.40 V/cell was performed at 0° C. for one year. Thereafter, while floating charging was continued under the same conditions for 11 days, 1 x 10-3 mol of hexammineplatinum (IV) ions were added to the alkaline electrolyte of the 5 g battery. The battery is referred to as Battery C), and 1XiO"" m01/m of chloroplatinic acid was added to the alkaline solution in the first pond of the other 5 cycles (hereinafter, the battery to which this chloroplatinic acid was added is referred to as a battery). ). The capacity of the remaining battery was examined by discharging it at a current rate of 1 hour at 20° C. (this battery containing no additives was referred to as Battery E). Batteries C and D to which the platinum compound had been added were discharged at a current rate of 1 hour at 20° C. every month to examine their capacity, and the speed of capacity recovery after the addition of the platinum compound was examined. The results are shown in FIG.

From FIG. 2, it can be seen that the capacity recovery of battery C to which a platinum ammine complex was added was faster than that of the battery to which chloroplatinic acid was added.

Effects of the Invention As described above, according to the present invention, it is possible to prevent a decrease in the capacity of a vented sintered alkaline storage battery that is subjected to floating charging at high temperatures for a long period of time. In addition, the capacity of a battery whose capacity has decreased can be quickly restored.

[Brief explanation of the drawing]

Fig. 1 is a characteristic diagram showing a comparison of the discharge capacity and life of a Ben 1-type sintered alkaline storage battery according to the present invention and a conventional alkaline storage battery of this type after being floated for a long period of time under high temperature.
The figure is a characteristic diagram showing the capacity recovery characteristics when the present invention is applied to a battery whose capacity has decreased due to long-term floating charging under high temperature, compared with a case where the present invention is not applied. fuck 1 figure

Claims (2)

[Claims] (1) A vent characterized in that the negative electrode active material is cadmium, and the alkaline electrolyte contains platinum in an amount of 1×10^-^5 mol/l or more, or platinum is deposited on the cadmium negative electrode plate. Shaped sintered alkaline storage battery. (2) The platinum contained in the alkaline electrolyte is tetraammineplatinum(II) ion [Pt(NH_3)_4]^2^
+ or hexaammine platinum (IV) ion [Pt(NH_3
)_6]^4^+ The vented sintered alkaline storage battery according to claim (1), which is an ammine complex such as _6]^4^+.