JPS62211860A - Nickel positive plate for alkaline storage battery - Google Patents

Abstract

PURPOSE:To increase very high rate discharge performance by forming a nickel oxide layer having a specified mean thickness on the surface of a nickel porous body, and containing a cobalt compound which does not form a solid solution with nickel hydroxide in the active material. CONSTITUTION:A porous sintered nickel substrate obtained by sintering carbonyl nickel powder in a reducing atmosphere is heated in an atmosphere of the air to form a nickel oxide layer having a mean thickness of 5-70Angstrom thereon. A cobalt compound which does not form a solid solution with nickel hydroxide which is a positive active material is contained in the active material. This active material is filled in the sintered substrate to form a nickel positive plate for an alkaline storage battery. By the synergistic effect, the dependency of active material utility and discharge voltage on the discharge rate is decreased. Since the performance drop in very high rate discharge is reduced, the battery is useful for the power source of a power tool or the like.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention is directed to a high-performance nickel-based alkaline storage battery that has very good characteristics in ultra-high rate discharge and exhibits almost no performance deterioration as the cycle progresses. This relates to the positive electrode plate.

Conventional technology Conventionally, most nickel positive electrode plates used in alkaline storage batteries are made by impregnating a porous nickel sintered substrate made by sintering carbonyl nickel powder in a reducing atmosphere with an acidic solution mainly composed of nickel salts, and then concentrating it. The nickel substrate is then immersed in a hot alkaline solution to fill the pores of the nickel substrate with a positive electrode active material whose main component is nickel hydroxide.

Recently, two methods have been proposed to improve the performance of nickel positive electrode plates. One of them is to include a cobalt compound that does not form a solid solution with nickel hydroxide in the positive electrode active material. According to this method, it is possible to increase the active material utilization rate during discharge by about 10 to 15% compared to the conventional method. For example, in the conventional positive electrode plate, the active material utilization rate for IOA discharge was about 70 to 80%, whereas in the above-mentioned improved method, it was about 85 to 90%, which is advantageous for increasing the capacity of the positive electrode plate. . The other method is to form a nickel oxide layer on the surface of the nickel sintered body. For example, when a nickel sintered substrate without a nickel oxide layer is used and the active material is filled by chemical impregnation, the nickel sintered body is eaten away by the acidic impregnating liquid, causing mechanical damage to the electrode plate. Strength decreases.

However, if a layer of nickel oxide is formed on the surface of the nickel sintered body based on the improved technique described above, it is possible to prevent the corrosion of the nickel sintered body as described above.

As a result of improvements that go beyond the problems that the invention aims to solve, the performance of recent nickel positive electrode plates has improved compared to conventional ones. The performance is still insufficient for ultra-high rate discharge such as when used as a battery. For example, for use in power tools, an alkaline storage battery requires a discharge current of about 3 OCA. Under such conditions, even with the recent improved nickel positive electrode plates as described above, polarization during discharge becomes considerably large, resulting in a significant drop in the terminal voltage of the storage battery. The same applies to the active material utilization rate.

Means for Solving the Problems The present invention relates to a nickel positive electrode plate that has a very small decrease in active material utilization rate and discharge rank in ultra-high rate discharge as described above, and has a high capacity. contains a cobalt compound that does not form a solid solution with nickel hydroxide in the active material, and a layer of nickel oxide with an average thickness of 5 to 70 people exists on the surface of the nickel porous body that holds the active material. It is characterized by this.

The nickel positive electrode plate is better than the cadmium negative electrode plate because the dependence of the active material utilization on the discharge rate is smaller, but it is even better in ultra-high discharge rate applications such as power tools as mentioned above. Discharge rate dependence is required.This applies not only to the active material utilization rate but also to the fourth discharge rate.

Of the two improvement techniques mentioned above, the method of improving the active material utilization rate, that is, the method of incorporating a cobalt compound that does not form a solid solution with nickel hydroxide into the active material, is attracting attention because of its large effect. However, no importance was placed on forming a nickel oxide layer on the surface of the other nickel sintered substrate. The reason for this is as follows. When filling the active material by chemical impregnation method,
Although it is necessary to repeat a series of steps such as impregnation with an acidic metal salt solution mainly containing nickel, neutralization, and drying several times, it has been desired to reduce the number of steps from the viewpoint of manufacturing costs. Therefore, in the past, the nickel sintered body was intentionally corroded to become an active material, and the amount of active material was increased. Forming a layer of nickel oxide on the surface of a nickel sintered body to prevent corrosion goes against this and becomes a factor in increasing costs.

The present inventor also studied this corrosion protection in detail, and found that
In addition to preventing corrosion of the nickel sintered body during the impregnation process, the thickness of the nickel oxide present on the surface of the nickel sintered body affects the discharge performance at the end of the nickel positive electrode plate manufacturing process. We found that it has a very important effect. In other words, a nickel positive electrode plate having a layer of nickel oxide with an average thickness of 5 to 70 people on the surface of a nickel sintered body has a very good active material utilization rate and a small dependence on the discharge rate of the fourth discharge, and has a very good 300△
It has been found that the deterioration in performance is small in Jf1 high rate discharge such as.

Furthermore, if the active material of the nickel positive electrode plate does not contain a cobalt compound that does not form a solid solution with nickel hydroxide, the discharge performance of the positive electrode plate will synergistically improve.
It was found that it is suitable for high rate discharge applications.

If the thickness of the nickel oxide layer is less than 5 or more than 70, it is not suitable for ultra-high rate discharge applications. For example 5
In the case of less than 100 liters, the initial JIJ performance of the positive electrode plate is good, but the performance gradually deteriorates as the charge/discharge cycle progresses. One of the reasons for this is considered to be the following effects caused by the use of sintered nickel as an active material. First, the composition of the active material filled externally in the impregnation process is usually a mixture of nickel, cobalt, and cadmium, with nickel hydroxide as the main component. This is because the active material utilization rate at the time is good.

However, only nickel hydroxide is produced by the nickel sintered body Ill IQ. In other words! 11! A layer of active material consisting of nickel hydroxide alone, which has low charging efficiency and low active material utilization during discharging, is formed between the nickel sintered body and the filled active material, which reduces the performance of the electrode plate. It is possible that there are.

Furthermore, since the active materials have different compositions, it is possible that the current distribution becomes non-uniform. The second problem is a decrease in current collection performance due to a decrease in the amount of nickel sintered body serving as a current collector. These problems are not limited to sintered positive electrode plates;
The same applies to the non-sintered type.

On the other hand, in the case of a positive electrode plate in which the thickness of the nickel oxide layer exceeds 70 mm, the discharge performance deteriorates from the beginning.

One reason for this is that as the nickel oxide layer becomes thicker, the properties of nickel oxide, which is originally an insulator, become more apparent, and the contact resistance between the active material and the nickel sintered substrate, which is the current collector, increases. is possible.

EXAMPLES Hereinafter, examples of the present invention and their effects will be explained in comparison with conventional examples.

Experiment 1 First, two types of nickel sintered substrates described below were used, and a nickel positive electrode plate according to the present invention and a conventional nickel positive electrode plate shown below were respectively produced.

Carbonyl nickel powder is kneaded with methyl cellulose and water to form a nickel slurry, and this nickel slurry is applied to a nickel-plated perforated steel plate, dried, and then sintered at 900°C in a reducing atmosphere containing water vapor to form a nickel sintered substrate. Created. Use this as a substrate. Furthermore, board A
was heat-treated at 250° C. in an air atmosphere to produce a nickel sintered substrate having a nickel oxide layer on the surface of the nickel sintered body. This will be referred to as substrate B. Although the average thickness of the nickel oxide layer of substrate B was about 80, the thickness of the oxide layer can be freely changed by changing the heat treatment conditions.

Positive electrode plate A (conventional product) Substrate A without a nickel oxide layer is immersed in a mixed aqueous solution of nitrates with a ratio of nickel, cobalt, and cadmium of 95:2:3, and then concentrated and neutralized. The conventional chemical impregnation process was repeated several times.

Positive electrode plate B (conventional product) Positive electrode plate B was prepared by using positive electrode plate A and further performing a normal chemical impregnation process once with a solution of cobalt nitrate alone to generate individual cobalt hydroxide in the active material.

Positive electrode plate C (conventional product) Positive electrode plate C was produced in the same manner as positive electrode plate A except that substrate B having a nickel oxide layer having an average thickness of 80 mm was used instead of substrate A in positive electrode plate A.

Positive electrode plate D (product of the present invention) This was produced in the same manner as positive electrode plate B except that substrate B having a nickel oxide base having an average thickness of 8 OA was used instead of the substrate in positive electrode plate B.

Note that the average thickness of the nickel oxide layer of positive electrode plates C and D measured after the completion of the active material impregnation step was about 60. In addition, in positive electrode plates A and B, 20% of the nickel sintered body was eaten by ffI during the active material impregnation process. In addition, regarding positive electrode plates B and D containing single cobalt hydroxide in the active material, it is known that the discharge performance of the positive plate is affected by the amount of the cobalt compound added.
Since the appropriate amount of cobalt compound has already been confirmed, that amount was set as the appropriate amount. For example, in a positive electrode plate that does not have a nickel oxide layer formed on the surface of the nickel sintered body, the amount of a single cobalt compound is higher than the amount of nickel hydroxide.
The discharge performance is good when the content is 2.0 to 8.0 mol%.

In the case of positive electrode plate B, the content was set to 5 mol %.

On the other hand, in a positive electrode plate having a nickel oxide layer on the surface of the nickel sintered body, the discharge performance is good when the amount of a single cobalt compound is 0.4 to 1.0 mol% relative to the amount of nickel hydroxide.

In the positive electrode plate and in Experiment 2, which will be described later, the amount was set at 4.2 mol%.

After cutting the 4F4 regular 144& produced as described above into predetermined dimensions, the
1-1 ft! In the solution, two cadmium negative plates having the same dimensions as the sample positive plate were used as counter electrodes to measure the discharge characteristics.

Charging is 0.20 A x 9 hours, and the base tst'FB
A mercury oxide electrode was used as the electrode. The dependence of the active material utilization rate on the discharge rate is shown in FIG. 1, and the dependence of the discharge intermediate potential on the discharge rate is shown in FIG. Note that the discharge intermediate potential in FIG. 2 is a value when the tli depth is 50% with respect to the theoretical capacity.

As can be seen from FIG. 1, the conventional positive bridge plate A has a lower active material utilization rate than any other positive electrode plate, and is also inferior in discharge rate dependence. On the other hand, positive electrode plate B containing cobalt hydroxide, which is impregnated with cobalt nitrate alone and does not form a solid solution with nickel hydroxide in the active material, has an active material utilization rate of about 15 to 2.
0% has improved. In addition, the positive electrode plate C, in which a layer of nickel oxide is formed on the surface of the nickel sintered body to prevent the nickel sintered body from corroding during the active material impregnation process, has not only the active material utilization rate but also its discharge rate dependence. has also improved.

Furthermore, the positive electrode plate of the present invention, which has a nickel oxide layer formed on the surface of the nickel sintered substrate and is impregnated with cobalt nitrate alone, has the best active material utilization rate and its discharge rate dependence, and has the best active material utilization rate and its discharge rate dependence. There is very little performance deterioration over time.

Such performance could not be obtained with conventional products, and is thought to be due to the synergistic effect of the two improved techniques mentioned above.

The same tendency as in Figure 1 is observed at the discharge intermediate potential in Figure 2, but it is important to form a nickel oxide layer on the surface of the nickel sintered body, especially for ultra-high rate discharge applications such as 30CA. I can say that.

As is clear from the diagrams in which the two initial characteristics were measured,
A layer of nickel oxide is formed on the surface of the nickel sintered body to prevent corrosion of the nickel sintered body during the active material impregnation process, and a cobalt compound that does not form a solid solution with nickel hydroxide is added to the active material. By containing it in
It is clear that the nickel positive electrode plate 19 has very good ultra-high rate discharge characteristics.

Experiment 2 Next, the thickness of the nickel oxide layer formed on the surface of the nickel sintered body and the discharge characteristics will be described.

The nickel sintered substrate used here is the base plate B used in Experiment 1.
The nickel sintered body was prepared using the same method as above, but the average thickness of the nickel oxide layer formed on the surface of the nickel sintered body was varied between 10 and 140 by changing the oxidation conditions. .

Impregnation of the active material followed the same method as positive electrode plates B and D of Experiment 1. In other words, the impregnating liquid is a mixed solution of nickel, cobalt, and cadmium nitrates, with nickel nitrate as the main component.This impregnating liquid is impregnated into a sintered nickel substrate, and then concentrated and neutralized, which is a typical chemical impregnation process. After repeating the steps several times, a final chemical impregnation step was performed once using a solution of cobalt Vn acid alone to form cobalt hydroxide alone.

After the active material impregnation process was completed, the thickness of the nickel oxide layer on the surface of the nickel sintered body was measured for each positive electrode plate, and it was found that the thickness had decreased by about 20 compared to before the active material impregnation process. In other words, it is considered that approximately 20 portions of the nickel oxide layer were dissolved during the active material impregnation process.

In addition, all of the positive electrode plates whose original nickel oxide layer had a thickness of less than 20 people had corrosion of the nickel sintered body, and therefore were excluded from the following tests.

The sample positive electrode plate was subjected to continuous cycles under the following conditions.

Charging ICAXL 2 hours pause 1 hour failure fi 3OCA + 0. IV Mat'vs, 1
-1a/HQ 0 pause 1 hour FIG. 3 shows the active material utilization rate during the 3rd cycle and the 100th cycle of discharge, and FIG. 4 shows the mid-discharge potential at that time. Note that the average thickness of the nickel oxide layer on the horizontal axis is the value after the completion of the active material impregnation step.

As can be seen from the results in FIG. 3, when the thickness of the nickel acid compound layer on the surface of the nickel sintered body exceeds 80, the active material utilization rate decreases. One of the reasons for this is considered to be the influence of the insulating properties of nickel oxide. On the other hand, in the 100+J-th cycle, the active material utilization rate also decreases when the thickness of the nickel oxide layer is less than 5 layers. One possible reason for this is that when the thickness of the nickel oxide layer is very thin, the nickel sintered body becomes an active material as the charge/discharge cycle progresses.

In other words, during the impregnation process, an active material consisting of nickel hydroxide alone, which has a different composition from the active material filled in, is generated between the nickel sintered body and the filled active material, resulting in poor plate performance such as uneven current distribution. This is thought to be one of the causes.

The same tendency as in Fig. 3 is observed at the discharge intermediate potential in Fig. 4, but when the thickness of the nickel oxide layer exceeds 70%, the performance decreases, and the active material utilization rate in Fig. 3 is lower than that of the nickel oxide layer. The effect of the oxide layer thickness seems to be large.

From the above, it is clear that when the average thickness of the nickel oxide layer on the surface of the nickel sintered body is 5 to 70, a nickel positive electrode plate with very good ultra-high rate discharge characteristics can be obtained.

Note that in Experiments 1 and 2 described above, the present invention was explained using a method in which a nickel sintered substrate was used and the active material was filled by a chemical impregnation method. It has been confirmed through experiments that similar results can be obtained even when using a substrate made of a porous nickel material. Furthermore, although cobalt hydroxide has been described as a single cobalt compound, it has been confirmed through experiments that similar results can be obtained with various cobalt salts and cobalt oxides.

Effects of the Invention As shown in the above examples, based on the present invention, the surface of the nickel porous body holding the active material has an average thickness of 5 to
70 layers of nickel oxide and the active material contains a cobalt compound that does not form a solid solution with nickel hydroxide, which improves the active material utilization rate and the discharge level at ultra-high rate of discharge. However, a very good nickel positive electrode plate can be obtained.

[Brief explanation of drawings]

FIG. 1 is a characteristic diagram showing an example of the discharge rate dependence of the active material utilization rate of a nickel positive electrode plate for alkaline storage batteries according to the present invention and a conventional nickel positive electrode plate of this type, and FIG. A characteristic diagram showing an example of the discharge rate dependence of the mid-discharge potential of a nickel positive electrode plate and a conventional nickel positive electrode plate of this type. Figure 3 shows the thickness of the nickel oxide layer on the surface of the nickel sintered body and the use of active materials during discharge. FIG. 4 is a characteristic diagram showing the relationship between the thickness of the nickel oxide layer on the surface of the nickel sintered body and the discharge intermediate potential. Central 1 Inichi 2 [F, 塘 (C＾) it is imaginary ((:A)

Claims (1)

[Claims] The porous nickel body holding the active material has a nickel oxide layer with an average thickness of 5 to 70 Å on the surface, and the active material further contains a cobalt compound that does not form a solid solution with nickel hydroxide. A nickel positive electrode plate for alkaline storage batteries characterized by: