JPH0656762B2 - Nickel positive electrode plate for alkaline storage battery - Google Patents

Description

TECHNICAL FIELD The present invention relates to a nickel positive electrode for a high-performance alkaline storage battery, which has very good characteristics in ultra-high-rate discharge and hardly causes performance deterioration with the progress of cycles. It is about boards.

2. Description of the Related Art Conventionally, many nickel positive electrode plates used in alkaline storage batteries are concentrated by impregnating a porous nickel sintered substrate obtained by sintering carbonyl nickel powder in a reducing atmosphere with an acidic solution containing nickel salt as a main component. After that, it is manufactured by a method of immersing in a hot alkaline solution and filling the positive electrode active material containing nickel hydroxide as a main component into the holes of the nickel substrate.

Recently, two proposals have been made for improving the performance of nickel positive electrode plates. One is to incorporate a cobalt compound that does not form a solid solution with nickel hydroxide into the positive electrode active material. According to this method, the utilization rate of the active material at the time of discharging can be increased by about 10 to 15% as compared with the conventional one. For example, the conventional positive electrode plate has an active material utilization rate of about 70 to 80% for 1 CA discharge, whereas the improved method described above is about 85 to 90%, which is advantageous for increasing the capacity of the positive electrode plate. . The other 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 the chemical impregnation method, the nickel impregnated body is corroded by the acidic impregnating solution, resulting in the mechanical strength of the electrode plate. Is reduced. However, when the nickel oxide layer is formed on the surface of the nickel sintered body based on the improved technique, it is possible to prevent the corrosion of the nickel sintered body as described above.

Problems to be Solved by the Invention As a result of the above improvements, the recent nickel positive electrode plate has improved performance as compared with the conventional one, but as a power source for power tools whose demand is rapidly increasing recently. Performance is still insufficient for ultra high rate discharge such as when used. For example, in electric power tool applications, the discharge current of an alkaline storage battery requires about 30 CA. Under such a condition, even in the recent nickel positive electrode plate which has been improved as described above, the polarization at the time of discharge becomes considerably large, and the terminal voltage of the storage battery significantly decreases. The same applies to the active material utilization rate.

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

The working nickel positive electrode plate has a smaller dependence on the discharge rate of the active material utilization rate than the cadmium negative electrode plate, and is good, but it has a better discharge rate in the applications of ultra-high-rate discharge such as the power tools described above. Dependency is required. This applies not only to the utilization rate of the active material but also to the discharge potential.

Among the above-mentioned two improved techniques, the method of improving the utilization rate of the active material, that is, the method of incorporating a cobalt compound which does not form a solid solution with nickel hydroxide into the active material is noted for its great effect. However, the formation of a nickel oxide layer on the surface of another nickel sintered substrate was not emphasized. The reason is as follows. When the active material is filled by the chemical impregnation method, it is necessary to repeat a series of steps such as impregnation, neutralization, and drying of an acidic metal salt solution mainly containing nickel, which is the number of times in terms of manufacturing cost. It was desired to reduce the Therefore, conventionally, the nickel sintered body has been intentionally corroded into an active material, and the amount of the active material filled has been increased.
Forming a layer of nickel oxide on the surface of the nickel sintered body to prevent corrosion is against this, and causes a cost increase.

The present inventor has also examined this anticorrosion in detail,
In addition to preventing corrosion of the nickel sintered body in the impregnation process, the thickness of the nickel oxide present on the surface of the nickel sintered body as the structure of the nickel positive electrode plate, which is the time when the manufacturing process of the nickel positive electrode plate is completed, affects its discharge performance. On the other hand, it has been found to have a very heavy effect. In other words, a nickel positive electrode plate having a nickel oxide layer with an average thickness of 5 to 70Å on the surface of a nickel sintered body has very small active material utilization rate and discharge rate existence at discharge level, and is very good. It was found that the performance degradation at such a very high rate discharge was small.

Further, when a nickel compound and a cobalt compound which does not form a solid solution are contained in the active material of the positive electrode plate of nickel described above, synergistically the discharge performance of the positive electrode plate is further improved, which is suitable for use in ultra-high rate discharge. I found out.

If the thickness of the nickel oxide layer is less than 5Å or exceeds 70Å, it is not suitable for ultra high rate discharge. For example, 5Å
When it is less than the above, the initial performance of the positive electrode plate is good, but the performance gradually decreases as the charge / discharge cycle progresses. As one of the factors, it is considered that the nickel sintered body is made into an active material as follows. First, the composition of the active material to be filled from the outside in the impregnation step is usually a mixture of nickel, cobalt and cadmium whose main component is nickel hydroxide. This is because the active material utilization rate at that time is good. However, only nickel hydroxide is produced by the corrosion of the nickel sintered body. In other words, an active material layer of nickel hydroxide alone, which has low charge efficiency and utilization rate of the active material at the time of discharge, is formed between the nickel sintered body which is the current collector and the filled active material, so that the performance of the electrode plate is deteriorated. It is possible that
Further, it is considered that the current distribution becomes non-uniform because the composition of the active material is different. Secondly, there is a decrease in current collecting performance due to a decrease in the amount of nickel sintered body which is a current collector. Such problems are not limited to the sintering type positive electrode plate,
The same applies to the non-sintered type.

On the other hand, the discharge performance of the positive electrode plate having a nickel oxide layer thickness of more than 70 Å has deteriorated from the beginning. One of the causes for this is that as the nickel oxide layer becomes thicker, the nature of the nickel oxide, which is originally an insulator, appears remarkably, and the contact resistance between the active material and the nickel sintered substrate, which is the current collector, becomes large. It is possible.

Example Hereinafter, an example of the present invention and its effect will be described in comparison with a conventional example.

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 described below were prepared.

Carbonyl nickel powder is kneaded with methylcellulose and water to form a nickel slurry.This nickel slurry is applied to a nickel-plated perforated steel sheet, dried, and then sintered at 900 ° C in a reducing atmosphere containing water vapor to form a nickel sintered substrate. It was made. This is substrate A. Further, the substrate A was heat-treated at 250 ° C. in an air atmosphere to prepare a nickel sintered substrate having a nickel oxide layer on the surface of the nickel sintered body. This is substrate B. The average thickness of the nickel oxide layer of the substrate B was about 80Å, but the thickness of the oxide layer can be freely changed by changing the heat treatment conditions.

Positive electrode plate A (conventional product) Substrate A on which a nickel oxide layer is not formed is immersed in a mixed aqueous solution of each of the nitrates in which the ratio of nickel, cobalt and cadmium is 95: 2: 3, and then concentrated and neutralized. The ordinary chemical impregnation process was repeated several times to produce the film.

Positive electrode plate B (conventional product) A positive electrode plate A was used, and a normal compound impregnation process was further performed once with a solution of cobalt nitrate alone to produce cobalt hydroxide alone in the active material.

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

Positive Electrode Plate D (Product of the Present Invention) A positive electrode plate B was produced in the same manner as in the positive electrode plate B, except that a substrate B having a nickel oxide layer having a flat thickness of 80 Å was used in place of the substrate A.

The average thickness of the nickel oxide layers of the positive electrode plates C and D measured at the end of the step of impregnating the active material were both about 60Å. Further, in the positive electrode plates A and B, 20% of the nickel sintered body was corroded during the step of impregnating the active material. Further, regarding the positive electrode plates B and D in which the active material contains a single cobalt hydroxide, it is known that the discharge performance of the positive electrode plate is affected by the addition amount of the cobalt compound, and it is already confirmed that the cobalt compound is suitable. Since the proper blending amount was confirmed, the proper blending amount was set. For example, in a positive electrode plate in which a nickel oxide layer is not formed on the surface of a nickel sintered body, the amount of a single cobalt compound is 2.0 to 2.0% with respect to the amount of nickel hydroxide.
When it is 8.0 mol%, the discharge performance is good. In the case of the positive electrode plate B, the amount is 5 mol%. On the other hand, in the positive electrode plate having the nickel oxide layer on the surface of the nickel sintered body, the discharge performance is good when the amount of the single cobalt compound is 0.4 to 7.0 mol% with respect to the amount of nickel hydroxide.
In the positive electrode plate D and Experiment 2 described later, the amount was 4.2 mol%.

After cutting the four types of positive electrode plates produced as described above into predetermined dimensions, two cadmium negative electrode plates having the same dimensions as the sample positive electrode plate were used as counter electrodes in a KOH electrolyte having a specific gravity of 1.250 (20 ° C). The discharge characteristics were measured. Charging was performed for 0.2 CA × 8 hours, and a mercury oxide electrode was used as a reference electrode. The discharge rate dependency of the active material utilization rate is shown in FIG. 1, and the discharge intermediate potential dependency of the discharge rate is shown in FIG. The discharge intermediate potential in FIG. 2 is the value when the discharge depth is 50% of the theoretical capacity.

As can be seen from FIG. 1, the positive electrode plate A of the conventional product has a lower active material utilization rate than any other positive electrode plate and is inferior in discharge rate dependency. On the other hand, the positive electrode plate B containing cobalt hydroxide which does not form a solid solution with nickel hydroxide by being impregnated with cobalt nitrate alone has an improved active material utilization rate of about 15 to 20%. Further, the positive electrode plate C in which a nickel oxide layer is formed on the surface of the nickel sintered body to prevent the nickel sintered body from corroding in the active material impregnation step has not only the active material utilization rate but also its discharge rate dependency. Is also improving. Further, the positive electrode plate D of the present invention in which the nickel oxide layer was formed on the surface of the nickel sintered substrate and which was impregnated with cobalt nitrate alone had the best utilization of the active material and its discharge rate dependency, and the discharge rate was 30 CA. Very little deterioration in performance. Such performance was not obtained with the conventional product, and it is considered that the synergistic effect of the above-described two improved techniques appeared.

The intermediate discharge potential shown in FIG. 2 has the same tendency as that shown in FIG. 1, but it is important to form a nickel oxide layer on the surface of the nickel sintered body especially in the case of ultra high rate discharge such as 30 CA. Can be said.

As is clear from the measurements of the above two initial characteristics,
A nickel oxide layer is formed on the surface of the nickel sintered body to prevent corrosion of the nickel sintered body in the step of impregnating the active material, and further nickel hydroxide and a cobalt compound which does not form a solid solution are contained in the active material. Thus, it is clear that a nickel positive electrode plate having an extremely high discharge characteristic can be obtained.

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

The nickel sintered substrate used here is the substrate B used in Experiment 1.
Was prepared in the same manner as in, but the average thickness of the nickel oxide layer formed on the surface of the nickel sintered body was changed between 10 and 140Å by changing the oxidation conditions. .

Impregnation with the active material was performed in the same manner as in the positive electrode plates B and D of Experiment 1. In other words, the impregnating solution is a mixed solution of nickel nitrate containing cobalt nitrate as a main component, cobalt nitrate, and cadmium nitrate. After repeating the above process several times, finally, the process of chemical impregnation was performed once using a solution of cobalt nitrate alone to produce cobalt hydroxide alone.

After the completion of the active material impregnation step, 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 decreased by about 20 Å compared to that before the active material impregnation step. In other words, it is considered that the nickel oxide layer was dissolved by about 20Å during the step of impregnating the active material. In the positive electrode plate in which the original nickel oxide layer had a thickness of less than 20 Å, the nickel sintered body was corroded in all cases, so it was excluded from the following test.

The sample positive electrode plate was continuously cycled under the following conditions.

Charging 1CA × 1.2 hours Pause 1 hour Discharge up to 30CA + 0.1V vs. Hg / Hg O Pause 1 hour Figure 3 shows the active material utilization rate during discharge at the 3rd and 100th cycles, and in Fig. 4 the discharge intermediate time. Indicates electric potential. The average thickness of the nickel oxide layer on the horizontal axis is a value after the completion of the step of impregnating the active material.

As can be seen from the results in FIG. 3, when the thickness of the nickel oxide layer on the surface of the nickel sintered body exceeds 80 Å, the active material utilization rate decreases. It is considered that one of the reasons for this is that the insulating property of nickel oxide has an influence. On the other hand, at the 100th cycle, the nickel oxide layer had a thickness of 5Å
The utilization rate of the active material is also reduced when the ratio is less than the above. As one of the reasons for this, it is conceivable that when the nickel oxide layer is very thin, the nickel sintered body becomes an active material as the charge / discharge cycle progresses. That is, an active material of nickel hydroxide alone having a composition different from the composition of the active material filled in the impregnation step is generated between the nickel sintered body and the filled active material, which deteriorates the electrode plate performance such as uneven current distribution. It is considered to be one of the causes.

The discharge intermediate potential in Fig. 4 shows the same tendency as in Fig. 3, but the performance deteriorates when the thickness of the nickel oxide layer exceeds 70Å, and the nickel oxidation rate is higher than the active material utilization rate in Fig. 3. It seems that the thickness of the material layer has a great influence.

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 70Å, a nickel positive electrode plate having very good ultra-high rate discharge characteristics can be obtained.

In the experiments 1 and 2 described above, the present invention has been described by the method of filling the active material by the chemical impregnation method using the sintered substrate of nickel, but when the filling method of the active material is the electrolytic impregnation method or the non-sintering method. It has been confirmed by experiments that similar results are obtained even when a substrate made of the nickel porous body of the formula is used. Further, although the cobalt compound alone has been explained with cobalt hydroxide, it has been confirmed by experiments that similar results can be obtained with various cobalt salts and cobalt oxides.

EFFECTS OF THE INVENTION Based on the present invention as shown in the above examples, the average thickness of 5 to 5 is provided on the surface of the nickel porous body holding the active material.
By having a 70Å layer of nickel oxide and further containing a cobalt compound that does not form a solid solution with nickel hydroxide in the active material, the active material utilization rate and discharge position are very good in super-efficient discharge. It is possible to obtain an excellent nickel positive electrode plate.

[Brief description of drawings]

FIG. 1 is a characteristic diagram showing an example of the discharge rate dependence of the active material utilization rate of the nickel positive electrode plate for alkaline storage batteries according to the present invention and the conventional nickel positive electrode plate of this kind, and FIG. 2 is the nickel for alkaline storage batteries according to the present invention. A characteristic diagram showing an example of the discharge rate dependence of the discharge intermediate potential of a positive electrode plate and a conventional nickel positive electrode plate of this kind, and FIG. 3 shows the thickness of the nickel oxide layer on the surface of the nickel sintered body and the utilization rate of the active material 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.

Claims (1)

[Claims] 1. A cobalt compound having a nickel oxide layer having an average thickness of 5 Å or more and 70 Å or less on the surface of a nickel porous body holding an active material, the cobalt compound not forming a solid solution with nickel hydroxide. A nickel positive electrode plate for an alkaline storage battery, which is characterized by being contained therein.