JPH07118331B2 - Nickel-cadmium storage battery - Google Patents

Description

Description: FIELD OF THE INVENTION The present invention relates to nickel-cadmium storage batteries.

Conventional technology and problems Since the discharge reaction of cadmium active material goes through the mechanism of dissolution and precipitation, the utilization rate of active material during discharge drops significantly as the discharge current increases. Although nickel-cadmium storage batteries using cadmium negative electrode plates are manufactured according to various applications, among them, storage batteries for high rate discharge applications that discharge at a high current depend on the discharge rate of the above cadmium negative electrode plate. Due to its higher performance than the nickel hydroxide electrode, the capacity was about 30% less than that of a general-purpose storage battery.

Therefore, it has been a problem to improve the problems caused by the characteristics of the negative polarity of cadmium and obtain a nickel-cadmium storage battery having excellent high rate discharge characteristics.

Means for Solving the Problems The present invention is characterized in that the electrolytic solution of a nickel-cadmium storage battery contains hydroxyethyl cellulose.

Actions In order to improve the discharge performance of nickel-cadmium storage batteries, methods using various additives such as carboxymethyl cellulose and sodium silicate have been proposed. However, the effect of the additives proposed hitherto has been slight.

The present inventor also investigated various additives, and by using an alkaline electrolyte containing hydroxyethyl cellulose in a storage battery, the active material utilization rate during high-rate discharge of cadmium active material was greatly improved, and the storage battery was improved. It has been found that the capacity of In addition, this effect was recognized for all those containing a cadmium active material regardless of the form of the negative electrode plate (sintering type, paste type, etc.). An example of the outline of the effect when the electrolytic solution containing hydroxyethyl cellulose is used is as follows.

The conventional sealed nickel-cadmium storage battery, which is called for general use, is usually used for discharging up to about 2 CA (1/2 hour rate). When this is discharged at, for example, 10 A (10 hour rate), it can be discharged by about 6 CA as compared with the case where the discharge rate dependence of the cadmium negative electrode plate allows the discharge of electricity at 1 CA (1 hour rate).
It drops to 0-70%.

On the other hand, when the same nickel-cadmium battery with an electrolyte containing hydroxyethyl cellulose was used,
The amount of electricity that can be discharged with CA is approximately 80 to 85 when discharged with 1 CA.
%, Which is an improvement from yes.

The reason for this effect is that when hydroxyethyl cellulose is used, the crystal form of the cadmium active material is γ, which is needle-like.
It is thought that it is because it is a mold.

Hydroxyethyl cellulose has already been used as a material for improving the charging efficiency of cadmium hydroxide at low temperature, as disclosed in JP-A-61-2405
It is a substance proposed in Japanese Patent Publication No. 79. In this proposal, hydroxyethyl cellulose is added when manufacturing a paste-type cadmium negative electrode plate, but the storage battery using the cadmium negative electrode plate manufactured in this manner has a charge and discharge cycle of several tens of cycles compared to the initial stage. It was found that the higher rate discharge has better performance, which is unstable.

Therefore, when the paste type cadmium negative electrode plate to which hydroxyethyl cellulose was added was further investigated, it was found that it had the following new problems.

Unlike methyl cellulose and carboxymethyl cellulose, hydroxyethyl cellulose is completely soluble in water. Therefore, in the process of drying the active material paste in the process of manufacturing the paste-type cadmium negative electrode plate, the hydroxyethyl cellulose is carried to the surface part of the electrode plate by the water moving from the inside of the electrode plate to the outside.

That is, the distribution of hydroxyethyl cellulose in the paste-type cadmium negative electrode that has completed the drying process is different depending on the site of the electrode plate, and that the amount of hydroxyethyl cellulose present on the surface of the electrode plate is very large. Due to this, the performance is unstable.

However, since hydroxyethyl cellulose is soluble in a high-concentration alkaline electrolyte used in nickel-cadmium storage batteries, such a paste-type cadmium negative electrode plate is left in the alkaline electrolyte for a long time of about one week, or
Alternatively, by repeating charging and discharging for about 20 cycles, the distribution of hydroxyethyl cellulose becomes uniform and the performance becomes stable.

However, as compared with the open type storage battery, the closed type requires less time for the electrode performance to stabilize because the amount of electrolyte is smaller.

The present invention solves the problems as described above, and is based on the finding that good characteristics can be stably obtained from the initial stage by using an electrolytic solution containing hydroxyethyl cellulose. . INDUSTRIAL APPLICABILITY The present invention is particularly effective in a sealed storage battery which has conventionally required a long period of time until the electrode performance becomes stable.
It can also be applied to a sintered cadmium negative electrode plate, which could not be applied in the invention disclosed in Japanese Unexamined Patent Publication No. 240579.

Examples The present invention will be described below with reference to preferred examples.

[Battery A] (conventional example) A nickel slurry prepared by kneading metallic nickel powder, methyl cellulose and water was applied to a nickel-plated perforated steel sheet, which was treated in a reducing atmosphere at 950 ° C. and then 200 A sintered substrate was produced by heat treatment at ℃. Next, after impregnating the sintered substrate with an aqueous solution of cadmium nitrate. The normal chemical impregnation step of neutralizing and filling the cadmium active material was repeated to prepare a sintered cadmium negative electrode plate. A nickel hydroxide positive electrode plate was also manufactured by a normal chemical impregnation process.

The negative electrode plate and the positive electrode plate manufactured as described above were stacked with a polypropylene separator interposed therebetween and then housed in a metal container to obtain a prismatic sealed nickel-cadmium storage battery having a negotiation capacity of 600 mAh. Specific gravity after electrolysis 1.30
A 0 (20 ° C.) KOH aqueous solution was used. This is storage battery A.

[Rechargeable Battery B] (Example of the present invention) The same operation was performed as in Rechargeable Battery A, except that 1.5 g of hydroxyethyl cellulose was dissolved in 1 liter of an aqueous KOH solution having a specific gravity of 1.300 (20 ° C.). This is storage battery B
And

[Battery C] (conventional example) 100 parts cadmium oxide powder, 20 parts metal cadmium powder,
Metallic nickel powder 10 parts, methyl cellulose 0.8 parts, potassium gluconate 0.4 parts, salt bee acrylonitrile short fibers
Cadmium paste was prepared by kneading 0.8 parts and 50 parts of water. A paste-type cadmium negative electrode plate was manufactured by applying this paste to a perforated steel plate plated with nickel and drying at 90 ° C.

The nickel hydroxide positive electrode plate was the same as that used in the storage battery A, and a storage battery was manufactured in the same manner as the storage battery A using the above electrode plate. This is referred to as a storage battery C. Specific gravity of electrolyte is 1.30
0 (20 ℃) KOH aqueous solution.

[Battery D] (conventional example) The same as Battery B except that 1.2 g of carboxymethylcellulose was dissolved in 1 liter of an aqueous KOH solution having a specific gravity of 1.300 (20 ° C.). This is referred to as a storage battery D.

[Rechargeable Battery E] (Example of the present invention) The same operation as in Rechargeable Battery C except that 1.2 g of hydroxyethyl cellulose cellulose was dissolved in 1 liter of an aqueous KOH solution having a specific gravity of 1.300 (20 ° C.). This is referred to as a storage battery E.

[Storage Battery E] (Comparative Example) Storage battery C was the same as storage battery C except that hydroxyethyl cellulose was used instead of methyl cellulose in the formulation of the cadmium paste. This is referred to as a storage battery F.

Water required for the hydration reaction of cadmium oxide is further added to the storage batteries C to F.

After charging / discharging the storage batteries A to F produced as described above for about 10 cycles, the relationship between the discharge current and the discharge electricity amount at room temperature was obtained.

The results are as shown in Fig. 1. The storage batteries B and E containing hydroxyethyl cellulose in the electrolytic solution clearly have a large amount of electricity at a high rate discharge as compared with the conventional storage batteries A, C and D, and the negative electrode It shows that it is hard to be a limit. Further, it is shown that the storage battery F of the comparative example has a smaller amount of discharged electricity than the storage batteries B and E of the present invention, and the performance is not sufficiently improved.

Next, among the storage batteries that have been tested, the conventional storage battery D and the storage battery E according to the present invention are disassembled, the cadmium negative electrode plate is taken out, washed with purified water, and the surface X-ray analysis pattern is measured using Cu K _α rays. Also, the crystal morphology of the active material was examined by using an electron microscope. The X-ray analysis figures of the storage battery D and the storage battery E are shown in FIGS. 2 and 3. Similar electron micrographs (× 2000) are shown in FIGS. 4 and 5.

As a result, in the cadmium negative electrode plate of the storage battery D in which carboxylmethyl cellulose is added to the electrolytic solution, the crystal form of the active material is β type, whereas in the cadmium negative electrode plate of the storage battery E in which hydroxyethyl cellulose is added to the electrolytic solution, needle-shaped γ It turns out that the mold is the main one.

As described above, it is clear that hydroxyethyl cellulose affects the crystal morphology of the cadmium active material, and it is considered that this is the reason why the active material utilization rate at the time of high rate discharge is improved.

Next, the amount of hydroxyethyl cellulose added to the electrolytic solution was examined. As the battery, a battery was manufactured based on the storage battery E and using an electrolytic solution in which the amount of hydroxyethyl cellulose added was changed variously, and the discharge performance thereof was measured. FIG. 6 shows the results, and it is considered that 0.2 g / or more and 9 g / or less is suitable as the amount of hydroxyethyl cellulose added.

In the examples of the present invention, the specific gravity of 1.300 (20 ° C.) was shown when using an aqueous KOH solution, but other than this, the specific gravity of 1.22 to 1.35 (20) which is generally used for nickel-cadmium storage batteries is shown.
(° C) It was confirmed that the same effect was obtained with KOH aqueous solution.
The same effect was also observed when the electrolyte was NaOH or a mixed system of KOH, NaOH and LiOH.

Effects of the Invention As described above, by using the alkaline electrolyte containing hydroxyethyl cellulose, it is possible to obtain a nickel-cadmium storage battery having excellent high rate discharge characteristics.

[Brief description of drawings]

FIG. 1 is a diagram comparing the discharge characteristics of the conventional product and the product of the present invention. FIG. 2 is an X-ray analysis pattern on the surface of the cadmium negative electrode plate of the conventional storage battery D, and FIG. 3 is a view showing an X-ray analysis pattern on the surface of the cadmium negative electrode plate of the storage battery E according to the present invention. FIG. 4 is an electron micrograph showing the structure of the crystal of the active material on the surface of the cadmium negative electrode plate of the conventional storage battery D. Fifth
The figure is an electron micrograph showing the structure of the crystal of the active material on the surface of the cadmium negative electrode plate of the storage battery E of the present invention. FIG. 6 is a diagram showing the effective range of the present invention.

Claims (2)

[Claims] 1. A nickel-cadmium storage battery comprising an alkaline electrolyte containing hydroxyethyl cellulose. 2. The nickel-cadmium battery according to claim 1, wherein the content of hydroxyethyl cellulose in the alkaline electrolyte is 0.2 g / g or more and 9 g / g or less.