JPH0685327B2 - Manufacturing method of cadmium negative electrode plate for alkaline storage battery - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for producing a paste type cadmium negative electrode plate for an alkaline storage battery.

Conventional technology and its problems When producing a paste type cadmium negative electrode plate, metal cadmium, cadmium hydroxide, and cadmium oxide can be considered as raw material active material powders. Among them, metal cadmium is not suitable as a main raw material of an active material because it is very expensive and its activity is low. Further, since cadmium hydroxide has a lower density than cadmium oxide or metal cadmium, there is a disadvantage that the energy density per volume of the negative electrode plate is low. On the other hand, cadmium oxide is most suitable as a raw material for the active material of the paste type negative electrode plate in terms of raw material cost, energy density and electrode plate performance.

On the other hand, as a solvent for dispersing the active material powder, an organic solvent and water can be considered, but when water with a low raw material cost is used, cadmium oxide reacts with water in a short time to change into cadmium hydroxide. Not only does the energy density per electrode plate volume decrease, but the active material paste solidifies. That is, it becomes impossible to apply the active material paste to the current collector or the core. For this reason, conventionally, an organic solvent has been used as a solvent. When an organic solvent is used, the reaction of changing cadmium oxide to cadmium hydroxide does not occur, so workability is good, and a paste type cadmium negative electrode plate with high energy density per electrode plate volume and high utilization rate of active material can be obtained. On the other hand, the cost of the solvent is higher than that of water, and various measures are required in handling in terms of pollution, fire, and working environment, which complicates the manufacturing process and considerably increases the manufacturing cost. There is.

Under such circumstances, one proposal has recently been made. The content is to add an intramolecular esterified product of hydroxycarboxylic acid or a salt thereof to an active material paste using cadmium oxide as an active material raw material. According to this method, the change of cadmium oxide to cadmium hydroxide is suppressed for a long time even when water, which is low in cost, is used as a solvent, so that the viscosity of the active material paste is stable and the workability is good. However, in the case of this method, if there is no external force applied to the active material paste, it will be about 24-50.
Although it has the effect of stabilizing the viscosity by suppressing the hydration reaction of cadmium oxide for a period of time, when stirring or shearing force is applied as in the case of actually applying the active material paste to the current collector,
This effect was considerably reduced, and the paste viscosity could be stabilized only for about 3 hours.

For these reasons, a new method for stabilizing an active material paste that enables continuous production of a paste type cadmium negative electrode plate has been demanded.

Means for Solving the Problems The present invention provides at least one of an intramolecular esterified product of hydroxycarboxylic acid or a salt thereof in an active material paste containing cadmium oxide and water in the production of a paste type cadmium negative electrode plate for an alkaline storage battery. One or more substances and at least one or more substances of boric acid or salts thereof are added to stabilize the viscosity of the active material paste for a long time and enable continuous production of a paste type cadmium negative electrode plate. Is.

Action If the intramolecular esterification product of hydroxycarboxylic acid or its salt is added to the active material paste containing cadmium oxide and water, the viscosity of the active material paste will stabilize when a force such as stirring is applied as described above. The time spent was about 3 hours. On the other hand, when boric acid or a salt thereof is added to the active material paste instead of the intramolecular esterified product of hydroxycarboxylic acid or a salt thereof, the time during which the viscosity of the active material paste is stable is 10 minutes or less. However, when both of these two substances are added to the active material paste, the time during which the viscosity of the active material paste is stable is dramatically increased to about 30 hours, during which the hydration reaction of cadmium oxide is suppressed. I found out that

The reason for this is not clear, but when boric acid or a salt thereof is added alone to the active material paste, the viscosity of the active material paste is slightly reduced as compared with the case where nothing is added, but oxidation The pot life until hydration of cadmium occurs and loses fluidity is almost the same as that when nothing is added.Therefore, boric acid or its salt has a function of suppressing the hydration of cadmium oxide. I don't think so. On the other hand, the intramolecular esterified product of hydroxycarboxylic acid and its salt have a function of suppressing the hydration reaction of cadmium oxide, although it varies depending on the stirring conditions and the like, and therefore boric acid and its salt. Is considered to have the effect of sustaining the action of the intramolecular esterified product of hydroxycarboxylic acid and its salt for a long time.

Comparing the method of the present invention with the conventional method from the technical point of view, in the conventional method, the pot life of the active material paste is about 3 hours as described above. When this method is used for producing a paste-type negative electrode plate, the net time used for manufacturing the negative electrode plate is approximately because the preparation time of the active material paste and the cleaning time for cleaning are included in about 3 hours. It is a very short time of about 1 hour. That is, in the case of this conventional method, it is almost impossible to continuously produce a paste-type negative electrode plate, and the productivity is low and the cost is low due to the low yield of raw materials and the difficulty in automation of production equipment. Becomes higher. On the other hand, in the case of the method of the present invention, since the pot life of the active material paste is about 30 hours as described above, continuous production of 8 hours, 12 hours or, in the maximum case, 24 hours is possible. Contrary to the conventional method, it is a revolutionary manufacturing method with high productivity and low cost, and its industrial value is extremely large.

Examples Hereinafter, the present invention will be described with reference to Examples.

First, as an example of the present invention, a negative electrode plate was manufactured as follows.

Example 1 (Example of the present invention) 100 parts by weight of cadmium oxide powder, metal cadmium powder 18
Parts by weight, methyl cellulose 0.6 parts by weight, vinyl chloride polymer latex emulsion 5 parts by weight, vinyl chloride-acrylic copolymer short fibers 0.8 parts by weight, and sodium ascorbate 0.3 parts by weight as a cadmium oxide hydration inhibitor. Then, 0.2 part by weight of potassium borate was added and kneaded to obtain an active material paste. This paste was applied to a perforated plate of nickel plated with iron using the paste applicator shown in FIG. 5, and then dried at 90 ° C. for 1 hour to prepare a negative electrode plate. This is designated as Sample A.

In FIG. 5, 1 is a bobbin for feeding a metal perforated plate, 2 is a perforated metal plate, 3 is an active material paste tank, 4 is an active material paste, 5 is a drying furnace, and 6 is an electrode plate winding bobbin. .

Example 2 (Example of the present invention) A negative electrode plate was produced in the same manner as in Example 1 except that ascorbic acid was used instead of sodium ascorbate in Example 1. This is designated as Sample B.

Example 3 (Example of the present invention) A negative electrode plate was produced in the same manner as in Example 1 except that tetronic acid was used instead of sodium ascorbate in Example 1. This is designated as Sample C.

Example 4 (Example of the present invention) A negative electrode plate was prepared in the same manner as in Example 1 except that 0.15 part by weight of sodium ascorbate and 0.15 part by weight of tetronic acid were used in place of 0.3 part by weight of sodium ascorbate in Example 1. It was made. This is designated as Sample D.

Example 5 (Example of the present invention) A negative electrode plate was prepared in the same manner as in Example 1 except that 0.1 part by weight of boric acid and 0.1 part by weight of potassium borate were used in place of 0.2 part by weight of potassium borate in Example 1. It was made. This is designated as Sample E.

Example 6 (Example of the present invention) 0.15 parts by weight of ascorbic acid and 0.15 parts by weight of sodium ascorbate were used in place of 0.3 parts by weight of sodium ascorbate in Example 1, and 0.1 parts by weight of boric acid was used instead of 0.2 parts by weight of potassium borate. Parts by weight and sodium borate 0.1
A negative electrode plate was produced in the same manner as in Example 1 except that parts by weight were used. This is designated as Sample F.

Next, as three comparative examples for the method of the present invention, conventional negative electrode plates were prepared as follows.

Example 7 (conventional method example) A negative electrode was manufactured in the same manner as in Example 1 except that 0.5 parts by weight of sodium ascorbate was used instead of 0.3 parts by weight of sodium ascorbate and 0.2 parts by weight of potassium phonate in Example 1. A plate was made. This is designated as Sample G.

Example 8 (Prior art example) 0.5 parts by weight of potassium borate alone was used in place of 0.3 parts by weight of sodium ascorbate and 0.2 parts by weight of potassium borate in Example 1, but the active material paste was fluidized during kneading. Was lost, and coating on the perforated plate was impossible.

Example 9 (conventional method example) The composition was the same as that of Example 1 except that sodium ascorbate and potassium borate were removed, but the active material paste lost fluidity during kneading, and was not applied to the porous plate. It was impossible.

As described above, in Examples 8 and 9, the hydration reaction of cadmium oxide could not be suppressed, and the fluidity of the paste was lost during the kneading and the paste did not solidify. I could not do it.

Next, FIGS. 1 and 2 in which the samples A to G produced in Examples 1 to 7 are compared will be described.

FIG. 1 is a diagram showing the relationship between the elapsed time after the start of coating on a porous plate and the coating amount of the active material per unit area of the porous plate (after drying). As is clear from this, Examples 1 to 6 of the present invention
It can be seen that in Samples A to F, the coating amount was constant for a long time and the paste viscosity was stable as compared with Sample G of Conventional Example 7.

FIG. 2 shows the results of measuring the cycle life of a cylindrical sealed nickel-cadmium storage battery having a nominal capacity of 1.9 Ah, which was prepared by combining the negative electrode plates of samples A to G and the sintered nickel positive electrode plate prepared by the usual method. Is. A to G in the figure correspond to Samples A to G of the negative electrode plate, respectively. As is clear from this, the batteries using Samples A to F of Examples 1 to 6 of the present invention maintained their capacities even after 1200 cycles, whereas Sample G of Conventional Example 7 had a negative electrode. The capacity of the battery used for the plate dropped significantly after about 800 cycles, and the life of the battery was exhausted.

When the battery after the above test was disassembled and the negative electrode plate was examined, no abnormalities were found in Samples A to F, but Sample G was tested.
However, the amount of active material applied varied depending on the part, and an internal short circuit occurred in the part with the highest amount applied. It is considered that this is because the original active material paste has poor viscosity and stability. That is, in the case of the production method of the present invention, since the active material paste has a long pot life and the viscosity of the active material paste is stable, uniform coating can be performed on the porous plate and the cycle life is improved. it is conceivable that.

Experiment Next, the results of studying the required addition amount of the cadmium oxide hydration-inhibiting substance in the present invention will be described.

Select sodium ascorbate from the group consisting of hydroxycarboxylic acid intramolecular esterification products or salts thereof, and potassium borate from the group consisting of boric acid or its salts. While applying (shearing force), the pot life until the fluidity of the paste disappeared was measured. The results are shown in FIG. The effect of adding potassium borate to sodium ascorbate is stable in the range of about 10 wt% to 220 wt%, but if continuous production for 24 hours is assumed, it is 5 to 5.
It is understood that the range is 230 wt%.

Next, the optimum addition amount of this two-component hydration reaction inhibiting substance to cadmium oxide was investigated. The result is the fourth
Shown in the figure. The amount of potassium borate added to sodium ascorbate was 5 wt%. The horizontal axis is the amount of the hydration reaction inhibitor for cadmium oxide, and the vertical axis is the pot life of the active material paste. As in the case of Fig. 3, assuming continuous production for 24 hours, the required addition amount of the hydration reaction inhibitor is 0.1 wt with respect to the weight of cadmium oxide.
% Or more, that is, sodium ascorbate is 0.095 wt%
The above is necessary. In combination with the above results, the addition amount of the hydration reaction-inhibiting substance needs to be in the following range.

Sodium ascorbate is required to be 0.095 wt% or more with respect to the weight of cadmium oxide, and potassium borate is 5 to 230 wt% with respect to the weight of sodium ascorbate.
Is the range.

Among the hydration reaction inhibitors, ascorbic acid as an intramolecular esterified product of hydroxycarboxylic acid or its salt, tetronic acid and each salt have the same effect, and boric acid as a boric acid system. In addition to potassium, it has been confirmed that boric acid and sodium borate have equivalent effects.

Effects of the Invention As described above, according to the present invention, the viscosity of the active material paste can be stabilized for a long time, continuous production of a paste-type cadmium negative electrode plate can be made possible, and productivity can be improved. Therefore, it is possible to achieve excellent advantages such as cost reduction.

[Brief description of drawings]

FIG. 1 is a diagram showing a relationship between a coating operation elapsed time and a coating amount of an active material paste of the present invention and an active material paste of a conventional method.
The figure shows the life characteristics of a nickel-cadmium storage battery using the negative electrode plate obtained by the present invention and the negative electrode plate obtained by the conventional method, and FIG. 3 is a blend of the two-component hydration reaction inhibiting substance of the present invention. Figure showing the relationship between the ratio and pot life of the active material paste,
FIG. 4 is a diagram showing the relationship between the compounding amount of the two-component system hydration reaction inhibiting substance of the present invention with respect to cadmium acid and the pot life of the active material paste, and FIG. 5 is an example of the paste applying apparatus used in the present invention. It is a schematic structure drawing.

Claims (3)

[Claims] 1. A method for producing a paste-type cadmium negative electrode plate by applying an active material paste containing cadmium oxide and water to a current collector or a core, and drying the paste to obtain a paste-type cadmium negative electrode plate, wherein molecules of hydroxycarboxylic acid are contained in the active material paste. A method for producing a cadmium negative electrode plate for an alkaline storage battery, characterized in that it contains at least one substance selected from internal esterification products or salts thereof and at least one substance selected from boric acid or salts thereof. . 2. The content of the intramolecular esterified product of the hydroxycarboxylic acid or its salt is 0.095% or more based on the weight of cadmium oxide, and the content of the boric acid or its salt is the molecule of the hydroxycarboxylic acid. 5 to 23 by weight relative to the content of the internal esterified product or its salt
It is 0%, The manufacturing method of the cadmium negative electrode plate for alkaline storage batteries of Claim (1). 3. The method for producing a cadmium negative electrode plate for an alkaline storage battery according to claim 1, wherein the intramolecular esterification product of the hydroxycarboxylic acid is ascorbic acid or tetronic acid.