JPH0555982B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a method for manufacturing a paste-type cadmium negative electrode plate for alkaline storage batteries.

Conventional technology and its problems When manufacturing a paste-type cadmium negative electrode plate, the raw material active material powder is metal cadmium,
Cadmium hydroxide and cadmium oxide are considered. Among these, metal cadmium is very expensive and has low activity, so it is not suitable as a main raw material for active materials. Furthermore, 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 an active material raw material for paste-type negative electrode plates in terms of raw material cost, energy density, and electrode plate performance.

On the other hand, as a solvent for dispersing active material powder,
Organic solvents and water are considered, but if water is used because the raw material cost is low, cadmium oxide will react with water in a short time and change to cadmium hydroxide, which will only lower the energy density per plate volume. Instead, the active material paste solidifies. In other words, it becomes impossible to apply the active material paste to the current collector or the core. For this reason, conventionally, organic solvents have been unavoidably used as solvents. When an organic solvent is used, a reaction in which cadmium oxide changes to cadmium hydroxide does not occur, so a paste-type cadmium negative electrode plate with good workability, high energy density per plate volume, and high active material utilization rate can be obtained. On the other hand, the cost of the solvent is higher than that of water, and various measures need to be taken when handling it in terms of pollution, fire, and the work environment, which makes the manufacturing process complicated and increases the manufacturing cost considerably. There is.

Under these circumstances, one proposal has been made recently. The content is that hydroxycarboxylic acid or its salt is added to an active material paste using cadmium oxide as an active material raw material. According to this method, even if inexpensive water is used as a solvent, the conversion of cadmium oxide to cadmium hydroxide is suppressed for a long time, so the viscosity of the active material paste is stabilized and workability is good. However, in this method, if no external force is applied to the active material paste, it is effective to suppress the hydration reaction of cadmium oxide and stabilize the viscosity for about 24 to 70 hours, but it does not actually become active. When agitation, shearing forces, etc. are applied, such as when applying a material paste to a current collector, this effect is considerably reduced, and the paste viscosity can only be stabilized for about 3 hours.

For these reasons, there was a need for a new method for stabilizing active material paste that would enable continuous production of paste-type cadmium negative electrode plates.

Means for Solving the Problems The present invention is directed to the production of paste-type cadmium negative electrode plates for alkaline storage batteries, in which at least one substance selected from hydroxycarboxylic acids and/or salts thereof is added to an active material paste containing cadmium oxide and water. By adding at least one substance selected from , boric acid, or a salt thereof, the viscosity of the active material paste can be stabilized for a long time, making continuous production of paste-type cadmium negative electrode plates possible.

Effect When hydroxycarboxylic acid or its salt is added to an active material paste containing cadmium oxide and water, when force such as stirring is applied as mentioned above,
The time period during which the viscosity of the active material paste is stable is approximately 3
It was time. On the other hand, when boric acid or its salt is added to the active material paste instead of hydroxycarboxylic acid or its salt, the time during which the viscosity of the active material paste is stable is 10 minutes or less. However, when both of these substances are added to the active material paste, the time that the viscosity of the active material paste remains stable increases dramatically to about 30 hours, and during that time, the hydration reaction of cadmium oxide is suppressed. The reason for this is not clear, but
When boric acid or its salt is added alone to the active material paste, the viscosity of the active material paste decreases somewhat compared to when nothing is added, but the hydration reaction of cadmium oxide occurs and the fluidity is improved. Since there is almost no difference in the pot life before loss compared to when nothing is added, it seems that boric acid or its salt has almost no effect on suppressing the hydration reaction of cadmium oxide. On the other hand, it is clear that hydroxycarboxylic acids and their salts have the effect of suppressing the hydration reaction of cadmium oxide, although there are differences depending on the stirring conditions, etc. Therefore, boric acid and its salts have a hydroxyl It is thought that it has the effect of sustaining the action of carboxylic acids and their salts for a long time.

Comparing the method of the present invention and the conventional method from a technical point of view, in the case of the conventional method, the pot life of the active material paste is about 3 hours, as mentioned above. When this method is used to produce a paste-type negative electrode plate, the time required to prepare the active material paste and the cleaning time is included in the approximately 3 hours, so the net time used to manufacture the negative electrode plate is approximately 3 hours. It's only a very short amount of time, about an hour. In other words, with this conventional method, it is almost impossible to continuously produce paste-type negative electrode plates, and productivity is low due to low yield of raw materials and difficulty in automating production equipment. Moreover, the cost increases. On the other hand, in the case of the method of the present invention, as mentioned above, the pot life of the active material paste is about 30 hours, so continuous production for 8 hours, 12 hours, or at most 24 hours is possible. Contrary to the conventional method mentioned above, this is a revolutionary manufacturing method with high productivity and low cost, and its industrial value is great.

Example The present invention will be explained below with reference to Examples.

First, as an example of the present invention, a negative electrode plate was produced in the following manner.

Example 1 (Example of the present invention) 100 parts by weight of cadmium oxide powder, 18 parts by weight of metal cadmium powder, 0.6 parts by weight of methyl cellulose,
5 parts by weight of vinyl chloride polymer latex emulsion, short fibers of vinyl chloride-acrylic copolymer
0.8 parts by weight, and 0.3 parts by weight of monosodium citrate as a hydration reaction inhibitor of cadmium oxide.
0.2 parts by weight of potassium borate was added and kneaded to form an active material paste. This paste was applied to a perforated plate made of nickel plated iron, and then dried at 90°C for 1 hour to produce a negative electrode plate. This is designated as sample A.

Example 2 (Example of the present invention) A negative electrode plate was produced in the same manner as in Example 1 except that boric acid was used instead of potassium borate in Example 1. This is designated as sample B.

Example 3 (Example of the present invention) A negative electrode was prepared in the same manner as in Example 1 except that sodium hydrogen tartrate was used instead of monosodium citrate in Example 1, and sodium borate was used instead of potassium borate. A board was made.
This is designated as sample C.

Example 4 (Example of the present invention) A negative electrode plate was produced in the same manner as in Example 1 except that citric acid was used instead of monosodium citrate in Example 1. This is designated as sample D.

Example 5 (Example of the present invention) Instead of 0.3 parts by weight of monosodium citrate in Example 1, 0.15 parts by weight of citric acid and 1 part by weight of citric acid
All Example 1 except that 0.15 parts by weight of potassium was used.
A negative electrode plate was prepared in the same manner as above. This is designated as sample E.

Example 6 (Example of the present invention) 0.15 parts by weight of tartaric acid and 0.15 parts by weight of potassium gluconate were used instead of 0.3 parts by weight of monosodium citrate in Example 1, and potassium borate
All Example 1 except that 0.1 part by weight of boric acid and 0.1 part by weight of sodium borate were used instead of 0.2 part by weight.
A negative electrode plate was prepared in the same manner as above. This is designated as sample F.

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

Example 7 (Example of conventional method) Everything was the same as in Example 1 except that 0.5 parts by weight of monosodium citrate was used instead of 0.3 parts by weight of monosodium citrate and 0.2 parts by weight of potassium borate in Example 1. A negative electrode plate was prepared. This is designated as sample G.

Example 8 (Example of conventional method) Only 0.5 parts by weight of potassium borate was used instead of 0.3 parts by weight of monosodium citrate and 0.2 parts by weight of potassium borate in Example 1, but the active material paste fluidized during kneading. It lost its properties, and it was impossible to apply it to a perforated plate.

Example 9 (Example of conventional method) A composition was used in which monosodium citrate and potassium borate were removed from the formulation in Example 1, but the active material paste lost fluidity during kneading and was difficult to coat on a porous plate. It was impossible to wear it.

As described above, in Examples 8 and 9, the hydration reaction of cadmium oxide could not be suppressed, and the paste lost its fluidity and solidified during kneading, so it was difficult to obtain a sample negative electrode plate. I couldn't do it.

Next, FIG. 1 and FIG. 2 will be explained, in which samples A to G prepared in Examples 1 to 7 are compared.

FIG. 1 is a diagram showing the relationship between the elapsed time after the start of coating onto a perforated plate and the amount of active material applied per unit area of the perforated plate (after drying). As is clear from this, compared to sample G of conventional method example 7, samples A to F of Examples 1 to 6 of the present invention have a constant coating amount for a long time, and the paste viscosity is stable. I understand.

Figure 2 shows the results of measuring the cycle life of a sealed cylindrical nickel-cadmium storage battery with a nominal capacity of 1.9 Ah by combining the negative electrode plates of Samples A to G with a sintered nickel positive electrode plate prepared by a conventional method. It is. A to G in the figure correspond to samples A to G of the negative electrode plate, respectively. As is clearer from this,
Batteries using Samples A to F of Examples 1 to 6 of the present invention for the negative electrode plate maintained their capacity even after 1200 cycles, whereas batteries using Sample G of Conventional Method Example 7 for the negative electrode plate had approximately Capacity decreases significantly after 800 cycles,
My life is over.

In addition, when the battery was disassembled after the above test and the negative electrode plate was examined, no abnormality was observed in samples A to F, but in sample G, the amount of active material applied differed depending on the part, and the amount of active material applied differed depending on the area. Internal short circuits were occurring in areas with large volumes. This is thought to be due to the poor viscosity and stability of the original active material paste. In other words, in the case of the manufacturing method of the present invention, in addition to the long pot life of the active material paste, the viscosity of the active material paste is stable, so it can be applied uniformly to the perforated plate, and the cycle life is improved. it is conceivable that.

Experiment Next, the results of a study on the necessary addition amount of the cadmium oxide hydration reaction inhibiting substance in the present invention will be described.

Select monosodium citrate from the group consisting of hydroxycarboxylic acids or their salts, and potassium borate from the group consisting of boric acids or their salts, change the mixing ratio to prepare an active material paste, and gently stir (shear force). The pot life until the paste lost its fluidity was measured while adding . The results are shown in FIG. The stable effect of adding potassium borate to monosodium citrate is approximately
The range is 10wt% to 240wt%, but it is understood that if continuous production is assumed for 24 hours, the range is 5 to 250wt%.

Next, we investigated the optimal amount of this two-component hydration reaction inhibitor to be added to cadmium oxide.
The results are shown in FIG. The amount of potassium borate added to monosodium citrate is 5wt%.
And so. The horizontal axis is the amount of the hydration reaction inhibitor against cadmium oxide, and the vertical axis is the pot life of the active material paste. As in the case of Figure 3, assuming 24-hour continuous production, the required amount of the hydration reaction inhibitor is 0.1wt relative to the weight of cadmium oxide.
% or more, that is, monosodium citrate is 0.095wt
% or more is required. In view of the above results, it is necessary that the amount of the hydration reaction inhibiting substance added is within the following range.

Monosodium citrate is required in an amount of 0.095 wt% or more based on the weight of cadmium oxide, and potassium borate is in a range of 5 to 250 wt% based on the weight of monosodium citrate.

Among the hydration reaction inhibitors, hydroxycarboxylic acids include citric acid, gluconic acid,
It has been confirmed that tartaric acid and its salts have equivalent effects, and that boric acid and sodium borate, in addition to potassium borate, have equivalent effects.

Effects of the Invention As described above, according to the present invention, it is possible to stabilize the viscosity of an active material paste for a long time, enable continuous production of paste-type cadmium negative electrode plates, and increase productivity. , it can provide excellent advantages such as lower costs.

[Brief explanation of the drawing]

Figure 1 is a diagram showing the relationship between the elapsed coating time and coating amount of the active material paste of the present invention and the active material paste of the conventional method. Figure 3 is a graph showing the relationship between the compounding ratio of the two-component hydration reaction inhibitor of the present invention and the pot life of the active material paste. FIG. 4 is a diagram showing the relationship between the amount of the two-component hydration reaction inhibiting substance of the present invention relative to cadmium acid and the pot life of the active material paste.

Claims (1)

[Scope of Claims] 1. A manufacturing method for obtaining a paste-type cadmium negative electrode plate by applying an active material paste containing cadmium oxide and water to a current collector or core and drying it, wherein a hydroxycarboxylic acid is added to the active material paste. or at least one substance thereof,
A method for producing a cadmium negative electrode plate for an alkaline storage battery, which comprises adding at least one substance selected from boric acid or a salt thereof. 2 The amount of the hydroxycarboxylic acid or its salt added is 0.095% based on the weight of cadmium oxide.
The cadmium negative electrode for an alkaline storage battery according to claim 1, wherein the amount of the boric acid or its salt added is 5 to 250% by weight relative to the amount of the hydroxycarboxylic acid or its salt added. Method of manufacturing boards. 3. The method for producing a cadmium negative electrode plate for an alkaline storage battery according to claim 1 or 2, wherein the hydroxycarboxylic acid is citric acid, gluconic acid, or tartaric acid.