JP2925764B2 - Manufacturing method of alkaline storage battery - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing an alkaline storage battery provided with a cadmium paste electrode.

[0002]

2. Description of the Related Art Conventionally, as a cadmium electrode plate used for an alkaline storage battery such as a nickel-cadmium storage battery, a non-sintering type cadmium electrode plate such as a paste type which is easy to manufacture and inexpensive has been widely used. A cadmium negative electrode of this kind is prepared by kneading a cadmium active material powder mainly composed of cadmium oxide powder, for example, with an appropriate solvent such as water and a kneading solution or a reinforcing fiber for imparting electrode plate strength to form an active material paste. The paste is prepared, applied to a conductive core, dried, subjected to a chemical conversion treatment of charging and discharging in an alkaline aqueous solution, and cut into appropriate dimensions to produce a paste.

When a chemical conversion treatment is performed as in this manufacturing method, the cadmium oxide is brought into contact with an alkaline aqueous solution during the chemical conversion treatment to change into cadmium hydroxide, and at the same time, the active material layer is hardened. When not performed, the active material layer is in a soft state. For this reason, when forming a spiral electrode body by winding an electrode using a pressure roller or the like without forming, in particular, the degree of pressure gradually increases as the electrode is closer to the end of winding than to the start of winding. As a result, the electrode thickness of such an unhydrated cadmium electrode decreases from the winding start portion to the winding end portion, and accordingly, the porosity of the electrode also decreases.

Accordingly, it is extremely difficult to form a spiral electrode body by winding a cadmium electrode while maintaining uniform porosity in the length direction of the electrode.

On the other hand, when a cadmium electrode having the same thickness is used, the average porosity of the unhydrated cadmium electrode after winding and the chemical conversion in which cadmium oxide has basically disappeared by chemical conversion. Comparing the average porosity of cadmium electrodes, the average porosity of unhydrated cadmium electrodes is generally smaller. For this reason, when trying to hold the same amount of electrolyte solution as a battery using a cadmium electrode that has undergone chemical formation in a battery using an unhydrated cadmium electrode, the unhydrated cadmium electrode has a small average porosity. In addition, the amount of electrolyte retained in the electrode is reduced, and the amount of electrolyte interposed between the positive electrode and the negative electrode is increased accordingly.

However, in this type of battery in which oxygen gas generated at the positive electrode during charging is absorbed by the cadmium electrode as the negative electrode, there is a suitable value for the amount of electrolyte interposed between the positive and negative electrodes. When a larger amount of electrolyte is interposed, it becomes difficult for oxygen gas to reach the negative electrode. This reduces the ability of the cadmium electrode to absorb oxygen gas, especially at the initial cycle stage immediately after battery assembly by charging and discharging.

Therefore, in order to set the oxygen gas absorption capacity to a value equal to or higher than a certain value, it is necessary to limit the amount of electrolyte injected. Then, the charge / discharge cycle proceeds to some extent, the amount of inactive, undischarged metal cadmium that is difficult to discharge in the cadmium electrode increases, is accumulated and increases the average porosity of the electrode, and the amount of electrolyte retained in the electrode. Increases as
The amount of electrolyte interposed between the negative electrodes decreases, and the discharge characteristics of the battery deteriorate. In order to prevent this, the above-described chemical conversion must be performed.However, since large-scale equipment is required to perform the chemical conversion, and the number of processes and manufacturing costs increase, a manufacturing method that can be said to be still sufficient has been developed. Absent.

In Japanese Patent Publication No. 2-139856, a paste of a kneaded active material mainly composed of cadmium oxide is applied to a conductive core to form a cadmium electrode plate, and then the cadmium oxide is hydroxylated. It has been proposed to hydrate in a sodium aqueous solution and then incorporate it into the battery. Here, as a specific method of hydration,
It states that it is preferable to immerse the cadmium electrode plate in a 60 ° C. aqueous sodium hydroxide solution.

However, as described above, when a battery that has been hydrated with an aqueous solution of sodium hydroxide is allowed to stand after assembly, there is a problem that the capacity is significantly deteriorated.

[0010]

SUMMARY OF THE INVENTION The present invention solves the above-mentioned problems, and aims to suppress the deterioration of the initial capacity of a battery due to being left after assembly and to provide an alkaline storage battery having excellent battery characteristics. is there.

[0011]

According to the method of manufacturing an alkaline storage battery of the present invention, a cadmium oxide is mainly used, and a paste active material containing a hydration inhibitor of the cadmium oxide is applied to a conductive core to form a cadmium oxide. A first step of forming an electrode plate;
A second step of hydrating the cadmium oxide with an aqueous solution of potassium hydroxide and sodium hydroxide to form cadmium hydroxide; and a third step of incorporating the hydrated cadmium electrode plate into a battery can. It is characterized by the following.

Here, it is preferable that the mixing ratio of potassium hydroxide to potassium hydroxide and sodium hydroxide in the aqueous alkali solution is 60% or more and 80% or less in molar ratio.

[0013]

[Function] It is well-known that cadmium hydroxide mainly composed of γ-type is obtained when an aqueous solution of sodium hydroxide is used as a hydration treatment solution when hydration treatment is performed at the time of producing an electrode plate, and the electrode characteristics are improved. is there.

However, if the battery is left after assembly, γ
The cadmium hydroxide changes into β-cadmium hydroxide by potassium hydroxide which is a main component of the electrolytic solution, and gradually becomes coarse. When this coarsened β-type cadmium hydroxide is generated, the charge acceptability is deteriorated, which causes a problem that the battery capacity is deteriorated.

Therefore, the present inventors have studied various types of the alkaline aqueous solution at the time of the hydration treatment and arrived at the present invention. That is, it has been found that cadmium hydroxide in which γ-type and β-type are mixed can be obtained by using a mixed alkaline aqueous solution of sodium hydroxide and potassium hydroxide as the alkaline aqueous solution during the hydration treatment. Β-type cadmium hydroxide generated during this hydration hardly becomes coarse due to standing. Therefore, even after the battery is assembled, even if the battery is left, the coarsening due to the formation of β-type cadmium hydroxide is small, and the decrease in charge acceptability is small.

The ratio of γ-type and β-type cadmium hydroxide to be formed varies depending on the mixing ratio of sodium hydroxide and potassium hydroxide.

When the molar ratio of potassium hydroxide to potassium hydroxide in the mixed aqueous alkali solution is not less than 60% and not more than 80%, deterioration of battery capacity after assembly can be suppressed, and It also has excellent characteristics.

[0018]

EXAMPLES Preparation of Cadmium Electrode (Base Electrode) 900 g of cadmium oxide powder as a main active material, 200 g of metal cadmium powder as a precharge active material, 6 g of methylcellulose as a binder, and a length as a reinforcing material 10 g of 6-nylon fiber having a thickness of about 1.5 mm and a thickness of 1 to 2 denier, and a 5% aqueous sodium phosphate solution 3 as an additive for suppressing hydration during kneading of the cadmium oxide 3
And then kneading to obtain an active material paste.

This active material paste is applied to both surfaces of a conductive core made of punched metal plated with nickel, dried, and cut to a predetermined size to obtain a base electrode plate.

Using this base electrode, a hydration temperature of 50
Mixed aqueous solution of potassium hydroxide aqueous solution and sodium hydroxide aqueous solution at various ratios (mixing ratio of potassium hydroxide to mixed aqueous alkali solution: 0, 20, 40, 6).
(0,80,100%) by immersion in a, b, c, d, e, f, hydration treatment,
b, c, d, e, and f were obtained.

These cadmium electrodes a, b, c, d,
e and f were combined with a known sintered nickel positive electrode and wound through a separator to form a spiral electrode body. This spiral electrode body was inserted into a battery can, a potassium hydroxide aqueous solution was injected as an electrolytic solution, and sealed to obtain batteries A, B, C, D, E, and F, respectively.

(Experiment 1) Mixed alkaline aqueous solutions a, d, f
FIG. 1 shows the relationship between the hydration treatment and the hydration completion time by changing the hydration treatment temperature. The hydration completion time is a time required for producing cadmium hydroxide by 85% or more. To determine whether 85% or more of cadmium hydroxide is generated, change in weight of the cadmium electrode before and after hydration is measured. That is, the ratio between the weight change amount and the theoretical weight change amount when all the cadmium oxide is changed to cadmium hydroxide is set to 85% or more. From FIG. 1, it can be seen that when the hydration treatment temperature is 30 ° C. or higher for any of the mixed aqueous alkali solutions, the progress of the hydration reaction is accelerated and the hydration completion time is shortened.

(Experiment 2) The cadmium electrodes a, b,
Using c, d, e, and f, the crystal structure of cadmium hydroxide was examined by X-ray diffraction intensity ratio. FIG. 2 shows this result.
The horizontal axis of FIG. 2 is the mixing ratio (molar ratio) of potassium hydroxide in the mixed alkaline aqueous solution, and the vertical axis is the X-ray diffraction intensity ratio of γ-cadmium hydroxide to β-cadmium hydroxide;
That is, it shows the generation ratio. From FIG. 2, it can be seen that the production ratio of β-type cadmium hydroxide increases as the mixing ratio of potassium hydroxide increases.

Therefore, it is understood that the formation of β-type cadmium hydroxide during hydration is promoted by potassium hydroxide.

(Experiment 3) The batteries A, B, C, D, E,
Using F, a comparison was made between the initial capacity after leaving the battery for one hour after assembling and the initial capacity after leaving the battery in a constant temperature bath at 40 ° C. for one week. FIG. 3 shows the result. The vertical axis in FIG. 3 represents 40% of the initial capacity one hour after battery assembly.
It shows the volume ratio of the initial capacity after one week standing in a constant temperature bath at ℃. As can be seen from FIG. 3, when the mixing ratio (molar ratio) of potassium hydroxide is 60% or more, capacity degradation after standing can be suppressed.

(Experiment 4) The batteries A, B, C, D, E,
Using F, the amount of gas generated when the battery was continuously charged was examined. The measurement conditions were as follows.
The battery is charged continuously for one week by the current of 2C. FIG. 4 shows the result. As shown in FIG. 4, when the mixing ratio (molar ratio) of potassium hydroxide is 80% or less, the amount of generated gas can be suppressed.

From the results of Experiments 1 to 4, the mixing ratio (molar ratio) of potassium hydroxide in the mixed alkaline aqueous solution during the hydration treatment is preferably 60% or more and 80% or less. 30 ° C. or higher is preferred.

[0028]

According to the production method of the present invention, the alkaline solution at the time of the hydration treatment is made into a mixed aqueous solution of potassium hydroxide and sodium hydroxide, so that the formation of β-type cadmium hydroxide by standing after the battery is produced. And the deterioration of the initial capacity can be suppressed, so that an alkaline storage battery with excellent battery characteristics can be provided, and its industrial value is extremely large.

[Brief description of the drawings]

FIG. 1 is a diagram showing the relationship between hydration treatment temperature and hydration completion time.

FIG. 2 is a view showing a relationship between a mixing ratio (molar ratio) of potassium hydroxide in a mixed alkaline aqueous solution and an X-ray diffraction intensity ratio.

FIG. 3 is a diagram showing a relationship between a mixing ratio (molar ratio) of potassium hydroxide in a mixed alkaline aqueous solution and an initial capacity ratio after battery assembly.

FIG. 4 is a diagram showing the relationship between the mixing ratio (molar ratio) of potassium hydroxide in a mixed alkaline aqueous solution and the amount of gas generated during continuous charging.

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int. Cl. ⁶ , DB name) H01M 4/24-4/26

Claims (2)

(57) [Claims] 1. A first step of forming a cadmium electrode plate by applying a paste-like active material mainly composed of cadmium oxide and containing a cadmium oxide hydration inhibitor to a conductive core,
A second step in which the cadmium oxide is hydrated with a mixed alkali aqueous solution of potassium hydroxide and sodium hydroxide to form cadmium hydroxide, and a third step in which the hydrated cadmium electrode plate is incorporated in a battery can. A method for producing an alkaline storage battery. 2. The mixing ratio of potassium hydroxide to the mixed aqueous alkali solution in the mixed aqueous alkali solution is 6 in molar ratio.
The method for producing an alkaline storage battery according to claim 1, wherein the content is 0% or more and 80% or less.