JPH1040918A - Paste type cadmium negative electrode and method for producing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a long-life alkaline storage battery which enhances oxygen gas absorption at a paste-type cadmium electrode, suppresses deformation of an electrode plate due to dissolution and precipitation of cadmium. SOLUTION: An organic compound layer 6 is provided on the surface of a cadmium active material layer 2 applied to a conductive core, and a nickel layer mainly composed of a porous nickel layer 4 is provided on the upper surface thereof. And the amount of magnesium hydroxide added was 0.1 to 3% by weight based on the cadmium active material.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a paste-type cadmium negative electrode used for an alkaline storage battery and a method for producing the same.

More specifically, it is a main object of the present invention to improve oxygen gas absorptivity of a paste-type cadmium negative electrode and to suppress deformation of an electrode plate due to dissolution and deposition of cadmium to improve the life.

[0003]

2. Description of the Related Art In recent years, a paste-type cadmium negative electrode in which a paste-like active material has been applied to a conductive core has been used because of its simple manufacturing process, low manufacturing cost, and high energy density. It has been widely used for storage batteries.

[0004] Such a paste-type cadmium negative electrode,
Unlike the sintering type cadmium negative electrode, since it does not have a conductive skeleton holding an active material, growth of metal cadmium generated at the time of battery charging occurs near the conductive core, and it is difficult to reach the electrode plate surface layer. As a result, the reaction between oxygen gas generated from the positive electrode and metal cadmium during overcharge is not efficiently performed, and when used in a sealed battery, the internal pressure of the battery increases due to insufficient oxygen gas elimination reaction. Having. In addition, cadmium was repeatedly dissolved and precipitated by repeated charge / discharge cycles, resulting in deformation of the negative electrode, which had a disadvantage that the life was likely to be shortened.

[0005]

In order to solve such a problem, there has been proposed a method of performing electrolytic nickel plating on an electrode surface as disclosed in Japanese Patent Publication No. 61-62727. Since nickel plating is performed directly,
There is a disadvantage that nickel on the surface is hard to be uniform and a sufficient effect cannot be obtained. When a nickel layer is provided on the electrode surface, the life characteristics can be improved by performing appropriate charging.However, when the electrode with this life is seen, the porous nickel layer formed on the electrode plate surface has It is recognized that coarse cadmium hydroxide crystals exist,
At the end of the life, it is considered that the movement of the electrolyte during charge and discharge is hindered by the coarse crystals of cadmium hydroxide. Therefore, it is considered that if the growth of cadmium hydroxide in the porous nickel layer can be suppressed, the life characteristics of the battery can be further improved.

As disclosed in Japanese Patent Application Laid-Open No. 60-63875 and US Pat. No. 4,614,696, a method of providing a conductive layer made of carbon powder on the surface of an electrode has been proposed. It is difficult to provide a uniform conductive layer, which also has a drawback that a sufficient effect cannot be obtained.

[0007]

The present invention provides an active material layer, a nickel-based conductive porous layer on the surface of the active material layer, and an organic compound layer located between the active material layer and the organic compound layer between the active material layer and the magnesium hydroxide. An object of the present invention is to provide a high-performance paste-type cadmium negative electrode which solves the above-mentioned conventional disadvantages.

[0008]

In this way, the generation of hydrogen gas as a side reaction during battery charging is suppressed, and the cadmium negative electrode absorbs oxygen gas generated from the positive electrode during overcharge, which is important when used in sealed nickel-cadmium storage batteries. Significantly improved characteristics, coarsening of the cadmium active material caused by repeated charge and discharge in a high-temperature atmosphere, deformation of the negative electrode due to dissolution and precipitation of the cadmium active material, and reduction in active material utilization due to dendrite growth Further, it is intended to prevent the life from being deteriorated due to the short circuit.

[0009]

FIG. 1 is an enlarged schematic view showing a cross section of a paste type cadmium negative electrode according to one embodiment of the present invention.

In FIG. 1, reference numeral 1 denotes a cadmium active material composed of cadmium hydroxide, cadmium oxide, metal cadmium, or the like. Reference numeral 2 denotes a layer made of these active materials. Reference numeral 3 denotes a conductive core supporting the active material 1, and here, a cross section of a perforated metal plate (punched metal sheet) is shown.

Reference numeral 4 denotes a porous nickel layer mainly composed of metallic nickel containing a small amount of metallic cadmium formed on the surface of the cadmium active material.

Reference numeral 5 denotes a porous nickel layer 4 in the active material layer 2.
Magnesium hydroxide provided in the middle and in the organic compound layer 6 formed between the active material layer 2 and the porous nickel layer 4.

FIG. 2 is a diagram showing changes in internal pressure of a sealed nickel-cadmium storage battery during charging and discharging.

In the drawing, a shows the internal pressure change of the battery using the negative electrode according to one embodiment of the present invention, b shows the internal pressure change of the battery using the conventional paste-type cadmium negative electrode, and c shows the internal pressure of the battery of the comparative example. The changes are shown respectively. A indicates the peak pressure of the battery internal pressure during charging, and B indicates the pressure due to the hydrogen gas remaining after the discharge is stopped.

As described above, the paste-type cadmium negative electrode has advantages in that it can be easily manufactured and has a high capacity density as compared with the sintered-type negative electrode, but has a conductive skeleton as in the sintered-type. Since it does not exist, the growth of metal cadmium generated during battery charging occurs near the core, and the metal cadmium hardly reaches the electrode plate surface layer. Therefore, the reaction with oxygen gas generated from the positive electrode at the time of overcharging is not efficiently performed, and when used in a sealed battery, the internal pressure of the battery increases.

However, when a conductive porous nickel layer is formed on the surface of the electrode plate as in the present invention, the generation of metal cadmium progresses due to the conduction of electricity from the conductive nickel layer on the surface of the electrode plate. A metal cadmium layer is also formed on the surface. Oxygen gas generated from the positive electrode during battery overcharge is mainly absorbed by the metal cadmium of the negative electrode according to the following equation.

2Cd + O ₂ + 2H ₂ 0 → 2Cd (OH) ₂ Therefore, the distribution of metal cadmium in the negative electrode is very important, and the negative electrode of the present invention in which a large amount of metal cadmium is distributed on the negative electrode surface has an oxygen gas absorbing property. It will be good.

The following points are particularly important as conditions for providing the conductive porous nickel layer on the surface of the negative electrode active material.

First, the conductive porous nickel layer is stable in a battery using a paste-type cadmium negative electrode. Since a battery using a cadmium negative electrode generally uses an alkaline electrolyte like a nickel-cadmium storage battery, it is required to have good alkali resistance and high conductivity. Considering the cost of the material, nickel is considered to be most suitable as the material of the conductive layer.

Second, it has sufficient adhesion to the cadmium active material layer and has an appropriate microporous structure for transferring the electrolyte during charge and discharge.

For example, when nickel powder or the like is applied to the surface of an active material layer, or when pressure is applied, the adhesion for energization is poor, and it is difficult to satisfy the above-mentioned conditions. It is thought that it is.

However, in the case of forming a porous nickel layer on the surface of the active material layer by electrolytic plating, it is necessary to thoroughly examine the method in order to ensure the uniformity and adhesion.

For example, when a nickel plating method using a usual watt bath is used, the nickel plating layer becomes uneven due to irregularities due to active material particles on the surface of the electrode plate or the presence of cadmium hydroxide as an insulator. Or the adhesion to the active material may not be ensured.

In the paste-type cadmium negative electrode according to the present invention, since the organic compound layer is formed on the surface of the active material of the electrode, the electrode surface is smooth and a uniform plating layer is easily formed during electrolytic plating. Become.

The organic compound, particularly an organic compound having a substituent, is generally known as a brightener for improving the uniform electrodeposition property and the smoothness of plating, and forms a porous nickel layer having good adhesion. It is possible to do.

Here, the selection of the organic compound used in the present invention depends on the film forming property on the electrode plate, the stability at the time of nickel plating, and the coating or impregnation of the electrode plate to form the organic compound layer. Industrial productivity and properties as an electrode plate (solubility when dissolving organic compounds in a solvent, stability when drying it later, properties that do not adversely affect electrode reactions when operating as a battery Etc.) must be considered.

When a charge / discharge cycle life test is performed using a negative electrode having a porous nickel layer formed on the surface of an electrode plate,
As described above, the life characteristics are significantly improved as compared with the conventional electrode having no porous nickel layer on the surface of the electrode plate. However, at the end of life, coarse cadmium hydroxide crystals are observed in the porous nickel layer on the surface of the electrode plate. The porous nickel layer prevents the growth of cadmium, which tends to extend out of the electrode plate as a dendrite, but the coarsened cadmium hydroxide in the nickel layer hinders the movement of the electrolyte that contributes to the electrode reaction. It is considered that the charge and discharge characteristics of the electrode deteriorate.

Magnesium compounds are described, for example, in JP-B-62
As disclosed in JP-A-159994, it is known that there is an effect of preventing cadmium crystals from becoming coarse.

In the present invention, an organic compound layer is disposed on the surface of an active material layer mainly composed of a cadmium compound, and a porous nickel layer is formed by electrolytic plating. , And impregnated in the porous nickel layer, and then treated with an alkali solution to fix the magnesium hydroxide in the cadmium active material layer, the organic compound layer, and the porous nickel layer.

This prevents the cadmium hydroxide from being coarsened in the cadmium active material layer and the porous nickel layer, and solves the above-mentioned problems caused by the cadmium hydroxide being coarsened in the nickel layer. Further, the life characteristics could be further improved.

Hereinafter, a specific example will be described in detail.

Example 1 An ethylene glycol solution of polyvinyl alcohol is added to cadmium oxide powder having an average particle diameter of 1 μm and kneaded to form a paste. This paste was applied to a nickel-plated apertured steel plate having a thickness of 0.1 mm as a conductive core and dried at about 140 ° C. for 30 minutes to obtain an electrode having a thickness of about 0.5 mm.

Next, phenylacetic acid (Phenylase)
This electrode was immersed in a xylene solution containing 0.5% by weight of (tic Acid) for about 10 seconds and dried at 80 ° C. to form a phenylacetic acid layer on the electrode surface. Further, this electrode was treated with 0.1 mol / l of nickel sulfate and 0.1 mol of boric acid.
Electroplating was performed for 30 seconds at a temperature of 20 ° C. and a current density of 10 A / dm ³ in a plating bath containing 5 mol / l to form a nickel plating layer on the surface.

Next, the electrode plate was treated with magnesium sulfate for 1.
It was immersed in an aqueous solution containing 5 mol / l, pulled up, and dried.

Next, this electrode was charged to about 40% of the theoretical capacity in an alkaline solution, washed with water and dried to obtain a paste-type cadmium negative electrode. This negative electrode is referred to as a.

A porous nickel layer 4 mainly composed of nickel formed by electrolytic plating is formed on the organic compound phenylacetic acid layer 6 shown in FIG.

After the nickel plating, the magnesium sulfate impregnated in the electrode plate reacts with the alkaline solution during the next chemical formation in the alkaline solution, is converted into magnesium hydroxide 5, and is converted into an organic compound in the active material layer. It is present in certain phenylacetic acid layers and in porous nickel layers.

The distribution of magnesium hydroxide in each component shown in FIG. 1 is confirmed by the following method.

That is, the distribution of magnesium hydroxide in the cadmium active material layer was determined by X-ray microanalysis (X-ray microanalysis) by observing the cross section of the electrode plate with a SEM photograph, and the distribution of magnesium hydroxide in the porous nickel layer and the organic compound layer. Electron Probe X-ray Mic
ro Analysis).

Using the negative electrode a obtained in this example, a sintered nickel positive electrode according to a conventional method, a separator made of a polyamide non-woven fabric, and a potassium hydroxide solution as electrolytes,
A sealed nickel-cadmium storage battery equivalent to 1.2 Ah was prepared, and the battery characteristics were evaluated.

The battery was evaluated by evaluating the internal pressure of the battery at the time of overcharging to evaluate the oxygen gas absorption characteristics of the negative electrode, the deformation of the negative electrode caused by repeated charging and discharging, or the dendrite formation caused by dissolution and deposition of the active material. The characteristics of the reduction in the utilization rate of the negative electrode due to growth and the deterioration in life due to short-circuit and the like were evaluated.

Here, the battery internal pressure characteristic at the time of overcharging is 20
The cycle life characteristics were evaluated by the internal pressure of the battery when overcharged at a current equivalent to 2 CmA in an atmosphere at 50 ° C.
The battery was charged with a current equivalent to 3 C for 4.5 hours, and was repeatedly charged and discharged to completely discharge with a resistance load equivalent to 1 CmA.

FIG. 2 is a diagram showing changes in the internal pressure of the battery during charging and discharging. The internal pressure of the battery begins to increase from the point when the battery enters the overcharged area, reaches a peak pressure, and decreases during discharging. The quality of the oxygen gas absorbing property of the negative electrode can be evaluated based on the internal pressure of the battery. That is, those having good oxygen gas absorbency have low battery internal pressure, and those having poor oxygen gas absorbency have high battery internal pressure.

FIG. 2A shows the internal pressure characteristics of the battery of this embodiment, and FIG. 2B shows the internal pressure characteristics of the battery using the conventional paste type negative electrode. Normally, oxygen generated during overcharge is completely absorbed by the negative electrode during discharging and at rest, so that the pressure in the battery returns to the initial charging state, but hydrogen gas is generated as a side reaction from the negative electrode during charging. In this case, hydrogen gas is not consumed inside the battery,
The residual pressure B remains as in the comparative example of FIG. 2c.

The oxygen gas absorptivity of the negative electrode was evaluated by AB, and the presence or absence of hydrogen gas was evaluated as the residual pressure B.

The charge / discharge cycle life was evaluated by repeating charge / discharge by the method described above, and comparing the initial capacity with 8 times.
Number of cycles where capacity has deteriorated to 0% (number of life cycles)
Was evaluated.

(Comparative Example 1) A coated battery was prepared in the same manner as in Example 1, and a similar battery was prepared using a negative electrode which had been formed without performing other treatments such as plating. 1
(B) and the same evaluation was performed. Table 1 shows the results of Example 1 and Comparative Example 1.

[0048]

[Table 1]

As described above, according to the present invention, it can be seen that the oxygen gas absorption characteristics of the negative electrode have been greatly improved, and the cycle life characteristics have also been greatly improved.

Next, an example in which only the type of the organic compound applied to the coated electrode plate is changed in the same manner as in Example 1 will be described. The purpose of providing organic compounds is, as described above,
It is for forming the plating layer which is dense and has good adhesion, like a brightening agent for ordinary plating, to make the surface of the coated electrode plate smooth, and the type thereof is a fatty acid having 5 to 30 carbon atoms. Or the salt thereof, and the solubility when dissolving the organic compound in a solvent, or the stability when drying it later, such as the industrial process for forming or applying the organic compound layer by coating or impregnating the electrode plate. In consideration of the productivity, it is a kind such as an aromatic carboxylic acid or a salt thereof in which one of the hydrogens bonded to the carbon of the fatty acid is substituted with a phenyl group or a phenoxy group.

As Examples 2 to 10, the following organic compounds were examined.

(Example 2) Atropic acid (Atropic Acid)

Embedded image

Example 3 Phenylpropiolic acid

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Example 4 Methyl p-hydroxybenzoate (Methyl PH)
hydroxybenzoate)

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Example 5 Vinyl Benzoic Acid (Vinylbenzoic Aci)
d)

Embedded image

(Example 6) sec-butylmalonic acid (sec-butylmalonic acid)
sonic Acid)

Embedded image

Example 7 Glycol Stearate
ate)

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(Example 8) Stearic acid (Stearine Acid)

Embedded image (Example 9) γ-phenylcrotonic acid (γ-Phenylcrto)
nic Acid)

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Example 10 Phenoxyacetic Ac
id)

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The same evaluation as in Example 1 was carried out on a negative electrode using each of the above compounds as the organic compound to be provided on the coated electrode plate. As a result, the battery internal pressure characteristics and the life characteristics were almost the same as those in Example 1. Similar results were obtained.

Example 11 Next, the amount of magnesium hydroxide present in the electrode plate was examined. Example 1
The amount of magnesium hydroxide in the negative electrode was 0.8% by weight based on the amount of the cadmium active material, but the appropriate range was determined by changing the concentration of magnesium sulfate impregnated in the electrode plate. In the preparation of the negative electrode, other conditions were the same, and only the magnesium sulfate concentration was changed. As a result, regarding the amount of magnesium hydroxide, the effect on the life becomes remarkable from about 0.1% by weight with respect to the amount of the cadmium active material, and when the amount becomes 3% by weight or more, the porous nickel on the electrode plate surface is reduced. Since the magnesium hydroxide present in the layer inhibits the movement of the electrolyte and degrades the discharge characteristics of the battery, the appropriate range is 0.1 to 3% by weight based on the cadmium active material. Appropriate. For the battery using the negative electrode prepared under these conditions, almost the same results as in Example 1 were obtained.

Example 12 A paste-type cadmium negative electrode was prepared by applying cadmium oxide or cadmium hydroxide as an active material to a conductive core, drying the cadmium oxide, and then adding metal cadmium as a preliminary charge. The coated electrode plate is subjected to negative electrolysis in an alkaline solution as in Example 1 to convert cadmium oxide or a part of cadmium hydroxide to metal cadmium.

However, recently, in order to omit this chemical conversion step, a method of using a mixture of cadmium oxide or cadmium hydroxide and metal cadmium as an active material paste applied to a conductive core has been proposed. I have. The following study was conducted on the premise of such a method.

Instead of the cadmium oxide used in Example 1, a metal cadmium powder corresponding to the metal cadmium formed during chemical formation was previously mixed into the active material paste, and the electrode plate was produced in the same manner as in Example 1. An electrode plate was prepared before impregnation with a magnesium sulfate salt solution, and a battery was prepared in the same manner as in Example 1 using this negative electrode, and the same battery characteristics were evaluated. In this case, the magnesium sulfate impregnated in the electrode plate is converted into magnesium hydroxide by the alkaline electrolyte in the battery, but almost the same results as in Example 1 are obtained as the battery characteristics. Was.

However, when this method is used, it is necessary to select, as the anion of the magnesium salt, a type that does not adversely affect the battery characteristics, such as sulfate ion, and avoids an anion that adversely affects the battery characteristics, such as nitrate ion. There is a need.

[0066]

As described above, in the paste-type cadmium negative electrode of the present invention, the oxygen gas absorbing property is improved, the cadmium is prevented from dissolving and depositing in the alkaline electrolyte, the electrode plate is prevented from being deformed, and the life is extended. Can be achieved.

[Brief description of the drawings]

FIG. 1 is an enlarged schematic view showing a cross section of a paste-type cadmium negative electrode according to one embodiment of the present invention.

FIG. 2 is a diagram showing changes in internal pressure of a sealed nickel-cadmium storage battery during charging and discharging;

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 active material 2 active material layer 3 conductive core 4 porous nickel layer 5 magnesium hydroxide 6 organic compound layer

Claims (2)

[Claims] 1. A cadmium compound comprising: an active material layer mainly composed of a cadmium compound applied to a conductive core; and a conductive porous layer mainly composed of metallic nickel provided on the surface thereof. In a paste-type cadmium electrode in which an organic compound layer is provided between an active material mainly containing nickel and a conductive porous layer mainly containing nickel, an active material layer mainly containing a cadmium compound, an organic compound layer, and a conductive porous layer mainly containing nickel are used. In addition, magnesium hydroxide is 0.1% with respect to the cadmium active material.
A paste-type cadmium negative electrode containing up to 3% by weight. 2. A paste-type cadmium in which an active material mainly composed of a cadmium compound is applied to a conductive core, impregnated with or coated with an organic compound, and then a porous nickel layer is formed by electrolytic plating. In the method for producing a negative electrode, a method for producing a paste-type cadmium negative electrode in which after a porous nickel layer is formed, an electrode plate is impregnated with a magnesium salt solution, and then converted into magnesium hydroxide by a reaction with an alkali solution and contained.