JPH1040908A - Manufacturing method of paste-type cadmium negative electrode - Google Patents

Abstract

(57) [Summary] A method for producing a paste-type cadmium electrode, comprising:
Provided is a method for efficiently forming a porous nickel layer containing a small amount of metal cadmium on the surface of a cadmium active material. SOLUTION: A paste-like active material mainly composed of a cadmium compound is applied to a conductive core material, and then impregnated or applied with an organic compound such as phenylacetic acid, and then a porous material containing a small amount of metal cadmium. A nickel layer is formed by electrolytic plating.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

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

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,
Since the formed nickel layer reduces the overvoltage of hydrogen generation, hydrogen is easily generated from the negative electrode during charging. In the case of sealed storage batteries, the generated hydrogen gas is not consumed inside the battery, so if the charging conditions are not appropriate, the hydrogen gas is gradually accumulated in the battery, and generally widely used explosion-proof safety devices for batteries May be activated to destroy the closed system of the battery. In such a case, the electrolyte solution is reduced, and the life of the battery is reduced. In addition, when a nickel layer is provided on the electrode surface, the life characteristics can be improved by performing appropriate charging. However, when the nickel layer is provided with this life, the porous nickel layer formed on the electrode plate surface can be improved. Among them, it is recognized that coarse cadmium hydroxide crystals are present, and at the end of life, the movement of the electrolyte during charge and discharge is hindered by the coarse cadmium hydroxide crystals. Conceivable. 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.

[0008]

SUMMARY OF THE INVENTION The present invention solves the above-mentioned conventional disadvantages and provides a high-performance paste-type cadmium negative electrode.

More specifically, a cadmium negative electrode having a dense porous nickel layer mainly composed of metal nickel and containing a small amount of metal cadmium is obtained on the surface of an active material mainly composed of a cadmium compound applied to a conductive core. The present invention provides a suitable production method that can be used.

[0010]

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 a sealed nickel-cadmium storage battery. 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 a short circuit.

[0011]

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.
An organic compound layer 6 formed in the middle and between the active material layer 2 and the porous nickel layer 4 for forming the layer 4 smoothly.
Magnesium hydroxide applied inside.

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

In the figure, 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 an advantage that it is easier to manufacture and has a higher capacity density than a sintered-type negative electrode, but has a conductive skeleton such as a sintered-type. Since it does not exist, the growth of metal cadmium generated during battery charging occurs near the core, and the metal cadmium does not easily reach 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 proceeds due to energization 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 O → 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.

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

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 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 its 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.

Since the paste-type cadmium negative electrode according to the present invention has an organic compound layer 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 surface, 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.

Further, when the porous nickel layer is provided on the electrode surface as described above, the formed nickel layer lowers the overvoltage of hydrogen generation, so that hydrogen gas is easily generated during charging. In the case of sealed storage batteries, the generated hydrogen gas is not consumed inside the battery.If charging conditions are not appropriate, hydrogen gas is gradually accumulated in the battery, and the explosion-proof safety device for the battery is activated to close the battery. This may destroy the system and shorten the life of the battery.

Therefore, it is necessary to suppress the generation of hydrogen gas as a side reaction of the negative electrode during this charging. Means for suppressing the generation of hydrogen gas from the negative electrode during charging is achieved by increasing the hydrogen generation overvoltage of the porous nickel layer formed on the surface of the electrode plate. Metal cadmium used as a negative electrode active material is a material having a high hydrogen generation overpotential.By applying metal cadmium also to the porous nickel layer on the surface of the electrode plate, the hydrogen generation overpotential of the porous nickel layer is reduced. Can be increased.

In the present invention, a cadmium salt is added to a nickel plating bath used for nickel plating on the surface of the negative electrode. Metal cadmium was provided in the layer to prevent a decrease in overvoltage of hydrogen generation in the porous nickel layer portion.

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, a porous nickel layer is formed on the surface of an electrode plate with a magnesium compound, then impregnated in a cadmium compound and a porous nickel layer as a magnesium salt solution, and then treated with an alkali solution. As magnesium hydroxide, it is fixed in the cadmium active material layer and in the porous nickel layer.

Thus, the cadmium compound in the cadmium active material layer and the porous nickel layer is prevented from being coarsened, and the problem caused by the cadmium hydroxide coarsening in the nickel layer as described above is solved. The life characteristics were further improved.

Hereinafter, a specific example will be described in detail.

Example 1 A solution of polyvinyl alcohol in ethylene glycol was added to cadmium oxide powder having an average particle size 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) is used.
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, the electrode was placed in a plating bath containing 0.1 mol / l of nickel sulfate, 10 ^-3 mol / l of cadmium sulfate and 0.5 mol / l of boric acid at a temperature of 20 ° C and a current density of 10 A / dm ³ .
Electroplating was performed for 0 seconds 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 indicated by 6 in FIG. Since the plating bath contains cadmium ions,
During electrolysis, metal cadmium is deposited on the surface of the electrode plate simultaneously with metal nickel. Therefore, the material forming the porous conductive layer 4 is metallic nickel containing a small amount of metallic cadmium.

After 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 the organic compound phenylacetic acid is contained in the active material layer. Layer and in the porous nickel layer.

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

That is, the porous nickel layer was determined by observing the cross section of the electrode plate with a SEM photograph, and the distribution state of metal cadmium, magnesium hydroxide or the organic compound in the porous nickel layer was determined by Cd, Mg, C, H, respectively. X-ray microanalysis (Electron)
Probe X-ray Micro Analysis
s).

Using the negative electrode a obtained in this example, a sintered nickel positive electrode by a conventional method, a separator made of a polyamide nonwoven 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 precipitation of the active material. The characteristics of the reduction in the utilization rate of the negative electrode due to growth and the deterioration of the life due to short-circuiting were evaluated.

Here, the battery internal pressure characteristic during overcharge 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 absorbency of the negative electrode was evaluated by AB, and the presence or absence of hydrogen gas was evaluated as residual pressure B.

The charge / discharge cycle life was evaluated by repeating the 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.

[0053]

[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,
This is for smoothing the surface of the coated electrode plate and forming a dense and good-adhesion plating layer, like a brightener for ordinary plating, the type of which is a fatty acid having 5 to 30 carbon atoms or a fatty acid thereof. Consisting of salt, and the solubility when dissolving the organic compound in a solvent, or the stability when drying it later,
Considering industrial productivity when forming or coating an organic compound layer by coating or impregnating an electrode plate, an aromatic carboxylic acid in which one of hydrogen bonded to carbon of a fatty acid is substituted with a phenyl group or a phenoxy group Or it will be of a kind like its salt.

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

Example 2 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)

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

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Example 7 Glycol Stearate
ate)

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Example 8 Stearic Acid

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Example 9 γ-phenylcrotonic acid (γ-Phenylcrot)
sonic Acid)

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Example 10 Phenoxyacetic Acid (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-mentioned compounds as the organic compound to be applied on the coated electrode plate.
Almost the same result was obtained.

(Example 11) In order to determine an appropriate value of the cadmium salt concentration contained in the nickel plating bath, several types of cadmium salt concentrations in the plating bath were changed in the same manner as in Example 1. A negative electrode was prepared, and the characteristics of the battery were evaluated.

The results are shown in (Table 2).

[0069]

[Table 2]

Cadmium salt concentration of 0 mol / l
This corresponds to the battery of the comparative example shown by c in FIG. 2. Since there is no metal cadmium in the porous nickel layer formed on the surface of the electrode plate, the overvoltage of hydrogen generation is low, This produces hydrogen gas. Therefore, it can be understood that hydrogen gas remains in the battery even after the battery is stopped from discharging, and the internal pressure of the battery has not returned to the initial state. The cadmium salt concentration in the plating bath, which has the effect of suppressing the generation of hydrogen gas during charging, is 10 ^-4 mol / l or more. However, if the cadmium salt concentration is too high, the nickel deposition efficiency decreases. Therefore, the oxygen gas absorption characteristics or the life characteristics are deteriorated. Therefore, the preferred concentration range is 10 ^-4.
〜１０10 ⁻² mol / l.

Example 12 Next, in order to determine appropriate conditions for electrolytic plating, a negative electrode similar to that of Example 1 was prepared in the same manner as in Example 1 except that only the plating energizing conditions were changed. An evaluation was performed.

The nickel salt aqueous solution used for electrolytic plating is
Usually, when performing nickel plating, it is about 1 mol / l, but in the present invention, it is 0.05 to 0.2 mol.
/ L range. When nickel plating is performed on the surface of the porous electrode, if the concentration of the aqueous nickel salt solution is high, the diffusion and supply of nickel are performed smoothly, and the nickel is plated in the pores more than the surface of the electrode. Plating is not formed sufficiently. The upper limit of the nickel concentration of the plating bath capable of forming a porous nickel plating layer on the surface of the porous electrode is about 0.2 mol / l. Conversely if too to low nickel concentration produces a hydrogen gas generation, since the reduced deposition efficiency of nickel it is not preferred. The lower limit of the concentration is about 0.05 mol / l. Therefore, the range of the nickel concentration in the appropriate plating bath is 0.05 to 0.2 mol /
l. There is a similar relationship between the plating current density and the apparent area of the electrode plate. When the current density is smaller than 5 A / dm ² at the above nickel concentration, nickel also precipitates inside the cadmium active material and nickel on the electrode plate surface. Precipitation decreases. Therefore, the lower limit of the current density is 5 A / d
About m ² is appropriate. Conversely, if the current density is too high, hydrogen gas is generated and nickel deposition efficiency is reduced, so the upper limit of the current density is preferably about 20 A / dm ² .

The following can be said about the amount of electricity supplied during plating.

When the amount of electricity supplied is small, a sufficient porous nickel layer cannot be secured, and the lower limit is 30 mAh / dm.
^{About 2} .

On the other hand, when the amount of electricity supplied is too large,
The plating layer becomes too thick, the ionic conductivity in the porous nickel layer is reduced, and when the battery is assembled, problems such as deterioration of discharge characteristics occur. Therefore, the upper limit of the amount of supplied electricity is about 500 mAh / dm ² .

The amount of electricity supplied during nickel plating is 30 m
The electrode plate of Ah / dm ² and the electrode plate of 500 mAh / dm ² were cut, and the thickness of the nickel plating layer was measured by observing the cross section with a SEM photograph.
The thicknesses of the nickel plating layers of 0 mAh / dm ² and 500 mAh / dm ² were about 0.5 μ and about 5 μ, respectively.

Further, the nickel plating layer is peeled off,
Was dissolved in nitric acid to determine the amount of nickel. in this way
From the amount of nickel obtained and the thickness of the nickel layer
As a result of calculating the porosity of the layer, the amount of electricity passed was 30 mAh /
dm^Two, 500mAh / dm ^TwoNickel layer of electrode plate
Had a porosity of about 70% and 40%, respectively.
Therefore, nickel plating which can sufficiently obtain the effects of the present invention
The conditions of the layer are as follows.
It is considered that the porosity is preferably about 40 to 70%. this
Such a nickel plating layer maintains appropriate plating energizing conditions.
Can be secured by

Therefore, the nickel concentration in the plating bath is 0.1.
05 to 0.2 mol / l, plating current density is 5 to 2
0 A / dm ² , plating electricity quantity is 30-500 mA
h / dm ² is appropriate, and a battery using a negative electrode plated under these conditions can obtain almost the same battery characteristics as in Example 1.

Example 13 Next, the amount of magnesium hydroxide impregnated in the electrode plate was examined. For the negative electrode of Example 1, the amount of magnesium hydroxide was 0.8% by weight based on the amount of cadmium active material, but the appropriate range was determined by changing the concentration of magnesium sulfate impregnating 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 14) 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 applying 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 generated during chemical formation was previously mixed in 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 solution, and a battery was prepared using this negative electrode in the same manner as in Example 1, 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 battery electrolyte in the battery. However, as the battery characteristics, almost the same results as in Example 1 are obtained. Was.

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

[0084]

As described above, in the paste-type cadmium negative electrode of the present invention, it is possible to improve the oxygen gas absorbability, suppress the dissolution and precipitation of cadmium, prevent the deformation of the electrode plate, and extend the life. Things.

[Brief description of the drawings]

FIG. 1 is an enlarged schematic view showing a cross section of a paste-type cadmium negative electrode obtained in one example 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 (7)

[Claims] 1. A paste-type cadmium negative electrode having an active material layer mainly composed of a cadmium compound coated on a conductive core, and a porous metal nickel layer containing a small amount of metal cadmium provided on the surface thereof. In the method for producing a conductive core, a cadmium compound-based active material is applied to a conductive core, and then impregnated with or coated with an organic compound, and then a porous nickel layer containing a small amount of metal cadmium by electrolytic plating. A method for producing a paste-type cadmium negative electrode for forming a negative electrode. 2. The plating bath according to claim 1, wherein said organic compound is impregnated or coated, and then a plating bath for forming a porous nickel layer by electrolytic plating has a nickel concentration of 0.05 to 0.2 mol / mol. 1, cadmium concentration 10 ^-4
A method for producing a paste-type cadmium negative electrode, which is a mixed solution containing from 10 to 10 ^-2 mol / l. 3. A method according to claim 1, wherein the current density of the electrolytic plating is 5 to 20 A / dm ² with respect to the apparent area of the electrode plate. 4. The method according to claim 1, wherein the amount of electricity supplied during electrolytic plating is 30 to 500 mA with respect to the apparent area of the electrode plate.
A method for producing a paste-type cadmium negative electrode of h / dm ² . 5. A paste-type cadmium negative electrode according to claim 1, wherein after the porous nickel layer is formed, the electrode plate is impregnated with a magnesium salt solution, and then converted into magnesium hydroxide by a reaction with an alkali solution. Law. 6. A paste according to claim 5, wherein the reaction between the magnesium salt and the alkali solution is carried out simultaneously with the formation of the electrode plate, in which the electrode plate is negatively electrolyzed in the alkaline solution to form metal cadmium in the electrode plate. A method for producing a cadmium negative electrode. 7. The method of producing cadmium paste according to claim 5, wherein the reaction between the magnesium salt and the alkaline solution is carried out in an alkaline solution which is a battery electrolyte.