JPH10172557A - Manufacture of active material for nickel electrode - Google Patents

Abstract

PROBLEM TO BE SOLVED: To efficiently obtain nickel hydroxide powder in which cobalt oxide is formed on the surfaces of particles while the physical property of the nickel hydroxide powder which is a raw material is kept by adding an alkali hydroxide solution to nickel hydroxide powder whose particle surface is covered with cobalt hydroxide, and at the same time hot air is blown to oxidize the cobalt hydroxide. SOLUTION: Nickel hydroxide powder which is a base material is dispersed in a dispersion medium such as water, usually 5-30wt.% slurry is prepared. The mean particle diameter of the nickel hydroxide, although it is variable by applications, is usually 2-50 microns, preferably 5-20 microns. The slurry is heated at 80 deg.C or less, and pH is adjusted to 8-11 by acid or alkali. In pH on the outside of the above range, unfavorably, the particle surface of the nickel hydroxide powder is not coated with cobalt hydroxide, and independent cobalt hydroxide particles are formed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a method for producing an active material for a nickel electrode.

[0002]

2. Description of the Related Art Conventionally, sintered and non-sintered nickel electrodes for alkaline secondary batteries have been known. In the sintering method, after a nickel powder slurry is applied to a substrate grid, a nickel sintered substrate obtained by sintering this is impregnated with an active material. As a method for impregnating the active material, an electrolytic impregnation method, a chemical impregnation method, and the like are known. For example, in the electrolytic impregnation method, a nickel hydroxide electrode is manufactured by immersing a nickel sintered substrate in a nickel nitrate solution and then using the substrate as a negative electrode to convert nitrate to nickel hydroxide in an alkaline solution. However, in each of these impregnation methods, the step of impregnating with nickel nitrate and the step of changing to nickel hydroxide need to be repeated several times in order to fill a sufficient amount of the active material into the nickel sintered substrate.

On the other hand, in the non-sintering method, an electrode substrate is directly filled with a paste of nickel hydroxide as an active material and manufactured. This non-sintered type electrode has a drawback that the utilization factor is lower than that of the sintered type electrode. For this reason, a method of further coating cobalt hydroxide on the particle surface of the nickel hydroxide powder has been proposed. According to this method, since a cobalt oxide having high conductivity is finally coated, it is possible to further enhance the conductivity of nickel hydroxide as an active material.

[0004]

However, there is still room for improvement in the above-mentioned method for forming a cobalt oxide in manufacturing on an industrial scale.

That is, in the above method, the particles of the obtained nickel hydroxide powder may be physically or chemically bonded to each other. In this case, the pulverizing step is required, and the workability is inevitably reduced. Moreover, when the bonded powder particles are crushed, the cobalt oxide at the bonded portion is peeled off, and as a result, the cobalt oxide cannot be completely covered.

Accordingly, it is a main object of the present invention to efficiently produce a cobalt hydroxide powder having a cobalt oxide formed on the particle surface while maintaining the physical properties of the nickel hydroxide powder as a raw material. And

[0007]

Means for Solving the Problems The present inventor has conducted intensive studies in view of the above-mentioned problems of the prior art, and as a result, has found that the above object can be achieved when cobalt oxide is formed by a specific method. The present invention has been completed.

That is, the present invention is characterized in that the above-mentioned cobalt hydroxide is oxidized by feeding heated air to a nickel hydroxide powder having a surface coated with cobalt hydroxide while adding an alkali hydroxide solution. The present invention relates to a method for producing a nickel electrode active material.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail along with its embodiments.

[0010] The method for producing a nickel electrode for an alkaline secondary battery according to the present invention is characterized in that the heated water is fed to a nickel hydroxide powder having a surface coated with cobalt hydroxide while adding an alkali hydroxide solution thereto. It is characterized by oxidizing cobalt oxide.

As the nickel hydroxide powder having a surface coated with cobalt hydroxide, a powder obtained by a known production method can be used. For example, a powder produced by the following method can be used.

First, a nickel hydroxide powder (raw material powder) serving as a base is dispersed in a dispersion medium such as water, and usually 5 to 30 minutes.
A slurry liquid of about weight% is used. As the nickel hydroxide powder, known powders can be used.
The nickel hydroxide powder disclosed in Japanese Patent Publication No. 18 can also be used. The average particle size of the nickel hydroxide powder can be appropriately changed depending on the application and the like, but is usually about 2 to 50 μm, preferably 5 to 20 μm.

Next, the above-mentioned slurry liquid is heated at room temperature or as required (usually 80 ° C. or lower), and the pH is adjusted to 8 to 11 with an acid (such as sulfuric acid) or an alkali (such as sodium hydroxide).
Adjust to the extent. If the pH is out of the above range, the surface of the particles of the nickel hydroxide powder is not coated with cobalt hydroxide, so that independent cobalt hydroxide particles are formed, which is not preferable.

While maintaining the above temperature and pH and stirring, a cobalt sulfate solution having a cobalt (Co) concentration of about 5 to 15% by weight and sodium hydroxide of about 5 to 40% by weight are added together. In the present invention,
The amount of cobalt hydroxide deposited can be appropriately adjusted according to the application and the like, but is usually 1 to 15% by weight, preferably 3 to 10% by weight based on the nickel hydroxide powder.

The obtained mixture is dehydrated with a centrifuge or the like,
Washing with water as necessary gives a nickel hydroxide powder containing cobalt hydroxide. This nickel hydroxide
Mainly, the particle surface is coated with cobalt hydroxide.

In the present invention, in addition to nickel hydroxide coated with cobalt hydroxide, cadmium, zinc,
Nickel hydroxide coated on the surface by using magnesium alone or in combination of two or more kinds can also be used. These surface coats can be formed in the same manner as described above. Further, not only a surface coat but also a solid solution of cadmium, zinc or the like in nickel hydroxide can be used. These can also be manufactured according to a known method.

Next, heated air is fed into the nickel hydroxide obtained above (hereinafter also referred to as “cobalt-coated nickel hydroxide”) while adding an alkali hydroxide solution.
Examples of the alkali hydroxide include potassium hydroxide and sodium hydroxide, and particularly preferred is sodium hydroxide.

The conditions for sending the heated air can be appropriately set depending on the cobalt-coated nickel hydroxide used, the final use, and the like. For example, the temperature of the heated air is usually 70 to 15
The temperature may be about 0 ° C, preferably 90 to 130 ° C. The feed rate of the heated air may be generally about 10 to 50 m ³ / m ² · min, preferably 20 to 35 m ³ / m ² · min.

The direction in which the heated air is fed is as long as the cobalt oxide can be formed while maintaining the physical properties of the primary particles of nickel hydroxide (base nickel hydroxide).
Either direction may be used. In the present invention, it is particularly preferable to feed from below. Here, the term “below” includes not only blowing heated air from directly below the raw material but also obliquely downward. As a result, the cobalt-coated nickel hydroxide powder soars by the air current of the heated air, and in some cases, forms a fluidized bed, so that cobalt oxide can be effectively formed in the state of primary particles.

The amount of the alkali hydroxide to be added can be appropriately set depending on the kind of the alkali hydroxide, the above conditions and the like, but is usually about 2 to 20% by weight based on the cobalt-coated nickel hydroxide (in terms of alkali hydroxide crystal). ), Preferably 5-
It may be 10% by weight. Although the concentration of the alkali hydroxide can be changed as appropriate, it is usually about 10 to 45% by weight, preferably 25 to 40% by weight.

Further, the amount of water retained in the above-mentioned cobalt-coated nickel hydroxide at least while the heated air is being fed in can be appropriately determined according to the use of the final product and the like. The content may be about 3 to 10% by weight, preferably 3 to 7% by weight. The amount of retained water can be adjusted by the amount of alkali hydroxide added (spray amount), the temperature of heated air, and the like. The period during which the heated air is being fed means, for example, when a fluidized bed dryer described below is used, mainly while a fluidized bed of primary particles is being formed. At the time when the supply of the heated air is completed, the water content may be outside the above range (for example, less than 3% by weight).

If the added amount of the alkali hydroxide or the water content is too small, the cobalt hydroxide on the particle surface is only partially dissolved, and a cobalt oxide having high conductivity is not formed. On the other hand, if the added amount of the alkali hydroxide or the retained water amount is too large, granulation occurs, and secondary particles may be formed, or the once formed cobalt oxide may be peeled off. is there.

The atmosphere in which the heated air is supplied is not particularly limited as long as the cobalt oxide can be formed, but may be in the air or in an oxidizing atmosphere.

The formation of the cobalt oxide by the above-mentioned heated air can also be carried out by using a known fluidized-bed dryer used in the production (granulation) of tableting granules, food granules and the like. FIG. 1 is a schematic diagram illustrating an example of the above dryer.
The cobalt-containing nickel hydroxide charged into the dryer flies up due to the heated air generated by the rotating disk and forms a fluidized bed. At the same time, the alkali hydroxide solution is sprayed from the spray nozzles on all sides. In the present invention, it is preferable to provide an infrared moisture meter for measuring the retained moisture content, thereby controlling the temperature and the like so that the retained moisture content in a state where the fluidized bed is formed is within the above range. Just do it. As shown in FIG. 1, it is preferable to further provide a temperature sensor and a pressure gauge in the tower inside the dryer to control the state. In addition, the measuring method of the water content is the drying loss method (JIS K 006).
8).

The nickel hydroxide on which the cobalt oxide has been formed is washed, if necessary, to remove excess alkali hydroxide. The washing method may be in accordance with a known method. For example, the washing can be carried out by charging the above nickel hydroxide into a washing can filled with warm water (about 50 to 80 ° C.) and stirring. After washing, dehydration may be performed by a known method such as centrifugation. Further, if necessary, it can be dried. The drying temperature may be usually about 80 to 120 ° C.

The nickel hydroxide powder particles obtained in this manner have primary surfaces of Co ₂ O ₃ , C ₂
Coated with a cobalt oxide (higher order cobalt oxide) such as oOOH, it can exhibit excellent conductivity. The average particle size of the powder depends on the raw material (nickel hydroxide serving as a base), the type of battery used, and the like, but is usually 2 to 50.
The thickness may be about μm, preferably 5 to 20 μm. In addition, its conductivity can be appropriately changed depending on the application and the like. For example, when it is used as an active material for an electrode of a nickel-metal hydride battery, it may be usually 30Ω or less, particularly 10Ω or less.

[0027]

According to the production method of the present invention, the nickel hydroxide powder particles are maintained while maintaining the physical properties (eg, particle size distribution) of the base nickel hydroxide powder, particularly in the state of primary particles. It becomes possible to form a cobalt oxide on the surface. Thereby, in the nickel hydroxide powder, excellent conductivity can be relatively easily secured without requiring a pulverizing step or the like.

The nickel hydroxide powder obtained by the production method of the present invention is useful as a non-sintered electrode active material in, for example, an alkaline secondary battery (a nickel-hydrogen battery, a nickel-cadmium battery, etc.). For example, if a slurry obtained by mixing this with an aqueous solution of a binder such as methyl cellulose is filled in nickel foam or the like, a nickel hydroxide electrode is obtained. As a result, it is possible to contribute to the improvement of the utilization rate of these batteries.

[0029]

EXAMPLES Examples and comparative examples are shown below to further clarify the features of the present invention.

Example 1 950 g of nickel hydroxide powder as a base was
0% by weight of the slurry liquid, and
The temperature was raised to ° C. Further, this slurry solution was adjusted to pH 9.0.
Was adjusted with a dilute sulfuric acid solution so that FIG. 2 shows the result of measuring the particle size distribution of the nickel hydroxide powder as a base. Microscopic photographs of the nickel hydroxide powder particles serving as the base are shown in FIGS. 5 and 6.

Next, while maintaining the pH at 9.0 and the temperature at 75 ° C., the slurry liquid is vigorously stirred to deposit 5% by weight of cobalt hydroxide on the nickel hydroxide surface (relative to the base nickel hydroxide powder). Thus, a fixed amount of the cobalt sulfate solution and the sodium hydroxide solution were simultaneously added dropwise. The concentration of the cobalt sulfate solution was 10% by weight, and the concentration of the sodium hydroxide solution was 25% by weight. In this way, a slurry of nickel hydroxide having a surface coated with cobalt hydroxide was obtained. FIG. 7 shows a micrograph of the cobalt-coated nickel hydroxide particles.

The slurry was dehydrated by a centrifugal separator and charged into a fluidized bed drier shown in FIG. Heated air at 100 ° C. was sent from below the dryer to dry the powder. As the drying progressed, the powder flew up, and the powder formed a fluidized bed in a state of primary particles inside the dryer. 200 g of a 35% by weight sodium hydroxide solution (7% by weight based on cobalt-coated nickel hydroxide) was sprayed toward the center of the fluidized bed. At this time, while measuring the water content of the powder with an infrared moisture meter, the spraying speed and the temperature were controlled so that the water content was kept at 7% by weight.

When the spraying of the sodium hydroxide solution was completed and the water content of the powder became 1% by weight or less, the powder was taken out, and excess sodium hydroxide was removed by washing with water. After dehydration, it was dried at 100 ° C. and then sieved with a 100 mesh sieve. At this time, all the particles passed through the sieve because they were oxidized in the state of primary particles. Press 4 g of the final product with a molding machine with a diameter of 15 mm (pressure 400 k
g / cm ² ) to obtain a cylindrical molded product (15φ
(× 10 mm), a highly conductive material of 1Ω was obtained. The measurement of the resistance value was 4
Using a terminal DC resistance meter, the terminals were brought into contact with the upper and lower sides of the molded body.

Further, the particle size distribution of the obtained nickel hydroxide powder was measured. The result is shown in FIG. 8 and 9 show micrographs of the powder and the powder particles, respectively. These results show that the obtained nickel hydroxide powder was able to form a cobalt oxide while maintaining the physical properties of the base nickel hydroxide powder.

Comparative Example 1 The procedure of Example 1 was repeated up to the step of coating the surface of the nickel hydroxide serving as a base with cobalt hydroxide.

In the same manner as in Example 1, the dehydrated product coated with cobalt hydroxide was put into a fluidized-bed dryer. Heated air at 100 ° C. was sent from below the dryer to dry the active material. As the drying progressed, the powder flew up, forming a fluidized bed inside the dryer. 600 g of a 35% by weight sodium hydroxide solution (21% by weight based on cobalt-coated nickel hydroxide) was sprayed toward the center of the fluidized bed. At this time, the water content of the powder was maintained at 7% by weight while observing the infrared moisture meter.

When the spraying of the sodium hydroxide solution was completed and the water content of the powder became 1% by weight or less, the powder was taken out, and excess sodium hydroxide was washed off with water to remove it. After dehydration, the product was dried at 100 ° C., and then sieved with a 100-mesh sieve. As a result, particles of 20% by weight of the original product remained on the sieve. In the same manner as in Example 1, 4 g of the final product that had all passed through the sieve was weighed 15 mm.
As a result of measuring the resistance value of the molded body, it was 1 Ω, which was a very conductive material. The particle size distribution of the nickel hydroxide powder before sieving was measured. FIG. 4 shows the results. FIG. 10 shows a micrograph of the powder. These results indicate that the obtained nickel hydroxide powder also contains secondary particles.

Comparative Example 2 The procedure was the same as in Example 1 up to the step of coating the surface of the nickel hydroxide serving as the base with cobalt hydroxide.

In the same manner as in Example 1, the dehydrated product coated with cobalt hydroxide was put into a fluidized-bed dryer. Heated air at 100 ° C. was sent from below the dryer to dry the active material. As the drying progressed, the powder flew up, forming a fluidized bed inside the dryer. 200 g of a 10% by weight sodium hydroxide solution (2% by weight based on cobalt-coated nickel hydroxide) was sprayed toward the center of the fluidized bed. At this time, the water content of the powder was maintained at 7% by weight while observing the infrared moisture meter.

When the spraying of the sodium hydroxide solution was completed and the water content of the powder became 1% by weight or less, the powder was taken out, and excess sodium hydroxide was removed by washing with water. After dehydration, it was dried at 100 ° C., and then sieved with a 100-mesh sieve, all passed through the sieve. In the same manner as in Example 1, 4 g of the final product was pressed with a molding machine having a diameter of 15 mm, and the resistance value of the molded product was measured.
It exceeded 200 kΩ and was a material with extremely low conductivity.

Further, the color of the product was brown compared to that of the example. This indicates that the cobalt hydroxide on the surface is oxidized without being dissolved, and a substance having low conductivity is generated.

Comparative Example 3 The procedure of Example 1 was repeated up to the step of coating the surface of the nickel hydroxide serving as a base with cobalt hydroxide.

In the same manner as in Example 1, the dehydrated product coated with cobalt hydroxide was put into a fluidized-bed dryer. Heated air at 100 ° C. was sent from below the dryer to dry the active material. As the drying progressed, the powder flew up, forming a fluidized bed inside the dryer. 280 g of a 25% by weight sodium hydroxide solution (7% by weight based on cobalt-coated nickel hydroxide) was sprayed toward the center of the fluidized bed. At this time, the water content of the powder was maintained at 12% by weight while observing the infrared moisture meter.

When the spraying of the sodium hydroxide solution was completed and the water content of the powder became 1% by weight or less, the powder was taken out, and excess sodium hydroxide was removed by washing with water. After dehydration, it was dried at 100 ° C., and then sieved with a 100-mesh sieve, most of which remained on the sieve. A micrograph of what remained on the screen is shown in FIG. For reference, a micrograph of the powder obtained in Example 1 observed at the same magnification is shown in FIG. 11 and 12
Thus, it can be seen that in Comparative Example 3, the nickel hydroxide powder was granulated to form secondary particles.

Comparative Example 4 The procedure was the same as in Example 1 up to the step of coating the surface of nickel hydroxide serving as a base with cobalt hydroxide.

In the same manner as in Example 1, a dehydrated product coated with cobalt hydroxide was charged into a fluidized-bed dryer. Heated air at 100 ° C. was sent from below the dryer to dry the active material. As the drying progressed, the powder flew up, forming a fluidized bed inside the dryer. 200 g of a 35% by weight sodium hydroxide solution (7% by weight based on cobalt-coated nickel hydroxide) was sprayed toward the center of the fluidized bed. At this time, the water content of the powder was maintained at 2% by weight while observing the infrared moisture meter.

When the spraying of the sodium hydroxide solution was completed and the water content of the powder became 1% by weight or less, the powder was taken out, and excess sodium hydroxide was removed by washing with water. After dehydration, it was dried at 100 ° C. and then sieved with a 100-mesh sieve, all of which passed through the sieve. What passed through the sieve was observed under a microscope. The result is shown in FIG. FIG. 13 shows that the state of the particle surface before the alkali oxidation is left, so that the cobalt hydroxide is not completely dissolved, and a part of the cobalt hydroxide remains on the particle.

[Brief description of the drawings]

FIG. 1 is a schematic view illustrating an example of a fluidized-bed dryer.

FIG. 2 is a view showing a particle size distribution of a raw material nickel hydroxide powder used in Example 1.

FIG. 3 is a view showing the particle size distribution of the powder obtained in Example 1.

FIG. 4 is a view showing the particle size distribution of the powder obtained in Comparative Example 1.

FIG. 5 is a photograph showing a particle structure of a raw material nickel hydroxide powder used in Example 1.

FIG. 6 is a photograph showing the particle structure of a raw material nickel hydroxide powder used in Example 1.

FIG. 7 is a photograph showing a particle structure of cobalt-coated nickel hydroxide powder in Example 1.

FIG. 8 is a photograph showing the particle structure of the powder obtained in Example 1.

FIG. 9 is a photograph showing the particle structure of the powder obtained in Example 1.

FIG. 10 is a photograph showing the particle structure of the powder obtained in Comparative Example 1.

FIG. 11 is a photograph showing the particle structure of the powder obtained in Comparative Example 3.

FIG. 12 is a photograph showing the particle structure of the powder obtained in Example 1.

FIG. 13 is a photograph showing the particle structure of the powder obtained in Comparative Example 4.

Claims (5)

[Claims] 1. A nickel electrode for a nickel electrode, characterized in that said cobalt hydroxide is oxidized by feeding heated air to a nickel hydroxide powder having a surface coated with cobalt hydroxide while adding an alkali hydroxide solution. Active material manufacturing method. 2. The addition amount of the alkali hydroxide solution is 2 to 20% by weight based on the nickel hydroxide powder.
The manufacturing method as described. 3. The water content of the nickel hydroxide powder at least during the supply of heated air is 3 to 1
2. The method according to claim 1, wherein the amount is 0% by weight. 4. The method according to claim 1, wherein the temperature of the heated air is 70 to 150 ° C. 5. A heating air supply amount of 10 to 50 m ³ / m ² · m.
The production method according to claim 1, wherein “in” is used.