JP2002029755A - Method for manufacturing nickel hydroxide powder for alkali secondary cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide nickel hydroxide powder the surface of which is uniformly coated with cobalt hydroxide having good crystallinity and to provide a method for manufacturing nickel hydroxide powder coated with cobalt hydroxide suitable for the manufacture of positive poles of alkali secondary cells by a paste method. SOLUTION: A reducing organic matter is made present in an aqueous solution containing nickel hydroxide powder and having the pH controlled to 10.5 to 12.5 with caustic alkali, to which further an aqueous solution containing cobalt and ammonium ion source material is continuously and quantitatively supplied so as to obtain 10 to 25 g/L ammonium ion concentration in the reaction liquid. In the coating process, the nickel ion concentration in the reaction solution is controlled to 10 to 300 mg/L and the total cobalt ion concentration is controlled to 5 to 300 mg/L. The solution contains hydrazine or formaldehyde by 1 to 10 vol.% as the reducing organic compound.

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 nickel hydroxide powder for an alkaline secondary battery, and more particularly, to a cobalt hydroxide having a high packing density suitable as an active material for a positive electrode of a non-sintered alkaline secondary battery. The present invention relates to a method for producing a nickel hydroxide powder coated with.

[0002]

2. Description of the Related Art As portable electronic devices have become smaller and lighter, batteries as a power source have been required to have higher energy density. To this end, a paste-type nickel electrode plate has been developed in which a metal fiber sintered body having a high porosity of 95% is used as a substrate, and a nickel hydroxide active material powder is filled in a paste form. In such a use, there is a problem that the utilization rate of the active material is lowered in exchange for the advantage that nickel hydroxide as the active material can be filled at a high density.

In order to improve the utilization, it is necessary to increase the conductivity between the electrode substrate and the nickel hydroxide particles. For this reason, a cobalt compound such as cobalt hydroxide is mixed and added during the production of the paste of the nickel hydroxide active material, and a highly conductive cobalt oxyhydroxide is formed by an electrode reaction to improve the conductivity between the electrode substrate and the nickel hydroxide particles. It is common to improve.

[0004] However, it is difficult to uniformly disperse the compound by mixing the cobalt compound with the nickel hydroxide particles, and improvement in conductivity cannot be expected by adding a small amount of the compound. Therefore, it is necessary to mix about 10% of the cobalt compound particles having a low filling density, and as a result, there is a problem that the filling amount of the nickel hydroxide particles as the active material itself is reduced.

[0005] Therefore, a method of coating various cobalt compounds on the surface of nickel hydroxide has been considered. For example, a method of coating the surface of nickel hydroxide with cobalt using electroless plating or the like as disclosed in JP-A-3-93161, or by a mechanochemical reaction as disclosed in JP-A-6-187984. A method of coating the surface with cobalt or the like has been proposed.

[0006] In particular, a method of coating the surface of nickel hydroxide particles with cobalt hydroxide is disclosed in, for example, JP-A-62-23.
No. 7667. This method
This is a method in which an aqueous solution of a cobalt salt such as cobalt sulfate is added to the nickel hydroxide suspension and neutralized with caustic alkali. However, according to this method, the generated cobalt hydroxide is not in a state of being gelled and coated on the nickel hydroxide surface, and the cobalt hydroxide-containing nickel hydroxide generated by the present method has a very small surface layer. Low density cobalt hydroxide particles are generated, the density of the particles is significantly reduced,
There was a problem that the tapping density was significantly reduced.

As a method for improving this, Japanese Patent Laid-Open Publication No.
In No. 3115, nickel hydroxide particles having a high tapping density are dispersed in water, an aqueous solution of cobalt sulfate and aqueous ammonia are simultaneously added thereto, and the reaction system is adjusted to a pH range of 11 to 13 with an aqueous solution of sodium hydroxide. A method of forming a cobalt hydroxide coating layer on the surface of nickel hydroxide particles while the nickel hydroxide particles are being described. This aims at forming a uniform cobalt hydroxide layer by increasing the solubility of the cobalt salt by causing ammonium ions to be present in the reaction system. However, as shown in the examples of the publication, the tapping density of the cobalt hydroxide-coated particles is lower than the density of the nickel hydroxide particles serving as nuclei by 0.2 g / ml or more. It was not fully satisfactory for the purpose of enabling filling.

[0008]

SUMMARY OF THE INVENTION The present invention relates to a nickel hydroxide powder having a surface uniformly coated with cobalt hydroxide having good crystallinity, which is suitable for producing a cathode of an alkaline secondary battery by a paste method. It is an object to provide a method for producing nickel hydroxide powder coated with cobalt hydroxide.

[0009]

According to the present invention, there is provided a method for producing a nickel hydroxide powder coated with cobalt hydroxide according to the present invention.
It is characterized in that a reducing organic substance is allowed to coexist in an aqueous solution adjusted to 12.5, and an aqueous solution containing cobalt and an ammonium ion donor is continuously added so that the ammonium ion concentration in the reaction solution becomes 10 to 25 g / liter. It is characterized in that it is quantitatively supplied quantitatively, and the total nickel ion concentration in the reaction solution during the coating treatment is 10 to 300
mg / liter, 5 to 5 for the total cobalt ion concentration
It is characterized by being 300 mg / liter.

In the coating treatment, the temperature of the reaction solution is set at 30.
It is preferable to add the cobalt salt aqueous solution at an addition rate of 0.6 g / min or less in terms of cobalt with respect to 1 kg of nickel hydroxide powder while maintaining the temperature at -55 ° C. Of hydrazine or formaldehyde.

In the method of the present invention, the cobalt and ammonium donors are added in the same solution, but the aqueous solution containing cobalt and the solution containing the ammonium ion donor are added separately and simultaneously. No problem.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION Under the conditions when coating with cobalt hydroxide according to the present invention, a preferable pH range is from 10.5 to 12.5. If the pH is less than 10.5, the anion of the used cobalt salt cannot be completely removed to form a basic salt, which results in the generation of impure cobalt hydroxide containing the salt. pH 1
If it exceeds 2.5, the solubility of cobalt ions is extremely reduced, and nucleation of cobalt hydroxide occurs instantaneously during neutralization.
Not only cannot uniform coating be obtained, but also single particles of cobalt hydroxide. More preferable pH range is 11 to 1
2.

In the present invention, since ammonium ions are introduced into the reaction solution in a high pH range, cobalt is present in the reaction solution as an ammine complex salt. Therefore, even in a high pH region, the solubility of cobalt is high, and the concentration of cobalt ions can be kept constant and high, so that the generation of crystal nuclei can be suppressed, and as a result, crystal growth can be promoted.

If the pH and ammonia ion concentration cannot be kept constant, the crystal nucleus generation rate of cobalt hydroxide and the like become irregular, so that the primary particle diameter of the produced cobalt hydroxide becomes uneven. . Therefore, not only the coating of the cobalt hydroxide on the surface of the nickel hydroxide particles becomes uneven, but also the tapping density of the produced particles decreases.

In addition, even if the pH is constant, if the pH exceeds 13, ammonia will be greatly diffused, and even if ammonia ions are present, the cobalt concentration cannot be adjusted to an optimum value, and uniform coating cannot be achieved. Disappears. Compared to the case where a raw material solution containing both a cobalt and an ammonium supplier is used, if an aqueous solution containing a cobalt and an aqueous solution containing an ammonium supplier are separately prepared and added at the same time, the pH and ammonia ion concentration can be minimized by stirring and mixing. Since the concentration can be kept constant and the cobalt concentration in the reaction tank is stabilized, it is possible to keep the crystal nucleus generation rate, the generation amount, and the crystal nucleus growth rate of cobalt hydroxide constant.

If the ammonia concentration in the tank is 10 g / l or less, it becomes difficult to maintain the appropriate cobalt concentration within the above-mentioned appropriate pH range, and if it is 25 g / l or more, the diffusion of added ammonia becomes severe. Is not practical because it consumes a large amount of the ammonium ion donor.

It is desirable that the addition rate of the aqueous solution of the cobalt salt, that is, the time for adding the aqueous solution containing cobalt to the reaction solution, is slow. However, an excessive decrease in the addition rate is not preferable because the addition rate directly affects the productivity. Conversely, if the addition rate is increased, non-uniformity due to the location of the concentration of cobalt ions in the reaction tank occurs,
The coating becomes uneven. Therefore, the addition rate of the aqueous cobalt salt solution is preferably 0.6 g / min or less as the amount of cobalt per 1 kg of nickel hydroxide in the liquid.

There is no particular upper limit on the amount of cobalt to be coated. However, if it exceeds 10%, the amount of nickel hydroxide as an active material is excessively reduced, and the battery capacity is extremely reduced. The advantage that a battery with a large capacity can be manufactured cannot be used. Coating with a large amount of cobalt contradicts the original purpose of uniformly dispersing a small amount of a cobalt compound in an electrode to form a conductive path. Further, if the amount of cobalt to be coated is 1% or less, the advantage of coating is lost, and the effect is not changed from the method of containing cobalt by solid solution, but the cost is increased and it is uneconomical.

During the reaction, it is necessary that a reducing organic compound coexist in the solution, and the presence of this organic compound causes the formation of trivalent cobalt ions in the cobalt hydroxide of the coating layer in a high pH region. Thus, the coating layer can be efficiently formed. The concentration of the organic compound in the reaction solution is desirably 1 to 10% by volume.

When the reaction temperature exceeds 55 ° C., the diffusion of ammonia from the solution becomes intense, which makes it difficult not only to keep the ammonia concentration in the tank constant, but also to increase the coexisting organic substance reducing power. Some metal is deposited. If the temperature is lower than 30 ° C., the reactivity of the coexisting reducing organic substance is reduced, the reducing power becomes insufficient, and trivalent ions of cobalt are generated.
Therefore, the temperature range of the reaction solution at the time of coating is preferably from 30 to 55 ° C, more preferably from 35 to 50 ° C.

It is desirable that the total nickel ion concentration in the reaction solution at the time of coating is 10 to 300 mg / liter. If it is less than 10 mg / liter, the tap density will decrease. There is no particular upper limit, but if it is too large, the recrystallization of nickel hydroxide causes a change in the pore size distribution and a decrease in the half-value width, degrading the powder characteristics. Furthermore, nickel is washed out of the system, which is uneconomical. 300mg for tap density improvement
Per liter is sufficient.

The total cobalt ion concentration in the reaction solution is 5 to
Desirably, it is 300 mg / liter. 5mg /
If the amount is less than 1 liter, not only a uniform coat cannot be formed but also a single particle of cobalt hydroxide is formed. If it exceeds 300 mg / liter, there is a problem that the tap density of the coated particles decreases.

Hereinafter, the present invention will be described based on examples.

[0024]

EXAMPLES [Production of Raw Material Nickel Hydroxide] The raw material of high bulk density nickel hydroxide is disclosed in, for example, Japanese Patent Application Laid-Open No. 9-0174.
29 can be produced. That is,
An aqueous solution containing nickel, an alkali hydroxide and ammonium water are simultaneously and continuously supplied to a reaction vessel equipped with a stirrer, the nickel ion concentration in the reaction solution is 1 to 50 mg / liter, and the reaction temperature is 40 to 70. ° C, the fluctuation range of the reaction temperature is ± 1 ° C, and the discharge head of the stirring blade of the stirrer is 14 to 7
This is a method in which 0 m ² / sec ² and the produced nickel hydroxide are kept in the reaction tank for a residence time of 6 hours or more.

[Preparation of Each Use Solution] A cobalt salt solution, a caustic alkali solution, and an ammonium ion donor aqueous solution to be used were prepared as follows. The cobalt salt aqueous solution was prepared by dissolving a special grade cobalt sulfate manufactured by Wako Pure Chemical in pure water to form a solution having a cobalt concentration of 1.6 mol / liter. The caustic alkali solution was prepared by dissolving reagent grade 1 caustic soda manufactured by Wako Pure Chemical in pure water to prepare a 3.2 mol / liter solution. As an ammonium ion supplier, reagent-grade ammonia water was used as it was.

Example 1 19 liters of pure water, 1.1
One liter of aqueous ammonia and 300 ml of hydrazine monohydrate were mixed and heated to 50 ° C. to suspend 5 kg of the high bulk density nickel hydroxide (tap density 2.15 g / ml). The pH of the obtained suspension was controlled to 12.0 with a sodium hydroxide solution while simultaneously adding the aqueous solution of cobalt sulfate and the aqueous ammonia adjusted by the above method while stirring the obtained suspension. The addition rate of the aqueous solution of cobalt sulfate is 3
0 ml / min, the addition rate of aqueous ammonia is 4.
It was 2 ml / min. Under the above conditions, the reaction was performed for a time (50 minutes) until the calculated cobalt content in the charged nickel hydroxide became 3%.

After the completion of the reaction, the formed product was immediately suction-filtered with a Buchner funnel, washed twice with 10 l of pure water and then filtered and dried. As a result of sampling and analyzing the reaction solution, the ammonium ion concentration in the solution was 9.6 g / liter. This dried product was dissolved in nitric acid and analyzed by atomic absorption spectroscopy.
Contained. The tap density was measured.
It was 11 g / milliliter, and as a result of SEM observation, it was confirmed that the presence of fine particles was small, that is, the amount of cobalt hydroxide single precipitate particles was small, and thus a nickel hydroxide-coated nickel hydroxide having a good coating state was obtained.

Example 2 19 liters of pure water, 1.1
One liter of aqueous ammonia and 260 milliliters of hydrazine monohydrate are mixed, heated to 50 ° C., and nickel hydroxide (tap density 2.19 g / ml) 3.5
kg were suspended. The pH of the resulting suspension was controlled at 11.0 with caustic soda while simultaneously adding the cobalt sulfate solution prepared by the above-described method and aqueous ammonia while stirring the suspension. The addition rate of the cobalt sulfate solution was 22 ml / min, and the addition rate of aqueous ammonia was 4.7 ml / min. The reaction was carried out for a time (85 minutes) at which the calculated cobalt content in the charged nickel hydroxide became 5%.
After the completion of the reaction, the resulting precipitate was immediately suction-filtered with a Buchner funnel, washed twice with 7 l of pure water and then filtered and dried. As a result of sampling and analyzing the reaction solution, the concentration of ammonium ion in the solution was 12.8 g /
Liters. The dried product was dissolved in nitric acid and subjected to atomic absorption analysis to find that it contained 4.93% of cobalt and had a tapping density of 2.05 g / ml.

Example 3 19 liters of pure water, 1.1
One liter of aqueous ammonia and 1.2 liter of hydrazine monohydrate were mixed and heated to 50 ° C. to suspend 5 kg of nickel hydroxide (tap density 2.19 g / ml). While stirring the obtained suspension, the pH was controlled at 11.5 with sodium hydroxide while simultaneously adding the cobalt sulfate and ammonium sulfate solutions prepared by the above-described method. The addition rate of the cobalt sulfate solution was 32 ml / min, and the addition rate of the aqueous ammonia was 4.8 ml / min. The reaction was allowed to proceed for a time (75 minutes) at which the calculated cobalt content in the charged nickel hydroxide was 4.5%.
After completion of the reaction, the formed precipitate was immediately suction-filtered with a Buchner funnel, washed twice with 1 liter of pure water and then filtered and dried. The concentration of ammonium ion in the solution was 1
It was 2.5 g / liter. The dried product was dissolved in nitric acid and analyzed by atomic absorption spectroscopy. As a result, it contained 4.41% by weight of cobalt and had a tapping density of 2.08 g / ml.

Comparative Example 1 1 liter of ammonia water, 19 liters of pure water and 5 liters of 5 kg of nickel hydroxide (tap density 2.15 g / ml) maintained at 40 ° C.
The suspension was suspended in a mixed solution with 0 ml of hydrazine monohydrate, and the pH was controlled at 11.5 with caustic soda while adding the cobalt sulfate solution prepared by the above method while stirring. The addition rate of the cobalt sulfate solution was 32 ml / min, and the addition rate of aqueous ammonia was 4.5 ml / min. The reaction was allowed to proceed for a time (67 minutes) at which the cobalt content in the charged nickel hydroxide was calculated to be 4%. After the completion of the reaction, the resulting precipitate was immediately suction-filtered with a Buchner funnel, washed twice with 10 liters of pure water, then filtered and dried. The ammonium ion concentration in the solution was 11.6 g / liter. The dried product was dissolved in nitric acid and subjected to atomic absorption analysis.
% And the tapping density was 1.97 g / ml. As a result of SEM observation, cobalt hydroxide partially covering nickel hydroxide was observed, but most of the cobalt hydroxide was present as single particles.

COMPARATIVE EXAMPLE 2 1.0 liter of ammonia water, 19 liter of pure water and 300 ml of hydrazine monohydrate containing 3.5 kg of nickel hydroxide (tap density 2.15 g / ml) kept at 25 ° C. The mixture was suspended in a mixed solution with sodium chloride, and the pH was adjusted to 10.0 with caustic soda while adding the cobalt sulfate solution prepared by the above method while stirring.
Was controlled. The addition rate of the cobalt sulfate solution is
32 ml / min, the addition rate of aqueous ammonia is
4.5 ml / min. Time (58) when the cobalt content in the charged nickel hydroxide is calculated to be 5%.
Min) reacted. After the completion of the reaction, the formed precipitate was immediately suction-filtered with a Buchner funnel, washed twice with 7 liters of pure water and then dried by filtration. The concentration of ammonium ion in the solution was 11.8 g / liter. The dried product was dissolved in nitric acid and subjected to atomic absorption analysis. The dried product contained 4.12% of cobalt and had a tapping density of 1.65.
g / milliliter. As a result of SEM observation, cobalt hydroxide partially covering nickel hydroxide was observed, but most of the cobalt hydroxide was present as single particles.

(Comparative Example 3) 1 liter of ammonia water, 19 liters of pure water and 3 liters of hydrazine monohydrate containing 3.5 kg of nickel hydroxide (tap density 2.15 g / milliliter) kept at 60 ° C. And the pH was controlled at 12.0 with caustic soda while adding the cobalt sulfate solution prepared by the above method while stirring. The addition rate of the cobalt sulfate solution was 32 ml / min, and the addition rate of the aqueous ammonia was 4.5 ml / min. The reaction was allowed to proceed for a time (58 minutes) at which the cobalt content in the charged nickel hydroxide was calculated to be 5%. After the completion of the reaction, the formed precipitate was immediately suction-filtered with a Buchner funnel, washed twice with 7 liters of pure water and then dried by filtration. The concentration of ammonium ion in the solution was 10.
It was 8 g / liter. The dried product was dissolved in nitric acid and subjected to atomic absorption analysis. As a result, it contained 4.97% of cobalt and had a tapping density of 1.83 g / ml. The obtained nickel hydroxide was black. This is considered to be because a large amount of reducing organic substances were contained and the processing temperature was high, so that the nickel hydroxide was reduced to a part of the nickel hydroxide, turned black, and the tap density decreased.

Table 1 shows the main constitutions of Examples 1 to 3 and Comparative Examples 1 to 3 and the tap densities of the core particles and the coating.

[0034]

[Table 1]

(Evaluation of Battery) Positive electrodes were prepared as follows using the nickel hydroxides of Examples 1 to 3 and Comparative Examples 1 and 2. Cobalt hydroxide (manufactured by Ise Chemical Co., Ltd.) is added to the cobalt hydroxide-coated nickel hydroxide so that the Co content in the positive electrode becomes 8 wt%, and H is added so that the binder amount becomes 2 wt%.
PC (hydroxypropyl cellulose 1000-400
0cP; Reagent Grade 1 made by Wako Pure Chemical Industries) Aqueous solution was added to form a paste using a non-babbling kneader (manufactured by Nippon Seiko), and nickel foam (Celmet manufactured by Sumitomo Electric: porosity 95)
%), Dried and isostatically pressed at a pressure of 2 ton / cm ² to obtain a positive electrode.

A cadmium electrode was used as the negative electrode, and a sulfonated polyolefin nonwoven fabric was used as the separator.
An 7.2 mol / liter potassium hydroxide aqueous solution was used as an electrolyte. The test cell was kept in a thermostat at 20 ° C., and charged at 0.1 C at 150 C of theoretical capacity (289 mA / g ⁻¹ ).
%, And discharge was performed at 0.2 C to 1.0 V.
At this time, the utilization is expressed as a percentage of the discharge capacity with respect to the theoretical capacity. Table 2 shows the utilization rate at the fifth cycle.

[0037]

[Table 2]

As described above, according to the present production method, it is possible to obtain a nickel hydroxide powder having a high tap density.
It can be seen that a battery with a high utilization rate can be manufactured.

[0039]

According to the present invention, it is possible to obtain a nickel hydroxide powder coated with cobalt hydroxide having a high availability suitable for the production of a paste type electrode.

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Masashi Kasai 3-5-3 Nishihara-cho, Niihama-shi, Ehime F-term in the Besshi Works of Sumitomo Metal Mining Co., Ltd. 4G048 AA03 AB04 AC06 AD03 AE05 AE07 5H050 AA08 AA12 BA13 CA03 CB14 DA02 DA10 EA12 FA17 FA18 GA14 GA15 HA10 HA14

Claims (4)

[Claims] 1. An aqueous solution containing nickel hydroxide powder and a reducing organic compound and adjusted to a pH of 10.5-12.5 with caustic alkali, and an aqueous solution containing a cobalt and ammonium ion donor in the reaction solution. And the total amount of nickel ions in the reaction solution is 10 to 300 mg / L, and the total concentration of cobalt ions is 5 to 300 mg / L. A method for producing nickel hydroxide powder for an alkaline secondary battery, comprising coating the nickel hydroxide with cobalt hydroxide. 2. Coating the cobalt hydroxide by maintaining the temperature of the reaction solution at 30 to 55 ° C. and adding an aqueous solution of a cobalt salt to 1 kg of nickel hydroxide powder at an addition rate of 0.6 g / min or less in terms of cobalt. The method for producing a nickel hydroxide powder for an alkaline secondary battery according to claim 1, wherein: 3. The method for producing a nickel hydroxide powder for an alkaline secondary battery according to claim 1, wherein the reducing organic compound is hydrazine or formaldehyde. 4. The method according to claim 1, wherein the concentration of the reducing organic compound in the reaction solution is 1 to 10% by volume.
The method for producing a nickel hydroxide powder for an alkaline secondary battery according to any one of the above.