JPH10247494A - Nickel hydroxide active material and its manufacture - Google Patents

Abstract

PROBLEM TO BE SOLVED: To develop the manufacturing method of a nickel hydroxide active material so that cobalt can be simply added and contained without forming a Ni-Co compound, and provide the nickel hydroxide active material further improved in its utilization factor. SOLUTION: Under agitation conditions, a nickel salt aqueous solution, an ammonia ion supplier, and an alkali hydroxide aqueous solution are added to an aqueous solution previously suspending granular metal cobalt. A particle of metal cobalt is used as a nucleus, nickel hydroxide is crystallized and developed on the surface of the particle. Thereby, a nickel hydroxide active material is provided containing the granular metal cobalt being localized close to the medial portion in the inside of a developed particle of nickel hydroxide.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a nickel hydroxide active material and a method for producing the same, and more particularly to a nickel hydroxide active material suitably used for a nickel positive electrode for an alkaline battery and a method for advantageously producing the same. suggest.

[0002]

2. Description of the Related Art Nickel hydroxide is an industrial product used for various applications. Particularly, for a non-sintered nickel positive electrode for an alkaline battery, the particle shape is spherical and its particle size is large. What has a narrow distribution is required. This is achieved by using such nickel hydroxide particles.
When the nickel positive electrode is filled into a carrier or the like as an active material, the particles do not fall off from the fine pores of the carrier and can be densely packed. In the case of using, the paste property such as fluidity is stabilized, so that the filling property and the filling rate are improved. Therefore, in each case, the utilization rate of the active material is improved, and an electrode having excellent performance can be obtained.

On the other hand, conventionally,. JP-A-5-21064 discloses that a nickel hydroxide active material containing 1 to 7 wt% of at least one of cadmium, calcium, zinc, magnesium, iron, cobalt and manganese as a nickel hydroxide active material having improved utilization characteristics and the like. In addition, there has been proposed a mixture of spherical or spherical-like particles and non-spherical particles. Also,. Japanese Patent Application Laid-Open No. 7-45282 discloses a nickel hydroxide active material that prevents a decrease in capacity per unit volume, such as zinc, cadmium, cobalt, and lead, which are in a corrosive area with an alkaline aqueous solution in pores of nickel hydroxide particles. There has been proposed a nickel hydroxide active material containing (diffused and fixed) a metal element of copper, silver, ruthenium, indium or tungsten.

[0004]

In the proposal according to the prior art, cobalt among the metal elements contained in nickel hydroxide certainly lowers the potential of the charging reaction of the nickel hydroxide active material. With.

However,. JP-A-5-21064
In the proposal according to the publication, a method in which a metal element such as cobalt is precipitated in nickel hydroxide particles and solid-dissolved in the particles at the same time, that is, a method in which the metal element is contained in the nickel hydroxide particles by so-called coprecipitation addition is adopted. ing. For this reason,
Cobalt forms a solid solution inside the nickel hydroxide crystal, and Ni-
By forming a Co compound, the crystal structure of nickel hydroxide is significantly changed, and cobalt acts as an impurity. This lowers the utilization ratio (actual discharge capacity / theoretical discharge capacity) and discharge potential of the nickel hydroxide active material.

In addition,. In the proposal according to JP-A-7-45282, a nickel electrode is immersed or electrochemically oxidized and reduced in a KOH electrolytic solution containing a metal element such as cobalt, A method has been adopted in which a compound of a metal element is coexistent and electrochemically redox-oxidized to diffuse and fix the metal element inside the pores of the nickel hydroxide particles. Therefore, the cobalt hydroxide is added to the nickel hydroxide active material without forming a Ni—Co compound, so that the utilization factor is improved. However, since the cobalt is not diffused to the center of the nickel hydroxide particles, a sufficient utilization rate cannot be obtained yet. In addition, the above-described method according to this proposal requires a metal element to be diffused and fixed after the nickel electrode is manufactured, and has a drawback that the process is complicated.

Accordingly, the present invention has developed a method for producing a nickel hydroxide active material which can easily add and contain cobalt without forming a Ni-Co compound, thereby further increasing the utilization factor as compared with the prior art. An object of the present invention is to provide a further improved nickel hydroxide active material.

[0008]

Means for Solving the Problems The inventors of the present invention have made intensive studies for realizing the above-mentioned object, and as a result, have completed the present invention having the following constitution as a summary. That is, the nickel hydroxide active material of the present invention is characterized in that granular metal cobalt is contained in a localized state from the central portion inside the nickel hydroxide particles. In another embodiment, the nickel hydroxide active material of the present invention is composed of an aggregate of granular metal cobalt surrounded by nickel hydroxide, and the metal cobalt is localized from the central portion inside the nickel hydroxide particles. It is characterized in that it is contained in a state. Here, the metal cobalt preferably has a particle size of 0.1 to 5 μm.

As a method for advantageously producing such a nickel hydroxide active material, the present invention provides a method in which an aqueous solution in which granular metallic cobalt is previously suspended, a nickel salt aqueous solution,
An ammonia ion supplier and an aqueous alkali hydroxide solution were added under stirring conditions, and the metal cobalt particles were used as nuclei to crystallize and grow nickel hydroxide on the surface of the particles, thereby growing granular metal cobalt. The present invention proposes a method for producing a nickel hydroxide active material, characterized in that the nickel hydroxide active material is contained in a localized state from the central portion inside the nickel hydroxide particles. Here, the metal cobalt preferably has a particle size of 0.1 to 5 μm.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION The method for producing a nickel hydroxide active material according to the present invention is characterized in that particles of metallic cobalt are used as nuclei, and nickel hydroxide is crystallized and grown on the surfaces of the core particles. According to such a method of the present invention, Ni-Co
It is possible to easily form a particle structure in which granular metal cobalt is included in nickel hydroxide without forming a compound, and as a result, cobalt is localized from the central portion inside the nickel hydroxide particles. To obtain a nickel hydroxide active material. Therefore, according to the present invention, it is possible to provide a nickel hydroxide active material whose utilization factor is further improved as compared with the related art.

In the present invention, metallic cobalt is used as core particles for crystallizing nickel hydroxide. The reason is that metallic cobalt does not react with the aqueous nickel salt solution to form a Ni—Co compound. In particular, when metal cobalt is used, the conductive substance is concentrated inside the nickel hydroxide particles, so that there is another effect that a resistance component is small and electricity is easily conducted (excellent in conductivity). It is desirable that such metal cobalt has a particle size of 0.1 to 5 μm. The reason for this is that if it is less than 0.1 μm, the metallic cobalt will agglomerate in the suspension, making it difficult to uniformly incorporate it in the central part of the nickel hydroxide, or the particle size of the nickel hydroxide active material generated. This is because a large amount of time is required to obtain a nickel hydroxide active material having a predetermined particle size. on the other hand,
If the thickness exceeds 5 μm, it is difficult to include the particles in the nickel hydroxide particles, and it is difficult to densify the nickel hydroxide.

In the present invention, the nickel hydroxide active material preferably has a spherical shape. The reason is that when a spherical nickel hydroxide active material is used, the filling property and the filling rate are improved, and as a result, the utilization rate as the active material is improved.

In the method of the present invention, an aqueous solution of various water-soluble nickel salts such as nickel nitrate, nickel sulfate and nickel chloride can be used as the nickel salt aqueous solution. The concentration of this nickel salt aqueous solution is usually 0.5 to
It is appropriate to use about 3 mol / l.

As the aqueous alkali hydroxide solution, sodium hydroxide, potassium hydroxide or the like can be used. This aqueous alkali hydroxide solution is usually preferably used as an aqueous solution of about 4 to 8 mol / l.

Ammonia water, ammonia gas, an aqueous solution of an ammonium salt such as ammonium nitrate, or the like can be used as the ammonia ion supplier. In the case of aqueous ammonia, it is appropriate to use one having a concentration of about 28% by weight. In the case of an aqueous solution of an ammonium salt,
Usually, it is appropriate to use one having a concentration of about 16 mol / l.

The method of supplying the reaction system is carried out with sufficient stirring, and the rate of addition depends on the capacity of the reaction vessel,
The residence time in the reaction system is usually 8
It is advisable to adjust appropriately so that the time is up to 20 hours.

The temperature of the reaction system at this time is 40 to 50 ° C.
Is kept constant. Usually, it is preferable to maintain the temperature at a predetermined value of about ± 2 ° C. Similarly, the pH of the reaction system is 11-1
It is kept at a constant value in the range of 1.5. Normally, the specified value ± 0.1
It is better to maintain to about.

[0018]

【Example】

(Example 1) Metal Co having an average particle size of 1.2 μm was added to a 20 l reaction layer.
40 g of the powder was dispersed in water and stirred, and then a 2 mol / l aqueous solution of nickel sulfate, 6.3% by weight of aqueous ammonia and a 6 mol / l aqueous solution of sodium hydroxide were supplied at a constant rate. The reaction was carried out at a constant value, and nickel hydroxide was crystallized and grown using metal Co as a seed crystal. The reaction was stopped 20 hours after the start of the reaction, and the obtained nickel hydroxide active material was washed and dried to obtain a sample A.

The obtained nickel hydroxide active material (sample A)
Had an average particle size of 7 μm and a tap density of 2.0 g / ml. The nickel hydroxide active material contained metal Co at a ratio of 3 wt% with respect to nickel hydroxide in the active material, and the cross section of the particles was observed by SEM. As shown in FIG. Had a plurality of metal Co particles incorporated therein.

To this nickel hydroxide active material (sample A), 5 wt% of water and CoO were added to form a paste, filled into a foamed Ni substrate having a porosity of 95%, dried at 100 ° C. for 1 hour, and then pressurized. A nickel positive electrode was obtained. The obtained nickel positive electrode was MH
Assemble the battery with the negative electrode of the alloy as the counter electrode, and
The positive electrode utilization rate (active material utilization rate) and the discharge potential in 0.2 C discharge were measured. Table 1 shows the results. Further, the battery after the charge / discharge test was disassembled, the positive electrode was taken out, and the cross section of the active material was observed by SEM. As shown in FIG. 2, metal Co inside the particles was reduced.

Comparative Example As a comparative example, an average particle diameter of a Co-free nickel hydroxide active material (Sample B) and a Co-free nickel hydroxide active material manufactured without adding a seed crystal of metal Co was 1.2. A nickel hydroxide active material (sample C) in which 3 μm of metallic Co was mixed at a ratio of 3 wt% and a nickel hydroxide active material (sample D) in which 3 wt% of Co was added in a solid solution state were prepared.
A positive electrode was prepared by adding CoO and water to each nickel hydroxide active material in the same manner as in the above example, and batteries were assembled. The positive electrode utilization rate (active material utilization rate) and discharge potential at 0.2 C discharge of each battery were measured. did. The results are shown in Table 1.

[0022]

[Table 1]

As is clear from the results shown in Table 1, Sample D to which Co was added in a solid solution state had a lower positive electrode utilization rate than the other samples. Sample D had a discharge potential of 15 mV compared to Sample B containing no Co compound containing no Co compound inside the particles.
It fell above. On the other hand, the samples (A and C) to which metal Co is added or mixed have a positive electrode utilization of 100% or more and a very small decrease in discharge potential.

In particular, as apparent from the results shown in Table 1, when the sample A in which the metal Co was added and contained in the nickel hydroxide particles was compared with the sample C in which the metal Co was simply added to nickel hydroxide and mixed, In the former according to the present invention, a higher positive electrode utilization rate was obtained. This means that the presence of the added metal Co inside the nickel hydroxide particles can effectively work to improve the utilization factor, and as shown in FIG. Metal inside particles
It is considered that Co is eluted and a uniform conductive network is formed over the entire nickel hydroxide, so that the particles are easily used even inside the particles.

Next, in the examples, in order to examine the optimum amount of metal Co to be present inside nickel hydroxide, 0, 1, 2, 3, 4, 5 wt.
A sample containing metal Co was prepared, and its positive electrode utilization was investigated. Table 2 shows the results.

[0026]

[Table 2]

As is clear from the results shown in Table 2,
The positive electrode utilization rate of the nickel hydroxide active material increases with the metal Co content, and becomes substantially constant at 4 wt% or more. On the other hand, when the amount of metal Co added as a seed crystal of nickel hydroxide increases, the proportion of nickel hydroxide in the positive electrode active material decreases, and the capacity density of the positive electrode decreases. Therefore, the addition amount of metal Co is preferably set to 4 wt% or less.

[0028]

As described above, according to the method of the present invention, cobalt can be easily added and contained without forming a Ni-Co compound, so that the utilization factor is further improved as compared with the prior art. The present invention can provide a nickel hydroxide active material that has been made to react.

[Brief description of the drawings]

FIG. 1 is a cross-sectional photograph showing a particle structure of a nickel hydroxide active material according to the present invention.

FIG. 2 is a cross-sectional photograph showing the particle structure of the nickel hydroxide active material according to the present invention after charge and discharge.

Claims (5)

[Claims] 1. A nickel hydroxide active material characterized in that granular metal cobalt is contained in a state localized at a central portion inside nickel hydroxide particles. 2. It is composed of an aggregate of granular metal cobalt surrounded by nickel hydroxide, and the metal cobalt is contained in a state localized at a central portion inside the nickel hydroxide particles. Nickel hydroxide active material. 3. The metal cobalt has a particle size of 0.1.
The nickel hydroxide active material according to claim 1, wherein the thickness is from 5 μm to 5 μm. 4. A nickel salt aqueous solution, an ammonia ion donor and an alkali hydroxide aqueous solution are added to an aqueous solution in which granular metallic cobalt is previously suspended under stirring conditions, and the metallic cobalt particles are used as nuclei to form the particles. A nickel hydroxide active material, characterized in that the metal hydroxide is crystallized and grown on the surface, so that the granular metal cobalt is contained in a localized state from the central portion inside the grown nickel hydroxide particles. Manufacturing method. 5. The metal cobalt has a particle diameter of 0.1.
The nickel hydroxide active material according to claim 5, wherein the thickness is from 5 to 5 m.