JPH10324523A - Production of cobalt oxide fine particulate powder - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain cobalt oxide fine particulate powder having a uniform particle size distribution and high reactivity. SOLUTION: An aq. cobalt salt soln. is neutralized with an excess aq. alkali soln. to obtain a cobalt hydroxide suspension in which the concn. ratio (R[OH<-> ]/2[Co<2+> ]) of the alkali to the cobalt salt is 1.0-1.2 and the concn. of the excess alkali is <=0.1 M. This suspension is heated to >=60 deg.C and cobalt ions are oxidized by blowing an oxygen-contg. gas to precipitate and form the objective cobalt oxide fine particulate powder having <=0.1 μm average particle diameter.

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 cobalt oxide fine particle powder, and more particularly, to a method for advantageously producing highly reactive cobalt oxide fine powder having fine particles, uniform particle size distribution, and high reactivity. Things.

[0002]

2. Description of the Related Art In recent years, transition metal oxide particles such as cobalt oxide particles are not used alone, but are mixed with other metal oxides and baked to be used as composite oxides in various applications. ing. Since what is produced by such a solid-phase reaction is mainly a sintered body of a polycrystal, it is used after being pulverized again into a powder and then molded into a desired mold. Recently, a lithium cobalt oxide (LiCoO) used as a positive electrode active material of a lithium battery has been used.
O ₂ ) is an example.

[0003] When the reactivity of the cobalt oxide particles is low, the progress of the solid phase reaction is slow, so that firing at a high temperature for a long time is necessary. When fired at high temperature for a long time, some metal ions evaporate and the composition is apt to fluctuate, or the particles are firmly fused and re-grinding is required, increasing the energy cost. It has been pointed out that the medium used in the method is worn and mixed.

[0004] In view of the above background, there is a need for a method of obtaining a highly reactive cobalt oxide particle powder which easily forms a compound with another metal oxide by firing at a low temperature for a short time.

[0005]

SUMMARY OF THE INVENTION In view of the above circumstances, it is an object of the present invention to provide a highly reactive cobalt oxide particle powder which can easily form a compound with another metal oxide by firing at a low temperature for a short time. And

[0006]

In order to solve the above-mentioned problems, the present invention is to neutralize an aqueous solution of a cobalt salt with an excess aqueous alkali solution to obtain a concentration ratio R between the alkali and the cobalt salt.
[OH ^-] / 2 [Co ^2+] is obtained cobalt suspension hydroxide concentration of excess alkali is 0.1M or less at 1.0 to 1.2, then the suspension 60 ° C. or higher This is a method for producing fine particles of cobalt oxide, comprising heating and blowing an oxygen-containing gas into the suspension to oxidize the cobalt ions to precipitate and form fine particles of cobalt oxide (Co ₃ O ₄ ).

Next, the present invention will be described in detail. Examples of the cobalt salt used in the present invention include cobalt sulfate, cobalt chloride, and cobalt nitrate. These can be used alone or in combination of two or more. Further, the alkaline aqueous solution used in the present invention,
Sodium hydroxide, potassium hydroxide, sodium carbonate,
Potassium carbonate and the like can be mentioned, and these can be used alone or in combination of two or more. The concentration ratio R of the alkali and the cobalt salt in the suspension of the cobalt (II) hydroxide in the present invention is represented by [OH ⁻ ] / 2 [Co ²⁺ ].
It is necessary that R = 1.0 to 1.2, preferably 1.01 to 1.10, and the excess alkali concentration be 1.0 M or less, preferably 0.5 or less. If the value of R or the excess alkali concentration is outside the above range, particles of the cobalt oxide single phase will not be obtained, resulting in a mixture.

[0008] The heating temperature of the suspension of cobalt (II) hydroxide in the present invention must be 60 ° C or higher, preferably 70 ° C or higher, more preferably 70 to 95 ° C. If the temperature is lower than 60 ° C., fine particles of a cobalt oxide single phase cannot be obtained, and a mixture may be formed. Although the upper limit of the heating temperature is not particularly limited, if the temperature exceeds 100 ° C., a high-pressure vessel is required, which increases the equipment cost, complicates the operation, and is not economical or industrial.
About 5 ° C. is preferable. Further, the oxidation method in the present invention is a method of blowing an oxygen-containing gas, for example, air into the suspension. If an oxidizing agent other than the oxygen-containing gas, such as hydrogen peroxide, is used, it is not possible to obtain fine particles of cobalt oxide single phase. Regarding the end point of the precipitation formation reaction of the cobalt oxide fine particle powder, O
By introducing an RP electrode and monitoring its potential, the degree of progress of the reaction can be sequentially tracked to determine the end point of the precipitation reaction. After confirming the end point of the reaction, the suspension is taken out, and the solid content is filtered off and dried.

As described above, fine particle powder, preferably fine particle powder having an average particle diameter of 0.1 μm or less,
In addition, cobalt oxide having a uniform particle size distribution can be obtained.

[0010]

The most important point in the present invention is that while heating a suspension of cobalt (II) hydroxide obtained by mixing an aqueous solution of a cobalt salt and an aqueous solution of an alkali that is more than neutralized,
Oxygen-containing gas is passed to oxidize cobalt ions to form precipitates, so that the average particle diameter is 0.1 μm.
This is a fact that a uniform cobalt oxide fine particle powder having the following particle size distribution can be obtained. This is presumably because cobalt oxide precipitates from cobalt hydroxide uniformly dispersed in the aqueous solution, so that uniform nuclei are not generated and fusion of particles does not occur.

[0011] When an oxidizing agent such as hydrogen peroxide is used instead of passing oxygen-containing gas, for example, the fine particles of cobalt oxide single phase cannot be obtained because the oxidizing ability is different from that of oxygen-containing gas. This is considered to be due to the fact that the oxidizing ability of the oxygen-containing gas is suitable for obtaining a particle powder of a cobalt oxide single phase. When a fine particle powder obtained by the present invention, particularly a uniform cobalt oxide fine particle powder having an average particle diameter of 0.1 μm or less and having a uniform particle size distribution is subjected to a solid phase reaction with, for example, a Li compound, the reaction is completed in a short time. It is considered that the solid phase reaction at the time of firing proceeds by mutual diffusion at the contact point between the raw material powder particles. When the average particle diameter of 0.1 μm or less of the cobalt oxide fine powder is used, the contact area increases, the reactivity of the cobalt raw material improves, and the reaction proceeds rapidly during firing.
It is considered that the reaction is completed in a short time.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A typical embodiment of the present invention is as follows. The identification of the reaction product fine particle powder and its crystal structure were performed by X-ray diffraction (RIGAKU, Mn-filtered Fe-K
α, 40 KV and 20 mA). The morphology and particle size distribution of the fine particles were examined by observation with a transmission electron microscope, and the average particle diameter was determined by statistical average from the particle image of the transmission electron microscope photograph.

[0013] <Production of cobalt oxide> cobalt sulfate (CoSO ₄ · 7H ₂ O) into an aqueous solution dissolved in water 2000 ml. To this aqueous solution, 2500 ml of a 0.756 M sodium hydroxide aqueous solution was added to prepare a suspension of cobalt (II) hydroxide (R = 1.05, excess NaOH).
Concentration = 0.02M). The suspension was heated to 80 ° C. with mechanical stirring. While keeping this temperature constant,
The oxidation reaction was performed for 20 hours by passing air through the suspension.
The obtained precipitate was separated by filtration, washed with water, and then dried at 60 ° C. to produce black fine particle powder. The obtained black powder was a spinel-type cobalt oxide Co ₃ O _{4 as} shown in the X-ray diffraction diagram of FIG. FIG. 2 shows a transmission electron micrograph showing the particle structure of the fine particle powder. The particle size distribution was uniform and the average particle size was about 0.03 μm.

<Sintering Reaction of Lithium Cobalt Oxide> 19.96 g of cobalt oxide fine powder having an average particle diameter of 0.03 μm obtained as described above and lithium carbonate powder 9.
19 g (Li / Co molar ratio = 1.0) was mechanically mixed in a mortar, and the obtained mixed powder was heated to 750 ° C. in air and reacted for 6 hours. The obtained powder was pulverized again in a mortar to obtain a black powder. The obtained black powder was a layered rock salt type lithium cobalt oxide powder as shown in the X-ray diffraction diagram of FIG.

[0015]

EXAMPLES Next, the present invention will be described in more detail with reference to Examples, Comparative Examples and Application Examples, but these do not limit the present invention at all.

Examples 1 to 5 and Comparative Examples 1 to 5 In Examples 1 to 5 and Comparative Examples 1 to 3, except that the concentration ratio R of the alkali and the cobalt salt, the excess alkali concentration, and the heating temperature were variously changed. A reaction product fine particle powder was obtained in the same manner as in the embodiment of the invention. In Comparative Examples 4 and 5, a reaction product powder was obtained by using hydrogen peroxide and nitrate ions as oxidizing agents instead of carrying out the oxidation reaction by passing air through. Table 1 shows the reaction conditions and the properties of the obtained reaction product powder. As is clear from Table 1, in Examples 1 to 5, fine spinel-type cobalt oxide fine particle powders having a fine and uniform particle size distribution were obtained. Comparative Examples 1 to
The powder obtained in Step 5 is a mixture of granular cobalt oxide and sheet-like cobalt oxyhydroxide [CoO (OH)], or sheet-like cobalt oxyhydroxide, unreacted cobalt hydroxide [Co (OH) ₂ ).

[0017]

[Table 1]

Application Examples 1 to 5 and Comparative Application Examples 1 to 5 Next, the reactivity between the cobalt oxide fine particle powders obtained in Examples 1 to 5 and Comparative Examples 1 to 5 and the lithium compound was evaluated in the practice of the invention. It examined similarly to a form. The results are shown in Table 2. From the results in Table 2, only when the fine spinel-type cobalt oxide fine particle powder having a uniform particle size distribution obtained in Examples 1 to 5 of the present invention was used, the layered rock salt was formed by a low-temperature, short-time firing reaction. It was confirmed that a lithium cobalt oxide single phase of the type was obtained.

[0019]

[Table 2]

[0020]

According to the present invention, it is possible to obtain a fine particle powder, particularly a cobalt oxide fine particle powder having an average particle diameter of 0.1 μm or less, and to obtain a uniform particle size distribution. When this cobalt oxide fine particle powder is used, the reactivity with other metal compounds is high due to the fact that it is fine particles and the particle size is uniform, and the reaction can be completed by firing at a low temperature for a short time. it can. That is, it becomes possible to provide a highly reactive cobalt oxide fine particle powder.

[Brief description of the drawings]

FIG. 1 is an X-ray diffraction diagram of a spinel-type cobalt oxide fine particle powder obtained in an embodiment of the present invention.

FIG. 2 is an electron micrograph (× 40000) showing the particle structure of the spinel-type cobalt oxide fine particle powder obtained in the embodiment of the present invention.

FIG. 3 is an X-ray diffraction diagram of a layered rock salt type lithium cobalt oxide powder obtained in the embodiment of the present invention.

Claims (2)

[Claims] 1. An aqueous solution of a cobalt salt is neutralized with an excess of an aqueous alkali solution, and the concentration ratio of alkali and cobalt salt, R [OH ⁻ ] / 2 [Co ²⁺ ], is excessively 1.0 to 1.2. Obtaining a cobalt hydroxide suspension having an alkali concentration of 0.1 M or less, then heating the suspension to 60 ° C. or higher, blowing an oxygen-containing gas into the suspension to oxidize cobalt ions,
A process for producing cobalt oxide fine particle powder, comprising forming a precipitate from cobalt oxide fine particle powder. 2. The average particle diameter of cobalt oxide is 0.1 μm.
2. The method according to claim 1, wherein: