JP3367152B2 - Method for producing nickel hydroxide powder coated with cobalt hydroxide - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing nickel hydroxide powder coated with cobalt hydroxide, which is used as a positive electrode material for non-sintered alkaline batteries. 2. Description of the Related Art In recent years, as portable electronic devices have become smaller and lighter, it has been desired that batteries as power sources have higher energy densities. Also, in a secondary battery, it is required to shorten the charging time. The first problem is to increase the energy density. The electrode of the conventional alkaline battery is called a sintered electrode, and the energy density of the positive electrode is limited to about 400 Ah / ml. Here, a paste-type electrode for the purpose of further increasing the capacity has recently been developed. In this method, a porous nickel body is used as an electrode substrate, and a mixture of a high bulk density nickel hydroxide powder and a metal cobalt powder as an additive for improving the utilization factor is formed into a paste, which is directly filled into the substrate to form a positive electrode. Is what you do. With the development of this method, the energy density has been increased to 500-600 Ah / ml. To reduce the second charging time, conventionally, a measure has been taken to add a solid solution of cobalt to nickel hydroxide powder to suppress adverse effects such as gas generation and swelling of the electrode during high-rate charging. It has been recognized that it is useful to add cobalt to the positive electrode in order to satisfy either property requirement. A paste type electrode is disclosed in Japanese Patent Application Laid-Open No. 60-1317.
65 and JP-A-60-131766, it is characterized in that nickel hydroxide, which is an active material, is densely packed as compared with the conventional positive electrode plate manufacturing. It is. In order to take advantage of this advantage, it is necessary that the nickel hydroxide particles used are also high in density and specific tapping density is high. Further, as described in JP-A-63-152866, not only the density but also its specific surface area and crystallinity are important for the charge / discharge characteristics of a battery. In order to achieve higher density and higher rate charging than the current state while satisfying such required basic physical properties, it is necessary to add at least 10% or more of cobalt to nickel hydroxide powder as a solid solution. However, when 10% or more of cobalt is made into a solid solution in nickel hydroxide, it becomes difficult to satisfy the above-mentioned necessary basic physical properties of nickel hydroxide for paste electrodes. This is presumably because the conditions for increasing the density of nickel hydroxide and the conditions for increasing the density of cobalt hydroxide are different. Therefore, in order to add 10% or more of cobalt to nickel hydroxide, a method is generally used in which particles such as cobalt hydroxide and cobalt oxyhydroxide are formed alone and mixed with nickel hydroxide at the time of electrode molding. there were. However, in the method of mixing with nickel hydroxide, it is difficult to uniformly disperse the cobalt hydroxide and the like, and since the cobalt hydroxide and the like to be mixed have a low bulk density, the amount of the active material filled in the electrode is reduced. It decreases significantly. Therefore, a method of coating the surface of nickel hydroxide with cobalt hydroxide or the like has been considered. As a method of coating nickel hydroxide with cobalt, Japanese Patent Application Laid-Open Nos. 1-267957 and 62-23
7667 and the like. JP-A-62-2
The method described in 237667 is a method in which an aqueous solution of a cobalt salt such as cobalt sulfate is added to a nickel hydroxide suspension and neutralized with a caustic alkali. In this method, the produced cobalt hydroxide is not in a state of being gelled and coated on the nickel hydroxide surface, but the cobalt hydroxide-containing nickel hydroxide produced by the present method has a very dense surface layer. Low cobalt hydroxide particles are formed, the density of the particles is significantly reduced, and the tapping density is also significantly reduced. In the method described in JP-A-1-267957, a cobalt salt is added to a battery electrolyte to precipitate cobalt hydroxide or the like on the surface of nickel hydroxide during the battery reaction. It is not a method of coating the nickel surface. [0005] The present invention relates to a nickel hydroxide powder whose surface is uniformly coated with cobalt hydroxide, which is suitable for producing a positive electrode of a battery by a paste method. An object of the present invention is to propose a method for producing nickel hydroxide powder coated with cobalt. According to the present invention, there is provided a method for producing a nickel hydroxide powder coated with cobalt hydroxide, comprising the steps of:
It is characterized in that an aqueous solution containing cobalt and an ammonium ion donor are continuously and quantitatively supplied to an aqueous solution continuously adjusted during the reaction . [0007] In the above-mentioned production method, the ammonium ion supplier may have an ammonium ion concentration of 10 to 10 in the reaction solution.
It is characterized in that it is supplied at 25 g / l. In order to neutralize various cobalt salts with caustic alkali, it is theoretically sufficient if the pH is 8 or more.
In Nos. To 11, the anion of the used cobalt salt cannot be completely removed to form a basic salt, and impure cobalt hydroxide containing the salt is generated. In order to suppress this, PH should be 11
It is necessary to do above. However, simply increasing the PH to 11
In this case, the produced cobalt hydroxide becomes gel-like, so that not only the nickel hydroxide cannot be firmly coated, but also the tapping density of the produced particles is remarkably reduced. this is,
At high pH, the solubility of cobalt ions drops extremely,
Crystal nucleation of cobalt hydroxide occurs instantaneously during neutralization,
This is probably because no crystal growth occurred. In the present invention, since ammonium ions are introduced into the reaction solution in the high pH range, cobalt becomes an ammine complex salt to increase the solubility of cobalt. Generation can be suppressed, and as a result, crystal growth can be promoted. Further, since each raw material solution is added individually and simultaneously, the PH and ammonia ion concentrations are kept as constant as possible, so that the cobalt concentration in the reaction vessel is kept constant and the crystal nucleation rate of cobalt hydroxide is increased. , Generation amount and crystal nucleus growth rate can be kept constant. Therefore, as in the case where the concentrations of PH and ammonia ions are not constant, the crystal nucleus generation rate of nickel hydroxide is irregular, and the primary particle diameter of the generated cobalt hydroxide is not uniform. Not only does the cobalt coating become non-uniform, but the tapping density of the formed particles also does not decrease. [0011] The diffusion of ammonia having a pH of 13 or more becomes severe, so that even if ammonia ions are present, the cobalt concentration cannot be set to an optimum value, and uniform coating cannot be performed. [0012] If the ammonia concentration in the tank is 10 g / l or less, an appropriate cobalt concentration cannot be maintained within the above-mentioned appropriate pH range. It is not practical because it consumes a lot. If the addition rate of the aqueous cobalt salt solution, that is, the time during which the aqueous solution containing cobalt is added to the reaction solution, is set to 1 hour or less, the concentration of the cobalt ions in the reaction tank becomes uneven depending on the location, and Becomes non-uniform. [0014] When the amount of cobalt to be coated is 50% or more, the amount of nickel hydroxide as an active material is excessively reduced, so that the battery capacity is extremely reduced. Thus, a battery having a higher capacity can be manufactured as compared with the conventional paste type electrode. The advantage of that is lost. If the amount of cobalt to be coated is 1% or less, the advantage of coating is lost,
It can be achieved by a method of containing cobalt by solid solution. When the reaction temperature is 80 ° C. or higher, the gas is diffused so strongly from the solution that it becomes difficult to keep the ammonia concentration in the tank constant. The preferred temperature range is 20-80C. EXAMPLES Preparation of Each Use Solution First, a cobalt salt solution, a caustic alkali solution, and an aqueous ammonia ion donor solution to be used were prepared as follows.
The cobalt salt aqueous solution was prepared by dissolving reagent grade 1 cobalt sulfate manufactured by Wako Pure Chemical Industries in pure water to prepare a solution having a cobalt concentration of 1.6 mol / l. Similarly, the concentration of reagent grade 1 cobalt chloride manufactured by Wako Pure Chemical Industries was adjusted to the same concentration. The caustic alkali solution is prepared by dissolving reagent grade 1 caustic soda made by Wako Pure Chemical in pure water, and adding 3.2 mol
A 1 / l solution was prepared. As the ammonia ion supplier, reagent grade 1 aqueous ammonia manufactured by Wako Pure Chemical Industries was used without dilution. In addition, a reagent primary grade ammonium sulfate manufactured by Wako Pure Chemical is dissolved in pure water, and the concentration of ammonia is 100 g / l.
Was prepared. Example 1 A conventional method, for example, as was filed by the applicant on May 28, 1993 (reference number KSMK0259-P), a nickel-containing solution and a caustic alkali were supplied simultaneously and continuously to supply water. High tapping density nickel hydroxide (tapping density 1.98 g / ml) 10 produced by a method for producing nickel oxide
0 g was suspended in 500 ml of pure water, and the pH was controlled at 11.5 with a caustic soda solution while simultaneously adding the cobalt sulfate solution prepared by the above method and aqueous ammonia while stirring. The addition rate of the aqueous solution of cobalt sulfate is 3 ml / mi.
n, the addition rate of ammonia water is 0.45 ml / min
And The time (62.3 min) at which the cobalt content in the added nickel hydroxide is calculated to be 15%.
After completion of the reaction, the formed product was immediately suction-filtered with a Buchner funnel, washed twice with 1 liter of pure water and then dried by filtration. As a result of sampling and analyzing the reaction solution, the ammonium ion concentration in the solution was 20 g /
l. The dried product was dissolved in nitric acid and subjected to atomic absorption analysis. As a result, the content of cobalt was 14.6%, and the tapping density was 1.76 g / ml. The average particle size was 10 μm. Also, this product is embedded in an epoxy resin, the surface of the embedded resin is polished, and then X-65 manufactured by Hitachi, Ltd.
As a result of performing surface qualitative analysis of nickel and cobalt on the cross section of the formed particles with a 0-type EPMA apparatus, it was found that the surface of the nickel hydroxide particles was uniformly coated with cobalt hydroxide. Example 2 500 g of nickel hydroxide 100 g as in Example 1
While suspending and stirring in pure water, the pH was controlled to 11.8 with caustic soda while simultaneously adding the cobalt chloride solution and the aqueous ammonia adjusted by the method described above. The addition rate of the cobalt chloride solution was 1.5 ml / min, and the addition rate of aqueous ammonia was 0.23 ml / min. The cobalt content in the nickel hydroxide with this addition was calculated to be 2
The reaction was carried out for 5 minutes (208 min), and after the reaction was completed, the formed product 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 15 g / l. The dried product was dissolved in nitric acid and atomic absorption analysis revealed that it contained 24.3% of cobalt and had a tapping density of 1.65 g / ml. The average particle size is 12 μm
Met. Further, this is embedded in an epoxy resin, and the surface of the embedded resin is polished, and then the X-650 type EP manufactured by Hitachi, Ltd. is polished.
As a result of performing surface qualitative analysis of nickel and cobalt on the cross section of the formed particles with the MA apparatus, it was found that the surface of the nickel hydroxide particles was uniformly coated with cobalt hydroxide. Example 3 500 g of nickel hydroxide 100 g similar to that of Example 1 was used.
While suspending and stirring in pure water, the pH was controlled to 11.8 with caustic soda while simultaneously adding the cobalt sulfate and ammonium sulfate solutions prepared by the method described above. The addition rate of the cobalt sulfate solution was 1.5 ml / min, and the addition rate of aqueous ammonia was 2.2 ml / min. After a period of time (416 min) at which the calculated cobalt content in the nickel hydroxide to which this addition was added becomes 50%, and the reaction was completed, the formed product was immediately suction-filtered with a Buchner funnel and filtered.
After being washed twice with 1 l of pure water and then filtered and dried. The ammonium ion concentration in the solution was 11 g / l. The dried product was dissolved in nitric acid and subjected to atomic absorption analysis. The dried product contained 48.4% of cobalt and had a tapping density of 1.45 g / ml. The average particle size is 8 μm
Met. Further, this is embedded in an epoxy resin, and the surface of the embedded resin is polished, and then the X-650 type EP manufactured by Hitachi, Ltd. is polished.
The surface qualitative analysis of nickel and cobalt on the cross section of the formed particles was performed by the MA apparatus. As a result, similarly to Examples 1 and 2, the surface of the nickel hydroxide particles was coated with cobalt hydroxide. However, some liberated cobalt hydroxide was also observed. Comparative Example 500 g of nickel hydroxide 100 g as in Example 1 was used.
While suspending and stirring in pure water, the pH was controlled at 11.8 with caustic soda while adding the cobalt sulfate solution prepared by the above method. The addition rate of the cobalt sulfate solution is
It was 1.5 ml / min. After the completion of the reaction, the formed product is immediately suction-filtered with a Buchner funnel, and filtered with 1 liter of pure water.
After repeated repulping with water, filtration and drying were performed. The dried product was dissolved in nitric acid and atomic absorption analysis revealed that cobalt was 49.8%.
Contained and the tapping density was 0.60 g / ml. Also, this is embedded in an epoxy resin, and the surface of the embedded resin is polished, and then the X-650 type EPMA manufactured by Hitachi, Ltd. is polished.
The surface qualitative analysis of nickel and cobalt on the cross section of the formed particles was performed by the apparatus. As a result, although cobalt hydroxide slightly coated on nickel hydroxide was observed, most of the cobalt hydroxide was present as single particles. According to the present invention, it is possible to obtain a nickel hydroxide powder coated with cobalt hydroxide suitable for the production of a paste electrode.

Claims (1)

(57) Claims 1. An aqueous solution containing nickel hydroxide powder and continuously adjusted to pH 11 to 13 with a caustic alkali during the reaction is mixed with an aqueous solution containing cobalt and an ammonium ion donor. Simultaneously and continuously, ammonium ion in the reaction solution
Constant supply so that the concentration of
A method for producing nickel hydroxide powder coated with cobalt hydroxide.