JP4271407B2 - Method for producing positive electrode active material for alkaline storage battery - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for producing a positive electrode active material for an alkaline storage battery.
[0002]
[Prior art]
Conventionally, in order to produce a positive electrode active material for an alkaline storage battery in which the surface of (oxy) nickel hydroxide is coated with cobalt oxyhydroxide, a step of coating the nickel hydroxide surface with a cobalt compound, It had to go through a plurality of steps, an oxidation step and an oxidation step.
[0003]
[Problems to be solved by the invention]
An object of this invention is to provide the manufacturing method of the positive electrode active material for alkaline storage batteries which coat | covered the nickel hydroxide surface with the cobalt oxyhydroxide.
[0004]
Moreover, an object of this invention is to provide the manufacturing method of the positive electrode active material for alkaline storage batteries which coat | covered the nickel hydroxide surface which a part of nickel hydroxide converted into nickel oxyhydroxide with cobalt oxyhydroxide.
Hereinafter, the present invention will be described in detail according to embodiments.
[0005]
[Means for Solving the Problems]
The production method of the present invention is characterized in that the surface of nickel hydroxide is coated with cobalt oxyhydroxide by a one-step wet reaction using nickel hydroxide as a starting material.
[0006]
More specifically, the method for producing a positive electrode active material for an alkaline storage battery in which the nickel hydroxide surface according to the present invention is coated with cobalt oxyhydroxide is used in an aqueous solution in which the pH is adjusted to 10 to 13.5 with an aqueous alkali metal hydroxide solution. Further, nickel hydroxide particles are added with stirring to form a slurry, and a cobalt sulfate solution and an oxidant solution are simultaneously dropped into the slurry.
[0007]
The production method according to the present invention is for an alkaline storage battery in which a part of nickel hydroxide is converted to nickel oxyhydroxide by dropping an oxidizing agent solution and the surface of nickel oxyhydroxide is coated with cobalt oxyhydroxide. It is also characterized by producing a positive electrode active material.
[0008]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, a manufacturing method according to the present invention will be described in detail with reference to embodiments.
A feature of the production method of the present invention is that nickel hydroxide particles are added to an aqueous solution adjusted to a pH of 10 to 13.5 with stirring to form a slurry, and a cobalt sulfate solution and an oxidant solution are simultaneously added dropwise thereto. It is characterized by this.
[0009]
There is no restriction | limiting in particular in the nickel hydroxide particle | grains which are the raw materials used by this invention, What is necessary is just the nickel hydroxide particle | grains normally utilized as a positive electrode active material for alkaline secondary batteries. Specifically, it is preferable to use one having a tapping density of 1.8 to 2.4 g / cc, a specific surface area of 5 to 30 m ² / g, and an average particle size of 5 to 20 μm. The nickel hydroxide particles include those containing appropriate amounts of various other metals as required. For example, B, Ca, Mg, Al, Si, Sc, Ti, V, Cr, Mn, Fe, Co, Cu, Zn, Ga, Y, Zr, Nb, Mo, Ru, Sn, Sb, La, Ce, Examples include Pr, Nd, Hf, Ta, W, and Pb. Among the above elements, one may be contained, or two or more may be contained.
[0010]
Although the dispersion amount of nickel hydroxide is not particularly limited, nickel hydroxide can usually be contained in a range of 1 to 30 mol per 1 L of water. More preferably, it is the range of 5-20 mol from the point of operativity in a manufacturing process, or economical efficiency.
[0011]
The method for adjusting the pH is not particularly limited, but it is preferable to use an aqueous alkali metal hydroxide solution. Specific examples include aqueous solutions of lithium, sodium, potassium, rubidium, cesium, and francium hydroxide. The preferred range of pH in the present invention depends on the stability of the nickel hydroxide particles and the oxidation reaction system used, particularly the type of oxidizing agent, and is usually in the range of 10 to 13.5. Specifically, when hypochlorite is used as the oxidizing agent, it is particularly preferable to maintain a pH of 13 or more.
[0012]
In the present invention, stirring is preferred, but the stirring device is not particularly limited. In the reaction vessel solution used in the present invention, nickel hydroxide as a raw material becomes a slurry (a slurry means a state in which nickel hydroxide particles are dispersed in the reaction solution by stirring to form a suspension), And since the oxidation reaction advances with an oxidizing agent, what can stir at the optimal rotation speed should just be used. Specifically, a marine three-blade type can be used. The stirring rotation speed in the reaction is not particularly limited. However, since the oxidation reaction is a contact reaction between a solid and a liquid, if the stirring is too slow, the nickel hydroxide powder is not uniformly dispersed in the aqueous solution and the oxidation reaction substantially proceeds. It becomes difficult to do. On the other hand, if the stirring is too fast, the decomposition of sodium hypochlorite proceeds and the oxidation reaction efficiency decreases. Therefore, it is important to select the rotation speed for the most effective stirring.
[0013]
The cobalt sulfate solution used for supplying cobalt ions used in the present invention is not limited to sulfate as long as it provides cobalt ions in the reaction aqueous solution. For example, chlorides and nitrates can be preferably used.
[0014]
Moreover, the oxidizing agent solution which can be used by this invention should just be a solution of the oxidizing agent which can oxidize the cobalt hydroxide produced during reaction to cobalt oxyhydroxide. Furthermore, any oxide solution capable of oxidizing a part of the nickel hydroxide particles to nickel oxyhydroxide may be used. Specifically, as the oxidizing agent solution, ozone; permanganate represented by permanganic acid (HMnO ₄ ), MMnO ₄ (M represents an alkali metal), etc .; chromic acid (CrO ₃ ), M ₂ Cr Chromic acid-related compounds represented by ₂ O ₇ , MCrO ₃ Cl (M represents an alkali metal), CrO ₂ Cl _2, etc .; F ₂ , Cl ₂ , Br ₂ , I ₂ halogen; Peroxo acid, M ₂ S ₂ O ₈ , M ₂ S ₂ O ₅ (M represents an alkali metal), a salt thereof represented by CH ₃ CO ₃ H, etc .; oxygen acid, MClO, MBrO, MIO, MClO ₃ , MBrO ₃ , MIO ₃ , It is a solution of a salt thereof represented by MClO ₄ , MIO ₄ (M represents an alkali metal), NaH ₂ IO ₆ , KIO ₄ or the like. Of these, oxygen acid is preferred. Two or more of these oxidizing agents may be used in combination. Particularly preferred is hypochlorous acid.
[0015]
The concentration of the oxidizing agent in the solution is not particularly limited, but is usually preferably 0.5 to 3.0 mol / L in terms of the oxidizing agent concentration. From the viewpoint of operability and economical efficiency in the production process, it is more preferably 1.5 to 2.5 mol / L. Specifically, the charging ratio of cobalt sulfate and sodium hypochlorite is preferably (sodium hypochlorite) / (cobalt)> 1.0 in terms of oxidation equivalent ratio. In addition, in order to oxidize nickel hydroxide to nickel oxyhydroxide, the nickel hydroxide can be oxidized to an arbitrary degree by adjusting the amount of oxidizing agent to nickel oxyhydroxide. In this case, the amount of oxidant required depends on the reaction conditions actually used, and can be easily selected by obtaining a correlation in advance between the oxidant added under the conditions and the degree of oxidation obtained.
[0016]
The reaction temperature depends on the type of oxidizing agent used, but is usually in the range of 30 to 70 ° C. When using a sodium hypochlorite solution especially, 40-60 degreeC is preferable. The oxidation time in the oxidation reaction varies depending on the kind of the oxidant and the reaction temperature, but when using a sodium hypochlorite solution, 3 to 8 hours, preferably 3 to 5 hours, acts on the reaction most effectively. It is advantageous also from economical efficiency.
[0017]
In the present invention, the dripping oxidant solution and the cobalt compound solution are added to the reaction solution so that the addition starts and ends at the same time and the oxidation equivalent ratio is always kept at a predetermined value. Is preferred.
[0018]
After completion of the reaction, the solution is filtered with the same pH (ie, pH 10 to 13.5), washed with water and dried. The drying of the product is not particularly limited. However, if the drying temperature is too high, there arises a problem that the obtained product is decomposed and the degree of oxidation is lowered. Accordingly, the product may be dried at a reduced pressure without raising the temperature, but is usually dried at 20 to 120 ° C., preferably 40 to 80 ° C.
[0019]
【Example】
The present invention will be described in more detail with reference to the following examples, but the present invention is not limited to these examples.
In the production of the target product, the stirring speed of the solution was 700 rpm, the water bath temperature was 50 ° C., and the pH was maintained at 13.0 by adding an 8 mol / L sodium hydroxide aqueous solution.
[0020]
(Measurement method of physical properties)
The average particle diameter, the amount of coated cobalt, the bulk density, the tapping density, the degree of oxidation, and the X-ray crystal diffraction pattern were measured by the following methods. The average particle size was measured using a laser microsizer “PRO7000S” manufactured by Seishin Corporation. The amount of coated cobalt was measured using ICP (SEPS Electronics SPS7000S). The bulk density and the tap density were measured with a tap denser “KYT-3000” manufactured by Seishin Corporation, before and after tapping 200 times using a 4 cm spacer. As for the degree of oxidation, a 0.2 g sample was collected and weighed, and after completely dissolving it in a sulfuric acid-potassium iodide (1: 1) solution, the liberated iodine was back titrated with a sodium thiosulfate solution. Calculated from the titer.
The X-ray crystal diffraction pattern was measured with an X-ray diffractometer (RINT2200 manufactured by Rigaku).
[0021]
(Example 1) Production of nickel hydroxide whose surface was coated with cobalt oxyhydroxide
In a cylindrical reaction tank (inner diameter 300 mm, height 300 mm, effective volume 10 L) equipped with a pH sensor, stirrer (3 marine blades, stirrer power 30 W, rotation speed 500-1000 rpm (variable)) and heater with temperature controller, 10 L of water was added and the temperature and pH were adjusted as described above.
Next, 1.0 kg of nickel hydroxide particles having a TAP density of 1.8 to 2.4 g / cc and an average particle size of 5 to 20 μm were added while stirring to obtain a nickel hydroxide slurry.
[0022]
To the above nickel hydroxide slurry, 350 ml of a 2 mol / L sodium hypochlorite solution and 320 ml of a 1.5 mol / L cobalt sulfate solution were added over 2 hours, and the mixture was further stirred for 1 hour.
This slurry was filtered using a Buchner funnel and dried at 80 ° C. for 12 hours using a blower dryer to obtain nickel hydroxide whose surface was coated with the target black cobalt oxyhydroxide.
[0023]
The yield is 99%, the average particle size is 11 μm, the amount of coated cobalt is 2.5% by weight, the bulk density is 1.4 g / cc, the tapping density is 2.0 g / cc, and the electromicrograph is shown in FIG. The X-ray diffraction pattern was as shown in FIG. The oxidation rate was 7.3%.
[0024]
Example 2 Production of nickel hydroxide having a surface coated with cobalt oxyhydroxide and partially converted to nickel oxyhydroxide 2 mol / L sodium hypochlorite under the same conditions as in Example 1 350 ml of the solution and 320 ml of a 1.5 mol / L cobalt sulfate solution were added over 2 hours. Thereafter, 150 ml of a 2 mol / L sodium hypochlorite solution was added to convert part of the nickel hydroxide into nickel oxyhydroxide. The mixture was further stirred for 1 hour, and the slurry was filtered, dehydrated and dried in the same manner as in Example 1. The surface was covered with the target black cobalt oxyhydroxide, and a portion thereof was converted to nickel oxyhydroxide. Nickel was obtained.
[0025]
Yield 99%, average particle size 11 μm, coated cobalt amount 2.5 wt%, bulk density 1.4 g / cc, tapping density 2.0 g / cc, nickel oxyhydroxide oxidation degree Was 12.5% and the X-ray diffraction pattern was as shown in FIG.
[0026]
Similarly, by adding 300 ml of a 2 mol / L sodium hypochlorite solution, the surface was coated with cobalt oxyhydroxide having an oxidation degree of 17.8%, and a part thereof was converted to nickel oxyhydroxide. Nickel hydroxide was obtained.
The X-ray diffraction pattern is FIG. 4, and the electric micrograph is FIG.
[0027]
Example 3 Production of nickel oxyhydroxide whose surface was coated with cobalt oxyhydroxide 350 ml of 2 mol / L sodium hypochlorite solution and 1.5 mol / L cobalt sulfate under the same conditions as in Example 1. 320 ml of solution was added over 2 hours. Then, nickel hydroxide was oxidized to nickel oxyhydroxide by further dropping 4 L of a 2 mol / L sodium hypochlorite solution. The slurry was further stirred for 1 hour, and this slurry was filtered, dehydrated and dried to obtain nickel oxyhydroxide whose surface was coated with the target black cobalt oxyhydroxide.
[0028]
Yield 99%, average particle size 11 μm, coated cobalt amount 2.5 wt%, bulk density 1.4 g / cc, tapping density 2.0 g / cc, nickel oxyhydroxide oxidation degree Was 100%, the electron micrograph was FIG. 6, and the X-ray diffraction pattern was FIG.
[0029]
【The invention's effect】
With the method for producing a positive electrode active material for an alkaline storage battery according to the present invention, the surface of nickel hydroxide can be coated with cobalt oxyhydroxide by a simple wet reaction using nickel hydroxide as a starting material.
[Brief description of the drawings]
1 is an electron micrograph of nickel hydroxide having a surface coated with cobalt oxyhydroxide produced in Example 1. FIG.
2 is an X-ray crystal diffraction pattern of nickel hydroxide having a surface coated with cobalt oxyhydroxide produced in Example 1. FIG.
FIG. 3 is an X-ray crystal diffraction pattern of nickel hydroxide produced in Example 2 and coated with cobalt oxyhydroxide having a degree of oxidation of 12.5% and partially converted to nickel oxyhydroxide. is there.
4 is an electron micrograph of nickel hydroxide produced in Example 2 and coated with cobalt oxyhydroxide having a degree of oxidation of 17.8% and partially converted to nickel oxyhydroxide. FIG.
FIG. 5 is an X-ray crystal diffraction pattern of nickel hydroxide prepared in Example 2 and coated with cobalt oxyhydroxide having a degree of oxidation of 17.8% and partially converted to nickel oxyhydroxide. is there.
6 is an electron micrograph of nickel oxyhydroxide having a surface coated with cobalt oxyhydroxide produced in Example 3. FIG.
7 is an X-ray crystal diffraction pattern of nickel oxyhydroxide having a surface coated with cobalt oxyhydroxide produced in Example 3. FIG.

Claims (2)

Nickel hydroxide particles are added with stirring to a solution adjusted to a pH of 10 to 13.5 with an alkali metal hydroxide aqueous solution, and a cobalt salt aqueous solution such as a cobalt sulfate solution and an oxidizing agent solution are added to the slurry. At the same time, a method for producing a positive electrode active material for an alkaline storage battery in which the surface of nickel hydroxide is coated with cobalt oxyhydroxide. Furthermore, the manufacturing method of the positive electrode active material for alkaline storage batteries of Claim 1 characterized by converting a part of nickel hydroxide into nickel oxyhydroxide by dripping an oxidizing agent solution.

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