JP2006160571A - Mg SOLID SOLUTION COBALT OXYHYDROXIDE PARTICLE AND ITS PRODUCING METHOD - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a cobalt oxyhydroxide particle where Mg is contained in a solid solution state and its producing method. <P>SOLUTION: The cobalt oxyhydroxide particle where Mg is contained in the solid solution state is obtained by adding an alkali aqueous solution to a divalent Co salt aqueous solution containing an Mg salt with agitation, by oxidizing it through contact with air under the existence of an oxidation catalyst and by precipitating the product as a spherical particle. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to cobalt oxyhydroxide particles containing Mg in a solid solution state. More specifically, the present invention relates to cobalt oxyhydroxide particles having a solid solution amount of 0.1 to 20 mol% and a substantially spherical shape. The present invention relates to cobalt oxyhydroxide particles having an oxidation degree of substantially 100% and a method for producing the same.

  In recent years, secondary batteries with high energy density have been eagerly desired in portable information devices such as mobile phones and notebook computers. Therefore, various positive electrode materials have been researched and developed to increase the capacity of such secondary batteries. For example, a conventional positive electrode material for an alkaline storage battery, which includes an active material powder containing nickel hydroxide and a powder composed of a cobalt compound, and the cobalt compound is β-cobalt oxyhydroxide, and the active material powder includes magnesium. A technique relating to nickel hydroxide containing such elements as a solid solution is known (see, for example, Patent Document 1).

However, it has not been known at all about cobalt oxyhydroxide particles containing elements such as magnesium in a solid solution state, and furthermore, a production method thereof.
Japanese Patent Laid-Open No. 2003-142087

  The problem to be solved by the present invention is a cobalt oxyhydroxide particle having a high density, a substantially spherical shape, and an oxidation degree of substantially 100%, containing magnesium element in a solid solution state. It is to find a manufacturing method capable of easily obtaining a new material in a single process.

  As a result of diligent research to establish a method for producing such a novel material, the present inventors have determined the elemental magnesium from a divalent Co salt aqueous solution containing magnesium salt in a single step by air oxidation in the presence of an oxidation catalyst. The present invention was completed by finding a method for precipitating cobalt oxyhydroxide contained in a solid solution state as spherical particles.

  That is, the present invention relates to cobalt oxyhydroxide particles containing magnesium element (Mg) in a solid solution state.

  Furthermore, this invention relates to the cobalt oxyhydroxide particle | grains of Claim 1 whose solid solution amount of Mg is 0.1-20 mol%.

  Further, the present invention oxidizes a mixture of an aqueous divalent Co salt solution containing Mg salt and an alkaline aqueous solution in contact with air in the presence of an oxidation catalyst, so that Mg is solid-dissolved and substantially spherical. It is related with the manufacturing method characterized by carrying out precipitation production of the cobalt oxyhydroxide particle | grains of this.

  Furthermore, the production method of the present invention is characterized in that the oxidation catalyst is a metal composed of at least one of iron, nickel, and chromium, or ions thereof.

  Since the production method according to the present invention is a method for obtaining cobalt oxyhydroxide particles from a divalent cobalt salt aqueous solution containing Mg salt in a single step, it is completely oxidized and has powder characteristics (density, grain size). It becomes possible to obtain novel cobalt oxyhydroxide particles containing substantially spherical Mg having a controlled diameter distribution and average particle size in a solid solution state.

Hereinafter, embodiments of the present invention will be described in detail.
(Cobalt oxyhydroxide particles containing Mg in solid solution)
The cobalt oxyhydroxide particles containing Mg of the present invention in a solid solution state are not merely coprecipitates of Mg compounds (for example, hydroxide) and cobalt oxyhydroxide particles, but the Mg element is in a eutectic or solid solution state. It is characterized by being included. This different state can be easily distinguished by, for example, a powder X-ray diffraction (XRD) method.

  There is no restriction | limiting in particular in the quantity of Mg contained in the cobalt oxyhydroxide particle | grains containing Mg of this invention in a solid solution state, According to the objective of use, it can change in a wide range. Preferably, it is expressed in terms of a molar ratio and ranges from 0.01 to 50 mol%, particularly preferably from 0.1 to 20 mol%.

  For the contained Mg, various commonly known quantitative analysis methods (wet or dry) of magnesium elements can be used. For example, an atomic absorption analysis method may be used as a wet method.

The cobalt oxyhydroxide particles containing Mg of the present invention in a solid solution state has a high density and a tapping density of at least 1.8 g / cm ³ , and in some cases, 2.2 g / cm 3. Having a density greater than ³ ; The bulk density is characterized by having a density of at least 1.3 g / cm ³ , and in some cases has a density exceeding 1.6 g / cm ³ .

  Furthermore, the shape is a substantially spherical secondary particle in which primary particles are gathered, and the average particle size is 5 μm to 15 μm. Such a shape can be easily observed using, for example, an electron microscope, and a generally known particle size measuring device can be used for the particle size distribution.

  The cobalt oxyhydroxide particles containing Mg of the present invention in a solid solution state are black, and the actually measured oxidation degree is substantially 100%. The degree of oxidation can be determined by a chemical analysis method such as oxidation-reduction titration or an X-ray diffraction method.

(Production method)
The production method according to the present invention comprises Mg according to the present invention described above in a eutectic or solid solution state, has a high density and a substantially spherical shape, and has an oxidation degree of substantially 100%. This is a method for producing certain cobalt oxyhydroxide particles, characterized in that it is produced as a precipitate in a single step starting from a divalent cobalt salt containing an Mg salt.

  That is, such a single step is to add cobalt oxyhydroxide as substantially spherical particles by adding an alkaline aqueous solution to a divalent Co salt aqueous solution containing Mg salt in the presence of a suitable oxidation catalyst and air while stirring. It is a process to make.

As the “divalent Co salt” that can be used in the present invention, specifically, cobalt nitrate (Co (NO ₃ ) ₂ ), cobalt chloride (CoCl ₂ ), cobalt sulfate (CoSO ₄ ) and the like are preferable. As an example. These Co salts may be used alone or in combination of two or more. Moreover, you may coexist a small amount of other metal salts as needed.

  Specific examples of the Mg salt that can be used in the present invention include magnesium nitrate, magnesium chloride, and magnesium sulfate. These Mg salts may be used alone or in combination of two or more.

It is possible to adjust the Mg content over a wide range by appropriately adjusting the kind of Mg salt and the concentration in the aqueous Co salt solution.
Further, according to the present invention, it is possible to easily adjust the particle size and density to a preferable range by changing the concentration of the divalent Co salt aqueous solution containing Mg salt. Specifically, the concentration can range from 10 g / L to 150 g / L in terms of cobalt, preferably from 40 g / L to 100 g / L, and more preferably from 60 g / L to 90 g / L. It is.

Generally, when the concentration of the divalent Co salt aqueous solution containing Mg to be reacted and the alkali concentration are lower, primary particles having a larger size are generated, and the density of the particles composed of the primary particles tends to be higher. For example, when a cobalt sulfate aqueous solution is used as the divalent Co salt aqueous solution, for example, when the concentration of cobalt sulfate is 90 g / L, almost spherical cobalt oxyhydroxide particles (density 1.8 g / L) composed of dense primary particles. cm ³ ), and in the case of 60 g / L, substantially spherical cobalt oxyhydroxide particles (density 2.3 g / cm ³ ) composed of finer primary particles are obtained.

  In addition, the granular characteristics (sphericity, average particle diameter, density, etc.) of the obtained particles are not only the concentration of these cobalt salt aqueous solutions, but also the concentration of the alkaline aqueous solution, the dropping time of the alkaline aqueous solution, the dropping amount of the alkaline aqueous solution, the reaction temperature, It can be controlled by the reaction time, the stirring speed, the type of catalyst, the amount of catalyst added, the air blowing speed, and the like. That is, it is easy for those skilled in the art to select these conditions as appropriate and obtain desired granular characteristics.

  Specific examples of the “alkaline aqueous solution” that can be used in the present invention include NaOH aqueous solution, KOH aqueous solution, aqueous ammonia, and the like, but the use of NaOH aqueous solution is more preferable. The aqueous alkaline solution is preferably added to maintain the pH of the reaction solution at 11 to 13 during the reaction. More preferably, it is preferably added to maintain the pH of the reaction solution at 12.0 to 12.8 during the reaction. The method for adding the alkaline aqueous solution is not particularly limited, and it is preferable that the pH of the reaction solution is quickly adjusted to a desired pH. In order to maintain the pH within a preferable range, it is preferable that a pH monitor can be used to automatically adjust the addition amount of the alkaline aqueous solution.

The catalyst that can be used in the present invention may be any catalyst that catalyzes an oxidation reaction by oxygen in the air under the condition of an alkaline aqueous solution. The mechanism of divalent cobalt salt by oxygen and catalyst being oxidized to cobalt oxyhydroxide at a predetermined pH in the presence of an alkali is considered to differ depending on the catalyst, but one mechanism is Co (OH) once formed in a solution. ) ₂ (particles, not limited to precipitation) is thought to be rapidly oxidized and produced as a precipitate. At that time, it is considered that Mg is incorporated in a eutectic or solid solution state.

  Specific examples of the oxidation catalyst include metals such as iron, chromium and nickel, or metal ions thereof. Such a catalyst is added to the reaction solution, and when the reaction is performed in an iron reaction vessel such as stainless steel, the reaction solution contacts the wall of the reaction vessel, or a very small amount of metal from the iron reaction vessel. It can also exist when ions are liberated in solution.

  Similarly, oxygen as an oxidizing agent that can be used in the present invention can be easily introduced by blowing air. Although there is no restriction | limiting in particular about the amount of blowing, It is preferable that it blows into a reaction solution sufficiently and always maintains a saturated state.

  Furthermore, it is preferable to sufficiently stir the reaction solution together with air in order to uniformly and rapidly react with oxygen.

  Although there is no restriction | limiting in particular about reaction temperature, Usually, the range of 40-60 degreeC is preferable.

  The reaction is initially in solution but becomes a slurry as a precipitate forms. For the purpose of aligning the particle shape and particle size within a desired range, it is preferable to continuously take out the slurry with an overflow device after a predetermined reaction time has passed and a steady state has been reached. The extracted particles can be separated by a normal method such as filtration and dried with hot air or the like.

  The cobalt oxyhydroxide particles containing Mg obtained in the present invention have a high density, an average particle size and a particle size distribution in a desired range, and are almost completely oxidized. It can be widely used for battery materials.

  Hereinafter, the present invention will be described with reference to examples.

(Example)
13 L of water was put into a stainless steel cylindrical reaction tank having an effective volume of 15 L equipped with a stirrer and an overflow pipe. SUS304 was used as the material for the reaction vessel. Next, a 30% sodium hydroxide solution was added until the pH reached 12.7, and the temperature was maintained at 50 ° C. with an electric heater. Next, the solution in the reaction tank was stirred at a constant speed so that air was sufficiently contained. Next, magnesium nitrate powder was dissolved in a cobalt sulfate aqueous solution containing 60 g of Co ions per liter so that the molar ratio of Mg to Co was 2 mol%, and the solution was continuously supplied at a constant rate of 10 cc / min. . Further, 30% sodium hydroxide was intermittently added so that the solution in the reaction vessel was maintained at pH 12.7 to form cobalt oxyhydroxide particles containing Mg.

  The particles obtained from the overflow pipe were collected for 24 hours continuously 72 hours after the inside of the reaction vessel became a steady state, washed with water, filtered, and dried at 100 ° C. for 15 hours to obtain a dry powder. The color tone of the powder was black.

Moreover, the analysis (XRD) by X-ray diffraction of the obtained powder was performed as follows.
Preparation of sample: Cobalt oxyhydroxide particles containing Mg obtained above were used as they were.
Measuring apparatus and conditions: RINT2000 (Cu-Kα) manufactured by Rigaku Corporation
Measurement result: A peak (Heterogenite-3R) due to cobalt oxyhydroxide represented by the chemical formula CoO (OH) was observed.

Further, the tapping density (TD) was measured as follows.
Sample preparation: The resulting powder was used as follows. The mass of the 20 mL cell was measured [A], and the crystal was spontaneously dropped into the cell and filled with a 48 mesh sieve. The mass [B] and the filling volume [D] of the cell after tapping 200 times were measured using “TAPDENSER KYT3000” manufactured by Seishin Enterprise Co., Ltd. with a 4 cm spacer. The following formula was used for calculation.
Tap density = (B−A) / D g / ml
Measurement result: 2.29 g / cc
The average particle diameter of the obtained cobalt oxyhydroxide was measured as follows.
Preparation of sample: The obtained powder was used as it was.
Measurement apparatus and conditions: LA-910 manufactured by HORIBA, Ltd. was used and the operation procedure manual was followed.
Measurement result: D50, 8.0 μm
The degree of oxidation of cobalt in the obtained powder was measured by an iodometry method. The degree of oxidation was expressed as a percentage of Co having a valence of 3 with respect to the total amount of Co contained in cobalt oxyhydroxide.
Measurement result: degree of oxidation = 100%
The surface structure of the obtained powder is shown in FIG. 1 using a scanning electron microscope (SEM). It can be seen that the primary particles gather to form a substantially spherical secondary particle.

(Comparative example)
The same procedure as in Example was performed except that no Mg salt was added.

  The analysis results of the powders obtained from Examples and Comparative Examples are summarized in Table 1.

  Although the embodiments of the present invention have been described in detail above, the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the gist of the present invention.

The electron micrograph (5000 times) of the cobalt oxyhydroxide particle | grains containing Mg obtained in Example 1 is shown. The XRD of the cobalt oxyhydroxide particle | grains obtained in Example 1 is shown.

Claims (4)

  Cobalt oxyhydroxide particles that are solid solution of Mg and are almost spherical.   The cobalt oxyhydroxide particle | grains of Claim 1 whose solid solution amount of Mg is 0.1-20 mol%.   A method for producing Mg solid solution and producing substantially spherical cobalt oxyhydroxide particles by stirring a mixture of an aqueous divalent Co salt solution containing Mg salt and an alkaline aqueous solution in the presence of an oxidation catalyst. A production method comprising oxidizing by contacting with air, solid-dissolving Mg, and precipitating substantially spherical cobalt oxyhydroxide particles.   The manufacturing method according to claim 3, wherein the oxidation catalyst is a metal composed of at least one of iron, nickel, and chromium or ions thereof.